Coated separator plate for an electrochemical system and method for producing a coated separator plate for an electrochemical system

Abstract

This document relates to a separator plate for an electrochemical system comprising a metallic substrate and a coating, wherein the coating comprises two different layers. The electrochemical system can, in particular, be a fuel cell system, an electrochemical compressor, an electrolyzer, or a flow battery, such as a redox flow battery. Furthermore, this document relates to a method for producing a coated separator plate for an electrochemical system.

Description

[0001] This document relates to a separator plate for an electrochemical system comprising a metallic substrate and a coating, wherein the coating comprises two different layers. The electrochemical system can, in particular, be a fuel cell system, an electrochemical compressor, an electrolyzer, or a flow battery, such as a redox flow battery. Furthermore, this document relates to a method for producing a coated separator plate for an electrochemical system.

[0002] Depending on the application, separator plates can have various functions. On the one hand, they ensure an electrically conductive connection to an adjacent layer, which might be, for example, a gas diffusion layer. On the other hand, separator plates typically serve to transport reactants and / or reaction products to and from the substrate, with a fluid guidance structure in the form of channels usually being provided for this transport. Furthermore, separator plates can be used to dissipate heat from the reaction, for example, by means of a coolant. This is often achieved by designing the separator plate as a two-layer plate, with the two layers defining an interior space through which a coolant flows. These layers are referred to as separator plates due to their function of separating the media.

[0003] The reaction conditions during operation of the electrochemical system often have a negative impact on the service life of the separator plates. For example, aggressive reaction conditions (e.g., the creation of hydrogen) can... + , H2 and O 2, which are already aggressive substances in themselves, as well as high cell voltages) often lead to corrosion of the separator plate, especially on the outside of a two-layer separator plate.

[0004] To counteract corrosion of the separator plate, it can be coated with an anti-corrosion layer, for example, in the electrochemically active area. To ensure long-term corrosion resistance, this coating should not be damaged during manufacturing or transport.

[0005] However, applying such anti-corrosion coatings can be expensive and complex due to the materials used in the coating and / or the additional process steps. When selecting a suitable anti-corrosion coating, the electrical contact resistance of the separator plate should also be considered, as the separator plate should be electrically conductive in the electrochemically active area. Precious metals would be suitable in principle due to their corrosion resistance and low electrical resistance, but their high cost makes their use uneconomical.

[0006] There is therefore a constant need to improve separator plates in terms of their corrosion resistance, electrical contact resistance, manufacturing costs and / or service life.

[0007] According to a first aspect of this disclosure, a separator plate for an electrochemical system is proposed.

[0008] The separator plate comprises a metallic substrate, a cover layer, and a mixed layer. The cover layer is positioned on top of the substrate, covering it, and contains a primary metal. The mixed layer is located on the side of the cover layer facing away from the substrate and contains a mixture of the primary metal and / or the cover layer material on the one hand, and a second metal on the other. The second metal is more noble than the primary metal and / or the metallic substrate.

[0009] The top layer can function, in particular, as an anti-corrosion layer and / or an adhesion promoter between the substrate and the second metal, while the mixed layer ensures sufficiently good electrical conductivity of the separator plate at its surface. Since the second metal is more noble than the first, a single layer of the second metal on the substrate would also be conceivable, as the second, more noble metal is more corrosion-resistant than the first. However, this is associated with the disadvantage of high manufacturing costs, for example, if the second metal is a platinum group metal or another noble metal. Furthermore, the intermediate top layer allows for better application and adhesion of the second metal, due to lattice matching.By combining the top layer and the mixed layer, the corrosion resistance and electrical conductivity of the separator plate can be improved, while at the same time the (material) costs for the separator plate can be kept low or at a level acceptable for mass production.

[0010] According to a standard definition, precious metals and semi-precious metals are metallic elements whose standard potential is positive relative to the hydrogen electrode. The second metal thus has a standard potential relative to the hydrogen electrode that is higher (more positive) than the standard potential of the first metal relative to the hydrogen electrode. The second metal can, for example, be a platinum group metal. Platinum group metals include platinum, iridium, ruthenium, rhodium, palladium, and osmium. Platinum and iridium are particularly prominent examples.

