Electrochemical Decomposition Of CO₂ In LiF-Li₂O Molten Salt System

With the rapid development of industry,the emission of greenhouse gas has been increasing year by year.The greenhouse effect is aggravating,causing the earth to be warmer and warmer,and the greenhouse gas emission reduction has become the focus of global research and attention.It is one of the hot topics in current research to find a way to convert and utilize CO2 in the atmosphere.The molten salt electrolysis method is used to decompose the CO2 which is absorbed in the molten salt.This way of obtaining carbon at the cathode and obtaining O2 at the anode is undoubtedly the best result for CO2 conversion and utilization.In this study,LiF-Li2O was used to absorb CO2.C and O2 were prepared by electrolysis of CO2 in LiF-Li2O-CO2 molten salt system and the related mechanism was discussed.LiF-Li2O molten salt can effectively absorb CO2 and converted into LiF-Li2CO3 molten salt electrolyte under atmospheric pressure.By using Ni wire as the working electrode,cyclic voltammetry tests were performed in LiF and LiF-Li2O-CO2 molten salts respectively.The results show that the reduction potential of Li+ in molten salt is-2.0V(vs.Pt),while the CO32-in molten salt begins to discharge at-0.5V.Carbon was obtained by electrolysis on Ni,Ti and Mo sustrate at different potentials(-1.2V,-1.4V,-1.6V)respectively.With the increase of potential,the deposited carbon on the Ni and Mo electrodes gradually appeared spherical.Raman analysis shows that most of the carbon with less sp2 hybridization and less graphitization obtained on the Ni and Ti electrodes are defects,and the carbon deposited on the Mo electrode has still a lot of defects.In addition,when electrolyzed on the Ti electrode,a substance whose phase is of TiO1.2 and Ti2O3 is formed between the surface of the Ti substrate and the carbon layer,and when the Mo electrode is electrolyzed,the Mo2C layer is formed on the surface of the Mo substrate with the deposited carbon.Cyclic Voltammetry tests indicate that the discharge potential of F-in molten salt was 2.15V(vs.Pt),while the potential for O2 evolution was 1.1 V in the LiF-Li2O-CO2 molten salt system.According to the steady state polar curve,and the behavior on platinum anode follows the tafel formula of η=0.171og|i|+1.49,the values of exchange current density,charge transfer coefficient and reaction order are iθ=22.14×10-9A/cm2,P=0.65 and P=0.65,respectively.Electrochemical impedance test results show that the control step is electrochemical reaction at both the low polarization potential and high polarization potential,mainly because the concentration of discharge ions on the surface of the Pt electrode in the electrolyte is high enough.O2 was collected anodcallye when the Pt wire and the Fe-Ni alloy were used as the anode to electrolyze the LiF-Li2O-CO2 molten salt,and the electrode reaction on the inert anode was CO32--2e-=CO2+0.5O2.The current efficiency of Pt electrode electrolysis can reach 68.83%.