U.S. patent application number 11/171730 was filed with the patent office on 2007-01-04 for integrally molded gasket for a fuel cell assembly.
This patent application is currently assigned to Freudenberg-NOK General Partnership. Invention is credited to Mark Allen Belchuk.
Application Number | 20070003821 11/171730 |
Document ID | / |
Family ID | 37589945 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070003821 |
Kind Code |
A1 |
Belchuk; Mark Allen |
January 4, 2007 |
Integrally molded gasket for a fuel cell assembly
Abstract
A fuel cell membrane electrode assembly (MEA) comprising first
and second gas diffusion layers and an ion exchange membrane
disposed between the diffusion layers. Each diffusion layer
includes an inner surface facing the membrane, an outer surface
opposite the inner surface, and a side surface defining a perimeter
of the diffusion layers. An outboard region extends about the
diffusion layers at the perimeter. The outboard region surrounds an
inboard region. The outboard region has a low density region
proximate to the side surface and a high density region between the
low density region and the inboard portion. A seal is mounted at
the low density region. The high density region prevents portions
of the seal from entering the inboard region thereby damaging the
MEA. The seal includes a first rim having a smaller radius than a
second rim. The smaller radius allows the seal to fit between
adjacent support plates and increases the durability of the
seal.
Inventors: |
Belchuk; Mark Allen;
(Windsor, CA) |
Correspondence
Address: |
FREUDENBERG-NOK GENERAL PARTNERSHIP;LEGAL DEPARTMENT
47690 EAST ANCHOR COURT
PLYMOUTH
MI
48170-2455
US
|
Assignee: |
Freudenberg-NOK General
Partnership
Plymouth
MI
|
Family ID: |
37589945 |
Appl. No.: |
11/171730 |
Filed: |
June 30, 2005 |
Current U.S.
Class: |
429/465 ;
429/483; 429/509; 429/532; 429/534; 429/535 |
Current CPC
Class: |
H01M 8/0286 20130101;
H01M 8/0273 20130101; H01M 2008/1095 20130101; H01M 8/0284
20130101; H01M 8/0271 20130101; H01M 4/88 20130101; H01M 8/1004
20130101; Y02E 60/50 20130101; H01M 8/0276 20130101 |
Class at
Publication: |
429/044 ;
429/035 |
International
Class: |
H01M 4/94 20060101
H01M004/94; H01M 2/08 20060101 H01M002/08 |
Claims
1. A fuel cell membrane electrode assembly comprising: a first gas
diffusion layer; a second gas diffusion layer opposite said first
gas diffusion layer; an ion exchange membrane disposed between said
first gas diffusion layer and said second gas diffusion layer; each
one of said first gas diffusion layer and said second gas diffusion
layer include: an inner surface facing said ion exchange membrane;
an outer surface opposite said inner surface; a side surface
between said outer surface and said inner surface defining a
perimeter of said first and said second diffusion layers
respectively; an outboard region extending about a periphery of
each of said first layer and said second layer at said perimeter;
and an inboard region at least substantially surrounded by said
outboard region, said inboard region including an inboard low
density region; said outboard region including: an outboard low
density region at least proximate to said side surface and said
perimeter; and an outboard high density region between said
outboard low density region and said inboard low density region,
said first and said second diffusion layers having a greater
density at said high density region than at said low density
regions; and a seal mounted to said outboard low density region so
as to cover said outer surface and said side surface of each of
said first and second diffusion layers at said outboard low density
region.
2. The membrane electrode assembly of claim 1, wherein said first
and said second gas diffusion layers include porous electrodes.
3. The membrane electrode assembly of claim 1, wherein said outer
surface is closer to said inner surface at said outboard high
density region than at said outboard and said inboard low density
regions, such that said first and said second diffusion layers are
thinner at said outboard high density region than at said outboard
and said inboard low density regions.
4. The membrane electrode assembly of claim 1, wherein said ion
exchange membrane extends laterally beyond said first and said
second gas diffusion layers.
5. The membrane electrode assembly of claim 1, wherein said seal
includes an elastomeric material.
6. The membrane electrode assembly of claim 1, wherein said seal
comprises at least one of silicone, fluorosilicone elastomer,
fluorocarbon elastomer, and ethylene propylene diene monomer
elastomer.
7. The membrane electrode assembly of claim 4, wherein said seal
covers said membrane.
8. The membrane electrode assembly of claim 1, wherein said seal
further comprises a first seal bead and a second seal bead; wherein
said first bead impregnates said first and said second gas
diffusion layers and said second bead is laterally offset from said
first and said second gas diffusion layers.
9. The membrane electrode assembly of claim 8, wherein said first
bead and said second bead are each at least substantially
cylindrical; and wherein said first bead has a smaller radius than
said second bead.
10. The membrane electrode assembly of claim 1, wherein said seal
impregnates said first gas diffusion layer and said second gas
diffusion layer to provide a barrier that is at least substantially
impermeable to gas.
