Promoting Charge Separation and Injection by Optimizing the Interfaces of GaN:ZnO Photoanode for Efficient Solar Water Oxidation.

Abstract

Photoelectrochemical water splitting is a promising route for converting solar energy into molecular hydrogen as a storable fuel. This study focused on improving the performance of GaN:ZnO photoanodes by addressing two key limiting factors: charge separation within the bulk material and charge injection at the electrode–electrolyte interface. Moisture-assisted nitridation combined with HCl acid treatment was applied to reduce recombination centers at internal interfaces within the GaN:ZnO solid solution particles. Additionally, a multimetal phosphide cocatalyst (NiCoFeP) was introduced at the photoanode surface to facilitate water oxidation and lower the overpotential for charge injection. The combined optimizations yielded a photocurrent density of 3.9 mA/cm² at 1.23 V versus the reversible hydrogen electrode and a solar-to-hydrogen conversion efficiency exceeding 1%, representing a notable benchmark for this class of photoanode materials.

Mechanism

Moisture-assisted nitridation and HCl acid treatment suppress recombination centers at internal GaN:ZnO interfaces, while the NiCoFeP multimetal phosphide cocatalyst reduces the overpotential at the photoanode–electrolyte interface, collectively enhancing charge separation and injection for water oxidation.