Layer system, flow field plate having layer system of this type, and fuel cell, electrolytic cell or redox flow cell

Abstract

The invention relates to a layer system (1) for coating a metal substrate (2a) to form a flow field plate (2), comprising:-at least one cover layer (1a) made of a metal oxide; -at least one intermediate layer (1b) supporting the cover layer (1a); and-a lower layer (1c) supporting the intermediate layer (s) (1b); wherein the cover layer (1a) is formed of an indium tin oxide; wherein the indium tin oxide is doped with at least one element from the group including carbon, nitrogen, boron, fluorine, hydrogen, silicon, titanium, tin, and zirconium; wherein the at least one intermediate layer (1b) is formed from titanium nitride and / or titanium carbide and / or titanium carbonitride and / or titanium niobium nitride and / or titanium niobium carbide and / or titanium niobium carbonitride and / or chromium nitride and / or chromium carbide and / or chromium carbonitride; and wherein the lower layer (1c) is formed of titanium or a titanium-niobium alloy or chromium. The invention also relates to a flow field plate having a layer system (1) of this type, and to a fuel cell (10), an electrolytic cell or a redox flow battery having a flow field plate (2, 2 ') of this type.

Description

[0001] The present application is a divisional application of the patent application with the application date of 16 April 2021, the application number 202180018242.1 (PCT / DE2021 / 100347), and the invention title “Layer system, flow field plate having a layer system of this type, and fuel cell, electrolyzer or redox flow cell”. TECHNICAL FIELD

[0002] The present invention relates to a layer system for coating a metal substrate to form a flow field plate, the layer system comprising at least one cover layer made of a metal oxide. The present invention further relates to a flow field plate comprising a metal substrate and such a layer system. Furthermore, the present invention relates to a fuel cell, electrolyzer or redox flow cell comprising at least one such flow field plate. BACKGROUND

[0003] From DE 100 58 337 A1 a flow field plate for a fuel cell or electrolyzer is known, wherein on at least one side of a metal sheet a conductive and corrosion-resistant protective coating made of a metal oxide is formed. The metal oxide is formed in particular from an oxide of an element or an alloy from the group comprising tin, zinc and indium.

[0004] US 2018 / 0053948 A1 describes a separator for a polymer electrolyte fuel cell. The separator made of ferritic stainless steel has an indium tin oxide coating. SUMMARY

[0005] It is an object of the present invention to provide an improved layer system for a flow field plate and to provide such a flow field plate. Furthermore, it is an object of the present invention to propose a fuel cell, electrolyzer or redox flow cell having at least one such flow field plate.

[0006] The object is achieved for a layer system for coating a metal substrate to form a flow field plate, which forms a layer system comprising at least one cover layer made of a metal oxide, at least one intermediate layer supporting the cover layer and a lower layer supporting the intermediate layer(s), the cover layer being formed of indium tin oxide (ITO), wherein the indium tin oxide is doped with at least one element from the group comprising carbon, nitrogen, boron, fluorine, hydrogen, silicon, titanium, tin and zirconium, wherein the at least one intermediate layer is formed of titanium nitride and / or titanium carbide and / or titanium carbonitride and / or titanium niobium nitride (TiNbN) and / or titanium niobium carbide (TiNbC) and / or titanium niobium carbonitride (TiNbCN) and / or chromium nitride (CrN) and / or chromium carbide (CrC) and / or chromium carbonitride (CrCN), and wherein the lower layer is formed of titanium (Ti) or titanium-niobium alloy (TiNb) or chromium (Cr).

[0007] This layer system is characterized by high long-term stability, high electrical conductivity, low cost, and the absence of precious metals. Furthermore, the layer system ensures excellent corrosion protection against the metal substrate or base plate of the flow field plate.

[0008] The layer system is preferably fabricated using PVD or CVD processes (PVD: Physical Vapor Deposition; CVD: Chemical Vapor Deposition).

[0009] A particularly preferred coating layer is made of indium tin oxide having an indium content in the range of 70 vol% to 90 vol%. An indium content in the range of 75 vol% to 85 vol% is also particularly preferred, as it has high conductivity.

[0010] Specifically, the lower layer serves as an adhesion promoter between the metal substrate and at least one intermediate layer. Furthermore, the lower layer forms a conductive oxide and thus provides electrochemical corrosion protection for the metal substrate of the flow field plate. The lower layer preferably has a layer thickness in the range of 1 nm to 300 nm.

