Fuel cell system and method for operating a fuel cell system

Abstract

The invention relates to a method for operating a fuel cell system (2) in a freezing start mode, wherein the fuel cell system (2) comprises at least one fuel cell (26) having an anode (28) and a cathode (30); and a jet pump (22) which is designed to return gas exiting the anode (28) of the at least one fuel cell (26) into the anode (28) of the at least one fuel cell (26) together with the hydrogen mass flow (mH2) in a manner driven by a hydrogen mass flow (mH2) supplied to the anode (28) of the at least one fuel cell (26). In the freezing start mode, the method comprises limiting the hydrogen mass flow (mH2) supplied to the jet pump (22) such that the hydrogen mass flow lies below a specified recirculation threshold of the jet pump (22) such that no relevant recirculation of gases exiting the anode (28) of the fuel cell (26) into the anode (28) of the fuel cell (26) takes place during the freezing start mode.

Description

[0001] R. 412806 - 1 - Description Method for Operating a Fuel Cell System The invention relates to a fuel cell system and a method for operating a fuel cell system, in particular for operating a fuel cell system in a freeze-start mode. The device also relates to a motor vehicle equipped with a fuel cell system according to the invention. Prior Art To reduce the environmentally harmful emissions of motor vehicles, electric motors are increasingly being used in motor vehicles instead of combustion engines. To supply the electric motors in the motor vehicles with electrical energy, batteries or fuel cell systems powered by hydrogen can be used. To increase the efficiency of a fuel cell system, the fuel cells are often operated with so-called anode recirculation.In this process, gas escaping from the anode of the fuel cell is returned to the anode inlet via a so-called anode recirculation circuit. However, during a freeze-start of a fuel cell system with anode recirculation, water and / or ice present in the anode recirculation circuit can enter the anode of the fuel cell and freeze there, which can impair the fuel cell's functionality. It is therefore an object of the invention to provide a fuel cell system and a method for operating a fuel cell system in freeze-start mode that makes it possible to prevent this from happening during freeze-start operation. 2 -Water and / or ice are introduced into the anode(s) of the fuel cell(s) of the fuel cell system. Disclosure of the invention: The invention comprises a method for operating a fuel cell system in freeze-start mode, wherein the fuel cell system comprises at least one fuel cell and a jet pump. The at least one fuel cell has an anode and a cathode. The jet pump is configured to return, driven by a hydrogen mass flow supplied to the anode of the at least one fuel cell, gas exiting the anode of the at least one fuel cell together with the hydrogen mass flow to the anode of the at least one fuel cell.A method according to the invention comprises limiting the hydrogen mass flow supplied to the jet pump during freeze-start operation in such a way that it lies below a predetermined recirculation threshold of the jet pump, so that during freeze-start operation no relevant return ("recirculation") of gases exiting the anode of the at least one fuel cell to the anode of the at least one fuel cell takes place.The invention also comprises a fuel cell system with at least one fuel cell having an anode and a cathode; a hydrogen supply valve configured to regulate a hydrogen mass flow supplied to the anode of the at least one fuel cell; a jet pump arranged between the hydrogen supply valve and the anode of the at least one fuel cell, configured to return gas discharged from the anode of the at least one fuel cell, together with the hydrogen mass flow, to the at least one fuel cell, driven by a hydrogen mass flow supplied to the anode of the at least one fuel cell; and a purge valve arranged at the outlet of the anode of the at least one fuel cell.The fuel cell system also includes a control device designed to control the hydrogen supply valve and the purge valve in such a way that the fuel cell system performs a method according to the invention R. 412806 -. 