Comparison of alkaline stability of quaternary ammonium- and 1,2-methylimidazolium-based alkaline anion exchange membranes

The alkaline stability of 1,2-dimethylimidazolium with various N3-substituents (including butyl, benzyl and vinylbenzyl) and corresponding quaternary ammonium small molecular compounds, and the 1,2-dimethylimidazolium- and quaternary ammonium-based membranes are systemically studied in the same condition. The spectroscopy (such as NMR, FT-IR, XPS and mass spectrum) results of the two kinds of small molecular compounds indicate that the quaternary ammonium cations are more stable than 1,2-dimethylimidazolium cations in 3   M KOH at elevated temperature, especially at 80   °C. Moreover, the alkaline stability of the 1,2-dimethylimidazolium cations would be influenced by the N3-substitutions of the imidazolium, and N3-butyl substituted cation shows a better alkaline stability. The quaternary ammonium-based membrane are also more stable than the 1,2-dimethylimidazolium-based membrane in 1   M KOH at 60   °C. In addition, the performance of the alkaline direct methanol fuel cell using quaternary ammonium-based membrane (22   mW   cm −2 ) is much better than that of the fuel cell using 1,2-dimethylimidazolium-based membrane (0.04   mW   cm −2 ).