Advanced catalytic materials for (photo)electrochemical energy conversion II

Resume : One of the most promising future sources of alternative energy involves water-splitting photoelectrochemical cells (PECs) – a technology that could potentially convert sunlight and water directly to a clean, environmentally friendly, and cheap hydrogen fuel. Practical PECmediated hydrogen production requires robust and highly efficient semiconductors, which should possess good light-harvesting properties, a suitable energy band position, stability in harsh conditions, and a low price. Despite significant progress in this field, new semiconductors that entail such stringent requirements are still sought after. Over the past few years, graphitic carbon nitride (CN) has attracted widespread attention due to its 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 a few reports regarded the utilization of CN in PECs due to the difficulty in acquiring a homogenous CN layer on a conductive substrate and to our lack of basic understanding of the intrinsic layer properties of CN. In this talk, I will introduce new approaches to grow CN layers with altered properties on conductive substrates for photoelectrochemical application1-4 . The growth mechanism and their chemical, photophysical, electronic, and charge transfer properties will be discussed.

Resume : Introduction The availability of technology for the direct and efficient conversion of solar energy into chemical fuel, will be one of the crucial elements for Europe to reach its ambitious climate goals by 2030 and 2050 and to fulfil the European Green Deal. Efficient light-to-fuel (solar fuels) technologies have the potential to significantly contribute to sector coupling by transferring renewable energy into chemical energy of synthetic energy carriers. This is especially valuable in areas of the energy system that do not have many options for using renewable electricity directly. These areas encompass heavy trucks, aviation and marine fuels, fuels for high-temperature industrial applications as well as the chemical feedstock as raw material basis for the chemical industry. The importance and the potential of using solar energy to create synthetic fuels is obvious when one considers the fact that using only 0.1% of the earth?s land space with solar collectors that operate with a collection efficiency of merely 20%, one could gather more than enough energy to supply the current yearly energy needs of all the citizens of the planet. Some other facts that speak out on behalf of solar energy for decarbonisation are: 1) the solar energy reserve is essentially unlimited and well distributed, 2) no particular individual or government owns it, 3) its utilisation is ecologically benign. The constantly increasing proportion of electricity supply that is accounted for by renewable energies, such as wind and solar energy, has led to the fact that on windy and/or sunny days, large amounts of power are already being produced this way. It is predicted that in a few years' time, in the middle of a windy summer day, Europe?s entire energy needs will be met by electricity generated from photovoltaics and wind. On such days however, the increasing expansion of renewable energies will produce more electricity than is needed at the time. The excess of electricity produced on such moments need to be stored in the form of batteries (electrical storage) or in the form of synthetic fuels (chemical storage). The development of batteries for variable renewable energy storage has made a lot of progress recently and is also supported and pushed by the European car industry. However, it mainly targets the short-term storage problem, like day/night storage. The long-term storage required to overcome the winter season, ?Dunkelflaute? (seasonal storage) is very difficult to address with batteries, as is the need to power heavy transport (trucks, ships and airplanes). Converting sunlight directly into chemicals has been investigated since decades. In 1972, Fujishima and Honda1 published the direct conversion from light to hydrogen using a wideband semiconductor (TiO2) in a photocatalytic process. Since then, many groups have worked on photocatalysis using more and more advanced devices and different embodiments of Photoelectrochemical cells (PEC)2. The efficiency of these approaches is increasing within the last years but they suffer from the principle problems of this approach: e.g. durability, due to the direct exposure of the photocatalyst material to the electrolyte, limited spectral range because of the limitation on the material choice and carrier recombination mechanisms within the PEC semiconductor material. Despite the effort and the recent improvements, the technology readiness level of the PEC technology is rather low (TRL 2-3) and the way to industrial application is not straightforward. On the other hand, PV and the electrolysis technologies are rather well developed and applied worldwide on ever larger scale. Building large-scale alkaline or PEM water splitting electrolysers in close proximity to the source of cheap green energy like solar or wind could bring the cost of green hydrogen below the 3 Euro/kg which is generally assumed to be the lowest cost of H2 production from Steam Methane Reforming (SMR). Nevertheless, the indirect nature of this approach leads to mainly resistive losses coming from cabling or other electrical connections and to significant investment costs for transmission and voltage conversion. In addition, the electrolyser approaches suffer from high CAPEX and sustainability issues due to the use of precious metals in Proton Exchange Membrane (PEM) electrolysers or relatively low current densities in Alkaline Electrolysis (AE). In imec, we will develop an integrated device consisting of a highly efficient solar module and a highly efficient electrolyser cell in order to provide a solution that combines the advantages of PV and electrolysis in one compact light-to-fuel device. Since several conversion steps are included, substantial investments are required and respective economies of scale lead to rather larger scale plants, from electricity generation, via electrolysis and electro-synthesis. All used technologies are introduced to the market and evolutionary developments can be expected, in particular cost scaling, as a consequence of classical technology learning. The key limitation of the state-of-the-art technologies is that the conversion from radiation to the final product takes place in several steps, which leads to not only efficiency drops, but also substantial investment requirements and respective industrial scaling in size of plants. In order to develop the necessary components of an integrated PV-EC system imec provides a technology toolbox including high efficiency Silicon-Perovskite Tandem modules and high efficiency electrochemical cells for water splitting with novel membrane electrode assembly concepts, a system simulation tool and advanced integration techniques using surface micromachining and micro fluidic. In the presentation we will give a status update on the technology toolbox highlighting the solar cell and the membrane electrode assembly development and show a first PV-EC system embodiment reaching 15% Solar to Hydrogen efficiency. Imec Technology Toolbox Electrochemical cell: Electrodes Porous metals with high surface area are broadly used as structural current collectors in multiple applications, such as catalysis2, ?ltration3, fuel cells4, batteries5, supercapacitors6, electrolyzers7, or sensors8. On the one hand, the high porosity of the porous metal is desired to accommodate greater volume of functional materials (e.g., energy-storing components in high-capacity batteries) or molecules (e.g., gas in fuel cell electrodes). On the other hand, the high surface area of the metal can enable higher reaction rates and lower internal resistance within the device, improving, for example, charging time of a battery9 or sensitivity of a sensor10. Importantly, high volumetric surface area (VSA) of the metal, also known as surface-to-volume ratio, allows to shrink the size of a porous current collector while keeping its total surface area high, facilitating device miniaturization and mechanical stability. To a big extent, such a trade-o? is a consequence of the random microstructure of these materials11. Electrode material is developed to provide high porosity and high volumetric surface area (VSA). For that reason, material like metal foams and metal coated carbon cloths are commonly used as electrodes. Nanostructured metals with large surface area have a great potential for multiple device applications. Although various metal architectures based on metal nano ligaments and nanowires are well known, they typically show a trade-off between mechanical robustness, high surface area, and high (macro)porosity, which, when combined, could significantly improve the performance of devices such as batteries, electrolysers, or sensors. In imec, we design templated networks of interconnected metal nanowires, combining high porosity of metal foams, narrowly distributed macropores, and a very high surface area of nano porous de-alloyed metals. Thanks to their structural uniformity, the few-micron thick nanowire meshes are also remarkably flexible and durable. In an exemplary application in electrolytic production of hydrogen, thanks to its high surface area, a few-micron thick nanomesh will outperform a thicker nickel foam. Furthermore, thanks to its high porosity, the Pt-doped nanomesh will surpass a microporous Pt/C cloth and will demonstrate benefits of the optimally designed nanowire structure for a simultaneous improvement and miniaturization of electrochemical devices. The development in this project will extend the potential of interconnected nanowires to multiple new research and industrial applications requiring highly porous and flexible conductive materials with a high surface-to-volume ratio. Si-Perovskite tandem cells The astonishingly fast increase of the power conversion efficiency (PCE) of perovskite solar cells in just a few years is the result of a unique combination of properties, including a high optical absorption coefficient12, long diffusion lengths13,14, low trap densities15. Beyond their ideal intrinsic optical and electrical proprieties, another key advantage of perovskite materials is that their bandgap can be tuned by varying their chemical composition. This is a unique benefit as compared to other PV materials. Indeed, this allows easy synthesis of a variety of perovskite absorbers whose energy bandgap can be optimally matched with the Silicon cell in multi-junction configurations to push the PCE over 30%, while still keeping the production costs at low to moderate level16,17. Perovskite-based tandem solar cells typically comprise a wide band gap (1.6-1.8 eV) perovskite top cell and a low band gap (1.0-1.1 eV) bottom cell. In the past 4-5 years, the mechanically stacked four-terminal (4T) perovskite/Si and perovskite/CIGS tandem solar cells have been intensively explored, due to the simplicity of independent fabrication and optimization of sub cells. However, this 4T design requires more transparent conductive oxide (TCO) electrodes and exterior electronics, making it impractical for large scale manufacturing and installation. On the other hand, the monolithic series interconnected (2T) tandem devices have attracted rapidly increasing interest as they involve a smaller number of substrates, layers, and interconnections. The best-in-class perovskite on silicon tandems have demonstrated PCEs of 28.2% and 29.12% in 4 terminals (4T) and 2 terminals (2T) respectively18. These results prove that the integration of perovskite and Si solar technology in a tandem configuration is a promising direction for high-efficiency PV development with still high potentials to be explored. Indeed, the theoretical limit for perovskite-Si tandem is well above 43%. Although these results are very promising for the development of innovative PV devices, all the very high PCEs have been demonstrated for devices typically not larger than 1 cm2 in the best cases. Additionally, for the 2T top result, a front-side polished Si bottom cell was used, while for industrial Si cells micron-sized textured surfaces are conventionally used. The current challenge for the 2T configuration is consequently how to grow device-quality perovskite material on the bottom cell with such surface roughness. The 2T configuration also enables generation of a high output voltage, which is specifically relevant for the application targeted in this project. It was shown that losses at the interfaces of the perovskite with adjacent layers like charge transporting materials are limiting the Voc of the final devices19. Therefore, to achieve the highest output voltages, it is important to passivate the perovskite film. Multiple routes have been suggested, like adding trace amounts of alkylamine ligands to the perovskite precursor solution, which have led to the improved orientation of the film, as well as efficient passivation of the surface20. PV-EC system integration The full monolithic integration of a PV cell and an electrochemical cell is identified as a solution to provide low cost device fabrication and reduce ohmic losses due to a short ionic pathway between the electrodes21. The short ionic pathway is realized by perforating the solar cell with holes filled with a proton exchange material. In literature silicon based multi-junction cells are proposed22,23, the holes are performed by reactive ion etching techniques, non-abundant materials (like Ir and Pt) are used as electrocatalysts, and Nafion (per(fluorosulfonic acid) poly(tetrafluoroethylene) copolymer) is used as membrane separator material. We are proposing an approach which concentrates on scalable processes and abundant materials. In this approach we will develop highly efficient silicon based perovskite multi-junction cells, the electrocatalyst material is based on a nanomesh made of abundant metals like Ni, or Cu, the membrane separator material will be a nano-composite electrolyte developed in imec24. In order to reach a monolithic integrated system, different intermediate embodiments are developed. We will present an embodiment with series connected shingled silicon solar cells and an electrochemical cell using a Ni nanomesh and an alkaline electrolyte. With this combination we could achieve StH efficiencies up to 15%. Outlook In a forthcoming embodiment Si-Perovskite tandem cells will substitute the silicon cells, dedicated catalysts are applied to the nanomesh electrode and a further reduction of the membrane thickness is implemented. References [1] Fujishima, A., Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode.?Nature?238,?37?38 (1972). https://doi.org/10.1038/238037a0 [2] Do?rfelt, C.; Kolvenbach, R.; Wirth, A. S.; Albert, M.; Ko?hler, K. Catalytic Properties of a Novel Raney-Nickel Foam in the Hydrogenation of Benzene. Catal. Lett. 2016, 146, 2425?2429. [3] Khosravanipour Mostafazadeh, A.; Zolfaghari, M.; Drogui, P. Electrofiltration Technique for Water and Wastewater Treatment and Bio-Products Management: A Review. J. Water Process Eng. 2016, 14, [4] Yuan, W.; Tang, Y.; Yang, X.; Wan, Z. Porous Metal Materials for Polymer Electrolyte Membrane Fuel Cells - A Review. Appl. Energy 2012, 94, 309?329. [5] Yang, G. F.; Song, K. Y.; Joo, S. K. A Metal Foam as a Current Collector for High Power and High Capacity Lithium Iron Phosphate Batteries. J. Mater. Chem. A 2014, 2, 19648?19652. [6] Xu, M.; Xu, R.; Zhao, Y.; Chen, L.; Huang, B.; Wei, W. Hierarchically Porous Ni Monolith@branch-Structured NiCo2O4 for High Energy Density Supercapacitors. Prog. Nat. Sci. Mater. Int. 2016, 26, 276?282. [7] Zhu, W.; Zhang, R.; Qu, F.; Asiri, A. M.; Sun, X. Design and Application of Foams for Electrocatalysis. ChemCatChem 2017, 9, 1721-1743 [8] Li, X.; Lu, X.; Kan, X. 3D Electrochemical Sensor Based on Poly(Hydroquinone)/Gold Nanoparticles/Nickel Foam for Dopa-mine Sensitive Detection. J. Electroanal. Chem. 2017, 799, 451?458. [9] Pikul, J. H.; Gang Zhang, H.; Cho, J.; Braun, P. V.; King, W. P. High-Power Lithium Ion Microbatteries from Interdigitated Three-Dimensional Bicontinuous Nanoporous Electrodes. Nat. Commun. 2013, 4, 1732. [10] Kumar, R.; Bhuvana, T.; Rai, P.; Sharma, A. Highly Sensitive Non-Enzymatic Glucose Detection Using 3-D Ni3(VO4)2 Nanosheet Arrays Directly Grown on Ni Foam. J. Electrochem. Soc. 2018, 165, [11] Juarez, T.; Biener, J.; Weissmu?ller, J.; Hodge, A. M. Nanoporous Metals with Structural Hierarchy: A Review. Adv. Eng. Mater. 2017, 19,1?23. [12] De Wolf, S., et al., Organometallic Halide Perovskites: Sharp Optical Absorption Edge and Its Relation to Photovoltaic Performance. J. Phys. Chem. Lett., 2014. 5: p. 1035. [13] Stranks, S.D., et al., Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber. Science, 2013. 342(6156): p. 341-344. [14] Xing, G., et al., Long-Range Balanced Electron- and Hole-Transport Lengths in Organic-Inorganic CH3NH3PbI3. Science, 2013. 342(6156): p. 344-347. [15] Shi, D., et al., Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals. Science, 2015. 347(6221): p. 519-522. [16] Tuning the Light Emission Properties by Band Gap Engineering in Hybrid Lead Halide Perovskite. Journal of the American Chemical Society, 2014. 136(51): p. 17730-17733. [17] Zhou, H., et al., Interface Engineering of Highly Efficient Perovskite Solar Cells. Science, 2014. 345: p. 542. [18] Kim, J., et al., Overcoming the Challenges of Large-Area High-Efficiency Perovskite Solar Cells. ACS Energy Letters, 2017. 2(9): p. 1978-1984. [19] C.M. Wolff et al., Adv. Mater. 31, (2019) 1902762. DOI: 10.1002/adma.201902762 [20] X. Zheng et al., Nat. Energy 5, (2020) 131. DOI: 10.1038/s41560-019-0538-4? [21] J. Newman, J. Electrochem. Soc. 2013, 160, F309 5 [22] W. Vijselaar, Adv. Energy Mater. 2019, 1803548 6 [23] C. Trompoukis, SOLMAT 182 (2018) 196-203 [24] S. Zankowski, ACS Appl. Mater. Interfaces 2018, 10, 44634-44644

