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WO1997034332A1 - Interconnector made from a metallic high-temperature material and with a lanthanum-containing surface - Google Patents

Interconnector made from a metallic high-temperature material and with a lanthanum-containing surface Download PDF

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Publication number
WO1997034332A1
WO1997034332A1 PCT/DE1997/000468 DE9700468W WO9734332A1 WO 1997034332 A1 WO1997034332 A1 WO 1997034332A1 DE 9700468 W DE9700468 W DE 9700468W WO 9734332 A1 WO9734332 A1 WO 9734332A1
Authority
WO
WIPO (PCT)
Prior art keywords
connecting element
temperature material
lanthanum
metallic high
metallic
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/DE1997/000468
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German (de)
French (fr)
Inventor
Willem J. Quadakkers
Michael Hänsel
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Forschungszentrum Juelich GmbH
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Forschungszentrum Juelich GmbH
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Priority to AU23797/97A priority Critical patent/AU2379797A/en
Publication of WO1997034332A1 publication Critical patent/WO1997034332A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/067—Borides
    • 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
    • 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
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/12—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte
    • H01M2008/1293—Fuel cells with solid oxide electrolytes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0065—Solid electrolytes
    • H01M2300/0068—Solid electrolytes inorganic
    • H01M2300/0071—Oxides
    • H01M2300/0074—Ion conductive at high temperature
    • 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
    • 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
    • H01M8/0204—Non-porous and characterised by the material
    • H01M8/0215—Glass; Ceramic materials
    • 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
    • H01M8/0215—Glass; Ceramic materials
    • H01M8/0217—Complex oxides, optionally doped, of the type AMO3, A being an alkaline earth metal or rare earth metal and M being a metal, e.g. perovskites
    • 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
    • H01M8/0215—Glass; Ceramic materials
    • H01M8/0217—Complex oxides, optionally doped, of the type AMO3, A being an alkaline earth metal or rare earth metal and M being a metal, e.g. perovskites
    • H01M8/0219—Chromium complex oxides
    • 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
    • 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

  • Interconnector made of a metallic high-temperature material with a surface containing lanthanum
  • the invention relates to a connecting element for high-temperature fuel cells consisting of a metallic high-temperature material.
  • the voltage that can be picked up from a single cell is quite low ( ⁇ IV).
  • ⁇ IV The voltage that can be picked up from a single cell
  • several cells have to be connected together.
  • the interconnection is effected by connecting elements which are known under the name "in connectors".
  • in connectors In contrast to the electrolyte and the electrodes, which are on the order of 100 ⁇ m thick, a connecting element designed as a bipolar plate is a few millimeters thick in SOFC flat cell concepts. Thus, this often represents not only the connecting link between the individual cells, but also the supporting component of the cell.
  • a bipolar plate has to have the following properties:
  • bipolar plates Two material groups are currently favored as the material for bipolar plates: ceramics based on LaCr0 3 and metallic high-temperature materials.
  • the metallic materials have the advantage over the ceramic materials that they have better toughness, better electrical conductivity and easier manufacture. Due to the required lower coefficient of thermal expansion (since the thermal expansion coefficient of the electrode Substances is approximately 11 * 10 "6 K " 1 ) and the required hot gas corrosion resistance and electronic conductivity of the oxide layers formed, chromium-forming alloys based on Cr or - for low temperatures - chromium oxide-forming alloys based on FeCr are particularly suitable Materials for bipolar plates viewed.
  • the oxidic layers (Cr 2 0 3 ) which arise at the contact points with the electrodes during operation can become so thick after long operating times that they impair the passage of current from the electrode to the bipolar plate.
  • the oxide layers that form on the walls in the gas channels exceed a critical layer thickness and flake off. This can impair the gas flow in the gas channels.
  • the object of the invention is to provide a connecting element which has the aforementioned properties, in particular with regard to durability and electrical conductivity, in a further improved manner.
  • the object according to the invention is therefore achieved by a connecting element, in particular by a bipolar plate, which, during long-term operation of the cell, has a layer based on LaCr0 3 or a double layer made of Cr 2 0 3 and LaCr0 3 instead of a Cr 2 0 3 layer in which the latter phase is at the oxide / gas interface.
  • a connecting element which has a layer consisting of LaB 6 on the surface.
  • a bipolar plate is made of a chromium oxide forming alloy z.
  • B. made of a Cr-based or FeCr-based alloy.
  • the typical shape (plate a few millimeters thick with gas channels) can be made in a conventional manner by machining a sheet metal material or by means of a near-net-shape manufacturing process using powder metallurgical methods, such as. B. the WPP process known from DE 41 20 706 can be produced.
  • the plate produced in this way is subjected to a coating process with a high-La-containing material on the contact side with the cathode.
  • the following compounds are suitable for this: metallic La, La 2 0 3 and LaCrO,.
  • Metallic La is very reactive at room temperature and oxidizes quickly to La 2 0 3 in contact with oxygen.
  • LaB 6 ie not La, La 2 0 3 or La chromite
  • LaB 6 is stable in air at room temperature and can be easily processed into layers.
  • a layer thickness of 1-10 ⁇ m, in particular 3 ⁇ m, is preferably applied to the surface of the bipolar plate, in particular in the region of the gas channels.
  • the coating is typically carried out using high-performance cathode sputtering. However, other coating methods can also be used.
  • a surface is formed on the surface modified in this way by a solid reaction of the coating material (LaB 6 ) with the material of the bipolar plate (chromium oxide-forming alloy based on Cr or FeCr such as Cr5FelY 2 0 3 ) Layer of LaCr0 3 or a double layer of Cr 2 0 3 and LaCr0 3 , in which the latter phase is on the outside.
  • the resulting layer has very good adhesion, is very thin and has good electrical conductivity.
  • the non-reacting parts from La 2 0 3 burst after cooling and contact with atmospheric moisture because of its hygroscopic character.
  • the bipolar plate coated in this way forms a layer on its surface which has good adhesion, good electrical conductivity, reduced evaporation of chromium-containing compounds and is compatible with the cathode material.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Fuel Cell (AREA)

