U.S. patent application number 09/736558 was filed with the patent office on 2002-11-07 for electrolyte creepage barrier for liquid electrolyte fuel cells.
Invention is credited to Farooque, Mohammad, Li, Jian, Yu, Chao-Yi.
Application Number | 20020164519 09/736558 |
Document ID | / |
Family ID | 24960345 |
Filed Date | 2002-11-07 |
United States Patent
Application |
20020164519 |
Kind Code |
A1 |
Li, Jian ; et al. |
November 7, 2002 |
Electrolyte creepage barrier for liquid electrolyte fuel cells
Abstract
A dielectric member for electrically insulating a manifold or
other component from a liquid electrolyte fuel cell stack wherein
the dielectric member is adapted to include a barrier which
chemically reacts with the liquid electrolyte to form solid
products which are stable in the liquid electrolyte.
Inventors: |
Li, Jian; (New Milford,
CT) ; Farooque, Mohammad; (Huntington, CT) ;
Yu, Chao-Yi; (New Milford, CT) |
Correspondence
Address: |
ROBIN BLECKER & DALEY
2ND FLOOR
330 MADISON AVENUE
NEW YORK
NY
10017
US
|
Family ID: |
24960345 |
Appl. No.: |
09/736558 |
Filed: |
December 13, 2000 |
Current U.S.
Class: |
429/458 ;
429/463; 429/464; 429/478; 429/516 |
Current CPC
Class: |
Y02E 60/50 20130101;
H01M 8/0282 20130101; H01M 8/145 20130101; H01M 8/2459 20160201;
H01M 8/242 20130101; H01M 8/2485 20130101; H01M 8/0273 20130101;
H01M 2008/147 20130101; H01M 8/2484 20160201 |
Class at
Publication: |
429/35 ;
429/38 |
International
Class: |
H01M 008/02 |
Claims
What is claimed is:
1. A dielectric member for use in electronically insulating a
manifold or other component from a liquid electrolyte fuel cell,
said dielectric member including a barrier which chemically reacts
with the liquid electrolyte to form solid products which are stable
in the electrolyte.
2. A dielectric member in accordance with claim 1, wherein said
barrier comprises one of CaAl.sub.2O.sub.4 powder,
MgAl.sub.2O.sub.3 powder, Al.sub.2O.sub.3 powder and calcium
aluminate cement.
3. A dielectric member in accordance with claim 1, wherein said
barrier is formed as a surface layer on a surface of the dielectric
member.
4. A dielectric member in accordance with claim 3, wherein said
surface of said dielectric member faces said manifold.
5. A dielectric member in accordance with claim 1, wherein said
barrier member is embedded in the sides of said dielectric
member.
6. A dielectric member in accordance with claim 1, wherein said
dielectric member has the shape of a frame.
7. A dielectric member in accordance with claim 6, wherein said
frame includes a plurality of segments joined at a joint and said
barrier is situated in the area of said joint.
8. A dielectric member in accordance with claim 7, wherein said
joint includes a keyway area for receiving a key for joining said
segments.
9. A liquid electrolyte fuel cell system comprising: a liquid
electrolyte fuel cell stack; a manifold member abutting a surface
of said liquid electrolyte fuel cell stack; a dielectric member
situated between said manifold member and said surface of said
liquid electrolyte fuel cell stack, said dielectric member
including a barrier which chemically reacts with the liquid
electrolyte to form solid products which are stable in the liquid
electrolyte.
10. A liquid electrolyte fuel cell system in accordance with claim
9, wherein: said liquid electrolyte is carbonate.
11. A liquid electrolyte fuel cell system in accordance with claim
9, wherein: said barrier members comprise one of CaAl.sub.2O.sub.4
powder, MgAl.sub.2O.sub.3 powder, Al.sub.2O.sub.3 powder and
calcium aluminate cement.
12. A liquid electrolyte fuel cell system in accordance with claim
9, wherein: the barrier is formed as a surface layer on a surface
of the dielectric member.
13. A liquid electrolyte fuel cell system in accordance with claim
12, wherein: said surface of said dielectric member faces said
manifold.
15. A liquid electrolyte fuel cell system in accordance with claim
9, wherein: said barrier member is embedded in the sides of said
dielectric member.
16. A liquid electrolyte fuel cell system in accordance with claim
9 further comprising: a gasket situated between said dielectric
member and said surface of said fuel cell stack.
