FUEL CELL WITH INTEGRATED DIFFUSER DEVICE

Abstract

Fuel cell (4), comprising: a pair of fuel cell plates (10, 12) defining an active area (8) and a supply area (6) of the fuel cell (4); an electrolyte membrane (14) arranged between the pair of fuel cell plates (10, 12) adjacent to the active area (8), wherein the electrolyte membrane (14) is arranged in a layered fashion between an anode (16) and a cathode (18); a pair of gas diffusion media (20) arranged between the electrolyte membrane (14) and the fuel cell plates (10, 12); and a lower sealing element (26) arranged between the pair of fuel cell plates (10, 12) and adjacent to the supply area (6), wherein the lower sealing element (26) has a barrier layer (28) with an elongated primary seal (30) formed integrally with it, wherein the seal (30) has at least an inwardly extending deflection device (32) formed integrally with the primary seal (30) and adapted to counteract reactant bypass flow between the seal (30) and the gas diffusion medium (20), wherein the barrier layer (28) has two opposite sides and is coupled to the electrolyte membrane (14).

Description

FIELD OF THE INVENTION

[0001] The present disclosure relates to a fuel cell and, more particularly, to a subgasket that prevents reactant bypass flow in the fuel cell. BACKGROUND OF THE INVENTION

[0002] A fuel cell has been proposed as a clean, efficient, and environmentally friendly energy source for various applications. Individual fuel cells can be stacked in series to form a fuel cell stack. The fuel cell stack is capable of producing sufficient electricity to power an electric vehicle. In particular, the fuel cell stack has been recognized as a desirable alternative to the conventional internal combustion engine used in modern vehicles.

[0003] One type of fuel cell stack is known as a proton exchange membrane (PEM) fuel cell stack. The typical PEM fuel cell comprises three basic components: a cathode, an anode, and an electrolyte membrane. The cathode and anode typically include a catalyst, such as platinum or another suitable material, to support the electrochemical fuel cell reaction. The electrolyte membrane is sandwiched between the cathode and anode. Porous diffusion media, such as carbon paper and the like, are generally disposed adjacent to the anode and cathode and assist in the delivery and distribution of reactants, such as hydrogen gas and air, to them.

[0004] The hydrogen gas supplied to the fuel cell reacts electrochemically in the presence of the anode to generate electrons and protons. The protons pass through the electrolyte membrane to the cathode, where oxygen from the air reacts electrochemically to generate oxygen anions. The oxygen anions react with the protons to form water as a reaction product. The electrons are transferred from the anode to the cathode through an electrical circuit arranged in between. This electrical circuit enables the fuel cell stack to be used as an electrical power source.

[0005] The electrolyte membrane, the electrodes, and the diffusion media are arranged between a pair of fuel cell plates and sealed, for example, with a subgasket element. The subgasket element typically has an elongated bead seal formed thereon, providing a substantially fluid-tight seal for the fuel cell, as is known from WO 2007 / 007708 A1 and US 2007 / 0264557 A1, wherein the subgasket of WO 2007 / 007708 A1, including the projections formed thereon, is a separate component from the electrolyte membrane. Each fuel cell plate has an active region to which the gaseous reactants are supplied for distribution to the electrodes. The fuel cell plate also includes a supply region configured to supply the gaseous reactants from a supply source to the active region.

[0006] In known fuel cell stacks, the diffusion media and the gasket of the subgasket element are spaced apart to accommodate manufacturing tolerances and prevent overlap of the diffusion media with the gasket. Overlap of the diffusion media and the gasket is known to result in undesirable leakage of gaseous reactants. However, the diffusion media and the spaced-apart gasket form a gap that allows a quantity of the reactants to bypass the active area of ​​the fuel cell plates in a phenomenon known as "reactant bypass flow." Reactant bypass flow is wasteful or uneconomical because the reactant is not delivered to the active area of ​​the fuel cell stack where the electrochemical fuel cell reaction takes place.Reactant bypass flow can also have an undesirable impact on the durability, reliability and performance of the fuel cell stack, particularly at lower reactant stoichiometric ratios when reactant starvation may occur.