Resume : Light absorption and charge transport in oxide semiconductors can be tuned by the introduction, during deposition, of a small quantity of foreign elements, leading to the improvement of the photoelectrocatalytic performance(1). In this work, both unmodified and vanadium-modified TiO2 thin films deposited by radio-frequency magnetron sputtering are investigated as photoanodes for photoelectrochemical water splitting. In particular, photoelectrocatalysis is discussed based on ultrafast transient absorbance spectroscopy measurements, performed at three different pump wavelengths from UV to the visible range are used (300, 390, and 530 nm) in order to cover the relevant photoactive spectral range of modified TiO2. Incident photon-to-current conversion efficiency spectra show that incorporation of vanadium in TiO2 extends water splitting in the visible range up to ?530 nm, a significant improvement compared to unmodified TiO2 that is active only in the UV range ?390 nm. However, transient absorbance spectroscopy clearly reveals that vanadium accelerates electron-hole recombination upon UV irradiation, resulting in a lower photon-to-current conversion efficiency in the UV spectral range with respect to unmodified TiO2. The new photoelectrocatalytic activity in the visible range is attributed to a V-induced introduction of intragap levels at ?2.2 eV below the bottom of the conduction band. This is confirmed by long-living transient signals due to electrons photoexcited into the conduction band after visible light (530 nm) pulses. The remaining holes migrate to the semiconductor-electrolyte interface where they are captured by long-lived traps and eventually promote water oxidation under visible light(2). (1) Rossi, G. et al. Charge carrier dynamics and visible light photocatalysis in vanadium-doped TiO2 nanoparticles. Appl. Catal. B Environ. 237, 603?612 (2018). (2) Piccioni, A. et al. Ultrafast Charge Carrier Dynamics in Vanadium-Modified TiO2 Thin Films and Its Relation to Their Photoelectrocatalytic Efficiency for Water Splitting. J. Phys. Chem. C (2020).

Resume : We report on the properties of metal-insulator-semiconductor (MIS) photoanodes for water splitting comprising thin RuO2 and IrO2-RuO2 films as top catalytic layers. RuO2 and IrO2 offer low resistivity, high optical transparency, work function as well as high catalytic efficiency. RuO2 and IrO2-RuO2 films with a thickness of 5 nm were grown using liquid injection metal-organic chemical vapour deposition, MOCVD. A thin SiO2 layer was prepared by ozone treatment of the n-Si substrate at 300 °C. The films have a low room temperature resistivity of 10?4 ?cm and transmittance up to 80% in the visible light region. The photocurrent and photovoltage of these MIS photoanodes were studied in 1 M aq. H2SO4 (pH=0), 0.5 M aq. Na2SO4 (pH=6), and 1 M aq. KOH (pH=14) electrolytes. The photoelectrochemical oxygen evolution reaction of the RuO2 and IrO2-RuO2 photoanodes follows a V-shape relationship with the pH. RuO2/SiO2/n-Si photoanode exhibited a photovoltage of 0.49 V and was able to generate a photocurrent of ~10 mA/cm2 at a thermodynamic water oxidation potential (1.23 V vs. normal hydrogen electrode, NHE) in 1 M aq. H2SO4 solution under 1 Sun intensity with AM 1.5 spectrum. A photovoltage of 0.42 V and a photocurrent of ~5 mA/cm2 were achieved for the IrO2-RuO2/SiO2/n-Si photoanode in acidic conditions. The stability of the photoanodes was examined in 1 M aq. H2SO4 and 1 M aq. KOH solutions. Chronoamperometry measurements on the RuO2/SiO2/n-Si photoanode in acidic solution under an applied voltage of 1.23 V vs. NHE showed the deterioration of the photoanode after 2 h of operation. Faster degradation was observed upon applying a higher voltage of 1.5 V vs. NHE. Similarly, stability measurements were performed on IrO2-RuO2/SiO2/n-Si photoanodes in 1 M aq. H2SO4 solution. In acidic conditions, at an applied bias of 1.23 V vs NHE, a photocurrent of ~2 mA/cm2 was observed which was stable for 24 h for the IrO2-RuO2 based photoanodes. X-ray photoelectron spectroscopy (XPS) measurements were carried out to understand the stability of the photoanodes in different electrolytes. The loss of RuO2 during the stability measurements in the acidic electrolyte was confirmed from the XPS studies. This study was performed during the implementation of the project Building-up Centre for advanced materials application of the Slovak Academy of Sciences, ITMS project code 313021T081 supported by Research & Innovation Operational Programme funded by the ERDF. The research was funded also by APVV (project APVV-17-0169).

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). Here we will show how coupling these sulphides with enzymes of hydrogenase, laccase or formate-dehydrogenase types allows photoevolving H2 or O2 or reducing CO2. 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). Some of us carried out recently work which coupled an electrode with a formate dehydrogenase enzyme (including W as active species; also obtained from Desulfovibrio vulgaris) so that it was possible to reduce electrocatalytically CO2 to formate (J. Álvarez-Malmagro et al., ACS Appl. Mater. Interfaces 2021, 13, 11891). Ongoing work will be shown here in which combining this latter enzyme with In2S3 nanoparticles allows to perform the same task photocatalytically.

