Multi-layer seal for harsh fuel cell applications

Abstract

The invention relates to a multilayer seal for harsh fuel cell applications. A fuel cell stack includes end plate units each having a metal plate, a dielectric plate, and a peripheral groove defined by edges of the dielectric plate and the metal plate. The stack further includes a gas inlet and a coolant inlet configured to receive a reactant gas and a coolant into the fuel cell stack, respectively; a fuel cell having a pair of bipolar plates; and a multilayer seal disposed on the end plate unit or the bipolar plate within the fuel cell stack. The multi-layer seal includes: a first layer constructed from a first material that is substantially impermeable to reactant gases; and a second layer constructed from a second material that is more corrosion resistant than the first material.

Description

Technical Field

[0001] The present disclosure relates to electrochemical fuel cell systems operable to convert gaseous reactants such as hydrogen into electricity. More specifically, aspects of the present disclosure relate to internal sealing of fuel cell systems. Background Art

[0002] Advanced hybrid electric and all-electric vehicles can employ fuel cell systems to generate current suitable for operating one or more electric traction motors. As understood in the art, a hydrogen (H2) fuel cell is an electrochemical device consisting of a negative electrode / anode that receives a supply of gaseous H2, a positive electrode / cathode that receives ambient air as an oxidant, and an electrolyte barrier interposed between the anode and the cathode. The induced electrochemical reaction oxidizes the H2 molecules on the anode side. The H2 gas is catalytically split to generate free electrons and protons. The free protons pass through the electrolyte barrier to the cathode side of the fuel cell and react with oxygen (O2) molecules. Water vapor and heat form inert byproducts of this reaction. The free electrons from the anode are then directed to a connected load, such as the above-mentioned (multiple) electric traction motors and accessories.

[0003] Fuel cell stacks for automotive and other high current applications typically utilize solid polymer electrolyte membranes (PEMs). The PEM provides the aforementioned ion transport between the anode and cathode. The combination of the catalyst layer of the anode, the catalyst layer of the cathode, and the electrolyte membrane defines a membrane electrode assembly (MEA). The MEA is disposed between gas diffusion layers (GDLs). The GDLs are in turn disposed between bipolar plates (BPPs) to form a fuel cell. Multiple fuel cells are assembled into a fuel cell stack to generate the necessary current and voltage for powering a given application. The BPPs collectively define a circuitous flow channel for distributing H2 and O2 reactant gases through the stack. Elastomeric seals or other types of seals (e.g., metal bead seals) are disposed around the edges of the MEA, the surfaces of the BPPs, and the end plate units of the stack to ensure effective separation of reactant and coolant flows while also preventing leakage and mixing of the various gases. Summary of the invention

[0004] A multi-layer seal for use in a fuel cell stack of the type described above is disclosed herein. While the solutions detailed herein may be particularly beneficial when applied to fuel cell systems (FCS) having relatively small size and complex geometry and / or having a variety of design requirements where press-in-place (PIP) seals and other types of seals are not suitable, the present teachings may be extended to larger or less complex FCSs without limitation.

[0005] The multi-layer seals contemplated herein include multiple sealing layers and are therefore suitable for use with FCS under severe application conditions, such as acidic or corrosive operating environments. In some embodiments, the multi-layer seals can be used to seal non-repetitive hardware (NRHW) components (e.g., end units of a fuel cell stack) or to seal repetitive hardware (such as bipolar plates (BPP)). Although adjacent sealing layers can be constructed of the same material, different materials are used in other embodiments to provide additional benefits as described below. The accompanying processes for applying the various sealing layers can also be the same or different, for example, one layer can be applied by a form-in-place gasket (FIPG) process, while other layers can be applied using a room temperature vulcanization (RTV) sealant process or a dispensing process. In addition to other possible embodiments, each sealing layer can be applied using a screen printing or dispensing process, for example for the BPP seals described above.

[0006] Between the sealing layers, the layer-to-layer interface of the structure can be strongly bonded or weakly bonded, or gaps can be formed between the layers to avoid interference between adjacent layers. The geometry, shape and / or thickness of each layer can vary depending on the application, wherein various possible configurations of the multi-layer seal are disclosed in detail below.

[0007] In particular, a fuel cell stack including a pair of end plate units is disclosed herein. Each end plate unit has a metal plate, a dielectric plate, and a peripheral groove defined by the edges of the dielectric plate and the metal plate. The fuel cell stack also includes: a gas inlet and a coolant inlet, which are configured to receive reactant gas and coolant into the fuel cell stack, respectively; a plurality of fuel cells, each of which has a pair of bipolar plates; and a multilayer seal, which is disposed on the end plate unit or the bipolar plate within the fuel cell stack. The multilayer seal includes a first and a second layer. In this embodiment, the first layer is constructed of a first material that is effectively impermeable to reactant gas and coolant. The second layer is constructed of a second material that is more corrosion resistant than the first material.

[0008] The multi-layer seal is disposed between the metal plate and the dielectric plate of each of the end plate units. In one or more embodiments, the bonding strength and maximum tensile elongation of the second layer to the dielectric plate are higher than the bonding strength and maximum tensile elongation of the first material to the dielectric plate.

[0009] The multi-layer seal may include an optional third layer disposed between the first layer and the third layer. The third layer may be constructed of a third material different from the first and second materials. The third material may include air, such that the third layer includes an air gap defined between the first and second layers in this particular non-repeating hardware embodiment. The third material according to aspects of the present disclosure may have a low bonding strength with the first material or the second material or both. The low bonding strength contemplated herein is sufficient to reduce chemical and bonding interference between the first and second layers.

