US-12620603-B2 - Bipolar plate, fuel cell, and method for producing a bipolar plate

Abstract

In order to provide a bipolar plate that has optimized electrical conductivity and can be produced as easily as possible, the invention proposes that the bipolar plate comprises an electrically conductive main body and an electrically conductive coating, wherein the electrically conductive coating comprises a binding material and one or more electrically conductive fillers, and wherein a pigment volume concentration in the coating corresponds at least to a pigment volume concentration required to achieve a percolation threshold.

Inventors

• Alexander Höflich

Assignees

• EKPO FUEL CELL TECHNOLOGIES GMBH

Dates

Publication Date

20260505

Application Date

20230131

Priority Date

20200812

Claims (19)

1. 1 . A bipolar plate comprising: an electrically conductive main body; and an electrically conductive coating, wherein the electrically conductive coating comprises a binding material and one or more electrically conductive fillers, a pigment volume concentration in the coating corresponds at least to a pigment volume concentration required to reach a percolation threshold, the one or more electrically conductive fillers have a surface modification, the binding material comprises an adhesion promoter component that serves as an adhesion promoter to the main body and which is coupled or couplable to the surface modification, and a degree of the surface modification and a content of the adhesion promoter component result in an adhesive strength between the coating and the main body of GT 1 or less.
2. 2 . The bipolar plate according to claim 1 , wherein the pigment volume concentration in the coating corresponds to 1.5 times or less a critical pigment volume concentration.
3. 3 . The bipolar plate according to claim 1 , wherein the coating is porous and/or open-pored.
4. 4 . The bipolar plate according to claim 1 , wherein the one or more electrically conductive fillers are selected from one or more carbon-based fillers, carbon black, acetylene black, flame black, furnace black, graphite, graphene, carbon nanotubes; and/or one or more fillers that comprise or are formed from an electrically conductive ceramic material, a carbide material, a transition metal carbide, a nitride material, a transition metal nitride, a boride material, a transition metal boride, or mixtures thereof.
5. 5 . The bipolar plate according to claim 1 , wherein the surface modification is a functionalization by hydroxy groups, carboxylic acid groups, amino groups, aldehyde groups, carbonyl groups, silane radicals or mixtures thereof.
6. 6 . The bipolar plate according to claim 1 , wherein the binding material is formed by means of a chemical reaction of at least two components, wherein a first component of the at least two components comprises or is formed from a bifunctional or polyfunctional isocyanate compound, and wherein a second component of the at least two components comprises or is formed from one or more compounds that have at least two free hydroxy groups or amino groups.
7. 7 . The bipolar plate according to claim 6 , wherein the first component is a bifunctional or polyfunctional isocyanate monomer, an oligomer of polyfunctional isocyanate monomers, or a prepolymer of polyfunctional isocyanate monomers and bifunctional or polyfunctional alcohols or amines.
8. 8 . The bipolar plate according to claim 6 , wherein the second component is selected from monomers, oligomers and prepolymers that have at least two free hydroxy groups or amino groups.
9. 9 . The bipolar plate according to claim 6 , wherein the second component comprises one or more fluorinated compounds that have a degree of fluorination of 5% or more and/or 40% or less.
10. 10 . The bipolar plate according to claim 1 , wherein the adhesion promoter component contains a carbodiimide.
11. 11 . The bipolar plate according to claim 1 , wherein the adhesion promoter component comprises or is formed from one or more aminosiloxanes.
12. 12 . The bipolar plate according to claim 1 , wherein adhesive strength between the coating and the main body is GT 0.
13. 13 . A fuel cell comprising one or more bipolar plates according to claim 1 .
14. 14 . A method for producing the bipolar plate, according to claim 1 , wherein the method comprising: providing an electrically conductive sheet material and/or an electrically conductive plate material; applying a coating material to the electrically conductive sheet material and/or the electrically conductive plate material; and drying and/or curing the coating material such that an electrically conductive coating is formed, wherein the coating material comprises a binding material or one or more precursors thereof and one or more electrically conductive fillers, and wherein a pigment volume concentration in the coating corresponds at least to a pigment volume concentration required to reach a percolation threshold.
15. 15 . The method according to claim 14 , wherein the coating material is applied to the electrically conductive sheet material and/or the electrically conductive plate material and wherein a forming method is subsequently carried out, thereby forming a bipolar plate.
16. 16 . The bipolar plate according to claim 1 , wherein the pigment volume concentration in the coating corresponds to 1.2 times or less a critical pigment volume concentration.
17. 17 . The bipolar plate according to claim 1 , wherein the pigment volume concentration in the coating corresponds to the critical pigment volume concentration.
18. 18 . The bipolar plate according to claim 3 , wherein the porosity is 0.01 or more.
19. 19 . The bipolar plate according to claim 3 , wherein the porosity is 0.35 or less.

