Coating system, electrode plate with such a coating system, method for producing same, and fuel cell, electrolytic cell or redox flow battery - Patents.com

Abstract

The present invention relates to a coating system (1) for coating a metal substrate (2a) to form an electrode plate (2), comprising at least one top coat (1a) made of a metal oxide, at least one intermediate coat (1b) supporting the top coat (1a), and a base coat (1c) supporting the one or more intermediate coats (1b). The top coat (1a) is formed by a network of nanofibers formed by either a) indium tin oxide, optionally with a third doping with at least one element from the group including carbon, nitrogen, boron, fluorine, hydrogen, phosphorus, sulfur, chlorine, bromine, aluminum, silicon, titanium, chromium, cobalt, nickel, copper, zircon, niobium, molybdenum, silver, antimony, hafnium, tantalum, tungsten, or b) doped tin oxide, the tin oxide having as a fourth doping at least one element from the group including niobium, tantalum, antimony, and fluorine. The invention also relates to an electrode plate having such a coating system, a method for producing it, and a fuel cell, an electrolyzer, or a redox flow battery having at least one electrode plate of such a coating system.

Description

[Technical field]

[0001] The present invention relates to a coating system for coating a metal substrate to form an electrode plate with at least one topcoat made of a metal oxide. The present invention further relates to an electrode plate with a metal substrate, such a coating system, and a method for manufacturing the same. Furthermore, the present invention relates to a fuel cell, an electrolyzer, or a redox flow battery comprising at least one such electrode plate. [Background technology]

[0002] A bipolar plate for a fuel cell or electrolyzer is already known from DE 100 58 337 A1, in which an electrically conductive and corrosion-resistant protective coating made of a metal oxide is formed on at least one side of a metal sheet. The metal oxide is in particular formed from an oxide of an element or an alloy from the group comprising tin, zinc and indium. A dopant, which ensures electrical conductivity and consists of at least one element from the group comprising aluminum, chromium, silver, boron, fluorine, antimony, chlorine, bromine, phosphorus, molybdenum and carbon, can be present in the metal oxide. The metal sheets used are metal sheets made of aluminum, copper, stainless steel, chromium-plated stainless steel, titanium, titanium alloys and iron-containing compounds, which may have a coating of at least one of the elements tin, zinc, nickel and chromium. Summary of the Invention [Problem to be solved by the invention]

[0003] The object of the present invention is to provide an improved coating system for electrode plates and to provide such an electrode plate. Furthermore, the object of the present invention is to provide a method for manufacturing an electrode plate and to propose a fuel cell, an electrolyzer or a redox flow battery comprising at least one such electrode plate. [Means for solving the problem]

[0004] This object is achieved by a coating system for coating a metal substrate to form an electrode plate, the coating system comprising at least one top coat made of a metal oxide, at least one intermediate coat supporting the top coat, and a base coat supporting one or more intermediate coats, The base coat is formed from titanium or a titanium-niobium alloy or chromium, at least one intermediate coat is formed from titanium niobium nitride and / or titanium niobium carbide and / or titanium niobium carbonitride and / or titanium carbide and / or titanium nitride and / or chromium carbide and / or chromium carbonitride and / or a homogeneous indium tin oxide optionally doped with a first dopant and / or a homogeneous tin oxide doped with a second dopant, -Top coat is a) indium tin oxide, optionally comprising a third dopant having at least one element from the group including carbon, nitrogen, boron, fluorine, hydrogen, phosphorus, sulfur, chlorine, bromine, aluminum, silicon, titanium, chromium, cobalt, nickel, copper, zirconium, niobium, molybdenum, silver, antimony, hafnium, tantalum, and tungsten; or b) doped tin oxide, which has as a fourth dopant at least one element from the group including niobium, tantalum, antimony, and fluorine; The nanofibers are formed from a network of nanofibers.

[0005] The coating system is characterized by a high long-term stability and at the same time a high electrical conductivity, and by the absence of precious metals, a low cost. In addition, the coating system ensures good corrosion protection for the metallic base material or substrate of the electrode plates, especially the bipolar plates. Indium tin oxide is also referred to below by the abbreviation ITO.

[0006] The coating system is preferably formed using a PVD or CVD process (PVD: Physical Vapor Deposition, CVD: Chemical Vapor Deposition) or a PACVD process (PACVD: Plasma-assisted Chemical Vapor Deposition).

