A Reduced Imidazolium Cation Layer Serves as the Active Site for Electrochemical Carbon Dioxide Reduction

Abstract Since Rosen et al. in 2011 found that imidazolium ionic liquid significantly increases the activity and selectivity of the electrochemical reduction of CO2 to CO, the catalytic role of imidazolium ionic liquid in CO2 reduction has been intensively investigated. To date, however, the molecular mechanism behind this activity and selectivity remains to be elucidated. Here, we report the role of a reduced imidazolium cation layer in facilitating CO2 reduction on a Cu electrode surface while simultaneously suppressing hydrogen evolution. The results of cyclic voltammetry and on-line differential electrochemical mass spectrometry, coupled with in-situ surface-enhanced Raman spectroscopy, indicated that the Cu surface is partially covered by the reduced imidazolium cations at potentials around ―0.8 V vs SHE. This potential is consistent well with the observed onset potential for the electroreduction of CO2, as well as the calculated one-electron reduction potential of imidazolium cations to form imidazolium radicals on Cu electrodes.