Photocatalytic hydrogen evolution over CuCrO2

We have been studying the technical feasibility of a photochemical H2 evolution based on a dispersion of CuCrO2 powder in aqueous electrolytes containing various reducing agents (S2−, SO32- and S2O32-). The title oxide combines a fair resistance to corrosion with an optimal band gap Eg of 1.32 eV. The intercalation of a small amount of oxygen should be accompanied by a partial oxidation of Cu+ into Cu2+ implying a p-type semiconductivity. The S2− oxidation inhibits the photocorrosion and the H2 evolution increases parallel to polysulfides Sn2- formation. Most of H2 is produced when p-CuCrO2 is connected to n-Cu2O formed in situ. H2 liberation proceeds mostly on CuCrO2 while the oxidation of S2− takes place over Cu2O surface and the hetero system Cu2O/CuCrO2 is optimized with respect to some physical parameters. The photoactivity is dependent on preparation conditions and lowering the synthesis temperature through nitrate route leads to an increase in specific surface area Ssp. The photoelectrochemical H2 production is a multistep process where the rate determining step is the arrival of electrons at the interface because of their low mobility. Prolonged irradiation (>80 min) leads to a pronounced decrease of the photoactivity; the tendency toward saturation is due to the undesired back reduction of polysulfides Sn2- in a closed system and to their strong absorption in the visible region (λmax = 520 nm).