U.S. patent application number 12/006336 was filed with the patent office on 2009-05-07 for membrane electrode assembly and method for making the same.
This patent application is currently assigned to Tsinghua University. Invention is credited to Shou-Shan Fan, Chang-Hong Liu.
Application Number | 20090117437 12/006336 |
Document ID | / |
Family ID | 40588393 |
Filed Date | 2009-05-07 |
United States Patent
Application |
20090117437 |
Kind Code |
A1 |
Liu; Chang-Hong ; et
al. |
May 7, 2009 |
Membrane electrode assembly and method for making the same
Abstract
The present invention relates to a membrane electrode assembly.
The proton exchange membrane includes two opposite surfaces. The
two electrodes are separately disposed on two the opposite surfaces
of the proton exchange membrane. The two electrodes are separately
disposed on two opposite surfaces of the proton exchange membrane.
Further, each electrode includes a catalyst layer and a gas
diffusion layer. The catalyst layer is configured for being
sandwiched between the gas diffusion layer and the proton exchange
membrane. The gas diffusion layer includes a carbon nanotube film.
The carbon nanotube film includes a plurality of carbon nanotubes
tangled with each other. And a method for making the membrane
electrode assembly is also included.
Inventors: |
Liu; Chang-Hong; (Bei-Jing,
CN) ; Fan; Shou-Shan; (Bei-Jing, CN) |
Correspondence
Address: |
PCE INDUSTRY, INC.;ATT. Steven Reiss
458 E. LAMBERT ROAD
FULLERTON
CA
92835
US
|
Assignee: |
Tsinghua University
Hon Hai Precision Industry Co., LTD.
|
Family ID: |
40588393 |
Appl. No.: |
12/006336 |
Filed: |
December 29, 2007 |
Current U.S.
Class: |
429/494 ;
101/129; 156/60; 264/299; 427/115; 977/742 |
Current CPC
Class: |
H01M 4/90 20130101; Y02P
70/50 20151101; H01M 4/9083 20130101; Y10T 156/10 20150115; H01M
2008/1095 20130101; H01M 8/0234 20130101; Y02E 60/50 20130101; H01M
8/1004 20130101 |
Class at
Publication: |
429/33 ; 264/299;
427/115; 156/60; 429/30; 101/129; 977/742 |
International
Class: |
H01M 8/10 20060101
H01M008/10; B05D 1/02 20060101 B05D001/02; B05D 1/18 20060101
B05D001/18; B41M 1/12 20060101 B41M001/12; B29C 39/00 20060101
B29C039/00; B32B 37/06 20060101 B32B037/06 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 2, 2007 |
CN |
200710124247.4 |
Claims
1. A membrane electrode assembly comprising: a proton exchange
membrane comprising two opposite surfaces; and two electrodes
disposing on the two opposite surfaces of the proton exchange
membrane, each electrode comprising a catalyst layer and a gas
diffusion layer, the catalyst layer configured for being sandwiched
between the gas diffusion layer and the proton exchange membrane,
and the gas diffusion layer comprising a carbon nanotube film, the
carbon nanotube film comprising a plurality of carbon nanotubes
entangled with each other.
2. The membrane electrode assembly as claimed in claim 1, wherein a
thickness of the carbon nanotube film is in an approximate range
from 1 micrometer to 2 millimeters, and a length of the carbon
nanotubes is above 10 micrometers.
3. The membrane electrode assembly as claimed in claim 1, wherein
the adjacent carbon nanotubes are combined and entangled by van der
Waals attractive force therebetween, thereby forming a network
structure/microporous structure.
4. The membrane electrode assembly as claimed in claim 3, wherein
the microporous structure comprises a plurality of micropores, and
a size of the micropores is less than 100 micrometers.
5. The membrane electrode assembly as claimed in claim 1, wherein
the carbon nanotubes in the carbon nanotube film are isotropic,
uniformly dispersed, and disorderly arranged.
6. The membrane electrode assembly as claimed in claim 1, wherein
the material of the proton exchange membrane is selected from the
group consisting of perfluorosulfonic acid, polystyrene sulfonic
acid, polystyrene trifluoroacetic acid, phenol formaldehyde resin
acid, and hydrocarbons.
7. The membrane electrode assembly as claimed in claim 1, wherein
the catalyst layer is composed of metal particles and carbon
particles.
