U.S. patent application number 11/483833 was filed with the patent office on 2006-11-09 for method for making catalysts for fuel cell oxygen electrodes.
Invention is credited to Michael A. Fetcenko, Cristian Fierro, Tim Hicks, William Mays, Stanford R. Ovshinsky, Benjamin Reichman, James Strebe, Avram Zallen.
Application Number | 20060252635 11/483833 |
Document ID | / |
Family ID | 33490366 |
Filed Date | 2006-11-09 |
United States Patent
Application |
20060252635 |
Kind Code |
A1 |
Ovshinsky; Stanford R. ; et
al. |
November 9, 2006 |
Method for making catalysts for fuel cell oxygen electrodes
Abstract
A method for making a catalyst having catalytically active
material supported on a carrier matrix. The catalytically active
material may be a mixed-valence, nanoclustered oxide(s), an
organometallic material or a combination thereof. In one method, a
metal salt solution is combined with a metal complexing agent to
form a metal complex. The metal complex is then combined with a
suspension that includes a carrier matrix and the system is
subjected to ultrasonic agitation. A base is then added to induce a
controlled crystallization of a catalytic nanocluster metal
material onto the carrier matrix. The supported catalytic material
is particularly useful for catalyzing oxygen reduction in a fuel
cell, such as an alkaline fuel cell.
Inventors: |
Ovshinsky; Stanford R.;
(Bloomfield Hills, MI) ; Fierro; Cristian;
(Northville, MI) ; Reichman; Benjamin; (West
Bloomfield, MI) ; Mays; William; (Commerce, MI)
; Strebe; James; (Clawson, MI) ; Fetcenko; Michael
A.; (Rochester, MI) ; Zallen; Avram; (West
Bloomfield, MI) ; Hicks; Tim; (Redford, MI) |
Correspondence
Address: |
ENERGY CONVERSION DEVICES, INC.
2956 WATERVIEW DRIVE
ROCHESTER HILLS
MI
48309
US
|
Family ID: |
33490366 |
Appl. No.: |
11/483833 |
Filed: |
July 10, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10457624 |
Jun 9, 2003 |
7097933 |
|
|
11483833 |
Jul 10, 2006 |
|
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Current U.S.
Class: |
502/101 ;
502/150; 502/152; 502/154; 502/185 |
Current CPC
Class: |
H01M 4/8605 20130101;
H01M 4/90 20130101; H01M 2004/8689 20130101; B01J 23/8892 20130101;
B01J 35/006 20130101; H01M 4/9083 20130101; H01M 8/08 20130101;
H01M 4/9008 20130101; B01J 23/75 20130101; Y02P 70/50 20151101;
B01J 21/18 20130101; H01M 4/9016 20130101; Y02E 60/50 20130101 |
Class at
Publication: |
502/101 ;
502/150; 502/152; 502/154; 502/185 |
International
Class: |
H01M 4/88 20060101
H01M004/88; B01J 21/18 20060101 B01J021/18; B01J 23/40 20060101
B01J023/40; B01J 23/74 20060101 B01J023/74 |
Claims
1. A method for making a catalytic material comprising the steps
of: providing a first metal complex, said first metal complex
including a first metal and a first complexing agent; combining
said first metal complex with a suspension, said suspension
including a carrier matrix suspended in a solvent; adding an agent
to said combination of said first metal complex and said
suspension, said agent inducing a breakdown of said first metal
complex, said breakdown causing said first metal to precipitate
onto said carrier matrix.
2. The method of claim 1, wherein said precipitate of said first
metal is in the form of a nanoclustered metal oxide.
3. The method of claim 2, wherein said nanoclustered metal oxide
includes said first metal in two or more oxidation states.
4. The method of claim 3, wherein said first metal is present in
three or more oxidation states.
5. The method of claim 1, wherein said first metal is Co or Mn.
6. The method of claim 1, wherein said first complexing agent
comprises nitrogen.
7. The method of claim 1, wherein said agent is a base.
8. The method of claim 7, wherein said base is a hydroxide.
9. The method of claim 1, further comprising the step of agitating
said combination of said first metal complex and said
suspension.
10. The method of claim 1, further comprising the steps of:
dissolving a metal salt to form a metal salt solution; adding said
complexing agent to said metal salt solution, said complexing agent
combining with said metal to form said first metal complex.
11. The method of claim 1, further comprising the steps of:
dissolving a metal salt to form a metal salt solution; adding said
complexing agent to said suspension; combining said metal salt
solution with said suspension containing said complexing agent,
said combining step forming said first metal complex.
12. The method of claim 1, further comprising the step of combining
a second metal complex with said combination of said first metal
complex and said suspension, said second metal complex including a
second metal and a second complexing agent, wherein said adding
agent step further induces a breakdown of said second metal
complex, said breakdown causing said second metal to precipitate on
said carrier matrix.
13. The method of claim 12, wherein said precipitate of said first
metal and said precipitate of second metal are layered on said
carrier matrix.
14. The method of claim 12, wherein said precipitate of said first
metal and said precipitate of said second metal are in the form of
nanoclustered metal oxides.
15. The method of claim 1, further comprising the step of combining
an organometallic with said combination of said first metal complex
and said suspension, said organometallic forming a layer on said
carrier matrix.
