U.S. patent application number 17/346481 was filed with the patent office on 2022-06-23 for gas diffusion layer for fuel cell, method of manufacturing the same, and unit cell for fuel cell including the same.
The applicant listed for this patent is Hyundai Motor Company, Kia Corporation. Invention is credited to Ji Han Lee, Seung Tak Noh, Jae Man Park.
Application Number | 20220200017 17/346481 |
Document ID | / |
Family ID | 1000005697031 |
Filed Date | 2022-06-23 |
United States Patent
Application |
20220200017 |
Kind Code |
A1 |
Lee; Ji Han ; et
al. |
June 23, 2022 |
Gas Diffusion Layer for Fuel Cell, Method of Manufacturing the
Same, and Unit Cell for Fuel Cell Including the Same
Abstract
A gas diffusion layer for a fuel cell constituting a unit cell
of the fuel cell includes a base layer including short carbon
fibers and having a reinforcing portion formed in a predetermined
area thereof in a thickness direction with continuous carbon fibers
oriented in the reinforcing portion. One method of manufacturing
the gas diffusion layer includes preparing a mixed dispersion in
which short carbon fibers are mixed, orienting continuous carbon
fibers on a conveyor belt, forming a paper having a reinforcing
portion in which the continuous carbon fibers are oriented by
supplying the prepared mixed dispersion to the conveyor belt on
which the continuous carbon fibers are oriented, and forming a base
layer by impregnating the paper with a hydrophobic agent.
Inventors: |
Lee; Ji Han; (Seongnam-si,
KR) ; Park; Jae Man; (Yongin-si, KR) ; Noh;
Seung Tak; (Suwon-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hyundai Motor Company
Kia Corporation |
Seoul
Seoul |
|
KR
KR |
|
|
Family ID: |
1000005697031 |
Appl. No.: |
17/346481 |
Filed: |
June 14, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 8/1004 20130101;
H01M 8/0234 20130101; H01M 8/0245 20130101 |
International
Class: |
H01M 8/0234 20060101
H01M008/0234; H01M 8/1004 20060101 H01M008/1004; H01M 8/0245
20060101 H01M008/0245 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2020 |
KR |
10-2020-0181244 |
Claims
1. A gas diffusion layer for a fuel cell constituting a unit cell
of the fuel cell, the gas diffusion layer comprising: a base layer
including short carbon fibers and having a reinforcing portion
formed in a predetermined area thereof in a thickness direction
with continuous carbon fibers oriented in the reinforcing
portion.
2. The gas diffusion layer of claim 1, wherein the continuous
carbon fibers of the reinforcing portion formed in the base layer
are oriented in one direction along a plane perpendicular to the
thickness direction, while being spaced apart from each other.
3. The gas diffusion layer of claim 1, wherein each of the
continuous carbon fibers of the reinforcing portion has a diameter
of 6 to 12 .mu.m.
4. The gas diffusion layer of claim 3, wherein: the continuous
carbon fibers of the reinforcing portion are formed in bundles,
each of the bundles including a plurality of the continuous carbon
fibers; and each of the bundles of the continuous carbon fibers has
a thickness of 50% or less of a total thickness of the base
layer.
5. The gas diffusion layer of claim 4, wherein each of the bundles
of the continuous carbon fibers in the reinforcing portion is
spaced apart from an adjacent bundle of the continuous carbon
fibers at a distance of 2 to 20 mm.
6. The gas diffusion layer of claim 1, wherein the reinforcing
portion is formed adjacent to a first surface of the base
layer.
7. The gas diffusion layer of claim 6, further comprising a micro
porous layer formed on a second surface of the base layer, wherein
the first surface of the base layer is opposite the second surface
of the base layer.
8. The gas diffusion layer of claim 6, further comprising a micro
porous layer formed on the first surface of the base layer.
9. A method of manufacturing a gas diffusion layer for a fuel cell
constituting a unit cell of the fuel cell, the method comprising:
preparing a mixed dispersion in which short carbon fibers are
mixed; orienting continuous carbon fibers on a conveyor belt;
forming a paper having a reinforcing portion in which the
continuous carbon fibers are oriented by supplying the prepared
mixed dispersion to the conveyor belt on which the continuous
carbon fibers are oriented; and forming a base layer by
impregnating the paper with a hydrophobic agent.
10. The method of claim 9, wherein in the orienting of the
continuous carbon fibers, the continuous carbon fibers are oriented
in one direction, while being spaced apart from each other.
11. The method of claim 9, wherein: in the orienting of the
continuous carbon fibers, the continuous carbon fibers are prepared
in bundles, each of the bundles including a plurality of the
continuous carbon fibers, and the bundles of the continuous carbon
fibers are oriented in close contact with or adjacent to a surface
of the conveyor belt; and in the forming of the paper, the mixed
dispersion is supplied to the surface of the conveyor belt at a
thickness greater than that of each of the bundles of the
continuous carbon fibers.
