Anion exchange membranes (AEMs) with good alkaline stability and ion conductivity are fabricated by incorporating quaternary ammonium-modified silica into quaternary ammonium-functionalized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO). Quaternary ammonium with a long alkyl chain is chemically grafted to the silica in situ during synthesis. Glycidyltrimethylammoniumchloride functionalization on silica (QSiO 2 ) is characterized by Fourier transform infrared and transmission electron microscopic techniques. The QPPO/QSiO 2 membrane having an ion exchange capacity of 3.21 meq·g –1 exhibits the maximum hydration number (λ = 11.15) and highest hydroxide ion conductivity of 45.08 × 10 –2 S cm –1 at 80 °C. In addition to the high ion conductivity, AEMs also exhibit good alkaline stability, and the conductivity retention of the QPPO/QSiO 2 -3 membrane after 1200 h of exposure in 1 M potassium hydroxide at room temperature is about 91% ascribed to the steric hindrance offered by the grafted long glycidyl trimethylammonium chain in QSiO 2 . The application of the QPPO/QSiO 2 -3 membrane to an alkaline fuel cell can yield a peak power density of 142 mW cm –2 at a current density of 323 mA cm –2 and 0.44 V, which is higher than those of commercially available FAA-3-50 Fumatech AEM (OCV: 0.91 V; maximum power density: 114 mW cm –2 at current density: 266 mA cm –2 and 0.43 V). These membranes provide valuable insights on future directions for advanced AEM development for fuel cells.

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In this study, blended anion exchange membranes were prepared using polyphenylene oxide containing quaternary ammonium groups and polyvinylidene fluoride. A polyvinylidene fluoride with high hydrophobicity was blended in to lower the vanadium ion permeability, which increased when the hydrophilicity increased. At the same time, the dimensional stability also improved due to the excellent physical properties of polyvinylidene fluoride. Subsequently, permeation of the vanadium ions was prevented due to the positive charge of the anion exchange membrane, and thus the permeability was relatively lower than that of a commercial proton exchange membrane. Due to the above properties, the self-discharge of the blended anion exchange membrane (30.1 h for QA–PPO/PVDF(2/8)) was also lower than that of the commercial proton exchange membrane (27.9 h for Nafion), and it was confirmed that it was an applicable candidate for vanadium redox flow batteries.

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