WO2006039802A1

WO2006039802A1 - Separator plate for fuel cell

Info

Publication number: WO2006039802A1
Application number: PCT/CA2005/001564
Authority: WO
Inventors: Truc Tran-Ngoc; Christopher Bennett
Original assignee: Polymer Technologies Inc.
Priority date: 2004-10-12
Filing date: 2005-10-12
Publication date: 2006-04-20
Also published as: CA2583569A1

Abstract

A separator plate for a fuel cell is provided. The separator plate includes a matrix and an insert. The matrix includes a polymeric material. The matrix has a first surface and a second surface. The insert is conductive and is positioned in the matrix. The insert includes at least one projection that extends towards the first surface at at least one location on the first surface. The insert includes at least one projection that extends towards the first surface at at least one location on the second surface. The at least one projection is unexposed on at least one of the surfaces. A quantity, of conductive material is embedded in any of the first and second surfaces at any locations of any unexposed projections.

Description

TITLE: Separator Plate for Fuel Cell

FIELD OF THE INVENTION

[0001] The present invention relates to fuel cells, and more particularly the invention relates to polymeric separator plates for fuel cells. BACKGROUND OF THE INVENTION

[0002] A polymer electrolyte membrane fuel cell (also known as a PEM fuel cell) is an electrochemical device capable of producing electricity from chemical reactions involving Hydrogen and Oxygen. Currently, PEM fuel cells are being considered or used in vehicles and in a variety of other applications such as, in stationary and mobile electricity generators.

[0003] A PEM fuel cell typically includes an anode electrode, a cathode electrode, and a polymer electrolyte membrane disposed there between. Typically, individual fuel cells are stacked together one on top of the other with electrically conductive separator plates disposed between adjacent fuel cells. [0004] The separator plate typically has a flow channel on each side for the transport of a fluid to each adjacent fuel cell. The fluid transported may be, for example, a reactant gas which is used by an adjacent fuel cell to produce electricity.

[0005] A commonly used material for the production of separator plates is graphite. However, graphite separator plates typically are expensive to manufacture, and are brittle. Other materials that are commonly used include polymer bound conductive materials such as, a graphite-polymer composite. However, separator plates manufactured from such composites typically possess a relatively low surface conductivity at their interface with adjacent fuel cell elements, due to the presence of a polymer "skin" that is generally the void of conductive material on their interface surfaces. Additionally, such plates typically have relatively high concentrations of graphite in them in order to achieve acceptable conductivity. As a result, graphite-polymer composite plates can be brittle. [0006] Some solutions have been proposed to improve the surface conductivity of such plates, whereby some or all of the skin is removed. For example, some proposed solutions include immersing the plate in a strong acidic solution, or blasting its contact surfaces with an abrasive material. While such processes may increase the surface conductivity of the plate, they can have detrimental effects on the quality of the finished part. Furthermore, these secondary processes increase the overall cost associated with the production of the plate.

[0007] There is, therefore, a need for an improved polymeric separator plate for use in a fuel cell, and for an improved method of manufacturing separator plates.

SUMMARY OF THE INVENTION

[0008] In a first aspect, the invention is directed to a separator plate for a fuel cell. The separator plate includes a matrix and an insert. The matrix includes a polymeric material. The matrix has a first surface and a second surface. The insert is conductive and is positioned in the matrix. The insert includes at least one projection that extends towards the first surface at at least one location on the first surface. The insert includes at least one projection that extends towards the first surface at at least one location on the second surface. The at least one projection is unexposed on at least one of the surfaces. A quantity of conductive material is embedded in any of the first and second surfaces at any locations of any unexposed projections.

[0009] Optionally, the quantity of conductive material extends to a depth below any of the first and second surfaces at any locations of any unexposed projections and any unexposed projections extend to within the depth below the first and second surfaces.

[0010] In a second aspect, the invention is directed to a separator plate for a fuel cell. The separator plate has a lower level of filler loading as a result of the provision of a conductive insert therein. [0011] In a third aspect, the invention is directed to a separator plate for a fuel cell, wherein the separator plate has a seal portion that is flexible and resilient.

[0012] In a fourth aspect, the invention is directed to fuel cell that is fully sealed and integrity tested prior to assembly in a fuel cell stack.

