Reduction of Carbon Dioxide to Formate at Low Overpotential Using a Superbase Ionic Liquid

A new low‐energy pathway is reported for the electrochemical reduction of CO2 to formate and syngas at low overpotentials, utilizing a reactive ionic liquid as the solvent. The superbasic tetraalkyl phosphonium ionic liquid [P66614][124Triz] is able to chemisorb CO2 through equimolar binding of CO2 with the 1,2,4‐triazole anion. This chemisorbed CO2 can be reduced at silver electrodes at overpotentials as low as 0.17 V, forming formate. In contrast, physically absorbed CO2 within the same ionic liquid or in ionic liquids where chemisorption is impossible (such as [P66614][NTf2]) undergoes reduction at significantly increased overpotentials, producing only CO as the product. The superbasic RTIL (room‐temperature ionic liquid) [P66614][124Triz] provides an alternative low‐energy pathway for conversion of CO2 into formate. This is the first time chemical binding of the CO2 molecule to the anion of a RTIL has been shown to decrease the activation energy for electrochemical reduction, by distortion of the CO2 geometry from linear to bent.