Layer and layer system and conductive plate and electrochemical cell

Abstract

The invention particularly relates to a layer (3a) for forming a conductive plate (1) for an electrochemical cell (50), which contains a first chemical element from the noble metal family in the form of ruthenium in a concentration ranging from 50 to 99 atomic % and at least one second chemical element in the form of silicon in a concentration of <10 atomic %. The invention further relates to the layer system, the conductive plate and the electrochemical cell.

Description

[Technical field]

[0001] The present invention relates to a layer for forming an electrically conductive plate, in particular for an electrochemical cell. Furthermore, the present invention relates to a layer system comprising such a layer, and to an electrically conductive plate comprising such a layer system. The present invention also relates to an electrochemical cell, in particular a fuel cell, an electrolyzer or a redox flow cell, comprising at least one such electrically conductive plate.

[0002] Electrochemical systems, particularly fuel cells, such as polymer electrolyte fuel cells, and electrically conductive current collecting plates for such fuel cells and electrolysers, as well as current collectors in galvanic cells and electrolysers, are known.

[0003] An example of this is the bipolar or monopolar plates in fuel cells, in particular in oxygen half-cells. Bipolar or monopolar plates are in the form of carbon plates (e.g. grafoil plates), which contain carbon as an essential element. These plates tend to be brittle and relatively thick, which significantly reduces the electrical charge of the fuel cell. Another drawback is that they lack physical (e.g. thermo-mechanical) and / or chemical and / or electrical stability.

[0004] It is known to manufacture the current collector plates of fuel cells from metals, especially austenitic stainless steels. The advantage of these plates is that plate thicknesses of less than 0.5 mm can be achieved. This thickness is desirable so that both the space and the weight of the fuel cell can be kept as small as possible. The problem with these plates is that surface oxides are formed during the operation of the fuel cell, which leads to an unacceptable increase in the surface resistance and / or electrochemical decomposition (corrosion, etc.).

[0005] German published patent applications 102010 / 026330 (A1), 102013 / 209918 (A1), 112005 / 001704 (T5) and 112008 / 003275 (T5) describe, for example, the coating of austenitic stainless steel as a carrier, which achieves the requirements for the use of bipolar plates in fuel cells with a gold layer in the band region up to 2 nm. There are some drawbacks to this solution to the requirements. For example, a gold layer, even with a thickness of only 2 nm, is very expensive for mass production. An even greater drawback can be found in the fundamental properties of gold, a chemical element. Gold is more valuable as a carrier material than stainless austenitic steel (stainless steel), and under unfavorable operating conditions in a fuel cell, the carrier dissolves (for example pitting or pitting corrosion), which leads to a reduced service life. Corrosion cannot be prevented, especially in chloride-containing environments (for example aerosols).

[0006] In particular, another drawback is that gold is not stable in high load applications, for example in electrolytic conditions above 1500 mV versus standard hydrogen units, in either acidic or basic environments.

[0007] Layers on carriers in the form of what are called hard material layers based on nitrides or carbides are also known in the prior art. An example of this is titanium nitride, which during the operation of the fuel cell tends to form metal oxide complexes through the sealed surface layer. As a result, similar to stainless steel, the surface resistance increases to high values. Processes for coating with chromium nitride or chromium carbonitride can be found, for example, in German Patent Specification No. 19937255 (B4) and European Patent Specification No. 1273060 (B1) and German Published Patent Application No. 10017200 (A1).

[0008] Depending on the composition, the hard material layer has very good operating properties (e.g. resistance to corrosion, resistance to friction, high contour accuracy), but it poses the risk of anodic dissolution when concentration chains form in the fuel cell under unfavorable operating conditions, when what are called local elements or unexpected and undesirable reaction elements occur during an internal electrochemical short circuit in the fuel cell, such as the formation of a water film between the active electrode and the bipolar plate of the membrane electrode assembly of the fuel cell.

