Bipolar plate for fuel cells, and production method

Patent metadata

Field	Value
Publication number	US-11114675-B2
Application number	US-201816484856-A
Country	US
Kind code	B2
Filing date	Feb 20, 2018
Priority date	Feb 20, 2017
Publication date	Sep 7, 2021
Grant date	Sep 7, 2021

Abstract

The bipolar plate of the invention for electrochemical cells, especially for proton-exchange membrane (PEM) fuel cells, is made with a metallic substrate and on the surface is made with an electrical contact resistance-reducing, carbon-based layer, a layer system or a boundary layer which is made of a near-surface, primarily sp2-bonded, carbon-based layer having a carbon fraction ranging from 50% to 100%, this layer being applied on a metallic substrate surface that is modified relative to the starting material. There may also be a surface region of the substrate in the form of an edge layer made with nitride and/or carbon by nitriding and/or carburizing. On the surface which is in touching contact with a gas-permeable element within the electrochemical cell, the metallic substrate may have a structuring made with elevations and/or depressions in the respective surface.

First claim

The invention claimed is:

1. A bipolar plate for proton-exchange membrane PEM fuel cells, which are made with a metallic substrate and on their surface with an electrical contact resistance-reducing carbon-based layer, a layer system or a boundary layer which is made of a near-surface sp2-bonded, carbon-based layer which has a carbon fraction ranging from 50% to 100% and which is applied on a metallic substrate surface modified relative to the starting material, and
a surface region of the metallic substrate is present as edge layer, which is made with nitride or carbon by nitriding or carburizing,
the metallic substrate has a surface which is in contact with a gas-permeable element within the PEM cells and the surface has elevations or depressions, wherein
the elevations or depressions on the metallic substrate surface have dimensions and geometrical design such that fibers, with which the gas-permeable element is made as a textile structure, which are
in touching contact over their periphery with at least 10% of their outer lateral surface, on the metallic substrate surface region in which the depression is present and in which the fibers and the substrate surface touch one another.

2. The bipolar plate as claimed in claim 1 , wherein an adhesion-promoting and corrosion-reducing layer of chromium or of titanium, or an adhesion-promoting layer enriched with chromium or nickel, having a thickness ranging from 2 nm to 200 nm, is formed on the surface of the metallic substrate as an interlayer beneath the carbon-based layer, the layer system or the boundary layer.

3. The bipolar plate as claimed in claim 1 , wherein the carbon-based layer or the carbon-enriched layer is formed on a chromium-enriched or nickel-enriched edge layer on a surface of the metallic substrate made from stainless steel.

4. The bipolar plate as claimed in claim 1 , wherein a transition zone with a carbon gradient is formed between the carbon-based layer or the carbon-enriched layer and the metallic substrate surface.

5. The bipolar plate as claimed in claim 1 , wherein depressions in the metallic substrate surface are formed with the same orientation and at constant distances between adjacent depressions.

6. A method for producing a bipolar plate as claimed in claim 1 , consisting of
vacuum coating the metallic substrate surface with a plasma, with a graphitic, carbon-based layer, a layer system or a boundary layer, and
positioning the metallic substrate surface in contact with the gas-permeable element in touching contact with the gas-permeable element in a PEM fuel cell and the metallic substrate surface is formed with elevations or depressions on its contact surface, which are formed by erosion of material or by an embossing method, the elevations or depressions on the metallic substrate surface have dimensions and geometric design such that fibers which make up the gas-permeable element are a textile structure in touching contact over their periphery with at least 10% of their outer lateral surface,
vacuum-coating the metallic substrate surface with a graphitic, carbon-based layer, a layer system or a boundary layer, which is made completely closed with a plurality of atomic layers disposed one above another, with a plasma which is generated with an electric arc discharge,
or
forming the edge layer by means of a plasma on the metallic substrate surface by a plasma nitriding, a plasma carburizing or a plasma carbonitriding process, while maintaining an atmosphere for this purpose.

