Oxygen-tolerant Electrochemical CO₂ Reduction from Bicarbonate Solutions toward Multicarbon Compounds (Supporting Information)

<p dir="ltr">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.</p>