16. The method of claim 15, wherein said organometallic layer is
formed over said precipitate of said first metal.
17. The method of claim 15, wherein said organometallic is combined
with said combination of said first metal complex and said
suspension after the addition of said agent.
18. The method of claim 15, wherein said organometallic comprises a
macrocycle.
19. The method of claim 1, wherein said carrier matrix comprises
carbon.
Description
RELATED APPLICATION INFORMATION
[0001] This application is a continuation of U.S. patent
applicataion Ser. No. 10/457,624, entitled "Catalyst for Fuel Cell
Oxygen Electrodes", filed on Jun. 9, 2003, the disclosure of which
is incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The present invention pertains generally to catalysts and
more particularly to oxygen reduction catalysts. In particular, the
present invention relates to catalysts that may be used in oxygen
electrodes of fuel cells.
BACKGROUND
[0003] With the increasing need to develop alternative forms of
energy to address the problems of pollution and the dependence on
oil, fuel cells have received increasing attention as a premier
source of clean and quiet power. However, due to the costs
associated with the materials that go into making these fuel cells,
they are not economically feasible for use in many
applications.
[0004] There are several competing fuel cell technologies. These
technologies include alkaline fuel cells, proton exchange membrane
(PEM) fuel cells, etc. Although each technology possesses certain
advantages over the other, alkaline fuel cells offer the potential
for higher power capability, high operating efficiency and lower
cost of manufacture.
[0005] In an alkaline fuel cell, the reaction at the hydrogen
electrode occurs between hydrogen and hydroxyl ions (OH.sup.-)
present in the electrolyte that form water and release electrons:
H.sub.2+2OH.sup.-.fwdarw.2H.sub.2O+2e.sup.-.
[0006] The oxygen reduction reaction typically takes place via a 2
step reaction, each step providing a 2 electron transfer. In other
cases, such as with the use of pure platinum, it has been reported
that oxygen reduction may be accomplished via a single step, 4
electron transfer. However, once the platinum is exposed to an
impurity, the direct 4-electron transfer may not be realized.
[0007] The consequence of the two-step reduction process is the
formation of peroxyl ions:
O.sub.2+H.sub.2O+2e.fwdarw.HO.sub.2.sup.-+OH.sup.-. (1)
HO.sub.2.sup.-+H.sub.2O+2e.fwdarw.3 OH.sup.-. (2) Overall:
O.sub.2+2H.sub.2O+4e.fwdarw.4OH.sup.-
[0008] Although the final reaction is ultimately hydroxyl ion
formation, the formation of intermediate species can be very
problematic. Peroxyl ions are very reactive and can oxidize many
materials. In a porous oxygen diffusion electrode where the
electrochemical reactions are taking place at the surface, the
formation of peroxyl ions becomes detrimental to the performance of
the fuel cell. The pores at the electrode surface provide sites for
oxygen reduction as long as the pores are accessible to the
electrolyte. Once the oxygen reduction takes place, peroxide
formation as an intermediate of the product of reaction occurs
within the pores. Since the pores are not through-hole pores, the
peroxide has no way to escape except by diffusion into the bulk.
Bulk diffusion can be a rather slow process. During this time,
peroxide can (1) oxidize the teflonized carbon, (2) decompose and
form gas bubbles that can block the pores causing a loss of surface
area, and (3) react with the active catalyst material to destroy
its character. All three of these factors can lead to gradual
flooding and a loss of performance within the oxygen electrode.
Thus, the effect of peroxide formation/reaction can be observed as
a gradual increase in polarization and a sudden loss of
performance.
[0009] Catalysis primarily occurs at certain favorable locations
called active sites. It has generally been taught that these active
sites can altered to increase the performance of catalysis. For
example, as described in U.S. Pat. No. 5,536,591, catalyst type,
state, size, proximity, porosity and topology are several factors
that can be altered to engineer new catalysts. The '591 patent and
its progeny, demonstrate that small sized catalytic particles, such
as 50 to 70 angstroms, can be formed in an oxide support within a
very small proximity to one another, such as within 2 to 300
angstroms. Such catalysts have revolutionized the NiMH battery
industry.
[0010] Catalysts can be either supported or non-supported.
Supported catalysts are those that have the catalyst fixed to a
carrier matrix, while non-supported catalysts are those that are
free from any carrier matrix. Examples of supported catalysts
include metals supported on carrier matrices such as refractory
oxides, carbon, or silicon dioxide. Examples of non-supported
catalysts include spongy metal catalysts, such as Raney nickel,
spinels, or other fine metal powders, such as platinum, gold,
palladium, silver, etc. There presently exist a multitude of
supported catalysts, which have been designed for specific uses.
Below are several examples of these catalysts.
[0011] Catalysts have been developed for the treatment of
wastewater. See for example, U.S. Pat. No. 4,670,360 to Habermann
et al., entitled Fuel Cell. Habermann et al., which discloses a
fuel cell having an activated carbon-containing anode and an
activated carbon-containing cathode for use in the oxidative
treatment of wastewaters containing oxygen or oxygen containing
compounds. The patent describes using graphite and active carbon as
a carrier support.
[0012] Catalysts have been developed for the cathodic evolution of
hydrogen in electrolysis plants. See for example, U.S. Pat. No.
