Method for operating a fuel cell system, and fuel cell system

Abstract

The invention relates to a method (100) for operating a fuel cell system (200), said method (100) comprising: introducing (101) hydrogen into an anode chamber (203) of a fuel cell stack (201) of the fuel cell system (200); applying (103) a starting voltage to the fuel cell stack (201), wherein the starting voltage has a reversed polarity relative to an operating voltage of the fuel cell stack (201); and opening (105) at least one cathode shut-off valve (207) of the fuel cell system (200). The invention also relates to a fuel cell system (200).

Description

[0001] R.415919

[0002] - 1 -

[0003] Description

[0004] title

[0005] Methods for operating a fuel cell system and fuel cell system

[0006] The present invention relates to an improved method for operating a fuel cell system and to a corresponding fuel cell system.

[0007] State of the art

[0008] Fuel cell systems are increasingly being used as alternative energy sources in various applications, particularly in the automotive industry. A faster and more efficient start-up of the fuel cell system is therefore of great importance to improve performance and user-friendliness.

[0009] For PEM fuel cells, a faster start-up time is particularly important, as it allows for a smaller battery to be used in the vehicle. This enables the fuel cell to provide power more quickly, eliminating the need to draw power from the battery.

[0010] A regular start-up of a fuel cell includes the following steps:

[0011] 1. Rinse the anode with hydrogen to increase the hydrogen concentration.

[0012] 2. Open the cathode valve to introduce air into the stack when sufficient hydrogen is present at the anode for operation. R.415919

[0013] - 2 -

[0014] However, a problem arises: during standstill and purging, hydrogen diffuses onto the cathode. This hydrogen is released when the cathode valve opens. Since only a limited hydrogen concentration is permissible in the exhaust gas, the cathode valves must be opened slowly to achieve sufficient dilution with air in the exhaust gas. This significantly increases the start-up time.

[0015] Disclosure of the invention

[0016] According to a first aspect of the invention, an improved method for operating a fuel cell system is provided, and according to a second aspect of the invention, a corresponding fuel cell system is provided. In particular, the invention is based on enabling a faster start-up of the fuel cell, which makes it possible to install a smaller battery in a corresponding vehicle.

[0017] The method for operating a fuel cell system according to the first aspect of the invention comprises introducing hydrogen into an anode compartment of a fuel cell stack of the fuel cell system, applying a starting voltage to the fuel cell stack, wherein the starting voltage has a polarity reversed relative to an operating voltage of the fuel cell stack, and opening at least one cathode shut-off valve of the fuel cell system.

[0018] In the context of the presented invention, an operating voltage is understood to be a voltage that is applied to a fuel cell stack during normal operation, i.e., when providing a requested power with optimized operating parameters.

[0019] This method enables a faster start-up of the fuel cell system. The hydrogen concentration in the cathode compartment before the opening of at least one cathode shut-off valve is reduced, and the safety during the fuel cell system start-up process is improved. R.415919

[0020] - 3 -

[0021] During anode purging, a voltage with the opposite polarity to that used during normal operation is preferably applied to the fuel cell stack. If there is sufficient hydrogen in the anode compartment and no oxygen in the cathode compartment, the hydrogen reacts on the cathode side when the starting voltage is applied and is then "pumped" back to the anode side or into the anode compartment. This principle is known as "electrochemical hydrogen pumping."

[0022] The reactions proceed as follows:

[0023] On the cathode side of the fuel cell stack or cathode compartment, which acts like an electrochemical anode:

[0024] H2 2H+ + 2e-

[0025] On the anode side of the fuel cell stack or the anode compartment, which acts like an electrochemical cathode:

[0026] 2H+ + 2e- H2

[0027] Accordingly, the anode compartment is purged with hydrogen, and after a short delay, the fuel cell stack is subjected to a negative voltage, ensuring that a necessary hydrogen concentration is already present in the anode compartment and that so-called "hydrogen pumping" occurs.

[0028] Once the required hydrogen concentration is reached in the anode compartment during purging, and hydrogen is pumped from the cathode compartment to the anode compartment, the cathode valves can be quickly opened to supply the fuel cell stack with air. The application of the negative starting voltage is then terminated.

