WO2001041243A1 - Fuel cell with oxidising agent circuit - Google Patents

Fuel cell with oxidising agent circuit Download PDF

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Publication number
WO2001041243A1
WO2001041243A1 PCT/EP2000/010925 EP0010925W WO0141243A1 WO 2001041243 A1 WO2001041243 A1 WO 2001041243A1 EP 0010925 W EP0010925 W EP 0010925W WO 0141243 A1 WO0141243 A1 WO 0141243A1
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WIPO (PCT)
Prior art keywords
fuel cell
circuit
cathode
oxidising agent
air
Prior art date
Application number
PCT/EP2000/010925
Other languages
German (de)
French (fr)
Inventor
Hendrik Dohle
Stefanie Von Andrian
Reinhard Menzer
Original Assignee
Forschungszentrum Jülich GmbH
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Publication of WO2001041243A1 publication Critical patent/WO2001041243A1/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
    • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
    • H01M8/04097—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with recycling of the reactants
    • 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
    • H01M8/04156—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying with product water removal
    • 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 fuel cell.
  • Several fuel cells are regularly mechanically and electrically connected to one another in order to achieve high voltages and / or electrical currents.
  • fuel cells which have a cathode, an electrolyte and an anode.
  • An oxidizing agent e.g. air
  • fuel e.g. hydrogen
  • the operating materials reach the electrodes and accumulate here.
  • the depleted resources then exit and are led out of the fuel cell.
  • Oxygen ions are formed in the presence of the oxidizing agent on the cathode of the high-temperature fuel cell known from DE 44 30 958 A1.
  • the oxygen ions pass through the solid electrolyte and recombine on the anode side with the hydrogen from the fuel to form water.
  • the recombination releases electrons and thus generates electrical energy.
  • Operating temperatures of a high-temperature fuel cell are typically around 800 degrees Celsius.
  • Protons are formed on the anode of the fuel cell known from DE 195 31 852 C1 in the presence of the fuel by means of a catalyst.
  • the protons pass through the membrane (electrolytes) and combine on the cathode side with the oxygen from the oxidizing agent to form water.
  • the electrons are released at the anode and consumed at the cathode, generating electrical energy.
  • a mixture of gases and / or liquids is usually present in an electrode space of a fuel cell. It can be fuel gases diluted with inert gases. By reforming and oxidizing a fuel such as a methanol-water mixture, further inert gases such as carbon dioxide can occur in the electrode space concerned. Air and thus the inert gas nitrogen are regularly fed to the cathode.
  • the gases or liquids on the respective electrodes should be mixed homogeneously in order to achieve good performance.
  • non-humidified gases that is to say gases which are not separately humidified in humidification devices
  • the electrode surfaces are to be supplied with operating means in a particularly uniform manner. Otherwise there is an increased risk of local drying out of an electrode and possibly an electrolyte membrane. Local dehydration results in loss of performance and can cause damage. If there is a temperature gradient can overheat the fuel cell locally. Local dehydration can result.
  • Thermal gradients should generally be avoided, since they can have a damaging effect and reduce the efficiency, since the operating temperature cannot necessarily be optimal.
  • Water is generated on the cathode side of fuel cells based on proton conductors. This must be removed regularly, as otherwise diff layers or channels will become clogged.
  • the equipment In order to achieve good efficiencies and to ensure operation, the equipment must be distributed and mixed spatially uniformly in a fuel cell. In addition, unwanted products such as water must be removed from the electrode compartments.
  • the publication DE 197 90 15 256 AI can be seen to provide distributor structures in an electrode space (space in which the electrode is located).
  • the distribution structures are designed like a comb. They should cause an even distribution of the equipment in the respective room.
  • German patent application DE 198 08 331 AI it has been proposed to provide a plurality of feed channels and adjacent discharge channels. These channels have holes that adjoin the electrode of the fuel cell. The equipment flows through the holes and thus reaches perpendicular to the electrode and to the interface between the electrolyte and the electrode. In the same way, they flow out again vertically.
  • the holes are also of different sizes in order to achieve an even distribution of the gases along the electrode surfaces.
  • the low intermixing is disadvantageous in particular when local, reaction-related temperature gradients occur.