11. A fuel cell membrane electrode assembly comprising: a first gas
diffusion layer; a second gas diffusion layer; an ion exchange
membrane disposed between said first and said second gas diffusion
layers; each one of said first diffusion layer and said second
diffusion layer include: an inner surface facing said ion exchange
membrane; an outer surface opposite said inner surface; a side
surface between said outer surface and said inner surface defining
a perimeter of said first and said second layers respectively; and
a seal having a first rim integral with a second rim, said first
rim is mounted to said outer surface and said side surface of each
of said first layer and said second layer, said second rim is
laterally offset from said first and said second layers; wherein
said seal impregnates said first gas diffusion layer and said
second gas diffusion layer to provide a barrier between said first
and said second gas diffusion layers that is at least substantially
impermeable to gas; and wherein said first rim has a smaller volume
than said second rim.
12. The membrane electrode assembly of claim 11, wherein said first
and said second gas diffusion layers comprise porous
electrodes.
13. The membrane electrode assembly of claim 11, wherein said first
and said second rims are at least substantially cylindrical, said
first rim having a smaller radius than said second rim.
14. The membrane electrode assembly of claim 11, each one of said
first layer and said second layer further comprising an outboard
region extending about a periphery of said first layer and said
second layer respectively at said side surface, each of said
outboard regions having a low density region proximate to said side
surface and a high density region distal to said side surface;
wherein said high density region is up to about 50% more dense than
said low density region.
15. The membrane electrode assembly of claim 14, wherein said first
rim impregnates said low density region.
16. The membrane electrode assembly of claim 15, wherein said
second rim extends laterally beyond said first and said second
diffusion layers.
17. The membrane electrode assembly of claim 11, wherein said ion
exchange membrane extends laterally beyond said first and said
second gas diffusion layers.
18. The membrane electrode assembly of claim 11, wherein said seal
includes an elastomeric material.
19. The membrane electrode assembly of claim 11, wherein said seal
comprises at least one of silicone, fluorosilicone elastomer,
fluorocarbon elastomer, and ethylene propylene diene monomer
elastomer.
20. A fuel cell comprising: a first support plate; a second support
plate; a membrane electrode assembly positioned between said first
support plate and said second support plate, said membrane
electrode assembly comprising: a first electrode adjacent said
first support plate; a second electrode opposite said first
electrode and adjacent said second support plate; and an ion
exchange membrane disposed between said first electrode and said
second electrode; each one of said first electrode and said second
electrode include: an inner surface facing said ion exchange
membrane; an outer surface opposite said inner surface, said outer
surface of said first electrode facing said first support plate and
said outer surface of said second electrode facing said second
support plate; a side surface between said outer surface and said
inner surface defining a perimeter of said first and said second
electrodes respectively; an outboard region extending about a
periphery of each of said first electrode and said second electrode
at said perimeter; an inboard region at least substantially
surrounded by said outboard region; said outboard region including
a low density region proximate to said side surface and a high
density region that is inboard of, and adjacent to, said low
density region; a seal mounted to said outboard low density region
so as to cover said outer surface and said side surface of each of
said first and said second diffusion layers; wherein said seal
impregnates said low density region of said outboard region to
provide a barrier between said first and said second gas diffusion
layers that is at least substantially impermeable to gas.
21. The fuel cell of claim 20, further comprising a fuel cell stack
including a plurality of said fuel cells.
22. The fuel cell of claim 20, wherein said first and said second
electrodes are porous.
23. The fuel cell of claim 20, wherein said outer surface is closer
to said inner surface at said high density region than at said low
density region.
24. The fuel cell of claim 20, wherein said inboard region and said
low density region have the same density.
25. The fuel cell of claim 20, wherein said seal comprises an
elastomeric material.
26. The fuel cell of claim 20, wherein said seal comprises at least
one of silicone, fluorosilicone elastomer, fluorocarbon elastomer,
and ethylene propylene diene monomer elastomer.
27. The fuel cell of claim 20, wherein said seal further comprises
a first annular projection and a second annular projection; wherein
said first projection impregnates said first and said second
electrodes and said second projection is laterally offset from said
first and said second electrodes.
28. The fuel cell of claim 27, wherein said first and said second
projections are at least substantially cylindrical, said first
projection having a smaller radius than said second projection.
29. A method for manufacturing a fuel cell membrane electrode
assembly having an ion exchange membrane affixed between a first
gas diffusion layer and a second gas diffusion layer, the method
comprising the steps of: positioning the first and the second gas
diffusion layers with the membrane in-between between two halves of
a thermo-mold assembly, each mold half having a protruding region
that mirrors the location of a high density region to be formed in
the first and second gas diffusion layers at an outboard region
that extends about a periphery of the first and second diffusion
layers; closing the mold halves under heat such that the protruding
regions of the mold halves compress the first and the second
diffusion layers at the high density regions to increase the
density of the first and second diffusion layers at the high
density regions; injecting an elastomeric material that is heated
to a liquid within a cavity of the closed mold, the cavity located
about the periphery of the membrane electrode assembly at a low
density region that is outboard of the high density region, the
liquid elastomer flows within and impregnates the first and second
diffusion layers at the low density region; and curing the liquid
elastomeric material to form an elastomeric seal that is
impregnated within the first and second diffusion layers at the low
density region and extends around side surfaces of the first and
second diffusion layers at a perimeter of the first and second
diffusion layers.
