Selective electrochemical reduction of CO2 into fuels or chemical feedstocks is a promising avenue to achieve carbon‐neutral goal, but its development is severely limited by the lack of highly efficient electrocatalysts. Herein, cation‐exchange strategy is combined with electrochemical self‐reconstruction strategy to successfully develop diethylenetriamine‐functionalized mosaic Bi nanosheets (mBi‐DETA NSs) for selective electrocatalytic CO2 reduction to formate, delivering a superior formate Faradaic efficiency of 96.87% at a low potential of −0.8 VRHE. Mosaic nanosheet morphology of Bi can sufficiently expose the under‐coordinated Bi active sites and promote the activation of CO2 molecules to form the OCHO−* intermediate. Moreover, in situ attenuated total reflectance infrared spectra further corroborate that surface chemical microenvironment modulation of mosaic Bi nanosheets via DETA functionalization can improve CO2 adsorption on the catalyst surface and stabilize the key intermediate (OCHO−*) due to the presence of amine groups, thus facilitate the CO2‐to‐HCOO− reaction kinetics and promote formate formation.

Challenges remain in the development of highly efficient catalysts for selective electrochemical transformation of carbon dioxide (CO2) to high‐valued hydrocarbons. In this study, oxygen vacancy‐rich Bi2O3 nanosheets coated with polypyrrole (Bi2O3@PPy NSs) are designed and synthesized, as precatalysts for selective electrocatalytic CO2reduction to formate. Systematic material characterization demonstrated that Bi2O3@PPy precatalyst can evolve intoBi2O2CO3@PPy nanosheets with rich oxygen vacancies (Bi2O2CO3@PPy NSs) via electrolyte‐mediated conversion and function as the real active catalyst for CO2 reduction reaction electrocatalysis. Coating catalyst with a PPy shell can modulate the interfacial microenvironment of active sites, which work in coordination with rich oxygen vacancies in Bi2O2CO3 and efficiently mediate directional selective CO2 reduction toward formate formation. With the fine‐tuning of interfacial microenvironment, the optimized Bi2O3@PPy‐2 NSs derived Bi2O2CO3@PPy‐2 NSs exhibit a maximum Faradaic efficiency of 95.8% at −0.8 V (versus. reversible hydrogen electrode) for formate production. This work might shed some light on designing advanced catalysts toward selective electrocatalytic CO2 reduction through local microenvironment engineering.

Rational design advanced electrocatalysts and innovative energy-efficient electrolysis systems for converting carbon dioxide (CO2) into value-added chemicals or fuels is of significance yet challenging. As for electrochemical CO2 reduction reaction...