[0010] In one or more embodiments, the bipolar plate may include a bead joint. In such a configuration, the multi-layer seal may include a thin layer seal disposed on a surface of the bead joint.

[0011] The first material of the multi-layer seal may optionally include foamed fluorocarbon-based synthetic rubber (FKM). The second layer may be applied to the surface of the bead joint as solid FKM.

[0012] A fuel cell system (FCS) is also disclosed herein. An example of an FCS includes a reactant supply tank containing a reactant gas, a fuel cell stack in fluid communication with the reactant supply tank and configured to receive a coolant and a reactant gas, and a load. The load is configured to be driven by an electric current from the fuel cell stack. The fuel cell stack includes: a pair of end plate units, each of which has a metal plate, a dielectric plate, and a peripheral groove defined by the dielectric plate and the metal plate; a coolant inlet and a gas inlet, which are configured to receive the coolant and the reactant gas into the fuel cell stack, respectively. The stack also includes a plurality of fuel cells, and each corresponding fuel cell in the plurality of fuel cells includes a bipolar plate. A multilayer seal is disposed in the fuel cell stack, including a first layer constructed of a first material that is effectively impermeable to the reactant gas and the coolant, and a second layer constructed of a second material that is more corrosion-resistant than the first material.

[0013] A method for sealing a fuel cell stack having a plurality of fuel cells disposed between end plate units includes applying a first material as a first layer to an end plate unit or a bipolar plate of the fuel cell. The first layer has low permeability to reactant gases and a specific coolant (e.g., water) used in the fuel cell stack. The method also includes applying a second material as a second layer to the end plate unit or the bipolar plate to form a multilayer seal, wherein the second material is more corrosion resistant than the first material. The method also includes curing the first layer and the second layer to form a multilayer seal.

[0014] In one or more possible embodiments, the method includes applying a third material as a third layer between the first and second layers. In this method, the third material is different from the first and second materials and has a low bonding strength with the first and second materials. The low bonding strength is sufficient to reduce chemical and bonding interference between the first and second layers.

[0015] Applying the first material may optionally include using a form-in-place gasket process, while applying the second material may include using a manual dispensing process.

[0016] The present invention provides the following technical solutions.

[0017] Technical Solution 1. A fuel cell stack, comprising:

[0018] a pair of end plate units, each having a metal plate, a dielectric plate, and a peripheral groove defined by the dielectric plate and the metal plate;

[0019] a coolant inlet and a gas inlet, respectively configured to receive a coolant and a reactant gas into the fuel cell stack;

[0020] a plurality of fuel cells, wherein each respective fuel cell of the plurality of fuel cells comprises a pair of bipolar plates; and

[0021] A multi-layer seal, which is arranged on the end plate unit or the bipolar plate in the fuel cell stack, and the multi-layer seal comprises:

[0022] a first layer constructed of a first material that is substantially impermeable to the reactant gas and the coolant; and

[0023] A second layer is constructed of a second material that is more corrosion resistant than the first material.

[0024] Technical Solution 2. The fuel cell stack according to Technical Solution 1, wherein the multi-layer seal is provided between the metal plate and the dielectric plate of each of the end plate units.

[0025] Technical Solution 3. A fuel cell stack according to Technical Solution 2, wherein the bonding strength and maximum tensile elongation of the second layer to the dielectric plate are higher than the bonding strength and maximum tensile elongation of the first material to the dielectric plate.

[0026] Technical Solution 4. A fuel cell stack according to Technical Solution 1, wherein the multi-layer seal includes a third layer arranged between the first layer and the third layer, and the third layer is constructed of a third material different from the first material and the second material.

[0027] Technical Solution 5. A fuel cell stack according to Technical Solution 4, wherein the third material is air, so that the third layer includes an air gap defined between the first layer and the second layer.

[0028] Technical Solution 6. A fuel cell stack according to Technical Solution 4, wherein the third material has a low bonding strength with the first material and the second material, and the low bonding strength is sufficient to reduce chemical and bonding interference between the first layer and the second layer.

[0029] Technical Solution 7. A fuel cell stack according to Technical Solution 1, wherein the bipolar plates each include a metal bead joint, and wherein the multi-layer seal includes a thin layer seal arranged on the surface of the metal bead joint.

[0030] Technical Solution 8. A fuel cell stack according to Technical Solution 7, wherein the first material of the multi-layer seal comprises foamed fluorocarbon-based synthetic rubber (FKM), and wherein the second layer applied to the surface of the metal bead joint comprises solid FKM.

[0031] Technical solution 9. A fuel cell system (FCS), comprising:

[0032] a reactant supply tank containing a reactant gas;

[0033] a fuel cell stack in fluid communication with the reactant supply tank and configured to receive a coolant and the reactant gas; and

[0034] a load configured to be driven by current from the fuel cell stack, wherein the fuel cell stack comprises:

[0035] a pair of end plate units, each having a metal plate, a dielectric plate, and a peripheral groove defined by the dielectric plate and the metal plate;

[0036] a gas inlet configured to receive reactant gas into the fuel cell stack;

[0037] a coolant inlet configured to receive the coolant into the fuel cell stack;

[0038] a plurality of fuel cells, wherein each respective fuel cell of the plurality of fuel cells comprises a pair of bipolar plates; and

[0039] A multi-layer seal disposed within the fuel cell stack, the multi-layer seal comprising:

[0040] a first layer constructed of a first material that is substantially impermeable to the reactant gas and the coolant; and

[0041] A second layer is constructed of a second material that is more corrosion resistant than the first material.

