s enElectrodialysis (ED) processes are limited in terms of practical current densities due to the emergence of concentration boundary layers. A great deal of research has focused on methods to promote mixing of these boundary layers, particularly through developing new spacer materials. Spacers are crucial to the performance of electrodialysis stacks, forming the flow channels between membranes and leading to hydrodynamic mixing that can reduce mass transport limitations. The conventional treatment of spacers in electrodialysis has focused on characterizing the hydrodynamic mixing resulting from spacer geometry and assessing how this impacts the overall stack resistance. In this work, we explore the electrokinetic aspect of spacer performance: how does the electric-field bending induced by polymeric spacers give rise to electro-osmotic mixing and how can we enhance this effect by increasing the surface charge of conventional spacer materials? In order to understand these effects, we carried out an experimental study to characterize the ED performance of a lab-scale stack using spacers with different surface charge densities, achieved through polyelectrolyte adsorption on the spacers. Our results show that in the limiting current regime, substantial increases in the current density or reductions in power consumption can be achieved when making use of this enhanced mixing due to electro-osmosis. We also explain this enhancement through the use of a simplified theoretical model to highlight the potential of utilizing electrokinetic mixing from spacers in electrodialysis.
ER -