A Z-scheme system constructed from WO3 modified TiO2 doped with Cr and Sb for visible light-driven overall water splitting

Abstract

An artificial Z-scheme system using powder photocatalysts and a reversible redox mediator for the overall water splitting has been attracting attention for producing renewable H2 using solar energy. For the efficient use of this system, the development of efficient photocatalysts utilizing longer wavelength light is essential. TiO2 doped with Cr and Sb (TiO2:Cr/Sb) is one of the visible-light-active photocatalysts which has a bandgap of ca. 2.2 eV and absorbs light up to near 600 nm. However, TiO2:Cr/Sb powder in the Fe3+/Fe2+ reversible redox mediator showed negligible activity under visible light irradiation (λ > 460 nm). In this work, it was found that the photocatalytic performance for O2 evolution over TiO2:Cr/Sb modified with WO3 (WO3-TiO2:Cr/Sb) using the Fe3+/Fe2+ mediator was more than 15 times higher than that without modification. The apparent quantum efficiency of WO3-TiO2:Cr/Sb was estimated to be ca. 0.8% at 510 nm. The overall water splitting activity of Z-scheme water splitting (H2/O2 = 2), in combination with Ru/SrTiO3:Rh, was 9 times improved by the WO3 modification compared to that without modification. From the results of photoelectrochemical measurements, it was surmised that the loaded WO3 on the surface of TiO2:Cr/Sb may promote both reduction of Fe3+ to Fe2+ and oxidation of H2O to O2.