Method for manufacturing a bipolar plate
The method of primary mechanical forming followed by secondary forming with heat and non-contact forces addresses the limitations of traditional methods, enabling complex bipolar plate geometries and reducing tooling costs in electrochemical cell manufacturing.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ROBERT BOSCH GMBH
- Filing Date
- 2025-12-19
- Publication Date
- 2026-07-23
AI Technical Summary
Existing methods for manufacturing bipolar plates for electrochemical cells face limitations in design flexibility due to primary mechanical forming, which restricts the creation of small functional geometries and requires costly tool changes for minor geometry adjustments, and result in visible forming marks.
A method involving primary mechanical forming followed by secondary forming using heat and non-contact forces, such as a laser beam or gas pressure, allows for the creation of complex geometries without visible forming marks and reduces the need for new tools.
Enables the production of bipolar plates with intricate geometries and reduced tooling costs, while minimizing visible forming defects, thereby enhancing design flexibility and efficiency in electrochemical cell assembly.
Smart Images
Figure EP2025088610_23072026_PF_FP_ABST
Abstract
Description
[0001] R. 416480
[0002] - 1 -
[0003] Description
[0004] title
[0005] Method for manufacturing a bipolar plate
[0006] The present invention relates to a method for producing a bipolar plate for an electrochemical cell unit according to the preamble of claim 1, a method for producing an electrochemical cell unit according to the preamble of claim 14 and an electrochemical cell unit according to the preamble of claim 15.
[0007] State of the art
[0008] Fuel cell units, as galvanic cells, convert continuously supplied fuel and oxidizing agent into electrical energy and water via redox reactions at an anode and cathode.
[0009] Fuel cells are used in a wide variety of stationary and mobile applications, for example in homes without a connection to the power grid, in motor vehicles, rail transport, aviation, space travel, and shipping. Fuel cell units consist of multiple fuel cells arranged in a stack.
[0010] In fuel cell units, a large number of fuel cells are arranged in a fuel cell stack. Within each fuel cell, there is a gas space for the oxidizer, that is, a flow space for the passage of the oxidizer, such as ambient air containing oxygen. The gas space for the oxidizer is formed by channels on the bipolar plate and by a gas diffusion layer for the cathode. The channels are thus formed by a corresponding channel structure of the bipolar plate, and the oxidizer passes through the gas diffusion layer. (R. 416480)
[0011] - 2 -
[0012] Oxidizing agent, namely oxygen, is supplied to the cathode of the fuel cells. Similarly, a gas space for fuel is provided.
[0013] Electrolysis cell units, consisting of stacked electrolysis cells, similar to fuel cell units, are used, for example, for the electrolytic production of hydrogen and oxygen from water. Furthermore, fuel cell units are known that can be operated as reversible fuel cell units and thus as electrolysis cell units.
[0014] Fuel cell units and electrolysis cell units form electrochemical cell units. Fuel cells and electrolysis cells form electrochemical cells.
[0015] For the manufacture and assembly of electrochemical cells, especially fuel cells, it is necessary to arrange the fuel cell components in a aligned stack. The disc-shaped components of the fuel cells are proton exchange membranes, anodes, cathodes, gas diffusion layers, and bipolar plates. The electrically conductive bipolar plates are an essential part of the stack. These function as current collectors, for water drainage, and for guiding the reaction gases as well as liquid or gaseous coolant through flow chambers, in particular channels or channel structures.
[0016] Bipolar plates are generally made of two or three stainless steel plates. In their manufacture, a first and second plate are placed on top of each other and then welded together to form weld seams. These weld seams not only create a material-bonded and electrically conductive connection between the plates, but also provide a fluid-tight seal for coolant channels located between each pair of plates. For each bipolar plate, a corrugated first and second plate are placed on top of each other and stacked so that their inner surfaces meet at strip-shaped contact points. The plates are manufactured from raw slats using a forming die and are supplied with the necessary components.For primary forming, a forming tool is necessary, and due to design constraints, undercuts are generally not possible with the primary forming process because of the necessary demoldability. R. 416480.
[0017] - 3 -
[0018] Contact-based mechanical forming is not possible. This reduces the design options, for example, on the flanks of channels. Manufacturing small functional geometries using primary mechanical forming results in very high tool wear, so for economic reasons, small functional geometries are generally not produced on the plates. Changing the geometry of the plates requires the manufacture of new forming tools, meaning that even very minor changes to the plate geometry using primary forming incur very high costs for entirely new forming tools.
[0019] KR 101324950 B1 shows a method for the continuous forming of a raw component by means of mechanically applied forming forces with rollers and electromagnetically applied forming forces, and with a laser beam the stiffness of the material is reduced.
[0020] US patent 11,773,003 B2 discloses a method for manufacturing a three-dimensional sleeve for a resonator from a substrate by heating the substrate with a laser beam and forming the heated substrate using a vacuum on a forming frame.
[0021] EP 1 826850 A2 discloses a method for joining bipolar plates, in particular for a fuel cell stack, wherein at least two plates, in particular embossed plates, are arranged in a predetermined joining position relative to each other and are joined materially and form-fit by welding.
[0022] Disclosure of the invention
[0023] Advantages of the invention
[0024] Inventive method for manufacturing a bipolar plate for an electrochemical cell unit for converting electrochemical energy into electrical energy as a fuel cell unit and / or for converting electrical energy into electrochemical energy as an electrolysis cell unit with stacked electrochemical cells, comprising the steps: R. 416480
[0025] - 4 -
[0026] from a first raw plate as a first plate element and a second raw plate as a second plate element, primary mechanical forming of the first raw plate into a first plate as a first plate element with a forming tool by applying a primary forming force to the first raw plate with the forming tool, in particular contact-based, and / or primary mechanical forming of the second raw plate into a second plate as a second plate element with a forming tool by applying a primary forming force to the second raw plate with the forming tool, in particular contact-based, stacking the first plate element and the second plate element on top of each other so that the inner surfaces of the first and second plate elements lie on top of each other at a contact area, producing at least one welded joint between the first and the second plate element,so that the bipolar plate is formed from the first and second plate elements connected to each other by the weld joint, wherein the first plate element and / or the second plate element is additionally secondarily formed by heating the first and / or second plate element, in particular to a temperature greater than 100 °C, 300 °C or 700 °C, to reduce the necessary secondary forming force, and with a secondary forming force the secondary forming is carried out in the heated state, in particular at a temperature greater than 100 °C, 300 °C or 700 °C,so that after the cooling of the first and / or second plate element, the first and / or second plate element was secondarily formed. "Plate element" is the generic term for the raw plate before primary forming, the plate after primary forming, and the plate after secondary forming. Heating the first and / or second plate element, due to the change in material properties in the heated state, allows for a smaller functional geometry (in terms of size and / or geometry) that can be achieved with secondary forming, and / or a greater maximum secondary forming than the expansion achieved with secondary forming compared to the expansion before secondary forming.
[0027] In another embodiment, the first and / or second plate element is heated, particularly locally, with a laser beam. R. 416480
[0028] - 5 -
[0029] In an additional variant, the laser beam is directed towards an inside and / or outside surface of the first and / or second plate element for heating, in particular locally.
[0030] In a further embodiment, the laser beam is moved across the surface of the first and / or second plate element by means of a relative movement between the first and / or second plate element and the laser beam. Preferably, a laser is moved along the surface of the first and / or second plate element by a robot to achieve the relative movement between the first and / or second plate element and the laser beam.
