Fuel cell system and method for operating the fuel cell system

Abstract

A fuel cell system (1) comprising a voltage-generating fuel cell (2), which comprises an anode, a cathode, and an ion-conductive membrane separating the cathode from the anode, and comprising a reservoir (3) in which at least one contaminant is or can be stored, wherein, at a time when a limit voltage is expected to be reached or exceeded or when the voltage generated by the fuel cell (2) actually reaches or exceeds a limit voltage, the reservoir is temporarily connectable or fluidically connected to the fuel cell (2) in such a way that the at least one contaminant is supplied to the fuel cell (2) from the reservoir (3), characterized in that the reservoir (3) is integrated into a supply line (4) fluidically connected to the fuel cell (2), and in that a bypass line (6) bridging the reservoir (3) is provided, via which bypass line an uncontaminated reactant can be supplied to the fuel cell (2).

Description

[0001] The invention relates to a fuel cell system with a voltage-generating fuel cell comprising an anode, a cathode, and an ion-conductive membrane separating the cathode from the anode. The fuel cell system also has a storage unit in which at least one contaminant is or can be stored. The invention also relates to a method for operating such a fuel cell system.

[0002] During operation, the fuel cell is continuously contaminated by impurities introduced into the fuel cell through the reactants. For example, contamination of the air supplied to the cathode side can reduce the fuel cell's performance. However, the hydrogen supplied to the anode side can also contain impurities that reduce the fuel cell's performance. Therefore, regular cleaning processes are performed to ensure full performance.

[0003] To prevent fuel cell contamination, EP 1 349 638 B1 proposes the use of an air filter device, specifically to filter out impurities from the air supplied to the cathodes. To clean the air filter device, the impurities can also be discharged again, but this only happens if the incoming air is below a predetermined contamination level. The performance of the fuel cell should not be impaired in this process. It has proven disadvantageous that operating the fuel cell at high voltage leads to accelerated aging of the fuel cell.

[0004] US Pat. No. 5,013,617 A describes a fuel cell system equipped with various nitrogen tanks for supplying a predefined mixture of nitrogen and oxygen to the stack on the cathode side. An ejector is used to generate the nitrogen-oxygen mixture. By adding nitrogen from the tanks, the potential of the fuel cell is reduced to between 0.3 and 0.7 V per cell, thus reversing or preventing reversible cell damage.

[0005] It is therefore the object of the present invention to further develop a fuel cell system of the type mentioned above in such a way that damage or aging of the fuel cell caused by excessive voltages is reduced. Furthermore, it is the object of the present invention to provide a corresponding method for operating such a fuel cell system.

[0006] The part of the problem concerning the fuel cell system is solved by a fuel cell system having the features of claim 1. Advantageous embodiments with expedient further developments of the fuel cell system are specified in the dependent claims.

[0007] The fuel cell system is characterized in particular in that, at a time when a limit voltage is expected to be reached or exceeded or when it is actually reached or exceeded by the voltage generated by the fuel cell, the storage device is temporarily connectable or fluidly connected to the fuel cell in such a way that the at least one contaminant is supplied from the storage device to the fuel cell.

[0008] This configuration allows for targeted contamination of the fuel cell, thereby reducing its potential. This allows for lower power levels, such as those typically found in urban traffic. Targeted contamination of the fuel cell increases overall efficiency and extends its service life.

[0009] Contaminants can include physical contaminants, such as those in the form of particles. Examples include dust, dirt, pollen, insects, wood splinters, sawdust, metal particles, and the like. However, they can also be chemical contaminants, such as those found in the atmosphere, such as NOx, HC, CO, etc.

[0010] A suitable contaminant is continuously collected in the storage unit and released at the appropriate time to reduce the potential of the fuel cell.

[0011] The release of the contaminant can be achieved, for example, by connecting the reservoir to a supply line fluidically connected to the fuel cell, and by introducing or allowing the at least one contaminant to be introduced into the supply line via a valve. This opens the valve, and the contaminant flows from the reservoir into the supply line and thus into the fuel cell, reducing the fuel cell's power and thus also its voltage.

