Selective Acidic CO₂ Electroreduction to Methane Using Crown Ether-Functionalized Copper-Based Electrodes

CO₂ electroreduction (CO₂R) using Cu catalysts under acidic conditions currently receives substantial attention as it allows to limit detrimental (bi)carbonate salts formation and precipitation. However, it usually requires high concentrations of K-based electrolytes for suppressing hydrogen evolution (HER) and favoring C₂ products formation. Here we used crown-ethers in order to immobilize alkali cations at the surface of the catalyst and show that this strategy not only allows suppressing HER with much less concentrated electrolyte but also orientates the reaction towards CH₄ formation during acidic CO₂R. The utilization of 10 different crown-ethers allowed to study the effect of the structure of the ligand and the nature of the cation on CO₂R selectivity. The largest Faradic Efficiency for methane (FE_CH4 = 55%) was obtained under an applied current density of -150 mA.cm^-2, using the 4'-amino-benzo-15-crown-5-Na⁺ complex.