[0029] If sufficient operating fluids are available, electricity can then be generated and power supplied by the fuel cell stack. R.415919

[0030] - 4 -

[0031] The reason for the accumulation of hydrogen in the cathode compartment is that the fuel cell stack has a very large surface area, allowing for diffusive gas exchange between the anode and cathode compartments. The driving force behind this process is the partial pressure difference between the individual gas components. This means that over a long shutdown period, the gas concentrations in the anode and cathode compartments equalize.

[0032] The goal when the system is switched off is to prevent oxygen from accumulating in the fuel cell stack, especially in the anode compartment, as this can damage the fuel cell stack during startup. To achieve this, the oxygen is released during the switched-off or deactivated state, and closed cathode shut-off valves prevent air from flowing into the cathode compartment or the fuel cell stack.

[0033] Since there is no oxygen in the cathode compartment when the unit is switched off, hydrogen can accumulate there as part of the partial pressure equalization process. If oxygen were present, it would react with hydrogen on the catalyst to form water.

[0034] Therefore, no voltage is initially applied. If hydrogen is added to the anode compartment during purging and the anode gas is recirculated, a high cell voltage results at the fuel cell stack if oxygen is present in the cathode compartment. If this is not the case, the described procedure can be carried out by applying the starting voltage.

[0035] During standby operation, the starting voltage can also be applied in the switched-off phase, i.e., during the standby phase or even before the purging process, in order to keep as much hydrogen as possible in the anode compartment.

[0036] Applying a voltage allows a current to flow in the reverse direction, which then causes the corresponding reaction, i.e., hydrogen pumping. R.415919

[0037] - 5 -

[0038] It can also be provided that the at least one cathode shut-off valve opens at a speed that is at least 20% higher than the speed at which the at least one cathode shut-off valve opens when the fuel cell system is started without the application of the start voltage. This enables even faster power delivery by the fuel cell system or a particularly fast start-up of the fuel cell system.

[0039] For example, it may be provided that at least one cathode shut-off valve, in particular all cathode shut-off valves, are opened at the highest possible speed.

[0040] Preferably, it can be provided that a hydrogen concentration in the anode compartment of the fuel cell stack is determined before the at least one cathode shut-off valve is opened, and that the at least one cathode shut-off valve is only opened if the hydrogen concentration in the anode compartment exceeds a predetermined anode threshold. This ensures a sufficient hydrogen concentration for the efficient operation of the fuel cell system. In particular, this prevents premature opening of the at least one cathode shut-off valve.

[0041] It can also be provided that, before opening at least one cathode shut-off valve, a hydrogen concentration in a cathode compartment of the fuel cell stack is determined, and that at least one cathode shut-off valve is only opened if the hydrogen concentration in the cathode compartment is below a predetermined cathode threshold. This ensures that the hydrogen has been successfully removed from the cathode. It can also increase safety when opening at least one cathode shut-off valve.

[0042] It can also be provided that the opening of at least one cathode shut-off valve occurs after a predetermined duration following the commencement of the application of the starting voltage to the fuel cell stack. The control of the fuel cell system's start-up process can thereby be R.415919

[0043] - 6 - can be simplified. Furthermore, this allows for a constant start time. The timing for opening the at least one cathode shut-off valve and applying the start voltage is optimized to ensure an efficient start process.

[0044] It can also be provided that the fuel cell stack is supplied with the starting voltage after a predetermined purge duration, following the initiation of hydrogen injection into the anode compartment. As previously mentioned, the timing for opening the at least one cathode shut-off valve and applying the starting voltage can be optimized to ensure an efficient start-up process. In particular, this ensures a sufficient hydrogen concentration in the anode compartment before the starting voltage is applied. Furthermore, this allows for the optimization of the start time of the electrochemical hydrogen pumping.

[0045] It may also be provided that after opening at least one cathode shut-off valve, the application of the start voltage to the fuel cell stack is stopped and the operating voltage is set on the fuel cell stack.

[0046] After opening at least one cathode shut-off valve, the start-up voltage is terminated and the normal operating voltage is set to allow a seamless transition to normal operation. This maximizes the efficiency of the fuel cell system.

