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 H) and O-2 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 Bi-6s, Sn-5s, and Ag-4d 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 H-2 and O-2 evolution, and the Fe3+/Fe2+ redox couple as an electron relay.