Method for manufacturing one half of a bipolar plate or one bipolar plate for a fuel cell

Abstract

Method for manufacturing one bipolar plate half or one bipolar plate (8) for a fuel cell (2), comprising the steps: - three-dimensional printing of ribs (15) onto a base plate (16) with a first printing material, wherein a channel (17) for an operating medium of the fuel cell (2) is formed between each pair of ribs (15), - prior to the completion of the printed bridges (15), three-dimensional printing of a form (18) to form an inner channel (19) within at least one of the bridges (15) with a second printing material which differs from the first printing material, and - following the completion of the webs (15), the form (18) formed with the second printing material is produced, characterized in that the webs (15) are triangular in cross-section, or that the cross-section of the form (18) of the inner channel (19) is formed in an ellipse.

Description

[0001] The invention relates to a method for manufacturing one half of a bipolar plate or one bipolar plate for a fuel cell, comprising the steps: - three-dimensional printing of struts onto a base plate with a first printing material, wherein a channel for an operating medium of the fuel cell is formed between each pair of struts, - prior to the completion of the printed bridges, three-dimensional printing of a form to create an inner channel within at least one of the bridges with a second printing material that differs from the first printing material, and - following the completion of the bridges, the form created with the second printing material is applied.

[0002] Fuel cell devices are used for the chemical reaction of a fuel with oxygen to produce water, thereby generating electrical energy. As a core component, fuel cells contain the so-called membrane electrode assembly (MEA), which consists of a proton-conducting membrane and two electrodes—an anode and a cathode—arranged on either side of the membrane. During operation of the fuel cell device, which uses multiple fuel cells grouped together in a fuel cell stack, the fuel, in particular hydrogen (H₂) or a hydrogen-containing gas mixture, is supplied to the anode, where electrochemical oxidation of H₂ to H₂ occurs. + This occurs with the release of electrons. The membrane allows the protons H + It passes through, but is impermeable to electrons. - At the anode, hydrogen splitting occurs according to the following reaction: 2H₂ → 4H₂ + + 4e -(Oxidation / Electron release).

[0003] While the protons pass through the membrane to the cathode, the electrons are conducted to the cathode via an external circuit. Cathode gas (for example, oxygen or oxygen-containing air) is supplied to the cathodes via cathode compartments within the fuel cell stack, so that the following reaction takes place on the cathode side: O₂ + 4H₂ + + 4e - → 2H2O (reduction / electron uptake), whereby in the cathode compartment the oxygen anions react with the protons transported across the membrane to form water. This water must be removed from the fuel cell and the fuel cell stack until a humidity level is reached that is necessary for the operation of the fuel cell system.

[0004] The distribution of the reaction media involved in the fuel cell reaction, as well as the distribution of the cooling medium, is achieved via bipolar plates. Each of these plates has a flow field on its two opposite sides, directing the reaction medium to the anode or cathode. Often, the bipolar plates are formed from two bipolar plate halves. Within the bipolar plates, there is always an additional flow field for the coolant, implemented through one or more coolant channels. At the perimeter of the fuel cell stack are unipolar plates, where only one of the two plate sides has a flow field for one of the reaction media.

[0005] Bipolar plates are often manufactured from metallic material that undergoes numerous forming processes. Rectangular channel geometries can only be achieved through very complex methods. Bipolar plates incorporating graphite are also available. Their production is particularly complex, and the manufacturing processes are very slow to start. Traditionally, it is difficult to create free-form geometries from the respective plate material.

[0006] German patent application DE 10 2018 211 187 A1 describes a method and a device for manufacturing one half of a bipolar plate for a fuel cell. The method includes applying a media distribution structure made of a media distribution material, for example graphite, to a substrate material of a bipolar plate using a screen printing process. German patent application DE 10 2019 135 785 A1 also describes a printing process in which an elastomeric material is printed onto a metallic bipolar plate, in particular using screen printing.

[0007] US patent 2019 0 319 291 A1 describes a component for an electrochemical cell that is manufactured using an additive manufacturing process. German patent DE 10 2013 108 413 A1 also describes a method for manufacturing a fuel cell stack, comprising the following steps: - Manufacturing a first component, comprising a first gas channel structure; - Manufacturing a second component, comprising a second gas channel structure; - Stacking the first and second components with gas channel structures facing each other, with an electrolyte unit separating the gas channel structures.