[0009] Also known are several coatings based on nitrides with very thin layers of gold or platinum. Satisfactory operating results for fuel cells can therefore be achieved with layer thicknesses of the precious metals greater than 2 μm. The basic problem of dissolution lies in the high anodic potentials. The layer thickness ensures an almost pore-free top layer and therefore reduces the risk of pitting corrosion.

[0010] Also known are so-called dimensionally stable anodes. Here, single-phase or multiphase oxides with ruthenium oxide and / or iridium oxide are formed with the aid of refractory metals. Layers of this type are very stable but have a very high electrical resistance. The same is also true when the surface of a carrier, generally made of a noble metal, is doped with iridium.

[0011] DE 10 2009 / 010279 (A1) describes a bipolar fuel cell plate comprising a conductive metal plate which is anodized and on which a conductive layer is subsequently deposited by an atomic layer deposition process, in particular the conductive layer comprises at least one of titanium oxynitride, gold, platinum, carbon, ruthenium or ruthenium oxide.

[0012] DE 10 2016 / 202372 (A1) discloses layers consisting of homogeneous or heterogeneous solid metal solutions or composites containing a first chemical element from the class of precious metals in the form of iridium and / or a second chemical element from the class of precious metals in the form of ruthenium, and at least one other non-metallic chemical element from the group consisting of nitrogen, carbon, boron, fluorine and hydrogen.

[0013] Therefore, the following requirements must be imposed on the metal carriers or bipolar plates of PEM fuel cells or electrolysers, especially designed for energy conversion in these electrochemical systems: - high corrosion resistance to the surrounding medium, and / or -High recovery ability against anode or cathode polarization load - low surface resistance of the surface of the carrier or its coating facing the electrolyte - Low manufacturing costs of carriers, in particular conductive conductors in the form of bipolar plates for use in fuel cells, for example for use in mobile phones.

[0014] WO2018 / 145720(A1) discloses plate-shaped electrodes made of composite materials for redox flow batteries that are structured for optimal distribution of fluids.

[0015] It is therefore an object of the present invention to provide an improved layer or an improved layer system in general for a bipolar plate for an energy converter, in particular for an electrode of a fuel cell or an electrolyser or a redox flow battery. It is further an object of the present invention to specify a conductive plate having the improved layer system, and an electrochemical cell equipped therewith.

[0016] The object is achieved according to the invention by a layer, in particular for forming an electrically conductive plate for an electrochemical cell, which contains a first chemical element from the precious metals family in the form of ruthenium in a concentration ranging from 50 to 99 atomic % and at least one second chemical element in the form of silicon in a concentration of less than <10 atomic %. Silicon forms stable compounds, especially oxides, which have a positive effect on the resistance of the layer to electrochemical attack. Silicon is preferably contained at a concentration in the range of 3 atomic % to <10 atomic %.

[0017] The object is also achieved according to the invention by a layer system, in particular for a conductive plate of an electrochemical cell, which comprises a cover layer and an undercoat layer system, the cover layer being designed in the form of a layer according to the invention.

[0018] The object is also achieved according to the invention by an electrochemical cell, in particular in the form of a fuel cell, an electrolyser or a redox flow cell, comprising at least one electrically conductive plate according to the invention.

[0019] Advantageous configurations using expedient and non-obvious developments of the invention are set out in the dependent claims.

[0020] The layers according to the invention are designed to be electrically conductive, electrocatalytically active and to protect against corrosion.

[0021] The layer according to the invention preferably contains at least one further second chemical element from the group consisting of nitrogen, carbon, boron, fluorine, hydrogen and oxygen.

[0022] said at least one further second chemical element is preferably present in the cover layer at a concentration in the range of 1 atomic % to 40 atomic %.

[0023] The at least one second chemical element is preferably dissolved in the metal lattice of ruthenium in such a way that the lattice type of the host metal or host metal alloy is essentially unchanged.

[0024] The layer according to the invention preferably comprises a) ruthenium, silicon, and carbon, or b) ruthenium, silicon, carbon, and hydrogen, or c) ruthenium, silicon, carbon, and fluorine, optionally hydrogen, or d) ruthenium, silicon, carbon, and oxygen, or e) Ruthenium, silicon, carbon, oxygen, and hydrogen.

