Performance Adjustment Of Electrochemical Reduction Of CO₂ By Functionalized Imidazolium Ionic Liquids

With the rapid development of industry,the global environment and ecology has severely affected by the greenhouse gas CO₂which increased year by year.The electrochemical method has been used to capture CO₂in the production of valuable compounds,at the same time,to achieve green environmental protection and renewable resources.Because of the good conductivity and high electrochemical window,imidazolium ionic liquids are used as electrolytes for the electrochemical reduction of CO₂.In this paper,we have studied the effect of the electrochemical reduction of CO₂by ionic liquids with alkyl imidazole cations and anions containing fluorine atoms on Pb,In,and Sn electrodes.The results and conclusions are as follows:We systematically study the viscosities and conductivities of the imidazolium ionic liquids[C_nmim]BF₄（n=3-5）and[C₃mim]OTf and their aqueous solutions.The results show that,the conductivities of ionic liquids and their aqueous solutions increase and viscosities decrease with the increasing of temperature.When the concentration range of imidazolium ionic liquid solution is 10-100 mg/m L,the viscosities of the ionic liquid aqueous solutions are lower than that of the pure ionic liquids,and the conductivities are opposite.In order to investigate the effect of imidazolium ionic liquids’anions and cations on the electrochemical reduction of CO₂,cyclic voltammetry and linear scanning voltammetry were conducted on Pb,In,and Sn electrodes in a three-electrode system.Using[C_nmim]BF₄（n=3-5）aqueous solution as the electrolyte,the onset potential for CO₂reduction shifts to the increasingly negative potential with the increase of the side chain length of the imidazole cycloalkyl group.Using[C₃mim]BF₄and[C₃mim]OTf aqueous solution as the electrolyte,the onset reduction potential of CO₂is more positive when the[C₃mim]BF₄aqueous solution as electrolyte.By means of constant potential electrolysis,we found that the anions and cations of imidazolium ionic liquids play important roles in the electrochemical reduction of CO₂.We have studied the electrochemical reduction of CO₂into HCOOH on Pb electrode in[C_nmim]BF₄（n=3-5）aqueous solution.Using 80 mg/m L[C₃mim]BF₄aqueous solution as the electrolyte,Faradaic efficiencies as high as 91.82%,was reached at-2.1 V（vs.Ag/Ag⁺）.We also have studied the electrochemical reduction of CO₂into HCOOH on Pb electrode in[C₃mim]BF₄and[C₃mim]OTf aqueous solution.Using 80 mg/m L[C₃mim]BF₄aqueous solution as the electrolyte,Faradaic efficiencies as high as 91.82%,was reached at-2.1 V（vs.Ag/Ag⁺）.The electrochemical reduction of CO₂to HCOOH on In electrode in[C_nmim]BF₄（n=3-5）aqueous solution have been studied.Using 60 mg/m L[C₅mim]BF₄aqueous solution as the electrolyte,Faradaic efficiencies as high as 92.27%,was reached at-2.1 V（vs.Ag/Ag⁺）.We also have studied the electrochemical reduction of CO₂into HCOOH on In electrode in[C₃mim]BF₄and[C₃mim]OTf aqueous solution.Using 10 mg/m L[C₃mim]BF₄aqueous solution as the electrolyte,Faradaic efficiencies as high as 92.08%,was reached at-2.1 V（vs.Ag/Ag⁺）.The electrochemical reduction of CO₂to HCOOH on Sn electrode in[C_nmim]BF₄（n=3-5）aqueous solution have been studied.Using 10 mg/m L[C₄mim]BF₄aqueous solution as the electrolyte,Faradaic efficiencies as high as 38.54%,was reached at-2.1 V（vs.Ag/Ag⁺）.We also have studied the electrochemical reduction of CO₂into HCOOH on Sn electrode in[C₃mim]BF₄and[C₃mim]OTf aqueous solution.Using 40 mg/m L[C₃mim]BF₄aqueous solution as the electrolyte,Faradaic efficiencies as high as 54.14%,was reached at-2.0 V（vs.Ag/Ag⁺）.