Towards the quantification of the chemical mechanism of light-driven water splitting on GaN photoelectrodes

We present results from a study addressing the unbiased water-splitting process and its side reactions on GaN-based photoelectrodes decorated with NiO x , FeO x , and CoO x nanoparticles. Observations involving physicochemical analyses of liquid and vapour phases after the experiments were performed in 1 M NaOH under ambient conditions. A water-splitting process with GaN-based photoelectrodes results in the generation of hydrogen gas and hydrogen peroxide. Quantification of the water-splitting chemical mechanism gave numerical values indicating an increase in the device performance and restriction of the GaN electrocorrosion with surface modifications of GaN structures. The hydrogen generation efficiencies are η H 2 (bare GaN) = 1.23%, η H 2 (NiO x /GaN) = 4.31%, η H 2 (FeO x /GaN) = 2.69%, and η H 2 (CoO x /GaN) = 2.31%. The photoelectrode etching reaction moieties Q etch / Q are 11.5%. 0.21%, 0.26% and 0.20% for bare GaN, NiO x /GaN, FeO x /GaN, and CoO x /GaN, respectively. We propose the chemical mechanism of the light-driven water-splitting process on MeO x /n-GaN (Me = Ni, Fe, Co) according to the reaction product analysis and discuss the photoelectrode etching and the interaction of oxide NPs with the reaction layer.