Electrodeposition of Copper Oxides as Cost-Effective Heterojunction Photoelectrode Materials for Solar Water Splitting

Photoelectrocatalytic hydrogen production is crucial to reducing greenhouse gas emissions for carbon neutrality and meeting energy demands. Pivotal advances in photoelectrochemical (PEC) water splitting have been achieved by increasing solar light absorption. P-type Cu-based metal oxide materials have a wide range of energy band gaps and outstanding band edges for PEC water splitting. In this study, we first prepared Cu₂O thin films using electrodeposition and fabricated a heterojunction structure of CuO/Cu₂O by controlling annealing temperatures. The surface morphological, optical, and electrochemical properties were characterized using various analytical tools. X-ray and Raman spectroscopic approaches were used to verify the heterojunction of CuO/Cu₂O, while surface analyses revealed surface roughness changes in thin films as the annealing temperatures increased. Electrochemical impedance spectroscopic measurements in conjunction with the Mott–Schottky analysis confirm that the CuO/Cu₂O heterojunction thin film can boost photocurrent generation (1.03 mA/cm² at 0 V vs. RHE) via enhanced light absorption, a higher carrier density, and a higher flat band potential than CuO and Cu₂O thin films (0.92 and 0.08 mA/cm², respectively).