Poly(benzimidazole)s containing trifluoromethyl substituents and aryl ether linkages for high-temperature proton exchange membrane fuel cell applications

A novel tetraamine, 4,4’-oxy-bis[4-(trifluoromethyl)-1,2-benzendiamine] (7), was synthesized through a seven-step synthetic procedure starting from 1-chloro-4-nitro-2-(trifluoromethyl)benzene (1). Polybenzimidazole CF₃-PBI-OO was prepared from 4,4’-oxybis(benzoic acid) (OBA) and tetraamine (7) using Eaton’s reagent as the solvent. To achieve a relatively high molecular weight, the temperature and concentration should be well controlled. 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 ℃. We provide a relatively fast method to fabricate membranes by dissolving them in MSA. CF₃-PBI-OO also required less time (2.7 h) to achieve a saturated PA uptake (271%), when immersed in a 75% phosphoric 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 compared to commercially available m-PBI when subjected to the same test conditions.