Abstract

The invention relates to a connecting element made from a chromium oxide-forming alloy and having at its surface a layer of LaB6. The connecting element has in particular high long-term stability and produces lower quantities of harmful volatile chromium oxides than conventional connecting elements made from chromium oxide-forming alloys.

Description

B e s c h r e i b u n g Description

Aus einem metallischen Hochtemperaturwerkstoff be¬ stehender Interkonnektor mit lanthanhaltiger OberflächeInterconnector made of a metallic high-temperature material with a surface containing lanthanum

Die Erfindung bezieht sich auf ein aus einem metallischen Hochtemperaturwerkstoff bestehendes Verbindungselement für Hochtemperatur-Brennstoffzellen.The invention relates to a connecting element for high-temperature fuel cells consisting of a metallic high-temperature material.

In einer Hochtemperatur-Brennstoffzelle (SOFC) wird chemische Energie unmittelbar in elektrische Energie umgewandelt. Brennstoff (H2, CH4, CO, etc.) wird von einem Oxidationsmittel (02, Luft) durch einen Sauer¬ stoffleitenden Festelektrolyt (Y-stabilisiertes Zr02) getrennt. Bei Betriebstemperatur der Zelle (ca. 950°C) werden Sauerstoffionen von der Kathodenseite durch den Elektrolyten geleitet, die an der Anode mit dem Brennstoff reagieren. Wegen des Ladungsausgleichs fließt ein Elektronenstrom in gleicher Richtung.In a high temperature fuel cell (SOFC) chemical energy is converted directly into electrical energy. Fuel (H 2 , CH 4 , CO, etc.) is separated from an oxidizing agent (0 2 , air) by an oxygen-conducting solid electrolyte (Y-stabilized Zr0 2 ). At the operating temperature of the cell (approx. 950 ° C), oxygen ions are passed through the electrolyte from the cathode side and react with the fuel at the anode. Because of the charge balance, an electron current flows in the same direction.

