The new oxide CuLaO2.62, synthesized through solid reaction under O-2 atmosphere from CuLaO2 at 380 degrees C, crystallizes in a pseudodelafossite structure. The formulation comes from thermal analysis and iodometric titrations. It exhibits a p-type semiconductivity; the resistivity rho(300) (K) (2485 Omega cm) and the thermopower S-300 K (93 mu V K-1) suggest a mechanism conduction by small polarons hopping between Cu2+/3+. The material is thermally stable up to similar to 500 degrees C beyond which it converts 3 aqueous solutions for H-2 production, has irreversibly to CuLa2O4. Its photocatalytic ability, in contact with S2- and SO2 been evaluated in connection with some physical parameters. The title oxide is chemically stable in KOH media, its conduction band (-1.46V(sce)), determined from photoelectrochemical measurements, lies below the H2O/H-2 level (-0.82V(sce)) leading to a spontaneous H-2-evolution under visible light. The most H-2, with a generation rate of 0.465ml h(-1) mg(-1), was obtained in an aqueous sulfite solution (0.1 M SO32-, pH 8.04) and increases parallel to S2O62- and/or SO42- formation. The thermal enhancement of the photoactivity is attributed to an increase in carrier doping moving in narrow bands of Cu-3d parentage. The whole photoelectrochemical process is limited by the supply of electrons at the interface. The photoactivity slows down with time because of competitive reductions of end products S2O62- and SO42- with H2O. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.