Method and apparatus for conditioning a fuel cell stack for a fuel cell system

Abstract

The present invention relates to a method (100) for conditioning a fuel cell stack (310) for a fuel cell system. The proposed method (100) comprises: - applying (101) an electrical load to the fuel cell stack (310); - operating (103) the fuel cell stack (310) in a first operating mode in which an air supply system for supplying air to a cathode subsystem (314) of the fuel cell stack (310) is actively operated while the load is applied; - operating (105) the fuel cell stack (310) in a second operating mode in which the air supply system is deactivated while the load is applied; and - cyclically switching (107) repeatedly between the first operating mode and the second operating mode.

Description

[0001] R.416149

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method and apparatus for conditioning a fuel cell stack for a fuel cell system

[0006] The presented invention relates to a method and a device for conditioning a fuel cell stack for a fuel cell system.

[0007] State of the art

[0008] A newly assembled PEM fuel cell stack (PEM-FC), called a "stack", requires a conditioning process to achieve its full performance.

[0009] During a conditioning process, the membrane and ionomer components in the catalyst area are hydrated. Furthermore, the catalyst is activated, particularly by reducing surface oxides on the Pt catalyst particles. Finally, impurities such as organic residues and particles are flushed out during initial operation.

[0010] For conditioning, fuel cell stacks are usually operated on a test bench according to a special program.

[0011] Typically, the conditioning process involves cyclical switching between a high-current point and a currentless state. This serves to create a continuous alternation between cathode-side water production, which diffuses into the membrane and further forms proton channels, and a subsequent currentless state without ion and mass transport. This alternation significantly accelerates the formation of new channels. R.416149

[0012] - 2 -

[0013] At the same time, the cells also pass through specific potential states due to the load change, which is particularly beneficial for catalyst activity.

[0014] Disclosure of the invention

[0015] Within the scope of the presented invention, a method and a device for conditioning a fuel cell system are introduced. Further features and details of the invention will become apparent from the respective dependent claims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the device according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention always refers, or can refer, to each other.

[0016] The invention presented here is particularly useful for the time- and energy-efficient conditioning of a fuel cell stack for a fuel cell system.

[0017] Thus, according to a first aspect of the presented invention, a method for conditioning a fuel cell stack for a fuel cell system is presented.

[0018] The presented method comprises applying an electrical load to the fuel cell stack, operating the fuel cell stack in a first operating mode in which an air supply is actively operated to provide air to a cathode subsystem of the fuel cell stack while the load is applied, operating the fuel cell stack in a second operating mode in which the air supply is deactivated while the load is applied, and repeatedly switching cyclically between the first operating mode and the second operating mode.

[0019] The presented invention is based on the operation of a fuel cell stack in which it cyclically switches between two different operating modes. Due to the second operating mode, in which R.416149

[0020] - 3 - when the air supply is deactivated, a hydrogen pumping effect is achieved, whereby hydrogen is pumped from an anode subsystem into the cathode subsystem of the fuel cell stack, resulting in a particularly fast activation of the fuel cell stack.

[0021] In the second operating mode, the airflow through the cathode subsystem is completely stopped and any residual oxygen remaining in the cathode subsystem is consumed, in particular completely consumed. Accordingly, the current flow from the fuel cell stack as well as water and heat production come to a standstill.

[0022] Additionally, switching between the first operating mode, i.e., a current-carrying operating mode, and the second operating mode, i.e., a current-free operation, promotes the formation of new proton channels in the ionomer of the fuel cell stack cells.

[0023] It may be provided that the electrical load is selected in such a way that the voltage at the fuel cell stack is at most 10 volts, in particular exactly 0 volts.

[0024] By applying a voltage to the fuel cell stack, i.e., a stack voltage, of at most 10 volts, in particular exactly 0 volts, the hydrogen pumping effect is achieved in the cells of the fuel cell stack, so that hydrogen is pumped from the anode subsystem into the cathode subsystem.

[0025] The voltage at the fuel cell stack can be adjusted, for example, via a minimum voltage limit of the electrical load.

[0026] It may also be stipulated that a 4-quadrant load is selected as the electrical load.

