| Carbon dioxide has been considered as the primary green-house gas, and it is an abundant, cheap and potential carbon resourse as well. Electrochemical reduction of CO2 to value-added chemicals has great significance in energy conservation, environmental protection, utilization of renewable energy. Ionic liquid （IL） is a novel solvent which has been considered as a promising electrolyte in electrochemistry. It possesses many desirable and unique properties for CO2 reduction, such as wide electrochemical potential window, good thermal and chemical stability and low vapor pressure. In this paper, using a H-type cell, we studied the kinetic characteristics of CO2 reduction in l-butyl-3-methylimidazolium trifluoromethan-esulfonate （[Bmim][CF3SO3]）/propylene carbonate （PC） solution. Also, the catalytic effect and mechanism of the imidazole ionic liquid towards CO2 electroreduction are analyzed. The main contents are as follows:（1） In Tetrabutylammonium bromide（Bu4NBr）/propylene carbonate （PC） and Tetrabutylammonium Trifluoromethanesulfonate（[Bu4N][CF3SO3]）/PC solution, the catalytic activity of Au electrode is higher than that of Ag electrode towards CO2 reduction. In Bu4NBr/PC solution, the faradaic efficiency of CO reached maximum when the potential is-2.45V, and the current density is maintained about 1.15mA/cm2 during the two hours electrolysis process. While in [Bu4N][CF3SO3]/PC solution, the faradaic efficiency of CO reached maximum when the potential is-2.6 V, and the current density is maintained about 3.33mA/cm2 during the two hours electrolysis process.（2）In [Bmim][CF3SO3] solution, the transfer coefficient a is 0.1476, exchange current density is 1.914x10"* A/cm2 and the charge transfer resistance is 67.07cm2. During the potentiostatic electrolysis process, the current density of CO2 reduction is maintained about 2.15mA/cm2, and the Faradaic efficiencie of CO is about 62%. The catholyte has the highst electrical conductivity 12.76 mS/cm when m（[Bmim][CF3SO3]） :m（PC）=4:6. In this catholyte, the faradaic efficiency of CO reached maximum when the potential is-2.2SV. During the long period electrolysis process, the current density is maintained about 5.2mA/cm2, and the Faradaic efficiencies of CO maintained more than 90%.（3）With the increase of water content in m（[Bmim][CF3SO3]）:m（PC）=4:6 solution, the cathode reaction current density increased gradually. The highest CO faradic efficiency reaches 96.5% when the water content is 2% in the catholyte. The optimum water content in the catholyte is 0%～10%.（4）In [Bmim][CF3SO3]/PC solution, the onset potential of CO2 reduction shifts positively by 239 mV comparing with that in [Bu4N][CF3SO3]/PC solution. Also, a higher current density is obtained in [Bmim][CF3SO3]/PC solution. The catalytic mechanism of ionic liquid is illucidated as follows:firstly, [Bmim]+absorbs on the cathode and form a film. And then, CO2 adsorbed on the surface of Au electrode after transfer through the ionic liquid film. After that, CO2 molecular was reduced to CO2-radicald via single electron transfer. Then, the generated CO2- radical interacts with cation [Bmim]+and inducing the formation of [Bmim-CO2]（ad）. Through this route, the energy state of CO2- is decreased and the activation energy of CO2 electrochemical reduction is reduced. Hence the overpotential of CO2 electrochemical reduction was reduced substantially. |
