DEVICE FOR SURFACE COATING A STRIP-SHAPED SUBSTRATE MADE OF METAL FOR THE PRODUCTION OF BIPOLAR PLATES, ELECTRODES OR ELECTRIC CIRCUITS

Description

[0001] The invention relates to a device for surface coating a ribbon-shaped metal substrate for the production of bipolar plates, electrodes, or electrical current collectors for electrochemical cells with a coating formed with carbon and / or metal. The electrochemical cells are primarily fuel cells or redox flow batteries.

[0002] The bipolar plate, electrodes, or electrical current collector of an electrochemical cell, especially a fuel cell, must fulfill two main functions. Firstly, it serves as the electrical contact of the electrochemical cell, requiring high electrical conductivity. Secondly, it ensures the uniform distribution of the process media (e.g., hydrogen, oxygen). During the operation of a fuel cell, the process media—fuel and oxidizer—react to form water vapor, which is carried away on the oxygen side. However, this often leads to an accumulation of water vapor and the formation of small water droplets that are difficult to remove. This results in a reduced oxygen supply, ultimately decreasing the power output. Therefore, surface coatings with improved electrical conductivity and water removal capabilities are required.

[0003] Currently, coatings for bipolar plates, electrodes, or electrical current collectors are produced in a time-consuming and costly batch process. Furthermore, a wide variety of deposition processes from the fields of CVD and PVD, such as low-pressure CVD, magnetron sputtering, and arc evaporation, are used to form surface coatings on substrates of bipolar plates, electrodes, or electrical current collectors. For future industrial scaling of production processes, a fully continuous manufacturing process, including the aforementioned surface functionalizations, is desired.

[0004] Up to now, attempts have been made to improve water drainage from the cell through novel but simultaneously manufacturing-intensive flowfield designs with adapted channel geometries.

[0005] Current solutions in the field of surface coatings almost exclusively address the problem of electrical conductivity. However, they do not adequately consider water accumulation.

[0006] While solutions exist that utilize electrically conductive and hydrophobic surface coatings made of or with carbon layers, these present problems that have a particularly negative impact on continuous production and the maintenance of consistent quality.

[0007] It is generally known to coat bipolar plates with carbon coatings consisting predominantly of sp² modification carbon, and to use the electric arc coating process for this purpose. However, difficulties have arisen with large-area coating using continuous flow coating processes. In particular, these result in inhomogeneous and uneven coatings.

[0008] Another problem with continuous and homogeneous coating application is that without a sufficiently high negative bias voltage applied to the substrate, losses of coating material can occur, as the necessary energy for the carbon ions to move across the surface being coated is not available. However, if a suitable bias voltage is applied to the moving substrate, problems such as stress fractures or short circuits can occur, which in turn can lead to inhomogeneities in the coating.

[0009] When carbon layers are formed using electric arc discharges, uneven material removal can occur without countermeasures. This is due to an uncontrolled movement of the electric arc on the surface of a carbon-based target connected as the cathode. This can also lead to non-homogeneous layer formation across the entire surface. Furthermore, the utilization rate of the carbon used is reduced, meaning that a graphite target has to be replaced more frequently than necessary, as uncontrolled cratering on the surface is particularly detrimental.

[0010] The currently used evaporation technology is characterized by an electrical potential difference between the cathode (coating material) and the strip-shaped substrate to be coated. However, applying a high electrical potential to a steel strip as a substrate for bipolar plates, electrodes, or electrical current collectors is not readily possible in continuous industrial production. This is due to plant and manufacturing constraints, such as the required vacuum technology, safety aspects (freestanding, energized coils), or a complex process sequence. The development of a new evaporation technology should enable potential-free strip coating using established coating processes.

[0011] The goal of coating a metallic bipolar plate, electrode, or electrical current collector is to further enhance the already good intrinsic electrical conductivity of the substrate material (preferably stainless steel). This can be achieved by depositing a carbon-based, graphite-like coating system with a high proportion of sp² bonds. Besides the composition of the chamber atmosphere, other process parameters, such as temperature (100 °C - 400 °C) and pressure (0.01 Pa - 1 Pa), have a significant influence on coating growth and the resulting properties. Therefore, the coating process should be individually adjustable to achieve specific coating properties (hydrophobicity, electrical conductivity of the coating).

[0012] US 2019 / 0316249 A1 describes a method for forming a layer on a substrate using magnetron sputtering.

