U.S. patent application number 10/369145 was filed with the patent office on 2004-01-29 for methods for forming catalytic coating on a substrate.
Invention is credited to Schoeneweiss, Michael R., Scozzafava, Michael, Trabold, Thomas A..
Application Number | 20040018937 10/369145 |
Document ID | / |
Family ID | 30769709 |
Filed Date | 2004-01-29 |
United States Patent
Application |
20040018937 |
Kind Code |
A1 |
Trabold, Thomas A. ; et
al. |
January 29, 2004 |
Methods for forming catalytic coating on a substrate
Abstract
The present invention is directed to methods for forming a
catalytic coating on a substrate. The method comprises preparing a
catalytic fluid and dispensing the catalytic fluid onto a substrate
by using a direct writing instrument. It is emphasized that this
abstract is provided to comply with the rules requiring an abstract
which will allow a searcher or other reader to quickly ascertain
the subject matter of the technical disclosure. It is submitted
with the understanding that is will not be used to interpret or
limit the scope or meaning of the claims. 37 CFR 1.72(b).
Inventors: |
Trabold, Thomas A.;
(Pittsford, NY) ; Schoeneweiss, Michael R.; (W.
Henrietta, NY) ; Scozzafava, Michael; (Rochester,
NY) |
Correspondence
Address: |
CARY W. BROOKS
General Motors Corporation
Legal Staff, Mail Code 482-C23-B21
P.O. Box 300
Detroit
MI
48265-3000
US
|
Family ID: |
30769709 |
Appl. No.: |
10/369145 |
Filed: |
February 18, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10369145 |
Feb 18, 2003 |
|
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10201828 |
Jul 24, 2002 |
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Current U.S.
Class: |
502/101 ;
427/115 |
Current CPC
Class: |
H01M 8/0247 20130101;
H01M 4/8803 20130101; H01M 4/8605 20130101; H01M 8/04291 20130101;
H01M 4/8807 20130101; H01M 4/8882 20130101; H01M 4/8814 20130101;
Y02E 60/50 20130101; H01M 4/8828 20130101; H01M 8/1004 20130101;
H01M 4/8647 20130101; H01M 4/881 20130101; H01M 8/0241
20130101 |
Class at
Publication: |
502/101 ;
427/115 |
International
Class: |
H01M 004/88; B05D
005/12 |
Claims
We claim:
1. A method of forming a catalytic coating on a substrate
comprising: preparing a catalytic fluid; and dispensing said
catalytic fluid onto a substrate, having a first side and a second
side, using a direct writing instrument that has been programmed to
dispense said catalytic fluid onto said substrate in a pattern that
forms a catalytic coating on said first side of said substrate.
2. A method as claimed in claim 1, wherein said method further
comprises drying said catalytic fluid after said catalytic fluid is
dispensed onto said first side of said substrate.
3. A method as claimed in claim 1, wherein said act of preparing a
catalytic fluid comprises: preparing a mixture of between about 30
grams and about 250 grams of solvent and between about 130 grams
and about 200 grams of water; and preparing a solution between
about 5 grams and about 30 grams of ionomer and between about 5
grams and about 20 grams of platinum supported on a high surface
area carbon in said mixture of solvent and water.
4. A method as claimed in claim 1, wherein said catalytic fluid
comprises at least one ionomer, at least one precious metal,
carbon, a solvent, and water.
5. A method as claimed in claim 4, wherein said at least one
ionomer comprises a perfluorinated polymer.
6. A method as claimed in claim 4, wherein said at least one
precious metal comprises platinum.
7. A method as claimed in claim 4, wherein said at least one
ionomer and at least one precious metal are supported by said
carbon.
8. A method as claimed in claim 4, wherein said solvent comprises
isopropyl alcohol.
9. A method as claimed in claim 1, wherein said catalytic fluid
comprises about 4% by wt. of platinum, about 4% by wt. of ionomer,
about 4% by wt. of carbon, about 28% by wt. of water and about 60%
by wt. of solvent.
10. A method as claimed in claim 1, wherein said catalytic fluid
comprises perfluorinated polymer and carbon and exhibits a
perfluorinated polymer to carbon ratio of about 0.8 to about
2.0.
11. A method as claimed in claim 1, wherein said catalytic fluid
exhibits a viscosity between about 70 cp and about 2000 cp.
12. A method as claimed in claim 1, wherein said catalytic fluid
exhibits a viscosity of about 300 cp.
13. A method as claimed in claim 1, wherein said catalytic fluid
comprises between about 8% and about 20% solids.
14. A method as claimed in claim 1, wherein said catalytic fluid
comprises about 12% solids.
15. A method as claimed in claim 1, wherein said catalytic fluid
supports hydrogen oxidation.
16. A method as claimed in claim 1, wherein said catalytic fluid
supports oxygen reduction.
17. A method as claimed in claim 1, wherein said substrate is
selected from an electrolyte material, a polytetrafluoroethlyene
sheet, and a gas diffusion media.
18. A method as claimed in claim 17, wherein said electrolyte
material comprises a proton conducting membrane.
19. A method as claimed in claim 17, wherein said electrolyte
material comprises perfluorinated sulfonic acid.
20. A method as claimed in claim 1, wherein said catalytic coating
is dispensed such that it has a substantially uniform thickness
across said first side of said substrate.
21. A method as claimed in claim 1, wherein said catalytic coating
is configured to increase the probability of ionization of a
hydrogen-based fuel.
22. A method as claimed in claim 1, wherein said catalytic coating
is configured to increase the probability of a reaction of a
hydrogen ion with oxygen.
23. A method as claimed in claim 1, wherein said direct writing
instrument is configured such that the width and thickness of a
line forming said pattern depends upon the diameter of the direct
writing instrument from which said catalytic fluid is dispensed and
the volumetric flowrate of said catalytic fluid.
24. A method as clamed in claim 23, wherein said line thickness t
is determined by: t=Q/(Vw), wherein Q represents volumetric flow
rate of said catalytic fluid, wherein V represents writing speed of
said direct writing instrument, and wherein w represents line
width.
