Materials for energyC
Advanced catalytic materials for (photo)electrochemical energy conversion II
This symposium will be the 2nd edition of E-MRS symposium with the same theme. Following the success of the 1st edition, the 2021 symposium aims to bring a wider spectrum of researchers who are interested in and actively working on catalytic materials and processes for use in various (photo)electrochemical energy conversion devices.
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 long time. 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 done, 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
List of invited speakers (in alphabetical order):
- Brian Seger (Technical University of Denmark, Denmark)
- Hongjin Fan (Nanyang Technological University, Singapore)
- James Durrant (Imperial College London, UK)
- Jordi Arbiol (Catalan Institute of Nanoscience and Nanotechnology, Spain)
- Jose Ramon Galan-Mascaros (Institut Catala dÍnvestigacio Quimica - ICIQ, Spain)
- Menny Shalom (Ben-Gurion University of the Negev, Israel)
- Teresa Andreu (Universitat de Barcelona, Spain)
List of SC members (in alphabetical order):
- Elena Más-Marzá (Universitat Jaume I, Spain)
- Friedhelm Finger (IEK-5, Forschungszentrum Juelich, Germany)
- Hyacinthe Randriamahazaka (University of Paris Diderot, France)
- Idan Hod (Ben Gurion University, Israel)
- Jihun Oh (Korean Advanced Institute of Science and Technology, South Korea)
- Joachim John (IMEC R & D, Belgium)
- Leszek Zaraska (Jagiellonian University, Poland)
- Matthew Mayer (Helmholtz Zentrum Berlin, Germany)
- Paulo Ferreira (International Iberian Nanotechnology Laboratory, Portugal)
- Salvador Eslava (Imperial College London, UK)
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Photoelectrocatalysis I : Lifeng Liu
Authors : James R Durrant
Affiliations : Department of Chemistry, Centre for Processable Electronics, Imperial College London, London W12 0BZ,
Resume : The kinetics of electrochemical reactions are typically analysed through Butler-Volmer analyses of current ? voltage data. Such analyses have been very effective at determining electrochemical kinetics on metal electrodes. However their application to the kinetics of (photo)electrocatalytic water oxidation / reduction on metal oxides can be more challenging, due to multiple redox transitions observed in such metal oxides, the localised nature of these transitions and the complexity of the water oxidation / reduction reactions. In my talk I will address the potential of operando spectrochemistry to determine redox state population densities in metal oxides electrodes and photoelectrodes, and the use of such data to undertake rate law analyses of water oxidation / reduction. These studies will primarily be applied to Ni/Fe oxyhydroxide electrocatalysts and hematite photoanodes for water oxidation, as well as comparison with other metal oxide for both water oxidation and reduction. These studies will address the nature of the states driving water oxidation / reduction and the reaction kinetics and dependence upon population density. For example for Ni(M)OOH electrocatalysts, these studies will address the impact of metal (M) substitution on both the population densities and reaction rate constants, and how these together impact upon the overall current / voltage behaviour. A key conclusion of my talk will be that for the systems studied the kinetics of water / oxidation appear to be primarily driven by the population of states driving these reactions ? and as such it more appropriate to employ rate law rather than Butler-Volmer models in analysing these kinetics.
Authors : Salvador Eslava
Affiliations : Department of Chemical Engineering, Imperial College London
Resume : Photoelectrochemical splitting of water using solar energy offers a clean solution to the world energy requirements of a sustainable future. Achieving its full potential depends on developing inexpensive photoelectrodes that can efficiently absorb solar light and drive the photoinduced charges to oxidise and reduce aqueous electrolytes. In this talk, I will present recent developments my team has achieved in the preparation of inexpensive ternary metal oxide photoelectrodes. For example, we have achieved nanostructured LaFeO3 and PrFeO3 photocathodes and observed how important it is to tune their porosity and annealing process to achieve the highest photocathodic response and leverage their exceptional photovoltage. We have also recently developed Fe2TiO5 pseudobrookite-based films by aerosol-assisted chemical vapor deposition and discovered the positive impact of Zn2+ doping in their formation and performance as photoanodes. The Zn2+ doping modifies the electronic properties of the films, increases their charge carrier concentration, and upshifts their Fermi level, significantly improving their anodic photocurrent response by a factor of three. An extended characterisation help us relate their physical and charge-transfer properties to their performance, guiding us in their rational design for their optimization and future application.
Authors : Amin Yourdkhani1*, Marjan Saeidi1, Reza Montahaei2, Niousha Mouchani1, Mehdi Rasouli1, Reza Poursalehi1 and S.A. Seyyed Ebrahimi2
Affiliations : 1 Materials Engineering Department, Faculty of Engineering, Tarbiat Modares University, Tehran, Iran 2 University of Tehran, Advanced Magnetic Materials Research Center, School of Metallurgy and Materials, College of Engineering, Tehran, Iran
Resume : Flame-treatment is an effective strategy, cost-effective and straightforward to enhance the photoelectrochemical (PEC) properties of metal oxides, especially hematite thin films. We have used candle, butane, and propane flames to post-treatment the liquid phase deposited hematite thin films doped with Ti, Zr, and Nb. The PEC properties considerably enhanced upon flame-treatment, i.e., the photocurrent density for the 4% Ti-doped sample (1.1 mA/cm2 at 1.8 V vs. RHE) was enhanced by thirteen-fold compared to the non-flame treatment counterpart. The mechanism behind the versatility of the flame-treatment was investigated. It was found that the oxygen vacancy formation and carbon diffusion into the films are most likely responsible for improving the PEC properties. Oxygen vacancies activate of donor doping which increases the concentration of weakly bound electrons in the lattice. In addition, the samples are exposed to a flame with high-temperature (900-1200 °C), which can increase the crystallinity of the hematite films. There is an optimum time for the flame-treatment that afterward, the PEC properties were decreased. Oxygen vacancies on the surface act as trap states which have a negative side effect with increasing the interfacial charge recombination. Therefore, the maximum photocurrent can be achieved by balancing the positive and negative effects of oxygen vacancies.
Authors : Hao WU
Affiliations : City University of Hong Kong
Resume : Cu2O-based photocathodes as stable and efficient photoelectrochemical energy conversion catalysts require protections due to their photocorrosion at the electrode liquid junction (ELJ). In this presentation, recent progress on the development of stabilized Cu2O-based photocathodes for photoelectrochemical conversion will be introduced. Particularly, pulsing electrodeposition as a scalable protecting technique developed by our group will be presented. Wide band gap n-type semiconductor films such as TiO2 with ultrathin thickness decorated on top of Cu2O can protect the photocorrosion of the Cu2O from the aqueous electrolyte, thereby ameliorate the performance in favor of solar energy conversion.1 But, TiO2 grown from titanium tetraisopropoxide and H2O is known to have issues with growing non-uniformly. Herein, a buffer interlayer is crucial to assist the uniform coating of the protecting layer of TiO2 on the Cu2O. Interlayers such as ZnO and Ga2O3 have been deposited between Cu2O and the protective layer of TiO2 by atomic layer deposition to afford the chemical stability.1,2 Atomic layer deposition technique is however too complicated the costly for a large scale application. Also, limited semiconductors are available that could conformably deposit by atomic layer deposition. Herein, we developed a pulsing electrodeposition method to introduce an ultrathin interlayer containing ZnOx (ZnO and Zn(OH)2) on the Cu2O layer. In combine with dip-coating of TiO2, the surface-protected Cu2O photoelectrode achieves a higher and more stable photoresponse under visible light illumination. Due to the ultrathin property of the coated overlayers containing ZnOx and TiO2, time-of-flight secondary ion mass spectrometer (TOF-SIMs) was utilized to investigate the composition and chemical state of our designed multilayer photoelectrodes. A systematic investigation of the enhanced visible light-induced charge extraction in protected Cu2O photoelectrodes was also studied by Nyquist and time-resolved photoluminescence (TRPL). The enhanced photocathodic performance demonstrates the great potential of pulsing electrodeposition as a versatile alternative coating technique in addressing the non-stable issue of photoelectrodes for photoelectrochemical conversion. References 1. Paracchino, A.; Laporte, V.; Sivula, K.; Grätzel, M.; Thimsen, E. Nat. Mater. 2011, 10 (6), 456. 2. Li, C.; Hisatomi, T.; Watanabe, O.; Nakabayashi, M.; Shibata, N.; Domen, K.; Delaunay, J.-J. Energy & Environ. Sci. 2015, 8 (5), 1493.
|10:20||Live Q&A Session 1|
Photoelectrocatalysis II : Byungha Shin
Authors : Prof. Roland Marschall
Affiliations : University of Bayreuth, Chair of Physical Chemistry III
Resume : Efficient conversion and storage of solar energy are crucial steps in the establishment of a renewable and carbon neutral energy supply. Photoelectrochemistry is considered promising to make use of the large amounts of sunlight that reach the surface of earth. It renders the direct conversion of light into chemical energy possible, circumventing the problem of expensive energy storage using batteries, that comes with the use of photovoltaics. In recent years, earth-abundant spinel ferrites have emerged as auspicious materials for applications in photoelectrochemistry and electrocatalysis. They have the inherent ability to absorb a large part of the visible light spectrum with band gaps around 2 eV, while being at the same time stable against photocorrosion. We developed a fast microwave-assisted synthesis yielding phase-pure spinel ferrite nanoparticles of e.g. MgFe2O4, CoFe2O4, NiFe2O4 and ZnFe2O4 at temperatures as low as 170-200 °C.[1-4] The crystallite size can be tailored by post-synthetic heat treatment, however the materials are already (partly) crystalline as-prepared, with specific surface areas of around 200 m²/g and good colloidal stability. Photocatalytic and electrocatalytic experiments will be presented, as well as the conversion of some spinel oxides into sulfides, e.g. pendladites. A new direct microwave synthesis for nickel-iron sulfides for electrocatalytic CO2 reduction will also be presented. Well-ordered mesoporous ZnFe2O4 and NiFe2O4 materials were fabricated by sol-gel synthesis, and utilised in (photo)electrochemical water oxidation.[7,8] Recently, we presented a low temperature synthesis of a p-type earth-abundant iron oxide photocathode, hierarchical porous thin films of fully crystalline and phase-pure CaFe2O4 were prepared and applied in photoelectrochemical hydrogen generation. For the first time, this material can be prepared at temperatures as low as 700 °C. A novel synthesis for macroporous CaFe2O4 foams will also be presented.  K. Kirchberg et al., J. Phys. Chem. C 121 (2017) 27126?27138  C. Simon et al., submitted  P. Dolcet et al., Inorg. Chem. Front. 6 (2019) 1527-1534  A. Bloesser et al., ACS Appl. Nano Mater. 3 (2020) 11587?11599  D. Tetzlaff et al., Faraday Discussions 215 (2019) 216-226  C. Simon et al, submitted  K. Kirchberg et al., Chem. Phys. Chem. 19 (2018) 2313-2320  C. Simon et al., ChemElectroChem 8 (2021) 227-239  K. Kirchberg et al., Sustainable Energy Fuels 3 (2019) 1150-1153  A. Bloesser et al., Solar RRL 4 (2020) 1900570
Authors : Zaraska, L* (1). Syrek, K. (1), Gurgul, M. (1), Mika, K. (1), Gawlak, K. (1), Zych, M. (1), Sulka, G.D. (1)
Affiliations : Jagiellonian University, Faculty of Chemistry, Krakow, Poland
Resume : Nanostructured semiconductors, such as nanowires, nanotubes or nanoporous layers, have been extensively investigated for years owing to their promising properties, e.g. ultrahigh surface-to-volume ratio, higher charge carrier mobilities compared to their bulk counterparts. Among various methods that have been already proposed for fabrication of nanostructured semiconductor oxides, electrochemical methods (e.g., simple electrochemical oxidation (anodization) of particular metals or cathodic electrodeposition of oxides) are especially attractive due to their simplicity, cost-effectiveness and versatility. For instance, a big advantage of the oxide layers obtained by anodization is their relatively good adhesion to the conductive metal substrate, as well as perpendicular orientation of the nanochannels, nanowires, or nanotubes to the substrate that significantly facilitates electron transfer path. Moreover, tailoring of morphology of electrochemically deposited film is also possible by careful adjustment of the process parameters, especially the applied potential/current, temperature, duration of the process, as well as composition, viscosity, and pH of the electrolyte. The aim of this presentation is to give an overview of some recent results on electrochemical fabrication of nanostructured semiconductor oxides, e.g., nanostructured tin oxide (SnOx) layers, porous iron oxides, nanporous and nanowire-like zinc oxide (ZnO), nanoporous tungsten oxide (WO3) films, and their applications in photoelectrochemical and photocatalytic systems.
Authors : C. Maurizio, L. Girardi, B. Kalinic, P. Ragonese, A. Faramawi, G.-A. Rizzi, G. Mattei
Affiliations : C. Maurizio, B. Kalinic, P. Ragonese, A. Faramawi, G. Mattei: Physics and Astronomy Department, University of Padova I-35131 L. Girardi; G.-A. Rizzi Chemistry Department, University of Padova I-35131
Resume : Transition metal oxides (TMOs) are promising materials to be coupled to silicon photoanodes for photoelectrochemical water splitting [1-3]. They can prevent Si corrosion in harsh conditions and their catalytic activity allows to reduce the overpotential. The possibility of TMO nanostructuring can largely increase the number of catalytic sites for a defined electrode area, so enhancing the PEC performances. Nevertheless, certainly, the overall working process also depends on the details of the electronic band structure at the interfaces (Si/TMO and TMO/electrolyte). In this work, we present new results on the photoelectrochemical water splitting using Si photoanodes coupled with cobalt oxide nanopetals, whose preparation is based on physical vapor deposition followed by suitable thermal annealing. The mechanism of nanopetal formation is unveiled, by using a combination of X-ray Absorption Spectroscopy (Co K-edge), Grazing Incidence X-ray Diffraction, Atomic Force and Scanning Electron Microscopies. The PEC experiments (Linear Sweep Voltammetry, CV measurements, and Electronic Impedance Spectra) indicate that the nanopetal structure leads to a large increase of the photocurrent. Moreover, depending on the film thickness, a subtle balancing can be found, between optical transparency and protective action. The photopotential is shown to be sensitive to the details of the TMO/Si interface. In particular, the effect of an interlayer between the Co-oxide nanopetals and the Si substrate has been considered. The interlayer, in form of native silicon oxide, ad-hoc regrown (doped) silicon oxide has been investigated by X-ray Photoelectron Spectroscopy, and it is shown to play a major role in the PEC properties, suggesting a pathway for the optimization.  J. Yang et al. J. Am. Chem. Soc. 136 (2014) 6191.  Sol A. Lee et al. ACS Catal. 10 (2020) 420.  Shu Hu et al., Science 344 (2014) 1005.
Authors : Brian Tam, Flurin Eisner, Anna Hankin, Jenny Nelson, Andreas Kafizas
Affiliations : Department of Physics Imperial College London, Department of Chemical Engineering Imperial College London, Department of Chemistry Imperial College London
Resume : Bismuth vanadate (BiVO4) is often studied as an earth-abundant, visible light absorbing metal oxide photoanode for water splitting. While water oxidation kinetics on this material are slow, they can be improved by depositing co-catalysts, such as cobalt phosphate. Lower-cost co-catalysts made of Fe and Ni compounds, such as FeOOH and NiOOH, have emerged as an attractive alternative.1 They were shown to effectively catalyse the water oxidation reaction,2 in contrast to cobalt phosphate, which instead primarily slows electron-hole back recombination.3 These co-catalyst materials are typically deposited by electrodeposition and photodeposition, which offer useful control but may be difficult to scale up to larger area photoanodes. Herein we demonstrate a facile atmospheric-pressure chemical vapour deposition method for producing FeOOH and NiOOH co-catalyst layers on nanostructured photoanodes consisting of BiVO4 coated onto WO3 nanoneedles. Under visible light illumination, co-catalyst coated photoanodes show up to 200 mV earlier onset for photoactivity and a ~60 % increase in photocurrent at an applied bias of 1.23 VRHE compared to uncoated photoanodes. One benefit of this technique is that layers may be deposited sequentially in large-scale batch processing, a common industry technique for semiconductor fabrication. This versatile approach yields a potentially transformative method for fabricating large-area thin film photoelectrodes. Modeling our photoelectrochemical (PEC) device coupled to standard crystalline silicon photovoltaic (PV) cells indicates how an unassisted, complete device could work. The optoelectrical response and overall performance of the combined device was simulated using a numerical model of the coupled PV cells and PEC device. This work culminates in the demonstration of a prototype large-area, unassisted water splitting device with 4 cm x 9 cm active area photoanodes deposited on FTO-coated glass, driven by two crystalline silicon PV cells in series. Routes to improve charge extraction from the large area photoanodes will be discussed. 1. Kim, T. W. & Choi, K.-S. Nanoporous BiVO4 photoanodes with dual-layer oxygen evolution catalysts for solar water splitting. Science 343, 990?994 (2014). 2. Francàs, L., Selim, S., Corby, S., Lee, D., Mesa, C. A., Pastor, E., Choi, K.-S. & Durrant, J. R. Water oxidation kinetics of nanoporous BiVO4 photoanodes functionalised with nickel/iron oxyhydroxide electrocatalysts. Chem. Sci. 12, 7442?7452 (2021). 3. Ma, Y., Le Formal, F., Kafizas, A., Pendlebury, S. R. & Durrant, J. R. Efficient suppression of back electron/hole recombination in cobalt phosphate surface-modified undoped bismuth vanadate photoanodes. J. Mater. Chem. A 3, 20649?20657 (2015).
|12:40||Live Q&A Session 2|
(Photo)electrochemical CO2 reduction I : Sixto Gimenez Julia
Authors : Seger, Brian Ma, Ming Larrazabal, Gaston
Affiliations : Seger, Brian; Larrazabal, Gaston Surface Physics and Catalysis (SurfCat) Section, Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark Ma, Ming School of Chemical Engineering and Technology, Xi?an Jiaotong University, Xi?an 710049, People?s Republic of China
Resume : Low temperature CO2 electrolysis allows us to take the dominant greenhouse gas and use cheap renewable electricity and convert it to useful chemicals and fuels, such as ethylene, ethanol, and CO. While there are also other renewable approaches towards CO, such as high temperature (i.e. solid oxide) CO2 electrolysis, biomass gasification, and H2 electrolysis followed by the reverse water-gas shift reaction with CO2, all of these struggle to produce products beyond CO. Thus CO electrolysis, while catalytically similar to CO2 electrolysis, is also a highly useful approach towards valuable chemicals. This talk will focus on comparing CO2 electrolysis versus CO electrolysis and understanding the systems holistically. We will show a carbon balance analysis on both a zero-gap reactor using Ag for primarily CO evolution and a gapped reactor using Cu for higher reduced products. The effects of pH and the implications of the CO2/bicarbonate/carbonate equilibrium will be discussed as well as the anode product distribution and what information can be gained about this relating to the cathode. Furthermore we will also show that detailed analysis allows the anode and cathode results to be compared to each other via two independent methods to validate results. As we transition to CO electrolysis, the equilibration with the buffering bicarbonate/carbonate electrolyte is lost, which we will show leads towards an increasingly alkaline solution with a concomitant change in selectivity. By analyzing results from CO2 reduction as well as the concomitant OH- production and scavenging of CO2 to carbonate, we can actually use variations in CO2 outlet flow rate for both CO2 and CO electrolysis to give us a means to determine pH. This very simple technique allows for monitoring local pH modification during electrolysis.
