Influence of electrolyte on concentration-induced conductivity-permselectivity tradeoff of ion-exchange membranes

In ion-exchange membranes (IEMs), the concentration-induced tradeoff between conductivity and permselectivity constrains process performance. This study investigates the impacts of different electrolytes on the conductivity-permselectivity tradeoff of commercial cation and anion exchange membranes. Nine different electrolyte solutions containing mono-, di-, and trivalent ions, and spanning 1.5 orders of magnitude in concentration were examined. Effective conductivity is found to be determined by valency and mobility of the counterion and is insensitive to the co-ion identity. Apparent permselectivity declines with higher valency of the counterion and with lower valency of the co-ion. Overall, the IEMs exhibited different conductivitypermselectivity tradeoff behaviors across the electrolyte solutions investigated. The disparate tradeoff trends are shown to be governed by counter- and co-ion valencies, and counterion diffusivity. The study sheds light on the principal factors underpinning the tradeoff and advances the understanding of attainable conductivitypermselectivity performance in more complex water chemistries that are pertinent for practical IEM applications.