[0042] Technical Solution 10. The FCS according to Technical Solution 9, wherein the multi-layer seal is disposed between the metal plate and the dielectric plate of each of the end plate units.

[0043] Technical Solution 11. An FCS according to Technical Solution 10, wherein the bonding strength and maximum tensile elongation of the second layer to the dielectric plate and the metal plate are higher than the bonding strength and maximum tensile elongation of the first material to the dielectric plate and the metal plate.

[0044] Technical Solution 12. The FCS according to Technical Solution 9, wherein the multi-layer seal includes a third layer arranged between the first layer and the third layer, and the third layer is constructed of a third material different from the first material and the second material.

[0045] Technical Solution 13. The FCS according to Technical Solution 12, wherein the third material is air, so that the third layer includes an air gap defined between the first layer and the second layer.

[0046] Technical Solution 14. An FCS according to Technical Solution 12, wherein the third material has a low bonding strength with the first material and the second material, and the low bonding strength is sufficient to reduce chemical and bonding interference between the first layer and the second layer.

[0047] Technical Solution 15. An FCS according to Technical Solution 9, wherein each of the bipolar plates includes a metal bead joint, and wherein the multi-layer seal is at least partially formed as a metal bead seal on a surface of the metal bead joint.

[0048] Technical Solution 16. An FCS according to Technical Solution 15, wherein the first material of the multi-layer seal comprises foamed fluorocarbon-based synthetic rubber (FKM), and wherein the second layer applied to the surface of the metal bead joint comprises solid FKM.

[0049] Technical Solution 17. An FCS according to Technical Solution 9, wherein the FCS is part of an electrified powertrain system having an electric traction motor as at least part of the load.

[0050] Technical Solution 18. A method for sealing a fuel cell stack having a plurality of fuel cells disposed between end plate units, comprising:

[0051] applying a first material as a first layer to an end plate unit of the fuel cell, wherein the first layer is substantially impermeable to reactant gases and coolants used in the fuel cell stack;

[0052] applying a second material as a second layer to the end plate unit to form a multi-layer seal, wherein the second material is more corrosion resistant than the first material; and

[0053] The first layer and the second layer are cured to form the multi-layer seal.

[0054] Technical Solution 19. The method according to Technical Solution 18 further includes:

[0055] A third material is applied between the first layer and the second layer as a third layer, wherein the third material is different from the first material and the second material and has a low bonding strength with the first material and the second material, and wherein the low bonding strength is sufficient to reduce chemical and bonding interference between the first layer and the second layer.

[0056] Technical Solution 20. A method according to Technical Solution 18, wherein applying the first material includes using a formed-in-place gasket process, and wherein applying the second material includes using a manual dispensing process.

[0057] The above summary and other features and advantages of the present teachings will become apparent from the following detailed description of some of the best modes and other embodiments for carrying out the present teachings as defined in the appended claims when considered in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 A representative automotive vehicle equipped with a powertrain system having a fuel cell system (FCS) constructed using a multi-layer sealing strategy according to the present disclosure is illustrated.

[0059] Figure 2 A representative fuel cell stack having a multi-layer seal according to the present disclosure is illustrated.

[0060] Figure 3A and Figure 3B yes Figure 1 and Figure 2 1 and 2. Corresponding plan and partial perspective views of a non-repeating hardware (NRHW) section of a fuel cell stack shown in FIG.

[0061] Figure 3C yes Figure 1 and Figure 2 Schematic diagram of a plan view of an exemplary bipolar plate (BPP) of a fuel cell stack shown in FIG.

[0062] Figure 4A , Figure 4B and Figure 4C yes Figure 1 A partial cross-sectional side view illustration of a portion of an NRHW section of a representative FCS shown in FIG. 1 , wherein a multi-layer seal is disposed in a perimeter joint between a steel plate and a representative dielectric plate of the NRHW section.

[0063] Figure 5 Can be used as Figure 1 and Figure 2 A cross-sectional side view of a representative metal bead of a portion of a bipolar plate (BPP) of an exemplary fuel cell stack shown in FIG.

[0064] Fig. 6A and Figure 6B is Figure 1 and Figure 2 The fuel cell stack is applied on top of the metal bead to Figure 3C Schematic diagram of multiple layers of thin sealing materials forming a BPP seal on BPP.

[0065] Fig. 7A and Figure 7B Exemplary pressure distributions on bead seals having different configurations are illustrated.

[0066] Figure 8 A dual layer elastomeric seal according to aspects of the present disclosure is illustrated.

[0067] The present disclosure may be modified or implemented in alternative forms, wherein representative embodiments are shown in the accompanying drawings and described in detail below. The inventive aspects of the present disclosure are not limited to the disclosed embodiments. On the contrary, the present disclosure is intended to cover alternatives within the scope of the disclosure defined by the appended claims. DETAILED DESCRIPTION

[0068] Referring to the drawings, wherein like reference numerals correspond to similar parts throughout the several views, Figure 1 1 shows a motor vehicle 10 equipped with a fuel cell system (FCS) 12. The motor vehicle 10 includes a vehicle body 14 connected to a set of wheels 16. As shown, the motor vehicle 10 is configured as a passenger vehicle, such as a sport utility vehicle, a car, a truck, a motorcycle, etc. However, the FCS 12 can be incorporated into a wide range of vehicles, such as ships, aircraft, rail vehicles, farm equipment, etc., non-vehicle mobile platforms or fixed systems, such as power plants, cranes, etc. Figure 1 The motor vehicle 10 is used hereinafter as an exemplary host system for the FCS 12 , but the present teachings are not limited to such use.

