Electronic Structure Engineering via Coordinatively Unsaturated Bismuth for Efficient CO ₂ Electroreduction

ABSTRACT Metal‐coordinated unsaturated sites are a common type of pivotal active sites in the area of electrocatalytic CO 2 reduction (CO 2 RR). Its distinctive electronic structure and coordination environment effectively lower the reaction energy barrier and optimize the adsorption energy of intermediates, significantly promoting the activation and conversion of CO 2 . In this work, coordinately unsaturated Bi nanosheets (Bi‐2 NSs) was synthesized. The Bi species exhibit an intermediate‐state characteristic with 0 < δ < 3, along with a concurrent maximum in oxygen vacancies content, which directly contributed to excellent catalytic performance. In an H‐cell configuration, the Bi‐2 NSs achieved an HCOOH faradaic efficiency of 71.6% at −0.8 V versus RHE. When evaluated in a flow cell equipped with a gas diffusion electrode, it demonstrated a stable operation for 17 h at −100 mA cm −2 while maintaining 89.4% HCOOH selectivity. This work not only elucidates the critical role of unsaturated sites in enhancing the activity and stability of CO 2 RR but also provides new insights for the design of industrial CO 2 RR catalysts that combine high activity and durability.