3,926,844 to Benczur-Urmossy, entitled Catalysts For The Cathodic
Hydrogen Development. Benczar-Urmossy, which describes depositing
X-ray-amorphous boride compound of nickel, cobalt or iron on a
supporting structure. The compound is deposited from an aqueous
solution having metallic ions such as nickel ions, cobalt ions, or
iron ions, with a complexing agent and a water-soluble borate or
borazane at a temperature of below 60.degree. C.
[0013] Catalysts have been developed for use in hydrocracking gas
oil. See for example U.S. Pat. No. 4,686,030 issued to Ward,
entitled Mild Hydrocracking with a Catalyst Having A Narrow Pore
Size Distribution, which discloses metal oxide catalysts supported
on a calcined oxide support. The catalyst may be made by extruding
a gamma alumina-containing material through a die, drying the
alumina, and breaking the alumina into pieces to form the support.
The support is then impregnated with nickel nitrate hexahydrate and
ammonium heptamolybdate dissolved in phosphoric acid, dried and
calcinated.
[0014] Catalysts have been developed for use in air cathodes for
electrochemical power generation. See for example, U.S. Pat. No.
6,368,751 B1 to Yao et al., entitled, Electrochemical Electrode For
Fuel Cell. Yao et al., which discloses an electrochemical cathode,
which includes a porous metal foam substrate impregnated with a
mixture of carbon, CoTMPP and Teflon.
[0015] A number of techniques for making catalysts have also been
developed. These techniques include impregnating, coating, or
simply mixing metal powder in with a support. See for example, U.S.
Pat. No. 4,113,658 to Geus, entitled Process for Homogeneous
Deposition Precipitation of Metal Compounds on Support or Carrier
Materials, which discloses a method of making supported catalysts
by precipitating a metal salt solution onto a carrier matrix.
[0016] Another technique for making catalyst was taught by
Ovshinsky et al. in U.S. Pat. No. 4,544,473, entitled Catalytic
Electrolytic Electrode, filed May 12, 1980, which describes making
amorphous, catalytic bodies by various deposition techniques.
[0017] Catalysts can also be made by depositing organometallic
catalysts onto a support and then removing the organic material by
heating at a relatively high temperature. See for example U.S. Pat.
No. 4,980,037, entitled Gas Diffusion Cathodes, Electrochemical
Cells and Methods Exhibiting Improved Oxygen Reduction Performance,
issued Dec. 25, 1990 to Hossain et al.
[0018] Because the design of each catalyst is often the limiting
factor to its ultimate end use, there continues to be a need for
new and improved catalysts and ways for making them. Furthermore,
if fuel cells are to become cost competitive with other forms of
power generation, high efficiency, low cost catalysts for use in
these fuel cells needs to be provided.
SUMMARY OF THE INVENTION
[0019] The present invention addresses one or more of the
above-mentioned deficiencies and/or others by providing atomically
engineered catalysts based on Ovshinsky's principles of atomic
engineering to produce unusual orbital interactions and new
chemical properties. The catalyst includes a catalytically active
material supported on a carrier matrix. The catalytically active
material may comprise mixed-valence nanoclustered metal oxide(s),
an organo-metallic material, or a combination thereof. These
catalysts may be particularly useful for improved oxygen reduction,
polarization, and peroxide decomposition in a cathode of a fuel
cell, such as an alkaline fuel cell.
[0020] In one embodiment of the present invention there is provided
a supported catalyst comprising a carrier matrix and catalytically
active material including a mixed-valence, nanoclustered metal
oxide. The catalytically active material is preferably
substantially uniformly distributed about and supported by the
carrier matrix.
[0021] In another embodiment of the present invention there is
provided a supported catalyst comprising a carrier matrix and
catalytically active material including an organometallic. The
catalytically active material is preferably substantially uniformly
distributed about and supported by the carrier matrix.
[0022] In another embodiment of the present invention there is
provided a supported catalyst comprising a carrier matrix and
catalytically active material distributed about the carrier matrix,
wherein the catalytically active material includes a mixed-valence,
nanoclustered metal oxide and an organometallic. The catalytically
active material is preferably substantially uniformly distributed
about and supported by the carrier matrix.
[0023] In another embodiment of the present invention there is
provided a supported catalyst comprising a carrier matrix and
catalytically active material including mixed-valence,
nanoclustered metal oxide and an organometallic, where the
mixed-valence, nanoclustered catalyst is supported on the
organometallic catalyst. Alternatively, the organometallic may be
supported on the mixed-valence nanoclustered metal oxide. The
catalytically active material is preferably uniformly distributed
about and supported by the carrier matrix.
[0024] In still another embodiment of the present invention there
is provided a composite catalyst. The composite catalyst includes a
first catalytically active material on a first carrier matrix and a
second catalytically active material on a second carrier matrix.
The carrier matrices with their respective catalysts are preferably
mixed or blended together. The composite catalyst preferably
includes mixed-valence, nanoclustered metal oxide substantially
uniformly distributed about and supported by a first carbon based
carrier matrix and an organometallic substantially uniformly
distributed about and supported by a second carbon based carrier
matrix.