[0013] In a fifth aspect, the invention is directed to a separator plate for a fuel cell, wherein the separator plate has a seal portion that is has a selected configuration permitting ultrasonic welding to adjacent plates in the fuel cell.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will now be described by way of example only, with reference to the attached drawings in which:

[0015] Figure 1 is an exploded perspective view showing a portion of a fuel cell stack incorporating a separator plate in accordance with a first embodiment of the present invention;

[0016] Figure 2 is a sectional side view of a system of several plates from the fuel cell shown in Figure 1;

[0017] Figure 3 is a magnified perspective view of a portion of a separator plate which can be used the fuel cell stack shown in Figure 1 ;

[0018] Figure 4 is a magnified sectional side view of a portion of an alternative separator plate which can be used with the fuel cell stack shown in Figure 1;

[0019] Figure 5 is sectional side view of a system of several plates from the fuel cell shown in Figure 1 , shown partially assembled;

[0020] Figure 6 is a sectional side view of a separator plate adjacent two gas diffusion layers in accordance with another embodiment of the present invention; - A -

[0021] Figure 7 is a sectional side view of a separator plate in accordance with yet another embodiment of the present invention;

[0022] Figure 8 is a side view of a system for embedding conductive material into a separator plate plank during production of one of the separator plates shown in Figure 1 ; and

[0023] Figure 9 is a perspective view of the system shown in Figure 8.

DETAILED DESCRIPTION OF THE INVENTION

[0024] This application claims priority from US provisional application 60/522,542, the entire contents of which are incorporated herein by reference.

[0025] Reference is made to Figure 1 , which illustrates a fuel cell stack

10 containing a plurality of fuel cells 11. Two fuel cells 11 are shown in Figure 1 in the fuel cell stack 10, however it is possible for the fuel cell stack 10 to contain a greater number of fuel cells 11. Each fuel cell 11 includes a catalyzed electrolyte membrane 12, a gas diffusion layer (GDL) 14 on each side of the membrane 12, and a separator plate 18 adjacent the outwardly facing surfaces of the gas diffusion layers 14 and the Teflon™ masks 16. One side of the fuel cell 10 is an anode side 20, and the other side is a cathode side 22, with the membrane 12 separating the anode and cathode sides 20 and 22 from each other.

[0026] The catalyzed membrane 12 permits the migration of electrochemically generated Hydrogen ions across its thickness from the anode side 20 to the cathode side 22. The GDLs 14 control the distribution of water on the surfaces of the membrane 12. [0027] The separator plates 18 provide electrical conductivity between adjacent fuel cells 11 and between the fuel cell stack 10 and current collector plates (not shown) at both ends of the fuel cell stack 10.

[0028] Reference is made to Figure 2, which shows a magnified view of two of the separator plates 18. Each separator plate 18 has a first surface 24 and a second surface 26. The first surface 24 has a first flow channel 28 thereon for the transport of a reactant gas. The second surface 26 has a second flow channel 30 thereon for the transport of a reactant gas. It will be appreciated that the routing of the flow channels 28 and 30 shown in the Figures is exemplary only and that any suitable routing may be made.

[0029] The portion of the separator plate 18 where the plate 18 contacts the GDL 14 is called the active region 33. The active regions 33 may each be recessed relative to a surrounding inactive region 36. A shoulder 34 separates the recessed active region 33 from the inactive region 36. Referring to Figure 5, when the fuel cell 11 is clamped or otherwise held together, the recessed active region 33 permits the gas diffusion layer 14 to be retained in place, while inhibiting excessive compression of the gas diffusion layers 14. The shoulder 34 surrounding the active region 33 is positioned to receive and position the outer perimeter of the GDL 14. [0030] The portions of the active regions 33 that contact the GDLs 14 when the fuel cell stack 10 (Figure 1) is assembled together make up the electrical transfer regions 35. The electrical transfer regions 35 are the portions of the first and second surfaces 24 and 26 that conduct electrical currents between the separator plates 18 and the adjacent GDLs 14. Put another way, the electrical transfer regions 35 are the portions of the active regions 33 outside of the channels 28 and 30.

