Electrolyte Structure with Explicit Solvent in Nanoslit Capacitors using Classical Density Functional Theory

Abstract

Understanding the effects of double layer formation on charged interfaces is integral in many disciplines such as electrochemistry, polymer science, and solution theory. Classical models to understand double layer thermodynamics is typically based on the Poisson-Boltzmann equation where solvent is treated implicitly as a dielectric background and ions are treated as point charges. Although this theory works well for macroscopic charge distributions, it is known to lead to problems in nanopores when finite size and interfacial effects play important roles. The advent of using nanoporous electrodes for increased surface interactions motivates us to build a more accurate model that can characterize electrolyte structure in nanoconfined regions.

This theses aims to understand the electrolyte structure and the effects of explicit solvent in nanopores through computations. We first start by giving a brief description on classical models in understanding the behavior of solvent and ions under external electric fields. We then elucidate the problems with these classical models when considering electrolyte structure in nanoconfined regions. Afterwards we give a discussion on classical density functional theory and a method to model three component electrolyte with steric interactions and mean-field electrostatics. This method allows us to construct a local relative permittivity that is a function of the molecular interactions. Using this model, we study the effects of solvent properties, temperature, surface charge, and slit geometry on the adsorption and structure of each component. This model can be used to help guide the design of capacitor systems and understand the underlying thermodynamics of confined double layer formation.