[0031] Preferably, the secondary forming force is applied to the first and / or second plate element without contact, in particular using a gas. Contactless forming is forming without mechanical contact between two solids.
[0032] In another embodiment, the secondary forming force is applied with the gas by applying a pressure difference of the gas, in particular the ambient air, between the outside and the inside to the outside and the inside of each plate element.
[0033] In a complementary variant, the secondary forming force is applied with the gas by applying a directed mass flow of gas, in particular compressed air, to the surface, especially only the outside or only the inside, of each plate element. Preferably, compressed air at a pressure greater than 5 bar, 10 bar, 20 bar, or 50 bar is supplied from a compressed air nozzle to generate the directed mass flow of gas.
[0034] In a further embodiment, the secondary forming force for the secondary forming process is applied to the first and / or second plate element by locally vaporizing the material of the first and / or second plate element using the laser beam, so that the locally vaporized material causes a pressure difference of the gas between the outside and the inside of each plate element due to R. 416480.
[0035] - 6 -
[0036] Volume expansion occurs during the transition of the material from the solid to the gaseous state, and the volume expansion on the outside of each plate element is greater than on the inside of each plate element, or the volume expansion on the inside of each plate element is greater than on the outside of each plate element. The local vaporization of the plate element material substantially, in particular to at least 70%, 80%, or 90%, on only one side, i.e., the inside or the outside of the plate element, locally increases the volume of the gas in the area of vaporization and thus also locally increases the pressure for generating the secondary forming force.
[0037] In a complementary variant, the secondary forming force is applied as gravity to the first and / or second plate element. Due to the local heating of the plate element, very low secondary forming forces are necessary and sufficient for the secondary forming process, so that the force of gravity acting on the plate element is also sufficient for the secondary forming force.
[0038] In an additional embodiment, the secondary forming is carried out before the primary mechanical forming as the secondary forming of the first and / or second raw plate.
[0039] In a further embodiment, the secondary forming is carried out after the primary mechanical forming, specifically the secondary forming of the first and / or second plate and / or at least one plate element of the bipolar plate. When the secondary forming is performed after the primary mechanical forming, it therefore takes place before or after the weld joint between the first and second plate elements. The bipolar plate is formed from the first and second plate elements.
[0040] Advantageously, at least one welded joint between the first and second plate elements is produced, in particular exclusively, by resistance welding. R. 416480
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[0042] In a supplementary variant, at least one, in particular local, functional geometry, preferably a spacer between the first and second plate and / or a flow guide element and / or at least one welding boss for resistance welding and / or a reservoir and / or a cavity for a fluid and / or a tear-off edge for a fluid and / or at least one channel, in particular a drainage channel with capillary effect, is formed as at least one secondary forming.
[0043] A method according to the invention for producing an electrochemical cell unit for converting electrochemical energy into electrical energy as a fuel cell unit and / or for converting electrical energy into electrochemical energy as an electrolysis cell unit with stacked electrochemical cells, comprising the steps of: providing layered components of the electrochemical cells, namely preferably proton exchange membranes, anodes, cathodes, preferably gas diffusion layers and bipolar plates, stacking the layered components to form electrochemical cells and a stack of the electrochemical cell unit, wherein the bipolar plates are provided by carrying out a method described in this patent application.
[0044] An electrochemical cell unit according to the invention for converting electrochemical energy into electrical energy as a fuel cell unit and / or for converting electrical energy into electrochemical energy as an electrolysis cell unit, comprising stacked electrochemical cells and the electrochemical cells each comprising stacked layered components, and the components of the electrochemical cells preferably being proton exchange membranes, anodes, cathodes, preferably gas diffusion layers and bipolar plates, wherein the electrochemical cell unit is manufactured using a method described in this patent application.During primary mechanical forming, forming marks are created on the surface of the plate element by the mechanical forming tool due to the contact-based primary forming process, and these are detectable in the electrochemical cell unit, for example, optically visible nicks, grooves, scratches, grinding marks or indentations and / or with methods R. 416480.
[0045] - 8 -
[0046] Changes in the structure detectable by material analysis on the surface and / or interior of the first and / or second plate element, in particular a change in the lattice structure of the atoms and / or molecules due to heating and secondary forming. The primary forming marks can be distinguished from the changes during non-contact secondary forming, so that secondary forming can be easily identified as the functional geometries produced by secondary forming, for example, because there are no optically visible nicks, grooves, scratches, grinding marks, or indentations on the surface of the secondary forming due to the non-contact secondary forming and / or the change in the lattice structure of the atoms and / or molecules during local heating for secondary forming.Furthermore, certain functional geometries, such as undercuts or very small cavities, for example as channels with capillary action, cannot be produced during primary mechanical forming to create primary deformations, so that, solely due to the geometry and / or size, certain functional geometries produced by secondary forming can be detected on the electrochemical cell unit.
[0047] In a supplementary embodiment, at least one primary forming operation is performed.
[0048] Preferably, at least one secondary forming operation is performed.
[0049] In a further embodiment, the length, in particular the maximum length, of each secondary forming operation is less than 50%, 30%, 20%, 10%, 5%, 3% or 1% of the length, in particular the maximum length, of each primary forming operation.
[0050] In a further embodiment, the diameter, in particular the maximum diameter, of each secondary forming operation is less than 50%, 30%, 20%, 10%, 5%, 3% or 1% of the diameter, in particular the maximum diameter, of each primary forming operation.
[0051] In another variant, a plate or a raw plate with at least one welded joint is used to manufacture each bipolar plate. R. 416480
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[0053] connected to each other, or two plates or three plates are connected to each other with at least one welded joint.
[0054] Advantageously, at least one welded joint between the first and second plate element is produced, in particular exclusively, by laser welding.
[0055] In an additional embodiment, power modulation of the laser beam generated by the laser is performed for heating in order to perform secondary forming.
[0056] In an additional embodiment, the first and / or second plate element is heated locally, such that a partial area of the total surface of the inside of the first and / or second plate element is heated to a temperature greater than 100 °C, 300 °C or 700 °C, and the size of each partial area is less than 50%, 30%, 20% or 10% of the total surface of the inside of the first and / or second plate element.
[0057] In an additional embodiment, the first and / or second plate element is heated locally, such that a partial area of the total surface of the outside of the first and / or second plate element is heated to a temperature greater than 100 °C, 300 °C or 700 °C, and the size of each partial area is less than 50%, 30%, 20% or 10% of the total surface of the outside of the first and / or second plate element.
[0058] In an additional embodiment, the first and / or second plate element is heated locally, such that a partial area of the total surface of the inside of the first and / or second plate element is heated to a temperature greater than 100 °C, 300 °C or 700 °C, and the size of each partial area is greater than 1%, 2%, 3% or 5% of the total surface of the inside of the first and / or second plate element.
[0059] In an additional embodiment, the first and / or second plate element is locally heated, such that a partial area of the total surface of the outside of the first and / or second plate element is heated to a temperature greater than 100 °C, 300 °C or 700 °C, and the size of each of these areas is increased. R. 416480
[0060] - 10 -
[0061] The partial area is larger than 1%, 2%, 3% or 5% of the total area of the outside of the first and / or second plate element.
[0062] In a supplementary variant, several partial surfaces formed at a distance, in particular at least 0.1 cm, 1 cm, 3 cm or 5 cm, from each other are locally heated to produce each bipolar plate.
[0063] In a supplementary variant, for the production of each bipolar plate, several partial areas formed at a distance, in particular at least 0.1 cm, 1 cm, 3 cm or 5 cm, from each other are locally deformed by secondary forming.
