Proton Conducting Nano Hybrid Membranes Synthesized from Temperature Tolerant Polydimethylsiloxane (PDMS) Polymers
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Proton Conducting Nano Hybrid Membranes Synthesized from Temperature Tolerant Polydimethylsiloxane (PDMS) Polymers Je-Deok KIM1 and Itaru HONMA1 1 Energy Electronics Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, 305-8568, Japan ABSTRACT Flexible and temperature tolerant nano-hybrid membranes consisting of zirconium (titanium) oxides and polydimethysiloxane (PDMS) with the different molecular mass of 4500 and 600 have been synthesized by sol-gel processes. The membrane of zirconium/PDMS=2 (in molar) showed enhanced thermal stability and flexibility up to 300 ℃ due to the presence of cross-linkable inorganic nano-phase in the hybrid macromolecular matrix. The membrane becomes proton conducting polymer electrolyte when doped with 12-phosphotungstic acid (PWA). The proton conducting properties of the hybrid membranes with various PWA concentration were measured in the temperature range from room temperature to 150℃ under saturated humidity conditions. A maximum conductivity of 2x10-2 S/cm was obtained at 150℃ when the PDMS/zirconium oxides hybrid matrix was changed to gel state due to the higher water activity at elevated temperatures. INTRODUCTION The sol-gel process has been carried out on the preparation of crystalline and non-crystalline ceramic oxides and glasses, and provided the possibility of incorporating organic components into an inorganic oxide network at the molecular level. Much of these works is correlated with the encapsulation of various organic and inorganic moieties into inorganic silicate materials prepared from Si(OEt)4 or reactive metal alkoxides. The flexibility of organic/inorganic hybrids can be provided by a controlled sol-gel process of tetraethoxysilane (TEOS) and silanol-terminated polydimethylsiloxane (PDMS) moieties.[1] Previous works of rubbery ORMOSILs by Schmidt [2] and CERAMERs by Wilkes [3] are examples of flexible and thermally stable organic/inorganic hybrids, where the inorganic parts are incorporated to cross-link flexible polymers and provide structural stability of the hybrid network.[2-6] Therefore, rubbery ORMOSILs can be thermally more stable than pure organic rubbers. Katayama et al. reported mechanical and optical properties of the dimithysiloxane/metal oxides hybrid materials.[5,6] The ion conducting hybrid macromolecules with cross linked organic/inorganic moieties were synthesized by molecularly controlled sol-gel processes.[7,8] Commonly, phosphotungstic acid H3PW12O40・nH2O (PWA) is one of good candidate moieties for being incorporated into hybrid matrixes. It belongs to a large group of polyoxometalates[9] and has a high protonic conductivity at room temperature,[10] in the order of 10-1 S/cm, and a high solubility in water and in many organic solvents. Therefore, these heteropoly anions have been frequently used for proton conductive polymer electrolyte, which are durable even at elevated temperatures. The electrolyte membranes with temperature tolerance have attracted much attention, recently, for its a
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