U.S. patent application number 12/652468 was filed with the patent office on 2010-04-29 for fuel cell comprising oxygen electrode with surface nanostructure.
This patent application is currently assigned to PANASONIC CORPORATION. Invention is credited to Mitsuru Hashimoto, Daisuke INO, Nobuyasu Suzuki, Akira Taomoto, Yuka Yamada.
Application Number | 20100104915 12/652468 |
Document ID | / |
Family ID | 41198914 |
Filed Date | 2010-04-29 |
United States Patent
Application |
20100104915 |
Kind Code |
A1 |
INO; Daisuke ; et
al. |
April 29, 2010 |
FUEL CELL COMPRISING OXYGEN ELECTRODE WITH SURFACE
NANOSTRUCTURE
Abstract
The present invention is aimed to realize, in a fuel cell with
an oxygen electrode (a catalytic electrode), both catalytic
function and immobilization of the catalyst nanoparticles when the
catalyst nanoparticles are very small nanoparticles in the size of
1-3 nm. Oxygen electrode used in the fuel cell according to the
present invention is an oxygen electrode comprising a plurality of
carbon particles, a carbon thin-film, and surface nanostructure,
wherein the carbon particles are bonded to one another with the
carbon thin-film 2, the surface nanostructure is formed on the
surface of the carbon thin-film, the surface nanostructure
comprises catalyst nanoparticles made of platinum (Pt) and carbon
nanoparticles, diameter of each of the carbon particles is 30 nm or
more and 100 nm or less, diameter of the catalyst nanoparticle is
1.7 nm or more and 3.1 nm or less, and diameter of the carbon
nanoparticle is 1.0 nm or more and 11.2 nm or less. According to
this combination of these elements, the catalyst nanoparticles are
confined within three-dimensional structure to be formed by the
carbon nanoparticles and are immobilized without losing space which
allows any reactant to be accessed to the surface of the catalyst
nanoparticles.
Inventors: |
INO; Daisuke; (Nara, JP)
; Hashimoto; Mitsuru; (Kanagawa, JP) ; Taomoto;
Akira; (Kyoto, JP) ; Suzuki; Nobuyasu; (Osaka,
JP) ; Yamada; Yuka; (Nara, JP) |
Correspondence
Address: |
McDERMOTT WILL & EMERY LLP
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Assignee: |
PANASONIC CORPORATION
Osaka
JP
|
Family ID: |
41198914 |
Appl. No.: |
12/652468 |
Filed: |
January 5, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2009/001319 |
Mar 25, 2009 |
|
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|
12652468 |
|
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Current U.S.
Class: |
429/532 |
Current CPC
Class: |
Y02E 60/50 20130101;
H01M 4/8657 20130101; H01M 4/92 20130101; H01M 4/8605 20130101 |
Class at
Publication: |
429/30 |
International
Class: |
H01M 8/10 20060101
H01M008/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 2008 |
JP |
2008-104424 |
Claims
1. A fuel cell comprising an oxygen electrode, a hydrogen electrode
and solid polyelectrolyte, wherein the solid polyelectrolyte is
sandwiched between the oxygen electrode and the hydrogen electrode,
the oxygen electrode is a layered electrode comprising (a) a
plurality of carbon particles, (b) a carbon thin-film and (c)
surface nanostructure, wherein (d) the carbon particles 1 are
bonded to one another with the carbon thin-film, (e) the surface
nanostructure is formed on the surface of the carbon thin-film, (f)
the surface nanostructure comprises catalyst nanoparticles made of
platinum and carbon nanoparticles, (g) diameter of each of the
carbon particles is 30 nm or more and 100 nm or less, (h) diameter
of the catalyst nanoparticle is 1.7 nm or more and 3.1 nm or less,
and (i) diameter of the carbon nanoparticle is 1.0 nm or more and
11.2 nm or less.
2. The fuel cell according to claim 1, wherein said catalyst
nanoparticles immobilized in the form of contacting with a
plurality of said carbon particles.
Description
[0001] This is a continuation application under U.S.C. 111(a) of
pending prior International application No. PCT/JP2009/001319,
filed on Mar. 25, 2009, which in turn claims the benefit of
Japanese Application No. 2008-104424 filed on Apr. 14, 2008, the
disclosures of which Application are incorporated by reference
herein.
1. TECHNICAL FIELD
[0002] The present invention relates to a fuel cell characterized
in surface structure of an oxygen electrode thereof.
