Reprocessing and Characterization of Polybenzimidazole for High-Temperature Polymer Electrolyte Membrane Fuel Cells
Abstract: A reprocessing method of poly(2,2’-(m-phenylene)-5,5’-bibenzimidazole) (PBI) membranes recovered from the production line of High-Temperature Polymer Electrolyte Membrane Fuel Cells (HT-PEMFC) at Blue World Technologies (BWT) has been developed in order to reduce material loss in the production. Redissolution of scrap PBI membranes in poly(phosphoric acid) (PPA) and phosphoric acid (PA) was successful and the subsequent washing procedure produced PBI that could be redissolved in N,N-dimethyl acetamide (DMAc) and suitable for solution casting of new membranes. The reprocessed PBI and the membranes cast from it were characterized with respect to molecular weight, structural purity, acid doping behavior, thermal stability, mechanical strength, proton conductivity and fuel cell performance using pristine PBI membranes as the reference point. A reduction of the molecular weight was observed after the redissolution, which was speculated to be caused by hydrolysis of weak amide bonds due to structural defects in the polymer backbone. After doping in 85 wt.% PA, the tensile properties and the ex-situ proton conductivity were slightly decreased in comparison to the pristine reference material which could reasonably be explained by deviations in the membrane thickness and doping level. No apparent difference in properties depending on which solvent was used in the redissolution was observed. Fuel cell testing indicated similar performance between reprocessed and pristine PBI membranes, thus demonstrating the viability of the attempted recycling method.
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