FUEL CELL STACK WITH END PLATE ASSEMBLY TO IMPROVE PRESSURE
DISTRIBUTION IN THE STACK
The present invention relates to methods and apparatus suitable for assembling an
electrochemical fuel cell stack.
Fuel cell stacks comprise a series of individual fuel cells built up layer by layer into a
stack anrangement. Each cell itself may include various layered components such as a
polymer electrolyte membrane, gas diffusion layers, fluid flow plates and various sealing
gaskets for maintaining fluid tightness and providing fluid fuel and oxidant distribution to
the active surfaces of the membrane. At each end face of the stack, a pair of pressure
end plates coupled together by tie bars is conventionally used to hold the stack together
and maintain compression on the cells in the stack.
It is most important that pressure applied by the end plates to the ends of the fuel cell
stack is sufficiently uniform across the surfaces of the stack that all of the individual
components of the stack are maintained in proper compressive relationship with one
another. Sealing gaskets in particular must be maintained in proper compression across
the entire area of each fuel cell to ensure that fluid flow paths are properly defined so
that fuel and / or oxidant are correctly conveyed to the active surfaces of each cell and
do not leak.
Conventionally, uniform pressure is maintained by providing substantial and robust end
plates capable of maintaining sufficient excess pressure across the entire surfaces of the
ends of the stack. This results in large and heavy end plates to ensure that they are
sufficiently robust that they will not significantly distort under the requisite pressures and
will not apply compression forces unevenly. Use of large and heavy end plates results in
heavier and larger fuel cell stacks than is desirable. An alternative approach is to use
lighter weight end plates but provide an additional mechanism for mitigating the effects
of end plate structure distortion when compressive forces are applied. This could be a
shim positioned centrally between an end plate and a first inner stack component.
One approach described in US 2006/0194094 uses an end plate having a pressure
shield which is curved convexly towards the stack and a bearing plate which acts as a
transition element to transmit compressive forces to a planar element of the fuel cell
stack. This document can be said to recognise the importance of maintaining a uniform
pressure distribution.
A problem exists as to how to maintain a uniform compressive relationship through the
fuel cell stack while also allowing fluid distribution to the fuel cells in the stack. Further,
minimising the size and weight of the end plates, as noted above, is desirable for
incorporation of smaller fuel cell stacks for certain applications.
It is an object of the present invention to provide an improved way of ensuring good
pressure distribution across the end faces of a fuel cell stack while providing flexibility in
supplying the required fluids to the fuel cells.
According to one aspect, the present invention provides a fuel cell stack assembly
comprising: a plurality of fuel cells in a stack, the stack defining two opposing parallel
end faces; an end plate assembly at each opposing end face of the stack, the end plate
assemblies being coupled together to thereby maintain the fuel cells in the stack under
compression; wherein at least one of the end plate assemblies comprises:
a master plate defining a master compression face having a first portion and a
second portion;
a first slave plate defining a first slave compression face;
a second slave plate defining a second slave compression face,
the first slave compression face facing the first portion of the master compression
face and when assembled, being in compressive relationship therewith,
the second slave compression face facing the second portion of the master
compression face and when assembled, being in compressive relationship therewith.
At least one of the slave plates may extend laterally from the master plate on at least
one side defining a lateral extension portion, the lateral extension portion comprising at
least one fluid distribution port communicating with a fluid distribution gallery passing
through or alongside the plurality of fuel cells in the stack.
Both the first and second slave plates may extend laterally from the master plate on at
least one side, each of the first and second slave plates thereby defining a lateral
extension portion, and each lateral extension portion comprising at least one fluid
B2013/051046
distribution port communicating with a fluid distribution gallery passing through or
alongside the plurality of fuel cells in the stack.
The at least one fluid distribution port may include at least one of a fuel distribution port,
a water distribution port, an oxidant distribution port and a coolant fluid distribution port.
The first and second slave plates respectively may include a different configuration of
fluid distribution port. The first slave plate may define at least one of a fuel distribution
port and a water distribution port, as the at least one fluid distribution port and the
second slave plate may define at least one of an oxidant distribution port and a coolant
fluid distribution port, as the at least one fluid distribution port.
