U.S. patent application number 11/613842 was filed with the patent office on 2007-05-24 for electrophoretically deposited hydrophilic coatings for fuel cell diffuser/current collector.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to John Charles Clark, Joseph William Frisk.
Application Number | 20070116950 11/613842 |
Document ID | / |
Family ID | 25543638 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070116950 |
Kind Code |
A1 |
Clark; John Charles ; et
al. |
May 24, 2007 |
ELECTROPHORETICALLY DEPOSITED HYDROPHILIC COATINGS FOR FUEL CELL
DIFFUSER/CURRENT COLLECTOR
Abstract
A method is provided for making a hydrophilic carbon fiber
construction, such as a fuel cell gas diffusion layer or
diffuser/current collector, by electrophoretic deposition of a
metal oxide selected from Type I or Type II, where Type I consists
of metal oxides having a negative zeta potential and Type II
consists of metal oxides having a positive zeta potential. A
hydrophilic carbon fiber construction is provided, such as a fuel
cell gas diffusion layer or diffuser/current collector, which is
coated with a metal oxide and capable of wicking 200 mg of water
per 40 mg of the hydrophilic carbon fiber construction.
Inventors: |
Clark; John Charles; (White
Bear Lake, MN) ; Frisk; Joseph William; (Oakdale,
MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
25543638 |
Appl. No.: |
11/613842 |
Filed: |
December 20, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09997081 |
Nov 28, 2001 |
7160424 |
|
|
11613842 |
Dec 20, 2006 |
|
|
|
Current U.S.
Class: |
428/364 ;
428/357 |
Current CPC
Class: |
Y10T 428/29 20150115;
C25D 13/16 20130101; H01M 8/0234 20130101; C25D 13/02 20130101;
Y10T 428/2913 20150115; H01M 8/0245 20130101; H01M 8/023 20130101;
H01M 8/0247 20130101; Y02E 60/50 20130101; Y02P 70/50 20151101 |
Class at
Publication: |
428/364 ;
428/357 |
International
Class: |
B32B 19/00 20060101
B32B019/00; D02G 3/00 20060101 D02G003/00 |
Claims
1. A hydrophilic carbon fiber construction made according to a
method comprising the steps of: a) immersing a carbon fiber
construction in an aqueous dispersion of a metal oxide selected
from Type I or Type II, wherein Type I consists of metal oxides
having a negative zeta potential and Type II consists of metal
oxides having a positive zeta potential; b) contacting said
dispersion with a counterelectrode; and c) electrophoretically
depositing said metal oxide on said carbon fiber construction by
applying electric current between said carbon fiber construction
and said counterelectrode, wherein, when said metal oxide is
selected from Type I said carbon fiber construction is the anode
and when said metal oxide is selected from Type II said carbon
fiber construction is the cathode.
2. A hydrophilic carbon fiber construction which is capable of
wicking 200 mg of water per 40 mg of said hydrophilic carbon fiber
construction in 60 seconds or less.
3. A hydrophilic carbon fiber construction which is capable of
wicking 250 mg of water per 40 mg of said hydrophilic carbon fiber
construction in 60 seconds or less.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Ser. No. 09/997,081
filed Nov. 28, 2001, now allowed, the disclosure of which is
incorporated by reference in its entirety herein.
FIELD OF THE INVENTION
[0002] This invention relates to a method of making a hydrophilic
carbon fiber construction such as a fuel cell gas diffusion layer
or diffuser/current collector by electrophoretic deposition of a
metal oxide selected from Type I or Type II, where Type I consists
of metal oxides having a negative zeta potential and Type II
consists of metal oxides having a positive zeta potential. This
invention additionally relates to a hydrophilic carbon fiber
construction which is coated with a metal oxide and capable of
wicking 200 mg of water per 40 mg of the hydrophilic carbon fiber
construction.
BACKGROUND OF THE INVENTION
[0003] U.S. Pat. No. 5,840,414 discloses a carbon plate for use in
a fuel cell system which is rendered hydrophilic by incorporation
of a metal oxide. The reference lists potential methods at col. 5,
lines 31-52. The reference describes in detail and exemplifies a
three-step method of incorporating metal oxide in a graphite plate
by treatment with a metal chloride, in situ conversion of the metal
chloride to metal hydroxide, and in situ conversion of the metal
hydroxide to metal oxide. (col 5, line 53-col. 6, line 21; and col.
7, lines 7-25).
