EP1310007A1 - Method for regulating the fuel concentration in the anode fluid of a fuel cell, and corresponding device - Google Patents

Method for regulating the fuel concentration in the anode fluid of a fuel cell, and corresponding device

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Publication number
EP1310007A1
EP1310007A1 EP01962605A EP01962605A EP1310007A1 EP 1310007 A1 EP1310007 A1 EP 1310007A1 EP 01962605 A EP01962605 A EP 01962605A EP 01962605 A EP01962605 A EP 01962605A EP 1310007 A1 EP1310007 A1 EP 1310007A1
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EP
European Patent Office
Prior art keywords
methanol
fuel
fuel cell
carbon dioxide
cathode
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.)
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Application number
EP01962605A
Other languages
German (de)
French (fr)
Inventor
Walter Preidel
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.)
Siemens AG
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Siemens AG
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Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Publication of EP1310007A1 publication Critical patent/EP1310007A1/en
Withdrawn legal-status Critical Current

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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
    • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
    • H01M8/0662—Treatment of gaseous reactants or gaseous residues, e.g. cleaning
    • 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
    • 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
    • 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
    • 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
    • H01M8/04194—Concentration measuring cells
    • 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
    • H01M8/1009—Fuel cells with solid electrolytes with one of the reactants being liquid, solid or liquid-charged
    • 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 method for regulating the fuel concentration in the anode liquid of a fuel cell with anode, membrane and cathode, in which an exhaust gas is produced on the anode on the one hand and on the cathode on the other hand.
  • the invention also relates to a device with the necessary means for carrying out the method.
  • the fuel is preferably, but not exclusively, methanol.
  • Fuel cells are operated with liquid or gaseous fuels. If the fuel cell works with hydrogen, a hydrogen infrastructure or a reformer is required to generate the gaseous hydrogen from the liquid fuel.
  • Liquid fuels are e.g. Gasoline or alcohol, such as ethanol or methanol.
  • a so-called DMFC Direct Methanol Fuel Cell * works directly with liquid methanol as a fuel. The function and status of the DMFC are described in detail in “VIK reports *, No. 214 (Nov. 1999), pages 55 to 62.
  • Fuel cell systems consist of a large number of individual fuel cell units, which together form a fuel cell stack, which in the technical field is also referred to as a fuel cell stack or simply as a “stack *”.
  • a fuel cell stack which in the technical field is also referred to as a fuel cell stack or simply as a “stack *”.
  • exhaust gases are produced in the fuel cell at the anode on the one hand and at the cathode on the other hand.
  • the fuel methanol is mixed with water on the anode side and pumped through the stack using a metering pump.
  • the metha- nol is partly consumed by the anode reaction and carbon dioxide is generated.
  • Another part of the methanol is transported through the membrane to the cathode by permeation and electro-osmosis and directly oxidized to carbon dioxide on the catalyst of the cathode.
  • the anode liquid with the gas / steam mixture is separated into gas and liquid after exiting the anode. As much more carbon dioxide as possible is removed from the liquid and then the liquid is returned to the anode by means of the pump. So that the methanol concentration of this liquid does not become too low, sufficient methanol must be added.