  • a temperature difference results in a lower efficiency because the operating temperature differs locally from an optimum temperature.
  • the construction with the separate inlet and outlet channels also basically halves the areas through which the operating materials enter the fuel cell or a stack of fuel cells.
  • This disadvantage can be compensated for by a higher throughput.
  • a higher throughput results in a higher pressure loss and thus a lower efficiency.
  • a fuel cell stack is formed by a plurality of fuel cells which are mechanically and electrically connected to one another via connecting elements.
  • a perforated plate is understood to mean a flat component provided with holes. This plate is parallel to the layers of the fuel cell (electrodes - and
  • Electrolyte layers arranged.
  • the corresponding equipment is fed in and out via the adjacent room or duct.
  • the holes in the plate are macroscopically large, so they are visible to the naked eye.
  • the density and / or the diameter of the holes in particular increases in the direction of flow of the gas. This equal distribution has the consequence that electrochemical reactions in the fuel cell are evenly distributed. The occurrence of a temperature gradient can thus be counteracted.
  • the gas supply is also the gas discharge.
  • Gases pass through the holes to the adjacent electrode.
  • the gases do not regularly flow out directly through an adjacent hole.
  • product water is removed from an electrode space in particular by briefly increasing the flow. This increase in flow requires an increase in operating pressure. This results in significant losses of usable energy.
  • the object of the invention is also to provide a method for a particularly efficient operation of the fuel cell as claimed.
  • the fuel cell as claimed has additional means for circulating the oxidizing agent. Circulation is understood to mean that oxidizing agent is fed to a circuit, the cathode space being part of the circuit.
  • a blower for example, is provided as a means for circulation, which is connected via lines to the inlet and outlet of the associated cathode compartment. A fuel cell in which the product water accumulates in the cathode compartment is particularly affected.
  • a water separator is arranged in the circulation circuit. Recirculated oxidizing agent is freed from excess product water carried by the water separator. This also prevents product water blockages.
  • the air ratio ⁇ characterizes the amount of air stoichiometrically required in relation to the required minimum amount of air n air stöchiom et driven is provided.
  • the circulation circuit can be switched on or off continuously, intermittently or depending on the operating state of the fuel cell. It can be left to the person skilled in the art to optimally design the operation of the circulation circuit in order to optimize the performance of the fuel cell.
  • a circulating circuit according to the requirements can also be provided on the anode side in order to optimize the performance.
  • a fuel cell is outlined which consists of an anode 1, a membrane 2 and a cathode 3.
  • An anode space 4 borders on anode 1.
  • the fuel is passed through anode space 4.
  • the cathode compartment 5 is adjacent to the cathode 3.
  • Air is fed into the cathode compartment 5 via an inlet 6.
  • the depleted air arrives at an outlet 7 and leaves the fuel cell via this.
  • the air is circulated through a circuit 8.
  • a blower 9 is provided for carrying out the circulation. Circuit 8 and blower 9 are connected to the cathode compartment in such a way that depleted air near the outlet 7 is led back to the inlet 6.
  • a water separator 10 is arranged within the circuit 8. Excess product water is removed from the air with the aid of the water separator 10.
  • the cathode side is preferably operated at air ratios of up to 2.
  • the pressures occurring at this air ratio are relatively low. There is therefore no need for large pump outputs.

Abstract

The invention relates to a fuel cell with a cathode (3), an electrolyte (2) and an anode (1). A means of introducing and exhausting an oxidising agent into and from the cathode chamber is provided. Furthermore, the fuel cell comprises a means of leading the oxidising agent into a circuit (8), the cathode volume (5) forming part of said circuit. According to the invention, the oxidising agent is introduced into the cathode volume during operation in such amounts that the air ratio μ can be as high as μ=2 and the oxidising agent is at least partly circulated around a circuit. An operation of such a capacity is possible, that a high pump power for production of a relatively high pressure in the cathode volume is not necessary.

Description

grenns offzelle mit Kreislauf des Oxidatioπs ittelsgrenns offzelle with circulation of the Oxidatioπs ittels
Die Erfindung betrifft eine Brennstoffzelle. Mehrere Brennstoffzellen werden regelmäßig mechanisch und elektrisch miteinander verbunden, um so zu hohen Spannungen und / oder elektrischen Strömen zu gelangen.The invention relates to a fuel cell. Several fuel cells are regularly mechanically and electrically connected to one another in order to achieve high voltages and / or electrical currents.
