CN115469240A

CN115469240A - Method, apparatus and computer program product for state of health monitoring of a fuel cell

Info

Publication number: CN115469240A
Application number: CN202110646472.4A
Authority: CN
Inventors: 常亚飞; 柳绪丹; 王凯
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2021-06-10
Filing date: 2021-06-10
Publication date: 2022-12-13

Abstract

The present invention relates to the field of fuel cells. The invention relates to a method for state of health monitoring of a fuel cell, comprising the steps of: acquiring current state data of the fuel cell in an oxygen depletion stage, wherein the current state data can represent the health state of the fuel cell; receiving historical state data relating to the current state data of the fuel cell; and determining a degree of degradation of the fuel cell based on the comparison of the current state data with the historical state data. The invention also relates to a device for state of health monitoring of a fuel cell and a computer program product. The invention aims to fully utilize data generated in the oxygen consumption stage of the fuel cell and provide a fuel cell health monitoring scheme which is easy to implement, low in cost and free of additional equipment.

Description

Method, apparatus and computer program product for state of health monitoring of a fuel cell

Technical Field

The present invention relates to a method for state of health monitoring of a fuel cell, an apparatus for state of health monitoring of a fuel cell and a computer program product.

Background

Fuel cells are widely used in the field of electric vehicles as clean energy capable of reducing greenhouse gas emissions. However, lifetime remains a major bottleneck faced by fuel cells. It is of great significance to develop a scheme for diagnosing the state of health (SOH) of a fuel cell.

In the prior art, the most popular diagnostic methods for achieving state of health monitoring of fuel cells are polarization curve measurement and Alternating Current (AC) impedance spectroscopy. However, both solutions still suffer from a number of disadvantages, in particular, polarization curve measurements are currently only feasible in experimental environments with specific test equipment and stable operating conditions, and are not suitable for conventional vehicle applications. High frequency ac impedance spectroscopy has been widely used in the automotive field, but has mainly been in the direction of research on water management. Although the medium-low frequency ac impedance spectrometry has been used for the degradation measurement of fuel cells in a laboratory environment, it is still not mature enough for the vehicle field because of the long measurement time and unstable working conditions.

In this context, it is desirable to provide a fuel cell health monitoring scheme that is easy to implement, low cost, and requires no additional equipment.

Disclosure of Invention

It is an object of the present invention to provide a method for state of health monitoring of a fuel cell, an apparatus for state of health monitoring of a fuel cell and a computer program product to solve at least some of the problems of the prior art.

According to a first aspect of the present invention, there is provided a method for state of health monitoring of a fuel cell, the method comprising the steps of:

acquiring current state data of the fuel cell in an oxygen depletion stage, wherein the current state data can represent the health state of the fuel cell;

receiving historical state data relating to the current state data of the fuel cell; and

based on the comparison of the current state data with the historical state data, the degree of degradation of the fuel cell is determined.

The invention comprises in particular the following technical concepts: by collecting data during the oxygen depletion phase, the invention enables existing measurement conditions in the vehicle to be exploited without adding any additional equipment and the battery degradation state to be determined quickly based on comparison with historical data. Thereby providing an easy to operate fuel cell state of health monitoring scheme.

Optionally, the current state data includes: the output voltage, the impedance, the time course of the output voltage and/or the time course of the impedance of the fuel cell during the oxygen depletion phase.

The following technical advantages are achieved in particular here: during the oxygen depletion stage, there are great changes in the oxygen concentration and humidity inside the battery, and under such fluctuating environmental factors, many structural degradations caused by battery aging can be more clearly reflected by the trend of voltage and impedance changes. By recording these physical quantities which are easy to measure for the vehicle fuel cell model, the degradation information of the fuel cell can be seen more intuitively, and therefore the degradation degree analysis is realized at a lower cost as a whole.

Optionally, the oxygen depletion phase refers to: a time period starting from the cessation of the supply of oxygen to the cathode of the fuel cell until the oxygen inside the fuel cell is depleted, wherein in particular the supply of reactant gas to the anode is maintained during said time period.

