U.S. patent application number 12/316806 was filed with the patent office on 2009-07-02 for ceramic interconnect for fuel cell stacks.
This patent application is currently assigned to Saint-Gobain Ceramics & Plastics, Inc.. Invention is credited to Guangyong Lin.
Application Number | 20090169958 12/316806 |
Document ID | / |
Family ID | 40474771 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090169958 |
Kind Code |
A1 |
Lin; Guangyong |
July 2, 2009 |
Ceramic interconnect for fuel cell stacks
Abstract
A fuel cell comprises a plurality of sub-cells, each sub-cell
including a first electrode in fluid communication with a source of
oxygen gas, a second electrode in fluid communication with a source
of a fuel gas, and a solid electrolyte between the first electrode
and the second electrode. The sub-cells are connected with each
other with an interconnect. The interconnect includes a first layer
in contact with the first electrode of each cell, and a second
layer in contact with the second electrode of each cell. The first
layer includes a (La,Mn)Sr-titanate based perovskite represented by
the empirical formula of
La.sub.ySr.sub.(1-y)Ti.sub.(1-x)Mn.sub.xO.sub.b. In one embodiment,
the second layer includes a (Nb,Y)Sr-titanate perovskite
represented by the empirical formula of
Sr.sub.(1-1.5z-0.5k.+-..delta.)Y.sub.zNb.sub.kTi.sub.(1-k)O.sub.d.
In another embodiment, the interconnect has a thickness of between
about 10 .mu.m and about 100 .mu.m, and the second layer of the
interconnect includes a (La)Sr-titanate based perovskite
represented by the empirical formula of
Sr.sub.(1-z.+-..delta.)La.sub.zTiO.sub.d.
Inventors: |
Lin; Guangyong; (Shrewsbury,
MA) |
Correspondence
Address: |
HAMILTON, BROOK, SMITH & REYNOLDS, P.C.
530 VIRGINIA ROAD, P.O. BOX 9133
CONCORD
MA
01742-9133
US
|
Assignee: |
Saint-Gobain Ceramics &
Plastics, Inc.
Worcester
MA
|
Family ID: |
40474771 |
Appl. No.: |
12/316806 |
Filed: |
December 16, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61063643 |
Feb 5, 2008 |
|
|
|
61009003 |
Dec 21, 2007 |
|
|
|
Current U.S.
Class: |
429/496 ;
29/623.1; 427/115 |
Current CPC
Class: |
C04B 2235/3262 20130101;
H01M 8/1226 20130101; H01M 8/2432 20160201; C04B 2235/3213
20130101; Y10T 29/49108 20150115; C04B 2235/3275 20130101; H01M
8/2435 20130101; C04B 2235/3225 20130101; H01M 8/0228 20130101;
C04B 2235/3227 20130101; C04B 2235/3232 20130101; C04B 2235/3251
20130101; H01M 2008/1293 20130101; C04B 35/2633 20130101; C04B
2235/768 20130101; H01M 8/0217 20130101; Y02E 60/50 20130101; C04B
35/47 20130101; H01M 8/2404 20160201; C04B 35/2641 20130101; H01M
8/243 20130101; H01M 8/0215 20130101; C04B 35/016 20130101 |
Class at
Publication: |
429/33 ; 429/30;
427/115; 29/623.1 |
International
Class: |
H01M 8/10 20060101
H01M008/10; B05D 5/12 20060101 B05D005/12; H01M 6/00 20060101
H01M006/00 |
Claims
1. A fuel cell, comprising: a) a plurality of sub-cells, each
sub-cell including i) a first electrode in fluid communication with
a source of oxygen gas, ii) a second electrode in fluid
communication with a source of a fuel gas, and iii) a solid
electrolyte between the first electrode and the second electrode;
and b) an interconnect between the sub-cells, the interconnect
including i) a first layer that includes a (La,Mn)Sr-titanate based
perovskite represented by the empirical formula of
La.sub.ySr.sub.(1-y)Ti.sub.(1-x)Mn.sub.xO.sub.b, wherein x is equal
to or greater than zero and equal to or less than 0.6, y is equal
to or greater than 0.2 and equal to or less than 0.8, and b is
equal to or greater than 2.5 and equal to or less than 3.5, wherein
the first layer is in contact with the first electrode of each
sub-cell, and ii) a second layer that includes a (Nb, Y)Sr-titanate
based perovskite represented by the empirical formula of
Sr.sub.(1-1.5z-0.5k.+-..delta.)Y.sub.zNb.sub.kTi.sub.(1-k)O.sub.d,
wherein each of k and z independently is equal to or greater than
zero and equal to or less than 0.2, d is equal to or greater than
2.5 and equal to or less than 3.5, and .delta. is equal to or
greater than zero and equal to or less than 0.05, wherein the
second layer is in contact with the second electrode of each
sub-cell.
2. The fuel cell of claim 1, wherein the (La,Mn)Sr-titanate based
perovskite is represented by the empirical formula of
La.sub.0.4Sr.sub.0.6Ti.sub.(1-x)Mn.sub.xO.sub.b.
3. The fuel cell of claim 1, wherein each of the first and second
electrodes is porous.
4. The fuel cell of claim 3, wherein the interconnect is
substantially planar.
5. The fuel cell of claim 4, wherein the solid electrolyte includes
at least one material selected from the group consisting of
ZrO.sub.2 based material, CeO.sub.2 based material and
lanthanide-gallate based material.
6. The fuel cell of claim 4, wherein the first electrode includes
at least one of a lanthanum strontium manganate (LSM) based
material and a lanthanum strontium cobalt ferrite (LSCF) based
material.
7. The fuel cell of claim 4, wherein the second electrode includes
a Ni cermet.
8. The fuel cell of claim 4, wherein the thickness of each of the
first and second electrodes of at least one of the cells is in a
range of between about 0.5 mm and about 2 mm.
9. The fuel cell of claim 8, wherein the thickness of the
interconnect is in a range of between about 5 .mu.m and about 1,000
.mu.m.
10. The fuel cell of claim 9, wherein the thickness of the
interconnect is in a range of between about 10 .mu.m and about 500
.mu.m.
11. The fuel cell of claim 10, wherein the thickness of the
interconnect is in a range of between about 10 .mu.m and about 200
.mu.m.
12. The fuel cell of claim 11, wherein the thickness of the
interconnect is in a range of between about 10 .mu.m and about 100
.mu.m.
