U.S. patent application number 09/891690 was filed with the patent office on 2002-12-26 for corrugated current collector for direct internal reforming fuel cells.
Invention is credited to Blanchet, Scott, Doyon, Joel, Novacco, Lawrence.
Application Number | 20020197518 09/891690 |
Document ID | / |
Family ID | 25398653 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020197518 |
Kind Code |
A1 |
Blanchet, Scott ; et
al. |
December 26, 2002 |
CORRUGATED CURRENT COLLECTOR FOR DIRECT INTERNAL REFORMING FUEL
CELLS
Abstract
A fuel cell corrugated current collector having successive
spaced rows of corrugations, with the corrugations in a given row
establishing successive peak and valley regions along the given row
and the spaced rows of corrugations being adapted so that
corresponding peak regions from row-to-row establish through
passages for receiving and supporting solid catalyst elements. The
spaced rows of corrugations are such that there is a given pitch
between successive peak regions. The corrugations in the rows are
also such that corresponding peak regions from row-to-row have a
finite off-set which is less than 50 percent of the pitch. This
establishes a plurality of through passages in the current
collector each extending from row-to-row for receiving and
supporting the solid catalyst elements. Also, the off-set is based
on the catalyst dimensions and is set such that the corrugations
engage the catalyst elements.
Inventors: |
Blanchet, Scott; (Monroe,
CT) ; Doyon, Joel; (Bantam, CT) ; Novacco,
Lawrence; (Brookfield, CT) |
Correspondence
Address: |
ROBIN BLECKER & DALEY
2ND FLOOR
330 MADISON AVENUE
NEW YORK
NY
10017
US
|
Family ID: |
25398653 |
Appl. No.: |
09/891690 |
Filed: |
June 26, 2001 |
Current U.S.
Class: |
429/456 ;
428/595 |
Current CPC
Class: |
H01M 8/0258 20130101;
H01M 4/92 20130101; H01M 2008/1293 20130101; H01M 8/026 20130101;
Y10T 428/12354 20150115; H01M 8/0254 20130101; H01M 8/241 20130101;
H01M 8/0625 20130101; Y02E 60/50 20130101 |
Class at
Publication: |
429/20 ; 429/34;
428/595 |
International
Class: |
H01M 008/06; H01M
008/02; H01M 008/24; B21C 037/02 |
Claims
What is claimed is:
1. A corrugated current collector having successive spaced rows of
corrugations, with the corrugations in a given row establishing
successive peak and valley regions along the given row and the
spaced rows of corrugations being adapted so that corresponding
peak regions from row-to-row establish through passages for
receiving and supporting solid catalyst elements.
2. A corrugated current collector in accordance with claim 1,
wherein the peak regions in each row of corrugations are spaced by
a pitch Pt and the corresponding peak regions from row-to-row of
the rows of corrugations are offset by an amount O.
3. A corrugated current collector in accordance with claim 2,
wherein the pitch Pt is the same from row-to-row and the offset O
is the same from row to row.
4. A corrugated current collector in accordance with claim 3,
wherein the offset direction alternates from right to left from
row-to-row.
5. A corrugated current collector in accordance with claim 3,
wherein the offset is finite and less than 50 percent of the pitch
Pt.
6. A corrugated current collector in accordance with claim 5,
further comprising a solid catalyst element disposed in each of
said through passages.
7. A corrugated current collector in accordance with claim 6,
wherein the peak regions establishing each through passage engage
the catalyst element received in that through passage.
8. A corrugated current collector in accordance with claim 6,
wherein the corrugated current collector is formed from a punched
plate, whereby the punched areas of the plate form the valley
regions and the areas between the punched areas form the peak
regions of the rows of corrugations.
9. A corrugated current collector in accordance with claim 2,
wherein the offset O is finite and less than 50 percent of the
pitch Pt.
10. A corrugated current collector having successively spaced rows
of corrugations, with the corrugations in a given row establishing
successive peak and valley regions such that the peak. regions in
each row are spaced by the same pitch Pt and the corresponding peak
regions from row-to-row are offset by the same amount O, and said
offset O is finite and less than 50 percent of the pitch so that
corresponding peak regions from row-to-row establish through
passages for receiving and supporting solid catalyst elements.
