Advanced catalytic materials for (photo)electrochem. energy conversion III

Resume : Electrochemical energy conversion devices such as fuel cells or water and CO2 electrolyzers, including photo-electrochemical cells, are the ultimate tools to test photo-electrocatalyst performance parameters. The latter include activity, stability, and selectivity. However, such measurements in real devices are time and labor-consuming, and prohibitory expensive. Moreover, the complexity of real catalyst layers and multeity of processes taking place there makes fundamental studies related to electrocatalyst performance challenging ? the separation of electrocatalytic processes from others is not straightforward. Aqueous model systems (AMS) are typically used to overcome this drawback. The most known AMS is the rotating disk electrode (RDE). If very thin catalyst layers are applied, extraction of kinetic parameters for studied electrocatalysts is possible using Levich and Koutecky-Levich equations [1]. Hence, the intrinsic activity of various electrocatalysts can be compared and benchmarked to the state-of-the-art electrocatalyst. If coupled with external analytics, RDE can also be successfully used to study selectivity and dissolution stability [2-4]. RDE is very slow when it comes to quick screening of different catalytic materials. Moreover, since catalyst layers are very thin and flooded in aqueous electrolytes, RDE does not allow studying of electrocatalyst performance at conditions resembling that of real devices. Two research directions will be discussed in my presentation to overcome these drawbacks. First, scanning flow cell (SFC) based techniques will be introduced as experimental tools allowing high-throughput screening but also fundamental studies of activity, stability, and selectivity of photo-electrocatalysts [5-7]. Second, gas diffusion electrode (GDE) based setups will be presented as experimental tools to test catalysts in real catalyst layers [8]. Recent representative examples of the utilization of both families of setups to study oxygen reduction and oxygen evolution reaction electrocatalysts will be given. References: [1] T.J. Schmidt, H.A. Gasteiger, G.D. Stäb, P.M. Urban, D.M. Kolb, R.J. Behm, Characterization of High?Surface?Area Electrocatalysts Using a Rotating Disk Electrode Configuration, Journal of The Electrochemical Society, 145 (1998) 2354-2358. [2] A.H. Wonders, T.H.M. Housmans, V. Rosca, M.T.M. Koper, On-line mass spectrometry system for measurements at single-crystal electrodes in hanging meniscus configuration, Journal of Applied Electrochemistry, 36 (2006) 1215-1221. [3] N. Todoroki, H. Tsurumaki, H. Tei, T. Mochizuki, T. Wadayama, Online Electrochemical Mass Spectrometry Combined with the Rotating Disk Electrode Method for Direct Observations of Potential-Dependent Molecular Behaviors in the Electrode Surface Vicinity, Journal of The Electrochemical Society, 167 (2020) 106503. [4] P.P. Lopes, D. Strmcnik, D. Tripkovic, J.G. Connell, V. Stamenkovic, N.M. Markovic, Relationships between Atomic Level Surface Structure and Stability/Activity of Platinum Surface Atoms in Aqueous Environments, ACS Catalysis, 6 (2016) 2536-2544. [5] S. Cherevko, K.J.J. Mayrhofer, On-Line Inductively Coupled Plasma Spectrometry in Electrochemistry: Basic Principles and Applications, in: K. Wandelt (Ed.) Encyclopedia of Interfacial Chemistry, Elsevier, Oxford, 2018, pp. 326-335. [6] O. Kasian, S. Geiger, K.J.J. Mayrhofer, S. Cherevko, Electrochemical On-line ICP-MS in Electrocatalysis Research, Chem Rec, 19 (2019) 2130-2142. [7] K.J. Jenewein, A. Kormányos, J. Knöppel, K.J.J. Mayrhofer, S. Cherevko, Accessing In Situ Photocorrosion under Realistic Light Conditions: Photoelectrochemical Scanning Flow Cell Coupled to Online ICP-MS, ACS Measurement Science Au, 1 (2021) 74-81. [8] K. Ehelebe, N. Schmitt, G. Sievers, A.W. Jensen, A. Hrnji?, P. Collantes Jiménez, P. Kaiser, M. Geuß, Y.-P. Ku, P. Jovanovi?, K.J.J. Mayrhofer, B. Etzold, N. Hodnik, M. Escudero-Escribano, M. Arenz, S. Cherevko, Benchmarking Fuel Cell Electrocatalysts Using Gas Diffusion Electrodes: Inter-lab Comparison and Best Practices, ACS Energy Letters, 7 (2022) 816-826.

Resume : The oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) play crucial roles in energy storage and conversion devices such as metal-air batteries. However, both ORR and OER possess show sluggish kinetics and high activation overpotentials, limiting the widespread deployment of these energy storage and conversion devices. Diatomic catalysts, particularly those having heteronuclear active sites, have lately attracted considerable attention for their advantages over single-atom catalysts in reactions involving multi-electron transfers. In this presentation, we report the bimetallic iridium-iron diatomic catalysts (IrFe-N-C), derived from metal organic frameworks in a facile wet chemical synthesis followed by post-pyrolysis [1]. Advanced materials characterization techniques including HAADF-STEM, XPS and synchrotron-based XAS have unambiguously confirmed the atomic dispersion of Ir and Fe and the presence of IrFe dual-atoms. The as-obtained IrFe-N-C shows substantially higher electrocatalytic performance for both ORR and OER when compared to the single-atom counterparts (i.e., Ir-N-C and Fe-N-C), revealing favorable bifunctionality. The excellent bifunctionality of IrFe-N-C for ORR and OER enables it to serve as a high-performance air cathode in Zn-air batteries, which shows substantially enhanced performance with respect to the commercial Pt/C+RuO2 benchmarks. Our synchrotron-based XAS experiments and density functional theory (DFT) calculations suggest that the IrFe dual-atoms exist likely in an IrFeN6 configuration where both Ir and Fe coordinate with four N atoms without the formation of an Ir-Fe bonding. The Fe site contributes mainly to the ORR, while the Ir site plays a more important role in the OER. The two work in synergy and altogether promote oxygen electrocatalysis, holding great potential for use in various electrochemical energy storage and conversion devices. Reference: [1] Z. P. Yu, C. W. Si, A. P. LaGrow, Z. X. Tai, W. A. Caliebe, A. Tayal, M. J. Sampaio, J. P. S. Sousa, I. Amorim, A. Araujo, L. J. Meng, J. L. Faria, J. Y. Xu*, B. Li* and L. F. Liu*, Iridium-Iron Diatomic Active Sites for Efficient Bifunctional Oxygen Electrocatalysis, ACS Catalysis (Under review).

Resume : High Entropy Alloys (HEAs) are multicomponent systems containing at least five different elemental components and exhibiting configurational entropy of higher than 1.5kB, where kB is the Boltzmann constant. These materials possess several unique features, such as multifunctionality, flexibility in the choice of elements, easily tailored electronic interactions, and the presence of active sites for a variety of reactions.[1] Moreover, HEA catalysts are expected to exhibit high stability.[2] However, this assumption is based only on theoretical works due to the lack of experimental data in the HEAs field, which is at the beginning of its development.[1] Furthermore, the stability of these materials was not studied under electrocatalytic conditions (potential window, pH, reactive gases, etc.) yet. Therefore, we performed a number of experiments to study the stability of HEAs based on Pt, Ru, Ir, Rh, and Pd (both carbon-supported nanoparticles (NPs) and thin films) or Os (unsupported NPs). Our study included mainly two protocols to ensure that the potential window (0.05-1.5 V vs. RHE) covers those typically applied for oxygen reduction and evolution reactions (ORR and OER, respectively), small organic molecule oxidation, etc. The measurements were performed using a scanning flow-cell (SFC) combined with inductively coupled plasma mass spectrometry (ICP-MS).[3] In this work, we tried to achieve four main goals. (1) Establishing the effect of each constituent in Pt-Ru-Ir-Rh-Pd on the stability of the alloy. For this, we systematically tested unary, binary, ternary, quaternary, and quinary alloys (all of them with an equimolar composition). (2) Studying the influence of pH on the dissolution characteristics. On-line ICP-MS measurements were performed in both acidic and alkaline electrolytes. (3) Revealing the role of the phase segregation. To achieve this, we carried out the dissolution experiments for single-phase and phase-segregated (up to three phases) Pt-Ru-Ir-Rh-Os alloys. (4) Finally, verifying whether our findings can be translated to systems closer to real applications. The measurements were carried out on both sputtered thin films and carbon-supported alloy NPs. [1] T. Löffler, A. Ludwig, J. Rossmeisl, W. Schuhmann, Angew. Chemie - Int. Ed. 2021, 60, 26894. [2] Y. Sun, S. Dai, Sci. Adv. 2021, 7, 1. [3] G. C. da Silva, K. J. J. Mayrhofer, E. A. Ticianelli, S. Cherevko, J. Electrochem. Soc. 2018, 165, F1376.

Resume : Transition metal chalcogenides (TMCs) are broadly investigated catalysts, limited by the relative inertness of their pristine basal plane. We propose that TMC single layers modified by substitutional non-metal heteroatoms can harvest the synergistic benefits of stably anchored single-atom sites and activated TMC basal planes. These solid-solution TMC catalysts offer advantages such as simple and versatile synthesis, unmatched active site density, and a stable and well-defined single-atom active site chemical environment. Oxygen substitution sites present all over the basal plane act as single-atom reaction centres, substantially increasing the catalytic activity of the entire MoS2 basal plane for the electrochemical H2 evolution reaction[1]. Besides versatile synthesis methods, TMC single-layer substrates with embedded heteroatoms also offer the benefit of site densities that are much higher than those reported previously in the literature for metal SACs on various substrates. Substitution of heteroatoms with different electronegativity as compared to the substituted chalcogenide atoms induces a local redistribution of the charge density. This can create a complex charge density landscape where ions can find their preferred sites for efficient adsorption and charge transfer[2]. The resulting active sites are of interest not only for their catalytic activity but also as anchoring sites for other metal atoms. cknowledgements: We thank National Science Foundation for KFIH OTKA grant K 132869, and Élvonal grant KKP 138144. References [1] Pet?, J., Ollár, T., Vancsó, P. et al. Nature Chemistry 10, 1246?1251 (2018). [2] Vancsó, P. et al ACS Energy Letters 2019, 4, 8, 1947?1953

Resume : The world energy consumption is mainly based on hydrocarbon fuels which are depleting, and the related carbon dioxide emission contributes greatly to global warming. Alternative clean energy sources are thus required for the development of sustainable environment and society. As a promising carbon-neutral fuel alternative, hydrogen energy has gained great interest over the past decades and clean and sustainable production of hydrogen is crucial for future hydrogen energy technologies. However, the transition toward this hydrogen technology is sluggish due to the challenge on the development of highly efficiency, environmental-friendly, and cost-effective energy materials. To tackle those challenges, new materials with engineered properties for various energy applications are required. Electrochemical energy technologies, including rechargeable metal?air batteries, regenerative fuel cells, and water splitting, have aroused a great interest as attractive alternatives for clean and efficient energy production. Water electrolysis by using sustainable electricity results in green hydrogen and it is the key process towards a circular economy. At present, only a small fraction of around 4% of hydrogen is produced by electrochemical water splitting. State-of-the-art catalysts are platinum (Pt) for the hydrogen gas production at cathode of water electrolyser and iridium (Ir) as well as ruthenium (Ru) oxides for the oxygen evolution reaction at anode. Despite the superior catalytic properties of such precious metal catalysts for water electrolysis, their poor stability, high cost, and scarcity make their commercial utilization both uneconomical and impractical. As such, cheaper yet high-performing earth-abundant materials, possessing high electrocatalytic activity, is paramount desirable. Amorphous metal boride prepared by chemical reduction of earth-abundant transition metals in aqueous media with sodium borohydride showed outstanding electrocatalytic properties in alkaline media. These materials are prepared by a simple approach but their electrocatalytic performance is superior to the state-of-the-art catalysts based on precious metals. By using this facile approach, highly active material have been developed and shows outstanding activity compared to state-of-the-art platinum and Ruthenium catalyst. In addition, this transition metal boride shows promising stability in harsh alkaline solutions. This work presents a facile approach for synthesizing active materials for water electrolysis and this approach can be extended to the synthesis of other earth-abundant materials for various applications in electrochemical energy conversion and storage technologies.

