Nanostructured Membranes for Vanadium Redox Flow Batteries

The vanadium redox flow battery (VRB) has received considerable attention due to potential for large-scale energy storage systems suitable for a wide range of renewable energy applications. The key constituent of VRB is an ion exchange membrane that separates two electrolyte solutions, while allowing the conduction of ions. This review summarizes efforts in developing nanostructured membranes with reduced vanadium ion permeability and improved proton conductivity in order to achieve high performance and long life of VRB systems. An overview of the VRB systems and membrane requirements is first introduced. Recent studies on a broad range of nanostructured membranes are then presented, focusing on their properties and performance of VRB employing them. Nafion hybrid membranes containing various nanofillers are discussed mainly in terms of their proton permselectivity. As alternatives to Nafion membrane, nanostructured membranes based on sulfonated hydrocarbon polymers and nonionic materials are also reviewed. The discussion will cover organic-inorganic nanocomposite, amphoteric membranes, and nanofiltration membranes.