[0047] It may also be provided that, prior to applying the start-up voltage to the fuel cell stack, a check is carried out in which, during the introduction of hydrogen into the anode compartment, the stack voltage applied to the fuel cell stack is determined and compared with a predetermined release threshold, whereby the process is aborted if the stack voltage exceeds the release threshold. R.415919

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[0049] Such a check before applying the starting voltage prevents potential damage to the fuel cell stack. In particular, it prevents the application of the starting voltage under unsuitable conditions. This increases safety and protects the fuel cell stack from damage.

[0050] It can also be envisaged that the procedure is carried out during a start-up phase of the fuel cell system and that the fuel cell stack is supplied with the start-up voltage after hydrogen has been introduced into the anode compartment. This optimizes the start-up process of the fuel cell system. In particular, it ensures that sufficient hydrogen is present in the anode before the start-up voltage is applied.

[0051] The procedure can be used both during a normal start-up phase and from a standby mode, which increases the flexibility of the system.

[0052] It can also be provided that, when the fuel cell system is switched to standby mode, the fuel cell stack is already supplied with the start voltage before hydrogen is introduced into the anode compartment. The advantage is that this enables even faster reactivation from standby mode.

[0053] According to a second aspect of the invention, a fuel cell system for converting energy is presented.

[0054] The presented fuel cell system comprises at least one fuel cell stack comprising a cathode compartment and an anode compartment, cathode shut-off valves movable between a closed position, in which they seal off the cathode compartment fluid-tight, and an open position, in which they allow fluid to flow through the cathode compartment, a hydrogen metering unit, a voltage source, and a computing unit, wherein the computing unit is configured to control the cathode shut-off valves, the hydrogen metering unit, and the voltage source. R.415919

[0055] - 8 - to control in order to carry out a method according to a first aspect of the invention.

[0056] 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.

[0057] Such a fuel cell system offers an integrated system for implementing an improved starting procedure for the fuel cell system.

[0058] The presented fuel cell system enables optimized control of all relevant components for an efficient start of the fuel cell system.

[0059] In summary, the present invention provides an improved method and system for operating a fuel cell system, enabling faster, more efficient, and safer start-up of the fuel cell system. This leads to improved performance and ease of use of fuel cell systems in various applications, particularly in the automotive industry.

[0060] This improved starting method contributes significantly to increasing the efficiency and practicality of fuel cell systems.

[0061] The fuel cell system is equipped with all the necessary components to efficiently carry out the described process.

[0062] The advantages of the fuel cell system are:

[0063] - It enables a faster start-up of the fuel cell system.

[0064] - The hydrogen concentration on the cathode can be reduced before opening the respective cathode shut-off valves.

[0065] - Safety during the start-up process of the fuel cell system is improved.

[0066] - The fuel cell system allows for the use of a smaller battery in a vehicle. R.415919

[0067] - 9 -

[0068] - Energy consumption during the start-up process of the fuel cell system is optimized.

[0069] This improved starting method contributes significantly to increasing the efficiency and practicality of fuel cell systems, especially in the automotive sector.

[0070] 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.

[0071] They each show schematically:

[0072] Figure 1 shows a possible embodiment of the presented method and

[0073] Figure 2 shows a possible embodiment of the presented

[0074] Fuel cell system.

[0075] Fig. 1 shows a method 100 for operating a fuel cell system 200 as shown, for example, in Fig. 2.

[0076] The method 100 comprises an introduction step 101 in which hydrogen is introduced into an anode compartment 203 of a fuel cell stack 201 of the fuel cell system 200, an application step 103 in which the fuel cell stack is supplied with a start voltage, wherein the start voltage has a polarity reversed relative to an operating voltage of the fuel cell stack, and an opening step 105 in which at least one cathode shut-off valve of the fuel cell system is opened.

