Issue 5, 2020

Polybenzimidazole co-polymers: their synthesis, morphology and high temperature fuel cell membrane properties

Abstract

Polybenzimidazole (PBI) random co-polymers containing alicyclic and aromatic backbones were synthesized using two different dicarboxylic acids (viz., cyclohexane dicarboxylic acid and terephthalic acid) by varying their molar ratios. The synthesized co-polymers were characterized by inherent viscosity (IV) measurements, Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance (1H NMR) spectroscopy, X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA). The co-polymer composition was determined by 1H NMR spectroscopy. The cyclohexyl based PBI possessed a lower proton conductivity (114 mS cm−1) than terephthalic acid based PBI (220 mS cm−1). The aromatic PBI had a high tensile modulus of 11 GPa, whereas the modulus of cyclohexyl PBI was only 2 GPa. By suitably selecting the monomer concentration, the co-polymer properties can be altered (both proton conductivity and mechanical properties). Among different co-polymers, one synthesized using 30 mol% cyclohexane dicarboxylic acid and 70 mol% terephthalic acid exhibited good elongation (8%) and modulus (10.5 GPa) values and improved proton conductivity (242 mS cm−1). In the doped condition, the co-polymer registered an elongation of 52% and a tensile modulus of 170 MPa. The high conductivity of this composition is attributed to the presence of ordered domains (shown by field emission scanning electron microscopy) present in the co-polymer in the doped condition. The co-polymers are thermally stable and the thermal stability increased with an increase in the aromatic content. Thus, alicyclic–aromatic co-polymerization is a viable technique to prepare high-temperature proton exchange membranes.

Graphical abstract: Polybenzimidazole co-polymers: their synthesis, morphology and high temperature fuel cell membrane properties

Supplementary files

Article information

Article type
Paper
Submitted
17 sep 2019
Accepted
30 nov 2019
First published
02 dec 2019

Polym. Chem., 2020,11, 1043-1054

Polybenzimidazole co-polymers: their synthesis, morphology and high temperature fuel cell membrane properties

S. Kumar B., B. Sana, G. Unnikrishnan, T. Jana and S. Kumar K. S., Polym. Chem., 2020, 11, 1043 DOI: 10.1039/C9PY01403A

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