Measuring the alkaline stability of anion-exchange membranes

One significant barrier in developing durable, robust anion-exchange membranes (AEMs) for liquid-electrolyte-free fuel cells (AEMFCs) and water electrolyzers (AEMWEs) is their limited chemical stability to alkali. To measure the alkaline stability of AEMs, ex-situ tests are commonly used where the AEMs are immersed for long durations in aqueous alkali solutions. However, such tests do not adequately simulate the liquid-electrolyte-free environment of AEMFCs and AEMWEs, as the hydration and alkaline conditions do not always mimic actual operando conditions, yielding misleading and inaccurate indications of degradation rates for relatively low hydration conditions. We recently reported a unique ex-situ method which determines the alkaline stability of AEMs under conditions that mimic in-situ operating environments. In this study, we apply this technique to determine the alkaline stability of several AEMs containing different functional group and backbone chemistries. The alkaline stability of HDPE-based radiation-grafted (RG)-AEMs containing different functional group chemistries follows the trend: TMA ≥ MPY ∼ MPIP ≫ DEMA > TEA. Radiation-grafted AEMs (and a non-radiation-grafted PPO benchmark) containing different backbones and the same stable TMA group follows the stability order: ETFE ≥ LDPE > HDPE ≫ PPO. This technique is recommended for ex-situ testing of the alkaline stability of AEMs for both AEMFC and AEMWE applications.