Resume : Significant depletion of fossil fuels has led to the urge of finding new renewable sources of energy, able to fulfill the current energy demands. Solar-based hydrogen produced from water is an appealing alternative fuel, which can be generated without extra CO2 emissions. Transition metal nanoparticles, such as nickel, are the benchmark catalysts for hydrogen evolution reaction, as they are highly active, stable and earth-abundant. One of the emerging fields of solar energy harvesting is enhancing the catalytic reaction through the local surface plasmon resonance (LSPR) effect of the catalyst. Most studied mechanisms of the energy transfer from plasmonic nanoparticles are based on hot electron injection and plasmon-induced resonant energy transfer. However, the photothermal effect of the plasmon in transition metal nanoparticles is still underestimated in the literature. In this work, we have synthetized Ni nanoparticles with an elongated average shape by wetness impregnation of the hard silica template. The high distribution of sizes results in a broad plasmonic absorption in the visible range, which leads to a significant photothermal effect under solar illumination. The local increase of the temperature under HER cathodic conditions leads to the increase of the hydrogen production up to 23%. We are also able to reduce the overpotential for 185mV under galvanostatic conditions. By applying pulsed illumination, we have observed two processes: fast (0.5-1 s) and slow (up to 40s). The fast one, presumably, is responsible for the local increase of the reaction rate on the surface of the Ni nanoparticles due to a fast local temperature increase as a consequence of a damped plasmon caused by solar illumination. The second process is attributed to an enhanced mass transport in the electrolyte due to the temperature redistribution and overall heating of the electrolyte. Based on the obtained results, we have shown that the illumination of the nanostructured nickel catalyst with solar light can lead to the enhanced HER rate, and, as a result, to improved hydrogen production. We expect the LSPR photothermal approach to pave way to a more efficient photoelectrochemical water splitting process, taking advantage of visible and near-IR illumination.

Resume : Energy barrier-free charge transfer of photogenerated carriers and high photoconversion efficiency are achieved by using a core-shell heterostructure of TiO2-ZnS:Co/Bi2S3 for photoelectrochemical (PEC) water splitting. The TiO2 nanorods are covered with Co doped ZnS coating, followed by the encapsulation with the Bi2S3 shell. Co doped ZnS and Bi2S3 coating shells enhance UV-vis light harvesting and increase the density of photogenerated carriers of TiO2 nanorods. The impurity energy state of Co in ZnS connects the conduction band edges of Bi2S3 and TiO2 to convey photogenerated electrons, without extra energy consumption for hopping to Zn orbits at higher energy position. The continuous valance band edge of three components ensures a swift transfer for photogenerated holes to photoanode surface, where the recombination of photogenerated carriers is suppressed. This work offers a new way for the enhancement of the photoelectrochemical water splitting via engineering of the photogenerated charge transportation using core-shell heterostructured photoanode like TiO2-ZnS:Co/Bi2S3.

Resume : The electrical conversion and storage of solar energy is crucial for assuring the world energy supply. Photoelectrochemical (PEC) energy storage devices offers the possibility to directly transfer the solar energy into several energy carriers, such as hydrogen, low-C fuels/chemicals from CO2 reduction or other redox pairs like batteries. However, PEC technology has as main drawback the fact that the photoelectrode can be in direct contact with the electrolyte, limiting the choice of materials [1]. In this contribution, it will presented our developments on the fabrication of stable photoelectrodes and integrated devices. It will be discussed how impedance analysis (EIS) is a fundamental tool to understand the charge transfer and identify the main bottlenecks that could limit photoelectrode efficiency, specially for the oxygen evolution reaction (OER) [2,3]. Concerning the integrated devices, depending on the system, its design is not seamless unless the light-absorber photovoltage is customized to the voltage needs of the redox pairs [4]. In the case of CO2 reduction, partial current polarization curves should be taken into account, since reaction selectivity usually depends on the applied potential under controlled photocurrent, which will depend on the solar irradiance. On the other hand, for PEC redox flow batteries, unlike artificial photosynthesis synthesis, the required photovoltage continuously increase with the state-of-charge. By using amorphous silicon tandem multijunction photocathodes, it has been demonstrated that for either CO2 reduction to syngas [5] or solar vanadium redox flow batteries [6], an unbiased solar-to-chemical conversion efficiency 10% is achievable. Each technology will have in the future its niche market, while the solar-to-electricity roundtrip is more favorable for redox flow devices than for hydrogen or solar fuels, there is an urgent need to decarbonize our chemical industry with green hydrogen and upcycled CO2. The work was funded by MINECO projects WINCOST (ENE2016-80788-C5-5-R) and CCU+OX (PID2019-108136RB-C33). [1] 2020. Journal of Materials Chemistry A 8 (21), 10625-10669 [2] 2019. ACS applied materials & interfaces 11 (33), 29725-29735 [3] 2019. Journal of Materials Chemistry A 7 (38), 21892-21902 [4] 2020. Sustainable Energy & Fuels 4 (3), 1135-1142 [5] 2017. Energy & Environmental Science 10 (10), 2256-2266 [6] 2018. Journal of Physics D: Applied Physics 52 (4), 044001

Resume : The decarbonization of the current energy system has been recognized as a key milestone due to the increase of the average temperature on Earth[1]. In this context, (photo)electrochemical processes are considered as low-cost procedures to produce green fuels. Until now, efforts have mainly been focused on two reactions, the formation of molecular hydrogen from water and the reduction of carbon dioxide to form more complex species [2-3]. Considering the high potentials, both reducing and oxidizing, that can be obtained from photoelectrochemical processes, these synthetic approaches are suitable candidates for designing synthetic routes that allow the preparation of high-added value products, which requires redox transformations of the starting reagents [4-10]. In the majority of the cases described, the desired product is generated in one of the (photo)electrodes, whereas in the other one the oxidation (or reduction) of a sacrificial agent takes place. A smart optimization of these systems would be a procedure which allow obtaining high-added value products at both electrodes. [1] Caldeira, K. et al. Science, 360, 1419 (2018) [2] Durrant, J. R. et al. Nature Photonics 6, 511 (2012) [3] Grätzel, M. Nature, 414, 338 (2014) [4] Cha, H. G. & Choi, K.-S. Nature Chemistry. 7,328, 2015 [5] Li, T. et al. Nature Communications 8, 390, 2017 [6] Tateno, H., et al. ChemElectroChem 4, 3283, 2017 [7] Tateno, H. et al. Chemical Communications 53, 4378, 2017 [8] Tateno, H. et al. Angewandte Chemie International Edition 57, 11238, 2018 [9] Liu, D. et al. Nature Communications 2019, 10, 1779. [10] Xile H. et al. Nature Catalysis 2, 366, 2019

Resume : The development of materials which can drive photocatalytic water splitting at high efficiency remains the central challenge for the production of renewable hydrogen using sunlight. Owing to advantages such as low cost, elemental abundance, and chemical stability, transition metal oxides (TMOs) are some of the most widely used materials for this purpose. The most efficient systems developed to date reach a solar-to-hydrogen conversion efficiencies (STH) of around 1%[1,2] and are based on wide bandgap TMOs such as SrTiO3 which has a bandgap of 3.2 eV and thus absorbs UV light only. However, the target for commercial applications is widely considered to be 10% STH, and extended visible light absorption is therefore key to bridge this activity gap.[3] While large research efforts have been devoted to TMOs with smaller bandgaps, efficiencies for such materials have typically remained relatively far from their theoretical limit. For example, Fe2O3 is one of the most studied TMOs in the field of solar fuel production, but it has so far reached only 1/3 of its theoretical maximum activity for water oxidation,[4] which raises the question whether there are limitations of more fundamental nature. In this talk, I will compare the photophysics of TMOs with extended visible light absorption to identify common patterns for this class of materials. To this end, Fe2O3, Cr2O3, and Co3O4, which have absorption onsets of around 2.1 eV, 1.9 eV, and 1.6 eV, respectively, are studied using time-resolved optical spectroscopic techniques where their excited state dynamics are probed on a timescale of femtoseconds to seconds following light absorption. I will show that the photophysics of these materials are remarkably similar when key material characteristics are taken into account, suggesting a common pathway for the localisation and recombination of photogenerated charges in this class of materials. Based on these results a more general photophysical model for TMOs with extended visible light absorption can be postulated, which provides insights into the performance limiting factors in TMOs with extended visible light absorption. References: [1] Wang, Q. et al. Scalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1%. Nat. Mater. 1?3 (2016). [2] Takata, T. et al. Photocatalytic water splitting with a quantum efficiency of almost unity. Nature 581, 411?414 (2020). [3] Chen, S., Takata, T. & Domen, K. Particulate photocatalysts for overall water splitting. Nat. Rev. Mater. 2, 17050 (2017). [4] Kim, J. Y. et al. Single-crystalline, wormlike hematite photoanodes for efficient solar water splitting. Sci. Rep. 3, 2681 (2013).

Resume : Water splitting has been proposed to be a promising approach to producing clean hydrogen fuel. The two half reactions of water splitting, i.e. the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), take place kinetically fast in solutions with completely different pH values. Enabling HER and OER to simultaneously occur under kinetically favorable conditions while using exclusively low-cost, earth-abundant electrocatalysts, is highly desirable but remains a challenge. In this presentation, we will show that with a bipolar membrane (BPM) we can accomplish HER in a strongly acidic solution and OER in a strongly basic solution, using bifunctional self-supported cobalt nickel phosphide nanowire (Co-Ni-P NW) electrodes to catalyze both reactions (Figure 1) [1]. Such asymmetric water electrolysis can be achieved at 1.567 V to deliver a current density of 10 mA cm-2 with ca. 100% Faradaic efficiency under the ?reverse bias? configuration. Moreover, in the ?forward bias? configuration, the voltage needed to afford 10 mA cm-2 can be reduced to only 0.841 V, due to the assistance of electrochemical neutralization between acid and alkaline. Furthermore, we demonstrate that BPM-based asymmetric water electrolysis can be accomplished in a circulated single cell electrolyzer delivering 10 mA cm-2 at 1.550 V and splitting water very stably for at least 25 h (Figure 2), and that water electrolysis is enabled by a solar panel operating at 0.908 V (@13 mA cm-2), under the ?forward bias? of the BPM. The same BPM approach is also extended to the CoTe2-CoP dual phase electrocatalysts [2], which demonstrate similar electrochemical performance with markedly reduced input voltage for overall water electrolysis in the ?forward bias? configuration. The BPM-based asymmetric water electrolysis is a promising alternative to conventional proton and anion exchange membrane water electrolysis. References: 1. J. Y. Xu, I. Amorim, Y. Li, J. J. Li, Z. P. Yu, B.S. Zhang, A. Araujo, N. Zhang, L. Liu, Carbon Energy 2 (2020) 646. 2. I. Amorim, J. Y. Xu, N. Zhang, Z. P. Yu, A. Araujo, F. Bento, L. Liu, Chem. Eng. J. 420 (2021) 130454.