[0011] The top layer and / or the mixing layer may be applied to the entire surface and / or only to sections of at least one surface of the separator plate. In particular, the top layer and / or the mixing layer are applied completely or exclusively in an electrochemically active area of ​​the separator plate, i.e., where the electrochemical reactions take place during operation of the separator plate. Outside the electrochemically active area, the top layer and the mixing layer need not necessarily be present.

[0012] There are several possible options for the material of the top layer. The top layer can be made primarily of the first metal or consist entirely of the first metal. Alternatively, the top layer material can be a metal compound containing the first metal. In one variation, the top layer can contain oxides, nitrides, and / or oxynitrides of the first metal, possibly mixed with the first metal, or consist entirely of these. The first metal could be, for example, niobium, titanium, or chromium, which are closely related in the electrochemical series. The top layer can be designed to contain at least one of these metals or a mixture or alloy of at least two of these metals. The two layers can be distinguished, among other things, by the fact that the top layer does not contain the second metal, while the second metal is present in the mixed layer.

[0013] The topcoat and the substrate can differ from each other in two ways: firstly, they may be made of different materials containing different metals, for example, when niobium is used as the first metal on a titanium substrate. Secondly, they may differ in that the topcoat material and the substrate material itself, even if they contain the same or an identical metal, are nevertheless different materials, as is the case, for example, with a chromium / chromium nitride mixture, where chromium is the first metal, on a stainless steel substrate that also contains chromium.

[0014] In one embodiment, the concentration of the second metal in the mixed layer, measured perpendicular to a separator plate plane, increases towards the side of the mixed layer facing away from the cover layer. Furthermore, the concentration of the first metal in the mixed layer, measured perpendicular to a separator plate plane, can decrease towards the side of the mixed layer facing away from the cover layer.

[0015] The mixed layer may also contain oxides, nitrides, and / or oxynitrides, particularly of the first metal. The nitrides can form as a result of the manufacturing process, for example, if the manufacturing process (e.g., PVD) takes place under a nitrogen atmosphere. Similarly, oxides and oxynitrides can be formed when using a suitable atmosphere during the manufacturing process (gas mixtures of O₂ and N₂ or O₂ alone). Alternatively, the oxides can form after a storage period of the separator plate or during operation of the separator plate.

[0016] To further improve electrical conductivity, it can be advantageous for the second metal to form electrically conductive paths extending from the top layer to the surface of the mixed layer. These conductive paths often form spontaneously (because they are energetically more favorable), for example, during a PVD or CVD manufacturing process. However, a full-surface layer of the second metal on the surface of the mixed layer is not necessary, at least not on the anode side.

[0017] The thickness of the top layer is often greater than the thickness of the composite layer, in particular at least twice, three times, or five times greater than the thickness of the composite layer. For example, the thickness of the top layer can be at least 50 nm, often at most 1000 nm or at most 1500 nm. Furthermore, an exemplary thickness of the composite layer can be at least 10 nm, usually at most 100 nm. The substrate is often made of stainless steel, steel, aluminum, or titanium. The material of the top layer typically differs from the material of the substrate. Furthermore, in embodiments, the substrate can be substantially free of the first metal. In an alternative embodiment, however, the first metal can be present in both the top layer and the substrate; this applies in particular to chromium. Usually, the substrate and the top layer are substantially free of the second metal.The substrate can have a thickness of at least 50 µm and is therefore significantly thicker than the two coatings.

[0018] The top layer is usually applied directly to the substrate. Furthermore, the mixing layer is typically applied directly to the top layer. "Directly" here means that each layer is in contact with the other, and there are no intermediate layers.

[0019] In one example, the separator plate can have an elastomer layer arranged on the mixing layer, whereby the elastomer layer is only applied in sections or not across the entire surface. The elastomer layer can, for example, be designed as a sealant to seal at least parts of the separator plate.

[0020] The separator plate can be coated on one or both sides. The top layer and the mixing layer can therefore be applied to both sides or only one side of the separator plate. It is also possible for the top layer to be applied to both sides, while the mixing layer is only applied to one side of the separator plate. For example, if the reaction conditions on one flat side of the separator plate are relatively or particularly aggressive, but have little influence on the corrosion behavior of the other flat side, only a single-sided coating is required.

