CA2429595A1 - Fuel cell stack - Google Patents
Fuel cell stack Download PDFInfo
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- CA2429595A1 CA2429595A1 CA002429595A CA2429595A CA2429595A1 CA 2429595 A1 CA2429595 A1 CA 2429595A1 CA 002429595 A CA002429595 A CA 002429595A CA 2429595 A CA2429595 A CA 2429595A CA 2429595 A1 CA2429595 A1 CA 2429595A1
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- fuel cell
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- cell stack
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- 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
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
- H01M8/04537—Electric variables
- H01M8/04544—Voltage
- H01M8/04559—Voltage of fuel cell stacks
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- 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
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- 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
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
- H01M8/04537—Electric variables
- H01M8/04544—Voltage
- H01M8/04552—Voltage of the individual fuel cell
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- 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
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
- H01M8/04746—Pressure; Flow
- H01M8/04753—Pressure; Flow of fuel cell reactants
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- 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
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
- H01M8/04791—Concentration; Density
- H01M8/04798—Concentration; Density of fuel cell reactants
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- 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
- H01M8/1011—Direct alcohol fuel cells [DAFC], e.g. direct methanol fuel cells [DMFC]
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- 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
- H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
- H01M8/249—Grouping of fuel cells, e.g. stacking of fuel cells comprising two or more groupings of fuel cells, e.g. modular assemblies
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- 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
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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
The invention relates to a fuel cell stack, whereby a regulation of the operational medium concentration may be effected by simple means. It is thus possible to automatically operate the fuel cell stack almost optimally, which means just above the minimum necessary operating medium concentration for operation, dependant upon the load. The invention is based upon the effect that an individual fuel cell under identical operating conditions produces a lesser cell voltage. The above is used as the adjustment parameter for the controlled addition of at least one operating medium, for example methanol or also air. According o the invention, the fuel cell stack can thus be operated with economical means at nearly optimal conditions.
Description
22539 ~ Transl. of PCT/DE01/044327 T R A N S L A T I O N
D a s c r i p t i o n ~ cs~ sTACx Technical Field The invention relates to a fuel cell stack, especially a control for an operating medium for a fuel cell stack.
A fuel cell comprises a cathode, an electrolyte and an anode. The cathode is supplied with an oxidizing agent, for example, air and the anode is supplied with fuel, for example, hydrogen.
A plurality of fuel cells are, as a rule, electrically and mechanically connected together by connecting elements to produce more electrical outputs. An example for such a connecting element is illustrated as the bipolar plate known from DE 44 10 711 C1. By means of bipolar plates, fuel cells stacked one above the other can be electrically connected in series. This arrangement is knows as a fuel cell stack. These are comprised of the bipolar plates and the electrode-electrolyte units.
In a liquid operated direct-methanol fuel cell, a water/methanol mixture is fed into the anode compartments. For producing technologically usable voltages, individual cells are electrically connected in series. Typical methanol concentrations 22539 ~ Transl. of PCT/DE01/04432 lie, in this case, in the range of 0.1 m to 2 m. As a rule, the methanol/water mixture is supplied in a substoichiometric amount.
Of special significance for an economical operation of the fuel cell is the correct adjustment of the methanol concentration. Too low a methanol concentration gives rise to a reduction is the cell efficiency because of a methanol deficiency, whereas too high a concentration reduces the efficiency because of the useless combustion of diffusing methanol to the cathode side. The methanol concentration must, therefore, be controlled.
As state of the art there is a control system for regulating the methanol concentration which comprises a methanol sensor.
Such an arrangement is described in DS 198 50 720 A1.
For example, a data set can be prograamned into a minicomputer to provide the optimal methanol concentration for a respective operating point (in terms of temperature electrical current and medium throughflow rates). Furthermore, a unit can be provided for metering the methanol. In conjunction with the methanol sensor and the methanol metering unit, the methanol concentration is the cell can be adjusted by means of a control algorithm.
The methanol regulation known from the state of the art is indeed satisfactory, but it is connected with significant structural and financial cost. 8specially for small systems in a power range of the order of 10 to 500 watts, the cost for such a control system is outside the economical range. Furthermore, the establishment of a data set for all possible operating conditions is connected with greater expense.
D a s c r i p t i o n ~ cs~ sTACx Technical Field The invention relates to a fuel cell stack, especially a control for an operating medium for a fuel cell stack.