[0031] The plate 18 includes a matrix 100 and an insert 102. The matrix 100 includes an active region matrix 104, which has a first composition in the active region 33 and an inactive region matrix 106, which may have a second, different composition in the inactive region 36. For example, the active region matrix 104 may be made from a composite of a polymer, such as a perfluorocarbon sulfonic acid ionomer (eg. Nafion™), and a conductive material, such as graphite. Alternatively, the active region matrix 104 may be made from a polymeric material, and may have a quantity of conductive material embedded in one or both of its surfaces 24 and 26, as will be described further below. [0032] Other polymer materials that may be used include LCP (Liquid

Crystal Polymer), Nylon™, Polyvinylidene fluoride (PVDF), polypropylene or any other suitable polymer, including polymers that are relatively non- conductive and can act as a carrier for a conductive filler, or polymers that are themselves intrinsically conductive.

[0033] The insert 102 is positioned in the active region 33. The insert

102 is conductive, and may be made from a suitable conductive, preferably metallic, material, such as, for example, SS 304 stainless steel, SS 316 stainless steel, Aluminum. One example of SS316 that would be suitable is known as E-brite™ 26-1 from Allegheny-Ludlum.

[0034] The insert 102 includes a plurality of projections 108 including first projections 108a that extend towards of the electrical transfer regions 35 at locations 110 on the first surface 24 of the plate 18, and second projections 108b that extend towards the electrical transfer regions 35 at locations 110 on the second surface 26 of the plate 18. On the surface 24 of the plate 18 shown in the left side of Figure 2, the channels 28 carry coolant and so the projections 108 may extend all the way to the surface 24 of the plate 18. On the surface 26 of the plate 18 shown in the left side of Figure 2, the channels 30 carry hydrogen. To protect the insert 102 from being attacked by the hydrogen, the projections 108 may be configured to not extend all the way to the surface 26.

[0035] For the separator plate 18 that is shown on the right side of

Figure 2, the first surface 24 has channels 28 which carry oxidant, and the second surface 26 has channels 30 which carry coolant. The insert 102 in the separator plate 18 on the right of Figure 2 has projections 108b that optionally extend all the way to the surface 26 at locations 110. However, the projections 108a extend towards the surface 24, but not all the way to the surface 24 at locations 110, such that they are not exposed at the surface 24, thereby protecting the insert 102 from attack by the oxidant in the channels 28. [0036] A quantity 54 of conductive material 56 is embedded into selected portions of the first and second surfaces 24 and 26, such as at the locations 110 wherein the projections 108 extend towards the surface 24 or 26 without being exposed at the surface 24 or 26. The quantity 54 of conductive material 56 provides a conductive path between the surface 24 or 26 of the plate 18 and the insert 102. [0037] The conductive material 56 extends to a depth D below the surface 24 and 26. Preferably, the projections 108 extend to within the depth D of the surface 24 or 26 so that the conductive material 56 provides a conductive path between the surface 24 or 26 of the plate 18 and the insert 102, without the need for conductive filler to be present in the active region matrix 104.

[0038] The conductive material 56 may be made up of any particles that provide suitable conductivity in a direction through the thickness of the separator plate 18. For example, the conductive material 56 may be graphite, carbon or Titanium carbide. The conductive material 56 can be referred to as a second conductive material, and it may be the same as or different than the conductive material used in the active region matrix 104.

[0039] The conductive material 56 may be in any suitable form, such as fibres, powder or granulate. For the purposes of this document, all of these are a type of particle. The selected portions of the first and second surfaces 24 and 26 may include some or all of one or both of the first and second surfaces 24 and 26.

[0040] The quantity 54 of conductive material 56 may be a contiguous layer. Alternatively, however, the quantity 54 may be made up of a plurality of separate 'islands' that cover portions of one or both surfaces 24 and 26 of the plate 18, but which are disconnected from each other. For example, they may be separated by the flow channels 28 or 30.

[0041] In an alternative embodiment, the quantity 54 of conductive material 56 may be provided over the entirety of the electrical transfer region 35. This alternative improves the in-plane conductivity at the surface 24 or 26. [0042] By embedding the surface conductive material 56 in the first and second surfaces 24 and 26 of the separator plate 18, the conductive material 56 can more easily conduct electricity to and from the interior of the plate 18, relative to a prior art coating that is not embedded in the surface. Embedding the surface conductive material 56 causes the conductive material 56 to break through the generally less-conductive 'skin' that can develop on the first and second plate surfaces 24 and 26 under some manufacturing conditions.

