Bipolar plate with multilayer structure; fuel cell; fuel cell system

Abstract

Bipolar plate (1) for a fuel cell (10), comprising a base body (2) made of fiber composite material and at least one metallic coating (3, 4) applied to the base body (2), wherein a copper-containing first coating (3) is applied directly to the base body (2) and a second coating (4) made of a stainless metal material is applied to this first coating (3).

Description

[0001] The invention relates to a bipolar plate (also referred to as a bipolar fuel cell plate) for a fuel cell, preferably a hydrogen-oxygen fuel cell. The invention further relates to a fuel cell and a fuel cell system, each equipped with several bipolar plates.

[0002] Conventional bipolar plates are usually manufactured as pure metal plates, such as aluminum. Coated bipolar plates are also known, particularly to provide corrosion protection. However, a disadvantage of known bipolar plates is that they are either relatively thick to achieve sufficient strength, or, conversely, lack sufficient strength to achieve the thinnest possible structure. Generic prior art is known, for example, from DE 10 2008 056 421 A1, DE 10 2010 051 964 A1, and KR 10 2005 0 105 784 A.

[0003] It is therefore an object of the present invention to provide a bipolar plate that, on the one hand, has the smallest possible thickness and, on the other hand, has sufficient strength to achieve a long service life of the fuel cell. Adequate electrical conductivity and corrosion resistance should be ensured.

[0004] This is achieved according to the invention by the features of claim 1, whereby a bipolar plate for a fuel cell is claimed, which has a (plate-shaped) base body made of fiber composite material and at least one metallic coating applied to the base body, wherein a copper-containing first coating is applied directly to the base body and in turn a second coating consisting of a stainless metal material is applied to this first coating.

[0005] Such a bipolar plate can be made as thin as possible, resulting in the entire fuel cell being significantly smaller while maintaining the same power output without compromising its efficiency. Nevertheless, the bipolar plate's other functions are still maintained. The base body forms robust support points to support and distribute the applied compressive forces when the fuel cell is fully assembled. The first coating forms a necessary electrical conductive structure for efficient operation of the fuel cell. Furthermore, the second coating protects the base body and the first coating against corrosion.

[0006] Further advantageous embodiments are claimed in the subclaims and explained in more detail below.

[0007] Therefore, it is advantageous if the first coating consists of a chemically, preferably electroplated, applied (pure) copper layer. This allows the thickness of the first coating to be adjusted as precisely as possible.

[0008] It's also advantageous for the second coating to be made of or made of rust-proof steel, such as stainless steel. This makes the second coating as durable as possible.

[0009] Furthermore, it is expedient if a channel structure (of the bipolar plate) designed for collecting and conducting fluids, in particular for supplying hydrogen and removing water, is directly incorporated into the base body or, alternatively, is attached to the base body. This further simplifies the manufacture of the bipolar plate.

[0010] If the channel structure is introduced directly into the base body using laser ablation, the channel structure can be designed as individually and finely as possible. On the other hand, unlike machining processes such as milling, no cooling medium, such as drilling fluid, is required, which would wet or contaminate the surface of the base body to be subsequently coated, which is either harmful to the fiber composite material or hinders sufficient adhesion of the applied coatings.

[0011] As an alternative to introducing the channel structure by laser ablation, it is also advantageous if the channel structure is introduced, for example, pressed / embossed, into one of the coatings (preferably in the form of a preformed film). Further preferably, the first coating is first bonded to the second coating before being applied to the base body and then subjected to embossing before being applied / attached to the base body, forming the channel structure. This allows the manufacturing process to be carried out as efficiently as possible.

[0012] In order to produce a bipolar plate that is as stiff as possible, it is also advantageous if the fiber composite material of the base body contains (several) carbon fibers implemented as long fibers.

[0013] In this regard, it is also beneficial for strength if the fiber composite material of the base body comprises first carbon fibers and second carbon fibers oriented obliquely / transversely, preferably perpendicularly, to the first carbon fibers. In a particularly preferred embodiment, the first carbon fibers are aligned along the longitudinal direction of the bipolar plate, and the second carbon fibers are aligned perpendicularly to the longitudinal direction of the bipolar plate.

[0014] It is also advantageous if the fiber composite material has multiple layers of a fiber fabric or multiple wound layers. This allows the stiffness of the bipolar plate to be cleverly adjusted.

