U.S. patent application number 11/984355 was filed with the patent office on 2008-03-27 for electrode catalyst for fuel cell and fuel cell using the same.
This patent application is currently assigned to Junichi OZAKI. Invention is credited to Akira Hamada, Asao Ooya, Junichi Ozaki.
Application Number | 20080076008 11/984355 |
Document ID | / |
Family ID | 28034788 |
Filed Date | 2008-03-27 |
United States Patent
Application |
20080076008 |
Kind Code |
A1 |
Ozaki; Junichi ; et
al. |
March 27, 2008 |
Electrode catalyst for fuel cell and fuel cell using the same
Abstract
To provide an electrode catalyst for a fuel cell comprising
inexpensive materials substituting for a precious metal catalyst
such as platinum, and a fuel cell using the same. Poly (furfuryl
alcohol) containing ferrocene is prepared by dissolving ferrocene
corresponding to 1 to 3 wt % on the iron atomic basis in furfuryl
alcohol, adding hydrochloric acid (2 mol/dm.sup.3) thereto as a
polymerization initiator, and then polymerizing them in the air at
70.degree. C. for 48 hours. Random layers 2 developed into
onion-like lamination layers around iron particles are produced by
heating this poly (furfuryl alcohol) up to 700.degree. C. at a
temperature rising rate of 150.degree. C./h, and then holding the
state for an hour to carbonize it. The iron carbon complex having
this structure of the random layers 2 is applied especially to the
cathode side as the electrode catalyst, to form the cells for the
fuel cell.
Inventors: |
Ozaki; Junichi; (Kiryu-shi,
JP) ; Ooya; Asao; (Kiryu-shi, JP) ; Hamada;
Akira; (Moriguchi-shi, JP) |
Correspondence
Address: |
KRATZ, QUINTOS & HANSON, LLP
1420 K Street, N.W.
Suite 400
WASHINGTON
DC
20005
US
|
Assignee: |
OZAKI; Junichi
Kiryu-shi
JP
OOYA; Asao
Kiryu-shi
JP
SANYO ELECTRIC CO., LTD.
Moriguchi-shi
JP
|
Family ID: |
28034788 |
Appl. No.: |
11/984355 |
Filed: |
November 16, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10371185 |
Feb 24, 2003 |
7320842 |
|
|
11984355 |
Nov 16, 2007 |
|
|
|
Current U.S.
Class: |
429/527 ;
423/445R; 429/532; 429/535; 502/182; 502/185; 977/734 |
Current CPC
Class: |
H01M 4/9041 20130101;
Y02E 60/50 20130101; H01M 4/8657 20130101; H01M 8/1004 20130101;
H01M 4/96 20130101; H01M 4/90 20130101 |
Class at
Publication: |
429/040 ;
423/445.00R; 502/182; 502/185; 977/734 |
International
Class: |
H01M 4/96 20060101
H01M004/96; B01J 21/18 20060101 B01J021/18; C01B 31/00 20060101
C01B031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 2002 |
JP |
2002-050381 |
Claims
1: An electrode catalyst for a fuel cell which is a carbon material
consisting essentially of graphitization-resistant carbon,
characterized in using as an electrode catalyst one having a random
layer structure at least in a part of the material structure.
2: An electrode catalyst for a fuel cell as claimed in claim 1,
characterized in using as an electrode catalyst one which is
obtained through carbonization processing by baking after having
added a metal compound to a raw material for producing the
graphitization-resistant carbon and mixed them, and which has the
random layer structure at least in a part of the material
structure.
3: An electrode catalyst for a fuel cell as claimed in claim 1,
characterized in that said random layer structure is carbon
nano-onion structure developed into onion-like lamination layers
around metal particles.
4: An electrode catalyst for a fuel cell as claimed in claim 2,
characterized in that the raw material for producing said
graphitization-resistant carbon are to be selected from a group of
the materials consisting of poly (furfuryl alcohol), furan resin or
thermosetting resin including phenol resin, brown coal, cellulose,
poly (vinylidene chloride) and lignin.
5: An electrode catalyst for a fuel cell as claimed in claim 2,
characterized in that said metal compounds contain at least one of
these metals of iron, cobalt, nickel, chromium, and manganese.