  • the amount of methanol corresponding to the electric current can be calculated from the current flow, but the additional amount, which replaces the loss via electroosmosis and permeation, cannot be determined qualitatively, so that the anode liquid would have a concentration that is too low.
  • the amount of methanol in the direct methanol fuel cell is calculated via the current flow and increased by a constant factor, for example 1.5 or 2.0. This compensates for the methanol losses, whereby it is accepted that the methanol concentration is not optimal for the current density. Since the methanol tends to doses must be metered in order to avoid undersupply and thus the risk of polarity reversal, the methanol loss is greater than necessary
  • the object of the invention is therefore to specify a method with which the regulation of the fuel concentration in the anode liquid of a direct methanol fuel cell is improved, and to create an associated device.
  • the fuel loss across the membrane is advantageously detected.
  • a commercially available sensor is used to measure the concentration. after cooler and pressure regulator is attached.
  • the single figure shows a schematic representation of a single unit, specifically a DMFC fuel cell, with the associated system components which are necessary for the operation of this fuel cell.
  • FIG. 1 shows a methanol tank 1 with a subsequent metering pump 2 and a heater 3, via which the liquid methanol as fuel reaches the fuel cell unit 10.
  • a cooler 4, a CO 2 separator 5, a unit 6 for rectification and a methanol sensor 7 are assigned to the anode part.
  • Another metering pump 8 is used to feed methanol back into the fuel circuit.
  • a compressor 14 for air On the cathode side there is a compressor 14 for air, a cooler or water separator 15 for the cathode liquid and a C0 2 sensor 16. Furthermore, a unit 25 for controlling the fuel cell unit 10 and optionally an electrical inverter 26 are provided for the operation of the system.
  • the DMFC shown has primary and secondary fluid circuits.
  • the methanol / water mixture is fed to the anode 11 and air to the cathode 13 of the fuel cell 10.
  • the C0 2 is separated from the residual fuel and this is returned to the fuel circuit.
  • the cathode exhaust gas is conducted via the cooler or water separator 15 in the exhaust gas-side fluid circuit.
  • the CO 2 content which is a measure of the methanol loss via the membrane 12 of the fuel cell, is then measured in the exhaust gas.
  • the measurement signal is fed back to the primary metering pump 2.
  • the C0 2 sensor 16 in the figure is a commercially available sensor, which is advantageously installed in the gas stream after the cooler 15 and the existing pressure regulator. The Co 2 concentration is thus measured in molar.
  • One mole of carbon dioxide also corresponds to one mole of methanol.
  • the amount of air on the cathode side is known from the compressor power or can be determined by measuring the air flow.
  • There is a certain systematic error in the amount of carbon dioxide determined with the sensor since a small proportion of the carbon dioxide that is generated at the anode by the electrochemical reaction can diffuse through the membrane to the cathode, so that the air used has a small and possibly also a little fluctuating carbon dioxide concentration. Since no additional electroosmosis is effective for the carbon dioxide, as is the case with methanol, this error can be tolerated.
  • the metering of the methanol results from the flow and is to be calculated additively from the carbon dioxide concentration on the cathode side.
  • MEA membrane-electrolyte-anode
  • stack properties can then this rule base of the ⁇ Faraday current one hand and the leakage current on the other hand, an additional flow of methanol are added.
  • the lambda for methanol is then increased to 1.05 to 1.5 as required.
  • the additive use of the carbon dioxide concentration on the cathode side in the exhaust air is essential for controlling the fuel cell system. It is no longer absolutely necessary to measure the methanol concentration in the fuel cycle.
  • the DMFC is equipped with a carbon dioxide sensor in the exhaust gas. Characteristic measurements were successfully carried out for verification.

