Bipolar plate assembly for a fuel cell stack

Abstract

The bipolar plate assembly (204-1, 204-2, 302-1, 2004) may include a cathode flow field plate (306, 310, 2008) and an anode flow field plate (308, 312, 2010). The cathode flow field plate (306, 310, 2008) has a first plurality of flow channels (502, 2106) defined between a first plurality of ribs (500) that function as pathways for an oxidant, and a second plurality of flow channels (406) defined between a second plurality of ribs (404) that function as pathways for a coolant. The anode flow field plate (308, 312, 2010) has a third plurality of flow channels (412, 2204) defined between the third plurality of ribs (410, 2202) that function as paths for fuel and a fourth plurality of flow channels (614, 2110) defined between the fourth plurality of ribs (612) that function as paths for coolant. The first inlet manifold (426, 2206) receives the oxidant, the coolant, or both, and the second inlet manifold (432, 2208) receives the fuel.

Description

[Technical Field]

[0001] The present invention relates generally to fuel cell stacks, and more particularly to bipolar plate assemblies for fuel cell stacks. [Background technology]

[0002] A fuel cell stack includes multiple fuel cells, in which a chemical reaction may occur between a fuel and an oxidant. The chemical reaction may convert the chemical energy of the fuel and the oxidant into electrical energy. The chemical reaction occurs at the anode and cathode of each fuel cell. The fuel cell stack includes a bipolar plate assembly for providing fuel and oxidant to the fuel cells. The bipolar plate assembly may include a cathode flow channel on one side and an anode flow channel on the opposite side. The bipolar plate assembly may be positioned between two adjacent cells, with the cathode flow channel providing oxidant to the cathode of one fuel cell and the anode flow channel providing fuel to the anode of the adjacent fuel cell. Thus, the bipolar plate assembly may separate the two adjacent fuel cells. Summary of the Invention [Problem to be solved by the invention]

[0003] The fuel cell stack may include a bipolar plate assembly positioned between adjacent fuel cells of the fuel cell stack, and the bipolar plate assembly may have a cathode flow channel on one side to provide oxidant to one fuel cell and an anode flow channel on the opposite side to provide fuel to the adjacent fuel cell.

[0004] In some applications of fuel cell stacks, such as transportation applications, bipolar plate assemblies are made from graphite due to its high corrosion resistance, high chemical stability, and high thermal conductivity. However, because graphite exhibits better mechanical properties only at large thicknesses, bipolar plate assemblies made from graphite can be relatively thick. The increased thickness can increase the size and weight of the fuel cell stack. Furthermore, the increased size and weight make it difficult to assemble the components of the fuel cell stack.

[0005] Fuel cells must be maintained within a specific temperature range to ensure satisfactory performance. However, chemical reactions occurring within each fuel cell release heat, thereby increasing the temperature of the fuel cell. To maintain the temperature of the fuel cell, coolant flow field plates may be provided within the fuel cell stack adjacent to some of the fuel cells. The coolant flow field plates include flow channels for circulating the coolant. However, providing coolant flow field plates increases the weight of the fuel cell stack. Furthermore, as the number of fuel cells increases, the number of coolant flow field plates also increases. This can result in an increased size of the fuel cell stack. Furthermore, configuring coolant flow field plates adjacent to some fuel cells results in cooling some fuel cells and leaving some fuel cells uncooled. This uneven cooling across the fuel cell stack reduces the performance of the fuel cell stack.

[0006] In some scenarios, air may be used as both a coolant and an oxidant, and a common manifold is provided for the oxidant and the coolant. Therefore, the coolant and the oxidant may need to be provided to the fuel cell stack with the same flow rate. In some scenarios, the oxidant and the coolant may need to be provided at different flow rates within the fuel cell stack. In particular, as the temperature of the fuel cell increases, the coolant flow rate may need to be increased to decrease the temperature of the fuel cell without increasing the oxidant flow rate. Having a common manifold for both the oxidant and the coolant may prevent the oxidant and the coolant from being provided at different flow rates, which may reduce the performance of the fuel cell stack. To prevent the common manifold from affecting the performance of the fuel cell, separate manifolds for the coolant and the oxidant are provided. However, in such cases, separate ducts for the oxidant and the coolant should be used. The use of separate ducts for the oxidant and the coolant increases the manufacturing and maintenance costs of the fuel cell. [Means for solving the problem]

[0007] The present invention relates to a bipolar plate assembly for a fuel cell stack. [Effects of the Invention]

[0008] Using embodiments of the present invention, the weight of the bipolar plate assembly and the weight of the fuel cell stack can be reduced. Furthermore, the use of separate coolant flow field plates can be eliminated. Moreover, uniform cooling can be produced across the fuel cell stack, thereby increasing fuel cell performance. [Brief explanation of the drawings]

[0009] [Figure 1a] 1 is a perspective view of a fuel cell stack according to one embodiment of the present invention; [Figure 1b] 1 is a side view of a fuel cell stack according to one embodiment of the present invention; [Figure 2] 1 is an exploded view of a fuel cell stack according to one embodiment of the present invention. [Figure 3] FIG. 2 is an exploded view of a first fuel cell and bipolar plate assembly according to one embodiment of the present invention. [Figure 4] FIG. 2 is an exploded view of a bipolar plate assembly according to one embodiment of the present invention. [Figure 5a] FIG. 1 is a perspective view of a bipolar plate assembly according to one embodiment of the present invention. [Figure 5b] FIG. 5b is a cross-sectional view of a bipolar plate assembly along section AA of FIG. 5a, according to one embodiment of the present invention. [Figure 6a] FIG. 2 is a perspective view of an anode flow field plate of a bipolar plate assembly according to one embodiment of the present invention. [Figure 6b] FIG. 6b is an enlarged view of a portion of the diagram shown in FIG. 6a, according to one embodiment of the present invention. [Figure 6c] FIG. 2 is a rear view of an anode flow field plate of a bipolar plate assembly according to one embodiment of the present invention. [Figure 7] FIG. 2 illustrates an anode flow field plate of a bipolar plate assembly according to one embodiment of the present invention. [Figure 8] FIG. 2 is a rear view of an anode flow field plate of a bipolar plate assembly according to one embodiment of the present invention. [Figure 9] FIG. 2 illustrates an anode flow field plate of a bipolar plate assembly according to one embodiment of the present invention. [Figure 10] FIG. 1 illustrates an anode gasket of a bipolar plate assembly according to one embodiment of the present invention. [Figure 11] FIG. 2 illustrates a cathode flow field plate of a bipolar plate assembly according to one embodiment of the present invention. [Figure 12] FIG. 2 is a perspective view of a cathode flow field plate of a bipolar plate assembly according to one embodiment of the present invention. [Figure 13] FIG. 1 illustrates a cathode gasket of a bipolar plate assembly according to one embodiment of the present invention. [Figure 14] FIG. 2 shows a membrane electrode assembly (MEA) of a fuel cell stack according to one embodiment of the present invention. [Figure 15] FIG. 2 shows a first current collector plate of a fuel cell stack according to one embodiment of the present invention. [Figure 16] FIG. 2 illustrates an inlet end plate of a fuel cell stack according to one embodiment of the present invention. [Figure 17a] 1 is a diagram illustrating a fuel cell system according to one embodiment of the present invention. [Figure 17b] 1 is an exploded view of a fuel cell system according to one embodiment of the present invention; [Figure 18] 1 illustrates a fuel cell stack according to one embodiment of the present invention. [Figure 19] 1 illustrates a fuel cell stack according to one embodiment of the present invention. [Figure 20] 1 is an exploded view of a fuel cell stack according to one embodiment of the present invention; [Figure 21] FIG. 2 is an exploded view of a bipolar plate assembly positioned between a first fuel cell and a second fuel cell, according to one embodiment of the present invention. [Figure 22] FIG. 2 is a perspective view of an anode flow field plate of a bipolar plate assembly according to one embodiment of the present invention. [Figure 23] FIG. 23 is an enlarged view of a portion of the diagram shown in FIG. 22, according to one embodiment of the present invention. [Figure 24] FIG. 2 illustrates an anode flow field plate of a bipolar plate assembly according to one embodiment of the present invention. [Figure 25] FIG. 2 shows an MEA of a fuel cell stack according to one embodiment of the present invention. [Figure 26a] FIG. 2 is a front view of a first current collector plate of a fuel cell stack according to an embodiment of the present invention. [Figure 26b]FIG. 2 is a rear view of a first current collector plate of a fuel cell stack according to an embodiment of the present invention. [Figure 27a] FIG. 2 is a front view of an inlet end plate of a fuel cell stack according to one embodiment of the present invention. [Figure 27b] 2 is a cross-sectional view of an inlet end plate of a fuel cell stack according to one embodiment of the present invention. [Figure 28a] FIG. 2 is a front view of an outlet end plate of a fuel cell stack according to one embodiment of the present invention. [Figure 28b] 2 is a cross-sectional view of an outlet endplate of a fuel cell stack according to one embodiment of the present invention. [Figure 29] FIG. 2 illustrates a recirculation unit for a fuel cell stack according to one embodiment of the present invention. [Figure 30] 1A-1D illustrate a method of manufacturing a bipolar plate assembly according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The detailed description is provided with reference to the accompanying drawings, in which the leftmost digit(s) of a reference number identifies the figure in which the reference number first appears, and the same numbers are used throughout the drawings to reference like features and components.

[0011] According to an exemplary embodiment, a bipolar plate assembly for a fuel cell stack includes a cathode flow field plate and an anode flow field plate. The cathode flow field plate may include a first cathode surface and a second cathode surface. The second cathode surface may be opposite the first cathode surface. The first cathode surface may have a first plurality of ribs. Flow channels may be defined between two adjacent ribs. The flow channels function as paths for an oxidant for a first fuel cell of the fuel cell stack. The flow channels on the first cathode surface may be referred to as the first plurality of flow channels. The oxidant may be, for example, air. The second cathode surface may have a second plurality of ribs. The flow channels may be defined between two adjacent ribs. The flow channels function as paths for a coolant. The flow channels on the second cathode surface may be referred to as the second plurality of flow channels. The coolant may be, for example, air.

[0012] The second plurality of channels can be complementary to the first plurality of ribs, and the second plurality of ribs can be complementary to the first plurality of channels. For example, the formation of ribs on the first cathode surface causes the formation of channels on the second cathode surface. Similarly, the formation of channels on the first cathode surface causes the formation of ribs on the second cathode surface.

[0013] Similar to the cathode flow field plate, the anode flow field plate may include a first anode surface and a second anode surface. The second anode surface may be opposite the first anode surface. The first anode surface may have a third plurality of ribs. Flow channels may be defined between two adjacent ribs. The flow channels function as paths for fuel for a second fuel cell in the fuel cell stack. The flow channels on the first anode surface may be referred to as the third plurality of flow channels. The fuel may be, for example, hydrogen. The second anode surface may have a fourth plurality of ribs. The flow channels on the second anode surface may function as paths for coolant. The flow channels on the second anode surface may be referred to as the fourth plurality of flow channels. The fourth plurality of flow channels may be complementary to the third plurality of ribs, and the fourth plurality of ribs may be complementary to the third plurality of flow channels. That is, the formation of ribs on the first anode surface causes the formation of flow channels on the second anode surface. The formation of flow channels on the first anode surface causes the formation of ribs on the second anode surface. The cathode flow feed plate and the anode flow field plate may be bonded together such that the second cathode surface faces and contacts the second anode surface. In one example, the cathode flow field plate and the anode flow field plate may be bonded together by laser welding.

[0014] In one example, the flow field plate may be made of metal. To achieve a given mechanical strength of the flow field plate, the metal flow field plate may have a relatively smaller thickness than a graphite flow field plate. The lower thickness of the metal flow field plate may facilitate complimentary structures of the channels and ribs.