Description

RELATED APPLICATION This application is a continuation of international application No. PCT/EP2021/072003 filed on Aug. 6, 2021 and claims the benefit of German application No. 10 2020 210 209.0 filed on Aug. 12, 2020, which are incorporated herein by reference in their entirety and for all purposes. FIELD OF DISCLOSURE The present invention relates to a bipolar plate, in particular for a fuel cell. The invention further relates to a fuel cell, in particular a low-temperature fuel cell. The present invention further relates to a method for producing a bipolar plate. Bipolar plates are in particular components of fuel cell stacks in fuel cells and preferably serve to separate the media (reaction gases and coolant) and distribute the reaction gases by means of flow fields via the electrochemically active surface of each fuel cell unit of the fuel cell stack, as well as for electrical conduction via the electrical fuel cell units connected in series in the fuel cell stack and for contacting the gas diffusion layers in each individual fuel cell unit. In addition, reaction heat is dissipated or transferred into the coolant via the bipolar plate units. To supply the media in an optimized manner, the bipolar plates preferably have an embossed structure comprising flow channels (flow field) through which, in particular, the best possible distribution of the media over the entire surface of the bipolar plate is possible. A bipolar plate unit is preferably produced by joining an anode bipolar plate and a cathode bipolar plate and can comprise further layers, in particular a layer having an electrically insulating layer for connection to an adjacent bipolar plate unit in the fuel cell stack. For example, in polymer electrolyte fuel cells, a bipolar plate unit comprising two bipolar plates is arranged alternately with a membrane electrode assembly (MEA). The membrane electrode assembly preferably comprises a polymer electrolyte and two electrodes formed as a gas diffusion layer. In order to ensure sufficient corrosion resistance under the respective electrochemical conditions, a coating of one of the surfaces of a main body of the bipolar plate facing the MEA in the assembled state is generally necessary. BACKGROUND The scientific article “Coating of stainless steel and titanium bipolar plates for anticorrosion in PEMFC: A review” by N. F. Asri et al. in the International Journal of Hydrogen Energy No. 42 (2017), pages 9135 to 9148, summarizes conventional coating methods. Application of a very thin noble metal layer is known from EP 2 469 634 B1. WO 2009/089376 A2 and EP 2 157 645 B1 disclose application of a thin layer of noble metal clusters or noble metal alloys. However, these methods have the disadvantage that they are associated with high costs and often form discontinuous layers. WO 2009/065545 A1, WO 2009/108102 A1, CA 2688483 A1, U.S. Pat. No. 5,624,769 A and DE 10 2014 016 186 A1 disclose the application of thin ceramic coatings or plastic coatings on a main body of a bipolar plate. The coatings are usually deposited on bipolar plates by physical vapor deposition (PVD) and/or chemical vapor deposition (CVD). Coatings produced in this way, however, have the disadvantage that they are brittle and bipolar plate main bodies must therefore be coated after a forming process (post-coating). Thus, each bipolar plate main body has to be coated individually, which results in increased production costs. In particular, coatings applied by wet-chemical methods often do not have sufficient adhesion to the main body of the bipolar plate and degrade comparatively quickly. Multilayer structures are disclosed in U.S. Pat. No. 6,291,094 B1 and U.S. Pat. No. 8,852,827 B2. However, complex pretreatment of the main body of the bipolar plate is regularly necessary here. SUMMARY OF THE INVENTION The object of the present invention is to provide a bipolar plate that has optimized electrical conductivity and can be produced as simply as possible. According to the invention, this object is solved by a bipolar plate according to claim 1. The bipolar plate, in particular for a fuel cell, comprises an electrically conductive main body and an electrically conductive coating. The coating comprises a binding material and one or more electrically conductive fillers. Preferably, a pigment volume concentration in the coating corresponds at least to a pigment volume concentration required to reach a percolation threshold. In particular, the pigment volume concentration in the coating is greater than the pigment volume concentration required to reach the percolation threshold. When the percolation threshold is reached or exceeded, a sudden increase in an electrical conductivity of the coating preferably occurs and steadily increases with a further increase in concentration. The one or more electrically conductive fillers preferably each comprise filler particles or are formed therefrom. The filler particles can be, for example, at least approxim