30. The method of claim 29, wherein said injecting step further
comprises injecting the liquid elastomeric material within the
cavity having an inner chamber connected to an outer chamber
surrounding the inner chamber such that the seal formed after said
curing step includes an inner rim and an outer rim, the inner rim
impregnates the first and second gas diffusion layers and the outer
rim extends laterally from the first and second gas diffusion
layers.
31. The method of claim 30, wherein the inner chamber has a smaller
volume than the outer chamber such that the inner rim of the seal
has a smaller diameter than the outer rim.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to fuel cells. More
particularly, the present invention relates to an integrally molded
gasket seal for a fuel cell membrane electrode assembly.
BACKGROUND OF THE INVENTION
[0002] Electrochemical fuel cells facilitate chemical reactions
between hydrogen and oxygen to generate electrical current. The
chemical reactions take place in one or more membrane electrode
assemblies ("MEA"). Each MEA typically includes an ion exchange
membrane disposed between two electrodes, which are also referred
to as gas diffusion layers. Between each electrode and the membrane
is a catalyst, the location of which defines an electrochemically
active area of the MEA.
[0003] One electrode functions as a cathode and the other electrode
functions as an anode. Typically, hydrogen is supplied to the anode
and oxygen is supplied to the cathode. The hydrogen and oxygen are
directed to the electrodes in separate manifolds.
[0004] The membrane acts as a barrier to isolate the hydrogen and
oxygen to prevent short-circuiting of the MEA. The membrane
restricts passage of oxygen and hydrogen, but permits protons to
pass between the anode and the cathode. In many MEA's, the membrane
extends laterally beyond the perimeter of each electrode layer.
Extending the membrane beyond the two electrodes helps to prevent
passage of oxygen and hydrogen between the electrodes at the
perimeter edges of the electrodes, which can short-circuit the
MEA.
[0005] To further isolate the hydrogen and oxygen molecules, a
gasket seal is provided around the perimeter edge of the electrodes
and over the portion of the membrane that extends beyond the
electrodes. To enhance the effectiveness of the seal, the seal is
impregnated within the electrodes, which are typically porous and
have a uniform density. The seal is made of an elastomeric material
and can include multiple beads or protrusions to further increase
the effectiveness of the seal.
[0006] In operation, hydrogen gas (H.sub.2) supplied to the anode
reacts with the catalyst to split the H.sub.2 molecule into two
H.sup.+ ions and two electrons. The electrons are conducted via the
anode to an external circuit to provide current to the circuit that
can be used for a variety of purposes, such as to power and turn a
motor. The circuit next directs the electrons to the cathode side
of the fuel cell.
[0007] Simultaneously, oxygen gas (O.sub.2) supplied to the cathode
reacts with the catalyst to form two oxygen atoms. Each of the
oxygen atoms have a strong negative charge. This negative charge
attracts the H.sup.+ ions through the membrane. The H.sup.+ ions
combine with an oxygen atom and two of the electrons from the
external circuit to form a water molecule (H.sub.2O).
[0008] A single MEA produces only a small voltage. To increase the
amount of voltage produced, multiple MEAs are often combined in a
fuel cell stack in a manner that is commonly known in the art. The
multiple MEA's are typically separated by flow field plates, which
are commonly referred to as separator plates.
[0009] While existing MEAs are suitable for their intended use,
they are subject to improvement. For example, portions of the
elastomeric seal sometimes enter the MEA active area during the
manufacturing process as the elastomer is impregnated within the
MEA. The presence of elastomer in the active area is undesirable
because it restricts movement of gases and other particles in the
active area, thereby decreasing the effective size of the active
area and decreasing the efficiency of the fuel cell. Therefore,
there is a need for a device and method that prevents portions of
the seal from entering the active area during the impregnation
process.
[0010] Existing MEA's also experience problems due to the size of
the gasket seal or the distance that the seal extends above or
below the MEA. For example, if the seal is too large and thus
protrudes too far above or below the MEA then the seal will not
properly fit between the MEA and the neighboring separator plates
of a fuel cell stack. Further, such large seals exert more stress
on the seal/MEA interlock than smaller seals due to numerous
factors, such as their volume and increased exposure to outside
forces that can highly strain the seal, thus making it more likely
that larger seals, rather than smaller seals, will become detached
from the MEA or damage the MEA. Still further, larger seals may
permit more hydrogen permeation as compared to smaller seals. On
the other hand, larger seals are more effective than smaller seals
at preventing gross leakage from the MEA into the surrounding
environment. Thus, there is a need for a seal that realizes the
advantages associated with both large and small seals, while at the
same time overcomes the disadvantages of each.
