Method for determining resistance of at least one fuel cell, fuel cell system and vehicle

Abstract

The invention relates to a method for determining the resistance of at least one fuel cell of a fuel cell stack (10), said method comprising the following steps: providing (320) a fuel cell system (100) having the fuel cell stack (10), the cathode gas on the cathode side of at least one fuel cell of the fuel cell stack (10) does not have an oxidizing agent. Furthermore, the method comprises, as a step, applying (360) at least one such electrical inspection signal to at least one fuel cell such that anode gas protons move from the anode side to the cathode side of the at least one fuel cell at least in the at least one fuel cell. Furthermore, the method comprises, as a step, detecting (380) at least one signal response of the at least one fuel cell as a reaction to the at least one applied electrical inspection signal. Furthermore, the method comprises, as a step, ascertaining (400) a resistance of at least one fuel cell of a fuel cell stack (10) of the fuel cell system (100) on the basis of at least one applied electrical test signal and at least one detected signal response.

Description

Background Art

[0001] A fuel cell is an electrochemical energy converter in which, for example, hydrogen (H2) and oxygen (O2) are converted into water (H2O), electrical energy, and heat.

[0002] The porous electrodes (commonly referred to as catalyst layers) of a polymer electrolyte membrane fuel cell can have platinum particles (catalysts) supported on larger carbon particles. This carbon phase ensures electron transport and heat transport. In addition, this layer can also be penetrated by an ionomer to ensure proton conduction ability. The electrochemical reaction requires a triple phase boundary (TPB), which is created by the encounter of platinum, ionomer, and reactants. The membrane is located at the center of this structure and can mainly consist of an ionomer. The function of the membrane is to transport hydrogen protons from the anode electrode to the cathode electrode with as little loss as possible, but also to separate the two gas spaces from each other (airtightness) and to provide electrical insulation. The proton conduction ability of a given membrane mainly depends on two parameters: temperature and water content, where the latter is very closely related to the fuel cell current and the humidity of the gas channels.

[0003] Since the membrane resistance is an important indicator of fuel cell performance, it is important to monitor this membrane resistance during operation. If the resistance is too high, the overall performance may be poor and there may be a risk of drying out (Austrocknung). In addition, the dry state is also not conducive to the service life because the membrane becomes warmer in the dry state than in the humid state at a given current. In extreme cases, a very humid state may indicate possible flooding effects (Flutungseffekte) of the electrodes. It is known to determine the membrane resistance by means of an alternating current measurement or an alternating voltage measurement, where an AC signal is superimposed on the DC state during operation and the response of the system is recorded. By means of the amplitude ratio and the phase shift, the electrochemical impedance (Electrochemical Impedance Spectroscopy, EIS) can be determined. Here, either a fixed frequency (High Frequency Resistance, HFR) can be continuously superimposed and measured simultaneously, or the complete electrochemical impedance spectrum can be measured in a given situation, where the frequencies typically ranging from the kilohertz range to the millihertz range are sampled, which can be very time-consuming.

[0004] Another known method is the so-called "Current Interruption" method. In this complex method, the load is interrupted and the response of the fuel cell is sampled at a high frequency. Then, the ohmic resistance is determined by mathematical analysis. Summary of the Invention

[0005] The present invention shows a method according to the features of claim 1, a fuel cell system according to the features of claim 10, and a vehicle according to the features of claim 12.

[0006] Other features and details of the present invention result from the dependent claims, the description, and the drawings. Here, the features and details described in the context of the method according to the present invention of course also apply in the context of the fuel cell system according to the present invention and the vehicle according to the present invention, and vice versa accordingly, such that there is always a cross-reference or a possible cross-reference between the disclosures of the individual inventive aspects.

[0007] According to a first aspect, the present invention shows a method for determining the resistance of at least one fuel cell of a fuel cell stack of a fuel cell system, wherein each of the plurality of fuel cells of the fuel cell stack has an anode side, a cathode side, and a membrane. As a first step, the method includes providing a fuel cell system having a fuel cell stack, wherein the cathode gas on the cathode side of at least one fuel cell of the fuel cell stack does not have an oxidant of the cathode gas or substantially does not have an oxidant of the cathode gas. Furthermore, the method includes, as a step, applying at least one such electrical test signal to at least one of the plurality of fuel cells of the provided fuel cell stack such that anodic gas protons move from the anode side through the membrane of at least one fuel cell to the cathode side of at least one fuel cell. Furthermore, the method includes, as a step, detecting at least one signal response of at least one fuel cell as a reaction to the at least one applied electrical test signal. Furthermore, the method includes, as a step, determining the resistance of at least one fuel cell of the fuel cell stack of the fuel cell system based on the at least one applied electrical test signal and the at least one detected signal response.