[0013] A vacuum arc coating device is known from EP 0 r492 592 A1.

[0014] AU 639 469 B2 relates to a method and a device for treating components with electric arc discharges.

[0015] It is therefore an object of the invention to provide methods for the continuous formation of surface coatings based on carbon, which are formed from crystalline, or at least predominantly crystalline, carbon, in which a consistent coating quality can be maintained within a predetermined surface area of ​​a substrate used for the production of bipolar plates, electrodes, or electrical current collectors, and over a longer period of time. Furthermore, interruptions of the coating process should be largely avoided.

[0016] According to the invention, this problem is solved with a device having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features specified in dependent claims.

[0017] To achieve efficient manufacturing of functionalized bipolar plates, electrodes, or electrical current collectors, a so-called roll-to-roll process can be used. This process involves continuously unwinding a strip-shaped substrate from a roll and, after the formation of a surface coating, either rewinding it or immediately processing it further. In particular, a separation process is used to create individual bipolar plates, electrodes, or electrical current collectors, possibly with additional shaping. The aim is to unwind a coil of the substrate material in air under normal ambient atmospheric conditions, then feed it into a vacuum chamber via airlocks for further processing steps, primarily coating processes, and finally rewind or further process the finished strip.

[0018] Typically, different, usually quite high bias voltages, in the range of several hundred volts, are applied to the strip as the substrate to be coated during the individual process steps. In a continuous process, this can lead to contact problems, potentially causing electrical arcing on the strip. This, in turn, can damage the substrate surface or result in uneven surface coatings, particularly affecting layer thickness and inhomogeneous material composition. To solve this problem, a technique for potential-free strip coating is proposed.This is to be achieved with a new evaporation technology in which the advantageous electrical potential difference is created by at least one auxiliary electrode positioned between the substrate and the actual evaporation source, in this specific case a target consisting of a metal or carbon, particularly graphite, and connected as the anode. The at least one auxiliary electrode allows the movement of ions from a pre-generated plasma towards the substrate surface to be influenced. This enables the creation of a homogeneous coating of metal and / or carbon over the desired electrically or electrochemically active area of ​​bipolar plates, electrodes, or electrical current collectors.

[0019] In the device according to the invention, a metallic ribbon substrate, preferably made of stainless steel, is coated in a vacuum chamber. It is preferably guided translationally through the vacuum chamber continuously at a constant speed. The ribbon substrate is arranged and aligned at a distance from and parallel to the longitudinal axis of a rod-shaped target, which consists of a pure metal such as Cr, Mo, Cu, Al, Ti, Ta, W, V, Au, Nb, Hf, Ag, or Zr, an alloy thereof, or carbon in the form of graphite. A nitride of one of these metals can also be used. The rod-shaped target can have a round or polygonal cross-section perpendicular to its longitudinal axis.

[0020] The rod-shaped target is connected to the negative terminal of a first electrical voltage source. An anode, or optionally an ignition electrode, is positioned at a distance from the rod-shaped target and connected to the positive terminal of the first electrical voltage source. The first electrical voltage source can be operated in pulsed or continuous mode to ignite and maintain electrical arc discharges between the anode and the rod-shaped target.

[0021] Furthermore, at least one auxiliary electrode, connected to the positive terminal of a second electrical voltage source, is positioned at a distance from the rod-shaped target, parallel to its longitudinal axis, and at least partially between the ribbon substrate and the surface of the rod-shaped target. By using an auxiliary electrode and / or an electrically conductive, strip- or grid-shaped element, aligned parallel to the surface of the ribbon substrate, positioned between the auxiliary electrode and the ribbon substrate, and connected to the negative terminal of the second electrical voltage source, the application of a negative bias voltage to the ribbon substrate can be avoided, thus eliminating the associated disadvantages.

[0022] The auxiliary electrode could be formed with at least one or at least two rectangular plate-shaped elements. At least two plate-shaped elements could be spaced apart from each other, with the rod-shaped target positioned between the plate-shaped elements. According to the invention, an auxiliary electrode is formed with a V-shaped or U-shaped concave curve towards the rod-shaped target, such that ions of the plasma generated by electric arc discharges are arranged between the plate-shaped elements or the legs of a V- or U-shaped curved auxiliary electrode and are additionally influenced in their movement towards the surface of the ribbon substrate to be coated by the electric field generated by the auxiliary electrode between the plate-shaped elements or the legs.It is advantageous if the plate-shaped elements or the legs are oriented at an oblique angle, such that the distance between the end faces of the longer sides of the plate-shaped elements or legs oriented towards the rod-shaped graphite target is smaller than the distance between their end faces oriented towards the ribbon-shaped substrate. Alternatively, several plate-shaped elements or curved auxiliary electrodes can be arranged in a row instead of a single plate-shaped element or a single curved auxiliary electrode. Two row arrangements can be positioned opposite each other, or an auxiliary electrode can be combined with a row arrangement of several V-shaped, U-shaped, or concavely curved plate-shaped elements, with the rod-shaped target, the anode, and the ignition electrode arranged analogously.

