High proton conductivity of sulfonated methoxyphenyl-containing poly(arylene ether ketone) for proton exchange membranes

Abstract

A series of sulfonated methoxyphenyl-containing poly(arylene ether ketone)s (SMP-PAEKs) were synthesized via polycondensation from 2-(3-methoxy)phenylhydroquinone and other commercial monomers, followed by a postsulfonation approach under mild reaction conditions. Controlled substituted sites and the degree of sulfonation were realized by using various quantities of 2-(3-methoxy)phenylhydroquinone, given that sulfonated polymers (SMP-PAEK) can be soluble in common organic solvents such as DMSO, NMP, and DMAc. The tough and transparent polymer membrane was prepared by a solution casting method, exhibiting excellent mechanical properties and high proton conductivities. The tensile stress at maximum load and elongation at break of these membranes are 30.0–32.4 MPa and 120–171% in a dry state respectively. The proton conductivities of these membranes are higher than that of Nafion 117 in water. In particular, SMP-PAEK-80 with an IEC of 1.62 mequiv. g⁻¹ exhibited the highest proton conductivity of 294 mS cm⁻¹ at 80 °C in water. In addition, SMP-PAEK-90 with an IEC of 1.83 mequiv. g⁻¹ exhibited suitable proton conductivities in different relative humidities (RHs) (30–98%) at 80 °C, which was higher than Nafion 117. The clear micro-phase separation morphology was observed by SAXS, which was powerful evidence to explain their high conductive behaviors. In addition, the current density of the SMP-PAEK-80 membrane was measured to be 235 mA cm⁻² at 0.36 voltage (V) under fully hydrated conditions at room temperature with 1.5 bar back pressure during a MEA cell performance test.