SUMMARY OF THE INVENTION
[0011] The present invention provides for a fuel cell membrane
electrode assembly (MEA) comprising first and second gas diffusion
layers and an ion exchange membrane disposed between the diffusion
layers. Each diffusion layer includes an inner surface facing the
membrane, an outer surface opposite the inner surface, and a side
surface defining a perimeter of the diffusion layers. An outboard
region extends about the diffusion layers at the perimeter. The
outboard region surrounds an inboard region. The outboard region
has a low density region proximate to the side surface and a high
density region between the low density region and the inboard
portion. A seal is mounted at the low density region. The high
density region prevents portions of the seal from entering the
inboard region during the manufacturing process, thereby damaging
the MEA.
[0012] Another aspect of the invention provides for a fuel cell
membrane assembly having a first gas diffusion layer, a second gas
diffusion layer, an ion exchange membrane disposed between the
first and second gas diffusion layers, and a seal. Each one of the
first and second gas diffusion layers include the following: an
inner surface facing the ion exchange membrane; an outer surface
opposite the inner surface; and a side surface between the outer
surface and the inner surface defining a perimeter of the first and
the second layers respectively. The seal has a first rim integral
with a second rim. The first rim is mounted to the outer surface
and the side surface of each of the first layer and the second
layer. The second rim is laterally offset from the first and the
second layers. The seal impregnates the first gas diffusion layer
and the second gas diffusion layer to provide a barrier between the
first and the second gas diffusion layers that is at least
substantially impermeable to gas. The first rim has a smaller
volume than the second rim.
[0013] A further aspect of the invention provides for a first
support plate, a second support plate, and a membrane electrode
assembly positioned between the first support plate and the second
support plate. The membrane electrode assembly includes a first
electrode, a second electrode, an ion exchange membrane, and a
seal. The first electrode is adjacent to the first support plate.
The second electrode is opposite the first electrode and adjacent
the second support plate. The ion exchange membrane is disposed
between the first electrode and the second electrode. Each one of
the first electrode and the second electrode include: an inner
surface facing the ion exchange membrane; an outer surface opposite
the inner surface, the outer surface of the first electrode faces
the first support plate and the outer surface of the second
electrode faces the second support plate; a side surface between
the outer surface and the inner surface defining a perimeter of the
first and the second electrodes respectively; an outboard region
extending about a periphery of each of the first electrode and the
second electrode at the perimeter; and an inboard region at least
substantially surrounded by the outboard region. The outboard
region includes a low density region proximate to the side surface
and a high density region that is inboard of, and adjacent to, the
low density region. The seal impregnates the low density region of
the outboard region to provide a barrier between the first and the
second gas diffusion layers that is at least substantially
impermeable to gas.
[0014] Yet an additional aspect of the invention provides for a
method for manufacturing a fuel cell membrane electrode assembly
having an ion exchange membrane affixed between a first gas
diffusion layer and a second gas diffusion layer. The method
comprises the following steps: positioning the first and the second
gas diffusion layers between two halves of a thermo-mold assembly,
each mold half having a protruding region that mirrors the location
of a high density region to be formed in the first and second gas
diffusion layers at an outboard region that extends about a
periphery of the first and second diffusion layers; closing the
mold halves under heat such that the protruding regions of the mold
halves compress the first and the second diffusion layers at the
high density regions to increase the density of the first and
second diffusion layers at the high density regions; injecting an
elastomeric material that is heated to a liquid within a cavity of
the closed mold, the cavity located about the periphery of the
membrane electrode assembly at a low density region that is
outboard of the high density region, the liquid elastomer flows
within the first and second diffusion layers at the low density
region; and curing the liquid elastomeric material to form an
elastomeric seal that is impregnated within the first and second
diffusion layers at the low density region and extends around side
surfaces at the periphery of the first and second diffusion
layers.
[0015] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating the preferred embodiment of the
invention, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0017] FIG. 1 is an exploded perspective view of a fuel cell
assembly according to the teachings of the present invention
comprising a membrane electrode assembly (MEA) disposed between two
support plates;
[0018] FIG. 2 is a perspective view of the MEA of FIG. 1;
[0019] FIG. 3 is an exploded view of the MEA of FIG. 1 illustrated
without the gasket seal for clarity; and
[0020] FIG. 4 is a cross-sectional view taken along line 4-4 of
FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] The following description of the preferred embodiments is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses.
[0022] A fuel cell assembly according to the teachings of the
present invention is illustrated in FIG. 1 at reference numeral 10.
The fuel cell 10 generally comprises a first support plate 12, a
second support plate 14, and a membrane electrode assembly (MEA) 16
disposed between the first and second support plates 12 and 14. The
plates 12 and 14 are mounted to opposite sides of the MEA 16.
