Abstract
A novel tetraamine, 4,4'-oxy-bis[3-(trifluoromethyl)-1,6-benzendiamine] (7), was synthesized through a serious of synthetic steps starting from 4-nitro-2-(trifluoromethyl)chlorobenzene (1). Polybenzimidazole CF3-PBI-OO was prepared from 4,4'-oxybis(benzoic acid) (OBA) and tetraamine (7) by using Eaton’s reagent as the solvent. Throughout this process, the temperature and the concentration of the polymer solution should be controlled in order to achieve a high molecular weight. CF3-PBI-OO exhibited a high inherent viscosity of 2.1 dL/g, measured in methanesulfonic acid (MSA) with a concentration of 0.2 g/dL at 35 ℃. The oxidative stability of CF3-PBI-OO is not improved by the incorporation of trifluoromethyl groups due to its higher water uptakes resulting from the aryl ether linkages on the polymer backbone. CF3-PBI-OO also required less time (2.7 h) to achieve a saturated PA uptake (271%), when immersed in a 75% phosphorous acid solution at room temperature. CF3-PBI-OO membrane with a PA uptake of 213% demonstrated the optimal combination of properties. The membrane exhibited a high proton conductivity of 115 mS/cm at 160 ℃. The single fuel cell based on CF3-PBI-OO demonstrated a peak power density of 691 mW/cm2 at 160 ℃. It showed superior performance in comparison to m-PBI and OPBIs when subjected to the same test conditions.