[0025] For a more complete understanding of the invention,
reference is now made to the following Brief Description of the
Drawings and Detailed Description of Preferred Embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a SEM of catalytically active material in
accordance with the present invention;
[0027] FIG. 2 is a selected area electron diffraction pattern of
(Co.sup.2+, Co.sup.3+).sub.3O.sub.4 mixed-valence, nanoclustered
metal oxide in accordance with an embodiment of the present
invention;
[0028] FIG. 3 is a three dimensional view of a crystal structure
for a (Co.sub.2+, Co.sup.3+).sub.3O.sub.4 mixed-valence,
nanoclustered metal oxide in accordance with an embodiment of the
present invention.
[0029] FIG. 4 is a TEM of a mixed-valence, catalytic material
supported on a carrier matrix in accordance with an embodiment of
the present invention;
[0030] FIG. 5 is a TEM of mixed-valence, catalytic material
supported on a carrier matrix in accordance with an embodiment of
the present invention;
[0031] FIG. 6 is a TEM of mixed-valence, catalytic material
supported on a carrier matrix in accordance with an embodiment of
the present invention;
[0032] FIG. 7 is a cross-sectional view of an oxygen electrode in
accordance with an embodiment of the present invention
[0033] FIG. 8 is a graphical comparison of the performance of a
catalyst in accordance with an embodiment of the present invention
and others; and
[0034] FIG. 9 is a graphical comparison of the performance of a
catalyst in accordance with an embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0035] In accordance with the present invention, there is described
herein a catalyst which can be used for oxygen reduction. The
catalyst comprises a catalytically active material supported on a
carrier matrix. The catalytically active material may comprise
mixed- valence, nanoclustered metal oxide(s), an organometallic
material, or a combination thereof. The catalytically active
material is preferably provided at a loading of: 30% by weight or
less, 20% by weight or less, 10% by weight or less, 5% by weight or
less, but more preferably at a loading of 1% to 5% by weight. The
catalyst may be particularly useful for enhancing the rate of
oxygen reduction in an oxygen electrode of a fuel cell. The
catalyst may also be useful for catalyzing hydrogenation,
hydro-cracking, hydrogen oxidation, reduction alkylation,
ammonolysis, and electrochemical reactions.
[0036] As mentioned above, the catalytically active material may
comprise a mixed-valence, nanoclustered metal oxide. Mixed-valence,
nanoclustered metal oxides can provide a diverse range of active
sites for enhancing the rate of a multi-step reaction.
Mixed-valence oxide is any mixture of oxides of more than one
valence state. The valence states preferably include more than one
of the +1, +2, +3, +4, +5 and +6 oxidation states. The
mixed-valence, nanoclustered metal oxide may include oxides having
a plurality of valence states, such as two, three, four or more
different valence states. The average valence of any particular
nanocluster may be between 0 and +5, 0 and +1, +1 and +2, +2 and
+3, +3 and +4 and +4 and +5. A preferred mixed-valence
nanoclustered metal oxide is from +1 to +3. The nanoclusters may
include a higher concentration of metal atoms in a lower oxidation
state than metal atoms in a higher oxidation state. The ratio of
atoms in the higher oxidation state to the atoms in the lower
oxidation state may range from 1:4 to 3:4, preferably 1:3 to 2:3,
or more preferably 1:2 to 2:3. Providing nanoclusters with a higher
concentration of metal atoms having a lower valence state than
higher valence state can allow for a more favorable reaction rate
in a multi-step reaction mechanism.
[0037] The mixed-valence, nanoclustered metal oxide may be
multi-functional. A multi-functional catalyst has one component
that provides a rate of reaction that favors a first reaction step
and another component that provides a rate of reaction that favors
a second reaction step over the first. By providing a
multi-functional catalytically active material, complex reactions
having multiple steps can be more effectively driven.
[0038] The mixed-valence, nanoclustered metal oxide may be
multicomponent. A multicomponent nanoclustered metal oxide has more
than one element. Preferred multicomponent nanoclustered metal
oxides have two or more, three or more or even four or more
elements. Preferred elements include those selected from the
transition metals, such as nickel, cobalt, manganese, etc.
Preferred elements include those that provide hydrogenation
catalysis. Mulitcomponent nanoclusters can provide improved
catalytic activity for complex reactions and can synergistically
interact to outperform single element, uniform clusters. The
multiple elements may be provided in solid solution to form the
multicomponent oxide. Preferred multicomponent oxides include those
that are mostly cobalt oxide, mostly nickel oxide or mostly
manganese oxide. Preferred multicomponent oxides include
cobalt-manganese oxide, cobalt-nickel, nickel-manganese oxide,
cobalt-manganese-nickel oxide. The multicomponent oxide may include
one or more of the noble metals, such as Ag, Au, Pt, etc. However,
due to the costs associated with using noble metals and the
performance that can be achieved without them, the multicomponent
oxide preferably includes less than 10%, more preferably less than
2% and more preferably less than 1% noble metals by weight. A
preferred multicomponent metal oxide is essentially noble metal
free.