Resume : The message from the latest IPCC report released in April this year on the topic of climate change is clear: urgent action is needed if we are to limit global warming to 1.5°C and the current climate change we are experiencing is due to human induced emissions. Efforts to reduce our CO2 emissions are currently being put in place but there is no doubt that we need to speed up if want to achieve our targets. This presentation confirms that we are rightly obsessed with reducing our CO2 emissions, but we should not forget some other climate change ‘allies’. If want to achieve the carbon neutral energy transition, we will need to have access to sufficient materials and metals and this in a sustainable way (environmentally and socially). Moreover, the energy transition will require large amounts of pure clean water which is a second climate change ally that will be touched upon. By the end of the presentation, the audience should be convinced that CO2 should not only be seen as a problem but also as a resource. Therefore, we should show it our affection since we will lots of it to succeed in our energy transition.

Resume : Photoactive electrodes offer clean solutions to exploit the solar energy in different applications for a sustainable future, from energy conversion to synthesis of fuels and feedstocks. Achieving the full potential of these photoelectrodes depend on finding effective approaches for their synthesis and tuning that achieve the highest incident photon-to-current efficiencies. In this talk, I will present recent developments we have achieved in the preparation of inexpensive photoanodes for water oxidation, a bottleneck in the development of water-splitting solar devices. We have developed different photoanodes based on BiVO4 functionalized with bismuthene and NiFeOOH and other cocatalysts, as well as halide perovskite photoanodes protected with graphite layers. An extended characterization helps us relate their physical and charge-transfer properties to their performance, guiding us in their rational design for their optimization and future application. For example, we find that bismuthene effectively works as an interlayer between BiVO4 and NiFeOOH, energetically filling electron trap states for a better photoanode performance. We also demonstrate how carbon inks can be exploited to protect novel, doped halide perovskite photoanodes that translate the high efficiencies achieved in solar cells to photoelectrochemical devices.

Resume : Solar-driven photoelectrochemical water splitting can provide a sustainable source of hydrogen as a clean and renewable form of energy. Semiconductors employed in water-splitting photoanodes can have large rates of recombination which ultimately reduces the amount of oxygen evolved and limits the solar-to-hydrogen conversion efficiency. Ferroelectric materials possess a permanent internal electric field which has been shown to increase the lifetime of charge carriers by an order of magnitude and has the potential to reduce recombination in ferroelectric semiconductors1. Here, BaTiO3 is studied as a wide-bandgap ferroelectric semiconductor and the effect of enhancing the ferroelectric properties by a method of poling is explored. The impact of the ferroelectric field on photocurrent generation and charge carrier dynamics is examined using steady state and transient spectroscopic techniques. Comparing as-grown films with little ferroelectric alignment to poled films, an increase of photocurrent from 30 to 145 Acm-2 at 1.23 V vs RHE and an increase in IPCE from 3.5 to 34% at excitation wavelengths (325 nm) was observed after poling. Heating above the Curie temperature for BaTiO3 to remove the polarisation was also shown to decrease the photocurrent in a reversible process. Transient absorption spectroscopy measurements demonstrate that the lifetime of probed electrons increases from t50% from 0.1 ms to 4 ms after poling. Simultaneous transient photocurrent measurements show

Resume : Solar fuels present a cheaper, more direct mode of storage for solar energy compared to electricity from photovoltaics. One scheme to produce solar fuels is the photoelectrochemical (PEC) reduction of CO2 to one- or two-carbon fuels, where a semiconductor configured as an electrode performs both the light absorption and charge transport functionalities necessary to drive the reduction reaction. A potential semiconductor for this application is the p-type copper bismuth oxide (CuBi2O4) with 1) band gap capable of visible light absorption and 2) conduction band edge position suitable for CO2 reduction. In this study, CuBi2O4 photocathodes on FTO were prepared via an electrodeposition-spray deposition-annealing route. By varying the number of spray cycles, photocathodes with varying Cu/Bi ratio (0.28, 0.57, 1.01, 1.86, 2.24) were obtained. Where the ratio exceeded the stoichiometric value of 0.5, a nanoparticulate copper (II) oxide (CuO) phase on top of the CuBi2O4 layer was present, forming a planar heterojunction between the two oxide layers. With increasing Cu/Bi ratio, the optical band gap of the photocathodes shifted to lower wavelengths while the flatband potential shifted to a more negative value (vs RHE). Analysis of the photocurrent-potential behavior of the photocathodes under chopped visible-light illumination showed a ~4-fold increase in the photocurrent (at 0 V vs RHE, for the 1.86 film) from an inert electrolyte to a CO2-saturated electrolyte, confirming activity for CO2 reduction of the the CuBi2O4/CuO photoelectrodes. A further ~12-fold increase under an electrolyte with an electron scavenger revealed that the photocurrent is severely limited by a slow interfacial charge transfer kinetics presumably. The transient photocurrent response of the photocathodes showed a ~3-fold decrease in the photocurrent after 30 mins of testing. These results indicate that while the CuBi2O4/CuO films can achieve PEC CO2 reduction, corrosion is still the main concern in cell stability.

Resume : Here, we report synthesis of Ag2S nanostructures of zig-zag geometry to achieve the improved photoelectrochemical (PEC) water splitting response for hydrogen generation. A two-step process was utilized for the fabrication of working electrodes. The synthesis of zig-zag nanorods was carried out using glancing angle deposition followed by sulfurization. The PEC performance was studied by varying the number of zig-zag arms of Ag2S. The as-prepared four arm Ag2S zig-zag electrodes exhibited superior optical absorption, as well as photocurrent density of 3.04 mA/cm2 (at 1 V vs Ag/AgCl), compared to one arm Ag2S nanorods with minimum charge transfer resistance at the semiconducting electrode/electrolyte interface. The improved photocurrent density of four arm Ag2S zig-zag nanorods electrode was attributed to increased optical trapping and hence, effective absorption of light due to its wavy structure. The theoretical simulations based on rigorous coupled wave analysis were performed to understand the light absorption mechanism for the zig-zag Ag2S nanorods structures. This work provides a simple and effective approach towards the development of an efficient PEC electrode by tuning the morphology of nanostructured materials.

Resume : The recent energy crisis is unveiling, once more, the urgent and dramatic need for a swift transition from a fossil fuels to a renewable energy-driven economy. To this aim, the conversion of the extremely abundant solar energy into chemical energy, by means of artificial photosynthetic architectures, is increasingly seen as an essential step towards a sustainable carbon-neutral society. Semiconductor-based solar fuel production can be accomplished with a photoelectrochemical (PEC) device, which contains a direct-semiconductor/liquid interface to promote a specific redox reaction. The production of hydrogen through the photoinduced water splitting process has been a scientific dream for long, but its application is yet to be effective. The limits are mainly related to the slow kinetics of the oxygen evolution reaction, due to its multi-electron character. Since the aim of the process is mostly the production of hydrogen, an effective workaround might be to replace the conventional water oxidation path with the oxidation of an organic compound to a molecule of industrial or pharmaceutical value, in order to improve the overall added-value of the photocatalytic process. In this study, Ti-doped ?-Fe2O3 nanostructured thin films were employed as photoanodes to promote organic oxidation reactions. In particular, based on a previous experience on the PEC conversion of benzylamine to N-benzylidenebenzylamine by such nanostructures1, we developed an analogous process for the conversion of a biomasses derivative, 5-hydroxymethylfurfural (HMF), into furandicarboxylic acid (FDCA), an important monomer for polymeric materials such as poly (ethylene 2,5-furandicarboxylate) (PET). The use of an electron mediator such as 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) is essential to drive the catalytic process towards FDCA, increasing dramatically selectivity and conversion rate, while the faradaic efficiency is still limited by the competition with water oxidation reaction due to the aqueous environment. Following previous reports on BiVO4 photoanodes2, the addition of a thick CoPi layer, which typically ?bottlenecks? water oxidation kinetics3, produced efficient hole transfer to TEMPO due to favoured kinetics. Finally, operando analysis of the charge carrier dynamics at the basis of this enhancement was studied by Intensity Modulated Photocurrent Spectroscopy, implementing a data analysis algorithm based on distribution of relaxation times (DRT) analysis4, able to resolve the time-domain contribution of the hole transfer mechanisms. 1 R. Mazzaro, S. Boscolo Bibi, M. Natali, G. Bergamini, V. Morandi, P. Ceroni and A. Vomiero, Nano Energy, 2019, 61, 36?46. 2 D. J. Chadderdon, L. Wu, Z. A. McGraw, M. Panthani and W. Li, ChemElectroChem, 2019, 6, 3387?3392. 3 G. M. Carroll and D. R. Gamelin, J. Mater. Chem. A, 2016, 4, 2986?2994. 4 D. Klotz, D. S. Ellis, H. Dotan and A. Rothschild, Phys. Chem. Chem. Phys., 2016, 18, 23438?23457.

Resume : A continuously rising of carbon dioxide (CO2) concentration in the atmosphere have lead to an increase of greenhouse gas responsible for global warming. Reducing CO2 to various hydrocarbons and oxygenates provides a method of converting an industrial waste product into a feedstock. Among various methods, photoelectrochemical CO2 reduction (PEC-CO2RR) using semiconductors can be considered a realistic solution, since it addresses simultaneously the problems of CO2 emissions and renewable energy storage [1]. Silicon (Si) constitutes a photoelectrode material of choice due to its bandgap and mature processing technique. An extra advantage of Si is the possibility to elaborate well-defined 3D microstructure networks (i.e. Si Micropillars, SiMPs [2]), allowing: (i) enhanced surface contact area with the electrolyte vs. flat electrodes, (ii) improved carrier separation and collection and (iii) reduced surface defects vs Si nanostructures [3]. Decorating p-type SiMPs with metal nanoparticles (NPs) (such as Pt, Cu, Ag, and Au) may allows a better collection of photogenerated charge carriers without blocking light from reaching the semiconductor. In addition, it can provide a relatively high current density at low overpotentials for PEC-CO2RR, due to the metal catalytic effect. Despite their interest, till now only one work has dealt with the PEC-CO2RR on metal decorated SiMPs, as far as we know [4]. In the present work, we report on the synthesis of bimetallic AgxCu100-x nanoparticles (NPs) directly on plain p-Si and p-SiMPs and their application as photocathodes for PEC-CO2RR. A one-step electroless deposition is used, based on Si metal-assisted chemical etching (MACE). SEM-EDS and XRD analysis demonstrate a phase-separated Ag/Cu crystalline structure and a worm-like morphology distributed uniformly over a whole surface and even on the sidewalls of SiMPs as shown in Fig 1. Our first PEC experiments performed in CO2-saturated 0.5 M NaHCO3 display a positive shift in onset of 0.59 and 0.74 V, for flat p-Si/Ag50Cu50 and p-SiMPs/Ag50Cu50, respectively, after bimetallic deposition. The effect of pitch (P20, P50, and P100 µm) and height (H1 = 64 µm and H2 = 107 µm) shows that smaller pitch and longer height provides a sightly higher photocurrent values. CH4 and CO are identified as the main CO2 conversion gas products. An important Cu loss is however observed after photoelectrolysis. Current studies are oriented to minimize this loss and to gain insights into the energetics of the Si and SiMPs/bimetallic/electrolyte interface. [1]. J. He, et al., ACS Energy Lett. 2020, 5, 1996?2014. [2] E. L. Warren, et al., J. Phys. Chem. C 2014, 118, 747. [3] E. Torralba, et al., ACS Catal. 2015, 5, 6138. [4] N. S. Lewis, et al., ACS Energy Lett. 2020, 5, 2528.

