EP1027743A2 - Method for the production of high temperature fuel cells - Google Patents

Method for the production of high temperature fuel cells

Info

Publication number
EP1027743A2
EP1027743A2 EP99950474A EP99950474A EP1027743A2 EP 1027743 A2 EP1027743 A2 EP 1027743A2 EP 99950474 A EP99950474 A EP 99950474A EP 99950474 A EP99950474 A EP 99950474A EP 1027743 A2 EP1027743 A2 EP 1027743A2
Authority
EP
European Patent Office
Prior art keywords
contact layer
contact
bipolar plate
pore former
contact material
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.)
Withdrawn
Application number
EP99950474A
Other languages
German (de)
French (fr)
Inventor
Belinda BRÜCKNER
Horst Greiner
Klaus Eichler
Winfried Schaffrath
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.)
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Siemens AG
Original Assignee
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Siemens AG
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV, Siemens AG filed Critical Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Publication of EP1027743A2 publication Critical patent/EP1027743A2/en
Withdrawn legal-status Critical Current

Links

Classifications

    • 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
    • H01M8/1213—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte characterised by the electrode/electrolyte combination or the supporting 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
    • H01M8/02—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
    • H01M8/0223—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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the invention relates to a method for producing a high-temperature fuel cell, which has a contact layer between the cathode and the bipolar plate, in which a contact material is applied to the bipolar plate for producing the contact layer and then a high temperature, which is in particular above 800 ° C. , is exposed.
  • the fuel cells are divided into low, medium and high temperature fuel cells, which in turn differ in different technical embodiments.
  • a fuel cell stack composed of a large number of high-temperature fuel cells (a fuel cell stack is also called “stack *” in the specialist literature)
  • at least one composite circuit board has a protective layer under an upper composite circuit board, which covers the high-temperature fuel cell stack , - a contact layer, an electrolyte electrode unit, a further contact layer, another composite printed circuit board, etc.
  • the electrolyte electrode unit comprises two electrodes and a solid electrolyte arranged between the two electrodes and designed as a membrane.
  • an electrolyte electrode unit lying between adjacent composite printed circuit boards forms a high-temperature fuel cell with the contact layers directly adjoining the electrolyte electrode unit on both sides, which also includes the sides of each of the two composite printed circuit boards adjacent to the contact layers.
  • This type and further types of fuel cells are known, for example, from the “Fuel Cell Handbook * by A. J. Appleby and F. R. Foulkes, 1989, pages 440 to 454.
  • a single cell is electrically connected to a metallic bipolar plate on the cathode side by means of a ceramic contact layer.
  • This contact layer has the task of compensating for unevenness in the production of the metallic and ceramic components in such a way that a full-surface, electronically conductive contact is produced between these components.
  • the aim is to keep the contact resistance between the bipolar plate and the cathode as small as possible and thus to keep the internal resistance of the entire high-temperature fuel cell stack as low as possible.
  • the requirements for the contact layer are also sufficient ductility to obtain the full-area contact mentioned.
  • the electrically conductive deformable contact layer can be applied to the bipolar plate using a cold spraying process (DE 44 36 456 C2).
  • the contact material applied to the bipolar plate is a spray suspension.
  • the contact layer can be applied to the bipolar plate by means of a screen printing process.
  • the contact material is a screen printing paste.
  • the unsintered contact layer has a dry density which is in the range from 2.9 to 3.9 g / cm 3 .
  • the object of the invention is to develop a method of the type mentioned at the outset in such a way that the deformability of the contact layer can assume a relatively high value.
  • This object is achieved according to the invention in that a pore former is added to the contact material before application.
  • a pore former is a substance that burns without residue during a temperature treatment and thus leads to an increase in the pore volume. Such a substance can be both in liquid form and in the form of a solid; in this form it can be supplied to the screen printing paste or spray suspension mentioned.
  • a substance is preferably chosen as the pore former, which is admixed as a solid to the screen printing paste or the spray suspension and which is insoluble in the solvent components of the screen printing paste or the spray suspension.
  • a substance thus takes up a corresponding volume fraction in the contact layer, which can be in the range from 0 to 54% by volume.
  • the dry density can be reduced to a value of 1.7 to 2.4 g / cm 3 . This allows a greater deformation of the contact layer.
  • a plastic such as a melamine resin, can be used as a pore-forming additive.
  • carbon can ⁇ material in the form of carbon, carbon black or graphite can be used.