[0043] The embedment of conductive material 56 in the surfaces 24 and/or 26 may be carried in accordance with any of the teachings of PCT application PCT/CA2005/000813 (Tran et al.), the entire contents of which are hereby incorporated by reference.

[0044] Preferably, the locations 110 for the projections 108 are well spread out over the active region 33. In this way, the plate 18 has numerous positions along its contact surfaces with the adjacent plates, eg. plate 14, or another plate 18 (see Figure 5), wherein a high conductivity electrical path is provided.

[0045] Reference is made to Figure 6, which shows an exemplary connection between three adjacent plates, and which illustrates the electrical flow from one plate to another. [0046] In this example, the plates are a separator plate 18 and GDLsI 4 and 14' on each side of the plate 18 (a configuration that is not specifically shown in Figure 1 , however it is a configuration that would nonetheless fall within the scope of the present invention). However, the plates could be any adjacent plates in the fuel cell stack 10. [0047] It will be noted that in the embodiment shown in Figure 6, the insert 102 is buried beneath both surfaces 24 and 26 of the separator plate 18, and conductive material 56 is embedded in both surfaces 56 to facilitate electrical conduction between the surfaces 24 and 26 and the insert 102.

[0048] The electrical conduction between the three plates 14, 18 and 14' is described. When the separator plate 18 is in contact with an adjacent plate, eg. GDL 14, there will be certain spots across the area of mutual contact wherein the contact is relatively strong and other spots wherein the contact is relatively weak, due to imperfect flatness of the plates 18 and 14. Additionally, there may be variability in the properties of the plate 14, such that certain spots on the surface of the plate 14 may have higher conductivity than other spots. As a result of the above, there may be 'hot¹ spots at the interface between the separator plate 18 and the plate 14 whereby the conductivity between the plates 18 and 14 is higher. By providing a plurality of locations 110 that are well spread over the active region 33, the likelihood is increased that a hot spot will coincide with a location 110, thus facilitating electrical flow into the plate 18 and through the plate 18 to the opposing surface.

[0049] On the other side of the plate 18 in Figure 6, the hot spots along the interface between the plates 18 and 14' may be at different locations than the hot spots at the interface of the plate 18 and 14. By providing a plurality of well spread locations 110 of the projections 108, and by having the insert 102 extend substantially over the entire active region 33, the plate 18 can provide a high conductivity electrical path from the hot spot on one side of the plate 18 to a hot spot at another location on the other side of the plate 18. [0050] The projections 108 preferably substantially cover the entirety of the active region 33 on both sides of the separator plate 18. The surface conductive material 56 is preferably provided on substantially all of the electrical transfer region 35 thus providing an increased chance of hot spot being positioned at a location 110. [0051] The surface conductive material 56 may be kept out of the first and second flow channels 28 and 30, so that the polymeric skin that is present in the channels 28 and 30 is undisturbed. In this way, the surface integrity of the first and second channels 28 and 30 is not compromised by embedded particles, so that the walls 31 and floor 32 of the channels 28 and 30 are resistant to degradation during use and the plate 18 is more effective as a barrier to separate fuel on one side from oxidant on the other side. [0052] The surface conductive material 56 may be kept out of the seal portion 44 and may further be kept entirely out of the inactive region 36. In so doing, the seal portion 44 in particular may be made from any suitable material for forming a seal with the adjacent fuel cell component (eg. the membrane 12), without the material properties of the seal portion 44 being negatively affected (eg. embrittled) by the presence of the surface conductive material 56. For example, the material of the seal portion 44 may be selected to have good weldability by ultrasonic means to the electrolyte membrane 12.

[0053] By providing increased surface conductivity for the separator plate 18, the GDL 14 may be maintained under relatively less compression when the fuel cell 11 or fuel cell stack 10 is assembled in order to achieve suitable conduction of electricity between the separator plate 18 and the GDL

14. This, in turn, provides improved long-term structural stability for the fuel cell stack 10. The depth of the recessed active region 33 may be selected to permit a selected amount of compression in the GDL 14 in the assembled fuel cell stack 10.

[0054] As a result of the presence of the insert 102, the concentration of conductive filler in the active region matrix 104 may be reduced, optionally to zero, relative to a separator plate lacking a conductive insert. As a result of the reduced filler loading, the separator plate 18 is relatively less brittle than a plate with a high filler loading. Additionally, the plate 18 with reduced filler loading may be manufactured more easily than a plate with a relatively high filler loading. For example, in embodiments wherein the plate 18 is manufactured by an injection molding process, the reduced filler loading provides reduced wear on certain components of the injection molding machine, such as the injection screw and the hot runner nozzle tips.

