Method for determining a state and fuel cell stack

Abstract

The invention relates to a method for determining the state (10) of a fuel cell, comprising the steps of providing (14) a fuel cell stack (16); establishing a reduced-reaction state (34) of the fuel cell stack (16) with limited availability of the oxidant in an anode chamber volume (Va) and cathode chamber volume (Vk); gas-tight sealing (36) of the fuel cell stack (16); operating the fuel cell stack (16) in reverse mode (42) by applying a predefined electrical reverse current (44) to electrodes (26, 28) of the fuel cell stack (16); measuring (54) at least one gas pressure in the anode chamber volume (Va) as a first gas pressure (56); measuring (54) at least one gas pressure in the cathode chamber volume (Vk) as a second gas pressure (58); calculating (60) a chemical amount of desorbed hydrogen as a desired chemical amount (nt) as a function of at least the first and second gas pressures (56, 58); and calculating (62) a state parameter (64) of the total active electrochemical surface of the fuel cell stack (16) as a function of at least the calculated desired chemical amount (nt). The invention also relates to a fuel cell stack (16).

Description

[0001] R. 416013

[0002] - 1 -

[0003] Description

[0004] title

[0005] Methods for condition monitoring and fuel cell stacks

[0006] The invention relates to a method for state detection according to claim 1. Furthermore, the invention relates to a fuel cell stack.

[0007] State of the art

[0008] In DE 10 2022 207 826 A1 a diagnostic procedure for a fuel cell is described, comprising self-inerting of the atmosphere at a working electrode, applying a constant current to a fuel cell stack and simultaneously measuring the electrical voltages at all individual cells in order to determine a state characteristic from the voltage curves.

[0009] The efficiency of the fuel cell can be reduced by age-related impairments. A significant age-related impairment is a reduction in the active electrochemical surface area (ECSA) of the fuel cell stack, for example through carbon corrosion and / or agglomeration of catalyst particles.

[0010] By knowing the active electrochemical surface, the fuel cell can be operated in a modified manner to maintain the highest possible efficiency.

[0011] Disclosure of the invention

[0012] According to the present invention, a method for condition monitoring with the features of claim 1 is proposed. This allows the condition of the active electrochemical surface of the entire fuel cell stack to be determined holistically, more easily, and more reliably. Individual cell voltage monitoring is no longer necessary. Age-related impairments R. 416013

[0013] - 2 -

[0014] The fuel cell can be determined more cost-effectively, easily, and accurately.

[0015] The fuel cell can be arranged in a stationary or mobile device, in particular a vehicle. The vehicle can be an electric vehicle. The fuel cell can provide drive energy for propelling the vehicle.

[0016] The fuel cell can be a PEM fuel cell (Proton Exchange Membrane Fuel Cell).

[0017] The fuel cell stack can be permeable to a reaction medium. The reaction medium can be gaseous or liquid. The reaction medium can be a fuel, in particular hydrogen. The reaction medium can be an oxidizing agent, in particular oxygen, preferably from air. The fuel cell stack can be permeable to a first reaction medium, in particular the fuel, and a second reaction medium, in particular the oxidizing agent.

[0018] The membrane electrode assembly (MEA) can comprise at least one electrolyte membrane, in particular a proton exchange membrane (PEM), which preferably separates the anode and cathode. Catalyst layers can be arranged on the electrolyte membrane. The catalyst layers can be located on both sides of the electrolyte membrane and, in particular, can form the anode and cathode, respectively. The membrane electrode assembly can comprise at least one gas diffusion layer (GDL), in particular on the anode and / or cathode.

[0019] The process can be performed regularly. This allows the operation of the fuel cell to be adjusted depending on the condition monitoring, thus extending the lifespan of the fuel cell.

[0020] The reaction reduction state is a controlled state in which the fuel cell is transitioned from its active, power-generating normal operating state to an inactive, voltage-free state in which no electrochemical reactions take place. An example of a reaction reduction state is oxygen depletion, as described in R. 416013.

[0021] - 3 -

[0022] The remaining oxygen at the cathode is removed or consumed to make the cathode chamber volume as inert as possible.

