Sustainable approaches for renewable energy conversion to fuels and chemicals

Resume : Climate change concerns have spurred a growing interest in developing environmentally friendly and sustainable technologies to utilize CO2. Along these lines, the electrocatalytic reduction of carbon dioxide (CO2RR) into value-added chemicals and fuels offers additional possibilities to close the anthropogenic carbon cycle and store renewable energy into chemical bonds. Thus, it is of special interest to design efficient and durable catalysts which are able to operate under milder conditions (i.e. reduced potential) and are highly selective towards specific products. In this talk I will provide new insight into the CO2RR with special focus on: (i) the reactivity of size- and shape-controlled NPs (Cu2O cubes, core/shell ZnO@Cu2O cubes), and (ii) the correlation between the dynamically evolving structure and composition of these electrocatalysts under operando reaction conditions, including pulse electrolysis treatments, and their activity and selectivity. Particularly, operando quick X-ray absorption spectroscopy (QXAFS), coupled with machine-learning based data analysis and surface-enhanced Raman spectroscopy (SERS) will be employed to investigate the time-dependent chemical and structural changes in mono and bimetallic (ZnO/Cu2O) catalysts under CO2RR conditions at high current densities. I will describe that the addition of Zn to a Cu-based catalyst has a crucial impact on the kinetics of subsurface processes, while redox processes of the Cu surface layer remain largely unaffected. Interestingly, the presence of Zn was found to contribute to the stabilization of cationic Cu(I) species, which is of catalytic relevance since disordered Cu(0)/Cu(I) interfaces have been reported beneficial for an efficient CO2 conversion to complex multicarbon products. At the same time, the increased C2+ product selectivity observed appears associated to the formation of Cu-rich CuZn alloys in samples with low Zn content, while Zn-rich alloy phases result in an increased formation of CO, paralleled by an increase of the parasitic hydrogen evolution reaction. Our results are expected to open up new routes for the reutilization of CO2 through its direct conversion into valuable chemicals and fuels such as ethylene and ethanol.

Resume : The electroreduction reaction of CO2 (CO2RR) into hydrocarbons over copper electrodes has been studied extensively for the past few decades. However, the CO2RR mechanism, the activation of CO2 and the exact surface structure of the copper electrode are still heavily debated.[1] Raman spectroscopy has shown great promise to elucidate structure-function relationships of catalyst at work, but the low signal intensity and resulting poor time resolution (often up to minutes) hampers the application of conventional Raman spectroscopy for the study of the reaction dynamics, which requires sub-second time resolution. In this presentation, I will discuss how we deploy in situ time-resolved Raman spectroscopy to investigate the electrocatalytic activation of CO2 and the dynamic chemical structure of the electrode surface.[2] References: [1] S. Nitopi et al. Chem. Rev. 2019, 119, 7610 [2] H. An et al. Angew. Chem. Int. Ed. 2021, 60, 16576

Resume : CO2 methanation is a competitive route to recycle and convert CO2, a greenhouse effect gas, into a renewable fuel, thus progressing towards a low-carbon-emission society able to counteract the climate change effects. For the catalytic conversion of CO2 into CH4, heterogeneous systems involving metal active species supported on metal oxides of different natures, very often in a powder form, have been widely investigated. Powder catalysts, however, present critical limitations when implemented in real devices. The aim of this study is to develop structured CeO2-based catalyst supports, easy to handle and to transport, able to reduce the pressure drop that powder catalysts can cause when packed in industrial reactors. We describe a scalable manufacturing process of mm-sized CeO2 pellets by extrusion-spheronization of CeO2-based pastes of different compositions. As a proof of concept, the so-obtained CeO2-based catalyst carriers have been impregnated with Ni species and evaluated in the catalytic conversion of CO2 into methane. The catalytic performance of the novel CeO2 carriers is hereby compared with analogous CeO2-promoted Al2O3 spheres, following previous studies in our group, which proved that the addition of a certain amount of CeO2 to Ni catalysts supported over commercial Al2O3 carriers significantly improved their activity in the methanation reaction. H2-TPR analysis revealed that a temperature of 350ºC is enough to completely reduce and activate the Ni/CeO2 catalyst, while temperatures above 700ºC are needed to reduce the Ni species when supported on the Al2O3 support. The possibility to reduce the catalyst at mild temperatures arises as technological advantage of the CeO2-based carriers with respect to Al2O3 ones, as most commercial reactors are incapable of heating the hydrogen gas above 400ºC. When evaluated in the methanation reaction, Ni/CeO2 displayed activities ca. 10% higher than those exhibited by the Al2O3 analogue at every temperature measured. These results open new avenues towards the preparation of catalytic materials for the industrial production of renewable fuels.

Resume : Cerium Oxide (CeO2) is one of the most interesting rare-earth material compounds for nanotechnology. When the size of grain is reduced to the nanometric regime, an increase of the surface area gives rise to the reversible removal of oxygen atoms from the exposed surface, generating a higher density of surface defects in the crystal structure. Electrons left behind by released oxygen localize on empty f states of cerium ions (formally reduced from Ce4+ to Ce3+) that are screened from the positive charge of the atom’s core by a high number of electrons localized in internal shells, preventing this change in oxidation state from altering the crystalline structure of the material at its surface. The ability to work as an “oxygen buffer” and electron scavenger is the core of the specific tasks it can be applied to, both in the nanocatalysis field and in biomedicine, where it is manly used as an antioxidant-like substance capable of the modulation of oxidative stress and inflammation-related processes. This work aims to go through the properties of colloidal CeO2 nanocrystals. The development of a strategy to obtain single-crystal nanoparticles, metal-oxide hybrids and other complex structures like different lanthanide-doped nanoparticles in aqueous media will be detailed by presenting a synthetic protocol for the system and a mechanistic description of the process. The applications of the presented nanomaterials within the fields of nanocatalysis and biomedicine will be discussed.

Resume : Reduction of carbon dioxide has as main objective the production of useful organic compounds and fuels - renewable fuels - in which solar energy would be stored. Molecular catalysts can be employed to reach this goal, either in electrochemical or photochemical contexts. They may in particular provide excellent selectivity thanks to easy tuning of the electronic properties at the metal and of the ligand second and third coordination sphere. Recently it has been shown that such molecular catalysts may also be tuned for generating highly reduced products such as methanol and methane, leading to new exciting advancements. Hybridization of these catalysts with conductive or semi-conductive materials may lead to enhance stability and new catalytic properties, as well as inclusion of molecular catalysts in devices for applications. This approach bridges between homogeneous and heterogeneous, and it raises new fundamental questions that may further lead to breakthrough in CO2 reduction chemistry. Our recent results will be discussed. References 1. Y. Wei, L. Chen, H. Chen, L. Cai, G. Tan, Y. Qiu, Q. Xiang, G. Chen, T.-C. Lau, M. Robert, Angew. Chem. Int. Ed., DOI:10.1002/anie.202116832, in press 2. B. Ma, M. Blanco, G. Drazic, L. Calvillo, L. Chen, G. Chen, T.-C. Lau, J. Bonin, G. Granozzi, M. Robert J. Am. Chem. Soc., 143, 8414-8425 (2021). 3. P. B. Pati, E. Boutin, R. Wang, S. Diring, S. Jobic, N. Barreau, F. Odobel, M. Robert, Nat. Commun., 11:3499 (2020). 4. B. Ma, G. Chen, C. Fave, L. Chen, R. Kuriki, K. Maeda, O. Ishitani, T-C. Lau, J. Bonin, M. Robert, J. Am. Chem. Soc., 142, 6188-6195 (2020). 5. S. Ren, D. Joulie, D. Salvatore, K. Torbensen, M. Wang, M. Robert, C. Berlinguette Science, 365, 367-369 (2019). 6. H. Rao, L. Schmidt, J. Bonin, M. Robert, Nature, 548, 74-77 (2017).

Resume : The extensive consumption of fossil fuels has caused the rapid increase in the CO2 level in the atmosphere, forcing people to find a clean and efficient technology of CO2 conversion to reduce CO2 emissions. Among the various CO2 conversion methods, the photoelectrochemical CO2 reduction reaction (PEC-CO2RR) is particularly interesting since it couples catalytic conversion of CO2 with solar energy storage in the form of solar fuels1. In the family of semiconductors, silicon (Si) is widely used due to its large abundance, nontoxicity and high energy bandgap (Eg = 1.2 eV). Modification of p-type Si with metal nanoparticles (NPs) such as Pt, Cu, Ag and Au has allowed to obtain relatively high current densities at low overpotentials for PEC-CO2RR, due to the metal catalytic effect, large number of active sites and band structure of the p-Si support. Among these metals, Ag and Cu are proven as good candidates for their low cost and ability to reduce CO2 to CO and formate and various hydrocarbons at low potentials (e.g. -1.05 V vs. SCE for H2 and CO and -0.58 V vs. RHE for CH4, C2H4 and CO) 2,3. Bimetallics are well known to boost the activity and selectivity of catalytic reactions, included CO2RR4. Despite their interest they have scarcely been exploited for PEC-CO2RR on Si supports. In the present work, we report on the synthesis of bimetallic AgxCu100-x NPs on p-Si supports and their application as photocathodes for PEC-CO2RR. These NPs are obtained by an innovative one-step method based on metal assisted chemical etching (MACE). We demonstrate that it offers good control of the bimetallic composition, allowing the synthesis of AgxCu100-x over the entire x range, and that it can be extended to any bimetallic system based on noble metals. Surprisingly, the morphology of AgCu NPs is very different from that of pure metals. Small spherical nanoparticles are obtained for Ag or Cu alone (25-30 nm in diameter) while elongated worm-like NPs (Feret diameter of ~145 nm) are formed with Ag and Cu together. XRD evidenced a phase-separated crystalline structure for this bimetallic system. Our first experiments on the PEC performance evidence a shift of 0.33 V towards positive potentials for p-Si/Ag50Cu50 with respect to p-Si in CO2-saturated 0.5 M NaHCO3 (aq.) electrolyte under illumination (0.2 AM1.5), which points out the potentiality of these photocathodes. However, SEM images show a significant loss in Cu content during electrolysis. Current work is being directed at understanding and eliminating this phenomenon. References 1. He, J. & Janáky, C. ACS Energy Lett. 5, 1996–2014 (2020). 2. Kempler, P. A., Richter, M. H., Cheng, W. H., Brunschwig, B. S. & Lewis, N. S. ACS Energy Lett. 5, 2528–2534 (2020). 3. Hinogami, R., Nakamura, Y., Yae, S. & Nakato, Y. J. Phys. Chem. B 102, 974–980 (2002). 4. Zhu, W., Tackett, B. M., Chen, J. G. & Jiao, F. Top. Curr. Chem. 376, 1–21 (2018).

Resume : The rapid increase of the greenhouse CO2 emissions due to human activities during the last century and as a consequence the climate warming is a matter of great concern for the scientific community. To overcome the problem, different CO2 capture, storage and conversion techniques were recently developed. Among the latter, the electrochemical CO2 conversion in molten salt electrolytes attracts considerable interest due to the possibility to synthesize value-added solid nanocarbon materials. It was shown that the variation of synthetic conditions, namely electrolyte composition, electrode material or reaction temperature results in synthesis of nanocarbons with different morphologies like graphene, carbon nanotubes or nanofibers, etc. The present study concerns the electrochemical CO2 conversion to nanocarbons in low temperature (500 oC) eutectic mixture of Li-K-Na carbonates. The emphasis is made on the effect of electrode material on the morphology of the deposited nanocarbons. It is an original report on preparation of tubular nanostructures at so low temperatures. The electrochemical CO2 conversion was performed in a vertical furnace. The eutectic mixture of Li2CO3-K2CO3-Na2CO3 (250-350 g) with a mole ratio 43.5:25.0:31.5 was placed into the furnace reactor in alumina crucible. The salts were dried initially at 250 oC for 16 h to remove moisture. Then, the temperature was raised to and kept at 700 oC for 0.5 h to ensure the complete melting of the salts. After that, the electrodes were inserted and CO2 was purged into the melt. The reaction temperature was left to drop to the desired 500 oC when a potential of 2.0-2.5 V was applied. The duration of the electrolysis was 4 h. After the reaction, the cathode with the deposited carbons was immersed in deionized water and stirred continuously until all the carbon was removed. The collected dry product was treated with 3.0 M HCl and then washed with water to remove residuals. Coiled wire from galvanized Fe was used as cathode while galvanized Fe, Ni, Cu, Ni-Cu and Ni-Cr coiled wires served as anodes. The conducted XRD analysis and Raman spectroscopy showed that the produced nanocarborns were generally amorphous. The SEM microscopy evidenced that the use of galvanized Fe anode resulted in formation of irregularly shaped nanocarbons. The Ni and Ni-Cr anodes stimulated deposition of honey-comb nanostructures while the deposits on the Cu and Ni-Cu anodes possessed tubular morphology. The lower potential (2.0-2.2 V) led to growth of long entangled tubes while at higher potential (2.5 V) short tubes were formed which in the case of the Cu anode resembled urchin-like agglomerates. Summarizing, the nature of electrode material influenced to a great extend the morphology of the deposited nanocarbons. The low temperature electrolysis in Li-K-Na molten salt electrolyte resulted in formation of tubular nanostructures when Cu-containing anodes were used.

