Method for producing a bipolar plate

Abstract

Method for producing a bipolar plate (2) for use in a fuel cell, comprising the steps of providing (100) a bipolar plate (2') made of a composite material (8) comprising an electrically conductive layer material (6) and an electrically non-conductive layer material (4), selectively removing (200) parts of the electrically non-conductive layer material (4) from the composite material (8) to expose regions of the electrically conductive layer material (6) on the surface (O) of the bipolar plate (2') by means of a first material removal method,applying (300) a functional layer (10) to the surface (O) of the bipolar plate (2') to functionalize the surface (O) of the bipolar plate (2') by means of a coating process, and selectively removing (400) parts of the functional layer (10) to expose regions of the electrically conductive layer material (6) by means of a second material removal process.

Description

State of the art

[0001] The present invention is based on a method for producing a bipolar plate and a bipolar plate, preferably produced using such a method. Furthermore, the invention relates to a fuel cell having a plurality of such bipolar plates. State of the art

[0002] Fuel cells are electrochemical energy converters in which reaction gases, such as hydrogen and oxygen, are converted into water, electrical energy, and heat. The reaction gases are separated by a polymer membrane, which provides the necessary insulation. A fuel cell has a typical symmetrical structure, with a catalyst layer and a gas distribution layer arranged on either side of the polymer membrane, each of which is followed by a bipolar plate. The bipolar plates arranged within the fuel cell fulfill several functions. They serve to electrically interconnect the cells, supply and distribute the reaction gases, and supply and distribute the coolant.

[0003] For reasons of weight, cost and durability, bipolar plates made of composite materials have become established today, in which electrically conductive particles are incorporated into plastic materials.

[0004] The disadvantage is that coating the electrically conductive particles with plastic reduces the electrical conductivity of the material and the wettability of the surface, which ultimately hinders the mass transport within a fuel cell and thus reduces the performance of fuel cells. Disclosure of the invention

[0005] According to a first aspect, the invention relates to a method having the features of the independent method claim and, according to a second aspect, to a bipolar plate according to the independent device claim. According to a third aspect, the invention further relates to a fuel cell having a plurality of bipolar plates according to the independent device claim. Further features and details of the invention emerge from the respective subclaims, the description and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the bipolar plate according to the invention or the fuel cell according to the invention and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is or can always be made reciprocal.

[0006] The method according to the invention for producing a bipolar plate for use in a fuel cell comprises the steps of providing a bipolar plate made of a composite material, comprising an electrically conductive layer material and an electrically non-conductive layer material, selectively removing parts of the electrically non-conductive layer material from the composite material to expose regions of the electrically conductive layer material on the surface of the bipolar plate by means of a first material removal method, applying a functional layer to the surface of the bipolar plate to functionalize the surface of the bipolar plate by means of a coating method, and selectively removing parts of the functional layer to expose regions of the electrically conductive layer material by means of a second material removal method.

[0007] The method according to the invention for producing a bipolar plate preferably serves to increase the electrical conductivity of bipolar plates made of composite material, in particular plastic-based bipolar plates, and to reduce the electrical contact resistance between a bipolar plate and other components when the bipolar plate is arranged within a fuel cell. Advantageously, a permanent hydrophilization of bipolar plates made of composite materials can be achieved, with the use of a (preferably porous) coating particularly supporting the mass transport of process gases and reaction water into or out of the composite material.By using non-layer-forming and layer-forming (plasma) processes, surface functionalization can be performed within a single system, allowing the process steps of cleaning a surface, exposing conductive particles, activating a composite material surface, and coating the composite material surface to render it hydrophilic to a single process. Furthermore, by removing and subsequently applying material (preferably in the nm-µm range), the dimensions of the bipolar plate can be maintained or only minimally altered.

[0008] The bipolar plate processed using the method according to the invention can preferably be used in a fuel cell or in a fuel cell system for a motor vehicle. Use in other fuel cell-powered means of transport or even stationary systems is also conceivable. It goes without saying that the bipolar plate in question can also be used in an electrolyzer. According to the invention, a functional layer can preferably be understood as a layer that fulfills a specific task or function, such as accelerating or ensuring mass transport, or the like.

[0009] Within the scope of the invention, it was recognized that by using a bipolar plate made of composite material and by selectively abrading the plastic surface, electrically conductive particles close to the surface can be exposed in a simple and cost-effective manner, and that the plastic surface can be activated. It was also recognized that by applying a thin, hydrophilic, and porous coating with good adhesion to the activated binder and poor adhesion to the conductive additives, easy removal of the layer components that adhere poorly to the conductive additives can be achieved.

[0010] With regard to a precisely controllable, selectable removal of electrically non-conductive layer regions of the composite material from the surface of a bipolar plate, it can be particularly advantageous if the first material removal process for selectively removing portions of the electrically non-conductive layer material takes the form of an etching process, preferably a plasma etching process. A plasma etching process can be a dry or wet etching process, or a combination of a dry and wet etching process. By selectively removing electrically non-conductive layer regions of the composite material from the surface of the bipolar plate to expose electrically conductive layer regions of the composite material, the surface energy of the composite material can be increased, in particular, so that temporary hydrophilization can be achieved.