[0039] Nanoclusters are small regions in the nanometer size range
of >0 nm to 1000 nm. Preferrably, the nanoclusters are 0.5-50 nm
in size, and more preferably 50 to 300 .ANG. in size. The
nanoclusters may be partially crystalline, polycrystalline,
microcrystalline, nanocrystalline, essentially amorphous, or
amorphous. The nanoclusters may be formed of small crystallites or
grains which themselves may be highly ordered oxides in the size
range of 10-1000 .ANG.. The nanoclusters may be agglomerated to
form a continuous or substantially continuous coating that has a
thickness that is on the nanometer scale, e.g. of >0 nm to 1000
nm thick. The nanoclusters may be regions of varying thickness or
density, such as thicker or denser towards the middle of a cluster.
Regions of varying thickness permit the topology of the
nanoclusters to be altered to increase surface area and catalytic
activity. The nanoclusters may include small grains of differing
orientation. Having nanoclusters with small grains of differing
orientation can permit stacking of grains to increase the number
and availability of grain boundaries to improve catalytic activity.
The nanoclusters may include 10 to 100 crystallites or grains each.
The grains may have a diameter of 150 .ANG. or less, preferably 100
.ANG. or less, but are preferably between 0 and 20 .ANG..
Nanoclusters having a small grain size permit greater accessibility
of reactants to the active sites. The grains may have a spinel
crystal structure. The nanoclusters may be highly ordered oxides,
such as 100 .ANG.-500 .ANG. in size. Highly ordered oxides can have
the properties of metals to provide enhanced catalytic activity,
but are not in the 0 oxidation state. The nanoclusters or
agglomerations of nanoclusters preferably have a high density. A
high density may be provided by having nanoclusters or
agglomerations of nanoclusters in close proximity to one another. A
high density of nanoclusters provides additional active sites for
improved catalytic activity. The proximity of nanoclusters and/or
agglomerations preferably includes spacing of 1 to 100 .ANG. and
more preferably 2 to 40 .ANG.. The shape, size, form, proximity,
density and ultimate activity of the nanoclusters may be controlled
by the method of forming. By changing the method of how the
nanoclusters are formed: the size, shape, density, grain stacking,
and topology of the clusters can be atomically engineered.
[0040] The mixed-valence, nanoclustered catalytic material may be
formed about the carrier matrix by any suitable means, such as by
precipitation, electrodepositing, impregnation, electroless
deposition, sputtering, etc. The catalytic material is preferably
formed with a low temperature deposition, such as below 80.degree.
C., or at a temperature suitable for forming the catalyst without
altering the catalytic material or the carrier matrix. The
nanoclusters may be formed on, absorbed to, bonded rigidly thereto,
dispersed about, electro-statically held, or simply contact the
carrier matrix. The carrier matrix in turn may support the
catalytically active material directly or indirectly. The
mixed-valence, nanoclustered metal oxides are preferably formed on
a carrier matrix via electroless deposition. More preferably, a
controlled precipitation process that includes forming a metal
complex and breaking down the complex in a controlled manner to
form the nanoclusters is used. By controlling the manner and rate
in which the catalytically active material is formed, different
properties for materials having the same chemical composition can
be provided.
[0041] A controlled precipitation process may be provided by
dissolving a metal salt into a solution to form a metal salt
solution and combining the metal salt solution with a complexing
agent to form a metal complex. The metal complex may then be
combined with a suspension of the carrier matrix. The complex may
be broken down in a controlled manner by reducing the strength of
the complex to electrolessly deposit an oxide about the carrier
matrix. For example, a carrier matrix, such as carbon black, may be
wetted with an organic solvent, such as a polar organic solvent
like acetone, to form a suspension. A metal complex can then be
combined with the wetted carbon and aggressively mixed. An agent,
such as an acid or base, can then be added to the combination to
break down the metal complex so that a catalyst forms on the
carbon. The formation of the catalyst may be done in an ultrasonic
bath using sonication. The catalyst may then be separated from any
excess solution, dried and/or heat treated as desired.
[0042] The controlled precipitation may be done at a fast or slow
rate. A fast deposition rate deposits the catalytically active
material about the carrier matrix in 24 hours or less, while a slow
deposition rate deposits the catalytically active material about
the carrier matrix in more than 24 hours. It has been found that by
altering the rate at which nanoclusters are formed, the activity of
the catalyst can be changed. Preferably, deposition is done at the
slow rate. Deposition rates may be adjusted in a number of ways,
such as by altering temperatures, concentrations, pH, the amount of
the complex present, etc. Deposition rate may also be controlled by
increasing or decreasing the rate at which the metal complex is
weakened. For example, a complex may be prepared by adding a metal
salt to excess ammonium hydroxide and then reducing the excess
ammonium ion. Further, the reaction may be controlled by adjusting
the concentration of ammonium in the headspace. By increasing or
decreasing the amount of ammonium in the headspace, the deposition
rate and/or crystallite size of the catalyst may be controlled.
[0043] The catalytically active material may include an
organometallic. The organometallic is preferably a macrocycle
including one or more transition metals, such as cobalt
tetramethoxyphenyl porphyrin (CoTMPP), manganese tetramethoxyphenyl
porphyrin (MnTMPP) or cobalt/manganese tetramethoxyphenyl porphyrin
(CoMnTMPP). The organometallic may be atomically layered on the
carrier matrix. Atomically layering the organometallic provides
active sites for catalytic activity without isolating the
underlying material. Atomic layering can also be used to adjust the
proximity of the organometallic to adjacent materials to alter the
overall chemistry of active sites, such as atomically layering the
organometallic next to nanoclusters or other catalytically active
materials.
