Improvement of CuO photostability with the help of a BiVO4 capping layer by preventing self-reduction of CuO to Cu2O

Abstract We fabricated BiVO4/CuO heterojunction photoelectrodes by depositing BiVO4 capping layers on CuO photoelectrodes and investigated the photocurrent density and photostability of the photoelectrodes according to the number of BiVO4 depositions using the spin coating method. The morphological, structural, optical, electrical and photoelectrochemical properties of the BiVO4/CuO photoelectrode were investigated using field-emission scanning electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, electrochemical impedance spectroscopy, and three-electrode potentiostat/galvanostat equipment. XRD and XPS results showed that the crystallinities and binding energies of BiVO4/CuO photoelectrodes were affected by BiVO4 compared to the CuO photoelectrode. In particular, XPS measurements showed that the Cu 2p3/2 peak binding energies of the CuO photoelectrode and BiVO4/CuO photoelectrodes with poor photostabilities shifted to those of Cu2O, showing self-reduction from CuO to Cu2O, after photostability measurement. In contrast, BiVO4/CuO photoelectrodes with proper BiVO4 deposition cycles showed good photostabilities without self-reduction. The BiVO4/CuO photoelectrode with 4 BiVO4 deposition cycles showed a high photostability of 76.2% via photocorrosion suppression, which is a much improved result compared to the single CuO photoelectrode with a photostability of 13.1%. However, the photocurrent density of −1.77 mA/cm2 (vs. SCE at −0.55 V) is still low, and further study is necessary.