[0069] Figure 1The FCS 12 includes a fuel cell stack 18 having a number of fuel cells 20 arranged therein suitable for the application, wherein an exemplary configuration of the fuel cell stack 18 is Figure 2 The multi-layer seal 15 is disposed in one or more locations within the fuel cell stack 18 and may include, for example, Figures 2 to 4C As shown in FIG. 1 , on or along the interface surfaces of the end plate units 30A and 30B or other non-repeating hardware (NRHW) sections 30, such as Fig. 6A and Figure 6B The bipolar plate 38 ( Figure 2 and Figure 3C ) between adjacent beads 60-1 and / or as Figure 8 , for example, as a press-in-place (PIP) seal or an elastomeric seal. Thus, the use of the multi-layer seal 15 as described increases the sealing integrity and overall durability of the fuel cell stack 18, and thus makes the fuel cell stack 18 more suitable for use in relatively harsh operating environments.

[0070] The multi-layer seal 15, for its part, is applied according to various processes specified herein, thus facilitating manufacturing. As contemplated herein, each respective layer of the multi-layer seal 15 serves a specific sealing function in order to meet a variety of sealing requirements. For example, Figure 3A and Figure 3B As shown in a non-repetitive hardware embodiment, as follows Figure 3B Cutting line 4-4 Figure 4A , Figure 4B and Figure 4C As shown in more detail in , the first layer 45 can be constructed of a first material (A) having a high density to meet hydrogen and coolant permeation requirements (i.e., low permeability / effectively impermeable to H2 and coolant, as defined herein), while the second layer 47 (B) can be used for high acid resistance and coolant corrosion resistance, for example, for sealing the end plate of a fuel cell stack. As used herein, "low permeability" and "effectively impermeable" refer to the ability to be sealed by, for example, or The gas diffusion rate of fluoropolymer materials is lower than that of DOWSIL TM The substantially impermeable material may have a diffusion rate of less than about 0.5-1.5 x 10 -10 (m 2 / s) of the gas permeability (diffusion rate) coefficient, which may be less than about 25% of the permeability coefficient of the second layer 47.

[0071] Likewise, material A may be used to form a primary seal, while material B serves as a protective layer for material A. Different materials may be used within the scope of the present disclosure to construct the respective first and second layers 45 and 47 of material A or B, such as polyolefin elastomers, silicone rubber, ethylene propylene diene monomer (EPDM), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), methyl vinyl silicone, benzyl, various fluoroelastomers / rubbers (moldable or non-moldable), polytetrafluoroethylene (PTFE), etc. These sealants may be cured at room temperature or at elevated temperatures, such as in an oven.

[0072] Except in FIG. 4A to FIG. 4C In addition to forming a peripheral seal in the end plate or other NRHW section 30, the multi-layer seal 15 described below can be combined with the bead seal 60-1 (see Fig. 6A and Figure 6B ) to increase seal thickness and reduce seal sensitivity to contamination. This helps provide a wider seal load range and optimal pressure distribution profile, such as Figure 7B In some embodiments, less expensive materials may be used for the inner layer or other protected or unexposed areas of the seal. The use of multi-layer seals may also reduce seal penetration and increase set loads through a harder and denser inner layer. FIG. 4A to FIG. 8 Such features and benefits are described in more detail.

[0073] Reference again Figure 1 , the motor vehicle 10 is only one possible host system for the FCS 12 and its resident fuel cell stack 18. Other types of vehicles and mobile systems may use a similarly configured FCS 12, for example, ships, rail vehicles, aircraft, farm equipment, mobile platforms, etc. Fixed systems including, for example, power plants, cranes, backup electrical power sources, etc. may also employ the FCS 12 and fuel cell stack 18. Thus, the motor vehicle 10 is an illustrative and non-limiting representative type of host system that can benefit from the sealing techniques described herein.

[0074] Figure 1 The FCS12 uses a fuel cell stack 18 to generate on-board electricity. As understood in the art, air and hydrogen (H2) or another suitable reactant gas 17R are supplied from a reactant supply tank 17 in fluid communication with the fuel cell stack 18, for example, via a series of valves, pressure regulators and accessories (not shown). A suitable coolant 19 is similarly circulated through the fuel cell stack 18 to regulate the temperature of the fuel cell stack 18. The fuel cell stack 18 itself is constructed of a number of fuel cells 20 suitable for the application. The fuel cell stack 18 ultimately produces electricity, and water vapor and heat are byproducts of its operation.

[0075] The electrified powertrain system 11 using the fuel cell stack 18 may include a direct current to direct current (DC / DC) converter 22 to convert the DC output voltage (V1) from the fuel cell stack 18 to a voltage (V2) suitable for the application. As understood in the art, this action may be performed via a boost operation facilitated by high speed switching of semiconductor power switches and transformers (not shown) residing within the DC / DC converter 22. The electrified powertrain system 11 may include an alternating current (AC) traction motor (M2) as shown as part of the driven load. E )25, in this case an electric traction motor connected to one or more of the wheels 16 via shaft 160.

