CuIn3Se5, prepared by the fusion technique crystallizes in the P-chalcopyrite structure and exhibits n-type conduction ascribed to indium excess. The electrical conductivity follows an Arrhenius-type law with activation energy of 0.35 eV and an electron mobility of 10(-4) cm(2) V-1 s(-1) in conformity with small polaron hopping. The optical gap (1.19 eV), determined from the diffuse reflectance spectrum, is properly matched to the sun spectrum. CuIn3Se5 is chemically stable and a corrosion rate of only 1.2 mu mol year(-1) is found at neutral pH. The slope and the intercept to C-2 = 0 of the Mott Schottky plot gives respectively an electron density of 3.75 x 10(16) cm(-3) and a flat band potential of -0.22 V-SCE. The conduction band (-0.74 V-SCE) therefore lies below the potential of H2O/H-2 couple and as application. H-2 photo-production is successfully achieved over CuIn3Se5. The best performance is obtained in S2O32- solution (10(-2) M, pH similar to 7) with an evolution rate of 0.54 mL g(-1) min(-1). The conversion efficiency (0.13%) is due to the formation of small depletion width (230 nm) and a large diffusion length compared to a very large penetration depth (similar to 1 mu m). Attempts have been made to improve the photoactivity and the hetero-system CuIn3Se5/WO3 is compared favorably with respect to CuIn3Se5. The photoactivity is ascribed to electrons transfer from the sensitizer CuIn3Se5-conduction band (CB), acting as electrons pump, to WO3-CB (-0.4 V-SCE) resulting in the enhanced water reduction. (C) 2012 Elsevier B.V. All rights reserved.