High-efficiency water oxidation and energy storage utilizing various reversible redox mediators under visible light over surface-modified WO3

Abstract

Tungsten trioxide (WO₃) powder, treated with various metal salt solutions, was used for the photocatalytic oxidation of water into O₂; the reaction was accompanied by the reduction of various redox oxidants. The photocatalytic activity of WO₃ was remarkably improved by thermal treatment with alkali metal and silver salt aqueous solutions. Cs-treated WO₃ showed the highest activity. The WO₃ particles were covered with a very thin layer of a cesium tungstate species, and the ion-exchangeable sites on the WO₃ surface were formed by Cs-treatment. The activity of Cs-treated WO₃ was further improved by ion exchange of H⁺ and Fe²⁺ ions and was 24 times higher than the activity of WO₃ without treatment. All methods of O₂ evolution using IO₃⁻ and VO₂⁺ on WO₃ were also significantly improved with Cs-treatment, which suppressed the reverse reaction of the oxidation of the various redox reductants. The optimized WO₃ in Fe(ClO₄)₃ aqueous solution had a high quantum yield (31% at 420 nm) and solar-to-chemical energy conversion efficiency (0.38%).