[0025] With carbon-containing layers, i.e. the semimetallic or nonmetallic chemical element carbon, the electrical conductivity of the layer is higher than that of gold, while its oxidative stability in acidic solutions is significantly greater than 2000 mV against the standard hydrogen electrode. Depending on the embodiment, the specific electrical resistance measured is 5 mΩ cm. -2 below (under standard conditions).

[0026] By comparison, the specific electrical resistivity of gold is approximately 10 mΩ cm at room temperature. -2 It is.

[0027] The layer also preferably further comprises at least one chemical element from the class of refractory metals, in particular titanium and / or zirconium and / or hafnium and / or niobium and / or tantalum and / or tungsten. At least one chemical element from the class of refractory metals is contained in the layer, in particular in a concentration range of 0.01-10 atomic %. The addition of a refractory metal has also been shown to control, in particular, H2O2 and ozone formed during electrolysis.

[0028] The layer also preferably contains at least one chemical element from the group of base metals, which is preferably formed by aluminum, iron, nickel, cobalt, zinc, cerium, tin. At least one further chemical element from the group of base metals is contained in the layer, in particular in a concentration range of 0.01 to 10 atomic %.

[0029] At least one chemical element from the class of base metals in the form of tin and at least one chemical element from the class of refractory metals are contained together in the layer, in particular in a concentration range of 0.01 to 10 atomic %.

[0030] The layer also preferably contains at least one additional chemical element from the group consisting of iridium, platinum, gold, silver, rhodium, palladium in a concentration range of 0.01 to 25 atomic %.

[0031] It is preferred if the layer has a layer thickness preferably in the range of 0.5 to 500 nm.

[0032] It has proven to be beneficial if all chemical elements from the precious metals class, ie together with ruthenium, are contained in the layer in a concentration range of more than 50 atomic % up to 99 atomic %.

[0033] Corrosion protection on metal substrates such as those made of steel, especially high-grade steel or titanium, is further improved by applying a layer according to the invention to the underlying system between the substrate and the layer, which is particularly advantageous when corrosive media are present, especially when the corrosive media contain chlorides.

[0034] Subjection to oxidation, i.e. oxidation of the surface of the support and of the layer applied thereon, usually leads to delamination of the precious metal layer deposited thereon.

[0035] The object is also achieved by a layer system, in particular for a conductive plate of an electrochemical cell, which comprises a cover layer and an undercoat layer system, the cover layer being in the form of a layer according to the invention.

[0036] In particular, the undercoat layer system comprises at least one undercoat layer having at least one chemical element from the group titanium, niobium, hafnium, zirconium, tantalum.

[0037] The undercoat layer system comprises in particular a first undercoat layer in the form of a metal alloy layer comprising the chemical elements titanium and niobium, in particular 20-50% by weight of niobium and the remainder titanium.

[0038] The undercoat layer system in particular comprises a second undercoat layer which also contains at least one chemical element from the group titanium, niobium, zirconium, hafnium, tantalum, and at least one non-metallic element from the group nitrogen, carbon, boron, fluorine.

[0039] In a particularly preferred embodiment, the undercoat layer system comprises a) titanium, niobium, and also carbon and fluorine, or b) In particular, (Ti 67 Nb 33 )N 0.8-1.1 Titanium, niobium, and also nitrogen, formed from The second undercoat layer comprises:

[0040] The second undercoat layer is preferably positioned between the first undercoat layer and the top layer.

[0041] The second undercoat layer may further contain up to 5 atomic % oxygen.

[0042] Advantageously, a thickness of less than 10 nm of the layer or cover layer according to the invention is sufficient to protect against oxidation, which increases the resistance of the second undercoat layer.To provide reliable protection against corrosion, some layers of the undercoat layer system are made of at least one high-melting metal, which is applied to at least two layers of steel, in particular stainless steel, first as a metal or alloy layer (=first undercoat layer) and then as a semimetal layer (=second undercoat layer).The double layer formed with the aid of a two-layer structure under the layer according to the invention ensures that, on the one hand, electrochemical adaptation to the substrate material, i.e. the material that forms the substrate for receiving the layer system, and, on the other hand, pore formation due to oxidation and hydrolysis processes is eliminated.

