Bipolar plate for a fuel cell and fuel cell system with a fuel cell stack with such a plate

Abstract

Bipolar plate (2) for a fuel cell, comprising: a first end (4), a second end (6), a first side (8) and a second side (10), the bipolar plate (2) further comprising an active region (12), a supply region (14), a peripheral region (16), a sealing region (18) and a hinge region (20), wherein the peripheral region (16) surrounds the active region (12) and the supply region (14) and wherein the sealing region (18) is arranged between the peripheral region (16) and both the active region (12) and the supply region (14), characterized in that a plurality of outwardly extending tabs (22) are arranged adjacent to the peripheral region (16) at both the first end (4) and the second end (6) of the bipolar plate (2), and the hinge region (20) is disposed between the peripheral region (16) and the outwardly extending tabs (22) at both the first end (4) and the second end (6) of the bipolar plate (2), extends from the first side (8) of the bipolar plate (2) to the second side (10) of the bipolar plate (2) and allows bending of the outwardly extending tabs (22) for connection to at least one peripheral electrical device without undesirably bending the sealing region (18) of the bipolar plate (2), to which: - an average thickness of the hinge region (20) is smaller than an average thickness of the tabs (22) and an average thickness of the peripheral region (16) arranged adjacent to the hinge region (20); - the peripheral region (16) has a raised reinforcement feature (24) and the tabs (22) also have a raised reinforcement feature (24), wherein a portion of the raised reinforcement feature (24) of the tabs is U-shaped, wherein an open end (26) of the U-shaped raised reinforcement feature (24) faces the hinge region (20); - and a score line (32) is formed in the hinge region (20) along a length of the hinge region (20) from the first side (8) to the second side (10) of the bipolar plate (2), the score line (32) assisting in bending the hinge region (20).

Description

FIELD OF THE INVENTION

[0001] The present disclosure relates, inter alia, to a bipolar plate for connection to peripheral electrical equipment of a fuel cell system according to the preamble of claim 1, as known, for example, from JP 2009-217 939 A.

[0002] Further prior art can also be found in US 6 933 069 B2. BACKGROUND OF THE INVENTION

[0003] A fuel cell has been proposed as a clean, efficient, and environmentally friendly energy source for electric vehicles and various other applications. Individual fuel cells can be stacked in series to form a fuel cell stack for various applications. The fuel cell stack is capable of delivering a quantity of electricity sufficient to power a vehicle. In particular, the fuel cell stack has been recognized as a potential alternative to the conventional internal combustion engine used in modern motor vehicles.

[0004] One type of fuel cell is the polymer electrolyte membrane (PEM) fuel cell. The PEM fuel cell comprises three basic components: an electrolyte membrane; and a pair of electrodes comprising a cathode and an anode. The electrolyte membrane is sandwiched between the electrodes to form a membrane electrode assembly (MEA). The MEA is typically sandwiched between porous diffusion media (DM), such as carbon fiber paper, which supports the delivery of reactants, such as hydrogen to the anode and oxygen to the cathode. An MEA and DM pre-assembled together with a subgasket to separate reactant fluids is known as a modular electrode assembly.

[0005] In the electrochemical fuel cell reaction, hydrogen is catalytically oxidized in the anode to produce free protons and electrons. The protons pass through the electrolyte to the cathode. The electrons from the anode cannot pass through the electrolyte membrane and are instead carried as an electric current to the cathode by an electrical load, such as an electric motor. The protons react with the oxygen and electrons in the cathode to produce water.

[0006] The electrolyte membrane is typically formed from a layer of an ionomer. The fuel cell electrodes are generally formed from a finely divided catalyst. The catalyst can be any electrocatalyst that catalytically supports the oxidation of hydrogen or methanol and / or the reduction of oxygen for the electrochemical fuel cell reaction. The catalyst is typically a noble metal, such as platinum or another platinum group metal. The catalyst is generally disposed on a carbon support, such as soot particles, and dispersed in an ionomer.

