Method for producing a bipolar plate

Abstract

The invention relates to a method for producing a bipolar plate (10, 51) for an electrochemical cell unit (53) as a fuel cell unit (1) for converting electrochemical energy into electrical energy and / or as an electrolytic cell unit (49) for converting electrical energy into electrochemical energy, comprising a stack of electrochemical cells (52), the method has the following steps: providing a first plate (64) and a second plate (65); stacking the first plate (64) and the second plate (65) one above the other such that the inner sides (66) of the first and second plates (64, 65) one above the other and an intermediate space (79) is formed between the first and second plates (64, 65); sealing the intermediate space (79) in a fluid-tight manner from the environment with at least one sealing means (84) in order to prevent fluid from flowing from the environment into the inner space (79); a contact force is applied to the first and / or the second plate (64, 65), such that, as a result of the applied contact force, the inner side (66) of the first and the second plate (64, 65) overlaps the additional pressure on the contact region (68) on the basis of the applied contact force in such a way that the intermediate space (79) is loaded with a negative pressure in relation to the ambient pressure and, as a result of the negative pressure in the intermediate space (79), the inner side (66) of the first and the second plate (64, 65) is pressed against the additional pressure on the contact region (68). A contact force applied by ambient pressure to the first and / or second plate (64, 65) is applied to the first and / or first plate (64, 65); a welded connection (69) is produced between the first and second plates (64, 55), and the interior space (79) is sealed with at least one membrane (85) as at least one sealing means (84).

Description

Technical Field

[0001] The invention relates to a method for producing a bipolar plate of an electrochemical cell according to the preamble of claim 1, a method for producing an electrochemical cell according to the preamble of claim 14 and an electrochemical cell according to the preamble of claim 15. Background Art

[0002] Fuel cell units as direct current cells convert continuously supplied fuel and oxidant into electrical energy and water by means of redox reactions at the anode and cathode. Fuel cells are used in a wide variety of stationary and mobile applications, for example in houses not connected to the power grid or in motor vehicles, in rail transport, in aviation, in space travel and in navigation. A large number of fuel cells are arranged in a stack in a fuel cell unit as a stack.

[0003] A large number of fuel cells are arranged in a fuel cell unit in the form of a fuel cell stack. There is a gas space for the oxidant inside each fuel cell, that is, a flow space for passing the oxidant (for example, air with oxygen from the environment). The gas space for the oxidant is composed of channels on the bipolar plate and by a gas diffusion layer for the cathode. Therefore, the channel is composed of the corresponding channel structure of the bipolar plate, and the oxidant (that is, oxygen) reaches the cathode of the fuel cell via the gas diffusion layer. In a similar manner, there is a gas space for the fuel.

[0004] Electrolytic cell units consisting of electrolytic cells arranged in a stack (analogously to fuel cell units) are used, for example, to electrolytically obtain hydrogen and oxygen from water. In addition, fuel cell units are known that can be operated as reversible fuel cell units and thus as electrolytic cell units. Fuel cell units and electrolytic cell units form electrochemical cell units. Fuel cells and electrolytic cells form electrochemical cells.

[0005] For the manufacture and assembly of electrochemical cells, especially fuel cells, it is necessary that the components of the fuel cells are arranged in an aligned stack. The sheet-like components of the fuel cells are proton exchange membranes, anodes, cathodes, gas diffusion layers and bipolar plates. An important component of the stack is the conductive bipolar plates. These act as current collectors to drain and guide the reaction gases and guide the liquid or gaseous coolant through the flow space, especially the pipeline or channel structure. The bipolar plates are placed flat on the contact surface on the gas diffusion layer.

[0006] Bipolar plates are usually constructed from two or three plates made of stainless steel. When manufacturing bipolar plates, the first and second plates are stacked one above the other, and then the plates are welded together to form a weld seam. The weld seam not only has the function of connecting the plates materially and electrically to each other, but also serves to seal the channels of the coolant in a fluid-tight manner, which are constructed between each two plates. For the corresponding bipolar plate, the first and second plates, which are shaped in a corrugated manner, are stacked one above the other and stacked, so that the inner sides of the first and second plates are stacked one above the other on the strip-shaped contact area, and there is a gap with a thickness between the inner sides on the strip-shaped contact area. In order to construct the weld seam reliably and fluid-tightly, it is necessary that the thickness of the gap is small, that is, the gap is constructed to be less than the technical zero gap of 20 μm. In addition, the first and second plates are stacked one above the other with the correct lateral relative position as the set position, so that the weld connection is only produced on the strip-shaped contact area as the joining area.

[0007] In the case of a large thickness of the gap, it is no longer possible to make a weld without interruption between the first and second plates, so that the fluid passes horizontally in the direction of the plane of the first and second plates due to the leak between the first and second plates. In addition, due to the rupture of the weld at the weld, the fluid can flow vertically and perpendicularly to the plane of the first and second plates along the weld. The leak of the weld can only be confirmed in the subsequent production process when the fuel cell unit is checked for leaks, so that in the case of a fuel cell unit with, for example, 500 fuel cells, only one weld has leaks, the entire fuel cell unit can no longer be used and must be removed. In order to avoid a large gap at the contact area, that is, in order to construct a technical zero gap, a contact force is applied to the first and second plates by a mechanical clamping device during the welding process, so that due to the applied contact force, the inner side of the first and second plates overlap each other due to the applied contact force and the additional pressure at the contact area. Due to the additional pressure, a technical zero gap is constructed on the contact area. However, mechanical hold-down devices hinder the construction of welded seams by means of laser welding, because the laser beam is blocked by the mechanical hold-down devices, so that the hold-down devices must be constantly released (i.e., deactivated) and placed on the plates (i.e., activated) during laser welding. Therefore, time-consuming constant changes of the hold-down devices (e.g., clamps) are required during welding. Therefore, a large amount of time is required to construct the welded connection between the first and second plates from a large number of welds. In addition, high costs for the hold-down devices are generated. In the industrial production of a large number of fuel cell units, high costs are generated due to the high time expenditure.

[0008] DE 10 2008 024 478 B4 shows a method for producing a bipolar plate assembly for a fuel cell stack, the method comprising the following steps: providing a first monopolar plate having a first inner surface; providing a second monopolar plate having a second inner surface; positioning the first inner surface adjacent to the second inner surface; and connecting the first monopolar plate and the second monopolar plate by means of a plurality of point-by-point conductive nodes, wherein, when connecting the first monopolar plate and the second monopolar plate, the plurality of point-by-point conductive nodes are distributed in a uniform 2D grid pattern on a surface of a coolant flow region constructed in an internal space of the bipolar plate assembly, and a step of connecting a first circumferential flange of the first monopolar plate to a second circumferential flange of the second monopolar plate is implemented by means of laser welding.

[0009] DE 10 2021 206 581 A1 shows a method for producing bipolar plates for an electrochemical cell unit, the method comprising the following steps: providing a first plate and a second plate; stacking the first plate and the second plate one above the other, so that the inner sides of the first and second plates are arranged one above the other and an intermediate space is formed between the first and second plates; applying a contact force to the first and second plates, so that the inner sides of the first and second plates are arranged one above the other due to the applied contact force and the additional pressure on the contact area; producing a welded connection between the first and second plates, wherein the intermediate space is loaded with a negative pressure relative to the ambient pressure, so that the contact force applied to the first and / or second plate by the ambient pressure is applied to the first and / or second plate. Summary of the invention

[0010] According to the method for manufacturing a bipolar plate of an electrochemical cell unit of the present invention, the electrochemical cell unit is used as a fuel cell unit for converting electrochemical energy into electrical energy and / or as an electrolysis cell unit for converting electrical energy into electrochemical energy, and the electrochemical cell unit has a stacked electrochemical cell, and the method comprises the following steps: providing a first plate and a second plate; stacking the first plate and the second plate one above the other, so that the inner sides of the first and second plates are stacked one above the other and an intermediate space is constructed between the first and second plates; sealing the intermediate space with at least one sealing device to seal the intermediate space against an ambient fluid to prevent the fluid from leaking into the intermediate space; and Flow from the environment into the interior space; exert a contact force on the first and / or second plate, so that the inner sides of the first and second plates are placed one above the other due to the applied contact force and the additional pressure on the contact area, in that the intermediate space is loaded with a negative pressure relative to the ambient pressure and the contact force applied by the ambient pressure to the first and / or second plate is applied to the first and / or second plate due to the negative pressure in the intermediate space; produce a welded connection between the first and second plates, wherein the interior space is sealed with at least one film as at least one sealing means. The at least one sealing means as at least one film can be easily placed on the outer side of the first and / or second plate, for example by means of a robot, and achieves a reliable sealing of the intermediate space. The welded connection between the first and second plates usually comprises a plurality of separate weld seams. Thus, in addition to the pressure caused by the weight force, the additional pressure caused by the weight force acts on the second plate.