[0008] German patent application DE 10 2015 224 835 A1 describes a method for manufacturing a performance-optimized fuel cell characterized by uniform electrical and thermal contact during operation and a simultaneously reduced system weight. The method comprises the additive manufacturing of the individual layers of the fuel cell. Therefore, the object of the present invention is to provide a method for manufacturing a bipolar plate half or a bipolar plate in which arbitrarily complex structures for guiding the operating media and for guiding the coolant can be realized.

[0009] This problem is solved by a method with the features of claim 1. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0010] The inventive and aforementioned method is characterized in particular by the fact that the bipolar plate half or the bipolar plate is now three-dimensionally printed from different materials, making it possible to realize an individual design for the channels of the operating media or for the inner channels for conveying the coolant.

[0011] While it would theoretically be possible to simply leave out the areas of the inner channels in the region of the webs during 3D printing with the first printing material, this would necessitate the insertion of support structures into the inner channels, as the bipolar plate half or bipolar plate could then deform undesirably during handling. Furthermore, it is very complex to subsequently remove such support structures from the inner channel area. For the same reason, a printing process is preferred because it avoids unwanted residues within the inner channels compared to machining. Instead, a (nearly cast-like) shape is formed inside the webs, providing the necessary stability for handling the bipolar plate half or bipolar plate. This shape is then subsequently applied (the so-called "lost-form" method).

[0012] It is advantageous to first 3D print the base plate before beginning the 3D printing of the webs. This avoids the need to join the webs to the base plate, and offers the added benefit of allowing the 3D printing of the webs to follow the base plate printing process immediately. If the base plate is also printed from the same material, there is no interface between the base plate and the webs that could lead to unwanted separation of the webs from the base plate, especially when the coolant is pumped through the internal channels at very high pressure.

[0013] Instead of printing the base plate, it is also possible for the material for the base plate to be provided on a roll (so-called "coil"), from which the base plate to be printed is then separated.

[0014] It is advantageous if the first printing material is a plastic or graphite, although metal is also suitable as the first printing material, especially if good electrical conductivity is desired. The latter is preferably achieved using a powder bed process, particularly an SLS process (selective laser sintering).

[0015] To reliably apply the shape for forming the inner channel after printing, it has proven advantageous to apply the shape by washing.

[0016] This method offers the advantage of creating a polymer-based mold that, after the webs are completed, is washed out with an acidic chemical. The initial printing material is acid-resistant, preventing it from being attacked by the acid and thus preserving the webs and base plate during the acid treatment. Only the mold located inside the webs is washed out by the chemical, exposing the internal channels.

[0017] To ensure that washing out the mold is straightforward, it has proven advantageous for the mold to be porous. In a preferred embodiment, the second printing material is therefore made of a polymer, which forms the mold from a polymer foam.

[0018] In order to maximize the coolant flow through the webs, it has proven advantageous to shape the cross-sectional shape of the inner channel according to the cross-sectional shape of its associated web.

[0019] According to the invention, it is possible for the webs to be triangular in cross-section.

[0020] However, in order to be able to selectively adjust the flow behavior of the coolant within the inner channel, it has proven advantageous - but not covered by the invention - if the cross-section of the shape of the inner channel is formed according to a polygon, whereby a rectangular shape of the cross-section of the inner channel is particularly advantageous.

[0021] If the webs are to be made particularly stable, the invention alternatively provides that the cross-section of the inner channel is formed in an elliptical shape. A circular cross-section has proven to be particularly preferred.

[0022] The inventive method now makes it possible to combine conventional channel structures with flow-influencing structures, such as a so-called "fine mesh," within a single component. Furthermore, freeform channel geometries in the coolant can be achieved using the present "lost-form" method.

[0023] The features and combinations of features mentioned above in the description, as well as those subsequently mentioned in the figure description and / or shown in the figures alone, can be used not only in the combinations specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments that are not explicitly shown or explained in the figures, but which can be derived and generated from the explained embodiments by separate combinations of features, are also to be considered as encompassed and disclosed by the invention.

