Study on Synthesis of Polybenzimidazole (PBI) Using Low Cost & High Impurity Industrial 3,3'-diaminobenzidine (DAB) for Application in High Temperature Proton Exchange Membrane Fuel Cells

Poly[2,2-(m-phenylene)−5,5-bibenzimidazole] (m-PBI), the most studied PBI, is close to practical application, however, the high cost of m-PBI restricts its application for HT-PEMFCs. The cost can be reduced by 85% if the low cost & high impurity industrial DAB can be used to synthesize m-PBI after pre-treatment. Herein, we study the influence of impurities in industrial 3,3'-diaminobenzidine (DAB) on the synthesis of polybenzimidazole (PBI), and the possibility of the synthesis of m-PBI based on purified low cost & high impurity industrial DAB. It is shown that impurities would reduce the molecular weight and thermal stability of PBI, and mechanical strength and oxidation stability of the according PBI and H3PO4/PBI membranes. Using industrial DAB (94.40%) without any treatment as a reactant, the molecular weight of the obtained PBI is too low to prepare a membrane. A simple method of purifying low cost & high impurity industrial DAB is proposed, by dissolution and recrystallization using the absorption effect of carbon powder. It is proven that the performances of PBI synthesized using purified DAB are near to the PBI synthesized using high-purity DAB. The peak power density of HT-PEMFC based on PBI from purified industrial DAB reached 426 mW cm−2 at 180 °C.