Oxygen-tolerant Electrochemical CO<sub>2</sub> Reduction from Bicarbonate Solutions toward Multicarbon Compounds

Electrochemical CO2 reduction to multicarbon products offers a promising pathway for closing the anthropogenic carbon cycle while producing value-added chemicals. However, conventional gaseous CO2 electrolysis suffers from severe performance losses when O2 impurities are present. In this study, we focused on a HCO3−-derived CO2 reduction system, in which gaseous CO2 is generated in-situ within the electrolyzer, enabling efficient formation of a three-phase interface required for high-rate C2+ synthesis. We have successfully achieved a faradaic efficiency of 67.4 % and a partial current density exceeding 300 mA cm−2 for C2+ compounds. Importantly, the HCO3−-derived CO2RR demonstrated excellent oxygen tolerance, maintaining both the faradaic efficiency and partial current density for C2+ products even when CO2 gas containing 20 % O2 was used as the source for HCO3− solutions.