Imidazolium ion-terminated self-assembled monolayer (SAM)-modified electrodes achieve CO₂ conversion while suppressing hydrogen evolution. Immobile imidazolium ion on gold (Au) electrodes reduce CO₂ at low overpotential. The distance between electrode and imidazolium ion separated by alkane thiol affects CO₂ reduction activity. CO₂ reduction current depends on the tunnel current rate. Although the product of CO₂ reduction at the bare Au electrode is CO, SAM-modified electrodes produce ethylene glycol in aqueous electrolyte solution without CO evolution. The faradaic efficiency reached a maximum of 87%. CO₂ reduction at SAM-modified electrodes is unaffected by reduction activity of Au electrode. This phenomenon shows that the reaction field of CO₂ reduction is not the electrode surface but the imidazolium ion monolayer.