Alkaline Ionic Liquid Microphase Promotes Deep Reduction of CO₂ on Copper

Abstract

Electrochemical reduction of CO₂ to multicarbon (C₂₊) products using renewable energy sources is an important route to storing sustainable energy and achieving carbon neutrality. It remains a challenge to achieve high C₂₊ product faraday efficiency (FE) at ampere-level current densities. Herein, we propose the immobilization of an alkaline ionic liquid on copper for promoting the deep reduction of CO₂. By this strategy, a C₂₊ FE of 81.4% can be achieved under a current density of 0.9 A·cm^-2 with a half-cell energy conversion efficiency of 47.4% at -0.76 V vs reversible hydrogen electrode (RHE). Particularly, when the current density is as high as 1.8 A·cm^-2, the C₂₊ FE reaches 71.6% at an applied potential of -1.31 V vs RHE. Mechanistic studies demonstrate that the alkaline ionic liquid plays multiple roles of improving the accumulation of CO₂ molecules on the copper surface, promoting the activation of the adsorbed CO₂, reducing the energy barrier of CO dimerization, stabilizing intermediates, and facilitating the C₂₊ product formation.