[0023] A plate-shaped auxiliary electrode can also be arranged in a V- or U-shaped concave curve, open towards the ribbon substrate, with the rod-shaped target positioned inside and at a distance from the V- or U-shaped convexly curved plate-shaped element. This influences the movement of the ions in the generated plasma towards the surface of the ribbon substrate to be coated. It is also possible to provide another electrically conductive element in the base region, below the rod-shaped target, positioned below the end faces of two plate-shaped elements facing in that direction. This creates an arrangement that can function similarly to a single curved auxiliary electrode. This additional electrically conductive element can be connected to the same electrical potential as the two plate-shaped elements.

[0024] An electrically conductive, grid- or strip-shaped element can be arranged, alone or additionally, between the surface of the rod-shaped target, on which the base points of electric arcs are formed, and the ribbon substrate, and connected to the negative terminal of a second electrical voltage source. This allows accelerated ions to pass through the mesh of a grid or between the strips of such a grid- or strip-shaped element towards the surface of the ribbon substrate to be coated, thus forming the coating. The strips should preferably be aligned parallel to each other and arranged equidistantly.The mesh size and the spacing of strips, as well as the material thickness of a grid or the width of strips with the spaces between them, should be chosen such that at least 50%, preferably at least 70% and particularly preferably at least 90% of the ions strike the corresponding surface of the ribbon-shaped substrate unhindered.

[0025] An electrically conductive grid- or strip-shaped element should have an area, including the spaces between meshes of a grid or between strips through which ions can pass to coat the surface of the ribbon-shaped material, that corresponds to at least 50%, preferably at least 70%, and particularly preferably at least 90% of the total area of ​​the surface of the ribbon-shaped substrate to be coated at the same time.

[0026] In an embodiment in which an auxiliary electrode with at least one plate-shaped element and a grid- or strip-shaped element are jointly present in a vacuum chamber, it is advantageous if an electrical voltage is applied to a plate-shaped auxiliary electrode, the absolute value of which is at least twice, preferably four times and particularly preferably at least ten times smaller than an electrical voltage applied to a grid- or strip-shaped element.

[0027] One or more preferably rectangular, plate-shaped elements of an auxiliary electrode arranged in a series should have a length on its long side that is at least 90% of the length of a respective rod-shaped target.

[0028] An electrical voltage between 5 V and 1500 V should be applied to at least one auxiliary electrode, which is formed with one or more plate-shaped elements, and / or an electrically conductive grid- or strip-shaped element.

[0029] In an advantageous embodiment, several permanent or electromagnets can be arranged in a series, at least on the side of the rod-shaped target facing away from the ribbon-shaped substrate, with a spacing between each permanent or electromagnet extending from one end of the rod-shaped target to its opposite end. They can thus be arranged similarly to a chain, where the individual links are not directly connected to one another, but advantageously in a common plane parallel to the longitudinal axis of the rod-shaped target.

[0030] The magnetic fields of the permanent or electromagnets arranged in this way can guide the base point of an ignited electric arc on the surface of the rod-shaped target from the end face of the rod-shaped target, which is located at the anode, towards the opposite end face of the rod-shaped target, so that a more uniform material removal can be achieved on the surface of the rod-shaped target over its length.

[0031] The use of permanent or electromagnets is particularly advantageous with a rod-shaped target made of carbon, preferably in the form of graphite.

