Synthesis and Properties of A Novel Polymer Electrolyte Membrane for High-Temperature PEMFC

• Main Authors: Li-Cheng Jheng, 鄭力誠
• Other Authors: Steve L.C. Hsu
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/85026182394142661391

碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 95 === Polybenzimidazole(PBI) membrane doped with phosphoric acid was proposed as an solid electrolyte membrane for PEMFC and DMFC. In this study, fluorine-pyridine containing PBI copolymers were synthesized by copolymerization of 3’3-diaminobenzidine , 2,5-Pyridinedicarboxylic- acid(2,5-PDA) and 2,2-Bis(4-carboxyphenyl)-hexafluoropropane(HFA) with different molar ratio. PBI membranes were prepared by solution- casting and then doped by immersion into phosphoric acid. The structures of PBI copolymers were characterized by FTIR, 1H-NMR and X-ray. The solubility of PBI was significantly improved by the introduction of a flexible bulky group, HFA, into polymer backbone. The excellent thermal stablility and dimension stability of PBI were completely maintained. Additionally, the PBI copolymers exhibited the methanol permeability of 3.1~4.2×10-8 cm2/s in 6wt% methanol solution which show that they were still good methanol barrier materials as expected. The proton conductivity of phosphoric acid doped PBI is dependent on doping level and temperatures. Under anhydrous condition, the proton conductivity of saturated acid doped PBI membranes was about 6×10-4 S/cm at 160℃. From the results, it can be suggested that the proton conduction in PBI copolymers is governed by Grotthuss mechanism rather than Vehicle mechanism. The PBI copolymers exhibited good mechanical properties with tensile strength at about 80MPa and Young’s modulus at 2GPa. However, the mechanical properties of the acid doped PBI membranes were decreased in the presence of phosphoric acid or water which act as plasticizers.