[0011] Specifically, the intermediate layer also acts as an adhesion promoter between the lower layer and the capping layer. Furthermore, at least one intermediate layer forms a conductive oxide, thus providing electrochemical corrosion protection for the metal substrate of the lower layer and the flow field plate. At least one intermediate layer also provides a barrier against hydrogen, preventing hydrogen from penetrating in the direction of the metal substrate and damaging it. The layer thickness of a single intermediate layer is preferably selected in the range of 0.1 μm to 3.0 μm. However, two or more intermediate layers may be present.

[0012] The capping layer mechanically protects the underlying layer and (one or more) intermediate layers from corrosion. The capping layer particularly has a layer thickness ranging from 0.01 μm to 15 μm, and more particularly from 0.1 μm to 3 μm.

[0013] The layer system according to the invention, comprising a lower layer, at least one intermediate layer, and a cover layer, preferably has a total thickness in the range of 0.1 μm to 20 μm.

[0014] Furthermore, it has been shown to be useful if the capping layer is doped with at least one element from the group consisting of carbon, nitrogen, boron, fluorine, hydrogen, silicon, titanium, tin, and zirconium, for a maximum of 35 atomic percent, particularly in the range of 0.1 atomic percent to 10 atomic percent, and especially preferably in the range of 1 atomic percent to 5 atomic percent. In this case, one or more doping elements are incorporated into the oxide lattice of indium tin oxide.

[0015] In this case, the dopant can be present uniformly across the thickness of the capping layer. Alternatively, the amount of (one or more) dopant elements can be increased in the direction of the free surface of the capping layer, thereby forming a gradient layer. One or more dopant elements can also be present only in the free surface of the capping layer.

[0016] A particularly preferred method is to use a carbon and / or silicon doped capping layer. Specifically, hydrogen is present only in the traces of the capping layer.

[0017] In particular, the following layer systems for coating metal substrates preferably made of steel, especially austenitic steel or austenitic stainless steel, have been shown to be advantageous for forming flow field plates: Example 1 Bottom layer: TiNb or Ti layer thickness: 100 nm Intermediate layer: TiNbN; Layer thickness: 300 nm Coating: Indium tin oxide with an indium content of 80% by volume Layer thickness: 100 nm Example 2 Bottom layer: TiNb or Ti layer thickness: 100 nm Intermediate layer: TiNbCN; Layer thickness: 300 nm Coating: Indium tin oxide with an indium content of 80% by volume Layer thickness: 100 nm Example 3 Bottom layer: TiNb or Ti layer thickness: 100 nm 1. Intermediate layer: TiNbN layer thickness: 200 nm 2. Intermediate layer: TiNbCN layer thickness: 200 nm Coating: Indium tin oxide with an indium content of 90% by volume Layer thickness: 100 nm Example 4 Bottom layer: TiNb or Ti layer thickness: 100 nm 1. Intermediate layer: TiNbCN layer thickness: 200 nm 2. Intermediate layer: TiNbN layer thickness: 200 nm Coating: Indium tin oxide with an indium content of 80% by volume Layer thickness: 100 nm Example 5 Bottom layer: TiNb or Ti layer thickness: 100 nm Intermediate layer: TiN layer thickness: 300 nm Coating: Indium tin oxide with an indium content of 80% by volume Layer thickness: 100 nm Example 6 Bottom layer: TiNb or Ti layer thickness: 100 nm Intermediate layer: TiC and / or TiNbC; Layer thickness: 300 nm Coating: Indium tin oxide with an indium content of 80% by volume Layer thickness: 100 nm Example 7 Bottom layer: TiNb or Ti layer thickness: 100 nm Intermediate layer: TiCN layer thickness: 300 nm Coating: Indium tin oxide with an indium content of 80% by volume Layer thickness: 100 nm Example 8 Bottom layer: Cr layer thickness: 100 nm Intermediate layer: CrN and / or CrCN; Layer thickness: 300 nm Coating: Indium tin oxide with an indium content of 80% by volume Layer thickness: 100 nm Example 9 Bottom layer: Cr layer thickness: 100 nm Intermediate layer: CrC and / or CrCN; Layer thickness: 300 nm Coating: Indium tin oxide with an indium content of 80% by volume Layer thickness: 100 nm This objective is achieved for a flow field plate comprising a metal substrate and a layer system according to the invention, wherein the flow field plate has a structure in the following order: metal substrate, Lower level, (One or more) intermediate layers, Overlay.

