Method for manufacturing bipolar plates for fuel cells

Abstract

Method for manufacturing bipolar plates for fuel cells, wherein at least one of the two electrodes of fuel cells is arranged as a bipolar plate on at least one side and is electrically connectable to a membrane-electrode arrangement, wherein the membrane forming an electrolyte is a polymer membrane, in which a metal strip (1) or two supplied metal strips are guided through a second device (3) and / or a third device (4), wherein the second device (3) for carrying out fine cleaning and / or nitriding of the metal strip and the third device (4) for carrying out a surface coating on one side of a surface are designed with an adhesion-enhancing metal layer, and A carbon layer is applied to the surface thus treated in a fourth device (5), and Subsequently, a forming of the two metal strips or a division of the one metal strip into two metal strips (1.1, 1.2) and a forming of these metal strips obtained by division (1.1, 1.2) is carried out, in which channels are formed for the supply of fuel and oxidizing agent as well as for the removal of reaction products of the electrochemical reactions, wherein The two metal strips subsequently formed, or the two metal strips obtained by division subsequently formed (1.1, 1.2), are moved and positioned towards each other in such a way that surface areas in which a material-bonded joining is to take place come into contact with each other, and the joining is achieved with at least one laser beam (13) which is directed into a gap between the formed metal strips or metal strips obtained by division (1.1, 1.2) moved towards each other at an angle, and a weld joint is formed only there, and thereby the individual steps that are carried out in the devices (3, 4, 5), the forming and joining are carried out successively in a continuous process.

Description

[0001] The invention relates to a method for producing bipolar plates for fuel cells, in particular fuel cells in which a bipolar plate is arranged on one side of at least one of the two electrodes of fuel cells and can be connected to a membrane-electrode arrangement, wherein the membrane forming an electrolyte is a polymer membrane.

[0002] Fuel cells are used, for example, to generate electricity in mobile applications by converting chemical energy into electrical energy. Currently, the production of fuel cells is still cost-intensive, meaning their use in the automotive sector, for example, is not yet economically viable. Bipolar plates (BIPs) in fuel cells supply hydrogen and oxygen, remove water and cooling water, and supply and collect released electrons. An anode (hydrogen supply) and a cathode (oxygen supply and water removal) are located between two bipolar plates, between which a polymer membrane (polymer electrolyte membrane - PEM) with an electrode coating containing, for example, platinum as a catalyst, and catalyst layers, and the gas diffusion layer are arranged. These form a so-called membrane electrode assembly (MEA).Additionally, appropriate seals are applied to the bipolar plate. This typically occurs before the MEA is applied. The PEM is an electrically insulating but proton-conducting polymer membrane. This allows hydrogen ions to diffuse through it, and electrical current can be conducted to the cathode via a load. The electrode layers are typically hot-pressed onto the PEM. So-called gas diffusion layers (GDLs) are arranged between the bipolar plates and the membrane / electrode. These layers are a knitted fabric, e.g., made of carbon fibers. The GDLs are designed to distribute the gases escaping from the BiP channels evenly and across the membrane and to conduct the electrons released by the hydrogen to or from the respective bipolar plate.

[0003] The fuel cell typically achieves a voltage of, for example, 0.5 V - 1.23 V between the two electrodes. However, due to losses, the usable electrical voltage is typically lower. It is important that the released electrons are absorbed as efficiently as possible on the hydrogen side and returned to the process as efficiently as possible on the oxygen side. The contact or passage resistance should be as low as possible. Electrical resistance at this point has a direct influence on the efficiency of the BIP. The operating temperature is maintained in an optimal range for the cell type, for example, < 100 °C. The cooling required for this can be achieved via a cooling circuit within the bipolar plate.

[0004] In the production of such fuel cells, a BIP half-shell is currently manufactured from a rolled steel or titanium sheet (thickness 0.05 mm - 0.2 mm). For this purpose, the sheet is cut out, for example, and formed using a single- or multi-stage stamping process. This half-shell is then joined to a second half-shell to form a BIP. The half-shells can have different geometries on the cathode and anode sides. The joining process for stainless steel BIP is typically laser welding. Adhesive joining processes are also used for titanium. After the plates are joined, they are surface coated on both sides. This can, for example, be a layer system that ends with a carbon layer.

