Ionic conductivity and thermal analysis of a high-temperature polymer
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A high-temperature polymer electrolyte based on lithium-doped pyromellitic dianhydride + Oxybis(aniline)/2,5-diaminobenzenesulfonic acid (PMDA-ODA/DABSA) copolymer has been synthesized and characterized by ac impedance analysis and differential scanning calorimetry. Its dc conductivity was found to reach 10~8 S/cm near 60 °C at ambient relative humidity and was confirmed to be of ionic nature. Besides the increase of the conductivity achieved by moisture uptake, the doping of lithium was found to yield enhancement of the ionic transport in the absence of water molecules as well. I. INTRODUCTION To recycle energy sources such as industrial waste steam, and to develop sensors durable at harsh environments, polymer electrolytes capable of operating around 350 °C are needed in the applications of reversible steam-electrolysis/fuel cells and sensor technology, in order to replace ceramic electrolytes which are limited by their low current density and low power density. The existing polyethylene oxides (PEO) and perfluorinated ionomers (NafionR, for example) used in solid-state polymer fuel cells and sensors are, however, not capable of high-temperature operation.1-2 Although they can be made into thin films to reduce internal energy loss and to produce much larger current density and power density than their ceramic counterparts, the low glass transition temperature (Tg) required by PEO to gain chain motion contribution to ion mobility,2-3 or the transport of a substantial amount of water in perfluorinated ionomer to facilitate ionic conduction, made their high-temperature (T > 150 °C) applications impossible.4'5 Among high-performance polymers possessing thermal stability at or above 300 °C, polyimides are a wellstudied example.6-7 Although they have high thermal and mechanical strength (shrinkage < 4 % at 400 °C and tensile strength >25 000 psi), their electric conductivities are very low at room temperature (
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