11. A fuel cell comprising: an anode section including a separator
plate and a corrugated current collector situated adjacent the
separator plate, said corrugated current collector having
successive spaced rows of corrugations, with the corrugations in a
given row establishing successive peak and valley regions along the
given row and the spaced rows of corrugations being adapted so that
corresponding peak regions from row-to-row establish through
passages for receiving and supporting solid catalyst elements.
12. A fuel cell in accordance with claim 11, wherein peak regions
in each row of corrugations are spaced by the same pitch Pt and the
corresponding peak regions form row-to-row of the rows of
corrugations are offset by the same amount 0, and the offset O is
finite and less than 50 percent of the pitch.
13. A fuel cell in accordance with claim 12, further comprising a
solid catalyst element disposed in each of said through
passages.
14. A fuel cell in accordance with claim 13, wherein the corrugated
current collector is formed from a punched plate, whereby the
punched areas of the plate form the valley regions and the areas
between the punched areas form the peak regions of the rows of
corrugations.
15. A fuel cell in accordance with claim 11 further comprising: a
cathode section; and an electrolyte member situated between said
anode and cathode sections.
16. A fuel cell system comprising: a first fuel cell including an
anode section having a separator plate and a corrugated anode
current collector situated adjacent to a first face of the
separator plate, said corrugated anode current collector having
successive spaced rows of corrugations, with the corrugations in a
given row establishing successive peak and valley regions along the
given row and the spaced rows of corrugations being adapted so that
corresponding peak regions from row-to-row establish through
passages for receiving and supporting solid catalyst elements; and
a second fuel cell including a cathode section having a corrugated
cathode current collector adjacent a second face of the separator
plate, said corrugated cathode current collector having successive
spaced rows of corrugations situated transverse to the spaced rows
of corrugations of the corrugated anode current collector, with the
corrugations in a given row establishing successive peak and valley
regions along the given row and the spaced rows of corrugations
being adapted so that corresponding peak regions from row-to-row
establish through passages.
17. A fuel cell system in accordance with claim 16, wherein peak
regions in each row of corrugations of the corrugated anode and
cathode current collectors are spaced by the same pitch Pt and the
corresponding peak regions from row-to-row of the rows of
corrugations of the corrugated anode and cathode current collectors
are offset by the same amount O, and the offset O is finite and
less than 50 percent of the pitch Pt.
18. A fuel cell system in accordance with claim 17, further
comprising a solid catalyst element disposed in each of said
through passages.
19. A fuel cell system in accordance with claim 16 wherein: said
first fuel cell further includes a cathode section and an
electrolyte member situated between the anode section and the
cathode section of that first fuel cell; and said second fuel cell
further includes an anode section and an electrolyte member
situated between the cathode section and the anode section of that
second fuel cell.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to current collector electrode
supports for fuel cells. More specifically, this invention relates
to corrugated current collectors for high temperature, internally
reforming, planar fuel cells.
[0002] A fuel cell is a device which directly converts chemical
energy stored in a fuel such as hydrogen or methane into electrical
energy by means of an electrochemical reaction. This differs from
traditional electric power generating methods which must first
combust the fuel to produce heat and then convert the heat into
mechanical energy and finally into electricity. The more direct
conversion process employed by a fuel cell has significant
advantages over traditional means in both increased efficiency and
reduced pollutant emissions.
[0003] In general, a fuel cell, similar to a battery, comprises a
negative (anode) electrode and a positive (cathode) electrode
separated by an electrolyte which serves to conduct electrically
charged ions between them. In contrast to a battery, however, a
fuel cell will continue to produce electric power as long as fuel
and oxidant are supplied to the anode and cathode, respectively. To
achieve this, gas flow fields are provided adjacent to the anode
and cathode through which fuel and oxidant are supplied. In order
to produce a useful power level, a number of individual fuel cells
must be stacked in series with an electrically conductive separator
plate between each cell.
