U.S. patent application number 10/762477 was filed with the patent office on 2007-11-22 for interconnect device, fuel cell and fuel cell stack.
Invention is credited to Jens Ulrik Nielsen, Christian Olsen, Harald Usterud.
Application Number | 20070269704 10/762477 |
Document ID | / |
Family ID | 32668645 |
Filed Date | 2007-11-22 |
United States Patent
Application |
20070269704 |
Kind Code |
A1 |
Olsen; Christian ; et
al. |
November 22, 2007 |
INTERCONNECT DEVICE, FUEL CELL AND FUEL CELL STACK
Abstract
The invention provides an interconnect device for a fuel cell
comprising an electrolyte, an anode and a cathode, the interconnect
device comprising a channel system having a plurality of channels,
each channel being closed in one end and having either an inlet
side or an outlet side at the open end of the channel, each channel
having an inlet side placed in alternating order with a channel
having an outlet side, the inlet side of each channel placed in
consecutive order on one side of the interconnect, and the outlet
sides of each channel placed in consecutive order on the opposide
side of the interconnect relative to the inlet side, and a second
layer of channels is located on the surface of the channel system.
The invention also provides a fuel cell and a fuel cell stack in
which the interconnect device is used.
Inventors: |
Olsen; Christian; (Ballerup,
DK) ; Usterud; Harald; (Horsholm, DK) ;
Nielsen; Jens Ulrik; (Soborg, DK) |
Correspondence
Address: |
DICKSTEIN SHAPIRO LLP
1825 EYE STREET NW
Washington
DC
20006-5403
US
|
Family ID: |
32668645 |
Appl. No.: |
10/762477 |
Filed: |
January 23, 2004 |
Current U.S.
Class: |
429/456 ;
429/478; 429/495 |
Current CPC
Class: |
H01M 2008/1293 20130101;
B01J 2219/00783 20130101; Y02E 60/566 20130101; H01M 8/12 20130101;
C01B 3/38 20130101; B01J 2219/00873 20130101; C01B 2203/0233
20130101; B01J 2219/00853 20130101; H01M 8/2484 20160201; H01M
8/244 20130101; C01B 2203/066 20130101; H01M 8/2483 20160201; B01J
2219/00869 20130101; H01M 8/0258 20130101; H01M 8/2457 20160201;
H01M 8/14 20130101; B01J 2219/00891 20130101; H01M 8/0254 20130101;
H01M 8/24 20130101; Y02E 60/50 20130101; H01M 8/0637 20130101 |
Class at
Publication: |
429/038 |
International
Class: |
H01M 2/14 20060101
H01M002/14 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 15, 2003 |
DK |
PA 2003 00232 |
Claims
1. An interconnect device for a fuel cell comprising an
electrolyte, an anode and a cathode, the interconnect device
comprising a channel system having a first plurality of channels,
each channel being closed in one end and having either an inlet
side or an outlet side at the open end of the channel, each channel
having an inlet side placed in alternating order with a channel
having an outlet side, the inlet side of each channel being placed
in consecutive order on one side of the interconnect, and the
outlet side of each channel being placed in consecutive order on
the opposite side of the interconnect relative to the inlet side,
and a second plurality of channels located on the surface of the
first plurality of channels of the channel system so that the
second plurality of channels is in a plan which is about parallel
to the first plurality of channels.
2. The interconnect device according to claim 1, wherein the first
plurality of channels of the channel system has a plurality of
straight, parallel channels.
3. The interconnect device according to claim 1, wherein channels
of the second plurality of channels intersect the channels in the
first plurality of channels of the channel system, the second
plurality of channels being closed at both ends and the channels of
the first plurality of channels remaining open throughout their
length.
4. The interconnect device according to claim 1, wherein the
channels of the second plurality of channels are closed at their
surface and at both ends, and are placed parallel to and directly
above the channels of the first plurality of channels, the closed
surface being perforated in the area of the channels.
5. The interconnect device according to claim 4, wherein the
closed, perforated surface of the channel system comprises a
separate interlayer placed on the surface of the channel
system.
6. The interconnect device according to claim 1, wherein the second
plurality of channels intersects the channels of the first
plurality of channels, the second plurality of channels being
closed at both ends, the first plurality of channels being partly
closed.
7. The interconnect device according to claim 3, wherein the second
plurality of channels comprises a separate interlayer placed on the
surface of the channel system.
8. The interconnect device according to claim 1, wherein the
channels of the first plurality of the channel system are provided
with distribution and collection holes.
9. A fuel cell comprising an electrolyte, an anode, a cathode and
an interconnect device according to claim 1.
10. The fuel cell according to claim 9, wherein the fuel cell is a
solid oxide fuel cell.
11. The fuel cell according to claim 9, wherein the fuel cell is a
molten carbonate fuel cell.
