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 O₂ 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 Cu_0.92Co_2.08O₄, but CuCoOx was a mixture of Cu_0.92Co_2.08O₄, 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 O₂ 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.