12. The method of claim 11, wherein in the forming of the paper,
the mixed dispersion is supplied at a thickness at least two times
greater than that of each of the bundles of the continuous carbon
fibers.
13. The method of claim 11, wherein: in the orienting of the
continuous carbon fibers, each of the continuous carbon fibers
forming the bundles has a diameter of 6 to 12 .mu.m; and each of
the bundles of the continuous carbon fibers is spaced apart from an
adjacent bundle of the continuous carbon fibers at a distance of 2
to 20 mm.
14. The method of claim 11, further comprising, after the forming
of the base layer, forming a micro porous layer by applying a
slurry in which a hydrophobic agent is mixed with carbon-based
powder onto a first surface of the base layer, wherein the first
surface is opposite a second surface of the base layer on which the
reinforcing portion is formed.
15. The method of claim 11, further comprising, after the forming
of the base layer, forming a micro porous layer by applying a
slurry in which a hydrophobic agent is mixed with carbon-based
powder onto a surface of the base layer on which the reinforcing
portion is formed.
16. A unit cell for a fuel cell, the unit cell comprising: a
membrane-electrode assembly; a pair of gas diffusion layers
disposed on outer surfaces of the membrane-electrode assembly,
respectively, wherein each of the gas diffusion layers includes a
base layer including short carbon fibers and having a reinforcing
portion formed in a predetermined area thereof in a thickness
direction with continuous carbon fibers oriented in the reinforcing
portion; and a pair of flow field type separators disposed on outer
sides of the gas diffusion layers, respectively, and bent so that
lands and channels are alternately formed.
17. The unit cell of claim 16, wherein the continuous carbon fibers
of the reinforcing portion formed in the base layers of the gas
diffusion layers are oriented in one direction, while being spaced
apart from each other.
18. The unit cell of claim 17, wherein: the lands and the channels
formed in the separators are formed to be aligned in one direction;
and a direction in which the continuous carbon fibers of the
reinforcing portion are oriented is kept at an angle of 45 to
90.degree. with respect to the direction in which the lands and the
channels of the separators are formed.
19. The unit cell of claim 16, wherein: the base layers of the gas
diffusion layers are disposed to face the separators; the gas
diffusion layers further include a micro porous layer formed on a
first surface of the base layers facing the membrane-electrode
assembly; and the reinforcing portions of the gas diffusion layers
are formed adjacent to a second surface of the base layers facing
the separators.
20. The unit cell of claim 16, wherein: the base layers of the gas
diffusion layers are disposed to face the separators; the gas
diffusion layers further include a micro porous layer formed on a
first surface of the base layers facing the membrane-electrode
assembly; and the reinforcing portions of the gas diffusion layers
are formed adjacent to the first surface of the base layer facing
the micro porous layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Korean Patent
Application No. 10-2020-0181244, filed on Dec. 22, 2020, which
application is hereby incorporated herein by reference.
TECHNICAL FIELD
[0002] The present disclosure relates to a gas diffusion layer for
a fuel cell, a method of manufacturing the same, and a unit cell
for a fuel cell including the same.
BACKGROUND
[0003] A fuel cell, which is a kind of power generation device
electrochemically reacting chemical energy of fuel in a stack to
convert the chemical energy into electrical energy, can be used for
industrial and household purposes, and used to not only supply
power for driving a vehicle but also supply power to a small
electronic product such as a portable device. Recently, the
applicable fields of the fuel cell have increasingly expanded
because the fuel cell is a highly efficient clean energy
source.
[0004] FIG. 1 is a view showing a typical unit cell for a fuel
cell.
[0005] As can be seen from FIG. 1, a membrane-electrode assembly
(MEA) 10 is located on the innermost area of the typical unit cell
for a fuel cell. The membrane-electrode assembly 10 includes a
polymer electrolyte membrane ii capable of moving hydrogen cations
(protons), and catalyst layers coated on both surfaces of the
electrolyte membrane for hydrogen and oxygen to react, that is, an
anode electrode layer (anode) 12 and a cathode electrode layer
(cathode) 13.
[0006] In addition, gas diffusion layers (GDLs) 20 are stacked on
outer sides of the membrane-electrode assembly 10, that is, on
respective outer sides of the anode electrode layer 12 and the
cathode electrode layer 13, and separators 30, each having a flow
field formed to supply fuel and discharge water generated by the
reaction, are located on respective outer sides of the gas
diffusion layers 20.
[0007] The separator 30 is a flow field type separator. The flow
field type separator is bent so that lands 31 and channels 32 are
alternately formed, the lands 31 are supported by the gas diffusion
layer 20, and reaction gas flows through the channels 32. In this
case, the lands 31 and the channels 32 are formed to be aligned in
one direction along a reaction gas flow direction.