8. The membrane electrode assembly as claimed in claim 7, wherein
the metal particles are selected from the group consisting of
platinum particles, gold particles, and ruthenium particles.
9. The membrane electrode assembly as claimed in claim 7, wherein
the carbon particles are selected from the group consisting of
graphite, carbon black, carbon fiber, and carbon nanotubes.
10. A method for making a membrane electrode assembly, the method
comprising the steps of: (a) fabricating a carbon nanotube film to
act as a gas diffusion layer; (b) forming a catalyst layer on the
carbon nanotube film to obtain an electrode; and (c) providing a
proton exchange membrane, and disposing two of the electrodes on
two opposite surfaces of the proton exchange membrane, thereby
forming the membrane electrode assembly.
11. The method as claimed in claim 10, wherein the fabricating
process of the carbon nanotube film comprises the substeps of: (a1)
providing a raw material of carbon nanotubes; (a2) adding the raw
material of carbon nanotubes to a solvent to get a floccule
structure; and (a3) separating the floccule structure from the
solvent, and shaping/molding the separated floccule structure to
obtain the carbon nanotube film.
12. The method as claimed in claim 11, wherein in step (a2), after
adding the raw material of carbon nanotubes to the solvent, a
process of flocculating is executed to get the floccule structure;
and the process of flocculating is selected from the group
consisting of ultrasonic dispersion and high-strength
agitating/vibrating.
13. The method as claimed in claim 11, wherein in step (a3), the
process of separating is executed by the substeps of: (a31) pouring
the solvent containing the floccule structure of carbon nanotubes
through a filter; and (a32) drying the floccule structure of carbon
nanotubes captured on the filter to obtain the separated floccule
structure of carbon nanotubes.
14. The method as claimed in claim 11, wherein in step (a3), the
process of shaping/molding is executed by the substeps of: (a33)
putting the separated floccule structure into a container, and
spreading the floccule structure to form a predetermined structure;
(a34) pressing the spread floccule structure to yield a desired
shape; and (a35) drying the spread floccule structure to remove the
residual solvent or volatilizing the residual solvent to form the
carbon nanotube film.
15. The method as claimed in claim 11, wherein the step (a3)
comprises a process of pumping filtration to obtain the carbon
nanotube film.
16. The method as claimed in claim 15, wherein the process of
pumping filtration comprises the substeps of: (a31') providing a
microporous membrane and an air-pumping funnel; (a32') filtering
the solvent containing the floccule structure of carbon nanotubes
through the microporous membrane into the air-pumping funnel; and
(a33') air-pumping and drying the floccule structure of carbon
nanotubes captured by the microporous membrane.
17. The method as claimed in claim 11, wherein in step (a3), a
process of cutting the carbon nanotube film is provided to form a
predetermined size of the gas diffusion layer.
18. The method as claimed in claim 10, wherein step (b) comprises
the substeps of: (b1) putting metal particles and carbon particles
into a dispersion solution; (b2) adding water and a surface active
agent to the dispersion solution to obtain a catalyst slurry; and
(b3) coating the catalyst slurry on the carbon nanotube film and
drying the catalyst slurry, thereby forming the catalyst layer on
the carbon nanotube film to obtain the electrode.
19. The method as claimed in claim 18, wherein in step (b3), the
process of coating is executed by a spraying method, an immersing
method, or a screen printing method.
20. The method as claimed in claim 10, wherein in step (c), the two
electrodes are attached on the two opposite surfaces of the proton
exchange membrane by a heat pressing process.
Description
[0001] This application is related to a commonly-assigned
application entitled, "MEMBRANE ELECTRODE ASSEMBLY AND METHOD FOR
MAKING THE SAME", filed ______ (Atty. Docket No. US17017).
Disclosure of the above-identified application is incorporated
herein by reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The invention generally relates to membrane electrode
assembly and method for making the same and, particularly, to a
carbon nanotube based membrane electrode assembly of a fuel cell
and method for making the same.
[0004] 2. Discussion of Related Art
[0005] Fuel cells can generally be classified into alkaline, solid
oxide, and proton exchange membrane fuel cells. The proton exchange
membrane fuel cell has received more attention and has developed
rapidly in recent years. Typically, the proton exchange membrane
fuel cell includes a number of separated fuel cell work units. Each
work unit includes a fuel cell membrane electrode assembly (MEA),
flow field plates (FFP), current collector plates (CCP), as well as
related support equipments, such as blowers, valves, and
pipelines.
