U.S. patent application number 17/117308 was filed with the patent office on 2021-04-08 for cathode for fuel cells and method of manufacturing membrane electrode assembly having the same.
The applicant listed for this patent is HYUNDAI MOTOR COMPANY, KIA MOTORS CORPORATION. Invention is credited to Hoon Hui LEE.
Application Number | 20210104765 17/117308 |
Document ID | / |
Family ID | 1000005279610 |
Filed Date | 2021-04-08 |
United States Patent
Application |
20210104765 |
Kind Code |
A1 |
LEE; Hoon Hui |
April 8, 2021 |
CATHODE FOR FUEL CELLS AND METHOD OF MANUFACTURING MEMBRANE
ELECTRODE ASSEMBLY HAVING THE SAME
Abstract
A cathode for fuel cells includes a carbon support, a platinum
catalyst supported on the carbon support and an ionomer surrounding
the carbon support and the platinum catalyst, wherein the ionomer
is removed from the surface of the platinum catalyst. The cathode
for fuel cells has a structure in which an ionomer film coating the
surface of the platinum catalyst and thus acting as oxygen transfer
resistance is removed from the surface of the platinum catalyst
and, thus, mass transfer resistance (oxygen diffusion resistance)
may be reduced and performance of a fuel cell may be improved.
Further, the cathode having a low amount of platinum used due to
improvement in platinum utilization may effectively execute oxygen
transfer and thus increase the amount of platinum participating in
catalysis, as compared to conventional cathodes.
Inventors: |
LEE; Hoon Hui; (Seoul,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HYUNDAI MOTOR COMPANY
KIA MOTORS CORPORATION |
Seoul
Seoul |
|
KR
KR |
|
|
Family ID: |
1000005279610 |
Appl. No.: |
17/117308 |
Filed: |
December 10, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15848880 |
Dec 20, 2017 |
10879550 |
|
|
17117308 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 2008/1095 20130101;
H01M 4/8882 20130101; H01M 8/1004 20130101; H01M 4/8878 20130101;
H01M 8/1018 20130101; H01M 4/8828 20130101; H01M 4/9083 20130101;
H01M 4/926 20130101; H01M 4/8825 20130101; Y02P 70/50 20151101;
H01M 4/8668 20130101; H01M 2004/8689 20130101; H01M 4/8605
20130101 |
International
Class: |
H01M 8/1004 20060101
H01M008/1004; H01M 4/86 20060101 H01M004/86; H01M 4/88 20060101
H01M004/88; H01M 4/90 20060101 H01M004/90; H01M 4/92 20060101
H01M004/92; H01M 8/1018 20060101 H01M008/1018 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2016 |
KR |
10-2016-0181660 |
Claims
1. A cathode for fuel cells comprising: a carbon support; a
platinum catalyst supported on the carbon support; and an ionomer
surrounding the carbon support and the platinum catalyst, wherein
the ionomer is removed from a surface of the platinum catalyst.
2. The cathode for fuel cells of claim 1, wherein the carbon
support is a highly crystalline carbon support having a high degree
of graphitization.
3. The cathode for fuel cells of claim 1, wherein the carbon
support and the platinum catalyst are surrounded with the ionomer
such that only the surface of the platinum catalyst is not coated
with the ionomer.
4. A membrane electrode assembly for fuel cells comprising the
cathode of claim 1.
5. A fuel cell comprising the membrane electrode assembly of claim
4.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional patent application of U.S.
patent application Ser. No. 15/848,880, filed on Dec. 20, 2017
based on and claims the benefit of priority to Korean Patent
Application No. 10-2016-0181660 filed on Dec. 28, 2016 with the
Korean Intellectual Property Office, the entire contents of which
are incorporated herein by reference.
TECHNICAL FIELD
[0002] The present disclosure relates to a cathode for fuel cells
and a method of manufacturing a membrane electrode assembly having
the same. More particularly, it relates to a cathode which improves
performance of a fuel cell by decreasing oxygen diffusion
resistance.
BACKGROUND
[0003] In general, a Polymer Electrolyte Membrane Fuel Cell (PEMFC)
includes a Membrane Electrode Assembly (MEA) including an anode, a
cathode and a polymer electrolyte membrane disposed between the
anode and the cathode. An oxidation reaction of fuel occurs at the
anode to which hydrogen or fuel is supplied, hydrogen ions
generated at the anode are conducted to the cathode through the
electrolyte membrane, and a reduction reaction of oxygen occurs at
the cathode to which oxygen is supplied, thus generating
current.