[0008] Meanwhile, the gas diffusion layer 20 is formed by forming a
micro porous layer (MPL) 22 on a base layer 21 made of carbon
fibers.
[0009] In this case, the base layer 21 is generally formed by
impregnating a carbon fiber paper with a hydrophobic agent such as
polytetrafluoroethylene (PTFE). As an example of the carbon fiber
paper, carbon paper, carbon cloth, or the like may be used.
[0010] In addition, the micro porous layer 22 may be manufactured
by mixing a hydrophobic agent such as PTFE with carbon powder such
as carbon black, acetylene black carbon, or black pearls carbon,
and then coated on one surface or both surfaces of the base layer
21 according to the purpose of use.
[0011] Meanwhile, the carbon fiber base of the base layer 21 is
formed in a paper type by forming a paper from short carbon fibers
dispersed in an aqueous solution on a conveyor belt. As a result,
the short carbon fibers are randomly oriented in a two-dimensional
(2D) direction. Subsequently, a binder is heat-treated, the carbon
fiber paper is impregnated with a hydrophobic agent, and the carbon
fiber paper is carbonized to form the base layer.
[0012] However, when the base layer is manufactured by a roll to
roll process according to a conventional method, there has been a
problem that the base layer is easily fractured by a small impact
or depending on roll driving conditions. The fracture of the base
layer causes a problem that the production process yield and
product quality deteriorate.
[0013] In particular, when a gas diffusion layer is formed as a
thin film according to the demand for making a fuel cell in a small
size, the fracture problem of the base layer has occurred more
easily. For this reason, it has been difficult to secure mass
productivity in manufacturing the gas diffusion layer to have a
thickness of 150 .mu.m or less.
[0014] The contents described as the related art have been provided
only to assist in understanding the background of the present
disclosure and should not be considered as corresponding to the
related art known to those having ordinary skill in the art.
SUMMARY
[0015] The present disclosure relates to a gas diffusion layer for
a fuel cell, a method of manufacturing the same, and a unit cell
for a fuel cell including the same. Particular embodiments relate
to a gas diffusion layer for a fuel cell having a continuous
reinforcing portion, a method of manufacturing the same, and a unit
cell for a fuel cell including the same.
[0016] An embodiment of the present disclosure provides a gas
diffusion layer for a fuel cell having a continuous reinforcing
portion, a method of manufacturing the same, and a unit cell for a
fuel cell including the same.
[0017] According to an embodiment of the present disclosure, a gas
diffusion layer for a fuel cell constituting a unit cell of the
fuel cell includes a base layer including short carbon fibers and
having a reinforcing portion formed in a predetermined area thereof
in a thickness direction with continuous carbon fibers oriented in
the reinforcing portion.
[0018] The continuous carbon fibers of the reinforcing portion
formed in the base layer may be oriented in one direction along a
plane perpendicular to the thickness direction, while being spaced
apart from each other.
[0019] Each of the continuous carbon fibers of the reinforcing
portion may have a diameter of 6 to 12 .mu.m.
[0020] The continuous carbon fibers of the reinforcing portion may
be formed in bundles, each including a plurality of continuous
carbon fibers, and each of the bundles of continuous carbon fibers
may have a thickness of 50% or less of a total thickness of the
base layer.
[0021] Each of the bundles of continuous carbon fibers in the
reinforcing portion may be spaced apart from an adjacent bundle of
continuous carbon fibers at a distance of 2 to 20 mm.
[0022] The reinforcing portion may be formed adjacent to a surface
of the base layer.
[0023] The gas diffusion layer may further include a micro porous
layer formed on one surface of the base layer, and the reinforcing
portion may be formed adjacent to a surface opposite to the surface
on which the micro porous layer is formed.
[0024] The gas diffusion layer may further include a micro porous
layer formed on one surface of the base layer, and the reinforcing
portion may be formed adjacent to the surface on which the micro
porous layer is formed.
[0025] According to another embodiment of the present disclosure, a
method of manufacturing a gas diffusion layer for a fuel cell
constituting a unit cell of the fuel cell includes preparing a
mixed dispersion in which short carbon fibers are mixed, orienting
continuous carbon fibers on a conveyor belt, forming a paper having
a reinforcing portion in which the continuous carbon fibers are
oriented by supplying the prepared mixed dispersion to the conveyor
belt on which the continuous carbon fibers are oriented, and
forming a base layer by impregnating the paper with a hydrophobic
agent.
[0026] In the orienting of the continuous carbon fibers, the
continuous carbon fibers may be oriented in one direction, while
being spaced apart from each other.
[0027] In the orienting of the continuous carbon fibers, the
continuous carbon fibers may be prepared in bundles, each including
a plurality of continuous carbon fibers, and the bundles of
continuous carbon fibers may be oriented in close contact with or
adjacent to a surface of the conveyor belt. In the forming of the
paper, the mixed dispersion may be supplied to the surface of the
conveyor belt at a thickness greater than that of each of the
bundles of continuous carbon fibers.