[0011] In a supplementary embodiment, the negative pressure in the intermediate space is at least 100 mbar, 300 mbar or 500 mbar less than the ambient pressure. The ambient pressure is usually about 1000 mbar, so that when there is a negative pressure of 300 mbar in the intermediate space, a pressure difference of 700 mbar occurs between the intermediate space and the environment. Thus, an ambient pressure of 1000 mbar acts on the outer sides of the first and second plates, and a negative pressure of 300 mbar acts on the inner sides of the first and second plates, so that due to this pressure difference, the pressure on the outer side is greater than the pressure on the inner side, and thus, as a result of the resulting total force, the first and second plates are placed one on top of the other with additional pressure without taking into account the force of gravity.

[0012] In another embodiment, the first plate is first placed on the carrier plate and then the second plate is placed on the first plate.

[0013] In an additional variant, after the second pane has been placed on the first pane, the intermediate space between the first and second pane is sealed with respect to the environment by at least one film.

[0014] In a supplementary embodiment, the intermediate space in the outer edge of the first and second plates arranged one above the other is sealed with at least one film. At the outer edge, there is a circumferential gap, in particular a technically zero gap, between the first and second plates, and this gap is sealed by the at least one film. The at least one film is preferably arranged completely circumferentially on the outer edge.

[0015] In a further embodiment, the intermediate space in the fluid opening leading to the first and second plates arranged one above the other is sealed with at least one film. At the fluid opening, there is a surrounding gap, in particular a technically zero gap, between the first and second plates, and the gap is sealed by at least one film.

[0016] Preferably, at least one film is placed on at least one outer side of the first and / or second plates stacked one on top of the other.

[0017] In a further embodiment, at least 30%, 50%, 70% or 90%, in particular completely, of at least one outer surface of the first and / or second plates stacked one above the other is provided with at least one film and is covered by the at least one film.

[0018] In an additional variant, at least one film is placed on at least one outer side of the first and / or second plates stacked one above the other by unrolling the at least one film from a roller and then placing it on at least one outer side of the first and / or second plates stacked one above the other.

[0019] In particular, the welded connection is produced by means of laser welding.

[0020] In another embodiment, at least one film is placed on at least one outer side of the first and / or second plate in a region where the laser beam emitted by the laser passes as a crossover point to produce the welded connection, so that during the production of the welded connection by the laser beam, the at least one film is penetrated and / or dissolved, in particular melted and / or evaporated by the laser beam. This facilitates the application of the film to the outer side of the first and / or second plate in terms of processing technology, since the at least one film can also be placed on the outer side of the first and / or second plate in a region where the welded connection is produced by means of the laser beam.

[0021] In a supplementary variant, after the weld connection is produced, at least one film is removed from at least one outer side of the first and / or second plates stacked one above the other, in particular completely removed. After the removal of the at least one film, the at least one film has no contact with the bipolar plate.

[0022] In an additional embodiment, during the production of the welded connection, the intermediate space is in particular continuously charged with a negative pressure relative to the ambient pressure. Preferably, the negative pressure in the intermediate space is continuously and substantially constant during the entire production of the welded connection. Preferably, substantially constant means having a deviation of less than 30%, 20% or 10%.

[0023] A method for manufacturing an electrochemical cell unit according to the present invention, wherein the electrochemical cell unit is used as a fuel cell unit for converting electrochemical energy into electrical energy and / or as an electrolysis cell unit for converting electrical energy into electrochemical energy, and the electrochemical cell unit has a stacked electrochemical cell, and the method has the following steps: providing layered components of the electrochemical cell (i.e., preferably a proton exchange membrane, an anode, a cathode, preferably a gas diffusion layer and a bipolar plate); stacking the layered components into an electrochemical cell and an electrochemical cell unit stack, wherein a bipolar plate is provided by implementing a method described in the present patent application.

[0024] According to the present invention, an electrochemical cell unit as a fuel cell unit for converting electrochemical energy into electrical energy and / or as an electrolysis cell unit for converting electrical energy into electrochemical energy comprises electrochemical cells arranged in a stack, and the electrochemical cells each comprise a layered component arranged in a stack, and the components of the electrochemical cell are preferably a proton exchange membrane, an anode, a cathode, preferably a gas diffusion layer and a bipolar plate, wherein the corresponding bipolar plate is constructed by a first and a second plate, wherein the electrochemical cell unit is manufactured by means of the method described in the present patent application and / or the first and / or the second plate does not have a clamping mark. In the prior art, the contact force is basically applied point by point to the outer side of the first and second plates by means of a clamping device as a clamp, thereby causing the clamping mark to be constructed. These clamping marks are, for example, visually visible cracks, grooves, wear marks or scratches and / or changes in the structure on the surface and / or in the interior of the first and / or second plate that can be detected by means of a material analysis method, in particular a change in the lattice structure of atoms and / or molecules.

[0025] In another embodiment, during the reduction of the pressure in the intermediate space to achieve a negative pressure in the intermediate space relative to the environment, the at least one membrane moves from the outside in the direction of the intermediate space due to the negative pressure on the outside of the first and / or second plate. The negative pressure causes the at least one membrane to be sucked into the intermediate space.

[0026] In another embodiment, at least one film is made of plastic, preferably polyolefin, such as polyethylene (PE) and / or polypropylene (PP). Preferably, at least one film is made of polyvinyl chloride (PVC) and / or polystyrene (PS) and / or polyester and / or polycarbonate (PC).

[0027] In another variant, the at least one film is constructed from cellophane.

[0028] In a supplementary variant, the at least one film is constructed from a bio-based plastic, preferably polylactic acid (PLA) and / or cellulose acetate and / or a starch blend.

[0029] Preferably, at least one film has a thickness and / or a wall thickness of between 2 μm and 2 mm, in particular between 2 μm and 1 mm.

[0030] In another embodiment, at least one film is configured as an adhesive film. Thus, at least one film adheres to the outer side of the first and / or second pane without adhesive, preferably by means of Van der Waals bonds.

[0031] In an additional embodiment, at least one film is designed as an adhesive film. The at least one film as an adhesive film has an adhesive coating on one side, and the side with the adhesive coating is placed on at least one outer side of the first and / or second pane, so that the at least one film adheres to at least one outer side of the first and / or second pane by means of an adhesive connection.

[0032] In a supplementary embodiment, the at least one film is placed on at least one outer side of the first and / or second pane by first unrolling the at least one film from a roll and then placing it on at least one outer side of the first and / or second pane.

[0033] Practically, at least one film is placed onto at least one outer side of the first and / or second pane by means of a robot.

[0034] In another variant, after the welding connection is made, the at least one film is not reused. Therefore, the at least one film is a disposable product. Due to the low production costs of the at least one film, the use of the at least one film as a disposable only results in negligible costs.

[0035] In an additional configuration, during and / or after placing at least one film on at least one outer side of the first and / or second plate, the set position of the at least one film on the outer side of the first and / or second plate is checked and / or detected with the aid of a camera and image processing software, and preferably, if there is a deviation between the actual position of the at least one film on at least one outer side of the first and / or second plate detected by the camera and image processing software and the set position, an error message is issued and / or the at least one film is additionally placed autonomously or automatically, so that the actual position of the at least one film on at least one outer side of the first and / or second plate is consistent with the set position.

