(41b) Enhanced CO2 Electroreduction in Selectivity Tuned By Anion Modification of the Ionic Liquids

Jianpeng Feng ^a,b, Shaojuan Zeng^a, Suojiang Zhang ^a , Xiangping Zhang ^a,*

^a Institute of Process Engineering, Chinese Academy of Sciences, 100190, Beijing, China

^bUniversity of Chinese Academy of Science, Beijing 100049, China

*Corresponding author: xpzhang@ipe.ac.cn

In the past hundreds years, the unrestrained combustion of non-renewable fossil fuels leads to an aggravated energy crisis and a continuously rising level of atmospheric carbon dioxide (CO₂). which has created serious environmental, social and global ecological issues^{1, 2}. However, CO₂ is also a cheap, abundant and renewable C1-feedstock that can be converted into useful chemicals. Electrochemical reduction was extensively studied owing to their mild reaction conditions and easy implementation for practical applications. Moreover, they can directly use the seasonal, geographical, and intermittent energy (tied, wind, and solar et al.). However, the low solubility of CO₂ and complicated reaction process in aqueous solution render CO₂ reduction inefficient. Ionic liquid (IL) has been proven to be a promising reaction medium for CO₂ electrochemical reaction because of its unique physicochemical properties (e.g., high CO₂ solubility, high intrinsic ionic conductivity, wide electrochemical potential windows )^{3, 4}

In this work, Herein, we present an efficient CO₂ electroreduction system based on a diverse class of imidazolium ILs, including a novel superbase IL 1-Butyl-3-Methylimidazolium 1,2,4-Triazolide ([Bmim][124Triz]). The superbase IL has a superior capacity of 0.726 mol CO₂ per mol IL, and the high concentration of dissolved CO₂ in the electrolyte is favorable for the fast transport of CO₂ to the cathode surface. On Pb electrode, the applied potential for CO₂ reduction to formic acid (HCOOH) was lowered from circa -1.97 V to -1.78 V (vs. Ag/Ag⁺) compared to [Bmim][PF₆] IL. For now it was widely reported that the reduced form from imidazolium cation, namely, imidazolium neutral radical serves as the reaction site for CO₂ reduction, nevertheless, we found that in the HCOOH formation on Pb electrode, the chemical binding of the [124Triz]^- anion and CO₂ molecule can decrease the activation energy, significantly. Furthermore, within the same strategy, the highest Faradaic efficiency (98.4%) at partial current density of 11.7 mA cm^-2 for CO was obtained on Ag in ILs system to date. Our finding about the role of the anion on CO₂ electroreduction will stimulate to develop more novel anions to enhance this reaction process and open a potential way for the efficient utilization of CO₂.

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