Poisson-Fermi Model of Single Ion Activities

TL;DR

This paper introduces a Poisson-Fermi model that accurately predicts single ion activity coefficients in electrolyte solutions by incorporating hydration effects, dielectric variations, and voids, with minimal adjustable parameters.

Contribution

The novel Poisson-Fermi model accounts for hydration shells, voids, and dielectric variations, improving prediction accuracy with only one adjustable parameter.

Findings

Model agrees with experimental activity coefficients.

Captures nonmonotonic behavior of activity with salt concentration.

Includes effects of water polarization and steric hindrance.

Abstract

A Poisson-Fermi model is proposed for calculating activity coefficients of single ions in strong electrolyte solutions based on the experimental Born radii and hydration shells of ions in aqueous solutions. The steric effect of water molecules and interstitial voids in the first and second hydration shells play an important role in our model. The screening and polarization effects of water are also included in the model that can thus describe spatial variations of dielectric permittivity, water density, void volume, and ionic concentration. The activity coefficients obtained by the Poisson-Fermi model with only one adjustable parameter are shown to agree with experimental data, which vary nonmonotonically with salt concentrations.