13. A fuel cell, comprising: a) a plurality of sub-cells, each
sub-cell including i) a first electrode in fluid communication with
a source of oxygen gas, ii) a second electrode in fluid
communication with a source of a fuel gas, and iii) a solid
electrolyte between the first electrode and the second electrode;
and b) an interconnect between the sub-cells and having a thickness
of between about 10 .mu.m and about 100 .mu.m, the interconnect
including i) a first layer that includes a (La,Mn)Sr-titanate based
perovskite represented by the empirical formula of
La.sub.ySr.sub.(1-y)Ti.sub.(1-x)Mn.sub.xO.sub.b, wherein x is equal
to or greater than zero and equal to or less than 0.6, y is equal
to or greater than 0.2 and equal to or less than 0.8, and b is
equal to or greater than 2.5 and equal to or less than 3.5, wherein
the first layer is in contact with the first electrode of each
sub-cell; and ii) a second layer that includes a (La)Sr-titanate
based perovskite represented by the empirical formula of
Sr.sub.(1-z.+-..delta.)La.sub.zTiO.sub.d, wherein z is equal to or
greater than zero and equal to or less than 0.4, d is equal to or
greater than 2.5 and equal to or less than 3.5, and .delta. is
equal to or greater than zero and equal to or less than 0.05,
wherein the second layer is in contact with the second electrode of
each sub-cell.
14. The fuel cell of claim 13, wherein the (La,Mn)Sr-titanate-based
perovskite is represented by the empirical formula of
La.sub.0.4Sr.sub.0.6Ti.sub.(1-x)Mn.sub.xO.sub.b.
15. The fuel cell of claim 13, wherein each of the first and second
electrodes is porous.
16. The fuel cell of claim 15, wherein the interconnect is
substantially planar.
17. The fuel cell of claim 16, wherein the solid electrolyte
includes at least one material selected from the group consisting
of ZrO.sub.2 based material, CeO.sub.2 based material and
lanthanide-gallate based material.
18. The fuel cell of claim 16, wherein the first electrode includes
at least one of a lanthanum strontium manganate (LSM) based
material and a lanthanum strontium cobalt ferrite (LSCF) based
material.
19. The fuel cell of claim 16, wherein the second electrode
includes a Ni cermet.
20. The fuel cell of claim 16, wherein the thickness of each of the
first and second electrodes of at least one of the cells is in a
range of between about 0.5 mm and about 2 mm.
21. The fuel cell of claim 20, wherein the thickness of the
interconnect is in a range of between about 10 .mu.m and about 75
.mu.m.
22. The fuel cell of claim 21, wherein the thickness of the
interconnect is in a range of between about 15 .mu.m and about 65
.mu.m.
23. A method of forming a fuel cell that includes a plurality of
sub-cells, comprising the step of connecting each of the sub-cells
with an interconnect, wherein each sub-cell includes: i) a first
electrode in fluid communication with a source of oxygen gas, ii) a
second electrode in fluid communication with a source of a fuel
gas, and iii) a solid electrolyte between the first electrode and
the second electrode, and wherein the interconnect includes i) a
first layer that includes a (La,Mn)Sr-titanate-based perovskite
represented by the empirical formula of
La.sub.ySr.sub.(1-y)Ti.sub.(1-x)Mn.sub.xO.sub.b, wherein x is equal
to or greater than zero and equal to or less than 0.6, y is equal
to or greater than 0.2 and equal to or less than 0.8, and b is
equal to or greater than 2.4 and equal to or less than 3.3, wherein
the first layer is in contact with the first electrode of each
sub-cell, and ii) a second layer that includes a
(Nb,Y)Sr-titanate-based perovskite represented by the empirical
formula of
Sr.sub.(1-1.5z-0.5k.+-..delta.)Y.sub.zNb.sub.kTi.sub.(1-k)O.sub.d,
wherein each of k and z independently is equal to or greater than
zero and equal to or less than 0.2, d is equal to or greater than
2.5 and equal to or less than 3.5, and .delta. is equal to or
greater than zero and equal to or less than 0.05, wherein the
second layer is in contact with the second electrode of each
sub-cell.
24. The method of claim 23, further including forming at least one
component of each sub-cell.
25. The method of claim 24, further including forming at least one
of the electrodes of each sub-cell, and forming the
interconnect.
26. The method of claim 25, wherein at least one of the electrodes
of each sub-cell is formed independently from the formation of the
interconnect.
27. The method of claim 25, wherein at least one of the electrodes
of each sub-cell is formed together with the formation of the
interconnect.
28. The method of claim 26, wherein the first electrode of a first
sub-cell of the plurality of sub-cells is formed together with the
first and the second layers of the interconnect, and wherein the
formation of the first electrode, the first layer and the second
layer includes: i) disposing a second-layer material of the
interconnect over the second electrode of a first sub-cell; ii)
disposing a first-layer material of the interconnect over the
second-layer material; iii) disposing a first-electrode material of
a second sub-cell over the first-layer of the interconnect; and iv)
heating the materials such that the first-layer and second-layer
materials of the interconnect form the first and second layers of
the interconnect, respectively, and that the first-electrode
material forms the first electrode.
29. A method of forming a fuel cell that includes a plurality of
sub-cells, comprising the step of connecting each of the sub-cells
with an interconnect having a thickness of between about 10 .mu.m
and about 100 .mu.m, wherein each sub-cell includes: i) a first
electrode in fluid communication with a source of oxygen gas, ii) a
second electrode in fluid communication with a source of a fuel
gas, and iii) a solid electrolyte between the first electrode and
the second electrode, and wherein the interconnect includes i) a
first layer that includes a (La,Mn)Sr-titanate-based perovskite
represented by the empirical formula of
La.sub.ySr.sub.(1-y)Ti.sub.(1-x)Mn.sub.xO.sub.b, wherein x is equal
to or greater than zero and equal to or less than 0.6, y is equal
to or greater than 0.2 and equal to or less than 0.8, and b is
equal to or greater than 2.5 and equal to or less than 3.5, wherein
the first layer is in contact with the first electrode of each
sub-cell, and ii) a second layer that includes a (La)Sr-titanate
based perovskite represented by the empirical formula of
Sr.sub.(1-z.+-..delta.)La.sub.zTiO.sub.d, wherein z is equal to or
greater than zero and equal to or less than 0.4, d is equal to or
greater than 2.5 and equal to or less than 3.5, and .delta. is
equal to or greater than zero and equal to or less than 0.05,
wherein the second layer is in contact with the second electrode of
each sub-cell.
30. The method of claim 29, further including forming at least one
component of each sub-cell.
31. The method of claim 30, further including forming at least one
of the electrodes of each sub-cell, and forming the
interconnect.
32. The method of claim 31, wherein at least one of the electrodes
of each sub-cell is formed independently from the formation of the
interconnect.
33. The method of claim 31, wherein at least one of the electrodes
of each sub-cell is formed together with the formation of the
interconnect.
