Hydrogen production from water on oxynitride photocatalysts

Oxynitrides are presented as effective non-oxide photocatalysts for overall water splitting. RuO2-loaded germanium nitride (beta-Ge3N4) is shown to achieve stoichiometric decomposition of H2O into H-2 and O-2 under ultraviolet irradiation (lambda > 200 nm). A novel solid solution of GaN and ZnO, (Ga1-xZnx)(N1-xOx), with a band gap of 2.4-2.8 eV (depending on composition) achieves overall water splitting under visible light (k > 400 nm) when loaded with an appropriate cocatalyst. The narrower band gap of the solid solution originates from the bonding between Zn and N atoms at the top of the valence band. The photocatalytic activity of (Ga1-xZnx)(N1-xOx) for overall water splitting is dependent strongly on both the cocatalyst and the crystallinity and composition of the material. The quantum efficiency of (Ga1-xZnx)(N1-xOx) with Rb and Cr mixed-oxide (Rh2-yCryO3) nanoparticles reaches 2-3 % at 420-440 nm, which is the highest reported efficiency for overall water splitting in the visible-light region.