[0036] In an additional embodiment, after the production of the welded connection, at least one film is removed mechanically and / or thermally and / or pneumatically from the outer sides of the first and second plates stacked one above the other. The mechanical removal is carried out, for example, by means of a rotating brush and / or a movable scraper. The thermal removal is carried out, for example, with a radiator and / or a gas flame. The pneumatic removal is carried out, for example, with the aid of compressed air from a nozzle. Preferably, the removal of the at least one film is carried out by a robot. For this purpose, a processing unit for removing the film, in particular a rotating brush, a radiator and / or a nozzle for compressed air, is fastened to the arm of the robot.

[0037] In a supplementary embodiment, the complete removal of the film from at least one outer side of the first and / or second plate is checked and / or detected by means of a camera and image processing software, and preferably, if film remnants are still present in areas of at least one outer side of the first and / or second plate, their position is correspondingly determined by means of the camera and image processing software and then removed automatically, in particular mechanically and / or thermally and / or pneumatically, for example by moving a rotating brush by an arm of a robot over the areas with film still present. Preferably, the camera is fastened to the arm of the robot, so that this monitoring of the complete removal of the film is automatically carried out by means of the robot.

[0038] In an additional embodiment, the support plate has an elastic sealing layer on the upper side, so that the first plate is placed on the elastic sealing layer of the support plate. Practically, the elastic sealing layer has a modulus of elasticity between 0.1 and 10 GPa. Preferably, the sealing layer is connected to the rest of the support plate in a materially bonded manner, in particular by means of injection molding and / or 3D printing. Preferably, the rest of the support plate is made of metal, in particular steel, and / or has a modulus of elasticity greater than 100 GPa.

[0039] In another embodiment, a processing intermediate space is formed between the first plate and the support plate, and the processing intermediate space is loaded with a negative pressure relative to the ambient pressure, so that the first plate lies flat on the support plate due to the negative pressure and the processing additional pressure, in particular without taking gravity into account. Preferably, the processing intermediate space is composed of a plurality of processing intermediate subspaces, which are preferably connected to each other in a fluid-conducting manner. For example, in the case of a negative pressure on the outer side of the first lower plate as the lower side and ambient pressure on the outer side of the second upper plate as the upper side, a contact force for the additional pressure is also mechanically applied to the outer side of the first lower plate as the lower side by means of the outer side of the first lower plate as the lower side lying flat on the support plate with the processing additional pressure.

[0040] In another embodiment, the intermediate space between the first and second plates comprises a channel for a coolant.Preferably, the intermediate space between the first and second plates comprises a technically zero gap at the contact area.

[0041] In another variant, the intermediate space is filled with a protective gas, in particular nitrogen or an inert gas, while the negative pressure in the intermediate space is maintained. The negative pressure in the intermediate space is established by sucking the protective gas from a container with the protective gas through the intermediate space with a vacuum pump, then establishing the negative pressure in the intermediate space, and optionally, then guiding the protective gas through the intermediate space while the negative pressure in the intermediate space is maintained.

[0042] In a supplementary embodiment, a protective gas is directed to the intersection point, in particular by means of a movable nozzle, while the laser beam impinges on the outer side of the first plate.

[0043] In another embodiment, the intermediate space is loaded with a negative pressure relative to the ambient pressure, so that the contact force exerted on the first and / or second plate is substantially exerted on the first and / or second plate by the ambient pressure. "Substantially" preferably means that at least 70%, 80% or 90% of the contact force is caused by the ambient pressure. In the absence of negative pressure, the second plate lies flat on the first plate only due to the weight force and the pressure acting on the second plate due to gravity.

[0044] In an additional embodiment, after stacking the first and second plates, the first plate with a partial area of ​​the inner side of the first plate lies on a partial area of ​​the inner side of the second plate at the contact area, and outside the contact area, due to the spacing between the inner sides of the first and second plates in a direction perpendicular to the virtual plane spanned by the bipolar plates, at least one channel, preferably a plurality of channels for the coolant is formed between the inner sides of the first and second plates. Preferably, after stacking, the virtual plane spanned by the first and second plates is oriented substantially parallel to each other, in particular with a deviation of less than 30°, 20° or 10°.

[0045] Preferably, the seal for sealing at least one channel for the coolant between the first and the second plate to the outside is formed by at least one weld seam produced by means of laser beam welding.

[0046] In a further embodiment, at least 90% of the bipolar plates, in particular all of the bipolar plates, are provided to the fuel cell unit by carrying out the method described in the present patent application.

[0047] In a supplementary variant, the first and second plates are at least partially, in particular completely, provided from metal, in particular stainless steel and / or aluminum and / or plastic and / or a composite material.

[0048] In a supplementary variant, the first and second plates are provided at least partially, in particular completely, in a corrugated and / or sheet-like and / or layered manner.

[0049] In a further embodiment, the bipolar plate is constructed from two or three plates, and these two or three plates are connected to one another by means of a welded connection by means of the method described in the present patent application.

[0050] In a supplementary variant, at least one welded connection of the bipolar plate is produced, in particular, only in the contact region.

[0051] In a further embodiment, the thickness of the first and second panes is between 5 μm and 1000 μm, in particular between 20 μm and 300 μm.

[0052] Preferably, the membrane electrode assembly is formed from a respective proton exchange membrane, a respective anode and a respective cathode, in particular as a CCM (catalyst coated membrane) with catalyst material in the anode and the cathode.

[0053] In another variant, the electrochemical cell unit comprises at least 50, 100, 200 or 400 stacked electrochemical cells.

[0054] Furthermore, the invention comprises a computer program having program code means which are stored on a computer-readable data carrier in order to carry out the method described in the present patent application when the computer program is executed on a computer or a corresponding processing unit.

[0055] Furthermore, an integral part of the invention is a computer program product having program code means which are stored on a computer-readable data carrier in order to carry out the method described in the present patent application when the computer program is executed on a computer or a corresponding processing unit.

[0056] In another variant, the electrochemical cell unit comprises a housing and / or a connecting plate. The stack is surrounded by the housing and / or the connecting plate.

[0057] The fuel cell system according to the present invention, in particular a fuel cell system for a motor vehicle, comprises a fuel cell unit as a fuel cell stack having a fuel cell, a compressed gas storage device for storing gaseous fuel, and a gas delivery device for delivering a gaseous oxidant to the cathode of the fuel cell, wherein the fuel cell unit is constructed as a fuel cell unit and / or an electrolysis cell unit described in the present patent application.

[0058] The electrolysis system and / or fuel cell system according to the present invention comprises an electrolysis cell unit as an electrolysis cell stack having electrolysis cells, a compressed gas storage device preferably for storing gaseous fuel, a gas delivery device preferably for delivering a gaseous oxidant to the cathode of the fuel cell, a storage container for a liquid electrolyte, and a pump for delivering the liquid electrolyte, wherein the electrolysis cell unit is constructed as the electrolysis cell and / or fuel cell unit described in the present patent application.

[0059] In a further embodiment, the fuel cell unit described in the present patent application additionally forms an electrolysis cell unit as a reversible fuel cell unit and preferably vice versa.

[0060] In a further variant, the electrochemical cell unit, in particular the fuel cell unit and / or the electrolysis cell unit, comprises at least one connecting device, in particular a plurality of connecting devices and a clamping element.

[0061] Practically, components for electrochemical cells, in particular fuel cells and / or electrolysis cells, are preferably insulating layers, in particular proton exchange membranes, anodes, cathodes, preferably gas diffusion layers and bipolar plates, in particular separator plates.

[0062] In a further embodiment, the connecting device is designed as a bolt and / or is rod-shaped and / or as a tensioning belt.

[0063] Practically, the clamping element is designed as a clamping plate.

[0064] In another variant, the gas conveying device is designed as a blower and / or a compressor and / or a pressure vessel with an oxidizing agent.

[0065] In particular, the electrochemical cell, in particular the fuel cell and / or the electrolysis cell, comprises at least 3, 4, 5 or 6 connection devices.

[0066] In a further embodiment, the clamping element is plate-shaped and / or lamellar and / or flat and / or is designed as a grid.