Resume : Achieving efficient and stable oxygen evolution reaction (OER) in acidic or neutral medium is of paramount importance for hydrogen production via proton exchange membrane water electrolysis (PEM-WE). Supported iridium based nanoparticles (NPs) are the state-of-the-art OER catalysts for PEM-WE, but the non-homogeneous dispersion of these NPs on the support together with their non-uniform sizes usually lead to catalyst migration and agglomeration under strongly corrosive and oxidative OER conditions, eventually causing the loss of active surface area and/or catalytic species and thereby the degradation of OER performance. Here, we design a catalyst comprising surface atomic-step enriched ruthenium-iridium (RuIr) nanocrystals homogeneously dispersed on a metal organic framework (MOF) derived carbon support (RuIr@CoNC) [1], which shows outstanding catalytic performance for OER with high mass activities of 2041, 970 and 205 A gRuIr-1 at an overpotential of 300 mV and can sustain continuous OER electrolysis up to 40, 45 and 90 hours at 10 mA cm-2 with minimal degradation, in 0.5 M H2SO4 (pH = 0.3), 0.05 M H2SO4 (pH = 1) and PBS (pH = 7.2) electrolytes, respectively. Comprehensive experimental studies and density functional theory (DFT) calculations reveal that the good performance of RuIr@CoNC can be attributed, on one hand, to the presence of abundant atomic steps which maximize the exposure of catalytically active sites and lower the limiting potential of the rate-determining step of OER; on the other hand, to the strong interaction between RuIr nanocrystals and the CoNC support which endows homogeneous dispersion and firm immobilization RuIr catalysts on CoNC. The RuIr@CoNC catalysts also show outstanding performance in a single cell PEM electrolyzer, and their large-quantity synthesis is demonstrated. References: [1] 11. J.Y. Xu, J. J. Li, Z. Lian, A. Araujo, Y. Li, B. Wei, Z. P. Yu, O. Bondarchuk, I. Amorim, V. Tileli, B. Li, Lifeng Liu*, ?Atomic-step enriched ruthenium-iridium nanocrystals anchored homogeneously on MOF-derived support for efficient and stable oxygen evolution in acidic and neutral media? ACS Catalysis 2021, 11, 3402-3413.

Resume : The small organic molecule electro-oxidation (OMEO) and the hydrogen evolution (HER) are two important half-reactions in direct alcohol fuel cells (DAFCs) and water electrolyzers, respectively, whose kinetics are largely hindered by the low activity and poor stability of electrocatalysts. Noble metals (e.g. Pt, Pd) are currently the state-of-the-art catalysts for the HER and OMEO; however, for practical applications their electrocatalytic performance needs to be improved. In this presentation, we report a simple phosphorization treatment of commercially available palladium-nickel (PdNi) catalysts that can result in the formation of multifunctional ternary palladium nickel phosphide (PdNiP) catalysts, exhibiting substantially enhanced electrocatalytic activity and stability for HER and a number of OMEO model reactions including the formic acid oxidation reaction (FAOR), methanol oxidation reaction (MOR), ethanol oxidation reaction (EOR), and ethylene glycol oxidation reaction (EGOR), in terms of not only apparent activity, but also of specific and mass activities, poisoning tolerance and catalytic stability. The improved performance results from the modification of electronic structure of palladium and nickel by the introduced phosphor and the enhanced corrosion resistance of PdNiP. The simple phosphorization approach reported here allows for mass production of highly-active OMEO and HER electrocatalysts, holding substantial promise for their large-scale application in direct alcohol fuel cells and water electrolyzers.

Resume : We study the effects of simulated outdoor illumination conditions on the performance of photovoltaic-biased electrosynthetic (PV?EC) systems used for the generation of hydrogen by means of solar water splitting. An integrated PV-EC cell consists of a photovoltaic cell (PV) directly combined with an electrolysis cell (EC), where the chemical reactions take place. In the present work, multijunction silicon based solar cells [1] were implemented for the PV part of the device together with an EC cell using a Pt/IrOx catalyst system. Annual variations in the solar illumination spectra influence the device performance together with long-term energy conversion. Both PV device and PV-EC device performance under varied spectral conditions differ from the performance obtained under standard AM1.5G illumination. Our model accounts for annual spectral changes in illumination and predicts the long-term (1 year) performance of PV?EC systems in terms of the hydrogen amount produced for a given geographical location for various types of multijunction photovoltaic systems (tandem, triple, and quadruple junctions). [1] F. Urbain, V. Smirnov, J.P. Becker et al, Energy Env. Sci. 2016, 9, 145?154 [2] K. Welter et al, Energy Fuels 2021, 35, 1, 839?846

Resume : Platinum in the form of nanocubes (NCs) were synthesized by colloidal method, and with a fast and simple drop-casting method Pt NCs were applied as hydrogen evolution reaction electrocatalysts to electrochemical (EC) and photoelectrochemical (PEC) systems. Our drop-casting method showed minimized loss of Pt (~6%) from Pt NC synthesis to EC cell fabrication, and we also achieved a remarkable Pt mass activity of 1.77 A/mg at -100 mV in EC systems (fluorine-doped tin oxide (FTO)/Pt NC cathode) with neutral electrolyte. In PEC systems (based on a Cu(In,Ga)Se2 (CIGS) photocathode), a maximum onset potential of 0.678 V against the reference hydrogen electrode was reached by carefully choosing amount of Pt NC loading to compromise between better light transmittance and the catalytic activity. The photoelectrodes also exhibited good long-term operational stability over 9.5 hours with negligible degradation of the photocurrent, and 11 hours stability with maintaining 80% current density against maximum. Our study presents an effective strategy to greatly reduce the use of expensive Pt without compromising the catalytic performance. It also presents an extra benefit of further reducing the usage of Pt because the drop-casting of Pt NC solutions is expected to waste less raw materials than vacuum deposition.

Resume : Our modern society demands new synthetic strategies environmentally benign and energy efficient. Besides, these synthetic procedures should also provide high reaction yields, high selectivity, as well as ensure low or even no greenhouse gas emissions. Organic electrosynthesis fulfills the previous requirements, furthermore allows achieving the replacement of dangerous and toxics chemical and the reduction of the quantity of solvents used. One of the key points in electrosynthesis is the design and preparation of stable and robust electrodes. In our group we have successfully tested Ti/Ni alloys for the oxygen evolution reaction (OER), observing low overpotentials and high-density currents. Moreover, our Ti/Ni electrodes exceeded the performance of commercially available electrodes for this reaction. (1) These Ti/Ni electrodes are easily prepared in a facile and scalable method based on powder metallurgy, showing high electrochemical surface area and high concentration of active species. Herein, we use of these Ti/Ni electrodes for the oxidation of organic substrates of a range of molecules to obtain high added value species. References (1) Guenani, N.; Barawi, M.; Villar-García, I. J.; Bisquert, J.; de la Peña O’Shea, V. A.; Guerrero, A. Sustainable Energy Fuels, 2020, 4, 4003-4007.

Resume : A thorough knowledge of the atomic structure and composition of catalyst nanoparticles is paramount to the development of advanced materials for proton exchange membrane fuel cells (PEMFC), one of the most promising energy conversion devices for automotive and stationary applications. Pt and Pt-based alloys nanoparticles (NPs) are currently used as the catalyst to promote the kinetics of the hydrogen oxidation and oxygen reduction reactions in the anode and cathode of the fuel cell, respectively. Yet, the durability of the catalysts remains the main issue for their commercialization. In this talk, the focus is to understand the behavior of Pt and Pt-alloy NPs during the various stages of fuel cell cycling. For this purpose a set-up was developed to simulate the effect of voltage cycling on the cathode side of the fuel cell. In this set up, catalyst NPs supported on carbon nanotubes and amorphous carbon were observed by advanced transmission electron microscopy, before and after cycling. The experiments show particle migration in conjunction with carbon corrosion during the initial cycles, whereas the appearance of single atoms and atomic clusters on the surface of the carbon support appear after additional voltage cycling as a result of surface dissolution of NPs. For the case of alloyed NPs, the experiments show a heterogeneous deposition of Pt on the NPs.

Resume : Herein, we reported the potential driven electrochemical transformation of two nickel salen polymers, poly(meso-NiSaldMe), and poly(NiSaltMe) into Ni(OH)2 type electrocatalytically active nanoparticles in basic solution. These two polymers, differ in the configuration of methyl substitution at imine bridge. The use of different electrochemical conditions for the preparation of two polymeric NPs precursors allowed us to establish the correlation between both morphology and chemical structure of polymeric precursors that governed the morphology and electrocatalytic efficiency of fabricated NPs. The morphology and electrocatalytic performance of prepared NPs were tuned by applying different electropolymerization conditions to prepare poly(meso-NiSaldMe) and poly(NiSaltMe). Interestingly, generated Ni(OH)2 type nanostructures from these two different poly (Ni-salen) precursors were electrocatalytically active towards ethanol oxidation at different extent. Moreover, we found that organic solvent electrolyte solutions stable poly(NiSalen)s film took a longer time to generate NPs in base electrolyte media. Poly(Ni-Salen)s and Ni(OH)2 type NPs were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

Resume : Several applications require to maximize an electrode electroactive surface (ECSA) relative to its volume. A popular option is to develop nanoscaled materials like nanoparticles (NPs). Fortunately, a range of synthesis methods allows to control composition, size and shape of nanomaterials, to best tune activity, selectivity and stability. Unfortunately, popular syntheses like colloidal approaches often require surfactants to avoid NPs agglomeration. The later typically need to be removed - e.g. by chemical or thermal steps, often with limited efficiency - in order to develop materials with clean (i.e. electroactive) surfaces. We developed surfactant-free colloidal syntheses to obtain readily active (electro)catalysts [1-4]. This talk will present the latest development in this regard, starting with Pt NPs for the oxygen reduction reaction (ORR) where we were able to show the importance of size and interparticle distance to optimize mass activity [5]. Furthermore, we recently developed a low boiling point synthesis of surfactant-free colloidal precious metals [6]. The latter is versatile and can lead to suitable materials such as Pt NPs for the methanol oxidation (MOR) reaction [6] or Pd NPs for the ethanol oxidation reaction (EOR) [7]. We here show the relevance of this synthesis approach to better study and benchmark electrocataysts. This presentation will detail the case of the optimal parameters to develop and study Ir based catalysts with high mass activity compared to state-of-the-art even at high loading for the oxygen evolution reaction (OER) [8, 9]. We studied the interplay between the solvents used for the synthesis of Ir NPs and the solvents used for supporting on carbon materials. We compared NPs prepared without surfactant in alkaline ethylene glycol, alkaline ethanol or alkaline methanol for the OER. The catalysts with the highest activity were obtained using ethanol as solvent. Interestingly, the high activity observed was related more to the influence of the solvent during the supporting steps than during the synthesis of the NPs. These examples illustrate the benefits of surfactant-free colloidal syntheses to not only develop various electrocatalysts, but also study and understand the influence of various steps in the preparation of supported electrocatalysts [1]. Overall, a better understanding of important parameters to develop precious metal based catalysts is gained to make the most of the limited resources that are Pt, Pd or Ir. References [1] Quinson et al. ChemCatChem. 2021, 13, 1692. [2] Alinejad, ACS Catal. 2020, 10, 21, 13040. [3] Du et al. ACS Catal. 2021, 11, 2, 820. [4] Arminio-Ravelo et al. ChemCatChem. 2020, 12, 5, 1282. [5] Inaba et al. ACS Catal. In press. [6] Quinson et al. Sustain. Chem. 2021, 2, 1, 1-7. [7] Schreyer et al. Inorganics 2020, 8, 11, 59. [8] Bizzotto et al. Catal. Sci. Technol., 2019, 9, 6345. [9] Bizzotto et al. Submitted.