34. The method of claim 33, wherein the first electrode of a first
sub-cell of the plurality of sub-cells is formed together with the
first and the second layers of the interconnect, and wherein the
formation of the first electrode, the first layer and the second
layer includes: i) disposing a second-layer material of the
interconnect over the second electrode of a first sub-cell; ii)
disposing a first-layer material of the interconnect over the
second-layer material; iii) disposing a first-electrode material of
a second sub-cell over the first-layer of the interconnect; and iv)
heating the materials such that the first-layer and second-layer
materials of the interconnect form the first and second layers of
the interconnect, respectively, and that the first-electrode
material forms the first electrode.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/063,643, filed on Feb. 5, 2008 and U.S.
Provisional Application No. 61/009,003, filed on Dec. 21, 2007. The
entire teachings of the above applications are incorporated herein
by reference.
BACKGROUND OF THE INVENTION
[0002] A fuel cell is a device that generates electricity by a
chemical reaction. Among various fuel cells, solid oxide fuel cells
use a hard, ceramic compound of metal (e.g., calcium or zirconium)
oxide as an electrolyte. Typically, in the solid oxide fuel cells,
an oxygen gas, such as O.sub.2, is reduced to oxygen ions
(O.sup.2-) at the cathode, and a fuel gas, such as hydrogen gas
(H.sub.2) gas, is oxidized with the oxygen ions to form water at
the anode.
[0003] Interconnects are one of the critical issues limiting
commercialization of solid oxide fuel cells. Currently, most
companies and researchers working with planar cells are using
coated metal interconnects. While metal interconnects are
relatively easy to fabricate and process, they generally suffer
from high power degradation rates (e.g. 10%/1,000 h) partly due to
formation of metal oxides, such as Cr.sub.2O.sub.3, at an
interconnect-anode/cathode interface during operation. Ceramic
interconnects based on lanthanum chromites (LaCrO.sub.3) have lower
degradation rates than metal interconnects partly due to relatively
high thermodynamic stability and low Cr vapor pressure of
LaCrO.sub.3 compared to Cr.sub.2O.sub.3 formed on interfaces of the
metal interconnects and electrode. However, lanthanum chromites
generally are difficult to fully densify and require high
temperatures, such as at or above about 1,600.degree. C., for
sintering. Although certain doped lanthanum chromites, such as
strontium-doped and calcium-doped lanthanum chromites, can be
sintered at lower temperatures, they tend to be either unstable or
reactive with an electrolyte (e.g., a zirconia electrolyte) and/or
an anode.
[0004] Therefore, there is a need for development of new
interconnects for solid oxide fuel cells, addressing one or more of
the aforementioned problems.
SUMMARY OF THE INVENTION
[0005] The invention is directed to a fuel cell, such as a solid
oxide fuel cell (SOFC), that includes a plurality of sub-cells and
to a method of preparing the fuel cell. Each sub-cell includes a
first electrode in fluid communication with a source of oxygen gas,
a second electrode in fluid communication with a source of a fuel
gas, and a solid electrolyte between the first electrode and the
second electrode. The fuel cell further includes an interconnect
between the sub-cells. The interconnect includes a first layer in
contact with the first electrode of each sub-cell, and a second
layer in contact with the second electrode of each sub-cell. The
first layer includes a (La,Mn)Sr-titanate based pertovskite
represented by the empirical formula of
La.sub.ySr.sub.(1-y)Ti.sub.(1-x)Mn.sub.xO.sub.b, wherein x is equal
to or greater than zero, and equal to or less than 0.6; y is equal
to or greater than 0.2, and equal to or less than 0.8; and b is
equal to or greater than 2.5, and equal to or less than 3.5. In one
embodiment, the second layer includes a (Nb,Y)Sr-titanate based
pertovskite represented by the empirical formula of
Sr.sub.(1-1.5z-0.5k.+-..delta.k)Y.sub.zNb.sub.kTi.sub.(1-k)O.sub.d,
wherein each of k and z independently is equal to or greater than
zero, and equal to or less than 0.2; d is equal to or greater than
2.5 and equal to or less than 3.5; and .delta. is equal to or
greater than zero, and equal to or less than 0.05. In another
embodiment, the interconnect has a thickness of between about 10
.mu.m and about 100 .mu.m, and the second layer of the interconnect
includes a (Sr)La-titanate based perovskite represented by the
empirical formula of Sr.sub.(1-z.+-..delta.)La.sub.zTiO.sub.d,
wherein z is equal to or greater than zero, and equal to or less
than 0.4; d is equal to or greater than 2.5, and equal to or less
than 3.5; and .delta. is equal to or greater than zero, and equal
to or less than 0.05.
[0006] In the invention, the first layer of (La,Mn)Sr-titanate
based perovskite, which is in contact with the first electrode
exposed to an oxygen source, can provide relatively high
sinterability (e.g., sinterability to over 95% of theoretical
density at a temperature lower than about 1,500.degree. C.),
stability in the oxidizing atmosphere and/or electrical
conductivity. The second layer of (Nb,Y)Sr-titanate based
perovskite and/or (La)Sr-titanate based perovskite, which is in
contact with the second electrode exposed to a fuel source, can
provide high electrical conductivity and stability in the reducing
atmosphere. The (La,Mn)Sr-titanate based perovskite and the
(Nb,Y)Sr-titanate based perovskite materials have similar thermal
expansion coefficients with each other. For example,
La.sub.0.4Sr.sub.0.6Ti.sub.0.4Mn.sub.0.6O.sub.3 has an average
thermal expansion coefficient of 11.9.times.10.sup.-6 K.sup.-1 at
30.degree. C.-1,000.degree. C. in air, and
Sr.sub.0.86Y.sub.0.08TiO.sub.3 has an average thermal expansion
coefficient of 11-12.times.10.sup.-6 K.sup.-1 at 25.degree.
C.-1,000.degree. C. in air. Thus, both of the first layer of
(La,Mn)Sr-titanate based perovskite and the second layer of
(Nb,Y)Sr-titanate based perovskite can be co-sintered at the same
time, minimizing process steps.
[0007] In another embodiment, the present invention is directed to
a method of forming a fuel cell that includes a plurality of
sub-cells. The method includes connecting each of the sub-cells
with an interconnect. Each sub-cell includes a first electrode in
fluid communication with a source of oxygen gas, a second electrode
in fluid communication with a source of a fuel gas, and a solid
electrolyte between the first electrode and the second electrode.
The interconnect includes a first layer that includes a
(La,Mn)Sr-titanate-based perovskite represented by the empirical
formula of La.sub.ySr.sub.(1-y)Ti.sub.(1-x)Mn.sub.xO.sub.b, wherein
x is equal to or greater than zero and equal to or less than 0.6, y
is equal to or greater than 0.2 and equal to or less than 0.8, and
b is equal to or greater than 2.5 and equal to or less than 3.5.