[0044] The organometallic may be formed about the carrier matrix in
any suitable way, such as directly onto the carrier matrix or onto
a material supported by the carrier matrix, such as onto
mixed-valence, nanoclustered metal oxides. The organometallic may
be formed about the carrier matrix by first preparing a solution of
organometallic material and then combining the solution with the
carrier matrix. The solution preferably includes an organic
solvent. A preferred solvent is a polar organic solvent, such as
acetone, however, other organic solvents may be substituted
depending upon the organometallic's solubility and the carrier
matrix.
[0045] A preferred embodiment of the method for making an
organometallic catalyst includes, creating a suspension of the
carrier matrix and adding a solution of organometallic to the
suspension. The resulting suspension is preferably agitated for a
substantial period of time, such as at least 24 hours. The catalyst
may then be separated from any excess solution (such as by
decanting or filtering), dried and/or heat treated as desired.
Heat-treating can be used to alter the organic support structure.
Heat-treating may be used to alter the catalytically active
material by removing organic portions of the organometallic.
Heat-treating may be accomplished by heating the catalyst in an
inert gas, or a reducing atmosphere, depending on the desired
valence states of the catalytically active material and the
residual surrounding organic structure.
[0046] The carrier matrix may be any suitable support material
based on the reaction medium of the ultimate end use. The carrier
matrix is preferably carbon based. A carbon based carrier matrix is
particularly useful for supporting catalytically active material in
a fuel cell oxygen electrode because of its ability to help
dissociate molecular oxygen into atomic oxygen. The carrier matrix
is preferably an agglomerated, filamentary carbon based material.
The carrier matrix may include a plurality of strands having a
diameter of 20 .mu.m or less. The carrier matrix preferably has a
low density and/or high surface area. The carrier matrix may be a
banded linear structure with an ill defined border, such as fluffy
carbon, or may be stratified in one or more directions. The carrier
matrix may be intertwined with non-distinct edges having a vertical
extent which goes into the middle of the carrier region with a more
dense matrix embedded towards the center of the mass. The carrier
matrix may also/or alternatively have a distinct up and down
wavelike pattern, may be uniform, diffuse or wispy with distinct
edges. By having a dispersed carbon matrix, increased surface area
can be provided while maintaining adequate support and
accessibility of the catalytically active material.
[0047] In a preferred embodiment of the present invention, the
catalyst comprises mixed-valence, nanoclustered metal oxide
distributed about and supported by a carrier matrix and
organometallic material distributed over the mixed-valence,
nanoclustered metal oxide. A catalyst having an organometallic
distributed over nanoclusters may be made by depositing the
nanoclusters about a carrier matrix and then supplying the
organometallic about the nanoclusters using one or more of the
above procedures. By using two or more different catalytically
active materials about the same carrier matrix in close proximity
to one another, new and different chemistries can be achieved.
[0048] In another preferred embodiment of the present invention,
the catalyst comprises organometallic material distributed about
and supported by a carrier matrix and mixed-valence, nanoclustered
catalysts substantially distributed over the organometallic
material. A catalyst having nanoclusters distributed over
organometallic material may be made by dispersing the
organometallic material over a carrier matrix and then supplying
the nanoclusters over the organometallic material using one or more
of the procedures described above. By using two or more different
catalytically active materials about the same carrier matrix in
close proximity to one another new and different chemistries can be
achieved.
[0049] In another preferred embodiment of the present invention
there is provided a composite mixture of catalytic material that
includes mixed-valence, nanoclustered metal oxides distributed
about and supported by a first carrier matrix and organometallic
material substantially uniformly distributed over and supported by
another carrier matrix. The composite catalyst may be made by
making mixed-valence, nanoclustered metal oxide catalyst as
described above and making an organometallic catalyst as described
above and blending the two together. A composite catalyst can
provide improved catalytic activity for complex reactions.
[0050] The catalysts described above may be used in an oxygen
electrode. The oxygen electrode may include a carbon matrix
supported by a current collector. A carbon matrix can provide 1) a
porous matrix with pathways for oxygen to travel to the electrolyte
contacting side of the oxygen electrode and 2) enhance the
dissociation of molecular oxygen into atomic oxygen. The current
collector provides a conductive pathway for current to travel. The
current collector preferably extends throughout the entire oxygen
electrode. The current collector is preferably in electrical
communication with the catalytically active material, and may be in
direct contact therewith. The current collector may comprise an
electrically conductive mesh, grid, foam, expanded metal, or
combination thereof. For example, a preferable current collector
comprises a conductive mesh having about 40 wires per inch or less
horizontally and about 20 wires per inch or less vertically. The
wires comprising the mesh may have a diameter between 0.005 inches
and 0.01 inches, preferably between 0.005 inches and 0.008 inches.
This design provides enhanced current distribution due to the
reduction of ohmic resistance.
[0051] The oxygen electrode may be formed in the same manner as a
conventional oxygen electrode, where the active catalyst material
described above is substituted at least partly for conventional
catalyst. In such a case, one or more catalyst as described above
may be formed into the porous carbon material of the conventional
electrode.