3 -for operating a fuel cell system in a freeze-start mode. The invention also includes a motor vehicle with at least one electric motor and a fuel cell system according to the invention, which is designed and configured to supply the electric motor with electrical energy. A fuel cell system according to the invention and a method according to the invention for operating a fuel cell system have at least the following advantages: Short drying time after shutdown, since water remaining in the anode recirculation circuit does not need to be completely removed. This also results in lower purge / hydrogen losses during anode drying. Increased service life of the fuel cell(s) and a reduction in hydrogen consumption. Prevention of circulation-induced anode icing. This prevents cell degradation, which further increases the service life of the fuel cells.Exemplary embodiments of the invention enable a robust freeze-start strategy, resulting in reliable starting behavior and thus higher customer satisfaction. Monitoring of the fuel cell voltage (CVM) can be omitted. This reduces the costs of the fuel cell system. However, if a system for monitoring the fuel cell voltage (CVM) is present, the degree of icing of individual fuel cells can be determined by monitoring the cell voltages during purging operation, thereby further improving the freeze-start performance. In one embodiment, the electrical current drawn from the at least one fuel cell during freeze-start operation is limited to prevent [R. 412806 -]. 4 - This results from recirculation by the jet pump. The electrical current density can be expected to reach a value in the range of 0.1 A / cm². 2 and 0.3 A / cm 2The method is limited. In one embodiment, the fuel cell system has a purge valve, and the method comprises purging the at least one fuel cell by temporarily opening the purge valve. The hydrogen mass flow rate supplied to the anode of the at least one fuel cell is kept constant during and after the purge is initiated. In other words, the hydrogen mass flow rate supplied to the anode of the at least one fuel cell is not changed when the purge valve is opened. This prevents the purge from triggering an undesirable anode recirculation during freeze-start operation. In another embodiment, the method comprises reducing the electrical current drawn from the at least one fuel cell during the purge process to prevent the purge from triggering an undesirable anode recirculation during freeze-start operation.In one embodiment, the method comprises reducing the electrical current drawn from the at least one fuel cell during the purging process to such an extent that the gas pressure at the anode of at least one fuel cell is at least 100 mbar, and in particular at least 100 mbar to 200 mbar, greater than the gas pressure at the cathode of at least one fuel cell. This prevents the mass flow through the purging valve from stopping. In another embodiment, the method comprises reducing the electrical current drawn from the at least one fuel cell before opening the purging valve. The method may in particular comprise reducing the electrical current drawn from the at least one fuel cell for 100 ms to 1000 ms before opening the purging valve.In one embodiment, the method comprises reducing the mass flow through the cathode of the at least one fuel cell during purging, analogous to the reduction of the electric current. This prevents the cell voltage of the at least one fuel cell from briefly dropping below the R. 412806 - level. 5 -This would reduce heat production and increase the risk of cathode icing. However, particularly in the case of individual very low cell voltages, it can also be beneficial as a recovery and regeneration measure to not reduce the mass flow through the cathode of at least one fuel cell during purging, thereby allowing the cell voltage to rise briefly during the purging process. A measured increase in cell voltage can also be used to determine the extent to which individual cells are already iced on the cathode side.In one embodiment, the method further comprises determining, in particular calculating, the maximum electrical current that can be drawn from the at least one fuel cell during freeze-start operation without activating recirculation by the