7. The method as claimed in claim 6 , in the case of carbonitriding, the edge layer is first nitrided and subsequently carburized.

8. The method as claimed in claim 6 , wherein the metallic substrate surface is vacuum-coated with the graphitic, the carbon-based layer, the layer system or the boundary layer, which is made completely closed with a plurality of atomic layers disposed one above another, by a plasma which is generated with an electric arc discharge.

9. The method as claimed in claim 8 , before the application of the graphitic, the carbon-based layer, the layer system or the boundary layer or before the formation of the edge layer, an oxide layer present on the metallic substrate surface is at least partially removed or reduced by an etching operation in argon or nitrogen or the oxide is reduced in a hydrogen-containing atmosphere.

10. The method as claimed in claim 8 , before the application of the graphitic, the carbon-based layer, the layer system or the boundary layer, an adhesion promoter layer of chromium or titanium or a layer made with chromium and titanium is formed on the metallic substrate surface by an electric arc discharge operation under vacuum.

11. The method as claimed in claim 6 , the graphitic, the carbon-based layer, the layer system or the boundary layer with ionized and accelerated carbon ions is formed, on carbon atoms present on the metallic substrate surface, at temperatures ranging from 80° C. to 600° C. with a layer thickness <80 nm.

12. The method as claimed in claim 11 , wherein almost 100% ionization of the carbon atoms is attained by means of a pulsed arc evaporator.

13. The method as claimed in claim 6 , a plasma nitrocarburizing for forming the edge layer in a near-vacuum, nitrogen-containing atmosphere at a pressure ranging from 10 −1 mbar to 10 −3 mbar by the nitriding treatment where nitrogen ions are accelerated in the direction of the substrate surface, the metallic substrate being subject to an electrically negative bias voltage ranging from 500 V to 1000 V or the metallic substrate is maintained having connection to ground potential, and a temperature ranging from 300° C.-500° C.

14. The method as claimed in claim 13 , nitrogen ions are generated by means of an electric arc discharge-assisted glow discharge and are accelerated in the direction of a cooled anode, while the nitrogen ions arising are shielded and accelerated in the direction of the metallic substrate surface.

15. The method as claimed in claim 6 , the erosion of material for forming elevations or depressions is attained with at least one laser beam in an irradiated region of the metallic substrate surface, or the roughness and specific surface area of the metallic substrate surface is increased by bombardment with ions.

16. The method as claimed in claim 15 , the elevations or depressions are attained by at least one laser beam, by interference of a plurality of laser beams, in an irradiated region of the metallic substrate surface, or roughness and specific surface area of the metallic substrate surface is increased by bombardment with ions having an energy ranging from 10 2 eV to 10 4 eV, under vacuum conditions.

17. The method as claimed in claim 6 , a plasma nitrocarburizing for forming the edge layer takes place in a near-vacuum, nitrogen-containing atmosphere at a pressure ranging from 10 −1 mbar to 10 −3 mbar by the nitriding treatment in which nitrogen ions are generated by the electrons of a carbon evaporator and are accelerated by an applied electric potential difference, in the direction of the metallic substrate surface, and the subplantation or implantation of carbon takes place in parallel by the same carbon evaporator.

Assignees

• Fraunhofer Ges Forschung
• Univ Dresden Tech

Inventors

• Topalski Slavcho
• Roch Teja
• Stucky Thomas
• Zwick Axel
• Maurizio Giorgio

Classifications

• H01M2008/1095

  Fuel cells with polymeric electrolytes · CPC title

• H01M8/0228 Primary

  in the form of layered or coated products · CPC title

• H01M8/021

  Alloys based on iron · CPC title

• H01M8/0247

  characterised by the form (characterised by a channel configuration H01M8/0258) · CPC title

• Y02P70/50

  Manufacturing or production processes characterised by the final manufactured product · CPC title