Molecular Dynamics Simulation Of Ionic Liquids In Industrial Application

In nowadays energy structures around the world, the fossil fuels still play an important role in developing countries like China. As we all know, the pollutants, such as CO₂, SO₂ or NOx, emission from the combustion of fossil fuels which contain sulfide or nitride will have a great impact on environment, like global warming. Recently, room temperature ionic liquids（RTILs） become kind of potential CO₂ absorbents due to their outstanding features. The studies on CO₂ capture using dicationic ionic liquids（DILs） demonstrated that DILs, in which each cation carries two unit charges, are promising absorbents for CO₂ uptake especially compared with monocationic ionic liquids（MILs）. However, DILs/CO₂ interfacial properties at the molecular level are still unknown. This work investigated the CO₂ absorption properties of representative DIL, 1-alkyl-3-dimethylimidazolium bis（trifluoromethylsulfonyl）imide, [Cn（mim）2]（Tf2N）2（n = 3, 6, 12）, using molecular dynamics（MD） simulations. The higher interfacial CO₂ density at DIL than that at MIL interfaces suggests the increased CO₂ interaction sites in DIL. The interfacial CO₂ density also exhibits an alkyl chain length dependence which decreases with the elongation of alkyl chain and proportionally correlates with the content of fluorine atoms at interfaces. Moreover, DIL shows a lower H2 O and N2 uptake from flue gas compared with MIL, implicating the higher CO₂/H2 O and CO₂/N2 selectivity.Although the capture of CO₂ can weaken the impact of global warming, these pollutants can be fully controlled if renewable energy resources can take dominant roles in the future energy structures. Recent studies show that the supercapacitors with RTIL electrolytes exhibit a good performance for the storage of intermittent renewable energy. Supercapacitors store energy by electrical double layers（EDLs）, thus the microstructure of ILs near the electrode surface will have a great impact on the EDLs structure. Previous theoretical studies which focused on the supercapacitors always used idealized electrode, thus ignored the defect on electrode surface. In this work, the MD simulations of ILs at different stepped graphite electrodes were performed to characterize the microstructure of ILs-electrode interface. It shows that the different relationships between the thickness of stepped surface and ion size, will result in a more evident or less defined interfacial layering structure of cation/anion. In addition, the ion layers exhibit different patterns and alignments of couterion/co-ion lattice between neutral and charged electrodes. These translations in the microstructure of ILs will have important significance in understanding the molecular mechanism of supercapacitors’ both static and dynamic properties.