[0008] As long as it is technically meaningful, the method steps described above and below can be carried out individually, together, once, multiple times, in parallel in time and / or successively in any order.

[0009] In particular, the above steps can be carried out repeatedly, for example, at least once during vehicle operation, in order to repeatedly determine, respectively, the resistance of at least one fuel cell of the fuel cell stack or the (total) resistance of the fuel cell stack of the fuel cell system based on the respective at least one applied electrical test signal and the respective at least one detected signal response. Thus, the resistance of the fuel cell, in particular the membrane resistance, can be monitored over time. By monitoring the membrane resistance, the fuel cell performance can be inferred.

[0010] In particular, the fuel cell stack includes bipolar plates and membrane electrode units, wherein the bipolar plates and the membrane electrode units are stacked alternately one above the other. At both ends of the fuel cell stack, the fuel cell stack may respectively have end plates. In particular, the membrane electrode unit includes a membrane having a first membrane side and a second membrane side opposite to the first membrane side, an anode electrode disposed on the first membrane side of the membrane, a cathode electrode disposed on the second membrane side of the membrane, a cathode electrode catalyst layer disposed on the anode electrode and / or a cathode electrode catalyst layer disposed on the cathode electrode and / or a cathode gas diffusion layer disposed on the cathode electrode and / or at least a cathode gas diffusion layer for distributing cathode gas to the cathode electrode and / or at least an anode gas diffusion layer for distributing anode gas to the anode electrode. In addition, in particular, the fuel cell stack is a polymer electrolyte membrane fuel cell stack.

[0011] The features and / or details and / or embodiments and / or advantages described for at least one fuel cell of the fuel cell stack or for a fuel cell of the fuel cell stack can also be transferred to the other fuel cells of the fuel cell stack, and vice versa.

[0012] In particular, the anode side of at least one fuel cell includes an anode plate half of the bipolar plate of the fuel cell stack, an anode electrode, and an anode electrode catalyst layer disposed on the anode electrode. Additionally, the anode side may also have an anode gas diffusion layer.

[0013] In particular, the cathode side of at least one fuel cell includes a cathode plate half of the bipolar plate of the fuel cell stack, a cathode electrode, and a cathode electrode catalyst layer disposed on the cathode electrode. Additionally, the cathode side may also have a cathode gas diffusion layer.

[0014] The resistance of at least one fuel cell in particular includes at least one (electrical or electronic) contact resistance, such as the (electrical or electronic) contact resistance between two components of the fuel cell (such as a bipolar plate and a gas diffusion layer), and / or includes at least one (electrical or electronic) layer resistance, such as the layer resistance of a gas diffusion layer, and / or includes at least one dynamic resistance, such as the resistance of oxygen kinetics or the resistance of hydrogen kinetics, and / or includes a membrane resistance. The membrane resistance can also be understood as a proton ohmic resistance. During the operation of the fuel cell system, the contact resistance and / or the layer resistance can remain almost constant, such that it is sufficient to determine the contact resistance and / or the layer resistance once and then subtract the contact resistance and / or the layer resistance from the resistance to be determined to obtain the membrane resistance. For example, the layer resistance of the anode gas diffusion layer can be realized on the anode gas diffusion layer as a single component before assembling the fuel cell stack. The layer resistance thus obtained can be stored in the acquisition unit of the fuel cell system according to the invention.

[0015] For example, a fuel cell system having a fuel cell stack can be provided on a vehicle, such as a fuel cell vehicle.