[0028] In the forming of the paper, the mixed dispersion may be
supplied at a thickness at least two times greater than that of
each of the bundles of continuous carbon fibers.
[0029] In the orienting of the continuous carbon fibers, each of
the continuous carbon fibers forming the bundles may have a
diameter of 6 to 12 .mu.m, and each of the bundles of continuous
carbon fibers may be spaced apart from an adjacent bundle of
continuous carbon fibers at a distance of 2 to 20 mm.
[0030] The method may further include, after the forming of the
base layer, forming a micro porous layer by applying a slurry in
which a hydrophobic agent is mixed with carbon-based powder onto
one surface of the base layer. In the forming of the micro porous
layer, the slurry may be applied onto a surface opposite to a
surface of the base layer on which the reinforcing portion is
formed.
[0031] The method may further include, after the forming of the
base layer, forming a micro porous layer by applying a slurry in
which a hydrophobic agent is mixed with carbon-based powder onto
one surface of the base layer. In the forming of the micro porous
layer, the slurry may be applied onto a surface of the base layer
on which the reinforcing portion is formed.
[0032] According to another embodiment of the present disclosure, a
unit cell for a fuel cell includes a membrane-electrode assembly
(MEA), a pair of gas diffusion layers (GDLs) disposed on both
surfaces of the membrane-electrode assembly, respectively, and a
pair of flow field type separators disposed on respective outer
sides of the gas diffusion layers and bent so that lands and
channels are alternately formed, wherein each of the gas diffusion
layers includes a base layer including short carbon fibers and
having a reinforcing portion formed in a predetermined area thereof
in a thickness direction with continuous carbon fibers oriented in
the reinforcing portion.
[0033] The continuous carbon fibers of the reinforcing portion
formed in the base layer of the gas diffusion layer may be oriented
in one direction, while being spaced apart from each other.
[0034] The lands and the channels formed in the separator may be
formed to be aligned in one direction, and a direction in which the
continuous carbon fibers of the reinforcing portion are oriented
may be kept at an angle of 45 to 90.degree. with respect to a
direction in which the lands and channels of the separator are
formed.
[0035] The base layer of the gas diffusion layer may be disposed to
face the separator, the gas diffusion layer may further include a
micro porous layer formed on one of both surfaces of the base layer
facing the membrane-electrode assembly (MEA), and the reinforcing
portion of the gas diffusion layer may be formed adjacent to the
other one of both surfaces of the base layer facing the
separator.
[0036] The base layer of the gas diffusion layer may be disposed to
face the separator, the gas diffusion layer may further include a
micro porous layer formed on one of both surfaces of the base layer
facing the membrane-electrode assembly (MEA), and the reinforcing
portion of the gas diffusion layer is formed adjacent to the one of
both surfaces of the base layer facing the micro porous layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is a view showing a typical unit cell for a fuel
cell.
[0038] FIGS. 2 and 3 are views showing a gas diffusion layer for a
fuel cell according to an embodiment of the present disclosure.
[0039] FIG. 4 is a view showing a gas diffusion layer for a fuel
cell according to another embodiment of the present disclosure.
[0040] FIG. 5 is a view for explaining a process of manufacturing
the gas diffusion layer for a fuel cell according to an embodiment
of the present disclosure.
[0041] FIGS. 6A to 8B are views for comparing the unit cell for a
fuel cell according to an embodiment of the present disclosure with
the typical unit cell for a fuel cell.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0042] Hereinafter, embodiments of the present disclosure will be
described in more detail with reference to the accompanying
drawings. However, the present disclosure is not limited to the
embodiments to be described below and may be implemented in
variously different forms. The embodiments are provided to complete
the present disclosure and for those skilled in the art to
completely understand the scope of the present disclosure. In the
drawings, like reference numerals denote like components.
[0043] FIGS. 2 and 3 are views showing a gas diffusion layer for a
fuel cell according to an embodiment of the present disclosure.
[0044] As illustrated in FIGS. 2 and 3, a gas diffusion layer 100
for a fuel cell according to an embodiment of the present
disclosure includes a base layer 120 including short carbon fibers
121 and having a reinforcing portion no formed in a predetermined
area thereof in a thickness direction (x-axis direction) with
continuous carbon fibers 111 oriented in the reinforcing portion
110, and a micro porous layer 130 formed on one surface of the base
layer 120.