[0004] In internally reforming fuel cells, a steam reforming
catalyst is placed within the stack of fuel cells to allow direct
use of hydrocarbon fuels (e.g., methane, coal gas, etc.) in the
fuel cells without the need for expensive and complex external
reforming equipment. Two forms of internal reforming have been
used. Indirect internal reforming is accomplished by placing
reforming catalyst in an isolated chamber within the stack and
routing the reformed gas from this chamber into the anode
compartment of each fuel cell. Direct internal reforming is
accomplished by placing reforming catalyst within the active anode
compartment of each fuel cell. This catalyst is then available to
reform fuel gas with steam formed by the electrochemical reactions
of the fuel cell and can result in very high reforming efficiency
and fuel utilization.
[0005] The particular geometry used for the anode chamber and
catalyst support is important for many reasons. The geometry should
be selected to minimize pressure drop for fuel flow as higher
pressure requires more auxiliary power and results in lower system
efficiency. In addition, for stacks with many cells, low variation
in flow restriction from cell to cell is critical to insure that
each cell receives the same fuel flow and thereby operates at the
same fuel utilization. As the efficiency of the fuel cell stack is
limited by the individual cell which receives the least amount of
fuel, uniform fuel flow is very important to achieve maximum fuel
utilization and stack electrical efficiency.
[0006] A major feature of a fuel cell which also relates to direct
internal reforming catalyst is the useful life of the cell. As the
cell ages, the activity of the reforming catalyst in the anode
chamber decays due to the poisoning effects of the electrolyte
vapor within the passage. This decay in activity reduces the
effectiveness of the catalyst and the reforming efficiency of the
cell. This, in turn, reduces the electrical efficiency of the cell
because less reformed fuel is available for the electrochemical
reactions. As the effectiveness of the catalyst is directly related
to the mass of catalyst available for reforming, one way to
increase the reforming efficiency and cell life is to increase the
catalyst mass in the anode chamber.
[0007] Another important characteristic of the components used to
form the fuel and oxidant flow fields of a fuel cell is the ability
of the components to apply uniform pressure to the active cell
components (i.e., anode, cathode and matrix). Uniform pressure is
important to insure uniform contact resistance over the cell active
area as well as to reduce the likelihood of gaps forming between
cell components during operation.
[0008] The direct internal reforming catalyst must also be
protected from deactivation by electrolyte wicking from the
abutting anode containing liquid electrolyte. One method to protect
the catalyst is to design the corrugated current collector so that
it shields the catalyst, acting as a barrier to electrolyte
migration from the adjacent anode component.
[0009] Many different component geometries have been proposed and
used by fuel cell manufacturers for providing the fuel and oxidant
flow fields and catalyst support for direct internally reforming
fuel cells. U.S. Pat. No. 4,548,876 describes a corrugated current
collector used for this purpose. In the current collector of the
'876 patent, particulate material is placed in the current
collector corrugations and is used for diffusion and support. The
particulate material faces a catalyst layer which, in turn, abuts
an active electrode. The particulate material is preferably made of
nonconducting alumina, but may also comprise the same material as
used in the catalyst layer. This geometry is limited in that a
considerable portion of the active electrode is blocked by the
particulate material and the gas is forced to flow around the
blockage away from the electrode.
[0010] U.S. Pat. No. 4,983,472 describes a corrugated current
collector with a plurality of corrugations forming dimples arranged
in a checkerboard pattern for use on the cathode side of the cell.
This configuration represents an improvement over the current
collector of the '876 patent by allowing the gas much better access
to the active electrode. However, the configuration has limitations
when used in an anode chamber which also houses a direct internal
reforming catalyst in the form of elongated solid elements. Due to
the checkerboard pattern, these catalyst elements can only be
loaded substantially perpendicular to the fuel gas flow. This
results in high flow restriction and susceptibility to large
variation in flow restriction from cell to cell.
[0011] Another disadvantage of the checkerboard pattern of dimples
used in the current collector of the '472 patent is that when
applied to both the anode and cathode chambers, a larger scale
checkerboard pattern of compressive load results on the cell active
area due to the periodic nesting of the corrugation feet through
the bipolar plate. This non-uniform pressure distribution could
result in variation in the cell contact resistance.
