U.S. patent application number 17/088732 was filed with the patent office on 2021-02-25 for support for fuel cell, method of preparing the same, and electrode for fuel cell, membrane-electrode assemby for a fuel cell and fuel cell system including same.
The applicant listed for this patent is KOLON INDUSTRIES, INC.. Invention is credited to Jun-Young KIM, Sung-Chul LEE, Myoung-Ki MIN, Yong-Bum PARK.
Application Number | 20210057761 17/088732 |
Document ID | / |
Family ID | 1000005195309 |
Filed Date | 2021-02-25 |
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United States Patent
Application |
20210057761 |
Kind Code |
A1 |
KIM; Jun-Young ; et
al. |
February 25, 2021 |
SUPPORT FOR FUEL CELL, METHOD OF PREPARING THE SAME, AND ELECTRODE
FOR FUEL CELL, MEMBRANE-ELECTRODE ASSEMBY FOR A FUEL CELL AND FUEL
CELL SYSTEM INCLUDING SAME
Abstract
A support for a fuel cell includes a substrate including highly
crystalline carbon, and a crystalline carbon layer on the
substrate.
Inventors: |
KIM; Jun-Young; (Yongin-si,
KR) ; LEE; Sung-Chul; (Yongin-si, KR) ; MIN;
Myoung-Ki; (Yongin-si, KR) ; PARK; Yong-Bum;
(Yongin-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOLON INDUSTRIES, INC. |
Seoul |
|
KR |
|
|
Family ID: |
1000005195309 |
Appl. No.: |
17/088732 |
Filed: |
November 4, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14069853 |
Nov 1, 2013 |
10862136 |
|
|
17088732 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/926 20130101;
H01M 2008/1095 20130101; H01M 4/921 20130101; H01M 4/92
20130101 |
International
Class: |
H01M 4/92 20060101
H01M004/92 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 4, 2013 |
KR |
10-2013-0022990 |
Claims
1. A method of preparing the support for a fuel cell, the method
comprising: adding a monomer for a graphitizable polymer to a
liquid containing a highly crystalline carbon suspended therein to
prepare a mixture, the highly crystalline carbon having a Raman
spectrum intensity ratio between a (1360) plane and a (1580) plane,
I.sub.D/I.sub.G ((I(1360 cm.sup.-1)/I(1580 cm.sup.-1)) of about
0.24 to about 0.91; adding a polymerization initiator to the
mixture to perform polymerization and prepare a polymerization
product; stabilizing the polymerization product to prepare a
stabilized product; first heat-treating the stabilized product to
provide a first heat-treated product; second heat-treating and
carbonizing the first heat-treated product to provide a resultant;
and third heat-treating and graphitizing the resultant.
2. The method of preparing the support for a fuel cell as claimed
in claim 1, wherein the polymerization product includes highly
crystalline carbon and a carbon layer in a form of a continuous
coating on the highly crystalline carbon, wherein the carbon layer
has a coating ratio represented by the following Equation 1 of
about 100% to about 800%: Coating
ratio=[(W.sub.f-W.sub.0)/W.sub.0].times.100(%) [Equation 1]
wherein, W.sub.0 denotes a weight (g) of highly crystalline carbon
in the substrate, and W.sub.f denotes a weight (g) of total
polymerization product in the substrate and carbon layer.
3. The method of preparing the support for a fuel cell as claimed
in claim 1, wherein the first heat-treating is performed at about
300.degree. C. to about 700.degree. C.
4. The method of preparing the support for a fuel cell as claimed
in claim 1, wherein the stabilizing is performed at about
220.degree. C. to about 280.degree. C.
5. The method of preparing the support for a fuel cell as claimed
in claim 1, wherein the second heat-treating includes a first
heating stage at about 400.degree. C. to about 800.degree. C., and
second heating stage at about 800.degree. C. to about 1200.degree.
C.
6. The method of preparing the support for a fuel cell as claimed
in claim 1, wherein the third heat-treating is performed at about
1200.degree. C. to about 2500.degree. C.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. application Ser.
No. 14/069,853, filed on Nov. 1, 2013, which claims priority to
Korean Patent Application No. 10-2013-0022990, filed on Mar. 4,
2013, in the Korean Intellectual Property Office, the entire
disclosure of which is incorporated by reference herein in its
entirety.
BACKGROUND
1. Field
[0002] Embodiments relate to a support for a fuel cell, method of
preparing the same, an electrode for a fuel cell, a
membrane-electrode assembly for a fuel cell including the same, and
a fuel cell system including the same.
2. Description of the Related Art
[0003] A fuel cell is a power generation system for producing
electrical energy through an electrochemical redox reaction of an
oxidant and a fuel such as hydrogen or a hydrocarbon-based material
such as methanol, ethanol, natural gas, and the like.
[0004] Such a fuel cell is a clean energy source that may replace
fossil fuels. A fuel cell may include a stack composed of unit
cells, and may produce various ranges of power output. The fuel
cell has a four to ten times higher energy density than a small
lithium battery and thus, has been high-lighted as a small portable
power source.
[0005] Representative exemplary fuel cells include a polymer
electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel
cell (DOFC). The direct oxidation fuel cell includes a direct
methanol fuel cell which uses methanol as a fuel.
[0006] The polymer electrolyte fuel cell has advantages of high
energy density and high power, and a direct oxidation fuel cell has
lower energy density than that of the polymer electrolyte fuel
cell, but has advantages of easy handling of the liquid-type fuel,
a low operation temperature, and no need for an additional fuel
reforming processor.
[0007] In the aforementioned fuel cell system, a stack that
substantially generates electricity includes several to scores of
unit cells stacked adjacent to one another, and each unit cell is
composed of a membrane-electrode assembly (MEA) and a separator
(also referred to as a bipolar plate). The membrane-electrode
assembly is composed of an anode (also referred to as a "fuel
electrode" or an "oxidation electrode") and a cathode (also
referred to as an "air electrode" or a "reduction electrode") that
are separated by a polymer electrolyte membrane.