[0011] For the controlled application of thin functional layers to substrates with targeted adjustment of layer properties, the invention can advantageously provide for the coating process for applying a functional layer to the surface of the bipolar plate to be designed in the form of a vacuum coating process, preferably a PVD or CVD process, in particular in the form of a plasma-based PVD or CVD process. By using a plasma-assisted process, increased layer quality can be achieved in particular through improved adhesion, more selective deposition, and lower contamination. A plasma-based PVD process can, for example, be designed in the form of a magnetron sputtering process or a reactive sputtering process. A plasma-based CVD process can also be designed in the form of an LPCVD process or a PE-CVD process.Alternatively, a spraying process can be used to apply the functional layer.

[0012] With a view to a stable bond of the functional layer in the desired areas, it can further be provided that the applied functional layer is dried before selectively removing parts of the functional layer. The drying of the applied functional layer is preferably carried out by introducing an air stream and / or by irradiation with a radiation source. The introduced air stream can preferably be in the form of a heated air stream. The radiation source can also preferably be designed as an IR radiation source for emitting electromagnetic radiation in the infrared frequency range.

[0013] Within the scope of a simple, cost-effective, and effective selective removal of the functional layer, it can advantageously be further provided that the second material removal method for selectively removing parts of the functional layer is designed in the form of a mechanical removal method, preferably using a doctor blade and / or a brush and / or compressed air. Due to the varying degrees of adhesion of the functional layer to electrically conductive or electrically non-conductive areas, the functional layer can be easily removed from the electrically conductive areas of the functional layer using the mechanical removal method, whereas the functional layer remains on the electrically non-conductive areas of the functional layer.

[0014] The invention also further relates to a bipolar plate for use in a fuel cell, preferably produced by processing a bipolar plate from a composite material comprising an electrically conductive layer material and an electrically non-conductive layer material, in particular according to a method described above. The bipolar plate according to the invention comprises a first layer comprising an electrically non-conductive layer material, and a second layer arranged on the first layer comprising an electrically conductive layer material and a functional layer material, wherein the functional layer material is arranged between the electrically conductive layer material. Thus, the bipolar plate according to the invention exhibits the same advantages as have already been described in detail with regard to the method according to the invention.

[0015] In the context of cost-effective production of stable and robust bipolar plates, it can advantageously be provided that the electrically non-conductive layer material is in the form of a plastic, optionally in the form of a thermoplastic or thermosetting plastic, in particular in the form of polyethylene (PE) or polypropylene (PP) as thermoplastics, or phenolic or epoxy resins as thermosetting plastics. The use of such plastic materials also promises, in particular, a weight-optimized design.

[0016] In the context of cost-effective production of weight-optimized bipolar plates for effective charge transport, it can advantageously be provided that the electrically conductive layer material is in the form of a carbon-containing material, preferably in the form of graphite. As an alternative to graphite, the carbon-containing material can also be in the form of graphene, carbon fibers, or the like.

[0017] To functionalize non-electrically conductive surface areas of the bipolar plate according to the invention, the functional layer material can advantageously comprise silicon-containing compounds, preferably siloxanes and / or silanes and / or aminosilanes and / or alkanethiols. With a view to achieving a particularly targeted functionalizable surface, the use of self-assembled monolayers (SAMs) can also be considered. The functionalization should, in particular, ensure a layer that is both porous and hydrophilic for optimal gas distribution and water drainage.

[0018] Within the scope of a particularly targeted control of the properties of a particular bipolar plate, it can advantageously be further provided according to the invention that the second layer has a layer thickness of < 100 µm, preferably < 10 µm, in particular < 1 µm.

[0019] The invention also further relates to a fuel cell comprising a plurality of bipolar plates as described above. Thus, the fuel cell according to the invention exhibits the same advantages as those already described in detail with regard to the method according to the invention and the bipolar plate according to the invention.

[0020] Further advantages, features, and details of the invention will become apparent from the following description, which describes exemplary embodiments of the invention in detail with reference to the drawings. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination.

[0021] They show: Fig. 1 a schematic representation of the individual steps of a method according to the invention for producing a bipolar plate for use in a fuel cell and Fig. 2 a schematic representation of a bipolar plate according to the invention for use in a fuel cell.

[0022] Fig. 1 shows a schematic representation of the individual steps of a method according to the invention for producing a bipolar plate 2 for use in a fuel cell.

[0023] As per Fig. 1, the method according to the invention comprises the steps of providing 100 a bipolar plate 2' made of a composite material 8, having an electrically conductive layer material 6 and an electrically non-conductive layer material 4, selectively removing 200 parts of the electrically non-conductive layer material 4 from the composite material 8 to expose regions of the electrically conductive layer material 6 on the surface O of the bipolar plate 2' by means of a first material removal method, applying 300 a functional layer 10 with a functional layer material 10' to the surface O of the bipolar plate 2' to functionalize the surface O of the bipolar plate 2' by means of a coating method, and selectively removing 400 parts of the functional layer 10 to expose regions of the electrically conductive layer material 6 by means of a second material removal method.

