Hydroxide Is Not a Promoter of C2+ Product Formation in the Electrochemical Reduction of CO on Copper

Abstract Highly alkaline electrolytes have been shown to improve the formation rate of C 2+ products in the electrochemical reduction of carbon dioxide (CO 2 ) and carbon monoxide (CO) on copper surfaces, with the assumption that higher OH − concentrations promote the C−C coupling chemistry. Herein, by systematically varying the concentration of Na + and OH − at the same absolute electrode potential, we demonstrate that higher concentrations of cations (Na + ), rather than OH − , exert the main promotional effect on the production of C 2+ products. The impact of the nature and the concentration of cations on the electrochemical reduction of CO is supported by experiments in which a fraction or all of Na + is chelated by a crown ether. Chelation of Na + leads to drastic decrease in the formation rate of C 2+ products. The promotional effect of OH − determined at the same potential on the reversible hydrogen electrode scale is likely caused by larger overpotentials at higher electrolyte pH.