Method for producing a bipolar plate

Abstract

The invention relates to a method for producing a bipolar plate (10, 51) for an electrochemical cell (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 comprises the following steps: providing a first plate (64) and a second plate (65), stacking the first plate (64) and the second plate (65) on each other in such a way that the inner sides (66) of the first and second plates (64, 65) lie on each other, applying a contact force to the first and second plates (64, 65) by means of a negative pressure in a negative pressure chamber (104) compared to ambient pressure, according to the invention, the first and second plate (64, 65) are arranged in such a way that the inner sides (66) of the first and second plate (64, 65) lie on each other on the contact region (68) by means of an additional pressure due to the applied contact force, which is generated by the contact force applied from the ambient pressure, at least one welded connection (69) is produced between the first plate (64) and the second plate (65) by means of a laser beam (74), and the first and / or second plate (64, 65) is welded to the first and / or second plate (64, 65) between the first and / or second plate (64, 65) by means of the laser beam (74). A connection channel (89) for a process fluid is formed on the first and / or second plate (64, 65), which connection channel opens into a fluid opening (41) on the bipolar plate (10, 51) and into a channel (12, 13, 14) for a process fluid on the bipolar plate (10, 51), the connection opening (93) being machined into the first and / or second plate (64, 65), the first plate and / or the second plate (64, 65) has a connection opening (93) which connects the connection channel (89) to a channel (12, 13, 14) for a process fluid on the bipolar plate (10, 51), the connection opening (93) being machined into the first plate and / or the second plate (64, 65) by means of a laser beam (74).

Description

Technical Field

[0001] The invention relates to a method for producing a bipolar plate for 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 are galvanic cells that 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 various stationary and mobile applications, for example in premises not connected to the power grid or in motor vehicles, rail transport, aviation, aerospace and shipping. In a fuel cell unit, a plurality of fuel cells are arranged in a stack as a stack.

[0003] In a fuel cell unit, a plurality of fuel cells are arranged in a fuel cell stack. In each fuel cell, there is a gas chamber for the oxidant, i.e., a flow space for guiding the oxidant, for example, air containing oxygen from the surrounding environment. The gas chamber for the oxidant is formed by the channels on the bipolar plates and the gas diffusion layer for the cathode. Therefore, the channels are formed by the corresponding channel structure of the bipolar plates and the oxidant, i.e., oxygen, passes through the gas diffusion layer to the cathode of the fuel cell. In a similar manner, there is a gas chamber for the fuel.

[0004] Electrolyzer units consisting of electrolyzers arranged in a stack are used, for example, similarly to fuel cell units, for electrolytically obtaining hydrogen and oxygen from water. In addition, fuel cell units are known which can be operated as reversible fuel cell units and thus as electrolyzer units. Fuel cell units and electrolyzer units form electrochemical cell units. Fuel cells and electrolyzers form electrochemical cells.

[0005] For the production and assembly of electrochemical cells, in particular fuel cells, it is necessary to arrange the components of the fuel cell in an aligned stack. The sheet-like components of the fuel cell are the proton exchange membrane, the anode, the cathode, the gas diffusion layer and the bipolar plates. The electrically conductive bipolar plates are an important component of the stack. These bipolar plates act as current collectors for discharging water and for guiding the reaction gases and liquid or gaseous coolants through the flow spaces, in particular the channels or channel structures. The bipolar plates rest on the contact surfaces on the gas diffusion layer.

[0006] Bipolar plates are usually composed of two or three plates made of stainless steel. When manufacturing bipolar plates, the first and second plates are placed on each other, and then the plates are welded to each other to form a weld. The weld not only has the function of connecting the plate materials to each other in a locking and conductive manner, but also serves to seal the channels for coolant formed between each two plates in a fluid-tight manner. For each bipolar plate, the first and second plates with corresponding corrugated shapes are placed on each other and stacked so that the inner sides of the first and second plates are located on each other on the strip-shaped contact area, and there is a gap with thickness between the inner sides on the strip-shaped contact area. For a reliable and fluid-tight construction of the weld, a small gap thickness is required, that is, the gap forms a technical zero gap of less than 20 μm. In addition, the first and second plates must be stacked on each other with the correct lateral relative position as the target 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 produce a weld seam between the first plate and the second plate without interruption, so that the fluid passes horizontally in the direction of the plane of the first and second plates at the leakage between the first and second plates. In order to avoid large gaps in the contact area, i.e. in order to form a technical zero gap, a contact force is applied to the first and second plates by means of a mechanical clamping device during the welding process, so that the inner sides of the first plate and the second plate are located on each other in the contact area due to the applied contact force with additional pressure. Due to the additional pressure, a zero gap is formed in the contact area. However, rod-shaped or pliers-shaped mechanical clamping devices hinder the formation of welds by means of laser welding, because the laser beam is blocked by the mechanical clamping device, so that the clamping device must be continuously loosened during laser welding, i.e. deactivated and another one placed on the plate, i.e. activated. Therefore, it is necessary to continuously replace the clamping device, such as a clamp, during welding, which is time-consuming.

[0008] In addition, it is known to utilize the negative pressure in the negative pressure chamber to apply the contact force from the ambient pressure to the first and second plates, so that there is no need to continuously replace the rod-shaped or clamp-shaped clamping device. The negative pressure chamber can be formed, for example, by the intermediate space between the first and second plates or the negative pressure chamber is limited by the lower side of the sheet-like mechanical clamping device and the upper side of the support plate for the first plate below. The larger ambient pressure acts on the upper side of the mechanical clamping device and forms a contact element on the mechanical clamping device, by means of which the contact force is applied to the first and / or second plate. The sheet-like mechanical clamping device is annularly configured with a surrounding contact protrusion as a contact element and does not hinder the guidance of the laser beam due to its geometric structure.

[0009] A connecting channel is formed in the bipolar plate for connecting the fluid openings as supply and discharge channels for process fluid fuel, oxidant and coolant to the transverse distribution channel and / or the channel for process fluid in a fluid-conductive manner. The connecting channel leads to the transverse distribution channel and / or to the channel for process fluid at the connecting opening. In order to manufacture the bipolar plate, before the first plate and the second plate are stacked on each other and the welded connection between the first and second plates is manufactured, the connecting opening is mechanically punched into the first plate and / or the second plate by means of a punch as a first plate and / or a second plate is provided. The disadvantage of this mechanical processing of the connecting opening is that it is expensive and has low manufacturing accuracy. In addition, changes in the geometric structure of the connecting opening require costly replacement of the stamping tool.

[0010] DE 10 2021 206 581 A1 shows a method for producing a bipolar plate for an electrochemical cell, comprising the following steps: providing a first and a second plate, stacking the first and the second plate on one another so that the inner sides of the first and second plates are located on one another and an intermediate space is formed between the first and the second plate, applying a contact force to the first and the second plate so that, as a result of the applied contact force, the inner sides of the first and the second plate are located on one another at the contact area with additional pressure due to the applied contact force, and a welded connection is produced between the first and the second plates, wherein the intermediate space as a negative pressure chamber is loaded with a negative pressure pressure compared to the ambient pressure, so that the contact force from the ambient pressure applied to the first and / or second plate is applied to the first and / or second plate. Summary of the invention

[0011] The method according to the invention for producing a bipolar plate of an electrochemical cell unit (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 has stacked electrochemical cells) comprises the following steps: providing a first plate and a second plate, stacking the first plate and the second plate on each other so that the inner sides of the first and second plates lie on each other, applying a contact force to the first and second plates by means of a negative pressure in a negative pressure chamber compared to the ambient pressure, so that the inner sides of the first and second plates lie on each other at the contact area with an additional pressure due to the applied contact force generated by the contact force applied from the ambient pressure, producing at least one welded connection between the first and second plates by means of a laser beam, forming a connecting channel for a process fluid on the first and / or second plate, the connecting channel leading to a fluid opening on the bipolar plate and to a channel for a process fluid on the bipolar plate, machining a connecting opening into the first and / or second plate, the connecting opening connecting the connecting channel to the channel for a process fluid on the bipolar plate, wherein the connecting opening is machined into the first and / or second plate by means of a laser beam. The connecting channel is preferably formed between the first and second plates as an intermediate space and / or on the outer side of the first plate and / or on the outer side of the second plate.Preferably, the process fluid is a fuel and / or an oxidant and / or a coolant and / or an electrolyte for the anode and / or an electrolyte for the cathode.

