2022 Fall Meeting
Materials for a sustainable transitionQ
Advanced catalytic materials for (photo)electrochem. energy conversion III
Catalysts are widely used to lower thermodynamic barriers and accelerate kinetics of reactions in many (photo)electrochemical energy conversion processes. The past few years have witnessed a rapid growth in catalytic materials research. This symposium aims to bring together researchers who are interested in, and actively working on, catalytic materials and processes for use in (photo)electrochemical energy conversion.
With the ever-growing deployment of renewable energy and the needs for load-levelling, rapid inter-conversion of electrical energy to chemical energy and vice versa provides an attractive solution to off-peak renewable energy storage and utilization. Using electrolyzers, water can be split producing hydrogen fuels that are clean and high-density energy carriers. Photoelectrochemical (PEC) water splitting using semiconductor photoelectrodes, including multi-junction architectures, offers a straightforward and potentially efficient means of hydrogen production, though formidable challenges for stable and un-assisted water splitting still remain and practical deployment of PEC cells may take a few decades. Electro-fuels, i.e. chemicals produced by electrolyzers, have recently provoked increasing interest: a great deal of work on electrocatalytic and photoelecatalytic CO2 reduction has been reported, and electrosynthesis of ammonia has lately emerged as an alternative to the energy-intensive Haber-Bosch process. As far as fuel cells are concerned, several European countries have announced a timetable for stopping the production and sales of petrol and diesel powered cars. This will open up a huge market for fuel-cell powered vehicles.
To achieve high conversion efficiency, the use of catalysts in (photo)electrolyzers and fuel cells is essential. Remarkable progress has been made in recent years towards the development of new catalytic materials, with particular emphasis on the substitution, either partially or completely, of precious noble metals. Recent advances in in-operando characterization techniques, as well as in theoretical approaches to the prediction of activity trends and catalyst screening allow for fundamental understanding of catalytic mechanisms and processes and rational design of efficient and durable catalytic materials.
This symposium will provide a platform for researchers working on catalytic materials to showcase and learn about the latest findings in this fast-growing field of research. The symposium covers, but is not limited to, both experimental and theoretical studies of advanced catalytic materials that can find applications in fuel cells and electrolyzers of different types. Contributions to the system design of these (photo)electrochemical energy conversion devices are also welcome.
Hot topics to be covered by the symposium:
- Water splitting and fuel cell catalysts
- Semiconductor materials including multijunctional/hybrid photoelectrodes
- Electrochemical and solar-driven CO2 reduction
- Catalytic materials for electro-fuel and chemical (e.g. methanol, ammonia) synthesis
- 2D materials for (photo)electrocatalysis
- Bi-functional and multi-functional electrocatalysts
- Reduction/replacement of critical metals by nano-design of abundant materials
- Theoretical and experimental approaches to catalyst screening and design
- Advanced characterization techniques (in particular in-operando) of photoelectrodes and catalysts
- Theoretical studies and computational modeling of catalytic mechanisms/processes
Confirmed invited speakers:
- Virgil Andrei, University of Cambridge, UK
- Ib Chorkendorff, Technical University of Denmark, Denmark
- Jan Mertens, CSO Engie and University of Gent, Belgium
- Joanna Kargul, University of Warsaw, Poland
- Joan Ramon Morante, Catalonia Institute for Energy Research – IREC, Spain
- Serhiy Cherevko, Helmholtz Institute Erlangen-Nuernberg for Renewable Energy, Germany
- Sonya Calnan, Helmholtz Zentrum Berlin, Germany
Confirmed scientific committee members:
- Athanasios Chatzitakis, University of Oslo, Norway
- Jianwu Sun, University of Linkoping, Sweden
- Mihalis Tsampas, DIFFER, The Netherlands
- Nina Plankensteiner, imec, Belgium
- Salvador Eslava, Imperial College London, UK
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Electrocatalysis I : Vladimir Smirnov
Authors : Ib Chorkendorff
Affiliations : Department of Physics Technical University of Denmark
Resume : In our current transition to rely on sustainable energy we have identified some of the most significant obstacles for making fuels and chemicals . One of the most challenging processes is the activation of molecular nitrogen, which is essential for life. We have for more than 15 years tried to activate molecular nitrogen electrochemically at ambient conditions and have made ammonia many times, however, when we performed the appropriate control experiments, we found that it was only impurities that were converting into ammonia. This also applies for many of the studies also published in the literature we tried to reproduce with one exception where we simultaneous depositing Li in an N2 atmosphere. Here it was proven that it was possible to activate N2 to synthesize ammonia . We have subsequently followed up on this process and a very simple model for the synthesis has been proposed and based on this insight devised experiments that significantly improved the Faradaic and energy efficiency  by oscillating the potential. Further improvements have been gained by controlling the oxygen content  and by synthesizing of high area electrodes  leading to Faradaic efficiency of ~80% and current densities towards 1A/cm2. Despite excellent recent progress there are still substantial outstanding questions concerning the energy efficiency which will also be discussed. 1. Z. W Seh, J. Kibsgaard, C. F. Dickens, I. Chorkendorff, J. K. Nørskov and T. F. Jaramillo, “Combining Theory and Experiment in Electrocatalysis: A Framework for Providing Insights into Materials Design” SCIENCE 355 (2017) 146. 2. S. Z. Andersen, V. Čolić, S. Yang, J. A. Schwalbe, A. C. Nielander, J. M. McEnaney, J. G. Baker, A. R. Singh, B. A. Rohr, M. J. Statt, S. J. Blair, S. Mezzavilla, K. Enemark-Rasmussen, J. Kibsgaard, P. C. K. Vesborg, M. Cargnello, S. F. Bent, T. F. Jaramillo, I. E. L. Stephens, J. K. Nørskov and I. Chorkendorff, “Benchmarking the Electrochemical Nitrogen Reduction Reaction” NATURE, 570 (2019) 504-508 3. S. Z. Andersen, M. J. Statt, V. J. Bukas, S.G. Shapel, J. B. Pedersen, K. Krempl, Mattia Saccoccio, D. Chakraborty, J. Kibsgaard, P. C. K. Vesborg, J. Nørskov, and I. Chorkendorff, “Increasing Stability and Efficiency of Lithium-Mediated Electrochemical Nitrogen Reduction” Energy & Environ. Sci. 13 (2020) 4291 4. K. Li, S. Z. Andersen, M. J. Statt, M. Saccoccio, V. J. Bukas, K. Krempl, R. Sažinas1, J. B. Pedersen, V. Shadravan, Y. Zhou, D. Chakraborty, J. Kibsgaard, P. C. K. Vesborg, J. K. Nørskov, and I. Chorkendorff, “Enhancement of Li-mediated Ammonia Synthesis by Addition of Oxygen”, Science 374 (2021) 1593-97. 5. K. Li, S. G. Shapel, D. Hochfilzer, J. B. Pedersen, K. Krempl, S. Z. Andersen, R. Sažinas, M. Saccoccio, S. Li, D. Chakraborty, J. Kibsgaard, P. C. K. Vesborg, J. K. Nørskov, and I. Chorkendorff, “Increasing current density of Li-mediated ammonia synthesis with high surface area copper electrodes” ACS Energy Lett. 7 (2022) 36-41.
Authors : Nuria Jiménez-Arévalo1, Jinan Hussein Awadh Al Shuhaib1, Rodrigo Bautista Pacheco1, Antonella Cutrupi2, Mahmoud M Saad Abdelnabi2, Riccardo Frisenda2, Maria Grazia Betti2, Carlo Mariani2, Yolanda Manzanares3, Cristina Gómez Navarro3,4, Antonio Martínez Galera1,4, Jose Ramón Ares1, Isabel Jiménez Ferrer1,4, Fabrice Leardini1,4
Affiliations : 1 Departamento de Fisica de Materiales, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049, Madrid, Spain. 2 Dipartimento di Física, Sapienza Università di Roma, I-00185, Italy. 3 Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049, Madrid, Spain. 4 Instituto Nicolas Cabrera, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049, Madrid, Spain.
Resume : The rational design of advanced electrocatalysts for green hydrogen production using electrical energy supply from renewable sources is a key issue that must be addressed to reduce CO2 emissions. Two-dimensional transition metal dichalcogenides such as MoS2 have been extensively investigated as cathodes for the electrolytic water splitting. The electrocatalytic activity of these layers is substantially improved by creating defects such as grain boundaries or sulfur vacancies . In this work, we investigate the growth of MoS2 layers onto different substrates (silicon, Si/SiO2, quartz, glassy carbon and highly oriented pyrolytic graphite (HOPG)) by a special salt-assisted chemical vapor deposition (CVD) method. Extensive characterizations of these layers based on Raman Spectroscopy, Photoluminescence, Scanning Tunneling Microscopy and Atomic Force Microscopy have shown that our CVD method allows the growth of flat ultrathin MoS2 nanoparticles (having 1-2 layers in thickness and a diameter of 2-3 nm). In addition, these seem highly defective due to the presence of sulfur vacancies, as revealed by X-ray Photoelectron Spectroscopy measurements. The electrochemical performances of the MoS2 layers for the HER have been studied in a three-electrode cell. The results evidence an activation effect after cycling as well as a high stability of the layers during electrolysis. Faradaic efficiencies close to 100% have been obtained by measuring the amount of evolved hydrogen by mass spectrometry. Moreover, our MoS2 samples present photo-electrochemical currents when illuminated with a halogen lamp. We also analyze the influence of growth conditions (in particular, the use of a H2 flow) on the sulfur vacancies content, the electrocatalytic properties of the samples and some characteristic features present in the Raman spectra (relative positions and intensities of E1g and A2g Raman bands and appearance of new Raman bands). This work may open new possibilities to tune the MoS2 properties by nano-structuring and defect-engineering by playing with growth conditions.  Jianqi Zhu, et al. ?Boundary activated hydrogen evolution reaction on monolayer MoS2?, Nature Communications, 2019, 10,1?7
Authors : Jorit Obenlüneschloß, David Zanders, Jan-Lucas Wree, Anjana Devi
Affiliations : Ruhr University Bochum
Resume : Pyrite type materials have been in the discussion to be used as catalysts in the hydrogen evolution reaction (HER). Out of this class ruthenium disulfide, RuS2, is one of the most promising candidates. RuS2 has previously been known as a very active catalyst for hydrodesulfurization and for the hydrogenation of organic compounds.[1,2] With the advent of renewable energy and the need to utilize new energy carriers hydrogen is among the top candidates. Its production however requires effective catalysts to overcome the high amount of energy currently needed. The commonly accepted descriptor for effective HER, one half reaction of the electrolysis of water, is the hydrogen adsorption energy which has been calculated as remarkably low for RuS2 with 0.069 eV. This renders it an effective catalyst which is at the same time believed to be very corrosion resistant and stable. To this day the fabrication of this material has been limited to solution chemical approaches for nanoparticles and sputtering methods for films, omitting the advantages chemical vapor deposition (CVD) provides.[5,6] This presentation demonstrates how it was possible to close this gap with the combination of the ruthenium amidinate precursor Ru(CO)2(tBuAMD)2 and elemental sulfur. The favorable reactivity of the chosen precursor allowed circumventing the use of toxic H2S often employed in CVD of sulfide films. A new thermal CVD process was developed, and the resulting polycrystalline thin films were fully characterized by means of XRD, SEM, RBS, NRA, UV/VIS, as well as XPS to reveal promising film properties. The optimal deposition temperature was found to be 600 °C on Si(100) substrates enabling homogeneous films with a high degree of crystallinity, and high purity with a near stochiometric Ru to S ratio. To explore the potential of the herein grown RuS2 films, electrocatalytic investigations were performed to test for the acidic HER. A promising HER activity could be observed for films deposited onto FTO at 600 °C when a low overpotential of 287 mV was applied that generated a current of 10 mAcm-2. The electrocatalytic reactions taking place afforded a Tafel slope of 85 mV/dec for the low potential region, indicating the proton reduction of the Heyrovsky step to be rate limiting. These proof of principle electrocatalytic studies show that the fabricated RuS2 thin films are effective HER catalysts and that CVD is a powerful tool which enlarges the accessibility of this pyrite material with a facile process.  M. Lacroix, et al., Journal of Catalysis 1989, 120, 473?477.  J. A. De Los Reyes, Appl. Catal., A 2007, 322, 106?112.  https://www.nrel.gov/research/eds-hydrogen.html  Z. Zhang, et al., Small 2021, 17, 2007333.  Y. Li, et al., Mater. Res. Bull. 2015, 65, 110?115.  S. Brunken, et al., Thin Solid Films 2013, 527, 16?20.