The first layer is in contact with the first electrode of each
sub-cell. The interconnect also includes a second layer that
includes a (Nb,Y)Sr-titanate-based perovskite represented by the
empirical formula of
Sr.sub.(1-1.5z-0.5k.+-..delta.)Y.sub.zNb.sub.kTi.sub.(1-k)O.sub.d,
wherein each of k and z independently is equal to or greater than
zero and equal to or less than 0.2, d is equal to or greater than
2.5 and equal to or less than 3.5, and .delta. is equal to or
greater than zero and equal to or less than 0.05. The second layer
is in contact with the second electrode of each sub-cell. In one
embodiment, the method includes forming at least one component of
each sub-cell. In another embodiment, the method includes forming
at least one of the electrodes of each sub-cell, and forming the
interconnect. In yet another embodiment, at least one of the
electrodes of each sub-cell is formed independently from the
formation of the interconnect, and at least one of the electrodes
of each sub-cell is formed together with the formation of the
interconnect. In one embodiment, the first electrode of a first
sub-cell of the plurality of sub-cells is formed together with the
first and the second layers of the interconnect, and the formation
of the first electrode, the first layer and the second layer
includes disposing a second-layer material of the interconnect over
the second electrode of a first sub-cell, disposing a first-layer
material of the interconnect over the second-layer material,
disposing a first-electrode material of a second sub-cell over the
first-layer, of the interconnect, and heating the materials such
that the first-layer and second-layer materials of the interconnect
form the first and second layers of the interconnect, respectively,
and that the first-electrode material forms the first
electrode.
[0008] In another embodiment, the present invention is directed to
a method of forming a fuel cell that includes a plurality of
sub-cells, comprising the step of connecting each of the sub-cells
with an interconnect having a thickness of between about 10 .mu.m
and about 100 .mu.m. Each sub-cell includes a first electrode in
fluid communication with a source of oxygen gas, a second electrode
in fluid communication with a source of a fuel gas, and a solid
electrolyte between the first electrode and the second electrode.
The interconnect includes a first layer that includes a
(La,Mn)Sr-titanate-based perovskite represented by the empirical
formula of La.sub.ySr.sub.(1-y)Ti.sub.(1-x)Mn.sub.xO.sub.b, wherein
x is equal to or greater than zero and equal to or less than 0.6, y
is equal to or greater than 0.2 and equal to or less than 0.8, and
b is equal to or greater than 2.5 and equal to or less than 3.5.
The first layer is in contact with the first electrode of each
sub-cell. The interconnect also includes a second layer that
includes a (La)Sr-titanate based perovskite represented by the
empirical formula of Sr.sub.(1-z.+-..delta.)La.sub.zTiO.sub.d,
wherein z is equal to or greater than zero and equal to or less
than 0.4, d is equal to or greater than 2.5 and equal to or less
than 3.5, and .delta. is equal to or greater than zero and equal to
or less than 0.05. The second layer is in contact with the second
electrode of each sub-cell. In one embodiment, the method includes
forming at least one component of each sub-cell. In another
embodiment, the method includes forming at least one of the
electrodes of each sub-cell, and forming the interconnect. In yet
another embodiment, at least one of the electrodes of each sub-cell
is formed independently from the formation of the interconnect, and
at least one of the electrodes of each sub-cell is formed together
with the formation of the interconnect. In one embodiment, the
first electrode of a first sub-cell of the plurality of sub-cells
is formed together with the first and the second layers of the
interconnect, and the formation of the first electrode, the first
layer and the second layer includes disposing a second-layer
material of the interconnect over the second electrode of a first
sub-cell, disposing a first-layer material of the interconnect over
the second-layer material, disposing a first-electrode material of
a second sub-cell over the first-layer of the interconnect, and
heating the materials such that the first-layer and second-layer
materials of the interconnect form the first and second layers of
the interconnect, respectively, and that the first-electrode
material forms the first electrode.
[0009] This invention has many advantages. Bi-layer ceramic
interconnects of the invention meet all the major requirements for
solid oxide fuel cell (SOFC) stack interconnects.
(La,Mn)Sr-titanate based perovskite is stable and its electrical
conductivity is high in an oxidizing atmosphere, and therefore this
material can be used on the air side in the bi-layer ceramic
interconnect. (Nb,Y)Sr-titanate based perovskite and
(La)Sr-titanate based perovskite is stable and its electrical
conductivity is high in a reducing atmosphere, and therefore this
material can be used on the fuel side in the bi-layer ceramic
interconnect. These materials also have the advantage that,
containing no chromium, they do not have the problems associated
with lanthanum chromites (LaCrO.sub.3). The present invention can
be used in a solid oxide fuel cell (SOFC) system, particularly in
planar SOFC stacks. SOFCs offer the potential of high efficiency
electricity generation, with low emissions and low noise operation.
They are also seen as offering a favorable combination of
electrical efficiency, co-generation efficiency and fuel processing
simplicity. One example of a use for SOFCs is in a home or other
building. The SOFC can use the same fuel as used to heat the home,
such as natural gas. The SOFC system can run for extended periods
of time to generate electricity to power the home and if excess
amounts are generated, the excess can be sold to the electric grid.
Also, the heat generated in the SOFC system can be used to provide
hot water for the home. SOFCs can be particularly useful in areas
where electric service is unreliable or non-existent.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic cross-sectional view of one embodiment
of the invention.
[0011] FIG. 2 is a schematic diagram of a fuel cell of the
invention in a planar, stacked design.
[0012] FIG. 3 is a schematic diagram of a fuel cell of the
invention in a tubular design.
[0013] FIG. 4 is a scanning electron microscopic (SEM) image of an
interconnect of the invention made of
La.sub.0.4Sr.sub.0.6Ti.sub.0.4Mn.sub.0.6O.sub.3-.delta. and
Sr.sub.0.86Y.sub.0.08TiO.sub.3-.delta. layers.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The foregoing will be apparent from the following more
particular description of example embodiments of the invention, as
illustrated in the accompanying drawings in which like reference
characters refer to the same parts throughout the different views.
The drawing is not necessarily to scale, emphasis instead being
placed upon illustrating embodiments of the present invention.
[0015] FIG. 1 shows fuel cell 10 of the invention. Fuel cell 10
includes a plurality of sub-cells 12. Each sub-cell 12 includes
first electrode 14 and second electrode 16. Typically, first and
second electrodes 14 and 16 are porous. In fuel cell 10, first
electrode 14 at least in part defines a plurality of first gas
channels 18 in fluid communication with a source of oxygen gas,
such as air. Second electrode 16 at least in part defines a
plurality of second gas channels 20 in fluid communication with a
fuel gas source, such as H.sub.2 gas or a natural gas which can be
converted into H.sub.2 gas in situ at second electrode 16.