[0012] In another embodiment, the production of the welded connection between the first and second plates is first carried out and subsequently the connection opening is processed into the first and / or second plate by means of a laser beam. Preferably, the vacuum chamber is not charged with negative pressure during the processing of the connection opening by means of a laser beam, since the first and second plates are connected to one another by means of a welded connection during the processing of the connection opening. Preferably, the vacuum chamber is charged with negative pressure during the processing of the connection opening by means of a laser beam.

[0013] In a supplementary embodiment, firstly the contact force is applied to the first and second plates by means of a negative pressure in the negative pressure chamber compared to the ambient pressure, and subsequently, simultaneously, the welded connection is produced between the first and second plates.

[0014] In an additional variant, the connecting channel geometry is introduced into the first and / or second plate by means of deformation, in particular embossing, so that after the first and second plates are stacked on top of each other, the connecting channel is formed as an intermediate space between the first and second plates due to the connecting channel geometry. As a method step for providing the first and / or second plate, the connecting channel geometry is introduced, for example, by means of a press.

[0015] Preferably, the connecting channel geometry is processed into the first and / or second plate before the first and second plates are stacked on top of each other.

[0016] In another embodiment, the correct position of the focus of the laser beam generated by the laser system for machining the connection opening on the first and / or second plate is detected optically, in particular by means of a laser scanner and / or by means of a camera and an image processing system. The laser beam is preferably aligned with the optically determined correct position of the focus. Data about the geometry of the first and / or second plate are additionally used to determine the optically correct position of the focus.

[0017] In a supplementary configuration, at least one connecting opening for each connecting channel is processed into the first plate and / or the second plate by means of a laser beam, in that the first and / or the second plate is separated at at least one flap geometry by means of a laser beam and at least a partial area of ​​the first and / or the second plate is subsequently moved, in particular pivoted, as at least one flap.

[0018] The movement of the at least one flap is expediently caused by an inherent stress or a prestress of the first and / or second plate.

[0019] In an additional embodiment, in particular before stacking the first and second plates, an inherent stress or a prestress of the first and / or second plate is introduced into the first and / or second plate by means of a pressing process.

[0020] In another variant, at least one connecting opening for each connecting channel is processed into the first and / or second plate by means of a laser beam, in that the first and / or second plate is separated at at least one notch geometry by means of a laser beam and at least a portion of the first and / or second plate is subsequently removed from the remaining first and / or second plate.

[0021] In particular, at least one connecting opening for each connecting channel is processed into the first and / or second plate by means of a laser beam in that the first and / or second plate is separated at least partially, preferably at least 90%, 95%, 98% or 99%, in particular completely, as a melt lip on an edge of the first and / or second plate that delimits the at least one connecting opening. In the case of substantially complete deposition or relocation, no deposition of molten material outside the melt lip occurs on the remaining bipolar plates, for example as splashes.

[0022] In an additional embodiment, at least one connecting opening is designed to be slot-shaped and / or circular and / or T-shaped.

[0023] Preferably, the laser beam used for processing the connecting opening has a power of between 200 W and 800 W, in particular between 400 W and 600 W, and / or the laser beam used for processing the connecting opening has a diameter of between 100 μm and 500 μm, in particular between 200 μm and 400 μm, and / or the relative speed between the first and / or the second plate and the focus of the laser beam used for processing the connecting opening is between 300 mm / s and 700 mm / s, in particular between 400 mm / s and 600 mm / s, and / or the thickness of the first plate and / or the second plate at the focus of the laser beam used for processing the connecting opening is between 25 μm and 125 μm, in particular between 50 μm and 100 μm.

[0024] The method according to the invention for producing an electrochemical cell unit (which is used as a fuel cell unit for converting electrochemical energy into electrical energy and / or as an electrolyzer unit for converting electrical energy into electrochemical energy, having stacked electrochemical cells) has the following steps: providing layered components of the electrochemical cell, namely preferably a proton exchange membrane, an anode, a cathode, a gas diffusion layer and a bipolar plate, stacking the layered components into a stack of electrochemical cells and electrochemical cell units, wherein the bipolar plate is provided by carrying out the method described in the present patent application.

[0025] According to the invention, the electrochemical cell unit, as a fuel cell unit for converting electrochemical energy into electrical energy and / or as an electrolyzer unit for converting electrical energy into electrochemical energy, comprises electrochemical cells arranged in a stack, and the electrochemical cells each comprise layered components arranged in a stack, and the components of the electrochemical cells are preferably a proton exchange membrane, an anode, a cathode, a gas diffusion layer and a bipolar plate, wherein on the bipolar plate, a connecting channel for a process fluid is formed between a first plate and a second plate, and the connecting channel leads into a fluid opening on the bipolar plate and into a channel for the process fluid on the bipolar plate, and a connecting opening is formed in the first and / or second plate of the bipolar plate, which connects the connecting channel to the channel for the process fluid on the bipolar plate, wherein the electrochemical cell is manufactured by means of the method described in the present patent application, and / or on the first plate and / or the second plate, the connecting opening is delimited by a melt lip, in particular, the melt lip has a greater thickness than the first and / or second plate outside the melt lip and / or the melt lip is formed from melted material of the first and / or second plate. Preferably, the thickness of the melt lip is at least 10%, 20% or 30% greater than the thickness of the first and / or second plate outside, on or near the melt lip.

[0026] In a further variant, the connecting channels each have a first end formed by at least one additional fluid opening and a second end formed by at least one connecting opening, wherein the additional fluid opening opens into the fluid opening and the connecting opening opens into the transverse distribution channel and / or into the channel for the process fluid.

[0027] In another variant, an intermediate space is formed between the first and second plates, in particular as a result of stacking the first and second plates on one another such that the inner sides of the first and second plates lie on one another.

[0028] In another embodiment, at least 2, 3, 5, 10 or 10 connecting openings are formed on each connecting channel.

[0029] In another variant, the contact force is applied to the first and / or second plate by means of the negative pressure in the negative pressure chamber and the ambient pressure acting directly and / or indirectly on the at least one mechanical clamping device. Due to the geometrical structure of the at least one clamping device, it is not necessary to replace the at least one clamping device during the production of the welded connection, because the at least one clamping device is constructed essentially two-dimensionally and / or lamellarly, so that the extension of the at least one clamping device in the direction of the virtual plane unfolded by the at least one mechanical clamping device is significantly greater than the extension perpendicular to the virtual plane, in particular at least 2, 5, 10 or 20 times greater. Preferably, the at least one mechanical clamping device and / or the virtual plane unfolded by the at least one mechanical clamping device are oriented essentially parallel to the first and / or second plate and / or to the virtual plane unfolded by the first and / or second plate during the production of the welded connection and / or during the processing of the connection opening, in particular with a deviation of less than 30°, 20° or 10°. Preferably, the contact force is essentially constant during the production of the welded connection, preferably with a deviation of less than 30%, 20% or 10%.