Die Spannung, die an einer Einzelzelle abgegriffen wer- den kann, ist recht niedrig (< I V) . Um die SOFC-Tech- nik für die Stromerzeugung nutzen zu können, müssen da¬ her mehrere Zellen zusammengeschaltet werden. Die Zu¬ sammenschaltung wird durch Verbindungselemente bewirkt, die unter der Bezeichnung „In erkonnektoren" bekannt sind. Im Gegensatz zum Elektrolyten und den Elektroden, die größenordnungsmäßig lOOμm dick sind, ist ein als bipolare Platte ausgestaltetes Verbindungselement bei SOFC-Flachzellenkonzepten einige Millimeter dick. Somit stellt dieses vielfach nicht nur das Verbindungsglied zwischen den Einzelzellen, sondern auch die tragende Komponente der Zelle dar.The voltage that can be picked up from a single cell is quite low (<IV). In order to be able to use the SOFC technology for power generation, several cells have to be connected together. The interconnection is effected by connecting elements which are known under the name "in connectors". In contrast to the electrolyte and the electrodes, which are on the order of 100 μm thick, a connecting element designed as a bipolar plate is a few millimeters thick in SOFC flat cell concepts. Thus, this often represents not only the connecting link between the individual cells, but also the supporting component of the cell.

Bei den gegebenen Betriebstemperaturen (ca. 950°C) muß eine bipolare Platte u.a. folgende Eigenschaften be- sitzen:At the given operating temperatures (approx. 950 ° C) a bipolar plate has to have the following properties:

• ausreichende Festigkeit;• sufficient strength;

• Gasdichtigkeit;• gas tightness;

• einfache (kostengünstige) Herstellbarkeit;• simple (inexpensive) manufacturability;

• thermische Ausdehnung, die ähnlich wie die der kera- mischen Elektrodenmaterialien ist;• thermal expansion that is similar to that of ceramic electrode materials;

• gute elektrische Leitfähigkeit;• good electrical conductivity;

• Korrosionsbeständigkeit in dem oxidierenden Gas (Luft) und dem Brennstoff (H20/H2) ;• Corrosion resistance in the oxidizing gas (air) and the fuel (H 2 0 / H 2 );

• Kompatibilität mit den Elektrodenmaterialien Zur Zeit werden zwei Werkstoffgruppen als Material für bipolare Platten favorisiert: Keramiken auf LaCr03-Ba- sis und metallische Hochtemperaturwerkstoffe. Die me¬ tallischen Werkstoffe weisen gegenüber den keramischen Materialien den Vorteil auf, über eine bessere Zähig- keit, bessere elektrische Leitfähigkeit und leichtere Herstellbarkeit zu verfügen. Aufgrund des geforderten geringeren thermischen Ausdehnungskoeffizienten (da der thermische Ausdehnungskoeffizient der Elektrodenwerk- Stoffe etwa 11*10"6 K"1 beträgt) und der erforderlichen Heißgaskorrosionsbeständigkeit und elektronischen Leit¬ fähigkeit der entstehenden Oxidschichten werden zur Zeit insbesondere chromoxidbildende Legierungen auf Cr- Basis oder - für niedrige Temperaturen - chromoxidbil¬ dende Legierungen auf FeCr-Basis als geeignete Werk¬ stoffe für bipolare Platten angesehen.• Compatibility with the electrode materials Two material groups are currently favored as the material for bipolar plates: ceramics based on LaCr0 3 and metallic high-temperature materials. The metallic materials have the advantage over the ceramic materials that they have better toughness, better electrical conductivity and easier manufacture. Due to the required lower coefficient of thermal expansion (since the thermal expansion coefficient of the electrode Substances is approximately 11 * 10 "6 K " 1 ) and the required hot gas corrosion resistance and electronic conductivity of the oxide layers formed, chromium-forming alloys based on Cr or - for low temperatures - chromium oxide-forming alloys based on FeCr are particularly suitable Materials for bipolar plates viewed.

Bipolare, aus chromoxidbildenden Legierungen herge¬ stellte Platten weisen folgende Nachteile auf:Bipolar plates made from chromium oxide-forming alloys have the following disadvantages:

Die oxidischen Schichten (Cr203) , die an den Kontakt¬ stellen mit den Elektroden während des Betriebes ent¬ stehen, können nach langen Betriebszeiten so dick wer¬ den, daß sie den Stromdurchgang von der Elektrode zur bipolaren Platte beeinträchtigen. Bei Langzeitbetrieb überschreiten die Oxidschichten, die auf den Wänden in den Gaskanälen entstehen, eine kritische Schichtdicke und platzen ab. Der Gasfluß in den Gaskanälen kann dadurch beeinträchtigt werden.The oxidic layers (Cr 2 0 3 ) which arise at the contact points with the electrodes during operation can become so thick after long operating times that they impair the passage of current from the electrode to the bipolar plate. In long-term operation, the oxide layers that form on the walls in the gas channels exceed a critical layer thickness and flake off. This can impair the gas flow in the gas channels.