[0015] The bipolar plate assembly may further include a first inlet manifold and a second inlet manifold. The first inlet manifold may receive an oxidant, a coolant, or both from a first source. In one example, the first inlet manifold may receive both the oxidant and the coolant from a source such as a blower. The second inlet manifold may receive fuel from a second source.

[0016] The present invention eliminates the use of separate coolant flow field plates by having coolant channels on the cathode flow field plate and the anode flow field plate. Therefore, the size of the fuel cell stack is reduced. Furthermore, by having such a configuration of coolant channels, the present invention ensures uniform cooling across the fuel cell stack. Therefore, the present invention enhances fuel cell performance. Also, because the thickness of the bipolar plate assembly is smaller, the present invention reduces the weight of the fuel cell stack and facilitates easy assembly of the fuel cell stack components. Using embodiments of the present invention, a common manifold can be used for the oxidant and coolant. Therefore, the present invention avoids the use of additional components, such as separate ducts for the oxidant and coolant, and reduces the cost of manufacturing the fuel cell stack.

[0017] The present invention is further described with reference to Figures 1a-30. It should be noted that the description and illustrations merely illustrate the principles of the invention. Various configurations can be devised that incorporate the principles of the invention, although not explicitly described or shown herein. Moreover, all statements herein reciting principles, aspects, and examples of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.

[0018] FIG. 1a shows a perspective view of a fuel cell stack 100 according to one embodiment of the present invention. The fuel cell stack 100 may include multiple fuel cells 102. The fuel cell stack 100 may be, for example, a low-temperature polymer electrolyte membrane fuel cell stack (LTPEMFC stack) or a high-temperature polymer electrolyte membrane fuel cell stack (HTPEMFC stack). In each fuel cell, a chemical reaction may occur between a fuel and an oxidant. The chemical reaction may convert the chemical energy of the fuel and the oxidant into electrical energy. Accordingly, a fuel and an oxidant may be supplied to each fuel cell. The fuel may be, for example, hydrogen. The oxidant may be, for example, air. Furthermore, the temperature of the fuel cell stack 100 may need to be maintained within a temperature range for satisfactory performance of the fuel cell stack 100. The performance of the fuel cell stack 100 may be measured by the electrical energy produced by the fuel cell stack 100 for a given amount of fuel and oxidant. To provide optimal performance, an LTPEMFC stack may need to be maintained at a temperature range of 30°C to 80°C, and an HTPEMFC stack may need to be maintained at a temperature range of 80°C to 160°C. However, the chemical reactions occurring within each fuel cell may increase the temperature of the fuel cell. To maintain the temperature of the fuel cell stack 100, a coolant is circulated within the fuel cell stack. The coolant may be, for example, air.

[0019] The fuel cell stack 100 may include an inlet end plate 103 positioned at a first end of the fuel cell stack 100 and an outlet end plate 104 positioned at another end of the fuel cell stack 100. The fuel cells 102 may be positioned between the inlet end plate 103 and the outlet end plate 104. The inlet end plate 103 may facilitate the entry of fuel, oxidant, and coolant into the fuel cell stack 100. Accordingly, the inlet end plate 103 may include a first inlet 106-1 through which fuel is provided to the fuel cell stack 100, and second inlets 106-2 and third inlets 106-3 through which oxidant and coolant are provided to the fuel cell stack 100. Furthermore, the first inlet 106-1 may be displaced in a direction perpendicular to the center of the inlet end plate 107 from the second inlet 106-2 and from the third inlet 106-3. The outlet endplate 104 may facilitate the removal of fuel, oxidant, and coolant. Thus, the outlet endplate 104 may include a first outlet 108-1 through which excess fuel is removed from the fuel cell stack 100, and second and third outlets 108-2, 108-3 through which excess oxidant and coolant are removed from the fuel cell stack 100. The locations of the outlets on the outlet endplate 104 may be similar to the locations of the inlets on the inlet endplate 103. That is, the second outlet 108-2 and the third outlet 108-3 may be positioned adjacent to one another. Furthermore, the first outlet 108-1 may be displaced from the second outlet 108-2 and the third outlet 108-3 in a direction perpendicular to the center of the outlet endplate 104 (not shown in FIG. 1a).

[0020] Fuel cell stack 100 may further include tie rods 109 and bolts 110 for assembling the components of fuel cell stack 100. In one example, fuel cell stack 100 may include guides 111, which may facilitate assembling the components of fuel cell stack 100 together.

[0021] 1b shows a side view of a fuel cell stack 100 according to one embodiment of the present invention. The fuel cell stack 100 may include multiple current collectors, which may collect electrical current from each fuel cell. For example, the fuel cell stack 100 may include a first current collector 112-1 and a second current collector 112-2. The first current collector 112-1 may be positioned adjacent to the inlet end plate 103, and the second current collector 112-2 may be positioned adjacent to the outlet end plate 104. In one example, a component such as a wire may be connected between the first current collector 112-1 and the second current collector 112-2 to extract electrical energy from the fuel cell stack 100.

[0022] FIG. 2 illustrates an exploded view of a fuel cell stack 100 according to one embodiment of the present invention. The plurality of fuel cells 102 includes fuel cells, such as a first fuel cell 202-1, a second fuel cell 202-2, and a third fuel cell 202-3. The fuel cell 202-2 is disposed at one end of the fuel cell stack 100, and the fuel cell 202-3 is disposed at the opposite end of the fuel cell stack 100. To provide fuel and oxidant to each fuel cell, the fuel cell stack 100 may include multiple bipolar plate assemblies, such as 204-1, 204-2, and 204-3, to provide oxidant or fuel to the fuel cells. For example, the bipolar plate assembly 204-1 may provide oxidant to the first fuel cell 202-1 and fuel to the second fuel cell 202-2. Thus, the bipolar plate assembly 204-1 may be positioned between two adjacent fuel cells, i.e., between the first fuel cell 202-1 and the second fuel cell 202-2. Bipolar plate assemblies 204-1, 204-2, 204-3 may be referred to as bipolar plate assembly 204. Each bipolar plate assembly 204 may have a cathode flow field plate (not shown in FIG. 2) that provides oxidant to one fuel cell and an anode flow field plate (not shown in FIG. 2) that provides fuel to another fuel cell.

[0023] In one example, fuel cells 202-2, 202-3 may be provided with oxidant or fuel by adjacent bipolar plates, so that fuel cells 202-2, 202-3 at the ends of fuel cell stack 100 may need to be provided with either fuel or oxidant. For example, fuel cell 202-3 may be provided with oxidant by bipolar plate assembly 204-2 and may need to be provided with fuel for a chemical reaction to occur in fuel cell 202-3. Similarly, a second fuel cell 202-2 may be provided with fuel by bipolar plate assembly 204-1 and may need to be provided with oxidant for a chemical reaction to occur in second fuel cell 202-2. Thus, to provide either fuel or oxidant to fuel cells 202-2, 202-3 at the ends of fuel cell stack 100, fuel cell stack 100 may include unipolar flow field plates, such as unipolar cathode flow field plate 210 and unipolar anode flow field plate 212. For example, the monopolar cathode flow field plate 210 may be disposed between the first current collector 112-1 and the second fuel cell 202-2 and may provide oxidant to the second fuel cell 202-2, and the monopolar anode flow field plate 212 may be disposed between the second current collector 112-2 and the third fuel cell 202-3 and may provide fuel to the third fuel cell 202-3.

[0024] In one example, the unipolar flow field plate and a portion of the bipolar plate assembly may form part of a fuel cell. For example, the unipolar cathode flow field plate 210 and the anode flow field plate of the bipolar plate assembly 204-1 may form part of the second fuel cell 202-2. Similarly, the unipolar anode flow field plate 212 and the cathode flow field plate of the bipolar plate assembly 204-2 may form part of the fuel cell 202-3.

[0025] As previously mentioned, the fuel cell stack 100 may include tie rods 109 and guides 111 to facilitate fastening the components of the fuel cell stack 100. The tie rods 109 may hold the components of the fuel cell stack 100 together and may extend from the inlet endplate 103 to the outlet endplate 104 without passing through the bipolar plate assembly of the fuel cell stack 100. Accordingly, to facilitate insertion of the tie rods 109, the inlet endplate 103 may include provisions such as openings 214, and the outlet endplate 104 may include provisions such as openings 216 that facilitate insertion of the tie rods 109. The tie rods may extend between openings on the inlet endplate 103 and corresponding openings on the outlet endplate 104 and may be fastened using bolts. In one example, the dimensions of the inlet end plate 103 and the outlet end plate 104 may be larger than the dimensions of the bipolar plate assembly, the fuel cell 102, the current collector plates 112-1, 112-2, and the monopolar flow field plates 210, 212. As will be appreciated, the dimensions of the bipolar plate assembly, the fuel cell, and the monopolar flow field plates 210, 212 may be substantially similar. The openings on the inlet end plate 103 and the outlet end plate 104 through which the tie rod 109 passes may be provided on portions of the end plates 103, 104 that do not contact the monopolar flow field plates 210, 212 to ensure that the tie rod 109 does not pass through the monopolar flow field plates 210, 212, the current collector plates 112-1, 112-2, the bipolar plate assembly, and the fuel cell. Additionally, the inlet endplate 103 may include guide tool holes 218, and the outlet endplate 104 may include guide tool holes (not shown in FIG. 2 ) to facilitate insertion of the guide tools 111. The guide tools may extend from the guide tool holes on the inlet endplate 103, pass through the components of the fuel cell stack 100, and to corresponding guide tool holes on the outlet endplate 104. The guide tools 111 can align the bipolar plate assemblies and MEAs during assembly. As will be appreciated, some fuel cells in the fuel cell stack 100 may receive fuel from one bipolar plate assembly and oxidant from an adjacent bipolar plate assembly.

[0026] 3 is an exploded view of a first fuel cell 202-1 and bipolar plate assemblies 204-1, 302-1 according to one embodiment of the present invention, where the first fuel cell 202-1 is positioned between the bipolar plate assemblies 302-1, 204-1. The bipolar plate assembly 204-1 may provide oxidant to the first fuel cell 202-1, and the bipolar plate assembly 302-1 may provide fuel to the first fuel cell 202-1.

[0027] As previously mentioned, bipolar plate assembly 204 may include a cathode flow field plate and an anode flow field plate. For example, cathode flow field plate 306 and anode flow field plate 308 may be part of bipolar plate assembly 204-1, and cathode flow field plate 310 and anode flow field plate 312 may be part of bipolar plate assembly 302-1. The cathode flow field plate and anode flow field plate may face and contact each other.

[0028] The anode flow field plate 308 may face the second fuel cell 202-2 (not shown in FIG. 3) and may provide fuel to the second fuel cell 202-2. The cathode flow field plate 306 may face the first fuel cell 202-1 and may provide oxidant to the first fuel cell 202-1. The anode flow field plate 312 may face the first fuel cell 202-1 to provide fuel to the first fuel cell 202-1, and the cathode flow field plate 310 may face another fuel cell (not shown in FIG. 3) to provide oxidant to that fuel cell.

