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

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.

Carbon Dioxide Capture by Aqueous Ionic Liquid Solutions

“…[17,[19][20][21]32] However,i no ur case, the carbamate pathway can be discardeda so nly two 13 C signals wereo bserved for the anion with chemical shifts very close to that displayed by the starting material. [17,[19][20][21]32] However,i no ur case, the carbamate pathway can be discardeda so nly two 13 C signals wereo bserved for the anion with chemical shifts very close to that displayed by the starting material.…”

“…[4,7,8] This is mainly owed to the high CO 2 solubility in ILs as well as the possibility to fine-tune the sorption properties of the ionic material. [16][17][18][19][20][21] This mechanism requires much more energy for CO 2 release than the noncovalent path, but because of the formation of a CO 2 derivative, these ILs have in turn ah igherc apacity for CO 2 capture. [9,10] However,t he use of traditional and neat ILs as physicals orbents for CO 2 is not particularly good because, in most of the cases, their noticeable high solubility resultsf rom their high molecular weight.…”

Recent Trends, Benchmarking, and Challenges of Electrochemical Reduction of CO2 by Molecular Catalysts

“…Thanks to the electrochemical nature of the CO 2 conversion to fuels and chemicals, the electrical energy invested to convert CO 2 in the form of a chemical fuel can be stored and redistributed using established supply chains for future use. [12][13][14] However, despite the low potentials offered by catalytic electrodes, the cost of electrodes is not always viable when upscaled to industrial levels. Converting CO 2 electrochemically into compounds with high energy densities, such as alcohols (methanol, ethanol), formates, and CO, represents a form of energy storage and is also adaptable to demand response or energy arbitrage technologies.…”

Sustainable Cyclic Carbonate Production, Utilizing Carbon Dioxide and Azolate Ionic Liquids

“…47 Even though they are more basic than common trialkylamines, the pKa values of their conjugate acids would not warrant them to qualify as superbasic substances. [48][49][50] Nevertheless, their associated anions possess sufficiently high nucleophilicity to attach weakly electrophilic CO2, enabling them to be used in CO2 gas capture and catalysis.…”

“…[48][49][50] Nevertheless, their associated anions possess sufficiently high nucleophilicity to attach weakly electrophilic CO2, enabling them to be used in CO2 gas capture and catalysis. 47,[51][52][53][54][55] In this paper, we refer to them as azolate ionic liquids (or salts).…”