U.S. patent application number 10/037506 was filed with the patent office on 2002-07-18 for method of integrally sealing an electronchemical fuel cell fluid distribution layer.
Invention is credited to Campbell, Stephen A., Davis, Michael T., Lamont, Gordon, Stumper, Juergen, Wilkinson, David P..
Application Number | 20020094470 10/037506 |
Document ID | / |
Family ID | 25298552 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020094470 |
Kind Code |
A1 |
Wilkinson, David P. ; et
al. |
July 18, 2002 |
Method of integrally sealing an electronchemical fuel cell fluid
distribution layer
Abstract
A fuel cell comprises a pair of separator plates and a pair of
fluid distribution layers interposed between the separator plates.
At least one of the fluid distribution layers comprises a sealing
region and an electrically conductive, fluid permeable active
region, and a polymeric material extending into each of the sealing
region and the active region. An ion exchange membrane is
interposed between at least a portion of the fluid distribution
layers, and a quantity of electrocatalyst is interposed between at
least a portion of each of the fluid distribution layers and at
least a portion of the membrane, thereby defining the active
region. Melt-bonding the thermoplastic and/or other polymeric
material in the sealing region renders the at least one fluid
distribution layer substantially fluid impermeable in a direction
parallel to the major planar surfaces. This approach reduces or
eliminates the need for separate gaskets or sealing components and
integrates several functions, such as sealing, fluid distribution,
and current collection in a single layer.
Inventors: |
Wilkinson, David P.; (North
Vancouver, CA) ; Stumper, Juergen; (Vancouver,
CA) ; Campbell, Stephen A.; (Maple Ridge, CA)
; Davis, Michael T.; (Port Coquitlam, CA) ;
Lamont, Gordon; (New Westminster, CA) |
Correspondence
Address: |
MCANDREWS HELD & MALLOY, LTD
500 WEST MADISON STREET
SUITE 3400
CHICAGO
IL
60661
|
Family ID: |
25298552 |
Appl. No.: |
10/037506 |
Filed: |
January 4, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10037506 |
Jan 4, 2002 |
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09384531 |
Aug 27, 1999 |
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6350538 |
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09384531 |
Aug 27, 1999 |
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09309677 |
May 11, 1999 |
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09309677 |
May 11, 1999 |
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08846653 |
May 1, 1997 |
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5976726 |
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Current U.S.
Class: |
429/509 ;
29/623.2; 429/514 |
Current CPC
Class: |
H01M 8/0263 20130101;
H01M 8/241 20130101; H01M 8/0271 20130101; H01M 8/0256 20130101;
H01M 8/0236 20130101; Y10T 29/4911 20150115; H01M 8/2483 20160201;
Y10T 428/30 20150115; H01M 8/0221 20130101; Y02E 60/50 20130101;
H01M 8/0213 20130101; H01M 8/0239 20130101; H01M 8/0245 20130101;
H01M 8/0206 20130101; H01M 8/0226 20130101; H01M 8/0232 20130101;
H01M 8/0243 20130101; H01M 2300/0082 20130101; H01M 8/0228
20130101 |
Class at
Publication: |
429/35 ;
29/623.2; 429/38 |
International
Class: |
H01M 002/08; H01M
008/02 |
Claims
What is claimed is:
1. A method of sealing at least one of a pair of fluid distribution
layers in a fuel cell, the fuel cell comprising: (a) a pair of
substantially fluid impermeable separator plates having associated
therewith a compressive mechanism for urging said plates towards
each other; (b) a pair of fluid distribution layers interposed
between said separator plates, each of said fluid distribution
layers having two major planar surfaces, at least one of said fluid
distribution layers comprising a sealing region and an electrically
conductive, fluid permeable active region, said at least one fluid
distribution layer comprising a preformed sheet material extending
into each of said sealing region and said active region; (c) an ion
exchange membrane interposed between at least a portion of said
fluid distribution layers; (d) a quantity of electrocatalyst
interposed between at least a portion of each of said fluid
distribution layers and at least a portion of said membrane,
thereby defining said active region; the method comprising
compressing said preformed sheet material by urging said pair of
plates towards each other, whereby said at least one fluid
distribution layer is rendered substantially fluid impermeable in a
direction parallel to said major planar surfaces, in said sealing
region.
2. The method of claim 1 wherein said at least one of said fluid
distribution layers is both of said pair of fluid distribution
layers.
3. The method of claim 1 wherein said membrane superposes at least
a portion of said sealing region.
4. The method of claim 1 further comprising electrically insulating
said at least one fluid distribution layer in said sealing
region.
5. The method of claim 1 wherein said preformed sheet material is a
mesh.