Aus der Druckschrift DE 44 30 958 Cl sowie aus der Druckschrift DE 195 31 852 Cl sind Brennstoffzellen bekannt, die eine Kathode, einen Elektrolyten sowie eine Anode aufweisen. In einen an die Kathode angrenzenden Kanal oder Raum - nachfolgend Kathodenraum genannt - wird ein Oxidationsmittel (z. B. Luft) und in einen an die Anode angrenzenden Kanal oder Raum wird Brennstoff (z. B. Wasserstoff) zugeführt.From the publication DE 44 30 958 Cl and from the publication DE 195 31 852 Cl, fuel cells are known which have a cathode, an electrolyte and an anode. An oxidizing agent (e.g. air) is fed into a channel or space adjacent to the cathode - hereinafter referred to as cathode space - and fuel (e.g. hydrogen) is fed into a channel or space adjacent to the anode.
Die Betriebsmittel gelangen zu den Elektroden und reichern sich hier ab. Anschließend treten die abgereicherten Betriebsmittel wieder aus und werden aus der Brennstoffzelle herausgeleitet.The operating materials reach the electrodes and accumulate here. The depleted resources then exit and are led out of the fuel cell.
An der Kathode der aus der Druckschrift DE 44 30 958 AI bekannten Hochtemperaturbrennstoffzelle bilden sich in Anwesenheit des Oxidationsmittels Sauerstoffionen. Die Sauerstoffionen passieren den Festelektrolyten und rekombinieren auf der Anodenseite mit dem vom Brennstoff stammenden Wasserstoff zu Wasser. Mit der Rekombination werden Elektronen freigesetzt und so elektrische Energie erzeugt. Betriebstemperaturen einer Hochtemperaturbrennstoffzelle liegen typischerweise um die 800 Grad Celsius. An der Anode der aus der Druckschrift DE 195 31 852 Cl bekannten Brennstoffzelle bilden sich in Anwesenheit des Brennstoffs mittels eines Katalysators Protonen. Die Protonen passieren die Membran (Elektrolyten) und verbinden sich auf der Kathodenseite mit dem vom Oxidationsmittel stammenden Sauerstoff zu Wasser. An der Anode werden die Elektronen freigesetzt und an der Kathode verbraucht und so elektrische Energie erzeugt.Oxygen ions are formed in the presence of the oxidizing agent on the cathode of the high-temperature fuel cell known from DE 44 30 958 A1. The oxygen ions pass through the solid electrolyte and recombine on the anode side with the hydrogen from the fuel to form water. The recombination releases electrons and thus generates electrical energy. Operating temperatures of a high-temperature fuel cell are typically around 800 degrees Celsius. Protons are formed on the anode of the fuel cell known from DE 195 31 852 C1 in the presence of the fuel by means of a catalyst. The protons pass through the membrane (electrolytes) and combine on the cathode side with the oxygen from the oxidizing agent to form water. The electrons are released at the anode and consumed at the cathode, generating electrical energy.
In einem Elektrodenraum einer Brennstoffzelle liegt in der Regel ein Gemisch aus Gasen und/oder Flüssigkeiten vor. Es kann sich um mit Inertgasen verdünnte Brenngase handeln. Durch Reformierung und Oxidation eines Brennstoffs wie einem Methanol-Wasser-Gemisch können im betreffenden Elektrodenraum weitere Inertgase wie Kohlendioxid auftreten. Der Kathode wird regelmäßig Luft und damit auch das Inertgas Stickstoff zugeführt.A mixture of gases and / or liquids is usually present in an electrode space of a fuel cell. It can be fuel gases diluted with inert gases. By reforming and oxidizing a fuel such as a methanol-water mixture, further inert gases such as carbon dioxide can occur in the electrode space concerned. Air and thus the inert gas nitrogen are regularly fed to the cathode.
Die an den jeweiligen Elektroden befindlichen Gase oder Flüssigkeiten sollten homogen durchmischt vorliegen, um zu guten Leistungen zu gelangen.The gases or liquids on the respective electrodes should be mixed homogeneously in order to achieve good performance.
