Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to flow field plates. Flow field
plates are typically used in fuel cell stacks in which they
perform several functions.
In a typical fuel cell stack of the membrane type as
described for example in U.S. Patent No. 3, 134, 696, membranes
are sandwiched between porous catalytic electrode layers, and
in turn between flow field plates which separate the cells in
the stack. The flow field plates perform multiple functions.
They act as current collectors for the electrodes and they
provide electrical continuity between adjacent cells. They
separately distribute reagent gases (oxygen and hydrogen)
across opposite faces of the plate in contact with opposite
polarity electrodes of adjacent cells They remove the
product of reaction (water) typically from the oxygen side,
and should supply adequate moisture to the hydrogen side to
prevent dehydration of the membrane. They act to conduct away
heat generated at the membrane during operation of the cello
These multiple functions result in such plates having a
complex structure and being expensive to produce. Flow field
plate construction of diverse types are exemplified by U.S.
Patents Nos. 3,814,631 (Warszawski et al); 4,125,676 (Maricle
et al); 4,649,091 (McElroy); 5,108,849 (Watkins et al);
5,300,370 (Washington et al); 5,445,904 ( Kaufman); 5,484,666
(Gibb et al); 5,514,487 (Washington et al); 5,683,828 (Spear
et al); 5,707,755 (Grot) and 5,709,961 (Cisar et al),
It is an object of the invention to provide a flow field
plate which is effective to carry out its function, but
relatively simple and economical to manufacture.
According to the invention, there is provided a flow field
plate comprising surface layers of electrically conductive
material, a core layer of electrically conductive material
between the surface layers within the thickness of the plate,
wherein the plate defines multiple sets of fluid passages
comprising first sets of passages, one set formed in the
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thickness of each surface layer and open to and parallel to
the surface of that layer, a second .set of passages formed in
the thickness of the core layer and extending transversely to
the passages of the first sets to provide points of
intersection with the latter when viewed in plan, ports
placing passages of the second set in communication with
passages of one or other of the first sets at points of
intersection of the passages, and a third set of passages
extending perpendicularly through the layers, without
intersecting passages of the first sets, and each
communicating with a passage or passages of the second set to
provide fluid paths into, out of, or through the first sets
of passages via the second set of passages. The surface or
core layers may be formed integrally or as a sandwich
construction. The first sets of passages are preferably
machined into the surface layer in a concentric circular or
helical pattern. The layers may be formed of graphite or
formed or metallized with a metal resistant to corrosion
under the operating conditions of a fuel cell.
Further features of the invention will be apparent from the
appended claims and from the following description of
presently preferred embodiments of the invention with
reference to the accompanying drawings, in which:
Figure 1 is an exploded view of a fuel cell stack
incorporating a first embodiment of flow field plate;
Figure 2 is a plan view of the flow field plate shown in
Figure 1;
Figure 3 is a plan view of a modification of the flow field
plate shown in Figure 2;
Figure 4 is a fragmentary cross-section on the line 4-4 in
Figure 3;
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Figures 5-7 are plan views from the same side of separately
formed layers of a second embodiment of flow field plate;
Figure 8 is an exploded isometric view of the embodiment of
Figures 5-7;
Figure 9 is a plan view of a third embodiment of flow field
plate;
Figure 10 is a cross-section of a variation of the embodiment
of Figure 9; and
Figure 11 is a plan view of a fourth embodiment of flow field
plate.
