Bipolarplatte

Abstract

Bipolar plate (2) for use in a fuel cell system, comprising a first plate half (2a) for arrangement on an anode side (AS) of a membrane electron unit (MEA) of the fuel cell system, a second plate half (2b) for arrangement on a cathode side (CS) of a membrane electron unit (MEA) of the fuel cell system, wherein the bipolar plate (2) has a basic structure (4) made of a base material which is at least partially coated with a conductive coating (6), wherein the conductive coating (6) has a metal oxide content.

Description

[0001] The present invention relates to a bipolar plate for use in a fuel cell system and to a fuel cell system comprising a plurality of such bipolar plates. State of the art

[0002] Fuel cells are electrochemical energy converters in which reactant gases, such as hydrogen and oxygen, are converted into water, electrical energy, and heat. The reactant gases are separated by a polymer membrane, which provides the necessary insulation. A typical fuel cell has a structure in which, following the polymer membrane, a catalyst layer and a gas diffusion layer (membrane electrode assembly) are arranged on both sides, each followed by a bipolar plate. The bipolar plates within the fuel cell perform several functions. They serve for the electrical interconnection of the cells, for the supply and distribution of the reactant gases, for the removal of the reaction products (water), and for the supply and distribution of the coolant.For the purpose of reducing contact resistance between a bipolar plate and the adjacent membrane electrode assembly to improve the electrical conductivity of fuel cells, it is known to coat bipolar plates with a conductive varnish.

[0003] A disadvantage is that the conductive coatings used are susceptible to the chemically aggressive environment in fuel cells. During fuel cell operation, radicals are formed that decompose the binders in the conductive coatings. This leads to an increase in contact resistance between a bipolar plate and an adjacent membrane electrode assembly, thus reducing the electrical conductivity of the fuel cells and significantly decreasing their performance. Disclosure of the invention

[0004] The invention relates, according to a first aspect, to a device with the features of the independent device claim, and according to a second aspect, to a system according to the independent system claim. Further features and details of the invention become apparent from the respective dependent claims, the description, and the drawings. Features and details described in connection with the device according to the invention naturally also apply in connection with the system according to the invention, and vice versa, so that the disclosure relating to the individual aspects of the invention always includes, or allows for, reciprocal reference.

[0005] The bipolar plate according to the invention is intended to guarantee higher stability and resistance to the chemically aggressive conditions within a fuel cell while maintaining the same performance. In particular, the bipolar plate according to the invention is intended to counteract the degradation of a conductive coating caused by the chemically aggressive conditions within a fuel cell and thus ensure stable, long-lasting and efficient operation of a fuel cell system.

[0006] The bipolar plate according to the invention for use in a fuel cell system comprises a first plate half for arrangement on an anode side of a membrane electron unit of the fuel cell system and a second plate half for arrangement on a cathode side of a membrane electron unit of the fuel cell system, wherein the bipolar plate has a basic structure made of a base material which is at least partially coated with a conductive coating, wherein the conductive coating has a metal oxide content.

[0007] The surface-optimized bipolar plate according to the invention can preferably be used in a fuel cell or in a fuel cell system.

[0008] The bipolar plate can also be used as a gas distribution plate in electrolysis processes. When used in a fuel cell system, the bipolar plate is preferably suitable for use in a motor vehicle or similar vehicle. It can also be used in other fuel cell-powered vehicles or stationary systems.

[0009] The first and second halves of a bipolar plate can be understood as the two halves that make up a bipolar plate. These halves can be joined together to form a complete bipolar plate. The anode side of a membrane electron unit (MEU) can be understood as the part of the MEU where the fuel (here, hydrogen) is split into protons and electrons, which is the first step in the electrochemical process of the fuel cell. Similarly, the cathode side of the MEU can be understood as the part of the MEU where oxygen is reduced by first accepting electrons and then reacting with protons to form water. This reaction is the final step in the electrochemical process of the fuel cell and contributes to the generation of electric current.

[0010] Within the scope of the invention, it has been recognized that the inclusion of metal oxides within the conductive coating can successfully counteract the decomposition of a binder or binding agent within the conductive coating. It has also been recognized according to the invention that metal oxides are suitable as effective radical scavengers. Furthermore, it has been recognized that hydroxyl radicals or hydroperoxyl radicals primarily contribute to the decomposition of the conductive coating of bipolar plates, which, due to their formation from hydrogen peroxide—catalyzed by free iron ions—preferentially arise in the immediate vicinity of iron-containing bipolar plates.

[0011] With a view to achieving a cost-effective, stable, and durable design for a bipolar plate used in an energy-efficient fuel cell system, it is advantageous to use an iron-containing material, preferably stainless steel, as the base material. Bipolar plates made of iron-containing base materials are particularly suitable for use in energy-efficient fuel cell systems due to their high electrical conductivity, which is essential for their function as current collectors and distributors. Such materials also guarantee high gas tightness and ease of machining. Alternatively, the bipolar plate can also be made of titanium or graphite.