[0055] While it has been described that the matrix 104 can be provided with no conductive filler, it is nonetheless optionally possible for the matrix 104 to be provided with a conductive filler in addition to the embedded conductive material on its surfaces 24 and/or 26. The conductive filler would be provided as a second quantity of conductive material. This conductive material may be the same or different than the conductive material that makes up the first quantity 54 embedded in the surfaces 24 and/or 26.

[0056] Reference is made to Figure 3, which shows a structure that can make up the insert 102. In the embodiment shown in Figure 3, the insert 102 is made up of a mesh 112 that is formed as necessary to provide the projections 108. A particular advantage to making the insert 102 out of a mesh is that when the active region matrix 104 is formed, eg. by a molding process around the mesh 110, the apertures, shown at 114, in the mesh 112 provide numerous holds for the matrix 104, to strengthen the connection between the matrix 104 and the insert 102.

[0057] Reference is made to Figure 4, which shows another optional structure that can make up the insert 102. In the embodiment shown in Figure 4, the insert 102 is made up a sheet of material, eg. a sheet of foil that has been stamped, punched and formed to provide the projections 108. In the embodiment shown in Figure 4, a plurality of apertures 114, and preferably many apertures 114, are provided in the insert 102 to provide holds for the matrix 104 when the matrix is molded onto the insert 102.

[0058] In the following Table 1, the electrical conductivities for selected materials are provided.

Table 1 : Electrical conductivities for selected materials

[0059] In the following Table 2, the thru-plane resistance of a graphite plate is compared with the resistance across other plates of various materials. The conductivities of the materials are provided to illustrate the filler loading that is present in the materials.

Table 2: Resistance of plates made with various materials

[0060] The resistances provided in the table are calculated per square centimeter of active region of the separator plate. The conductivities of the materials listed in the MATERIAL column are in Siemens per centimeter and are representative of the amount of conductive filler loading present in the material. The formed insert used in Examples 4 and 5 is the insert shown in Figure 3. The stamped insert used in Examples 6, 7 and 8 is the insert shown in Figure 4. A plate thickness of 1 mm was used for the plates in Examples 2- 8 because it is contemplated that at least some of the plates 18 in Examples 2-8 may be able to be made thinner than a comparable graphite plate of Example 1 (which has a thickness of 2 mm). The potentially thinner construction may be possible at least as a result of the reduced brittleness that accompanies the lower filler loading.

[0061] As can be see in Example 8 of the table, the filler loading of the material can be reduced by the addition of the stainless steel insert, while providing a resistance that is approximately the same as that of the graphite plate of Example 1.

[0062] Table 2 above does not take into account the presence of the polymer skin that can develop at the surfaces 24 and 26 of the plate 18 and is thus not necessarily a perfect representation of the resistances that would exist with an actual product. The table is intended, however, to illustrate that the resistance of the plate 18 can be brought to acceptable levels as a result of the insert, even with a lower conductive filler loading of the matrix 104.

[0063] In embodiments wherein the projections 108 of the insert 102 are either exposed at the plate surface 24 or 26 or extend sufficiently close to the surface 24 or 26, (eg. to within the selected depth of the embedded material 56 below the surface 24 or 26), the active region matrix 104 may provide acceptable conductivity even without containing any conductive filler.

However, it is anticipated that the active region matrix 104 will possess some conductive filler throughout in addition to having the embedded conductive material on at least one of the surfaces 24 and 26.

[0064] In the inactive region 36, the conductive filler may be omitted, so that the entirety of the inactive region matrix 106 is made from a polymer. The polymer of the inactive region 36 need not be the same polymer as is used for the active region 33.

