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Hybrid membranes of sulfonated poly ether ether ketone, ionic liquid and organically modified montmorillonite for proton exchange membranes with enhanced ionic conductivity and ionic liquid lixiviation protection

Arias, Jose Jonathan Rubio, Carlos Dutra, José, Gomes, Ailton de Souza
Journal of membrane science 2017 v.537 pp. 353-361
X-ray diffraction, artificial membranes, cations, clay, electrochemistry, impedance, ionic liquids, models, montmorillonite, nuclear magnetic resonance spectroscopy, transmission electron microscopy
Through the fabrication of hybrid membranes, composed by the protic ionic liquid diethylmethylammonium trifluomethane sulfonate (demaTfO), sulfonated poly (ether ether kethone) with degree of sulfonation 73% (sPEEK73) and montmorillonite modified with dema⁺ cation (Mmtdema), this work evaluates the effect exerted by the compatibilization between clay and ionic liquid on the morphology and performance of membranes, as a function of Mmtdema proportion. This system of membranes showed high conductivity (78 mS/cm at 70°C) with some issues, due to the plasticization effect caused by montmorillonite and ionic liquid; these effects were confirmed through electrochemical impedance spectrometry (EIS), dynamic mechanical analysis (DMA) and proton relaxometry. The membranes showed resistance to ionic liquid lixiviation, which was confirmed through static water immersion and this effect was attributed to the protection effect that interlamellar spaces can provide to the ionic liquid, as it was visualized through TEM and XRD. The conjugation of results from several different techniques as SAXS, EIS, NMR, TEM and XRD permitted to obtain evidences for a proposed descriptive model of proton transporting process, which turns out to be a synergy between Grotthuss mechanism and vehicular mechanism, favored by the structure of Mmtdema and the preparation method, leading thus to high conductivity membranes with lixiviation protection for application as proton exchange membranes.