Authors : Ebrahim Sadeghi (a,b), Naeimeh Sadat Peighambardoust (a), Sanaz Chamani (a) Umut Aydemir (a,c)
Affiliations : a Koç University Boron and Advanced Materials Application and Research Center (KUBAM), Sariyer, ?Istanbul, 34450, Turkey ? b Graduate School of Sciences and Engineering, Koç University, Sariyer, Istanbul, 34450, Turkey c Department of Chemistry, Koç University, Sariyer, Istanbul, 34450, Turkey
Resume : Developing high-performance electrocatalysts for hydrogen evolution and oxygen evolution reactions ??(HER/OER) is of paramount importance to secure the future of clean and sustainable hydrogen energy, ?yet still challenging. Recently metal-organic frameworks (MOFs) have intrigued the electrocatalytic ?community on account of their versatile catalytic activities, remarkable structural diversity, high surface ?areas, and tunable pore sizes. However, MOFs are generally considered to be poor electrocatalysts for ?electrochemical reactions such as the OER and HER. To overcome these impacts, 2D structured MOFs ?with rapid electron and mass transport and larger specific surface have been proposed and received ?increasing attention. The prime and utmost objective of this study is to develop in-situ growth of 2D ?MOFs directly on conductive substrates such as nickel?a cheap commercial material, that has already ?been widely used as a substrate and support for electrode materials because of its high electronic ?conductivity, desirable 3D open-pore structure, and high specific surface area. In addition to this, mixed ?metal oxides have been the center of attention for decades due to their remarkable electrocatalytic ?features. To date, the combination of MOFs/metal oxides has largely remained unexplored. Herein, we ?systematically examine a series of MOFs/metal oxides composites as outstanding HER, OER, and ?overall water splitting candidates. The primary results demonstrated that we could drive water ?oxidation/reduction with an ultra-small OER/HER overpotential of 120 mV/170 mV at 10 mA cm-2 ?current density. The exceptional OER and HER electrodes were combined to build an overall water ?splitting cell, affording 10 mA cm-2 at a cell potential of 1.58 V. We believe the unique properties??including extraordinary stability (~ 50 h)?developed within the in-situ growth of these composites ?possess the capacity for large-scale implementation.?
Photoelectrocatalysis I : Byungha Shin
Authors : Virgil Andrei
Affiliations : Yusuf Hamied Department of Chemistry, University of Cambridge, United Kingdom
Resume : Metal halide perovskites have emerged as promising alternatives to commonly employed light absorbers for solar fuel synthesis, enabling unassisted photoelectrochemical (PEC) water splitting[1,3] and CO2 reduction to syngas.[2,4] While the bare perovskite light absorber is rapidly degraded by moisture, recent developments in the device structure have led to substantial advances in the device stability. Here, we give an overview of the latest progress in perovskite PEC devices, introducing design principles to improve their performance and reliability. For this purpose, we will discuss the role of charge selective layers in increasing the device photocurrent and photovoltage, by fine-tuning the band alignment and enabling efficient charge separation. A further beneficial effect of hydrophobicity is revealed by comparing devices with different hole transport layers (HTLs).[1,3] On the manufacturing side, we will provide new insights into how appropriate encapsulation techniques can extend the device lifetime to a few days under operation in aqueous media.[1,2] To this end, we replace low melting alloys with graphite epoxy paste as a conductive, hydrophobic and low-cost encapsulant.[3,5] The combined advantages of these approaches are demonstrated in a perovskite-BiVO4 tandem device archiving selective unassisted CO2 reduction to syngas. These design principles are successfully applied to an underexplored BiOI light absorber, increasing the photocathode stability towards hydrogen evolution from minutes to months. Finally, we take a glance at the next steps required for scalable solar fuels production, showcasing our latest progress in terms of device manufacturing. A suitable choice of materials can decrease the device cost tenfold and expand the device functionality. Such materials are compatible with large-scale, automated fabrication processes, which present the most potential towards future real-world applications.  Andrei, V. et al. Adv. Energy Mater. 2018, 8, 1801403.  Andrei, V.; Reuillard, B.; Reisner, E. Nat. Mater. 2020, 19, 189?194.  Pornrungroj, C.; Andrei, V et al. Adv. Funct. Mater. 2021, 31, 2008182.  Rahaman, M.; Andrei, V. et al. Energy Environ. Sci. 2020, 13, 3536?3543.  Andrei, V.; Bethke, K.; Rademann, K. Phys. Chem. Chem. Phys. 2016, 18, 10700?10707.  Andrei, V.; Jagt, R. A. et al. Nat. Mater. 2022. DOI: 10.1038/s41563-022-01262-w.  Andrei, V. et al. in press.  Sokol, K. P.; Andrei, V. Nat. Rev. Mater. 2022, 7, 251?253.
Authors : Ahmed Chnani, Mario Kurniawan, Andreas Bund, and Steffen Strehle
Affiliations : Ahmed Chnani; Steffen Strehle: Technische Universität Ilmenau, Institute of Micro and Nanotechnologies, Microsystems Technology Group, Max Planck Ring 12, 98693 Ilmenau, Germany Mario Kurniawan; Andreas Bund: Technische Universität Ilmenau, Institute of Electrochemistry and Electroplating Technology , Gustav Kirchhoff Str. 6 , 98693 Ilmenau, Germany
Resume : Photoelectrochemical (PEC) water splitting, as one of the most promising sustainable methods for solar hydrogen production, is still impractical due to the lack of stable, cost-effective and efficient photoanode materials. The n-type semiconductor hematite is considered as a promising candidate as photoanode material with suitable bandgap, availability, non-toxicity and stability in pH > 3 but suffers still from a low PEC efficiency. We addressed this issue by an improved material synthesis strategy targeting explicitly the short lifetime of photogenerated charge carriers as well as the overall electrical conductivity. We present in this regard a relatively simple but highly effective rapid annealing approach of iron thin films in ambient air for fabricating nanometer-thick hematite films with an optimized thickness of 90 nm. We show that these hematite films suffice to absorb sufficient light and exhibit a high PEC efficiency, as well as a superior stability studied for over 1000 h in 1 M NaOH electrolyte at temperature 60 ± 5 °C. The measured improvement of the charge carrier concentration from 1.28 to 5.74 × 10^19 cm-3 should rely on the thermal stress developed during the rapid heating and cooling. In particular, our ultra-thin hematite photoanodes exhibit a real photocurrent density of 2.35 mA cm-2 at 1.23 V versus RHE, and an oxygen evolution reaction with a Faradaic efficiency of 99.8 % at potential as low as 1 V versus RHE.
Authors : Thomas Emmler, Andreas Elsenberg, Steffen Fengler, Charline Wolpert, Mauricio Schieda, Thomas Klassen
Affiliations : Thomas Emmler (Helmholtz-Zentrum Hereon, Geesthacht, Germany); Andreas Elsenberg (Helmut-Schmidt-Universität, Hamburg, Germany); Steffen Fengler (Helmholtz-Zentrum Hereon, Geesthacht, Germany); Charline Wolpert (Helmut-Schmidt-Universität, Hamburg, Germany); Mauricio Schieda (Helmholtz-Zentrum Hereon, Geesthacht, Germany); Thomas Klassen (Helmholtz-Zentrum Hereon, Geesthacht, Germany & Helmut-Schmidt-Universität, Hamburg, Germany)
Resume : One of the key steps towards a decarbonized energy economy is to replace fossil fuels as energy carriers for ships, cars or stationary power consuming devices. Hydrogen can easily replace fossil fuels in many of these use cases, while in other cases it can be used as feedstock to produce methane and synthetic liquid fuels such as ammonia and methanol. Hydrogen can be produced renewably and with minimal environmental impact in photoelectrochemical water splitting cells. While significant research effort is still necessary to develop optimal photoelectrode materials, some scalable components are commercially available, one example being bismuth vanadate (BiVO4), a promising photoabsorber. Aerosol Deposition (AD) is a scalable coating method that enables the use pre-synthesized semiconductor powders to generate films without the use of solvents. This method is a variant of the Cold Gas Spraying process, but incorporates a vacuum chamber, which enables operation at lower kinetic energies, and hence the use of smaller particles (resulting in sub-micrometer coatings), and fragile substrates (such as FTO-coated glass). Here we report on our recent investigations on aerosol deposited water splitting photoelectrodes, based on BiVO4 layers, comparing them with electrodes produced by cold gas spraying. Photoelectrochemical experiments, including voltammetry under chopped illumination, electrochemical impedance spectroscopy and Mott-Schottky analysis, reveal the advantage of Aerosol Deposition over Cold Gas Spraying when coating oxides featuring small carrier lifetimes, as in the case of BiVO4. Furthermore, preliminary correlations can be extracted between efficiency of the coated electrodes and parameters used in the Aerosol Deposition process. Surface Photo Voltage measurements enable the construction of defect layer models for the BiVO4 coatings. To further enhance the efficiency of the electrodes, we construct BiVO4/WO3 heterojunctions, reaching photocurrent densities above 5 mA/cm^2 (under 1 Sun, with CoPi decoration and in citrate pH7 electrolyte). Additionally, we show preliminary results on up-scaled aerosol-deposited photoelectrodes, for use in prototype cells with illuminated area of 100 cm^2.
Authors : Haozhen Yuan, Joe Briscoe
Affiliations : School of Engineering and Material Science and Materials Research institute, Queen Mary University of London, London, E1 4NS
Resume : BiFeO3 thin films have been widely studied for photoelectrochemical water splitting because of its narrow bandgap and good ferroelectricity which can promote the separation of photo-generated charges. Bismuth is well known as volatile and excess bismuth is usually added into the precursor to compensate the loss of bismuth during heat treatment. But how much excess bismuth and how excess bismuth will affect its PEC performance have not been well studied. Herein, self-doped Bi1+xFeO3 (x from 0 to 0.3) thin films are prepared via simple chemical solution deposition method. The grain size of films increases firstly and then decreases with increasing x. The loss of bismuth after annealing is confirmed by EDX and it estimates that a stoichiometric BiFeO3 thin film can be achieved between x=0.05 and 0.1. Enhanced photocathodic photocurrent density is observed in slightly bismuth-rich films (x=0.15 and 0.2) which can be ascribed to the co-existence of rhombohedral and orthorhombic crystal structures. Our work offers a simple and low-cost approach to enhance the photocathodic current density by up to 52.2%, which could help the further development of BiFeO3-based thin films for PEC water splitting application.
Authors : Verena Streibel, Johanna Schönecker, Laura I. Wagner, Ian D. Sharp
Affiliations : Walter Schottky Institute and Physics Department, Technical University Munich, Garching, Germany
Resume : Photoelectrochemical (PEC) water splitting provides a direct means of harvesting the sun?s energy and converting it into valuable fuels. The major bottleneck in efficiently driving water electrolysis is the sluggish oxygen evolution reaction (OER) that is catalyzed at the photoanode of a PEC cell. Promising novel photoanode absorber materials are transition metal (TM) oxynitrides, which are a wide and relatively underexplored compound space. Compared to TM oxides, oxynitrides have smaller band gaps ? enabling more efficient light harvesting ? and compared to TM nitrides, oxynitrides are more stable under the harsh OER conditions ? yielding increased life times. Prime examples for promising nitride- and oxynitride-based photoanode materials are Ta3N5 and TaON. Tantalum, however, largely stems from conflict regions, prompting the search for alternative materials. In this contribution, we report on the reactive sputter deposition of Zr oxynitride thin films and their optoelectronic and PEC characterization. To tune the film characteristics, we systematically vary several deposition parameters, with a particular emphasis on understanding the roles of oxygen and nitrogen in the reactive sputter gas. As controlled amounts of oxygen are introduced at otherwise fixed deposition conditions, we observe a transition from metallic ZrN to a disordered semiconducting nitrogen-rich zirconium nitride to a crystalline bixbyite-type Zr2N2O-like phase to nitrogen-doped cubic ZrO2. These investigations show that, while a critical amount of oxygen is required to induce the formation of crystalline oxynitride phases, oxygen concentrations in the sputter gas mixture as low as 1 % already lead to the formation of dominantly oxidic crystal phases, alluding to the high oxophilicity of Zr and ZrN. For our materials library, we show that we can tune the band gap of the semiconducting films, where increasing amounts of incorporated oxygen lead to larger band gaps. In particular, our crystalline Zr2N2O-like films have band gaps in the visible range, are intrinsically n-type, and their calculated valence band maximum position is favorable relative to the water oxidation potential, making them viable candidates for PEC photoanodes. Based on chopped linear sweep voltammetry measurements of crystalline Zr2N2O-like films functioning as photoanodes, we indeed show that these films are photoelectrocatalytically active for the OER in alkaline electrolyte. While their oxophilicity complicates post-deposition annealing treatments, we show that high-vacuum annealing is a promising means to further increase their crystallinity and boost their PEC performance. While the observed photocurrent is still about one order of magnitude lower than for TaON, further material optimization could potentially close this gap and provide a more sustainable materials system for PEC applications.
