Improvement of Photoelectrochemical and Stability Properties of Electrodeposited Cu2O Thin Films by Annealing Processes

The synthesization of Cu 2 O thin films by electrodeposition for photoelectrochemical water splitting is reported. The synthesized Cu 2 O samples are annealed at different temperatures between 300 and 500 °C. The XRD analysis and SEM images indicate that the sample without annealing includes Cu 2 O grains with pyramid shape. With annealing to more than 300 °C, due to the oxidization of the sample, a thin layer of CuO appears on the original Cu 2 O film and the crystalline signatures of such CuO structure increase with annealing at higher temperatures. The photoelectrochemical measurements indicate that annealing pure Cu 2 O by more than 300 °C, remarkably increases the photocurrent achieved from this photocathode. The effect is accompanied with considerable improvement of chemical stability of the original Cu 2 O electrode during water splitting. Such protection effect, which is originated from generation of CuO on the samples, increases with the annealing temperature up to 500 °C. However, the best photocurrent from the Cu 2 O/CuO composite is obtained from the annealing temperature of about 400 °C. The results of impedance analysis of various annealed samples indicate that annealing at a higher temperature, better charge transfer occurs both at the interface of photocathode/electrolyte and inside the photocathode.