[0016] At least one applied electrical inspection signal can be a voltage signal, wherein a current signal as a response to the at least one signal is detected as a reaction to the voltage signal (as the at least one applied electrical inspection signal). For example, the voltage signal as the electrical inspection signal can be detected by means of a voltage measuring unit (such as a voltmeter), and / or the current signal as a response to the at least one signal can be detected by means of a current measuring unit (such as an ammeter). Alternatively or additionally, it can also be considered that at least one applied electrical inspection signal is a current signal, wherein a voltage signal as a response to the at least one signal is detected as a reaction to the current signal (as the at least one applied electrical inspection signal). For example, the current signal as the electrical inspection signal can be detected by means of a current measuring unit (such as an ammeter), and / or the voltage signal as a response to the at least one signal can be detected by means of a voltage measuring unit (such as a voltmeter). In particular, the detection unit of the fuel cell system according to the invention includes a current measuring unit and / or a voltage measuring unit. Advantageously, existing components are used as the voltage measuring unit and / or the current measuring unit for operating or monitoring the fuel cell system.

[0017] In particular, such an electrical inspection signal is applied to at least one of a plurality of fuel cells, which at least temporarily has a first signal level and at least temporarily has a second signal level different from the first signal level, wherein for both the first signal level and the second signal level (respectively), the anode gas protons move from the anode side to the cathode side of at least one fuel cell via the membrane of at least one fuel cell. The movement of the anode gas protons can also be understood as proton pumping. In particular, such an electrical inspection signal is applied to at least one of a plurality of fuel cells such that the fuel cell stack at least temporarily has a negative fuel cell stack potential difference, wherein in particular, the value of the negative fuel cell stack potential difference changes at least once, in particular significantly changes at least once, over time. For example, a stepped current signal can be applied as the at least one electrical inspection signal, wherein sometimes, for example, 5 amperes and sometimes, for example, 10 amperes are applied to at least one fuel cell. A stepped or substantially stepped voltage signal can be detected as the signal response of at least one fuel cell as a reaction to the stepped current signal. The resistance of the fuel cell can be determined from the stepped current signal as the at least one (applied) electrical inspection signal and the stepped voltage signal as the at least one signal response.

[0018] In particular, by means of Ohm's law, for example, by means of an evaluation unit of a fuel cell system according to the invention, based on at least one applied electrical check signal and at least one detected signal response, the resistance of at least one fuel cell of a fuel cell stack of the fuel cell system is determined.

[0019] Since a fuel cell system having a fuel cell stack does not have an oxidant for the cathode gas or has substantially no oxidant for the cathode gas, the amount of the reactant (Reaktionspartner) is kept particularly low, and the resistance of at least one fuel cell of the fuel cell stack can be determined in a particularly simple manner, and thus the monitoring of the fuel cell stack can also be achieved particularly simply and / or cost-effectively and / or quickly. For example, the cathode gas can be air, where the oxygen in the air is the oxidant for the cathode gas. Advantageously, in addition, by the determination of the resistance according to the invention, the cathode catalyst layer can also be cleaned additionally.

[0020] It can be advantageous that in the method according to the invention, at least the fuel cell stack of the fuel cell system in a defined state is provided. Thus, the determination of the resistance of at least one fuel cell of the fuel cell stack or of the fuel cell stack can be achieved particularly accurately, and the resistance of at least one fuel cell or of the fuel cell stack, in particular the membrane resistance, can be monitored particularly advantageously over time. For example, the fuel cell stack may have been operated for a specifiable duration, and / or the membrane of the fuel cell stack has a specifiable minimum humidity, and / or the fuel cell stack has a specifiable minimum temperature.

[0021] It may be advantageous that, in the method according to the invention, the cathode gas supply of the fuel cell system is interrupted in a fluid-technical manner, the cathode gas supply being used to supply cathode gas to the cathode sides of a plurality of fuel cells, and in particular, the fuel cell stack is electrically loaded at least temporarily so that the cathode gas on the cathode side of at least one fuel cell of the fuel cell stack does not have or substantially does not have an oxidant of the cathode gas. Thus, it is possible in a particularly simple manner to cause the cathode gas on the cathode side of at least one fuel cell of the fuel cell stack not to have or substantially not to have an oxidant of the cathode gas. Prior to this, the power of the fuel cell stack can also be reduced in an additional step. The interruption of the cathode gas supply of the fuel cell system in a fluid-technical manner can be achieved by closing a valve at the cathode input of the fuel cell stack, the cathode gas supply being used to supply cathode gas to the cathode sides of a plurality of fuel cells. Additionally, by current interruption, it is possible to force a fuel cell reaction between the oxidant of the cathode gas and the reductant of the anode gas such that the oxidant (e.g., oxygen) of the cathode gas is completely or substantially completely reduced and the cell potential is zero or substantially zero. For example, it is possible to identify whether the oxidant has been depleted or substantially depleted by detecting and analyzing the potential difference of the fuel cell stack and / or by detecting and analyzing the current passing through the fuel cell stack. Additionally, a reductant (e.g., hydrogen) can flow on the respective anode sides of the plurality of fuel cells, where, in particular, water and nitrogen or substantially water and nitrogen (in the case of air as the cathode gas) are located on the respective cathode sides of the plurality of fuel cells.