The following technical advantages are achieved in particular here: during use in a vehicle, in order to suppress the fuel cell system from generating an oxygen-hydrogen interface on the anode side, it is often the aim to control the fuel gas supply sequence during the start-stop phase in order to prevent air ingress. This measure, in turn, creates a very favorable environment for fuel cell state of health monitoring, during which no additional equipment needs to be introduced, thus reducing the costs of the overall solution and providing operability.

Optionally, in the step of determining the degree of degradation, the current state data within a predefined time interval of the oxygen depletion phase is selected to perform the comparison.

The following technical advantages are achieved in particular here: by intercepting the time interval for performing the measurement and comparison, it is excluded that the specific state data (e.g., voltage characteristic curve) is less changed at the initial or end stage, thereby easily causing erroneous judgment. Thus, the accuracy of the method is further improved.

Optionally, a constant current is applied to the fuel cell during the oxygen depletion phase by in-situ cathodic discharge measurement, in particular by means of a DC/DC converter in a fuel cell electric vehicle.

The following technical advantages are achieved in particular here: the DC/DC converter is a component which can directly access the fuel cell stack and directly control the output current of the fuel cell stack in the power assembly of the fuel cell electric automobile, so that the original equipment in a vehicle fuel system can be fully utilized to provide disturbance current for the fuel cell stack, and observation of specific parameters can be realized. Thus, experimental conditions for monitoring the state of health of the battery locally in the vehicle are provided in a simple manner.

Alternatively, the current state data is acquired and the degree of degradation is determined for each section of the fuel cell, in particular for each cell.

The following technical advantages are achieved in particular here: by taking the state data of the fuel cells into account in sections, replacement can be carried out only for fuel cell sections or cells which are severely degraded locally, without the need to recall the entire fuel cell stack, so that assembly and maintenance costs can be saved in particular.

Optionally, the historical state data includes: status data measured once at the oxygen depletion stage when the fuel cell has not deteriorated; and/or a collection of state data measured during an oxygen depletion phase a plurality of times during use of the fuel cell.

The following technical advantages are achieved in particular here: on the one hand, by saving the measurement result of the oxygen depletion stage when no deterioration has occurred as the reference standard, the degree of deterioration can be intuitively inferred by looking at the degree of deviation of the current state data from the historical state data. On the other hand, by cumulatively storing the measurement results as historical state data, the previous cycle measurement results can be recalled multiple times each time the degradation analysis is performed, whereby the temporal behavior of the fuel cell degradation can be advantageously identified, and remedial action can be taken more specifically.

Alternatively, the degree of deterioration of the fuel cell is determined as follows: the faster the currently measured output voltage drops over time, the higher the degree of degradation of the fuel cell, as compared to historical state data; and/or the more the time course of the currently measured impedance shifts upward overall, the higher the degree of degradation of the fuel cell, as compared to the historical state data.

Optionally, in the step of obtaining current status data, the ambient temperature, humidity, purge rate, reactant flow rate and/or pressure are controlled to meet preset conditions associated with measurement conditions of historical status data.

The following technical advantages are achieved in particular here: it is possible to advantageously exclude the environmental factor interference from the health monitoring result of the fuel cell, further improving the accuracy of the deterioration degree determination.

According to a second aspect of the present invention, there is provided an apparatus for state of health monitoring of a fuel cell, the apparatus being for performing the method according to the first aspect of the present invention, the apparatus comprising:

an acquisition module configured to acquire current state data of the fuel cell during an oxygen depletion phase, the current state data being indicative of a state of health of the fuel cell;

a receiving module configured to be able to receive historical state data related to current state data of the fuel cell; and

an analysis module configured to determine a degree of degradation of the fuel cell based on a comparison of the current state data and the historical state data.

According to a third aspect of the present invention, there is provided a computer program product, wherein the computer program product comprises a computer program for implementing the method according to the first aspect of the present invention when executed by a computer.