[0018] This is preferably a flow field plate having a metal substrate or metal support plate, which is preferably made of steel, particularly austenitic steel or stainless steel. The support plate can be designed as one or more parts. Attached Figure Description

[0019] Figures 1 to 3The purpose of this illustration is to demonstrate the layer system according to the invention, the flow field plate formed using the layer system, and the fuel cell. In the accompanying drawings: Figure 1 A flow field plate with a layered system is shown; Figure 2 A fuel cell system comprising multiple fuel cells is schematically illustrated. Figure 3 An enlarged view of a cross section through the layer system shown by way of example is presented. Detailed Implementation

[0020] Figure 1 A flow field plate 2 with a layer system 1 is shown, wherein the flow field plate has a metal substrate 2a or a metal support plate made of austenitic steel. The flow field plate 2 has an inlet region 3a with openings 4 and an outlet region 3b with additional openings 4', these openings being used to supply process gases to the fuel cell and to remove reaction products from the fuel cell. The flow field plate 2 also has a gas distribution structure 5 on each side, providing a gas distribution structure for use with a polymer electrolyte membrane 7 (see...). Figure 2 )touch.

[0021] Figure 2 A fuel cell system 100 comprising multiple fuel cells 10 is schematically shown. Each fuel cell 10 includes a polymer electrolyte membrane 7 adjacent to both sides of flow field plates 2, 2'. Figure 1 The same reference numerals in the figures indicate the same elements.

[0022] Figure 3 It shows crossing according to Figure 1 A cross-section of the layer system 1 is shown. It can be seen that there are a cover layer 1a, intermediate layers 1b, and a lower layer 1c. The lower layer 1c is disposed on side B of the layer system 1, which is arranged to face the substrate 2a of the flow field plate 2. The cover layer 1a is disposed on side A of the layer system 1, which is arranged to face away from the substrate 2a of the flow field plate 2. Alternatively, the layer system 1 may also have multiple intermediate layers 1b.

[0023] List of reference numerals Layer 1 system 1a Covering layer 1b Intermediate Layer 1c Lower layer 2,2' Flow field plate 2a Metal substrate 3a Inflow area 3b Export Area 4, 4' Opening 5. Gas distribution structure 7 Polymer electrolyte membrane 10 Fuel Cells 100 Fuel Cell System The side of layer A system 1 facing away from substrate 2a The side of layer B system 1 facing substrate 2a

Claims

1. A layer system (1) for coating a metal substrate (2a) to form a flow field plate (2, 2'), comprising at least one cover layer (1a) made of metal oxide, at least one intermediate layer (1b) supporting the cover layer (1a) and a lower layer (1c) supporting the intermediate layer (1b). in, The capping layer (1a) is formed of indium tin oxide, wherein the indium tin oxide is doped with at least one element from the group consisting of carbon, nitrogen, boron, fluorine, hydrogen, silicon, titanium, tin and zirconium. Wherein, the at least one intermediate layer (1b) is formed of titanium nitride and / or titanium carbide and / or titanium carbonitride and / or titanium niobium nitride and / or titanium niobium carbide and / or titanium niobium carbonitride and / or chromium nitride and / or chromium carbide and / or chromium carbonitride, and The lower layer (1c) is formed of titanium or a titanium-niobium alloy or chromium.

2. The layer system (1) according to claim 1, wherein, The capping layer (1a) made of indium tin oxide has an indium content in the range of 70% to 90% by volume.

3. The layer system (1) according to any one of the preceding claims, wherein, The lower layer (1c) has a layer thickness in the range of 1 nm to 300 nm.

4. The layer system (1) according to any one of the preceding claims, wherein, The at least one intermediate layer (1b) has a layer thickness in the range of 0.1 μm to 3.0 μm.

5. The layer system (1) according to any one of the preceding claims, wherein, The cover layer (1a) has a thickness in the range of 0.01 μm to 15 μm.

6. The layer system (1) according to any one of the preceding claims, wherein, The capping layer (1a) is doped with at least one element from the group consisting of carbon, nitrogen, boron, fluorine, hydrogen, silicon, titanium, tin and zirconium, in an amount of up to 35 atomic percent, particularly in the range of 0.1 atomic percent to 10 atomic percent.

7. A flow field plate (2, 2') comprising a metal substrate (2a) and a layer system (1) according to any one of claims 1 to 6, the flow field plate having a structure of the flow field plate (2, 2') in the following order: Metal substrate (2a). Lower layer (1c) (One or more) intermediate layers (1b), Covering layer (1a).

8. The flow field plate (2, 2') according to claim 7, wherein, The metal substrate (2a) is formed of steel.

9. A fuel cell (10), wherein the fuel cell is particularly an oxygen-hydrogen fuel cell, or an electrolyzer or redox flow cell, the fuel cell comprising at least one flow field plate (2, 2') according to claim 7 or 8.

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

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