Engineering single-atom Co on defective bismuth oxychloride to construct asymmetric Bi-O-Co-Vo interfacial sites with strong spin polarization for boosted CO2 photoreduction.
Abstract
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 (Vo), thereby constructing well-defined asymmetric Bi-O-Co-Vo interfacial catalytic units with robust spin polarization. Structural characterizations verify that Co atoms substitutionally occupy lattice Bi sites, and neighboring Vo 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 Vo 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-Vo 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.