[0027] By using a 4-quadrant load as the electrical load, negative cell voltages or a negative voltage at the fuel cell stack can also be implemented in the second operating mode. Accordingly, using a 4-quadrant load, it is possible to operate the R.416149 fuel cell stack.

[0028] - 4 - to operate continuously at a voltage below 0 volts, whereby the 4-quadrant load "engages" once the voltage at the fuel cell stack falls below 0 volts and provides the electrons for the hydrogen pumping effect. This causes all cells of the fuel cell stack to pump hydrogen and thus effectively activates all cells. No oxygen is required in the cathode subsystem for this, as the reaction at the cells is forced by the electron supply from the 4-quadrant load. The intensity of the hydrogen pumping effect during the second operating mode can be defined or adjusted via the negative voltage limit, e.g., in the range of -10 volts to 0 volts.

[0029] Accordingly, it can be provided that the electrical load is selected in such a way that a voltage below 0 volts is established at the fuel cell stack.

[0030] It may also be provided that during the second operating mode a hydrogen concentration in the cathode subsystem is set to a value between 1 vol% and 30 vol%.

[0031] By applying a negative voltage to the fuel cell stack, such strong hydrogen pumping is achieved that the hydrogen concentration in the cathode subsystem settles at a value between 1 vol.% and 30 vol.%.

[0032] It may still be provided that the electrical load is between 1.5 A / cm² 3 and 2 A / cm 3 lies.

[0033] To adjust the electrical load such that a voltage below 0 volts is established on the fuel cell stack, an electrical load of between 1.5 A / cm² has been used. 3 and 2 A / cm 3 proved to be particularly advantageous.

[0034] It may also be provided that the air system is deactivated by deactivating a fan of the air system. R.416149

[0035] - 5 -

[0036] By deactivating the blower, the entry of oxygen into the cathode subsystem can be effectively and quickly stopped, and by activating the blower, it can be restarted.

[0037] It may also be provided that the air system is deactivated by closing the cathode shut-off valves of the fuel cell stack.

[0038] Closing the cathode shut-off valves effectively and quickly stops the entry of oxygen into the cathode subsystem, while opening the cathode shut-off valves restarts the process.

[0039] It may also be provided that in the second operating mode each cell of the fuel cell stack is operated at a voltage of less than 0 volts at least temporarily.

[0040] By operating each cell of the fuel cell stack at least temporarily with a voltage below 0 volts, effective conditioning of the entire fuel cell stack or of each cell of the fuel cell stack is achieved.

[0041] According to a second aspect, the presented invention relates to a device for conditioning a fuel cell stack.

[0042] The presented device comprises a fuel supply system, a blower, a computing unit and an electrical load.

[0043] The computing unit is configured to adjust the fuel cell stack and the blower in such a way that they execute one possible embodiment of the presented method.

[0044] In the context of the presented invention, a computing unit is understood to be a computer, a processor, a control unit, or any other programmable circuit. R.416149

[0045] - 6 -

[0046] It may be provided that the computing unit is further configured to adjust the electrical load in such a way that, in the second operating mode, each cell of the fuel cell stack is operated at least temporarily with a voltage below 0 volts.

[0047] Advantages described in detail with respect to the method for conditioning a fuel cell stack for a fuel cell system according to the first aspect of the invention apply equally to the device for conditioning a fuel cell stack according to the second aspect of the invention and vice versa.

[0048] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description can each be essential to the invention individually or in any combination.

[0049] They each show schematically:

[0050] Figure 1 shows a possible embodiment of the presented method,

[0051] Figure 2 shows a stress profile during the process according to Fig. 1 and

[0052] Figure 3 shows a device for conditioning a fuel cell stack.

[0053] Figure 1 shows a method 100 for conditioning a fuel cell stack for a fuel cell system.

[0054] Procedure 100 includes a debit 101 in which an electrical load is applied to the fuel cell stack.

[0055] Furthermore, the process 100 includes a first operating step 103 in which the fuel cell stack is operated in a first operating mode, in which an air supply is provided to supply a cathode subsystem of the R.416149

[0056] - 7 -

[0057] The fuel cell stack is actively operated with air while the load is applied.