[0006] The MEA generally includes a proton exchange membrane and
two electrodes separately disposed on two opposite surfaces of the
proton exchange membrane. Further, each electrode includes a
catalyst layer and a gas diffusion layer. The catalyst layer is
configured for being sandwiched between the gas diffusion layer and
the proton exchange membrane. The material of the proton exchange
membrane is selected from the group consisting of perfluorosulfonic
acid, polystyrene sulfonic acid, polystyrene trifluoroacetic acid,
phenol formaldehyde resin acid, and hydrocarbons. The catalyst
layer includes catalyst materials and carriers. The catalyst
materials are selected from the group consisting of metal
particles, such as platinum particles, gold particles, and
ruthenium particles. The carriers are generally carbon particles,
such as graphite, carbon black, carbon fiber or carbon nanotubes.
The gas diffusion layer is constituted of treated carbon cloth and
carbon paper.
[0007] The gas diffusion layer of MEA is mainly formed by a carbon
fiber paper. A process of making the carbon fiber paper is by the
steps of: mixing carbon fibers, wood pulp, and cellulose fibers;
using the mixture to obtain a paper pulp; and then forming the
carbon fiber paper from the paper pulp. However, the process of
making the carbon fiber paper has the following disadvantages:
Firstly, the carbon fibers in the carbon fiber paper are not
uniformly dispersed, thereby the gaps therein are uneven resulting
in the carbon fibers having a small specific surface area. Thus,
the structure restricts the gas diffusion layer to uniformly
diffuse the gases, which is needed for the MEA. Secondly, the
carbon fiber paper has high electrical resistance, thus,
restricting the transfer of electrons between the gas diffusion
layer and the external electrical circuit, thereby reducing the
reaction activity of the MEA. Thirdly, the carbon fiber paper has
poor tensile strength, and is difficult to process.
[0008] What is needed, therefore, is a membrane electrode assembly
having excellent reaction activity and method for making the same
being simple and easy to be applied.
SUMMARY
[0009] A membrane electrode assembly includes a proton exchange
membrane and two electrodes. The proton exchange membrane includes
two opposite surfaces. The two electrodes are separately disposed
on the opposite surfaces of the proton exchange membrane. Further,
each electrode includes a catalyst layer and a gas diffusion layer.
The catalyst layer is configured for being sandwiched between the
gas diffusion layer and the proton exchange membrane. The gas
diffusion layer includes a carbon nanotube film. The carbon
nanotube film includes a plurality of carbon nanotubes entangled
with each other. And a method for making the membrane electrode
assembly is also included
[0010] Other advantages and novel features of the present membrane
electrode assembly and the method for making the same will become
more apparent from the following detailed description of present
embodiments when taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Many aspects of the present membrane electrode assembly and
the method for making the same can be better understood with
reference to the following drawings. The components in the drawings
are not necessarily to scale, the emphasis instead being placed
upon clearly illustrating the principles of the present membrane
electrode assembly and the method for making the same.
[0012] FIG. 1 is a schematic view of a membrane electrode assembly,
in accordance with the present embodiment.
[0013] FIG. 2 is a flow chart of a method for making the membrane
electrode assembly shown in FIG. 1.
[0014] FIG. 3 shows a Scanning Electron Microscope (SEM) image of a
flocculated structure of carbon nanotubes formed by the method of
FIG. 2.
[0015] FIG. 4 shows a Scanning Electron Microscope (SEM) image of a
carbon nanotube film formed by the method of FIG. 2 wherein the
carbon nanotube film has a predetermined shape.
[0016] FIG. 5 shows a Scanning Electron Microscope (SEM) image of a
carbon nanotube film formed by the method of FIG. 2 wherein the
carbon nanotube film has been folded.
[0017] FIG. 6 is a schematic view of a fuel cell in accordance with
the present embodiment.
[0018] Corresponding reference characters indicate corresponding
parts throughout the several views. The exemplifications set out
herein illustrate at least one present embodiment of the membrane
electrode assembly and the method for making the same, in at least
one form, and such exemplifications are not to be construed as
limiting the scope of the invention in any manner.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0019] Reference will now be made to the drawings, in detail, to
describe embodiments of the membrane electrode assembly and the
method for making the same.
[0020] Referring to FIG. 1, a membrane electrode assembly 10 is
provided in the present embodiment. The membrane electrode assembly
10 includes a proton exchange membrane 12 and two electrodes 14.