[0023] In the reduced reaction state, at least near-inert conditions can exist within the fuel cell stack. The anode and cathode chamber volumes can then consist primarily of hydrogen, nitrogen, and possibly water vapor, with oxygen present only in a significantly reduced proportion compared to the normal operating state of the fuel cell.

[0024] Before reversing operation and after gas-tight sealing, an equilibrium state of the gases in the fuel cell stack can exist, in which there is the same partial pressure and the same concentration of the gases in the anode chamber volume compared to the cathode chamber volume, and in particular, an electrochemically induced electrical voltage at the electrodes is zero.

[0025] When reference is made above and below to the anode or cathode, even in the case of reversing operation, the components of the anode or cathode in the normal operation of the fuel cell are meant.

[0026] The anode chamber volume is the entire interior space of the fuel cell stack for distributing the fuel to the anodes, in particular including associated connections and distribution structures at least within the fuel cell stack.

[0027] The cathode chamber volume is the entire interior space of the fuel cell stack for distributing the oxidizing agent to the cathodes, in particular including associated connections and distribution structures at least within the fuel cell stack.

[0028] With gas-tight sealing, the anode chamber volume and the cathode chamber volume are sealed off from the outside. The lines connected to the anode chamber volume can be closed by valves. The lines connected to the cathode chamber volume can also be closed by valves. This ensures that the total amount of all gases is contained within the chamber. R. 416013

[0029] - 4 -

[0030] in the cathode chamber volume and the anode chamber volume.

[0031] The reverse current can be an inverted current compared to the current generated by the electrochemical reaction during normal operation of the fuel cell stack. The reverse current can cause oxidative processes to occur in the half-cell where cathodic (reductive) processes take place during normal operation. Conversely, the applied reverse current can cause reductive processes to occur in the half-cell where anodic (oxidative) processes take place during normal operation.

[0032] During reversing operation, the total electrical voltage at the electrodes and / or the electrical cell voltage at at least one individual cell can be measured. At least one duration of the reversing operation and / or a current parameter of the reversing current value, in particular a current value, a current value curve, and / or a current gradient of the reversing current, can depend on the measured total voltage or cell voltage.

[0033] The current parameter can be set such that each individual cell, during reversing operation, maintains an electrical cell voltage at least within a specified voltage range, in particular from 0.45 V to 0.65 V. The smaller the reversing current gradient, the more accurate the pressure measurement of the respective gas pressure can be for a given sampling rate. Reversing operation can be stopped when the total voltage, divided by the number of individual cells, reaches a limit, for example, a value of 0.8 V.

[0034] The temperature in the anode chamber volume and the cathode chamber volume can be constant, at least during reversing operation. The volume of the anode chamber and the volume of the cathode chamber are preferably constant and / or known during reversing operation.

[0035] The applied reverse current can cause protons to be transported across the electrolyte membrane from the cathode to the anode. The amount of hydrogen supplied to the anode chamber volume by the pumping process can be removed from the cathode chamber volume. The protons can be released at the cathode by the oxidation of hydrogen molecules (R. 416013).

[0036] - 5 -

[0037] Protons are formed. At the anode, the protons can recombine with electrons to form hydrogen molecules.

[0038] The desorbed hydrogen can be generated through a desorption process, particularly at the cathode. In this process, hydrogen stored in solid (adsorbed) form on the cathode, especially the catalyst surface, can be released through electrochemical reactions. The adsorbed hydrogen may be bound as atoms on the surface of the cathode, particularly the catalyst, for example, platinum. The applied reverse current can drive an electrochemical desorption reaction. The released hydrogen atoms recombine on the anode side to form hydrogen molecules. The anode chamber volume can thereby be enriched with additional hydrogen. However, the desorption process may be limited by the amount of adsorbed hydrogen available at the cathode. Once all the adsorbed hydrogen at the cathode has been desorbed, the desorption process may be complete.The amount of adsorbed hydrogen can depend directly on the active electrochemical surface area. A larger active electrochemical surface area can form more adsorption sites and can therefore store and release more hydrogen.

[0039] The desorption process of a single cell can be completed when an electrical threshold voltage is reached at the single cell, for example 0.45 V.