Drawings

The principles, features and advantages of the present invention may be better understood by describing the invention in more detail below with reference to the accompanying drawings. The drawings comprise:

FIG. 1 shows a schematic diagram of various forms of internal damage after fuel cell decay;

FIG. 2 shows a schematic diagram of the effect of fuel cell decay on internal catalytic layer structure;

FIG. 3 shows a block diagram of an apparatus for state of health monitoring of a fuel cell in accordance with an exemplary embodiment of the present invention;

FIG. 4 shows a schematic diagram of an exemplary scenario for generating an oxygen depletion process according to one embodiment of the present invention;

FIG. 5 shows a flow chart of a method for state of health monitoring of a fuel cell in accordance with an exemplary embodiment of the present invention;

FIG. 6 shows a schematic diagram representing the overall degree of degradation by a time characteristic curve of the output voltage of the fuel cell stack during the oxygen depletion phase;

fig. 7 shows a schematic diagram representing the degree of local degradation by means of a time characteristic of the output voltage of the fuel cell during the oxygen depletion phase;

fig. 8 shows a schematic diagram representing the degree of degradation of the fuel cell by the impedance characteristic curve of the fuel cell at the oxygen depletion stage; and

fig. 9 shows a schematic diagram for characterizing the degree of degradation of a fuel cell by means of an oxygen concentration profile of the fuel cell during an oxygen depletion phase.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings and exemplary embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of the invention.

Fig. 1 shows a schematic diagram of various forms of destruction of the interior of a fuel cell after degradation.

After frequent load changes or start-stops of the fuel cell stack, a severe internal damping occurs, and the effect of this damping is illustrated in respective sub-diagrams (a) to (e) of fig. 1 in conjunction with different structural parts of the fuel cell.

In sub-diagram (a) the internal basic structure of a fuel cell is shown, which for example comprises cathode-side and anode-side

gas diffusion layers

101, 105, a cathode catalyst layer 102, a proton exchange membrane 103, an anode catalyst layer 104.

The electrolyte variation in the cathode catalytic layer is shown in sub-diagram (b). For example, as temperature humidity cycles and freezing and thawing cycles occur at low temperature conditions, migration of the liquid electrolyte 107 in the catalytic layer may occur. Since the solid electrolytes (e.g., pt) 106, 108 are not free-flowing, a substantial portion of the surface of the Pt 106 is left free from the liquid electrolyte 107, while another portion of the surface of the Pt 108 is left with excess liquid electrolyte 107.

The internal structural changes in the cathode catalyst layer are shown in subfigure (c). Fuel cells can lead to carbon corrosion, for example during start-up or during a gas shortage, leading to cracks 110 in the catalyst layers.

In sub-diagram (d) is shown the separation between the catalytic layer and the proton exchange membrane resulting from the degradation of the fuel cell.

The internal structural changes in the proton exchange membrane are shown in subfigure (e). When no degradation occurs, there is no crack in the proton exchange membrane 103 between the cathode 112 and the anode 113 of the fuel cell. When deterioration occurs, crack pinholes 111 occur in the proton exchange membrane 103.

Fig. 2 shows a schematic diagram of the effect of fuel cell decay on the internal catalytic layer structure.

The catalytic layer of the fresh electrode is shown on the left side of fig. 2, and it can be seen that the catalytic layer as a whole assumes a very complete state. The right side of fig. 2 shows the catalytic layer after 60 freeze-thaw cycles, and the gas diffusion layer is exposed due to the large area of exfoliation caused by the local destruction of the catalytic layer.

In general, these structural changes shown in fig. 1 and 2 result in a decrease in mass transfer performance and an increase in ohmic impedance of the electrode structure of the fuel cell.

Fig. 3 shows a block diagram of an apparatus for state of health monitoring of a fuel cell according to an exemplary embodiment of the present invention.

The device 10 for state of health monitoring of a Fuel cell may be, for example, part of a Fuel Cell Control Unit (FCCU), but it may also be a separately provided device for health monitoring purposes.

