Electrical-Double-Layer Charging in a Complex Network of Pores

Ion transport in charged porous media plays a pivotal role in applications ranging from capacitive deionization to electrochemical capacitors. Three factors affect transport: double-layer thickness, ionic properties (valences and diffusivities), and the geometry of the porous network. While experimental reports suggest that the porous-network geometry dictates the transport of ionic species, modeling approaches that can predict such dependencies are scarce due to the complexity of the porous geometry and the coupled nature of governing equations.

In this talk, we present a new framework that models ion transport in a complex network of charged pores while also accounting for arbitrary double-layer thickness, ionic valences, and ionic diffusivities. The framework is based upon a perturbation expansion of the Poisson-Nernst-Planck equations for low applied potentials and long pores. We study the impact of porous geometry by generating a range of pore networks by modeling them as semi-regular lattices of bonds and sites. We show that the charging timescales of each pore become coupled and can be controlled via ionic diffusivities, valences, and porous geometry.