Synthesis and Characterization of Rich Delafossite CuYO2+X Application for Solar Energy Conversion

Here we report the synthesis and some physical properties of superoxides CuYO2.51 and CuYO2.25 prepared from the delafossite CuYO2 respectively by thermal oxidation at 380 °C under O2-flow and soft chemistry in NaBrO (5N) solution and their applications as catalysts for solar energy conversion in a chemical H2 evolution, upon visible light. The oxygen insertion was accompanied by partial oxidation of Cu+ lattice. For CuYO2.25, the chemical analyses as well as magnetic data reveal the presence of mixed valent states containing at least formally an equal number of Cu+ and Cu2+. In air, CuYO are thermally stable up to 500 °Cabove wich they undergo . an irreversible 2+X conversion into CuY2O5. The oxides are chemically stable in basic media and under illumination, they are stabilizsd by hole consumption reactions involving SO32- and S2- as holes scavengers. The flat band potentials lying between 0,17 and 0,17 eV, are located above the H2O/H2 level, leading to a spontaneous H2- evolution. The rate of H2-formation is altered by the oxygen insertion and the best photoactivity is obtained over CuYO2.25 immersed at 0.025 M sulfide S2- solution. A photoelectrochemical study is reported for comparison with photoactivity results.