6: An electrode catalyst for a fuel cell as claimed in claim 2,
characterized in that an amount of said metal compound to be added
to the graphitization-resistant carbon is in the range of 0.5 to 15
wt % on the basis of the metal component(s) contained in said metal
compounds.
7: An electrode catalyst for a fuel cell as claimed in claim 2,
characterized in that said metal compound has one of the forms of
nitrate, chloride, acetyl-acetate or acetyl-acetate complex, and
metallocene and its derivatives.
8-12. (canceled)
13: An electrode catalyst for a fuel cell as claimed in claim 2,
characterized in that said random layer structure is carbon
nano-onion structure developed into onion-like lamination layers
around metal particles.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electrode catalyst for a
fuel cell using a carbonaceous material of a special structure as
an alternative catalyst for a precious metal catalyst such as
platinum and relates to a fuel cell using the same.
[0003] 2. Detailed Description of the Prior Art
[0004] As already known, in a solid polymer type fuel cell, a cell
to be built in a cell module is comprised of a sheet-like solid
polymer electrolyte film, an anode (fuel electrode) and a cathode
(oxidant electrode) which are placed to oppose each other so as to
hold this solid polymer electrolyte film in-between.
[0005] As the above-mentioned solid polymer electrolyte film, a
fluorinated ion-exchange resin film representing a
per-fluoro-sulfonic acid resin film (for example, Nafion film
manufactured by DuPont) is used. Moreover, it is usual that the
anode and the cathode (hereafter, simply called electrode(s)) are
constructed comprising a catalyst layer and an electrode substrate
containing a catalytic material, and are bonded on both principal
surfaces of the solid polymer electrolyte film on the catalyst
layer side by hot pressing.
[0006] For the electrode substrate mentioned above, a porous sheet
(for example, carbon paper), which not only supports the catalyst
layer, but also supplies and discharges reactant gases (fuel gas
and oxidizer gas), and has also a function as a collector, is used.
And, when the reactant gases are supplied to each of the
above-mentioned electrodes, a three phase boundary of a gas phase
(reactant gas), a liquid phase (solid polymer electrolyte film),
and a solid phase (catalysts of both electrodes) is formed in the
boundary between the catalyst layer carrying a platinum precious
metal provided on both electrodes and the solid polymer electrolyte
film, and thus an electrochemical reaction is caused to generate
direct current power.
[0007] In the above-mentioned electrochemical reaction, the
following reactions are caused, namely, [0008] on the anode side:
H.sub.2.fwdarw.2H.sup.++2e.sup.- [0009] on the cathode side:
(1/2)O.sub.2+2H.sup.++2e.sup.-.fwdarw.H.sub.2O, and H.sup.+ ion
generated on the anode side moves toward the cathode side in the
solid polymer electrolyte film, and e.sup.- (electron) moves to the
cathode side via an external load. On the other hand, on the
cathode side, the oxygen contained in the oxidizer gas reacts with
H.sup.+ ion and e.sup.- having moved from the anode side, and
thereby water is produced. Thus, a solid polymeric fuel cell
generates direct current power from hydrogen and oxygen, and
produces water.
SUMMARY OF THE INVENTION
[0010] In the above-mentioned conventional solid polymeric fuel
cell, platinum or an expensive precious metal catalyst such as
platinum alloy catalysts (Pt--Fe, Pt--Cr, Pt--Ru, etc.) or the like
has been used for an electrode, and the amount of use for a cell is
about 1 mg/cm.sup.2 which is relatively large, and this makes an
electrode catalyst costly in a cell module. Therefore, it is one of
the main technical purposes for practical use to reduce the amount
of use of the precious metal catalyst.
[0011] In order to solve such a problem, various kinds of precious
metal catalysts have been examined to decrease the amount of use,
and as one of the methods, a method for forming an electrode by
using a precious metal catalyst highly dispersed on carbon black
having a high specific surface area in particles of a few
nano-meters in particle diameter. However, in this proposal,
decrease in catalytic performance due to sintering or elution of
the catalyst becomes a problem, and even if such a method is used,
0.5 to 1 mg/cm.sup.2 of the catalyst is necessary and the high cost
problem still remains unsolved.
