Coarse-grained simulations of an ionic liquid-based capacitor: II. Asymmetry in ion shape and charge localization

J Phys Condens Matter. 2014 Jul 16;26(28):284114. doi: 10.1088/0953-8984/26/28/284114. Epub 2014 Jun 12.

Abstract

In this work, which is a continuation of part I, we introduce a primitive model for an ionic liquid (IL) that can account for the planar shape of cations typical for ILs like imidazolium. The model consists of a spherical anion and a triangular cation consisting of three spheres, where one or all three vertices of the triangle can carry electric charge. We use molecular dynamics simulations to study the differential capacitance Cd of an ionic liquid confined between two planar electrodes. Our goal is to elucidate the complex dependence of Cd on the electrode potential U in terms of simple entities such as the shape and charge distribution of the ions. For this purpose, we compare the results from the current model to the results based on the models with spherical cations that possess asymmetry in ion valence and shape that were analyzed in detail in part I of this work. We show that the various possible stackings of the triangles near the cathode lead to noticeable new features in Cd(U) as compared to the spherical models. Different distributions of charges on the triangle lead to different preferred orientations of the cations near the cathode that are moreover potential dependent.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Computer Simulation
  • Electric Capacitance*
  • Ionic Liquids / chemistry*
  • Models, Chemical*
  • Models, Molecular*
  • Molecular Conformation
  • Static Electricity*

Substances

  • Ionic Liquids