A fuel cell comprises a cathode, an electrolyte and an anode. The cathode is supplied with an oxidizing agent, for example, air and the anode is supplied with fuel, for example, hydrogen.
A plurality of fuel cells are, as a rule, electrically and mechanically connected together by connecting elements to produce more electrical outputs. An example for such a connecting element is illustrated as the bipolar plate known from DE 44 10 711 C1. By means of bipolar plates, fuel cells stacked one above the other can be electrically connected in series. This arrangement is knows as a fuel cell stack. These are comprised of the bipolar plates and the electrode-electrolyte units.
In a liquid operated direct-methanol fuel cell, a water/methanol mixture is fed into the anode compartments. For producing technologically usable voltages, individual cells are electrically connected in series. Typical methanol concentrations 22539 ~ Transl. of PCT/DE01/04432 lie, in this case, in the range of 0.1 m to 2 m. As a rule, the methanol/water mixture is supplied in a substoichiometric amount.
Of special significance for an economical operation of the fuel cell is the correct adjustment of the methanol concentration. Too low a methanol concentration gives rise to a reduction is the cell efficiency because of a methanol deficiency, whereas too high a concentration reduces the efficiency because of the useless combustion of diffusing methanol to the cathode side. The methanol concentration must, therefore, be controlled.
As state of the art there is a control system for regulating the methanol concentration which comprises a methanol sensor.
Such an arrangement is described in DS 198 50 720 A1.
For example, a data set can be prograamned into a minicomputer to provide the optimal methanol concentration for a respective operating point (in terms of temperature electrical current and medium throughflow rates). Furthermore, a unit can be provided for metering the methanol. In conjunction with the methanol sensor and the methanol metering unit, the methanol concentration is the cell can be adjusted by means of a control algorithm.
The methanol regulation known from the state of the art is indeed satisfactory, but it is connected with significant structural and financial cost. 8specially for small systems in a power range of the order of 10 to 500 watts, the cost for such a control system is outside the economical range. Furthermore, the establishment of a data set for all possible operating conditions is connected with greater expense.
22539 Transl. of PCT/DE01/04432 Similar problems arise in the control of the operating medium on the oxidizing side (cathode side) of the fuel cell which is not limited only to the case of direct methanol fuel cells.
The oxidizing agent, especially oxygen or air, is supplied to the fuel cell generally under pressure with the aid of a compressor. On cost grounds here as well a control for an optimum operating range is advantageous.
Obiect and solution of the Invention The invention has as its object to provide a simple and cost effective method of controlling at least one operating medium for a fuel call stack as well as a fuel cell stack suitable for this method.
The object is attained with a method according to the main claim as well as an apparatus for carrying out the method according to the auxiliary claim.
Advantageous embodiments can be deduced from the dependent claims which relate back to them.
Subject of the Invention The invention is based upon the concept that an individual fuel cell of a fuel cell stack can be so selected and, optionally, so modified that it requires a somewhat higher operating medium concentration for a predetermined cell voltage than the remaining individual cells of the fuel cell stack. For the same available operating medium concentration for all cells, the voltage of a so modified individual cell can, as a rule, be 22539 ~ Transl. of PCT/DE01/04432 lower than that of the other cells. When the voltage of this individual cell falls below a predetermined threshold, utilizing a simple electronic circuit, an operating medium can be additionally fed into the operating medium circulation until the cell voltage of the modified fuel cell rises above threshold or a further threshold.
The method of the invention according to claim 1 thus is provided for a fuel cell stack with a multiplicity of fuel cells.
These fuel cells are connected with at least one operating medium circulation through which the fuel cells are supplied with the operating medium. The method of the invention provides that the metering of an operating medium into the operating medium circuit is effected in dependence upon the detected cell voltage.
In an advantageous embodiment according to claim 2, the feed of the operating medium is effected directly upstream of the fuel cell whose cell voltage is detected. The regulating mechanism thus occurs especially rapidly because the direct feed of the operating medium into the fuel cell can immediately provide an increased conversion and thus an increase in the cell voltage.
Advantageously, the metering or feed of the operating medium according to claim 3 is controlled by a valve. Thus especially the overstepping or understepping of the threshold for the cell voltage is directly converted into an electrical signal which controls the valve.