[0016] Although, in FIG. 1, first electrodes 14 and second
electrodes 16 define a plurality of gas channels 18 and 20, other
types of gas channels, such as a microstructured channel (e.g.,
grooved channel) at each of the electrodes or as a separate layer
in fluid communication with the electrode, can also be used in the
invention. For example, referring to FIG. 2, first gas channel 18
is defined at least in part by first electrode 14 and by at least
in part by interconnect 24, and second gas channel 20 is defined at
least in part by second electrode 16 and by at least in part by
interconnect 24.
[0017] Any suitable cathode materials known in the art can be used
for first electrode 14. In one embodiment, first electrode 14
includes a La-manganate (e.g, La.sub.1-aMnO.sub.3, where a is equal
to or greater than zero, and equal to or less than 0.1) or
La-ferrite based material. Typically, the La-manganate or
La-ferrite based materials are doped with one or more suitable
dopants, such as Sr, Ca, Ba, Mg, Ni, Co or Fe. Examples of doped
La-manganate based materials include LaSr-manganates (LSM) (e.g.,
La.sub.1-kSr.sub.kMnO.sub.3, where k is equal to or greater than
0.1, and equal to or less than 0.3, (La+Sr)/Mn is in a range of
between about 1.0 and about 0.95 (molar ratio)) and LaCa-manganates
(e.g., La.sub.1-kCa.sub.kMnO.sub.3, k is equal to or greater than
0.1, and equal to or less than 0.3, (La+Ca)/Mn is in a range of
between about 1.0 and about 0.95 (molar ratio)). Examples of doped
La-ferrite based materials include LaSrCo-ferrite (LSCF) (e.g.
La.sub.1-qSr.sub.qCo.sub.1-jFe.sub.jO.sub.3, where each of q and j
independently is equal to or greater than 0.1, and equal to or less
than 0.4, (La+Sr)/(Fe+Co) is in a range of between about 1.0 and
about 0.95 (molar ratio)). In one specific embodiment, first
electrode 14 includes at least one of a LaSr-manganate (LSM) (e.g.,
La.sub.1-kSr.sub.kMnO.sub.3) and a LaSrCo-ferrite (LSCF). Common
examples include
(La.sub.0.8Sr.sub.0.2).sub.0.98MnO.sub.3.+-..delta. (.delta. is
equal to or greater than zero, and equal to or less than 0.05) and
La.sub.0.6Sr.sub.0.4Co.sub.0.2Fe.sub.0.8O.sub.3.
[0018] Any suitable anode materials known in the art can be used
for second electrode 16. In one embodiment, second electrode 16
includes a nickel (Ni) cermet. As used herein, the phrase "Ni
cermet" means a ceramic metal composite that includes Ni, such as
about 20 wt %-70 wt % of Ni. Examples of Ni cermets are materials
that include Ni and yttria-stabilized zirconia (YSZ), such as
ZrO.sub.2 containing about 15 wt % of Y.sub.2O.sub.3, and materials
that include Ni and Y-zirconia or Sc-zirconia. An additional
example of anode materials include Cu-cerium oxide. Specific
examples of Ni cermet include 67 wt % Ni and 33 wt % YSZ, and 33 wt
% Ni and 67 wt % YSZ.
[0019] Typically, the thickness of each of first and second
electrodes 14 and 16 is independently is in a range of between
about 0.5 mm and about 2 mm. Specifically, the thickness of each of
first and second electrodes 14 and 16 is, independently, in a range
of between about 1 mm and about 2 mm.
[0020] Solid electrolyte 22 is between first electrode 14 and
second electrode 16. Any suitable solid electrolytes known in the
art can be used in the invention. Examples include ZrO.sub.2 based
materials, such as Sc.sub.2O.sub.3-doped ZrO.sub.2,
Y.sub.2O.sub.3-doped ZrO.sub.2, and Yb.sub.2O.sub.3-doped
ZrO.sub.2; CeO.sub.2 based materials, such as Sm.sub.2O.sub.3-doped
CeO.sub.2, Gd.sub.2O.sub.3-doped CeO.sub.2, Y.sub.2O.sub.3-doped
CeO.sub.2 and CaO-doped CeO.sub.2; Ln-gallate based materials (Ln=a
lanthanide, such as La, Pr, Nd or Sm), such as LaGaO.sub.3 doped
with Ca, Sr, Ba, Mg, Co, Ni, Fe or a mixture thereof (e.g.,
La.sub.0.8Sr.sub.0.2Ga.sub.0.8Mg.sub.0.2O.sub.3,
La.sub.0.8Sr.sub.0.2Ga.sub.0.8Mg.sub.0.15Co.sub.0.05O.sub.3,
La.sub.0.9Sr.sub.0.1Ga.sub.0.8Mg.sub.0.2O.sub.3, LaSrGaO.sub.4,
LaSrGa.sub.3O.sub.7 or La.sub.0.9A.sub.0.1Ga.sub.3 where A=Sr, Ca
or Ba); and mixtures thereof. Other examples include doped
yttrium-zirconate (e.g., YZr.sub.2O.sub.7), doped
gadolinium-titanate (e.g., Gd.sub.2Ti.sub.2O.sub.7) and
brownmillerites (e.g., Ba.sub.2In.sub.2O.sub.6 or
Ba.sub.2In.sub.2O.sub.5). In a specific embodiment, electrolyte 22
includes ZrO.sub.2 doped with 8 mol % Y.sub.2O.sub.3 (i.e., 8 mol %
Y.sub.2O.sub.3-doped ZrO.sub.2.)
[0021] Typically, the thickness of solid electrolyte 22 is in a
range of between about 5 .mu.m and about 20 .mu.m, such as between
about 5 .mu.m and about 10 .mu.m. Alternatively, the thickness of
solid electrolyte 22 is thicker than about 100 .mu.m (e.g., between
about 100 .mu.m and about 500 100 .mu.m). In this embodiment
employing solid electrolyte 22 having a thickness greater than
about 100 .mu.m, solid electrolyte 22 can provide structural
support for fuel cell 10.