12. A fuel cell stack comprising at least two fuel cells according
to claim 9.
Description
[0001] The invention concerns a high temperature fuel cell, in
particular a Solid Oxide Fuel Cell (SOFC) or a Molten Carbonate
Fuel Cell (MCFC), in which reforming of hydrocarbons takes place in
the anode chamber or within the anode itself. In particular it
concerns an interconnect device in a SOFC or MCFC fuel cell in
which the mechanical tension within the fuel cell is reduced.
BACKGROUND OF THE INVENTION
[0002] A SOFC comprises an oxygen-ion conducting electrolyte, a
cathode at which oxygen is reduced and an anode at which hydrogen
is oxidised. The overall reaction in a SOFC is that hydrogen and
oxygen electrochemically react to produce electricity, heat and
water.
[0003] The anode also comprises a high catalytic activity for the
steam reforming of hydrocarbons into hydrogen, carbon dioxide and
carbon monoxide. Steam reforming can be described by the reaction
of a fuel such as natural gas with steam and the reactions which
take place can be represented by the following equations:
CH.sub.4+H.sub.20.fwdarw.CO+3H.sub.2
CH.sub.4+CO.sub.2.fwdarw.2CO+2H.sub.2
CO+H.sub.20.fwdarw.CO.sub.2+H.sub.2
[0004] The fuel gas supplied to the fuel cell contains in most
cases steam, thus enabling the steam reforming process to occur
according to the above equations at the anode surface. The hydrogen
produced then reacts in above electro-chemical reaction. The steam
reforming reaction is, however, very endothermic and a large heat
input is therefore required.
[0005] A typical temperature distribution in a fuel cell stack with
a hydrocarbon feedstock therefore shows a dramatic temperature drop
near the inlet of the fuel cell due to the fast endothermic
reforming reaction resulting in severe temperature gradients within
the cell.
[0006] The SOFC is a ceramic composite of three different
materials. Ceramic SOFCs have low mechanical strength and in
particular low tensile strength. The tensile strength within a SOFC
is closely connected to temperature gradients and it is therefore
highly important to minimise the temperature gradients and thereby
the tensile strength of the SOFC. When the tensile strength in the
fuel cell exceeds a given threshold value the cell will crack and
the fuel cell will malfunction.
[0007] It is to some extent possible to control the tensile
strength to an acceptable level by using a hydrogen feed-stock, but
in the future it is foreseen that natural gas and other hydrocarbon
feedstock will become dominant. This will increase the problem
dramatically as the endothermic reforming of hydrocarbons will
reduce the temperature of the fuel cell in the fuel-inlet area
significantly, thereby increasing the temperature gradients and the
tensile strength in the fuel cell to an unacceptable level.
[0008] Several methods of reducing the temperature gradients are
known. Most of these methods involve changes in operation
parameters of the fuel cell system such as enhanced airflow to the
cathode. Such changes are often connected to increased operation
cost of the fuel cell system.
SUMMARY OF THE INVENTION
[0009] The objective of the invention is to reduce the thermal
gradients and the tensile strength of the fuel cell by using an
interconnect device which divides the fuel into a number of micro
fuel cells. This is achieved by distributing the fuel gas supply to
the fuel cell over the cell's entire surface. In this way many
small electrochemical cells are created on one fuel cell. Due to
the shorter distance between the heat requiring reforming reaction
and the heat producing electrochemical reaction, the tensile
strength of the cell is reduced considerably.
[0010] According to the invention there is therefore provided an
interconnect device for a fuel cell comprising an electrolyte, an
anode and a cathode, the interconnect device comprising a channel
system having a plurality of channels each channel being closed in
one end and having either an inlet side or an outlet side at the
open end of the channel each channel having an inlet side placed in
alternating order with a channel having an outlet side, the inlet
side of each channel placed in consecutive order on one side of the
interconnect, and the outlet sides of each channel placed in
consecutive order on the opposide side of the interconnect relative
to the inlet side, and a second layer of channels is locatedon the
surface of the channel system.
[0011] The invention also provides a fuel cell comprising an
electrolyte, an anode, a cathode and an interconnect device.
[0012] Furthermore, the invention provides a fuel cell stack
comprising at least two fuel cells.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIGS. 1 and 1a show an interconnect device with open gas
supply and collection channels.
[0014] FIGS. 2 and 2a show an interconnect device with open gas
supply and collection channels with surface channels at right
angles.
[0015] FIGS. 3 and 3a show an interconnect device with closed gas
supply and collection channels and perforations in the interconnect
surface.
[0016] FIGS. 4 and 4a show an interconnect device with partly
closed gas supply and collection channels with surface channels at
right angles.
[0017] FIG. 5 shows a top view of an interconnect device.
[0018] FIG. 6 shows a section of an assembled fuel cell stack.
