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

Abstract

The invention presented relates to a method (100) for conditioning a fuel cell stack (310) for a fuel cell system. The presented procedure (100) includes: - 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 is actively operated to supply a cathode subsystem (314) of the fuel cell stack (310) with air 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 - repeated cyclic switching (107) between the first operating mode and the second operating mode.

Description

[0001] The presented invention relates to a method and a device for conditioning a fuel cell stack for a fuel cell system. State of the art

[0002] A newly assembled PEM fuel cell stack (PEM-FC), called a "stack", requires a conditioning process to achieve its full performance.

[0003] 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.

[0004] For conditioning, fuel cell stacks are usually operated on a test bench according to a special program.

[0005] Typically, the conditioning process involves cyclical switching between a high-current state and a currentless state. This serves to create a constant 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, with this alternation significantly accelerating the formation of new channels.

[0006] At the same time, the cells also pass through specific potential states due to the load change, which is particularly beneficial for catalyst activity. Disclosure of the invention

[0007] 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.

[0008] The invention presented here is particularly useful for the time- and energy-efficient conditioning of a fuel cell stack for a fuel cell system.

[0009] 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.

[0010] 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.

[0011] 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 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, thereby achieving particularly rapid activation of the fuel cell stack.

[0012] In the second operating mode, airflow through the cathode subsystem is completely stopped, and any residual oxygen remaining in the cathode subsystem is consumed, in particular, completely consumed. Consequently, the current flow from the fuel cell stack, as well as water and heat production, cease.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] The voltage at the fuel cell stack can be adjusted, for example, via a minimum voltage limit of the electrical load.

[0017] It may also be stipulated that a 4-quadrant load is selected as the electrical load.

[0018] By using a 4-quadrant load as an electrical load, negative cell voltages or a negative voltage across 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 fuel cell stack continuously at a voltage below 0 volts. Once the voltage across the fuel cell stack falls below 0 volts, the 4-quadrant load "engages" and provides the electrons for the hydrogen pumping effect. This causes all cells of the fuel cell stack to pump hydrogen, thus effectively activating 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. Beyond the negative voltage limit, e.g.,In the range of -10 volts to 0 volts, the intensity of the hydrogen pump effect during the second operating mode can be defined or adjusted.

[0019] 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.

[0020] 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%.

[0021] 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.%.

[0022] It may still be provided that the electrical load is between 1.5 A / cm² 3 and 2 A / cm 3 lies.

[0023] 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.

[0024] It may also be possible to deactivate the air system by deactivating a fan of the air system.

[0025] 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.

[0026] It may also be provided that the air system is deactivated by closing the cathode shut-off valves of the fuel cell stack.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] According to a second aspect, the presented invention relates to a device for conditioning a fuel cell stack.

[0031] The presented device comprises a fuel supply system, a blower, a computing unit and an electrical load.

[0032] 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.

[0033] In the context of the presented invention, a computing unit is to be understood as a computer, a processor, a control unit or any other programmable circuit.

[0034] 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.

[0035] Advantages described in detail for the method of 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.

[0036] 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.

[0037] They each show schematically: Fig. 1. A possible design of the presented procedure, Fig. 2 a voltage profile during the procedure according to Fig. 1 and Fig. 3 a device for conditioning a fuel cell stack.

[0038] In Fig. Figure 1 shows a method 100 for conditioning a fuel cell stack for a fuel cell system.

[0039] The procedure 100 includes a load step 101 in which an electrical load is applied to the fuel cell stack.

[0040] Furthermore, the procedure 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 actively operated to supply a cathode subsystem of the fuel cell stack with air while the load is applied.

[0041] 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.

[0042] Furthermore, the procedure 100 includes a switching step 107 in which the first operating mode and the second operating mode are repeatedly switched cyclically.

[0043] In Fig. 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.

[0044] 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.

[0045] 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.

[0046] In Fig. Figure 3 shows a device 300 for conditioning a fuel cell stack 310.

[0047] 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 fuel cell stack 310, a computing unit 305 and an electrical load 307.

[0048] The computing unit 305 is configured to adjust the fuel cell stack 310, the fuel supply system 301 and the blower 303 such that they perform the procedure 100 according to Fig. Execute step 1.

Claims

[1] Method (100) for conditioning a fuel cell stack (310) for a fuel cell system, the method (100) comprising: - 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 is actively operated to supply a cathode subsystem (314) of the fuel cell stack (310) with air 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 - repeated cyclic switching (107) between the first operating mode and the second operating mode. [2] Method (100) according to claim 1, characterized by, that the electrical load is chosen such that a voltage is applied to the fuel cell stack (310) which is at most 10 volts, in particular exactly 0 volts. [3] Method (100) according to claim 1 or 2, characterized by , that a 4-quadrant load is chosen as the electrical load. [4] Method (100) according to claim 3, characterized by , that the electrical load is selected such that a voltage is established at the fuel cell stack (310) which is below 0 volts. [5] Method (100) according to any one of the preceding claims, characterized by , that during the second operating mode a hydrogen concentration in the cathode subsystem (314) is set to a value between 1 vol% and 30 vol%. [6] Method (100) according to any one of the preceding claims, characterized by , that the electrical load is between 1.5 A / cm 3 and 2 A / cm 3 lies. [7] Method (100) according to any of the preceding claims, characterized by , that the air system is deactivated by deactivating a blower (303) of the air system. [8] Method (100) according to any one of the preceding claims, characterized by , that the air system is deactivated by closing the cathode shut-off valves of the fuel cell stack (310). [9] Method (100) according to any of the preceding claims, characterized by , 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 adjust the fuel cell stack (310), the fuel supply system (301) and the blower (303) such that they perform a method (100) according to any one of claims 1 to 9. [11] Device (300) according to claim 10, characterized by , 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 below 0 volts.

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