Photoelectrochemical Properties of GaN Photoanodes with Cobalt Phosphate Catalyst for Solar Water Splitting in Neutral Electrolyte

Cyclic voltamrnetry measurements are carried out in neutral phosphate-buffered electrolyte using n-type Ga-polar GaN thin-film photoelectrodes with and without cobalt phosphate (Co-Pi) modification. Without CO-Pi, the variation of the photo current with the bias potential exhibits a two-step behavior and under chopped illumination spikes occur at low bias potential. Thus in this regime surface recombination is dominant. Co-Pi modification suppresses surface recombination and significantly increases the photocurrent, especially for low bias potentials. At the same time, stability tests reveal that Co-Pi does not protect GaN against photocorrosion. Experiments using H2O2 imply that this photocorrosion is a reductive process and probably related to the presence of charged surface defects.