Ammonium based ionic liquids immobilized in large pore zeolites: Encapsulation procedures and proton conduction performance

Ammonium based ionic liquids immobilized in Y (FAU framework code) and beta (BEA framework code) type zeolites by different solution methods have been comprehensively characterized for their potential applications as hydrophilic-conducting fillers for PEM. In particular (2-hydroxymethyl) trimethylammonium dimethyl phosphate (IL1) and N,N-dimethyl-N-(2-hydroxyethyl) ammonium bis(trifluoromethanesulfonyl) imide (IL2) encapsulated into commercial NaY (Si/Al = 1.5) and NH4-BEA (Si/Al = 12.5) type zeolites have been investigated. X-ray diffraction, N2 physisorption, TGA analysis, ATR–FTIR and Raman spectroscopy techniques have been used to assess about the goodness of the encapsulation procedures. Finally, A.C. impedance spectroscopy measurements of tablets prepared from PVDF/composite (1:9 wt. ratio) were performed in order to evaluate their conduction properties. The conduction properties of the composites as a function of temperature and water partial pressure have been finally chosen as analytical tool to define the best encapsulation procedure and IL/Z composite for PEMFCs applications. A possible conduction mechanism, where synergic-inhibition effects between ILs and H2O molecules coupled to IL dragging by water desorption take place, is also presented.