[0005] A seal is then applied to the BIP, which can be achieved, for example, using a spraying process. It is then cured. Alternatively, a prefabricated seal can be applied. The MEA is then applied. Fuel cells or fuel cell stacks are formed by stacking such BIPs + MEAs. The process described sometimes involves intermediate steps, for example, for quality assurance. This testing also includes testing for the tightness of individual cells and, ultimately, the entire cell stack.

[0006] DE 10 2017 205 523 A1, DE 10 2017 202 679 A1 and DE 10 2011017 417 A1 disclose possibilities for the production of bipolar plates that can be used in PEM fuel cells.

[0007] It is therefore an object of the invention to provide possibilities for increasing labor productivity in the production of bipolar plates for fuel cells.

[0008] According to the invention, this object is achieved by a method having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features defined in subordinate claims.

[0009] One improvement is the approach to fuel cell manufacturing, where the entire production can be carried out in a single process chain or in a single belt process. To achieve this, as many production steps as possible should be carried out in the belt process, and the belt should be separated into BIPs, BIP + GDL, or BIP + MEAs as late as possible in the process chain. In this case, it is a roll-to-plate process. From these separated BIPs, an entire fuel cell stack consisting of a multitude of stacked BIPs + MEAs and the corresponding sealing technology and end pieces can be constructed at the end of the process chain.

[0010] In the method, one metal strip or two metal strips can be passed through a first device designed for pre-cleaning the metal strip or the two metal strips if pre-cleaning is required.

[0011] Following any pre-cleaning, the one or two metal strips are passed through a second device and / or a third device. The second device is designed to perform fine cleaning and / or nitriding of the metal strip, and the third device is designed to apply a surface coating to one side of a surface with an adhesion-enhancing metal layer.

[0012] A carbon layer is applied to the treated surface in a fourth device.

[0013] Subsequently, during the feed movement of one of the metal strips pretreated in this way, a preferably central division in the feed axis direction and rotation of one of the divided metal strips by 180 ° can be carried out.

[0014] If two metal strips are used and pretreated in this way, it may be necessary to rotate one of the two pretreated metal strips by 180°.

[0015] Again following any division and / or rotation that may have been carried out, or directly after the formation of the carbon layer, the metal strips are formed to create channels for the supply of fuel and oxidant, as well as for the removal of reaction products from the electrochemical reactions. These formed strips are therefore no longer planar, but have a three-dimensional surface structure with elevations and / or depressions. Channel widths in the range of, for example, 0.1 mm - 2 mm and channel depths of 0.05 - 1.5 mm can be achieved. Strips formed in this way can also have openings and thus no closed surface, for example in the area of ​​the channel structure. In this case, the channel structure can also be designed as a lattice structure.

[0016] The formed metal strips are moved toward each other and positioned so that surface areas where a material bond is to be created come into contact with each other. The bond is then formed with at least one laser beam directed into a gap between the formed metal strips that are moving toward each other, forming a welded joint only there. This welding process can also be combined with a welding process in which one of the metal strips is joined to the other in the form of a welded joint.

[0017] The individual steps of pretreatment in the devices, if necessary dividing and turning as well as forming and joining should be carried out one after the other in a continuous process.

[0018] Before coating, a metal strip should be cleaned, as oil residues from the rolling process may still be present. Cleaning can generally be achieved using wet chemical processes.

[0019] If only very thin oil films are present on the surface, cleaning can also be achieved by carbonizing the remaining oil and simultaneously preheating the strip. Temperatures for this are approximately 150 °C. In this way, for example, hydrocarbon compounds can be oxidized during heat treatment, and the oxidation products can then be removed.

[0020] If the metal strip is already cleaned or oil-free, pre-cleaning may not be necessary.

[0021] After pre-cleaning and simultaneous preheating of one or both metal strips, nitriding and / or plasma fine cleaning of the surfaces is performed. For this purpose, the metal strip or two metal strips should be heated to temperatures of 320 °C - 450 °C. Plasma fine cleaning can be advantageously performed in combination with nitriding, whereby plasma fine cleaning can be performed first before nitrogen is added for nitriding. If plasma fine cleaning is not performed in combination with nitriding, the achievable nitriding depth per unit time may be reduced.

