Method for manufacturing bipolar plates for fuel cells

Abstract

The present invention relates to a method for producing a bipolar plate (10) for a fuel cell (1), the bipolar plate comprising a plate body (11) for separating the fuel cell (1) from an adjacent fuel cell (1) or a housing, wherein the plate body (11) comprises a flow field structure (1b) for introducing reactants into the fuel cell (1). To this end, the method comprises the following steps: providing a mass block (D1) and a polymer-based adhesive, the mass block consisting of electron-conducting particles, applying the applied mass block (D1) in the form of the flow field structure (1b) to the plate body (11) of the bipolar plate (10), pyrolyzing the applied mass block (D1), and the mass block remaining as a shaped element in the form of the flow field structure (1b) on the plate body (11) of the bipolar plate (10) and connected to the bipolar plate.

Description

Technical Field

[0001] The invention relates to a method for producing a bipolar plate for a fuel cell according to the independent method claim, a corresponding bipolar plate according to the independent device claim, and a corresponding fuel cell according to the parallel independent device claim. Background Art

[0002] To date, flow field structures for fuel cells have been provided as cavity structures in the millimeter range. To this end, the later cavity structure or channel can be milled into the bipolar plate as a recess, or can be applied to the bipolar plate as a protrusion or tab structure. In addition, the bipolar plate can be deformed to produce the cavity structure. Then, a gas distributor structure composed of particles or fibers, such as a gas diffusion layer (GDL), is placed on the cavity structure or channel that is open toward the membrane of the fuel cell. The gas distributor structure can optionally have a microporous layer (MPL) in the direction of the membrane. When stacking, each of the layers must be positioned relative to each other in order to form a properly functioning fuel cell. It is also known to produce a gas distributor structure by printing. Subsequently, this printed gas distributor structure is connected to the airtight bipolar plate, for example, by bonding after a curing process. However, electrical and thermal resistances are formed at the contact points between the printed gas distributor structure and the bipolar plate. Summary of the Invention

[0003] According to a first aspect, the present invention provides a method for producing a bipolar plate for a fuel cell having the features of an independent method claim. Furthermore, according to a second aspect, the present invention provides a corresponding bipolar plate having the features of an independent device claim, and according to a third aspect, a corresponding fuel cell having the features of a parallel independent device claim. Further advantages, features, and details of the invention can be derived from the dependent claims, the description, and the drawings. Features and details described in the context of the method according to the invention naturally also apply in the context of the bipolar plate according to the invention and / or the fuel cell according to the invention, and vice versa, so that the disclosure of the individual inventive aspects always refers to or can refer to one another.

[0004] The present invention provides a method for manufacturing a bipolar plate for a fuel cell. The bipolar plate comprises a plate body for separating a fuel cell from an adjacent fuel cell or a housing, wherein the plate body has a flow field structure for introducing reactants into the fuel cell. To this end, the method according to the present invention comprises the following steps:

[0005] - providing a (first) mass consisting of electron-conducting particles, in particular a printing paste or dispersion and a polymer-based binder,

[0006] - applying the provided mass in the form of the flow field structure on the plate body of the bipolar plate, in particular printing it,

[0007] The applied mass is pyrolyzed, and remains as a shaped element in the form of the flow field structure on the plate body of the bipolar plate and is connected to the bipolar plate.

[0008] The fuel cells according to the invention can be combined to form a fuel cell stack, a so-called fuel cell stack, which has a plurality of stacked repeating units in the form of individual fuel cells, preferably PEM fuel cells.

[0009] The bipolar plate according to the present invention provides a cavity structure or channel structure in the millimeter range for introducing reactants and for their rough distribution in the fuel cell. The bipolar plate can be used in particular in conjunction with a flat or planar plate body, which is particularly advantageous in terms of production.

[0010] Subsequently or together with the flow field structure (coarse channel structure and high porosity), a porous gas diffusion layer (GDL, fine porosity) and optionally a microporous layer (MPL, very fine porosity) can be provided (e.g. printed or deposited) on the plate.

[0011] The flow field structure according to the invention has, in addition to an external cavity structure or channel structure in the millimeter range, an internal porosity for improved gas transport near the plate body of the bipolar plate. The flow field structure according to the invention can preferably be used on the cathode side of a fuel cell.

[0012] The bipolar plate according to the invention can be suitable for use in mobile applications, for example in vehicles, or for stationary applications, for example in generators.

