Cross-linked high temperature polymer electrolytes through oxadiazole bond formation and their applications in HT PEM fuel cells

Chemical cross-linking of linear, high molecular weight polymer electrolytes has been performed herein, using thermally stable cross-linking bonds. Aromatic copolymeric or terpolymeric polyethers combining polar main chain pyridine units with side cross-linkable carboxylic acid groups were employed. The selected cross-linking chemistry was that of oxadiazole ring formation due to the synthetic versatility and the exceptional thermal and chemical stability of the formed linkages. Membranes of increased robustness and thermal stability were obtained after cross-linking that moreover presented higher doping levels than their linear analogues. Selected cross-linked membranes were formulated into membrane electrode assemblies (MEAs) that were tested in a single cell at temperatures up to 220 degrees C for 350 hours showing stable operation and high ionic conductivities close to 10(-1) S cm(-1). These facts point to the superiority of the cross-linked materials and their great potential as PEMs for fuel cells operating well above 180 degrees C.