The first and second portions of the master compression face may be at a first angle
relative to one another and the first and second slave compression faces may be at a
second angle to one another. The first angle may be reflex and the second angle may be
obtuse, or the first angle may be obtuse and the second angle may be reflex.
The first angle and the second angle may be selected such that the first portion and
second portion of the master compression face and respectively the first and second
slave compression faces are non-parallel prior to application of a load to the end plate
assemblies whereas, under the application of the load to maintain the fuel cells under
compression, a bending moment in the master plate may cause the first portion of the
master compression face and the first slave compression face to come into parallel
relationship with one another by distortion of the master plate, and cause the second
portion of the master compression face and the second slave compression face to come
into parallel relationship with one another by distortion of the master plate.
The first angle may be greater than 80 degrees such that master compression face
defines a convex surface. The convex surface may be configured such that under the
application of the load to maintain the fuel cells under compression, the bending moment
in the master plate causes the first portion of the master compression face and the first
slave compression face to come into parallel relationship with one another by distortion
of the master plate, and the second portion of the master compression face and the
second slave compression face to come into parallel relationship with one another by
distortion of the master plate.
13 051046
The second angle may be greater than 180 degrees such that the first and second slave
compression faces together define a convex surface. The convex surface may be
configured such that under the application of the load to maintain the fuel cells under
compression, the bending moment in the master plate causes the first portion of the
master compression face and the first slave compression face, and the second portion of
the master compression face and the second slave compression face, to come into
parallel relationship with one another by distortion of the master plate.
The first and second portions of the master compression face may both form part of a
continuous convex surface and the first and second slave compression faces may be
contiguous so as to form a concave surface by abutting the first and second slave plates
against one another along one edge.
The master plate may be formed from metallic material. The slave plates may be formed
from non-metal material.
Both of the end plate assemblies may comprise a master plate and a first and a second
slave plate.
A plurality of tie bars may be arranged to pass through the lateral extension portions of
the first and second slave plates at opposing ends of the fuel cell stack. The tie bars may
be configured to couple the end plate assemblies together to thereby maintain the fuel
cells in the stack under compression. The plurality of tie bars may be located inwards of
the at least one fluid distribution port proximal the plurality of fuel cells in order to
maintain the fuel cell stack under compression.
According to another aspect, the present invention provides a method of forming a fuel
cell stack assembly comprising: forming a plurality of fuel cells in a stack, the stack
defining two opposing parallel end faces; positioning first and second slave plates of an
end plate assembly at one end face of the stack, the first and second slave plates each
having respective first and second slave compression faces facing outwardly from the
stack; positioning a master plate defining a master compression face at the end face of
the stack such that the master compression face is proximal the first and second slave
compression faces; positioning a second end plate assembly at the opposing end face of
the stack; and coupling the end plate assemblies together to bring the first and second
stave compression faces into compressive relationship with the master compression
face and to maintain the stack under compression.
Embodiments of the present invention will now be described by way of example and with
reference to the accompanying drawings in which:
Figure 1 shows a perspective exploded view of a master plate and five
exemplary pairs of first and second slave plates, each pair having different fluid
distribution ports;
Figure 2 shows a perspective sectional view of a master plate and first and
second slave plates showing relative positions of the three elements in an assembled
fuel cell stack;
Figure 3a shows a front perspective view of an exemplary fuel cell stack
assembly;
Figure 3b shows a rear perspective view of the fuel cell stack assembly of figure
3a;
Figure 3c shows a rear view of the fuel cell stack assembly of figures 3a and 3b;
Figure 4a shows a schematic cross-sectional view of a master plate with a
convex master compression face and reflex first angle , and first and second slave
plates with an obtuse angle Qs between the first and second slave compression faces;
and
Figure 4b shows a schematic cross-sectional view of a master plate with a
concave master compression face and obtuse first angle , and first and second slave
plates with a reflex angle S between the first and second slave compression faces; and
Figure 5 shows a flow diagram of a method suitable for forming a fuel cell stack
assembly.
Fundamental to a fuel cell stack assembly is the parallel relationship of the monopolar /
bipolar fuel cel plates to one another. Uniform contact forces maintained across the
electrodes contribute towards optimum electrode performance. The end plate (which
may be an end plate assembly) is an important component governing the parallel
relationship in the stack assembly, but the end plate itself will likely go through a physical
distortion once a load is applied to the end plate in order to maintain the fuel cell stack
under compression and bring the fuel cells into compressive relationship. Preferably, any
distortion of the end plate should not be transmitted to the electrode plates of the fuel
cells.