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

Abstract

In the case of a fuel cell, in which a waste gas develops on the anode and on the cathode, the invention provides that the carbon dioxide concentration in the cathode waste gas is measured and the measured result is used to determine the loss of fuel that results via the membrane of the fuel cell. To this end, the corresponding device is provided with a carbon dioxide sensor (16) that is arranged inside the gas stream.

Description

Beschreibungdescription
Verfahren zur Regelung der Brennstoffkonzentration in der Anodenflüssigkeit einer Brennstoffzelle und zugehörige Vor- richtungMethod for regulating the fuel concentration in the anode liquid of a fuel cell and associated device
Die Erfindung bezieht sich auf ein Verfahren zur Regelung der Brennstoffkonzentration in der Anodenflüssigkeit einer Brennstoffzelle mit Anode, Membran und Kathode, bei der an der Anode einerseits und an der Kathode andererseits jeweils ein Abgas anfällt. Daneben bezieht sich die Erfindung auch auf eine Vorrichtung, mit den notwendigen Mitteln zur Durchführung des Verfahrens. Bei der Erfindung ist der Brennstoff vorzugsweise, aber nicht ausschließlich Methanol.The invention relates to a method for regulating the fuel concentration in the anode liquid of a fuel cell with anode, membrane and cathode, in which an exhaust gas is produced on the anode on the one hand and on the cathode on the other hand. In addition, the invention also relates to a device with the necessary means for carrying out the method. In the invention, the fuel is preferably, but not exclusively, methanol.
Brennstoffzellen werden mit flüssigen oder gasförmigen Brennstoffen betrieben. Sofern die Brennstoffzelle mit Wasserstoff arbeitet, ist eine Wasserstoff-Infrastruktur oder ein Reformer zur Erzeugung des gasförmigen Wasserstoffes aus dem flüs- sigen Brennstoff notwendig. Flüssige Brennstoffe sind z.B. Benzin oder Alkohol, wie Ethanol oder Methanol. Eine sog. DMFC („Direct Methanol Fuel Cell* ) arbeitet direkt mit flüssigem Methanol als Brennstoff. Funktion und Status der DMFC sind im Einzelnen in „VIK-Berichte* , Nr. 214 (Nov. 1999), Seiten 55 bis 62, beschrieben.Fuel cells are operated with liquid or gaseous fuels. If the fuel cell works with hydrogen, a hydrogen infrastructure or a reformer is required to generate the gaseous hydrogen from the liquid fuel. Liquid fuels are e.g. Gasoline or alcohol, such as ethanol or methanol. A so-called DMFC (“Direct Methanol Fuel Cell *) works directly with liquid methanol as a fuel. The function and status of the DMFC are described in detail in “VIK reports *, No. 214 (Nov. 1999), pages 55 to 62.
Brennstoffzellenanlagen bestehen aus einer großen Anzahl einzelner Brennstoffzelleneinheiten, die zusammen einen Brennstoffzellenstapel bilden, welcher in der Fachwelt auch als Brennstoffzellenstack oder auch kurz als „Stack* bezeichnet wird. Bei der mit Methanol als Brennstoff betriebenen Direkt- Methanol-Brennstoffzelle fallen in der Brennstoffzelle an der Anode einerseits und an der Kathode andererseits Abgase an.Fuel cell systems consist of a large number of individual fuel cell units, which together form a fuel cell stack, which in the technical field is also referred to as a fuel cell stack or simply as a “stack *”. In the case of the direct methanol fuel cell operated with methanol as fuel, exhaust gases are produced in the fuel cell at the anode on the one hand and at the cathode on the other hand.
In der Direkt-Methanol-Brennstoffzelle (DMFC) wird auf der Anodenseite der Brennstoff Methanol mit Wasser gemischt und mittels einer Dosierpumpe durch den Stack gepumpt. Das Metha- nol wird dabei zum Teil durch die Anodenreaktion verbraucht und es entsteht Kohlendioxid. Ein anderer Teil des Methanols wird durch Permeation und Elektroosmose durch die Membran zur Kathode transportiert und am Katalysator der Kathode direkt zu Kohlendioxid oxidiert.In the direct methanol fuel cell (DMFC), the fuel methanol is mixed with water on the anode side and pumped through the stack using a metering pump. The metha- nol is partly consumed by the anode reaction and carbon dioxide is generated. Another part of the methanol is transported through the membrane to the cathode by permeation and electro-osmosis and directly oxidized to carbon dioxide on the catalyst of the cathode.