[0022] It may be advantageous that, in the method according to the invention, a stepped signal and / or a ramp signal and / or a jump signal and / or a discrete signal are applied at least temporarily as at least one electrical test signal. In particular, the at least temporarily stepped signal and / or the at least temporarily ramp signal and / or the at least temporarily jump signal and / or the at least temporarily discrete signal have at least a first signal height and a second signal height different from the first signal height. Additionally, it can be considered to apply different electrical test signals successively in time.

[0023] It may be advantageous that, in the method according to the invention, a current signal with an increasing current intensity is applied as at least one electrical test signal, where the voltage is detected as at least one signal response. Thus, it is possible in a particularly simple manner to determine the resistance of at least one fuel cell. For example, in the case of a stepped signal, at least one first signal height and a second signal height different from the first signal height can be applied as at least one electrical test signal.

[0024] It may be advantageous that, in the method according to the invention, at least one electrical inspection signal is applied to at least two of the plurality of fuel cells of the provided fuel cell stack such that the anode gas protons move from the respective anode sides through the respective diaphragms of the respective fuel cells to the respective cathode sides of the respective fuel cells in the at least two fuel cells. Thus, the resistances of the plurality of fuel cells of the fuel cell stack can be determined, and the monitoring of the fuel cell stack can be achieved particularly accurately. It may be advantageous that, in the method according to the invention, based on at least one applied electrical inspection signal and the corresponding detected signal response, the resistance is determined for each of the at least two fuel cells respectively, or based on at least one applied electrical inspection signal and the detected signal response, the total resistance is determined for the at least two fuel cells. If the resistance is determined for each of the at least two fuel cells respectively based on at least one applied electrical inspection signal and the corresponding detected signal response, then each of the at least two fuel cells can be monitored, and a defective fuel cell can be located particularly easily, for example. If the total resistance is determined for the at least two fuel cells based on at least one applied electrical inspection signal and the detected signal response, then it is possible to monitor particularly easily and with particularly little effort whether, for example, there is a defective diaphragm in the fuel cell stack. For example, in order to determine the total resistance, the electrical inspection signal can be applied to two current collectors of the fuel cell stack.

[0025] It may be advantageous that, in the method according to the invention, based on at least one applied electrical inspection signal, at least one detected signal response, and additionally based on at least one layer resistance and / or at least one contact resistance and / or at least one kinetic resistance of at least the fuel cell stack (especially at least one fuel cell), the diaphragm resistance of the diaphragm of at least one fuel cell of the fuel cell stack is determined. In particular, at least one layer resistance and / or at least one contact resistance and / or at least one kinetic resistance of at least the fuel cell stack (especially at least one fuel cell) can be determined or measured in advance and stored respectively in the determination unit of the fuel cell system according to the invention. In order to determine the diaphragm resistance, at least one layer resistance and / or at least one contact resistance and / or at least one kinetic resistance can be subtracted.

[0026] It may be advantageous that, in the method according to the invention, when a reduction in the electrical power demand for the fuel cell stack is recognized and / or predicted, a method for determining the resistance is carried out. Thus, for example, the determination of the resistance can also be carried out during vehicle operation, for example when stationary at a traffic light. Alternatively or additionally, when it is recognized that the electrical power demand for the fuel cell stack can be buffered by a buffer unit of the fuel cell system, a method for determining the resistance can be carried out. The buffer unit can be a battery, such as a vehicle battery. By the expression "carrying out a method for determining the resistance" it is meant that the starting conditions for the following steps can be the recognition and / or prediction of a reduction in the electrical power demand for the fuel cell stack and / or the ability to buffer the electrical power demand for the fuel cell stack by a buffer unit of the fuel cell system: providing a fuel cell system, wherein the cathode gas on the cathode side of at least one fuel cell of the fuel cell stack does not have an oxidant of the cathode gas or essentially does not have an oxidant of the cathode gas, and applying an electrical check signal, and detecting at least one signal response of at least one fuel cell, and determining the resistance.