[0007] The electrolyte membrane, the electrodes, the DM, and a subgasket, for example in the form of the UEA, are arranged between a pair of fuel cell plates. The pair of fuel cell plates form an anode plate and a cathode plate. Each of the fuel cell plates may have a plurality of channels formed therein for distributing the reactants and coolant to the fuel cell. The fuel cell plate is typically formed, for example, by a conventional sheet metal forming process such as stamping or punching, machining, compression molding, or photoetching through a photolithographic mask. In the case of a bipolar fuel cell plate, the fuel cell plate is typically formed from a pair of unipolar plates, which are then joined together to form the bipolar fuel cell plate.

[0008] The fuel cell stack is generally connected to peripheral equipment for transferring electrical power to electric motors and circuitry and for monitoring the performance of the fuel cell stack. Typical peripheral equipment includes cell voltage monitoring (CVM) equipment. Dimensional variations in the various fuel cell components, as well as dimensional variations in the peripheral equipment, can lead to overlap. This overlap results in difficulties in establishing proper electrical connections between the fuel cell stack and the peripheral equipment.

[0009] Previous multi-cell connector-to-plate CVM interface concepts have utilized oversized contact pads or outward-facing contacts in individual rows, individually connected to each bipolar fuel cell plate. Such edge-mounted assembly concepts impose undesirable limitations on the stack repeat distance and thus the number of bipolar fuel cell plates that can be driven by each electrical interconnect board or assembly.

[0010] There is a continuing need for a bipolar fuel cell plate that allows coupling of the bipolar fuel cell plate and peripheral equipment despite dimensional variations. SUMMARY OF THE INVENTION

[0011] According to the invention, a bipolar plate for a fuel cell is presented, wherein the bipolar plate is characterized by the features of claim 1.

[0012] By constructing a hinge region into the bipolar plates of the present disclosure, a cell voltage monitoring tab of each bipolar plate can be deflected to adjust the connector spacing without affecting the load on an adjacent bipolar plate seal. To maintain control of the coarse arrangement of the tabs, the spacing in the finger regions is carefully dimensioned. Rather than attempting to precisely match the spacing, the connector is undersized so that no overlap is created. The connector then narrows the tab spacing to accommodate it. Because certain neighboring connectors overlap in the stacking direction, the overlap ends are not positioned side by side, allowing the plate to twist over a longer span. A wide-spread, narrow-slot arrangement is also used to improve in-plane position control.

[0013] In one embodiment, a bipolar plate for a fuel cell has a first end, a second end, a first side, and a second side. The bipolar plate also has an active region, a feed region, a peripheral region, a sealing region, and a hinge region. The peripheral region surrounds both the active region and the feed region. The sealing region is disposed between the peripheral region and both the active region and the feed region. A plurality of outwardly extending tabs are disposed adjacent to the peripheral region at both the first end and the second end of the plate. The hinge region is disposed between the peripheral region and the outwardly extending tabs at both the first end and the second end of the bipolar plate. The hinge region extends from the first side of the plate to the second side of the bipolar plate.The hinge area allows the outwardly extending tabs to be bent for connection to a peripheral electrical device without undesirably bending the sealing area.

[0014] In another embodiment, a fuel cell stack includes a pair of bipolar plates. The fuel cell stack also includes a modular electrode assembly with a subgasket and a membrane electrode assembly disposed between a pair of diffusion media layers. The membrane electrode assembly and the diffusion media layers are disposed between the bipolar plates to form the fuel cell stack.

