Anion exchange membrane based on poly(arylene ether sulfone)s functionalized with quinuclidinium-piperidinium dual cations for vanadium redox flow battery applications

Vanadium redox flow batteries (VRFBs) have gained significant interest as a prospective energy storage solution due to their scalability and extended cycle durability. The efficient functioning of VRFBs relies significantly on anion exchange membranes (AEMs), which facilitate the selective transport of ions while preventing crossover. In this study, we present a novel AEM based on poly(arylene ether sulfone)s (PAES) functionalized with dual cations (quinuclidinium-piperidinium) (DC-PAES) bearing a butyl spacer, explicitly designed for VRFB applications. The DC-PAES membrane containing dual cations separated by a butyl spacer results in a balanced combination of hydrophilicity and hydrophobicity, which enables efficient ion transport across the membrane. The DC-PAES membrane showed hydroxide conductivity of 0.085 S/cm at 80 °C, having an ion exchange capacity (IEC) of 1.42 mmol/g. The resulting DC-PAES membrane displayed low permeability (2.1×10-7 cm2 min-1) and high selectivity (12.3×105 S min cm-3) to vanadium. The performance of the AEMs fabricated for VRFB application showed better Coulombic (97.1%), energy (90.0%), and voltage efficiency (92.63%) at 40 mAcm-2 higher than Nafion 117. The reported AEMs revealed excellent stability due to the steric and ring constraints of quinuclidinium and piperidinium cation, hindering the attack of oxidative species. Furthermore, the DC-PAES membrane demonstrated improved battery cycling performance lasting up to 150 cycles under in-situ conditions, making it a promising separator material for VRFB applications.