The control of the metering of the operating medium is effected according to claim 4, as soon as the cell voltage of the fuel cell falls below a predetermined value. This simple control 22539 Transl. of PCT/DE01/04432 mechanism allows the operating medium metering to be controlled in dependence upon the conversion which occurs is this cell and thus optimize the operating medium metering. Advantageously, the operating medium metering according to the method of the invention is effected directly via the conversion of the fuel cell and thus the cell voltage and not as is customary in the state of the art via control of the concentration of the operating medium. Con-sequently, it is also not necessary for the method of the invention for different operating states and operating parameters to determine data sets for the concentration of an operating medium.
In order to prevent an overdosing of the operating medium into the operating medium circulation, a further embodiment according to claim 5 provides that the feed of the operating medium is terminated as soon as a call voltage of the fuel cell exceeds a predetermined value, for example, as upper limiting value.
The monitoring of the cell voltage with respect to the upper and lower limiting values is advantageously effected in a single modified fuel cell to minimize the apparatus costs. The upper and lower limiting values can be either identical or also slightly different. Even with identical limiting values, a control mechanism is provided since operating medium dosing and the resultant increase is the cell voltage occur only with a time delay. For the operation of the fuel cell stack, as optimum range of the cell voltage can be established. The closer the feed of the operating medium to the fuel cell, the smaller is the time delay and thus the more closely the upper and lower limiting values can be matched to the optimum range.
The oxidizing agent, especially oxygen or air, is supplied to the fuel cell generally under pressure with the aid of a compressor. On cost grounds here as well a control for an optimum operating range is advantageous.
Obiect and solution of the Invention The invention has as its object to provide a simple and cost effective method of controlling at least one operating medium for a fuel call stack as well as a fuel cell stack suitable for this method.
The object is attained with a method according to the main claim as well as an apparatus for carrying out the method according to the auxiliary claim.
Advantageous embodiments can be deduced from the dependent claims which relate back to them.
Subject of the Invention The invention is based upon the concept that an individual fuel cell of a fuel cell stack can be so selected and, optionally, so modified that it requires a somewhat higher operating medium concentration for a predetermined cell voltage than the remaining individual cells of the fuel cell stack. For the same available operating medium concentration for all cells, the voltage of a so modified individual cell can, as a rule, be 22539 ~ Transl. of PCT/DE01/04432 lower than that of the other cells. When the voltage of this individual cell falls below a predetermined threshold, utilizing a simple electronic circuit, an operating medium can be additionally fed into the operating medium circulation until the cell voltage of the modified fuel cell rises above threshold or a further threshold.
The method of the invention according to claim 1 thus is provided for a fuel cell stack with a multiplicity of fuel cells.
These fuel cells are connected with at least one operating medium circulation through which the fuel cells are supplied with the operating medium. The method of the invention provides that the metering of an operating medium into the operating medium circuit is effected in dependence upon the detected cell voltage.
In an advantageous embodiment according to claim 2, the feed of the operating medium is effected directly upstream of the fuel cell whose cell voltage is detected. The regulating mechanism thus occurs especially rapidly because the direct feed of the operating medium into the fuel cell can immediately provide an increased conversion and thus an increase in the cell voltage.
Advantageously, the metering or feed of the operating medium according to claim 3 is controlled by a valve. Thus especially the overstepping or understepping of the threshold for the cell voltage is directly converted into an electrical signal which controls the valve.
The control of the metering of the operating medium is effected according to claim 4, as soon as the cell voltage of the fuel cell falls below a predetermined value. This simple control 22539 Transl. of PCT/DE01/04432 mechanism allows the operating medium metering to be controlled in dependence upon the conversion which occurs is this cell and thus optimize the operating medium metering. Advantageously, the operating medium metering according to the method of the invention is effected directly via the conversion of the fuel cell and thus the cell voltage and not as is customary in the state of the art via control of the concentration of the operating medium. Con-sequently, it is also not necessary for the method of the invention for different operating states and operating parameters to determine data sets for the concentration of an operating medium.
In order to prevent an overdosing of the operating medium into the operating medium circulation, a further embodiment according to claim 5 provides that the feed of the operating medium is terminated as soon as a call voltage of the fuel cell exceeds a predetermined value, for example, as upper limiting value.