[0021] In some applications, two separator plates are joined to form a bipolar plate, for example, in a fuel cell stack. A cooling chamber for holding a coolant can extend between the separator plates. In these cases, the side of the separator plate(s) facing the cooling chamber can be provided without the aforementioned cover layer and the mixing layer, since no significant chemical reactions take place in the cooling chamber. In electrolyzer applications, the bipolar plate is usually a single layer. In this case, the separator plate designed as a bipolar plate can be coated on both sides with the cover layer and the mixing layer. However, it is also possible to provide both the cover layer and the mixing layer on one side and only the cover layer on the other, particularly the hydrogen-carrying side.

[0022] Often, the top layer and / or the mixed layer are applied using PVD or CVD.

[0023] According to another aspect, a method for manufacturing the separator plate is provided. This method may, for example, include the following steps: - Providing a metallic substrate; - Applying a top layer of a first metal to the substrate, for example by means of PVD or CVD, in particular by sputtering the first metal onto the substrate; - Co-sputtering of the first metal with a second metal to create the mixed layer.

[0024] Sputtering or co-sputtering can take place under a nitrogen and / or oxygen atmosphere or under an argon atmosphere. The process may include further steps: - Formation of conduction paths of the second metal in the mixed layer, the conduction paths extending from the cover layer to the surface of the mixed layer.

[0025] According to another aspect of this document, an electrochemical system is provided which comprises a plurality of stacked separator plates according to one of the aforementioned embodiments. The electrochemical system in which the separator plate is used can be, for example, a fuel cell system or an electrolyzer.

[0026] Exemplary embodiments of the separator plate and the electrochemical system are shown in the accompanying figures and are explained in more detail below. They show: Fig. 1. Schematic representation in a perspective view of an electrochemical system with a plurality of bipolar plates arranged in a stack; Fig.2 schematically in a perspective view two bipolar plates of the system according to the prior art consisting of two separator plates with a membrane electrode arrangement (MEA) arranged between the bipolar plates; Fig. 3 an exploded view of a single cell of an electrolyzer with two separator plates limiting it, according to the prior art; Fig. 4 a sectional view of a separator plate according to one embodiment; Fig. 5 a sectional view of a separator plate according to a further embodiment; and Fig. 6 A schematic representation of a method for producing a separator plate according to embodiments.

[0027] Here and in the following, recurring features in various figures are designated with the same or similar reference symbols. For the sake of clarity, the repeated use of reference symbols in subsequent figures is sometimes omitted.

[0028] Fig.Figure 1 shows an electrochemical system 1 with a plurality of identical metallic bipolar plates 2, which here consist of two separator plates 2a, 2b and together with membrane electrode units 10 and gas diffusion layers 14 form electrochemical cells arranged in a stack 6 and stacked along a z-direction 7. The bipolar plates 2 of the stack 6 are clamped between two end plates 3, 4. The z-direction 7 is also called the stacking direction. In this example, the system 1 is a fuel cell stack. Each pair of adjacent separator plates 2a, 2b of two neighboring bipolar plates 2 of the stack defines an electrochemical cell, which serves, for example, to convert chemical energy into electrical energy. To form the electrochemical cells of the system 1, a membrane electrode unit (MEA) 10 is arranged between each adjacent bipolar plates 2 of the stack.The MEAs typically each contain at least one membrane, e.g., a catalyst-coated electrolyte membrane, and a frame-shaped membrane reinforcement layer that surrounds and reinforces the membrane. Furthermore, a gas diffusion layer (GDL) can be arranged on one or both surfaces of the MEA. Fig. 1 and 2 are not shown.

[0029] In alternative embodiments, system 1 can also be configured as an electrolyzer. Separator plates can also be used in this case. The design of these separator plates can then correspond to the design of the separator plates described in more detail here, even though the media guided on or through the separator plates in an electrolyzer may differ from the media used in a fuel cell system. Furthermore, electrolyzers often do not require an additional cooling medium. Exemplary separator plates 20, 20' of an electrolyzer are shown in the Fig. 3 shown, see also explanations below.