Sollen unbefeuchtete Gase, das heißt, nicht getrennt in Befeuchtungseinrichtungen befeuchtete Gase in eine Polymerelektrolytmembran-Brennstoffzelle eingeleitet werden, so sind die Elektrodenflächen besonders gleichmäßig mit Betriebsmitteln zu versorgen. Andernfalls droht verstärkt ein lokales Austrocknen einer Elektrode und gegebenenfalls einer Elektrolytenmembran. Lokales Austrocknen hat Leistungsverluste zur Folge und kann Schäden verursachen. Bei Vorliegen eines Temperaturgradienten kann die Brennstoffzelle lokal überhitzen. Lokales Austrocknen kann die Folge sein.If non-humidified gases, that is to say gases which are not separately humidified in humidification devices, are to be introduced into a polymer electrolyte membrane fuel cell, the electrode surfaces are to be supplied with operating means in a particularly uniform manner. Otherwise there is an increased risk of local drying out of an electrode and possibly an electrolyte membrane. Local dehydration results in loss of performance and can cause damage. If there is a temperature gradient can overheat the fuel cell locally. Local dehydration can result.
Strömen Betriebsmittel parallel zu den Elektroden über längere Bereiche hinweg, so verbrauchen sie sich zunehmend. Entsprechend unterscheiden sich die ablaufenden Reaktionen ortsabhängig in quantitativer Hinsicht. Das Auftreten von Temperaturgradienten in einer Brennstoffzelle sind die Folge.If equipment flows parallel to the electrodes over longer areas, they are increasingly used up. Accordingly, the reactions taking place differ from place to place in quantitative terms. The result is the occurrence of temperature gradients in a fuel cell.
Thermische Gradienten sind generell zu vermeiden, da sich diese schädigend auswirken können und den Wirkungsgrad herabzusetzen, da die Betriebstemperatur zwangsläufig nicht gleichmäßig optimal sein kann.Thermal gradients should generally be avoided, since they can have a damaging effect and reduce the efficiency, since the operating temperature cannot necessarily be optimal.
Kathodenseitig wird bei Brennstoffzellen, die auf Protonenleitern basieren, Wasser erzeugt. Dieses muß regelmäßig entfernt werden, da sonst Diff sionsschichten oder auch Kanäle verstopfen.Water is generated on the cathode side of fuel cells based on proton conductors. This must be removed regularly, as otherwise diff layers or channels will become clogged.
Zur Erzielung guter Wirkungsgrade und zur Sicherstellung des Betriebesnmüssen die Betriebsmittel räumlich gleichmäßig in einer Brennstoffzelle verteilt und durchmischt werden. Ferner müssen unerwünschte Produkte wie entstehendes Wasser aus den Elektrodenräumen entfernt werden.In order to achieve good efficiencies and to ensure operation, the equipment must be distributed and mixed spatially uniformly in a fuel cell. In addition, unwanted products such as water must be removed from the electrode compartments.
Der Druckschrift DE 197 90 15 256 AI ist zu entnehmen, in einem Elektrodenraum (Raum, in dem sich die Elektrode befindet) Verteilerstrukturen vorzusehen. Die Verteilerstrukturen sind kammartig ausgestaltet. Sie sollen eine gleichmäßige Verteilung der Betriebsmittel im jeweiligen Raum bewirken. Es ist gemäß der deutschen Patentanmeldung DE 198 08 331 AI vorgeschlagen worden, eine Mehrzahl an Zuführungskanälen und hieran angrenzende Abführungskanäle vorzusehen. Diese Kanäle weisen Löcher auf, die an die Elektrode der Brennstoffzelle angrenzen. Die Betriebsmittel durchströmen die Löcher und gelangen so senkrecht zur Elektrode sowie zur Grenzfläche zwischen Elektrolyt und Elektrode. In gleicher Weise strömen dieses senkrecht wieder ab.The publication DE 197 90 15 256 AI can be seen to provide distributor structures in an electrode space (space in which the electrode is located). The distribution structures are designed like a comb. They should cause an even distribution of the equipment in the respective room. According to German patent application DE 198 08 331 AI, it has been proposed to provide a plurality of feed channels and adjacent discharge channels. These channels have holes that adjoin the electrode of the fuel cell. The equipment flows through the holes and thus reaches perpendicular to the electrode and to the interface between the electrolyte and the electrode. In the same way, they flow out again vertically.