Die Anodenflüssigkeit mit dem Gas/Dampf-Gemisch wird nach Austritt aus der Anode in Gas und Flüssigkeit getrennt. Soviel weiteres Kohlendioxid wie möglich wird aus der Flüssig- keit entfernt und dann wird die Flüssigkeit mittels der Pumpe wieder der Anode zugeführt. Damit die Methanolkonzentration dieser Flüssigkeit nicht zu gering wird, muss Methanol im ausreichenden Ausmaß hinzudosiert werden. Die dem elektrischen Strom entsprechende Menge des Methanols kann aus dem Stromfluss errechnet werden, die zusätzliche Menge, die den Verlust über die Elektroosmose und Permeation ersetzt, ist aber qualitativ nicht fassbar, so dass die Anodenflüssigkeit eine zu geringe Konzentration aufweisen würde.The anode liquid with the gas / steam mixture is separated into gas and liquid after exiting the anode. As much more carbon dioxide as possible is removed from the liquid and then the liquid is returned to the anode by means of the pump. So that the methanol concentration of this liquid does not become too low, sufficient methanol must be added. The amount of methanol corresponding to the electric current can be calculated from the current flow, but the additional amount, which replaces the loss via electroosmosis and permeation, cannot be determined qualitatively, so that the anode liquid would have a concentration that is too low.
Letzteres Problem kann mit einem konstanten Überschussfaktor gelöst werden. Da aber die Verluste im Einzelnen von der Betriebsweise der methanolgespeisten Brennstoffzelle abhängen, da sich die Elektroosmose und die Permeation je nach Stromdichte in der Zelle unterschiedlich überlagern, wird sich über längere Zeit entweder Methanol anreichern oder bei zu geringem Überschuss die Methanolkonzentration nicht ausrei-' chend sein. In diesem Fall ist die Gefahr des Umpolens der schlechter versorgten Zellen des Brennstoffzellenstacks sehr hoch. Ein Umpolen der Zellen kann aber zu nicht regenerier- barer Schädigung der Zelle führen.The latter problem can be solved with a constant excess factor. But since the losses in detail of the operation of the methanol-powered fuel cell depend, as the electro-osmosis and permeation superimpose different depending on the current density in the cell will accumulate over time either methanol or not enough surplus not sufficient, the methanol concentration 'accordingly his. In this case, the risk of reversing the polarity of the poorly supplied cells of the fuel cell stack is very high. Reversing the polarity of the cells can lead to non-regenerable damage to the cell.
Beim Stand der Technik wird die Methanolmenge bei der Direkt- Methanol-Brennstoffzelle über den Stromfluss berechnet und um einen konstanten Faktor, z.B. 1,5 oder 2,0, erhöht. Damit werden die Methanolverluste ausgeglichen, wobei in Kauf genommen wird, dass die Methanolkonzentration nicht optimal für die jeweilige Stromdichte ist. Da das Methanol eher im Über- schuss dosiert werden uss, um die Unterversorgung und damit die Gefahr des Umpolens zu vermeiden, ist der Methanolverlust größer als notwendigIn the prior art, the amount of methanol in the direct methanol fuel cell is calculated via the current flow and increased by a constant factor, for example 1.5 or 2.0. This compensates for the methanol losses, whereby it is accepted that the methanol concentration is not optimal for the current density. Since the methanol tends to doses must be metered in order to avoid undersupply and thus the risk of polarity reversal, the methanol loss is greater than necessary
Ganz allgemein gilt, dass der Wirkungsgrad des beschriebenen Brennstoffzellensystems mit obigem Betriebskonzept nicht optimal ist und einer Verbesserung bedarf.In general, the efficiency of the described fuel cell system with the above operating concept is not optimal and needs to be improved.
Aufgabe der Erfindung ist es daher, ein Verfahren anzugeben, mit dem die Regelung der Brennstoffkonzentration in der Anodenflüssigkeit einer Direkt-Methanol-Brennstoffzelle verbessert wird, und eine zugehörige Vorrichtung zu schaffen.The object of the invention is therefore to specify a method with which the regulation of the fuel concentration in the anode liquid of a direct methanol fuel cell is improved, and to create an associated device.
