WO2003026036A2 - Coated metal object in the form of a plate and used as component of a fuel cell stack - Google Patents

Coated metal object in the form of a plate and used as component of a fuel cell stack Download PDF

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Publication number
WO2003026036A2
WO2003026036A2 PCT/EP2002/010481 EP0210481W WO03026036A2 WO 2003026036 A2 WO2003026036 A2 WO 2003026036A2 EP 0210481 W EP0210481 W EP 0210481W WO 03026036 A2 WO03026036 A2 WO 03026036A2
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WO
WIPO (PCT)
Prior art keywords
coating
metal object
metal
layer
fuel cell
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PCT/EP2002/010481
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German (de)
French (fr)
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WO2003026036A3 (en
Inventor
Petra Koschany
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Manhattan Scientifics, Inc.
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Application filed by Manhattan Scientifics, Inc. filed Critical Manhattan Scientifics, Inc.
Priority to AU2002362328A priority Critical patent/AU2002362328A1/en
Publication of WO2003026036A2 publication Critical patent/WO2003026036A2/en
Publication of WO2003026036A3 publication Critical patent/WO2003026036A3/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/0204—Non-porous and characterised by the material
    • H01M8/0223—Composites
    • H01M8/0228—Composites in the form of layered or coated products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/0204—Non-porous and characterised by the material
    • H01M8/0206—Metals or alloys
    • H01M8/0208—Alloys
    • H01M8/021—Alloys based on iron
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/023—Porous and characterised by the material
    • H01M8/0232—Metals or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/023—Porous and characterised by the material
    • H01M8/0241—Composites
    • H01M8/0245—Composites in the form of layered or coated products
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the invention relates to a coated plate-shaped metal object as a component of a fuel cell stack, and to a method for its production.
  • the plate-shaped metal object is used in particular in fuel cells as a bipolar plate, cooling layer or gas distribution structure.
  • Certain types of fuel cells are made with a polymer electrolyte membrane (PEM).
  • PEM polymer electrolyte membrane
  • This is provided with a catalyst layer on both sides and is located between two gas diffusion layers. It is also possible for the two gas diffusion layers to be provided with the catalyst layer instead of the membrane.
  • a fuel e.g. B. hydrogen gas
  • an oxidizing agent e.g. B. oxygen supplied.
  • Form on the anode due to of the catalyst protons, which cross the membrane acting as an electrolyte and combine with the oxygen in the cathode-side catalyst layer to form water. In this process, a potential difference arises between the two catalyst layers, which is used in an external circuit.
  • the fuel cell stack may contain additional layers that are formed from plate-shaped metal objects, such as. B. a coolant layer for cooling the fuel cell stack or gas distribution structures, provided with flow channels, for improved introduction of the reaction gases to the reaction site.
  • Bipolar plates, cooling layers and gas distribution layers have in common that, in order to ensure a conductive contact between the individual cells or their individual components, they must be very electrically conductive and only have a low contact resistance to the neighboring components of the fuel cell. In addition, it must be ensured that oxidation does not result in water-soluble products in the base materials used, which, when in contact with the catalyst, could block the catalyst or limit the ionic conductivity of the electrolyte. For this reason, carbon materials are often used, the contact resistances of which do not increase as a result of partial oxidation during operation of the fuel cell compared to the use of metal and which are chemically inert to blockages in the catalyst or poisoning of the electrolyte. The disadvantage of this is the high cost of the carbon materials.
  • the invention is intended to avoid all of the disadvantages listed above by using inexpensive, coated metallic components.
  • the use of metallic components in fuel cells is to be made possible, for which purpose simple and inexpensive coating processes are applied to these metallic coating objects, which keep the contact resistances to other components low and constant despite changing operating modes over time.
  • the invention enables a cost reduction by the coating being only partially and on average not thicker than 0.04 ⁇ m. or preferably as 0.01 ⁇ m.
  • a surface-covering conductive coating of the metallic coating object is not necessary for use in fuel cells in order to ensure a low contact resistance between the components used. The use of the coating material can thus be reduced.
  • the risk of the formation of water-soluble oxidation products with their negative consequences for the fuel cell can be avoided by suitable selection of the material of the coating object, or a further protective layer can be added to the coating.
  • components consisting of a metal can be used in fuel cells.
  • These are preferably bipolar plates, but also gas distribution structures, for example made of perforated structural sheets, or cooling layers.
  • the metal object to be coated it should preferably be ensured in advance that water-soluble products do not result from its oxidation, which could block the catalyst or would limit the ionic conductivity of the membrane when it comes into contact with it; otherwise this restriction of the choice of material can become unnecessary through appropriate additional protective layers.
  • Stainless steel or titanium is very suitable as a base material for the metal object due to its chemical inertness in the above sense, but the latter is less preferred due to the high cost.
  • an additional protective layer is advantageous due to the possible risk of water-soluble oxidation products.
  • a protective layer is particularly suitable for a graphite foil.
  • the coating is not applied to the entire surface of the metal object, but is a non-closed coating. This means that the entire surface of the metal object is not covered with the coating metal and its oxides.
  • Suitable coating metals are metals which can have compounds with oxygen atoms to a variable degree (MO x ), although other compounds can also be covalently bonded to the oxygen atoms, for example MO x (OH) y , and their oxides have good electrical conductivity, for example tin, indium, antimony or the platinum metals ruthenium, rhodium, osmium, palladium, iridium and platinum or alloys of such metals. It is important to ensure that the metal oxide (MO x ) conducts electricity well in as many of the oxidation states that occur in different operating modes. Ruthenium and ruthenium oxide are therefore particularly preferably used.
  • the oxidation levels of the coating vary depending on the place of use within the fuel cell and the respective operating mode.
  • a fuel cell is supplied with hydrogen gas on the anode side and oxygen-containing gas on the cathode side; in the switched-off state, air penetrates through the membrane into the anode compartment.
  • metallic components in a fuel cell stack these are alternately in an oxidizing and reducing atmosphere depending on the place of use and the selected operating mode.
  • the coating of such components must therefore have a sufficiently good electrical conductivity both in elemental-metallic and in the oxidation state MO ⁇ in order to ensure the greatest possible reduction in the contact resistance to other components.