Resume : The production of alternative fuels and chemicals from green electricity and simple feedstock molecules (water, CO2, nitrogen) represents an important pathway towards carbon neutrality of the European industry – besides the need for an increase in resource circularity and a massive electrification. Conversion of renewable energy into chemical energy carriers and feedstock enables: • the increase of renewable energy sources in the energy mix, • a long-term seasonal storage of intermittent energy sources, • a reduction of GHG emissions from existing assets (industrial and power plants), • and facilitates the storage and transport of energy through a local, decentralized production. An inherent characteristic of the production of these so-called e-molecules is their complex value chains, involving multiple stakeholders – ranging from the CO2 provider, the conversion technology developer to the off-takers. For a cost-efficient and sustainable production, all the bricks of this chain must be optimized with respect to each other. Due to the complexity of the processes and their innovative nature, no single actor is positioned on managing the whole chain alone; players develop a brick of the process and advance through collaboration. For all the bricks, material science plays a crucial role for future energy and cost savings. Taking the example of CO2 provision, sustainable, cost-efficient CO2 is central to the production of renewable fuels and chemicals. CO2 sources are multiple and can differ significantly in terms of size, type and origin of emissions. On the short-term, CO2 from concentrated sources will be the major source of CO2 providing the opportunity for capturing CO2 at lower cost and environmental impact. On the long-term, direct atmospheric CO2 capture can play a key role in decentralized e-fuel production - provided significant cost reductions through innovation. Concerning the conversion steps, hydrogen from water splitting is often hailed as one of the most promising elements to replace fossil fuels. Together with carbon monoxide from CO2, it is the main ingredient for syngas – a versatile intermediate compound that can be transformed in a multitude of chemicals and fuels. Hydrogen is mostly found in water, but the chemical process to transform it into fuel is still inefficient and breakthroughs in material science are urgently needed. For next generation conversion technologies, solar fuels are a highly promising: Rather than using renewable electricity, these devices combine everything necessary to go directly from sunlight to the final chemical product. Also, Direct Atmospheric CO2 Capture & Conversion would lead to a breakthrough: CO2 capture technologies have in common one major challenge – the energy use. Most of the energy use is linked to the regeneration step where pure, gaseous CO2 is released. The best strategy is to avoid this step and to develop a technology allowing the direct conversion from the captured CO2 solution.

Resume : Carbon dioxide (CO2) and carbon monoxide (CO) electrochemical reduction reactions (CO2RR and CORR) offer ways to recycle CO2, and produce energy-rich chemicals that can replace petrochemicals and fossil fuels contributing to the global decarbonization goals. Combining these technologies with renewable electricity enables the storage of intermittent renewable sources and leads to carbon emission-free chemicals feedstocks (P. De Luna et al., Science 2019, 364, eaav3506). Liquid hydrocarbons from CO2RR such as formate, ethanol, acetate, and propanol are widely employed commodity chemicals, which offer high energy density, straightforward storage, separation, and transportability. Moreover, the success of the electrochemical reduction approaches will require advances in reaction rates (current density) to decrease the capital contribution on product cost. A partial current density of 200 mA cm−2 to single products is considered a threshold for industrialization (S. Verma, ChemSusChem 2016, 9, 1972). Therefore, our studies sought to develop electrocatalysts for the selective production of liquid at high reaction rates and selectivity from the CO2RR. Inspired by the high selectivity to formate of indium-based catalysts and by the high activities achieved using nanostructured catalysts, we pursued InP colloidal quantum dots (CQDs) in the fabrication of cathodes for formate production. InP CQDs-based cathodes assembled by depositing the InP CQDs ink on a carbon-based gas diffusion layer generate formate as the only liquid product in the 0.5 - 1.5 A cm-2 range (I. Grigioni, ACS Energy Lett. 2020, 6, 79). Selectivity, measured as Faradaic Efficiency (FE), maintained above 90% in a wide current density range with a formate production rate as high as 17.4 mmol h-1 cm-2 at 1 A cm-2. A set of operando electrochemical and in situ Raman characterizations, together with ex-situ XPS analyses on fresh and spent cathodes, reveals that the active catalyst presents coexistence of surface sulfur derived from the CQDs thiol-ligand and metal In. Cooperative catalysis between In metal and surface sulfur sites allows for the high performance of this InP CQDs derived catalyst. The ability to operate with high FE in a wide range of current density and low applied voltage makes InP CQDs a versatile catalyst candidate for practical electrochemical CO2 reduction.

Resume : Photo-electrocatalytic (PEC) processes, which rely on solar light as energy source so as to drive highly selective chemical reactions, are a promising approach for CO2 reduction (CO2RR) into value-added fuels or chemicals. However, in current systems (which yet remain relatively rare), the conversion efficiency is still orders of magnitude below industrial requirements. To achieve a high solar-to-fuel conversion efficiency, new strategies yielding high photocurrent along with sufficient photo-voltage should be developed. Recent advances in photovoltaic on one hand and in molecular catalysis on the other hand open up new possibilities for improving photo-conversion of CO2. We have developed transparent and conductive nanostructured layers integrating an earth-abundant metal-based molecular catalyst into a ZnO matrix, which can be simultaneously used as a window and a protective layer for solar cells, creating a complete photo-electrode for solar to fuel conversion. More specifically, hybrids ZnO/catalyst layers were prepared by a simple one step electrochemical deposition on ZnO:Al window layers of Cu(In,Ga)Se2 based solar cells (CIGS). Combination of hybrid ZnO with a very low concentration of encapsulated molecular catalyst inside the oxide layer can lead to a high catalytic response for the CO2 reduction to CO with a selectivity of 97% and high current density (up to ca. 5 mA cm-2). These results will be discussed.

Resume : One of the environmental problems is the release of CO2 to air mainly by human activities. An increase in the CO2 amount in the atmosphere causes serious environmental problems. There are research activities to solve this problem and an approach is photocatalytic CO2 reduction with numerous semiconductors. Layered perovskites, in particular, are attractive materials due to their stable perovskite slabs containing numerous metal cations and flexible interlayer galleries that enable easy modification. The photocatalytic activity of layered perovskites is generally increased by modifying their surface with co-catalysts, in general, noble metals. In this research, we investigated the effect of single-site atom doping in the perovskite structure and modification of the bandgap with nitridation. The synthesis of Dion-Jacobson phase three-layer perovskite CsCa2Ta3O10 crystals was performed with conventional solid-state reaction and their [Ca2MxTa3-xO10-yNy]- (M: Pd, Pt or Ru) nanosheets through a nitridation-protonation-exfoliation approach for photocatalytic CO2 reduction application. In comparison to non-exfoliated perovskites, the 2D layered perovskite nanosheets benefit from a shorter transfer pathway for charge carriers to quickly reach their surface without a recombination process, resulting in improved efficiency. For bulk layered perovskites, this article introduces those that have been modified via elemental noble metal doping (Pt, Pd, Ru, and Rh) to the crystal structure to create a single-site metal domain-doped on the 2D nanosheets materials for photocatalytic applications to the literature. These phases were synthesized successfully according to structural and chemical characterization methods. The effect of dopant on photocatalytic activity for CO2 reduction was revealed.

Resume : One of the main challenges in the development of photoelectrochemical devices for solar energy conversion is the design and engineering of solid/solid and solid/liquid interfaces to achieve optimal charge transfer and good long-term stability. Even if one would design a ‘perfect’ interface on paper, it may be difficult to fabricate or it might undergo (ir)reversible changes during device operation. X-ray photoelectron spectroscopy offers a powerful tool to study these aspects, and I will show two examples. The first one is the BiVO4/electrolyte interface, which we studied with ambient pressure XPS using tender X-rays. We previously showed that an ultra-thin (~2 nm) BiPO4 layer forms at the surface under illumination. More recent results, however, reveal that this formation depends on the surface structure of BiVO4 and can be avoided for well-crystallized samples [1]. In the second example, we use hard X-ray photoelectron spectroscopy to study the -SnWO4/NiOx interface. The NiOx prevents passivation of the -SnWO4 absorber and introduces favorable upward bend bending. However, it also oxidizes part of the Sn2+ to Sn4+ during its deposition. This results in a thin SnO2 layer that pins the Fermi level and reduces the photovoltage [2]. This example also serves as a reminder that the photocurrent is only one of the performance indicators; the photovoltage is at least as important for energy conversion applications. References: [1] M. Favaro et al., J. Phys. D. Appl. Phys. 54 (16), 164001 (2021). [2] P. Schnell et al, Adv. Energy Mater. 2003183 (2021).

Resume : Solar fuels materials have attracted tremendous attention, as viable path towards a green and renewable source of fuel. The solar energy can be transformed to chemical energy by a proper combination of solar cells coupled with efficient catalysts, splitting water into H2 and O2. Solar cells provide the voltage required for the water splitting which is facilitated by efficient less expensive metal catalysts reducing the overpotential losses. The optimization of the performance includes adapting solar cell voltage and current to the precise needs of the catalytic reaction, which vary for different catalysts, water pH factor, electrolytes. In this work we will focus on bifunctional oxygen evolution catalysts (OEC) and hydrogen evolution catalysts (HEC) based on earth abundant materials such as, NiMoFe system, synthesized by physical vapor deposition (PVD) and discussion of results on particular cases. The HER and OEC of Ni, Mo, MoNi, NiFe, MoFe and NiMoFe intermetallic compounds supported on Glass, Ni foil and Ni foam, were investigated in acidic and alkaline water electrochemical device. The impact of deposition conditions on the structure and composition of different catalysts were characterized by XRD, GD-OES and SEM. Coupled water electrolyzer with photovoltaics (PV) have appeared as a very promising way to improve the efficiencies of solar-to-fuel energy conversion. Different simple and tandem solar cells such as CIGS and Si/Perovskite developed in our institute were involved for solar to hydrogen generation. Recent results showed that with bifunctional bimetallic and trimetallic water splitting catalysts are possible to highly reduce the over potential to drive a 10 mA cm2 current density with nonprecious and commercially ready materials.

Resume : The low efficiency of water electrolysis can be greatly improved by rationally designing low cost and efficient oxygen and hydrogen evolution materials. Herein, we report the synthesis of Ni–P alloys adopting a facile electroless plating method under mild conditions on Ni foam (NF) substrates. A fine tuning of the synthesis parameters allowed us to realize Ni–P catalysts with high performance for the oxygen evolution reaction (OER), yielding a current density of 10 mA cm−2 at an overpotential as low as 335 mV, exhibiting charge transfer resistances of only a few Ohms and a remarkable turnover frequency (TOF) value of 0.62 s−1 at 350 mV. To boost the hydrogen evolution reaction (HER), we developed ultra-low amount Pt-decorated Ni-P catalysts on NF (Pt/Ni-P/NF) via decoration of electroless deposited Ni-P alloys with very small amount of Pt nanoparticles (NPs) through a dip-coating procedure. This hybrid metal/non noble metal catalyst unfolds outstanding activity toward HER, requiring an overpotential of only 22 mV to attain a current density of 10 mA cm–2 with noteworthy Tafel slope of ~30 mV dec–1 and TOF of 1.78 s-1 at 50 mV. Finally, we realize an alkaline electrolyzer using the undecorated Ni-P as anode and Pt-decorated Ni-P electrode as cathode, respectively. We demonstrate that this full electrolyzer can sustain a current density of 10 mA cm–2 with a low potential of 1.64 V for at least 15 h with no discernible performance degradation. The present achievements provide a doable platform paving the way for development of cost competitive and highly efficient electrocatalysts for widespread water electrocatalysis application.

