Graphite Formation From CO2 Electroreduction in a Synergistic Ionic Liquid–Liquid Metal System

Abstract

Electrochemical CO₂ reduction at catalytic liquid metal (LM) surfaces offers a promising route for sustainable carbon conversion, yet suboptimal electrolyte formulations limit its practical implementation. We demonstrate CO₂ reduction at a cerium-containing liquid metal (LM-Ce) using, for the first time, an ionic liquid-based electrolyte that combines high CO₂ solubility, electrochemical stability, and high solution conductivity. Using 1 M 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM-TfO) with 2 M H₂O in N,N-dimethylformamide (DMF), and under an applied potential of –1.44 V versus standard hydrogen electrode (SHE), the system achieves a high current density while CO₂ reduction to graphite proceeds with an overall faradaic efficiency of 73.2 ± 3.3% and a high degree of graphitization (I_G/I_D ≈ 5). These results demonstrate that ionic liquids (ILs) function not only as excellent supporting media but may also serve as active and potentially tunable components to improve CO₂ reduction rates at LM-Ce interfaces.