Method for operating an electrochemical cell and vehicle with electrochemical cell

Abstract

The invention relates to a method for operating an electrochemical cell. The method comprises at least the following steps: S1: Measuring at least one cell parameter (11) of the electrochemical cell; S2: Determining at least one comparison parameter (15) with a model (13) of the electrochemical cell based on data (14) about a past operation of the electrochemical cell; S3: Comparing at least one cell parameter (11) and at least one comparison parameter (15); S4: Selecting an operating mode (21, 22) based on the comparison; and S5: Operating the electrochemical cell in the selected operating mode (21, 22). Furthermore, the invention relates to a vehicle with an electrochemical cell.

Description

[0001] The invention relates to a method for operating an electrochemical cell. Furthermore, the invention relates to a vehicle with an electrochemical cell.

[0002] From DE 10 2023 120 282 A1 a method for diagnosing the functionality of a fuel cell system and a method for controlling a fuel cell system are known.

[0003] The inventive method for operating an electrochemical cell, for example a fuel cell, comprises the following steps: S1: Measuring at least one cell parameter of the electrochemical cell; S2: Determine at least one comparison parameter with a model of the electrochemical cell based on data about a past operation of the electrochemical cell; S3: Comparing at least one cell parameter and at least one comparison parameter; S4: Selecting an operating mode based on the comparison; and S5: Operating the electrochemical cell in the selected operating mode.

[0004] By determining a reference parameter with a model of the electrochemical cell based on data from past operation, it is possible to predict or quantify the expected state of health of the electrochemical cell at the current operating time, based on its operating history. From this state of health, expected values ​​for the current cell behavior can be derived. By comparing these expected values ​​with the actual cell behavior, which is quantified by at least one measured cell parameter, conclusions can be drawn about whether the electrochemical cell is functioning correctly. If deviations from the expected values ​​are detected, these can be interpreted as indications of a fault or operation under unfavorable conditions.By selecting and setting a suitable operating mode based on the comparison, corrective action can be taken. This can prevent damage and / or further deterioration of the cell condition. At least partial regeneration of the electrochemical cell is also possible.

[0005] In one variant of the method, at least one cell parameter is measured using electrochemical impedance spectroscopy (EIS). Electrochemical impedance spectroscopy is an established method in the field of electrochemical cells, particularly fuel cells, which provides valuable information about the electrochemical cell and the processes occurring within it, quantifying it, for example, in the form of an AC resistance (impedance). By applying electrochemical impedance spectroscopy, at least one cell parameter can be determined in a technically simple and equally reliable manner.

[0006] Another aspect stipulates that at least one comparison parameter is determined based on measurement influencing factors recorded during the measurement of at least one cell parameter and on data about the past operation of the electrochemical cell.

[0007] Measurement influencing variables are quantities or parameters that affect the AC resistance of the electrochemical cell and / or have a direct impact on the measurement. For electrochemical cells designed as fuel cells, measurement influencing variables include, for example, air temperature, cell temperature, charge air pressure, fuel gas pressure, humidity, stoichiometry, and / or an AC signal applied to the electrochemical cell during measurement. In principle, one or more of these measurement influencing variables can be recorded during the measurement of at least one cell parameter. Alternatively, one or more of these measurement influencing variables can also be recorded shortly before or shortly after the measurement.

[0008] The data on the past operation of the electrochemical cell includes, for example, load profiles with which the electrochemical cell was operated and / or regeneration phases, in the case of fuel cells, for example, purging intervals in which the fuel cell was purged with hydrogen or an inert gas.

[0009] The examples mentioned for measurement influencing factors and the data on past operation are, of course, not to be understood as limiting. In principle, a wide variety of other data can be collected and analyzed.

[0010] Furthermore, the electrochemical cell model, used to determine at least one comparative parameter, may include an aging module that predicts the aging state of the electrochemical cell based on data from its past operation. For example, in electrochemical cells designed as fuel cells, it may be possible to determine, or at least estimate, how a catalyst surface has changed during past operation and how large the catalyst surface area is that is still available at the current operating time.

[0011] The comparison parameter is, for example, a virtual AC resistance of the electrochemical cell, which is preferably determined by simulation using the model based on the measured influencing factors at the given aging state. In simplified terms, a virtual AC resistance of the electrochemical cell can be determined as a comparison parameter based on the operating history and then compared with at least one cell parameter, which is preferably an actually measured AC resistance of the electrochemical cell. Thus, two similar parameters are compared. This is technically simple and can be implemented with minimal computing resources.