[0004] The anode and the cathode of the fuel cell require a
catalyst for oxidation and reduction reactions of the fuel, and a
Pt/C catalyst or a Pt/alloy/C catalyst is generally used for the
catalyst. An electrode of the fuel cell includes an ionomer formed
of the same component as the electrolyte membrane, together with
the catalyst for oxidation and reduction reactions, so as to
transfer hydrogen ions generated at the anode to the cathode. Such
an ionomer serves as both a hydrogen ion conductor and a binder
that physically binds Pt/C catalyst particles of the electrode.
[0005] The oxidation and reduction reactions should effectively
occur at the cathode. However, if the ionomer located at the
cathode coats catalyst particles to an excessively thick thickness,
resistance to oxygen gas transmission is increased. On the other
hand, if the ionomer coats catalyst particles to an excessively
thin thickness or does not coat catalyst particles, resistance to
hydrogen gas transmission is increased and, thus, there is a
tradeoff. Therefore, the amount of the ionomer is generally
controlled so as to coat the catalyst layer to a proper
thickness.
[0006] Furthermore, the amount of platinum used for the catalyst
should be decreased to lower the cost of the fuel cell. However, if
the amount of platinum in an electrode layer is decreased,
particularly for the cathode, an ionomer film coating catalyst
particles has greater resistance to diffusion of oxygen to the
catalyst particles. Performance of the fuel cell having a greatly
reduced amount of platinum is thereby lowered.
SUMMARY
[0007] The present disclosure has been made in an effort to solve
the above-described problems associated with the related art and
thus the present disclosure provides a cathode of a Polymer
Electrolyte Membrane Fuel Cell (PEMFC) which improves performance
of the fuel cell by decreasing oxygen diffusion resistance.
[0008] In one aspect, a cathode for fuel cells may include a carbon
support, a platinum catalyst supported on the carbon support, and
an ionomer surrounding the carbon support and the platinum
catalyst, wherein the ionomer is removed from a surface of the
platinum catalyst.
[0009] In a preferred embodiment, the carbon support may be a
highly crystalline carbon support having a high degree of
graphitization.
[0010] In one aspect, a method of manufacturing a membrane
electrode assembly for fuel cells includes coating a surface of a
platinum catalyst supported on a carbon support with an amorphous
carbon layer by mixing the platinum catalyst supported on the
carbon support with a polymer containing carbon and a solvent and
carbonizing the platinum catalyst mixed with the polymer and the
solvent, preparing an electrode forming slurry by mixing the
carbonized platinum catalyst with an ionomer, preparing a cathode
using the slurry, manufacturing a membrane electrode assembly using
the prepared cathode, an electrolyte membrane and an anode, and
removing the ionomer from the surface of the platinum catalyst of
the cathode by oxidizing the amorphous carbon layer coating the
surface of the platinum catalyst.
[0011] In a preferred embodiment, the carbon support may be a
highly crystalline carbon support having a high degree of
graphitization, and the polymer containing carbon may be
polydopamine.
[0012] In another preferred embodiment, in carbonization of the
platinum catalyst mixed with the polymer containing carbon and the
solvent, the polymer containing carbon coating the platinum
catalyst may form the amorphous carbon layer by drying a mixing
solution, acquired by mixing the platinum catalyst supported on the
carbon support with the polymer containing carbon and the solvent,
and then heating an acquired powder under a nitrogen atmosphere, or
the polymer containing carbon coating the platinum catalyst may
form the amorphous carbon layer by heating a mixing solution,
acquired by mixing the platinum catalyst supported on the carbon
support with the polymer containing carbon and the solvent, under a
nitrogen atmosphere until the solvent is dried, raising the
temperature of an acquired mixing solution to 700 to 900.degree. C.
and then maintaining the temperature of the mixing solution.
[0013] In still another preferred embodiment, the amorphous carbon
layer may be an amorphous carbon layer having a low degree of
graphitization.
[0014] In yet another preferred embodiment, oxidization of the
amorphous carbon layer may be carried out by applying a voltage of
1.2 to 1.4 V to the cathode while supplying nitrogen gas and
hydrogen gas to the cathode and the anode, respectively, or be
carried out by maintaining the membrane electrode assembly for 5 to
20 minutes while supplying nitrogen gas and air to the cathode and
the anode, respectively, and extracting a current of 0.1 to 0.2
A/cm.sup.2 from the cathode.
[0015] Other aspects and preferred embodiments of the invention are
discussed infra.
[0016] The above and other features of the invention are discussed
infra.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above and other features of the present disclosure will
now be described in detail with reference to certain exemplary
embodiments thereof illustrated in the accompanying drawings which
are given hereinbelow by way of illustration only, and thus are not
limitative of the present disclosure, and wherein:
[0018] FIG. 1 is an illustrative view showing the structure of a
conventional fuel cell;
[0019] FIG. 2 is an illustrative view showing the structure of a
cathode of the conventional fuel cell; and
[0020] FIG. 3 is an illustrative view showing the structure of a
cathode, from which an ionomer is removed, in accordance with the
present disclosure.
