Tailoring Different Molecular Weight Phenylene–Polybenzimidazole Membranes with Remarkable Oxidative Stability and Conductive Properties for High-Temperature Polymer Electrolyte Fuel Cells

Polybenzimidazole (ph-PBI) polymer was synthesized with different molecular weights (MWs) and casted into conductive films for use in high-temperature fuel cells (FCs). A comprehensive study on the influence of polymer MW on membrane cast efficiency, chemical stability, thermal behavior, tensile strength, conductivity, FC performance, and durability was reported. The synthesized materials were characterized by different techniques, including, nuclear magnetic resonance spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, impedance microscopy, and scanning electron microscopy. The results showed the importance of manufacturing ph-PBI membranes with controlled properties to achieve high efficiency FCs. High MW ph-PBI membrane (119 kDa) showed a slower rate of chemical degradation, remarkable mechanical properties, and an improved FC performance compared to low MW ph-PBI membrane (39 kDa), thanks to the architecture of high MW ph-PBI. A gain of 91% in proton conductivity with a 47% in FC power density was obtained for the ph-PBI membrane with MW 119 kDa.