Enhancing Fuel Cell Performance: The Role of a Copper Metal–Organic Framework in Phosphoric Acid-Doped Polybenzimidazole Proton Exchange Membranes

Abstract

Fuel cells using proton exchange membrane (PEM) technology, which exhibit superior performance across a wide temperature range, have attracted significant interest in fuel cell vehicle development. Poly(2,2′-m-phenylene-5,5′-benzimidazole) (m-PBI) serves as a pivotal component in the construction of membranes for polymer electrolyte membrane fuel cells (PEMFCs). m-PBI was synthesized via the melt polycondensation method from its monomers. The structure and molecular weight of m-PBI were examined by proton Nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC) techniques, respectively. Herein, we prepared a copper metal−organic framework (MOF) from its precursor and loaded it into the m-PBI membranes. Phosphoric acid (PA) doping strategically enhances the inherent properties of m-PBI, significantly improving the ionic conductivity within the PEM. The MOF loading improved PEM's PA uptake with extended, uninterrupted proton transport channels. The membranes' physicochemical attributes showed a direct correlation with MOF concentration, surpassing that of pristine m-PBI membranes. Due to their strong PA and water uptake abilities, the MOF-loaded m-PBI membranes exhibited enhanced conductivity over a wide range of temperatures (up to 80 °C) compared to the bare m-PBI membrane. At 80 °C, the PAdoped 3 wt % MOF-loaded m-PBI showed a peak power density of 371 mW/cm 2 , while the PA-doped m-PBI had a power density of 255 mW/cm 2 . This innovative PEM outperforms conventional materials due to its superior design when compared with current m-PBI-based PEMFC systems.