[0040] The first gas pressure can be measured by at least one pressure sensor. The second gas pressure can be measured by at least one pressure sensor. The first and second gas pressures can be measured and, in particular, recorded during reversing operation, especially continuously.

[0041] The target amount of substance can be determined in moles.

[0042] From the characteristic value of the entire active electrochemical surface, an average characteristic value can be calculated for the individual cells.

[0043] In a preferred embodiment of the invention, it is advantageous if the calculation of the target amount of substance depends on a difference between an R. 416013

[0044] - 6 -

[0045] This involves a total change in the amount of hydrogen molecules on the anode side and a total change in the amount of hydrogen molecules on the cathode side.

[0046] The target amount of substance n t can depend on the difference between the total amount of substance changed on the anode side. a on hydrogen molecules and the total change in amount of substance on the cathode side. k can be calculated for hydrogen molecules as follows

[0047] |n t | = |Δn a | − |Δn k |

[0048] The total substance change on the anode side and the total substance change on the cathode side can be the respective change during and / or as a result of the reversing operation. The total substance change on the anode side and the total substance change on the cathode side can each be the change from the start of the reversing operation. The total substance change on the anode side can be an increase in the total substance quantity. The total substance change on the cathode side can be a decrease in the total substance quantity.

[0049] In a preferred embodiment of the invention, the total change in the amount of substance on the anode side is calculated as a function of at least one first gas pressure value of the first gas pressure, and the total change in the amount of substance on the cathode side is calculated as a function of at least one second gas pressure value of the second gas pressure. The first gas pressure value can be the first gas pressure measured at a first measurement time. The second gas pressure value can be the second gas pressure measured at a second measurement time. The first and second measurement times can be the same or different.

[0050] In a particular embodiment of the invention, it is advantageous if the total amount of substance changed on the anode side can be determined by applying the general equation for ideal gases with known temperature T in the anode chamber volume, with known anode chamber volume V. a, calculated with known gas constant R and the first gas pressure value. The temperature can be measured by at least one temperature sensor on the fuel cell stack. R. 416013

[0051] - 7 -

[0052] The anode chamber volume may have been determined by prior measurement.

[0053] The total amount of substance changed on the anode side a can be calculated as follows

[0054] (p1- p 1,0 ) · V a

[0055] Δn a =

[0056]

[0057] R • T

[0058] with the first initial pressure value p 10 as the first gas pressure measured at an initial time, in particular immediately before reversing operation and at equilibrium.

[0059] In a preferred embodiment of the invention, it is advantageous if the total amount of substance change on the cathode side can be determined by applying the general equation for ideal gases with known temperature T in the cathode chamber volume, with known cathode chamber volume V. k , with known gas constant R and with the second gas pressure value p2. The total change in substance on the cathode side An k can be calculated as follows

[0060] (p2- p 2,0 ) · V k

[0061] Δn k =

[0062]

[0063] R • T

[0064] with the second output pressure value p 2,0 as the second gas pressure measured at an initial point in time, in particular immediately before reversing operation and at equilibrium. The first and second initial pressure values ​​Pi,o, P2,o can be equal.

[0065] In a preferred embodiment of the invention, the first gas pressure value is the first gas pressure measured at a given measurement time, and the second gas pressure value is the second gas pressure measured at that same measurement time. The measurement time is determined based on a pressure gradient of the first gas pressure (the first pressure gradient) and a pressure gradient of the second gas pressure (the second pressure gradient). The measurement time is specifically within the reversing operation. The first and second pressure gradients can be continuously recorded during the reversing operation. R. 416013

[0066] - 8 -

[0067] In a preferred embodiment of the invention, a pressure gradient ratio is calculated from the first and second pressure gradients and compared with a volume ratio of cathode chamber volume to anode chamber volume. The pressure gradient ratio can be continuously recorded during reversing operation. The comparison of the volume ratio and the pressure gradient ratio can be continuously recorded during reversing operation.

