Anion exchange membranes with clusters of alkyl ammonium group for mitigating water swelling but not ionic conductivity

Crosslinked ionomers containing clusters of alkyl ammonium group at side chain was synthesized by attaching an unique amine (tris[2-(dimethylamino)ethyl]amine) on poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) polymer backbone. These molecular structures show a dramatic enhancement in water resistance (low water uptake (9–13%) and dimensional swelling (4–6%) in water at room temperature) compared with non-cluster-shaped PPOs. Moreover, the temperature had less of an influence on the water uptake and swelling ratio of the membranes. The resulting anion exchange membranes exhibit good ionic (OH-) conductivities in water (up to 25.4 mS cm−1 at 25 °C) and represent a new class of anion exchange membranes. A test of the alkaline stability of membranes (in 1 M KOH at 60 °C for 480 h) showed hydroxide conductivity about 51% of the original conductivity and indicated that these membranes are good candidates for application in alkaline fuel cells (AFCs). Membrane electrode assembly made from the as-fabricated membrane showed moderate fuel cell performance reaching peak power density 77 mW cm−2 at 60 °C in a H2/O2 alkaline fuel cell. This simplistic synthetic tactic enables the preparation of densely functionalized materials with the potential to meet the demands of AFCs.