[0030] In a supplementary configuration, the negative pressure chamber is limited by at least one mechanical clamping device, so that due to the negative pressure in the negative pressure chamber and the ambient pressure, negative pressure is indirectly and / or directly applied to the clamping device, and the negative pressure is transmitted by at least one mechanical clamping device at least partially, in particular completely, as at least one contact force to the first and / or second plate.

[0031] In an additional variant, the vacuum chamber is delimited by an upper side of the support plate, which is acted upon by vacuum, and by at least one lower side of the at least one mechanical hold-down device, which is acted upon by vacuum.

[0032] In another embodiment, the intermediate space between the first plate and the second plate is loaded with a negative pressure compared to the ambient pressure as a negative pressure chamber, so that the contact force from the ambient pressure applied to the first and / or second plate is applied to the first and / or second plate. Preferably, the disclosure of DE 10 2021 206 581 A1 is accepted in the present patent application.

[0033] In a supplementary embodiment, the negative pressure in the negative pressure chamber is 100 mbar, 300 mbar or 500 mbar less than the ambient pressure. The ambient pressure is generally about 1000 mbar, so that when the negative pressure in the intermediate space is 300 mbar, a pressure difference of 700 mbar occurs between the intermediate space and the surrounding environment. Therefore, when the negative pressure chamber is configured as an intermediate space, 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 the pressure difference, the pressure on the outer side is greater than the pressure on the inner side and thus as a result of the total force generated, the first plate and the second plate are located on each other with additional pressure, without taking into account the gravity.

[0034] In a supplementary variant, the first plate is first placed on the support plate and the second plate is subsequently placed on the first plate.

[0035] Preferably, the intermediate space between the first and second pane is sealed against the surroundings by means of at least one sealing agent, in particular after the second pane has been placed on the first pane.

[0036] 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 technical zero gap over the contact area.

[0037] In a supplementary variant, the welded connection is produced by means of laser welding.

[0038] In an additional embodiment, the negative pressure chamber is charged with a negative pressure compared to the ambient pressure, in particular continuously, during the production of the welded connection. Preferably, the negative pressure in the negative pressure chamber remains continuous and substantially constant during the entire production of the welded connection. Substantially preferably means with a deviation of less than 30%, 20% or 10%.

[0039] In a supplementary embodiment, when the laser beam impinges on the focal point on the outer side of the first plate, a protective gas is directed to the focal point, in particular by means of a movable nozzle.

[0040] Preferably, a seal is formed by at least one weld seam produced by means of laser beam welding for sealing at least one channel for the coolant to the outside between the first and the second plate.

[0041] 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.

[0042] In a supplementary variant, the first and second plates are at least partially, in particular completely, made of metal, in particular stainless steel and / or aluminum, and / or plastic and / or a composite material.

[0043] In a supplementary variant, the first plate and the second plate are provided at least partially, in particular completely, in corrugated and / or sheet-like and / or layer-like.

[0044] In another embodiment, the bipolar plate consists of two or three plates, and the 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.

[0045] In a supplementary variant, at least one welded connection of the bipolar plate is produced, in particular, only at the contact region.

[0046] In another variation, the electrochemical cell comprises at least 50, 100, 200, or 400 stacked electrochemical cells.

[0047] The invention also comprises a computer program having program code means 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 computing unit.

[0048] Furthermore, an integral part of the invention is also a computer program product having program code means stored on a computer-readable data medium 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 computing unit.

[0049] In another variation, the first species is oxygen and the second species is hydrogen.

[0050] In another variant, the electrolysis cell of the electrolysis cell unit is a fuel cell.

[0051] In another variant, the electrochemical cell comprises a housing and / or a connecting plate. The stack is surrounded by the housing and / or the connecting plate.

[0052] In a further embodiment, the fuel cell unit described in the present patent application additionally forms an electrolyser unit as a reversible fuel cell unit, and preferably vice versa.

[0053] Components for electrochemical cells, in particular fuel cells and / or electrolyzers, are preferably expediently insulating layers, in particular proton exchange membranes, anodes, cathodes, preferably gas diffusion layers and bipolar plates, in particular separator plates.

[0054] Preferably, the fuel is hydrogen, hydrogen-rich gas, reformed gas or natural gas.

[0055] The fuel cell and / or the electrolysis cell is expediently designed to be essentially flat and / or lamellar.

[0056] In a supplementary variant, the oxidant is air containing oxygen or pure oxygen.

[0057] 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

[0058] Embodiments of the present invention are described in more detail below with reference to the accompanying drawings. The accompanying drawings show:

[0059] Figure 1 : A greatly simplified exploded view of an electrochemical cell system as a fuel cell system and an electrolyzer system with components of an electrochemical cell as a fuel cell and an electrolyzer,

[0060] Figure 2 : A three-dimensional view of a portion of a fuel cell and an electrolyzer,

[0061] Figure 3 : Longitudinal section of an electrochemical cell as a fuel cell and electrolyzer,

[0062] Figure 4 : Electrochemical cell units as fuel cell units and electrolyzer units as a three-dimensional view of a fuel cell stack and an electrolyzer stack,

[0063] Figure 5 : Electrochemical cell units as fuel cell units and electrolyzer units as side views of fuel cell stacks and electrolyzer stacks,

[0064] Figure 6 : A three-dimensional view of the bipolar plate,

[0065] Figure 7 : Enlarged longitudinal section of the fuel cell and electrolysis cell in the weld area,

[0066] Figure 8 : A longitudinal section of a bipolar plate comprising two plates which are connected to one another by means of a weld seam as a through-weld and also form a weld-in,

[0067] Fig. 9 : A longitudinal section through a bipolar plate comprising 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,

[0068] Fig.10 : Longitudinal section of the two plates when placed on the support plate during the welding process,

[0069] Fig.11 : horizontal section of the bipolar plate in the region of the flow opening as discharge channel for the oxidant,

[0070] Fig.12 : Fig.11 The enlarged part,

[0071] Fig.13 : vertical cross section of the bipolar plate in the region of the connecting channels,

[0072] Fig.14 : vertical longitudinal section of the bipolar plate in the region of the connecting channel,

[0073] Fig.15 : A partial three-dimensional view of a bipolar plate at a connection opening in a first embodiment, the connection opening being used to guide a process fluid into or out of a connection channel,

[0074] Fig.16 :The second plate of the bipolar plate having a connection opening is based on Fig.15 AA section,

[0075] Fig.17 : A partial three-dimensional view of a bipolar plate at a connection opening in a second embodiment, the connection opening being used to guide a process fluid into or out of a connection channel,

[0076] Fig.18 : A partial three-dimensional view of a bipolar plate at a connection opening in a third embodiment, the connection opening being used to guide a process fluid into or out of a connection channel,

[0077] Fig.19 :The second plate of the bipolar plate having a connection opening is based on Fig.18 BB cross section,

[0078] Fig. 20 : A partial three-dimensional view of a bipolar plate at a connection opening in a fourth embodiment, wherein the connection opening is used to guide a process fluid into or out of a connection channel;

[0079] Fig.21 : A partial three-dimensional view of a bipolar plate at a connecting opening in a fifth embodiment, the connecting opening being used to guide a process fluid into or out of a connecting channel. DETAILED DESCRIPTION

[0080] 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 H 2 The gaseous fuel is introduced to the anode 7 and the anode 7 forms the negative electrode. The gaseous oxidant, i.e. air containing oxygen, is introduced to the cathode 8, i.e. the oxygen in the air provides the necessary gaseous oxidant. Reduction (absorption of electrons) occurs at the cathode 8. Oxidation is carried out at the anode 7 as the release of electrons.