[0076] In this configuration, a direct current-alternating current (DC / AC) inverter 24 is disposed between the DC-DC converter 22 and the traction motor 25. The internal switching operation of the inverter 24 ultimately converts the DC input voltage (V2) into an alternating current voltage (VAC) suitable for exciting the phase windings of the traction motor 25, thereby resulting in machine rotation and motor output torque (T O ) is transmitted to the wheels 16. Other possible components of the electrified powertrain system 11 may include an auxiliary power module 26, i.e., another DC / DC converter, which is operable to reduce the voltage level (V2) from the DC bus to an auxiliary voltage level (V3), which is nominally about 12-15V. Thus, the low voltage auxiliary battery (B AUX ) 28 is supplied with an auxiliary voltage ( V3 ) to power onboard low-voltage functions of the motor vehicle 10 .

[0077] Brief reference Figure 2 , a fuel cell stack 18 is shown in simplified form herein using a multi-layer seal 15 to achieve its sealing. FIG. 3A to FIG. 3B and FIG. 4A to FIG. 4C The NRHW section 30 of the embodiment of the present invention includes a pair of end plate units 30A and 30B, between which a plurality of fuel cells 20 and electrodes E1 and E2 are arranged. Each fuel cell 20 includes a pair of bipolar plates (BPP) 38, between which a membrane electrode assembly (MEA) 36 is disposed. One or more gas inlets 32 are configured to receive a suitable reactant gas flow, such as hydrogen (H2), into the fuel cell stack 18. One or more gas outlets 34 also allow water vapor and heat to be discharged to the surrounding ambient environment. Other ports for supplying coolant and air are omitted for simplicity, but are not shown in the drawings. Figure 3A and Figure 3BAs shown, a positive electrode and a negative electrode having a suitable dielectric coating are arranged at opposite ends of a fuel cell stack 18. The multi-layer seal 15 can be used in various positions within the fuel cell stack 18 to optimize the sealing integrity of the fuel cell stack 18 under oxidative, acidic or other severe operating conditions, as will now be explained with reference to the remaining figures.

[0078] refer to Figure 3A and Figure 3B , the NRHW section 30 is shown in plan view and partial perspective view, respectively, to include a collector plate 31 disposed within a coated metal plate 40 ("SUS plate"), which is in turn connected to a dielectric plate 42, as shown in FIG. Figure 3B The current collector 31 is surrounded by a peripheral groove 400, which can be filled by a press-in-place (PIP) seal as understood in the art. Figure 3A In a representative configuration, the metal plate 40 defines a plurality of fluid ports or passages, including Figure 2 The gas inlet 32 ​​and the gas outlet 34 are shown in different configurations. Figure 3A Also illustrated in FIG. 3 are coolant inlet port 33C, air inlet port 33A, air outlet port 133A, and coolant outlet port 133C. The specific number, location, and shape of the various fluid ports or passages may vary depending on the configuration of the NRHW section 30, and thus the specific configuration of FIG. 3A is illustrative of the present invention and is not limiting.

[0079] According to the present disclosure, the NRHW section 30 thus presents various interface surfaces that would benefit from the multi-layer sealing approach described herein. For example, Figure 3B The gas inlet 32 ​​and coolant inlet port 133C visible in the figure are surrounded by a peripheral groove 35, which is in turn defined by the edges of the dielectric plate 42 and the metal plate 40. Therefore, the flange portion 142 of the dielectric plate 42 protrudes through the gas inlet 32, the coolant inlet port 133C and the metal plate 40 as shown in the figure. Figure 3A The other ports of the peripheral groove 35 surround the flange portion 142. Figure 3C and Figures 5 to 8 Other locations of the disclosed sealing method are described.

[0080] Reference now Figure 4A , Figure 4B and Figure 4C The multi-layer seal 15 can be Figure 3A and Figure 3B The NRHW section 30 is used to provide the accompanying benefits in a variety of ways. As shown, for example, the NRHW section 30 includes Figure 230A and 30B of the end plate units, a partial cross-sectional view of which is depicted. As understood in the art, such a structure represents an interface portion of a fuel cell stack 18 in which different materials are positioned in close proximity to each other. In this case, a metal plate 40 (e.g., 304 or 316 stainless steel (about 1 mm to about 10 mm thick)) can be compressed against a dielectric plate 42 (e.g., polyphenylene sulfide (PPS) reinforced with fiberglass or another electrically insulating material). When the respective metal plates 40 and dielectric plates 42 are brought into close proximity with each other by such compression, the bead edge of the sealing material initially disposed between the metal plates 40 and the dielectric plates 42 is forced away from or squeezed into a peripheral groove 35 defined by the edges and surfaces of the dielectric plates 42 and the metal plates 40, the peripheral groove having a width dimension (DD) of about 1 mm to about 5 mm or more. The peripheral groove 35 is sealed via a multi-layer seal 15, as described below.

[0081] The materials in this portion of the fuel cell stack 18 differ in composition (i.e., metal vs. dielectric) as well as surface roughness, with the dielectric plate 42 being nominally "rough" and the metal plate 40 being nominally "smooth" in a relative context. Such materials have very different coefficients of thermal expansion, thus making locations such as the representative NRHW section 30 difficult to properly seal. Thus, in such sealing applications or similar applications, the use of the multi-layer seal 15 of the present disclosure will provide various attendant benefits, and various locations for the multi-layer seal 15 may be constructed as a form-in-place gasket (FIPG), or via dispensing, room temperature vulcanization (RTV), or injection molding processes.

[0082] refer to Figure 4A For example, after the above-mentioned compression of the metal plate 40 and the dielectric plate 42, a thin layer of the sealing material remains between them, and most of it is discharged into the peripheral groove 35. In this case, a plurality of sealing materials can be used as the constituent layers of the multi-layer seal 15. Then, the multi-layer seal 15 will be arranged between the metal plate 40 and the dielectric plate 42 of each of the end plate units 30A and 30B.