[0068] In a preferred embodiment of the invention, the measurement point is defined as the point in time at which the difference between the pressure gradient ratio and the volume ratio reaches a predetermined differential threshold, particularly after the pressure gradient ratio has previously exceeded a predetermined ratio threshold. The ratio threshold can be predetermined such that the pressure gradient ratio is higher than the pressure gradient ratio resulting from the pumping process. The ratio threshold can be a pressure gradient ratio value that is 50% or more higher than the pressure gradient ratio value present at the beginning of the reversing operation.

[0069] The difference threshold can be positive. The difference threshold can be zero. The measurement point can be the point in time at which the ratio difference, coming from higher values, reaches the difference threshold.

[0070] If the ratio difference is negative or the difference threshold is not reached, a failed state detection can be concluded. An excessively high cell voltage can be the reason why the difference threshold is not reached, as, for example, some individual cells may undergo catalyst oxidation at excessively high cell voltage, which can produce further gaseous hydrogen.

[0071] If the ratio difference is negative or the difference threshold is not undershot, the reversing operation can be repeated, particularly with a modified predefined current parameter for the reversing current. For example, the current value can be increased to raise the cell voltages more uniformly. R. 416013

[0072] - 9 -

[0073] In an advantageous embodiment of the invention, the state parameter is a roughness factor and / or an area of ​​the active electrochemical surface. The roughness factor can indicate the ratio of the area of ​​the total active electrochemical surface to the total geometric electrochemical surface.

[0074] The surface area can be calculated based on Faraday's law, according to which the electric charge Q transferred in an electrochemical reaction is proportional to the amount of substance reacted, here the target amount n. t , is. For example, the electric charge

[0075] Q = (2 • n t ) • F

[0076] with the Faraday constant F.

[0077] Since the electric charge is proportional to the active electrochemical surface area, the area A of the total active electrochemical surface area can be calculated from the electric charge if the reference charge density <7 of the electrochemical surface area is known. For example, the area is

[0078] A = Q / σ

[0079] Furthermore, a computer program is proposed that contains machine-readable instructions executable on at least one computer, the execution of which triggers the described state monitoring procedure. A storage unit, also machine-readable and accessible by at least one computer, on which the computer program is stored, is further proposed.

[0080] According to the present invention, a fuel cell stack with the features according to claim 10 is further proposed.

[0081] Further advantages and advantageous embodiments of the invention will become apparent from the description of the figures and the illustrations. R. 416013

[0082] - 10 -

[0083] Character description

[0084] The invention is described in detail below with reference to the illustrations. These show, in detail:

[0085] Figure 1: A method for state detection in a special embodiment of the invention.

[0086] Figure 2: A time course of measured values ​​during execution of the method for condition detection in a further special embodiment of the invention.

[0087] Figure 1 shows a method for state detection in a special embodiment of the invention. The method for state detection 10 of a fuel cell comprises providing 14 a fuel cell stack 16, which includes several individual cells 18, each with a membrane electrode assembly 24 comprising at least one electrolyte membrane 19, an anode 20 and a cathode 22, an anode-side electrode 26 electrically connected to the anodes 20 and a cathode-side electrode 28 electrically connected to the cathodes 22, and an anode chamber volume V. a for the distribution of hydrogen to the anodes 20 and a cathode chamber volume V kfor the distribution of an oxidizing agent, in particular oxygen, to the cathodes 22.

[0088] Due to the fuel cell stack entering a state of reduced reaction 34, there is a limited availability of oxygen in the cathode chamber volume V. k The anode chamber volume V a and the cathode chamber volume V k They therefore mainly comprise hydrogen, nitrogen and, if applicable, water vapor, and if oxygen, then with a much reduced proportion compared to the normal operating state of the fuel cell stack 16.

[0089] Subsequently, the fuel cell stack 16 is sealed gas-tight 36. This involves the anode chamber volume V being supplied. a connected lines 38 and those connected to the cathode chamber volume V k The connected lines 38 are closed, for example, by valves 40. This prevents R. 416013

[0090] - 11 -

[0091] that mass flows between the anode chamber volume V a and the cathode chamber volume V k the trapped gas phase and the environment are exchanged.

[0092] Subsequently, the fuel cell stack 16 is reversed by applying a predetermined electrical reversing current 44 to the electrodes of the fuel cell stack 16. The reversing current 44 is inverted compared to the electrical current generated by the electrochemical reaction during normal operation of the fuel cell stack 16.

