Electrochemical Desalination Using a Hybrid Redox-Flow Cell with a Ceramic Ion Conductor

Abstract

Electrochemical desalination is a potentially energy-efficient strategy for distributed, small-scale purification of brackish sources, especially as compared to conventional processes that are reliant on heat or reverse osmosis. One promising subcategory of electrochemical desalination systems features a combination of sodium-intercalating electrodes and polymer-based anion-exchange membranes. Although desalination is technically feasible with this design, polymer-based ion-exchange membranes tend to have imperfect permselectivities and to be susceptible to water crossover between diluate and concentrate streams. These issues result in parasitic losses that increase the energetic cost of desalination.We propose a hybrid flow cell design that features a redox-active electrolyte separated from a solid, anion-converting or anion-intercalating electrode with a solid ceramic ion-exchange membrane. By making use of a dense, ceramic membrane with a far greater selectivity for sodium ion conduction than analogous polymeric ion-exchange membranes, the parasitic issues described above are avoided. 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.