title: Aliphatic/aromatic polyimide ionomers as a proton conductive membrane for fuel cell applications.
abstract: To produce a proton conductive and durable polymer electrolyte membrane for fuel cell applications, a series of sulfonated polyimide ionomers containing aliphatic groups both in the main and in the side chains have been synthesized. The title polyimide ionomers 1 with the ion exchange capacity of 1.78-2.33 mequiv/g were obtained by a typical polycondensation reaction as transparent, ductile, and flexible membranes. The proton conductivity of 1 was slightly lower than that of the perfluorinated ionomer (Nafion) below 100 degrees C, but comparable at higher temperature and 100% RH. The highest conductivity of 0.18 S cm(-)(1) was obtained for 1 at 140 degrees C. Ionomer 1 with high IEC and branched chemical structure exhibited improved proton conducting behavior without sacrificing membrane stability. Microscopic analyses revealed that smaller (<5 nm) and well-dispersed hydrophilic domains contribute to better proton conducting properties. Hydrogen and oxygen permeability of 1 was 1-2 orders of magnitude lower than that of Nafion under both dry and wet conditions. Fuel cell was fabricated with 1 membrane and operated at 80 degrees C and 0.2 A/cm(2) supplying H(2) and air both at 60% or 90% RH. Ionomer 1 membrane showed comparable performance to Nafion and was durable for 5000 h without distinct degradation.
authors.affiliation: Clean Energy Research Center, and Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, 4 Takeda, Kofu 400-8510, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Asano
authors.forename: Makoto
authors.initials: M
authors.lastname: Aoki
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Suzuki
authors.forename: Kenji
authors.initials: K
authors.lastname: Miyatake
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Uchida
authors.forename: Masahiro
authors.initials: M
authors.lastname: Watanabe