Bei hohen Temperaturen und hohen, auf der Kathodenseite herrschenden Sauerstoffpartialdrücken bildet Cr203 flüchtige Oxide (z.B. Cr03) oder Hydroxide (z.B. CrO(OH)2) . Diese reagieren mit dem Kathodenwerkstoff (MnLa-Perowskit) und schädigen deren katalytische Funk¬ tion oder kondensieren an der Grenzfläche Ka- thode/Elektrolyt. Durch letztgenannten Effekt findet bei längerem Einsatz schließlich keine Kathodenreaktion mehr statt. Aus der Druckschrift DE 44 22 624 AI ist eine bipolare Platte bekannt, die aus einem metallischen Hochtemperaturwerkstoff besteht und auf der Oberfläche mit einer Verbindung des Lanthans beschichtet ist . Die Beschichtung soll das Abdampfen von flüchtigen Chromverbindungen bei hohen Temperaturen unter oxidierenden Bedingungen vermeiden.At high temperatures and high oxygen partial pressures prevailing on the cathode side, Cr 2 0 3 forms volatile oxides (eg Cr0 3 ) or hydroxides (eg CrO (OH) 2 ). These react with the cathode material (MnLa perovskite) and damage their catalytic function or condense at the cathode / electrolyte interface. As a result of the last-mentioned effect, there is no longer any cathode reaction after prolonged use. From the document DE 44 22 624 AI a bipolar plate is known which consists of a metallic high temperature material and is coated on the surface with a compound of lanthanum. The coating is intended to prevent volatile chromium compounds from evaporating at high temperatures under oxidizing conditions.

Aufgabe der Erfindung ist die Schaffung eines Verbindungselementes, das über erforderliche vorgenannte Eigenschaften, insbesondere bezüglich Langlebigkeit sowie elektrische Leitfähigkeit, in weiter verbesserter Weise verfügt.The object of the invention is to provide a connecting element which has the aforementioned properties, in particular with regard to durability and electrical conductivity, in a further improved manner.

Die Aufgabe wird durch ein Verbindungselement mit den Merkmalen des Hauptanspruchs gelöst. Versuche haben gezeigt, daß die elektrische Leitfähig¬ keit von Cr203-Schichten auf metallischen Hochtemperaturwerkstoffen durch Dotierung mit La verbessert werden kann: Deckschichten auf LaCr03-Basis weisen eine gute elektrische Leitfähigkeit und einen niedrigen Abdampfdruck von flüchtigen Cr-Spezies (ca. 100 mal geringer als über Cr203) bei hohem Sauerstoffpartialdruck auf. Nachteilhafte chemische Wechselwirkungen von Schichten auf LaCr03-Basis mit dem Kathodenwerkstoff sind außerdem geringer als die von Cr203 mit dem Kathodenwerkstoff. Der Einbau von La in die Cr203-Schicht verbessert die Haftung des Chromoxids. 5The object is achieved by a connecting element with the features of the main claim. Experiments have shown that the electrical conductivity of Cr 2 0 3 layers on metallic high-temperature materials can be improved by doping with La: top layers based on LaCr0 3 have good electrical conductivity and a low evaporation pressure of volatile Cr species (approx 100 times less than over Cr 2 0 3 ) at high oxygen partial pressure. Adverse chemical interactions of layers based on LaCr0 3 with the cathode material are also less than that of Cr 2 0 3 with the cathode material. The incorporation of La into the Cr 2 0 3 layer improves the adhesion of the chromium oxide. 5