[0022] Fuel cell 10 further includes interconnect 24 between
sub-cells 12. Interconnect 24 includes first layer 26 in contact
with first electrode 14, and second layer 28 in contact with second
electrode 16. First layer 26 includes a (La,Mn)Sr-titanate based
perovskite represented by the empirical formula of
La.sub.ySr.sub.(1-y)Ti.sub.(1-x)Mn.sub.xO.sub.b, wherein x is equal
to or greater than zero, and equal to or less than 0.6; y is equal
to or greater than 0.2, and equal to or less than 0.8; and b is
equal to or greater than 2.5, and equal to or less than 3.5. In one
specific embodiment, the (La,Mn)Sr-titanate based perovskite is
represented by the empirical formula of
La.sub.0.4Sr.sub.0.6Ti.sub.(1-x)Mn.sub.xO.sub.b, wherein values of
x and b are as described above. Specific examples of suitable
(La,Mn)Sr-titanate based perovskites include
La.sub.0.4Sr.sub.0.6TiO.sub.b,
La.sub.0.4Sr.sub.0.6Ti.sub.0.8Mn.sub.0.2O.sub.b,
La.sub.0.4Sr.sub.0.6Ti.sub.0.6Mn.sub.0.4Ob and
La.sub.0.4Sr.sub.0.6Ti.sub.0.4Mn.sub.0.6O.sub.b. In another
specific embodiment, a
La.sub.0.4Sr.sub.0.6Ti.sub.(1-x)Mn.sub.xO.sub.b material is
employed, and the material has an electrical conductivity of
between about 20 S/cm and about 25 S/cm in air (e.g. about 22.6
S/cm) at about 810.degree. C., and has an average density equal to
or greater than 95% theoretical density.
[0023] Second layer 28 includes a (Nb,Y)Sr-titanate based
perovskite represented by the empirical formula of
Sr.sub.(1-1.5z-0.5k.+-.k)Y.sub.zNb.sub.kTi.sub.(1-k)O.sub.d, or a
(La)Sr-titanate based perovskite represented by the empirical
formula of Sr.sub.(1-z.+-..delta.)La.sub.zTiO.sub.d, wherein each
of k and z independently is equal to or greater than zero, and
equal to or less than 0.4; and d is equal to or greater than 2.5,
and equal to or less than 3.5 (e.g., equal to or greater than 2.9,
and equal to or less than 3.2); and .delta. is equal to or greater
than zero, and equal to or less than 0.05. Specific examples of the
(Nb,Y)Sr-titanate based perovskite include
Sr.sub.0.86Y.sub.0.08TiO.sub.3.+-..delta., and
Sr.sub.0.995Ti.sub.0.99Nb.sub.0.01O.sub.3.+-..delta. (wherein
.delta. is equal to or greater than zero, and equal to or less than
0.05). A specific example of the (La)Sr-titanate based perovskites
includes Sr.sub.0.67La.sub.0.33TiO.sub.3.+-..delta. (wherein
.delta. is equal to or greater than zero, and equal to or less than
0.05). In a further specific embodiment, a
Sr.sub.0.86Y.sub.0.08TiO.sub.3.+-..delta. or
Sr.sub.0.995Ti.sub.0.99Nb.sub.0.01O.sub.3.+-..delta. material is
employed, and has an average density equal to or greater than 95%
theoretical density. In another further specific embodiment, the
Sr.sub.0.86Y.sub.0.08TiO.sub.3.+-..delta. and
Sr.sub.0.995Ti.sub.0.99Nb.sub.0.01O.sub.3.+-..delta. materials have
an electrical conductivity of about 82 S/cm and 10 S/cm,
respectively, in a reducing environment (oxygen partial pressure of
10.sup.-19 atm) at about 800.degree. C.
[0024] As used herein, "perovskite" has the perovskite structure
known in the art. The perovskite structure is adopted by many
oxides that have the chemical formula of ABO.sub.3. The general
crystal structure is a primitive cube with the A-cation in the
center of a unit cell, the B-cation at the corners of the unit
cell, and the anion (i.e., O.sup.2-) at the centers of each edge of
the unit cell. The idealized structure is a primitive cube, but
differences in ratio between the A and B cations can cause a number
of different so-called distortions, of which tilting is the most
common one. As used herein, the term "perovskite," with or without
other terms in combination therewith (e.g., "(La,Mn)Sr-titanate
based perovskite, ""(Nb,Y)Sr-titanate based perovskite," and
"(La)Sr-titanate based perovskite") also includes such distortions.
Also, as used herein, the term "(La,Mn)Sr-titanate based
perovskite" means a La- and/or Mn-substituted SrTiO.sub.3
(Sr-titanate) having the perovskite structure. In one example,
La-substituted, Sr-titanate based perovskites have the perovskite
structure of SrTiO.sub.3 wherein a portion of the Sr atoms of
SrTiO.sub.3 are substituted with La atoms. In another example,
Mn-substituted, Sr-titanate based perovskites have the perovskite
structure of SrTiO.sub.3 wherein a portion of the Ti atoms of
SrTiO.sub.3 are substituted with Mn atoms. In yet another example,
La- and Mn-substituted, Sr-titanate based perovskites have the
perovskite structure of SrTiO.sub.3 wherein a portion of the Sr
atoms of SrTiO.sub.3 are substituted with La atoms, and a portion
of the Ti atoms of SrTiO.sub.3 are substituted with Mn atoms. Also,
as used herein, the term "(Nb,Y)Sr-titanate based perovskite" means
a Nb- and/or Y-substituted, SrTiO.sub.3 (Sr-titanate) having the
perovskite structure. In one example, Y-substituted, Sr-titanate
based perovskites have the perovskite structure of SrTiO.sub.3
wherein a portion of the Sr atoms of SrTiO.sub.3 are substituted
with Y atoms. In another example, Nb-substituted, Sr-titanate based
perovskites have the perovskite structure of SrTiO.sub.3 wherein a
portion of the Ti atoms of SrTiO.sub.3 are substituted with Nb
atoms. In yet another example, Nb- and Y-substituted, Sr-titanate
based perovskites have the perovskite structure of SrTiO.sub.3
wherein a portion of the Sr atoms of SrTiO.sub.3 are substituted
with Y atoms, and a portion of the Ti atoms of SrTiO.sub.3 are
substituted with Nb atoms. Also, as used herein, the term
"(La)Sr-titanate based perovskite" means La-substituted SrTiO.sub.3
(Sr-titanate) having the perovskite structure, wherein a portion of
the Sr atoms of SrTiO.sub.3 are substituted with La atoms.
Generally, in the (La,Mn)Sr-titanate based perovskites, La and Sr
atoms occupy the A-cation sites, while Ti and Mn atoms occupy the
B-cation sites. Generally, in the (Nb,Y)Sr-titanate based
perovskites, Sr and Y atoms occupy the A-cation sites, while Ti and
Nb atoms occupy the B-cation sites. Generally, in the
(La)Sr-titanate based perovskite, Sr and La atoms occupy the
A-cation sites, while Ti atoms occupy the B-cation sites.
[0025] In a specific embodiment, first layer 26 includes
La.sub.0.4Sr.sub.0.6Ti.sub.0.4Mn.sub.0.6O.sub.3.+-..delta. and
second layer 28 includes Sr.sub.0.86Y.sub.0.08TiO.sub.3.+-..delta..