[0007] There is a continuing need for a fuel cell with a sub-gasket element that counteracts inefficient reactant bypass flow in a fuel cell stack. The sub-gasket element is designed to direct a higher percentage of reactant to the active areas of the fuel cell stack, optimizing fuel cell stack durability, reliability, and performance during low reactant stoichiometric operation.

[0008] The invention is based on the task of meeting this need. SUMMARY OF THE INVENTION

[0009] This object is achieved with a fuel cell having the features of claim 1 and with a fuel cell stack having the features of claim 16.

[0010] According to the present disclosure, a sub-gasket element has been developed that counteracts inefficient reactant bypass flow in a fuel cell stack, directs a higher percentage of reactant flow to the active regions of the fuel cell stack, and optimizes durability, reliability, and performance of the fuel cell stack during low reactant stoichiometric ratios.

[0011] In another embodiment, a fuel cell stack comprises a plurality of the fuel cells arranged in a stack and having the subgasket member with the elongated primary seal and at least one inwardly extending baffle. DRAWINGS

[0012] 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 below, in which: Fig. 1 shows a schematic exploded perspective view of an illustrative fuel cell stack according to the present disclosure, with only two cells shown; Fig. 2 a fragmentary perspective view of the Fig. 1, showing a seal of the sub-seal element with a deflector; Fig. 3 a side sectional view in elevation of one of the Fig. 1, showing a sub-gasket seal with a canted baffle according to an embodiment of the present disclosure; Fig. 4 a fragmentary plan view of the Fig. 1 showing a plurality of baffles according to another embodiment of the present disclosure; Fig. 5 a fragmentary perspective view of the Fig. 1, further showing the subgasket element assembled with the gas diffusion medium and the electrolyte membrane according to an embodiment of the present disclosure; Fig. 6 a plan view of the Fig. 5 shown sub-sealing element; Fig. 7 a fragmentary perspective view of the Fig. 1, further showing the subgasket element assembled with the gas diffusion medium and the electrolyte membrane according to another embodiment of the present disclosure; Fig. 8 a side sectional view in elevation of the Fig. 7, further assembled with a pair of fuel cell plates and having the deflector on an anode side of the fuel cell; and Fig. 9 a side sectional view in elevation of the Fig. 7, which is further assembled with a pair of fuel cell plates and has the deflector on a cathode side of the fuel cell. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following description is merely exemplary in nature. It should also be understood that corresponding reference characters indicate like or corresponding parts and features throughout the drawings.

[0014] Fig. 1 shows an exemplary fuel cell stack 2 according to the present disclosure. For illustrative purposes, only two fuel cells 4 are shown, it being understood that a typical fuel cell stack 2 includes many more fuel cells 4. The fuel cells 4 are typically stacked together between a pair of clamping plates (not shown) and a pair of unipolar end plates (not shown). Each of the fuel cells 4 has a feed region 6 configured to transport gaseous reactants to or from an active region 8 of the fuel cell 4. An electrochemical reaction occurs at the active region 8 of the fuel cells 4, resulting in the fuel cell stack 2 generating electrical power.

[0015] Each fuel cell 4 includes a pair of first and second fuel cell plates 10, 12. The first and second plates 10, 12 may, for example, be unipolar or bipolar plates having a plurality of flow channels and a plurality of lands formed thereon. The first and second fuel cell plates 10, 12 define the feed region 6 and the active region 8 of the fuel cell 4. For example, the flow channels are configured to deliver gaseous reactants to the active region 8 of the fuel cell 4. The active region 8 is disposed between the first and second plates 10, 12 adjacent the flow channels when the plates 10, 12 are assembled to form the fuel cell 4. Likewise, it should be understood that the feed region 6 is disposed between the first and second plates 10, 12 and adjacent the active region 8 when the fuel cell 4 is assembled.

