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

Abstract

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.

Microstructural and Dynamical Heterogeneities in Ionic Liquids

“…Both freezing and thawing phase transitions of ILs in CNTs are strongly influenced by geometric constraints and strong interactions of ILs with CNT walls . The interior radius and chiralities of CNTs and doping atoms in CNTs can affect the melting temperatures of confined ILs. , ILs inside smaller CNTs are more stable than those in larger CNTs, which is attributed to enhanced interactions of ILs with CNT walls. In addition, ILs inside zigzag CNTs have lower energy and are more stable than those in armchair configurations and therefore have higher melting temperatures.…”

Measurement and Modeling of Thermodynamic Properties for Ternary Mixtures Containing 1-Butyl-3-methylimidazolium-Based Ionic Liquids with Acetophenone and Acetic or Propionic Acid

“…The hydrogen atoms attached to an imidazolium ring can be substituted with another atom or compound to produce desired properties. The imidazolium-based ILs show promising applications in various fields and are considered as heat transfer fluids, corrosion inhibitors, lubricants, and electrolytes in electrochemical apparatus such as batteries, photoelectrical, fuel, and solar cells, capacitors, and media for gas chromatography. − For the current study, we choose to focus on ILs 1-butyl-3- methylimidazolium tetrafluoroborate ([BMIM]­[BF 4 ]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]­[PF 6 ]) based on their industrial application in various fields. − Acetophenone is the simplest polar aromatic ketone and it was chosen in the present study due to its wide range of applicability as a solvent in various applications and used as a chemical intermediate in pharmaceuticals and agrochemicals . Carboxylic acids are versatile compounds that are widely used in the manufacture of insecticides, pesticides, cleaning detergents, plastics, rubber, and pharmaceutical products and in the food and beverage industries where they are used as flouring agents, as natural pigment for food, and as acidulants to preserve food and beverages. − The structure of carboxylic acids contains a hydroxyl group (−OH) and carbonyl group (CO).…”

Effect of Shear Flow on Nanoparticles Migration near Liquid Interfaces

“…Taherkhani et al used classical molecular dynamics (MD) simulations 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), and they also studied the effect of nitrogen as a doping element in CNT on these properties of [EMIM][PF6] by MD simulation. It was shown that in the presence of nitrogen, ion transfer uses a hydrogen bonding mechanism, while in its absence, ion transfer uses a diffusion mechanism in which the cation has a significant effect on the ion transfer and electrical conductivity [ 11 ].…”