Authors : Jihun Oh
Affiliations : Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Republic of Korea
Resume : Electrochemical CO2 reduction reaction (CO2RR) at Cu surfaces is a promising carbon capture and utilization (CCU) technology since it can convert CO2 to value-added chemical fuels and feedstocks such as ethylene. Cu is only metal that can reduce CO2 to multi-carbon products with significant amounts. However, CO2RR on Cu suffers low selectivity in an aqueous solution as it can also produce CO, CH4 and other minor products. Here, I’ll talk about the important role of local CO2RR environment to promote C-C coupling on Cu surfaces. Based on a systematic study, we show that C-C coupling occurs by the Langmuir-Hinshelwood mechanism and the optimum surface coverage of CO2 is needed to maximize C-C coupling. I’ll present that strategies to control the local environment based on steady-state modeling and monodisperse Cu2O nanoparticles as a model catalyst system. Based on this approach, we can produce C2+ products (ethylene and ethanol) with > 70% Faraday efficiency at > 300 mA/cm2 in near neutral electrolyte.
Authors : Tandava. V.S.R.K., Dr. Sebastián Murcia-López, Dr. Joan Ramón Morante*
Affiliations : Catalonia Institute for Energy Research (IREC), Sant Adrià de Besos, 08930, Barcelona, Spain.
Resume : Circular economy of CO2 is the hot issue amid the global warming. The quest to attain a Carbon Neutral economy relies upon exploring favourable strategies to mitigate CO2 emissions. Having the strong requisite to meet the global energy demands and to curb the ever-increasing levels of CO2 in the atmosphere, the urge to develop reliable systems for CO2 conversion is quite important. Electrocatalytic CO2 reduction (ECO2R) is proven to be one of several promising strategies explored and still has plenty of room to work on. Developing functional advanced nanostructured catalyst materials and systems for electrochemical conversion of CO2 to alternative fuels or value-added products is the necessity to accomplish. The unique capability of copper and copper-based heterogeneous electrocatalysts that are highly selective towards hydrocarbons had led them to be the ?benchmark materials?. In the present work Copper and Copper Oxide-based materials supported over Carbon Black (Vulcan XC-72) were synthesized via a facile hydrothermal method. Initial X-Ray Diffraction studies revealed the presence of Cu, CuO, and Cu2O particles with varied crystallographic orientation (111, 200) and found to be selective towards ethylene and C2 products. SEM analysis showed the platelet like morphology of copper adhered over widely dispersed Vulcan XC-72 The as-synthesized material ink was prepared and directly deposited on a 3D porous substrate, Carbon Toray with PTFE acting as a Gas Diffusion Electrode (GDE) and tested in a flow filter-press cell under both neutral and alkaline electrolyte conditions. Tuning the GDE was carried out in the preparation of catalyst inks involving ionomers and PTFE content indicating the modifications to the GDE with tuned hydrophobicity. The flow effects of both CO2 and electrolyte flows were investigated alongside consideration of the pH variations during the electrolysis. A strong correlation between working voltage, structural electrocatalyst properties, pH, and product distribution was observed with enhanced selectivity towards ethylene generally obtained at intermediate potentials. The undesired Hydrogen Evolution Reaction (HER) was considered and evaluated in terms of overall Faradaic efficiency. Preliminary results indicated the effect of the composition parameters in modifying the GDE like ionomers and PTFE can have a strong influence on selectivity and long-term stability of the electrodes in the long run. Potential solutions to the aforementioned factors were addressed. Keywords: CO2, Electrocatalytic CO2 reduction, Copper, Gas Diffusion electrodes, Tunable hydrophobicity Ethylene. This work is supported by European Union's Horizon 2020 DOC-FAM program under the Marie Sk?odowska-Curie Actions Grant Agreement No 754397.
Authors : Nina Plankensteiner [1,2], Sara Andrenacci [1,3], 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 : An attractive solution towards net-zero carbon emission is the electrocatalytic CO2 reduction with its ability to convert the greenhouse gas CO2 with renewable energy and appropriate catalytic materials to useful chemicals and fuels to store energy. Depending on the number of electrons transferred a variety of oxygenates and hydrocarbons can be obtained. Among used catalytic materials, such as metals, alloys or composites, copper has shown the unique property to electrocatalytically convert CO2 into a wide variety of valuable C2+ products such as ethylene or alcohols. In recent literature various efforts are directed towards improving the catalytic activity and the selectivity of Cu catalysts to obtain specific products. A common pathway to improve the catalytic activity and at the same time significantly alter the product selectivity is by using nanostructured porous materials that increase the number of specific surface sites and can temporarily trap reaction intermediates. However, the majority of nanostructured porous Cu electrodes under investigation consist of ill-defined pore sizes and shapes (porous Cu is mainly made by reducing oxidized Cu) or as randomly ordered nanoparticles loaded on porous (carbon-based) supports. In addition to that, many porous materials studied, such as Cu foams, exhibit high porosity, but a rather low surface area enhancement. In this work we propose for the first time regular-ordered 3D-interconnected Cu nanowire networks (called Cu nanomesh) with a significantly enhanced electrochemical surface area to systematically study the electrochemical CO2 reduction. These unique electrodes show a surface area enhancement (compared to planar Cu) by a factor of ~80, while providing a high porosity of ~70% together with sufficient mechanical stability, an important aspect towards their practical implementation in flow cells. Cu nanomeshes were fabricated through electrochemically plating in 3D-porous anodic aluminum oxide templates. To demonstrate their ability towards the electrochemical CO2 reduction, planar and nanomesh Cu electrodes were electrochemically characterized in various carbon-containing electrolyte solutions. The product analysis showed a significant difference in selectivity between polycrystalline (same crystallographic orientation) planar and nanostructured Cu electrodes with an enhanced potential-dependent formation of CO observed, when using nanomesh electrodes. The beneficial effect of the high electrochemical surface area was demonstrated by a significant increase in the current density on the nanostructured Cu electrodes.
Authors : Shiyuan LIU (1), Ce ZHANG (1), Wei YAO (1), Zhaolong Wang (2)
Affiliations : (1)Qian Xuesen Laboratory of Space Technology China Academy of Space, P.R. China; (2) National Research Center for High-Efficiency Grinding, College of Mechanical and Vehicle Engineering, Hunan University, P.R. China
Resume : Electrochemical CO2 reduction reaction (CO2RR) with a variety of products such as HCOOH, C2H4 and etc. is a promising technology for CO2 recycling and utilization powered by renewable energy. In order to improve the faradic efficiency, product selectivity and stability to meet the requirements of large-scale application, novel catalysts as well as electrodes have been designed and prepared.(references) However, the state-of-the-arts gas diffusion electrode (GDE) for CO2RR could not solve the CO2 surface concentration limitation in aqueous electrolyte, which is considered as an essential factor to hinder the performance of CO2RR. Modifying the electrode geometry is an effective method to accelerate the mass transfer in the local electrode-electrolyte interface. In this study, a novel kind of 3D-printing micro-array GDEs has been fabricated by photosensitive resin based on Stereo lithography Appearance (SLA), which enables fast fabricating, designable and delicate structure, and accurate controllable for related electrochemical CO2RR processes. The obtained electrode was in form of micro arrays and coated with micron-layered Cu catalyst. For better exploring the geometry and size effects, various shape and size of micro arrays were prepared and systematically studied. Compared with the conventional GDEs, the regularly micro array electrodes can effectively promote the detachment of product bubbles and confine the bubble size by optimizing the size spacing between tow array among the electrode. As a result, the novel 3D micro arrays electrode could accelerate the evolution of bubbles by means of a thinner diffusion layers and ensure a fast mass transfer, which is beneficial for CO2RR process to solve the concentration limitation and impel this technology from lab-scale study to industrialization.
|15:35||Live Q&A Session 3|
Poster Session I : Vladimir Smirnov, Lifeng Liu
Authors : Gurgul, M.*; Orczykowski, B.; Kocwa, P.; Zaraska, L. (1)
Affiliations : Department of Physical Chemistry and Electrochemistry, Faculty of Chemistry, Jagiellonian University Gronostajowa 2, 30-387 Cracow, Poland
Resume : In recent years, nanostructured oxides obtained during an anodic oxidation process have gathered much interest mainly due to their unique physicochemical properties that enable them to be considered in many different energy conversion and storage devices . Among them, in the past few years, anodic tin oxide also has drawn great attention especially in the field of photoelectrochemical water splitting devices, solar cells, and photocatalysis [2,3]. Moreover, lately it was proven that controlled thermal treatment of the anodic tin oxide allows strict tailoring of the structure and Sn2+ content, and hence also its’ semiconducting properties . However, regarding a relatively low melting point of the metallic Sn substrate (~ 230 °C) on which the nanostructured oxides mostly are being obtained, this path is strongly limited. For this purpose, in this work a novel strategy based on synthesis of anodic SnOx on the conductive glass (FTO) is proposed. According to this, some preliminary results concerning optimization of the anodizing conditions (e.g. anodizing potential, time) enabling to obtain stable oxide layers together with an impact of thermal treatment conditions on the photoelectrochemical activity of such kind of materials were verified. Morphology and composition of the materials were verified by FE-SEM, and XRD techniques. Moreover, semiconducting properties of the materials were investigated using UV-Vis reflectance spectra and photoelectrochemical measurements under both monochromatic and simulated solar light irradiation. References 1. G.D. Sulka (Ed.), Nanostructured Anodic Metal Oxides; Synthesis and Applications, 1st ed., Elsevier 2020. 2. H. Bian, Z. Li, X. Xiao, P. Schmuki, J. Lu, Y.-Y. Li, Anodic synthesis of hierarchical SnS/SnOx hollow nanospheres and their application for high-performance Na-ion batteries, Adv. Funct. Mater. 29 (2019) 1901000. 3. L. Zaraska, K. Gawlak, M. Gurgul, D.K. Chlebda, R.P. Socha, G.D. Sulka, Controlled synthesis of nanoporous tin oxide layers with various pore diameters and their photoelectrochemical properties, Electrochim. Acta 254 (2017) 238 – 245. 4. A. Palacios-Padrós, M. Altomare, K. Lee, I. Diéz-Pérez, F. Sanz, P. Schmuki, Controlled thermal annealing tunes the photoelectrochemical properties of nanochanneled tin-oxide structures, ChemElectroChem 1 (2014) 1133 – 1137.
Authors : Pierpaolo Vecchi (1), Alberto Piccioni (1), Serena Berardi (2), Vito Cristino (2), Michele Mazzanti (2), Stefano Caramori (2), Paola Ceroni (3) & Luca Pasquini (1).
Affiliations : (1) Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, 40127, Bologna, Italy; (2) Department of Chemical and Pharmaceutical Sciences, University of Ferrara, via Luigi Borsari 46, 44121, Ferrara, Italy; (3) Department of Chemistry ?Giacomo Ciamician?, University of Bologna, via Selmi 2, 40126, Bologna, Italy
Resume : The WO3/BiVO4 heterojunction is a promising candidate for photoelectrochemical (PEC) water splitting, for its good charge transfer and light absorbing properties. A variable affecting the PEC efficiency of the photoelectrode is the surface morphology, and can be manipulated during the deposition using different techniques. Electrochemical impedance spectroscopy (EIS) is a common technique used to characterize charge transfer processes in the space charge layer of the electrode by modulating the applied potential. Instead, light intensity modulation allows to study charge transfer and recombination due to surface states only. Using EIS combined with intensity modulated photocurrent spectroscopy (IMPS) and transient photocurrent (TPC) measurements, the carrier dynamics in colloidal and solvothermal WO3 photoelectrodes, with and without an additional electrodeposited BiVO4 layer, were investigated. The characteristic time constants and the equivalent circuits determined from EIS and IMPS have been applied to interpret the transient dynamics observed in TPC experiments. Significant changes in the recombination rates were observed in the different electrodes. These results aim to explain the relation between the processes occurring at the surface and the electrode morphology to find the best deposition parameters for the heterojunction.
Authors : Choongman Moon, Filipe M. A. Martinho, Jihoon Jung, Byungha Shin
Affiliations : Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea; Department of Photonics Engineering, Technical University of Denmark, DK-4000 Roskilde, Denmark; Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea; Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea;
Resume : Silicon photoelectrode has been widely investigated as a bottom cell of a tandem photoelectrochemical (PEC) water-splitting device because its bandgap (1.12 eV) is close to the lower bandgap of the ideal tandem bandgap combination (~1.9 eV / ~1.1 eV). While the silicon cell based on a p-n junction shows 500 ~ 570 mV of photovoltage, a top cell made of a large bandgap material, such as Fe2O3, BiVO4 or Cu2O, can combine with the silicon bottom junction to drive the water-splitting reaction without any external power supply. However, when considering the catalytic activity of the state-of-art water-splitting catalysts, photovoltages from such tandem PEC devices are barely enough to carry out the unassisted water-splitting reaction. Furthermore, silicon p-n junction can be easily damaged by a high processing temperature often required for depositing a large bandgap material, and it severely limits the choice of materials for the top cell. In this study, we demonstrate silicon photoelectrodes based on a tunnel oxide passivated contact (TOPCon) on silicon photoelectrodes to generate a photovoltage higher than 630 mV. Both photocathode for hydrogen evolution and photoanode for oxygen evolution are tested over a broad range of pH (0 ~ 14), and show a reasonably good Tafel slope depending on catalysts. The enhanced photovoltage compared to silicon p-n junction would be able to provide a higher efficiency when it is applied to a tandem device. In addition, the TOPCon silicon photoelectrodes maintain good performance after annealing at a high temperature (> 400 °C). The high thermal stability shows that the TOPCon Si would be compatible with many other large bandgap materials processed at a high temperature.
Authors : M. Einert, A. Waheed, D. Moritz, S. Lauterbach, H. Schlaad, and J.P. Hofmann
Affiliations : 1 Department of Materials and Earth Sciences, Surface Science Laboratory, Technical University of Darmstadt, Otto-Bernd-Strasse 3, 63287 Darmstadt (Germany) 2 Institute of Chemistry, University of Potsdam, Karl-Liebknecht-Strasse 24-25, 14476 Potsdam (Germany)
Resume : In the search for sustainable and economical affordable materials as photoabsorber for photo-assisted solar water splitting, copper-based metal oxide photoelectrodes are promissing class of materials. Copper-based metal oxide photoelectrodes with defined mesopore structure were prepared via a sol-gel synthesis. The influence of the used polymeric porogen on the (pore-) morphology of the materials was evaluated by means of wide-angle-X-ray scattering, scanning and transmission electron microscopy and was further correlated to the photoelectrochemical performance of the mesoporous photoelectrodes. By combining intensity-modulated photocurrent and photovoltage spectroscopy, charge-carrier dynamics and lifetimes were attributed to the experimentally observed photoresponse of the thin-film photoelectrodes. A detailed comparison of XPS- and Mott-Schottky-Analysis gives insight into the electronic band structures of these promising photoabsorbers and contributes therefore to the overall understanding of charge carrier dynamics in copper-based photolelectrodes in particular and for mesoscopic structured energy materials in general.
Authors : Gihun Jung, Segi Byun, Byungha Shin
Affiliations : Korea Advanced Institute of Science and Technology, Gihun Jung; Byungha Shin Korea Institute of Energy Research, Segi Byun
Resume : Among various synthesis methods for bismuth vanadate, a two-step process including electrodeposition of Bi precursor film followed by drop-casting of V containing organic solution and annealing has been widely adopted to fabricate bismuth vanadate photoanode with high photoelectrochemical(PEC) oxidation performance. However, careful removal of excess vanadium oxide on bismuth vanadate after the annealing process is required and conventionally highly basic solution such as 1 M sodium hydroxide solution has been used for the etchant. Due to the weak chemical stability of bismuth vanadate under high pH solution, unintended dissolution of bismuth vanadate also occurs during the vanadium oxide etching process, which results in poor reproducibility and areal uniformity of the PEC oxidation performance. Here, we developed a selective etching method for excess vanadium oxide without any damage on bismuth vanadate, which is named as electrochemical etching. Compared with conventional chemical etching method by sodium hydroxide solution, our own method shows better uniformity and reproducibility PEC performance. Detail analyses of bismuth vanadate films after two etching methods (chemical vs electrochemical) will be delivered.
