Synergy of porous structure and cation doping in Ta₃N₅ photoanode towards improved photoelectrochemical water oxidation

Herein, a cross-linked porous Ta₃N₅ film was prepared via a simple solution combustion route followed by a high-temperature nitridation process for photoelectrochemical (PEC) water oxidation. Meanwhile, the metal cations (Mg²⁺ and Zr⁴⁺) were incorporated into the porous Ta₃N₅ to enhance the PEC performance. The porous Mg/Zr co-doped Ta₃N₅ photoanode yielded a photocurrent density of 1.40 mA cm⁻² at 1.23 V vs RHE, which is 5.6 times higher than that of the dense Ta₃N₅ photoanode. The enhanced performance should be ascribed to the synergistic effect of porous structure and cation doping, which can enlarge the electrochemical active surface area and accelerate the charge transfer by introducing O_N substitution defects. Subsequently, Co(OH)₂ cocatalyst was loaded on the Mg/Zr-Ta₃N₅ photoanode to negatively shift the onset potential to 0.45 V vs RHE and further improve the photocurrent density to 3.5 mA cm⁻² at 1.23 V vs RHE, with a maximum half-cell solar to hydrogen efficiency of 0.45%. The present study provides a new strategy to design efficient Ta₃N₅ photoelectrodes via the simultaneous control of the morphology and composition.