Resume : WO3-based nanostructures have emerged as one of the most promising candidates for electrocatalytic hydrogen evolution reaction (HER) due to their low cost, electrochemical durability, and high stability in an acidic environment. A powder of WO3 nanorods (400 nm long, 5 nm large) is produced by hydrothermal synthesis and thermal annealed. In depth, an investigation is performed involving transmission electon microscopy and electrochemical analysis with linear sweep voltammetry (LSV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The catalytic activity for hydrogen evolution reaction (HER) is investigated both for as-prepared and annealed WO3 nanorods demonstrating the peculiar HER dependence on crystalline phase, energy gap, and oxygen vacancy density. The annealed nanostructures show the best performance in terms of overpotential (173 mV), Tafel slope (140 mV/dec), and turn-over frequency (TOF).

Resume : It has been estimated that the energy captured in one hour of sunlight that reaches our planet is equivalent to annual global energy production by human population. To efficiently capture the practically inexhaustible solar energy and convert it into high energy density solar fuels provides an attractive ‘green’ alternative to running our present day economies on rapidly depleting fossil fuels, especially in the context of ever growing global energy demand. In this lecture I will overview our recent research to construct an operational semi-synthetic ‘artificial leaf’ based on photosystem I macromolecular machine interfaced with various electrode materials for production of green electricity and fuel. The performance of such semi-synthetic devices can be greatly improved by a rational design of organic conductive interface assuring unidirectional electron transfer whilst minimising back reactions. I will show how such custom-made interfaces can be further improved by adding metal redox centres and metallic nanoparticles in order to enhance not only the light-harvesting functionality but also increase the product output of photoconversion. Such highly interdisciplinary research carries a great potential for generation of viable and sustainable technologies for solar energy conversion into fuel and other carbon-neutral chemicals.

Resume : With Magic-angle spinning NMR, cryo-Electron microscopy, and accurate computer simulations we resolve universal mechanisms of biological photosynthesis across taxonomies and species and study how to transfer biological design principles to chiral biomimetic nanomaterials for high yield artificial photosynthesis. Photosynthetic complexes are activated in the ground state by local mismatches that selectively enhance conformational dynamics to perform the biological functions of light-harvesting, charge separation, and catalysis upon excitation by light. This leads us into a function-based framework of limited complexity for the design of semisynthetic and biomimetic artificial photosynthesis components for the conversion and storage of solar energy into chemicals. Conformational twisting promotes energy transfer and mixing of charge transfer character into the excited state coupled to protonation change of a variety of responsive matrices by a quasi quantum coherent mechanism denoted Non-adiabatic Conversion by Adiabatic Passage (NCAP). In this mechanism, an adiabatic sweep induces nonadiabatic matrix elements between reactant and a product states with resonant coupling to a vibration that is self-selected from the vibrational background. This process is best described in a doubly rotating interaction frame to reveal the coherent conversion of a reactant into a product with near-unity yield. To make the step to artificial photosynthesis we study for many years chlorosome bacteriochlorophyll antenna aggregates. This is a rather unique biological system without protein. Starting from an idealized symmetric model for the structure determined by cryo-EM and MAS NMR, we have added static and dynamic heterogeneity to track how ultrafast energy transfer can be stimulated by NCAP. Very recently, we have prepared chiral semisynthetic peptide-porphyrin antenna constructs, and the data indicate that a chiral packing may be sufficient to activate NCAP processes. For water oxidation catalysis we also project the biological system on a function-based framework to reduce the complexity. Here we study the level crossings between reactant and product intermediate states and the possibility to induce nonadiabatic transitions while conserving electronic spin angular momentum. A first experimental example of vibrationally assisted rapid catalysis was found in copper oxide nano leaves with induced asymmetry. All in all, our portfolio of experimental and theoretical results leads us to conclude that with the function-based framework of the biological paradigms, we can build on principles of coherent rotations in spin space in a magnetic field to establish quantum principles of high yield NCAP by the crossing of reactant and product states for a novel class of asymmetric responsive matrix materials that perform semiclassical chemical conversions by twisting, as in chiral biological systems.

Resume : The ammonia production (Haber-Bosch) is recognized as one of the largest and crucial process in the current chemical industry. However, with the rising concerns related to the related large CO2 emissions and extensive energy inputs, the full electrification of the Haber-Bosch process is becoming an attractive sustainable alternative. As a result, the concept of electrochemical nitrogen reduction reaction (eNRR) has been theoretically and practically demonstrated in the last couple of years. The eNRR typically comprises an electrochemical cell, where at the anodic site protons are produced and at the cathodic side the dinitrogen molecule is reduced to NH3. With respect to the latter, the development of an efficient cathodic electrocatalyst is a crucial aspect in the eNRR. In this respect, the electrocatalysts should be able to efficiently bind N2 and mediate its transformation to NH3. In the last years, single-site heterogeneous catalysts have been demonstrated to outperform the parental nanostructured materials in many (electro)catalytic process. However, as a general issue, their production is still challenging: multi-steps synthesis involving relatively expensive starting materials are usually employed. In this contribution we describe the development of a Ru-based nitrogen-doped carbon-supported materials which feature single atomic Ru sites. As a crucial point, their manufacturing consists of just two synthetic steps and three starting materials. Here, we demonstrated how the increased amount of the nitrogen-dopant constitutes the key-ingredient to create the single sites. Additionally, it is possible to easily vary the carbonaceous support (e.g. carbon black, carbon nanotubes) and to scale-up the preparation. The so-obtained materials have been characterized both structurally/morphologically (XRPD, XPS, Raman, physisorption) and electrochemically in the eNRR (Linear Sweep Voltammetry, Chronoamperometry and related control experiments).

Resume : There is a burgeoning interest in the development of a green method of ammonia synthesis; ammonia, already critical for fertilisers in the agricultural industry, is also being touted as a possible future energy vector or carbon-free fuel. The current method of production - the Haber Bosch process - is highly environmentally damaging and energy intensive but to date no viable alternative has been demonstrated. An electrochemical method operating under ambient conditions would be particularly attractive, as it would enable ammonia to be produced on a decentralised basis on-site and on-demand.[1] Thus far, amongst solid electrodes, only lithium based electrodes in organic electrolytes can unequivocally reduce nitrogen to ammonia.[2,3] Even so, at present, the lithium based system is far too inefficient for practical uses; moreover, it is highly unstable. In the current contribution, we will explore the underlying reasons why lithium is unique in its ability to reduce nitrogen to ammonia.[4] We use a combination of electrochemical experiments, Raman spectroscopy, time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy and density functional theory. By drawing from the adjacent fields of enzymatic nitrogen reduction and battery science, we will aim to build a holistic picture of the factors controlling nitrogen reduction. [1] Nilsson, A. & Stephens, I. E. L. in Research needs towards sustainable production of fuels and chemicals (eds J.K. Nørskov, A. Latimer, & C. F. Dickens) 49 (Energy-X, Brussels, Belgium, 2019). [2] Andersen, S. Z., Colic, V., Yang, S., Schwalbe, J. A., Nielander, A. C., McEnaney, J. M., Enemark-Rasmussen, K., Baker, J. G., Singh, A. R., Rohr, B. A., Statt, M. J., Blair, S. J., Mezzavilla, S., Kibsgaard, J., Vesborg, P. C. K., Cargnello, M., Bent, S. F., Jaramillo, T. F., Stephens, I. E. L., Norskov, J. K. & Chorkendorff, I. Nature 570, 504, (2019). [3] Westhead, O., Jervis, R. & Stephens, I. E. L. Science 372, 1149, (2021). [4] Bagger, A., Wan, H., Stephens, I. E. L. & Rossmeisl, J. ACS Catalysis 11, 6596, (2021).

Resume : The interest in heterogenization of molecular catalysts for electrosynthesis has been rapidly increasing in recent years. This approach enables the combination of easily characterized and optimized active sites via the molecular catalyst with the practical advantages of heterogeneous catalysis. Typically, the ligands of the molecular catalyst are modified with anchoring moieties such as carboxylates or phosphonates to facilitate covalent bonding to the (typically oxide) electrode surface. Other approaches involve the use of polymers or modifying the catalyst with an aromatic moiety to facilitate pi-stacking interactions with a carbon electrode. In this talk, I will discuss our new approach for interfacing molecular catalysts with electrodes via host–guest interactions.[1] Using a cyclodextrin-modified Au or ITO electrode along with transition-metal complexes featuring a naphthalene binding group, we observe facile charge transfer between the anchored molecular catalysts and the electrode, even though no covalent or pi-stacking interaction is present in the system. The approach allows for recycling of degraded catalysts through desorption of the guest molecules followed by resorption of fresh ones. New developments using this approach will also be discussed. [1] Sevéry, L.; Szczerbiński, J.; Taskin, M; Tuncay, I.; Nunes, F. B.; Cignarella, C.; Tocci, G.; Blacque, O.; Osterwalder, J.; Zenobi, R.; Lannuzzi, M.; Tilley, S. D.* Immobilization of molecular catalysts on electrode surfaces using host–guest interactions Nature Chemistry, 2021, 13, 523-529. doi.org/10.1038/s41557-021-00652-y

Resume : The energy transition and a hydrogen-based economy depend on the availability of energy in forms that allow long-term storage and transport from remote areas with abundance of renewable energy (RE) sources, and liquefied forms are the preferred option. Ammonia has potential to meet several requirements and to constitute one of the best energy carrier alternatives, besides being an important feedstock for the fertilizer and chemical industries. While current industrial processes rely on fossil fuels for H2 generation and a catalytic reaction (Haber-Bosch) at high temperature and pressure, new green paths with H2 providing from water electrolysis have emerged as best short-term solution. However, this approach faces certain incompatibilities between the two processes and limitations to tolerate RE intermittency. Direct electro-synthesis of ammonia from N2 (N2RR), H2O and RE has the potential to simplify the entire process, to be easily implemented in islanded and remote areas, to endure energy intermittency and curtailment, to accept less pure raw materials and to require less energy deriving in lower costs. However, the initial N2 adsorption and first electron transfer steps have intrinsic high-energy barriers, which might favor competing HER and impact the final NH3 productivity. As alternative, nitrogen oxyanions such as nitrates, mostly present as dissolved anions in polluted water from industrial sources, domestic sewage, sodium nitrate ore, and nitrification of bacteria, constitute a promising nitrogen source to synthesize ammonia via electrochemical route (NO3RR). This route has potential to achieve higher productivity values, as mass transfer limitations and inherent stability of molecular N2 are avoided, while at the same time constitutes an environmental remediation strategy. In this work, several strategies at material, electrode and cell levels are addressed towards the electrochemical generation of ammonia from NO3RR (and N2RR). Bimetallic electrocatalysts based on materials with different intrinsic activities (i.e. Cu for higher nitrate conversion; Ti for higher faradaic efficiency to ammonia) have been evaluated, by also considering the influence of electrolyte composition. The specific performance of single-metal and bimetallic electrodes strongly depends on pH and nitrate concentration conditions. Finally, FENH3>85% and productivities of 14.5 mgNH3·h-1·cm-2 are achieved with a Ti electrode decorated with Cu nanoparticles, demonstrating the implicit potential of this approach in comparison to direct N2RR with values in the order of μgNH3·h-1·cm-2. This work has been funded by MINECO under projects RESOL (ENE2017-85087-C3-2-R) and CERES (PID2020-116093RB-C42).

Resume : Billions of tons of solid waste are generated throughout the world each year and either end up in landfills or are processed in energy-intensive and polluting recycling strategies causing significant environmental damage. The use of sunlight-driven technologies to utilise these abundant waste resources as feedstocks for the generation of sustainable fuels and value-added chemicals emerges as a lucrative strategy to mitigate environmental pollution, tackle our energy crisis and create a circular economy. However, the existing solar waste conversion systems are not yet suitable for practical applications owing to their low efficiencies, poor selectivity and non-reusability. Here, we introduce a Cu30Pd70|perovskite|Pt photoelectrochemical (PEC) system, which can reform a diverse range of waste streams, including biomass, industrial by-products, and plastic waste, into industrially relevant value-added chemicals and clean hydrogen fuel, simultaneously without any external bias. A novel Cu30Pd70 oxidation catalyst is integrated in the PEC device to generate value-added products using simulated solar light, achieving 60–90% product selectivity and ~70–130 µmol cm^–2 h^–1 product rates, which corresponds to 10^2–10^4 times higher activity than conventional particulate photoreforming systems. The single-light absorber device offers versatility in terms of substrate scope, sustaining unassisted photocurrents of 4–9 mA cm^–2 for plastic, biomass, and glycerol conversion, in either a 'two-compartment' or integrated ‘artificial leaf’ configuration. These configurations enable an effective reforming of non-transparent waste streams and facile device retrieval from the reaction mixture enabling reuse for multiple cycles. The prototype device demonstrates the potential of PEC assemblies toward waste valorisation, accompanied by sustainable fuel production, approaching the thresholds required for commercial implementation.