6. The method of claim 5 wherein said mesh is electrically
conductive.
7. The method of claim 6 wherein said mesh contains an electrically
conductive filler at least in said active region.
8. The method of claim 6 wherein said mesh consists essentially of
a metal.
9. The method of claim 8 wherein said metal is selected from the
group consisting of nickel, stainless steel, niobium and
titanium.
10. The method of claim 5 wherein said mesh is an electrical
insulator, said mesh containing an electrically conductive filler
at least in said active region.
11. The method of claim 10 wherein said mesh consists essentially
of a polymeric material.
12. The method of claim 11 wherein said polymeric material is
selected from the group consisting polyethylene, polypropylene and
polytetrafluoroethylene.
13. The method of claim 1 wherein said preformed sheet material is
a substantially fluid impermeable sheet material, the method
further comprising rendering said sheet material fluid permeable in
said active region.
14. The method of claim 13 wherein said substantially fluid
impermeable sheet material is rendered fluid permeable by
perforating said sheet material at least in said active region.
15. The method of claim 14 wherein said substantially fluid
impermeable sheet material is electrically conductive.
16. The method of claim 15 wherein said substantially fluid
impermeable sheet material is graphite foil.
17. The method of claim 15 wherein said at least one fluid
distribution layer comprises an electrically conductive filler
within perforations in said perforated active region.
18. The method of claim 14 wherein said substantially fluid
impermeable sheet material is an electrical insulator, and said at
least one fluid distribution layer comprises an electrically
conductive filler within perforations in said perforated active
region.
19. The method of claim 18 wherein said substantially fluid
impermeable sheet material consists essentially of a polymeric
material.
20. The method of claim 1 further comprising forming at least one
channel in at least one of said major planar surfaces of said at
least one fluid distribution layer, said at least one channel
traversing said active region and adapted to direct a fluid
reactant stream therein.
21. The method of claim 1 further comprising forming at least one
channel in at least one of said major planar surfaces of said at
least one fluid distribution layer, said at least one channel
adapted to direct a fluid reactant stream in contact with said
layer.
22. A method of sealing at least one of a pair of fluid
distribution layers in a fuel cell, the fuel cell comprising: (a) a
pair of substantially fluid impermeable separator plates; (b) a
pair of fluid distribution layers interposed between said separator
plates, each of said fluid distribution layers having two major
planar surfaces, at least one of said fluid distribution layers
comprising a sealing region and an electrically conductive, fluid
permeable active region, said at least one fluid distribution layer
comprising a porous electrically insulating sheet material
extending into each of said active region and said sealing region;
(c) an ion exchange membrane interposed between at least a portion
of said fluid distribution layers; (d) a quantity of
electrocatalyst interposed between at least a portion of each of
said fluid distribution layers and at least a portion of said
membrane, thereby defining said active region; the method
comprising disposing an electrically conductive filler in said
active region and a sealing filler in said sealing region, whereby
said fluid distribution layer is rendered substantially fluid
impermeable in said sealing region.
23. The method of claim 22 wherein said porous electrically
insulating sheet material consists essentially of a polymeric
material.
24. The method of claim 23 wherein said polymeric material is
microporous.
25. The method of claim 23 wherein said polymeric material is
selected from the group consisting polyethylene, polypropylene and
polytetrafluoroethylene
26. The method of claim 22 wherein said porous electrically
insulating sheet material is a mesh.
27. The method of claim 22 wherein said porous electrically
insulating sheet material is glass fiber mat.
28. The method of claim 22 wherein said sealing filler comprises a
flow processible material.
29. The method of claim 28 wherein said flow processible material
is an elastomer.
30. The method of claim 29 wherein said elastomeric flow
processible material is silicon rubber.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/384,531, filed on Aug. 27, 1999, entitled
"Electrochemical Cell With Fluid Distribution Layer Having Integral
Sealing Capability". The '531 application is, in turn, a
continuation-in-part of U.S. patent application Ser. No.
09/309,677, filed on May 11, 1999, also entitled "Electrochemical
Cell With Fluid Distribution Layer Having Integral Sealing
Capability". The '677 application is, in turn, a continuation of
U.S. patent application Ser. No. 08/846,653, filed on May 1, 1997,
also entitled "Electrochemical Cell With Fluid Distribution Layer
Having Integral Sealing Capability", now U.S. Pat. No. 5,976,726
issued Nov. 2, 1999. Each of the '531 and '653 applications is
hereby incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to a fuel cell with a fluid
distribution layer having integral sealing capability.