[0029] As will be appreciated, a portion of bipolar plate assembly 204-1 and a portion of bipolar plate assembly 302-1 may form part of first fuel cell 202-1. That is, anode flow field plate 312 and cathode flow field plate 306 may be part of first fuel cell 202-1. First fuel cell 202-1 may include a membrane electrode assembly 314, in which a chemical reaction between fuel and oxidant occurs. MEA 314 may include a cathode 316 on a first side and an anode on a side opposite the first side. In the illustrations shown herein, the anode may be behind cathode 316. Cathode 316 may receive oxidant from cathode flow field plate 306, and the anode may receive fuel from anode flow field plate 312. Thus, the anode may face the bipolar plate assembly 302-1, and the cathode 316 may face the bipolar plate assembly 204-1. Additionally, the MEA 314 may include a polymer electrolyte membrane (PEM) (not shown in FIG. 3) positioned between the cathode 316 and the anode. The MEA 314 may also include multiple gas diffusion layers (not shown in FIG. 3). A gas diffusion layer may be positioned between the cathode flow field plate 306 and the cathode 316, and a gas diffusion layer may be positioned between the anode flow field plate 312 and the anode. The gas diffusion layers may diffuse reactant gases, such as fuel and oxidant, across the anode and cathode 316, respectively, to facilitate chemical reactions across the surface of the cathode 316 and across the surface of the anode.

[0030] During operation, at the anode, hydrogen provided by the anode flow field plate 312 may be split into hydrogen ions and electrons. The hydrogen ions may pass through the PEM to reach the cathode 316. Meanwhile, the electrons may not be allowed to pass through the PEM. Electrons from the anode of each fuel cell may reach the first current collector 112-1 (not shown in FIG. 3). From the first current collector 112-1, these electrons may flow through an external circuit to the second current collector 112-2 (not shown in FIG. 3). This provides power to the external circuit. From the second current collector 112-2, the electrons may reach the cathode of each fuel cell. At the cathode 316, the hydrogen ions, electrons, and oxygen from the oxidant may react to form water and release heat energy.

[0031] In one example, cathode flow field plate 306 and anode flow field plate 308 may be welded together. The welding may be performed, for example, on the anode flow field plate, where weld seam 318 may be on anode flow field plate 308 and weld seam 320 may be on anode flow field plate 312.

[0032] Additionally, bipolar plate assembly 204-1 may include a gasket 322 (referred to as an anode gasket) on anode flow field plate 308 to prevent fuel leakage, and a gasket 324 (referred to as a cathode gasket) on cathode flow field plate 306 to prevent oxidant leakage. Similarly, bipolar plate assembly 302-1 may include an anode gasket 326 on anode flow field plate 312 and a cathode gasket 328 on cathode flow field plate 310.

[0033] The bipolar plate assemblies may be described with reference to bipolar plate assembly 204-1. However, it will be understood that the bipolar plate assemblies may be described with reference to other bipolar plate assemblies of fuel cell stack 100.

[0034] FIG. 4 illustrates an exploded view of a bipolar plate assembly 204-1 according to one embodiment of the present invention. The cathode flow field plate 306 may include a first cathode surface (not shown in FIG. 4) and a second cathode surface 402. The second cathode surface 402 may be opposite the first cathode surface. The first cathode surface may have a first plurality of ribs (not shown in FIG. 4). A flow channel (not shown in FIG. 4) may be defined between two adjacent ribs to serve as a pathway for an oxidant for the first fuel cell 202-1. The flow channels on the first cathode surface may be referred to as a first plurality of flow channels. The second cathode surface 402 may have a second plurality of ribs 404. A flow channel may be defined between two adjacent ribs to serve as a pathway for a coolant. The channels, such as channels 406-1, 406-2, and 406-3, on the second cathode surface 402 may be collectively referred to as a second plurality of channels 406. The formation of ribs on the first cathode surface causes the formation of channels on the second cathode surface 402. The formation of channels on the first cathode surface causes the formation of ribs on the second cathode surface 402. Thus, the second plurality of channels 406 may be complementary to the first plurality of ribs, and the second plurality of ribs 404 may be complementary to the first plurality of channels.

[0035] The anode flow field plate 308 may include a first anode surface 408 and a second anode surface (not shown in FIG. 4). The second anode surface may be opposite the first anode surface 408. The first anode surface 408 may have a third plurality of ribs 410. Flow channels may be defined between two adjacent ribs. The flow channels, such as 412-1, 412-2, and 412-3, on the first anode surface 408 may be referred to as a third plurality of flow channels 412. The third plurality of flow channels 412 may function as paths for fuel for the second fuel cell 202-2. The second anode surface may have a fourth plurality of ribs (not shown in FIG. 4). Flow channels may be defined between two adjacent ribs to function as paths for coolant. The flow channels on the second anode surface may be referred to as a fourth plurality of flow channels (not shown in FIG. 4). In one example, the first and second plurality of flow paths 406 may be oriented perpendicular to the third and fourth plurality of flow paths 412 and 414 .

[0036] The formation of ribs on the first anode surface 408 causes the formation of channels on the second anode surface. The formation of channels on the first anode surface 408 causes the formation of ribs on the second anode surface. Thus, the fourth plurality of channels can be complementary to the third plurality of ribs 410, and the fourth plurality of ribs can be complementary to the third plurality of channels 412.

[0037] As previously mentioned, the cathode flow field plate 06 and the anode flow field plate 308 may face each other and may be in contact with each other. In particular, the second cathode surface 402 may face and be in contact with the second anode surface.

[0038] To achieve a predetermined mechanical strength of the flow field plates, each flow field plate may have a small thickness. For example, a metal sheet having a thickness ranging from 50 microns to 100 microns may be stamped to form flow field plates having a thickness of 0.3 mm to 1 mm. In one example, each flow field plate may have a thickness of 0.8 mm. Thus, each bipolar plate assembly 204, including a cathode flow field plate and an anode flow field plate, may have a thickness of 1.6 mm. Flow field plates made from metals having a small thickness may possess properties such as high mechanical strength, high electrical conductivity, high thermal conductivity, and high gas impermeability, along with their small thickness. The small thickness of metal flow field plates may facilitate the efficient construction of channels and ribs. That is, the formation of channels on one surface of a flow field plate by the formation of ribs on another surface of the flow field plate is achieved by using flow field plates with a small thickness. Thus, in one example, the cathode flow field plate 306 and the anode flow field plate 308 may be made from metal.

[0039] Additionally, for each fuel cell, a coolant may need to be circulated through the fuel cell stack to prevent the temperature of the fuel cell from increasing due to chemical reactions. In the present subject matter, the bipolar plate assembly may facilitate the flow of coolant through the second plurality of flow paths 406 and through the fourth plurality of flow paths. Thus, the present subject matter reduces the size and weight of the fuel cell stack 100 when compared to scenarios in which the fuel cell stack uses separate coolant plates to facilitate the flow of coolant through the fuel cell stack.

[0040] Additionally, when the cathode flow field plate 306 and the anode flow field plate 308 are assembled, the first openings 422 in the cathode flow field plate 306 and the second openings 424 in the anode flow field plate 308 form a first inlet manifold 426. The first inlet manifold 426 may receive an oxidant, a coolant, or both from a first source (not shown in FIG. 4), such as a blower, through the second inlet 106-2 (not shown in FIG. 4) and the third inlet 106-3 (not shown in FIG. 4). Thus, to provide the oxidant and the coolant, the first inlet manifold 426 may be coupled to the first plurality of flow paths, to the second plurality of flow paths 406, and to the fourth plurality of flow paths.

[0041] Furthermore, when the cathode flow field plate 306 and the anode flow field plate 308 are assembled, the third opening 428 of the cathode flow field plate 306 and the fourth opening 430 of the anode flow field plate 308 may together form a second inlet manifold 432. The second inlet manifold 432 may receive fuel from a second source. For example, the second inlet manifold 432 may receive fuel from a fuel source through the first inlet 106-1 (not shown in FIG. 4 ). Thus, to provide fuel, the second inlet manifold 432 may be coupled to the third plurality of flow channels 412. In particular, the fourth opening 430 may be coupled to an inlet of the third plurality of flow channels 412.

[0042] The first inlet manifold 426 and the second inlet manifold 432 may be positioned perpendicular to one another when viewed from the center of the bipolar plate assembly 204-1. For example, the first opening 422 may be offset from the second opening 424 on the cathode flow field plate 306 relative to the center of the cathode flow field plate 306 (not shown in FIG. 4 ), and the second opening 424 may be offset from the fourth opening 430 on the anode flow field plate 308 relative to the center of the anode flow field plate 308. Positioning the first inlet manifold 426 perpendicular to the second inlet manifold 432 may prevent mixing of the fuel and oxidant.

[0043] The oxidant and coolant entering the fuel cell stack 100 through the second inlet 106-2 and the third inlet 106-3 may reach each fuel cell through a first inlet manifold 426 in the bipolar plate assembly 204-1 for supply to the fuel cell 202-1 (not shown in FIG. 4). The fuel entering the fuel cell stack 100 through the first inlet 106-1 may reach each bipolar plate assembly 204-1 through a second inlet manifold 432 for supply to the fuel cell 202-1 (not shown in FIG. 4).

[0044] Additionally, in an assembled state, i.e., when the cathode flow field plate 306 and the anode flow field plate 308 are assembled together, the fifth opening 438 in the cathode flow field plate 306 and the sixth opening 440 in the anode flow field plate 308 may together form a first outlet manifold 441. Similarly, the seventh opening (not shown in FIG. 4 ) in the cathode flow field plate 306 and the eighth opening 442 in the anode flow field plate 308 may together form a second outlet manifold 443. The first outlet manifold 441 may remove oxidant and coolant from the bipolar plate assembly 204-1. The second outlet manifold 443 may remove excess fuel from the bipolar plate assembly 204-1.

[0045] The cathode flow field plate 306 and the anode flow field plate 308 may be joined together by welding on the first anode surface 408. The welding may be, for example, a continuous weld performed on the first anode surface 408. The continuous weld performed on the first anode surface 408 may prevent leakage that may be caused by an increase in pressure within the fuel cell stack 100. The welding may be performed on the first anode groove 444 on the first anode surface 408. As a result of the welding, a weld seam 318 may be formed on the first anode groove 444. An anode gasket 322 may be positioned on the weld seam 318 to prevent fuel leakage. For example, a liquid sealant may be poured onto the weld seam and allowed to solidify to form the anode gasket 322 on the first anode surface 408. Similar to the anode flow field plate 308, the cathode flow field plate 306 may include a first cathode groove (not shown in FIG. 4 ). A cathode gasket 324 may be positioned over the first cathode groove to prevent oxidant leakage. To ensure that the welds of the bipolar plate assembly 204-1 are intact, continuous welds may be applied adjacent the edge of the anode flow field plate 308 and around the second inlet manifold 432 and the second outlet manifold 443. Additionally, welds may be applied around the first inlet manifold 426 and the first outlet manifold 441 to facilitate coolant entry and removal from the second plurality of flow channels 406 and the fourth plurality of flow channels. In particular, continuous welds may be applied around three sides of the first inlet manifold 426 and three sides of the first outlet manifold 441, respectively. Additionally, welding may not be performed on the fourth side 445 of the first inlet manifold and on the fourth side 446 of the first outlet manifold 441. Welding may prevent leakage of coolant from the second anode surface and the second cathode surface 402. Thus, welding may prevent the use of gaskets between the anode and cathode flow field plates.Providing welds around three sides of the first inlet manifold 426 and no welds around the fourth side creates a gap between the second anode surface and the second cathode surface 402. The gap between the second anode surface and the second cathode surface 402 streamlines the flow of coolant.

[0046] In one example, instead of welding on the anode flow field plate 308, welding may be performed on the cathode flow field plate 306. For example, welding may be performed on the first cathode groove. This causes the formation of a weld seam (not shown in FIG. 4 ) on the first cathode groove. In such an example, a cathode gasket 324 may be placed on the weld seam. For example, a liquid sealant may be poured on the weld seam and allowed to solidify to form the cathode gasket 324 on the first cathode surface. In such an example, an anode gasket 322 may be placed on the first anode groove 444. In the present invention, a single groove (i.e., either the first anode groove 444 or the first cathode groove) may be used for both welding and sealing purposes. Thus, the present subject matter may increase the flow field area for fuel and oxidant and simplify the manufacturability of bipolar plate assemblies.