[0023] The support plates 12 and 14 are substantially similar.
Therefore, like reference numbers are used to designate features of
the plates 12 and 14 that are similar or the same. When it is
necessary to distinguish between the first and second plates 12 and
14, such as in the figures, the letter "a" is used to designate
features of the first support plate 12 and the letter "b" is used
to designate features of the second support plate 14.
[0024] Each of the support plates 12 and 14 include multiple
manifold ports 18. The ports 18 can take a variety of different
forms and can be provided at a variety of different locations
within the plates 12 and 14. As illustrated, the ports 18 are
located along an edge of each of the plates 12 and 14 and extend
through each of the plates 12 and 14. Each of the ports 18 are
separate passageways that keep different gases of the different
ports 18 isolated from each other. The ports 18 of each of the
plates 12 and 14 are in vertical alignment with each other.
[0025] Each of the support plates 12 and 14 further include flow
field channels 20. The channels 20 are located within a surface of
the plates 12 and 14 respectively that abuts the MEA 16. The
channels 20 are in communication with one or more of the ports 18.
The channels 20 are operable to distribute the gases supplied
through the ports 18 to the MEA 16.
[0026] With additional reference to FIGS. 2-4, the MEA 16 generally
includes a first gas diffusion layer 22, a second gas diffusion
layer 24, an ion exchange membrane 26 disposed between the first
and second gas diffusion layers 22 and 24, a seal 28 (not shown in
FIG. 3 for clarity) mounted to the diffusion layers 22 and 24, and
MEA manifold ports 30.
[0027] The first and second gas diffusion layers 22 and 24 are
substantially the same. Therefore, like reference numbers are used
to designate features of the diffusion layers 22 and 24 that are
similar or the same. When it is necessary to distinguish between
the first and second diffusion layers 22 and 24, such as in the
figures, the letter "a" is used to designate features of the first
diffusion layer 22 and the letter "b" is used to designate features
of the second diffusion layer 24.
[0028] The first and second diffusion layers 22 and 24 each include
an inner surface 32 and an outer surface 34 that is opposite the
inner surface 32. The inner surfaces 32 face the membrane 26. The
outer surface 34a of the first diffusion layer 22 faces the first
support plate 12 and the outer surface 34b of the second gas
diffusion layer 24 faces the second support plate 14.
[0029] Each of the diffusion layers 22 and 24 include a side
surface 36 that is located between the inner surface 32 and the
outer surface 34. Specifically, the side surfaces 36 are located at
an outer edge of the inner and outer surfaces 32 and 34
respectively. The side surfaces 36 define an outer perimeter of the
first and second diffusion layers 22 and 24.
[0030] The gas diffusion layers 22 and 24 each further include an
inboard region 38 and an outboard region 40. The inboard regions 38
are at a center of the diffusion layers 22 and 24. The outboard
regions 40 are at a periphery of the diffusion layers 22 and 24 and
extend about the perimeter of the diffusion layers 22 and 24 at the
side surfaces 36. The outboard regions 40 surround the inboard
regions 38. Thus, the outboard regions 40 are proximate to the side
surfaces 36 and the inboard regions 38 are distal to the side
surfaces 36.
[0031] With particular reference to FIG. 4, the outboard regions 40
each include a low density region 42 and a high density region 44.
The low density regions 42 are at, or at least proximate to, the
side surfaces 36. The low density regions 42 extend about the
entire, or substantially the entire, perimeter of the diffusion
layers 22. The low density regions 42 extend from between about 0.5
mm to about 10 mm, preferably about 4 mm, inward from the side
surfaces 36 toward the inboard regions 38. The thickness of the low
density regions 42, which is the distance between the outer surface
34a of the first diffusion layer 22 and the outer surface 34b of
the second diffusion layer 24 including the thickness of the
membrane 26, is approximately 0.48 mm.
[0032] The high density regions 44 are between each of the inboard
regions 38 and the low density regions 42. The high density regions
44 extend about the entire, or substantially the entire, perimeter
of the diffusion layers 22 and are more dense than the low density
regions 42. The high density regions 44 can be of most any
structural form that is sufficient to provide the diffusion layers
22 and 24 with an increased density at the high density regions 44
as compared to the low density regions 42.
[0033] The diffusion layers 22 and 24 are generally porous. The
diffusion layers 22 and 24 can be made of a variety of materials
known in the art, such as carbon fiber paper, which is generally
comprised of a plurality of intertwined carbon fibers.
[0034] In applications where the diffusion layers 22 and 24 are
made of carbon fiber paper, the increased density of the high
density regions 44 can be due to decreased spacing between the
carbon fibers in the high density regions 44 as compared to the low
density regions 42. This decreased spacing can be provided in a
variety of different ways, such as by compressing or "pinching" the
layers 22 and 24 during the MEA 16 manufacturing process.