BACKGROUND OF THE INVENTION
[0003] Electrochemical fuel cells convert fuel and oxidant to
electricity and reaction product. Solid polymer fuel cells
generally employ a membrane electrode assembly ("MEA") comprising a
solid polymer electrolyte or ion exchange membrane disposed between
two fluid distribution (electrode substrate) layers formed of
electrically conductive sheet material. The fluid distribution
layer has a porous structure across at least a portion of its
surface area, which renders it permeable to fluid reactants and
products in the fuel cell. The electrochemically active region of
the MEA also includes a quantity of electrocatalyst, typically
disposed in a layer at each membrane/fluid distribution layer
interface, to induce the desired electrochemical reaction in the
fuel cell. The electrodes thus formed are electrically coupled to
provide a path for conducting electrons between the electrodes
through an external load.
[0004] At the anode, the fluid fuel stream moves through the porous
portion of the anode fluid distribution layer and is oxidized at
the anode electrocatalyst. At the cathode, the fluid oxidant stream
moves through the porous portion of the cathode fluid distribution
layer and is reduced at the cathode electrocatalyst.
[0005] In fuel cells employing hydrogen as the fuel and oxygen as
the oxidant, the catalyzed reaction at the anode produces hydrogen
cations (protons) from the fuel supply. The ion exchange membrane
facilitates the migration of protons from the anode to the cathode.
In addition to conducting protons, the membrane isolates the
hydrogen-containing fuel stream from the oxygen-containing oxidant
stream. At the cathode electrocatalyst layer, oxygen reacts with
the protons that have crossed the membrane to form water as the
reaction product. The anode and cathode reactions in
hydrogen/oxygen fuel cells are shown in the following
equations:
Anode reaction: H.sub.2.fwdarw.2H.sup.++2e.sup.-
Cathode reaction: 1/2O.sub.2+2H.sup.++2e.sup.-H.sub.2O
[0006] In fuel cells employing methanol as the fuel supplied to the
anode (so-called "direct methanol" fuel cells) and an
oxygen-containing stream, such as air (or substantially pure
oxygen) as the oxidant supplied to the cathode, the methanol is
oxidized at the anode to produce protons and carbon dioxide.
Typically, the methanol is supplied to the anode as an aqueous
solution or as a vapor. The protons migrate through the ion
exchange membrane from the anode to the cathode, and at the cathode
electrocatalyst layer, oxygen reacts with the protons to form
water. The anode and cathode reactions in this type of direct
methanol fuel cell are shown in the following equations:
Anode reaction:
CH.sub.3OH+H.sub.2O.fwdarw.6H.sup.++CO.sub.2+6e.sup.-
Cathode reaction: 3/2O.sub.2+6H.sup.++6e.sup.-.fwdarw.3H.sub.2O
[0007] In fuel cells, the MEA is typically interposed between two
separator plates or fluid flow field plates (anode and cathode
plates). The plates typically act as current collectors, provide
support to the MEA, and prevent mixing of the fuel and oxidant
streams in adjacent fuel cells, thus, they are typically
electrically conductive and substantially fluid impermeable. Fluid
flow field plates typically have channels, grooves or passages
formed therein to provide means for access of the fuel and oxidant
streams to the surfaces of the porous anode and cathode layers,
respectively.
[0008] Two or more fuel cells can be connected together, generally
in series but sometimes in parallel, to increase the overall power
output of the assembly. In series arrangements, one side of a given
plate serves as an anode plate for one cell and the other side of
the plate can serve as the cathode plate for the adjacent cell,
hence the plates are sometimes referred to as bipolar plates. Such
a series connected multiple fuel cell arrangement is referred to as
a fuel cell stack. The stack typically includes manifolds and inlet
ports for directing the fuel and the oxidant to the anode and
cathode fluid distribution layers, respectively. The stack also
usually includes a manifold and inlet port for directing the
coolant fluid to interior channels within the stack. The stack also
generally includes exhaust manifolds and outlet ports for expelling
the unreacted fuel and oxidant streams, as well as an exhaust
manifold and outlet port for the coolant fluid exiting the
stack.
[0009] The fluid distribution layer in fuel cells has several
functions, typically including:
[0010] (1) to provide access of the fluid reactants to the
electrocatalyst;
[0011] (2) to provide a pathway for removal of fluid reaction
product (for example, water in hydrogen/oxygen fuel cells and water
and carbon monoxide in direct methanol fuel cells);
[0012] (3) to serve as an electronic conductor between the
electrocatalyst layer and the adjacent separator or flow field
plate;
[0013] (4) to serve as a thermal conductor between the
electrocatalyst layer and the adjacent separator or flow field
plate;
[0014] (5) to provide mechanical support for the electrocatalyst
layer;
[0015] (6) to provide mechanical support and dimensional stability
for the ion exchange membrane.