[0047] FIG. 5a shows a perspective view of the bipolar plate assembly 204-1 of the fuel cell stack 100 according to one embodiment of the present invention. The first cathode surface may include a first plurality of ribs 500-1, 500-2, 500-3 and a first plurality of channels 502-1, 502-2, 502-3. The plurality of ribs 500-1, 500-2, 500-3 may be collectively referred to as the first plurality of ribs 500. The first plurality of channels 502-1, 502-2, 502-3 may be collectively referred to as the first plurality of channels 502. The first plurality of channels 502 may function as a pathway for oxidant for the fuel cell 202-1 (not shown in FIG. 5). Additionally, the oxidant may enter the first plurality of channels 502 through the first inlet manifold 426. Accordingly, the inlets of the first plurality of flow channels 502 may be coupled to the first inlet manifold 426. Further, through the first outlet manifold 441, excess oxidant may exit the bipolar plate assembly 204-1. Accordingly, the outlets of the first plurality of flow channels 502 may be coupled to the first outlet manifold 441. Through the second inlet manifold 432, fuel may enter the third plurality of flow channels 412. Accordingly, the inlets of the third plurality of flow channels 412 may be coupled to the second inlet manifold 432. Further, through the second outlet manifold 443, excess fuel may exit the bipolar plate assembly 204-1. Accordingly, the outlets of the third plurality of flow channels 412 may be coupled to the second outlet manifold 443. In particular, the eighth opening 442 may be coupled to the outlets of the third plurality of flow channels 412 to facilitate removal of excess fuel from the bipolar plate assembly 204-1.

[0048] Figure 5b shows a cross-sectional view of bipolar plate assembly 204-1 along section AA of Figure 5a, according to one embodiment of the present invention. In the view shown here, anode flow field plate 308 is above cathode flow field plate 306. Here, enlargements 504, 505 show portions of the cross-sectional view.

[0049] In the enlarged view 504, the first plurality of ribs 500 is complimentary to the second plurality of channels 406, and the first plurality of channels 502 is complimentary to the second plurality of ribs 404. Channels 502-1, 502-2, 502-3 are shown in the figures herein. As will be appreciated, the third plurality of channels 412 and the fourth plurality of channels are not visible in the views shown herein because the cross-sectional view is along section AA, which is a direction parallel to the first plurality of channels.

[0050] As shown in enlarged view 505, an anode gasket 322 may be disposed over the weld seam 318 of the first anode surface 408. The anode gasket 322 may prevent leakage of fuel. Similarly, a cathode gasket 324 may be disposed over the first cathode groove 510 of the first cathode surface 512. The cathode gasket 324 may prevent leakage of oxidant.

[0051] 6a shows a perspective view of the anode flow field plate 308 of the bipolar plate assembly 204-1 in accordance with one embodiment of the present invention. The third plurality of ribs 410 may be in a serpentine pattern. Accordingly, the third plurality of channels 412 may be in a serpentine pattern. Furthermore, the fourth plurality of ribs (not shown in FIG. 6) and the fourth plurality of channels (not shown in FIG. 6) are complementary to the third plurality of channels 412 and the third plurality of ribs 410, respectively, such that the fourth plurality of ribs and the fourth plurality of channels may be in a serpentine pattern.

[0052] Fuel entering the inlets of the third plurality of flow channels 412 through the second inlet manifold 432 may follow a serpentine path and reach the gas diffusion layer positioned adjacent to the anode flow field plate 308. As will be appreciated, in the illustrations shown herein, the gas diffusion layer may be disposed above the anode flow field plate 308. Fuel that does not reach the gas diffusion layer may reach the outlets of the third plurality of flow channels 412 and exit the bipolar plate assembly 204-1 through the second outlet manifold 443.

[0053] Furthermore, the second opening 424 and the fourth opening 430 of the anode flow field plate 308 may be disposed perpendicular to one another when viewed from the center 604 of the anode flow field plate 308. Similarly, the sixth opening 440 and the eighth opening 442 of the anode flow field plate 308 may be disposed perpendicular to one another when viewed from the center 604 of the anode flow field plate 308. This may facilitate the fuel manifold and the oxidant manifold being perpendicular to one another. Therefore, mixing of the fuel and the oxidant within the bipolar plate assembly 204-1 may be prevented.

[0054] The first inlet manifold 426 and the second inlet manifold 432 may be disposed perpendicular to one another when viewed from the center of the bipolar plate assembly 204-1. As previously mentioned, guides 111 (not shown in FIG. 6a) may facilitate assembly of the various components of the fuel cell stack 100. Accordingly, the anode flow field plate 308 may have a plurality of guide holes 608 that facilitate insertion of the guides 111.

[0055] FIG. 6b shows an enlarged view of the portion of the diagram shown in FIG. 6a, according to one embodiment of the present invention. A rib- and channel-free area 609 may be formed on the first anode surface 408 to prevent fuel flow on the second anode surface (not shown in FIG. 6b). The area 609 may be closer to the fourth opening 430 than the center 604 (not shown in FIG. 6b) of the anode flow field plate 308. The area 609 may be referred to as a first flat area. The first flat area 609 may be provided over a predetermined length near the fourth opening 430. Furthermore, a rib 410-1 that is part of the third plurality of ribs 410 may extend from the first flat area 609. The positioning of the first flat area 609 and the rib 410-1 may ensure that fuel entering the third plurality of flow channels 412 from the fourth opening 430 does not flow across the second anode surface (not shown in FIG. 6b), as will be described with reference to FIG. 6c.

[0056] FIG. 6c shows a rear view of the anode flow field plate 308 of the bipolar plate assembly 204-1 according to one embodiment of the present invention. The second anode surface 610 is shown. The fourth plurality of ribs 612 may be complementary to the third plurality of channels 412 (not shown in FIG. 6c), and the fourth plurality of channels 614 may be complementary to the third plurality of ribs 410 (not shown in FIG. 6c). Displacement of the ribs 410-1 from the second inlet manifold 432 may displace the paths 614-1 of the fourth plurality of channels 614 a distance from the second inlet manifold 432. The first flat area 609 (not shown in FIG. 6c) has a corresponding area 616 formed on the second anode surface 610. The area 616 may be closer to the second inlet manifold 432 than to the center 604 (not shown in FIG. 6c) of the anode flow field plate 308. Area 616 may be free of ribs and channels and may hereinafter be referred to as the second flat area. Area 616 may alternatively be referred to as the anode flat area.

[0057] Similar to the anode flow field plate 308, the cathode flow field plate 310 (not shown in FIG. 6c) may include a region on the first cathode surface 512. The region on the first cathode surface 512 may be closer to the third opening 428 than the center of the cathode flow field plate 310. The region may be free of ribs and channels and may be referred to as a third flat region. The cathode flow field plate 310 may include a region on the second cathode surface 402 (not shown in FIG. 6c). The region on the second cathode surface 402 may be closer to the third opening 428 than the center of the cathode flow field plate 310. Furthermore, the region on the second anode surface 402 may be free of ribs and channels and may be referred to as a fourth flat region. The fourth flat region may alternatively be referred to as a cathode flat region. As will be appreciated, the formation of the third flat region may cause the formation of a fourth flat region. The fourth flat area may be positioned on the cathode flow field plate 310 at a location corresponding to the location of the second flat area 616 on the anode flow field plate 312. Thus, the bipolar plate assembly 204-1 may be welded such that the second flat area 616 faces and contacts the fourth flat area of ​​the second cathode surface 402. Because fuel enters through the second inlet manifold 432, the weld may prevent the fuel from flowing over the second anode surface 610. That is, fuel reaching the second inlet manifold 432 may enter the first anode surface 408 and may not reach the second anode surface 610 due to the weld. Thus, the present invention prevents mixing of the fuel and coolant.

[0058] In some cases, the gas diffusion layer adjacent to the anode flow field plate 308 may be damaged due to factors such as increased temperature or excessive compression during assembly of the fuel cell stack components. Additionally, in some cases, the hydrogen fuel may be humidified to maintain hydration of the MEA in order to improve fuel cell performance. As a result, water clogging may occur within the third plurality of flow channels 412. Water clogging may lead to blockage of the path for the hydrogen fuel. Therefore, in such instances, to prevent blockage of the anode flow field plate 308, the anode flow field plate 308 may include an additional path for the fuel, as described below.

[0059] FIG. 7 illustrates the anode flow field plate 308 of the bipolar plate assembly 204-1 according to one embodiment of the present invention. To prevent fuel blockage within the anode flow field plate 308, the anode flow field plate may include a bypass path 700 between adjacent ribs of the third plurality of ribs 410. For example, a first rib 702-1 and a second rib 702-2 may be disconnected and displaced from one another, with the bypass path 700 formed between the first rib 702-1 and the second rib 702-2 at the displaced portions. The bypass path 700 may function as an additional path for fuel. If one or more flow paths of the third plurality of flow paths 412 are blocked, the fuel may enter the bypass path 700 to flow to another path that may not be blocked. For example, consider fuel flowing through flow path 706-1 and moving toward flow path 706-2. Further, consider flow path 706-2 to be blocked. Fuel flowing from flow path 706-1 may pass through bypass path 700 to reach flow path 706-3, which may prevent fuel flow from being impeded by blockage of flow path 706-2.

[0060] FIG. 8 illustrates a rear view of the anode flow field plate 308 of the bipolar plate assembly 204-1 according to one embodiment of the present invention. Here, the second anode surface 610 is illustrated. In one example, the ribs on the first anode surface 408 (not shown in FIG. 8) may be disposed adjacent to the second inlet manifold 432 without a flat area between the second inlet manifold 432 and the ribs. As will be appreciated, the ribs may be part of a third plurality of ribs 410 (not shown in FIG. 8). A third plurality of flow channels 412 (not shown in FIG. 8) may extend from the second inlet manifold 432. Due to the formation of the third plurality of ribs 410 extending from the second inlet manifold 432, a fourth plurality of flow channels 614 may extend from the second inlet manifold 432 on the second anode surface 610. Because the fourth plurality of flow channels 614 extends from the second inlet manifold 432, fuel arriving at the second inlet manifold 432 may enter the fourth plurality of flow channels 614 on the first anode surface 408 (not shown in FIG. 8 ). As will be appreciated, the extension of the third plurality of ribs 410 from the second inlet manifold 432 may prevent intrusion of fuel on the second anode surface 610. Thus, fuel may flow over the first anode surface 408 and may not flow over the second anode surface 610.

[0061] However, in some examples, fuel may still enter the second anode surface 610. To prevent fuel flow on the second anode surface 610, the ribs extending from the second inlet manifold 432 on the first anode surface 408 (not shown in FIG. 8 ) may be discontinuous. The ribs extending from the second inlet manifold 432 on the first anode surface 408 may be referred to as third ribs. The third ribs may have a discontinuity closer to the second inlet manifold 432 than the center 604 of the anode flow field plate 308 (not shown in FIG. 8 ). As will be understood, the discontinuity is devoid of ribs and flow channels. The discontinuity may be referred to as a fifth flat area. In some examples, the fifth flat area may also function as an additional path for fuel flow on the first anode surface 408.

[0062] Due to the discontinuity of the third rib, the flow passage 802 extending from the second inlet manifold 432 may have a discontinuity 804. The flow passage 802 may be part of the fourth plurality of flow passages 614 and may have a discontinuity closer to the second inlet manifold 432 than the center 604 of the anode flow field plate 308. The flow passage 802 may be referred to as a first flow passage. The first flow passage 802 may be complementary to the third rib. The discontinuity 804 in the first flow passage 802 may be devoid of a rib and a flow passage and may be referred to as a sixth flat area. The sixth flat area 804 may prevent further flow of fuel over the second anode surface 610. For example, fuel entering the second anode surface 610 through the first flow passage 802 may be blocked by the sixth flat area 804. That is, fuel entering portion 805-1 of first flow path 802 may be blocked by sixth flat area 804 and may not flow into portion 805-2 of first flow path 802. Thus, mixing of fuel and coolant is prevented.

