Organic electrochemical transistors (OECTs) have recently been investigated intensively due to their switching and sensing functionality in an electrolytic environment which is compatible with biological systems. The working principle of OECTs differs significantly from the classical electrostatically gated field-effect transistors (FET) due the volumetric capacity control of charge carrier concentration in the channel by ionic motion. The mixed electron-ion transport of the devices has consequence for many parameters of the devices including dynamics and hysteresis. In this talk, our recent work on a better understanding of OECT operation is reviewed. We discuss the properties of a wide variety of devices including solid state electric devices and vacuum-processed devices. It turns out that entropic terms play a major role in the operation of the devices due to the entirely different statistical properties of the ions in the channel. The results show that the often observed hysteresis of OECT can be separated in an intrinsic bistable behavior and a conventional hysteresis behavior related to ion dynamics and other effects. The bistability of the devices offers interesting device applications.

Doping of organic semiconductor films enhances their conductivity for applications in organic electronics, thermoelectrics and bioelectronics. However, much remains to be learnt about the properties of the conductive charges in order to optimize the design of the materials. Electrochemical doping is important for organic electrochemical transistors (OECTs) used in biomedical sensors. Benefits of doping via electrochemistry include controllable doping levels, reversibility and high achievable carrier densities. We introduce a new technique, applying in-situ terahertz (THz) spectroscopy directly to electrochemically doped polymers in combination with time-resolved spectro-electrochemistry, chronoamperometry and OECT device measurements. We evaluate the intrinsic short-range transport properties of the polymers (without the effects of long-range disorder, grain boundaries and contacts), while precisely tuning the doping level via the applied oxidation voltage. Moreover, temperature-dependent measurements allow to extract the thermodynamic and activation parameters of the electrochemical processes. Results will be shown for a variety of polymers based on polythiophene backbones with different sidechains, aligned polymer chains and novel 2D organic films.

Organic mixed ionic-electronic conductors (OMIECs) have recently risen as a promising material choice for bioelectronic devices due to their low impedance, soft mechanical properties, and ability to transduce ionic signals to electronic currents. These properties have enabled the development of high-performance devices for electrophysiological recordings, chemical sensing, cell monitoring, and neuromorphic devices. The unique behaviour of OMIECs arises from “electrochemical doping” where ion intercalation through the bulk of the material modifies the oxidation state, and therefore charge carrier concentration, of the conjugated polymer. However, the current understanding of electrochemical gating remains limited. To address this knowledge gap, we use a newly developed hyperspectral differential transmission microscopy technique to probe electrochemical gating in operando.

First, I will present a comprehensive drift-diffusion model to describe mixed ionic-electronic transport in OMIECs using the data collected from in operando microscopy which captures the complex behaviours of electrochemical doping. The proposed model captures several features observed for electrochemical (de)doping of OMIECs including diffusion-like rather than drift-like ion transport and the voltage-dependence of ion kinetics. The results suggest that diffusion of electronic carriers (holes) down electrochemical potential gradients plays a significant role in operation of OMIEC-based devices. In the second part of the presentation, I will show that electrochemical doping consists of two distinct kinetic regimes. Generally, electrochemical doping is assumed to be limited by motion of ions due to their large mass compared to electrons/holes. However, in a state-of-the-art polythiophene, electrochemical doping speeds can be limited by poor hole transport at low doping levels, leading to substantially slower switching speeds than expected. We show that the timescale of hole-limited doping can be controlled by the degree of microstructural heterogeneity, enabling the design of OMIECs with improved electrochemical performance. The framework for understanding the driving forces and kinetics of mixed ionic-electronic transport provides guidance for device design as well as optimization of new materials for improved performance in bioelectronic devices.

Organic semiconductors with polar side groups are capable of mixed electronic and ionic conduction, making them candidates for electrodes in electrochemical devices. In the case of conjugated polymers, electrochemical and redox properties can be tuned through choice of polymer backbone and side chain [1, 2].  Conjugated polymer electrodes can show excellent charging and discharging rates, high coulometric efficiency, efficient charge transport and reversible charging in simple aqueous electrolytes, making them interesting for different applications including energy storage. However, the specific capacity and operational stability need to be improved [3]. We use molecular modelling together with electrochemical measurements to investigate the relationship between polymer chemical structure and the redox properties, charging behaviour and cycling stability of the polymer electrodes. We use molecular dynamics simulations to explore how the side chain structure influences polymer packing, film swelling and stability [4]; how structure influences polymer-ion interactions; and how these interactions influence electronic transport properties. Finally, we use simulations to explore how chemical structure influences specific capacity. The findings can help to develop chemical designs for improved conjugated polymer electrodes for aqueous environments.

The charge-transport properties of conjugated polymers have been studied intensively for both electronic and optoelectronic device applications. Some polymer semiconductors not only support the ambipolar transport of electrons and holes, but do so with comparable carrier mobilities. This opens the possibility of gaining deeper insight into the charge-transport physics of these complex materials via comparison between electron and hole dynamics while keeping other factors, such as polymer microstructure or vibrational fluctuations, equal. Field-induced electron spin resonance spectroscopy has been recently used to compare the spin relaxation behavior of electron and hole polarons in three ambipolar conjugated polymers, showing three spin relaxation regimes as a function of temperature. We interpret these findings on the basis of calculated electronic structure calculations and state-of-the-art numerical propagation of the hole and electron carrier wavefunctions coupled to nuclear motion in these polymers.

In the second part of the talk, we will report on recent simulations of ion intake and diffusion in crystalline microstructures of conjugated polymers equipped with glycolated side chains for organic electrochemical transistor applications. All-atom simulations support a crystal phase transition upon doping that occurs via a zipping mechanism. We will also describe preliminary phenomenological calculations aiming at describing the changes in electrical conductivity with increasing carrier concentration and that take into account the electrostatic interactions with the ions. 

Engineering conjugated polymers with glycol-based side chains has been the main strategy used to improve the performance of mixed ionic-electronic conductors (OMIECs), a promising material class for interfacing biological systems with electronics. Organic electrochemical transistors (OECTs) are a solution for this task and are often used to benchmark OMIECs performance. Different studies have showed that polymers designed with hydrophilic solubilizing chains show better OECT performance, mostly due to their higher ionic uptake and stability in aqueous environments. [1]

In this work, we explore how side chain engineering in poly(3-hexylthiophene) (P3HT) and in indacenodithiophene-co-benzothiadiazole (IDTBT) impact their ionic transport properties. We used time-resolved spectroelectrochemistry to measure the kinetics of doping in these materials with high time resolution. We observe that for thicker films (around 100-200 nm), the films with more glycol content are doped faster, confirming that the ion transport is better in more polar polymers. However, for thinner films (around 20nm), we observe that the kinetics becomes independent of glycol content. We hypothesize that the kinetics in thin films are less dependent on the ion transport and closer to the electrochemical limit. Therefore, the polar content does not affect the intrinsic electrochemical reactions rate and the doping favorability, which remain controlled by the polymer backbone.

Organic electrochemical transistors (OECTs) are a rapidly advancing technology that plays a crucial role in the development of next-generation bioelectronic devices. Recent advances in p-type/n-type organic mixed ionic-electronic conductors (OMIECs) have enabled power-efficient complementary OECT technologies for various applications, such as chemical/biological sensing, large-scale logic gates, and neuromorphic computing. However, ensuring both high performance and long-term operational stability remains a significant challenge that hinders their widespread adoption. Ladder-type conjugated polymers, with their rigid backbone structure composed of double-strand chains linked by condensed π-conjugated units, can sustain high electrochemical doping levels without any conformational disorder, which leads to exceptional operational stability, high charge carrier mobility, and large volumetric capacitance. In this report, we demonstrate our recent development on ladder-type conjugated polymers, with p-type/n-type high mixed ionic-electronic conducting performance and high stability in long-term OECT operation. Reasonable molecular design and improvement of synthesis methods have enabled the synthesis of high-performance p-type/n-type ladder polymers with mobility increased by more than 10 times. Their unique ladder-type structure enables them to have long-term stability within >90% current remain after 6 hours continues operation, and enables them to accommodate more carrier injections with of up to two charges per repeat unit. Density of states filling and opening of a hard Coulomb gap around the Fermi energy at high electrochemical doping levels enable the ion-tunable antiambipolarity in these ladder polymers. The development of ladder-based polymer ink formulations has also enabled printed electronics. With these ladder-type polymers, we developed complementary inverters with a record-high DC gain of 194 V/V and excellent stability. We report the first organic electrochemical neurons (OECNs) with ion-modulated spiking, based on all-printed complementary organic electrochemical transistors. We demonstrate facile bio-integration of OECNs with Venus Flytrap (Dionaea muscipula) to induce lobe closure upon input stimuli. We report a biorealistic conductance-based organic electrochemical neuron (c-OECN) using a mixed ion–electron conducting ladder-type polymer with stable ion-tunable antiambipolarity. The latter is used to emulate the activation/inactivation of sodium channels and delayed activation of potassium channels of biological neurons. These c-OECNs can spike at bioplausible frequencies nearing 100 Hz, emulate most critical biological neural features, demonstrate stochastic spiking and enable neurotransmitter-/amino acid-/ion-based spiking modulation, which is then used to stimulate biological nerves in vivo.

Conductive polymers combine high ionic and electronic conductivities with soft mechanical properties, and achieve the conversion of electrochemical processes in liquid environment to mechanical formalization.^[1] The resulting material electroactivity has been exploited in electrochemical actuators with low-voltage drive and nanoscale precision, leading to the development of bioelectronics soft actuators.^[2] On the other hand, the electrically-induced swelling of conductive polymer layers can be detrimental for applications such as thin film neuromodulation devices, where shear stresses with the substrate can lead to delamination and device failure.^[3] During volume change, electroactive polymers translate an external stimulus to a change of the physical properties on a nanometer scale, but the intrinsic mechanism of actuation is not completely understood. In this work, we address this gap of knowledge introducing quantitative measurements of electroswelling using atomic force microscopy (AFM). We exploit AFM as a local probe for volume changes and interface forces that provides transient data on dynamical effects related to electroactuation. We combine electroswelling measurements in the frequency domain with electrochemical impedance spectroscopy on a model conductive polymer, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) to correlate morphological changes with information on ionic uptake and local electrochemical potential. Through the development of a mathematical theory, we describe electroswelling in terms of transport and accumulation of hydrated ions, and we achieve multimodal AFM experiments mapping electroswelling amplitude and phase on soft polymer thin films. Our findings highlight the physicochemical mechanisms limiting actuation width and timescales and can be crucial to develop functional materials with enhanced electroactive properties.

The polyelectrolyte complex of poly(3,4-ethylene dioxythiophene) with poly(styrene sulfonate), PEDOT:PSS, is ubiquitous in the field of organic electronics. Yet, its complex structure in water and in the solid state make it challenging to understand structure-property relationships for optimization or functionalization. Our group focuses on developing a better understanding of PEDOT:PSS, particularly for using it as a mixed ionic-electronic conductor for organic electrochemical transistors (OECTs). In this talk, I will share two recent projects. The first project will describe how to increase the OECT performance of common formulations of PEDOT:PSS without sacrificing stability in water by using a surface functionalization method instead of blending with a crosslinker. For a simple formulation of PEDOT:PSS with ethylene glycol and a dodecylbenzene sulfonic acid (DBSA) surfactant, we found that surface functionalization with (3-glycidyloxypropyl)trimethoxysilane (GOPS) led to a [μC*] value of 376 ± 74 F cm^‒1 V^‒1 s^‒1 instead of 104 ± 20 F cm^‒1 V^‒1 s⁻¹ when blended with GOPS (the most commonly used approach to maintain water stability). In the second part, I will describe the use of polyethylene oxide (PEO) as either a polymeric additive to commercial formulations or as a block copolymer with PSS to increase the volumetric capacitance of PEDOT:PSS, up to 200 F cm⁻³ (after washing the films in water) and 120 F cm⁻³ respectively. When using a relatively low molecular weight PEO, 400 Da, the PEDOT:PSS:PEO blend led to a [μC*] value up to  632 F cm^‒1 V^‒1 s^‒1 after washing with water, close to that obtained for crystalline PEDOT but without having to use sulfuric acid. For both projects, I will describe our approach for the preparation of different formulations, how the additives or block copolymers affect the chemical composition, and detailed microstructure characterization to tease out structure-property relationships in PEDOT:PSS-based mixed conductors.

Organic mixed ionic/electronic conductors (OMIECs) have gained considerable interest in bioelectronics, power electronics, circuits and neuromorphic computing. These organic, often polymer-based, semiconductors rely on a combination of ionic transport, electronic transport, and high volumetric charge storage capacity. Despite recent progress and a rapidly expanding library of new materials, a full understanding of fundamental processes of OMIECs remains largely unexplored. Critically, useful studies require us to probe these systems in device-relevant conditions, fully considering the effects of ions and solvent on microstructure and transport. To this end, we report on recent efforts towards structure/composition-property relations in high performance organic mixed conductors using ex-situ, in-situ, and operando scattering and spectroscopic techniques. We use a combination of GIWAXS, GISAXS, XPCS, E-QCMd, UV-Vis, XRF, as well as device measurements to explore kinetics, composition, and structural evolution during electrochemical operation. Importantly, these findings provide insights into materials design for enhancing device performance and stability.

Conjugated polymers (CPs) with hydrophilic side chains are capable of simultaneously conducting electronic and ionic charges, making them interesting materials for applications in bioelectronics, electrochromics, electrocatalysis and energy storage. Whilst numerous p-type mixed-conducting polymers have shown excellent stability and performance, n-type mixed-conducting polymers usually suffer from poor stability in aqueous environments and in air. To date, most reported solution processable n-type mixed conducting polymers that show good stability, high electron mobility and high specific capacity, involve the naphthalenediimide (NDI) unit. [1-3] However, the electrochemical stability of NDI-based mixed-conducting polymers varies with the specific chemical structure and choice of electrolyte. The underlying mechanisms by which ionic charging/discharging deteriorates the electrochemical stability are not properly understood. In this work, we study several NDI-based n-type mixed conducting polymers with different side chain and backbone structures operating in aqueous electrolytes of systematically varying concentrations to control the electrochemical stabilities. We observe that increasing electrolyte concentration and replacing a small fraction of hydrophilic side chains with hydrophobic ones largely improve the electrochemical stability of the NDI-based n-type mixed conducting polymers. To understand the phenomena, we use spectroelectrochemical and electrogravimetric characterisation tools and molecular dynamic (MD) simulations to explore the impact of side chains and electrolytes on the electrochemical stabilities of the polymers. We show that the improvement in stability can be tentatively attributed to a reduction in swelling, which avoids excessive electrolyte uptake, thereby improving the environment for ion transport and maintaining the intermolecular connections. We propose design rules for both material and electrolyte to maximise reversible multi-electron charging of n-type mixed conducting polymers.

The development of organic electrochemical transistors (OECTs) capable of maintaining their high amplification, fast transient speed, and operational stability in harsh environments will advance the growth of next‐generation wearable electronics, robotics and biological electronics. In this study, a high-performance solid-state OECT (SSOECT) is successfully demonstrated, showing a recorded high transconductance of 220 ± 59 S cm−1, ultrafast device speed of ≈10 kHz with excellent operational stability over 10 000 switching cycles, and thermally stable under a wide temperature range from −50 to 110 °C. The developed SSOECTs are successfully used to detect low-amplitude physiological signals, showing a high signal-to-noise-ratio of 32.5 ± 2.1 dB. For the first time, the amplifying power of these SSOECTs is also retained and reliably shown to collect high-quality electrophysiological signals even under harsh temperatures. The demonstration of high-performing SSOECTs and its application in harsh environment are core steps toward their implementation in next-generation wearable electronics and bioelectronics. We also will present our recent work on developing fibrous electrolyte containing polymer matrix and ionic liquid, which is highly robust, breathable, waterproof, and conformal with human skin is reported. Serving as fibrous substrate and electrolyte of OECTs, a high transconductance of ≈0.8 mS, stability over pulsing and time (≈1000 cycles and 30 days) are achieved. The softness of fibrous OECTs enables a comfortable contact after attaching to human skin, which can reduce the interfacial impedance to achieve a high-quality local amplification of the electrocardiography signals (signal-to-noise ratio of 21.7 dB) even in skin squeezed state or after one week. These results indicated that our fibrous OECTs have huge potential for versatile on-skin electronics such as non-invasive medical monitoring, soft sensors, and textile electronics.

The presentation will give an overview over recent studies in my group about design and processing of polymeric mixed-ionic-electronic conductors for opto-electronic and switchable technologies including actuators, electrochromic displays and electrically switchable metasurfaces.

In the first part, electrochemistry will be shown as versatile tool to control the doping level of semiconducting polymer films. Data on tunable absorption properties, electrical conductivities and wetting behavior will be presented for p-type materials.[1] Both, in-situ as well as ex-situ electrochemical techniques will be presented and correlations to the morphology of the films will be drawn. For energy level determination within fully organic solar cells particularly in-situ spectroelectrochemistry of blend films proved to be highly useful.[2]

In the second part, poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) will be presented as multifunctional material. Electrochemical switching in organic and in aqueous electrolytes results in different degrees of volume swelling as characterized by in-situ spectroscopic ellipsometry.[3] The humidity dependence of the PSS polyelectrolyte phase further allows to prepare volume changes by water uptake. The bending behavior of “intelligent” humidity-triggered bilayer actuators with poly(dimethylsiloxane) (PDMS) passive layers can be explained by the humidity-dependent mechanical behavior of PEDOT:PSS.[4]

Chemical and electrochemical doping are widely used to modulate the electrical properties of conjugated polymers. Doping of thin films facilitates fundamental spectroscopic studies and, ultimately, is important for the operation of devices from transistors to solar cells. However, some applications such as thermoelectrics and wearable electronics require bulk materials, which complicates doping processes and mass transport, limiting the performance of devices. This talk will explore some of the fundamentals of doping of both thin films and bulk materials. The impact of doping on the electrical as well as mechanical properties will be discussed, and it is shown how doping can be used to tune both the conductivity and stiffness of conjugated polymers. Finally, strategies are explored that permit to decouple the effect of doping on the electrical and mechanical properties, which can be used to prepare a variety conducting bulk materials, from stiff composites and foams to hydrogels and stretchable fibers.

Electrolyte-Gated Transistors (EGTs) have emerged as an integral part of numerous applications in biosensing and bioelectronics, owing to their remarkable ability to efficiently transduce biological events into amplified electronic signals while stably operating in aqueous electrolytes. EGT are three-terminal devices consisting of a semiconducting channel between source and drain electrodes capacitively coupled with the gate electrode through ions in the electrolyte. Understanding these devices at the nanoscale is paramount in order to leverage their respective, or combined, functionality for various applications. An optimized level of crystallinity or a balance between ionic and electronic conduction within the semiconductor might be desired, which directly relates to the physical and chemical nature of the semiconducting material and its response to applied electric fields. However, probing the nanoscale properties under operating conditions has been challenging due to the complications arising from the electrolyte environment. In this communication, I will review the progress made in our research group towards developing an advanced scanning probe microscopy technique able to probe different functional properties of the semiconductor materials (morphological, electrical and mechanical) at the nanoscale in operating electrolyte-gated transistors (EGTs). The technique is based on in-Liquid Scanning Dielectric Microscopy (in-Liquid SDM) to which we added automated functionalities and multiparametric characterization capabilities for comprehensive and simultaneous probing of the nanoscale electrical, mechanical and morphological properties in operating EGTs. Examples of applications to Electrolyte Gated Organic Field Effect Transistors (EGOFETs) [1] and Organic Electrochemical Transistors (OECTs) will be presented.

We explore the concept of constructing microscopic electronic neurons that mimic natural brain systems in order to create brain-inspired computational artificial systems. We discuss the essential material and device properties required for these spiking neurons, which can be characterized using impedance spectroscopy and small perturbation equivalent circuit elements. We identify the structural conditions necessary for smooth oscillations, which depend on the dynamics of a conducting system with internal state variables. We emphasize the significance of detecting the Hopf bifurcation, a critical point for achieving spiking behavior, through spectral features of the impedance. We focus on the mixed ionic-electronic conductors in which the slow ionic motion introduces a internal state variable that controls the electronic conductivity. Our findings reveal that the minimal neuron system requires a capacitor, a chemical inductor, and a negative resistance, which can be integrated into the physical response of the device rather than being built from separate circuit elements. Thus, we propose a method to quantify the physical and material properties of devices in order to produce the dynamic properties of neurons that are necessary for a specific computational scheme. We present a novel approach towards building brain-inspired artificial systems and provides insights into the important material and device considerations for achieving spiking behavior in electronic neurons [1].

In recent years, there has been continuous progress in the development of n-type organic thermoelectrics (OTE) due to the synthesis of new conjugated polymers and dopants. The primary focus of most designs has been to enhance doping efficiency and increase electrical conductivity, resulting in values surpassing 102 S cm^-1. Although effective, doping encounters limitations because of the inherent inverse relationship between the properties that determine the figures of merit in thermoelectric materials. To advance the field further, alternative approaches are needed beyond optimizing doping efficiency and the host:dopant ratio. In this study, we propose the concept of self-induced anisotropy as a solution to overcome the inverse coupling between electrical conductivity and Seebeck coefficient in n-type OTEs. Previous research has suggested methods like rubbing and drawing to induce anisotropy in p-type OTEs based on thiophenes. In our work, we exploit the interactions between solvent, host, and dopant to induce a preferential orientation. This orientation increases the in-plane delocalization length, thereby improving electrical conductivity whitout hindering the Seebeck coefficient. By adopting this approach, we have achieved promising results in the 2DPP-2CNTVT:N-DMBI system. At room temperature, we obtained a Power Factor of 115 μW m^-1 K^-2 and a figure of merit of 0.17, which further increased to 188 μW m^-1 K^-2 and 0.36, respectively, at 105 ºC. To explain the origin of self-induced anisotropy, we utilized Hansen Solubility Parameters and established guidelines for formulating solvent-host-dopant systems that can achieve a similar effect. This discovery opens new possibilities for advancing n-type OTEs.

Conjugated porous polymers (CPPs) are solely organic members of porous materials family. They are very promising compounds for photocatalytic and electronic applications thanks to their the electron rich and porous backbone offering high accessible surface areas and advanced photophysical properties.[1,2] Moreover, their high dimensionality make them particularly interesting for organic electronic devices due to the possibility of orientation independent electron/hole mobility through their 2D/3D skeleton.[3,4] Additionally, the open voids along the porous backbone are perfectly separated phases to introduce guest molecules to form charge-transfer complexes (i.e. doping), which leads improved electrical conductivities.[4]

We have previously reported formation of charge-transfer complexes of electron rich CPPs after iodine treatment.[5–7] In a particular example, we showed that a thiophene based CPP became more conductive after iodine exposure when compared to its linear analogue whereas the latter outperformed the former before the doping.[7]

In this communication, chemical doping an electron rich CPP by using different techniques (i.e. mixing dopant+CPP in solution or vacuum impregnation) will be presented. The spectral (e.g. UV, IR, NMR, EDX, XPS) and physical characterizations (thermal elemental analysis, TGA, and porosity measurements) of the pristine and doped forms indicated the successful incorporation of the guest molecules in the pores. Furthermore, effect of the doping on the electrical impedance and conductivity will also be discussed.

We present a novel concept for cuff electrodes that greatly simplifies the insertion procedure on nerves as small as 100 µm. Cuff electrodes serve as peripheral nerve interfaces for neural stimulation or recording, with various applications including chronic pain management, sleep apnea treatment, and high blood pressure control. Existing methods for securing cuff electrodes on larger nerves in the millimeter range rely on surgical threading, zip tie-like closing mechanisms, or prefolded spiral cuff geometries. While these approaches are effective for larger nerves containing multiple fibers branching out to different target regions, they present challenges when targeting smaller nerves with diameters of 100 µm or below. The fragility of such nerves and the difficulties in handling small probes make interfacing with typical cuff electrode systems a challenging task.

To overcome these challenges, our approach leverages 3D and 4D printing techniques, in combination with flexible and superabsorbent materials. These materials readily conform to the shape of the nerve upon contact with body fluid, allowing the electrodes to wrap around the nerve without requiring manual deformation [1]. This approach reduces the risk of nerve damage during implantation. Notably, we have successfully implanted these devices in a locust model and demonstrated their efficacy in recording and stimulating neural activity as well as associated muscle activation. The geometric design of our cuff electrodes features electrodes distributed along both the axial and circumferential directions, enabling enhanced spatially selective sensing and stimulation capabilities.

In summary, our nerve cuff electrode concept offers a transformative solution for the implantation of electrodes on ultra-small nerves, streamlining the procedure and minimizing potential harm. Through the utilization of state-of-the-art rapid fabrication techniques and adaptable materials, we have developed a simple procedure for recording and stimulating of neural activity. The incorporation of electrodes distributed along multiple directions further enhances the potential for selective sensing and stimulation.

Biomaterial scaffolds have emerged as a tool to build 3D cultures of cells which better resemble biological systems, while advancements in bioelectronics have enabled the modulation of cell proliferation, differentiation, and migration.

Here, we first describe a porous conductive hydrogel with the same mechanical modulus and viscoelasticity as neural tissue. Electrical conductivity is achieved by incorporating low amounts (<0.3% weight) of carbon nanomaterials in an alginate hydrogel matrix, and then freeze-drying to self-organize into highly porous networks. The mechanical and electrical properties of the material can be carefully tuned and used to modulate the growth and differentiation of neural progenitor cells (NPCs). With increasing hydrogel viscoelasticity and conductivity, we observe the formation of denser neurite networks and a higher degree of myelination.

To investigate the functionality of neurite networks in 3D, we begin by placing a polydimethylsiloxane (PDMS) microstructure on an underlying multielectrode array (MEA). We then explore different materials and techniques to integrate hydrogels into the PDMS microstructures, such that the hydrogel can facilitate neurons to form 3D networks while still confined by the PDMS. This platform can be used to support the growth of human iPSC-derived sensory neurons, with and without a co-culture of human Schwann cells. Additionally, our platform is compatible with various methods to assess neuronal functionality (e.g. MEA electrical recordings), and can be used to understand the effect(s) of hydrogel properties on the resulting neuronal networks. Both described biomaterial systems can support the growth of neuronal cells for over 12 weeks to investigate neuronal development and disease progression. Further, we have demonstrated the use of these materials for the fabrication of implantable surface electrode arrays which can seamlessly interface with electrically active tissues such as the brain and heart.

Bioelectronic medicine have enormous potential not only to replace lost body function but also for guiding and encouraging regenerative processes, helping the body to self-repair. The ability of our skin to self-heal is something so integral to our everyday life that we barely reflect on how remarkable this is. Other parts of our bodies have very limited healing capability, especially the very complex structures of brain and spinal cord. Furthermore, while most of us take our self-repairing skin for granted, old age and certain diseases can drastically reduce this ability, greatly increasing the risk that seemingly uncomplicated wounds develop into chronic ones.  

Together wiht my team I have shown how electrical field stimulation can have a guiding effect on skin cell migration, which could be of great significance to speed up wound closure and reduce the risk for chronic wounds. Together with collaboration partners we now explore how similar principles can be used to promote more constructive repair after traumatic injury. The common denominator for these therapeutic concepts is electrical field stimulation, in other words direct current injected into the tissue. This places special constraints on the electrode materials used to ensure biocompatible and reversible direct current injection mechanisms. My talk will outline some material concepts that we have developed for this and which electrochemical boundary conditions that apply to ensure that direct current stimulation can be sustained in tissue even with fully implantable systems. I will showcase how we employ conducting polymer hydrogels for direct current stimulation, and how such technology allows for new discoveries as well as potential future therapies.

From extracellular matrices (ECM) in connective tissues, to silks spun by spiders, and textile fibers weaved in fabrics, small diameter fibers widely exist in nature and have been closely associated with our daily life. These individual fibers have quasi-one-dimensional flexible structures, with diameters smaller than ~100 µm, and length to width aspect ratios greater than ~100. Orderly assembling fibers into arrays and three-dimensional architectures with designable chemical properties and sensing capabilities could open a range of bioelectronics and biointerface applications. In this presentation, I will demonstrate biofabrication and fiber printing techniques that enable the patterning of functional fiber architectures in three dimensions. These fiber printing techniques extend the materials libraries and device designs, which underpin technological capabilities from enabling fundamental studies in cell migration, to customizable and eco-friendly fabrication of wearable sensors. Finally, I will provide an outlook on the strategic pathways for developing next-generation bioelectronics using fibers as architectural building blocks.

Use of light for selective and spatio-temporally resolved control of cell functions (photoceutics) is emerging as a valuable alternative to standard electrical and chemical methods. Here, we propose the use of smart materials, and in particular of organic semiconductors, as efficient and biocompatible optical transducers in the field of regenerative medicine.

Devices able to selectively and precisely modulate the fate of living cells, from adhesion to proliferation, from differentiation up to specific function, upon visible light will be presented. Examples of practical applications, recently reported by our group, include optical modulation of the activity of both excitable and non-excitable cells, control of essential cellular switches like transient receptor potential channels and other cationic channels, as well as effective modulation of intracellular calcium signaling for precise control of cell metabolic processes. We describe fabrication and optimization of micro- and nano-structured polymeric interfaces, in the form of beads and 3D scaffolds, with different cell models. As representative examples, we report on (i) functional interaction with intracellular proteins, leading to non-toxic modulation of the cell redox balance [1,2]; (ii) a novel strategy to gain optical control of Endothelial Progenitor Cell (EPC) fate and to optically induce angiogenesis in vitro [3]; (iii) optical modulation of mesenchymal stem cells and human-induced pluripotent stem cells physiological pathways [4]; (iv) effects of light-sensitive 3D scaffolds on neurogenesis [5]. Current knowledge about the photo-activated processes occurring at the conjugated polymer/living cell interface, obtained by complementing several physical/chemical/biological characterization techniques, is also critically discussed.  The above mentioned study-cases represent, to the best of our knowledge, first reports on use of organic semiconductors for optical modulation of the cell fate, with disruptive perspectives in cell-based therapies. Future opportunities and perspective applications in regenerative medicine will be critically evaluated in the conclusions.

Photovoltaic implants introduce a new wireless method for precise electrical stimulation of tissue using the conversion of light into electrical energy, employing thin layers of organic semiconductors on a flexible substrate. With their remarkable potential for biomedical applications, these implants offer a versatile platform capable of delivering targeted electrical stimuli in the brain, facilitating the development of neuronal networks, and fostering regeneration and neuroprotection following traumatic brain injury [1]. Applications include devices that can be placed on the surface of the brain, or in the form of cuffs wrapped around nerves, which have already been showcased in numerous studies [2,3].

However, these principles may be applied in many other areas. They hold promise for use in electrical nerve conduits. By simultaneously providing guidance and stimulation to regenerating nerves, these conduits can help promote axonal regrowth, reconnection, and functional recovery. The precise control over electrical parameters through light enables tailored interventions, allowing for targeted treatment strategies in cases of nerve damage, peripheral neuropathies, or even spinal cord injuries [4]. On the other hand, the use of optoelectronic devices as capacitive sensors opens up avenues for monitoring tissue properties, neuronal activity and nerve growth, and for investigating brain-diseases in both research and clinical settings.

Our studies emphasize general essential requirements for these different clinical applications. Notably, our focus lies on fabrication methods of new devices, biocompatibility, the distribution of the electric field in biological tissue, and their ability to influence cellular growth.

To assess biocompatibility, Chick Chorioallantoic Membrane (CAM) assays were conducted and tissue was sampled for immunohistochemical studies. Furthermore, colorimetric LDH cytotoxicity assays were used to quantify possible adverse effects of the devices when in contact with primary cell cultures of cortical neurons [5].

In addition to quantifying the biocompatibility of these photovoltaic implants, investigating their generated electric field and long-term stability is imperative to optimize their performance. Therefore, a custom measurement system was employed to characterize the spatial distribution of the electric field in an aqueous solution during stimulation over the span of several hours to several days. By precisely mapping the electric field, we gained insights into the long-term stability of the device, and efficacy and intensity of the stimulation to optimize precise targeting of specific areas with low light intensities while minimizing potential damage to the surrounding tissue.

Furthermore, we utilized in vitro experiments to observe the effects of photovoltaic stimulation on the intrinsic electrical activity, signal transmission and morphology of neuronal cell cultures. Voltage-sensitive dyes provide real-time feedback on the neuronal response to optoelectronic stimulation. Long-term observations of morphological changes using a microscopy setup were used to investigate the phenomenon of electrotropism to give insights into directional cell growth patterns and structural alterations in response to electrical stimulation, to further support the potential of these electrodes to guide and manipulate cellular growth [6].

Through our studies encompassing biocompatibility assessments, electric field mapping, and in vitro experiments, we aim to optimize fabrication steps, increase their performance and promoting research on optoelectronics in biomedical engineering.

