Electrochemical CO2 reduction reaction (eCO2RR) is a viable approach to achieve carbon neutrality. Bismuth-based electrocatalysts demonstrate exceptional selectivity in CO2-to-formate conversion, but their reconstruction mechanisms during the eCO2RR remain elusive. Herein, the reconstruction processes of bismuth molybdate (Bi2MoO6) nanoplates are elucidated during the eCO2RR. Operando and ex situ measurements reveal the in situ partial reduction of Bi2MoO6 to Bi metal, forming Bi@Bi2MoO6 at negative potentials. Meanwhile, CO32- ions in the electrolyte spontaneously exchange with MoO42- in Bi2MoO6. The obtained Bi@Bi2MoO6/Bi2O2CO3 delivers a formate Faradaic efficiency (FE) of 95.2% at -1.0 V. Notably, high formate FEs (>90%) are maintained within a wide 500 mV window. Although computational calculations indicate a higher energy barrier for *OCHO formation on Bi2O2CO3, the prevention of excessive reduction to metal Bi significantly enhances long-term stability. Furthermore, the CO32- ion exchange process occurs in various 2D Bi-containing precatalysts, which should be emphasized in further studies.
Keywords: Bi2MoO6; CO2 reduction; formate; in situ reconstruction; ion exchange.