High thermomechanical stability and ion-conductivity of anion exchange membranes based on quaternized modified poly(oxyndoleterphenylene)

Abstract

Novel anion exchange membranes (AEMs) were synthesized by superacid-catalyzed step-growth polycondensation of isatine and p-terphenyl at room temperature. The materials obtained were functionalized by a highly efficient nucleophilic substitution reaction to introduce different cationic side chain lengths, this way, different degrees of functionality (DF) were achieved through modifying the molar ratios of the functionalization agent and the polymer precursor. The high solubility of the cationic polymers allowed NMR studies, additionally, the water uptake (WU), morphology, ion exchange capacity (IEC), ion-conductivity, thermal and mechanical stabilities were investigated. The membranes displayed high conductivities due to the well-defined structures and high phase segregation observed, the membrane with the longest pendant quaternary ammonium (QA) group had a conductivity of 118.7 mS cm−1 at 80 °C demonstrating its potential applicability in electrochemical devices in which ionic membranes were required. The novel AEMs were tested in a hydrogen fuel cell (HFC) and a direct methanol fuel cell (DMFC) observing high open circuit voltages (OCV) of about 1.03 V and 0.6 V for HFC and DMFC, respectively. These results are promising for fuel cells and different electrochemical devices, according to the ion conductivity observed, resistance and mechanical properties of the reported membranes.