Electrocatalysis II : Anna Staerz, Joachim John
Authors : J.R.Morante
Affiliations : IREC Jardins de les Dones de Negre,1. Sant Adrià del Besòs 08930. Spain University of Barcelona, C/ Martí Franquès 1, Barcelona 08028. Spain
Resume : Nanoreactors are structures of materials defined at the nano level scale with a zone, 2D or 3D, and the ability to encapsulate one or more molecules guests. Encapsulation can not only isolate the guest molecule from the rest, but also help to induce specific conformation of the guest(s). Furthermore, confined space associated to a nanoreactor increases the concentration of reactants in this zone and can effectively influence the reaction rate taking place in this zone or nanoreactor through binding interactions. These features become essentials to define the nanoreactors concept, specially, concerning to oxidation and reduction reactions needed in many energy systems like electrochemical cells where multistep processes are needed. For example, the processes required for CO2 or nitrates reductions to obtain green products as alternative to the currently considered as standards based on fossil feed stocks. Correct choice of ligands and/or catalyst metal ions, are essential conditions for the assembly of these nanoreactors. Two kinds of ligands (one-dimensional and two-dimensional ligands) can be used. One-dimensional ligands which form the edges of the coordination cage can bridge two metal centers, while the faces of the final structure can be formed by two-dimensional ligands which are like bridge between parts with different functional catalyst appropriate for the different steps of the overall catalytic process. It is known that the higher wall-to-volume ratio in nanoreactors with respect to conventional routes allows to effectively quenching radical-type reactions and runaway effects. In this contribution we will be focused on examples for sustainable chemistry and more eco-efficient chemical syntheses routes. The reported nanoreactor examples facilitate safer and more energy-efficient production routes, higher-yield, cleaner and more resource-efficient synthesis of large volumes of chemicals: reduction of CO2, reduction of nitrate and even application in Lithium Sulphur, LS, batteries will be assessed and discussed, showing with these examples, the advantages in the use of this approach and demonstrating that the nanoreactor concept as catalysis constitutes a rational approach for its design. Thus, it is a key factor towards scientific and technological breakthrough in electrochemical or synthesis processes for a sustainable energy system.
Authors : Isilda Amorim, Zhipeng Yu, Fátima Bento and Lifeng Liu
Affiliations : Isilda Amorim; Zhipeng Yu; Lifeng Liu - Clean Energy Cluster, International Iberian Nanotechnology Laboratory (INL), Avenida Mestre Jose Veiga, 4715-330 Braga, Portugal Isilda Amorim; Fátima Bento - Centre of Chemistry, University of Minho, Gualtar Campus, Braga, 4710-057, Portugal
Resume : Renewable energy powered electrochemical water splitting has been recognized as a sustainable and environmentally-friendly way to produce green hydrogen which can substitute conventional fossil fuels to decarbonize different sectors of our economy, able to contribute to achieving global carbon neutrality. The development of inexpensive and earth-abundant new materials and components that can be integrated into electrolyzers is important in order to improve the overall performance and lower H2 production cost. Despite substantial progress, the operational voltage of water splitting in a single electrolyte system is still high. To this end, the recently developed bipolar membrane water electrolysis (BPM-WE) seems promising in lowering the energy demand which can help save system costs, enabling the hydrogen evolution reaction (HER) to occur in kinetically favorable acidic solution in the cathodic compartment and the oxygen evolution reaction (OER) to simultaneously take place in kinetically favorable alkaline solution in the anodic compartment. In this presentation we demonstrate the development of a heterostructured dual-phase cobalt phosphide-cobalt ditelluride (CoP-CoTe2) nanowires, which can be used as efficient bifunctional electrocatalysts for both HER and OER using acid-alkaline dual electrolytes in a two-compartment cell separated by a bipolar membrane (BPM). Using the BPM under reverse bias configuration, the bipolar membrane overall water splitting can be accomplished with a voltage of 1.72 V to deliver 10 mA cm-2. A significant reduction in the applied external cell voltage can be achieved, e.g. 1.01 V at 10 mA cm-2, when a forward bias condition was used due to the assistance of electrochemical neutralization. Moreover, this electrolyzer can sustain water splitting for at least 100 h without performance decay. The bipolar membrane water electrolysis, particularly with the ?forward bias? configuration, shows great promise as an alternative to the current technologies for low-cost, energy-saving production of green hydrogen.
Authors : Irmak Karakaya , Ömer Dag
Affiliations : Department of Chemistry, Bilkent University, Ankara 06800, Turkey. ; Department of Chemistry, Bilkent University, Ankara 06800, Turkey. UNAM-National Nanotechnology Research Center, Bilkent University, Ankara 06800, Turkey.
Resume : Noble transition metal oxides such as IrO2 and RuO2 are highly efficient electrocatalysts for oxygen evolution reaction (OER).  However, these materials have high cost and low abundancy in earth crust, compared to first raw transition metal based oxides (TMOs). The lithiated first raw transition metal oxides (LTMO) are efficient candidates for energy applications, particularly as water oxidation electrocatalysts. De-intercalation of lithium ion from LTMOs during catalytic process produces highly active surface distinct from common TMOs and brings stability and efficiency under harsh catalytic conditions.  In this study, a two-step method is introduced, based on earth abundant manganese to produce mesoporous spinel LiMn2(x)M(x)O4 (M: Co, Ni) (x = 0,1) thin films, having high surface area. Modification of the catalytic surface to enhance the amount of active transition metals such as, cobalt and nickel on the electrode surface amplifies the OER performance through synergistic electronic effects.  In the first step, molten salt-assisted self-assembly (MASA) process has been employed to produce mesoporous spinel LiMn2?xM?xO4 thin films over FTO glasses. The spinel LiMn2?xCoxO4 electrodes (x=0, 0.5, and 1) were prepared and tested as electro-catalysts that display Tafel slope values of 130, 67 and 64 mV/dec, respectively. The overpotential also drops from 491 mV to 304 mV at 1 mA/cm2 going from LiMn2O4 to LiMnCoO4. Tafel slope of the spinel LiMn1.5Ni0.5O4, is 47 mV/dec with an overpotential values of 262 mV at 1 mA/cm2 and 578 mV at 10 mA/cm2. In the second step, the LiMn2(x)M(x)O4 (x = 0?0.5) electrodes were modified by a systematic incorporation of Co(II) or Ni(II) into the structure using successive ionic layer adsorption (SILAR) followed by an annealing process. To increase the amount of deposited active species, SILAR process could be repeated many times. Tafel slope of mesoporous spinel LiMn2O4 thin film decreased from 130 to 82 mV/dec upon employing the SILAR/annealing process once using cobalt species. Modification of the LiMn2O4 using nickel by once, three, and five times gave Tafel slopes of 44, 37,34 mV/dec, respectively. The five times nickel modified LiMn2O4 electrode displays an overpotential of 268 mV at 1mA/cm2 and 634 mV at 10 mA/cm2 and results high efficiency and catalytic stability in long term OER experiments. References  B. M. Hunter et al., Earth-abundant heterogeneous water oxidation catalysts,? Chem. Rev., vol. 116, pp. 14120?14136, 2016  F. M. Balci et al., ?Synthesis of mesoporous LiMn2O4 and LiMn(2?x)Co(x)O4 thin films using the MASA approach as efficient water oxidation electrocatalysts,? J. Mater. Chem. A, vol. 6, pp. 13925?13933, 2018  I. Karakaya et al., ?Modification of Mesoporous LiMn2O4 and LiMn2?xCoxO4 by SILAR Method for Highly Efficient Water Oxidation Electrocatalysis,? Adv. Mater. Technol., vol. 5, no. 8, pp. 1?12, 2020
Authors : Faria Rafique, Muhammad sadaf Hussain, Dr. Joe Briscoe, Dr Habib ur Rehman
Affiliations : Queen Mary University of London Lahore university of the Management sciences, LUMS, Lahore, Pakistan University of the Punjab, Lahore, Pakistan
Resume : Ever-growing global energy demand and the associated environmental concerns of our current energy supplies have accelerated the search for new energy resources and conversion technologies that are sustainable, environmentally safe, low cost, and offer improved performance. Among the various options being explored, hydrogen is one of the most sustainable, environmentally benign and clean fuel resources on the planet. Currently, more than 95% of world?s hydrogen is being produced through steam reforming of fossil fuels and biomass. There is an urgent need for an alternative process for the synthesis of hydrogen that is cheap and uses carbon neutral resources. Water electrolysis is an e?ective and decisive method to produce hydrogen fuel, because it is abundant, carbon free, clean, and renewable energy source, however the process to convert water into hydrogen (water electrolysis) is a hugely challenging from thermodynamic and kinetics viewpoints as it requires significant amount of energy (?237.2 kJ mol?1) under normal operating conditions. Electrocatalysts have been used to lower kinetic barriers and enhance energy conversion efficiency of this process. Platinum, ruthenium and iridium-based catalysts have been found to be most effective for water splitting. However, due to their low natural abundance, electrocatalysts from these materials are prohibitively expensive. Lots of work has been done to explore cheap materials as a replacement for rare-earth metals. Oxides, hydroxides, nitrides, sulfides and borides of first row transition metals have been extensively explored for this purpose.
Authors : Xingyu Ding1, Freddy E. Oropeza2, Giulio Gorni3, Mariam Barawi2, Miguel García-Tecedor2, Victor A. de la Peña O?Shea2, Jan P. Hofmann4, Jianfeng Li1, Jun Cheng1, Kelvin H. L. Zhang1
Affiliations : 1State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China 2Photoactivated Processes Unit, IMDEA Energy Institute, Parque Tecnológico de Móstoles, Avda. Ramón de la Sagra 3, 28935 Móstoles, Madrid, Spain. 3CELLS-ALBA Synchrotron, Carrer de la Llum 2-26, 08290 Cerdanyola del Vallès, Spain 4Surface Science Laboratory, Department of Materials and Earth Sciences, Technical University of Darmstadt, Otto-Berndt-Strasse 3, 64287 Darmstadt, Germany
Resume : Transition metal chalcogenides have been identified as low-cost and efficient electrocatalysts to promote the hydrogen evolution reaction (HER) in alkaline media. However, the nature of active sites and the underlying catalytic mechanism remain elusive. We have been recently working on series of transition metal (TM) sulphides, which exhibit high HER activity. Interestingly, we often observed that these materials require a period of activation at the beginning of the electrochemical test in order to achieve high HER activity. In this talk, I will describe a study of NiS electrodes in which, by virtue of operando X-ray absorption spectroscopy (XAS) and electrochemical characterization, we elucidate an in-situ phase transition of nickel sulfide (NiS) to an intimately mixed phase of Ni3S2 and amorphous NiO under alkaline HER conditions. Such phase transition generates highly active synergistic dual sites at the NiO/Ni3S2 interface that greatly enhances the HER rate. Experimental mechanistic studies and near-ambient presure spectroscopy indicate that, at the NiO/Ni3S2 interface of the mixed phase catalysts, Ni in NiO is the active site for water dissociation and OH* adsorption, and S in Ni3S2 acts as the active site for H* adsorption and H2 evolution. By promoting the in-situ formation of NiOx/Ni3S2 interfaces, we achieved highly active electrocatalysts able to drive the HER with overpotential of only 95 mV to reach a current density of 10 mA cm-2. Our work shows that, although the chemistry of transition metal chalcogenides is highly dynamic, a careful control of the working conditions may lead to the in-situ formation of catalytic species that enhance the performance of this type of materials.