[0012] Further, as a catalyst substitute for platinum, an
organometallic compound of a chelate structure or a metallic oxide
of a pyrochlore structure is also being examined for the use,
however, the actual situation is the fact that these are inferior
to the platinum catalyst in catalytic activity.
[0013] Therefore, the purpose of the present invention, which has
been worked out considering the situation of the conventional
catalysts as described above, is to provide an electrode catalyst
for a fuel cell which is made of an inexpensive material as a
substitute for an expensive precious metal catalyst such as
platinum and is high in catalytic activity.
[0014] Moreover, another purpose of the present invention is to
provide a fuel cell using the highly active electrode catalyst made
of the inexpensive material.
[0015] In order to achieve the purposes mentioned above, as a
result of the zealous researches conducted by the inventors, they
have found out that a carbon material obtained by adding an iron
group compound such as ferrocene to a raw material for producing
graphitization-resistant carbon such as poly (furfuryl alcohol),
furan resin, and phenol resin, heating them at 700.degree. C. to
3000.degree. C. in an inert atmosphere such as in helium, argon,
and vacuum, and controlling the carbonization reaction, contains a
phase having a structure analogous to graphite (a kind of a random
layer structure having parallel lamination layer structure in the
direction of a carbon hexagonal mesh plane and having no regularity
in the three-dimensional directions) developed into onion-like
lamination layers around metallic particles such as those of
nano-order iron.
[0016] It has been found out that this carbon nano-onion phase
manifests a high oxygen reducing performance considered to be
caused by the crystallographic structure of the surface different
from that of normal graphite. Therefore, the inventors have found
out that the above-mentioned problem can be solved by applying a
material containing this carbon nano-onion phase to the electrode
catalyst for a fuel cell (in particular, a cathode side electrode
catalyst), and making this carbon nano-onion phase act as the
catalyst in the cathodic reaction (oxygen reduction and water
production), and thus they have achieved the present invention.
[0017] The electrode catalyst for a fuel cell as claimed in claim 1
of the present invention is a carbon material consisting
essentially of the graphitization-resistant carbon, and is
characterized in using as an electrode catalyst one having a random
layer structure at least in a part of the material structure.
[0018] The electrode catalyst for a fuel cell as claimed in claim 2
of the present invention is obtained through carbonization
processing by baking after having added and mixed a metallic
compound to the raw material for producing the
graphitization-resistant carbon, and is characterized in using as
an electrode catalyst one having a random layer structure at least
in a part of the material structure.
[0019] The electrode catalyst for a fuel cell as claimed in claim 3
of the present invention is characterized in that the random layer
structure is a carbon nano-onion structure developed into
onion-like lamination layers around the metal particles.
[0020] The electrode catalyst for a fuel cell as claimed in claim 4
of the present invention is characterized in that the raw material
for producing the graphitization-resistant carbon is to be selected
from a group of the materials consisting of poly (furfuryl
alcohol), furan resin or thermosetting resin including phenol
resin, brown coal, cellulose, poly (vinylidene chloride) and
lignin.
[0021] The electrode catalyst for a fuel cell as claimed in claim 5
of the present invention is characterized in that the metal
compound contain at least one of these metals of iron, cobalt,
nickel, chromium, and manganese.
[0022] The electrode catalyst for a fuel cell as claimed in claim 6
of the present invention is characterized in that an amount of the
metal compound to be added to the graphitization-resistant carbon
is in the range of 0.5 to 15 wt % on the basis of the metal
component contained in the metal compound.
[0023] The electrode catalyst for a fuel cell as claimed in claim 7
of the present invention is characterized in that the metal
compound has one of the forms of nitrate, chloride, acetyl-acetate
or acetyl-acetate complex, metallocene and its derivatives.
[0024] The method for preparing the electrode catalyst for a fuel
cell as claimed in claim 8 of the present invention is
characterized in that the raw material for producing the
graphitization-resistant carbon is added and mixed with a
metallocene derivative containing at least one of these metals of
iron, cobalt, nickel, chromium, and manganese and having a
copolymerizing functional group, and after both of them have been
copolymerized and mixed, they are carbonization-processed by
baking.
[0025] The fuel cell as claimed in claim 9 of the present invention
is characterized in using the electrode catalyst for the fuel cell
as claimed in claim 1.