Resume : Photoelectrochemical cells (PECs) have been developed as environmentally friendly systems that can directly utilize photogenerated electron-hole pairs for water splitting, fuel production, conversion of carbon dioxide, and pollutant degradation. Most reports on the photocatalytic or PEC hydrogen (H2) evolution via water splitting have focused on the H2 reduction half-reaction by generating on the photoanode a non-valuable oxygen or using sacrificial agents to consume the generated h+, resulting in a a significant waste of energy. Lately, much effort is invested into the synthesis of valuable chemicals on the photoanode while retaining the production of H2 on the cathode. Over the past few years, polymeric carbon nitrides (CN) attract widespread attention due to their outstanding electronic properties, which have been exploited in various applications, including photo- and electro-catalysis, heterogeneous catalysis, CO2 reduction, water splitting, light-emitting diodes, and PV cells. CN comprises only carbon and nitrogen, and it can be synthesized by several routes. Its unique and tunable optical, chemical, and catalytic properties, alongside its low price and remarkably high stability to oxidation (up to 500 °C), make it a very attractive material for photoelectrochemical applications. However, only few reports regarded CN utilization in PECs due to the difficulty in acquiring a homogenous CN layer on a conductive substrate and our lack of basic understanding of the intrinsic layer properties of CN. This talk will introduce new approaches to grow CN layers with altered properties on conductive substrates for photoelectrochemical applications. The growth mechanism and their chemical, photophysical, electronic, and charge transfer properties will be discussed. I will show the utilization of PEC with a CN-based photoanode as a stable and efficient platform for the oxidation of organic molecules to added-value chemicals, with hydrogen co- production. The second part of the talk will be focused on the electrocatalytic oxidative upgrading of organic molecules by NiFe-oxide into valuable chemicals.

Resume : Power-to-C2-C4 technology is a new route based on the production of light hydrocarbons (C2, C3, and C4) from renewable hydrogen and using different carbon sources (CO2 and CO) derived from raw materials such as biomass or simply captured from the air. The synthesis of C2-C4 hydrocarbons is considered an intermediate process between Power-to-Gas (Sabatier (CH4)) and Power-to-Liquid (Fischer-Tropsch (C5+)) and of great interest since the products obtained can be used widely as fuels in heating appliances, cooking equipment, and vehicle transportation. The main advantage of using a mixture of light gases and alkanes, compared to methane alone, is its higher calorific value. In this context, the scope of this work is to develop a novel catalytic formulation that is selective to C2-C4 hydrocarbons, with the aim of producing synthetic natural gas with high calorific value. For this, a series of catalysts composed of an active bimetallic phase (X-Co; X=Ni, Pt, and Fe) promoted by lanthanum oxide (La2O3) and supported on alumina microspheres (Al2O3) was synthesized. In order to identify the optimal process conditions, the hydrogenation of different carbon sources (CO2 or CO) was carried out using a constant molar ratio H2:CO2 or Co=3, maintaining a Gas hourly space velocity (GHSV=40000 NmL g-1 h-1) and varying the temperature (T=200-400ºC) and pressure (P=0-20 bar g). Then, the catalytic performance of the catalysts was carried out at the previously optimized conditions (T=200-300ºC and P=10 bar·g). In parallel, in order to better understand the chemistry and structural nature of the catalysts and to be able to establish a link between the catalyst properties and its C2-C4 selectivity, different characterization techniques were used (SEM-EDX, N2-Physisorption, He-Pycnometry, H2-TPR, XRD, and CO-Chemisorption). Additionally, in situ DRIFT spectroscopy measurements were performed on the catalysts to propose the hydrogenation reaction mechanism for both CO2 and CO. As optimal conditions to carry out the CO2 and CO hydrogenation process, it was identified that the catalysts should be evaluated at a pressure of 10 bar g and using a temperature range between 200-300ºC. Temperatures and pressures higher than those proposed result in a higher selectivity to CH4. At the optimized reaction conditions, the highest selectivities to C2-C4 were reached at T=250 ºC and using CO as a carbon source. In the CO2 hydrogenation, the Pt-Co bimetallic catalyst reached the highest selectivity (≈15%), being preferentially C2 and C3 hydrocarbons. On the other hand, in the CO hydrogenation, it was detected that all the bimetallic catalysts exhibited an improved selectivity (>37%) to C2-C4. The trend at 250ºC follows the order: Ni-Co>Fe-Co>Pt-Co>Co, suggesting that the implementation of a second metal in the Co-La2O3-Al2O3 system is positive and influences the selectivity of hydrocarbons. A selectivity to C2-C4 of approximately 50% was estimated in the Ni-Co bimetallic catalyst, the remaining 50% distributed between CH4 (≈40%), CO2 (≈5%), and even C5 (≈5%). The results of TPR, XRD, and DRIFT confirmed that the selectivity to C2-C4 strongly depends on the formation, reduction, and interaction of the formed species. This study can provide systematic guidance to the utilization of high-efficiently bimetallic catalysts for higher hydrocarbon formation with high yield from CO2 or CO.

Resume : The production of cheap energy from renewable sources, like solar or wind energy, provides the opportunity to use electrochemistry for the synthesis of chemical products in a cost-effective manner. The development of photoelectrochemical systems and electrolyzers to produce H2 from water has been the most studied as a means to store renewable energy and thus solve the inherent problem of the source intermittency. Lately, the reduction of CO2 to energy-rich chemicals (CO, formic acid, methane, etc.) is gaining increasing attention. However, none of these routes have become competitive with conventional, but less environmentally friendly, production methods yet. To overcome this gap, there are other alternative chemical routes, such as the synthesis of products with added value for the chemical industry which may combine both environmental and economical interests, despite being much less developed. One chemical transformation of interest is the oxidation of 5-hydroxymethyl-furfural (HMF), obtained from biomass, to produce 2,5-furandicarboxylic acid (FDCA), a precursor of poly-ethylene 2,5-furandicarboxylate (PEF) a polymer called to substitute polyethylene terephthalate (PET) thanks to its renewable origin. Among reduction reactions, the production of aniline from nitrobenzene has a great interest as this species is widely employed as a building block for the production of aniline-based dyes, explosives, pesticides and drugs. This is a 3-steps mechanism that involves the insertion of 2e- and 2H+ species in each of the hydrogenation steps of the NO2 group of the molecule. Electrodes made of Cu and Cu-based compounds have efficiently been used for the electro-reduction of nitrobenzene in aqueous media due to their high energy of activation for the competing hydrogen evolution reaction (HER). Compared with copper, palladium shows high activity for the hydrogenation of organic compounds, mainly due to its affinity for the adsorption and storage of H* species. In this work, decoration of Cu foil surface with Pd by galvanic replacement technique was used to improve the catalytic properties of the reduction electrode. An enhancement of the performance and selectivity of this electrode was obtained with respect to pure Cu, achieving a complete reduction nitrobenzene solution and obtaining aniline with 70% yield for aniline. Finally, a detailed analysis using Impedance Spectroscopy has revealed the improvement in the catalytic performance of Cu with Pd electrodes by increasing the adsorption of hydrogen in the electrode surface, which favours the selectivity in the reduction of nitrobenzene to aniline in a simple three-electrode system like batch reactor type, using inexpensive Cu subtract and an easy modification technique. In conclusion, developing materials capable of producing and stabilize H* in the electrode surface is key to reach an effective reduction and hydrogenation of organic species.

Resume : Hydrogen is considered a promising vector to store energy, especially considering the unpredictability of electricity generation based on renewable sources. Per molecule, hydrogen can store one of the largest amounts of chemical energy. This energy can be transformed into electricity in an environmentally clean procedure using a fuel cell. However, the challenge of storing such hydrogen in a small volume, as well as the lack of a hydrogen distribution infrastructure represent major drawbacks for a deployment of a hydrogen based economy. For this reason, new alternatives for hydrogen storage must been studied and developed and, in this line, graphene oxide (GO) presents a great potential. Hydrogenated graphene lattice offers safe and high capacity for hydrogen storage and can be obtained directly from the electrochemical reduction of graphene oxide (GO). In certain conditions, protons can be chemically bonded to carbon atoms to form reduced GO (rGO-H), which in turn, can be stored safely and can be easily transported wherever the electricity generation is needed. The GO electrochemical reduction can result in two major different products depending on the mechanism involved, the proton incorporation and consequent formation of C-H bonds, or the dehydration of the epoxy/hydroxyl groups and restoring of the double bond, which would lead to the rebuilding of the graphene-like lattice. In this work, we present different rGO-H samples prepared at different electrochemical conditions, showing how the electrolyte and the applied potential and time, play a decisive role in the hydrogen incorporation in the structure, with the final goal of optimize the process and make a feasible alternative for hydrogen storage.

Resume : Achieving a sustainable and cost-effective energy supply is very challenging today. Water splitting can be a scalable solution, however, still critical materials are typically used as catalysts. In particular, highly efficient oxygen evolution reaction (OER) is achieved with Ir and Ru based catalysis [1]. Transition metals (e.g. Ni, Fe) have been attracted lot of attention due to their natural abundance, low cost and good chemical stability. Among them, Ni-based nanostructures have shown excellent catalytic performance for OER. Typically, Ni-based structures are synthesized by harsh chemical methods (hydrothermal, solvothermal). Here we present the catalytic performance of NiO nanoparticles (NP) realized by pulsed laser ablation in liquid (PLAL) with a Nd: YAG (10 ns) high power laser. A large amount of NP is produced in few minutes of treatments. The NPs morphological and compositional properties have been analysed by Scanning Electron Microscopy, Energy Dispersive X-ray techniques, Rutherford Backscattering Spectrometry. The anode was realized by drop-casting of NiO NP onto graphene paper, and the OER features were tested via electrochemical techniques (cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy) under alkaline conditions (1 M KOH). An overpotential of 308 mV at 10 mA cm−2 was measured with a Tafel slope of 48 mV dec−1. These results are promising for the fabrication of low-cost Ni-based nanostructures for high-efficiency and sustainable electrocatalysts. [1] J. Kibsgaard, I. Chorkendorff, Considerations for the scaling-up of water splitting catalysts, Nature Energy 2019, 4, 430. https://doi.org/10.1038/s41560-019-0407-1

Resume : The production of clean and sustainable energy is one of the key open challenges to combat climate change and meet the ever-increasing global energy demand. In this context, a valuable and environmentally friendly method for the production of molecular hydrogen, considered as the energy carrier of the future, is water electrolysis. The sluggish kinetics and high energy barrier of the oxygen evolution reaction (OER) have stimulated the search for stable, efficient and cost-effective electrocatalysts, taking into account that the benchmark Ir and Ru-based materials, in spite of the excellent activity in alkaline media, suffer from high cost, low abundance, and poor long-term stability. In this work, Mn2O3 nanostructures decorated with Fe, Co and Ni oxides are fabricated on low-cost nickel foam substrates, favorably acting as current collectors and favoring electrolyte diffusion and gas evolution during OER, thanks to their inherent porosity. After the initial plasma enhanced-chemical vapor deposition (PE-CVD) of manganese oxide, Fe2O3, Co3O4, and NiO nanoparticles were introduced by radio frequency (RF)-Sputtering, and the obtained systems were annealed under an inert atmosphere to yield the phase-selective formation of pure Mn2O3. A multi-technique characterization by means of complementary analytical tools revealed the formation of high area quasi-1D arrays, characterized by an intimate contact between Mn2O3 and the functionalizing agents. The best Fe2O3-MnO2 systems achieved an overpotential as low as 350 mV vs. the reversible hydrogen electrode at a current density of 10 mAxcm-2, and a low Tafel slope of 70 mVxdec-1, which are among the best values reported for manganese oxide OER catalysts in alkaline media. This result was traced back to the peculiar system morphology and the interplay between the single oxides, maximized for Fe2O3-containing systems thanks to the even spatial dispersion of low-sized iron(III) oxide nanoaggregates throughout Mn2O3. Overall, the presently reported results candidate the proposed preparation route as an effective strategy to improve the intrinsic activity of manganese(III) oxide nanostructures, opening the door to a promising nano-engineering of electrocatalysts based on earth-abundant and non-precious materials. L. Bigiani, C. Maccato, T. Andreu, A. Gasparotto, C. Sada, E. Modin, O.I. Lebedev, J.R. Morante, D. Barreca, ACS Applied Nano Materials, 2020, 3, 9889.