2. BACKGROUND ART
[0003] Power generation performance of fuel cell is strongly
depended on net surface area of catalyst contained in a catalytic
electrode. When the surface area is increased, the current density
at electrical generation is increased to improve the output
voltage. Downsizing of catalyst in the form of several nanometer
particles is an effective method to increase the surface area of
the catalyst per unit mass. Thus, nanoparticles of metal or alloy
with a diameter of about 5 nm have usually been used as catalyst
nanoparticles.
[0004] On the other hand, there was a problem of reducing the total
surface area of the catalyst due to mutual aggregation of the
catalyst nanoparticles during electrical generation by fuel cell.
In order to suppress such aggregation by dispersing the catalyst
nanoparticles into the catalytic electrode, the catalytic electrode
with large surface area, comprising acetylene black with a diameter
of 30-100 nm as a main constitutive element, has generally been
used. Since the catalyst nanoparticles were produced on the
acetylene black according to reduction-precipitation method or the
like, they were physically adsorbed on the catalytic electrode
surface. However, due to a week interaction between the catalytic
electrode surface and the catalyst nanoparticles, this method is
not capable of preventing the aggregation of smaller catalyst
nanoparticles especially with a diameter of 1-3 nm. Large surface
area of the catalyst nanoparticles fails to be kept during
electrical generation. Excellent power generation performance which
appeared at the earlier stage therefore rapidly disappears.
[0005] In order to solve this problem, proposed were a method for
immobilizing platinum nanoparticles by degrading carbon monoxide or
hydrocarbons at the surface of the platinum nanoparticles which
serve as catalyst nanoparticles and adsorbing carbon to the site
adjacent thereto (Patent Publication 1) and a method for implanting
platinum into the carbon nanoparticles by simultaneously
evaporating carbon and platinum with arc discharge (Patent
Publication 2). Also there was a method for introducing chemical
bonding force based on molecular cross-linked structure or the like
at an interface between the catalyst nanoparticles and the carbon
nanoparticles such as acetylene black and immobilizing those
(Patent Publication 3).
[0006] Patent Publication 1: Japanese Patent Laid-Open Publication
No. Sho 54-82394
[0007] Patent Publication 2: Japanese Patent Laid-Open Publication
No. 2006-140017
[0008] Patent Publication 3: Japanese Patent Laid-Open Publication
No. 2004-207228
[0009] Patent Publication 4: Japanese Patent Laid-Open Publication
No. 2005-087864
[0010] Patent Publication 5: Japanese Patent Laid-Open Publication
No. 2005-129369
[0011] Patent Publication 6: Japanese Patent Laid-Open Publication
No. 2006-156366
SUMMARY OF THE INVENTION
[0012] According to the foregoing conventional methodologies, since
the platinum nanoparticles were completely embedded below carbon
overlayers at the earlier stage, any reactive element (oxygen,
hydrogen) is not capable of being accessed to the surface thereof
to lose any catalytic function. In order to reactivate platinum
surface without losing any immobilizing function by carbon
overlayers, it is necessary to remove such carbons in angstrom
accuracy, however, this needs very precise operation. According to
a method of removing carbons with oxidation, carbons exposed at the
surface will be removed at substantially uniform reaction rate. On
the other hand, under the nanometer scale, adsorption level and
vapor deposition level on carbons for the platinum nanoparticles
are inhomogeneous locally. Thus, it is substantially impossible to
apply similar immobilizing treatment to the numerous platinum
nanoparticles, any desired immobilizing effect would not be
realized thereby.
[0013] When chemical bonding force based on molecular cross-linked
structure was employed to immobilize the catalyst nanoparticles,
there are problems both of significantly changing the surface
property of the catalyst nanoparticles with chemical bonding and of
significantly reducing the surface area with catalytic
activity.
[0014] The present invention is to solve the foregoing problems
known in the prior arts and is aimed to provide a fuel cell with an
oxygen electrode which realizes both catalytic function and
immobilization of the catalyst nanoparticles simultaneously even if
they are very small nanoparticles.