The monitoring of the cell voltage with respect to the upper and lower limiting values is advantageously effected in a single modified fuel cell to minimize the apparatus costs. The upper and lower limiting values can be either identical or also slightly different. Even with identical limiting values, a control mechanism is provided since operating medium dosing and the resultant increase is the cell voltage occur only with a time delay. For the operation of the fuel cell stack, as optimum range of the cell voltage can be established. The closer the feed of the operating medium to the fuel cell, the smaller is the time delay and thus the more closely the upper and lower limiting values can be matched to the optimum range.
" CA 02429595 2003-05-22 22539 Transl. of PCT/DE01/04432 Advantageously, the detection of the cell voltage is effected for a modified fuel cell according to claim 6. The modified fuel cell used in the method according to claim 6 has, by comparison with the remaining fuel cells of the fuel cell stack, a diffusion resistance which is greater by at least 5% so that an correspondingly altered cell voltage will be obtained. The "modification" in the sense of the invention is that this modified fuel cell at optimal fuel concentration for the remaining fuel cells of the cell stack produces a call voltage which is at least 10% less. Such a modification can be obtained by the use of a thicker diffusion layer. Stated otherwise, the modified fuel cell requires for its optimum operating point, a methanol concentration which is greater by about 5 to 10% than that of the remaining fuel cells of the stack.
Advantageously the method is used in a direct methanol fuel cell with methanol as a fuel.
It is also conceivable to use the method for control of the oxidizing agent. For example, the air or oxygen feed to the fuel cells can be effected in dependence upon the cell voltage of a modified cell. In that case the modified cell serves to control, for example, an air compressor and its output.
A further advantageous embodiment of the method according to claim 9 proposes to detect the cell voltage of a further fuel cell within the fuel cell stack. This fuel call is advantageously not modified. The dosing of the operating medium is then controlled additionally as a function of the cell voltage of this fuel cell.
Advantageously the method is used in a direct methanol fuel cell with methanol as a fuel.
It is also conceivable to use the method for control of the oxidizing agent. For example, the air or oxygen feed to the fuel cells can be effected in dependence upon the cell voltage of a modified cell. In that case the modified cell serves to control, for example, an air compressor and its output.
A further advantageous embodiment of the method according to claim 9 proposes to detect the cell voltage of a further fuel cell within the fuel cell stack. This fuel call is advantageously not modified. The dosing of the operating medium is then controlled additionally as a function of the cell voltage of this fuel cell.
22539 Transl. of PCT/DE01/04432 The method according to the invention is is principle usable with all direct methanol fuel cell stacks. It can thus control not only the metering of the fuel (pure methanol or also highly concentrated methanol-water mixture) but also can be used for the control of the oxidizing agent. It especially allows control by regulating a compressor which supplies the requisite oxidation medium at a corresponding pressure.
For carrying out the method according to the invention, a direct methanol fuel cell stack with a multiplicity of fuel cell according to claim 11 is suitable in which at least one of the fuel calls is provided with a diffusion resistance which is increased by comparison with that of the remaining fuel cells of the stack.
This means that this modified fuel cell at optimum operating conditions of the remaining fuel cells will produce as a rule a cell voltage which is at least 10% less.
According to claim 12, the means [providing the increased diffusion resistance] can advantageously be a thicker diffusion layer or an additionally arranged diffusion layer. A thicker diffusion layer or an additional diffusion layer generally will reduce the access of methanol to the anode. As a result there is also usually a reduced conversion. To the extent that the remaining fuel cells of the stack operate with approximately optimal conditions, there is a reduction as a consequence of the cell voltage in this modified fuel cell against that of the remaining fuel cells.
Advantageously the fuel cell stack according to claim 13 has an electrically switchable valve which is disposed in the feed 22539 '' Transl. of PCT/DE01/04432 of the operating medium. The valve can thus be located within the operating medium circulation or also outside it.
In an advantageous refinement of the fuel call stack according to claim 14, the modified cell is connected with the electrically switchable valve so that the modified cell is capable of controlling the valve via an electric signal.
Special Descrit>tive Part The invention is described below in greater detail in conjunction with Figures and exemplary embodiments.
Figure 1: A schematic illustration of the automatic operating medium concentration control, for example for a direct methanol fuel cell stack.
Figure 2: Current/voltage graphs of different methanol concentrations for a direct methanol fuel cell.
Figure 1 shows the configuration of the fuel cell stack according to the invention. From a supply vessel 1, the methanol is supplied to the anode circulation 2 of the fuel cell stack comprising the fuel cells BZ with the bipolar plates 5a to 5e. A
circulation tank 4 and a circulation pump 3 serve for the uniforan flow to the anode. 'Via the bipolar plate 5d, the cell voltage is additionally detected. With this cell voltage a circuit 6 is activated which controls the valve (pump) 7 for metering the methanol.
