Insight into the Role of Entropy in Promoting Electrochemical CO2 Reduction by Imidazolium Cations.

Abstract

The electroreduction of CO2 plays an important role in achieving a net-zero carbon economy. Imidazolium cations can be used to enhance the rate of CO2 reduction reactions, but the origin of this promotion remains poorly understood. In this work, we show that in the presence of 1-ethyl-3-methylimidazolium (EMIM+), CO2 reduction on Ag electrodes occurs with an apparent activation energy near zero, while the applied potential influences the rate through the pre-exponential factor. Our findings suggest that the CO2 reduction rate is controlled by the initial state entropy, which depends on the applied potential through the organization of cations at the electrochemical interface. Further characterization shows that the C2-proton of EMIM+ is consumed during the reaction, leading to the collapse of the cation organization and a decrease in the catalytic performance. Our results have important implications for understanding the effect of potential on reaction rates, as they indicate that the common picture based on vibrational activation of electron transfer reactions is insufficient for describing the impact of potential in complex systems, such as CO2 reduction in the presence of imidazolium cations.