[0016] The fuel cell 4 comprises an electrolyte membrane 14, an anode 16, and a cathode 18. The anode 16 is disposed on a first side of the electrolyte membrane 14, and the cathode 18 is disposed on a second side of the electrolyte membrane 14. The anode 16 and the cathode 18 sandwich the electrolyte membrane to form a membrane electrode assembly (MEA). The electrolyte membrane 14 is further sandwiched between a pair of gas diffusion media 20. The MEA can be configured as a catalyst-coated membrane (CCM) or a catalyst-coated diffusion media (CCDM), as required. The electrolyte membrane 14 and the gas diffusion media 20 extend substantially to an edge of the active region 8 of the fuel cell 4.

[0017] The fuel cell stack 2 includes a manifold formed by aligning respective manifold openings 22 in the fuel cell plates 10, 12. The manifold is in fluid communication with a source of the gaseous reactant, such as an air compressor or a hydrogen storage tank. The manifold is configured to supply the gaseous reactant to the fuel cell stack 2 as needed. For example, the first fuel cell plate 10 has a plurality of passages 24 formed therein. At least one of the passages 24 is in fluid communication with the manifold. It should be understood that the passages 24 may include an inlet passage configured to supply gaseous reactants to the active region 8 of the fuel cell 4 or an outlet passage configured to remove gaseous reactants from the active region 8.

[0018] The fuel cell 4 includes a subgasket element 26 disposed between the first and second fuel cell plates 10, 12. The subgasket element 26 may be used alone or in conjunction with a polymeric sealing element (not shown), as desired, to provide a substantially fluid-tight seal of the fuel cell 4. The subgasket element 26 is generally disposed within the feed region 6 of the fuel cell 4. The subgasket element 26 includes a barrier layer 28 that counteracts mixing of the various gaseous reactants supplied to the fuel cell 4. In certain embodiments, the barrier layer 28 is formed from a substantially inert polymeric material and coupled to the electrolyte membrane 14. As a non-limiting example, the barrier layer 28 may be coupled to the electrolyte membrane 14 via an adhesive.Other suitable means for coupling the barrier layer 28 to the electrolyte membrane 14 may also be used. In other embodiments, the barrier layer 28 is formed from the same material as the electrolyte membrane 14 and has a laminated or layered structure. For example, a portion of the electrolyte membrane 14 may extend into the feed region 6 and be coated or laminated with a substantially inert material to counteract any undesirable interaction with the first and second fuel cell plates 10, 12. The undesirable interaction may include corrosion of the first and second fuel cell plates 10, 12 as well as damage to the electrolyte membrane 14. Other suitable means for forming the barrier layer 28 may also be used.

[0019] The sub-gasket element 26 includes an elongated primary seal 30 formed on the barrier layer 28. For example, the primary seal 30 may be an elongated bead disposed on the barrier layer 28. The primary seal 30 is integrally formed with the barrier layer 28. The primary seal 30 generally surrounds the feed region 6 and the active region 8 of the fuel cell 4 and counteracts unwanted leakage of the gaseous reactants from the fuel cell 4. The primary seal 30 of the sub-gasket element 26 may be disposed adjacent to the manifold and further counteracts unwanted leakage of the gaseous reactant into the fuel cell 4. It should be noted that when the fuel cell 4 is fully assembled, a gap (in Fig. 3) between the primary seal 30 and the gas diffusion medium 20. The gap is generally used to assist in the substantially fluid-tight sealing of the first and second fuel cell plates 10, 12 in forming the fuel cell 4. However, if this is ignored, the gap acts as a bypass region, facilitating undesirable reactant bypass flow in the fuel cell 4 around the active region 8 from the passages 24 of the first and second fuel cell plates 10, 12.

[0020] As in Fig. 2, the sub-gasket element 26 of the present disclosure includes at least one inwardly extending baffle 32 adapted to counteract reactant bypass flow within the fuel cell 4. For example, the baffle 32 extends laterally inward from the primary seal 30 and toward the active region 8 of the fuel cell 4. In Fig. 2, a pair of baffles 32 are shown having a substantially T-shaped cross-section and disposed on a first side and a second side of the barrier layer 28. In another embodiment, the baffle 32 is a rib having a substantially rectangular cross-section. It should be noted that the baffle 32 may have any cross-sectional shape suitable for counteracting reactant bypass flow by minimizing the gap between the primary seal 30 and the gas diffusion media 20.