Resume : To counter the threat of continuously dwindling energy resources and climate change, there is a need to steer the energy and chemical sectors away from a dependence on fossil fuels. Sustainable hydrogen provides an alternative but its generation demands the use of abundant catalyst materials and non-depletable energy sources. However, renewable energy sources such as solar, wind and wave energy are intermittent and fluctuating in nature. This requires energy conversion and storage infrastructure that are able to accommodate dynamic loads with variations spanning time scales of seconds to hours. Here, the effects of dynamic operation, typical of directly coupled photovoltaic electrolysis, on electro-catalyst performance for hydrogen generation by water splitting are discussed. Nickel-iron and nickel-molybdenum thin films were grown on various supports by electrodeposition as electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. The Ni-Fe and Ni-Mo catalyst depositions were scaled up from 1 cm² to 225 cm² and the catalyst activity is comparable to that reported in the literature for similar materials and largely unaffected by the deposition scale. Stability tests revealed that the OER catalyst was the most vulnerable to degradation, especially, in the absence of iron. To counter this effect, we adjusted the deposition conditions and were able to identify a catalyst that is stable under variable voltage levels. The catalysts were used to build a 3-stack liquid alkaline electrolyser reaching a capacity of 14 A (320 ml/min of hydrogen produced) at room temperature. Two such stacks were directly coupled to photovoltaic modules and operated for at least 700 hours each outdoors without significant reduction in the performance. The same catalysts have been incorporated in a smaller single cell anion exchange electrolyser that reaches a current density of 500 mA/cm² at 2.22 V at room temperature with reductions in the cell voltage expected with an improved cell design. Acknowledgements The contributions of various colleagues at HZB are appreciated. The author is grateful for financial support from the German Federal Ministry of Education and Research in the framework of the CatLab project (03EW0015A) and H2DEMO project (03SF0619A). Funding for PECSYS Project from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 735218 is also acknowledged. This Joint Undertaking receives support from the European Union?s Horizon 2020 Research and Innovation programme and Hydrogen Europe and N.ERGHY. The project started on the 1st of January 2017 with a duration of 48 months.

Resume : Ruthenium thin films are garnering interest as next-generation interconnects to replace Cu in future nanoelectronic devices. Especially in the back end of line (BEOL) and middle of line (MOL), ongoing scale down has motivated alternative metallization approaches such as semi-damascene in which Ru outperforms Cu and Co.[1,2] Beyond that, Ru catalysts are arousing significant attention in the context of electrocatalysis for the production of hydrogen through water splitting. This interest is based on their distinguished performance in the oxygen evolution reaction (OER), which is one of the half-reactions for hydrogen generation.[3] For thin film fabrication, chemical vapor-based techniques such as chemical vapor deposition (CVD) have been established as a most viable approach to deposit coatings of a plethora of material systems in thicknesses as low as sub-nanometers. A paramount factor in each CVD process is the choice of precursors and their chemistry that governs layer formation and material quality. A review of the current CVD processes for Ru shows that a considerable number of often closely related precursors with their individual advantages and drawbacks have been employed.[4] Hitherto, none of them could fully satisfy academic and industrial demands alike. This presentation introduces an alternative Ru precursor class, namely Ru diazadienyl cymenes [Ru(DAD)(Cym)] and underlines their potential for vapor deposition-based applications by the demonstration of a single source precursor (SSP) and ammonia assisted (NH3) CVD process. Ru thin films obtained by these two processes from the Ru(tBu2DAD)(Cym) precursor are subjected to complementary analyses including XRD, AFM, SEM, RBS, NRA as well as XPS. The NH3 assisted process is shown to produce Ru thin films with superior purity (< 90 at.%), and on SiO2 substrates 30 ? 35 nm thick Ru layers with resistivity values in the range of 12 ? 16 ?? cm (Ru bulk = 8 ?? cm) are successfully grown. This is in par with established Ru CVD processes relying on problematic, oxidative film growth chemistry. In a consecutive case study, CVD grown Ru thin films are subjected to catalysis assessment in the acidic OER. Promising performance of the layers is demonstrated with overpotentials as low as 240 mV and Tafel slopes of 45 ? 50 mV dec-1. The effect of the OER conditions on the layers is critically evaluated by a combination of XRD, XPS, SEM and TEM investigations. This proof of concept investigation supports the utilization of chemical vapor-based deposition processes for the synthesis or decoration of catalyst materials with thin layers of Ru. [1] G. Murdoch, et al., in 2020 IEEE IITC 1052020, p. 4. [2] https://www.imec-int.com/en/press/imec-presents-alternative-metals-advanced-interconnect-and-contact-schemes-path-2nm. [3] Y. Li, et al, Adv. Energy Mater. 2020, 10, 1903120. [4] https://www.atomiclimits.com/alddatabase/.

Resume : The CO2 reduction reaction (CO2RR) has shown promise for producing C1-based feedstocks, including formic acid, CO, and syngas at ambient conditions. A great challenge in this effort is product selectivity and tunability, which researchers have commonly addressed by combining different CO2RR-active metals, functionalising the surface, or optimising electrochemical reaction parameters. A synthetically simpler approach would use active sites from a single metallic species embedded in different coordination environments to tune product selectivity. For this aim, carbon-supported, nitrogen-coordinated metal single atom catalysts (SACs) are a promising class of electrocatalysts. Given their well-defined atomic structure and tunable coordination environment, these material systems are also valuable model systems for decoding reaction pathways and identifying favourable atomic arrangements. Within the same system, the coordination environment can be altered by varying synthesis conditions. Bismuth is well-known to be an efficient CO2RR catalyst, producing formic acid as major product in aqueous electrolyte. However, a recent report also revealed its efficiency for CO generation. It has been hypothesised that this differing CO2RR product selectivity may arise from different Bi coordination environments in the respective catalyst systems. Since these results stem from dissimilar systems, we aim to test this hypothesis on the same catalyst system to exclude other influences on selectivity. For a system of Bi SACs within a carbon-nitrogen framework, we can tune the CO2RR selectivity towards formic acid or syngas production by choosing tailored annealing treatments. Bismuth SACs anchored on commercially available carbon black (Bi@CB) were synthesized via a solution-based chemical method followed by inert atmosphere annealing. Corresponding X-ray diffraction patterns show no obvious crystalline metallic reflections. X-ray photoelectron spectroscopy, however, confirmed the presence of Bi metal along with lattice N, O, and C, where O and N are integrated into the carbon framework during the wet-chemical synthesis procedure. A single-atomic nature of Bi is indicated by both scanning transmission electron microscopy and corresponding energy-dispersive X-ray spectroscopy mapping. Depending on chosen synthesis parameters, Bi@CB shows different product selectivity: Low-temperature annealing (300 oC) promotes formic acid generation with a Faradaic efficiency of above 80 %, while high-temperature annealing (800 oC) favours syngas formation. Further atomic scale structural characterizations are currently underway to rationally verify whether this change in selectivity is truly caused by a changed coordination environment of the SACs. Since the versatility of a single CO2RR catalyst system to producing two different major products has rarely been reported, our work opens up a new direction of tuning the CO2RR C1 product selectivity using Bi SACs.

Resume : Electrochemical carbon dioxide (eCO2) reduction provides a promising route from greenhouse gas to fuels and feedstocks. However, the reduction mechanisms, especially in a flow cell system, are ambiguous. Most of the reported in-situ characterizations are established under non-real working condition, including lower current densities, different cell designs, or different flow rates of CO2 gas and electrolytes compared with real eCO2 performance testing. Here, we use proton transfer reaction-time of flight-mass spectrometry (PTR-TOF-MS) to perform real-time operando analysis of the products generated by high-current-density CO2 electrolysis under actual working conditions in GDE-based flow cells with Cu-based electrocatalysts. The high mass resolution, ppbv-level sensitivity, minimal fragmentation, sub-second response time, and multi-product detection ability of PTR-TOF-MS allow for tracing of C1-C4 minor and major intermediates and products, measurement of their 13C isotope composition, and identification of onset time.

Resume : Water electrolysis is expected to play a crucial role to the transition towards a hydrogen-based, low carbon economy. Among the various technologies for water electrolysis technologies, the one using proton exchange membranes (PEM) holds promise due to its high efficiency, load flexibility and compact design. However, the acidic environment in the PEM creates a harsh operating environment which entails the use of scarce and expensive metals (Pt and Ir) which account for 38% of the cost of a catalyst coated membrane (CCM). Moreover, the high scarcity of Ir is considered as the grand challenge of this technology. To relieve high raw material costs and to mitigate the Ir-dependence of PEM electrolysis, the development of advanced CCMs with improved Ir utilization is essential. Most of studies so far have focused on the development of high-structured catalysts, either by maximizing the Ir dispersion with using high surface area supports or by using alternative catalyst nanostructures. In all these conventional routes, the CCM manufacturing process is multi-step and primarily ink-based. Steps include ink preparation (from metallic nanoparticles), ink application onto the PEM to yield the catalyst-coated product, and several intermediate drying stages. The use of improved catalyst layer manufacturing techniques has been proposed as an alternative route to produce catalyst-coated membranes (CCMs) with low Ir loadings, without compromising in activity or durability. However, such concepts are less represented in literature. Despite this, the use of vapor-based processes for the manufacturing of nanomaterials for PEM electrolysers has key benefits over ink-based processes including the simplification of the production process, the reduction of catalyst loading, and the deposition of more uniform thin layers of material. In this work, we prepared CCMs using a solvent free, gas-phase method, comprising spark ablation and impaction, to produce iridium-based nanoparticles (IrNPs) for PEM water electrolysers. IrNPs were produced at ambient temperature and pressure conditions in the gas phase using Ir rods as the nanomaterial source. The nanoparticle aerosol was then directed towards a nozzle and deposited onto a Nafion 115 membrane via inertial impaction. The prepared CCMs were characterized using RBS, ICP, SEM, HR-TEM, XRD, and XPS. The Ir-based CCMs were employed in a single-cell PEM water electrolyser and complete performance assessment was performed at 60 °C, focusing both on activity and durability. Our results show that the CCMs prepared with spark ablation outperform the benchmark (commercial) CCM despite using considerably less Ir. Overall, our results showcase the feasibility of the spark ablation technology as a scalable and efficient method to achieve reduced Ir loading and better performing CCMs for PEM water electrolysis. Taking into account the simplicity of the process, this technology has also the potential to relieve the high CCM manufacturing costs of conventional approaches, which currently account for 42% of the total CCM cost.