[0043] Electrochemical adaptation to the substrate material is necessary, since both the semimetallic layer (=second undercoat layer) and the layer or top layer according to the invention are very valuable. In the event of pore formation, the potential of the high local elements increases, resulting in unacceptable corrosion currents. The metallic first undercoat layer is preferably formed from titanium or niobium or zirconium or tantalum or hafnium, or from alloys of these metals, which are less valuable than the substrate material in the form of steel, especially stainless steel, and reacts first with the corrosion process, forming insoluble oxides or large amounts of sometimes gel-like hydroxocomplexes of these high-melting metals. As a result, the pores are filled and protect the substrate from corrosion. This process represents a self-healing of the layer system.

[0044] The second undercoat layer, in particular in the form of a nitride layer, acts as a hydrogen barrier and thus protects the substrate, the bipolar plate and the metallic first undercoat layer, in particular made of stainless steel, from hydrogen embrittlement.

[0045] The object is also achieved by an electrically conductive plate, in particular a bipolar plate of an electrode of a fuel cell or an electrolyser or a redox flow battery, comprising a metallic substrate and a layer system according to the invention applied to at least a partial area of ​​the surface of the substrate.

[0046] In particular, the layer system is applied over the entire area to one or both faces of the substrate. The metal substrate is in particular made of steel or titanium, preferably of high-grade steel. The thickness of the substrate is preferably less than 1 mm, in particular equal to 0.5 mm.

[0047] Finally, the object is achieved by an electrochemical cell, in particular in the form of a fuel cell, an electrolyser or a redox flow cell, comprising at least one electrically conductive plate according to the invention.

[0048] The fuel cells according to the invention, in particular polymer electrolyte fuel cells comprising at least one conductive plate according to the invention in the form of a bipolar plate, have proven to be particularly advantageous in terms of electrical value and corrosion resistance, such fuel cells therefore having a long service life of more than 10 years and vehicle operating times of more than 5000 hours.

[0049] Comparably long service lives can be achieved with electrolysers according to the invention, which work with the opposite operating principle with respect to fuel cells and in which chemical reactions, i.e. material transformations, are brought about with the aid of an electric current. In particular, the electrolysers are those which are suitable for hydrogen electrolysis.

[0050] Long service lives and power densities can be achieved with a redox flow battery according to the invention comprising at least one conductive plate in the form of an electrode according to the invention.

[0051] Further features, advantages and details of the invention will become apparent from the following description of preferred embodiments of the invention. The features and combinations of features described above in the description can be used not only in the combination specified in each case, but also in other combinations or alone, without departing from the scope of the invention. [Brief description of the drawings]

[0052] [Figure 1] 1 shows a cross-sectional view of a conductive plate. [Diagram 2] The electrodes are shown along with the flux fields. [Diagram 3] 1 shows a redox flow battery having a redox flow cell or a redox flow battery. [Figure 4] The electrolytic cell is shown in cross section. [Diagram 5] 1 shows a fuel cell stack in a three-dimensional view.

[0053] 1 shows in cross-section a conductive plate 1 comprising a substrate 2 made of stainless steel and a layer system 3 applied to the entire surface of one side of the substrate 2. The layer system 3 comprises a cover layer 3a and an undercoat layer system 4 comprising a first undercoat layer 4a and a second undercoat layer 4b.

[0054] In a first exemplary embodiment, here the metal substrate 2 in the form of a conductor for a bipolar plate of a polymer electrolyte fuel cell for converting (reformed) hydrogen is made of stainless steel, in particular that referred to as authentic steel, which has known very high requirements for corrosion resistance, for example DIN ISO material number 1.4404.