[0064] Advantageously, at least one welded connection between the first and second plate elements is produced after the primary mechanical forming and / or after the secondary forming.
[0065] In an additional embodiment, the temperature of the first and / or second plate element in the area of secondary forming during the forming process, in particular on the inside and / or outside of the first and / or second plate element, is greater than 100 °C, 300 °C or 700 °C.
[0066] Preferably, the pressure in the vacuum chamber during secondary forming is less than 900 mbar, 700 mbar, 500 mbar, 300 mbar or 100 mbar.
[0067] In another embodiment, the pressure in the overpressure chamber during secondary forming is greater than 1 bar, 3 bar, 5 bar, 10 bar, 20 bar, 30 bar or 50 bar.
[0068] In an additional embodiment, the mass flow rate of the directed gas is changed.
[0069] In another embodiment, the secondary forming is carried out before and / or after the welding of the joint between the first and second plate elements. R. 416480
[0070] - 11 -
[0071] In a supplementary variant, the laser and / or the compressed air nozzle / or the vacuum wall and / or the positive pressure wall is moved by a robot, in particular an industrial robot.
[0072] In another variant, the negative pressure wall and / or positive pressure wall is placed on the inside and / or outside of the plate element using a robot, especially an industrial robot.
[0073] In another variant, the weld joint is produced by resistance welding by placing the inner surfaces of the first and second plates against each other at a contact area, applying a contact force to the first and / or second plate with at least one mechanical holding device, so that, as a result of the applied contact force acting as a joining force, the inner surfaces of the first and second plates lie against each other with a compressive force at the contact area, the contact area at least partially forming a joining area for producing the weld joint, producing the weld joint between the first and second plates at the joining area by resistance welding by passing a current through the first plate and second plate with a first electrode and a second electrode.
[0074] In an additional embodiment, the thickness, in particular the maximum and / or minimum, of the first and / or second plate element is between 50 pm and 140 pm, in particular between 70 pm and 110 pm and / or less than 0.2 mm.
[0075] In a supplementary variant, at least one weld joint is performed using KE resistance welding as capacitor discharge resistance welding with a welding time of the current pulse of less than 30 ms or 10 ms.
[0076] In a further embodiment, after stacking the first and second plate elements on top of each other, a gap is formed between the first and second plate elements due to the geometry of the first and / or second plate element. R. 416480
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[0078] In a further embodiment, at least 90% of the bipolar plates, in particular all bipolar plates, are made available to the electrochemical cell unit by carrying out a method described in this patent application.
[0079] In a supplementary variant, the first and second raw plates are provided at least partially, in particular completely, made of metal, especially stainless steel and / or aluminum, and / or plastic and / or composite material.
[0080] In particular, the at least one plate element and / or the bipolar plate is at least partially, and in particular completely, made of metal, in particular stainless steel and / or aluminum, and / or plastic and / or composite material.
[0081] In a supplementary variant, the first and second plates are provided at least partially, in particular completely, in a wave-like and / or disc-like and / or layer-like form and / or are produced with the primary forming process.
[0082] In a supplementary variant, at least one weld connection of the bipolar plate is made, in particular exclusively, at the contact area.
[0083] In another variant, the electrochemical cell unit comprises at least 50, 100, 200 or 400 stacked electrochemical cells.
[0084] The invention further comprises a computer program with program code means stored on a computer-readable data carrier to carry out a method described in this patent application when the computer program is executed on a computer or a corresponding computing unit.
[0085] The invention also includes a computer program product with program code means stored on a computer-readable data carrier to execute a method described in this patent application R. 416480.
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[0087] to be carried out when the computer program is run on a computer or a corresponding computing unit.
[0088] In another variant, the electrochemical cell unit comprises a housing and / or a connection plate. The stack is enclosed by the housing and / or the connection plate.
[0089] In a further embodiment, the fuel cell unit described in this patent application additionally forms an electrolysis cell unit as a reversible fuel cell unit and preferably vice versa.
[0090] In another 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 several connecting devices, and clamping elements.
[0091] Suitable 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.
[0092] In another embodiment, the connecting device is designed as a bolt and / or is rod-shaped and / or is designed as a tension strap.
[0093] The clamping elements are appropriately designed as clamping plates.
[0094] In another variant, the gas conveying device is designed as a blower and / or a compressor and / or a pressure vessel containing an oxidizing agent.
[0095] In particular, the electrochemical cell unit, especially the fuel cell unit and / or electrolysis cell unit, comprises at least 3, 4, 5 or 6 connecting devices.
[0096] In a further embodiment, the clamping elements are plate-shaped and / or disc-shaped and / or flat and / or designed as a grid. R. 416480
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[0098] Preferably, the fuel is hydrogen, hydrogen-rich gas, reformate gas or natural gas.
[0099] Fuel cells and / or electrolysis cells are typically designed to be essentially flat and / or disc-shaped.
[0100] In a complementary variant, the oxidizing agent is air with oxygen or pure oxygen.
[0101] Preferably, the fuel cell unit is a PEM fuel cell unit with PEM fuel cells, or a SOFC fuel cell unit with SOFC fuel cells, or an alkaline fuel cell (AFC).
[0102] Brief description of the drawings
[0103] Exemplary embodiments of the invention are described in more detail below with reference to the accompanying drawings. These show:
[0104] Fig. 1 shows a highly simplified exploded view of an electrochemical cell system as a fuel cell system and electrolysis cell system with components of an electrochemical cell as a fuel cell and electrolysis cell.
[0105] Fig. 2 shows a perspective view of part of a fuel cell and electrolysis cell.
[0106] Fig. 3 shows a longitudinal section through electrochemical cells as fuel cells and electrolysis cells,
[0107] Fig. 4 a perspective view of an electrochemical cell unit as a fuel cell unit and electrolysis cell unit as a fuel cell stack and electrolysis cell stack, R. 416480
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[0109] Fig. 5 shows a side view of the electrochemical cell unit as a fuel cell unit and electrolysis cell unit as a fuel cell stack and electrolysis cell stack.
[0110] Fig. 6 a perspective view of a bipolar plate,
[0111] Fig. 7 shows an enlarged longitudinal section through a fuel cell and electrolysis cell in the area of a weld seam,
[0112] Fig. 8 shows a longitudinal section through a bipolar plate comprising two plates joined together by a weld seam as a weld lens.
[0113] Fig. 9 shows a side view of a raw slab,
[0114] Fig. 10 shows a highly simplified representation of a forming device,
[0115] Fig. 11 shows a side view of part of a first and second plate before they are placed on top of each other.
[0116] Fig. 12 shows a side view of part of a plate element during heating with a laser beam.
[0117] Fig. 13 shows a side view of part of the plate element during the application of a secondary forming force, with a symbolic representation of the forming force as arrows.
[0118] Fig. 14 shows a side view of part of the plate element during the application of a secondary forming force with a mass flow of gas as compressed air.
[0119] Fig. 15 shows a side view of part of the plate element during the application of a secondary forming force with ambient pressure using a vacuum chamber.
[0120] Fig. 16 shows a side view of part of the plate element during the application of a secondary forming force with a pressure chamber, R. 416480
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[0122] Fig. 17 shows a side view of part of the plate element after secondary forming and
[0123] Fig. 18 shows a stress-strain diagram with the strain in % indicated on the abscissa and the stress in MPa indicated on the ordinate of the material of the plate element for different temperatures.
