Performance and stability comparison of Aemion™ and Aemion+™ membranes for vanadium redox flow batteries

Anion exchange membranes (AEMs) have shown a significant rise in performance and durability within recent years for applications such as electrolysis and fuel cells. However, in vanadium redox-flow batteries, their use is of particular interest to lower costs and self-discharge rates compared to conventional perfluorinated sulfonic acid-based ionomers such as Nafion. In this work we evaluate the properties of two commercial AEMs, Aemion™ and Aemion+™, based on ex situ characterizations, an accelerated stress test degradation study (>1000 hours storage in highly oxidizing VO₂ ⁺ electrolyte at 35 °C) and electrochemical battery cycle tests. All membranes feature low ionic resistances of below 320 mΩ cm², enabling battery cycling at 100 mA cm^-2. Aemion shows considerable VO²⁺ formation within a VO₂ ⁺ stress test, whereas Aemion+ remains almost unaffected in the 1058 h stress test. Evaluating self-discharge data, cycling performance and durability data, Aemion+™ (50 μm thickness) features the best properties for vanadium redox-flow battery operation.