[0016] The fluid distribution layer is electrically conductive
across at least a portion of its surface area to provide an
electrically conductive path between the electrocatalyst reactive
sites and the current collectors. Materials that have been employed
in fluid distribution layers in solid polymer fuel cells
include:
[0017] (a) carbon fiber paper;
[0018] (b) woven and non-woven carbon fabric optionally filled with
electrically conductive filler such as carbon particles and a
binder;
[0019] (c) metal mesh or gauze - optionally filled with
electrically conductive filler such as carbon particles and a
binder;
[0020] (d) polymeric mesh or gauze, such as polytetrafluoroethylene
mesh, rendered electrically conductive, for example, by filling
with electrically conductive filler such as carbon particles and a
binder.
[0021] (e) microporous polymeric film, such as microporous
polytetrafluoroethylene, rendered electrically conductive, for
example, by filling with electrically conductive filler such as
carbon particles and a binder.
[0022] Thus, fluid distribution layers typically comprise preformed
sheet materials that are electrically conductive and fluid
permeable in the region corresponding to the electrochemically
active region of the fuel cell.
[0023] Conventional methods of sealing around MEAs within fuel
cells include framing the MEA with a resilient fluid impermeable
gasket, placing preformed seal assemblies in channels in the fluid
distribution layer and/or separator plate, or molding seal
assemblies within the fluid distribution layer or separator plate,
circumscribing the electrochemical active region and any fluid
manifold openings. Examples of such conventional methods are
disclosed in U.S. Pat. Nos. 5,176,966 and 5,284,718. Disadvantages
of these conventional approaches include difficulty in assembling
the sealing mechanism, difficulty in supporting narrow seal
assemblies within the fluid distribution layer, localized and
uneven mechanical stresses applied to the membrane and seal
assemblies, and seal deformation and degradation over the lifetime
of the fuel cell stack.
[0024] Such gaskets and seals, which are separate components
introduced in additional processing or assembly steps, add
complexity and expense to the manufacture of fuel cell stacks.
SUMMARY OF THE INVENTION
[0025] The invention includes a fuel cell with a fluid distribution
layer having integral sealing capability and a method for effecting
sealing. The fuel cell comprises:
[0026] (a) a pair of substantially fluid impermeable separator
plates;
[0027] (b) a pair of fluid distribution layers interposed between
the separator plates, each of the fluid distribution layers having
two major planar surfaces, at least one of the fluid distribution
layers comprising a sealing region and an electrically conductive,
fluid permeable active region, the at least one fluid distribution
layer comprising polymeric material extending into each of the
sealing region and the active region;
[0028] (c) an ion exchange membrane interposed between at least a
portion of the fluid distribution layers;
[0029] (d) a quantity of electrocatalyst interposed between at
least a portion of each of the fluid distribution layers and at
least a portion of the membrane, thereby defining the active
region.
[0030] The polymeric material is melt-bonded in the sealing region,
thereby rendering the at least one fluid distribution layer
substantially fluid impermeable in a direction parallel to the
major planar surfaces, in the sealing region. Thus, the polymeric
material included in the at least one fluid distribution layer has
intrinsic sealing capability.
[0031] The polymeric material included in the at least one fluid
distribution layer may be melt-bonded to the adjacent separator
plate.
[0032] In a preferred fuel cell, each of the fluid distribution
layers comprises a sealing region and an electrically conductive,
fluid permeable active region, and each of the fluid distribution
layers comprises polymeric material extending into each of the
sealing region and the active region.
[0033] In preferred embodiments the membrane superposes at least a
portion of the sealing region. Advantageously, therefore, the
polymeric material in the sealing region of the fluid distribution
layer may be melt-bonded to the ion exchange membrane.
[0034] In preferred embodiments, the polymeric material comprises a
polyolefin material, such as, for example polyethylene or
polypropylene.
[0035] The fluid distribution layer may be electrically insulating
in the sealing region.
[0036] The polymeric material may be a preformed sheet. In a first
embodiment of a fuel cell, the preformed sheet is a mesh, which may
optionally contain an electrically conductive filler at least in
the active region. The term mesh as used herein includes woven
meshes and expanded mesh materials. In a second embodiment of a
fuel cell, the preformed sheet is a microporous sheet material.
[0037] Alternatively, the polymeric material (before melt-bonding)
may comprise particulates dispersed throughout the fluid
distribution layer. In some embodiments, the particulates may be or
include fibers.
[0038] In any of the embodiments described above, at least one of
the fluid distribution layers may comprise at least one channel,
for directing a fluid reactant stream, formed in at least one of
the major planar surfaces thereof. The at least one channel
preferably traverses the active region.