Authors : Laura Montañés, Camilo A. Mesa, Beatriz Julián-López, Sixto Giménez
Affiliations : Institute of Advanced Materials (INAM), Universitat Jaume I, 12006, Castelló, Spain
Resume : The capture of solar energy and its direct conversion into chemical energy using artificial photosystems is one of the most promising routes to provide the global demand for energy in a sustainable way. Among the different existing approaches, the photoelectrochemical energy conversion (PEC) has attracted considerable interest for solar energy storage through the formation of chemical bonds in form of dihydrogen molecules or carbon-based fuels.  These systems are normally based on semiconductors that absorb solar energy, that is, photoanodes (photooxidation reaction) and photocathodes (photoreduction reaction), coupled to catalyst and connected by an aqueous electrolyte. However, the main challenge lies in the lack of efficient, inexpensive, stable and scalable semiconductors, particularly in the photoanode, where the oxygen evolution reaction (OER) takes place. Metal oxides are the most studied as photoanodes since they have a valence band with a thermodynamically favourable energy for the OER. Numerous types of semiconductors have been tested, such as titanium dioxide (TiO2), hematite (?-Fe2O3), bismuth vanadate (BiVO4) and tungsten trioxide (WO3) among others.  Bismuth vanadate (BiVO4), has attracted attention in the last two decades as one of the most robust, efficient, and inexpensive photoanode for water electrolysis. BiVO4 is characterized by having a bandgap of 2.4 eV, allowing it to absorb a greater amount of solar energy compared to the previously mentioned oxides.  In this poster, I will present a novel synthesis to obtain bismuth vanadate nanoparticles using a surfactant as distribution agent and to control the size. This synthesis offers the advantage of being carried out at low temperature, in an aqueous medium and using inexpensive precursors. These nanoparticles provide a high surface area in addition to multiple photoelectrodes designs to obtain efficient devices.  T. Hisatomi, J. KubotaK. Domen. Recent advances in semiconductors for photocatalytic and photoelectrochemical water splitting. Chem. Soc. Rev. 2014, 43, 7520. DOI: 10.1039/c3cs60378d  D. K. Lee, D. Lee, M. A. Lumley, K. S. Choi. Progress on ternary oxide-based photoanodes for use in photoelectrochemical cells for solar water splitting. Chem. Soc. Rev. 2019, 48, 2126. DOI: 10.1039/c8cs00761f  J.H. Kim, J.S. Lee. Elaborately Modified BiVO4 Photoanodes for Solar Water Splitting. Adv. Mater. 2019, 32(20), 1521-4095. DOI: 10.1002/adma.201806938
Authors : Jiaming Ma, Giulia Tagliabue
Affiliations : Laboratory of Nanoscience for Energy Technologies (LNET), STI, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
Resume : TiO2 is a promising photocatalyst with remarkable chemical and photo corrosion resistance that has been widely used in many applications including dye-sensitized solar cells (DSSC), photoelectrical cells (PEC) and, more recently, solar-powered redox flow batteries (RFBs). However, its wide bandgap (3.2 V) restricts light absorption and limits efficiency under solar illumination. Localized surface plasmon resonances (LSPR), i.e. collective oscillations of the electron cloud in metallic nanoparticles, have emerged as a viable solution to overcome such limitations. While their use in DSSC and PEC water splitting devices has shown promising results, applications to solar RFBs have remained largely unexplored. In particular, the understanding of the role of plasmonic nanoparticles during both the charging and discharging processes remains to be clarified. Here, we report the engineering of plasmon-enhanced solar powered redox cells towards studying their impact on both charging and discharging processes. In particular we compare the performance of TiO2/gold photoanodes with increasing gold content, i.e. a TiO2/Au layer and a TiO2/Au nanoparticles (NPs). As the thickness of Au layer and the content of Au NPs increase, we can see an enhancement in light absorption in the Vis-to-NIR (400-750 nm) range. Interestingly, the relationship between photocurrent and Au content is not linear, the photocurrent of modified photoanodes can be even lower than the bare one under continuously increasing Au. In particular, we observe the photocurrent of the plasmonic TiO2/Au NPs structure has a significant enhancement (0.08 mA/cm2), which is twice higher than the bare one (0.04 mA/cm2), thus increasing the solar to chemical (STC) efficiency. Concurrently, we observe that the gold loading has an impact on the discharge process that needs to be taken into account for the optimization solar powered redox cells and solar redox flow batteries. Keywords: Plasmonic structure, TiO2/Au NPs, TiO2/Au layer, STC, solar powered redox cells
Authors : Anna A. Wilson a, Benjamin Moss a, Takashi Hisatomi b, Kazunari Domen b,c, James R. Durrant a
Affiliations : a The Department of Chemistry, Imperial College London, South Kensington, London SW7 2AZ, U.K. b Center for Energy & Environmental Science, Interdisciplinary Cluster for Cutting Edge Research, Shinshu University, 4-17-1 Wakasato, Nagano-shi, Nagano 380-8553, Japan c Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
Resume : Photocatalytic water splitting driven by sunlight offers an up-scalable route to a renewable source of hydrogen fuel. The particulate nature of the photocatalyst panels studied herein enables the panels to be manufactured by low-cost and large scale manufacturing processes. Al 3+ doped SrTiO3 modified with a RhCrOx proton reduction co-catalyst (Al:SrTiO3/RhCrOx) is one of the most promising photocatalytic systems to date for overall water splitting. Al:SrTiO3/RhCrOx sheets, where RhCrOx is deposited via impregnation, achieve an apparent quantum yield of 56% at 365 nm. 1 Impressive stability is observed following modification with a CoOy overlayer, with water splitting activity maintained at 80% of initial activity over 1300 hours. 2 More recently, apparent quantum yields near to unity have been achieved for Al:SrTiO3/RhCrOx powder where cocatalysts were deposited selectively onto facets. 3 This work aims to explore the functions of Al 3+ doping and RhCrOx, to identify what enables the efficient photocatalyst operation without external bias or scavengers present. To this end, the photocatalyst sheets and their components are characterised, in particular by XPS, and their charge carrier dynamics are investigated in operando by employing photoinduced absorption spectroscopy (PIAS) and diffuse reflectance transient spectroscopy (DRTS). Through XPS studies, we identify the successful suppression of Ti 3+ recombination centres following fluxmediated Al 3+ doping and a lowering of the Fermi level that significantly decreases the n-type character. The combination of Al 3+ doping and RhCrOx deposition results in increased charge densities under steady-state conditions, in addition to greatly extended charge carrier lifetimes. Efficient electron extraction to the RhCrOx proton reduction catalyst is confirmed by scavenger studies, whilst the charges remaining in the bulk are predominantly assigned to hole species. This spatial separation results in a charge imbalance, where holes accumulate and persist in bulk Al:SrTiO3 regions without detriment to water splitting activity. The intensity dependence of the PIAS decay kinetics identifies a broad distribution of hole states being accessed under accumulation conditions. Under background illumination (as would be the case for device operation in sunlight), the deep states responsible for the longest-lived charges are saturated and passivated, assisting the subsequent generation of reactive charges to contribute to water splitting activity. 1. Y. Goto, T. Hisatomi, Q. Wang, T. Higashi, K. Ishikiriyama, T. Maeda, Y. Sakata, S. Okunaka, H. Tokudome, M. Katayama, S. Akiyama, H. Nishiyama, Y. Inoue, T. Takewaki, T. Setoyama, T. Minegishi, T. Takata, T. Yamada and K. Domen, Joule, 2018, 2, 509–520. 2. T. Minegishi, H. Nishiyama, T. Hisatomi, M. Yoshida, H. Lyu, M. Katayama, K. Domen, Y. Goto, K. Asakura, Y. Sakata, T. Yamada, T. Higashi and T. Takata, Chem. Sci., 2019, 10, 3196–3201. 3. T. Takata, J. Jiang, Y. Sakata, M. Nakabayashi, N. Shibata, V. Nandal, K. Seki, T. Hisatomi and K. Domen, Nature, 2020, 581, 411–414.
Authors : David Carvajal, Ramón Arcas, Camilo Mesa, Elena Mas-Marzá, Francisco FabregatSantiago
Affiliations : Institute of Advanced Materials, Universitat Jaime I, 12006, Avda. V. Sos Baynat s/n, Castelló, Spain
Resume : The production of cheap energy from renewable sources, like solar energy, provides the opportunity to use electrochemistry for the synthesis of added-value products in a costeffective manner. Thus, the combination of electrochemical cells with photovoltaic devices, either as independent or integrated devices, has widely been studied for the transformation of photons to electricity and then to chemical energy through the oxidation of species such as water and alcohol to oxygen or aldehydes respectively. The reduction half-reaction, on the other hand, has typically been used to produce molecular hydrogen, which is considered as a mean to store energy due to its high-density energy per weight unit. Additionally, the reduction of CO2, to energy-rich chemicals (CO, formic acid, methane, methanol, etc.), is gaining increasing attention these days. In this line, there are other alternative chemical routes, such as the synthesis of products for the chemical industry, which despite being much less developed, may present a good intrinsic economical interest. The production of aniline by reduction of nitrobenzene is a very useful transformation, as this species are widely employed as building blocks for the production of aniline-based dyes, explosives, pesticides and drugs. The electrochemical reduction of nitrobenzene to aniline is a 3-steps mechanism, involving a 6 electron and 6 proton process. Electrodes made of Cu and Cu based compounds have efficiently been used for the electro-reduction of nitrobenzene in aqueous media due to their high energy of activation for the competing hydrogen evolution reaction (HER), thus enhancing the reactivity of the hydrogen radical in the organic reduction and increasing the coulombic efficiency for the organic transformation. Compared with copper, noble metals as palladium show high activity for the hydrogenation of organic compounds, mainly due to their affinity for the adsorption and storage of H* species as hydrides. In this work, we present the electro-reduction of nitrobenzene using Cu electrodes decorated with Pd by a galvanic replacement technique. We have observed that the introduction of Pd in the Cu surface enhanced the performance and selectivity of the electrode. A detailed analysis using Impedance Spectroscopy has also been performed showing the improvement in the catalytic performance of Cu with Pd decorated electrodes due to the incorporation of Pd.
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Celebration of the 50th anniversary of photoelectrochemical water splitting : Sixto Gimenez Julia, Byungha Shin, Salvador Eslava
Authors : Menny Shalom
Affiliations : Chemistry Department, Ben-Gurion University of the Negev, Beer-Sheva, Israel
Resume : One of the most promising future sources of alternative energy involves water-splitting photoelectrochemical cells (PECs) – a technology that could potentially convert sunlight and water directly to a clean, environmentally friendly, and cheap hydrogen fuel. Practical PECmediated hydrogen production requires robust and highly efficient semiconductors, which should possess good light-harvesting properties, a suitable energy band position, stability in harsh conditions, and a low price. Despite significant progress in this field, new semiconductors that entail such stringent requirements are still sought after. Over the past few years, graphitic carbon nitride (CN) has attracted widespread attention due to its outstanding electronic properties, which have been exploited in various applications, including photo- and electro-catalysis, heterogeneous catalysis, CO2 reduction, water splitting, light-emitting diodes, and PV cells. CN comprises only carbon and nitrogen, and it can be synthesized by several routes. Its unique and tunable optical, chemical, and catalytic properties, alongside its low price and remarkably high stability to oxidation (up to 500 °C), make it a very attractive material for photoelectrochemical applications. However, only a few reports regarded the utilization of CN in PECs due to the difficulty in acquiring a homogenous CN layer on a conductive substrate and to our lack of basic understanding of the intrinsic layer properties of CN. In this talk, I will introduce new approaches to grow CN layers with altered properties on conductive substrates for photoelectrochemical application1-4 . The growth mechanism and their chemical, photophysical, electronic, and charge transfer properties will be discussed.
Authors : Joachim John, Nina Plankensteiner, Arvid Van der Heide, Jonathan Govaerts, Loic Tous, Tom Aernouts, Jef Poortmans, Philippe Vereecken
Affiliations : imec, Kapeldreef 75, 3001 Leuven, Belgium KU Leuven, 3000 Leuven, Belgium
Resume : Introduction The availability of technology for the direct and efficient conversion of solar energy into chemical fuel, will be one of the crucial elements for Europe to reach its ambitious climate goals by 2030 and 2050 and to fulfil the European Green Deal. Efficient light-to-fuel (solar fuels) technologies have the potential to significantly contribute to sector coupling by transferring renewable energy into chemical energy of synthetic energy carriers. This is especially valuable in areas of the energy system that do not have many options for using renewable electricity directly. These areas encompass heavy trucks, aviation and marine fuels, fuels for high-temperature industrial applications as well as the chemical feedstock as raw material basis for the chemical industry. The importance and the potential of using solar energy to create synthetic fuels is obvious when one considers the fact that using only 0.1% of the earth?s land space with solar collectors that operate with a collection efficiency of merely 20%, one could gather more than enough energy to supply the current yearly energy needs of all the citizens of the planet. Some other facts that speak out on behalf of solar energy for decarbonisation are: 1) the solar energy reserve is essentially unlimited and well distributed, 2) no particular individual or government owns it, 3) its utilisation is ecologically benign. The constantly increasing proportion of electricity supply that is accounted for by renewable energies, such as wind and solar energy, has led to the fact that on windy and/or sunny days, large amounts of power are already being produced this way. It is predicted that in a few years' time, in the middle of a windy summer day, Europe?s entire energy needs will be met by electricity generated from photovoltaics and wind. On such days however, the increasing expansion of renewable energies will produce more electricity than is needed at the time. The excess of electricity produced on such moments need to be stored in the form of batteries (electrical storage) or in the form of synthetic fuels (chemical storage). The development of batteries for variable renewable energy storage has made a lot of progress recently and is also supported and pushed by the European car industry. However, it mainly targets the short-term storage problem, like day/night storage. The long-term storage required to overcome the winter season, ?Dunkelflaute? (seasonal storage) is very difficult to address with batteries, as is the need to power heavy transport (trucks, ships and airplanes). Converting sunlight directly into chemicals has been investigated since decades. In 1972, Fujishima and Honda1 published the direct conversion from light to hydrogen using a wideband semiconductor (TiO2) in a photocatalytic process. Since then, many groups have worked on photocatalysis using more and more advanced devices and different embodiments of Photoelectrochemical cells (PEC)2. The efficiency of these approaches is increasing within the last years but they suffer from the principle problems of this approach: e.g. durability, due to the direct exposure of the photocatalyst material to the electrolyte, limited spectral range because of the limitation on the material choice and carrier recombination mechanisms within the PEC semiconductor material. Despite the effort and the recent improvements, the technology readiness level of the PEC technology is rather low (TRL 2-3) and the way to industrial application is not straightforward. On the other hand, PV and the electrolysis technologies are rather well developed and applied worldwide on ever larger scale. Building large-scale alkaline or PEM water splitting electrolysers in close proximity to the source of cheap green energy like solar or wind could bring the cost of green hydrogen below the 3 Euro/kg which is generally assumed to be the lowest cost of H2 production from Steam Methane Reforming (SMR). Nevertheless, the indirect nature of this approach leads to mainly resistive losses coming from cabling or other electrical connections and to significant investment costs for transmission and voltage conversion. In addition, the electrolyser approaches suffer from high CAPEX and sustainability issues due to the use of precious metals in Proton Exchange Membrane (PEM) electrolysers or relatively low current densities in Alkaline Electrolysis (AE). In imec, we will develop an integrated device consisting of a highly efficient solar module and a highly efficient electrolyser cell in order to provide a solution that combines the advantages of PV and electrolysis in one compact light-to-fuel device. Since several conversion steps are included, substantial investments are required and respective economies of scale lead to rather larger scale plants, from electricity generation, via electrolysis and electro-synthesis. All used technologies are introduced to the market and evolutionary developments can be expected, in particular cost scaling, as a consequence of classical technology learning. The key limitation of the state-of-the-art technologies is that the conversion from radiation to the final product takes place in several steps, which leads to not only efficiency drops, but also substantial investment requirements and respective industrial scaling in size of plants. In order to develop the necessary components of an integrated PV-EC system imec provides a technology toolbox including high efficiency Silicon-Perovskite Tandem modules and high efficiency electrochemical cells for water splitting with novel membrane electrode assembly concepts, a system simulation tool and advanced integration techniques using surface micromachining and micro fluidic. In the presentation we will give a status update on the technology toolbox highlighting the solar cell and the membrane electrode assembly development and show a first PV-EC system embodiment reaching 15% Solar to Hydrogen efficiency. Imec Technology Toolbox Electrochemical cell: Electrodes Porous metals with high surface area are broadly used as structural current collectors in multiple applications, such as catalysis2, ?ltration3, fuel cells4, batteries5, supercapacitors6, electrolyzers7, or sensors8. On the one hand, the high porosity of the porous metal is desired to accommodate greater volume of functional materials (e.g., energy-storing components in high-capacity batteries) or molecules (e.g., gas in fuel cell electrodes). On the other hand, the high surface area of the metal can enable higher reaction rates and lower internal resistance within the device, improving, for example, charging time of a battery9 or sensitivity of a sensor10. Importantly, high volumetric surface area (VSA) of the metal, also known as surface-to-volume ratio, allows to shrink the size of a porous current collector while keeping its total surface area high, facilitating device miniaturization and mechanical stability. To a big extent, such a trade-o? is a consequence of the random microstructure of these materials11. Electrode material is developed to provide high porosity and high volumetric surface area (VSA). For that reason, material like metal foams and metal coated carbon cloths are commonly used as electrodes. Nanostructured metals with large surface area have a great potential for multiple device applications. Although various metal architectures based on metal nano ligaments and nanowires are well known, they typically show a trade-off between mechanical robustness, high surface area, and high (macro)porosity, which, when combined, could significantly improve the performance of devices such as batteries, electrolysers, or sensors. In imec, we design templated networks of interconnected metal nanowires, combining high porosity of metal foams, narrowly distributed macropores, and a very high surface area of nano porous de-alloyed metals. Thanks to their structural uniformity, the few-micron thick nanowire meshes are also remarkably flexible and durable. In an exemplary application in electrolytic production of hydrogen, thanks to its high surface area, a few-micron thick nanomesh will outperform a thicker nickel foam. Furthermore, thanks to its high porosity, the Pt-doped nanomesh will surpass a microporous Pt/C cloth and will demonstrate benefits of the optimally designed nanowire structure for a simultaneous improvement and miniaturization of electrochemical devices. The development in this project will extend the potential of interconnected nanowires to multiple new research and industrial applications requiring highly porous and flexible conductive