[0081] The redox equation of the electrochemical process is:

[0082] cathode:

[0083] O 2 +4H + +4e - --》2H 2 O

[0084] anode:

[0085] 2H 2 --》4H + +4e -

[0086] The overall reaction equation at the cathode and anode is:

[0087] 2H 2 +O 2 --》2H 2 O

[0088] The normal potential difference of the electrode pair under standard conditions as a reversible fuel cell voltage or no-load voltage of an unloaded fuel cell 2 is 1.23 V. In practice, this theoretical voltage of 1.23 V cannot be achieved. In the static state and at low currents, voltages of more than 1.0 V can be achieved, and when operating at high currents, voltages between 0.5 V and 1.0 V can be achieved. A fuel cell unit 1 of a fuel cell stack 1 of a plurality of fuel cells 2 connected in series, in particular a plurality of fuel cells 2 arranged in a stack, has a higher voltage, which corresponds to the number of fuel cells 2 multiplied by the individual voltage of each fuel cell.

[0089] The fuel cell 2 further includes a proton exchange membrane 5 (PEM) arranged between an anode 7 and a cathode 8. The anode 7 and the cathode 8 are constructed in a layered or sheet-like manner. The PEM 5 acts as an electrolyte, a catalyst carrier and a separator for the reaction gas. The PEM 5 also acts as an electrical insulator and prevents an electrical short circuit between the anode 7 and the cathode 8. Typically, a 12 μm to 150 μm thick proton conducting membrane made of a perfluorinated and sulfonated polymer is used. The PEM 5 conducts protons H + and essentially blocks the removal of protons H + ions other than PEM5, which is responsible for the proton H + The permeability of PEM5 enables charge transport. 2 and hydrogen H 2 Essentially impermeable, i.e., blocking oxygen O 2 and hydrogen H 2 In the case of hydrogen fuel H 2 The gas chamber 31 on the anode 7 is connected to the gas chamber 31 with air or oxygen O2 The gas flows between the chambers 32 on the cathode 8 as an oxidant. The proton conductivity of the PEM 5 increases with increasing temperature and increasing water content.

[0090] Electrodes 7, 8 are located as anode 7 and cathode 8 on both sides of PEM 5 facing gas chambers 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 against PEM 5. Electrodes 7, 8 are carbon fiber, glass fiber or plastic mats attached to PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene-propylene copolymer), PFA (perfluoroalkoxy), PVDF (polyvinylidene fluoride) and / or PVA (polyvinyl alcohol) and hot pressed into microporous. Catalyst layer 30 is usually applied to the side facing gas chambers 31, 32 on electrodes 7, 8 respectively (not shown). The catalyst layer 30 on the anode 7 on the gas chamber 31 with fuel includes nano-dispersed platinum-ruthenium on graphitized soot particles bonded to a binder. The catalyst layer 30 on the cathode 8 on the gas chamber 32 with oxidant similarly includes nano-dispersed platinum. For example, using Polytetrafluoroethylene emulsion or polyvinyl alcohol is used as adhesive.

[0091] In contrast, the electrodes 7, 8 are made of ionomers, such as The electrodes 7, 8 with ionomers are electrically conductive because the carbon particles are also conductive to protons H. + And because the platinum-containing carbon particles additionally act as a catalyst layer 30 ( Figure 2 and Figure 3 The membrane electrode assembly 6 having the electrodes 7 and 8 including the ionomer constitutes a membrane electrode assembly 6 as a CCM (catalyst coated membrane).

[0092] A gas diffusion layer 9 (GDL) is located on the anode 7 and the cathode 8. The gas diffusion layer 9 on the anode 7 evenly distributes the fuel from the channel 12 for the fuel to the catalyst layer 30 on the anode 7. The gas diffusion layer 9 on the cathode 8 evenly distributes the oxidant from the channel 13 for the oxidant to the catalyst layer 30 on the cathode 8. The GDL 9 also draws away the reaction water in the direction opposite to the flow direction of the reaction gas, i.e. in the direction from the catalyst layer 30 or the electrodes 7, 8 to the channels 12, 13, respectively. In addition, the GDL 9 keeps the PEM 5 moist and conducts current. The GDL 9 is composed, for example, of a hydrophobic carbon paper as a carrier and a base layer and a bonded carbon powder layer as a microporous layer.

[0093] The bipolar plate 10 is located on the GDL 9. The electrically conductive bipolar plate 10 is used as a current collector for discharging water and for guiding the reaction gas as a process fluid through the channel structure 29 and / or the flow field 29 and for discharging waste heat, which occurs especially at the cathode 8 during the exothermic electrochemical reaction. In order to discharge the waste heat, the channel 14 is processed into the bipolar plate 10 as a channel structure 29 for guiding the liquid or gaseous coolant as a process fluid through. The channel structure 29 on the gas chamber 31 for fuel is composed of channels 12. The channel structure 29 on the gas chamber 32 for oxidant is composed of channels 13. For example, metals, conductive plastics and composite materials and / or graphite are used as materials for the bipolar plate 10.

[0094] In the fuel cell unit 1 and / or the fuel cell stack 1 and / or the fuel cell stack 1, a plurality of fuel cells 2 are stacked and arranged in an aligned manner ( Figure 4 and Figure 5 ).exist Figure 1 2 shows an exploded view of two fuel cells 2 arranged in an aligned stack. The seal 11 seals the gas chambers 31 , 32 or the channels 12 , 13 in a fluid-tight manner. Hydrogen H 2 The fuel is stored in the compressed gas storage 21 at a pressure of, for example, 350 bar to 700 bar. Figure 1 ). The fuel is led from the compressed gas reservoir 21 via the high-pressure line 18 to the pressure reducer 20 for reducing the pressure of the fuel in the medium-pressure line 17 to about 10 bar to 20 bar. The fuel is led 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. From the injector 19, the fuel is supplied to the supply line 16 for fuel ( Figure 1 ) and is supplied from the supply line 16 to the channel 12 for fuel, which constitutes the channel structure 29 for fuel. The fuel thus flows through the gas chamber 31 for fuel. The gas chamber 31 for fuel is constituted by the channel 12 and the GDL 9 on the anode 7. After flowing through the channel 12, the fuel that is not consumed in the redox reaction on the anode 7 and the water that may come from the controlled humidification of the anode 7 are discharged from the fuel cell 2 through the discharge line 15.