[0067] Preferably, the fuel is hydrogen, a hydrogen-rich gas, reformed gas or natural gas.

[0068] Practically, the fuel cell and / or the electrolysis cell is / are of substantially flat and / or lamellar design.

[0069] In a supplementary variant, the oxidant is air containing oxygen or pure oxygen.

[0070] Preferably, the fuel cell unit is a PEM fuel cell unit having a PEM fuel cell or a SOFC fuel cell unit having a SOFC fuel cell or an alkaline fuel cell (AFC). BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Subsequently, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. It is shown that:

[0072] Figure 1 A greatly simplified exploded view of an electrochemical cell system as a fuel cell system and an electrolysis cell system, which has components of electrochemical cells as fuel cells and electrolysis cells,

[0073] Figure 2 A three-dimensional view of a portion of a fuel cell and an electrolysis cell,

[0074] Figure 3 Longitudinal section of an electrochemical cell as a fuel cell and an electrolysis cell,

[0075] Figure 4 A perspective view of an electrochemical cell unit as a fuel cell unit and an electrolytic cell unit as a fuel cell stack and an electrolytic cell stack,

[0076] Figure 5 A side view of an electrochemical cell unit as a fuel cell unit and an electrolysis cell unit of a fuel cell stack and an electrolysis cell stack,

[0077] Figure 6 A three-dimensional view of a bipolar plate.

[0078] Figure 7 Enlarged longitudinal section of the fuel cell and electrolysis cell in the area of ​​the weld seam,

[0079] Figure 8 A longitudinal section through a bipolar plate, which comprises two plates which are connected to one another by means of a weld seam as a through-weld and further embodied with a weld-in,

[0080] Fig. 9 A longitudinal section of a bipolar plate, which comprises two plates which are connected to one another by means of a weld seam as a weld-in during a welding process by means of a laser beam, and

[0081] Fig.10 Longitudinal section through the two plates when lying flat on the support plate during the welding process,

[0082] Fig.11 In the first embodiment, after the film as a sealing device is placed, the Figure 6 The longitudinal section AA, without the support plate shown,

[0083] Fig.12 In the second embodiment, after the film as a sealing device is placed, the Figure 6 The longitudinal section AA, without the support plate shown,

[0084] Fig.13 In the third embodiment, after the film as a sealing device is placed, the Figure 6 The longitudinal section AA, without the support plate shown,

[0085] Fig.14 Strongly simplified illustration of a robot with a roller of a film. DETAILED DESCRIPTION

[0086] exist Figures 1 to 3 The basic structure of a fuel cell 2 as a PEM fuel cell 3 (polymer electrolyte fuel cell 3) is shown in FIG. The principle of the fuel cell 2 is to generate electrical energy or electric current by means of an electrochemical reaction. Hydrogen H2 is introduced to the anode 7 as a gaseous fuel and the anode 7 constitutes the negative electrode. A gaseous oxidant (i.e., air with oxygen) is introduced to the cathode 8, that is, the oxygen in the air provides the necessary gaseous oxidant. Reduction (electron absorption) occurs at the cathode 8. Oxidation as electron release is carried out at the anode 7.

[0087] The content of the redox equation for the electrochemical process is:

[0088] cathode:

[0089] O2+4H + +4e - →2H2O

[0090] anode:

[0091] 2H2→4H + +4e -

[0092] The overall reaction equation at the cathode and anode is:

[0093] 2H2+O2→2H2O

[0094] The difference between the normal potential of the electrode pair under standard conditions and the reversible fuel cell voltage or no-load idling voltage of the unloaded fuel cell 2 is 1.23 V. In practice, this theoretical voltage of 1.23 V cannot be achieved. In a stationary state and with a small current, a voltage exceeding 1.0 V can be achieved, and when running with a larger current, a voltage between 0.5 V and 1.0 V is achieved. A series circuit of multiple fuel cells 2, in particular a fuel cell unit 1 of a fuel cell stack 1 of multiple stacked fuel cells 2, has a higher voltage, which is equivalent to the number of fuel cells 2 multiplied by the single voltage of the corresponding fuel cell 2.

[0095] In addition, the fuel cell 2 includes a proton exchange membrane 5 (PEM), which is arranged between the anode 7 and the cathode 8. The anode 7 and the cathode 8 are layered or sheet-like. The PEM 5 acts as an electrolyte, a catalyst carrier and a separator for the reaction gas. In addition, the PEM 5 also acts as an electrical insulator and prevents electrical short circuits between the anode 7 and the cathode 8. Generally, a proton-conducting membrane made of a perfluorinated and sulfonated polymer with a thickness of 12 μm to 150 μm is used. The PEM 5 conducts protons H + and substantially blocks H + ions, thus due to the PEM 5 protons H + The PEM 5 is substantially impermeable to the reactant gases oxygen O2 and hydrogen H2, that is, it blocks the flow of oxygen O2 and hydrogen H2 between the gas space 31 at the anode 7 with the fuel hydrogen H2 and the gas space 32 at the cathode 8 with the air or oxygen O2 as the oxidant. The proton conductivity of the PEM 5 increases with increasing temperature and increasing water content.

[0096] Electrodes 7, 8 as anode 7 and cathode 8 are placed flat on both sides of PEM 5 facing gas spaces 31, 32 respectively. The unit composed of PEM 5 and electrodes 7, 8 is called membrane electrode assembly 6 (MEA). Electrodes 7, 8 are pressed with PEM 5. Electrodes 7, 8 are platinum-containing carbon particles, which are bonded to PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene propylene copolymer), PFA (perfluoroalkoxy), PVDF (polyvinylidene fluoride) and / or PVA (polyvinyl alcohol) and are hot pressed in a microporous carbon fiber mesh, glass fiber mesh or plastic mesh. On electrodes 7, 8, a catalyst layer 30 (not shown) is usually applied on the side facing gas space 31, 32 respectively. The catalyst layer 30 at the gas space 31 with fuel at the anode 7 includes nano-dispersed platinum ruthenium on graphitized carbon black particles (which are bonded to a binder). The catalyst layer 30 at the gas space 32 with oxidant at the cathode 8 includes similar nano-dispersed platinum. As a binding agent, e.g. PTFE emulsifier or polyvinyl alcohol.

[0097] In contrast, the electrodes 7, 8 are made of ionomers (eg These electrodes 7, 8 with ionomers are electrically conductive due to the carbon particles and also conduct protons H + , and additionally also acts as a catalyst layer 30 due to the platinum-containing carbon particles ( Figure 2 and 3The membrane electrode assembly 6 having these electrodes 7, 8 including ionomers constitutes a membrane electrode assembly 6 as a CCM (catalyst coated membrane, CCM).

[0098] Gas diffusion layer 9 (Gas Diffusion Layer, GDL) is placed flat on anode 7 and cathode 8. Gas diffusion layer 9 on anode 7 distributes fuel from channel 12 for fuel uniformly to catalyst layer 30 on anode 7. Gas diffusion layer 9 on cathode 8 distributes oxidant from channel 13 for oxidant uniformly to catalyst layer 30 on cathode 8. In addition, GDL 9 draws reaction water in the direction opposite to the flow direction of reaction gas, that is, in the direction from catalyst layer 30 or electrode 7, 8 to channel 12, 13, respectively. In addition, GDL 9 keeps PEM 5 moist and conducts current. For example, GDL 9 is constructed of hydrophobic carbon paper as carrier and base layer and a combined carbon powder layer as microporous layer.

[0099] The bipolar plate 10 is located on the GDL 9. The electrically conductive bipolar plate 10 serves as a current collector for drainage and for guiding the reaction gas as a process fluid through the channel structure 29 and / or the flow field 29 and for dissipating the waste heat, which is generated in particular in the exothermic electrochemical reaction at the cathode 8. In order to dissipate the waste heat, channels 14 are added to the bipolar plate 10 as channel structures 29 to guide a liquid or gaseous coolant as a process fluid through them. The channel structure 29 on the gas space 31 for the fuel is composed of channels 12. The channel structure 29 on the gas space 32 for the oxidant is composed of channels 13. As materials for the bipolar plate 10, metals, electrically conductive plastics and composite materials and / or graphite are used, for example.