[0008] Electricity is generated as follows. A fuel is supplied to
the anode and adsorbed on catalysts of the anode and then, oxidized
to produce protons and electrons. The electrons are transferred
into the cathode via an external circuit, while the protons are
transferred into the cathode through the polymer electrolyte
membrane. In addition, an oxidant is supplied to the cathode. Then,
the oxidant reacts with the protons and the electrons on the
catalysts of the cathode to produce electricity along with
water.
SUMMARY
[0009] Embodiments are directed to a support for a fuel cell
including a substrate including highly crystalline carbon, and a
crystalline carbon layer on the substrate.
[0010] The crystalline carbon layer may have a thickness of about 1
nm to about 40 nm.
[0011] The highly crystalline carbon may have a Raman spectrum
intensity ratio between a (1360) plane and a (1580) plane,
I.sub.D/I.sub.G ((I(1360 cm.sup.-1)/I(1580 cm.sup.-1)) of about
0.24 to about 0.91.
[0012] The highly crystalline carbon may include carbon nanotube,
carbon nanowire, heat-treated carbon black, graphite, graphene, or
a combination thereof.
[0013] Embodiments are also directed to a method of preparing the
support for a fuel cell including adding a monomer for a
graphitizable polymer to a highly crystalline carbon liquid to
prepare a mixture, adding a polymerization initiator to the mixture
to perform polymerization and prepare a polymerization product,
stabilizing the polymerization product to prepare a stabilized
product, first heat-treating the stabilized product to provide a
first heat-treated product, second heat-treating and carbonizing
the first heat-treated product to provide a resultant, and third
heat-treating and graphitizing the resultant.
[0014] The polymerization product may include highly crystalline
carbon and a carbon layer. The carbon layer may have a coating
ratio represented by the following Equation 1 of about 100% to
about 800%.
Coating ratio=[(W.sub.f-W.sub.0)/W.sub.0].times.100(%) [Equation 1]
[0015] wherein, W.sub.0 denotes a weight (g) of highly crystalline
carbon in the substrate, and [0016] W.sub.f denotes a weight (g) of
total polymerization product in the substrate and carbon layer.
[0017] The first heat-treating may be performed at about
300.degree. C. to about 700.degree. C.
[0018] The stabilizing may be performed at about 220.degree. C. to
about 280.degree. C.
[0019] The second heat-treating may include a first heating stage
at about 400.degree. C. to about 800.degree. C. and second heating
stage at about 800.degree. C. to about 1200.degree. C.
[0020] The third heat-treating may be performed at about
1200.degree. C. to about 2500.degree. C.
[0021] Embodiments are also directed to an electrode for a fuel
cell including an electrode substrate, and a catalyst layer on the
electrode substrate, the catalyst layer including the support as
disclosed above and an active metal supported on the support.
[0022] The active metal may include platinum, ruthenium, osmium, a
platinum-ruthenium alloy, a platinum-osmium alloy, a
platinum-palladium alloy, or a platinum-M alloy, wherein M is at
least one transition element selected from Ga, Ti, V, Cr, Mn, Fe,
Co, Ni, Cu, Zn, Sn, Mo, W, Rh, and Ru.
[0023] Embodiments are also directed to a membrane-electrode
assembly for a fuel cell including a cathode and an anode facing
each other and a polymer electrolyte membrane between the cathode
and anode. At least one of the cathode and anode may be the
electrode disclosed above.
[0024] Embodiments are also directed to fuel cell system including
at least one electricity generating element including the
membrane-electrode assembly disclosed above and a separator
positioned at each side of the membrane-electrode assembly, a fuel
supplier that supplies the electricity generating element with a
fuel, and an oxidant supplier that supplies the electricity
generating element with an oxidant.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Features will become apparent to those of skill in the art
by describing in detail exemplary embodiments with reference to the
attached drawings in which:
[0026] FIG. 1 illustrates a schematic view showing a fuel cell
system according to one embodiment;
[0027] FIG. 2 illustrates a TEM photograph of the support obtained
from Example 1;
[0028] FIG. 3 illustrates a graph showing FT-IR of the support
precursor obtained from Preparation Example 1;
[0029] FIG. 4 illustrates a graph showing XPS (X-ray photoelectron
spectroscopy) survey spectra of the support obtained from
Comparative Example 1 and the support precursor obtained from
Preparation Example 1;
[0030] FIG. 5 illustrates a high-resolution transmission electron
microscope (HR-TEM) photograph of the catalyst obtained by
supporting Pt nanoparticles in the support obtained from Example
2;
[0031] FIG. 6 illustrates a high-resolution transmission electron
microscope (HR-TEM) photograph of the support obtained from Example
2;
[0032] FIG. 7 illustrates a graph showing XPS C1s core-level
spectra of the carbon support obtained from Example 1 (a); and FIG.
7B is a graph showing XPS Pt4f core-level spectra of the catalyst
obtained from Example 3(b);
[0033] FIG. 8 illustrates a graph showing a decreasing rate of
electrochemical active area of a half cell obtained using the
catalysts obtained from Examples 3, 4 and Comparative Examples 4 to
6;
[0034] FIG. 9 illustrates a graph showing an electrochemical
surface area of a half cell obtained using the catalysts obtained
from Examples 3, 4 and Comparative Examples 4 to 6;
[0035] FIG. 10 illustrates a graph showing a Raman spectrum of the
supports obtained from Examples 1 and 2 and Comparative Examples 1,
2 and the catalysts obtained from Comparative Example 6 and a
Control; and
[0036] FIG. 11 illustrates a graph showing the Raman spectrum area
ratio and intensity ratio of supports obtained from Examples 1 to 2
and Comparative Examples 1, 2 and the catalysts obtained from
Comparative Example 6 and a Control.
