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.