Electrochemical Reduction of CO 2 on a Cu Electrode under High Pressure: Factors that Determine the Product Selectivity

Abstract

The selectivity of the electrochemical reduction products of CO 2 on a Cu electrode in aqueous KHCO 3 solution depended remarkably on the CO 2 pressure (<60 atm), stirring condition, and the current density. As the flux of CO 2 to the Cu electrode surface was increased by increasing CO 2 pressure and/or by stirring, the main reduction product was changed in the order of H 2 → hydrocarbons → CO and/or HCOOH . On the other hand, the selectivity of the reduction products was changed in the order of CO and/or HCOOH → hydrocarbons → H 2 by increasing the current density. From these results, it was concluded that the balance between the flux of CO 2 from the bulk solution to the electrode surface and the current density determines which reduction products are produced. Hydrocarbon formation was preferential when the current density was comparable to the maximum CO 2 flux under given condition. The partial current density for maximum hydrocarbon formation occurred at 375 mA cm −2 under CO 2 pressure at 30 atm.