[0024] Further advantages, features, and details of the invention will become apparent from the claims, the following description of preferred embodiments, and the drawings. These show: Fig. 1 a schematic representation of a fuel cell device, Fig. 2 a schematic and perspective section of a raw part of a bipolar plate, Fig. 3 a schematic and perspective section of the finished bipolar plate made of Fig. 2, Fig. 4 a schematic and perspective section of another raw part of a bipolar plate, in which the shape in cross-section was printed as polygonal, in particular rectangular, Fig. 5 one of the Fig. 4. Corresponding representation of a raw part of a bipolar plate, in which the shape in cross-section was printed as a polygon, in particular hexagonal, Fig. 6 one of the Fig. 4. Corresponding representation of a raw part of a bipolar plate, in which the shape in cross-section was printed elliptical, in particular circular.

[0025] In the Fig. Figure 1 schematically shows a fuel cell device 1 that can be used, for example, in a motor vehicle or in a ship, wherein it comprises a plurality of fuel cells 2 grouped in a fuel cell stack 3, to which the media required for operation, including the coolant, are supplied and removed via media ports.

[0026] Each of the fuel cells 2 comprises an anode, a cathode, and a proton-conducting membrane separating the anode from the cathode. The membrane is formed from an ionomer, preferably a modified polytetrafluoroethylene (PTFE) backbone with sulfonic acid groups on its side chains. Alternatively, the membrane can also be formed as a sulfonated hydrocarbon membrane.

[0027] A catalyst may be added to the anodes and / or the cathodes, wherein the membranes are preferably coated on their first side and / or on their second side with a catalyst layer made of a precious metal or a mixture comprising precious metals such as platinum, palladium, ruthenium or the like, which serve as reaction accelerators in the reaction of the respective fuel cell 2.

[0028] Fuel (for example, hydrogen) can be supplied to the anode from a fuel tank 13 via an anode compartment. In a polymer electrolyte membrane fuel cell (PEM fuel cell), fuel or fuel molecules are split into protons and electrons at the anode. The PEM allows the protons to pass through but is impermeable to the electrons. The reaction that occurs at the anode, for example, is: 2H₂ → 4H₂ + + 4e -(Oxidation / Electron Release). While the protons pass through the PEM to the cathode, the electrons are conducted to the cathode or to an energy storage device via an external circuit.

[0029] The cathode gas (for example, oxygen or oxygen-containing air) can be supplied to the cathode via a cathode compartment, so that the following reaction takes place on the cathode side: O2 + 4H + + 4e - → 2H2O (reduction / electron uptake).

[0030] Since several fuel cells 2 are combined in the fuel cell stack 3, a sufficiently large quantity of cathode gas must be supplied. A compressor 11 provides a large mass flow of cathode gas or fresh gas flow, which increases significantly in temperature as a result of compression. The conditioning of the cathode gas or fresh gas flow, i.e., its adjustment with respect to the desired temperature and humidity in the fuel cell stack 3, takes place in a charge air cooler 5 downstream of the compressor 11 and an external humidifier 4 downstream of the compressor 11. This humidifier saturates the membranes of the fuel cells 2 with moisture to increase their efficiency, as this promotes proton transport.

[0031] The supply of the operating media and the coolant to the fuel cells 2 is ensured via so-called bipolar plates 8, which are provided with flow fields for the two reactants on their two opposite sides. Within the bipolar plates, there is a further flow field for coolant, which is realized by one or more coolant channels.

[0032] The bipolar plate halves, or bipolar plates 8, are manufactured using a lost-form method, as shown by Fig. 2 will be explained in more detail. Fig. Figure 2 shows a raw part of a bipolar plate half or a bipolar plate 8 for a fuel cell 2. Here, three-dimensional ribs 15 were printed three-dimensionally onto a base plate 16 using a first printing material, with a channel 17 for an operating medium of the fuel cell 2 being formed between each pair of ribs 15. Prior to the completion of the printed ribs 15, a form 18 for forming an inner channel 19 within at least one of the ribs 15 was printed three-dimensionally using a second printing material, which differs from the first printing material. Subsequently, the ribs 15 were completed so that the form 18 is positioned within the ribs 15, as shown in the Fig. 2. The first printing material is either metal, plastic, or graphite, all three components being acid-resistant. The mold 18 can be produced by washing, which then forms the inner channels 19. In this case, the mold 18 is preferably formed on a polymer base, which is washed with an acidic chemical after the completion of the webs 15. The base plate 16 and the webs 15 are acid-resistant, so that they are not dissolved during acid treatment. Preferably, the second printing material, which forms the mold 18, is made of a polymer foam, so that the washing with an acidic chemical is improved or accelerated due to the porosity of the foam.