[0083] Here, a nominal first material A and a second material B may be used to form the respective first layer 45 and second layer 47. As described above, in one or more embodiments, materials A and B may have different material compositions and / or properties. For example, the first material A may be substantially impermeable to H2 or another reactant gas and the coolant used in the fuel cell stack 18, with "low permeability" and "effectively impermeable" as used herein meeting the desired H2 and coolant permeation specifications for the selected embodiment. For example, when H2 is used as Figure 1When the reactant gas 17R is introduced, the first material A may have a high density to prevent H2 penetration, or to prevent the penetration of the corresponding coolant. The second material B may itself be more corrosion-resistant than the first material / material A, thereby resisting the corrosion caused by Figure 1 The FCS 12 may be exposed to corrosion caused by coolants and acids in its working environment. In this way, the multi-layer seal 15 will improve Figure 2 The fuel cell stack 18 is ruggedized and durable to relatively harsh or severe operating environments.

[0084] In this or other embodiments, the second material B used to form the second layer 47 may have a higher bonding strength and maximum allowable shear / compression deformation or tensile elongation than the first layer 45 and its first material A, but may have a higher H2 permeability. Therefore, the synergistic effect of materials A and B will be Figure 2 The desired sealing quality is provided at various locations on and within the fuel cell stack 18 .

[0085] Figure 4B A multilayer seal 15 is depicted with an additional third layer 51, indicated as material C. In some embodiments, material C may be different from the first material / material A of the first layer 45 and the second material / material B of the second layer 47, which is disposed between the aforementioned first layer 45 and the second layer 47. In this optional three-layer approach, the third layer 51 is thinly applied between the first layer 45 and the second layer 47. Here, the third layer 51 constructed of the third material C has a low bonding strength with the first material A or the second material B or both A and B. The introduction of the third layer 51 when forming the end unit seal as shown can reduce the chemical and bonding interference between the first material A and the second material B of the corresponding first layer 45 and the second layer 47. Therefore, the failure of the first layer 45 will not adversely affect the sealing performance of the second layer 47, and vice versa. In this exemplary embodiment, material A and material B can be the same material.

[0086] Figure 4C In itself, it depicts Figure 4B Basically the same structure, where the third layer 51 / third material C is replaced by an air gap. Therefore, in this case, the "material" of the third layer 51 is air, that is, the air-filled gap or air pocket located between the first layer 45 and the second layer 47. Such an approach will achieve the same Figure 4B The third layer 51 has a similar effect. Figure 4C A potential difficulty with the solution includes maintaining separation of the respective first and second layers 45, 47, thus possibly requiring the use of a jig, tool, or sacrificial element therebetween.

[0087] Brief reference Figure 3C , Figure 1 and Figure 2 The fuel cell stack 18 may also include one or more bead joints 60 disposed on the bipolar plate (BPP) 38 (see Figure 2 ). As is understood in the art, FIG. 4A to FIG. 4C In contrast to the NRHW section 30 shown in FIG. 1 , the BPP 38 is a duplicate hardware element. The BPP 38 is separated Figure 2 The fuel cell stack 18 shown in FIG. 1 is composed of fuel cells 20, and the fuel cells 20 are connected in series to form the fuel cell stack 18. The BPP 38 can also be a hydrogen (H2), oxygen (O 2) and coolant 19 flow to provide various flow channels 62, thereby Figure 1 The reactant gas 17R is distributed on the surface of the fuel cell 20.

[0088] The BPP 38 may include a bead joint 60 formed of a metallic material suitable for the application (e.g., stainless steel, titanium, aluminum, or another metal or metals). As is understood in the art, the bead joint 60 may be constructed of non-metallic materials such as graphite, and thus the bead joint 60 is not limited to a metallic construction. Figure 3A and Figure 3B Undesirable fluid leakage between the metal plates 40, the beaded joint 60 can be Figure 5 The beaded joint 60 may be provided along the peripheral edge of the BPP 38 and / or the periphery of the various ports 33C, 33A, 34, 133A, 32 and 133C.

[0089] like Figure 5 As shown in , each bead joint 60 can be formed in one or more configurations by interfacing metal sheets 600A and 600B to form a flow channel 62 therebetween. Flat ends 66 are joined (e.g., laser welded) or sealed (e.g., bonded) together to further define the flow channel 62. Surfaces 64A and 64B of the bead joint 60 can be sealed via the multi-layer seal 150 of the present disclosure. Thus, as Figures 1 to 4C In an embodiment of the multi-layer seal 15 , the multi-layer seal 150 may be formed as a metal bead seal disposed on the surface 64A and / or 64B of the metal bead joint 60 .

[0090] Reference now Fig. 6A and Figure 6B For example, such a bead seal is shown in the figure Figure 5The bead seal 60-1 of the bead joint 60 is shown. The bead seal 60-1 has a multi-layer seal 150 located on the surface 64 (i.e., surface 64A and / or 64B) that serves as the bead seal. When properly formed, the multi-layer seal 150 prevents Figure 1 The leakage of the reactant gas 17R. In terms of structure, the bead seal can be taken along the surface (for example, Figure 2 When the fuel cell stack 18 is finally assembled, the multi-layer seals 150 (bead seals) of adjacent BPPs 38 are pressed together, which in turn compresses the multi-layer seals 150. As a result, H2 does not escape from the fuel cell stack 18. As is understood in the art, there are active areas (e.g., Figure 3C 62) in the opening (not shown).

