Poly(terphenylene) anion exchange membranes with high conductivity and low vanadium permeability for vanadium redox flow batteries (VRFBs)

In this study, we demonstrate a new class of poly(terphenylene) based anion exchange membranes (AEMs) with improved chemical stability and anion conductivity in vanadium redox flow batteries (VRFBs). A series of terphenyl- and biphenyl-based polymers with pendant quaternary ammonium alkyl groups were synthesized and characterized for VRFB applications. When the arrangement of the polymer backbone and cation-tethered alkyl chains was varied, the prepared AEM membranes exhibited extremely low vanadium permeance while maintaining high conductivity. These properties further provided a high coulombic efficiency close to 100% at all current densities as well as high voltage efficiency. The single cell VRFB performance with the poly(terphenylene) based AEMs showed 2-5% higher coulombic efficiency than those of commercial AEMs and similar voltage efficiency to those of commercial PEMs (Nafion (R) 212). The highest EE value of 93.64% was achieved at the current density of 20 mA/cm(2) (vs. 72% EE for Nafion212). In addition, poly(terphenylene) based AEMs showed superior cycle stability and high capacity retention, thus demonstrating their high performance as promising IEMs for VRFB application.