Zr-Doped Mesoporous Ta₃N₅ Microspheres for Efficient Photocatalytic Water Oxidation

Tantalum nitride (Ta₃N₅) has been considered as a promising candidate for photocatalytic water splitting because of its strong visible-light absorbance as far as 600 nm. However, its catalytic activity is often hampered by various intrinsic/extrinsic defects. Here, we prepared a series of Zr-doped mesoporous tantalum nitride (Ta₃N₅) via a template-free method and carried out a detailed investigation of the role of Zr doping upon the photocatalytic performance. Various physicochemical properties including crystal structure, optical absorption, and so on were systematically explored. Our results show that doping Zr into Ta₃N₅ induces an enhancement of oxygen content and a suppression of absorption band around 720 nm, indicating an increase of O_N^• defects and a decrease of V_N^••• defects in the structure. Introduction of Zr significantly boosts the photocatalytic oxygen production of Ta₃N₅. The optimized photocatalytic oxygen production rate approaches 105 μmol h^-1 under visible light illumination (λ ≥ 420 nm), corresponding to an apparent quantum efficiency as high as 3.2%. Photoelectrochemical analysis and DFT calculation reveal that the superior photocatalytic activity of Zr-doped Ta₃N₅ originates from a high level of O_N^• defects' concentration, which contributes to a high electron mobility, and a low level of V_N^••• defects' concentration, which often act as charge recombination centers.