Co-catalysts loaded on SrTiO3:Rh in visible-light-driven Z-scheme photocatalysis systems consisting of SrTiO3:Rh for H2 evolution, BiVO4 for O2 evolution, and Fe3+/Fe2+ for an electron mediator were investigated. The activity of the system using a Ru co-catalyst for overall water splitting was as high as that of the system using a Pt co-catalyst. The photocatalytic activity of the system using the Pt co-catalyst decreased as the partial pressures of evolved H2 and O2 were increased. In contrast, such deactivation was not observed for the system using the Ru co-catalyst. The investigation of the back-reactions revealed that water formation from H2 and O2, reduction of Fe3+ by H2, and oxidation of Fe2+ by O2 were significantly suppressed in the system using the Ru co-catalyst, resulting in good photocatalytic performance for water splitting. The (Ru/SrTiO3:Rh)-(BiVO4)-(Fe3+/Fe2+) photocatalysis system gave a quantum yield of 0.3% and a stable activity more than 70 h. This system was confirmed to be active for water splitting using a solar simulator.
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