  • the side of a bipolar plate facing the cathode of a fuel cell is exposed to an oxidizing atmosphere
  • the side facing the anode is exposed to a reducing atmosphere on the one hand during operation of the fuel cell stack and, on the other hand, to an oxidizing atmosphere when it is at a standstill.
  • the latter also applies to cooling layers which are located in the anode compartment or to gas distribution structures which are arranged in the same way and which can be produced, for example, from perforated structural sheets.
  • the composition of the coating more precisely the respective oxidation state of the metal oxide MO x , therefore changes depending on the operating modes, ie on the duration of operation or standstill of the fuel cell stack and on the chosen place of use. In order to achieve a consistently low contact resistance despite this changing composition, it is advantageous if both the metal and its variable oxidation levels have sufficient electrical conductivity.
  • All common application methods in particular electrolytic deposition, or the usual PVD (e.g. sputtering) or CVD methods are suitable for applying the metal layer to the coating object.
  • the parameters of the corresponding coating process are selected so that a thin, non-closed layer of the coating metal is formed on the surface of the coating object.
  • partial oxidation can take place. This can be done using all common methods and treatments.
  • the partial oxidation of the coating could take place by treatment with atmospheric oxygen or by Tempering in an oxygen-containing atmosphere.
  • the coating metal is tempered preferably in air at a temperature preferably between 100 ° C. and 800 ° C., particularly preferably between 200 ° C. and 400 ° C.
  • the tempering additionally improves the adhesion of the coating, since the resultant Connects coating metal oxide with oxide layers present on the coating object before the coating.
  • Further methods for partial oxidation are, for example, the electrochemical treatment of the applied coating metal or the sputtering of the coating metal in an atmosphere with a fixed oxygen content.
  • an additional protective layer is expedient, as explained above.
  • All materials that are highly conductive and chemically inert in the above sense are suitable as protective layers. They preferably consist of a thin, possibly gas-permeable graphite foil that can be attached to one or both surfaces of the component. Since a low contact resistance between the metal component and the protective layer is also essential here, the coating according to the invention can be used advantageously.
  • the composite of coated metal component and protective layer can be produced by all common methods, for example by simply laying on or pressing on, possibly at elevated temperature. If conductive bonding is chosen as the connection method, a suitable adhesion promoter is required. Further details and embodiments of the coating according to the invention are described below using examples:
  • the bipolar plates for a fuel cell stack consist of a 50 ⁇ m thick stainless steel foil, which is coated with the coating according to the invention. Ruthenium is used as the coating metal. After cleaning, degreasing and grinding the passivation layer on the surface of the stainless steel foil, the ruthenium coating is electrolytically deposited from a ruthenium chloride solution on the stainless steel foil.
  • the aqueous electrolyte solution contains 0.25% by mass of ruthenium chloride and approx. 5% by mass of isopropanol. With an electrolysis voltage of 1.48 V, a current of approx. 1.5 mA / cm 2 surface of the metal object, that is the stainless steel foil, results. 60 seconds are selected as the duration of the electrolytic deposition. This creates a non-closed coating with metallic ruthenium on the stainless steel foil. After the coated bipolar plate has dried, it is annealed for 30 minutes at 300 ° C. in an oxygen-containing atmosphere for partial oxidation.
  • the contact resistance of individual components can be determined using the following method:
  • the component to be examined is placed between two carbon fiber papers with a thickness of 0.3 mm and this in turn between two gold-plated copper electrodes of a tensioning device.
  • a defined pressure can be exerted on the component to be examined.
  • the voltage falling between the copper electrodes is determined as a function of a direct current flowing through the tensioning device, from which the area-specific resistance of the component to be examined can be determined.
  • a contact resistance can be created including the resistance of the carbon fiber papers of 16.3 m ⁇ cm 2 at a contact pressure of 11.5 bar, which is only slightly above the contact resistance of 13.3 m ⁇ cm 2 at the same contact pressure of a corresponding bipolar plate with elemental-metallic coating.
  • an untreated bipolar plate made of 50 ⁇ m stainless steel foil has a contact resistance of 188 m ⁇ cm 2 at a contact pressure of 11.5 bar.
  • the average layer thickness is less than 0.025 ⁇ m, that is to say it has less than 100 atomic layers on average. It is therefore not dense, but there are empty, uncoated areas between atomic accumulations.
  • the same coating process with ruthenium can also be used for perforated structural sheets made of stainless steel, which can advantageously be used as gas distribution structures in a fuel cell stack.
  • the aluminum bipolar plate or cooling layer is provided with a layer of elemental platinum or ruthenium by sputtering, which is then partially oxidized by tempering in an oxygen-containing atmosphere becomes.
  • a thin 0.85 mm graphite foil which is hydrophobic, serves as a protective layer.
  • the composite of coated aluminum bipolar plate or cooling layer and graphite foil is produced by means of conductive gluing.
  • epoxy resin is applied in small quantities (approx. 1.5 mg / cm 2 ) to the graphite foil and cured by means of hot pressing at 110 ° C and a pressure of approx. 35 bar.
  • a graphite foil according to Example 2 is not completely, but interrupted, for. B. applied in the form of individual webs or preferably connected web structures.
  • the contact resistance of such a bipolar plate with gas distribution channels measured using the method shown in Example 1 is in the range of approximately 22 m ⁇ cm 2 at a contact pressure of 14 bar.
  • the contact resistance of a bipolar plate with graphite foil glued to the entire surface is typically up to approx. 15 m ⁇ cm 2 at a contact pressure of also 14 bar.

Abstract

The invention concerns a coated metal object in the form of a plate designed to be used as component of a fuel cell stack. The coat of said object consists of an open thin layer, having a maximum thickness of 0.04 νm and containing a metal such as tin, indium, antimony or a metal of the platinum group (Ru, Rh, Os, Pa, Ir, Pt), which comprises, in variable amount, bonds with oxygen atoms in said layer. The coat metal has, as such or in all the variable oxidation states, a sufficiently good electroconductivity. Said coat enables economical use of metal components in fuel cells as bipolar plates, gas distribution layers, or refrigerating layers. It is possible to use inexpensive materials whereof the contact resistance levels remain low more or less continuously, even when the operating modes of the fuel cells changes and the oxidation levels of the coat, which are related to said different operating modes, vary.