Resume : To fulfill the ambitious targets towards a net-zero economy the electrocatalytic conversion of water or CO2 to H2, CO, syngas, formic acid, alcohols or even to more complex chemicals through the organic electrosynthesis will be among the key technologies. Although water electrolysis is already a mature technology, widely deployed mass production of green H2 through electrolysis is still limited due to its high costs associated with use of scarce catalyst materials and costly corrosion-resistant components or low conversion efficiencies. Similar shortcomings are seen for the still at an early-stage CO2 conversion in which product selectivity and low catalyst durability introduce even more challenges. Currently a major research focus is directed towards superior (nano)catalyst materials with significant less attention on the electrode architecture itself. Often, ill-defined electrodes with nano-catalysts mixed with ion-conducting polymeric-binders coated on membranes or porous electrodes are investigated, missing fundamental studies on simple well-defined model systems. Imec has an extensive know-how on nano-patterning, nano-structuring and surface-texturing by techniques such as nano-imprint lithography, lift-off and/or controlled vapor-phase grain growth, electrochemical anodization and plating of metals and metal-oxides. In this talk we show how this knowledge was exploited by fabricating nanopatterns of catalyst arrays and regular-ordered 3D-nanowire networks [1,2] as electrodes for water electrolysis and CO2 reduction. Regular nanopattern arrays with controlled pitch made by nano-imprint lithography & lift-off and surface-textured copper wafers served as model (metal) catalyst structures to study fundamentals of the CO2 reduction mechanism. The 3D-nanowire networks (so-called ?nanomeshes?) were applied as high-surface area electrodes to demonstrate high-throughput electrocatalysis. Freestanding porous nanomesh electrodes can be obtained by electrochemical metal plating in 3D-porous anodic aluminum oxide templates. Due to the high number of catalytic sites on nickel nanomeshes we see a pronounced shift towards lower HER and OER onset potentials in the alkaline environment. The nanomesh electrodes were tested in an alkaline membrane-electrode assembly in an electrolyzer up to 1A/cm2 and outperform commercial nickel foams. Electrocatalytic CO2 reduction was studied on copper nanomesh electrodes. CO and C2H4 were identified as major CO2RR products and a significant increase in the current density compared to planar copper-based electrodes was determined. [1] ACS Appl. Mater. Interfaces 10, 44634?44644 (2018) [2] J. Phys. Chem. C 119, 2105?2112 (2015)

Resume : Hydrogen is a clean alternative to carbon-based fuels, that can be produced in an environmentally friendly way via electrolysis of water. However, the sluggish oxygen evolution reaction (OER) kinetics at the anode are still a bottleneck since practical water electrolysers require operating cell voltages of 1.8 to 2 V at ~ 25°C, even though the thermodynamic voltage is 1.23 V vs. SHE. In this context, urea oxidation reaction (UOR) with a thermodynamic potential of 0.37 V vs. SHE is an interesting alternative anode reaction to OER [1, 2]. Thus, the energy requirement for H2 production by conventional water electrolysis can potentially be reduced by up to 70 % with a urea electrolyser. Moreover, by using waste water containing urea from organisms and by-products of industrial activities, simultaneous water treatment during electrolysis is possible. So far, nickel, its alloys and other noble metals have been reported as electrocatalysts for UOR [3, 4, 5]. In this work, Nickel-Copper (Ni-Cu) alloy is studied for low temperature UOR in alkaline medium. By varying the electrolyte composition for electrodeposition, we achieved the highest catalytic activity with a Ni:Cu ratio of 2:1 in solution. The catalytic onset potential of the best NiCu alloy proceeded at 1.22 V vs. RHE (0.33 V vs. Hg/HgO) when 0.33 M urea was added to the 1.0 M KOH electrolyte, proving significant urea electrooxidation at room temperature. The oxygen evolution due to water electrolysis of KOH for the same NiCu alloy occurred at 0.6 V vs. Hg/HgO. The overpotential required for a geometric current density of 50 mA/cm² at room temperature was 0.43 V and 0.65 V (vs. Hg/HgO) for UOR and OER, respectively. Using solutions to which either Fe or Fe(CN)6 were added to the Ni precursor instead of Cu, for electrodeposition of the electrocatalyst, increased the onset potential of UOR to 0.37 V or 0.40 V vs Hg/HgO respectively. Since the element Fe and its compounds are well-known for O2 evolution catalyst, the addition of Fe or Fe(CN)6 reduced the OER onset potential to 1.4 V vs. RHE (0.5 V vs. Hg/HgO, less negative than NiCu) which correspondingly reduced the current density of UOR. Tafel plot investigations and electrochemical impedance studies shall be used to understand the mechanisms of UOR process. Also demonstration of hydrogen generation using UOR as at the anode under dynamic conditions shall be presented and implications for catalyst stability shall be discussed. References: 1. Boggs, B.K., Chem Commun, 2009, 4859-4861. 2. Yue, Z. H., et al., Electrochim Acta, 2018, 268, 211-217. 3. Vedharathinam, V; Botte GG., Electrochim Acta, 2012, 81, 292–300. 4. Sun, X., et al., Catal Sci Technol 2020, 10, 1567–1581. 5. Ye, K., et al., In: Shao, M. (eds) Electrocatalysis. Topics in Current Chemistry Collections Springer, Cham 2020, 41-79. DOI: 10.1007/978-3-030-43294-2_2.

Resume : With the need to reduce global CO2 emissions, significant interest has been dedicated to the electrochemical reduction of CO2 to more valuable products such as carbon monoxide, methane, formic acid, or C?C bonded hydrocarbons. The electroreduction of CO2 using traditional heterogeneous catalysts often faces significant challenges, namely high overpotentials and a suboptimal selectivity towards the desired products. These challenges can be overcome by the use of enzymes such as carbon monoxide dehydrogenases (CODH), which have been shown to catalyze the reduction of CO2 to CO at minimal overpotentials. The implementation of CODH enzymes in electrocatalysis, however, relies on their immobilization on appropriately structured electrodes of high surface area. We present the preparation of micro- and nanostructured electrodes by electrospinning of polyacrylonitrile fiber mats. After a carbonization step in inert atmosphere, a homogeneous, electrically conductive mat is obtained with tunable geometric parameters including fiber diameter, porosity, and total mat thickness. We subsequently modify the surface chemistry of these fibers by coating them with different conductive semiconductors by atomic layer deposition (ALD). ALD is a chemical vapor deposition process defined by repetitive self-limiting surface reactions and uniquely suited to the conformal coating of complex geometries such as the fiber mats considered here. Finally, the electrodes are functionalized with extracts containing different recombinant CODHs, the CO2 reduction activity of which can be verified and quantified in a preliminary step using a colorimetric assay. Under anaerobic conditions, electrolysis is carried out in aqueous electrolytes containing a redox mediator, which enables electron transfer. The electrolysis product carbon monoxide is detected and quantified selectively in the electrolytic solution using low-energy ionization mass spectrometry.

Resume : Of the many metals studied for electrochemical CO2 reduction (CO2RR), copper is the only one known to produce C2-products making it preferred. Since the early work of Hori et al., potassium phosphate buffers have been studied as electrolytes for CO2RR.1 Beyond being key for elucidating CO2RR mechanisms, the interaction between the electrolyte and copper must be understood to ensure long-term stability. It is known that under oxidizing conditions, copper dissolves from the electrode.2 Using electrochemical on-line inductively coupled plasma mass spectrometer, Speck et al. found a peak Cu dissolution at 0.5VRHE which they attribute to oxidation to CuI followed by a second more intense peak at 0.78V RHE for CuII.2 This phenomenon is used to create roughened electrode surfaces, i.e. a anodization step followed by redeposition under cathodic conditions. In addition to being dependent on the pH, the Cu-dissolution in the phosphate buffer is reportedly influenced by the amount of dissolved inorganic carbon warranting more research.3 Model systems based on high purity Cu-films (180 nm) deposited using PVD on Si-wafers, allows the precise monitoring of the dissolution rate. The interaction with fresh electrolyte and after purging with CO2 or argon will be studied. Based on x-ray fluorescence, after 5 h in 0.5 M fresh phosphate buffer the Cu-layer had thinned to 100.0±1.4. while after both argon and CO2 purging the rate was significantly lower (163.0±4.2 nm for CO2 and 160.0±7.0 for argon). This finding already indicates that, like in DI water, dissolved oxygen facilitates the Cu-dissolution reaction.2,4 To correlate dissolution trends to differences in crystal plane surface structure energies and coordination, both (111) and (200) oriented films will be examined.5 Controlling Cu-dissolution during inevitable periods at open circuit is critical. Not only could it result in the misinterpretation of ex situ determined morphological changes, but preferential dissolution of certain facets would change product selectivity.2,6 1. Hori, Y., Murata, A. & Takahashi, R. Formation of hydrocarbons in the electrochemical reduction of carbon dioxide at a copper electrode in aqueous solution. Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases 85, 2309?2326 (1989). 2. Speck, F. D. & Cherevko, S. Electrochemical copper dissolution: A benchmark for stable CO2 reduction on copper electrocatalysts. Electrochemistry Communications 115, (2020). 3. Dartmann, J., Sadlowsky, B., Dorsch, T. & Johannsen, K. Copper corrosion in drinking water systems - Effect of pH and phosphate-dosage. Materials and Corrosion 61, 189?198 (2010). 4. Gambino, J. et al. Etching of copper in deionized water rinse. in Proceedings of the International Symposium on the Physical and Failure Analysis of Integrated Circuits, IPFA (2008). doi:10.1109/IPFA.2008.4588209. 5. Sandbeck, D. J. S. et al. Dissolution of Platinum Single Crystals in Acidic Medium. ChemPhysChem 20, 2997?3003 (2019). 6. Hochfilzer, D. et al. The Importance of Potential Control for Accurate Studies of Electrochemical CO Reduction. ACS Energy Letters 6, 1879?1885 (2021).

Resume : Water splitting using electrochemical reactions is an attractive technique for clean, efficient energy conversion and storage, but requires a highly efficient non-precious metal electrocatalyst to reduce wide overpotentials. Among them, the development of high-efficiency oxygen evolution reaction (OER) catalyst is very important because the OER has a higher kinetic barrier than the hydrogen evolution reaction. Here, we rationally designed the K-doped NiCo2O4 (NCO) catalyst derived from the metal organic framework structure of prussian blue analogue (PBA) and demonstrated it as a high-performance OER electrode. We controlled the doping concentration of K through a simple hydrothermal synthesis method using the K precursor present in the PBA. The synthesized K-doped NCO catalyst showed the increased active oxygen vacancies and the higher conductivity. The cyclic voltammetry (CV) scan of the K-doped NCO catalyst showed a low overpotential value of 0.292 V at a current density of 10 mA cm-2 and a Tafel value of 49.9 mV dec-1, outperforming a commercial OER catalyst (Ir). The synthesized K-doped NCO can be utilized as high performance electrode materials for metal-oxide batteries and supercapacitors.

Resume : Photoelectrochemical (PEC) water splitting is an alternative to fossil fuel combustion involving the generation of renewable hydrogen without environmental pollution or greenhouse gas emissions. Cuprous oxide (Cu2O) is a promising semiconducting material for the simple reduction of hydrogen from water, in which the conduction band edge is slightly negative compared to the water reduction potential. However, the solar-to-hydrogen conversion efficiency of Cu2O is lower than the theoretical value due to a short carrier-diffusion length under the effective light absorption depth. Thus, increasing light absorption in the electrode?electrolyte interfacial layer of a Cu2O photoelectrode can enhance PEC performance. In this study, a Cu2O 3D photoelectrode comprised of pyramid arrays was fabricated using a two-step method involving direct-ink-writing of graphene structures. This was followed by the electrodeposition of a Cu current-collecting layer and a p?n homojunction Cu2O photocatalyst layer onto the printed structures. The performance for PEC water splitting was enhanced by increasing the total light absorption area (Aa) of the photoelectrode via controlling the electrode topography. The 3D photoelectrode (Aa = 3.2 cm2) printed on the substrate area of 1.0 cm2 exhibited a photocurrent (Iph) of ?3.01 mA at 0.02 V (vs. RHE), which is approximately three times higher than that of a planar photoelectrode with an Aa = 1.0 cm2 (Iph = ?0.91 mA). Our 3D printing strategy provides a flexible approach for the design and the fabrication of highly efficient PEC photoelectrodes.