[0039] In any of the embodiments described above, at least one of
the separator layers may comprise at least one channel formed in a
major surface thereof facing a fluid distribution layer, for
directing a fluid reactant stream in contact with the layer.
[0040] In any of the embodiments described above, a fluid
distribution layer may comprise one or more layers of material.
[0041] In any of the embodiments described above, a fluid
distribution layer may comprise an electrically conductive filler
in the active region. Preferred electrically conductive fillers
comprise a binder and electrically conductive particles, such as,
carbon particles and/or boron carbide particles. The electrically
conductive filler may comprise a catalyst and/or an ionomer.
[0042] In any of the above embodiments, the sealing region may have
at least one fluid manifold opening formed therein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1 is an exploded sectional view of a conventional
(prior art) solid polymer fuel cell showing an MEA interposed
between two flow field plates.
[0044] FIG. 2A is an exploded sectional view, in the direction of
arrows A-A in FIG. 2B, of a fuel cell that includes a pair of fluid
flow field plates and a pair of fluid distribution layers with
integral sealing capability. The fluid distribution layers include
a polymeric mesh sheet material that has been melt-bonded in the
sealing region. FIG. 2B is an exploded isometric view of a portion
of the fuel cell of FIG. 2A.
[0045] FIG. 3A is an exploded sectional view, in the direction of
arrows B-B in FIG. 3B, of an electrochemical fuel cell which
includes a pair of fluid flow field plates and a pair of fluid
distribution layers with integral sealing capability. The fluid
distribution layers include a substantially fluid impermeable sheet
material having plurality of perforations formed in the
electrochemically active region thereof. FIG. 3B is an exploded
isometric view of a portion of the fuel cell of FIG. 3A.
[0046] FIG. 4A is an exploded sectional view, in the direction of
arrows C-C in FIG. 4B, of an electrochemical fuel cell which
includes a pair of separator plates and a pair of fluid
distribution layers with integral sealing capability. The fluid
distribution layers include a substantially fluid impermeable sheet
material having plurality of perforations in the electrochemically
active region thereof, and fluid flow channels formed in a major
surface thereof. FIG. 4B is an exploded isometric view of a portion
of the fuel cell of FIG. 4A.
[0047] FIG. 5 is a schematic diagram illustrating a fabrication
process suitable for manufacture of fuel cells with fluid
distribution layers with integral sealing capability.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)
[0048] FIG. 1 illustrates a typical (prior art) solid polymer fuel
cell 10. Fuel cell 10 includes an MEA 12 including an ion exchange
membrane 14 interposed between two electrodes, namely, an anode 16
and a cathode 17. Anode 16 includes a porous electrically
conductive fluid distribution layer 18. A thin layer of
electrocatalyst 20 is disposed at the interface with the membrane
14, thereby defining an electrochemically active region of fluid
distribution layer 18. Cathode 17 includes a porous electrically
conductive fluid distribution layer 19. A thin layer of
electrocatalyst 21 is disposed at the interface with the membrane
14, thereby defining an electrochemically active region of fluid
distribution layer 19. The MEA is interposed between anode flow
field plate 22 and cathode flow field plate 24. Anode flow field
plate 22 has at least one fuel flow channel 23 formed in its
surface facing the anode fluid distribution layer 18. Cathode flow
field plate 24 has at least one oxidant flow channel 25 formed in
its surface facing the cathode fluid distribution layer 19. When
assembled against the cooperating surfaces of the fluid
distribution layers 18 and 19, channels 23 and 25 form reactant
flow field passages for the fuel and oxidant, respectively.
Membrane electrode assembly 12 also includes preformed gaskets 26
placed within channels 27, which extend through the thickness of
the fluid distribution layers 18 and 19. When the fuel cell 10 is
assembled and compressed, by urging plates 22 and 24 towards each
other, the gaskets 26 cooperate with the plates 22, 24 and the
membrane 14 to form a seal circumscribing the electrochemically
active region of each fluid distribution layer 18, 19.
[0049] FIG. 2A is an exploded sectional view of a fuel cell 210, a
portion of which is shown in FIG. 2B in an exploded isometric view.
Fuel cell 210 includes a membrane electrode assembly 212, which
includes an ion exchange membrane 214 interposed between a pair of
fluid distribution layers 218 and 219. A quantity of
electrocatalyst is disposed in a layer 220, 221 at the interface
between each fluid distribution layer 218, 219 and membrane 214 in
the electrochemically active region 230 of the fluid distribution
layers 218, 219. The catalyst may be applied to the membrane or to
the fluid distribution layer. The MEA 212 is interposed between a
pair of flow field plates 222 and 224. Each plate 222, 224 has an
open-faced channel 223, 225 formed in its surface facing the
corresponding fluid distribution layer 218, 219, respectively, and
traversing a portion of each plate that superposes the
electrochemically active region 230. When assembled against the
cooperating surfaces of the fluid distribution layers 218 and 219,
channels 223 and 225 form reactant flow field passages for the fuel
and oxidant, respectively.
