Recent Advances in (Oxy)sulfide Photocatalysts for Solar-driven Water Splitting and CO2 Reduction

Abstract

Metal sulfides are an attractive material group as photocatalysts in terms of utilizing visible light in sunlight. However, S2− in metal sulfides are oxidized by photogenerated holes. Hence, the metal sulfides rarely oxidize water to O2 under photoirradiation. To achieve water splitting and CO2 reduction as artificial photosynthetic reactions in which water is used as a sole electron donor, application of metal sulfides to photoelectrode and Z-scheme systems is one useful strategy. In both systems, metal sulfides are used as a reduction part that is photocathode and photocatalyst for the reduction of water and CO2. Although metal sulfides only contain S2− as the anion, metal oxysulfides contain S2− and O2−. The valence band maximum formed by the O 2p and S 3p hybridized orbitals of oxysulfides stabilizes S2− ions when compared to those in the sulfides. Such metal oxysulfides are active for photocatalytic water oxidation to O2.