Different Annealing Atmosphere Gases on the Growth and Photocurrent Performance of CuO Films Grown on FTO Substrate

Improvement in photocurrent performance remains the key subject to prepare a stable and efficient photocathode in photoelectrochemical cell (PEC) water splitting. Different to the ordinary methods, various annealing atmosphere gases were used to study the growth of CuO films on fluorine-doped tin oxide substrate; then, the photocurrent performance was studied when those CuO films were used as photocathodes in PEC. The scanning electron microscopy images indicate that all of the CuO films are composed of vertically arrayed CuO nanosheets, each individual nanosheet with a thickness of 100–500 nm. Those hierarchical CuO photoelectrodes in the PEC exhibit quite different photoelectrochemical activities in visible light, where the air-annealed CuO film has nearly 6 times enhancement in photocurrent (108 μA) at 0 V compared to that of film under oxygen atmosphere, and 34 times of argon. It has an acceptor concentration of 2.9 × 1021 cm–3 from Mott–Schottky analysis, which is more than 2 times larger than that of the oxygen-annealed CuO film, and 37 times larger than that of the argon-annealed film. Ultraviolet photoelectron spectroscopy measurements were carried out to explain the improved photocurrent performance of the air-annealed CuO films, where the obtained valence band of 0.44 eV and work function of 4.92 eV well match the reduction reaction of electrolyte (H2O).