Materials and processes for production of solar hydrogen

“Materials and processes for production of solar hydrogen”

Book of abstracts

05-07th May, 2021

Project “Complex of online and onsite lectures on materials for hydrogen generation by solar water splitting” med acronym” (COOL LONGBOAT)

Stavanger, May 2021

“Materials and processes for production of solar hydrogen”

Program

05-07th May, 2021 Project “Complex of online and onsite lectures on materials for hydrogen generation by solar water splitting” med acronym” (COOL LONGBOAT)

Day1

09:00-13:00 Session leader: Smagul Karazhanov

09:00-09:05 Smagul Karazhanov. Opening.

09:05-09:30 Arve Holt. Research Director, Institute for Energy Technology, Kjeller, Norway. Welcome speech.

09:30-10:30 Athanasios Chatzitakis “Fuel(s) from the Sun”

10:30-11:10 Questions/answers, presentation by students 10:45 – 10:55 Henrik Petlund // University of Oslo // “Modification of double perovskite BGLC587 with Fe, Ni and Mn for the oxygen evolution reaction (OER)” 10:55 – 11:05 Xiaolan Kang // University of Oslo // “Water vapor photoelectrolysis operating Under Varying Atmospheric Humidity in a Solid-State Photoelectrochemical Cell”

11:10-11:20 Coffee break

11:20-12:20 Nicolas Alonso Vante “Photo(electro)catalysis - Introductory aspects: Electrochemical and Photoelectrochemical cells”

12:20-13:00 Questions/answers, presentation by students

12:35 – 12:45 Karla Vega-Granados // University of Poitiers // “Modulating methanol tolerance of soft-chemistry selenization of carbon supported palladium nanoparticles “

Day 2

09:00-13:00 Session leader: Santanu Das

09:00-10:00 Hiroshi Kageyama “Mixed anion materials”

10:00-10:40 Questions/answers, presentation by students 10:15 – 10:25 Zefeng Wei // University of Kyoto // “Formation of PbCl2-type AHF (A = Ca, Sr, Ba) with Partial Anion Order at High Pressure” 10:25 – 10:35 Yu Cao // University of Kyoto // “Vanadium Hydride as an Ammonia Synthesis Catalyst”

10:40-11:40 Smagul Karazhanov “Oxyhydrides: synthesis, characterization and applications”

11:40-12:20 Questions/answers, presentation by students 11:55 – 12:05 Dicel, A. // Istanbul Technical University // “Encapsulation of YHO with PVB and PVP”


12:30-13:30 Truls Norby “Electrode kinetics in fuel cells and electrolyzers”

13:30-14:10 Questions/answers, presentation by students 13:45 – 13:55 Kevin G. Both // University of Oslo // “Plasmonically-assisted Photocatalysis by Au-nanoparticles on STO created by galvanic replacement and exsolution” 13:50 – 14:00 Morito Namba // Kyoto University // “Protonation of rutile oxides”

Day 3

09:00-13:00 Session leader: Athanasios Chatzitakis

09:00 – 09:10 Arunachala M. Kannan // Arizona State University // “H2 generation by enhancing interfacial charge transfer in WO3/BiVO4 photoanode for photoelectrochemical water splitting”

09:10-10:10 Bernt Thorstensen “Titania photocatalysis. What can we learn, both process wise and material wise, from simple experiments”?

10:00-10:40 Questions/answers, presentation by students 10:15 – 10:25 Bhagyasree G. S. // Calicut University // “Characterization of Silica/Metal Oxides and Silica/Graphite Oxide Photonic crystals for Enhancing Efficiency of Solar Cells”

10:40-11:40 Santanu Das "Pt-free electrodes for applications in electrochemical hydrogen generation".

11:40-12:20 Questions/answers, presentation by students


12:30-13:30 Olena Zavorotynska “Structural characterization of energy-related materials”

13:30-14:10 Questions/answers, presentation by students 13:40 – 13:50 Tina Knudsen // University of Stavanger // “Characterisation of YHO films with Raman spectroscopy” 13:50 – 14:00 Damir Z. Mamedov // Institute for Energy Technology // “Theoretical study of electronic structure, optical properties and wettability of CeO2

14:00 – 14:10 ”Temitope Boriwaye // University of Ibadan // “Theoretical investigation of lead-free perovskites”

14:10-14:20 Closing session

Plenary lectures

COOL LONGBOAT 1st Summer school 2021: “Materials and Processes for Production of Solar Hydrogen”

May 5-7, 2021 // Online

Fuel(s) from the sun 1Chatzitakis A. [email protected], University of Oslo, Centre for Materials Science and Nanotechnology, Department of Chemistry, Gaustadalléen 21, NO-0349, Oslo, Norway In order to address the intermittent nature of sunlight, solar energy can be converted and stored as chemical energy. This process is inspired by the natural photosynthetic mechanism and it is referred to as artificial photosynthesis (AP). Semiconducting materials play a pivotal role in AP systems as they can absorb sunlight and in turn catalyze chemical reactions. In this talk the main functionality of such photocatalysts, as well as the overall concept of AP are introduced (Figure 1). Among the plethora of solar-generated fuels, we will focus on the production of a very important one, the hydrogen gas (H2). A general introduction of H2 as a renewable and “green” fuel will be given, accompanied by a few key developments from the literature. To that direction, developments in the University of Oslo will also be presented and the concept of H2 production through photo-electrolysis of water vapor will also be introduced and discussed. As Jules Verne said back in 1874, “Water will be the coal of the future”.

Figure 1 An illustration of photocatalytic devices producing solar fuels with sunlight as the only energy input.


