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) comprises a base.

Description

[0001] The present invention relates to a bipolar plate for use in a fuel cell system, a method for manufacturing a bipolar plate, and 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.To reduce contact resistance between a bipolar plate and the adjacent membrane electrode assembly, thereby improving the electrical conductivity of fuel cells, it is known to coat bipolar plates with a conductive coating. Additionally, the conductive coating protects the surface of the bipolar plates from oxidation.

[0003] A disadvantage is that the conductive coatings used are susceptible to the chemically aggressive environment in fuel cells. The binders in these coatings degrade due to the acidic conditions. 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, according to a second aspect to a method according to the independent method claim, and according to a third aspect to a system according to the independent system claim. Further features and details of the invention will 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 method and the system according to the invention, and vice versa, so that the disclosure of 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 by hydrolysis 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 lacquer coating, wherein the conductive lacquer coating contains a proportion of a base.

[0007] The bipolar plate according to the invention can preferably be used in a fuel cell or in a fuel cell system. Likewise, the use of the bipolar plate as a gas distribution plate in electrolysis processes is conceivable. When used in a fuel cell system, the bipolar plate can preferably be used in a motor vehicle or the like. Likewise, use in other fuel cell-powered vehicles or stationary systems is conceivable.

[0008] 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.

[0009] Within the scope of the invention, it has been discovered that the inclusion of a base within the conductive coating can successfully counteract the hydrolysis of a binder or binding agent within the conductive coating. In this context, the base acts particularly as an acid scavenger to hinder or prevent the catalytic hydrolysis of a binder in the conductive coating, thus preventing or at least hindering its hydrolytic decomposition. For the purposes of this invention, a base can be understood to be, in particular, a Brønsted base, i.e., a proton acceptor, and / or a Lewis base, i.e., an electron pair donor.

[0010] 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.

[0011] For particularly effective protection of a bipolar plate, especially the conductive coating of a bipolar plate, it is advantageous to provide that the base is in the form of an amine or polyamine, preferably in the form of basic binders such as polyethyleneimine and / or polyvinylamine and / or polyvinylpyridine. These basic binders may preferably be present in the conductive coating at a proportion of 30 to 100 wt.%. To increase the stability of the added base, it may also be chemically cross-linked. Additives such as organic or inorganic salts, e.g., carbonates or hydrogen carbonates, may also be used as bases. Similarly, additives such as imides, e.g., bis-(2,6-diisopropylphenyl)carbodiimide, or acrylates, such as trimethylolpropane triacrylate, may be added as acid scavengers to prevent hydrolysis. The additives may be present in the conductive coating at a proportion of < 10 wt.%, preferably < 5 wt.%.It is understood that the conductive coating may contain only basic binders or additives or mixtures of basic binders and additives, preferably consisting of mixtures of basic binders (polymers), additives and classic polymers (polyurethanes, polyamide-imides, polyimides, acrylates, etc.).

[0012] 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.

[0013] 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, the binder preferably being in the form of a plastic, particularly a thermosetting plastic. Suitable thermosetting plastics include, in addition to the plastics according to the invention, polyurethanes (PU), polyamide-imides (PAls), polyimides (PI), acrylates, polyvinylidene fluoride (PVDF), polyethylene (PE), similar polymers, and mixtures thereof. The use of such plastic materials also promises, in particular, a weight-optimized design.

[0014] To ensure the most effective possible acid neutralization while avoiding any negative impact on other processes, it can be advantageous for the base content to be between 10 and 100 wt.% based on the dry fraction of a binder in the conductive coating (e.g., basic binders: 30 to 100 wt.% and additives: 5 to 10 wt.%). Preferably, the base content in the conductive coating can be at least 50 wt.% based on the dry fraction of a binder in the conductive coating, and in particular at least 60 wt.%.

[0015] 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.

