Polybenzimidazole/zwitterion-coated polyamidoamine dendrimer composite membranes for direct methanol fuel cell applications

• PBI/ZC-PAMAM dendrimer (containing sulfonic acid and amine groups) composite membranes was synthesized for DMFC applications.
• Water uptake and ionic conductivity results showed good prospects for use in DMFC.
• The methanol permeability of PBI/ZC-PAMAM composite membranes is much lower than that of Nafion-117.

The zwitterion-coated polyamidoamine (ZC-PAMAM) dendrimer with ammonium and sulfonic acid groups has been synthesized and used as filler for the preparation of PBI-based composite membranes for direct methanol fuel cells. Polybenzimidazole (PBI)/ZC-PAMAM dendrimer composite membranes were prepared by casting a solution of PBI and ZC-PAMAM dendrimer, and then evaporating the solvent. The presence of ZC-PAMAM dendrimer was confirmed by FT-IR and energy-dispersive X-ray spectroscopy (EDS) mapping of sulfur and oxygen elements. The water uptake, swelling degree, proton conductivity, and methanol permeability of the membranes increased with the ZC-PAMAM dendrimer content. For the PBI/ZC-PAMAM-20 membrane with 20 wt% of ZC-PAMAM, it shows a proton conductivity of 1.83 × 10−2 S/cm at 80 °C and a methanol permeability of 5.23 × 10−8 cm2 s−1. Consequently, the PBI/ZC-PAMAM-20 demonstrates a maximum power density of 26.64 mW cm−2 in a single cell test, which was about 2-fold higher than Nafion-117 membrane under the same conditions.

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