Photoelectrocatalysis II : Athanasios Chatzitakis
Authors : Jianwu Sun
Affiliations : Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping 58183, Sweden E-mail: firstname.lastname@example.org
Resume : Solar-driven photoelectrochemical (PEC) conversion of carbon dioxide (CO2) and water into renewable chemical fuels has attracted much interest due to its great potential to mitigate climate change. In this work, we show that high-quality, large-area, uniform graphene layers can be grown on cubic silicon carbide (3C-SiC). Through tuning the number of graphene layers, we demonstrate that the Schottky junction formed at the interface of graphene/3C-SiC can be atomically tailored for solar-driven CO2 conversion [1-3]. High-quality and uniform graphene layers were epitaxially grown on 3C-SiC surface. 3C-SiC has a relatively small bandgap of 2.36 eV, which is favorable for visible sunlight absorption. Most importantly, the conduction and valence band positions of 3C-SiC ideally straddle the water redox potentials, indicating that the photogenerated carriers have enough energy to overcome the energetic barrier of water splitting [4-5]. We show that the Schottky barrier and the built-in electric field of the graphene/3C-SiC junction can be tailored by atomically tuning the number of graphene layers . The tuned graphene/3C-SiC Schottky junction was demonstrated to promote charge separation and transport in a PEC CO2 conversion system for solar-to-fuel conversion with a high selectivity . References:  Hao Li, Y. Shi, H. Shang, W. Wang, J. Lu, A.A. Zakharov, L. Hultman, R. I. G. Uhrberg, M. Syväjärvi, R. Yakimova, L. Zhang, and Jianwu Sun*, ?Atomic-Scale Tuning of Graphene/Cubic SiC Schottky Junction for Stable Low-Bias Photoelectrochemical Solar-to-Fuel Conversion?, ACS Nano, 14, 4905?4915, (2020).  Y. Shi, A. A Zakharov, I. G Ivanov, G Reza Yazdi, V. Jokubavicius, M.Syväjärvi, R.Yakimova, Jianwu Sun*, ?Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3CSiC (111)?, Carbon, 140, 533-542, (2018).  W. Wang, Y. Shi, A A Zakharov, M.Syva?ja?rvi, R.Yakimova, R.IG Uhrberg, Jianwu Sun*, ?Flat-band electronic structure and interlayer spacing influence in rhombohedral four-layer graphene?, Nano letters, 18, 5862-5866, (2018).  J. Jian, Y. Shi, M. Syvajarvi, R.Yakimova, Jianwu Sun*, ?Cubic SiC Photoanode Coupling with Ni:FeOOH Oxygen-Evolution Cocatalyst for Sustainable Photoelectrochemical Water Oxidation? Solar RRL 4, 1900364, (2020).  Jing-Xin Jian, Valdas Jokubavicius, Mikael Syväjärvi, Rositsa Yakimova, and Jianwu Sun*, ?Nanoporous Cubic Silicon Carbide Photoanodes for Enhanced Solar Water Splitting?, ACS Nano, 15, 5502?5512 (2021).
Authors : A. Rioja Cabanillas(1,2), P. Fernández-Ibáñez(1) , R. Hauser(2) and J.A. Byrne(1)
Affiliations : 1 Nanotechnology and Integrated Bioengineering Centre, Ulster University, Shore Road, Newtownabbey, BT37 0QB, United Kingdom 2 Delft Intensified Materials production, Molengraaffsingel 10, 2629 JD Delft, Netherlands
Resume : Nutrient pollution due to intense human activities, affects the quality of the soil, air and water and have a detrimental impact on the ecosystems. Nutrient pollution in water bodies occurs due to excess of nitrogen compounds. Nitrogen excess is typically removed in wastewater treatment plants by several biological treatment steps. However, spatial and economical constrains prevent the full implementation of these processes for the required discharge limits in some plants. Moreover, wastewater has a great potential for energy recovery, which is not exploited at present. Consequently, there is a need to develop technologies that could improve the management of the nutrient cycle with a more cost efficient, sustainable and effective use of resources (1). In this work, we study the use of WO3 and P25 materials for the photoelectrochemical degradation of urea and energy recovery in the form of H2. The P25 photoanode was fabricated by immobilizing P25 onto a transparent conducting electrode, doped tin oxide coated glass (FTO), while the WO3 photoanode was synthesized by a hydrothermal method where the nanoplates were grown directly in the FTO glass. The experiments were carried out in a custom-made 2 compartment photoelectrochemical cell separated by a Nafion membrane and using platinized Ti mesh as cathode. The photoelectrochemical experiments showed that the WO3 photoanode generated 8 times higher photocurrent than P25, was able to absorb light up to 480 nm, and reached a IPCE of 36 % at 340 nm. The WO3 photoanode also showed considerable higher urea removal when compared to P25. The better performance of WO3 was attributed to an improved charges pathway, light absorption in the visible range and increased radical generation. Urea oxidation products were identified and the production of H2 analysed using GC. This research shows the potential of using WO3 photoanodes for the removal of nitrogen pollutants and energy recovery from wastewater as valuable alternative to conventional water treatment processes. References: (1) Rioja-Cabanillas, Adriana, David Valdesueiro, Pilar Fernandez-Ibañez, and John Byrne. 2020. ?Hydrogen from Wastewater by Photocatalytic and Photoelectrochemical Treatment.? Journal of Physics: Energy 3: 012006. https://doi.org/10.1088/2515-7655/abceab. Acknowledgement: We wish to acknowledge funding for the REWATERGY project from the European Union under the Marie Sk?odowska-Curie Actions (MSCA) ? Innovative Training Networks (Call: H2020-MSCA-ITN-2018). Project N. 812574
Authors : Yusuf Yuda Prawira1,2, Theodoros Dimopoulos1, Thomas Wicht2, Selina Götz1, Günther Rupprechter2, Rachmat Adhi Wibowo1
Affiliations : 1 AIT Austrian Institute of Technology GmbH, Center for Energy, Energy Conversion and Hydrogen, Giefinggasse 2, 1210, Vienna, Austria 2 Institute of Materials Chemistry, TU Wien, Getreidemarkt 9/BC, 1060 Vienna, Austria
Resume : A novel architecture of a Cu2ZnSnS4 (CZTS)-based heterojunction photocathode is proposed to enhance the performance in photoelectrochemical water reduction. The CZTS photoactive layers on Mo-coated soda-lime glass substrates were prepared first via spin-coating of CZTS precursor followed by subsequent sulfurization at 620 °C. The CZTS precursor used in this contribution contains dimethyl sulfoxide solvent, salts of Cu, Zn and Sn as well as sulfur source of thiourea. Subsequent sputter deposition of ZnO, Zn(O,S), Nb-doped TiO2 and Pt overlayers was carried out on the as-prepared CZTS photoactive layer. These overlayers were directly sputtered from their respective sputter targets, simplifying and speeding up the overall heterojunction photocathode preparation through a single sputtering run. All layers encompassing the heterojunction photocathode were structurally characterized by SEM, FT-Raman, Grazing-Incidence XRD and FT-IR. XPS analysis was additionally performed to quantify the composition of the photoactive layer. It is demonstrated that the CZTS photoresponse in the photoelectrochemical (PEC) water reduction increased appreciably with an additionally sputtered Zn(O,S) overlayer, indicated by an increase of PEC photocurrent density. Further photocurrent enhancement was achieved by the implementation of subsequent intrinsic ZnO, Nb-doped TiO2 and Pt. Nevertheless, it was found that the presence of the ZnO layer in the heterojunction photocathode reduced the photocurrent density, probably due to the existence of additional interfaces in the photocathode multilayer structure. The maximum PEC photocurrent density was delivered by the photocathode with CZTS/Zn(O,S)/Nb:TiO2/Pt architecture in 0.2 M Na2SO4 electrolyte, yielding ~16 mA/cm² at 0 VRHE and pH 10. To the best of our knowledge, this represents the highest photocurrent achieved for a Cd-free CZTS PEC device so far.
Authors : Alberto Piccioni1-2, Pierpaolo Vecchi1, Raffaello Mazzaro1-2, Michele Mazzanti3, Vito Cristino3, Stefano Caramori3, Luca Pasquini1-2
Affiliations : 1. Department of Physics and Astronomy, Università di Bologna, viale C. Berti Pichat 6/2, 40127 Bologna, Italy. 2. Institute for Microelectronics and Microsystems, National Research Council, via Gobetti 101, 40129, Bologna, Italy 3. Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Via Fossato di Mortara 17, 44121 Ferrara, Italy
Resume : The understanding of charge carrier dynamics followed by light absorption in heterojunction-based photoanodes is of the utmost importance for the performance optimization of photoelectrochemical (PEC) cells, especially under operando conditions. Intensity-modulated photocurrent spectroscopy (IMPS) is a powerful tool to this aim, but the information content provided by this technique can be further enhanced by means of excitation sources with different wavelengths. This innovative approach allows to selectively probe different layers of the heterojunction and identify the electron transport properties in each layer and at their interface. Herein, WO3/BiVO4 heterojunction decorated with a thin layer of cobalt hexacyanoferrate catalysts, the cobalt?iron analogue of Prussian Blue (CoFe-PB), was used in a conventional three electrode PEC cell for water splitting and its charge carrier dynamics was studied using Wavelength-Dependent IMPS. To gain a detailed and consistent picture of the processes occurring at such a complex heterojunction, the behaviour of WO3/BiVO4/CoFe-PB is compared with pristine colloidal WO3 and WO3/BiVO4 with and without the addition of a CoFe-PB catalyst. The proposed data analysis allows to identify the occurrence of interface recombination processes affecting the semiconductor junction, as well as the positive contribution of the inorganic complex catalyst on the charge separation efficiency of the BiVO4 layer. The deep understanding of the fate of charge carriers in the studied photoanode validates WD-IMPS as a straightforward method to widen the understanding of such structures.1 References: 1. Vecchi, P. et al. Charge Separation Efficiency in WO3/BiVO4 Photoanodes with CoFe Prussian Blue Catalyst Studied by Wavelength?Dependent Intensity Modulated Photocurrent Spectroscopy . Sol. RRL 2200108, (2022).
Authors : Farabi Bozheyev(1,2), Steffen Fengler(1), Jiri Kollmann(1), Thomas Klassen(1,3), Mauricio Schieda(1)
Affiliations : (1) Institute of Photoelectrochemistry, Helmholtz-Zentrum Hereon GmbH, Max-Planck-Str. 1, 21502 Geesthacht, Germany; (2) National Nanolaboratory, Al-Farabi Kazakh National University, 71 Al-Farabi Ave., 050000 Almaty, Kazakhstan; (3) Institute of Materials Technology, Helmut-Schmidt University, Holstenhofweg 85, 22043 Hamburg, Germany
Resume : A promising way to store solar energy is to convert it into chemical energy. In this respect, hydrogen (H2) generation via water splitting is one of the optimal routes. This can be achieved directly using semiconducting photoelectrodes, that through sunlight absorption generate charge carriers, which drive the electrolysis reaction. In order to achieve efficient solar water splitting, the physicochemical properties of the semiconductors used must be understood, particularly, the mechanisms and processes limiting the photovoltage. Transient surface photovoltage (TSPV) spectroscopy is a unique technique that can help identify potential and limitations in materials for solar hydrogen evolution. In this work, ammonium thiomolybdate (ATM: (NH4)2Mo3S13), tungsten diselenide (WSe2), and their heterojunction ATM/WSe2 are studied by TSPV spectroscopy. The separate photoelectrochemical performances of the ATM and WSe2 thin films investigated here are very limited. However, their combination ATM/WSe2 significantly increased the photocurrent density by two orders of magnitude. Using TSPV, the changes leading to such an effect are interpreted in terms of charge carrier generation, separation, and recombination processes. References:  Bozheyev F. et al. ACS Appl. Mater. Interfaces, 2022 (10.1021/acsami.2c01623).
Authors : Adriana Augurio(1), Qian Guo (1), Alberto Alvarez-Fernandez (2), Vishal Panchal (3), Bede Pittenger (4), Peter Dewolf (4), Stefan Guldin (2), Ana Belen Jorge Sobrido (1) and Joe Briscoe*(1)
Affiliations : (1) Queen Mary University of London, London, UK; (2) University College London, London, UK; (3) Bruker, Coventry, UK; (4) Bruker Nano Surfaces, Santa Barbara, USA;
Resume : Low-cost, oxide-based photo-electrocatalysts (PEC), such as Fe2O3, BiVO4, CuWO4, are gaining increased attention to achieve unassisted water splitting to produce solar fuels. Although they possess ideal bandgaps in the range of 2-2.5 eV, they suffer from a high level of surface recombination and low carrier mobility . Ferroelectric polarization has emerged as a new strategy in photocatalysis to induce opposite band bending at material surfaces facilitating increased charge separation and promoting selective redox reactions . However, most ferroelectric have wide bandgaps, and therefore do not absorb visible light, and are insulating therefore cannot transport photogenerated charges. Therefore, herein, we combine ferroelectric BaTiO3 with the photocatalyst Fe2O3 in parallel at the nanoscale to combine the benefits of ferroelectrics and photocatalysts in a nanocomposite film. To produce this structure, porous BaTiO3 (pBTO) thin films were synthesized by the soft template-assisted sol-gel method. Using different concentrations of organic template, the porosity of pBTO was controlled to obtain suitable thin films for photocatalyst integration. The overall porosity and surface area of the pBTO thin films is determined by SEM analysis and ellipsometry. The ferroelectric phase of pBTO is confirmed by XRD analysis and Raman spectroscopy. The switching of spontaneous polarization of pBTO by an electric field is verified by Piezoresponse Force Microscopy (PFM). The alignment of polar dipoles to the ferroelectric surface (Pup or Pdown) is evaluated by testing the PEC performance of pBTO after electrochemical (EC) poling at +-8V, which show that the photoanode performance is improved for Pdown. Lastly, the pBTO/Fe2O3 thin film shows an enhancement of the photocurrent density compared to either the bare Fe2O3 (by ?2 times) and pBTO thin films (by ?20 times), which could be correlated to the upward band bending induced by the ferroelectric polarization of pBTO. The PEC response in pBTO/Fe2O3 is accordingly regulated by EC poling without altering the Fe2O3 layer chemically (as confirmed by XPS), leading to further enhancement of the photocurrent. This research work shows a facile and low-cost approach for the development of novel ferroelectric/photocatalyst photoanodes with switchable control of their PEC performance, which possess a great potential for photoelectrochemical applications. References 1. S. Kment, Chem. Soc. Rev., 2017, 46, 3716. 2. F. Chen, Angew. Chem. Int. Ed., 2019, 58, 10061-10073.