May 5-7, 2021 // Online

Photo(electro)catalysis - Introductory aspects: Electrochemical and Photoelectrochemical cells

Nicolas Alonso-Vante

e-mail: [email protected], IC2MP – UMR CNRS 7285 University of Poitiers, France This 1-hour lecture is best suited for an attendee who has basic knowledge of electrochemistry, and also welcomes chemists, physicists, materials scientists with an interest in applying materials science to Electrocatalysis and photoelectrocatalysis. About the lecture: It will start giving an overview of materials, energy challenges. The chemical and electrochemical principles will be given as a starting point to discuss concept of electrocatalysis and photoelectrocatalysis of the water splitting process, mechanisms, and criteria to choose nanomaterials for an efficient conversion. The subjects to be covered are: (i) redox reactions of water, (ii) the hydrogen electrode and catalysts, (iii) the oxygen reduction reaction and catalysts, (iv) the catalyst challenge by design, and (v) perspectives.


May 5-7, 2021 // Online

Mixed-anion Materials 1*Kageyama, H. [email protected], Kyoto University, Japan Mixed anion compounds, which contain several different anions, began to draw attention as game-changing inorganic materials. Since, compared with conventional inorganic compounds such as oxides, mixed-anion compounds may exhibit unique coordination and resultant extended structures, from which fundamentally different chemical and physical property may emerge. My talk aims at describing the current status and scope as well as outlining prospects and challenges surrounding mixed-anion compounds, focusing on crucial roles of multiple anions in synthesis, characterization, and properties [1]. Understanding of mixed-anion compounds is still growing, but recent studies have unveiled several key features that are otherwise inaccessible in traditional single-anion compounds. We show several examples, such as titanium perovskite oxyhydrides that can act as a precursor for topochemical anion exchange reaction [2] and as a catalyst [3]. Our recent efforts to extend the research on mixed-anion compounds to non-oxide-based materials will be also presented [4, 5].

Figure 1 Mixed-anion concepts (taken from Ref. 1).


May 5-7, 2021 // Online

1) H. Kageyama et al., Nat. Commun. 2018, 772. 2) Y. Yajima et al., Nat. Chem. 7, 1017 (2015). 3) Y. Kobayashi et al., J. Am. Chem. Soc. 139, 18240 (2017). 4) S. Gao et al., Nat. Commun. 12, 201 (2021) 5) H. Ubukata et al., Sci. Adv., in press.


May 5-7, 2021 // Online

Oxyhydrides: synthesis, characterization and applications

Smagul Zh. Karazhanov Department for Solar Energy, Institute for Energy Technology, Norway

E-mail: [email protected] Oxyhydrides are emerging class of materials with mixed oxide and hydride anions sharing the same sites in the lattice [1-4]. They exhibit exciting properties that are available neither in pure oxides nor in hydrides. Yttrium oxyhydride (YHO) is one of the representatives of the class of materials that was discovered by Trygve Mongstad [5]. The material exhibits UV-light induced reversible color change that takes place at room temperature and ambient pressures, the property that has attracted interest for applications in smart windows, medicine, photocatalysis, energy storage devices [5-8]. Later on some other rare earth metal oxyhydrides are reported to exhibit similar materials properties [9-10]. The aim of the talk is to report overview of latest results about materials properties and applications. UV light induced oxygen release from the films, lattice contraction, and mechanism of the photochromic effect, the relationship of the structural, optical, and electrical properties of the films on deposition conditions. The present talk includes overview on status of research on the topic and ongoing research activity in the Institute for Energy Technology. The results obtained from X-ray diffraction, transmission and reflectance spectra for the films before and after illumination of the films with UV light. Photoluminescence studies have been performed at low and room temperature that shows weak luminescence properties of the films. X-ray photoelectron spectroscopic studies as well as micro Raman measurements support the idea about light induced oxygen release from the films. Also, the results of theoretical studies, ion beam results and synchrotron results will be presented. UV light-induced lattice contraction, mechanism of the lattice contraction, UV-light induced oxygen/hydrogen release from the films will be presented. The films have been deposited by reactive magnetron sputtering of yttrium in the H2/Ar atmosphere that has led to formation of YH2±δ. The films then were taken out of the chamber and are oxidized in the air. Thus, the YHO has been formed. Structural, electrical, optical, morphological, and vibrational properties of the films have been studied. Ab initio modelling has been performed by the software VASP.

References 1 K. Hayashi, P. V. Sushko, et al. Nature Communications. 5, 3515, (2014). 2 Y. Kobayashi, O. J. Hernandez, et al. Nature Materials. 11, 507, (2012). 3 Y. Kobayashi, O. Hernandez, et al. Sci. Technol. Adv. Mater. 18(1), 905-918, (2017). 4 H. Kageyama, K. Hayashi, et al. Nature Communications. 9(1), 772, (2018). 5 T. Mongstad, C. Platzer-Bjorkman, et al. Solar Energy Mater. Solar Cells. 95(12), 3596-

3599, (2011). 6 F. A. Martinsen, J. M. Amenedo, et al. Photochromic Device. US Patent Application

NO20160106, 2016. 7 C. C. You, D. Moldarev, et al. Solar Energy Mater. Solar Cells. 166, 185-189, (2017). 8 D. Moldarev, M. V. Moro, et al. Phys. rev. Mater. . 2, 115203, (2018). 9 M. La, N. Li, et al. Scripta Materialia. 142, 36-40, (2018). 10 S. Cornelius, G. Colombi, et al. J. Phys. Chem. Lett., 1342-1348, (2019).

mailto:[email protected]


May 5-7, 2021 // Online

Electrode kinetics in fuel cells and electrolyzers 1Truls Norby 1 [email protected] , University of Oslo, Norway Fuel cells constitute the technology of choice to convert hydrogen to electricity, while electrolyzers will be a major technology for producing that hydrogen from electricity from renewable sources, notably indirect (hydroelectric, wind, wave) and direct (photovoltaic) solar energy. They are hence not directly the topic of a workshop on solar fuels, but photoelectrochemical (PEC) electrode kinetics is such a complex matter that it is useful to have electrode kinetics of fuel cells and electrolyzers as kind of reference. Both PEC and fuel cells and electrolyzers have in common that established state-of-the-art versions have aqueous liquid electrolytes, while solid-state electrolytes are of increasing interest. We will cover both, and dwell on various intermediate cases. While various charge carrying ions are in use in different ranges of temperature (O2-, CO3