  • the grain size is preferably in the range below 10 ⁇ .
  • a screen printed contact ⁇ layer whose thickness is between 50 microns and 150 microns and is in 38 vol .-% carbon black contains a grain size of about 50 nm, can be determined by annealing at a temperature below 800 ° C in the cooled Condition by cold forming by 20% due to a weight load of 420 p / cm 2 . If the layer contains 54% by volume of soot, a cold deformation of 40% is achieved.
  • a layer that has been sintered in the contact material with the aid of a pore former has, despite its increased porosity, a sufficiently high bulk conductivity so that this does not make any significant contribution to the overall resistance of the entire stack at operating temperature.
  • FIGS. 1 and 2 Exemplary embodiments of a high-temperature fuel cell, in which use is made of a contact layer with high deformation, are shown in the attached FIGS. 1 and 2.
  • Figure 1 shows a section of such a high-temperature fuel cell, in which the contact layer is applied by a screen printing process
  • FIG. 2 shows a section of a high-temperature fuel cell in which the contact layer is applied as a suspension using a cold spray process.
  • a bipolar plate 2 which can consist, for example, of CrFe 5 2 ⁇ 3 l, is provided with a number of operating medium channels 4 which run parallel to the paper plane. These channels 4 are with a fuel gas, such as Hydrogen, charged.
  • the bipolar plate 2 is electrically conductively connected to a nickel network 8, for example by spot welding.
  • a thin anode 10 adjoins this nickel mesh 8.
  • the anode 10 bears against a solid electrolyte 12.
  • This electrolyte 12 is delimited at the top by a cathode 14 in the form of a thin, electrically conductive, in particular ceramic, layer.
  • a ceramic contact layer 16 connects to the cathode 14. This contact layer 16 serves to compensate for unevenness in the production of the metallic and ceramic components.
  • the contact layer 16 consists of a number of individual parallel webs which have a width of, for example, 1 mm and a thickness of, for example, 80 ⁇ m. As is immediately clear, the formation of the webs is provided due to the geometry of the high-temperature fuel cell.
  • a further bipolar plate 18 is connected to the ceramic contact layer 16 via a ceramic protective layer 22.
  • This has a number of operating device channels 20 which run parallel to one another and perpendicular to the paper plane. They carry oxygen or air during operation.
  • the protective layer 22 completely lines the channels 20.
  • the protective layer 22 is first applied to the channel side of the bipolar plate 18 in a vacuum plasma spraying process.
  • the contact layer 16 is then applied to the webs between the channels 20 on the contact layer 22 using the screen printing method. It also contains a pore former. Alternatively, the contact layer 16 can also be applied to the cathode 14 using the screen printing method in the form of webs or strips.
  • Figure 2 largely corresponds to that of Figure 1, so that it is sufficient to the differences explain.
  • a protective layer 22 is applied to the channel side of the bipolar plate 18.
  • the contact layer 16 is applied in a cold spraying process.
  • the contact layer 16 thus completely lines the channels 20.
  • the cathode 14 is in electrical contact with the webs of the contact layer 16.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Sustainable Energy (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Sustainable Development (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Composite Materials (AREA)
  • Fuel Cell (AREA)
  • Inert Electrodes (AREA)

Abstract

The high-temperature fuel cell has a contact layer (16) disposed between the cathode (14) and a bipolar plate (18). During production of the contact layer (16), a contact material is applied on the bipolar plate (18), which may be fitted with a ceramic protective layer (22). Said material is then exposed to a high temperature, especially above 800 °C. In order to ensure high deformability of the ceramic contact layer (16), a pore-forming material, e.g. a granular plastic or a fine particle carbon, is added to the contact material before application.

Description

Beschreibungdescription
Verfahren zur Herstellung einer Hochtemperatur-BrennstoffzelleMethod of manufacturing a high temperature fuel cell
Die Erfindung bezieht sich auf ein Verfahren zur Herstellung einer Hochtemperatur-Brennstoffzelle, die eine Kontaktschicht zwischen Kathode und bipolarer Platte aufweist, bei dem zur Herstellung der Kontaktschicht ein Kontaktmaterial auf die bipolare Platte aufgebracht und danach einer hohen Temperatur, die insbesondere über 800 °C liegt, ausgesetzt wird.The invention relates to a method for producing a high-temperature fuel cell, which has a contact layer between the cathode and the bipolar plate, in which a contact material is applied to the bipolar plate for producing the contact layer and then a high temperature, which is in particular above 800 ° C. , is exposed.
