Understanding the role of imidazolium-based ionic liquids in the electrochemical CO(2) reduction reaction

The development of efficient CO(2) capture and utilization technologies driven by renewable energy sources is mandatory to reduce the impact of climate change. Herein, seven imidazolium-based ionic liquids (ILs) with different anions and cations were tested as catholytes for the CO(2) electrocatalytic reduction to CO over Ag electrode. Relevant activity and stability, but different selectivities for CO(2) reduction or the side H(2) evolution were observed. Density functional theory results show that depending on the IL anions the CO(2) is captured or converted. Acetate anions (being strong Lewis bases) enhance CO(2) capture and H(2) evolution, while fluorinated anions (being weaker Lewis bases) favour the CO(2) electroreduction. Differently from the hydrolytically unstable 1-butyl-3-methylimidazolium tetrafluoroborate, 1-Butyl-3-Methylimidazolium Triflate was the most promising IL, showing the highest Faradaic efficiency to CO (>95%), and up to 8 h of stable operation at high current rates (−20 mA & −60 mA), which opens the way for a prospective process scale-up.