2-, H+, OH-, H3O+), protonic electrolytes are most central to PEC and we will focus on them, with examples from proton ceramics, proton exchange membranes (PEMs), hydroxide ion conducting polymers, and surface protonic conduction. The electrode reaction comprises faradaic charge transfer over the electrolyte-electrode interface. This can be an electron transfer (redox) or – in the case of mixed ion electron conducting electrodes – ion transfer, in which case the electron transfer must take place somewhere else, e.g. on the electrode surface. The charge transfer – which is our means of driving the reaction with a voltage or recording a current in a chemically driven fuel cell – may be hindered by the supply of reactants, making adsorption and dissociation appear in the polarization resistance. In addition, diffusion in gas phase, over surfaces, and in the bulk of the electrode or electrolyte slows the reaction further and may eventually limit the current. While charge transfer takes place over the double layer capacitance of the electrolyte-electrode interface, the other processes may store reactants and products as much higher chemical capacitance, whereby the different processes have different time constants and may be separated in impedance spectroscopy. The talk will go through materials, processes, and methods, look to general principles that can be applied across systems and technologies, where possible also photoelectrochemical cells for solar hydrogen and artificial photosynthesis.


COOL LONGBOAT 1st Summer school 2021:

“Materials and Processes for Production of Solar Hydrogen”

May 5-7, 2021 // Online

Pt-free electrodes for applications in electrochemical hydrogen generation *1 Das, Santanu *Lead presenter 1 [email protected], Indian Institute of Technology (BHU), Varanasi, UP, India 221005 Abstract Hydrogen is the most promising energy carrier and a suitable alternative for

conventional fossil fuels, with relatively high gravimetric energy density (~140 MJ

kg-1), Zero carbon footprints, and a renewable source available in the form of water.

Currently, hydrogen-based technologies are critical alternatives to replace

conventional coal, oil, and natural gas. Although hydrogen can be produced using a

few industrial processes, including catalytic steam reforming, partial oxidation, and

coal gasification, all of these processes significantly contribute to global CO2

emissions. Thus, meeting all of the criteria for future universal energy demands,

among other hydrogen production approaches, the electrocatalytic hydrogen

evolution reaction (HER) from water splitting is the most economical and feasible

path for the hydrogen fuel-based ecosystem. To date it is essential to develop active

electrocatalysts for achieving accelerated HER kinetics along with minimum

overpotential for hydrogen evolution reactions (HER). Primarily, electrolysis of

water (Water splitting) could be an eco-friendly method to generate pure hydrogen

(H2O → H2 + 1/2 O2) whereas in other industrial techniques are highly energy

consuming as well as emitting CO2 in atmosphere causes severe environmental

issues. As standard, platinum (Pt) exhibits zero overpotential for HER, thereby,

highly adopted in current hydrogen evolution reactions in various water

electrolyzers. In particular, platinum-based materials serve as the best catalysts of

choice in practice for room-temperature (RT) water electrolysis, which can be carried

out both in acidic and alkaline mediums. However, low thermal efficiency for the

HER (1.223 V), high cost, scarcity, and low corrosion resistance are the fundamental

limitations of Pt-based electrode systems. Thus, there is a continuous search for Pt-

free electrodes to be developed for efficient RT-HER. In this presentation, a broad

overview will be presented for the Pt-free electrodes for the HER while a focus will

be kept thoroughly on illustrating the current status and future prospects for various

other materials for HER, including metals, metal alloys, metals modified with

transition-metal, carbides, chalcogenides, nitrides, phosphides, and heteroatom

doped carbon nanostructures, etc.


May 5-7, 2021 // Online

Titania UV photocatalysis. What can we learn, both process wise and material wise, from simple experiments.

Bernt Thorstensen [email protected], KeraNor AS, Brobekkveien 104, NO-0582 Oslo, NORWAY The big class of photoelectric and photoelectrochemical components is including several well-known components like solar cells and electrochemical cells, photocatalytic cells, sensors, light emitting diodes (LEDs), lasers etc. Particularly the branch of this class, which deals with transforming optical energy to electric or electrochemical energy, are all based upon solid-state technology and semiconductor physics. The importance of understanding the basics of solid-state physics is essential for the work with these components, combined with the understanding of the process reaction kinetics that is often controlling the surface of the component in an ambient environment. Photocatalysis is in some way the “simplest” of the photoelectrochemical processes, in the sense that they do not have external electrical contacts, and apparently are not exposed to external current or voltage. However, as will be seen, also these cells develop internal current and voltage during catalytic operation under illumination. We have for more than a decade been working with the development of photocatalysis, with titania as the photocatalyst and with UVA as light. An interesting question is whether we can learn something general from these limited experiments and characteristics we have gained from our work with titania UV-photocatalysis. This presentation will therefore briefly cover the following issues:

1. Some basic principles from semiconductor physics: band gap, Fermi level, direct and

indirect band gap, p-n diode structure, Schottky diode.

2. The light source and the light absorption: Solar light, UV light, absorption coefficient, Urbach tails, band gap states.

3. The loss mechanisms: Thermalization losses, spectral losses, Shockley-Queisser limit, thickness dependent losses.

4. Photocatalysis: Generation of radicals. Titania photocatalyst, preparation, calcination, doping. Colloidal titania coating properties. Familiarity with dye-sensitized solar cells.

5. Operation characteristics of the photocatalytic component: Schottky diode, Gärtner-Butler equation, the space charge layer (Debye length), electron-hole generation, light generated additional charges, lifetime, recombination.