[0124] Figures 1 to 3 illustrate the basic structure of a fuel cell 2, specifically a PEM fuel cell 3 (polymer electrolyte fuel cell 3). The principle of fuel cells 2 is that electrical energy, or electric current, is generated by means of an electrochemical reaction. Hydrogen (H₂) is supplied as a gaseous fuel to an anode 7, which forms the negative terminal. A gaseous oxidizing agent, namely air containing oxygen, is supplied to a cathode 8; that is, the oxygen in the air provides the necessary gaseous oxidizing agent. Reduction (electron uptake) takes place at the cathode 8. Oxidation, the release of electrons, occurs at the anode 7.
[0125] The redox equations for the electrochemical processes are:
[0126] Cathode:
[0127] O2+ 4 H + + 4 e- -» 2 H2O
[0128] Anode:
[0129] 2 H2-» 4 H+ + 4 e-
[0130] Total reaction equation of cathode and anode:
[0131] 2 H2 + O2- → 2 H2O
[0132] The difference between the normal potentials of the electrode pairs under standard conditions, as the reversible fuel cell voltage or open-circuit voltage of the unloaded fuel cell 2, is 1.23 V. This theoretical voltage of 1.23 V is not reached in practice. In the resting state and at low currents, voltages above 1.0 V can be reached, and during operation with higher currents, voltages between R. 416480 are observed.
[0133] - 17 -
[0134] The voltages reached are 0.5 V and 1.0 V. A series connection of several fuel cells 2, in particular a fuel cell unit 1 as a fuel cell stack 1 of several stacked fuel cells 2, exhibits a higher voltage, which corresponds to the number of fuel cells 2 multiplied by the individual voltage of each fuel cell 2.
[0135] Fuel cell 2 also includes a proton exchange membrane 5 (PEM), which is positioned between the anode 7 and the cathode 8. The anode 7 and cathode 8 are layered and disc-shaped, respectively. The PEM 5 acts as an electrolyte, catalyst support, and separator for the reaction gases. The PEM 5 also functions as an electrical insulator, preventing an electrical short circuit between the anode 7 and cathode 8. Generally, proton-conducting films made of perfluorinated and sulfonated polymers, with thicknesses of 12 pm to 150 pm, are used. The PEM 5 conducts the protons H + and blocks ions other than protons H + essentially, so that due to the permeability of PEM 5 to the protons H +The charge transport can take place. The PEM 5 is essentially impermeable to the reaction gases oxygen O2 and hydrogen H2, i.e., it blocks the flow of oxygen O2 and hydrogen H2 between a gas chamber 31 at the anode 7 containing hydrogen H2 as fuel and the gas chamber 32 at the cathode 8 containing air or oxygen O2 as the oxidizing agent. The proton conductivity of the PEM 5 increases with increasing temperature and increasing water content.
[0136] On both sides of the PEM 5, facing the gas spaces 31 and 32, the electrodes 7 and 8 are positioned as the anode 7 and cathode 8, respectively. A unit consisting of the PEM 5 and the electrodes 7 and 8 is referred to as a membrane electrode assembly (MEA). The electrodes 7 and 8 are pressed onto the PEM 5. The electrodes 7 and 8 are platinum-containing carbon particles bonded to PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene propylene copolymer), PFA (perfluoroalkoxy), PVDF (polyvinylidene fluoride), and / or PVA (polyvinyl alcohol) and hot-pressed into microporous carbon fiber, glass fiber, or plastic mats. A catalyst layer 30 is typically applied to each electrode 7 and 8 on the side facing the gas spaces 31 and 32 (not shown). The catalyst layer 30 in the gas space 31 with fuel at the anode 7 comprises nanodispersed R. 416480
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[0138] Platinum-ruthenium on graphitized carbon black particles bound to a binder. The catalyst layer 30 on the gas space 32 with oxidizing agent at the cathode 8 comprises nanodispersed platinum analogously. Examples of binders used include Nation®, a PTFE emulsion, or polyvinyl alcohol.
[0139] In contrast, electrodes 7 and 8 are composed of an ionomer, for example Nation®, platinum-containing carbon particles, and additives. These electrodes 7 and 8, with their ionomer, are electrically conductive due to the carbon particles and also conduct protons H. + and also function as a catalyst layer 30 (Figs. 2 and 3) due to the platinum-containing carbon particles. Membrane electrode assemblies 6 with these electrodes 7, 8 comprising the ionomer form membrane electrode assemblies 6 as CCM (catalyst-coated membrane).
[0140] A gas diffusion layer 9 (GDL) is located on the anode 7 and the cathode 8. The gas diffusion layer 9 at the anode 7 distributes the fuel from fuel channels 12 evenly onto the catalyst layer 30 at the anode 7. The gas diffusion layer 9 at the cathode 8 distributes the oxidant from oxidant channels 13 evenly onto the catalyst layer 30 at the cathode 8. The GDL 9 also draws off water of reaction in the opposite direction to the flow direction of the reaction gases, i.e., in one direction each from the catalyst layer 30 or electrodes 7, 8 to the channels 12, 13. Furthermore, the GDL 9 keeps the PEM 5 moist and conducts the current. The GDL 9 is composed, for example, of a hydrophobic carbon paper as a support and substrate layer and a bonded carbon powder layer as a microporous layer.
[0141] A bipolar plate 10 rests on the GDL 9. The electrically conductive bipolar plate 10 serves as a current collector, for water drainage, and for guiding the reaction gases as process fluids through the channel structures 29 and / or flow fields 29, as well as for dissipating the waste heat, which occurs particularly during the exothermic electrochemical reaction at the cathode 8. For heat dissipation, channels 14 are incorporated into the bipolar plate 10 as channel structures 29 for the passage of a liquid or gaseous coolant as process fluid. The channel structure 29 at the gas space 31 for fuel is from R. 416480.
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[0143] Channels 12 are formed. The channel structure 29 at the gas space 32 for oxidizing agent is formed by channels 13. Materials used for the bipolar plates 10 include, for example, metal, conductive plastics, composite materials, and / or graphite.
[0144] In a fuel cell unit 1 and / or a fuel cell stack 1, several fuel cells 2 are arranged in a straight line (Figs. 4 and 5). Fig. 1 shows an exploded view of two fuel cells 2 arranged in a straight line. Seals 11 provide a fluid-tight seal for the gas spaces 31, 32 and channels 12, 13, respectively. Hydrogen H2 is stored as fuel in a pressurized gas storage tank 21 (Fig. 1) at a pressure of, for example, 350 bar to 700 bar. From the pressurized gas storage tank 21, the fuel is conveyed through a high-pressure line 18 to a pressure reducer 20 to reduce the fuel pressure in a medium-pressure line 17 from approximately 10 bar to 20 bar. From the medium-pressure line 17, the fuel is conveyed to an injector 19. At injector 19, the fuel pressure is reduced to an injection pressure between 1 bar and 3 bar.Fuel is fed from injector 19 to a fuel supply line 16 (Fig. 1) and from the supply line 16 to the fuel channels 12, which form the fuel channel structure 29. The fuel thus flows through the fuel gas space 31. The fuel gas space 31 is formed by the channels 12 and the gas flow channel 9 at the anode 7. After passing through the channels 12, the fuel not consumed in the redox reaction at the anode 7, and any water from controlled anode humidification, is discharged from the fuel cells 2 through a discharge line 15.
