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.　©　2024　Hydrogen　Energy　Publications　LLC