[0012] In one embodiment of the method, the at least one measured cell parameter and the at least one reference parameter are compared by creating a first Nyquist diagram based on the at least one measured cell parameter and a second Nyquist diagram based on the at least one reference parameter. Any deviation in the position and / or shape of the first and second Nyquist diagrams is then determined. It has been shown that the causes underlying the cell behavior deviating from the expected value can be directly and reliably deduced from the positional and / or shape deviations of the Nyquist diagrams. To illustrate, for example, in electrochemical cells designed as fuel cells, a shift of the first Nyquist diagram to the right can indicate excessively high membrane resistance.By evaluating the positional and / or shape deviation of the two Nyquist diagrams, specific problems can be identified, which in turn enables the initiation of targeted countermeasures.

[0013] For example, it can be stipulated that a first operating mode is selected if the deviation in the position and / or shape of the two Nyquist diagrams is below a predefined threshold, and that a second operating mode is selected if the deviation exceeds the predefined threshold. This allows an optimal operating strategy to be selected and applied depending on the observed cell behavior.

[0014] Alternatively, Bode plots can be used instead of Nyquist plots to compare the at least one measured cell parameter and the at least one comparison parameter. For example, a first Bode plot can be created based on the at least one measured cell parameter, and a second Bode plot can be created based on the at least one comparison parameter. Differences between the two Bode plots can then be determined and evaluated to select a more advantageous operating mode.

[0015] For example, the first operating mode is optimized for performance and / or efficiency. In contrast, the second operating mode may be geared towards troubleshooting and / or regenerating the electrochemical cell.

[0016] It is conceivable that at least the second operating mode defines at least one of the following operating parameters for the electrochemical cell: a maximum operating load, an operating temperature, an operating humidity, an operating charge air pressure, an operating fuel gas pressure, and an operating stoichiometry. These examples are not intended to be exhaustive. A multitude of other operating parameters that influence cell behavior can be defined. This allows the second operating mode to counteract further deterioration of cell behavior and / or even actively improve it, which in turn has a positive effect on the overall efficiency averaged over the lifespan of the electrochemical cell.

[0017] Another aspect stipulates that process steps S1 to S5 are repeated at predetermined and / or regular intervals, for example, at fixed time intervals or, in the case of vehicle integration, after a certain distance has been traveled. This ensures that an operating mode appropriate to the current cell state of the electrochemical cell is always selected and that the electrochemical cell is operated optimally throughout its entire service life.

[0018] The vehicle according to the invention comprises at least one electrochemical cell, for example a fuel cell, a detection device for detecting at least one cell parameter of the electrochemical cell and a computing unit configured to carry out a method according to the invention.

[0019] The advantages mentioned for the method apply equally to the vehicle according to the invention.

[0020] Preferred embodiments are explained in more detail with reference to the following figures. These show - Fig. 1 a schematic representation of an embodiment of a vehicle according to the invention; - Fig. 2 a schematic representation of a method according to the invention in an exemplary embodiment; and - Fig. 3 A diagram showing a first Nyquist diagram and a second Nyquist diagram of a fuel cell.

[0021] Fig. Figure 1 shows a vehicle according to the invention.

[0022] The vehicle 1 is a truck comprising at least one electrochemical cell 2 designed as a fuel cell and at least one, preferably several, electric motors 3. The electric motors 3 are supplied with electrical energy by the at least one electrochemical cell 2 to drive the wheels of the vehicle 1. Optionally, further energy supply devices for providing the electric motors 3 with electrical energy may be provided, for example, an electrical energy storage device 4.

[0023] Furthermore, the vehicle 1 has at least one detection device 5 for detecting at least one cell parameter of the electrochemical cell 2. In the case of the Fig. In the variant shown in Figure 1, the detection device 5 is an impedance spectrometer with which an alternating current resistance of the electrochemical cell 2 can be measured.

[0024] Furthermore, the vehicle 1 includes several sensors, including an air temperature sensor 6, which measures the temperature of the charge air used for the operation of the electrochemical cell 2; an air pressure sensor 7, which measures the charge air pressure; a cell temperature sensor 8, which measures the temperature of the electrochemical cell 2; and a humidity sensor 9, which measures the membrane moisture of the electrochemical cell 2. These examples are not intended to be exhaustive. In principle, the vehicle 1 can have a variety of additional sensors to record various parameters of the vehicle environment and / or the electrochemical cell 2.

[0025] Furthermore, the vehicle 1 includes a computing unit 10 which is configured to execute a method according to the invention for operating the electrochemical cell 2.

[0026] Fig. Figure 2 shows a schematic representation of an exemplary embodiment of the method.

[0027] In a first step S1 of the method, a cell parameter 11 is measured using the detection device 5. More precisely, the AC resistance of the electrochemical cell 2 is measured over a defined frequency range using the impedance spectrometer. For this purpose, the electrochemical cell 2 is exposed to AC signals with different frequencies, which are preferably modulated onto a current supplied by the electrochemical cell 2.

