Visible Light-Driven Z-Scheme Water Splitting Using Oxysulfide H2 Evolution Photocatalysts

A Sm2Ti2S2O5 (STSO) oxysulfide photocatalyst prepared by a novel flux method showed a higher degree of crystallinity and greater photocatalytic activity than that prepared by conventional polymerized complex and sulfurization processes. Co-loading with both IrO2 as an oxidative cocatalyst, and Pt, as a reductive cocatalyst, was found to be essential for promoting the photocatalytic activity of the STSO. Visible light-driven Z-scheme water splitting into H-2 and O-2 was realized by utilizing the STSO photocatalyst for H-2 evolution in conjunction with a WO3 photocatalyst treated with H+ and Cs+ and loaded with PtOx for O-2 evolution, and a triiodide/iodide (I-3(-)/I-) redox couple as a shuttle electron mediator. Various other narrow band gap oxysulfide photocatalysts with H-2 evolution activity, such as La5Ti2CuS5O7 and La6Ti2S8O5, were also shown to be applicable as H-2 evolution photocatalysts in the present Z-scheme water splitting system.