17. A liquid electrolyte fuel cell system in accordance with claim
9 wherein: said dielectric member has the shape of a frame.
18. A liquid electrolyte fuel cell system in accordance with claim
17, wherein: said frame includes a plurality of segments joined at
a joint and said barrier is situated in the area of said joint
19. A liquid electrolyte fuel cell system in accordance with claim
18, wherein: said joint includes a keyway area for receiving a key
for joining said segments.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to dielectric members and, in
particular, to dielectric members for electrically isolating
manifolds and other components, from a liquid electrolyte fuel cell
stack.
[0002] In a carbonate (liquid electrolyte) fuel cell stack with
external manifolds for gas supply and discharge, the manifolds are
electrically isolated from the fuel cell stack by a dielectric
member in the form of a picture frame. The dielectric frame must be
capable of operating at a voltage difference of between 100 and
1000 volts depending on the number of cells in a stack and the
electrical configuration of the stacks when arranged in a power
plant. A dielectric frame formed of Al.sub.2O.sub.3 has been found
capable of providing electrical isolation to thousands of
volts.
[0003] However, at the fuel cell operating temperature of
650.degree. C., the liquid electrolyte in the fuel cell stack tends
to creep over the surface of the dielectric frame. The frame and
the stack are only separated by a thin porous gasket for gas
sealing. The porous gasket becomes filled with electrolyte and as
the dielectric frame comes in contact with the liquid electrolyte,
the frame becomes wetted.
[0004] Once this occurs, a thin continuous layer of conductive
liquid electrolyte film forms on the surface of the dielectric.
Consequently, the electrical isolation provided by the dielectric
frame can be compromised and can lead to stack malfunction. As a
result, designers of these frames have looked to develop techniques
to prevent or reduce the electrolyte creepage. The aim of these
designers is to realize a dielectric frame able to provide stable
long-term dielectric insulation of the liquid electrolyte fuel cell
stack from the metallic manifold.
[0005] It is, therefore, an object of the present invention to
provide a dielectric member which overcomes the above
disadvantages.
[0006] It is a further object of the present invention to provide a
dielectric member which exhibits increased resistance to dielectric
creepage.
SUMMARY OF THE INVENTION
[0007] In accordance with the principles of the present invention,
the above and other objects are realized in a dielectric member for
electrically insulating a manifold or other component from a liquid
electrolyte fuel cell stack wherein the dielectric member is
adapted to include a barrier which chemically reacts with the
liquid electrolyte to form solid products which are stable in the
liquid electrolyte. In this way, the barrier inhibits flow or
creepage of electrolyte from reaching the metallic manifolds.
BRIEF DESCRIPTION OF THE DRAWING
[0008] The above and other features and aspects of the present
invention will become more apparent upon reading the following
detailed description in conjunction with the accompanying drawings,
in which:
[0009] FIG. 1 shows a fuel cell stack incorporating a dielectric
member having a barrier in accordance with the principles of the
present invention;
[0010] FIG. 2 illustrates schematically one form of the dielectric
member of FIG. 1;
[0011] FIG. 3 shows a test configuration for testing a dielectric
member having a barrier in accordance with the principles of the
present invention;
[0012] FIG. 4 shows test results for a dielectric member of FIG.
3;
[0013] FIGS. 5 and 6 show further configurations for the dielectric
member of FIG. 1; and
[0014] FIGS. 7 and 8 illustrate application of the invention to a
dielectric frame.
DESCRIPTION OF THE INVENTION
[0015] FIG. 1 shows a fuel cell stack 1 in which a metallic
manifold 2 abuts a face 1A of the stack. The manifold 2 can either
serve to input gas or to extract gas from the stack 1.
[0016] Situated between the stack 1 and the manifold 2 are a gasket
3 and a dielectric member 4. The gasket 3 contacts the face 1A of
the stack, while the dielectric member is situated between the
gasket 3 and manifold 2. The dielectric member 4, typically, may
have the form of a picture frame.
[0017] The dielectric member electrically isolates the metallic
manifold 2 from the stack 1. As shown in FIG. 2, the dielectric
member 4 includes a barrier 5 which is situated in the path of the
liquid electrolyte flowing from the stack 1 through the gasket 3.
In accordance with the invention, the barrier 5 is adapted to
chemically react with the liquid electrolyte (e.g., carbonate
electrolyte) of the stack 1 to produce solid products which are
stable in the electrolyte. As can be appreciated, the production of
these products inhibits flow of the electrolyte along the surface
of the dielectric member. As a result, electrolyte creepage is
reduced and the insulating characteristics of the dielectric member
are preserved.