[0015] The present invention is directed to a fuel cell comprising
an oxygen electrode, a hydrogen electrode and solid
polyelectrolyte,
[0016] wherein the solid polyelectrolyte is sandwiched between the
oxygen electrode and the hydrogen electrode, [0017] the oxygen
electrode is a layered electrode comprising [0018] (a) a plurality
of carbon particles 1, [0019] (b) a carbon thin-film 2, and [0020]
(c) surface nanostructure 3, wherein [0021] (d) the carbon
particles 1 are bonded to one another by the carbon thin-film 2,
[0022] (e) the surface nanostructure 3 is formed on surface of the
carbon thin-film 2, [0023] (f) the surface nanostructure 3
comprises catalyst nanoparticles 4 made of platinum and carbon
nanoparticles 5, [0024] (g) diameter of each of the carbon
particles 1 is 30 nm or more and 100 nm or less, [0025] (h)
diameter of the catalyst nanoparticle 4 is 1.7 nm or more and 3.1
nm or less, and [0026] (i) diameter of the carbon nanoparticle 5 is
1.0 nm or more and 11.2 nm or less.
[0027] According to the present invention with regard to the oxygen
electrode, since the catalyst nanoparticles are arranged at vacancy
and recess formed with the carbon nanoparticles in the
three-dimensional surface nanostructure, the catalyst nanoparticles
is capable of receiving reactant molecules and offer their
catalytic activities. In addition, the catalyst nanoparticles are
located into surface and inner of the three-dimensional structure
formed with the carbon nanoparticles and are immobilized
thereby.
[0028] Furthermore, by immobilizing the catalyst nanoparticles in
the form of contacting with a plurality of carbon nanoparticles,
the catalyst nanoparticles will not be allowed to pass any opening
among carbon nanoparticles, and aggregation thereof can duly be
suppressed.
[0029] According to the fuel cell of the present invention,
improved and stable power generation performance will be realized
without reducing reactive area in the catalyst.
[0030] These and other objects, additional aspects and advantages
of the present invention will become apparent from the following
detailed description on the preferred embodiments by referring to
the drawings attached hereto.
[0031] According to the fuel cell of the present invention, by
using therein the oxygen electrode with the surface nanostructure,
the catalyst nanoparticles with a diameter of about 1-3 nm fail to
aggregate substantially when they contact with adjacent
nanoparticles. Since it is not necessary to cover surface of the
catalyst nanoparticles with molecules or carbon overlayers,
reactant molecules are capable of reaching the surface of the
catalyst nanoparticles and their catalytic activities are also not
be inhibited. Therefore, it comes to be possible to realize both
catalytic function and immobilization of the catalyst nanoparticles
on the surface of the catalytic electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a cross-sectional view of the oxygen electrode
with surface nanostructure according to Embodiment 1.
[0033] FIG. 2 is a view illustrating relation between size of
carbon nanoparticles and that of catalyst nanoparticles according
to Embodiment 1.
[0034] FIG. 3 is a picture taken with scanning tunneling microscope
(STM) for surface nanostructure according to Reference Example.
[0035] FIG. 4 is a graph illustrating STM height profile on carbon
nanoparticles according to Reference Example.
[0036] FIG. 5 is an picture taken with cross-sectional transmission
electron microscope (TEM) on surface nanostructure according to
Reference Example.
[0037] FIG. 6 is a view illustrating plots on upper limit and lower
limit of carbon nanoparticles with respect to catalyst
nanoparticles according to Embodiment 1.
[0038] FIG. 7 is a view illustrating Raman spectrum on carbon
nanoparticles according to Reference Example.
[0039] FIG. 8 is a cross-sectional view illustrating cell for the
fuel cells according to Example 1 and Comparative Example 1.
[0040] FIG. 9 is a graph illustrating the experiment results on
stability of platinum nanoparticles contained in the oxygen
electrode according to Example 1 and Comparative Example 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] Embodiments of the present invention are described as
follows with reference to the drawings attached hereto.
Embodiments
[0042] FIG. 1 is a cross-sectional view of the oxygen electrode (a
catalytic electrode) with surface nanostructure according to
Embodiment 1. In FIG. 1, 1 indicates the carbon particles of
conductive powder, 2 indicates the carbon thin-film of conductive
thin-film, and 3 indicates the surface nanostructure. Carbon
particles 1 are bonded to one another with the carbon thin-film 2,
and the surface nanostructure 3 is formed on the surface of the
carbon thin-film 2. Such constitutive elements increase the surface
nanostructure 3 per unit volume of the oxygen electrode.
