SEM analysis of an MEA sample from a failed stack showing the ruptured membrane as a result of mechanical failures... fIgure .0 SEM analysis of an MEA sample from a failed stack showing
Trang 1edges.were.first.introduced.by.Gore,.and.they.are.now.available.from.all.major.MEA
suppliers
Reinforced membranes have been shown to delay crack initiation and
propa-gation.232–239 PTFE-based porous films, woven fibers, and microfibers are widely
fIgure . SEM analysis of an MEA sample from a failed stack showing the ruptured
membrane as a result of mechanical failures.
Trang 2but with improved durability Johnson Matthey presented a reinforced membrane.
that.gave.a.sixfold.increase.in.durability.for.a.30-cell.stack.operated.under.dynamic
operation.conditions.239.DuPont.recently.introduced.Nafion.XL™
,.a.reinforced.mem-
brane.made.from.a.chemically.stabilized.ionomer.(see.below) It.has.achieved.a.10-fold.increase.in.lifetime.under.low.RH.and.potential.cycling.conditions.242
... Improvement in Pfsa Chemical stability
through end-group modification
Peroxide radicals from decomposition of H2O2 are believed to be responsible for
Rf-CF2·.+.·OH.→.[Rf-CF2OH] → Rf-COF.+.HF (20)
Trang 3fIgure .0 SEM analysis of an MEA sample from a failed stack showing the thinned
membrane (from 45 μm to ~9 μm).
Table .
rh effect on the frr and the rate of voltage degradation at °C, 0. a/
cm , and ./.0 reformate-air stoichiometry
rh(%) Testing Time(h) Total
frr(0–/g·h·cm)
degradation rate(μv/h)
Trang 4... modification of Pfsa membrane
Many.research.groups.are.actively.engaged.in.modifying.existing.membrane.struc-tures.to.improve.durability.and.expand.the.range.of.operating.temperatures.while
retaining the desirable membrane properties.30,240,245,246.However, chemical
modi-fication is largely limited to the side chains because the perfluorinated backbone
Trang 5using.air.and.oxygen,.respectively.267
Although much progress has been made on PFSA-based membranes, there
remain many challenges For automotive applications, a membrane is required to
12.3.2 p OlybenZimidaZOle m embrane m aterialS
Plug Power, working with its European partners PEMEAS (now BASF Fuel Cell
Trang 7F2C CF
F2C CF
F2C CF
F2C CF
R n
Trang 8.by.Solvay.Advanced.Polymers.and.vari-ous types of poly(arylene ether and ether ketone)s under the trade name PEEK™
by Victrex® In most cases, the sulfonated groups are introduced by subjecting
the polyarylenes to direct electrophilic sulfonation Others are prepared through
Trang 10. gas dIffusIon layer maTerIals
external contact angle measurements were more indicative of the GDL surface
roughness than the capillary forces in the GDL pores (which reflects the real
measurement of water removal capacity).315 They presented a new method for
P N O
R
SO 3
P N O
Trang 12water from the system To fulfill these functions, an ideal bipolar plate material
should have minimal gas permeability, high electrical conductivity, high thermal
material for its good electron conductivity, low density, and high corrosion
resis-tance.(e.g.,.680.S/cm.and.1.78.g/cm3.for.POCO.AXF-5Q).329.However,.due.to.its.poor
composite.should.have.good.thermal.stability,.high.chemical.stability,.and.low.per-meability to the reactant gases The electrical conductivity of graphite composite
materials is lower than that of a pure graphite material (with the extent
Trang 13fIgure . Comparison of liquid water transport for two 50-cm2 single-cell PEM fuel
cells using commercial graphite composite bipolar plates: (a) surface modified and (b) as
received (0.1 A/cm 2 , 1.5/2.0 H 2 –air stoichiometry, 100% RH).
Trang 14Silva’s study showed that although Ni-based alloys have a contact resistance.
comparable to that of graphite, their corrosion resistance in an acidic medium is
hydrophilic/hydrophobic character.4 Stanic and Hoberecht linked membrane edge
fIgure . Impact of system components on fuel cell performance (From Du, B et al.,
JOM, 58, 44, 2006 With permission.)
Trang 15failure and pinhole formation, two primary causes of premature stack failure, to.
materials For example, we found that a plate sample with a particular
combina-tion of graphitic particles and resin binders emitted 7.2 and 1.7 µg/g plate·day of
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