Die Löcher sind ferner unterschiedlich groß, um so eine Gleichverteilung der Gase entlang der Elektrodenflächen zu erzielen.The holes are also of different sizes in order to achieve an even distribution of the gases along the electrode surfaces.
Nachteilhaft ist der beschriebene Aufbau aufgrund der Vielzahl der Kanäle relativ aufwendig. Erwünschte Durchmischungen sind recht gering.The construction described is disadvantageous due to the large number of channels. Desired mixes are quite low.
Insbesondere bei Auftreten lokaler, reaktionsbedingter Temperaturgradienten ist die geringe Durchmischung von Nachteil. Ein Temperaturunterschied bewirkt einen geringeren Wirkungsgrad, da die Betriebstemperatur lokal von einem Temperaturoptimum abweicht.The low intermixing is disadvantageous in particular when local, reaction-related temperature gradients occur. A temperature difference results in a lower efficiency because the operating temperature differs locally from an optimum temperature.
Nachteilhaft hat der Aufbau mit den getrennten Zu - und Abführungskanälen ferner grundsätzlich eine Halbierung der Flächen zur Folge, durch die die Betriebsmittel in die Brennstoffzelle oder einen Stapel von Brennstoffzellen eintreten. Dieser Nachteil kann zwar durch einen höheren Durchsatz ausgeglichen werden. Ein höherer Durchsatz hat jedoch einen höheren Druckverlust und damit einen schlechteren Wirkungsgrad zur Folge. Vergleichbares gilt für die Flächen, durch die die abgereicherten Betriebsmittel aus der Brennstoffzelle oder dem Brennstoffzellenstapel austreten.Disadvantageously, the construction with the separate inlet and outlet channels also basically halves the areas through which the operating materials enter the fuel cell or a stack of fuel cells. This disadvantage can be compensated for by a higher throughput. However, a higher throughput results in a higher pressure loss and thus a lower efficiency. The same applies to the areas through which the depleted resources emerge from the fuel cell or the fuel cell stack.
Zwar können bei einer Brennstoffzelle die Stege zwischen getrennten Zu - und Abführungskanälen sehr klein gehalten werden, um so zu großen Eintritts - und Austrittsflächen zu gelangen. Hierdurch würde sich jedoch der elektrische Kontakt zwischen den Brennstof zellen eines Brennstoffzellenstapels und damit der Wirkungsgrad verschlechtern. Ein Brennstoffzellenstapel wird durch mehrere Brennstoffzellen gebildet, die über verbindende Elemente miteinander mechanisch und elektrisch verbunden sind.In the case of a fuel cell, the webs between separate inlet and outlet channels can be kept very small in order to achieve large entry and exit areas. As a result, however, the electrical contact between the fuel cells of a fuel cell stack and thus the efficiency would deteriorate. A fuel cell stack is formed by a plurality of fuel cells which are mechanically and electrically connected to one another via connecting elements.
Gemäß einer weiteren deutschen Patentanmeldung DE 1985 3911 AI ist vorgeschlagen worden, die Elektrode einer Brennstoffzelle von einem an die Elektrodenoberfläche angrenzenden Kanal oder Raum durch eine gelochte Platte zu trennen. Unter einer gelochten Platte wird ein flächiges, mit Löchern versehenes Bauelement verstanden. Diese Platte ist parallel zu den Schichten der Brennstoffzelle (Elektroden - undAccording to another German patent application DE 1985 3911 AI, it has been proposed to separate the electrode of a fuel cell from a channel or space adjacent to the electrode surface by means of a perforated plate. A perforated plate is understood to mean a flat component provided with holes. This plate is parallel to the layers of the fuel cell (electrodes - and
Elektrolytschichten) angeordnet. Über den angrenzenden Raum oder Kanal wird das entsprechende Betriebsmittel zu - und abgeführt. Die Löcher in der Platte sind makroskopisch groß, also mit bloßem Auge sichtbar.Electrolyte layers) arranged. The corresponding equipment is fed in and out via the adjacent room or duct. The holes in the plate are macroscopically large, so they are visible to the naked eye.
