Mechanically Robust Anion Exchange Membranes via Long Hydrophilic Cross-Linkers

Mechanically tough, cross-linked anion exchange membranes (AEM) based on poly(2,6-dimethylphenylene oxide) (PPO) were achieved by introducing a hydrophilic and flexible Jeffamine (O,O′-bis(2-aminopropyl)polypropylene glycol-block-poly(ethylene glycol)-block-polypropylene glycol 500) cross-linker into the cationic macromolecular network. The Jeffamine cross-linked AEMs demonstrated outstanding strength and flexibility and were mechanically tougher than AEM samples based on benzyltrimethylammonium (BTMA) functionalized PPO alone. The hydrated BTMA40 membrane showed 52% elongation at break, while the Jeffamine-based J10PPO sample had a 167% elongation at break. In addition, the hydroxide (OH–) conductivity of the J10PPO sample was 52 mS/cm at 80 °C with a swelling ratio of 61%, while BTMA60 suffered severe swelling above 60 °C. The alkaline stabilities of the AEMs with different degrees of Jeffamine cross-linking were evaluated in 1 M NaOH at 80 °C for 500 h. During the 500 h degradation test, J10PPO exhibited the greatest cation stability. The OH– conductivity of this membrane decreased by 30% over 500 h. In contrast, the OH– conductivity of BTMA40 decreased to 9.6 mS/cm at 20 °C, which is 60% lower than the value measured for the sample before the stability test. Based on the high-performance Jeffamine cross-linked AEM, a Pt-catalyzed fuel cell with a peak power density of 314 mW/cm2 was demonstrated at 60 °C under 100% related humidity.