[0063] 9 illustrates the anode flow field plate 308 of the bipolar plate assembly 204-1 in accordance with one embodiment of the present invention. In some instances, both the bypass passage 700 and the discontinuous ribs extending from the second inlet manifold 432 may be omitted. As previously mentioned, the fifth flat area 902 is formed in the third rib 904 between the portion 905-1 of the third rib 904 and the portion 905-2 of the third rib 904. The formation of the fifth flat area 902 on the first anode surface 408 may form the sixth flat area 804 (not shown in FIG. 9 ) on the second anode surface 610 (not shown in FIG. 9 ). Thus, in such an example, as previously mentioned with reference to FIG. 8 , impediment to fuel movement may be prevented by the bypass path 700, and fuel flow on the second anode surface 610 (not shown in FIG. 9 ) may be prevented by the formation of discontinuous ribs closer to the second inlet manifold 432 than to the center 604 of the anode flow field plate 308.

[0064] FIG. 10 illustrates an anode gasket 322 of a bipolar plate assembly 204-1 according to one embodiment of the present invention. In one example, to form the anode gasket 322, a liquid sealant may be applied to the weld seam 318 (not shown in FIG. 10) on the first anode surface 408 (not shown in FIG. 10). Solidification of the liquid sealant forms the anode gasket 322. The liquid sealant may be, for example, acrylated urethane, RTV silicone, Loctite 5883 (polyacrylate), Loctite 5910 (oxime silicone), or any combination thereof. In one example, to prevent fuel leakage, the anode gasket 322 may have different segments, such as 1002-1 through 1002-6, surrounding different portions of the anode flow field plate 308. For example, segment 1002-1 surrounds the first inlet manifold 426, segment 1002-2 extends adjacent to the edge of the anode flow field plate 308, segment 1002-3 surrounds the second inlet manifold 432, segment 1002-4 surrounds the third plurality of flow paths 412, segment 1002-5 surrounds the first outlet manifold 441, and segment 1002-6 surrounds the second outlet manifold 443.

[0065] 11 shows the cathode flow field plate 306 of the bipolar plate assembly 204-1 in accordance with one embodiment of the present invention, where the first cathode surface 512 is shown. Here, the second cathode surface 402 is behind the first cathode surface 512.

[0066] Each of the first plurality of ribs 500 and each of the first plurality of channels 502 may pass between the first inlet manifold 426 and the first outlet manifold 441 on the first cathode surface 512. Thus, each of the first plurality of ribs 500 and each of the first plurality of channels 502 may be parallel to one another. The first inlet manifold 426 may be coupled to the inlets of the first plurality of channels 502 so that the oxidant enters the first plurality of channels 502. For example, the first openings 422 of the cathode flow field plate 306 may be coupled to the inlets of the first plurality of channels 502.

[0067] Additionally, because the ribs and channels on one surface of the flow field plate are complementary to the channels and ribs on the opposing surface of the flow field plate, a second plurality of ribs 404 (not shown in FIG. 11 ) and a second plurality of channels 406 (not shown in FIG. 11 ) may also run from the first inlet manifold 426 to the first outlet manifold 441 on the second cathode surface 402 (not shown in FIG. 11 ). The first inlet manifold 426 may be coupled to the inlets of the second plurality of channels 406 on the second cathode surface 402 such that coolant enters the second plurality of channels 406. For example, the first opening 422 may be coupled to the inlets of the second plurality of channels 406.

[0068] In one example, each of the second plurality of flow paths 406 may be parallel to one another, and the fourth plurality of flow paths 614 may be serpentine. Thus, the coolant entering the bipolar plate assembly 204-1 may have both serpentine and parallel flow. This may ensure that the pressure loss within the bipolar plate assembly 204-1 due to the coolant flow may be smaller. The reduced pressure loss may enhance the performance of the fuel cell.

[0069] Similar to the anode flow field plate 308 (not shown in FIG. 11 ), the cathode flow field plate 306 may also include a plurality of guide tool holes 1102 to facilitate the insertion of guide tools 111 to assemble the various components of the fuel cell stack 100.

[0070] Here, the first cathode groove 510 is shown. As mentioned previously, the cathode gasket 324 may be disposed over the first cathode groove 510. For clarity, the cathode gasket 324 is not shown in this view. In some instances, welding may be performed on the cathode flow field plate 306 to form a weld seam. The first inlet manifold 426 includes weld points around its periphery. In such instances, the cathode gasket 324 may be disposed over the weld seam.

[0071] 12 shows a perspective view of the cathode flow field plate 306 of the bipolar plate assembly 204-1 in accordance with one embodiment of the present invention. The first inlet manifold 426 can provide both oxidant and coolant to the bipolar plate assembly 204-1. The oxidant and coolant provided from a single source (not shown in FIG. 12) can enter the first inlet manifold 426. From the first inlet manifold 426, air can enter the first plurality of flow channels 502 and the second plurality of flow channels 406 (not shown in FIG. 12).

[0072] 13 illustrates the cathode gasket 324 of the bipolar plate assembly 204-1 according to one embodiment of the present invention. In one example, a liquid sealant may be dispensed onto the first cathode groove 510 (not shown in FIG. 13) to form the cathode gasket 324. Solidification of the liquid sealant forms the cathode gasket 324. The liquid sealant may be, for example, acrylated urethane, RTV silicone, Loctite 5883 (polyacrylate), Loctite 5910 (oxime silicone), or any combination thereof.

[0073] To prevent oxidant leakage, the cathode gasket 324 may have different segments, such as 1302-1 and 1302-2, that surround various components of the cathode flow field plate 306 (not shown in FIG. 12 ). For example, segment 1302-1 may surround the first plurality of flow channels 502, the first inlet manifold 426, the first outlet manifold 441, the second inlet manifold 432, and the second outlet manifold 443, while segment 1302-2 may extend adjacent to the edge of the cathode flow field plate 306. FIG. 14 shows an MEA 314 of a fuel cell stack 100 according to one implementation of the present subject matter. The MEA 314 may include an anode 1402 and a cathode 316 behind the anode 1402. A PEM may be positioned between the cathode and the anode. The MEA 314 may include a plurality of guide holes 1404 to facilitate insertion of guides 111 (not shown in FIG. 14). The MEA 314 may also include openings, such as opening 1406 for the inlet of fuel to pass to the adjacent bipolar plate assembly 302-1 (not shown in FIG. 14), and opening 1408 for the inlet of oxidant and coolant to pass to the adjacent bipolar plate assembly 302-1. Similarly, openings 1410, 1412 facilitate the exit of fuel and oxidant removed from the adjacent bipolar plate assembly 302-1 (not shown in FIG. 14) from the fuel cell stack 100.

[0074] FIG. 15 illustrates a first current collector 112-1 of a fuel cell stack 100 according to one embodiment of the present invention. As previously mentioned, electrons flowing from the anode of each bipolar plate may reach the first current collector 112-1 and may flow from the first current collector 112-1 to the second current collector 112-2 (not shown in FIG. 15) through an external circuit, such as a wire connected between the first current collector 112-1 and the second current collector 112-2, which may result in electrical current through the fuel cell stack 100. In this regard, to conduct the flow of electrons, the first current collector 112-1 may include a protrusion 1502. The protrusion 1502 may further include an opening 1504 through which a wire may be coupled.

[0075] Additionally, first current collector 112-1 may include openings, such as opening 1506 to facilitate the flow of fuel, opening 1508 to facilitate the flow of oxidant and coolant, and opening 1510. Additionally, first current collector 112-1 may also include guide hole 1512 to facilitate the insertion of guide 111 (not shown in FIG. 15).

[0076] The second current collector 112-2 may have a similar configuration to the first current collector 112-1. For example, the second current collector 112-2 may also include a protrusion that includes an opening. A wire may be connected between the opening 1504 on the first current collector 112-1 and the opening on the second current collector 112-2. When the fuel cell stack 100 is assembled, the protrusions on the first current collector 112-1 and the second current collector 112-2 may extend beyond the other components of the fuel cell stack 100.

[0077] 16 illustrates an inlet end plate 103 of a fuel cell stack 100 according to one embodiment of the present invention. The inlet end plate 103 may include openings, such as 1602 for the inlet of fuel, and openings 1604 and 1606 for the inlet of air, which is used as both an oxidant and a coolant. Additionally, the inlet end plate 103 may also include openings 214 to facilitate the insertion of tie rods and guide tool holes 218 to facilitate the insertion of guide tools 111 (not shown in FIG. 16 ). In one example, the dimensions of the inlet end plate 103 may be taller than the other components of the fuel cell stack 100.

[0078] In the above examples, the end plates are described with respect to the inlet end plate 103, but the end plates may also be described with respect to the outlet end plate 104. Accordingly, the outlet end plate 104 may include openings for the removal of fuel, oxidant, and coolant, respectively, from the fuel cell stack 100. Additionally, the outlet end plate 104 may include openings for tie rods 109 and guide holes for guides 111. In some examples, the fuel cell stack 100 may be sealed in a casing, as described below.

[0079] FIG. 17a illustrates a fuel cell system 1700 according to one embodiment of the present invention. In one example, the fuel cell stack 100 (not shown in FIG. 17a) may be sealed within a casing 1702 and may be referred to as the fuel cell system 1700. The casing 1702 may be, for example, a metal casing. Chemical reactions occurring within the fuel cell stack 100 may increase pressure within the casing 1702. If the pressure increases beyond a certain value, the fuel cell system 1700 may explode. To avoid pressure buildup within the casing 1702 and prevent an explosion, the fuel cell system 1700 may include a pressure relief valve 1704 disposed within the casing 1702. Additionally, the opening 1706-1 may facilitate coupling of a fuel source to the first inlet 106-1, and the openings 1706-2, 1706-3 may facilitate coupling of an air source to the second inlet 106-2 and the third inlet 106-3.

[0080] FIG. 17b shows an exploded view of a fuel cell system 1700 according to one embodiment of the present invention. The casing 1702 may include multiple segments, such as segments 1708-1, 1708-2, 1708-3, and 1708-4. The segments may be fastened together using, for example, fasteners (not shown in FIG. 17b) to form an enclosure surrounding the fuel cell stack 100. The casing 1702 may include an opening 1709 through which a pressure relief valve 1704 may be coupled to the casing 1702. The fuel cell system 1700 may include a hydrogen sensor 1710 to detect hydrogen leaks. The hydrogen sensor 1710 may be provided within the casing 1702.

[0081] In some examples, as described below, sources of oxidant and coolant, such as an air source, may be positioned above the fuel cell stack 100 .

[0082] 18 shows a fuel cell stack 1800 according to one embodiment of the present invention. In some examples, oxidant and coolant supplies may be coupled to the top of fuel cell stack 1800. Fuel cell stack 1800 may be similar to fuel cell stack 100.

