Photocatalytic hydrogen production over new oxide

The new oxide CuLaO 2.62 , synthesized through solid reaction under O 2 atmosphere from CuLaO 2 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 ρ 300 K ( 2485 Ω cm ) and the thermopower S 300 K ( 93 μ V K - 1 ) suggest a mechanism conduction by small polarons hopping between Cu 2 + / 3 + . The material is thermally stable up to ∼ 500 ∘ C beyond which it converts irreversibly to CuLa 2 O 4 . Its photocatalytic ability, in contact with S 2 - and SO 3 2 - aqueous solutions for H 2 production, has been evaluated in connection with some physical parameters. The title oxide is chemically stable in KOH media, its conduction band ( - 1.46 V sce ) , determined from photoelectrochemical measurements, lies below the H 2 O / H 2 level ( - 0.82 V sce ) leading to a spontaneous H 2 -evolution under visible light. The most H 2 , with a generation rate of 0.465 ml h - 1 mg - 1 , was obtained in an aqueous sulfite solution ( 0.1 M SO 3 2 - , pH 8.04) and increases parallel to S 2 O 6 2 - and/or SO 4 2 - 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 S 2 O 6 2 - and S n 2 - with H 2 O .