Long-branched and densely functionalized anion exchange membranes for fuel cells

To achieve a better performance of anion exchange membranes (AEMs), AEMs of a unique structure with flexible and dense side chains are prepared by taking amino groups on poly (aryl ether ketone)s (PAEKs) as reaction sites and grafting four long side chains on each repeat unit of main chains. This chemical synthetic route for the unique structure is simple and controllable, with no obvious side reactions happening during synthetic process. Three different kinds of cycloaminium cations are used as functional groups. The AEMs with this unique structure exhibit limited swelling ratios and improved hydroxide conductivities, of which the highest attains 74.4 mS cm−1 at 80 °C when using N-Methylmorpholine (Mm) as the cation group. The high conductivities are due to the formation of connective ion conducting channels facilitated by this kind of structure inside the membranes. No obvious changes in chemical structures of AEMs with different cations happen after alkali treatment for 768 h at 60 °C, indicating a good alkaline stability of AEMs with such specific structure. Moreover, the PAEK-MmOH yields a maximum power density of 302 mW cm−2 at 640 mA cm−2 when operating in a single fuel cell. Overall, these long-branched and densely functionalized AEMs with cycloaminium cation groups possess good application prospects in fuel cells.