Resume : Valorisation of biomass to fuel/chemicals will be one of the main routes for the reduction of carbon emissions [1]. Electrocatalytic reduction of biomass-derived feedstocks represents a good alternative to the classic reductive valorisation processes carried out via thermal hydrogenation processes. Electrocatalytic hydrogenation can bypass the problem of activating H2, thanks to in situ generation of Hads from protons/water. Furthermore, it eliminates the need for using H2 at high purity and pressure, thus lowering operational costs. However, electrochemical processes require the design of electrocatalyst materials capable of achieving high efficiency, high selectivity and, in the case of biomass processing, also display high tolerance to complex feeds and impurities. [2] Here, we report on the design and synthesis of carbon-based electrode materials based on heteroatom-doped carbons for the reduction of unsaturated organic substrates. A hydrothermal method was developed for the synthesis of porous materials containing nitrogen functionalities and non-precious metal encapsulated nanoparticles (M@C). A nanocarbon scaffold was included in the synthesis to ensure high conductivity while a soft polymeric template was used to develop porosity. A combination of structural and spectroscopic methods was used to characterise the M@C composite materials, including X-ray photoelectron spectroscopy, X-ray crystallography, scanning electron microscopy and thermogravimetric analysis. Voltammetry and potential step experiments were used to investigate the efficiency and selectivity of organic hydrogenations achieved with these materials. Finally, we discuss the potential of these carbon-based nanocomposite materials as electrocatalysts for transformations of unsaturated organics. [1] Du, L.; Shao, Y.; Sun, J.; Yin, G.; Du, C.; Wang, Y., Electrocatalytic valorisation of biomass derived chemicals. Catal Sci Technol 2018, 8 (13), 3216-3232. [2] Weber, R. S., Effective Use of Renewable Electricity for Making Renewable Fuels and Chemicals. ACS Catal. 2019, 9 (2), 946-950.

Resume : Herein, CuO/NiO/ZrO2 (CNZr) composites exhibiting superior photocatalytic and electrocatalytic water reduction activities were calcined at various temperatures and synthesized through a hydrothermal route. The CNZr600 composite had an H2 production rate (14.27 mmol g?1 h?1) advanced than that of CNZr400 and CNZr500 under stimulated solar light irradiation. The prepared mixed metal oxide composites (CNZr600/NF) with fine-tuned electronic structures and multiple integrated active sites exhibited small overpotentials of 218, 400 mV for HER & OER at 10 mA cm-2 in 1.0 M KOH medium. A fully self-assembled water splitter using these electrodes as anode and cathode attains a current density (10 mA cm-2) at a cell voltage as low as 1.79 V. This finding may open new possibilities of designing bifunctional electrocatalysts for practical electrolysis of water. The exceptional morphology (confirmed using TEM, SAED, and energy dispersive X-ray analyses), meaningfully improved charge carrier separation, and synergistic effects of the mixed metal oxide composite system should be accountable for the outstanding catalytic activity. These outcomes suggest a new unexplored path for the production of extremely active and low-cost catalyst for practical H2 production.

Resume : Direct seawater electrolysis is proposed to be a potential low-cost approach to green hydrogen production, taking advantage of the vastly available seawater and large-scale offshore renewable energy being deployed. However, developing efficient, earth-abundant electrocatalysts that can survive under harsh corrosive conditions for long time is still a significant technical challenge. In this presentation, we report the fabrication of self-supported nickel-iron phosphosulfide (NiFeSP) nanotube array electrode through a two-step sulfurization/phosphorization approach [1]. Advanced transmission electron microscopy and X-ray absorption spectroscopy characterization confirmed that the NiFeSP nanotubes are enriched with NiFeS/NiFeP heterointerfaces and under-coordinated metal sites. Thus-fabricated electrode combines several merits including multiple metal/non-metal components, 3D hierarchical architecture, and abundant heterointerfaces and under-coordinated active sites, which can work in synergy boosting the electrocatalytic performance, with an overpotential of 380 (for HER) and 260 mV (for OER) at a large current density of 500 mA cm-2 and outstanding durability of 1000 hours in simulated alkaline-seawater solution (KOH + NaCl). Theoretical calculations demonstrate that the heterointerface and under-coordinated metal sites synergistically lower the energy barrier to the rate-determining step of reactions, rationally explaining the experimentally observed outstanding performance. The NiFeSP electrode also shows good catalytic performance for the urea oxidation reaction (UOR). By coupling UOR with HER, the bifunctional NiFeSP electrode pair can efficiently catalyze the overall urea-mediated alkaline-saline water electrolysis at 500 mA cm-2 under 1.938 V for 1000 hours without notable performance degradation, showing significant potential for energy-saving production of green hydrogen. This work provides an effective strategy for the design and synthesis of highly-active and stable catalytic electrodes for saline water electrolysis, which will find applications in massive production of low-cost renewable hydrogen. Reference: [1] Z. P. Yu, Y. F. Li, V. M. Diaconescu, L. Simonelli, J. Ruiz, I. Amorim, A. Araujo, L. J. Meng, J. L. Faria and L. F. Liu*, Highly efficient and stable saline water electrolysis enabled by self-supported nickel-iron phosphosulfide nanotubes with heterointerfaces and under-coordinated metal active sites, Advanced Functional Materials (Under review).

Resume : Since the discovery by Kroto et al. of buckminsterfullerene C60 and the first use of its derivatives as an electron acceptor in bulk heterojunction polymer:fullerene solar cells, a great number of new fullerene materials have been proposed to date in search of the most affordable photon-to-electron conversion. But it is well known that fullerene basically collect and transport the electrons formed by the dissociation of excitons primarily generated along the donor phase. And the fullerene-based acceptor materials, suffer from a photo-degradation due to the charge carrier trapping under illumination. One of the way to deal with problems with recombination and photodecomposition could be replacing the blend form of polymer-fullerene material with a layer formed by electropolymerization or electrocopolymerization of both components. It could be straight way to obtain a thin conducting layer with fullerene, with good conductivity and controllable thickness. In this work we have studied a some groups of new C60 and C70 derivatives. The main aim was to check the influence of substituent for electropolymeryzation and alignment of orbital energies. The first group of derivatives was pyrene-fullerene systems. It was interesting because of their planar aromatic hydrocarbon fused rings which made them especially attractive candidates for numerous applications. The second group was analogous to the first one, but in the place or pirydine rings, there was a thiophene rings. It was expected that the presence of this substituent will improve the electropolymerization process, to cover the whole surface with fullerens. In each group, three C60 ([C60]P1, [C60]B1, [C60]B2) and corresponding three C70 fullerene derivatives ([C70]P1, [C70]B1, [C70]B2) were synthesized using Prato and Bingel procedures. All of them was characterized by electrochemical methods. Part of these derivatives undergo electropolymerization reactions with themselves or electrocopolymeryzation with another monomers. The influence of the size of fullerene and of the type of a linker between fullerene and substituent was examined. The HOMO and LUMO energies as well as band gap energies determined from cyclic voltammograms, were correlated with the theoretical data (obtained by DFT calculations) and spectrophotometric results.

Resume : Oxygen evolution reaction plays important role in water split process, as it is inevitable for reduction of hydrogen from aqueous solutions. Usage of effective catalysts improves kinetics of oxygen evolution reaction and allows exploitation of solar light energy for improving energetic efficiency of hydrogen fuel production. Layers consisting of tungsten and iron oxides are promising materials as OER photocatalysts[1]. Two step procedure of preparation of semi-transparent layers based on tungsten and iron oxides was proposed. In the first step, tungsten alloy layer was electrodeposited, and then it was transformed into oxides layers by annealing in oxygen atmosphere. For this purpose several novel alloys of tungsten were proposed, especially W-Fe-Zn and W-Fe-Cu, to be formed by electrodeposition from tungstate-citrate galvanic baths[2] on FTO. The method leads to formation of well adherent, mechanically and chemically stable catalytic film of transition metal oxides attached to conductive and transparent substrate. Usage of the galvanostatic method for formation of the layer precursors enables to fully control the film thickness, while modulating contents of metal precursors in the galvanic bath allows to control the final composition of the catalyst layer. Optimal conditions for obtaining the layers were studied, including plating bath composition, temperature and current density of electrodeposition, as well as duration and temperature of thermal modification of the material. At high electrode potentials, photocurrent measured on W-Fe-Zn layers do exceed that observed for WO3 layers made by sol-gel deposition. Proposed method of obtaining selected photocatalytic layers containing transition metal oxides is advantageous due to its simplicity and inexpensiveness in comparison to methods based on vapor deposition, and simultaneously due to precise control of layer thickness in comparison to other methods. [1] Solarska R. et al., Nanoporous WO3?Fe2O3 films; structural and photo-electrochemical characterization, Functional Materials Letters, 7(06), 1440006 [2] Tsyntsaru N. et al. Modern trends in tungsten alloy electrodeposition with iron group metals, Surface Engineering and Applied Electrochemistry 48(6):491?520

Resume : The metal oxide semiconductor copper (I) oxide has attracted attention for its unique optical and electrochemical properties, which have led to a variety of applications, including photocatalysis, gas sensors, solar cells, and water splitting. Thin film formation is necessary for actual application, and the electrodeposition has been studied as one of the methods. We have established electrodeposition of inorganic semiconductor /organic dye hybrid thin films. Recent work has been accomplished in the electrodeposition of copper (I) thiocyanate/Neutral Red hybrid thin films, which show CO2RR catalytic activity through concerted functional enhancement. In this study, we examined the electrodeposition of copper (I) oxide using organic dyes and the properties of the obtained thin films. Potentiostatic electrolysis at an F-doped SnO2 (FTO) coated glass rotating disk electrode (RDE, ? = 500 rpm) was carried out at -350mV (vs. Ag/AgCl) in an nitrogen-saturated aqueous electrolyte (60ºC) containing 10 mM Copper sulfate pentahydrate,75 mM lactic acid, 1.4M sodium hydroxide and 1?M methylene blue (MB) for 5min. In electrodeposition of copper (I) oxide, a concentrated solution is generally used to achieve a sufficient deposition rate, but in this experiment, electrodeposition was achieved in a dilute solution by controlling the diffusion of the active species using a rotating electrode. Potentiostatic electrolysis at -350mV vs. Ag/AgCl, where the diffusion-limiting current is observed, resulted in the deposition of an orange thin film. The XRD pattern of the deposited film showed a peak of copper suboxide, indicating successful electrolytic deposition of copper (I) oxide. When MB was added to the copper (I) oxide electrodeposition bath, orange thin films were obtained as well. The absorption spectrum of the thin film also showed no MV-derived absorption peaks, indicating that hybridization did not occur.Since copper (I) oxide exhibits p-type semiconductivity due to copper vacancies, we thought that cationic dyes would be introduced by substitution. On the other hand, it has been reported that the cathodic electrodeposited copper (I) oxide is often n-type semiconducting, so we will investigate the conditions for complexation with various types of organic molecules, including anionic dyes.

Resume : Solar-driven water splitting for hydrogen production could become a crucial technology in future sustainable energy scenarios. Photoelectrochemical (PEC) water splitting, which combines solar energy harvesting and water electrolysis in a single process, is a promising option that has the potential to be cost-effective. PEC photoelectrodes should simultaneously satisfy many requirements for efficient hydrogen production, such as light-harvesting, fast charge separation, efficient catalysis, low cost and high stability. Thus research efforts in the field are mainly focused on material optimization and/or discovery to create almost exclusively thin film photoelectrodes. Our group efforts are mainly directed on a parallel direction, i.e. what kind of cell design should be used for scaling up the concept as materials breakthroughs are achieved. In this direction, the inspiration for our device design is based on the well-established polymeric electrolyte membrane (PEM) electrolyzers. Their design has several advantages with the most important to be the efficient product separation, the scalability and the minimization of the ohmic losses due to the zero-gap design. The latter means that the electrodes are in direct contact with the polymeric electrolyte and thus allowing a very short distance for the ionic transfer. Due to the zero-gap design porous photoelectrodes are necessary to allow gas flow. Thus our early efforts on PEM-PEC were focused on the development of alternative fabrication techniques to go from thin film to porous photoelectrodes (including materials such as TiO2, WO3, BiVO4) and their implementation on proton-conducting polymeric electrolytes. In this work, we are utilizing anion exchange polymeric membranes as the basis for the development of PEM-PEC cells based on abundant materials and state-of-the-art photoabsorbers to allow bias-free operation. In particular, W-doped BiVO4 porous photoanodes are developed on porous conductive substrates using the SILAR (successive ionic layer adsorption and reaction) approach. This method is selected due to its simplicity, cost-effectiveness and scalability. To improve activity and stability we modified the BiVO4 photoanode surface by decorating it with a boron-treated ultrathin FeOOH/NiOOH layer using a simple pH-modulated immersion approach. The resulting photoanodes in combination with commercially purchased Ni cathodes have achieved current densities > 1.5 mA cm-2 with over 100 h photostability in the anion exchange PEM-PEC set-up. Additionally, to enable bias-free operation a Si PV cell was integrated. Overall, this research permits the practical achievable solar-hydrogen device with cheap, earth-abundant and non-toxic electrodes.