[0043] Surface nanostructure 3 formed on the carbon thin-film 2
further comprises the catalyst nanoparticles 4 and the carbon
nanoparticles 5. Right column of FIG. 1 is the enlarged view of the
outermost of the surface nanostructure 3. Quasi-spherical carbon
nanoparticles 5 form three-dimensional structure where the catalyst
nanoparticles 4 are confined at vacancies and recess. This surface
structure has pathways to surface of catalyst nanoparticles which
reactant molecules pass through, even though catalyst nanoparticles
are located in subsurface vacancy. In addition, the catalyst
nanoparticles 4 are preventing from passing through opening among
the carbon nanoparticles 5 and are duly immobilized.
[0044] Surface nanostructure 3 is capable of offering their
function when at least two or three carbon nanoparticles are
stacked along with the depth direction. Thus, any kind and shape of
a substrate for forming the surface nanostructure 3 can be used if
they are available for fuel cell. For example, acetylene black with
a diameter of 30 nm or more and 100 nm or less is available as the
carbon particles 1 as noted in the column of BACKGROUND ART. Then,
the carbon thin-film produced by heat-treating polymer containing
carbon is available as the carbon thin-film 2.
[0045] The relation between the size of the catalyst nanoparticles
and that of the carbon nanoparticles is described. In FIG. 2, the
denotation 6 is a plan view showing the relation between the size
of the carbon nanoparticles and that of the catalyst nanoparticles.
The denotation 7 is a cross-sectional view of the plan view 6. In
FIG. 2, 8 indicates a carbon nanoparticle, and the opening made by
aligning and closest packing three carbon nanoparticles 8 is
indicated therein as the denotation 9. In order to immobilize the
catalyst nanoparticles in a space made by the carbon nanoparticles
8, it is necessary that the diameter of the catalyst nanoparticles
is at least larger than the opening 9. Namely, with regard to the
size of the catalyst nanoparticles (diameter a nm) to that of the
carbon nanoparticles 8 (diameter b nm), it is necessary that b is
less than 3/(2- 3)a in order to realize the minimum size which
allows immobilization of them with the opening 9.
[0046] On the other hand, the minimum size of the carbon
nanoparticles is preferably 1 nm or more in order to pass the
reactant molecules (gaseous molecules such as hydrogen or oxygen)
through the opening 9. Diameter b in the carbon nanoparticles
should therefore meet the equation of 1.ltoreq.b.ltoreq. 3/(2-
3)a.
Reference Example
Preparation of Surface Nanostructure
[0047] Platinum (Pt) nanoparticles with a diameter of 1.7-3.1 nm
were prepared as the catalyst nanoparticles 4, and the surface
nanostructure 3 was produced on the 12 mm square of Highly Oriented
Pyrolytic graphite (NT-MDT, Russia).
[0048] The catalyst precursor solution containing platinum was
prepared by mixing 0.95 g of chloroplatinic acid (IV)hexahydrate
(Wako Pure Chemical Industries, Ltd.), 7.85 g of polyamic acid
solution and 17.5 g of dimethylacetamide (Wako Pure Chemical
Industries, Ltd.; Guaranteed Reagent). Polyamic acid was prepared
by synthesizing 4,4'-diaminodiphenylether (Tokyo Chemical Industry
Co., Ltd.) and pyromellitic acid anhydride (Tokyo Chemical Industry
Co., Ltd.). Synthesis was performed by mixing 5.00 g of
4,4'-diaminodiphenylether and 120 g of dimethylacetamide, then
dissolving those, adding thereto 5.45 g of pyromellitic acid
anhydride, and agitating them for about three hours.
[0049] In the Reference Example, the catalyst precursor solution
was diluted four-fold with dimethylacetamide, then it was dropped
on the freshly cleaved graphite. Excess solution on the graphite
was removed with spin coating method (5,000 rpm revolution, 150
seconds), and the solvent was evaporated in the low-vacuum chamber.
Then the graphite base was heated with the low-vacuum dryer.
Temperature was elevated from the room temperature to 200.degree.
C. in 40 minutes and the elevated temperature was kept for two
hours. Finally, this graphite was transferred to an infrared
imaging furnace under the argon atmosphere and was heated for 30
minutes at arrival temperature of 800.degree. C. which was elevated
in the range of 1-20.degree. C. per second. As a result of these
procedures, the surface nanostructure 3 consisting of both the
carbon nanoparticles and the platinum nanoparticles is
prepared.
