Regulating Electronic Structure of Transition Metal Single-Atoms in COFs for Enhanced Photocatalytic CO₂ Reduction

The rational regulation of the electronic structure in single-atom catalysts (SACs) is pivotal yet challenging for enhancing photocatalytic CO₂ reduction. Herein, we elaborately designed a series of M₁N₂ sites (M = Au, Pt, Pd, Ru, Mo) anchored on a vinylene-linked covalent organic framework (sp²c-COF) to construct M/COF SACs for gas-solid CO₂ photoreduction. The M/COF SACs revealed a d-orbital electronic configuration-dependent activity, where the d-band center exhibiting strong correlation with CO₂ adsorption energy (R² = 0.98). Notably, the Mo/COF catalysts delivered a superior CO rate of 294.43 µmol·g^-1·h^-1 with near-unity selectivity under pure CO₂ and sustained 146.6 µmol·g^-1·h^-1 under simulated flue gas (15% CO₂). The superior activity originates from the synergistic interplay of its highest d-band center (-0.314 eV) and strongest spin polarization among the series. This unique electronic structure, featuring abundant single-atom states near the Fermi level and half-occupied d orbitals, facilitates optimal σ-donation (via d_z2) and π-back-donation (via d_xz/d_yz) for CO₂ activation, thereby significantly lowering the energy barriers for *COOH formation and *CO desorption. This work establishes a design principle for high-performance SACs through the co-modulation of d-band configuration and spin polarization.