From high-purity synthesis to key experimental considerations for evaluating functionalized ionic liquids for combined capture and electrochemical conversion of CO2

Ionic liquids (ILs) are considered functional electrolytes for the electrocatalytic reduction of CO2 (ECO2R) due to their role in the double-layer structure formation and increased CO2 availability at the electrode surface, which reduces the voltage requirement. However, not all ILs are the same considering the purity and degree of the functionality of the IL. Further, there are critical experimental factors that impact the evaluation of ILs for ECO2R including the reference electrode, working electrode construction, co-solvent selection, cell geometry, and whether the electrochemical cell is a single compartment or a divided cell. Here, we describe improved synthesis methods of imidazolium cyanopyrrolide IL for electrochemical studies in consideration of precursor composition and reaction time. We explored how IL dilution within acetonitrile, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), propylene carbonate (PC), and n-methyl-2-pyrrolidone (NMP) affected conductivity and CO2 mass transport, and ECO2R activation overpotential, as well as surveyed effects of electrode material (Sn, Ag, Au and glassy carbon). Acetonitrile was found to be the best solvent for lowering the onset potential and increasing the catalytic current density for the production of CO owing to the enhanced ion mobility in combination with the silver electrode. Further, the ECO2R activity of molecular catalysts Ni(cyclam)Cl2 and iron tetraphenylsulfonato porphyrin (FeTPPS) on carbon cloth electrode maintained high Faradaic efficiencies for CO in the presence of the IL. This study presents best practices for examining non-traditional multifunctional electrolytes amenable to integrated CO2 capture and conversion technologies for homogenous and heterogenous ECO2R.