Comparing Charge Transport Predictions for a Ternary Electrolyte Using the Maxwell–Stefan and Nernst–Planck Equations

Abstract

In this work, we investigate and compare the Maxwell-Stefan and Nernst-Planck equations for modeling multicomponent charge transport in liquid electrolytes. Specifically, we consider charge transport in the Li + / I - / I 3 - /ACN ternary electrolyte originally found in dye-sensitized solar cells. We employ molecular dynamics simulations to obtain the Maxwell-Stefan diffusivities for this electrolyte. These simulated diffusion coefficients are used in a multicomponent charge transport model based on the Maxwell-Stefan equations, and this is compared to a Nernst-Planck based model which employs binary diffusion coefficients sourced from the literature. We show that significant differences between the electrolyte concentrations at electrode interfaces, as predicted by the Maxwell-Stefan and Nernst-Planck models, can occur. We find that these differences are driven by a pressure term that appears in the Maxwell-Stefan equations. We also investigate what effects the Maxwell-Stefan diffusivities have on the simulated charge transport. By incorporating binary diffusivities found in the literature into the Maxwell-Stefan framework, we show that the simulated transient concentration profiles depend on the diffusivities; however, the simulated equilibrium profiles remain unaffected. © 2010 The Electrochemical Society.