[0004] U.S. Pat. No. 6,080,504 discloses a method of
electrodeposition of catalytic metal on a substrate to form a gas
diffusion electrode using a pulsed electric current.
[0005] U.S. Pat. No. 4,175,165 discloses a fuel cell system that
includes bipolar plates having hydrophilic surfaces. The surfaces
may be made hydrophilic by application of wetting agents such as
silica sols, alumina, or silica-alumina. ('165 at col. 6, lines
13-22).
[0006] WO 01/17050 discloses a method of making a structural fuel
cell component hydrophilic by use of a metal oxyhydroxide,
oxyhydroxide hydrate, or oxide hydrate.
[0007] U.S. Pat. Nos. 5,298,348 and 5,389,471 disclose a separator
for an alkaline battery system.
[0008] U.S. Pat. No. 6,083,638 discloses a fuel cell system that
includes a current collector that includes hydrophilic materials
and can also include hydrophobic materials. The current collector
may be made of fibers such as carbon, glass or resin fibers. The
hydrophilic material or bulking agent may be particles of materials
such as carbon powder, metal powder, glass powder, ceramic powder,
silica gel, zeolite or non-fluorinated resin. The hydrophobic
material or bulking agent may be particles of materials such as
fluorinated resin. (see, '638 FIG. 10).
[0009] U.S. Pat. No. 5,998,058 discloses an electrode backing layer
for a polymer electrolyte membrane fuel cell formed from a carbon
fiber substrate treated so as to contain both "hydrophilic" and
"hydrophobic" pores. The reference describes a method of making
pores more hydrophilic by immersion in a solution of tin
tetrachloride pentahydrate followed by immersion in ammonia.
[0010] U.S. Pat. No. 6,024,848 discloses a porous support plate for
an electrochemical cell which includes a contact bilayer adjacent
to an electrode including a hydrophobic and a hydrophilic phase.
The reference discloses a hydrophilic phase comprised of a mixture
of carbon black and a proton exchange resin.
SUMMARY OF THE INVENTION
[0011] Briefly, the present invention provides a method of making a
hydrophilic carbon fiber construction such as a fuel cell gas
diffusion layer or diffuser/current collector comprising the steps
of: a) immersing a carbon fiber construction in an aqueous
dispersion of a metal oxide selected from Type I or Type II, where
Type I consists of metal oxides having a negative zeta potential
such as SnO.sub.2 and SiO.sub.2, and Type II consists of metal
oxides having a positive zeta potential such as ZrO.sub.2; b)
contacting the dispersion with a counterelectrode; and c)
electrophoretically depositing the metal oxide on the carbon fiber
construction by applying electric current between the carbon fiber
construction and the counterelectrode, where carbon fiber
construction is the anode when the metal oxide is selected from
Type I and carbon fiber construction is the cathode when the metal
oxide is selected from Type II.
[0012] In another aspect, the present invention provides a
hydrophilic carbon fiber construction such as a fuel cell gas
diffusion layer capable of wicking 200 mg of water per 40 mg of the
hydrophilic carbon fiber construction.
[0013] What has not been described in the art, and is provided by
the present invention, is a method of manufacturing a hydrophilic
gas diffusion layer for use in a fuel cell by electrophoretic
deposition of a metal oxide selected from Type I or Type II,
defined herein, to provide a hydrophilic carbon fiber construction
with high water absorption speed and capacity.
[0014] It is an advantage of the present invention to provide a
quick and convenient method of manufacturing a hydrophilic gas
diffusion layer having a uniform coating of a metal oxide.
BRIEF DESCRIPTION OF THE DRAWING
[0015] FIG. 1 is a schematic depiction of a electrophoresis
apparatus useful in the method according to the present
invention.
[0016] FIG. 2 is a graph of water absorbed vs. time in a water
wicking analysis of carbon papers treated according to the method
of the present invention as well as two comparative carbon
papers.
[0017] FIG. 3 is a graph of water absorbed vs. time in a water
wicking analysis of carbon fibers treated according to the method
of the present invention as well as comparative untreated carbon
fibers.
[0018] FIG. 4 is an electron micrograph of a carbon fiber treated
with tin oxide according to the method of the present
invention.
[0019] FIG. 5 is a graph of water absorbed vs. time in a water
wicking analysis of carbon papers treated according to the method
of the present invention as well as a comparative carbon paper.
[0020] FIG. 6 is an electron micrograph of a carbon fiber treated
with zirconia according to the method of the present invention.
