Enhancing photoelectrocatalytic activity and stability of p-Cu₂O photocathode through n-TiO₂ coating for improved H₂ evolution reaction

This article presents a novel approach to improve both the photoelectrocatalytic activity and stability of the p-Cu2O photocathode. The approach involves the coating of an n-type TiO2 layer using e-beam evaporation with precise controllability of the coating thickness onto the p-type Cu2O electrode, forming a TiO2/Cu2O p/n heterojunction. Such a p/n junction enhances the photoelectrocatalytic activity of the Cu2O electrode by promoting the separation of the photo-generated charge carriers. Additionally, the large bandgap TiO2 coating layer serves as protection, reducing the photocorrosion of Cu2O, thereby improving the stability of the electrode. The n-TiO2/p-Cu2O photocathode shows superior photoelectrochemical H-2 evolution activity in comparison to the pristine p-Cu2O photocathode. We have found that the thickness and annealing temperature of TiO2 influence strongly the photocurrent and stability of the resultant TiO2/Cu2O photocathode. The best TiO2/Cu2O photocathode was achieved by coating a 50 nm thick TiO2 layer onto the Cu2O, followed by annealing at 350 degrees C. This configuration exhibited a large onset photovoltage of 0.58 V vs RHE and a catalytic current density of similar to 0.9 mA center dot cm(-2) at 0 V vs RHE in a pH 7 phosphate buffer, under standard 1 Sunlight illumination.