[0065] Referring to Figure 2, the inactive region 36 surrounds the active region 33 and includes a seal portion 44. The seal portion 44 seals against an adjacent fuel cell component, such as the catalyzed membrane 12 to inhibit leakage of reactant gases out of the active region 33. As more clearly shown in Figure 3, the seal portion 44 may include a projection 46 that extends outwardly from the first and second surfaces 24 and 26 of the separator plate 18. The projection 46 may be made from a polymeric material that is suitably deformable for use as a seal means. A plurality of projections 46 may be provided instead of one projection 46, thereby forming a labyrinth seal with the catalyzed membrane 12 to prevent leakage of reactant gases. [0066] Recesses 47 located on either side of the seal projections 46 accommodate deformation of the projections 46 during compression of the fuel cell stack 10 or when the seal tip is melted during ultrasonic welding of the projections 46 to the membrane 12 (see Figure 3a). This allows plates to sit firmly flat against each other in a FC stack assembly.

[0067] In an alternative embodiment, the projections 46 may be made from a material that is ultrasonically weldable to the adjacent fuel cell component, such as the catalyzed membrane 12. The shape of the projections 46 may be such that they are of relatively large cross-section at their base, shown at 48, and are of relatively small cross-section at their tip, shown at 50. This feature permits ultrasonic power to be concentrated in the tip 50 for welding the projections 46 to the adjacent fuel cell component, thereby forming a seal therewith. The projections 46 may generally taper from their bases 48 to their tips 50. [0068] As a result of the improved seal provided by the seal portion 44, the fuel cell stack 10 need not incorporate Teflon™ seals that are typically used in some fuel cell stacks.

[0069] Referring to Figure 1 , a first inlet aperture 40a passes through the first separator plate 18 in the inactive region 36. The first inlet aperture 40a is an inlet aperture for the first flow channel 28 and communicates fluidically therewith (see Figure 1). A first outlet aperture 42a also passes through the separator plate 18 in the inactive region 36 and is an outlet aperture for the first flow channel 28 and communicates fluidically therewith. Similarly, a second inlet aperture 40b and a second outlet aperture 42b for the second flow channel 30 pass through. Additionally, for the fuel cell stack 10 shown in Figure 1 , a third inlet aperture 40c and a third outlet aperture 42c pass through the separator plate 18 to connect to the second separator plate 18. The first, second and third inlet apertures 40a, 40b and 40c carry a fuel, coolant and oxygen to the separator plates 18 respectively. [0070] In the embodiment shown in Figure 2, the GDLs 14 are bonded to the catalyzed membrane 12 to form a membrane electrode assembly (MEA).

[0071] Referring to Figure 2, each separator plate 18 is shown as having flow channels 28 and 30 on both surfaces 24 and 26. Such plates 18 may be used as bipolar plates with either fuel or oxidant on one side and coolant on the other side. It is alternatively possible for the separator plates

18 to have reactant gas channels 28 on their first side and a oxidant 30 on their second side 26. In such an embodiment, coolant would not be provided, or would be provided via some other means.

[0072] It is further possible that the plates 18 could be made with a reactant gas channel 28 on one surface (eg. surface 24), and no channels on their other surface (eg. surface 26). For example, in the fuel cell stack 10, the outermost separator plate 18 at each end of the stack 10 may lack flow channels on its outward-facing surface.

[0073] Reference is made to Figure 7, which shows a magnified side sectional view of a separator plate 140 in accordance with another embodiment of the present invention. The separator plate 140 is similar to the separator plate 18 except that the separator plate 140 has embedded into its surfaces, shown at 144 and 146, a conductive material 56 in the form of a conductive mesh 142. The mesh 142 may be formed in any suitable way. For example, the mesh 142 may be an expanded metal. Alternatively, the mesh 142 may be made from screen material.

[0074] A piece of mesh 142 having a selected size and shape may be provided and embedded in the first and second plate surfaces 144 and 146 in the regions where the plate 140 contacts the GDLs 14. The mesh 142 may be embedded directly as it is applied by means of ultrasonic power. The mesh 142 may cover the first and second flow channels shown at 148 and

150, however, the mesh 142 may be configured to not contact the channel walls or floor, shown at 152 and 154 respectively, as shown in Figure 7. [0075] The structure of the separator plates 18 lends itself to a semi- automated production process, in particular where the plates are welded together, the fuel cell stack 10 may be pre-tested to determine if any leaks are present. [0076] The plates 18, 140 may be made by any suitable fuel plate manufacturing process, and may include processes such as extrusion and/or injection molding and/or compression molding. The embedment of mesh 142 or of particles may be accomplished by any suitable means, including, for example, heat embedment or pressure embedment. Alternatively, the particle embedment may be carried out by the method taught in co-pending PCT application PCT/CA2005/000813 (Tran et al.).