Resume : Transition metal oxides such as NiOx and MnOx are considered promising candidates to replace noble metals as electrocatalysts for the oxygen evolution reaction (OER). Improvements in these initially inactive materials require mechanistic and kinetic knowledge of the four-electron transfer steps of OER. X-ray photoelectron spectroscopy, a widely used tool to characterize the electronic structure of thin films, is used in combination with surface-enhanced Raman spectroscopy. This leads to a deeper understanding of the changing structural properties and chemical compositions which determine the catalytic activity. Using operando Raman spectroscopy, it was demonstrated that various MnOx films in alkaline medium exhibit birnessite-type MnO2 motifs at an applied potential. Their activity correlates with two shifting vibrational modes, one associated with the formation of MnIII species and one associated with the expansion of layers containing MnO6 octahedra. A special activation treatment results in a highly amorphous mixed valence oxide that exhibits the highest OER activity regardless of the starting material. While several studies have shown that iron impurities promote the activity of nickel-based catalysts, the effects of intrinsic defects are not well-understood. NiOx thin films were prepared at different temperatures and therefore varied in chemical composition and crystalline order. Raman spectroscopy was used to follow the characteristic oxidation of nickel species from NiII(OH)2 to NiIIIOOH and NiIVOO? under electrochemical cycling conditions. A stronger oxide-to-hydroxide conversion, consistent with the post-electrochemical study, was associated with the presence of initial NiIII impurities and oxygen vacancies and was beneficial for the electrocatalytic activity.

Resume : Tailoring of Catalyst Surfaces for Energy Conversion ? In-situ Studies of Electrochemical driven Nanoparticle Exsolution R. Rameshan(a), L. Lindenthal(a), F. Schrenk(a), T. Ruh(a), A. Nenning(b), A.K. Opitz(b), C. Rameshan(a) a Institute of Materials Chemistry, TU Wien, Austria b Institute of Chemical Technologies and Analytics, TU Wien, Austria 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-?, 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)

Resume : The efficient electrocatalytic degradation of environmental pollutants and synthesis of oxidizing species requires an electrode with a large surface area, high electrocatalytic activities, long-term stability, and a low cost. Thus, the introduction of nanotechnology seems to be an imperative factor to intensify the synergic effects of electrocatalytic materials to produce strong oxidant species or to increase the active sites on their surfaces. Recently, a new type of diamond electrodes was discovered–boron-doped carbon nanowalls manufactured using the microwave plasma-assisted chemical vapor deposition (CVD) process. Thus, we report, for first time, the results regarding the applicability of a BDD-boron-doped carbon nanowalls anode to degrade organic pollutants and electro-synthetize peroxodisulfate anion (PDS) in sulfate solutions in order to answer relevant questions from both fundamental and practical point-of-views. Carbon nanoarchitectures were synthesized as the core with a uniform BDD film. Since these carbon nanowalls combined both features of BDD and carbon, they are utilized as the electrode for the efficient electrocatalytic degradation of environmental pollutants. Dye-model pollutant was degraded below the limit of detection within 1.5 h using these anodes. For other various organic pollutants, this anode exhibited excellent degradation capacity. Such a high performance of electrocatalytic degradation of these environmental pollutants originates from increased surface areas and active sites by the three-dimensional carbon nanoarchitectures as well as the decreased charge-transfer resistance by the core-diamond-carbon structure. These kind of diamond films are thus promising as a new electrode material or an electrocatalyst for various catalytic applications in the environmental and energy fields. Acknowledgements: Financial supports from Conselho Nacional de Desenvolvimento Científico e Tecnológico (Brazil), 439344/2018-2, and from Fundação de Amparo à Pesquisa do Estado de São Paulo (Brazil), FAPESP 2014/50945-4 and 2019/13113-4, are gratefully acknowledged. [1] J. Davis, J.C. Baygents, J. Farrell, Understanding persulfate production at boron dopeddiamondfilm anodes, Electrochim. Acta 150 (2014) 68–74 [2] P.A. Michaud, E. Mahe, W. Haenni, A. Perret, C. Comninellis, Electrochem.Solid-State Lett. 3 (2000) 77–79 [3] K. Serrano, P.A. Michaud, C. Comninellis, A. Savall, Electrochim.Acta 48 (2002) 431–436. [4] P.A. Michaud, M. Panizza, L. Ouattara, T. Diaco, G. Foti, C. Comninellis, J. Appl. Electrochem. 33 (2003) 151–154. [5] J.R. Davis, J.C. Baygents, J. Farrell, J. Appl.Electrochem. 44 (2014) 841–848. [6] D. Khamis, E. Mahé, F. Dardoize, D. Devilliers, J. Appl. Electrochem. 40 (2010) 1829–1838. [7] C. Comninellis, G. Chen, Electrochemistry for the Environment,first ed. Springer, NewYork, 2010. [8] C.A. Martínez-Huitle, M. Panizza, Curr. Opin. Electrochem. 11 (2018) 62-71. [9] K.C.F. Araújo, D.R. da Silva, E.V. dos Santos, H. Varela, C.A. Martínez-Huitle, J. Electroanal. Chem. 860 (2020) 113927.

Resume : For past decade, we are looking for an alternative to fossil energy supplies. One of the alternatives are fuel cells and metal/air battery. In the case of metal/air battery, oxygen electrochemistry plays a key role. To improve the oxygen reduction reaction (ORR), manganese oxides (MnxOy) can be considered promising substitutes to platinum who is the best catalyst. Our project aims to prepare non-noble catalysts based on manganese oxide. To this end, we used electrospinning process. Electrospun nanofibers had a great potential for removal of contaminants from aqueous solutions owing to their large specific surface area, high porosity, easy modification, and good compatibility with other functional materials. The catalyst was prepared by an electrospun manganese acetate/PVP nanofiber, followed by a thermal treatment. The thermal treatment was a key point to optimize the electrocatalytical properties of the obtained manganese oxides /Carbon nanofiber catalysts (MnxOy/CF). Our studies were demonstrated that the MnxOy/CF catalysts prepared at 500°C exhibit exceptional selectivity toward 4 electron pathway.

Resume : Commercial proton exchange membrane fuel cells (PEMFCs) use platinum as the catalyst, a too scarce and precious metal for sustainable energy supply through PEMFCs. Pt-free catalysts are actively searched for, both at the cathode and at the anode. With huge advancements in current density, lower overpotential and higher stability in the past few years, molecular engineered bio-inspired catalysts hold promise for the next generation of PEMFC [1, 2]. Yet, their implementation in catalytic layers faces nanocomposite formulation issues [3]. Here, we use carbon nanotube immobilized DuBois nickel catalysts to exemplify how self-assembly at the mesoscale affects performances of H2 oxidation anodes. Copied on the conserved functional features of the active site of hydrogenases, the nickel catalysts created by Dubois et al. [4] show impressive turn-over frequency with no over-potential for hydrogen oxidation in solution. Not only has the central part of the catalyst, but also its outer sphere has a strong influence on the catalytic capacity [5]. Modification of the outer sphere can be used to immobilize the catalyst on a conductive matrix [6-8], a requirement for further implementation in PEMFC [9]. However, long-term ion transport in PEMFC requires creating ion conductive paths in the electrode, a task usually fulfilled by the addition of an ionomer. Although it allowed us to assemble the first fully Pt-free PEMFC [3], the current density was very low when the anode contained ionomer. The electrode microstructure thus appears critical to the system performance, yet it was hardly studied. THere, we show that molecular engineering coupled with three-dimensional structuring of the carbon electrode plays a major role on the catalytic activity through enhancement of catalyst grafting and substrate/product diffusion inside the electrode. In particular, we compare the effect of Nafion ionomer addition on the performances of bioinspired catalytic layers produced via three distinct surface chemistries [6-9]. We use microscopy as well as small angle neutron scattering techniques to characterize the self-assembly of the ionomer [10] with the carbon nanotubes/catalyst composite. A strong correlation appears between current drop in the presence of ionomer, and absence of ionomer hydrophilic/hydrophobic nanostructure. We propose a model that describes how the surface charge of the functionalized nanotubes drives the structuration of the Nafion ionomer and impacts diffusion of protons and gas to and from catalytic centres. [1] N. Coutard, N. Kaeffer, V. Artero, Chem. Commun., 2016, 52, 13728-13748. [2] F. Jaouen, D. Jones, N. Coutard, V. Artero, P. Strasser, A. Kucernak, Johnson Matthey Technology Review, 2018, 62, 231-255. [3] P.D. Tran, A. Morozan, S. Archambault, J. Heidkamp, P. Chenevier, H. Dau, M. Fontecave, A. Martinent, B. Jousselme, V. Artero, Chem. Sci., 2015, 6, 2050-2053. [4] M. Rakowski Dubois and D. L. Dubois, Acc. Chem. Res., 2009, 42, 1974?1982 [5] A. Dutta, J.A.S. Roberts, W.J. Shaw, Angew. Chem. Int. 2014, 53, 6487-6491 [6] A. Le Goff, V. Artero, B. Jousselme, P.D. Tran, N. Guillet, R. Metaye, A. Fihri, S. Palacin, M. Fontecave, Science, 2009, 326, 1384-1387. [7] P.D. Tran, A. Le Goff, J. Heidkamp, B. Jousselme, N. Guillet, S. Palacin, H. Dau, M. Fontecave, V. Artero, Angew. Chem. Int. Ed., 2011, 50, 1371-1374. [8] T.N. Huan, R.T. Jane, A. Benayad, L. Guetaz, P.D. Tran, V. Artero, Energy Environ. Sci., 2016, 9, 940-947. [9] S. Gentil, N. Lalaoui, A. Dutta, Y. Nedellec, S. Cosnier, W.J. Shaw, V. Artero, A. Le Goff, Angew. Chem. Int. Ed., 2017, 56, 1845-1849 [10] L. Rubatat, G. Gebel, O. Diat, Macromolecules 2004, 37, 7772