A direct methanol fuel cell stack is supplied via an anode circulation, comprised of a circulating pump and circulating tank with fuel. One cell of the stack has a thicker anodic _ g 22539' Transl. of PCT/DE01/04432 diffusion layer than the other cells. As the methanol concentration approaches the minimum required methanol concentration within the cells as a result of the utilization [of methanol], the cell voltage within the modified cell falls because of the anodic diffusion over voltage. The cell voltage is detected by an electronic circuit and sets a pump in operation which feeds methanol from a vessel into the circulation.
Advantageously the modified cell is protected by a diode to exclude pole reversal. Furthermore, it is advantageous to meter the methanol directly into the feed line of the cell. In this manner a rapid reaction time for the control is ensured. A further advantageous feature is found in the connection of a resister is parallel to the poles of the modified fuel cell. When the fuel cell stack is operated in an idling mode, this can ensure that the adjustment of a methanol concentration to zero will be avoided and which could lead to difficulties is startup.
As a modification of the cell, apart from the increase in the thickness of the diffusion layer, there are other possibilities for decreasing the effective diffusion coefficient within the anode. For example with the use of identical electrodes, a reduction in the active area can serve the purpose as well. The method advantageously does not require calibration.
In as advantageous embodiment, the cell voltage of a further fuel cell is detected. The detected cell voltage of the nonmodified fuel cell thus serves as an additional parameter for the regulation of the metering. In this manner the metering of _ g _ 2259 - Transl. of PCT/DE01/04432 fuel can be prevented in the case in which, for example, there is afailure of the supply of the oxidation medium for the entire stack and a consequent drop in the cell voltage of the modified fuel cell. The detection of the cell voltage of a further fuel cell ensures that onlyin the case of a relative drop of the cell voltage of the modified cell because of a reduction in the fuel concentration, will there by the addition of fuel. Thus also an overdosing can be precluded for example since in such a case both the cell voltage of the modified cell as wall as that of the nonmodified cell will drop.
The following table shows an advantageous possibility of the switching logic for a direct methanol fuel cell stack.
Cell Voltage of the Cell voltage of a Metering of Modified Fuel Cell Further Fuel Cell Additional Fuel > 0.3 V > 0.3 V No < 0.3 v > 0.3 v Yes < 0.3 V < 0.3 V No In Figure 2, four current/voltage curves are shows for a direct methanol fuel cell whereby the fuel concentration varies in the range of 0.5 M to 4 M of methanol in water. Both too low and too high concentrations of methanol give rise to a drop in the cell voltage and thus make the system uneconomical. The goal is to operate the system with an optimal fed methanol concentration depending upon the operating conditions (for example predetermined current draw). The term "optimal" as used hare means with the least possible methanol concentration to produce the highest possible cell voltage in the fuel cell.
For carrying out the method according to the invention, a direct methanol fuel cell stack with a multiplicity of fuel cell according to claim 11 is suitable in which at least one of the fuel calls is provided with a diffusion resistance which is increased by comparison with that of the remaining fuel cells of the stack.
This means that this modified fuel cell at optimum operating conditions of the remaining fuel cells will produce as a rule a cell voltage which is at least 10% less.
According to claim 12, the means [providing the increased diffusion resistance] can advantageously be a thicker diffusion layer or an additionally arranged diffusion layer. A thicker diffusion layer or an additional diffusion layer generally will reduce the access of methanol to the anode. As a result there is also usually a reduced conversion. To the extent that the remaining fuel cells of the stack operate with approximately optimal conditions, there is a reduction as a consequence of the cell voltage in this modified fuel cell against that of the remaining fuel cells.
Advantageously the fuel cell stack according to claim 13 has an electrically switchable valve which is disposed in the feed 22539 '' Transl. of PCT/DE01/04432 of the operating medium. The valve can thus be located within the operating medium circulation or also outside it.
In an advantageous refinement of the fuel call stack according to claim 14, the modified cell is connected with the electrically switchable valve so that the modified cell is capable of controlling the valve via an electric signal.
Special Descrit>tive Part The invention is described below in greater detail in conjunction with Figures and exemplary embodiments.
