Photocatalytic hydrogen production over new oxide CuLaO2.62CuLaO2.62

The new oxide CuLaO2.62CuLaO2.62, synthesized through solid reaction under O2O2 atmosphere from CuLaO2CuLaO2 at 380∘C, crystallizes in a pseudodelafossite structure. The formulation comes from thermal analysis and iodometric titrations. It exhibits a p-type semi-conductivity; the resistivity ρ300K(2485Ωcm) and the thermopower S300K(93μVK-1) suggest a mechanism conduction by small polarons hopping between Cu2+/3+Cu2+/3+. The material is thermally stable up to ∼500∘C beyond which it converts irreversibly to CuLa2O4CuLa2O4. Its photocatalytic ability, in contact with S2-S2- and SO32- aqueous solutions for H2H2 production, has been evaluated in connection with some physical parameters. The title oxide is chemically stable in KOH media, its conduction band (-1.46Vsce), determined from photoelectrochemical measurements, lies below the H2O/H2H2O/H2 level (-0.82Vsce) leading to a spontaneous H2H2-evolution under visible light. The most H2H2, with a generation rate of 0.465mlh-1mg-1, was obtained in an aqueous sulfite solution (0.1MSO32-, 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 Sn2- with H2OH2O.