Resume : Finding a material with all the desired properties for a photocatalytic water splitter is a challenge yet to be overcome, requiring both a surface with ideal energetics for all steps in the Hydrogen and Oxygen evolution reactions (HER and OER) and a bulk band gap large enough to mediate said steps. We want to develop a process to separate these challenges by separating the surface adsorption properties from the bulk light absorption properties. We aim to do this by investigating the energetic properties of two-dimensional transition metal dichalcogenides (TMDCs) that have been theorised to be good candidates for water splitting catalysts [1,2], and could be used as a surface coating to a material with a large enough bulk band gap. 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 these adsorptions under standard conditions. The absorption properties of the Hetero-bilayer has been investigated to determine how suitable it is for water splitting in the regard, and band edge positions have been calculated to determine if the charge carriers are driven towards the surface. 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 : Solid-state photoelectrochemical (SSPEC) cells enable the production of dry hydrogen gas (H2) directly through the photoelectrolysis of water vapor. Moreover, they introduce a safe way to utilize toxic, yet efficient photocatalysts such as CdS. Here, polyol made CdS and CdSe crystalline nanoparticles (NPs) are loaded on TiO2 nanotube arrays (TNTAs) for solar-simulated light driven photoelectrochemical (PEC) water vapor splitting and dry H2 production. The principle of operation of a SSPEC cell is the surface protonic conduction mechanism on TiO2 due to adsorbed water molecules on its surface. In combination with polymeric electrolytes, such as Nafion instead of liquid ones, gaseous reactants, like water vapor from ambient humidity can be utilized. Here, we study the effects of the operating conditions in gaseous ambient atmospheres (80%, 40% and 0% relative humidity (RH) at room temperature) and the surface modifications of TNTAs based photoanodes with well-crystallized CdX NPs (CdS or CdSe). The latter show 3.6 and 2.5 times increase in the photocurrent density of defective TNTAs modified with CdS and CdSe, respectively, when compared to the pristine TNTAs. Electrochemical impedance spectroscopy and structural characterizations elucidate that the improved performance is due to the higher electronic conductivity, as well as to the enhanced charge carrier separation at the TiO2/CdX heterojunction under gaseous operating conditions. More importantly, we evaluate the PEC activity of the SSPEC cells by cycling between high RH (80%) and low RH levels (40%), directly evidencing the effect of RH and, in turn, adsorbed water, on the cell performance. Online mass spectrometry indicates the expected difference in dry H2 production rate (halved) corresponding perfectly with the amount of water vapor (80% vs 40% RH). Moreover, a complete restoration of the SSPEC cell performance from low to high RH levels is achieved and the activity in the high RH case is comparable with operation of the TNTAs/CdX in liquid electrolytes (0.5 M Na2SO4). Such SSPEC cells can play a central role in off-grid, water depleted, and air-polluted areas for the production of hydrogen from renewable energy and provides a solution for the safe use of toxic, yet efficient photocatalysts.

Resume : With the harsh consequences that fossil fuels pose to the environment, there is a significant shift in both research and industrial communities towards green and renewable fuels, reducing the carbon footprint. With the diurnal nature of renewable energy resources (i.e. sun and wind), there is an inherent mismatch between the energy supply and demand. Therefore, the necessity of efficient energy storage is crucial to cover the uninterrupted supply, especially during peak hours. Energy can be stored in different ways ranging from flywheels and supercapacitors to storage in chemical bonds namely in batteries and hydrogen. However, the batteries are lacking behind hydrogen in terms of energy density to weight ratio. And this is why hydrogen is considered the most promising energy vector in the near to long future. Green hydrogen is obtained from water electrolysis which can also be solar light assisted to yield the photoelectrochemical (PEC) water splitting. The classical PEC approach with photoabsorber electrodes has been studied since the 1970s but the efficiency and cost limit its practical widespread implementation. Furthermore, the demand for high purity water for solar-driven electrolysis in arid areas around the world is substantial. The viable solution to this would be a combination of the solar-driven water splitting with the water absorption only from ambient humidity. Here, in this work, we demonstrate solar-driven hydrogen production by harvesting water obtained from air humidity. To reach this objective, we have developed and functionalized porous WO3 photoanodes with Aquivion® ionomer coating. This functionalization has a dual role (i) allowing water absorption from the ambient and transferring it to the active sites for water oxidation reaction and (ii) promoting the proton transfer between the photoanode and the polymer electrolyte membrane (PEM) to the cathode for the hydrogen evolution reaction. By introducing an alternative functionalized membrane photoelectrode assemblies (MPEA) architecture, we are able (under simulated LED illumination) to validate the concept of making hydrogen out of thin air at photocurrent density ~ 8 mA cm-2 that is required to achieve the 10% solar to hydrogen efficiency (STH) goal of PEC field. Further, we demonstrate 90% of performance in ambient humidity compared to liquid operation, the highest reported so far. The functionalized PEM-PEC reactor demonstrated herein is expected to be instrumental for future stand-alone devices that could deliver hydrogen for a decentralized hydrogen economy.

Resume : BiVO4 is a perspective semiconductor photocatalyst used for water oxidation and degradation of organic water pollutants [1]. However, the exact positions of the conduction and valence band edges of BiVO4 is still a matter of controversy in the literature, and therefore quite different mechanisms of the photocatalytic processes are proposed. Therefore, the aim of this work was to shed more light on the mechanism of photocatalytic and photoelectrocatalytic processes at the surface of BiVO4 in aqueous solutions and clarify the exact role of hydroxyl radicals, superoxide anion radicals and photogenerated holes in the degradation of the organic pollutant (such as caffeine; CAF). The obtained results were confronted with the literature data. The second goal of this work was to determine the influence of the surface modification of BiVO4 with a cobalt phosphate (Co-Pi) co-catalyst, on the rate of CAF photodegradation [2]. The photodegradation rate constant of caffeine, used as a model compound, was improved 2.2 times by deposition of Co-Pi co-catalyst on the surface of the semiconductor. The presence of Co-Pi resulted in the increase of the electron life-time and suppression of the electron-hole recombination. The 26-fold increase of the degradation rate constant was achieved by application of an external potential of 0.6 V vs Ag/AgCl to the BiVO4 electrode and the mechanism of photoelectrocatalytic process is proposed. BiVO4 was also combined with graphitic carbon nitrate (g-C3N4) to obtain better separation of photogenerated e-h pairs [3]. [1] Y. Park, K.J. McDonald, K.-S. Choi, Progress in bismuth vanadate photoanodes for use in solar water oxidation, Chem. Soc. Rev. 42 (2013) 2321?2337. doi:10.1039/C2CS35260E. [2] T.??cki, H. Hamad, K. Zar?bska, E. Kwiatkowska, M. Skompska publication under review. [3] V. Rathi, A. Panneerselvam, R. Sathiyapriya, A novel hydrothermal induced BiVO4/g-C3N4 heterojunctions visible-light photocatalyst for effective elimination of aqueous organic pollutants, Vacuum. 180 (2020) 109458. doi:10.1016/j.vacuum.2020.109458.

Resume : Photoelectrochemical (PEC) reactions provide means of splitting water into H2 and O2, and of converting CO2. Both hydrogen and CCU (carbon capture and utilization) are considered to hold high potential for decarbonization and the energy transition towards renewables. However, new materials compositions and morphologies are sought for, in order to boost the efficiency of the photoelectrochemical process. In order to obtain such new materials, synthesis routes which allow versatile compositions are needed. After a brief introduction into aqueous solution gel, covering its advantages and limitations to the synthesis of metal oxides, its application to PEC oxide materials will be shown in this presentation. The synthesis of metal oxides is carried out by means of an aqueous solution-gel route, which uses simple chemical operations in ambient air. This route has been developed in the group over the past 2 decades, which by now, enables us to synthesize precursors for all the relevant metal ions in the periodic system. After optimization the precursors can be mixed at will, to allow combinations of several metal ions in any desired stoichiometry. After drying, decomposition, and crystallization at elevated temperatures in air, the precursors are transformed into metal oxide powders. Besides, the precursors can also be spin-coated, spray-coated or dip-coated to create thin films on various substrates. Several metal oxides were selected because of their interesting properties as photoelectrodes for PEC devices: e.g. copper based oxides including copper bismuth oxide or copper iron oxides besides bismuth tungsten oxide. The precursors are synthesized, their structure is assessed and their transformation into the oxide is investigated as well. Optimization of the crystallization temperature leads to improved phase purity and morphology. Furthermore, the optical characteristics are reported(including optical absorption and Mott-Schottky analysis of the charge carrier transport. Finally photocurrent measurements are employed to demonstrate the material?s activity. This demonstrates the synthesis route?s versatility for photoelectrode fabrication. With the first materials having been tested, the road now lies open towards the fabrication of dual absorber devices, other materials compositions as well as other morphologies. The authors acknowledge financial support by the Flemish Research Foundation (FWO, project number G053519N), by SYNCAT, a Flemish cSBO Catalisti MOT3 Moonshot project, and the Federal government within the ETF project BeHyFE.

Resume : Semiconductor materials used in photoelectrochemical applications have often poor stability under operating conditions. One strategy implemented in recent years for corrosion protection of photoelectrodes is the application of thin films of titanium dioxide (TiO2), coated by Atomic Layer Deposition (ALD). However, the stability of these coatings in photoelectrochemical conditions is also limited. We are using spectroscopic ellipsometry (SE) and in-situ atomic force microscope (AFM) characterization[1, 2] in order to quantify the influence of operational parameters on the degradation of these layers. Here we show our recent investigations under anodic operation in acidic environment. For fully amorphous TiO2 layers, a significant contributor to the corrosion is a purely chemical process, with an activation energy of 57 kJ/mol. Furthermore, the degradation rate doubles upon illumination under simulated sunlight. At increasing pH the stability increases significantly. For operation in sulfuric acid, further passivation can be achieved in partially crystalline protection layers. References: [1] Kriegel H. et al. J. Mater. Chem. A, 2020, 8, 18173. [2] Raudsepp R. et al. (in preparation).

Resume : An innovative 2D MAX structure comprising of Ti3AlC2 multilayers and copper oxide (CuO)/nickel oxide (NiO) (CN) composite was fabricated via a facile chemical route for improving photocatalytic hydrogen evolution activity. The physicochemical properties of the synthesized nanocomposites were analysed through various structural, morphological, and elemental techniques. The 2D Ti3AlC2/CuO/NiO composite showed a maximum H2 generation rate of 20.7 mmol g-1 h-1, which is greater than that of the CN nanocomposite. This improved activity can be attributed to the presence of Ti3AlC2 multilayers on CuO/NiO, which showed excellent photoinduced charge carrier separation. As an electron-bridge, CN NC can support the photoelectrons to transfer from the CB of MAX to the CB of CN, from where the photoelectrons respond with hydrogen ion to release hydrogen. The time-resolved photoluminescence measurement results showed that the CuO/NiO/MAX (CNM) composite had a charge carrier lifetime of 3 ns. The outcomes of this study will be beneficial in realizing the industrial applications of Ti3AlC2 MAX-based structured catalysts for hydrogen evolution and other ecological energy systems.

