Synthesis and Properties of Quaternary Phosphonium‐based Anion Exchange Membrane for Fuel Cells

Quaternary phosphonium‐based polyelectrolyte was synthesized from bromomethylated poly(2,6‐dimethyl‐1,4‐ phenylene oxide) (BPPO) by functionalization with tris(2,4,6‐trimethoxyphenyl) phosphine (TTMPP). Typically, excellent solubility of the polyelectrolyte in polar solvents, such as NMP and DMSO, allowed a solution‐casting strategy for preparation of anion exchange membrane (AEM) with properly ordered hydrophilic/hydrophobic nano‐scale phase separation morphology, which was visible in atomic force microscopic phase images. Accordingly, the optimized ionmeric AEM exhibited excellent hydroxide conductivity of 110 mS/cm at 70°C, but extremely restricted linear expansion ratio of below 7% at the same temperature. Additionally, such membrane could maintain flexibility and conductivity after an immersion treatment in 1 mol/L NaOH solution at 60°C for about 100 h, implying its potential in alkaline fuel cells.