[0027] According to a second aspect, the invention shows a fuel cell system for a vehicle. The fuel cell system includes a fuel cell stack having a plurality of fuel cells, wherein each of the plurality of fuel cells has an anode side, a cathode side, and a membrane. In addition, the fuel cell system includes a control unit for controlling the fuel cell system having the fuel cell stack, wherein the control unit is configured to cause the cathode gas on the cathode side of at least one fuel cell of the fuel cell stack not to have an oxidant of the cathode gas or essentially not to have an oxidant of the cathode gas. The fuel cell system includes a check signal generator unit for applying at least one such electrical check signal to at least one of the plurality of fuel cells such that anodic gas protons can move from the anode side via the membrane of at least one fuel cell to the cathode side of at least one fuel cell. In particular, the check signal generator unit is furthermore configured to apply such a check signal such that at least one electrical check signal has (at least) a first signal level at least temporarily and has a second signal level different from the first signal level at least temporarily, in order to cause anodic gas protons to move from the anode side via the membrane of at least one fuel cell to the cathode side of at least one fuel cell. In addition, the fuel cell system includes a detection unit for detecting at least one signal response of at least one fuel cell as a reaction to at least one applied electrical check signal. In addition, the fuel cell system includes a determination unit for determining at least one resistance of at least one fuel cell of the fuel cell stack of the fuel cell system, in particular the membrane resistance of the membrane of at least one fuel cell, based on at least one applied electrical check signal and at least one detected signal response.

[0028] Advantageously, a fuel cell system according to the invention is configured to carry out the method according to the invention.

[0029] Thus, a fuel cell system according to the second aspect of the invention has the same advantages as those already described for the method according to the first aspect of the invention.

[0030] According to a third aspect, the invention shows a vehicle, in particular a motor vehicle, having a fastening interface, wherein the fuel cell system is constructed according to the invention and is arranged on the fastening interface of the vehicle by means of a mating fastening interface.

[0031] The vehicle is in particular a motor vehicle, such as a passenger car or a truck or a motorcycle.

[0032] Thus, a vehicle according to the third aspect of the invention has the same advantages as those already described for the method according to the first aspect of the invention or for the fuel cell system according to the second aspect of the invention.

[0033] Other measures for improving the invention result from the following description of some embodiments of the invention, which are schematically shown in the drawings. All features and / or advantages resulting from the description or the drawings, including structural details, spatial arrangements and method steps, can be important for the invention either individually or in different combinations. It should be noted here that the drawings only have the described features and are not considered to limit the invention in any way. Description of the Drawings

[0034] The drawings schematically show:

[0035] Figure 1 a fuel cell system is shown,

[0036] Figure 2 a vehicle is shown,

[0037] Figure 3 a method is shown. Detailed Description

[0038] In the following drawings, even the same technical features of different embodiments are denoted by the same reference numerals.

[0039] Figure 1 A fuel cell system 100 for a vehicle 200 is schematically disclosed.

[0040] The fuel cell system 100 includes a fuel cell stack 10 having a plurality of fuel cells, wherein each of the plurality of fuel cells has an anode side, a cathode side, and a membrane. In addition, the fuel cell system 100 includes a control unit 20 for controlling the fuel cell system 100 having the fuel cell stack 10, wherein the control unit 20 is configured to cause the cathode gas on the cathode side of at least one fuel cell of the fuel cell stack 10 to have no oxidant of the cathode gas or substantially no oxidant of the cathode gas, for example, by interrupting the supply of the cathode gas in a fluid-technical manner. The interruption of the supply of the cathode gas in a fluid-technical manner can be achieved by closing the valve 111 in the cathode gas supply. In addition to the cathode gas supply, the fuel cell stack 10 has an anode gas supply with a valve 112. Furthermore, the fuel cell system 100 includes an inspection signal generator unit 40 for applying at least one such electrical inspection signal to at least one of the plurality of fuel cells such that anodic gas protons can move from the anode side through the membrane of at least one fuel cell to the cathode side of at least one fuel cell. In addition, the fuel cell system 100 includes a detection unit 50 for detecting at least one signal response of at least one fuel cell as a reaction to at least one applied electrical inspection signal. In addition, the fuel cell system 100 includes an evaluation unit 60 for evaluating at least one resistance, in particular the membrane resistance of the membrane of at least one fuel cell, of the fuel cell stack 10 of the fuel cell system 100 based on at least one applied electrical inspection signal and at least one detected signal response.