[0050] Fluid distribution layers 218, 219 each have a sealing
region 240. In the illustrated embodiment, ion exchange membrane
214 superposes sealing region 240 and may be melt-bonded thereto.
In the electrochemically active region 230, the fluid distribution
layers 218, 219 are electrically conductive and fluid permeable, to
permit the passage of reactant fluid between the two major planar
surfaces thereof to access the electrocatalyst layer 220, 221
respectively. In the embodiment illustrated in FIGS. 2A and 2B,
fluid distribution layers include an electrically insulating
preformed polymeric mesh sheet material 250 extending into each of
the active and sealing regions 230, 240, respectively. The fluid
distribution layer is rendered electrically conductive in the
active region 230, for example, it may contain an electrically
conductive filler, at least in the region 230. Polymeric mesh sheet
material 250 is melt-bonded at locations 245 in the sealing region
240 thereby rendering the fluid distribution layers substantially
fluid impermeable in a direction parallel to their major planar
surfaces. Further, polymeric mesh sheet material 250 is melt-bonded
to ion exchange membrane 214 at locations 245 thereby also
effecting a seal between fluid distribution layers 218, 219 and
membrane 214. The melt-bonding within mesh sheet material 250 at
locations 245 and the melt-bonding of mesh sheet material 250 to
membrane 214 may desirably be accomplished in one step. A suitable
melt-bond may be obtained using a conventional technique
appropriate for the joining of thermoplastics and/or other
polymeric materials generally, such as heat bonding or ultrasonic
welding. Where appropriate, solvent bonding may also be employed
(for example, where a solvent is used to dissolve the polymeric
sheet material after which the solvent is removed, leaving a
melt-bonded polymeric seal). Seals between the melt-bonded membrane
electrode assembly 212 and plates 222, 224 are effected by
compression of the fluid distribution layers 218, 219 in the
sealing region 240 between plates 222, 224. Thus, complete sealing
around the periphery of the active region 230, is accomplished
partly by melt-bonding of the thermoplastic and/or other polymeric
material, and partly by compression. Suitable mesh materials
include expanded polyolefin materials, such as expanded
polypropylene or polyethylene.
[0051] As shown in FIG. 2B, each of membrane 214, fluid
distribution layer 219, reactant flow field plate 224, has a
plurality of openings 260 formed therein, which align when
assembled to form manifolds for directing inlet and outlet fluid
streams through fuel cell 210. For example, oxidant fluid flow
field channel 225 extends between oxidant inlet manifold opening
260a and oxidant outlet manifold 260b formed in plate 224. The
fluid manifold openings 260 in fluid distribution layers 218, 219
are formed in sealing region 240. Openings, 260, need not
necessarily be formed in the mesh material of the fluid
distribution layer, as the fluid passing through the manifold can
generally readily pass through the mesh material. Melt-bonded
locations 245 appear between active region 230 and openings
260.
[0052] In FIG. 2A, other polymeric preformed sheets (for example,
suitable microporous films) may be employed in the fluid
distribution layers 218, 219 instead of the expanded polymeric mesh
sheet material 250. Further, in principle, polymeric particulate
filled fluid distribution layers might also be sealed in this way.
Thus, polymeric particulates (for example, plastic fibers)
dispersed throughout the fluid distribution layer may be employed
instead of a mesh.
[0053] In the embodiment of FIG. 2A, melt-bonding of the fluid
distribution layers to the membrane is preferred since this
provides a seal at the fluid distribution layer/membrane interface
and may result in simpler overall manufacture of an MEA. However,
this interfacial seal may instead be effected by compression where
desired (for instance if the membrane and polymeric material in the
fluid distribution layer are not suitably compatible).
[0054] FIG. 3A is an exploded sectional view of an electrochemical
fuel cell 310, a portion of which is shown in FIG. 3B in an
exploded isometric view. Again, fuel cell 310 includes a membrane
electrode assembly 312, including an ion exchange membrane 314
interposed between a pair of fluid distribution layers 318 and 319,
with a quantity of electrocatalyst disposed in a layer 320, 321 at
the interface between each fluid distribution layer 318, 319 and
membrane 314 in the electrochemically active region 330 of the
fluid distribution layers 318, 319. The MEA 312 is interposed
between a pair of flow field plates 322 and 324, each plate having
an open-faced channel 323, 325 formed in its surface facing the
corresponding fluid distribution layer 318, 319, respectively, as
described for FIGS. 2A and 2B above.