[0022] Plasma nitriding is a thermochemical surface treatment, particularly of steels, using nitrogen, for example, and is typically used to improve wear properties. However, at low nitriding temperatures, corrosion resistance can also be improved. The long nitriding times required are particularly critical for achieving great nitriding depths. However, these are not required for the invention.

[0023] However, to simply improve the adhesion of a subsequent carbon coating and create a nitriding zone close to the edge, short nitriding times with correspondingly reduced nitriding depths of, for example, a few µm are sufficient. Alternatively, nitriding can be omitted and replaced by, for example, a sputtering process or another coating process. Such a sputtering process can be carried out as metal ion sputtering, for example, by generating chromium ions using an arc process and accelerating them onto the surface to be coated. This allows a chromium layer to be formed that improves adhesion and corrosion protection.

[0024] Subsequently, and as the final coating process, a carbon layer with a thickness of <200 nm, but preferably <50 nm, is applied to the metal strip or two metal strips in the fourth device. During this process, the metal strip or strips should be kept at a temperature T >300 °C, and the carbon ions should be implanted into the surfaces of the metal strip or strips.

[0025] After the coating process, one metal strip is split into at least two metal strips, one of which becomes the anode side of the BIP and the other the cathode side of the respective BIP. One of the metal strips obtained by the split is then rotated 180°. Alternatively, the two metal strips can be split before coating and coated in the same or two different systems. In this case, no strip splitting takes place. Since the coating of the two metal strips is typically applied from below, one of these two metal strips, from which a BIP half-shell is formed, should be turned 180° before the forming process. This can also be done inline.Preferably, the pretreatment of two metal strips is carried out in such a way that the two metal strips are moved in parallel alignment to one another and at the same speed through the devices and a device for rotating one of two metal strips, wherein this speed should preferably also be maintained during the forming and a joining to be carried out thereafter.

[0026] Alternatively, the strip can also be guided vertically during coating. In this case, a metal strip could be coated on both sides, for example, or the two sides of the metal strip could be coated in different areas on the front and back, eliminating the need to rotate the metal strip 180° before forming or joining.

[0027] The forming process for metal strips can be carried out using various well-known methods such as deep drawing, roll stamping, embossing, punching, or media-based forming processes, for example, hydroforming. For this purpose, at least one forming tool can be designed, for example, in the form of an embossing roller or an embossing die. In contrast to rolling or deep drawing, hydroforming requires only one embossing tool, in the form of a die, for each of the cathode and anode sides.

[0028] During hydroforming, an active medium is fed onto the side of the sheet facing the die, which presses the metal strip against the contour of the die; in principle, this can also be done in several stages.

[0029] For roll stamping, at least two rolls of a roll pair should be used, one for the cathode side and one for the anode side. A roll pair can consist of a female and a male die, whose radially outer surfaces have been appropriately structured. For a multi-stage forming process, several roll pairs can also be arranged in series. The forming process for one anode side and one cathode side should be carried out synchronously in one strip run. The stamping structures for the cathode and anode sides are typically different.

[0030] For non-continuous forming processes followed by continuous further processing, for example, using laser welding, it should be possible to provide strip storage before and after forming, for example in the form of loops that can vary the path of the metal strip between coating or strip slitting and forming, or even between forming and laser welding. For all of the forming processes described, this offers the advantage of being able to join the formed metal strips with a precise fit during laser welding. "Precise fit" here means that the metal strip sections to be joined are brought together and positioned in such a way that they come into contact with one another.

[0031] With at least one laser beam from the direction of one of the two metal strips, the metal strips can be joined at their outer edges at least in the edge area of ​​the bipolar plate and the media supply.

