Ion selective redox active anion exchange membrane: Improved performance of vanadium redox flow battery

Abstract

In-sight understanding of synergetic and trade-off behaviour between chemical and structural properties of emerging redox active membrane separator for batteries is necessary for high performance and widespread adoption of technologies. Our aim is to provide sustainable solution such as stable membrane with fast ionic-transport (low resistivity), and impervious nature for redox active species that leads to deleterious capacity fade and materials underutilization. We report architecture of redox active anion exchange membranes (AEMs) by free radical polymerization using tert-butylmethaacrylate (tBuMA), vinylimidazole (VIm) and vinyl ferrocene (VFc). The VFc acts as redox responsive species (ferrocenium ion) due to protonation under operating conditions. These ion selective redox active membranes offer chemical modularity, high conductivity, stability, and prevents VO2+ cross-over, necessary for improved vanadium redox flow battery (VRFB) performance. The fundamental electrochemistry of redox active membranes is fascinating, due to redox peaks (Fc/Fc+) in voltammetry. Suitable redox-active membrane separator exhibits 98.0% current efficiency corresponding to 85.0% voltage efficiency at 60 mA cm−2 in VRFB operation. Therefore, AEMs with redox active functional moieties can open a new avenue for efficient VRFB and various electrochemical applications.