[0012] In the context of particularly effective protection of a bipolar plate, especially the conductive coating of a bipolar plate, it can also be advantageously provided that the metal oxide is cerium oxide (Ce x O Y, e.g. as Ce2O3, preferably as CeO2) and / or silver oxide (Ag X O Y , e.g. as AgO, Ag3O4 or Ag2O3, preferably as Ag2O) and / or platinum oxide (Pt X O Y , e.g. as PtO or PtO3, preferably as PtO2). PtO2, Ag2O and especially CeO2 have proven to be particularly effective radical scavengers in the course of developing the present invention, especially as scavengers of hydroxyl and hydroperoxyl radicals, which were identified within the scope of the invention as the main cause of the destruction of the conductive coating of a bipolar plate.

[0013] With a view to ensuring high electrical conductivity, high thermal conductivity, and high corrosion resistance, the conductive coating can advantageously further be provided according to the invention to comprise a carbon-containing material, preferably a mixture of carbon black and graphite. Alternatively to the mixture of carbon black and graphite, the carbon-containing material can also be in the form of graphene, carbon fibers, or the like, and mixtures thereof.

[0014] In the context of cost-effective production of stable and robust bipolar plates, it is advantageously possible for the conductive coating to include a binder, preferably in the form of a plastic, particularly a thermosetting plastic. Suitable thermosetting plastics include, for example, polyurethanes (PU), polyamide-imides (PAls), polyimides (PI), acrylates, polyvinylidene fluoride (PVDF), polyethylene (PE), and / or similar polymers and mixtures thereof. The use of such plastic materials also promises, in particular, a weight-optimized design.

[0015] To ensure the most effective possible scavenging of radicals, while avoiding any negative impact on other processes such as proton conductivity, it can be advantageous for the metal oxide content to be between 0.1 and 10 wt% based on the dry fraction of the conductive coating. With appropriate distribution of the metal oxide particles, this can preferably be achieved at a concentration of 10–500 µg / cm². 2 Advantageously, the metal oxide content is < 10 wt.%, in particular < 1 wt.% based on the dry fraction of the conductive coating.

[0016] Furthermore, to ensure the most effective possible scavenging of radicals, it is advantageous to provide that the metal oxides are present in the conductive coating in the form of nanoparticles, the size of which is preferably < 100 nm, and in particular < 50 nm. Using metal oxides in the form of nanoparticles increases their specific surface area, leads to a more uniform distribution, and thus enables improved interaction between the metal oxides and radicals.

[0017] With a view to minimizing manufacturing and cost effort, the bipolar plate can further be provided with a corrugated profile with outer and inner areas, wherein the conductive coating is preferably arranged only in the outer areas. It has been recognized within the scope of the invention that for significantly improved electrical conductivity, it is sufficient to arrange the conductive coating in the immediate boundary areas between the bipolar plate and the gas diffusion layer.

[0018] Similarly, to minimize manufacturing and cost effort, the metal oxide-containing conductive coating can be applied only to the second half of the plate for placement on the cathode side of a membrane electron unit of the fuel cell system. It has been recognized within the scope of the invention that the main site of formation of harmful radicals is located on the cathode-side part of the bipolar plate. It can also be provided that the basic structure is coated differently on the anode and cathode sides, with the cathode-side part preferably being coated with a metal oxide-containing conductive coating and the anode-side part with a coating to increase contact conductivity.

[0019] For additional protection of a conductive coating, in particular for protecting a binder of a conductive coating from hydrolysis, it can advantageously be further provided that the conductive coating comprises a base, preferably an amine, and / or that the conductive coating comprises a π-binder as a binder, preferably a polyimide. A π-binder can in particular be understood to be a molecule that has π-electrons via which the molecule can interact with other molecules or atoms.

[0020] The invention also relates to a fuel cell system comprising a plurality of bipolar plates described above. The fuel cell system according to the invention thus has the same advantages as those already described in detail with regard to the bipolar plate according to the invention.

[0021] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description can each be essential to the invention individually or in any combination.

[0022] They each show schematically: Fig. 1 a representation of a fuel cell of a fuel cell system according to the invention, comprising a plurality of bipolar plates according to a first embodiment, and Fig. 2 a representation of a cross-section of a bipolar plate according to the invention for use in a fuel cell or a fuel cell system according to a first embodiment.

[0023] Fig. Figure 1 shows a schematic representation of a fuel cell BSZ of a fuel cell system according to the invention, comprising a plurality of bipolar plates 2 according to a first embodiment.

[0024] The bipolar plates 2 comprise a first plate half 2a for arrangement on an anode side AS of a membrane electron unit (MEA) of the fuel cell system and a second plate half 2b for arrangement on a cathode side CS of a membrane electron unit (MEA) of the fuel cell system. The membrane electron unit (MEA) further consists of the centrally arranged polymer electrolyte membrane (PEM), to which the anode catalyst layer (ACL) is attached on the anode side. a middle porous layer MPL and a gas diffusion layer GDL are arranged, whereas on the cathode side the cathode catalyst layer CCL, a middle porous layer MPL and a gas diffusion layer GDL are arranged.

