Direct water photoelectrolysis with patterned n-GaN

Direct photoelectrolysis of water was observed using a structured $n\text{-}\mathrm{Ga}\mathrm{N}$ photoanode, aqueous NaOH solution, and platinum cathode. The structured $n\text{-}\mathrm{Ga}\mathrm{N}$ was formed by selective area regrowth using metal stripes defined by photolithography. Gas evolution from both the $n\text{-}\mathrm{Ga}\mathrm{N}$ anode and the platinum cathode was observed under UV irradiation without external bias. The metal stripes eliminated current crowding and the $n\text{-}\mathrm{Ga}\mathrm{N}$ regrowth increased specific surface area. As a result, distinct improvements in photocurrent were achieved. The origin of the photocurrent and the conversion efficiency are discussed based on water-splitting reactions and etching reactions.