[0145] A gas supply device 22, for example designed as a blower 23 or a compressor 24, supplies ambient air as an oxidizing agent into an oxidizing agent supply line 25. From the supply line 25, the air is fed into the oxidizing agent channels 13, which form a channel structure 29 on the bipolar plates 10 for the oxidizing agent, so that the oxidizing agent flows through the oxidizing agent gas space 32. The oxidizing agent gas space 32 is formed by the channels 13 and the gas distribution plate 9 at the cathode 8. After flowing through the channels 13 and the gas space 32, the oxidizing agent 32 is not discharged at the cathode 8R. 416480
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[0147] The consumed oxidizing agent and the reaction water generated at the cathode 8 due to the electrochemical redox reaction are drained from the fuel cells 2 via a discharge line 26. A supply line 27 serves to supply coolant to the coolant channels 14, and a discharge line 28 serves to drain the coolant passed through the channels 14. For the sake of simplicity, the supply and discharge lines 15, 16, 25, 26, 27, 28 are shown as separate lines in Fig. 1. At the end region near the channels 12, 13, 14, aligned fluid openings 41 are formed in the stack of the fuel cell unit 1 on sealing plates 39 as an extension at the end region 40 of the superimposed bipolar plates 10 (Fig. 6) and membrane electrode assemblies 6 (not shown). The fuel cells 2 and the components of the fuel cells 2 are disk-shaped and span essentially parallel fictitious planes 59.The aligned fluid openings 41 and seals (not shown) in a direction perpendicular to the fictitious planes 59 between the fluid openings 41 thus form a supply channel 42 for oxidant, a discharge channel 43 for oxidant, a supply channel 44 for fuel, a discharge channel 45 for fuel, a supply channel 46 for coolant, and a discharge channel 47 for coolant. The supply 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 supply and discharge lines 15, 16, 25, 26, 27, 28 outside the fuel cell unit stack 1 open into the supply and discharge channels 42, 43, 44, 45, 46, 47 inside the fuel cell unit stack 1. The fuel cell stack 1 together with the pressurized gas storage 21 and the gas supply device 22 forms a fuel cell system 4.
[0148] In the fuel cell unit 1, the fuel cells 2 are arranged between two clamping elements 33, which act as clamping plates 34. A first clamping plate 35 rests on the first fuel cell 2, and a second clamping plate 36 rests on the last fuel cell 2. The fuel cell unit 1 comprises approximately 200 to 400 fuel cells 2, not all of which are shown in Figures 4 and 5 for illustrative purposes. The clamping elements 33 exert a compressive force on the fuel cells 2; that is, the first clamping plate 35 rests with a compressive force on the first fuel cell 2, and the second clamping plate 36 rests with a compressive force on the last fuel cell 2. R. 416480
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[0150] The fuel cell stack 2 is thus clamped to ensure the tightness of the fuel, oxidizer, and coolant, particularly due to the elastic seals 11, and also to minimize the electrical contact resistance within the fuel cell stack 1. To clamp the fuel cells 2 with the clamping elements 33, four connecting devices 37 are formed as bolts 38 on the fuel cell unit 1, which are subjected to tensile stress. The four bolts 38 are connected to the chipboard panels 34.
[0151] Figure 6 shows the bipolar plate 10 of the fuel cell 2. The bipolar plate 10 comprises the channels 12, 13, and 14 as three separate channel structures 29. The channels 12, 13, and 14 are not shown separately in Figure 6, but are simplified as a layer of a channel structure 29. The fluid openings 41 on the sealing plates 39 of the bipolar plates 10 and membrane electrode assemblies 6 (not shown) are arranged in a stacked, aligned position within the fuel cell unit 1, forming supply and discharge channels 42, 43, 44, 45, 46, 47. Seals (not shown) are arranged between the sealing plates 39 to provide a fluid-tight seal for the supply and discharge channels 42, 43, 44, 45, 46, 47 formed by the fluid openings 41.The bipolar plate 10 has a length of 61 and a width of 62. It features a feed channel 42 for oxidizing agent, a discharge channel for oxidizing agent, a feed channel 44 for fuel, a discharge channel 45 for fuel, a feed channel 46 for coolant, and a discharge channel 47 for coolant.
[0152] Since the bipolar plate 10 also fluidly separates the gas chamber 31 for fuel from the gas chamber 32 for oxidant and furthermore also fluidly seals the channel 14 for coolant, the term separator plate 51 can additionally be chosen for the bipolar plate 10 for the fluid-tight separation of process fluids. Thus, the term separator plate 51 is also subsumed under the term bipolar plate 10 and vice versa. The channels 12 for fuel, the channels 13 for oxidant, and the channels 14 for coolant of the fuel cell 2 are also formed on an electrochemical cell 52, but with a different function. R. 416480
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[0154] In another embodiment, not shown, the fuel cell unit 1 is configured as an alkaline fuel cell unit 1. Potassium hydroxide solution is used as the mobile electrolyte. The fuel cells 2 are stacked. A monopolar or bipolar cell configuration is possible. The potassium hydroxide solution circulates between an anode and a cathode, carrying 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, i.e., as an electrolysis cell unit 49.
[0155] Fuel cell unit 1 can also be used and operated as electrolysis cell unit 49, i.e., it forms a reversible fuel cell unit 1. The following describes some features that enable the operation of fuel cell unit 1 as electrolysis cell unit 49. For 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) is also required. + The liquid electrolyte is necessary for electrolysis.
[0156] The following redox reactions occur during electrolysis:
[0157] Cathode:
[0158] 4 H3O + + 4 e- -» 2 H2+ 4 H2O
[0159] Anode:
[0160] 6 H2O — » O2 + 4 H3O + + 4 e'
[0161] Total reaction equation of cathode and anode:
[0162] 2 H2O → 2 H2 + O2
[0163] The polarity of electrodes 7, 8 is reversed during electrolysis when operating as an electrolysis cell unit 49 (not shown) compared to operation as a fuel cell unit 1, so that hydrogen H2 is formed as a second substance at the cathodes in the fuel channels 12, through which the liquid electrolyte is passed, and the hydrogen H2 is released from the liquid electrolyte. R. 416480
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[0165] The liquid electrolyte is absorbed and transported in solution. Similarly, the liquid electrolyte is passed through the channels 13 for oxidant, and oxygen (O2) is formed as the first substance at the anodes in or on the channels 13 for oxidant. The fuel cells 2 of the fuel cell unit 1 function as electrolysis cells 50 during operation as electrolysis cell unit 49. The fuel cells 2 and electrolysis cells 50 thus form electrochemical cells 52. The oxygen (O2) formed is absorbed by the liquid electrolyte and transported in solution. The liquid electrolyte is stored in a storage container 54. For the sake of graphical simplification, Fig. 1 shows two storage containers 54 of the fuel cell system 4, which also functions as an electrolysis cell system 48.The 3-way valve 55 on the fuel supply line 16 is switched during operation as an electrolysis cell unit 49, so that instead of fuel from the pressurized gas storage tank 21, the liquid electrolyte is introduced into the fuel supply line 16 by a pump 56 from the storage tank 54. A 3-way valve 55 on the oxidizer supply line 25 is switched during operation as an electrolysis cell unit 49, so that instead of air from the gas supply unit 22, the liquid electrolyte is introduced into the oxidizer supply line 25 by a pump 56 from the storage tank 54.The fuel cell unit 1, which also functions as an electrolysis cell unit 49, optionally features modifications to the electrodes 7, 8 and the gas diffusion layer 9 compared to a fuel cell unit 1 that can only be operated as a fuel cell unit 1: for example, the gas diffusion layer 9 is non-absorbent, so that the liquid electrolyte drains away easily and completely, or the gas diffusion layer 9 is not formed, or the gas diffusion layer 9 is a structure, preferably metallic, in particular a honeycomb or grid structure, on the bipolar plate 10. The electrolysis cell unit 49 with the storage tank 54, the pump 56, the separators 57, 58, and preferably the 3-way valve 55, forms an electrochemical cell system 60.
