Highly Active GaN-Stabilized Ta₃ N₅ Thin-Film Photoanode for Solar Water Oxidation

Ta₃ N₅ is a very promising photocatalyst for solar water splitting because of its wide spectrum solar energy utilization up to 600 nm and suitable energy band position straddling the water splitting redox reactions. However, its development has long been impeded by poor compatibility with electrolytes. Herein, we demonstrate a simple sputtering-nitridation process to fabricate high-performance Ta₃ N₅ film photoanodes owing to successful synthesis of the vital TaO_δ precursors. An effective GaN coating strategy is developed to remarkably stabilize Ta₃ N₅ by forming a crystalline nitride-on-nitride structure with an improved nitride/electrolyte interface. A stable, high photocurrent density of 8 mA cm^-2 was obtained with a CoPi/GaN/Ta₃ N₅ photoanode at 1.2 V_RHE under simulated sunlight, with O₂ and H₂ generated at a Faraday efficiency of unity over 12 h. Our vapor-phase deposition method can be used to fabricate high-performance (oxy)nitrides for practical photoelectrochemical applications.