[0032] A further permanent or electromagnet can also be arranged at the end face of the rod-shaped target, opposite the end face where the anode or, preferably, an ignition electrode is located, and be configured or operated such that an ignited electric arc is extinguished when its base point on the surface of the rod-shaped target reaches the area of ​​the magnetic field of the further permanent or electromagnet arranged at the end face of the rod-shaped target. After or at a point before the extinguishing of this electric arc, a subsequent electric arc can be ignited at the side of the rod-shaped target by means of an ignition electrode arranged there, which is connected to a positive pole of the first or a further electrical voltage source.When multiple electric arcs are operated simultaneously, it should be ensured that at least their base points on the surface of the rod-shaped target do not interfere with each other. This can be achieved, for example, by using a suitable pulse frequency for the ignition of the electric arcs. The ignition electrode should be operated with an electrical voltage in the range of 20 V to 30 V, preferably 25 ± 1 V. An electrical voltage in the range of 60 V to 80 V can be used for the ignition of an electric arc. The resulting electric current depends on the material of the rod-shaped target and can range from 50 A to 400 A.

[0033] Advantageously, the auxiliary electrode, which is formed with a curved or several plate-shaped elements, can be cooled. For this purpose, a suitably tempered fluid can be used and applied directly to the auxiliary electrode as a gas stream or in the form of liquid cooling.

[0034] For improved guidance of the base points of electric arcs, permanent or electromagnets can generate magnetic fields with the same field line orientation from the end face of the rod-shaped target where the ignition electrode or anode is located to the opposite end face of the rod-shaped target. The field strength of the magnetic fields generated by the permanent or electromagnets should preferably increase continuously from the end face of the rod-shaped target where the anode is located to the opposite end face of the rod-shaped target, and / or the distance between adjacent permanent or electromagnets should decrease.This allows for better influence on the movement of the respective base point of an electric arc, depending on the distance from the anode, using the force of the magnetic fields.

[0035] The additional permanent or electromagnet can generate a magnetic field whose polarity is opposite to that generated by the permanent or electromagnets, and / or the magnetic field generated by the additional permanent or electromagnet can have a greater field strength than the magnetic fields generated by the permanent or electromagnets. Alone or in addition to these measures, the additional permanent or electromagnet can extend beyond the surface of the rod-shaped target facing the ribbon-like substrate.

[0036] The permanent or electromagnets arranged in series can be U-shaped and aligned so that their open side points towards the ribbon-shaped substrate, allowing the effect of their magnetic fields to be used to hold the base point of the ignited electric arc on a specific surface area of ​​the rod-shaped target between the respective legs of the permanent or electromagnets.

[0037] In the invention, several vacuum chambers, which can be designed as described above, can advantageously be arranged successively in a series arrangement in the feed direction of the ribbon-shaped substrate for forming the coating, which is formed with metal and / or carbon and / or a modification on the surface of the ribbon-shaped substrate in the form of nitriding, carburizing and / or nitriding-carburizing.

[0038] Thus, a first vacuum chamber, designed for plasma fine cleaning, can be arranged in the feed direction of the ribbon substrate, followed by a second vacuum chamber, designed for modification of the surface of the ribbon substrate in the form of nitriding and / or for the formation of a metallic intermediate layer, and subsequently by at least one further vacuum chamber, designed for coating the ribbon substrate with the metal of the rod-shaped target or with carbon.This allows for successive steps of fine cleaning, nitriding of the surface of the ribbon substrate, and then the formation of the coating on the substrate. Alternatively, after fine cleaning of the surface of the ribbon substrate, a metallic intermediate layer can be applied, which, for example, can improve adhesion or prevent diffusion, before the coating is formed on the surface of the ribbon substrate. However, it is also possible to perform fine cleaning, preferably in the form of plasma fine cleaning, in a vacuum chamber, followed by coating formation in a further vacuum chamber.

[0039] In at least one of the vacuum chambers, the rod-shaped target can be coated with the metal or carbon. To ensure a completely homogeneous coating of the metal or carbon across the desired surface of the ribbon substrate, at least two vacuum chambers arranged sequentially in the feed direction of the ribbon substrate can be used for this purpose. Multiple such vacuum chambers also enable continuous coating if a rod-shaped target needs to be exchanged within one of the vacuum chambers.

[0040] In at least one vacuum chamber, a surface treatment of the ribbon-like substrate can also be performed before the carbon coating is formed. For this purpose, a suitable reactive gas containing nitrogen and / or carbon can be introduced into the respective vacuum chamber to achieve nitration, carburization, or both on the surface. In this case, a target can be omitted in a suitably designed vacuum chamber; only a cathode is used, which does not directly influence the surface modification process with the reactive gas and simply provides the necessary energy.

