Imidazolium-functionalized anion exchange polymer containing fluorine group for fuel cell application

Abstract

In this paper, two series of novel anion exchange membranes based on poly(arylene ether ketone)s and poly(arylene ether ketone sulfone)s containing fluorine group were successfully synthesized via polycondensation, brominated, methyl imidazolium functionalization, and the subsequent alkalization reactions. Bromination rather than chloromethylation was used for the conversion of CH3 to reactive CH2Br. 1-methylimidazole was used for the preparation of target anion exchange membranes (AEMs). The structures of poly(arylene ether ketone)s (PAEKs), brominated poly(arylene ether ketone)s (BPAEKs), poly(arylene ether ketone sulfone)s(PAEK-SFs), brominated poly(arylene ether ketone-sulfone)s(BPAEK-SFs), methyl imidazolium-functionalized poly(arylene ether ketone)s (MIPAEKs) and methyl imidazolium-functionalized poly(arylene ether ketone sulfone)s (MIPAEK-SFs) were confirmed by 1H-NMR spectroscopy. Thermal stability of the MIPAEKs membranes and the MIPAEK-SFs membranes were characterized by thermo gravimetric analysis (TGA). The water uptakes, swelling ratio, hydroxide ion conductivities, ion exchange capacities (IEC), chemical stabilities, and mechanical properties of the membranes derived from the synthesized membranes were assessed as anion exchange membranes. The IEC of the MIPAEKs membranes varied from 1.670 to 2.568 meq g−1, however, as for the MIPAEK-SFs membranes which varied from 1.033 to 1.892 meq g−1, which can be controlled by brominated reaction conditions. The ion conductivities of the membranes increase dramatically with increasing temperature. The MIPAEK-c membrane with IEC value of 2.568 meq g−1, derived from copolymer BPAEK-c bearing methyl imidazolium functionalization structure, displayed the highest hydroxide ion conductivity of 38.6 mS cm−1 at 80 °C and showed strong tensile strength (23 MPa) at 25 °C and hydroxide ion conductivity of 33.1 mS cm−1 after being conditioned with 3 M NaOH at 60 °C for 24 h. These properties of the ionomers membranes show their potential as an anion exchange membrane of alkaline fuel cells.