DETAILED DESCRIPTION OF THE INVENTION
[0019] A reduction of the thermal gradients within the fuel cell is
accomplished by ensuring a fuel gas distribution to the entire cell
surface, thereby enabling the endothermic reforming reaction and
the exothermic electrochemical reaction to take place uniformly
over the cell surface. The pressure gradients ensure a uniform gas
flow over the majority of the cell area.
[0020] The interconnect device of the invention is primarily for
high temperature application at the fuel gas side, i.e. the anode
side, of the fuel cell. The oxygen side of the interconnect, i.e.
the cathode side, can have any geometry suitable for the transport
of the oxygen. This can for instance be straight, parallel channels
or any other type known in the art.
[0021] The exact path of the fuel flow can vary and several fuel
paths are given. Different embodiments of the interconnect of the
invention are described below, each embodiment depicting a
different construction of the interconnect and thus a different
fuel flow path.
[0022] The table below gives an overview of the numbering of the
different parts of the interconnect shown in the figures:
TABLE-US-00001 Number Interconnect Section 1 supply hole 2 supply
channel 3 interconnect surface 4 collection channel 5 exit hole 6
second layer of channels 7 distributing hole 8 collecting hole
[0023] FIG. 1 shows a simple interconnect geometry, where the fuel
flows from supply holes 1 and through the porous anode placed on
the surface of the interconnect 3 on its way from the supply
channel 2 to the collection channel 4. This embodiment has a
channel system with an open gas supply and collection channels. By
open channel is meant that the upper surface of the channel is not
covered or closed throughout its length. By closed channel is meant
that the upper surface of the channel is covered throughout its
length.
[0024] The fuel gas path across the anode side is explained in more
detail as follows:
[0025] Fuel enters the interconnect from one or more fuel supply
holes 1. Fuel is distributed across the anode by supply channels 2
in the interconnect. The fuel is exposed to the anode material. If
the fuel is a hydrocarbon, it reforms with steam in an endothermic
reaction upon contact with the anode material. The fuel is then
spent electrochemically in an exothermic reaction to produce
electricity. These two reactions occur close to each other, and
will benefit from each other as the reforming reaction can draw on
the heat produced by the electrochemical reaction. The spent fuel
exhaust is collected by channels 4 in the interconnect and led to
exit holes 5 at the cell perimeter.
[0026] FIG. 1a shows a side view of the path followed by the fuel
gas through the interconnect and the anode. The anode is placed on
the surface of the interconnect 3 and the gas transport occurs from
the supply channel 2 through the anode to the collection channel
4.
[0027] In the embodiment shown in FIG. 1 the supply and collection
channels are straight, parallel channels. The channels are not
limited to being straight and parallel, but can have another
geometry for instance diagonally placed.
[0028] In a second embodiment the flow of the fuel is not limited
to occur entirely through the porous anode material. It can also
flow partly through gaps created between the anode surface and the
interconnect surface. This reduces the pressure drop. Such gaps are
obtained by making a second layer of channels 6 in the interconnect
surface 3, which are at an angle to the supply and collection
channels 2 and 4, i.e. they intersect the channels of the channel
system, and located on the surface of the channel system shown in
FIG. 1. This is shown in FIG. 2, where the interconnect has open
supply and collection channels with surface channels 6 created
perpendicular to the supply and collection channels. Other angles
can be chosen such that the second layer of surface channels 6 are
not at right angles to the supply and collection channels 2 and 4.
The second layer of surface channels 6, which are closed at both
ends, can for instance be diagonally placed relative to the supply
and collection channels 2 and 4.
[0029] FIG. 2a shows a side view of the path followed by the fuel
gas. Gas transport occurs from the supply channels through the
second layer of channels 6 to the collection channels. During its
journey the gas contacts the anode placed on the interconnect
surface 3 and is steam reformed.
[0030] In a third embodiment the supply channels are closed and the
closed interconnect surface 3 is perforated in the area of the
channels. In this embodiment the closed, perforated surface 3
corresponds to the second layer of channels being closed at their
surface and at both ends, and perforated in the area of the
channels. The channels of the second layer are placed parallel to
and directly above those of the channel system. This ensures that
fuel passing through a perforation will be reformed only in the
vicinity of the perforation. FIG. 3 shows an interconnect with
closed gas supply and collection channels, where the fuel flows
through perforations made in the interconnect surface 3 above the
supply channels and into the porous anode material. The reformed
gas leaves the anode and enters the collection channel through the
perforations placed above the collection channels 4.
[0031] FIG. 3a shows the presence of small fuel distribution holes
7 in the supply channel 2 and fuel exhaust collecting holes 8 in
the collection channel 4.
