U.S. patent application number 11/208903 was filed with the patent office on 2006-08-03 for ni-al alloy anode for molten carbonate fuel cell made by in-situ sintering the ni-al alloy and method for making the same.
Invention is credited to Eun Ae Cho, Heung Yong Ha, Jonghee Han, Seong Ahn Hong, Jaeyoung Lee, Tae Hoon Lim, Suk-Woo Nam, In Hwan Oh, Sung Pil Yoon.
Application Number | 20060171839 11/208903 |
Document ID | / |
Family ID | 36756757 |
Filed Date | 2006-08-03 |
United States Patent
Application |
20060171839 |
Kind Code |
A1 |
Yoon; Sung Pil ; et
al. |
August 3, 2006 |
Ni-Al alloy anode for molten carbonate fuel cell made by in-situ
sintering the Ni-Al alloy and method for making the same
Abstract
Disclosed is a Ni--Al alloy anode for molten carbonate fuel cell
made by in-situ sintering the Ni--Al alloy. Further, disclosed is a
method for preparing the same comprising steps of preparing a sheet
with Ni--Al alloy powders (S1); and installing the sheet in a fuel
cell without any heat treatment for sintering the Ni--Al alloy in
the sheet and then in-situ sintering the Ni--Al alloy in the sheet
during a pretreatment process of the cell with the sheet (S2),
wherein a reaction activity of the Ni--Al alloy anode can be
maintained, the method is simple and economic, and a mass
production of the Ni--Al alloy anode and a scale-up in the method
are easy.
Inventors: |
Yoon; Sung Pil;
(Seongnam-si, KR) ; Hong; Seong Ahn; (Seoul,
KR) ; Oh; In Hwan; (Seoul, KR) ; Lim; Tae
Hoon; (Seoul, KR) ; Nam; Suk-Woo; (Seoul,
KR) ; Ha; Heung Yong; (Seoul, KR) ; Han;
Jonghee; (Seoul, KR) ; Cho; Eun Ae; (Seoul,
KR) ; Lee; Jaeyoung; (Incheon, KR) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
US
|
Family ID: |
36756757 |
Appl. No.: |
11/208903 |
Filed: |
August 22, 2005 |
Current U.S.
Class: |
419/57 |
Current CPC
Class: |
H01M 4/8875 20130101;
H01M 8/141 20130101; B22F 5/00 20130101; H01M 4/8605 20130101; H01M
4/90 20130101; H01M 4/8885 20130101; Y02P 70/50 20151101; Y02E
60/50 20130101 |
Class at
Publication: |
419/057 |
International
Class: |
B22F 3/10 20060101
B22F003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 1, 2005 |
KR |
10-2005-0008954 |
Claims
1. A Ni--Al alloy anode for molten carbonate fuel cell wherein a
sheet made of Ni--Al alloy powders is directly installed in the
cell without any heat treatment for sintering the Ni--Al alloy in
the sheet and then the Ni--Al alloy in the sheet is in-situ
sintered during a pretreatment process of the cell with the
sheet.
2. The Ni--Al alloy anode according to claim 1, wherein an inert
gas is injected so as to control an oxidation of nickel during the
in-situ sintering process.
3. The Ni--Al alloy anode according to claim 1, wherein, during the
in-situ sintering process, the inert gas is injected up to the
point before a temperature at which organic binders used to prepare
the sheet are removed, then air is injected in such a temperature
scope wherein the organic binders are removed, and then hydrogen
and carbon dioxide are simultaneously injected after the removal of
the organic binders and up to the point before an operating
temperature of the cell.
4. A method for preparing a Ni--Al alloy anode for molten carbonate
fuel cell comprising steps of: preparing a sheet with Ni--Al alloy
powders (S1); and installing the sheet in a fuel cell without any
heat treatment for sintering the Ni--Al alloy in the sheet, and
then in-situ sintering the Ni--Al alloy in the sheet during a
pretreatment process of the cell with the sheet (S2).
5. The method according to claim 4, wherein, in the step of S2, an
inert gas is injected so as to control an oxidation of nickel
during the in-situ sintering process.
6. The method according to claim 5, wherein, In the step of S2,
during the in-situ sintering process, the inert gas is injected up
to the point before a temperature at which organic binders used to
prepare the sheet are removed, then air is injected in such a
temperature scope wherein the organic binders are removed, and then
hydrogen and carbon dioxide are simultaneously injected after the
removal of the organic binders and up to the point before an
operating temperature of the cell.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a Ni--Al alloy anode for
molten carbonate fuel cell made by in-situ sintering the Ni--Al
alloy and a method for making the Ni--Al alloy anode.