6. The Langmuir mechanism: Eley-Rideal mechanism, probe molecule, radical generation, kinetic rate constant, transformation of photons to radicals, radical utilization.



May 5-7, 2021 // Online

Structural Characterization of Energy-Related Materials Olena Zavorotynska

Department of Mathematics and Physics, University of Stavanger, P.O.Box 8600, NO-4036 Forus, Norway e-mail: [email protected]

Hydrogen-rich solids, or hydrides, are versatile systems with a wide range of exciting properties relevant to storage and conversion of energy. They can store hydrogen with high energy density that is very compelling if compared to that of battery,1,2 and possess other fascinating properties potentially interesting for applications within a wide range of solutions for energy technology and catalysis. The numerous potential applications owe in part to an astonishing chemical bonding flexibility of hydrogen, which can be ionic (H─, H+), covalent (Hcov), neutral for the atoms at interstitial sites, or intermediate between these. Balance between the different contributions defines thermodynamic3 and electric4 properties of hydrides. Hydrogen is an important constituent of other energy-related materials as well. Understanding the structure and dynamics in hydrogen-rich solids is not an easy task.

This presentation overviews some common and less common techniques for characterisation, in particular, hydrogen-containing compounds. The talk will focus on vibrational spectroscopy methods, such as FTIR, Raman, and Inelastic neutron scattering, as well as X-ray-based methods such as X-ray diffraction and absorption techniques. The examples of compounds covered in this talk will include metal alloys, metal hydrides, mixed-anion compounds, and high-surface area porous materials for adsorption of hydrogen.

References

1. George, L., et al., Int J Hydrogen Energy 2010, 35 (11), 5454. 2. Chu, Steven, “Get Ready For 1.5¢ Renewable Electricity, Steven Chu Says, Which

Could Unleash Hydrogen Economy”, https://www.forbes.com/sites/jeffmcmahon/2019/04/02/get-ready-for-1-5%C2%A2-renewable-electricity-steven-chu-says-which-could-unleash-hydrogen-economy/#7147b36b1c01, accessed 09.04.2019.

3. a) Takagi, S., et al., Scripta Mater 2015, 109, 1, b) Humphries, T. D., et al., PCCP 2015, 17 (12), 8276.

4. Orgaz, E., et al., Phys Rev B 1996, 54 (22), 16124.

https://www.forbes.com/sites/jeffmcmahon/2019/04/02/get-ready-for-1-5%C2%A2-renewable-electricity-steven-chu-says-which-could-unleash-hydrogen-economy/#7147b36b1c01



Contributions from participants


May 5-7, 2021 // Online

Modification of double perovskite BGLC587 with Fe, Ni and Mn for the oxygen evolution reaction (OER)

1*Henrik Petlund, 2Truls Norby & 2Athanasios Chatzitakis *Lead presenter [email protected], Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, FERMiO, Gaustadalléen 21, NO-0349 Oslo, Norway 2Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, FERMiO, Gaustadalléen 21, NO-0349 Oslo, Norway Photoelectrochemical cells (PECs) for room temperature water splitting needs better electrocatalysts for the OER in order to be economically viable. Rare earth double perovskite cobaltites previously investigated as positrode material in high temperature PCECs and PCFCs has recently been shown to have intrinsic catalytic activities (ICAs) towards the OER exceeding that of state-of-the-art IrO2 [1]. In my master thesis I investigate how the electrocatalytic properties towards the OER of the double perovskite Ba0.5Gd0.8La0.7Co2O6-δ (BGLC587) is influenced by B-site substitution of Fe, Ni and Mn. Tafel slopes and overpotentials from linear sweep voltammetry (LSV) show that substitution with Fe can significantly improve the activity, whereas implementation of Ni and Mn gives a less prominent change. The intrinsic catalytic activity (ICA) is also addressed by the RctCdl product obtained from electrochemical impedance spectroscopy (EIS) as argued by Papaderakis et al. [2] and Chatzitakis et al. [3]. This further supports the results extracted from LSV.

Top 5 performing B-site substituted BGLC587

Tafel slope (mV dec-1) η10 (mV) RctCdl (s)

BGLCF55 52.9 BGLCF73 443 BGLCF55 3.6 x 10-4

BGLCF73 58.7 BGLCF55 456 BGLCN91 4.8 x 10-4

BGLCF91 60.6 BGLCF91 461 BGLCM55 5.2 x 10-4

BGLF 61.2 BGLCN55 490 BGLCF91 5.7 x 10-4

BGLCN55 67.0 BGLC587 495 BGLC587 5.9 x 10-4

Figure 1 The top 5 performing B-site substituted BGLC587 electrocatalysts in terms of Tafel slope, overpotential at 10 mA/cm2 and the RctCdl product representing the intrinsic catalytic activity (ICA).

REFERENCES: 1. Andersen, H., et al., A highly efficient electrocatalyst based on double perovskite

cobaltites with immense intrinsic catalytic activity for water oxidation. Chemical

Communications, 2020. 56(7): p. 1030-1033. 2. Papaderakis, A., et al., Electrochemical impedance studies of IrO2 catalysts for

oxygen evolution. Journal of Electroanalytical Chemistry, 2015. 757: p. 216-224.

3. Chatzitakis, A., et al., Comparison of the photoelectrochemical performance of

particulate and nanotube TiO2 photoanodes. Catalysis Today, 2017. 280: p. 14-20.