[0045] In this case, the micro porous layer 130 is formed to be
identical or similar to a general micro porous layer applied to a
typical gas diffusion layer. For example, the micro porous layer
130 is formed by applying a slurry, in which a hydrophobic agent
such as polytetrafluoroethylene (PTFE) is mixed with carbon-based
powder such as carbon black, onto one surface of the base layer
120. Then, the micro porous layer 130 is formed in such a manner
that some of the slurry applied remains on one surface of the base
layer 120 and the other of the slurry applied permeates into the
surface of the base layer 120 by a predetermined depth. The micro
porous layer 130 is not limited to the above-described embodiment,
and may be modified in various manners as long as micro pores are
formed to allow reaction gas to flow while being diffused
therethrough.
[0046] Meanwhile, the base layer 120 is similar to a general base
layer manufactured by impregnating a base in the form of carbon
fiber paper or the like made of short carbon fibers 121 with a
hydrophobic agent such as PTFE for imparting hydrophobicity, but
the reinforcing portion no is formed in the predetermined area of
the base layer 120 in the thickness direction (x-axis direction)
with the continuous carbon fibers 111 oriented therein.
[0047] The continuous carbon fibers 111 constituting the
reinforcing portion 110 formed in the base layer 120 are preferably
oriented in one direction, while being spaced apart from each
other, so that tensile properties of the continuous fibers are
exhibited.
[0048] In this case, it is preferable that the direction in which
the continuous carbon fibers 111 are oriented is variously modified
depending on structures of the lands 31 and the channels 32 formed
in the separator 30. For example, the direction in which the
continuous carbon fibers 111 are oriented in the reinforcing
portion 110 is preferably kept at an angle of 45 to 90.degree. with
respect to a direction (y-axis direction) in which the lands 31 and
the channels 32 of the separator 30 are formed. Thus, the
continuous carbon fibers 111 may be oriented in the reinforcing
portion no in various directions, on a plane (y-z plane)
perpendicular to the thickness direction (x-axis direction),
depending on the structures of the lands 31 and the channels 32 of
the separator 30.
[0049] In addition, each of the continuous carbon fibers 111
forming the reinforcing portion 110 preferably has a diameter of 6
to 12 .mu.m. It is preferable to maintain the diameter of the
continuous carbon fiber in within the proposed range for smooth
diffusion and flow of reaction gas and generated water passing
through the base layer 120. In particular, it is more preferable
that the continuous carbon fiber in has a smaller diameter within
the proposed range. However, if the diameter of the continuous
carbon fiber 111 is smaller than 6 .mu.m, a desired level of
tensile properties is not achieved.
[0050] In addition, the continuous carbon fibers 111 in the
reinforcing portion 110 are most preferably used as single strands,
but may be formed and used in bundles, each including a plurality
of continuous carbon fibers 111, to express the tensile properties
of the continuous carbon fibers 111 at a desired level. In this
case, each of the bundles of continuous carbon fibers 111
preferably has a thickness d2 of 50% or less of a total thickness
of the base layer 120.
[0051] In addition, each of the bundles of continuous carbon fibers
111 in the reinforcing portion no is preferably kept spaced apart
from an adjacent bundle of continuous carbon fibers 111 at a
distance d1 of 2 to 20 mm. If the distance d1 between the bundles
of continuous carbon fibers 111, which are spaced apart from each
other, is smaller than 2 mm, the continuous carbon fibers 111 are
of high density, resulting in an increase in flow resistance of the
reaction gas and generated water. If the distance d1 between the
bundles of continuous carbon fibers 111, which are spaced apart
from each other, is greater than 20 mm, a mechanical stiffness
increasing effect of the reinforcing portion no is
insignificant.
[0052] Meanwhile, as illustrated in FIG. 3, the reinforcing portion
110 is preferably formed adjacent to a surface of the base layer
120.
[0053] In this case, the reinforcing portion 110 is preferably
formed adjacent to one of both surfaces of the base layer 120
opposite to the other one of both surfaces of the base layer 120 on
which the micro porous layer 130 is formed. When forming a fuel
cell stack, since the reinforcing portion 110 of the base layer 120
faces the separator 30, the base layer 120 reinforced by the
reinforcing portion no may be suppressed from intrusion into the
channels of the separator 30.
[0054] On the other hand, the location at which the reinforcing
portion is formed in the base layer may be changed.
[0055] FIG. 4 is a view showing a gas diffusion layer for a fuel
cell according to another embodiment of the present disclosure.
[0056] As illustrated in FIG. 4, like the gas diffusion layer in
the above-described embodiment, a gas diffusion layer 200 includes
a base layer 220 including short carbon fibers 221 and having a
reinforcing portion 210 formed in a predetermined area thereof in a
thickness direction (x-axis direction) with continuous carbon
fibers 211 in the reinforcing portion 210, and a micro porous layer
230 formed on one surface of the base layer 220.