DETAILED DESCRIPTION
[0037] Example embodiments will now be described more fully
hereinafter with reference to the accompanying drawings; however,
they may be embodied in different forms and should not be construed
as limited to the embodiments set forth herein. Rather, these
embodiments are provided so that this disclosure will be thorough
and complete, and will fully convey exemplary implementations to
those skilled in the art.
[0038] In the drawing figures, the dimensions of layers and regions
may be exaggerated for clarity of illustration. It will also be
understood that when a layer or element is referred to as being
"on" another layer or substrate, it can be directly on the other
layer or substrate, or intervening layers may also be present.
Further, it will be understood that when a layer is referred to as
being "under" another layer, it can be directly under, and one or
more intervening layers may also be present. In addition, it will
also be understood that when a layer is referred to as being
"between" two layers, it can be the only layer between the two
layers, or one or more intervening layers may also be present. Like
reference numerals refer to like elements throughout.
[0039] One embodiment provides a support for a fuel cell that
includes a substrate including highly crystalline carbon and a
crystalline carbon layer disposed on the substrate.
[0040] The highly crystalline carbon may be carbon nanotube, carbon
nanowire, heat-treated carbon black, graphite, graphene, or a
combination thereof.
[0041] If heat-treated carbon black is used, the heat-treated
carbon black may be prepared by heat-treating the carbon black at
about 1000.degree. C. to about 2500.degree. C. for about 30 minutes
to about 1 hour. The heat treatment atmosphere may be N.sub.2, Ar,
or a combination thereof. The heat treatment may be performed at a
heat-up rate of about 1.degree. C./min to about 6.degree. C./min.
When the heat treatment is performed with a rising temperature, the
heat treatment may be performed in 3 steps from the low temperature
to the high temperature. In this case, the heat-up rate may be
changed in each step so that the heat-up rate is decreased as
increasing the temperature.
[0042] The thickness of the substrate including highly crystalline
carbon and the crystalline carbon layer may be appropriately
adjusted according to the kind of carbon that is used. According to
an implementation, the crystalline carbon layer may have a
thickness of about 1 nm to about 40 nm.
[0043] In one embodiment, the highly crystalline carbon may have a
Raman spectrum intensity ratio between a (1360) plane and a (1580)
plane, I.sub.D/I.sub.G ((I(1360 cm.sup.-1)/I(1580 cm.sup.-1)) of
about 0.24 to about 0.91. When the highly crystalline carbon has
the Raman spectrum intensity ratio within this range, the high
crystalline and the high graphitization degree may be obtained, so
as to provide advantages of low carbon oxidation rate.
[0044] In one embodiment, the highly crystalline carbon may have an
interlayer spacing (d002) of a (002) plane of 3.35 .ANG. to 3.55
.ANG..
[0045] The support according to one embodiment has a structure that
includes a highly crystalline carbon substrate and a crystalline
carbon layer disposed on the substrate. Such a structure may have
improved durability. The crystalline carbon layer may be formed
from the graphitizable polymer, and a functionalized carbon
structure having a high graphitization degree may be formed while
crystallizing the graphitizable polymer. Accordingly, resistance to
oxidation corrosion may be improved if the functionalized carbon
has a high crystallinity. In addition, the support according to one
embodiment may effectively suppress the support corrosion if fewer
defects are present on the surface of support, and the support may
have improved stability due to the high resistance. As the gaps
between re bond of the functional carbon acts as an anchoring
center, the adherence between the support and the catalyst may be
increased, and the support aggregation may be suppressed. In
addition, the stable structure and the anchoring site of the
functionalized carbon may suppress the phenomenon that the catalyst
is aggregated or detached from the support, so as to prevent or
reduce catalyst corrosion.
[0046] Generally, a Pt/C catalyst supporting Pt nanoparticle in the
carbon support is widely used as a catalyst for a fuel cell, but
the electrochemical surface area (ECSA) of Pt is shapely decreased
by the phenomenon of carbon support corrosion, Pt nanoparticle
decomposition, Ostwald ripening, and aggregation. As a result, the
durability of the catalyst may remarkably deteriorate.
[0047] According to an embodiment, the support may have improved
durability, such that deterioration may be prevented or
hindered.
[0048] Another embodiment provides a method of preparing the
support for a fuel cell. The method includes adding a monomer for a
graphitizable polymer to a highly crystalline carbon liquid (for
example, a highly crystalline carbon dissolved or suspended in a
liquid) to prepare a mixture, adding a polymerization initiator to
the mixture to perform polymerization and prepare a polymerization
product, stabilizing the polymerization product to prepare a
stabilized product, first heat-treating the stabilized product,
second heat-treating and carbonizing the first heat-treated
product, and third heat-treating and graphitizing the resultant.
Hereinafter, a method of preparing the support for a fuel cell
according to one embodiment is described in detail.
[0049] First, a precursor for forming a graphitizable polymer is
added to the highly crystalline carbon liquid.
[0050] The highly crystalline carbon liquid may be prepared by
adding a highly crystalline carbon in a solvent. The carbon liquid
may be a carbon suspension. After adding the highly crystalline
carbon into the solvent, the ultrasonic wave treatment may be
carried out. The ultrasonic wave treatment may be performed for
about 5 minutes to about 60 minutes.
[0051] The highly crystalline carbon may be added to the solvent in
an amount of about 1 wt % to about 70 wt % based on 100 percent by
weight of the solvent.
[0052] The highly crystalline carbon may be carbon nanotube, carbon
nanowire, heat-treated carbon black, graphite, graphene, or a
combination thereof.
[0053] The precursor for forming a graphitizable polymer may be a
diarylacetylene derivative, an alkyl derivative, an alkoxy
derivative (benzophenone, phosphate), a 1,6-heptadiene-based
compound, a dihalohetero compound, an ethynyl compound or a
combination thereof. According to an implementation, the precursor
be any precursor being capable of forming of a polymer of
polyacrylonitrile, polycaprolactone, polyvinylene, polynaphthalene,
polyimide, polyketone, polyarylene derivative, polyarylene-vinylene
or a combination thereof.