[0013] The invention is based on the idea of ​​pyrolyzing the entire bipolar plate together with the plate body of the bipolar plate, which comprises a plate body having a flow field structure according to the invention applied thereto and, if necessary, an optionally adjacent gas diffusion layer (GDL) and / or, if necessary, an optionally adjacent microporous layer (MPL). In other words, with the aid of the method according to the invention, the bipolar plate is provided as a pyrolyzed composite component consisting of the plate body, the porous (sintered and therefore coherent) flow field structure and, if necessary, the gas diffusion layer and / or the microporous layer. Thus, a bipolar plate can be provided having significantly improved electrical and thermal conductivity between the plate body of the bipolar plate, the porous flow field structure and, if necessary, the gas diffusion layer and / or the microporous layer.

[0014] The method according to the present invention enables the use of bipolar plate bodies that are flat on one or both sides and therefore cost-effective, without requiring complex cavity structures or channels. This results in significant cost savings. Such plates can also be cost-effectively printed as a continuous strip in a continuous process and separated into individual plates only before stacking. However, it is also conceivable in principle that the bipolar plate bodies may have a specific pre-structure, for example, by producing a negative structure (e.g., embossing, etching, or printing).

[0015] By coating the bipolar plate body with a first mass containing electron-conducting particles, a composite structure with very good electrical conductivity can be produced. By using a suitable printing technique, such as screen printing, it is also possible to achieve that the surface tolerance of the printed flow field structure is essentially determined by the accuracy of the printing mold, such as the screen. If the bipolar plate or layer is slightly wavy, for example, when printing the next layer, the wavy shape is not reinforced by the next screen, but is smoothed out again. As a result, thicker multilayer structures with good thickness tolerances can also be produced, which is conducive to uniform gas flow and uniform electrical contact of the catalyst layer.

[0016] When printing multiple layers, large particles (first mass) are selected for the particle layer close to the bipolar plate. The large particles not only lead to large pores, but also lead to large pore gaps in the layer, and ensure good drainage, gas transport and high stability. In the direction of the diaphragm, the last thin printed layer can have finer particles (second mass), for example, in the case of the previous microporous layer. Since thin and uniform layers are printed according to the present invention, insignificant layer mixing (if any) occurs here. When processing multiple layers, layers with possible condensation sites (Keimstelle) for product water can be formed. Other layers can be formed by materials that can be further burned (such as PMMA), which intentionally produce large pores.

[0017] The flow field structure can be formed as a wave-like structure, which has, for example, a substantially semicircular or arc-shaped cross-section on the web. The semicircular cross-section can extend in the direction of the membrane to achieve a uniform, preferably reduced, supporting force there. The flow field structure can have a porosity of approximately 50% to 70%. Weak points / interference points in the flow field structure can be monitored directly during printing and thus virtually eliminated.

[0018] Subsequently, only a small number of components need to be handled when assembling the fuel cell, which significantly facilitates and simplifies the production of the fuel cell.

[0019] Furthermore, the present invention can propose in a method for producing a bipolar plate for a fuel cell that a burnable negative structure is applied to the plate body of the bipolar plate before the flow field structure is applied, in particular printed, on the plate body of the bipolar plate. The burnable negative structure is later decomposed as completely as possible into gaseous components during sintering / pyrolysis. This can be achieved by appropriately selecting the particles and adhesive to be printed. In this way, the production of a flow field structure with the desired cavity structure or channel can be simplified. The printing of the cavity by means of a microporous particle mixture after pyrolysis is significantly facilitated. This is because the particle mixture cannot enter the cavity of the gas channel.

[0020] Furthermore, the present invention can provide, in a method for producing a bipolar plate for a fuel cell, that the calcinable negative structure is provided as a mixture of particles and a binder, in particular a dry dispersion, wherein the particles and the binder have similar softening temperatures and / or decomposition temperatures, which are preferably lower than the decomposition temperature of the (first) mass (in particular, the electron-conducting particles and / or the polymer-based binder or adhesive of the printed mass). This ensures that, after pyrolysis of the flow field structure on the plate body of the bipolar plate, the negative structure is completely decomposed, thereby exposing the desired cavity structure or channels within the flow field structure.

[0021] Furthermore, the present invention can provide, in a method for producing a bipolar plate for a fuel cell, that the particles of the burnable negative structure comprise at least one of the following elements: polymethyl methacrylate, polystyrene, polycarbonate, and / or polyetheretherketone, and / or that the binder of the burnable negative structure comprises at least one of the following elements: polyethylene glycol, polyvinylidene fluoride, and / or an acrylate adhesive. These materials make it possible to provide a mixture of particles and binder that has similar softening and / or decomposition temperatures, which in turn are lower than the decomposition temperature of the electron-conducting particles of the mass and / or the polymer binder used therein.

