Cation Effect on the Dynamics of Intermediates in Electroreduction of Carbon Dioxide in Acids

In the electrochemical reduction of CO2, the employment of an acidic electrolyte with an alkali metal cation could reduce carbon loss. However, how the alkali metal cation activates CO2 and promotes the following proton-coupled electron transfer steps remains ambiguous. Here, from a rigorous analysis of CO2 reduction and CO reduction, we reveal that the kinetics of the CO2 electro-activation step and the following C–C coupling step both correlate positively with the concentration of K+, except that the promotion effect of K+ on the CO2-to-*CO step reaches a plateau when the concentration of K+ is ≥0.7 M under a high overpotential. The activity toward multicarbon products is determined by the dual cationic effect of K+ on the two steps, as evidenced in in situ Raman spectroscopy. The spectroscopic investigation shows that the adsorption of *CO shifts from atop configuration to bridge configuration as a net result of the dual cation effect, and the amount of adsorbed *OH increases with the rise of K+ concentration.