Synthesis and fabrication of Cu-trimesic acid MOF anchored sulfonated Poly(2,5-benzimidazole) membranes for PEMFC applications

Abstract

Porous metal–organic frameworks (MOFs) have started to gain attention because of their high crystallinity, porosity and structural designability, and they can facilitate proton conduction, but the poor membrane forming ability of MOFs limits their application. In this work, composite membranes based on poly (2,5-benzimidazole) (ABPBI) are focused, and the polymer ABPBI was synthesized from its monomer by solution polycondensation method using polyphosphoric acid (PPA) as solvent. Copper-trimesic acid (Cu-TMA) based metal-organic framework (MOF) was prepared by solvothermal synthesis. Varying ratios of MOF were incorporated into the ABPBI polymer matrix to develop a polymer electrolyte membrane (PEM) by solvent casting technique. Sulfonated composites were obtained by immersing the membranes in 20% sulfuric acid and the membranes were used to characterize the crystallographic structure and surface morphology by XRD and SEM. The membrane's mechanical, thermal and physicochemical properties, like tensile strength, thermogravimetric analysis, contact angle, water uptake, swelling ratio, ion exchange capacity, oxidative stability and proton conductivity, have also been evaluated. The 3 wt% Cu-TMA loaded membrane exhibited the highest proton conductivity of 0.039 S cm−1 at 80 °C, whereas the neat sABPBI showed 0.024 S cm−1. Cu-TMA/sABPBI based PEMs are good candidates for polymer electrolyte membrane fuel cells, as shown by their water uptake and ion exchange capacity values of 21.58% and 1.66 meq g−1.