Poly(arylene ether nitrile) anion exchange membranes with dense flexible ionic side chain for fuel cells

To resolve the excessive swelling and undesirable alkaline stability of densely functionalized type anion exchange membranes (AEMs) and to obtain high performance AEMs, quaternary ammonium-functionalized poly(arylene ether nitrile) (QPAEN) AEMs with dense flexible ionic side chain are prepared via nucleophilic substitution polycondensation, demethylation reaction and Williamson reaction. The densely pendent flexible long side chains with QA groups at the end provide a high conductivity and the introduced strong polar nitrile groups result in lower water uptake, excellent dimensional stability and strong alkali resistance of the AEMs. The QPAEN membrane with IEC of 1.78 meq g−1 exhibits the highest hydroxide conductivity of 116.0 mS cm−1 at 80 °C. The high conductivity is attributed to the well-developed hydrophilic/hydrophobic phase separated morphology that constructs efficient ion conducting pathways in the membranes. High retention of hydroxide conductivity (80.2%) and ionic exchange capacity (IEC) (86.0%) was observed for the QPAEN-0.4 membrane in the degradation test in a 2 M aqueous KOH solution for 480 h. Moreover, the single cell performance of the as-prepared AEMs was greatly enhanced and a high peak power density of 251.3 mW cm−2 at 60 °C was observed.