[0057] However, concerning the reinforcing portion 210 formed
adjacent to a surface of the base layer 220, in this case, the
reinforcing portion 210 is formed adjacent to one of both surfaces
of the base layer 220 on which the micro porous layer 230 is
formed. Accordingly, when the gas diffusion layer 200 is
manufactured, the micro porous layer 230 can be formed relatively
uniformly, and it is possible to reduce damage to a
membrane-electrode assembly (MEA) caused by ends of the short
carbon fibers 221 forming the base layer 220. In addition, a pore
gradient is formed sequentially in a direction from the micro
porous layer 230 through the reinforcing portion 210 and the base
layer 220 to the separator 30, thereby smoothly discharging the
generated water and supplying the reaction gas.
[0058] Next, a unit cell to which the gas diffusion layer according
to embodiments of the present disclosure is applied will be
described.
[0059] Like a typical unit cell for a fuel cell, the unit cell for
a fuel cell to which the gas diffusion layer 100 having the
reinforcing portion no formed therein is applied includes a
membrane-electrode assembly 10; a pair of gas diffusion layers 100
disposed on both surfaces of the membrane-electrode assembly 10,
respectively; and a pair of flow field type separators 30 disposed
on respective outer sides of the gas diffusion layers 100 and bent
so that lands 31 and channels 32 are alternately formed.
[0060] In this case, as proposed in the above-described embodiment,
the gas diffusion layer 100 includes a base layer 120 including
short carbon fibers 121 and having a reinforcing portion 110 formed
in a predetermined area thereof in a thickness direction (x-axis
direction) with continuous carbon fibers 111 oriented in the
reinforcing portion no, and a micro porous layer 130 formed by
impregnating a surface of the base layer 120 with a slurry in which
a hydrophobic agent is mixed with carbon-based powder.
[0061] As the separator 30, a flow field type separator is applied.
For example, the separator 30 is bent so that the lands 31 and the
channels 32 are alternately formed, the lands 31 are supported by
the gas diffusion layer 100, and reaction gas flows through the
channels 32. In this case, the lands 31 and the channels 32 are
formed to be aligned in one direction along a reaction gas flow
direction.
[0062] In this case, a direction in which the continuous carbon
fibers 111 of the reinforcing portion 110 are oriented is
preferably kept at an angle of 45 to 90.degree. with respect to a
direction (y-axis direction) in which the lands 31 and the channels
32 of the separator 30 are formed. When forming a fuel cell stack,
since the continuous carbon fibers 111 of the reinforcing portion
110 are disposed to cross the channels 32 of the separator 30, the
base layer 120 may be suppressed from intrusion into the channels
32 of the separator 30.
[0063] If the angle between the direction in which the continuous
carbon fibers 111 of the reinforcing portion no are oriented and
the direction in which the lands 31 and the channels 32 of the
separator 30 are formed is smaller than 45.degree., the channels 32
of the separator 30 may be disposed to be aligned with the
direction in which the continuous carbon fibers 111 are oriented,
thereby causing a problem that the continuous carbon fibers 111
intrude into the channels 32 of the separator 30.
[0064] In addition, it is preferable that the base layer 120 of the
gas diffusion layer 100 is disposed to face the separator 30, and
the reinforcing portion no of the gas diffusion layer 100 is formed
adjacent to one of both surfaces of the base layer 120 facing the
separator 30. Since the base layer 120 is reinforced by the
reinforcing portion 110, the base layer 120 can be suppressed from
intrusion into the channels 32 of the separator 30.
[0065] Also, as in the above-described gas diffusion layer 200
according to another embodiment, the base layer 220 of the gas
diffusion layer 200 may be disposed to face the separator 30, and
the reinforcing portion 210 of the gas diffusion layer 200 may be
formed adjacent to one of both surfaces of the base layer 120
facing the micro porous layer 230. Accordingly, a pore gradient may
be formed sequentially in the direction from the micro porous layer
230 through the reinforcing portion 210 and the base layer 220 to
the separator 30.
[0066] Next, a method of manufacturing the above-described gas
diffusion layer will be described.
[0067] FIG. 5 is a view for explaining a process of manufacturing
the gas diffusion layer for a fuel cell according to an embodiment
of the present disclosure.
[0068] A method of manufacturing a gas diffusion layer according to
an embodiment of the present disclosure includes preparing a mixed
dispersion 121a in which short carbon fibers 121 are mixed,
orienting continuous carbon fibers 111 on a conveyor belt 1,
forming a paper having a reinforcing portion 110 in which the
continuous carbon fibers 111 are oriented by supplying the prepared
mixed dispersion 121a to the conveyor belt 1 on which the
continuous carbon fibers 111 are oriented, forming a base layer 120
by impregnating the paper with a hydrophobic agent, and forming a
micro porous layer 130 by applying a slurry in which a hydrophobic
agent is mixed with carbon-based powder onto a surface of the base
layer 120.
[0069] The preparing of the mixed dispersion is preparing a mixed
dispersion 121a in which short carbon fibers 121 are dispersed to
form a base layer 120. The mixed dispersion 121a is prepared by
mixing short carbon fibers 121, a binder, and a dispersant in a
solvent.