[0052] Referring now to FIG. 7, depicted therein at 10 is a fuel
cell oxygen electrode according to a preferred embodiment of the
present invention. As shown therein, the electrode 10 has a layered
structure. A layered structure promotes oxygen dissociation and
resistance to flooding within the oxygen electrode. The oxygen
electrode 10 includes a gas diffusion layer 11, an active material
layer 12, and at least one current collector 13. The active
material layer contains a catalyst. The gas diffusion layer and the
active material layer may be placed adjacent to one another with
the current collector 13 being placed in contact with the active
material layer. Alternatively, the current collector may be placed
outside the gas diffusion layer 11 and the active material layer 12
to form a sandwich configuration. When used inside a fuel cell, the
active material layer 12 may be placed in contact with the
electrolyte solution while the gas diffusion layer 11 may be placed
in contact with the air or oxygen stream.
[0053] The oxygen electrode preferably has a hydrophobic component,
which provides a barrier for isolating the electrolyte, or wet,
side of the oxygen electrode from the gaseous, or dry, side of the
oxygen electrode. The hydrophobic component may include a
halogenated organic polymer compound, such as
polytetrafluoroethylene (PTFE). The hydrophopic component may be
combined with carbon particles in the gas diffusion layer 11 to
provide the barrier. The barrier may also be formed with carbon
particles coated with a polymer compound, such as PTFE coated
carbon particles. The carbon particles may be carbon black, such as
Vulcan XC-72 carbon (Trademark of Cabot Corp.), Acetylene Black,
etc. The gas diffusion layer may contain approximately 30-60
percent by weight of polymer with the remainder consisting of
carbon particles.
[0054] The active material layer 12 is supported by the current
collector and may be composed of coated carbon particles and
catalytically active material as described above. The coated carbon
particles are preferably coated with polytetrafluoroethylene, which
preferably contain approximately >0-20% polytetrafluoroethylene
by weight. The catalytically active material may be blended with
the coated carbon particles, deposited on the coated carbon
particle or deposited directly to the electrode to form a layer of
the active catalyst material on the surface of the active material
layer. The thickness of this layering may be anywhere from 30
Angstroms or less to as thick as 2 microns or more, depending upon
the activity of the chosen material and the requirements of the end
use (i.e. such as a fuel cell).
EXAMPLES
1. 5 wt % CoOx Loaded on Carbon (o)
[0055] I. 250 cc of NH.sub.4OH (ammonia) was added to 25 g of
carbon under ultrasonic agitation.
[0056] II. 3.75 g CoSO.sub.4 was dissolved in 100 ml of water.
[0057] III. Once the carbon was completely wetted, II was added to
I under ultrasonic agitation.
[0058] IV. Dilute NaOH solution was added to III under ultrasonic
agitation over several hours.
[0059] V. The end material was filtered and then rinsed with
water.
[0060] VI. The rinsed material was dried overnight at
.about.80.degree. C.
[0061] The procedure produced supported, mixed-valence
nanoclustered Co oxide catalyst. A catalyst produced in accordance
with Example 1 above was submitted to SEM testing and the results
are shown FIG. 1. The material was also submitted to X-ray analysis
to determine crystal structure. FIG. 2 shows a selected area
electron diffraction pattern and FIG. 3 shows a model of a crystal
structure for a mixed-valence, metal oxide. The sample was
submitted to TEM analysis and the images are shown in FIGS. 4, 5,
and 6 under various magnifications.
2. 5 wt % MnOx Loaded on Carbon (.box-solid.)
[0062] I. 250 cc of NH.sub.4OH (ammonia) was added to 25 g of
carbon under ultrasonic agitation.
[0063] II. 2.49 g MnSO.sub.4xH.sub.2O was dissolved in 100 ml of
water.
[0064] III. Once the carbon was completely wetted, II was added to
I under ultrasonic agitation.
[0065] IV. Dilute NaOH solution was added to III under ultrasonic
agitation over several hours.
[0066] V. The resulting material was filtered and then rinsed with
water.
[0067] VI. The rinsed material was dried overnight at .about.80
.degree. C.
[0068] The procedure produced supported 5 wt % nanoclustered,
mixed-valence, Mn oxide catalyst.
[0069] The supported catalysts above were formed into oxygen
electrodes for use in a power generating alkaline fuel cell and
compared in side-by-side tests, of current Density (mA/cm2) vs.
Potential (V) as shown in FIG. 8. As shown, the electrodes, even
though formed without noble metal or platinum catalysts, performed
well.
3. 10 wt % MnOx Loaded on Carbon (.tangle-solidup.)
[0070] I. 250 cc of NH.sub.4OH (ammonia) was added to 25 g of
carbon under ultrasonic agitation.
[0071] II. 5.28 g MnSO.sub.4xH.sub.2O was dissolved in 100 ml of
water
[0072] III. Once the carbon was completely wetted, II was added to
I under ultrasonic agitation.
[0073] IV. Dilute NaOH solution was added to III under ultrasonic
agitation over several hours.
[0074] V. The resulting material was filtered and then rinsed with
water.
[0075] VI. The rinsed material was dried overnight at
.about.80.degree. C.
4. 5 wt % MnOx+5 wt % CoOx Loaded on Carbon (.diamond-solid.)
