Photocatalytic water splitting under visible light utilizing I3−/I− and IO3−/I− redox mediators by Z-scheme system using surface treated PtOx/WO3 as O2 evolution photocatalyst

Abstract

Water oxidation reactions over a surface treated PtO_x/WO₃ photocatalyst in the presence of IO₃⁻ or I₃⁻ ions were investigated. When the IO₃⁻ ion was used as an electron acceptor, PtO_x/WO₃ treated by thermal treatment using Cs₂CO₃ aqueous solution followed by H⁺-exchange-treatment (PtO_x/H-Cs-WO₃) showed ca. 4 times higher activity compared with PtO_x/WO₃ without surface treatment. The apparent quantum yield at 420 nm was 20%. Moreover, when the I₃⁻ ion was used as the electron acceptor, the activity of PtO_x/WO₃ was negligible, while PtO_x/H-Cs-WO₃ showed a high activity for water oxidation. The cesium surface treatment also had an excellent effect for the improvement of photocatalytic performance of TiO₂. The activity of a water splitting reaction under visible light by the Z-scheme system that combined Pt/SrTiO₃:Cr/Ta with PtO_x/H-Cs-WO₃ was 3 times higher than that using PtO_x/WO₃ as an O₂ evolution photocatalyst. Moreover, owing to the contribution from both IO₃⁻ and I₃⁻ ions as redox mediators, the water splitting reaction stoichiometrically proceeded in a wider pH region (pH 2–9).