Another function of the end plate is to allow the transmission of fluids to the electrode
plates of the stack. Preferably these fluids should be isolated from metallic surfaces, for
example to avoid corrosion or reaction with the metallic component which may require
replacement of the affected component.
Dependent on the requirements of the fuel cell stack assembly, and how the fuel cell
stack assembly is to be integrated into a particular system, there are often bespoke and /
or specific requirements for the end plate components. Such requirements may include
particular fluid distribution port arrangements, provision for the coupling of the end plates
to the fuel cell stack (for example, via the use of tie bars, clips, or bands for maintaining
the stack under compression), and preferred properties of the fuel cell stack assembly
(for example, making the stack as light, or as small, as possible).
Figure 1 illustrates an exemplary master plate 1 and five exemplary pairs of a first slave
plate 5 and a second slave plate 7. The first slave plate 5 and the second slave plate 7
are discrete (i.e. physically separate) elements. A master plate 1 and a pair of first and
second slave plates 5, 7 together comprise an end plate assembly 30. The master plate
1 defines a master compression surface 2 which, in this embodiment comprises a first
portion 3 and a second portion 4. The first slave plate 5 comprises a first slave
compression face 6 and the second slave plate 7 comprises a second slave
compression face 8. An end plate assembly comprising a master plate 1 and first and
second slave plates 5, 7 may be located at one end, or at both ends, of the fuel cell
stack depending on the particular requirements.
Each slave plate 5, 7 includes a planar back surface 14 configured for engagement with
an end face of a stack of fuel cells. The planar back surface 14 may be uniformly flat or
may comprise a series of pressure elements which together define a series of coplanar
pressure surfaces distributed across the area of the plate which collectively define the
planar back surface 14.
When assembled together to form an end plate assembly 30 as in figure 3a for example,
the first slave compression face 6 faces the first portion 3 of the master compression
face 2 and the second slave compression face 8 faces the second portion 4 of the
master compression face 2. When the fuel cell stack is assembled, the first slave
compression face 6 and first portion 3 of the master compression face 2 are in
compressive relationship. Similarly, the second slave compression face 8 and the
second portion 4 of the master compression face 2 are in compressive relationship.
Figure 2 illustrates the master plate 1 and first and second slave plates 5, 7 assembled
to form an end plate assembly 30.
As best seen in figure 3a, both first and second slave plates 5, 7 extend laterally from or
beyond the edges 22 of the master plate 1 on both sides of the master plate 1 in figure
1, where all the illustrated slave plates 5, 7 have a lateral extension portion 9 extending
to the top of the first slave plates 5 and to the bottom of the second slave plates 7,
beyond the boundary edges 22 of the master plate . In other examples, depending on
the chosen assembly of slave plates, only one slave plate might extend laterally beyond
the edges 22 of the master plate 1, on at least one side.
Lateral extension portions 9 can be seen in figure 1 to comprise at least one fluid
distribution port 10, 11, 12, 13, 17. Such fluid distribution ports 10, 11, 12, 13, 17 can
each communicate with a fluid distribution gallery passing through or down the sides of
the plurality of fuel cells in the stack. Fluid distribution galleries are required for delivery
of fuel and / or oxidant and / or water to the cells in the stack in a known manner. The
lateral extension portions 9 may also comprise further features, such as ports, recesses,
grooves or channels, for example for the attachment of an air box 25 to the fuel cell
assembly 20.
The master plate 1 may be formed as an open cell structure with voids 16 and
connecting limbs 18 for a lighter weight construction for any given strength. It is not
required to locate any fluid distribution port apertures 10, 11, 12, 13, 17 in the master
plate 1. Such apertures 10, 11, 12, 3, 17 can be located in the lateral extension portions
9 of the slave plates 5, 7.
As well as including fluid distribution ports, the first and second slave plates 5, 7 include
a number of apertures for the passage of tie bars 35 (the ends of which can be seen in
figures 3a-3c) for assembling the stack and for maintaining the stack in compression.