[0026] The fuel cell as claimed in claim 10 of the present
invention is characterized in that the electrode catalyst for the
fuel cell as claimed in claim 1 is produced like layers at least on
one side of a solid polymer electrolyte film and is thereby used as
electrode reaction layers.
[0027] The fuel cell as claimed in claim 11 of the present
invention is characterized in that the electrode reaction layers
are produced from a mixture of the electrode catalyst for the fuel
cell as claimed in claim 1 and the solid polymer electrolyte.
[0028] The fuel cell as claimed in claim 12 of the present
invention is characterized in that the electrode reaction layers as
claimed in claim 10 or claim 11 are applied to the cathode side of
the fuel cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] These and other objects and advantages of the present
invention will become clear from the following description with
reference to the accompanying drawings, wherein:
[0030] FIG. 1 is a part of a TEM image observed by the transmission
electron microscope showing a carbonized state of an iron carbon
complex prepared from ferrocene-poly (furfuryl alcohol) relating to
the embodiment of the present invention.
[0031] FIG. 2 is a TEM image enlarging a part of the random layers
of a structure analogous to graphite developed into onion-like
lamination layers around the iron particles, and a schematic view
of a part thereof.
[0032] FIG. 3 is an X-ray diffraction (XRD) patterns of iron carbon
complex or the like using Cu-K.alpha. rays.
[0033] FIG. 4 is an enlarged view of the diffraction line peak
parts of Fe (3)-PFA which is one of iron carbon complexes.
[0034] FIG. 5 is a graph showing the test results of a cell of a
fuel cell using an iron carbon complex as an electrode
catalyst.
[0035] FIG. 6 is a part of a TEM image observed by the transmission
electron microscope showing a carbonized state of iron carrying
brown coal relating to an alternate embodiment of the present
invention.
[0036] FIG. 7 is an X-ray diffraction (XRD) patterns of iron
carrying brown coal using Cu-K.alpha. rays.
[0037] FIG. 8 is a graph showing the test results of a cell of a
fuel cell using iron carrying brown coal as an electrode
catalyst.
Explanation of References:
[0038] 1 iron particles
[0039] 2 random layers
[0040] 2a plane-like carbide
[0041] 3 amorphous
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0042] Next, preferred embodiments of the present invention will be
described in details referring to the drawings.
Embodiment 1
[0043] Firstly, an iron carbon complex is prepared by mixing
ferrocene with furfuryl alcohol (hereafter, abbreviated to FA) and
carbonizing the mixture. For this purpose, poly (furfuryl alcohol)
(hereafter, abbreviated to PFA) containing ferrocene is prepared by
dissolving ferrocene corresponding to 1 to 3 wt % on the iron atom
basis in FA, adding hydrochloric acid (2 mol/dm.sup.3) as a
polymerization initiator thereto, and then polymerizing them at
70.degree. C. for 48 hours in the air. Following this, PFA is
heated up to 700.degree. C. at a programming rate of 150.degree.
C./h in an atmosphere of helium circulation, and then PFA is
maintained in this state for an hour to be carbonized.
[0044] FIG. 1 shows a part of a TEM image of a carbonized state of
the iron carbon complex observed by a transmission electron
microscope, and it is possible to confirm from this image that a
random layer 2 of a structure analogous to graphite developed into
an onion-like lamination has been produced around a nano-order (nm)
minute iron particle 1. Such a random layer structure has occupied
about 60% of the whole. The remaining part is regarded as being
composed of an amorphous structure and a little of a graphitized
structure.
[0045] FIG. 2 is a TEM image of the random layer 2 which is partly
magnified, and, a plurality of plane-like carbide 2a is present in
parallel in the same plane and is also a structure multilaminated
like an onion, as it is partly illustrated in a schematic form.
Each plane-like carbide 2a is in the form of two-dimensional chain
of hexagonally-linked carbon atoms. Such a random layer 2 has been
obviously different from the graphitized structure in the point
that there is no regularity in the three-dimensional direction
(direction of lamination). The spacing between the faces in the
direction of lamination is 3.40 .ANG. that is narrower than those
of PFA (3.9 .ANG.) and pitch coke PC (3.45 .ANG.), and shows an
approximate value of graphite for electrode GE (3.38 .ANG.).