[0021] FIG. 7 is a graph of water absorbed vs. time in a water
wicking analysis of carbon papers treated according to the method
of the present invention as well as a comparative carbon paper.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0022] The present invention provides an electrophoretic method of
making a hydrophilic carbon fiber construction such as a fuel cell
gas diffusion layer or diffuser/current collector. Briefly, the
present method comprises the steps of: a) immersing a carbon fiber
construction in an aqueous dispersion of a metal oxide selected
from Type I or Type II, where Type I consists of metal oxides
having a negative zeta potential such as SnO.sub.2 and SiO.sub.2,
and Type II consists of metal oxides having a positive zeta
potential such as ZrO.sub.2; b) contacting the dispersion with a
counterelectrode; and c) electrophoretically depositing the metal
oxide on the carbon fiber construction by applying electric current
between the carbon fiber construction and the counterelectrode,
where carbon fiber construction is the anode when the metal oxide
is selected from Type I and carbon fiber construction is the
cathode when the metal oxide is selected from Type II.
[0023] Fuel cells are electrochemical cells which produce usable
electricity by the catalyzed combination of a fuel such as hydrogen
and an oxidant such as oxygen. Typical fuel cells contain layers
known as gas diffusion layers or diffuser/current collector layers
adjacent to catalytically reactive sites. These layers must be
electrically conductive yet must be able to allow the passage of
reactant and product fluids. Typical gas diffusion layers comprise
porous carbon materials. In some fuel cell systems, it is
advantageous to use a gas diffusion layer which is more hydrophilic
than untreated carbon. The present invention concerns the
manufacture of hydrophilic gas diffusion layers.
[0024] Any suitable carbon fiber construction may be used.
Typically the carbon fiber construction is selected from woven and
non-woven carbon fiber constructions. Carbon fiber constructions
which may be useful in the practice of the present invention may
include: Toray.TM. Carbon Paper, SpectraCarb.TM. Carbon Paper,
AFN.TM. non-woven carbon cloth, Zoltek.TM. Carbon Cloth, and the
like.
[0025] Any suitable electrodeposition equipment may be used. FIG. 1
is a schematic depiction of a electrophoresis apparatus useful in
the method according to the present invention including a current
source (1), a cathode (2), an anode (3), and a bath (4) containing
the metal oxide particles (5). A Hull Cell may be used. A typical
counterelectrode is mild steel plate. Any suitable source of
electric current may be used.
[0026] Any suitable aqueous dispersion of metal oxide particles may
be used. The dispersion may be a colloidal suspension or a latex.
Average particle size in the dispersion is typically less than 100
nm, more typically less than 70 nm, more typically less than 50 nm,
and most typically less than 30 nm. The metal oxide is selected
from one of two groups, Type I and Type II. Type I metal oxides
have a negative zeta potential when measured in aqueous suspension.
Type I metal oxides include SnO.sub.2, SiO.sub.2. Type II consists
of metal oxides having a positive zeta potential when measured in
aqueous suspension. Type II metal oxides include ZrO.sub.2.
[0027] Where the metal oxide is a Type I metal oxide, the electric
current is applied between the carbon fiber construction, as anode,
and the counterelectrode, as cathode. Where the metal oxide is a
Type II metal oxide, the carbon fiber construction is the cathode
and the counterelectrode is the cathode. The electric current
applied is sufficient to deposit the desired amount of metal oxide.
Typically, the electric current is driven by a voltage of at least
6 volts, more typically at least 12 volts, and most typically at
least 24 volts. Typically, the electric current density is at least
0.3 .mu.A/cm.sup.2, more typically at least 3 .mu.A/cm.sup.2, and
most typically at least 30 .mu.A/cm.sup.2.
[0028] It is an advantage of the present method that it can be
performed in a speedy manner and is therefore suitable for
commercial production. Typically, the duration of the
electrodeposition step is not more than 30 minutes, more typically
not more than 15 minutes.
[0029] Typically the metal oxide is deposited onto the carbon fiber
construction in the amount of at least 0.1 weight percent per
weight of carbon fiber construction, more typically at least 1
weight percent, more typically at least 2 weight percent, and most
typically at least 5 weight percent.
[0030] Typically, the treated carbon fiber construction is
subsequently rinsed and dried.