Es ist bekannt, daß bei der Elektrolyse von Wasser die Wassermoleküle durch elektrischen Strom in Wasserstoff (H2) und Sauerstoff (02) zerlegt werden. In einer Brennstoffzelle läuft dieser Vorgang in umgekehrter Richtung ab. Durch die elektrochemische Verbindung von Wasserstoff (H2) und Sauerstoff (02) zu Wasser entsteht elektrischer Strom mit hohem Wirkungsgrad. Wenn als Brenngas reiner Wasserstoff (H2) ein- gesetzt wird, geschieht dies ohne Emission von Schadstoffen und Kohlendioxid (C02) . Auch mit einem technischen Brenngas, beispielsweise Erdgas oder Kohlegas, und mit Luft (die zusätzlich mit Sauerstoff (02) angereichert sein kann) anstelle von reinem Sauerstoff (02) erzeugt eine Brennstoffzelle deut- lieh weniger Schadstoffe und weniger Kohlendioxid (C02) als andere Energieerzeuger, die mit fossilen Energieträgern arbeiten. Die technische Umsetzung des Prinzips der Brennstoffzelle hat zu unterschiedlichen Lösungen, und zwar mit verschiedenartigen Elektrolyten und mit Betriebstemperaturen zwischen 80 °C und 1000 °C, geführt.It is known that in the electrolysis of water, the water molecules are broken down into hydrogen (H 2 ) and oxygen (0 2 ) by electric current. In a fuel cell, this process takes place in the opposite direction. The electrochemical connection of hydrogen (H 2 ) and oxygen (0 2 ) to water creates electrical current with high efficiency. If pure hydrogen (H 2 ) is used as the fuel gas, this happens without emission of pollutants and carbon dioxide (C0 2 ). (May be enriched additionally with oxygen (0 2)) Even with an industrial fuel gas, for example natural gas or coal gas, and with air instead of pure oxygen (0 2), a fuel cell German lent less pollution and less carbon dioxide (C0 2) than other energy producers that work with fossil fuels. The technical implementation of the principle of the fuel cell has led to different solutions, namely with different types of electrolytes and with operating temperatures between 80 ° C and 1000 ° C.
In Abhängigkeit von ihrer Betriebstemperatur werden die Brennstoffzellen in Nieder-, Mittel- und Hochtemperatur- Brennstoffzellen eingeteilt, die sich wiederum durch ver- schiedene technische Ausführungsformen unterscheiden. Bei dem aus einer Vielzahl von Hochtemperatur-Brennstoffzellen sich zusammensetzenden Hochtemperatur-Brennstoffzellen- stapel (in der Fachliteratur wird ein Brennstoffzellenstapel auch „Stack* genannt) liegen unter einer oberen Verbundleiterplatte, welche den Hochtemperatur-Brennstoffzellenstapel abdeckt, der Reihenfolge nach wenigstens eine Verbundleiterplatte eine Schutzschicht,- eine Kontaktschicht, eine Elektrolyt-Elektroden-Einheit, eine weitere Kontaktschicht, eine weitere Verbundleiterplatte, usw.Depending on their operating temperature, the fuel cells are divided into low, medium and high temperature fuel cells, which in turn differ in different technical embodiments. In the case of the high-temperature fuel cell stack composed of a large number of high-temperature fuel cells (a fuel cell stack is also called “stack *” in the specialist literature), at least one composite circuit board has a protective layer under an upper composite circuit board, which covers the high-temperature fuel cell stack , - a contact layer, an electrolyte electrode unit, a further contact layer, another composite printed circuit board, etc.
Die Elektrolyt-Elektroden-Einheit umfaßt dabei zwei Elektroden und einen zwischen den beiden Elektroden angeordneten, als Membran ausgeführten Festelektrolyten. Dabei bildet jeweils eine zwischen benachbarten Verbundleiterplatten lie- gende Elektrolyt-Elektroden-Einheit mit den beidseitig an der Elektrolyt-Elektroden-Einheit unmittelbar anliegenden Kontaktschichten eine Hochtemperatur-Brennstoffzelle, zu der auch noch die an den Kontaktschichten anliegenden Seiten jeder der beiden Verbundleiterplatten gehören. Dieser Typ und weitere Brennstoffzellen-Typen sind beispielsweise aus dem „Fuel Cell Handbook* von A. J. Appleby und F. R. Foulkes, 1989, Seiten 440 bis 454, bekannt.The electrolyte electrode unit comprises two electrodes and a solid electrolyte arranged between the two electrodes and designed as a membrane. In each case, an electrolyte electrode unit lying between adjacent composite printed circuit boards forms a high-temperature fuel cell with the contact layers directly adjoining the electrolyte electrode unit on both sides, which also includes the sides of each of the two composite printed circuit boards adjacent to the contact layers. This type and further types of fuel cells are known, for example, from the “Fuel Cell Handbook * by A. J. Appleby and F. R. Foulkes, 1989, pages 440 to 454.