Description

Beschichtetes plattenförmiges Metallobjekt als Komponente eines Brennstoffzellenstapels Coated plate-shaped metal object as a component of a fuel cell stack
Die Erfindung bezieht sich auf ein beschichtetes plattenförmiges Metallobjekt als Komponente eines Brennstoffzellenstapels, sowie auf ein Verfahren zu seiner Herstellung. Das plattenförmige Metallobjekt findet insbesondere Einsatz in Brennstoffzellen als Bipolarplatte, Kühlschicht oder Gasverteilungsstruktur.The invention relates to a coated plate-shaped metal object as a component of a fuel cell stack, and to a method for its production. The plate-shaped metal object is used in particular in fuel cells as a bipolar plate, cooling layer or gas distribution structure.
Bestimmte Typen von Brennstoffzellen sind mit einer Polymerelektrolyt- Membran (PEM) hergestellt. Diese ist auf beiden Seiten mit einer Katalysatorschicht versehen und befindet sich zwischen zwei Gasdiffusionsschichten. Es ist auch möglich, daß anstelle der Membran die beiden Gasdiffusionsschichten mit der Katalysatorschicht versehen sind. Auf der Anodenseite der Membran wird ein Brennstoff, z. B. Wasserstoffgas, und auf der Kathodenseite ein Oxidationsmittel, z. B. Sauerstoff, zugeführt. An der Anode bilden sich aufgrund des Katalysators Protonen, welche die als Elektrolyt wirkende Membran durchqueren und sich in der kathodenseitigen Katalysatorschicht mit dem Sauerstoff zu Wasser verbinden. Bei diesem Prozeß entsteht zwischen den beiden Katalysatorschichten eine Potentialdifferenz, die in einem äußeren Stromkreis genutzt wird. In der Regel werden zur Erzeugung größerer Leistung mehrere Brennstoffzellen hintereinander geschaltet und zu einem Brennstoffzellenstapel verbunden. Die auch als Separatoren bezeichneten Bipolarplatten sind die Elemente in den Brennstoffzellenstapeln, die den Anoden-Gasraum einer Einzelzelle vom Kathoden-Gasraum der anschließenden Zelle trennen. Sie müssen daher gasdicht sein. Des weiteren kann der Brennstoffzellenstapel zusätzliche Schichten enthalten, die aus plattenförmigen Metallobjekten gebildet sind, wie z. B. eine Kühlmittel führende Schicht zur Kühlung des Brennstoffzellenstapels oder Gasverteilstrukturen, versehen mit Strömungskanälen, zur verbesserten Heranführung der Reaktionsgase an den Reaktionsort.Certain types of fuel cells are made with a polymer electrolyte membrane (PEM). This is provided with a catalyst layer on both sides and is located between two gas diffusion layers. It is also possible for the two gas diffusion layers to be provided with the catalyst layer instead of the membrane. On the anode side of the membrane, a fuel, e.g. B. hydrogen gas, and on the cathode side an oxidizing agent, e.g. B. oxygen supplied. Form on the anode due to of the catalyst protons, which cross the membrane acting as an electrolyte and combine with the oxygen in the cathode-side catalyst layer to form water. In this process, a potential difference arises between the two catalyst layers, which is used in an external circuit. As a rule, several fuel cells are connected in series and connected to form a fuel cell stack in order to generate greater power. The bipolar plates, also called separators, are the elements in the fuel cell stacks that separate the anode gas space of a single cell from the cathode gas space of the adjoining cell. You must therefore be gas-tight. Furthermore, the fuel cell stack may contain additional layers that are formed from plate-shaped metal objects, such as. B. a coolant layer for cooling the fuel cell stack or gas distribution structures, provided with flow channels, for improved introduction of the reaction gases to the reaction site.
Bipolarplatten, Kühlschichten und Gasverteilschichten ist gemeinsam, daß sie, um einen leitenden Kontakt zwischen den Einzelzellen bzw. deren einzelnen Komponenten zu gewährleisten, elektrisch sehr gut leitfähig sein müssen und nur einen geringen Übergangswiderstand zu den benachbarten Komponenten der Brennstoffzelle aufweisen dürfen. Darüber hinaus muß gewährleistet werden, daß bei den eingesetzten Grundmaterialien nicht durch Oxidation wasserlösliche Produkte entstehen, die bei Kontakt mit dem Katalysator diesen blockieren oder die Ionenleitfähigkeit des Elektrolyten einschränken könnten. Aus diesem Grunde kommen vielfach Kohlenstoffmaterialien zum Einsatz, deren Übergangswiderstände im Vergleich zum Einsatz von Metall nicht durch partielle Oxidation während des Betriebes der Brennstoffzelle zunimmt und die chemisch inert gegenüber Blockaden des Katalysators oder Vergiftungen des Elektrolyten sind. Nachteilig daran sind die hohen Kosten der Kohlenstoffmaterialien. Denkbar wäre der Einsatz von metallischen Komponenten nach GB1285417. So offenbart die britische Druckschrift ein Verfahren zur anodischen Oxidation einer geschlossenen Rutheniumbeschichtung auf einem metallischem Leiter zum Zweck der Reduktion der Korrosionsgefahr. Diese Beschichtung besteht aus elementarem Ruthenium und Rutheniumoxid. Da zum Schutz des beschichteten Metalls eine kontinuierliche Bedeckung notwendig ist, folgt daraus ein relativ hoher Verbrauch von Ruthenium.Bipolar plates, cooling layers and gas distribution layers have in common that, in order to ensure a conductive contact between the individual cells or their individual components, they must be very electrically conductive and only have a low contact resistance to the neighboring components of the fuel cell. In addition, it must be ensured that oxidation does not result in water-soluble products in the base materials used, which, when in contact with the catalyst, could block the catalyst or limit the ionic conductivity of the electrolyte. For this reason, carbon materials are often used, the contact resistances of which do not increase as a result of partial oxidation during operation of the fuel cell compared to the use of metal and which are chemically inert to blockages in the catalyst or poisoning of the electrolyte. The disadvantage of this is the high cost of the carbon materials. The use of metallic components according to GB1285417 would be conceivable. For example, the British publication discloses a process for the anodic oxidation of a closed ruthenium coating on a metallic conductor in order to reduce the risk of corrosion. This coating consists of elemental ruthenium and ruthenium oxide. Since continuous protection is necessary to protect the coated metal, this results in a relatively high consumption of ruthenium.
