WO2003001621A2 - Bipolar plate for a fuel cell - Google Patents

Bipolar plate for a fuel cell Download PDF

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Publication number
WO2003001621A2
WO2003001621A2 PCT/DE2002/001733 DE0201733W WO03001621A2 WO 2003001621 A2 WO2003001621 A2 WO 2003001621A2 DE 0201733 W DE0201733 W DE 0201733W WO 03001621 A2 WO03001621 A2 WO 03001621A2
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WO
WIPO (PCT)
Prior art keywords
channel
bipolar plate
fuel cell
distribution channel
supply
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PCT/DE2002/001733
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German (de)
French (fr)
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WO2003001621A3 (en
Inventor
Andrei Kulikovsky
Hendrik Dohle
Alexei Kornyshev
Jürgen Mergel
Original Assignee
Forschungszentrum Jülich GmbH
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Publication of WO2003001621A2 publication Critical patent/WO2003001621A2/en
Publication of WO2003001621A3 publication Critical patent/WO2003001621A3/en

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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
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
    • 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
    • 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
    • H01M2300/0082—Organic polymers
    • 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
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
    • H01M8/04119—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying
    • 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
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04186—Arrangements for control of reactant parameters, e.g. pressure or concentration of liquid-charged or electrolyte-charged reactants
    • 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 bipolar plate for a fuel cell, in particular for a low-temperature fuel cell.
  • Low-temperature fuel cells such as the hydrogen fuel cell or the direct methanol fuel cell, regularly require an even supply of operating materials.
  • this includes the fuel, for example H or
  • Methanol or a methanol-water mixture
  • the oxidizing agent for example air or oxygen.
  • a uniform distribution of the operating materials can be achieved by using a bipolar plate with a channel structure or with a meandering structure.
  • a bipolar plate in which a meandering channel is formed. This type of bipolar plate ensures good uniform distribution of the operating materials on the electrode surface both at low flow rates (part-load operation) and at high flow rates (full-load operation).
  • a gas distributer design for proton-exchange-membrane fuel cells J. Electrochem. Soc, Vol. 143, No. 5, L103-L105 (1996) a gas distribution system with comb-like and interlocking inlet and outlet channels, which are closed at their ends, is known. The operating medium is distributed in the inlet channels closed at their ends, flows to the end thereof, and is guided to a porous electrode. A comparatively large pressure difference is built up between the inlet channels and the outlet channels, and the operating medium or the reaction product flows through a diffusion layer of the electrode bordering the bipolar plate.
  • a homogeneous moistening of the membrane represents a problem that has not yet been finally resolved, since only this ensures the effective transport of the ions.
  • this is done regularly when using methanol, a methanol-water mixture or humidified hydrogen.
  • the use of non-humidified gases can disadvantageously dry out individual membrane areas.
  • a disadvantage of the bipolar plates on the oxidizing agent side cited in the prior art is not regularly the problem of solving the water accumulating in the channels to a sufficient extent.
  • water does not only escape on the cathode side. stands, but also from the anode side water by electro-osmosis through the membrane, or the electrolyte. If one channel is full, the flow resistance increases there and the flow switches to the other channels.
  • This disadvantageously creates an uneven distribution of the oxidizing agent within the fuel cell.
  • There is an inhibition of transport with regard to the oxidizing agent with the result that the performance and the efficiency of the fuel cell are adversely affected.
  • the object of the invention is to create a bipolar plate for a fuel cell with which inhomogeneous moistening of the membrane electrode unit is achieved
  • the bipolar plate for a fuel cell has at least one distribution channel for distributing an item of equipment via an electrode, a supply channel and a discharge channel, via which the item of equipment can be guided into or out of the distribution channel. Furthermore, the bipolar plate comprises at least one additional supply channel which opens directly into the distribution channel. This has the advantage that in the case of non-humidified gas as the operating material, the area or the length of the distribution channel on which the gas flowing through is relatively dry and thus disadvantageously leads to drying out of the membrane can be minimized. In the case of liquid fuels as operating resources, an additional inlet (feed) means that lower concentrations can advantageously be used.
