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

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.