[0030] The z-axis 7, together with the x-axis 8 and y-axis 9, defines a right-handed Cartesian coordinate system. The separator plates 2a, 2b define a plate plane at their point of contact, with each plate plane being parallel to the xy-plane and thus perpendicular to the stacking direction or to the z-axis 7. The end plate 4 has a multitude of media connections 5, 5a, through which media can be supplied to and discharged from system 1. These media can include, for example, fuels such as molecular hydrogen or methanol, reaction gases such as air or oxygen, reaction products such as water vapor or depleted fuels, or coolants such as water and / or glycol. Gases are often supplied by means of blowers and / or compressors, while the supply of coolants is usually carried out with the aid of at least one pump and via the connections 5a.The cooling connections 5a are optional, especially when the electrochemical system 1 is configured as an electrolyzer.

[0031] Fig. Figure 2 shows, in perspective, two adjacent bipolar plates 2 of an electrochemical system of the type of system 1. Fig. 1 and a membrane electrode assembly (MEA) 10 arranged between these adjacent bipolar plates 2, known from the prior art, wherein the MEA 10 is in Fig. 2 is largely obscured by the bipolar plate 2 facing the viewer. The bipolar plate 2 is formed from two separator plates 2a, 2b joined together, of which in Fig.In each case, only the first separator plate 2a, facing the viewer, is visible, concealing the second separator plate 2b. The separator plates 2a and 2b can each be made of a single metal sheet, e.g., a stainless steel sheet. The separator plates 2a and 2b can be welded together, e.g., by laser welding. Two adjacent separator plates 2a and 2b of different bipolar plates, together with the MEA 10 and any GDLs present (not shown here), form an electrochemical cell.

[0032] The separator plates 2a, 2b have aligned through-holes that form through-holes 11a-c of the bipolar plate 2. When a plurality of plates of the type of bipolar plate 2 are stacked, the through-holes 11a-c form conductors that extend through the stack 6 in the stacking direction 7 (see Fig.1) Typically, each of the conduits formed by the through-openings 11a-c is in fluid connection with one of the ports or media connections 5 and, if applicable, 5a in the end plate 4 of system 1. Coolant, for example, can be introduced into or discharged from the stack via the conduits formed by the through-openings 11a. The conduits formed by the through-openings 11b and 11c, on the other hand, can be configured to supply the electrochemical cells of the fuel cell stack 6 of system 1 with fuel and reaction gas, as well as to discharge the reaction products from the stack. The media-carrying through-openings 11a-11c are essentially parallel to the plane of the individual bipolar plates 2.

[0033] In an electrochemically active area 18, the first separator plates 2a exhibit, to the observer, the Fig.On the front side facing 2, a flow field 17 with structures for guiding a reaction medium along the front side of the separator plate 2a is located. These structures are in Fig. 2 is given by a multitude of footbridges and channels 16 running between and bounded by the footbridges. At the viewer's Fig. On the front side of the bipolar plates 2 facing the first separator plates 2a, each separator plate also has a distribution and collection area 15. Distribution or collection areas 15 each comprise structures designed to distribute a medium introduced into the distribution area 15 from one of the first of the two through-openings 11b across the active area 18, or to collect or concentrate a medium flowing from the active area 18 towards the second of the through-openings 11b. The fluid guide structures of both distribution or collection areas 15 are arranged in Fig.2 channels also run through footbridges and between the footbridges and are bordered by the footbridges.

[0034] To seal the through-openings 11a-c from the interior of the stack 6 and from the environment, the first separator plates 2a each have sealing arrangements in the form of sealing beads 12a-c, which are arranged around the through-openings 11a-c and which completely enclose the through-openings 11a-c. The second separator plates 2b have, on the side visible to the observer, Fig. 2 corresponding sealing beads for sealing the through openings 11a-c on the opposite back side of the bipolar plates (not shown).

[0035] The first separator plates 2a each have a further sealing arrangement in the form of a perimeter bead 12d, which surrounds the flow field 17 of the active area 18, the distribution and collection areas 15, and the through-openings 11b, 11c, and seals them against the through-opening 11a, i.e., against the coolant circuit, and against the environment of the system 1. The second separator plates 2b each include corresponding perimeter beads. All beads 12a-12d can have a section of an elastomer-based coating 52, which is Fig. 2, however, is only hinted at.