[0003] 2. Description of the Related Art
[0004] A fuel cell is used for directly converting chemical energy
into electric energy. There are various kinds of the fuel cell,
such as a molten carbonate fuel cell, a solid polymer electrolyte
fuel cell, and a solid oxide fuel cell etc. The molten carbonate
fuel cell is a fuel cell using the molten carbonate as its
electrolyte and comprises a cathode, an electrolyte, a support and
an anode etc.
[0005] A high temperature fuel cell operating at 500.degree. C. or
more, such as the molten carbonate fuel cell and the solid oxide
fuel cell, mainly uses nickel for an electrode. For example, the
molten carbonate fuel cell uses nickel for an anode and nickel
oxide (NiO) for a cathode.
[0006] The anode in which an oxidation reaction of fuel occurs has
serious problems of sintering and creep phenomena at an operating
condition of high temperature and high load of 2 kg/cm.sup.2 or
more. That is, the reduction of porosity and the change of
micro-structure such as a shrinkage etc. occur in the anode due to
the sintering and the creep phenomena, thereby causing a
degradation of the performance of the fuel cell.
[0007] In particular, the nickel electrode is manufactured to be
porous so as to enlarge a reaction area and to provide a gas
passage. When such a porous nickel electrode is used at a high
temperature for a long time, the surface area and reaction rate of
the nickel electrode are reduced due to the sintering. In addition,
when a fuel cell having stacks of several unit cells using the
porous nickel electrode is operated for a long time, there occurs a
creep in the porous nickel electrode due to the load of the fuel
cell, thereby reducing the performance of the fuel cell.
[0008] In the prior art for solving the above-mentioned problems of
the sintering and the creep, a chromium of about 10 wt % was added
to the nickel or an oxide such as Cr.sub.2O.sub.3 and LiCrO.sub.2
was formed on the surface of the nickel electrode in order to
improve the resistance of the nickel electrode to the sintering and
the creep. It is known that a creep strain of Ni+10% Cr anode is 5%
or less. However, the LiCrO.sub.2 formed on the surface of the
nickel electrode is dissolved in the electrolyte, thereby
deteriorating the resistance of the nickel electrode to the
sintering and the creep when the fuel cell is operated for a long
time.
[0009] In order to improve the creep characteristic, there has been
used an oxide dispersion strengthened (ODS) method of dispersing a
metal oxide such as alumina in the nickel electrode since the
mid-1980's. Further, there have been extensive studies for an
electrode consisting of Ni--Al based alloy containing a small
amount of aluminum, which is oxidized prior to nickel. It is known
that the electrode consisting of Ni--Al based alloy has a creep
strain of 0.5% or less and an increase of contact resistance is
very slight even in a size of 1 m.sup.2, which is a size of a
commercial electrode.
[0010] However, the prior Ni--Al alloy electrode is expensive
compared to the electrode using the existing material and has such
a problem that the Ni--Al alloy electrode is not sintered in a
general manufacturing process of the electrode. That is, the
aluminum formed as a solid solution is primarily oxidized on the
surface of the nickel electrode, thereby forming an alumina oxide
having a very high melting point on the surface. Due to the alumina
oxide, the sintering between the nickel particles becomes
difficult.
[0011] Under the circumstances, there has been used a method of
sintering the electrode through a partial oxidation-reduction
wherein the surface of the electrode is partially oxidized under
the condition that the nickel particle can be oxidized, and then
the surface of the electrode is reduced again.
[0012] The partial oxidation-reduction method uses a phenomenon
that when the nickel is oxidized into a nickel oxide, the density
is changed and a volume is thus expanded. According to the partial
oxidation-reduction method, the nickel particles can easily contact
with each other due to the surface oxidation of the nickel, so that
it is possible to progress a sintering process despite the
formation of the alumina oxide and to manufacture an electrode
having a proper strength. In the partial oxidation-reduction
method, it is very important to control a partial pressure of
oxygen, thereby preventing an occurrence of excessive micro-pores
due to the volume change between nickel and nickel oxide resulting
from the excessive oxidation of the nickel particle. The
micro-pores eventually cause a re-distribution of the electrolyte,
thereby exerting very bad influence on the life of the fuel
cell.
[0013] As mentioned above, since the partial pressure of oxygen
should be controlled, there have been such problems in the partial
oxidation-reduction method that it is very difficult to introduce a
continuous process required for a mass production and that
necessary equipments become very complicated.
SUMMARY OF THE INVENTION
[0014] Accordingly, the present invention has been made to solve
the above-mentioned problems occurring in the prior art. The object
of the present invention is to provide a Ni--Al alloy anode for
molten carbonate fuel cell made by in-situ sintering the Ni--Al
alloy and a method for making the same, wherein a reaction activity
of the Ni--Al alloy anode can be maintained, the method is simple
and economic, and a mass production of the Ni--Al alloy anode and a
scale-up in the method are easy.
