Bipolar plates and fuel cell stacks

Abstract

The present invention relates to a bipolar plate having an inactive plate portion and an active plate portion for dispensing reactants, the inactive plate portion having a plurality of dielectric ports, wherein the inactive plate portion and the active plate portion are coupled to each other by means of at least one spring element. The invention also relates to a fuel cell stack.

Description

Technical Field

[0001] The present invention comprises a bipolar plate having an inactive plate portion and an active plate portion for dispensing reactants, the inactive plate portion having a plurality of dielectric ports, wherein the inactive plate portion and the active plate portion are coupled to each other by means of at least one spring element. The present invention also relates to a fuel cell stack. Background Technology

[0002] Fuel cells are used to provide electrical energy through an electrochemical reaction, where multiple fuel cells can be combined in series to form a fuel cell stack in order to increase the available power. Each of these fuel cells includes an anode, a cathode, and a proton-conducting membrane separating the anode and cathode, which is coated with a catalyst to facilitate the electrochemical reaction.

[0003] The electrodes of these fuel cells are supplied with reactant gases via bipolar plates, specifically hydrogen on the anode side and oxygen or oxygen-containing gases, particularly air, on the cathode side. When supplying reactants to the fuel cell, these reactants are guided into the bipolar plates via media ports. The bipolar plates are designed to distribute these reactants to the active regions using one or more channels, so as to supply the entire electrode surface as uniformly as possible by means of a flow field. In addition to the reactant gases, a cooling medium is also guided through the bipolar plates, necessitating that the three different media be guided in a technically tightly separated manner within a minimal space. Therefore, two metal forming parts are typically welded together to form the bipolar plates. Furthermore, a gas diffusion layer is used to ensure that the reactants introduced into the bipolar plates are distributed as uniformly as possible across the entire surface of the catalyst-coated membrane.

[0004] The multiple fuel cells combined in the fuel cell stack are typically pressed together by the tension element of a clamping system with a force in the range of several tons in order to achieve sufficient contact pressure at the catalyst-coated membrane to reduce ohmic losses and to avoid unsealing of the seals used by means of high compression.

[0005] However, it should be noted that during fuel cell stack operation, forces may arise that can increase or decrease the clutch force. Increased clutch force is due to the thermal expansion of the components used, the pressure used to supply and distribute reactants, and the expansion of the membranes used during hydration.

[0006] The reduction in clamping force may occur due to negative thermal expansion at lower temperatures or low temperatures, or due to sedimentation behavior of the gas diffusion layer, which increases with the lifespan of the fuel cell stack and the resulting aging. Therefore, it is necessary to compensate for sedimentation behavior throughout the entire lifespan of the fuel cell stack. This involves equipping the clamping system with spring elements such as disc springs or helical springs; however, this requires additional structural space, increases the weight of the fuel cell stack, and raises costs and development expenses. Furthermore, it is necessary to distribute the clamping force evenly across the surface of the fuel cell stack, which typically requires additional components between the clamping system and these spring elements.

[0007] DE 102013011412 A1 discloses a bipolar plate having a cathode plate and an anode plate, wherein the cathode plate has a spring region that is substantially elastically deformable in the height direction of the bipolar plate, and a seal is injection-molded in the spring region. DE 102013011422A1 discloses a bipolar plate in which both the cathode plate and the anode plate have regions that are substantially elastically deformable in the height direction, and these regions are equipped with reinforcing structures. FR 2899386 A1 shows bipolar plate halves equipped with ribs on which conductive, elastic conductive components are supported to ensure electrical contact. Summary of the Invention

[0008] The objective of this invention is to provide an improved bipolar plate and an improved fuel cell stack.

[0009] This task is solved by a bipolar plate according to the invention and a fuel cell plate according to the invention. Advantageous designs of the invention with suitable extensions are described below.