  • One embodiment of the bipolar plate provides at least two further supply channels in the distribution channel. The more additional feeds are provided, the more even the moisture or Concentration curve of the equipment when using the bipolar plate in a fuel cell. Both of these advantageously result in improved performance.
  • a particularly advantageous embodiment provides a meandering distribution channel.
  • In the case of direct methanol fuel cells for a bipolar plate often only one distribution channel in the form of a tightly wound meander is provided. Additional supply channels provided allow comparatively lower flow velocities to be set during the supply of the oxidizing agent during the operation of the fuel cell. The flow speed along the distribution channel then increases in the direction of flow due to the further feeds. Due to the increasing flow velocity at the end of the distribution channel, the product water formed is discharged from the distribution channel particularly effectively.
  • Figure 1 Exemplary embodiments of a bipolar plate according to the invention in supervision.
  • Figure 2 Schematic diagram of the degree of moisture of an operating gas against the length of the distribution channel (in the direction of flow of the operating medium) using the example of a polymer electrolyte membrane (PEM) cathode. Comparison of a single supply of the non-humidified gas and supply via two further feeds according to the invention.
  • Figure 3 Schematic diagram of the concentration of a methanol-water mixture against the length of the distribution channel using the example of a direct methanol fuel cell (DMFC) anode. Comparison between a single supply of the fuel and a supply via two further feeds according to the invention.
  • DMFC direct methanol fuel cell
  • FIG. 1 Two embodiments of a bipolar plate are shown in FIG.
  • the first has a meandering distribution channel 3 as well as a feed channel 1 and a discharge channel 2.
  • feed channels 4 are provided at two further locations.
  • the flow of the equipment for. B. a gas at the beginning of the distribution channel can be set lower.
  • the pressure is only a third of the pressure without further feed.
  • the equipment is thus distributed at a lower flow rate in the first part of the distribution channel.
  • the degree of moisture in the gas increases due to the chemical conversion due to the low flow velocity in the first part, much faster than without a further additional feed.
  • the flow velocity within the distribution channel increases to values that would have been set at the beginning in the case of no further feeds.
  • the gas inside the distribution channel is therefore more humid than without further feed. But this is advantageously a uniform achieved greater moistening of the membrane and, as a result, improved performance of the fuel cell.
  • Feed-in initially results in a kind of dilution effect, which is even more than compensated for in the further course.
  • the increasing flow velocity along the length of the distribution channel has the additional advantage that the product water formed is quickly removed from the distribution channel.
  • An additional feed also has a similar advantage on the anode side of a polymer membrane fuel cell (PEM), as is shown schematically in FIG.
  • PEM polymer membrane fuel cell
  • a methanol-water mixture with a concentration C max of methanol is used as fuel.
  • the chemical conversion of the fuel cell consumes methanol.
  • the concentration of methanol along the distribution channel drops significantly. This leads disadvantageously to an inhomogeneous implementation.
  • the concentration gradient along the distribution channel is significantly reduced, although overall lower methanol concentrations are used. As a result, such a fuel cell has a more homogeneous and thus improved performance profile.
  • a bipolar plate with the size 100 x 100 mm 2 is provided with a meander 3 with the geometric dimensions 1 x 1 x 1 mm 3 with a web width of 1 mm.
  • the meander 3 has three further supply bores (inlet channels) 4 through which the air can be guided into the meander 3.
  • the arrangement of the supply bores (feed channel 1 and additional feed channels 4) is such that the path length in the meander 3 from one feed bore to the next is the same.

Abstract

The invention relates to a bipolar plate for a fuel cell, in particular for a low-temperature fuel-cell, which in addition to a distribution channel (3) and a supply channel (1) and discharge channel (2), which open into said distribution channel, also has an additional supply channel (4), which is used to supply an operating medium directly to the distribution channel (3). This promotes improved flow guidance for the operating medium. The distribution channel area, in which the adjoining membrane is in danger of drying out as a result of the low humidity of the operating medium, is minimised in a uniform manner and the yield of product water that is formed is significantly increased.