materials with a high surface-to-volume ratio. Si-Perovskite tandem cells The astonishingly fast increase of the power conversion efficiency (PCE) of perovskite solar cells in just a few years is the result of a unique combination of properties, including a high optical absorption coefficient12, long diffusion lengths13,14, low trap densities15. Beyond their ideal intrinsic optical and electrical proprieties, another key advantage of perovskite materials is that their bandgap can be tuned by varying their chemical composition. This is a unique benefit as compared to other PV materials. Indeed, this allows easy synthesis of a variety of perovskite absorbers whose energy bandgap can be optimally matched with the Silicon cell in multi-junction configurations to push the PCE over 30%, while still keeping the production costs at low to moderate level16,17. Perovskite-based tandem solar cells typically comprise a wide band gap (1.6-1.8 eV) perovskite top cell and a low band gap (1.0-1.1 eV) bottom cell. In the past 4-5 years, the mechanically stacked four-terminal (4T) perovskite/Si and perovskite/CIGS tandem solar cells have been intensively explored, due to the simplicity of independent fabrication and optimization of sub cells. However, this 4T design requires more transparent conductive oxide (TCO) electrodes and exterior electronics, making it impractical for large scale manufacturing and installation. On the other hand, the monolithic series interconnected (2T) tandem devices have attracted rapidly increasing interest as they involve a smaller number of substrates, layers, and interconnections. The best-in-class perovskite on silicon tandems have demonstrated PCEs of 28.2% and 29.12% in 4 terminals (4T) and 2 terminals (2T) respectively18. These results prove that the integration of perovskite and Si solar technology in a tandem configuration is a promising direction for high-efficiency PV development with still high potentials to be explored. Indeed, the theoretical limit for perovskite-Si tandem is well above 43%. Although these results are very promising for the development of innovative PV devices, all the very high PCEs have been demonstrated for devices typically not larger than 1 cm2 in the best cases. Additionally, for the 2T top result, a front-side polished Si bottom cell was used, while for industrial Si cells micron-sized textured surfaces are conventionally used. The current challenge for the 2T configuration is consequently how to grow device-quality perovskite material on the bottom cell with such surface roughness. The 2T configuration also enables generation of a high output voltage, which is specifically relevant for the application targeted in this project. It was shown that losses at the interfaces of the perovskite with adjacent layers like charge transporting materials are limiting the Voc of the final devices19. Therefore, to achieve the highest output voltages, it is important to passivate the perovskite film. Multiple routes have been suggested, like adding trace amounts of alkylamine ligands to the perovskite precursor solution, which have led to the improved orientation of the film, as well as efficient passivation of the surface20. PV-EC system integration The full monolithic integration of a PV cell and an electrochemical cell is identified as a solution to provide low cost device fabrication and reduce ohmic losses due to a short ionic pathway between the electrodes21. The short ionic pathway is realized by perforating the solar cell with holes filled with a proton exchange material. In literature silicon based multi-junction cells are proposed22,23, the holes are performed by reactive ion etching techniques, non-abundant materials (like Ir and Pt) are used as electrocatalysts, and Nafion (per(fluorosulfonic acid) poly(tetrafluoroethylene) copolymer) is used as membrane separator material. We are proposing an approach which concentrates on scalable processes and abundant materials. In this approach we will develop highly efficient silicon based perovskite multi-junction cells, the electrocatalyst material is based on a nanomesh made of abundant metals like Ni, or Cu, the membrane separator material will be a nano-composite electrolyte developed in imec24. In order to reach a monolithic integrated system, different intermediate embodiments are developed. We will present an embodiment with series connected shingled silicon solar cells and an electrochemical cell using a Ni nanomesh and an alkaline electrolyte. With this combination we could achieve StH efficiencies up to 15%. Outlook In a forthcoming embodiment Si-Perovskite tandem cells will substitute the silicon cells, dedicated catalysts are applied to the nanomesh electrode and a further reduction of the membrane thickness is implemented. References  Fujishima, A., Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode.?Nature?238,?37?38 (1972). https://doi.org/10.1038/238037a0  Do?rfelt, C.; Kolvenbach, R.; Wirth, A. S.; Albert, M.; Ko?hler, K. Catalytic Properties of a Novel Raney-Nickel Foam in the Hydrogenation of Benzene. Catal. Lett. 2016, 146, 2425?2429.  Khosravanipour Mostafazadeh, A.; Zolfaghari, M.; Drogui, P. Electrofiltration Technique for Water and Wastewater Treatment and Bio-Products Management: A Review. J. Water Process Eng. 2016, 14,  Yuan, W.; Tang, Y.; Yang, X.; Wan, Z. Porous Metal Materials for Polymer Electrolyte Membrane Fuel Cells - A Review. Appl. Energy 2012, 94, 309?329.  Yang, G. F.; Song, K. Y.; Joo, S. K. A Metal Foam as a Current Collector for High Power and High Capacity Lithium Iron Phosphate Batteries. J. Mater. Chem. A 2014, 2, 19648?19652.  Xu, M.; Xu, R.; Zhao, Y.; Chen, L.; Huang, B.; Wei, W. Hierarchically Porous Ni Monolith@branch-Structured NiCo2O4 for High Energy Density Supercapacitors. Prog. Nat. Sci. Mater. Int. 2016, 26, 276?282.  Zhu, W.; Zhang, R.; Qu, F.; Asiri, A. M.; Sun, X. Design and Application of Foams for Electrocatalysis. ChemCatChem 2017, 9, 1721-1743  Li, X.; Lu, X.; Kan, X. 3D Electrochemical Sensor Based on Poly(Hydroquinone)/Gold Nanoparticles/Nickel Foam for Dopa-mine Sensitive Detection. J. Electroanal. Chem. 2017, 799, 451?458.  Pikul, J. H.; Gang Zhang, H.; Cho, J.; Braun, P. V.; King, W. P. High-Power Lithium Ion Microbatteries from Interdigitated Three-Dimensional Bicontinuous Nanoporous Electrodes. Nat. Commun. 2013, 4, 1732.  Kumar, R.; Bhuvana, T.; Rai, P.; Sharma, A. Highly Sensitive Non-Enzymatic Glucose Detection Using 3-D Ni3(VO4)2 Nanosheet Arrays Directly Grown on Ni Foam. J. Electrochem. Soc. 2018, 165,  Juarez, T.; Biener, J.; Weissmu?ller, J.; Hodge, A. M. Nanoporous Metals with Structural Hierarchy: A Review. Adv. Eng. Mater. 2017, 19,1?23.  De Wolf, S., et al., Organometallic Halide Perovskites: Sharp Optical Absorption Edge and Its Relation to Photovoltaic Performance. J. Phys. Chem. Lett., 2014. 5: p. 1035.  Stranks, S.D., et al., Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber. Science, 2013. 342(6156): p. 341-344.  Xing, G., et al., Long-Range Balanced Electron- and Hole-Transport Lengths in Organic-Inorganic CH3NH3PbI3. Science, 2013. 342(6156): p. 344-347.  Shi, D., et al., Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals. Science, 2015. 347(6221): p. 519-522.  Tuning the Light Emission Properties by Band Gap Engineering in Hybrid Lead Halide Perovskite. Journal of the American Chemical Society, 2014. 136(51): p. 17730-17733.  Zhou, H., et al., Interface Engineering of Highly Efficient Perovskite Solar Cells. Science, 2014. 345: p. 542.  Kim, J., et al., Overcoming the Challenges of Large-Area High-Efficiency Perovskite Solar Cells. ACS Energy Letters, 2017. 2(9): p. 1978-1984.  C.M. Wolff et al., Adv. Mater. 31, (2019) 1902762. DOI: 10.1002/adma.201902762  X. Zheng et al., Nat. Energy 5, (2020) 131. DOI: 10.1038/s41560-019-0538-4?  J. Newman, J. Electrochem. Soc. 2013, 160, F309 5  W. Vijselaar, Adv. Energy Mater. 2019, 1803548 6  C. Trompoukis, SOLMAT 182 (2018) 196-203  S. Zankowski, ACS Appl. Mater. Interfaces 2018, 10, 44634-44644
Authors : Alberto Piccioni(1), Daniele Catone(2), Alessandra Paladini(3), Patrick O?Keeffe(3), Alex Boschi(4), Alessandro Kovtun(4), Maria Katsikini(5), Federico Boscherini(1), Luca Pasquini(1)
Affiliations : (1) Department of Physics and Astronomy, Alma Mater Studiorum ? Università di Bologna, viale C. Berti Pichat 6/2, 40127 Bologna, Italy; (2) Istituto di Struttura della Materia - CNR (ISM-CNR), EuroFEL Support Laboratory (EFSL), Via del Fosso del Cavaliere 100, Rome, 00133 Italy; (3) Istituto di Struttura della Materia - CNR (ISM-CNR), EuroFEL Support Laboratory (EFSL), Monterotondo Scalo 00015, Italy; (4) Istituto per la Sintesi Organica e la Fotoreattività, Consiglio Nazionale delle Ricerche, Via P. Gobetti 101, 40129 Bologna, Italy; (5) School of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
Resume : Light absorption and charge transport in oxide semiconductors can be tuned by the introduction, during deposition, of a small quantity of foreign elements, leading to the improvement of the photoelectrocatalytic performance(1). In this work, both unmodified and vanadium-modified TiO2 thin films deposited by radio-frequency magnetron sputtering are investigated as photoanodes for photoelectrochemical water splitting. In particular, photoelectrocatalysis is discussed based on ultrafast transient absorbance spectroscopy measurements, performed at three different pump wavelengths from UV to the visible range are used (300, 390, and 530 nm) in order to cover the relevant photoactive spectral range of modified TiO2. Incident photon-to-current conversion efficiency spectra show that incorporation of vanadium in TiO2 extends water splitting in the visible range up to ?530 nm, a significant improvement compared to unmodified TiO2 that is active only in the UV range ?390 nm. However, transient absorbance spectroscopy clearly reveals that vanadium accelerates electron-hole recombination upon UV irradiation, resulting in a lower photon-to-current conversion efficiency in the UV spectral range with respect to unmodified TiO2. The new photoelectrocatalytic activity in the visible range is attributed to a V-induced introduction of intragap levels at ?2.2 eV below the bottom of the conduction band. This is confirmed by long-living transient signals due to electrons photoexcited into the conduction band after visible light (530 nm) pulses. The remaining holes migrate to the semiconductor-electrolyte interface where they are captured by long-lived traps and eventually promote water oxidation under visible light(2). (1) Rossi, G. et al. Charge carrier dynamics and visible light photocatalysis in vanadium-doped TiO2 nanoparticles. Appl. Catal. B Environ. 237, 603?612 (2018). (2) Piccioni, A. et al. Ultrafast Charge Carrier Dynamics in Vanadium-Modified TiO2 Thin Films and Its Relation to Their Photoelectrocatalytic Efficiency for Water Splitting. J. Phys. Chem. C (2020).
Authors : Prangya P. Sahoo1, Miroslav Mikolá?ek2, Kristína Hu?eková1,3, Edmund Dobro?ka3, Ján ?oltýs3, Peter Ondrejka2, Martin Kemény2, Ladislav Harmatha2, Matej Mi?u?ík 4, Karol Fröhlich1,3
Affiliations : 1 Centre for Advanced Materials Application, Slovak Academy of Sciences, Dúbravská cesta 5807/9, 845 11 Bratislava, Slovakia 2 Institute of Electronics and Photonics, Slovak University of Technology, Ilkovi?ova 3, 812 19 Bratislava, Slovakia 3 Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04, Bratislava, Slovakia 4 Polymer Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 845 41, Bratislava, Slovakia
Resume : We report on the properties of metal-insulator-semiconductor (MIS) photoanodes for water splitting comprising thin RuO2 and IrO2-RuO2 films as top catalytic layers. RuO2 and IrO2 offer low resistivity, high optical transparency, work function as well as high catalytic efficiency. RuO2 and IrO2-RuO2 films with a thickness of 5 nm were grown using liquid injection metal-organic chemical vapour deposition, MOCVD. A thin SiO2 layer was prepared by ozone treatment of the n-Si substrate at 300 °C. The films have a low room temperature resistivity of 10?4 ?cm and transmittance up to 80% in the visible light region. The photocurrent and photovoltage of these MIS photoanodes were studied in 1 M aq. H2SO4 (pH=0), 0.5 M aq. Na2SO4 (pH=6), and 1 M aq. KOH (pH=14) electrolytes. The photoelectrochemical oxygen evolution reaction of the RuO2 and IrO2-RuO2 photoanodes follows a V-shape relationship with the pH. RuO2/SiO2/n-Si photoanode exhibited a photovoltage of 0.49 V and was able to generate a photocurrent of ~10 mA/cm2 at a thermodynamic water oxidation potential (1.23 V vs. normal hydrogen electrode, NHE) in 1 M aq. H2SO4 solution under 1 Sun intensity with AM 1.5 spectrum. A photovoltage of 0.42 V and a photocurrent of ~5 mA/cm2 were achieved for the IrO2-RuO2/SiO2/n-Si photoanode in acidic conditions. The stability of the photoanodes was examined in 1 M aq. H2SO4 and 1 M aq. KOH solutions. Chronoamperometry measurements on the RuO2/SiO2/n-Si photoanode in acidic solution under an applied voltage of 1.23 V vs. NHE showed the deterioration of the photoanode after 2 h of operation. Faster degradation was observed upon applying a higher voltage of 1.5 V vs. NHE. Similarly, stability measurements were performed on IrO2-RuO2/SiO2/n-Si photoanodes in 1 M aq. H2SO4 solution. In acidic conditions, at an applied bias of 1.23 V vs NHE, a photocurrent of ~2 mA/cm2 was observed which was stable for 24 h for the IrO2-RuO2 based photoanodes. X-ray photoelectron spectroscopy (XPS) measurements were carried out to understand the stability of the photoanodes in different electrolytes. The loss of RuO2 during the stability measurements in the acidic electrolyte was confirmed from the XPS studies. This study was performed during the implementation of the project Building-up Centre for advanced materials application of the Slovak Academy of Sciences, ITMS project code 313021T081 supported by Research & Innovation Operational Programme funded by the ERDF. The research was funded also by APVV (project APVV-17-0169).
Authors : J.C. Conesa(1), M. del Barrio(1), J. Álvarez-Malmagro(1), M. Pita(1), S. Zacarias(2), I. A. C. Pereira(2), S. Shleev(3), A. L. De Lacey(1)
Affiliations : (1)Instituto de Catálisis y Petroleoquímica, CSIC, Madrid, Spain; (2)ITQB, Universidade Nova de Lisboa, Oeiras, Portugal; (3)Biomedical Science, Faculty of Health and Society, Malmö University, Malmö, Sweden
Resume : Many sulphide semiconductors are photocatalytically active in significant ranges of the visible spectrum; our group has shown this, specifically, for In2S3, with a bandgap of 2.0-2.1 eV, and SnS2, with a bandgap of 2.2 eV (R. Lucena et al., Catal. Commun. 2012, 20, 1; ibid. Appl. Catal. A: General, 2012, 415-416, 111). Here we will show how coupling these sulphides with enzymes of hydrogenase, laccase or formate-dehydrogenase types allows photoevolving H2 or O2 or reducing CO2. First, we could show that combining In2S3 with a mutated hydrogenase obtained from Desulfovibrio vulgaris (having Fe and Ni as active species) it was possible to generate photocatalytically H2 in presence of a sacrificial agent (C. Tapia et al., ACS Catalysis 2016, 6, 5691). Then, we showed that combining In2S3 with a laccase obtained from Trametes hirsuta (including a Cu-oxide cluster as active species) it was possible to generate O2 photoelectrochemically (C. Tapia et al., ACS Catalysis 2017, 17, 4881), this being the first time that such enzyme-sulphide combination allowed photoevolution of O2. A similar photoelectrochemical generation of O2 could be shown subsequently by combining SnS2 with the same laccase enzyme (C. Jarne et al., ChemElectroChem 2019, 9, 2755). Some of us carried out recently work which coupled an electrode with a formate dehydrogenase enzyme (including W as active species; also obtained from Desulfovibrio vulgaris) so that it was possible to reduce electrocatalytically CO2 to formate (J. Álvarez-Malmagro et al., ACS Appl. Mater. Interfaces 2021, 13, 11891). Ongoing work will be shown here in which combining this latter enzyme with In2S3 nanoparticles allows to perform the same task photocatalytically.
Authors : Fallahpour,M.*(1), Poursalehi,R.(1), Yourdkhani,A.(1)
Affiliations : (1) Department of Materials Engineering, Tarbiat Modares University, Tehran, Iran
Resume : In recent years pollution of water resources with different organic and inorganic contaminants, and its harmful side effects on human health has become a significant challenge. Photocatalytic degradation is a biocompatible method for the wastewater treatment process. This work aims to immobilize g-C3N4/ZnO nanocomposite on a transparent substrate to use for urban municipal landfill pitch-dark wastewater leachate treatment. Immobilization on a transparent substrate can provide a pathway to the efficient coupling of light to photocatalyst nanoparticles, even pitch-dark media, and an appropriate recovery condition. In this study, ZnO nanoparticles were first prepared by a DC arc discharge synthesis method. Two zinc rods as electrodes were immersed in DI water, and an 80 A current was applied. After completion of oxidation process, white precipitate dried and mixed with urea. g-C3N4/ZnO nanocomposite was synthesized by pyrolysis of the mixture at the rate of 5°C/min to 550 °C for four h; then, the composition was fixed on a glass substrate. The physicochemical properties of g-C3N4/ZnO were mainly characterized by XRD, UV-vis spectroscopy, and SEM. The photocatalytic activity of immobilized g-C3N4/ZnO nanostructure was evaluated by decomposing dark methylene blue solution under backlight visible irradiation. After 90 minutes of irradiation, the degradation efficiency of the nanocomposite was about 95%. Results showed enhanced photocatalytic activity of the nanocomposite compared with g-C3N4 and ZnO even in pitch-dark conditions. Such an enhanced photoactivity could be assigned to the well-established heterojunction between g-C3N4 and ZnO.
Authors : E. Hashemi*(1), R. Poursalehi.(1) & H. Delavari.(1).
Affiliations : (1)Department of Materials Engineering, Tarbiat Modares University, Tehran,14115-143, Iran
Resume : Bismuth oxide (Bi2O3) photocatalytic nanoparticles are produced via oxidation of bismuth (Bi) nanoparticles, which are synthesized by DC electrical arc discharge in water as oxidative media by applying a 60A DC currents between two bismuth electrodes. Powder X-ray diffraction (XRD) pattern reveals formation of both bismuth and bismuth oxide phases. Field emission scanning electron microscopy (FE-SEM) image indicates the formation of spherical nanoparticles with average size of 17 nm. The optical transmission spectra of colloidal sample demonstrates the optical characteristics of both bismuth and bismuth oxide. In addition, oxidation mechanism of nanoparticles are explained by XRD and UV-Visible spectroscopy. The photocatalytic performance of synthesized nanoparticles are studied by degradation of methyl orange under visible light irradiation during 180 min. The synthesized nanoparticles shows an efficient photocatalytic activity. To sum up, synthesis of bismuth oxide nanoparticles by electrical arc discharge in water with high purity and controllable oxidation process introduced a relatively simple and flexible method for synthesis of environmentally friendly photocatalytic nanoparticles.
Authors : V. Golovanova, T. Andreu, J.R. Morante
Affiliations : Catalonia Institute for Energy Research (IREC); Department of Materials Science and Physical Chemistry, University of Barcelona; Department of Electronics, University of Barcelona
Resume : Significant depletion of fossil fuels has led to the urge of finding new renewable sources of energy, able to fulfill the current energy demands. Solar-based hydrogen produced from water is an appealing alternative fuel, which can be generated without extra CO2 emissions. Transition metal nanoparticles, such as nickel, are the benchmark catalysts for hydrogen evolution reaction, as they are highly active, stable and earth-abundant. One of the emerging fields of solar energy harvesting is enhancing the catalytic reaction through the local surface plasmon resonance (LSPR) effect of the catalyst. Most studied mechanisms of the energy transfer from plasmonic nanoparticles are based on hot electron injection and plasmon-induced resonant energy transfer. However, the photothermal effect of the plasmon in transition metal nanoparticles is still underestimated in the literature. In this work, we have synthetized Ni nanoparticles with an elongated average shape by wetness impregnation of the hard silica template. The high distribution of sizes results in a broad plasmonic absorption in the visible range, which leads to a significant photothermal effect under solar illumination. The local increase of the temperature under HER cathodic conditions leads to the increase of the hydrogen production up to 23%. We are also able to reduce the overpotential for 185mV under galvanostatic conditions. By applying pulsed illumination, we have observed two processes: fast (0.5-1 s) and slow (up to 40s). The fast one, presumably, is responsible for the local increase of the reaction rate on the surface of the Ni nanoparticles due to a fast local temperature increase as a consequence of a damped plasmon caused by solar illumination. The second process is attributed to an enhanced mass transport in the electrolyte due to the temperature redistribution and overall heating of the electrolyte. Based on the obtained results, we have shown that the illumination of the nanostructured nickel catalyst with solar light can lead to the enhanced HER rate, and, as a result, to improved hydrogen production. We expect the LSPR photothermal approach to pave way to a more efficient photoelectrochemical water splitting process, taking advantage of visible and near-IR illumination.
