title: Size asymmetric hard spheres as a convenient model for the capacitance of the electrical double layer of an ionic liquid.
abstract: Even though ionic liquids are composed of nonspherical ions, it is shown here that the general features of the capacitance of an electrical double layer can be obtained using a charged hard sphere model. We have shown in our earlier studies that at high electrolyte concentrations or large magnitudes of the electrode charge density the fact that the ions have a finite size, and are not point ions, cause the capacitance near the potential of zero charge to increase and change from a minimum to a maximum as the ionic concentration is increased and to decrease as the magnitude of the electrode charge density increases. Here, we show that the asymmetry of the capacitance of an ionic liquid can be explained qualitatively by using spherical ions of different size without attempting to introduce the ionic shape in a detailed manner. This means that the general features of the capacitance of the double layer of an ionic liquid can be studied without using a complex model, although the study of the density or charge profiles of an ionic fluid would require one. However, this is often unnecessary in the analysis of many experiments.
authors.affiliation: Department of Physical Chemistry, Adam Mickiewicz University of Poznań, Umultowska 89b, 61-614 Poznań, Poland.
authors.forename: Stanisław
authors.initials: S
authors.lastname: Lamperski
authors.affiliation: Department of Physical Chemistry, Adam Mickiewicz University of Poznań, Umultowska 89b, 61-614 Poznań, Poland.
authors.forename: Joanna
authors.initials: J
authors.lastname: Sosnowska
authors.affiliation: Laboratory of Theoretical Physics, Department of Physics, University of Puerto Rico, San Juan, Puerto Rico 00931-3343, USA.
authors.forename: Lutful Bari
authors.initials: LB
authors.lastname: Bhuiyan
authors.affiliation: Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602-5700, USA.
authors.forename: Douglas
authors.initials: D
authors.lastname: Henderson