[0095] The gas delivery device 22, which is configured as a blower 23 or a compressor 24 or a turbo compressor, for example, delivers air from the surrounding environment as an oxidant into a supply line 25 for the oxidant. From the supply line 25, the air is supplied to the channel 13 for the oxidant, which is formed in the channel structure 29 for the oxidant on the bipolar plate 10, so that the oxidant flows through the gas chamber 32 for the oxidant. The gas chamber 32 for the oxidant is composed of the channel 13 and the GDL 9 on the cathode 8. After flowing through the channel 13 for the oxidant 32 or the gas chamber 32, the oxidant that is not consumed on the cathode 8 and the reaction water formed on the cathode 8 due to the electrochemical redox reaction are discharged from the fuel cell 2 through the discharge line 26. The supply line 27 is used to supply the coolant to the channel 14 for the coolant, and the discharge line 28 is used to discharge the coolant guided through the channel 14. The supply and discharge lines 15, 16, 25, 26, 27, 28 are connected in a manner similar to the supply and discharge lines 15, 16, 25, 26, 27, 28. Figure 1 For simplicity, it is shown as a separate pipeline. At the end regions near the channels 12, 13, 14, the fluid openings 41 on the sealing plate 39, which are aligned in the stack as a stack of fuel cell units 1, are configured as extensions on the end regions 40 of the bipolar plates 10 and the membrane electrode assemblies 6 (not shown) located on each other. The fuel cell 2 and the components of the fuel cell 2 are sheet-shaped and unfold a virtual plane 59 that is oriented substantially parallel to each other. Therefore, the aligned fluid openings 41 and the seals (not shown) form a supply channel 42 for the oxidant, a discharge channel 43 for the oxidant, a supply channel 44 for the fuel, a discharge channel 45 for the fuel, a supply channel 46 for the coolant, and a discharge channel 47 for the coolant between the fluid openings 41 in a direction perpendicular to the virtual plane 59. The supply and discharge lines 15, 16, 25, 26, 27, 28 outside the stack of fuel cell units 1 are configured as process fluid lines. Supply and discharge lines 15, 16, 25, 26, 27, 28 outside the stack of fuel cell units 1 lead to supply and discharge channels 42, 43, 44, 45, 46, 47 within the stack of fuel cell units 1. The fuel cell stack 1 together with the compressed gas storage 21 and the gas delivery device 22 forms a fuel cell system 4.

[0096] 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 is located on the first fuel cell 2 and a second clamping plate 36 is located on the last fuel cell 2. The fuel cell unit 1 includes approximately 200 to 400 fuel cells 2, which are shown in Figure 1 for illustration purposes. Figure 4 and Figure 5Not all fuel cells 2 are shown in the figure. The clamping element 33 applies pressure to the fuel cells 2, i.e. the first clamping plate 35 bears against the first fuel cell 2 with pressure, and the second clamping plate 36 bears against the last fuel cell 2 with pressure. Thus, the fuel cell stack 2 is clamped in order to ensure the tightness for the fuel, oxidant and coolant, in particular due to the elastic seal 11, and also to keep the contact resistance within the fuel cell stack 1 as low as possible. In order to clamp the fuel cells 2 with the clamping element 33, four connecting devices 37 as bolts 38 are constructed on the fuel cell unit 1. The four bolts 38 are connected to the clamping plate 34.

[0097] 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 separate 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 sealing plates 39 of the bipolar plates 10 and the fluid openings 41 on the membrane electrode assembly 6 (not shown) are arranged in an aligned stack in the fuel cell unit 1 so that supply and discharge channels 42, 43, 44, 45, 46, 47 are formed. Here, a seal not shown is arranged between the sealing plates 39 for fluid-tightly sealing the supply and discharge channels 42, 43, 44, 45, 46, 47 formed by the fluid openings 41. The bipolar plate 10 has a length 61 and a width 62. The channel 14 or the channel 14 for the coolant 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%.

[0098] Since the bipolar plate 10 also separates the gas chamber 31 for the fuel from the gas chamber 32 for the oxidant in a fluid-tight manner and also from the channel 14 for the coolant in a fluid-tight manner, the term "separator plate 51" can also be selected for the fluid-tight separation or separation of the process fluid in addition to the bipolar plate 10. Therefore, the term bipolar plate 10 also includes the term separator plate 51, and vice versa. The channel 12 for the fuel, the channel 13 for the oxidant and the channel 14 for the coolant of the fuel cell 2 are also constructed on the electrochemical cell 52, but have different functions.

[0099] The fuel cell unit 1 can also be used and operated as an electrolysis cell unit 49, i.e. a reversible fuel cell unit 1 is formed. Some features that enable the fuel cell unit 1 to be operated as an electrolysis cell unit 49 are described below. For the electrolysis, a liquid electrolyte is used, i.e. a liquid electrolyte having a concentration of about c(H 2 SO 4 ) = 1 mol / l of strongly diluted sulfuric acid. A sufficient concentration of hydronium ions H in the liquid electrolyte 3O+ is essential for electrolysis.

[0100] The following redox reaction occurs during electrolysis:

[0101] cathode:

[0102] 4H 3 O + +4e - --》2H 2 +4H 2 O

[0103] anode:

[0104] 6H 2 O--》O 2 +4H 3 O + +4e -

[0105] The overall reaction equation at the cathode and anode is:

[0106] 2H 2 O--》2H 2 +O 2

[0107] When operating as an electrolysis cell unit 49, the polarity of the electrodes 7, 8 is opposite to that when operating as a fuel cell unit 1 (not shown), so that hydrogen H is formed at the cathode in the channel 12 for conducting the liquid electrolyte for the fuel. 2 As the second substance, and hydrogen H 2 is absorbed by the liquid electrolyte and transported together in dissolved form. Similarly, the liquid electrolyte is guided through the channel 13 for the oxidant and oxygen O is formed at the anode in or on the channel 13 for the oxidant. 2 As the first substance. When operating as an electrolysis cell unit 49, the fuel cell 2 of the fuel cell unit 1 functions as an electrolysis cell 50. Therefore, the fuel cell 2 and the electrolysis cell 50 form an electrochemical cell 52. The oxygen O formed 2 The liquid electrolyte is absorbed and transported together in a dissolved form. The liquid electrolyte is stored in a storage container 54. Figure 1, two storage containers 54 of a fuel cell system 4 are shown for the sake of simplicity of the drawing, which also functions as an electrolyzer system 48. When operating as an electrolyzer unit 49, a three-way valve 55 on the supply line 16 for the fuel is switched so that instead of the fuel from the compressed gas reservoir 21, a liquid electrolyte is introduced from the storage container 54 into the supply line 16 for the fuel by means of a pump 56. When operating as an electrolyzer unit 49, a three-way valve 55 on the supply line 25 for the oxidant is switched 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 supply line 25 for the oxidant by means of a pump 56. Compared to a fuel cell unit 1 that can only be operated as a fuel cell unit 1, a fuel cell unit 1 that is also used as an electrolytic cell unit 49 optionally has modifications to the electrodes 7, 8 and the gas diffusion layer 9: for example, the gas diffusion layer 9 does not have suction properties, so that the liquid electrolyte easily flows out 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 electrolytic cell unit 49 forms an electrochemical cell system 60 together with a storage container 54, a pump 56 and separators 57, 58 and preferably a three-way valve 55.

[0108] 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 introduces the separated hydrogen into the compressed gas reservoir 21 by means of a compressor not shown. Subsequently, the electrolyte discharged from the separator 57 for hydrogen is supplied to the storage container 54 for electrolyte by means of a pipeline. 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 introduces the separated oxygen into the compressed gas reservoir not shown for oxygen by means of a compressor not shown. By guiding the oxygen into the supply line 25 for the oxidant by means of a pipeline not shown when operating as a fuel cell unit 1, the oxygen in the compressed gas reservoir not shown for oxygen can be optionally used for operating the fuel cell unit 1. The electrolyte discharged from the separator 58 for oxygen is then supplied to the storage container 54 for electrolyte by means of a pipeline. The channels 12, 13 and the discharge and supply lines 15, 16, 25, 26 are designed so that after use as an electrolyzer 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 electrolyzer unit 49 and before use as a fuel cell unit 1, an inert gas is passed through the channels 12, 13 and the discharge and supply lines 15, 16, 25, 26 in order to completely remove the liquid electrolyte before passing the gaseous fuel and oxidant. The fuel cell 2 and the electrolyzer 2 thus form an electrochemical cell 52. The fuel cell unit 1 and the electrolyzer unit 49 thus form an electrochemical cell unit 53. The channel 12 for the fuel and the channel for the oxidant thus form the channels 12, 13 for passing the liquid electrolyte when operating as an electrolyzer unit 49, and this applies similarly to the supply and discharge lines 15, 16, 25, 26. For process technology reasons, the electrolysis cell 49 normally does not require any channels 14 for conducting the coolant through. In the electrochemical cell 49, the channels 12 for the fuel also form channels 12 for conducting the fuel and / or electrolyte through, and the channels 13 for the oxidant also form channels 13 for conducting the fuel and / or electrolyte through.