In another specific embodiment, first layer 26 includes
La.sub.0.4Sr.sub.0.6Ti.sub.0.4Mn.sub.0.6O.sub.3.+-..delta. and
second layer 28 includes
Sr.sub.0.995Ti.sub.0.99Nb.sub.0.01O.sub.3.+-..delta.. In yet
another specific embodiment, first layer 26 includes
La.sub.0.4Sr.sub.0.6Ti.sub.0.4Mn.sub.0.6O.sub.3.+-..delta. and
second layer 28 includes
Sr.sub.0.67La.sub.0.33TiO.sub.3.+-..delta.. In these embodiments,
specifically, first electrode 14 includes
(La.sub.0.8Sr.sub.0.2).sub.0.98MnO.sub.3.+-..delta. or
La.sub.0.6Sr.sub.0.4Co.sub.0.2Fe.sub.0.8O.sub.3, and second
electrode 16 includes 67 wt % Ni and 33 wt % YSZ. In these
embodiments, more specifically, first electrode 14 includes
(La.sub.0.8Sr.sub.0.2).sub.0.98MnO.sub.3.+-..delta. or
La.sub.0.6Sr.sub.0.4Co.sub.0.2Fe.sub.0.8O.sub.3; second electrode
16 includes 67 wt % Ni and 33 wt % YSZ; and electrolyte 22 includes
8 mol % Y.sub.2O.sub.3-doped ZrO.sub.2.
[0026] Typically, the thickness of each of first layer 26 and
second layer 28 is in a range of between about 5 .mu.m and about
1000 .mu.m. Specifically, the thickness of each of first layer 26
and second layer 28 is in a range of between about 10 .mu.m and
about 1000 .mu.m. In one specific embodiment, the thickness of
second layer 28 is about 0.005 to about 0.5 of the total thickness
of interconnect 24.
[0027] Interconnect 24 can be in any shape, such as a planar shape
(see FIG. 1) or a microstructured (e.g., grooved) shape (see FIG.
2). In one specific embodiment, at least one interconnect 24 of
fuel cell 10 is substantially planar.
[0028] In one embodiment, the thickness of interconnect 24 is in a
range of between about 10 .mu.m and about 1,000 .mu.m.
Alternatively, the thickness of interconnect 24 is in a range of
between about 0.005 mm and about 2.0 mm. In one specific
embodiment, the thickness of interconnect 24 is in a range of 10
.mu.m and about 500 .mu.m. In another embodiment, the thickness of
interconnect 24 is in a range of 10 .mu.m and about 200 .mu.m. In
yet another embodiment, the thickness of interconnect 24 is between
about 10 .mu.m and about 100 .mu.m. In yet another embodiment, the
thickness of interconnect 24 is between about 10 .mu.m and about 75
.mu.m. In yet another embodiment, the thickness of interconnect 24
is between about 15 .mu.m and about 65 .mu.m.
[0029] In one specific embodiment, first electrode 14 and/or second
electrode 16 has a thickness of between about 0.5 mm and about 2 mm
thick; and interconnect 24 has a thickness of between about 10
.mu.m and about 200 .mu.m, specifically between about 10 .mu.m and
about 200 .mu.m, and more specifically between about 10 .mu.m and
about 100 .mu.m.
[0030] In another specific embodiment, second layer 28 includes a
SrLa-titanate based perovskite described above; and interconnect 24
has a thickness of between about 10 .mu.m and about 100 .mu.m,
specifically between about 10 .mu.m and about 75 .mu.m, and more
specifically between about 15 .mu.m and about 65 .mu.m.
[0031] In yet another specific embodiment, at least one cell 12
includes porous first and second electrodes 14 and 16, each of
which is between about 0.5 mm and about 2 mm thick; solid
electrolyte 22 has a thickness of between about 5 .mu.m and about
20 .mu.m; and interconnect 24 is substantially planar and has a
thickness of between about 10 .mu.m and about 200 .mu.m.
[0032] In yet another specific embodiment, interconnect 24 is
substantially planar; first layer 26 of interconnect 24 includes
La.sub.0.4Sr.sub.0.6Ti.sub.(1-x)Mn.sub.xO.sub.b (e.g., x=0, 0.2,
0.4 or 0.6); and each of first and second electrodes 14 and 16 is
porous.
[0033] In yet another specific embodiment, interconnect 24 is
substantially planar; first layer 26 of interconnect 24 includes
La.sub.0.4Sr.sub.0.6Ti.sub.(1-x)Mn.sub.xO.sub.b (e.g., x=0, 0.2,
0.4 or 0.6); and each of first and second electrodes 14 and 16 is
porous; and first electrode 14 includes a La-manganate or
La-ferrite based material described above, such as
La.sub.1-kSr.sub.kMnO.sub.3 or
La.sub.1-qSr.sub.qCo.sub.jFe.sub.1-jO.sub.3 (wherein values of each
of k, q and j independently are as described above).
[0034] In yet another specific embodiment, interconnect 24 is
substantially planar; first layer 26 of interconnect 24 includes
La.sub.0.4Sr.sub.0.6Ti.sub.(1-x)Mn.sub.xO.sub.b (e.g., x=0, 0.2,
0.4 or 0.6); and each of first and second electrodes 14 and 16 is
porous; and first electrode 14 includes a La-manganate or
La-ferrite based material (e.g., La.sub.1-kSr.sub.kMnO.sub.3 or
La.sub.1-qSr.sub.qCo.sub.jFe.sub.1-jO.sub.3, values of each of k, q
and j independently are as described above), and second electrode
16 includes a Ni cermet (e.g., 67 wt % Ni and 33 wt % YSZ). In one
aspect of this specific embodiment, electrolyte 22 includes 8 mol %
Y.sub.2O.sub.3-doped ZrO.sub.2.
[0035] Fuel cell 10 of the invention can include any suitable
number of a plurality of sub-cells 12. In one embodiment, fuel cell
10 of the invention includes at least 30-50 sub-cells 12. Sub-cells
12 of fuel cell 10 can be connected in series or in parallel.
[0036] A fuel cell of the invention can be a planar stacked fuel
cell, as shown in FIG. 2. Alternatively, as shown in FIG. 3, a fuel
cell of the invention can be a tubular fuel cell. Fuel cells shown
in FIGS. 2 and 3 independently have the characteristics, including
specific variables, as described for fuel cell 10 shown in FIG. 1
(for clarity, details of cell components are not depicted in FIGS.
2 and 3). Typically, in the planar design, as shown in FIG. 2, the
components are assembled in flat stacks, with air and fuel flowing
through channels built into the interconnect. Typically, in the
tubular design, as shown in FIG. 3, the components are assembled in
the form of a hollow tube, with the cell constructed in layers
around a tubular cathode; air flows through the inside of the tube
and fuel flows around the exterior.