[0031] The treated carbon fiber construction may also be heated to
further dry the metal oxide particles, typically to a temperature
of at least 150.degree. C., more typically at least 250.degree. C.,
and most typically at least 350.degree. C. Heating time is
typically at least 10 minutes, more typically at least 20 minutes,
and most typically at least 30 minutes.
[0032] Additional coatings may be added to the carbon fiber
construction. Hydrophobic coatings may be added to the carbon fiber
construction, such as fluoropolymer/carbon coatings.
[0033] Metal oxide coatings produced according to the method of the
present invention are highly uniform. FIGS. 4 and 6 are micrographs
of substrates coated according to the present invention. It can be
seen that the particles form a uniform layer on the surface of the
fibers.
[0034] The uniformity of metal oxide coatings produced according to
the method of the present invention is believed to contribute to
the high degree of water absorption exhibited by the hydrophilic
carbon fiber constructions according to the present invention.
Hydrophilic carbon fiber constructions according to the present
invention can typically absorb or wick at least 200 mg of water per
40 mg of the construction. More typically, theses constructions can
absorb or wick at least 250 mg of water per 40 mg of the
construction. Typically, the hydrophilic carbon fiber construction
according to the present invention can wick 200 mg of water per 40
mg of the construction in 60 seconds or less. More typically, the
hydrophilic carbon fiber construction according to the present
invention can wick 250 mg of water per 40 mg of the construction in
60 seconds or less.
[0035] This invention is useful in the manufacture of hydrophilic
fuel cell gas diffusion layers.
[0036] Objects and advantages of this invention are further
illustrated by the following examples, but the particular materials
and amounts thereof recited in these examples, as well as other
conditions and details, should not be construed to unduly limit
this invention.
EXAMPLES
[0037] Unless otherwise noted, all reagents were obtained or are
available from Aldrich Chemical Co., Milwaukee, Wis., or may be
synthesized by known methods.
Examples 1 and 2C
[0038] In Example 1, Toray.TM. Carbon Paper 060 (Toray
International Inc., Tokyo, Japan) was treated with Nalco.RTM. 2327
colloidal silica (Ondeo Nalco Company, Naperville, Ill.), nominally
having a particle size 20 nm, using an electrophoretic deposition
process. The particle size (diameter) was found to be 27 nm when
measured using a ZetaPlus dynamic light scattering apparatus
(Brookhaven Inst. Corp., Holtville, N.Y.). When the suspension was
diluted to 1% by weight with deionized water, the zeta potential on
the particles was found to be -26 mV measured using a ZetaPALS
instrument (Brookhaven Inst. Corp., Holtville, N.Y.). Since the
zeta potential is negative, the carbon paper was used as the anode
of the electrolytic cell, as shown in FIG. 1, and a mild steel
plate was used as the cathode. The silica suspension was diluted to
1% by weight with deionized water. A 30 volt potential was applied
between the anode and cathode for 10 minutes to deposit the silica
particles on the carbon paper. A current of about 5 microamps was
generated during the deposition. The sample was dried and weighed.
The add-on was 2.8 weight %.
[0039] A 40 mg coupon was cut from the dried sample and contact
angle and wicking were measured using deionized water and a Cahn
DCA-322 Dynamic Contact Angle Analyzer (Thermo Cahn, Madison,
Wis.). The coated carbon paper had both a zero degree advancing and
a zero degree receding contact angle. Wicking of water was almost
instantaneous.
[0040] In Comparative Example 2C, the same Toray carbon paper as
used in Example 1 was dipped in the same Nalco.RTM. 2327 colloidal
silica, diluted to 1% by weight with deionized water, for 10
minutes. After this procedure the sample was dried and tested for
contact angle and wicking as above. The contact angle for the paper
in water was 127 advancing and 18 receding. Wicking of water into
the sample was not apparent.
[0041] FIG. 2 is a graph of water absorbed vs. time in a water
wicking analysis of carbon papers treated according to this example
and comparative carbon papers. Trace 16 is a comparative uncoated
paper. Trace 15 is the comparative paper according to Example 2C.
Trace 12 is the initial result for a paper treated according to
Example 1. Trace 13 is the result for a paper treated according to
Example 1 and subsequently wet and dried. Trace 14 is a similar
paper wet and dried twice. Trace 11 is a similar paper wet and
dried four times and vigorously. Trace 17 is a similar paper which
was heated to 380.degree. C. for 10 minutes. The resulted disclosed
in the graph indicate that the coating according to Example 1 is
durable.
