A high performance, stable anion exchange membrane for alkaline redox flow batteries

Abstract

The development of cost-effective, safe, and low-corrosion alkaline aqueous redox flow batteries, such as alkaline zinc-iron flow batteries, has motivated the research of hydrocarbon-based anion exchange membranes. These membranes, characterized by their positively charged functional groups, facilitate the transport of hydroxide anions (OH−) in alkaline environments, rendering them as potential alternatives to conventional proton exchange membranes in emerging alkaline redox flow batteries. Herein, a facilely synthesized anion exchange membrane (AEM) with superior chemical stability in alkaline media and outstanding ion conductivity has been developed for use in an alkaline redox flow battery. The membrane consists of a partially imidazolium substituted poly (vinylbenzyl chloride) polymer matrix and low molecular weight polyethylene glycol (PEG) additive. The membrane provides positively charged polymer backbone with hydroxide anion as counter ions. The additive PEG not only augments membrane flexibility through interaction with the rigid polymer backbone, but also enhances the conductivity through conducting ions by the alkalized-ether functionality. The optimized anion exchange membrane demonstrates better ionic conductivity of 58.2 mS cm−1 and comparable permeability compared with commercially Nafion117 membrane, enabling promoted energy efficiency (83.5 %), coulombic efficiency (99.85 %) and excellent stability (280 cycles with negligible capacity degradation) of a zinc-iron flow battery at 80 mA cm−2.