Figure 1: A schematic illustration of the automatic operating medium concentration control, for example for a direct methanol fuel cell stack.
Figure 2: Current/voltage graphs of different methanol concentrations for a direct methanol fuel cell.
Figure 1 shows the configuration of the fuel cell stack according to the invention. From a supply vessel 1, the methanol is supplied to the anode circulation 2 of the fuel cell stack comprising the fuel cells BZ with the bipolar plates 5a to 5e. A
circulation tank 4 and a circulation pump 3 serve for the uniforan flow to the anode. 'Via the bipolar plate 5d, the cell voltage is additionally detected. With this cell voltage a circuit 6 is activated which controls the valve (pump) 7 for metering the methanol.
A direct methanol fuel cell stack is supplied via an anode circulation, comprised of a circulating pump and circulating tank with fuel. One cell of the stack has a thicker anodic _ g 22539' Transl. of PCT/DE01/04432 diffusion layer than the other cells. As the methanol concentration approaches the minimum required methanol concentration within the cells as a result of the utilization [of methanol], the cell voltage within the modified cell falls because of the anodic diffusion over voltage. The cell voltage is detected by an electronic circuit and sets a pump in operation which feeds methanol from a vessel into the circulation.
Advantageously the modified cell is protected by a diode to exclude pole reversal. Furthermore, it is advantageous to meter the methanol directly into the feed line of the cell. In this manner a rapid reaction time for the control is ensured. A further advantageous feature is found in the connection of a resister is parallel to the poles of the modified fuel cell. When the fuel cell stack is operated in an idling mode, this can ensure that the adjustment of a methanol concentration to zero will be avoided and which could lead to difficulties is startup.
As a modification of the cell, apart from the increase in the thickness of the diffusion layer, there are other possibilities for decreasing the effective diffusion coefficient within the anode. For example with the use of identical electrodes, a reduction in the active area can serve the purpose as well. The method advantageously does not require calibration.
In as advantageous embodiment, the cell voltage of a further fuel cell is detected. The detected cell voltage of the nonmodified fuel cell thus serves as an additional parameter for the regulation of the metering. In this manner the metering of _ g _ 2259 - Transl. of PCT/DE01/04432 fuel can be prevented in the case in which, for example, there is afailure of the supply of the oxidation medium for the entire stack and a consequent drop in the cell voltage of the modified fuel cell. The detection of the cell voltage of a further fuel cell ensures that onlyin the case of a relative drop of the cell voltage of the modified cell because of a reduction in the fuel concentration, will there by the addition of fuel. Thus also an overdosing can be precluded for example since in such a case both the cell voltage of the modified cell as wall as that of the nonmodified cell will drop.
The following table shows an advantageous possibility of the switching logic for a direct methanol fuel cell stack.
Cell Voltage of the Cell voltage of a Metering of Modified Fuel Cell Further Fuel Cell Additional Fuel > 0.3 V > 0.3 V No < 0.3 v > 0.3 v Yes < 0.3 V < 0.3 V No In Figure 2, four current/voltage curves are shows for a direct methanol fuel cell whereby the fuel concentration varies in the range of 0.5 M to 4 M of methanol in water. Both too low and too high concentrations of methanol give rise to a drop in the cell voltage and thus make the system uneconomical. The goal is to operate the system with an optimal fed methanol concentration depending upon the operating conditions (for example predetermined current draw). The term "optimal" as used hare means with the least possible methanol concentration to produce the highest possible cell voltage in the fuel cell.
Claims (14)
1. A method of operating a fuel cell stack with a plurality of fuel cells whereby the fuel cells are connected by at least one operating medium circulation, with the steps of detecting the cell voltage of a fuel cell, in dependence on this cell voltage metering an operating medium into the operating medium circulation.
2. The method according to the preceding claim characterized in that the operating medium is metered directly into the feed line of the modified fuel cell.
3. The method according to one of the preceding claims characterized in that the metering of the operating medium is effected into the operating medium circulation through a valve.
4. The method according to one of the preceding claims characterized in that the operating medium is metered into the circulation as soon as the cell voltage of the modified fuel cell falls below a predetermined value.
5. The method according to one of the preceding claims characterized in that the metering of the operating medium into the circulation is terminated as soon as the cell voltage of the individual fuel cell exceeds a predetermined value.
6. The method according to one of the preceding claims characterized in that the cell voltage of a modified fuel cell is detected, the modified fuel cell having a diffusion resistance which is at least 5% higher than that of the remaining fuel cells of the fuel cell stack.