25. A method as claimed in claim 1, wherein said pattern comprises
a configuration selected from a rectangular spiral, a straight
line, a series of lines, or a single continuous coating over the
entire substrate.
26. A method as claimed in claim 1, wherein said pattern comprises
a series of lines configured to align with at least one flow field
channel of a fuel cell.
27. A method as claimed in claim 1, wherein said catalytic coating
forms a conductive layer on said first side of said substrate.
28. A method as claimed in claim 1, wherein said method further
comprises applying ultrasonic energy to said substrate.
29. A method as claimed in claim 28, wherein said ultrasonic energy
is applied to said first side of said substrate after said
dispensing of said catalytic fluid on said first side of said
substrate.
30. A method as claimed in claim 28, wherein said ultrasonic energy
is applied to said second side of said substrate after said
dispensing of said catalytic fluid on said first side of said
substrate.
31. A method as claimed in claim 1, wherein said method further
comprises dispensing a second fluid onto said first side of said
substrate using a direct writing instrument that has been
programmed to dispense said second fluid onto said substrate in a
pattern that forms a second coating on said first side of said
substrate.
32. A method as claimed in claim 31, wherein said second fluid
comprises a noncatalyic fluid.
33. A method as claimed in claim 31, wherein said second fluid
comprises a precious metal.
34. A method as claimed in claim 33, wherein said precious metal
comprises platinum.
35. A method as claimed in claim 31, wherein said second fluid is
deposited at the periphery of the first side of said substrate.
36. A method as claimed in claim 1, wherein said method further
includes dispensing said catalytic fluid onto said second side of
said substrate using a direct writing instrument that has been
programmed to dispense said catalytic fluid onto said substrate in
a pattern that forms a catalytic coating on said second side of
said substrate.
37. A method as claimed in claim 36, wherein said method further
comprises dispensing a second fluid onto said second side of said
substrate using a direct writing instrument that has been
programmed to dispense said second fluid onto said substrate in a
pattern that forms a second coating on said second side of said
substrate.
38. A method as claimed in claim 37, wherein said second fluid
comprises a noncatalytic fluid.
39. A method as claimed in claim 38, wherein said noncatalytic
fluid is dispensed in a shadow pattern of said catalytic fluid to
form a second coating on said first side of said substrate.
40. A method as claimed in claim 37, wherein said second fluid
comprises a precious metal.
41. A method as claimed in claim 40, wherein said precious metal
comprises platinum.
42. A method as claimed in claim 40, wherein said second fluid is
deposited at the ends of the second side of said substrate.
43. A method of forming a catalytic coating on a substrate
comprising: providing a catalytic fluid; dispensing said catalytic
fluid onto a substrate, having a first and second side, using a
direct writing instrument that has been programmed to dispense said
catalytic fluid onto said first side of said substrate in a pattern
that forms a catalytic coating on said first side of said
substrate; and dispensing a noncatalytic fluid onto said first side
of said substrate using said direct writing instrument that has
been programmed to dispense said noncatalytic fluid in a shadow
pattern of said first coating to form a noncatalytic coating on
said first side of said substrate.
44. A method as claimed in claim 43, wherein said noncatalytic
fluid comprises a carbonaceous material.
45. A method as claimed in claim 44, wherein said carbonaceous
material comprises a material exhibiting high electrical
conductivity.
46. A method as claimed in claim 44, wherein said carbonaceous
material comprises a material exhibiting high thermal
conductivity.
47. A method as claimed in claim 44, wherein said carbonaceous
material comprises a material exhibiting low porosity.
48. A method as claimed in claim 44, wherein said carbonaceous
material comprises carbon black, graphite, and combinations
thereof.
49. A method as claimed in claim 43, wherein said shadow pattern
fills any spaces in the pattern of said first coating.
50. A method as claimed in claim 43, wherein said noncatalytic
fluid is dispensed simultaneously with said catalytic fluid.
51. A method as claimed in claim 43, wherein said noncatalytic
coating and said catalytic coating are formed simultaneously.
52. A method as claimed in claim 43, wherein said noncatalytic
coating is formed after the formation of said catalytic
coating.
53. A method as claimed in claim 43, wherein said catalytic and
said noncatalytic coatings are dispensed independently from said
direct writing instrument.
54. A method as claimed in claim 43, wherein said noncatalytic
fluid has a higher viscosity than said catalytic fluid.
55. A method as claimed in claim 43, wherein said noncatalytic
fluid exhibits a viscosity between about 300 cp and about 10,000
cp.
56. A method as claimed in claim 43, wherein said noncatalytic
fluid is thicker than said catalytic fluid.
57. A method as claimed in claim 43, wherein said catalytic fluid
exhibits a viscosity between about 70 cp and about 2000 cp.
58. A method as claimed in claim 43, wherein said catalytic fluid
exhibits a viscosity of about 300 cp.
59. A method as claimed in claim 43, wherein said catalytic coating
on said first side of said substrate is configured to align with
flow field channels of a fuel cell.
60. A method as claimed in claim 43, wherein said noncatalytic
coating on said first side of said substrate is configured to align
flow field lands of a fuel cell.
61. A method as claimed in claim 43, wherein said catalytic coating
on said first side of said substrate is configured to align with
flow field channels of a fuel cell while said noncatalytic coating
on said first side of said substrate is configured to align with
flow field lands of a fuel cell.
62. A method as claimed in claim 43, wherein said method further
comprises: dispensing said catalytic fluid onto said second side of
said substrate using a direct writing instrument that has been
programmed to dispense said catalytic fluid onto said second side
of said substrate in a pattern that forms a catalytic coating on
said second side of said substrate; and dispensing said
noncatalytic fluid onto said second side of said substrate using
said direct writing instrument, wherein said direct writing
instrument has been programmed to dispense said noncatalytic fluid
on said second side of said substrate in a shadow pattern of said
catalytic fluid to form a noncatalytic coating on said second side
of said substrate.
63. A method as claimed in claim 62, wherein said catalytic coating
on said second side of said substrate is configured to align with
flow field channels of a fuel cell.