[0028] For example, a sinusoidal voltage of a specific frequency can be applied to electrochemical cell 2 to modulate a corresponding AC signal onto the current supplied by the electrochemical cell. A phase shift between the voltage and the AC signal can then be detected and evaluated. This process is repeated for several frequencies, as is common practice in the art, until the frequency-dependent AC resistance is characterized with sufficient accuracy. The operating point of electrochemical cell 2 is kept at least approximately constant for all frequencies throughout the entire measurement period to ensure good comparability of the recorded data.

[0029] Alternatively, it is also possible to expose electrochemical cell 2 to several frequencies simultaneously to measure the frequency-dependent AC resistance. For example, a voltage can be applied to electrochemical cell 2 that is generated by superimposing several sinusoidal voltages of different frequencies. The current response of electrochemical cell 2 can then be recorded and evaluated, for example, using a Fourier transform, to determine the phase shifts of the current and voltage for the individual frequencies and thus characterize the frequency-dependent AC resistance. In simpler terms, the cell response for several frequencies can be recorded simultaneously, thereby significantly reducing the overall measurement time, for example, from 5 minutes to 30 seconds.

[0030] Simultaneously with the cell parameter 11, a plurality of measurement influencing variables 12 are recorded.

[0031] At the in Fig. In the example shown, the air temperature sensor 6 measures the charge air temperature, the charge air pressure sensor 7 measures the charge air pressure, the electrochemical cell temperature sensor 8 measures the temperature of the electrochemical cell 2, and the membrane moisture of the electrochemical cell 2 measures the humidity sensor 9. Furthermore, the current supplied by the electrochemical cell 2 during the measurement and information about the alternating current signals applied to the electrochemical cell 2 during the measurement are recorded. The measurement parameters 12 are transmitted to the processing unit 10.

[0032] In a second step S2 of the procedure, the computing unit 10, using a model 13 of the electrochemical cell 2, for example a digital twin, determines a comparison parameter 15 based on the measurement influencing variables 12 and on data 14 about a past operation of the electrochemical cell 2. The comparison parameter 15 is used in the Fig. In the variant of the method shown in section 2, a virtual alternating current resistance of the electrochemical cell 2 is used.

[0033] The data 14 concerning past operation includes, for example, load profiles under which the electrochemical cell 2 was operated and / or regeneration phases, such as purging intervals, of the electrochemical cell 2. This is, of course, not to be understood as a limitation. A wide variety of other data 14 concerning past operation can be included in the calculation of the comparison parameter 15.

[0034] As in Fig. As shown in Figure 2, the model 13 of the electrochemical cell 2 comprises an aging module 16 and a functional module 17. Using the aging module 16, the computing unit 10 predicts the aging state of the electrochemical cell 2 at the time of measurement of the cell parameter 11, based on the data 14 about the past operation of the electrochemical cell 2.

[0035] For example, the aging module 16 uses data 14 on the past operation of electrochemical cell 2 to predict how a catalyst surface of electrochemical cell 2 has changed during the past operation and how large the catalyst surface area is still available at the time of measurement. This is, of course, not to be understood as a limitation. In principle, other parameters or operating variables can also be determined that quantify the aging and / or health status of electrochemical cell 2.

[0036] The results from the aging module 16 are then transferred to the function module 17, which determines at least one comparison parameter 15 based on these and the measurement influencing variables 12 recorded during the measurement.

[0037] In a third step S3 of the procedure, the computing unit 10 compares the at least one recorded cell parameter 11 with the at least one comparison parameter 15. More precisely, the computing unit 10 compares the AC resistance measured in step S1 of the procedure with the virtual AC resistance determined by simulation in step S2 of the procedure.

[0038] For this purpose, the computing unit 10 creates a first Nyquist diagram 18 based on at least one measured cell parameter 11 and a second Nyquist diagram 19 based on at least one comparison parameter 15.

[0039] Fig. Figure 3 shows a diagram in which the first Nyquist diagram 18 and the second Nyquist diagram 19 are graphically represented.

[0040] In a fourth step S4 of the procedure, the computing unit 10 selects an operating mode 21, 22 based on the comparison.

[0041] For this purpose, the calculation unit 10 determines deviations 20 of the position and shape of the two Nyquist diagrams 18, 19.

[0042] If the deviations 20 are below a predefined limit, the computing unit 10 selects a first operating mode 21. The first operating mode 21 is, for example, geared towards performance- or efficiency-optimized operation of the electrochemical cell 2.

[0043] In simplified terms, the first operating mode 21 is selected when the actual measured AC resistance corresponds at least approximately to the virtual AC resistance of the electrochemical cell 2 expected on the basis of historical data 14 and determined by simulation, and the two Nyquist diagrams 18, 19 accordingly differ only slightly from each other.

[0044] If, on the other hand, the deviations 20 exceed the specified limit, the computing unit 10 selects a second operating mode 22. The second operating mode 22 is intended, for example, for troubleshooting and / or regenerating the electrochemical cell 2.