[0058] Furthermore, the procedure 100 includes a second operating step 105 in which the fuel cell stack is operated in a second operating mode in which the air supply is deactivated while the load is applied.

[0059] Furthermore, the procedure 100 includes a switching step 107 in which the first operating mode and the second operating mode are repeatedly switched cyclically.

[0060] Figure 2 shows a diagram 200 which spans time on its abscissa and a voltage on a cell voltage of a cell of a fuel cell stack on its ordinate.

[0061] A curve represented by measuring points 201 shows a change in voltage during the second operating step 105, in which the fuel cell stack is operated in a second operating mode in which the air supply is deactivated while the load is applied.

[0062] It is evident that the trend of measurement points 201 assumes negative values ​​at time t1, resulting in electrode pumping, in which hydrogen is transferred from the anode side of the cell to its cathode side. Due to this electrode pumping, the cell is conditioned particularly effectively and quickly, e.g., in just a few minutes, and especially in under 10 minutes.

[0063] Fig. 3 shows a device 300 for conditioning a fuel cell stack 310.

[0064] The device 300 comprises a fuel supply system 301 for metering hydrogen into an anode subsystem or an anode compartment 312 of the fuel cell stack 310, a blower 303 for conveying air into a cathode subsystem or a cathode compartment 314 of the R.416149

[0065] - 8 -

[0066] fuel cell stack 310, a computing unit 305 and an electrical load 307.

[0067] The computing unit 305 is configured to adjust the fuel cell stack 310, the fuel supply system 301 and the blower 303 so that they perform the procedure 100 according to Fig. 1.

Claims

R.416149 - 9 - Claims 1. Method (100) for conditioning a fuel cell stack (310) for a fuel cell system, wherein the method (100) comprises: Applying (101) an electrical load to the fuel cell stack (310), Operating (103) the fuel cell stack (310) in a first operating mode in which an air supply to provide air to a cathode subsystem (314) of the fuel cell stack (310) is actively operated while the load is applied, operating (105) the fuel cell stack (310) in a second operating mode in which the air supply is deactivated while the load is applied, and repeatedly cyclically switching (107) between the first operating mode and the second operating mode.

2. Method (100) according to claim 1 , characterized in that the electrical load is selected such that a voltage is established on the fuel cell stack (310) which is at most 10 volts, in particular at exactly 0 volts.

3. Method (100) according to claim 1 or 2, characterized in that a 4-quadrant load is selected as the electrical load.

4. Method (100) according to claim 3, characterized in that the electrical load is selected such that a voltage is established on the fuel cell stack (310) which is below 0 volts. R.416149 - 10 - 5. Method (100) according to one of the preceding claims, characterized in that during the second operating mode a hydrogen concentration in the cathode subsystem (314) is reduced to a value between The concentrations are set to 1% by volume and 30% by volume.

6. Method (100) according to one of the preceding claims, characterized in that the electrical load is between 1.5 A / cm² 3 and 2 A / cm 3 lies.

7. Method (100) according to one of the preceding claims, characterized in that the air system is deactivated by deactivating a blower (303) of the air system.

8. Method (100) according to one of the preceding claims, characterized in that the air system is deactivated by closing cathode shut-off valves of the fuel cell stack (310).

9. Method (100) according to one of the preceding claims, characterized in that in the second operating mode each cell of the fuel cell stack (310) is operated at least temporarily with a voltage of less than 0 volts.

10. Device (300) for conditioning a fuel cell stack, the device (300) comprising: a fuel supply system (301), a blower (303), a computing unit (305) and an electrical load (307), wherein the computing unit (305) is configured to control the fuel cell stack (310), the fuel supply system (301) and R.416149 - 11 - to adjust the blower (303) such that it performs a method (100) according to any one of claims 1 to 9.

11. Device (300) according to claim 10, characterized in that the computing unit (305) is further configured to adjust the electrical load (307) such that in the second operating mode each cell of the fuel cell stack (310) is operated at least temporarily with a voltage of less than 0 volts.

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