[0035] In applications where the high density regions 44 are
provided by compressing the diffusion layers 22 and 24, as
illustrated in the figures, the high density regions 44 have a
reduced thickness or height as compared to the low density regions
42 and the inboard regions 38 when the diffusion layers 22 are
viewed in the cross-section of FIG. 4. In other words, the outer
surfaces 34 are closer to the inner surfaces 32 in the area of the
high density regions 44 than in the area of the low density regions
42 or the inboard regions 38.
[0036] The thickness of the overall MEA at the high density region
44, which is the distance from the outer surface 34a of the first
diffusion layer 22 to the outer surface 34b of the second diffusion
layer 24 including the thickness of the ion exchange membrane 26,
is approximately 0.43 mm, but can be any other suitable thickness.
The high density region 44 can be located, for example, from
between about 0.5 mm to about 10 mm, preferably about 4 mm, inboard
from the side surface 36 and can be approximately 1.5 mm in length,
or any other suitable thickness.
[0037] While the high density region 44 is illustrated as having a
reduced height or thickness as compared to the low density region
42 in the cross-section of FIG. 4, the high density region 44 can
have a thickness that is uniform with the remainder of the
diffusion layers 22 and 24 as long as the high density region 44
has a higher density than the low density region 42. The high
density region 44 can be of a variety of different densities, such
as up to about 50% more dense than the inboard region 38 and/or the
low density region 42.
[0038] In most applications the inboard regions 38 have a density
that is approximate to, or the same as, the low density regions 42
of the outboard region 40. The inboard region 38 is therefore a low
density region 46 itself. However, in some applications the inboard
region 38 can have a density that is greater or less than the low
density region 42 of the outboard region 40. The thickness of the
overall MEA 16 at the low density region 46, which is the distance
from the outer surface 34a of the first diffusion layer 22 to the
outer surface 34b of the second layer 24 including the thickness of
the ion exchange membrane 26, can be approximately 0.48 mm or any
other suitable thickness.
[0039] The first and second gas diffusion layers 22 and 24 are
electrically conductive. As a result, the diffusion layers 22 and
24 are commonly referred to as electrodes.
[0040] The ion exchange membrane 26 is typically a polymer
electrolyte membrane that conducts only positively charged ions.
The membrane 26 prohibits the passage of electrons. Any suitable
fuel cell membrane known in the art can be used. The membrane 26
typically includes a top surface 48 and a bottom surface 50. The
top surface 48 abuts the inner surface 32a of the first gas
diffusion layer 22 and the bottom surface 50 abuts the inner
surface 32b of the second gas diffusion layer 24.
[0041] As best illustrated in FIG. 4, the membrane 26 is sized to
extend laterally beyond the diffusion layers 22 and 24. In other
applications, the membrane 26 can be coextensive with the first and
second diffusion layers 22 and 24 such that it terminates at the
side surfaces 36. The membrane 26 can also be sized to terminate
inboard of the side surfaces 36.
[0042] The portion of the membrane top surface 48 facing the
inboard region 38a of the first gas diffusion layer 22 is coated
with an anode catalyst (not shown). The portion of the bottom
surface 50 facing the inboard region 38b of the second gas
diffusion layer 24 is coated with a cathode catalyst (not shown).
The catalysts can be any suitable catalyst known in the art, such
as Nafion.RTM.. The portions of the ion exchange membrane 26 that
oppose the outboard regions 40 of the gas diffusion layers 22 and
24 may not be, but in some applications can be, coated with the
catalyst.
[0043] The areas of the MEA 16 where the catalyst opposes the
inboard regions 38 of the gas diffusion layers 22 and 24 are the
active regions of the MEA 16. The areas of the MEA 16 where the
portions of the membrane 26 not covered with the catalyst oppose
the outboard regions 40 are the inactive regions of the MEA 16. The
chemical reactions generating electrons and water take place in the
active regions. No reactions take place in the inactive
regions.
[0044] As most clearly illustrated in FIGS. 2 and 4, the seal 28 is
mounted about the peripheral edge of the MEA 16. Specifically, the
seal 28 is mounted to the outer surfaces 34a and 34b at the
outboard low density region 42 and to the side surfaces 36a and
36b. In applications where the membrane 26 extends from beyond the
first and second diffusion layers 22 and 24, as illustrated in FIG.
4, the seal 28 is also mounted to and mounted over the portion of
the membrane 26 that protrudes from between the first and second
diffusion layers 22 and 24. The seal 28 applies a compression force
to the membrane 26.
[0045] The seal 28 impregnates the diffusion layers 22 and 24 at an
impregnation region 52. Specifically, the seal is impregnated
within the outboard low density regions 42 and within the side
surfaces 36. Impregnating the seal 28 at the impregnation region 52
enhances the interface between the seal 28 and the diffusion layers
22 and 24.
