Layer system, electrode plate comprising such a layer system, process for its production, and fuel cell, electrolyzer or redox flow battery - Patents.com

Abstract

The invention relates to a layer system (1) for coating a substrate (2a) to form an electrode plate (2), the layer system (1) comprising at least one coating (1a) of a metal oxide, the coating (1a) comprising a homogeneous polycrystalline doped indium tin oxide layer, the top of which being a polycrystalline doped indium tin oxide layer consisting of a network of nanofibers (6), the indium tin oxide being doped with at least one element from the group comprising carbon, nitrogen, boron, fluorine, hydrogen, phosphorus, sulfur, chlorine, bromine, aluminum, silicon, titanium, chromium, cobalt, nickel, copper, zirconium, niobium, molybdenum, silver, antimony, hafnium, tantalum, tungsten. The invention further relates to an electrode plate comprising such a layer system, to a process for its production and to a fuel cell, electrolytic cell or redox flow battery comprising at least one such electrode plate.

Description

[Technical Field]

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

[0002] German Patent Application Publication No. DE 10058337 discloses a bipolar plate for a fuel cell or electrolyzer, in which a 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 formed, in particular, from an oxide of an element or alloy from the group including tin, zinc, and indium. A doping that ensures electrical conductivity and consists of at least one element from the group including aluminum, chromium, silver, boron, fluorine, antimony, chlorine, bromine, phosphorus, molybdenum, and carbon can be present in the metal oxide. The metal sheet used may be made of aluminum, copper, stainless steel, chromium-plated stainless steel, titanium, titanium alloys, or iron-containing compounds, and may be coated with at least one of 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 layer system for an electrode plate and to provide such an electrode plate. Furthermore, the object of the present invention is to provide a method for the production of 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] The purpose is for a layer system for coating a substrate to form an electrode plate, the layer system comprising: The at least one first coating is made of a metal oxide, the at least one first coating being a homogeneous polycrystalline doped indium tin oxide layer, on which a top layer is formed in the form of a polycrystalline doped indium tin oxide layer made of a network of nanofibers, the at least one first coating and the indium tin oxide of the top layer being doped 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, zirconium, niobium, molybdenum, silver, antimony, hafnium, tantalum, and tungsten.

[0005] This layer system is characterized by a high level of long-term stability and simultaneously high electrical conductivity and low cost due to the use of a large amount of precious metals or no precious metals. In addition, this layer system ensures excellent corrosion protection for the metallic base material or substrate of the electrode plates, especially bipolar plates. Indium tin oxide is also referred to below as ITO (indium tin oxide).

[0006] The layer system is preferably formed by a PVD or CVD process (PVD: Physical Vapour Deposition, CVD: Chemical Vapour Deposition) or a PACVD process (PACVD: Plasma-Assisted Chemical Vapour Deposition).

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

[0008] The formation of the top layer made from a network of nanofibers is referred to in this document in the publication “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 used non-reactive sputtering techniques to produce ITO nanofibers for fuel cells, electrolyzers, and redox flow bipolar plates from targets made with a 90:10 atomic % In2O3:SnO2 ratio at a deposition rate of 40 Å / min. Temperature and SnO2 content are key growth factors in the production of ITO nanofibers. Growth occurs via atoms evaporating from the target and depositing on the substrate. The growth temperature range is 150°C to 500°C. With increasing temperature, the average fiber length and average fiber diameter increase, the adjacent distance decreases, and the number of fibers per unit area increases. The SnO2 content is preferably up to 30 atomic %. The change in the average nanofiber length and average diameter depends on the deposition time. ITO nanofibers are preferably grown on a thin, dense ITO layer.

[0010] The preferred total layer thickness of the layer system is <1 μm, in particular in the range of 0.01 to 0.5 μm.

[0011] The concentration of the doping element in the indium tin oxide is in particular in the range of <0 to 20 atomic %.

[0012] Particularly preferably, the first coating and top layer herein are made of indium tin oxide with an indium content in the range of 70-90 atomic %. Particularly preferably, the indium content is in the range of 75-85 atomic %, which has a high level of electrical conductivity.