[0093] Before the reversing operation 42 and after the gas-tight sealing 36, in particular an equilibrium state of the gases in the fuel cell stack 16 exists, in which there is an equal partial pressure and an equal substance concentration of the gases in the anode chamber volume V a compared to the cathode chamber volume V kis present and in particular the electrochemically induced electrical voltage at electrodes 26, 28 is zero.

[0094] During the reversing operation 42, the total electrical voltage 48 is measured 46 at the electrodes 26, 28. At least a duration 50 of the reversing operation 42 and / or a current parameter 52 of the reversing current value, in particular a reversing current value magnitude, a reversing current value profile, and / or a reversing current gradient of the reversing current 44, can depend on the measured total voltage 48. The current parameter 52 can be specified such that each individual cell 18 assumes an electrical cell voltage during the reversing operation 42 with at least one voltage value within a specified voltage range, in particular from 0.45 V to 0.65 V.

[0095] During the reversing operation 42, a measurement 54 of at least one gas pressure in the anode chamber volume V is also carried out. aas the first gas pressure 56 and a measurement 54 of at least one gas pressure in the cathode chamber volume V k as second gas pressure 58.

[0096] The reversing operation 42 can effect a pumping process and a desorption process.

[0097] The applied reverse current 44 can cause protons in the single cell 18 to flow through the electrolyte membrane from the cathode 22 to the anode 20. R. 416013

[0098] - 12 -

[0099] are transported. The volume of the anode chamber V is increased by the pumping process. a The amount of hydrogen supplied can be distributed across the cathode chamber volume V k Protons can be extracted at the cathode 22 through the oxidation of hydrogen molecules. At the anode 20, the protons can recombine with electrons to form hydrogen molecules.

[0100] In the desorption process, hydrogen, which is stored in solid (adsorbed) form on the surface of the cathode 22, particularly the catalyst surface, is released by electrochemical reactions. The adsorbed hydrogen can be bound to the surface of the cathode 22 in the form of atoms or molecules, particularly the catalyst, for example, platinum. The applied reverse current 44 can drive an electrochemical desorption reaction. The released hydrogen atoms form hydrogen molecules on the anode side. The anode chamber volume V aThe desorption process can be enriched with additional hydrogen. However, the desorption process may be limited by the available amount of adsorbed hydrogen at cathode 22. Once all the adsorbed hydrogen has been desorbed, the desorption process may be complete. The amount of adsorbed hydrogen may depend directly on the active electrochemical surface area. A larger active electrochemical surface area can form more adsorption sites and can therefore store and release more hydrogen.

[0101] Furthermore, a calculation is performed to determine the amount of substance 60 of desorbed hydrogen molecules as the target amount of substance n. t at least dependent on the first and second gas pressures 56, 58. The target amount of substance n is determined in this process. t depending on a difference between a total change in substance on the anode side. a on hydrogen molecules and a total change in substance on the cathode side. kcalculated on hydrogen molecules as follows

[0102] |n t | = |Δn a | − |Δn k |

[0103] The total change in substance on the anode side Δn a This includes, in particular, an increase in the total amount of substance and the change in the total amount of substance on the cathode side Δn. k The pumping process results in a reduction of the total amount of substance. This reduction in the total amount of substance on the cathode side, caused by the pumping process, leads to an increase in the amount of substance on the anode side. The excess R. 416013

[0104] - 13 -

[0105] The target amount of substance n can therefore be determined from the difference. t as the amount of hydrogen released by the desorption process.

[0106] The total change in substance on the anode side Δn aThe total amount of substance on the cathode side is calculated depending on a first gas pressure value p1 of the first gas pressure 56, and the total amount of substance on the cathode side is calculated depending on a second gas pressure value p2 of the second gas pressure 58. The change in the total amount of substance on the anode side An a is obtained by applying the general equation for ideal gases with known temperature T in the anode chamber volume V a , with known anode chamber volume V a , with known gas constant R and with the first gas pressure value p, calculated as follows

[0107] (p1− p 1,0 ) · V a

[0108] Δn a =

[0109]

[0110] R • T

[0111] with the first initial pressure value p 10 as the first gas pressure 56 measured at an initial time, in particular immediately before the reversing operation 42 and at the equilibrium state.

