Reconstructed Bismuth Oxide through in situ Carbonation by Carbonate‐containing Electrolyte for Highly Active Electrocatalytic CO2 Reduction to Formate

The catalyst‐reconstruction makes it challenging to clarify the practical active sites and unveil the actual reaction mechanism during the CO2 electroreduction reaction (CO2RR). However, currently the impact of the electrolyte microenvironment in which the electrolyte is in contact with the catalyst is overlooked and might induce a chemical evolution, thus confusing the reconstruction process and mechanism. In this work, the carbonate adsorption properties of metal oxides were investigated, and the mechanism of how the electrolyte carbonate affect the chemical evolution of catalysts were discussed. Notably, Bi2O3 with weak carbonate adsorption underwent a chemical reconstruction to form the Bi2O2CO3/Bi2O3 heterostructure. Furthermore, in situ and ex situ characterizations unveiled the formation mechanism of the heterostructure. The in situ formed Bi2O2CO3/Bi2O3 heterostructure with strong electron interaction served as the highly active structure for CO2RR, achieving a formate Faradaic efficiency of 98.1 % at −0.8 Vvs RHE. Theoretical calculations demonstrate that the significantly tuned p‐orbit electrons of the Bi sites in Bi2O2CO3/Bi2O3 optimized the adsorption of the intermediate and lowered the energy barrier for the formation of *OCHO. This work elucidates the mechanism of electrolyte microenvironment for affecting catalyst reconstruction, which contributes to the understanding of reconstruction process and clarification of the actual catalytic structure. The carbonate in the electrolyte was found to affect the chemical evolution of the catalyst and further lead to changes in the catalyst performance. Especially, the Bi2O3 with weak CO32− adsorption underwent an in situ carbonation to form surface Bi2O2CO3 layer in CO2 purged KOH electrolyte. The reconstructed Bi2O2CO3/Bi2O3 heterostructure with strong electron interaction served as a highly active structure and promoted the formation of formate.