[0010] In the bipolar plate according to the invention, the bipolar plate has an inactive plate portion and an active plate portion for dispensing reactants. The inactive plate portion has multiple media ports, and the inactive plate portion and the active plate portion are coupled to each other by means of at least one spring element. This provides the advantage that the spring function is integrated into the bipolar plate, saving additional springs or spring elements and the structural space required for them. That is, the spring function is transferred from the clamping system comprising the fuel cell stack to the fuel cell with the bipolar plate, wherein the spring function is assigned to a specific region of the bipolar plate, namely between the inactive plate portion and the active plate portion, wherein the inactive plate portion circumferentially surrounds the active plate portion having a flow field. It should be noted that the inactive plate portion has media guiding, sealing, and insulating functions, while the active plate portion has a flow field and is subjected to sedimentation behavior, especially the sedimentation behavior of the gas diffusion layer, and is reliably abutted against the gas diffusion layer due to the spring element.

[0011] Preferably, especially when the cathode and anode plates are made of metal or metal alloy, the cathode and anode plates are combined together and the at least one spring element is formed by a leaf spring arranged between the inactive and active sub-plates, formed by partial areas of the cathode and anode plates. Due to the principle of a two-part structure with sheet-like areas and the use of sufficiently elastic materials, the leaf spring principle can be realized without other components, wherein the spring constant of the leaf spring can be adjusted by the shape fit between partial areas of the cathode and anode plates, i.e., the force flow between the metal layers can be altered, for example, by different welds or adapted surface roughness.

[0012] Alternatively or additionally, the spring constant of the leaf spring can be adjusted by increasing the frictional force between certain areas of the cathode and anode plates.

[0013] There is also the possibility that the spring constant of the leaf spring can be adjusted by means of an intermediate element arranged between a portion of the cathode plate and the anode plate.

[0014] Especially when the bipolar plate is not made of metal but is implemented as a graphite composite bipolar plate, it is advantageous that these partial areas are at least partially replaced by elastic elements, which are connected to the inactive and active plate portions by injection molding or vulcanization. Here, the adjustment of the spring characteristics can be achieved in the design by adapting the resistance torque against bending or by adapting the material properties.

[0015] Since the medium must be guided and dispensed into the bipolar plate from the inactive plate portion with the medium ports without alteration, it is stipulated that channels for guiding the medium between these medium ports be formed in the elastic element, wherein these channels are preferably used for cooling the medium, because the reactive gas can also be guided to the active subplate through a suitable gas diffusion layer.

[0016] It is also possible that: two medium ports for guiding the cooling medium are arranged in the inactive plate section, from which coolant channels are guided through these partial areas, that is, in particular, the intermediate element can only partially replace the function, where the coolant channel is in the unreplaced area, or the intermediate element itself may have the coolant channel.

[0017] By comparison, the aforementioned advantages and effects also apply to fuel cell stacks having at least one such bipolar plate and to fuel cell devices or fuel cell vehicles having such fuel cell stacks.

[0018] The features and combinations of features mentioned in the foregoing description, as well as those mentioned subsequently in the description of the drawings and / or shown separately in the drawings, can be applied not only in the corresponding described combinations but also in other combinations or individually, without departing from the scope of protection of the invention. Therefore, embodiments not explicitly shown or illustrated in the drawings, but which can be derived from the combinations of features selected from the illustrated embodiments, should be considered as included and disclosed by the invention. Attached Figure Description

[0019] Other advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the accompanying drawings. Hereinafter:

[0020] Figure 1 A plan view of a bipolar plate is shown, illustrating a non-active plate portion with a medium port and an active plate portion with a flow field.

[0021] Figure 2 A schematic diagram of a longitudinal section of a bipolar plate is shown, in which the inactive plate portion and the active plate portion are coupled to each other by means of a spring element;

[0022] Figure 3 It shows the corresponding Figure 2 An illustration of an unclamped spring element presented in a non-realistic manner;

[0023] Figure 4 It shows the corresponding Figure 3 A diagram showing a clamped spring element;

[0024] Figure 5 It shows the corresponding Figure 2 A symbolic representation of friction;

[0025] Figure 6 It shows the corresponding Figure 2 A diagram with intermediate elements;

[0026] Figure 7 It shows the corresponding Figure 2 An illustration of a region where the elastic element has replaced the portion of the image.