[0046] FIG. 3 shows X-ray diffraction patterns (XRD) of an iron
carbon complex etc. by using Cu-K.alpha. rays, and the pattern A
shows a case of 0 wt % addition of iron atomic basis, the pattern B
shows a case of 1 wt % addition, and the pattern C shows 3 wt %
addition. Moreover, for comparison with these PFA carbons, a
graphite electrode (GE) manufactured by Toshiba Ceramics Co., Ltd.
pitch coke (PC) manufactured by Nippon Steel Chemical Co., Ltd. and
a sample of polyvinyl acetate (PVAc 1050) carbonized at
1,050.degree. C. have been used.
[0047] Looking at these XRD patterns, any of GE, PC, PVAc 1050,
Fe(3)-PFA, and Fe (1)-PFA shows a large diffraction line peak near
2.theta.=26.degree.. However, Fe (0)-PFA does not show a large
diffraction line peak. According to this result, PFA carbon
prepared by mixing iron therein obviously brings a difference from
PFA carbon without iron in the characteristic, and this difference
is considered to be caused by the random layers 2. Moreover, it has
also been found out that the more iron is added, the larger the
diffraction line peak is. Scattering in the neighborhood of the
(002) diffraction of Fe (1)-PFA and Fe (3)-PFA is about 1/10 in the
case of PC and GE. Thus, the iron carbon complex prepared in this
embodiment is considered to have a random layer structure that has
mostly been undeveloped in graphitization but is partly
graphitized.
[0048] FIG. 4 is an enlarged view of the diffraction line peak part
of the above-mentioned Fe (3)-PFA pattern C, and it is considered
that the oblique line area shows the random layer structure 2, and
the dotted area shows the amorphous structure 3. The measurement
conditions of this case are; a powder X-ray diffraction device:
RINT 2100 V/PC manufactured by Rigaku, a heat source: Cu-K.alpha.,
voltage: 32 kV, current: 20 mA, scanning speed: 0.2.degree./min,
and sampling width: 0.010.degree..
[0049] Since PFA carbon provided with the random layer structure
has been found out to have an electrode characteristic as GE, a
test electrode was made by the method as described below.
[0050] (1) The carbon material obtained was ground in an agate
mortar and was passed through a 100-mesh sieve.
[0051] (2) A 5% solution of Nafion.TM. manufactured by Aldrich Co.,
Ltd. was mixed with the carbon material and made into paste so that
P/(P+Q) was 25% [P: mass of the solid polymer electrolyte, Q: mass
of the carbon material].
[0052] (3) The paste made by the step (2) was applied to the carbon
paper (TGP-H060) manufactured by Toray Industries, Inc. coated with
a thin layer consisting of carbon black (VulcanXC-72) and PTFE. In
this case, a carrying quantity of carbon material was adjusted to
10 mg/cm.sup.2.
[0053] (4) Thereafter, drying treatment was carried out at a room
temperature and 60.degree. C.
[0054] Next, a test cell was manufactured by the following
method.
[0055] (1) An electrode made by using conventional carbon carrying
platinum as a catalyst was employed as an anode, and the electrode
made by the above-mentioned method was employed as a cathode
(dimensions of the electrodes: 1 cm.times.1 cm).
[0056] (2) Nafion.TM. 112 manufactured by DuPont was used as the
solid polymer electrolyte film and the anode and cathode made by
the step (1) were arranged on both sides of the film.
[0057] (3) These electrodes and the laminated body of the solid
polymer electrolyte film were was hot-pressed at 150.degree. C. and
5 MPa for 30 sec to make it into an electrode-solid polymer
electrolyte film connection body (MEA).
[0058] (4) The MEA obtained was assembled in a fuel cell and used
as a cell for evaluating the performance.
