Proton Conducting Organic/Inorganic Nanocomposite Polymer Electrolytic Membrane Synthesized by Sol-Gel Process
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I. Honma, *S. Nomura and H. Nakajima Energy Fundamental Division, Electrotechnical Laboratory, AIST, Umezono, Tsukuba, Ibaraki, 3058568, Japan, [email protected] * Minase Research Institute, Sekisui Chemical Co.,Ltd., Osaka 618-8589, Japan
ABSTRACT In this paper, new synthetic routes have been investigated for the preparation of Organic/inorganic nanocomposite polymer membranes consisting of Si0 2 /PTMO(polytetramethylene oxide) hybrids and novel proton conducting materials. These materials have been synthesized through sol-gel processes in flexible, ductile, free-standing thin membrane form. The hybrid membrane has been found to be thermally stable up to 160 C and possesses proton conductivities of approximately 10-4 S/cm from a room temperature to 160 C.
INTRODUCTION Recently, new synthetic routes have been developed for the preparation of organic/inorganic hybrid materials as realistic ionic conducting membranes for electrochemical devices such as fuel cells and batteries( 1 -13). In those materials, the structure of the hybrid has been designed at a molecular scale to possess fast proton as well as Lithium ion conduction through mostly manipulating organic ligand to inorganic surfaces(1-13) In this paper, a new class of organic/inorganic nanocomposite membranes consisting of SiO 2 / Polymer (PEO: Polyethylene Oxides; PPO: polypropylene oxide; PTMO: polytetrapropylene oxide) hybrids have been synthesized through sol-gel processes. Membranes doped with an acidic moiety such as 12-phosphotungstic acid (PWA) show high proton conductivities at temperatures up to 160 °C and were found to be flexible, as well as, thermally stable due to the closs-linking with temperature tolerant polymer frameworks in the hybrids. The effect of molecular structure and molecular weight of the polymers have been studied on the thermal stability and proton conducting properties of the membranes.
EXPERIMENT Molecular Design of the Hybrid Membrane Molecular precursors designed for organic/inorganic hybrid membranes have been developed in our previous papers(9- 12 ). Organic polymers of polyethylene oxide (PEO), polypropylene oxide (PPO), and polytetramethylene oxide (PTMO) have been closs-linked with alkoxysilanes through isocyanato coupling. These precursors then hydrolyze and condense to form macromolecules of flexible, glassy hybrid materials as shown in fig. 1. In the present work, the molecular weight of PEO, PPO, and PTMO have been systematically changed to control the thermal stability and proton
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Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society
conductivity of the hybrid electrolyte membranes. In particular, PEO600 (molecular weight of PEO is 600), PPO700, PTMO250, PTMO650 and PTMO2000 (Wako Pure Chemical) have been used for studying the effects of molecular structure and molecular weight on the thermal and conductive properties of the membrane. Membrane Synthetic procedure Figure 2 inset shows a synthetic route of the production of a silica/PTMO hybrid membrane. Endcapped precursor, i.e., tri
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