The fluid distributions ports 10, 11, 12, 13, 17 can include one or more of any or all of
fuel distribution ports, water distribution ports, oxidant distribution ports and coolant fluid
distribution ports. For example, as shown in figures 1, 2 and 3a-3c, ports for the inflow
and outflow of air 10, 13 are included in the slave plates 5, 7, which may provide for the
cooling of, and / or supply of oxidant (e.g. air) to, the fuel cells. Also shown are fluid
distribution ports 11, 12 for the supply and distribution of fuel (e.g. hydrogen). Fluid
distribution ports 11, 12 could be drillings to provide different positional options for
coupling pipe connectors t o the same distribution gallery, e.g. to supply the anode plates
in the stack with fuel. Also shown is a water distribution port 17 for the supply and
distribution of water to the fuel cells in the stack. The water distribution port 1 could be
for the purpose of direct cooling by injection into the anodes or cathodes of the fuel cells
or for a separate cooling circuit between fuel cell anode / cathode plates. Other possible
arrangements of different ports in the lateral extension portions may also be envisaged.
Some fluid distribution ports (e.g. that indicated by reference numeral 2) may be wholly
or partly contained within a portion of the respective slave plate that lies within the
footprint defined by the master plate, rather than being wholly contained in the lateral
extension portion 9.
An advantage to the use of first and second slave plates 5, 7 is the flexibility of possible
arrangements for making up the end plate assembly. As illustrated in figure 1, a first
slave plate 5 and a second slave plate 7 used together may have different fluid
distribution ports. Therefore it is possible to choose the required porting arrangements
for each side of the fuel cell stack by choosing individual first and second slave plates 5,
7 with different porting arrangements.
For example, it may be required to allow cooling gas / oxidant to flow into and out of
diagonally opposite edges of the fuel cell assembly. Therefore, particular coolant fluid
(air flow) port requirements are needed at those two opposite edges. As another
example, a first slave plate pair (that is, on one end of the fuel cell stack) may be
required to define a fuel distribution port and/or a water distribution port, and a second
slave plate pair (on the other end of the fuel cell stack) may be required to define an
oxidant distribution port and/or a coolant fluid distribution port.
The modular adaptability of the end plate assembly achieved by having two slave plates
5, 7 allows for greater flexibility in selecting the porting arrangements of a fuel cell stack
assembly. Having the option of arranging different configurations of the fuel cell stack
using two slave plates with possibly different fluid distribution port arrangements means
T/GB2013/051046
that fuel cell stacks can be assembled with increased adaptability, for example to match
a particular system layout, without the need for custom components to be included.
Such modularity of the slave plates 5, 7 also provides for lower levels of end plate stock
required to be held by a manufacturer / assembler to achieve a particular porting
arrangement, and reduce component costs, inventory costs, and procurement costs
while improving build response and delivery lead times.
Various configurations of First and second slave plates 5, 7 containing fluid ports 10, 11,
12, 13, 17 in different positions and / or different proportions may be provided to suit a
particular stack. The first and second slave plates 5, 7 may however have the same first
and second slave compression faces 6, 8 designed to mate with the master compression
face 2. The slave plates can be manufactured by moulding.
Figures 3a-3c show three views of an exemplary fuel cell stack assembly 20 including a
master plate 1 and first and second slave plates 5, 7 at both ends of the plurality of fuel
cells 15. Tie bars 35 (the ends of which are visible in the figures) are included in the fuel
cell stack assembly, and each stack has two air boxes 25 included. The exemplary fuel
cell stack assembly 20 in figures 3a-3c has an asymmetric cathode delivery to exhaust,
e.g. where cathode air enters port 10 at the top right as viewed in figure 3a and exits a
corresponding port at bottom left of figure 3a.
As shown in figures 3a-3c, a fuel cell stack assembly 30 comprises a plurality of fuel
cells 15 in a stack, the stack defining two opposing parallel end faces. The individual fuel
cells are not shown separately. The stack has each cell parallel to the planar back
surfaces 1 of the first and second slave plates 5, 7. The planar back surfaces 14 of the
slave plates 5, 7 are the surfaces on the opposite sides of the slave plates 5, 7 to the
slave compression faces 6, 8. The stack of cells therefore defines two opposing parallel
end faces each of which engages with a respective pair of first and second slave plates
5, 7 .