[0012] According to the invention, however, the reservoir is integrated into a supply line that is fluidly connected to the fuel cell, which offers space advantages. For this purpose, a bypass line can be provided that bridges the reservoir, through which an uncontaminated reactant can be supplied to the fuel cell. Thus, depending on the performance requirements, the fuel cell system can be operated in contaminated mode with low power output or in uncontaminated mode with high power output.

[0013] In order to be able to realize a stepped or intermediate power operation in this context, it has proven advantageous if a multi-way valve is arranged at a connection point of the bypass line with the supply line in order to supply a first portion of the reactant to be supplied to the fuel cell to the bypass line and to supply a second portion of the reactant to be supplied to the fuel cell into or through the storage with the at least one contaminant.

[0014] Since a large number of contaminants can often be found in the ambient air, it has proven advantageous if the supply line is a cathode supply line that is fluidly connected to the cathode of the fuel cell.

[0015] The object relating to the method is achieved by a method according to the features of claim 4. Advantageous embodiments with expedient further developments of the method are specified in the dependent claims.

[0016] The method for operating a fuel cell system with a fuel cell comprising an anode, a cathode and an ion-conductive membrane separating the anode from the cathode is characterized by the following steps: - Predicting a voltage or measuring a voltage generated by the fuel cell, and - Introducing at least one contaminant into the fuel cell, thereby contaminating the fuel cell, when the predicted voltage or the measured voltage of the fuel cell reaches or exceeds a threshold voltage.

[0017] This also has the advantage that contamination of the fuel cell is specifically caused when the voltage generated by the fuel cell is too high, which leads to undesirable increased aging of the cell.

[0018] In order to be able to identify at an early stage those locations or points on the route where an increased voltage leads to accelerated aging of the fuel cell, the invention provides that the voltage generated by the fuel cell is forecast depending on a route selected using a navigation system. For example, the section of road that is located within a city or town can be identified in advance as a section of road where the fuel cell will be subject to accelerated aging, since only a low level of power is drawn from the fuel cell on this section of road. The contaminant is therefore supplied to the fuel cell at this point or while driving along the corresponding section of road in order to reduce the voltage of the fuel cell.

[0019] The fuel cell system or the navigation system preferably has a data receiving device in order to be able to receive data from a data service. The data retrieved via the data service can, for example, be the emission levels at a specific location or the traffic situation on a specific section of the route. In this context, it has therefore proven advantageous if the forecast of the voltage generated by the fuel cell is created as a function of traffic data determined along a section of the route. This way, for example, on a route prone to traffic jams, the contaminant can be supplied to the fuel cell in advance in order to prevent excessively high voltages on this section of the route, which would lead to accelerated aging of the fuel cell.

[0020] Alternatively or additionally, it is also possible to predict the voltage generated by the fuel cell based on historical operation of the fuel cell system. For example, a processor unit with a data memory containing data on the operation of the fuel cell system can be provided for this purpose. This data can be time- and / or date-related, so that the fuel cell system is informed in advance, for example, that a driver is about to leave for rush hour or travel. Even in such cases, increased traffic volumes are to be expected, meaning only a slight reduction in fuel cell performance is to be expected.

[0021] Alternatively or additionally, it has proven advantageous to both predict and measure the voltage generated by the fuel cell, and to interrupt or terminate fuel cell contamination when the predicted voltage has reached or exceeded the threshold voltage, but the actual measured voltage falls below the threshold voltage. This accommodates cases where a low power requirement is expected but a high power requirement is actually desired, thus preventing fuel cell contamination.

[0022] Further advantages, features, and details of the invention will become apparent from the claims, the following description of preferred embodiments, and the drawings. These show: Fig. 1 a schematic representation of a fuel cell system, Fig. 2 a schematic section of a fuel cell system - not covered by the invention - with a storage device which is connected via a valve to a supply line of the fuel cell stack, and Fig. 3 a schematic section of a fuel cell system with a storage unit that is integrated into a supply line and can be bridged by means of a bypass line.

[0023] In Fig. Figure 1 shows a fuel cell system 1 connected to a navigation system 9 via a communication link 10. The system comprises a fuel cell stack 11 having a plurality of fuel cells 2 connected in series. The series connection of the fuel cells 2 is only indicated schematically in all figures. The fuel cell system 1 and the navigation system 9 are parts of a fuel cell vehicle (not shown in detail).