Bei einer Hochtemperatur-Brennstoffzelle im planaren Design (vgl. DE 44 36 456 C2) wird jeweils eine Einzelzelle mit einer metallischen bipolaren Platte auf der Kathodenseite mittels einer keramischen Kontaktschicht elektrisch verschaltet. Diese Kontaktschicht hat die Aufgabe, Fertigungsunebenheiten der metallischen und keramischen Bauteile derart auszuglei- chen, daß ein vollflächiger, elektronisch leitender Kontakt zwischen diesen Bauteilen hergestellt wird. Dadurch soll der Kontaktwiderstand zwischen der bipolaren Platte und der Kathode möglichst klein und somit der Innenwiderstand des gesamten Hochtemperatur-Brennstoffzellen-Stapels möglichst ge- ring gehalten werden. Die Anforderungen an die Kontaktschicht sind neben einer ausreichenden elektrischen Leitfähigkeit bei der Betriebstemperatur der Hochtemperatur-Brennstoffzelle auch eine genügende Verformbarkeit, um den genannten vollflächigen Kontakt zu erhalten.In the case of a high-temperature fuel cell in the planar design (cf. DE 44 36 456 C2), a single cell is electrically connected to a metallic bipolar plate on the cathode side by means of a ceramic contact layer. This contact layer has the task of compensating for unevenness in the production of the metallic and ceramic components in such a way that a full-surface, electronically conductive contact is produced between these components. The aim is to keep the contact resistance between the bipolar plate and the cathode as small as possible and thus to keep the internal resistance of the entire high-temperature fuel cell stack as low as possible. In addition to sufficient electrical conductivity at the operating temperature of the high-temperature fuel cell, the requirements for the contact layer are also sufficient ductility to obtain the full-area contact mentioned.
Beim bisher üblichen "Stack"-Aufbau wird der Kontakt zwischen der bipolaren Platte und der Kathode abhängig vom Absetzvor¬ gang des Stacks während des Fügevorgangs erst bei einer Te - peratur oberhalb von 800 °C hergestellt. Bei diesen Temperaturen muß die Verformbarkeit der Kontaktschicht in ausreichendem Maße gewährleistet sein. Es hat sich herausgestellt, daß die Kontaktschicht um ca. 30% ihrer ursprünglichen Dicke verformbar sein sollte.When usual "stack" configuration of the contact between the bipolar plate and the cathode is dependent on Absetzvor ¬ transition of the stack during bonding only at a Te - temperature above made of 800 ° C. At these temperatures, the deformability of the contact layer must be ensured to a sufficient degree. It has been found that the contact layer should be deformable by approximately 30% of its original thickness.
