Covalent cross-linking in phosphoric acid of pyridine based aromatic polyethers bearing side double bonds for use in high temperature polymer electrolyte membrane fuelcells

Cross-linkable aromatic polyethers combining main and side chain pyridine units as well as side double bonds were successfully synthesized and characterized. Aiming at the use of these materials as electrolytes at high temperature fuel cells, these polymers were subjected to covalent cross-linking in order to improve their mechanical properties and their stability in the doped state. The cross-linking was obtained via cationic polymerization of the double bonds, during the impregnation of the produced membranes in phosphoric acid. The cross-linking was confirmed by the increased glass transition temperatures, the improved thermal stability and the insolubility of the cross-linked membranes compared to their undoped non cross-linked counterparts. Selected cross-linked membranes were used for membrane electrode assembly (MEA) preparation and tested in a single cell at temperatures between 180 and 220 °C. Long-term durability tests were also performed at 180 °C and at a current density of 0.2 A/cm2. The experiment showed a stable operation without degradation for 1000 h. The promising performance and the durability of the tested materials in combination with the simple and convenient technique which used to produce cross-linked membranes, demonstrates the feasibility of this type of electrolytes to be used in high temperature PEM fuel cell applications.