[0077] Figure 2 shows a 200-unit fuel cell system for converting energy. R.415919

[0078] - 10 -

[0079] The fuel cell system 200 comprises at least one fuel cell stack 201, which includes an anode compartment 203 and a cathode compartment 205, cathode shut-off valves 207, which can be switched between a closed position, in which they seal off the cathode compartment 205 in a fluid-tight manner, and an open position, in which they allow flow through the

[0080] cathode space 205 with fluid, are movable, a hydrogen dosing unit 209 and a voltage source 211, in particular a bidirectional voltage source, such as a battery and a computing unit 213.

[0081] The computing unit 213 is configured to control the cathode shut-off valves 207, the hydrogen dosing unit 209 and the voltage source 211 in order to carry out the procedure 100 according to Fig. 1.

Claims

R.415919 - 11 - Claims 1. Method (100) for operating a fuel cell system (200), wherein the method (100) comprises: Introducing (101) hydrogen into an anode compartment (203) of a fuel cell stack (201) of the fuel cell system (200), applying (103) to the fuel cell stack (201) a starting voltage, wherein the starting voltage has a polarity reversed relative to an operating voltage of the fuel cell stack (201), and Opening (105) at least one cathode shut-off valve (207) of the fuel cell system (200).

2. Method (100) according to claim 1 , characterized in that at least one cathode shut-off valve (207) is opened at a speed that is at least 20% higher than the speed at which the at least one cathode shut-off valve (207) is opened when the fuel cell system (200) is started without applying the start voltage.

3. Method (100) according to claim 1 or 2, characterized in that before opening (105) the at least one cathode shut-off valve (207) a hydrogen concentration in the anode compartment (203) of the fuel cell stack (201) is determined and the at least one cathode shut-off valve (207) is only opened if the hydrogen concentration in the anode compartment (203) is above a predetermined anode threshold value.

4. Method (100) according to one of the preceding claims, characterized in that R.415919 - 12 - that before opening (105) the at least one cathode shut-off valve (207) a hydrogen concentration in a cathode chamber (205) of the fuel cell stack (201) is determined and that the at least one cathode shut-off valve (207) is only opened if the hydrogen concentration in the cathode chamber (205) is below a predetermined cathode threshold.

5. Method (100) according to claim 1 or 2, characterized in that the opening (105) of the at least one cathode shut-off valve (207) takes place after a predetermined duration following the commencement of the application of the start voltage to the fuel cell stack (201).

6. Method (100) according to one of the preceding claims, characterized in that the application of the starting voltage to the fuel cell stack (201) is initiated after a predetermined purging period following the initiation of the introduction of hydrogen into the anode compartment (203).

7. Method (100) according to one of the preceding claims, characterized in that after opening the at least one cathode shut-off valve (207) the imprinting of the start voltage onto the fuel cell stack (201) is terminated and the operating voltage on the fuel cell stack (201) is set.

8. Method (100) according to one of the preceding claims, characterized in that before applying (103) the fuel cell stack (201) with the start voltage, a check is carried out in which, during the introduction of hydrogen into the anode compartment (203), a stack voltage applied to the fuel cell stack (201) is determined and compared with a predetermined release threshold value, wherein, in the event that the stack voltage is above the release threshold value, the method (100) is terminated. R.415919 - 13 - 9. Method (100) according to one of the preceding claims, characterized in that the method (100) is carried out during a start-up phase of the fuel cell system (200) and the application of the start-up voltage to the fuel cell stack (201) takes place after hydrogen has been introduced into the anode space (203).

10. Method (100) according to one of claims 1 to 9, characterized in that, when the fuel cell system (200) is switched to standby mode, the fuel cell stack (201) is already supplied with the start voltage before hydrogen is introduced into the anode compartment (203).

11. Fuel cell system (200) for converting energy, wherein the fuel cell system (200) comprises: - at least one fuel cell stack (201) comprising a cathode compartment (205) and an anode compartment (203), - Cathode shut-off valves (207) which are movable between a closed position, in which they seal off the cathode chamber (205) in a fluid-tight manner, and an open position, in which they allow fluid to flow through the cathode chamber (205), - a hydrogen dosing unit (209), - a voltage source (211) and - a computing unit (213) wherein the computing unit (213) is configured to control the cathode shut-off valves (207), the hydrogen metering unit (209) and the voltage source (211) to carry out a method (100) according to any one of claims 1 to 10.

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