Imidazolium- and Pyrrolidinium-Based Ionic Liquids as Cocatalysts for CO₂ Electroreduction in Model Molecular Electrocatalysis

The structure effect on the role of different ionic liquids (ILs) as a simultaneous supporting electrolyte and cocatalyst for CO2 electroreduction in the presence of a model molecular catalyst [Re(bpy)(CO)3Cl] has not been addressed yet. In particular, we varied the nature of the cation, anion, and cation alkyl chain by a choice of five different ILs, including imidazolium and pyrrolidinium cations, and we compared their results to benchmark the supporting electrolyte. We report an overpotential diminution of 0.33 V for CO2 to CO conversion in the presence of ILs under CO2 catalytic conditions. We prove the IL cation-dependent overpotential diminution due to the electrostatic stabilization of the negatively charged active form of the catalyst, with the π–π stacking interaction provided by imidazolium cations responsible for their outstanding performance. Finally, a mechanistic explanation is provided to justify a weaker IL cocatalytic effect when CO2 electroreduction takes place in the presence of a proton source.