Ammonium-functionalized poly(arylene ether)s as anion-exchange membranes

The recent progress of our research on anion-exchange membranes (AEMs) for alkaline fuel cell applications is reviewed. The anion conductivity and the mechanical, thermal and chemical stability of AEMs are insufficient. To address these issues, we have designed and synthesized a novel series of poly(arylene ether)-based AEMs with quaternized ammonium groups. First, the effect of the sequence of the polymer main chain (random or block) on the AEM properties, especially the anion conductivity, is discussed. We emphasize that fluorenyl groups serve effectively as scaffolds for the ammonium groups. We then discuss the alkaline stability of both the polymer backbone and the quaternized ammonium groups. Partial fluorination improves the alkaline stability of the polymer main chains. Among the several ammonium groups investigated, we propose that pyridinium groups are seemingly more stable than the typical aliphatic ammonium (for example, trimethylammonium) groups. The results imply that aromatic AEMs are potentially applicable to alkaline fuel cells that use hydrogen or hydrazine as a fuel.