[0070] In this case, water may be used as the solvent, and
PAN-based short carbon fibers each having a length of 6 mm or 12 mm
are used as the short carbon fibers 121. Further, a PVA-based
binder is used as the binder.
[0071] The mixed dispersion 121a prepared in this way is filled
into a hopper 3 provided above the conveyor belt 1.
[0072] The orienting of the continuous carbon fibers 111 is
orienting continuous carbon fibers 111 in one direction to
manufacture a reinforcing portion 110 to be formed in the base
layer 120. In this case, continuous carbon fibers 111 are unwound
from a winding roll 2 around which the continuous carbon fibers 111
are wound, and the unwound continuous carbon fibers 111 are
oriented in one direction in close contact with or adjacent to a
surface of the conveyor belt 1 while being spaced apart from each
other.
[0073] Here, the continuous carbon fibers 111 are most preferably
oriented as single strands, but may be formed in bundles, each
including a plurality of continuous carbon fibers in, and supplied
to the conveyor belt 1.
[0074] In this case, each of the continuous carbon fibers 111
forming the bundles has a diameter of 6 to 12 .mu.m, and the
continuous carbon fibers 111 are oriented so that each of the
bundles of continuous carbon fibers 111 is spaced apart from an
adjacent bundle of continuous carbon fibers 111 at a distance of 2
to 20 mm.
[0075] In forming of the paper, the mixed dispersion 121a is
supplied from the hopper 3 provided above the conveyor belt 1 to
the surface of the conveyor belt 1 on which the continuous carbon
fibers 111 are oriented. In this case, the mixed dispersion 121a is
preferably supplied at a thickness greater than that of each of the
bundles of continuous carbon fibers 111. More preferably, the mixed
dispersion 121a is supplied at a thickness at least two times
greater than that of each of the bundles of continuous carbon
fibers 111.
[0076] After supplying the mixed dispersion 121a, in which the
short carbon fibers 121 are mixed, to the continuous carbon fibers
111 as described above, the mixed dispersion 121a is dried so that
the short carbon fibers 121 and the continuous carbon fibers 111
are bound to each other, while the short carbon fibers 121 mixed in
the mixed dispersion 121a are primarily bound together, thereby
forming the paper. The formed paper may be cut to a desired
size.
[0077] The forming of the base layer 120 is forming a base layer
120 in which the reinforcing portion no is formed. In forming of
the base layer 120, first of all, the paper, that is, a carbon
fiber web, is impregnated with a resin in which an inorganic filler
is mixed, such that the short carbon fibers 121 mixed therein are
secondarily bound together. Thereafter, the paper is carbonized
through heat treatment at a temperature of about 1200 to
1400.degree. C. Subsequently, in order to increase carbon
crystallinity of carbon components constituting the paper, the
carbon components are graphitized by additionally heat-treating the
paper at a temperature of 2000 to 2400.degree. C.
[0078] The paper graphitized in this way is impregnated with a
hydrophobic agent such as PTFE.
[0079] Thereafter, heat treatment is performed at a temperature
corresponding to a melting point or higher of PTFE, e.g. about
350.degree. C., to activate PTFE, thereby forming a base layer with
water repellency imparted to the paper.
[0080] The forming of the micro porous layer 130 is forming a micro
porous layer 130 by applying a slurry in which a hydrophobic agent
is mixed with carbon-based powder onto a surface of the base layer
120. First, the slurry is prepared by mixing carbon-based powder
such as carbon black and a hydrophobic agent such as PTFE in a
solvent. The prepared slurry is applied onto the surface of the
base layer 120, and then the slurry is dried to form a micro porous
layer 130 on the surface of the base layer 120.
[0081] Thereafter, heat treatment is performed at a temperature
corresponding to a melting point or higher of PTFE, e.g. about
350.degree. C., to activate PTFE, thereby imparting water
repellency to the base layer 120 and the micro porous layer
130.
[0082] Meanwhile, in the forming of the micro porous layer 130, the
slurry may be applied onto a surface opposite to the surface of the
base layer 120 on which the reinforcing portion 110 is formed, or
applied onto the surface of the base layer 120 on which the
reinforcing portion no is formed.
[0083] Next, the unit cell for a fuel cell in which the
reinforcement portion is formed in the base layer according to an
embodiment of the present disclosure will be compared with the
typical unit cell for a fuel cell in which no reinforcement portion
is formed in the base layer.
[0084] FIGS. 6A to 8B are views for comparing the unit cell for a
fuel cell according to an embodiment of the present disclosure with
the typical unit cell for a fuel cell. In this case, FIGS. 6A, 7A,
and 8A are views showing the typical unit cell for a fuel cell in
which no reinforcement portion is formed in the base layer, and
FIGS. 6B, 7B, and 8B are views showing the unit cell for a fuel
cell in which the reinforcement portion is formed in the base layer
according to an embodiment of the present disclosure. In addition,
FIGS. 7A and 7B show cross-sections cut along line A-A' of FIGS. 6A
and 6B, respectively, and FIGS. 8A and 8B show cross-sections cut
along line B-B' of FIGS. 6A and 6B, respectively.
