A new oxynitride, Ga-Zn-In-O-N, having a d(10) electronic configuration was prepared, and its behavior as a visible-light-driven photocatalyst for water splitting was examined. It is found to have an absorption band edge near 600 nm and photocatalyze H-2 and O-2 evolution under visible light (lambda > 400 nm) in the presence of an appropriate electron donor or accepter. Unmodified Ga-Zn-In-O-N is somewhat unstable in the water oxidation reaction, but the catalytic system is stabilized and improved by modi. cation with cobalt oxide as an oxygen evolution promoter. (C) 2009 Elsevier B.V. All rights reserved.