The proton exchange membrane 12 includes two opposite surfaces. The
two electrodes 14 are separately disposed on the two opposite
surfaces of the proton exchange membrane 12. Further, each of the
electrodes 14 includes a catalyst layer 18 and a gas diffusion
layer 16. The catalyst layer 18 is configured for being sandwiched
between the gas diffusion layer 16 and the proton exchange membrane
12.
[0021] The gas diffusion layer 16 includes a carbon nanotube film.
The carbon nanotube film includes a plurality of carbon nanotubes
tangled with each other. The adjacent carbon nanotubes are combined
and entangled by van der Waals attractive force, thereby forming a
network structure/microporous structure. Further, the carbon
nanotubes in the carbon nanotube film are isotropic, uniformly
dispersed, and disorderly arranged. Due to the carbon nanotube film
having a plurality of carbon nanotubes entangled with each other
and the microporous structure, the carbon nanotube film has good
tensile strength, thereby having a free-standing structure. It is
understood that the carbon nanotube film is very microporous. Sizes
of the micropores are less of 100 micrometers. Length and width of
the carbon nanotube film are not limited. A thickness of the carbon
nanotube film is in an approximate range from 1 micrometer to 2
millimeters.
[0022] The catalyst materials includes metal particles and carbon
particles. The metal particles are selected from the group
consisting of platinum particles, gold particles, and ruthenium
particles. The carbon particles are selected from the group
consisting of graphite, carbon black, carbon fiber, and carbon
nanotubes. Quite suitably, the metal particles are platinum; and
the carbon particles are carbon nanotubes. The metal particles are
dispersed in the carbon particles, thereby forming the catalyst
layer 18. The loading of the metal particles is less of 0.5
mg/cm.sup.2 (milligram per square centimeter). The material of the
proton exchange membrane 12 is selected from the group consisting
of perfluorosulfonic acid, polystyrene sulfonic acid, polystyrene
trifluoroacetic acid, phenol-formaldehyde resin acid, and
hydrocarbons.
[0023] Referring to FIG. 2, a method for making the above-described
membrane electrode assembly 10 are provided in the present
embodiment. The method includes the steps of: (a) fabricating a
carbon nanotube film to act as a gas diffusion layer; (b) forming a
catalyst layer on the carbon nanotube film to obtain an electrode;
and (c) providing a proton exchange membrane, and disposing two of
the electrodes on opposite surfaces of the proton exchange membrane
respectively, thereby forming the membrane electrode assembly.
[0024] The carbon nanotube film is formed by the substeps of: (a1)
providing a raw material of carbon nanotubes; (a2) adding the raw
material of carbon nanotubes to a solvent to get a floccule
structure; and (a3) separating the floccule structure from the
solvent, and shaping/molding the separated floccule structure to
obtain a carbon nanotube film.
[0025] In step (a1), a raw material of carbon nanotubes is an array
of carbon nanotubes, quite suitably, a super-aligned array of
carbon nanotubes. The array of carbon nanotubes contains a
plurality of carbon nanotubes, which are selected from the group
consisting of single-walled carbon nanotubes, double-walled carbon
nanotubes, and multi-walled carbon nanotubes. The given
super-aligned array of carbon nanotubes can be formed by the steps
of: (a11) providing a substantially flat and smooth substrate;
(a12) forming a catalyst layer on the substrate; (a13) annealing
the substrate with the catalyst layer in air at a temperature in
the approximate range from 700.degree. C. to 900.degree. C. for
about 30 to 90 minutes; (a14) heating the substrate with the
catalyst layer to a temperature in the approximate range from
500.degree. C. to 740.degree. C. in a furnace with a protective gas
therein; (a15) supplying a carbon source gas to the furnace for
about 5 to 30 minutes and growing a super-aligned array of carbon
nanotubes on the substrate; and (a16) separating the array of
carbon nanotubes from the substrate to get the raw material of
carbon nanotubes.
[0026] In step (a11), the substrate can, beneficially, be a P-type
silicon wafer, an N-type silicon wafer, or a silicon wafer with a
film of silicon dioxide thereon. Preferably, a 4-inch P-type
silicon wafer is used as the substrate.
[0027] In step (a12), the catalyst can, advantageously, be made of
iron (Fe), cobalt (Co), nickel (Ni), or any alloy thereof.
