Anion Effect on CO2 Electrochemical Reduction in Acidic Media

The CO 2 electroreduction reaction (CO 2 RR) in acidic media offers a promising route to convert renewable electricity into value-added chemicals with high carbon utilization, yet its selectivity is severely limited by competing hydrogen evolution reaction. Despite extensive investigations into cation effects in acidic CO 2 RR, the role of anions remains underexplored. Here, we systematically investigate the effect of three common electrolyte anions—Cl − , SO 4 2− , and H 2 PO 4 − —on acidic CO 2 RR. Theoretical studies suggest that Cl − induces the most negative surface charge on Cu relative to SO 4 2− and H 2 PO 4 − , which enhances C–C coupling and thereby improves selectivity toward C 2+ products. Electrochemical evaluation shows that Cu catalysts in Cl − -containing electrolytes deliver the highest C 2+ selectivity, surpassing those in SO 4 2− and H 2 PO 4 − environments. Specifically, we achieve a peak C 2+ Faradaic efficiency of 82% at 300 mA cm −2 . The promotional role of Cl − is further observed on Ag catalysts in acidic CO 2 RR. In situ Raman spectroscopy reveals that Cl − enhances the adsorption of *CO intermediates on Cu surfaces, thereby promoting C–C coupling and C 2+ product generation. This work reports an effective anion electrolyte engineering strategy to enhance CO 2 RR performance under acidic conditions. Graphical The type of anions in the electrolyte affects the performance of acidic CO 2 electroreduction. Compared to SO 4 2− and H 2 PO 4 − anions, the presence of Cl − anions facilitates *CO intermediate adsorption and thus promotes C–C coupling toward C 2+ products in acidic media on Cu catalysts.