[0015] It has also proven particularly advantageous if the carbon fibers are pitch fibers, preferably tar pitch fibers, and more preferably coal tar fibers, such as hard coal tar fibers. This results in the highest possible stiffness of the bipolar plate.

[0016] Furthermore, it is advantageous if the two coatings are applied to a first side surface ( / underside) of the base body, and the base body is left uncoated on a second side surface ( / top side) facing the first side surface (i.e., the fiber composite material is exposed to the environment or merely coated with a protective coating) or is coated with an electrical insulation layer, preferably in the form of a glass fiber laminate layer. This allows the bipolar plate to be inserted into the fuel cell as efficiently as possible.

[0017] Furthermore, the invention relates to a fuel cell with two bipolar plates according to the invention arranged opposite one another according to at least one of the previously described embodiments, between which bipolar plates an anode, a cathode and gas diffusion layers are arranged.

[0018] In this regard, it is also advantageous if the fuel cell has a plurality of sub-units, each of which has two oppositely arranged bipolar plates according to the invention according to at least one of the previously described embodiments, an anode, a cathode and gas diffusion layers.

[0019] Furthermore, the invention relates to a fuel cell system comprising a fuel cell according to at least one of the previously described embodiments, a tank connected to an inlet of the fuel cell, and a cooling device arranged and designed to cool the fuel cell.

[0020] In order to construct the fuel cell system as simply as possible, it is also advantageous if the cooling device is designed as a (pure) air cooler.

[0021] Furthermore, a method for producing a base body for a bipolar plate is disclosed, which is preferably designed according to at least one of the previously described embodiments, wherein in a (first) step a) a core shaped as a polyhedron is provided, in a (second) step b) the core is covered or wrapped with carbon fibers designed as long fibers, in a (third) step c) an adhesive penetrating the carbon fibers is cured to form an intermediate product, forming a polyhedron having a plurality of flat plate sections, and in a (fourth) step d) the plate sections are separated such that each plate section forms an individual plate-shaped base body. This results in the most efficient possible production of the base body and ultimately also of the bipolar plate that benefits from it.

[0022] Furthermore, a method for producing a bipolar plate according to the invention according to at least one of the previously described embodiments is disclosed, wherein firstly a plate-shaped base body formed on a fiber composite material is provided and then this base body is coated with a copper-containing first coating on a first side surface, wherein in turn subsequently a second coating consisting of a stainless metal material is applied to the first coating.

[0023] The invention will now be explained in more detail below with reference to figures.

[0024] They show: Fig. 1 a perspective view of a bipolar plate according to the invention, cut in the transverse direction and shown individually with respect to several coatings, according to a preferred embodiment, Fig. 2 a plan view of the finished bipolar plate according to the invention, Fig. 3 a perspective view of a base body used to manufacture the bipolar plate, Fig. 4 a detailed view of a in the base body of the Fig. 3 introduced channel structure, Fig. 5 several different channel structures that are located in the base body of the Fig. 3 and Fig. 4 are recoverable, Fig. 6 a schematic sectional view of two bipolar plates according to the invention of Fig. 1 fuel cell, Fig. 7 is a further sectional view of the fuel cell comprising the bipolar plates according to the invention, wherein the gas diffusion layers are opposite Fig. 6 are shown in more detail, Fig. 8 a schematic diagram of a fuel cell system which, among other things, comprises several fuel cells according to Fig. 6 and Fig. 7, Fig. 9 a flow chart illustrating a manufacturing method of a base body of the bipolar plate according to the invention, and Fig. 10 is a flow chart illustrating a manufacturing method of the bipolar plate according to the invention.

[0025] The figures are merely schematic in nature and therefore serve solely to clarify the invention. The same elements are designated by the same reference numerals.

[0026] When considering the Fig. 6 and Fig. 7, a structure of a fuel cell 10 is shown. The fuel cell 10 is designed as a hydrogen-oxygen fuel cell 10. The fuel cell 10 has, in the usual way, several of the Fig. 6 and Fig. 7. However, for the sake of simplicity, only one subunit 9 is shown.

[0027] The fuel cell 10, i.e., the illustrated subunit 9 of the fuel cell 10, has two opposing bipolar plates 1 spaced apart from each other. Each bipolar plate 1 has a channel structure 5 that is incorporated into the bipolar plate 1 on a first side surface 6 (underside). In their assembled state in the fuel cell 10 / subunit 9, the bipolar plates 1 face each other with their first side surfaces 6.

