Influence of crosslinking in phosphoric acid-doped poly(phenylene oxide) membranes on their proton exchange membrane properties

Abstract

Phosphoric acid (PA)-doped membranes are promising electrolytes for high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, long-term durability issues have been an obstacle to their commercialization. Herein, we report a series of poly(phenylene oxide) (PPO)-based crosslinked membranes containing quaternary ammonium (QA) groups and exhibiting enhanced physicochemical stability and PA retention via ion-pair interactions between QA and PA. The degree of crosslinking in PPO by diamine crosslinker was controlled at 20, 30, and 40. The membranes were also crosslinked (degree = 20) using diamine crosslinkers with variable alkyl chain length (ethyl, butyl, and hexyl). All membranes exhibited sufficient thermal stability (5% weight loss temperatures (TD5%) = -230 degrees C) and oxidative stability (-85% in the Fenton test). The PA uptake of the resulting membranes was controlled between 110 and 154% depending on their crosslinked structures. The membrane with the lowest degree of crosslinking (20) and shortest crosslinker exhibited the highest PA uptake and highest anhydrous proton conductivity (0.043 S/cm at 150 degrees C) in doped state. The proton conductivity was found to be significantly influenced by the PA uptake and crosslinked membrane structures. The highest PA retention of 89% was exhibited by the PA-doped membrane with the highest degree of crosslinking (40). (c) 2021 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.