[0091] Fig. 6A and Figure 6B The representative multi-layer seal 150 includes the first layer 45 and the second layer 47 described above, Figure 6B The embodiment also includes an optional third layer 51. As understood in the art, a typical single-layer seal used at the indicated location is screen printed to a desired thickness, such as about 30-40 microns. This limits the allowable contaminant size that will be smaller than the seal thickness, Figure 6B A representative contaminant 63 is shown in the multi-layer seal 250 having a thickness greater than that of a single layer seal.

[0092] It is recognized herein that a single layer approach does not provide the desired sealing pressure at the center of the seal 150 when the seal loads are high and the top surface of the metal bead deforms. Fig. 7A This potential problem with a typical single bead seal 15* is illustrated by the uneven or "M-shaped" pressure distribution profile 70, which indicates that the pressure is lowest in the middle of the single bead seal 15*. Therefore, the seal integrity or sealing performance of this center area is lower.

[0093] Fig. 6A and Figure 6B The multi-layer seals 150 and 250 help to solve this problem. A thicker seal is applied along the central area of ​​the surface 64 via multi-path / multi-layer screen printing or via a combination of screen printing and dispensing. As understood in the art, screen printing involves the use of a fine mesh screen that is stretched over a frame and blocks certain areas where printing is not desired. Dispensing, for its part, includes the controlled application of sealant in the form of a continuous bead or line of sealant material along the surface to be sealed. The materials of the respective first layer 45, second layer 47 and third layer 51 can be the same or different materials to provide the desired sealing properties.

[0094] By way of illustration, the second layer 47 may be constructed of foamed fluorocarbon-based synthetic rubber (FKM) to reduce the Fig. 7A The pressure profile of the type shown in the pressure trace 70 is changed and the sensitivity to contamination is reduced. In terms of the lateral bead pressure profile, for example, Figure 7B A flatter or more uniform pressure distribution 700 (herein Figure 6B An optional three-layer version of the multi-layer seal 250 is shown in FIG. Fig. 6A or Figure 6B The multi-layer seal 150 or 250 is bonded to the BPP 38 (see Figure 2 ) in a structure to obtain the potential result of better sealing. As mentioned above, the first layer 45 and the third layer 51 can be solid FKM to reduce H2 or coolant penetration. Other screen printable / dispensable materials can be used for similar end results within the scope of the present disclosure.

[0095] Reference now Figure 8 , Figure 1 The fuel cell stack 18 may also include a multi-layer seal 350, or Figure 2 A "press-in-place" or PIP seal is provided on a surface 80 of a fuel cell stack 18, which surface 80 may be anywhere on or within the fuel cell stack 18. Such a multi-layer seal 350 may be used between various components of the fuel cell stack 18 (e.g., the BPP 38, the MEA 36, and the end plate units 30A, 30B). The assembly of the fuel cell stack 18 results in a force being applied to such an elastomeric seal, which in turn compresses to form a leak-proof seal. However, typical approaches use a single layer seal for this purpose, which may be too soft or too hard for the application, and due to the thick elastomer, the gas permeation properties may also be less than ideal.

[0096] like Figure 8 As shown in , the present method uses a multi-layer seal 350 as a thin layer seal to address this potential problem. This representative embodiment uses a first layer 45 and a second layer 47, with an optional layer 51 also depicted between them. In this case, the use of two or more elastomeric layers for the respective materials A and B alleviates the above-mentioned problems. For example, the first layer 45 / material A can be selected to be a relatively hard and relatively inexpensive material to reduce cost and H2 permeation, and increase seal stiffness. The second layer 47 / material B, which works in this same example, can be softer and more corrosion resistant than material B. "More corrosion resistant" means that material B of the second layer 47 is more resistant to corrosion than the first layer 45 in the presence of coolant and acidic liquids / vapors. FIG. 4A to FIG. 4C Both the dielectric (eg, PPS) and the metal plate 40 maintain a higher bonding strength.

[0097] As previously described, materials A and B can be dispensed or injection molded, thereby facilitating the manufacturability of the fuel cell stack. Likewise, the combination of the first and second materials will provide the desired load deflection curve, permeability, corrosion resistance at an optimal cost. In yet another embodiment, when used, an optional third layer 51 can be added between the respective first layer 45 and second layer 47 to provide the additional sealing benefits described above.

[0098] For sealing Figure 1 A method of manufacturing a fuel cell stack 18 or another such stack having a plurality of fuel cells 20 disposed between end plate units 30A, 30B (generally referred to as NRHW 30) may generally include applying a first material A as a first layer 45 to the NRHW section 30. As described above, the first layer 45 is impermeable to H2 or another reactant gas 17R or coolant 19 used in the fuel cell stack 18. For example, the H2 permeability of the first layer 45 may be less than about 2e-13 mole·m / (m 3 ·s·Pa). For example, when the coolant 19 is water, the coolant permeability may be less than about 2 g / m at 25°C. 2 / 24 hours. Other values ​​may be used in other embodiments.

[0099] The method also includes applying a second material B as a second layer 47 to the NRHW section 30. As described above, the second material B may be more corrosion resistant than the first material A. The method may then proceed to form the multi-layer seal 15 by curing the first layer 45 and the second layer 47, for example, in an oven (or in air) at a suitable curing temperature.

