Alkaline anion exchange membrane from poly(arylene ether ketone)-g-polyimidazolium copolymer for enhanced hydroxide ion conductivity and thermal, mechanical, and hydrolytic stability

A series of alkaline anion exchange membranes (AAEMs) are synthesized from poly (arylene ether ketone) -poly (vinyl-1-butylimidazolium) graft copolymers (PAEK-g-[PBVIm-OH]) with different [PBVIm-OH] cationic chain lengths. The chemical structure of the synthesized polymers is confirmed by 1H NMR and FTIR analysis. Several essential properties of AAEMs such as water uptake, hydroxide ion conductivity, and thermal, mechanical and dimensional stability for fuel cell applications are investigated and correlated to the ion cluster dimension examined by small-angle x-ray scattering. The PAEK-g-[PBVIm-OH]-based AAEMs show excellent thermal, mechanical, and dimensional stability, as they have the thermal degradation temperature of 250 °C, the tensile strength of 7.7 MPa and the planar swelling ratio of 12% at 40 °C. The hydroxide ion conductivity increases with increasing PBVIm-OH graft chain length. The AAEM membrane with the longest PBVIm-OH chain length (MW of ∼7000 g mol−1) exhibits the highest hydroxide conductivity of 0.00878 S cm−1 at 40 °C and the highest elongation of 206.7% in the hydrate state. The membrane electrode assembly fabricated from this membrane shows the highest power density of 22 mW cm−2 at a current density of 55 mA cm−2, which is very promising for fuel cell applications.