[0015] In another embodiment, a fuel cell system includes the fuel cell stack with the bipolar plates. The fuel cell system also includes a plurality of peripheral electrical devices. Each of the peripheral electrical devices has a plurality of electrical connectors. At least a portion of the electrical connectors is in electrical communication with at least a portion of the tabs of the bipolar plates. The hinge region allows the outwardly extending tabs to be bent for connection to the electrical connectors of the peripheral electrical device without undesirably bending the sealing region of the bipolar plates. DRAWINGS

[0016] The above and other advantages of the present disclosure will be readily apparent to those skilled in the art from the following detailed description, particularly with reference to the drawings described herein. Fig. 1 is a fragmentary top perspective view of a bipolar fuel cell plate according to an embodiment of the present invention, wherein the bipolar fuel cell plate is disposed adjacent an electrical connection assembly, for illustrative purposes; Fig. Figure 2 is an enlarged fragmentary plan view of the bipolar fuel cell plate shown in circle 2 of Fig. 1 is shown; Fig. 3 is another enlarged fragmentary plan view of the bipolar fuel cell plate shown in rectangle 3 of Fig. 1 is shown; Fig. 4 is a fragmentary perspective side view of a fuel cell stack having a plurality of the Fig. 1, with some of the bipolar plates omitted for illustrative purposes; and Fig. 5 is a fragmentary perspective side view of the Fig. 4, wherein the electrical connector assemblies are shown in electrical communication with the bipolar plates. DETAILED DESCRIPTION OF THE INVENTION

[0017] The following detailed description and the accompanying drawings describe and illustrate various embodiments of the invention. The description and drawings are intended to enable those skilled in the art to make and use the invention.

[0018] With reference to the Fig. 1 to 5, a bipolar plate 2 of the present disclosure has a first end 4, a second end 6, a first side 8, and a second side 10. The bipolar plate 2 further includes an active region 12, a feed region 14, a peripheral region 16, a sealing region 18, and a hinge region 20. The peripheral region 16 surrounds the active region 12 and the feed region 14. The sealing region 18, also known as a "sealing disk," is disposed between the peripheral region 16 and both the active region 12 and the feed region 14.

[0019] A plurality of outwardly extending tabs 22 are arranged adjacent the hinge region 20 at both the first end 4 and the second end 6 of the bipolar plate 2. The end of the Fig. 1 can be the first end 4 or the second end 6 as needed. Since either the first end 4 or the second end 6 can provide the tabs 22 for electrical connection and the bipolar plate 2 can be reversible, it should be noted that the positioning of the tabs 22 on both the first end 4 and the second end 6 of the bipolar plate 2 simplifies various diagnostics while reducing parts counts during assembly of a fuel cell stack 34 (in the Fig. 4 and Fig. 5 shown) can be saved.

[0020] The hinge portion 20 is disposed between the peripheral portion 16 and the outwardly extending tabs 22 at both the first end 4 and the second end 6 of the bipolar plate 2. The hinge portion 20 extends from the first side 8 of the bipolar plate 2 to the second side 10 of the bipolar plate 2. The hinge portion 20 advantageously allows bending of the outwardly extending tabs 22 for connection to electrical connectors 25 of at least one peripheral electrical device 27 without undesirably bending the sealing portion 18. The undesirable bending of the sealing portion 18 may result in unsealing of the sealing portion 18 and leakage during operation when the bipolar plate 2 is disposed within the fuel cell stack 34.

[0021] In certain embodiments, an average thickness of the hinge region 20 may be less than an average thickness of the tabs 22 and an average thickness of the peripheral region 16, each disposed adjacent to the hinge region 20. It should be understood that the smaller average thickness of the hinge region 20 assists in bending the bipolar plate 2 at the hinge region 20 during manufacture and handling of the bipolar plate 2 and assembly with the peripheral electrical device 27. The thickness of the hinge region 20 is also selected to minimize susceptibility of the bipolar plate 2 to deformation during handling during manufacture. As a non-limiting example, the average thickness of the hinge region 20 is about 150 micrometers, and the average thickness of each of the tabs 22 and the adjacent peripheral region 16 is between about 450 micrometers to about 750 micrometers.A skilled person may select alternative thicknesses of the peripheral region 16, the hinge region 20 and the tabs 22 as required.

