Synthesis and characterization of acid-doped polybenzimidazole membranes by sol–gel and post-membrane casting method

Polybenzimidazoles (p-PBI and m-PBI) were synthesized by the reaction of 3,3-diaminobenzidine with terephthalic acid or isophthalic acid in polyphosphoric acid at 220 °C for 20 h. These PBI membranes were prepared by two methods: conventional casting (post-membrane fabrication) and direct casting (in situ fabrication). Their properties were found to be dependant on their polymer structure as well as the membrane casting method used in the fabrication process. p-PBI demonstrated higher ion conductivity and greater mechanical properties than m-PBI. The membrane produced by the direct casting method resulted in higher ion conductivity than that produced by the conventional casting method. For these reasons, p-PBI membrane formed by a direct casting method promises to enhance the performance of proton exchange membrane fuel cells (PEMFCs).