[0012] A further concern when using the current collector of the
'472 patent relates to the flow field formed by placing the solid
catalyst elements perpendicular to the flow direction. The
resulting geometry is characterized by nearly equal resistance to
flow parallel and perpendicular to the primary flow direction. This
means that as gas is generated in high current producing areas of
the cell it is allowed to expand laterally, apparently enhancing
mixing within the cell. However, this also tends to supply high
current producing areas of the cell with even more fresh fuel
resulting in high current density and temperature gradients within
the cell.
[0013] U.S. Pat. No. 5,795,665 describes an alternate corrugated
current collector design wherein the current collector is combined
with a separator plate to form gas passages and support for solid
catalyst elements. In this design, all the cell components are
formed in a corrugated pattern and nested together. As a result
forming the cell components is a complex operation. Also, the space
available for the reforming catalyst elements is limited.
[0014] It is therefore an object of the present invention to
provide a novel corrugated current collector design which overcomes
the disadvantages of the prior art designs.
[0015] It is also an object of the present invention to provide a
corrugated current collector which allows solid direct internal
reforming catalyst elements to be loaded substantially parallel to
the primary direction of gas flow.
[0016] It is a further object of the present invention to provide a
corrugated current collector which allows the space provided for
solid reforming catalyst elements to be maximized.
[0017] It is yet a further object of the present invention to
provide a corrugated current collector which results in more
uniform pressure distribution to the cell active components.
[0018] It is still a further object of the present invention to
provide a corrugated current collector which results in a pattern
flow field geometry characterized by high transverse flow
resistance and low axial flow resistance thus resulting in more
uniform current and temperature distributions within the cell.
[0019] It is also an object of the present invention to provide a
corrugated current collector which results in better shielding of
the direct internal reforming solid catalyst elements from the cell
electrolyte and holding these catalyst elements away from the
electrolyte containing electrode.
SUMMARY OF THE INVENTION
[0020] In accordance with the principles of the present invention,
the above and other objectives are realized in a current collector
having successive spaced rows of corrugations, with the
corrugations in a given row establishing successive peak and valley
regions along the given row and the spaced rows of corrugations
being adapted so that corresponding peak regions from row-to-row
establish through passages for receiving and supporting solid
catalyst elements.
[0021] In the embodiment of the invention to be described
hereinafter, the spaced rows of corrugations are such that there is
a given pitch between successive peak regions in a row and a given
offset in the peak regions from row-to-row. In particular, the
offset is selected to be finite and to be less than 50 percent of
the pitch, so as to establish the plurality of through passages for
the solid catalyst elements. Also, the offset is further selected
based on the catalyst dimensions and is such that the corrugations
engage the catalyst elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The above and other features and aspect of the present
invention will become more apparent upon reading the following
detailed description in conjunction with the accompanying drawings,
in which:
[0023] FIG. 1 shows in perspective view a corrugated current
collector in accordance with the principles of the present
invention;
[0024] FIG. 2 shows in perspective view a prior art corrugated
current collector of the type disclosed in the '472 patent;
[0025] FIG. 3 shows an end view of the corrugated current collector
of FIG. 1;
[0026] FIG. 4 shows an end view of the prior art corrugated current
collector of FIG. 2;
[0027] FIG. 5.shows the measured pressure drop as a function of gas
flow for the corrugated current collector of FIG. 1 and for the
prior art corrugated current collector of FIG. 2;
[0028] FIG. 6 shows a plot of the predicted distribution of flow
resistance for 5000 cells using the corrugated current collector of
FIG. 1 and the prior art corrugated current collector of FIG.