[0036] The structures of the active area 18, the distribution structures of the distribution and collection areas 15, and the sealing beads 12a-d are each formed integrally with the separator plates 2a and molded into the separator plates 2a, e.g., in an embossing or deep-drawing process or by means of hydroforming. The same applies to the corresponding structures of the second separator plates 2b.

[0037] The two through-openings 11b and the conduits formed by the through-openings 11b through the stack of plates of system 1 are each connected via feedthroughs 13b in the sealing grooves 12b, via the distribution structures of the distribution or collection area 15 and via the flow field 17 in the active area 18 of the viewer of the Fig.The first separator plates 2a facing each other are in fluid contact. Similarly, the two through-openings 11c and the conduits formed by the through-openings 11c through the plate stack of system 1 are each connected via corresponding corrugated penetrations 13c, via corresponding distribution and collection structures, and via a corresponding flow field on an outer side of the surface visible to the observer. Fig. The two separator plates 2b facing away from each other are in fluid contact. The through-openings 11a, or the channels formed by the through-openings 11a through the plate stack of system 1, are each in fluid contact via feedthroughs 13a and a cavity 19 enclosed or surrounded by the separator plates 2a, 2b. This cavity 19 serves to guide a coolant through the bipolar plate 2, in particular to cool the electrochemically active area 18 of the separator plates 2a, 2b.

[0038] Fig. Figure 3 shows an exploded view of an electrochemical single cell 60, where the single cell 60 is part of an electrolyzer. Electrolyzers typically comprise a plurality of stacked single cells 60, which together form a stack comparable to the stack 6 made of Fig.1. The single cell 60 comprises two separator plates 20 and 20' (each comprising half of a single cell 60), two cell frames 42 and 44, media diffusion structures 41 and 43, and a membrane-electrode assembly 40 with a membrane 45. The media diffusion structure 43 comprises, for example, layers of carbon fleece, while the media diffusion structure 41 comprises metal, e.g., titanium. The separator plate 20' is, for example, arranged on the anode side of the single cell 60. In the illustrated embodiment, the separator plate 20 is arranged on the cathode side of the single cell 60. The individual layers are pressed together to form a single cell. Each layer has fluid feedthroughs 46, 47, 50, 51 arranged in alignment above one another for the introduction and removal of water, oxygen and hydrogen, as well as positioning holes 48.

[0039] A flow field 17 of the separator plate 20 is defined by projecting the cell frame 44, or the area 27 recessed in it, onto the separator plate 20. A flow field 17 of the separator plate 20' is also defined by projecting the cell frame 42, or the area 27' recessed in it, onto the separator plate 20'. The through-openings 46, 47 of the separator plates 20, 20' are in fluid contact with the flow field 17, so that a medium can be directed from the through-opening 46 to the flow field 17, or active area 18, or from the flow field 17, or active area 18, to the through-opening 47. When a potential is applied, hydrogen can be produced from the supplied water in the electrolyzer. This hydrogen can leave the cell through the through-openings 50. The through-openings 50, 51 are sealed on the sides of the separator plates 20, 20' facing the viewer by means of an elastomer profile 52'.Analogous, but not visible here, elastomer profiles surround the through-openings 46, 47 on the sides of the separator plates 20, 20' facing away from the viewer. While the in . Fig. Although the 3 separator plates 20, 20' shown have a square outer contour, other shapes are also possible. For example, the separator plates 20, 20' can have a round or other outer contour.

[0040] The separator plates 2a, 2b and 20, 20' are made of Fig. 1, Fig. 2 to Fig. 3 are exemplary separator plates according to the state of the art.

[0041] In the following, the reference symbol 30 is generally used for separator plates. This can refer to one of the separator plates 20, 20' or one of the separator plates 2a, 2b, unless otherwise clearly indicated.

[0042] During operation of the electrochemical system 1, for example an electrolyzer or a fuel cell system, aggressive reaction conditions prevail which can lead to corrosion of the separator plates 30. This corrosion, in turn, is accompanied by reduced electrical conductivity, causing the separator plates 30 to lose functionality over time.

