In Situ-Doped Sulfonated Schiff-Base Networks in SPEEK Composite Membranes with Enhanced Proton Conductivity

Sulfonated polyether ether ketone (SPEEK) has been widelyinvestigatedin proton exchange membrane fuel cells (PEMFCs) due to its excellentthermal stability, chemical stability, and low cost compared withNafion. However, excessive degree of sulfonation will easily leadto the decrease in thermal stabilities and mechanical properties ofSPEEK membranes, which limits the enhancement of proton conductivity.In this work, a series of Schiff-base networks (SNWs) with differentcontents are in situ synthesized in the SPEEK membrane by a Schiff-baseco-condensation reaction, and then, the composite membranes are soakedin sulfonic acid for further improvement of proton conductivity. Thehighest doping amount of the SNW filler in SPEEK can reach 20 wt %.High loading and low leaching rate of H2SO4 areeasily achieved owing to the similar size between sulfuric acid moleculesand micropores in SNW. Moreover, abundant amino and imine groups inSNW networks contribute to the anchoring of H2SO4 into the pores by acid-base interactions. The proton conductivityof the SPEEK/S-SNW-15 composite membrane can reach 115.53 mS cm(-1) at 80 degrees C and 100% RH. Meanwhile, the compositemembrane also exhibits satisfied stability and mechanical property.