Aromatic Ester-Functionalized Ionic Liquid for Highly Efficient CO2 Electrochemical Reduction to Oxalic Acid
Yingliang Yang1,2, Hongshuai Gao1, Jiaqi Feng1,3
1Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, P. R. China.
Abstract:
Electrochemical reduction of CO2 into valuable chemicals is a significant route to utilize CO2 resources. Among various electroreduction products, oxalic acid (H2 C2 O4 ) is an important chemical for pharmaceuticals, rare earth extraction, and metal processing. Here, an aprotic aromatic ester-functionalized ionic liquid (IL), 4-(methoxycarbonyl) phenol tetraethylammonium ([TEA][4-MF-PhO]), was designed as an electrolyte for CO2 electroreduction into oxalic acid. It exhibited a large oxalic acid partial current density of 9.03 mA cm-2 with a faradaic efficiency (FE) of 86 % at -2.6 V (vs. Ag/Ag+ ), and the oxalic acid formation rate was as high as 168.4 μmol cm-2 h-1 , which is the highest reported value to date. Moreover, the results of density functional theory calculations demonstrated that CO2 was efficiently activated to a -COOH intermediate by bis-active sites of the aromatic ester anion via the formation of a [4-MF-PhO-COOH]- adduct, which finally dimerized into oxalic acid.
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