[0037] The invention also includes a method of forming fuel cells
as described above. The method includes forming a plurality of
sub-cells 12 as described above, and connecting each sub-cell 12
with interconnect 24. Fabrication of sub-cells 12 and interconnect
24 can employ any suitable techniques known in the art. For
example, planar stacked fuel cells of the invention can be
fabricated by particulate processes or deposition processes.
Tubular fuel cells of the invention can be fabricated by having the
cell components in the form of thin layers on a porous cylindrical
tube, such as calcia-stabilized zirconia.
[0038] Typically, a suitable particulate process, such as tape
casting or tape calendering, involves compaction of powders, such
as ceramic powders, into fuel cell components (e.g., electrodes,
electrolytes and interconnects) and densification at elevated
temperatures. For example, suitable powder materials for
electrolytes, electrodes or interconnects of the invention, are
made by solid state reaction of constituent oxides. Suitable high
surface area powders can be precipitated from nitrate and other
solutions as a gel product, which are dried, calcined and
comminuted to give crystalline particles. The deposition processes
can involve formation of cell components on a support by a suitable
chemical or physical process. Examples of the deposition include
chemical vapor deposition, plasma spraying and spray pyrolysis.
[0039] In one specific embodiment, interconnect 24 is prepared by
laminating a first-layer material of interconnect 24, and a
second-layer material of interconnect 24, side by side at a
temperature in a range of between about 50.degree. C. and about
80.degree. C. with a loading of between about 5 and about 50 tons,
and co-sintered at a temperature in a range of 1,300.degree. C. and
about 1,500.degree. C. for a time period sufficient to form
interconnect layers having a high theoretical density (e.g.,
greater than about 90% theoretical density, or greater than about
95% theoretical density), to thereby form first layer 26 and second
layer 28, respectively.
[0040] Alternatively, interconnect 24 is prepared by sequentially
forming first layer 26 and then second layer 28 (or forming second
layer 28 and then first layer 26). Typically, each of the first and
second slurries can be sintered at a temperature in a range of
1,300.degree. C. and about 1,500.degree. C. For example, the first
slurry of La.sub.0.4Sr.sub.0.6Ti.sub.0.4Mn.sub.0.6Ob is sintered at
about 1300.degree. C. in air, and the second slurry of
Sr.sub.0.86Y.sub.0.08TiO.sub.d or
Sr.sub.0.995Ti.sub.0.99Nb.sub.0.01O.sub.d is sintered at about
1400.degree. C. in air.
[0041] In the invention, sub-cells 12 are connected via
interconnect 24. In one embodiment, at least one of the electrodes
of each sub-cell 12 is formed independently from interconnect 24.
Formation of electrodes 14 and 16 of each sub-cell 12 can be done
using any suitable method known in the art, as described above. In
one specific embodiment: i) a second-layer material of interconnect
24 is disposed over second electrode 16 of a first sub-cell; ii) a
first-layer material of interconnect 24 is disposed over the
second-layer material, and iii) first electrode 14 of a second
sub-cell is then disposed over the first-layer material of
interconnect 24. In another specific embodiment: i) a first-layer
material of interconnect 24 is disposed over first electrode 14 of
a second sub-cell; ii) a second-layer material of interconnect 24
is disposed over the first-layer material of interconnect 24; and
iii) second electrode 16 of a first sub-cell is disposed over the
second-layer material. In these specific embodiments, sintering the
first-layer and second-layer materials forms first layer 26 and
second layer 28 of interconnect 24, respectively.
[0042] Alternatively, one or more electrodes of sub-cells 12 (e.g.,
electrode 14 or 16, or electrodes 14 and 16) are formed together
with formation of interconnect 24. In one specific embodiment, i) a
second-layer material of interconnect 24 is disposed over a
second-electrode material of a first sub-cell; ii) a first-layer
material of interconnect 24 is then disposed over the second-layer
material; iii) a first-electrode material of a second sub-cell is
disposed over the first-layer of interconnect 24; and iv) heating
the materials such that the first-layer and second-layer materials
of interconnect 24 form first layer 26 and second layer 28 of
interconnect 24, respectively, and that the first-electrode and
second-electrode materials form first electrode 14 and second
electrode 16, respectively.
[0043] In another specific embodiment: i) a second-layer material
of interconnect 24 is disposed over second electrode 16 of a first
sub-cell; ii) a first-layer material of interconnect 24 is disposed
over the second-layer material; iii) disposing a first-electrode
material of a second sub-cell over the first-layer of interconnect
24, and iv) heating the materials such that the first-layer and
second-layer materials of the interconnect form first layer 26 and
second layer 28 of interconnect 24, respectively, and that the
first-electrode material forms first electrode 14.
[0044] The fuel cells of the invention, such as SOFCs, can be
portable. Also, the fuel cells of the invention, such as SOFCs, can
be employed as a source of electricity in homes, for example, to
generate hot water.
EXEMPLIFICATION
Example
Bi-layer Interconnect of
La.sub.0.4Sr.sub.0.6Ti.sub.0.4Mn.sub.0.6O.sub.3-.delta. ("LSTM")
and Sr.sub.0.86Y.sub.0.08TiO.sub.3-.delta. ("YST")
[0045] A small amount of (La,Mn)Sr-titanate,
La.sub.0.4Sr.sub.0.6Ti.sub.0.4Mn.sub.0.6O.sub.3-.delta. (LSTM),
powder (2.0 grams) was added on the top of (Nb,Y)Sr-titanate,
Sr.sub.0.86Y.sub.0.08TiO.sub.3-.delta. (YST), powder (1.0 gram).
The LSTM/YST powders were die-pressed together using a steel die
with a diameter of 1.125 inches at a load of 10,000 lbs. The
La.sub.0.4Sr.sub.0.6Ti.sub.0.4Mn.sub.0.6O.sub.3-.delta. powder was
binderized before die-pressing with 0.5 wt % polyethylene glycol
(PEG-400) and 0.7 wt % polyvinyl alcohol (PVA 21205) in order to
increase the strength of the green body for handling. The
die-pressed LSTM/YST powders with a bi-layer structure were then
co-sintered pressurelessly at 1350.degree. C. for one hour in air.
The LSTM/YST bi-layer structure was cross sectioned, mounted in an
epoxy, and polished for SEM (scanning electron microscope)
examination. FIG. 4 shows an SEM result of the fabricated LSTM/YST
bi-layer structure. As shown in FIG. 4, both LSTM and YST materials
were bonded very well to each other, and had a very high density.
The total thickness of the LSTM-YST bi-layer structure was about
1.20 mm; the thickness of LSTM layer was about 0.72 mm, and the
thickness of YST layer was about 0.48 mm. The relative densities of
the LSTM layer and the YST layer were about 98% and about 94%,
respectively.
EQUIVALENT
[0046] While this invention has been particularly shown and
described with references to example embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
* * * * *