[0021] With reference to Fig. 3, the baffle 32 may be canted with respect to the primary seal 30. Canting the baffle 32 may be used to minimize a volume of the gap 33 on either the anode side or the cathode side of the fuel cell 4. For example, the baffle 32 may include a leg 34 that cants the baffle 32 at a desired angle. The baffle 32 may also be canted or biased to either side of the fuel cell 4 due to an asymmetry of the primary seal 30, such as when the primary seal 30 is a double-bead seal having a first bead and a second bead, and the first bead is larger than the second bead.In a particular embodiment, the primary seal 30 is asymmetrical and includes baffles 32 only on the cathode side of the fuel cell 4, which are further biased toward the cathode side of the fuel cell 4 and counteract reactant bypass flow primarily on the cathode side. Those skilled in the art will appreciate that other suitable means for skewing or biasing the baffle 32 with respect to the primary seal 30 may be used.

[0022] The sub-gasket member 26 may include a plurality of baffles 32. Each of the plurality of baffles 32 is intermittently arranged in a spaced-apart arrangement along the primary seal 30. It should be noted that the plurality of baffles 32 arranged in a spaced-apart arrangement does not significantly increase the required compression load for the fuel cell 4, as would occur, for example, if the baffle 32 were arranged in the gap 33 substantially continuously along the primary seal 30.

[0023] The plurality of baffles 32 may be disposed on the first side of the barrier layer 28 and / or the second side of the barrier layer 28, as desired. In certain embodiments, a first portion of the baffles 32 may be disposed on the first side of the barrier layer 28. A second portion of the baffles 32 may be disposed on the second side of the barrier layer 28. The first and second portions of the baffles 32 are disposed in an offset relationship from one another across the barrier layer 28. Regarding the opposed and offset relationship, it should be understood that the barrier layer 28, on which the baffle 32 is disposed, is deflected upon assembly of the fuel cell 4, further minimizing the volume of the gap 33 opposite the baffle 32.Thus, the deflectors 32, which are arranged in opposite and offset relationship, can further counteract the reactant bypass flow in the fuel cell 4.

[0024] In a Fig. 4, one of the deflection devices 32 extends further inward than other of the deflection devices 32. The plurality of deflection devices 32 may be arranged so that, for example, a length is increased in sequence. As best shown in the Fig. 5 and Fig. 6, a portion of the baffles 32 may extend inwardly to a length sufficient for the baffles 32 to contact the gas diffusion media 20. In certain embodiments, at least one of the baffles 32 extends inwardly to abut the gas diffusion media 20 without substantial deflection. In other embodiments, the baffles 32 that contact the gas diffusion media 20 are collapsible and can be pressed, bent, bent, and / or folded against the gas diffusion media 20. The baffles 32 may have a thickness that allows the baffles 32 to be flexible and to be bent against the gas diffusion media 20 under conventional assembly pressures for the fuel cell 4. The contact of the deflection devices 32 with the gas diffusion medium 20 provides a barrier that counteracts the reactant bypass flow.

[0025] In certain embodiments, a portion of the baffles 32 that extends inward toward the gas diffusion medium 20 and is not in contact with the gas diffusion medium 20 causes the reactant bypass flow to assume a tortuous path, such as a serpentine path. The portion of the baffles 32 that is not in contact with the gas diffusion medium 20 also reduces a volume of the gap 33 available for the reactant bypass flow to pass through. Therefore, it should be noted that a portion of the baffles 32 that is not in contact with the gas diffusion medium 20 also counteracts the reactant bypass flow.

[0026] In a further embodiment, which is described in the Fig. 7 to 9, the gas diffusion medium 20 of the fuel cell 4 may have a notch 36 formed therein. The notch 36 receives the baffle 32. It should be noted that the gas diffusion medium 20 may have a plurality of notches 34 adapted to receive the plurality of baffles 32 when assembled to form the fuel cell 4. Suitable dimensions of the notch 36 may be selected as needed, for example, to substantially adapt a cross-sectional shape of the baffle 32. As shown in the Fig. 8 and Fig.As shown in Figure 9, the deflector 32 can be arranged on the first side of the barrier layer 28, for example, the anode side, and / or the second side of the barrier layer 28, for example, the cathode side. It should be noted that the notch 36 allows the deflector 32 to counteract reactant bypass flow while also counteracting undesirable tenting of the deflector 32 that can result when the deflector 32 is in contact with an edge of the gas diffusion medium 20. The notch 36 also counteracts undesirable pressure on the gas diffusion medium 20 that can result from contact of the deflector 32 therewith.

