Engineering single-atom Co on defective bismuth oxychloride to construct asymmetric Bi-O-Co-V_o interfacial sites with...

Engineering spin-polarized interfacial sites is central to gas-solid photocatalytic CO₂ reduction, yet how such sites govern interfacial charge transfer and CO₂ activation remains poorly understood. Herein, atomically dispersed Co atoms were incorporated into ultrathin bismuth oxychloride (BiOCl) nanosheets with adjacent oxygen vacancies (V_o), thereby constructing well-defined asymmetric Bi-O-Co-V_o interfacial catalytic units with robust spin polarization. Structural characterizations verify that Co atoms substitutionally occupy lattice Bi sites, and neighboring V_o reconstruct the local coordination environment of Co centers. Comprehensive in situ/operando characterizations unravel that the built-in polarization field originating from these asymmetric interfacial sites drives directional charge transfer and effectively suppresses photogenerated carrier recombination. Density functional theory (DFT) calculations reveal that synergistic hybridization between Co d states and V_o states breaks spin degeneracy and optimizes the electronic structure for enhanced CO₂ activation. Benefiting from the synergistic effects of optimized charge separation and spin-polarized surface reaction kinetics, the optimized 3Co-BOC-V_o achieves a CO evolution rate of 152.31 ± 6.28 μmol g^-1 h^-1 with 96.0% CO selectivity under visible light, which is 7.06 times higher than pristine BiOCl. Notably, external magnetic field further enhances CO production by 58.4%, providing strong evidence for the spin-polarized catalytic mechanism. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) together with climbing image nudged elastic band (CI-NEB) calculations demonstrate that spin polarization lowers the energy barrier of the rate-determining *COOH formation step. This work demonstrates that engineering spin-asymmetric interfacial microenvironments via single-atom substitution and defect engineering is a general and effective strategy for boosting photocatalytic CO₂ reduction performance, providing guidance for the rational design of high-efficiency layered bismuth oxyhalide photocatalysts toward practical solar-driven CO₂ conversion.