[0041] For a continuous coating process, it is particularly advantageous to exchange cathode material made of metal or carbon (graphite) within a vacuum chamber as "inline" as possible and without significant delays, or to change the target. For this purpose, a multi-chamber system can be used on a vacuum chamber, which can be constructed similarly to a turret. This system allows for the exchange of a used rod-shaped target for a new one without significantly interrupting the coating process and without requiring any interruption of the vacuum conditions within the respective vacuum chamber. A multi-chamber system can be flanged to a vacuum chamber. Within the multi-chamber system, individual chambers can be provided to hold rod-shaped targets. By moving the multi-chamber system, an empty chamber can be positioned to receive a used rod-shaped target.Subsequently, a further movement can take place in which another chamber is positioned so that a new, unused, rod-shaped target can be moved from this chamber into its desired position within the vacuum chamber. The multi-chamber system should form a vacuum lock and / or the individual chambers should be able to be moved into their respective desired positions by means of a rotating motion.

[0042] By coating the ribbon-shaped substrate for the production of bipolar plates, electrodes, or electrical current collectors with a metallic or graphite-like carbon layer (GLC) on its surface, a significant increase in electrical conductivity can be achieved. Furthermore, an improvement in corrosion resistance can be expected if suitable metallic intermediate layers are formed in a known manner (e.g., Cr, Mo, Ti, Ag, Ta, Nb, Ru, Rh, W, V, Au, Zr, Al, Cu, Hf). For the aforementioned intermediate coatings, the cathodic arc deposition process can also be used in principle, both in pulsed and, preferably, in unpulsed mode under high vacuum.

[0043] In electric arc discharges, a high-current discharge (short circuit) can be induced by a preferably short-term mechanical contact on the cathode, advantageously with an ignition electrode. This ignites an electric arc between an anode and the target, which acts as the cathode. The base of the arc can move on the cathode surface. The energy of the electric arc generates a plasma on the surface of the target, and the ions in this plasma can form the surface coating on the respective substrate surface. The atoms ejected during plasma formation are ionized as a result of collisions with emitted electrons, and the released ions are accelerated towards the substrate. This technique is characterized by high deposition rates of several tenths of micrometers per minute and the very high ionization levels achievable, sometimes up to 95%.

[0044] In contrast, other deposition processes in the field of CVD often require very high process temperatures (> 500 °C) and sometimes use toxic or otherwise safety-critical gases. Furthermore, they often have a very long process duration of several hours and require complex treatment of the process-related exhaust gases.

[0045] In addition to a metallic intermediate layer, other options are available to increase corrosion resistance, such as plasma nitriding using the AEGD process followed by carbon coating. In the AEGD process, an aperture is positioned in front of a metal evaporator, trapping the ions and allowing only the emitted electrons to reach the auxiliary electrode (AEGD). This excites the plasma. The nitriding process is then initiated by introducing nitrogen. The plasma intensity can be increased by raising the AEGD voltage. The subsequent coating with metal or carbon can be carried out using the arc welding process described above.

[0046] By carrying out the individual process steps in a continuous conveyor process using a roll-to-roll method, costs are reduced and productivity is increased.

[0047] This can be advantageously used in fuel cells in the automotive industry, in hydrogen electrolysis, and in battery applications (e.g., redox flow batteries).

[0048] Additionally, for a smooth process flow in future production, it is advantageous to achieve the longest possible service life per cathode (target) made of metal or carbon (graphite). Using a multi-chamber airlock system, rod-shaped graphite targets can be exchanged in a high vacuum, i.e., during operation. A system similar to a turret magazine with several movable, preferably rotatable, chambers, each holding a rod-shaped target, is one possible implementation for maintaining the most continuous process possible.

[0049] To ensure a homogeneous coating, several vacuum chambers designed and operated according to the invention can be arranged in series one after the other in the direction of movement of the ribbon-shaped substrate. The vacuum chambers can be equipped with an airlock system to maintain the vacuum conditions.

[0050] With the aid of intelligent control between the actual evaporation unit (anode, cathode, and belt conveyor), the ignition times of an electric arc can be adapted to the respective feed rate of the ribbon substrate, thus achieving synchronization. If an electric arc between the anode and the rod-shaped target (acting as the cathode) is extinguished, a vacuum chamber located downstream in the feed direction, containing a rod-shaped target, anode, and a grid- or strip-shaped electrically conductive element and / or auxiliary electrode, can be activated immediately afterward and used for layer formation on the substrate surface. This prevents defects and ultimately increases process stability.However, several vacuum chambers arranged in this way can also be operated simultaneously to compensate for incontinences during the respective coating processes and to obtain a homogeneous carbon layer of uniform thickness.