The device 10 comprises an acquisition module 11, a receiving module 12 and an analysis module 13. The acquisition module 11 may communicate with various sensors arranged at the fuel cell system 20 in order to receive current state data of the fuel cell system 20 during an oxygen depletion phase, the so-called oxygen depletion phase, which is capable of characterizing the state of health of the fuel cell. Such current state data may be the output voltage V of the fuel cell _FC And its time course, impedance Z and its time course, output current i _FC The concentration distribution of oxygen in the gas diffusion layer and the catalyst layer, the oxygen diffusion rate and other physical parameters.

The receiving module 12 can communicate with a server 30 (in particular arranged in the cloud), for example, in order to retrieve historical state data of the fuel cell therefrom. It is also possible that the historical state data is stored in a local controller of the fuel cell system 20. Depending on the type of current state data that is obtained, the historical state data that is expected to be called up can be present here in the form of data points or else in the form of characteristic curves.

After the current status data and the historical status data have been acquired, these data are transmitted to the analysis module 13, where the current status data and the historical status data can be subjected to corresponding signal processing and analysis operations, so that the state of health of the fuel cell can be determined. Such a state of health can be characterized, inter alia, by information on the degree of degradation, the lifetime, etc. of the fuel cell.

As shown in fig. 3, a high voltage DC/DC converter 40, which is a component of a powertrain of a fuel cell electric vehicle that can directly access the fuel cell stack and directly control the output current of the fuel cell stack, is also illustratively externally connected to the output of the fuel cell system. Generally, the DC/DC converter is used to convert the output voltage of the fuel cell and transfer the generated energy to the DC bus. In order to build up an experimental environment for monitoring the state of health of the battery, i.e. a so-called in-situ cathodic discharge condition, locally in the vehicle, a perturbation current may be applied to the fuel cell, for example by means of the DC/DC converter.

In the case of cathode discharge, by providing the high-voltage DC/DC converter with a specified reference current i _ref The output current of the fuel cell can be controlled to create different current steps, and the current density can be freely adjusted. Accordingly, the current response and the voltage response of the fuel cell stack may also be measured by the DC/DC converter. These data are transmitted to an evaluation module 13 or other control unit of the device 10 by means of a communication bus, such as a CAN bus, so that the generated data are available for diagnosis and maintenance of the fuel cell.

In addition, in order to make the current state data comparable to the historical state data, it is necessary to control the measurement conditions to be consistent with or satisfy a certain relationship with the measurement conditions of the historical state data each time the current state data is measured at the oxygen depletion stage. This can be achieved, for example, by the apparatus 10 appropriately matching and adjusting a plurality of subsystems 50 (e.g., thermal management system, reactant gas pressure management system, humidity management system) to achieve the desired measurement conditions required. As an example, the temperature, humidity, reactant flow rate, purge rate, pressure, etc. may be controlled to remain substantially constant at each measurement instant, thereby effectively removing interference from environmental factors on the measurement results.

FIG. 4 shows a schematic diagram of an exemplary scenario for generating an oxygen depletion process according to one embodiment of the present invention.

After shutdown of the fuel cell system 20, hydrogen gas may remain in the anode 22, and as the hydrogen gas is slowly consumed, air gradually diffuses from the cathode 21 to the anode 22, thereby forming an oxygen-hydrogen interface, which may lead to, among other things, corrosive degradation of the carbon support of the cell, and ultimately, fuel cell performance degradation.

In order to avoid the formation of a hydrogen-oxygen interface as much as possible or to reduce the maintenance time of the hydrogen-oxygen interface as much as possible, it is possible to limit the access of air to the interior of the fuel cell and thus the consumption of residual oxygen by adjusting the reaction gas shut-off sequence (air shut-off before hydrogen shut-off), which also constitutes an advantageous measurement condition for monitoring the state of health of the fuel cell.