Mit der Erfindung sollen alle oben aufgeführten Nachteile durch den Einsatz kostengünstiger, beschichteter metallischer Komponenten vermieden werden. Es soll der Einsatz metallischer Komponenten in Brennstoffzellen ermöglicht werden, wozu einfache und kostengünstige Beschichtungsprozesse auf diese metallischen Beschichtungsobjekte angewandt werden, welche die Übergangswiderstände zu anderen Komponenten niedrig und trotz sich zeitlich ändernder Betriebsmodi konstant halten.The invention is intended to avoid all of the disadvantages listed above by using inexpensive, coated metallic components. The use of metallic components in fuel cells is to be made possible, for which purpose simple and inexpensive coating processes are applied to these metallic coating objects, which keep the contact resistances to other components low and constant despite changing operating modes over time.
Dies wird, ausgehend von einem plattenförmigen Metallobjekt, das beim Einsatz in Brennstoffzellen in Bezug auf Blockaden des Katalysators oder der Ionenleitfähigkeit des Elektrolyten entweder chemisch inert ist oder durch zusätzliche Maßnahmen geschützt wird, dadurch erreicht, daß die Beschichtung eine nicht geschlossene und elektrisch leitfähige Schicht, die ein partiell oxidiertes Metall enthält, bildet. Gemäß einer speziellen Ausführung wird dies z. B. erreicht durch Abscheidung einer dünnen, nicht geschlossenen Schicht, enthaltend ein Metall wie Zinn, Indium, Antimon oder ein Platin-Metall (Ru, Rh, Os, Pa, Ir, Pt), welches in der Schicht in variablem Maße Verbindungen zu Sauerstoffatomen besitzt, oberflächig auf dem Beschichtungsobjekt, wobei das Beschichtungsmetall und all seine variablen Oxidationszustände, die von den wechselnden Betriebsbedingungen abhängen, eine ausreichend gute elektrische Leitfähigkeit besitzen. Durch die Erfindung wird eine Kostenreduktion möglich, indem die Beschich- tung nur teilweise und im Mittel nicht dicker als 0,04 μm. oder vorzugsweise als 0,01 μm erfolgt. Ein flächendeckende leitfähige Beschichtung des metallischen Beschichtungsobjektes ist für den Einsatz in Brennstoffzellen nicht notwendig, um einen geringen Übergangswiderstand zwischen den eingesetzten Komponente zu gewährleisten. Somit kann der Einsatz des Beschichtungs- materials verringert werden. Weiterhin kann die Gefahr der Entstehung wasserlöslicher Oxidationsprodukte mit ihren negativen Folgen für die Brennstoffzelle durch geeignete Materialauswahl des Beschichtungsobjekts vermieden werden, oder es kann noch eine weitere Schutzschicht zur Beschichtung hinzugefügt werden.This is achieved on the basis of a plate-shaped metal object which, when used in fuel cells, is either chemically inert with regard to blockages of the catalyst or the ionic conductivity of the electrolyte or is protected by additional measures in that the coating has a non-closed and electrically conductive layer, which contains a partially oxidized metal. According to a special embodiment, this is e.g. B. achieved by deposition of a thin, non-closed layer containing a metal such as tin, indium, antimony or a platinum metal (Ru, Rh, Os, Pa, Ir, Pt), which compounds in the layer to varying degrees to oxygen atoms has, superficially on the coating object, the coating metal and all its variable oxidation states, which depend on the changing operating conditions, have a sufficiently good electrical conductivity. The invention enables a cost reduction by the coating being only partially and on average not thicker than 0.04 μm. or preferably as 0.01 μm. A surface-covering conductive coating of the metallic coating object is not necessary for use in fuel cells in order to ensure a low contact resistance between the components used. The use of the coating material can thus be reduced. Furthermore, the risk of the formation of water-soluble oxidation products with their negative consequences for the fuel cell can be avoided by suitable selection of the material of the coating object, or a further protective layer can be added to the coating.
Bevorzugte Weiterbildungen der Erfindung finden sich in den Unteransprüchen.Preferred developments of the invention can be found in the subclaims.
Mit Hilfe des erfindungsgemäßen Beschichtungsverfahrens können aus einem Metall bestehende Komponenten in Brennstoffzellen zum Einsatz kommen. Bevorzugt handelt es sich um Bipolarplatten, aber auch um Gasverteilstrukturen beispielsweise aus perforierten Strukturblechen oder um Kühlschichten.With the aid of the coating method according to the invention, components consisting of a metal can be used in fuel cells. These are preferably bipolar plates, but also gas distribution structures, for example made of perforated structural sheets, or cooling layers.
Bei der Auswahl des zu beschichtenden Metallobjekts ist vorzugsweise vorab sicherzustellen, daß nicht durch seine Oxidation wasserlösliche Produkte entstehen, welche bei Kontakt mit dem Katalysator diesen blockieren könnten oder die Ionenleitfähigkeit der Membran einschränken würden; andernfalls kann durch entsprechende zusätzliche Schutzschichten diese Einschränkung der Materialauswahl unnötig werden. Sehr gut geeignet als Grundmaterial für das Metallobjekt ist aufgrund seiner chemischen Inertheit im obigem Sinne Edelstahl oder Titan, Letzteres ist aber aufgrund der hohen Kosten weniger bevorzugt. Beim Einsatz beispielsweise von Aluminium für das Metallobjekt ist aufgrund der möglichen Gefahr des Entstehens von wasserlöslichen Oxida- tionsprodukten eine zusätzliche Schutzschicht von Vorteil. Für die eventuelle Schutzschicht eignet sich insbesondere eine Graphitfolie.When selecting the metal object to be coated, it should preferably be ensured in advance that water-soluble products do not result from its oxidation, which could block the catalyst or would limit the ionic conductivity of the membrane when it comes into contact with it; otherwise this restriction of the choice of material can become unnecessary through appropriate additional protective layers. Stainless steel or titanium is very suitable as a base material for the metal object due to its chemical inertness in the above sense, but the latter is less preferred due to the high cost. When using aluminum for the metal object, for example, an additional protective layer is advantageous due to the possible risk of water-soluble oxidation products. For the eventual A protective layer is particularly suitable for a graphite foil.