[0050] FIG. 3 shows the surface nanostructure taken by scanning
tunneling microscope (STM). The observation was performed under the
air atmosphere, and bias voltage for the sample was 0.3 V and
tunnel current was 0.3 nA. The surface was covered with particulate
substances. Ratio of the elements contained in this surface was
0.0006 atom of platinum to one atom of carbon. Thus, almost all of
the observed particles were carbon nanoparticles. Twenty carbon
nanoparticles were randomly sampled from FIG. 3 and the diameter of
the carbon nanoparticles were determined with height profile of
STM. FIG. 4 shows a cross section height profile taken from
X.sub.1-X.sub.2 line in FIG. 3. When a peak was fitted by using
Gaussian function and full width at half maximum was regarded as
the diameter of the carbon nanoparticles, the average value was
determined to be 6.1 nm. Then, when distribution of the diameter
was regarded as normal distribution and confidence interval was
0.997, 3.sigma.=5.1 nm was obtained. Therefore, 99.7% of the carbon
nanoparticles shown in FIG. 3 each have a diameter of 1.0 nm or
more and 11.2 nm or less.
[0051] FIG. 5 shows the result of observation on cross-section of
the surface nanostructure with transmission electron microscope
(TEM) to determine the diameter of the platinum nanoparticles
contained in the surface nanostructure. In order to observe the
cross-section, a carbon vapor-deposited film was formed on the
outermost of the surface nanostructure. Three area (i), (ii) and
(iii) were identified in this picture, namely, they were (i) the
carbon deposited film for TEM observations, (ii) the surface
nanostructure and (iii) graphite substrate, respectively. Thickness
of the surface nanostructure was about 20 nm. In the area (ii),
there were dark spots in size of about several nm, and they were
identified as platinum by using electron diffraction. One thousand
platinum nanoparticles were sampled in the optional sites, then the
average diameter thereof was determined as 2.4 nm and 3.sigma.=0.7
nm was obtained. Therefore, 99.7% of the carbon nanoparticles may
each have a diameter of 1.7 nm or more and 3.1 nm or less.
[0052] FIG. 6 shows the relation between the diameter of the carbon
nanoparticles and that of the platinum nanoparticles according to
Embodiment 1. In FIG. 6, the hatched area denoted as 11 is the
diameter range of the carbon nanoparticles and of the platinum
nanoparticles determined respectively in Reference Example. The
hatched area is fallen within the diameter range of
1.ltoreq.b.ltoreq. 3(2- 3)a for realizing the surface nanostructure
3.
[0053] FIG. 7 shows the result obtained by measuring, with Raman
spectroscopy analysis, the ratio of graphite of the carbon
nanoparticles 5 which are the constitutive element of the surface
nanostructure 3. Analysis was performed under the air atmosphere,
and wavelength of the excitation light was 488 nm. Intensity area
ratio F/G of Peak F at 1,375 cm.sup.-1 and Peak G at 1,595
cm.sup.-1 was 3.0.
Example 1
Production of Oxygen Electrode
[0054] Oxygen electrode was produced by bonding acetylene black of
the carbon particles 1 with the carbon thin-film produced by
heat-treating macromolecule as the carbon thin-film 2 and forming
on their surface the surface nanostructure 3 as shown in Reference
Example.
[0055] Then, 4.0 g of acetylene black (DENKI KAGAKU KOGYO KABUSHIKI
KAIHSA) with a diameter of about 50 nm, 2.0 g of polyacrylonitrile
(Sigma-Aldrich Corporation) and 54.6 g of dimethylacetamide (Wako
Pure Chemical Industries, Ltd.) were mixed and the mixture was
agitated for 20 hours with a ball mill. 1.69 g of this mixture was
dropped on 19.6 cm.sup.2 of carbon paper (Toray), and the solvent
was evaporated in the low-vacuum chamber. Then the carbon paper was
heated with the low-vacuum dryer. Temperature was elevated from the
room temperature to 120.degree. C. in 40 minutes and the elevated
temperature was kept for 2 hours. Finally, this carbon paper was
transferred to an infrared imaging furnace under the argon
atmosphere and was heated for 30 minutes at arrival temperature of
800.degree. C. which was elevated in the range of 1-20.degree. C.
per second. As a result of foregoing procedures, the carbon paper
comprising a layer formed by the acetylene black bound with the
carbon thin-film was produced.