An end plate assembly 30, for example as described above, may be located at each
opposing end face of the fuel cell stack as shown. In the example of figures 3a-3c, the
three-piece end plate assembly 30 is used at both ends of the fuel cell stack. However, it
will be appreciated that such a three-piece end plate assembly 30 could be used only at
2013/051046
one end of a fuel cell stack, with the other end having a conventional end plate. The end
plate assemblies may be coupled together to maintain the fuel cells in the stack under
compression. The coupling may be achieved using any suitable method, for example, via
the use of clips, bands, or tie bars / tie rods. A plurality of tie bars may be arranged as
shown in figures 3a-3c to pass through the master plate 1 and first and second slave
plates 5, 7, at opposing ends of the fuel cell stack. The tie bars 35 can be configured to
couple the end plate assemblies 30 together to thereby maintain the fuel cells in the
stack under compression.
Stack fixing points, such as the ports for locating tie bars 35 in the fuel cell stack
assembly 20, are located along axes along the top and bottom edges of the master plate
(as viewed in figures 3a - 3c) thereby substantially containing distortion of the master
plate 1 under compression to distortion about an axis parallel thereto.
The plurality of tie bars 35 as shown in figures 3a-3c are preferably located inwards of
the fluid distribution ports 10, 11, 12, 13, 17 proximal the plurality of fuel cells 5 in order
to maintain the fuel cell stack under compression. Locating the tie bars in this way closer
to the fuel cells in the stack concentrates the compression of the slave plates 5, 7 onto
the body of the fuel cell stack where it is most required, rather than onto the air boxes 25
via the lateral extension portions 9.
It may be that around 95% of the applied force to the plate / electrode assembly 20,
applied due to compression of the fuel cell stack, is required for the (more central)
electrode region, and outside of this centralised area only 5% of the total applied force is
required (typically in the manifold regions where fluid distribution ports 10, 11, 12, 13
may be located). Such pressure distribution may be the optimal distribution to cause
desirable uniform pressure loading across the fuel cells in the stack.
By avoiding significantly extending the master plate 1 beyond the footprint of the fuel cell
plates 5, as shown in figures 3a-3c, it is possible to reduce the bending moment applied
to the master plate 1 because the overall height of the end plate 1 is reduced or
minimised. Correspondingly if the height of the master plate is reduced or minimised,
then the thickness of the master plate may also be reduced or minimised. The lateral
extension portions 9 of the slave plates 5, 7 can be configured for the transmission of
around 5% of the compressive force required to the outer manifold regions.
In the above examples, the end plate assemblies may have the master plate formed
from metal (for example, for strength, durability and/or ease of manufacture) and the
slave plates may be fomned from a non-metal material, such as a plastic or toughened
glass materials, e.g. for passivity.
Figures 4a and 4b illustrate schematic cross sectional views of two possible profiles for
the master plate 1 and first and second slave plates 5, 7. The first portion 3 and the
second portion 4 of the master compression face 2 are at a first angle relative to one
another; the first slave compression face 6 and second slave compression face 8 are at
a second angle 0S to one another.
Introducing a reflex angle to the master plate 1 strengthens the master plate 1 in a
critical area (along the centre angled region of the master plate 1). Such an arrangement
as shown in figure 4a, for example, also allows for a larger mass of slave plate 5, 7
material at the outer edges of the end plate assembly 30.
With the lateral extension portions 9 of the first and second slave plates 5, 7 as shown in
figures 4a and 4b, a larger mass of non-metal or plastic material can be dedicated to
providing fluid distribution ports in the slave plates 5, 7. Having non-metallic fluid
distribution ports in the slave plates 5, 7 allows fluids supplied to the fuel cell assembly
to be isolated from metallic surfaces in the end plate assembly 30. This can reduce
corrosion which might otherwise occur in end plate assembly parts made from corrodible
metal that are exposed to fluid flows. This also limits or avoids the use of expensive
corrosion resistant metal (e.g. stainless steel) in the end plate assembly.