[0085] As illustrated in FIG. 6B, the membrane-electrode assembly
10, the gas diffusion layer 100, and the separator 30 are
sequentially stacked in the unit cell for a fuel cell. In this
case, the base layer 120 forming the gas diffusion layer 100 faces
the separator 30, and the micro porous layer 130 faces the
membrane-electrode assembly 10. In addition, as the separator 30, a
flow field type separator in which lands 31 and channels 32 are
formed is applied.
[0086] In particular, in the gas diffusion layer 100 of the unit
cell for a fuel cell according to an embodiment of the present
disclosure, as illustrated in FIG. 6B, the reinforcing portion 110
including the continuous carbon fibers 111 oriented in one
direction is disposed adjacent to a surface of the base layer 120
facing the separator 30.
[0087] In the unit cell for a fuel cell according to an embodiment
of the present disclosure, the gas diffusion layer 100 and the
separator 30 are stacked so that the direction in which the
continuous carbon fibers 111 are oriented is kept at an angle of
90.degree., that is orthogonal, with respect to the direction
(y-axis direction) in which the channels 32 of the separator 30 are
formed.
[0088] As illustrated in FIG. 7A, in the typical unit cell for a
fuel cell, while the gas diffusion layer 20 is stacked to face the
separator 30, the base layer 21 partially intrudes into the
channels of the separator 30 (I), resulting in a deformation of the
gas diffusion layer 20. The deformation of the gas diffusion layer
20 causes a differential pressure between the channels 32,
resulting in a problem that the performance of the fuel cell stack
deteriorates.
[0089] On the other hand, as illustrated in FIG. 7B, in the unit
cell for a fuel cell according to an embodiment of the present
disclosure, while the gas diffusion layer 100 is stacked to face
the separator 30, the reinforcing portion no formed in the base
layer 120 of the gas diffusion layer 100 suppresses the base layer
120 from partially intruding into the channels 32 of the separator
30, thereby preventing a differential pressure between the channels
32.
[0090] In addition, as illustrated in FIG. 8A, in the typical unit
cell for a fuel cell, when the base layer 21 of the gas diffusion
layer 20 and the channels 32 of the separator 30 are in contact
with each other, a separate water discharge passage for the
generated water is not formed. In contrast, as illustrated in FIG.
8B, in the unit cell for a fuel cell according to an embodiment of
the present disclosure, a passage for discharging the generated
water W is formed in a space between the continuous carbon fibers
111 forming the reinforcing portion 110, which are spaced apart
from each other. Thus, it is possible to expect an inducing effect
for the generated water W to be smoothly discharged.
[0091] According to the embodiments of the present disclosure, the
following effects can be expected.
[0092] First, due to the tensile properties of the continuous
carbon fibers applied to the reinforcing portion, it is easy to
produce a base in a roll type with excellent handling properties,
thereby increasing a production yield in the gas diffusion layer
manufacturing process and lowering a failure rate in the stack
formation process. As a result, productivity can be increased and
cost can be reduced.
[0093] Second, the reinforcing portion formed in the base layer
increases a shear strength of the gas diffusion layer. Thus, even
if the base layer for the gas diffusion layer is manufactured to
have a thickness of 100 .mu.m or less, no fracture occurs.
Accordingly, mass productivity can be secured in manufacturing gas
diffusion layers as thin-film in a roll to roll type.
[0094] Third, by stacking the gas diffusion layer and the separator
so that the angle between the direction in which the continuous
carbon fibers of the reinforcing portion formed in the base layer
are oriented and the direction in which the lands and the channels
of the flow field type separator are formed is kept within the
range of 45 to 90.degree., when forming a fuel cell stack, the gas
diffusion layer can be suppressed from intrusion into the channels
of the separator, thereby reducing a differential pressure between
the channels. As a result, the performance of the fuel cell stack
can be improved.
[0095] Fourth, by stacking the gas diffusion layer and the
separator so that the angle between the direction in which the
continuous carbon fibers of the reinforcing portion formed in the
base layer are oriented and the direction in which the lands and
the channels of the flow field type separator are formed is kept
within the range of 45 to 90.degree., a surface pressure against
reaction formed in the channels of the separator can be increased,
thereby reducing a contact resistance. As a result, the performance
of the fuel cell stack can be improved.
[0096] Although the present disclosure has been shown and described
with respect to specific embodiments, it will be apparent to those
having ordinary skill in the art that the present disclosure may be
variously modified and altered without departing from the spirit
and scope of the present disclosure as defined by the following
claims.
* * * * *