[0007] Nanofibers are elongated or rod-like structures with diameters up to 200 nm and lengths up to 1000 nm. Nanofibers may be tapered.

[0008] To form a topcoat from a network of nanofibers, reference is made herein to “3D ITO-nanowire networks as transparent electrode for all terrain substrate”, Qiang Li et al., Scientific Reports (2019) 9:4983. See: https: / / doi.org / 10.1038 / s41598-019-41579-2

[0009] Applicant has also deposited a 90:10 atomic % InN film using a non-reactive sputtering technique with a deposition rate of 40 Å / min. 2 O 3 :SnO 2 It has also been possible to produce ITO nanofibers for fuel cells, electrolyzers, and redox flow batteries from targets made of SnO. 2The content is the main growth factor in the production of ITO nanofibers. Growth occurs by atoms evaporating from the target and depositing on the substrate. The temperature range for growth is 150°C to 500°C. Increasing the temperature increases the average fiber length and average diameter of the fibers, decreases the neighborhood distance, and increases the number of fibers per unit area. SnO 2 The content is preferably up to 30 atomic %. The increase in the average length and average diameter of the nanofibers depends on the deposition time. The ITO nanofibers are preferably grown on a thin and dense ITO layer.

[0010] The production of such nanofibers can also be based on doped tin oxide.

[0011] The first dopant preferably corresponds to the third dopant, and the second dopant preferably corresponds to the fourth dopant.

[0012] The concentration of the first dopant and / or third dopant element in the indium tin oxide is in particular in the range from >0 to 20 atomic %, preferably in the range from 0.5 to 20 atomic %.

[0013] The concentration of the second and / or fourth dopant elements in the tin oxide is in particular in the range from >0 to 20 atomic %, preferably in the range from 0.5 to 20 atomic %.

[0014] In this case, a topcoat made from indium tin oxide having an indium content in the range of 70-90 atomic % is particularly preferred, while an indium content in the range of 75-85 atomic % is particularly preferred, as it provides a high level of electrical conductivity.

[0015] The base coat is used in particular as an adhesion promoter between the metal substrate and at least one intermediate coat. Furthermore, the base coat forms a conductive oxide and thus provides galvanic corrosion protection to the metal substrate of the bipolar plate. The base coat preferably has a coating thickness in the range of 1 nm to 300 nm.

[0016] In particular, the intermediate coat is also used as an adhesion promoter between the base coat and the top coat. Furthermore, depending on the selection, the at least one intermediate coat can also form a conductive oxide and thus provide galvanic corrosion protection to the base coat and the metal substrate of the electrode plate. The at least one intermediate coat also provides a barrier against hydrogen, so that hydrogen cannot penetrate into the metal substrate and damage it. The coat thickness of each intermediate coat is preferably selected in the range of 0.1 to 3.0 μm. However, there may be two or more intermediate coats.

[0017] The top coat provides mechanical and corrosion protection to the base coat and to the intermediate coat(s) and has in particular a coat thickness in the range of 0.01 to 15 μm, in particular in the range of 0.1 to 3 μm.

[0018] The coating system according to the invention comprising the base coat, at least one intermediate coat and the top coat preferably has a total thickness in the range of 0.1 to 20 μm.

[0019] In particular, the following coating systems for coating metal substrates, preferably metal substrates made of steel, in particular austenitic steel or austenitic stainless steel, have proven advantageous for forming electrode plates.

[0020] Example 1: Base coat: TiNb Coat thickness: 100nm Intermediate coat: TiNbN Coat thickness: 300nm Topcoat: Indium tin oxide nanofiber with 80% indium content by volume Coating thickness: 100nm

[0021] Example 2: Base coat: TiNb Coat thickness: 100nm 1. Intermediate coating: TiNbN Coating thickness: 200nm 2. Middle coat: Uniform indium tin oxide coat thickness: 200nm Topcoat: Indium tin oxide nanofiber with indium content of 90% by volume Coating thickness: 100nm

[0022] Example 3: Base coat: TiNb Coat thickness: 100nm 1. Intermediate coating: TiNbCN Coating thickness: 200nm 2. Intermediate coat: TiNbN Coat thickness: 200nm Topcoat: Doped tin oxide nanofibers Coating thickness: 100nm

[0023] The purpose of this is to Metal substrate, Base coat, One or more intermediate coats, and Top Coat This is achieved for an electrode plate comprising a metal substrate and a coating system according to the invention having an electrode plate structure in the order of:

[0024] Preferably, the electrode plate comprises a metal substrate or metal carrier plate, preferably made of steel, in particular made of austenitic steel or stainless steel. Alternatively, the substrate may be formed of titanium or a titanium alloy or aluminium or an aluminium alloy or zinc or a zinc alloy or a tin alloy or copper or a copper alloy or nickel or a nickel alloy or silver or a silver alloy or chromium or a chromium alloy.

