Durable Sulfonated Poly(benzothiazole-<i>co</i>-benzimidazole) Proton Exchange Membranes
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Abstract
Two series of random sulfonated poly(benzothiazole-<i>co</i>-benzimidazole) polymers (sPBT-BI) with 70% and 60% degree
of sulfonation
were evaluated as proton exchange membranes. sPBT was also prepared
for a comparative study. The mechanical properties of sPBT-BI were
greatly enhanced by incorporation of benzimidazole (BI); sPBT-BI70-10
showed a tensile strength of 125 MPa and elongation at break of 38.9%,
an increase of 56.5% and 145%, respectively, compared with sPBT. The
solubility, dimensional stability, thermal properties, and oxidative
stability of sPBT-BI were also improved. The ionic clusters of sPBT-BI
membranes in both AFM phase images and TEM images became narrower
with increasing amounts of BI while containing the same molar amount
of sulfonic acid groups. This resulted in lower dimensional swelling
and higher mechanical strength, but the proton conductivity decreased.
However, high proton conductivity was achieved by incorporating an
appropriate content of BI. PEMFC H<sub>2</sub>/air single cell performances
and durabilities were improved by incorporation of 5% of BI units
in sPBT