Authors : Zhongrui Yu, Hui Guo, Zulin Sun, Yi Li, Yihao Liu, Weiguang Yang, Lingyan Feng, Ying Li, Wenxian Li , Shengqiang Zhou, Slawomir Prucnal
Affiliations : Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden, Germany; Institute of Materials, Shanghai University, Shanghai 200444, China; School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China; Materials Genome Institute, Shanghai University, Shanghai 200444, PR China; Institute for Sustainable Energy, Shanghai University, Shanghai 200444, China;
Resume : Energy barrier-free charge transfer of photogenerated carriers and high photoconversion efficiency are achieved by using a core-shell heterostructure of TiO2-ZnS:Co/Bi2S3 for photoelectrochemical (PEC) water splitting. The TiO2 nanorods are covered with Co doped ZnS coating, followed by the encapsulation with the Bi2S3 shell. Co doped ZnS and Bi2S3 coating shells enhance UV-vis light harvesting and increase the density of photogenerated carriers of TiO2 nanorods. The impurity energy state of Co in ZnS connects the conduction band edges of Bi2S3 and TiO2 to convey photogenerated electrons, without extra energy consumption for hopping to Zn orbits at higher energy position. The continuous valance band edge of three components ensures a swift transfer for photogenerated holes to photoanode surface, where the recombination of photogenerated carriers is suppressed. This work offers a new way for the enhancement of the photoelectrochemical water splitting via engineering of the photogenerated charge transportation using core-shell heterostructured photoanode like TiO2-ZnS:Co/Bi2S3.
|11:35||Live Q&A Session 5|
Photoelectrocatalysis III : Joachim John
Authors : Teresa Andreu
Affiliations : University of Barcelona (UB). Dept. Materials Science and Physical Chemistry. C/Martí i Franquès, 1. 08028-Barcelona. Spain. Catalonia Institute for Energy Research (IREC)
Resume : The electrical conversion and storage of solar energy is crucial for assuring the world energy supply. Photoelectrochemical (PEC) energy storage devices offers the possibility to directly transfer the solar energy into several energy carriers, such as hydrogen, low-C fuels/chemicals from CO2 reduction or other redox pairs like batteries. However, PEC technology has as main drawback the fact that the photoelectrode can be in direct contact with the electrolyte, limiting the choice of materials . In this contribution, it will presented our developments on the fabrication of stable photoelectrodes and integrated devices. It will be discussed how impedance analysis (EIS) is a fundamental tool to understand the charge transfer and identify the main bottlenecks that could limit photoelectrode efficiency, specially for the oxygen evolution reaction (OER) [2,3]. Concerning the integrated devices, depending on the system, its design is not seamless unless the light-absorber photovoltage is customized to the voltage needs of the redox pairs . In the case of CO2 reduction, partial current polarization curves should be taken into account, since reaction selectivity usually depends on the applied potential under controlled photocurrent, which will depend on the solar irradiance. On the other hand, for PEC redox flow batteries, unlike artificial photosynthesis synthesis, the required photovoltage continuously increase with the state-of-charge. By using amorphous silicon tandem multijunction photocathodes, it has been demonstrated that for either CO2 reduction to syngas  or solar vanadium redox flow batteries , an unbiased solar-to-chemical conversion efficiency 10% is achievable. Each technology will have in the future its niche market, while the solar-to-electricity roundtrip is more favorable for redox flow devices than for hydrogen or solar fuels, there is an urgent need to decarbonize our chemical industry with green hydrogen and upcycled CO2. The work was funded by MINECO projects WINCOST (ENE2016-80788-C5-5-R) and CCU+OX (PID2019-108136RB-C33).  2020. Journal of Materials Chemistry A 8 (21), 10625-10669  2019. ACS applied materials & interfaces 11 (33), 29725-29735  2019. Journal of Materials Chemistry A 7 (38), 21892-21902  2020. Sustainable Energy & Fuels 4 (3), 1135-1142  2017. Energy & Environmental Science 10 (10), 2256-2266  2018. Journal of Physics D: Applied Physics 52 (4), 044001
Authors : Ramón Arcas, David Carvajal, Francisco Fabregat-Santiago, Elena Mas-Marzá
Affiliations : Institute of Advanced Materials (INAM)
Resume : The decarbonization of the current energy system has been recognized as a key milestone due to the increase of the average temperature on Earth. In this context, (photo)electrochemical processes are considered as low-cost procedures to produce green fuels. Until now, efforts have mainly been focused on two reactions, the formation of molecular hydrogen from water and the reduction of carbon dioxide to form more complex species [2-3]. Considering the high potentials, both reducing and oxidizing, that can be obtained from photoelectrochemical processes, these synthetic approaches are suitable candidates for designing synthetic routes that allow the preparation of high-added value products, which requires redox transformations of the starting reagents [4-10]. In the majority of the cases described, the desired product is generated in one of the (photo)electrodes, whereas in the other one the oxidation (or reduction) of a sacrificial agent takes place. A smart optimization of these systems would be a procedure which allow obtaining high-added value products at both electrodes.  Caldeira, K. et al. Science, 360, 1419 (2018)  Durrant, J. R. et al. Nature Photonics 6, 511 (2012)  Grätzel, M. Nature, 414, 338 (2014)  Cha, H. G. & Choi, K.-S. Nature Chemistry. 7,328, 2015  Li, T. et al. Nature Communications 8, 390, 2017  Tateno, H., et al. ChemElectroChem 4, 3283, 2017  Tateno, H. et al. Chemical Communications 53, 4378, 2017  Tateno, H. et al. Angewandte Chemie International Edition 57, 11238, 2018  Liu, D. et al. Nature Communications 2019, 10, 1779.  Xile H. et al. Nature Catalysis 2, 366, 2019
Authors : Hao WU
Affiliations : School of Energy and Environment City University of Hong Kong
Resume : Here we demonstrate that the direct transfer of photogenerated electrons from the Cu2O nanowires to the non-excited Cu3(BTC)2 (LUMO level) by time-resolved photoluminescence, inducing a long-lived charge-separated state following bandgap excitation, thus improving the charge separation efficiency and stability of the Cu2O applied in photocatalytic CO2 reduction. The design of stable and selective photocatalysts for CO2 reduction with H2O as the direct electron donor is still challenging. Particularly, Cu2O is endowed with efficient visible-light absorption and a suitable conduction band position favorable for CO2 reduction. However, insufficient stability and low CO2 uptake impede its photocatalytic activity for CO2 reduction. Moreover, Cu2O possesses the appropriate band edge positions to realize CO and CH4 production simultaneously. Compared to the CO production, the CH4 formation requires eight electrons which is more challenging from a kinetic point of view.[3,4] In the presented work, we described a system with water-vapor as the electron donor for the selective CO2 reduction to CH4 without the assistance of electrical bias and scavenger. Cu2O nanowires were encapsulated by metal-organic frameworks (MOFs) of Cu3(BTC)2 via a surfactant-free method. Benefiting from the protection of the framework of Cu3(BTC)2 which suppressed the water-induced corrosion of Cu2O, the Cu2O@Cu3(BTC)2 composite achieved a selective reduction of CO2 to CH4 with improved stability and activity compared to the bare Cu2O sample, under visible-light irradiation. A sevenfold increase of the maximum CO2 uptake was also achieved upon the decoration of Cu3(BTC)2. This study extends the understanding of the relationships between MOFs and metal oxides beyond their conventional physisorption/chemisorption type of interactions to now include charge separation. References:  Y. A. Wu, et al., Nat. Energy 2019, 4, 957?968.  C. Y. Toe, et al., Angew. Chemie Int. Ed. 2018, 57, 13613?13617. Angew. Chemie. 2018, 57, 13613?13617.  X. Deng, et al., J. Am. Chem. Soc. 2019, 141, 10924?10929.  X. Li, et al., Nat. Energy 2019, 4, 690?699.
Authors : Michael Sachs,1,2 Liam Harnett-Caulfield,3 Bernadette Davies,1 Daniel Sowood,1 Ernest Pastor,1,4 Jenny Nelson,2 Aron Walsh,3,5 James R. Durrant1
Affiliations : 1 Molecular Sciences Research Hub, Imperial College London, London W12 0BZ, U.K.; 2 Department of Physics, Imperial College London, London SW7 2BW, U.K.; 3 Department of Materials, Imperial College London, London SW7 2AZ, U.K.; 4 ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain; 5 Department of Material Science and Engineering, Yonsei University, Seoul 03722, Korea
Resume : The development of materials which can drive photocatalytic water splitting at high efficiency remains the central challenge for the production of renewable hydrogen using sunlight. Owing to advantages such as low cost, elemental abundance, and chemical stability, transition metal oxides (TMOs) are some of the most widely used materials for this purpose. The most efficient systems developed to date reach a solar-to-hydrogen conversion efficiencies (STH) of around 1%[1,2] and are based on wide bandgap TMOs such as SrTiO3 which has a bandgap of 3.2 eV and thus absorbs UV light only. However, the target for commercial applications is widely considered to be 10% STH, and extended visible light absorption is therefore key to bridge this activity gap. While large research efforts have been devoted to TMOs with smaller bandgaps, efficiencies for such materials have typically remained relatively far from their theoretical limit. For example, Fe2O3 is one of the most studied TMOs in the field of solar fuel production, but it has so far reached only 1/3 of its theoretical maximum activity for water oxidation, which raises the question whether there are limitations of more fundamental nature. In this talk, I will compare the photophysics of TMOs with extended visible light absorption to identify common patterns for this class of materials. To this end, Fe2O3, Cr2O3, and Co3O4, which have absorption onsets of around 2.1 eV, 1.9 eV, and 1.6 eV, respectively, are studied using time-resolved optical spectroscopic techniques where their excited state dynamics are probed on a timescale of femtoseconds to seconds following light absorption. I will show that the photophysics of these materials are remarkably similar when key material characteristics are taken into account, suggesting a common pathway for the localisation and recombination of photogenerated charges in this class of materials. Based on these results a more general photophysical model for TMOs with extended visible light absorption can be postulated, which provides insights into the performance limiting factors in TMOs with extended visible light absorption. References:  Wang, Q. et al. Scalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1%. Nat. Mater. 1?3 (2016).  Takata, T. et al. Photocatalytic water splitting with a quantum efficiency of almost unity. Nature 581, 411?414 (2020).  Chen, S., Takata, T. & Domen, K. Particulate photocatalysts for overall water splitting. Nat. Rev. Mater. 2, 17050 (2017).  Kim, J. Y. et al. Single-crystalline, wormlike hematite photoanodes for efficient solar water splitting. Sci. Rep. 3, 2681 (2013).
|15:20||Live Q&A Session 6|
Poster Session II : Salvador Eslava, Leszek Zaraska
Authors : Isilda Amorim, Junyuan Xu, Lifeng Liu
Affiliations : International Iberian Nanotechnology Laboratory
Resume : Water splitting has been proposed to be a promising approach to producing clean hydrogen fuel. The two half reactions of water splitting, i.e. the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), take place kinetically fast in solutions with completely different pH values. Enabling HER and OER to simultaneously occur under kinetically favorable conditions while using exclusively low-cost, earth-abundant electrocatalysts, is highly desirable but remains a challenge. In this presentation, we will show that with a bipolar membrane (BPM) we can accomplish HER in a strongly acidic solution and OER in a strongly basic solution, using bifunctional self-supported cobalt nickel phosphide nanowire (Co-Ni-P NW) electrodes to catalyze both reactions (Figure 1) . Such asymmetric water electrolysis can be achieved at 1.567 V to deliver a current density of 10 mA cm-2 with ca. 100% Faradaic efficiency under the ?reverse bias? configuration. Moreover, in the ?forward bias? configuration, the voltage needed to afford 10 mA cm-2 can be reduced to only 0.841 V, due to the assistance of electrochemical neutralization between acid and alkaline. Furthermore, we demonstrate that BPM-based asymmetric water electrolysis can be accomplished in a circulated single cell electrolyzer delivering 10 mA cm-2 at 1.550 V and splitting water very stably for at least 25 h (Figure 2), and that water electrolysis is enabled by a solar panel operating at 0.908 V (@13 mA cm-2), under the ?forward bias? of the BPM. The same BPM approach is also extended to the CoTe2-CoP dual phase electrocatalysts , which demonstrate similar electrochemical performance with markedly reduced input voltage for overall water electrolysis in the ?forward bias? configuration. The BPM-based asymmetric water electrolysis is a promising alternative to conventional proton and anion exchange membrane water electrolysis. References: 1. J. Y. Xu, I. Amorim, Y. Li, J. J. Li, Z. P. Yu, B.S. Zhang, A. Araujo, N. Zhang, L. Liu, Carbon Energy 2 (2020) 646. 2. I. Amorim, J. Y. Xu, N. Zhang, Z. P. Yu, A. Araujo, F. Bento, L. Liu, Chem. Eng. J. 420 (2021) 130454.
Authors : Junyuan Xu, Lifeng Liu
Affiliations : International Iberian Nanotechnology Laboratory
Resume : Achieving efficient and stable oxygen evolution reaction (OER) in acidic or neutral medium is of paramount importance for hydrogen production via proton exchange membrane water electrolysis (PEM-WE). Supported iridium based nanoparticles (NPs) are the state-of-the-art OER catalysts for PEM-WE, but the non-homogeneous dispersion of these NPs on the support together with their non-uniform sizes usually lead to catalyst migration and agglomeration under strongly corrosive and oxidative OER conditions, eventually causing the loss of active surface area and/or catalytic species and thereby the degradation of OER performance. Here, we design a catalyst comprising surface atomic-step enriched ruthenium-iridium (RuIr) nanocrystals homogeneously dispersed on a metal organic framework (MOF) derived carbon support (RuIr@CoNC) , which shows outstanding catalytic performance for OER with high mass activities of 2041, 970 and 205 A gRuIr-1 at an overpotential of 300 mV and can sustain continuous OER electrolysis up to 40, 45 and 90 hours at 10 mA cm-2 with minimal degradation, in 0.5 M H2SO4 (pH = 0.3), 0.05 M H2SO4 (pH = 1) and PBS (pH = 7.2) electrolytes, respectively. Comprehensive experimental studies and density functional theory (DFT) calculations reveal that the good performance of RuIr@CoNC can be attributed, on one hand, to the presence of abundant atomic steps which maximize the exposure of catalytically active sites and lower the limiting potential of the rate-determining step of OER; on the other hand, to the strong interaction between RuIr nanocrystals and the CoNC support which endows homogeneous dispersion and firm immobilization RuIr catalysts on CoNC. The RuIr@CoNC catalysts also show outstanding performance in a single cell PEM electrolyzer, and their large-quantity synthesis is demonstrated. References:  11. J.Y. Xu, J. J. Li, Z. Lian, A. Araujo, Y. Li, B. Wei, Z. P. Yu, O. Bondarchuk, I. Amorim, V. Tileli, B. Li, Lifeng Liu*, ?Atomic-step enriched ruthenium-iridium nanocrystals anchored homogeneously on MOF-derived support for efficient and stable oxygen evolution in acidic and neutral media? ACS Catalysis 2021, 11, 3402-3413.
Authors : Zhipeng Yu, Junyuan Xu, Isilda Amorim, Yue Li, Lifeng Liu
Affiliations : Zhipeng Yu; Junyuan Xu; Isilda Amorim; Yue Li; Lifeng Liu International Iberian Nanotechnology Laboratory (INL), Avenida Mestre Jose Veiga, 4715-330 Braga, Portugal Zhipeng Yu Laboratory of Catalysis and Materials (LSRE-LCM), Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal Isilda Amorim Department of Chemistry, University of Minho, Gualtar Campus, 4715-057 Braga, Portugal
Resume : The small organic molecule electro-oxidation (OMEO) and the hydrogen evolution (HER) are two important half-reactions in direct alcohol fuel cells (DAFCs) and water electrolyzers, respectively, whose kinetics are largely hindered by the low activity and poor stability of electrocatalysts. Noble metals (e.g. Pt, Pd) are currently the state-of-the-art catalysts for the HER and OMEO; however, for practical applications their electrocatalytic performance needs to be improved. In this presentation, we report a simple phosphorization treatment of commercially available palladium-nickel (PdNi) catalysts that can result in the formation of multifunctional ternary palladium nickel phosphide (PdNiP) catalysts, exhibiting substantially enhanced electrocatalytic activity and stability for HER and a number of OMEO model reactions including the formic acid oxidation reaction (FAOR), methanol oxidation reaction (MOR), ethanol oxidation reaction (EOR), and ethylene glycol oxidation reaction (EGOR), in terms of not only apparent activity, but also of specific and mass activities, poisoning tolerance and catalytic stability. The improved performance results from the modification of electronic structure of palladium and nickel by the introduced phosphor and the enhanced corrosion resistance of PdNiP. The simple phosphorization approach reported here allows for mass production of highly-active OMEO and HER electrocatalysts, holding substantial promise for their large-scale application in direct alcohol fuel cells and water electrolyzers.
Authors : Mehran Sarafzade, Amin Yourdkhani, Rasoul Sarraf-Mamoory
Affiliations : Materials Engineering Department, Tarbiat Modares University, Theran, Iran
Resume : In this research, titania thin films were deposited by the liquid phase decomposition (LPD) method at 55±5 °C for 100 minutes. Then, the as-deposited films were flame-treated by using a candle flame. Other sets of samples also were furnace annealed at 500 °C. The photoelectrochemical (PEC) characterizations showed that the furnace annealed samples are not visible active, whereas the candle-flame treated samples are visible active photocatalysts. The indirect optical band gap for furnace annealed and candle-flame treated samples were measured 3.65 and 3.06 eV, respectively, showing the visible active characteristics of the candle-flame treated sample. Carbon diffusion into the films via a solid-state diffusion process during the candle-flame treatment with temperatures as high as 1000 °C is most likely responsible for the visible activity.
Authors : Katharina Welter 1, Jan-Philipp Becker 1, Wolfram Jaegermann 2, Friedhelm Finger 1 , Vladimir Smirnov 1
Affiliations : 1 IEK-5 Photovoltaik, Forschungszentrum Jülich GmbH, D-52425, Jülich, Germany; 2 Institute of Materials Science, TU Darmstadt, D-64287 Darmstadt, Germany;
Resume : We study the effects of simulated outdoor illumination conditions on the performance of photovoltaic-biased electrosynthetic (PV?EC) systems used for the generation of hydrogen by means of solar water splitting. An integrated PV-EC cell consists of a photovoltaic cell (PV) directly combined with an electrolysis cell (EC), where the chemical reactions take place. In the present work, multijunction silicon based solar cells  were implemented for the PV part of the device together with an EC cell using a Pt/IrOx catalyst system. Annual variations in the solar illumination spectra influence the device performance together with long-term energy conversion. Both PV device and PV-EC device performance under varied spectral conditions differ from the performance obtained under standard AM1.5G illumination. Our model accounts for annual spectral changes in illumination and predicts the long-term (1 year) performance of PV?EC systems in terms of the hydrogen amount produced for a given geographical location for various types of multijunction photovoltaic systems (tandem, triple, and quadruple junctions).  F. Urbain, V. Smirnov, J.P. Becker et al, Energy Env. Sci. 2016, 9, 145?154  K. Welter et al, Energy Fuels 2021, 35, 1, 839?846
Authors : Jinwoo Chu, Bonhyeong Koo, Byungha Shin
Affiliations : Korea Advanced Institute of Science and Technology (KAIST)
Resume : Platinum in the form of nanocubes (NCs) were synthesized by colloidal method, and with a fast and simple drop-casting method Pt NCs were applied as hydrogen evolution reaction electrocatalysts to electrochemical (EC) and photoelectrochemical (PEC) systems. Our drop-casting method showed minimized loss of Pt (~6%) from Pt NC synthesis to EC cell fabrication, and we also achieved a remarkable Pt mass activity of 1.77 A/mg at -100 mV in EC systems (fluorine-doped tin oxide (FTO)/Pt NC cathode) with neutral electrolyte. In PEC systems (based on a Cu(In,Ga)Se2 (CIGS) photocathode), a maximum onset potential of 0.678 V against the reference hydrogen electrode was reached by carefully choosing amount of Pt NC loading to compromise between better light transmittance and the catalytic activity. The photoelectrodes also exhibited good long-term operational stability over 9.5 hours with negligible degradation of the photocurrent, and 11 hours stability with maintaining 80% current density against maximum. Our study presents an effective strategy to greatly reduce the use of expensive Pt without compromising the catalytic performance. It also presents an extra benefit of further reducing the usage of Pt because the drop-casting of Pt NC solutions is expected to waste less raw materials than vacuum deposition.
Authors : Fatemeh Parveh, Amin Yourdkhani, Reza Poursalehi
Affiliations : Materials Engineering Department, Tarbiat Modares University, Tehran, Iran.
Resume : In this work, hematite (?-Fe2O3) photoanodes thin films with a 25 nm thickness were deposited on ?uorine-doped tin oxide (FTO) coated glass substrates by liquid phase deposition (LPD) method followed by annealing at 800 ° C for 20 minutes. Then, the iron phosphate (FePO4.2H2O) co-catalyst was loaded on hematite thin films by the LPD method. Photoelectrochemical (PEC) investigations revealed that the hematite thin films loaded with iron phosphate co-catalyst exhibit a higher photocurrent density than that for the bare hematite thin films. The highest optical current density was obtained for 30 minutes of loading the Iron Phosphate co-catalyst on the hematite film, which is 0.51 mA/cm2 at 1.23 V vs. RHE, 70% higher than the bare hematite sample. Under solar illumination, iron phosphate co-catalyst can e?ciently collect and store photogenerated holes from the ?-Fe2O3 electrode. This charge separation reduces surface state recombination, leading to an enhancement of PEC properties.