Description

Beschreibung description
Bipolare Platte für eine BrennstoffzelleBipolar plate for a fuel cell
Die Erfindung betrifft eine bipolare Platte für eine Brennstoffzelle, insbesondere für eine Niedertemperatur-Brennstoffzelle .The invention relates to a bipolar plate for a fuel cell, in particular for a low-temperature fuel cell.
Stand der TechnikState of the art
Niedertemperatur-Brennstoffzellen, wie beispielsweise die Wasserstoff-Brennstoffzelle oder auch die Direkt- Methanol-Brennstoffzelle, benötigen regelmäßig eine gleichmäßige Versorgung mit Betriebsstoffen. Dazu gehö- ren zum einen der Brennstoff, beispielsweise H oderLow-temperature fuel cells, such as the hydrogen fuel cell or the direct methanol fuel cell, regularly require an even supply of operating materials. On the one hand, this includes the fuel, for example H or
Methanol, bzw. ein Methanol-Wassergemisch, und zum anderen das Oxidationsmittel, beispielsweise Luft oder auch Sauerstoff.Methanol, or a methanol-water mixture, and on the other hand the oxidizing agent, for example air or oxygen.
Eine gleichmäßige Verteilung der Betriebsstoffe kann durch Einsatz einer bipolaren Platte mit einer Kanal- Struktur oder auch mit einer Mäanderstruktur erfolgen.A uniform distribution of the operating materials can be achieved by using a bipolar plate with a channel structure or with a meandering structure.
Aus US-4 988 583 ist eine bipolare Platte bekannt, bei der ein mäanderförmig verlaufender Kanal ausgebildet ist. Diese Art von bipolarer Platte gewährleistet sowohl bei niedrigen Durchflüssen (Teillastbetrieb) , als auch bei hohen Durchflußraten (Vollastbetrieb) eine gute Gleichverteilung der Betriebsstoffe auf die Elektro- denoberflache . Aus T. V. Nguyen : A gas distributer design for proton- exchange-membrane fuel cells, J. Electrochem. Soc, Vol. 143, No. 5, L103-L105 (1996) ist ein Gasverteilersystem mit kammartigen und miteinander verzahnten Ein- laß- und Auslaßkanälen, die an ihren Enden geschlossenen sind, bekannt . Das Betriebsmittel wird in den an ihren Enden geschlossenen Einlaßkanälen verteilt, strömt bis zu deren Ende, und wird an eine porös ausgestaltete Elektrode geführt. Dabei wird ein ver- gleichsweise großer Druckunterschied zwischen den Einlaßkanälen und den Auslaßkanälen aufgebaut und das Betriebsmittel, bzw. das Reaktionsprodukt strömt durch eine Diffusionsschicht der an die bipolare Platte grenzenden Elektrode.From US-4 988 583 a bipolar plate is known in which a meandering channel is formed. This type of bipolar plate ensures good uniform distribution of the operating materials on the electrode surface both at low flow rates (part-load operation) and at high flow rates (full-load operation). From TV Nguyen: A gas distributer design for proton-exchange-membrane fuel cells, J. Electrochem. Soc, Vol. 143, No. 5, L103-L105 (1996) a gas distribution system with comb-like and interlocking inlet and outlet channels, which are closed at their ends, is known. The operating medium is distributed in the inlet channels closed at their ends, flows to the end thereof, and is guided to a porous electrode. A comparatively large pressure difference is built up between the inlet channels and the outlet channels, and the operating medium or the reaction product flows through a diffusion layer of the electrode bordering the bipolar plate.