In Strömungsrichtung des Gases nimmt die Dichte und/oder der Durchmesser der Löcher insbesondere zu. Diese Gleichverteilung hat zur Folge, daß elektrochemische Reaktionen in der Brennstoffzelle gleichmäßig verteilt ablaufen. Dem Entstehen eines Temperaturgradientens kann so entgegengewirkt werden.The density and / or the diameter of the holes in particular increases in the direction of flow of the gas. This equal distribution has the consequence that electrochemical reactions in the fuel cell are evenly distributed. The occurrence of a temperature gradient can thus be counteracted.
Bei dieser Ausgestaltung ist die Gaszuführung zugleich die Gasableitung.In this embodiment, the gas supply is also the gas discharge.
Gase gelangen durch die Löcher zur angrenzenden Elektrode. Die Gase strömen regelmäßig nicht unmittelbar durch ein benachbartes Loch wieder ab. Es treten im Vergleich zu einer Brennstoffzelle mit getrennten Zu- und Abführungskanälen stärkere Durchmischungen (Verwirbelungen) auf. Temperaturgradienten werden so vermieden.Gases pass through the holes to the adjacent electrode. The gases do not regularly flow out directly through an adjacent hole. Compared to a fuel cell with separate inlet and outlet channels, there is more thorough mixing (swirling). This avoids temperature gradients.
Produktwasser wird gemäß dem Stand der Technik insbesondere durch kurzfristige Durchflußerhöhung aus einem Elektrodenraum entfernt. Diese Durchflußerhöhung erfordert eine Erhöhung des Betriebsdrucks. Deutliche Verluste an nutzbarer Energie sind nachteilhaft die Folge.According to the prior art, product water is removed from an electrode space in particular by briefly increasing the flow. This increase in flow requires an increase in operating pressure. This results in significant losses of usable energy.
Gegenüber dem vorgenannten Stand der Technik ist es Aufgabe der Erfindung, eine Brennstoffzelle mit verbesserter Leistung bereitzustellen. Aufgabe der Erfindung ist ferner die Angabe eines Verfahrens für einen besonders leistungsfähigen Betrieb der anspruchsgemäßen Brennstoffzelle .Compared to the aforementioned prior art, it is an object of the invention to provide a fuel cell with improved performance. The object of the invention is also to provide a method for a particularly efficient operation of the fuel cell as claimed.
Die Aufgabe wird durch eine Vorrichtung mit den Merkmalen des ersten Anspruchs sowie durch ein Verfahren mit den Merkmalen des Nebenanspruchs gelöst. Vorteilhafte Ausgestaltungen ergeben sich aus den Unteransprüchen.The object is achieved by a device with the features of the first claim and by a method with the features of the subsidiary claim. Advantageous refinements result from the subclaims.
Die anspruchsgemäße Brennstoffzelle weist neben den Mitteln zur Zu- und Abführung eines Oxidationsmittels zusätzliche Mittel zur Umwälzung des Oxidationsmittels auf. Unter Umwälzung wird verstanden, daß Oxidationsmittel einem Kreislauf zugeführt wird, wobei der Kathodenraum Teil des Kreislaufes ist. Als Mittel zur Umwälzung ist beispielsweise ein Gebläse vorgesehen, welches über Leitungen mit dem Ein- und Ausgang des zugehörigen Kathodenraums verbunden ist. Betroffen ist insbesondere eine Brennstoffzelle, in der das Produktwasser im Kathodenraum anfällt.In addition to the means for supplying and removing an oxidizing agent, the fuel cell as claimed has additional means for circulating the oxidizing agent. Circulation is understood to mean that oxidizing agent is fed to a circuit, the cathode space being part of the circuit. A blower, for example, is provided as a means for circulation, which is connected via lines to the inlet and outlet of the associated cathode compartment. A fuel cell in which the product water accumulates in the cathode compartment is particularly affected.