Initially, both the cathode 21 and the anode 22 of the fuel cell 20 are filled with the reaction gas. Then, the supply of the reaction gas on the cathode 21 side is interrupted, which can be achieved, for example, by closing the shut-off

valves

23, 24 in the intake line and the exhaust line on the cathode 21 side, respectively, thereby forming a closed space with respect to the outside air. On the anode 22 side, the supply of hydrogen gas at the original flow rate and pressure is continued while the gas discharged from the anode 21 side is recirculated to the fuel cell stack via the hydrogen circulation line. Then, as the redox reaction proceeds, the remaining oxygen inside the fuel cell stack is gradually consumed, and thus the oxygen concentration becomes lower and lower, which is referred to as an oxygen depletion process in the sense of the present invention.

Here, in order to detect the current state data of the fuel cell at the oxygen depletion stage, for example, after the

cutoff valves

23, 24 on the cathode 21 side are switched to the closed state, the output (e.g., current/voltage) of the fuel cell stack may be controlled by the high-voltage DC/DC converter. For example, a constant perturbation current may be applied to the fuel cell stack by means of a DC/DC converter, and the output voltage response of the fuel cell during the oxygen depletion phase may then be measured, in addition to measuring the impedance characteristic of the fuel cell in conjunction with a corresponding purge operation. Such output voltage responses or impedance characteristics can be recorded not only as current state data, but also stored in a local or cloud server in association with the measurement time, so that they can be provided in the form of historical reference data for later state of health analysis of the fuel cell.

Fig. 5 shows a flow chart of a method for state of health monitoring of a fuel cell according to an exemplary embodiment of the invention. The method according to the invention is explained here with the aid of the apparatuses and scenarios shown in fig. 3-4.

In step S11, the supply of oxygen to the fuel cell is stopped. Here, for example, the shut-off

valves

23, 24 in the reactant gas line on the fuel cell cathode 21 side are closed.

In step S12, the environmental condition of the fuel cell is controlled to satisfy a preset condition. In order to obtain the desired output voltage response and impedance characteristics, a perturbation current can be applied to the fuel cell and the current can be maintained constant, for example, by means of in-situ cathodic discharge measurement. As an example, a constant current in the form of a current step can be provided by means of a high voltage DC/DC converter as shown in fig. 3. In addition, the measurement conditions can meet the preset environmental conditions by controlling the set parameters of the corresponding subsystems such as the thermal management system, the humidity management system, the reaction gas flow rate control system, the purging mechanism, the pressure control system and the like, so that the influence of environmental factors on the health state monitoring of the fuel cell can be eliminated to a certain extent.

In step S13, current state data of the fuel cell during the oxygen depletion phase, which is capable of characterizing the state of health of the fuel cell, is acquired.

Here, the oxygen depletion phase refers to: a time period from the time when the introduction of oxygen into the cathode is stopped until the oxygen content in the fuel cell is exhausted. Such an oxygen depletion process can be produced, for example, by controlling the shut-off

valves

23, 24 shown in fig. 4 accordingly, and measures are usually taken to establish this condition before each shut-down of the fuel cell in order to avoid the occurrence of an oxygen-hydrogen interface, so that, in particular, no additional equipment or separate experimental conditions need to be introduced for the health monitoring of the fuel cell, which greatly reduces the expenditure.

In the sense of the present invention, such current state data may be physical quantities that can be measured directly or intermediate results that are obtained on the basis of the measurement by data analysis or signal processing.

Thus, on the one hand, the current state data can be characterized by the voltage, the impedance and their time course. For the fuel cell model, both of these (voltage/impedance) belong to physical quantities that can be directly measured. On the other hand, there are physical quantities which cannot be measured directly or are difficult to measure directly, but which can likewise reflect the deterioration of the fuel cell in principle, and which can be used as an intermediate result or as an analytical product as an indicator for the state of health of the fuel cell, also during the oxygen depletion phase. This includes, for example: the concentration distribution of oxygen in the Gas Diffusion Layer (GDL) and/or the Catalytic Layer (CL) in the fuel cell, the diffusion capacity of oxygen between the electrodes, and the like.