[0032] The forming of the pretreated metal strips should be carried out in such a way that areas of the metal strips that are to be joined using laser radiation are either not formed or are formed in such a way that these surface areas are positioned relative to one another following the forming process during joining such that they come into contact with one another and converge at an angle before joining, so that a gap is formed between the formed metal strips to be joined, into which gap the at least one laser beam is directed onto the surface areas to be joined. A tight, integral connection can be created in these areas by welding using the at least one laser beam. The heat input from the laser beam should be minimized in order to minimize thermal distortion of the BIP.

[0033] For a laser welding process, jig rolls or forming rolls with geometric structures can be used, such as those used in the forming process on the side facing the coating on one or both metal strips. In a multi-stage embossing process, the rolls can also be designed differently from the previously used embossing tools on their forming surfaces. The jig rolls should each have a raised surface at the positions where a weld seam or weld spot is to be formed.

[0034] The two fixture rollers cannot be designed as a male and female die.

[0035] When welding the pretreated and formed metal strips to be joined, the functional coating on the BIP should not be damaged. To achieve this, a weld seam or spot weld should be located within a BIP. This prevents the corrosion-reducing effect of the coating at the weld points from being reduced.

[0036] If necessary, an additional weld can be performed around the bipolar plate, and at material feed points, an overlap weld can be performed. This may also damage the coating.

[0037] After joining the BIP half-shells, they can be further processed either individually or in a strip process, preferably to complete complete fuel cells.

[0038] The semi-finished products can be separated in coated, formed and bonded form and then further processed into fuel cells.

[0039] Before separation, which can be performed using a separation process such as laser cutting, a seal and, if necessary, the materials of an MEA can be applied individually or a complete MEA can be applied to a BIP. These process steps can also be incorporated into the manufacturing process according to the invention.

[0040] Metal strips of varying thicknesses can also be used for production. This allows for influencing the strength and operating conditions, particularly the locally varying thermal conditions of fuel cells.

[0041] For example, a BIP can be produced using the individual processes described below: Laser welding for joining the pretreated and formed metal strips can be performed, for example, using an IR (wavelength, e.g., 1000 nm - 1100 nm) single-mode fiber laser. Between the laser source and the surface, the laser beam can be guided via a fiber, collimated at the end of the fiber, and deflected via a scanner with at least one reflective element. The scanner can be designed, for example, as a galvo scanner with two reflective elements. The laser beam can then be focused using f-theta optics. The focal width is typically 10 µm - 200 µm.

[0042] In metal ion sputtering for fine cleaning in a second device, the surface of one or more at least pre-cleaned metal strips can be cleaned by bombardment with ions with sufficient energy (10 2eV to several tens 3 eV). This is based on a momentum transfer between the respective incident ion and the surface. Through elastic "nuclear collisions," the momentum is introduced into the material at the surface of the respective metal band, initiating a collision cascade. This can cause surface atoms to receive an outward-directed momentum. If the kinetic energy of the incident ions exceeds the binding energy of the material atoms of the respective metal band, they are dispersed from the solid surface, primarily in atomic form but also in the form of atom clusters.

[0043] By applying a high electrical voltage in the range between 100 V and 1000 V to the respective metal strip, ideally in a vacuum chamber of a second device in the pressure range of 10 -3 mbar - 10 2mbar, a low-pressure plasma can be generated using noble gases. With a mixture of excited metal and gas ions, the high-energy particles are accelerated toward the substrate by the applied electric current potential, abrading the surface. This allows for fine plasma cleaning of the substrate and increases the metal strip surface roughness.

[0044] In potential-free fine cleaning, the metal ions are accelerated onto the surface of a particular metal strip via additional electrodes. Alternatively, an electrical potential can be applied to the metal ion source.

[0045] The metallization of metallic surfaces for passivation is well known. For example, metal surfaces are galvanized or chrome-plated to provide long-term protection against corrosion. Depending on the operating conditions, high redox potentials sometimes occur in a fuel cell, creating a very aggressive environment. If metallic BIPs are used, they can corrode. The goal of metallic BIPs is to increase corrosion resistance and achieve good electrical conductivity.

[0046] Corrosion resistance can be achieved or improved by a corrosion-reducing coating or nitriding of the metal strip.

