Triggering Asymmetric Layer Displacement Polarization and Redox Dual‐Sites Activation by Inside‐Out Anion Substitution for Efficient CO₂ Photoreduction

Abstract Sluggish bulk charge transfer and barren catalytic sites severely hinder the CO₂ photoreduction process. Seeking strategies for accelerating charge dynamics and activating reduction and oxidation sites synchronously presents a huge challenge. Herein, an inside‐out chlorine (Cl) ions substitution strategy on the layered polar Bi₄O₅Br₂ is proposed for achieving layer structure‐dependent polarization effect and redox dual‐sites activation. Cl ions in the bulk phase shrink the halogen layer interspace by 8‰, triggering asymmetric [Bi₄O₅]²⁺ layer displacement polarization, prolonging the average photocharge lifetime to 201.8 ps. Meanwhile, surface substituted Cl ions enhance the electron‐donating capability of neighboring Bi atoms, activating the intrinsic Bi reduction sites, and increasing H₂O molecule adsorption on nearby intrinsic O oxidation site (cal. by 0.105 eV), also self‐donating as an alien oxidation site. Besides, Cl upshifts the p‐band center closer to the Fermi level, facilitating the reactant adsorption. Therefore, the energy barrier for CO₂ activation and rate‐limiting ^*COOH intermediate formation steps are significantly decreased. Without cocatalysts and sacrificial reagents, inside‐out Cl‐substituted Bi₄O₅Br₂ delivers a remarkable CO₂‐to‐CO photoreduction rate of 50.18 µmol g⁻¹ h⁻¹, being one of the state‐of‐the‐art catalysts. This finding offers insights into exploiting polarization at the molecular‐level and enhances understanding of catalytic site activation.