Synthesis and Characterization of Rich Delafossite CuYO_(2+x) Application for Solar Energy Conversion

摘要

Here we report the synthesis and some physical properties of superoxides CuYO_(2.51) and CuYO_(2.25) 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 CuYO_(2.25), 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 Cu~(2+)'. In air, CuYO_(2+x) are thermally stable up to 500 °Cabove wich they undergo an irreversible conversion into CuY2O5. The oxides are chemically stable in basic media and under illumination, they are stabilizsd by hole consumption reactions involving SO32- and S~(2-) 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 Lb-evolution. The rate of H2-formation is altered by the oxygen insertion and the best photoactivity is obtained over CuYO_(2.25) immersed at 0.025 M sulfide S~(2-) solution. A photoelectrochemical study is reported for comparison with photoactivity results.