Insight into the Improvement Mechanism of Copper Oxide/BiVO4 Heterojunction Photoanodes for Solar Water Oxidation

N-type BiVO4 films coupled with p-type copper oxide nanoparticles were investigated as photoanodes for water oxidation. Compared with the BiVO4 film, the Cu2O/BiVO4, CuO/BiVO4 and CuxO/BiVO4 films all showed significantly improved photoelectrochemical water oxidation activity and stability. As expected, the radiative recombination of charge on the three kinds of copper oxide/BiVO4 films was decreased due to the p-n junction effect between copper oxide and BiVO4. However, our investigations indicated that the electrocatalytic water oxidation on the copper oxide could be initiated when the copper oxide/BiVO4 photoanodes were irradiated by solar light; therefore, the copper oxide-coupling resulted in a more obvious improvement in the water oxidation kinetics of BiVO4 than the thermodynamic improvement in the charge separation of BiVO4. Of the three kinds of copper oxide/BiVO4 films, the CuxO/BiVO4 film comprising BiVO4 film coupled with a combination of Cu2O/CuO nanoparticles showed the best solar water oxidation performance due to the better electrocatalytic activity for water oxidation of CuxO compared with Cu2O or CuO alone. The kinetic investigations and analyses in the present work provide comprehensive insight into the mechanism of the copper oxide/BiVO4 photoanodes for solar water oxidation. (C) 2019 The Electrochemical Society.