[0021] FIG. 4 is a flow chart showing the method steps in claim
6.
[0022] It should be understood that the appended drawings are not
necessarily to scale, presenting a somewhat simplified
representation of various preferred features illustrative of the
basic principles of the invention. The specific design features of
the present disclosure as disclosed herein, including, for example,
specific dimensions, orientations, locations, and shapes will be
determined in part by the particular intended application and use
environment.
[0023] In the figures, reference numbers refer to the same or
equivalent parts of the present disclosure throughout the several
figures of the drawing.
DETAILED DESCRIPTION
[0024] Hereinafter reference will now be made in detail to various
embodiments of the present disclosure, examples of which are
illustrated in the accompanying drawings and described below. While
the invention will be described in conjunction with exemplary
embodiments, it will be understood that the present description is
not intended to limit the invention to the exemplary embodiments.
On the contrary, the invention is intended to cover not only the
exemplary embodiments, but also various alternatives,
modifications, equivalents and other embodiments within the spirit
and scope of the invention as defined by the appended claims. In
the following description of the present disclosure, a detailed
description of known functions and configurations incorporated
herein will be omitted when it may make the subject matter of the
present disclosure rather unclear.
[0025] A cathode for fuel cells in accordance with one embodiment
of the present disclosure may include a carbon support, a platinum
catalyst supported on the carbon support, and an ionomer
surrounding the carbon support and the platinum catalyst. The
cathode may have a structure in which the ionomer is removed from
the surface of the platinum catalyst.
[0026] In a conventional platinum catalyst supported on a carbon
support, an ionomer, i.e., a proton conductor, coats the surface of
the platinum catalyst so that resistance to movement of oxygen to
the platinum catalyst is increased.
[0027] Therefore, the inventor(s) of the present disclosure
confirmed through tests that, in a structure of a fuel cell in
which an ionomer surrounds a carbon support and a platinum
catalyst, if the ionomer is removed only from the surface of the
platinum catalyst, performance of the fuel cell may be improved due
to decrease in mass transfer resistance (oxygen diffusion
resistance).
[0028] Hereinafter, a cathode for fuel cells and a method of
manufacturing a membrane electrode assembly having the same in
accordance with one embodiment of the present disclosure will be
described in more detail.
[0029] The method of manufacturing the membrane electrode assembly
in accordance with one embodiment of the present disclosure
includes coating the surface of a platinum catalyst supported on a
carbon support with an amorphous carbon layer by mixing the
platinum catalyst with a polymer containing carbon and a solvent
and carbonizing the platinum catalyst mixed with the polymer and
the solvent; mixing the carbonized platinum catalyst with an
ionomer and preparing an electrode forming slurry; preparing a
cathode using the slurry; manufacturing a membrane electrode
assembly using the prepared cathode, an electrolyte membrane and an
anode; and removing the ionomer from the surface of the platinum
catalyst of the cathode by oxidizing the amorphous carbon layer
coating the surface of the platinum catalyst.
[0030] The carbon support and the platinum catalyst supported
thereon are mixed with a polymer containing carbon and a solvent,
thus preparing a mixing solution.
[0031] Here, a carbon support having a high degree of
graphitization, i.e., a carbon support having high crystallinity,
is used as the carbon support. The reason for this is to cause a
difference in resistance to oxidation with a carbon layer, which
will subsequently coat the platinum catalyst.
[0032] Further, polydopamine may be used as the polymer containing
carbon.
[0033] In order to carbonize the mixing solution, first, the mixing
solution may be dried, thus forming a powder. When the acquired
powder is heated to a temperature of 400 to 900.degree. C. for 30
minutes to 2 hours in a furnace under a nitrogen atmosphere, the
polymer containing carbon coating the surface of the platinum
catalyst forms an amorphous carbon layer.
[0034] Otherwise, such carbonization is carried out by heating the
mixing solution, acquired by mixing the platinum catalyst supported
on the carbon support with the polymer containing carbon and the
solvent, under a nitrogen atmosphere until the solvent is dried,
raising the temperature of the mixture to 400 to 900.degree. C. and
then maintaining the temperature of the mixture for 30 minutes to 2
hours, thereby causing the polymer containing carbon coating the
surface of the platinum catalyst to form the amorphous carbon
layer.
[0035] The formed amorphous carbon layer is an amorphous carbon
layer having a low degree of graphitization. Such an amorphous
carbon layer has much lower resistance to oxidization than the
highly crystalline carbon support.
[0036] Thereafter, the carbonized platinum catalyst (the surface of
which is coated with the amorphous carbon layer) is mixed with an
ionomer and an electrode forming slurry is prepared, thus preparing
a cathode.
[0037] Thereafter, a membrane electrode assembly is manufactured
using the prepared cathode, an electrolyte membrane and an anode.