May 5-7, 2021 // Online

Water vapor photoelectrolysis operating Under Varying Atmospheric Humidity in a Solid-State Photoelectrochemical Cell

1 Xiaolan Kang, 1* Larissa Chaperman, 2 Fayna Mammeri, 2 Souad Ammar Merah, 2 Athanasios Chatzitakis, 1 *lead presenter 1 [email protected], Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, FERMiO, Oslo, Norway 2 Interfaces Traitements Organisation et Dynamique des Systèmes (ITODYS), Université de Paris, Paris, France. A solid-state photoelectrochemical (SSPEC) cell is an elegant approach for solar water electrolysis, especially when it comes to monolithic device design. In a SSPEC cell, the use of polymer-based membranes alleviates the need for liquid and in many cases corrosive electrolytes, while the electrodes distance is minimized due to a tandem configuration. Furthermore, the use of gaseous reactants, such as water vapor enables the integration of efficient, yet toxic photocatalysts, such as CdS. In this work, we evaluate the performance of a SSPEC cell, which is a layered structure composed of a thin TiO2 layer on a Ti mesh substrate as the photoanode electrode, a Nafion® membrane as the electrolyte and a Pt/C electrode as the cathode. We studied the effects of both the operating conditions in gaseous ambient atmospheres and the surface modification of TiO2 nanotubes (TNTs)-based photoanode with well-crystallized CdS and CdSe quantum dots (QDs). The SSPEC cell was cycled between high relative humidity (RH) (80%) and low RH levels (40%) providing direct evidence of the effect of the water content in air on the cell performance. TNTs modified with CdS QDs exhibited enhanced photocurrent density as compared to the unmodified one, and this photoanode showed excellent cyclability between low and high RH levels. Such a monolithic design highlights its importance and applicability in off-grid areas, as well as areas where clean water sources are scarce.

Figure 1 Schematic of the SSPEC cell working mechanism with rTNTAs60CdS as the photoanode


May 5-7, 2021 // Online

Modulating methanol tolerance of soft-chemistry selenization of carbon supported palladium nanoparticles

1*Vega-Granados, Karla, 1Alonso-Vante, Nicolas *lead presenter 1 [email protected] , IC2MP, UMR-CNRS 7285, University of Poitiers, 4 rue Michel Brunet, F-86073 Poitiers Cedex 9, France.

Carbon-supported Palladium nanoparticles were selenized using a simple aqueous phase method to provide tolerance to methanol during its use as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium. Surface electrochemistry results showed that an initial completely selenized surface evolves into a stable Pd@PdxSey structure, as consecutive potential cycles are applied in the potential region limited by H2 and O2 evolution. The selenization process confers material’s selectivity in the presence of methanol, as well as an active surface for the ORR.



May 5-7, 2021 // Online

Formation of PbCl2-type AHF (A = Ca, Sr, Ba) with Partial Anion Order at High Pressure

1‡Yumi Tsuchiya, 1‡*Zefeng Wei, 1Thibault Broux, 1Cédric Tassel, 1Hiroki Ubukata, 2Yuuki Kitagawa, 2Jumpei Ueda, 2Setsuhisa Tanabe, & 1Hiroshi Kageyama. *lead presenter ‡These authors contributed equally to this work. [email protected], Graduate of School of Engineering, Kyoto University, Japan 2 Graduate School of Human and Environmental Studies, Kyoto University, Japan Recently, the hydride anions are shown high compressibility in size, twice as compressible as the oxide anions [1], which drives anion order-disorder transition in fluorite-type structure oxyhydrides LnHO (Ln = lanthanide) and unprecedented coordination number decrease around hydride anions in LaHO upon higher external pressure [2],[3]. The effect of size flexibility of hydride anions may also appear in other mixed anions compounds besides oxyhydrides. Here, the high-pressure polymorphs of alkaline earth metal hydride-fluorides AHF (A = Ca, Sr, Ba) were studied up to 8 GPa. While AHF adopts the fluorite-type structure at ambient pressure with complete anion disorder, the PbCl2-type structure is formed by pressurization. The critical pressure from the fluorite-type structure to the PbCl2-type structure of AHF shows a declining trend, as the ionic radius of the A2+ cation increases. In contrast to PbCl2-type LaHO and LaOF with complete anion order [3],[4], H–/F– anions in the PbCl2-type SrHF and BaHF are partially ordered, with a preferential occupation of the hydride anions at the square-pyramidal site (vs. tetrahedral site), which is partially supported by First-principles calculations. These results provide a strategy for controlling anion ordering and local structure by external pressure in mixed-anion compounds.

Figure 1 The PbCl2-type AHF (A = Ca, Sr, Ba) with partial anion order is obtained by pressurization of fluorite-type AHF whose anions are fully disordered


May 5-7, 2021 // Online

Reference [1] T. Yamamoto, D. Zeng, T. Kawakami, V. Arcisauskaite, K. Yata, M. A. Patino, N. Izumo, J. E. McGrady, H. Kageyama and M. A. Hayward, Nat. Commun., 2017, 8, 1217. [2] H. Yamashita, T. Broux, Y. Kobayashi, F. Takeiri, H. Ubukata, T. Zhu, M. A. Hayward, K. Fujii, M. Yashima, K. Shitara, A. Kuwabara, T. Murakami and H. Kageyama, J. Am. Chem. Soc., 2018, 140, 11170–11173. [3] T. Broux, H. Ubukata, C. J. Pickard, F. Takeiri, G. Kobayashi, S. Kawaguchi, M. Yonemura, Y. Goto, C. Tassel and H. Kageyama, J. Am. Chem. Soc., 2019, 141, 8717-8720. [4] M. Glätzle, M. Schauperl, C. Hejny, M. Tribus, K. R. Liedl and H. Huppertz, Z. Anorg. Allg. Chem., 2016, 642, 1134–1142.


