Reconstructed Bismuth Oxide through in situ Carbonation by Carbonate-containing Electrolyte for Highly Active Electrocatalytic CO 2 Reduction to Formate.

The catalyst-reconstruction makes it challenging to clarify the practical active sites and unveil the actual reaction mechanism during the CO 2 electroreduction reaction (CO 2 RR). 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, Bi 2 O 3 with weak carbonate adsorption underwent a chemical reconstruction to form the Bi 2 O 2 CO 3 /Bi 2 O 3 heterostructure. Furthermore, in situ and ex situ characterizations unveiled the formation mechanism of the heterostructure. The in situ formed Bi 2 O 2 CO 3 /Bi 2 O 3 heterostructure with strong electron interaction served as the highly active structure for CO 2 RR, achieving a formate Faradaic efficiency of 98.1 % at -0.8 V vs RHE . Theoretical calculations demonstrate that the significantly tuned p-orbit electrons of the Bi sites in Bi 2 O 2 CO 3 /Bi 2 O 3 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.