Alkaline Durable Anion-Conducting Electrolyte Membranes Prepared by Radiation Induced Grafting of 2-Methyl-4-vinylimidazole for Non-Platinum Direct Hydrazine Hydrate Fuel Cells

For Pt-free alkaline-type fuel cells, anion-conducting polymer electrolyte membranes (AEMs) having a weak base imidazolium group, which scarcely damages the polymer backbones, have been developed. To prevent ring opening hydrolysis and β-elimination reactions, which are the main degradation routes, we conducted the radiation-induced grafting of 2-methyl-4(5)-vinylimidazole (2Me4VIm), which possesses methyl protecting group at imidazole C2 position and no β-protons, with styrene into a poly(ethylene-co-tetrafluoro-ethylene) (ETFE) film and subsequent N-alkylation and ion exchange reactions to obtain 2Me4VIm/St-AEM (Im/St = 75/25) with ion exchange capacity of 1.35 mmol g-1. The conductivity and water uptake are 157 mS cm-1 and 86%, respectively. In 1 M KOH at 80°C, the initial rapid decrease of conductivity was clearly suppressed; then, the membrane maintained the conductivity above 15 mS/cm until 600 h. The semi-logarithmic plots of conductivity show 1st order kinetics, indicating the no β-elimination but only slow ring-opening hydrolysis in the alkaline condition.