Die Aufgabe ist erfindungsgemäß durch die Maßnahmen des Pa- tentanspruches 1 gelöst. Eine zugehörige Vorrichtung ist durch den Patentanspruch 6 gekennzeichnet. Weiterbildungen des erfindungsgemäßen Verfahrens bzw. der erfindungsgemäßen Vorrichtung sind in den jeweils abhängigen Ansprüchen angegeben.According to the invention, the object is achieved by the measures of patent claim 1. An associated device is characterized by claim 6. Further developments of the method according to the invention and the device according to the invention are specified in the respective dependent claims.
Bei der Erfindung wird durch die Messung der Kohlendioxidkonzentration im Kathodenabgas vorteilhafterweise der Brennstoffverlust über die Membran erfasst werden. Zur Messung der Konzentration wird ein handelsüblicher Sensor verwendet, der im Gasstrom z.B. nach Kühler und ordruckregler angebracht ist.In the invention, by measuring the carbon dioxide concentration in the cathode exhaust gas, the fuel loss across the membrane is advantageously detected. A commercially available sensor is used to measure the concentration. after cooler and pressure regulator is attached.
Weitere Vorteile und Einzelheiten der Erfindung ergeben sich durch die Figurenbeschreibung an Hand der Zeichnung in Ver- bindung mit den Patentansprüchen. Die einzige Figur zeigt in schematischer Darstellung eine einzelne Einheit speziell einer DMFC-Brennstoffzelle mit den zugehörigen Systemkomponenten, die für den Betrieb dieser Brennstoffzelle notwendig sind.Further advantages and details of the invention result from the description of the figures on the basis of the drawing in conjunction with the patent claims. The single figure shows a schematic representation of a single unit, specifically a DMFC fuel cell, with the associated system components which are necessary for the operation of this fuel cell.
In der Figur 1 ist ein Methanoltank 1 mit einer nachfolgenden Dosierpumpe 2 und einer Heizung 3 dargestellt, über die das flüssige Methanol als Betriebsstoff zur Brennstoffzellen- Einheit 10 gelangt. Die Brennstoffzellen-Einheit 10 ist in der Modifikation als Direkt-Methanol-Brennstoffzelle (DMFC = Direct Methanol Fuel Cell) realisiert und im Wesentlichen durch eine Anode 11, eine Membran 12 und eine Kathode 13 charakterisiert. Dem Anodenteil ist ein Kühler 4, ein C02-Ab- scheider 5, eine Einheit 6 zur Rektifikation und ein Methanolsensor 7 zugeordnet. Eine weitere Dosierpumpe 8 dient zur Rückspeisung von Methanol in den Brennstoffkreislauf.FIG. 1 shows a methanol tank 1 with a subsequent metering pump 2 and a heater 3, via which the liquid methanol as fuel reaches the fuel cell unit 10. The fuel cell unit 10 is implemented in the modification as a direct methanol fuel cell (DMFC = Direct Methanol Fuel Cell) and is essentially characterized by an anode 11, a membrane 12 and a cathode 13. A cooler 4, a CO 2 separator 5, a unit 6 for rectification and a methanol sensor 7 are assigned to the anode part. Another metering pump 8 is used to feed methanol back into the fuel circuit.
Auf der Kathodenseite ist ein Verdichter 14 für Luft, ein Kühler bzw. Wasserabscheider 15 für die Kathodenflüssigkeit und ein C02-Sensor 16 vorhanden. Weiterhin sind für den Betrieb der Anlage eine Einheit 25 zur Steuerung/Regelung der Brennstoffzellen-Einheit 10 sowie gegebenenfalls ein elektrischer Wechselrichter 26 vorhanden.On the cathode side there is a compressor 14 for air, a cooler or water separator 15 for the cathode liquid and a C0 2 sensor 16. Furthermore, a unit 25 for controlling the fuel cell unit 10 and optionally an electrical inverter 26 are provided for the operation of the system.
Bei der dargestellten DMFC sind primäre und sekundäre Fluid- kreisläufe vorhanden. Im primären Kreislauf wird das Metha- nol-/Wasser-Gemisch der Anode 11 und Luft der Kathode 13 der Brennstoffzelle 10 zugeführt. Im sekundären Kreislauf wird das C02 aus dem Restbrennstoff abgetrennt und dieser dem Brennstoffkreislauf zurückgeführt. Weiterhin wird das Kathodenabgas über den Kühler bzw. Wasserabscheider 15 im abgas- seitigen Fluidkreislauf geführt. Danach wird im Abgas der C02-Gehalt, der ein Maß für den Methanolverlust über die Membran 12 der Brennstoffzelle ist, gemessen. Das Messsignal wird auf die primäre Dosierpumpe 2 zurückgeführt. Der C02- Sensor 16 in der Figur ist ein handelsüblicher Sensor, der im Gasstrom vorteilhafterweise nach dem Kühler 15 und dem vorhandenen Vordruckregler angebracht ist. Die Co2-Konzentration wird damit molar gemessen.The DMFC shown has primary and secondary fluid circuits. In the primary circuit, the