Cardo-Polyetherketone Anion Exchange Membranes with Suitable Chemical/Mechanical Stability and Performance for All-Vanadium Redox Flow Battery

Abstract

Cardo-polyethereketone (PEK-C) based anion exchange membrane (AEM) was prepared by quaternization using trimethylammonium. The structures of intermediates and AEMs were confirmed by NMR spectroscopy. The ion exchange capacity of the PEK-C AEMs was 1.4±0.1 mmol g-1, which resulted in membranes with an ionic conductivity (sulfate form, 30 oC) of 5.6 ± 0.5 mS cm-1 and a vanadium (IV) permeability (at room temperature) of 8.2±0.2 ×10-9 cm2 s-1. Stability tests performed by immersion of PEK-C based AEMs in 1.5M VO2 + oxidizing solution during two months resulted in no change in the chemical structure of the polymer as demonstrated by 1H NMR, 13C NMR and 1H-13C heteronuclear multiple quantum correlation (HMQC). PEK-C based AEMs were also stable during vanadium redox flow battery operation (30 mAcm-2) for 50 charge/discharge cycles and showed coulombic and energy efficiency of 98% and 80%, respectively.