Electrochemical approach to evaluate the mechanism of photocatalytic water splitting on oxide photocatalysts

Photoelectrochemical measurements of TiO2, NaTaO3, and Cr or Sb doped TiO2 and SrTiO3 photocatalysts were carried out in H2 and O2 saturated electrolytes in order to evaluate the reverse reactions during water photolysis. The poor activity of TiO2 as a result of reverse photoreactions of O2 reduction and H2 oxidation was revealed with the respective high cathodic and anodic photocurrents. The rise in the photocurrents at NaTaO3 after La doping was in harmony with the doping-induced increase in the photocatalytic activity. NiO loading suppresses the O2 photoreverse reactions, which declines photocatalytic activity, and/or promotes the photo-oxidation of water, because the O2 photo-reduction current was scarcely observed near the flatband potential. Photocurrents of O2 reduction and H2 oxidation were observed under visible light for the Cr and Sb doped SrTiO3 and TiO2, respectively. These phenomena are in harmony with the previous reports on the photocatalysts examined with sacrificial reagents.