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Vanadium Hydride as an Ammonia Synthesis Catalyst 1*Cao, Y., 1Kobayashi, Y., 1Ubukata, H. & 1Kageyama, H. *lead presenter [email protected], Department of Energy and Hydrocarbon Chemistry, Kyoto University, Kyoto 615-8510 Ammonia is not only vital for the production of fertilizers and industrial chemicals, but also a potential hydrogen storage material and future fuel alternative.[1] In general, active elements are limited to mid-to-late transition metals (e.g., Ru, Fe, Co, etc.), and only a few early 3d transition metals (e.g., from Sc to Mn) are capable to catalyze ammonia synthesis efficiently. There are a few cases of breaking scaling rules, such as our previous study TiH2, BaTiO2.5H0.5,[2] and by Kitano et al. with BaCeO3-xHyNz,[3] there is evidence of a Mars van Krevelen mechanism of hydride (and nitride). This requires the facile diffusion of hydride/nitride species throughout the bulk lattice. TiH2, and more indirectly, the perovskites BaTiO2.5H0.5 and BaCeO3-xHyNz are all based on face-centered cubic (fcc) type close-packed structures. We suspected that if all other conditions are the same, then the transition metals and their hydrides, such as V, V2H, Nb, and NbH, with more open bcc-based structures should have better hydride/nitride diffusion, and hence higher catalytic activity. Here, single-phase hydrides of V and Nb have been found to break scaling rules and have relatively robust activity for ammonia synthesis, as shown in Figure 1. The activity of VH0.39, most likely with an active composition of VH0.44N0.16, is superior to the previously reported BaTiO2.5H0.5, and comparable to TiH2 and Cs-Ru/MgO at 400 °C under 5 MPa.[4] The metal benefits from bcc related structure which enhance hydride diffusion, in addition to having relatively lower M-N bond strength. References [1] Y. Tang, Y. Kobayashi, N. Masuda, Y. Uchida, H. Okamoto, T. Kageyama, S. Hosokawa, F. Loyer, K. Mitsuhara, K. Yamanaka, Y. Tamenori, C. Tassel, T. Yamamoto, T. Tanaka, H. Kageyama, Adv. Energy Mater. 2018, 8, 1801772. [2] Y. Kobayashi, Y. Tang, T. Kageyama, H. Yamashita, N. Masuda, S. Hosokawa, H. Kageyama, J. Am. Chem. Soc. 2017, 139, 18240–18246. [3] M. Kitano, J. Kujirai, K. Ogasawara, S. Matsuishi, T. Tada, H. Abe, Y. Niwa, H. Hosono, J. Am. Chem. Soc. 2019, 141, 20344–20353. [4] Y. Cao, A. Saito, Y. Kobayashi, H. Ubukata, Y. Tang, H. Kageyama, ChemCatChem 2021, 13, 191–195.

Figure 1 Catalytic activities for NH3 synthesis at 400 °C, 5 MPa.



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Encapsulation of YHO with PVB and PVP 1A. Dicel, 2Elbruz Murat Baba, 3Esra Özkan Zayim, 2S. Zh. Karazhanov *Ayşe Dicel [email protected], Department of Nanoscience and Nanoengineering, Istanbul Technical University Faculty of Science and Letters, 34469, Istanbul, Turkey 2 Department for Solar Energy, Institute for Energy Technology, NO-2027, Kjeller, Norway 3 Physics Engineering Department, Istanbul Technical University Faculty of Science and Letters, 34469, Istanbul, Turkey Chromogenic materials are considered as smart materials and they are very useful in energy saving applications.[1] One of the widely researched topic at this subject is the smart windows. Smart windows are preferred for modifying the incoming light and solar energy in buildings. Yttrium oxyhydride is a good alternative for photochromic applications because YHO is an emerging inorganic contender that exhibits photochromic properties.[2][3][4] In this work, polymers (PVB and PVP) are deposited via spin coating. The optimal deposition parameters are determined according to their optical properties. The photochromic performance for long cycle measurements of encapsulated coatings are investigated. The aim of the work is producing photochromic films encapsulated by polymers, investigating optical performance of double layer films and characterization of optical properties. Spin coating parameters play a key role in terms the optical performance of the double layer coating. In this case, dynamic spin coating is used for PVP and PVB encapsulation on top of YHO coated glass. Solutions are prepared as 1%, 5% and 10% solute for each polymer. All percentages were easily dissolved in 1ml of ethanol.The optimized parameters are given in the table down below: Solution Percentage (%) Amount of PVB powder (mg) Amount of PVP powder (mg)

1 26.025 26.662

5 126.99 133.685

10 233.59 269.04

Table 1: Spin coating solution parameters for PVB and PVP. After the deposition, the long cycle optical properties are investigated by using an Ocean Optics QE6500 spectrophotometer. Average transmittance measured between 600 and 900 nm during 0.5 h illumination followed by 1 h darkness in a sample kept in N2 atmosphere.


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Figure 1: Time varying optical contrast of YHO encapsulated by polymers. (PVB and PVP From this graph, it is detected that the long cycle transmission performance of PVB encapsulated YHO is better than PVP encapsulated YHO. It is found experimentally that PVB increase the optical performance of YHO photochromic films in terms of long cycle testing. References: [1] E. Materials, Introduction to Chromogenics, (2017) 1–11.

https://doi.org/10.1016/B978-0-08-101747-0.00001-5. [2] C.C. You, S.Z. Karazhanov, Effect of temperature and illumination conditions

on the photochromic performance of yttrium oxyhydride thin films, J. Appl. Phys. 128 (2020). https://doi.org/10.1063/5.0010132.

[3] E.M. Baba, J. Montero, E. Strugovshchikov, E.Ö. Zayim, S. Karazhanov, Light-induced breathing in photochromic yttrium oxyhydrides, Phys. Rev. Mater. 4 (2020) 1–8. https://doi.org/10.1103/physrevmaterials.4.025201.

[4] E.M. Baba, P.M. Weiser, E.Ö. Zayim, Temperature-Dependent Photochromic Performance of Yttrium Oxyhydride Thin Films, Phys. Status Solidi Rapid Res. Lett. 2000459 (2020) 1–5. https://doi.org/10.1002/pssr.202000459.