[0054] A polymerization initiator may be added to the mixture to be
polymerized. The polymerization initiator may be ammonium
persulfate ((NH.sub.4).sub.2S.sub.2O.sub.8), potassium persulfate
(K.sub.2S.sub.2O.sub.8), azobisisobutyronitrile
(C.sub.8H.sub.12N.sub.4), or a combination thereof, as examples.
The polymerization initiator may be added in a suitable amount for
initiating the polymerization reaction of the monomer for a
graphitizable polymer.
[0055] The polymerization may be performed by agitating under an
atmosphere of nitrogen, argon, or a combination thereof at a
temperature of about 0.degree. C. to about 70.degree. C. for about
1 hour to about 48 hours.
[0056] The polymerization product may be cleaned according to a
general washing process. In addition, the polymerization product
may be vacuum-dried at about 60.degree. C. to about 120.degree.
C.
[0057] The polymerization product includes highly crystalline
carbon and a carbon layer. The carbon layer may be formed on the
highly crystalline carbon. The carbon layer may have a coating
ratio represented by the following Equation 1 of about 100% to
about 800%. In an implementation, the carbon layer may have a
coating ratio of about 110% to about 800%.
Coating ratio=[(W.sub.f-W.sub.0)/W.sub.0].times.100(%) [Equation 1]
[0058] (W.sub.0: weight (g) of highly crystalline carbon in the
substrate, and [0059] W.sub.f: weight (g) of total polymerization
product including the substrate and a crystalline carbon layer)
[0060] When the coating ratio of carbon layer is within this range,
the carbon layer may be uniformly coated on the substrate including
the highly crystalline carbon, and the highly crystalline graphitic
layer structure may be easily formed without deteriorating the
characteristics of high crystalline carbon.
[0061] Then, the substrate coated with graphitizable polymer may be
stabilized. The stabilizing may include a chemical reaction such as
crosslinking, oxidation, aromatization, dehydrogenation, or
cyclization of graphitizable polymer.
[0062] The stabilizing may be performed with a rising temperature
at a heat-up rate of about 3.degree. C./min to about 5.degree.
C./min under the air atmosphere to a final temperature of about
220.degree. C. to about 280.degree. C. and then continuing at the
final temperature for about 30 minutes to about 2 hours.
[0063] According to the stabilizing process, the graphitizable
polymer may adsorb oxygen from the air as part of the cycling and
the crosslinking linkage, so as to provide a thermally stable
ladder polymer structure in the following carbonizing process
according to the reaction. If the temperature of the stabilizing
process is lower than the range, the reaction may occur too slowly,
and the stabilization may be incompletely performed, so as to
deteriorate the carbon physical properties. On the other hand, if
the temperature of the stabilization process is higher than the
range, the graphitizable polymer may be excessively heated to be
melted or combusted, which is unfavorable.
[0064] Then, the stabilized substrate may be subjected to a first
heat-treating process. The first heat-treating process may be
performed under a N.sub.2 or Ar atmosphere at a heat-up rate of
about 3.degree. C./min to about 5.degree. C./min and maintained at
about 300.degree. C. to about 700.degree. C. for about 30 minutes
to about 6 hours. According to the first heat-treating process, the
carbon content may be increased to be greater than or equal to
about 90 wt % by exhausting various gases, or a three dimensional
carbon structure having molecular and fibrillar orientation may be
formed. In addition, the polymer chain maybe rearranged according
to the first heat-treatment so that the parallel molecular chain
may form a three dimensional bond. In addition, the effects
according to the first heat-treating process may be further
effectively obtained when the heat-treatment is performed under the
above-mentioned conditions.
[0065] Then, the first heat-treated substrate may be subjected to a
second heat-treating process to be carbonized. According to the
carbonizing process, the polymer coated on the substrate may be
carbonized. The second heat-treating process includes a first step
of heating at about 400.degree. C. to about 800.degree. C. and a
second step of heating at about 800.degree. C. to about
1200.degree. C. When the second heat-treating process is performed
in the first and the second steps within the temperature range,
structures such as graphite oxide may be removed, and carbon with
an sp.sup.2 structure may be developed.
[0066] The substrate that has undergone the carbonizing process may
be subjected to a third heat-treating process to be graphitized.
According to the graphitization, the carbonized polymer is finally
graphitized to provide graphite, which is a crystalline carbon
layer, on the substrate. The third heat-treating process may be
performed by heating at about 1200.degree. C. to about 2500.degree.
C.
[0067] When performing a third heat-treating process, the formed
graphitic layer structure may be further developed and arranged,
and graphene sheets may be stacked together well. Accordingly, a
uniform graphitic layer may be provided that may slow the kinetics
of carbon oxidation to improve the anti-corrosion properties of
carbon. The high temperature graphitization process may remove an
amorphous phase to enhance the graphitized structure arrangement,
so that a mesoporous channel aligned with graphene layers may be
well developed.
[0068] When third heat-treatment is performed within the
temperature range, the effects of the third heat-treatment may be
more effectively obtained, and mesopore channels aligned together
with the arranged graphitized structure may be more readily formed
and may be well developed.
[0069] Another embodiment provides a catalyst for a fuel cell
including the support and an active metal supported on the
support.