[0022] Furthermore, the present invention can provide, in a method for producing a bipolar plate for a fuel cell, that the electron-conducting particles of the mass include graphite particles and / or graphite fibers, and / or that at least a portion of the electron-conducting particles of the mass (preferably greater than 10% by weight relative to the finished layer) have a diameter in the order of 0.5 μm to 50 μm, preferably 3 μm to 15 μm. This allows for a porous flow field structure with advantageous stability. Furthermore, such a flow field structure ensures improved distribution of reactants and improved removal of product water due to its internal porosity.

[0023] Furthermore, the present invention can provide, in a method for producing a bipolar plate for a fuel cell, that the polymer-based adhesive of the mass (to be coated) comprises at least one of the following elements: an acrylate adhesive and / or polytetrafluoroethylene and / or polyvinylidene fluoride. This allows sintering between the electron-conducting particles during pyrolysis.

[0024] Furthermore, the present invention can provide, in a method for producing a bipolar plate for a fuel cell, that the mass comprises calcinable particles, such as polymethyl methacrylate, for forming macroscopic pores within the flow field structure. This can improve the internal porosity within the flow field structure.

[0025] Furthermore, the present invention can provide a method for manufacturing a bipolar plate for a fuel cell by applying a provided mass block in the form of a flow field structure to the bipolar plate body using printing technology, particularly screen printing technology. Thus, a precise technique for providing the flow field structure can be provided.

[0026] Furthermore, the present invention can provide, in a method for producing a bipolar plate for a fuel cell, that after pyrolysis of a mass applied in the form of a flow field structure on the plate body of the bipolar plate, a gas diffusion layer and / or a microporous layer is applied (in particular, printed or placed) onto the flow field structure, which is formed from a second mass that is different from the first mass and in particular finer. In particular, the electron-conducting particles of the second mass can be embodied as fine soot particles and / or can have a size, for example, of the order of 0.5 μm to 3 μm. In any case, the electron-conducting particles of the second mass have a smaller diameter and / or a different shape than the particles of the first mass. Thus, multiple layers with different particle sizes can be printed, which facilitates improved introduction of reactants into the fuel cell and a more uniform distribution of the reactants on the fuel cell membrane.

[0027] Furthermore, within the scope of the present invention, it is conceivable that the gas diffusion layer and the microporous layer together with the flow field structure formed by the (first) mass are applied to the plate body of the bipolar plate, in particular printed. This allows for a bipolar body that is particularly cost-effective and simple to manufacture.

[0028] The present invention also proposes a bipolar plate for a fuel cell, comprising a plate body for separating a fuel cell from an adjacent fuel cell or a housing, wherein the plate body has a flow field structure for introducing reactants into the fuel cell. To this end, the present invention provides that the flow field structure is applied, in particular printed, onto the bipolar plate using a mass or dispersant composed of electron-conducting particles and a polymer-based adhesive and then pyrolyzed there (along with the plate body of the bipolar plate). The bipolar plate according to the present invention achieves the same advantages as those described above in the context of the method according to the present invention. In the present case, these advantages are fully cited.

[0029] Advantageously, bipolar plates can be produced using a method that can be carried out as described above. In this way, the bipolar plates can acquire the special properties brought about by the method according to the invention, such as improved stability, electrical conductivity (especially electronic conductivity) and / or thermal conductivity, and improved distribution of reactants in the fuel cell, and the fuel cell is also simple and cost-effective to produce.

[0030] The present invention also provides a fuel cell having at least one corresponding bipolar plate. The fuel cell according to the present invention achieves the same advantages as those described above in the context of the method according to the present invention and the bipolar plate according to the present invention. In the present case, these advantages are fully cited. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention and its developments and advantages are explained in more detail below with reference to the accompanying drawings. The accompanying drawings schematically show:

[0032] Figure 1 An exemplary configuration of a fuel cell within the meaning of the present invention,

[0033] Figure 2 An exemplary configuration of a fuel cell with bipolar plates within the meaning of the present invention, and

[0034] Figure 3 A top view of a bipolar plate within the meaning of the present invention with multiple side views. DETAILED DESCRIPTION

[0035] In the different figures, identical components of the invention are always provided with the same reference numerals and are therefore generally described only once.

[0036] Figures 1 to 3 The method for manufacturing the bipolar plate 10 for the fuel cell 1 according to the present invention will be described.