Referring first to Figure 1, there is shown in exploded view
components of a fuel cell stack incorporating flow field
plates 1 in accordance with the invention; end flow field
plates la in the stack may, as shown, be single rather than
double sided since the face adjacent an end cap will not form
part of a cell. The cells in the stack are formed by
electrode assemblies, of which only one is shown, inserted
between adjacent flow field plates. Each electrode assembly
comprises in this example, a semipermeable proton exchange
membrane B, on each side of which are located porous
graphitic electrode layers C&F. It should be understood that
flow field plates in accordance with the invention could also
be utilized with other types of electrode assembly presenting
planar electrode surfaces to the plates, and in other types
of electrochemical cell stacks, for example cells using
electrical power to disassociate electrolytes into gases
rather than the reverse process that takes place in fuel
cells, although fuel cells are presently seen as a primary
electrochemical application for the plates. Further possible
application are in filter presses or fluid purification units
in which the electrode assembly would be replaced by a
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suitable filter element of osmotic membrane, or ion transfer
a l ement
The membrane B is clamped adjacent its outer periphery and
adjacent a central aperture by 0-rings 31b and 31e located in
grooves 31d (see Figure 4) in the adjacent flow field plates
when the stack of flow field plates and electrode assemblies
is clamped between end plates (of which only one is shown) by
an axial tie rod (not shown) passing through a central bore
12 in a core member 20 on which the electrode assemblies and
flow field plates are assembled. Elastomeric collars G within
the central bores 9 of the flow field plates interact with
the apices of core 20 to define three channels 4d, 5d and 6d
extending through the bores 12 longitudinally of the stack
forming fluid passages for oxygen, hydrogen and water, these
passages communicating with ports J in the end cap H.
Washers E may optionally or alternatively be used to seal the
passages so formed at the membranes B.
Opposite surface layers of the plates 1 are formed with a
series of concentric grooves forming first sets of channels
covering an annular area between the O-rings 31b and 31e,
this area corresponding to that of the electrodes C and Fo On
the sides of the plates seen in Figures 1 and 2, the-set of
grooves comprises alternating grooves 2 and 3, while on the
opposite side (see Figure 4) there is one set of grooves 10.
Drilled radial bores 4, 5 and 6, forming a second set of
channels, extend through core layers of the plates 1 between
the surface layers, and communicate respectively with the
grooves 2, 3 and 10 through ports or vias 4a, 5a and 6a
respectively The bores 4, 5 and 6 communicate with the
channels 4d, 5d and 6d, forming a third set of channels
though ports of which only port 6c is referenced. The
channels 4d, 4 and 2 of each plate conduct oxygen to fields
adjacent the electrodes F adjoining electrode assemblies on
one side of the plates, and the channels 6d, 6 and 10 of each
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plate conduct hydrogen to fields adjacent the electrodes of
the electrode assemblies adjoining the other sides of the
plates. The channels 3, 5a and 5d conduct water, formed by
reaction between the oxygen and the hydrogen of the membrane
under the influence of the catalyst treated electrodes, away
from the reaction zone. The width and shape of lands 3a
between the grooves 2 and 3 may be controlled (compare Figure
10) so as to maximize the area of the electrodes exposed to
the reagent fields, and having regard to the porosity of the
electrode material to allow oxygen and water to migrate the
channels 2 towards the channels 3. The width and shape of
lands between the channels 10 may be similarly controlled.
Since the channels nearest the centre of the plate are
shorter, it may be desirable to make these channels narrower
so as to reduce the fluid flow through these channels
compared to those of greater radius.
The drillings forming channels 4, 5 and 6 are closed at their
outer ends by a further 0-ring 31 retained in a channel 8
around the periphery of each plate 1.
The reaction between the hydrogen and the oxygen at the
membrane is exothermic, and it may be desirable to provide
additional cooling of the assembly during operation. This is
facilitated by the modification of the plate shown in Figure
2 as illustrated in Figure 3. As compared with the plate of
Figure 2, the core member 20, instead of being approximately
triangular, is in the form of a five pointed star so as to
define five rather than three passages within the bores 9.
The additional passages 11 and lla communicate with
additional radial bores llc and lld in the plate, while the
0-ring 31 is replaced by a sealing collar 31c so as to
enclose the channel 8 around the periphery of the plate. The
channels 4, 5 and 6 are closed at their outer ends by plugs
4c, 5c and 6c. Cooling liquid may be fed to the stack
through the channel 11 and exit through the channel 11a after
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passing through the plates via the channels llc, lld and 8.