Poster session I : Vladimir Smirnov, Byungha Shin, Joachim John
Authors : Hyunjoong Kim, Taeghwan Hyeon
Affiliations : School of Chemical and Biological Engineering, Seoul National University, 08826 Seoul, Republic of Korea
Resume : Building interface between metal and oxide has been importantly investigated to achieve superior catalytic performance. Despite the synergy effect of the metal-oxide interface, carbon-based materials have been widely used as supports in electrocatalysis instead of the oxide materials, due to electroconductivity. However, the carbon has been thought to be inert support that hardly interacts with metal nanoparticles. Herein, we report a facile method for hybridizing metal-oxide-carbon in an aqueous medium at room temperature. The method features self-termination of reaction and the absence of additional surfactant. The results from X-ray photoelectron spectroscopy reveals that our method formulates a large number of interface and metal-oxide interaction. The hybrid structure exhibits highly improved hydrogen oxidation activity in alkaline conditions, compared to catalyst without oxide. Moreover, by combining the interface formation with active metal tuning, the activity and stability of the catalyst can be further enhanced.
Authors : Isilda Amorim, Zhipeng Yu, Fátima Bento and Lifeng Liu
Affiliations : Isilda Amorim; Zhipeng Yu; Lifeng Liu - Clean Energy Cluster, International Iberian Nanotechnology Laboratory (INL), Avenida Mestre Jose Veiga, 4715-330 Braga, Portugal Isilda Amorim; Fátima Bento - Centre of Chemistry, University of Minho, Gualtar Campus, Braga, 4710-057, Portugal
Resume : Achieving efficient and stable oxygen evolution reaction (OER) in acidic medium is of paramount importance for hydrogen production via proton exchange membrane water electrolysis (PEM-WE). However, to enable efficient PEM-WE in acidic media, platinum group metal (PGM) based catalysts such as iridium (Ir) or ruthenium (Ru) are critical to drive the thermodynamically and kinetically demanding OER. As a consequence, the use of high cost and scarce PGM catalysts constrains the large-scale deployment of PEM-WE technology and therefore developing electrocatalysts containing significantly reduced PGM without compromised performance becomes a pressing need. In this work, Ir nanoparticles were produced by chemical reduction on cobalt-nickel phosphide nanowires self-supported on carbon paper (CoNiP-Ir/CP). EDX analysis showed an arity of Ir of around 4% on the CoNiP/CP surface. Preliminary results indicate a good catalytic activity of CoNiP-Ir/CP toward OER in 0.5 M H2SO4, presenting an overpotential of 289 mV at current density of 10 mA cm-2. Moreover, the CoNiP-Ir/CP is able to sustain continuous OER electrolysis up to 70 h at 10 mA cm?2.
Authors : Robbe Jacops, Davino De Bruyn, Bjorn Joos, Pieter Levecque, Marlies Van Bael, Tom Breugelmans, An Hardy
Affiliations : UHasselt, Hasselt University, Institute for Materials Research and imec division imomec, Materials Chemistry, DESINe group, Diepenbeek, Belgium / Research Group Applied Electrochemistry & Catalysis, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium; Research Group Applied Electrochemistry & Catalysis, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium; UHasselt, Hasselt University, Institute for Materials Research and imec division imomec, Materials Chemistry, DESINe group, Diepenbeek, Belgium; Research Group Applied Electrochemistry & Catalysis, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium; UHasselt, Hasselt University, Institute for Materials Research and imec division imomec, Materials Chemistry, DESINe group, Diepenbeek, Belgium; Research Group Applied Electrochemistry & Catalysis, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium; UHasselt, Hasselt University, Institute for Materials Research and imec division imomec, Materials Chemistry, DESINe group, Diepenbeek, Belgium
Resume : To reach the EU goal of being climate neutral by 2050, the energy network needs to be decarbonized. This raises a need for a sustainable method to store and transport large amounts of renewable energy. Green hydrogen is one of the key elements for the transition to renewable energy storage. Splitting water to form hydrogen gas is a way to convert renewable energy to a chemical that can be used for energy storage and transport or as a building block for other chemicals. Photoelectrochemical (PEC) water splitting technology is an interesting alternative to conventional electrolysis for hydrogen generation. The concept of PEC water splitting is to directly convert incident sunlight to electrical energy and split water to form hydrogen and oxygen gas. One of the main challenges for this technology is to develop photoelectrode materials that are highly efficient at converting sunlight to hydrogen and are stable during operation. This work focuses on Bi2WO6 as a possible photoactive material for PEC water splitting. Bi2WO6 microspheres are synthesized utilizing a hydrothermal method. Thin film Bi2WO6 is prepared by spin coating and subsequent thermal treatment of an aqueous solution containing citrato-complexes of Bi3+ and W6+. By combining both methods i.e. mixing the microspheres in the solution before spin coating, a complex photoelectrode of embedded Bi2WO6 microspheres in a continuous Bi2WO6 thin film is prepared. This electrode has a higher specific surface area compared to the standard thin film, and it shows better particle to substrate adhesion compared to depositing the particles without thin film?s precursor solution. The effects of the hydrothermal synthesis parameters (temperature, time, pH and concentration) and the effects of the spin coating parameters (particle loading, precursor concentration/composition and spin speed/time) are studied by examining the crystal structure, morphology, stability, optical properties and photoelectrochemical performance of the photoelectrode. The techniques used to study these properties are XRD, UV-VIS, SEM, TGA, ICP-OES, and (photo)electrochemical analysis techniques. This research is part of the BE-HyFE project, which is a Belgian academic collaboration project, funded by the federal Energy Transition Fund by FPS Economy.
Authors : Stetsyuk T.1, Malyshev V.2, Gab A.2, Shakhnin D.2, Korolkevich A.2
Affiliations : 1 Frantsevich Institute for Problems of Materials Science of NAS of Ukraine 2 Open International University of Human Development ?Ukraine?
Resume : An analysis of the experimental data of the chronovoltammetric study of the electroreduction of cobalt (II), molybdenum (VI), and tungsten (VI) against the background of a tungstate melt confirms the possibility of implementing the electrowinning of cobalt, molybdenum, and tungsten. Na2WO4?1.5 mol. % WO3 melt was used as the base electrolyte for the deposition of alloys of a wide composition. The electrodeposition of tungsten coatings with a tungsten anode was carried out within the temperature range 1123?1173 K at a cathode current density from 0.04 to 0.14 A/cm2. It was found that at a current density 0.04?0.10 A/cm2, tungsten coatings have a columnar structure and a thickness of up to 150?200 µm with a microhardness of 3.33?4.12 GPa. The maximum coating thickness is up to 500 µm. For the cathodic co-deposition of metals with the alloy formation, the tungsten anode was replaced by a more noble cobalt anode, and the electrolysis was carried out at cathodic current densities 0.05?0.12 A/cm2. The WO3 concentration was maintained within the range 0.1?1.5 mol. %, while the CoO concentration was changed from 0.01 up to 1.0 mol. %. In this case, the molar ratio of tungsten and cobalt ions varied from 150 to 0.1. An increase in CoO concentration or temperature and a decrease in the cathode current density lead to an increase in the cobalt content in the deposit. From melts containing 0.08?1.0 mol. % CoO, at temperatures 1123?1173 K, continuous layers of CoW and Co3W intermetallic compounds with a finely crystalline or layered structure and a microhardness 4.90?8.24 GPa are successively deposited onto the cathode. From melts without WO3, at current densities up to 0.05 A/cm2, solid cobalt layers of a block or columnar-block structure are formed, up to 50 ?m thick and with a microhardness 1.47?1.77 GPa. The method of cobalt - molybdenum alloys deposition is similar to the described above. The only difference is that the initial melt was Na2WO4?5.0 mol. % MoO3. In this case, the alloys deposition patterns are similar to those of W-Co. The MoO3 concentration was maintained within the range 0.1?5.0 mol. %, while the CoO concentration was changed from 0.01 to 2.0 mol. %. In this case, the molar ratio of molybdenum and cobalt ions varied from 500 to 0.05. From melts containing 0.1?0.8 mol. % CoO, at a temperature 1123?1173 K, continuous layers of intermetallic compounds CoMo and Co3Mo are successively deposited onto the cathode. Their microhardness in this series decreases from 6.37 down to 3,82 GPa. From melts containing no MoO3, at current densities up to 0.05 A/cm2, continuous cobalt layers of a block or columnar-block structure are formed. The study of the electrochemical behavior of molybdenum, tungsten and cobalt in a tungsten melt and of the effect of electrolysis conditions on the composition and structure of deposits of cobalt-molybdenum (tungsten) alloys showed that, with a decrease in the concentration of cobalt and an increase in the concentration of molybdenum (tungsten) in the melt, the phase composition of cathode deposits changes from cobalt through cobalt-molybdenum (tungsten) alloys of various compositions to pure molybdenum (tungsten).
Authors : Yuya Harada, Daiki Kono, Dai Xinjie, Tsukasa Yoshida
Affiliations : Yamagata University
Resume : Electric power supplied by renewable sources such as solar and wind has become viable due to their significant cost reduction, but their intermittent electricity demands required the urgent development of large-scale storage technologies. Electrolysis of water is the ideal way to convert electrical energy into hydrogen, but noble metals and their oxides are used as electrocatalysts due to their stability and activity. For sustainable technological development, it is necessary to develop alternative electrocatalysts made from abundant elements. Some metal-free organic conductive polymers with hydrogen bonding capabilities have shown high electrocatalytic activities toward hydrogen evolution reactions (HER). In our recent study, we successfully electropolymerized neutral red (NR) to form conductive poly-NR (PNR) with high catalytic activity for HER. PNR hydrogen-bonding N atoms annealed into phenazine aromatic systems as well as amino substituents. The mechanism and kinetics of HER electrocatalysis by PNR have been clarified by electrochemical analysis combined with in situ spectroscopy and DFT calculations. The films of PNR were prepared by electropolymerization on F-doped tin oxide coated conductive glass (FTO, Asahi Glass) and SIGRATHERM® GFA5 Carbon felt at 50 mV s-1 for 50 times in a 5 mM NR - 0.1 M sulfuric acid aqueous solution under nitrogen. Polyaniline (PANI) was also obtained by the same method for comparison. HER catalysis was investigated by linear sweep voltammetry (LSV) in 1 M trifluoromethanesulfonic acid (TfOH) under N2. Infrared spectroscopy, UV-visible spectroscopy, and Fourier transform infrared spectroscopy were used to characterize the film samples. UV-visible spectroelectrochemical monitoring of the reaction intermediate was conducted to determine the rate of HER. Under acidic conditions, PNR undergoes a pseudo-reversible reduction that shifts -61.8 mV/pH, and HER takes off at this point. From the observed Nernstian relationship, the same number of protons and electrons should pair together, resulting in a single reduced PNR-H or a double reduced PNR-H2. The DFT calculation also suggests protonation of N atoms. It is possible to associate the hydrogen atoms stabilized in the reaction intermediate with the release of Hydrogen (Tafel mechanism), which completes the electrocatalytic cycle. PNR reduction is actually associated with a change in color. When -0.15 V vs. RHE is continuously applied to PNR, the broad reddish absorption peaking around 500 nm attenuates to a pale yellow, producing PNR-H and/or PNR-H2. Under open circuit under Nitrogen, a gradual recovery of the original red PNR was observed. Therefore, the rate of spectral change is analyzed to determine the rate of the Tafel process. The pseudo-first order reaction rate law can be applied since proton is abundant and its concentration is constant, so that the rate of HER is simply the rate of consumption of PNR-H or PNR-H2. From the absorbance at 545 nm before and after reduction, the ratio of PNR-H and PNR-H2 is defined. A reaction rate constant k of 9.98×10-4 /s for this rate-limiting step.good fit of the experimental data was obtained to yield a pseudo-first-order.