Resume : Co-based ordered mesoporous oxides and their electrocatalytic performance have been very well studied [1]. Other transition metals added in the Co-based oxide structure are known to improve its electrocatalytic activity [2]. Here, we develop a series of ordered mesoporous Cu/Ni/Co oxides (CNCO) with various Cu/Ni ratios to assess the role of these added metals and possible synergy effects on the electrocatalytic performance toward oxygen evolution and reduction reactions (OER and ORR, respectively). Physicochemical and electrocatalytic properties of the materials were characterized in detail. Most Cu and Ni were incorporated into the spinel structure of cobalt oxide, resulting in (Cu,Ni)xCo(3-x)O4 with small amounts of other phases such as CuO and NiO. Regarding the activity and stability of the catalysts toward OER, it was found that Ni-rich CNCO outperforms binary Ni/Co and Cu/Co oxides in 1M KOH electrolyte, being activated over 200 CVs. As a result, the most active material CNCO-2-8 (Cu/Ni~1/4) exhibits a current density of 411 mA cm-2 at the potential of 1.7 V vs RHE and an overpotential of 312 mV at the current density of 10 mA cm-2 after the activation process. After, the measurements were repeated in the purified 1M KOH excluding any activation due to the interaction of Ni with Fe impurities present in the electrolyte and thus exploring the intrinsic role of Cu. CNCO-2-8 outperforms Ni/Co oxide highlighting that the addition of Cu improves the electrocatalytic activity of the material. Furthermore, CNCO-2-8 indicates excellent long-term stability in 1M KOH. The combination of Cu and Ni in Co oxide also improves its activity toward ORR and reduces the side reaction facilitating the 4e- reaction path. CNCO-5-5 (Cu/Ni~1/1) demonstrates the best activity and long-term stability in 0.1M KOH. Summarizing, we observed that Cu/Ni inclusions in Co oxide provide a high number of active sites resulting in the highly efficient and stable bifunctional catalyst for both OER and ORR. [1] Priamushko, T.; Guillet-Nicolas, R.; Kleitz, F. Mesoporous Nanocast Electrocatalysts for Oxygen Reduction and Oxygen Evolution Reactions. Inorganics 2019, 7 (8), 98. [2] Wu, Z. P.; Lu, X. F.; Zang, S. Q.; Lou, X. W. Non-Noble-Metal-Based Electrocatalysts toward the Oxygen Evolution Reaction. Advanced Functional Materials 2020, 30, 1910274.

Resume : Using semiconductor photoelectrodes to directly drive electrocatalytic CO2 conversion using sunlight is an attractive route to an integrated solar-to-chemicals device. But it is not as simple as just combining semiconductors with catalysts. The differences between metallic and semiconductor electrodes, plus the complex interplay at the electrode-catalyst-electrolyte interfaces, present challenges and opportunities in device design. Our studies focus on differences between metallic and semiconducting electrodes which can alter the behavior of electrocatalytic CO2 reduction. This includes differences observed when using a semiconductor photoelectrode to drive a molecular catalyst, where catalyst immobilization can enable efficient turnover (1). Additionally, photoelectrodes allow a decoupling of current and potential which is not possible on metallic electrodes, a phenomenon we exploit to demonstrate new routes for controlling product selectivity. (1) Schreier, et al. J. Am. Chem. Soc. 2016, 138, 6, 1938. doi: 10.1021/jacs.5b12157

Resume : CO2 emitted into the atmosphere by fossil hydrocarbons combustion is responsible for the current climate change. Its capture and conversion thus constitute a major challenge. Among different possible technologies, the sunlight-assisted photoelectrochemical (PEC) conversion of CO2 into renewable fuels (e.g., CH4, C2H4, CH3OH?) using semiconductors (solar to chemical energy), is a sustainable solution of major interest for the energy transition [1]. Despite recent advances, the PEC reduction of CO2 remains a challenge. The main problems to be solved are (i) the high overpotential required (binding energy C=O 803 kJ/mol), (ii) the modest selectivity for hydrocarbons and alcohols vs. CO and HCOOH (i.e., separation costs), (iii) the low PEC performances (photocurrent densities < 10 mA/cm² for limiting diffusion conditions and < 1 mA/cm2 at modest overpotentials) and (iv) CO poisoning of the catalytic surfaces. Finding new photoelectrocatalysts combining efficiency, selectivity and stability still requires significant efforts [2]. Bulk or nanostructured bimetallics have been tested for the CO2 reduction reaction for which the ability to tune the selectivity is well established. Among them, the PdCu system has demonstrated higher performances for fuel production (FE ~ 60% for C2 chemicals like C2H4 and C2H5OH) [3,4]. As far as we know, this system has never been combined with a photoactive support. In this work we proposed an innovative method for the synthesis of PdCu nanoparticles directly on Si supports by metal assisted chemical etching (MACE), a well-known electroless deposition process used for single metal nanoparticles but never applied to bimetallic systems. It relies on coupled electrochemical reactions between Si and metal cations in HF media. From XRD, SEM-EDX and XPS measurements, we demonstrate that this method allows precise control of the PdxCu100 x nanoparticle composition and their microstructure which can be set as phase-separated or solid solution. It could be extended to any bimetallic system to be deposited on Si (if single metals are susceptible of MACE). It also allows to load bimetallic catalyst on Si substrates with micro and macrostructures of high aspect ratio. The PEC responses of the synthetized photocathodes are explored for the conversion of CO2 (and HER) as a function of the PdxCu100-x catalyst composition in solid solutions. Pd50Cu50 is the composition providing the highest photocurrent density. SEM-EDX analysis of the electrode surface before and after electrochemistry reveals a certain degree of nanoparticles coalescence. Product analysis by gas chromatography and RMN with the new photocathodes is currently being performed. [1] F. Marken, D. Fermin, RSC Energy & Environment Series (2018) [2] J. He, C. Janáky, ACS Energy Lett. 5, 1996 (2020) [3] W. Zhu, et al., Top Curr. Chem. (Z) 376, 41 (2018) [4] E. Torralba, et al., Electrochim. Acta 354, 136739 (2020)

Resume : Efficient synthesis of solar fuels is attracting great attention now-a-days as it opens up the possibility to convert the greenhouse gas CO2 into value-added products where solar energy is stored as chemical energy. Despite recent advancements in solar energy conversion research, design of selective catalyst materials for long-term performance and assembly of bias-free solar devices for efficient CO2-to-fuel synthesis still remains challenging. Here, we demonstrate a novel approach of integrating an inexpensive Cu96In4 metal alloy catalyst into a state-of-the-art lead halide triple cation perovskite?BiVO4 tandem photoelectrochemical (PEC) device for unassisted CO production from aqueous CO2. CO is an extremely important CO2 reduction product as it can be further converted into long-chain hydrocarbon fuels by the Fischer Tropsch process. The bimetallic Cu96In4 alloy catalyst, synthesized by a template-assisted galvanostatic electrodeposition method, has a microporous 3D dendritic morphology and it shows excellent CO2 electroreduction activity towards selective CO production at low overpotentials (>70% CO selectivity at ?0.3 V vs. reversible hydrogen electrode (RHE)). Operando Raman spectroscopy reveals a weaker *CO adsorption on the Cu96In4 alloy surface compared to pure Cu which supports the immediate release of CO as a gaseous product from the alloy surface. The BiVO4?perovskite?Cu96In4 tandem PEC device shows an excellent (~75%) selectivity towards solar CO production from CO2 and H2O under bias-free conditions where the solar-to-CO conversion efficiency reached 0.19% after 10 h operation. Furthermore, the perovskite?Cu96In4 cathode shows robust PEC activity under different solar light intensities (varied from 0.1 Sun to 1 Sun) which indicates that the device can be used under different daylight conditions or even on a cloudy day with diffused sunlight. Reference: Rahaman, M.; Andrei, V.; Pornrungroj, C.; Wright, D.; Baumberg, J. J.; Reisner, E. Energy Environ. Sci., 2020, 13, 3536-3543

Resume : Photoelectrochemical cells (PEC) are one of the most promising approaches for the production of alternative energy carrier in the global effort to diminish the usage of fossil fuels [1]. In this context, III-V nanowires (NW) based photoelectrodes [2-5] are particularly attractive thanks to their high surface/volume ratio and their efficient charge separation and collection. However III-V NWs suffer from corrosion in aqueous electrolyte that prevents their utilization for long period. In order to avoid the surface degradation of the III-V NW under working conditions, a particular attention has to be given to their surfaces. We proposed to grow an oxide shell transparent to visible light and compatible with the carrier transfer from the III-V semiconductor to the electrolyte to increase the viability of these photoelectrodes. GaP and GaAs NWs were grown by molecular beam epitaxy (MBE) using the vapor-liquid-solid (VLS) mechanism on silicon substrate and a TiO2 shell was deposited by atomic layer deposition (ALD). The morphology, interface, and structure of the NWs were studied by scanning transmission electron microscopy and electron energy loss spectroscopy before and after the measurements of their photoelectrochemical activity after combination with suitable hydrogen or oxygen evolution catalysts. 1 N. Armaroli et al, Angew. Chem. 46, (2007), 52 2 M. G. Kibria et al, Nat. Commun. 5 (2014), 3825 3 J. Kamimura et al, Semicond. Sci. Technol. 31 (2016), 074001 4 K. T. Fountaine et al, ACS Photonics 3 (2016), 1826 5 N. Kornienko et al, ACS Nano 10 (2016), 5525

Resume : Water electrolysis, fuel cells, and metal-air batteries all require efficient and cheap electrocatalysts that can significantly lower the reaction overpotentials. Defects due to doping or alloy are pivotal to tailoring the electrocatalytic activities of the electrode materials. In this talk, I will discuss about effect of composition engineering and doping of electrocatalysts in their performance in water splitting and meal-ion batteries. First, we show dual anion doping, or metal-anion co-doping in alloy compounds can simultaneously modulate key parameters in water dissociation and hydrogen adsorption energies, leading to evident enhancement in both hydrogen and oxygen evolution reactions activities. Second, tuning the local defect configurations can promote the intrinsic HER activity of the basal plane of MoS2. And doping of Sn and Sb bi-atoms with different electronegativities can enhance the stability of amorphous MoSxO2-x catalyst for acidic HER. Finally, we show the effectiveness of local configuration of bi-metal atomic catalysts in boosting the ORR function.