[0028] The shape / course of the channel structure 5 of the bipolar plates 1 running in one plane can in principle be designed in different ways, as in Fig. 5. Accordingly, it is possible, for example, to provide a grid-like channel structure 5 with a large number of intersecting row and column sections (image top left). The channel structure 5 can also run in a meandering manner (image top right and image bottom left). Furthermore, the channel structure 5 can be designed with a constant depth. However, a depth profile that changes in the transverse direction is also possible (image top right). The channel structure 5 can also have several parallel channel sections that are connected to transversely running transverse channels at their respective ends facing the same direction (image bottom center). The channel structure 5 can also be designed in a labyrinthine manner (image bottom right).

[0029] The channel structure 5 always serves to supply hydrogen to the anode 11 or oxygen / air to the cathode 12 and to remove water.

[0030] In addition to the schematically indicated anode 11 and cathode 12, several gas diffusion layers 13a, 13b are also present in the usual way between the bipolar plates 1 of the sub-unit 9.

[0031] As already mentioned, several of these sub-units 9 are stacked on top of each other in the usual way as a fuel cell 10. These are then used together with other components of a fuel cell system 15, which is Fig. 8 is indicated schematically.

[0032] The fuel cell 10 used in an exemplary fuel cell system 15 is in Fig. 8. In addition to the actual fuel cell 10, several further components are provided in the usual way to generate electrical drive energy during operation. A tank containing hydrogen is designated by the reference numeral 17. This tank 17 / hydrogen tank is connected (fluidically) to an inlet 16 of the fuel cell 10. In addition, an air / oxygen supply device 23 is provided outside the fuel cell 10, which is also connected to the fuel cell 10. On the output side, the fuel cell 10 is connected to an HV module 24, which represents an electrical power output and is also connected, for example, to a battery. Furthermore, a controller 25 is provided to electrically control the corresponding processes for operating the fuel cell 10. A cooling device 18 as an air cooler is provided to cool the fuel cell 10.

[0033] According to the invention, the respective bipolar plate 1 of the fuel cell 10 is designed according to the invention Fig. 1 to 5, as explained below. The bipolar plate 1 according to the invention is thus present in duplicate for each subunit 9 of the fuel cell 10. The bipolar plates 1 of the fuel cell 10 are realized as identical parts.

[0034] The bipolar plate 1 has a multi-material and multi-layer structure. According to the invention, the bipolar plate 1 has a Fig. 3 and Fig. 4 has a clearly visible base body 2. The base body 2 is made directly from a fiber composite material.

[0035] In the illustrated embodiment, the base body 2 already has the finished outer shape of the bipolar plate 1 produced therefrom. The base body 2 thus already has the channel structure 5 on the first side surface 6. The channel structure 5 is introduced by means of a laser ablation process.

[0036] On a second side surface 7 (top side) of the base body 2, which is not shown here for the sake of clarity and faces opposite the first side surface 6, the base body 2 is preferably left untreated. The fiber composite material is thus exposed to the environment on the second side surface 7. The fiber composite material may then be coated with a (non-metallic) protective coating.

[0037] It is also in connection with the Fig. 1 and Fig. 2 that the base body 2 is provided with a plurality of recesses 26, 27 positioned laterally of the channel structure 5. These recesses 26, 27 are particularly preferably formed by laser cutting or, alternatively, by laser drilling. The first recesses 26 are designed as elongated holes with rounded ends.

[0038] Viewed in a longitudinal direction of the bipolar plate 1 / the base body 2, which is Fig. 2 is marked with the reference arrow 14, the first recesses 26 are positioned in end regions 29a, 29b next to the channel structure 5. The first recesses 26 are partially connected to the channel structure 5 by means of connecting passages 28 running in the plane of the channel structure 5. Two first recesses 26 are provided in each end region 29a, 29b of the base body 2, and the two first recesses 26 of each end region 29a, 29b are in turn spaced from one another in a direction transverse to the longitudinal direction, i.e. in a transverse direction of the base body 2. A second recess 27 is also present in the transverse direction between the first recesses 26 of each end region 29a, 29b. The second recess 27 is larger than the respective first recess 26 and has a rectangular cross-section. The recesses 26, 27 are each implemented as through holes that completely penetrate the base body 2.