[0028] In step (a14), the protective gas can, beneficially, be made
up of at least one of nitrogen (N.sub.2), ammonia (NH.sub.3), and a
noble gas. In step (a15), the carbon source gas can be a
hydrocarbon gas, such as ethylene (C.sub.2H.sub.4), methane
(CH.sub.4), acetylene (C.sub.2H.sub.2), ethane (C.sub.2H.sub.6), or
any combination thereof.
[0029] The super-aligned array of carbon nanotubes can,
opportunely, have a height more than 100 microns and include a
plurality of carbon nanotubes parallel to each other and
approximately perpendicular to the substrate. Because the length of
the carbon nanotubes is very long, portions of the carbon nanotubes
are bundled together. Moreover, the super-aligned array of carbon
nanotubes formed under the above conditions is essentially free of
impurities such as carbonaceous or residual catalyst particles. The
carbon nanotubes in the super-aligned array are closely packed
together by the van der Waals attractive force.
[0030] In step (a16), the array of carbon nanotubes is scraped from
the substrate by a knife or other similar devices to obtain the raw
material of carbon nanotubes. Such a raw material is, to a certain
degree, able to maintain the bundled state of the carbon
nanotubes.
[0031] In step (a2), the solvent is selected from the group
consisting of water and volatile organic solvent. After adding the
raw material of carbon nanotubes to the solvent, a process of
flocculating is executed to get the floccule structure. The process
of flocculating is selected from the group consisting of ultrasonic
dispersion and high-strength agitating/vibrating. Quite usefully,
in this embodiment ultrasonic dispersion is used to flocculate the
solvent containing the carbon nanotubes for about 10.about.30
minutes. Due to the carbon nanotubes in the solvent having a large
specific surface area and the bundled carbon nanotubes having a
large van der Waals attractive force, the flocculated and bundled
carbon nanotubes form a network structure (i.e., floccule
structure).
[0032] In step (a3), the process of separating the floccule
structure from the solvent includes the substeps of: (a31) pouring
the solvent containing the floccule structure through a filter into
a funnel; and (a32) drying the floccule structure on the filter to
obtain the separated floccule structure of carbon nanotubes.
[0033] In step (a32), a time of drying can be selected according to
practical needs. Referring to FIG. 3, the floccule structure of
carbon nanotubes on the filter is bundled together, so as to form
an irregular flocculate structure.
[0034] In step (a3), the process of shaping/molding includes the
substeps of: (a33) putting the separated floccule structure into a
container (not shown), and spreading the floccule structure to form
a predetermined structure; (a34) pressing the spread floccule
structure with a certain pressure to yield a desirable shape; and
(a35) drying the spread floccule structure to remove the residual
solvent or volatilizing the residual solvent to form a carbon
nanotube film.
[0035] It is to be understood that the size of the spread floccule
structure is, advantageously, used to control a thickness and a
surface density of the carbon nanotube film. As such, the larger
the area of a given amount of the floccule structure is spread
over, the less the thickness and density of the carbon nanotube
film.
[0036] Referring to FIG. 4, bundling of the carbon nanotubes in the
carbon nanotube film, provides strength to the carbon nanotube
film. Therefore, the carbon nanotube film is, advantageously, easy
to be folded and/or bent into arbitrary shapes without rupture. In
the embodiment, the thickness of the carbon nanotube film is in the
approximate range from 1 micrometer to 2 millimeters, and the width
of the carbon nanotube film is in the approximate range from 1
millimeter to 10 centimeters.
[0037] Further, the step (a3) can be accomplished by a process of
pumping filtration to obtain the carbon nanotube film. The process
of pumping filtration includes the substeps of: (a31') providing a
microporous membrane and an air-pumping funnel; (a32') filtering
the solvent containing the floccule structure of carbon nanotubes
through the microporous membrane into the air-pumping funnel; and
(a33') air-pumping and drying the floccule structure of carbon
nanotubes captured on the microporous membrane.
[0038] In step (a31'), the microporous membrane has a smooth
surface. And the diameters of micropores in the membrane are about
0.22 microns. The pumping filtration can exert air pressure on the
floccule structure, thus, forming a uniform carbon nanotube film.
Moreover, due to the microporous membrane having a smooth surface,
the carbon nanotube film can, beneficially, be easily separated
from the membrane.