Es ist bekannt, daß die elektrisch leitende verformbare Kontaktschicht mit Hilfe eines Kaltspritzverfahrens auf der bipolaren Platte aufgebracht werden kann (DE 44 36 456 C2) . Hierbei ist das auf die bipolare Platte aufgebrachte Kontakt- material eine Spritzsuspension. Es ist auch bekannt, daß die Kontaktschicht mittels eines Siebdruckverfahrens auf die bipolare Platte aufgebracht werden kann. Hierbei ist das Kontaktmaterial eine Siebdruckpaste. Bei beiden Verfahren besitzt die ungesinterte Kontaktschicht eine Trockendichte, die im Bereich von 2,9 bis 3,9 g/cm3 liegt. Untersuchungen haben nun ergeben, daß sich die Siebdruckschichten im Temperaturbereich von Raumtemperatur bis 1000 °C bei einer Belastung von 400 p/cm2 kaum, die naßpulver-gespritzten Schichten im Temperaturbereich von 200 °C bis 300 °C bei derselben Belastung von 400 p/cm2 nur um 10% verformen lassen. Dies wird auf den Ausbrand der Binderbestandteile des Kontaktmaterials beim Sintern zurückgeführt. Diese Werte liegen weit von dem gewünschten Wert von ca. 30% entfernt. Ab 850 °C werden Sintereffekte wirksam, die zu einer Verfestigung des Gefüges füh- ren. Die Verformung der Kontaktschicht um die geforderten 30% bei Temperaturen oberhalb von 900 °C (das ist der Temperaturbereich, in dem der Absetzvorgang des Stacks stattfindet) ist somit nicht gewährleistet. Rasteraufnahmen von Querschliffen, die nach einem Stack-Test von der Kontaktschicht angefertigt wurden, haben dies bestätigt. Sie zeigen, daß nur etwa ein Drittel der Kontaktfläche als stromtragende Fläche zur Verfü- gung steht. Dies führt im Laufe der Zeit unweigerlich zu einer Vergrößerung des Übergangswiderstands und damit zu einer Verschlechterung der Stack-Leistung.It is known that the electrically conductive deformable contact layer can be applied to the bipolar plate using a cold spraying process (DE 44 36 456 C2). The contact material applied to the bipolar plate is a spray suspension. It is also known that the contact layer can be applied to the bipolar plate by means of a screen printing process. The contact material is a screen printing paste. In both methods, the unsintered contact layer has a dry density which is in the range from 2.9 to 3.9 g / cm 3 . Studies have now shown that the screen printing layers in the temperature range from room temperature to 1000 ° C with a load of 400 p / cm 2 hardly, the wet powder-sprayed layers in the temperature range from 200 ° C to 300 ° C with the same load of 400 p / cm 2 Only allow cm 2 to be deformed by 10%. This is attributed to the burnout of the binder components of the contact material during sintering. These values are far from the desired value of approx. 30%. From 850 ° C, sintering effects take effect, which lead to a solidification of the structure. The deformation of the contact layer by the required 30% at temperatures above 900 ° C (this is the temperature range in which the stack is deposited) therefore not guaranteed. This has been confirmed by grid scans of cross sections that were made by the contact layer after a stack test. They show that only about a third of the contact area is available as a current-carrying area. Over time, this inevitably leads to an increase in contact resistance and thus a deterioration in stack performance.
Aufgabe der Erfindung ist es, ein Verfahren der eingangs ge- nannten Art derart auszubilden, daß die Verformbarkeit der Kontaktschicht einen relativ hohen Wert annehmen kann.The object of the invention is to develop a method of the type mentioned at the outset in such a way that the deformability of the contact layer can assume a relatively high value.
Die Lösung dieser Aufgabe gelingt erfindungsgemäß dadurch, daß vor dem Aufbringen dem Kontaktmaterial ein Porenbildner zugesetzt wird.This object is achieved according to the invention in that a pore former is added to the contact material before application.
Durch die Zugabe des Porenbildners zum Material der keramischen Kontaktschicht wird die Porosität dieser Kontaktschicht erhöht. Somit ist die Voraussetzung für eine große Schicht- Verformung geschaffen. Ein Porenbildner ist ein Stoff, der während einer Temperaturbehandlung rückstandsfrei verbrennt und somit zu einer Erhöhung des Porenvolumens führt. Ein solcher Stoff kann sowohl in flüssiger Form als auch in Form eines Feststoffes vorliegen; er kann in dieser Form der erwähn- ten Siebdruckpaste oder der erwähnten Spritzsuspension zugeführt werden.The porosity of this contact layer is increased by adding the pore former to the material of the ceramic contact layer. This creates the prerequisite for a large layer deformation. A pore former is a substance that burns without residue during a temperature treatment and thus leads to an increase in the pore volume. Such a substance can be both in liquid form and in the form of a solid; in this form it can be supplied to the screen printing paste or spray suspension mentioned.