64. A method as claimed in claim 62, wherein said noncatalytic
coating on said second side of said substrate is configured to
align with flow field lands of a fuel cell.
65. A method as claimed in claim 62, wherein said catalytic coating
on said second side of said substrate is configured to align with
flow field channels of a fuel cell while said second coating on
said second side of said substrate is configured to align with flow
field lands of a fuel cell.
66. A method of preparing an electrolyte membrane for use in a
membrane electrode assembly comprising: preparing a catalytic
fluid; dispensing said catalytic fluid onto an intermediate
material using a direct writing instrument that has been programmed
to dispense said catalytic fluid onto said intermediate material in
a pattern that forms a catalytic coating on said intermediate
material; and transferring said catalytic coating from said
intermediate material to an electrolyte membrane.
67. A method as claimed in claim 66, wherein said method further
comprises drying said catalytic fluid after said catalytic fluid is
dispensed onto said substrate.
68. A method as claimed in claim 66, wherein a secondary ionomer
solution is applied to said intermediate material.
69. A method as claimed in claim 68, wherein said secondary ionomer
solution is applied to said intermediate material by spraying.
70. A method as claimed in claim 68, wherein said intermediate
material is dried after said secondary ionomer solution is
applied.
71. A method as claimed in claim 66, wherein said intermediate
material is selected from polytetrafluoroethylene or ethylene
tetrafluoroethylene, or variations thereof.
72. A method as claimed in claim 66, wherein said transferring said
first coating from said intermediate material to said electrolyte
membrane is performed by a hot-press.
73. A method as claimed in claim 72, wherein said hot-press is set
at a temperature between about 140.degree. C. to about 165.degree.
C.
74. A method as claimed in claim 72, wherein said hot-press uses a
pressure between about 1300 kPa to about 4000 kPa.
75. A method as claimed in claim 66, wherein said electrolyte
membrane comprises perfluorinated sulfonic acid or some variation
thereof.
76. A method as claimed in claim 66, wherein said method further
comprises dispensing a noncatalytic fluid onto said intermediate
material using said direct writing instrument that has been
programmed to dispense said noncatalytic fluid in a shadow pattern
of said first coating to form a noncatalytic coating on said
intermediate material.
77. A method of preparing an electrolyte membrane for use in a
membrane electrode assembly comprising: preparing a catalytic
fluid; and dispensing said catalytic fluid onto an electrolyte
material using a direct writing instrument that has been programmed
to dispense said catalytic fluid onto said electrolyte material in
a pattern that forms a catalytic coating on said electrolyte
material.
78. A method as claimed in claim 77, wherein said method further
comprises drying said electrolyte material after said catalytic
fluid is dispensed on said electrolyte material.
79. A method of preparing a diffusion media for use in a fuel cell
comprising: preparing a catalytic fluid; and dispensing said
catalytic fluid onto a diffusion media using a direct writing
instrument that has been programmed to dispense said catalytic
fluid onto said diffusion media in a pattern that forms a catalytic
coating on said diffusion media.
80. A method as claimed in claim 79, wherein said method further
comprises drying said diffusion media after said catalytic fluid is
dispensed on said diffusion media.
81. A method as claimed in claim 79, wherein said diffusion media
comprises carbon fiber, carbon cloth, and combinations thereof.
82. A system for preparing a membrane electrode assembly
comprising: a first coating station comprising a first substrate
holding device, and at least one coating head for applying a
coating to a first side of a substrate; a first drying station; a
second coating station comprising a second substrate holding
device, and at least one coating head for applying a coating to a
second side of a substrate; a second drying station; a cutting
station; and a carrier device configured to carry said substrate to
each station.
83. A system as claimed in claim 82, wherein said first substrate
holding device comprises a vacuum table.
84. A system as claimed in claim 82, wherein said first coating
station forms a conductive coating on said first side of said
substrate.
85. A system as claimed in claim 82, wherein said second substrate
holding device comprises a vacuum table.
86. A system as claimed in claim 82, wherein said second coating
station forms a conductive coating on said second side of said
substrate.
87. A system as claimed in claim 82, wherein said first drying
station comprises a heat source.
88. A system as claimed in claim 87, wherein said heat source is
selected from an infrared heat source, heated jets, convection
oven, and combinations thereof.
89. A system as claimed in claim 82, wherein said second drying
station comprises a heat source.
90. A system as claimed in claim 89, wherein said heat source is
selected from an infrared heat source, heated jets, convection
oven, and combinations thereof.
91. A system as claimed in claim 82, wherein said cutting station
comprises a die-cutting station.
92. A system as claimed in claim 82, wherein said carrier device
comprises a feed roll.
93. A system as claimed in claim 82, wherein said substrate is
selected from an intermediate material, an electrolyte material,
and a diffusion media material.
94. A system as claimed in claim 93, wherein said intermediate
material is selected from polyfluorotetraethlyene or ethylene
tetrafluoroethylene.
95. A system as claimed in claim 93, wherein said electrolyte
membrane comprises perfluorinated sulfonic acid or variations
thereof.
96. A system as claimed in claim 93, wherein said diffusion media
comprises carbon fiber, carbon cloth, and combinations thereof.
97. A method of fabricating an article incorporating a fuel cell,
said method comprising: providing a fuel supply manifold; providing
an oxidant supply manifold; preparing a membrane electrode assembly
by acts comprising, preparing a catalytic fluid, dispensing said
catalytic fluid onto an intermediate material using a direct
writing instrument that has been preprogrammed to dispense said
catalytic fluid onto said intermediate material in a pattern that
forms a catalytic coating on said intermediate material,
transferring said catalytic coating from said intermediate material
to a first side of an electrolyte membrane, dispensing said
catalytic fluid onto an intermediate material using a direct
writing instrument that has been preprogrammed to dispense said
catalytic fluid onto said intermediate material in a pattern that
forms a catalytic coating on said intermediate material, and
transferring said catalytic coating from said intermediate material
to a second side of said electrolyte membrane; and positioning said
membrane electrode assembly between said fuel supply manifold and
said oxidant supply manifold.
