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.