[0070] The active metal may be platinum, ruthenium, osmium, a
platinum-ruthenium alloy, a platinum-osmium alloy, a
platinum-palladium alloy, a platinum-M alloy (M is at least one
transition element selected from Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu,
Zn, Sn, Mo, W, Rh, and Ru), or a combination thereof. The catalyst
according to one embodiment may be used in an anode and/or a
cathode. The anode and cathode may include the same catalyst. In an
implementation, a direct oxidation fuel cell may include a
platinum-ruthenium alloy catalyst as an anode catalyst in order to
prevent catalyst poisoning in the anode reaction. Specific examples
of the catalyst may include one selected from Pt, Pt/Ru, Pt/W,
Pt/Ni, Pt/Sn, Pt/Mo, Pt/Pd, Pt/Fe, Pt/Cr, Pt/Co, Pt/Ru/W, Pt/Ru/Mo,
Pt/Ru/V, Pt/Fe/Co, Pt/Ru/Rh/Ni, and Pt/Ru/Sn/W.
[0071] The process of supporting the active metal in a support may
be carried out by any suitable process.
[0072] Yet another embodiment provides an electrode for a fuel cell
including a catalyst layer including the catalyst and an electrode
substrate.
[0073] The catalyst layer may further include a binder resin to
improve its adherence and proton transfer properties.
[0074] The binder resin may be a proton conductive polymer resin.
Examples of the binder resin may include a polymer resin having a
cation exchange group selected from a sulfonic acid group, a
carboxylic acid group, a phosphoric acid group, a phosphonic acid
group, and derivatives thereof at its side chain. Examples of the
polymer resin may include at least one proton conductive polymer
selected from a fluoro-based polymer, a benzimidazole-based
polymer, a polyimide-based polymer, a polyetherimide-based polymer,
a polyphenylenesulfide-based polymer, a polysulfone-based polymer,
a polyethersulfone-based polymer, a polyetherketone-based polymer,
a polyether-etherketone-based polymer, and a
polyphenylquinoxaline-based polymer.
[0075] The hydrogen (H) in the cation exchange group of the proton
conductive polymer may be substituted with Na, K, Li, Cs, or
tetrabutylammonium. When the H in the cation exchange group of the
terminal end of the proton conductive polymer side chain is
substituted with Na or tetrabutylammonium, NaOH or
tetrabutylammonium hydroxide may be used during preparation of the
catalyst composition, respectively. When the H is substituted with
K, Li, or Cs, suitable compounds for the substitutions may be
used.
[0076] The binder resin may be used singularly or in combination.
The binder resin may be used along with non-conductive polymers to
improve adherence with a polymer electrolyte membrane. The binder
resin may be used in a controlled amount.
[0077] Examples of the non-conductive polymers include at least one
selected from polytetrafluoroethylene (PTFE),
tetrafluoroethylene-hexafluoropropylene copolymer (FEP),
tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA),
ethylene/tetrafluoroethylene (ETFE),
ethylenechlorotrifluoro-ethylene copolymer (ECTFE),
polyvinylidenefluoride, a
polyvinylidenefluoride-hexafluoropropylene copolymer (PVdF-HFP),
dodecylbenzenesulfonic acid, and sorbitol.
[0078] The electrode substrate plays a role of supporting an
electrode and diffusing a fuel and an oxidant into a catalyst
layer, so that the fuel and the oxidant may easily approach the
catalyst layer. The electrode substrates may be formed from a
material such as carbon paper, carbon cloth, carbon felt, or a
metal cloth (a porous film composed of metal fiber or a metal film
disposed on a surface of a cloth composed of polymer fibers), as
examples.
[0079] The electrode substrates may be treated with a
fluorine-based resin to be water-repellent to prevent deterioration
of diffusion efficiency due to water generated during operation of
a fuel cell. The fluorine-based resin may be one selected from
polytetrafluoroethylene, polyvinylidene fluoride,
polyhexafluoropropylene, polyperfluoroalkylvinylether,
polyperfluorosulfonylfluoride alkoxyvinyl ether, fluorinated
ethylene propylene, polychlorotrifluoroethylene, and a copolymer
thereof.
[0080] In order to increase reactant diffusion effects between the
electrode substrates and catalyst layer, the anode or cathode may
further include a microporous layer on an electrode substrate. The
microporous layer may include conductive powders with a certain
particle diameter. The conductive material may include, but is not
limited to, carbon powder, carbon black, acetylene black, activated
carbon, a carbon fiber, fullerene, carbon nanotubes, carbon
nanowires, carbon nanohorns, carbon nanorings, or combinations
thereof.
[0081] The microporous layer is formed by coating a composition
including a conductive powder, a binder resin, and a solvent on the
conductive substrate. The binder resin may include, for example,
polytetrafluoroethylene, polyvinylidenefluoride,
polyhexafluoropropylene, polyperfluoroalkylvinylether,
polyperfluorosulfonylfluoride, alkoxyvinyl ether, polyvinylalcohol,
cellulose acetate, or a copolymer thereof. The solvent may include,
for example, an alcohol such as ethanol, isopropyl alcohol,
n-propyl alcohol, butanol, etc., water, dimethyl acetamide,
dimethyl sulfoxide, N-methylpyrrolidone, or tetrahydrofuran. The
coating method may include, for example, screen printing, spray
coating, doctor blade methods, gravure coating, dip coating, silk
screening, painting, etc., depending on the viscosity of the
composition.
[0082] According to another embodiment, a membrane-electrode
assembly for a fuel cell including the electrode as either one of a
cathode or an anode is provided. The membrane-electrode assembly
for a fuel cell includes a cathode and an anode facing each other,
and a polymer electrolyte membrane interposed between the cathode
and anode.
[0083] The polymer electrolyte membrane may be any generally-used
polymer electrolyte membrane made of a proton conductive polymer
resin. The proton conductive polymer resin may be a polymer resin
having a cation exchange group selected from a sulfonic acid group,
a carboxylic acid group, a phosphoric acid group, a phosphonic acid
group, and derivatives thereof, at its side chain.