[0047] Plasma nitriding is a thermo-chemical treatment of the surface of steels, for example with nitrogen at temperatures of approx. < 550° C. It is normally used to improve wear properties. Especially in stainless steels, the passivating effect of chromium is lost when chromium sets to form chromium nitride (CrN). This reduces corrosion resistance. By plasma nitriding at lower temperatures of < 420 °C, the formation of CrN can be largely avoided and corrosion resistance can even be improved. The introduction of nitrogen atoms into the area of ​​the metal strip close to the surface leads to a lattice expansion of the cubic austenitic atom structure. For this purpose, the nitrogen is ionized in a negative pressure nitrogen atmosphere at pressures of approx. 0.1 Pa and accelerated towards the metal strip.

[0048] The improvement in electrical conductivity can be achieved by deposition of a carbon-based, graphite-like layer system in a fourth device.

[0049] By deposition using a non-pulsed or pulsed carbon ion source, e.g., arc evaporation of a carbon target in a vacuum chamber, electrically conductive, corrosion-resistant layers can be deposited. With a simultaneous increase, especially of the temperature during carbon deposition, fewer metastable sp 3 -bonds and increased sp 2 -bonds of the carbon in the layer. The generated carbon ions should be accelerated to high average ion energies >100 eV, ideally approximately 300 eV, via a potential difference (> 400 V) between the metal strip and the carbon evaporator or accelerated via auxiliary electrodes, in order to achieve implantation of the carbon ions.

[0050] Carburizing, through the subsequent addition of carbon, can increase not only corrosion resistance but also electrical conductivity. The material of the metal strips used to produce the BIPs can therefore have a lower electrical contact resistance. At pressures in the range of 0.01 Pa - 10 Pa, surface modification is achieved using ionized gas or plasma. To generate the plasma, an electrical voltage of several hundred volts can be applied in a vacuum between a cathode and an anode in a second device or another device arranged upstream of the fourth device in the feed direction of the respective metal strip. Depending on the electrical conductivity of at least one carbon-containing gas used, a specific electrical current density results when the electrical voltage is applied.Auxiliary anodes provide additional acceleration to the free electrons released by an electron source via arc discharge, allowing plasma intensification. Carbon-containing gases that can be used are preferably carbon dioxide, methane, propane, or carbon-containing gas mixtures, such as hydrogen, nitrogen, and carbon monoxide.

[0051] Carburizing can prevent a reduction in corrosion protection in the area of ​​the laser weld seam.

[0052] In the process according to the invention, surfaces of one metal strip or two metal strips can also be carbonitrided.

[0053] Strip handling can be simplified by the strip process and the use of rollers to fix the metal strips during joining.

[0054] The heat input through joining and thus thermal distortion of the BiP can be minimized because, on the one hand, the rollers can dissipate heat and, on the other hand, the weld seams or points can be made finer.

[0055] Thanks to the described solution, the carbon-coated metal strips no longer need to be wound up after coating (reducing damage), and potential contamination can be prevented. One or both metal strips can be unwound from a single reel and, if necessary, guided over deflection rollers. The feed motion can at least be supported by pairs of drive rollers. The feed motion can also be achieved solely by pairs of rollers for the aforementioned forming process.

[0056] The required process times can be minimized and contamination of the materials or components during transport can be avoided.

[0057] Fuel cells with BIP produced according to the invention can be used in the automotive, aircraft, transportation industries or mobile applications.

[0058] The invention will be explained in more detail below by way of example.

[0059] Showing: Fig. 1 shows in schematic form an example of the implementation of the method according to the invention and Fig. 2 a possibility for joining two pretreated metal strips.

[0060] In the Fig. In the example shown in Figure 1, a metal strip 1 is unwound from a roll 8 and introduced via a deflection roll 9 into a first device 2 for carrying out a rough cleaning.

[0061] From there, the metal strip 1 is conveyed to a second device 3, where fine cleaning and nitriding are performed using plasma. The thus-treated metal strip 1 is then conveyed to the third device 4, where a chromium layer is applied to the surfaces of the metal strip 1 to improve adhesion and provide corrosion protection.

[0062] A carbon layer is then formed in the fourth device 5.