[0015] In order to accomplish the object, there is provided a
Ni--Al alloy anode for molten carbonate fuel cell wherein a sheet
made of Ni--Al alloy powders is directly installed in the cell
without any heat treatment for sintering the Ni--Al alloy in the
sheet and then the Ni--Al alloy in the sheet is in-situ sintered
during a pretreatment process of the cell with the sheet.
[0016] In the Ni--Al alloy anode for molten carbonate fuel cell
according to the present invention, an inert gas is injected so as
to control an oxidation of nickel during the in-situ sintering
process.
[0017] In the Ni--Al alloy anode for molten carbonate fuel cell
according to the present invention, during the in-situ sintering
process, the inert gas is injected up to the point before a
temperature at which organic binders used to prepare the sheet are
removed, then air is injected in such a temperature scope wherein
the organic binders are removed, and then hydrogen and carbon
dioxide are simultaneously injected after the removal of the
organic binders and up to the point before an operating temperature
of the cell.
[0018] In order to accomplish the object, there is provided a
method for preparing a Ni--Al alloy anode for molten carbonate fuel
cell comprising steps of preparing a sheet with Ni--Al alloy
powders (S1); and installing the sheet in a fuel cell without any
heat treatment for sintering the Ni--Al alloy in the sheet and then
in-situ sintering the Ni--Al alloy in the sheet during a
pretreatment process of the cell with the sheet (S2).
[0019] In the step of S2, an inert gas is injected so as to control
an oxidation of nickel during the in-situ sintering process.
[0020] In the step of S2, during the in-situ sintering process, the
inert gas is injected up to the point before a temperature at which
organic binders used to prepare the sheet are removed, then air is
injected in such a temperature scope wherein the organic binders
are removed, and then hydrogen and carbon dioxide are
simultaneously injected after the removal of the organic binders
and up to the point before an operating temperature of the
cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a graph showing heat treatment conditions and
atmospheres when a tape made of nickel-aluminum alloy powders is
directly installed in a cell without any separate heat treatment
for sintering the nickel-aluminum alloy in the tape and then a
nickel-aluminum alloy anode is prepared with in-situ sintering the
nickel-aluminum alloy in the tape according to the present
invention.; and
[0022] FIG. 2 is a graph showing a long time performance of a unit
cell using a nickel-aluminum alloy anode for molten carbonate fuel
cell made by in-situ sintering the nickel-aluminum alloy according
to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] Hereinafter, the present invention will be described in
detail by describing preferred embodiments with reference to the
accompanying drawings.
[0024] In the present invention, "a pretreatment process of cell"
is a pretreatment process of cell having a sheet made of
nickel-aluminum alloy powders installed therein directly without
any heat treatment for sintering the nickel-aluminum alloy in the
sheet, and means a process of removing an organic material such as
a binder and a plasticizer, etc. used to prepare the sheet or a
process comprising the removing of the organic material and a
heating up to the point before an operating temperature of the
cell.
[0025] According to the invention, a sheet is prepared by, for
example, the tape-casting of nickel-aluminum alloy powders, which
are difficult to be sintered as mentioned above (S1). Subsequently,
the sheet is directly installed to a cell without any heat
treatment for sintering the nickel-aluminum alloy in the sheet, and
then the nickel-aluminum alloy in the sheet is in-situ sintered in
a process of removing an organic material such as a binder or a
plasticizer added for preparing the sheet, or in a process of
heating up to the point before an operating temperature of the cell
after removing the organic material (S2). Thereby, the method for
preparing the nickel-aluminum alloy anode according to the present
invention is simple and economic, and a scale-up in the method and
a mass production of the nickel-aluminum alloy anode are easy while
a reaction activity of the nickel-aluminum alloy anode is
maintained.
[0026] In particular, during the in-situ sintering of the
nickel-aluminum alloy, an oxidation control is performed by
injecting an inert gas such as nitrogen or argon in a specific
temperature range so as to prevent an excessive oxidation of the
nickel. Further, at this time, a temperature at which the inert gas
is injected is determined by a temperature at which the organic
materials such as an organic binder and plasticizer, etc. added in
the tape-casting process are removed by a thermal decomposition and
an oxidation, etc.
[0027] That is, the organic binder added in the tape-casting
process is mostly removed at 300.degree. C..about.400.degree. C. If
the pretreatment is performed with the inert gas such as nitrogen
or argon in the temperature range for a long time, there can occur
carbon deposits, which may exert a bad influence on a cell
performance.