[0109] The bipolar plate 10 is manufactured by laser beam welding from a first plate 64 and a second plate 65 as monopolar plates 64, 65. To this end, for each bipolar plate 10, the corresponding corrugated first plate 64 and the second plate 65 are placed on each other and stacked so that the inner sides 66 of the first plate 64 and the second plate 65 are placed on each other on a strip-shaped contact area 68 as a joint. Subsequently, the virtual planes 59 unfolded by the sheet-like first plate 64 and the second plate 65 are oriented substantially parallel to each other. The first plate 64 and the second plate 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, strip-shaped channels 14 for coolant are formed outside the strip-shaped contact area 68 between the inner sides 66 of the first plate and the second plate 64, 65, and these strip-shaped channels form an intermediate space 79. Providing the first and second plates 64 , 65 with a plurality of corrugations results in a plurality of channels 14 being formed between the contact areas 68 .

[0110] The first plate 64 and the second plate 65 as the monopolar plates 64, 65 are connected to each other in a material-locking manner to form the bipolar plate 10 by means of laser beam welding, so that a welded connection 69 as a plurality of weld seams 70 is produced between the first plate 64 and the second plate 65. The laser system includes 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 irradiates the outer side 67 of the second plate 65 at a focus having a diameter of about 100 μm. A motion unit not shown moves the laser beam 74 over the outer side 67 of the second plate 65 and / or moves the first plate 64 and the second plate 65 under the laser beam 74, so that a relative feed direction 78 of the laser beam 74 relative to the first plate 64 and the second plate 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 plate 64 and the second plate 65 is increased to above the melting temperature, and thereby a liquid melt 77 is formed during the welding process, which is then cooled and solidified into a welded connection 69 as a weld seam 70. In addition, optionally, a small hole 76 is formed in the liquid melt 76 as a steam capillary along the beam direction of the laser beam 74, and the small hole is formed as a hose-shaped cavity composed of metal vapor and / or partially ionized metal vapor respectively below the laser beam 74 moving along the feed direction 78 relative to the first plate 64 and the second plate 65. The through-weld portion 71 or the weld-in portion 72 ( Figure 8 ). The width B of the weld 70 ( Figure 8 ) corresponds essentially to the diameter of the laser beam 74 or the focus.

[0111] The weld seam 70 is implemented completely continuously and fluid-tightly at the edge regions near the length and width sides of the bipolar plate 10 for sealing the intermediate space 79 with the coolant so that the coolant cannot flow outward. In the bipolar plate 10, transverse distribution channels 94 are formed between the first plate 64 and the second plate 65 for guiding the coolant from the supply channel 46 for the coolant into the channel structure 29 and from the channel structure 29 into the discharge channel 47 for the coolant. Therefore, the weld seam 70 also acts as a seal to seal the channel 14 for the coolant outwardly outside the channel 14. Figure 6 In the figure, a weld seam 70 as a seal for the coolant is shown in a very simplified manner as a continuous straight line. Optionally, a further weld seam 70 of sectional design can be produced on the contact area 68, which has no sealing function for the coolant to enter the environment or to the outside and serves only for the material connection of the two plates 64, 65 and optionally also serves to seal between the two channels 14 for the coolant.

[0112] In order to manufacture the bipolar plate 10, a first plate 64 and a second plate 65 made of stainless steel are first provided. The first plate 64 and the second plate 65 have a thickness of about 70 μm. A horizontal and flat support plate 80 made of steel 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, which respectively form vacuum sub-chambers 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 vacuum sub-chamber 83 by means of a vacuum pump not shown. For this purpose, a suction channel 88 is constructed in the support plate 80. The suction channel 88 is connected to all vacuum sub-chambers 83 in a fluid-conducting manner, and the vacuum sub-chamber 83 constitutes a vacuum chamber 82 as a whole. On the one hand, the negative pressure in the vacuum chamber 82 is very small between the outer side 67 of the first plate 64 and the upper side of the support plate 80 and is 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 the negative pressure in the vacuum chamber 82, the first plate 64 rests against the upper side of the support plate 80 with the process additional pressure. Therefore, the outer side 67 of the first plate 64 rests against the support plate 80 with a pressure formed by the sum of the process additional pressure and the weight of the first plate 64. As a result, a reliable positive and / or non-positive connection is formed 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 positioned in an immovable manner relative to the support plate 80, so that the weld seam 70 can be produced precisely at the correct position.

[0113] Subsequently, the second plate 65 is placed on the first plate 64 with precise positioning. A sealing agent 84 is then arranged at the outer edge 87 of the two plates 64, 65 stacked on top of each other, namely a multi-part sealing frame 85 (not shown) with an inner sealing ring made of rubber and an outer metal frame. In addition, all fluid openings 41 are sealed by means of a process seal 86 as a further sealing agent 84, except for the outlet channel 47 for the coolant. The process seal 86 is located at the outer edge 87 of the two plates 64, 65 stacked on top of each other. Figure 6 . Subsequently, a large negative pressure is generated on the discharge channel 47 for the coolant by means of a vacuum pump (not shown), which is formed by two aligned fluid openings 41 of the first plate 64 and the second plate 65 on the sealing plate 39. 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 outer side 67 as the first plate 64 in a fluid-conducting manner. The outer side 67 as the upper side of the second plate 65 is sealed with a sealing medium in a fluid-tight manner. Because 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 formed essentially by the channel 14 for the coolant. Therefore, the pressure difference between the ambient pressure and the negative pressure in the intermediate space 79 as the negative pressure chamber 104 is about 600 mbar. Therefore, the ambient pressure of the air 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 here, so that the outer side 67 of the second plate 65 is loaded with a constant pressure in an advantageous manner. The negative pressure in the vacuum chamber 82 is less than the negative pressure in the intermediate space 79, so that the contact force per unit area acting on the lower outer side 67 of the first plate 64 is smaller than the contact force per unit area acting on the upper outer side 67 of the second plate 65, and the difference resulting from this is applied as a pressure from the first plate 64 to the support plate 80, without taking into account the gravity. The contact force is therefore a pressure. Therefore, in the contact area 68, the inner side 66 of the first plate 64 and the second plate 65 rest against each other with additional pressure, and due to the size of these additional pressures, a technical zero gap of less than 20 μm is essentially present in the contact area 68. The weld seam 70 is then produced by means of a laser 73.

[0114] Optionally, before the negative pressure is generated in the intermediate space 79 as the negative pressure chamber 104, the intermediate space 79 is filled with a protective gas, in particular nitrogen or a rare gas, and preferably, the protective gas is continuously guided through the intermediate space 79 also during the generation and maintenance of the negative pressure. This is implemented in the following way: for example, during the suction by means of a vacuum pump, a small amount of protective gas is additionally guided through the supply channel 46 on the discharge channel 47 for the coolant. Since the sealing of the outer edge 87 and the remaining fluid openings 41 cannot be completely sealed technically, it is necessary to continuously introduce the 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 focus on the outer side 67 of the second plate 65, that is, the outer side of the location irradiated by the laser beam 74, is continuously supplied with protective gas. Thereby, the weld seam 70 can be produced completely with surrounding flushing of the protective gas.