[0100] A plurality of fuel cells 2 are arranged in an aligned and stacked manner in a fuel cell unit 1 and / or a fuel cell group 1 and / or a fuel cell stack 1 ( Figure 4 and Figure 5 ).exist Figure 1 1 shows an exploded view of two fuel cells 2 arranged in an aligned stack. The seal 11 seals the gas spaces 31, 32 or the channels 12, 13 in a fluid-tight manner. Hydrogen H2 is stored as fuel in a compressed gas storage 21 ( Figure 1 ). The fuel is conducted from the compressed gas storage 21 via the high-pressure line 18 to the pressure reducer 20 in order to reduce the fuel pressure of about 10 bar to 20 bar in the medium-pressure line 17. The fuel is conducted from the medium-pressure line 17 to the injector 19. At the injector 19, the pressure of the fuel is reduced to an injection pressure of between 1 bar and 3 bar. The fuel is supplied from the injector 19 to the supply line 16 for fuel ( Figure 1 ) and feeds it from the supply line 16 into the channel 12 for fuel, which constitutes the channel structure 29 for fuel. As a result, the fuel flows through the gas space 31 for fuel. The gas space 31 for fuel is constituted by the channel 12 on the anode 7 and the GDL 9. After flowing through the channel 12, the fuel that is not consumed in the redox reaction at the anode 7 and the water that may come from the controlled humidification of the anode 7 are discharged from the fuel cell 2 via the discharge line 15.

[0101] A gas delivery device 22 (for example, configured as a blower 23 or a compressor 24) delivers air from the environment as an oxidant into a supply line 25 for the oxidant. The air is supplied from the supply line 25 into the channel 13 for the oxidant (the channel forms a channel structure 29 at the bipolar plate 10 for the oxidant), so that the oxidant flows through a gas space 32 for the oxidant. The gas space 32 for the oxidant is formed by the channel 13 at the cathode 8 and the GDL 9. After flowing through the channel 13 for the oxidant 32 or the gas space 32, the oxidant that is not consumed at the cathode 8 and the reaction water produced by the electrochemical redox reaction at the cathode 8 are discharged from the fuel cell 2 through the discharge line 26. The supply line 27 is used to supply the coolant into the channel 14 for the coolant, and the discharge line 28 is used to discharge the coolant guided through the channel 14. For the sake of simplicity, the supply and discharge lines 15, 16, 25, 26, 27, 28 are arranged in a manner similar to the embodiment of the present invention. Figure 1 In the end region near the channels 12, 13, 14, the stack is formed as a fuel cell unit 1, and aligned fluid openings 41 are formed on the sealing plate 39, as the bipolar plates 10 ( Figure 6 ) and an extension on the end region 40 of the membrane electrode assembly 6 (not shown). The fuel cell 2 and the components of the fuel cell 2 are of sheet-like design and span virtual planes 59 oriented substantially parallel to each other. Therefore, the aligned fluid openings 41 and the seals (not shown) between the fluid openings 41 in a direction perpendicular to the virtual plane 59 form a feed channel 42 for an oxidant, a discharge channel 43 for an oxidant, a feed channel 44 for a fuel, a discharge channel 45 for a fuel, a feed channel 46 for a coolant and a discharge channel 47 for a coolant. The feed and discharge lines 15, 16, 25, 26, 27, 28 outside the stack of the fuel cell unit 1 are designed as process fluid lines. The feed and discharge lines 15, 16, 25, 26, 27, 28 outside the stack of the fuel cell unit 1 lead to the feed and discharge channels 42, 43, 44, 45, 46, 47 inside the stack of the fuel cell unit 1. The fuel cell stack 1 together with the compressed gas storage device 21 and the gas delivery device 22 forms a fuel cell system 4 .

[0102] In the fuel cell unit 1, the fuel cells 2 are arranged between two clamping elements 33 as clamping plates 34. A first clamping plate 35 lies on the first fuel cell 2, while a second clamping plate 36 lies on the last fuel cell 2. The fuel cell unit 1 comprises approximately 200 to 400 fuel cells 2, which are arranged in a row for drawing reasons. Figure 4 and 5 Not all are shown. The clamping element 33 applies pressure to the fuel cell 2, that is, the first clamping plate 35 is pressed against the first fuel cell 2, and the second clamping plate 36 is pressed against the last fuel cell 2. In this way, the fuel cell stack 2 is tightened to ensure the tightness to the fuel, oxidant and coolant, especially based on the elastic seal 11, and furthermore to keep the contact resistance inside the fuel cell stack 1 as small as possible. In order to tighten the fuel cell 2 with the clamping element 33, four connecting devices 37 are constructed as bolts 38 on the fuel cell unit 1, which are loaded with tensile force. The four bolts 38 are connected to the tensioning plate 34.

[0103] exist Figure 6 2 shows a bipolar plate 10 of a fuel cell 2. The bipolar plate 10 includes channels 12, 13 and 14 as three separated channel structures 29. The channels 12, 13 and 14 are arranged in a Figure 6 2 is not shown separately, but only simplified as a layer of the channel structure 29. The fluid openings 41 on the bipolar plate 10 and the sealing plate 39 of the membrane electrode assembly 6 (not shown) are arranged in an aligned stacked manner inside the fuel cell unit 1, so as to form supply and discharge channels 42, 43, 44, 45, 46, 47. Here, a seal not shown is arranged between the sealing plates 39 to seal the supply and discharge channels 42, 43, 44, 45, 46, 47 formed by the fluid openings 41 in a fluid-tight manner. The bipolar plate 10 has a length 61 and a width 62. The channel 14 or the channel 14 as the channel structure 29 has a length 63, and the width of the channel structure 29 substantially corresponds to the width 62 of the bipolar plate 10, in particular with a deviation of less than 20% or 10%.

[0104] Since the bipolar plate 10 also separates the gas space 31 for the fuel from the gas space 32 for the oxidant in a fluid-tight manner and also seals the channels 14 for the coolant in a fluid-tight manner, the term "separator plate 51" can also be selected as a supplement to the bipolar plate 10 to separate or separate the process fluid in a fluid-tight manner. Therefore, the term "separator plate 51" is also included in the term "bipolar plate 10" and vice versa. The channels 12 for the fuel, the channels 13 for the oxidant and the channels 14 for the coolant of the fuel cell 2 are also constructed on the electrochemical cell 52, but have other functions.

[0105] In another embodiment not shown, the fuel cell unit 1 is constructed as an alkaline fuel cell unit 1. As a flowing electrolyte, potash lye is used as potassium hydroxide solution. The fuel cells 2 are arranged in a stack. Here, a monopolar battery structure or a bipolar battery structure can be constructed. The potassium hydroxide solution circulates between the anode and the cathode and transports away reaction water, heat and impurities (carbonates, dissolved gases). The fuel cell unit 1 can also be operated as a reversible fuel cell unit 1, that is, as an electrolysis cell unit 49.

[0106] The fuel cell unit 1 can also be used and operated as an electrolysis cell unit 49, that is, it is a reversible fuel cell unit 1. Some features are described below, which enable the fuel cell unit 1 to be operated as an electrolysis cell unit 49. For the electrolysis, a liquid electrolyte is used, namely highly diluted sulfuric acid with a concentration of approximately c(H2SO4)=1 mol / l. A sufficient concentration of hydronium ions H3O4 in the liquid electrolyte + Necessary for electrolysis.