[0051] Prior to the actual treatment and coating of a ribbon-shaped substrate, wet chemical cleaning can be carried out to remove grease, oil, and production residues. The respective surfaces can also be cleaned of surface contaminants, preferably as a fine cleaning process, either alone or additionally, using plasma or ion bombardment in a manner known per se.

[0052] A high vacuum of up to 0.01 Pa should be maintained in the respective vacuum chambers, with airlocks at the inlet and outlet of each vacuum chamber being designed accordingly to maintain this vacuum permanently during a continuously operated coating process.

[0053] The vacuum chamber should be heated to a temperature between 100 °C and 300 °C for degassing before coating begins. Ion sputtering (etching) can also be performed in the vacuum chamber prior to coating for additional cleaning and activation of the substrate surface. For this purpose, metal ions in an argon atmosphere (via gas inlet) can be used at high electrical voltages of 500 V to 1500 V at at least one auxiliary electrode and within a pressure range of 0.1 Pa to 1 Pa. The maximum electrical voltage can be reduced to 1000 V for continuous operation of electric arcs and to a maximum of 1500 V for pulsed operation.

[0054] Adhesion-promoting intermediate layers can be formed in a known manner by deposition of metal ions (e.g. Cr, Mo, Ti, Ag, Ta, Nb, Ru, Rh, W, V, Au, Zr, Al, Cu, Hf) in a pressure range between 0.1 Pa and 1 Pa and bias voltages of 0 - 500 V on an auxiliary electrode and / or grid- or strip-shaped element prior to the formation of a carbon layer.

[0055] The vacuum chamber(s) and the ribbon-shaped substrate should be connected to ground potential.

[0056] A vacuum chamber should also be brought to or maintained at temperatures of 100 °C to 400 °C before carrying out subsequent process steps.

[0057] A carbon layer can be formed by deposition at high electrical voltages of 50 V to 1000 V at the anode within a pressure range of 0.01 Pa to 1 Pa. This allows for subplantation. When an electric arc is ignited, an electric current of 5 A to 30 A flows.

[0058] An electrical voltage in the range of 5 V to 1500 V should be applied to a grid- or strip-shaped element.

[0059] Plasma nitriding, which can be performed before the formation of the carbon layer on the substrate surface, is a thermochemical treatment of the surface of steels with, for example, nitrogen at relatively low temperatures (T < 600 °C) and is typically used to improve wear resistance. Subsequent carburizing by carbon deposition can improve not only the corrosion resistance but also the electrical conductivity of the bipolar plate. However, lower nitriding temperatures should be used for this purpose.

[0060] Both process steps can be carried out under the aforementioned vacuum conditions. Applying a high electrical voltage between the cathode and anode generates the required plasma (ionized gas). In the case of plasma nitriding, this is a nitrogen plasma. During carbon deposition, an additional process gas, such as fluorine or nitrogen, can be introduced into the vacuum chamber for the desired doping. This creates a mixed plasma of ionized carbon and dopant atoms. Carbon subplantation allows for the structuring of the substrate surface, resulting in nanocrystalline (doped) carbon within the nitrided layer. This improves the desired properties of the bipolar plate, electrode, or electrical current collector, and ultimately, the electrochemical cell.

[0061] The invention will be explained in more detail below using an example.

[0062] This shows: Figure 1 schematically depicts a part of a vacuum chamber that can be used in the invention, in a side view; Figure 2A a front view of the in Figure 1 shown part; Figure 2B a front view of the in Figure 1 shown part with an electrically conductive grid- or strip-shaped element; Figure 3A a schematic sectional view of a vacuum chamber that can be used in the device according to the invention and Figure 3B Another example of a vacuum chamber that can be used in the device according to the invention, each in a schematic sectional view.

[0063] In Figure 1 and 2A and 2BThe schematic shows how a rod-shaped graphite target 3a can be arranged in principle in relation to an anode 3b and an ignition electrode 5, an auxiliary electrode 6, 6a, 6b, permanent or electromagnets 7, and another permanent or electromagnet 8. The two plate-shaped elements 6a and 6b, which form the auxiliary electrode 6, are oriented at an oblique angle and parallel to the longitudinal axis of the rod-shaped graphite target 3a, so that they can exert a reverse funnel effect for the ions with which the carbon layer is formed as a coating. Advantageously, the ions can thus be directed towards the respective surface to be coated of the target 3a. Figure 1 and 2 The process is accelerated on the ribbon-shaped substrate 1 made of stainless steel (not shown).