[0037] exist Figure 1An exemplary fuel cell 1 is shown in FIG. This fuel cell comprises a membrane M, which is provided with electrode layers EA on both sides. In the cathode region K of the fuel cell 1, a microporous layer MPL and a gas diffusion layer GDL adjoin the electrode layers EA. The distributed structure for the fuel cell 1, which has a corresponding cavity structure 11 in the millimeter range, forms a bipolar plate 10 having a cavity structure 11 in the form of a protrusion. Furthermore, the known bipolar plate 10 can be provided with the cavity structure 11 by forming.

[0038] The method according to the invention is used to produce a bipolar plate 10 for a fuel cell 1 which is Figure 2 , and the fuel cell has a (preferably flat) plate 11, which is used to separate the fuel cell 1 from other fuel cells 1 or a housing, wherein the plate 11 has a flow field structure 1b, which is used to introduce reactants into the fuel cell 1.

[0039] To this end, the method according to the invention comprises the following steps:

[0040] - providing a (first) mass D1 consisting of electron-conducting particles and a polymer-based binder, said mass being, for example, a printing paste or a dispersion,

[0041] - applying the provided mass D1 or the dispersant in the form of a flow field structure 1b to the plate body 11 of the bipolar plate 10, for example by a printing technique, in particular a screen printing technique,

[0042] The applied mass D1 or dispersant is pyrolyzed, and remains as a shaped element in the form of a flow field structure 1 b on the plate body 11 of the bipolar plate 10 and is connected to the bipolar plate.

[0043] The fuel cells 1 according to the invention can be stacked to form a fuel cell stack, a so-called fuel cell stack, which has a plurality of stacked repeating units, for example in the form of PEM fuel cells.

[0044] The bipolar plate 10 according to the invention provides a cavity structure or channel structure in the millimeter range for coarse distribution of the reactants in the fuel cell 1. The bipolar plate 10 according to the invention can advantageously be used with a flat or planar plate body 11, which is particularly advantageous in terms of production.

[0045] Subsequently or together with the flow field structure 1 b , the porous gas diffusion layer GDL and, if appropriate, the microporous layer MPL can be applied, in particular printed, on the plate body 11 (see Figure 3 ).

[0046] like Figure 2 and Figure 3As shown, the flow field structure 1b according to the invention has an internal porosity in addition to an external cavity structure or channel structure in the millimeter range. The flow field structure 1b according to the invention can preferably be used in the cathode region K of the fuel cell 1 in order to facilitate the discharge of product water there.

[0047] According to the present invention, a bipolar plate 10 having a flow field structure 1b according to the present invention and, if necessary, an optionally adjacent gas diffusion layer GDL and / or an optionally adjacent microporous layer MPL is pyrolyzed together with the plate body 11. Thus, a bipolar plate 10 can be provided that exhibits improved electrical (especially electronic) and thermal bonding properties between the plate body 11, the porous flow field structure 1b, and the gas diffusion layer GDL and / or the microporous layer MPL.

[0048] like Figure 2 and Figure 3 As shown, the flow field structure 1b can have a corrugated structure with, for example, a semicircular cross section on the webs. This allows for a uniform, preferably reduced, supporting force on the membrane M. The flow field structure 1b can have a porosity of approximately 50% to 70%.

[0049] like Figure 2 and Figure 3 As schematically shown, a burnable negative structure 1a can be applied to the body 11 of the bipolar plate 10 before the flow field structure 1b is applied, in particular printed, thereon. This negative structure subsequently decomposes as completely as possible into gaseous components during pyrolysis. The burnable negative structure 1a can be provided as a mixture of particles and a binder (e.g., a dry dispersion). The particles and binder have similar softening and / or decomposition temperatures, preferably lower than the decomposition temperature of the electron-conducting particles and / or the polymer-based binder of the mass D1. The particles of the burnable negative structure 1a can include at least one of the following: polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC), and / or polyetheretherketone (PEEK). The binder of the burnable negative structure 1a can include at least one of the following: polyethylene glycol (PEO), polyvinylidene fluoride (PVDF), and / or an acrylate adhesive.

[0050] The electron-conducting particles of mass D1 can in turn comprise graphite particles and / or graphite fibers, wherein the electron-conducting particles of mass D1 can have a size in the order of 10 μm to 50 μm. The polymer-based adhesive of mass D1 can comprise at least one of the following elements: an acrylate adhesive and / or polytetrafluoroethylene (PTFE) and / or polyvinylidene fluoride (PVDF).

[0051] Alternatively, it is conceivable that the mass D1 may include burnable particles, for example polymethyl methacrylate (PMMA), in order to form macroscopic holes in the flow field structure 1 b.