Durch die zusätzliche Umwälzung im Kathodenraum wird eine Gleichverteilung des Sauerstoffpartialdrucks sowie ein Wasseraustrag verbessert bzw. eine Verstopfung durch Produktwasser vermieden. Einer Verarmung des Sauerstoffpartialdrucks vom Lufteinlaß zum Luftauslaß, welcher insbesondere bei kleinen Luftzahlen stattfindet, und hiermit einhergehende inhomogene Leistungen der Brennstoffzelle werden so entgegengewirkt .Due to the additional circulation in the cathode compartment, an even distribution of the oxygen partial pressure and a water discharge are improved or a blockage by product water is avoided. A depletion of the oxygen partial pressure from the air inlet to the air outlet, which takes place in particular with low air numbers, and the associated inhomogeneous outputs of the fuel cell are thus counteracted.
Es ist dadurch möglich, auch bei kleinen Luftzahlen bzw. geringem Druck im Kathodenraum gute Leistungen zu erzielen. Kann die Brennstoffzelle bei kleinen Luftzahlen wirtschaftlich sinnvoll betrieben werden, so müssen keine hohen Pumpleistungen erbracht werden. Verluste von nutzbarer Energie werden so im Vergleich zum vorgenannten Stand der Technik vermieden, obwohl eine zusätzliche Umwälzung durchgeführt wird. In einer vorteilhaften Ausgestaltung der Erfindung ist im Umwälzkreislauf ein Wasserabscheider angeordnet . Durch den Wasserabscheider wird umgewälztes Oxidationsmittel von mitgeführtem überschüssigen Produktwasser befreit. Verstopfungen durch Produktwasser werden so weiter vermieden.This makes it possible to achieve good performances even with small air numbers or low pressure in the cathode compartment. If the fuel cell can be operated in an economically sensible manner with small air ratios, it is not necessary to provide high pumping capacities. Losses of usable energy are avoided in comparison to the aforementioned prior art, although an additional circulation is carried out. In an advantageous embodiment of the invention, a water separator is arranged in the circulation circuit. Recirculated oxidizing agent is freed from excess product water carried by the water separator. This also prevents product water blockages.
Bevorzugt wird die anspruchsgemäße Brennstoffzelle bei Luftzahlen bis zu λ=2 betrieben. Die Luftzahl λ charakterisiert die Luftmenge, die im Verhältnis zur benötigten stöchiometrisch erforderlichen Mindestluftmenge nLuft,stöchiometrisch bereitgestellt wird. λ=l bedeutet, daß gerade die Luftmenge vorhanden ist, um die gewünschten Reaktionen im Kathodenraum durchzuführen. Es gilt λ=nLuft/nLuft,stöchiometrisch-The fuel cell as claimed is preferably operated at air ratios up to λ = 2. The air ratio λ characterizes the amount of air stoichiometrically required in relation to the required minimum amount of air n air stöchiom et driven is provided. λ = l means that there is just the amount of air to carry out the desired reactions in the cathode compartment. The following applies: λ = n air / n air , stoichiometric
Der Umwälzkreislauf kann ständig, intermittierend oder in Abhängigkeit vom Betriebszustand der Brennstoffzelle zugeschaltet oder abgeschaltet werden. Es kann dem Fachmann überlassen bleiben, den Betrieb des Umwälzkreislaufes optimal zu gestalten, um die Leistungsfähigkeit der Brennstoffzelle zu optimieren.The circulation circuit can be switched on or off continuously, intermittently or depending on the operating state of the fuel cell. It can be left to the person skilled in the art to optimally design the operation of the circulation circuit in order to optimize the performance of the fuel cell.
Ergänzend kann ein anspruchsgemäßer Umwälzkreislauf auch auf der Anodenseite vorgesehen sein, um die Leistung zu optimieren.In addition, a circulating circuit according to the requirements can also be provided on the anode side in order to optimize the performance.
Anhand der Figur wird die Erfindung näher verdeutlicht.The invention is illustrated in more detail with the aid of the figure.