[0033] In Fig. Figure 3 shows the bipolar plate half or bipolar plate 8, in which the mold 18 has now been washed out, creating the inner channels 19 for the coolant flow 21. Channels 17, which serve the flow 20 of the reaction medium, are arranged between each pair of webs 15.

[0034] It is based on the Fig. 2 and Fig. 3. It can be seen that the cross-sectional shape of the inner channel 19 corresponds to the cross-sectional shape of its associated web 15, which serves to maximize the coolant flow 21. In this case, the webs 15 and also the inner channels 19 have a triangular cross-section.

[0035] The Fig. 4 and Fig. However, paragraph 5 points to the possibility that the cross-section of shape 18 of the inner channel 19 is formed according to a polygon. In Fig. 4 The cross-section of the inner channel 19 is shaped like a rectangle. Fig. Figure 5 shows the cross-section of shape 18 of the inner channel 19, which corresponds to a hexagon. However, the present application is not limited to a square or hexagonal shape, so a polygonal shape with more than four or more than six corners is also possible.

[0036] Fig. Section 6 refers to the possibility that the cross-section of the shape 18 of the inner channel 19 can be formed according to an ellipse, whereas in this case a cross-section in the form of a circular disk is present. Such a design increases the stability of the webs 15 when they are subjected to a coolant flow under high pressure.

[0037] As a result, the bipolar plate half or bipolar plate 8 produced according to the inventive method is characterized by more effective cooling of the fuel cell rod 2 because the coolant channels, namely the inner channels 19, are located closer to the heat source, namely the membrane electrode assembly. The printing process provided for in the invention reduces the manufacturing time, and the development time is also shorter due to the elimination of tool manufacturing time. The stacking properties of the fuel cell stack 3 are also improved because pressure losses are reduced.

[0038] This increases the long-term stability of each unit cell within the fuel cell stack 3, particularly through the use of hybrid materials. The inventive method allows for the creation of multiple channels or inclusions within a single component without additional joining steps, thus improving gas transport to the reactive sites of the electrode. On the cathode side, improved removal of product water results in more robust operating behavior of the fuel cell stack 3. The latter is particularly important in the case of a frost start. REFERENCE MARK LIST: 1 Fuel cell device 2 Fuel cell 3 fuel cell stacks 4 humidifiers 5 intercoolers 8 Bipolar plate 9 Fresh air duct 10 Cathode exhaust line 11 compressors 12 Fuel line 13 Fuel tank 14 Recirculation line 15 Bridge 16 Base plate 17 channels (operating medium) 18 Form 19 Inner channel (coolant) 20 Flow of the reaction medium (e.g. air or H2) 21 Coolant flow

Claims

[1] Method for manufacturing one bipolar plate half or one bipolar plate (8) for a fuel cell (2), comprising the steps: - three-dimensional printing of ribs (15) onto a base plate (16) with a first printing material, wherein a channel (17) for an operating medium of the fuel cell (2) is formed between each pair of ribs (15), - prior to the completion of the printed bridges (15), three-dimensional printing of a form (18) to form an inner channel (19) within at least one of the bridges (15) with a second printing material which differs from the first printing material, and - following the completion of the bridges (15), application of the form formed with the second printing material (18), characterized by that the webs (15) are triangular in cross-section, or that the cross-section of the shape (18) of the inner channel (19) is formed according to an ellipse. [2] Method according to claim 1, characterized by , that the base plate (16) is first printed three-dimensionally before the three-dimensional printing of the bridges (15) begins. [3] Method according to claim 1 or 2, characterized by that the first printing material is a metal, a plastic, or graphite. [4] Method according to any one of claims 1 to 3, characterized by , that the form (18) is produced by washing. [5] Method according to claim 4, characterized by , that the form (18) is formed on a polymer basis and is washed out with an acidic chemical after completion of the webs (15). [6] Method according to any one of claims 1 to 3, characterized by , that the second printing material is formed from a polymer, by which the shape (18) is created from a polymer foam. [7] Method according to any one of claims 1 to 6, characterized by, that the cross-sectional shape of the inner channel (19) is shaped according to the cross-sectional shape of its associated web (15).

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