[0027] It has surprisingly been discovered that the use of the deflection device 32 causes a higher percentage of the gaseous reactants supplied to the fuel cell 4 to reach the active region 8. This counteracts uneconomical and inefficient reactant bypass flow. The increased availability of the gaseous reactants at the active region 8 optimizes the long-term durability, reliability, and performance of the fuel cell 4. In particular, at low stoichiometric ratios, where a shortage can otherwise occur, the increased availability of the gaseous reactants counteracts undesirable damage to the fuel cell 4, such as carbon corrosion of the electrodes 16, 18.A voltage drop of the fuel cell 4 at low stoichiometric ratios of the anode and cathode is further counteracted due to the increased availability of the gaseous reactants with the deflection device 32 of the present disclosure.

Claims

[1] Fuel cell (4), comprising: a pair of fuel cell plates (10, 12) defining an active region (8) and a supply region (6) of the fuel cell (4); an electrolyte membrane (14) disposed between the pair of fuel cell plates (10, 12) adjacent to the active region (8), the electrolyte membrane (14) being sandwiched between an anode (16) and a cathode (18); a pair of gas diffusion media (20) disposed between the electrolyte membrane (14) and the fuel cell plates (10, 12); and a sub-gasket element (26) disposed between the pair of fuel cell plates (10, 12) and adjacent the feed region (6), the sub-gasket element (26) comprising a barrier layer (28) having an elongated primary seal (30) integrally formed therewith, the seal (30) comprising at least one inwardly extending baffle (32) integrally formed with the primary seal (30) and adapted to counteract reactant bypass flow between the seal (30) and the gas diffusion medium (20), the barrier layer (28) having two opposing sides and being coupled to the electrolyte membrane (14). [2] Fuel cell according to claim 1, wherein the deflection device (32) is in contact with the gas diffusion medium (20). [3] Fuel cell according to claim 2, wherein the deflection device (32) is pressed, kinked, bent and / or folded. [4] A fuel cell according to claim 1, wherein the barrier layer (28) is inclined toward the anode side or the cathode side of the electrolyte membrane (14). [5] The fuel cell of claim 1, wherein the gas diffusion medium (20) has a notch (36) formed therein that receives the deflector (32). [6] The fuel cell of claim 1, wherein the deflector (32) extends laterally inwardly from the primary seal (30). [7] The fuel cell of claim 1, wherein the primary seal (30) is an elongated bead disposed on the barrier layer (28). [8] Fuel cell according to claim 1, wherein the barrier layer (28) and / or the deflector (32) are inclined with respect to the primary seal (30). [9] Fuel cell according to claim 1, wherein the at least one deflection device (32) comprises a plurality of deflection devices. [10] A fuel cell according to claim 9, wherein one of the deflection means (32) extends further inward than other of the deflection means (32). [11] Fuel cell according to claim 9, wherein the deflection devices (32) are arranged on a first side or a second side of the barrier layer (28). [12] The fuel cell of claim 9, wherein a first portion of the deflection means (32) is disposed on a first side of the barrier layer (28) and a second portion of the deflection means (32) is disposed on a second side of the barrier layer (28). [13] A fuel cell according to claim 12, wherein the first portion of the deflection means (32) is offset with respect to the second portion of deflection means (32). [14] The fuel cell of claim 1, wherein the primary seal (30) is asymmetrical and adapted to bias the barrier layer (28) in a desired direction. [15] The fuel cell of claim 14, wherein the asymmetric primary seal (30) is a double bead seal having a first bead and a second bead, the first bead being larger than the second bead. [16] Fuel cell stack (2) comprising a plurality of fuel cells (4) according to claim 1 arranged in a stack.

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