All throughout life, from early embryonic development through the operation and interaction of cells and tissues in the adult body up to the process of regeneration, biophysical signals, particularly mechanosensation, play a crucial role. Extracellular mechanical stimuli cause tissue regeneration, which includes processes including cell division, differentiation, migration, and ejection [1,2,3]. Age causes the body's ability to rejuvenate to decline, which negatively impacts on our lives.

The techniques for modulating or controlling mechanical stimulation of cells that are currently available frequently lack the effectiveness, dependability, reversibility, and spatial sensitivity needed for in vitro and in vivo applications. Here, we demonstrate a cutting-edge method for manipulating mechanosensitive ion channels using exogenous organic semiconductors. Materials of this class may be readily processed into a variety of forms, such as thin films, microstructured devices, or nanoparticles, and are totally biocompatible, providing the potential for in vivo use. However, their particular opto-electrical characteristics stand out the most, offering exceptional visible light responsivity as well as electron and ion conductivity.

In this study, we investigate the potential for accurate and efficient regulation of the activation of mechanosensitive ion channels using organic semiconductors, particularly conjugated polymers. We critically examine the outcomes produced by various techniques, such as microstructured devices and polymer thin films.

Our findings may pave the way for the development of cutting-edge smart materials for tissue regeneration triggered by physical stimuli.

An organic photoelectrochemical transistor (OPECT) is an organic electrochemical transistor (OECT), where the output current is controlled by light. OPECT has promising performance in biosensing with transconductance improved up to the physical limit, enhancing sensor sensitivity. However, to render an OECT photosensitive, photoactive materials should be integrated into the device, relying on additional metals, sophisticated nanostructures, and tedious synthetic approaches. This study developed an all-in-one OPECT structure, where a single photosensitive polymeric mixed ionic-electronic conductor was used as the photoactive gate and the channel material. A range of n-type polymeric mixed conductors was studied to understand the material requirements. The OPECT performance was investigated by evaluating the photoelectrochemical characteristics in electrode configuration and inherent OECT properties in dark conditions. We find that the photovoltage induced by light mainly controls the OECT output, the extent of which is controlled by the lifetime of photoinduced species. Using photosensitive polymers with long exciton lifetimes is key to maximizing OPECTs performance for light-gated bioelectronic devices.

The field of Bioelectronics aims to integrate electronics and biology, offering promising opportunities in various domains. However, a major hurdle in this field is the mechanical mismatch between rigid electronics and the soft nature of living tissues. Bioelectronic devices based on soft and flexible materials, developed by using microfabrication and printing techniques, aim to bridge the mismatch between the two worlds. In contrast, biological processes polymerize small molecules to create intricate micromachines. Inspired by biology, we utilize enzymatic processes and thiophene-based oligomer building blocks to in vivo generate organic conductors. By harnessing the advantages of this approach, we successfully achieved the in-situ formation of conducting polymer gels within living organisms. These gels exhibited soft mechanical properties that closely resemble those of natural tissues. Furthermore, we demonstrated the enzymatic construction of organic conductors in various tissues and their application as active materials in organic transistors. Our alternative approach overcomes the limitations of conventional methods, providing opportunities for the development of novel, soft, and bio-compatible electronic interfaces. This paradigm shift in the development of organic bioelectronics opens avenues for healthcare, bioengineering, and beyond.

2D MXenes exhibit a range of interesting properties that make them suitable for healthcare-related applications. These include efficient electronic and ionic charge transport, hydrophilicity, redox activity, biocompatibility, antimicrobial effects, vis-NIR plasmon resonance, photothermal effect (light to heat conversion), tunable surface terminal groups, and structural and chemical tunability.  In addition, MXenes can be synthesized using solution processing in water providing a simple method for low-cost processing of 2D flakes, thin and thick films, aerogels, and hydrogels at scale. Recently, the applications of MXene in healthcare and biomedical applications have seen tremendous activity covering areas such as biosensing, electrophysiology, tissue engineering, antimicrobial and antiviral treatments, and therapeutics.

In this talk, I will discuss the use of MXenes in several devices for biomedical applications. This includes using MXene-based hydrogels as physical and electromechanical sensors (e.g., physical motion, body artifacts, muscle fatigue) including wearable and stand-alone sensors.  The talk will also cover using MXene-based composites as wearable sweat sensors with a unique modular design that enabled a simple exchange of the specific sensing electrode to tailor to the desired analytes to detect multiple biomarkers in sweat. The talk also includes leveraging the ability of MXene hydrogels to absorb ultrasound energy to develop an implantable battery that can be charged remotely from medical ultrasound probes. Promising new directions for MXenes and related composition will be discussed.

Our understanding of the brain and general neural systems is based on models of increasing complexity, from 2D cell culture to organoids and organotypic slices to animal models. These models provide significant insight into neuronal information processing in the brain, but require advanced electrophysiological measurement technologies to achieve long-term stable recordings with single-cell and millisecond space-time resolution. Thus, challenges remain to study information processing between neurons with high spatiotemporal resolution and high signal-to-noise ratio (SNR). These challenges are overcome by well-established planar multichannel devices, but at the expense of signal-to-noise ratio. Without sufficient electrode-cell coupling, planar microelectrode arrays (MEAs) provide low-amplitude signals that are difficult to correctly assign by spike sorting algorithms. Furthermore, the unresolved subthreshold signals lose valuable information that is essential for direct estimation of synaptic weights and correct generation of connectivity matrices in neural networks.

To yield better cell-electrode coupling, numerous vertical nanostructures and nanoelectrodes have been developed by several groups. Here we present the concept of nanocavity (NC) MEAs with vertical nanostraws. High aspect ratio nanostraws (NS) were engineered to initiate tight cell-structure coupling, while the nanocavity reduces the electrode impedance. This combination yields a spontaneous tight mechanical coupling and results in long-term recordings with increased signal amplitude, with no poration-inducing external forces or surface functionalization [1]. Moreover, simultaneous patch-clamp and MEA recordings of the coupled neuron directly demonstrated the capability of our device to record post-synaptic potentials. Here we show that PSP resolution persisted throughout the measurements, indicating a stable and long-term subthreshold amplitude sensitivity.

Simultaneous electrical recordings with good spatial and temporal resolution from 3D neuronal structures (organoids or organotypical slices) is also technological limited. Here we present our recent developments to overcome this limitations by 3D MEA which allow the recording from inside the neuronal tissue [Shihada et al, submitted].

Understanding and modulating neural networks requires high-resolution acquisition of neural activity over time, real-time analysis, and minimally invasive stimulation methods with high specificity. Such procedures are particularly needed for treatment of sensory disfunction (e.g. hearing loss), and certain neurological diseases (e.g. epilepsy). The lack of soft, biocompatible, hybrid and smart neural interfaces hinders our capacity to study complex neural dynamics and efficiently apply responsive neuromodulation therapy. Here, I am presenting the vision of Neural Waves lab towards designing and developing materials and novel fully implantable, contained and responsive neural interfaces that will allow long-term acquisition and closed-loop manipulation of neural circuits with high spatiotemporal resolution over extended period of time to reveal neural dynamics in different neurological pathways and alleviate disfunctions and diseases. I will cover our studies on i) creating artificial basilar membrane based on acousto-sensitive ion-based transistors and soft electronics, ii) innovating electroencephalography interfaces, and iii) utilizing organic perforated multielectrode arrays to investigate the effect of photopharmacological interventions on Cortical Seizures.

Minimally-invasive neuromodulation using low-intensity focused ultrasound (LIFU) holds great promise for treating various neurological disorders. It has been demonstrated to modulate neural activity, promoting both excitatory and inhibitory effects. This capability allows for restoring aberrant neural circuitry or suppressing hyperactive regions, thereby alleviating symptoms associated with conditions such as Parkinson's disease, epilepsy, chronic pain, and depression.

One of the key advantages of LIFU neuromodulation is its combination of high spatial resolution, minimal invasiveness, and extensive coverage of the nervous system. Unlike traditional electrical, magnetic, or optical neuromodulation techniques, which can achieve high-spatial resolution at the expense of high invasiveness and reduced brain coverage, ultrasound waves benefit from low wavelengths, scattering, and absorption in brain tissue and hence, can be focused virtually anywhere in the brain, with high-spatial-resolution and without requiring brain surgery. This reduces the risk of infection, tissue damage, and other complications associated with invasive procedures, making it a safer option for patients, and also allows for accessing a broader range of neural circuits with high precision.

Despite the abovementioned promise, there is still a knowledge and technological gap in LIFU neuromodulation to maximize its potential. LIFU neuromodulation is achieved by means of an ultrasound transducer. These transducers generate low-intensity focused ultrasound waves that can penetrate deep into tissues while maintaining spatial specificity. By adjusting the parameters of the ultrasound waves, specific regions of the brain or peripheral nerves can be targeted with precision. However, similar to their use in medical diagnostic imaging, conventional ultrasound transducers used in LIFU neuromodulation have hand-held form factors and require off-the-shelf equipment. These bulky setups lead to two severe limitations:  in pre-clinical research, the mismatch of size between bulky transducers and in-vitro/in vivo models (mice, rats) impose severe limitations in understanding the effects of ultrasound on the nervous system and how to better apply LIFU neuromodulation for different disease models; secondly, in clinical applications, the use of LIFU neuromodulation can only be applied in a bed-side scenario, where the patient either would visit the clinic once or twice per week to receive a treatment or would operate a LIFU neuromodulation system at home.

This talk will describe the recent research in the field of ultrasound microsystems towards developing the next generation of LIFU neuromodulation systems that can be seamlessly integrated into in vitro/in vivo experimental setups in pre-clinical settings and used as wearable and minimally-invasive devices for clinical treatments. This description will answer two questions: how to massively integrate all the necessary LIFU neuromodulation functionality into a single-miniaturized and battery-powered microsystem? How can ultrasound microsystems be designed to be mechanically flexible to better adjust to the body's natural curvature?

To answer these questions, the talk will focus on novel ultrasound microfabrication and microsystem integration methods and the next-generation ultrasound electronics, while showing a few examples of ongoing projects featuring in vitro and in vivo validation showcasing the potential of LIFU microsystems for minally invasive and precise neuromodulation for the treatment of neurological diseases.

The effectiveness of many chemotherapeutic agents in treating cancer is limited by poor delivery efficiency and systemic toxicity. Local chemotherapy approaches utilizing iontronic devices present a promising solution for efficient interference with cancer growth and tumor size reduction. We use iontronic devices with incorporated membranes to enable the continuous delivery of chemotherapeutics with high spatiotemporal resolution. We operate freestanding iontronic pumps with the the chemotherapeutics Gemcitabe (Gem) named GemIPs to treat a GBM model on the chicken chorioallantoic membrane. In addition, we compare results with a conventional topical daily treatment. We see that both administration techniques induce G2-phase cell cycle arrest and apoptosis. Remarkably, growth inhibition was achieved only with the steady Gem dosing with GemIPs, but not with daily topical drug administration at the maximum dosage amounts that was not lethal for the chick embryo. I will discuss how the different transient concentration profiles between the techniques generates this difference in outcome. 

The generation of in vitro platforms capable of mimicking the in vivo situation as an alternative to animal models and/or monitoring cellular processes is necessary for medicine and drug discovery [1]. In this sense, Smart Bioelectronics arise from the combination of smart functional materials, bioelectronics and microfluidics, making Smart Bioelectronics a powerful tool to control cellular microenvironments.

Smart functional materials such as poly(N-isopropylacrylamide) (pNIPAAm) can undergo structural changes due to their inherent lower critical solution temperature (LCST) phase transition in water at 32 ºC. On its side, poly(3,4-ethylenedioxythiopene):poly(styrene sulfonate) (PEDOT:PSS) is a widely used conducting polymer in the bioelectronics field, due to its mixed ionic and electronic conduction properties. When mixing both polymers, the developed PEDOT:PSS/pNIPAAm co-polymer modulates cellular adhesion/detachment of cancer cells and the electrochemical monitoring of the process [2-3].

Moreover, PEDOT can be tailored biochemically and mechanically to replicate a specific tissue. PEDOT polymers made in combination with biopolymers and glycosaminoglycans such as collagen and hyaluronic acid can be used in the generation of 3D bioelectronic interfaces with physiologically relevant conditions [4-5]. On the other hand, microfluidic devices offer optical transparency, miniaturization, and controlled media perfusion required in organ-on-a-chip models. The interface between 3D bioelectronics and microfluidic devices enables the real-time electrical and optical monitoring of cellular processes in a controlled microenvironment.

Here, we present an overview of different 2D and 3D Smart Bioelectronic interfaces for the simultaneous electrical and optical monitoring of cancer cell migration.

Research on electrolyte-gated and organic electrochemical transistor (OECT) architectures is motivated by the prospect of a highly biocompatible interface capable of amplifying bioelectronic signals at the site of detection. Despite many demonstrations in these directions, a quantitative model for OECTs as impedance biosensors is still lacking. We overcome this issue by introducing a model experiment where we simulate the detection of a single cell by the impedance sensing of a dielectric microparticle. The highly reproducible experiment allows us to study the impact of transistor geometry and operation conditions on device sensitivity. With the data we rationalize a mathematical model that provides clear guidelines for the optimization of OECTs as single cell sensors, and we verify the quantitative predictions in an in-vitro experiment. In the optimized geometry, the OECT-based impedance sensor allows to record single cell adhesion and detachment transients,  showing a maximum gain of 20.2±0.9 dB with respect to a single electrode-based impedance sensor.

The common methods for in-vivo delivery of biomolecules  are strongly limited by invasiveness and/or lack of quantitative delivery control. These limitations can be overcome by the Organic Electronic Ion Pump (OEIP), that electrophoretically delivers ions without fluid flow and ions backflow from tissue, enabling quantitative studies. The capillary-based OEIPs have been demonstrated to be minimally invasive, however, the micro-scale glass capillaries are brittle, thus tend to break during insertion in harder tissues. In this work, we developed flexible and robust OEIPs based on polyimide-coated glass capillaries, enabling their insertion in a wide range of biological tissues. We provide evidence that sufficient intensity of blue light penetrates via the polyimide coating, although it is commonly accepted that polyimide’ high optical absorption prevents polymerization using high energy light. Using low cost, water soluble photoinitiators and blue light, we established a cheap and environmentally safe system for photo-crosslinking via polyimide coating.

The resulting OEIP devices can reliably deliver abscisic acid (ABA), the so-called plant stress hormone, one of the most challenging substances delivered using iontronic devices. The developed OEIP was applied to deliver ABA directly into the petiole of intact Arabidopsis leaves, establishing an advanced petiole feeding tool. In contrary to the conventional petiole feeding assays, OEIP enables ion delivery to intact plants with a high control of the delivered dose and elimination of the disturbances induced by convective delivery. By delivering ABA to the petiole, we triggered immediate and long-lasting stomata closure, without observable wound effect, demonstrating the high potential of the developed bioactuator. The mechanism of the induced stomata closure was studied by delivering endogenously absent deuterium-labeled ABA, confirming that the closure was induced by the delivered ABA ions that were distributed to the leaf blade by the plant vasculature.

Bacterial infections are one of the major threats to public health, food safety and development which makes it is necessary develop materials and strategies that limit or prevent these bacterial proliferations and biofilm infections.[1] Although, medical implants have led to dramatic improvement in patient's health and well-being, they are accompanied by drawbacks that include surgical risks during placement or removal, implant failure and more specifically microbial infections. These implant-associated infections are mainly caused by the bacterial bio-films in which bacteria are more recalcitrant towards treatments. Indeed, implant surfaces are non-vascularized abiotic materials rendering the common strategies inappropriate and ineffective.[2] In this context we have designed and developed innovative and smart interfaces based on phosphonium self-assembled monolayers (SAMs)  that can be electrically activated on-demand for eradicating bacterial infections on solid surfaces. Hence, upon electroactivation, a successful eradication of gram-positive and gram-negative bacterial strains has been clearly highlighted on SAM-modified titanium surfaces. Subsequently, we observed 95% and 90% antibacterial efficiencies against Staphylococcus aureus and Klebsiella pneumoniae. More importantly, no cytotoxicity has been observed towards eukaryotic cells which clearly demonstrates the biocompatible character of these novel surfaces for further implementation.

Additionally, in our ongoing work, we have explored the synergistic relationship between electrical stimulus for drug delivery and wound healing. Our bodies naturally generate endogenous electrical fields in order to facilitate the migration of fibroblasts, keratinocytes, macrophages, epithelial cells and ions to the wound site to speed up the healing process.[3] In this regard, we have designed and developed electrochemically polymerized polypyrrole films deposited on ITO substrates encapsulated with antimicrobial peptides, which can be released in a controlled manner upon electrical application. Apart from exploring the phenomenon of electrotaxis in wound healing as a consequence of applying an exogenous electrical field, the bioelectric effect is also being studied in depth to understand the mechanisms by which applied electrical fields render the surface antimicrobial. We highlight the advantages of using electrochemical deposition as a technique for film formation as it allows for precise control over film thickness, surface roughness and homogeneity, and can expand the application for these films to not only as electrically responsive wound healing patches, but also as coatings for food packaging and other wearable electronics. These films have been characterized and their properties have been thoroughly studied using various techniques which further support the successful antimicrobial encapsulation throughout its internal framework. Finally, the biocompatible nature of these films supports their potential in various applications.

1.Tacconelli, E.; Carrara, E.; Savoldi, A.; Harbarth, S.; Mendelson, M.; Monnet, D. L.; Pulcini, C.; Kahlmeter, G.; Kluyt-mans, J.; Carmeli, Y.; Ouellette, M.; Out-terson, K.; Patel, J.; Cavaleri, M.; Cox, E. M.; Houchens, C. R.; Grayson, M. L.; Hansen, P.; Singh, N.; Theuretzbacher, U.; Magrini, N. (2018) Lancet Infect. Dis.18, 318-327.

2. Carrara, S.; Rouvier, F.; Auditto, S.; Brunel, F.; Jeanneau, C.; Camplo, M.; Sergent, M.; About, I.; Bolla, J.-M.; Raimundo, J.-M. Int. J. Mol. Sci. 2022, 23, 2183. https://doi.org/10.3390/ijms23042183

3. Farber, P. L., Isoldi, F. C., & Ferreira, L. M. (2021). Electric Factors in Wound Healing. Advances in wound care, 10(8), 461–476. https://doi.org/10.1089/wound.2019.1114

Inherited retinal dystrophies and late-stage age-related macular degeneration, for which treatments remain limited, are among the most prevalent causes of legal blindness. Retinal prostheses have been developed to stimulate the inner retinal network; however, lack of sensitivity and resolution, and the need for wiring or external cameras, have limited their application. Here I report on the use of conjugated polymer nanoparticles (P3HT NPs), showing that they mediate light-evoked stimulation of retinal neurons and persistently rescue visual functions when subretinally injected in a rat model of retinitis pigmentosa. In particular I will report on recent results showing that the organic liquid prosthesis is effective also in retinas that have undergone a process of rewiring caused by the loss of photoreceptor function. I will discuss a numerical model that trys to capture the essential nature of the photostimulation mechanism by numerically solving the Poisson-Nernst-Planck (drift-diffusion)  equation with proper boundary conditions taking into account theelectron transfer processes occuring at the interface. 
 

Currently, on-skin wearable or on-skin devices mainly rely on power sources such as non-rechargeable batteries, which are often toxic and harmful to the environment. Therefore, there is a strong need to develop new self-powered energy sources that possess human- and eco-friendly characteristics, including biocompatibility, degradability, and breathability. In this context, biofriendly and sustainable triboelectric nanogenerators (TENGs) emerge as excellent candidates for the next generation of green energy sources. TENG devices harness mechanical energy from various activities and environments, such as biomechanical motions and convert it into electrical energy. They are are cost-effective, easy to fabricate, and highly efficient, making them suitable for self-powered electronics and independent power source modules. Although there is a wide range of triboelectric materials available, many TENGs still rely on fluorinated polymers, which are known to be non-environmentally friendly and may cause discomfort and skin infections when used in on-skin wearables. To address these challenges, we demonstrate a cellulose-based tribopositive layer that enhances the TENG power output by introducing different surface functional groups through nano-coating or chemical/mechanical reduction to form nano-crystals or fibers. Additionally, we report on a new bio-polymer-based tribonegative layer, mimicking the chemical structure of conventional non-biodegradable materials. In the pursuit of a completely biodegradable TENG, we replace the substrate with a biopolymer film and employ carbon-based electrodes. These bio-TENGs offer flexibility, biocompatibility, and breathability, making them suitable for use as wearable devices that can harvest energy from biomechanical motions. Notably, these devices exhibit high performance with output voltage values surpassing 1 kV. This represents a twofold increase compared to conventional substrates and electrode materials employing polyimide as a negative triboelectric layer. Additionally, in the case of all-biopolymers-baed TENGs, the device output exceeds 500 V, which outperforms other reported bio-TENG devices in terms of voltage output generation. 

Bioelectronic devices show great promise in healthcare and environmental sensing due to their ability to provide longitudinal monitoring to maintain optimal status and evaluate physical and (bio)chemical changes. Electrochemical (bio)sensors are at the centre of this effort and offer a vast potential to revolutionize conventional diagnostics and environmental sensing methods that uses traditional laboratory tests-based evaluations, that are slow and mainly require in-person visits or frequent sampling if the long-term analysis is necessary.

In this presentation, I will give a brief overview of our recently developed electrochemical methodologies targeting of sensing and monitoring of various metabolites, hormones and microorganisms to acquire better knowledge on diagnosis and disease progression of diseases and environmental changes. This talk will summarize how to design sustainable sensors, and integrated electronics and how to use them in clinical and environmental settings with our unique access to patient materials and environmental samples, which creates an unprecedented opportunity to address fundamental questions in medical and environmental monitoring.   

The plant cell is protected by a complex polysaccharide cell wall composed primarily of cellulose, hemicellulose and pectin. This wall stabilizes a semi-permeable barrier, the plasma membrane (PM) that serves two main roles: (1) transport of essential molecules in and out of the cell, and (2) sensory transduction of environmental stimuli. Considerable progress has been made over the past two decades in understanding plant membrane proteins from a genetic perspective, but complementary tools for physiological, electrophysiological, and biochemical characterization necessary for studying protein functions are lacking. This work promotes a new cell-free, bioelectronic platform that captures the properties of green plant PMs and enables the measurement of plant transporter functions.

Monitoring the flux of metal ions across plant cell membranes through protein transporters embedded within them is a significant challenge today, but is fundamental for assigning function to unknown transporter genes; tackling transporter substrate specificities and modes of regulation; and eventually linking metabolic pathways to cellular compartments, plant growth and development, and bridging the genotype to phenotype gap. Today's technologies are inadequate for a number of reasons, including low throughput and lack of sensitivity, especially for transporters, which have fluxes several orders of magnitude lower than ion channels.

            In this presentation, I will share a new technology that combines planar green plant membranes with transparent, electrically conducting polymer electrodes for the dual-mode (optical or electrical) measurement of plant protein functions. Organic electrochemical transistors (OECT) based on the conductive polymer PEDOT:PSS offer biocompatibility, high-quality electrical signals, and optical monitoring due to the transparency of PEDOT:PSS thin films. We demonstrate here the application of the OECT to the measurement of copper transporter 1 (COPT1), which maintains plant copper homeostasis, but its function has not been wholly characterized. We formed a supported lipid bilayer (SLB) with membranes from transient GFP and GFP-COPT1-transfected Arabidopsis thaliana mesophyll protoplasts on the surface of the OECT. We measure copper flux through COPT1 in a specific and concentration-dependent manner. After data analysis, we obtain kinetic parameters of transport for COPT1 and report on the coupling of COPT1 with another protein, a copper reductase.

This new kind of plant-derived sensor device is amenable to scale up and we anticipate that it can be highly multiplexed for the collection of large data sets on plant transporter systems in a way that has not been possible before. With this capability, such large data sets can be fed into big data science approaches for enabling discoveries and breakthroughs in our understanding of how plants adapt to genetic perturbations, extreme weather conditions, pathogen pressures, and other critical aspects important for flourishing ecosystems.

The possibility to control living matter with exogenous stimuli can have tremendous impact on synthetic biology, medicine and materials science, among others. For instance achieving control over cells behaviour remains a challenge at the interface between living and non-living matter,^[1] and would enable the development of new bio-mimetic and bio-enabled materials able to perform tasks.^[2] Within this context, bacteria have arisen as “active and actively-controllable materials”, exhibiting neuro-like behaviour, extended bioelectric signalling^[3,4] and tunable assembly properties.^[5] In the last decade, it has been observed that the regulatory element of such an active behaviour is the electrical potential across the membrane, which governs bacteria electrophysiology, metabolisms and bioenergetics.^[6] Light can be a powerful tool in these regards, as one can control the membrane potential and, thus, cell function and behaviour remotely and with relatively high spatiotemporal precision.

Here, I will show that a membrane-targeted azobenzene can be used to photo-modulate precisely the membrane potential in cells of the Gram-positive bacterium Bacillus subtilis. We found that upon exposure to blue- green light, the isomerization reaction in the bacteria membrane induces hyperpolarisation of the potential (ΔV = 20 mV), within a bio-mimetic mechanism reproducing the initial fate of retinal. Apart from being promising results in the view to photocontrol bacterial motion and assembly behavior in consortia, this approach also highlights the role of previously uncharacterized ion channels in bacteria electrophysiology.^[7]

The interface between biological cells and non-biological materials has profound influences on cellular activities, chronic tissue responses, and ultimately the success of medical implants and bioelectronic devices. For instance, electroactive materials in contact with cells can have very different composition, surface topography and dimensionality. Dimensionality defines the possibility to have planar (2D), pseudo-3D (planar with nano-micropatterned surface) and 3D conductive materials (i.e., scaffolds) in bioelectronics devices. Their success for both in vivo and in vitro applications lie in the effective coupling/adhesion of cells/tissues with the devices’ surfaces. It is known how a large cleft between the cellular membrane and the electrode surface massively affects the quality of the recorded signals or ultimately the stimulation efficiency of a device. In fact, the shape and the composition of these newly designed electrodes recalls those features of neuronal cells to ultimately induce biomimetic recognition. Furthermore, conductive materials that exhibit dynamic properties and organic composition might better recapitulate the native environment of tissue. However, engineering such new platforms still require materials synthesis, integration into microfabricated platforms and stable cell interfacing. Here, we propose a new class of organic conductive materials which resemble the biomimetic architecture of neurite and dendritic spines, can undergo dynamic reshaping and can be functionalized with artificial membrane to enhance cell coupling and outgrowth. The cell response can be monitored and eventually is adapting to the substrate changes over time. These new electrodes can pave the way to adaptive microdevices of use in bioelectronic applications such as electrophysiology and sensing.

Traditional electronic devices are made of non-renewable and often toxic materials, which can lead to serious environmental contamination upon their disposal. A promising strategy for producing sustainable electronics is the direct writing of laser-induced graphene (LIG) electrically conductive patterns on biological and bio-based substrates. However, high ablation rates, the need to use controlled atmosphere, toxic fire retardants and multiple lasing steps limit the applicability of conventional LIG processes to produce sustainable electronic devices.

We have introduced iron-catalyzed laser-induced graphitization (IC-LIG) as an innovative technique enabling to engrave large-scale electrically conductive patterns on thermally sensitive substrates such as wood and wood-derived materials [1]. Our approach makes use of an aqueous bio-based coating, inspired by the historical iron-gall ink, which protects the wood surface from laser ablation and thermal damage while preserving its mechanical properties. Thanks to our approach, it is possible to engrave highly conductive (up to 2500 S m-1) patterns even on thinnest wood veneers (> 400 µm) and cellulose paper within a single lasing step in ambient atmosphere using a conventional CO2 laser setup.

Here, we explore further the possibilities offered by our IC-LIG approach by elucidating the catalytic effect of iron under different lasing conditions. We can control the iron-carbon composite structure at the nano- and microscale level, e.g., by tuning the concentration of iron in the ink. This, in turn, allows us to tune the iron phases in the resulting IC-LIG materials. By precisely controlling the laser parameters and setup we are able to fabricate bio-inspired surface patterns at the meso- and macroscale, controlling the structure as well as the electrical properties on a multiscale level, allowing us to fabricate sustainable electrodes for prospective uses as energy storage and electrochemical devices.

[1] C. H. Dreimol et al., Nat. Commun. 2022, 13, 3680 (12 pp.).]

In vitro studies have a significant impact on the progression of novel therapies, cancer and stem cell research, and the drug discovery process. However, the current standard for in vitro models primarily relies on two-dimensional (2D) cell cultures, which fail to fully replicate the intricate cellular architecture and response to microenvironmental cues. To address this limitation, three-dimensional (3D) cell cultures have emerged as more accurate representations of the in vivo cellular environment. Tissue-engineered scaffolds are particularly promising in this regard. However, existing technologies for assessing 3D cell cultures are predominantly limited to endpoint assays, offering only a snapshot of cellular behavior. In this study, our goal is to overcome this challenge by employing continuous electrical assessment of 3D cell cultures cultivated on electroactive composite scaffolds composed of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and MXenes. The scaffold architectures are created using the freeze-drying technique, and we investigate the influence of different scaffold compositions on electrochemical performance, morphology, swelling, biocompatibility. By combining the electroactive properties of PEDOT:PSS with the distinctive characteristics of MXenes, we aim to develop scaffolds that not only support cell growth but also enable real-time, non-invasive monitoring of cellular behavior. Our study surpasses conventional optical-based assessments by introducing continuous electrical measurements as a means of tracking the dynamics of 3D cell cultures. The electroactive composite scaffolds facilitate the detection of electrical signals associated with crucial cellular activities like attachment, proliferation, and differentiation. To evaluate the performance of the electroactive composite scaffolds, we culture them with Human Dermal Fibroblasts and assess parameters such as cell attachment, viability, and growth. By integrating the benefits of 3D cell culture and continuous electrical assessment, our study aims to comprehensively characterize scaffold-cell interactions and their potential applications in tissue engineering and regenerative medicine.

Biofilm, the predominant lifestyle of all bacterial species, is a form of bacterial growth that enhances survival in wetted natural and artificial environments. The accompanying resilience, including decreased susceptibility to disinfectants and antibiotics, increases the need for prevention of biofilm formation, particularly on implanted medical devices and on food contact surfaces. This has prompted a revision of traditional methods and practices, re-evaluating them in relation to bacterial adherence and growth. The metabolism of bacteria growing in biofilms compared to those undergoing planktonic growth differs vastly. One important determinant is the redox state of the microenvironment in which bacteria exist. Sensing of the environmental redox state controls the switch between aerobic and anaerobic metabolism as well as bacterial virulence. We showed previously that electrically charged surfaces with high charge storage capacity, like PEDOT-based conducting polymers, can be used to modulate biofilm formation by altering the redox states of the surfaces [1, 2]. To gain better understanding of this finding, we performed an in-depth analysis of the process of biofilm formation on redox-challenged PEDOT:PSS surfaces using GFP-expressing Salmonella and the optotracer EbbaBiolight 680. The latter is a non-toxic fluorescent tracer that allowed us to monitor and quantify the production of extracellular matrix components (ECM) in real-time by semi-quantitative spectroscopy and microscopy [3]. Redox challenge performed in a fast-charging electrochemical setup promoted bacterial production of higher amounts of cells and ECM on oxidized PEDOT:PSS surfaces compared to their reduced counterpart. When electrodes were separated and charging was carried out with respect to a Pt electrode, the slower charging process resulted in increased cell numbers as well as increased amount of ECM on the reduced surfaces. When isogenic Salmonella mutants unable to produce the ECM components curli and/or cellulose were tested, none of them responded to the redox challenge. This demonstrates a novel use of surface redox potential to modulate ECM curli production and accordingly biofilm formation. Anti-biofouling surfaces directly affecting ECM production may find use in sensitising biofilm forming strains to the effect of antibiotics and antimicrobial compounds.

Leveraging the biocatalytic machinery of living organisms for in-vivo fabrication of functional bioelectronic interfaces enables seamless integration of devices in tissue and formation of biohybrid systems. Previously we have demonstrated that plants can polymerize conjugated oligomers in-vivo forming conductors within their structure. We showed that the polymerization is enzymatically catalyzed by endogenous peroxidases, and we developed a series of conjugated oligomers that can be enzymatically polymerized in physiological conditions. The conjugated polyelectrolytes integrate within the plant cell wall structure adding electronic functionality into the plant that is then explored for energy storage. Recently we demonstrated intact plants with electronic roots that continue to grow enabling plant-biohybrid systems that maintain fully their biological processes. The electronic roots are used to build supercapacitors and biohybrid circuits to power low power electrochemical devices. Furthermore, we have extended this concept into an animal model system. We demonstrated that Hydra, an invertebrate animal, can polymerize intracellularly conjugated oligomers in cells that expresses peroxidase activity. The conjugated polymer forms electronically conducting and electrochemically active domains in the µm range integrated within the hydra tissue. Our work paves the way for self-organized electronics in plant and animal tissue for modulating biological functions and in-vivo bio-fabrication of hybrid functional materials and devices.