[0059] A reaction gas was supplied to the anode and the cathode of
the cell for evaluating the performance, and experiments were
performed on power generation. The addition amount of ferrocene
(addition amount of iron) to the carbon material was made to 0.5 wt
%, 1 wt %, 2 wt %, and 3 wt % on iron atomic basis. FIG. 5 shows
the results of the experiment, and the cell voltages were 470 mV
with 0.5 wt %, 580 mV with 1 wt %, 605 mV with 2 wt %, and 620 mV
with 3 wt %, respectively. In this case, the current density was
0.01 A/cm.sup.2. The power generation was increased in performance
as ferrocene was increased in the addition amount, and although the
power generation performance was low with the addition amount of
0.5 wt %, catalytic activity appeared. With the addition amount of
3 wt %, the best power generation performance was shown, a
significant increase in power generation cannot be expected even if
the addition amount is increased further. Moreover, with an
addition mount less than 0.5 wt %, a substantial decrease in power
generation is foreseen. Thus, an addition amount of ferrocene is
preferred to be 0.5 to 3 wt %.
Embodiment 2
[0060] Next, an example of having prepared an iron carbon complex
by using brown coal will be described below.
[0061] In this embodiment, the particle diameters were arranged to
2 to 5.6 mm, and Loy Yang coal (hereafter, abbreviated to LY) which
was from Australia and stored in the air was used as a coal sample.
This LY coal had 41.8% water, 63.9% carbon, 4.8% hydrogen, 0.6%
nitrogen, and 30.7% O.sub.diff by weight, respectively.
[0062] The above-mentioned LY coal was made to carry 0 to 10 wt %
Fe (NO.sub.3).sub.3.9H.sub.2O of iron atomic basis from its water
solution as an iron catalyst by an impregnation method. The
carbonization was carried out by heating the sample up to
1000.degree. C. at a temperature rising rate of 150.degree. C./min
in the atmosphere of helium, and keeping it at the temperature for
an hour.
[0063] The structure of the iron carbon complex obtained was
examined by X-ray diffraction measurement and observation through a
transmission electron microscope. Cu-K.alpha. rays were used for
the XRD measurement. The TEM observation was performed on the
sample which had been ground in an agate mortar, dispersed in
acetone, and prepared by scooping it with a micro grid for TEM.
[0064] FIG. 6 is a TEM image showing the carbonized state of the
iron carbon complex, and it could be confirmed from the image that
the random layers 2 of the structure analogous to graphite and
developed into onion-like or bamboo-like lamination layers were
produced. As the measuring conditions in this case, JEM-1200 EXS
Transmission Electron Microscope manufactured by JEOL.Ltd was used,
and accelerating voltage was 100 kV. Micro iron particles were not
present, but they are considered that they were vaporized and
disappeared at the time of the high temperature processing.
[0065] FIG. 7 shows the patterns of X-ray diffraction (XRD) of the
iron carbon complex using Cu-K.alpha. rays, and the pattern D is
the one for a 0 wt % addition amount of
Fe(NO.sub.3).sub.3.9H.sub.2O on an iron atomic basis; E is the
pattern for 0.5 wt %; F is the pattern for 6 wt %; G is the pattern
for 10 wt %; and H is the pattern for 15 wt %, respectively.
[0066] According to these XRD patterns, the pattern G and the
pattern H have a large diffraction line peak around at
2.theta.=26.degree.. In the pattern F, a slight diffraction line
peak was observed, but in the other patterns, no significant
diffraction line peak was observed. From these results, the random
layer structure is produced in the case that an addition amount of
Fe(NO.sub.3).sub.3.9H.sub.20 on an iron atomic basis is 5 to 15 wt
%. It was also found out that the more an addition amount of
Fe(NO.sub.3).sub.3.9H.sub.20 is, the larger diffraction line peak
appears, however, when the addition amount reaches 15 wt %, there
was an upward tendency of diffraction peak sharpness considered to
originate from graphite. Therefore, an addition amount of
Fe(NO.sub.3).sub.3.9H.sub.20 is preferred to be 5 to 15 wt % on an
iron atomic basis.
[0067] Moreover, the carbonization processing was carried out at
the temperature of 1000.degree. C. in the present embodiment,
however, the sample carbonized at 1000.degree. C. was further
heat-treated in a vacuum in a Tammann furnace at 1500.degree. C.
and 2000.degree. C., and was also heat-treated in an argon flow at
3000.degree. C. for 30 min. As the heat treating temperature rose,
the diffraction lines were increased in sharpness, and new
diffraction lines appeared at 2.theta.=26.4.degree. in addition to
the previous main diffraction line peak at 2.theta.=26.degree. at
2000.degree. C. Moreover, the peak originating from iron
disappeared then due to evaporation of iron. Thus, it was found out
that any of the samples were graphitized in multiple phases by the
high-temperature heat treatment.