jet pump, and limiting the electrical current drawn from the at least one fuel cell during freeze-start operation to this maximum electrical current. When determining / calculating the maximum electrical current that can be drawn from the at least one fuel cell during freeze-start operation, purging and the interaction of the purging with the hydrogen mass flow supplied to the at least one fuel cell can be taken into account. This allows the freeze-start operation of a fuel cell system according to the invention to be further improved.In one embodiment, the method comprises controlling the purge valve such that the increased amount of hydrogen supplied to the at least one fuel cell, caused by the opening of the purge valve, is limited. In one embodiment, the purge valve is a stepwise or continuously variable purge valve, and the method comprises controlling the purge valve so that it opens fully or partially to adjust the mass flow through the purge valve. R. 412806 -. 6 -In one embodiment, the purge valve is a switching valve that can only be switched between a fully open state and a fully closed state, and the method comprises periodically controlling the purge valve so that it opens and closes periodically in order to vary the average mass flow rate through the purge valve. An embodiment of the invention is described below with reference to the accompanying figures. Brief description of the figures: Figure 1 shows a schematic view of a motor vehicle with a fuel cell system according to the invention. Figure 2 shows a schematic view of a fuel cell system according to the invention. Figure 3 shows a schematic representation of the mass flow rate delivered by the jet pump as a function of the pressure difference at the anode. Figure 4 shows a flowchart illustrating the sequence of a method according to the invention.Figure description: Figure 1 shows a schematic view of a motor vehicle 1 driven by an electric motor 5, which is supplied with electrical energy by a fuel cell system 2. The motor vehicle 1 has four wheels 3 and at least one electric motor 5, which is provided for driving at least two of the four wheels 3 of the motor vehicle 1. The electric motor 5 can also be provided for driving all four wheels 3 of the motor vehicle 1. In an alternative embodiment, which is not explicitly shown in the figures, an electric motor 5 can be provided at at least one of the wheels 3, in particular at each of the wheels 3, of the motor vehicle 1 for driving the respective wheel 3. R. 412806 -. 7 -The electric motor 5 is supplied with electrical energy via a motor control unit 7, which is provided by the fuel cell system 2. A fuel cell system 2 according to the invention can also be used in motor vehicles 1 that have more or fewer than four wheels 3. Figure 2 shows a schematic view of a fuel cell system 2 according to the invention. The fuel cell system 2 comprises a hydrogen reservoir 12, for example a hydrogen tank 12, which provides hydrogen gas for operating the fuel cell system 2. Through a shut-off valve 14, the hydrogen gas from the hydrogen reservoir 12 is fed to a heating device 16, which makes it possible to heat the hydrogen gas to a desired temperature.From the heating device 16, the hydrogen gas passes through a pressure regulator 18, which allows the desired pressure of the hydrogen gas to be set, to a hydrogen supply valve ("HGI valve") 20, which allows the supply of the hydrogen gas to at least one fuel cell 26 of the fuel cell system 2 to be regulated. The hydrogen gas is supplied, in particular, to an anode 28 of the at least one fuel cell 26. The at least one fuel cell 26 also includes a cathode 30, to which oxygen, for example in the form of ambient air, is supplied via an oxygen supply system not explicitly shown in Figure 2. A membrane 24, in particular a polymer electrolyte membrane 24, is arranged between the anode 28 and the cathode 30 of the at least one fuel cell 26. For the sake of simplicity, only a single fuel cell 26 is shown in Figure 1. A fuel cell system 2 according to the invention can also be R. 412806-.8 - The fuel cell 26 comprises several fuel cells, which can be arranged in a fuel cell stack. The hydrogen and oxygen supplied to the fuel cell 26 react within the fuel