Bicarbonate Rebalances the *COOH/*OCO^– Dual Pathways in CO₂ Electrocatalytic Reduction: <i>In Situ</i> Surface-Enhanced Raman Spectroscopic Evidence

Abstract

Understanding the reactive site/CO₂/electrolyte interfacial behaviors is very crucial for the design of an advantageous CO₂ electrocatalytic reduction (CO₂ER) system. One important but unrevealed question is how the CO₂ER process is influenced by the high concentration of HCO₃^-, which is deliberately added as electrolyte or from the inevitable reaction between dissolved CO₂ and OH^-. Here, we provide unambiguous <i>in situ</i> spectroscopic evidence that on Ag-based catalysts, HCO₃^- is apt to facilitate *OCO^- generation and therefore rebalances CO₂ER pathways. By employing an alternative acid electrolyte to restrict the exchange between CO₂ and HCO₃^- and eliminating the effect of solution pH, we reveal that HCO₃^- can decrease the onset potential of *OCO^- and promote further formate production. Theoretical calculations indicate HCO₃^- can stabilize the adsorption of *OCO^- instead of *COOH. The renewed understanding of the role of HCO₃^- could facilitate the judicious selection of electrolytes to regulate the CO₂ER pathway and product distribution.