Hydrothermal-synthesized SrTiO3 photocatalyst codoped with rhodium and antimony with visible-light response for sacrificial H2 and O2 evolution and application to overall water splitting

The codoping effect of antimony on the photocatalytic activity of visible-light-driven SrTiO 3 doped with rhodium (SrTiO 3 :Rh) was investigated. SrTiO 3 doped with rhodium and antimony (SrTiO 3 :Rh/Sb) prepared by a hydrothermal method was found to be active for photocatalytic H 2 evolution from an aqueous methanol solution and O 2 evolution from an aqueous silver nitrate solution under visible light irradiation, although SrTiO 3 doped with rhodium and no antimony was active only for the H 2 evolution. Photocatalytic activities of SrTiO 3 :Rh/Sb were strongly dependent on the ratio of codopant to dopant (Sb/Rh). Diffuse reflection spectroscopy (DRS), electron spin resonance (ESR), Raman, and action spectrum analyses revealed the contribution of rhodium and antimony to visible-light response of SrTiO 3 :Rh/Sb. Unstable and reversible Rh 3+ ions in oxidation state were the superior species for the H 2 evolution. On the other hand, Rh 3+ ions stabilized by codoping of antimony without the formation of Rh 4+ ions and oxygen defects which would work as undesirable recombination sites between photogenerated electrons and holes played an important role in the O 2 evolution. Moreover, when an IrO X cocatalyst was loaded on the surface of the SrTiO 3 :Rh/Sb photocatalyst, the photocatalytic activity of the O 2 evolution drastically increased. The apparent quantum yield for the H 2 evolution over Pt(0.3 wt%)/SrTiO 3 :Rh(1%)/Sb(1%) and the O 2 evolution over IrO X (3.0 wt%)/SrTiO 3 :Rh(1%)/Sb(1%) at 420 nm were 0.8% and 4.5%, respectively. The Z -scheme system composed of Ru(1.0 wt%)/SrTiO 3 :Rh(2%) as a H 2 -evolving photocatalyst, IrO X (3.0 wt%)/SrTiO 3 :Rh(1%)/Sb(1%) as an O 2 -evolving photocatalyst, and an Fe 3+ /Fe 2+ redox couple as an electron mediator showed photocatalytic activity for overall water splitting under visible light irradiation.