[0107] In electrolysis, the following redox reactions take place:

[0108] cathode:

[0109] 4H3O + +4e - →2H2+4H2O

[0110] anode:

[0111] 6H2O→O2+4H3O + +4e -

[0112] The overall reaction equation at the cathode and anode is:

[0113] 2H2O→2H2+O2

[0114] The polarization of the electrodes 7, 8 is carried out by electrolysis when operating as an electrolytic cell unit 49, in contrast to when operating as a fuel cell unit 1 (not shown), so that in the channel 12 for the fuel (through which the liquid electrolyte is conducted), hydrogen H2 is formed as the second substance at the cathode, and the hydrogen H2 is absorbed by the liquid electrolyte and is transported together in a dissolved state. Similarly, the liquid electrolyte is conducted through the channel 13 for the oxidant, and at the anode, in or on the channel 13 for the oxidant oxygen O2, oxygen O2 is formed as the first material. When operating as an electrolytic cell unit 49, the fuel cell 2 of the fuel cell unit 1 acts as an electrolytic cell 50. Therefore, the fuel cell 2 and the electrolytic cell 50 form an electrochemical cell 52. The formed oxygen O2 is absorbed by the liquid electrolyte and is transported together in a dissolved state. The liquid electrolyte is stored in a storage container 54. In Figure 1 , for the sake of simplicity of the drawing, two storage containers 54 of a fuel cell system 4 are shown, which also functions as an electrolysis cell system 48. During operation, a three-way valve 55 on the feed line 16 for the fuel is switched to an electrolysis cell unit 49, so that instead of the fuel from the compressed gas storage 21, a liquid electrolyte is introduced from the storage container 54 into the feed line 16 for the fuel by means of a pump 56. During operation, a three-way valve 55 on the feed line 25 for the oxidant is switched to an electrolysis cell unit 49, so that instead of the oxidant being air from the gas supply device 22, a liquid electrolyte is introduced from the storage container 54 into the feed line 25 for the oxidant by means of a pump 56. Compared to a fuel cell unit 1 that can be operated only as a fuel cell unit 1, a fuel cell unit 1 that also functions as an electrolysis cell unit 49 optionally has modifications to the electrodes 7, 8 and the gas diffusion layer 9: for example, the gas diffusion layer 9 is not adsorptive, so that the liquid electrolyte can flow away easily and completely, or the gas diffusion layer 9 is not formed, or the gas diffusion layer 9 is a structure on the bipolar plate 10. The electrolysis cell unit 49 forms an electrochemical battery system 60 with a storage container 54, a pump 56 and separators 57, 58 and preferably a three-way valve 55.

[0115] A separator 57 for hydrogen is arranged on the discharge line 15 for fuel. The separator 57 separates hydrogen from the electrolyte containing hydrogen and the separated hydrogen is introduced into the compressed gas storage 21 by means of a compressor (not shown). Subsequently, the electrolyte discharged from the separator 57 for hydrogen is fed back into the storage container 54 for electrolyte by means of the line 21. A separator 58 for oxygen is arranged on the discharge line 26 for fuel. The separator 58 separates oxygen from the electrolyte containing oxygen and the separated oxygen is introduced into the compressed gas storage container (not shown) for oxygen by means of a compressor (not shown). The oxygen in the compressed gas storage container (not shown) for oxygen can be optionally used for the operation of the fuel cell unit 1 by conducting the oxygen into the supply line 25 for the oxidant by means of a line (not shown) when operating as a fuel cell unit 1. Subsequently, the electrolyte discharged from the separator 58 for oxygen is fed back into the storage container 54 for electrolyte by means of a line (not shown). The channels 12, 13 and the discharge and supply lines 15, 16, 25, 26 are designed as follows: after use as an electrolytic cell unit 49 and after the pump 56 is switched off, the liquid electrolyte flows completely back into the storage container 54 due to gravity. Optionally, after use as an electrolytic cell unit 49 and before use as a fuel cell unit 1, an inert gas is conveyed through the channels 12, 13 and the discharge and supply lines 15, 16, 25, 26 in order to completely remove the liquid electrolyte before the gaseous fuel and oxidant are passed through. Thus, the fuel cell 2 and the electrolytic cell 2 form an electrochemical cell 52. The fuel cell unit 1 and the electrolytic cell unit 49 thus form an electrochemical cell unit 53. Therefore, the channel 12 for the fuel and the channel for the oxidant thus form the channels 12, 13 for passing through the liquid electrolyte when operating as an electrolytic cell unit 49, and this applies similarly to the supply and discharge pipes 15, 16, 25, 26. For process engineering reasons, the electrolytic cell unit 49 usually does not require a channel 14 for passing through the coolant. In the electrochemical cell unit 49, the channel 12 for the fuel also forms the channel 12 for passing through the fuel and / or electrolyte, and the channel 13 for the oxidant also forms the channel 13 for passing through the fuel and / or electrolyte.

[0116] The bipolar plate 10 is manufactured by laser beam welding of a first plate 64 and a second plate 65 as monopolar plates 64, 65. To this end, for the corresponding bipolar plate 10, the first and second plates 64, 65 formed in a corrugated manner are placed one above the other and stacked, so that the inner sides 66 of the first and second plates 64, 65 are placed one above the other as a joining point on a strip-shaped contact area 68. Then, the virtual planes 59 opened by the disc-shaped first and second plates 64, 65 are oriented substantially parallel to each other. The first and second plates 64, 65 made of stainless steel each have an outer side 67 opposite to the inner side 66. After the two plates 64, 65 are arranged as the initial plates 64, 65 for manufacturing the bipolar plate 10, a strip-shaped channel 14 for a coolant is constructed between the inner sides 66 of the first and second plates 64, 65 outside the strip-shaped contact area 68, and the strip-shaped channel constructs an intermediate space 79. The geometry of the first and second plates 64 , 65 provided with a large number of corrugations results in a large number of channels 14 being formed between the contact areas 68 .

[0117] The first and second plates 64, 65 as monopolar plates 64, 65 are connected to each other in a material-locking manner by means of laser beam welding to form a bipolar plate 10, so that a welded connection 69 is produced between the first and second plates 64, 65 as a plurality of weld seams 70. The laser system comprises a laser 73 ( Fig. 9 ). The laser 73 emits a laser beam 74 as a focused electromagnetic wave. The laser beam 74 is emitted onto the outer side 67 of the second plate 65 by means of an optical system 75, so that the laser beam 74 hits the outer side 67 of the second plate 65 at an intersection point having a diameter of about 70 μm. A movement unit not shown either moves the laser beam 74 over the outer side 67 of the second plate 65 and / or moves the first and second plates 64, 65 under the laser beam 74, so that a relative feed direction 78 of the laser beam 74 relative to the first and second plates 64, 65 is generated. The laser beam 74 is absorbed by the outer side 67 of the second plate 65, so that during the welding process, the temperature of the stainless steel of the first and second plates 64, 65 rises to above the melting temperature, and thus during the welding process, a liquid melt 77 is formed, which then cools again and solidifies to form a welded connection 69 as a weld seam 70. In addition, optionally, the keyhole 76 is configured as a steam capillary in the liquid melt 76 in the beam direction of the laser beam 74, and the steam capillary is configured as a tubular hollow space formed by metal vapor and / or partially ionized metal vapor under the laser beam 74, and the laser beam moves relative to the first and second plates 64, 65 along the feed direction 78. According to the depth of the optional keyhole 76 and the liquid melt 77, the through-weld portion 71 or the weld-in portion 72 ( Figure 8 ). The width B of the weld 70 ( Figure 8 ) is substantially equivalent to the diameter of the laser beam 74 or the intersection point.

[0118] The weld seam 70 extends completely through the channel 14 for the coolant at the edge region near the longitudinal side of the channel structure 29 (at Figure 6 The channel structure 29 is designed as a continuous straight line and has one or more interruptions (in the edge region near the broad side of the channel structure 29) starting from the channel 14 for the coolant toward the feed channel. Figure 6 The bipolar plate 10 is manufactured in a manner that is not shown in the figure as a dashed straight line, so that the coolant can be introduced from the supply channel 46 for the coolant into the channel structure 29 and can be discharged from the channel structure 29 into the outlet channel 47 for the coolant. For this purpose, a structure not shown is formed in the bipolar plate 10, which is used to guide the coolant from the supply channel 46 for the coolant into the channel structure 29 and from the channel structure 29 into the outlet channel 47 for the coolant. The fully through weld seam 70 is additionally (not shown in full) preferably circumferentially configured so that the intermediate space 79 is sealed from the environment. Therefore, the weld seam 70 (not shown in full) also acts as a seal, and the channel 14 for the coolant is sealed from the environment outside the channel 14 to the outside. Optionally, a further, segmented weld seam 70 can be produced at the contact region 68 which has no sealing function for the coolant to the environment or to the outside and serves only to connect the two plates 64 , 65 in a materially bonded manner and optionally also serves in addition to sealing between the two channels 14 for the coolant.