98. A method as claimed in claim 97, wherein said article comprises
a vehicle at least partially powered by said fuel cell.
99. A method as claimed in claim 97, wherein said article comprises
a power supply at least partially powered by said fuel cell.
100. A method of fabricating an article incorporating a fuel cell,
said method comprising: providing a fuel supply manifold; providing
an oxidant supply manifold; preparing a membrane electrode assembly
by acts comprising, preparing a catalytic fluid, dispensing said
catalytic fluid onto an electrolyte material, having a first and
second side, using a direct writing instrument that has been
preprogrammed to dispense said catalytic fluid onto said
electrolyte material in a pattern that forms a catalytic coating on
said first side of said electrolyte material, and dispensing said
catalytic fluid onto said electrolyte material using a direct
writing instrument that has been preprogrammed to dispense said
catalytic fluid onto said electrolyte material in a pattern that
forms a catalytic coating on said second side of said electrolyte
material; and positioning said membrane electrode assembly between
said fuel supply manifold and said oxidant supply manifold.
101. A method as claimed in claim 100, wherein said article
comprises a vehicle at least partially powered by said fuel
cell.
102. A method as claimed in claim 100, wherein said article
comprises a power supply at least partially powered by said fuel
cell.
103. A method of fabricating an article incorporating a fuel cell,
said method comprising: providing a fuel supply manifold; providing
an oxidant supply manifold; dispensing a catalytic fluid onto a
diffusion media using a direct writing instrument that has been
preprogrammed to dispense said catalytic fluid onto said first
diffusion media in a pattern that forms a catalytic coating on said
first diffusion media; placing said first diffusion media adjacent
said first manifold; dispensing said catalytic fluid onto a second
diffusion media using a direct writing instrument that has been
preprogrammed to dispense said catalytic fluid onto said second
diffusion media in a pattern that forms a catalytic coating on said
second diffusion media; placing said second diffusion media
adjacent said second manifold; and placing an electrolyte material
between said first and second diffusion medias.
104. A method as claimed in claim 103, wherein said article
comprises a vehicle at least partially powered by said fuel
cell.
105. A method as claimed in claim 103, wherein said article
comprises a power supply at least partially powered by said fuel
cell.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/201,828, filed Jul. 24, 2002.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to fuel cells and
particularly, to methods for forming a catalytic coating on a
substrate.
SUMMARY OF THE INVENTION
[0003] According to the present invention, methods for forming a
catalytic coating on a substrate are provided.
[0004] In one embodiment, a method of forming a catalytic coating
on a substrate is provided. According to the method, a catalytic
fluid is prepared and dispensed onto a substrate using a direct
writing instrument that has been programmed to dispense the
catalytic fluid onto the substrate in a pattern that forms a
catalytic coating on the first side of the substrate.
[0005] In another embodiment, a method of forming a catalytic
coating on a substrate is provided. According to the method, a
catalytic fluid is dispensed onto a substrate using a direct
writing instrument that has been programmed to dispense the
catalytic fluid onto the substrate in a pattern that forms a first
coating on a first side of the substrate. A noncatalytic fluid is
also dispensed onto the first side of the substrate using the same
direct writing instrument in a shadow pattern of the first coating
to form a second coating on the first side of the substrate.
[0006] In still another embodiment, a method of preparing an
electrolyte membrane for use in a membrane electrode assembly is
provided. According to the method a catalytic fluid is dispensed
onto an intermediate material using a direct writing instrument
that has been programmed to dispense the catalytic fluid in a
pattern that forms a catalytic coating on the intermediate
material. The catalytic coating is then transferred from the
intermediate material to an electrolyte membrane.
[0007] In still yet another embodiment, a method of preparing an
electrolyte membrane for use in a membrane electrode assembly is
provided. According to the method, a catalytic fluid is dispensed
onto an electrolyte material using a direct writing instrument.
[0008] In still another embodiment, a method of preparing a
diffusion media for use in a fuel cell is provided. According to
the method, a catalytic fluid is dispensed onto a diffusion media
using a direct writing instrument.
[0009] In yet another embodiment, a system for preparing a membrane
electrode assembly is provided. The system comprises first and
second coating stations, first and second drying stations, a
cutting station and a carrier device. The first coating station
comprises a first substrate holding device, and at least one
coating head for applying a coating to a first side of a substrate.
The second coating station comprises a second substrate holding
device, and at least one coating head for applying a coating to a
second side of a substrate. The carrier device is configured to
carry the substrate from station to station.
[0010] These and other features and advantages of the invention
will be more fully understood from the following description of the
invention taken together with the accompanying drawings. It is
noted that the scope of the claims is defined by the recitations
therein and not by the specific discussion of features and
advantages set forth in the present description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The following detailed description can be best understood
when read in conjunction with the following drawings, where like
structure is indicated with like reference numerals and in
which:
[0012] FIG. 1 is a schematic illustration of a fuel cell
system.
[0013] FIG. 2 is a schematic illustration of a vehicle including a
fuel cell system.
[0014] FIG. 3 is a schematic illustration of a fuel cell stack
employing two fuel cells.
[0015] FIG. 4 is an exploded view of a membrane electrode
assembly.
[0016] FIG. 5 is a block diagram of a direct writing instrument
according to one embodiment of the present invention.
[0017] FIG. 6 is an illustration of the nozzle and nozzle tip of a
direct writing instrument forming a pattern on a substrate
according to one embodiment of the present invention.
[0018] FIG. 7 is an illustration of a pattern according to one
embodiment of the present invention.
[0019] FIG. 8 is an illustration of a pattern according to one
embodiment of the present invention.
[0020] FIG. 9 is an illustration of a membrane electrode assembly
according to one embodiment of the present invention.
[0021] FIG. 10 is an illustration of one side of a membrane
electrode assembly having a first and a second coating according to
one embodiment of the present invention.
[0022] FIG. 11 is an illustration of a membrane electrode assembly
system according to one embodiment of the present invention.