Advancements in synthetic biology have pushed the frontier of materials science into the realm of engineering living materials. This presentation focuses on bioengineering strategies for coupling the electronic metabolisms of living cells with electrodes. Building on recent discoveries in the extracellular electron transfer mechanisms of S. oneidensis, our research focuses on the heterologous expression of key cytochromes in a facultative anaerobe (E. coli) [1-2]. We employ a combination of colorimetric and electrochemical techniques to characterize extracellular electron transfer in these engineered microbes. Interestingly, the bioengineered strains exhibit enhancements in both mediated and non-mediated extracellular electron transfer, with the extent varying with the specific combinations of expressed proteins. This platform was used to demonstrate enhanced electricity production for applications such as waste water treatment. Importantly, this work represents the first demonstration of the complete electron conduit from S. oneidensis fo bioeletcricity genertaion in a foreign cell. This demonstartion significantly broadens the range of exoelectrogenic microbes, unlocking new applications in microbial electronics across various fields such as biotechnology, environmental science, chemical synthesis, and energy conversion.

Inspired by biocatalysts in nature, artificial catalyst systems with behavior similar to or exceeding the activity of biocatalysts have been widely studied for different healthcare and environmental applications. In this work, a hybrid organic-inorganic approach is used to combine conducting polymer with inorganic materials for biocatalysis. Three different MoS2 nanosheets (MSNSs) were synthesized based on different methodologies. Methodology 1:  ammonium tetra thiomolybdate (NH4)2MoS4 and hydrazine hydrate (N2H4·4H2O) were sonicated and transferred to an autoclave for the hydrothermal process. Methodology 2: MoS2 nanosheets were synthesized through a hydrothermal method using sodium molybdate Na2-MoO4.2H2O and L-cysteine. Methodology 3: MoS2 nanosheets were prepared through exfoliating of bulk MoS2 in N, N-Dimethylformamide (DMF) by sonication process. The morphology, and structural information of MSNSs were analyzed by TEM, SEM, XRD and Raman spectroscopy. Initial results show excellent catalytic performance of the MSNs with different concentrations of hydrogen peroxide ranging from 1µM to 10M. The catalytic behavior of the MSNSs were then compared with the performance of hydrogen peroxidase within the same range of concentration values.

Eman Aljawi, Akbota Kurmangaliyeva, Muhammad Jamali, Bushara Fatma, Waqas Waheed, Dean Everett, Charalampos Pitsalidis, Anas Alazzam, and Anna Maria Pappa.

“Bioelectrocatalytic lab on chip device for infection biomarker monitoring”

Viruses can easily mutate, as evidenced with SARS-Cov2, hence prevention and early detection of infection seems to be the most reliable strategies to cope with pandemics. The current available diagnostics tools, such as real-time polymerize chain reaction (RT-PCR), are not compatible with early detection as they are time-consuming, expensive, don’t offer multiplexing, and don’t offer on-site detection. To tackle these issues, Lab-on-Chip (LoC) biosensors have emerged, overcoming the limitations of conventional methods. Electrochemical biosensors mainly consist of electrodes integrated into a platform to offer portable, on-site, cost-effective, specific, and fast detection. This project introduces a multiplexing LoC biosensor for the simultaneous detection of 4 infection biomarkers; glucose, lactate, hydrogen peroxide, and C-reactive protein (CRP) all in one device using biocatalytic enzymes for the three metabolies and an antigen for CRP as biorecognition elements. Optimization on the electrode materials in terms of bioelectrocatalytic performance leads to the optimum sensing capabilities while allowing for multiplexing on a chip. This work compbines LoC technologies based on microfluidics and the recent advancements in materials science, combining conducting polymers with 2D electronic materials for the electrode fabrication.

The assembly of supramolecular structures within living systems is an innovative approach for introducing artificial constructs and developing bio-materials capable of influencing and/or regulating the biological responses of living organisms. By integrating chemical, photophysical, morphological, and structural characterizations, we show that the cell-driven assembly of DTTO into fibers results in the formation of a 'biological assisted' polymorphic form, hence the term bio-polymorph. Indeed, X-ray diffraction revealed that cell-grown DTTO fibers present a unique molecular packing leading to specific morphological, optical, and electrical properties. Monitoring the process of fibers formation in cells with time-resolved photoluminescence, we established that cellular machinery is necessary for fibers production and postulated a non-classical nucleation mechanism for their growth. These biomaterials may have different applications for the stimulation and sensing of living cells, but more crucially, the study of their genesis and properties broadens our understanding of life beyond the native components of cells.[GL1]

[GL1]Questa frase è bella, ma va oltre il contributo che stiamo dando, mi pare. Lascio a te decidere, ma noi la toglieremmo.

Signaling in physiological environments relies on physicochemical cues and biomolecular that are all processed by the cellular machinery to execute a specific response. In this presentation, designer functional peptides will be discussed as synthetically engineered materials that could enable the transduction of light to cellular cues for controlling the behavior and anisotropy of excitable cells such as cardiomyocytes. First, the structural tunability of the assembly behavior of peptides bearing optoelectronic π-conjugated units in aqueous solutions and on surfaces to generate nano- and micropatterns are discussed. While the supramolecular assemblies of these peptides can have dynamic structures in physiologically relevant solutions, on surfaces that have anisotropic topography, the resulting self-assembled optoelectronic peptides can be directed to form 1-D nanostructures with ordered molecular interactions between π-units. Additionally, fabrication approaches that allow for the generation of micropatterns of π-conjugated peptides that are stable under electrolytic cell culture media will be shown. The distinct capability of these patterned π-conjugated peptides to align cardiomyocytes interfaced with these materials will also be discussed. This property provides the potential opportunity for directional stimulation of excitable cells with spatiotemporal control, especially when the stimulation is initiated using light. Finally, material design insights that allow for enhanced photoconduction by these designer peptides will also be presented. Overall, we envision these functional peptides as transducer biomaterials that can offer a new paradigm for having systematically controlled cell-material interactions towards tissue engineering and in vitro modeling applications for excitable cells.

The employment of organic semiconductors (OSCs) promises to widen the realm of electronics to countless new applications, thanks to the advantageous properties of organics. Effectively, the field of organic electronics has been forging ahead from its initial proof-of-concept devices towards increasingly diverse materials and applications.

State-of-the-art high performance OSCs are derived from petrochemicals. Nevertheless, this class of materials can also be based on renewable, natural resources. Indeed, nature offers an extraordinary variety of systems that exhibit diverse opto-electronic functionalities. For instance, colours can vary in plants depending on the specific function, weather conditions and health/life cycle stage. Molecules responsible for this property are often dyes and pigments that show π-electron delocalization within their molecular structure and hence, that are potentially prone to showing optimal charge carrier transport properties and frontier energy levels compatible for charge injection.

Effectively, different natural molecules have been reported to display semiconducting properties and few of them have been used as active layers for electronic devices, e.g., organic thin film transistors (OTFTs). For instance, carotenoids are an interesting class of molecules, owing to their widespread availability in a large range of plants, algae, bacteria and fungi. They are hence compatible with a circular economy model, unravelling novel sustainable scenarios in organic electronics, besides being edible, thus contributing to the growth of the rising field of edible electronics. In this work we will show how a fine microstructural tuning of these materials can lead to the fabrication of efficient OTFTs with reasonable stability. Such results indicate that options for sustainable, edible semiconductors are available and can be exploited towards the integration into logic circuits.

The use of light to control the activity of different cell-types has recently come at the forefront of the scientific community thanks to a series of key-enabling features (i.e. spatial/temporal selectivity, and lower invasiveness). Optogenetics is probably the prime example of this approach and since its initial development in neuroscience has been extended to other fields. However, the need of viral gene transfer, required to induce light-sensitivity in the target organism, strongly impairs the clinical translation of optogenetics-based systems. To overcome this issue, non-genetic (geneless) optostimulation is a growing and multidisciplinary field of research at the border among physics, material science and biology that aims to achieve light sensitivity with photoactive actuators. I will present promising photoactuators for cardiac applications, focusing in particular on excitation-contraction coupling modulation. Future clinical perspectives in contexts where the possibility of obtaining precise control of cardiac cell activity could offer new insights (e.g. resynchronization and arrhythmia termination) will also be discussed.

Nature has evolved in a hierarchical manner to achieve outstanding material properties and complex organismal behaviours. Hierarchy is a ubiquitous organizing and functional principle of natural systems, which are controlled in size, shape and pattern. The properties of skeletal muscles mainly rely on their hierarchical structure, composed of fibrous actuators organized in different levels of aggregation (from cm down to nm). This strong hierarchical organization gives muscles their remarkable time-dependent viscoelastic properties, and their efficient hierarchical actuating organization at different levels, from the single sarcomere to the muscle fascicle. 

Muscles are an optimized mechanism over a million years of evolution, and have inspired artificial actuators [1]. Despite that, current actuation technologies are not able to recapitulate the features of natural skeletal muscles. The possibility to grow fully functional living muscles in vitro and use them to power soft machines has the potential to revolutionize robotics, in the long term.

Biohybrid actuation is born as a new and extremely promising actuation method, which combines a live entity, like muscle cells, with an artificial substrate to produce a mechanical movement generated by the contraction of muscle cells. Attractive advantages feature this kind of biological actuator as performance invariance with scalability (from nm to mm), high transduction efficiency, and high power-to-weight ratio. Biohybrid actuators have the potential to deliver remarkable performance with life-like movements at the macroscale to artificial devices. Biohybrid actuators usually rely on a bottom-up approach and include systems based on cardiomyocytes, insect self-contractile tissues, and engineered skeletal muscle tissues (from both mammals and insects), which can convert chemical energy from the environment into mechanical energy. Skeletal muscle cells are the muscle cell types that have generated the most interest because they may be regulated to contract in response to specific stimuli, such as chemical, electrical, or optical signals, following suitable optogenetic changes [2]. There are several examples of bio-hybrid actuators and robots in literature, as the bio-bots can walk or swim [3]. Despite that, the use of a bio-hybrid actuator to actuate a medical device as a catheter has never been explored, so far.

Catheterization is one of the most promising approaches for the targeted treatment of several diseases, including cancer. Indeed, the local administration of medications or chemicals in the area of interest may maximize the therapy efficacy, reducing side effects. Here, we report the concept and an early investigation of a novel intravascular steerable catheter powered by an on-board biohybrid actuator on its tip to navigate deep and tortuous regions within the cardiovascular systems. The catheter performance has been analyzed by analytical and numerical analyses, assessing the influence of the catheter geometrical (e.g., inner and outer radii, wall thickness) and physical (e.g., stiffness) parameters, the actuator geometrical parameters (e.g., length and positioning over the catheter tip) and contractile force. The findings demonstrate the necessity to lower the outer diameters and decrease wall thickness to maximize the catheter deflection. Also, we assessed the influence of the positioning of the biohybrid actuator as the applied forces. These preliminary results hold a lot of promise in light of future experiments using this type of actuation to drive microcatheters through the cardiovascular network, even though the performance of this concept still needs to be improved to match relevant anatomical targets, as the radius of curvature of the inner branches of organs.

The vast expansion of available synthetic biology tools has led to explosive developments in the field of materials science. The increased accessibility of these tools has pushed the frontier of materials science into the field of engineering biological and even living materials. By coupling the tunability of nanomaterials with the prospect of re-programming living devices, one can re-purpose biology to fulfil needs that are otherwise intractable using traditional engineering approaches.

Optical technologies in particular stand to benefit from the untapped potential in coupling the optical properties of nanomaterials with the specificity and scalability of biological materials. This presentation highlights applications in sensing and energy technologies that exploit the synergistic coupling of nanobio-hybrid materials. This talk will focus on the development of living electronics, such as photovoltaics based on photosynthetic organisms with augmented capabilities. The development include advancements in electrode engineering as well as biological engineering of living organisms. The talk will also discuss nanobionic approaches that focus oin infusing synthetic nanoparticle with living cells.

The control of biological functions is crucial for the in-depth understanding of physiological/pathogenic processes, as for the development of novel, ad hoc therapeutic modalities to fight specific diseases. In this regard, light-induced cell control is characterized by lower invasiveness, better space and time resolution, with respect to more traditional electrical-based methods. Exogenous inorganic and organic semiconducting materials have attracted considerable interest, since they can be employed as photoactive transducers to trigger the biological activity, without any need for viral transfection [1]. In particular, semiconducting polymers offer great biocompatibility and stability together with geometrical adaptability. Among them, the green light-absorbing poly(3-hexylthiophene) (P3HT) was successfully employed for the modulation of the physiological activity of different cell models [2-4], including the boosting of both proliferation and tubulogenesis of endothelial cells [5]. The latter result is particularly appealing in view of the regeneration of the cardiovascular tissue for application in cardiovascular disease therapies.

Here, we realize smart biointerfaces between red-light absorbing conjugated polymers and cardiovascular cells. The aim of our work is to study the cellular response both to the polymers alone and in combination with red light excitation. The latter is particularly favorable in view of in vivo applications, given the higher penetration of red light within living tissues, as compared to lower visible wavelengths. We show that conjugated polymers in form of nanoparticles lead to either enhancement or reduction of the angiogenic response of model endothelial cells, depending on the material type and the presence/absence of the light stimulus. Furthermore, we observe that semiconducting polymer thin films efficiently modulates, upon red light photoexcitation, the physiological properties of Cardiomyocytes. In particular, we demonstrate that polymer-mediated photostimulation modulates both the Ca²⁺ dynamics and the electrical properties of the cells. Very interestingly, we observe an anti-arrhythmogenic effect, unequivocally triggered by polymer photoexcitation.

Overall, our results support the possibility to employ red light-responsive conjugated polymers to regulate cardiovascular functions, in a drug-free, touchless, repeatable, and spatio-temporally controlled manner.

With the recent trends in hydrogen technologies, scale-up fabrication of membrane electrode assemblies (MEAs) for the electrochemical systems such as fuel cells and electrolyzers is gaining significant attention. Companies and researchers are focusing on diverse large-scale electrode fabrication processes, such as roll-to-roll and screen-printing. However, optimizing such processes is not trivial, and a number of parameters, including but not limited to catalyst type, solvent, ink mixing, electrode coating and drying, play a role in the quality of the final product. Correlations between the fabrication parameters and resulting electrode microstructure, properties and performance are important to understand, in order to better control the processes. Advanced imaging and spectroscopy techniques, together with image and data processing to quantify important structural and compositional parameters, play an important role in this understanding. Information about catalyst distribution, composition, and surface chemistry can be correlated to ink characteristics, and finally to electrode structures, component distribution and properties, and their effect on MEA performance can be investigated. This talk will offer a plethora of examples of these advanced characterization and quantification techniques within a collaborative project on Overall Research on Electrode Coating Processes (OREO) between four institutions: University of Connecticut, Colorado School of Mines, National Renewable Energy Lab and Fraunhofer ISE.

The extended commercialization of electrochemical energy conversion devices (i.e., fuel cells and (co-)electrolyzers) relies on the development of improved catalysts for the reactions taking place in their electrodes (i.e., O₂-reduction/evolution, H₂-oxidation/evolution or CO₂-reduction). This in turn passes by deepening our understanding of these reactions’ mechanisms and of the parameters that determine the performance and stability of the electrocatalysts speeding up their kinetics. As a result, great efforts are being devoted to investigate these reactions and materials under operation-relevant conditions. Such in situ / operando studies are often carried out using X-ray absorption spectrocospy (XAS), which is a bulk-sensitive technique realizable at atmospheric pressure and that can provide insight on an analyte’s oxidation state, electronic properties and coordination environment. Moreover, recent developments in fast X-ray energy scanning and spectral acquisition have resulted in a surge of interest in time-resolved XAS studies that can yield additional information on the changes undergone by the catalysts in the course of the reaction [1]. However, the large majority of these works are performed using electrochemical cells and/or experimental conditions (e.g., convective properties, catalyst loadings) optimized to assure the successful completion of the spectroscopic measurements, but that may significantly differ from those encountered by these materials in the real devices. Most importantly, little is known about how these differences can affect the results derived from such spectroelectrochemical studies, as well as on the extent to which their conclusions are amenable to application-relevant operative conditions.

With this motivation, this contribution will start by discussing how XAS-results may be affected by the thickness of the studied catalyst layers (CLs). This was achieved by studying the formation of palladium hydride on electrodes with similar Pd-loadings but ≈ 5-fold different CL-thicknesses, which were prepared using an unsupported Pd-aerogel vs. a carbon-supported Pd-nanoparticle catalyst [2]. In a subsequent step, we will show how this CL-thickness and the intensity of the incident X-ray beam can caused the accumulation of evolved O₂-bubbles within the pores of an Ir-oxide-based CL, leading to a localized loss of potential control that can ultimately result in an erroneous assignment of the catalyst’s oxidation state [3]. Finally, we will present our recent efforts at developing a novel electrochemical cell allowing operando spectroscopic studies with ultra-low catalyst loadings, enhanced mass transport properties and the online analysis of the reaction products.

In summary, this contribution will provide novel insight on the impact of various experimental parameters on operando XAS measurements, while providing guidelines for the successful completion of such experiments and the subsequent interpretation of their results.

One of the main challenges to tackle for the widespread adoption of proton exchange membrane fuel cells (PEMFCs) is minimise the use of PGM catalysts while keeping high activity and durability.  

Great advances have been made in the fundamental understanding and experimental development of electrocatalysts [1]. One strategy to address this challenge consists in nano-engineering morphology and composition of the catalysts to increase their ORR mass activity and durability upon prolonged cycling. Another approach consists in the modification of the support material, which can bring enhanced stability to corrosion as well as promote electrocatalysis via interactions with the metal catalyst.

Our group is developing novel electrocatalysts and support materials to enhance performance and durability of PEMFC cathodes.

A range of chemical and electrochemical synthesis techniques to prepare Pt nanoparticles and thin films [2] are investigated to prepare highly active ultra-low PGM loaded electrodes. A solid-phase synthesis is used to prepare Pt-rare earth metal alloys of controlled stoichiometry [3, 4].

In parallel, we are developing functionalised carbons and metal oxide-based support materials with high corrosion resistance combined with electronic electrocatalyst-support interactions beneficial for activity and durability [5, 6]. The morphology of the supports also plays a crucial role. Nanostructured electrodes are prepared by electrospinning allowing control over structure and porosity [2, 5].

In this work, the advances in understanding the role of materials composition and architecture on electroactivity and durability of PEMFC cathodes will be presented.

Metal halide perovskites have emerged as promising alternatives to commonly employed light absorbers for solar fuel synthesis, enabling unassisted photoelectrochemical (PEC) water splitting^[1,3] and CO₂ reduction to syngas.^[2,4] While the bare perovskite light absorber is rapidly degraded by moisture, recent developments in the device structure have led to substantial advances in the device stability. Here, we give an overview of the latest progress in perovskite PEC devices, introducing design principles to improve their performance and reliability. For this purpose, we will discuss the role of charge selective layers in increasing the device photocurrent and photovoltage, by fine-tuning the band alignment and enabling efficient charge separation. A further beneficial effect of hydrophobicity is revealed by comparing devices with different hole transport layers (HTLs).^[1,3] On the manufacturing side, we will provide new insights into how appropriate encapsulation techniques can extend the device lifetime to a few days under operation in aqueous media.^[1,2] To this end, we replace low melting alloys with graphite epoxy paste as a conductive, hydrophobic and low-cost encapsulant.^[3,5] These design principles are successfully applied to an underexplored BiOI light absorber, increasing the photocathode stability towards hydrogen evolution from minutes to months.^[6] Finally, we take a glance at the next steps required for scalable solar fuels production, showcasing our latest progress in terms of device manufacturing. A suitable choice of materials can decrease the device cost tenfold and expand the device functionality, resulting in flexible, floating artificial leaves.^[4] Those materials are compatible with large-scale, automated fabrication processes, which present the most potential towards future real-world applications.^[7,8] Similar PEC systems approaching a m² size can take advantage of the modularity of artificial leaves,^[9] whereas thermoelectric generators can further bolster water splitting by utilizing waste heat to provide an additional Seebeck voltage.^[10,11]

Fe-N-C catalysts have made considerable advancements in their initial activity. However, their stability in acidic mediums presents a challenge that must be addressed to replace Pt in fuel cell cathodes. Unfortunately, the complicated phenomena present in fuel cells make it difficult to understand the deactivation mechanisms of Fe-N-C cathodes, hindering the development of prolonged stability solutions. Herein, we show time-resolved changes in active site density (SD) and turnover frequency (TOF) of Fe-N-C catalysts. These changes occur simultaneously with a decrease in oxygen reduction reaction (ORR) current in a temperature/gas controllable gas-diffusion electrode (GDE) flow cell. We identified a strong dependence of SD changes on operating parameters by conducting in operando diagnosis of Fe leaching. Furthermore, we drew a lifetime-dependent stability diagram that reveals a shift in the prime degradation mechanism during operations. We propose a stabilizer concept utilizing ORR-inactive site-isolated Pt ions to suppress undesirable Fe loss during ORR. Through this proof-of-concept strategy, we verified enhanced fuel cell stability with reduced Fe dissolution, offering a new design principle for durable Fe-N-C catalysts.

Low temperature proton exchange membrane fuel cells (PEMFCs) powered by green hydrogen provide a means to sustainable energy production for stationary and transport applications. Their widespread commercialization is limited by the cost of the platinum catalyst at the cathode, where oxygen reduction occurs. Atomic Fe sites within nitrogen-doped carbon (Fe-N-C) offer a cheap and sustainable alternative, exhibiting the most promising non-precious metal activity for oxygen reduction. However, their stability is still below commercial realization owing to several degradation routes. Steps can be taken to minimize these pathways, [1,2] however, demetallation of FeN_x active sites is still suggested as a primary performance degradation mechanism in PEMFCs. [3]

To shed new light into Fe demetallation, in this work we focus on monitoring Fe dissolution in 0.1 M HClO₄ from our recently reported highly porous and >50% FeN_x utilization Fe-N-C catalyst. [4] We compare operando Fe dissolution under O₂ (active) and Ar (inert) conditions in both room temperature flow cell (FC) and gas diffusion electrode (GDE) setups, coupled to online inductively-coupled plasma mass spectrometry (ICP-MS). We also monitor the impact of high temperature on Fe dissolution using ex situ rotating disc electrode (RDE) and operando GDE measurements.

Fe dissolution was detected under both atmospheres in FC-ICP-MS configuration, with the amount dependent on potential, electrolyte, and gas atmosphere. After aging test performed at 80^oC in O₂-saturated electrolyte in RDE post-mortem X-ray absorption spectroscopy and transmission electron microscopy (TEM) analysis show the formation of Fe₂O₃ nanoparticles. Operando GDE-ICP-MS measurement show reduced Fe dissolution under room temperature O₂, but small increase or negligible change at 70^oC. Meanwhile, under Ar at room temperature, high Fe dissolution is detected.. Post-mortem TEM and high angle annular dark field scanning TEM shows formation of Fe_xO_y nanoparticles under room temperature O₂, and limited formation under Ar, in GDE setup. We propose under O₂ reduction GDE conditions a degradation mechanism of Fe dissolution from FeN_x sites and subsequent reprecipitation into Fe_xO_y, which we explore with microkinetic modelling.

Hydrogen is an important energy vector and plays a key role in global plans to achieve net zero targets and low temperature water electrolysis is a viable technology to produce hydrogen at scale. The efficiency of water electrolysers, however, is limited by the sluggish kinetics of the oxygen evolution reaction (OER) at the anode, which contributes to a significant potential loss [1]. The search for new catalysts, has been largely focussed on optimising the binding energetics of the reaction intermediates on the surface by altering the materials chemistry. However, the role of the interfacial solvent on the OER kinetics is a largely unexplored lever to tune catalytic activity.

In this work, we investigate the influence of the nature of cations in the electrolyte on the OER kinetics on an iridium oxide catalyst in alkaline condition, in order to gain fundamental insight into the polarised solid-liquid interface. The activity in 0.1 M MOH (M = Li, Na, K, Cs) shows marked differences depending on the nature of the cation, with the OER activity being higher for larger cations. We performed operando uv-vis spectroscopy to quantify the potential-dependent redox transitions on the surface from 0.35 V_RHE to 1.55 V_RHE, and identify the binding energetics and the degree of interaction between surface adsorbates. In order to rationalise the trends in redox kinetics observed, laser-induced current transient measurements were employed to study the behavior of the interfacial water at the electrode surface. In particular, the potential of maximum entropy (PME) was determined for the different electrolyte compositions. This work provides a holistic picture of the electrified interface and allows us to determine how the nature of the electrolyte modulates the OER kinetics. 

Iridium oxide is the state-of-the-art electrocatalyst for water oxidation in polymer electrolyte membrane (PEM) electrolysers for green hydrogen production. Understanding what controls the reaction rate on such benchmark metal oxides is central to designing more active and stable electrocatalysts for water oxidation in PEM electrolysers.^[1]

In this talk, I will present our work on probing active sites and the intrinsic water oxidation rate on iridium-based catalysts using a combination of time-resolved operando optical spectroscopy, X-ray absorption spectroscopy (XAS), and electrochemical mass spectrometry (ECMS). This talk will focus on comparing two state-of-the-art iridium oxides structures- amorphous IrO_x versus crystalline rutile IrO₂. I will first discuss the intermediate states and catalytically active states on iridium oxides and show how we can use optical spectroscopy to identify and quantify these states . The nature of these states, including Ir oxidation state and surface absorbates on iridium sites, will be elucidated using a combination of XAS and Density Function Theory (DFT). The interaction between these states and its effect on controlling the free energy of elementary reaction steps in water oxidation will also be discussed. Finally, based on the resulting molecular level understanding, I will present a modified Sabatier volcano model to describe trends in OER activity that takes into account the effect of absorbate-absorbate interactions on binding energetics. 

Electrocatalytic water splitting is a topic of investigation of numerous research groups for decades. Oxygen evolution reaction (OER), as a more complex and more demanding reaction, is more frequently studied, despite of the fact that the simpler hydrogen evolution reaction (HER), is generally not well understood. Nowadays, recurrent approach to electrocatalysis is conquest for more active and more stable electrode materials, very often lacking significant input to better understanding of reaction mechanisms or understanding of what are the drivers of electrocatalytic activity [1].

Importantly, if one asks the key question from the conceptual point of view, and that is: what are the origins of electrocatalytic activity? - the answer will be, in the predominant majority of cases, like 70 years ago. Namely, paradigm of electrocatalysis is Sabatier principle, that suggests optimal (“not too strong, not too weak”) binding of intermediates as main precondition of high reaction rate [2]. Conventional wisdom suggests that confirmation of this should be relatively simple. Namely, Brönsted-Evans-Polanyi (BEP) relations suggest linear relationship between adsorption energy of key intermediates and activation energy. In other words, if we have reliable values of adsorption energies relevant for the electrochemical environment [3], they should form linear dependence with experimentally obtained activation energies.

However, high-temperature hydrodynamic experiments on HER indicate that reducing of activation energy by tuning of adsorption energy of intermediates is not necessarily beneficial for enhancement of HER rate. Namely, HER rate is strongly influenced by preexponential frequency factor. Therefore, we propose discussion that will analyse several key aspects of HER electrocatalysis: 1) interplay of activation energy and preexponential factor as a driver of electrocatalytic activity 2) are BEP relations relevant for electrocatalysis 3) can we assess adsorption energies experimentally 4) what are relevant descriptors that shed light on HER activation process, 5) what else is important beyond Sabatier principle for rate of HER [1-5].

The key procedure in designing and understanding of electrocatalysts is identifying active sites with optimal adsorption properties towards reaction intermediates. However, such identification under reaction conditions is often very complicated and indirect. Normally, ex-situ experiments are used. In alternatives, the available resolution today is rather low, hiding the true structural origin of the activity at the atomic level. Therefore, the nature of active centers is currently known for only a few electrocatalytic reactions and a limited number of catalyst surfaces. In the presentation, I will explain the principles of identification of active sites using electrochemical scanning tunneling microscopy under reaction conditions for several reactions essential for PEMFCs and electrolysers [1-3]. The working principles are based on the analysis of the fluctuations of the tunneling current at different sites when the reaction cannot take place or is enabled due to the right electrode potential being applied. Examples will include metal, metal oxide, and non-metallic (e.g. HOPG and MoS₂) electrocatalysts.

Despite fossil fuels having brought forth the dawn of civilisation as we know it, they have also left an enduring effect on the Earth’s climate. To address this, it is imperative that we devise renewable technologies to decarbonise our economy. For example, one could envision using sunlight to drive (photo)electrochemical water splitting devices to produce H2, a highly energy-dense fuel when compressed and stored. A major roadblock in realizing this, however, is the lack of affordable and efficient catalysts for the oxygen evolution reaction (OER).

In this talk I will describe our recent efforts to rationalize the activity of OER electrocatalysts^[1,2] by means of reaction descriptors and how to utilize this knowledge to guide the design of more efficient materials. In addition, I will discuss how this approach can be translated to molecular systems^[3] and present a series of catalyst design principles to accelerate the discovery of “ideal” molecular OER catalysts via high-throughput^[4] and machine learning studies.^[5] Finally, I will present a new platform that we have developed to automate the generation of bottom-up molecular OER databases to boost the discovery of molecular systems which can be ultimately immobilized onto solid supports to design hybrid OER materials.

Complex oxides have evolved as a major class of functional energy materials applied in a wide range of energy conversion and storage approaches which harvest the ability to precisely tailor and combine oxides on the nanoscale. Heterogeneous interfaces of oxides typically possess distinctly different material properties as compared to the bulk [1] and allow tailoring and tuning of ionic-electronic properties by intentional design of interfaces. Here, we will discuss how dedicated design and understanding of interfacial space charge phenomena can be used to tailor electronic and ionic charge transport along and across electrochemically active oxide interfaces and surfaces, with particular focus on the role of space charge at solid-liquid interfaces operating in alkaline water splitting. We will discuss materials engineering strategies that allow to overcome the limitations of ‘bulk catalyst’ owing to intrinsic scaling relations and the typically observed inverse relationship of catalyst activity and long term stability. [2] As we elaborate the choice and combination of select oxides in from of defined multilayers and superlattices can lead to superior stability compared to the parent materials. [3,4] In this way, the control of space charge and electronic structure can be used to realize hybrid catalysts that attempt to break classical relations of electrochemical activity and stability.

In the future energy scenario, hydrogen is seen as a promising alternative to currently used fossil fuels. Proton exchange membrane (PEM) electrolysis is recognized as the best technology for the sustainable production of hydrogen, however, its widespread utilization is jeopardized by the fact that the catalyst, used for the anodic oxygen evolution reaction, is based on scarce iridium. One of the strategies to reduce its loading in the electrolyzer is the dispersion of Ir-based nanoparticles on ceramic supports, which can withstand harsh conditions in the electrolyzer.

The newly designed materials for electrocatalytic applications, pursuing this goal, are generally first tested on the laboratory scale. The most critical parameters that reveal their viability are their activity, stability, and selectivity. The best metric, indicating the activity of the catalyst is the so-called turnover frequency (TOF), which is in reality difficult to obtain. Instead, normalization of the current by the electrochemically active surface area (ECSA) is used. Unfortunately, there are currently no methodologies for its determination in the case of supported Ir-based catalysts. A promising methodology was recently proposed by Watzele et al. [1], which suggested the use of electrochemical impedance spectroscopy (EIS) to measure the so-called adsorption capacitance of reaction intermediates, which is directly related to the active surface area. In their work, the authors showcased this methodology on thin films.

Here, we applied this methodology to a commercial catalyst Ir on Vulcan (Premetek) to test its suitability for the measurement of ECSA of supported nanostructured catalysts. We prepared electrodes with different loadings of the investigated material and performed a detailed analysis of the impedance spectra. Results showed significant discrepancies between expected and measured values of obtained parameters, which cannot be attributed solely to the experimental errors. Based on the results, we discuss possible reasons for the anomalies and confirm the main hypotheses by impedance simulations using the full physical model ‐ instead of the simplified equivalent circuit.

The scarcity of iridium has been the bottle neck of the large-scale implementation of proton exchange membrane (PEM) electrolysers, where high loading of iridium oxide is used to catalyse water oxidation and to sustain an integrated conductive layer. The loading of iridium at the anode can be reduced by introducing a catalyst support.^1,2 However, finding materials that are stable and conductive under the oxidative and acidic conditions of the oxygen evolution reaction (OER) is extremely challenging.  Most materials suffer from oxidation, and subsequent passivation and/or dissolution during the OER.³ Titanium-based materials have shown excellent corrosion-resistant properties. Titanium metal has been employed as a porous transport layer (PTL) in the PEM electrolysers, and titanium nitride is predicted to be stable in a wide range of pH.^4,5 These features indicate that titanium-based materials have potential applicability as catalyst supports for iridium oxide water oxidation catalysts.