The plates 1 may be constructed in various ways. In one
presently preferred form, a disc of graphite is machined on
its opposite faces to form the grooves 2, 3 and 10 and on its
periphery to form the channel 8. Such circular grooves are
readily machined even in a material such as graphite. The
radial bores are drilled. Rather than graphite, the plate
may be formed of metal such as a noble metal or corrosion
resistant alloy, but noble metals are very costly, and
corrosion resistant alloys or metal may have inadequate
corrosion resistance, or, in the case of metals such as
titanium or tantalum, may be costly and difficult to machine.
Another possible approach is to mould or cast the plate with
at least the surface grooves, drill the radial passages, and
metallize the completed plate using a noble metal. In this
case the plate may be machined, cast or moulded from base
metal or synthetic resin, provided that the integrity of the
metallization of the various passages can be assured if the
substrate material is not itself corrosion resistant. In the
drawings the ports or vias 4a, 5a and 6a are shown as
separately formed, but it may be practical to displace the
radial drillings sufficiently towards the relevant surfaces
of the plate that the primary and secondary passages
intersect without additional drillings. If the plates are
used in a non-electrochemical application, then their
conductivity may be immaterial, and they can be moulded or
machined from synthetic resin.
In use in a fuel cell, the stack incorporating the plates is
preferably operated with the passages 2 and 3 facing
upwardly, so that water formed by interaction at the membrane
of oxygen and hydrogen accumulates in and is drained from the
passages 3.
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Turning now to Figures 5 to 8, an alternative embodiment of
plate is shown, in which the same reference numerals are
utilized to indicate similar parts. The opportunity has been
taken in the several figures to illustrate variations of this
embodiment, but collectively the Figure shows respectively a
first surface layer 100, a core layer 101 and a second
surface layer 102 which are assembled in the relationship
shown in Figure 8 to form a complete plate. Each layer may
for example be formed by either as already described above,
or by embossing a sheet of a deformable graphitic composition
to the various passages. For example, the grooves 2, 3 and 10
may be pressed into the outer layers, and the secondary
passages pressed into the appropriate side of the centre
layer 10. Such pressed passages, such as the passage 50o in
the centre layer will weaken it less than punched or drilled
slots such as 6 or 40. The passage may communicate with a
central passage 9, divided by a core 20, through ports 40d,
50d, or with off-centre through passages such as 13. As seen
in Figure 6, the arrangement may incorporate cooling
passages, as described above with reference to Figure 3.
Referring now to Figures 9 and 10, these Figures illustrate
an embodiment incorporating certain variations of the
embodiments of Figures 1-4. For example, the drilled
passages in the core layer of the plate need not be radial,
so long as they can intersect the passages 1, 2 and 3.
Moreover, the third passages extending longitudinally of the
stack need not be located in the centre portions of the
plates. In Figure 8, a non radial passage 90 extends between
longitudinal passages 70, 80, sealed to passages of adjacent
plates by 0-rings 70b, 80b. The passages 70, 80 are radially
outward of the 0-rings 31b. In Figures 9 and 10 a group of
longitudinal passages 13 sealed by 0-rings 13a provide for
admission of hydrogen, oxygen and cooling water, while an
central passage 12 provides for drainage of water produced by
reaction, and for the passage of a tie-rod (not shown).
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Figure 11 shows how multiple stacks of cells may be assembled
using a single set of plates 1. The plates in this case are
rectangular, the stack being held together by the rods (not
shown) through passages 12. The drillings 4, 5 and 6 (closed
at the edge of the plate by plugs such as 6c) may be
connected to longitudinal passages formed either by the
passages 12, or segments of a central (relative to the
grooves 2, 3) core 20, as previously described.
Although the passages 1, 2 and 3 have been described as
circular and concentric, helical grooves could be employed to
form the passages and are easily machined. Separation of the
passages 2 and 3 can be achieved in this case by use of a
multi-start helix. In cases where the grooves must be
machined from a material such as graphite, complex groove
layouts should be avoided.
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