The first angle on the master plate 1 and the second angle S formed by the first and
second slave plates 5, 7, are preferably selected so that when the master plate
undergoes distortion under compression, the second angle Q plus the first angle 
(which may vary due to the compressive force applied to the stack) will tend towards a
value of 360 degrees. This compressive force and resulting distortion in the master plate
will also tend to bring the first and second slave compression faces 6, 8 and the
corresponding portions 3 , 4 of the master compression face into a parallel relationship,
while the planar back surfaces 14 of the first and second slave plates 5, 7 adjacent to the
fuel cell plate/electrode assembly remain planar and parallel with the fuel cells in the
stack.
As shown in figure 4a, the first angle between the two portions 3, 4 of the master
compression face 2 is preferably reflex (greater than 180 degrees) and the second angle
s between the first and second slave compression faces 6, 8 is preferably obtuse
(between 90 degrees and 180 degrees). In figure 4b, the first angle between the two
portions 3, 4 of the master compression face 2 is obtuse (between 90 degrees and 180
degrees) and the second angle S between the first and second slave compression
faces 6, 8 is reflex (greater than 180 degrees).
The first angle and the second angle Q are preferably selected such that: the first
portion 3 of the master compression face 2 and the first slave compression face 6 are
non-parallel prior to application of a load to the end plate assemblies; similarly, the
second portion 4 of the master compression face 2 and the second slave compression
face 8 are non-parallel prior to application of a load to the end plate assemblies. That is,
prior to the application of a load to the end plate assemblies to compress the fuel cell
stack, the portions 3, 4 of the master compression face 2 and respectively the first and
second slave compression faces 6, 8 converge on one another at the centre angled
portion of the master compression face 2 (where the two portions 3, 4 of the master
compression face 2 meet). However, under the application of the load to maintain the
fuel cells under compression, a bending moment in the master plate 1 causes: the first
portion 3 of the master compression face 2 and the first slave compression face 6; and
the second portion 4 of the master compression face 2 and the second slave
compression face 8, to come into parallel relationship with one another by distortion of
the master plate 1.
Figure 4a illustrates the case where the first angle is greater than 180 degrees such
that master compression face 2 defines a convex surface, the convex surface being
configured such that under the application of the load to maintain the fuel cells under
compression, the bending moment in the master plate 1 causes the first portion 3 of the
master compression face and the first slave compression face 6 to come into parallel
relationship with one another by distortion of the master plate 1 and causes the second
portion of the master compression face 4 and the second slave compression face 8 to
come into parallel relationship with one another by distortion of the master plate .
Figure 4b illustrates the case where the second angle Qs is greater than 180 degrees
such that the first and second slave compression faces 6, 8 together define a convex
surface, the convex surface being configured such that under the application of the load
to maintain the fuel cells under compression, the bending moment in the master plate 1
causes the first portion of the master compression face 3 and the first slave compression
face 6 to come into parallel relationship with one another by distortion of the master plate
1, and causes the second portion of the master compression face 4 and the second
slave compression face 8 t o come into parallel relationship with one another by distortion
of the master plate 1.
The angles and S may be selected to suit any particular design of master plate and
slave plate, taking into account many different factors such as the degree of stiffness of
the master plate, the volume of material required in the slave plates for the required fluid
porting and fluid delivery conduits, the desired mass and/or volume of the end plate
assembly and the type of materials used.
In another exemplary configuration to those shown in figures 4a and 4b each of the first
portion 3 and second portion 4 of the master compression face 2 need not be planar but
could be curved surfaces. For example, each of the first portion 3 and second portion 4
could present a convex surface respectively towards the first and second slave
compression faces 6, 8. The surfaces 3, 4 may be concave rather than convex. In other
examples, the first and second slave compression faces 6, 8 may also, or alternatively,
present concave (or convex) surfaces towards the respective portions of the master
compression face 2. In a further example, the first and second slave compression faces
6, 8 may be contiguous by abutting the first and second slave plates 5, 7 together along
one edge. The master compression face 2 may also be a planar surface in some
examples.
The transition between the first portion 3 and second portion 4 of the master
compression face 2 need not necessarily be a sharp angle as shown in figures 4a and
4b. The transition can be a smooth rounded transition portion between the two portions
3, 4. For example, a rounded transition portion in the master compression face 2 may
follow a cylindrical profile with the flat first and second portions 3, 4 at tangents to the
radius of the cylindrical transition portion. The first and second portions 3, 4 of the
13 051046
master compression face 2 can both form part of a continuous convex (or in other
examples, concave) surface.
