Keynote Lecture
Stability Study of Cation Moieties in Alkaline Anion Exchange Membranes for Fuel Cell Applications

There is an increasing worldwide interest in anion exchange membrane fuel cells (AEMFCs) due to the potential of this technology to use low cost electrocatalysts, promising a considerable cost reduction for new generation of fuel cell devices. However, the stability of anion conducting polymers for durable anion exchange membranes (AEMs) and anion exchange ionomers (AEIs) is still a great concern.

Here we present a novel methodology to measure the true alkaline stability of anion conducting polymers to be used in AEMFCs. The new ex-situ technique simulates the environment of an AEMFC during operation, where nucleophilic and basic OH^- species in the absence, or with scarce amount of water, attack the functional groups of the ionic polymer. Using this technique we clearly show the critical effect of water molecules on the alkaline stability of quaternary ammonium (QA) cations commonly used as functional groups in AEMFCs.

The results show that as the water content is reduced, the QA cations are more rapidly degraded in the presence of OH^- at room temperature. With increasing number of water molecules solvating the hydroxide, its nucleophilicity and basicity are hindered and the QA degradation is significantly slowed. These results indicate that the currently used aqueous alkali ex-situ tests to measure AEM stability may lead to false positive stability results where anion conducting polymers may appear more alkali stable than they really are.

We strongly recommend the adoption of this novel developed technique to measure the true stability of anion conducting polymers to be used for AEMFCs. We believe that this new ex-situ protocol will rapidly lead to development and selection of best stable polymers for durable and robust AEMFCs.