Electrochemical Desalination Using a Hybrid Redox Flow Cell

Abstract

Electrochemical desalination is an attractive, energy-efficient strategy for small-scale, distributed water purification systems, as compared to conventional thermal desalination or reverse osmosis. Many incumbent electrochemical desalination cells feature a combination of sodium-intercalating electrodes and polymer-based anion-exchange membranes with non-ideal permselectivities. We propose a hybrid flow cell design that features a redox-active electrolyte separated by a cation exchange membrane from a solid, anion-converting or anion-intercalating electrode. This design makes use of a dense, ceramic membrane with a greater selectivity for sodium ion conduction than polymeric ion-exchange membranes, which are also susceptible to energy losses from water crossover between dilute and concentrated salt streams. We discuss considerations that will impact the relationship among electrode and electrolyte properties, operational parameters (e.g. current density, concentration factor and water recovery percentage) and the energetic cost of desalination.