Die Beschichtung ist nicht vollflächig auf dem Metallobjekt aufgebracht, sondern ist eine nicht geschlossenen Beschichtung. Darunter ist zu verstehen, daß nicht die gesamte Oberfläche des Metallobjekts mit dem Beschichtungsmetall und dessen Oxiden bedeckt ist.The coating is not applied to the entire surface of the metal object, but is a non-closed coating. This means that the entire surface of the metal object is not covered with the coating metal and its oxides.
Als Beschichtungsmetall eignen sich Metalle, welche in variablem Maße Verbindungen zu Sauerstoff atomen besitzen können (MOx), wobei an den Sauerstoffatomen auch noch weitere Verbindungen kovalent gebunden sein können, beispielsweise MOx(OH)y, und deren Oxide gute elektrische Leitfähigkeit aufweisen, also beispielsweise Zinn, Indium, Antimon oder die Platin- Metalle Ruthenium, Rhodium, Osmium, Palladium, Iridium und Platin bzw. Legierungen aus derartigen Metallen. Dabei ist darauf zu achten, daß das Metalloxid (MOx) in möglichst vielen der bei verschiedenen Betriebsmodi auftretenden Oxidationsstufen elektrisch gut leitet. Besonders bevorzugt kommen deshalb Ruthenium und Rutheniumoxid zur Anwendung.Suitable coating metals are metals which can have compounds with oxygen atoms to a variable degree (MO x ), although other compounds can also be covalently bonded to the oxygen atoms, for example MO x (OH) y , and their oxides have good electrical conductivity, for example tin, indium, antimony or the platinum metals ruthenium, rhodium, osmium, palladium, iridium and platinum or alloys of such metals. It is important to ensure that the metal oxide (MO x ) conducts electricity well in as many of the oxidation states that occur in different operating modes. Ruthenium and ruthenium oxide are therefore particularly preferably used.
Die Oxidationsstufen der Beschichtung variieren beim Einsatz in Brennstoffzellen in Abhängigkeit vom Einsatzort innerhalb der Brennstoffzelle und dem jeweiligen Betriebsmodus. Einer Brennstoffzelle wird während des Betriebs anodenseitig Wasserstoffgas und kathodenseitig sauerstoffhaltiges Gas zugeführt, im ausgeschaltetem Zustand dringt Luft durch die Membran in den Anodenraum ein. Beim Einsatz metallischer Komponenten in einem Brennstoffzellenstapel befinden sich diese abhängig vom Einsatzort und dem gewähltem Betriebsmodus abwechselnd in oxidierender, wie auch reduzierender Atmosphäre. Die Beschichtung solcher Komponenten muß demnach sowohl in elementar-metallischem, wie im Oxidationszustand MO^ eine ausreichend gute elektrische Leitfähigkeit besitzen, um jeweils eine möglichst große Reduktion des Übergangswiderstands zu anderen Komponenten zu gewährleisten. So ist beispielsweise die der Kathode einer Brennstoffzelle zugewandte Seite einer Bipolarplatte einer oxidierenden Atmosphäre, die der Anode zugewandte Seite einerseits während des Betriebs des Brennstoffzellenstapels einer reduzierenden und andererseits bei Stillstand einer oxidierenden Atmosphäre ausgesetzt. Letzteres gilt auch für Kühlschichten, die sich im Anodenraum befinden, oder für ebenda angeordnete Gasverteilstrukturen, die beispielsweise aus perforierten Strukturblechen hergestellt sein können. Es ändert sich also abhängig von den Betriebsmodi, d. h. von der Dauer des Betriebs oder Stillstands des Brennstoffzellenstapels sowie vom gewählten Einsatzort die Zusammensetzung der Beschichtung, genauer die jeweilige Oxidationsstufe des Metalloxids MOx. Um trotz dieser sich verändernden Zusammensetzung einen gleichbleibend geringen Übergangswiderstand zu erreichen, ist es vorteilhaft, wenn sowohl das Metall sowie seine variablem Oxidationsstufen eine ausreichende elektrische Leitfähigkeit besitzen.When used in fuel cells, the oxidation levels of the coating vary depending on the place of use within the fuel cell and the respective operating mode. During operation, a fuel cell is supplied with hydrogen gas on the anode side and oxygen-containing gas on the cathode side; in the switched-off state, air penetrates through the membrane into the anode compartment. When using metallic components in a fuel cell stack, these are alternately in an oxidizing and reducing atmosphere depending on the place of use and the selected operating mode. The coating of such components must therefore have a sufficiently good electrical conductivity both in elemental-metallic and in the oxidation state MO ^ in order to ensure the greatest possible reduction in the contact resistance to other components. So is For example, the side of a bipolar plate facing the cathode of a fuel cell is exposed to an oxidizing atmosphere, the side facing the anode is exposed to a reducing atmosphere on the one hand during operation of the fuel cell stack and, on the other hand, to an oxidizing atmosphere when it is at a standstill. The latter also applies to cooling layers which are located in the anode compartment or to gas distribution structures which are arranged in the same way and which can be produced, for example, from perforated structural sheets. The composition of the coating, more precisely the respective oxidation state of the metal oxide MO x , therefore changes depending on the operating modes, ie on the duration of operation or standstill of the fuel cell stack and on the chosen place of use. In order to achieve a consistently low contact resistance despite this changing composition, it is advantageous if both the metal and its variable oxidation levels have sufficient electrical conductivity.
