Effects of electrostatic correlations on ion dynamics in alternating current voltages

Abstract

Motivated by recent progress on the inclusion of ion-ion correlations through continuum models applied to mobile charge dynamics analysis, we present a modified Poisson–Nernst–Planck (mPNP) model to include both steric and electrostatic correlation effects on ion dynamics near charged parallel blocking electrodes. The first contribution appears directly on chemical potential of each ion in solution as a non-electrostatic term, whereas the latter is addressed by a modified fourth-order Poisson equation, proposed by Bazant et al. (Bazant, M. Z.; Storey, B. D.; Kornyshev, A. A. Phys. Rev. Lett.2011, 106, 46,102). Monte Carlo simulation results for implicit water 1:1 and 2:1 electrolytes were properly described with this continuum framework without the aid of fitting parameters. Moreover, the model predicts overscreening for 2:1 electrolytes, which was not properly accessed by classical PNP-like approaches. Alternating current (ac) voltage simulations were carried out and show a meaningful effect of electrostatic correlations on mobile charge dynamics, especially for 2:1 electrolytes where ion-ion correlations are stronger near the electrodes. The methodology proposed here allows the inclusion of new contributions in the PNP model framework for ion dynamics, as well as to solve transient ac voltage problems, taking advantage of the EMSO (Environment of Modeling, Simulation and Optimization) software simulator features.