3 years ago

Effect of Nitrogen Doping on Glass Transition and Electrical Conductivity of [EMIM][PF6] Ionic Liquid Encapsulated in a Zigzag Carbon Nanotube

Effect of Nitrogen Doping on Glass Transition and Electrical Conductivity of [EMIM][PF6] Ionic Liquid Encapsulated in a Zigzag Carbon Nanotube
Babak Minofar, Farid Taherkhani
Molecular level understanding of the properties of ionic liquids inside nanopores is needed in order to use ionic liquids for many applications such as electrolytes for energy storage in electric double-layer capacitors and dye-sensitized solar cells for conversion of solar energy. In this study, classical molecular dynamics (MD) simulations have been performed to investigate the radial distribution, glass transition, ionic transfer number, and electrical conductivity of the ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate [EMIM][PF6] ionic liquid encapsulated in carbon nanotube (CNT). The effect of nitrogen as a doping element in CNT on these properties of [EMIM][PF6] was also investigated by MD simulation, and the configurational entropy of [EMIM][PF6] encapsulated in CNT was calculated in absence and presence of nitrogen as a doping element. The configurational entropy of [EMIM][PF6] encapsulated in CNT is nonmonotonic versus temperature in both the presence absence of nitrogen doping. The glass transition of [EMIM][PF6] encapsulated in CNT is shifted to high temperature with doped nitrogen. The Green–Kubo formalism was used to calculate the ionic transfer number of [EMIM][PF6] encapsulated in CNT. Ionic transfer numbers show a maximum peak for cation transfer and a minimum peak for anion transfer with temperature. Electrical conductivity of [EMIM][PF6] encapsulated in CNT decreases with increasing temperature in the presence of doped nitrogen and increases in absence of nitrogen. The cationic conductivity also increases with temperature in the presence vs absence of nitrogen doping. The MD findings for electrical conductivity and glass transition with temperature are in good agreement with available experimental data. The MD data shed new light on the effect of nitrogen doping on the mechanism of ion transfer. In the presence of nitrogen, ion transfer uses a hydrogen bonding mechanism, and in its absence, ion transfer uses a diffusion mechanism in which the cation has a significant effect on ion transfer and electrical conductivity.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b00911

DOI: 10.1021/acs.jpcc.7b00911

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