cell 26 to form water (H2O). This reaction releases electrical energy, which is used by the fuel cell 26 as an electric current I. Stack and voltage U Stack is provided. A jet pump 22 is provided between an outlet 20b of the hydrogen supply valve 20 and an inlet 28a of the anode 28 of the fuel cell 26. A first inlet 22a of the jet pump 22 is fluidically connected to an outlet 20b of the hydrogen supply valve 20, so that the jet pump 22 is supplied with a hydrogen mass flow m Ḣ2, which flows from the outlet 20b of the hydrogen supply valve 20 through the jet pump 22 to the inlet 28a of the anode 28 of the fuel cell 26, is driven. A second inlet (suction inlet) 22b of the jet pump 22 is fluidically connected via an anode gas return line 32 to an outlet 28b of the anode 28, so that when the jet pump 22 is operated, gas exiting the anode 28 through outlet 28b is drawn through the anode gas return line 32 into the suction inlet 22b of the jet pump 22 and, together with the freshly supplied hydrogen gas, is fed to the inlet 28a of the anode 28. Furthermore, a purge valve 34 is provided at the outlet 28b of the anode 28, which allows the anode 28 to be purged by opening the purge valve 34. The purge valve 34 can be a stepped or continuously adjustable purge valve 34, which allows the purge mass flow rate m flowing through the purge valve 34 to be controlled. H ̇ 2,PurgeThe flow rate can be varied in stages or continuously by varying the geometry of the flushing valve 34. Alternatively, the flushing valve can be a switching valve that can only be switched between a fully open state and a fully closed state. In this case, the flow rate averaged over time can be varied by the flushing valve R. 412806 - 9 - 34 flowing flushing mass flow m H ̇ 2,PurgeThe flow rate can be varied by controlling the purge valve 34 to open and close periodically, with the opening time of the purge valve 34 being adjusted in the duty cycle to the desired flow rate through the purge valve 34. The fuel cell system 2 also includes a control device 36, which is configured to control the valves 14, 20, the heating device 16, the pressure regulator 18, and the purge valve 34 in order to operate the fuel cell system 2 in a desired operating mode with predefined operating parameters. During a freeze start of the fuel cell system 2, it is desirable to prevent as much recirculation of gas as possible from the anode 28 of the fuel cell 26 through the anode gas return line 32 and the jet pump 22 into the inlet 28a of the anode 28, so that no water or ice from the anode circuit can enter the anode 28 of the fuel cell 26.This is achieved by appropriately controlling the hydrogen supply valve 20 to determine the hydrogen mass flow rate m supplied to the jet pump 22 during freeze-start operation. HThe circulation is limited so that it lies below a predetermined circulation threshold of the jet pump 22. This means that during freeze-start operation, no relevant recirculation of gases exiting the anode 28 of the fuel cell 26 into the anode 28 of the fuel cell 26 occurs. In this way, it can be reliably prevented that water or ice from the recirculation circuit enters the anode 28 of the fuel cell 26. The circulation threshold can be determined during the development phase of the jet pump 22 or the fuel cell system 2 by calculations, simulations, or component tests and, if necessary, verified by measurements during the application phase of the fuel cell system 2 on a test bench equipped with additional measuring technology. A suitable measurement parameter for this purpose is the pressure difference Δp. Anbetween input 28a and output 28b of anode 28, which can be determined by existing or additional pressure sensors. Alternatively, this pressure difference Δp can be used. An Measured in real-world operation and used to determine the area below the recirculation threshold. R. 412806 - 10 - Theoretical calculations and simulations for determining the circulation threshold can incorporate geometric parameters of the jet pump 22, such as its diameter, angle, and / or length, as well as surface properties and operating conditions, such as the inlet pressure at the hydrogen metering valve 20 and the gas composition in the recirculation circuit (concentrations