Authors : Daiki Kono1,Yuya Harada1, Xinjie Dai1, Tsukasa Yoshida1
Affiliations : 1.Yamagata University
Resume : Conductive polymers with hydrogen bonding sites can act as metal-free electrocatalysts for hydrogen evolution reaction (HER). Neutral red (NR) is a kind of phenazine dyes and known as a pH indicator. NR is also an analogue to aniline (ANI) and thus can be polymerized into PNR by oxidative radical coupling as ANI becomes PANI. While the presence of peripheral amino group makes the above-mentioned polymerization possible, the presence of N atoms annulated in the aromatic system are expected to act as the sites for protonation, so that PNR can exhibit HER catalysis unlike PANI. One of the best ways to obtain PNR film should be electropolymerization deposition (EPD), triggered by electrochemical oxidation of NR to its radical, just like it is commonly done for PANI. However, EPD was only considered as a recipe to obtain materials, and its process was not studied in depth. For the convenience of monitoring the film growth, potential cycling (just like cyclic voltammetry to count increment of charges associated with the redox of the polymer) was almost always used, even though polymer growth is only expected from oxidation of monomer. In this study, we have carried out EPD of PNR with various electrolysis protocols; potential sweep/cycling (CV), potentiostatic electrolysis (chronoamperometric, CA), and pulsed potential electrolysis (PP), to compare growth rate as well as growth/charge. Reddish-black thin films of PNR were obtained on F-doped SnO2 (FTO) conductive glass, so that we could quantify PNR by vis-absorbance. The oxidation of NR occurs at around +1 V vs. Ag/AgCl, whereas the reduction around -0.1 V. While potential cycling between +1.2 and -0.2 V yielded good PNR thin films with stable CVs, potentiostatic electrolysis at +1.05 V resulted in a quick decrease of the anodic current in CA, caused by slowdown of charge transfer kinetics, not by depletion of NR as confirmed by experiments employing an RDE. The increment of the optical density (O.D.) per charge was the same for CV and CA methods, when integra of anodic charge from CV and CA were compared to O.D., despite that the latter was much slower per time. When negative end of the potential cycling was varied for the CV method, we realized that de-doping of PNR at around +0.3 V resulted in improvement of charge transfer kinetics for oxidation of NR, not the reduction of PNR at ca. -0.1 V. Consequently, PP to apply alternating potentials at +1.05 V for oxidation of NR and +0 V for de-doping of PNR to refresh the surface resulted in the most efficient (fastest) EPD of PNR. Interestingly, these PNR thin films showed slight differences in their absorption spectra to reflect their differences of electronic structures. The conditions of EPD can therefore be optimized to achieve high catalytic activity and stability for HER.
Authors : Olga Malinowska, dr Kamila Zar?bska
Affiliations : University of Warsaw
Resume : In recent years, the population growth and industrial development have contributed to the increase in water pollution. Organic dyes constitute a large group of pollutants. The biological methods of water purification used are insufficient because these compounds are difficult to decompose in the natural environment due to their inhibitory effects on the growth and activity of microorganisms. Therefore, more effective methods are needed. Many publications have reported that semiconductor heterogeneous photocatalysis has a great potential in the struggle against hard-to-decompose organic pollutants in water. The first studies focused on TiO2, but due to its relatively large energy bandgap and the photocatalytic action only in the UV radiation range, the search for an equally easily available photocatalyst that would also absorb visible light and thus be more efficient, cheaper and easier in obtaining has started. One of the promising materials is Ag3PO4, n-type semiconductor that can efficiently oxidize water by releasing oxygen and degrade organic pigments when exposed to visible radiation due to adequate energies of valence and conduction bands. The present research describes the synthesis, characterization and exploration of the photocatalytic activity of Ag3PO4. Its nanoparticles were synthesized by electrochemical methods following the literature recipe. The influence of factors such as the presence of citrate ions in the electrolyte solution or the applied potential on the synthesis process was discussed. Based on the UV-Vis spectrum and using the Tauc method, the band energy gap was determined (2.36 eV). The EVB and the ECB were also determined, which were respectively: 2.81 eV and 0.45 eV vs. SHE. These values became the basis for predictions about the mechanism of the photocatalytic process. However, the photostability measurements have shown that Ag3PO4 is unstable due to photocorrosion caused by photo-generated electrons from the conduction band. This effect can be avoided by using the electron scavengers and creating a heterojunction. To check the behavior of the semiconductor as the photocatalyst, a test was performed with an OH? scavenger - terephthalic acid. The changes in the concentration of OH? caused by the photocatalytic action of Ag3PO4 were monitored using the fluorescence spectroscopy. A comparison of the photocatalytic decomposition of MO dye with the use of Ag3PO4 and the composite Ag3PO4/g-C3N4 has shown that the tested photocatalyst, Ag3PO4, shows good photocatalytic properties in visible light. The heterojunction, however, showed greater photostability. Improving the photostability of a given semiconductor may result in obtaining a good and effective photocatalyst capable of purifying water under visible radiation. Combining the photocatalytic potential of Ag3PO4 with renewable energy in the form of natural sunlight can be an environmentally friendly, inexpensive and widely available method of wastewater treatment.
Authors : Xiaolan Kang (1), Vilde Mari Reinertsen (2), Kevin Gregor Both (1), Augustinas Galeckas (2), Thomas Aarholt (2), Øystein Prytz (2), Truls Norby (1), Dragos Neagu (3), Athanasios Chatzitakis (1)*
Affiliations : (1) Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, Gaustadalléen 21, NO-0349 Oslo, Norway; (2) Centre for Materials Science and Nanotechnology, Department of Physics, University of Oslo, P. O. Box 1048 Blindern, NO-0316, Oslo, Norway; (3) Department of Chemical and Process Engineering, University of Strathclyde, 75 Montrose St, G1 1XJ, Glasgow, United Kingdom
Resume : In situ metal exsolution is a powerful method to prepare well-anchored and catalytically active nanoparticles (NPs) supported on perovskite oxide-based supports. These exsolved NPs are directly socketed on the perovskite?s surface and can be re-shaped without changing their initial location and structural arrangement, but this usually involves lengthy treatments and use of toxic gasses (CO, NH3). In this work, we hybridize exsolved Ni NPs on SrTiO3 with Au or Pt through the galvanic replacement/deposition method, which is simpler and safer, leading to a wealth of new bimetallic nanostructures. In the case of AuNi we achieve, among other, supported antenna-reactor nanostructures, which show high activity in plasmon-assisted photoelectrochemical (PEC) water splitting in strongly alkaline conditions. In order to highlight the versatility of our method, a simple tuning of the galvanic replacement step allows the formation of socketed PtNi bimetallic nanoparticles of low Pt loadings and high electrocatalytic activity for the hydrogen evolution reaction (HER) in alkaline conditions. This powerful methodology enables the design and synthesis of multimetallic and well-adhered catalysts with tunable catalytic functionality through minimal engineering.
Authors : Maida Aysla Costa de Oliveira1, Hugo Nolan1, Christian Schröder1, Marc Brunet-Cabré1, Kim McKelvey1,2 and Paula E. Colavita1
Affiliations : 1School of Chemistry, Trinity College Dublin and 2School of Chemical and Physical Science, Victoria University of Wellington College Green, Dublin 2, Ireland email@example.com
Resume : Vanadium redox flow batteries (VRFBs) stand out as promising electrochemical systems for coupling storage to renewables due to advantages such as low environment impact, large-scale energy storage, long cycle life, and deep discharge capability. A VRFB consists of two tanks with vanadium redox couples, separated by an ion-exchange membrane and circulated through a cell composed of porous electrodes at which the charge/discharge reactions take place . Nevertheless, kinetics barriers for vanadium redox processes and understanding of the reaction mechanism at the electrode/electrolyte interface for both oxidation and reduction process of vanadium remain critical for the design of high performing VRFB devices . Conventional graphitic carbon electrodes are often employed to achieve the required high efficiency mass transfer rates and charge transfer of V+3/V+2 and VO+2/VO2+ couples at the electrode surfaces as this minimizes high overpotentials and undesirable efficiency losses. However, the kinetics of vanadium species is generally sluggish at these surfaces and the intrinsic activity of conventional carbons can limit performance . Nitrogenated active sites and surface properties are beneficial for achieving fast kinetics and high selectivity of species during vanadium redox, due to the strong capability to provide more active sites and hydrophilic C-N bonds . In this study, we developed carbon nanoarchitectures with controlled N-site density and distribution, for the fundamental understanding of the chemical, structural and electronic effects on charge transfer kinetics at the positive electrode. A combination of surface chemistry, nanoscale electrochemistry, and conventional electrochemical methods were performed to evaluate the performance of N-doped carbons towards the VO2+/VO2+ couples. Electrochemical voltammetry and impedance methods show that both N-site type and carbon organization affect charge transfer impedances and rate determining steps involved in the VO2+/VO2+ charge/discharge process. Thus, from the proposed materials we will discuss the implications of our findings for the design of carbon model surface for VRFB performance. References:  Meskinfam, et al., Interaction of vanadium species with a functionalized graphite electrode: A combined theoretical and experimental study for flow battery applications (2018), 420,142.  Choi, et al., Understanding the redox reaction mechanism of vanadium electrolytes in all-vanadium redox flow batteries, J Energy Storage (2019), 21, 327.  Behan, et al., Combined optoelectronic and electrochemical study of nitrogenated carbon electrodes. J Phys Chem C (2017), 121, 6596.  Tripathi et al., Interfacial co-polymerization derived nitrogen doped carbon enables high-performance carbon felt for vanadium flow batteries. J. Electrochem (2021), 168, 110548.
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Electrocatalysis III : Salvador Eslava
Authors : Serhiy Cherevko
Affiliations : Helmholtz-Institute Erlangen-Nuremberg for Renewable Energy (IEK-11), Forschungszentrum Jülich Cauerstr. 1, 91058, Erlangen, Germany
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 . 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 . Recent representative examples of the utilization of both families of setups to study oxygen reduction and oxygen evolution reaction electrocatalysts will be given. References:  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.  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.  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.  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.  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.  O. Kasian, S. Geiger, K.J.J. Mayrhofer, S. Cherevko, Electrochemical On-line ICP-MS in Electrocatalysis Research, Chem Rec, 19 (2019) 2130-2142.  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.  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.
Authors : Zhipeng Yu,a,b,c Chaowei Si,d Alec P. LaGrow,a Zhixin Tai,a Wolfgang A. Caliebe,e Akhil Tayal,e Maria J. Sampaio,b,c Juliana P.S. Sousa,a Isilda Amorim,a Ana Araujo,a.b,c Joaquim L. Faria,b,c Junyuan Xu,a,g,* Bo Lid,* and Lifeng Liua,*
Affiliations : a International Iberian Nanotechnology Laboratory (INL), Avenida Mestre Jose Veiga, 4715-330 Braga, Portugal b Laboratory of Catalysis and Materials (LSRE-LCM), Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal c Associate Laboratory in Chemical Engineering, Faculty of Engineering (ALiCE), University of Porto, Rua Dr. Roberto Frias s/n 4200-465 Porto, Portugal d Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China e Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, D-22607 Hamburg, Germany g Laboratory of Advanced Spectro-electrochemistry and Li-on Batteries, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 116023 Dalian, China.
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 . 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:  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).
Authors : Tatiana Priamushko, Attila Kormányos, Rebecca Pittkowski, Qi Dong, Bin Xiao, Maria Minichova, Valentin Briega-Martos, Alan Savan, Ken J. Jenewein, Thomas Böhm, Liangbing Hu, Alfred Ludwig, Matthias Arenz, Serhiy Cherevko
Affiliations : Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (IEK-11), Forschungszentrum Jülich, 91058 Erlangen, Germany; Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (IEK-11), Forschungszentrum Jülich, 91058 Erlangen, Germany; Department of Chemistry, University of Copenhagen, DK-2100 Copenhagen O, Denmark; Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA; Materials Discovery and Interfaces, Institute for Materials, Ruhr-Universität Bochum, 44801 Bochum, Germany; Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (IEK-11), Forschungszentrum Jülich, 91058 Erlangen, Germany; Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (IEK-11), Forschungszentrum Jülich, 91058 Erlangen, Germany; Materials Discovery and Interfaces, Institute for Materials, Ruhr-Universität Bochum, 44801 Bochum, Germany; Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (IEK-11), Forschungszentrum Jülich, 91058 Erlangen, Germany; Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (IEK-11), Forschungszentrum Jülich, 91058 Erlangen, Germany; Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA; Materials Discovery and Interfaces, Institute for Materials, Ruhr-Universität Bochum, 44801 Bochum, Germany; NanoElectroCatalysis Group, Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, 3012 Bern, Switzerland; Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (IEK-11), Forschungszentrum Jülich, 91058 Erlangen, Germany.
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. Moreover, HEA catalysts are expected to exhibit high stability. 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. 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). 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.  T. Löffler, A. Ludwig, J. Rossmeisl, W. Schuhmann, Angew. Chemie - Int. Ed. 2021, 60, 26894.  Y. Sun, S. Dai, Sci. Adv. 2021, 7, 1.  G. C. da Silva, K. J. J. Mayrhofer, E. A. Ticianelli, S. Cherevko, J. Electrochem. Soc. 2018, 165, F1376.
