Ternary Ionic-Liquid-Based Electrolyte Enables Efficient Electro-reduction of CO2 over Bulk Metal Electrodes

Using bulk metals as catalysts to get high efficiency in electro-reduction of CO₂ is ideal but challenging. Here, we report the coupling of bulk metal electrodes and a ternary ionic-liquid-based electrolyte, 1-butyl-3-methylimidazolium tetrafluoroborate/1-dodecyl-3-methylimidazolium tetrafluoroborate/MeCN to realize highly efficient electro-reduction of CO₂ to CO. Over various bulk metal electrodes, the ternary electrolyte not only increases the current density but also suppresses the hydrogen evolution reaction to obtain a high Faradaic efficiency (FE) toward CO. FE_CO could maintain ∼100% over a wide potential range, and metal electrodes showed very high stability in the ternary electrolyte. It is demonstrated that the aggregation behavior of the ternary electrolyte and the arrangement of two kinds of IL cations with different chain lengths in the electrochemical double layer not only increase the wettability to electrode and CO₂ adsorption but also extend the diffusion channel of H⁺, rendering the high current density and FE_CO.