Non-Local Electronic Perturbation at Low-Coordinated Ru Sites Boosts N₂ Photoreduction

Atomic-level regulation of the coordination environment in single-atom catalysts (SACs) remains a significant challenge in heterogeneous photocatalysis. This study presents a second-shell engineering strategy through the insertion of oxygen into the secondary coordination sphere of low-coordinated Ru-N₂ sites, creating a non-local electronic perturbation distinct from conventional first-shell modification. The distal oxygen atom functions as a remote electron pump through the C─O─N bridging network, increasing the electron density at the Ru site and enhancing Ru dπ-N pπ back-donation interactions. This strengthened π-back-donation induces an asymmetric charge distribution between the proximal and distal nitrogen atoms of adsorbed N₂, weakening the N≡N bond and reducing the rate-determining step barrier from 1.034 to 0.822 eV while maintaining optimal product desorption. Consequently, Ru─O─CN achieves an ammonia evolution rate of 767.52 µmol ·g^{- 1} ·h^{- 1} under visible light irradiation, representing a 2.64-fold enhancement over Ru─CN and approximately 150-fold improvement compared to pristine g-C₃N₄. This work demonstrates that non-local coordination engineering through second-shell heteroatom doping provides an effective approach for fine-tuning the electronic structure of SACs.