[0022] The average thickness of both the peripheral region 16 and the tabs 22 may be based on a raised reinforcement feature 24 disposed thereon. As a non-limiting example, the raised reinforcement features 24 may have a height between about 150 micrometers to about 300 micrometers above the surface of the planar bipolar plate 2, although other heights may be used. When both the peripheral region 16 and the tabs 22 have the raised reinforcement features 24, the hinge region 20 is disposed between the raised reinforcement features 24 of the peripheral region 16 and the tabs.

[0023] The raised reinforcement features 24 on the tabs 22 may also be configured to contact the electrical connectors 25 of the at least one peripheral electrical device 27. For example, as shown in Fig. 2, the raised reinforcement features 24 on the outwardly extending tabs 22 represent a plurality of elongated rows oriented substantially orthogonal to an orientation axis of the outwardly extending tabs 22. Other shapes and orientations of the raised reinforcement features 24 on the peripheral region 16 and the tabs 22 may be used as desired.

[0024] In a Fig. 2, a portion of the raised reinforcement feature 24 of the tabs 22 may be substantially U-shaped. An open end 26 of the U-shaped raised reinforcement feature 24 may be oriented to face the hinge region 20 of the bipolar plate 2. A weld 28 is formed in the U-shaped raised reinforcement feature 24. The weld 28 may be used, at least in part, to join a first unipolar plate to a second unipolar plate to form the modular bipolar plate 2. The weld 28 does not extend into the hinge region 20 because the weld 28 would otherwise undesirably impair the flexibility of the hinge region 20.

[0025] As further stated in Fig. 3, the bipolar plate 2 of the present disclosure may include a recess 30. The recess 30 is disposed in the hinge region on both the first side 8 and the second side 10 of the bipolar plate 2. In certain embodiments, the recess 30 is substantially V-shaped. The bipolar plate 2 may also have a score line 32 formed therein. The score line 32 is formed in a hinge region 20 along a length of the hinge region 20. The score line 32 may extend from the first side 8 to the second side 10 of the bipolar plate 2. Both the recesses 30 and the score line 32 may be stamped into the hinge region 20 as a non-limiting example. It should be noted that the recesses 30 in the bipolar plate 2 and the score line 32 extending between the first and second sides 8, 10 of the bipolar plate 2 assist the desired bending of the hinge region 20.

[0026] Now referring to the Fig. 4 and Fig. 5, the present disclosure further includes the fuel cell stack 34 having a plurality of bipolar plates 2 and a plurality of modular electrode assemblies 36. Each of the modular electrode assemblies 36 includes a subgasket and a membrane electrode assembly disposed between a pair of diffusion media layers. The membrane electrode assembly and the diffusion media layers are disposed between the bipolar plates 2. The bipolar plates 2 and the modular electrode assemblies 36 are stacked in an alternating manner and compressed to form the fuel cell stack 34.

[0027] With particular reference to the Fig. 1 and Fig.5, the present disclosure also includes a fuel cell system 38 having the fuel cell stack 34 and a plurality of peripheral electrical devices 27. Each of the peripheral electrical devices 27 includes the plurality of electrical connectors 25. At least a portion of the electrical connectors 25 are in electrical communication with at least a portion of the tabs 22 of the bipolar plates 2 of the fuel cell stack 34. As further explained hereinabove, the hinge portion 20 allows the outwardly extending tabs 22 to be flexed for connection to the electrical connectors 25 of the peripheral electrical devices 27 without undesirably flexing the seal portion 18 of the bipolar plates 2.

[0028] In a particular embodiment, the peripheral electrical devices 27 are embedded measurement module (EMM) assemblies. The EMM assemblies are arranged in a first vertical row 40 and a second vertical row 42 along one end of the fuel cell stack 34. The EMM assemblies are arranged to eliminate overlap effects. For example, the first vertical row 40 is arranged in a staggered relationship relative to the second vertical row 42. The use of the dual row arrangement has been found desirable for efficient electronics packaging. Because certain electrical connectors 25 on one assembly overlap the electrical connectors 25 on the next assembly in the stacking direction, the overlapping electrical connectors 25 are not positioned side by side, allowing the bipolar plates 2 to twist over an extended span.It should be noted that the use of other peripheral electrical devices 27 is possible.