[0039] With regard to the fiber composite material of the base body 2, it should be noted that it is made of a long fiber fabric for the thinnest possible construction and a relatively high strength / stiffness. In particular, carbon fibers 20 are used for this purpose, which are schematically shown in Fig. 9. Those carbon fibers 20 are preferably designed as coal tar fibers.

[0040] The carbon fibers 20 comprise, in particular, first carbon fibers that are aligned in the longitudinal direction 14 of the bipolar plate 1 and second carbon fibers that are aligned perpendicular to the longitudinal direction 14, i.e., in the transverse direction. As described below in connection with Fig. As explained in Figure 9, these carbon fibers 20 are pre-consolidated and pre-impregnated as a fiber fabric in the form of a prepreg during production. Alternatively, however, it is also possible in principle to process the carbon fibers 20 as a wound layer in a winding process. In other words, the base body 2 is thus made of a CFRP material.

[0041] With regard to the fiber composite material of the base body 2, it should also be noted that this can be manufactured using a multi-step process. Accordingly, it is possible to first apply a hydrogen-impermeable barrier layer to the core 19 and then lay down a (first) layer of pre-impregnated carbon fibers 20, after which this (first) layer of carbon fibers 20 is initially cured together with the barrier layer. In a further step, an additional barrier layer is then applied to the previously cured (first) layer of fiber composite material, and a further (second) layer of carbon fibers 20 is then applied. This (second) layer of carbon fibers 20, together with the additional barrier layer, is then also cured. This process can, in principle, be repeated several more times, so that the base body 2 is built up layer by layer according to the onion principle.

[0042] In principle, it is also possible to not form the respective barrier layer as a separate layer, but to integrate its function directly into an adhesive processed into the carbon fiber 20. This ultimately results in the fiber composite material becoming impermeable to hydrogen. Like the barrier layer, this adhesive then contains platelet-shaped filler particles, such as those made of montmorillonite. These filler particles have a platelet structure and generate a high barrier density, thus creating a layer impermeable to hydrogen.

[0043] The channel structure 5 is introduced directly into the fully cured fiber composite material and the recesses 26, 27 are formed.

[0044] On the base body 2, as then in Fig. As can be seen in Figure 1, a first coating 3 has been applied. This first coating 3 is designed as a purely copper-containing layer (consisting of almost 100% copper). The first coating 3 is applied chemically, namely electroplated. The first coating 3 is preferably applied over the entire first side surface 6.

[0045] In a further preferred embodiment, it is also expedient to apply the first coating 3 to the entire base body 2 / to completely envelop the base body 2 with the first coating 3 and thus to apply the first coating 3 to both the first side surface 6 and the second side surface 7. In the present embodiment, however, the second side surface 7 is left free of the first coating 3.

[0046] Again on the first coating 3 according to Fig. 1, a second coating 4 is applied. The second coating 4 is implemented as a stainless steel coating. The second coating 4 is applied to the entire first side surface 6 and completely covers the first coating 3 towards the surrounding area. In this embodiment, the second side surface 7 is also free of the second coating 4, although in further embodiments, this second coating 4 can alternatively completely envelop the base body 2.

[0047] In a preferred embodiment, a glass fiber laminate is applied to the second side surface 7, forming an electrical insulation layer 8, as shown in Fig. 1 is indicated schematically. The insulation layer 8 and the second coating 4 then together form a complete / all-encompassing enclosure against the environment.

[0048] According to an alternative embodiment, it is also advantageous if the base body 2 is initially shaped such that it does not itself have a channel structure 5. The base body 2 can thus be provided without a channel structure 5. In a subsequent step, the first coating 3 and / or the second coating 4 are provided with the channel structure 5 before being applied to the base body 2. This can be achieved, for example, by embossing. The two coatings 3, 4 are then implemented, for example, as films. Subsequently, the two coatings 3, 4, comprising the channel structure 5, are attached to the base body 2, for example by adhesive bonding.