[0115] In the region of the fluid opening 41, a weld seam 70 is produced around the fluid opening 41 by means of laser welding (only in Fig.11 and Fig.12 ), in order to prevent the process fluid from flowing uncontrolled into the intermediate space 79 between the first plate 64 and the second plate 65. The process fluid is introduced into the fluid opening 41 or discharged from the fluid opening 41 by means of the connecting channel 89. However, the weld seam 70 on the fluid opening 41 is not formed on the connecting channel 89. Fig.11 4 shows, for example, an outlet channel 43 for the oxidant. The oxidant is guided through the channels 13 on the outer side 67 of the first plate 64 in the region of the membrane electrode assembly 5. After flowing through the channels 13, the oxidant flows into the transverse distribution channels 94 on the outer side 67 and is guided from the transverse distribution channels 94 to the connecting channels 89 at the outlet channel 43. The connecting channels 89 ( Figures 11 to 14 ) is formed between the first plate 64 and the second plate 65. For this purpose, before the second plate 65 is stacked on the first plate 64 and before the weld seam 70 is produced, a corrugated connecting channel geometry 102 is processed into the first plate 64 by means of forming, for example, embossing. The connecting channel 89 has a first end 90 that opens into the fluid opening 41 and a second end 91 that opens directly into the transverse distribution channel 89 and indirectly into the channels 12, 13 and 14 for the process fluid. The connecting channel 89 opens into the fluid opening 41 at an additional fluid opening 92 as the first end 90. The connecting channel 89 opens directly into the transverse distribution channel 89 and directly into the channels 12, 13 and 14 for the process fluid at a connecting opening 92 as the second end 91. Here, a plurality of connecting openings 93 are also formed on each connecting channel 89. Therefore, in Fig.11In the shown discharge channel 43, the oxidant flows from the transverse distribution channel 94 through the connecting opening 93 into the connecting channel 89 and from the connecting channel 89 through the additional fluid opening 92 into the discharge channel 43 as the fluid opening 41. In the fluid opening 41 as the supply channel 42 for the oxidant, the oxidant flows through the connecting channel 89 in the opposite direction, i.e. from the supply channel 42 through the additional fluid opening 92 into the connecting channel 89 and from the connecting channel 89 through the connecting opening 93 directly into the transverse distribution channel 94 and indirectly into the channel 13 for the oxidant. The channel 13 for the oxidant and the transverse distribution channel 94 for the oxidant are constructed on the outer side 67 of the first plate 64.

[0116] The process fluid fuel is guided through the fluid openings 41 as supply channels 44 and discharge channels 45 for the fuel through the connecting channels 89, the transverse distribution channels 94 and the channels 12 for the fuel in a similar manner to the process fluid oxidant. The transverse distribution channels 94 and the channels 12 for the fuel are formed on the outer side 67 of the second plate 65.

[0117] The guidance of the process fluid coolant through the fluid opening 41 serving as a supply channel 46 and an outlet channel 47 for the coolant through the connecting channel 89, the transverse distribution channel 94 and the channel 14 for the coolant is implemented similarly to the process fluid oxidant, but the transverse distribution channel 94 and the channel 14 for the coolant are limited by the inner side 66 of the first plate 64 and the second plate 65, that is, they are constructed between the first plate 64 and the second plate 65.

[0118] exist Fig.15 and Fig.16 , a first embodiment of a connection opening 93 configured as a slit-shaped connection opening 100 is shown. The connection opening 93 is processed into the second plate 65 by means of a laser beam 74 from a laser 73. This processing of the connection opening 93 is carried out after the production of the welded connection 69 with the weld seams 70, in particular after all weld seams 70 have been produced between the first plate 64 and the second plate 65, and thus also in time by exerting a contact force between the first plate 64 and the second plate 65 by means of the negative pressure in the negative pressure chamber 104 as the intermediate space 79. The laser beam 74 melts and separates the second plate 65 at the remelting geometry 99, and this is carried out as follows: the slit-shaped connection opening 100 is formed. The material of the second plate 65 melted at the slit-shaped connection opening 100 is completely redistributed and melted at the edge or boundary area of ​​the slit-shaped connection opening 100 of the second plate 65 which delimits the connection opening 93, so that the melting lip 101 ( Fig.16) is formed around the connecting opening 93. This has the advantage that already melted material of the second plate 65 in the intermediate space 73, ie in particular in the connecting channel 89, is not deposited on the connecting opening 93, for example in the form of material splashes.

[0119] For this complete relocation and remelting of the material of the second plate 65 melted by means of the laser beam 74, the parameters of the laser beam 74 and thus of the focus of the laser beam 74 on the outer side 67 of the first plate 64 are selected accordingly: a power of 500 W with a spot size of 300 μm, a relative speed v of 500 mm / s between the first plate 64 and the laser beam 74 during the machining of the connection opening 93 and a thickness of 75 μm of the first plate 64 in the region of the connection opening. The position of the laser beam 74 on the first plate 64 is optically detected by means of a laser scanner of the laser system. Due to the known geometry of the second plate 65 and the welded connection 69 already implemented between the first plate 64 and the second plate 65, the correct position for machining the connection opening 93 can be precisely aligned by means of the geometry of the first plate 64 and / or the second plate 65 and the data of the optical detection result of the laser beam 74. If the width of the slit-shaped connecting opening 100 is greater than the spot size of the laser beam 74 , the laser beam is guided multiple times along the longitudinal direction of the slit-shaped connecting opening 100 to melt, separate and displace the material of the first plate 64 multiple times.

[0120] exist Fig.17 A second embodiment in which the connection opening 93 is configured as a slit-shaped connection opening 100 is shown. Fig.15 and Fig.16 The slit-shaped connecting opening 93 is not oriented horizontally but approximately vertically, ie approximately at a right angle to the first embodiment.

[0121] exist Fig.18 and Fig.19 A third embodiment for constructing a connection opening 93 is shown in FIG. Fig.15 and Fig.16 The connection opening 93 is substantially circular in design.

[0122] exist Fig. 20 A fourth embodiment for constructing a connection opening 93 is shown in FIG. Fig.15 and Fig.16 The connection opening 93 is essentially H-shaped. During the processing with the aid of the laser beam 74 , the material of the first plate 64 is not completely remelted, but is only separated and remelted along the completely surrounding notch geometry 97 as a remelting geometry 99 , and a partial region 98 of the second plate 65 is removed from the connection opening 93 .

[0123] exist Fig.21 A fifth embodiment for constructing a connection opening 93 is shown in FIG. Fig.15 and Fig.16 The connecting opening 93 is designed to be substantially rectangular. In this case, the material of the second plate 65 is not completely remelted during processing by means of the laser beam 74, but is only separated and remelted along the U-shaped, incompletely surrounding flap geometry 95 as a remelting geometry 99 and a partial area of ​​the flap 96 of the second plate 65 is pivoted outwardly about the pivot axis 103 as an unseparated section. Before the second plate 65 is stacked on the first plate 64, inherent stresses and / or prestresses are mechanically introduced into the second plate 65 by means of a stamping process, so that the flap 96 automatically pivots outwardly after the U-shaped cutout has been formed.

