Fuel cell stacks and methods for their manufacture

Abstract

Fuel cell stack comprising a plurality of stacked fuel cell units and at least one stack termination element (1), characterized in that the stack termination element (1) is formed from a metal part (1.1) and a stiffening part made of plastic (1.2), wherein the stack termination element (1) is manufactured in one piece as a metal-plastic hybrid component using the plastic injection molding process.

Description

[0001] The invention relates to a fuel cell stack according to the preamble of claim 1.

[0002] Furthermore, the invention relates to a method for manufacturing a fuel cell stack according to the preamble of claim 7.

[0003] Fuel cell stacks typically consist of multiple fuel cells, a clamping device, and at least one end plate that seals the stack at its front. To ensure the necessary tightness and functionality of the fuel cell stack, the end plates and the fuel cells are clamped together. The end plate serves to absorb and / or transmit high clamping forces, connect the fuel cell stack to media inlets / outlets, and seal and electrically contact the fuel cell stack. Furthermore, the end plate can serve as an interface and / or sealing surface to a housing and connect the fuel cell stack to supporting structures, such as the vehicle body. The requirements for the end plates are therefore correspondingly high and necessitate a very robust design to ensure the required bending and torsional stiffness.To meet these requirements, the end plate is usually made of a solid metal plate, a special plastic or a fiber-reinforced epoxy resin.

[0004] Another approach is known from US 2005 / 0095485 A1, which discloses a fuel cell current collection system comprising a fuel cell stack with a number of fuel cells stacked in a predetermined direction and an end plate assembly. The end plate assembly is arranged at one end of the fuel cell stack and comprises an end plate and a current collector that passes through the end plate and is electrically coupled to the fuel cell stack to collect the current from the fuel cell stack. One embodiment provides that the end plate has a metal reinforcement structure that is overmolded with plastic.

[0005] DE 10 2011 088 103 A1 describes an end plate for a fuel cell with an anti-bending plate, in which the anti-bending plate is assembled with an insert having a sandwich structure and the insert is injection-molded. This prevents the insert from easily bending due to pressure during injection molding. The end plate contains a sandwich insert comprising two or more stacked plates, each with a specific shape. An anti-bending plate is coupled to the sandwich insert and then injection-molded. This prevents the sandwich insert from easily bending due to resin pressure during the injection molding process, unlike a conventional integral metallic insert.

[0006] US 2009 / 0117416 A1 describes an end plate for a fuel cell stack and a method for manufacturing it, wherein the end plate, which is connected to both ends of a fuel cell stack, is manufactured in a hybrid structure using two types of materials with different coefficients of thermal expansion, thereby providing a uniform surface pressure in the fuel cell stack.

[0007] The invention is based on the objective of providing a fuel cell stack that is improved compared to the prior art and a method for manufacturing a fuel cell stack that is improved compared to the prior art.

[0008] With regard to the fuel cell stack, the problem is solved according to the invention by the features specified in claim 1 and with regard to the method by the features specified in claim 7.

[0009] Advantageous embodiments of the invention are the subject of the dependent claims.

[0010] A fuel cell stack comprises a plurality of stacked fuel cell units and at least one stack termination element. The stack termination element is formed from a metal part and a stiffening part, and is manufactured as a single metal-plastic hybrid component using a plastic injection molding process.

[0011] Designing the stack termination element as a hybrid component allows for the combination of the positive properties of two different materials. The metal part enables the transfer of clamping forces over a large area into the fuel cell units and facilitates connection points to supporting structures, such as the vehicle body. Furthermore, the metal part exhibits excellent dimensional and temperature stability. A metallic alloy, such as steel, is also suitable as the metal material.

[0012] The stiffening element enables electrical insulation of the fuel cell stack from the environment. Furthermore, it provides an interface to a housing for the fuel cell stack, a connection and inlet for gaseous or liquid media to and from the fuel cell stack, and insulation of these media, both electrically and for corrosion protection. The stiffening element thus optimizes the metal component. Suitable plastics for this purpose are organic polymers, particularly thermoplastics.

[0013] The stack termination element can therefore be advantageously implemented as a cost-, space- and function-optimized component without additional processing and / or assembly costs.

[0014] Exemplary embodiments of the invention are explained in more detail below with reference to drawings.

[0015] This shows: Fig. 1 schematically a top view of a stack termination element of a fuel cell stack, and Fig. 2 schematically a sectional view of the stack termination element according to Fig. 1.

[0016] Corresponding parts are marked with the same reference symbols in all figures.

[0017] The Fig. 1 and Fig. Figures 2 each show a stack termination element 1 of a fuel cell stack not shown in detail, wherein Fig. 1 a top view and Fig. Figure 2 shows a cross-sectional view of the stack termination element 1.

[0018] A fuel cell stack typically consists of a plurality of stacked fuel cell units, the structure and function of which is described, for example, in the aforementioned US 2005 / 0095485 A1.

[0019] The fuel cell stack can, for example, comprise high-temperature fuel cell units, e.g., solid oxide fuel cells, or low-temperature fuel cell units, e.g., polymer electrolyte fuel cells, with polymer electrolyte fuel cells (PEMFC) being preferred.

[0020] The stack termination element 1 defines one end face of the fuel cell stack. In a particularly advantageous embodiment of the invention, the fuel cell stack has a further stack termination element 1, so that it is bounded on both sides by a stack termination element 1.

