Z-Schematic Solar Water Splitting Using Fine Particles of H₂-Evolving (CuGa)_0.5ZnS₂ Photocatalyst Prepared by a Flux Method with Chloride Salts

We successfully improved a (CuGa)_0.5ZnS₂ metal sulfide photocatalyst by preparation in a molten LiCl-CsCl flux for sacrificial H₂ evolution compared to the counterpart prepared by a solid-state reaction. The particle size of the metal sulfide was controlled by changing the synthetic temperature of the flux method. The particle size of (CuGa)_0.5ZnS₂ as the H₂-evolving photocatalyst drastically affected the Z-schematic water splitting activity driven by interparticle electron transfer with RGO-(CoO_x/BiVO₄) as an O₂-evolving photocatalyst. When the (CuGa)_0.5ZnS₂ photocatalyst with a small particle size was used, the Z-schematic water splitting was enhanced by an increase in the collision frequency between Pt/(CuGa)_0.5ZnS₂ and RGO-(CoO_x/BiVO₄) particles for accelerating the interparticle electron transfer. This Z-scheme photocatalyst system gave an apparent quantum yield (AQY) of 0.80% at 440 nm and a solar-to-hydrogen conversion efficiency (STH) of 0.024% for water splitting into H₂ and O₂.