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Bismuth vanadate (BiVO4) offers high photon efficiencies in solar photo-anodes, due to its suitable semiconductor band gap energies and associated visible light absorption. In well-tuned conditions, such anodes enable green hydrogen generation in photoelectrochemical water splitting cells. Bismuth vanadate films have to ensure high efficiencies in electron/hole pair generation and sufficiently high rates of charge transfer to the conducting substrate and the electrolyte, respectively. Thus, the tuning of coating properties has to aim for high phase purity, good layer integrity as well as optimum diffusion path lengths. In order to explore the potential of aerosol deposition to produce BiVO4 films with high photoelectrochemical activity and to elucidate influences on microstructure and application properties, powder sizes and spraying parameters had to be tailored. By ball milling over durations of up to 20 min, particles sizes in the range from 8.3 down to 0.6 µm were obtained. With respect to spray conditions, the process gas pressure was varied from 1.0 to 2.1 bar corresponding to gas flow rates of 10-40 l/min. The wide range of powder sizes and parameters in aerosol deposition allowed for developing a window of deposition in order to derive the most promising combinations for layer build-up. Optimum parameter sets in application on stainless steel substrates were transferred to FTO-coated glass substrates for backlit cell layouts. The thickness and conductivity of the layers were adjusted to a layer thickness range of 200-500 nm in order to achieve maximum photocurrents. The production of homogeneous, large-scale prototypes demonstrates that aerosol deposition is suitable for processing layers for solar energy harvesting with high photo current densities of up to 3.55 mA/cm2. [ABSTRACT FROM AUTHOR]

Amorphous TiO2 films deposited by Atomic Layer Deposition (ALD) are recently being employed as corrosion protection coatings for photoanodes and photocathodes. However, these protective films are not immune to degradation. We have applied spectroscopic ellipsometry to quantify the loss of material, and the corresponding etch rates, for amorphous TiO2 in photoelectrochemical cells under a wide range of conditions, at open- and short-circuit, in darkness and under illumination with different wavelength ranges. In 0.5 M sulfuric acid, we found corrosion to proceed via two routes: a chemical process, with an activation energy of 57 kJ mol−1, and photoelectrochemically, once excess generated charge carriers are extracted. Compared to the dark condition, the combined degradation rate is more than doubled under illumination at 100 mW cm−2 and at pH 0.3–2. The observed etch processes are highly dependent on the acidic pH values and largely suppressed at pH > 4. This has important implications for the selection of operating conditions for practical photoelectrochemical cells using amorphous TiO2 protective coatings. [ABSTRACT FROM AUTHOR]

An essential step toward enabling the production of renewable and cost-efficient fuels is an improved understanding of the performance of energy conversion materials. In recent years, there has been growing interest in ternary metal oxides. Particularly, α-SnWO 4 exhibited promising properties for application to photoelectrochemical (PEC) water splitting. However, the number of corresponding studies remains limited, and a deeper understanding of the physical and chemical processes in α-SnWO 4 is necessary. To date, charge-carrier generation, separation, and transfer have not been exhaustively studied for SnWO 4 -based photoelectrodes. All of these processes depend on the phase composition, not only α-SnWO 4 but also on the related phases SnW 3 O 9 and WO 3 , as well as on their spatial distributions resulting from the coating synthesis. In the present work, these processes in different phases of tin tungstate films were investigated by transient surface photovoltage (TSPV) spectroscopy to complement the analysis of the applicability of α-SnWO 4 thin films for practical PEC oxygen evolution. Pure α-SnWO 4 films exhibit higher photoactivities than those of films containing secondary SnW 3 O 9 and WO 3 phases due to the higher recombination of charge carriers when these phases are present.

