Redox Desalination Using Flow Battery Architectures

Abstract

The water-energy nexus presents new opportunities for redox flow systems to make a large impact on our energy economy. Current efforts to make redox flow batteries commercially viable have traditionally focused on lowering capital costs; an alternative strategy is to increase the revenues associated with battery operation by creating a valuable product like desalinated water. By placing one or more intervening water chambers, bounded by ion-selective membranes, between the anode and cathode of a traditional flow battery, the system becomes capable of simultaneous water desalination and electrical energy storage. A symmetric flow cell that uses the same redox couple at both electrodes is no longer able to store electrical energy, but enables lowered specific energy consumption for salt removal, as well as greatly lowered reactant capital costs relative to the storage mode. Certain cell designs can additionally be switched reversibly between both operating modes, thereby allowing the stack to be utilized even when a conventional flow battery would normally be idled. We present several examples of devices that use flow battery architectures to perform redox water desalination for energy storage applications as well as nontraditional novel applications with large energy savings.