Authors : Nihal El Guenani1, Jose Solera-Rojas1, Antonio Guerrero1, Elena Mas-Marzá1
Affiliations : 1 Institute of Advanced Materials (INAM), Universitat Jaume I, 12006 Castelló, Spain
Resume : Our modern society demands new synthetic strategies environmentally benign and energy efficient. Besides, these synthetic procedures should also provide high reaction yields, high selectivity, as well as ensure low or even no greenhouse gas emissions. Organic electrosynthesis fulfills the previous requirements, furthermore allows achieving the replacement of dangerous and toxics chemical and the reduction of the quantity of solvents used. One of the key points in electrosynthesis is the design and preparation of stable and robust electrodes. In our group we have successfully tested Ti/Ni alloys for the oxygen evolution reaction (OER), observing low overpotentials and high-density currents. Moreover, our Ti/Ni electrodes exceeded the performance of commercially available electrodes for this reaction. (1) These Ti/Ni electrodes are easily prepared in a facile and scalable method based on powder metallurgy, showing high electrochemical surface area and high concentration of active species. Herein, we use of these Ti/Ni electrodes for the oxidation of organic substrates of a range of molecules to obtain high added value species. References (1) Guenani, N.; Barawi, M.; Villar-García, I. J.; Bisquert, J.; de la Peña O’Shea, V. A.; Guerrero, A. Sustainable Energy Fuels, 2020, 4, 4003-4007.
|17:20||Live Q&A Session 7|
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Fuel cells catalysts : Leszek Zaraska
Authors : Christine RANJAN and Hyacinthe RANDRIAMAHAZAKA
Affiliations : Université de Paris, CNRS, ITODYS, SIELE Group, 45 Rue des Saints-Pères, 75006 Paris, FRANCE
Resume : For past decade, we are looking for an alternative to fossil energy supplies. One of the alternatives are fuel cells and metal/air battery. In the case of metal/air battery, oxygen electrochemistry plays a key role. To improve the oxygen reduction reaction (ORR), manganese oxides (MnxOy) can be considered promising substitutes to platinum who is the best catalyst. Our project aims to prepare non-noble catalysts based on manganese oxide. To this end, we used electrospinning process. Electrospun nanofibers had a great potential for removal of contaminants from aqueous solutions owing to their large specific surface area, high porosity, easy modification, and good compatibility with other functional materials. The catalyst was prepared by an electrospun manganese acetate/PVP nanofiber, followed by a thermal treatment. The thermal treatment was a key point to optimize the electrocatalytical properties of the obtained manganese oxides /Carbon nanofiber catalysts (MnxOy/CF). Our studies were demonstrated that the MnxOy/CF catalysts prepared at 500°C exhibit exceptional selectivity toward 4 electron pathway.
Authors : N. Coutard,1 A. Ghedjatti,1,2 S. Lyonnard,2 H. Okuno,3 L. Guetaz,4 V. Artero,1 P. Chenevier 2
Affiliations : a Univ. Grenoble Alpes, CEA, CNRS, IRIG, LCBM lab, 38000 Grenoble, France b Univ. Grenoble Alpes, CEA, CNRS, IRIG, SyMMES lab, 38000 Grenoble, France c Univ. Grenoble Alpes, CEA, IRIG, MEM lab, 38000 Grenoble, France b Univ. Grenoble Alpes, CEA, LITEN, DTNM, Lab. Nanocaractérisation et Nanosécurité, 38000 Grenoble, France
Resume : Commercial proton exchange membrane fuel cells (PEMFCs) use platinum as the catalyst, a too scarce and precious metal for sustainable energy supply through PEMFCs. Pt-free catalysts are actively searched for, both at the cathode and at the anode. With huge advancements in current density, lower overpotential and higher stability in the past few years, molecular engineered bio-inspired catalysts hold promise for the next generation of PEMFC [1, 2]. Yet, their implementation in catalytic layers faces nanocomposite formulation issues . Here, we use carbon nanotube immobilized DuBois nickel catalysts to exemplify how self-assembly at the mesoscale affects performances of H2 oxidation anodes. Copied on the conserved functional features of the active site of hydrogenases, the nickel catalysts created by Dubois et al.  show impressive turn-over frequency with no over-potential for hydrogen oxidation in solution. Not only has the central part of the catalyst, but also its outer sphere has a strong influence on the catalytic capacity . Modification of the outer sphere can be used to immobilize the catalyst on a conductive matrix [6-8], a requirement for further implementation in PEMFC . However, long-term ion transport in PEMFC requires creating ion conductive paths in the electrode, a task usually fulfilled by the addition of an ionomer. Although it allowed us to assemble the first fully Pt-free PEMFC , the current density was very low when the anode contained ionomer. The electrode microstructure thus appears critical to the system performance, yet it was hardly studied. THere, we show that molecular engineering coupled with three-dimensional structuring of the carbon electrode plays a major role on the catalytic activity through enhancement of catalyst grafting and substrate/product diffusion inside the electrode. In particular, we compare the effect of Nafion ionomer addition on the performances of bioinspired catalytic layers produced via three distinct surface chemistries [6-9]. We use microscopy as well as small angle neutron scattering techniques to characterize the self-assembly of the ionomer  with the carbon nanotubes/catalyst composite. A strong correlation appears between current drop in the presence of ionomer, and absence of ionomer hydrophilic/hydrophobic nanostructure. We propose a model that describes how the surface charge of the functionalized nanotubes drives the structuration of the Nafion ionomer and impacts diffusion of protons and gas to and from catalytic centres.  N. Coutard, N. Kaeffer, V. Artero, Chem. Commun., 2016, 52, 13728-13748.  F. Jaouen, D. Jones, N. Coutard, V. Artero, P. Strasser, A. Kucernak, Johnson Matthey Technology Review, 2018, 62, 231-255.  P.D. Tran, A. Morozan, S. Archambault, J. Heidkamp, P. Chenevier, H. Dau, M. Fontecave, A. Martinent, B. Jousselme, V. Artero, Chem. Sci., 2015, 6, 2050-2053.  M. Rakowski Dubois and D. L. Dubois, Acc. Chem. Res., 2009, 42, 1974?1982  A. Dutta, J.A.S. Roberts, W.J. Shaw, Angew. Chem. Int. 2014, 53, 6487-6491  A. Le Goff, V. Artero, B. Jousselme, P.D. Tran, N. Guillet, R. Metaye, A. Fihri, S. Palacin, M. Fontecave, Science, 2009, 326, 1384-1387.  P.D. Tran, A. Le Goff, J. Heidkamp, B. Jousselme, N. Guillet, S. Palacin, H. Dau, M. Fontecave, V. Artero, Angew. Chem. Int. Ed., 2011, 50, 1371-1374.  T.N. Huan, R.T. Jane, A. Benayad, L. Guetaz, P.D. Tran, V. Artero, Energy Environ. Sci., 2016, 9, 940-947.  S. Gentil, N. Lalaoui, A. Dutta, Y. Nedellec, S. Cosnier, W.J. Shaw, V. Artero, A. Le Goff, Angew. Chem. Int. Ed., 2017, 56, 1845-1849  L. Rubatat, G. Gebel, O. Diat, Macromolecules 2004, 37, 7772
Authors : Tatiana Priamushko, Eko Budiyanto, Claudia Weidenthaler, Harun Tüysüz, Freddy Kleitz
Affiliations : Department of Inorganic Chemistry - Functional Materials, Faculty of Chemistry, University of Vienna, Währinger Straße 42, A-1090 Wien, Vienna, Austria; Department of Heterogeneous Catalysis, Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Muelheim an der Ruhr, Germany; Department of Heterogeneous Catalysis, Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Muelheim an der Ruhr, Germany; Department of Heterogeneous Catalysis, Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Muelheim an der Ruhr, Germany; Department of Inorganic Chemistry - Functional Materials, Faculty of Chemistry, University of Vienna, Währinger Straße 42, A-1090 Wien, Vienna, Austria.
Resume : Co-based ordered mesoporous oxides and their electrocatalytic performance have been very well studied . Other transition metals added in the Co-based oxide structure are known to improve its electrocatalytic activity . Here, we develop a series of ordered mesoporous Cu/Ni/Co oxides (CNCO) with various Cu/Ni ratios to assess the role of these added metals and possible synergy effects on the electrocatalytic performance toward oxygen evolution and reduction reactions (OER and ORR, respectively). Physicochemical and electrocatalytic properties of the materials were characterized in detail. Most Cu and Ni were incorporated into the spinel structure of cobalt oxide, resulting in (Cu,Ni)xCo(3-x)O4 with small amounts of other phases such as CuO and NiO. Regarding the activity and stability of the catalysts toward OER, it was found that Ni-rich CNCO outperforms binary Ni/Co and Cu/Co oxides in 1M KOH electrolyte, being activated over 200 CVs. As a result, the most active material CNCO-2-8 (Cu/Ni~1/4) exhibits a current density of 411 mA cm-2 at the potential of 1.7 V vs RHE and an overpotential of 312 mV at the current density of 10 mA cm-2 after the activation process. After, the measurements were repeated in the purified 1M KOH excluding any activation due to the interaction of Ni with Fe impurities present in the electrolyte and thus exploring the intrinsic role of Cu. CNCO-2-8 outperforms Ni/Co oxide highlighting that the addition of Cu improves the electrocatalytic activity of the material. Furthermore, CNCO-2-8 indicates excellent long-term stability in 1M KOH. The combination of Cu and Ni in Co oxide also improves its activity toward ORR and reduces the side reaction facilitating the 4e- reaction path. CNCO-5-5 (Cu/Ni~1/1) demonstrates the best activity and long-term stability in 0.1M KOH. Summarizing, we observed that Cu/Ni inclusions in Co oxide provide a high number of active sites resulting in the highly efficient and stable bifunctional catalyst for both OER and ORR.  Priamushko, T.; Guillet-Nicolas, R.; Kleitz, F. Mesoporous Nanocast Electrocatalysts for Oxygen Reduction and Oxygen Evolution Reactions. Inorganics 2019, 7 (8), 98.  Wu, Z. P.; Lu, X. F.; Zang, S. Q.; Lou, X. W. Non-Noble-Metal-Based Electrocatalysts toward the Oxygen Evolution Reaction. Advanced Functional Materials 2020, 30, 1910274.
|14:50||Live Q&A Session 8|
Electrocatalyst synthesis and characterization : Paulo Ferreira, Lifeng Liu
Authors : Paulo Ferreira
Affiliations : 1INL – International Iberian Nanotechnology Laboratory, Av. Mestre José Veiga s/n, 4715-330 Braga, Portugal. 2 Materials Science and Engineering Program, The University of Texas at Austin, Austin, Texas 78712, United States 3 Mechanical Engineering Department and IDMEC, Instituto Superior Técnico, University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
Resume : A thorough knowledge of the atomic structure and composition of catalyst nanoparticles is paramount to the development of advanced materials for proton exchange membrane fuel cells (PEMFC), one of the most promising energy conversion devices for automotive and stationary applications. Pt and Pt-based alloys nanoparticles (NPs) are currently used as the catalyst to promote the kinetics of the hydrogen oxidation and oxygen reduction reactions in the anode and cathode of the fuel cell, respectively. Yet, the durability of the catalysts remains the main issue for their commercialization. In this talk, the focus is to understand the behavior of Pt and Pt-alloy NPs during the various stages of fuel cell cycling. For this purpose a set-up was developed to simulate the effect of voltage cycling on the cathode side of the fuel cell. In this set up, catalyst NPs supported on carbon nanotubes and amorphous carbon were observed by advanced transmission electron microscopy, before and after cycling. The experiments show particle migration in conjunction with carbon corrosion during the initial cycles, whereas the appearance of single atoms and atomic clusters on the surface of the carbon support appear after additional voltage cycling as a result of surface dissolution of NPs. For the case of alloyed NPs, the experiments show a heterogeneous deposition of Pt on the NPs.
Authors : Monika Char??ka, Kamila ??picka, Jakub Kalecki, Wojciech Lisowski, Piyush Sindhu Sharma*
Affiliations : Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
Resume : Herein, we reported the potential driven electrochemical transformation of two nickel salen polymers, poly(meso-NiSaldMe), and poly(NiSaltMe) into Ni(OH)2 type electrocatalytically active nanoparticles in basic solution. These two polymers, differ in the configuration of methyl substitution at imine bridge. The use of different electrochemical conditions for the preparation of two polymeric NPs precursors allowed us to establish the correlation between both morphology and chemical structure of polymeric precursors that governed the morphology and electrocatalytic efficiency of fabricated NPs. The morphology and electrocatalytic performance of prepared NPs were tuned by applying different electropolymerization conditions to prepare poly(meso-NiSaldMe) and poly(NiSaltMe). Interestingly, generated Ni(OH)2 type nanostructures from these two different poly (Ni-salen) precursors were electrocatalytically active towards ethanol oxidation at different extent. Moreover, we found that organic solvent electrolyte solutions stable poly(NiSalen)s film took a longer time to generate NPs in base electrolyte media. Poly(Ni-Salen)s and Ni(OH)2 type NPs were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).
Authors : Jonathan Quinson, Francesco Bizzotto, Masanori Inaba, Maria Escudero-Escribano, Matthias Arenz
Affiliations : Chemistry Department, University of Copenhagen, 2100 Universitetsparken, Copenhagen, Denmark; Chemistry-Biochemistry Department, University of Bern, Freiestrasse 3 CH-3012 Bern, Switzerland; Chemistry-Biochemistry Department, University of Bern, Freiestrasse 3 CH-3012 Bern, Switzerland; Chemistry Department, University of Copenhagen, 2100 Universitetsparken, Copenhagen, Denmark; Chemistry-Biochemistry Department, University of Bern, Freiestrasse 3 CH-3012 Bern, Switzerland
Resume : Several applications require to maximize an electrode electroactive surface (ECSA) relative to its volume. A popular option is to develop nanoscaled materials like nanoparticles (NPs). Fortunately, a range of synthesis methods allows to control composition, size and shape of nanomaterials, to best tune activity, selectivity and stability. Unfortunately, popular syntheses like colloidal approaches often require surfactants to avoid NPs agglomeration. The later typically need to be removed - e.g. by chemical or thermal steps, often with limited efficiency - in order to develop materials with clean (i.e. electroactive) surfaces. We developed surfactant-free colloidal syntheses to obtain readily active (electro)catalysts [1-4]. This talk will present the latest development in this regard, starting with Pt NPs for the oxygen reduction reaction (ORR) where we were able to show the importance of size and interparticle distance to optimize mass activity . Furthermore, we recently developed a low boiling point synthesis of surfactant-free colloidal precious metals . The latter is versatile and can lead to suitable materials such as Pt NPs for the methanol oxidation (MOR) reaction  or Pd NPs for the ethanol oxidation reaction (EOR) . We here show the relevance of this synthesis approach to better study and benchmark electrocataysts. This presentation will detail the case of the optimal parameters to develop and study Ir based catalysts with high mass activity compared to state-of-the-art even at high loading for the oxygen evolution reaction (OER) [8, 9]. We studied the interplay between the solvents used for the synthesis of Ir NPs and the solvents used for supporting on carbon materials. We compared NPs prepared without surfactant in alkaline ethylene glycol, alkaline ethanol or alkaline methanol for the OER. The catalysts with the highest activity were obtained using ethanol as solvent. Interestingly, the high activity observed was related more to the influence of the solvent during the supporting steps than during the synthesis of the NPs. These examples illustrate the benefits of surfactant-free colloidal syntheses to not only develop various electrocatalysts, but also study and understand the influence of various steps in the preparation of supported electrocatalysts . Overall, a better understanding of important parameters to develop precious metal based catalysts is gained to make the most of the limited resources that are Pt, Pd or Ir. References  Quinson et al. ChemCatChem. 2021, 13, 1692.  Alinejad, ACS Catal. 2020, 10, 21, 13040.  Du et al. ACS Catal. 2021, 11, 2, 820.  Arminio-Ravelo et al. ChemCatChem. 2020, 12, 5, 1282.  Inaba et al. ACS Catal. In press.  Quinson et al. Sustain. Chem. 2021, 2, 1, 1-7.  Schreyer et al. Inorganics 2020, 8, 11, 59.  Bizzotto et al. Catal. Sci. Technol., 2019, 9, 6345.  Bizzotto et al. Submitted.
Authors : Hannes Radinger*(1,2), Paula Connor (2), Sven Tengeler (2), Robert Stark (3), Wolfram Jaegermann (2) & Bernhard Kaiser (2)
Affiliations : (1) Institute for Applied Materials, Karlsruhe Institute of Technology, Germany (2) Surface Science Laboratory, TU Darmstadt, Germany (3) Physics of Surfaces, TU Darmstadt, Germany
Resume : Transition metal oxides such as NiOx and MnOx are considered promising candidates to replace noble metals as electrocatalysts for the oxygen evolution reaction (OER). Improvements in these initially inactive materials require mechanistic and kinetic knowledge of the four-electron transfer steps of OER. X-ray photoelectron spectroscopy, a widely used tool to characterize the electronic structure of thin films, is used in combination with surface-enhanced Raman spectroscopy. This leads to a deeper understanding of the changing structural properties and chemical compositions which determine the catalytic activity. Using operando Raman spectroscopy, it was demonstrated that various MnOx films in alkaline medium exhibit birnessite-type MnO2 motifs at an applied potential. Their activity correlates with two shifting vibrational modes, one associated with the formation of MnIII species and one associated with the expansion of layers containing MnO6 octahedra. A special activation treatment results in a highly amorphous mixed valence oxide that exhibits the highest OER activity regardless of the starting material. While several studies have shown that iron impurities promote the activity of nickel-based catalysts, the effects of intrinsic defects are not well-understood. NiOx thin films were prepared at different temperatures and therefore varied in chemical composition and crystalline order. Raman spectroscopy was used to follow the characteristic oxidation of nickel species from NiII(OH)2 to NiIIIOOH and NiIVOO? under electrochemical cycling conditions. A stronger oxide-to-hydroxide conversion, consistent with the post-electrochemical study, was associated with the presence of initial NiIII impurities and oxygen vacancies and was beneficial for the electrocatalytic activity.