In step 21, a data call request is sent to a history database disposed at the cloud server or local. Such a data call request comprises, for example, the type of data to be requested (output voltage, output current, impedance, oxygen concentration profile and/or oxygen diffusion rate, etc.) and a predefined time interval or measurement instant.

In response to such a call request, corresponding historical state data may be extracted from the historical database and sent to the receiving module 12 of the device 1 in step 22.

Next, in step S31, the acquired historical state data is compared with the current state data, and the deterioration rate, the degree of deterioration, and/or the remaining life of the fuel cell are calculated according to the result of the comparison. This comparison may be performed qualitatively, but may also be accomplished by quantitatively analyzing the relationship between the current state data and the historical state data and building a corresponding mathematical expression or physical model. By such an analysis of the comparison results, the state of health of the fuel cell can be understood in a more intuitive manner.

In step S32, it is determined whether the calculated parameter characterizing the state of health of the fuel cell is higher than a tolerable limit. As an example, the calculated deterioration rate is compared with a deterioration rate limit value, for example, and it is thus determined whether the degree of deterioration of the fuel cell has become very severe and therefore further measures need to be taken.

If this is the case, remedial action may be taken in step S33. For example, the fuel cell may be shut down or disabled to avoid further adverse effects on the normal operation of the vehicle. For example, an alarm can be sent to the mobile terminal of the vehicle user through the corresponding communication interface to remind the vehicle user to take measures as soon as possible, so that a travel scheme is reasonably arranged or a battery maintenance plan is made in advance.

If the tolerable limit has not been exceeded, further measures can be taken in step S34. For example, the fuel cell may continue to be used and the above steps may be repeated at certain intervals in order to continuously monitor the state of health of the fuel cell.

Fig. 6 shows a schematic diagram representing the overall degree of degradation by a time characteristic curve of the output voltage of the fuel cell stack in the oxygen depletion phase.

Fig. 6 shows the course of the output voltage of the entire fuel cell stack over time U1, U2, U3, U4 measured several times during the oxygen depletion phase, the first three measurements U1 to U3 being storable in a cloud server, for example, as historical state data. The last measurement U4 is taken as the current state data of the fuel cell, which is used to characterize the current state of health of the fuel cell.

As can be seen by observing the trend of the variation of the individual voltage characteristic curves, the voltage value of the entire fuel cell stack is at a relatively high level in response to the applied constant disturbance current at the time of the initial stop of the supply of oxygen. As the oxygen in the fuel cell stack is gradually depleted, the residual oxygen concentration becomes lower and lower, and thus the output voltage of the entire fuel cell stack also continues to drop. Finally, when the oxygen is completely depleted, the output voltage is maintained at a lower level.

By comparing the latest measured output voltage variation process U4 with the historical voltage variation processes U1-U3, it is found that as the degradation of the fuel cell proceeds, the gas diffusion capacity of the fuel cell becomes worse and worse due to the decrease in the mass transfer performance of the electrode structure, which results in the more and more significant loss of the output voltage of the fuel cell. Therefore, as indicated by arrows in fig. 6, the output voltage of the fuel cell decreases to the minimum level more and more rapidly during the oxygen depletion period due to the increasing degree of deterioration. It can be seen in particular that the most recently measured voltage curve U4 decreases to a steady value as quickly as possible in comparison with the state data U1 to U3 recorded at the historical time, so that the degradation trend of the fuel cell can be reflected unambiguously from the output voltage response of the oxygen depletion phase.

As an example, to more effectively analyze the state of health of the fuel cell, only the linear portions of the voltage characteristic curves U1-U4 may be of interest. This can be achieved, for example, by defining the time interval t1-t3 during the oxygen depletion phase. During this predetermined time interval (indicated by a grey square in fig. 6), a measurement point p1, p2, p3, p4 can be selected on each voltage characteristic curve U1 to U4 at a specific time t2 relative to the starting time. Then, the corresponding deterioration degree can be judged by comparing the voltage magnitudes corresponding to the measurement points p1, p2, p3, and p4.