[0046] As most clearly illustrated in FIG. 4, the seal 28 includes
an inner projection, rim, or bead 54a and an outer projection, rim,
or bead 54b. The beads 54 extend completely around the seal 28. The
beads 54 are connected by an interconnecting bridge region 56 and
are thus integral with each other. As illustrated, each bead 54 is
substantially cylindrical. However, the beads 54 can be of most any
suitable shape. While the present invention is illustrated as
including two beads 54, the seal 28 can include a single bead 54,
more than two beads 54, or no beads 54 at all.
[0047] The beads 54 can be of various different sizes depending on
numerous factors, such as the size of the fuel cell 10 and the
application. Preferably, the inner bead 54a has a smaller area or
radius than the outer bead 54b. In many applications the inner bead
has as radius of approximately 0.3 mm and the outer bead 54b has a
radius of approximately 0.69 mm.
[0048] The seal 28 can be made of a variety of different materials
known in the art that are at least substantially impermeable to
gas, such as oxygen and hydrogen. The seal 28 is typically an
elastomer, such as a thermosetting liquid injection moldable
compound. For example, the seal 28 can be made of one or more of
the following materials: silicone, fluorosilicone elastomer,
fluorocarbon elastomer, and ethylene propylene diene monomer
elastomer.
[0049] The MEA 16 further includes MEA manifold ports 30. As
illustrated in FIGS. 1 and 2, the MEA ports 30 are integral with
the seal 28 and made of the same material as the seal 28. The MEA
ports 30 are aligned with the manifold ports 18a and 18b of the
first and second plates 12 and 14. The MEA ports 30 are individual
passageways that permit the passage of gases between the manifold
ports 18a and 18b.
[0050] An exemplary process for manufacturing the fuel cell 10 will
now be described in detail. To manufacture the MEA 16, the gas
diffusion layers 22 and 24 are laminated to opposite sides of the
membrane 26 using any of a variety of different devices and methods
known in the art.
[0051] The diffusion layers 22 and 24 and the membrane 26 are
placed in a suitable molding tool (not shown) to form the high
density region 44 and install the seal 28. The molding tool can
also be used to laminate the diffusion layers 22 to the membrane
26, as is known in the art. The molding tool can be any suitable
molding tool that is commonly used in the art, such as an injection
molding tool. The molding tool includes a mold with two mold halves
that mirror the diffusion layers 22 and 24.
[0052] The mold includes protruding features that mirror the high
density regions 44. The protruding features extend from both halves
of the mold to a distance equal to the difference in thickness
between the high density region 44 and the low density regions 42
and 46. Therefore, when the mold halves are closed and heat is
applied, the protruding regions compress the first and second
diffusion layers 22 and 24 at the high density regions 44.
Compressing the first and second diffusion layers 22 and 24
increases the density of the diffusion layers 22 and 24 to form the
high density regions 44.
[0053] The mold halves each further include an annular recess that
extends about the perimeter of the mold and mirrors the areas where
the MEA manifold ports 30 are to be formed. When the mold halves
are closed the recesses form a cavity at the low density regions
42, at the portion of the membrane 26 that protrudes from between
the first and second diffusion layers 22 and 24, and form cavities
in the areas where the MEA manifold ports 30 are to be formed. The
cavity at the low density regions includes an inner chamber and an
outer chamber. The inner chamber receives the low density region 42
and the protruding portion of the membrane 26. The outer chamber is
laterally spaced apart from the first and second diffusion layers
22 and 24. The inner chamber is smaller than the outer chamber.
[0054] To form the seal 28 and the MEA ports 30 the elastomer is
heated to a liquid and is injected within the mold cavities formed
by the recesses present in each mold half. The liquid elastomer
flows within, or impregnates, the porous diffusion layers 22 and 24
at the outboard low density regions 42. Impregnation of the
diffusion layers 22 and 24 with the liquid elastomer is enhanced
due to the decreased density of the low density regions 42, as
compared to the high density regions 44.
[0055] The inner and outer chambers receive the heated elastomer to
form the inner and outer seal beads 54a and 54b respectively. The
smaller volume of the inner chamber provides the inner bead 54a
with a smaller volume or radius than the outer seal bead 54b.
[0056] The high density regions 44 are advantageous because they
restrict passage of the liquid elastomer. Compressing the diffusion
layers 22 and 24 in this region 44 presses the fibers of the
diffusion layers 22 and 44 closer together and closes the pores
between the fibers. Therefore, no passages are available through
the high density regions 44 and the liquid elastomer is confined to
the low density regions 42. Restricting the elastomer to the low
density regions 42 keeps the elastomer out of the inboard regions
38 and the active areas where the presence of the elastomer may
render the MEA 16 inactive.
[0057] The elastomer is next heat cured solid to form the seal 28
and the MEA ports 30. The portion of the elastomer impregnated
within the diffusion layers 22 and 24 hardens to form a mechanical
interlock between the seal 28 and the diffusion layers 22 and 24.