[0076] I. 600 cc of NH.sub.4OH (ammonia) was added to 60 g of
carbon under ultrasonic agitation
[0077] II. Dissolve 6.3 g MnSO.sub.4xH.sub.2O+10.2 g CoSO.sub.4 in
100 ml of water
[0078] III. Once the carbon was completely wetted, II was added to
I under ultrasonic agitation
[0079] IV. Dilute NaOH solution was added to III under ultrasonic
agitation over several hours.
[0080] V. The resulting material was filtered and then rinsed with
water.
[0081] VI. The rinsed material was dried overnight at
.about.80.degree. C.
5. 2.5 wt % MnOx+7.5 wt % CoOx Loaded on Carbon
(.circle-solid.)
[0082] I. 600 cc of NH.sub.4OH was added to 60 g of carbon under
ultrasonic agitation
[0083] II. 3.15 g MnSO.sub.4xH.sub.2O+15.46 g CoSO.sub.4 were
dissolved in 100 ml of water
[0084] III. Once the carbon was completely wetted, II was added to
I under ultrasonic agitation.
[0085] IV. Dilute NaOH solution was added to III under ultrasonic
agitation over several hours.
[0086] V. The resulting material was filtered and then rinsed with
water.
[0087] VI. The rinsed material was dried overnight at
.about.80.degree. C.
6. 7.5 wt % MnOx+2.5 wt % CoOx Loaded on Carbon (.box-solid.)
[0088] I. 600 cc of NH.sub.4OH (ammonia) was added to 60 g of
carbon under ultrasonic agitation.
[0089] II. 9.5 g MnSO.sub.4xH.sub.2O+5.13 g CoSO.sub.4 were
dissolved in 100 ml of water
[0090] III. Once the carbon was completely wetted, II was added to
I under ultrasonic agitation
[0091] IV. Dilute NaOH solution was added to III under ultrasonic
agitation over several hours.
[0092] V. The resulting material was filtered and then rinsed with
water.
[0093] VI. The rinsed material was dried overnight at
.about.80.degree. C.
[0094] The above supported catalysts were formed into oxygen
electrodes for use in a power generating alkaline fuel cell and
compared in side-by-side tests, of current Density (mA/cm2) vs.
Potential (V) as plotted in FIG. 8. As shown, the electrodes, even
though formed without noble metal or platinum catalysts, performed
well.
7. 20 wt % Co-TMPP on Carbon (Not Plotted)
[0095] I. 300 cc of NH.sub.4OH (ammonia) was added to 20 g of
carbon under ultrasonic agitation.
[0096] II. 5 g of Co-TMPP was combined with 300 cc of acetone.
[0097] III. II was added to I under ultrasonic agitation over
several hours.
[0098] IV. The resulting material was filtered and dried.
8. 15 wt % CoOx+5 wt % MnOx Loaded on Carbon (Not Plotted)
[0099] I. 400 cc of NH.sub.4OH (ammonia) was added to 30 g of
carbon under ultrasonic agitation
[0100] II. 3.56 g MnSO.sub.4xH.sub.2O+17.39 g CoSO.sub.4 were
dissolved in 100 ml of water.
[0101] III. Once the carbon was completely wetted, II was added to
I under ultrasonic agitation
[0102] IV. Dilute NaOH solution was added to III under ultrasonic
agitation over several hours.
[0103] V. The resulting material was filtered and then rinsed with
water.
[0104] VI. The rinsed material was dried overnight at
.about.80.degree. C.
[0105] To increase the multi-functional activity of the catalyst,
material from Example 9 was produced from material produced in
accordance with Examples 7 and 8.
9. 50/50 Blend of 20 wt % Co-TMPP/15 wt % CoOx+5 wt % MnOx ( )
[0106] An electrode was prepared by blending 5.0 g of a 20 wt %
Co-TMPP on carbon with 5.0 g 15 wt % CoOx+5 wt % MnOx on
carbon.
10. 2.5 wt % MnOx+7.5 wt % CoOx Loaded on Carbon
(.diamond-solid.)
[0107] I. 600 cc of NH.sub.4OH was added to 60 g of carbon under
ultrasonic agitation
[0108] II. 3.15 g MnSO.sub.4xH.sub.2O+15.46 g CoSO.sub.4 were
dissolved in 100 ml of water
[0109] III. Once the carbon was completely wetted, II was added to
I under ultrasonic agitation.
[0110] IV. Dilute NaOH solution was added to III under ultrasonic
agitation over several hours.
[0111] V. The resulting material was filtered and then rinsed with
water.
[0112] VI. The rinsed material was dried overnight at
.about.80.degree. C.
[0113] The above supported catalysts from examples 9 and 10 were
formed into oxygen electrodes for use in a power generating
alkaline fuel cell and compared in side-by-side tests, of current
Density (mA/cm2) vs. Potential (V) as plotted in FIG. 9. As shown,
the electrodes, even though formed without noble metal or platinum
catalysts, performed well, and better when the multi-functionality
of the catalysts were increased.
[0114] While the invention has been illustrated in detail in the
drawings and the foregoing description, the same is to be
considered as illustrative and not restrictive in character, as it
is appreciated that these catalysts may be useful in other types
applications, such as those described above. Further, it is
understood that only the preferred embodiments have been shown and
described in detail and that all changes and modifications that
come within the spirit of the invention are desired to be
protected.
* * * * *