[0023] FIG. 12a is an illustration of an ultrasonic probe applied
above to a substrate.
[0024] FIG. 12b is an illustration of an ultrasonic probe applied
below a substrate.
[0025] Skilled artisans appreciate that elements in the figures are
illustrated for simplicity and clarity and have not necessarily
been drawn to scale. For example, the dimensions of some of the
elements in the figures may be exaggerated relative to other
elements to help to improve understanding of embodiments of the
present invention.
DETAILED DESCRIPTION
[0026] Referring to FIG. 1, a fuel cell system 2 for automotive
applications is shown. It is to be appreciated, however, that other
fuel cell system applications, such as for example, in the area of
residential systems, may benefit from the present invention. As
illustrated, the fuel cell system 2 includes a primary reactor 4, a
water-gas shift reactor 6, a preferential oxidation (PrOx) reactor
7, at least one heat exchanger 8, a tail gas combustor 9, and a
fuel cell 10. An explanation of these components and the operation
of the fuel cell system 2 follows. It is to be appreciated that
while one particular fuel cell system design is described, the
present invention may be applicable to any fuel cell system design
where catalytic coatings are utilized.
[0027] In the primary reactor 4 a hydrocarbon fuel, such as
gasoline or methane, air and steam are mixed, heated, and delivered
to a catalyzed substrate. Here, the mixture is split into hydrogen,
carbon monoxide, and other process gases, as the mixture flows over
and reacts with the catalyst, forming a hydrogen-rich stream.
Suitable catalyst materials include platinum group metals and base
metals. This reaction occurs at temperatures in the range between
about 700.degree. C. and about 800.degree. C.
[0028] The hydrogen-rich stream leaving the primary reactor 4
enters the water-gas shift reactor 6. Oxygen from water is used to
convert carbon monoxide to carbon dioxide leaving additional
hydrogen and increasing system efficiency. Operating temperatures
of the shift reactor 6 range from about 250.degree. C. to about
450.degree. C. The hydrogen-rich stream leaving the shift reactor 6
then enters into the PrOx reactor 7, where the final cleanup of
carbon monoxide takes place before the hydrogen-rich stream enters
the fuel cell stack. Air is added to supply the oxygen needed to
convert most of the remaining carbon monoxide to carbon dioxide,
leaving additional hydrogen behind. Operating temperatures in the
PrOx reactor 7 range from about 80.degree. C. to about 200.degree.
C. Combined, the three reactors extract hydrogen from the fuel, and
reduce or eliminate harmful emissions.
[0029] The three reactors are quickly heated to their operating
temperatures before the fuel is introduced. The heat exchanger 8 is
therefore used to regulate the various temperatures throughout the
fuel cell system 2. Typically, the heat exchanger 8 preheats the
steam and air streams before entering into the primary reactor 4.
The waste heat from the hydrogen-rich stream exits the primary
reactor 4.
[0030] The hydrogen-rich stream then is supplied to the fuel cell
10, which may comprise a stack of fuel cells, and reacted with
oxygen from a source, such as air, to produce electricity, which
can be used to power a load 11. The small quantities of unused
hydrogen that leave the fuel cell 10 are consumed in the tail gas
combustor 9 which operates at a temperature between about
300.degree. C. to about 800.degree. C. It is to be appreciated that
while a series of reactors is described as being the hydrogen
source, any hydrogen source is applicable to the present
invention.
[0031] Referring to FIG. 2, a vehicle is shown having a vehicle
body 90, and a fuel cell system having a fuel cell processor 4 and
a fuel cell stack 15. A discussion of the present invention as
embodied in a fuel cell stack and a fuel cell, is provided
hereafter in reference to FIGS. 3-9.
[0032] FIG. 3 depicts a fuel cell stack 15 having a pair of
membrane-electrode-assemblies (MEAs) 20 and 22 separated from each
other by an electrically conductive fluid distribution plate 30.
Plate 30 serves as a bi-polar plate having a plurality of fluid
flow channels 35, 37 for distributing fuel and oxidant gases to the
MEAs 20 and 22. By "fluid flow channel" we mean a path, region,
area, or any domain on the plate that is used to transport fluid
in, out, along, or through at least a portion of the plate. The
MEAs 20 and 22, and plate 30, are stacked together between clamping
plates 40 and 42, and electrically conductive fluid distribution
plates 32 and 34. Plates 32 and 34 serve as end plates having only
one side containing channels 36 and 38, respectively, for
distributing fuel and oxidant gases to the MEAs 20 and 22, as
opposed to both sides of the plate.
[0033] Nonconductive gaskets 50, 52, 54, and 56 provide seals and
electrical insulation between the several components of the fuel
cell stack. Gas permeable diffusion media material 60, 62, 64, and
66 press up against the electrode faces of the MEAs 20 and 22.
Plates 32 and 34 press up against the diffusion media material 60
and 66 respectively, while the plate 30 presses up against the
diffusion media material 62 on the anode face of MEA 20, and
against diffusion media material 64 on the cathode face of MEA
22.
[0034] An oxidizing fluid, such as O.sub.2, is supplied to the
cathode side of the fuel cell stack from storage tank 70 via
appropriate supply plumbing 86. While the oxidizing fluid is being
supplied to the cathode side, a reducing fluid, such as H.sub.2, is
supplied to the anode side of the fuel cell from storage tank 72,
via appropriate supply plumbing 88. The reducing fluid may be
derived from a mixture of methane or gasoline, air, and water
according to a reforming process in the presence of a catalyst.
Exhaust plumbing (not shown) for both the H.sub.2 and O.sub.2/air
sides of the MEAs will also be provided. Additional plumbing 80,
82, and 84 is provided for supplying liquid coolant to the plate 30
and plates 32 and 34. Appropriate plumbing for exhausting coolant
from the plates 30, 32, and 34 is also provided, but not shown.
