Strategies for the Development of Visible-light-driven Photocatalysts for Water Splitting

Photocatalysts for water splitting developed by the present authors are reviewed. A NiO (0.2 wt %)/NaTaO3:La (2%) photocatalyst with a 4.1-eV band gap showed high activity for water splitting into H2 and O2 with an apparent quantum yield of 56% at 270 nm. Many visible-light-driven photocatalysts have also been developed through band engineering by doping of metal cations, forming new valence bands with Bi6s, Sn5s, and Ag4d orbitals, and by making solid solutions between ZnS with wide band gap and narrow band gap semiconductors. Overall water splitting under visible light irradiation has been achieved by construction of a Z-scheme photocatalysis system employing the visible-light-driven photocatalysts for H2 and O2 evolution, and the Fe3+/Fe2+ redox couple as an electron relay.