2;
[0029] FIG. 7 shows the measured flow non-uniformity for a thirty
cell stack made with the corrugated current collector of FIG. 1
illustrating less than +/-15% variation;
[0030] FIG. 8 shows the measured flow non-uniformity for a thirty
cell stack made with the prior art corrugated current collector of
FIG. 2 illustrating greater than +/-30% variation;
[0031] FIG. 9 shows a perspective view of an anode current
collector with catalyst elements having the form of the corrugated
current collector of FIG. 1 and a cathode current collector also
having the form of the corrugated current collector of FIG. 1
situated adjacent opposing sides of a bipolar separator plate to
illustrate the contact regions of the peak regions of the current
collectors on the separator plate;
[0032] FIG. 10 shows a plan view of the contact pattern achieved
with the corrugated current collector of FIG. 1 demonstrating the
general uniformity of the resulting distribution;
[0033] FIG. 11 shows a plan view of the contact pattern achieved
with the prior art corrugated current collector of FIG. 2
demonstrating the resulting checkerboard pattern of high and low
pressure;
[0034] FIG. 12 shows the measured temperature distribution in a
plan view of a thirty fuel cell stack made with the corrugated
current collector of FIG. 1 illustrating a temperature range of
70.degree. C.;
[0035] FIG. 13 shows the measured temperature distribution in a
plan view of a thirty fuel cell stack made with the prior art
corrugated collector of FIG. 2 illustrating a temperature range of
99.degree. C.; and
[0036] FIG. 14 shows the formation of a fuel stack using the
corrugated current collector of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0037] FIG. 1 shows a corrugated current collector 1 in accordance
with the principles of the present invention. As shown, the current
collector 1 includes a plurality of spaced rows of corrugations
2-7. Each row of corrugations establishes successive peak and
valley regions P and V along the length of the corrugation. These
are labeled P2, V2 through P7, V7 for the corrugation rows 2-7.
[0038] The successive peaks in a given row of corrugations define a
given pitch for the given row. In the case shown, the pitch for
each of the rows is the same Pt. Moreover, each row of corrugations
2-7 is offset by a finite amount from the preceding and succeeding
rows of corrugations, with the offset alternating in opposite
directions from row-to-row. Thus, the row of corrugations 3 is
offset to the right from the row of corrugations 2 and the row of
corrugations 4 is offset to the left from the row of corrugations
3. Again, in the case shown the offset O is the same from
row-to-row.
[0039] In accordance with the principles of the present invention,
the offset O for the rows is selected to be less than 50 percent of
the pitch Pt. With this selection for the offset, the rows of
corrugations 2-7 define a plurality of through passages each of
which extends from row-to-row and each of which is adapted to
receive and support a solid catalyst element.
[0040] More particularly, the rows of corrugations 2-7 define the
through passages 11-14, as shown in FIG. 3, each of which receives
and supports a solid catalyst element 15. As seen in FIG. 3, a
catalyst element 15 is engaged by a segment of each of the
corrugations establishing its respective through passage. The
succession of segments engaging an element 15 extend over the
length of the element, thereby providing the desired support of the
element via the current collector 1.
[0041] Establishing the through passages 11-14 so that they extend
transverse to the length of the rows of corrugations 2-7 permits
the catalyst elements 15 received in the passages to also be
situated transverse to the length of the corrugations. This
positioning of the catalyst elements 15 has considerable advantages
when the corrugated current collector 1 is used as the current
collector on the anode side of a direct internal reforming fuel
cell in which the catalyst elements 15 serve as the internal
reforming catalyst.
[0042] Specifically, when used as such an anode side current
collector, the catalyst elements 15 become situated parallel to the
axial flow direction of the fuel gas, so that there remains
enlarged free flow areas for the passage of the gas. These free
flow areas 16 can be seen in FIG. 3. As the flow restriction for
the fuel gas of a fuel cell is a function of the minimum free flow
areas available to the gas, the free flow areas 16 of the current
collector 1 result in a significantly lower flow restriction of the
fuel gas, as compared with that of prior art corrugated current
collector configurations.
[0043] This can be seen by comparing the free flow areas 16 of the
current collector 1 with the free flow areas of a prior art
corrugated current collector of the type disclosed in the '472
patent. Such a prior art corrugated current collector 21 is shown
in FIG. 2 as having rows of corrugations 22-27 formed to provide a
checkerboard pattern of peak and valley regions, PP and VV. This
checkerboard pattern is a result of selecting the offset O1 of the
corrugations from row-to-row to be equal to 50 percent of the pitch
Pt1.
