Monte-Carlo Simulation of the Ionic Transport of Electrolyte Solutions at High Concentrations Based on the Pseudo-Lattice Model

Abstract

The theoretical understanding of the ionic transport in electrolyte solutions is not yet well-established at high concentrations, such as at C/M > 1. In our present study, two transport phenomena---self-diffusion and ionic conduction---of the electrolyte solution at high concentrations (roughly 0.05 ≤ C/M ≤ 3) are computationally simulated by a kinetic Monte-Carlo scheme. A swap mechanism in the three-dimensional pseudo-lattice is proposed to model the movement of ions and solvent, in which only the nearest-neighbor interaction is considered. The energy difference between the before- and after-swap states, based on which the stochastic Monte-Carlo process occurs, is found to be expressed in only two energetic terms; the coulombic repulsion between ions with the identical sign, +εii, and the heat of dissolution of the ionic crystal, Δdiss H. The self-diffusion coefficients of both ions and solvent decrease with the increase in the ionic concentration, which qualitatively agree with the experimental observation. The asymmetric bell-shape of the specific conductivity, σ, principally originates from the coulombic repulsion. The ionic concentration at which the maximum σ occurs well coincides with that of the experimentally observed results. The Δdiss H-dependency reveals that, ceteris paribus, σ marks the highest at around -2kT < Δdiss H< 0, out of the range of which σ is attenuated by either the ion-ion or ion-solvent interaction. Finally, the limitations in the model are addressed. The detail of the study is in press at the date of 15 April 2016 in J. Electrochem. Soc. Figure 1