[0077] Reference is made to Figure 8, which shows a system 58 for the embedment of particles in the separator plate 18. The system 58 includes a station 74, a station 80 and a station 84. The station 74 is a conductive particle application station, which includes an upper conductive particle application station portion 74a and a lower conductive particle application station portion 74b. The conductive particle application station portions 74a and 74b have conductive particle application devices 76a and 76b respectively, which may be, for example, spray nozzles, which apply conductive particles to the first and second surfaces 62a and 62b of the plate blank 62. The spray nozzles may be movable as necessary to thoroughly apply the conductive particles over the selected surface areas.

[0078] The conductive particles may be applied as dry particles, or alternatively, they may be applied with a carrier liquid that can assist them in adhering to the plate blank 62. In particular, some form of adhesion assistance, such as incorporating a carrier liquid is contemplated for the conductive particle application device 76b applying conductive particles to the second plate blank surface 62b.

[0079] The application of conductive particles to the first and second plate blank surfaces 62a and 62b may be kept within a selected surface area by including seal members 78a and 78b on the upper and lower conductive particle application station portions 74a and 74b. The seal members 78a and 78b surround the conductive particle application devices 76a and 76b and seal against the plate blank surfaces 62a and 62b to control where conductive particles are applied to the plate blank 62. For example, the seal members 78a and 78b could be rubber seals that form a seal on the plate blank 62 to prevent the conductive particles from being applied to the seal portions 44 that are formed on the plate blank 62 (see Figure 9).

[0080] A selected portion of the conductive particles applied to the upper and lower plate blank surfaces 62a and 62b is embedded into the surfaces 62a and 62b at a particle embedment station 80, which includes an upper particle embedment station portion 80a and a lower particle embedment station portion 80b. At the particle embedment station 80, the conductive particles may be embedded in the surfaces 62a and 62b by any suitable means. For example, they may be embedded ultrasonically. A first device 82a may be positioned in the upper particle embedment station portion 80a. The first device 82a may be configured to operate either as a sonotrode or as an anvil in an ultrasonic heating operation. A second device 82b may be positioned in the lower particle embedment station portion 80a, and is also configurable to operate either as a sonotrode or as an anvil in an ultrasonic heating operation.

[0081] The upper and lower devices 82a and 82b each have a plate contacting surface with a selected pattern so that, when each device 82a or 82b acts as a sonotrode, it applies ultrasonic energy through the pattern onto a selected portion of the plate blank surfaces 62a and 62b, thereby embedding a selected portion of the particles into the surfaces 62a and 62b. For example, the patterns on the devices 82a and 82b may be such that particles are embedded into the portions of the plate blank surfaces 62a and 62b that will ultimately contact the GDL 14 (see Figure 1) without being embedded in the flow channels 28 and 30. [0082] When the first and second devices 82a and 82b are brought into contact with the first and second plate blank surfaces 62a and 62b and power is applied to the first device 82a, the first device 82b acts as a sonotrode and ultrasonically embeds conductive particles into the first plate blank surface 62a, while the other device 82a or 82b acts as an anvil. Similarly, when power is applied to the second device 82b, the second device acts as a sonotrode and ultrasonically embeds conductive particles into the second plate blank surface 62b.

[0083] When a portion of the plate blank 62 is in the particle embedment station 80, power may be first sent to one of the devices 82a and 82b to embed particles into one of the plate blank surfaces 62a and 62b. Power may then be sent to the other of the devices 82a and 82b to embed particles into the other of the plate blank surfaces 62a and 62b.

[0084] Instead of providing the first and second devices 82a and 82b which are capable of acting as either a sonotrode or an anvil, it is possible that a first particle embedment station could be provided, having a sonotrode for contacting the first plate blank surface 62a and an anvil for contacting the second plate blank surface 62b, and that a second particle embedment station could be provided, having a sonotrode for contacting the second plate blank surface 62b and an anvil for contacting the first plate blank surface 62a.

[0085] It is optionally possible for the entire plate blank surfaces 62a and 62b to receive a conductive particle coating, instead of the coating being omitted from selected areas.