[0044] As can be seen from FIG. 2, with the prior art current
collector 21, as an anode side current collector, the solid
catalyst elements 28 must be situated along the length of the
corrugations and, therefore, transverse to the gas flow direction.
This results in free flow areas 29 of limited extent, as can be
seen in the end view of the prior art current collector 21 shown in
FIG. 4.
[0045] Due to the free flow areas 29 of limited extent, the gas
flow restriction in a fuel cell using the prior art current
collector 21 is almost four times that of current collector 1 of
the invention. This is shown in FIG. 5 which depicts the measured
pressure drop of the current collector 1 in comparison to the
measured pressure drop of the prior art current collector 21.
[0046] The current collector 1 of the invention is preferably
formed from a single sheet of suitable material compatible with the
particular fuel cell (e.g., stainless steel, Inconel, nickel-clad
stainless steel, etc.). The material is punched using a die and
press to form the valley regions or feet and the peak regions. The
depth of the punching operation determines the height of the
resulting gas flow field. The orientation of the valley regions is
selected so that in the axial direction of gas flow the least
amount of cross sectional area will be obstructed by the valley
regions in order to minimize gas flow restriction.
[0047] The specific dimensions of the valley regions and the
stamped pattern are selected to yield adequate strength under
compressive load and to provide adequate access area for the gas to
the active electrode. Another consideration in specifying the size
of the valley region is to insure that the hole or empty area which
the active electrode must span not be so large that the electrode
sags into the flow field.
[0048] The pitch Pt and the offset O are, in turn, selected as
above-described to obtain the advantages previously discussed.
Further, by basing the offset O on the diameter of catalyst element
15, the catalyst diameter, and, therefore, mass, can be maximized
thereby maximizing the useful life of the cell. The peak regions,
as above-described, can also be made to engagingly lock the regions
17 the catalyst elements 15 against the bipolar separator and away
from the electrolyte containing electrode.
[0049] Because the minimum free flow areas 29 of the prior art
current collector 21 are significantly affected by the diameter of
the catalyst and this diameter can be difficult to control in a
manufacturing plant, the variation in flow restriction for the
prior art current collector 21 in manufactured fuel cells can be
significant. For the current collector of 1 of the invention,
however, the minimum free flow areas 16 are much less affected by
the catalyst diameter and the resulting variation in flow
restriction from cell to cell is greatly reduced.
[0050] FIG. 6 shows the results of a Monte Carlo simulation which
predicts the flow restriction of a large number of cells using a
mathematical model for pressure drop and normally distributed,
randomly selected values for the inputs. The results indicate that
for cells using the current collector 1 of the invention the
distribution of flow restriction from cell to cell is five to six
times tighter than that for cells using the prior art current
collector 21.
[0051] FIGS. 7 and 8 show measured distributions of flow for two
thirty cell stacks, one made using the current collector 1 of the
invention and the other made by using the current collector 21 of
the prior art. These results demonstrate, experimentally, a two to
three-fold reduction in flow non-uniformity achieved by using the
current collector of the invention.
[0052] As mentioned above, the row to row offset O of the
corrugations of the current collector 1 can be varied from a finite
value (i.e., a value greater than zero percent of the pitch Pt) to
a value of less than 50 percent of the pitch Pt. This allows for
catalyst of different diameters. Moreover, while an offset O of 0%
of the pitch would allow a catalyst of maximum diameter to be used,
this is undesirable for two reasons. First, the catalyst would be
situated very close to the anode electrode of the fuel cell and
could potentially wick liquid electrolyte directly from the anode.
Second, with 0% offset the interference of the corrugations with
the catalyst elements 15 which helps hold the catalyst in place
would then be lost.
[0053] Another important advantage of the corrugated current
collector of the invention is the desirable contact distribution
realized with the collector. FIG. 9 shows current collectors 91 and
92, configured similarly to the current collector 1 of FIG. 1, used
on the anode and cathode sides, respectively, of a bipolar plate 93
of a fuel cell. As can be seen, the anode side current collector 91
supports catalyst elements 94 for internal reforming.