[0025] The carrier plate can be designed as a single-part or multi-part, in particular the electrode plate is designed as a bipolar plate.

[0026] According to the invention, the method for manufacturing an electrode plate according to the invention comprises the following steps: Providing a metal substrate; forming a base coat on a surface of a metal substrate; forming at least one intermediate coat on the base coat; forming a top coat on a side of at least one intermediate coat facing away from the base coat; The coating system is formed on the metal substrate by non-reactive sputtering. This is a deposition process that can be performed cost-effectively on a continuous manufacturing scale and can also be used to produce nanofibers.

[0027] The object is further achieved for a fuel cell, in particular an oxygen-hydrogen fuel cell, or for an electrolyser, in particular for the production of hydrogen and oxygen from water, or for a redox flow battery, in particular comprising at least one organic electrolyte, comprising at least one electrode plate according to the invention. The fuel cell preferably comprises at least one polymer electrolyte membrane.

[0028] In the tests, the coating system was treated with 0.5 mM H 2 SO 4 It exhibits stability out of the device under harsh fuel cell conditions in electrolyte +0.1 ppm HF up to at least 1.4 V vs Ag / AgCl, and is therefore comparable to precious metal coatings. The contact resistance before and after this electrochemical load (see parameters above) is less than 100 N / cm 2 3mOhm cm at a contact pressure of 1.0 and a measurement temperature of 24°C 2 is less than.

[0029] The corrosion current was measured at 10 -7 A / cm 2 No corrosion on the coating or substrate was detected optically or microscopically up to at least 1.4 V vs. Ag / AgCl. Stainless steel substrates according to DIN, material number 1.4404, were used as substrates.

[0030] In the test, the coating system was diluted with H 2 SO 4 Under harsh electrolytic conditions in electrolyte, the contacts exhibited a stability of at least up to 2.2 V vs. the normal hydrogen electrode (NHE) outside the device. The contact resistance before and after this electrochemical load (see parameters above) was 100 N / cm 2 3mOhm cm at a contact pressure of 1.0 and a measurement temperature of 24°C 2 is less than.

[0031] No corrosion in the coating or substrate was detected optically or microscopically up to at least 2.2 V vs. NHE. Stainless steel substrates according to DIN, material number 1.4404, were used as substrates.

[0032] 1 to 4 are intended to illustrate, by way of example, a coating system according to the invention, an electrode plate in the form of a bipolar plate and produced using the coating system, and a fuel cell. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 is a diagram of a bipolar plate including a coating system. [Diagram 2] FIG. 1 is a schematic diagram of a fuel cell system comprising multiple fuel cells. [Diagram 3] FIG. 2 is an enlarged cross-sectional view of an example coating system. [Figure 4] 1 is a scanning electron microscope photograph of the top coat. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Figure 1 shows an electrode plate 2 in the form of a bipolar plate with a coating system 1, the plate having a metal substrate 2a or metal carrier plate, here made of austenitic stainless steel. The bipolar plate has an inlet area 3a with openings 4 and an outlet area 3b with further openings 4' used to supply process gases to the fuel cell and to remove reaction products from the fuel cell. The bipolar plate also has gas distribution structures 5 on both sides, which are provided for contact with a polymer electrolyte membrane 7 (see Figure 2).

[0035] Figure 2 is a schematic diagram of a fuel cell system 100 comprising a number of fuel cells 10. Each fuel cell 10 comprises a polymer electrolyte membrane 7 having adjacent electrode plates 2, 2' on either side in the form of bipolar plates. The same reference numbers as in Figure 1 denote the same elements.

[0036] Figure 3 shows a cross-section of the coating system 1 according to Figure 1. It can be seen that there is a top coat 1a, an intermediate coat 1b and a base coat 1c. The base coat 1c is arranged on a side B of the coating system 1, which faces the substrate 2a of the bipolar plate 2. The top coat 1a is arranged on a side A of the coating system 1, which faces away from the substrate 2a of the electrode plate 2. Alternatively, the coating system 1 may also have several intermediate coats 1b.

