Electrochemical Impedance Studies of CO2 Reduction in Ionic Liquid/Organic Solvent Electrolyte on Au Electrode

Electrochemical reduction of CO2 has been studied in 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([Bmim][CF3SO3])/propylene carbonate (PC) solution on Au electrode. The linear sweep voltammetry measurements show that [Bmim][CF3SO3] has significant catalytic effect toward CO2 reduction. In order to study the mechanism of CO2 reduction in [Bmim][CF3SO3]/PC on Au electrode, the electrochemical impedance spectroscopy is employed. The experiment results show that the electrochemical impedance spectroscopy detected in [Bmim][CF3SO3]/PC is different from that detected in tetrabutylammonium trifluoromethanesulfonate ([Bu4N][CF3SO3])/PC solution. The reasonable explanation is that [Bmim]+ is absorbed on the Au electrode, leading to the formation of ionic liquid film. During the CO2 reduction process, absorbed CO2 is reduced to CO2− radical via single electron transfer. The generated CO2− radical interacts with [Bmim]+ and inducing the formation of [Bmim-CO2](ad). Thus, the activation energy and overpotential of CO2 reduction are reduced. The electrochemical impedance spectroscopy can be used as a methods to investigate the mechanism of CO2 reduction in non-aqueous solution.