Viscosity effects for ion transport in electrochemical systems

Abstract

Ion transport in a fluid medium is often described by the Poisson-Nernst-Planck (PNP) equation, a time-dependent mean-field theory that ignores the ion excluded-volume effects and electrostatic correlations, and a number of theoretical procedures have been recently proposed to alleviate the mean-field approximation. In this work, we investigate the charging kinetics of an electric double layer (EDL) of organic electrolytes using the dynamic density functional theory (DDFT). Unlike the PNP equation, DDFT predicts a nonlinear dependence of the surface charge density on the charging voltage. For systems with low solvent viscosity, the collective behaviors caused by inertial effects lead to an oscillatory variation of the surface charge density, occurrences in the charging process of the electrochemical system. Both the strength and frequency of charge oscillation are affected by the solvent viscosity and the degree of EDL overlap.