Enhancement of Photocatalytic Activity of Electrodeposited Cu₂O by Reducing Oxygen Vacancy Density

Oxygen vacancies (OVs) are common in cuprous oxide (Cu2O), and the effect of OVs on photocatalytic activity remains unclear. In this study, the photocatalytic activity of Cu2O photoanode with varying OV densities was investigated. The OV density in Cu2O was controlled by adjusting the Cu(CH3COO)2 concentration in a precursor solution used for the electrodeposition of Cu2O. The oxygen deficiency decreased from 5.2 to 0.4%, characterized through X-ray diffraction, when the Cu(CH3COO)2 concentration was reduced from 0.04 to 0.005 M due to the decrease in the mismatch between the concentrations of Cu(CH3COO)2 and OH–. The decrease in the OV density increased the excess photocharge density of Cu2O, as verified by photoluminescence and photovoltage measurements. Furthermore, the decrease in the OV density resulted in the enhancement of the spectral response and photocatalytic activity; this was attributed to the increase in the excess photocharge density. OVs in Cu2O mainly mediated the photocharge recombination and played a negative role in photocatalytic activity.