[0043] The present invention aims to improve the corrosion resistance and electrical conductivity of the separator plates 2, 2' at reasonable cost in order to improve the functionality and service life of the separator plates 30.

[0044] According to one aspect of the invention, the separator plate 30 comprises a metallic substrate 31, a cover layer 32, and a mixing layer 33. The cover layer 32 is arranged on the substrate 31, covers the substrate 31, and contains a first metal.

[0045] The mixed layer 33 is arranged on a side of the cover layer 32 facing away from the substrate 31 and contains a mixture of the first metal and a second metal. Additionally or alternatively, the mixed layer can contain a mixture of the material of the cover layer 32 and the second metal. The second metal is more noble than the first metal and / or the metallic substrate 31. The cover layer 32 is arranged directly on the substrate 31, while the mixed layer 33 is arranged directly on the cover layer 32.

[0046] In the Fig. Figures 4-5 illustrate the difference between the top layer 32 and the mixing layer 33 by means of hatching. While the top layer 32 is in the Fig.Layer 4-5 is completely black, while layer 33 has a hatching pattern. The presence or relative concentration of the first metal is indicated by black color, while the presence or relative concentration of the second metal is indicated by white color.

[0047] It can be provided that the concentration of the second metal in the mixed layer 33, measured perpendicular to a separator plate plane, i.e., parallel to the z-direction 7, increases towards one side of the mixed layer 33 facing away from the cover layer 32. This is also evident from the hatching in the figures. Often, the concentration of the first metal in the mixed layer 33, measured perpendicular to a separator plate plane and parallel to the z-direction, decreases towards one side of the mixed layer 33 facing away from the cover layer 32.

[0048] The mixed layer 33 may also contain oxides, nitrides and / or oxynitrides, for example oxides, nitrides and / or oxynitrides of the first metal.

[0049] In the Fig. Figure 5 shows that the second metal forms electrically conductive paths 34 extending from the top layer 32 to the surface of the mixed layer 33. These electrically conductive paths 34 ensure permanent electrical conductivity in the z-direction. However, a full-surface coating of the second metal on the surface is not necessary, at least not on the anode side.

[0050] In the Fig.Figures 4-5 indicate that the thickness of the top layer 32 is greater than the thickness of the mixed layer 33, in particular at least twice as great as the thickness of the mixed layer 33. In the example shown, the thickness of the top layer 32 is 100 nm to 500 nm, while the thickness of the mixed layer 33 is at least 10 nm and at most 20 nm. The thickness of the substrate 31 is considerably greater and can, for example, be at least 50 µm. Fig. Figures 4-5 show, for better illustration of layers 32 and 33, only a part of the substrate 31 in the z-direction.

[0051] The substrate 31 can be made of stainless steel, steel, aluminum, or titanium. Because the coating consisting of the top layer 32 and the mixed layer 33 protects the substrate 31 of the separator plate 30 against corrosion, materials can be used for the substrate 31 that cannot be used in conventional separator plates 30, such as aluminum or non-stainless steel.

[0052] The top layer 32 can be made essentially of, or consist of, the first metal. The phrase "essentially" here includes material impurities of up to 5%. Alternatively, the top layer 32 can contain or consist of oxides, nitrides, and / or oxynitrides of the first metal, possibly in mixture with the first metal.

[0053] For the first metal, niobium, titanium, or chromium, for example, are suitable. Niobium is particularly suitable for electrolyzer applications, while mixtures of chromium and chromium nitride can be advantageous, especially in fuel cell applications such as high-temperature PEM fuel cells. However, the invention is not limited to these applications. The material of the cover layer 32 should differ from the material of the substrate 31. For example, the boundary between a cover layer of chromium and chromium nitride and a stainless steel substrate with a substantial chromium content can be defined by the presence or absence of iron atoms. Sometimes, however, the substrate 31 is essentially free of the first metal, for example, in the case of a titanium substrate in combination with niobium as the first metal.