[0039] The carbon nanotube film produced by the method has the
following virtues. Firstly, through flocculating, the carbon
nanotubes are bundled together by van der Walls attractive force to
form a network structure/floccule structure. Thus, the carbon
nanotube film is very durable. Secondly, the carbon nanotube film
is very simply and efficiently produced by the method. A result of
the production process of the method, is that thickness and surface
density of the carbon nanotube film are controllable.
[0040] The adjacent carbon nanotubes are combined and tangled by
van der Waals attractive force, thereby forming a network
structure/microporous structure. Thus, the carbon nanotube film has
good tensile strength. Referring to FIG. 5, the carbon nanotube
film obtained in the present embodiment is folded without rapture.
As such, the carbon nanotube film is easy to process, and can,
beneficially be folded in most any desired shape.
[0041] In practical use, the carbon nanotube film can,
beneficially, be cut into any desired shape and size. As such, it
is easily applied to use in a fuel cell, especially, in a
micro-type of fuel cell acting as a gas diffusion layer.
[0042] In step (b), the catalyst layer 18 is formed by the substeps
of: (b1) putting metal particles and carbon particles into a
dispersion solution; (b2) adding water and a surface active agent
to the dispersion solution to obtain a catalyst slurry; (b3)
coating the catalyst slurry on the carbon nanotube film and drying
the catalyst slurry, thereby forming the catalyst layer on the
carbon nanotube film to obtain the electrode.
[0043] In step (b1), the metal particles are selected from the
group consisting of platinum particles, gold particles and
ruthenium particles. The carbon particles are selected from the
group consisting of graphite, carbon black, carbon fibers, and
carbon nanotubes. The metal particles load on surfaces of the
carbon particles. Further, loading of the metal particles is less
of 0.5 mg/cm.sup.2. The carbon particles have the properties of
high conductivity, a high specific surface area, and good corrosion
resistance. In order to enhance the dispersion of carbon particles
in the dispersion solution, a ball mill refiner is used to mill the
carbon particles. CHF 1000 resin is dissolved in dimethyl acetamide
to form the dispersion solution. A mass percent of the CHF 1000
resin in the dispersion solution is about 5%.
[0044] In step (b2), the surface active agent is used to restrain
agglomeration of the carbon particles. Thus, in the present
embodiment, isopropanol is used as the surface active agent. After
the water and the surface active agent are added into the
dispersion solution, a process of dispersing the dispersion
solution is executed by an ultrasonic dispersing or an
agitating.
[0045] In step (b3), a process of coating is executed by a spraying
method, an immersing method, or a screen printing method. The
above-described methods can, opportunely, ensure that the catalyst
slurry is uniformly and densely coated on the carbon nanotube film.
In order to reduce the cracks and voids in the catalyst layer 18,
the drying method is executed at a low temperature. The drying
process is selected from the group consisting of an oven drying
method and a sintering method.
[0046] In step (c), the two electrodes 14 are attached on the two
opposite surfaces of the proton exchange membrane 12 by a heat
pressing process. Further, the catalyst layer 18 is configured for
being sandwiched between the gas diffusion layer 16 and the proton
exchange membrane 12. The material of the proton exchange membrane
12 is selected from the group consisting of perfluorosulfonic acid,
polystyrene sulfonic acid, polystyrene trifluoroacetic acid, phenol
formaldehyde resin acid, and hydrocarbons.
[0047] Referring to FIG. 6, a fuel cell 600 is further provided in
the present embodiment. The fuel cell 600 includes a membrane
electrode assembly (MEA) 618, two flow field plates (FFP) 610, two
current collector plates (CCP) 612, as well as related support
equipment 614. The MEA 618 includes a proton exchange membrane 602
and two electrodes 604 separately disposed on two opposite surfaces
of the proton exchange membrane 602. Further, each electrode
includes a catalyst layer 608 and a gas diffusion layer 606. The
catalyst layer 608 is configured for being sandwiched between the
gas diffusion layer 606 and the proton exchange membrane 602. The
proton exchange membrane 602 is selected from the group consisting
of perfluorosulfonic acid, polystyrene sulfonic acid, polystyrene
trifluoroacetic acid, phenol-formaldehyde resin acid, and
hydrocarbons. The proton exchange membrane 602 is used to conduct
the protons generated in the MEA 618, and separate the fuel gases
and the oxidant gases. The catalyst layer 608 includes catalyst
materials and carriers. The catalyst materials are selected from
the group consisting of metal particles, such as platinum
particles, gold particles or ruthenium particles. The carrier is
generally carbon particles, such as graphite, carbon black, carbon
fiber or carbon nanotubes. The gas diffusion layer 606 is the
carbon nanotube film produced in the present embodiment. The FFP
610 is made of metals or conductive carbon materials. Each FFP 610
is disposed on a surface of each electrode 604 facing away from the
proton exchange membrane 602. The FFP 610 has at least one flow
field groove 616. The flow field groove 616 is contacted with the
gas diffusion layer 606. Thus, the flow field groove 616 is used to
transport the fuel gases, the oxidant gases, and the reaction
product (i.e. water). The CCP 612 is made of conductive materials.
