CuBi2O4/CuO photocathode with conformal CQD@Ni(OH)2 coating for stable solar water splitting

Abstract

CuBi2O4 exhibits a high onset potential and theoretically high photocurrent density due to its well-matched bandgap for solar water splitting. However, factors such as low charge carrier mobility and severe charge recombination prevent CuBi2O4 from reaching its ideal photoelectrochemical performance, while photocorrosion of the Cu element severely compromises its stability. Herein, a convenient and low-cost chemical bath deposition method has been employed to combine carbon quantum dots (CQDs) with Ni(OH)2, resulting in the preparation of a conformal CQD@Ni(OH)2 layer-coated CuBi₂O₄/CuO heterojunction photocathode. Under AM 1.5G illumination, CuBi2O4/CuO/CQD@Ni(OH)2 illustrates a photocurrent density of −1.36 mA cm−2, which is 2.12 times higher than that of CuBi2O4/CuO. More importantly, the conformal coating of CQD@Ni(OH)2 effectively prevents photocorrosion induced by oxidation-reduction reactions of Cu2+/Cu. At 0.3 VRHE, the photocurrent of CuBi2O4/CuO/CQD@Ni(OH)2 remains at 76.4% after 10000 s of chopped light illumination, significantly outperforming the 48.9% retention observed for CuBi2O4/CuO photocathode after 3600 s of chopped light illumination. This work demonstrates that the CQDs and Ni(OH)2 are good candidates for the photoelectrode overlayer with significant synergetic effects.