[0055] The layer system 3 is formed by a coating process, for example a vacuum-based coating process (PVD), on the substrate 2, which is coated in one step first with a first undercoat layer 4a in the form of a titanium layer 1.5 μm thick, then with a second undercoat layer 4b in the form of a titanium nitride layer of approximately equal thickness, and finally with a top layer 3a having the composition RuSiC. The cover layer 3a corresponds to a layer coating open on one side, and is designed so that only one cover layer surface of a further layer, here the second undercoat layer 4b, is in contact with it. Thus, in the fuel cell the free surface 30 of the cover layer 3a is arranged facing the electrolyte, in particular the polymer electrolyte.

[0056] In a second exemplary embodiment, the metal substrate 2 is firstly provided with a metal alloy layer of a few hundreds of nm in thickness, of composition Ti 0.9 Nb 0.1 The substrate is coated with a first undercoat layer 4a in the form of a metal alloy layer having the composition Ti. The further application of a second undercoat layer 4b is a few hundred nm thicker. 0.9 Nb 0.1 N 1-x A cover layer 3a having the composition RuSiC and a thickness of a few nm is then applied.

[0057] The advantage is the particularly high stability against oxidation of the plate 1 according to the invention: even with a constant load of +3000 mV against the standard hydrogen electrode, no increase in resistance is found in a sulfuric acid solution with a pH value of 3.

[0058] The cover layer 3a according to the invention of the first and second exemplary embodiments can be applied both by sputtering technique and by cathodic ARC coating method, also known as vacuum arc deposition. Despite the large number of droplets, in other words an increased number of metal droplets compared to the sputtering technique, the cover layer 3a according to the invention produced with the cathodic ARC process also has the advantageous property of high corrosion resistance, with a surface conductivity stable over time of the cover layer 3a according to the invention produced using the sputtering technique.

[0059] In a third exemplary embodiment, the layer system 3 according to the invention is applied on a substrate 2 in the form of a structured perforated stainless steel sheet metal. The substrate 2 is electropolished in a H2SO4 / H3PO4 bath before the layer system 3 is applied. After application of a single undercoat layer in the form of a tantalum carbide layer several thousand nm thick, a cover layer 3a in the form of RuSiCHO is applied.

[0060] The advantage of the undercoat layer formed from tantalum carbide lies not only in its exceptional resistance to corrosion, but also in the fact that it does not absorb any hydrogen and therefore acts as a hydrogen barrier for the substrate 2. This is particularly advantageous when titanium is used as the substrate material.

[0061] The layer system 3 according to the invention in a third exemplary embodiment has a current density of 500 mA cm -2 It is suitable for use in electrolytic cells to produce hydrogen at higher current densities.

[0062] The advantage of semi-metallic layers placed sealed between and / or on both sides within the layer system or in the simplest case of a second undercoat layer, made for example of titanium nitride, is that they have a resistivity of 10-12 mΩ cm -2Likewise, the layer or cover layer according to the invention can also be formed without a second undercoat layer or semi-metallic layer, with a possible increase in resistance.

[0063] Table 1 lists some coating systems along with their properties. [Table 1]

[0064] Table 1 shows only a few exemplary layer systems. Advantageously, the layer systems according to the invention show no increase in resistance over several weeks at temperatures of 70-80° C. in sulfuric acid solution and an anodic load of +2000 mV vs. the standard hydrogen electrode. The layer systems applied in high vacuum using the sputtering or or ARC method, or in excellent vacuum using the PECVD method (plasma enhanced chemical vapor deposition), partially darkened after this exposure time. However, there were no visible signs of corrosion or significant changes in the surface resistance.

[0065] Figure 2 shows a three-dimensional view of a plate 1 in the form of an electrode, comprising a substrate 2 in the form of a metal plate, made of stainless steel, with a profile 40 forming a flux field 7. The substrate 2 has profiles 40 on both sides in order to form in each case a flux field 7, resulting in a three-dimensional structuring of the surface of the electrode. The substrate 2 is covered on both sides with a layer system 3 over which the electrolyte flows in the redox flow battery 8 (see Figure 3).