As another example, it is also possible to calculate the slopes of the linear portions of the respective voltage characteristic curves U1 to U4, respectively, and quantitatively describe the degree of degradation of the fuel cell by comparing the relationship between the calculated slopes. For example, the larger the value of the slope of the voltage characteristic curve, the more serious the degradation degree.

Fig. 7 shows a schematic diagram representing the degree of local degradation by means of a time characteristic curve of the output voltage of the fuel cell during the oxygen depletion phase. The difference from fig. 6 is that fig. 7 shows not the time course of the output voltage of the entire fuel cell stack, but the time course of the output voltage for the cells in the fuel cell stack.

In the embodiment shown in fig. 7, after the fuel cell has been in use for a certain period of time, the cells are taken in the middle and end regions of the fuel cell stack (near the exhaust line), respectively, and the voltage characteristic curves U5, U6 of these cells are measured during the oxygen depletion phase, respectively. For the sake of clarity, the course U5 of the output voltage of the battery cells in the middle region over time is shown in the upper part of fig. 7. At the same time, fig. 7 shows the course U6 of the output voltage of the battery cells in the end region over time. For reference, voltage characteristic curves U1', U1 ″ of the respective battery cells when no degradation occurs are also shown, respectively.

By contrast, it can be seen that the voltage U6 of the end cell close to the exhaust line drops to a minimum value more quickly than the cell in the central region, which means, for example: the cells in the end regions of the fuel cell stack are subject to more severe or more rapid deterioration. This may be caused in particular by the fact that the cells in the vicinity of the location of the inlet or outlet of the reactive gases are more susceptible to contaminants. However, it is also possible that during the actual measurement, for example, due to an uneven cooling distribution, the cells in the central region of the stack deteriorate more severely.

Fig. 8 shows a schematic diagram for characterizing the degree of degradation of the fuel cell by the impedance characteristic curve of the fuel cell at the oxygen depletion stage.

Fig. 8 shows the course of the impedance of the fuel cell over time Z1, Z2, Z3, Z4 measured several times during the oxygen depletion phase. As an example, the impedance characteristic curve Z1 measured for the first time (for example, in the case where the battery has not deteriorated) may be stored as the history state data. As another example, it is also possible to store a plurality of, for example, the previous three measurements Z1, Z2, Z3 as historical state data, and to consider the last measurement Z4 as current state data of the fuel cell for characterizing the current state of health of the fuel cell.

As can be seen by observing the trend of the individual impedance characteristics, the reduction in the number of redox reactions and the corresponding purging process leads to a gradual reduction in the internal humidity of the cell during the oxygen consumption phase, and therefore to a consequent increase in the impedance.

When a plurality of impedance characteristics Z1, Z2, Z3, Z4 are observed simultaneously, it is found that the impedance characteristics Z4 measured last are shifted overall upwards with respect to the previous measurement results Z1, Z2, Z3. This is caused inter alia by the following reasons: the aging of the fuel cell is accompanied by many structural changes such as carbon corrosion, collapse of the catalytic layer, separation of the catalytic layer from the membrane, and the like, which cause an increase in resistance. However, during normal cell use, such changes in impedance due to structural degradation are often difficult to observe because the impedance is typically at a relatively stable value due to the normal operating conditions of the fuel cell. In the oxygen depletion stage, the impedance changes significantly with a large change in the humidity inside the battery, and the information on the decay of the battery state can be seen more clearly by observing this trend of change (the entire impedance characteristic curve shifts upward).

It follows that the oxygen depletion state provides a very advantageous monitoring condition for the health diagnosis of the fuel cell.

Fig. 9 shows a schematic diagram representing the degree of degradation of the fuel cell by the oxygen concentration profile of the fuel cell at the oxygen depletion stage.