7. The method according to one of the preceding claims characterized in that methanol is the operating medium which is metered into the circulation.
8. The method according to one of the preceding claims characterized in that the metering of the operating medium is effected by controlling an air compressor.
9. The method according to one of the preceding claims characterized in that the cell voltage of a further fuel cell is detected and the metering of the operating medium is effected additionally in dependence upon this cell voltage.
10. The method according to one of the preceding claims which is used for a direct methanol fuel cell stack.
11. A fuel cell stack with a plurality of direct methanol fuel cells and at least one operating medium circulation characterized by at least one modified fuel cell which by comparison to the remaining fuel cells of the fuel cell stack has a diffusion resistance which is at least 5% greater.
12. The fuel cell stack according to the preceding claim characterized in that the modified fuel cell has an additional or thicker anodic diffusion layer than the remaining fuel cell.
13. The fuel cell stack according to one of the preceding claims 11 to 12 characterized by a valve in the operating medium feed.
14. The fuel cell stack according to the preceding claim characterized by an electric contacting between the modified fuel cell and the valve.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE10058083A DE10058083A1 (en) | 2000-11-23 | 2000-11-23 | fuel cell stack |
| DE10058083.1 | 2000-11-23 | ||
| PCT/DE2001/004432 WO2002043175A2 (en) | 2000-11-23 | 2001-11-21 | Fuel cell stack |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2429595A1 true CA2429595A1 (en) | 2002-05-30 |
Family
ID=7664334
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002429595A Abandoned CA2429595A1 (en) | 2000-11-23 | 2001-11-21 | Fuel cell stack |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP1340279A2 (en) |
| CA (1) | CA2429595A1 (en) |
| DE (1) | DE10058083A1 (en) |
| WO (1) | WO2002043175A2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7166379B2 (en) | 2000-12-27 | 2007-01-23 | Plug Power Inc. | Technique to regulate an efficiency of a fuel cell system |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102004061656A1 (en) * | 2004-12-22 | 2006-07-06 | Forschungszentrum Jülich GmbH | Direct-methanol-fuel cell stack operating method, comprises controlling controller, which regulates methanol dosing pump, so that two operating points are alternatively set to adjust inflow of methanol concentrations in anode area of stack |
| DE102005010497B4 (en) * | 2005-03-08 | 2014-05-28 | Forschungszentrum Jülich GmbH | A method of operating a direct methanol fuel cell stack |
| DE102005015660B4 (en) * | 2005-04-06 | 2013-03-28 | Forschungszentrum Jülich GmbH | Low-temperature fuel cell stack and method for operating the same |
| DE102007062165A1 (en) * | 2007-12-21 | 2009-06-25 | Sabik Informationssysteme Gmbh | Method and device for operating a fuel cell |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3542597A (en) * | 1967-12-04 | 1970-11-24 | Monsanto Res Corp | Fuel cell with automatic means for feeding reactant and method |
| JPS59114769A (en) * | 1982-12-22 | 1984-07-02 | Toshiba Corp | Fuel cell system |
| JPH0719615B2 (en) * | 1987-09-30 | 1995-03-06 | 株式会社日立製作所 | Fuel cell power generation system |
-
2000
- 2000-11-23 DE DE10058083A patent/DE10058083A1/en not_active Withdrawn
-
2001
- 2001-11-21 CA CA002429595A patent/CA2429595A1/en not_active Abandoned
- 2001-11-21 WO PCT/DE2001/004432 patent/WO2002043175A2/en not_active Application Discontinuation
- 2001-11-21 EP EP01997861A patent/EP1340279A2/en not_active Withdrawn
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7166379B2 (en) | 2000-12-27 | 2007-01-23 | Plug Power Inc. | Technique to regulate an efficiency of a fuel cell system |
| US7166378B2 (en) | 2000-12-27 | 2007-01-23 | Plug Power Inc. | Technique to regulate an efficiency of a fuel cell system |
Also Published As
| Publication number | Publication date |
|---|---|
| WO2002043175A2 (en) | 2002-05-30 |
| DE10058083A1 (en) | 2002-06-20 |
| WO2002043175A3 (en) | 2002-11-28 |
| EP1340279A2 (en) | 2003-09-03 |
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| Date | Code | Title | Description |
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| FZDE | Dead |