[0041] Figure 2 Schematically disclosed is a vehicle 200, in particular a motor vehicle, which has a fastening interface 201, wherein the fuel cell system 100 is arranged on the fastening interface 201 of the vehicle 200 by means of a mating fastening interface 101, and the fuel cell system is in particular as described for Figure 1 above.

[0042] Figure 3 Disclosed is a method for evaluating the resistance of at least one fuel cell of a fuel cell stack 10 of a fuel cell system 10, and the fuel cell system is in particular as described for Figure 1As described, each of the plurality of fuel cells in the fuel cell stack 10 has an anode side, a cathode side, and a membrane. The method includes, as a step: providing 320 a fuel cell system 100 having the fuel cell stack 10, wherein the cathode gas on the cathode side of at least one fuel cell of the fuel cell stack 10 does not have an oxidant of the cathode gas or substantially does not have an oxidant of the cathode gas. In this method, additionally, optionally, it can be considered to provide 321 at least the fuel cell stack 10 of the fuel cell system 100 in a defined state. Furthermore, the method includes, as a step: applying 360 at least one such electrical inspection signal, for example, applying 362 a current signal with an increasing current intensity, to at least one of the plurality of fuel cells of the provided fuel cell stack 10, such that anodic gas protons move from the anode side through the membrane of at least one fuel cell to the cathode side of at least one fuel cell. In this method, as a step, additionally, optionally, it can be considered to apply 361 at least a stepped signal and / or at least a ramp signal and / or at least a jump signal and / or at least a discrete signal as at least one electrical inspection signal, at least temporarily. Furthermore, the method includes, as a step: detecting 380 at least one signal response of at least one fuel cell, for example, detecting 382 the voltage of at least one fuel cell, as a reaction to at least one applied electrical inspection signal. Furthermore, the method includes, as a step: determining 400 the resistance of at least one fuel cell of the fuel cell stack 10 of the fuel cell stack 100 based on at least one applied electrical inspection signal and at least one detected signal response. In this method, as a step, additionally, optionally, it can be considered to perform the method for determining the resistance when it is recognized and / or predicted 301 that the electrical power demand for the fuel cell stack decreases, and / or when it is recognized 302 that the electrical power demand for the fuel cell stack 10 can be met by a buffer unit of the fuel cell system 100, such as a battery buffer. For example, this recognition or prediction can be achieved by a control unit of the fuel cell system 100. In this method, as a step, additionally, optionally, it can be considered to apply 363 at least one electrical inspection signal to at least two of the plurality of fuel cells of the provided fuel cell stack 10 such that anodic gas protons move from the respective anode sides through the respective membranes of the respective fuel cells to the respective cathode sides of the respective fuel cells among the at least two fuel cells.In this method, as a step, additionally, i.e., optionally, it is possible to consider, for each of the at least two fuel cells, determining 401 the resistance based on at least one applied electrical inspection signal and the corresponding detected signal response, or determining 402 the total resistance for the at least two fuel cells based on at least one applied electrical inspection signal and the detected signal response. In this method, as a step, additionally, i.e., optionally, it is possible to consider, determining 420 the membrane resistance of the membrane of at least one fuel cell of the fuel cell stack 10 based on at least one applied electrical inspection signal, at least one detected signal response, and additionally based on at least one layer resistance and / or at least one contact resistance and / or at least one dynamic resistance of at least the fuel cell stack (in particular at least one fuel cell).

Claims

1. A method for determining the electrical resistance of at least one fuel cell of a fuel cell stack (10) of a fuel cell system (10), wherein: Each of the plurality of fuel cells of the fuel cell stack (10) has an anode side, a cathode side and a membrane, wherein the method comprises: providing (320) a fuel cell system (100) having the fuel cell stack (10), wherein a cathode gas on a cathode side of at least one fuel cell of the fuel cell stack (10) is free of an oxidant for the cathode gas or is substantially free of an oxidant for the cathode gas, applying (360) at least one such electrical inspection signal to at least one fuel cell of a plurality of fuel cells of the provided fuel cell stack (10) so that anode gas protons move from the anode side to the cathode side of the at least one fuel cell via a membrane of the at least one fuel cell at least in the at least one fuel cell, detecting (380) at least one signal response of the at least one fuel cell in response to at least one applied electrical check signal, Based on at least one applied electrical test signal and at least one detected signal response, a resistance of at least one fuel cell of a fuel cell stack (10) of the fuel cell system (100) is determined (400).

