The effect of surface transport on water desalination by porous electrodes undergoing capacitive charging

TL;DR

This paper develops a theoretical model incorporating surface transport in porous electrodes during capacitive deionization, revealing that surface transport can both accelerate and slow down water desalination depending on conditions.

Contribution

It introduces a novel theory including surface transport effects in CDI modeling, which was not previously considered in charge and salt dynamics.

Findings

Surface transport can enhance CDI charging rate under certain conditions.

Surface transport can slow down CDI charging at other conditions.

The model provides new insights into the complex role of surface transport in desalination.

Abstract

Capacitive deionization (CDI) is a technology in which water is desalinated by ion electrosorption into the electric double layers (EDLs) of charging porous electrodes. In recent years significant advances have been made in modeling the charge and salt dynamics in a CDI cell, but the possible effect of surface transport within diffuse EDLs on these dynamics has not been investigated. We here present theory which includes surface transport in describing the dynamics of a charging CDI cell. Through our numerical solution to the presented models, the possible effect of surface transport on the CDI process is elucidated. While at some model conditions surface transport enhances the rate of CDI cell charging, counter-intuitively this additional transport pathway is found to slow down cell charging at other model conditions.