Original blend membranes of partially fluorinated copolymers bearing azole functions with sulfonated PEEK for PEMFC operating at low relative humidity

International audienceOriginal proton conducting fluorocopolymers grafted by azole functions (imidazole, benzimidazole, 1H-1,2,4-triazole) were synthesized through grafting poly(iodoethyl vinyl ether–alt–chlorotrifluoroethylene) copolymers by 4(5)-hydroxymethylimidazole, 2-mercaptobenzimidazole or 1H-1,2,4-triazole-3-thiol. Imidazole, benzimidazole and 1,2,4-triazole functionalized copolymers were characterized by 1H and 19F NMR spectroscopy and by thermal analyses (DSC and TGA), and were used in the preparation of blend membranes with sulfonated PEEK (sPEEK). Properties of the three series of membranes were comprehensively studied to evidence the influence of the nature of the azole group on membrane microstructure, thermal properties, and water uptake. Proton conductivities of blend membranes comprising a fluorinated polymer component functionalized with triazole is significantly higher than those with imidazole or benzimidazole moieties, and detailed characterizations have identified an optimal composition in terms of the basic (-NH):acidic (-SO3H) groups ratio of 1.7 in this system, where the proton conductivity at 140 °C and at low relative humidity (< 25 %) reached 7 mS.cm-1 for a blend membrane containing 60 %-wt of s-PEEK and 40 %-wt of poly(IEVE-alt-CTFE)-g-1H-1,2,4-triazole-3-thiol95% copolymer