Influence of SnWO₄, SnW₃O₉, and WO₃ Phases in Tin Tungstate Films on Photoelectrochemical Water Oxidation

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-SnWO₄ 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-SnWO₄ is necessary. To date, charge-carrier generation, separation, and transfer have not been exhaustively studied for SnWO₄-based photoelectrodes. All of these processes depend on the phase composition, not only α-SnWO₄ but also on the related phases SnW₃O₉ and WO₃, 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-SnWO₄ thin films for practical PEC oxygen evolution. Pure α-SnWO₄ films exhibit higher photoactivities than those of films containing secondary SnW₃O₉ and WO₃ phases due to the higher recombination of charge carriers when these phases are present.