Influence of protic ionic liquid on structure of proton-conducting sPEEK-zirconia membranes for anhydrous fuel cell application

Full text: Operation in higher temperatures, under anhydrous conditions, is vital for the future of Polymer Electrolyte Fuel Cell (PEFC) technology. In this work, hybrid sPEEK / ZrO₂ membranes, comprising the protic ionic liquid (PIL) diethylmethylamine triflate in different contents were synthesized via sol-gel method. The membranes showed good thermal stability and the presence of ZrO₂ nanoparticles enabled PIL retention. Their structural features have been investigated at 70°C by XRD and SAXS. For pure sPEEK, a SAXS broad peak is observed, attributed to spatial correlation between polymer nanodomains rich in SO₃H groups, consistent with a Guinier regime. Incorporation of ZrO₂ (4 wt.%) increases the crystallinity of sPEEK, but does not affect the correlation between SO₃H-rich nanodomains, suggesting weak interactions between ZrO₂ and SO₃H groups. PIL interacts with SO₃H domains, illustrated by the SAXS peak intensity decrease. Another interesting feature is that incorporation of 10 and 40 wt.% PIL leads to an increase in conductivity by the membranes: the former shows a decrease in spatial correlation between ZrO₂ nanoparticles. The structure of the latter exhibits small spatial correlation between ZrO₂ nanoparticles, lower polymer crystallinity and higher conductivity. A study of the evolution of structure, thermomechanical properties and proton conductivity of the membranes in temperatures up to 160°C is in course, aiming the practical use of these materials in PEFCs. (author)