In–depth understanding on the mechanism of ionic liquid-assisted enhancement of electrochemical CO2 reduction to formic acid

Although extensive research has been conducted on the electrochemical CO2 reduction reaction (CO2RR) using ionic liquid (IL) + acetonitrile and ILs + acetonitrile + H2O systems, it is a challenge to explain why ILs facilitate electrochemical CO2 reduction and why different ILs exhibit varying catalytic effects. In this paper, we utilized commercially available copper electrodes as the working electrode and employed three ILs (i.e., 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), and 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([BMIM][Tf2N])) as one of the additive components of electrolytes for electrochemical CO2RR. The relationship between the performance of electrochemical CO2RR to formic acid (FA) and different IL structures in binary and ternary systems was investigated through experiments. The mechanism of performance of electrochemical CO2RR to FA enhanced by ILs in the binary systems was explored at the molecular level through density functional theory (DFT) calculations. Furthermore, the role of H2O was elucidated in the ternary IL + acetonitrile + H2O system.