Defect‐Driven Reconstruction of Bismuth Nanoflowers via Precursor Engineering for Highly Efficient CO₂‐to‐Formate Electrochemical Reduction

Electrochemical reduction of CO 2 represents a promising strategy for converting CO 2 into value‐added chemical products. Currently, significant efforts have been devoted to developing more efficient Bi‐based catalysts to reduce CO 2 to formate. However, the role of precursor defects in directing the electrochemical reconstruction of Bi‐based catalysts is yet to be thoroughly investigated. Herein, a strong alkali‐induced strategy, coupled with electrochemical reduction for controllable morphology and defect engineering to achieve Bi 2 O 3 reconstruction with oxygen vacancies (O v ‐Bi 2 O 3 ) into defect‐rich Bi nanoflowers (Bi (O v ‐Bi 2 O 3 )) featuring small‐angle grain boundaries, is reported. Over a wide potential range (from −0.87 to −1.17 V vs. reversible hydrogen electrode [RHE]) in an H‐type cell, Bi (O v ‐Bi 2 O 3 ) exhibits a high Faradaic efficiency of formate (>95%). Moreover, it displays a high current density (−340 mA cm −2 ) at −1.08 V versus RHE and a formate production rate of 6.09 mmol h −1 cm −2 in a flow cell, thus highlighting its potential for industrial applications. In situ attenuated total reflectance surface‐enhanced infrared absorption spectroscopy offers detailed insights into the reaction mechanism, verifying that formate formation predominantly occurs through the *OCHO intermediate. This study reveals the role of precursor‐derived defects in catalytic properties, clarifying mechanisms and guiding performance optimization.