[0054] The second metal can be, for example, a platinum group metal such as platinum or iridium. These metals are relatively expensive, which is why a complete coating of the substrate 31 with these metals is not feasible for practical applications and mass production. The substrate 31 and the top layer 32 are typically essentially free of the second metal. The mixed layer 33 is not, in particular, a continuous layer of the second metal, but contains at least some of the first metal or the material of the top layer. The first and second metals can be matched to each other in such a way that they form the most stable and solid mixed layer possible. Furthermore, the first metal should be matched to the material of the substrate 31. Advantageous material combinations include, for example: Table 1: possible material combinations for substrate 31, the first metal and the second metal substrate first metal second metal aluminum niobium platinum aluminum titanium platinum Steel niobium platinum Steel titanium platinum Steel Titanium (especially mixed with titanium oxynitride) platinum stainless steel Chromium (especially mixed with chromium nitride) platinum titanium niobium platinum titanium niobium iridium

[0055] The invention is not limited to the aforementioned material combinations; rather, other metal combinations are also conceivable.

[0056] Optionally, an elastomer layer can be provided on the mixing layer 33, cf. the elastomer-based bead sections 52 in Fig. 2 and the elastomer profiles 52' in Fig. 3 (not shown in the Fig. 4-5). The elastomer layer may be applied only in sections or not over the entire surface, for example in the area of ​​the sealing beads 12a-d, and may, for example, be designed as a micro-seal. If provided, the elastomer layer preferably extends outside the electrochemically active area 18.

[0057] In Fig. Figure 6 shows an exemplary flowchart for a process for manufacturing the separator plate 30, which may, for example, include the following steps: - Providing a metallic substrate 31 (step S); - Applying a top layer 32 with a first metal to the substrate 31, for example by means of PVD or CVD, in particular by sputtering the first metal onto the substrate 31 (step D); - Co-sputtering of the first metal with a second metal to create the mixed layer 32 (step M).

[0058] Before applying the top layer 32, an optional passivation layer of the substrate 31 can be removed, e.g., mechanically or chemically, in a step P. The top layer 32 can then be applied directly to the native material of the substrate 31.

[0059] Sputtering or co-sputtering can take place under a nitrogen and / or oxygen atmosphere or under an argon atmosphere. The process can optionally include further steps: - Forming conduction paths 34 of the second metal in the mixed layer 33, wherein the conduction paths 34 extend from the cover layer 31 to the surface of the mixed layer 33 (step L).

[0060] The top layer 32 and / or the mixing layer 33 can be applied over the entire surface and / or only in sections to at least one surface of the separator plate 30. For example, the outer surface 22 of the separator plate 2a of the Fig. 2, i.e., the area outside the perimeter groove 12d should be free of the top layer 32 and the mixed layer 33. If the layers 32 and 33 are only present in sections on the separator plate 30, at least one electrochemically active area 18 of the separator plate 30 should be coated with the layers 32 and 33. The top layer 32 and the mixed layer 33 can be arranged on both sides of the separator plate 30 or only on one side, as required.

[0061] The separator plate 30 is suitable, for example, for use in a fuel cell system or an electrolyzer. The [material / component] Fig. 4 and Fig. The 5 separator plates 30 shown can therefore be used in the systems of Fig. 1-3 are used. Features that are only in the Fig. As shown in 1-3, the separator plates 30 can be used. Fig. 4-5 can be combined and vice versa.

[0062] According to another aspect, an electrochemical system 1 is comparable to the Fig. 1 provided, which comprises a large number of stacked separator plates 30 of the type described above. Reference symbol list 1 electrochemical system 2, 2' Bipolar plate 2a first separator plate 2b second separator plate 3 End plate 4 End plate 5, 5a Media connection 6 stacks 7 z-direction 8 x-direction 9 y-direction 10 Membrane electrode unit 11a-c Through openings 12 Sealing arrangement 12a-d sealing beads 13a-c procedures 15 Distribution or collection area 16 channels 17 fluid-carrying area, flow field 18 electrochemically active areas 19 Cavity 20, 20' separator plate 27, 27' recessed area 30 separator plates 31 metallic substrate 32 Top layer 33 Mixed layer 34 electrically conductive path 40 Membrane electrode array 41 Media diffusion structure 42 cell frames 43 Media diffusion structure 44 cell frames 45 Membran 46 Fluid passage opening 47 Fluid passage opening 48 positioning holes 50 Fluid passage opening 51 Fluid passage opening 52 elastomer-based coating 52' Elastomeric sealing profile 60 electrochemical cells