Resume : Electrochemical water splitting represents a promising way to produce carbon-free renewable energy. Water splitting is composed of two half reactions: the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), taking place at the anode and cathode, respectively. The OER is considered the limiting process of the overall water electrolysis, because it involves four sequential electron transfer, thereby having slow kinetics and a large energy barrier for water splitting. One important issue is the availability of raw materials. Although their significant economic importance for key sectors in the global economy, they have a high-supply risk and there is a lack of (viable) substitutes, due to the unique and reliable properties of these materials for existing. Oxides and hydroxides of non-precious transition metals (e.g., Fe, Co, Ni) have been extensively investigated and are currently prevailing electrocatalysts used in the OER. Among these, Ni oxide represents a promising candidate as anode material with enhanced electrochemical performances. NiO nanostructures (such as oriented arrays, multilayers, or interconnected networks) increase electrolyte permeability through the active material, facilitating the mass transport at the interface. Thanks to unique size dependent properties, mass diffusion, and high surface area, nanostructured NiO is often used as a high-performance OER catalyst. In our work NiO microflowers (prepared by a low-cost and environmentally friendly chemical method) were dispersed onto a graphene paper (GP) substrate with different mass loading. The effect of the variation of the catalyst amount was evaluated through electrochemical analyses and the role of surface active sites was elucidated. Polarization curves, Tafel plot and Turnover frequencies were used as important parameters to evaluate the overall intrinsic activity of the dispersed catalysts. The NiO catalyst with optimized mass loading and material dispersion on GP required only 314 mV to deliver a current density of 10 mA cm^(-2) for the OER under alkaline conditions, with the charge transfer resistance of 4 ohms, and a TOF of 6.98 s^(-1). A deep understanding of the effect of the variation of the mass loading of NiO microflowers elucidated the influence of the amount of catalyst in the OER. The presented low-cost and reproducible approach can provide a significant platform for the future development of high-efficiency electrocatalysts. [1] Bruno, L.; Scuderi, M.; Malandrino, G.; Priolo, F.; Mirabella, S. Enhanced Electrocatalytic Intrinsic Activity of NiO Microflowers on Graphene Paper for Oxygen Evolution Reaction (paper in preparation)

Resume : Electrocatalytic oxygen evolution reaction (OER) plays a key role in sustainable energy conversion and storage, but is severely hampered by the lack of efficient catalysts, whose development remains a critical and challenging issue. Herein, it is reported for the first time that pure and Fe2O3-containing Co3O4-based OER electrocatalysts are grown on highly porous Ni foams by plasma enhanced-chemical vapor deposition and/or radiofrequency sputtering. Thanks to the inherent advantages of cold plasma synthesis routes, Ni foam supports are efficiently infiltrated by Co3O4 nanostructures and eventually nanosized Fe2O3, allowing a fine-tuning of their mutual content, nano-organization, and oxygen defectivity. For Co3O4-Fe2O3 systems, these issues enable current densities up to ≈120 mA cm−2at 1.79 V versus the reversible hydrogen electrode, an overpotential of ≈350 mV at 10 mA cm−2 and a Tafel slope as low as 60 mV dec−1, favorably comparing with literature values for most cobalt-based OER catalysts reported so far. Such features, accompanied by a good time stability, represent an important goal for eventual practical applications and candidate the proposed fabrication route as a valuable tool for the design of efficient electrocatalysts with precisely engineered properties and based on naturally abundant transition elements.

Resume : Water electrolysis is a promising method for the synthesis of green hydrogen. Nickel-based materials are considered to be a low-cost and efficient electrocatalyst for water oxidation. The current strategies for enhancement have been centered around on the modification of the metallic phase of nickel, forming phosphide or boride with excellent water oxidation efficiency. However, these phosphide and boride have been reported leaching out from the nickel electrode during water oxidation, indicating the challenges in elemental compatibility using such strategy. Most importantly, an oxide layer is frequently reported on the pristine nickel electrode, thus confusing the functionality of the active species, i.e. metallic nickel or surface nickel oxides, that are responsible for water oxidation. In this presentation, I report our recent work of the kinetics of active species on a metallic nickel anode for water oxidation employing a step-potential spectroelectrochemical (SEC) technique. An amorphous nickel oxide oxidised by the environmental oxygen was identified on the surface of metallic nickel using X-ray photoelectron spectroscopy. Such surface nickel oxide shows a SEC feature similar to the nickel oxyhydroxide (NiOOH). The kinetics of water oxidation in the nickel oxide on metallic nickel are observed to be more efficient than NiOOH in terms of rate constants and turnover frequencies (i.e. 1-7.6 s-1 of Ni/FTO than 0.6-2.3 s-1 of NiOOH at overpotential from 0.29 V to 0.39 V) for water oxidation. These results uncover the mechanism of the higher water oxidation efficiency of nickel oxide derived from metallic nickel, and emphasise the function of surface oxidized nickel, in terms of the structural and chemical consideration, to optimise the water oxidation performance using nickel-based materials.

Resume : The fabrication and mechanistic considerate of cost effective and efficient catalysts for water electrolysis are the center of water splitting technologies. We hypothesized the development of 3D mesoporous thin film of semiconductors by chemical solution deposition (CSD) for use as self-supported catalyst for electrochemical (EC) water electrolysis. These mesoporous supports can shows enhanced performance by deposition of metal catalyst via heat induction method. For characterization of electrode materials, various techniques have been applied such as, optical and surface analysis carried out by Scanning electron microscopy, Energy Dispersive X-Ray, X-Ray Diffraction, and Fourier Transform Infrared Spectroscopy. Potentiostat used for electrochemical activity and stability tests. To obtain the Faraday efficiency, hydrogen and oxygen gas collection will accomplish using a eudiometric gas collection system.

Resume : Photoelectrochemical (PEC) hydrogen evolution reaction (HER) is one of the most promising methods to achieve solar-to-hydrogen conversion [1-2]. Tin selenide (SnSe) is a good candidate for PEC HER due to its appropriate conductive band edge position to drive the water reduction process and high absorption coefficient to absorb solar light [3-4]. Liquid phase exfoliation (LPE) method is one of the most applied approaches to produce suspension of nanoflakes from its bulk counterpart with low-cost and high yield [5]. In this study, SnSe nanoflakes were prepared by using LPE method in different solvents, namely isopropanol (IPA) and the mixture of IPA/H2O with different H2O contents. The SnSe nanoflakes exfoliated in IPA exhibited 10 times higher PEC activity than those made in the mixture of IPA/H2O. The PEC performance of SnSe nanoflakes increased with the decreasing H2O content in the solvent mixture. The existence of SnSe2 domains in SnSe nanoflakes was proved by Raman spectroscopy and X-ray diffraction, which decreased the PEC performance of SnSe. Additionally, a sieving system was used to separate as-received SnSe crystals to select large, medium, and small crystals before LPE process, which further improved the PEC performance of SnSe electrodes. The electrodes prepared from the medium-sized SnSe crystal, exfoliated in isopropanol, showed the highest photocurrent of 2.4±0.4 mA cm–2 at –0.74 V versus RHE. Overall, these results indicate the applicability of SnSe electrodes in PEC HER, and allow us to explore other photoelectrocatalytic reactions on the exfoliated SnSe. References [1] S. E. Hosseini, et al., Renewable Sustainable Energy Rev. 2016, 57, 850-866. [2] M. Marwat, et al., ACS Appl. Energy Mater. 2021, 4, 12007-12031. [3] R. Wang, et al., J. Mater. Chem. A. 2020, 8, 5342-5349. [4] D. Zheng D, et al., ACS Nano. 2018, 12, 7239-7245. [5] Y. Ye, et al., Adv. Optical Mater. 2019, 7, 1800579.

Resume : Electrocatalytic decomposition of water is a promising route for hydrogen production, which nowadays is one of the best candidates as energy vector for a future carbon-free economy. In an electrolyzer for water splitting, hydrogen is produced in the cathode, and simultaneously oxygen is generated in the anode, then catalytic materials for both half-reactions are required. They must have high electrocatalytic activity (and high selectivity) for lowering the applied voltage to the cell and long-term stability for the durability of the device. Apart from that, the materials should be composed by Earth-abundant elements and be environmentally friendly. Besides, the synthetic route should be cheap and scalable for industrial production. For the oxygen evolution reaction (OER), the Ir/Ru oxides show excellent electrocatalytic performance for water oxidation in alkaline media, however, the scarcity of these metals and their high cost are detrimental for practical applications. Fueled by a growing interest in new materials that could be advantageous against precious metal-based catalysts, metal phosphides have attracted particular attention. Cobalt and iron elements have been reported as electrocatalysts active centers enhancing OER. In this work, we investigate the use of CoFeP nanoparticles to obtain disperse CoFeP particles supported on metallic foam. It allows achieving high current densities with lower overpotentials as the prepared electrode are showing a low Tafel slope. Under operando conditions for OER in alkaline media, chemical species are found to be different from the ones present in the freshly prepared electrode due to the reactivity of the electrodic material under anodic conditions. Nonetheless, after few initial minutes, the electrodes were stable for long-time tests under anodic currents. Oxyhydroxides are found to be the active species for OER after detailed characterization by HR-TEM, EELS, EDX and XPS analysis and their functional role is discussed taking into account the initial composition of the freshly prepared catalyst.

Resume : To keep our society sustainable, we need new technologies to replace the existing ones based on fossil fuels. Light driven water splitting to produce protons and electrons is the key to generate solar fuels, by the reduction of CO2 and N2 for instance, and one major challenge is to create highly efficient water oxidation catalyst. Inspired by the structure and function of OEC in PSII and man-made molecular water oxidation catalysts, strategies to design and synthesize advanced water oxidation material catalysts including transition metal oxides/hydroxides, and organic polymers with well-defined molecular structures of the catalytic active sites will be presented. Recent progress on photoelectrochemical (PEC) cells for water splitting and sustainable production of fine chemicals by using water as the oxygen and hydrogen source for respective oxygenation and hydrogenation of organic substrates will also be demonstrated in this symposium. Related publications: J. Yang et al, Nat. Commun. 2021, 12, 373. F. Li et al, Angew. Chem. Int. Ed. 2021, 60, 1976-1985. J. Hou et al, Angew. Chem. Int. Ed. 2021, 60, 2-11. X. Zhang et al, J. Am. Chem. Soc. 2021, 143, 49, 20657–20669.

Resume : 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 has been devoted to this topic recently. 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[1] can be designed to capture light and oxidize water and reduce protons, CO2 or other compounds to generate useful chemical fuels and feedstocks. In this context, this contribution will describe the preparation of efficient molecular water oxidation catalysts both in homogeneous phase and confined into solid conductive or semiconductive supports. Further the nature of the anchoring strategy on the performance of these molecular (photo)anode will be further discussed as well their implications for the generation of solar fuels.[2] [1] (a) Berardi, S.; Drouet, S.; Francàs, L.; Gimbert-Suriñach, C.; Guttentag, M.; Richmond, C.; Stoll, T.; Llobet, A. Chem. Soc. Rev., 2014, 43, 7501-7519. (b) Matheu, R.; Ertem, M. Z.; Gimbert-Suriñach, C; Sala, X.; Llobet, A. Chem. Rev. 2019, 119, 3453–3471. (c) Matheu, R.; Garrido Barros, P.; Gil Sepulcre, M.; Ertem, M. Z.; Sala, X; Gimbert-Suriñach, C; Llobet, A. Nat. Rev. Chem. 2019, 3, 331–341. [2] (a) Matheu, R.; Gray, H. B.; Brunschwig, B. S.; Llobet, A; Lewis, N. S. et al., J. Am. Chem. Soc. 2017, 139, 11345-11348. (b) Garrido-Barros, P.; Gimbert-Suriñach, C.; Llobet, A. et al., J. Am. Chem. Soc. 2017, 139, 12907–12910. (c) Hoque, Md. A.; Gil-Sepulcre, M.; Llobet, A. et al. Nat. Chem. 2020, 12, 1060–1066. (d) Schindler, D.; Gil‐Sepulcre, M.; Llobet, A.; Würthner, F. Adv. Energy Mater. 2020, 2002329. (e) Gil-Sepulcre, M.; Llobet, A. et al. J. Am. Chem. Soc. 2021, 143, 11651–11661. (f) Gil-Sepulcre, M.; Llobet, A. Nat. Catal. 2022, in press. DOI: 10.1038/s41929-022-00750-1.