[0035] Referring to FIG. 4, an exploded view of membrane electrode
assembly 20 is shown comprising an anode layer 102, a cathode layer
106, and an electrolyte 104 separating the anode layer 102 and the
cathode layer 106. Membrane electrode assembly 20 and membrane
electrode assembly 22 are identical. For simplicity purposes, the
present invention is being described in relation to membrane
electrode assembly 20, it is to be appreciated that the present
invention can be applied to membrane electrode assembly 22 and
membrane electrode assemblies in general.
[0036] Generally, the anode layer 102 and the cathode layer 106 are
coatings formed in such a manner that they are in intimate contact
with the electrolyte material once the fuel cell 10 (FIG. 1) is
assembled. Methods of forming a catalytic coating on a substrate
will now be explained. The first step in the method is to prepare a
catalytic fluid. Generally, the catalytic fluid is a solution of
ionomer, precious metal catalyst, solvent and water. A solution of
ionomer and precious metal catalyst istypically prepared on a
support in a mixture of the solvent and water. Different amounts
maybe used depending on the desired viscosity of the catalytic
fluid and the carbon to ionomer ratio desired. Generally, between
about 30 grams and about 250 grams of solvent is mixed with between
about 130 grams and about 200 grams of water and between about 5
grams and about 30 grams of ionomer and between about 5 grams and
about 20 grams of precious metal catalyst are mixed together to
form a solution. The support used for the solution of the ionomer
and precious metal catalyst is typically carbon having a high
surface area. The amount of carbon is generally between about 5
grams and about 20 grams. More specifically, the catalytic solution
comprises about 4% by wt. of precious metal, about 4% by wt. of
ionomer, about 4% by wt. of carbon, about 28% by wt. of water and
about 60% by wt. of solvent.
[0037] The precious metal catalyst can be selected from platinum,
platinum alloys and combinations thereof. The solvent can be
selected from isopropyl alcohol, ethanol, butanol, and combinations
thereof. The catalytic fluid can be prepared to exhibit a viscosity
between about 70 cp and about 2000 cp, and more specifically, a
viscosity of about 300 cp. The catalytic fluid can be prepared to
exhibit an ionomer to carbon ratio of about 0.8 to about 2.0. The
amount of solid in the solution is between about 8% by wt. and
about 20% by wt., and more specifically about 12% by wt.
[0038] Once the catalytic fluid is prepared, it is dispensed onto a
substrate 110 using a direct writing instrument. By "direct
writing," we mean depositing fluid directly onto a surface of a
substrate in a pattern defined by the motion of the instrument, the
motion of the substrate, or both. In direct writing, the deposited
fluid forms a relatively well-defined line or area of deposition,
relative to the overall dimensions of the deposition surface or the
deposited pattern. Relative motion between the fluid source and the
deposition substrate increases the extent of the well-defined line
or area of deposition to create a more extensive deposited
pattern.
[0039] FIG. 5 shows one embodiment of a direct writing instrument
according to the present invention. The direct writing instrument
150 comprises a design system 152, a writing system controller 154
and a writing system 160. The writing system 160 further comprises
a fluid dispensing system 168, a nozzle 166, a nozzle tip 167, and
a substrate holding device 162. The design system 152 stores a
pattern that is drawn on a graphic display. The design system 152
electronically communicates with the writing system controller 154
such that the writing system controller 154 knows the pattern and
controls the writing system 160 in a manner that allows the writing
system 160 to draw the pattern stored in the design system 152 on
the substrate 110.
[0040] Referring to FIGS. 5 and 6, the writing system controller
154 electronically communicates with the fluid dispensing system
168 and the substrate holding device 162. Therefore, the writing
system controller 154 allows the fluid dispensing system 168 to
deliver the catalytic fluid to the nozzle 166. The catalytic fluid
is dispensed through the nozzle tip 167 onto the substrate 110. The
catalytic fluid may be carried to the fluid dispensing system 168
by any suitable means.
[0041] The writing system controller 154 allows the substrate
holding device 162 to move in a variety of positions that form the
pattern 170 stored in the design system. By moving the substrate
holding device 167 in various positions, the substrate 110 is
accurately placed under the nozzle tip 167 while the catalytic
fluid is being dispensed onto the substrate 110. In this manner,
the nozzle 166 and the nozzle tip 167 do not move, but remain
stationary while dispensing the catalytic fluid. Also, the pressure
of the nozzle tip 167 is controlled such that no direct surface
contact with the substrate 110 occurs. In another embodiment, the
substrate holding device 162 remains stationary while the nozzle
166 and nozzle tip 167 move over the substrate 110 while dispensing
the catalytic fluid.
[0042] The design system 152 may be any computer-aided-design (CAD)
interface that allows the design of a pattern via a graphics
editor, digitizing tablet, or interface through a generic photo
plotter interface. The nozzle 166 may be heated to allow the
catalytic fluid to remain in a molten state so that it will easily
dispense through the nozzle tip 167. The width and thickness of the
line, or lines, 169 forming the pattern 170 depend upon the nozzle
tip diameter, the volumetric flowrate of the fluid to the nozzle
tip, and the writing speed. The writing speed may vary depending
upon the movement of the substrate 110 relative to the nozzle tip
167 or the movement of the nozzle tip 167 the substrate. Thus, the
line thickness can be determined by the following equation:
t=Q/(Vw), wherein Q=volumetric flow rate, w=line width, V=writing
speed, and t=the line thickness. Viscosity of the fluid determines
how close the line width is to the nozzle tip diameter, i.e. a low
viscosity fluid will flow, therefore the line width is greater than
the nozzle tip diameter while a high viscosity fluid does not flow
as well, therefore, the line width is about equivalent to the
nozzle tip diameter.
[0043] The nozzle tip 167 can produce at least one line having a
width between about 0.002 inches to about 0.25 inches. If more than
one line is desired, a space up to about 0.0005 inches can be made
between the lines. The line thickness can be up to 0.010 inches per
pass with the nozzle. The line can have tolerances of about
+/-0.000025 inches. The instrument writes at a speed between about
0.05 inches per second to about 5.0 inches per second. The
instrument 150 operates on a minimum grid pitch of 0.0005
inches.