[0166] A hydrogen separator 57 is arranged on the fuel discharge line 15. The separator 57 separates the hydrogen from the electrolyte containing hydrogen, and the separated hydrogen is introduced into the pressurized gas storage tank 21 by means of a compressor (not shown). The electrolyte drained from the hydrogen separator 57 is then returned to the system. R. 416480
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[0168] The electrolyte is supplied to the storage tank 54 via a line. An oxygen separator 58 is arranged on the fuel discharge line 26. The separator 58 separates the oxygen from the electrolyte containing oxygen, and the separated oxygen is introduced into a compressed gas storage tank for oxygen (not shown) by means of a compressor (not shown). The oxygen in the compressed gas storage tank for oxygen (not shown) can optionally be used for the operation of the fuel cell unit 1 by conveying the oxygen via a line (not shown) into the supply line 25 for oxidant when operating as fuel cell unit 1. The electrolyte drained from the oxygen separator 58 is then returned to the electrolyte storage tank 54 via a line.Channels 12, 13 and the discharge and supply lines 15, 16, 25, 26 are designed such that, after use as an electrolysis cell unit 49 and the switching off of pump 56, the liquid electrolyte completely returns to the storage container 54 due to gravity. Optionally, after use as an electrolysis cell unit 49 and before use as a fuel cell unit 1, an inert gas is passed through channels 12, 13 and the discharge and supply lines 15, 16, 25, 26 to completely remove the liquid electrolyte before the passage of gaseous fuel and oxidizer. Fuel cells 2 and electrolysis cells 2 thus form electrochemical cells 52. Fuel cell unit 1 and electrolysis cell unit 49 therefore form an electrochemical cell unit 53.The channels 12 for fuel and the channels for oxidant thus form channels 12, 13 for conveying the liquid electrolyte when operating as an electrolysis cell unit 49, and this applies analogously to the supply and discharge lines 15, 16, 25, 26. For process-related reasons, an electrolysis cell unit 49 does not normally require channels 14 for conveying coolant. In an electrochemical cell unit 49, the channels 12 for fuel also form channels 12 for conveying fuel and / or electrolyte, and the channels 13 for oxidant also form channels 13 for conveying fuel and / or electrolyte.
[0169] The bipolar plates 10 are produced by resistance welding from the first plate 64 and the second plate 65 as monopolar plates 64, 65. For this purpose, a correspondingly corrugated first and second plate 65 are produced for each bipolar plate 10. 416480
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[0171] Plates 64, 65 are placed one on top of the other and stacked so that the inner surfaces 66 of the first and second plates 64, 65 lie against each other at strip-shaped contact areas 68 as a butt joint. The fictitious planes 59, spanned by the disc-shaped first and second plates 64, 65, are then essentially aligned parallel to each other, in particular with a deviation of less than 30°, 20°, or 10°. The first and second plates 64, 65, made of stainless steel, each have an outer surface 67 opposite the inner surfaces 66. After the two plates 64, 65 are arranged one on top of the other to produce the bipolar plates 10, strip-shaped channels 14 for coolant are formed outside the strip-shaped contact areas 68 between the inner surfaces 66 of the first and second plates 64, 65, forming an intermediate space 75 as an inner area 74.The geometry of the provided first and second plates 64, 65 with a large number of waves necessitates that a large number of channels 14 are formed between the contact areas 68.
[0172] The first and second plates 64, 65 as monopolar plates 64, 65 are joined together by resistance welding to form a bipolar plate 10, so that a welded connection 69 is produced as a large number of welds 70 between the first and second plates 64, 65.
[0173] The weld 70, optionally produced by laser welding, is formed as a continuous, circumferential weld 72 at the edge of the bipolar plate 10 or the first and second plates 64, 65 near the longitudinal and broad sides (shown as a continuous line in Fig. 6) to seal the space 75 between the first and second plates 64, 65 to the outside for the coolant. A further weld 69, 70, shown as a dashed line in Fig. 6, is interrupted and permeable to coolant, allowing the coolant to be introduced from the coolant supply channel 46 into the channel structure 29 and discharged from the channel structure 29 into the coolant discharge channel 47. For this purpose, structures (not shown) are formed in the bipolar plate 10 to guide the coolant from the coolant supply channel 46 into the channel structure 29 and from the channel structure 29 into the coolant discharge channel 47.
[0174] In addition, there are further, section-by-section trained R. 416480
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[0176] Additional welds 73 (shown as a continuous straight line in Fig. 6) are present on an inner area 74. These welds do not provide a sealing function for the coolant to the environment or to the outside and serve only to create a material-bonded connection between the two plates 64, 65. Optionally, they can also serve to seal between two channels 14 for coolant. An inner area 74 is framed by the circumferential weld 72.
[0177] To manufacture the bipolar plate 10, the first plate 64 and the second plate 65, made of stainless steel, are first provided. The first and second plates 64, 65 have a thickness 87 of approximately 70 µm. The first plate 64 is placed on a lower first electrode (not shown) as a support. The second plate 65 is then precisely positioned on top of the first plate 64. Furthermore, all fluid openings 41 are sealed with a process seal 77, using a sealing medium 76, for example, a rubber sealing ring. The process seals 77 are shown with dashed lines in Fig. 6. At the contact area 68, the inner surfaces 66 of the first and second plates 64, 65 thus rest against each other, exerting pressure forces. Fig. 11 shows the first plate 64 and the second plate 65 shortly before they rest against each other and make contact at the contact area 68.A large number of grooves were incorporated into the first and second plates 64, 65 by primary mechanical forming. Fig. 11 shows only a small part of the first and second plates 64, 65, so that in Fig. 1 only three grooves for each plate 64, 65 are visible. In fact, however, as already mentioned, the first and second plates 64, 65 have a large number of grooves forming waves, so that the first and second plates 64, 65 as a whole have a wave-like shape. The width 88 of the local geometry of the groove and the depth 89 of the local geometry of the groove determine the aspect ratio. This aspect ratio is defined as the width 88 divided by the depth 89 and the maximum aspect ratio depends on parameters, for example the thickness 87 of the first and second plate 64, 65 as well as the yield strength, the tensile strength, the transverse contraction and the modulus of elasticity of the material of the plate element 85, 86 as plate 64, 65.A second upper electrode is then placed on the second plate 65. A current is passed through the first and second plates 64, 65 via the electrodes, and the weld joint 69 is formed by resistance welding at the contact area 68 as R. 416480.
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[0179] Joining area formed as a welding lens 71 without formation on the outer sides 67.
[0180] In Fig. 9, a raw plate 83, 84 is shown in a side view as a first raw plate 83 or a second raw plate 84. The raw plate 83, 84 is designed as a flat plate. The first plate 64 is produced by mechanically forming the first raw plate 83 into the first plate 64 with a corrugated or channel-shaped structure using a mechanical contact forming device 78 (Fig. 10). The second plate 65 is produced analogously by mechanically forming the second raw plate 84 in the forming device 78. The forming device 78 shown in Fig. 10 is designed as a mechanical forming tool 79, namely a deep-drawing tool 80. The deep-drawing tool 80 comprises a lower press plate 81 as a die 81, which is stationary.An upper press plate 82, acting as a press punch 82, is movable in a vertical direction by means of a hydraulic device (not shown). The blank plate 83, 84 is inserted between the die 81 and the stamping punch 82, and then the die 81 is moved downwards towards the stamping punch 82 to apply a primary forming force by means of mechanical contact between the blank plate 83, 84 and at least one forming tool 81, 82, namely the die 81 and the stamping punch 82. The term "plate element 85, 86" is the generic term for both the blank plate 83, 84 and the plates 64, 65. The first plate element 85 is formed by both the first plate 64 and the first blank plate 83. The second plate element 86 is thus formed by both the second plate 65 and the second blank plate 84.