[0084] Examples of the polymer resin include at least one selected
from a fluoro-based polymer, a benzimidazole-based polymer, a
polyimide-based polymer, a polyetherimide-based polymer, a
polyphenylenesulfide-based polymer, a polysulfone-based polymer, a
polyethersulfone-based polymer, a polyetherketone-based polymer, a
polyether-etherketone-based polymer, and a
polyphenylquinoxaline-based polymer. According to implementations,
the polymer resin may include poly(perfluorosulfonic acid)
(commercially available as "NAFION"), poly(perfluorocarboxylic
acid), a copolymer of tetrafluoroethylene having a sulfonic acid
group and fluorovinylether, defluorinated polyetherketone sulfide,
an aryl ketone, or
poly[(2,2'-m-phenylene)-5,5'-bibenzimidazole].
[0085] The hydrogen (H) in the cation exchange group of the proton
conductive polymer may be substituted with Na, K, Li, Cs, or
tetrabutylammonium. When the H in the cation exchange group of the
terminal end of the proton conductive polymer side chain is
substituted with Na or tetrabutylammonium, NaOH or
tetrabutylammonium hydroxide may be used during preparation of the
catalyst composition, respectively. When the H is substituted with
K, Li, or Cs, suitable compounds for the substitutions may be used.
Such a Na, K, Li, Cs, or tetrabutylammonium may be converted into a
proton during a subsequent acid treatment of a catalyst layer, and
thus, a proton form (H.sup.+-form) polymer electrolyte membrane may
be provided.
[0086] Another embodiment provides a fuel cell system including at
least one electricity generating element, a fuel supplier, and an
oxidant supplier.
[0087] The electricity generating element may include the
membrane-electrode assembly according to one embodiment and a
separator (referred to as a bipolar plate). The electricity
generating element may generate electricity through oxidation of a
fuel and reduction of an oxidant.
[0088] The fuel supplier may supply the electricity generating
element with a fuel, while the oxidizing agent supplier may supply
the electricity generating element with an oxidizing agent such as
oxygen or air.
[0089] In an implementation, the fuel may include liquid or gaseous
hydrogen or a hydrocarbon fuel. The hydrocarbon fuel, for example,
may be methanol, ethanol, propanol, butanol, or natural gas.
[0090] FIG. 1 illustrates the schematic structure of a fuel cell
system according to an embodiment, which will be described in
details with the reference to this accompanying drawing as follows.
Although FIG. 1 shows a fuel cell system supplying a fuel and an
oxidizing agent to an electrical generating element using a pump,
in other implementations, the fuel cell system of the embodiment
may include a structure wherein a fuel and an oxidant are provided
by diffusion.
[0091] A fuel system 1 of the embodiment may include at least one
electricity generating element 3 that generates an electrical
energy by oxidation of a fuel and reduction of an oxidizing agent,
a fuel supplier 5 that supplies the fuel, and an oxidant supplier 7
that supplies an oxidant to the electricity generating element
3.
[0092] In addition, the fuel supplier 5 may be equipped with a tank
9, which stores fuel, and a pump 11, which is connected therewith.
The fuel pump 11 may supply fuel stored in the tank 9 with a
predetermined pumping power.
[0093] The oxidant supplier 7, which supplies the electricity
generating element 3 with an oxidant, may be equipped with at least
one oxidant pump 13 for supplying an oxidant with a predetermined
pumping power.
[0094] The electricity generating element 3 may include a
membrane-electrode assembly 17, which oxidizes hydrogen or a fuel
and reduces an oxidant, and separators 19 and 19' that are
respectively positioned at opposite sides of the membrane-electrode
assembly and that supply hydrogen or a fuel, and an oxidant,
respectively. The stack 15 may be provided by stacking at least one
of the electricity generating elements 3.
[0095] The following Examples and Comparative Examples are provided
in order to highlight characteristics of one or more embodiments,
but it will be understood that the Examples and Comparative
Examples are not to be construed as limiting the scope of the
embodiments, nor are the Comparative Examples to be construed as
being outside the scope of the embodiments. Further, it will be
understood that the embodiments are not limited to the particular
details described in the Examples and Comparative Examples.
Preparation Example 1
[0096] 2.0 g of a highly crystalline carbon in the form of carbon
nanotube was treated with an ultrasonic wave in 20 ml of deionized
water for 20 minutes to provide a carbon suspension. 33 ml of
acrylonitrile was added to the carbon suspension and agitated for
30 minutes. 1.08 g of ammonium persulfate
((NH.sub.4).sub.2S.sub.2O.sub.8) was added thereto, and agitated
under the nitrogen atmosphere at 65.degree. C. for 24 hours to
provide emulsion polymerization.
[0097] After the polymerization, the polymerized product was
centrifuged and washed with deionized water and ethanol. Then, the
washed product was vacuum-dried at 60.degree. C. to provide a
carbon substrate coated with polyacrylonitile (PAN) layer as a
support precursor.
Preparation Example 2
[0098] A support precursor, in the form of a carbon substrate
coated with a polyacrylonitrile layer, was prepared in accordance
with the same procedure as in Preparation Example 1, except that
after the 1.08 g of ammonium persulfate
((NH.sub.4).sub.2S.sub.2O.sub.8) was added, the agitating under the
nitrogen atmosphere at 65.degree. C. was carried out for 1 hour to
provide the emulsion polymerization.
Preparation Example 3
[0099] A support precursor, a carbon substrate coated with a
polyacrylonitrile layer, was prepared in accordance with the same
procedure as in Preparation Example 1, except that after the 1.08 g
of ammonium persulfate ((NH.sub.4).sub.2S.sub.2O.sub.8) was added,
the agitating under the nitrogen atmosphere at 65.degree. C. was
carried out for 2 hours to provide the emulsion polymerization.
Preparation Example 4
[0100] A support precursor, a carbon substrate coated with a
polyacrylonitrile layer, was prepared in accordance with the same
procedure as in Preparation Example 1, except that after the 1.08 g
of ammonium persulfate ((NH.sub.4).sub.2S.sub.2O.sub.8) was added,
the agitating under the nitrogen atmosphere at 65.degree. C. was
carried out for 6 hours to provide the emulsion polymerization.