of H2, N2, water vapor), and temperatures in the gas phase of the recirculation circuit. Figure 3 shows a schematic representation of the mass flow rate m delivered by the jet pump 22 through the anode gas return line 32. R ̇ as a function of the pressure difference Δp Anbetween the inlet 28a and the outlet 28b of the anode 28. Below a minimum pressure difference Δp specified by the design of the jet pump 22. minThe recirculation capacity of the jet pump 22 is so low that it can be disregarded. In this range, there is no risk of water and / or ice being conveyed through the recirculation circuit to the inlet 28a of the anode 28 of the fuel cell 26. The absence of recirculation during a freeze start is unproblematic, since the nitrogen level in the anode 28 has not yet risen shortly after start-up and / or a sufficiently high overall pressure can ensure that a sufficiently high hydrogen partial pressure is always present at the membrane 24 of the fuel cell 26. Water produced by the operation of the fuel cell 26 initially remains in the cathode 30 at low temperatures, especially below freezing, and freezes there.Only at higher temperatures of the fuel cell 26, especially at temperatures above 30°C, does water bound in the membrane 24 evaporate on the anode side of the membrane 24 and can then freeze at the still-cold outlet areas, leading to blockages. Therefore, the risk of icing of the anode 28 by water produced on the cathode side of the fuel cell 26 is low as long as the fuel cell 26 has not yet heated up significantly. R. 412806 -. 11 -Figure 4 shows a flowchart illustrating the sequence of a method according to the invention for operating a fuel cell 26 in freeze-start mode. After starting the freeze-start operation in step 100, step 200 first checks whether a purging or drainage process is currently being carried out on the at least one fuel cell 26 and whether the purging valve 34 or a drain valve (not shown in the figures) is open. If this is not the case, step 300 is skipped and the method continues with step 400. In step 400, it is checked whether the hydrogen mass flow rate m H ̇2 below a predetermined recirculation threshold m m ̇ ax lies (m H ̇2< m m ̇ ax If this is the case, the current draw I Stack from at least one fuel cell 26 and thus also the hydrogen supply m HThe hydrogen mass flow rate m is increased to the anode 28 of the fuel cell 26 in step 500. Steps 200, 400, and 500 are repeated cyclically until, in step 400, it is determined that the hydrogen mass flow rate m H ̇2 the specified recirculation threshold mṁax has been reached or exceeded (mḢ2 ≥ mṁax). In this case, the current draw I Stack from at least one fuel cell 26 and thus also the hydrogen mass flow m H The hydrogen mass flow rate is reduced again to the anode 28 of the fuel cell 26 in order to achieve a certain level. H ̇2 the specified recirculation threshold m m ̇ ax does not exceed. If, in step 200, it is determined that a purging or drainage process is being carried out on the at least one fuel cell 26, with the purging valve 34 or the drainage valve open, the current draw I StackThe current draw from at least one fuel cell 26 is directly reduced, since a constant current draw with the purge valve 34 / drain valve open would result in an increased hydrogen supply from the hydrogen reservoir 12. This could initiate an undesirable recirculation of gas from the outlet 28b of the anode 28 of the fuel cell 26 through the anode gas return line 32 and the jet pump 22 during a freeze start. R. 412806 - 12 - The method for operating the fuel cell system 2 may in particular include the electrical current I extracted from the at least one fuel cell 26 during a rinsing or dewatering process. Stack to reduce too much so that the gas pressure p AnThe pressure at the anode 28 of the fuel cell 26 must be at least 100 mbar, and in particular between 100 mbar and 200 mbar, greater than the gas pressure pKat at the cathode 40 of the fuel cell 26, as otherwise there is a risk that the purging or dewatering process will cease. It is advantageous if the electrical current I drawn from the at least one fuel cell 26 Stack The flow rate is reduced before the purge valve 34 is opened. This can lead to a brief drop in the hydrogen