Enhancing the Photoelectrochemical Activity of CuO/ZnO Junction Photocathodes for Water Splitting

To facilitate fast transfer of photogenerated electrons and surface stability, the CuO photocathode needs to be coupled with another heterojunction material. Here, we propose CuO/ZnO heterojunctions as photocathodes for photoelectrochemical (PEC) water splitting. First, CuO was grown on a Cu substrate, either in the form of a foil or mesh gauge, via anodization followed by postheating treatment. Subsequently, ZnO was electrodeposited on the grown CuO. The grown CuO film was composed of two-dimensional nanoplates aligned vertically against the substrate. The film morphology changed to flower-like or nearly spherical when ZnO was deposited by electrodeposition. Based on its open-circuit potential (OCP), overpotential and current density, CuO/ZnO grown on the Cu mesh exhibited better PEC performance than its counterpart grown on the Cu foil. When the mesh substrate was used, the surface area of the grown nanostructures was high and reached approximately 102.42 m² g^-1. The OCP of the CuO/ZnO mesh reached a low value of approximately -137 mV; this value quantitatively indicated that its PEC activity was more favorable for the hydrogen evolution reaction (HER). Moreover, the overpotential at the benchmark current density of 10 mA cm^-2 for the Cu mesh was 379 mV, and this value was lower than those of the other photocathode materials.