Resume : To efficiently capture the practically inexhaustible solar energy and convert it into green electricity and high energy density solar fuels provides an attractive ‘green’ alternative to the present-day fossil fuel-based energy systems, especially in the context of ever-growing global energy demand. This approach, dubbed ‘artificial photosynthesis’ carries great potential for the green energy transition from the centralised to decentralised systems for energy production. In this lecture, I will overview the concept of the biomolecular artificial photosynthesis devices and show how their bottom-up rational design can yield the increased solar conversion efficiency and stability. The biophotocatalyst in these devices is the photosystem I (PSI) complex from an extremophilic microalga C. merolae, interfaced with various transparent electrode materials for production of green electricity and fuel. I will show that the performance of PSI-based devices can be greatly improved by tailoring the structure of the organic conductive interface to ensure the generation of unidirectional electron flow and minimisation of wasteful back reactions. Specifically, incorporating transitional metal redox centres together with plasmonic nanoparticles in the bio-organic interface significantly improves not only the light-harvesting functionality of the PSI photoenzyme but also increases its photostability and the overall photoconversion output of the biomolecular devices. Such highly interdisciplinary and multifaceted rational design paves the way for generation of viable and sustainable technologies for solar energy conversion into fuel and other carbon-neutral chemicals.

Resume : Photocatalysis is considered as one of the most attractive and promising process in harvesting and converting solar energy for environmental applications. The selection of proper semiconductor or hybrid semiconductor-based system is challenging. During last two decades, a great effort has been devoted to develop new types of photocatalysts based on metal oxides, sulfides and salts, as well as metal-free organic semiconductors[1]. Graphitic carbon nitride (g-C3N4) is a perspective material of the band gap of about 2.7 eV, easy to obtain in the form of powder by thermal condensation of urea or melamine, stable in water and photocorrosion resistant. Unfortunately, g-C3N4 has also some disadvantages, such as average catalytic activity, because of high recombination rate, and poor electron mobility, but those can be overcome by formation of a hybrid system with other semiconductors, such as BiVO4, CdS, Cu2O[2]. In this work we modified the properties of g-C3N4 by reduction it with NaBH4[3]. It was proven in the literature that band gap become narrower along with the reduction degree [4]. The defects in the reduced C3N4 (r-C3N4) were determined using FTIR and XPS methods. Till now the reports on the electrochemical properties of g-C3N4 and r-C3N4 are very scarce. Therefore, we discuss in detail the influence of reduction degree on the photocurrent-potential curves, photocurrent transients, open circuit potential characteristics and electrochemical impedance spectra (EIS) as well as on n-type and p-type properties of C3N4. Finally, g-C3N4 and r-C3N4 were combined with BiVO4 and the hybrid systems were characterized by spectroscopic, microscopic and electrochemical methods. The preliminary photocatalytic results for water splitting and caffeine degradation with the use of BiVO4/r-C3N4 are also presented. [1] Recent Advances and Applications of Semiconductor Photocatalytic Technology, Zhang F., Wang X., Liu H., Liu C., Wan Y., Long Y. and Cai Z., Appl. Sci. 2019, 9, 2489. [2] A review on graphitic carbon nitride (g-C3N4) based hybrid membranes for water and wastewater treatment Li X., Huang G., Chen X., Huang J., Li M., Yin J., Liang Y., Yao Y., Li Y., Science of the Total Environment 2021, 792, 148462. [3] Defective g-C3N4 Prepared by the NaBH4 Reduction for High-Performance H2 Production, Wen Y., Qu D., An L., Gao X., Jiang W., Wu D., Yang D., Sun Z., ACS Sustainable Chem. Eng. 2019, 2, 2343. [4] Synergy of Dopants and Defects in Graphitic Carbon Nitride with Exceptionally Modulated Band Structures for Efficient Photocatalytic Oxygen Evolution, Zhao D., Dong Ch-L., Wang B., Chen C., Huang Y.-C., Diao Z., Li S. , Guo L., Shen S., Adv. Mater. 2019, 31, 1903545.

Resume : Surface plasmonic resonance effect happening on metal nanoparticle surfaces has enhanced the photocatalyst?s activity in the visible light region, making plasmonic photocatalysis the hallmark for solar hydrogen evolution reaction (HER). Nickel is one of the promising plasmonic candidates for the photocatalysis due to their low-cost and abundance in the earth. Moreover, in typical plasmonic photocatalytic systems, semiconducting support provide trapping sites for the plasmon-excited electrons, which further promotes the water oxidation or reduction reaction on the semiconductors [1]. However, the bare Ni metallic particles are not ideal for HER, Ni-based heterogeneous catalysts such as Ni@NiO core@shell offer promising HER catalytic activity for an efficient water splitting. Another attractive compound of Ni for photocatalysis is the nickel carbonate (NiCO3) in charge of oxygen evolution but rather rarely explored [2]. Herein, the varied sizes of Ni@NiO/NiCO3 core@shell hybrid nanostructures and their vacuum annealed counterparts have been studied for surface plasmon driven photocatalytic solar H2 generation without any co-catalyst [2]. Huge variation in the photocatalytic activity has been observed in the pristine vs post-vacuum annealed samples with the maximum H2 yield (~ 80 µmol/g/h) for vacuum annealed sample (N70-100/2h) compared to ~ 40 µmol/g/h for the pristine (N70) photocatalyst under white light irridiation. The results of XRD, FESEM/TEM-EELS and XPS spectroscopy demonstrate a core-shell structure of these samples consist of a core of Ni and a shell of crystalline NiO and amorphous NiCO3 [3]. Based on the results, it was found that an amount of NiCO3 in the shell has effect on the amount of H2 evolution and N70-100/2h shows the highest activity due to the highest amount of carbonate. Time-resolved PL further evidence that the plasmonic electrons originated from Ni tend to transfer to NiCO3 via NiO. As per the proposed mechanism, amorphous NiCO3 in the shell has been suggested to serve as the active site due to its favorable electronic structure [4]. Along with materials innovation and in-depth study of catalytic mechanism, this work is hoped to inspire a materials engineering route focused on non-noble but cheap SPR-related photocatalysts for sunlight hydrogen evolution. [1] Y. Shi, et al. J. Am. Chem. Soc. 2015, 137, 23, 7365?7370 [2] Sh.G. Patra, et al. Acc. Chem. Res. 2020, 53, 10, 2189?2200 [3] P. Talebi, et al. RSC Adv., 2021, 11, 2733?2743 [4] P. Talebi, et al. Appl. Energy., 2022, Under revision

Resume : Polydopamine (PDA) is a biomimetic material discovered in 2007 [1], which gained significant scientific interest due to numerous advantages- e.g. photocatalytic properties- and easy synthesis via auto oxidation [2]. Potentially new and unexplored topic are PDA films obtained at the air/water (a/w) interface, but the breakthrough discover was possible 2D-like macromolecular arrangement in these polymeric films reported by our team [3]. What is important, these films can be obtained on a large scale, preserving high quality, homogeneity and continuity after transferring onto various substrates [4]. In turn, TiO2 nanostructures have been one of the most important candidates for photocatalytic applications (i.e. water pollution removal, water splitting) but simultaneously they have several disadvantages limiting their applicational potential. In our experiment, we examine nano-laminar combination of PDA with TiO2 in sentimetre-scale towards photocatalytic performance enhancement. The films synthesis conditions were optimized and described in our recent work [4]. With the use of these conditions for production of PDA, and atomic layer deposition (ALD) for production of TiO2, we prepared centimeter-scale Si/TiO2/PDA and Quartz/TiO2/PDA laminar composites. Obtained materials were examined by means of: X-ray diffractometry, Raman spetroscopy, profilometry, transient absorption spectroscopy in femtosecond range and transmission UV-Vis spectroscopy. The electrochemical methods used include: light-sweep voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. Finally, photocatalytic performance was investigated in UV-Vis spectrum towards degradation of methylene blue (MB). Successful PDA deposition on the semiconductor interface was confirmed. Thereafter, we provide evidence of decreasing contribution of shallow defects states in TiO2. Moreover, significant improvement of electrochemical properties and the charge carrier's recombination rate reduction was revealed. Later, photocatalytic degradation of MB show remarkable efficiency enhancement. Next, we investigated whether it is possible to obtain multilayer composites (1, 2 and 3 layers of TiO2/PDA on Si(100) and quartz substrates) and we studied the influence of the number of stacking layers onto structural, morphological and optical properties of the resulting materials. The new insights about functional polymer/inorganic semiconductor laminar structures were revealed. The authors acknowledge the financial support from the National Science Centre (NCN) of Poland by the OPUS grant 2019/35/B/ST5/00248. J.S. Acknowledges Financial Support of the French Government Scholarship. [1] Lee et al. (2007) doi: 10.1126/science.1147241 [2] Aguilar-Ferrer et al. (2021) doi: 10.1016/j.cattod.2021.08.016 [3] Coy et al. (2021) doi: 10.1021/acsami.1c02483 [4] Szewczyk et al. (2022) doi: 10.1016/j.mtchem.2022.100935

Resume : Photocatalysis can be used to convert CO2 to formic acid and to produce zero carbon hydrogen from sunlight, but the efficiency of current photocatalysts needs to be increased for widespread utilisation. A photocatalyst must convert photon energy to electron-hole pairs and prevent the electron-hole pairs from recombining for the time it takes to transfer the charges to the reactants at its surface. Anatase TiO2 is effective in transferring the charged particles to reactants, because of its oxygen terminated surfaces. Facetted TiO2 nanoparticles separate electrons and holes to different facet surfaces, which prevents them from recombining for long enough to transfer the charges to the reactants. However, the anatase TiO2 bandgap is 3.2 eV, which requires photons with wavelengths of 375 nm or less to produce electron-hole pairs. Therefore, TiO2 is limited to using a small part of the solar spectrum. Applying a TiO2 shell to tetragonal ZrO2 nanoparticles causes large strains in the TiO2 shell, which reduces its bandgap while also maintaining facets for charge separation and oxygen terminated surfaces for catalysis of reactants. Finite element analysis shows that shell thicknesses of 4-10 nm are effective in obtaining large strains in a large portion of the shell, with the largest strains occurring next to the ZrO2 surface. The strains reduce the bandgap in anatase TiO2 by 0.05-0.4 eV, which allows the use of a larger part of the solar spectrum. Overall, the electron-hole pair creation in the TiO2 shell can be increased by up to 25% in sunlight. The TiO2 shells retain their beneficial aspects for photocatalysis including a porous outer surface for increased surface area. The photocatalytic performance could be further increased many-fold by combination of the core/shell nanoparticles with surface plasmon resonance from metal nanoparticles as has been done with TiO2 nanoparticles.

Resume : For most catalysts, the limited catalytic efficiency and difficulty in recovering astrict their development and practical applications. Plenty of strategies have the potential to improve the catalytic efficiency of catalysts. Piezo-catalysis is a newly developed technology, which combines a piezoelectric effect with catalysis. Piezoelectric materials can convert mechanical energy into electric energy, and they have recently attracted much attention in the application of energy harvesting and sensing devices. Among them, piezoelectric polymers have special advantages, such as lightweight, deformability, and flexibility, which make them have the potential to become soft electronics. PVDF has become the most widely investigated piezoelectric polymer material because of its excellent characteristics and acceptable price. Electrospinning can produce nano- or micro-fiber membranes with high surface area; moreover, the mechanical stretching and electric polarization during the process can improve the in situ piezoelectric property of PVDF. Therefore, electrospinning becomes an effective and simple method for preparing a piezoelectric-related PVDF membrane. Here are some ideas to improve the two main weaknesses of catalysts: 1). when the catalysts are combined with a matrix, the catalysts are easily recycled and reused, meantime the uniform distribution of catalysts on a substrate with a high surface-area-to-volume ratio can reduce aggregation and increase the surface area of catalysts; 2). when a piezoelectric material is used as a catalyst or combined with a catalyst, since the piezoelectric field formed in the piezoelectric material can accelerate the migration of electrons and reduce the recombination between electrons and holes, the catalytic efficiency can be improved. The current work aims to show the production, characterization, and photocatalytic performance of nanostructured membranes based on electrospun PVDF matrix and TiO2 catalysts. PVDF-TiO2 core-sheath nanofiber membrane is prepared by coaxial electrospinning with PVDF solution and TiO2 suspension as the core and sheath. Two steps are carried out in order to investigate the piezo-catalytic activity of the proposed nanofibrous membranes: 1. Evaluation of TiO2 suspensions with different TiO2 mass fractions, solvents, and the feed rate of core and sheath solution in order to find the proper parameters for achieving good morphology PVDF-TiO2 core-sheath nanofibers with a uniform TiO2 coverage; 2. Evaluation of the core-polymer solution: PVDF and PAN are used as core solutions in coaxial electrospinning for investigating the performance of core-sheath nanofiber membranes with different piezoelectric properties. The obtained results present that a PVDF-TiO2 core-sheath nanofibers with good morphology can be prepared and the catalytic efficiency can be influenced by the external stain when PVDF, the piezoelectric material, is applied as the core polymer. This work allowed us to consider the proposed approach, piezo-catalysis, as a valid solution in the development of a new advanced catalyst.