[0027] Figure 8 shows a schematic diagram of a fuel cell stack known from the prior art, clamped between two end plates, wherein one of these end plates is supported by a spring element against a spring cap; and

[0028] Figure 9 shows the corresponding... Figure 2 The illustration is based on a bipolar plate known from the prior art, wherein the inactive plate portion and the active plate portion are connected to each other in some areas without spring elements. Detailed Implementation

[0029] Figure 8 schematically illustrates a fuel cell stack 2, which consists of multiple fuel cells 3 connected in series. Each of these fuel cells 3 includes an anode and a cathode, as well as a proton-conducting membrane separating the anode and cathode. This membrane is formed from an ionomer, preferably a sulfonated tetrafluoroethylene polymer (PTFE), or a polymer of perfluorosulfonic acid (PFSA). Alternatively, the membrane can be formed as a sulfonated hydrocarbon membrane. A catalyst can be additionally added to the anode and / or cathode, wherein the membrane is preferably coated with a catalyst layer on its first side and / or its second side, the catalyst layer being composed of a noble metal or a mixture of noble metals including platinum, palladium, ruthenium, etc., which act as reaction accelerators in the reaction of the respective fuel cell.

[0030] Fuel (e.g., hydrogen) is supplied to the anode as an anode gas via the anode region within the fuel cell stack 2. In a polymer electrolyte membrane fuel cell (PEM fuel cell), at the anode, the fuel or fuel molecules are broken down into protons and electrons. Protons (e.g., H+) + (e) passes through the membrane, but the membrane is sensitive to electrons (e) - It cannot pass through. Here, the following reaction occurs at the anode: 2H₂ → 4H₂ + +4e - (Oxidation / Electron Release). Protons pass through the membrane to the cathode, while electrons are conducted to the cathode via external circuitry or to the energy storage device. Cathode gas (e.g., oxygen or oxygen-containing air) can be supplied to the cathode via the cathode region within the fuel cell stack 2, causing the following reaction to occur on the cathode side: O₂ + 4H₂O + +4e - →2H2O (reduction / electron absorption).

[0031] The reactant gases are transferred to bipolar plates 7, in which channels are formed and combined into a flow field for distributing the reactant gases onto the membrane. Additionally, these bipolar plates 7 are configured to deliver a cooling medium, thereby guiding three different media in a minimal space.

[0032] Here, Figure 1 A typical division of a bipolar plate 7 is shown, comprising an inactive plate portion 9 with multiple medium ports 8 and an active plate portion 10 for dispensing reactants, wherein the inactive plate portion 9 circumferentially surrounds the active plate portion 10 having a flow field. In the illustrated embodiment, three pairs of medium ports are shown on the edge side of the flow field in the inactive plate portion 9, namely two medium ports 8 for supplying and discharging the cooling medium and two medium ports respectively for supplying and discharging the two reactant gases. Furthermore, the inactive plate portion is provided with seals 11 so that the inactive plate portion 9 can perform its sealing, insulating, and medium guiding functions.

[0033] The fuel cell stack 2, schematically shown in Figure 8 and known from the prior art, has a plurality of fuel cells 3 arranged between two end plates 1. In the illustrated embodiment, the upper end plate 1 is symbolically provided with a spring pack 4, which supports the end plate 1 on a spring cap 5, wherein on the side of the fuel cell stack 2, two straps 6 extend from the spring cap 5 through the first end plate 1 to the second end plate 1, such that the fuel cells 3 are clamped together in the fuel cell stack 2 by a compressive force.

[0034] According to the present invention, the spring pack 4 along with the spring cap 5 can be saved by integrating the spring function into at least one of the bipolar plates 7, preferably into all the bipolar plates 7 of the fuel cell stack 2, by means that the inactive plate portion 9 and the active plate portion 10 are coupled to each other by means of at least one spring element 12, as this is in Figure 3 The diagram illustrates, using a symbolic spring, the unclamped state, which transitions to the clamped state during the assembly of fuel cell stack 2. Figure 4 The clamping state shown provides sufficient subsequent tension reserve to compensate for, for example, this settling behavior.