[0025] Fig. Figure 2 shows a schematic representation of a cross-section of a bipolar plate 2 according to the invention for use in a fuel cell (FCC) or a fuel cell system according to a first embodiment. Fig. 2 is also the intended electron flow (e - ) as well as the locally separated supply of H2 and O2.

[0026] As per Fig. As can be seen in Figure 2, the bipolar plate 2 according to the invention comprises a first plate half 2a for arrangement on an anode side AS of a membrane electron unit (MEA) of the fuel cell system and a second plate half 2b for arrangement on a cathode side CS of a membrane electron unit (MEA) of the fuel cell system, wherein the bipolar plate 2 has a base structure 4 made of a base material which is at least partially coated with a conductive coating 6, wherein the conductive coating 6 contains a metal oxide component. (It can also be provided that the base structure is coated differently on the anode side and the cathode side, wherein the cathode-side part may preferably be coated with a conductive coating containing a metal oxide and the anode-side part with a coating to increase the contact conductivity.)

[0027] The base material is in the form of an iron-containing material, preferably in the form of stainless steel.

[0028] The metal oxide can preferably be in the form of CeO2 and / or Ag2O, wherein the metal oxide content can advantageously be between 0.1 and 10 wt.% based on the dry fraction of the conductive coating 6. The metal oxides can be present in the conductive coating 6 in the form of nanoparticles, wherein the size of the nanoparticles is preferably < 100 nm, in particular < 50 nm.

[0029] As per Fig. As can be seen in Figure 2, the bipolar plate 2 has a wave-shaped profile with outer areas 8a and inner areas 8b, with the conductive coating 6 being arranged only in the outer areas 8a.

[0030] The metal oxide-containing conductive coating 6 can also be arranged - unlike as shown here - only on the second half of the plate 2b for arrangement on a cathode side CS of a membrane electron unit MEA of the fuel cell system, since this location has been identified as the main location for the presence of harmful radicals.

[0031] Furthermore, it can be provided that the conductive coating 6 has a base, preferably an amine and / or that the conductive coating 6 has a π-binder as a binder, preferably a polyimide.

[0032] By means of the bipolar plate 2 according to the invention, it is particularly possible to guarantee higher stability and resistance to the chemically aggressive conditions within a fuel cell (FCC) with the same performance and to counteract degradation of a conductive coating 6 by the chemically aggressive conditions within a fuel cell (FCC), thus ensuring stable, durable and efficient operation of a fuel cell system.

Claims

[1] Bipolar plate (2) for use in a fuel cell system, comprising: - a first plate half (2a) for arrangement on an anode side (AS) of a membrane electron unit (MEA) of the fuel cell system, - a second plate half (2b) for arrangement on a cathode side (CS) of a membrane electron unit (MEA) of the fuel cell system, - wherein the bipolar plate (2) has a basic structure (4) made of a base material which is at least partially coated with a conductive lacquer coating (6), characterized by , that the conductive coating (6) contains a metal oxide content. [2] Bipolar plate (2) according to claim 1, characterized by that the base material is an iron-containing material, preferably stainless steel. [3] Bipolar plate (2) according to claim 1 or 2, characterized by that the metal oxide is formed as CeO2, Ag2O, PtO2 or mixtures thereof. [4] Bipolar plate (2) according to any one of the preceding claims, characterized by , that the conductive coating (6) comprises a carbon-containing material, preferably a mixture of carbon black and graphite. [5] Bipolar plate (2) according to any one of the preceding claims, characterized by , that the conductive coating (6) comprises a binder, wherein the binder is preferably in the form of a plastic, in particular in the form of a thermosetting plastic. [6] Bipolar plate (2) according to any one of the preceding claims, characterized by , that the metal oxide content is between 0.1 and 10 wt.% based on the dry fraction of the conductive coating (6). [7] Bipolar plate (2) according to any one of the preceding claims, characterized by that the metal oxides are present in the form of nanoparticles within the conductive coating (6), wherein the size of the nanoparticles is preferably < 100 nm, in particular < 50 nm. [8] Bipolar plate (2) according to any one of the preceding claims, characterized by , that the bipolar plate (2) has a wave-shaped profile with outer areas (8a) and inner areas (8b), wherein preferably the conductive coating (6) is arranged only in the outer areas (8a). [9] Bipolar plate (2) according to any one of the preceding claims, characterized by , that the conductive coating (6) is arranged only on the second plate half (2b) for arrangement on a cathode side (CS) of a membrane electron unit (MEA) of the fuel cell system. [10] Bipolar plate (2) according to any one of the preceding claims, characterized by , that the conductive coating (6) has a base, preferably an amine and / or that the conductive coating (6) has a π-binder as a binder, preferably a polyimide. [11] Fuel cell system comprising a plurality of bipolar plates (2) according to any one of the preceding claims.

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