[0181] In addition to the primary contact-based mechanical forming of the raw plate 83, 84 into the plate 64, 65, a secondary contactless forming of the plate element 84, 85 is performed with a secondary forming force. The secondary forming can be performed before the primary forming as a forming of the raw plate 83, 84 into the plate element 85, 86 followed by primary forming. The secondary forming can be performed after the primary forming as a forming of the first and / or second plate 64, 65 as the first and / or R. 416480
[0182] - 28 -
[0183] second plate element 85, 86 before or after the production of the weld joint 69.
[0184] Before applying the secondary forming force to the plate element 85, 86, the plate element 85, 86 is locally heated. This local heating is preferably carried out with a laser beam 90 (Fig. 12) and / or by means of thermal radiation and / or a warm air stream. Fig. 12 shows a temperature profile 91 of the plate element 85, 86. The laser beam 90 is directed at the outer surface 67 of the first and / or second plate 64, 65 (only partially shown in Fig. 12) and absorbed at the outer surface 67, causing the plate element 85, 86 to heat up locally. A first temperature layer 92 immediately adjacent to the area where the laser beam 90 strikes the outer surface 87 has a temperature of 1000 °C. A subsequent temperature layer 93 has a temperature of 800 °C. A subsequent temperature layer, 94, has a temperature of 650 °C.The last temperature layer 95, which also partially forms the inner side 66, has a temperature of 500 °C.
[0185] This local heating of the plate element 85, 86 with the laser beam 90 reduces the yield strength and increases the yield strength of the stainless steel sheet of the plate element 85, 86. Furthermore, the transverse contraction is improved. The material of the plate element 85, 86 can thereby reach a near-molten state, enabling secondary forming without cracking. The stiffness and / or strength of the material of the plate element 85, 86 is significantly reduced at elevated temperatures. Due to the elevated temperature, the material of the plate element 85, 86 exhibits no yield strength, allowing secondary forming to be carried out in a flow- or melt-like material state without cracking. Figure 18 shows a stress-strain diagram for the material of the plate element 85, 86 at various temperatures, namely 25 °C, 500 °C, 650 °C, 800 °C, and 1000 °C. In Fig.12. The heating of the plate elements 85, 86 takes place only on the outer surface 67. Alternatively, the heating can also be carried out simultaneously with two laser beams 90 on both the inner surface 66 and the outer surface 67 of the plate element 85, 86 (not shown). R. 416480.
[0186] - 29 -
[0187] During and / or after the local heating of the plate element 85, 86, the secondary forming force 96 is applied to the plate element 85, 86 (Fig. 13). In Fig. 13, the secondary forming force 96 is symbolically represented by arrows, which is applied to the outer surface 67. Optionally, depending on the embodiment, a counterforce 97 can act on the opposite side 66, i.e., the inner surface 66, in the opposite direction to the secondary forming force 96. The secondary forming creates a secondary deformation 111, which in particular forms a functional geometry 112, for example, a spacer between the first and second plate element 85, 86.
[0188] Figure 14 shows a first embodiment for applying the secondary forming force. The secondary forming force is applied by means of a directed mass flow of gas, namely compressed air. An air compressor 101 compresses ambient air into a compressed air reservoir 100 to a pressure of, for example, 10 to 100 bar. From the compressed air reservoir 100, the compressed air is supplied to a compressed air nozzle 98 via a compressed air hose 99. The compressed air nozzle 98 directs the mass flow of compressed air as a pressure jet 102 onto the outer surface 67 of the plate element 85, 86, thereby applying the secondary forming force to the outer surface 67 without contact. The secondary forming force is thus applied locally to the outer surface 67 due to the mass flow of compressed air, which is deflected from the outer surface 67 of the plate element 85, 86. The ambient pressure nevertheless acts on the inside 66 as the counterforce 97 (not shown in Fig. 14).Preferably, in the first embodiment according to Fig. 14, the laser (not shown) is used to generate the laser beam 90, and at a distance from it, the compressed air nozzle 98 is moved along the outer surface 67 at a predetermined constant distance by an industrial robot. This allows both the local heating with the laser beam 90 and the application of the secondary forming force locally with the compressed air jet 102 to be carried out simultaneously.
[0189] Figure 15 shows a second embodiment for applying the secondary forming force. A local negative pressure or vacuum is applied to the inner surface 66 of the plate element 85, 86. For this purpose, a surface 66R is applied to the inner surface 66. 416480
[0190] - 30 -
[0191] A completely gas-tight vacuum wall 104 is placed around the entire circumference, and then the vacuum chamber 103 is evacuated using a vacuum line 105 and a vacuum pump 106, i.e., a vacuum of, for example, 100 mbar is created in the vacuum chamber 103. The ambient pressure of approximately 1000 mbar continues to act on the outer surface 67, so that the secondary forming force 96 on the outer surface 67 is applied by the ambient pressure of approximately 1000 mbar, and the counterforce 97 is applied by the residual pressure in the vacuum chamber 103 at a pressure of approximately 100 mbar. The local heating of the outer surface 67 with the laser beam 90 takes place before the creation of the vacuum in the vacuum chamber 103 and / or while maintaining the vacuum in the vacuum chamber 103. The size of the vacuum chamber 103 can be significantly larger than the area onto which the laser beam 90 is directed on the outer surface 67.However, local forming only occurs in those areas, despite the presence of the vacuum chamber 103, onto which the laser beam 90 has been applied, because only the locally heated material of the plate element 85, 86 has a correspondingly reduced stiffness for secondary forming with the small secondary forming force 96. The secondary forming force relevant for secondary forming is determined by the pressure difference between the inner surface 66 with the vacuum chamber 103 and the outer surface 67 at ambient pressure.
[0192] Figure 16 shows a third embodiment for applying the secondary forming force. A gas-tight pressure wall 108 rests completely around the outer surface 67, forming a pressure chamber 107. Compressed air is introduced into the pressure chamber 107 from the compressed air reservoir 100 via a compressed air line 109, thereby pressurizing the pressure chamber 107 to an overpressure of, for example, 2, 3, or 5 bar. The ambient pressure also acts on the inner surface 66 of the plate element 85, 86. The compressed air in the pressure chamber 107 thus applies the secondary forming force 96 to the outer surface 67, and the ambient pressure applies the counterforce 97 to the inner surface 66 of the plate element 85, 86. The secondary forming force 96, which is decisive for the secondary forming process, is determined by the pressure difference between the pressure on the outside 67 in the overpressure chamber 107 and the pressure at the R. 416480
[0193] - 31 -
[0194] The inner surface 66 is heated to a temperature higher than the ambient pressure. Local heating of the outer surface 67 and / or inner surface 66 with the laser beam 90 occurs before the overpressure is generated in the overpressure chamber 107 and / or while maintaining the overpressure in the underpressure chamber 103. For simultaneous local heating with the laser beam 90 and maintaining the overpressure in the overpressure chamber 107, the laser beam 90 is directed at the inner surface 66. In Fig. 17, the extent 110 of the local secondary deformation 111 is shown as the functional geometry 112.