[0049] Combined with Fig. Figure 9 illustrates a preferred manufacturing method for a base body 2. For this purpose, a core 19 is first provided in a (temporally first) step a). The core 19 is shaped as a polyhedron / cube. The moldable fiber composite material for forming the base body 2 is then applied to this core 19 in a (temporally second) step b). For this purpose, the carbon fibers 20 are first applied or wound accordingly. The carbon fibers 20, as already mentioned, can be pre-impregnated before application or only impregnated after application / winding. Finally, at the end of step b), the adhesive-impregnated carbon fiber is cured, after which a fully cured polyhedron (as intermediate product 22) is formed in a (temporally third) step c).Subsequently, the core 19 can optionally be removed as a soluble core before the subsequent (step d)) cutting open the polyhedron / disassembling the polyhedron. Preferably, however, the polyhedron is disassembled into several plate sections 21 directly after step c), and only then is the core 19 removed or reused. The plate sections 21 each form a blank for forming the base body 2. Subsequently, according to the preferred embodiment of the . Fig. 1, the channel structure 5 is introduced directly into this plate section 21 to form the finished base body 2. The recesses 26, 27 are also introduced.

[0050] According to Fig.10, that base body 2 is then used to produce a bipolar plate 1. The base body 2 is thus prepared in a step I). After step I), the first coating 3 is applied in a step II). Subsequently, the second coating 4 is applied in a step III). List of reference symbols 1 bipolar plate 2 base bodies 3 first coating 4 second coating 5 Channel structure 6 first side surface 7 second side surface 8 Insulation layer 9 subunits 10 fuel cell 11 Anode 12 Cathode 13a first gas diffusion layer 13b second gas diffusion layer 14 Longitudinal direction 15 Fuel cell system 16 Entrance 17 tanks 18 Cooling device 19 core 20 carbon fiber 21 plate section 22 Intermediate product 23 Feeding device 24 HV module 25 Control 26 first recess 27 second recess 28 Connecting Passage 29a first end area 29b second end area QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2008 056 421 A1

[0002] DE 10 2010 051 964 A1

[0002] KR 10 2005 0 105 784 A

[0002]

Claims

[1] Bipolar plate (1) for a fuel cell (10), with a base body (2) made of fiber composite material and at least one metallic coating (3, 4) applied to the base body (2), wherein a copper-containing first coating (3) is applied directly to the base body (2) and in turn a second coating (4) consisting of a rust-proof metal material is applied to this first coating (3). [2] Bipolar plate (1) according to claim 1, characterized by that a channel structure (5) designed to collect and guide fluids is introduced directly into the base body (2) or is fastened to the base body (2). [3] Bipolar plate (1) according to claim 2, characterized by that the channel structure (5) is introduced directly into the base body (2) by means of laser ablation. [4] Bipolar plate (1) according to claim 2, characterized by that the channel structure (5) is embossed into one of the coatings (3, 4). [5] Bipolar plate (1) according to one of claims 1 to 4, characterized by that the fiber composite material of the base body (2) contains carbon fibers (20) converted into long fibers. [6] Bipolar plate (1) according to claim 5, characterized by that the fiber composite material comprises first carbon fibers and second carbon fibers aligned obliquely to the first carbon fibers. [7] Bipolar plate (1) according to claim 5 or 6, characterized by that the carbon fibers (20) are pitch fibers. [8] Bipolar plate (1) according to one of claims 1 to 7, characterized by that the fiber composite material has several layers of a fiber fabric or several winding layers. [9] Bipolar plate (1) according to one of claims 1 to 8, characterized bythat the two coatings (3, 4) are applied to a first side surface (6) of the base body (2) and the base body (2) is left uncoated on a second side surface (7) facing opposite the first side surface (6) or is coated with an electrical insulation layer (8). [10] Fuel cell (10) with two oppositely arranged bipolar plates (1) according to one of claims 1 to 9, between which bipolar plates (1) an anode (11), a cathode (12) and gas diffusion layers (13a, 13b) are arranged. [11] Fuel cell (10) according to claim 10, characterized by that several sub-units (9), each having two oppositely arranged bipolar plates (1), an anode (11), a cathode (12) and gas diffusion layers (13a, 13b), are present. [12] Fuel cell system (15) with a fuel cell (10) according to claim 10 or 11, a tank (17) connected to an inlet (16) of the fuel cell (10) and a cooling device (18) arranged and designed to cool the fuel cell (10). [13] Fuel cell system (15) according to claim 12, characterized by that the cooling device (18) is designed as an air cooler.

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