Authors : R. Rameshan(a), L. Lindenthal(a), F. Schrenk(a), T. Ruh(a), A. Nenning(b), A.K. Opitz(b), C. Rameshan(a)
Affiliations : (a) Institute of Materials Chemistry, TU Wien, Austria (b) Institute of Chemical Technologies and Analytics, TU Wien, Austria
Resume : Tailoring of Catalyst Surfaces for Energy Conversion ? In-situ Studies of Electrochemical driven Nanoparticle Exsolution R. Rameshan(a), L. Lindenthal(a), F. Schrenk(a), T. Ruh(a), A. Nenning(b), A.K. Opitz(b), C. Rameshan(a) a Institute of Materials Chemistry, TU Wien, Austria b Institute of Chemical Technologies and Analytics, TU Wien, Austria In heterogeneous catalysis surfaces decorated with uniformly dispersed, catalytically highly active (nano)particles are a key requirement for excellent performance. We present here an innovative, time efficient route to obtain and tailor the formation of nanoparticles on the catalyst surface directly during reaction by combining catalysis and electrochemistry. Perovskite-type catalysts can incorporate catalytically highly active guest elements as dopants. When applying reductive conditions (gas atmosphere or applied electric potential) these dopants emerge from the oxide lattice to form catalytically active nanoparticles on the surface (by exsolution), causing a strong enhancement of catalytic reactivity. For the newly synthesized perovskite materials Nd0.6Ca0.4Fe0.9Co0.1O3-?, we show by in-situ near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) combined with electrochemical impedance spectroscopy (EIS) how we can control the formation of catalytically active nanoparticles on the surface. With Scanning Electron Microscopy (SEM) the size of the formed particles could be determined. The crucial factor to trigger exsolution is the oxygen partial pressure (pO2), which can be adjusted and controlled either by the reaction environment or by the applied electrochemical potential. For reverse water gas shift reaction (rWGS) the formed nanoparticles are strongly enhancing the catalytic activity. Acknowledgement This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement n° 755744 / ERC - Starting Grant TUCAS)
Authors : Karla Caroline de Freitas Araújo1, Djalma Ribeiro da Silva1, Elisama Vieira dos Santos1, Carlos A. Martínez-Huitle1, Robert Bogdanowicz2
Affiliations : 1 Instituto de Química, Universidade Federal do Rio Grande do Norte, Natal, Rio Grande do Norte, Brasil. 2 Department of Metrology and Optoelectronics, Faculty of Electronics, Telecommunication and Informatics, Gdańsk University of Technology, Gdańsk 80-233, Poland.
Resume : The efficient electrocatalytic degradation of environmental pollutants and synthesis of oxidizing species requires an electrode with a large surface area, high electrocatalytic activities, long-term stability, and a low cost. Thus, the introduction of nanotechnology seems to be an imperative factor to intensify the synergic effects of electrocatalytic materials to produce strong oxidant species or to increase the active sites on their surfaces. Recently, a new type of diamond electrodes was discovered–boron-doped carbon nanowalls manufactured using the microwave plasma-assisted chemical vapor deposition (CVD) process. Thus, we report, for first time, the results regarding the applicability of a BDD-boron-doped carbon nanowalls anode to degrade organic pollutants and electro-synthetize peroxodisulfate anion (PDS) in sulfate solutions in order to answer relevant questions from both fundamental and practical point-of-views. Carbon nanoarchitectures were synthesized as the core with a uniform BDD film. Since these carbon nanowalls combined both features of BDD and carbon, they are utilized as the electrode for the efficient electrocatalytic degradation of environmental pollutants. Dye-model pollutant was degraded below the limit of detection within 1.5 h using these anodes. For other various organic pollutants, this anode exhibited excellent degradation capacity. Such a high performance of electrocatalytic degradation of these environmental pollutants originates from increased surface areas and active sites by the three-dimensional carbon nanoarchitectures as well as the decreased charge-transfer resistance by the core-diamond-carbon structure. These kind of diamond films are thus promising as a new electrode material or an electrocatalyst for various catalytic applications in the environmental and energy fields. Acknowledgements: Financial supports from Conselho Nacional de Desenvolvimento Científico e Tecnológico (Brazil), 439344/2018-2, and from Fundação de Amparo à Pesquisa do Estado de São Paulo (Brazil), FAPESP 2014/50945-4 and 2019/13113-4, are gratefully acknowledged.  J. Davis, J.C. Baygents, J. Farrell, Understanding persulfate production at boron dopeddiamondfilm anodes, Electrochim. Acta 150 (2014) 68–74  P.A. Michaud, E. Mahe, W. Haenni, A. Perret, C. Comninellis, Electrochem.Solid-State Lett. 3 (2000) 77–79  K. Serrano, P.A. Michaud, C. Comninellis, A. Savall, Electrochim.Acta 48 (2002) 431–436.  P.A. Michaud, M. Panizza, L. Ouattara, T. Diaco, G. Foti, C. Comninellis, J. Appl. Electrochem. 33 (2003) 151–154.  J.R. Davis, J.C. Baygents, J. Farrell, J. Appl.Electrochem. 44 (2014) 841–848.  D. Khamis, E. Mahé, F. Dardoize, D. Devilliers, J. Appl. Electrochem. 40 (2010) 1829–1838.  C. Comninellis, G. Chen, Electrochemistry for the Environment,first ed. Springer, NewYork, 2010.  C.A. Martínez-Huitle, M. Panizza, Curr. Opin. Electrochem. 11 (2018) 62-71.  K.C.F. Araújo, D.R. da Silva, E.V. dos Santos, H. Varela, C.A. Martínez-Huitle, J. Electroanal. Chem. 860 (2020) 113927.
|17:20||Live Q&A Session 9|
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(Photo)electrochemical CO2 Reduction II : Vladimir Smirnov
Authors : Matthew T. Mayer
Affiliations : Helmholtz Zentrum Berlin für Materialien und Energie
Resume : Using semiconductor photoelectrodes to directly drive electrocatalytic CO2 conversion using sunlight is an attractive route to an integrated solar-to-chemicals device. But it is not as simple as just combining semiconductors with catalysts. The differences between metallic and semiconductor electrodes, plus the complex interplay at the electrode-catalyst-electrolyte interfaces, present challenges and opportunities in device design. Our studies focus on differences between metallic and semiconducting electrodes which can alter the behavior of electrocatalytic CO2 reduction. This includes differences observed when using a semiconductor photoelectrode to drive a molecular catalyst, where catalyst immobilization can enable efficient turnover (1). Additionally, photoelectrodes allow a decoupling of current and potential which is not possible on metallic electrodes, a phenomenon we exploit to demonstrate new routes for controlling product selectivity. (1) Schreier, et al. J. Am. Chem. Soc. 2016, 138, 6, 1938. doi: 10.1021/jacs.5b12157
Authors : E. Chopard, Z. Ait Rahhou, D. Muller-Bouvet, C. Cachet-Vivier, S. Bastide, E. Torralba
Affiliations : East - Paris Institute of Chemistry and Materials, 2-8, rue Henri Dunant 94320 THIAIS-FRANCE
Resume : CO2 emitted into the atmosphere by fossil hydrocarbons combustion is responsible for the current climate change. Its capture and conversion thus constitute a major challenge. Among different possible technologies, the sunlight-assisted photoelectrochemical (PEC) conversion of CO2 into renewable fuels (e.g., CH4, C2H4, CH3OH?) using semiconductors (solar to chemical energy), is a sustainable solution of major interest for the energy transition . Despite recent advances, the PEC reduction of CO2 remains a challenge. The main problems to be solved are (i) the high overpotential required (binding energy C=O 803 kJ/mol), (ii) the modest selectivity for hydrocarbons and alcohols vs. CO and HCOOH (i.e., separation costs), (iii) the low PEC performances (photocurrent densities < 10 mA/cm² for limiting diffusion conditions and < 1 mA/cm2 at modest overpotentials) and (iv) CO poisoning of the catalytic surfaces. Finding new photoelectrocatalysts combining efficiency, selectivity and stability still requires significant efforts . Bulk or nanostructured bimetallics have been tested for the CO2 reduction reaction for which the ability to tune the selectivity is well established. Among them, the PdCu system has demonstrated higher performances for fuel production (FE ~ 60% for C2 chemicals like C2H4 and C2H5OH) [3,4]. As far as we know, this system has never been combined with a photoactive support. In this work we proposed an innovative method for the synthesis of PdCu nanoparticles directly on Si supports by metal assisted chemical etching (MACE), a well-known electroless deposition process used for single metal nanoparticles but never applied to bimetallic systems. It relies on coupled electrochemical reactions between Si and metal cations in HF media. From XRD, SEM-EDX and XPS measurements, we demonstrate that this method allows precise control of the PdxCu100 x nanoparticle composition and their microstructure which can be set as phase-separated or solid solution. It could be extended to any bimetallic system to be deposited on Si (if single metals are susceptible of MACE). It also allows to load bimetallic catalyst on Si substrates with micro and macrostructures of high aspect ratio. The PEC responses of the synthetized photocathodes are explored for the conversion of CO2 (and HER) as a function of the PdxCu100-x catalyst composition in solid solutions. Pd50Cu50 is the composition providing the highest photocurrent density. SEM-EDX analysis of the electrode surface before and after electrochemistry reveals a certain degree of nanoparticles coalescence. Product analysis by gas chromatography and RMN with the new photocathodes is currently being performed.  F. Marken, D. Fermin, RSC Energy & Environment Series (2018)  J. He, C. Janáky, ACS Energy Lett. 5, 1996 (2020)  W. Zhu, et al., Top Curr. Chem. (Z) 376, 41 (2018)  E. Torralba, et al., Electrochim. Acta 354, 136739 (2020)
Authors : Motiar Rahaman, Virgil Andrei, Chanon Pornrungroj, Demelza Wright, Jeremy J Baumberg, and Erwin Reisner
Affiliations : Rahaman, M.; Andrei, V.; Pornrungroj, C.; Wright, D.; Reisner, E. Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom Wright, D.; Baumberg, J. J. NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
Resume : Efficient synthesis of solar fuels is attracting great attention now-a-days as it opens up the possibility to convert the greenhouse gas CO2 into value-added products where solar energy is stored as chemical energy. Despite recent advancements in solar energy conversion research, design of selective catalyst materials for long-term performance and assembly of bias-free solar devices for efficient CO2-to-fuel synthesis still remains challenging. Here, we demonstrate a novel approach of integrating an inexpensive Cu96In4 metal alloy catalyst into a state-of-the-art lead halide triple cation perovskite?BiVO4 tandem photoelectrochemical (PEC) device for unassisted CO production from aqueous CO2. CO is an extremely important CO2 reduction product as it can be further converted into long-chain hydrocarbon fuels by the Fischer Tropsch process. The bimetallic Cu96In4 alloy catalyst, synthesized by a template-assisted galvanostatic electrodeposition method, has a microporous 3D dendritic morphology and it shows excellent CO2 electroreduction activity towards selective CO production at low overpotentials (>70% CO selectivity at ?0.3 V vs. reversible hydrogen electrode (RHE)). Operando Raman spectroscopy reveals a weaker *CO adsorption on the Cu96In4 alloy surface compared to pure Cu which supports the immediate release of CO as a gaseous product from the alloy surface. The BiVO4?perovskite?Cu96In4 tandem PEC device shows an excellent (~75%) selectivity towards solar CO production from CO2 and H2O under bias-free conditions where the solar-to-CO conversion efficiency reached 0.19% after 10 h operation. Furthermore, the perovskite?Cu96In4 cathode shows robust PEC activity under different solar light intensities (varied from 0.1 Sun to 1 Sun) which indicates that the device can be used under different daylight conditions or even on a cloudy day with diffused sunlight. Reference: Rahaman, M.; Andrei, V.; Pornrungroj, C.; Wright, D.; Baumberg, J. J.; Reisner, E. Energy Environ. Sci., 2020, 13, 3536-3543
Authors : Dursap, T.*(1), Regreny, P.(1), Tapia Garcia, C.(2), Fadel, M.(2), Chevalier, C.(3), Chauvin, N.(3), Gendry, M.(1), Danescu, A.(1), Koepf, M.(2), Artero, V.(2), Bugnet, M.(4), Penuelas, J.(1)
Affiliations : (1) Univ Lyon, CNRS, INSA Lyon, ECL, UCBL, CPE Lyon, INL, UMR 5270, 69130 Ecully, France ; (2) Univ. Grenoble Alpes, CNRS, CEA, IRIG, Laboratoire de Chimie et Biologie des Métaux, 38000 Grenoble, France ; (3) Univ Lyon, INSA Lyon, ECL, CNRS, UCBL, CPE Lyon, INL, UMR 5270, 69621 Villeurbanne, France ; (4) Univ Lyon, CNRS, INSA Lyon, UCBL, MATEIS, UMR 5510, 69621 Villeurbanne, France
Resume : Photoelectrochemical cells (PEC) are one of the most promising approaches for the production of alternative energy carrier in the global effort to diminish the usage of fossil fuels . In this context, III-V nanowires (NW) based photoelectrodes [2-5] are particularly attractive thanks to their high surface/volume ratio and their efficient charge separation and collection. However III-V NWs suffer from corrosion in aqueous electrolyte that prevents their utilization for long period. In order to avoid the surface degradation of the III-V NW under working conditions, a particular attention has to be given to their surfaces. We proposed to grow an oxide shell transparent to visible light and compatible with the carrier transfer from the III-V semiconductor to the electrolyte to increase the viability of these photoelectrodes. GaP and GaAs NWs were grown by molecular beam epitaxy (MBE) using the vapor-liquid-solid (VLS) mechanism on silicon substrate and a TiO2 shell was deposited by atomic layer deposition (ALD). The morphology, interface, and structure of the NWs were studied by scanning transmission electron microscopy and electron energy loss spectroscopy before and after the measurements of their photoelectrochemical activity after combination with suitable hydrogen or oxygen evolution catalysts. 1 N. Armaroli et al, Angew. Chem. 46, (2007), 52 2 M. G. Kibria et al, Nat. Commun. 5 (2014), 3825 3 J. Kamimura et al, Semicond. Sci. Technol. 31 (2016), 074001 4 K. T. Fountaine et al, ACS Photonics 3 (2016), 1826 5 N. Kornienko et al, ACS Nano 10 (2016), 5525
|10:05||Live Q&A Session 10|
HER and OER electrocatalysts : Hyacinthe Randriamahazaka
Authors : Hong Jin Fan
Affiliations : School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore
Resume : Water electrolysis, fuel cells, and metal-air batteries all require efficient and cheap electrocatalysts that can significantly lower the reaction overpotentials. Defects due to doping or alloy are pivotal to tailoring the electrocatalytic activities of the electrode materials. In this talk, I will discuss about effect of composition engineering and doping of electrocatalysts in their performance in water splitting and meal-ion batteries. First, we show dual anion doping, or metal-anion co-doping in alloy compounds can simultaneously modulate key parameters in water dissociation and hydrogen adsorption energies, leading to evident enhancement in both hydrogen and oxygen evolution reactions activities. Second, tuning the local defect configurations can promote the intrinsic HER activity of the basal plane of MoS2. And doping of Sn and Sb bi-atoms with different electronegativities can enhance the stability of amorphous MoSxO2-x catalyst for acidic HER. Finally, we show the effectiveness of local configuration of bi-metal atomic catalysts in boosting the ORR function.
Authors : HuangJingWei Li, Min Liu
Affiliations : State Key Laboratory of Powder Metallurgy, Hunan Provincial Key Laboratory of Chemical Power Sources, School of Physics and Electronics, Central South University, Changsha 410083, P. R. China.
Resume : Electrocatalytic hydrogen evolution reaction (HER) in alkaline media is a promising electrochemical energy conversion strategy. Ruthenium (Ru) is an efficient catalyst with a desirable cost for HER; however, the sluggish H2O dissociation process, due to the low H2O adsorption on its surface, currently hampers the performances of this catalyst in alkaline HER. Herein, we demonstrate that the H2O adsorption/dissociation improves significantly by the construction of Ru?O?Mo sites. We prepared Ru/MoO2 catalysts with Ru?O?Mo sites through a facile thermal treatment process and assessed the creation of Ru?O?Mo interfaces by transmission electron microscope (TEM) and extended X-ray absorption fine structure (EXAFS). By using Fourier-transform infrared spectroscopy (FTIR) and H2O adsorption tests, we proved Ru?O?Mo sites have tenfold stronger H2O adsorption ability than that of Ru catalyst. The catalysts with Ru?O?Mo sites exhibited a state-of-the-art overpotential of 16 mV at 10 mA cm?2 in 1 M KOH electrolyte, demonstrating a threefold reduction than the previous bests of Ru (56 mV) and commercial Pt (32 mV) catalysts. We proved the stability of these performances over 40 hours without decline. These results could open a new path for designing efficient and stable catalysts.
Authors : Roser Fernández-Climent, Miguel García-Tecedor, Camilo A. Mesa, Sixto Giménez
Affiliations : Institute of Advanced Materials (INAM), Universitat Jaume I, Avenida de Vicent Sos Baynat, s/n, 12006 Castelló de la Plana, Spain; Photoactivated Processes Unit, IMDEA Energy Institute, Parque Tecnológico de Móstoles, Avda. Ramón de la Sagra 3, 28935 Móstoles, Madrid, Spain; Institute of Advanced Materials (INAM), Universitat Jaume I, Avenida de Vicent Sos Baynat, s/n, 12006 Castelló de la Plana, Spain; Institute of Advanced Materials (INAM), Universitat Jaume I, Avenida de Vicent Sos Baynat, s/n, 12006 Castelló de la Plana, Spain
Resume : Hydrogen evolution reaction (HER) is a sustainable and promising alternative technology to overcome the use of fossil fuels that cause substantial harmful environmental impact worldwide. Recently, many works have reported electrocatalysts based on metallic earthabundant and cost-effective materials (Ni1, 2, Co3, Mo4, 5, Fe6, Cu7, 8) as promising alternatives to the state-of-the-art Pt catalysts for HER. In this talk, I will present a cost-effective and facile route to synthetize highly efficient Cu2S electrocatalyst, exhibiting 400 mA cm-2 at -1V vs RHE and exceptional stability under operation conditions. Different structural characterization techniques were employed to analyze the as-prepared and post-mortem electrodes coupled to detailed electrochemical characterization and mechanistic analysis This Cu-based electrocatalyst represents a great step towards scalability for industrial hydrogen production.