[0013] In particular, the following layer system for coating a metal substrate, preferably made of steel, in particular austenitic steel or austenitic stainless steel, has proven advantageous for forming electrode plates.

[0014] Example 1: First coating: ITO Layer thickness: 100nm Doping: 10 atomic % nitrogen Top layer: Indium tin oxide nanofibers with 80% indium content by volume Layer thickness: 100nm Doping: 3-5 atomic percent copper

[0015] Example 2: First coating: ITO Layer thickness: 100nm Doping: 5 atomic % titanium Further first coating: ITO Layer thickness: 200 nm Doping: 5 atomic % nitrogen Top layer: Indium tin oxide nanofibers with 90% indium content by volume Layer thickness: 100nm Doping: 3-5 atomic percent carbon

[0016] The object is to make an electrode plate having a metal substrate and substrate, at least one first coating made from a metal oxide; and Top layer made from nanofibers a layer system according to the invention, having a structure of electrode plates in the order This is achieved for the electrode plate comprising:

[0017] The structure preferably has a layer thickness in the range of 0.001 to 5 mm.

[0018] In particular, the substrate is made of an iron alloy, in particular steel, or titanium or a titanium alloy, or aluminum or an aluminum 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, or is based on graphite.

[0019] This is preferably an electrode plate with a metal substrate or a metal carrier plate, which can consist of one or more parts, in particular the electrode plate is designed as a bipolar plate.

[0020] According to the invention, the method for producing an electrode plate according to the invention comprises the steps of: Providing a substrate; forming a bottom layer on a surface of an electrode plate; forming at least one first coating on a substrate; forming a top layer on the at least one first coating, wherein the at least one first coating and the top layer of a metal oxide are formed on the substrate having an amorphous structure using non-reactive sputtering; annealing the at least one first coating and the top layer at a temperature in the range of 220-400°C so that the amorphous structure is converted to a polycrystalline structure; Includes:

[0021] This is a deposition process that can be performed cost-effectively on a continuous scale and can also be used to produce nanofibers.

[0022] The object is further achieved with a fuel cell, in particular an oxygen-hydrogen fuel cell, or an electrolyzer, in particular for producing hydrogen and oxygen from water, or in particular a redox flow battery 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.

[0023] In tests, the layer system exhibited stability up to at least 1.4 V vs. Ag / AgCl under harsh fuel cell conditions in a 0.5-mM H2SO4 electrolyte with pH 3 + 0.1 ppm HF, ex situ, thus comparable to precious metal coatings. The contact resistance (see parameters above) before and after this electrochemical load was 0.01 V at a contact pressure of 100 N / cm 2 , and at a measurement temperature of 24°C, <3mOhm*cm 2 is.

[0024] Corrosion currents are <10 under relevant fuel cell application potentials up to 1.0 V with respect to Ag / AgCl. -7 A / cm 2 is. No attack of the layer or the substrate was detected optically or microscopically up to at least 1.4 V vs. Ag / AgCl. Stainless steel substrates of material number 1.4404 according to DIN were used as substrates.

[0025] In tests, the layer system showed stability up to at least 2.2 V compared to an ex-situ NHE (normal hydrogen electrode) under harsh electrolytic conditions in H2SO4 electrolyte at pH 4. The contact resistance (see parameters above) before and after this electrochemical load was 0.01 V at a contact pressure of 100 N / cm 2 , and at a measurement temperature of 24°C, <3mOhm*cm 2 is.

[0026] No attack of the layer or substrate was detected optically or microscopically up to at least 2.2 V with respect to the NHE. A stainless steel substrate of material number 1.4404 according to DIN was used as substrate.

[0027] 1 to 4 are intended to illustrate, by way of example, the layer system according to the invention, the electrode plate in the form of a bipolar plate formed therewith, and the fuel cell. [Brief explanation of the drawings]

[0028] [Figure 1]1 shows a bipolar plate with a layer system. [Figure 2] 1 shows a schematic representation of a fuel cell system comprising a plurality of fuel cells. [Figure 3] 1 shows an enlarged cross section of an electrode plate 2 with an exemplary layer system. [Figure 4] A scanning electron micrograph of the top layer is shown. DETAILED DESCRIPTION OF THE INVENTION

[0029] 1 shows an electrode plate 2 in the form of a bipolar plate with a layer system 1, which comprises a metal substrate 2a or metal carrier plate, here made from 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 gas 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 FIG. 2).