Similarly, the transition between the first and second slave compression faces 6, 8 need
not necessarily be a sharp angle as shown in figures 4a and 4b. The transition can be a
smooth rounded transition portion between the two faces 6, 8. Thus, the first and second
slave compression faces 6, 8 can together provide contiguous concave (or in other
examples, convex) surfaces by abutting the first and second slave plates 5, 7 against
one another along one edge.
If the master plate 1 has a more complex shaped master compression face 2, this may
lead to greater accuracy in the master compression face 2 and the first and second slave
compression faces 6, 8 being in parallel relationship with one another under stack
compression than having only planar master and slave compression faces. Such a form
of master compression face 2 having a rounded transition between the two master
compression face portions 3, 4 may be able to accommodate the distortion in the master
plate 1 more accurately during compression of the stack, thus resulting in flat
compression faces 3, 4 being offered to the corresponding slave plate compression
faces 6, 8 in operation.
Further, having first and second slave compression faces 6, 8 forming contiguous
surfaces having, for example, a rounded transition between the first and second
compression faces 6, 8 (e.g. a swept contour profile of the first and second slave plates
together) may be used to better match the distorted face of the master plate 1 under
compression.
Other possible profiles of the master compression face, and of the slave compression
face (formed by the first and second slave compression faces 6, 8 together when the first
and second slave plates 5, 7 are abutted along one edge) include one single curved
profile (where the curve may be, for example, spherical, parabolic, or another shape
suitable for achieving uniform pressure distribution to the fuel cell stack upon
compression of the stack) or the master compression face 2 being substantially flat and
facing a curved slave compression face formed from the first and second slave
compression faces 6, 8.
The swept form / inclusion of rounded or curved portions in the master compression face
2 and / or the first and second slave compression faces 6, 8 may be achieved by
performing, bending, casting or an extrusion, according, for example, to cost
requirements.
Other features may be included in the master and slave plates, such as a mechanism or
structure by which the slave plates can be registered with the master plate. An
exemplary arrangement is shown in figures 1 to 3c in which a tenon 23 or projection or
series of projections is formed on the master plate 1 which engages with / into a mortise
24 or corresponding recess or groove in a surface of the slave plate 5, 7. It will be
understood that the mortise and tenon structures can be reversed between the master
and slave plates.
Figure 5 shows a flow diagram of a method suitable for forming a fuel cell stack
assembly including the steps of: forming a plurality of fuel cells in a stack, the stack
defining two opposing parallel end faces (step 51); positioning first and second slave
plates of an end plate assembly at one end face of the stack, the first and second slave
plates each having respective first and second slave compression faces facing outwardly
from the stack (step 52); positioning a master plate defining a master compression face
at the end face of the stack such that the master compression face is proximal the first
and second slave compression faces (step 53); positioning a second end plate assembly
at the opposing end face of the stack (step 54); and coupling the end plate assemblies
together to bring the first and second slave compression faces into compressive
relationship with the master compression face and to maintain the stack under
compression (step 55), and is self-explanatory.
Other embodiments are intentionally within the scope of the accompanying claims.
CLAIMS
. A fuel cell stack assembly comprising:
a plurality of fuel celts in a stack, the stack defining two opposing parallel end
faces;
an end plate assembly at each opposing end face of the stack, the end plate
assemblies being coupled together to thereby maintain the fuel cells in the stack under
compression;
wherein at least one of the end plate assemblies comprises:
a master plate defining a master compression face having a first portion
and a second portion;
a first slave plate defining a first slave compression face;
a second slave plate defining a second slave compression face,
the first slave compression face facing the first portion of the master
compression face and when assembled, being in compressive relationship therewith,
the second slave compression face facing the second portion of the
master compression face and when assembled, being in compressive relationship
therewith.
2. The fuel cell stack assembly of claim 1 in which at least one of the slave plates
extends laterally from the master plate on at least one side defining a lateral extension
portion, the lateral extension portion comprising at least one fluid distribution port
communicating with a fluid distribution gallery passing through or alongside the plurality
of fuel cells in the stack.