Authors : Boon Chong Ong, ZhiLi Dong
Affiliations : School of Material Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798
Resume : Hydrogen production from water splitting is often as regarded the ?Holy Grails? of chemistry. Water oxidation is the kinetic bottleneck of overall water splitting reaction because of the sluggish kinetic and complex multistep electron transfer process. The development of effective materials for water oxidation reaction is indeed a challenging field. Metal-organic framework (MOF) with high surface area and porosity has become a promising catalyst for various reaction. Polyoxometalates (POMs) are molecular oxide aggregates with diversified structure and chemical versatility. The metal-oxygen framework in POMs which can undergo reversible redox reaction has increased their popularity in the field of catalysis. In this study, a hybrid compound of MOF/POMs is fabricated by crystallization mechanism, with the addition of POMs during MOF formation. Prior to that, POMs are synthesized by self-assembly process. All the materials are synthesized under mild condition, without the usage of strong acid and strong base. Characterization tests such as field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) are performed to elucidate the properties of the hybrid compounds. In the electrocatalytic water oxidation reaction experiment, MOF/POMs hybrid compounds show enhancement in performance compared to pristine MOF, indicating the potential of the newly synthesized compounds as efficient catalysts. Keywords: Polyoxometalate, Metal-organic Framework, Hybrid compound, Electrocatalysis, Water oxidation
Authors : Zhipeng Yu, Francisco Javier Escobar-Bedia, Maria J. Sabater, Isilda Amorim, Ana Araujo, Joaquim L. Faria, Patricia Concepcion, Lifeng Liu
Affiliations : Zhipeng Yu; Isilda Amorim; Ana Araujo; Lifeng Liu International Iberian Nanotechnology Laboratory (INL), Av. Mestre Jose Veiga, 4715-330 Braga, Portugal Zhipeng Yu; Ana Araujo; Joaquim L. Faria 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 Francisco Javier Escobar-Bedia; Maria J. Sabater; Patricia Concepcion Instituto de Tecnología Química, Universitat Politècnica de València-Consejo Superior de Investigaciones Científicas (UPV-CSIC), Avenida de los Naranjos s/n, 46022 Valencia, Spain Isilda Amorim Center of Chemistry, Chemistry Department, University of Minho, Gualtar Campus, Braga, 4710-057, Portugal
Resume : Electrocatalysts play a crucial role in hydrogen production via water electrolysis. However, developing efficient catalysts to reduce the high reaction overpotentials caused by the sluggish kinetics of the anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER) remains a formidable challenge. In this presentation, we report the synthesis of atomically dispersed ruthenium (Ru) supported on nitrogen-doped carbon (Ru-NC) with an ultra-low Ru loading (0.2 wt%), which is realized by a two-step deposition-pyrolysis method. Extensive transmission electron microscopy investigations reveal that Ru is dispersed on the NC support in the form of both single atoms and small clusters. The as-prepared Ru-NC exhibits superior electrocatalytic activity and good stability for both HER and OER, showing bifunctionality. It only requires a low overpotential of 47.1 and 72.8 mV to deliver a current density of 10 mA cm-2 for HER in 0.5 M H2SO4 and 1.0 M KOH, respectively, and 300 mV for OER in 1.0 M KOH. Considering the superior bifunctional electrocatalytic HER and OER activities, the overall water electrolysis performance has been investigated in alkaline solution using Ru-NC as both HER and OER catalysts in the presence of a bipolar membrane (BPM). This configuration enables water electrolysis to occur in acid-alkaline dual electrolytes (BPM-WE), where HER is accomplished in a kinetically favorable acidic solution and OER in a kinetically favorable basic solution. Such asymmetric acid-alkaline BPM-WE operates under a low cell voltage of only 0.89 V to deliver a current density of 10 mA cm-2 and can sustain over 100 hours without significant performance decay due to the assistance of electrochemical neutralization resulting from the crossover of the electrolytes, which shows a great potential for energy-saving hydrogen production.
|12:30||Live Q&A Session 11|
2D materials for (photo)electrocatalysis : Idan Hod
Authors : Jordi Arbiol,* Ting Zhang, Zhifu Liang, Maria Chiara Spadaro
Affiliations : 1. Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Catalonia, Spain 2. ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Catalonia, Spain
Resume : Technology at the nanoscale has become one of the main challenges in science as new physical effects appear and can be modulated at will. Especially 2D nanomaterials can be designed and engineered in order to improve their performance and efficiency for energy and environmental applications. In this way, a proper selection of defects, grain boundaries and surfaces, or the right selection of dopants allow a major increase on the properties of a new generation of (photo)electrocatalysts. In the present work, by using powerful advanced electron microscopy related techniques, we will move to the atomic scale in order to visualize the beauty of such nanostructures. Modified nanostructures as support for single atom catalysts with a great enhancement on lithium-sulphur batteries stability and performance or CO2 Reduction will be shown . Nanoengineered atom-thin transition metal dichalcogenides (MoS2 and WS2) showing a high density of grain boundaries acting as efficient active sites for the hydrogen evolution reaction (HER) will be also studied at the atomic scale . Atomic resolution electron microscopy analyses will help us to visualize such fancy nanostructures and allow us to create 3D atomic models in order to understand not only the growth mechanisms implied, but also to be used as input models for further DFT simulations, which will allow us to gain knowledge on the novel catalytic mechanisms achieved. We will show our latest results on direct visualization and modelling of nanomaterials at atomic scale, which will help to understand their growth mechanisms (sometimes complex) and also correlate their chemical properties ((photo)electrocatalytic) at sub-nanometer scale with their atomic scale structure.  Y. He, et al. Nature Communications, 11, 57 (2020)  Z. Liang et al., Advanced Energy Materials, 11, 2003507 (2021)
Authors : Evgeniya Kovalska
Affiliations : University of Chemistry and Technology, Prague, Czech Republic
Resume : Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have been demonstrated as promising catalysts for water splitting, hydrogen reduction, and water oxidation. The unique chemical-physical properties of 2D TMDs are shown by their small size enriched by the number of edge active sites, band-edge position, quantum confinement effect, and photo-induced catalytic efficiency. TMDs are considered the most promising cost-effective catalysts, and their properties are determined by the TMDs? polymorph type (hexagonal 2H, trigonal 1T). Tantalum disulfide (TaS2) as a member of the TMD family has been subject to numerous studies due to various material?s unique structural and electronic phases. Its initial metallicity and electrical conductivity lead to potential applications such as a light-responsive electrode. Albeit the study of TaS2 mainly focuses on the superconductivity and field emission, photo-induced features of the material for hydrogen evolution reaction (HER) and photosensing have not been explored yet. Several methods have been demonstrated to produce 2D TaS2, using chemical vapor deposition (CVD), mechanical cleavages, intercalation, ultrasonication, or liquid-phase exfoliation. However, the CVD method remains to be improved before it can be used to produce large-domain homogeneous TaS2 films. The mechanical cleavage is not scalable and misses control over product thickness and size. Alternatively, electrochemical exfoliation (ECE) is the most convenient, controlled, and straightforward method employed in ambient temperature for large-scale production of 2D TaS2. In this study, the light-induced efficiency of electrochemically exfoliated TaS2 nanosheets for hydrogen generation catalysis and photodetectors has been presented for the first time. The ECE of TaS2 crystals toward a few-layer derivative has been pioneered in anhydrous tetrabutylammonium hexafluorophosphate in N, N dimethylformamide. Comprehensive analysis of exfoliated TaS2 revealed the formation of nanoparticles and nanosheets with a lateral size of about several nanometers and micrometers, correspondingly. Observed mutual twisting of 2H-TaS2 flakes leads to the redistribution of charge density induced by interlayer interaction of the individual nanosheets. External light irradiation on the TaS2 surface influences its conductivity, making it feasible for photoelectrocatalysis (PEC) and photodetection (PD). The TaS2-based catalyst demonstrates high HER PEC activity with the onset overpotential below 575 mV, which can be lowered by thorough catalyst preparation. Finally, the TaS2-integrated PD in the acidic medium represents its broadband light sensing capability with the highest photoresponsivity toward 420 nm light illumination. This finding will pave the way to a new realization of exfoliated twist-angle stacked TaS2 for photo-induced electrochemistry and sensing.
Authors : Mingming Li, Yibo Wang, Tengfei Li, Jinghan Li, Lujun Huang, Qinglei Liu, Jiajun Gu and Di Zhang
Affiliations : State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University
Resume : As an eco-friendly and renewable energy source, hydrogen energy has attracted widespread attention. MoS2 nanomaterials are typical catalysts for the electrocatalytic hydrogen evolution reaction (HER), but their performances are limited by their poor conductivity and spontaneous agglomeration. Here, we prepared few-layer fluorine-free Ti3C2TX (T = O, OH) as a conductive substrate of MoS2 for HER catalysis, and the as-prepared hybrid catalyst exhibits high catalytic activity with a small overpotential of 139 mV at -10 mA cm-2, a Tafel slope of 78 mV dec-1, and a negligible decay after 3000 cycles at a scan rate of 100 mV s-1 in an acidic solution. The excellent performance in HER activity can be attributed to the improved electrical conductivity, increased O active sites and optimized 2D masstransport channels of the unique few-layer fluorine-free structure. Interestingly, the few-layer fluorine-free Ti3C2TX/MoS2 catalyst also performs well under neutral and alkaline conditions. This work demonstrates that few-layer fluorine-free Ti3C2TX (T = O, OH) can be used as an excellent conductive substrate to further improve the HER performances of other nanoscale electrocatalysts.
Authors : Junyi Cui, and Salvador Eslava*
Affiliations : Imperial College London
Resume : Two-dimensional (2D) VA group materials, including black phosphorene and bismuthene, attract considerable attention in energy devices because of their unique properties, such as tunable bandgap and superhigh carrier mobility. However, their application in photoelectrochemical devices is rarely reported. In this presentation, we present the successful design of a co-catalyst/2D VA material/semiconductor composite photoanode consisting of NiFeOOH/bismuthene/BiVO4 that achieves 3.7 mA cm-2 at 0.8 VRHE. Characterization techniques such as electrochemical impedance spectroscopy, intensity modulated photocurrent spectroscopy, cyclic voltammetry, and open circuit potential, were comprehensively employed to identify the roles of bismuthene and NiFeOOH on BiVO4. We found that bismuthene can (1) increase hole concentration at the surface, (2) modulate surface oxygen vacancies, and (3) accelerate oxygen evolution reaction kinetics. Indeed, kinetics studies show the composite photoanode has an effective hole injection into the electrolyte. Moreover, we found that the improvement from bismuthene strongly depends on the co-catalyst used. We assign this dependence to the permeability and conductivity of the different co-catalysts.
Authors : Edward Allery David Baker, Joe Pitfield, Steven Paul Hepplestone
Affiliations : Department of Physics, University of Exeter
Resume : Two dimensional materials, such as the transition metal dichalcogenides (TMDCs) are a good candidate for water splitting catalysts [1,2], as they often have larger band gaps than their bulk counterparts. However, this had to be balanced by the thin layers having a small absorption cross section and difficulties in mounting on a suitable substrate. PdSe2 is being suggested as a potential water splitting candidate . 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 both adsorptions and substitutions, in both air and water environments. 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.
|15:00||Live Q&A Session 12|
Electrocatalysts based on earth-abundant elements : Matthew Mayer
Authors : Jose Ramon Galan-Mascarosa, Felipe Garcés-Pineda, Jiahao Yu, Ilario Gelmetti
Affiliations : Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and Technology (BIST) Av. Països Catalans, 16, Tarragona, 43007, Spain; ICREA, Passeig Lluís Companys, 23, Barcelona, 08010, Spain.
Resume : The establishment of a sustainable renewable fuels technology will depend on the electrocatalytic reduction of substrates into fuels, but also on the electrocatalytic oxidation of water or other feedstock to extract the needed electrons and protons. The requirements for the oxidation electrocatalysts are typically more demanding regarding long term stability, since these catalysts must be fast, selective and efficient, but also robust to high oxidation potentials, water, oxygen, electrolytes, acids or bases, etc. Several earth abundant metal oxides are excellent electrocatalysts in neutral and basic conditions, with multiple examples from different labs.1 However, most active transition metal oxides are unstable in acidic media, where they just dissolve even in open circuit conditions. Only noble metal oxides, such as IrO2, are able to exhibit competitive electrooxidation activity in aqueous acidic conditions (pH < 3), where reduction electrochemistry is easier and faster, and proton exchange membrane (PEM) technology may facilitate high current density performance in compact electrolyzer architectures. In this communication we will report our latest results in the search for efficient, low cost oxidation electrocatalysts from earth abundant, non-critical raw materials able to work in aqueous acidic media. We showed how Co-containing polyoxometalates (POMs), are active electrocatalysts for the oxygen evolution reaction (OER) in acidic conditions when stabilized by a partially hydrophobic support.2 Although with some limitations, a hybrid composite of an insoluble salt of the polyoxoanion [Co9(H2O)6(OH)3(PW9O34)3]16? blended with a carbon paste electrode exhibited superior performance and higher current densities than the corresponding IrO2-based electrodes in the low overpotential range. We are extending this same strategy to bulk and nanostructured transition metal oxides to provide fast and robust OER at pH < 1. Furthermore we will show how some of these metal oxides can also catalyze alternative electrochemical oxidation processes of high interest for the chemical industry, such as the selective oxidation of alcohols to aldehydes or carboxylic acids.
Authors : Subhabrata Mukhopadhyay, Ran Shimoni, and Idan Hod*
Affiliations : Department of Chemistry at Ben-Gurion University of the Negev (BGU), Israel
Resume : In recent years, there is a growing interest in the incorporation of Metal-Organic Frameworks (MOFs) based thin films into electrochemical energy conversion schemes. In principle, MOF-based electrocatalytic systems hold several key virtues, such as the ability to immobilize unparalleled amount of catalytic sites; intrinsic inclusion of mass-transport channels; the ability to add molecular shuttles to deliver redox equivalents to and from the MOF-tethered catalytic sites; and finally, much like in catalytic enzymes, MOFs offer the possibility to modulate the catalyst’s secondary chemical environment. Indeed, over the last years several reports have demonstrated the concept of using electroactive MOF thin films as the catalytic component in the electrocatalytic cell, either through (a) the use of the MOF structural elements themselves (ligands or nodes) as electroactive catalysts, or (b) the immobilization of high concentration of active molecular catalysts within the MOF pores (for a wide variety of energyrelated catalytic reactions as hydrogen evolution, water oxidation, oxygen reduction, and CO2 reduction). Yet, up to this point, the notion of using MOFs to precisely tune and manipulate the properties of the electrocatalytically active site and its surrounding chemical environment was overlooked. In this talk, we will demonstrate for the first time that a non-electrocatalytic MOF can be used as a porous membrane layered over a solid heterogeneous electrocatalyst. Following this principle, a suitably designed MOF membrane has the potential to modify the microenvironment of the underlying heterogeneous catalyst and affect its electrocatalytic properties in a wide variety of proton-coupled electron transfer (PCET) reactions.
Authors : Camilo A. Mesa (1) Miguel García-Tecedor (1) Jaime Noguera-Gómez (2) Felipe Pineda (4) Rafael Abargues (2) James R. Durrant (3) Jose Ramón Galán (4) Sixto Giménez (1)
Affiliations : 1. Institute of Advanced Materials (INAM), Universitat Jaume I, 12006 Castelló, Spain 2. UMDO, Instituto de Ciencia de los Materiales, Universidad de Valencia, P.O. Box 22085, Valencia 46071, Spain 3. Department of Chemistry and Centre for Plastic Electronics, MSRH, White City Campus, Imperial College London, London W12 0BZ, United Kingdom 4. Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and Technology (BIST), Tarragona, Spain
Resume : Electrocatalytic hydrogen production via water splitting is considered a promising technology to store renewable energy into chemical bonds. In this process, the oxygen evolution reaction (OER) water acts as electron donor and it is considered to be the bottleneck of the process when using metal-oxide anodes. The efficiency of these catalysts does not only depend on the nature of the metal oxide, but also on their physical characteristics such as composition, magnetic susceptibility and doping variations, amongst others. However, the mechanism of the OER on metal oxides as well as the nature of the efficiency loses remains elusive. In this talk, I will present recent advances on the understanding of the kinetics of OER on different metal-oxide electrocatalysts, focusing particularly on Ni-based anodes. Kinetic and mechanistic analyses of the OER on Ni-based electrocatalysts will be presented under different physicochemical conditions, Fe doping on facile synthesised Ni-oxide anodes [1-3] as well as the effect of applying a magnetic field on ferrite type Ni-oxide catalysts on the OER kinetics will be shown.
Authors : Patrick Guggenberger, Tatiana Priamushko, Freddy Kleitz
Affiliations : Department of Inorganic Chemistry?Functional Materials, Faculty of Chemistry, University of Vienna, Währinger Straße 42, A-1090 Wien, Vienna, Austria ; Department of Inorganic Chemistry?Functional Materials, Faculty of Chemistry, University of Vienna, Währinger Straße 42, A-1090 Wien, Vienna, Austria ; Department of Inorganic Chemistry?Functional Materials, Faculty of Chemistry, University of Vienna, Währinger Straße 42, A-1090 Wien, Vienna, Austria
Resume : The development of new low-cost water splitting electrocatalysts to replace the expensive and scarce established noble metal Pt and RuO2/IrO2 catalysts is a major challenge on the way to green hydrogen production. Ordered mesoporous transition metal oxides, and especially the Co3O4 derived ones, were hence studied extensively owing to their good performance and stability in alkaline electrolytes for OER . The preparation of bimetallic transition metal oxides like NiCo2O4, but also the addition of small amounts of transition metals - as dopants - led to improved electrocatalysts due to synergistic effects between the metal oxide species [2, 3]. In this work, we synthesized Mn and Fe-doped ordered mesoporous nickel cobalt oxides via one-step impregnation using KIT-6 aged at 40°C as a hard template to obtain electrocatalysts exhibiting high porosity and surface area. By implementation of a low-temperature calcination approach, the temperature necessary to obtain spinel-type transition metal oxides was significantly reduced from typical 500°C to 200°C. This was achieved by exploiting the ?container effect? described by Sun et al . Detailed materials characterization was performed to ascertain elemental and phase compositions and determine porosity and mesoporous characteristics. Further, the effects of iron and manganese-doping upon the electrocatalytic activity of ordered mesoporous Ni0.5Co2.5O4 were investigated and the stability of the catalysts was demonstrated in a 72h galvanostatic experiment. Wide-angle XRD revealed spinel structure for Co3O4, Ni0.5Co2.5O4, and the Fe and Mn-doped samples, meaning that Fe and Mn substituted Ni in the spinel structure of the multimetallic oxide. SAXS and nitrogen physisorption confirmed a high mesopore ordering, a bimodal pore size distribution (typical for KIT-6-40 replicas), high BET surface area around 130 m²/g, and a total pore volume of approximately 0.3 cm³/g for all electrocatalysts. Further, the electrocatalytic performance was ascertained for the OER in 1M KOH electrolyte. All electrocatalysts prepared at 200°C performed superior to the Co3O4 references which were calcined at 200°C and 500°C respectively. With a low overpotential of only 359 mV (@10 mA/cm2) and a high current density of 279 mA/cm2 @1,7 V vs. RHE, the Mn0.1Fe0.1Ni0.3Co2.5Ox composition exhibited the best OER performance among the samples. The high stability of the catalysts was confirmed by a stable working electrode potential during a 72h galvanostatic polarization at 5 mA in 1 M KOH electrolyte at room temperature. In summary, a low-temperature calcination approach was successfully used to prepare Mn and Fe-doped mesoporous nickel cobalt oxide without the formation of any detectable phases except the spinel structure. The success of this procedure is attributed to the low calcination temperature as higher temperatures usually lead to the formation of different oxide phases and result in poor replica quality . It was shown that the activity of the oxides toward OER increases with the addition of Mn- and/or Fe- into Ni/Co oxides as a result of the synergistic effect between metals. Moreover, the catalysts demonstrate excellent stability, which makes them attractive candidates for further research. 1. Zhao, Q., Yan, Z., Chen, C. & Chen, J. Spinels: Controlled Preparation, Oxygen Reduction/Evolution Reaction Application, and beyond. Chem. Rev. 117, 10121?10211 (2017). 2. Fang, L. et al. Crystal-plane engineering of NiCo2O4 electrocatalysts towards efficient overall water splitting. J. Catal. 357, 238?246 (2018). 3. Li, Y., Hasin, P. & Wu, Y. NixCo3-XO4 nanowire arrays for electrocatalytic oxygen evolution. Adv. Mater. 22, 1926?1929 (2010). 4. Sun, X. et al. Container effect in nanocasting synthesis of mesoporous metal oxides. J. Am. Chem. Soc. 133, 14542?14545 (2011). 5. Priamushko, T. et al. Nanocast Mixed Ni-Co-Mn Oxides with Controlled Surface and Pore Structure for Electrochemical Oxygen Evolution Reaction. ACS Appl. Energy Mater. 3, 5597?5609 (2020).
|17:20||Live Q&A Session 13 & Closing remarks|
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