[0119] To manufacture the bipolar plate 10, first a first plate 64 and a second plate 65 made of stainless steel are provided. The first and second plates 64, 65 have a thickness of about 70 μm. A horizontal and flat support plate 80 ( Fig.10 ) has an elastic sealing layer 81 made of rubber on the upper side. A plurality of recesses are formed in the elastic sealing layer 81, each of which forms a processing intermediate subspace 83 after the first plate 64 is placed on the elastic sealing layer 81. After the first plate 64 is placed on the elastic sealing layer 81 of the support plate 80, a vacuum is generated in the processing intermediate subspace 83 by means of a vacuum pump (not shown). For this purpose, a suction channel 88 ( Fig.10). The suction channel 88 is connected to all the process intermediate subspaces 83 in a fluid-conducting manner, and the process intermediate subspaces 84 constitute the process intermediate space 82 as a whole. On the one hand, the negative pressure in the process intermediate space 82 between the outer side 67 of the first plate 64 and the upper side of the support plate 80 is small and is located in the range of about 800 mbar, that is, the difference between the negative pressure and the ambient pressure is about 200 mbar. Due to this negative pressure in the process intermediate space 82, the first plate 64 lies flat on the upper side of the support plate 80 with the process additional pressure. Therefore, the outer side 67 of the first plate 64 lies flat on the support plate 80 with a pressure (which is composed of the sum of the process additional pressure and gravity). As a result, a reliable form-locking and / or force-locking connection is established between the lower outer side 67 of the first plate 64 and the upper side of the support plate 80, so that the first plate 64 is precisely and immovably positioned relative to the support plate 80 and the weld 80 can therefore be precisely produced at the correct position.

[0120] Next, the second plate 65 is placed onto the first plate 64 in an accurately positioned manner. Next, a sealing device 84 is arranged on the outer edge 87 of the two plates 64, 65 arranged one above the other. In addition, all fluid openings 41 are sealed with the sealing device 84, except for the outlet channel 47 for the coolant. Next, a large negative pressure is generated at the outlet channel 47 for the coolant (which is formed by two aligned fluid openings 41 of the first and second plates 64, 65 on the sealing plate 39) by means of a vacuum pump (not shown). For this purpose, the vacuum pump is connected to a negative pressure hose (not shown) and the negative pressure hose is connected to the lower side of the first plate 64 as the outer side 67 for fluid conduction. The outer side 67 of the second plate 65 as the upper side is closed in a fluid-tight manner by means of the sealing device 84. Since the outer edge 87 and the remaining fluid openings 41 are sealed, a strong negative pressure of about 400 mbar is generated in the intermediate space 79, which is essentially formed by the channel 14 for the coolant. The pressure difference between the ambient pressure and the negative pressure in the intermediate space 79 is therefore about 600 mbar. The ambient pressure of the air therefore exerts a substantially constant contact force on the outer side 67 of the second plate 65. This contact force is substantially constant per unit area, so that the outer side 67 of the second plate 65 is advantageously loaded with a constant pressure. The negative pressure in the intermediate space 82 is less than the negative pressure in the intermediate space 79, so that, with respect to the negative pressure in the intermediate space 82, a smaller contact force per unit area acts on the lower outer side 67 of the first plate 64 than on the upper outer side 67 of the second plate 65, and the resulting difference is applied as a pressure by the first plate 64 to the support plate 80, without taking into account the force of gravity. The contact force is therefore a pressure. Thus, in the contact region 68, the inner sides 66 of the first and second plates 64, 65 are placed one above the other with additional pressures and, due to the magnitude of these additional pressures, a technical zero gap of less than 20 μm is substantially present in the contact region 68. Subsequently, the weld seam 70 is produced by a laser 73. In addition, the first plate 64 lies mechanically on the support plate 80 with a contact force.

[0121] Optionally, before the negative pressure is generated in the intermediate space 79, the intermediate space 79 is filled with a protective gas, in particular nitrogen or an inert gas, and preferably, the protective gas is continuously guided through the intermediate space 79 during the generation and maintenance of the negative pressure. This is implemented by, for example, introducing additional traces of protective gas through the supply channel 46 during the suction at the outlet channel 47 for the coolant with a vacuum pump. Since the sealing of the outer edge 87 and the remaining fluid openings 41 cannot be achieved technically in a completely sealed manner, it is necessary to continuously introduce protective gas into the intermediate space 79 during the maintenance of the negative pressure so that the protective gas is continuously present in the intermediate space 79 during welding. In addition, the protective gas is continuously fed in on the outside at the intersection point on the outer side 67 of the second plate 65, that is, at the location where the laser beam 74 strikes. Thus, the weld seam 70 can be produced completely by flushing with protective gas.

[0122] The sealing means 84 for sealing the intermediate space 79 is designed as a film 85 made of plastic. For this purpose, the film 85 wound on a roller 86 is unwound from the roller 86 by means of a robot 89 or manually and placed on the outer side 67 of the first and / or second plate 64, 65. The film 85 is thus placed completely around the outer edge 87 of the first and / or second plate 64, 65 and additionally on all fluid openings 41 except for the fluid opening 41 (as a discharge channel 47 for the coolant) in order to generate a negative pressure in the intermediate space 79. The film 85 is an adhesive film 85, so that the adhesive film 85 adheres to the outer side 67 by means of adhesive forces without adhesive. The thickness or wall thickness of the film 85 made of plastic is designed sufficiently so that the film reliably seals the intermediate space 79 in a fluid-tight manner relative to the surroundings during the negative pressure in the intermediate space 79, that is, no damage to the film 85 occurs during the maintenance of the negative pressure in the intermediate space 79. For this purpose, the film 85 has a thickness of approximately 0.5 mm.

[0123] For placing the film 85 on the outer sides 67 of the first and second plates 64, 65, Fig.11 A first embodiment is shown in FIG. Fig.11 In the first embodiment shown in FIG. , the entire outer side 67 is covered by the film 85 . Fig.12 In the second embodiment shown in FIG. 8 , not the entire outer side 67 is covered by the film 85 . The outer side 67 of the first plate 64 is excluded from being covered with the film 85 in the region of the channels 14 for the coolant. Fig.13 In the third exemplary embodiment shown in FIG, the film 85 is placed only on the areas of the outer sides 67 of the first and second plates 64, 65 that are necessary for sealing the intermediate space 79. These are the outer circumferential edge 87 and the fluid opening 41 on the first and second plates 64, 65.

[0124] The film 85 is designed to be light-transmissive. Therefore, the film 85 can also be placed on the area of ​​the outer side 67 of the second plate 65 at which the welded connection 69 is produced by means of the laser beam 74. The laser beam 74 directed at the film 85 passes through the film 85 and dissolves the film 85 due to the high temperature, that is, the film 85 melts and / or evaporates. During the application of the film 85 to the outer side 67 of the first and second plates 64, 65, this simplifies the processing step, because it is not necessary to ensure that no film 85 is placed on the area of ​​the outer side 67 of the second plate 65 that is impinged by the laser beam 74.

[0125] The film 85 can be manually or by Fig.14 The robot 89 shown in the figure is placed on the outer side 67 of the first and second plates 64, 65. In addition, a camera is arranged on the robot 89 or on another robot 89 not shown. The color of the film 85 is clearly different from the color of the first and second plates 64, 65, so that the position (actual position) of the film 85 on the outer side 67 of the first and second plates 64, 65 can be detected by the camera and corresponding image processing software in a computer not shown. Therefore, during and after the film 85 is placed on the outer side 67 of the first and second plates 64, 65, it can be continuously monitored and checked whether the film 85 is applied to the required area (set position) of the outer side 67 as required. If defects occur, they can be automatically repaired by the robot 89 and covered with the film 85.