[0083] Similar to fuel cell stack 100, fuel cell stack 1800 may include an inlet end plate 1802 to facilitate the supply of fuel, oxidant, and coolant from their respective sources. Inlet end plate 1802 may include a first inlet (not shown in FIG. 18 ) and a second inlet 1804. The first inlet may supply both oxidant and coolant to fuel cell stack 1800 from a first source 1806, which may be, for example, a blower. Below, the first source may be described with reference to a blower. The first inlet may be coupled to blower 1806. For example, the first inlet may be coupled to a first duct 1808 of the blower. In one example, blower 1806 may be supported by inlet end plate 1802. For example, blower 1806 may be coupled to an upper surface of inlet end plate 1802 using a blower bracket 1810. The second inlet 1804 may provide fuel to the fuel cell stack 1800 from a fuel source (not shown in FIG. 18 ). Accordingly, the second inlet 1804 may be coupled to the fuel source. The fuel cell stack 1800 may further include an outlet end plate 1812. Excess fuel, excess oxidant, and excess coolant from the fuel cell stack 1800 may be removed through the outlet end plate 1812. Accordingly, the outlet end plate 1812 may include a first outlet 1814 and a second outlet 1816. The first outlet 1814 may remove excess hydrogen from the fuel cell stack 1800, and the second outlet 1816 may remove excess air from the fuel cell stack 1800. Furthermore, in one example, the excess air removed from the fuel cell stack 1800 may be recirculated to the fuel cell stack 1800 through a recirculation unit 1818 of the fuel cell stack 1800.

[0084] In the above example, a single inlet (first inlet) is provided for both the oxidant and the coolant. In some examples, separate inlets may be provided for both the oxidant and the coolant. Furthermore, in the above example, the oxidant and the coolant may be provided through a single duct (first duct 1808), and in some examples, the oxidant and the coolant may be provided from separate ducts from the blower 1806.

[0085] FIG. 19 shows a fuel cell stack 1800 according to one embodiment of the present invention. The blower 1806 may include a second duct 1902. In such an example, the inlet end plate 1802 may include a third inlet (not shown in FIG. 19). The second inlet (not shown in FIG. 19) may provide oxidant to the fuel cell stack 1800, and the third inlet may provide coolant to the fuel cell stack 1800. To provide coolant to the fuel cell stack 1800, a first duct 1808 may be coupled to the first inlet, and a second duct 1902 may be coupled to the third inlet.

[0086] The outlet end plate 1812 includes a third outlet (not shown in FIG. 19). The first outlet may remove excess oxidant from the fuel cell stack, and the third outlet may remove excess coolant. Additionally, to recirculate air, an end of a recirculation unit 1818 may be coupled to the third outlet, and another end of the recirculation unit may be coupled to a second duct 1902.

[0087] 20 shows an exploded view of a fuel cell stack 1800 according to one embodiment of the present invention. The fuel cell stack 1800 may include multiple fuel cells, such as a first fuel cell 2002-1 and a second fuel cell 2002-2. The fuel cell stack 1800 may include a bipolar plate assembly 2004, a first current collector 2006-1, and a second current collector 2006-2. The first current collector 2006-1 may be similar to the first current collector 112-1, and the second current collector 2006-2 may be similar to the second current collector 112-2.

[0088] The bipolar plate assembly 2004 may be positioned between the first fuel cell 2002-1 and the second fuel cell 2002-2. The bipolar plate assembly 2004 may provide oxidant to the first fuel cell 2002-1 and fuel to the second fuel cell 2002-2. Thus, the bipolar plate assembly 2004 may include a cathode flow field plate 2008, which may provide oxidant to the first fuel cell 2002-1, and an anode flow field plate 2010, which may provide fuel to the second fuel cell 2002-2. The cathode flow field plate and the anode flow field plate may be made of a metal such as stainless steel. The cathode flow field plate 2008 and the anode flow field plate 2010 may face each other and may be in contact with each other. The bipolar plate assembly 2004 may include multiple gaskets, such as an anode gasket 2012 on the anode flow field plate 2010 to prevent fuel leakage and a cathode gasket 2014 on the cathode flow field plate 2008 to prevent oxidant leakage. Additionally, in one example, the bipolar plate assembly 2004 may include a provision for coolant flow within the bipolar plate assembly 2004. A third gasket 2016 may be disposed between the cathode flow field plate 2008 and the anode gasket 2012 where the cathode flow field plate 2008 and the anode gasket 2012 face each other. The third gasket 2016 may prevent coolant leakage. Additionally, the bipolar plate assembly 2004 may include a cathode edge gasket (not shown in FIG. 20) disposed along the edge of the cathode flow field plate 2008 and an anode edge gasket 2017 disposed along the edge of the anode flow field plate 2010. The edge gaskets may prevent fracture of the bipolar plate assembly 2004 during compression of the fuel cell stack 1800.

[0089] In one example, at the ends of the fuel cell stack 1800, a flow field plate may need to face a fuel cell on only one of its sides and provide fuel or oxidant to that fuel cell. Thus, at the ends of the fuel cell stack 1800, the fuel cell stack 1800 may include monopolar flow field plates, such as a monopolar anode flow field plate 2018-1 and a monopolar cathode flow field plate 2018-2. For example, the monopolar anode flow field plate 2018-1 may be positioned adjacent to the first current collector plate 2006-1 and may provide fuel to the fuel cell 2002-1. The monopolar cathode flow field plate 2018-2 may be positioned adjacent to the second current collector plate 2006-2 and may provide oxidant to the fuel cell 2002-2.

[0090] In one example, the monopolar flow field plates and portions of the bipolar plate assembly 2004 may form part of each fuel cell. For example, the cathode flow field plate 2008 and the monopolar anode flow field plate 2018-1 of the bipolar plate assembly 2004 may be part of the first fuel cell 2002-1. Similarly, the monopolar cathode flow field plate 2018-2 and the anode flow field plate 2010 of the bipolar plate assembly 2004 may form part of the second fuel cell 2002-2.

[0091] Each fuel cell may include an MEA, where chemical reactions occur that convert chemical energy into mechanical energy, where MEA 2019-1 is part of the first fuel cell 2002-1 and MEA 2019-2 is part of the second fuel cell 2002-2, and each MEA may include an anode, a cathode, and a PEM.

[0092] 21 shows an exploded view of a bipolar plate assembly 2004 disposed between a first fuel cell 2002-1 and a second fuel cell 2002-2, according to one embodiment of the present invention. Each MEA may also include a gas diffusion layer (not shown in FIG. 21) adjacent to the cathode and a gas diffusion layer (not shown in FIG. 12) adjacent to the anode. The gas diffusion layers may spread the fuel or oxidant across the anode or anode to have a uniform chemical reaction across the cathode and anode.

[0093] The cathode flow field plate 2008 may include a first cathode surface 2104 and a second cathode surface (not shown in FIG. 21 ). The second cathode surface may be opposite the first cathode surface 2104. The first cathode surface 2104 may include a first plurality of ribs. A flow channel may be defined between two adjacent ribs. The flow channels on the first cathode surface 2104 may be referred to as a first plurality of flow channels 2106. The first plurality of flow channels 2106 may function as a pathway for an oxidant. In one example, the first cathode surface 2104 may face the cathode (not shown in FIG. 21 ) of the MEA 2019-1 to provide oxidant to the cathode. The second cathode surface may include a second plurality of ribs (not shown in FIG. 21 ). A flow channel may be defined between two adjacent ribs. The flow channels on the second cathode surface may be referred to as a second plurality of channels. The second plurality of channels may function as a pathway for a coolant.

[0094] The anode flow field plate 2010 may include a first anode surface (not shown in FIG. 21 ) and a second anode surface 2108. The second anode surface 2108 may be opposite the first anode surface. The first anode surface may include a third plurality of ribs. Flow channels may be defined between two adjacent ribs. The flow channels on the first anode surface may be referred to as a third plurality of channels. The third plurality of channels may function as pathways for fuel. In one example, the first anode surface may face the anode 2102 of the MEA 2019-2 to provide fuel to the anode. The second anode surface 2108 may include a fourth plurality of ribs (not shown in FIG. 21 ). Flow channels may be defined between two adjacent ribs. The flow channels on the second anode surface 2108 may be referred to as a fourth plurality of channels 2110. The fourth plurality of channels 2110 may function as a pathway for a coolant.

[0095] The cathode flow field plate 2008 and the anode flow field plate 2010 are made from a small thickness of metal, and the channels on one side may be complimentary to the ribs on the opposite surface, i.e., a first plurality of ribs may be complementary to a second plurality of channels, the first plurality of channels 2106 may be complementary to the second plurality of ribs, the third plurality of ribs may be complementary to a fourth plurality of channels 2110, and the third plurality of channels may be complementary to the fourth plurality of ribs.

[0096] Additionally, as previously mentioned, anode edge gasket 2017 and cathode edge gasket 2112 may prevent anode flow field plate 2010 and cathode flow field plate 2008 from breaking during compression of the components of fuel cell stack 1800 together.

[0097] 22 shows a perspective view of an anode flow field plate 2010 of a bipolar plate assembly 2004-1 in accordance with one embodiment of the present invention. A first anode surface 2200 is shown. As will be appreciated, the second anode surface 2108 may be behind the first anode surface 2200. The first anode surface 2200 may include a third plurality of ribs, such as 2202-1, 2202-2, and 2202-3, and a third plurality of channels 2204-1, 2204-2, and 2204-3. The third plurality of ribs may be collectively referred to as the third plurality of ribs 2202, and the third plurality of channels may be collectively referred to as the third plurality of channels 2204. In one example, the third plurality of ribs 2202 and the third plurality of channels 2204 are triple serpentine shaped. Because the ribs on one surface are complementary to the channels on the opposite surface and the channels on one surface are complementary to the ribs on the opposite surface, the fourth plurality of ribs and the fourth plurality of channels 2110 can be serpentine shaped. Similarly, the first plurality of ribs (not shown in FIG. 22), the first plurality of channels 2106 (not shown in FIG. 22) can be triple serpentine shaped. Due to the complementarity of the ribs and channels, the second plurality of ribs (not shown in FIG. 22) and the second plurality of channels can be triple serpentine shaped.

[0098] The bipolar plate assembly 2004 may include a first inlet manifold 2206 that provides oxidant and coolant from the blower 1806 (not shown in FIG. 22 ) and a second inlet manifold 2208 that provides fuel from a fuel source (not shown in FIG. 22 ). A first opening (not shown in FIG. 22 ) in the cathode flow field plate 2008 and a second opening 2210 in the anode flow field plate 2010 may together form the first inlet manifold 2206. A third opening (not shown in FIG. 22 ) in the cathode flow field plate 2008 and a fourth opening 2212 in the anode flow field plate 2010 may together form the second inlet manifold 2208. In one example, the first inlet manifold 2206 may be coupled to the inlets of the first plurality of flow channels 2106 (not shown in FIG. 20) to provide oxidant, and the second inlet manifold 2208 may be coupled to the inlets of the third plurality of flow channels 2204. In one example, the first inlet manifold 2206 may be coupled to the inlets of the second plurality of flow channels (not shown in FIG. 24) and the fourth plurality of flow channels 2110 to provide coolant. Further, to remove excess fuel from the bipolar plate assembly 2004, the bipolar plate assembly 2004 may include a first outlet manifold 2214. Similarly, to remove excess oxidant and coolant from the bipolar plate assembly 2004, the bipolar plate assembly 2004 may include a second outlet manifold 2216. The fifth opening (not shown in FIG. 22) in the cathode flow field plate 2008 and the sixth opening 2218 in the anode flow field plate 2010 may together form a first outlet manifold 2214. The seventh opening (not shown in FIG. 22) in the cathode flow field plate 2008 and the eighth opening 2220 in the anode flow field plate 2010 may together form a second outlet manifold 2216.

[0099] In some examples, the coolant and oxidant are provided separately. In such examples, the oxidant may be provided using the first inlet manifold 2206, and excess oxidant may exit using the first outlet manifold 2214. Additionally, the bipolar plate assembly 2004 may include a third inlet manifold 2221-1 through which coolant may be provided to the bipolar plate assembly 2004, and a third outlet manifold 2221-2 through which excess coolant may exit the bipolar plate assembly 2004.

