(486b) Membranes With Sulfonated Perfluorocyclobutane (PFCB) Ionomer for Fuel Cells

Membranes with Sulfonated Perfluorocyclobutane (PFCB) Ionomer
for Fuel Cells

Ruichun Jiang,
Timothy Fuller, Craig Gittleman

Global Fuel Cell
Activities, General Motors Company

895
Joslyn Ave, Pontiac, MI 48340, USA

Ruichun.Jiang@GM.com

     Polymer
electrolyte fuel cells (PEFC) have been regarded as one of the most promising
power sources for various applications. As the heart of PEFC, the proton
exchange membrane, or PEM, plays a critical role in proton transport,
electrical isolation and reactant gas separation between anode and cathode
components of a fuel cell. Perfluorosulfonic Acid (PFSA) ionomers, such as
Nafion^® from Dupont, are the most commonly used materials for PEMs
because of their favourable proton conductivity, and mechanical and chemical
durability characteristics. There are, however, drawbacks associated with the
use of PFSA membranes. These include high cost and high gas permeability which
contributes to reductions in both fuel cell efficiency and durability. To
overcome these deficiencies, hydrocarbon membranes with aromatic backbones have
received considerable attention as PEM materials due to their lower gas
permeability and decreased production costs.

     A new class
of hydrocarbon block copolymer membrane based on perfluorocyclobutane (PFCB)
chemistry was developed at General Motors for fuel cell PEM applications. The
PEMs with sulfonated PFCB ionomer demonstrate benefits of low production costs,
good proton conductivity, and lower gas (H₂, O₂, N₂)
permeability than PEM with PFSA ionomer. One of the challenges for sulfonated
PFCB based PEMs is enhancing their mechanical stability. Several strategies,
including blending PFCB ionomer with a poly(vinylidene fluoride) (PVDF)
elastomer, and introducing reinforcement layer containing expanded polytetrafluoroethylene
(ePTFE) have been investigated to develop composite PFCB PEMs with improved
mechanical properties.

Performance
and durability of fuel cell membranes based on PFCB ionomer are greatly
influenced by the content of PVDF, as well as by the properties of ePTFE
reinforcement layer. The figure on the right shows that the mechanical
durability in RH cycling tests of the sulfonated PFCB/PVDF blend membranes were
improved with increasing level of PVDF content. More performance and durability
information of PFCB/PVDF and PFCB/PVDF-ePTFE types of fuel cell membranes will
be reported and discussed.