Z-Scheme Water Splitting Utilizing Fe2O3 as an Oxygen-Evolving Photocatalyst

Fe2O3 is a widely studied material as a photoanode and O2 evolution photocatalyst responsive to visible light. Although Z-scheme systems employing Fe2O3-based photocatalysts have been reported, the kind of combined H2-evolving photocatalyst is limited to C3N4. In this study, we demonstrated water splitting by the Z-scheme systems utilizing Ti-doped Fe2O3 (Fe2O3:Ti) and Rh-doped SrTiO3 (SrTiO3:Rh). Z-scheme water splitting (Z-WS) was achieved by the interparticle electron transfer from Fe2O3:Ti to SrTiO3:Rh. Ti doping was essential to achieve Z-WS. Doping Ti into Fe2O3 increased the carrier density, causing improvement of electronic conductivity and enhancement of charge separation through band bending. These factors remarkably improved the photoelectrochemical property, resulting in achievement of Z-WS. The Ru/SrTiO3:Rh-Fe2O3:Ti system was active for water splitting even without cocatalyst modification of Fe2O3:Ti. The activity was improved by the IrOx deposition, while modification with MnOx, FeOx, CoOx, and RhOx decreased activity. The impregnation method involving heat treatment at 500–600 °C and the adsorption method followed by heat treatment at 500 °C were found to be an appropriate condition for IrOx deposition through systematic characterization. The external quantum yield of the present system was determined to be 0.23% at 430 nm.