NAMS 2002 Workshop - ICOM 2008

Fuel Cells I – 5
Monday July 14, 4:30 PM-5:00 PM, Honolulu/Kahuku
Sulfonated Polyimide Membranes for Polymer Electrolyte Fuel Cells
K. Okamoto (Speaker), Yamaguchi University, Ube, Yamaguchi, Japan, okamotok@yamaguchiu.ac.jp
K. Matsuda, Yamaguchi University, Ube, Yamaguchi, Japan
Z. Hu, Yamaguchi University, Ube, Yamaguchi, Japan
K. Chen, Yamaguchi University, Ube, Yamaguchi, Japan
N. Endo, Yamaguchi University, Ube, Yamaguchi, Japan
M. Higa, Yamaguchi University, Ube, Yamaguchi, Japan
Polymer electrolyte membrane (PEM) is the key component of polymer
electrolyte fuel cell (PEFC). Many sulfonated hydrocarbon polymer membranes
have been developed as alternatives for sulfonated perfluoropolymer
membranes. Sulfonated polyimides (SPIs) are one of the promising candidates
for PEMs because of their low fuel permeation, good film-forming ability and
excellent mechanical, thermal and chemical properties. However, they have a
disadvantage of rather easy hydrolysis of imide ring. We investigated the
relationship between the chemical structure of SPIs and the water stability of
their membranes, and developed SPI membranes with reasonably high water
stability and high PEFC performance. In this presentation, we report on
preparation of novel sulfonated polyimide membranes with excellent water
stability and their applications for PEFCs.
SPIs bearing sulfophenoxy side groups were successfully prepared from 1,4,5,8naphthalene-tetracarboxylic
dianhydride (NTDA), 2,2-bis(4sulfophenoxy)benzidine
(2,2-BSPOB) and a non-sulfonated diamine such as 4,4bis(4-aminophenoxy)biphenyl.
The dry SPI membranes in proton form were
immersed into the medium of phosphorous pentoxide/methanesulfonic acid to
form cross-linking. Their uncross-linked and cross-linked membranes were
evaluated as polymer electrolyte membranes for polymer PEFCs.
They maintained high mechanical strength and high proton conductivity after
aging in water at 130 °C for 500 h, indicating their high water stability. PEFCs
with the SPI membranes showed high performances at 90 °C and 0.3 MPa with
air supply; for example, a cell voltage of 0.67 V at 0.5 A/cm 2 under 85 %RH.
They also showed fairly high performances even at a low humidity of 30%RH due
to the back diffusion of water formed at the cathode, for example, a cell voltage
of 0.63 V at 0.5 A/cm 2 . PEFCs with the cross-linked SPI membranes were
operated under a constant current density of 0.5 A/cm 2 at 90 °C and 85 %RH for
1600 h without any reduction in cell performance, indicating their high fuel cell
durability. The SPI membranes have high potential for PEFCs at higher
temperatures above 80 °C.