[0068] In the present embodiment also, a test electrode was made by
the method as described below.
[0069] (1) The carbon material obtained was ground by an agate
mortar, and was passed through a 100-mesh sieve.
[0070] (2) A 5% solution of Nafion.TM. manufactured by Aldrich Co.,
Ltd. was mixed with the carbon material and made into paste so that
P/(P+Q) was 25% [P: mass of the solid polymer electrolyte, Q: mass
of the carbon material].
[0071] (3) The paste made by the step (2) was applied to the carbon
paper (TGP-H060) manufactured by Toray Industries, Inc. coated with
a thin layer consisting of carbon black (VulcanXC-72) and PTFE on
one side thereof. In this case, a carrying quantity of carbon
material was adjusted to 10 mg/cm.sup.2.
[0072] (4) Thereafter, drying treatment was carried out at a room
temperature and 60.degree. C.
[0073] Next, a test cell was made by the following method.
[0074] (1) An electrode made by using conventional carbon carrying
platinum as a catalyst was employed as an anode, and the electrode
made by the above-mentioned method was employed as a cathode
(dimensions of the electrodes: 1 cm.times.1 cm).
[0075] (2) Nafion.TM. 112 manufactured by DuPont was used as the
solid polymer electrolyte film and the anode and cathode made by
the step (1) were arranged on both sides of the film.
[0076] (3) These electrodes and the laminated body of the solid
polymer electrolyte film were hot-pressed at 150.degree. C. and 5
MPa for 30 sec to make it into an electrode-solid polymer
electrolyte film connection body (MEA).
[0077] (4) The MEA obtained was assembled in a fuel cell and used
as a cell for evaluating the performance.
[0078] A reaction gas was supplied to the anode and the cathode of
the cell for evaluating the performance, and experiments were
performed on power generation. The addition amounts of
Fe(NO.sub.3).sub.3.9H.sub.20 (addition amount of iron) to the
carbon material were made to 5 wt %, 10 wt %, and 15 wt % on iron
atomic basis. FIG. 8 shows the results of the experiments, and the
cell voltages were 200 mV with 5 wt %, 595 mV with 10 wt %, and 550
mV with 15 wt %, respectively. In this case, the current density
was 0.01 A/cm.sup.2. Although the power generation performance was
low with the addition amount of 15 wt %, catalytic activity
appeared. With the addition amount of 10 wt %, the best power
generation performance was presented, however, the power generation
performance was lower than that in the case using the poly
(furfuryl alcohol). Thus, an addition amount of
Fe(NO.sub.3).sub.3.9H.sub.20 is preferred to be 10 wt %.
[0079] In the embodiments 1, 2 described above, the production of
graphitization-resistant carbon was explained by the examples using
poly (furfuryl alcohol) or brown coal as a raw material therefor,
however, thermosetting resin including furan resin or phenol resin,
cellulose, poly (vinylidene chloride), lignin, or the like can be
used other than the aforementioned materials. Moreover, both of the
embodiments 1, 2 were explained by the examples using an iron
carbon complex, however, cobalt, nickel, chromium, manganese, or
the like can be used other than iron. As metal compounds, they can
take the forms of nitrates, chlorides, acetylacetonato or
acetylacetenato complex, metallocene and its derivatives.
[0080] Moreover, a metal-carbon complex may be produced by adding
and mixing a metallocene derivative containing at least one of
iron, nickel, chromium, and manganese and also having a
copolymerizing functional group with a raw material for producing
graphitization-resistant carbon, and coploymerizing and mixing both
of them.
[0081] Further, in the embodiments 1, 2, an electrode catalyst is
formed in a thin layer form on the solid polymer electrolyte film
surface as an electrode reaction layer, however, the electrode
reaction layer can also be formed from the mixture of the electrode
catalyst and the solid polymer electrolyte.
[0082] The electrode catalyst for a fuel cell as claimed in claim 1
of the present invention is a carbon material consisting
essentially of graphitization-resistant carbon, and uses the one
having a random layer structure at least in a part of the structure
of the carbon material as the electrode catalyst, therefore, it can
be provided as an electrode catalyst with high catalyst activity at
an inexpensive price as a substitute for a precious metal catalyst
such as platinum or platinum compound or the like.