Ein noch nicht endgültig gelöstes Problem stellt die homogene Befeuchtung der Membran dar, da nur sie den effektiven Transport der Ionen gewährleistet . Auf der Brennstoffseite erfolgt dies regelmäßig beim Einsatz von Methanol, einem Methanol-Wassergemisch oder befeuchtetem Wasserstoff. Auf der Oxidationsmittelseite kann es jedoch bei Einsatz von nicht befeuchteten Gasen nachteilig zu einem Austrocknen einzelner Membranbereiche kommen.A homogeneous moistening of the membrane represents a problem that has not yet been finally resolved, since only this ensures the effective transport of the ions. On the fuel side, this is done regularly when using methanol, a methanol-water mixture or humidified hydrogen. On the oxidant side, however, the use of non-humidified gases can disadvantageously dry out individual membrane areas.
Nachteilig wird auch bei den im Stand der Technik zitierten bipolaren Platten auf der Oxidationsmittelseite regelmäßig das Problem nicht gelöst, das in den Kanälen anfallende Wasser in ausreichendem Maße abzuführen. Bei Niedertemperatur-Brennstoffzellen tritt zusätzlich das Problem auf, daß nicht nur kathodenseitig Wasser ent- steht, sondern auch von der Anodenseite her Wasser durch Elektroosmose durch die Membran, bzw. den Elektrolyten übertritt. Läuft ein Kanal voll, so steigt dort der Strömungswiderstand an und die Strömung weicht auf die übrigen Kanäle aus. Dadurch entsteht nachteilig eine Ungleichverteilung des Oxidationsmittels innerhalb der Brennstoffzelle. Es kommt zu einer Transporthemmung hinsichtlich des Oxidationsmittels mit der Folge, daß dadurch die Leistung und der Wirkungsgrad der Brenn- stoffzelle negativ beeinflußt wird.A disadvantage of the bipolar plates on the oxidizing agent side cited in the prior art is not regularly the problem of solving the water accumulating in the channels to a sufficient extent. In the case of low-temperature fuel cells, there is also the problem that water does not only escape on the cathode side. stands, but also from the anode side water by electro-osmosis through the membrane, or the electrolyte. If one channel is full, the flow resistance increases there and the flow switches to the other channels. This disadvantageously creates an uneven distribution of the oxidizing agent within the fuel cell. There is an inhibition of transport with regard to the oxidizing agent, with the result that the performance and the efficiency of the fuel cell are adversely affected.
Aufgabe und LösungTask and solution
Aufgabe der Erfindung ist es eine bipolare Platte für eine Brennstoffzelle zu schaffen, mit der eine inhomo- gene Befeuchtung der Membran-Elektroden-Einheit beiThe object of the invention is to create a bipolar plate for a fuel cell with which inhomogeneous moistening of the membrane electrode unit is achieved
Einsatz von nicht befeuchtetem Gas weitgehend verhindert wird.Use of non-humidified gas is largely prevented.
Weiterhin ist es Aufgabe der Erfindung ein Verfahren zum Betreiben einer Brennstoffzelle bereit zu stellen, bei dem eine Leistungsreduzierung aufgrund ungleicher Befeuchtung einer Membran-Elektroden-Einheit vermieden wird.Furthermore, it is an object of the invention to provide a method for operating a fuel cell in which a power reduction due to uneven moistening of a membrane electrode unit is avoided.