Zur Aufbringen der Metallschicht auf das Beschichtungsobjekt eignen sich alle gängigen Aufbringungsverfahren, insbesondere die elektrolytische Abscheidung, oder die üblichen PVD- (z. B. Sputtern) oder CVD-Methoden. Dabei werden die Parameter des entsprechenden Beschichtungsverfahrens so gewählt, daß eine dünne, nicht geschlossene Schicht des Beschichtungs-Metalls auf der Oberfläche des Beschichtungsobjekts entsteht. Somit ist nur ein geringer Verbrauch des Beschichtungs-Metalls notwendig, was zu einer erheblichen Reduzierung der Kosten im Vergleich zu einer vollflächigen Beschichtung beiträgt, zumal eine geschlossene Schicht zur Reduzierung der Übergangswiderstands zu anderen Komponenten nicht notwendig ist.All common application methods, in particular electrolytic deposition, or the usual PVD (e.g. sputtering) or CVD methods are suitable for applying the metal layer to the coating object. The parameters of the corresponding coating process are selected so that a thin, non-closed layer of the coating metal is formed on the surface of the coating object. Thus, only a low consumption of the coating metal is necessary, which contributes to a considerable reduction in costs compared to a full-surface coating, especially since a closed layer to reduce the contact resistance to other components is not necessary.
Nach Aufbringung der elementar-metallischen Beschichtung kann eine partielle Oxidation erfolgen. Diese kann mittels aller gängigen Verfahren und Be- handlungsweisen geschehen. Beispielsweise könnte die partielle Oxidation der Beschichtung durch Behandlung mit Luftsauerstoff erfolgen oder durch Temperung in sauerstoffhaltiger Atmosphäre. Das Tempern des Beschichtungs- metalls geschieht bevorzugt in Luft bei einer Temperatur bevorzugt zwischen 100° C und 800° C, besonders bevorzugt zwischen 200° C und 400° C. Durch die Temperung wird zusätzlich eine verbesserte Haftung der Beschichtung erreicht, da sich das entstehende Beschichtungsmetalloxid mit vor der Be- schichtung auf dem Beschichtungsobjekt vorhandenen Oxidschichten verbindet. Weitere Methoden zur partiellen Oxidation sind beispielsweise die elektrochemische Behandlung des aufgebrachten Beschichtungsmetalls oder das Sputtern des Beschichtungsmetalls in einer Atmosphäre mit festgelegtem Sauerstoffgehalt.After the elementary metallic coating has been applied, partial oxidation can take place. This can be done using all common methods and treatments. For example, the partial oxidation of the coating could take place by treatment with atmospheric oxygen or by Tempering in an oxygen-containing atmosphere. The coating metal is tempered preferably in air at a temperature preferably between 100 ° C. and 800 ° C., particularly preferably between 200 ° C. and 400 ° C. The tempering additionally improves the adhesion of the coating, since the resultant Connects coating metal oxide with oxide layers present on the coating object before the coating. Further methods for partial oxidation are, for example, the electrochemical treatment of the applied coating metal or the sputtering of the coating metal in an atmosphere with a fixed oxygen content.
Diese Oxidationsschritte können sogar zu einem Mischoxid bestehend aus Metallatomen des beschichteten Metallobjekts und der Beschichtung selbst führen.These oxidation steps can even lead to a mixed oxide consisting of metal atoms of the coated metal object and the coating itself.
Falls durch Materialauswahl für das Metallobjekt die Gefahr des Entstehens von wasserlöslichen Oxidationsprodukten mit seinen negativen Folgen für die Brennstoffzelle nicht vermieden werden kann, ist wie oben erläutert eine zusätzliche Schutzschicht zweckmäßig. Als Schutzschichten eignen sich alle Materialien, die gut leitfähig und chemisch inert im obigen Sinne sind. Bevorzugt bestehen sie aus einer dünnen, möglicherweise gasdurchlässigen Graphitfolie, die auf einer oder beiden Oberflächen der Komponente angebracht werden kann. Da auch hier ein niedriger Übergangswiderstand zwischen der Metallkomponente und der Schutzschicht unerläßlich ist, kann die erfindungsgemäße Beschichtung vorteilhaft eingesetzt werden. Der Verbund aus beschichteter Metallkomponente und Schutzschicht kann dabei mittels aller gängigen Verfahren hergestellt werden, so etwa mittels einfachem Auflegen oder Aufpressen eventuell bei erhöhter Temperatur. Wird als Verbindungsverfahren das leitfähige Aufkleben gewählt, so bedarf es eines geeigneten Haftvermittlers. Weitere Einzelheiten und Ausführungsformen der erfindungsgemäßen Beschichtung werden im folgenden anhand von Beispielen beschrieben:If the risk of water-soluble oxidation products with their negative consequences for the fuel cell cannot be avoided by the choice of material for the metal object, an additional protective layer is expedient, as explained above. All materials that are highly conductive and chemically inert in the above sense are suitable as protective layers. They preferably consist of a thin, possibly gas-permeable graphite foil that can be attached to one or both surfaces of the component. Since a low contact resistance between the metal component and the protective layer is also essential here, the coating according to the invention can be used advantageously. The composite of coated metal component and protective layer can be produced by all common methods, for example by simply laying on or pressing on, possibly at elevated temperature. If conductive bonding is chosen as the connection method, a suitable adhesion promoter is required. Further details and embodiments of the coating according to the invention are described below using examples:
Beispiel 1:Example 1:
Die Bipolarplatten für einen Brennstoffzellenstapel bestehen aus einer 50 μm dicken Edelstahlfolie, welche mit der erfindungsgemäßen Beschichtung überzogen wird. Als Beschichtungsmetall wird Ruthenium verwendet. Nach Reinigung, Entfettung und Abschleifen der Passivierungsschicht auf der Oberfläche der Edelstahlfolie wird die Rutheniumbeschichtung aus einer Rutheniumchlorid-Lösung auf der Edelstahlfolie elektrolytisch abgeschieden. Die wässerige Elektrolytlösung enthält 0,25 Massenprozent Rutheniumchlorid und ca. 5 Massenprozent Isopropanol. Bei einer Elektrolysespannung von 1,48 V ergibt sich ein Strom von ca. 1,5 mA/cm2 Oberfläche des Metallobjekts, also der Edelstahlfolie. Als Dauer der elektrolytischen Abscheidung werden 60 Sekunden gewählt. Dadurch wird eine nicht geschlossene Beschichtung mit metallischem Ruthenium auf der Edelstahlfolie erzeugt. Nach Trocknen der beschichteten Bipolarplatte wird diese zur partiellen Oxidation für 30 Minuten bei 300° C in sauerstoffhaltiger Atmosphäre getempert.The bipolar plates for a fuel cell stack consist of a 50 μm thick stainless steel foil, which is coated with the coating according to the invention. Ruthenium is used as the coating metal. After cleaning, degreasing and grinding the passivation layer on the surface of the stainless steel foil, the ruthenium coating is electrolytically deposited from a ruthenium chloride solution on the stainless steel foil. The aqueous electrolyte solution contains 0.25% by mass of ruthenium chloride and approx. 5% by mass of isopropanol. With an electrolysis voltage of 1.48 V, a current of approx. 1.5 mA / cm 2 surface of the metal object, that is the stainless steel foil, results. 60 seconds are selected as the duration of the electrolytic deposition. This creates a non-closed coating with metallic ruthenium on the stainless steel foil. After the coated bipolar plate has dried, it is annealed for 30 minutes at 300 ° C. in an oxygen-containing atmosphere for partial oxidation.