[0064] Out of Figures 2A and 2BA wedge-shaped arrangement of plate-shaped elements 6a and 6b can be extracted as an auxiliary electrode. The rod-shaped target 3a and the anode 3b are arranged between the plate-shaped elements 6a and 6b, which are arranged conically widening towards the ribbon-shaped substrate 1. The permanent or electromagnets 7 are schematically indicated below the rod-shaped target 3a. The horizontal arrow above the ribbon-shaped substrate 1 indicates the direction of feed motion of the substrate 1.

[0065] The plate-shaped elements 6a and 6b forming the auxiliary electrode can also be replaced, in a form not shown, by a single plate-shaped element, which is then formed or deformed in a V-shape, U-shape, or concave shape, and similarly to the one shown in Figures 2A and 2B It can be arranged.

[0066] In Figure 2B is that in Figure 2AThe example shown is supplemented with a grid- or strip-shaped element 11, which is arranged between the arrangement with the rod-shaped target 3a, the anode 3b, the ignition electrode 5 and the upper edge in the direction of the substrate 1 and the surface of the ribbon-shaped substrate 1 to be coated. The element 11 is arranged with its grid or strips parallel to the surface of the substrate 1 and is connected to the negative terminal of the second electrical voltage source 9.

[0067] The absolute magnitude of the negative electrical voltage acting on the grid- or strip-shaped element 11 is considerably greater than that acting on the auxiliary electrode formed with the plate-shaped elements 6a and 6b.

[0068] In an embodiment not shown, an auxiliary electrode 6b formed with at least one plate-shaped element can also be dispensed with, and only the further grid- or strip-shaped element 11 can be used for accelerating ions towards the surface of the ribbon-shaped substrate 1 to be coated.

[0069] With the schematic representations in Figures 3a and 3b It can be illustrated how other elements of a device can be arranged and designed in relation to each other.

[0070] The first electrical voltage source 4 is electrically connected on one side to the negative pole of the rod-shaped graphite target 3a and on the other side to a positive pole on an end face of the rod-shaped graphite target 3 at a distance from this fixedly installed ignition electrode or anode 5.

[0071] Parallel to the surface of the rod-shaped graphite target 3, on which the base points of ignited electric arc discharges between ignition electrode or anode 5, auxiliary electrode 6 and rod-shaped graphite target 3 are guided to plasma formation, the ribbon-shaped substrate 1 is guided translationally through the vacuum chamber 2 in order to form a carbon layer on a surface of the ribbon-shaped substrate 1.

[0072] Below the rod-shaped graphite target 3, eight permanent or electromagnets 7 are arranged in a row in this example. On the opposite end face, to the end face where the anode 5 is located, another permanent or electromagnet 8 is arranged, which extinguishes an electric arc when its base point enters the area of ​​influence of the magnetic field generated by the other permanent or electromagnet 8.

[0073] The plate-shaped elements 6a and 6b, with which the auxiliary electrode 6 is formed, or a concavely curved auxiliary electrode 6 is / are attached to the positive connected to the positive pole of a second electrical voltage source 9.

[0074] The vacuum chamber 2 and / or the ribbon-shaped substrate 1 are at ground potential.

[0075] Vacuum chamber 2 also has a connection 10 through which pumping is possible to maintain a sufficient vacuum in vacuum chamber 2.

Claims

1. Device to surface coat a ribbon-shaped substrate of a metal for the manufacture of bipolar plates, electrodes or electrical current conductors for electrochemical cells with a coating formed with metal or carbon, in which the ribbon-shaped substrate (1) is arranged in a vacuum chamber (2) at a distance from a rod-shaped target (3a) and is aligned parallel to the longitudinal axis of the rod-shaped target (3a), which is made of a metal or carbon; the rod-shaped target (3a) is connected to the negative pole of a first electrical voltage source (4), and an anode (3b), which is connected to the positive pole of the first electrical voltage source (4), is arranged at a distance from the rod-shaped target (3a), wherein the first electrical voltage source (4) is operated in pulsed or continuous mode to ignite and maintain electrical arc discharges between the anode (3b) and the rod-shaped target (3a), and at least one auxiliary electrode (6, 6a, 6b), which is connected to a positive pole of a second electrical voltage source (9), and the rod-shaped target (3a) is arranged within the legs of an auxiliary electrode (6) concavely curved in a V-shape or a U-shape towards the rod-shaped target (3a) or in a gap between an auxiliary electrode formed with at least two plate-like elements (6a, 6b) at a distance from the auxiliary electrode (6) concavely curved in a V-shape or a U-shape or the plate-like elements (6a, 6b) so that metal or carbon ions released by electric arc discharges from the rod-shaped target (3a) pass through the auxiliary electrode (6, 6a, 6b), which is open towards the rod-shaped target (3a), to the ribbon-shaped substrate (1).

