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 CO(2) to formate and syngas at low overpotentials, utilizing a reactive ionic liquid as the solvent. The superbasic tetraalkyl phosphonium ionic liquid [P(66614)][124Triz] is able to chemisorb CO(2) through equimolar binding of CO(2) with the 1,2,4-triazole anion. This chemisorbed CO(2) can be reduced at silver electrodes at overpotentials as low as 0.17 V, forming formate. In contrast, physically absorbed CO(2) within the same ionic liquid or in ionic liquids where chemisorption is impossible (such as [P(66614)][NTf(2)]) undergoes reduction at significantly increased overpotentials, producing only CO as the product.