[0055] Fluid distribution layers 318, 319 each have a sealing
region 340. In the illustrated embodiment, ion exchange membrane
314 superposes only a portion of the sealing region 340
circumscribing the active region 330. The membrane 314 does not
superpose entire sealing region 340. In the electrochemically
active region 330, the fluid distribution layers 318, 319 are
electrically conductive and fluid permeable. In the embodiment
illustrated in FIGS. 3A and 3B, fluid distribution layers include
substantially fluid impermeable sheet material 350 extending into
each of the active and sealing regions 330, 340, respectively. The
sheet material 350 is perforated at least in the electrochemically
active region, rendering it fluid permeable, to permit the passage
of reactant fluid between the two major planar surfaces thereof for
access to the electrocatalyst layer 320, 321 respectively. In the
illustrated embodiment, the substantially fluid impermeable sheet
material 350 is formed from an electrically insulating polymeric
material such as polytetrafluoroethylene or an elastomer such as
Santoprene brand rubber available through Monsanto Company. As the
sheet material 350 is electrically insulating, the fluid
distribution layer is rendered electrically conductive in the
active region 330. For example, the perforations 352 may contain an
electrically conductive filler 354. Compression of sheet material
350 in fluid distribution layers 318, 319 between membrane 314 and
plates 322, 324 respectively, renders the fluid distribution layers
substantially fluid impermeable in a direction parallel to their
major planar surfaces in the sealing region 340, by virtue of the
fluid impermeability of the sheet material 350 which extends into
the sealing region 340.
[0056] As shown in FIG. 3B, each of the fluid distribution layers
318, 319, and reactant flow field plates 322, 324, has a plurality
of openings 360 formed therein, which align when assembled to form
manifolds for directing inlet and outlet fluid streams through fuel
cell 310, as described above. For example, oxidant fluid flow field
channel 325 extends between oxidant inlet manifold opening 360a and
oxidant outlet manifold 360b formed in plate 324. The two fluid
distribution layers 318, 319 and the reactant flow field plates
322, 324 cooperate to form a seal circumscribing the manifold
openings 360. Whereas sealing around the periphery of the active
region 340 in the embodiment of FIGS. 3A and 3B, is accomplished by
utilizing the intrinsic sealing capability of the sheet material
350 when it is interposed and compressed between the plates 322,
324 and the membrane 314. If the fluid distribution layers 318, 319
are electrically conductive in sealing region 340 and membrane 314
does not superpose the entire sealing region 340, an electrical
insulator would need to be interposed between layers 318, 319 to
prevent short circuiting.
[0057] FIG. 4A is an exploded sectional view of an electrochemical
fuel cell 410, a portion of which is shown in FIG. 4B in an
exploded isometric view. Fuel cell 410 is very similar to fuel cell
310 of FIGS. 3A and 3B, again including a membrane electrode
assembly 412, including an ion exchange membrane 414 interposed
between a pair of fluid distribution layers 418, 419, with
electrocatalyst-containing layers 420, 421 defining the
electrochemically active region 430 of the fluid distribution
layers 418, 419. The MEA 412 is interposed between a pair of
separator plates 422 and 424.
[0058] Fluid distribution layers 418, 419 each have a sealing
region 440. In the illustrated embodiment, ion exchange membrane
414 superposes sealing region 440. In the electrochemically active
region 430, the fluid distribution layers 418, 419 are electrically
conductive and fluid permeable. In the embodiment illustrated in
FIGS. 4A and 4B, fluid distribution layers include substantially
fluid impermeable sheet material 450 extending into each of the
active and sealing regions 430, 440, respectively. The sheet
material 450 is perforated at least in the electrochemically active
region, rendering it fluid permeable, to permit the passage of
reactant fluid between the two major planar surfaces thereof for
access to the electrocatalyst layer 420, 421 respectively. In the
illustrated embodiment, the substantially fluid impermeable sheet
material 450 is formed from an electrically conductive material
such as graphite foil, carbon resin or a metal. The perforations
452 preferably contain an electrically conductive filler 454.
[0059] In the illustrated embodiment, each fluid distribution layer
418, 419 has an open-faced channel 423, 425 formed in its surface
facing the corresponding separator plate 422, 424, respectively,
and traversing the electrochemically active region 430. When
assembled against the cooperating surfaces of the plates 422 and
424, channels 423 and 425 form reactant flow field passages for the
fuel and oxidant, respectively.