[0063] At least the second to fourth devices 3 to 5 should have an internal pressure that is lower than the ambient pressure and is suitable for carrying out the respective process in the respective device.

[0064] A lock is provided between each device 2 to 5. Lock 6.2 provides the transition from the first device 2 to the second device 3, in this example, with an internal pressure below ambient pressure. Lock 6.3 provides the transition between the third device 4 with reduced internal pressure. Lock 6.4 provides the transition from a fourth device 5 with reduced internal pressure relative to the ambient atmosphere. A lock 6.1 is also provided upstream of the first device 2.

[0065] A device 10 is arranged downstream of the fourth device 5 in the feed direction of the metal strip 1, with which the metal strip 1 is divided into two pretreated metal strips 1.1 and 1.2. The metal strip 1 can preferably be cut centrally, parallel to the feed axis of the metal strip 1.

[0066] One of the two pretreated metal strips 1.2 thus obtained is fed to a device 11, by which it is rotated by 180°. Since usually only one surface of the metal strip is pretreated, the rotation is performed in such a way that the pretreated surfaces of metal strips 1.1 and 1.2 do not face each other.

[0067] In this example, each of the metal strips 1.1 and 1.2 is fed to at least one forming device 7 and conveyed further. After forming, the strip is no longer planar but has a wavy, typically three-dimensional surface with depressions or elevations.

[0068] The forming device can, for example, consist of embossing rollers structured to deform the metal strips 1.1 and 1.2 to create depressions and, if necessary, elevations in the form of channels or hills for the supply and removal of operating materials and reaction products and their distribution within fuel cells. The rollers each consist of pairs, one forming the die and one forming the male die.

[0069] The metal strips 1.1 and 1.2 thus formed are fed to a device 12 for material-to-material joining, which can preferably be carried out using laser radiation.

[0070] Subsequently, separation and further production of fuel cells can be carried out, as explained in the general part of the description.

[0071] In Fig.Figure 2 shows how two formed metal strips 1.1 and 1.2, which have been suitably twisted relative to each other, one of which has the anode-side channel structure and the other the cathode-side channel structure, are moved together into the gap between the two rollers 7.1 and 7.2. As the rollers 7.1 and 7.2 rotate, they also continue to move.

[0072] If rollers 7.1 and 7.2 bring surface areas of the formed metal strips 1.1 and 1.2 into contact where a material bond is to be created, a laser beam 13 is directed into the gap between rollers 7.1 and 7.2 onto the facing surfaces of the pretreated and formed metal strips 1.1 and 1.2, so that a material bond is created at these positions. At these positions, surface areas of the metal strips 1.1 and 1.2 come into contact with each other. The channel structure created between the metal strips 1.1 and 1.2 can form the cooling channels.

[0073] The laser beam 13 can be directed to the respective positions for establishing the bonded connection using two reflective elements 14.1 and 14.2, which form a scanner or galvo scanner, and with which it can be deflected to the respective positions where the bonded connections are to be formed. Using an f-theta optics 15, the focal length and thus the position of the focal plane of the laser beam 13 can be precisely influenced.

