Efficient and Selective Electroreduction of CO 2 to HCOOH over Bismuth-Based Bromide Perovskites in Acidic Electrolytes.

Metal halide perovskites, primarily used as optoelectronic devices, have not been applied for electrochemical conversion due to their insufficient stability in moisture. Herein, two bismuth-based perovskites are introduced as novel electrocatalysts to convert CO 2 into HCOOH in aqueous acidic media (pH 2.5), exhibiting a high Faradaic efficiency for HCOOH of >80 % in a wide potential range from -0.75 to -1.25 V. Their structural evolution against water was dynamically monitored by in situ spectra. Theoretical calculations further reveal that the formation of intermediate OCHO* on bismuth sites of Cs 3 Bi 2 Br 9 (111) play a pivotal role toward HCOOH production, which has a lower energy barrier than that on Cs 2 AgBiBr 6 (001) surfaces. Significantly, CO 2 reacts with protons instead of water which can enhance CO 2 reduction rate and suppress hydrogen evolution by avoiding carbonate formation in acidic electrolytes. This work paves the way for the extensive investigation of halide perovskites in aqueous systems.