Highly Stable Alkaline Polymer Electrolyte Based on a Poly(ether ether ketone) Backbone

Alkaline polymer electrolyte fuel cells (APEFCs) promise the use of nonprecious metal catalysts and thus have attracted much research attention in the recent decade. Among the challenges of developing practical APEFC technology, the chemical stability of alkaline polymer electrolytes (APEs) seems to be rather difficult. Research found that, upon attachment of a cationic functional group, an originally stable polymer backbone, such as polysulfone (PSF), would degrade in an alkaline environment. In the present work, we try to employ poly(ether ether ketone) (PEEK), a very inert engineering plastic, as the backbone of APEs. The PEEK is functionalized with both a sulfonic acid (SA) group and a quaternary ammonia (QA) group, with the latter as the majority amount. Ionic cross-linking between SA and QA has rendered the thus-obtained membrane (xQAPEEK) with high mechanical strength and low swelling degree. More importantly, the xQAPEEK membrane exhibits outstanding stability in a 1 mol/L KOH solution at 80 °C for a test period of 30 days: the total weight loss of xQAPEEK is only 6 wt %, in comparison to a large degradation of quaternary ammonia PSF (more than 40 wt %) under the same conditions. Our findings not only have demonstrated an effective approach to preparing PEEK-based APE but also cast a new light on the development of highly stable APEs for fuel-cell application.