mass flow rate. H2 from the hydrogen supply valve 20 enters the jet pump 22. However, this is unproblematic for the operation of the fuel cell system 2 and the recirculation through the anode gas return line 32. The electrical current drawn from the at least one fuel cell can, for example, be reduced 100 ms to 1000 ms before the purge valve opens. In the case of cathode operation with air depletion to increase heat production, it can also be advantageous if the oxygen mass flow through the cathode 39 is briefly reduced analogously to the electrical current I. Stack, which is drawn from the fuel cell 26, is reduced. Otherwise, the cell voltage of the fuel cell 26 would briefly increase, which would reduce the heat production of the fuel cell 26 and thus increase the risk of cathode 30 icing. On the other hand, particularly in the case of individual, very low cell voltages, it can be useful as a recovery and regeneration measure to briefly increase the cell voltages during purging. Optionally, such a sudden increase in cell voltage can be used to detect the extent to which the cathodes 30 of individual fuel cells 26 are already iced. R. 412806 - 13 - The freeze-start behavior of the fuel cell system 2 can be further improved by reducing the maximum electrical current I Stack,maxis determined, which can be taken from the at least one fuel cell 26 without increasing the recirculation to such an extent that there is a risk of unacceptably high water ingress and thus a risk of icing at the anode 28, and the electrical current I taken from the fuel cell 26 or from the fuel cell stack Stack to the maximum electric current I thus determined Stack,max is limited: I Stack ≤ I Stack,max The maximum permissible water ingress is determined experimentally and / or through simulations during the development / application of the system and stored in the control device 36 as a fixed limit or in a table depending on state variables, such as the electrical load. For the hydrogen mass flow rate m H ̇ 2,HGI , which flows through the hydrogen supply valve 20, applies in normal operation, i.e. with the purge valve 34 closed: and in flushing mode, i.e. with the flushing valve 34 open: This is m H ̇2,Consumedder mass flow rate of the hydrogen consumed in the chemical reaction in the at least one fuel cell 26. m H ̇2,Consumedergült is derived from the Faraday equation and is proportional to the electric current I Stack , which is taken from at least one fuel cell 26 or the fuel cell stack. m H ̇2,Crossover,Leakage: the mass flow lost through losses, e.g., leaks, in fuel cell system 2. m H ̇2,Crossover,Leakage during the freezing start not significantly influenced. R. 412806 - 14 - m H ̇ 2,Purge is the mass flow rate of hydrogen that exits through the purge valve 34 during purge operation. m H ̇ 2,Purge depends on the flushing strategy used and the flushing valve 34. For the maximum electrical current I Stack,max, which, without recirculation, can be taken from the fuel cell 26 or the fuel station stack, then applies in normal operation, with the purge valve 34 closed: and during rinsing operation, with the rinsing valve 34 open: In practical application, the maximum current I depends Stack,max the specific geometry of the hydrogen supply valve 20, the jet pump 22, and the fuel cell(s) 26, as well as the materials used, particularly their interaction with water droplets, are crucial. Preferably, the maximum flow rate m is controlled by actuating the purge valve 34. HThe pressure of the hydrogen supply valve 20 is significantly limited compared to normal operation in order to limit the hydrogen supply valve 20 and thus also the recirculation capacity. To achieve this, it is advisable to keep the pressure differential between the inlet 20a and the outlet 20b of the hydrogen supply valve 20 as small as possible, especially below the critical pressure ratio of 2, and / or to purge more frequently but only briefly. As soon as the temperature of at least one fuel cell 26 is reliably above a predetermined freezing temperature level, e.g., when a coolant inlet temperature is above 5°C or more, the freeze-start operation is terminated, and the fuel cell system 2 is operated in normal operation with an active recirculation circuit.