[0056] Then, 1.26 g of the catalyst precursor solution noted in
Reference Example was dropped on the carbon paper prepared
previously, and the solvent was evaporated in the low-vacuum
chamber. Then the carbon paper was heated with the low-vacuum
dryer. Temperature was elevated from the room temperature to
200.degree. C. in 40 minutes and the elevated temperature was kept
for 2 hours. Finally, heating was conducted in an infrared imaging
furnace under the argon atmosphere for 30 minutes at arrival
temperature of 800.degree. C. which was elevated at 10.degree. C.
per second.
[0057] As a result of foregoing procedures, the oxygen electrode
(the catalytic electrode) with the surface nanostructure is
produced.
Comparative Example 1
Production of Comparative Electrode
[0058] For a comparative example on stability of the platinum
nanoparticles with a diameter of about 2 nm, a conventional oxygen
electrode (a catalytic electrode) used in fuel cell was prepared as
a comparative electrode. Main elements of the comparative electrode
are the carbon paper and acetylene black with a diameter of about
50 nm. Platinum nanoparticles were produced with
reduction-precipitation method and were physically adsorbed onto
the acetylene black. Average diameter of the platinum nanoparticles
was 2.3 nm and was comparable to those referred to in Reference
Example. Relation between average diameter of the acetylene black
and that of the platinum nanoparticles according to Comparative
Example 1 is shown as the denotation 12 in FIG. 6. Average diameter
of the acetylene black is larger than the upper limit of the
appropriate diameter to realize the surface nanostructure 3.
[0059] [Evaluation of Oxygen Electrode]
[0060] A fuel cell installed the oxygen electrodes and evaluation
experiments of the oxygen electrodes are described. FIG. 8 is the
cross-sectional view showing the structure of the cell.
Constitutive elements of the cell are the oxygen electrode 15, the
hydrogen electrode 16, the solid polyelectrolyte membrane (Nafion,
DuPont) 14, the separator 13 which sandwich these elements, the gas
passage 17 for the oxygen electrode, and the gas passage 18 for the
hydrogen electrode. As the oxygen electrode 15, the oxygen
electrode and the comparative electrode respectively noted in
Example 1 and Comparative Example 1 were used. 10 mg/cm.sup.2 of
Nafion disperse solution (Sigma-Aldrich Corporation) was dropped
onto surface of the oxygen electrode 15 and was incorporated into
the cell. Hydrogen electrode 16 was produced by using
platinum-ruthenium as a material for the catalyst nanoparticle and
dropping those prepared along with ink method onto carbon
paper.
[0061] FIG. 9 shows the result of the experiment on stability of
the platinum nanoparticles contained in the oxygen electrode 15.
Nitrogen and hydrogen were introduced respectively into the gas
passage 17 for the oxygen electrode and the gas passage 18 for the
hydrogen electrode at the flow rate of 50 ml/minutes. Aggregation
and deterioration of the platinum nanoparticles were accelerated by
repeatedly sweeping electrical potential of the oxygen electrode 15
to the hydrogen electrode 16 in the range of from 0.1 V to 1.0 V.
Number of this electrical potential cycle was represented as the
horizontal axis in FIG. 9. Vertical axis represented the normalized
surface area of the platinum nanoparticles in the oxygen electrode
15. Surface area was determined with the hydrogen adsorption
desorption peak in cyclic voltammetry, and it was corresponding to
the area of electrochemically active surface. Change on this
surface area is very preferable index on the aggregation of the
platinum nanoparticles. When such electrical potential cycle was
performed 4,000 times, about half of the surface area 20 in the
comparative electrode was deactivated, but the surface area 19 in
the oxygen electrode was substantially kept. It is apparent that,
due to the surface nanostructure which constitutes the outermost
surface of the oxygen electrode according to Example 1, the
catalytic activity and the stability of the platinum nanoparticles
were maintained.
[0062] It is obvious for one skilled in the art from the foregoing
disclosure that numerous modification of the present invention and
the other embodiments of the present invention. Accordingly, the
foregoing disclosure should be regarded as an illustration only and
is presented in order to teach one skilled in the art as to how to
realize the best mode of the present invention. Details of the
structure and/or function of the present invention can
substantially be changed without departing from the spirit
thereof.
[0063] The fuel cell according to the present invention comprises
the oxygen electrode comprising the surface nanostructure which
allows both the catalytic function and immobilization of the
catalyst nanoparticles with a diameter of about 1-3 nm, and offers
improved stability on such catalytic function.
* * * * *