A one-dimensional model for water desalination by flow-through electrode capacitive deionization

Abstract

Capacitive deionization (CDI) is a fast-emerging water desalination technology in which a small cell voltage of ~1V across porous carbon electrodes removes salt from feedwaters via electrosorption. In flow-through electrode (FTE) CDI cell architecture, feedwater is pumped through macropores or laser perforated channels in porous electrodes, enabling highly compact cells with parallel flow and electric field, as well as rapid salt removal. We here present a one-dimensional model describing water desalination by FTE CDI based on modified Donnan electric double layer theory, and employing simple cell boundary conditions derived via scaling arguments. We further provide a comparison of model results to data obtained from a custom-built FTE CDI cell. We show good model-to-equilibrium data fits with reasonable values for fitting parameters such as the Stern layer capacitance, micropore volume, and attraction energy. Further, the model well-describes dynamic effluent salt concentration and cell current obtained from the experimental cell. Thus, we demonstrate that from an engineering modeling perspective, an FTE CDI cell can be described with simpler one-dimensional models, unlike more typical flow-between electrodes architecture where 2D models are required.