Design and synthesis of side-chain optimized poly(2,6-dimethyl-1,4-phenylene oxide)-g-poly(styrene sulfonic acid) as proton exchange membrane for fuel cell applications: Balancing the water-resistance and the sulfonation degree

• Published in: International journal of hydrogen energy 2021-06, Vol.46 (39), p.20664-20677
• Main Authors: Zeng, Guangbo, Zhang, Dongqing, Yan, Liuming, Yue, Baohua, Pan, Ting, Hu, Yidong, He, Shufa, Zhao, Hongbin, Zhang, Jiujun
• Format: Article
• Language: English
• Subjects: Proton exchange membrane; Structure design; Sulfonation degree; Water-resistance
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2021.03.173

Side-chain optimized poly (2,6-dimethyl-1,4-phenylene oxide)-g-poly (styrene sulfonic acid) (PPO-g-PSSA) is designed with balanced water-resistance and sulfonation degree. The PPO-g-PSSA is synthesized by controlled atom-transfer radical polymerization (ATRP) from brominated poly (2,6-dimethyl-1,4-phenylene oxide) (PPO-xBr) and ethyl styrene-4-sulfonate and followed by hydrolysis. A series of PPO-g-PSSA are prepared possessing different bromination degree (x) of PPO-xBr and polymerization degree (m) of the side-chains and the water-resistances of the fabricated membranes are investigated. The results show that a PPO-g-PSSA at relatively low x (x  4) exhibits good balance between the water-resistance and the sulfonation degree. Namely, it displays suitable proton conductivity with compromised water-resistance. Moreover, a maximum ion exchange capacity (IEC) of 3.24 mmol g−1 is reached without the sacrifice of water-resistance. In addition, PPO-g-0.08PSSA-13 and PPO-g-0.14PSSA-4 are chosen characterized by thermogravimetric analysis, proton conductivities and mechanical properties. At 90% RH, the optimized PPO-g-0.08PPSA-13 possesses a proton conductivity of 37.9 mS cm−1 at 40 °C and 45.5 mS cm−1 at 95 °C, respectively. •Sulfonated graft PPO is designed and optimized by molecular dynamics simulation.•The maximum ion exchange capacity is achieved at 3.24 mmol g−1.•Some membranes obtain a balance between water-resistance and sulfonation degree.•Relatively low bromination degree and high polymerization degree are recommended.