[0083] The electrode catalyst for a fuel cell as claimed in claim 2
of the present invention is obtained through carbonization
processing by baking after having added and mixed a metallic
compound to the raw material for producing the
graphitization-resistant carbon, and uses the one having a random
layer structure at least in a part of the structure of the carbon
material as the electrode catalyst, therefore, it can be
manufactured with ease and also a carbon material provided with a
catalytic function just as desired by controlling the carbonizing
process. As the control method, for example, the conditions such as
a raw material, a reaction atmosphere, a treating temperature, or
the like are selectable.
[0084] The electrode catalyst for a fuel cell as claimed in claim 3
of the present invention has a carbon nano-onion structure
developed into onion-like lamination layers around the metal
particles from the random layer structure, and is obtainable as a
catalyst excellent in performance.
[0085] For the electrode catalyst for a fuel cell as claimed in
claim 4 of the present invention, a raw material for producing the
graphitization-resistant carbon is to be selected from a group of
the materials consisting of poly (furfuryl alcohol), furan resin or
thermosetting resin including phenol resin, brown coal, cellulose,
poly (vinylidene chloride) and lignin, therefore, the costs can be
reduced by selecting those materials as necessary.
[0086] Since the electrode catalyst for a fuel cell as claimed in
claim 5 of the present invention is characterized in that the metal
compound contains at least one of these metals of iron, cobalt,
nickel, chromium, and manganese, it is possible to select a metal
suitable for the manufacturing conditions.
[0087] In the electrode catalyst for a fuel cell as claimed in
claim 6 of the present invention, an amount of the metal compound
to be added to the graphitization-resistant carbon is in the range
of 0.5 to 15 wt % on the basis of the metal component(s) contained
in the metal compound, therefore, an electrode provided with a
desired catalytic activity can be made by altering the addition
amount of the metal compound as necessary.
[0088] In the electrode catalyst for a fuel cell as claimed in
claim 7 of the present invention, the metal compound has one of the
forms of nitrate, chloride, acetyl-acetate or acetyl-acetate
complex, metallocene and its derivatives, therefore, the metal
compound suitable for the manufacturing costs and conditions can be
selected.
[0089] In the method for preparing the electrode catalyst for a
fuel cell as claimed in claim 8 of the present invention, the raw
material for producing the graphitization-resistant carbon is added
and mixed with a metallocene derivative containing at least one of
these metals of iron, cobalt, nickel, chromium, and manganese and
having a copolymerizing functional group, and after both of them
have been copolymerized and mixed, they are carbonization-processed
by baking, therefore, a desired electrode catalyst can easily be
prepared.
[0090] The fuel cell as claimed in claim 9 of the present invention
can be reduced in the cell module cost by using the electrode
catalyst for the fuel cell as claimed in claim 1.
[0091] In the fuel cell as claimed in claim 10 of the present
invention, the electrode catalyst for the fuel cell as claimed in
claim 1 is formed into layer-like one at least on one side of a
solid polymer electrolyte film and is used as electrode reaction
layers, therefore, the electrode-film connection body can be
reduced in cost.
[0092] In the fuel cell as claimed in claim 11 of the present
invention, the electrode reaction layers are formed from a mixture
of the electrode catalyst for the fuel cell as claimed in claim 1
and the solid polymer electrolyte, therefore, the electrolyte
network can be developed also in the direction of thickness of the
catalyst layers rather than one simply arranging the electrode
catalyst on the surface of the solid polymer electrolyte film. It
is possible to substantially increase the number of three-phased
interfaces acting as a reaction site and obtain a high electrode
activity by forming the electrode catalytic layers into such a
structure.
[0093] In the fuel cell as claimed in claim 12 of the present
invention, the electrode reaction layers as claimed in claim 10 or
claim 11 are applied to the cathode side of the fuel cell,
therefore, the cathode side manifests a high oxygen reducing
performance, and thereby the power generation performance can be
improved.
[0094] While the presently preferred embodiment of the present
invention has been shown and described, it will be understood that
the present invention is not limited thereto, and that various
changes and modifications may be made by those skilled in the art
without departing from the scope of the invention as set forth in
the appended claims.
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