3 . The fuel cell stack assembly of claim 1 in which both the first and second slave
plates extend laterally from the master plate on at least one side, each of the first and
second slave plates thereby defining a lateral extension portion, and each lateral
extension portion comprising at least one fluid distribution port communicating with a
fluid distribution gallery passing through or alongside the plurality of fuel cells in the
stack.
4. The fuel cell stack assembly of claim 2 or claim 3 in which the at least one fluid
distribution port includes at least one of a fuel distribution port, a water distribution port,
an oxidant distribution port and a coolant fluid distribution port.
5. The fuel cell stack assembly of claim 3 in which the first and second slave plates
respectively include a different configuration of fluid distribution port.
6. The fuel cell stack assembly of claim 3 in which
the first slave plate defines at least one of a fuel distribution port and a water
distribution port, as the at least one fluid distribution port and;
the second slave plate defines at least one of an oxidant distribution port and a
coolant fluid distribution port, as the at least one fluid distribution port.
7. The fuel cell stack assembly of claim 1 in which:
the first and second portions of the master compression face are at a first angle
relative to one another; and
the first and second slave compression faces are at a second angle to one
another.
8. The fuel cell stack assembly of claim 7 in which the first angle is reflex and the
second angle is obtuse, or the first angle is obtuse and the second angle is reflex.
9. The fuel cell stack assembly of claim 7 in which the first angle and the second
angle are selected such that the first portion and second portion of the master
compression face and respectively the first and second slave compression faces are
non-parallel prior to application of a load to the end plate assemblies whereas, under the
application of the load to maintain the fuel cells under compression, a bending moment
in the master plate causes the first portion of the master compression face and the first
slave compression face to come into parallel relationship with one another by distortion
of the master plate, and cause the second portion of the master compression face and
the second slave compression face to come into parallel relationship with one another by
distortion of the master plate.
10. The fuel cell stack assembly of claim 8 in which the first angle is greater than 180
degrees such that master compression face defines a convex surface, the convex
surface being configured such that under the application of the load to maintain the fuel
cells under compression, the bending moment in the master plate causes the first
portion of the master compression face and the first slave compression face to come into
parallel relationship with one another by distortion of the master plate, and causes the
second portion of the master compression face and the second slave compression face
to come into parallel relationship with one another by distortion of the master plate.
. The fuel cell stack assembly of claim 8 in which the second angle is greater than
180 degrees such that the first and second slave compression faces together define a
convex surface, the convex surface being configured such that under the application of
the load to maintain the fuel cells under compression, the bending moment in the master
plate causes the first portion of the master compression face and the first slave
compression face, and the second portion of the master compression face and the
second slave compression face, to come into parallel relationship with one another by
distortion of the master plate.
12. The fuel cell stack assembly of claim 1 in which the first and second portions of
the master compression face both form part of a continuous convex surface and the first
and second slave compression faces are contiguous so as to form a concave surface by
abutting the first and second slave plates against one another along one edge.
13. The fuel cell stack assembly of claim 1 in which the master plate is formed from
metallic material and the slave plates are formed from non-metal material.
4 . The fuel cell stack assembly of claim 1 in which both of the end plate assemblies
comprise a master plate and a first and second slave plate as defined in claim 1.
15. The fuel cell stack assembly of claim 3 in which a plurality of tie bars are
arranged to pass through the lateral extension portions of the first and second slave
plates at opposing ends of the fuel cell stack, the tie bars configured to couple the end
plate assemblies together to thereby maintain the fuel cells in the stack under
compression.
16. The fuel cell stack assembly of claim 15 in which the plurality of tie bars are
located inwards of the at least one fluid distribution port proximal the plurality of fuel cells
in order to maintain the fuel cell stack under compression.
17. A method of forming a fuel cell stack assembly comprising:
forming a plurality of fuel cells in a stack, the stack defining two opposing parallel
end faces;
positioning first and second slave plates of an end plate assembly at one end
face of the stack, the first and second slave plates each having respective first and
second slave compression faces facing outwardly from the stack;
positioning a master plate defining a master compression face at the end face of
the stack such that the master compression face is proximal the first and second slave
compression faces;
positioning a second end plate assembly at the opposing end face of the stack;
and
coupling the end plate assemblies together to bring the first and second slave
compression faces into compressive relationship with the master compression face and
to maintain the stack under compression.