Charge Carrier Molecular Sieve (CCMS) Membranes with Anti-aging Effect for Long-Life Vanadium Redox Flow Batteries

Vanadium crossover hinders widespread commercial adoption of vanadium redox flow batteries (VRFBs). Superglassy polymers have the potential to offer high selectivity needed to control the crossover but as yet do not possess the requisite proton conductivity and stability. Here, we explore nanocomposite separators that can improve this selectivity. We report a dual-function charge carrier molecular sieve (CCMS) membrane, consisting of a high free volume microporous glassy polymer, poly[1-(trimethylsilyl)-1-propyne] (PTMSP)/sulfonated PAF (PAF-1-SO3H), that effectively hinders the migration of hydrated vanadium ions. Furthermore, ideally placed PAF-1-SO3H pores not only proved excellent for developing proton conductive channels but also suppressed physical aging within the separator. Experiments then linked this to an increased battery cycle life. As a consequence of achieving higher and more stable VRFB performance compared to benchmarked Nafion (Coulombic efficiencies of 97 vs 87% and capacity retention values of 85 vs 58% at a current density of 60 mA cm–2, respectively), our integrated design heralds a class of stable separators for hydrogen-based energy technologies.