Synthesis and properties of fluorine-containing polybenzimidazole for high-temperature proton exchange membrane fuel cells

• Main Authors: Shih-Wei Chuang, 莊士緯
• Other Authors: Steve Lien-Chung Hsu
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/24594324213739993147

博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 96 === First, an amorphous, organosoluble fluorine-containing polybenzimidazole (PBI) was synthesized from 3,3’-diaminobenzidine and 2,2-bis(4-carboxyphenyl)-hexafluoropropane. The 5 % weight loss temperature of the polymer is at 520 oC. In the methanol permeability measurement, the PBI membranes showed a lot better methanol barrier ability than the Nafion® membrane. The proton conductivity of the acid-doped PBI membranes increased with increasing temperatures and doping level of phosphoric acid in the polymer. The PBI membranes show higher proton conductivity than Nafion® 117 membrane at high temperature(~160 ℃). Second, PBI/montmorillonite(MMT) nanocomposite membranes were prepared from fluorine-containing PBI with an organically modified MMT(m-MMT). Both X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses showed that the m-MMT was well dispersed in the PBI matrix on a nanometer scale. The mechanical properties and the methanol barrier ability of the PBI films were significantly improved by the addition of m-MMT. The m-MMT in the phosphoric acid doped PBI could effectively inhibit the plasticizing effect of the phosphoric acid. The conductivity of the acid-doped PBI/m-MMT nanocomposites was slight lower than the acid-doped pure PBI. Third, PBI/silica nanocomposite membranes were prepared via sol-gel process from fluorine-containing PBI copolymer with tetraethyl orthosilicate (TEOS) precursor and a bonding agent. The introduction of the bonding agent results in the reinforcing interfacial interaction between PBI chains and silica nanoparticles. Transmission electron microscopy (TEM) analyses showed that the silica particles were well dispersed in the PBI matrix on a nanometer scale. The mechanical properties and the methanol barrier ability of the PBI films were improved by the addition of silica. The conductivities of the acid-doped PBI/silica nanocomposites were slightly lower than the acid-doped pure PBI. Fourth, PBI/imidazole(Im) hybrid membranes were prepared from fluorine-containing PBI with Im. The thermal decomposition of the PBI/Im hybrid membranes occurred at about 160 oC. The conductivities of the acid doped PBI/Im hybrid membranes increased with both the temperatures and the Im content. The addition of Im could reduce the mechanical properties and methanol barrier ability of the PBI membranes.