Resume : Water electrolysis is a promising and environmentally friendly means for renewable electricity storage. Proton exchange membrane (PEM) water electrolysis has numerous advantages but relies on scarce and expensive Ir anode catalysts. Thanks to the recent progress in the development of anion-exchange membranes (AEM), the AEM-based electrolysis is becoming an attractive alternative which could allow the replacement of Ir anodes by more abundant transition metal oxides (TMO). Despite numerous publications devoted to the investigation of TMOs during the oxygen evolution reaction (OER), the nature of the active sites is not fully understood yet, hindering the development of active and stable electrode materials for AEM electrolysis. This is largely due to the heterogeneity of electrocatalytic materials, and lack of in situ information regarding the evolution of the surface composition in the course of electrocatalysis. TMOs with spinel structure constitute a promising class of materials due to a relatively low synthesis temperature (hence high surface area) and to their composition-dependent and widely tunable properties. Numerous studies have been devoted to the investigation of mixed Co/Fe and Ni/Co/Fe oxides in the OER and they showed that while cobalt spinel such as Co3O4 is active in the OER, its low electrical conductivity requires the addition of carbon. This reduces the applicability of such anode materials due to the corrosion instability of carbon under the OER conditions. Fe3O4 possesses higher electrical conductivity but is less OER active. Hence it was decided to combine these interesting properties to synthetize core shell cobalt iron oxide nanoparticles (Fe3O4@CoFe2O4) by thermal decomposition and to study their activity for the OER using cyclic voltammetry and impedance techniques. They are showing an activity as high as 150 A/goxide at 1.65V vs RHE. Additionally, despite numerous publications on spinel materials for the OER, the nature of the active sites is still being disputed. (Near) ambient pressure photoemission spectroscopy (NAP-PES), and NEXAFS (near edge absorption fine structure) has recently proven to be a powerful tool for the operando investigation of electrocatalytic materials. These nanoparticles have been studied operando under potential and are exhibiting some changes in the oxidation states of cobalt and iron.

Resume : Ever-growing global energy demand and the associated environmental concerns of our current energy supplies have accelerated the search for new energy resources and conversion technologies that are sustainable, environmentally safe, low cost, and offer improved performance. Among the various options being explored, hydrogen is one of the most sustainable, environmentally benign and clean fuel resources on the planet. Currently, more than 95% of world’s hydrogen is being produced through steam reforming of fossil fuels and biomass. There is an urgent need for an alternative process for the synthesis of hydrogen that is cheap and uses carbon neutral resources. Water electrolysis is an effective and decisive method to produce hydrogen fuel, because it is abundant, carbon free, clean, and renewable energy source, however the process to convert water into hydrogen (water electrolysis) is a hugely challenging from thermodynamic and kinetics viewpoints as it requires significant amount of energy (≈237.2 kJ mol−1) under normal operating conditions. Electrocatalysts have been used to lower kinetic barriers and enhance energy conversion efficiency of this process. Platinum, ruthenium and iridium-based catalysts have been found to be most effective for water splitting. However, due to their low natural abundance, electrocatalysts from these materials are prohibitively expensive. Lots of work has been done to explore cheap materials as a replacement for rare-earth metals. Oxides, hydroxides, nitrides, sulfides and borides of first row transition metals have been extensively explored for this purpose. In our research, the synthesis approach was modified where Ni foam used as support material on which Fe precursors were deposited by drop casting followed by thermal reduction. The prepared electrode (Fe-NFAs-NF) shows excellent performance in overall water splitting with a cell voltage of 1.58 V at 20 mA cm-2. For the hydrogen evolution reaction it requires an overpotential of only 27 mV at 10 mA cm-2 and gives a Tafel slope of 99 mV dec-1, while for oxygen evolution reaction (OER), it requires overpotential of 288 mV at 100 mA cm-2, with a Tafel slope of 42 mV dec-1. The enhanced electrochemical activity of these catalysts is attributed to the large surface area, porosity, abundant active sites and efficient electron pathway. Overall, the strategies presented in this study are simple yet effective for making composite structures which can be further explored for the fabrication of other metal/metal oxides over nickel foam substrates with potential applications in energy generation, energy storage and environmental remediation.

Resume : In the urgent quest for green energy vectors, the generation of hydrogen by water splitting with sunlight occupies a preeminent standpoint. The highest solar-to-hydrogen (STH) efficiencies have been achieved with photovoltaic-electrochemical (PV-EC) systems. However, most PV-EC water-splitting devices are required to work at extreme conditions, such as in concentrated solutions of HClO4 or KOH or under highly concentrated solar illumination. In this work, a molecular catalyst-based anode is incorporated for the first time in a PV-EC configuration, achieving an impressive 21.2% STH efficiency at neutral pH. Moreover, as opposed to metal oxide-based anodes, the molecular catalyst-based anode allows us to work with extremely small catalyst loadings (< 16 nmol/cm2) due to a well-defined metallic center, which is responsible for the fast catalysis of the reaction in the anodic compartment. This work paves the way for integrating molecular materials in efficient PV-EC water-splitting systems.

Resume : The energy requirement of the world is constantly increasing and the studies for the alternative energy sources are ongoing. The hydrogen energy is one of the promising solutions for these alternative energy sources due to the high abundance of the hydrogen on the earth. However, the hydrogen must be produced and the photocatalytic hydrogen production is one of the methods to generate hydrogen from water using sun light. For photocatalytic hydrogen production, the photocatalysis must have a suitable band gap and appropriate valence and conduction bands potentials to reduction and oxidations reactions [1]. In this study, the selenium based chevrel phase CoW6Se8 has been considered for the water splitting performance. The Chevrel phases that are discovered by Chevrel and Sergent have superior properties composing with three refractory metals [2]. The Chevrel phases have MxMoyCh8 formula where M is a metal and Ch is a chalcogen with y as 3 or 6 and x as 0, 1, 2, 3, or 4 values in a Chevrel phase [3]. In literature, the sulphur based Chevrel phases have been investigated for the superconductivity, cathode material properties, hydrogen production properties, etc. [4-6]. However, there is a lack of interest for selenium based Chevrel phases in the literature. In addition, the Chevrel phases are considered with molybdenum atoms where tungsten atoms could be used instead of molybdenum atoms. In this study, CoW6Se8 have been examined using the Density Functional Theory (DFT) [7,8] to reveal its structural and electronic properties. The DFT is a powerful theory to get the materials properties without any input from experimental values. To get detailed water splitting performance, the hybrid functional [9] calculations have been performed and the results have been analyzed. The selenium based chevrel phase CoW6Se8 is a potential candidate material for water splitting applications. This work is supported by TUBITAK under project number 120F305. References [1] Kudo, A., Miseki, Y. 2009. “Heterogeneous photocatalyst materials for water splitting”. Chemical Society Reviews, 38(1), 253-278. [2] Chevrel, R., Sergent, M., Prigent, J. 1971. “Sur de nouvelles phases sulfurées ternaires du molybdène”, J Solid State Chem, 3, 515–9. [3] Perrin, A., Perrin, C., Chevrel, R. 2019. “Chevrel Phases: Genesis and Developments”. [4] Fischer Ø. 1978. “Chevrel phases: Superconducting and normal state properties”, Appl Phys, 16, 1–28. [5] Mitelman, A., Levi, M. D., Lancry, E., Levi, E., Aurbach, D. 2007. “New cathode materials for rechargeable Mg batteries: Fast Mg ion transport and reversible copper extrusion in CuyMo6S8 compounds”, Chem Commun, 4212–4214. [6] Wu, Z., Guo, J., Wang, J., Liu, R., Xiao, W., Xuan, C., Wang, D. 2017. “Hierarchically porous electrocatalyst with vertically aligned defect-rich CoMoS nanosheets for the hydrogen evolution reaction in an alkaline medium”. ACS applied materials & interfaces, 9(6), 5288-5294. [7] Kresse, G., Furthmüller, J. 1996. “Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set”, Phys. Rev. B., 54, 11169-11186. [8] Kresse G, Furthmüller J. 1996. “Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set”, Comput Mater Sci 6:15–50. [9] Heyd J, Scuseria GE, Ernzerhof M. 2003. “Hybrid functionals based on a screened Coulomb potential”, J Chem Phys 2003;118:8207.

Resume : Ferroelectric materials have been widely studied in the area of photoelectrochemistry as the internal electrical field of ferroelectric materials can support the separation of photo-generated charges under illumination. Ferroelectric BiFeO3 has attracted much attention as it has a suitable bandgap around 2.6 eV which is active in visible range while other traditional ferroelectric materials such as BaTiO3 and PbTiO3 have wide bandgap larger than 3 eV. However, it has been reported that xBiFeO3-(1-x)PbTiO3 solid solutions have the lowest bandgap around 2.2 eV at x = 0.71. Herein, xBFO-(1-x)PTO binary films have been prepared via chemical solution deposition for photoelectrochemical water splitting application. Highly pure BiFeO¬3 (x=1) with a rhombohedral structure is obtained without any presence of impurity phases, such as Bi2Fe4O9 and Bi25FeO40 that are usually found using hydrothermal and solid states method. The bandgap of xBFO-(1-x)PTO is found to keep increasing with more and more PTO introduced into BFO, which is shifted from 2.64 eV (x=1) to 3.13 eV (x=0). The pure PTO here has cubic structure and the as-prepared binary films all exhibit orthorhombic structure while tetragonal crystal was observed in both pure PTO and solid solutions in Wu’s report1. In addition, the photo-generated current of binary films is much lower than pure films, which can be also explained by the transformation from ferroelectric rhombohedral to paraelectric orthorhombic structure. Our results indicate it is crucial to control the crystal structure of BiFeO3 to achieve good photoelectrochemical performance, particularly when undertaking band gap engineering via solid solutions.

Resume : Photoelectrochemical (PEC) devices have been shown to achieve high efficiencies1 with promising cost estimations for hydrogen production due to their integrated device structure2. Researchers have typically focused on monolithic, thin film photoelectrodes on substrates such as fluorine-doped tin oxide coated glass. However, studies have shown that these structures have high ionic resistance upon scale up, resulting in a reduced current density3. In other electrochemical devices (such as fuel cells and electrolysers), porous gas diffusion layers are used to prevent this scaling issue. However, the preparation of photoelectrodes on porous substrates requires the development of new semiconductor deposition techniques, transparent catalyst layers and transparent gas diffusion layers. The realisation of such a device is targeted in the H2020 funded Sun-To-X project4, where we aim to build a large area PEC device for solar hydrogen production. The produced hydrogen will be then stored in a silicon-hydride-based liquid hydrogen storage material (HydroSil5) for which the thermochemical hydrogen ?charging? process will be developed in the scope of the project. The charging process to form HydroSil involves the reaction of hydrogen and a SiOx precursor at high temperatures, which will be generated by concentrated solar light. Compared to state-of-the-art hydrogen carriers, this has the advantage of being non-toxic, liquid at ambient conditions and having an exothermic release process. Finally, we will investigate another use of the Si-H bonds in the HydroSil molecule for the reductive depolymerisation of plastics for the formation of hydrocarbons. 1. W.-H. Cheng, ACS Energy Lett. 2018, 3, 1795?1800 2. M. R. Shaner et al. Energy Environ. Sci., 2016, 9, 2354-2371 3. I. Y. Ahmet et al. Sustainable Energy Fuels, 2019, 3, 2366-2379 4. https://sun-to-x.eu/ 5. https://www.hysilabs.com/

Resume : It is well known that the storage of Hydrogen (H2) occurs through the use of hydrides by means a solid-gas type reaction. This method is a very attractive alternative given its enormous versatility and greater security. The considerable gravimetric capacity of hydrides for the storage of H2 (>6%) makes these materials very attractive for portable applications of this gas. However, it is necessary to use light compounds/elements to guarantee the greatest gravimetric capacity of the compound, supposes a restriction that leads, in many cases, to very stable compounds with a slow kinetics of absorption and desorption of H2. Alkali alanate family are a very attractive for portable hydrogen applications and, specifically sodium alanate (NaAlH4), has been intensively investigated [1] because desorbs the hydrogen through two reactions at not very high temperatures (150-250ºC). For several years, many attempts have been made to reduce the temperature of these reactions through nanostructuring or the use of different catalysts. However, the different reaction pathways that have been explored trying to find the non-thermal activation of the sorption/desorption reactions of H2 in hydrides (by mechanical energy or by electromagnetic radiation) aim to promote these reactions avoiding the use of thermal energy [2]. The non-thermal H2 desorption mechanism is not clear enough, suggesting that this mechanism is due to different causes: generation of desorption channels, catalytic effects, etc. This could avoid undesired phenomena (phase segregation, recrystallization, etc.) improving, therefore, the processes of hydrogen sorption. In this context, it was observed that mechanical energy is very effective for the desorption of H2 in vacuum at room temperature (RT) in very stable hydrides (when temperatures higher than 300oC are needed for thermal dehydrogenation) [3] such as magnesium hydride. In this work, the destabilization of sodium alanate pellet under mechanical forces at RT has been investigated and compared with other families of hydrides. The released gases were analyzed in operando using a quadrupole mass spectrometer coupled to a dynamic expansion system to investigate the Mechanical Stimulated Gas Emission (MSGE-MS) technique. First, the tribodesorption of NaAlH4 gases showed different species compared to the exhibited thermal desorption experiments. The most significant finding was that the tribological mechanical activation showed a significant amount of hydrogen ( >99%) , AlxHy, among other gases at various proportions, ruling out thermal pathways. This study was complemented with ex situ characterization of confocal µ-Raman spectrometry, microultraidentation, COF, TPD-MS, etc. The Raman spectra showed the characteristic bands of abraded (mechanical effect zone) and pristine surface that were exclusively assigned a phase corresponding to NaAlH4. This analysis rules out the thermal effect. The influence of load on the emission rate will be pointed out. Finally, the main differences between tribochemical reactions and thermal desorption reaction pathways will be discussed. [1] T. J. Frankcombe, Chem. Rev. 112, 2164 (2012) [2] J.R. Ares et al, ChemPhysChem, 20, 10, 1248 (2019) [3] R. Nevshupa et. al, J Phys. Chem. Lett. 6, 2780 (2015)

