Rational design of metal-single-atom decorated CaTaO₂N as multifunctional photocatalysts for water splitting and CO₂...

Perovskite oxynitrides, exemplified by CaTaO₂N, have emerged as promising visible-light photocatalysts for solar fuel generation, including overall water splitting and CO₂ reduction. Loading cocatalysts is a proven strategy to enhance performance, yet the systematic design of highly dispersed metal cocatalysts with tailored multi-functionality remains underexplored. Herein, we employ first-principles density functional theory (DFT) calculations to systematically screen twelve single metal atoms (M = Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au) anchored onto the CaTaO₂N(010) surface as single-atom cocatalysts for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and CO₂ reduction reaction (CO₂RR). Our calculations reveal distinct catalytic functionalities governed by the electronic structure of the metal adatoms. We identify several high-performance candidates based on activity descriptors: Fe-, Cu-, Rh-, Ag-, and Os-adsorbed systems exhibit ΔG_H* values superior to the benchmark Pt-adsorbed system, indicating their potential as efficient and cost-effective HER catalysts; the Au-modified surface exhibits a relatively lower theoretical overpotential for the OER, identifying it as an effective OER catalyst; the Rh-decorated surface shows outstanding activity for both the HER and OER; most notably, Co-, Ni-, and Pd-decorated systems exhibit superior and balanced activities for the HER, OER, and CO₂RR, making them exceptional candidates for integrated solar fuel production systems that couple water splitting with CO₂ conversion. Mechanistic analysis elucidates the origin of selectivity, linking it to the metal-dependent binding strengths of key reaction intermediates and the modulated charge transfer at the metal-support interface. This work not only provides a library of efficient single-atom cocatalysts for CaTaO₂N but also establishes a design principle for developing multifunctional, noble-metal-free photocatalytic systems for sustainable energy applications.