Photoelectrochemical water-splitting using GaN pyramidal dots and their long-term stability in the two-electrode configuration

We report the high solar-to-hydrogen conversion efficiency (STH) and long-term stability of a photoelectrochemical water-splitting (PEC-WS) system using GaN pyramidal dots (PDs) coated with oxidized tungsten sulfide (OTS) as the photoanode material (GaN-PD/OTS photoanode). After PEC-WS of seven days in the three-electrode configuration, the current density of the GaN-PD/OTS photoanode decreased slightly to 95.8% compared with immediately after the reaction started. In the more practical two-electrode configuration, the STH of the GaN-PD/OTS photoanode was calculated to be 1.54% immediately after the reaction started and was slightly lower at 1.50% after 20 hours of PEC-WS. This conversion efficiency and stability are much higher than those of previously reported photoanodes. The current density retention rate was also measured to be 97% after 20 hours of PEC-WS under the same conditions. A photoanode with stable STH characteristics and a high current density retention rate has not yet been reported for the two-electrode configuration.