Engineering Under‐Coordinated Active Sites with Tailored Chemical Microenvironments over Mosaic Bismuth Nanosheets for Selective CO2 Electroreduction to Formate

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. Diethylenetriamine‐functionalized mosaic Bi nanosheets (mBi‐DETA NSs) are synthesized via combining cation exchange with electrochemical self‐reconstruction. Mosaic nanosheet structure can afford abundant under‐coordinated Bi active sites for the activation of CO2. Moreover, surface chemical microenvironment modulation of mosaic Bi nanosheets by diethylenetriamine can improve CO2 adsorption and stabilize the key intermediate (OCHO−*), thus facilitating the CO2‐to‐HCOO− reaction kinetics and promoting formate formation.