Browsing by Author "Vittadello, M."

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    Ormosil/Sulfonated Polyetheretherketone-Based Hybrid Composite Proton Conducting Membranes
    (Journal of Electrochemical Society, 2006) Licoccia, S.; Vona, M.L.D.; Epifonia, A.D.; Marani, D.; Vittadello, M.; Greenbaum, S.G.
    A modi?ed silane bearing a sulfonic acid function (?sulfonated diphenylsilanediole, SDPSD?)was prepared and characterized. The resulting ormosil was mixed with sulfonated polyetheretherketone ?SPEEK? with high degree of sulfonation (?0.9)? leading to homogeneous composite membranes. The formation of the composite substantially modi?ed the properties of SPEEK in terms of water uptake and solubility. The structural and electrochemical performance of the components and of the composite were investigated with thermogravimetric analysis, ?eld emission scanning electron microscopy,1H and 29Si nuclear magnetic resonance, both in solution and in the solid state, and electrochemical impedance spectroscopy. Both conductivity values, as high as 0.1 S cm?1, and 1H diffusion coef?cients of the composite SPEEK/SDPSD demonstrated that it possesses good proton transport characteristics up to 120�C, and it is then suitable for application as an electrolyte in polymer electrolyte fuel cells operating at intermediate temperature.
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    Two new siloxanic proton conducting membranes: Part II. Proton conductivity mechanism and NMR study
    (Electrochimica Acta, 2005) di Noto, V.; Vittadello, M.; Kalfan, A.N.; Greenbaum, S.G.
    The synthesis and structural characterization of two types of membranes with formulas {Si(CH3)3O[Si(CH3)HO]21.26-[Si(CH3)((CH2)3SO3H)O]1.8-[Si(CH3)((CH2)3Si(CH3)2O-)-O]14-Si(CH3)3}n (A) and {Si(CH3)3O[Si(CH3)HO]21.26-[Si(CH3)((CH2)3SO3H)O]1.8-[Si(CH3)((CH2)3(Si(CH3)2O-w))-Ov][Si(CH3)((CH2)3Si(CH3)2O-)-O]14?vSi(CH3)3}n (B), (w=20.31), were previously proposed. The ac electrical response of A and B was fully characterized in the 40 Hz?2 MHz frequency region by studying the impedance spectra in the medium and low frequency regions by equivalent circuits and complex dielectric spectra at high frequency in terms of dielectric relaxation modes. Results demonstrated that A and B conduct ionically by means of a proton exchange event which occurs via a vehicular mechanism between neighboring water clusters formed by water molecules aggregated around each sulfonic acid group of the siloxane side chains. The proton conductivities at 115�C of ca. 1.9 ? 10?3 and 1.8 ? 10?4 S cm?1 of fully hydrated membranes A and B, respectively, classify these silicone networks as good proton conductors. Membrane B was chosen for a closer investigation using NMR spectroscopy. Solid state 29Si MAS NMR experiments gave further insight about the three-dimensional structure. Proton diffusion measurements provided some encouraging results about proton dynamics of this membrane signaling the great potential of siloxanic based proton conductors.