[0024] Each of the fuel cells 2 comprises an anode and a cathode, as well as an ion-conductive, particularly proton-conductive, membrane separating the anode from the cathode. The membrane is formed from an ionomer, preferably a sulfonated tetrafluoroethylene polymer (PTFE) or a perfluorinated sulfonic acid polymer (PFSA). Alternatively, the membrane can be formed as a hydrocarbon membrane.

[0025] A catalyst may additionally be admixed with the anodes and / or the cathodes, wherein the membranes are preferably coated on their first side and / or on their second side with a catalyst layer made of a noble metal or of mixtures comprising noble metals such as platinum, palladium, ruthenium or the like, which serve as reaction accelerators in the reaction of the respective fuel cell 2.

[0026] The anode or fuel (e.g., hydrogen) is supplied via anode compartments within the fuel cell stack 11. In a polymer electrolyte membrane fuel cell (PEM fuel cell), fuel or fuel molecules are split into protons and electrons at the anode. The membrane allows the protons (e.g., H + ) but is impermeable to the electrons (e - ). The following reaction takes place at the anode: 2H2 → 4H + + 4e - (Oxidation / electron release). While the protons pass through the membrane to the cathode, the electrons are conducted to the cathode or an energy storage device via an external circuit.

[0027] Cathode gas (e.g. oxygen or oxygen-containing air) can be supplied to the cathodes via cathode spaces within the fuel cell stack 11, so that the following reaction takes place on the cathode side: O2 + 4H + + 4e -→ 2H2O (reduction / electron uptake).

[0028] In this case, the anode chambers are connected via an anode supply line 12 to a fuel reservoir 13 that provides the fuel. Fuel that has not reacted at the anodes can be resupplied to the anode chambers via an anode recirculation line 14. A recirculation fan (not shown in detail) is assigned to the anode recirculation line 14 or is fluidically coupled into the anode recirculation line 14. To regulate the fuel supply, a fuel actuator 15 is assigned to the anode supply line 12 or is arranged in the anode supply line 12. This fuel actuator 15 is preferably designed as a pressure control valve. Upstream of the pressure control valve, a heat exchanger 16 in the form of a recuperator is arranged for (pre-)heating or conditioning the fuel.

[0029] On the air or cathode side, there is a compressor 17, which in this case draws in ambient air and compresses it. Due to this compression, the temperature of the drawn-in cathode gas increases, so that it is first passed via a compressor line 18 to a charge air cooler 19 to be cooled back down to a desired temperature. Starting from the charge air cooler 19, the drawn-in, compressed cathode gas is fed to a humidifier 20. In the humidifier 20, the dry cathode gas is mixed with the moisture in the cathode exhaust gas, which is fed to the humidifier 20 via a cathode exhaust gas line 21, and thus also humidified before being fed to the cathode chambers of the fuel cell stack 11 via the cathode supply line 8. Furthermore, the humidifier 20 is connected to an exhaust line 22, via which the remaining cathode exhaust gas is discharged from the fuel cell system 1.

[0030] In the present case, a reservoir 3 is provided on the cathode or air side, in which at least one contaminant is stored, at least temporarily. The one or more contaminants can be supplied to the fuel cell 2 in a targeted manner in order to reduce the potential of the fuel cell 2, thereby preventing accelerated aging of the fuel cell 2. The contaminant is supplied to the fuel cell 2 or the fuel cell stack 11 at a time when a limit voltage is expected to be reached or exceeded, or when the voltage generated by the fuel cell 2 actually reaches or exceeds it. In the present case, a voltmeter is provided to measure the voltage of the fuel cell 2. This voltmeter can be a single-cell voltmeter or a stack voltmeter for measuring the entire voltage provided by the fuel cell stack 11.

[0031] In Fig. Figure 2 shows an exemplary variant—not covered by the invention—for the storage and release of contaminants. This variant includes a supply line 4 that is fluidly connected to the fuel cell 2 or to the fuel cell stack 11. In this case, the supply line 4 is the cathode supply line 8, with the reservoir 3 containing the contaminant being connected to the cathode supply line 8 via a valve 5. If this valve 5 is opened, the contaminant is transferred from the reservoir 3 into the fuel cell stack 11, where it lowers the stack potential or one or more individual cell potentials of individual fuel cells 2.

