Efficient electrocatalytic reduction of CO2 on an Ag catalyst in 1-ethyl-3-methylimidazolium ethylsulfate, with its co-catalytic role as a supporting electrolyte during the reduction in an acetonitrile medium

CO₂ electrochemical reduction reactions (CO₂ERR) has shown great promise in reducing greenhouse gas emissions while also producing useful chemicals. In this contribution, we describe the CO₂ERR at different catalysts using 1-ethyl-3-methylimidazolium ethyl sulfate [emim][EtSO₄] ionic liquid (IL) as a solvent and as a supporting electrolyte. CO₂ERR occurs at Ag and Cu catalysts at a lower overpotential than that at Au, Pt, and boron-doped diamond (BDD) catalysts. In addition, we report that ILs play a better co-catalytic role when used as a supporting electrolyte during CO₂ERR in an acetonitrile (AcN) medium than the conventional supporting electrolyte, tetrabutylammonium hexafluorophosphate [TBA][PF₆] in AcN. Furthermore, it is found that imidazolium-based cations ([emim]⁺) play a significant co-catalytic role during the reduction compared to [TBA]⁺ and pyrrolidinium [empyrr]⁺ cations, while anions of the ILs play no such role. The formation of CO from the CO₂ERR was detected using cyclic voltammetry at an Ag catalyst both in [emim][EtSO₄] as well as in an AcN solvent containing [emim][EtSO₄] as a supporting electrolyte. The product of the CO₂ reduction in this IL medium at the Ag catalyst is CO, which can be converted to synthetic liquid fuels by coupling the process with the Fischer-Tropsch process or through the conversion of CO₂ into fuels based on green hydrogen by the Sabatier process, that is, methanation of CO₂ on industrial scale, in the future.