Ta3N5 thin-film photoelectrodes were prepared using a reactive sputtering technique, and their properties for photoelectrochemical water splitting under visible light were investigated. The crystal phases of the films were dependent on the sputtering conditions, such as the N-2/O-2 ratio of the sputtering atmosphere and the substrate temperature (T-s). Single-phase Ta3N5 films were obtained by sputtering at N-2/O-2 = 30 and T-s = 1013 K with post-annealing in an NH3 flow. The Ta3N5 photoelectrodes had an anodic photoresponse in water photoelectrolysis, although the photocurrent rapidly decreased because of self-oxidation of the photoanode by photogenerated holes. However, modification of the NH3-treated Ta3N5 films with IrO2 promoted the oxidation of water and suppressed the self-oxidation of Ta3N5. (C) 2010 Elsevier B.V. All rights reserved.