[0044] The pattern 170 formed on the substrate 110 can be selected
from a rectangular spiral, a straight line, a series of lines, or
any suitable geometric pattern. An example of a pattern 170 having
a line, or series of lines, 169 forming a rectangular spiral is
shown in FIG. 7. The spacing between adjacent lines can be
adjusted. For the case of no spacing between adjacent lines, the
pattern 170 would form a single continuous coating over the entire
substrate 110. FIG. 8 shows a pattern 170 having a series of lines
169 formed by a direct writing instrument according to one
embodiment of the present invention.
[0045] Typically, after the pattern is formed on the substrate 110,
the substrate 110 is dried by a heat source having a temperature
between about 70.degree. C. and about 100 .degree. C. The pattern,
once dried, forms a coating on the substrate 110. The heat source
is selected from an infrared heater, convective oven, heated jets,
or any other suitable heating device for removing solvent from the
catalytic fluid. The substrate 110 is subjected to the heat for a
time sufficient to evaporate primarily all of the solvent in the
coating, more specifically between about 2 minutes to about 10
minutes.
[0046] The method of making the membrane electrode assembly may
vary depending upon the substrate upon which the catalytic fluid is
dispensed. The substrate is generally selected from an intermediate
material, a diffusion media material, or electrolyte membrane
material.
[0047] If the substrate is an intermediate material then the
catalytic solution is deposited in the programmed pattern onto the
intermediate material by a direct writing instrument. The coated
substrate is then dried at a temperature between about 70.degree.
C. to about 100.degree. C., typically in an oven. After the
substrate is dry, a secondary ionomer solution may be applied to
the substrate and dried. The application of the ionomer solution is
typically performed by spraying. The coating formed on the
intermediate material is then transferred to an electrolyte
membrane material typically using a hot-press transfer. In one
embodiment of the present invention, a second fluid that is
nonreactive may be applied onto the intermediate material after the
deposition of catalytic fluid or simultaneously with the catalytic
fluid. The coating formed on the intermediate material is then
transferred to an electrolyte membrane material. The intermediate
material is typically selected from polytetrafluoroethlyene,
ethylene tetrafluoroethylene, or variations thereof. The
noncatalytic fluid is described in detail below.
[0048] A second substrate that can be used in the present invention
is a diffusion media material. If the diffusion media material is
used, the catalytic fluid is prepared as described above and then
deposited onto the diffusion media material using a direct writing
instrument as described above in any of the patterns described
above. The coated diffusion media material is then subjected to
drying. The diffusion media material can be any suitable diffusion
media material used in fuel cells. In one embodiment of the present
invention, a second fluid that is noncatalytic fluid may be applied
onto the diffusion media material after the deposition of catalytic
fluid or simultaneously with the catalytic fluid.
[0049] As an alternative, the substrate can be the electrolyte
membrane material. Therefore, the catalytic fluid is deposited
directly onto the electrolyte membrane material. The coated
electrolyte membrane material is then subjected to drying. The
electrolyte membrane material may be a proton conducting membrane,
such as perfluorinated sulfonic acid, or some variation
thereof.
[0050] In one embodiment of the present invention, a second fluid
that is noncatalytic may be applied onto the electrolyte membrane
material after the deposition of catalytic fluid or simultaneously
with the catalytic fluid, thereby forming a catalytic coating and a
noncatalytic coating on one side of the electrolyte membrane
material. Referring to FIG. 9, an MEA 180 having both the catalytic
coating 182 and the noncatalytic coating 184 is shown. The
noncatalytic fluid forms a noncatalytic coating 184 when dried. The
noncatalytic fluid is deposited in such a manner that it "shadows"
the catalytic fluid. By "shadow" we mean that one fluid follows the
outline of the other fluid such that one fluid is not deposited
directly over the other fluid. When used, the noncatalytic fluid
fills in the spaces between the lines of catalytic fluid on the
substrate 202.
[0051] The noncatalytic fluid comprises a material that exhibits a
high electrical conductivity, a high thermal conductivity, and low
porosity. The noncatalytic fluid may be a carbonaceous material,
carbon black, graphite, or combinations thereof. The carbonaeous
material may also comprise a polymeric binder such as polyimide,
polyethylene terephthalate, and combinations thereof. The viscosity
of the noncatalytic fluid can be adjusted as appropriate to readily
fill regions between catalytic coatings illustrated in FIG. 9.
Generally, the noncatalytic fluid exhibits a viscosity between
about 300 cp and about 10,000 cp. The noncatalytic fluid can be
dispensed such that it is thicker on the substrate than the
catalytic fluid.
[0052] Referring to FIG. 10, one embodiment of an MEA 180 having a
catalytic coating 182 and a noncatalytic coating 184 is shown. The
catalytic fluid can be deposited in a pattern that allows the lines
of the catalytic coating 182 to align with channels in a flow field
plate. The noncatalytic fluid can then be deposited in pattern that
allows the lines of the noncatalytic coating 184 to align with the
lands 186 in the flow field plate. This can be accomplished on both
sides of the substrate 202 such that the catalytic fluid forming
the catalytic anode coating 182a is aligned with the channels 185
of the anode flow field plate. Therefore, the noncatalytic coating
184 lies between the spaces of the catalytic fluid or catalytic
anode coating 182a, forming a noncatalytic coating 184 on the lands
186 of the anode flow field plate. Similarly on the cathode side of
the MEA 180, the catalytic fluid forming the catalytic cathode
coating 182b is aligned with the channels 187 of the cathode flow
field plate. Thus, the noncatalytic fluid is deposited between the
spaces of the catalytic fluid or catalytic cathode coating 182b,
forming a noncatalytic coating 184 on the lands 186 of the cathode
flow field plate. The catalytic anode coating 182a and catalytic
cathode coating 182b are shown to be narrower than the opening of
the channels 185, 187, respectively. It is to be appreciated that
the catalytic anode coating 182a and the catalytic cathode coating
182b may be formed such that the coating is as wide as channels
185, 817 or wider. This concept is explained in more detail in
application Ser. No. 10/201,828.
