Optimizing Polybenzimidazole Binders for High-Temperature Proton Exchange Membrane Fuel Cells

The binders in the catalyst layers (CLs) of high-temperature proton exchange membrane fuel cells (HT-PEMFCs) play a critical role in obtaining an excellent cell performance. However, commercial poly(tetrafluoroethylene) (PTFE) binders lack sufficient proton conductivity, while polybenzimidazole (PBI) ionomer binders result in poor fuel cell performance. Herein, ImPBI, Py-PBI, and NH2-PBI as ionomer binders were synthesized by introducing the imidazole, pyridine, and aniline groups into the main chain of PBI, and the effect on fuel cell performance of the binders was discussed. The strong interaction between the nitrogen-rich groups and free phosphoric acid (PA) molecules enhanced proton transport, prevented catalyst “acid flooding,” and significantly improved the fuel cell performance. The 50_50ImPBI binder exhibited the best performance, and a single cell with 50_50ImPBI (2.5 wt %) achieved a peak power density of 969.3 mW cm–2 at 160 °C (1120.3 mW cm–2 at 180 °C), surpassing commercial binder performance. These findings suggested that developing binder architectures represents a pivotal pathway to enhancing fuel cell performance.