[0086] After a selected portion of the particles are embedded into the plate blank surfaces 62a and 62b, the particles that are not embedded are removed from the plate blank surfaces 62a and 62b, at a particle removal station 84, which includes an upper particle removal station portion 84a and a lower particle removal station portion 84b. The upper and lower particle removal station portions 84a and 84b include air outlets 86a and 86b respectively for directing pressurized air from a source of pressurized air (not shown) onto the plate blank surfaces 62a and 62b to remove unembedded conductive particles therefrom. In order to improve the removal efficiency of the air outlets 86a and 86b, it is possible that they may be movable to facilitate their access to all necessary portions of the plate blank surfaces 62a and 62b.

[0087] Depending on the type of conductive particles used for the coating, a liquid may be included in the pressurized air to assist in particle removal. For example, where the conductive particles are applied to one or both plate blank surfaces 62a and 62b using a carrier liquid, particle removal may be facilitated by the use of a liquid entrained in the pressurized air. The entrained liquid may be any suitable liquid, and may be selected specifically based on the conductive material used for the coating, and also based on how the conductive material was itself applied to the surfaces 62a and 62b. The liquid should be selected to avoid damaging the plate blank surfaces, and should itself not be adherent to the plate blank surfaces 62a and 62b.

[0088] The particle removal station portions 84a and 84b further include dust collection inlets 88a and 88b respectively, which extend back to a dust collection system (not shown). The dust collection inlets 88a and 88b may surround the blasting air outlets 86a and 86b to contain and capture any dust generated during air blasting of the plate blank surfaces 62a and 62b.

[0089] After the conductive particles have been removed from the plate blank surfaces 62a and 62b, other operations may be performed on the plate blank 62.

[0090] The upper station portions 74a, 80a and 84a may be connected together in a common upper member 92. The upper member 92 is movable to bring the station portions 74a, 80a and 84a into contact and away from contact with the first plate blank surface 62a. Similarly, the lower station portions, 74b, 80b and 84b may be connected together in a common lower member 94.

[0091] The upper and lower members 92 and 94 may operate together similarly to a stamping press and may be configured so that any patterned members therein, such as the plates with the flow channel pattern thereon in the feature forming station 72 can be easily interchanged with other plates having a different pattern thereon, facilitating the production of different configurations, sizes and shapes of separator plate.

[0092] It has been shown and described that the palte 18 have flow channels on both surfaces 24 and 26. It is alternatively possible, however, for the plates 18 to have flow channels on one side only, eg. on surface 24, or on surface 26.

[0093] The above described manufacturing method is exemplary only.

Any method of making the separator plates 18, 140 may be used.

[0094] As will be apparent to persons skilled in the art, various modifications and adaptations of the apparatus described above may be made without departure from the present invention, the scope of which is defined in the appended claims.

Claims

CLAIMS:

1. A separator plate for a fuel cell, comprising: a matrix, wherein the matrix includes a polymeric material, wherein the matrix has a first surface and a second surface, an insert, wherein the insert is conductive, wherein the insert is positioned in the matrix; wherein the insert includes at least one projection that extends towards the first surface at at least one location on the first surface, wherein the insert includes at least one projection that extends towards the second surface at at least one location on the second surface, and wherein the at least one projection is unexposed on at least one of the surfaces, and wherein a quantity of conductive material is embedded in any of the first and second surfaces at any locations of any unexposed projections.

2. A separator plate as claimed in claim 1 , wherein the quantity of conductive material extends to a depth below any of the first and second surfaces at any locations of any unexposed projections and wherein any unexposed projections extend to within the depth below the first and second surfaces.

3. A separator plate as claimed in claim 1 , wherein the matrix is made from a homogenous mixture of the polymeric material and a second quantity of conductive material.

4. A separator plate as claimed in claim 1 , wherein at least one of the surfaces has a flow channel therein, and wherein said quantity of conductive material is outside of the flow channel.

5. A separator plate as claimed in claim 1 , wherein the first surface includes an active region surrounded by an inactive region and wherein the active region is recessed relative to the inactive region.

6. A separator plate as claimed in claim 1 , wherein the quantity of conductive material includes at least one conductive mesh.

7. A separator plate as claimed in claim 6, wherein at least one of the surfaces has a flow channel therein, and wherein the at least one conductive mesh extends across the flow channel.

8. A separator plate as claimed in claim 1 , wherein the quantity of conductive material includes a quantity of conductive particles.