The long-term operation of refractory-metal-based metamaterials is crucial for applications such as thermophotovoltaics. The metamaterials based on refractory metals like W, Mo, Ta, Nb, and Re fail primarily by oxidation. Here, the use of the noble metal Ir is proposed, which is stable to oxidation and has optical properties comparable to gold. The thermal endurance of Ir in a 3-layer-system, consisting of HfO 2 /Ir/HfO 2 , by performing annealing experiments up to 1240 °C in a pressure range from 2 × 10 -6  mbar to 1 bar, is demonstrated. The Ir layer shows no oxidation in a vacuum and inert gas atmosphere. At temperatures above 1100 °C, the Ir layer starts to agglomerate due to the degradation of the confining HfO 2 layers. An in situ X-ray diffraction experimental comparison between 1D multilayered Ir/HfO 2 and W/HfO 2 selective emitters annealed at 1000 °C, 2 × 10 -6  mbar, over 100 h, confirms oxidation stability of Ir while W multilayers gradually disappear. The results of this work show that W-based metamaterials are not long-term stable even at 1000 °C. However, the oxidation resistance of Ir can be leveraged for refractory plasmonic metamaterials, such as selective emitters in thermophotovoltaic systems with strong suppression of long wavelength radiation., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Hydrogen produced from solar energy has the potential to replace petroleum in the future. To this respect, there is a need in the abandoned and efficient materials that can continuously split water molecules using solar energy. In this report, an ammonium thiomolybdate (ATM: (NH 4 ) 2 Mo 3 S 13 ) is evaluated as a p-type semiconductor film photocathode for hydrogen evolution reaction. The ATM thin films are prepared by spin-coating on fluorine-doped tin oxide substrates, and their structural, morphological, optical, photoelectrical, and photoelectrochemical (PEC) properties are studied. Transient surface photovoltage (TSPV) spectroscopy and spectroscopic ellipsometry indicate the band gap E g = 1.9 eV for the ATM thin films. Furthermore, the photovoltage of the ATM thin films measured by TSPV is correlated to the photocurrents measured by the PEC characterization that can be used to evaluate the material potential for hydrogen generation. The films exhibit a low photocurrent density of 46 μA cm -2 at 0 V RHE . However, its combination with WSe 2 thin-film photocathodes results in a significant increase in photocurrent density up to 4.6 mA cm -2 at 0 V RHE (100 times). The reason for such a strong charge carrier transfer effect for ATM/WSe 2 heterojunction photocathodes is studied by TSPV spectroscopy that allows a comprehensive evaluation of potential photovoltaic materials toward PEC hydrogen production. Furthermore, the photovoltage generated by a WSe 2 thin film is 30 times lower than that of its single crystal, which indicates that the quality of WSe 2 thin films should be improved for faster PEC hydrogen evolution.

Electronic properties and charge transfer processes were studied in an n-Si(n ++ )/TiO 2 (ALD) system at an amorphous TiO 2 /anatase transition by transient surface photovoltage spectroscopy at constant photon flux. The TiO 2 layers were deposited by atomic layer deposition (ALD) onto highly doped silicon (c-Si(n ++ )), and the phase composition of the TiO 2 layers changed with increasing thickness from amorphous to the anatase polymorph as anatase crystallites started to grow at the surface. Depending on phase composition, the band gap of TiO 2 correlated with the characteristic energy of exponential tails. In most cases, photogenerated electrons were separated toward the back contact. For photogeneration in c-Si(n ++ ), electron back transfer was limited by Auger recombination with holes in the surface space charge region of c-Si(n ++ ), and by electron transfer across the interface, either via exponentially distributed states near the conduction band edge of amorphous TiO 2 or via distance-dependent recombination with holes trapped in anatase. For photogeneration in TiO 2 , electron back transfer was limited by trapping in TiO 2 . Under strong light absorption in amorphous TiO 2 with anatase crystallites on top, electrons were preferentially separated toward the TiO 2 surface.

Conductive metal oxides represent a new category of functional material with vital importance for many modern applications. The present work introduces a new conductive metal oxide V 13 O 16 , which is synthesized via a simplified photoelectrochemical procedure and decorated onto the semiconducting photocatalyst BiVO 4 in controlled mass percentages ranging from 25% to 37%. Owing to its excellent conductivity and good compatibility with oxide materials, the metallic V 13 O 16 -decorated BiVO 4 hybrid catalyst shows a high photocurrent density of 2.2 ± 0.2 mA cm -2 at 1.23 V versus reversible hydrogen electrode (RHE). Both experimental characterization and density functional theory calculations indicate that the superior photocurrent derives from enhanced charge separation and transfer, resulting from ohmic contact at the interface of mixed phases and superior electrical conductivity from V 13 O 16 . A Co-Pi coating on BiVO 4 -V 13 O 16 further increases the photocurrent to 5.0 ± 0.5 mA cm -2 at 1.23 V versus RHE, which is among the highest reported for BiVO 4 -based photoelectrodes. Surface photovoltage and transient photocurrent measurements suggest a charge-transfer model in which photocurrents are enhanced by improved surface passivation, although the barrier at the Co-Pi/electrolyte interface limits the charge transfer., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In the highly competitive market of fuel cells, solid alkaline fuel cells using liquid fuel (such as cheap, non-toxic and non-valorized glycerol) and not requiring noble metal as catalyst seem quite promising. One of the main hurdles for emergence of such a technology is the development of a hydroxide-conducting membrane characterized by both high conductivity and low fuel permeability. Plasma treatments can enable to positively tune the main fuel cell membrane requirements. In this work, commercial ADP-Morgane® fluorinated polymer membranes and a new brand of cross-linked poly(aryl-ether) polymer membranes, named AMELI-32®, both containing quaternary ammonium functionalities, have been modified by argon plasma treatment or triallylamine-based plasma deposit. Under the concomitant etching/cross-linking/oxidation effects inherent to the plasma modification, transport properties (ionic exchange capacity, water uptake, ionic conductivity and fuel retention) of membranes have been improved. Consequently, using plasma modified ADP-Morgane® membrane as electrolyte in a solid alkaline fuel cell operating with glycerol as fuel has allowed increasing the maximum power density by a factor 3 when compared to the untreated membrane.