Nafion-like structured perfluoropoly(diphenylene) graft polymers microphase separated anion exchange membranes

Abstract

Perfluorinated poly(diphenyl) graft polymers with alkoxy side chains of piperidinium quaternary ammonium salts were synthesized by two-step trifluoromethanesulfonic acid and lanthanum trifluoromethanesulfonate catalyzed and Williamson ether-forming reactions. Its grafted hydrophilic side chains can form a good microphase separation structure, as demonstrated by small angle X-ray scattering and atomic force microscope. The good phase separation structure improves the ionic conductivity while ensuring a smaller swelling ratio. The ionic conductivity of long side chain polymer (PF4) reached 80 mS cm−1 at 80 °C, while the swelling ratio was only 17.1 %. The maximum power density of PF4 was 1.008 W cm−2 at a gas flow rate of 200 sccm and a gas back pressure of 0.1 MPa. In addition, due to the perfluorinated substituted backbone and the non-N-site bonded piperidine cation, all the anion exchange membranes prepared in this paper possess good alkaline stability, with a conductivity drop of no more than 11 % after 1000 h of immersion in 4 M NaOH solution, and essentially no change in mechanical properties. The PF4 was operated at a current density of 200 mA cm−2 for 250 h with a voltage drop of only 97 mV and a resistance increase of 12 %.