Vorzugsweise wird als Porenbildner ein Stoff gewählt, der als Feststoff der Siebdruckpaste bzw. der Spritzsuspension zuge- mischt wird und der in den Lösemittelbestandteilen der Siebdruckpaste bzw. der Spritzsuspension unlöslich ist. Ein solcher Stoff nimmt dadurch in der Kontaktschicht einen entsprechenden Volumenanteil ein, der im Bereich von 0 bis 54 Vol.-% liegen kann. Nach dem Ausbrennen des Zusatzes erhöht sich die Porosität. Die Trockendichte kann sich auf einen Wert von 1,7 bis 2,4 g/cm3 reduzieren. Somit wird eine größere Verformung der Kontaktschicht zugelassen. Als porenbildender Zusatz kann ein Kunststoff, wie z.B. ein Melaminharz, eingesetzt werden. Alternativ kann auch Kohlen¬ stoff in Form von Kohle, Ruß oder Graphit verwendet werden. Die Korngröße liegt vorzugsweise im Bereich unter 10 μ .A substance is preferably chosen as the pore former, which is admixed as a solid to the screen printing paste or the spray suspension and which is insoluble in the solvent components of the screen printing paste or the spray suspension. Such a substance thus takes up a corresponding volume fraction in the contact layer, which can be in the range from 0 to 54% by volume. After the additive has burned out, the porosity increases. The dry density can be reduced to a value of 1.7 to 2.4 g / cm 3 . This allows a greater deformation of the contact layer. A plastic, such as a melamine resin, can be used as a pore-forming additive. Alternatively, carbon can ¬ material in the form of carbon, carbon black or graphite can be used. The grain size is preferably in the range below 10 μ.
Versuche haben folgendes ergeben: Eine siebgedruckte Kontakt¬ schicht, deren Dicke zwischen 50 μm und 150 μm liegt und die 38 Vol.-% Ruß einer Körnung von etwa 50 nm enthält, läßt sich nach einer Temperung bei einer Temperatur unter 800 °C im abgekühlten Zustand durch eine Gewichtslast von 420 p/cm2 um 20% kaltverformen. Enthält die Schicht 54 Vol.-% Ruß, wird eine Kaltverformung um 40% erreicht.Experiments have the following result: a screen printed contact ¬ layer whose thickness is between 50 microns and 150 microns and is in 38 vol .-% carbon black contains a grain size of about 50 nm, can be determined by annealing at a temperature below 800 ° C in the cooled Condition by cold forming by 20% due to a weight load of 420 p / cm 2 . If the layer contains 54% by volume of soot, a cold deformation of 40% is achieved.
Eine Schicht, die unter Zuhilfenahme eines Porenbildners im Kontaktmaterial gesintert wurde, besitzt trotz ihrer erhöhten Porosität eine noch genügend hohe Bulk-Leitfähigkeit, so daß diese zum Gesamtwiderstand des gesamten Stacks bei Betriebstemperatur keinen wesentlichen Beitrag liefert.A layer that has been sintered in the contact material with the aid of a pore former has, despite its increased porosity, a sufficiently high bulk conductivity so that this does not make any significant contribution to the overall resistance of the entire stack at operating temperature.
Ausführungsbeispiele einer Hochtemperatur-Brennstoffzelle, bei der von einer Kontaktschicht mit hoher Verformung Gebrauch gemacht wird, sind in den beigefügten Figuren 1 und 2 dargestellt .Exemplary embodiments of a high-temperature fuel cell, in which use is made of a contact layer with high deformation, are shown in the attached FIGS. 1 and 2.
Figur 1 zeigt dabei einen Ausschnitt einer solchen Hochtemperatur-Brennstoffzelle, bei der die Kontaktschicht nach einem Siebdruckverfahren aufgebracht ist, undFigure 1 shows a section of such a high-temperature fuel cell, in which the contact layer is applied by a screen printing process, and
Figur 2 zeigt einen Ausschnitt einer Hochtemperatur-Brennstoffzelle, bei der die Kontaktschicht als Suspension mit einem Kaltspritzverfahren aufgebracht ist.FIG. 2 shows a section of a high-temperature fuel cell in which the contact layer is applied as a suspension using a cold spray process.
