PPOs having piperidinium-based conducting head groups with extra molecular interaction sites as new anion exchange membranes

Abstract

Poly(2,6-dimethyl-1,4-phenylene oxide)s [PPOs] with 4-hydroxy-piperidinium and tropinium conducting head groups are developed, and corresponding membranes are investigated as new anion exchange membranes (AEMs). Their properties are compared with piperidinium-functionalized PPO membranes. The additional OH group in the piperidinium unit further enhances the chemo-physical stability of the corresponding membrane (OH-Pip-PPO) due to physical crosslinking through hydrogen bonding. The bulky structure of tropinium provides additional free volume in the corresponding membrane (Trop-PPO). Hydrogen bonding between the polymers and water causes well-developed morphology and high dimensional stability. These membranes also contain ion-conducting highways, facilitating efficient ion transport, in agreement with molecular dynamics simulations. The 4-hydroxy-piperidinium-functionalized PPO showed the highest dimensional and alkaline stability, with slightly lower conductivity and cell performance than piperidinium-functionalized-PPO (Pip-PPO) and Trop-PPO. Trop-PPO further increases free volume and water uptake, resulting in the highest normalized conductivity among the three PPO-based membranes and fuel cell performance similar to Pip-PPO.