Resume : The deployment of carbon-free energy technologies that could compete with the price of fossil fuels is expected to be a key factor for sustaining the future energy requirements of the world population. In this regard, hydrogen is a promising energy vector that could be produced directly using renewable energy in an electrolyzer. Among the electrode materials used as cathodes, iron phosphide has engaged interest in the last years. Apart from the fact that it is composed of two elements highly abundant in the Earth’s crust, the new synthetic routes are making its synthesis simpler and cheaper. In this work, a 3D electrode composed by FeP directly deposited on carbon fibers is fabricated by a simple impregnation method and subsequent heat treatment. The intermediate iron species are converted to FeP by in situ phosphine generation at 300-400 ˚C. High coverage of the carbon fibers is achieved as observed by SEM, leading to a highly porous cathode with a high surface area. Optimized FeP electrodes exhibit high activity toward hydrogen evolution reaction (HER) in both acidic and alkaline electrolytes displaying low overpotentials and excellent stability. The FeP deposition using the same synthetic route was also performed in a nickel foam substrate leading to analogous reaction kinetics towards HER. Electrodes under the most outperformed conditions will be tested in a flow cell using proton exchange membranes (PEM) or alkaline anion exchange membranes (AAEM) to evaluate the feasibility of the cathodes for HER in continuous operation.

Resume : Anthropogenic greenhouse gas CO2 can be modified to alternative fuels and value-added products by Electrochemical CO2 Reduction. Cathodes based on GDE-deployed CO2 electrolysers are most attractive and found to be highly efficient in achieving a carbon-neutral economy. Copper and copper-based catalysts are proved as the star materials in producing greater than 2e- carbon products. In this particular work, the main focus is on developing the catalyst layer modified Gas Diffusion Electrodes and subsequent deployment of two cell approach in attaining enhanced faradaic efficiencies and higher current densities. Firstly, we report a simple Cu/CuOx based catalyst synthesised by a facile hydrothermal method supported over carbon. CuOx platelet-like structures partially surrounded by carbon-black are obtained facilitating the enhanced CO2 diffusion and electrical conductivity. Initial X-Ray Diffraction studies revealed the presence of Cu, Cu2O and CuO particles with varied crystallographic orientation (111, 200) and were found to be selective towards ethylene. HR-TEM analysis revealed the polymorphic Cu particles that are majorly surrounded by Carbon. Compositional modifications to the catalysts and catalyst layer deposited over the GDE are carried out and the optimum ratios of Cu/C are reported. Tailored catalyst layers over the GDE exhibited high current densities greater than -150 mA cm-2 for ethylene selectivity with FE > 30% are observed at a maximum cathodic potential of -1.5 V vs RHE. Optimization studies are also performed by altering the preparation of catalyst inks involving binders and varying PTFE content to tune the hydrophobicity. In the successive experiments, two-cell approach is executed in a series mode wherein the first cell is deployed with CO selective catalyst having Zn and Ag-based materials and the converted CO is directly supplied as the feed for the second cell having C2 selectivity attaining overall high conversion rates. Flow-by and flow-through configurations were also assessed and quantified results are reported. A systematic study in the flow concentration of CO2 and electrolyte is carried out monitoring the pH of the electrolyte both pre and post-electrolysis on both cells. It is inferred that the two or multi-cell approach definitely aids in attaining industrially relevant current densities and enhanced conversion rates with long term stability and is proposed to have high commercial viability. Keywords: CO2, Electrocatalytic CO2 reduction, Copper, Zn-Ag, Gas Diffusion electrodes, Ethylene, Multi-cell approach. This work is supported by European Union's Horizon 2020 DOC-FAM programme under the Marie Skłodowska-Curie Actions Grant Agreement No 754397.

Resume : Electrochemistry will play an important role in the transition to renewable alternatives as a source for chemicals and materials production. In the development of electrochemical processes for industrial application, the design and scale-up of the electrochemical reactor is very important. Avantium has been using its knowledge and technology on catalyst research to develop an integrated electrochemical process for the production of chemicals from CO2. We work on the development of continuous processes with high degrees of automation, control and real-time data monitoring. Scale up in electrochemical reactors is achieved by using multiple cells or as commonly known a stack configuration. By participating in several European consortia we are able to collaborate on the integration of tandem electrolysis and the scaling up of our CO2 reduction technology which will be demonstrated on actual industrial sites with integrated CO2 capture and purification.

Resume : The design and development of environmentally friendly and robust anodes for photoelectrochemical (PEC) water splitting plays a critical role for the efficient conversion of radiant energy into hydrogen fuel. In this regard, quasi-1D copper vanadates (CuV2O6) were grown on conductive substrates by a hydrothermal procedure and processed for use as anodes in PEC cells, with the idea of understanding the role exerted by cobalt oxide (CoOx) overlayers deposited by radio frequency (RF) sputtering. The target materials were characterized in detail by a multi-technique approach with the aim at elucidating the interplay between their structure, composition, morphology, and the resulting activity as photoanodes. Functional tests were performed by standard electrochemical techniques like linear sweep voltammetry, impedance spectroscopy, and by the less conventional intensity modulated photocurrent spectroscopy (IMPS), yielding an important insight into the material PEC properties in terms of kinetic constants for charge injection, electron-hole recombination and charge transfer efficiency. The obtained results highlight that, even though the supposedly favourable band alignment between CuV2O6 and Co3O4 did not yield a net current density increase, cobalt oxide-functionalized anodes presented a remarkable durability enhancement, an important prerequisite for their eventual real-world applications. The concurrent phenomena accounting for the observed behaviour are presented and discussed in relation to material physico-chemical properties.

Resume : Global efforts to reduce pollution due to an excess emission of CO2 require a completely revised approach to energy production. Green hydrogen is the most promised energy carrier which can be generated by means of water splitting in a climate-neutral manner. Water splitting in a system containing TiO2 photoanode has been demonstrated exactly 50 years ago by Fujishima and Honda [1]. Since that time, many efforts including incorporation of cationic or anionic dopants have been undertaken in order to use this material for green hydrogen generation. However, all these attempts have led to a moderate success, only. Too large band gap of TiO2 that is badly adapted to the visible range of the light spectrum remains the main problem. Recently, a completely new strategy has been proposed to manipulate light [2] instead of modification of the photoanode material. This idea is based on nonlinear up-conversion effect (UP) that involves two or more photons of lower frequency that can be absorbed in optically active medium to produce one photon of higher frequency better matched to the wide band gap of TiO2. Optically active materials can be formed by incorporation of lanthanide ions such as Er3+ and Yb3+ into TiO2 [3]. In this review, we will present the recent advances in this field of studies including our own contribution to the up-conversion in lanthanide-doped TiO2 deposited by reactive rf magnetron sputtering [4]. TiO¬2:Er,Yb thin film photoanodes have been grown on different substrates, e.g. Si, amorphous silica, ITO, Ti foil, from metallic Ti/Er (90/10 at.%), Ti/Er/Yb (98/1/1 at.%), and Ti/Er/Yb (88/2/10 at.%) targets in Ar:O2 atmosphere. The influence of Er3+ and Yb3+ on TiO2 thin films morphology, electronic structure and optical properties was investigated. Scanning electron microscopy, SEM, X-ray absorption spectroscopy with synchrotron radiation, XAS and UV-VIS-NIR spectrophotometry were employed. Functional measurements of current-voltage characteristics were carried out. Correlation between the photocurrent density and up-conversion intensity will be discussed. The general conclusion is that the UP emission is highly sensitive to the local atomic and electronic structure of lanthanides ions as well as to their localization in TiO2 matrix. [1] Fujishima, A.; Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode, Nature 1972, 238, 37–38 [2] Yang M-Q.; Gao M.; Hong M. and Ho G.W. Visible-to-NIR Photon Harvesting: Progressive Engineering of Catalysts for Solar-Powered Environmental Purification and Fuel Production, Advanced Materials 2018, 30, 1802894 [3] Mazierski P.; Juganta K.; Royc J.K.; Mikolajczyk A.; Wyrzykowska E.; Grzyb T.; Caicedoa P.N.; Weib Z.; Kowalska E.; Zaleska-Medynska A.; Nadolna J. Systematic and Detailed Examination of NaYF4-Er-Yb-TiO2 Photocatalytic Activity under Vis–NIR Irradiation: Experimental and Theoretical Analyses, Applied Surface Science 2021, 536, 1477805 [4] Kot A.; Radecka M.; Dorosz D.; Zakrzewska K. Optically Active TiO2:Er Thin Films Deposited by Magnetron Sputtering Materials 2021, 14, 4085 Acknowledgement: The National Science Centre NCN Poland is acknowledged for supporting this research under the project no. UMO-2020/37/B/ST8/02539.

Resume : The exploration of transition metal-based electrocatalyst for overall water splitting is becoming important as hydrogen becomes an integral part of the energy landscape. Recently, a new class of compounds i.e. layered double-hydroxides (LDHs), also known as anionic clays, are have shown tremendous promise for use as electrocatalysts. The lamellar morphology of LDHs accommodates higher active sites, which contributes to the facile electron transfer and thus attracts a great deal of interest in catalysis application. Moreover, the high catalytic activity of LDHs are also linked to their facile anion exchange, specific electronic structures, and versatile chemical compositions. Herein, we have developed a series of ternary layered double hydroxide (LDH) using pH-adjusted co-precipitation method with varying ratio of Cu, Ni and Co, which are used as an electrocatalyst for overall water splitting. (Cu3-xNix)Co2-LDHs (x = 0, 1, 2, and 3) were systematically characterized using XRD, XPS, SEM, FTIR, TEM, and BET techniques. The synergistic contributions from the electrocatalytically active metals and lamellar morphology of LDHs promote water dissociation, facilitate faster release of H2-O2 gas bubbles, ameliorate electrolyte ion diffusion, and improve electron transfer rate. It is further observed that the (Cu2Ni)Co2-LDH showed excellent electrocatalytic activity for both hydrogen evolution (HER) and oxygen evolution reaction (OER) with an overpotential of 162 and 218 mV for HER and OER, respectively at 10 mA cm-2. Tafel slope was found to be lowest for (Cu2Ni)Co2-LDH. Further, the durability of the materials was also analyzed by performing chronoamperometry for over 12 h. The overall water electrolytic cell using (Cu2Ni)Co2-LDH as both electrodes can reach 100 mA cm−2 at 1.65 V with outstanding durability.