[0032] Another exemplary variant for the storage and release of contaminants is in Fig.3, wherein the reservoir 3 is integrated into the supply line 4, and wherein a bypass line 6 is provided that bridges the reservoir 3. An uncontaminated reactant can be supplied to the fuel cell 2 or the fuel cell stack 11 via this bypass line 6. In the present case, a multi-way valve 7 is arranged at a connection point between the bypass line 7 and the supply line 4 in order to supply a first portion of the reactant to be supplied to the fuel cell 2 to the bypass line 6 and to supply a second portion of the reactant to be supplied to the fuel cell 2 into or through the reservoir 3 containing the at least one contamination. The multi-way valve 7 can preferably be controlled and switched automatically by means of a control unit.The portion that is fed into or through the storage 3 is also fed to the fuel cell 2 with its impurities, whereby the cell potential is reduced and increased aging of the fuel cell 2 is avoided.

[0033] The solution according to the invention is therefore characterized by the fact that the fuel cell system 1, and in particular the fuel cell 2, exhibits increased efficiency. This leads to reduced aging of the fuel cells 2 in the fuel cell stack 11. LIST OF REFERENCE SYMBOLS: 1 fuel cell system 2 fuel cells 3 storage 4 Supply line 5 Valve 6 Bypass line 7 Multi-way valve 8 Cathode supply line 9 Navigation system 10 Communication connection 11 Valve 12 Bypass line 13 Cathode supply line 14 Anode recirculation line 15 Fuel actuator 16 heat exchangers 17 compressors 18 Compressor line 19 intercooler 20 humidifiers 21 Cathode exhaust line 22 exhaust pipe 23 Data receiving device

Claims

[1] Fuel cell system (1) with a voltage-generating fuel cell (2), which comprises an anode, a cathode and an ion-conductive membrane separating the cathode from the anode, and with a storage (3) in which at least one contaminant is storable or stored, wherein at a time of an expected reaching or exceeding or an actual reaching or exceeding of a limit voltage by the voltage generated by the fuel cell (2), the storage is temporarily connectable or fluidly connected to the fuel cell (2) in such a way that the at least one contaminant is supplied to the fuel cell (2) from the storage (3), characterized by that the reservoir (3) is integrated into a supply line (4) which is fluidly connected to the fuel cell (2), and that a bypass line (6) bridging the reservoir (3) is present, via which an uncontaminated reactant can be supplied to the fuel cell (2). [2] Fuel cell system (1) according to claim 1, characterized by that a multi-way valve (7) is arranged at a connection point of the bypass line (7) to the supply line (4) in order to supply a first portion of the reactant to be supplied to the fuel cell (2) to the bypass line (6) and to supply a second portion of the reactant to be supplied to the fuel cell (2) into or through the reservoir (3) with the at least one contaminant. [3] Fuel cell system (1) according to claim 1 or 2, characterized by that the supply line (4) is a cathode supply line (8) fluidly connected to the cathode of the fuel cell (2). [4] Method for operating a fuel cell system (1) with a fuel cell (2) comprising an anode, a cathode and an ion-conductive membrane separating the anode from the cathode, characterized by the steps: - creating a forecast of a voltage generated by the fuel cell (2), and - supplying at least one contaminant to the fuel cell (2) and thus contaminating the fuel cell (2) when the predicted voltage of the fuel cell (2) reaches or exceeds a limit voltage, wherein the prediction of the voltage generated by the fuel cell (2) is made as a function of a route selected by means of a navigation system (9). [5] Method according to claim 4, characterized by that the forecast of the voltage generated by the fuel cell (2) is made as a function of traffic data determined along a section of the route. [6] Method according to claim 4 or 5, characterized by that the forecast of the voltage generated by the fuel cell (2) is made as a function of historical operation of the fuel cell system (1). [7] Method according to claim 5 or 6, characterized bythat the voltage generated by the fuel cell (2) is both predicted and measured, and that the contamination of the fuel cell (2) is interrupted or terminated when the predicted voltage has reached or exceeded the limit voltage, but the actual measured voltage remains below the limit voltage.

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