Nach Figur 1 ist eine bipolare Platte 2, die z.B. aus CrFe5 2θ3l bestehen kann, mit einer Anzahl von Betriebsmittel- Kanälen 4 versehen, die parallel zur Papierebene verlaufen. Diese Kanäle 4 werden mit einem Brenngas, wie beispielsweise Wasserstoff, beschickt. Die bipolare Platte 2 ist mit einem Nickelnetz 8 elektrisch leitend verbunden, z.B. durch Punktschweißen. An dieses Nickelnetz 8 grenzt eine dünne Anode 10 an. Die Anode 10 liegt an einem Feststoff-Elektrolyten 12 an. Dieser Elektrolyt 12 wird oben von einer Kathode 14 in Form einer dünnen elektrisch leitenden, insbesondere keramischen Schicht begrenzt. An die Kathode 14 schließt sich eine keramische Kontaktschicht 16 an. Diese Kontaktschicht 16 dient dazu, Fertigungsunebenheiten der metallischen und keramischen Bauteile auszugleichen. Sie ist, wie bereits erläutert, so gefertigt, daß sie ausreichend verformbar ist. Sie ist vor dem Aufbringen mit einem Porenbildner versetzt, z.B. mit Ruß, so daß sich bei höheren Temperaturen Poren bilden. Die Kontaktschicht 16 besteht aus einer Anzahl einzelner paralleler Stege, die eine Breite von z.B. 1 mm und eine Dicke von z.B. 80 μm aufweisen. Wie sogleich deutlich wird, ist die Ausbildung der Stege infolge der Geometrie der Hochtemperatur- Brennstoffzelle vorgesehen.According to FIG. 1, a bipolar plate 2, which can consist, for example, of CrFe 5 2θ 3 l, is provided with a number of operating medium channels 4 which run parallel to the paper plane. These channels 4 are with a fuel gas, such as Hydrogen, charged. The bipolar plate 2 is electrically conductively connected to a nickel network 8, for example by spot welding. A thin anode 10 adjoins this nickel mesh 8. The anode 10 bears against a solid electrolyte 12. This electrolyte 12 is delimited at the top by a cathode 14 in the form of a thin, electrically conductive, in particular ceramic, layer. A ceramic contact layer 16 connects to the cathode 14. This contact layer 16 serves to compensate for unevenness in the production of the metallic and ceramic components. As already explained, it is manufactured in such a way that it is sufficiently deformable. Before application, it is mixed with a pore former, for example with soot, so that pores form at higher temperatures. The contact layer 16 consists of a number of individual parallel webs which have a width of, for example, 1 mm and a thickness of, for example, 80 μm. As is immediately clear, the formation of the webs is provided due to the geometry of the high-temperature fuel cell.
An die keramische Kontaktschicht 16 schließt sich über eine keramische Schutzschicht 22 eine weitere bipolare Platte 18 an. Diese besitzt eine Anzahl von Betriebsmittel-Kanälen 20, die parallel zu einander und senkrecht zur Papierebene verlaufen. Sie führen im Betrieb Sauerstoff oder Luft. Die Schutzschicht 22 kleidet die Kanäle 20 vollständig aus.A further bipolar plate 18 is connected to the ceramic contact layer 16 via a ceramic protective layer 22. This has a number of operating device channels 20 which run parallel to one another and perpendicular to the paper plane. They carry oxygen or air during operation. The protective layer 22 completely lines the channels 20.
Bei der Herstellung wird zunächst die Schutzschicht 22 im Vakuum-Plasma-Sprühverfahren auf die Kanalseite der bipolaren Platte 18 aufgetragen. Anschließend wird die Kontaktschicht 16 im Siebdruckverfahren auf die Stege zwischen den Kanälen 20 auf die Kontaktschicht 22 aufgebracht. Auch sie enthält wieder einen Porenbildner. Alternativ kann die Kontaktschicht 16 auch auf die Kathode 14 im Siebdruckverfahren in Form von Stegen oder Streifen aufgetragen werden.During manufacture, the protective layer 22 is first applied to the channel side of the bipolar plate 18 in a vacuum plasma spraying process. The contact layer 16 is then applied to the webs between the channels 20 on the contact layer 22 using the screen printing method. It also contains a pore former. Alternatively, the contact layer 16 can also be applied to the cathode 14 using the screen printing method in the form of webs or strips.
Die Ausführungsform nach Figur 2 entspricht weitgehend derjenigen von Figur 1, so daß es ausreicht, die Unterschiede zu erläutern. Hier ist ebenfalls eine Schutzschicht 22 auf die Kanalseite der bipolaren Platte 18 aufgebracht. Anschließend ist hierauf die Kontaktschicht 16 im Kaltspritzverfahren aufgetragen. Die Kontaktschicht 16 kleidet somit die Kanäle 20 vollständig aus. Auf den Stegen der Kontaktschicht 16 liegt elektrisch kontaktierend die Kathode 14. The embodiment of Figure 2 largely corresponds to that of Figure 1, so that it is sufficient to the differences explain. Here, too, a protective layer 22 is applied to the channel side of the bipolar plate 18. Subsequently, the contact layer 16 is applied in a cold spraying process. The contact layer 16 thus completely lines the channels 20. The cathode 14 is in electrical contact with the webs of the contact layer 16.