methanol / water mixture is fed to the anode 11 and air to the cathode 13 of the fuel cell 10. In the secondary circuit, the C0 2 is separated from the residual fuel and this is returned to the fuel circuit. Furthermore, the cathode exhaust gas is conducted via the cooler or water separator 15 in the exhaust gas-side fluid circuit. The CO 2 content, which is a measure of the methanol loss via the membrane 12 of the fuel cell, is then measured in the exhaust gas. The measurement signal is fed back to the primary metering pump 2. The C0 2 sensor 16 in the figure is a commercially available sensor, which is advantageously installed in the gas stream after the cooler 15 and the existing pressure regulator. The Co 2 concentration is thus measured in molar.
Einem Mol Kohlendioxid entspricht dabei auch ein Mol Metha- nol. Die Luftmenge auf der Kathodenseite ist bekannt durch die Kompressorleistung bzw. kann durch die Messung des Luftdurchflusses bestimmt werden. Ein gewisse systematischer Fehler steckt in der mit dem Sensor bestimmte Kohlendioxidmenge, da ein geringer Anteil des Kohlendioxids, das an der Anode durch die elektrochemische Umsetzung entsteht, durch die Membran zur Kathode diffundieren kann, so dass die verwendete Luft eine geringe und unter Umständen auch geringfügig schwankende Kohlendioxidkonzentration besitzt. Da für das Kohlendioxid aber keine zusätzliche Elektroosmose wirksam wird, wie es bei dem Methanol der Fall ist, ist dieser Fehler tolerierbar.One mole of carbon dioxide also corresponds to one mole of methanol. The amount of air on the cathode side is known from the compressor power or can be determined by measuring the air flow. There is a certain systematic error in the amount of carbon dioxide determined with the sensor, since a small proportion of the carbon dioxide that is generated at the anode by the electrochemical reaction can diffuse through the membrane to the cathode, so that the air used has a small and possibly also a little fluctuating carbon dioxide concentration. Since no additional electroosmosis is effective for the carbon dioxide, as is the case with methanol, this error can be tolerated.
Die Dosierung des Methanols ergibt sich aus dem geflossenen Strom und ist additiv aus der Kohlendioxidkonzentration auf der Kathodenseite zu berechnen. Für einen zuverlässigen Be- trieb, je nach Membran-Elektrolyt-Anode (MEA) - und Stackeigenschaften, kann dann dieser Basis aus dem Faraday Λschen Strom einerseits und dem Verluststrom andererseits ein zusätzlicher Methanolfluss hinzugefügt werden. Das Lambda für Methanol wird dann je nach Erfordernis auf 1,05 bis 1,5 er- höht.The metering of the methanol results from the flow and is to be calculated additively from the carbon dioxide concentration on the cathode side. For a reliable operation, depending on the membrane-electrolyte-anode (MEA) - and stack properties, can then this rule base of the Λ Faraday current one hand and the leakage current on the other hand, an additional flow of methanol are added. The lambda for methanol is then increased to 1.05 to 1.5 as required.
Bei dem in der Figur dargestellten System und dem an Hand der Figur beschriebenen Betriebskonzept ist die additive Verwendung der Kohlendioxidkonzentration auf der Kathodenseite in der Abluft zur Steuerung des BrennstoffZellensystems wesentlich. Es ist nicht mehr zwingend erforderlich, die Methanolkonzentration im Brennstoffkreislauf zu messen.In the system shown in the figure and the operating concept described with reference to the figure, the additive use of the carbon dioxide concentration on the cathode side in the exhaust air is essential for controlling the fuel cell system. It is no longer absolutely necessary to measure the methanol concentration in the fuel cycle.
In der Praxis wird die DMFC mit einem Kohlendioxidsensor im Abgas ausgerüstet. Zur Verifizierung wurden Kennlinienmessungen erfolgreich durchgeführt.In practice, the DMFC is equipped with a carbon dioxide sensor in the exhaust gas. Characteristic measurements were successfully carried out for verification.
Die vorstehend anhand einer mit Methanol als Brennstoff betriebenen DMFC beschriebene Problemlösung lässt sich auf mit anderen Brennstoffen betriebene Brennstoffzellen übertragen. The problem solution described above on the basis of a DMFC operated with methanol as fuel can be transferred to fuel cells operated with other fuels.