Die Aufgabe wird gelöst durch eine bipolare Platte gemäß Hauptanspruch sowie durch ein Verfahren gemäß Nebenanspruch. Vorteilhafte Ausführungsformen finden sich in den jeweils darauf rückbezogenen Ansprüchen. Gegenstand der ErfindungThe object is achieved by a bipolar plate according to the main claim and by a method according to the secondary claim. Advantageous embodiments can be found in the claims referring back to each. Subject of the invention
Die bipolare Platte für eine Brennstoffzelle weist wenigstens einen Verteilerkanal zur Verteilung eines Betriebsmittels über eine Elektrode, einen Zuführungska- nal und einen Abführungskanal auf, über die das Betriebsmittel in bzw. aus dem Verteilerkanal geführt werden kann. Weiterhin umfaßt die bipolare Platte wenigstens einen zusätzlichen Zuführungskanal, der direkt in den Verteilerkanal mündet. Dies hat den Vorteil, daß im Fall von nicht befeuchtetem Gas als Betriebsstoff, der Bereich, bzw. die Länge des Verteilerkanals, auf der das durchströmende Gas relativ trocken ist und damit nachteilig zu einer Austrocknung der Membran führt, minimiert werden kann. Im Fall von flüssigen Brennstoffen als Betriebsmittel führt ein zusätzlicher Einlass (Zuführung) dazu, daß vorteilhaft mit geringeren Konzentrationen gearbeitet werden kann.The bipolar plate for a fuel cell has at least one distribution channel for distributing an item of equipment via an electrode, a supply channel and a discharge channel, via which the item of equipment can be guided into or out of the distribution channel. Furthermore, the bipolar plate comprises at least one additional supply channel which opens directly into the distribution channel. This has the advantage that in the case of non-humidified gas as the operating material, the area or the length of the distribution channel on which the gas flowing through is relatively dry and thus disadvantageously leads to drying out of the membrane can be minimized. In the case of liquid fuels as operating resources, an additional inlet (feed) means that lower concentrations can advantageously be used.
Eine Ausführungsform der bipolaren Platte sieht mindestens zwei weitere Zuführungskanäle in den Verteilerkanal vor. Je mehr zusätzliche Zuführungen vorgesehen werden, desto gleichmäßiger verläuft die Feuchtigkeitsbzw. Konzentrationskurve der Betriebsmittel bei Einsatz der bipolaren Platte in einer Brennstoffzelle. Beides führt vorteilhaft zu einer verbesserten Leistung.One embodiment of the bipolar plate provides at least two further supply channels in the distribution channel. The more additional feeds are provided, the more even the moisture or Concentration curve of the equipment when using the bipolar plate in a fuel cell. Both of these advantageously result in improved performance.
Eine besonders vorteilhafte Ausführungsform sieht einen mäanderförmigen Verteilerkanal vor. Je länger ein Ver- teilerkanal ist, desto vorteilhafter wirken sich zusätzliche Einspeisungen im Betrieb einer Brennstoffzelle aus. Bei den Direkt-Methanol-Brennstoffzellen ist für eine bipolare Platte häufig nur ein Verteilerkanal in Form eines eng geschlungenen Mäanders vorgesehen. Durch zusätzliche vorgesehene Zuführungskanäle lassen sich während des Betriebs der Brennstoffzelle ver- gleichsweise geringere Strömungsgeschwindigkeiten bei der Zuführung des Oxidationsmittels einstellen. In Strömungsrichtung nimmt dann die Strömungsgeschwindigkeit entlang des Verteilerkanals aufgrund der weiteren Zuführungen zu. Durch die ansteigende Strömungsge- schwindigkeit zum Ende des Verteilerkanals wird das gebildete Produktwasser besonders effektiv aus dem Verteilerkanal ausgeschleust.A particularly advantageous embodiment provides a meandering distribution channel. The longer a distribution channel is, the more advantageous additional feeds have in the operation of a fuel cell. In the case of direct methanol fuel cells for a bipolar plate often only one distribution channel in the form of a tightly wound meander is provided. Additional supply channels provided allow comparatively lower flow velocities to be set during the supply of the oxidizing agent during the operation of the fuel cell. The flow speed along the distribution channel then increases in the direction of flow due to the further feeds. Due to the increasing flow velocity at the end of the distribution channel, the product water formed is discharged from the distribution channel particularly effectively.
Spezieller Beschreibungsteil Nachfolgend wird der Gegenstand der Erfindung anhand von drei Figuren und einem Ausführungsbeispiel näher erläutert, ohne daß der Gegenstand der Erfindung dadurch beschränkt wird.Special description part The subject matter of the invention is explained in more detail with reference to three figures and an exemplary embodiment, without the subject matter of the invention being restricted thereby.