Die Übergangswiderstände einzelner Komponenten können mit folgender Methode ermittelt werden: Die zu untersuchende Komponente wird zwischen zwei Kohlefaserpapiere mit einer Stärke von 0,3 mm und diese wiederum zwischen zwei vergoldete Kupfer-Elektroden einer Spannvorrichtung gelegt. Dadurch kann ein definierter Druck auf die zu untersuchende Komponente ausgeübt werden. In Abhängigkeit von einem durch die Spannvorrichtung fließenden Gleichstrom wird die zwischen den Kupfer-Elektroden abfallende Spannung ermittelt, woraus sich der flächenspezifische Widerstand der zu untersuchenden Komponente ermitteln läßt. So kann bei der eben beschriebenen Bipolarplatte mit partiell oxidierter Beschichtung ein Übergangswiderstand beinhaltend den Widerstand der Kohlefaserpapiere von 16,3 mΩcm2 bei einem Anpreßdruck von 11,5 bar gemessen werden, der nur unwesentlich über dem Übergangswiderstand von 13,3 mΩcm2 bei gleichem Anpreßdruck einer entsprechenden Bipolarplatte mit elementar-metallischer Beschichtung liegt. Zum Vergleich dazu besitzt eine unbehandelte Bipolarplatte aus 50 μm Edelstahlfolie einen Übergangswiderstand von 188 mΩcm2 bei ebenfalls 11,5 bar Anpreßdruck.The contact resistance of individual components can be determined using the following method: The component to be examined is placed between two carbon fiber papers with a thickness of 0.3 mm and this in turn between two gold-plated copper electrodes of a tensioning device. As a result, a defined pressure can be exerted on the component to be examined. The voltage falling between the copper electrodes is determined as a function of a direct current flowing through the tensioning device, from which the area-specific resistance of the component to be examined can be determined. In the bipolar plate with partially oxidized coating just described, a contact resistance can be created including the resistance of the carbon fiber papers of 16.3 mΩcm 2 at a contact pressure of 11.5 bar, which is only slightly above the contact resistance of 13.3 mΩcm 2 at the same contact pressure of a corresponding bipolar plate with elemental-metallic coating. For comparison, an untreated bipolar plate made of 50 μm stainless steel foil has a contact resistance of 188 mΩcm 2 at a contact pressure of 11.5 bar.
Aus den angegebenen Werten läßt sich errechnen, daß die mittlere Schichtdicke weniger als 0,025 μm beträgt, also durchschnittlich weniger als 100 Atomlagen aufweist. Sie ist damit nicht dicht, sondern zwischen Atomanhäufungen befinden sich leere, unbeschichtete Stellen.It can be calculated from the values given that the average layer thickness is less than 0.025 μm, that is to say it has less than 100 atomic layers on average. It is therefore not dense, but there are empty, uncoated areas between atomic accumulations.
Das selbe Beschichtungsverfahren mit Ruthenium kann auch bei perforierten Strukturblechen aus Edelstahl zum Einsatz kommen, welche vorteilhaft als Gasverteilungsstrukturen in einem Brennstoffzellenstapel eingesetzt werden können.The same coating process with ruthenium can also be used for perforated structural sheets made of stainless steel, which can advantageously be used as gas distribution structures in a fuel cell stack.
Beispiel 2:Example 2:
Bei Verwendung von Aluminium als Grundmaterial für eine Bipolarplatte oder eine Kühlschicht bedarf es wegen der möglichen Gefahr der Entstehun wasserlöslicher Produkte aufgrund der Oxidation bedingt durch die entsprechenden Betriebsmodi, welche bei Kontakt mit dem Katalysator diesen blockieren oder die Ionenleitfähigkeit der Membran einschränken könnten, bevorzugt zusätzlicher Schutzschichten.If aluminum is used as the base material for a bipolar plate or a cooling layer, additional protective layers are required because of the possible risk of water-soluble products being formed due to the oxidation due to the corresponding operating modes, which could block the catalyst or limit the ionic conductivity of the membrane ,
Zunächst wird die Aluminium-Bipolarplatte oder -Kühlschicht durch Sputtern mit einer Schicht aus elementarem Platin oder Ruthenium versehen, welche anschließend durch Tempern in sauerstoffhaltiger Atmosphäre partiell oxidiert wird. Als Schutzschicht dient eine dünne Graphitfolie der Stärke 0,85 mm, welche hydrophob ist. Dadurch können sich Oxidationsprodukte des Aluminiums nicht im Produktwasser lösen, was Schäden an Katalysator oder Membran hervorrufen würde. Der Verbund aus beschichteter Aluminium-Bipolarplatte oder -Kühlschicht und Graphitfolie wird mittels leitfähigen Aufklebens hergestellt. Als Haftvermittler wird Epoxidharz in geringen Mengen (ca. 1,5 mg/cm2) auf die Graphitfolie aufgetragen und mittels Heißpressen bei 110° C und einem Druck von ca. 35 bar ausgehärtet.First, the aluminum bipolar plate or cooling layer is provided with a layer of elemental platinum or ruthenium by sputtering, which is then partially oxidized by tempering in an oxygen-containing atmosphere becomes. A thin 0.85 mm graphite foil, which is hydrophobic, serves as a protective layer. As a result, oxidation products of aluminum cannot dissolve in the product water, which would damage the catalyst or membrane. The composite of coated aluminum bipolar plate or cooling layer and graphite foil is produced by means of conductive gluing. As an adhesion promoter, epoxy resin is applied in small quantities (approx. 1.5 mg / cm 2 ) to the graphite foil and cured by means of hot pressing at 110 ° C and a pressure of approx. 35 bar.