[0124] Overall, the method for manufacturing a bipolar plate 10 according to the invention, the method for manufacturing an electrochemical cell 53 according to the invention, and the electrochemical cell 53 according to the invention have significant advantages. After the material-locked connection between the first plate 64 and the second plate 65 as the bipolar plate 10 is produced, the connection opening 93 on the connection channel 89 is processed by means of a laser 73. Processing by means of a laser 73 has the following advantages: the connection opening 93 can be processed very accurately and with little effort and low cost, because the laser system for generating the laser beam 73 for producing the weld seam 70 is already available. Therefore, it is not necessary to perform laborious mechanical punching of the connection opening 93 by means of a high-cost punching machine for providing the second plate 65. Therefore, the cost for manufacturing the bipolar plate 10 can be reduced in an advantageous manner with a higher precision of the geometric structure of the connection opening 93. In addition, very small connection openings 93 can also be processed, which cannot be manufactured by means of a mechanical punching process for reasons of manufacturing precision and material technology. Therefore, a plurality of connection openings 93 can be formed in each connection channel 89. Changing the geometry of the connecting opening 93 so that the laser beam 74 executes a different movement path on the second plate 65 can be achieved inexpensively and with little effort simply by changing the software and / or reprogramming the laser system.

Claims

1. A method for producing a bipolar plate (10, 51) for an electrochemical cell (53) as a fuel cell cell (1) for converting electrochemical energy into electrical energy and / or as an electrolyzer cell (49) for converting electrical energy into electrochemical energy, the electrochemical cell 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) on each other so that the inner sides (66) of the first and second plates (64, 65) are located on each other, - applying a contact force to the first and second plates (64, 65) by means of a negative pressure in the negative pressure chamber (104) compared to the ambient pressure, so that the inner sides (66) of the first and second plates (64, 65) lie on each other at the contact area (68) with an additional pressure due to the applied contact force resulting from the ambient pressure, - producing at least one welded connection (69) between the first and second plates (64, 65) by means of a laser beam (74), - forming a connecting channel (89) for a process fluid on the first plate and / or the second plate (64, 65), the connecting channel opening into the fluid opening (41) on the bipolar plate (10, 51) and into the channel (12, 13, 14) for the process fluid on the bipolar plate (10, 51), - processing a connection opening (93) into the first plate and / or the second plate (64, 65), said connection opening connecting the connection channel (89) to a channel (12, 13, 14) for a process fluid on the bipolar plate (10, 51), It is characterized in that The connecting opening (93) is processed into the first plate and / or the second plate (64, 65) by means of a laser beam (74).

2. The method according to claim 1, It is characterized in that First, a welded connection (69) is produced between the first and second plates (64, 65), and subsequently the connection opening (93) is processed into the first and / or second plates (64, 65) by means of the laser beam (74).

3. The method according to one or more of the preceding claims, It is characterized in that Firstly, a contact force is applied to the first and second plates (64, 65) by means of a negative pressure in a negative pressure chamber (104) compared to the ambient pressure, and subsequently and simultaneously a welded connection (70) is produced between the first and second plates (64, 65).

4. The method according to one or more of the preceding claims, It is characterized in that A connecting channel geometry (102) is worked into the first plate and / or the second plate (64, 65) by means of deformation, in particular pressing, so that after the first plate (64) and the second plate (65) are stacked on one another, the connecting channel (89) is constructed as an intermediate space (79) between the first plate and the second plate (64, 65) due to the connecting channel geometry (102).

5. The method according to claim 4, It is characterized in that The connecting channel geometry (102) is processed into the first plate and / or the second plate (64, 65) before the first plate (64) and the second plate (65) are stacked on top of each other.

6. The method according to one or more of the preceding claims, It is characterized in that The correct position of the focus of a laser beam (74) generated by a laser system for machining the connection opening (93) on the first and / or second plate (64, 65) is detected optically, in particular by means of a laser scanner.

7. The method according to one or more of the preceding claims, It is characterized in that At least one connecting opening (93) for each connecting channel (89) is processed into the first plate and / or the second plate (64, 65) by means of the laser beam (74) in such a way that: The first and / or second plate (64, 65) is separated at at least one flap geometry (95) by means of the laser beam (74), and at least one partial region of the first and / or second plate (64, 65) is subsequently moved, in particular pivoted, as the at least one flap (96).

8. The method according to claim 7, It is characterized in that The movement of the at least one flap (96) is caused by the inherent stress or prestress of the first plate and / or the second plate (64, 65).

9. The method according to claim 8, It is characterized in that The inherent stress or prestress of the first plate and / or the second plate (64, 65) is introduced into the first plate and / or the second plate (64, 65) by means of a pressing process.

10. The method according to one or more of the preceding claims, It is characterized in that At least one connecting opening (93) for each connecting channel (89) is processed into the first plate and / or the second plate (64, 65) by means of the laser beam (74) in such a way that: The first and / or second plate (64, 65) is separated at at least one notch geometry (97) by means of the laser beam (74), and at least one partial region (98) of the first and / or second plate (64, 65) is subsequently removed from the remaining first and / or second plate (64, 65).

11. The method according to one or more of the preceding claims, It is characterized in that At least one connecting opening (93) for each connecting channel (89) is processed into the first plate and / or the second plate (64, 65) by means of the laser beam (74) in such a way that: The first plate and / or the second plate (64, 65) are separated on at least one remelting geometry (99) by means of the laser beam (74), and material of the first plate and / or the second plate (64, 65) melted during the separation is at least partially, in particular completely, deposited as a melt lip (101) at an edge of the first plate and / or the second plate (64, 65) that delimits the at least one connecting opening (93).

12. The method according to one or more of the preceding claims, It is characterized in that The at least one connecting opening (93) is slit-shaped and / or circular and / or T-shaped.

13. The method according to one or more of the preceding claims, It is characterized in that The laser beam (74) used for processing the connection opening has a power between 200 W and 800 W, in particular between 400 W and 600 W, and / or The laser beam (74) for machining the connection opening has a diameter between 100 μm and 500 μm, in particular between 200 μm and 400 μm, and / or The relative speed between the first plate and / or the second plate (64, 65) and the focus of the laser beam (74) for machining the connection opening is between 300 mm / s and 700 mm / s, in particular between 400 mm / s and 600 mm / s, and / or The thickness of the first plate and / or the second plate (64, 65) at the focus of a laser beam (74) for machining the connection opening is between 25 μm and 125 μm, in particular between 50 μm and 100 μm.

14. A method for producing an electrochemical cell (53) as a fuel cell cell (1) for converting electrochemical energy into electrical energy and / or as an electrolysis cell cell (49) for converting electrical energy into electrochemical energy, the electrochemical cell 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), 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 into a stack of 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 (53) as a fuel cell cell (1) for converting electrochemical energy into electrical energy and / or as an electrolysis cell cell (49) for converting electrical energy into electrochemical energy, comprising: - electrochemical cells (52) arranged in a stack, and the electrochemical cells (52) each comprise layered components (5, 6, 7, 8, 9, 10, 51) arranged in a stack, and - components (5, 6, 7, 8, 9, 10, 51) of the electrochemical cell (52), preferably a proton exchange membrane (5), an anode (7), a cathode (8), a gas diffusion layer (9) and a bipolar plate (10, 51), wherein on the bipolar plate (10, 51), a connecting channel (89) for a process fluid is formed between the first plate and the second plate (64, 65), and the connecting channel (89) opens into a fluid opening (41) on the bipolar plate (10, 51) and into a channel (12, 13, 14) for a process fluid on the bipolar plate (10, 51), and a connecting opening (93) is formed in the first plate and / or the second plate (64, 65) of the bipolar plate (10, 51), which connects the connecting channel (89) to the channel (12, 13, 14) for a process fluid on the bipolar plate (10, 51), It is characterized in that The electrochemical cell (53) is produced by means of the method according to claim 14, and / or On the first plate and / or the second plate (64, 65), the connecting opening (93) is limited by a melt lip (101), in particular, the melt lip (101) has a greater thickness than the first plate and / or the second plate (64, 65) outside the melt lip (101), and / or the melt lip (101) is constructed from melted material of the first plate and / or the second plate (64, 65).

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