Abstract
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.
Highlights
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 high overpotential for CO2 reduction is related to the large reorganization energy associated with reduction of linear CO2 to the bent [CCO2]À radical anion
Initial reports on CO2 reduction in room-temperature ionic liquids (RTILs) formed dialkyl carbonates through generation of CCO2 radicals, which were reacted with alcohols using 1-alkyl-3-methylimidazolium ([Cnmim]+) based RTILs with a range of non-coordinating anions.[7]
Summary
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. Rosen et al reported the use of Ag electrodes in [C2mim][BF4], which was found to decrease the energy of formation of the [CCO2]À radical anion through the complexation of CO2 with the [C2mim]+ cation.[8] This significantly reduced the overpotential for CO2 reduction to CO to < 0.2 V.
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