CuCoOx/BiVO4 multifunctional catalyst for organics degradation, water oxidation, and O2 reduction under visible light

Monoclinic BiVO4 (BiV) is an excellent photoanode for water oxidation, but it is a poor photocatalyst for organic oxidation due to slow O-2 reduction. Herein we report a 94-fold increased photocatalytic activity of BiV through a surface deposited CuCoOx. The model reaction was phenol degradation in aqueous solution under visible light. CuCoOx, CuOx, and CoOx were prepared in butanol, separately, while CuCo2O4 was prepared in aqueous solution. Solid characterization showed that CuCo2O4 was Cu0.92Co2.08O4, but CuCoOx was a mixture of Cu0.92Co2.08O4, CuOx, and CoOx. Notably, the rate of phenol oxidation on CuCoOx/BiV was not only larger than those on Pt/BiV, CuCo2O4/BiV, CuOx/BiV, and CoOx/BiV, but also larger than the sum of the rates obtained for the latter three. Photoluminescence study revealed that all co-catalysts improved the efficiency of charge separation of BiV, with the trend similar to that for phenol photo-oxidation. Electrochemical study with a BiV film electrode showed that among four co-catalysts, CuOx was the most active for O-2 reduction, CoOx for water oxidation, and CuCo2O4 for water photo-oxidation. According to the measured band edge potentials for semiconductors, a possible charge transfer from BiV to co-catalyst is proposed, including the electron transfer for CuOx/BiV, the hole transfer for CoOx/BiV and CuCo2O4/BiV, and the sequential electron transfer for CuCoOx/BiV.