Claims

Patentansprüche claims
1. Verfahren zur Regelung der Brennstoffkonzentration in der Anodenflüssigkeit einer Brennstoffzelle mit Anode, Membran und Kathode, bei der an der Anode einerseits und an der Kathode andererseits jeweils ein Abgas anfällt, d a d u r c h g e k e n n z e i c h n e t , dass die Kohlendioxidkonzentration im Kathodenabgas gemessen wird und der über der Membran anfallende Brennstoffverlust erfasst wird.1. A method for regulating the fuel concentration in the anode liquid of a fuel cell with anode, membrane and cathode, in which an exhaust gas is produced on the anode on the one hand and on the other hand on the cathode, characterized in that the carbon dioxide concentration in the cathode exhaust gas is measured and that accumulating over the membrane Fuel loss is recorded.
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 der Brennstoff Methanol ist.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 the fuel is methanol.
3. Verfahren nach Anspruch 1 oder Anspruch 2, d a d u r c h g e k e n n z e i c h n e t , dass die Kohlendioxidkonzentration mittels eines Sensors, der im Gasstrom angeordnet ist, gemessen wird.3. The method according to claim 1 or claim 2, that the carbon dioxide concentration is measured by means of a sensor which is arranged in the gas stream.
4. Verfahren nach Anspruch 3, d a d u r c h g e k e n n - z e i c h n e t , dass die Kathodendioxidkonzentration im4. The method of claim 3, d a d u r c h g e k e n n - z e i c h n e t that the cathode dioxide concentration in
Gasstrom noch im Fluidkreislauf vorhandenen Einheiten zum Kühlen und Regelung des Vordruckes gemessen wird.Gas flow is still measured in the fluid circuit existing units for cooling and control of the admission pressure.
5. Verfahren nach Anspruch 2, d a d u r c h g e k e n n - z e i c h n e t , dass die bei der Messung ermittelte Kohlendioxidkonzentration in Methanol umgerechnet wird, wobei ein Mol Kohlendioxid einem Mol Methanol entspricht.5. The method of claim 2, d a d u r c h g e k e n n - z e i c h n e t that the carbon dioxide concentration determined during the measurement is converted into methanol, wherein one mole of carbon dioxide corresponds to one mole of methanol.
6. Vorrichtung zur Durchführung des Verfahrens nach Anspruch 1 oder einem der Ansprüche 2 bis 4, mit einem Kohlendioxidsensor (16), der im Gasstrom angeordnet ist.6. Device for performing the method according to claim 1 or one of claims 2 to 4, with a carbon dioxide sensor (16) which is arranged in the gas stream.
7. Vorrichtung nach Anspruch 6, d a d u r c h g e k e n n z e i c h n e t , dass der Sensor (16) im Gasstrom nach einem darin angebrachten Kühler (15) eines ggf. vorhandenen Vordruckreglers angebracht ist. 7. The device as claimed in claim 6, so that the sensor (16) is attached in the gas flow after a cooler (15), which may be present, of a pre-pressure regulator which may be present.
EP01962605A 2000-08-16 2001-08-03 Method for regulating the fuel concentration in the anode fluid of a fuel cell, and corresponding device Withdrawn EP1310007A1 (en)

Applications Claiming Priority (3)

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DE10039959A DE10039959A1 (en) 2000-08-16 2000-08-16 Method for regulating the fuel concentration in the anode liquid of a fuel cell and associated device
DE10039959 2000-08-16
PCT/DE2001/002976 WO2002015314A1 (en) 2000-08-16 2001-08-03 Method for regulating the fuel concentration in the anode fluid of a fuel cell, and corresponding device

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CA2419452A1 (en) 2003-02-14
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WO2002015314A1 (en) 2002-02-21
CN1446385A (en) 2003-10-01

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