[0112] The total change in substance on the cathode sidek is obtained by applying the general equation for ideal gases with known temperature T in the cathode chamber volume V k , with known cathode chamber volume V k , with known gas constant R and with the second gas pressure value p2, calculated as follows

[0113] (P2~ P2,o) • Vk

[0114] Δn k =

[0115]

[0116] R • T

[0117] with the second output pressure value p 2,0 as the second gas pressure measured at the initial time 58.

[0118] The first gas pressure value p is that at a measurement time t. x The first measured gas pressure is 56, and the second gas pressure value p2 is the one at the measurement time t. x measured second gas pressure 58. The measurement time t x The time frame lies within the reversing operation 42. The recording of the measurement time t x This will be explained in more detail with reference to Figure 2.

[0119] Finally, a state characteristic value 64 of the total active electrochemical surface of the fuel cell stack 16 R is calculated. 416013

[0120] - 14 -

[0121] at least depending on the calculated target substance amount n t The state parameter can be an area A of the active electrochemical surface. The area A can be calculated using Faraday's law, according to which the electric charge Q transferred in an electrochemical reaction is proportional to the amount of substance reacted, here the target amount n. t For example, the electric charge is

[0122] Q = (2 • n t ) • F,

[0123] with the Faraday constant F.

[0124] Since the electric charge Q is proportional to the active electrochemical surface area, the area A of the total active electrochemical surface area can be calculated from the electric charge, given a known reference charge density <7 of the electrochemical surface, as follows.

[0125] A = Q / σ

[0126] The surface area A can therefore indicate a state of the entire active electrochemical surface.

[0127] Figure 2 shows a time course of measured values ​​during execution of the state monitoring method in a further specific embodiment of the invention. The upper time diagram shows the first and second gas pressures 56, 58, the middle diagram shows the pressure gradient of the first gas pressure 56 as the first pressure gradient 66 and the pressure gradient of the second gas pressure 58 as the second pressure gradient 68, and the lower diagram shows the magnitude of the pressure gradient ratio 70 of the first and second pressure gradients 66, 68. The pressure gradient ratio r can, for example, be expressed as follows, with the first pressure gradient dp1 / dt and the second pressure gradient dp2 / dt:

[0128] dp1 / dt

[0129] r = -

[0130]

[0131] dp2 / dt

[0132] The reversing operation begins at the initial time t0. Before the reversing operation and after gas-tight sealing, an equilibrium state of the gases exists in the fuel cell stack, in which the partial pressure and the concentration of the gases in the anode chamber volume R are the same. 416013

[0133] - 15 -

[0134] The first and second gas pressures 56, 58 are equal to the volume of the cathode chamber. The first and second pressure gradients 66, 68 are zero. The first and second pressure gradients 66, 68 and the pressure gradient ratio 70 are recorded continuously during reversing operation.

[0135] The measurement time t xThe pressure gradients 66 and 68 are determined as follows, depending on the first and second pressure gradients. With the reversing operation starting at the initial time t0, the first gas pressure 56 increases, while the second gas pressure 58 decreases. The first pressure gradient 66 is greater than zero, and the second pressure gradient 68 is less than zero. The measurement time t x is recorded as the time at which an amount of the difference 72 between the pressure gradient ratio 70 and the volume ratio 74 of cathode chamber volume to anode chamber volume reaches a predetermined difference threshold, which is in particular zero, after the pressure gradient ratio 70, here at time t1, has exceeded a predetermined ratio threshold 76, here the volume ratio 74 of cathode chamber volume to anode chamber volume.