[0029] An extended protrusion / narrow slot arrangement is used according to the present disclosure to improve position control within the plane of the fuel cell stack 34. For example, each of the portions of the tabs 22 in electrical communication with the electrical connectors 25 may be wider than adjacent slots between the tabs 22 of the bipolar plate 2. The electrical connectors 25 are also narrower than the portions of the tabs 22 in electrical communication with the electrical connectors 25. This minimizes the opportunity for interference between the tabs 22 and the electrical connectors 25 during assembly of the fuel cell system 38.Excessive alignment variation is avoided by pairing an extended protrusion with a narrow slot, providing a single alignment feature in the lateral direction while avoiding redundant and potentially overlapping constraints.

[0030] Advantageously, the bipolar plate 2 of the present disclosure allows coupling of the bipolar plate 2 to the peripheral electrical devices 27 despite variations in tolerances and stack repeat distance.

Claims

[1] Bipolar plate (2) for a fuel cell, comprising: a first end (4), a second end (6), a first side (8) and a second side (10), the bipolar plate (2) further comprising an active region (12), a supply region (14), a peripheral region (16), a sealing region (18) and a hinge region (20), wherein the peripheral region (16) surrounds the active region (12) and the supply region (14) and wherein the sealing region (18) is arranged between the peripheral region (16) and both the active region (12) and the supply region (14), characterized by , that a plurality of outwardly extending tabs (22) are arranged adjacent to the peripheral region (16) at both the first end (4) and the second end (6) of the bipolar plate (2), and the hinge region (20) is disposed between the peripheral region (16) and the outwardly extending tabs (22) at both the first end (4) and the second end (6) of the bipolar plate (2), extends from the first side (8) of the bipolar plate (2) to the second side (10) of the bipolar plate (2) and allows bending of the outwardly extending tabs (22) for connection to at least one peripheral electrical device without undesirably bending the sealing region (18) of the bipolar plate (2), to which: - an average thickness of the hinge region (20) is smaller than an average thickness of the tabs (22) and an average thickness of the peripheral region (16) arranged adjacent to the hinge region (20); - the peripheral region (16) has a raised reinforcement feature (24) and the tabs (22) also have a raised reinforcement feature (24), wherein a portion of the raised reinforcement feature (24) of the tabs is U-shaped, wherein an open end (26) of the U-shaped raised reinforcement feature (24) faces the hinge region (20); - and a score line (32) is formed in the hinge region (20) along a length of the hinge region (20) from the first side (8) to the second side (10) of the bipolar plate (2), the score line (32) assisting in bending the hinge region (20). [2] The bipolar plate of claim 1, wherein at least one of the raised reinforcement features (24) of the tabs (22) is configured to contact adjacent electrical connectors of the at least one peripheral electrical device. [3] The bipolar plate of claim 1, wherein a weld (28) is formed in the U-shaped raised reinforcement feature (24), the weld (28) extending to the hinge region (20). [4] Bipolar plate according to claim 1, comprising a recess (30) formed in the hinge region (20) on the first side (8) and the second side (10) of the bipolar plate (2), the recesses (30) assisting the bending of the hinge region (20). [5] Fuel cell system comprising: a fuel cell stack having a pair of bipolar plates (2), each bipolar plate (2) being formed according to claim 1; a modular electrode assembly (36) comprising a subgasket and a membrane electrode assembly disposed between a pair of diffusion medium layers, the membrane electrode assembly and the diffusion medium layers being disposed between the bipolar plates (2); and a plurality of peripheral electrical devices, each of the peripheral electrical devices having a plurality of electrical connectors, at least a portion of the electrical connectors being in electrical communication with at least a portion of the tabs (22) of the bipolar plates (2).

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