[0028] Accordingly, a plasticizer, which has a low volatilization
temperature, among the organic materials added in the tape-casting
process should be primarily volatilized in the temperature range
(200.degree. C..about.300.degree. C.), and then the pretreatment
should be performed with air or oxygen instead of nitrogen etc. in
the temperature range (300.degree. C..about.400.degree. C.) at
which the organic binders are removed. Further, the air or oxygen
treatment should be performed only for a minimal time for which the
organic binder is completely removed.
[0029] According to the invention, when preparing a nickel-aluminum
alloy anode for a molten carbonate fuel cell, it is possible to
simplify the preparing process of the anode since an additional
heat treatment process is not necessary. In addition, the method is
economic, and the scale-up in the method and the mass production of
the nickel-aluminum alloy anode are easy while a reaction activity
of the nickel-aluminum alloy anode is maintained.
EXAMPLE
[0030] A tape of nickel-aluminum alloy powders (i.e., a green
sheet) was prepared as follows:
[0031] At first, a binder, a solvent, a plasticizer and a defoamer
were primary-mixed and ball-milled for 24 hours, and then
nickel-aluminum alloy powders (5 wt % or less aluminum) and a
disperant were secondary-mixed and ball-milled for 2.about.48
hours, thereby making a slurry.
[0032] Methyl cellulose 1500 (Hayashi Pure Chemical) was used as
the binder. Water was used as the solvent. Glycerol (Junsei
Chemical) was used as the plasticizer. SN 154 (San Nopco Korea) and
Cerasperse 5468 (San Nopco Korea) were used as the defoamer and the
disperant, respectively.
[0033] Based on 100 g of the nickel-aluminum alloy powders,
1.about.2 g of the binder, 40.about.50 g of the solvent, 1.about.2
g of the plasticizer, 0.1.about.1 g of the defoamer and 0.1.about.1
g of the disperant were respectively used.
[0034] It could be checked through a slurry deposition experiment
that the materials added when performing the second ball-mill were
uniformly mixed. By regulating the second ball-mill time, a
porosity property of the anode could be regulated to a level
required for a molten carbonate fuel cell. Pores in the slurry,
which were generated when performing the ball-mill, were removed
through a defoaming process, and a viscosity was regulated to about
10,000.about.15,000 cP so as to maintain a thickness of the green
sheet uniformly.
[0035] A green sheet slip was prepared with a tape-casting process
using a doctor blade, and a drying was performed at a room
temperature. After preparing and drying the green sheet, a green
sheet cut to a size of 10 cm.times.10 cm was directly installed to
a unit cell. Then, an in-situ sintering was performed in the
pretreatment process of the unit cell.
[0036] FIG. 1 is a graph showing heat treatment conditions and
atmospheres when a tape made of nickel-aluminum alloy powders is
directly installed in a cell without any separate heat treatment
for sintering the nickel-aluminum alloy in the tape and then a
nickel-aluminum alloy anode is prepared with in-situ sintering the
nickel-aluminum alloy in the tape according to the present
invention
[0037] As shown in FIG. 1, an inert gas such as nitrogen (or argon)
was injected from a room temperature to 250.degree. C. (for 96
hours) during a heating process comprising a process for removing
the binder and the plasticizer, etc. of the tape so as to remove
the plasticizer having a low volatilization temperature and to
prevent an excessive oxidation of nickel in the nickel-aluminum
alloy. Then, air was blown in the temperature range of 250.degree.
C..about.450.degree. C. (for 24 hours) so as to completely remove
the organic binder. Then, hydrogen and carbon dioxide were
simultaneously injected in the temperature range of 450.degree.
C..about.650.degree. C. (for 24 hours) so as to prevent an
excessive nickel oxidation of the nickel-aluminum particles.
[0038] FIG. 2 is a graph showing a long time performance of a unit
cell using a nickel-aluminum alloy anode for molten carbonate fuel
cell made by in-situ sintering the nickel-aluminum alloy according
to the present invention.
[0039] As shown in FIG. 2, the unit cell using a nickel-aluminum
alloy anode for molten carbonate fuel cell made by in-situ
sintering the nickel-aluminum alloy according to the present
invention exhibits a constant performance for 1,000 hours.
[0040] Further, the cell exhibits an electrical conductivity and a
nitrogen cross-over, etc., which are equal or superior to those of
an anode made by an ex-situ sintering method such as the existing
partial oxidation-reduction method.
[0041] Many alterations and modifications may be made by those
having ordinary skill in the art without departing from the spirit
and scope of the invention. Therefore, it must be understood that
the embodiment and example described above should not be taken as
limiting the invention as defined by the following claims. The
claims are thus to be understood to include what is specifically
described above, what is conceptionally equivalent, what can be
obviously substituted and also what essentially incorporates the
essential idea of he invention.
* * * * *