Pore-scale investigation on ion transport and transfer resistance in charged porous media with micro-macro structure

Abstract

Capacitive deionization is an electrochemical desalination technology, in which ions are removed from aqueous solution using porous carbon electrodes. Poisson-Nernst-Planck equations are fully solved by the lattice Boltzmann method to investigate the dynamic ion transport and adsorption processes from macropores between carbon particles into micropores inside carbon particles. Effects of potential, ion concentration and thickness of the microporous zone on the dynamic ion transport processes are investigated. Pore-scale results show that the ion transport first occurs at the micropore/macropore interface and then extends to the inner part of the microporous zone. Adsorption of Na+ ion consumes more time to reach the equilibrium state compared with expulsion of Cl− ion, and the ion concentrations of microporous zones in the steady state predicted by simulations agree well with the results obtained by the Donnan model. The kinetic rate parameters of the finite-rate ion transport model are obtained using data fitting based on the individual ion transfer fluxes into micropores calculated by the pore-scale simulation. It is found that identified kinetic rate parameters are constant showing the validity of the model, and the thickness of the microporous zone has a great influence on the values.