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Plasmonically-assisted Photocatalysis by Au-nanoparticles on STO created by galvanic replacement and exsolution

1*Kevin G. Both, 2Vilde M. Reinertsen, 2Thomas Aarholt, 2Truls Norby,2Øystein Prytz, 2Athanasios Chatzitakis *lead presenter 1 [email protected], Centre for Materials Science and Nanotechnology, University of Oslo, Gaustadalléen 21, NO-0349 Oslo Norway 2 Centre for Materials Science and Nanotechnology, University of Oslo, Gaustadalléen 21, NO-0349 Oslo Norway As part of the transition towards renewable energy sources for the production of fuels, photocatalysis has been in the interest of researchers for decades1–3. Photocatalytic water splitting is one of the reactions widely studied and of great interest, because it would allow the storage of the photon energy in chemical energy, as hydrogen and oxygen gasses1. One requirement for a photocatalyst used for water splitting is to possess a bandgap larger than 1.23 eV, with 1.9 – 2.3 eV being the ideal range due to kinetic and thermodynamic losses1. However, materials stable during photocatalytic water splitting operation typically have larger bandgaps, decreasing the catalysts' efficiency due to limited light absorption3. A way to tackle this challenge is to introduce plasmonic nanoparticles that can enhance the efficiency of the wide band gap photocatalysts by extending the light absorption edge towards the visible region. Three main mechanisms contribute to the energy transfer from the nanoparticle to the semiconductor: The scattering/trapping mechanism, the plasmon-induced energy transfer (PIRET), and the hot electron injection mechanism1,3. The combination of plasmonic nanoparticles and semiconductors, forming a heterojunction, affects the photoconversion in four different ways: (i) strong light absorption, (ii) intensive far-field light scattering, (iii) abundant hot carrier generation, and (iv) plasmonic heating effect1. Here we present a novel method of preparing such nanoparticles by a combination of in-situ metal exsolution followed by galvanic deposition. The photocatalyst under study is strontium titanate of the general formula of, Sr1+xTi1-xNixO3-δ (STO), while the nanoparticles are based on Ni and Au. In literature, Ni particles are exsolved routinely4, but they do not possess significant plasmonic activity5. On the other hand, Au exhibits high plasmonic activity but cannot be substituted into the STO4,5. We show that our proposed method successfully deposits plasmonically active nanoparticles on the surface of STO leading to increased photocatalytic activity. 1. Wu, N. Plasmonic metal–semiconductor photocatalysts and photoelectrochemical

cells: a review. Nanoscale 10, 2679–2696 (2018). 2. Walter, M. G. et al. Solar Water Splitting Cells. Chem. Rev. 110, 6446–6473 (2010).


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3. Zhang, Q. et al. Recent advancements in plasmon-enhanced visible light-driven water splitting. J. Materiomics 3, 33–50 (2017).

4. Neagu, D. et al. Nano-socketed nickel particles with enhanced coking resistance grown in situ by redox exsolution. Nat. Commun. 6, 8120 (2015).

5. Kreibig, U. & Vollmer, M. Optical Properties of Metal Clusters. (Springer Berlin Heidelberg, 2013).


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Protonation-induced Spin Frustration in Rutile Oxides 1*Namba, M., 1Takaoka, K., 1Li, H., 1Ishida, K., 1Takatsu, H. & 1Kageyama, H. 1 Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Japan. We have synthesized the protonated rutile compounds, H0.75Rh0.5V0.5O2 and H0.5Cr0.5V0.5O2, by low-temperature hydrogen gas treatment. This reaction selectively reduced nonmagnetic V5+ (d0) ions and gave H0.75Rh0.5V0.5O2 with Rh3+ (low-spin d6) and V3.5+ (d1.5), and H0.5Cr0.5V0.5O2 with Cr3+ (d3) and V4+ (d1). H0.75Rh0.5V0.5O2 with nonmagnetic Rh3+ ions has weak magnetic interactions; a spin glass transition occurs at Tf = 6 K. In contrast, protonation of Cr0.5V0.5O2 induces enhanced antiferromagnetic interactions, with the Weiss temperature of θ = −199(1) K. However, a spin glass transition takes place at lower temperature than the precursor (Cr0.5V0.5O2; Tf = 15 K, H0.5Cr0.5V0.5O2; Tf = 10 K), giving a highest frustration factor of 20 among rutile oxides (Figure 1). This strong frustration is caused by competition of the magnetic interactions in which two kinds of magnetic ions are randomly distributed. Protonation of rutile oxides and other oxides can be a useful tool to open possibilities to explore novel magnetic properties.

Figure 1 Temperature dependence of the FC (circles) and ZFC (squares) magnetic susceptibility of Cr0.5V0.5O2 (red) and H0.5Cr0.5V0.5O2 (blue) measured at 0.1 T. The inset expands the low-temperature part around the cusps.


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Characterization of Silica/Metal Oxides and Silica/Graphite Oxide Photonic crystals for Enhancing Efficiency Of Solar Cells

1Bhagyasree G. S.*, 2Dr.Nithyaja B. 1*[email protected], Govt. College Madappally, Calicut, Kerala, India-673102 2 Govt. College Madappally, Calicut, Kerala, India-673102

Photonic crystals are novel focus of the technological interest. Due to their specific response to the light, photonic crystals are being subjected for numerous applications including optical filters , Bragg mirrors etc.. Many theoretical and experimental studies show that photonic crystals have the ability to enhance the efficiency of solar cells. Her we have designed one dimensional photonic crystals of silica incorporated with metal oxides and graphite oxides. We proposed two types of photonic crystals of silica.; one dimensional multi-layers of silica incorporated with metal oxides and the left is incorporated with graphite oxide. The structures consisted of multi-layers of thin films of silica, metal oxides and graphite oxide respectively. The proposed nano photonic crystals of Silica/ Metal oxides are synthesized by sol-gel method and graphite oxide is prepared by modified Hummer’s process. The metal oxides used are alumina (Al2O3) , Zinc oxide (ZnO) and Silver oxide (Ag2O) respectively. We subjected them for theoretical and experimental analysis for understanding the optical response of the proposed photonic crystals . The SEM images of the thin films have taken and surface characterization has been carried out. UV of the thin films has been taken for analyzing the optical parameters such as reflectance, transmittance and absorption in the UV- IR and visible region. The theoretical studies are also carried out using transfer matrix method and finite difference time domain method.