[0100] In one example, the cathode flow field plate 2008 and the anode flow field plate 2010 may be bonded together by welding. For example, the flow field plates may be welded such that the second anode surface 2108 (not shown in FIG. 22) and the second cathode surface may face each other and may be in contact with each other. The weld may be, for example, a spot weld and may be made on the first anode surface 2200. The weld may have to ensure that the bond between the anode flow field plate 2010 and the cathode flow field plate 2008 is intact and that there is sufficient clearance for coolant to flow over the second anode surface 2108 and the second cathode surface. Thus, in one example, spot welds, indicated by weld spot 2226, may be made adjacent the edges of the anode flow field plate 2010, such as the first edge 2222 and the second edge 2224, and around the third inlet manifold 2221-1 and the third outlet manifold 2221-2. The weld spots may prevent leakage of coolant from the bipolar plate assembly 2004. Additionally, the weld spot provided around the third inlet manifold 2221-1 may provide a path for coolant entering through the third inlet manifold 2221-1 to flow into the second and fourth plurality of flow channels 2110. Similarly, the weld spot provided around the third outlet manifold 2221-2 may provide a path for excess coolant to exit the second and fourth plurality of flow channels 2110 through the third outlet manifold 2221-2. Providing spot welds can enhance the electrical conductivity of the bipolar plate assembly 2004 during operation. In some examples, to weld the anode flow field plate 2010 and the cathode flow field plate 2008 together, the weld may be made on the first cathode surface 2104 instead of on the first anode surface 2200.

[0101] The anode gasket 2012 may be disposed on the first anode groove 2230. In one example, the anode gasket 2012 may be shaped similarly to the shape of the gasket 322. The anode edge gasket 2017 may be disposed on the second anode groove 2232. As will be appreciated, a liquid sealant may be disposed on the first anode groove 2230 and the second anode groove 2232 and allowed to solidify to form the gasket. Similar to the anode gasket 2012, the cathode gasket 2014 may be disposed on the first cathode groove (not shown in FIG. 22 ) on the first cathode surface 2104 (not shown in FIG. 22 ). The cathode edge gasket 2112 may be disposed on the second cathode groove (not shown in FIG. 22 ) on the first cathode surface 2104.

[0102] The anode flow field plate 2010 may have a plurality of guide tool holes 2234 to facilitate the insertion of guide tools, which may facilitate assembly of the various components of the fuel cell stack 1800. Similarly, the cathode flow field plate 2008 may have a plurality of guide tool holes to facilitate the insertion of guide tools.

[0103] Similar to bipolar plate assembly 204-1, bipolar plate assembly 2004 may include a bypass path 2236, which may act as an additional path for fuel and prevent fuel blockage.

[0104] 23 shows an enlarged view of a portion of the diagram shown in FIG. 22, according to one embodiment of the present invention. Here, the first anode surface 2200 is shown. A bypass path 2236 may be formed between two adjacent ribs that are displaced from one another. For example, a first rib 2302-1 and a second rib 2302-2 of the third plurality of ribs 2202 are displaced from one another to form the bypass path 2236.

[0105] In some examples, the flow channels may be in different patterns to increase the residence time of the fuel and oxidant to ensure that a maximum amount of fuel and oxidant reaches the respective gas diffusion layers.

[0106] FIG. 24 illustrates an anode flow field plate 2010 of a bipolar plate assembly 2004 according to one embodiment of the present invention. In one example, in addition to having a triple serpentine shape, each rib of the third plurality of ribs 2202 may have a corrugated configuration. Thus, the third plurality of ribs 2202 may be referred to as having a wavy triple serpentine configuration. Because the third plurality of ribs 2202 has a wavy triple serpentine configuration, the third plurality of channels 2204 may have a wavy triple serpentine configuration. Similarly, the first plurality of channels 2106 (not shown in FIG. 24), the second plurality of channels (not shown in FIG. 24), and the fourth plurality of channels 2110 (not shown in FIG. 24) may have a wavy triple serpentine configuration. The wavy triple serpentine configuration may increase the residence time of the fuel and oxidant. That is, the wavy triple serpentine configuration of the channels may increase the time that the fuel and oxidant reside within their respective channels. Thus, the undulating triple serpentine configuration allows more time for the fuel and oxidant to reach the respective gas diffusion layers of the fuel cells before reaching the respective outlet manifolds. Such increased residence time can increase the amount of fuel and oxidant available for reaction. Thus, in the present subject matter, the efficiency of the fuel cell stack 1800 is enhanced.

[0107] FIG. 25 illustrates MEA 2019-1 of fuel cell stack 1800 according to one embodiment of the present invention. Shown here is gas diffusion layer 2500 on MEA 2019-1. As will be appreciated, the anode may be behind gas diffusion layer 2500, the PEM may be behind the anode, the cathode may be behind the PEM, and a first gas diffusion layer may be behind the cathode. The MEA may include openings, such as openings 2502-1 through 2502-6, for the entry and removal of fuel, oxidant, and coolant. Additionally, MEA 2019-1 may also include a plurality of guide holes 2504. While in the examples above, the MEA is described with reference to MEA 2019-1, in some examples, the MEA may be described with reference to MEA 2019-2.

[0108] FIG. 26a shows a front view of the first current collector 2006-1 of the fuel cell stack 1800 according to one embodiment of the present invention.

[0109] Similar to the first current collector 112-1, electrons from the first current collector 2006-1 may flow through an external circuit to the second current collector 2006-2 (not shown in FIG. 26) and become current from the fuel cell stack 1800. In this regard, the first current collector 2006-1 may include a feature 2600, which may include an opening 2602 for connecting wires to a similar opening in the second current collector 2006-2 (not shown in FIG. 26). Additionally, the first current collector 2006-1 may include openings such as 2604-1 through 2604-6 for the inlet and outlet of fuel, oxidant, and coolant. The first current collector may include a plurality of guide holes 2606.

[0110] 26b shows a rear view of the first current collector 2006-1 of the fuel cell stack 1800 according to one embodiment of the present invention. The first current collector 2006-1 may include multiple gaskets to prevent leakage of fuel, oxidant, and coolant. For example, a gasket 2606-1 around the opening 2602-1 corresponding to the fuel inlet to prevent fuel leakage, a gasket 2606-2 around the opening 2602-2 corresponding to the oxidant inlet to prevent oxidant leakage, a gasket 2606-3 around the opening 2602-3 corresponding to the fuel outlet to prevent fuel leakage, a gasket 2606-4 around the opening 2602-4 corresponding to the oxidant outlet to prevent oxidant leakage, a gasket 2606-5 around the opening 2602-5 corresponding to the coolant inlet, and a gasket 2606-6 around the opening 2602-6 corresponding to the coolant outlet to prevent coolant leakage. As can be appreciated, the second current collector 2006-2 may have a similar configuration to the first current collector 2006-1.

[0111] Figure 27a shows a front view of an inlet end plate 1802 of a fuel cell stack 1800 according to one embodiment of the present invention. The inlet end plate 1802 may include a plurality of openings 2700 for insertion of tie rods (not shown in Figure 27) and openings such as 2702-1 through 2702-3 for fuel inlets, oxidant inlets, and coolant inlets, respectively.

[0112] 27b shows a cross-sectional view of an inlet end plate 1802 of a fuel cell stack 1800 according to one embodiment of the present invention, showing a second inlet 1804 through which hydrogen fuel can be provided to the fuel cell stack 1800.

[0113] FIG. 28a shows a front view of an outlet end plate 1812 of a fuel cell stack 1800 according to one embodiment of the present invention.

[0114] Similar to the inlet end plate 1802, the outlet end plate 1812 may include a plurality of openings 2800 for the insertion of tie rods (not shown in FIG. 28a) and a plurality of guide holes 2802 for the insertion of guides (not shown in FIG. 28a), and may include openings such as opening 2804-1 for the outlet of coolant, an opening for the outlet of fuel (not shown in FIG. 28a), and an opening for the outlet of oxidant (not shown in FIG. 28a).

[0115] 28b shows a cross-sectional view of the outlet end plate 1812 of a fuel cell stack 1800 according to one embodiment of the present invention. Shown here is a first outlet 1814 and a second outlet 1816. Excess fuel may exit the fuel cell stack 1800 through the first outlet 1814, and excess air may exit the fuel cell stack 1800 through the second outlet 1816. In one example, excess air exiting the fuel cell stack 1800 may be recirculated within the fuel cell stack 1800 as a coolant through a recirculation unit 1818.

[0116] FIG. 29 illustrates a recirculation unit 1818 of a fuel cell stack 1800 according to one embodiment of the present invention. The recirculation unit 1818 may receive excess oxidant and excess coolant from the fuel cell stack 1800. To receive the excess oxidant and coolant, the recirculation unit 1818 may include an oxidant inlet duct 2902 coupled to the first outlet 1814 and a coolant inlet duct 2904 coupled to a third outlet (not shown in FIG. 29 ). Excess oxidant from the fuel cell stack 1800 may enter the oxidant inlet duct 2902 through the first inlet 2906, and excess coolant from the fuel cell stack 1800 may enter the coolant inlet duct 2904 through the second inlet 2908. Thus, the oxidant air and the coolant air may be mixed together in the duct 2910 of the recirculation unit 1818. Furthermore, the temperatures of the coolant air and the oxidant air may be higher than optimal due to increased temperatures within the fuel cell stack 1800. In this regard, to reduce the temperature of the air within the recirculation unit 1818, the recirculation unit 1818 may include a heat exchanger 2912. The heat exchanger 2912 may cool the air flowing therethrough. In one example, a coolant may flow through the heat exchanger 2912 to reduce the temperature of the air flowing therethrough. As will be appreciated, the coolant flowing through the heat exchanger may remove thermal energy from the air flowing therethrough, reducing the temperature of the air. To facilitate circulation of the coolant through the heat exchanger 2912, the heat exchanger may include a heat exchanger coolant inlet 2914 to facilitate entry of the coolant into the heat exchanger 2912 and a heat exchanger coolant outlet 2916 to facilitate removal of the coolant from the heat exchanger 2912.

[0117] Further, upon flowing through the heat exchanger 2912, the air may exit the recirculation unit 1818 through a coolant outlet 2918. The coolant outlet 2918 may be coupled to a second duct 1902 (not shown in FIG. 29 ) so that the recirculated air may flow back to the fuel cell stack 1800 as a coolant. Through the use of the recirculation unit 1818, the amount of coolant to be circulated inside the fuel cell stack 1800 may be increased without having to increase the power of the blower 1806 that provides the coolant.

[0118] 30 illustrates a method 3000 for manufacturing a bipolar plate assembly for a fuel cell stack, according to one embodiment of the present invention. The order in which the method blocks are described is not intended to be limiting, and some of the described method blocks may be combined in any order to implement method 3000 or alternative methods. Additionally, some of the individual blocks may be deleted from method 3000 without departing from the scope of the inventions described herein.

[0119] In block 3002, a first plurality of ribs and a first plurality of flow channels defined between the first plurality of ribs may be formed on a first cathode surface of a cathode flow field plate of a bipolar plate assembly. The formation of the first plurality of ribs may cause the formation of a second plurality of flow channels on a second cathode surface of the cathode flow field plate, and the formation of the first plurality of flow channels may cause the formation of a second plurality of ribs on the second cathode surface. The second cathode surface may be opposite the first cathode surface. The first plurality of flow channels may function as paths for an oxidant, and the second plurality of flow channels may function as paths for a coolant. The bipolar plate assembly may correspond to bipolar plate assembly 204-1 or bipolar plate assembly 2004. The cathode flow field plate may correspond to cathode flow field plate 306 or cathode flow field plate 2008. The first plurality of ribs may correspond to first plurality of ribs 500. The first plurality of channels may correspond to first plurality of channels 502 or first plurality of channels 2106. The second plurality of ribs may correspond to second plurality of ribs 404. The second plurality of channels may correspond to second plurality of channels 406.

