Surface engineering of CuO-Cu2O heterojunction thin films for improved photoelectrochemical water splitting

The efficient production of green hydrogen poses a significant challenge that requires the development of active, low-cost, and stable catalysts. Copper oxide has emerged as a highly effective photocatalyst for water splitting, offering the advantages of being nontoxic, abundant, and inexpensive. Nonetheless, the photoelectrochemical water splitting (PEC) process can be enhanced through surface modification. In this study, we utilized single-source precursors for aerosol-assisted chemical vapor deposition (AACVD) in order to deposit thin films of copper oxide (CuO-Cu2O) heterojunctions onto a substrate composed of fluorine-doped tin oxide (FTO). The chosen precursor for this purpose was copper (II) nitrate hemi(pentahydrate). To further optimize the CuO-Cu2O films, a novel acid treatment involving the addition of varying quantities of acetic acid (AA) to the precursor solution was employed. Remarkably, this acid treatment resulted in a significant improvement in the photocurrent density of the CuO-Cu2O heterojunction. Notably, a 3 mL acid-treated CuO-Cu2O thin film exhibited an impressive photocurrent measure of −6.8 mA/cm2 at 0.0 V vs RHE in 0.5 M Na2SO4 electrolyte, compared to the performance of the untreated CuO-Cu2O thin film (−2.8 mA/cm2 at 0.0 V vs RHE). This catalyst demonstrated stability and a threefold increase in hydrogen production performance. The increase in photocurrent densities is closely linked to the influence of AA on two key factors: particle growth and structural defects, such as oxygen vacancies. This relationship has been confirmed through the examination of SEM, AFM, and PL spectra results. The findings of this study not only offer a novel approach to catalyst design but also propose a practical method for photoelectrochemical water splitting. This method holds great promise for achieving sustainable and renewable energy sources, as well as efficient green hydrogen production.