Claims

Separator plate (30) for an electrochemical system (1), comprising a metallic substrate (31), a cover layer (32) and a mixed layer (33), wherein the cover layer (32) is arranged on the substrate (31), covers the substrate (31) and contains a first metal,- wherein the mixed layer (33) is arranged on a side of the cover layer (32) facing away from the substrate (31) and contains a mixture of the first metal and / or the material of the cover layer (32) on the one hand and a second metal on the other hand,- wherein the second metal is more noble than the first metal and / or the metallic substrate (31). Separator plate (30) according to claim 1, wherein the concentration of the second metal in the mixing layer (33) increases perpendicular to a separator plate plane towards a side of the mixing layer (33) facing away from the cover layer (32). Separator plate (30) according to one of the preceding claims, wherein the concentration of the first metal in the mixing layer (33) decreases as measured perpendicular to a separator plate plane towards a side of the mixing layer (33) facing away from the cover layer (32). Separator plate (30) according to one of the preceding claims, wherein the mixing layer (33) further contains oxides, nitrides and / or oxynitrides. Separator plate (30) according to one of the preceding claims, wherein the second metal forms electrically conductive paths (34) which extend from the cover layer (32) to the surface of the mixing layer (33). Separator plate (30) according to one of the preceding claims, wherein the thickness of the cover layer (32) is greater than the thickness of the mixing layer (33), in particular at least twice as great as the thickness of the mixing layer (33). Separator plate (30) according to the preceding claim, wherein the thickness of the cover layer (32) is at least 50 nm and wherein the thickness of the mixing layer (33) is at least 10 nm. Separator plate (30) according to one of the preceding claims, wherein the substrate (31) is made of stainless steel, steel, aluminium or titanium. Separator plate (30) according to one of the preceding claims, wherein the cover layer (32) is substantially made of or consists of the first metal. Separator plate (30) according to one of claims 1 to 8, wherein the cover layer (32) contains or consists of oxides, nitrides and / or oxynitrides of the first metal, optionally in mixture with the first metal. Separator plate (30) according to one of the preceding claims, wherein the first metal is niobium, titanium or chromium. Separator plate (30) according to one of the preceding claims, wherein the second metal is a platinum group metal such as platinum or iridium. Separator plate (30) according to one of the preceding claims, wherein the material of the cover layer (32) differs from the material of the substrate (31), and / or wherein the substrate (31) is substantially free of the first metal and / or wherein the substrate (31) and the cover layer (32) are substantially free of the second metal. Separator plate (30) according to one of the preceding claims, wherein the cover layer (32) is arranged directly on the substrate (31) and / or wherein the mixing layer (33) is arranged directly on the cover layer (32). Separator plate (30) according to one of the preceding claims, wherein the top layer (32) and / or the mixing layer (33) are applied by means of PVD or CVD. Separator plate (30) according to one of the preceding claims, wherein the top layer (32) and / or the mixing layer (33) are applied over the entire surface and / or only in sections to at least one surface of the separator plate (30). Separator plate (30) according to one of the preceding claims, wherein the cover layer (32) and the mixing layer (33) are arranged on both sides of the separator plate (30) or only on one side of the separator plate (30). Electrochemical system (1) comprising a plurality of stacked separator plates (30) according to one of the preceding claims, wherein the electrochemical system is a fuel cell system, an electrolyzer, an electrochemical compressor or a flow battery. Method for producing a separator plate (30), in particular according to one of claims 1 to 17, comprising the following steps: providing a metallic substrate (31); applying a cover layer (32) with a first metal to the substrate (31), for example by means of PVD or CVD, in particular by sputtering the first metal onto the substrate (31); co-sputtering the first metal with a second metal to produce the mixed layer (33), in particular under a nitrogen and / or oxygen atmosphere or under an argon atmosphere. Method for producing the separator plate (30) according to claim 19, further comprising: forming electrically conductive paths (34) of the second metal in the mixed layer (33), wherein the conductive paths (34) extend from the cover layer (32) to the surface of the mixed layer.

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