[0066] FIG. 3 shows an electrochemical cell 50 in the form of a redox flow cell 8 or a redox flow battery with a redox flow cell 8. The redox flow cell 8 comprises two plates 1a, 1b in the form of electrodes, a first reaction chamber 10a and a second reaction chamber 10b, each reaction chamber 10a, 10b being in contact with one of the electrodes. The reaction chambers 10a, 10b are separated from each other by an ion exchange membrane 9a. A liquid anolyte 11a is pumped from a tank 13a to the first reaction chamber 10a via a pump 12a and is fed between the electrode section 1a and the ion exchange membrane 9a. A liquid catholyte 11b is pumped from a tank 13b to the second reaction chamber 10b via a pump 12b and is fed between the electrode section 1b and the ion exchange membrane 9a. An ion exchange occurs across the ion exchange membrane 9a and electrical energy is released by redox reactions at the electrodes.

[0067] 4 shows an electrochemical cell 50 in the form of an electrolysis cell 20 of an electrolyser, with a polymer electrolyte membrane 9 separating the anode side A and the cathode side K from each other. The catalyst layers 21a, 21b each comprise a catalyst material and fluid diffusion layers 22a, 22b, which are arranged adjacent to the catalyst layers 21a, 21b on both sides of the polymer electrolyte membrane 9. The fluid diffusion layers 22a, 22b are placed adjacent to conductive plates 24a, 24b, respectively, which are made of expanded metal. The plates 24a, 24b each have channels 23a, 23b on the side facing the fluid diffusion layers 22a, 22b to improve the supply of the reaction medium (water) and the removal of the reaction products (water, hydrogen, oxygen).

[0068] FIG. 5 shows diagrammatically a fuel cell stack 100 comprising a number of electrochemical cells 50 in the form of fuel cells 90. Each fuel cell 90 comprises a polymer electrolyte membrane 9 adjacent to both sides of a plate 1c, 1d in the form of a bipolar plate. Each bipolar plate comprises a substrate 2 made of stainless steel, which is covered on both sides with a layer system 3 (see FIG. 1). The bipolar plates have an inlet area with openings 80a and an outlet area with further openings 80b used to supply the fuel cells 90 with process gases and coolant and to remove reaction products from the fuel cells 90 and the coolant. The bipolar plates also have gas distribution structures 7′ on both sides, which are arranged facing the polymer electrolyte membrane 9. [Explanation of symbols]

[0069] 1, 1a, 1b, 1c, 1d, 24a, 24b Conductive plates 2. Board Three-tier system 3a layer, cover layer 4 Undercoat Layer System 4a First undercoat layer 4b Second undercoat layer 7. Flux Field 7' Gas distribution structure 8. Redox flow battery 9 Polymer electrolyte membrane 9a Ion exchange membrane 10a First reaction chamber 10b Second reaction chamber 11a Anolite 11b Catholyte 12a, 12b Pump 13a, 13b Tank 20 electrolyte battery 21a, 21b catalyst layer 22a, 22b Fluid diffusion layer 23a, 23b flow conduit 30 free surface 40 Profiles 50 Electrochemical Cells 80a, 80b opening 90 Fuel Cell 100 Fuel Cell Stack K Cathode side A Anode side

Claims

1. A layer (3a) for forming a conductive plate (1) for an electrochemical system, the layer (3a) containing a composition of a first chemical element from the precious metals family in a concentration range of 50 to 99 atomic % and a second chemical element which is silicon in a concentration of <10 atomic %.

2. 2. The layer (3a) according to claim 1, containing at least one further second chemical element from the group consisting of nitrogen, carbon, boron, fluorine, hydrogen and oxygen.

3. The layer (3a) according to claim 2, wherein said at least one second chemical element is present in said layer (3a) in a concentration ranging from 1 atomic % to 40 atomic %.

4. a) comprising ruthenium, silicon, and carbon; b) containing ruthenium, silicon, carbon, and hydrogen; c) containing ruthenium, silicon, carbon, and fluorine; d) containing ruthenium, silicon, carbon, and oxygen, or e) A layer (3a) according to any one of claims 1 to 3, comprising ruthenium, silicon, carbon, oxygen and hydrogen.