Beispiel 3:Example 3:
Bei Verwendung einer glatten Edelstahl-Bipolarplatte mit partiell oxidierter Rutheniumbeschichtung nach Beispiel 1 kann es vorteilhaft sein, eine Kanalstruktur zur Verteilung der Reaktionsgase hin zu ihren Reaktionsorten herzustellen. Dazu wird eine Graphitfolie nach Beispiel 2 nicht vollflächig, sondern unterbrochen z. B. in Form von einzelnen Stegen oder bevorzugt zusammenhängenden Stegstrukturen aufgebracht.When using a smooth stainless steel bipolar plate with partially oxidized ruthenium coating according to Example 1, it can be advantageous to produce a channel structure for distributing the reaction gases to their reaction sites. For this purpose, a graphite foil according to Example 2 is not completely, but interrupted, for. B. applied in the form of individual webs or preferably connected web structures.
Der mittels dem in Beispiel 1 dargestelltem Verfahren gemessene Übergangswiderstand einer solchen Bipolarplatte mit Gasverteilungskanälen liegt im Bereich von ca. 22 mΩcm2 bei einem Anpreßdruck von 14 bar. Im Vergleich dazu beträgt der Übergangswiderstand einer Bipolarplatte mit vollflächig aufgeklebten Graphitfolie typischerweise bis zu ca. 15 mΩcm2 bei einem Anpreßdruck von ebenfalls 14 bar. The contact resistance of such a bipolar plate with gas distribution channels measured using the method shown in Example 1 is in the range of approximately 22 mΩcm 2 at a contact pressure of 14 bar. In comparison, the contact resistance of a bipolar plate with graphite foil glued to the entire surface is typically up to approx. 15 mΩcm 2 at a contact pressure of also 14 bar.

Claims

Patentansprüche: claims:
1. Beschichtetes plattenförmiges Metallobjekt als Komponente eines Brennstoffzellenstapels, dadurch gekennzeichnet, daß die Beschichtung eine nicht geschlossene und elektrisch leitfähige Schicht, die ein partiell oxidiertes Metall enthält, bildet.1. Coated plate-shaped metal object as a component of a fuel cell stack, characterized in that the coating forms a non-closed and electrically conductive layer which contains a partially oxidized metal.
2. Beschichtetes Metallobjekt nach Anspruch 1, dadurch gekennzeichnet, daß die Beschichtung in einem ganzen Bereich von Oxidationsgraden elektrisch leitfähig ist.2. Coated metal object according to claim 1, characterized in that the coating is electrically conductive in a whole range of degrees of oxidation.
3. Beschichtetes Metallobjekt nach Anspruch 2, dadurch gekennzeichnet, daß das partiell oxidierte Metall RuOx (0 < x < 4) ist.3. Coated metal object according to claim 2, characterized in that the partially oxidized metal is RuO x (0 <x <4).
4. Beschichtetes Metallobjekt nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß die mittlere Schichtdichte der durch die Beschichtung gebildeten Schicht geringer als 0,04 μm und vorzugsweise unter 0,01 μm ist.4. Coated metal object according to one of claims 1 to 3, characterized in that the average layer density of the layer formed by the coating is less than 0.04 microns and preferably less than 0.01 microns.
5. Beschichtetes Metallobjekt nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß das beschichte Metallobjekt aus Edelstahl besteht.5. Coated metal object according to one of claims 1 to 4, characterized in that the coated metal object consists of stainless steel.
6. Beschichtetes Metallobjekt nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß das mit der Beschichtung versehene Metallobjekt noch mit einer weiteren Beschichtung versehen ist, die außen auf der Beschichtung aus dem partiell oxidiertem Metall sitzt, elektrisch leitfähig ist und aus hydrophobem Material besteht.6. Coated metal object according to one of claims 1 to 3, characterized in that the metal object provided with the coating is also provided with a further coating which sits on the outside of the coating of the partially oxidized metal, is electrically conductive and consists of hydrophobic material ,
7. Verfahren zur Herstellung eines beschichteten plattenförmigen Metall- objekts als Komponente eines Brennstoffzellenstapels nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß auf das zunächst unbeschichtete Metallobjekt oberflächig eine nicht geschlossene Schicht abgeschieden wird und dann partiell oxidiert wird.7. Process for producing a coated plate-shaped metal Object as a component of a fuel cell stack according to one of claims 1 to 6, characterized in that a non-closed layer is deposited on the surface of the initially uncoated metal object and then partially oxidized.
8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, daß die Abscheidung elektrochemisch oder mittels CVD- oder PVD -Verfahren erfolgt.8. The method according to claim 7, characterized in that the deposition is carried out electrochemically or by means of CVD or PVD processes.
9. Verfahren nach Anspruch 7 oder 8, dadurch gekennzeichnet, daß die partielle Oxidation mittels Tempern erfolgt.9. The method according to claim 7 or 8, characterized in that the partial oxidation takes place by means of annealing.
10. Verfahren nach einem der Ansprüche 7 bis 9 zur Herstellung eines Metallobjekts nach Anspruch 6, dadurch gekennzeichnet, daß eine zusätzliche Schutzschicht auf die partiell oxidierte Schicht aufgebracht wird. 10. The method according to any one of claims 7 to 9 for producing a metal object according to claim 6, characterized in that an additional protective layer is applied to the partially oxidized layer.
PCT/EP2002/010481 2001-09-18 2002-09-18 Coated metal object in the form of a plate and used as component of a fuel cell stack WO2003026036A2 (en)

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