The chemical stability of the cationic functional groups in anion-exchange membranes (AEMs) in AEM Fuel Cells (AEMFCs) has been the limiting parameter restricting the commercialization of these devices. Degradation of the cationic functional groups in the anion-exchange membranes by the transported hydroxide leads to severe decrease in anion conductivity and in turn, to a rapid reduction in cell performance. Therefore, understanding the reason behind this decay is important, as is to exploit novel chemistries and materials for the development of stable AEMs with improved lifetimes. In recent years, our group has shown that the water content in the operating fuel cell plays a significant role in the kinetics of the hydroxide attacks. In this talk, I will show that water microsolvation of hydroxide anions affect different faces of hydroxide reactivity differently - it's role as a nucleophile, a base, and as a reducing agent. Moreover, I'll describe the development of quaternary ammonium functional groups in which all carbons connected to the nitrogen atom are sp<sup>2</sup>, inhibiting S<sub>N</sub>2 and E2 reactions. I’ll show that, even with these structural features, these quaternary ammonium salts can decompose quite rapidly under the severe dry and alkaline conditions typically found in operating AEMFCs. Yet, by understanding the single-electron transfer decomposition mechanism and addressing this with electron-donating groups, these molecules can be further improved to become the most stable functional groups tested to date.

Chemical stability of anion-exchange membranes for alkaline fuel cells

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