Resume : Understanding and quantifying transport in (photo)electrochemical devices and components is essential for their characterization and optimization. This is particularly important when experiments are able to provide only limited and locally averaged information. Multi-scale, multi-dimensional and multi-physics numerical models have the ability to provide locally resolved information and, therefore, become an indispensable tool for the quantitative analysis and characterization. Here, I will discuss three computational example cases on multiple scales that provide insights into the details of transport and heterogeneity of it. First, I describe an electrical double layer (EDL) model which allowed to identify the role of non-reactive cations (e.g. potassium) in electrochemical CO2 reduction in acidic environments [1]. The EDL model solved for the transport of ionic species in the diffusion layer and charge distribution in Stern layer and provided locally resolved potential and concentration distributions in close vicinity of the electrode. We observed that the potassium cations migrate to the electrode surface and modulate the electric field strength, and therefore, reduce the migration of protons towards the electrode, highlighting the importance of controlled transport at/towards the electrode surface. Second, I will show a pore-scale model of catalyst layers for electrochemical CO2 reduction that provides insights into the heterogeneity and transport throughout the layer. We utilize a combined experimental-numerical approach [2], where a physical sample is analysed by FIB-SEM nano-tomography, the obtained data segmented and the structure digitalized, and the used as input to the pore-level simulations. We provide quantitative effective transport properties and discuss heterogeneity. Finally, I will review a multi-scale photoanode degradation model [3] that provides insight into the importance of operating conditions and their effect on the stability of photoanodes. Also on the device scale, heterogeneity is observed to be critical, indicating that variation in local operating conditions will translate into variation of stability. These three examples serve to show the importance of modelling, and I will end by highlighting the desire to provide connected multi-scale models that are able to account for these effect throughout all relevant scales (device, electrode, interface, molecule, atom-scales). References: [1] J. Gu, S. Liu, W. Ni, W. Ren, S. Haussener, X. Hu. Modulating Electric Field Distribution by Alkali Cations for CO2 Electroreduction in Strongly Acidic Medium, Nature Catalysis, accepted, 2022. [2] S. Suter, M. Catoni, Y. Gaudy, S. Pokrant, S. Haussener, Linking Morphology and Multi-Physical Transport in Structured Photoelectrodes, Sustainable Energy & Fuels, doi: 10.1039/C8SE00215K, 2018. [3] F. Nandjou, S. Haussener, Modeling photostability of solar water splitting devices and stabilization strategies, in review, 2022.

Resume : A long-standing challenge is the development of artificial photosynthetic approaches for capturing and storing the energy of sunlight in the chemical bonds of a fuel, e.g. molecular hydrogen, offering a clean, sustainable and abundant source of energy. In this respect, colloidal nanostructured semiconductor materials are explored extensively as photosensitizers and photocatalysts. To push forward the development of functional materials based on semiconductor nanocrystals, function immanent exciton and charge-separation/recombination dynamics in relation to structural parameters need to be understood. Factors like composition, structure and dimensions of the semiconductor particles, the nature of cocatalysts and the type of surface ligands are severely influencing the efficiencies for solar to hydrogen conversion. By applying time-resolved transient absorption and photoluminescence spectroscopy we strive to reveal the connections between structure, charge carrier dynamics and the targeted function. To illustrate this approach, I will give a brief overview on the results of our studies on CdSe@CdS seeded nanorods functionalized with metal particles of varying composition and morphology as cocatalyst and the insights gained on the connection between charge separation at the nanosized semiconductor/metal interface and activity for hydrogen evolution.[1, 2] Besides the transfer of electrons to the cocatalyst, a key step in these heterostructures is hole localization in the CdSe seed which enables the formation of long-lived charge separation supporting charge accumulation at the catalytic reaction centers necessary to drive multi-electron redox reactions. Latest results revealed the influence of the nature of the surface ligands on the efficiency of the hole localization process.[3] Finally, interfacing semiconductor nanocrystals with molecular reaction centers presents an attractive alternative to metal particles and equally high charge transfer rates as at semiconductor/metal interfaces can be reached in principle.[4] Nevertheless, anchoring strategies with sufficient stability and supporting efficient transfer of multiple charge carriers and reducing unwanted charge recombination, e.g. by anchoring units serving as electron relay, still need to be established. First results indicate that bioinspired redox-active polymer matrices could play an important role in the future design of photocatalytically active inorganic/organic hybrid materials.[5] References: [1] J. Phys. Chem. C 2016, 120, 24491-24497. [2] Nano Lett. 2018, 18, 357-364. [3] Catalysts 2020, 10, 1143. [4] J. Phys. Chem. Lett. 2021, 12, 4385-4391. [5] ACS Appl. Nano Mat., 2021, 4, 12913-12919. Acknowledgement: Financial support is acknowledged by the German Research Foundation (DFG) – TRR234 CataLight (project number 364549901, project B4, Z2), the Fonds der Chemischen Industrie (FCI), the COST Action CM1202 PERSPECT-H2O and the Chinese Scholarship Council Scholarship (CSC).

Resume : The electrocatalytic oxygen reduction (ORR) and evolution reactions (OER) are pivotal processes in a variety of sustainable energy conversion systems, including hydrogen fuel cells, electrolysers, photoelectrochemical water splitting and metal-air batteries. These electrocatalysis of these complex multi-electron transfer acid-base reactions have led to the exploration of a wide range of materials, in particular complex transition metal oxides (TMOs) [1-3]. TMOs exhibit a plethora of structural and electronic properties, which are acutely dependent on composition and crystal structure. Many studies have attempted to establish activity descriptors based on the electronic structure as probed by DFT and spectroscopic methods [2-4]. However, more recent studies have shown that orbital occupancy is acutely dependent on the electrode potential which have a significant impact in the activity and stability of strongly TMOs [6-8]. Consequently, the atomistic rationalization of the activity of transition metal oxides towards oxygen electrocatalysis has turned into one of the most complex challenges in the field of electrochemical energy conversion. In this contribution, we performed a detailed experimental and computational study of LaMnxNi1-xO3 perovskites nanostructures, establishing an unprecedented correlation between oxygen electrocatalytic activity and orbital composition. A key element of our strategy is tuning the orbital composition of the material while keeping the same crystal phase. Our synthesis approach led to the formation of single-phase rhombohedral nanocrystals in the range of 17 to 35 nm across the whole composition range (x) as probed by XRD, XAS, XPS and electron microscopy. Systematic electrochemical analysis of pseudocapacitive responses in the potential region relevant to the ORR and OER shows the evolution of Mn and Ni d-orbitals as a function of the perovskite composition. We rationalize these observations employing DFT with HSE06 functionals, establishing the electron occupancy of d¬-orbitals under operational conditions. The link between electrochemical responses and the nature of the orbitals are further confirmed by in-situ spectroscopic techniques [8]. Our analysis clearly shows a linear correlation between the OER kinetics and the integrated density of states (DOS) of Ni and Mn 3d states, while the ORR kinetics is characterised by a second-order dependence. For the first time, our study identifies the relevant DOS dominating both reactions and the importance of understanding orbital occupancy under operational conditions. 1. Stamenkovic, V. R.; et al. Nat. Mater. 2017, 16, 69 2. Song, J.; et al. Chem. Soc. Rev. 2020, 49, 2196 3. Li, H.; et al. Nat. Catal. 2021, 4 (6), 463 4. Hwang, J.; et al. Science 2017, 358, 751 5. Grumelli, D.; et al. Angew. Chem. Int. Ed. 2020, 59, 21904 6. Mefford, J. T.; et al. Nature 2021, 593, 67 7. Celorrio, V.; et al. ACS Appl. Energy Mater. 2021, 4, 176 8. Celorrio, V.; et al. ACS Catal. 2021, 11 (11), 6431

Resume : Strontium titanate (SrTiO3) is an ultraviolet active photocatalyst which can be engineered by doping to improve the photocatalytic activity. The effect of Al-monodoping and (Ir,Al)-codoping on the electronic and optical properties of oxygen deficient SrTiO3 are investigated in order to evaluate their performance towards the photocatalytic water splitting. We use the first-principles methods with Hubbard U corrections within the framework of density functional theory (DFT). To find the appropriate U values, we match the electronic structure of pristine, Al-doped and (Ir, Al)-codoped SrTiO3 with that obtained using hybrid functional. The main objective of this work is to extend the spectral response of SrTiO3 to the visible region of sunlight through codoping and to understand the factors that affect the photocatalytic efficiency of it. In general, the band gap decreases with the substitution of these dopants at cationic host sites, by introducing dopant associated states which can serve as charge recombination centers depending on their position in forbidden region and electron occupancy. We have also studied the effect of codoping (Ir and Al) in different ratios (1:2 and 1:1). For 1:2(Ir,Al)-codoped oxygen deficient SrTiO3, the absorption curve extends over a wide region of visible light solar spectrum. On reducing Ir4+ to Ir3+, the position of dopant induced states and optical signature changes, with absorption (in visible light spectrum) limited to the 350 - 550 nm wavelength region. To further investigate the impact of (Ir, Al) codoping on water splitting activity, we calculate the overpotential for oxygen evolution reaction (OER) to take place and it is found that there is reduction in overpotential with codoping. We hope that these results will pave the way for the design of (Ir, Al)-codoped SrTiO3 -based photocatalysts for the generation of solar hydrogen.

Resume : Many sulphide semiconductors are photocatalytically active in significant ranges of the visible spectrum. Our group has shown this, specifically, for In2S3, with a bandgap of 2.0-2.1 eV, and SnS2, with a bandgap of 2.2 eV (R. Lucena et al., Catal. Commun. 2012, 20, 1; ibid. Appl. Catal. A: General, 2012, 415-416, 111). In addition, by partially substituting these sulphides with vanadium (R. Lucena et al. J. Mater. Chem. A, 2014, 2, 8236; P. Wahnón et al. PCCP 2011, 13, 20401) we will show how this substitution widens the wavelength range of their activity. The main work will consist then in coupling these sulphides with enzymes of hydrogenase, laccase or formate dehydrogenase types in order to show how these enzymes allow photoevolving H2 or O2. First, we could show that combining In2S3 with a mutated hydrogenase obtained from Desulfovibrio vulgaris (having Fe and Ni as active species) it was possible to generate photocatalytically H2 in presence of a sacrificial agent (C. Tapia et al., ACS Catalysis 2016, 6, 5691). Then, we showed that combining In2S3 with a laccase obtained from Trametes hirsuta (including a Cu-oxide cluster as active species) it was possible to generate O2 photoelectrochemically (C. Tapia et al., ACS Catalysis 2017, 17, 4881), this being the first time that such enzyme-sulphide combination allowed photoevolution of O2. A similar photoelectrochemical generation of O2 could be shown subsequently by combining SnS2 with the same laccase enzyme (C. Jarne et al., ChemElectroChem 2019, 9, 2755). In addition, work in which In2S3 (a type n semiconductor, in suspension combined with a sacrificial agent), or ongoing work using different oxides of Cu and Fe (p-type semiconductors, combined with carbon fibers in electrochemical setups), are coupled with a formate dehydrogenase enzyme having W in the active centre, will show how CO2 can be reduced to formate ions.

Resume : Because of their low cost and abundance, catalysts incorporating 3d transition metals have recently gained popularity. Heavy and 3d transition metal alloys are being used in electrochemical reactions such as the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Another advantage of using such materials is that they introduce a new parameter that may be exploited to control the chemical reactions: the spin moments of 3d transition metals. From the theoretical point of view in heterogeneous catalysis the trend of the chemical reactivity is often explained in terms of the so called d-band model. We propose a generalized d-band center model where the chemical reactivity of the majority and minority spin-band electrons are separately evaluated [1]. We demonstrate that to understand the catalytic properties of spin-polarized materials one has to consider the d-band center model reformulated by us. We also studied the paramagnetic oxygen atoms adsorbed on PdFe surfaces and showed that the oxygen reduction reaction can be controlled using magnetic field, particularly the overpotential [2]. Finally, we discuss the problem of chemisorption of molecules on metal surfaces by using an approach that combines the Newns-Anderson-Grimely model with the Stoner model of metallic ferromagnetism. We studied for the ferromagnetic surfaces, how the strength of chemisorption is related to the magnitude of the surface moments and vice versa [3]. We also discussed how chemisorption affects Stoner’s criterion for the appearance of ferromagnetism and therefore allows the non-magnetic surface to become ferromagnetic [4].

Resume : In heterogeneous catalysis surfaces decorated with uniformly dispersed, catalytically highly active (nano)particles are a key requirement for excellent performance. We present here an innovative, time efficient route to obtain and tailor the formation of nanoparticles on the catalyst surface directly during reaction by combining catalysis and electrochemistry. Perovskite-type catalysts can incorporate catalytically highly active guest elements as dopants. When applying reductive conditions (gas atmosphere or applied electric potential) these dopants emerge from the oxide lattice to form catalytically active nanoparticles on the surface (by exsolution), causing a strong enhancement of catalytic reactivity. For the newly synthesized perovskite materials Nd0.6Ca0.4Fe0.9Co0.1O3-δ, we show by in-situ near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) combined with electrochemical impedance spectroscopy (EIS) how we can control the formation of catalytically active nanoparticles on the surface. With Scanning Electron Microscopy (SEM) the size of the formed particles could be determined. The crucial factor to trigger exsolution is the oxygen partial pressure (pO2), which can be adjusted and controlled either by the reaction environment or by the applied electrochemical potential. For reverse water gas shift reaction (rWGS) the formed nanoparticles are strongly enhancing the catalytic activity. Acknowledgement This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement n° 755744 / ERC - Starting Grant TUCAS)