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

Electrochemical reduction of CO₂ represents a promising strategy for converting CO₂ into value-added chemical products. Currently, significant efforts have been devoted to developing more efficient Bi-based catalysts to reduce CO₂ 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 Bi₂O₃ reconstruction with oxygen vacancies (O_v-Bi₂O₃) into defect-rich Bi nanoflowers (Bi (O_v-Bi₂O₃)) 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-Bi₂O₃) 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.