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.