[0030] Figure 2 shows a schematic representation of a fuel cell system 100 comprising a number of fuel cells 10. Each fuel cell 10 comprises a polymer electrolyte membrane 9 adjacent to both sides of electrode plates 2, 2' in the form of bipolar plates. The same reference numerals as in Figure 1 denote the same elements.

[0031] Figure 3 shows a cross section of the electrode plate 2 according to Figure 1. It can be seen that there is a substrate 2a, a first coating 1a and a top layer 1b. The first coating 1a is arranged on the side B of the layer system 1, which is arranged facing the substrate 2a. The top layer 1b is arranged on the side A of the layer system 1, which is opposite the substrate 2a of the electrode plate 2. Alternatively, the layer system 1 can also have multiple first coatings 1a.

[0032] FIG. 4 shows a scanning electron micrograph of the surface of the top layer 1b, which is made from a network of nanofibers 6, here made from indium tin oxide. [Explanation of symbols]

[0033] One-tier system 1a First Coating 1b Top layer 2, 2' electrode plate 2a 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: the side of the layer system 1 opposite the substrate 2a B. Side of layer system 1 facing substrate 2a

Claims

1. 1. A layer system (1) for coating a substrate (2a) to form an electrode plate (2, 2'), said layer system (1) comprising at least one first coating (1a) made of a metal oxide, said at least one first coating (1a) being a homogeneous polycrystalline doped indium tin oxide layer, on which a top layer (1b) is formed in the form of a polycrystalline doped indium tin oxide layer made of a network of nanofibers (6), said indium tin oxide of said at least one first coating (1a) and of said top layer (1b) comprising at least one element from the group comprising 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.

2. 2. The layer system (1) according to claim 1, wherein the layer thickness of the layer system (1) is less than 1 μm.

3. The layer system (1) according to claim 1 or 2, wherein the concentration of doping elements in the indium tin oxide is in the range of 0 to 20 atomic %.

4. 2. The layer system (1) according to claim 1, wherein the indium tin oxide has an indium content in the range of 70 to 90 atomic %.

5. An electrode plate (2, 2'), in particular a bipolar plate, comprising a substrate (2a) and a layer system (1) according to claim 1, Substrate (2a), at least one first coating (1a) made from a metal oxide, and Top layer made of nanofibers (1b) The electrode plates (2, 2') have a structure in the order of the electrode plates (2, 2').

6. 6. The electrode plate (2, 2') according to claim 5, wherein the substrate (2a) has a thickness in the range of 0.001 to 5 mm.

7. 7. The electrode plate (2, 2') according to claim 5 or 6, wherein the substrate (2a) is made of an iron alloy, in particular steel, or titanium or a titanium alloy, or aluminum or an aluminum 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, or is based on graphite.

8. 6. The electrode plate (2, 2') according to claim 5, wherein the substrate (2a) is a metal substrate (2a).

9. A fuel cell (10), in particular an oxygen-hydrogen fuel cell, or an electrolyzer, or a redox flow battery, comprising at least one electrode plate (2, 2') according to claim 5.

10. 10. The fuel cell (10) according to claim 9, comprising at least one polymer electrolyte membrane (7).

11. A method for producing an electrode plate (2, 2') according to claim 5, comprising the steps of: Providing a substrate (2a); forming at least one first coating (1a) on said substrate (2a); forming a top layer (1b) on said at least one first coating (1a), wherein said at least one first coating (1a) and said top layer (1b) are formed on said substrate (2a) by non-reactive sputtering so as to have an amorphous structure; annealing said at least one first coating (1a) and said top layer (1b) at a temperature in the range of 220 to 400°C in such a way that said amorphous structure is transformed into a polycrystalline structure; A method comprising:

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