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H2 generation by enhancing interfacial charge transfer in

WO3/BiVO4 photoanode for photoelectrochemical water splitting

Umesh Prasad and Arunachala M. Kannan* The Polytechnic School, Ira A. Fulton Schools of Engineering, Arizona State University, Mesa,

AZ 85212, USA

Abstract

Photoanodes containing a WO3/BiVO4 heterojunction have demonstrated promising photoelectrochemical water splitting performance, but the ability to effectively passivate the WO3/BiVO4 interface has limited charge transport and collection. Here, the WO3/BiVO4 interface is passivated with a sulfur-modified Bi2O3 interfacial layer with staggered band edge alignment to facilitate charge transfer and lifetime. Additionally, BiVO4 was co-doped with Ga3+ at Bi3+ sites and W6+ at V5+ sites (i.e., (Ga,W):BiVO4) to improve the light absorption and photogenerated charge carrier concentration. The optimized WO3/S:Bi2O3/(Ga,W):BiVO4 photoanode exhibited a photocurrent of 4.0±0.2 mA.cm-2 compared to WO3/(Ga,W):BiVO4 with 2.8±0.12 mA.cm-2 at 1.23 VRHE in K2HPO4 under simulated AM 1.5G illumination. Time-resolved photoluminescence spectroscopic analysis of the WO3/S:Bi2O3/(Ga,W):BiVO4 electrode validated the enhanced interfacial charge transfer kinetics. In operando femto- and nano-second transient absorption spectroscopy confirmed the presence of long-lived photogenerated charge carriers and revealed lower recombination initially due to rapid charge separation for WO3/S:Bi2O3/(Ga,W):BiVO4. The distribution and role of sulfur was further investigated using EDAX, XPS and TOF-SIMS depth profiling. The Co-Pi co-catalyst layer was added to achieve photocurrent 5.1±0.25 mA.cm-2 and corresponding H2 generation rate 67.3 µmol.h-1cm-2 for WO3/S:Bi2O3/(Ga,W):BiVO4/Co-Pi photoanode.


Raman spectroscopic characterization of thin films of YHO

1*Knudsen, T., 2Baba, E.M., 2Karazhanvov, S. & 1Zavorotynska, O.

*Mrs. T. Knudsen, [email protected] Department of Mathematics and Physics, University of Stavanger, P.O.Box 8600, NO-4036 Forus, Norway2 Department for Solar Energy, Institute for Energy Technology, 2027 Kjeller, Norway

Mixed-anion compounds are the compounds that contain multiple anions in the structure. Due to the different nature of individual anions, the compounds may exhibit properties different from those of the corresponding single-anion compounds. Oxyhydrides represent one class of the mixed-anion compounds that contain both H− and O2−. In this work we studied a rare-earth oxyhydride (RE-O-H) yttrium oxyhydride (YHO). This compound has interesting photochromic (PC) properties when illuminated by UV and visible light. A complete understanding of the origin of the PC effect and its limitations has not yet been established.

In this work, we studied thin films of YHO before and after UV-illumination with an aim to understand the color-changing mechanism. Thin films of YHO were synthesized by magnetron sputtering and studied by Raman spectroscopy, X-ray diffraction (XRD), and cyclic optical testing. Several samples coated with palladium (Pd) were studied with regards to electrical resistivity in an attempt of revealing if hydrogen diffusion takes part in the photodarkening. The electrical measurements were done with a four-point probe.

Thin films of YHO were illuminated with lasers of 532, 633 and 1030 nm wavelengths. For all the samples and the wavelengths, a certain sample damage was observed depending on the laser power. Depth profile studies indicated that the laser beams had penetrated through the samples. Thus, a large part of the Raman studies was focused on optimizing the measurement conditions. The peaks in the Raman spectra before and after UV exposure were assigned basing on factor group analysis (FGA) of the relevant crystalline structures and the literature. The average grain size of the samples was estimated by the Scherrer equation from properties of the XRD patterns. Average grain size decreased with increasing deposition pressure of the sputtering process.

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Theoretical study of electronic structure, optical properties and wettability of CeO2

1,2*Mamedov, D, 1Karazhanov, S.Zh. *lead presenter [email protected], Department for Solar Energy, Institute for Energy Technology, Norway 2Department of Materials Science, National Research Nuclear University, Russia Due to its advanced surface properties and many technologically important applications cerium dioxide (CeO2, ceria) has become under the focus of extensive research. This work presents a study of structural, electronic, optical properties as well as hydrophobicity of the material by first-principles calculations. In the first part, we have focused our research for bulk stoichiometric and non-stoichiometric CeO2. Study of O vacancy showed that the Ce-4f orbitals become partially occupied with electrons while in ideal crystal they remain empty. Additionally, wetting properties of CeO2 have been considered in terms of water contact angle. The calculation predicts intrinsic hydrophilicity of ceria which is confirmed by numerous experiments. In the last part the influence of the tetravalent impurities has been considered such as zirconium, silicon, titanium, and tin. It is found that all mentioned impurity atoms reduce lattice parameter, formation energy of O-vacancy and intrinsic wettability of ceria, and significantly modify its optical absorption. It allows to control photocatalytic activity of CeO2 in the wide range.


Materials and processes for production of solar hydrogen

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