Herein, a series of titanium-based thin films (titanium oxide, titanium metal, titanium nitride and titanium-niobium alloy) were synthesised by reactive sputtering and their performance as a support for iridium oxide OER catalysts was examined by electrochemistry mass spectrometry (EC-MS) to measure the O₂ evolved in real time. The dissolution of both the catalyst and the supports, i.e., iridium, titanium and niobium, were tested by an inductively coupled plasma mass spectrometry (ICP-MS). The supports’ capability of remaining conductivity was found to directly correlate with catalytic activity of iridium oxide. The activity and stability of iridium oxide was strongly dependent on the support. Therefore, through this study, we couple EC-MS and ICP-MS to rigorously benchmark the performance of the support and catalysts for the OER reaction in acidic electrolyte.

Efficient and long-lasting electrocatalysts for the oxygen reduction reaction (ORR) play a crucial role in ensuring the continuous functionality of advanced energy technologies like proton-exchange membrane fuel cells (PEMFCs). Among the elements, platinum stands out as the most effective and stable electrocatalyst for the ORR so far. However, even platinum is not entirely resistant to degradation under a hostile electrochemical environment of the cathode leading to an irreversible detrimental effect on performance during fuel cell operation. Studies of the degradation mechanisms of ORR catalysts and their underlying principles pointed out that the inhibition of Pt dissolution is crucial for suppressing their deterioration.

Targeting that aim, we investigated Pt–Au alloy model catalysts with various compositions (Pt₉₅Au₅, Pt₉₀Au₁₀, and Pt₈₀Au₂₀) prepared by magnetron sputtering. The promising stability improvement of the Pt–Au catalyst, manifested in suppressed platinum dissolution with increasing Au content, was documented over an extended potential range up to 1.5 V_RHE. On the other hand, at elevated concentrations, Au showed a detrimental effect on ORR activity.

A systematic study involving multiple complementary characterization techniques such as Synchrotron Radiation Photoelectron Spectroscopy (SRPES), Energy-dispersive X-ray spectroscopy (EDX), X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Rotation Disc Electrode (RDE), Scanning Flow Cell coupled to an Inductively Coupled Mass Spectrometer (SFC-ICP-MS), and Monte Carlo (MC) simulations based on Density Functional Theory (DFT) data enabled us to gain a comprehensive understanding of the composition–activity–stability relationship to find optimal Pt–Au alloying for maintaining the activity of monometallic platinum and improving its resistance to dissolution.

The results showed that Pt–Au alloy with 10% gold represents the most promising composition retaining the activity of monometallic Pt while suppressing Pt dissolution by 50% at the upper potential limit of 1.2 V_RHE and by 20% at devastating 1.5 V_RHE.

                Decarbonisation is one of the main current goals of humanity. One of the most promising ways to achieve this is the establishment of the so-called hydrogen circular economy. Namely, while abundant and renewable energy from the sun and wind can be used to run the water electrolysers to produce the hydrogen, on the other hand, this hydrogen can be used to produce electricity for almost every end-use energy requirements. In particular, the conversion of hydrogen into electricity in fuel cells can be used for a wide range of applications, including light-duty and heavy-duty vehicles. However, there are still challenges that make massive adoption of these vehicles unfeasible. In addition to hydrogen fuel storage and transportation, the electrocatalyst issues are also an important obstacle to building a hydrogen-powered transportation system. Although the very high cost of platinum-based electrocatalysts can be solved by alloying platinum (Pt) with a less noble and less expensive metal (e.g. Co, Cu, Fe, Ni) thus enabling even higher oxygen reduction reaction (ORR) activity, the stability of these Pt-nanoalloy systems is still an open question, usually inappropriately addressed. Hence, a deeper insight into stability of Pt-nanoalloy electrocatalysts is essential.^1,2

                Here, the latest findings on the stability of the carbon supported intermetallic Pt-alloy nanoparticles (Pt-M/C, where M = Co, Cu or Ni) obtained using advanced, in-house designed methodologies such as the high-temperature accelerated degradation tests (HT-ADTs) and the high-temperature electrochemical flow cell coupled to an inductively coupled plasma mass spectrometry (HT-EFC-ICP-MS), will be presented.^2,3 Whereas the former enables ADT to be performed in a liquid electrolyte half-cell by utilisation of a standard rotating disc electrode at temperatures of up to 75 °C, the latter allows for precise (ppb range) time-temperature-and-potential resolved measurements of dissolution of metals. By simulation of close-to-real operational conditions, these technologies enabled to prove that in addition to the carbon corrosion, which follows the Arrhenius law and increases exponentially with temperature,^2,4 also Pt dissolution, as well as less noble metal dissolution, increases with increasing temperature.^2,3 This applies not only to the operational potential window (0.6-1.0 V) where the metal dissolution is expected to be dominant but also to a wide potential window such as 0.4-1.2 V where both degradation mechanisms (carbon corrosion as well as metal dissolution) can be expected.^2–4 Essentially, expanding the potential window results in an exponential growth of temperature impact on metals dissolution.^2,3 Nevertheless, with an increase in temperature, not only the dissolution of Pt, but also the rate of its re-deposition (due to the Ostwald ripening) is increased at the same time, resulting in concealment of Pt dissolution.^2,3,5 These previous findings about the dependence of the stability of Pt and less noble metal on the temperature and potential window³ will be upgraded with guidelines on how to control stability of Pt-alloy nanoparticles. In other words, the improvement of the stability of Pt-alloy nanoparticles via adjusting non-intrinsic (i.e. potential window) as well as intrinsic properties (i.e. electrocatalyst composition and structure) will be discussed.

Pt/C and PtRu/C catalysts are widely used in fuel cells and electrolysers in acidic and alkaline media. Considering only anode reactions, both catalysts can be used to oxidise hydrogen or other organic fuels in fuel cells. ^1-3 Looking at their application in electrolysers, on the other hand, some organic molecules can also be oxidised on the anode in an electrolyser resulting in value-added products and competitive reaction to oxygen evolution. ^{4, 5} This widespread use and potential of these catalysts lead to a question of long-term stability in real conditions. Therefore, in this work, we focus on the fundamental investigation of dissolution and degradation of Pt/C and PtRu/C catalysts using a rotating disc electrode and scanning flow cell coupled to ICP-MS. To cover the broad application of these catalysts, we applied different upper potential limits of CVs in 24h accelerated stress tests. The aspect of real conditions was addressed by elevated temperature in these studies. Post-Morten catalyst analysis was carried out in order to understand the catalyst degradation in described conditions. Activity decrease was also evaluated. The obtained data can be used to estimate the stability window of Pt/C and PtRu/C and minimize the degradation of these catalysts in real applications.  

Surface modification using nanoparticles has been widely applied to enhance catalytic activity and stability of the oxygen electrode in solid oxide electrochemical cells, whereas there is still a long way to go for preparing uniform and scalable nanoparticles. Herein, an ultrasonic spray infiltration technique was introduced to produce electrocatalytically reactive nano-sized ceria or double perovskite oxide decorated oxygen electrodes. The uniform nano-sized infiltrates prepared improved oxygen catalytic activity by increasing oxygen vacancies and enlarging reaction sites on the electrode surface. The solid oxide electrochemical cells with tailored oxygen electrodes revealed a performance enhancement during reversible operation in fuel cell and electrolysis cell modes. In addition, ultrasonic spray infiltration-based nanoparticles were applied to a large-area cell (100 cm²), which indicated increased power output and stable performance for long-term operation. Thus, this study proved a scalable and feasible method to tailor bifunctional oxygen electrodes using uniform infiltrates for solid oxide electrochemical cells.

Polymer electrolyte membrane fuel cells (PEMFCs) offer a promising zero-emission energy conversion solution for various applications, including automotive. However, the widespread adoption of PEMFC technology faces challenges that must be addressed. One significant performance bottleneck is the oxygen reduction reaction (ORR), which has led to the use of Pt-alloy nanoparticles on high surface area (HSA) carbon black (CB) supports as state-of-the-art electrocatalysts. Achieving high carbon support and the catalyst layer durability remains a major challenge, particularly for heavy-duty vehicle (HDV) applications that aim to meet the ambitious U.S. Department of Energy (DoE) goal of 30,000 hours of system lifetime. Two research trends focus on improving carbon durability: (i) enhancing existing HSA CB supports and (ii) exploring alternative carbon candidates with desirable properties. Graphene derivatives (GDs) such as reduced graphene oxide (rGO), and graphene nanoribbons (GNRs) have shown potential as alternative carbon supports with improved durability against carbon corrosion.

This presentation investigates the correlation between carbon support properties of graphene derivatives (rGOs, GNRs) and carbon black in Pt-based fuel cell electrocatalysts. Nanoparticulate intermetallic-based electrocatalysts were analyzed, revealing comparable metallic components but notable variations in the carbon support. Specially designed electrochemical accelerated degradation tests (HT-ADTs) demonstrated that rGO-supported catalysts exhibited superior electrochemical durability compared to carbon black-supported counterparts. The results were further validated through direct online measurements using electrochemical cell-mass spectrometry (EC-MS). This study provides valuable insights into the relationship between carbon support properties and electrocatalyst durability, offering guidance for developing more stable carbon supports in line with the Department of Energy (DoE) objectives. The findings contribute to the advancement of fuel cell technology by enhancing the understanding of carbon support properties and their impact on electrocatalyst performance.

Proton exchange membrane fuel cells are a viable alternative to conventional combustion engines running on fossil fuels. Using hydrogen as fuel, they do not contribute carbon emissions during operation, and can thus make the mobility sector a lot cleaner. However, the electrocatalyst cost still poses an issue, as those advanced materials commonly contain scarce noble metals, like platinum. To catalyze the oxygen reduction reaction inside the fuel cell, supported Pt-alloy nanoparticles are now commonly used to lower the amount of Pt. However, such nanoparticle ensembles are far from uniform, and the effect of certain structural features remains unexplored.

In this contribution, I will present a recent study focusing on carbon-supported platinum-copper nanoparticles containing anti-phase boundaries. Those planar defects, contributing to chemical disorder, were previously described for a bulk alloy, but not how they manifest themselves in a nanoscale catalyst. Experimental and simulated X-ray powder diffraction was used to determine the defect placement, and in-situ high-temperature scans were used to observe their temperature-dependent evolution. Electron diffraction and atomically resolved scanning transmission electron microscopy were used to confirm the defect presence locally, and the oxygen reduction reaction performance was evaluated for several platinum-copper analogs with and without anti-phase boundaries. This study is a step towards a more detailed understanding of the structure-property relationship of nanoparticulate electrocatalysts.

Investigating the water oxidation mechanism using operando spectroelectrochemistry

Efficient (photo)electrochemical oxidation of water is central to the production of energy carriers such as hydrogen. Hydrogen plays a critical role in the energy transformation to a sustainable future, due to its widespread applications as a fuel for transport, feedstock to chemical industries and a heat source for buildings and industry. Low temperature water electrolysis can enable hydrogen production renewably and at scale; however, the efficiencies of these technologies are currently limited by poor kinetics of the water oxidation reaction at the anode.

State-of-the-art catalysts such as iridium-based oxides in acidic electrolyte and nickel oxyhydroxides in alkaline electrolyte exhibit complex redox chemistry, which cannot be understood using electrochemical measurements alone. Particularly, the redox transitions on these catalysts can exhibit non-Nernstian behaviour, resulting in the redox transitions being dependent on pH. In this talk, I will demonstrate how optical spectroscopy and X-ray absorption spectroscopy can be used to identify and quantify the density of potential-dependent intermediates, the interaction between them, and the intrinsic rate of water oxidation, as a function of pH. In addition to determining the changes in the catalyst, I will also show how the nature of interfacial water can be probed using surface enhanced infrared absorption spectroscopy.  Therefore, using a combination of operando spectroscopic techniques, I will elucidate the factors controlling water oxidation kinetics on these materials.

Hydrogen is regarded as a future energy vector powering society needs fully from renewable sources. In this respect, proton exchange membrane hydrogen fuel cells (PEMFC) are key devices, where energy of hydrogen molecules is transformed to electricity with relatively high efficiency. Pt based catalysts, used at the cathode to speed up the oxygen reduction reaction (ORR), is one of the most expensive parts of the device and in the last two decades scientists are finding a way to limit Pt loading without compromising the performance. This effort led to deep understanding of ORR electrocatalysis and development of a new class of catalysts, where various schemes (alloying, morphology) are used to facilitate the reactions. In spite of these efforts, incorporation of these catalysts in the MEA and optimizing device operation remains a challenge, mainly because of low catalyst stability and various structural and chemical inhomogeneities. In this contribution we will assess the stability issues of bimetallic PtNi catalysts during its lifetime, from the cradle to the grave, using high energy X-rays as an universal in-situ and operando probe.

Water electrolysers (WE) with proton-conducting electrolytes, especially those based on the polymer electrolyte membranes (PEM), present many important technological advantages over the traditional alkaline-based electrolyte systems. On a negative side, efficient and practically robust operation of the PEMWEs is challenging to achieve without the use of the oxygen evolution reaction (OER) catalysts based iridium, typically introduced to the anodes at mg cm^-2 levels of loading. The key limitation here is not just the very high cost of Ir, but also the availability of this very scarce metal that is mined on a scale of only few tonnes per annum.

Aiming to resolve this challenge, our work has focused on the development of iridium-free OER catalysts capable of robust operation at low pH and elevated temperatures on an extended timescale. Towards this aim, we have implemented a “catalyst-in-matrix” design concept, which is based on combining the catalytically active oxide species, e.g. cobalt or manganese, with an electrically conductive matrix that is thermodynamically stable under the target operating conditions, e.g. oxides of lead and antimony. The talk will present several examples of such systems based on various “catalyst” and “matrix” elements, with a specific focus on the durability of the materials in operation. Integration of some of the most promising catalyst, including those operating in a self-healing mode, into the anodes of the devices for the low-pH water electrolysis will be highlighted.

In order to enable mass production and global commercialization of automobiles powered by hydrogen fuel cells it is imperative to reduce the platinum loading from the current 25-30g_{Pt stack}, which translates to 0.315 mg Pt/cm² cathode loading.¹ The use of alloy cathode catalysts is currently considered one of the few viable paths towards decreasing the PGM content in fuel cell stacks that can get very close to the loadings used in internal combustion engines (2-8 g Pt / Veh). However, their performance and durability at high current densities (i.e. > 1.0 W/cm²) under real world driving conditions is still not sufficient.

In this presentation we will show recent strategies that will document the challenges of Pt/C and Pt-alloy/C cathodes for high power operation, via investigations of catalyst and layer design. Results will document the importance of tailoring alloy catalyst composition, surface area as well as particle location on existing commercial supports. Advanced characterization and diagnostics techniques will be presented that will determine key differences between different Pt-alloy variants in terms of performance and durability against state of the art Pt/C catalyst.  Emphasis will be given to the role of dissolved metal ions during ink formulation and their impact on performance for automotive applications. These results have helped identify the mechanisms that compromise catalyst stability as well as activity and allowed the synthesis of new materials and layers that could be capable of thrifting Pt loading to levels that will help mass commercialization and advance the technology in order to reach the challenging target of 1.8 W/cm².

1. R. Borup, K. More, A. Weber, DOE FC135: FC-PAD Fuel Cell Performance and Durability

The conversion of renewable energy into valuable chemicals and fuels requires water and CO₂ electrolysis. To make these technologies more accessible and affordable worldwide, we need to find catalysts that are cheap, abundant, active, and stable. The catalysts’ performance depends not only on their intrinsic properties but also on the electrolyzer’s design and the type of electrolyte used. However, in CO₂ electrolysis, the catalyst may exhibit rapid degradation in a certain electrolyte because of the pH change over time due to ion movement across the membrane.¹ Therefore, the anode materials should resist corrosion in a wide range of pH values and/or in electrolytes rich in carbonate. Most of the non-noble transition metals and their compounds are very stable at high pH, but they are less durable than Ir or Pt at low and (near-) neutral pH.² Interestingly, some recent studies have shown that oxides based on Co can maintain good stability even at low pH.^{3, 4} However, we still do not understand how this stability works and how non-noble metal oxides catalyze the oxygen evolution reaction (OER) at low or near-neutral pH. In this work, we tried to answer some of the questions. We use a scanning flow cell (SFC) combined with inductively coupled plasma mass spectrometry (ICP-MS) and differential electrochemical mass spectrometry (DEMS) to study the stability of cobalt oxide under different electrochemical conditions at low and mild pH. With these techniques, we can monitor the dissolution of Co online and identify possible narrow stability windows before and during the OER. Moreover, going one step further toward the industrial application of such materials, we tested various Co₃O₄-based electrodes as anodes in CO₂ electrolyzers. Based on our results, we suggest and discuss the dissolution of cobalt oxide and provide perspectives on improving its stability.

Extracting electrons from water through the oxygen evolution reaction (OER) is a crucial element of carbon neutral fuel generation and other energy storage technologies.^1–3 Large overpotential losses in the OER arise from kinetic barriers associated with multiple proton and electron transfer steps.³ Lowering this barrier is key to improving performance, however a general understanding of the fundamental factors controlling OER kinetics has not yet been reached.

Broadly, two general classes of OER mechanism link applied potential to the rate of catalysis. Electrochemical mechanisms, where the rate determining step (RDS) involves an electron leaving the catalytic intermediate and surface site to be conducted away by the electrode, and chemical mechanisms where no net electron transfer occurs during the RDS.⁴ In the electrochemical mechanism, the current (rate) scales exponentially with the applied potential, as electrode potential is directly correlated to activation energy; whereas in a purely chemical mechanism, voltage only drives the accumulation of catalytic intermediates.⁴ In the simplest case, the rate of a chemical RDS would scale with the coverage of the rate limiting intermediate to the power of its stoichiometric coefficient.⁴ However, more complex behaviour may also arise through interactions between adsorbates changing with coverage, leading to a dependence of activation energy on coverage.⁵

 Beyond fundamental considerations, mechanistic understanding of the OER is challenging due to the complexity of many OER catalysts. For example, despite decades of study, the phase transitions, active oxidation states, active sites and mechanism of cobalt hydroxide/oxyhydroxide – one of the most intensely studied electrocatalysts - remain controversial.^6-9 The position, degree of oxidation and chemical nature of the active sites in CoOOH remains a topic of intense debate - obscuring considerations of the fundamental mechanism of operation in this material.

Such conflicting results reflect a crucial unmet technical challenge in electrocatalysis: there does not exist a widely accessible method of simultaneously measuring populations of catalytic intermediates and proving that the measured intermediate drive current through direct measurement of OER kinetics. Herein, we demonstrate the power of spectroelectrochemical analysis built around employing a multi-channel detector to  measure continuous spectral changes during the polarisation curve at all points of the polarisation curve to overcome this challenge. We  use the example of cobalt oxyhydroxide (hereafter CoOOH) and cobalt-iron Prussian Blue (hereafter CoFe-PB) – another cobalt based catalyst with contrasting behaviour to CoOOH,  This capacity is combined with time resolved measurement of the kinetics of implicated catalytic intermediates as they decay under open circuit conditions to verify turnover frequencies. The richness of the resulting dataset enables us to extract quantitative, operando coverages and turnover frequencies of intermediates, reconstruct the polarisation curve, and prove that the intermediates measured turn over quickly enough to support the measured current. Using this approach, we quantify the extent of energetic destabilisation of the rate limiting intermediate of both catalysts as a function of coverage. Supported by molecular level insight gained from density functional theory calculations we show that the interacting chemical mechanism contributes significantly to the current in both catalysts, despite disperate kinetics and electroadsorpative properties. In light of our conclusions, we examine the contribution this destabilisation makes to OER current as well as examine the validity of simple mechanistic interpretations of Tafel slopes.

Water electrolysis remains the most promising pathway towards the sustainable provisioning of H₂ at the terawatt scale. Unfortunately, a competitive hydrogen pricing against that derived from fossil fuels remains limited by the capital and ongoing expenditures of current state-of-the-art water electrolyser technologies. It is therefore necessary for future sustainable hydrogen economies that the development of noble-metal-free electromaterials be made to withstand the harsh electrolytic conditions imposed by efficient proton exchange membrane water electrolysis (PEMWE). However, the advancement of cost-effective anode catalysts for industrially relevant PEMWE has thus far been infrequent and relatively unsuccessful. Of the trivial sum of sufficiently stable modes of the oxygen evolution reaction (OER) within low-pH electrolytes, self-healing systems demonstrate a potential towards earth-abundant OER under industrially relevant PEMWE conditions. Self-healing mechanisms are defined by a quasi-equilibrated state between surface and dissolved catalytic components, whether added intentionally or corroded from the catalyst itself, and can therefore provide a perceptible means for long-lifetime electrolytic operation. From this perspective, detailing such a mode of electrocatalysis proves highly useful within a range of electrolytic applications including but not limited to water oxidation, as a large sum of electromaterials and electrochemical pathways often rely on the equilibration between surface and dissolved electroactive species. Here at Monash University, Swinburne University of Technology and Max-Planck-Institut for Chemical Energy Conversion, operando X-ray spectroscopic and voltammetric techniques have been developed in order to track a self-healing water oxidation mechanism.^1-2 Using a highly stable and high performance Co-based OER catalyst within low-pH conditions,³ utilisation of in situ Co K and L₃-edge X-ray absorption spectroscopy (XAS) in conjunction with electrochemical Quartz Crystal Microbalance (eQCM) and Fourier Transformed alternating current Voltammetry (FTacV) has allowed the successful tracking of the oxidative changes within the catalysts electronic structure. From a predominant Co(II) ground state to its catalytically relevant Co(III) oxidative structure under operation, the charge- and mass-transfer processes have also been compared against the redox events occurring during the self-healing OER mechanism, providing in detail, the potentials at which both the electron- and mass-transfers begin and the effect of catalytic loading on cobalt selective process. Further details of the mechanistic insights into both static and dynamic electro- and spectroelectrochemical techniques will be elaborated on through both poster submission and oral presentation.  

The Oxygen Reduction Reaction (ORR) serves as the fundamental reaction in electrocatalysis systems like fuel cells, metal-air batteries, and hydrogen peroxide (H2O2) electro-generation. The ORR reaction mechanism encompasses two potential pathways: a two-electron (2e-) process and a four-electron (4e-) process, which respectively result in the reduction of oxygen to H2O2 or water (H2O). While fuel cells ideally prefer a direct 4e- ORR pathway, a sequential pathway involving the exchange of 2e- can be an environmentally friendly approach for decentralized H2O2 production [1, 2]. H2O2 holds significant importance for various applications and has been recognized as one of the top 100 most significant chemicals. Current methods for H2O2 production, such as the anthraquinone process or direct synthesis, face challenges due to their complex and hazardous nature. Therefore, electrochemical H2O2 synthesis via 2e- ORR presents a more environmentally friendly, safer, and faster alternative to existing technologies. Carbon-based materials modified with heteroatoms, specifically nitrogen-doped carbon (N-C), are considered promising substitutes for expensive noble metal catalysts like Pt for ORR in fuel cells and Au for ORR to H2O2 [1, 3]. The synthesis of N-C typically involves a carbonization process performed at temperatures ranging from 500-1200°C for a duration of one to tens of hours, under various gas atmospheres such as air, nitrogen, argon, ammonia, etc. [4]. The thermal carbonization process is characterized by high energy consumption and long preparation time.

Alternatively, microwave (MW) irradiation offers a more energy-efficient and environmentally sustainable method for synthesizing porous carbon-based materials, making it economically viable as well. This study investigates the impact of both thermal and microwave heating on the properties of porous carbon derived from polyaniline. Additionally, the electrocatalytic performance of these porous carbons in alkaline media for the ORR is examined. The objective is to identify the optimal carbonization conditions during MW heating, resulting in a structure with a chemical composition that complements that obtained through conventional thermal pyrolysis methods.

Under optimal conditions of 450 W power and 140 seconds of exposure, a one-step MW synthesis yields disordered graphite structures with nitrogen and oxygen functionalities. This sample exhibits a comparable chemical structure to the polyaniline sample thermally carbonized at a temperature of 700-800°C, as confirmed by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Both the MW (450 W, 140 s) and thermally (700°C, 1 min) prepared samples demonstrate catalyzed electrochemical ORR, with a selectivity of approximately 58±1% towards H2O2.

By replacing thermal carbonization with microwave-based methods, the overall synthesis time and energy consumption for porous carbon derived from polyaniline can be reduced by a factor of 71 and 93, respectively.

The results indicate that the C-450W_140s sample demonstrates comparable performance in alkaline ORR to the thermally prepared samples, highlighting the effectiveness of the MW-carbonization synthesis approach. These findings pave the way for expanding the application of MW carbonized samples in diverse fields such as electrocatalysis, supercapacitors, and zinc-air batteries, thereby complementing sustainable synthesis methods.

Pyrolized iron-based catalysts are one of the most promising alternatives to platinum, for the oxygen reduction reaction (ORR) taking place at the cathode of fuel cells. However, the pyrolysis step leads to the formation of a plethora of iron sites. Characterizing these sites under reaction conditions is challenging, and thus complicates fundamental studies of the catalyst. In turn, this hinders the rational optimization of pyrolized Fe-based catalysts.

On the other hand, iron macrocycles, with their well-defined structures, offer a platform for the study of the oxygen reduction reaction on FeN₄ active sites. These macrocycles exhibit one or two distinctive peaks in their cyclic voltammograms, the origin of which is still debated. There have also been reports suggesting that the position of the high-potential peak correlates with the activity of the motif, making it a powerful performance descriptor and a tool to obtain structure-property relationships of FeN₄ sites.

in this study, several iron macrocycles with different ligands and active sites were investigated, using electrochemistry, operando optical spectroscopy and DFT simulations. Optical spectroscopy results (shown in the TOC for the molecule FePC) show potential-dependent spectral changes in concomitance with the CV peaks. This, with the help DFT simulations, allowed us to identify the origin of the spectral change and to propose the existence of two families of macrocycles, with drastically different ORR activity.  One group is characterized by two CV peaks, high ORR activity and low peroxide yield, while the other features a single CV peak, poor catalytic performance and higher peroxide production.

This study provides a first step in understanding what controls the activity of FeN4 sites and offers a tool to unravel fundamental properties of pyrolized FeN_x catalysts.   

The extensive application of proton exchange membrane fuel cells (PEMFC) is conditioned by the limited supply and high cost of the Pt used in commercial PEMFC catalysts. To make PEMFC more widely available, new electrocatalysts with low Pt loading and high Pt efficiencies must be developed.

An important, but little explored aspect of this, is the interaction between the carbon support, proton conductive ionomer and catalyst. Catalyst support with optimal porosity is suggested to protect the Pt particles from direct ionomer poisoning but still provide the particles with good accessibility to the protons and oxygen.

In our project, carbon nanospheres with highly ordered mesoporous channels have been synthesised sustainably from biomass.  Pt nanoparticles were deposited via polyol method onto the as synthesised mesoporous carbon sphere (MCS) and another two commercially widely used carbon substrates (porous Ketjenblack and non-porous Vulcan). Characterization of the catalysts were carried out with SEM/TEM, BET, XPS, XRD, revealing that the Pt nanoparticles are same in geometric and electronic structure while the difference of these catalysts solely arises from the different support porosity thus the different local environment of Pt NPs in the catalysts. All the Pt/C catalysts were tested under a gas diffusion half cell configuration for their oxygen reduction performance. Pt/MCS shows supreme performance where the Pt NPs sit inside the mesoporous channels of the carbon sphere.

To understand the outstanding activity of Pt/MCS, operando X-ray Absorption Spectroscopy was used to evaluate the ionomer coverage on the Pt surface by monitoring the Pt electronic structure change in the potential range of 0.1-1 V (vs RHE).  Together with comprehensive nanostructure analysis via gas sorption, we proved that the oxygen reduction performance was boosted via the ideal interaction of Pt and Nafion ionomer, where direct contact in-between these two is eliminated without sacrificing the accessibility of Pt active sites. This will then guild the design strategy for future electrocatalysts development.

Alkali metal cation (AM⁺) is commonly used as counterions for anions in aqueous solutions due to its high solubility and ionic conductivity. This cation is typically situated near the electrode and constitute a key component of the electric double layer (EDL) structure, which is traditionally perceived as spectator species in electrochemical reactions. However, recent studies have shown the modulation of aqueous electrocatalysis depending on the identity and concentration of AM⁺. Several hypotheses have been proposed to explain the role of AM⁺ in electrocatalysis, while it is still under discussion. Here, we demonstrate that AM⁺s can directly participate on the model reaction of oxygen reduction reaction (ORR), forming chemical bonds with reactions intermediates and governing kinetics. This conclusion is corroborated by observing the NaO₂ intermediate via advanced in situ spectroscopic analysis during the ORR on carbon surface. The Nernstian shift of polarization curve with varying AM⁺ concentrations and the significantly diminished ORR activity without free AM⁺, further demonstrate the pivotal role of AM⁺ in directly interacting with reaction intermediates in aqueous environments.   

Activating of molecular Nitrogen is an extremely important process as it supplies in the form of fertilizer the nitrogen that it is a prerequisite for building all amino acids and nucleic acids essential for life. After brief review of the history of activating nitrogen[1] I shall concentrate on the ammonia synthesis and motivate why an alternative route to the current commercial Haber-Bosch could be attractive Recently we found that a method published by Tsuneto et al. 25 years ago worked and proved that by simultaneous depositing Li in an N2 atmosphere it was indeed possible to activate N2 to synthesize ammonia[2]. We have subsequently followed up on this process and a very simple model for the synthesis has been proposed. Based on this insight we devised experiments that significantly improved the Faradaic and energy efficiency[3]  by oscillating the potential. Further improvements have been gained by controlling the oxygen content[4]  and by synthesizing of high area electrodes[5] and design of the SEI layer leading to Faradaic efficiency of ~80% and current densities towards 1A/cm2 [6]. Despite excellent recent progress there are still substantial outstanding problems. All data so far were relying on using the electrolyte as a sacrificial proton conductor. This issue was solved in a fuel cell type setup, but now we are back to 6 mA/cm2 and 60 % Faradaic efficiency on the other hand we can now talk about energy efficiencies of some 15% [7]. Further progress is under way and will be discussed

Over only few years of intense research, the lithium redox-mediated nitrogen reduction reaction (NRR) has proven to enable electrosynthesis of ammonia at practical yield rates and faradaic efficiencies approaching 100 %. Today, it remains the one and only practical approach towards sustainable electrosynthesis of ammonia. However, further significant research and development efforts are required to translate the redox-mediated NRR into a technology of applied significance, in the first place by addressing the two current major challenges: (i) insufficient stability in operation, and (ii) energy efficiency that is thermodynamically limited to approximately 33% (under standard conditions).

Both of these limitations stem from the need for the operation under strongly reductive conditions defined by the reversible potential of the Li⁺ + N₂ / Li₃N redox couple. Under unoptimised conditions, continuous and uncontrollable degradation of the electrolyte solution components results in progressive poisoning of the N₂-reducing cathode surface, rapid loss in the performance, and impossibility of passing charge more than few hundred C cm^-2 in typically reported experiments. Our research aims to resolve this through understanding the mechanism of operation of the NRR cathodes and design of the electrolyte solutions that prevent reductive degradation pathways while sustaining high rates and faradaic efficiencies of the ammonia production.

The talk will present some of our recent findings in this domain, in particular outcomes of the studies exploring the effects of the chemical nature of the electrolyte, proton carriers and mass-transport on the NRR performance. Feasibility of increasing the energy efficiency of the process will be briefly highlighted.

Electrochemical reduction of NO_x, CO₂, N_2, and combinations hold the promise to be a cornerstone for the sustainable production of fuels and chemicals. Importantly, all reactions share a direct competition with hydrogen, and furthermore, several products are formed from each reactant of these reactants.

For electrochemical N₂ reduction to ammonia (NH₃) the interest at ambient conditions is burgeoning [1-3]. Most interesting for the direct electrochemical N₂ reduction in aqueous, there is no working catalyst similar to “copper” for CO₂ reduction catalyst [4-6]. Instead, the electrochemical reaction is today limited to the non-aqueous lithium-mediated system.

In this talk, I will give a unified approach to these reduction reactions versus hydrogen in aqueous and discuss what it takes to reduce nitrogen electrochemically.

[1] Andersen, Čolić, Yang, Schwalbe, Nielander, McEnaney, Enemark-Rasmussen, Baker, Singh, Rohr, Statt, Blair, Mezzavilla, Kibsgaard, Vesborg, Cargnello, Bent, Jaramillo, Stephens, Nørskov, Chorkendorff, Nature, 2019, 570, 504-508.

[2] H.-L. Du, M. Chatti, R. Y. Hodgetts, P. V. Cherepanov, C. K. Nguyen, K. Matuszek, D- R. MacFarlane, A. N. Simonov. Nature, 2022, 609, 722–727

[3] M. Spry, O. Westhead, R. Tort, B. Moss, Y. Katayama, M.-M. Titirici, I. E. L. Stephens, and A. Bagger, ACS Energy Letters, 2023, 8 (2), 1230-1235

[4] Y. Hori et. al., Journal of the Chemical Society, Faraday Transactions, 1989, 85, 2309-2326.

