Hydrogen evolution from p-GaN cathode in water under UV light irradiation

Hydrogen is evolved at a zero bias when a p-type GaN cathode in an electrolyte solution is irradiated with UV light, although both hydrogen evolution rate and photocurrent decrease during the irradiation. Spontaneous hydrogen evolution indicates that the conduction bandedge of p-GaN is above the reduction potential of H+(aq). From the relationship between the volume of generated hydrogen and the number of electrons traveling from the Pt anode to the p-GaN cathode, the reaction efficiency of electrons injected from the conduction band of the p-GaN cathode with H+(aq) in a neutral Na2SO4 electrolyte solution is larger than 70%. As a result, the overall quantum efficiency for the hydrogen generation before degradation is estimated to be 4-6% at a wavelength of 340 nm by considering the incident photon-to-current efficiency of p-GaN.