[0016] Similarly, to minimize manufacturing and cost effort, the conductive coating can be applied only to the first half of the plate for placement on the anode side of a membrane electron unit of the fuel cell system. Within the scope of the invention, it has been recognized that the highest acid concentration is localized on the anode-side part of the bipolar plate.

[0017] For additional protection of a conductive coating, particularly for additional protection of a binder in a conductive coating against radicals, it can advantageously be further provided that the conductive coating comprises a metal oxide, preferably CeO₂, Ag₂O, PtO₂, analogous salts of other oxidation states, and / or the respective mixtures thereof. Likewise, with a view to effective protection of a binder in a conductive coating, it can be provided 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.

[0018] The invention also relates to a method for producing a bipolar plate as described above, wherein the base is added to the conductive coating before the conductive coating is applied to the base structure of the bipolar plate. The method 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. It can also advantageously be provided that a fuel cell or fuel cell system is purged with a base, such as an amine, during maintenance in order to regenerate the base within the conductive coating.

[0019] 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 and the method according to the invention.

[0020] 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. The drawings schematically show: 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, 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, and Fig. 3 An electron microscopic image of a bipolar plate coated with a conductive varnish.

[0021] 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.

[0022] 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, on the anode side, the anode catalyst layer (ACL), 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.

[0023] 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.

[0024] 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 basic 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 base. It can also be provided that the basic structure is coated differently on the anode side and the cathode side, i.e., each with a coating of a different composition.

[0025] The base material is in the form of an iron-containing material, preferably in the form of stainless steel.

[0026] The base can also be in the form of an amine or polyamine, preferably in the form of polyethyleneimine and / or polyvinylamine and / or polyvinylpyridine, wherein the proportion of base can advantageously be between 10 and 100 wt.% based on the dry fraction of a binder of the conductive coating 6 (e.g. basic binders: 30 to 100 wt.% and additives 5 to 10 wt.%).

[0027] 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.

[0028] The conductive coating 6 can also – contrary to the present description – be arranged only on the first half of the plate 2a for placement on an anode side AS 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 acid. It is understood that a different type of coating can then preferably be arranged on the second half of the plate.

[0029] Furthermore, it can be provided that the conductive coating 6 comprises a metal oxide, preferably CeO2, Ag2O, PtO2, analogous salts of other oxidation states and / or the respective mixtures thereof and / or that the conductive coating 6 comprises a π-binder as a binder, preferably a polyimide.

[0030] Fig.Figure 3 shows an electron microscopic image of a bipolar plate 2 coated with a conductive lacquer, in which it can be clearly seen that due to the hydrolytic decomposition of the binder of the conductive lacquer coating 6 cavities have formed within the conductive lacquer coating 6, which drastically reduce the electrical conductivity of the bipolar plate 2.

[0031] 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 proportion of a base. [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 bythat the base is in the form of an amine or polyamine, preferably in the form of polyethyleneimine and / or polyvinylamine and / or polyvinylpyridine. [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 proportion of base is between 10 and 100 wt.% based on the dry fraction of a binder of the conductive coating (6). [7] 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). [8] Bipolar plate (2) according to any one of the preceding claims, characterized by , that the conductive coating (6) is arranged only on the first plate half (2a) for arrangement on an anode side (AS) of a membrane electron unit (MEA) of the fuel cell system. [9] Bipolar plate (2) according to any one of the preceding claims, characterized by , that the conductive coating (6) comprises a metal oxide, preferably CeO2, Ag2O, PtO2, analogous salts of other oxidation states and / or the respective mixtures thereof and / or that the conductive coating (6) comprises a π-binder as a binder, preferably a polyimide. [10] Method for manufacturing a bipolar plate (2) according to any one of the preceding claims, characterized by, that the base is supplied to the conductive paint before the conductive paint is coated onto the base structure of the bipolar plate (2). [11] Fuel cell system comprising a plurality of bipolar plates (2) according to any one of the preceding claims.

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