In Situ Structural Reconstruction to Generate the Active Sites for CO2 Electroreduction on Bismuth Ultrathin Nanosheets

Abstract Electrochemical structural reconstruction of catalysts may generate real active sites that differ from the initial catalyst, but is often ignored. Herein, combining in situ and ex situ techniques, it is identified that the bismuth nanosheets (NS) dotted with large numbers of coordinatively unsaturated pit sites is produced via the in situ structural reconstruction of Bi(OH)3 NS. Such reconstructed Bi NS shows greatly improved catalytic activity toward CO2 electroreduction, with a 2.6‐fold increase in current density compared with intact Bi NS, high Faradaic efficiency for HCOO− production (>95%), and an extraordinary turnover frequency of 0.35 s−1 at −0.98 VRHE. In addition, it delivers industrial‐relevant current density of 325 mA cm−2 without compromising selectivity in a flow cell. The mechanistic studies demonstrate that these coordinatively unsaturated sites acting as the real active sites favor the stabilization of key intermediate *OCHO, which thus facilitate the reaction kinetics for HCOO− production. This work not only provides a unique perspective on the construction of efficient catalysts for CO2 electroreduction, but also implies the importance in recognition of structural reconstruction.