Pyrazolium Ionic Liquid Co-catalysts for the Electroreduction of CO2

Pyrazolium ionic liquids (Pz ILs) were employed as co-catalysts for electrochemical conversion of CO2 to CO on a silver disk electrode, leading to a significant decrease in the onset potential for the reduction (ca. 500 mV). The electrochemical conversion of CO2 to CO proceeds in acetonitrile-based electrolytes containing Pz IL co-catalysts with Faradaic efficiencies (FEs) of nearly 100% over a range of at least 0.5 V, and the Pz cations remain intact over prolonged CO2 electrolysis. The impact of alkyl substituents on the Pz ring and the influence of water on the process are also discussed.