Structurally Well-Defined Anion-Exchange Membranes Containing Perfluoroalkyl and Ammonium-Functionalized Fluorenyl Groups

Mizuki Ozawa, Taro Kimura, Kanji Otsuji, Ryo Akiyama, Junpei Miyake, Makoto Uchida, Junji Inukai, Kenji Miyatake

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Novel anion-conductive polymers containing perfluoroalkyl and ammonium-functionalized fluorene groups were synthesized and characterized. The quaternized polymers synthesized using a dimethylaminated fluorene monomer had a well-defined chemical structure in which each fluorenyl group was substituted with two ammonium groups at specific positions. The resulting polymers had a high molecular weight (Mn = 8.9-13.8 kDa, Mw = 13.7-24.5 kDa) to provide bendable thin membranes with the ion-exchange capacity (IEC) ranging from 0.7 to 1.9 mequiv g-1 by solution casting. Both transmission electron microscopy images and small-angle X-ray scattering patterns suggested that the polymer membranes possessed a nanoscale phase-separated morphology based on the hydrophilic/hydrophobic differences in the polymer components. Unlike typical anion-exchange membranes found in the literature, hydroxide ion conductivity of the membranes did not increase with increasing IEC because of their high swelling capability in water. The membrane with IEC = 1.2 mequiv g-1 showed balanced properties of high hydroxide ion conductivity (81 mS cm-1 at 80 °C in water) and mechanical strength (>100% elongation and 14 MPa maximum stress at 80 °C, 60% relative humidity). The polymer main chains were stable in 4 M KOH for 1000 h, whereas the trimethylbenzyl-type ammonium groups degraded under the conditions to cause loss in the hydroxide ion conductivity. An H2/O2 fuel cell with the membrane with IEC = 1.2 mequiv g-1 exhibited a maximum power density of 242 mW cm-2 at 580 mA cm-2 current density.

Original languageEnglish
Pages (from-to)16143-16149
Number of pages7
JournalACS Omega
Volume3
Issue number11
DOIs
Publication statusPublished - 2018 Nov 28
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)

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