Claims

Patentansprüche claims
1. Verfahren zur Herstellung einer Hochtemperatur-Brennstoffzelle, die eine Kontaktschicht (16) zwischen Kathode (14) und bipolarer Platte (18) aufweist, bei dem zur Herstellung der Kontaktschicht (16) ein Kontaktmaterial auf die bipolare Platte (18) aufgebracht und danach einer hohen Temperatur, die insbesondere über 800 °C liegt, ausgesetzt wird, d a d u r c h g e k e n n z e i c h n e t , daß vor dem Aufbringen dem Kontaktmaterial ein Porenbildner zugesetzt wird.1. A method for producing a high-temperature fuel cell which has a contact layer (16) between the cathode (14) and the bipolar plate (18), in which a contact material is applied to the bipolar plate (18) for producing the contact layer (16) and then a high temperature, which is in particular above 800 ° C, is characterized in that a pore former is added to the contact material before application.
2. Verfahren nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t , daß ein im Kontaktmaterial unlöslicher Porenbildner verwendet wird.2. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that a pore former insoluble in the contact material is used.
3. Verfahren nach Anspruch 1 oder 2, d a d u r c h g e k e n n z e i c h n e t , daß als Kontaktmaterial eine keramische Siebdruckpaste oder eine kerami- sehe Spritzgußsuspension verwendet wird, und das Kontaktmaterial zusammen mit dem zugegebenen Porenbildner auf die bipolare Platte (18) nach einem Siebdruckverfahren bzw. nach einem Kaltspritzverfahren aufgebracht wird.3. The method according to claim 1 or 2, characterized in that a ceramic screen printing paste or a ceramic see injection molding suspension is used as the contact material, and the contact material is applied together with the added pore former to the bipolar plate (18) by a screen printing process or by a cold spraying process becomes.
4. Verfahren nach einem der Ansprüche 1 bis 3, d a d u r c h g e k e n n z e i c h n e t , daß als Porenbildner ein Feststoff eingesetzt wird.4. The method according to any one of claims 1 to 3, d a d u r c h g e k e n n z e i c h n e t that a solid is used as the pore former.
5. Verfahren nach einem der Ansprüche 1 bis 4, d a d u r c h g e k e n n z e i c h n e t , daß als Porenbildner ein Kunststoff, wie ein Melaminharz, eingesetzt wird.5. The method according to any one of claims 1 to 4, that a plastic, such as a melamine resin, is used as the pore former.
6. Verfahren nach einem der Ansprüche 1 bis 4, d a d u r c h g e k e n n z e i c h n e t , daß als Porenbildner Kohlenstoff, insbesondere in Form von Kohle, Ruß oder Graphit, eingesetzt wird. 6. The method according to any one of claims 1 to 4, characterized in that carbon, in particular in the form of coal, carbon black or graphite, is used as the pore former.
7. Verfahren nach einem der Ansprüche 1 bis 6, d a d u r c h g e k e n n z e i c h n e t , daß ein Porenbildner verwendet wird, der eine Korngröße besitzt, die unterhalb von lOμm liegt.7. The method according to any one of claims 1 to 6, d a d u r c h g e k e n n z e i c h n e t that a pore former is used which has a grain size which is below 10 microns.
8. Verfahren nach einem der Ansprüche 1 bis 7, d a d u r c h g e k e nn z e i c h n e t , daß die Kontaktschicht (16) vorzugsweise eine Dicke von 80 bis 100 μm besitzt .8. The method according to any one of claims 1 to 7, so that the contact layer (16) preferably has a thickness of 80 to 100 microns.
9. Verfahren nach einem der Ansprüche 1 bis 9, d a d u r c h g e k e n n z e i c h n e t , daß die Kontaktschicht (16) auf eine Schutzschicht (22) aufgetragen wird.9. The method according to any one of claims 1 to 9, so that the contact layer (16) is applied to a protective layer (22).
10. Verfahren nach einem der Ansprüche 1 bis 9, dahingehend abgeändert, daß das Kontaktmaterial nicht auf die bipolare Platte (18), sondern auf die Kathode (14) aufgebracht wird. 10. The method according to any one of claims 1 to 9, modified so that the contact material is not applied to the bipolar plate (18), but on the cathode (14).
EP99950474A 1998-08-04 1999-07-30 Method for the production of high temperature fuel cells Withdrawn EP1027743A2 (en)

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DE19835253 1998-08-04
DE19835253A DE19835253A1 (en) 1998-08-04 1998-08-04 High-temperature fuel cell manufacturing method
PCT/DE1999/002351 WO2000008701A2 (en) 1998-08-04 1999-07-30 Method for the production of high temperature fuel cells

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