[0032] In a fourth embodiment the flow is partly through a second
layer of channels 6 in the interconnect surface 3 at an angle to
the supply and collection channels 2 and 4. This reduces the
pressure drop. This is shown in FIG. 4 where the second layer of
channels 6 are perpendicular to the supply and collection channels
2 and 4 of the channel system. The channels 2 and 4 are partly
closed. The second layer of channels 6 can also be at another angle
to channels 2 and 4, for instance diagonal. They are closed at both
ends.
[0033] FIG. 4a shows a side view of the path followed by the fuel
gas indicating the presence of fuel distributing holes 7 in the
supply channel 2 and exhaust collecting holes 8 in the collection
channel 4.
[0034] In the various embodiments, it can be practical to construct
the anode side of the interconnect from two or more interlayers
instead of a single layer. This can for instance be done by
constructing an interlayer provided with the channel system, and
placing a second interlayer provided with a second layer of
channels on the surface of the first interlayer.
[0035] FIG. 5 shows a top view of the anode side of an
interconnect. This view illustrates the embodiment described in
FIG. 4, where the interconnect has partly closed gas supply and
collection channels. It illustrates the formation of many small
electrochemical cells created on one fuel cell.
[0036] A fuel cell is placed on the upper surface of the
interconnect 3 with the anode side towards the interconnect. The
fuel cell should be sealed firmly along the edges of the
interconnect to prevent the overall fuel gas flow from following
any other path than the prescribed path.
[0037] The hydrocarbon containing fuel gas is supplied to the
interconnect through a number of supply holes 1 connected to a
closed fuel gas supply channel 2. A number of small fuel supply
distribution holes 7 in the supply channel 2 allow the fuel to flow
out from the supply channels 2, thus exposing it to the anode side
of the fuel cell lying on top of the interconnect. The fuel will
flow from the distribution holes 7 across the surface of the second
layer of channels 6 to the fuel exhaust collection holes 8, which
connect the gas to the closed fuel exhaust collection channels 4.
During its journey the gas contacts the anode and is steam
reformed. From the collection channels 4 the reformed fuel gas
exits the interconnect through the fuel exhaust exit holes 5. The
reformed fuel gas includes hydrogen, which reacts in an overall
electrochemical reaction with oxygen to produce electricity, heat
and water. The exhaust products exiting the anode side of the
interconnect are therefore primarily carbon dioxide and water. The
fuel gas flow is controlled by the pressure difference between the
fuel gas supply and the fuel gas exhaust.
[0038] The interconnect of the invention can have distribution
holes 7 and collecting holes 8 placed in the supply and collection
channels 2 and 4 when required. This ensures that a supply of fresh
fuel gas, before exposure to the anode, is distributed out all over
the surface of the fuel cell. By employing the interconnect in a
fuel cell, in cases where the fuel gas contains hydrocarbons, the
endothermic reforming reactions are distributed uniformly over the
surface of the fuel cell. The simultaneously occurring
electrochemical reaction is distributed uniformly over the surface
of the fuel cell allowing the waste heat from this reaction to be
used for the reforming reaction. The temperature differences
between the fuel supply distribution holes 7 and the fuel exhaust
collecting holes 8, which arise due to variations between the waste
heat production from the electrochemical reaction and heat
consumption from the reforming, are minimised due to the short
distances for the heat transport. The heat transport will mainly be
through heat conduction in the interconnect and in the fuel
cell.
[0039] As a result of the minimised temperature gradients it is
furthermore obtained that the mechanical stress in the fuel cell
due to temperature gradients are minimised, thereby decreasing the
probability for a mechanical failure of the fuel cell. The
gradients will be minimised for any type of fuel gas applied, but
the advantage will typically be highest in cases in which a
hydrocarbon feedstock is reformed in contact with the anode.
[0040] FIG. 6 illustrates a section of an assembled fuel cell stack
showing the position of the interconnect relative to the other
components of the fuel cell. Five layers are shown--the top layer
shows the interconnect placed on the cathode 10. The oxygen supply
channels 9 provide oxygen for reaction at the cathode, and they are
located on the cathode side of the interconnect. The geometry of
the oxygen supply channels 9 are chosen to facilitate the transfer
of the required amounts of oxygen to the cathode. They can for
instance be formed as straight, parallel channels. Other geometries
known in the art are applicable.
[0041] The cathode 10 is placed between the interconnect and the
electrolyte layer 11. This is followed by the anode layer 12, which
has its other surface in contact with the interconnect surface
3.
[0042] The two contact surfaces of the interconnect can be provided
for in different ways, for example by contacting two interlayers
with each other, one interlayer having an anode side with a fuel
gas supply system as described in the variuos embodiments of the
invention, the other interlayer having a cathode side with an
oxygen supply system that is conventionally applied in the art. The
two interlayers together provide the interconnect in this case.
[0043] The interconnect of the invention can be applied in fuel
cells utilising either internal or external manifolds.
* * * * *