Experimental Studt Of Ionic Liquid-water-Acetonitrile Electrolytic Liquid Used In CO₂ Electrochemical Reduction

With the consumption of traditional fossil fuels,the amount of carbon dioxide(CO2)in the atmosphere is increasing year by year,which brings about increasingly serious environmental problems.At the same time,CO2 is also a rich and cheap carbon resource,which can be used to produce high value-added chemical products.Therefore,CO2 fixation is of great significance.CO2 electrochemical reduction has the characteristics of mild conditions,environment friendly,which can realize the resource utilization of CO2.In traditional inorganic salt aqueous solution electrolyte,because of severe hydrogen evolution reaction,product Faraday efficiency and current density are low.Ionic liquid electrolytic liquid system has lots of advantages,such as well CO2 absorption performance,less side effect,high Faraday efficiency and current density.Therefore,ionic liquid electrolytic liquid system has good performance in the CO2 electrochemical reduction.Firstly,a series of imidazole and proton ionic liquids were synthesized by one-step method and two-step method in this paper.The physical properties of the synthesized ionic liquids,such as viscosity,conductivity,electrochemical window and CO2 absorption capacity,were tested.The synthesized ionic liquid was configured into IL-H2O-MeCN electrolyte.At the same time,four kinds of Cu-based catalysts were synthesized.The effects of concentration of[Bmim][BF4]and H2O,electrolytic potential and electrolytic time on electrochemical reduction of CO2 were studied in[Bmim][BF4]-1MH2O-MeCN electrolyte.The addition of an appropriate amount of H2O can significantly improve the Faraday efficiency and stabilize the electrolytic liquid system.The optimal conditions for the electrochemical reduction of CO2 in the[Bmim][BF4]-1MH2O-MeCN electrolyte were:[Bmim][BF4]content was 0.5mol/L,water content was lmol/L,electrolytic potential was-1.7V(vs.Ag/AgCl),and electrolysis time was 4h.Under above conditions,the Faraday efficiencies of formic acid and acetic acid were the highest(60%and 12.3%,respectively),and the current densities were 3.01mA·cm-2 and 0.63mA·cm-2,respectively.In the-1.7V(vs.Ag/AgCl),electrolysis time 4h,0.5M[Bmim][BF4]-1MH2O-MeCN system,the influence of catalyst type on the electrochemical reduction of CO2 was compared.Although the products selectivity of copper-based catalysts is different,higher Faraday efficiency and current density can be obtained under Cu2(CuTCPP)catalysis.Finally,the influence of the electrolyte on the electrochemical reduction of CO2 was studied at the electrolytic potential of-1.7v(vs.Ag/AgCl)and the electrolytic time was 4h.The performance of 0.5M[Bmim][BF4]-1MH2O-MeCN was the best in the electrolytes with different imidazole cationic alkyl carbon chain lengths.In the different anionic electrolytic liquid systems,0.5M[Bmim][PF6]-1MH2O-MeCN,formic acid and acetic acid had the highest Faraday efficiency(63.4%and 15.3%,respectively).The current densities were 6.82mA·cm-2 and 1.65mA·cm-2,respectively.The electrochemical reduction performance of CO2 in protic ionic liquid was poor,and Faraday efficiency was only 23.4%and 3.7%.Compared with ionic liquid electrolysis system,the electrochemical reduction performance of CO2 in inorganic salt solution is poor,and Faraday efficiency and current density of the product are low.Therefore,ionic liquid electrolytic liquid system has a good application prospect in the electrochemical reduction of CO2.