[0060] An embodiment such as the one illustrated in FIGS. 4A and 4B
integrates several functions including sealing, fluid distribution
including provision of a flow field, and current collection, in a
single layer or component.
[0061] Compression of sheet material 450 in fluid distribution
layers 418, 419 between membrane 414 and plates 422, 424,
respectively, renders the fluid distribution layers 418, 419
substantially fluid impermeable in a direction parallel to their
major planar surfaces in the sealing region 440, by virtue of the
fluid impermeability of the sheet material 450 which extends into
the sealing region 440.
[0062] As shown in FIG. 4B, each of the membrane 414, fluid
distribution layers 418, 419, reactant flow field plates 422, 424,
has a plurality of openings 460 formed therein, which align when
assembled to form manifolds for directing inlet and outlet fluid
streams through fuel cell 410, as described above.
[0063] A wide variety of fabrication processes may be used to
manufacture and assemble fuel cells of the present design. The
design is believed to be suited for high throughput manufacturing
processes, such as the reel-to-reel type process disclosed in the
aforementioned U.S. patent application Ser. No. 08/846,653
incorporated herein by reference. Such a reel-to-reel process may
consolidate several webs consisting of the fluid distribution
layers, a catalyzed membrane, and a separator layer. The
consolidation step could include a thermal lamination (thereby
effecting the melt-bonding between the fluid distribution layers
and the membrane) and a pressure bonding process.
[0064] FIG. 5 is a schematic diagram illustrating a possible
fabrication approach for a fuel cell similar to that illustrated in
FIGS. 4A and 4B. FIG. 5 shows schematically the preparation of a
fluid distribution layers 518, and the consolidation of two such
layers 518, 519 with a catalyzed membrane 514 and a separator layer
522, in a reel-to-reel type process. For example, fluid
distribution layers 518 are formed by selectively perforating a
substantially fluid impermeable preformed sheet material 550 in the
active region, in a perforation step 580. The sheet material could,
for example, be graphite foil. In a subsequent step 585, the
perforations are at least partially filled with an electrically
conductive filler, such as carbon particles and a polymeric binder.
A layer of conductive filler may also be deposited on one or both
major surfaces of the perforated sheet material 550. Reactant flow
field channels 523 may be formed in one or both major surfaces of
the fluid distribution layer in step 590, for example, by
embossing. A multi-layer fuel cell assembly 510 may be formed by
bringing together, in a consolidation step 595, two fluid
distribution layers 518, 519, with an ion exchange membrane 514,
and a substantially fluid impermeable separator layer 522. The
consolidation step could include a thermal lamination and/or
pressure bonding process. The ion exchange membrane 514 has a
electrocatalyst-containing layer on a portion of both of its major
surfaces, defining the electrochemically active region.
Alternatively, the electrocatalyst could be deposited on the fluid
distribution layers 518, 519 prior to consolidation step 595. The
assemblies may then optionally be cut into single cell units, and
layered to form a fuel cell stack, wherein separator layers 522
will serve as bipolar plates. FIG. 5 illustrates how the present
fuel cell design with fluid distribution layers with integral seal
capability, is suitable for fabrication via a continuous, high
throughput manufacturing process, with little material wastage and
few individual components and processing steps.
[0065] The practical advantages of the present fuel cell with a
fluid distribution layer having integral sealing capability is the
combination of the sealing and fluid distribution functions into
one fluid distribution layer, thereby reducing cost, simplifying
the components, and improving their reliability. This approach
reduces or eliminates the need for separate sealing components in a
fuel cell assembly.
[0066] In all of the above embodiments, the fuel cell may include
additional layers of material interposed between those shown, or
the components shown may be multi-layer structures. Such additional
layers may or may not superpose both the electrochemically active
region and the sealing region. The separator plates may have
optionally have raised sealing ridges projecting from the major
surfaces thereof in the sealing region. In a fuel cell assembly
under compression, the sealing ridges will compress the fluid
distribution layer.
[0067] Those in the art will appreciate that the general principles
disclosed in the preceding can be expected to apply to both gas and
liquid feed fuel cells, for example, gaseous hydrogen/air solid
polymer fuel cells and liquid methanol/air or "direct methanol"
solid polymer fuel cells. However, it is expected that fewer
polymers will be suitable for use in the latter since a suitable
polymer would have to be compatible with liquid methanol.
[0068] While particular elements, embodiments and applications of
the present invention have been shown and described, it will be
understood, of course, that the invention is not limited thereto
since modifications may be made by those skilled in the art,
particularly in light of the foregoing teachings. It is therefore
contemplated by the appended claims to cover such modifications as
incorporate those features that come within the scope of the
invention.
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