[0035] To achieve according to Figure 2 The spring element 12 is formed by combining the cathode plate 13 and the anode plate 14 together and by a leaf spring 16 formed by a portion of the cathode plate 13 and the anode plate 14 arranged between the inactive sub-plate 9 and the active sub-plate 10. That is, by the two-part structure of the bipolar plate 7, the leaf spring principle can be realized by the integrated, monolithically formed leaf spring 16, especially in the case of the metal bipolar plate 7.

[0036] Here, the spring constant of leaf spring 16 can be obtained by corresponding to Figure 2 The shape fit 17 between a portion of the cathode plate 13 and the anode plate 14 is adjusted or by corresponding to Figure 5 The increased friction 18 between a portion of the cathode plate 13 and the anode plate 14 is adjusted.

[0037] Alternatively, there also exist Figure 6 The possibility shown is that the spring constant of the leaf spring 16 can be adjusted by an intermediate element 19 arranged between a portion 15 of the cathode plate 13 and the anode plate 14.

[0038] at last, Figure 7It is suggested that these partial regions 15 may be at least partially replaced by elastic elements 20, which are connected to the inactive plate portion 9 and the active plate portion 10 by injection molding or vulcanization, wherein channels for guiding media, particularly coolant, between these media ports 8 are formed in the elastic element 20. These reactive gases may be guided via an expanded gas diffusion layer.

[0039] In accordance with Figure 2 , 5 In embodiments 6 and 7, a channel for a cooling medium can be created in the shape of the leaf spring 16 from the portion 15, wherein the channel size and shape can be used to adapt to the characteristics of the spring.

[0040] List of reference numerals

[0041] 1. End plate

[0042] 2. Fuel Cell Stack

[0043] 3. Fuel Cells

[0044] 4 Spring Pack

[0045] 5. Spring Caps

[0046] 6. Lace-up

[0047] 7 Bipolar plates

[0048] 8 Media Ports

[0049] 9 Inactive board areas

[0050] 10 Active Board Areas

[0051] 11. Seals

[0052] 12 Spring Elements

[0053] 13 Cathode Plate

[0054] 14 Anode Plates

[0055] 15 Partial Areas

[0056] 16 leaf springs

[0057] 17 Shape Matching

[0058] 18. Friction

[0059] 19 Intermediate Components

[0060] 20. Elastic element.

Claims

1. A bipolar plate (7) having an inactive plate portion (9) with a plurality of dielectric ports (8) and an active plate portion (10) for dispensing reactants, wherein the inactive plate portion (9) and the active plate portion (10) are coupled to each other by means of at least one spring element (12), wherein a cathode plate (13) and an anode plate (14) are combined together and the at least one spring element (12) is formed by a leaf spring (16) arranged between the inactive plate portion (9) and the active plate portion (10) and formed by a portion (15) of the cathode plate (13) and the anode plate (14), characterized in that, The cathode plate (13) and the anode plate (14) are combined together and the at least one spring element (12) is formed by a leaf spring (16) arranged between the inactive plate portion (9) and the active plate portion (10), which is formed in a sheet-like manner by a portion (15) of the cathode plate (13) and the anode plate (14), and the spring constant of the leaf spring is adjusted by a shape fit between the portion of the cathode plate and the anode plate.

2. The bipolar plate (7) according to claim 1, characterized in that, The spring constant of the leaf spring (16) is adjusted by the increased friction (18) between a portion (15) of the cathode plate (13) and the anode plate (14).

3. The bipolar plate (7) according to claim 2, characterized in that, The spring constant of the leaf spring (16) is adjusted by an intermediate element (19) arranged between a portion (15) of the cathode plate (13) and the anode plate (14).

4. The bipolar plate (7) according to claim 2 or 3, characterized in that, The cathode plate (13) and the anode plate (14) are made of metal or metal alloy.

5. The bipolar plate (7) according to any one of claims 1 to 3, characterized in that, Two medium ports (8) for guiding the cooling medium are arranged in the inactive plate portion (9), from which coolant channels are guided through the portion area (15).

6. A fuel cell stack (2) having at least one bipolar plate (7) according to any one of claims 1 to 5.

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