[5] A. Bagger, W. Ju, AS Varela, P. Strasser, J. Rossmeisl., ChemPhysChem, 2017, 18, 3266–3273.

[6] A. Bagger, H. Wan, I.E.L. Stephens, J. Rossmeisl, ACS Catalysis, 2021, 11 (11), 6596-6601

While the fixation of dinitrogen to ammonia at ambient conditions has undergone remarkable advances in recent years, the direct use of dinitrogen for the synthesis of other nitrogenous products, such as amines, nitriles or nitro compounds, is a challenging task. Furthemore, catalytic protocols remain unknown.

The reductive splitting of dinitrogen into transition metal nitride complexes represents a potential entry towards N₂ fixation beyond ammonia. Over the past years, we have examined the mechanisms of chemically, photochemically, and electrochemically driven reductive N₂ splitting by group 6 and 7 metal complexes as a path for the direct conversion of N₂ into several products beyond ammonia, such as nitriles, amides and N₂O. In this contribution, the reductive splitting of dinitrogen will be presented. Electro- and photochemically driven pathways are discussed that are based on detailed mechanistic studies and electronic structure/reactivity relationships of key intermediates. Synthetic strategies for selectivity control that are guided by N–H proton-coupled electron transfer thermochemistry of intermediates are presented.

Energy-intensive thermochemical processes within chemical manufacturing are a major contributor to global CO₂ emissions. With the increasing push for sustainability, the scientific community is striving to develop renewable energy-powered electrochemical technologies in lieu of CO₂-emitting fossil-fuel-driven methods. However, to fully electrify chemical manufacturing, it is imperative to expand the scope of electrosynthetic technologies, particularly through the innovation of reactions involving nitrogen-based reactants as products from water/CO₂ electrolysis do not cover the full scope of industrial needs.

To this end, this talk focuses on my lab’s efforts nitrogen fixation to ammonia through the use of innovative electrochemical interfaces. I will proceed to detail new efforts in nitrogen fixation through the co-electrolysis of CO₂ with N-reactants (N₂, NO₃^2-…) in generating products with C-N bonds like amides, urea that are important as commodity and fine chemicals in the chemical industry.  In particular, I will discuss several new reaction pathways discovered towards C-N products and the application of operando techniques to understand the key C-N coupling steps in the reaction process.

Nitrogen reduction to ammonia stands amongst the hardest processes to decarbonise, with the Haber-Bosch process dominating the market. In that regard, electrochemical ammonia synthesis can meet this unmet need, towards sustainable and decentralised production of fertilisers and carbon-neutral fuel.

So far, the lithium-mediated synthesis is the sole process to unambiguously generate ammonia from nitrogen on a solid electrode.^1,2 Tremendous progress has been made in just a few years, both in terms of the underpinning fundamentals,^3,4 and in terms of device engineering.^5,6 However, all these improvements are burdened with the need to operate at lithium plating potential. This results in enormous overpotentials (>3.2 V) and energy losses (>70% due to lithium plating).^7,8 A solution is to identify new catalytic systems with lower intrinsic overpotential, which is highly challenging.⁹

In this talk, I will walk us through the periodic table of elements, bringing together physical descriptors obtained from theoretical calculations and literature meta-analysis. This exploration will aim at unifying the comparison of electrochemical systems for nitrogen reduction to ammonia, and pinpoint candidate elements which I will investigate experimentally. Electrochemical testing, ex situ / operando characterisation and model experiments will be performed to explore promising catalytic systems. Learning from those, I will provide fundamental explanations to the unique features of lithium and suggest pathways to breach the bottleneck of the lithium chemistry, opening the discussion for more energy efficient and sustainable chemistries.

Ammonia (NH₃), being the basis of all nitrogen fertilizers, constitutes one of the pillars of modern society, without which nearly half of the population would not be present on Earth.¹ Furthermore, thanks to its properties (high energy content and density), it is recently emerging as a backbone fuel towards decarbonisation.² Up-to-date, NH₃ is mainly produced via the energy-intensive Haber-Bosch process and, to meet the future NH₃ demand, new green synthesis techniques need to be developed.³

To this end, electrochemical nitrogen and nitrate reduction reactions (E-NRR and E-NO₃RR) have received considerable attention since, among other advantages, they permit the utilization of electricity from renewables. Also, taking into account that molybdenum and sulphur play key roles in nitrogenase-based nitrogen fixation, molybdenum disulphide (MoS₂) is expected to be active toward E-NRR, even if it has already demonstrated good catalytic activity toward hydrogen evolution reaction (HER, the main competitor of E-NRR).⁴

In this work, MoS₂ has been tested for E-NRR and E-NO₃RR in combination with different formulated electrolytes (LiSO₄ and K₂SO₄ at different concentrations and pH values). A flow cell with a gas diffusion electrode, on which the catalyst is immobilized through air-brushing technique, has been used to perform all the experiments.  Regarding E-NRR, encouraging results were obtained when employing Li⁺ as an additive in the electrolyte, leading to Faradaic efficiencies between 5 and 10%, as well as 85-301 μmol g^-1 h^-1 yield at -0.6 V vs. RHE. Further, since NH₃ was detected not only in the cathodic site, but also in the anodic one, as well as absorbed within the cationic membrane, the interactions between the Nafion membrane and NH₃ were also studied, observing that NH₃ adsorption decreased when the size of the cation raised (around 60% of NH₃ was absorbed when employing Li₂SO₄, ca. 20% when employing K₂SO₄).

Finally, in the case of NO₃RR, design of the experiment and surface response methodology (DoE/RSM) were employed to gain further insight onto the influence of operational conditions (potential, catalyst loading and salt concentration in the electrolyte) on the Faradaic efficiency and NH₃ yield of the NO₃RR, as well as the possible interaction between those parameters.

The Haber-Bosch (HB) reaction is definitely one of the most important reaction of the 20th century with tremendous impact on significant, for mankind, sectors, such as fertilizers, chemical industry, medicine, bio-fuels and ammonia production [1]. It is now well accepted that the relative activity of metallic HB catalysts can be correlated to their binding energies with N-containing species in terms of a volcano-shaped relationship. Metals that bind nitrogen too strongly or too weakly are on either side of the volcano [2]. Thus, it is important to devise a knowledge-based catalyst design that could potentially replace the Haber-Bosch method, while achieving high efficiency and energy saving towards sustainable NH3 production under ambient conditions. In this regard, herein we present two approaches for understanding the N2 acivation and conversion: (a) density functional theory (DFT) calculations are used in order to screen the N2 activation capacity and the accompanied electronic interactions for a portfolio of bimetallic alloys based on Mo, Ru and Fe metals, while using those metals as reference ones. (b) the role of defects in a new family of ceria-based oxide catalysts is explored from both experimental and computational point of view. These new type of oxide systems quickly enhance the ability to form and eliminate oxygen through redox reactions. 

Over the last decade there has been a growing interest in generating ammonia from nitrate with the aim of reducing eutrophication and acidication of water sources that has been exacerbated by anthropogenic activities.[1] In nature, the reduction of nitrate and nitrite ions is governed by Mo- and Fe-containing enzymes as a part of the nitrogen cycle. The key steps in the reduction of nitrate to nitrite are driven by nitrate reductase (Nars) enzymes involving the parent Mo(VI) oxo active site.[2] Subsequently, reduction of the nitrite to ammonium can be catalyzed by cytochrome c nitrite reductase (NrfA) enzymes, which features an Fe heme active site.[3] Inspired by this process, in the present work we introduce an Fe-substituted, two-dimensional molybdenum carbide of the MXene family (Mo₂CT_x:Fe, where T_x = O, OH, or F surface termination groups) for the electrochemical reduction of nitrate to ammonia.

Recent studies have demonstrated that MXenes efficiently enable various electrocatalytic reactions due to a high degree of control over the structure of their surface sites.[4] In this case, Mo₂CT_x:Fe contains isolated Fe sites in Mo positions of the host MXene (Mo₂CT_x), and as discussed above, the combination of these metals is known to facilitate the nitrate reduction reaction in naturally occurring reductase enzymes. Mo₂CT_x:Fe is shown here to outperform monometallic Mo₂CT_x for the electrochemical reduction of nitrate in both acidic and neutral electrolytes. Close examination of the electronic and local structure via operando X-ray absorption spectroscopy (Mo K-edge) reveals that substitution of Mo with Fe in the Mo₂CT_x lattice facilitates the defunctionalization of surface T_x groups upon reduction. This is shown to generate T_x vacancies, which then bind nitrate ions that subsequently fill the vacancies with O* via oxygen transfer. In accordance with experimental observations, density functional theory calculations provide further evidence that Fe sites promote the formation of T_x vacancies, which are thus identified as active sites and function in NO₃RR in a close analogy to the mechanism of the natural Mo-based nitrate reductase enzymes.

The intermittent availability of renewable energy poses a significant challenge that must be overcome to fully harness its potential. One promising solution is the storage of excess renewable energy in the form of carbon-free chemical fuels like hydrogen (H₂) and ammonia (NH₃). These energy-dense alternatives provide the means to transport renewable energy independently, without relying on traditional power grids. However, the current production of NH₃ primarily relies on the costly Haber-Bosch process, limiting its use as a chemical fuel. To address this limitation, there is a need for a sustainable production method, such as the electrochemical reduction of nitrogen gas (N₂) into NH₃. Among various electrochemical processes, the lithium-mediated nitrogen reduction reaction (Li-NRR) currently stands out as the sole method capable of achieving this conversion.¹

At Monash University, we have made significant advancements in Li-NRR, achieving close to 100% faradaic efficiency for NH₃ selectivity.^2,3 However, our focus now lies on reducing the energy demands and enhancing the overall sustainability of the Li-NRR process. This calls for the intelligent design of catalysts and electrolytes, which can be facilitated by expanding our knowledge of the solid electrolyte interface (SEI) which forms atop the reactive lithium deposit. Similar SEI layers have been extensively demonstrated to play a critical role in enhancing cell efficiency and lifespan in lithium-ion batteries. However, in the context of the lithium-mediated nitrogen reduction reaction (Li-NRR) system, the SEI may also hold the key to achieving NH₃ selectivity and preventing the undesired hydrogen evolution reaction.

This presentation covers the preliminary efforts of our ongoing work using in situ neutron reflectometry to gain insight into the Li-NRR mechanism occurring at the electrode interface and characterize the SEI environment that contributes to achieving exceptional faradaic efficiency.

Using NR, we have been able to observe dynamic surface changes in the scattering length density (SLD) profile of the catalytic deposit during Li-NRR, operating at a modest 10% faradaic efficiency, limited by the experimental constraints of the NR cell. To further deepen our understanding, we are utilizing operando galvanostatic electrochemical impedance spectroscopy to establish correlations between these surface changes and the electrochemical response of the cell. This multidimensional approach allows us to unlock crucial insights into the intricate processes taking place at the electrode interface, paving the way for more efficient and sustainable ammonia production through Li-mediated electrochemical reduction of nitrogen gas.

With 170 MT produced in 2020, ammonia is one of the most produced chemicals in the world [1]. However, it is currently produced using the Haber-Bosch process which contributes >1 % of global CO2 emissions. Continuous electrochemical nitrogen Reduction Reaction may not be able to completely replace the Haber-Bosch process but it has numerous advantages which may secure its place in green ammonia production. Continuous electrochemical nitrogen reduction reaction can be done at ambient pressures and temperatures, run directly from (renewable) electricity and enables ammonia production in smaller decentralised facilities. However, research into this field is still relatively new, performance is unoptimised and many important scientific questions remain unanswered. In particular, efficiency and current density are too low for commercial application and the key mechanisms by which the reaction occurs are still unknown. Recently, there have been significant advances which have focused on electrolyte optimisation [2-3] and cell design [4]. 

Optimising performance through the use of dynamic operating conditions is attractive because it can be done at little extra cost while achieving substantial improvements. Dynamic operating conditions have already been demonstrated to increase activity and selectivity towards desired products in the electrochemical CO2 Reduction Reaction [5-6] and increase electrode stability in electrochemical  [7]. 

In this work, dynamic operating conditions are investigated in the continuous electrochemical nitrogen reduction system using Electrochemistry-Mass Spectrometry, a technique which allows subsecond detection of gases and volatile species in real-time. This work builds on Krempl et al.’s work by improving detection times reducing noise which allows dynamic conditions to be investigated [8]. By monitoring H2 evolution (a key parasitic product) at different voltages, the point at which it is minimised was found. However, operating at this new optimal led to the accumulation of a reaction intermediate (lithium) which was not reacting quickly enough to form ammonia. Dynamic operating conditions were utilised to alternate between this H2 evolution minimum and an ammonia forming maximum. With this combination, ammonia selectivity was found to increase substantially from 7.9 % to 18 %. 

Lithium-mediated nitrogen reduction reaction (Li-NRR) is recognised as a high rate and selectivity pathway for green ammonia synthesis.^[1] However, practical implementation requires further advancements in yield rate and stability.^[1-3] Our previous study established a stable phosphonium cation/ylide proton shuttling cycle in a LiBF₄ electrolyte, achieving a faradaic efficiency (FE) of 69 ± 1%.^[4] Recently, the phosphonium-based proton shuttle in our robust high-concentration LiNTf₂ electrolyte outperformed LiBF₄, with doubled yield rate and improved FE of 75 ± 4%.^[5],[6] Despite the performance of the ethanol proton shuttle is still better, which is near 100 % FE and ca. 0.5 μmol s^-1 cm^-2 yield rate,^[5] the phosphonium cation is beneficial over the ethanol for no side products through tetrahydrofuranylation.^[6] This motivated us to deeply investigate the paramteres affecting the phosphonium cation shuttle’s performance in the high-concentration LiNTf₂ electrolyte.

Herein, we explored the relationship between the mass-transport characteristics of the electrolyte solution and the Li-NRR performance with three smaller relatives of the originally studied phosphonium cation, [P_6,6,6,14]⁺, specifically  [P_1,2,2,2]⁺, [P_1,4,4,4]⁺, [P_4,4,4,8]⁺ where the subscripted numbers represent the number of carbons in each of the four alkyl chains. An increase in the phosphonium alkyl chain length results in a noticeable decrease in the ionic conductivity and increase in the viscosity of the electrolyte solution. Furthermore, the diffusion coefficient of phosphonium cations measured by pulsed field gradient NMR techniques decreases as the alkyl chain length increases, with [P_6,6,6,14]⁺ having half the diffusion coefficient (0.93 × 10^-12 m² s^-1) of [P_1,2,2,2]⁺. The Li⁺ diffusion coefficient follows a similar, but less pronounced trend as it is moderately reduced from 0.74 × 10^-12 m² s^-1 in the [P_1,2,2,2]⁺ containing solution to 0.67 × 10^-12 m² s^-1 when using [P_6,6,6,14]⁺ shuttle. Interestingly, the type of phosphonium cations has minimal impact on the NTf₂^- diffusion coefficient. Based on these transport behaviours, one might expect that the longer phosphonium alkyl chain would adversely affect the Li-NRR performance because of the lower lithium diffusion. However, contrary to this expectation, the ammonia yield rate and the FE of the process increases steadly in the order [P_1,2,2,2]⁺ < [P_1,4,4,4]⁺ < [P_4,4,4,8]⁺ < [P_6,6,6,14]⁺. This suggests that the size of phosphonium cation directly affects a delicate balance of transport rates of the Li⁺, the proton shuttle and the N₂ transport at the electrolyte|electrode interface. Moreover, differential capacitance analysis demonstrated that the longer phosphonium alkyl chain, the more stable and compact ionic layer on the electrode surface. This well-structured ionic assembly acts as a protective layer that defines the structure of the solid electrolyte interphase and controls the Li⁺ electroreduction.

Optimising the Li-NRR performance with the best-performing [P_6,6,6,14]⁺ shuttle requires a decrease in the LiNTf₂ concentration from 2 to 1.5 M, which leads to an increase in the Li⁺ diffusion coefficient equal to that of the [P_1,2,2,2]⁺ system. Under this condition, the process is remarkably stable over 68 h with an invariable 80 ± 1% FE and an average yield rate of 300 ± 10 μmol s^-1 cm^-2.

Our study emphasises the complexity of the Li-NRR relationship to the mass-transport processes through correlations with bulk electrolyte properties, and to the ordering of the ionic species at the electrode surface. To achieve a 100 % FE target  with the robust phosphonium cation proton shuttles, future investigations will utilise hydrodynamic and computational modeling techniques.

Electrocatalytic NO_x reduction is a promising way to help restore the natural balance of the nitrogen cycle [1]. Various works agree that nitrate reduction to NH₄⁺/NH₃ involves NO as an intermediate, and NO hydrogenation is the potential-limiting step of NO reduction. However, debates on whether *NO hydrogenation produces *NHO or *NOH hamper catalyst optimization and rational design for NO_x electroreduction [2,3].

In this contribution, I will provide a simple classification of late transition metals for *NO hydrogenation: Cu, Ag, and Au (group 11 of the periodic table) primarily yield *NHO; Ni, Pd, and Pt (group 10) prefer to form *NOH or a combination of *NOH and *NHO. In turn, Co, Rh, and Ir (group 9) predominantly produced *NHO, particularly on adsorption sites with undercoordinated and/or square symmetry. Additionally, Cu and other group 11 elements prove very active for *NO hydrogenation and NO reduction to NH₄⁺/NH₃, while the (100) terraces of various transition metals should display reasonable activities. Statistical analysis enabled qualitative and quantitative conclusions through the use of “catalytic matrices”. These matrices identify that active catalysts for *NO electroreduction statistically favor *NHO over *NOH and possess undercoordinated sites [4].

To conclude, the matrices help uncover that highly active materials for NO reduction should typically contain undercoordinated Cu sites and be mediated by *NHO. The power of the matrices lies in their ability to rapidly extract information and use it to identify active sites with enhanced NO_x electroreduction.

The rising share of renewable electricity is testament to the increasing importance of solar/wind-electric routes to harvest sun light in form of potential differences and free electrons. While some electricity is used directly or stored capacitively, an increasing portion calls for direct conversion into valuable molecular solar fuels or chemicals. This “dark” e-conversion is made possible by heterogeneous electrocatalysis on the surface of solid electrodes coupled to mass and charge transport processes. Sustainable materials synthesis pathways coupled to novel advanced characterization techniques result in a deeper understanding of the origin of reaction kinetic barriers and the origin of transport limitations. This is critically needed for the design of more efficient, electrochemical materials, interfaces, and electrodes for practical electrolytic devices for the production of e-fuels and e-chemicals.

In this presentation, I will report on recent advances in our design and understanding of electrocatalytic materials, interfaces and electrodes relevant to the electrochemical conversion and valorization of CO2 into value-added molecular compounds. Focus will be placed on CO and ethylene as key target e-compounds in conventional liquid cells and Gas Diffusion Electrodes.

Many industrial chemical processes involve a high-energy demand (often still derived from fossil fuels), Urea is an important chemical for the agricultural industry, which accounts for 70% of the global nitrogen-containing fertilizer usage. Currently, urea is produced by the reaction of liquid NH₃ and CO₂^[1] in a process known as the Haber-Meiser process. Despite its importance, this process suffers from high energy demand and CO₂ emissions, mainly due to the NH₃ synthesis step (Haber- Bosch process), which relies on fossil fuel resources. Making urea with electrochemical methods has recently gained interest from the scientific community as this approach provides a way to reduce the high CO₂ emissions currently associated with urea production. Among the various nitrogen sources being explored for urea electrosynthesis, nitrate (NO₃^-) is an attractive one because of its high solubility in water, low dissociation energy and potential to mitigate NO₃⁻ contaminations in water. Even though the mechanism of urea synthesis via CO₂ and NO₃^- coupling is still controversial and not broadly studied, most reports implicate CO* and NH₂* surface intermediates in urea synthesis.^[2] Cu is an attractive electrocatalyst as it can reduce CO₂ to CO and further products and it is also an active catalyst for the reduction of nitrate to ammonia Previous reports on Cu and Cu-based materials showed that urea can be obtained from NO₂^-.^[3,4]  Early research by Shibata et al. with various catalysts demonstrated that the highest faradaic efficiency towards urea from NO₃^- was achieved with a Zn catalyst.^[5] In this presentation, I will show our latest results on the development of Cu bimetallic catalysts (CuZn and CuRh) for urea electrosysnthesis from CO₂ and NO₃^-.

References:

[1]        P. N. Cheremisinoff, Waste Minimization Cost Reduct. Process Ind. 1995, 222–284.

[2]        X. Liu, Y. Jiao, Y. Zheng, M. Jaroniec, S. Z. Qiao, Nat. Commun. 2022, 13, 1–9.

[3]        S. Liu, S. Yin, Z. Wang, Y. Xu, X. Li, L. Wang, H. Wang, Cell Reports Phys. Sci. 2022, 3, 100869.

[4]        N. Cao, Y. Quan, A. Guan, C. Yang, Y. Ji, L. Zhang, G. Zheng, J. Colloid Interface Sci. 2020, 577, 109–114.

[5]         M. Shibata, K. Yoshida, N. Furuya, J. Electrochem. Soc. 1998, 145, 595–600.

Carbon dioxide (CO₂) electrolysis to produce hydrocarbons and oxygenates using copper (Cu) based catalysts has attracted substantial interest due to the direct production of versatile C₂+ feedstocks . Inside the reactor, however, CO₂ electrolyzers produce C2+ compounds occur via a two-step tandem CO₂ to CO and CO to C₂+ steps. Such knowledge has been utilized in catalyst and cathode-to-anode reactor design, but sparingly in the in-plane design of the system. Here we use the knowledge that CO₂ reduction on copper is primarily a tandem reaction, and through modulation of the reactor flow rate achieve C2+ selectivity 84% at CO₂ utilizations of 31%, exceeding theoretical CO₂ utilization efficiencies of 25% for C₂₊ products. We show that higher utilizations are possible when a subset of the reactor performing only CO reduction, instead of CO₂ reduction, preventing excess CO₂ conversion to carbonates. Through use of varied flow field (serpentine, parallel, interdigitated) and pure CO-fed electrolysis, we link these our results to CO residence time. Notably we find that while ethylene production is constant with flow rate (~40%), oxygenates increase substantially at lower flow rates, reaching 45% at 10 SCCM. Finally, we posit that researchers should switch to combined ethylene + ethanol selectivity as a qualifying metric due to the ease of dehydrating ethanol to form ethylene and a demonstrated inability to fully control ethylene:oxygenate branching pathways. Efforts should then shift to the removal of ethanol from membrane electrode assembly systems and downstream recovery through existing commercial processes.

The synthetic methane from hydrogen derived from renewable energy and captured CO₂, so-called e-methane, is one of the promising ways to decarbonize gaseous fuel necessary for realizing carbon neutrality. The e-methane can utilize existing city gas infrastructure, and is particularly effective for high-temperature heat demand of 200°C or higher, which is difficult to replace with electricity. To meet the above-mentioned requirement, Tokyo Gas has started developing electrochemical CO₂ reduction technology using a polymer electrolyte membrane to synthesize e-methane with Osaka University under the “Green Innovation Fund project” in Japan.

Since the CO₂ electrochemical reduction yields chemical species such as CO, ethylene, formic acid, and hydrogen in addition to methane, one of the most important technical challenges is improving methane selectivity.

To solve this challenge and optimize the cell structure, the copper-based catalysts, known to have a potential for methane synthesis, have been designed and evaluated. The progress of catalyst and cell development for improved methane selectivity will be discussed.

In this talk, I will summarize various results on CO electroreduction to the C₂ species ethylene, ethanol and acetaldehyde on Cu-based catalysts.

I will start presenting a pathway for CO electroreduction to ethylene, ethanol and acetaldehyde [1]. An early intermediate in this pathway can be spectroscopically detected, and DFT helps elucidate its structure [2].

Moreover, the pathway predicts that the late stages of ethanol production correspond to the reduction of acetaldehyde [3], while the late stages of ethylene production coincide with the reduction of ethylene oxide [4]. Because these two reactions have different structural sensitivity, one can elucidate the structure of ethanol-producing sites on the rough surface of oxide-derived Cu [5].

Finally, previous work postulated that a *CHO dimer is part of the CO reduction pathway to ethanol [6]. We put that idea to the test by electroreducing glyoxal and determined that the *CHO dimer is unlikely to be a key intermediate of that pathway [7].

Time permitting, I will show that Ag-Cu tandem catalysts open an alternative, ethanol-selective pathway by virtue of their large surface coverage of *CO [8, 9], the structure sensitivity of which can be capitalized on to design active catalysts [10].

A multi-scale first-principles reaction-transport model is derived for the electrochemical reduction of CO2 to fuels and chemicals on polycrystalline copper electrodes. The model utilizes a continuous stirred-tank reactor (CSTR) approximation that captures the relative timescales for mesoscale stochastic processes at the electrode/electrolyte interface
that determine product selectivity. The model is built starting from a large experimental dataset obtained under a broad range of well-defined transport regimes in a gastight rotating cylinder electrode cell. Product distributions under different conditions of transport, applied potential, bulk electrolyte concentration, temperature and catalyst porosity are rationalized by introducing dimensionless numbers that reduce complexity and capture relative time scales for mesoscopic and microscopic dynamics of electrocatalytic reactions on copper electrodes of any porosity. This work demonstrates that one CO2 reduction mechanism can explain differences in selectivity reported for copper-based electrocatalysts when mass transport, concentration polarization effects, and primary and secondary current distributions are taken into account. The reaction-transport model presented in this talk should enable the rational design of CO2 electrolyzers.

Climate change concerns have spurred a growing interest in developing environmentally friendly technologies for energy generation, and the electrochemical reduction of CO₂ (CO₂RR) into value-added chemicals offers a possibility to store renewable energy into chemical bonds. It is therefore of particular interest to develop efficient, selective and durable electrocatalysts. The latter requires fundamental understanding of their structure and surface composition under reaction conditions.

This talk will illustrate how of a multi-technique in-situ/operando experimental approach is able provide in depth mechanistic insights into CO₂RR. A synergistic combination of LC-TEM, EC-AFM, NAP-XPS, XAS, XRD, GC/MS, and Raman Spectroscopy, coupled with machine learning-based data analysis, has been employed to investigate the evolution of the structure/composition of mono (Cu₂O) and bimetallic (ZnO@Cu₂O) cubic nanoparticles and single atom (M-N-C, with M=Fe, Sn, Cu, Co, Ni, Zn) CO₂RR electrocatalysts under reaction conditions.

A main aspect that I will discuss is the use of periodic potential pulses to alter the product selectivity toward desired high order hydrocarbons and alcohols. By screening a variety of product-steering pulse-length conditions for pre-reduced Cu₂O nanocubes, we identified a critical role of the formation of Cu-O_ad or CuOx/(OH)_y species as well as the importance of having an optimal OH_ad versus CO_ad catalyst surface coverage during CO₂RR. For the ZnO@Cu₂O system, we have further unveiled the role of the dynamic interplay between Zn Oxide, CuZn alloy, and metallic Zn formation, the evolution of Cu crystallites, and the adsorption behavior of CO and OH species. These findings pave the road toward improved catalyst design for non-conventional dynamic CO₂RR reaction conditions.

In addition, metal-nitrogen-doped carbons (M-N-C) will be discussed as emerging cost-effective CO₂RR catalysts, with emphasis in the study of their stability during operation. Here operando XAS data revealed drastic differences in the structural evolution of the different M-N-C materials, including reversibly formation of metallic clusters for some of the M-N-Cs studied that can be used to rationalize their distinct electrocatalytic performance and durability.

Finally, our studies are expected to open up new routes for the reutilization of CO₂ through its direct conversion into industrially valuable chemicals and fuels.

Gas diffusion electrodes (GDEs) improve the performance of CO₂ reduction by enhancing the gaseous species transport. GDEs also increase the accessibility of the catalyst and the reaction surface area. A membrane electrode assembly (MEA) electrolyzer is advantageous due to its ease of assembly and low ohmic loss. However, the impact of operational conditions on cell performance and the local variations of mass and charge transfer in the GDE MEA electrolyzer is not well understood, and studies typically focus on individual components rather the complete cell. This study aims to investigate CO₂ electrolysis in a GDE MEA configuration using a porous Ni-based single-site catalyst through a combined computational and experimental approach.

The approach followed here was: i) we developed a model based on the assembly structure and geometry of the MEA cell to represent the experimental setup; ii) we extracted morphological information of the catalyst layer and the diffusion layer by pore-level investigations utilizing the exact mesostructured obtained from tomography, as well as kinetics parameters extracted by a boundary layer model that was fit to the H-cell experiments with the same catalytic material as the one used in the MEA cell; iii) we fed these parameters into the MEA cell model that accounts for the three relevant phases (gas phase for reactant/product transport, membrane phase for ion transport, and solid phase for electron transport) and predicted the cell performance; and iv) we compared the predicted results with the experimental data obtained with the MEA cell to validate our model.

The computational model of the GDE MEA cell was able to predict the behavior of the experiments with less than 15% error. The computed potential was about 0.2 V to 0.4 V lower than the potential in the experiment at the same current, mainly attributed to contact resistances in the system. The model provides local distributions of gaseous species and current density at the catalyst layer and diffusion layer interface. At 15 sccm flow rate, the total current density decreased along the gas flow direction and reached 100 mA/cm² at 50% downstream of the channel. CO₂ concentration depleted after 50% of the channel length. To operate at more negative cell potentials, it was necessary to increase the flow rate or reduce the gas channel length to avoid the competing hydrogen evolution reaction becoming the dominant reaction. For a cell running at 15 sccm, the conversion was approaching 99% at a cell potential of -2.7 V. This was also near the point (-2.6 V) where maximum Faradaic efficiency was reached. Beyond this potential, the additional charge will not contribute to CO evolution but rather hydrogen evolution, because of the depletion of CO₂.

This work offers a practical methodology to provide first insights into the performance-significant design and operational choices of GDE-MEA CO₂ reduction devices. Differences between the model and the experiment are attributed to: i) Competitive adsorption between reactant CO₂ and H₂O on catalytic sites in the experiment; ii) bypass of flow along the GDE, especially at high flow rate, and iii) contact resistance induced potential drops in the cell in between each component (cathode, membrane, anode, current collector, etc). Future work will account for these factors.

CO2 electroreduction into valuable hydrocarbons with high selectivity is of high market interest yet challenging. Cu-based catalysts have a unique catalytic activity towards hydrocarbon (C2+) products in the CO2 electroreduction reaction and are widely studied to promote the corresponding selectivity and activity. The control of the oxidation state of the catalyst is essential in controlling the desired hydrocarbon production. Herein, we steer CO2 electroreduction towards ethylene production with high selectivity in an alkaline flow cell configuration from a copper phosphate catalyst. An optimum faradaic efficiency of 55% for ethylene production was obtained in a 7 M KOH electrolyte for a total current density of 150 mA.cm-2. A high faradaic efficiency for C2+ products of 60% was also obtained. The investigation of the mechanism shows that Cu nanoparticles are derived during electrolysis which may favour the dimerization of *CO to ethylene formation. This work provides new insights into designing catalysts for high-selectivity hydrocarbon formation.

CO₂ reduction provides a carbon neutral means of converting waste CO₂ and surplus electricity into valuable fuels and chemicals to reach the net zero global goal. Only Cu can yield valuable high energy C₂₊ products, due to its unique binding energy with *CO and *H intermediate [1], but only at the Faradaic Efficiencies of up to 52% for ethanol [2] and 87% for ethylene [3], and under high over-potentials and harsh conditions. Single crystal studies have shown that Cu(100) with surface defects (under-coordinated atoms) favours such C₂₊ products even oxygenated products, because of both the correct binding and low barriers for protonation and C-C coupling. Therefore, we hypothesise that by synthesizing nano-porous Cu with (100) orientation, its catalytic activity will be maximised [4 – 6].

Nano-porous materials have many potential applications as sensors, actuators, catalysis, etc, because of their large surface-to-volume ratio and high surface distortion. These structures can be produced by (electro)chemically dealloying a bimetallic alloy, in a regime where one of the components is much more chemically active than the other. As the active species are removed, the remaining material forms a nano-porous ‘sponge’ that has a bi-continuous structure, of which the amount of under-coordinated atoms is significant [7 – 8]. Inspired by the work from Chattot et al [9], where a linear relationship between the surface distortion of Pt and its oxygen reduction reactivity was found, we hypothesise that the CO₂ reduction reactivity of Cu surface could also be tailored by introducing surface distortion via dealloying.

Herein, we systematically studied the corrosion behaviour of Cu₂₀Zn₈₀ brass, using cryo-atomic probe tomography (cryo-APT) and in situ synchrotron X-ray diffraction (XRD), as shown by Figure 1. We successfully synthesised a series of nano-porous Cu materials with different ligament sizes, ranging from tens of nanometres to micrometres, via chemical dealloying by just changing temperatures. Synchrotron XRD measurement indicates that there is a huge but different micro-strain on these dealloyed nano-porous Cu, which is caused by the under-coordinated atoms. Electrochemical CO₂ and CO reduction measurement was then conducted, showing their significantly different catalytic activities, which correlated well with their micro-strains measured.

