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

A Sm 2 Ti 2 S 2 O 5 (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 IrO 2, 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 WO 3 photocatalyst treated with H + and Cs + and loaded with PtO x 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 La 5 Ti 2 CuS 5 O 7 and La 6 Ti 2 S 8 O 5, were also shown to be applicable as H 2 evolution photocatalysts in the present Z-scheme water splitting system.