[0053] When the noncatalytic fluid is used, to form a noncatalytic
coating 184 on the substrate 202 and the substrate is an
electrolyte membrane material, the fuel cell may eliminate the use
of the diffusion media material in a fuel cell. Thus, the resulting
fuel cell would be identical to the fuel cell 10 shown in FIG. 3,
however, the diffusion media 60, 62, 64, and 66 would not be
present.
[0054] Referring to FIG. 11, an MEA fabrication system 200
according to one embodiment of the present invention is shown. The
system has three primary stations: a first coating station, a
second coating station, and a die cutting station. The substrate
202 is placed on a feed roll 212 where the substrate 202 is pulled
from station to station by rollers 216, 218, 224, and 226. At the
first coating station the substrate 202 is pulled over a first
substrate holding device 214. Once over the first substrate holding
device 214, a nozzle 210a dispenses catalytic fluid directly onto
the first side 202a of the substrate 202. The catalytic fluid is
typically dispensed in the form of a pattern, as described above.
The substrate 202 is then pulled to first drying area 215. The
first drying area 215 can be an array of heated jets, an infrared
heater, convection oven, or any other suitable device for removing
a majority of solvent from the catalytic fluid. The first drying
area 215 typically maintains a temperature between about 70.degree.
C. and about 100.degree. C. While in first drying area 215 the
catalytic fluid dries to the substrate 202 and forms a catalytic
coating on the substrate 202. The catalytic coating may be either
an anode coating or a cathode coating.
[0055] Next, the substrate 202 is pulled to a second coating
station. In the second coating station, the substrate 202 is pulled
over a second substrate holding device 228. A catalytic fluid is
deposited onto the second side 202b of the substrate 202. The
catalytic fluid may be dispensed onto the substrate 202 in a manner
that forms a pattern as discussed above. While being pulled through
first drying area 215, the substrate 202 is turned in a manner that
allows the first side 202a of the substrate 202 to face the
opposite side such that nozzle 220a is placing catalytic fluid on
the second side 202b of the substrate 202. After the catalytic
fluid is placed onto the second side 202b of the substrate 202, the
substrate 202 is pulled to a second drying area 222. The second
drying area 222 can be an array of heated jets, an infrared heater,
convection oven, or any other suitable device for removing a
majority of solvent from the catalytic fluid. The second drying
area 222 typically maintains a temperature between about 70.degree.
C. to about 100.degree. C. While in second drying area 222, the
catalytic fluid deposited on the second side 202b of the substrate
202 forms a catalytic coating over the substrate 202. The catalytic
coating may be either an anode coating or a cathode coating.
[0056] The substrate 202 is then pulled to a cutting station 230
where the substrate 202 is cut into separate pieces such that each
piece of substrate 202 has both an anode coating and a cathode
coating. The substrate 202 may be further cut in such a manner as
to not interrupt a pattern that may have been formed on the
substrate 202 by the fluid.
[0057] As FIG. 11 shows, more than one nozzle 210a, 210b, 220a, and
220b can be used at each station to deposit more than one fluid
onto the substrate 202 at a time. While only two nozzles are shown
at each station, it is to be appreciated that an array of nozzles
can be present. When more than one fluid is deposited at a time,
one fluid may shadow the other fluid. Although the noncatalytic
fluid is described above as being the second fluid, it is to be
appreciated that the second fluid can be any desired fluid. For
example, the second fluid can be a fluid containing a high amount
of precious metal that is deposited near the inlet and exit of the
MEA. Then a fluid have a lower amount of precious metal can be
deposited in the center of the MEA, thereby, alleviating a portion
of the durability and mass transfer losses.
[0058] The nozzles 210a, 210b, 220a, and 220b are typically
attached to a direct writing instrument as described above. The
fluid is typically dispensed onto the substrate 202 in the form of
one of the patterns as described above. The catalytic fluid is
prepared as described above. The first and second substrate holding
devices 214 and 228 can be vacuum tables or any other suitable
device for holding the substrate in place.
[0059] Referring to FIGS. 12a and 12b, an additional step to the
method of applying more than one fluid to the substrate is shown.
Ultrasonic energy can be applied to assist with coating of the
substrate 202. An ultrasonic probe 250 can be placed over the
catalytic fluid 240 and the noncatalytic fluid 242 as the fluids
are dispensed from nozzles 210a and 210b onto the substrate 202.
The ultrasonic probe 250 transmits acoustic energy 251 through the
air above the contact line 241 of the catalytic fluid 240 and the
noncatalytic fluid 242 as shown in FIG. 12a. Referring specifically
to FIG. 12b, the ultrasonic probe 250 can be placed below the
substrate 202 to transmit acoustic energy 251 through the substrate
202 as the catalytic fluid 240 and the noncatalytic fluid 242 are
dispensed from nozzles 210a and 210b. The acoustic energy 251 is
transmitted at the contact line 241 of the catalytic fluid 240 and
the noncatalytic fluid 242.
[0060] The acoustic energy 251 is applied continuously to the
contact line 241, such that surface tension at the liquid-liquid
interface is continuously lowered at the point of application,
thereby enabling better fluid flow and creating a smooth interface
between fluids 240 and 242. It is to be appreciated that while
FIGS. 12a and 12b are shown using nozzles 210a and 210b which
operate at the first coating station, it is to be appreciated that
FIGS. 12a and 12b also show nozzles 220a and 220b which operate at
the second coating station. It is also to be appreciated that the
acoustic energy 251 can be used in any suitable method system for
making the MEA having two fluids, comprising both a catalytic and
noncatalytic fluid, dispensed onto a substrate both a catalytic
fluid and a noncatalytic fluid. It is further to be appreciated
that while this step is explained using acoustic energy from an
ultrasonic probe, any instrument or energy that can relieve surface
tension at the liquid-liquid interface can be used.
[0061] While the invention has been described by reference to
certain preferred embodiments, it should be understood that
numerous changes could be made within the spirit and scope of the
inventive concepts described. Accordingly, it is intended that the
invention not be limited to the disclosed embodiments, but that it
have the full scope permitted by the language of the following
claims.
* * * * *