Understanding the role of imidazolium-based ionic liquids in the electrochemical CO2 reduction reaction

The development of efficient CO2 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 CO2 electrocatalytic reduction to CO over Ag electrode. Relevant activity and stability, but different selectivities for CO2 reduction or the side H-2 evolution were observed. Density functional theory results show that depending on the IL anions the CO2 is captured or converted. Acetate anions (being strong Lewis bases) enhance CO2 capture and H-2 evolution, while fluorinated anions (being weaker Lewis bases) favour the CO2 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. Room-temperature ionic liquids are increasingly investigated as electrolytes for electrocatalytic CO2 reduction thanks to their high intrinsic ionic conductivities, wide electrochemical potential windows, and high CO2 absorption capacities and solubilities. Here, seven imidazolium-based ionic liquids are investigated as electrolytes for the electrochemical conversion of CO2 to CO using a silver foil cathode, with their stability, co-catalytic effects, and varying selectivities elucidated.