Claims

[1] Method for the production of bipolar plates of fuel cells, in which a bipolar plate is arranged on at least one side of at least one of the two electrodes of fuel cells and can be electrically connected to a membrane-electrode arrangement, wherein the membrane forming an electrolyte is a polymer membrane, in which a metal strip (1) or two supplied metal strips is / are guided through a second device (3) and / or a third device (4), wherein the second device (3) for carrying out a fine cleaning and / or nitriding of the metal strip and the third device (4) is designed to carry out a surface coating on one side of a surface with an adhesion-improving metal layer, and a carbon layer is applied to the surface thus treated in a fourth device (5), and subsequently, a forming of the two metal strips or a division of one metal strip into two metal strips (1.1, 1.2) and a forming of these metal strips (1.1, 1.2) obtained by division is carried out, in which channels for the supply of fuel and oxidizing agent as well as the removal of reaction products of the electrochemical reactions are formed, wherein the then formed two metal strips or the then formed two metal strips obtained by division (1.1, 1.2) are moved towards each other and positioned in such a way that surface areas in which a material-locking joining is to take place come into contact with each other and the joining is achieved with at least one laser beam (13), which is directed into a gap between the formed metal strips or metal strips obtained by division (1.1, 1.2) moved towards each other at an angle and only there a welded connection is formed, and in this case the individual steps carried out in the devices (3, 4, 5), the forming and joining, are carried out one after the other in a continuous flow process. [2] Method according to claim 1, characterized by that the second device (3), third device (4) and a fourth device (5) are operated under an internal pressure reduced compared to the environment and are separated from the environment and / or from each other by locks (6). [3] Method according to one of the preceding claims, characterized by that the metal strip (1) or the two metal strips is / are guided in the conveying direction upstream of the second device (3) or third device (4) through a first device (2) which is designed for pre-cleaning the metal strip (1) or the two metal strips. [4] Method according to one of the preceding claims, characterized bythat during the feed movement of one of the metal strips (1) pretreated in this way, after formation of the carbon layer, a preferably central division in the feed axis direction and rotation of one of the divided metal strips (1.2) by 180 ° or a rotation of one of two metal strips pretreated in this way by 180 ° is carried out. [5] Method according to one of the preceding claims, characterized by that with the fourth device (5) by means of a non-pulsed ion implantation at high ion energies, a carbon layer formed with sp2-hybridized carbon is formed on a surface of the one metal strip (1) or the two metal strips, wherein ion energies greater than 100 eV are maintained. [6] Method according to one of claims 3 to 5, characterized bythat the pre-cleaning is carried out by wet chemical means or by means of a heat treatment in which hydrocarbon compounds are oxidised and then the oxidation products are removed. [7] Method according to one of the preceding claims, characterized by that the fine cleaning and / or nitriding is carried out with a plasma, whereby the metal strip(s) have been heated to a temperature in the range 320 °C to 450 °C. [8] Method according to one of the preceding claims, characterized by that an adhesive layer is formed by accelerating metal ions, in particular chromium ions, onto the surface to be coated by means of an arc process. [9] Method according to one of the preceding claims, characterized bythat for the forming of the pretreated metal strips or metal strips obtained by division (1.1, 1.2), at least two forming tools (7.1, 7.2) of at least one tool pair are used, through which the pretreated metal strips are moved and the surfaces of the tool pair facing each other are designed to form the pretreated metal strips or metal strips obtained by division (1.1, 1.2). [10] Method according to one of the preceding claims, characterized bythat the forming of the metal strips or metal strips obtained by division (1.1, 1.2) is carried out in such a way that areas of the metal strips or metal strips obtained by division (1.1, 1.2) which are to be joined by means of a material bond using laser radiation are either not formed or are formed in such a way that these surface areas are positioned relative to one another following the forming process during the joining process in such a way that they come into contact with one another and before the joining process a gap is formed between the formed metal strips to be joined or the metal strips obtained by division (1.1, 1.2), into which gap the at least one laser beam (13) can be directed onto the surface areas to be joined. [11] Method according to the preceding claim, characterized bythat the metal strips or the metal strips obtained by division (1.1, 1.2) are joined with at least one laser beam from the direction of one of the two metal strips or one of the metal strips obtained by division (1.1, 1.2) and at least in the edge region of the bipolar plate and the media supply. [12] Method according to one of the preceding claims, characterized by that nitriding is carried out at temperatures below 450 °C in a nitrogen atmosphere in the second device (3) for a maximum period of 5 minutes. [13] Method according to one of the preceding claims, characterized by that a metal band (1) or two metal bands made of steel or titanium are used. [14] Method according to one of the preceding claims, characterized bythat two metal strips are moved in parallel alignment to one another and at the same speed through the devices (2, 3, 4, 5) and a device (12) for joining the metal strips, wherein this speed is preferably also maintained during the forming and, if necessary, during a strip turn or rotation. [15] Method according to one of the preceding claims, characterized by that in the second device (3) or a further device which is arranged in the feed direction of the one metal strip or the two metal strips in front of the fourth device (5), an additional carborization is carried out with the supply of carbon. [16] Method according to one of the preceding claims, characterized by that metal strips of different thicknesses are used.

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