Insight\ninto the Rate-Determining Step in Photocatalytic\nZ‑Scheme Overall Water Splitting by Employing A Series of Perovskite\nRTaON<sub>2</sub> (R = Pr, Nd, Sm, and Gd) as Model Photocatalysts

Photocatalysis\nis an intricate process that involves a multitude\nof physical and chemical factors operating across diverse temporal\nand spatial scales. Identifying the dominant factors that influence\nphotocatalyst performance is one of the central challenges in the\nfield. Here, we synthesized a series of perovskite RTaON<sub>2</sub> semiconductors with different A-site rare earth atoms (R = Pr, Nd,\nSm, and Gd) as model photocatalysts to discuss the influence of the\nA-site modulation on their local structures as well as both physical\nand chemical properties and to get insight into the rate-determining\nstep in photocatalytic Z-scheme overall water splitting (OWS). It\nis interesting to find that, with a decreasing ionic radius of the\nA-site cations, the RTaON<sub>2</sub> compounds exhibit continuous\nblue shift of light absorption and a concomitant reduction in the\nlifetime of photogenerated carriers, revealing a significant influence\nof A-site atoms on the light absorption and charge separation processes.\nOn the other hand, the A-site atomic substitution was revealed to\nsignificantly modulate the valence band positions as well as surface\noxidation kinetics. By employing the Pt-modified RTaON<sub>2</sub> as H<sub>2</sub>-evolving photocatalysts, the activity of photocatalytic\nZ-scheme OWS for hydrogen production on them is found to be determined\nby its surface oxidation process instead of light absorption or charge\nseparation. Our results give the first experimental demonstration\nof the rate-determining step during the photocatalytic Z-scheme OWS\nprocesses, as should be instructive for the design and development\nof other efficient solar-to-chemical energy conversion systems.