Dynamic ion exchange engineering BiOI-derived Bi2O2CO3 to promote CO2 electroreduction for efficient formate production

Prompt production of bismuth subcarbonate (Bi2O2CO3) intermediate is crucial for high-efficiency formate production and preservation of the bismuth-oxygen (Bi-O) structures during electrochemical CO2 reduction reaction (CO2RR) catalyzed by Bi-based catalyst. In this work, we investigate the CO2RR performance of bismuth oxyhalide (BiOX, including BiOCl, BiOBr and BiOI) catalysts with nanosheet-assembling microsphere morphology and develop an effective strategy of engineering BiOI-derived Bi2O2CO3 through dynamic ion exchange reaction to promote formate production from CO2RR. Among investigated BiOX catalysts with nanosheet-assembling microsphere morphology, BiOI exhibits the highest ion exchange rate due to the large interlayer spacing and low binding energy between [Bi2O2]2+ layer and I− ion. The produced BiOI-derived Bi2O2CO3 inherits the large interlayer spacing of BiOI and thus facilitates diffusion of HCO3– ions to promote CO2RR for formate production. By comparison with BiOCl and BiOBr, BiOI exhibits better CO2RR performance, achieving faradaic efficiency of 98 % with a current density of 42.0 mA cm−2 and excellent long-term durability. Mechanism studies demonstrate that the sufficient supply of HCO3– ions resulted from large interlayer spacing of BiOI-derived Bi2O2CO3 significantly promotes formate production and, in turn, improves the resistance of Bi-O structures to electroreduction. This work provides a deep insight into the mechanism of BiOX-catalyzed CO2RR for formate production, opening up new opportunities for developing high-performance CO2RR catalysts.