Effect of Pre-sodium Hydroxide and Post-heat Treatments on Copper Oxide-Based Photocathode: A Perspective on Photoelectrochemical Water Splitting and CO₂ Reduction

CuO photocathodes are p-type semiconductors used in photoelectrochemical cells to split water molecules into H₂ and O₂ gases and reduce CO₂ molecules to valuable chemical products such as carbon monoxide (CO), methane (CH₄), or even hydrocarbons. This work demonstrates pre- and post-treatment using the electrochemical deposition method for CuO photocathodes. Cu ions were deposited on a fluorine-doped tin oxide substrate by applying electricity. Next, the prepared Cu film was ultrasonically treated with 1 M NaOH. The as-prepared Cu film was clear and transparent. The structure and surface properties of the thin films were characterized by x-ray diffraction, scanning electron microscopy, and x-ray photoelectron spectroscopy. The results showed that the prepared Cu was transformed to Cu₂O. The film was then annealed in an O₂ atmosphere for different durations. As a result, the structure of Cu₂O was transformed to CuO. Electrochemical impedance spectroscopy revealed that the annealing time influenced the charge carrier density and affected the photocathode performance. The CuO photocathode was also preliminarily investigated for its ability to reduce CO₂ into a valuable chemical product.