Resume : To improve sustainability of earth?s resources discovery of new catalysts is a pressing issue. Most catalysts are prepared by wet chemical synthesis, which results in chemical waste and can be too slow for industrial use. Furthermore, the morphology of the materials is important because it affects their catalytic properties as higher surface areas yield more catalytic active sites, surface energetics change, leading to improved reaction rates, and other differences that affect catalytic activity. These reasons emphasize the motivation to accelerate the process of finding new materials with different nanostructures and optimized functionality, using fast and robust methods that do not involve wet chemistry. Glancing angle deposition (GLAD) is a physical vapor deposition (PVD) shadow growth technique where the substrate is positioned at an oblique angle to the vapor source and can be manipulated with regard to substrate tilt angle and rotation, during the deposition. The thin films obtained by GLAD have unique micro- or nanostructures, which depend on ballistic shadowing of the substrate, and are formed as nano- or micro-columnar films, leading to 3D nanostructure fabrication. Here, we present the first original results obtained by using GLAD to form nanoporous ultra-thin mesh structures, in a unique dry synthesis method. The nanostructured mesh films are highly porous and extremely pure, with high curvatures and different crystal motifs, suitable for catalytic activity. The different nanoporous mesh films were studied for their electrocatalytic performance in the O2 evolution as well as CH3OH oxidation reactions and show extremely high activity and stability. The insights gained, show a dependence of catalytic activity on nanostructuring and purity, which the standard experimental techniques cannot achieve or explore, thus illustrating the importance and impact that GLAD has, and will have, on developing sustainable catalysts.

Resume : The discovery of new materials with well-defined set of properties is a work-intensive and time-consuming task, when relying on conventional experimental routines. The employment of high-throughput techniques speeds up the screening of material properties and facilitates the generation of material libraries for data-driven optimization. To this end, combinatorial deposition is combined with automatized materials characterization and machine-learning approaches. Ultrasonic spray pyrolysis (USP) is a well-suited technique to create combinatorial thin films, enabling 2D variation of the film composition and/or thickness. In this work, we upgraded a commercial USP tool with a custom-built, electronically controlled pump system that allows for a gradual composition change of the precursor solution during the deposition process. The capabilities of the realized equipment are demonstrated by depositing a 2D composition gradient of copper-gallium-iron oxides on glass substrates. Oxide-based delafossite and wurtzite materials, with a bandgap in the 1-2 eV range, are highly relevant as earth-abundant light absorbers in photovoltaics (PV) and photoelectrochemical water splitting [1?3]. Spatially resolved elemental quantification of the 2D deposits is performed by automatized SEM/EDS which validates the targeted concentration distribution of the metal oxides over the sample area. Further, the optical properties of the thin films are determined by FTIR transmission measurements, yielding a map of band gap energies. The film thickness distribution is measured using a tactile profilometer and verified with cross-section SEM images. Crystallographic information is gathered through XRD point measurements over the whole sample area and changes of identified reflexes are evaluated. Finally, the comprehensive data from the chemical, optical and structural characterization is used to feed machine learning models for deriving dependencies over the covered parameter space. These findings will help to optimize the desired properties and design a compound that is suitable for the envisaged application as light absorber in PV and water-splitting devices. [1] Sullivan, Ian, Brandon Zoellner, and Paul A. Maggard. "Copper (I)-based p-type oxides for photoelectrochemical and photovoltaic solar energy conversion." Chemistry of Materials 28.17 (2016): 5999-6016. [2] Suzuki, Issei, et al. "First-principles study of CuGaO2 polymorphs: delafossite ?-CuGaO2 and wurtzite ?-CuGaO2." Inorganic chemistry 55.15 (2016): 7610-7616. [3] Liu, Qing-Lu, et al. "Fundamental properties of delafossite CuFeO2 as photocatalyst for solar energy conversion." Journal of Alloys and Compounds 819 (2020): 153032.

Resume : Titanium (IV) oxide (TiO2) nanoparticles show a broad variety of possible applications in the field of solar cells, biomedicine, (photo)catalysis and sensing. For these applications, the crystal phase of TiO2 particles (e.g., anatase, rutile and brookite) plays a major role to achieve high performance [1]. Various preparation methods (physical and chemical) have been shown in the literature to precisely control the crystal phase of TiO2. New studies showed that TiO2 performance (especially photocatalytic activity) can be also improved by combining with noble metals (Au, Au, etc.) [2] or oxide structures (like CeO2) [3]. Therefore, controlling the crystal phase and producing a hybrid structure in a single step would be highly beneficial. The production of nanoparticles via gas aggregation cluster source (GAS) offers the option to be combined with further PVD or CVD processes to create composite structures of controlled crystal phase for achieving better performance. The aggregation of TiO2 nanoparticles is influenced by the oxygen partial pressure pO2 inside the GAS [4]. The TiO crystallites and the short-range order in the mostly amorphous nanoparticles formed in this aggregation process act as crystallization precursors for the following heating process. pO2 is considered highly relevant to this aggregation process and hence the resulting crystal phase. It is influenced by the adjusted oxygen flow as well as the gettering of oxygen by TiOx species on the GAS walls. Therefore, the oxygen flow is not equivalent to pO2. Instead, we found that the target voltage changes with the target oxidation which is related to pO2 and the resulting TiO2 phase. A constant target voltage results in a reproducible phase formation. Full oxidation and crystallization of the particles is achieved by heating samples under atmospheric conditions. Heating of particles that were deposited at constant target voltages results in anatase phase for a broad range of temperatures. Particles produced at voltages outside an anatase formation window formed non-anatase phase at the same heating temperatures. The magnetron voltage can be seen as an indicator parameter for the oxygen partial pressure inside the GAS and the resulting particle phase after heat treatment. This concept is likely to be applicable to further reactive GAS processes. The production of high performance TiO2-CeO2 mixed oxide nanoparticles by GAS is under development. First particles have been produced and photocatalytic measurements have been started. [1] A. Sclafani, J. M. Herrmann, J. Phys. Chem., 1996, 100, 13655?13661 [2] S. Veziroglu et al., ACS Appl. Mater. Interfaces, 2020, 12, 14983?14992 [3] S. Veziroglu et al., Nanoscale, 2019, 11, 9840-9844 [4] Amir Mohammad Ahadi et al., J. Phys. D: Appl. Phys., 2015, 48, 035501

Resume : Liquid-cell transmission electron microscopy (LC-TEM) is a highly advanced method for real time observations of nanostructures synthesis in liquid environment. It allows to analyse their growth dynamics and the provided information enables to control the efficiency of the process and the quality of the obtained structure. However, it is challenging to estimate how the electron beam affects the synthesis, since it influences the particles diffusion and modifies the pH of the solution. It is widely reported that the beam may damage the nanostructure, as well as stimulate the nucleation, depending on the materials and the liquid environment. In the presented research, LC-TEM was used for imaging of PtNi alloyed nanoparticles synthesis. They were electrodeposited using cyclic voltammetry on the working carbon electrode of the liquid cell holder E-chip. In situ observations of the growing film morphology were correlated with cyclic voltammograms for better understanding of the process. The analysis showed that the film growth was very dynamic at the beginning and was slowing down with each cycle. It was also observed, how the nanostructure grows on the electrode and how the aggregates flow towards the electrode. Furthermore, ex-situ experiments of electrodeposition of nanoparticle PtNi films were performed for understanding, how voltammetry parameters affect the whole synthesis. Eventually, various precursor concentrations, scanning rates, cycle numbers and scanning ranges resulted in different thickness, homogeneity, nanoparticles size and surface structure. It was also noticed, that different elemental compositions of nanoparticles have been achieved, with lower or higher concentration of one metal, in favor of the other. Those differences were confirmed by SEM imaging and EDS mapping. The results were correlated with the voltammograms. The obtained data shows, that the growth process in the liquid cell is slower than the synthesis on the glassy carbon electrode, but the information provided by SEM imaging, STEM analysis and EDS mapping confirm that the nanoparticle films from both experiments exhibit the same nanostructures and chemical compositions.

Resume : Semiconductor (photo-)electrocatalysts like ZnO[1], Cu2-xSe[2], MoS2[3] and TiO2[4], and their composites have come up as promising candidates for CO2 electrolysis. While many different morphologies and varied thicknesses of these catalysts are employed, often only their bulk properties are used in proposing possible reaction pathways. As an example, bulk band edge positions are typically determined by Mott-Schottky (MS) experiments. In these measurements, a change in the applied potential bias across a semiconductor-electrolyte interface alters the depletion width within the semiconductor. Since the change in the depletion width alters the capacitance, this can be measured. Mapping capacitance changes with the potential applied gives a method to obtain the flatband potential for the material and thus its band edges. With growing inclination towards using nanostructured semiconductor electrodes for electrocatalytic CO2 reduction, like thin films or nanoparticles coated on a conducting substrate, we realize that doing MS may not be an appropriate strategy to determine the semiconductor band edge position. This is because a nano-semiconductor may be fully depleted by a very small potential and any additional bias does not alter the depletion width anymore. Additionally, insights on the electrolyte-(nano)semiconductor interface that will affect the CO2 reduction mechanism are important. We thus propose an alternate strategy of using reversible redox probes to determine these band edge locations in nano-semiconductors. In this regard, we develop a model thin film system with TiO2 (anatase) and show the feasibility to investigate the electrolyte-(nano)semiconductor interface by using Ru, Fe, Cr based redox probes in H2O. Based on whether the reversible nature of the redox probes is seen or not during a cyclic voltammetry experiment, and the peak current potential values, we can successfully estimate the band edge location of TiO2 (deposited on TiN by atomic layer deposition) as a function of the pH of the electrolyte. References: [1] Zeng et al. ChemSusChem, 13, 4128 ?4139 (2020) [2] Yang. et al. Nat Commun 10, 677 (2019) [3] Asadi et al. Nat Commun 5, 4470 (2014) [4] Yu et al. J. Mater. Chem. A, 6, 4706 (2018)

Resume : Platinum-based bimetallic alloys are known to possess unique activities exceeding those of pure platinum. Nevertheless, as a complex multi-component system, it suffers from structural reorganization under operating conditions, strongly affecting its lifetime performance. The better understanding on the structural dynamics of a bimetallic catalyst during its interaction with reactive environments is a prerequisite for the catalyst development. Herein we provide an operando electrochemical and spectroscopic study of the surface composition changes in a PtNi catalyst during repetitive oxidation/reduction cycles representing inherent working conditions for numerous redox reactions. Using cyclic voltammetry and near-ambient pressure X-ray photoelectron spectroscopy, a quantitative surface characterization under both realistic environments, i.e. electrified liquid and gaseous at elevated pressure and temperature, is obtained and correlated. We observed that, regardless of the operating environment, the PtNi alloy does not maintain its chemical integrity and undergoes irreversible change in composition profile reflected in surface nickel enrichment and consequent catalyst deactivation.