[0126] After the production of the welded connection 69, the film 85 is no longer used, that is, it is a disposable item. However, for reasons of processing technology, it is necessary that the film 85 is completely removed from the outer side 67 after the production of the welded connection 69. The removal of the film 85 from the outer side 67 is carried out mechanically and / or pneumatically and / or thermally. In the case of mechanical removal of the film 85, the film is removed, for example, by a rotating brush on the arm of a robot 89. In the case of pneumatic removal of the film 85, the film is removed, for example, by compressed air from a nozzle fastened to the arm of the robot 89, with a high pressure of, for example, 40 bar. In the case of thermal removal of the film 85 from the outer side 67 of the first and / or second plate 64, 65, the heating and removal of the film 85 is carried out locally, for example, by a radiator or a gas flame. Preferably, after the thermal removal of the film 85 with compressed air, the combustion products and residual products of the film 85 are removed.

[0127] Optionally, the complete removal of the film 85 from the outer side 67 of the first and / or second plate 64, 65 can be additionally checked with a camera and image processing software. As long as the film 85 is not removed on individual areas, the areas identified with the camera and image processing software with the film 85 still present can be additionally processed.

[0128] Overall, the method for manufacturing a bipolar plate 10 according to the present invention, the method for manufacturing an electrochemical cell unit 53 according to the present invention, and the electrochemical cell unit 52 according to the present invention have important advantages. The necessary high contact force on the contact area 68 is basically generated by means of the negative pressure in the intermediate space 79. Therefore, in an advantageous manner, it is not necessary to set a mechanical clamping device on the area above the second plate 65. Therefore, the laser beam 74 can be guided on the outer side 67 of the second plate 65 without hindering and activating and deactivating the mechanical clamping device. Therefore, a large number of welds 70 between the first plate 64 and the second plate 65 can be manufactured in a very short time (only limited by the speed for manufacturing the weld 70). The sealing device 84 as a film 85 can be simply arranged on the outer side 67 of the first and second plates 64, 65, so that low costs are generated for the sealing device 84 under high reliability. The film 85 as a disposable is cheap in production and use, and due to the automated method of applying the film 85 with a robot 89, low costs are generated for the application of the film 85. Therefore, as a disposable, cleaning of the sealing means 84 as a film 85 after the production of the welded connection 69, for example, cleaning of the metal deposited at points due to the production of the welded connection 69, is not necessary. The costs for the production of the bipolar plate 10 are therefore low, since on the one hand no mechanical hold-down device has to be maintained and additionally the welding process for producing the weld seam 70 can also be carried out in a very short time and therefore also very cheaply.

Claims

1. A method for producing a bipolar plate (10, 51) of an electrochemical cell unit (53), the electrochemical cell unit being used as a fuel cell unit (1) for converting electrochemical energy into electrical energy and / or as an electrolysis cell unit (49) for converting electrical energy into electrochemical energy, the electrochemical cell unit having stacked electrochemical cells (52), the method comprising the following steps: - providing a first plate (64) and a second plate (65), - stacking the first plate (64) and the second plate (65) one above the other so that the inner sides (66) of the first and second plates (64, 65) are arranged one above the other and an intermediate space (79) is formed between the first and second plates (64, 65), - sealing the intermediate space (79) in a fluid-tight manner relative to the surroundings by means of at least one sealing means (84) in order to prevent a fluid from flowing from the surroundings into the inner space (79), - applying a contact force to the first and / or second plate (64, 65), so that, as a result of the applied contact force, the inner sides (66) of the first and second plates (64, 65) are arranged one above the other in a contact area (68) due to the applied contact force and the additional pressure, in that the intermediate space (79) is loaded with a negative pressure relative to the ambient pressure, and, due to the negative pressure in the intermediate space (79), the contact force applied by the ambient pressure to the first and / or second plate (64, 65) is applied to the first and / or second plate (64, 65), - producing a welded connection (69) between said first and second plates (64, 65), It is characterized in that The interior space (79) is sealed by at least one film (85) as the at least one sealing means (84).

2. The method according to claim 1, characterized in that The negative pressure in the intermediate space (79) is at least 100 mbar, 300 mbar or 500 mbar lower than the ambient pressure.

3. The method according to claim 1 or 2, characterized in that: First, the first plate (64) is placed on the support plate (80), and then the second plate (65) is placed on the first plate (64).

4. The method according to any one or more of the preceding claims, characterized in that After the second plate (65) has been placed on the first plate (64), the intermediate space (79) between the first and second plates (64, 65) is sealed with respect to the environment by means of the at least one film (85).

5. The method according to any one or more of the preceding claims, characterized in that The at least one film (85) seals an intermediate space (79) in the outer edges (87) of the first and second plates (64, 65) arranged one above the other.

6. The method according to any one or more of the preceding claims, characterized in that The at least one film (85) seals an intermediate space (79) in a fluid opening (41) leading to a first and a second plate (64, 65) arranged one above the other.

7. The method according to any one or more of the preceding claims, characterized in that The at least one film (85) is placed on at least one outer side (67) of the first and / or second plates (64, 65) stacked one above the other.

8. The method according to any one or more of the preceding claims, characterized in that The at least one film (85) is placed at least 30%, 50%, 70% or 90%, in particular completely, on the surface of at least one outer side (67) of the first and / or second plates (64, 65) stacked one above the other and is covered by the at least one film (85).

9. The method according to any one or more of the preceding claims, characterized in that The at least one film (85) is placed on at least one outer side (67) of the first and / or second plates (64, 65) stacked one above the other by unrolling the at least one film (85) from a roller (86) and then placing it on at least one outer side (67) of the first and / or second plates (64, 65) stacked one above the other.

10. The method according to any one or more of the preceding claims, characterized in that The welded connection (69) is produced by means of laser welding.

11. The method according to claim 8, characterized in that The at least one film (85) is placed on the following area of ​​at least one outer side (67) of the first and / or second plate (64, 65): the laser beam (74) emitted by the laser (73) is transferred to this area as a crossover point to produce the welding connection (69), so that during the production of the welding connection (69) by the laser beam (74), the at least one film (85) is penetrated and / or dissolved, in particular melted and / or evaporated by the laser beam (74).

12. The method according to any one or more of the preceding claims, characterized in that After the welded connection (69) has been produced, the at least one film (85) is removed, in particular completely removed, from at least one outer side (67) of the first and / or second plates (64, 65) stacked one above the other.

13. The method according to any one or more of the preceding claims, characterized in that During the production of the welded connection (69), the intermediate space (79) is in particular continuously subjected to a negative pressure relative to the ambient pressure.

14. A method for producing an electrochemical cell unit (53), the electrochemical cell unit being used as a fuel cell unit (1) for converting electrochemical energy into electrical energy and / or as an electrolysis cell unit (49) for converting electrical energy into electrochemical energy, the electrochemical cell unit having stacked electrochemical cells (52), the method comprising the following steps: - providing the layered components (5, 6, 7, 8, 9, 10, 30, 51) of the electrochemical cell (52), namely preferably a proton exchange membrane (5), an anode (7), a cathode (8), preferably a gas diffusion layer (9) and a bipolar plate (10, 51), - stacking the layered components (5, 6, 7, 8, 9, 10, 30, 51) into electrochemical cells (52) and stacking into a stack of the electrochemical cell units (53), It is characterized in that The bipolar plate (10, 51) is provided by carrying out a method according to one or more of the preceding claims.

15. An electrochemical cell unit (53) used as a fuel cell unit (2) for converting electrochemical energy into electrical energy and / or used as an electrolysis cell unit (49) for converting electrical energy into electrochemical energy, the electrochemical cell unit comprising: - electrochemical cells (52) arranged in a stack, and the electrochemical cells (51) each comprise layered components (5, 6, 7, 8, 9, 10, 51) arranged in a stack, and - the components (5, 6, 7, 8, 9, 10, 51) of the electrochemical cell (52) are preferably a proton exchange membrane (5), an anode (7), a cathode (8), preferably a gas diffusion layer (9) and a bipolar plate (10, 51), wherein the respective bipolar plate (10, 51) is constructed from a first and a second plate (64, 65), It is characterized in that The electrochemical cell (53) is produced by means of the method according to claim 14, and / or The first and / or second plate (64, 65) has no clamping markings.

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