Polybenzimidazolium-Based Solid Electrolytes

A series of methyl, benzyl, and mixed polybenzimidazolium halides was synthesised and characterised by NMR spectroscopy. Membranes were formed and ion exchanged with hydroxides. These membranes are of interest for use in potentially platinum-free anionic exchange membrane fuel cells. Crosslinked membranes were obtained by the addition of alpha,alpha'-dibromo-p-xylene to the casting solution. The ion conductivity of membranes was determined by impedance spectroscopy. A hydroxide conductivity of 29 mS . cm(-1) at 26 degrees C and 58 mS . cm(-1) at 60 degrees C was obtained. The thermal and hydrolytic stability was investigated and a pathway for hydrolytic degradation proposed. Hydroxide ions react at the 2 position, the intermediate carbinol opens to the amine-amide, and further degrades under chain scission to diamine and carboxylic acid.