Proton conductive polyimide electrolytes containing trifluoromethyl groups: Synthesis, properties, and DMFC performance

Kenji Miyatake, Hua Zhou, Takashi Matsuo, Hiroyuki Uchida, Masahiro Watanabe

Research output: Contribution to journalArticle

163 Citations (Scopus)

Abstract

A series of sulfonated polyimide copolymers (FSPIH-X; X refers to molar percentage of bis(trifluoromethyl)biphenylene content) with X from 0 to 60 mol % were synthesized, of which electrolyte properties were investigated and compared to those of the perfluorinated ionomer (Nafion 112). FSPIH-X membranes are thermally stable with no glass transition temperature observed below the decomposition temperature (280°C). Oxidative stability of the membranes is improved with an increase in the content of trifluoromethyl substituents in the copolymer structure. FSPIH-60 endured for more than 9 h in Fenton's reagent at 80°C. Bis(trifluoromethyl)biphenylene groups with the molecular size of 6.1 Å make each polymer chain separate and produce space to hold water molecules despite their hydrophobic property so that the maximum water uptake was observed for FSPIH-20. Unlike the fluorene groups containing polyimides (SPIH-X), a strong water confinement effect was not obtained for FSPIH-X. The optimum composition of bis(trifluoromethyl)biphenylene groups was 30 mol%, and the FSPIH-30 membrane showed higher proton conductivity than 0.2 S cm -1 at 30-140°C. A direct methanol fuel cell (DMFC) using FSPIH-30 membrane has revealed that the methanol crossover through the membrane equivalent to the current density of methanol oxidation at cathode (j(CH 3OH)) is 64 mA/cm2 and merely 30% of that of Nafion 112 at open-circuit potential. A terminal voltage of 0.38 V was obtained at 200 mA/cm2 by the operation at 80 and 90°C with supplying dry and humidified oxygen.

Original languageEnglish
Pages (from-to)4961-4966
Number of pages6
JournalMacromolecules
Volume37
Issue number13
DOIs
Publication statusPublished - 2004 Jun 29
Externally publishedYes

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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