[0100] Optionally, the method may include applying or forming a third material C as a third layer 51 ( Figure 4C ). The third material C, which may be different from the first material 45 and the second material 47, also has a low bonding strength with the first material 45 and the second material 47, and the low bonding strength contemplated herein is sufficient to reduce chemical and bonding interference between the first layer 45 and the second layer 47, as described above. Applying the first material A may include using a formed-in-place gasket (FIPG) process, while applying the second material or the third material C may include using a manual dispensing process, among other possible methods.

[0101] As explained above, the present disclosure enables Figure 1 The fuel cell stack 18 is used in various positions within the FIG. 4A to FIG. 8 The multi-layer seal 15 and its embodiments 150, 250 and 350. For example, for FIG. 4A to FIG. 4CFor NRHW sections 30 or end units 30A, 30B, a first layer 45 / material A may be applied using the FIPG method and then a second layer 47 / material B may be applied using manual dispensing assisted by a syringe, for example, followed by low temperature curing.

[0102] For the formation of Fig. 6A and Figure 6B For a bead seal of a multi-layer seal 150 or 250 of the type shown in the drawings, respectively, screen printing can be used to apply the first layer 45 / material A, and possibly the optional third layer 51 / material C, followed by low temperature pre-curing and drying. Then, screen printing can be used to apply the second layer 47 / material B, followed by low temperature pre-curing / drying. After these steps, the final cure can be carried out at a temperature appropriately higher than the temperature used to pre-cure the previously applied layers.

[0103] This solution can also be extended to Figure 8 The elastomeric seal / PIP seal shown in the multi-layer seal 350 is shown (e.g., by dispensing a first layer 45 / material A and pre-curing it, followed by dispensing a second layer 47 / material B and pre-curing it as described above). An optional layer 51 / material C can be applied between material A and material B to further optimize the sealing characteristics and tightness. The final curing can then be started at a higher temperature. Thus, at Figure 1 Improved gas permeation and corrosion resistance benefits may be realized in a number of different locations and types of seals within a representative FCS 12 .

[0104] The detailed description and the accompanying drawings or figures are support and description of the present teaching, but the scope of the present teaching is limited only by the claims. Although some best modes and other embodiments for implementing the present teaching have been described in detail, there are various alternative designs and embodiments for implementing the present teaching defined in the appended claims.

Claims

1. A fuel cell stack, comprising: a pair of end plate units, each having a metal plate, a dielectric plate, and a peripheral groove defined by the dielectric plate and the metal plate; a coolant inlet and a gas inlet, respectively configured to receive a coolant and a reactant gas into the fuel cell stack; a plurality of fuel cells, wherein each respective fuel cell of the plurality of fuel cells comprises a pair of bipolar plates; and A multi-layer seal, which is arranged on the end plate unit or the bipolar plate in the fuel cell stack, and the multi-layer seal comprises: a first layer constructed of a first material that is substantially impermeable to the reactant gas and the coolant; and A second layer is constructed of a second material that is more corrosion resistant than the first material.

2. The fuel cell stack according to claim 1, wherein: The multi-layer seal is provided between the metal plate and the dielectric plate of each of the end plate units.

3. The fuel cell stack according to claim 2, wherein: The bonding strength and maximum tensile elongation of the second layer to the dielectric plate are higher than the bonding strength and maximum tensile elongation of the first material to the dielectric plate.

4. The fuel cell stack according to claim 1, wherein: The multi-layer seal includes a third layer disposed between the first layer and the third layer, the third layer being constructed of a third material different from the first material and the second material.

5. The fuel cell stack according to claim 4, wherein: The third material is air such that the third layer includes an air gap defined between the first layer and the second layer.

6. The fuel cell stack according to claim 4, wherein: The third material has a low bonding strength with the first material and the second material, the low bonding strength being sufficient to reduce chemical and bonding interference between the first layer and the second layer.

7. The fuel cell stack according to claim 1, wherein: The bipolar plates each include a metal bead joint, and wherein the multi-layer seal includes a thin layer seal disposed on a surface of the metal bead joint.

8. The fuel cell stack according to claim 7, wherein: The first material of the multi-layer seal comprises foamed fluorocarbon-based elastomer (FKM), and wherein the second layer applied to the surface of the metal bead joint comprises solid FKM.

9. A fuel cell system (FCS), comprising: a reactant supply tank containing a reactant gas; a fuel cell stack in fluid communication with the reactant supply tank and configured to receive a coolant and the reactant gas; and a load configured to be driven by current from the fuel cell stack, wherein the fuel cell stack comprises: a pair of end plate units, each having a metal plate, a dielectric plate, and a peripheral groove defined by the dielectric plate and the metal plate; a gas inlet configured to receive reactant gas into the fuel cell stack; a coolant inlet configured to receive the coolant into the fuel cell stack; a plurality of fuel cells, wherein each respective fuel cell of the plurality of fuel cells comprises a pair of bipolar plates; and A multi-layer seal disposed within the fuel cell stack, the multi-layer seal comprising: a first layer constructed of a first material that is substantially impermeable to the reactant gas and the coolant; and A second layer is constructed of a second material that is more corrosion resistant than the first material.

10. A method for sealing a fuel cell stack having a plurality of fuel cells disposed between end plate units, comprising: applying a first material as a first layer to an end plate unit of the fuel cell, wherein the first layer is substantially impermeable to reactant gases and coolants used in the fuel cell stack; applying a second material as a second layer to the end plate unit to form a multi-layer seal, wherein the second material is more corrosion resistant than the first material; and The first layer and the second layer are cured to form the multi-layer seal.

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