Improved charge carrier mobility in a copper oxide heterostructure enhances the photocatalytic partial oxidation of benzyl alcohol to benzaldehyde†

Copper oxides have been studied over the past decade for their potential in heterogeneous photocatalysis. However, fundamental issues regarding charge carrier behavior remain largely unexplored. In this study, we investigate the charge carrier mobility of CuO, CuO/Cu₂O, and Cu₂O using time-resolved microwave conductivity in relation to their photocatalytic performance in the partial oxidation of benzyl alcohol to benzaldehyde under visible light at 455 nm. The photoconductivity-lifetime product shows a good correlation with the conversion of benzyl alcohol and the yield of benzaldehyde, with CuO/Cu₂O exhibiting the highest performance. The favorable behavior of charge carriers in CuO/Cu₂O for photocatalysis is attributed to the presence of CuO impurity, which enables more efficient separation of photoexcited electrons and holes via the S-scheme heterojunction. The charge carrier mobility and photocatalytic performance are strongly influenced by the optoelectronic properties rather than by physical properties. By introducing a small amount of CuO (5.3 mol% based on X-ray absorption near edge structure), the charge carrier mobility of Cu₂O is improved, enhancing performance even when the specific surface area decreases. Based on the photoconductivity-lifetime product, we reveal how a heterostructured photocatalyst exhibits enhanced performance. This photophysical parameter is a promising indicator for evaluating and designing future photocatalysts.