Skizziert wird eine Brennstoffzelle, die aus einer Anode 1, einer Membran 2 und einer Kathode 3 besteht. An die Anode 1 grenzt ein Anodenraum 4. Durch den Anodenraum 4 wird der Brennstoff geleitet. Der Kathodenraum 5 grenzt an die Kathode 3. Über einen Einlass 6 wird Luft in den Kathodenraum 5 geleitet. Die abgereicherte Luft gelangt nach Passieren des Kathodenraums 5 zu einem Auslass 7 und verläßt hierüber die Brennstoffzelle. Zusätzlich wird die Luft durch einen Kreislauf 8 umgewälzt. Für die Durchführung der Umwälzung ist ein Gebläse 9 vorgesehen. Kreislauf 8 und Gebläse 9 sind so an den Kathodenraum angeschlossen, daß abgereicherte Luft nahe beim Auslass 7 zurück zum Einlass 6 geführt werden. Innerhalb des Kreislaufes 8 ist ein Wasserabscheider 10 angeordnet. Überschüssiges Produktwasser wird mit Hilfe des Wasserabscheiders 10 aus der Luft entfernt.A fuel cell is outlined which consists of an anode 1, a membrane 2 and a cathode 3. An anode space 4 borders on anode 1. The fuel is passed through anode space 4. The cathode compartment 5 is adjacent to the cathode 3. Air is fed into the cathode compartment 5 via an inlet 6. After passing through the cathode chamber 5, the depleted air arrives at an outlet 7 and leaves the fuel cell via this. In addition, the air is circulated through a circuit 8. A blower 9 is provided for carrying out the circulation. Circuit 8 and blower 9 are connected to the cathode compartment in such a way that depleted air near the outlet 7 is led back to the inlet 6. A water separator 10 is arranged within the circuit 8. Excess product water is removed from the air with the aid of the water separator 10.
Bevorzugt wird die Kathodenseite bei Luftzahlen von bis zu 2 betrieben. Die bei dieser Luftzahl auftretenden Drücke sind relativ gering. Es müssen daher keine großen Pumpleistungen erbracht werden. The cathode side is preferably operated at air ratios of up to 2. The pressures occurring at this air ratio are relatively low. There is therefore no need for large pump outputs.

Claims

Ansprüche Expectations
1. Brennstoffzelle mit einer Kathode (3), einem Elektrolyten (2) sowie einer Anode (1), einem Mittel zur Zu- und Abführung eines Oxidationsmittels sowie mit zusätzlichen Mitteln (8, 9) zur Führung von Oxidationsmittel in einem Kreislauf, wobei der Kathodenraum (5) Teil des Kreislaufs ist.1. Fuel cell with a cathode (3), an electrolyte (2) and an anode (1), a means for supplying and removing an oxidizing agent and with additional means (8, 9) for guiding oxidizing agent in a circuit, the Cathode compartment (5) is part of the circuit.
2. Brennstoffzelle nach Anspruch 1 mit einem im Kreislauf angeordneten Gebläse (9).2. Fuel cell according to claim 1 with a blower arranged in the circuit (9).
3. Brennstoffzelle nach Anspruch 1 oder 2, bei der der Kreislauf eine oder mehrere Leitungen umfaßt, die mit dem Ein- und Ausgang des zugehörigen Kathodenraums verbunden sind.3. Fuel cell according to claim 1 or 2, wherein the circuit comprises one or more lines which are connected to the input and output of the associated cathode space.
4. Brennstoffzelle nach Anspruch 1, 2, 3 oder 4, bei der im Kreislauf (8) ein Wasserabscheider (10) angeordnet ist.4. Fuel cell according to claim 1, 2, 3 or 4, in which a water separator (10) is arranged in the circuit (8).
5. Verfahren zum Betreiben einer Brennstoffzelle nach einem der vorhergehenden Ansprüche, bei dem das Oxidationsmittel dem Kathodenraum (5) während des Betriebs in einer solchen Menge zugeführt wird, daß die Luftzahl λ bis zu λ=2 beträgt und das Oxidationsmittel zumindest teilweise über einen Kreislauf (8) umgewälzt wird. 5. A method of operating a fuel cell according to one of the preceding claims, wherein the oxidizing agent is supplied to the cathode compartment (5) during operation in such an amount that the air ratio λ is up to λ = 2 and the oxidizing agent is at least partially via a circuit (8) is circulated.
PCT/EP2000/010925 1999-11-29 2000-11-06 Fuel cell with oxidising agent circuit WO2001041243A1 (en)

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