Preparation Example 5
[0101] A support precursor, a carbon substrate coated with a
polyacrylonitrile layer, was prepared in accordance with the same
procedure as in Preparation Example 1, except that after 1.08 g of
ammonium persulfate ((NH.sub.4).sub.2S.sub.2O.sub.8) was added, the
agitating under the nitrogen atmosphere at 65.degree. C. was
carried out for 12 hours to provide the emulsion
polymerization.
[0102] The coating ratio of polyacrylonitrile layer (carbon layer)
of each support precursors obtained from the Preparation Examples 1
to 5 was calculated, and the results are shown in the following
Table 1.
TABLE-US-00001 Polymerization Coating time (hour) ratio (%)
Preparation Example 1 24 790 Preparation Example 2 1 135
Preparation Example 3 2 195 Preparation Example 6 420 Preparation
Example 5 12 680
Comparative Example 1
[0103] The carbon substrate formed with the PAN coating layer
obtained from Preparation Example 1 was stabilized at a heat-up
rate of 3.degree. C./min at 280.degree. C. for 1 hour to provide a
carbon support coated with a PAN layer.
Comparative Example 2
[0104] The carbon substrate formed with the PAN coating layer
obtained from Preparation Example 1 was stabilized at a heat-up
rate of 3.degree. C./min at 280.degree. C. for 1 hour and subjected
to a first heat-treatment under a N.sub.2 atmosphere at a heat-up
rate of 3.degree. C./min at 400.degree. C. for 2 hours. Then, the
first heat-treated product was subjected to a second heat-treatment
to provide a carbon support coated with a PAN layer. The second
heat-treatment was performed with a first step of heating at
450.degree. C. and second step of heating at 800.degree. C.
Example 1
[0105] The carbon substrate formed with a PAN coating layer
obtained Preparation Example 1 was stabilized at 280.degree. C. for
1 hour with a heat-up rate of 3.degree. C./min, and the obtained
product subjected to a first heat-treatment at a heat-up rate of
3.degree. C./min under an N.sub.2 atmosphere at 400.degree. C. for
2 hours, and the first-treated product was subjected to a second
heat-treatment. The second heat-treatment was performed with a
first step of heating at 450.degree. C. and a second step of
heating at 800.degree. C. Then the second heat-treated product was
subjected to a third heat-treatment at 2000.degree. C. to provide a
carbon support coated with a crystalline carbon layer. FIG. 2 is a
TEM photograph of the obtained carbon support coated with a
crystalline carbon layer, from which it may be determined that the
crystalline carbon layer had a thickness of about 15 nm. The
crystalline carbon has an interlayer spacing (d002) of a (002)
plane of 3.4 .ANG..
Example 2
[0106] A carbon support coated with the crystalline carbon layer
was fabricated in accordance with the same procedure as in Example
1, except that the third heat-treatment was performed at
2500.degree. C.
Comparative Example 3
[0107] A carbon support coated with a PAN layer was fabricated in
accordance with the same procedure as in Comparative Example 2,
except that the second step of heating during the second
heat-treatment was performed at 1000.degree. C.
[0108] The support precursor obtained from Preparation Example 1
was analyzed by FT-IR, and the results are shown in FIG. 3. As
shown in FIG. 3, the support precursor obtained from Preparation
Example 1 showed a strong peak corresponding to the stretching
vibration of a CN group around 2240 cm.sup.-1. Thereby, it may be
determined that the polyacrylonitrile (PAN) chain was formed on the
crystalline carbon surface according to the chemical
polymerization.
[0109] XPS Analysis
[0110] The support obtained from the Comparative Example 1 and the
support precursor obtained from Preparation Example 1 were analyzed
by X-ray photoelectron spectroscopy (XPS), and the results are
shown in FIG. 4. As shown in FIG. 4, in addition to a C1s (about
285 eV) signal and an O1s (about 532 eV) signal, a N1s (about 399
eV) signal was also observed. From the results, it may be
determined that the PAN coating layer introduced by the chemical
polymerization was formed on the surface of crystalline carbon.
[0111] A Pt nanoparticle was supported on the support obtained from
Example 2 to provide a catalyst. The catalyst was imaged by HR
(high resolution)-TEM, and the results are shown in FIG. 5. From
the results shown in FIG. 5, it may be seen that the Pt nano
particles were uniformly supported on the support. In addition,
FIG. 6 shows an HR-TEM image of the support obtained from Example
2. As shown in FIG. 6, it may be seen that the obtained support had
a structure of a substrate and a crystalline carbon layer disposed
on the substrate.
Comparative Example 4
[0112] A catalyst for a fuel cell was fabricated by supporting Pt
on the support obtained from Comparative Example 1 according to the
chemical reduction.
Comparative Example 5
[0113] A catalyst for a fuel cell was fabricated by supporting Pt
on the support obtained from Comparative Example 2 according to the
chemical reduction.
Example 3
[0114] A catalyst for a fuel cell was fabricated by supporting Pt
on the support obtained from Example 1 according to the chemical
reduction.
Example 4
[0115] A catalyst for a fuel cell was fabricated by supporting Pt
on the support obtained from Example 2 according to the chemical
reduction.
Comparative Example 6
[0116] A catalyst (Pt/CNT) for a fuel cell was fabricated by
supporting Pt on a carbon nanotube support formed with no carbon
layer according to the chemical reduction.
[0117] The carbon support obtained from Example 1 was analyzed by
high resolution XPS C1s core-level spectroscopy, and the results
are shown in (a) of FIG. 7. In addition, the catalyst obtained from
Example 3 was measured by high resolution XPS Pt4f core-level
spectroscopy, and the results are shown in (b) of FIG. 7. As shown
in (a) and (b) of FIG. 7, it may be determined that, in the
catalyst obtained from Example 3, Pt nanoparticle was uniformly
supported on the support including a high crystalline carbon
graphitized layer.