Die erfindungsgemäße Aufgabe wird daher durch ein Verbindungselement, insbesondere durch eine bipolare Platte gelöst, das bei Langzeitbetrieb der Zelle auf der Oberfläche anstatt einer Cr203-Schicht eine Schicht auf LaCr03-Basis oder eine Doppelschicht aus Cr203 und LaCr03 aufweist, bei der sich die letztgenannte Phase an der Oxid/Gas-Grenzfläche befindet. Bewirkt wird dies gemäß Anspruch 1 durch ein Verbindungselement, welches auf der Oberfläche eine aus LaB6 bestehende Schicht aufweist.The object according to the invention is therefore achieved by a connecting element, in particular by a bipolar plate, which, during long-term operation of the cell, has a layer based on LaCr0 3 or a double layer made of Cr 2 0 3 and LaCr0 3 instead of a Cr 2 0 3 layer in which the latter phase is at the oxide / gas interface. This is achieved according to claim 1 by a connecting element which has a layer consisting of LaB 6 on the surface.

Vorteilhafte Ausgestaltungen ergeben sich aus den rückbezogenen Ansprüchen.Advantageous embodiments result from the related claims.

Ausführungsbeispiel : Eine bipolare Platte wird aus einer chromoxidbildenden Legierung z. B. aus einer Cr-Basis- oder FeCr-Basisle- gierung hergestellt. Die typische Form (Platte von ei¬ nigen Millimetern Dicke mit Gaskanälen) kann nach her¬ kömmlicher Art durch zerspannende Bearbeitung eines Blechmaterials oder mittels eines endkonturnahen Herstellungsverfahrens nach pulvermetallurgischen Methoden, wie z. B. das aus DE 41 20 706 bekannte WPP- Verfahren, hergestellt werden.Embodiment: A bipolar plate is made of a chromium oxide forming alloy z. B. made of a Cr-based or FeCr-based alloy. The typical shape (plate a few millimeters thick with gas channels) can be made in a conventional manner by machining a sheet metal material or by means of a near-net-shape manufacturing process using powder metallurgical methods, such as. B. the WPP process known from DE 41 20 706 can be produced.

Die so hergestellte Platte wird auf der Kontaktseite mit der Kathode einem Beschichtungsvorgang mit einem hoch La-haltigen Werkstoff unterzogen. Dazu bieten sich folgende Verbindungen an: metallisches La, La203 und LaCrO, . Metallisches La ist bei Raumtemperatur sehr reaktiv und oxidiert in Kontakt mit Sauerstoff schnell zu La203.The plate produced in this way is subjected to a coating process with a high-La-containing material on the contact side with the cathode. The following compounds are suitable for this: metallic La, La 2 0 3 and LaCrO,. Metallic La is very reactive at room temperature and oxidizes quickly to La 2 0 3 in contact with oxygen.

Versuche mit La203-Schichten zeigten weniger befriedi¬ gende Ergebnisse . Die Schichten neigen wegen des hygroskopischen Charakters dazu, während derExperiments with La 2 0 3 layers showed less satisfactory results. The layers tend to be hygroscopic in nature during the

Auslagerung vollständig abzuplatzen. Die Schichten waren des weiteren sehr unregelmäßig ausgebildet, und die Haftung war problematisch. Außerdem zeigte sich, daß selbst bei anfänglich guter Haftung die LaCr03- Schichten bei der Bildung von Mikrorissen keine Ausheilfähigkeit besitzen.Completely wipe out outsourcing. The layers were also very irregular and the adhesion was problematic. In addition, it was found that even with initially good adhesion, the LaCr0 3 layers have no healing ability when microcracks are formed.

Als vorteilhaft erwies sich die Verwendung anderer La- Verbindungen und zwar insbesondere die Verwendung von aus LaB6 bestehende Schichten (also nicht La, La203 oder La-Chromit) .The use of other La compounds proved to be advantageous, in particular the use of layers consisting of LaB 6 (ie not La, La 2 0 3 or La chromite).

LaB6 ist an Luft bei Raumtemperatur stabil und läßt sich gut zu Schichten verarbeiten. Bevorzugt wird eine Schichtdicke von 1- 10 μm, insbesondere 3 μm auf die Oberfläche der bipolaren Platte, insbesondere im Be- reich der Gaskanäle, aufgebracht. Die Beschichtung er¬ folgt typischerweise mittels Hochleistungskathodenzer- stäuben. Jedoch können auch andere Beschichtungsverf h- ren eingesetzt werden.LaB 6 is stable in air at room temperature and can be easily processed into layers. A layer thickness of 1-10 μm, in particular 3 μm, is preferably applied to the surface of the bipolar plate, in particular in the region of the gas channels. The coating is typically carried out using high-performance cathode sputtering. However, other coating methods can also be used.

