New polymeric proton conductors for water-free and high temperature fuel cells

Polyelectrolyte membranes containing imidazole groups were studied by conductivity, thermal, and mechanical measurements to determine their suitability for use as proton conducting membranes, which do not rely on the presence of water. Two types of polymer matrix were studied, i.e., a high Tg material, Nafion® and a polyether polyelectrolyte with a low Tg but suitable for attaching imidazole groups by covalent bonding. Both polyelectrotytes were doped with free imidazoles by solvent casting and by vapor sorption. The conductivity of the N-methyl imidazole doped materials was lower and the temperature dependence differed, indicating a different mechanism of proton transport for the imidazole. The imidazoles were covalently tethered to the polyether polyelectrolyte to provide a solid state membrane containing no mobile solvent. Voltammetry at platinum showed poisoning only when excess imidazole was present. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA, 8/22-26/2004).