[0021] To clamp the fuel cell units to the stack termination element 1, the fuel cell stack preferably has at least one clamping device (not shown). This advantageously enables the application of the necessary sealing and contact forces during operation of the fuel cell stack.

[0022] In the present embodiment, the stack termination element 1 is designed according to the invention as a hybrid component, which is formed from a metal part 1.1 and a stiffening part 1.2 made of a plastic or organic polymer.

[0023] In the present embodiment, the metal part 1.1 is formed as a shell-shaped sheet metal part, which is manufactured in casting, extrusion, or forging processes. Alternatively, the metal part 1.1 can also have a frame-shaped profile or a U-shaped profile.

[0024] The shell-shaped design increases the bending and torsional stiffness of the metal part 1.1. Furthermore, connecting elements (retaining elements) for attaching the fuel cell stack to supporting structures and fastening elements for clamping the fuel cell stack using thermal or mechanical joining methods can be arranged.

[0025] Preferably, the metal component 1.1 is made of a metallic alloy, such as steel. The advantage of using a metallic alloy lies particularly in the material's high dimensional stability and high temperature resistance. Furthermore, metallic alloys exhibit a high modulus of electric current, low coefficients of thermal expansion, good electrical conductivity, and ductile behavior in the event of damage, such as a collision involving a vehicle in which the fuel cell stack is located. Moreover, metal components made of a metallic alloy can be manufactured easily and cost-effectively using the processes mentioned above.

[0026] The stiffening element 1.2 is preferably made of a thermoplastic and is particularly preferably applied to an outer surface of the metal part 1.1 by injection molding, i.e., to a side facing away from the fuel cell stack. Alternatively, the stiffening element 1.2 can also be molded onto an inner surface of the metal part 1.1 and / or onto the inside of the metal part 1.1.

[0027] The thermoplastic can be solid or have cavities. In the present embodiment, the stiffening part 1.2 has a cross-rib structure which is enclosed in a frame-like manner corresponding to a circumferential profile of the metal part 1.1.

[0028] The cross-rib structures of the stiffening element 1.2 enable structural reinforcement of the metal part 1.1, where complex structures are very time-consuming and expensive to produce due to the material used. Furthermore, organic polymers are lightweight, so that when the fuel cell stack is used in a vehicle, its weight can be reduced, thus enabling energy savings.

[0029] The organic polymer is also electrically insulating and can be used as a sealing material; it is corrosion-resistant and therefore ideally suited for transporting media such as air, hydrogen, and / or cooling water. Furthermore, structures 1.2.1 are formed into the cross-rib structure of the stiffening element 1.2. In the present embodiment, these structures are cuboid and circular and serve to supply and discharge media into and out of the fuel cell stack.

[0030] For the production of the stack termination element 1 as a one-piece metal-plastic hybrid component, a plastic injection molding process is particularly suitable, so that the stiffening part 1.2 forms a material-bonded connection with the metal part 1.1.

[0031] To ensure an optimal, material-bonded connection between the stiffening element 1.2 and the metal part 1.1, even under high dynamic loads, a stress distribution for a stack termination element 1 is determined, and the shape of the stiffening element 1.2 is adjusted accordingly. Openings, indentations, and overmolding advantageously create a mechanically stable connection between the two materials.

[0032] By means of the stack termination element 1 according to the invention, positive material properties of two different materials are thus combined, so that the stack termination element 1 can be advantageously realized as a cost-, space- and function-optimized component without additional processing and / or assembly costs.

[0033] Furthermore, it is possible to arrange pipes and / or other components for the operation of the fuel cell stack on a side of the stack termination element 1 facing away from the fuel cell stack.

[0034] Furthermore, a space-saving arrangement of the fuel cell stack housing is possible, and the stack termination element 1 can preferably take on the functions of a support frame structure. This eliminates the need for support frame structures, thereby reducing, for example, the weight of a vehicle.

Claims

[1] Fuel cell stack comprising a plurality of stacked fuel cell units and at least one stack termination element (1), characterized by , that the stack termination element (1) is formed from a metal part (1.1) and a stiffening part made of plastic (1.2), wherein the stack termination element (1) is manufactured in one piece as a metal-plastic hybrid component using the plastic injection molding process. [2] Fuel cell stack according to claim 1, characterized by , that the metal part (1.1) is formed from a metallic sheet part as a frame profile, U-shaped profile, shell. [3] Fuel cell stack according to claim 1 or 2, characterized by , that the stiffening part (1.2) is formed from an organic polymer. [4] Fuel cell stack according to any one of the preceding claims, characterized by , that the metal part (1.1) is stiffened by forming and / or incorporating the stiffening part (1.2). [5] Fuel cell stack according to any one of the preceding claims, characterized by , that the stiffening part (1.2) is molded into and / or attached to the metal part (1.1) on the inside and / or outside. [6] Fuel cell stack according to any one of the preceding claims, characterized by , that the stiffening part (1.2) has a rib structure, in particular a cross-rib structure. [7] Method for producing a fuel cell stack, wherein a plurality of fuel cell units are stacked and a stack termination element (1) is arranged at at least one end of the stacked fuel cell units, characterized by , that the stack termination element (1) is formed from a metal part (1.1) and a stiffening part made of plastic (1.2), wherein the stack termination element (1) is manufactured in one piece as a metal-plastic hybrid component using the plastic injection molding process.

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