Improvement of Electrochemical Reduction of CO2 Using the Potential-Pulse Polarization Method

Abstract

Electrochemical conversion of CO2 gas emitted to the atmosphere to useful chemicals has been expected to suppress the global greenhouse effect and to conserve the natural resources. For the electrochemical reduction of CO2 on an Ag electrode, the effect of the addition of 1-ethyl-3-methylimidazolium ethyl sulfate (EMISE) ionic liquid to the aqueous solution of 0.1 mol dm−3 K2CO3, and the effect of the polarization methods, i.e., the potentiostatic polarization and the potential-pulse polarization, on the reduction efficiency were investigated. From the gas chromatography measurement, CO as the main product of CO2 reduction and H2 as a by-product of water decomposition were obtained. Faraday efficiency of CO formation obtained by the potential-pulse polarization was considerably higher than that obtained by the potentiostatic polarization. The addition of EMISE could add further improvement in the efficiency of CO formation higher than 70%. Such improvement provided by the potential-pulse polarization method and the addition of EMISE was interpreted by the depletion and recovery of the reactants on the electrode in the pulse cycle and promotion of CO2 molecular formation from HCO3− ions in the dense adsorption layer of EMIM cations on the electrode surface.

Keywords

• pulse polarization
• electrochemical reduction
• ionic liquid
• silver electrode