Up to such an operation, the surface of the platinum catalyst is
coated with the amorphous carbon layer and the ionomer surrounds
the platinum catalyst coated with the amorphous carbon layer.
[0038] Finally, the ionomer is removed from the surface of the
platinum catalyst by oxidizing the amorphous carbon layer.
[0039] Oxidization of the amorphous carbon layer may be carried out
by applying a voltage of 1.2 to 1.4 V to the cathode while
supplying nitrogen gas to the cathode and hydrogen gas to the
anode.
[0040] That is, since there is a remarkable difference in
resistance to oxidization between the amorphous carbon layer and
graphitized carbon particles used as a support of the platinum
catalyst, when a voltage of 1.2 to 1.4 V is applied to the cathode
of the manufactured membrane electrode assembly while supplying
nitrogen gas to the cathode and hydrogen gas to the anode of the
membrane electrode assembly, the amorphous carbon layer is oxidized
due to a difference in crystallinity between the amorphous carbon
layer and graphitized carbon particles and is thus removed together
with the ionomer, but the graphitized carbon particles used as the
catalyst support are not oxidized.
[0041] Further, oxidization of the amorphous carbon layer may be
carried out by maintaining the membrane electrode assembly for 5 to
20 minutes while supplying nitrogen gas to the cathode and air to
the anode and extracting a current of 0.1 to 0.2 A/cm.sup.2 from
the cathode.
[0042] That is, when the manufactured membrane electrode assembly
is maintained for a designated time (5 to 20 minutes) while
supplying nitrogen gas to the cathode and air to the anode and
extracting a current of 0.1 to 0.2 A/cm.sup.2 from the cathode
using a potentiostat, the amorphous carbon layer may be more
rapidly oxidized, thus removing the ionomer.
[0043] A cathode for fuel cells in accordance with another
embodiment of the present disclosure may include a carbon support,
a platinum catalyst supported on the carbon support, and an ionomer
surrounding the carbon support and the platinum catalyst, and have
a structure in which the ionomer is removed from the surface of the
platinum catalyst.
[0044] In this case, an ionomer film coating the surface of the
platinum catalyst and thus acting as oxygen transfer resistance is
removed from the surface of the platinum catalyst and, thus, oxygen
diffusion resistance may be reduced and performance of a fuel cell
may be improved.
[0045] The cathode prepared by the above-described method may have
the above-described structure and be thus configured such that the
carbon support and the platinum catalyst are surrounded with the
ionomer but the ionomer is removed from the surface of the platinum
catalyst.
[0046] Hereinafter, reference will be made in detail to various
embodiments of the present disclosure, examples of which are
illustrated in the accompanying drawings and described below. While
the invention will be described in conjunction with exemplary
embodiments, it will be understood that the present description is
not intended to limit the invention to the exemplary
embodiments.
Example
[0047] The following example illustrates the invention and is not
intended to limit the same.
[0048] A platinum catalyst supported on a highly crystalline carbon
support having a high degree of graphitization is mixed with
polydopamine and a solvent, thus preparing a mixing solution. After
the mixing solution is dried, an acquired powder is heated to a
temperature of 800.degree. C. in a furnace for 2 hours, thus being
carbonized.
[0049] After slurry is prepared by mixing the carbonized platinum
catalyst with an ionomer, a cathode is prepared. A membrane
electrode assembly (MEA) is manufactured using the prepared
cathode, an electrolyte membrane and an anode.
[0050] Thereafter, the ionomer is removed from the surface of the
platinum catalyst by oxidizing an amorphous carbon layer coating
the platinum catalyst by applying a voltage of 1.3 V to the cathode
while supplying nitrogen gas to the cathode and hydrogen gas to the
anode of the MEA.
[0051] Thereby, a cathode structure, in which the carbon support
and the platinum catalyst are surrounded with the ionomer but the
ionomer is removed from the surface of the platinum catalyst, may
be acquired.
[0052] As apparent from the above description, a cathode for fuel
cells manufactured in accordance with one embodiment of the present
disclosure has a structure in which an ionomer film coating the
surface of a platinum catalyst and thus acting as oxygen transfer
resistance is removed from the surface of the platinum catalyst
and, thus, mass transfer resistance (oxygen diffusion resistance)
may be reduced and performance of a fuel cell may be improved.
[0053] Further, the cathode having a low amount of platinum used
due to improvement in platinum utilization may effectively execute
oxygen transfer and thus increase the amount of platinum
participating in catalysis, as compared to conventional
cathodes.
[0054] The invention has been described in detail with reference to
preferred embodiments thereof. However, it will be appreciated by
those skilled in the art that changes may be made in these
embodiments without departing from the principles and spirit of the
invention, the scope of which is defined in the appended claims and
their equivalents.
* * * * *