Mitigating Electrode Inactivation during CO₂ Electrocatalysis in Aprotic Solvents with Alkali Cations

CO₂ electrochemical reduction (CO₂R) in aprotic media is a promising alternative to aqueous electrocatalysis, as it minimizes the competing hydrogen evolution reaction while enhancing CO₂ solubility. To date, state-of-the-art alkali salts used as electrolytes for selective aqueous CO₂R are inaccessible in aprotic systems due to the inactivation of the electrode surface from carbonate deposition. In this work, we demonstrate that an acidic nonaqueous environment enables sustained CO₂ electrochemical reduction with common alkali salts in dimethyl sulfoxide. Electrochemical and spectroscopic techniques show that at low pH carbonate buildup can be prevented, allowing CO₂R to proceed. Product distribution with a copper electrode revealed up to 80% Faradaic efficiency for CO₂R products, including carbon monoxide, formic acid, and methane. By understanding the mechanism for electrode inactivation in an aprotic medium and addressing that challenge with dilute acid addition, we pave the way toward the development of more efficient and selective electrolytes for CO₂R.