[0118] Electrochemical Characteristic Evaluation
[0119] 0.25 mg/cm 2 of each catalyst obtained from Examples 3, 4
and Comparative Examples 4 to 6 was added to a solvent including
water mixed with dipropylene glycol at a weight ratio of 50:50. An
ionomer of 5 wt % Nafion (Dupont) was added to provide a catalyst
composition for an electrode. The ionomer was included in an amount
of 40 wt % based on the total amount of the ionomer and catalyst.
The catalyst composition was coated onto a glassy carbon electrode
to provide a half-cell electrode for cyclic voltammetry (CV).
Cyclic voltammetry (CV) was carried out with respect to the
half-cell, and the decreasing rate of an electrochemical active
surface area (ECSA) was measured. The decreasing ratio of the
electrochemical active surface area after carrying out the CV
compared to the initial electrochemical active surface area before
carrying out the CV was calculated in terms of a percentage (%),
and the results are shown in FIG. 8. The CV test was performed by
using a potentiostat (VSP, Bio-Logic SA), and a rotation control
(Pine) in a setup of a temperature controller standard
three-compartment electrode. In this case, a Pt-mesh electrode and
an Ag/AgCl electrode were used as a counter electrode and a
reference electrode, respectively. The electrochemical active
surface area was calculated as the average of the peak area of
hydrogen adsorption and desorption excepting the double layer
charge values. Using an N.sub.2-saturated 0.1M HClO.sub.4 solution,
cycles were repeated at 0.6V to 1.4V for 1000 times, and ECSA was
measured in each 100 cycles at a scan rate of 20 mW/s.
[0120] As shown in FIG. 8, the decreasing ratio of electrochemical
active surface area of Examples 3 and 4 was less than that of
Comparative Examples 4 to 6. Particularly, it may be determined
that, in the case of Example 4, the electrochemical active surface
area barely decreased.
[0121] In addition, the half-cell was measured with respect to
electrochemical surface area, and the results are shown in FIG. 9.
As shown in FIG. 9, it may be determined that the catalysts of
Examples 3 and 4 had a significantly smaller decreasing ratio of
electrochemical surface area than the catalysts of Comparative
Examples 4 to 6. Particularly, it may be determined that the
electrochemical surface area was barely decreased even after the
1000th cycle in Example 4. Accordingly, it may be estimated that
the catalysts of Examples 3 and 4 had superior electrochemical
stability and durability to those of Comparative Examples 4 to
6.
[0122] Measuring Raman Spectrum
[0123] The supports obtained from Examples 1 and 2 and Comparative
Examples 1 and 2 were analyzed by Raman spectroscopy, and the
results are shown in FIG. 10. For the comparison, the catalyst
according to Comparative Example 6 and a Control including only CNT
were measured for Raman spectrum, and the results are also shown in
FIG. 10. As shown in FIG. 10, the similar results are shown in all
of Examples 1 and 2 and Comparative Examples 1, 2, 6, and CNT, so
it may be determined that the support according to Examples 1 and 2
maintained a similar structure to those of the conventional
supports.
[0124] Measuring Raman Spectrum Intensity Ratio
[0125] The supports of Examples 1 and 2 to Comparative Examples 1
and 2, and, for the comparison, the catalyst obtained from
Comparative Example 6 and the Control of CNT were measured to
determine a Raman spectrum area ratio (area integral ratio) and an
intensity ratio at a (1580 cm.sup.-1) plane and (1360 cm.sup.-1)
plane. From these measurements, the I.sub.D/I.sub.G area ratio
(area (1360 cm.sup.-1)/area (1580 cm.sup.-1)) and the
I.sub.D/I.sub.G intensity ratio (intensity (1360
cm.sup.-1)/intensity (1580 cm.sup.-1)) were calculated. The results
are shown in FIG. 11. From the results shown in FIG. 11, it may be
confirmed that the catalyst of Comparative Example 6 had a
I.sub.D/I.sub.G area ratio of about 0.91, a I.sub.D/I.sub.G
intensity ratio of about 0.69; and the catalysts of Control and
Comparative Examples 1 and 2 had a I.sub.D/I.sub.G area ratio of
about 0.78 to about 0.93, a I.sub.D/I.sub.G intensity ratio of
about 0.53 to about 0.65. On the other hand, the catalysts of
Examples 1 to 2 had a I.sub.D/I.sub.G area ratio of about 0.35, a
I.sub.D/I.sub.G intensity ratio of about 0.24. According to the
results, the supports according to Examples 1 to 2 had a different
Raman spectrum area ratio and intensity ratio from those of
Comparative Examples 1, 2, 6 and the Control. In addition, it may
be determined that the supports according to Examples 1 to 2 had a
I.sub.D/I.sub.G area ratio of about 38%, a I.sub.D/I.sub.G
intensity ratio of about 35% relative to the catalyst according to
Comparative Example 6.
[0126] By way of summation and review, embodiments provide a
support for a fuel cell being capable of improving catalyst
activity. Embodiments provide a method of preparing the support for
a fuel cell. Embodiments provide an electrode for a fuel cell
including the support for a fuel cell. Embodiments provide a
membrane-electrode assembly for a fuel cell including the
electrode. Embodiments provide a fuel cell system including the
membrane-electrode assembly.
[0127] Example embodiments have been disclosed herein, and although
specific terms are employed, they are used and are to be
interpreted in a generic and descriptive sense only and not for
purpose of limitation. In some instances, as would be apparent to
one of ordinary skill in the art as of the filing of the present
application, features, characteristics, and/or elements described
in connection with a particular embodiment may be used singly or in
combination with features, characteristics, and/or elements
described in connection with other embodiments unless otherwise
specifically indicated. Accordingly, it will be understood by those
of skill in the art that various changes in form and details may be
made without departing from the spirit and scope thereof as set
forth in the following claims.
* * * * *