2. The device according to claim 1, characterised in that an ignition electrode (5) connected to the positive pole of the first electrical voltage source (4) for igniting electrical arc discharges is arranged at a distance from the rod-shaped target (3a) on an end face of the rod-shaped target (3a).

3. The device according to any one of the preceding claims, characterised in that an electrically conductive strip- or grid-shaped element (11) is aligned parallel to the surface of the strip-shaped substrate (1), arranged between the auxiliary electrode (6, 6a, 6b) and the strip-shaped substrate (1) and is connected to the negative pole of the second electrical voltage source.

4. The device according to any one of the preceding claims, characterised in that a plurality of permanent or electromagnets (7) are arranged in a row at least on the side of the rod-shaped target (3a) facing away from the strip-shaped substrate (1), with a distance between the individual permanent or electromagnets (7) starting from one end face of the rod-shaped target (3a) to its opposite end face.

5. The device according to any one of the preceding claims, characterised in that a further permanent magnet or electromagnet (8) is arranged at the end face of the rod-shaped target (3a), which is opposite the end face at which the anode (3b) is arranged, and is configured or can be operated such that an ignited electric arc is extinguished when its base point on the surface of the rod-shaped target (3a) reaches the area of the magnetic field of the further permanent or electromagnet (8), located at the end face of the rod-shaped target (3a).

6. The device according to any one of the preceding claims, characterised in that the permanent or electromagnets (7) generate magnetic fields with field lines of the same orientation from the front end of the rod-shaped graphite target (3) on which the anode (5) is arranged, up to the oppositely arranged front end of the rod-shaped target (3a), generating magnetic fields with field lines that are each aligned in the same direction, whereby the field strength of the magnetic fields generated by the permanent or electromagnets (7) starting from the end face of the rod-shaped target (3a) to which the anode (3b) is attached, to the opposite end face of the rod-shaped target (3a), and / or the distance between permanent or electromagnets (7) arranged directly next to each other decreases in this direction.

7. The device according to any one of the preceding claims, characterised in that the further permanent magnet or electromagnet (8) generates a magnetic field whose polarity is opposite to that of the magnetic fields generated by the permanent or electromagnets (7) and / or the magnetic field generated by the further permanent or electromagnet (8) has a greater field strength than the magnetic fields generated by the permanent or electromagnets (7) and / or the further permanent magnet or electromagnet (8) protrudes beyond the surface of the rod-shaped graphite target facing the strip-shaped substrate (1).

8. The device according to any one of the preceding claims, characterised in that a plurality of vacuum chambers (2) according to any one of the preceding claims are in a row arrangement in the feed direction of the strip-shaped substrate (1) to form the coating, which is formed with the metal or carbon of the rod-shaped target (3a), a first vacuum chamber designed for plasma fine cleaning, followed by a second vacuum chamber designed for modifying the surface of the strip-shaped substrate (1) in the form of a nitration, carburisation and / or nitration-carburisation and / or for forming a metallic intermediate layer, and then at least one further vacuum chamber configured for coating the strip-shaped substrate (1) with the metal of the rod-shaped target (3a) or with the carbon.

9. The device according to one of the preceding claims, characterised in that a vacuum chamber (2) in which rod-shaped targets (3a) are accommodated and by manipulating the multi-chamber system, a used rod-shaped target (3a) can be replaced with a new, unused rod-shaped target (3a) without any interruption of the vacuum conditions in the respective vacuum chamber (2).

10. The device according to one of the preceding claims, characterised in that an electrical voltage between 5 V and 1500 V is applied to the at least one auxiliary electrode (6, 6a, 6b, 11).

11. The device according to any one of the preceding claims, characterised in that the auxiliary electrode (6, 6a, 6b) has been cooled.