[0037] FIG. 4 shows a scanning electron micrograph of the surface of a topcoat 1a made of a network of nanofibers 6, here made of indium tin oxide. [Explanation of symbols]

[0038] 1. Coating System 1a Top coat 1b One or more intermediate courts 1c Base coat 2, 2' electrode plate 2a metal board 3a Inflow area 3b Exit area 4, 4' opening 5 Gas distribution structure 6 Nanofibers 7 Polymer electrolyte membrane 10 fuel cell 100 Fuel Cell System A: Side of the coating system 1 facing away from the substrate 2a B: Side of coating system 1 facing substrate 2a

Claims

1. A coating system (1) for coating a metal substrate (2a) to form an electrode plate (2, 2'), comprising at least one top coat (1a) made of a metal oxide, at least one intermediate coat (1b) supporting said top coat (1a), and a base coat (1c) supporting one or more of said intermediate coats (1b), said base coat (1c) is formed from titanium or a titanium-niobium alloy or from chromium, said at least one intermediate coat (1b) is formed from titanium niobium nitride and / or titanium niobium carbide and / or titanium niobium carbonitride and / or titanium carbide and / or titanium nitride and / or chromium carbide and / or chromium carbonitride and / or homogeneous indium tin oxide optionally doped with a first dopant and / or homogeneous tin oxide doped with a second dopant, said top coat (1a) a) indium tin oxide, optionally comprising a third dopant having at least one element from the group including carbon, nitrogen, boron, fluorine, hydrogen, phosphorus, sulfur, chlorine, bromine, aluminum, silicon, titanium, chromium, cobalt, nickel, copper, zirconium, niobium, molybdenum, silver, antimony, hafnium, tantalum, and tungsten; or b) doped tin oxide, said tin oxide having as a fourth dopant at least one element from the group including niobium, tantalum, antimony, and fluorine; The coating system (1) is formed from a network of nanofibers (6) of any one of the above.

2. 2. The coating system (1) according to claim 1, wherein the first dopant corresponds to the third dopant and the second dopant corresponds to the fourth dopant.

3. 3. The coating system (1) according to claim 1 or 2, wherein the concentration of the first dopant and / or the third dopant element in the indium tin oxide is in the range of from >0 to 20 atomic %.

4. 2. The coating system (1) according to claim 1, wherein the concentration of the second dopant and / or the fourth dopant element in the tin oxide is in the range of from >0 to 20 atomic %.

5. 2. The coating system (1) according to claim 1, wherein the top coat (1a) made from indium tin oxide has an indium content in the range of 70-90 atomic %.

6. 2. The coating system (1) according to claim 1, wherein the base coat (1c) has a coat thickness in the range of 1 to 300 nm.

7. The coating system (1) according to claim 1, wherein said at least one intermediate coat (1b) has a coat thickness in the range of 0.1 μm to 3.0 μm.

8. The coating system (1) according to claim 1, wherein the top coat (1a) has a coat thickness in the range of 0.01 μm to 15 μm.

9. An electrode plate (2, 2'), in particular a bipolar plate, comprising a metal substrate (2a) and a coating system (1) according to claim 1, metal substrate (2a), Base coat (1c), one or more intermediate coats (1b), and Top Coat (1a) The electrode plates (2, 2') have a structure in the order of the electrode plates (2, 2').

10. 10. The electrode plate (2, 2') according to claim 9, wherein the metal substrate (2a) is made of steel.

11. A fuel cell (10), in particular an oxy-hydrogen fuel cell, or an electrolyser, or a redox flow battery, comprising at least one electrode plate (2, 2') according to claim 9 or 10.

12. The fuel cell (10) according to claim 11, comprising at least one polymer electrolyte membrane (7).

13. A method for manufacturing an electrode plate (2, 2') according to claim 9, said method comprising the steps of: Providing the metal substrate (2a); forming the base coat (1c) on the surface of the metal substrate (2a); forming said at least one intermediate coat (1b) on said base coat (1c); forming said top coat (1a) on the side of said at least one intermediate coat (1b) remote from said base coat (1c); A method, wherein the coating system (1) is formed on the metal substrate (2a) by non-reactive sputtering.

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