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

The synthesization of Cu2O thin films by electrodeposition for photoelectrochemical water splitting is reported. The synthesized Cu2O samples are annealed at different temperatures between 300 and 500 degrees C. The XRD analysis and SEM images indicate that the sample without annealing includes Cu2O grains with pyramid shape. With annealing to more than 300 degrees C, due to the oxidization of the sample, a thin layer of CuO appears on the original Cu2O film and the crystalline signatures of such CuO structure increase with annealing at higher temperatures. The photoelectrochemical measurements indicate that annealing pure Cu2O by more than 300 degrees C, remarkably increases the photocurrent achieved from this photocathode. The effect is accompanied with considerable improvement of chemical stability of the original Cu2O 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 degrees C. However, the best photocurrent from the Cu2O/CuO composite is obtained from the annealing temperature of about 400 degrees 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.