Es zeigenShow it
Figur 1 : Ausführungsbeispiele einer erfindungsgemäßen bipolaren Platte in der Aufsicht . Figur 2 : Schematisches Diagramm des Feuchtegrads eines Betriebsgases gegen die Länge des Verteiler- kanals (in Strömungsrichtung des Betriebsmittels) am Beispiel einer Polymer-Elektrolyt- Membran (PEM) Kathode. Vergleich einmalige Zuführung des nicht befeuchteten Gases und Zuführung über zwei weitere erfindungsgemäße Einspeisungen. Figur 3: Schematisches Diagramm der Konzentration eines Methanol-Wassergemisches gegen die Länge des Verteilerkanals am Beispiel einer Direkt- Methanol-Brennstoffzelle (DMFC) Anode. Ver- gleich zwischen einer einmaligen Zuführung des Brennstoffs und einer Zuführung über zwei weitere erfindungsgemäße Einspeisungen.Figure 1: Exemplary embodiments of a bipolar plate according to the invention in supervision. Figure 2: Schematic diagram of the degree of moisture of an operating gas against the length of the distribution channel (in the direction of flow of the operating medium) using the example of a polymer electrolyte membrane (PEM) cathode. Comparison of a single supply of the non-humidified gas and supply via two further feeds according to the invention. Figure 3: Schematic diagram of the concentration of a methanol-water mixture against the length of the distribution channel using the example of a direct methanol fuel cell (DMFC) anode. Comparison between a single supply of the fuel and a supply via two further feeds according to the invention.
In der Figur 1 werden zwei Ausführungsformen einer bi- polaren Platte gezeigt. Die erste weist einen mäander- förmigen Verteilerkanal 3 sowie einen Zuführungskanal 1 und einen Abführungskanal 2 auf. Zusätzlich sind an zwei weiteren Stellen Zuführungskanäle 4 vorgesehen. Durch diese zusätzlichen Einspeisungsmöglichkeiten über die Zuführungen 4 kann die Strömung des Betriebsmittels, z. B. eines Gases am Anfang des Verteilerkanals geringer eingestellt werden. In diesem Fall beträgt der Druck nur ein Drittel des Drucks ohne weiter Einspeisung. Die Verteilung des Betriebsmittels erfolgt somit mit einer geringeren Strömungsgeschwindigkeit im ersten Teile des Verteilerkanals.Two embodiments of a bipolar plate are shown in FIG. The first has a meandering distribution channel 3 as well as a feed channel 1 and a discharge channel 2. In addition, feed channels 4 are provided at two further locations. Through these additional supply options via the feeds 4, the flow of the equipment, for. B. a gas at the beginning of the distribution channel can be set lower. In this case, the pressure is only a third of the pressure without further feed. The equipment is thus distributed at a lower flow rate in the first part of the distribution channel.
Im Fall eines nicht befeuchteten Oxidationsgases erhöht sich der Feuchtegrad des Gases durch die chemische Umsetzung aufgrund der geringen Strömungsgeschwindigkeit im ersten Teil sehr viel schneller als ohne eine weitere Zusatzeinspeisung. Durch die weiteren Einspeisungen erhöht sich die Strömungsgeschwindigkeit innerhalb des Verteilerkanals auf Werte, die im Fall ohne weitere Einspeisung schon zu Beginn eingestellt worden wären. Im Mittel weist das Gas somit innerhalb des Verteilerkanals eine höhere Feuchtigkeit auf, als ohne weitere Einspeisung. Damit wird aber vorteilhaft eine gleichmä- ßigere Befeuchtung der Membran und als Folge eine verbesserte Leistungsbereitstellung der Brennstoffzelle erzielt .In the case of a non-humidified oxidizing gas, the degree of moisture in the gas increases due to the chemical conversion due to the low flow velocity in the first part, much faster than without a further additional feed. As a result of the further feeds, the flow velocity within the distribution channel increases to values that would have been set at the beginning in the case of no further feeds. On average, the gas inside the distribution channel is therefore more humid than without further feed. But this is advantageously a uniform achieved greater moistening of the membrane and, as a result, improved performance of the fuel cell.