Electrochemical CO₂ reduction is a candidate for reduced CO₂ concentration in the atmosphere and changes to usable compounds. Zero-gap reactor for CO₂ reduction is expected to realization due to its low applied voltage and high current density.

The zero-gap reactor for CO₂ reduction requires an anion exchange membrane and an anolyte. These requirements are different from the polymer electrolyte electrochemical cell for water electrolysis. Although the membrane is an anion exchange, cations in anolyte pass through from anode to cathode. The existence of a cation in the cathode is also known to be essential for CO₂ reduction, thus, the cation in the cathode has a possibility to affect the properties of CO₂ reduction. This report discusses the effects of the anolyte of KHCO₃ concentration.

 The KHCO₃ concentration was 0.01, 0.1, and 1.0 mol/L, the catalysts of the cathode for CO₂ reduction and the anode for water oxidation were Cu and IrOx, respectively. The electrode area was 5 cm². Since the catalyst for the cathode was Cu, the products in the cathode were mainly CO, CH₄, and C₂H₄, with the satellite reaction product of H₂ from water reduction.

The applied voltage under a constant current density of 200 mA/cm² was lowest at the KHCO₃ concentration of 1.0 mol/L. The maximum faradaic efficiencies of C₂H₄ around 35% were obtained at 4.2, 3.6, and 3.2 V for 0.01, 0.1, and 1.0 mol/L, respectively. From these results, the higher anolyte concentration shows the lower applied voltage at the same current density and at the highest faradaic efficiency of C₂H₄. The reliability was, however, the best at the concentration of 0.1 mol/L because the CO₂ gas flow was strangled by the precipitation of the salt at 1.0 mol/L and the current density increased at 0.01 mol/L. The anolyte concentration affects the CO2 reduction and the 0.1 mol/L KHCO₃ was the best considering all the results.

Electrochemical CO reduction (ECOR) can act as a potential bridge between CO2-to-CO technologies and renewable production of C2+ chemicals. Along with the development of catalyst materials for selective and efficient CO reduction, it is imperative to optimize electrolysis conditions and cell parameters to efficiently reduce CO at industrially relevant current density and produce pure concentrated product streams. In this work, we study ECOR is three different cell configurations, firstly, microfluidic configuration, secondly, a hybrid configuration with anode zero gap, and lastly, a zero gap configuration. We establish the optimal working conditions for each configuration and compare the fundamental differences in each configuration.
The zero gap configuration is optimal for producing a stable product stream of ethylene, acetate, ethanol and propanol for current densities upto 1 Acm-2 at reasonable cell potentials and can sustain long term C2+ production of >70% for upto 10 hours at a current density of 200 mAcm-2. The catalytic activity in this configuration is insensitive to anolyte pH and the cell can run at relatively lower alkaline concentrations. On the other hand, the product selectivity in hybrid cell configuration changes with catholyte concentrations. The catholyte ensures a high local pH near the cathode and therefore the product selectivity can be altered by changing alkaline concentration. This hybrid configuration works stable with anode catalyst coated membranes for current densities of upto 0.8 Acm-2, however the flowing catholyte makes the long term operation difficult. It is interesting to note the substantial consequence on catalytic activity by altering cell configuration and electrolysis conditions. These results stress on the importance of optimising cell configuration and measurement parameters for attaining optimum working conditions for reaching industrially relevant current densities.

Electrochemical reduction of CO2 presents an attractive way to store renewable energy in chemical bonds in a potentially carbon-neutral way. However, current electrolyzers suffer from intrinsic problems, like flooding and salt accumulation, that must be overcome to industrialize the technology. To resolve flooding and salt precipitation issues, researchers have used ultra-hydrophobic electrodes based on either polytetrafluoroethylene (PTFE) gas-diffusion layers (GDL’s), or carbon-based GDL’s with added PTFE. While the PTFE backbone is highly-resistant to flooding, the non-conductive nature of PTFE means that without additional current collection the catalyst layer itself is responsible for electron-dispersion, which penalizes system efficiency and stability. In this work, we present operando results that illustrate the poor current/potential distribution in thin catalyst layers (~50 nm) deposited onto PTFE GDL’s. We then compare the effects of thicker catalyst layers (~500 nm) and a newly developed non-interfering current collector (NICC). The NICC can maintain even current distribution with 10-fold thinner catalyst layers while improving stability towards ethylene (≥ 30%) by approximately two-fold. 

CO2 electrolysis using silver (Ag) and copper (Cu) based catalysts have been widely studied due to their ability to produce CO and multi-carbon products respectively. In industrially relevant membrane electrode assembly configurations, long term operational stability is hampered due to (bi) carbonate precipitation at the cathode triggered by alkali metal cation crossover from the anode. In this work, we investigate the role of cation crossover for Ag and Cu based catalysts by varying cation concentrations and the cation identity. We find that cation crossover from the anode is essential for CO2 activation and cation identity (K+, Na+) affect CO2RR selectivities significantly as shown in a number of previous studies. Further, we find that cation concentration do not alter product selectivity for a Ag catalyst producing CO, but alter product distribution significantly for a Cu catalyst, showing that C-C coupling rates are significantly affected by local cation concentration at the cathode. In contrast, cation crossover is detrimental for long term operation due to (bi) carbonate precipitation at the electrolyte free cathode, that induces flooding of the gas diffusion electrode over time. These results reveal that a proper management of local cation and water concentrations are essential in order to acheive long term operational stability in zero gap CO2 electrolyzers. 

The membrane-electrode assembly (MEA) approach appears to be the most promising technique to realize the high-rate CO2/CO electrolysis, however there are major challenges related to the crossover of ions and liquid products from cathode to anode via the membrane and the concomitant anodic oxidation reactions (AORs). In this perspective, by combining experimental and theoretical analyses, we elaborate on several impacts of anodic oxidation of liquid products in terms of performance evaluation. Firstly, we analyzed the crossover behavior of several typical liquid products through an anion-exchange membrane. Subsequently, two instructive examples (introducing formate or ethanol oxidation during electrolysis) reveals that the dynamic change of the anolyte (i.e., pH and composition) not only brings a slight shift of anodic potentials (i.e., change of competing reactions), but also affects the chemical stability of the anode catalyst. Anodic oxidation of liquid products can also cause either over- or under-estimation of the faradaic efficiency, leading to an inaccurate assessment of overall performance. To comprehensively understand fundamentals of AORs, we further develop a theoretical guideline with hierarchical indicators to predict and regulate the possible AORs in an electrolyzer. We conclude by giving some suggestions on rigorous performance evaluations for high-rate CO2/CO electrolysis in the MEA-based setup.

This talk will analyze CO₂ electrolysis from a device perspective to provide insight into what are the bottlenecks in the field and how to resolve them.  In particular we will focus on our results using synchrotron based wide angle x-ray scattering to observe CO₂ electrolysis devices in real time while concomitantly measuring anode and cathode product distributions.  During higher current density (>100 mA/cm²) CO₂ electrolysis devices are prone to cathodic ‘flooding’ leading to greatly enhanced hydrogen production.  We show that during this degradatory issue there is chaotic oscillatory fluctuations in potential, and product distribution.¹  By analyzing these fluctuations in the presence of a synchrotron, we can monitor salt deposition and even electrolyte penetration by a shift in the background scattering signal.  From the comprehensive analysis we have developed a hypothesis of why we both see the oscillations as well as flooding.  Interestingly, salt solubility and precipitation has a strong role in flooding issues. 

We then analyzed various salts (Li, Na, K, Cs) of differing solubility while doing CO₂ electrolysis.²  The synchrotron analysis clearly demonstrates the importance of salt solubility on stable operation.  We then switched to CO electrolysis as this allowed for more soluble hydroxides compared to the carbonates used during CO₂ electrolysis.  While this allowed for more stable hydration management, it did corrode the anode, as evidenced by IrO2 appearing on the cathode.  This was resolved by switching to a Ni anode, though long term acetate build-up caused pH issues.  The acetate issues was resolved by simply removing the acetate from the anolyte during testing.   This allowed for multiple tests with over 100 hour stability.³

CO₂ electrolysis to value-added products is a promising technology to close the carbon cycle and sequester anthropogenic CO₂ into chemical feedstocks; increasing the current density for multi-carbon products is one of the requirements for practical implementation. [1] The use of gas diffusion electrodes (GDEs) that allow the CO₂ reduction reactions (CO₂RR) to occur at the solid-catalyst/liquid-electrolyte/gaseous-CO₂ interface, effectively accelerates the CO₂RR by solving the problem of the mass transport limitation due to the inherently low diffusion and solubility of CO₂ in water. However, CO₂RR at the three-phase interface is complex, and guidelines for catalyst design toward its high activity have not been fully established. Since macrostructure significantly influences activity, it is challenging to distinguish between surface reactivity at the microscale (molecular level) and material transport properties at the macroscale (three-phase interface level). This presentation summarises our recent studies on high-rate CO₂RR from the point of view of both novel electrocatalyst designs and appropriate electrode assembly.

We successfully applied various metal-doped covalent triazine frameworks (M-CTFs) as platforms for CO₂RR electrocatalysts on GDEs [2-5]. In addition, we conducted systematic first-principles calculations and found that this reaction selectivity correlates with the adsorption energy of the intermediates. As M-CTFs possess the same framework, it is possible to vary only the metal center (catalytic active center) with the identical macrostructure of the catalyst layer. Thus, as we can directly compare the catalytic activity of the metal centers, M-CTFs serve as a model catalyst for establishing design guidelines for gaseous CO₂ electrocatalysts consisting of single metal centers.

We also achieved the ultra-high-rate CO₂ electrolysis to multicarbon products (C₂₊) by designing the triple phase interface composed of ordinary materials. We successfully increased the partial current density for C₂₊ over cupric oxide (CuO) nanoparticles on gas diffusion electrodes in neutral electrolytes to a record value of 1.7 A/cm² [6,7]. Specifically, we highlighted that the thickness of the catalyst layers is a crucial parameter that impacts the maximum current density for C₂₊. Although the GDE and electrocatalyst used in this case are not unique, the optimized assembly elicits their potential.

Electrochemical CO₂ reduction reaction, is the conversion of CO₂ to products through the application of charge in an electrolysis cell. If CO₂ could be selectively converted to a particular high value product at low overpotential and high current density, CO₂ would be turned into an energy storage molecule and/or a chemical feedstock, driving society closer to closing the carbon loop.

Since the early-mid 90s, research into CO₂ reduction reaction materials has primarily centred around copper^1-3.  Copper has the unique ability to bind to key intermediates *CO and H* moderately⁴, improving the chance of hydrogenation or coupling reaction steps⁵. Incremental improvements in cell design and nano structuring have improved the partial current density towards high value C₂₊ products. Size control⁶, oxide derived copper⁷ and facets⁸ among others effects have been tested, but questions remain whether the intrinsic activity towards the CO₂ reduction reaction on copper has been improved. A possible work around, is to alter the localized concentration of key intermediates. Therefore, multiple groups have paired Cu with a secondary, CO producing active site, to form a tandem mechanism^9-11.

In this talk I will be highlighting the advantages of using atomic layer deposition (ALD) in electrocatalysis and how it can form a method towards altering selectivity for the CO₂ reduction reaction.  I will initially present the requirement for altering copper activity through relating activity towards CO₂ reduction reaction to surface roughness of nanostructured copper and oxide-derived copper. Subsequently, trends in selectivity with different metal oxide nanoclusters atop copper nanoparticles are shown towards the CO₂ reduction reaction, with CO reduction reaction being used as a mechanistic tool. Further characterization techniques both ex and in situ will be presented to shed light on the changes in selectivity including XPS, in-situ contact angle measurements and FTIR amongst others.

The electrochemical conversion of CO2 (CO₂RR) into value-added chemicals using renewable energy sources is seen as one of the most promising approaches to achieve defossilization of the chemical industry.[1] The main targets are the direct production of multicarbon products such as ethylene and ethanol and the generation of syngas (CO+H₂), a feedstock in the Fischer Tropsch process. However, even though the CO₂RR process has been extensively investigated for the last 30 years,[2] its industrial application still faces significant challenges. To meet the industrial requirements, many operational parameters must be optimized besides the catalyst material such as the electrode configuration, the reaction microenvironment, and the electrolyzer design.[3] The state-of-the-art CO2RR setups, which consist of gas diffusion electrodes (GDEs) in flow cells and membrane electrode assembly (MEA) electrolyzers, already achieve relevant current densities (≥ 200 mA/cm2) but further research is needed to enhance the GDEs stability during long-term operation.

In this contribution, we present the synthesis of Ni and Cu-based electrocatalysts with high conversion to syngas and multicarbon products, respectively. These materials are synthesized via a single pyrolysis using a benzoxazine monomer (BO) as a precursor,[4] which leads to more active and stable catalyst materials than those produced with just the metal precursor. Besides the catalyst synthesis, we will discuss how the gas diffusion layer, and the hydrophobic/ion conductivity properties of the catalyst layer, strongly influence the GDEs’ stability and suppress the parasitic hydrogen evolution reaction. We show that, upon optimization, the Ni-BO-based GDE exhibits syngas production at -200 mA/cm² with a minimum stability of 2 h while the Cu-BO-based GDE is able to reach current densities up to -600 mA/cm² with high selectivity for ethanol and ethylene. The present work provides insight into important parameters that must be considered to fabricate stable GDEs for the conversion of CO₂ into valuable products at industrially-relevant current densities.

The Single-site MNC catalysts offer a ground-breaking non-precious-metal platform for CO₂ electrolysis, demonstrating exceptional faradaic efficiency towards CO (> 90% FE_CO) at industrial-relevant current densities (> 250 mA cm^-2) in regular membrane electrode assembly electrolyzer.[1] However, achieving such performance requires a cell potential (E_Cell) above 3 V, resulting in energy efficiency (EE) below 40% (EE = E_CO2-to-CO * FE_CO / E_Cell) [2, 3]. To address this challenge, a crucial technical solution involves further enhancing the catalyst material to minimize catalytic potential loss (for reduced E_Cell).

The metal center highly influences the intrinsic activity-potential relationship of the MNC catalysts. FeNx exhibits superior binding energy to the crucial intermediate, *COOH, for CO formation, compared to other metal centers. However, the FeNC ones suffer poisoning during the reaction, restricting their practical application in large-scale electrolyzers at high current densities.[4] Hence, to address this limitation, we designed a novel experimental approach to deactivate and reactivate the FeNC catalyst under CO2 electrolysis conditions using pulsed potentials. Interestingly, coupled with a millisecond-resolution differential electrochemical mass spectrometer, we defined an uncommon but potential-dependent recoverable CO₂ poisoning phenomenon on the FeNC catalyst. This comprehensive investigation unravels the mechanisms of CO₂ poisoning and recovery of the FeNC catalyst at the molecular level. Also, it offers practical guidance for mitigating the poisoning issue in large-scale applications.

The CO₂ reduction reaction (CO2RR) has shown promise for producing C1-based feedstocks, including formic acid, CO, and syngas, under ambient conditions. A great challenge in this effort is to achieve control over the reaction path in order to define the product selectivity. In this work, we exploit the well-defined atomic structure and tunable coordination environment of Bi-based single atom catalysts (SACs)[1] embedded in carbon-nitrogen frameworks to show that the coordination environment of a single metallic species can be used to tune product selectivity. Bi is well-known to be an efficient CO2RR catalyst to produce formic acid,[2, 3] but has also recently been reported for CO generation.[4] While it has been hypothesised that this differing CO2RR product selectivity may arise from different Bi coordination environments, these different products stem from dissimilar catalytic systems. Here, we aim to test this hypothesis on the same catalyst system to exclude other influences on selectivity.

Using Bi SACs within a carbon-nitrogen framework, we find that the CO2RR selectivity can be tuned towards formic acid or syngas production by choosing tailored annealing treatments. Bi SACs anchored on commercially available carbon black were synthesized via a solution-based chemical method followed by inert atmosphere annealing. The single-atomic nature of Bi is confirmed by both scanning transmission electron microscopy and X-ray absorption spectroscopy. Low-temperature (300 °C) annealing of these samples results in oxygen-coordinated Bi SACs and promotes formic acid generation, while high-temperature annealing (800 °C) favours formation of nitrogen-coordinated Bi SACs and syngas production. Since the versatility of a single CO2RR catalyst system for producing two different major products has rarely been reported, our work opens up a new direction of tuning the CO2RR C1 product selectivity using SACs.

Nanoparticle composites are widely used as catalysts in various chemical transformations. However, large-scale production of these materials is crucial for their practical implementation, and more efficient methods are needed. This presentation highlights recent advancements in the production of metal nanoparticles on carbon nanofibers through microwave heating. To achieve this, metal ions were deposited onto the carbon nanofiber surfaces using ethanol solutions, which were subsequently exposed to hexane, an antisolvent for metal ions. The carbon fibers were then rapidly and locally heated via Joule heating, resulting in the instantaneous formation of metal nanoparticles on the substrate surfaces in just a few seconds of microwave exposure, all in an ambient environment.
Furthermore, if nickel salt was used to produce nickel nanoparticles, carbon nanotubes (CNTs) were also produced on the carbon fibers during the process. This was due to several factors, including the vaporization of solvent residue that created a local environment for the reduction of metal salt, the decomposition of carbonaceous precursors on nanoparticle catalysts, and the fast cooling related to the condensation of hexane. We are exploring using the system to conver carbon dioxide to CNTs. Overall, this technique holds great promise for the scalable production of supported nanoparticle composites with potentially significant applications in the field of catalysis.

The intermittent photovoltaic (PV) power generation requires long term storage to stabilize energy system. Conversion of the excess PV power into valuable chemicals (products of CO₂ reduction, for example) represents an attractive solution for the problem. We address this challenge via ‘artificial leaf’ approach – photovoltaic driven conversion of carbon dioxide (CO₂) and water (H₂O) into valuable chemicals. In our experiment an electrochemical cell (EC), responsible for the CO₂ reduction, was directly connected to the highly efficient silicon heterojunction PV module that generates the sunlight-based electricity.

In this work, we study the performance of the directly coupled PV-driven CO₂ reduction cell with emphasis on the effects of realistic temperatures (25-65°C) and irradiances (0.2 to 1 sun) for the PV module. During the experiment we characterized coupling efficiency in the system and product selectivity of the electrolyzer, catalyst stability and finally solar-to-chemical (STC) efficiency. Coupling efficiency in the directly connected PV-EC system is an important performance parameter and is characterized by the coupling factor C_PV-EC, the ratio between the operating power and the maximum power deliverable by the PV device. The current-voltage parameters of both PV and EC system components were preselected to ensure high power coupling factor under standard test conditions of PV (1 sun irradiance A.M 1,5G and 25°C). A 5-cells silicon heterojunction PV module with maximum power point voltage of 3.2V, current of 383.7 mA, aperture area of 51.7 cm², and power conversion efficiency of 23.82% was connected to a commercially available EC cell with an 8.8 cm² CO-targeted silver catalyst [1].

The directly connected PV-EC device withstands realistic temperature and irradiance variation of the PV module maintaining high coupling factor C_PV-EC for the PV-EC device between 0.89 and 1.00. Furthermore, while temperature minimally affects PV-EC working points (V_WP, I_WP), the variations in irradiance between 0.2 and 1 sun significantly influence the voltage at working point (between 2.55 V and 3.44V respectively) and therefore affect electrolyzer products selectivity. The effect of operating voltage on the electrolyzer product selectivity is studied in a separate experiment with constant voltage steps with 1 hour duration using a potentiostat. As the voltage is increased between 2.6 to 3.4V the product selectivity for CO increases from 80% to 95%. In the operation stability study, we have observed high CO selectivity of approximately 90% over 7 hours of experiment at 3.4V and 330 mA. Performance of the EC cell characterized with the potentiostat suggests that under proper coupling, the PV-EC system can operate with solar to chemical efficiency for CO of approximately 10% over the operating voltage range.

In the ongoing experiments we investigate the CO-selectivity, operating stability and solar to CO efficiency with the directly connected PV-EC device in realistic irradiance and temperature conditions. In addition to that, the catalyst degradation rate on microstructure scale is studied using electron microscopy.

The electrochemical reduction of CO₂ (CO₂R) holds tremendous potential as a pivotal component in future energy systems reliant on renewable fuels. CO₂R proceeds through a complex reaction scheme consisting of multiple proton-electron steps with numerous possible intermediates and products, out of which many have been detected only recently. An additional level of complexity arises from the surface dynamics of the Cu catalysts undergoing structural transformations under potential,  with rapid changes in size, shape, and activity. By combining electrochemical measurements with high-resolution imaging, we identify and track dynamic active sites on the surface of electrodes during electrocatalysis.

In this talk, I will show you examples on the surface dynamics of Cu, Cu oxides and Cu electrodes covered by 2D materials during CO2 electroreduction. I will discuss the use of scanning probe microscopy and solid state spectroscopy to track the surface dynamics of electrocatalysts in-situ, and present a few unconventional strategies to reach significant boosts in the catalytic activity of 2D materials, using spin-selective mechanisms.

In the presentation I will go throught the latest developments that we have been developing in the group on one side on the type of materials and how they reconstruct under reaction conditions and how the relationships with the electrolyte can affect the chemistry taking place. The model systems investigated will allow to understand the particularities of highly reconstructed materials under relevant reaction conditions, this is a very crucial point when trying to go beyond the standard traditional models materials. Additionally the electrolytes can change the complete picture of the reactivity due to the generation of low energy paths, alternative paths that might contribute to the reactivity and more importantly new ways that reaction can be driven in different ways. The relevance of the results indicate that there are ways to allow some of the constraints that are limiting the technical implementation of CO2 reduction technologies in a short time.

Concentrated irradiation enables the production of solar fuels using smaller and inexpensive devices, resulting in decreased costs for solar fuel production. Additionally, by carefully selecting optimal operating conditions, it might be possible to enhance the performance of photoelectrochemical (PEC) devices [1]. A large proportion of the research on semiconducting materials for solar-driven water splitting has focused on their behaviour at room temperature and under 1 sun illumination. Hence, the utilization of high photon fluxes presents new possibilities for solar fuel production, as it has been demonstrated for integrated PV+EC devices [2]. Nevertheless, many obstacles hinder the design and testing of PEC cells intended for operation under concentrated irradiation. The potentially advantageous synergy between higher temperatures and irradiation makes the system complex and difficult to study.

In that regard, the effect of temperature alone on the properties of photoelectrodes has been reported recently for α-Fe₂O₃ [3], showing increased photocurrent densities at high potentials and increased recombination rates at low electrode potentials. In a similar study, BiVO₄ photoelectrodes have shown substantial increase in photocurrent densities across all electrode potentials [4]. The behaviour of photoelectrodes under high irradiations has been performed under relatively low irradiances (<30 kW m^‑2, c.f. 1 sun ≈ 1 kW m^-2) and usually for very stable photoelectrodes, e.g. Fe₂O₃ [5].

The combined effects of temperature and high irradiations on the properties of photoelectrode materials has been rarely investigated experimentally. With the aim to tackle this challenge, we designed and developed a PEC cell for operation under high irradiations (30 – 360 kW m^-2) complemented with a multiphysics model to predict the surface temperature, and the effects of ohmic drop due to bubble evolution, substrate resistance, and current density distributions. The High-Flux PEC cell (HF-PEC) comprises a stainless body steel acting as counter electrode, a high transmission quartz window and a modified Luggin capillary for the reference electrode. To avoid extreme temperatures at the surface of the photoelectrode, the electrolyte was recirculated at the back of the substrate to keep it at lower temperatures. Two photoelectrode materials were investigated: Sn-doped α-Fe₂O₃ and BiVO₄, both deposited on FTO or Ti substrates via spray pyrolysis.

In the case of Ti|α-Fe₂O₃ photoelectrodes, it was found that at high temperatures under 1 sun illumination, the charge transfer efficiencies decreased with temperature at low potentials (< 1.2 V vs. RHE), but increased at higher potentials; in contrast, impedance spectroscopy under high irradiations indicated that charge transfer efficiencies increased for all electrode potentials, even when the surface of the photoelectrode was at higher temperatures. This suggests, that although e-h recombination kinetics increased with temperature, the increased charge transport kinetics and higher exciton concentration could ultimately favour the charge transfer at the semiconductor-electrolyte interface. For FTO|BiVO₄ photoelectrodes, it was found that photocurrent densities do not scale proportionately with irradiance, and that degradation rates for this material are the result of complex interactions between increased transfer efficiencies, high temperatures and high photocurrent densities; it was found that the highest (irradiance-normalized) current density for BiVO₄ was achieved at ca. 120 kW m^-2.

Photoelectrochemical water splitting is a promising way of solar hydrogen generation. However, in order to achieve inexpensive, efficient, and stable photoelectrodes significant further improvements are needed. Perovskite and organic photoactive materials have attracted great scientific interest by reaching record high single-junction solar cell efficiencies, but their photoelectrode performance is currently limited by their instability in an aqueous environment. In this presentation, we will show a cost-effective way of protecting halide perovskite, as well as organic photoactive layers used for solar water splitting to reach both stable (>100 hours) and remarkably high photocurrents (>8 mA cm^‑2 and >25 mA cm^‑2 at 1.23 V_RHE, respectively). The perovskite photoelectrodes were developed using a low annealing temperature carbon paste with tuned energy level CsPbBr₃ photoactive layer. The effect of 2-dimensional (CsPb₂Br₅) and 0-dimensional (Cs₄PbBr₆) perovskite phases on efficiency and stability will be discussed including ways to control their formation. The organic photoanodes applied a ternary bulk heterojunction blend (non-fullerene acceptor and polymer donor) and the interlayers were optimised for stability under 1 sun illumination. Importantly, the lifetime of the photoelectrodes was increased by applying a protective graphite sheet functionalised with electrodeposited oxygen evolution catalyst (NiFeOOH), allowing to reach remarkable stability of several days – instead of the often-reported few hours – at high photocurrent densities, far beyond the current state-of-the art levels.

Transition metal (TM) nitrides are an emerging class of catalytic and photoelectrocatalytic materials.[1],[2] In general, nitrogen-poor TM nitrides are usually refractory materials with metallic character while nitrogen-rich nitrides often possess semiconducting character.[3] Hence, while the former are potential electrocatalyst candidates, the latter may qualify as photoelectrode absorber materials. For example, ZrN has recently been proposed as an electrocatalyst for both the electrochemical nitrogen[4] and oxygen[5] reduction reactions (ORR and NRR), while Zr₃N₄ and also Zr₂N₂O have been suggested as potential photoanode materials in photoelectrochemical water oxidation.[2] In this contribution, we test these hypotheses regarding the (photo)electrochemical characteristics of Zr-based (oxy)nitrides by experiment. To this end, we investigate reactively sputtered thin films for the electrochemical NRR/ORR and the photoelectrochemical oxygen evolution reaction (OER). Previous experiments on Ta-based nitrides have shown that addition of oxygen during the reactive sputter process is necessary to access higher metal oxidation states.[6] Indeed, as we introduce controlled amounts of oxygen at otherwise fixed deposition conditions, we observe a transition from metallic ZrN to a disordered nitrogen-rich Zr_xN_y to a crystalline bixbyite-type Zr₂N₂O to nitrogen-doped cubic ZrO₂. Crystalline Zr₃N₄ was not accessible under the used experimental conditions. While we observe a lack of electrocatalytic activity for ZrN in NRR and ORR and instabilities of the disordered nitrogen-rich Zr_xN_y in the photoelectrochemical OER, introducing more oxygen into the structure leads to a more stable crystalline structure (Zr₂N₂O), the opening of a band gap in the visible range, and the emergence of photoelectrochemical activity for oxidation reactions. Based on chopped linear sweep voltammetry measurements, we show that Zr₂N₂O films are photoactive for the OER in alkaline electrolyte with low onset potentials, indicating an overall favorable band alignment of the material with respect to the water oxidation and reduction potentials. While the observed photocurrents are still significantly lower than for the benchmark oxynitride TaON, further material optimization could potentially close this gap and provide a materials system functioning as sustainable photoanode.

Harnessing solar energy through photoelectrochemical (PEC) water splitting approach offers a promising and sustainable pathway to produce green hydrogen (H₂). However, to ensure the viability, cost-effectiveness, and long-term stability of this approach, fabricating an abundant and durable photoelectrode is crucial. Barium stannate (BaSnO₃) has not been considered promising material for PEC water splitting applications due to its wide band gap (˃3 eV) and limited solar absorption characteristics.[1] In this study, we optimized a spray pyrolysis method to fabricate phase pure BaSnO₃ photoanodes with a smaller optical gap of ∼2.2 eV. By annealing these photoanodes in a mild H₂ gas environment, we observed a significant decrease in the optical gap to ~1.5 eV. This led to an enhanced photoelectrochemical performance, with a 5-fold increase in the photocurrent density reaching ~0.5 mAcm^-2 at 1.23 V vs. RHE and an improved onset potential of ~0 V vs. RHE. To understand the reason behind this enhancement, we have used a combination of spectroscopy techniques, including photoluminescence (PL), time-resolved surface photovoltage analysis (TR-SPV), and time-resolved microwave photoconductivity (TRMC) measurements. We find that mild H₂ annealing of BaSnO₃ generates a set of mid-gap defect states associated with oxygen vacancies and Sn²⁺ centres.[2] Increasing the population of these mid-gap states, shifts the optical onset of photocurrent collection and mobile charge carrier generation to photon energies as low as ~1.5 eV. Furthermore, the transient signals of charge carriers show the extended lifetime after H₂ treatment and provides the evidence that carriers are transported via tunnelling through delocalized defect states. We show here that BaSnO₃ is a promising material with tunable optical properties and electronic structure.

The recent emergence of ultrathin oxide layers in catalysis has led to more corrosion-resistant photoelectrodes and enhanced catalytic selectivity – suppressing side reactions and catalyst poisoning [1]  Silica nanolayers for example demonstrated enhanced proton transfer [2] and electron transfer [3] across solid-solid interfaces when embedding molecular wires. The nanoscale integration of incompatible catalytic environments of CO₂ reduction and H₂O oxidation – similar to a thylakoid membrane – can potentially be achieved by such ultrathin oxide layers, provided we can maintain directional electronic and protonic communication across the layer.

Here, we investigate the proton conductivity and O₂ impermeability of ultrathin, dense, and amorphous Al₂O₃ layers and find that the diffusivity of protons is strongly dependent on the flux due to induced morphological changes in the alumina layer over time. Dense amorphous alumina layers were prepared via pulsed laser deposition (PLD; 2.5 nm, 3 nm, and 5 nm) and the porosity was varied via the oxygen background pressure of the chamber. We used electrochemical impedance spectroscopy to determine diffusion coefficients and charge transfer resistances, and complementary electrochemical FT-Infrared reflection-absorption spectroscopy was applied to analyze the dynamic structural changes of alumina over time in-situ (Figure 1b). In fact, we observe that initially, 2.5 nm of alumina can block both protons and oxygen, whereas over time the proton permeation improves while we can exclude dissolution of the Al₂O₃ layer (Figure 1c)

These discoveries facilitate the integration of incompatible catalytic functions on the nanoscale, thereby opening a new design space for developing macroscale systems. The core–shell nanotube array geometry for developing an artificial photosystem with the goal of placing CO₂ reduction inside the tubes and H₂O oxidation outside of them is just one among many opportunities to pursue.

During my talk I will discuss four topics, over which I have felt concern over the past few years:

- The concept of applied bias photon-to-current efficiency (ABPE).

The ABPE is described as ‘a diagnostic measurement in materials development’. However, the widely accepted ABPE equation is not formulated as a true energetic efficiency. Furthermore, negative ABPEs are obtained for applied potentials > 1.23 V, resulting in increasingly negative efficiencies for increasingly high photocurrents, which is non-sensical. Both of these issues invalidate the ABPE equation for the very condition it is designed to represent. It is also noticeable that a lot of recent reviews and systematic studies of photoelectrode materials in biased systems do not use the ABPE as an effective way to compare their performances. I will discuss the issues of the currently accepted ABPE formulation and suggest a more rigorous formulation.

- The perpetual reporting of incident radiation on photoelectrochemical cells as AM 1.5 G and 100 mW cm^-2

The accepted basic requirement for the characterisation of solar water splitting systems is the same as for benchmarking the performances of solar cells: the incident spectral irradiance has to match that of the Air Mass 1.5 Global (AM 1.5 G) spectrum of natural sunlight, amounting to 100 mW cm^-2 when integrated. The spectra of light sources is rarely an exact match to the AM 1.5 solar spectrum, even if an AM 1.5 filter is used.  I will discuss the importance rigorous calibration and the need to report the actual spectra of light sources used during the characterization of photoactive materials and assessment of photoelectrochemical devices.