Claims

R. 416013 - 16 - Patent claims 1. Method for state monitoring (10) of a fuel cell, comprising the steps Providing (14) a fuel cell stack (16) comprising several individual cells (18) each with a membrane electrode unit (24) comprising at least one anode (20) and one cathode (22), furthermore an anode-side electrode (26) electrically connected to the anodes (20) and a cathode-side electrode (28) electrically connected to the cathodes (22) and an anode chamber volume (V a ) for the distribution of hydrogen to the anodes (20) and a cathode chamber volume (V k ) for the distribution of an oxidizing agent to the cathodes (22) includes, Reaching a state of reduced reaction (34) of the fuel cell stack (16) with limited availability of the oxidant in the anode chamber volume (V) a ) and cathode chamber volume (V k), gas-tight sealing (36) of the fuel cell stack (16), reversing operation (42) of the fuel cell stack (16) by applying a predetermined electrical reversing current (44) to the electrodes (26, 28) of the fuel cell stack (16), Measurement (54) of at least one gas pressure in the anode chamber volume (V) a ) as the first gas pressure (56), Measurement (54) of at least one gas pressure in the cathode chamber volume (V) k ) as second gas pressure (58), Calculation (60) of an amount of desorbed hydrogen as the target amount of substance (n t ) at least dependent on the first and second gas pressures (56, 58) and Calculation (62) of a state characteristic (64) of the total active electrochemical surface of the fuel cell stack (16) at least dependent on the calculated target amount of substance (n) t ).

2. Method for state detection (10) according to claim 1, characterized in that the calculation (60) of the target substance quantity (n) t ) depending on a difference between a total change in substance on the anode side (Δn a ) on hydrogen molecules and a total change in the amount of substance on the cathode side (Δn k ) on hydrogen molecules. R. 416013 - 17 - 3. Method for state detection (10) according to claim 2, characterized in that the total change in the amount of material on the anode side (Δn a ) depending on at least one first gas pressure value (p,) of the first gas pressure (56) and the total amount of substance change on the cathode side (Δn k ) is calculated depending on at least one second gas pressure value (p2) of the second gas pressure (58).

4. Method for state detection (10) according to claim 3, characterized in that the total change in the amount of substance on the anode side (Δn) is determined by applying the general equation for ideal gases with known temperature (T) in the anode chamber volume (V). a ), with known anode chamber volume (V a ), with known gas constant (R) and with the first gas pressure value (p1).

5. Method for state detection (10) according to claim 3 or 4, characterized in that the total change in the amount of substance on the cathode side (Δn k ) by applying the general equation for ideal gases with known temperature (T) in the cathode chamber volume (V) k ), with known cathode chamber volume (V k ), with known gas constant (R) and with the second gas pressure value (p2).

6. Method for state detection (10) according to one of claims 3 to 5, characterized in that the first gas pressure value (p,) at a measurement time (t x ) measured first gas pressure (56) and the second gas pressure value (p2) at the time of measurement (t x ) measured second gas pressure (58) is and the measurement time (t x ) depending on a pressure gradient of the first gas pressure (56) as first pressure gradient (66) and a pressure gradient of the second gas pressure (58) as second pressure gradient (68).

7. Method for state detection (10) according to claim 6, characterized in that a pressure gradient ratio (70) is formed from the first and second pressure gradients (66, 68) and is combined with a volume ratio (74) of cathode chamber volume (V) k ) to anode chamber volume (V a ) is compared. R. 416013 - 18 - 8. Method for condition detection (10) according to claim 7, characterized in that the measurement time (t x ) is recorded as the point in time at which an amount of the difference (72) between the pressure gradient ratio (70) and the volume ratio (74) reaches a predetermined difference threshold, after the pressure gradient ratio (70) has previously exceeded a predetermined ratio threshold (76).

9. Method for condition detection (10) according to one of the preceding claims, characterized in that the condition parameter is a roughness factor and / or an area size (A) of the active electrochemical surface.

10. Fuel cell stack (16) for a fuel cell, comprising several individual cells (18) each comprising a membrane electrode unit (24) comprising at least one anode (20) and one cathode (22), an anode-side electrode (26) electrically connected to the anodes (20), a cathode-side electrode (28) electrically connected to the cathodes (22), an anode chamber volume (V a ) for the distribution of hydrogen to the anodes (20) and a cathode chamber volume (V k ) for the distribution of an oxidizing agent to the cathodes (22), wherein a state characteristic of the entire active electrochemical surface of the fuel cell stack (16) can be determined by a state detection method (10) according to one of the preceding claims.

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