Für die zweite Ausführung einer bipolaren Platte mit geraden parallel angeordneten Verteilerkanälen ergibt sich die gleiche vorteilhafte Wirkungsweise.The same advantageous mode of operation results for the second embodiment of a bipolar plate with straight distribution channels arranged in parallel.
Die Figur 2 erläutert den Zusammenhang zwischen demFigure 2 explains the relationship between the
Feuchtegrad (φ) eines Betriebsgases und der Länge des Verteilerkanals in Strömungsrichtung am Beispiel einer PEM Kathode. Durch die vergleichsweise geringe Strömungsgeschwindigkeit wird das Gas zu Beginn schneller mit Feuchtigkeit angereichert. Durch die zusätzlicheDegree of humidity (φ) of an operating gas and the length of the distribution channel in the direction of flow using the example of a PEM cathode. Due to the comparatively low flow velocity, the gas is enriched with moisture faster at the beginning. By the additional
Einspeisung tritt zwar zunächst eine Art Verdünnungseffekt ein, der aber im weiteren Verlauf sogar mehr als kompensiert wird. Die entlang der Länge des Verteilerkanals zunehmende Strömungsgeschwindigkeit weist den zusätzlichen Vorteil auf, daß das gebildete Produktwasser schnell aus dem Verteilerkanal entfernt wird.Feed-in initially results in a kind of dilution effect, which is even more than compensated for in the further course. The increasing flow velocity along the length of the distribution channel has the additional advantage that the product water formed is quickly removed from the distribution channel.
Ähnlich vorteilhaft zeigt sich eine zusätzliche Einspeisung auch auf der Anodenseite einer Polymermembran- Brennstoffzelle (PEM) , wie in Figur 3 schematisch gezeigt wird. Als Brennstoff wird beispielsweise eine Methanol-Wassermischung mit einer Konzentration Cmax an Methanol eingesetzt. Durch die chemische Umsetzung der Brennstoffzelle wird Methanol verbraucht. Als Folge sinkt die Konzentration an Methanol entlang des Verteilerkanals deutlich ab. Dies führt nachteilig zu einer inhomogenen Umsetzung. Durch die erfindungsgemäße weitere Einspeisung einer Methanol-Wassermischung wird das Konzentrationsgefalle entlang des Verteilerkanals deutlich reduziert, obwohl insgesamt niedrigere Methanolkonzentrationen eingesetzt werden. Als Folge weist eine solche Brennstoffzelle ein homogeneres, und damit verbessertes Leistungsprofil auf .An additional feed also has a similar advantage on the anode side of a polymer membrane fuel cell (PEM), as is shown schematically in FIG. For example, a methanol-water mixture with a concentration C max of methanol is used as fuel. The chemical conversion of the fuel cell consumes methanol. As a result, the concentration of methanol along the distribution channel drops significantly. This leads disadvantageously to an inhomogeneous implementation. As a result of the further feeding of a methanol / water mixture according to the invention, the concentration gradient along the distribution channel is significantly reduced, although overall lower methanol concentrations are used. As a result, such a fuel cell has a more homogeneous and thus improved performance profile.
Ausführungsbeispiel : Eine bipolare Platte der Größe 100 x 100 mm2 wird mit einem Mäander 3 mit den geometrischen Abmessungen 1 x 1 x 1 mm3 mit einer Stegbreite von 1 mm versehen. Der Mäander 3 weist zusätzlich zum Einlass 1 und Auslass 2 drei weitere Versorgungsbohrungen (Einlasskanäle) 4 auf, durch die die Luft in den Mäander 3 geführt werden kann. Die Anordnung der Versorgungsbohrungen (Zuführungskanal 1 und zusätzliche Zuführungskanäle 4) erfolgt derart, dass die Weglänge im Mäander 3 von einer Zuführungsbohrung zur nächsten gleich ist. Exemplary embodiment: A bipolar plate with the size 100 x 100 mm 2 is provided with a meander 3 with the geometric dimensions 1 x 1 x 1 mm 3 with a web width of 1 mm. In addition to inlet 1 and outlet 2, the meander 3 has three further supply bores (inlet channels) 4 through which the air can be guided into the meander 3. The arrangement of the supply bores (feed channel 1 and additional feed channels 4) is such that the path length in the meander 3 from one feed bore to the next is the same.