This mechanical interlock greatly enhances the sealing properties
of the seal 28. The hardened seal 28 also exerts pressure on the
portion of the membrane 26 that protrudes within the seal 28 to
increase the effectiveness of the seal 28 about the membrane
26.
[0058] The completed MEA 16 is next secured between the support
plates 12 and 14 to complete the fuel cell 10. The MEA 16 is
orientated such that the manifold ports 18 of the support plates 12
and 14 are aligned with the MEA manifold ports 30. The MEA 16 is
held in place between the support plates 12 and 14 by an external
loading mechanism that is known in the art (not shown).
[0059] Multiple fuel cells 10 can be combined to form a fuel cell
stack (not shown), as is known to those skilled in the art. In a
fuel cell stack, the electrical output of each fuel cell 10 is
combined to increase the voltage potential.
[0060] The operation of the fuel cell 10 will now be described.
Hydrogen is supplied to the first support plate 12 through one of
the manifold ports 18a of the first plate 12. Oxygen is supplied to
the second support plate 14 through one of the manifold ports 18b
of the second plate 14. To cool the fuel cell 10, coolant can be
supplied to one or both of the plates 12 and 14 through the
manifold ports 18. The hydrogen and oxygen are distributed through
different ports 18 to insure that the hydrogen and oxygen remain
separate. The MEA manifold ports 30 provide a channel for the
passage of gas past the MEA 16, which is particularly useful when
the fuel cell 10 is part of a fuel cell stack to permit the
distribution of oxygen, hydrogen, and air across the different fuel
cells 10.
[0061] Hydrogen supplied to the first plate 12 via the ports 18a
travels throughout the flow field channels 20a where the hydrogen
is distributed to the first gas diffusion layer 22. Therefore, the
first diffusion layer 22 serves as the anode. Oxygen supplied to
the second plate 14 via the ports 18b travels throughout the flow
field channels 20b where the oxygen is distributed to the second
diffusion layer 24. Therefore, the second gas diffusion layer 24
serves as the cathode.
[0062] The hydrogen gas (H.sub.2) diffuses through the first
diffusion layer 22 where it reacts with the catalyst. The reaction
with the catalyst yields two H.sup.+ ions and two electrons. The
electrons are conducted via the first diffusion layer 22 to a
circuit to provide current to the circuit. The current can be used
for a variety of purposes, such as to power and turn a motor. The
electrons are directed via the circuit to the second diffusion
layer 24.
[0063] Simultaneously, the oxygen gas (O.sub.2) supplied to the
second diffusion layer 24 reacts with the catalyst to yield two
oxygen atoms. The oxygen atoms have a strong negative charge. This
negative charge attracts the H.sup.+ ions through the membrane 26.
The H.sup.+ ions bond with an oxygen atom and two of the electrons
from the circuit to form a water molecule (H.sub.2O).
[0064] The membrane 26 isolates the hydrogen and oxygen molecules
to prevent a reaction between the two. The portion of the membrane
26 that extends beyond the first and second diffusion layers 22
prevents migration of oxygen and/or hydrogen around the side
surfaces 36, thereby further isolating the hydrogen and oxygen.
[0065] The seal 28 also helps to isolate the hydrogen and oxygen
and prevent escape of these gases into the surrounding atmosphere.
As illustrated in FIG. 4, the seal 28 covers and seals the
diffusion layers 22 and 24 at the low density regions 42. The seal
is impregnated within the outer surfaces 34 and the side surfaces
36 of each of the diffusion layers 22 and 24. The seal 28 also
applies a compression force to the portion of the ion exchange
membrane 26 that extends beyond the first and second diffusion
layers 22 and 24.
[0066] The position of the seal 28 over the membrane 26 prevents
cross migration of oxygen and gas between the first and second
layers 22 and 24 around the membrane 26. Impregnation of the inner
seal bead 54a within the diffusion layers 22 at the impregnation
region 52 prevents hydrogen and oxygen from escaping from the MEA
16 into the surrounding atmosphere. The outer bead 54b provides
redundancy to further prevent the escape of hydrogen and oxygen
into the atmosphere.
[0067] In some applications, the inner seal bead 54a is smaller
than the outer bead 54b. More specifically, the inner bead 54b can
have a smaller radius than the outer bead 54b, as illustrated in
the cross-sectional view of FIG. 4. Providing an inner bead 54a
with a smaller radius than the outer bead 54b is advantageous
because it allows the inner bead 54a to fit between the two support
plates 12 and 14 without being damaged. Further, because the inner
bead 54a is of a reduced size, it is not subject to as much
movement or disruption from external forces as a larger bead is
subject to, thereby preserving the integrity of the inner bead 54a
and the integrity of the interlock between the inner bead 54a and
the diffusion layers 22 and 24.
[0068] The description of the invention is merely exemplary in
nature and, thus, variations that do not depart from the gist of
the invention are intended to be within the scope of the invention.
Such variations are not to be regarded as a departure from the
spirit and scope of the invention.
* * * * *