The oxygen concentration distributions in the Gas Diffusion Layer (GDL) and the Catalytic Layer (CL) of the undegraded and degraded fuel cells are shown on the left and right sides of fig. 9, respectively. As the deterioration of the fuel cell progresses, the diffusion ability of the reaction gas in the gas diffusion layer and the catalytic layer of the fuel cell deteriorates, thereby causing the nonuniformity of the distribution of the oxygen concentration inside the fuel cell. For example, in a new cell, the initial oxygen concentration at one end of the gas diffusion layer is C0, the oxygen concentration reaches C1 when reaching the other end of the gas diffusion layer, and the oxygen concentration decreases to C2 after passing through the catalytic layer. However, for an aged cell, less oxygen reaches the other end of the gas diffusion layer, so the oxygen concentration C1 'at that location is significantly lower than the historical data C1, while the oxygen passing through the catalytic layer is further reduced to C2' due to the deterioration of the electrode structure itself, which is significantly lower than the concentration C2 recorded at the historical moment. Such nonuniformity of the gas concentration distribution caused by the deterioration of the internal structure directly causes a loss of the output voltage of the fuel cell.

It will be appreciated by those skilled in the art that the above given choices of parameters characterizing the degradation of the fuel cell are merely exemplary, and as technology evolves, more parameters may be used to characterize the degradation of the fuel cell. However, the present invention is not directed to selecting which parameters, and thus the technical idea of the present invention is not limited by the specific parameters.

Although specific embodiments of the invention have been described herein in detail, they have been presented for purposes of illustration only and are not to be construed as limiting the scope of the invention. Various substitutions, alterations, and modifications may be devised without departing from the spirit and scope of the present invention.

Claims

1. A method for state of health monitoring of a fuel cell, the method comprising the steps of:

2. The method of claim 1, wherein the current state data comprises: the output voltage, the impedance, the time course of the output voltage and/or the time course of the impedance of the fuel cell during the oxygen depletion phase.

3. The method of claim 1 or 2, wherein the oxygen depletion phase refers to: a period of time starting from the cessation of the passage of oxygen to the cathode (21) of the fuel cell until the oxygen inside the fuel cell is depleted, wherein during said period of time the supply of the reactant gas to the anode (22) is maintained in particular.

4. Method according to any of claims 1 to 3, wherein in the step of determining the degree of deterioration, the current state data within a predefined time interval of an oxygen depletion phase is selected for performing the comparison.

5. The method according to any one of claims 1 to 4, wherein in the oxygen depletion phase a constant current is applied to the fuel cell by in-situ cathodic discharge measurement, in particular by means of a DC/DC converter (40) in a fuel cell electric vehicle.

6. The method according to one of claims 1 to 5, wherein the current state data are acquired and the degree of degradation is determined individually for each section of the fuel cell, in particular for each cell.

7. The method of any of claims 1-6, wherein the historical state data comprises: status data measured once at the oxygen depletion stage when the fuel cell has not deteriorated; and/or a collection of state data measured during an oxygen depletion phase a plurality of times during use of the fuel cell.

8. The method according to any one of claims 1 to 7, wherein the degree of degradation of the fuel cell is determined as follows: the faster the currently measured output voltage drops over time, the higher the degree of degradation of the fuel cell, as compared to historical state data; and/or, the more the time course of the currently measured impedance shifts upward overall, the higher the degree of degradation of the fuel cell, as compared to the historical state data.

9. The method according to any one of claims 1 to 8, wherein in the step of acquiring current status data, the ambient temperature, humidity, reactant flow rate and/or pressure are controlled to satisfy preset conditions associated with measurement conditions of historical status data.

10. A device (10) for state of health monitoring of a fuel cell, the device being adapted to perform the method according to any one of claims 1 to 9, the device comprising:

an acquisition module (11) configured to be able to acquire current state data of the fuel cell during an oxygen depletion phase, which data are able to characterize the state of health of the fuel cell;

a receiving module (12) configured to be able to receive historical status data relating to current status data of the fuel cell; and

an analysis module (13) configured to be able to determine a degree of degradation of the fuel cell based on a comparison of the current status data with the historical status data.

11. A computer program product, wherein the computer program product comprises a computer program for implementing the method according to any one of claims 1 to 9 when executed by a computer.