- The construction of Pourbaix diagrams to predict photoelectrode and catalyst stability – example of BiVO₄ degradation

There are some puzzling aspects in the Pourbaix diagrams being used for demonstrating the reactions responsible for light-induced BiVO₄ degradation. I will present the published Pourbaix diagrams for the combined aqueous bismuth and vanadium systems and discuss why some postulated reactions that are presented as electrochemical (i.e. involving a change in oxidation state) cannot actually be so. I will also consider why chemical speciation in different electrolytes can contribute to electrode degradation.  

- Effect of temperature on (photo)electrolyser performance

Solar cells must be maintained at 25 °C during characterisation and here the characterisation of water splitting systems ceases to follow the same standards. The question is whether this matters. The deviation of photoabsorber temperature from 25°C in solar water splitting systems is not necessarily unreasonable or preventable, since the presence of electrolyte makes it harder to fix the photoabsorber temperature to one specific constant value; photoelectrochemical cells are not usually jacketed or designed to be immersed in water baths and so the electrolyte (and hence photoabsorber) temperature could readily vary by > 5 °C, depending on the ‘room temperature’ of a laboratory at the start of the experiment, and can increase by > 10 °C relative to the starting temperature, depending on the photocurrent density, size of the absorber relative to the volume of electrolyte and the duration of the experiment. It therefore seems more important for the electrolyte temperature to be measured, rather than controlled, since temperature affects Gibbs free energy of formation of the water splitting reaction and the volumetric molar densities of evolving gases. I will show, from the thermodynamic viewpoint, the importance of electrolyte temperature in (photo)electrolysis.

Millions of families around the world remain vulnerable to water scarcity and have no access to drinking water. Advanced oxidation processes (AOPs) are an effective way towards water purification with qualified reactive oxygen species (ROSs) while are impeded by the high-cost and tedious process in either input of consumable reagent, production of ROS, and the pre-treatment of supporting electrolyte. Herein, we couple solar light-assisted H2O2 production from water and photo-Fenton-like reactions into a self-cyclable system by using artificial leaf, achieving an unassisted H2O2 production rate of 0.77 μmol/(min·cm2) under 1 Sun AM 1.5 illumination. Furthermore, a large (70 cm2) artificial leaf was used for an unassisted solar-driven bicarbonate-activated hydrogen peroxide (BAP) system with recycled catalysts for real-time wastewater purification with requirements for only water, oxygen and sunlight. This demonstration highlights the feasibility and scalability of photoelectrochemical technology for decentralized environmental governance applications from laboratory benchtops to industry.

Nitriles are interesting class of organic compounds included in a wide variety of natural products and industrial processes, that have been explored as potential Liquid Organic Hydrogen Carriers (LOHCs) due to their high hydrogen capacity and stability.  Conventional methods for nitrile synthesis suffer from low atom economy, the use of toxic reagents, and limited selectivity. An alternative approach involves the oxidation of primary amines through organic electrosynthesis, which offers a safer and more environmentally friendly alternative by utilizing electric current and reducing hazardous solvents. Our research focuses on developing a green, selective, and gentle method for synthesizing nitriles in aqueous media, based on electrochemical procedures that allow eliminating the need for harsh reaction conditions. To that end, we have devised a facile alternative process for synthesizing electrodes through the electrodeposition of nickel on various supports for the electrooxidation of amines to nitriles.

In the electrooxidation of primary amines to nitriles with Ni based electrodes, hydrogen in produced at the cathode, whereas de amine is oxidized at the anode due to the redox par Ni²⁺/Ni³⁺ formed at the anode. To evaluate the effectiveness of different nickel-based electrodes, we conducted screening tests involving the electrooxidation of different aromatic and aliphatic primary amines. The electrodes tested include Ni foil (NiF), Ni45^[1], Ni foam (NF), Ni electrodeposited on NF (NieNF), and Ni electrodeposited on a graphite pencil rod (NieGPR). Among these, the NieNF electrode demonstrated the most favorable results in terms of high yields (>95%) and substrate tolerance. Notably, our proposed electrodes exhibit a significant advantage over Ni/Se electrodes reported in the literature^[2] , enabling a reduction of the reaction time for complete amine oxidation by half.

To sum up, the current project paves the way to produce both nitriles and H₂ with low cost and high   efficiency, thus grasping great potentials in the future energy conversion and storage technologies, sustainable environmental issues and beyond.

Solar hydrogen generation by photoelectrochemical (PEC) water splitting allows for direct photon-to-molecule conversion in a standalone system. Although it is one of the most promising approaches to generate renewable hydrogen, it is also the most challenging because of the multitude of processes occurring concurrently and at very short time scales.

Bismuth vanadate (BiVO₄) is an ideal photoanode material because of its favourable band gap of 2.4 eV [1], which allows it to absorb photons in the visible region of the solar spectrum and has a theoretical solar to hydrogen (STH) efficiency of ~ 9.2%. It has suitable band edges for the water redox process, is durable in aqueous solution, good crystallinity and made up of earth abundant materials. However, BiVO₄ photoanodes suffer from poor charge separation in the bulk of the material and at the electrolyte interface during the PEC water splitting process [2]. Doping of BiVO₄ is a common strategy used to improve charge separation [3]. Doping by electron donors can improve the electrical conductivity by increasing the electron density of BiVO₄ [4]. Doping of BiVO₄ with hexavalent Molybdenum (Mo⁶⁺) has been shown to enhance photocurrent generation due to more efficient charge separation [5].

In this work, we compare the charge separation efficiency of a homogenous doping concentration profile to a gradient doping concentration profile of Mo-doped BiVO₄. Gradient doping induces an upward band bending which amplifies charge separation within the bulk of the BiVO₄ film. Mo-doped BiVO₄ thin films are deposited on FTO-coated glass substrates by ultrasonic spray pyrolysis (USP). Morphological characterisations reveal controlled successive layered films, wherein the number of layers correspond to the number of cycles using our USP deposition process. Gradient doping is achieved by depositing controlled successive Mo-doped BiVO₄ layers that contain increasing dopant concentrations using this method. Their improvement in optical absorption and PEC performance is elucidated by material, optical, Mott-Schottky characterisations and electrochemical impedance spectroscopy.

Gas diffusion electrodes are essential components of common fuel and electrolysis cells that use gas phase reactants and products, but are typically made from graphitic carbon or metallic materials, which do not allow light transmittance, and thus limit the development of photoelectrode membrane assemblies for gas-phase solar fuel production. In this presentation, the application of solar H₂ production from humid air is motivated and the simple and scalable preparation of transparent gas-diffusion layers using F-doped SnO₂ (FTO) coated SiO₂ interconnected fiber felt substrates is introduced[1]. The resulting substrates have a porosity of 90 %, a roughness factor of 15.8 and a Young’s Modulus of 0.2 GPa. A sheet resistivity of 20 ± 3 Ω sq⁻¹ and a loss of incident light of 41% at an illumination wavelength of 550 nm is found with FTO coating. The application of various semiconductors on the substrates was established including Fe₂O₃ (chemical bath deposition), CuSCN and Cu₂O[2] (electrodeposition ), and semiconducting polymers[3] (dip coating ) and the liquid-phase photoelectrochemical performance commensurate with flat FTO substrates was confirmed. Finally, gas phase H₂ production was demonstrated with a polymer semiconductor photocathode membrane assembly at 1-Sun photocurrent density on the order of 1 mA cm^–2 and Faradaic efficiency of 40%.

A fundamental understanding of processes occurring at the electrode-electrolyte interface is essential for the development of optimized materials in sustainable energy production. In this talk, I will present two examples that highlight the relevance of atomistic studies on model electrocatalytic systems in understanding existing structure-function relationships and reaction-mechanism.

Firstly, I will introduce our custom experimental setup, which enables a comprehensive characterization of structural, chemical, and electrochemical properties on the same sample. This setup facilitates the transfer of electrodes from ultra-high vacuum conditions, ideal for surface science tools, to an electrochemical cell in an inert atmosphere. By employing this approach, we investigated potential-induced changes on Au(111) surfaces in acidic media. We monitored chemical transformations using ex-situ X-ray photoemission spectroscopy (XPS), providing insights into the electrochemical response, including oxide formation during the onset of the oxygen evolution reaction. Additionally, I will discuss the influence of various electrolyte anions on surface electro-oxidation.

Secondly, I will provide an overview of the local properties of point defects in transition metal dichalcogenide semiconductors (MX₂, M = transition metal, X = chalcogen) that have been proposed as active sites for the hydrogen evolution reaction (HER). By combining 4K scanning tunneling microscopy and spectroscopy (STM/STS), and non-contact atomic force microscopy (nc-AFM), we achieved atomic-scale correlation between the morphology and electronic properties of different types of structural defects in MoSe₂ and WS₂ monolayers. Our investigations unveiled the predominance of substitutional oxygen as the point defect in these semiconductors, effectively suppressing deep in-gap states associated with chalcogen vacancies [1, 2], which have been discussed to mediate the HER. These findings highlight the critical role of local properties in determining the functionality of materials for hydrogen production, ultimately governing the underlying reaction mechanism.

Photoelectrochemical (PEC) water splitting is a promising approach for generating solar hydrogen. To realize inexpensive PEC devices, TiO₂ has been considered a potential photoanode material because of its abundance, stability, and suitable valence-band energy edge for water oxidation. In this work, we will present results on post-treatment strategies to extend the high efficiencies of these photoanodes to the visible region of the solar spectrum. Our research paper details the successful introduction of different point defects (V_O and V_Ti) in TiO₂ photoanodes using a chemical treatment process. We utilized a range of advanced techniques, including surface photovoltage signal measurement (SPV), electron paramagnetic resonance measurement (EPR), and proton magic angle spinning nuclear magnetic resonance (¹H MAS NMR) to investigate the intrinsic band energy structure and surface state of synthesized TiO₂ photoanodes. Our finding indicates that V_O and V_Ti have favorable effects on photoanodes, leading to enhanced PEC performance. The enhancement is attributed to the interplay of collective and localized effects of point defects on TiO₂. The increased point defects narrow the bandgap and enhance donor density in TiO₂, which increases light absorption, conductivity, and photovoltage, as well as reducing the flat-band potential of TiO₂ photoanodes. Additionally, our results show that the presence of localized surface V_Ti surrounded by O^- increases the amount of surface hydroxyls and creates a more basic environment for Ti-OH species. This facilitates the water oxidation process by serving as trapping sites and self-reduction sites during OER. Our study on OER kinetics, using photoelectrochemical impedance spectroscopy (PEIS) and intensity modulated photocurrent spectroscopy (IMPS), demonstrates that the interaction between collective and localized effects of point defects can decrease the charge transfer resistance on the TiO₂-electrolyte junction and increase the concentration of interface hole flux on TiO₂ photoanodes. This is consistent with the observed higher photovoltage after chemical treatment. Our study has revealed that the interaction between V_O and V_Ti has a significant impact on the PEC performance of TiO₂ photoanodes. We believe that these findings will make a valuable contribution to the development of efficient and stable TiO₂ photoanodes and provide valuable insights into the development of higher performance photoanodes for sustainable energy conversion applications.

Water oxidation photoanodes based on earth-abundant metal oxide semiconductors are actively studied due to their limited environmental impact, the stability to photo-corrosion and the tunable optoelectronic properties [1]. BiVO₄/WO₃ heterostructures are now emerging as one of the most promising photoanode, but the activity is limited by surface recombination and sluggish charge transfer kinetics. Cobalt-iron mixed compounds, such as CoFeOx and CoFe hexacyanoferrate, a Prussian blue analogue, proved to effectively enhance photocurrent when coupled to BiVO₄/WO₃ photoanodes as water oxidation co-catalyst. The origin of the increased efficiency is still debated, but recent studies suggest an enhancement of charge separation efficiency within the semiconductor [2], rather than improved water oxidation kinetics, underlying possible charge accumulation on the co-catalyst leading to transient modification of the local structure. X-ray Absorption Spectroscopy (XAS) provides a unique view of the structural features of ultrathin catalyst layers, however often limited to a steady state ex-situ characterization of the catalyst local structure and valence state. To achieve structural understanding of the catalyst activity in the actual PEC operating conditions, a custom PEC-XAS cell was specifically designed to allow for operando monitoring of Co-Fe based co-catalysts deposited on  BiVO₄/WO₃ photoanodes, upon bias and illumination stimuli fully replicating the ex-situ conditions. The developed setup (Fig 1a), providing limited x-ray photons interaction path with the controlled-flow electrolyte (<100 μ m), prevents bubbles formation and enhances mass transfer (Fig 1a), allowing for stable, real-time correlation of the structural features with the photoelectrochemical response. The activity of CoFeOx and CoFe-PB  was investigated by either performing fixed potential spectroscopy (Fig 1b) at Co K-edge, or fixed X-ray energy absorption voltammograms [3] (FEXRAV, Fig 1c). The resulting characterization displayed a drastic modification of the structure between operando and ex-situ analysis, as well as a dependence on bias and illumination. In addition, despite the apparent similarities between CoFeOx and CoFe-PB in terms of composition and PEC activity, their operando-XAS behaviour displays a different enhancement mechanism, further correlated to the charge dynamics characteristics, investigated by IMPS and PEIS.

Organic semiconductors heterojunctions have recently gained significant interest in solar fuel production. In contrast to widely studied inorganic photocatalysts, the synthetic tunability of organic semiconductors, such as conjugated polymers and covalent organic framework (COF), allows the design of materials with tuned bandgaps for photocatalysts that can absorb a wider proportion of solar spectrum. Recently, heterojunctions nanoparticles prepared from a blend of conjugated polymer and non-fullerene small molecules, as those used in the organic photovoltaic field, have shown promising efficiency for hydrogen production in the visible. [1,2]  Our previous transient and operando studies have shown remarkably long-lived charge generation within the donor:acceptor heterojunction nanoparticles on timescales useful for photocatalysis (microsecond-millisecond).[3] Using a similar approach, 2D templated polymer heterojunctions were explored as a photocatalyst for hydrogen production, prepared by combining donor and acceptor 2D polymers in a templated growth method. Transient absorption spectroscopy on timescales ranging from picoseconds to seconds were employed to monitor the kinetics of photogenerated charges in the 2D heterojunction and single 2D polymer components and their correlation with hydrogen production.[4] In this talk, the charge carrier dynamics of the novel 2D templated polymer photocatalyst with improved hydrogen evolution rates will be discussed, including the effect of charge trapping and metal cocatalyst on charge extraction.

The pursuit of efficient, earth-abundant and stable photocatalysts has been the holy grail since TiO₂ was discovered as a water-splitting photocatalyst more than 50 years ago.[1,2] Ever since, wide bandgap absorbers such as TiO₂, SrTiO₃ or Ga₂O₃ have dominated the field of particulate photocatalyst development predominantly due to their deep valence bands driving water oxidation and remarkable stability.[3] However, with less than 5% UV light in our solar spectrum, the overall solar energy conversion efficiency of such wide-bandgap systems is by default limited to efficiencies below 1%. Even with the most outstanding Al:SrTiO₃ photocatalyst achieving one of the highest quantum yields reported, the overall solar-to-hydrogen conversion efficiency was only 0.65%.[4]

Tremendous efforts have been undertaken to extend the absorption into the visible to maximise the light-harvesting efficiency. On this quest, countless oxide and nitride as well as some oxynitride and oxysulfide materials with smaller bandgaps have been intensively studied with varying success.[3,5] In the novel visible light absorber (La,Sr)(Rh,Ti)O₃ employed in the Z-scheme photocatalyst sheet device from Profs. Wang and Domen, the controlled A and B site substitutions led to a record 1% solar-to-hydrogen efficiency.[6]

Substitution on A and B-sites of the perovskite ABX₃ crystal structure creates interesting defect chemistry widely studied in photo- and electrocatalysis. However, as our recent work on the La,Rh-co-doped SrTiO₃ showed, attention to the formation of undesired trap states is particularly important when attempting to induce visible light absorption into wide-bandgap semiconducting photocatalysts.[7]

In this talk, I will dive into defect engineering and chemistry of a small series of oxide perovskites that we employ in photo- and electrocatalysis and discuss challenges and ambiguities in such defect engineering approaches as well as considerations when operating under reducing conditions.

A key challenge in photocatalysis is to generate sufficiently long-lived excited states capable of driving the desired transformations but with a minimal energy cost. In Photosystem II, extending lifetimes is achieved with a series of redox co-factors. This enables the oxygen evolution reaction to take place, but at a high energy penalty (approx. loss of 40% of the energy of a red photon). Similarly, in artificial systems recombination reactions are suppressed by applying external biases or by using sacrificial reagents. This enables carriers to live long enough to react but lowers the overall energy efficiency of the system. While many photo-absorbers can be prepared, there is still no clear blueprint for the design of materials with intrinsically long-lived carriers that maximise photo-conversion efficiencies. In this talk, I will present an experiment systematically characterising the excited state lifetime and recombination dynamics in a series of energy conversion materials. Our data reveals a correlation between the achievable lifetime and the solid’s electronic configuration pointing towards intrinsic factors limiting performance. I will discuss the implications and opportunities that such intrinsic behaviour has in our ability to generate long-lived excited states for catalysis and other energy conversion systems.

High performance, light absorbing semiconductors are of intense interest for the solar-driven generation of sustainable fuels in photocatalytic and photoelectrochemical systems. Whilst metal oxides are the most-studied photoactive materials for the evolution of hydrogen from water and methanol from carbon dioxide and water, organic semiconductors can advantageously be synthesised from abundant sources; offer control over microstructure, light harvesting properties and redox potentials; and have the potential to be used in technologically simple devices. Despite substantial increases in the activities of organic photo-driven systems over the last five years, few studies[1] have managed to deconvolute the many factors (structural, optical, and electronic) that define the performance of these materials.

In this talk, I will primarily use transient absorption spectroscopy to demonstrate that generating charges which can live for microseconds is critical to the performance of a wide variety of different carbon nitride and linear conjugated polymer photocatalyst and photoelectrode systems [2-5]. However, generating large yields of these long-lived charges is a serious challenge in organic materials as excitons and charges typically recombine on the picosecond-nanosecond timescale. I will present several design strategies which can be employed to retard these processes, with particular focus on the timescales at which sacrificial agents and water influence the photophysics of the polymer system.

I will first use a series of novel sulfone-containing linear conjugated polymer photocatalysts to demonstrate that excitonic hole transfer from the polymer to the sacrificial donor can occur on the picosecond timescale, strongly competing with exciton recombination [2]. Crucially, the ability of the best-performing polymer to generate long-lived electrons is dependent on the thermodynamic driving force for hole transfer to the sacrificial donor.

Alternatively, excitons can be separated using an organic heterojunction. However, whilst a PM6:Y6 photoanode can efficiently separate excitons on the picosecond timescale with no applied bias, long-lived active charges are only observed when spatially separated by an applied bias [3]. We similarly find that low charge mobility in carbon nitride photoanodes limits their ability to physically separate charges, and can be improved by introducing a conductive network into the electrode [4]. Building on these observations, we demonstrate that the lifetime and yield of PM6 hole polarons can be improved in the PM6:Y6 photoanode by adding a PM6 overlayer on top of the bulk heterojunction. The PM6 overlayer aids the spatial separation of charges, retarding bimolecular recombination [3]. Finally we show that the inclusion of oligo(ethylene glycol) side chains to a polymer photocatalyst also extends the lifetime and yield of the active electrons relative to its alkylated analogue [5]. In this case, the hydrophilicity of the side chains causes substantial swelling, with the resulting spatial separation again reducing recombination.

Overall, I aim to show that a wide range of photo(electro)chemical organic materials and device structures can be improved through several common design themes.

Intensity Modulated Photocurrent Spectroscopy (IMPS) has been largely employed in semiconductors characterization, to probe the operando behavior with widely available facilities. However, the implementation of IMPS data analysis to complex structures, such as the semiconductor-electrolyte interface or buried heterojunctions, is generally limited to qualitative evaluation of the steady-state conversion efficiency. In this work, a new algorithm for the analysis of IMPS data is developed, providing unprecedented insights into the time resolved charge transfer/recombination paths in semiconductors for solar energy conversion, from photoelectrochemical (PEC) water splitting to photovoltaics. The algorithm, based on the previously developed Distribution of Relaxation Times (DRT) analysis, here modified with Lasso regression method, is validated on different PEC systems, such as Ti modified hematite photoanode for PEC water oxidation, identified as a standard platform in the field, but also CoPi modified hematite for valorization of biomass derivated and CIGS based photocathodes for water reduction. The application of the L-DRT algorithm to IMPS data provides several advantages compared to the conventional kinetic analysis, including straightforward identification of multiple charge transfer and recombination paths, improved time resolution, providing precise and reliable description of the characteristic lifetime of each process and extension of the potential window suitable to kinetic analysis due to the deconvolution of subtle recombination peaks [1], [2].

The development of sustainable strategies to produce added-value chemicals and fuels using renewable resources is particularly attractive to promote a transition towards a more sustainable energetic landscape, overcoming the dependence of fossil fuels at a global scale. One of the most promising alternatives involves the use of renewable electricity (wind, solar, hydropower, etc…) to power electrochemical conversion processes, which convert abundant molecules (e.g., water, carbon dioxide, and nitrogen) into higher-value products (e.g., hydrogen, hydrocarbons, oxygenates, and ammonia). In this context, the use of materials based on earth-abundant elements (Fe, Ni, Cu, etc…) is key to ensure the scalability and large-scale implementation. We will discuss the use of some earth-abundant (photo)electrocatalysts based on these elements for different reactions of wide technological interest, also focusing on the mechanistic understanding of the physical-chemical processes taking place during operation.

Photoelectrochemical (PEC) water splitting is an attractive method for the production of hydrogen from renewable energy sources. We have in recent years focused on both oxygen evolution reaction and hydrogen evolution reaction materials. In this talk, we want to summarize photoelectrode and surface engineering paths to high-performance electrodes for water splitting.

Firstly, we will report on BiFeO₃ (BFO) which has recently been identified as a promising photocathode material due to its light absorption and photo-electrochemical properties [1-3]. For practical applications, however, the PEC performance of BFO needs to be improved, which requires understanding of the aspects that limit its activity. We will present the effect of the ratio of Bi to Fe in the precursor solution of the sol-gel synthesis on the properties of BFO thin films [4]. Thin films with a stoichiometric ratio of Bi:Fe and thin films with 10% excess of Bi are prepared on fluorine-doped tin oxide. While bulk characterization techniques (XRD, RBS) show the formation of phase-pure BFO, surface characterization techniques (XPS, LEIS, TEM, ToF-SIMS) indicate Bi enrichment on the surface. The light absorption and band gap do not change upon adding 10% excess Bi in the precursor solution. However, the current density of the excess Bi samples is nearly two times larger than that of the stoichiometric BFO film at 0.6 V vs RHE. Electrochemical impedance spectroscopy explains this improved performance in terms of a lower recombination rate and a lower charge transfer resistance in Bi excess films. The lower recombination rate is attributed to less defects in the thin films, i.e. less Bi and O vacancies (XPS, TOF-SIMS). The low charge transfer resistance is attributed to a distinct Bi-oxide top layer that was detected on all samples (XPS, TOF-SIMS, LEIS, TEM). In summary, we can conclude that adjusting the Bi:Fe ratio is an effective manner to enhance the PEC performance of BFO thin films for hydrogen evolution reaction. 

Secondly, we will discuss a series of papers where we use WO₃ as oxygen evolution material for photo-electrochemical water splitting [5-8]. We start with discussing physical and chemical defects in WO₃ thin films and their impact on photo-electrochemical water splitting. We then transfer the thin film to scalable substrates, such as Si wafers, and discuss how the performance is boosted with WO₃/n-Si heterostructures. The role of Si and its impact on interface engineering is investigated. Then, we extend the study to the third dimension by investigating micro-pillars and nanowires and the impact of the three dimensional structure through surface area and light management on the performance.

We will conclude with sketching our further efforts to high-performance electrodes via photoelectrode and surface engineering using and developing further paths to scalable methods.

Moving from materials to devices is unthinkable without a preceding thorough assurance of the durability of all of their constituent components. Considering the crucial green energy technologies, photovoltaic cells for renewable electricity generation and water electrolyzers for hydrogen production using renewables already demonstrate the required operational stability over years, if not decades. Unfortunately, the same cannot be said for the cells used for the photoelectrochemical water splitting. As for now, with numerous efforts toward optimizing the activity, the more significant challenge of tailoring the durability of photoelectrodes to meet industrially relevant levels remains. Considerable research efforts are necessary in order to improve our understanding of the degradation processes and develop mitigation strategies. Dissolution (as part of corrosion) is one of the degradation processes. This talk will present our most recent results on the dissolution of representative photoelectrodes (photoabsorbers with or without co-catalysts) during water splitting.

Over the last years, the dissolution stability of different electrocatalysts has been investigated in our group using an inductively coupled plasma mass spectrometer (ICP-MS) directly connected to an electrochemical cell [1]. In this configuration, time- and potential-resolved dissolution analysis is possible. Recently, such a cell was equipped with a solar simulator, Air Mass 1.5 G filter, and monochromator, allowing standardized photoelectrochemical measurements [2]. The dissolution stability of representative WO₃, BiVO₄, and Fe₂O₃ photoabsorbers was investigated in different electrolytes with or without a co-catalyst overlayer [3-5]. With the help of electrolyte and interface engineering, stabilization of the photoabsorbers was demonstrated. The gained insights can then be utilized to advance synthesis and operation approaches of novel materials with improved photostability.

Besides dedicated fundamental studies on well-defined electrodes, flow cell setups are well-suited for operation in a high-throughput manner [6]. This potential was realized in a proof-of-concept study on Fe–Ti–W–O thin film materials libraries using  fully automated activity-stability measurements [7]. Such a platform would enable material discovery, which is tailored to search not only for the most active but also for the most stable material.

Photovoltaic-coupled photoelectrochemical (PV-PEC) water splitting devices offer a route to high efficiency solar-to-hydrogen (STH) conversion with low-cost and non-toxic materials, in particular given the recent advances in efficient and earth-abundant PEC (e.g. metal-oxide) and PV (e.g. organic, perovskite) materials. [1][2][3] However, achieving STH efficiencies relevant for commercialisation (~15-20%) requires careful optimisation of the electronic and optical properties of the constituent materials, as well of the device configuration to minimise parasitic optical and electrical losses.

Here, we present a optical-electronic model for simulating the current-voltage curves of PV-PEC tandem cells, and which includes descriptions of important (optical and electronic) loss mechanisms. PV operation is modelled using diode equations that incorporate loss estimates due to radiative and non-radiative recombination. For describing PEC operation, we extend the Gärtner formulism for PEC photocurrent generation to treat surface recombination due to charge trapping and correct for Fermi level pinning due to an overpotential drop over the Helmholtz layer. We then study the effect of changing semiconductor properties, including conduction and valence band levels, electron and hole masses, charge-diffusion length, Fermi level and trap densities, as well as optical considerations (e.g. parasitic light absorption due to electrolyte and bubble formation) on PV-PEC operation. This allows us to determine the PEC and PV semiconductor properties and device configurations that are required to reach STH efficiencies relevant for commercialisation, in particular using state-of-the-art metal-oxide, organic and perovskite semiconductors.

Hydrogen generated from solar-driven water-splitting process has the potential to be a clean, sustainable and abundant energy storage option [1,2]. The devices implemented in an integrated design approach, i.e., submerged in the electrolyte, pose a significant limitation when it comes to up-scaling [2]. The performance decreases due to added ohmic losses in the electrode or electrolyte and local pH gradients represents a significant challenge to overcome. The presence of the hydrogen gas bubbles at electrolyte/photoelectrode interface may assist in managing low pH gradients, if engineered properly. Beyond the state of the art, introducing a porosity to the photoelectrodes has been proposed as a shortcut to minimize the losses associated with up-scaling [2,3]. To study the optimal porous configuration of the water splitting device, mathematical modeling simulations were performed for various pore size (d_pore = 10–400 μm) and pitch of 1mm. The overall impact of tailoring the d_pore indicates that increasing porosity of the decreases the ohmic loss but increases the product bubble crossover (see Figure below). For the device to be operable with acceptable voltage loss of ~100 mV, the pore size should be less than 200 µm in diameter. These investigations are expected to contribute to advancing the development of large-scale water-splitting technology.

Figure 1 (a) Color map of total voltage losses for 10 cm long electrode with different size of pores. (b) Percentage of H₂ crossovers due to porous structures of electrodes.

Halide perovskites received significant attention in the photovoltaic community owing to its higher power conversion efficiency, high absorption coefficient, and bandgap tunability. However, their stability in aqueous medium is poor making them unsuitable to employ for direct water splitting. Various protective layers coupled with halide perovskite are utilized to prevent the exposure of the absorber to aqueous medium. However, these protective layers are susceptible to failure with prolonged operation. So, employing a water stable absorber material is found to be the key for successful photoelectrochemical (PEC) water splitting.

Vacancy ordered double perovskites with the formula A₂BX₆ are a promising alternative to conventional ABX₃ perovskites due to excellent stability, comparable absorption coefficient and bandgap tunability. This class of materials have their alternate octahedra being vacant enabling a wider range of B-site elements due to rotational freedom. Here, we have reported the most stable vacancy ordered halide perovskite Cs₂PtCl₆ and Cs₂PtBr₆ which showed extraordinary stability in air and even in extreme acidic and basic mediums. Furthermore, these materials exhibit absorption properties that encompass a substantial portion of visible light. The capability of the material to undergo anion exchange from Cs₂PtCl₆ to Cs₂PtBr₆ via core-shell mechanism to form Type-II heterostructure is demonstrated. These materials are successfully employed as photoanode for PEC water oxidation which displayed photocurrent density of >0.2 mA/cm² at 1.23 V vs. RHE.

While hydrogen production via photoelectrochemical water splitting has been demonstrated on a small scale, developing an industrial scale device is a challenge that brings together researchers from a range of disciplines, including engineers, material scientists and chemists. Development of photoelectrochemical water splitting devices requires an understanding of semiconductor physics, optics, (photo)electrochemistry (including catalysis and corrosion) and chemical engineering (e.g. fluid mechanics, heat and mass transport). These are all critical to the development of efficient and robust devices.

I will discuss our in-house developed photoelectrochemical (PEC) device, with a total photo-absorbing area in excess of 100 cm². The device operates with photoanodes fabricated by chemical vapour deposition, a prevalent and scalable method, of sequential layers of WO₃ nanorods and BiVO₄, to form a staggered heterojunction on FTO. The 2.4 to 2.5 eV bandgap of BiVO₄ enables light absorption up to 517 nm in wavelength and a theoretical solar-to-hydrogen efficiency (ɳ_STH) of up to 9.2 %. The WO₃/BiVO₄ heterojunction system is one of the most promising in terms of performance, cost and durability. Combined with a Ni mesh cathode and an externally mounted homojunction Si PV, and operated in a pH neutral phosphate buffer solution, this creates a cost-effective and scalable photoelectrochemical-photovoltaic (PV-PEC) device with a commercially viable fabrication method. In initial experiments, we have achieved a spontaneous solar-to-hydrogen efficiency (ɳ_STH) of 4.0 %.

Scale-up of PEC devices comes with numerous challenges which must be addressed by both computational and experimental approaches. I will discuss the ways in which we have combined these approaches in our research and initial progress to-date. I will also show strategies we have been developing towards mitigating performance losses within our device, including reducing severe potential and current gradients across poorly conducting photoelectrodes. I will discuss other aspects critical to the scale-up of photoelectrochemical devices, including heat and mass transfer, fluid dynamics and safety challenges associated with increasing product and precursor volumes.

Despite the urgent need for engineering progress in this area to accelerate this type of solar hydrogen technology, there are relatively few academic publications that address this topic. With a lack of demonstration prototypes, it remains difficult to envisage what an industrial-scale installation for clean hydrogen production might look like. Ultimately, availability of green hydrogen is expected to result in the hydrogen market expansion. This research seeks to elucidate engineering challenges of developing large-scale water splitting devices, to facilitate the pathway to commercially viable photoelectrochemical hydrogen production.

Key words

Photoelectrochemistry, hydrogen, scale-up, electrochemical engineering, BiVO₄

BiVO₄ is considered one of the most promising metal oxide semiconductors for photoelectrochemical water oxidation. Many studies focus on addressing the inherent material limitations, such as charge carrier mobility and slow water oxidation kinetics. For example, it has been shown that doping with some metals and non-metals increases the charge carrier mobility and the addition of a co-catalyst improves the water oxidation kinetics. These techniques are effective in such a way that ninety percent of the theoretical AM1.5 photocurrent of BiVO₄ has been achieved. This progress has shifted some focus towards scaling up, in which it has unfortunately been reported that the scale-up process significantly impacts the photocurrent and stability. Identifying and addressing the scale-up losses and optimizing the associated overpotential is therefore crucial.  In this study, we scaled-up sulfur incorporated BiVO₄ photoelectrodes using a screen printing technique. Photoelectrodes with area up to 100 cm² were fabricated uniformly, and the performance was evaluated using a continuous flow photoelectrochemical cell. Specifically, the effect of scale-up on the overall overpotential of the cell, which includes ohmic and concentration overpotentials, was considered. Strategies to minimize these losses, such as increasing the substrate conductivity and electrolyte engineering (modifying the concentration and the flow rate of electrolyte), were implemented. As a result, we successfully minimize the photocurrent loss to only ~12% when the photoelectrode area is increased by more than two orders of magnitude, from 0.24 to 100 cm². Further optimization of the ionic and concentration overpotential associated with scale-up is ongoing and will be discussed.