2. The method according to claim 1, It is characterized in that A fuel cell stack (10) of at least the fuel cell system (100) in a defined state is provided (321).

3. The method according to any one of the preceding claims, It is characterized in that A cathode gas supply (1) of the fuel cell system (100) for supplying cathode gas to the cathode side of the plurality of fuel cells is interrupted (338) in a fluidic manner and, in particular, the fuel cell stack (10) is at least temporarily electrically loaded (339) so that the cathode gas on the cathode side of at least one fuel cell of the fuel cell stack (10) is free of or substantially free of an oxidant for the cathode gas.

4. The method according to any one of the preceding claims, It is characterized in that in, A step-shaped signal and / or a ramp-shaped signal and / or a jump-shaped signal and / or a discrete signal are applied at least temporarily as the at least one electrical test signal (361).

5. The method according to any one of the preceding claims, It is characterized in that A current signal with increasing current intensity is applied (362) as the at least one electrical test signal, wherein a voltage is detected (382) as the at least one signal response.

6. The method according to any one of the preceding claims, It is characterized in that The at least one electrical inspection signal is applied (363) to at least two of the plurality of fuel cells of the provided fuel cell stack (10) in such a way that anode gas protons move from the corresponding anode side in the at least two fuel cells via the corresponding membranes of the corresponding fuel cells to the corresponding cathode side of the corresponding fuel cells in the at least two fuel cells.

7. The method according to claim 6, It is characterized in that Based on at least one applied electrical test signal and a corresponding detected signal response, a resistance is determined (401) for each of the at least two fuel cells, or based on at least one applied electrical test signal and a detected signal response, a total resistance is determined (402) for the at least two fuel cells.

8. The method according to any one of the preceding claims, It is characterized in that in, Based on at least one applied electrical test signal, at least one detected signal response and additionally based on at least one layer resistance and / or at least one contact resistance and / or at least one dynamic resistance of at least the fuel cell stack, in particular at least one fuel cell, the membrane resistance of the membrane of at least one fuel cell of the fuel cell stack (10) is determined (420).

9. The method according to any one of the preceding claims, It is characterized in that When a reduction in the electrical power demand for the fuel cell stack is identified and / or predicted (301), the method for determining the resistance is performed. and / or Therein, the method for ascertaining the resistance is performed when it is detected (302) that an electrical power demand for the fuel cell stack (10) can be buffered by a buffer unit of the fuel cell system (100).

10. A fuel cell system (100) for a vehicle (200), wherein: The fuel cell system (100) comprises: A fuel cell stack (10), the fuel cell stack comprising a plurality of fuel cells, wherein each of the plurality of fuel cells comprises an anode side, a cathode side and a membrane, A control unit (20) for controlling a fuel cell system (100) having the fuel cell stack (10), wherein the control unit (20) is configured to cause the cathode gas on the cathode side of at least one fuel cell of the fuel cell stack (10) to be free of or substantially free of an oxidant for the cathode gas, and a check signal generator unit (40) for applying at least one such electrical check signal to at least one fuel cell of the plurality of fuel cells so that anode gas protons can move from the anode side via a membrane of the at least one fuel cell to the cathode side of the at least one fuel cell at least in the at least one fuel cell, a detection unit (50) for detecting at least one signal response of the at least one fuel cell as a reaction to at least one applied electrical test signal, A determination unit (60) is used to determine at least one resistance of at least one fuel cell of a fuel cell stack (10) of the fuel cell system (100), in particular a membrane resistance of a membrane of at least one fuel cell, based on at least one applied electrical test signal and at least one detected signal response.

11. The fuel cell system (100) according to claim 10, It is characterized in that It is characterized in that The fuel cell system (100) is designed to carry out the method according to any one of claims 1 to 9.

12. A vehicle (200), in particular a motor vehicle, having a fastening interface (201), wherein: The fuel cell system (100) according to claim 10 or 11 is arranged on a fastening interface (201) of the vehicle (200) by means of a mating fastening interface (101).

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