Resume : Electrocatalytic hydrogen evolution reaction (HER) in alkaline media is a promising electrochemical energy conversion strategy. Ruthenium (Ru) is an efficient catalyst with a desirable cost for HER; however, the sluggish H2O dissociation process, due to the low H2O adsorption on its surface, currently hampers the performances of this catalyst in alkaline HER. Herein, we demonstrate that the H2O adsorption/dissociation improves significantly by the construction of Ru?O?Mo sites. We prepared Ru/MoO2 catalysts with Ru?O?Mo sites through a facile thermal treatment process and assessed the creation of Ru?O?Mo interfaces by transmission electron microscope (TEM) and extended X-ray absorption fine structure (EXAFS). By using Fourier-transform infrared spectroscopy (FTIR) and H2O adsorption tests, we proved Ru?O?Mo sites have tenfold stronger H2O adsorption ability than that of Ru catalyst. The catalysts with Ru?O?Mo sites exhibited a state-of-the-art overpotential of 16 mV at 10 mA cm?2 in 1 M KOH electrolyte, demonstrating a threefold reduction than the previous bests of Ru (56 mV) and commercial Pt (32 mV) catalysts. We proved the stability of these performances over 40 hours without decline. These results could open a new path for designing efficient and stable catalysts.

Resume : Hydrogen evolution reaction (HER) is a sustainable and promising alternative technology to overcome the use of fossil fuels that cause substantial harmful environmental impact worldwide. Recently, many works have reported electrocatalysts based on metallic earthabundant and cost-effective materials (Ni1, 2, Co3, Mo4, 5, Fe6, Cu7, 8) as promising alternatives to the state-of-the-art Pt catalysts for HER. In this talk, I will present a cost-effective and facile route to synthetize highly efficient Cu2S electrocatalyst, exhibiting 400 mA cm-2 at -1V vs RHE and exceptional stability under operation conditions. Different structural characterization techniques were employed to analyze the as-prepared and post-mortem electrodes coupled to detailed electrochemical characterization and mechanistic analysis This Cu-based electrocatalyst represents a great step towards scalability for industrial hydrogen production.

Resume : Hydrogen production from water splitting is often as regarded the ?Holy Grails? of chemistry. Water oxidation is the kinetic bottleneck of overall water splitting reaction because of the sluggish kinetic and complex multistep electron transfer process. The development of effective materials for water oxidation reaction is indeed a challenging field. Metal-organic framework (MOF) with high surface area and porosity has become a promising catalyst for various reaction. Polyoxometalates (POMs) are molecular oxide aggregates with diversified structure and chemical versatility. The metal-oxygen framework in POMs which can undergo reversible redox reaction has increased their popularity in the field of catalysis. In this study, a hybrid compound of MOF/POMs is fabricated by crystallization mechanism, with the addition of POMs during MOF formation. Prior to that, POMs are synthesized by self-assembly process. All the materials are synthesized under mild condition, without the usage of strong acid and strong base. Characterization tests such as field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) are performed to elucidate the properties of the hybrid compounds. In the electrocatalytic water oxidation reaction experiment, MOF/POMs hybrid compounds show enhancement in performance compared to pristine MOF, indicating the potential of the newly synthesized compounds as efficient catalysts. Keywords: Polyoxometalate, Metal-organic Framework, Hybrid compound, Electrocatalysis, Water oxidation

Resume : Electrocatalysts play a crucial role in hydrogen production via water electrolysis. However, developing efficient catalysts to reduce the high reaction overpotentials caused by the sluggish kinetics of the anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER) remains a formidable challenge. In this presentation, we report the synthesis of atomically dispersed ruthenium (Ru) supported on nitrogen-doped carbon (Ru-NC) with an ultra-low Ru loading (0.2 wt%), which is realized by a two-step deposition-pyrolysis method. Extensive transmission electron microscopy investigations reveal that Ru is dispersed on the NC support in the form of both single atoms and small clusters. The as-prepared Ru-NC exhibits superior electrocatalytic activity and good stability for both HER and OER, showing bifunctionality. It only requires a low overpotential of 47.1 and 72.8 mV to deliver a current density of 10 mA cm-2 for HER in 0.5 M H2SO4 and 1.0 M KOH, respectively, and 300 mV for OER in 1.0 M KOH. Considering the superior bifunctional electrocatalytic HER and OER activities, the overall water electrolysis performance has been investigated in alkaline solution using Ru-NC as both HER and OER catalysts in the presence of a bipolar membrane (BPM). This configuration enables water electrolysis to occur in acid-alkaline dual electrolytes (BPM-WE), where HER is accomplished in a kinetically favorable acidic solution and OER in a kinetically favorable basic solution. Such asymmetric acid-alkaline BPM-WE operates under a low cell voltage of only 0.89 V to deliver a current density of 10 mA cm-2 and can sustain over 100 hours without significant performance decay due to the assistance of electrochemical neutralization resulting from the crossover of the electrolytes, which shows a great potential for energy-saving hydrogen production.

Resume : Technology at the nanoscale has become one of the main challenges in science as new physical effects appear and can be modulated at will. Especially 2D nanomaterials can be designed and engineered in order to improve their performance and efficiency for energy and environmental applications. In this way, a proper selection of defects, grain boundaries and surfaces, or the right selection of dopants allow a major increase on the properties of a new generation of (photo)electrocatalysts. In the present work, by using powerful advanced electron microscopy related techniques, we will move to the atomic scale in order to visualize the beauty of such nanostructures. Modified nanostructures as support for single atom catalysts with a great enhancement on lithium-sulphur batteries stability and performance or CO2 Reduction will be shown [1]. Nanoengineered atom-thin transition metal dichalcogenides (MoS2 and WS2) showing a high density of grain boundaries acting as efficient active sites for the hydrogen evolution reaction (HER) will be also studied at the atomic scale [2]. Atomic resolution electron microscopy analyses will help us to visualize such fancy nanostructures and allow us to create 3D atomic models in order to understand not only the growth mechanisms implied, but also to be used as input models for further DFT simulations, which will allow us to gain knowledge on the novel catalytic mechanisms achieved. We will show our latest results on direct visualization and modelling of nanomaterials at atomic scale, which will help to understand their growth mechanisms (sometimes complex) and also correlate their chemical properties ((photo)electrocatalytic) at sub-nanometer scale with their atomic scale structure. [1] Y. He, et al. Nature Communications, 11, 57 (2020) [2] Z. Liang et al., Advanced Energy Materials, 11, 2003507 (2021)

Resume : Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have been demonstrated as promising catalysts for water splitting, hydrogen reduction, and water oxidation. The unique chemical-physical properties of 2D TMDs are shown by their small size enriched by the number of edge active sites, band-edge position, quantum confinement effect, and photo-induced catalytic efficiency. TMDs are considered the most promising cost-effective catalysts, and their properties are determined by the TMDs? polymorph type (hexagonal 2H, trigonal 1T). Tantalum disulfide (TaS2) as a member of the TMD family has been subject to numerous studies due to various material?s unique structural and electronic phases. Its initial metallicity and electrical conductivity lead to potential applications such as a light-responsive electrode. Albeit the study of TaS2 mainly focuses on the superconductivity and field emission, photo-induced features of the material for hydrogen evolution reaction (HER) and photosensing have not been explored yet. Several methods have been demonstrated to produce 2D TaS2, using chemical vapor deposition (CVD), mechanical cleavages, intercalation, ultrasonication, or liquid-phase exfoliation. However, the CVD method remains to be improved before it can be used to produce large-domain homogeneous TaS2 films. The mechanical cleavage is not scalable and misses control over product thickness and size. Alternatively, electrochemical exfoliation (ECE) is the most convenient, controlled, and straightforward method employed in ambient temperature for large-scale production of 2D TaS2. In this study, the light-induced efficiency of electrochemically exfoliated TaS2 nanosheets for hydrogen generation catalysis and photodetectors has been presented for the first time. The ECE of TaS2 crystals toward a few-layer derivative has been pioneered in anhydrous tetrabutylammonium hexafluorophosphate in N, N dimethylformamide. Comprehensive analysis of exfoliated TaS2 revealed the formation of nanoparticles and nanosheets with a lateral size of about several nanometers and micrometers, correspondingly. Observed mutual twisting of 2H-TaS2 flakes leads to the redistribution of charge density induced by interlayer interaction of the individual nanosheets. External light irradiation on the TaS2 surface influences its conductivity, making it feasible for photoelectrocatalysis (PEC) and photodetection (PD). The TaS2-based catalyst demonstrates high HER PEC activity with the onset overpotential below 575 mV, which can be lowered by thorough catalyst preparation. Finally, the TaS2-integrated PD in the acidic medium represents its broadband light sensing capability with the highest photoresponsivity toward 420 nm light illumination. This finding will pave the way to a new realization of exfoliated twist-angle stacked TaS2 for photo-induced electrochemistry and sensing.

Resume : As an eco-friendly and renewable energy source, hydrogen energy has attracted widespread attention. MoS2 nanomaterials are typical catalysts for the electrocatalytic hydrogen evolution reaction (HER), but their performances are limited by their poor conductivity and spontaneous agglomeration. Here, we prepared few-layer fluorine-free Ti3C2TX (T = O, OH) as a conductive substrate of MoS2 for HER catalysis, and the as-prepared hybrid catalyst exhibits high catalytic activity with a small overpotential of 139 mV at -10 mA cm-2, a Tafel slope of 78 mV dec-1, and a negligible decay after 3000 cycles at a scan rate of 100 mV s-1 in an acidic solution. The excellent performance in HER activity can be attributed to the improved electrical conductivity, increased O active sites and optimized 2D masstransport channels of the unique few-layer fluorine-free structure. Interestingly, the few-layer fluorine-free Ti3C2TX/MoS2 catalyst also performs well under neutral and alkaline conditions. This work demonstrates that few-layer fluorine-free Ti3C2TX (T = O, OH) can be used as an excellent conductive substrate to further improve the HER performances of other nanoscale electrocatalysts.