[0018] The material used for the barrier 5 can take on a variety of
forms. One material found usable is calcium aluminate cement
(Secar, available from LaFarge Corp.) At 650.degree. C., Secar
quickly reacts with Li.sub.2CO.sub.3 to form solid products
consisting of LiAlO.sub.2, CaO and K.sub.2CO.sub.3. These products
are chemically stable in the liquid electrolyte (molten carbonate)
environment. Another material is .gamma.-Al.sub.2O.sub.3. Further
common materials, such as MgAl.sub.2O.sub.4 powder and
CaAl.sub.2O.sub.4 powder, can also be used.
[0019] The effectiveness of the above-mentioned materials as
barriers depends not only on the chemical nature of the materials,
but also on the amount of the material used. As long as there is
sufficient reactive material, the electrolyte from the stack 1 will
not creep over the entire surface of the dielectric member 4 so as
to be able to reach the manifold 2.
EXAMPLE 1
[0020] A dielectric member using a barrier 5 comprised of Secar
(mechanical mixtures of A1.sub.2O.sub.3 and CaO) was fabricated.
The dielectric member comprised a grooved Al.sub.2O.sub.3
rectangular bar in a dimension of 4".times.1".times.0.625" with Ra
29 surface finishing (Ra: the average deviation of the profile from
the mean line, in .mu.in). The Secar was embedded in grooves on
both sides of the bar, as shown in FIG. 3.
[0021] The effect of Secar as a reactive barrier was then evaluated
in an accelerated electrolyte pool test. In the test, the bottom of
the dielectric member was submerged in a liquid electrolyte pool
(infinite electrolyte supply), and a piece of gasket, serving as
electrolyte absorbent, was laid on the top surface to collect the
creeping electrolyte. The results from this test are shown in FIG.
4, and demonstrate that the production of reaction products caused
significant delay in electrolyte creepage.
EXAMPLE 2
[0022] A dielectric member 4 as shown in FIG. 3 was formed in this
case with the barrier comprised of .gamma.-Al.sub.2O.sub.3 powder.
This member was similarly tested as described in Example 1 and the
results are also shown in FIG. 4. These results similarly indicate
that the barrier caused significant reduction in electrolyte
creepage.
EXAMPLE 3
[0023] In a liquid carbonate fuel cell stack, a dielectric frame as
described in the U.S. Pat. No. 4,414,294 may be employed. This
dielectric frame, as shown in FIGS. 7 and 8, includes straight
segments 71 which are connected at joints. The joint area, shown as
forming a keyway 72 in FIGS. 7 and 8, has the highest liquid
electrolyte creepage due to increased creepage surfaces in the
joint and possible capillaries formed between the straight bars and
the connecting key 73 inserted in the keyway 72. A barrier 5 made
of Secar cement, with a dimension 1.50".times.0.625".times.0.031",
was placed at the top of the joint area on the surface facing the
manifold in a 250 kW molten carbonate fuel stack(340) cells. In
approximately 12,000 hours of operation, the barrier partially
reacted with the liquid electrolyte, and no electrolyte crossed the
barrier and reached the manifold. This example confirmed the
effectiveness of the use of a dielectric member provided with a
chemically reactive barrier in actual fuel cell operation.
[0024] FIGS. 5 and 6 illustrate different configurations for the
dielectric member 4 and the barrier 5. In the dielectric member 4
of FIG. 5, the barrier 5 comprises barrier inserts 5A and 5B which
are embedded in the sides of the dielectric member. In the
dielectric member 4 of FIG. 6, the barrier 5 comprises a layer
situated on the surface of the member 4 facing the manifold 2.
[0025] The barriers 5 of the dielectric member 4 of the invention
can be fabricated by various processes. Thus, the barriers 5 can be
formed with high temperature ceramic binders using a painting or a
casting process. They can also be formed by the standard tape
casting technique. In both dielectric members 5 of FIGS. 5 and 6,
the presence of the barrier 5 results in reducing electrolyte flow
and, thereby prolonging dielectric life.
[0026] In all cases it is understood that the above-described
arrangements are merely illustrative of the many possible specific
embodiments which represent applications of the present invention.
Numerous and varied other arrangements can be readily devised in
accordance with the principles of the present invention without
departing from the spirit and scope of the invention.
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