[0052] like Figure 3 In side view Figure 1 ), after pyrolyzing the flow field structure 1b on the plate body 11 of the bipolar plate 10, a gas diffusion layer GDL and / or a microporous layer MPL can be printed or placed on the flow field structure 1b, and the flow field structure is composed of a second mass block D2 that is different from the (first) mass block D1 and is particularly finer. It is conceivable that the electron-conducting particles of the finer mass block D2 can have a smaller particle size than the (first) mass block D1. Therefore, a bipolar plate 10 having multiple layers with different particle sizes and pore sizes can be realized, so as to facilitate the introduction of reactants into the fuel cell 1 in an improved manner and the subsequent uniform distribution of the reactants on the membrane M of the fuel cell 1.

[0053] like Figure 3 In side view Figure 2 ), the gas diffusion layer GDL and / or the microporous layer MPL can be printed together with the flow field structure 1b composed of the (first) mass block D1 on the plate body 11 of the bipolar plate 10. Therefore, a particularly cost-effective and simple bipolar plate 10 can be realized.

[0054] The above description of the drawings describes the invention only within the framework of examples. Of course, the individual features of the embodiments can be freely combined with one another as long as they are technically reasonable, without leaving the framework of the invention.

Claims

1. A method for producing a bipolar plate (10) for a fuel cell (1), the bipolar plate comprising: a plate body (11) for separating the fuel cell (1) from an adjacent fuel cell (1) or a housing, wherein: The plate body (11) has a flow field structure (1b) for introducing reactants into the fuel cell (1), characterized in that the method comprises the following steps: - providing a first mass block (D1) consisting of electron-conducting particles and a polymer-based adhesive, - applying the provided first mass block (D1) in the form of the flow field structure (1b) to the plate body (11) of the bipolar plate (10), - The applied first mass block (D1) is pyrolyzed, and the mass block remains as a shaped element on the plate body (11) of the bipolar plate (10) in the form of the flow field structure (1b) and is connected to the bipolar plate, wherein, after the applied first mass block (D1) in the form of the flow field structure (1b) on the plate body (11) of the bipolar plate (10) is pyrolyzed, a gas diffusion layer (GDL) and / or a microporous layer (MPL) is applied to the flow field structure (1b) composed of a second mass block (D2) different from the first mass block (D1), the second mass block having a smaller particle size than the first mass block (D1), so that large pores are generated by the large particles of the first mass block (D1).

2. The method according to claim 1, characterized in that Before applying the flow field structure (1b) to the plate body (11) of the bipolar plate (10), a burnable negative structure (1a) is laid on the plate body (11) of the bipolar plate (10).

3. The method according to claim 2, characterized in that The burnable negative structure (1a) is provided as a mixture of particles and a binder, wherein the particles and the binder have similar softening temperatures and / or decomposition temperatures, wherein the decomposition temperature is lower than the decomposition temperature of the electron-conducting particles of the mass, wherein the particles of the burnable negative structure (1a) have at least one of the following elements: polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC) and / or polyetheretherketone (PEEK), and / or the binder of the burnable negative structure (1a) has at least one of the following elements: polyethylene glycol (PEO), polyvinylidene fluoride (PVDF) and / or an acrylate adhesive.

4. The method according to any one of claims 1 to 3, characterized in that The electron-conducting particles of the mass comprise graphite particles and / or graphite fibers, and / or at least some of the electron-conducting particles of the mass have a diameter in the order of 10 μm to 50 μm.

5. The method according to any one of claims 1 to 3, characterized in that The polymer-based adhesive of the mass comprises at least one of the following elements: an acrylate adhesive and / or polytetrafluoroethylene (PTFE) and / or polyvinylidene fluoride (PVDF).

6. The method according to any one of claims 1 to 3, characterized in that The mass has particles that can be burned to form holes in the flow field structure (1b).

7. The method according to any one of claims 1 to 3, characterized in that The provided mass block is applied to the plate body (11) of the bipolar plate (10) in the form of the flow field structure (1b) by printing technology.

8. The method according to claim 6, characterized in that The particles capable of cauterization are polymethyl methacrylate.

9. A bipolar plate (10) for a fuel cell (1), the bipolar plate being produced by means of a method according to any one of claims 1 to 8, wherein: The bipolar plate (10) comprises a plate body (11) for separating the fuel cell (1) from an adjacent fuel cell (1) or a housing, wherein the plate body (11) comprises a flow field structure (1b) for introducing reactants into the fuel cell (1), wherein the flow field structure (1b) is applied to the plate body (11) of the bipolar plate (10) by means of a mass block consisting of electron-conducting particles and a polymer-based adhesive and is pyrolyzed.

10. A fuel cell (1) comprising at least one bipolar plate (10) according to claim 9.

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