Each CCP 612 is disposed on a surface of each FFP 610 facing away
from the proton exchange membrane 602. Thus, the CCP 612 is used to
collect and conduct the electrons in the work process of MEA 618.
The related support equipments 614 include blowers, valves, and
pipelines. The blower is connected with the flow field plate 610 by
the pipelines. The fuel gases and the oxidant gases are blown by
the blowers
[0048] In work process of the fuel cell 600, fuel gases (i.e.
hydrogen) and oxidant gases (i.e. pure oxygen or air containing
oxygen) are respectively applied to a surface of each electrode
through the flow field plates 610 by the related equipments 614.
Specifically, hydrogen is applied to an anode; and oxygen to a
cathode. In one side of the MEA 618, after the hydrogen is applied
to the catalyst layer 608, a reaction of each hydrogen molecule is
as follows: H.sub.2.fwdarw.2H.sup.++2e. The hydrogen ions generated
by the above-described reaction reach the cathode through the
proton exchange membrane 602. At the same time, the electrons
generated by the reaction also arrive at the cathode by an external
electrical circuit. In the other side of the MEA 618, oxygen is
also applied to the cathode. Thus, the oxygen is reacted with the
hydrogen ions and electrons as follows:
1 2 O 2 + 2 H + + 2 e .fwdarw. H 2 O . ##EQU00001##
In the electrochemical reaction process, the electrons form an
electrical current, thereby being able to output electrical energy.
Accordingly, the water generated by the reaction penetrates the gas
diffusion layer 606 and the flow field plate 610, thereby removing
out of the MEA 608. From the above-described process, it is known
that the gas diffusion layer 606 reacts as a channel for the fuel
gases, oxidant gases, as well as the electrons. Fuel gas and
oxidant gases from the gas diffusion layer 606 arrive at the
catalyst layer; and the electrons through the gas diffusion layer
606 are connected with the external electrical circuit.
[0049] In the present embodiment, the gas diffusion layer 606
includes the carbon nanotube film. The carbon nanotube film
includes a plurality of carbon nanotubes tangled with each other.
The adjacent carbon nanotubes are combined and tangled by van der
Waals attractive force, thereby forming a network
structure/microporous structure. Further, the carbon nanotubes in
the carbon nanotube film are isotropic, uniformly dispersed, and
arranged in disorder. Thus, the carbon nanotube film has the
microporous structure and a large specific surface area. As such,
in one side of MEA 618, the hydrogen can be effectively and
uniformly diffused in the carbon nanotube film. The hydrogen fully
contacts with metal particles in the catalyst layer 608. Thus, the
catalytic reaction activity of the metal particles with the
hydrogen is enhanced. In another side of the MEA 618, the oxidant
gases are also uniformly diffused to the catalyst layer 608 through
the carbon nanotube film, thereby fully contacting with the metal
particles of the catalyst layer 608. Thus, the catalytic reaction
activity of the metal particles with the hydrogen ions and
electrons is enhanced. Due to the carbon nanotube film having good
conductivity, the electrons needed or generated in the reactions
are quickly conducted by the carbon nanotube film.
[0050] Moreover, a method for making the carbon nanotube film to be
used as the gas diffusion layer 606 has the following virtues.
Firstly, through flocculating, the carbon nanotubes are bundled
together by van der Walls attractive force to form a network
structure/floccule structure. Thus, the carbon nanotube film is
very durable. Secondly, the carbon nanotube film is very simply and
efficiently produced by the method. A result of the production
process of the method, is that thickness and surface density of the
carbon nanotube film are controllable.
[0051] Finally, it is to be understood that the above-described
embodiments are intended to illustrate rather than limit the
invention. Variations may be made to the embodiments without
departing from the spirit of the invention as claimed. The
above-described embodiments illustrate the scope of the invention
but do not restrict the scope of the invention.
* * * * *