Claims

R. 412806 - 15 -Claims 1. Method for operating a fuel cell system (2) in a freeze-start operation, wherein the fuel cell system (2) comprises: at least one fuel cell (26) with an anode (28) and with a cathode (30); and a jet pump (22) configured to return, driven by a hydrogen mass flow (mḢ2) supplied to the anode (28) of the at least one fuel cell (26), gas exiting from the anode (28) of the at least one fuel cell (26) together with the hydrogen mass flow (mḢ2) to the anode (28) of the at least one fuel cell (26);wherein the method comprises limiting the hydrogen mass flow rate (mḢ2) supplied to the jet pump (22) during freeze-start operation such that it lies below a predetermined recirculation threshold of the jet pump (22), so that no relevant recirculation of gases or liquids exiting the anode (28) of the fuel cell (26) or other components (22, 32) of the anode circuit into the anode (28) of the fuel cell (26) occurs during freeze-start operation.

2. Method according to claim 1, wherein the method comprises limiting the electric current (I) drawn from the at least one fuel cell (26) during freeze-start operation; Stack ) to limit, the method in particular comprising limiting the electric current density to a value between 0.1 A / cm² 2 and 0.3 A / cm 2to limit.

3. Method according to claim 1 or 2, wherein the fuel cell system (2) has a purge valve (34) and wherein the method comprises cleaning the at least one fuel cell (26) by at least temporarily opening the R. 412806 - 16 - to flush the flushing valve (34) and to keep the hydrogen mass flow rate (mḢ2) supplied to the anode (28) of the at least one fuel cell (26) constant during and after the initiation of the flushing.

4. Method according to claim 3, wherein the method comprises, during the flushing process, controlling the electrical current (I) drawn from the at least one fuel cell (26). Stack ) to reduce; wherein the method in particular comprises reducing the electrical current (I) withdrawn from the at least one fuel cell (26) during the purging process Stack ) to reduce too much so that the gas pressure (p An) in the anode (28) of the fuel cell (26) is at least 100 mbar greater than the gas pressure at the cathode (30) of the fuel cell (26).

5. Method according to claim 4, wherein the method comprises extracting the electric current (I) from at least one fuel cell (26). Stack ) before opening the purge valve (34), wherein the method particularly comprises reducing the electrical current (IStack) drawn from the at least one fuel cell (26) 100 ms to 1000 ms before opening the purge valve (34).

6. Method according to one of claims 4 or 5, wherein the method comprises reducing the mass flow through the cathode (30) of the at least one fuel cell (26) during purging analogously to reducing the electrical current (I). Stack ) to reduce.

7. Method according to any one of claims 3 to 6, wherein the method comprises reducing the maximum electric current (I Stack,max), which can be taken from the at least one fuel cell (26) during the freeze-start operation without activating the recirculation by the jet pump (22), in particular to calculate, and to determine the electric current (I Stack ), which is taken from the at least one fuel cell (26) during freeze-start operation, to the maximum electrical current (I) thus determined Stack,max ) to limit.

8. Method according to claim 7, wherein when determining the maximum electric current (I Stack,max ) in particular the purging and the interaction of the purging with the hydrogen mass flow (mḢ2), which R. 412806 - 17 -9. A method according to any one of claims 3 to 8, wherein the method comprises controlling the purge valve (34) such that the increased amount of hydrogen supplied to the at least one fuel cell (26) caused by purging is limited.

10. A method according to claim 9, wherein the purge valve (34) is a stepwise or continuously adjustable purge valve (34) and wherein the method comprises controlling the purge valve (34) so ​​that it opens fully or partially.

11. A method according to claim 9, wherein the purge valve (34) is a switching valve and wherein the method comprises periodically controlling the purge valve (34) so ​​that it opens and closes periodically. 12.Fuel cell system (2) comprising: at least one fuel cell (26) with an anode (28) and a cathode (30); a hydrogen supply valve (20) configured to regulate a hydrogen mass flow (mḢ2) supplied to the anode (28) of the at least one fuel cell (26); a jet pump (22) arranged between the hydrogen supply valve (20) and the anode (28) of the at least one fuel cell (26) and configured to be driven by a hydrogen mass flow (m. H ̇2), which is supplied to the anode (28) of the at least one fuel cell (26), gas which is discharged from the anode (28) of the at least one fuel cell (26), together with the hydrogen mass flow (m H 2) to the at least one fuel cell (26); a purge valve (34) arranged at the outlet (28b) of the anode (28) of the at least one fuel cell (26); and R. 412806 - 18 -a control device (36) configured to control the hydrogen supply valve (20) and the purge valve (34) such that the fuel cell system (2) performs a method for operating a fuel cell system (2) in a freeze-start mode according to one of the preceding claims.

13. Fuel cell system (2) according to claim 12, wherein the purge valve (34) is a single-stage or continuously adjustable purge valve (34).

14. Fuel cell system according to claim 13, wherein the purge valve (34) is a switching valve that can be switched between a fully closed state and a fully open state.

15. Motor vehicle (1) with at least one electric motor (5) and a fuel cell system (2) according to claims 12 to 14, wherein the fuel cell system (2) is designed and configured to supply the electric motor (5) with electrical energy.

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