Densely functionalized proton exchange membrane from sulfonated poly(aryl ether ketone) containing multiple flexible side chains for fuel cell

Abstract

Proton exchange membranes play a pivotal role in boosting the efficiency of fuel cells and hence focused research in this area is highly desirable. Here we report that a series of poly(aryl ether ketone)s with amino and trifluoromethyl units (AFPAEK) were synthesized by nucleophilic substitution polycondensation. Subsequently, sulfonated poly(aryl ether ketone) (SAFPAEK) membranes were prepared with amino groups of AFPAEKs as reaction sites to densely graft alkyl sulfonate side chains. This special structure of hydrophilic backbone containing trifluoromethyl groups and hydrophilic sulfonic acid groups generated nano-sized proton channels. The facilitated transportation of protons and cations through these membranes enables the prepared membranes to obtain high IEC and desirable proton conductivity. In particular, the SAFPAEK-50 membrane exhibits high proton conductivity from 0.077 to 0.179 S cm−1, which is higher than that of Nafion 115 over the entire temperature range. Meanwhile, SAFPAEK membranes possess excellent mechanical properties and favorable stability (thermal stability and oxidation stability). Importantly, SAFPAEK-50 displays a peak power density of 70.9 mW cm−2 at 158.8 mA cm−2 in a direct borohydride‑hydrogen peroxide fuel cell, which is higher than that of Nafion 115 (60.9 mW cm−2 at 151.2 mA cm−2). Therefore, the results reveal that the prepared densely functionalized membranes become good candidate proton exchange membrane materials for evaluation in fuel cell applications.