Claims

Patentansprüche claims
1. Bipolare Platte für eine Brennstoffzelle mit wenigstens einem Verteilerkanal (3) zur Verteilung eines Betriebsmittels, über eine Elektrode, in den ein Zuführungskanal (1) und ein Abführungskanal (2) münden, gekennzeichnet durch wenigstens einen zusätzlichen Zuführungskanal (4) , der direkt in den Verteilerkanal (3) mündet.1. Bipolar plate for a fuel cell with at least one distribution channel (3) for distributing an operating medium, via an electrode, into which a supply channel (1) and a discharge channel (2) open, characterized by at least one additional supply channel (4), which directly opens into the distribution channel (3).
2. Bipolare Platte nach Anspruch 1 mit wenigstens einem mäanderfδrmigen Verteilerkanal .2. Bipolar plate according to claim 1 with at least one meandering distribution channel.
3. Bipolare Platte nach Anspruch 1 oder 2 mit wenigstens zwei zusätzlichen Zuführungskanälen (4) pro Verteilerkanal .3. Bipolar plate according to claim 1 or 2 with at least two additional supply channels (4) per distribution channel.
4. Bipolare Platte nach Anspruch 1 bis 3, bei dem die Zuführungskanäle in gleichen Abständen in den Verteilerkanal münden.4. Bipolar plate according to claim 1 to 3, in which the supply channels open into the distribution channel at equal intervals.
5. Brennstoffzelle mit wenigstens einer bipolaren Platte gemäß Anspruch 1 bis 3.5. A fuel cell with at least one bipolar plate according to claims 1 to 3.
6. Niedertemperatur-Brennstoffzelle als Brennstoffzel- le nach vorhergehendem Anspruch.6. Low-temperature fuel cell as a fuel cell according to the preceding claim.
7. Verfahren zum Betreiben einer Brennstoffzelle, umfassend wenigstens eine bipolare Platte gemäß einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß ein Betriebsmittel über wenigstens zwei Zufuhrungs- kanäle direkt in einen Verteilerkanal zur Vertei- lung des Betriebsmittels über eine Elektrode eingeleitet wird.7. A method of operating a fuel cell comprising at least one bipolar plate according to one of claims 1 to 4, characterized in that an item of equipment is introduced via at least two supply channels directly into a distribution channel for distributing the item of equipment via an electrode.
8. Verfahren nach vorhergehendem Anspruch 7, bei dem ein Gas als Betriebsmittel an jedem Einlasskanal unter gleichem Druck eingeleitet wird.8. The method according to the preceding claim 7, wherein a gas is introduced as the operating medium at each inlet channel under the same pressure.
9. Verfahren nach Anspruch 7, bei dem eine Methanol- Wassermischung als Betriebsmittel an jedem Einlasskanal mit gleicher Konzentration eingeleitet wird. 9. The method according to claim 7, in which a methanol-water mixture is introduced as operating material at each inlet channel with the same concentration.
PCT/DE2002/001733 2001-06-21 2002-05-15 Bipolar plate for a fuel cell WO2003001621A2 (en)

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DE10129810A DE10129810A1 (en) 2001-06-21 2001-06-21 Bipolar plate for a fuel cell

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Publication number Priority date Publication date Assignee Title
WO2007017115A1 (en) * 2005-07-27 2007-02-15 Daimler Ag Pem fuel cell with charging chamber
JP2009503772A (en) * 2005-07-27 2009-01-29 ダイムラー・アクチェンゲゼルシャフト PEM fuel cell with filling chamber
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