[0045] The based on Fig. The implementation of process steps S3 and S4 described in section 3 is, of course, not to be understood as restrictive. In principle, both process steps can also be implemented without creating and evaluating Nyquist diagrams 18, 19. For example, in step S3 of the process, the computing unit 10 can also compare a measured voltage of the electrochemical cell 2 or other parameters derived from the measurement with a corresponding reference parameter 15.

[0046] In a fifth step S5 of the procedure, the computing unit 10 sets the selected operating mode 21, 22, so that the electrochemical cell 2 is operated with this mode in a subsequent operation.

[0047] At the in Fig.In the variant of the procedure shown in Figure 2, the second operating mode defines 22 setpoints and maximum values ​​for various operating parameters of the electrochemical cell 2, for example a maximum operating load, an operating temperature and / or an operating humidity.

[0048] In principle, one or more operating parameters can also be adjusted depending on the observed deviations 20 of the position and / or shape of the two Nyquist diagrams 18, 19. For example, it can be provided that the maximum operating load of the electrochemical cell 2 is more severely limited as the size of the deviations 20 increases.

[0049] Optionally, a frequency and / or duration of rinsing processes of the electrochemical cell 2 can also be determined based on the observed deviations 20 of the Nyquist diagrams 18, 19.

[0050] By adjusting or limiting the aforementioned operating parameters, the electrochemical cell 2 is protected during operation in the second operating mode 22, thereby preventing further deterioration of its aging and / or health condition. Operating the electrochemical cell 2 in the second operating mode 22 can even lead to an improvement in the aging and / or health condition of the electrochemical cell 2, for example, to at least a partial regeneration of the active catalyst surface.

[0051] Preferably, steps S1 to S5 of the method are repeated at regular intervals, for example at regular time intervals or after a certain distance has been traveled by the vehicle 1. This ensures that the electrochemical cell 2 is always operated in an operating mode 21, 22 appropriate to the current cell state, which in turn increases the overall lifetime as well as the averaged overall efficiency of the electrochemical cell 2. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2023 120 282 A1

[0002]

Claims

[1] Method for operating an electrochemical cell (2) comprising the steps: S1: Measuring at least one cell parameter (11) of the electrochemical cell (2); S2: Determining at least one comparison parameter (15) with a model (13) of the electrochemical cell (2) based on data (14) about a past operation of the electrochemical cell (2); S3: Comparing at least one cell parameter (11) and at least one comparison parameter (15); S4: Selecting an operating mode (21, 22) based on the comparison; and S5: Operating the electrochemical cell (2) in the selected operating mode (21, 22). [2] Method according to claim 1, wherein the at least one cell parameter (11) is measured by electrochemical impedance spectroscopy (EIS). [3] Method according to claim 1 or 2, wherein the at least one comparison parameter (15) is determined based on measurement influencing variables (12) recorded during the measurement of the at least one cell parameter (11) and the data (14) on the past operation of the electrochemical cell (2). [4] Method according to claim 3, wherein, when measuring the at least one cell parameter (11), the following are recorded as measurement parameters (12): air temperature, cell temperature, charge air pressure, fuel gas pressure, humidity, stoichiometry and / or an alternating current signal impressed into the electrochemical cell (2). [5] Method according to one of the preceding claims, wherein the model (13) of the electrochemical cell (2) with which the at least one comparison parameter (15) is determined comprises an aging module (16) which, based on the data (14) about the past operation of the electrochemical cell (2), predicts an aging state of the electrochemical cell (2). [6] Method according to one of the preceding claims, wherein the at least one measured cell parameter (11) and the at least one comparison parameter (15) are compared by creating a first Nyquist diagram (18) based on the at least one measured cell parameter (11) and creating a second Nyquist diagram (19) based on the at least one comparison parameter (15) and subsequently determining a deviation (20) of the position and / or shape of the first Nyquist diagram (18) and the second Nyquist diagram (19). [7] Method according to claim 6, wherein a first operating mode (21) is selected when the deviation (20) is below a predetermined limit, and wherein a second operating mode (22) is selected when the deviation (20) is above the predetermined limit. [8] Method according to claim 7, wherein at least the second operating mode (22) specifies at least one of the following operating parameters for the operation of the electrochemical cell (2): A maximum operating load, an operating temperature, an operating humidity, an operating charge air pressure, an operating fuel gas pressure, an operating stoichiometry. [9] A method according to any of the preceding claims, wherein the method steps S1 to S5 are repeated at predetermined and / or regular intervals. [10] Vehicle comprising at least one electrochemical cell (2), a detection device (5) for detecting at least one cell parameter (11) of the electrochemical cell (2) and a computing unit (10) configured to perform a method according to one of the preceding claims.

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