Resume : Two-dimensional (2D) VA group materials, including black phosphorene and bismuthene, attract considerable attention in energy devices because of their unique properties, such as tunable bandgap and superhigh carrier mobility. However, their application in photoelectrochemical devices is rarely reported. In this presentation, we present the successful design of a co-catalyst/2D VA material/semiconductor composite photoanode consisting of NiFeOOH/bismuthene/BiVO4 that achieves 3.7 mA cm-2 at 0.8 VRHE. Characterization techniques such as electrochemical impedance spectroscopy, intensity modulated photocurrent spectroscopy, cyclic voltammetry, and open circuit potential, were comprehensively employed to identify the roles of bismuthene and NiFeOOH on BiVO4. We found that bismuthene can (1) increase hole concentration at the surface, (2) modulate surface oxygen vacancies, and (3) accelerate oxygen evolution reaction kinetics. Indeed, kinetics studies show the composite photoanode has an effective hole injection into the electrolyte. Moreover, we found that the improvement from bismuthene strongly depends on the co-catalyst used. We assign this dependence to the permeability and conductivity of the different co-catalysts.

Resume : Two dimensional materials, such as the transition metal dichalcogenides (TMDCs) are a good candidate for water splitting catalysts [1,2], as they often have larger band gaps than their bulk counterparts. However, this had to be balanced by the thin layers having a small absorption cross section and difficulties in mounting on a suitable substrate. PdSe2 is being suggested as a potential water splitting candidate [3]. However its bulk band gap is too small for water splitting [4]. We propose to use this structure as a surface coating to a second TMDC with a larger band gap such as MoS2 and use this as an example of how such heterostructures could function. Using density functional theory, implemented in the Vienna Ab-initio Simulation Package, we have investigated the surfaces of TMDC monolayers MoS2 and PdSe2, and a Hetero-bilayer of the two, for their potential application as photocatalytic water splitters. The different functional groups involved in the Hydrogen and Oxygen evolution reactions have been added to the monolayers and the hetero-bilayer to determine their energetics. In addition to this, we have looked at how stable these materials are, to both adsorptions and substitutions, in both air and water environments. References: [1] Qing Tang and De En Jiang. ACS Catalysis, 6(8):4953?4961, Aug 2016. [2] B. Amin, et al . Phys. Rev. B, 92:075439, Aug 2015. [3] C. Long, et al . ACS Appl. Energy Mater., 2, 1, 513-520, 2019. [4] G. Zhang, et al . Appl. Phys. Lett., 114, 253102, June 2019.

Resume : The establishment of a sustainable renewable fuels technology will depend on the electrocatalytic reduction of substrates into fuels, but also on the electrocatalytic oxidation of water or other feedstock to extract the needed electrons and protons. The requirements for the oxidation electrocatalysts are typically more demanding regarding long term stability, since these catalysts must be fast, selective and efficient, but also robust to high oxidation potentials, water, oxygen, electrolytes, acids or bases, etc. Several earth abundant metal oxides are excellent electrocatalysts in neutral and basic conditions, with multiple examples from different labs.1 However, most active transition metal oxides are unstable in acidic media, where they just dissolve even in open circuit conditions. Only noble metal oxides, such as IrO2, are able to exhibit competitive electrooxidation activity in aqueous acidic conditions (pH < 3), where reduction electrochemistry is easier and faster, and proton exchange membrane (PEM) technology may facilitate high current density performance in compact electrolyzer architectures. In this communication we will report our latest results in the search for efficient, low cost oxidation electrocatalysts from earth abundant, non-critical raw materials able to work in aqueous acidic media. We showed how Co-containing polyoxometalates (POMs), are active electrocatalysts for the oxygen evolution reaction (OER) in acidic conditions when stabilized by a partially hydrophobic support.2 Although with some limitations, a hybrid composite of an insoluble salt of the polyoxoanion [Co9(H2O)6(OH)3(PW9O34)3]16? blended with a carbon paste electrode exhibited superior performance and higher current densities than the corresponding IrO2-based electrodes in the low overpotential range. We are extending this same strategy to bulk and nanostructured transition metal oxides to provide fast and robust OER at pH < 1. Furthermore we will show how some of these metal oxides can also catalyze alternative electrochemical oxidation processes of high interest for the chemical industry, such as the selective oxidation of alcohols to aldehydes or carboxylic acids.

Resume : In recent years, there is a growing interest in the incorporation of Metal-Organic Frameworks (MOFs) based thin films into electrochemical energy conversion schemes. In principle, MOF-based electrocatalytic systems hold several key virtues, such as the ability to immobilize unparalleled amount of catalytic sites; intrinsic inclusion of mass-transport channels; the ability to add molecular shuttles to deliver redox equivalents to and from the MOF-tethered catalytic sites; and finally, much like in catalytic enzymes, MOFs offer the possibility to modulate the catalyst’s secondary chemical environment. Indeed, over the last years several reports have demonstrated the concept of using electroactive MOF thin films as the catalytic component in the electrocatalytic cell, either through (a) the use of the MOF structural elements themselves (ligands or nodes) as electroactive catalysts, or (b) the immobilization of high concentration of active molecular catalysts within the MOF pores (for a wide variety of energyrelated catalytic reactions as hydrogen evolution, water oxidation, oxygen reduction, and CO2 reduction). Yet, up to this point, the notion of using MOFs to precisely tune and manipulate the properties of the electrocatalytically active site and its surrounding chemical environment was overlooked. In this talk, we will demonstrate for the first time that a non-electrocatalytic MOF can be used as a porous membrane layered over a solid heterogeneous electrocatalyst. Following this principle, a suitably designed MOF membrane has the potential to modify the microenvironment of the underlying heterogeneous catalyst and affect its electrocatalytic properties in a wide variety of proton-coupled electron transfer (PCET) reactions.

Resume : Electrocatalytic hydrogen production via water splitting is considered a promising technology to store renewable energy into chemical bonds. In this process, the oxygen evolution reaction (OER) water acts as electron donor and it is considered to be the bottleneck of the process when using metal-oxide anodes. The efficiency of these catalysts does not only depend on the nature of the metal oxide, but also on their physical characteristics such as composition, magnetic susceptibility and doping variations, amongst others. However, the mechanism of the OER on metal oxides as well as the nature of the efficiency loses remains elusive. In this talk, I will present recent advances on the understanding of the kinetics of OER on different metal-oxide electrocatalysts, focusing particularly on Ni-based anodes. Kinetic and mechanistic analyses of the OER on Ni-based electrocatalysts will be presented under different physicochemical conditions, Fe doping on facile synthesised Ni-oxide anodes [1-3] as well as the effect of applying a magnetic field on ferrite type Ni-oxide catalysts on the OER kinetics will be shown.

Resume : The development of new low-cost water splitting electrocatalysts to replace the expensive and scarce established noble metal Pt and RuO2/IrO2 catalysts is a major challenge on the way to green hydrogen production. Ordered mesoporous transition metal oxides, and especially the Co3O4 derived ones, were hence studied extensively owing to their good performance and stability in alkaline electrolytes for OER [1]. The preparation of bimetallic transition metal oxides like NiCo2O4, but also the addition of small amounts of transition metals - as dopants - led to improved electrocatalysts due to synergistic effects between the metal oxide species [2, 3]. In this work, we synthesized Mn and Fe-doped ordered mesoporous nickel cobalt oxides via one-step impregnation using KIT-6 aged at 40°C as a hard template to obtain electrocatalysts exhibiting high porosity and surface area. By implementation of a low-temperature calcination approach, the temperature necessary to obtain spinel-type transition metal oxides was significantly reduced from typical 500°C to 200°C. This was achieved by exploiting the ?container effect? described by Sun et al [4]. Detailed materials characterization was performed to ascertain elemental and phase compositions and determine porosity and mesoporous characteristics. Further, the effects of iron and manganese-doping upon the electrocatalytic activity of ordered mesoporous Ni0.5Co2.5O4 were investigated and the stability of the catalysts was demonstrated in a 72h galvanostatic experiment. Wide-angle XRD revealed spinel structure for Co3O4, Ni0.5Co2.5O4, and the Fe and Mn-doped samples, meaning that Fe and Mn substituted Ni in the spinel structure of the multimetallic oxide. SAXS and nitrogen physisorption confirmed a high mesopore ordering, a bimodal pore size distribution (typical for KIT-6-40 replicas), high BET surface area around 130 m²/g, and a total pore volume of approximately 0.3 cm³/g for all electrocatalysts. Further, the electrocatalytic performance was ascertained for the OER in 1M KOH electrolyte. All electrocatalysts prepared at 200°C performed superior to the Co3O4 references which were calcined at 200°C and 500°C respectively. With a low overpotential of only 359 mV (@10 mA/cm2) and a high current density of 279 mA/cm2 @1,7 V vs. RHE, the Mn0.1Fe0.1Ni0.3Co2.5Ox composition exhibited the best OER performance among the samples. The high stability of the catalysts was confirmed by a stable working electrode potential during a 72h galvanostatic polarization at 5 mA in 1 M KOH electrolyte at room temperature. In summary, a low-temperature calcination approach was successfully used to prepare Mn and Fe-doped mesoporous nickel cobalt oxide without the formation of any detectable phases except the spinel structure. The success of this procedure is attributed to the low calcination temperature as higher temperatures usually lead to the formation of different oxide phases and result in poor replica quality [5]. It was shown that the activity of the oxides toward OER increases with the addition of Mn- and/or Fe- into Ni/Co oxides as a result of the synergistic effect between metals. Moreover, the catalysts demonstrate excellent stability, which makes them attractive candidates for further research. 1. Zhao, Q., Yan, Z., Chen, C. & Chen, J. Spinels: Controlled Preparation, Oxygen Reduction/Evolution Reaction Application, and beyond. Chem. Rev. 117, 10121?10211 (2017). 2. Fang, L. et al. Crystal-plane engineering of NiCo2O4 electrocatalysts towards efficient overall water splitting. J. Catal. 357, 238?246 (2018). 3. Li, Y., Hasin, P. & Wu, Y. NixCo3-XO4 nanowire arrays for electrocatalytic oxygen evolution. Adv. Mater. 22, 1926?1929 (2010). 4. Sun, X. et al. Container effect in nanocasting synthesis of mesoporous metal oxides. J. Am. Chem. Soc. 133, 14542?14545 (2011). 5. Priamushko, T. et al. Nanocast Mixed Ni-Co-Mn Oxides with Controlled Surface and Pore Structure for Electrochemical Oxygen Evolution Reaction. ACS Appl. Energy Mater. 3, 5597?5609 (2020).