[0120] In block 3004, a first opening on the cathode flow field plate may be provided. The first opening may correspond to first opening 422. In block 3006, a third plurality of ribs and a third plurality of flow channels defined between the third plurality of ribs may be formed on a first anode surface of an anode flow field plate of the bipolar plate assembly. The formation of the third plurality of ribs may cause the formation of a fourth plurality of flow channels on a second anode surface of the anode flow field plate. The formation of the third plurality of flow channels may cause the formation of a fourth plurality of ribs on the second anode surface. The second anode surface may be opposite the first anode surface. The third plurality of flow channels may function as paths for fuel, and the fourth plurality of flow channels may function as paths for coolant. The anode flow field plate may correspond to anode flow field plate 308 or anode flow field plate 2010. The third plurality of ribs may correspond to third plurality of ribs 410 or third plurality of ribs 2202. The third plurality of channels may correspond to third plurality of channels 412 or third plurality of channels 2204. The fourth plurality of ribs may correspond to fourth plurality of ribs 612. The fourth plurality of channels may correspond to fourth plurality of channels 614 or fourth plurality of channels 2110. In block 3008, a second opening may be provided on the anode flow field plate. The second opening may correspond to second opening 424 or second opening 2210.

[0121] In block 3010, the cathode flow field plate and the anode flow field plate may be welded together so that the second cathode surface faces and contacts the second anode surface, and so that the first opening and the second opening together form a first inlet manifold that receives oxidant, coolant, or both from a first source.

[0122] Method 3000 may further include providing a first cathode groove on the first cathode surface and a first anode groove on the first anode surface. The first anode groove may correspond to first anode groove 444 or first anode groove 2230. The first cathode groove may correspond to first cathode groove 510. Furthermore, the cathode flow field plate and the anode flow field plate may be welded together by welding over the first cathode groove. The welding may form a weld seam over the first cathode groove. Moreover, a cathode gasket of the bipolar plate assembly may be provided over the weld seam to prevent oxidant leakage, and an anode gasket of the bipolar plate assembly may be provided over the first anode groove to prevent fuel leakage. The anode gasket may correspond to anode gasket 322 or anode gasket 2012, and the cathode gasket may correspond to cathode gasket 324 or cathode gasket 2014.

[0123] In the above examples, the welding is performed on the first cathode surface. However, in some examples, the welding may be performed on the first anode surface. In such examples, the method 3000 may include providing a first anode groove on the first anode surface and a first cathode groove on the first cathode surface. Further, the cathode flow field plate and the anode flow field plate may be welded together by welding on the first anode groove. The welding may form a weld seam on the first anode groove. Moreover, in such examples, an anode gasket may be provided on the weld seam to prevent fuel leakage, and a cathode gasket may be provided on the first cathode groove to prevent oxidant leakage.

[0124] The present invention eliminates the use of separate coolant flow field plates by having coolant channels on the cathode flow field plate and the anode flow field plate. Therefore, the size of the fuel cell stack is reduced. Furthermore, by having such a configuration of coolant channels, the present invention ensures uniform cooling across the fuel cell stack. Therefore, the present subject matter enhances fuel cell performance. Also, because the thickness of the bipolar plate assembly is smaller, the present invention reduces the weight of the fuel cell stack and facilitates easy assembly of the fuel cell stack components. Using embodiments of the present invention, a common manifold can be used for the oxidant and coolant. Therefore, the present invention avoids the use of additional components, such as separate ducts for the oxidant and coolant, and reduces the cost of manufacturing the fuel cell stack.

[0125] While the present invention has been described with respect to particular embodiments, this specification is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention, will become apparent to those skilled in the art upon reference to the description of the invention.

Claims

1. A bipolar plate assembly (204-1, 204-2, 302-1, 2004) for a fuel cell stack (100, 1800), comprising: a first cathode surface (512, 2104) having a first plurality of ribs (500) and a first plurality of flow channels (502, 2106) defined between the first plurality of ribs (500) to serve as pathways for oxidant for a first fuel cell (202-1, 2002-1) of the fuel cell stack (100, 1800); a cathode flow field plate (306, 310, 2008) comprising: a second cathode surface (402) opposite said first cathode surface (512, 2104) having a second plurality of ribs (404) and a second plurality of flow channels (406) defined between said second plurality of ribs (404) to serve as paths for a coolant, said second plurality of flow channels (406) being complementary to said first plurality of ribs (500) and said second plurality of ribs (404) being complementary to said first plurality of flow channels (502, 2106); a first anode surface (408, 2200) comprising a third plurality of ribs (410, 2202) and a third plurality of flow channels (412, 2204) defined between the third plurality of ribs (410, 2202) to serve as paths for fuel for a second fuel cell (202-2, 2002-2) of the fuel cell stack (100, 1800); a second anode surface (610, 2108) opposite the first anode surface (408, 2200), the second anode surface (610, 2108) having a fourth plurality of ribs (612) and a fourth plurality of flow channels (614, 2110) defined between the fourth plurality of ribs (612) to serve as paths for a coolant, the fourth plurality of flow channels (614, 2110) being complementary to the third plurality of ribs (410, 2202) and the fourth plurality of ribs (612) being complementary to the third plurality of flow channels (412, 2204), the second anode surface (610, 2108) facing and in contact with the second cathode surface (402); an anode flow field plate (308, 312, 2010) comprising: a first inlet manifold (426, 2206) for receiving at least one of the oxidant and the coolant from a first source (1806) provided on the cathode flow field plate (306, 310, 2008); a second inlet manifold (432, 2208) for receiving the fuel from a second source provided on the anode flow field plate (308, 312, 2010); a first outlet manifold (441, 2214) for discharging the oxidant and the coolant; each of the third plurality of flow paths (412, 2204) and each of the fourth plurality of flow paths (614, 2110) are in a serpentine pattern, and the first plurality of flow paths (502, 2106) and the second plurality of flow paths (406) are parallel to each other and extend from the first inlet manifold (426, 2206) to the first outlet manifold (441, 2214); the first inlet manifold (426, 2206) is connected to the inlets of the first plurality of flow paths (502, 2106) and the inlets of the second plurality of flow paths (406); Bipolar plate assembly (204-1, 204-2, 302-1, 2004).

2. 2. The bipolar plate assembly (204-1, 204-2, 302-1, 2004) of claim 1, wherein the first inlet manifold (426, 2206) is connected to the inlets of the first plurality of flow paths (502, 2106) to receive the oxidant, and the bipolar plate assembly (204-1, 204-2, 302-1, 2004) comprises a third inlet manifold (2221-1) connected to the inlets of the second plurality of flow paths (406) to receive the coolant.

3. a weld seam formed on the first cathode groove (510) of the first cathode surface (512, 2104) by welding the anode flow field plate (308, 312, 2010) to the cathode flow field plate (306, 310, 2008); a cathode gasket (324, 328, 2014) on the weld seam to prevent leakage of oxidant; and an anode gasket (322, 326, 2012) on the first anode groove (444, 2230) of the first anode surface (408, 2200) to prevent leakage of the fuel.

4. The bipolar plate assembly (204-1, 204-2, 302-1, 2004) of claim 1, wherein the anode flow field plate (308, 312, 2010) and the cathode flow field plate (306, 310, 2008) are made from metal.

5. The first plurality of ribs (500) a first rib (702-1) and a second rib (702-2) that are not connected and are displaced from each other; The first plurality of flow paths (502, 2106) a bypass passage (700, 2236) between said first rib (702-1) and said second rib (702-2) that serves as an additional path for said fuel; The bipolar plate assembly (204-1, 204-2, 302-1, 2004) of claim 1, comprising:

6. the second inlet manifold (432, 2208) is disposed on the cathode flow field plate (306, 310, 2008) and the anode flow field plate (308, 312, 2010); the second anode surface (610, 2108) comprises an anode flat area (616) closer to the second inlet manifold (432, 2208) than the center (604) of the anode flow field plate (308, 312 2010); the second cathode surface (402) comprises a cathode flat area closer to the second inlet manifold (432, 2208) than to the center of the cathode flow field plate (306, 310, 2008); 2. The bipolar plate assembly of claim 1, wherein the anode flow field plate and the cathode flow field plate are welded together such that the anode flat area faces and contacts the cathode flat area to prevent flow of the fuel over the second anode surface.

7. the third plurality of ribs (410, 2202) a third rib (904) extending from the second inlet manifold (432, 2208) and having a discontinuity (902) closer to the second inlet manifold (432, 2208) than a center (604) of the anode flow field plate (308, 312, 2010); the fourth plurality of flow paths (614, 2110) 2. The bipolar plate assembly of claim 1, comprising: a first flow channel extending from the second inlet manifold and having a discontinuity closer to the second inlet manifold than to the center of the anode flow field plate, the first flow channel being complementary to the third rib, and the discontinuity of the first flow channel being capable of preventing fuel flow over the second anode surface.

8. a first fuel cell (202-1, 2002-1); a second fuel cell (202-2, 2002-2); a bipolar plate assembly (204-1, 204-2, 302-1, 2004) between the first fuel cell (202-1, 2002-1) and the second fuel cell (202-2, 2002-2), a first cathode surface (512, 2104) having a first plurality of ribs (500) and a first plurality of flow channels (502, 2106) defined between said first plurality of ribs (500) to serve as pathways for oxidant for said first fuel cell (202-1, 2002-1); a second cathode surface (402) opposite the first cathode surface (512, 2104) having a second plurality of ribs (404) and a second plurality of flow channels (406) (406) defined between the second plurality of ribs (404) to serve as paths for a coolant, the second plurality of flow channels (406) being complementary to the first plurality of ribs (500) and the second plurality of ribs (404) being complementary to the first plurality of flow channels (502, 2106); a cathode flow field plate (306, 310, 2008) comprising: a first anode surface (408, 2200) comprising a third plurality of ribs (410, 2202) and a third plurality of flow channels (412, 2204) defined between said third plurality of ribs (410, 2202) to serve as paths for fuel for a second fuel cell (202-2, 2002-2); a second anode surface (610, 2108) opposite the first anode surface (408, 2200) having a fourth plurality of ribs (612) and a fourth plurality of flow channels (614, 2110) defined between the fourth plurality of ribs (612) to serve as paths for a coolant, the fourth plurality of flow channels (614, 2110) being complementary to the third plurality of ribs (410, 2202) and the fourth plurality of ribs (612) being complementary to the third plurality of flow channels (412, 2204), and a second cathode surface (402) facing and in contact with the second anode surface (610, 2108); an anode flow field plate (308, 312, 2010) comprising: a first inlet manifold (426, 2206) that receives at least one of the oxidant and the coolant from a blower (1806); a second inlet manifold (432, 2208) for receiving said fuel from a fuel source; a first outlet manifold (441, 2214) for discharging the oxidant and the coolant; each of the third plurality of flow paths (412, 2204) and each of the fourth plurality of flow paths (614, 2110) is in a serpentine pattern; a bipolar plate assembly (204-1, 204-2, 302-1, 2004) in which the first plurality of flow channels (502, 2106) and the second plurality of flow channels (406) are parallel to each other and extend from the first inlet manifold (426, 2206) to the first outlet manifold (441, 2214); said blower (1806) supplying oxidant and coolant; and a fuel cell stack (100, 1800) comprising the fuel source.

9. the first inlet manifold (426, 2206) is capable of receiving both the oxidant and the coolant, the first inlet manifold (426, 2206) is connected to the inlets of the first plurality of flow paths (502, 2106) and the second plurality of flow paths (406), and the fuel cell stack (100, 1800) is a first duct (1808) coupled to the blower (1806) on one end and to the first inlet manifold (426, 2206) on another end for providing the oxidant and the coolant to the fuel cell stack (100, 1800); The fuel cell stack (100, 1800) of claim 8, comprising:

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