Example 3
[0042] Textron 1071 HCB carbon fiber (Textron Inc., Providence,
R.I.) was electrophoretically deposited with Nalco.RTM. 2327
colloidal silica by the method disclosed in Example 1. The carbon
fibers were coated, dried and tested for contact angle and wicking.
The contact angle of the treated carbon cloth was zero advancing
and zero receding. FIG. 3 shows wicking results for comparative
untreated fibers (23) and for treated fibers measured in four
successive wicking trials, first (20), second (21), third (22), and
fourth (24). Again, an effective and durable wet ability treatment
was shown.
Examples 4 and 5C
[0043] In Example 4, Toray.TM. Carbon Paper 060 (Toray
International Inc., Tokyo, Japan) was treated with Nyacol.RTM.
SN15CG SnO.sub.2 dispersion (Nyacol Nano Technologies, Inc.,
Ashland, Mass.) using an electrophoretic deposition process. The
particle size (diameter) was found to be 41 nm when measured using
a ZetaPlus dynamic light scattering apparatus (Brookhaven Inst.
Corp., Holtville, N.Y.). When the suspension was diluted to 1% by
weight with deionized water, the zeta potential on the particles
was found to be -21 mV measured using a ZetaPALS instrument
(Brookhaven Inst. Corp., Holtville, N.Y.). Since the zeta potential
is negative, the carbon paper was used as the anode (3) of the
electrolytic cell, as shown in FIG. 1, and a mild steel plate was
used as the cathode (2). The tin oxide suspension (4) was diluted
to 1% by weight with deionized water. A 10 volt potential (1) was
applied between the anode and cathode for 10 minutes to deposit the
silica particles (5) on the carbon paper. The sample was dried and
weighed. The add-on was 4.3 weight %.
[0044] Contact angle and water wicking was tested as described
above. The contact angle of the treated paper was 58 degrees
advancing and zero degrees receding. A 4.3% by weight add-on of the
SnO2 was determined for this experiment. FIG. 4 is an electron
micrograph of a carbon fiber thus treated with tin oxide
demonstrating the uniformity of the coating obtained.
[0045] In Comparative Example 5C, a dip-coated sample was made by
following the same procedure as Comparative Example 2C and
substituting a Nyacol.RTM. SN15CG SnO.sub.2 dispersion, diluted to
1% by weight with deionized water, for the Nalco.RTM. 2327
colloidal silica.
[0046] FIG. 5 compares wicking results for the paper of Comparative
Example 5C (30), Example 4 (32), Example 4 repeated after 24 hours
(31), and Example 1 (33).
Example 6
[0047] In this example, Toray.TM. Carbon Paper 060 (Toray
International Inc., Tokyo, Japan) was treated with Nalco.RTM.
colloidal zirconia (Ondeo Nalco Company, Naperville, Ill.). The
particle size (diameter) was found to be 66 nm when measured using
a ZetaPlus dynamic light scattering apparatus (Brookhaven Inst.
Corp., Holtville, N.Y.). When the suspension was diluted to 1% by
weight with deionized water, the zeta potential on the particles
was found to be +30 mV measured using a ZetaPALS instrument
(Brookhaven Inst. Corp., Holtville, N.Y.). Since the zeta potential
is positive, the carbon paper was used as the cathode of the
electrolytic cell, and a mild steel plate was used as the anode.
The silica suspension was diluted to 1% by weight with deionized
water. A 20 volt potential was applied between the anode and
cathode for 10 minutes to deposit the silica particles on the
carbon paper. A current of 9.0 microamps was generated during the
deposition. The sample was dried and weighed. The add-on was 6.8
weight %.
[0048] FIG. 6 is an electron micrograph of a carbon fiber thus
treated with zirconia demonstrating the uniformity of the coating
obtained.
[0049] FIG. 7 compares wicking results for a comparative untreated
paper (42), Example 4 using tin oxide (43), Example 6 using
zirconia (40), and Example 1 using silica (41). Silica appears the
most effective at generating a wicking surface, zirconia is the
second most effective and SnO.sub.2 is the third. Any of these
treatments will substantially improve wettability.
[0050] Various modifications and alterations of this invention will
become apparent to those skilled in the art without departing from
the scope and principles of this invention, and it should be
understood that this invention is not to be unduly limited to the
illustrative embodiments set forth hereinabove. All publications
and patents are herein incorporated by reference to the same extent
as if each individual publication or patent was specifically and
individually indicated to be incorporated by reference.
* * * * *