[0024] The first material removal process for selectively removing 200 parts of the electrically non-conductive layer material 4 can be implemented, for example, in the form of an etching process, preferably in the form of a plasma etching process.

[0025] The coating method for applying 300 a functional layer 10 to the surface O of the bipolar plate 2' can also be designed in the form of a vacuum coating method, preferably a PVD or CVD method.

[0026] The second material removal method for selectively removing 400 parts of the functional layer 10 may further preferably be designed in the form of a mechanical removal method, for example using a squeegee and / or a brush and / or compressed air.

[0027] Fig. 2 shows a schematic representation of a bipolar plate 2 according to the invention for use in a fuel cell.

[0028] As per Fig. 2, the bipolar plate 2 comprises a first layer 12 comprising an electrically non-conductive layer material 4 and a second layer 14 arranged on the first layer 12, comprising an electrically conductive layer material 6 and a functional layer material 10', wherein the functional layer material 10' is arranged between the electrically conductive layer material 6.

[0029] The electrically non-conductive layer material 4 can, for example, be in the form of a plastic, optionally in the form of a thermoplastic (polyethylene or polypropylene) or thermosetting plastic (phenol or epoxy resin).

[0030] The electrically conductive layer material 6 can also be in the form of a carbon-containing material, preferably in the form of graphite.

[0031] The functional layer material 10' may further comprise silicon-containing compounds, preferably siloxanes and / or silanes and / or aminosilanes and / or alkanethiols.

Claims

[1] Method for producing a bipolar plate (2) for use in a fuel cell, comprising the steps: - Providing (100) a bipolar plate (2') made of a composite material (8), comprising an electrically conductive layer material (6) and an electrically non-conductive layer material (4), - selective removal (200) of parts of the electrically non-conductive layer material (4) from the composite material (8) to expose regions of the electrically conductive layer material (6) on the surface (O) of the bipolar plate (2') by means of a first material removal process, - applying (300) a functional layer (10) to the surface (O) of the bipolar plate (2') for functionalizing the surface (O) of the bipolar plate (2') by means of a coating process and - selective removal (400) of parts of the functional layer (10) to expose regions of the electrically conductive layer material (6) by means of a second material removal process. [2] Method according to claim 1, characterized by that the first material removal process for selectively removing (200) parts of the electrically non-conductive layer material (4) is designed in the form of an etching process, preferably in the form of a plasma etching process. [3] Method according to claim 1 or 2, characterized by that the coating method for applying (300) a functional layer (10) to the surface (O) of the bipolar plate (2') is designed in the form of a vacuum coating method, preferably a PVD or CVD method, in particular in the form of a plasma-based PVD or CVD method. [4] Method according to one of the preceding claims, characterized bythat before a selective removal (400) of parts of the functional layer (10), the applied functional layer (10) is dried, wherein the drying of the applied functional layer (10) is preferably carried out by introducing an air stream and / or by irradiation with a radiation source. [5] Method according to one of the preceding claims, characterized by that the second material removal method for selectively removing (400) parts of the functional layer (10) is designed in the form of a mechanical removal method, preferably using a squeegee and / or a brush and / or compressed air. [6] Bipolar plate (2) for use in a fuel cell, preferably produced by machining a bipolar plate (2') from a composite material (8) comprising an electrically conductive layer material (6) and an electrically non-conductive layer material (4), in particular according to a method according to one of the preceding claims, comprising: - a first layer (12) comprising an electrically non-conductive layer material (4), - a second layer (14) arranged on the first layer (12), comprising an electrically conductive layer material (6) and a functional layer material (10'), - wherein the functional layer material (10') is arranged between the electrically conductive layer material (6). [7] Bipolar plate (2) according to claim 6, characterized bythat the electrically non-conductive layer material (4) is in the form of a plastic, optionally in the form of a thermoplastic or thermosetting plastic, in particular in the form of polyethylene or polypropylene as thermoplastic plastic or in the form of phenolic or epoxy resin as thermosetting plastic. [8] Bipolar plate (2) according to claim 6 or 7, characterized by that the electrically conductive layer material (6) is in the form of a carbon-containing material, preferably in the form of graphite. [9] Bipolar plate (2) according to one of claims 6 to 8, characterized by that the functional layer material (10') comprises silicon-containing compounds, preferably siloxanes and / or silanes and / or aminosilanes and / or alkanethiols. [10] Bipolar plate (2) according to one of claims 6 to 9, characterized bythat the second layer (14) has a layer thickness of < 100 µm, preferably < 10 µm, in particular < 1 µm. [11] Fuel cell comprising a plurality of bipolar plates (2) according to one of claims 6 to 10.

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