[0195] Overall, the inventive method for manufacturing the bipolar plate 10, the inventive method for manufacturing the electrochemical cell unit 53, and the inventive electrochemical cell unit 53 offer significant advantages. Heating the first and / or second plate element 85, 86 to a high temperature during the secondary forming process allows for a greater degree of secondary forming 111 due to the resulting changes in material properties. Advantageously, undercuts and very small functional geometries 112, for example, smaller than 3 mm, 2 mm, 3 mm, or 0.5 mm, can also be produced using secondary forming. This opens up new design possibilities that would not be achievable with purely mechanical primary forming.The secondary forming geometries 111 produced by secondary forming, in particular as secondary functional geometries 112, can be easily modified at low cost by changing the location of local heating and the location of application of the local forming force by modifying the programming of a robot that moves the laser and / or the compressed air nozzle 98 and / or places and / or moves the vacuum wall 104 onto the plate element 85, 86 and / or places and / or moves the positive pressure wall 108 onto the plate element 85, 86. This advantageously enables high flexibility and variability for the production of forming geometries 111 at low cost.
Claims
R. 416480 - 32 - Claims 1. Method for manufacturing a bipolar plate (10, 51) for an electrochemical cell unit (53) for converting electrochemical energy into electrical energy as a fuel cell unit (1) and / or for converting electrical energy into electrochemical energy as an electrolysis cell unit (49) with stacked electrochemical cells (52) comprising the steps: providing a first raw plate (83, 85) as a first plate element (85) and a second raw plate (84, 86) as a second plate element (86), Primary mechanical forming with a forming tool (79, 80, 81, 82) of the first raw plate (83, 85) to a first plate (64, 85) as a first plate element (85) by applying a primary forming force to the first raw plate (83, 85) with the forming tool (79, 80, 81, 82) and / or primary mechanical forming with a forming tool (79, 80, 81, 82) of the second raw plate (84, 86) to a second plate (65, 86) as a second plate element (86) by applying a primary forming force to the second raw plate (84, 86) with the forming tool (79, 80, 81, 82). Stacking the first plate element (64, 85) and the second plate element (65, 86) on top of each other, so that the inner surfaces (66) of the first and second plate elements (85, 86) lie on top of each other at a contact area (68), Producing at least one welded joint (69, 70, 71, 72) between the first and second plate elements (85, 86), such that the bipolar plate (10, 51) is formed from the first and second plate elements (85, 86) connected to each other by the welded joint (69, 70, 71, 72), characterized by the fact that R. 416480 - 33 - the first plate element (85) and / or the second plate element (86) is additionally formed by heating the first and / or second plate element (85, 86) to reduce the necessary secondary forming force and by carrying out the secondary forming in the heated state with a secondary forming force, so that after cooling the first and / or second plate element (85, 86) the first and / or second plate element (85, 86) has been formed secondarily.
2. Method according to claim 1, characterized by the fact that the first and / or second plate element (85, 86) is heated locally, in particular with a laser beam (90).
3. Method according to claim 2, characterized by the fact that the laser beam (90) is directed to an inside (66) and / or outside (67) as the surface of the first and / or second plate element (85, 86) for the purpose of heating, in particular locally, the first and / or second plate element (85, 86).
4. Method according to claim 2 or 3, characterized by the fact that the laser beam (90) is moved by means of a relative movement between the first and / or second plate element (85, 86) and the laser beam (90) over the surface (66, 67) of the first and / or second plate element (85, 86).
5. Method according to one or more of the preceding claims, R. 416480 - 34 - characterized by the fact that the secondary forming force for the secondary forming is applied contactlessly, in particular with a gas, to the first and / or second plate element (85, 86).
6. Method according to claim 5, characterized by the fact that The secondary forming force is applied with the gas by applying a pressure difference of the gas, in particular air as ambient air, between the outside (67) and the inside (66) to the outside (67) and the inside (66) of each of a plate element (85, 86).
7. Method according to claim 6, characterized by the fact that The secondary forming force is applied with the gas by applying a directed mass flow of gas, in particular compressed air, to the surface (66, 67), in particular only the outside (67) or only the inside (66), of each plate element (85, 86).
8. Method according to one or more of claims 5 to 7, characterized by the fact that The secondary forming force for the secondary forming process with the gas is applied to the first and / or second plate element (85, 86) by locally vaporizing the material of the first and / or second plate element (85, 86) using the laser beam (90), so that the locally vaporized material causes a pressure difference of the gas between the outside (67) and the inside (66) of each plate element (85, 86) due to the volume increase during the transition of the R. 416480 - 35 - material from the solid state of matter to the gaseous state of matter and the increase in volume on the outside (67) of each plate element (85, 86) is greater than on the inside (66) of each plate element (85, 86) or the increase in volume on the inside (66) of each plate element (85, 86) is greater than on the outside (67) of each plate element (85, 86).
9. Method according to one or more of the preceding claims, characterized by the fact that the secondary forming force for the secondary forming is applied as gravity to the first and / or second plate element (85, 86).
10. Method according to claim one or more of the preceding claims, characterized by the fact that the secondary forming is carried out before the primary mechanical forming than the secondary forming of the first and / or second raw plate (83, 84).
11. Method according to one or more of the preceding claims, characterized by the fact that The secondary forming is carried out after the primary mechanical forming as the secondary forming of the first and / or second plate (64, 65) and / or at least one plate element (85, 86) of the bipolar plate (10, 51).
12. Method according to one or more of the preceding claims, characterized by the fact that R. 416480 - 36 - which at least one welded joint (69, 70, 71, 72) between the first and the second plate element (85, 86) is produced, in particular exclusively, by resistance welding.
13. Method according to one or more of the preceding claims, characterized by the fact that with the secondary forming at least one, in particular local, functional geometry (112), preferably a spacer between the first and second plate (66, 67) and / or a flow guide element, is formed as at least one secondary forming (111).
14. Method for manufacturing an electrochemical cell unit (53) for converting electrochemical energy into electrical energy as a fuel cell unit (1) and / or for converting electrical energy into electrochemical energy as an electrolysis cell unit (49) with stacked electrochemical cells (52) comprising the steps: providing layered components (5, 6, 7, 8, 9, 10, 30, 51) of the electrochemical cells (52), namely preferably proton exchange membranes (5), anodes (7), cathodes (8), preferably gas diffusion layers (9) and bipolar plates (10, 51), Stacking the layered components (5, 6, 7, 8, 9, 10, 30, 51) to form electrochemical cells (52) and to form a stack of the electrochemical cell unit (53), characterized by the fact that the bipolar plates (10, 51) are provided by carrying out a method according to one or more of the preceding claims.
15. Electrochemical cell unit (53) for converting electrochemical energy into electrical energy as a fuel cell unit (2) and / or for R. 416480 - 37 - Conversion of electrical energy into electrochemical energy as an electrolysis cell unit (49), comprising - stacked electrochemical cells (52) and the electrochemical cells (52) each comprise stacked layered components (5, 6, 7, 8, 9, 10, 51) and - the components (5, 6, 7, 8, 9, 10, 51) of the electrochemical cells (52) are preferably proton exchange membranes (5), anodes (7), cathodes (8), preferably gas diffusion layers (9) and bipolar plates (10, 51), characterized by the fact that the electrochemical cell unit (53) is manufactured by a method according to claim 14.