Steering Geometric Reconstruction of Bismuth with Accelerated Dynamics for CO₂ Electroreduction

Bismuth-based materials have emerged as promising catalysts in the electrocatalytic reduction of CO₂ to formate. However, the reasons for the reconstruction of Bi-based precursors to form bismuth nanosheets are still puzzling, especially the formation of defective bismuth sites. Herein, we prepare bismuth nanosheets with vacancy-rich defects (V-Bi NS) by rapidly reconstructing Bi₁₉Cl₃S₂₇ under negative potential. Theoretical analysis reveals that the introduction of chlorine induces the generation of intrinsic electric field in the precursor, thereby increasing the electron transfer rate and further promoting the metallization of trivalent bismuth. Meanwhile, experimental tests verify that Bi₁₉Cl₃S₂₇ has a faster reconstruction rate than Bi₂S₃. The formed V-Bi NS exhibits up to 96 % HCOO^- Faraday efficiency and 400 mA cm^-2 HCOO^- partial current densities, and its electrochemical active surface area normalized formate current density and yield are 2.2 times higher than those of intact bismuth nanosheets (I-Bi NS). Density functional theory calculations indicate that bismuth vacancies with electron-rich aggregation reduce the activation energy of CO₂ to *CO₂ ^- radicals and stabilize the adsorption of the key intermediate *OCHO, thus facilitating the reaction kinetics of formate production.