Bei Hochtemperatureinsatz in oxidierenden Medien bildet sich auf der so modifizierten Oberfläche durch Festkör¬ perreaktion des Beschichtungsmaterials (LaB6) mit dem Material der bipolaren Platte (chromoxidbildende Legierung auf Cr oder FeCr Basis wie Cr5FelY203) , eine Schicht aus LaCr03 oder eine Doppelschicht aus Cr203 und LaCr03, bei der die letztgenannte Phase sich an der Außenseite befindet. Durch die Reaktion/Interdiffusion des LaB6 mit Cr203 weist die resultierende Schicht eine sehr gute Haftung auf, ist sehr dünn und hat eine gute elektrische Leitfähigkeit. Die nicht reagierenden Teile aus La203 platzen nach Abkühlen und Kontakt mit Luft¬ feuchtigkeit wegen dessen hygroskopischen Charakters ab. Die derart beschichtete bipolare Platte bildet bei Langzeitbetrieb der Zelle auf ihrer Oberfläche eine Schicht, die eine gute Haftung, eine gute elektrische Leitfähigkeit, ein reduziertes Abdampfen chromhaltiger Verbindungen besitzt und kompatibel mit dem Kathoden- erkstoff ist. When used at high temperatures in oxidizing media, a surface is formed on the surface modified in this way by a solid reaction of the coating material (LaB 6 ) with the material of the bipolar plate (chromium oxide-forming alloy based on Cr or FeCr such as Cr5FelY 2 0 3 ) Layer of LaCr0 3 or a double layer of Cr 2 0 3 and LaCr0 3 , in which the latter phase is on the outside. As a result of the reaction / interdiffusion of the LaB 6 with Cr 2 0 3 , the resulting layer has very good adhesion, is very thin and has good electrical conductivity. The non-reacting parts from La 2 0 3 burst after cooling and contact with atmospheric moisture because of its hygroscopic character. During long-term operation of the cell, the bipolar plate coated in this way forms a layer on its surface which has good adhesion, good electrical conductivity, reduced evaporation of chromium-containing compounds and is compatible with the cathode material.

Claims

P a t e n t a n s p r ü c h e Patent claims 1. Aus einem metallischen Hochtemperaturwerkstoff be¬ stehendes Verbindungselement für Hochtemperatur- Brennstoffzellen, g e k e n n z e i c h n e t d u r c h eine aus LaB6 bestehende Schicht auf ihrer Oberfläche.1. A connecting element for high-temperature fuel cells consisting of a metallic high-temperature material, characterized by a layer consisting of LaB 6 on its surface. 2. Verbindungselement nach einem der vorhergehenden An¬ sprüche, d a d u r c h g e k e n n z e i c h n e t , daß sich die aus LaB6 bestehende Schicht an der Oxid/Gas-Grenzfläche befindet.2. Connecting element according to one of the preceding claims, characterized in that the layer consisting of LaB 6 is located at the oxide / gas interface. 3. Verbindungselement nach einem der vorhergehenden An- sprüche, d a d u r c h g e k e n n z e i c h n e t , daß eine chromoxidbildende Legierung als metallischer Hochtemperaturwerkstoff vorgesehen ist, 3. Connecting element according to one of the preceding claims, namely that a chromium oxide-forming alloy is provided as the metallic high-temperature material,
PCT/DE1997/000468 1996-03-13 1997-03-11 Interconnector made from a metallic high-temperature material and with a lanthanum-containing surface Ceased WO1997034332A1 (en)

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Applications Claiming Priority (2)

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DE19609813A DE19609813C1 (en) 1996-03-13 1996-03-13 Long life high temperature fuel cell interconnector
DE19609813.0 1996-03-13

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DE10211042A1 (en) * 2002-03-13 2003-10-02 Andreas Schubert Bipolar plate for fuel cell stack has porous parts manufactured using powder metallurgical techniques and/or combination of powder metallurgical and conventional manufacturing techniques
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