Authors : Tamás Ollár1*, Antal A. Koós2, Péter Vancsó2, Zakhar I. Popov3, Gergely Dobrik2, Pavel B. Sorokin3, and Levente Tapasztó2
Affiliations : 1 Centre for Energy Research, Institute for Energy Security and Environmental Safety, Surface Chemistry and Catalysis Department, Centre for Energy Research, 1121 Budapest, Hungary; 2Centre for Energy Research, Institute of Technical Physics and Materials Science, 1121 Budapest, Hungary; 3National University of Science and Technology MISiS, 119049 Moscow, Russia
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. 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. 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  Pet?, J., Ollár, T., Vancsó, P. et al. Nature Chemistry 10, 1246?1251 (2018).  Vancsó, P. et al ACS Energy Letters 2019, 4, 8, 1947?1953
Authors : Dr. Jean Marie Vianney Nsanzimana, Prof. Benjamin Butz, Prof. Manuela Killian, Dr. Julian Muller, Dr. Sina Hejazi, Dr. Yilmaz Sakalli, Marco Hepp, Charles Ogolla, and Dr. Christian Wiktor.
Affiliations : University of Siegen
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.
Photoelectrocatalysis III : Nina Plankensteiner, Joachim John
Authors : Jan Mertens
Affiliations : Engie, Simon Bolivar Laan 34, 1000 Brussels, Belgium Ghent University, Ghent, Belgium
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.
Authors : Salvador Eslava
Affiliations : Department of Chemical Engineering, Imperial College London, United Kingdom
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.
Authors : Chloe Forrester,a Adriana Augurio,a James Durrant,b Joe Briscoe a
Affiliations : a Queen Mary University of London, London, UK; b Imperial College London, London, UK
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
Authors : Ian Lorenzo E. Gonzaga, Candy C. Mercado
Affiliations : Department of Engineering Science, University of the Philippines Los Baños, Department of Mining, Metallurgical, and Materials Engineering, University of the Philippines Diliman; Department of Mining, Metallurgical, and Materials Engineering, University of the Philippines Diliman
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.
Authors : JYOTI YADAV, PARUL RATURI, SARJANA YADAV, J.P.SINGH
Affiliations : IIT DELHI
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.
Authors : Raffaello Mazzaro(a,b), Irene Carrai(a), Alberto Piccioni(a,b), Pierpaolo Vecchi(a), Giacomo Morselli(c), Elena Bassan(c), Paola Ceroni(c), Silvia Grandi(d), Serena Berardi(d), Stefano Caramori(d), Luca Pasquini(a,b).
Affiliations : (a) Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, 40127, Bologna, Italy (b) Institute for Microelectronics and Microsystems, National Research Council, via Gobetti 101, 40129, Bologna, Italy (c) Department Chemistry, University of Bologna, Selmi 2, 40129, Bologna, Italy (d) Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Via Fossato di Mortara 17, 44121 Ferrara, Italy
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.
Authors : Harsh Chaliyawala1, Labibe Soilihi1, Diane Muller-Bouvet1, Christine Cachet-Vivier1, Stephane Bastide1, Tarik Bourouina2, Fréderic Marty2, Abir Rezgui2, Sylvain Le Gall3, Encarnacion Torralba1*
Affiliations : (1) Univ Paris Est Creteil, CNRS, Institut de Chimie et des Matériaux Paris-Est (ICMPE), UMR 7182, 2 rue Henri Dunant, 94320 Thiais, France (2) ESYCOM - Electronique, Systèmes de communication et Microsystèmes (Université de Paris-Est - Marne-la-Vallée) Cité Descartes, 77454 Marne-la-Vallée Cedex 2, France (3) Group of electrical engineering Paris, UMR CNRS 8507, Centrale Supélec, (Univ. Paris Sud) 91192 Gif sur Yvette CEDEX, France
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 . 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 ), 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 . 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 . 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. . J. He, et al., ACS Energy Lett. 2020, 5, 1996?2014.  E. L. Warren, et al., J. Phys. Chem. C 2014, 118, 747.  E. Torralba, et al., ACS Catal. 2015, 5, 6138.  N. S. Lewis, et al., ACS Energy Lett. 2020, 5, 2528.
Electrocatalysis IV : Mihalis Tsampas
Authors : Dr Sonya Calnan
Affiliations : Competence Centre Photovoltaics Berlin (PVcomB), Helmholtz-Zentrum Berlin fu?r Materialien und Energie, Schwarzschildstraße 3, 12489 Berlin, Germany
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.
Authors : David Zanders, Jan-Lucas Were, Jorit Obenlüneschloss, Michael Gock, Anjana Devi
Affiliations : Inorganic Materials Chemistry, Ruhr University Bochum, Universitätsstraße 150, Bochum, Germany 44780 (for DZ, JLW, JO, AD) Global Business Unit Heraeus Precious Metals, Heraeus Deutschland GmbH & Co. KG, Heraeusstraße 12-14, Hanau, Germany 63450 (for MG)
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. 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. 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.  G. Murdoch, et al., in 2020 IEEE IITC 1052020, p. 4.  https://www.imec-int.com/en/press/imec-presents-alternative-metals-advanced-interconnect-and-contact-schemes-path-2nm.  Y. Li, et al, Adv. Energy Mater. 2020, 10, 1903120.  https://www.atomiclimits.com/alddatabase/.
Authors : Saswati Santra1, Verena Streibel1, Siyuan Zhang2 and Ian D. Sharp1*
Affiliations : 1Walter Schottky Institute and Physics Department, Technical University of Munich, Am Coulombwall 4, Garching, 85748 Germany 2Max-Planck-Institut für Eisenforschung, Max-Planck-Straße 1, Düsseldorf 40237, Germany
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.
Authors : Hangjuan Ren, Shik Chi Edman TSANG, Alexei A. Lapkin, Joel W. Ager
Affiliations : University of Oxford; University of Oxford; University of Cambridge; Lawrence Berkeley National Laboratory, University of California, Berkeley
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.
Electrocatalysis V : An Hardy, Joachim John
Authors : M.N. Tsampas1, M. Lavorenti1, W. L. Vrijburg2, S. Dimitriadou2, T. V. Pfeiffer2, F.M. Sapountzi1,3
Affiliations : 1 Dutch Institute For Fundamental Energy Research (DIFFER), De Zaale 20, 5612 AJ, Eindhoven, the Netherlands 2 VSPARTICLE BV, Molengraaffsingel 10, 2629 JD, Delft, the Netherlands 3 Syngaschem BV, Syncat@DIFFER, PO Box 6336, 5600 HH, Eindhoven, the Netherlands
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.
Authors : Nina Plankensteiner [1,2] Tibor Kuna , Alexandra Galetova [1,3] Anna Staerz , Rico Rupp , Patrick Steegstra , Joachim John , Philippe M. Vereecken [1,2]
Affiliations :  Imec, Kapeldreef 75, 3001 Leuven, Belgium  KULeuven, cMACS, Celestijnenlaan 200F, 3001 Leuven, Belgium  Chemistry Department, KU Leuven, Celestijnenlaan 200f, 3001 Heverlee, Belgium
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.  ACS Appl. Mater. Interfaces 10, 44634?44644 (2018)  J. Phys. Chem. C 119, 2105?2112 (2015)
Authors : Dr. rer. nat. Karuppasamy Dharmaraj, Rania Hanna, Prof. Dr. Rutger Schlatmann, Dr. Sonya Calnan
Affiliations : Institut Kompetenz-Zentrum Photovoltaik Berlin (PVcomB), Helmholtz-Zentrum Berlin für Materialien und Energie, Schwarzschildstraße 3, 12489 Berlin, Germany
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.
Authors : Jonas Englhard(1), Rebecca Bährle(2), Stefanie Böhnke-Brandt(2), Mirjam Perner(2), Julien Bachmann(1)
Affiliations : (1) Department of Chemistry and Pharmacy, Friedrich-Alexander University of Erlangen-Nürnberg, Cauerstrasse 3, D ? 91058 Erlangen, Germany (2) Geomicrobiology, GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3, D ? 24148 Kiel
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.
Authors : Anna Staerz, Nina Plankensteiner, Stanley Bus, Alexandra Galetova, Sukhvinder Singh, Maarten Mees, Philippe M. Vereecken
Affiliations : IMEC, Leuven, 3000, Belgium: KU Leuven, Leuven, 3001, Belgium
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).
Poster session II : Vladimir Smirnov, Byungha Shin, Joachim John
Authors : Nam-Woon Kim, Jeong Bae Kim, Jihun Oh, Hyunung Yu
Affiliations : Nam-Woon Kim; Jeong Bae Kim; Hyunung Yu-Korea Research Institute of Standards and Science (KRISS), Daejeon 34113, Republic of Korea ;Jihun Oh-Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
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.
Authors : Sanghyeon Lee
Affiliations : Yonsei University KIURI Institute
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.
Authors : Filippo Pota, Christian Schroder, Swapnil Ingle, Hugo Noland, Paula E. Colavita
Affiliations : School of Chemistry, Trinity College Dublin
Resume : Valorisation of biomass to fuel/chemicals will be one of the main routes for the reduction of carbon emissions . 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.  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.  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.  Weber, R. S., Effective Use of Renewable Electricity for Making Renewable Fuels and Chemicals. ACS Catal. 2019, 9 (2), 946-950.
Authors : Karthik Kannan1,2, Debabrata Chanda1,2, Jagadis Gautam1,2, Mikiyas Mekete Meshesha1,2, Jang Seok Gwon1,2, Myungsik Choi3, BeeLyong Yang1,2*
Affiliations : 1. School of Advanced Materials Science and Engineering, Kumoh National Institute of Technology, 61 Daehak-ro, Gumi-si, Gyeongbuk, 39177, Republic of Korea 2. GHS Co., Ltd. Gumi-si, Republic of Korea. 3. SJ Tech. Co., Ltd, 1026-1 Daecheon-Dong, Dalseo-Gu, Daegu City, Republic of Korea *Corresponding author: Tel: +82-(54)-478-7741, E-mail: firstname.lastname@example.org
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.
Authors : Zhipeng Yu,a,b,c Yifan Li,d Vlad M. Diaconescu,e Laura Simonelli,e Jonathan R. Esquius,a Isilda Amorim,a Ana Araujo,a,b,c Joaquim L. Faria,b,c and Lifeng Liu,a,*
Affiliations : a Clean Energy Cluster, International Iberian Nanotechnology Laboratory (INL), Av. Mestre Jose Veiga, 4715-330 Braga, Portugal b Laboratory of Separation and Reaction Engineering ? Laboratory of Catalysis and Materials (LSRE-LCM), Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n 4200-465 Porto, Portugal c Associate Laboratory in Chemical Engineering, Faculty of Engineering (ALiCE), University of Porto, Rua Dr. Roberto Frias s/n 4200-465 Porto, Portugal d School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao 266033, P.R. China e ALBA Synchrotron, Carrer Llum 2-26, Cerdanyola del Valles, Barcelona 08290, Spain
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 . 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:  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).
Authors : Kamila Zar?bska, Piotr Piotrowski, Magdalena Skompska
Affiliations : University of Warsaw, Faculty of Chemistry
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.
Authors : Tomasz K. Ratajczyk, Krzysztof Miecznikowski, Miko?aj Donten
Affiliations : Warsaw University, Faculty of Chemistry (all)
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. 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 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.  Solarska R. et al., Nanoporous WO3?Fe2O3 films; structural and photo-electrochemical characterization, Functional Materials Letters, 7(06), 1440006  Tsyntsaru N. et al. Modern trends in tungsten alloy electrodeposition with iron group metals, Surface Engineering and Applied Electrochemistry 48(6):491?520
Authors : Haruto Morinaga, Tensho Nakamura, Hana Kudo, Tsukasa Yoshida.
Affiliations : Yamagata University
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.
Authors : Pramod. Kunturu1, M. Lavorenti1, P. Varadhan1, S. Bera1, H. Johnson2, S. Kinge2, M.C.M. van de Sanden1,3, M.N. Tsampas1
Affiliations : 1 Dutch Institute for Fundamental Energy Research (DIFFER), 5612AJ Eindhoven, the Netherlands 2 Toyota Motor Europe NV/SA, Hoge Wei 33, 1930 Zaventem, Belgium 3 Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, the Netherlands
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.
Authors : Edward Allery David Baker, Joe Pitfield, Conor Jason Price, Steven Paul Hepplestone
Affiliations : Department of Physics, University of Exeter, Exeter, EX4 4QL, UK
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 . However its bulk band gap is too small for water splitting . 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:  Qing Tang and De En Jiang. ACS Catalysis, 6(8):4953?4961, Aug 2016.  B. Amin, et al . Phys. Rev. B, 92:075439, Aug 2015.  C. Long, et al . ACS Appl. Energy Mater., 2, 1, 513-520, 2019.  G. Zhang, et al . Appl. Phys. Lett., 114, 253102, June 2019.