5. A layer (3a) according to any one of claims 1 to 4, further comprising at least one chemical element of the refractory metal class consisting of titanium, zirconium, hafnium, niobium, tantalum and tungsten.

6. Layer (3a) according to claim 5, wherein said at least one chemical element of the refractory metal class is contained in said layer (3a) in a concentration range of 0.01 to 10 atomic %.

7. Layer (3a) according to any one of the preceding claims, wherein said layer (3a) further comprises at least one chemical element of the base metal class.

8. 8. Layer (3a) according to claim 7, wherein said at least one chemical element of the base metal group is from the base metal group aluminum, iron, nickel, cobalt, zinc, cerium and tin.

9. A layer (3a) according to claim 7 or 8, wherein the at least one base metal chemical element is contained in the layer (3a) in a concentration range of 0.01 to 10 atomic %.

10. 7. Layer (3a) according to any one of claims 5 or 6, in conjunction with any one of claims 7 to 9, wherein the at least one chemical element of the base metal group, which is tin, and the at least one chemical element of the refractory metal group are contained together in the layer (3a) in a concentration range of 0.01 to 10 atomic %.

11. Layer (3a) according to any one of the preceding claims, further comprising at least one additional chemical element from the group consisting of iridium, platinum, gold, silver, rhodium and palladium in a concentration range of 0.01 to 25 atomic %.

12. Layer (3a) according to any one of the preceding claims, characterized in that said layer (3a) has a layer thickness in the range of 0.5 nm to 500 nm.

13. A layer system (3) for a conductive plate (1) of an electrochemical cell (50), comprising a cover layer (3a) and an undercoat layer system (4), wherein the cover layer (3a) is designed in the form of a layer (3a) described in any one of claims 1 to 12.

14. 14. The layer system (3) according to claim 13, wherein the undercoat layer system (4) comprises at least one undercoat layer (4a, 4b) comprising at least one chemical element from the group of titanium, niobium, hafnium, zirconium and tantalum.

15. 15. The layer system (3) according to claim 14, wherein said undercoat layer system (4) comprises at least one first undercoat layer (4a) in the form of a metal alloy layer containing the chemical elements titanium and niobium.

16. 16. The layer system (3) according to claim 14 or 15, wherein the undercoat layer system (4) comprises a second undercoat layer (4b) also comprising at least one chemical element from the group titanium, niobium, hafnium, zirconium, tantalum and at least one non-metallic element from the group nitrogen, carbon, boron and fluorine.

17. 17. The layer system (3) according to claim 16, characterized in that the second undercoat layer (4b) is arranged between the first undercoat layer (4a) and the cover layer (3a).

18. 18. A layer system according to claim 16 or 17, characterized in that the second undercoat layer (4b) contains up to 5 atomic % oxygen.

19. A conductive plate (1, 1a, 1b, 1c, 1d, 24a, 24b) which is a bipolar plate of an electrode of a fuel cell (90) or an electrolytic cell (20) or a redox flow battery (8), comprising a metal substrate (2) and a layer system (3) according to any one of claims 13 to 18 applied to at least a partial area of ​​the surface of the substrate (2).

20. An electrochemical cell (50) in the form of a fuel cell (90), an electrolytic cell (20) or a redox flow battery (8), comprising at least one conductive plate (1, 1a, 1b, 1c, 1d, 24a, 24b) as described in claim 19.

21. An electrochemical cell (50) as described in claim 20, which is a polymer electrolyte fuel cell comprising at least one plate (1c, 1d) as described in claim 19 in the form of a bipolar plate.

22. 21. An electrochemical cell (50) according to claim 20, which is an electrolytic cell (20) comprising at least one plate (1a, 1b) according to claim 19 in the form of a bipolar plate.

23. 21. An electrochemical cell (50) according to claim 20, which is a redox flow battery (8) comprising at least one plate (24a, 24b) according to claim 19 in the form of an electrode.

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