[0054] As can be seen in FIG. 9, due to the configuration of the
current collectors 91 and 92, the valleys regions in the rows of
corrugations 91A, 91C, 91E and 91G of the anode side collector
91contact the bipolar plate 93 at positions aligned with the
positions at which the valley regions of the rows of corrugations
92A, 92C, 92E and 92G of the cathode side current collector 92
contact the plate 93. On the other hand, the valley regions in the
rows of corrugations 91B, 91D, 91F and 91H of the anode side
current collector 91 contact the bipolar plate 93 at positions
which are misaligned from the positions at which the valley regions
of the rows of corrugations 92B, 92D, 92F and 92H of the cathode
side current collector 92 contact the bipolar plate 93.
[0055] In the latter areas where the valley regions of the
corrugations of the anode and cathode current collectors do not
align, the separator plate 93 is allowed to flex making the
structure soft. In areas of the current collectors where the valley
regions do align the separator 93 is in compression making the
structure firm.
[0056] FIGS. 10 and 11, respectively, show schematically the
resulting pattern of soft and firm areas for the current collectors
of the invention compared with the same areas using the prior art
current collector of FIG. 2 for the anode and cathode side current
collectors. As can be seen from FIG. 10, the pattern formed by
using the current collectors in accordance with the invention, is
generally uniform with only very localized points of alignment and
misalignment. FIG. 11, on the other hand, shows that the pattern
resulting from using the prior art current is a more large scale,
checkerboard pattern of alignment which results in large areas of
high (30) and low (31) pressure applied to the active cell
components.
[0057] Another advantage of the current collector 1 of the
invention also derives from placing the reforming catalyst
substantially parallel to the gas flow direction. With the catalyst
loaded parallel to the gas flow, the transverse flow restriction is
much higher than the axial flow restriction (see, FIGS. 1, 3 and
4). However, with the catalyst loaded perpendicular to the flow,
the transverse flow restriction is nearly the same as the axial
flow restriction (see, FIGS. 2, 9 and 10). This difference in
transverse flow restriction results in the temperature gradient of
fuel cells using the current collector of the invention being less
than that of fuel cells using the prior art current collector
[0058] More particularly, since the electrical current is
necessarily non-uniform for large area fuel cells, the generation
of gas in the anode chamber is also non-uniform. For fuel cells
using the current collector of the invention, the localized gas
generated cannot easily expand laterally and, therefore, fresh fuel
is caused to be delivered to other, lower current areas of the
cell. In fuel cells using the current collector of the prior art,
the gas generated is allowed to expand laterally which causes high
current areas to be fed even more fresh fuel, thereby increasing
current maldistribution.
[0059] The result is that fuel cells using the current collector of
the invention display less temperature gradient than fuel cells
using the current collector of the prior art. This can be seen from
the experimental data set forth in FIGS. 12 and 13. These figures
show temperature gradient data performed in thirty cell stacks
using the current collector 1 of the invention and the current
collector 21 of the prior art, respectively. As can be seen, the
temperature gradient for the stack using the current collector of
the invention had a maximum of 70.degree. C. temperature gradient,
while the stack using the prior art current collector had a maximum
of 99.degree. C. temperature gradient for the same operating
conditions.
[0060] FIG. 14 shows schematically a direct internal reforming fuel
stack comprised of fuel cells 101 and 102. The fuel cells 101 and
102 are formed using the stacked configuration of anode and cathode
current collectors 91 and 92 and bipolar plate 93 shown in FIG. 9.
As can be seen, each fuel cell includes an anode section formed by
an anode electrode 111, an anode current collector 91 and a part of
a bipolar plate 93. Each fuel cell also includes a cathode section
comprised of a cathode electrode 112, a cathode current collector
92 and a part of a bipolar plate 93. Finally, each fuel cell also
includes an electrolyte member 113 situated between the anode and
cathode sections 111 and 112.
[0061] 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.
* * * * *