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Photoelectrocatalysis IV : Vladimir Smirnov
Authors : Kang Xiaolan,(1) Chaperman Larissa,(2) Galeckas Augustinas,(3) Merah Souad Ammar,(2) Mammeri Fayna,(2) Norby Truls,(1) Chatzitakis Athanasios,(1)
Affiliations : (1) Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, Oslo, Norway; (2) Interfaces Traitements Organisation et Dynamique des Systèmes (ITODYS), Université de Paris, Paris, France; (3) Centre for Materials Science and Nanotechnology, Department of Physics, University of Oslo, Oslo, Norway
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.
Authors : Marek Lavorenti (1), Pramod Kunturu (1), Purushothaman Varadhan (1), Hannah Johnson (2), Michail N. Tsampas (1)
Affiliations : 1) Dutch Institute for Fundamental Energy Research (DIFFER), 5612AJ Eindhoven, the Netherlands 2) Toyota Motor Europe NV/SA, Hoge Wei 33, 1930 Zaventem, Belgium
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.
Authors : T.??cki, H. Hamad, K. Zar?bska, E. Kwiatkowska, M. Skompska
Affiliations : University of Warsaw; Advanced Technology and New Materials Research Institute; University of Warsaw; University of Warsaw; University of Warsaw
Resume : BiVO4 is a perspective semiconductor photocatalyst used for water oxidation and degradation of organic water pollutants . 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 . 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 .  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.  T.??cki, H. Hamad, K. Zar?bska, E. Kwiatkowska, M. Skompska publication under review.  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.
Authors : A. Hardy 1, B. Joos 1, N. Debusschere 1, R. Jacops1,2, M.K. Van Bael 1
Affiliations : 1 UHasselt, Institute for Materials Research and imec division imomec, Materials Chemistry, DESINe group, Diepenbeek, Belgium 2 UAntwerp, ELCAT, Applied electrochemistry and catalysis, Wilrijk, Antwerp
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.
Authors : Jiri Kollmann(1), Herman Kriegel(1), Ragle Raudsepp(1), Maryam Pourmahdavi(1), Thomas Klassen(1,2), Mauricio Schieda(1)
Affiliations : (1) Helmholtz-Zentrum Hereon, Max-Planck-Str. 1, 21502 Geesthacht, Germany; (2) Helmut-Schmidt University, Holstenhofweg 85, 22043 Hamburg, Germany
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:  Kriegel H. et al. J. Mater. Chem. A, 2020, 8, 18173.  Raudsepp R. et al. (in preparation).
Authors : Karthik Kannan1,2, Debabrata Chanda1,2, Jagadis Gautam1,2, Mikiyas Mekete Meshesha1,2, Jang Seok Gwon1,2, Myungsik Choi3, BeeLyong Yang1,2*
Affiliations : 1. School of Advanced Materials Science and Engineering, Kumoh National Institute of Technology, 61 Daehak-ro, Gumi-si, Gyeongbuk, 39177, Republic of Korea 2. GHS Co., Ltd. Gumi-si, Republic of Korea. 3. SJ Tech. Co., Ltd, 1026-1 Daecheon-Dong, Dalseo-Gu, Daegu City, Republic of Korea *Corresponding author: Tel: +82-(54)-478-7741, E-mail: email@example.com
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.
Photocatalysis V : Sonya Calnan, Joachim John
Authors : Joanna Kargul
Affiliations : Solar Fuels Laboratory, Centre of New Technologies, University of Warsaw, Banacha 2C, 02-097 Warsaw, Poland
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.
Authors : Ewelina Kwiatkowska, Tomasz ??cki, Bartosz Furtak, Magdalena Skompska
Affiliations : Faculty of Chemistry, University of Warsaw Pasteura 1 02-093 Warsaw
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. 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. In this work we modified the properties of g-C3N4 by reduction it with NaBH4. It was proven in the literature that band gap become narrower along with the reduction degree . 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.  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.  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.  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.  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.
Authors : Parisa Talebi1, Harishchandra Singh1, Ekta Rani1, Vladimir Pankratov2, Viktorija Pankratova2,1, and Wei Cao1
Affiliations : 1Nano and Molecular Systems Research Unit, University of Oulu, FIN-90014, Finland; 2 Institute of Solid-State Physics, University of Latvia, 8 Kengaraga iela, 1063 Riga, Latvia;
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 . 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 . 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 . 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 . 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 . 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.  Y. Shi, et al. J. Am. Chem. Soc. 2015, 137, 23, 7365?7370  Sh.G. Patra, et al. Acc. Chem. Res. 2020, 53, 10, 2189?2200  P. Talebi, et al. RSC Adv., 2021, 11, 2733?2743  P. Talebi, et al. Appl. Energy., 2022, Under revision
Authors : Jakub Szewczyk1&2, Marcin Zió?ek3, Igor Iatsunskyi1, Katarzyna Siuzdak4, Syreina Sayegh2, Fida Tanos2&5, Mikhael Bechelany2, Emerson Coy1
Affiliations : 1NanoBioMedical Centre, Adam Mickiewicz University, Wszechnicy Piastowskiej 3, 61-614, Pozna?, Poland; 2Institut Europeen des Membranes, IEM, UMR 5635, Univ Montpellier, ENSCM, Centre national de recherche scientifique (CNRS), Place Eugene Bataillon, 34095 Montpellier, France; 3Faculty of Physics, Adam Mickiewicz University, ul. Uniwersytetu Pozna?skiego 2, 61-614, Pozna?, Poland; 4Centre of Laser and Plasma Engineering, The Szewalski Institute of Fluid-Flow Machinery, Fiszera 14 Str., 80-231 Gdansk, Poland; 5Laboratiore d'Analyses Chimiques, Faculty of Sciences, LAC-Lebanese University, Jdeidet 90656, Lebanon
Resume : Polydopamine (PDA) is a biomimetic material discovered in 2007 , which gained significant scientific interest due to numerous advantages- e.g. photocatalytic properties- and easy synthesis via auto oxidation . 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 . What is important, these films can be obtained on a large scale, preserving high quality, homogeneity and continuity after transferring onto various substrates . 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 . 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.  Lee et al. (2007) doi: 10.1126/science.1147241  Aguilar-Ferrer et al. (2021) doi: 10.1016/j.cattod.2021.08.016  Coy et al. (2021) doi: 10.1021/acsami.1c02483  Szewczyk et al. (2022) doi: 10.1016/j.mtchem.2022.100935
Authors : Greg Swadener
Affiliations : Aston University
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.
Authors : Jiayi Yina, Martina Rosoa, Michele Modesti
Affiliations : University of Padova, Department of Industrial Engineering, Via Marzolo, 9, 35131 Padova Italy.
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.
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Catalysis synthesis and characterization : Byungha Shin
Authors : Hannah-Noa Barad, Hyunah Kwon, Alex Ricardo Silva Olaya, Mariana Alárcon-Correa, Gunther Wittstock, Peer Fischer
Affiliations : Hannah-Noa Barad, Max Planck Institute for Intelligent Systems, Stuttgart, Germany, and Department of Chemistry, Center of Nanotechnology & Advanced Materials, Bar Ilan University, Ramat Gan, Israel; Hyunah Kwon, Max Planck Institute for Intelligent Systems, Stuttgart, Germany, and Institute for Molecular Systems Engineering, Heidelberg University, Heidelberg, Germany; Alex Ricardo Silva Olaya, School of Mathematics and Science, Department of Chemistry, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany; Mariana Alárcon-Correa, Max Planck Institute for Intelligent Systems, Stuttgart, Germany, and Institute for Molecular Systems Engineering, Heidelberg University, Heidelberg, Germany; Gunther Wittstock, School of Mathematics and Science, Department of Chemistry, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany; Peer Fischer, Max Planck Institute for Intelligent Systems, Stuttgart, Germany, and Institute for Molecular Systems Engineering, Heidelberg University, Heidelberg, Germany;
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.
Authors : Maximilian Wolf, Theodoros Dimopoulos
Affiliations : AIT Austrian Institute of Technology, Center for Energy, Energy Conversion and Hydrogen, 1210 Wien, Austria. TU Wien, Institut für Materialchemie, 1060 Wien, Austria.; AIT Austrian Institute of Technology, Center for Energy, Energy Conversion and Hydrogen, 1210 Wien, Austria.
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.  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.  Suzuki, Issei, et al. "First-principles study of CuGaO2 polymorphs: delafossite ?-CuGaO2 and wurtzite ?-CuGaO2." Inorganic chemistry 55.15 (2016): 7610-7616.  Liu, Qing-Lu, et al. "Fundamental properties of delafossite CuFeO2 as photocatalyst for solar energy conversion." Journal of Alloys and Compounds 819 (2020): 153032.
Authors : Marie Elis, Marius Kamp, Martin Hicke, Jonas Drewes, Franz Faupel, Oral Cenk Aktas, Salih Veziroglu, Lorenz Kienle
Affiliations : AG-Synthesis and Real Structure, Institute for Materials Science, Technical Faculty of the Christian-Albrechts-University of Kiel, Kaiserstrasse 2, 24143 Kiel, Germany; AG-Synthesis and Real Structure, Institute for Materials Science, Technical Faculty of the Christian-Albrechts-University of Kiel, Kaiserstrasse 2, 24143 Kiel, Germany; AG-Multicomponent Materials, Institute for Materials Science, Technical Faculty of the Christian-Albrechts-University of Kiel, Kaiserstrasse 2, 24143 Kiel, Germany; AG-Multicomponent Materials, Institute for Materials Science, Technical Faculty of the Christian-Albrechts-University of Kiel, Kaiserstrasse 2, 24143 Kiel, Germany; AG-Multicomponent Materials, Institute for Materials Science, Technical Faculty of the Christian-Albrechts-University of Kiel, Kaiserstrasse 2, 24143 Kiel, Germany; AG-Multicomponent Materials, Institute for Materials Science, Technical Faculty of the Christian-Albrechts-University of Kiel, Kaiserstrasse 2, 24143 Kiel, Germany; AG-Multicomponent Materials, Institute for Materials Science, Technical Faculty of the Christian-Albrechts-University of Kiel, Kaiserstrasse 2, 24143 Kiel, Germany; AG-Synthesis and Real Structure, Institute for Materials Science, Technical Faculty of the Christian-Albrechts-University of Kiel, Kaiserstrasse 2, 24143 Kiel, Germany
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 . 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.)  or oxide structures (like CeO2) . 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 . 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.  A. Sclafani, J. M. Herrmann, J. Phys. Chem., 1996, 100, 13655?13661  S. Veziroglu et al., ACS Appl. Mater. Interfaces, 2020, 12, 14983?14992  S. Veziroglu et al., Nanoscale, 2019, 11, 9840-9844  Amir Mohammad Ahadi et al., J. Phys. D: Appl. Phys., 2015, 48, 035501
Authors : Tomasz Tarnawski, Joanna Depciuch-Czarny, Miros?awa Pawlyta, Robin Schaeublin, Kamil Sobczak, Magdalena Parli?ska-Wojtan
Affiliations : Institute of Nuclear Physics Polish Academy of Sciences, PL-31-342 Krakow, Poland; Institute of Nuclear Physics Polish Academy of Sciences, PL-31-342 Krakow, Poland; Silesian University of Technology, Institute of Engineering Materials and Biomaterials, Konarskiego 18A, 44100 Gliwice, Poland; ScopeM-Scientific Center for Optical and Electron Microscopy, ETH Zu?rich, 8093 Zu?rich, Switzerland; Faculty of Chemistry, Biological and Chemical Research Centre, Warsaw, Poland
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.
Authors : Divyansh Khurana, Nina Plankensteiner, Philippe Vereecken
Affiliations : cMACS, KULeuven, Leuven 3001, Belgium imec, Leuven 3001, Belgium ; cMACS, KULeuven, Leuven 3001, Belgium imec, Leuven 3001, Belgium ; cMACS, KULeuven, Leuven 3001, Belgium imec, Leuven 3001, Belgium
Resume : Semiconductor (photo-)electrocatalysts like ZnO, Cu2-xSe, MoS2 and TiO2, 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:  Zeng et al. ChemSusChem, 13, 4128 ?4139 (2020)  Yang. et al. Nat Commun 10, 677 (2019)  Asadi et al. Nat Commun 5, 4470 (2014)  Yu et al. J. Mater. Chem. A, 6, 4706 (2018)
Authors : Ivan Khalakhan, Xianxian Xie, Mykhailo Vorokhta, Iva Matolínová
Affiliations : Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma Science, V Hole?ovi?kách 2, 18000 Prague, Czech Republic
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.
|10:30||Award ceremony of the Best Oral/Poster Prizes and closing remarks|
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