Direct connection of PV devices to electrochemical (EC) water-splitting cells or batteries (B) is a highly efficient and material-saving solution to stabilize intermittent PV generation on long- and short-time scales. In our study, we address a hybrid device with EC water splitting cell in parallel connection to a battery. The first obvious advantage of this PV-EC-B system is the much more stable operating conditions of the electrolyzer. A sufficiently scaled battery keeps the EC cell running overnight and shaves peak load during the daytime. In our works, we have shown the feasibility of the self-sustained operation of the PV-EC-B system [1, 2]. Besides the foreseeable stabilizing effects, we have found theoretically [1] and confirmed experimentally [2] that batteries can improve solar-to-hydrogen efficiency (STH) in PV-EC-B devices as compared to the PV-EC reference. Batteries can boost STH in PV-EC-B systems because, under periodic irradiance conditions, the battery transfers part of the daytime PV energy to the night, reducing EC cell power and suppressing related overpotential (kinetics) losses. The gain is synergistic – even despite additional potential losses in the battery, the EC-B combination has lower losses than the EC cell operating alone [1, 2]. From the point of view of the system design the reduction of operating power and its stability allows for the use of a smaller electrolyzer at the same nominal PV capacity.

In our report we will present details of the PV-EC-B operation, principles behind the gain in STH attained with battery, and our recent experimental study. An increased average STH efficiency per cycle (11.4 % vs. 10.5 % without the battery) has been observed in the PV-EC-B system of a Si heterojunction PV module, bifunctional NiFeMo electrolyzer, and a commercial Li-ion NMC battery. The results are discussed in the context of the generalized STH limit analysis developed earlier for PV-EC combinations [3].

Applying our analysis to different literature sources using PV-EC without batteries we present an analysis of what could be achieved if a battery is applied to these systems in the figure below. We calculate the STH limit with and without a battery for each experimentally reported system in literature as well as the STH gain with a battery.

Each system reported in the literature is represented by four symbols: filled blue circles show the reported experimental STH of each PV-EC system; open blue circles indicate the STH limit calculated for each system using the reverse analysis [3]; horizontal dashes represent the estimate for the STH limit in this system if the battery is included; finally, the red circles show the estimate of the STH gain for each system.

A separate set of points denoted “this work” represents the experiment on the PV-EC-B system in this work.

For approximately half of the reported systems STH gain of 0.5%_abs – 1%_abs can be expected, several systems can gain 1%_abs – 2%_abs, while several systems can gain 2%_abs – 4%_abs. There is a general trend for higher STH gain at higher PV efficiencies, but the data presented in Figure 4 does not constitute any dependence.

Suitable photo-electrode materials are known to be the main bottleneck for large scale deployment of devices for solar fuel production. These semiconducting materials must be efficient, stable and scalable, although, usually two out three of these qualities are met. Hematite is an extensively researched photoelectrode material, known for its long-lasting properties and facile synthesis. However, the position of its band edges and high recombination rates, resulting in low efficiencies, preclude hematite to be used in real applications. On the other hand, complex photo-electrodes with laborious synthesis, e.g. III-V tandems absorbers (GaInP/GaAs), coupled with RuO_x and PtRu catalysts, have proven to be highly efficient for water splitting [1].

With the aim to improve scalability, concentrated light sources allow the use of smaller photoelectrodes, provided they are stable and efficient at operating conditions. However, the use of higher irradiation (>100 kW m^-2) unlocks additional constraints related to heat management, ohmic drop due to inordinate current densities, and unknown electron/hole transfer kinetics under high photon flux and at higher temperatures. It is expected that these effects could be alleviated by careful reactor design, and choosing suitable substrates and operating conditions. However, these issues have been seldom investigated and only a few studies on photoelectrochemical cells for irradiations typically below 30 suns have been reported [2].

Here, we present the model and preliminary experimental validation of a photo-electrochemical cell operating under concentrated irradiation (>100 kW m^-2), using metal oxides (Fe₂O₃ and BiVO₄) as photoelectrode materials, which were selected due to their well-known and predictable photoelectrochemical behavior [3,4]. The effects of the substrate material (Ti or transparent conductive oxides deposited on glass), electrode configuration, electrolyte flow and spectrally resolved photon intensities on the performance of the cell will be presented. Initial predictions indicate that conductive glass is not a suitable substrate due to its low thermal conductivity, resulting in undesirable high temperatures (>80 °C) when operating under irradiations of 600 kW m^-2.

References:

[1] Young, J., Steiner, M., Döscher, H. et al. Nat Energy 2017, 2, 17028.

[2] Vilanova, Mendes, A. Journal of Power Sources 2020, 454, 227890.

[3] Bedoya-Lora, F. Hankin, A. Kelsall, G. J. Mater. Chem. A, 2017, 5, 22683-22696

[4] Gaudy, Y. Haussener, S. et al. J. Mater. Chem. A, 2018, 6, 17337-17352

In my talk I will revise the recent efforts done in my group regarding the integration of first principles studies into more advanced multiscale simulations. I will show the main difficulties and bottlenecks for the implementation of a more robust computational framework that can be used in a more general manner and that should give us access to more adequate models in the field. For instance I will address the main difficulties in the modeling of excited states and how they are more ubiquotous and diverse than previously considered and how modeling can address some of the challenges ahead of us to obtain proper representations. Also I will revise the types of approaximations when attempting multiscale approaches and how they need to be tuned and supported by machine learning techniques in some of the cases to reduce the dimensionality problems and the low energy events that typically consume the simulation times.

Green H₂ has been recognized as an important element in efforts to decarbonize our fossil fuel-dependent society. One approach to produce green H₂ is solar water splitting in a photoelectrochemical (PEC) device. Solar-to-hydrogen (STH) efficiencies of up to 30% have been demonstrated[1] but studies have shown that this approach still results in a relatively high levelized cost of hydrogen (LCOH) of ~10 US$ per kg of H₂.[2-3] This is ca. one order of magnitude higher than that of hydrogen produced via steam methane reforming (SMR), which forms the bulk of the currently produced H₂. A possible solution is to incorporate an upgrading process of biomass feedstock that generates valuable chemicals into the solar water splitting device. This is expected to not only decrease the overall LCOH but also introduce an alternative renewable pathway in chemical manufacturing. In this study, we propose the concept of solar-driven hydrogenation of biomass-derived feedstock. Photoelectrochemically generated H₂ in our solar water splitting device is coupled in situ with the homogenously catalyzed hydrogenation of itaconic acid (IA) to methyl succinic acid (MSA). IA has been identified by the US Department of Energy as one of the twelve building blocks that possess the potential to be transformed subsequently into several high-value bio-based chemicals or materials. MSA is a valuable chemical compound with an estimated global market size of up to ~15,000 tonnes, whose derivatives are ubiquitously used as solvents in cosmetics, polymer synthesis, binders in powder coatings, and organic synthesis, especially for pharmaceutical synthesis.[4-5] Our coupled hydrogenation approach—performed in the PV-electrolyzer and PEC configurations using III-V PV cells and BiVO₄-based photoelectrode, respectively—successfully demonstrate solar-driven H₂-to-MSA conversion as high as 60%. In comparison to the non-coupled approach (i.e., direct hydrogenation), our coupled system offers synergistic benefits in terms of prolonged durability and a higher degree of flexibility toward other important chemical transformation reactions. In addition, life-cycle net energy assessment and technoeconomic analysis results show that adding the coupled hydrogenation process significantly lowers the energy payback time and the LCOH, respectively, to a point that is competitive even with SMR-produced H₂.[6] Further implications and optimization potentials of the coupled PEC hydrogenation approach, also beyond the demonstrated hydrogenation of IA to MSA, will be discussed.

Green hydrogen is a key future energy resource, and its generation through electrochemical water splitting is a prominent option for industrial applications. This calls for robust and low-cost electrocatalyst to facilitate the kinetically and thermodynamically demanding oxygen evolution reaction (OER) which remains a challenging bottleneck of water splitting. In order to use the full potential of abundant transition metal-based catalysts, their structural design is only one part of the development process. In addition, their dynamic behavior and restructuring over longer operational periods during water splitting needs to be understood.[1]

Over the past years, we have brought forward a broad spectrum of 3d transition metal-based OER catalysts covering a wide range of compound types: from single atom catalysts [2] over molecules and coordination polymers [3, 4] to nanostructured and chalkogenide/phosphide-derived catalysts.[5] Selected examples of these catalyst types will be presented and their operando monitoring through X-ray absorption spectroscopy (XAS) and complementary methods will be discussed to provide in-depth insights into the dynamics of their active sites. This information is vital for the rational design of high-performance and robust electrocatalysts.

We performed a series of studies on Ni/Fe-based electrocatalysts to elucidate the interaction and optimal coordination environments of this highly active metal combination. We first constructed dual-site NiFe single atom catalysts (SACs) via a convenient synthesis protocol using g-C₃N₄ and glucose as precursors.[2] Their OER performance was superior to single site Ni-, Fe- and Co-SACs and the underlying structural reconstruction of the dual-site NiFe catalysts was investigated with a combination of operando XAS, high resolution HAADF-STEM investigations and DFT calculations. These results revealed that the Ni environment mainly underwent reconstruction towards active Ni-O-Fe moieties wherein both metal centers participate on the *OH deprotonation process, resulting in the formation of bridging O₂ species. The improved OER performance of dual-site NiFe SACs is assisted by the formation of spin channels via the Ni-O-Fe bonds. We furthermore designed ultra-thin NiFe-based coordination polymer derivatives for high OER performance.[3] Upon mild reduction with NaBH₄, the emerging reduced R-Ni₈Fe₂-CPs with sub-2 nm layered morphologies excelled through optimal exposure of active sites and fast electron transfer. The performance or their Ni-O-Fe active sites was further enhanced through the targeted incorporation of O and Ni deficiencies. In our next study, these materials were strategically optimized through controlled introduction of sulfur into the oxygen deficiencies around the Ni centers to generate S-R-NiFe-CPs with superior OER performance.[4] Their investigation through operando XAS revealed that sulfur tuning facilitates the formation of active Ni^IV-O-Fe^IV moieties, while their reconstruction was hindered in the sulfur-free materials, thereby confirming the benefits of anionic engineering strategies for the OER performance.

For overall water splitting, we developed a Fe-doped cobalt phosphide (Co@CoFe–P) catalyst for both hydrogen evolution reaction (HER) and OER. Low HER overpotentials at 10 mA/cm² were observed over a wide pH range (0~14), such as 83 mV in 0.5 M H₂SO₄ or 104 mV in 1.0 M KOH and a good OER activity with a low overpotential of 266 mV for 10 mA/cm² was obtained in 1.0 M KOH.[5] Operando XAS investigations demonstrated that partial Fe doping promoted the formation of HER active P–Co–O–Fe–P configurations in Co@CoFe–P with a lower energy barrier for water dissociation and  H* intermediate adsorption. Under OER conditions, a reconstruction process into OER active intermediates with Co^IV–O–Fe^IV  moieties was observed, while the formation of these active unites was hindered in P-free reference Co-FeOOH, thereby underlining the efficiency of anionic substitution strategies.

The talk will be concluded with an outlook on molecular and related Co-based OER catalysts to bridge the design perspectives between molecular and heterogeneous catalysts.

The replacement of fossil fuels by a clean and renewable energy source is one of the most urgent and challenging issues our society is facing today, which is why intense research is devoted to this topic.[1] Nature has been using sunlight as the primary energy input to oxidize water and generate carbohydrates (a solar fuel) for over a billion years. Inspired but not constrained by nature, artificial systems can be designed to capture light and oxidize water and reduce protons or other compounds such as CO₂ to generate useful chemical fuels. One of the key aspects for the efficient design of useful devices for the making solar fuels is the understanding and mastering of the anodic reaction involving the oxidation of water to dioxygen. The talk will describe the initial developments up to the state of the art, of molecular water oxidation catalysts and their anchoring on conductive and semiconductive surfaces. The latter is crucial for the generation of powerful hybrid molecular anodes for the production of solar fuels.[2]

[1] (a) Matheu, R.; Llobet, A. et al. Nat. Rev. Chem. 2019, 3, 331–341.

(b) Vereshchuk, N.; Llobet, A. et al. Chem. Soc. Rev. 2023, 52, 196-211

[2] (a) Hoque, Md. A.; Gil-Sepulcre, M.; Llobet, A. et al. Nat. Chem. 2020, 12, 1060–1066. (b) Schindler, D.; Gil‐Sepulcre, M.; Llobet, A.; Würthner, F. et al. Adv. Energy Mater. 2020, 2002329. (c) Gil-Sepulcre, M.; Llobet, A. et al. J. Am. Chem. Soc. 2021, 143, 11651–11661. (d) Gil-Sepulcre, M.; Llobet, A. Nat. Catal. 2022, 5, 79-82.

Molecular catalysts play a significant role in chemical transformations, utilizing changes in redox states to facilitate reactions. In the broadening field of carbon dioxide (CO2) electrolysis to value-added products, catalyst choice strongly impacts product formation. To date molecular electrocatalysts have efficiently produced single-carbon products from CO2 but have struggled to achieve the carbon-carbon coupling step needed to reach highly valued multi-carbon products. Conversely, copper acts as the only reliable bulk metal that enables carbon-carbon coupling, but leads to broad C2+ product spectrums.

Here we designed a molecular electrocatalyst system that subverts the traditional redox-mediated reaction mechanisms of organometallic compounds, facilitating electrochemical CO2-to-ethanol yields of 96% at optimal conditions with trace methanol and C3 products. By coupling iron tetraphenylporphyrin (Fe-TPP) with a nickel electrode, we fixed the iron oxidation state during electrocatalytic CO2 reduction to enable further reductions and coupling of *CO intermediates. This represents a marked behavioural shift compared to the same metalloporphyrin deposited onto carbon-based electrodes. Extending the approach to a 3D porous nickel support with adsorbed Fe-TPP, we attain ethanol faradaic efficiencies of 68% +/- 3.2% at -0.3 V vs a reversible hydrogen electrode (pH = 7.7) with partial ethanol current densities of -21 mA cm-2. Separately we demonstrate maintained ethanol production over 60 hours of operation. Further consideration of the wide parameter space of molecular catalyst and metal electrodes shows promise for additional novel chemistries and achievable metrics.1

Electrocatalysis has emerged as a promising process to store renewable energy into fuels and high added-value chemicals to decarbonise the energy and fine chemical sectors. As such, the water splitting process to generate H2 and O2 is of particular interest, even though both hydrogen and oxygen evolution reactions (HER and OER, respectively) are kinetically challenging, especially when using Earth-abundant metal oxide and chalcogenide catalysts. The efficiency of these catalysts does not only depend on the nature of the metal oxide/chalcogenide, but also on their physical characteristics such as composition, magnetic susceptibility and doping variations, amongst others. However, the reaction mechanism of the HER and OER on metal oxides/chalcogenides as well as the nature of the efficiency loses remains elusive. Obtaining such detailed mechanistic and kinetic knowledge requires the use of operando spectroscopic techniques that can probe the system under operating conditions. In this talk, I will present the characterisation of a Cu2-xS cathode for HER that increases its ECSA as a function of time and a NiFeOx anode for OER that changes its reaction mechanism when a magnetic field is applied to the system.

The search for highly efficient carbo-catalysts with novel compositions usually follows a two-step process. Initially, proof of concept is established using conventional fine powders. Subsequently, the focus shifts to the feasibility of scaling up the material and shaping it into practical catalyst forms. This last aspect, often overlooked, plays nonetheless a vital role in determining which catalysts have the potential for industrial application.[1] Previous works already settled the interest of phosphorus-doped carbons for alcohol oxidation reactions, acid catalysis biomass upgrade or as support for electrocatalysis.[2-3] However, little attempts have been made thus far in the direction of a technical catalyst.

We present here a straightforward production of P-doped carbon porous pellets on a multi-gram scale by simply using phytic acid ( and cellulose, both extracted from biomass and combined with a noodle pasta machine for extrusion. The so-formed spaghetti undergo a carbonization at 800 °C yielding a carbonaceous material in the shape of pellets. These latter exhibit good mechanical stability and a high phosphorus content (13 wt.%), predominantly in the form of surface phosphoric acid groups (-OPO₃H₂). Upon calcination, the carbonization of cellulose leads to the evolution of gases, creating extensive macroporosity beneficial for mass transport. Additionally, the release of phosphoric acid also generates micro- and mesopores (pores < 3 nm, SBET = 1000 m²/g), thereby increasing the density of available reactive sites. These characteristics would ultimately allow for the development of a flow-through catalytic structure.

The so-formed material was studied as a metal-free acid solid catalyst for the pyrolysis of waste cooking oil into biofuel. The resulting organic liquid fraction exhibits an interesting balance between alkanes and aromatics, suitable for an application as a jet fuel. Although the interest of the porous monoliths was demonstrated here in the context of thermo-catalysis, we envision to employ a similarly prepared material as a porous self-standing electrode. This approach would leverage the electronic conductivity of the pellets and the presence of abundant surface chelating groups.

In the transition towards Net-Zero, there is significant interest in phasing out fossil fuels as both the energy source and precursor for petrochemicals. Biomass is recognised as an ideal CO₂ neutral, abundant, and renewable resource substitute for fossil fuels.¹ The rich proton content in most biomass-derived materials endows it to be an effective hydrogen carrier. The inherent chemical structure allows them to be easily catalysed to produce valuable commodity chemicals that can be used in applications such as biodegradable polymers and pharmaceuticals. Although historically biomass has been regarded as waste stream, recent years have seen increasing attention in valorising it into useful products.²

In this talk, I present biomass electrolysis, specifically glycerol (the waste by-product from the bio-diesel industry), as an alternative route to producing hydrogen and value-added chemicals.³ The process resembles water electrolysis, with H₂ produced on the cathode via a hydrogen evolution reaction. On the anode, however, instead of oxidising water, partial oxidation of glycerol takes place, with a much lower thermodynamic requirement that can cut the electricity input by half. Here I present the fundamental knowledge on the general reaction mechanisms, acquired through advanced material characterisations and DFT calculation. At the same time, details on catalyst requirements and recent advances for the future strategic design of the processing system will be provided.

Looking beyond, besides utilising biomass, an even higher urgency lies in recycling the accumulating plastic waste into useful products. Mechanochemistry has emerged as a safe, efficient, and green technique. Using just mechanical energy, this process can cleave chemical bonds and depolymerise long-chain molecules such as cellulose and plastics, revealing huge potential in industrial applications.⁴ By transforming a liquid process into a solid-state reaction, this technique can also significantly reduce solvent consumption. Therefore, this talk will also cover the recent advances in mechanochemical catalysis for plastic recycling, and present the possibility of coupling mechanochemistry with electrochemistry for valorising waste into green hydrogen and value-added chemicals.

The steady increase in anthropogenic carbon dioxide (CO₂) emissions and atmospheric concentration continues to generate interest in using CO₂ as a precursor for fuels and commodity chemicals. The conversion of CO₂ has the dual benefit of addressing its associated negative environmental effects and the diminishing supply of petrochemical feedstocks. Likewise, the electrocatalytic reduction of dioxygen (O₂), has relevance to the development of more efficient fuel cells and chemical oxidations, as well as our understanding of how bioinorganic systems convert energy-rich molecules during respiration. At the heart of efficient reductive transformations are proton-coupled electron transfer (PCET) reactions, where electrons and protons move in a concerted way to mitigate kinetic and thermodynamic penalties. Mechanistic understanding of these reactions can inform the design of optimized catalyst structures with improved activity and selectivity for specific products. Molecular systems are well-positioned to provide a better understanding of these reactions because of the relative fidelity with which they can be characterized, as well as the possibility for systematic testing of structure-function relationships through iterative molecular design. In addition to developing new Co-, Fe-, Mn-, and Cr-based molecular electrocatalysts for these reactions, we are exploring the use of redox mediators and flow-based electrochemical reactors to understand how these reactions can be scaled relative to comparable heterogeneous systems.

Making fuels and chemicals directly from the sun is a highly promising approach to provide high economic efficiency by complete integration of the working modules. Directions taken include both synthetic and biomolecular or biohybrid photoelectrochemical devices characterised by various degrees of integration. Implementation of the synthetic artificial photosynthetic systems (APS) is often hampered by the necessity to apply harsh conditions for the catalysis in each half-cell to occur efficiently, photocorrosion of electrode materials, often-limited product selectivity and catalyst instability [1]. Moreover, the best performing inorganic and molecular catalysts usually encompass rare/toxic elements, which precludes such APS systems from large-scale implementation. Therefore, the field of biomolecular and biohybrid artificial photosynthesis has emerged through combining the biotic components, which have been evolutionary optimised in their photocatalytic performance, and non-toxic and cost-effective synthetic materials for selective production of target chemicals at ambient conditions [1].

Here, I present the bottom-up rational design that can yield the increased solar conversion efficiency and stability in biomolecular systems based on the robust photoenzyme, photosystem I (PSI). The PSI biophotocatalyst in these devices is interfaced with various cost-efficient, transparent electrode materials for production of green electricity and fuel. The performance of PSI-based devices can be greatly improved by tailoring the structure of the organic conductive interface, based on pyrene-NTA, terpirydine or diazonium salt ligands, to ensure the generation of unidirectional electron flow and minimisation of wasteful back reactions [2-5]. Specifically, incorporating transitional metal redox centres together with plasmonic nanoparticles in the bio-organic molecular wires significantly improves not only the light-harvesting functionality of the PSI photoenzyme but also increases its photostability and the overall photoconversion performance [2-7]. Such rational design paves the way for generation of viable and sustainable technologies for solar energy conversion into fuel and other carbon-neutral chemicals.

The rising share of renewable electricity is testament to the increasing importance of solar/wind-electric routes to harvest sun light in form of potential differences and free electrons. While some electricity is used directly or stored capacitively, an increasing portion calls for direct conversion into valuable molecular solar fuels or chemicals. This “dark” e-conversion is made possible by heterogeneous electrocatalysis on the surface of solid electrodes coupled to mass and charge transport processes. Sustainable materials synthesis pathways coupled to novel advanced characterization techniques result in a deeper understanding of the origin of reaction kinetic barriers and the origin of transport limitations. This is critically needed for the design of more efficient, electrochemical materials, interfaces, and electrodes for practical electrolytic devices for the production of e-fuels and e-chemicals.

In this presentation, I will report on recent advances in our design and molecular understanding of carbon-embedded, N-coordinated single metal atom (MNC) catalyst materials. MNC have long been attracted attention as porphyrin-inspired O₂-activating reduction catalysts for hydrogen fuel cell cathodes, yet have recently been proposed by our group as highly efficient and stable CO₂ – activating reduction catalysts for use at cathodes of CO₂ electrolyzers. I will describe ways to characterize MNC active sites and their reactivity, and will compare and contrast their reactivity and reaction mechanisms compared to metal surfaces.

The development of cheap and environmentally friendly fuels and chemicals whose production will be based on abundant and renewable resources appears as one of the main challenges in our society. Among different approaches, the direct use of sunlight for the valorisation of abundant resources, such as H2O, N2 or CO2, has been proposed as an appealing approach for the environmentally friendly and sustainable production of high added-value fuels and chemicals, such as H2, NH3, CH3OH or CH2CH2, among others, the so-called “solar fuels”. In this context, the photochemical solar fuels production is currently limited by the low light-to-chemical efficiency and the fact that in semiconductor-based photocatalysts light harvesting is usually restricted to the UV and visible blue light, and typically is affected by low charge separation efficiency and high recombination rates. In an alternative mechanism, photons from the visible and near infra-red (NIR) regions may interact with metal nanoparticles supported on thermally insulating materials by localized metal surface plasmon resonance (LSPR). In this pathway, much higher production rates and conversions have been reported since photon absorption promotes a localized heating in the active sites due to photon energy thermalization and generation of “hot carriers”, which influence the electronic structure of the species involved in the reaction.

In this presentation, it will be shown the design and fabrication of advanced multifunctional materials for the photothermal CO2 hydrogenation and NH3 production reactions in continuous flow. Moreover, mechanistic studies aimed to unravel which are the actual acfive sites and operational mode will be commented in detail. These research has the potential to advance the field and pave the way for the sustainalbe production of fuels and chemicals.

Roughly 95 % of the hydrogen consumed in Europe and over 95% of organic chemicals still rely on fossil resources. Therefore, finding alternative resources and clean technologies to mine those chemicals is instrumental to secure a sustainable chemical industry. The prospects of sourcing hydrogen from water and upcycling carbon dioxide and lignocellulosic biomass into chemical commodities and fine chemicals has paved the way for the advent of a new generation of technologies and concepts in this chemical space. Among them, (photo)electrochemical and photocatalytic approaches have gained in recent years capitalizing on their scalability, competitive performance and low-cost. To date, however, these technologies still remain at an early stage of development displaying conversion efficiencies below the expectations. A better understanding of the fundamental processes that govern the catalytic transformations at the reactive interface, together with innovative manufacturing protocols to engineer the materials holds the key to rationally advance these promising technologies. 

In this talk, we will discuss our most recent progress in the fields of photoelectrochemical (PEC) water splitting and carbon dioxide conversion, as well as new electrochemical and photocatalytic platforms for biomass valorization. Firstly, we will describe various methodologies to improve the performance of photoelectrodes (chalcogenides, metal oxides) for solar water splitting while identifying the key processes that limit the catalytic response. Likewise, we will show the prospects of driving the PEC CO₂ conversion directly at the semiconductor-liquid interface when using chalcopyrite electrodes and how the nature of the solvent dictates the response. Secondly, we will present various photocatalytic reactors, based on semiconductor nanocrystals and photoredox systems, capable of driving the selective fragmentation of lignocellulosic biomass into simple aromatics. In addition, electrochemical reactors for lignin valorization will be presented including a detailed mapping of the catalytic activity – composition relationships of the electrodes.

Photoelectrochemical and photocatalytic conversion of water and carbon dioxide using solar energy offers a clean solution to the world energy requirements of a sustainable future. Achieving its full potential depends on developing inexpensive photoelectrodes and photocatalysts that can efficiently absorb solar light and drive the photoinduced charges to react with water and carbon dioxide. In this talk, I will present recent developments we have achieved in the group in the preparation of inexpensive photoanodes, photocathodes and photocatalyst composites. For example, we have achieved nanostructured BiVO₄ functionalized with bismuthene and NiFeO_x that influence surface states and boost 6 times their photocurrent performance, as well as BiVO₄ with Ni and Co phosphide co-catalysts that offer a useful series of samples to understand semiconductor-electrocatalyst synergies. We have also achieved halide perovskites CsPbBr₃ photoanodes protected with printed carbon layers and graphite sheets and functionalized with NiFeO_x water-oxidation electrocatalyst, achieving photoanodes of low onset potential of +0.4 V vs. RHE and photocurrents around 8 mA cm^-2 at 1.23 V vs. RHE for water oxidation. These, moreover, achieve operational stabilities for oxygen evolution above 100 h, inexpensively extended to weeks by replacement of the graphite protection. We will also briefly present photocathodes made of oxide perovskites and composites of halide perovskites, such as Cs₂AgBiBr₃/bismuthene and Cs₃Bi₂Br₉/g-C₃N₄, for their use in the photocatalytic reduction of CO₂. An extended characterization helps us relate their physical and charge-transfer properties to their performance, guiding us in their rational design for their optimization and future application.

The carbon dioxide reduction reaction (CO₂RR), in particular electrochemically, to produce carbonaceous fuels is considered as a viable approach to store energy and to enable a CO₂-neutral carbon management. Besides CO₂RR, there is an additional strong demand for benign electrochemical reduction of other important heavy nonmetal oxo species (e.g., SiO₂, phosphine oxides, SO₂) with thermodynamically stable E-O bonds, which accrue in large quantities in industry. In this respect, the energy-intense deoxygenation of oxo compounds of silicon, phosphorus and sulfur is of particular technological importance because they represent one of the main feedstocks to produce important molecules and functional materials. For example, the release of elemental silicon, phosphorus (P₄) and sulfur (S₈) from naturally occurring minerals (e.g., silicate, phosphate, sulfate) follows energy-intensive chemical routes.

Thus, the established chemical reduction routes to deoxygenate such oxo precursors produce tons of reagent waste or, in the case of carbothermal treatment of minerals, afford a lot of CO₂. On the contrary, electrochemical strategies developed for the selective deoxygenation of E-O compounds remain as a feasible alternative powered by renewable electricity instead of fossil energy. Moderate reaction conditions, a large scope in experiment design for selective reactions, easy product isolation and zero reagent waste by applying electrochemical methods offer a promising solution to overcome the drawbacks of chemical reduction routes. This talk summarizes the emergence of electrochemical strategies developed for the reduction of selected examples of E-O/E=O compounds with E = silicon, phosphorus and sulfur in the past few decades and highlights opportunities and future challenges. ^[1]

Photocatalytic conversion of CO2 and H2O is an interesting route to produce fuels and chemicals; this process is also known as Artificial Photosynthesis (AP). In last years, extensive efforts have been made to develop efficient catalytic systems capable of harvesting light absorption and reducing CO2 especially when using water as the electron donor.

Herein, we report different strategies and modifications of photocatalysts to increase process performance. Among them, an interesting approach to improve charge separation in photocatalytic systems is the use of heterojunctions. In this line, the combination of different semiconductors with noble metal nanoparticles or organic semiconducting polymers leads to a separation of the photogenerated charge carriers to increasing their life time, facilitating charge transfer to adsorbed molecules.

The main products, using bare TiO2, were CO and H2, with low concentrations of CH4. The deposition of surface plasmon nanoparticles (SP-NPs) leads to changes in the selectivity to higher electron-demanding products, such as CH4. TAS measurements confirm that this behavior is due to the electron scavenging ability of SP-NPs [2].

Organo-inorganic hybrid materials show a dramatic reactivity improvement in CO2 photoreduction, enhancing methane selectivity. Reaction pathways are not well defined for this reaction and several uncertains are still unsolved [3]. To explain this behavior a combination of in-situ NAP-XPS, FTIR, TAS spectroscopies and theoretical tools has been used, showing a more efficient light absorption and charge transfer in the hybrid photocatalyst compared with bare materials.

Sodium ion batteries (SIBs) are a potential alternative to diversify the energy landscape, beyond Lithium-ion batteries (LIBs), due to their similar storage mechanism and easy technology transfer. Currently, the benchmark anodes for SIBs are hard carbons (HCs), since sodium ions do not intercalate into graphite. HCs can be produced from a variety of waste precursors and therefore are more sustainable and less geopolitically compromised than natural graphite, mainly concentrated in China. 

The electrochemical degradation of SIBs occurs at a higher rate than in LIBs. This can be attributed to the larger electrochemical reactivity of the HC anodes. A deeper operando understanding of the degradation mechanisms in SIBs, coupled with engineering of the materials and electrolyte to ensure that a better and more protective solid electrolyte interface (SEI) is formed, is needed for an accelerated scale up of this technology. In this talk I will show you some of the strategies we have developed for these aims.

Increasing the operating voltage of batteries brings additional challenges to the electrolyte, as it should be stable at higher potentials. Therefore, investigating the electrochemical stability window (ESW) of electrolytes is extremely important. While this could be considered an easy task with liquid electrolytes because mass transport limitation is seldom an issue, it is more complicated with solid polymer electrolytes. Common techniques used are cyclic voltammetry (CV) and linear sweep voltammetry (LSV). However, the main drawback of these methods is that the electrochemical stability of electrolytes is often arbitrarily determined and using conditions far from realistic. Therefore, alternative or complementary methods are required.

Herein, we investigate alternative techniques to determine the oxidative stability of solid polymer electrolytes. Staircase voltammetry (SV) is used to avoid the mass transport limitation and it is combined with electrochemical impedance spectroscopy to simultaneously detect changes in resistance and interfacial degradation. Synthetic charge–discharge profile voltammetry (SCPV) is used to apply the real voltage profile of the active material of interest. Finally, to include the effect of the active material, cut-off increase cell cycling method (CICC) has been developed where the upper cut-off voltage is gradually increased up to 5 V. Monitoring the voltage profile and the Coulombic efficiency can provide information of side reactions occurring at different voltages. The feasibility of these different methods has been investigated with two model solid polymer electrolytes: poly(ethylene oxide) and poly(trimethylene carbonate).[1]