Diagnostic device and electrochemical reaction system

Abstract

A diagnostic device (30, 30A) diagnoses a reactor (FC, EC). The diagnostic device comprises an impedance measurement unit (32, 32A) that measures the internal impedance of the reactor, and a storage unit (M) in which there is stored an equivalent circuit model simulating the electrochemical characteristics of the reactor. The diagnostic device furthermore comprises: a parameter identification unit (34, 34A) that identifies parameters within the equivalent circuit model; and a state diagnosis unit (36, 36A) that diagnoses the internal state of the reactor on the basis of the equivalent circuit model, in which the parameters identified by the parameter identification unit (34, 34A) are used. The equivalent circuit model includes one or more anode diffusion resistors and one or more anode diffusion capacitances as parameters indicating the gas transport characteristics of an anode of the reactor. The parameter identification unit identifies parameters including an anode diffusion resistor and an anode diffusion capacitance on the basis of a physical quantity having a correlation with the gas diffusion rate in the anode of the reactor.

Description

Diagnostic equipment, electrochemical reaction systems CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Patent Application No. 2024-62196, filed on April 8, 2024, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a diagnostic device and an electrochemical reaction system including the diagnostic device.

[0003] Conventionally, a method and apparatus for evaluating gas transport characteristics at the anode have been known, which incorporate an anode diffusion impedance, which is formed by connecting a resistor and a capacitor in parallel, into an equivalent circuit model of a fuel cell (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2007-66589

[0005] However, the frequency response frequency band of the gas transport characteristics at the anode is close to that at the cathode, making it difficult to distinguish between the gas transport characteristics at the anode and the gas transport characteristics at the cathode based on the internal impedance. Therefore, even if a diffusion impedance formed by connecting a resistor and a capacitor in parallel is simply incorporated into an equivalent circuit model of a fuel cell, it is difficult to appropriately evaluate the gas transport characteristics at the anode or the cathode. This is true not only for fuel cells, but also for reaction devices such as electrolysis devices that generate fuel by electrolysis of gases such as water vapor.

[0006] An object of the present disclosure is to provide a diagnostic device and an electrochemical reaction system that are capable of appropriately evaluating the gas transport characteristics of at least one of an anode and a cathode.

[0007] The present inventors have conducted extensive research into solutions to the above problems. As a result of this research, they have discovered that the gas diffusion speeds at the anode and cathode are different. The present disclosure was devised based on this finding.

[0008] According to one aspect of the present disclosure, a diagnostic device diagnoses a reaction device that outputs electric energy through an electrochemical reaction of a first gas that serves as an oxidant and a second gas that serves as a reductant, or that receives as input a first gas that serves as a reductant and a second gas that serves as an oxidant and electrolyzes the second gas using electric energy to output fuel, and includes: an impedance measurement unit that measures an internal impedance of the reaction device based on an AC signal including a plurality of frequencies output from the reaction device; a memory unit that stores an equivalent circuit model that simulates the electrochemical characteristics of the reaction device; a parameter identification unit that compares the internal impedance measured by the impedance measurement unit with the equivalent circuit model to identify a plurality of parameters that constitute the equivalent circuit model; and a condition diagnosis unit that diagnoses an internal condition of the reaction device based on the equivalent circuit model that reflects the parameters identified by the parameter identification unit, wherein the equivalent circuit model includes one or more anode diffusion resistances and one or more anode diffusion capacitances as parameters that indicate gas transport characteristics of an anode of the reaction device, and the parameter identification unit identifies the parameters including the anode diffusion resistance and the anode diffusion capacitance based on a physical quantity that has a correlation with the gas diffusion rate in the anode.

[0009] In this way, if the configuration is such that parameters including the anode diffusion resistance and the anode diffusion capacitance are identified based on physical quantities correlated with the gas diffusion rate at the anode, the difference in the gas diffusion rates at the anode and cathode is reflected in the equivalent circuit model. Use of such an equivalent circuit model makes it easier to understand the gas transport characteristics at the anode separately from the gas transport characteristics at the cathode, thereby enabling appropriate evaluation of the gas transport characteristics at the anode.

[0010] According to another aspect of the present disclosure, a diagnostic device diagnoses a reaction device that outputs electric energy through an electrochemical reaction of a first gas that serves as an oxidant and a second gas that serves as a reductant, or that receives as input the first gas that serves as a reductant and the second gas that serves as an oxidant and electrolyzes the second gas using electric energy to output fuel, and includes: an impedance measurement unit that measures an internal impedance of the reaction device based on an AC signal including a plurality of frequencies output from the reaction device; a memory unit that stores an equivalent circuit model that simulates electrochemical characteristics of the reaction device; a parameter identification unit that compares the internal impedance measured by the impedance measurement unit with the equivalent circuit model to identify a plurality of parameters that constitute the equivalent circuit model; and a condition diagnosis unit that diagnoses an internal condition of the reaction device based on the equivalent circuit model that reflects the parameters identified by the parameter identification unit, wherein the equivalent circuit model includes one or more cathode diffusion resistances and one or more cathode diffusion capacitances as parameters that indicate gas transport characteristics of a cathode of the reaction device, and the parameter identification unit identifies the parameters including the cathode diffusion resistance and the cathode diffusion capacitance based on a physical quantity that has a correlation with a gas diffusion rate in the cathode.

[0011] In this way, if the configuration is such that parameters including the cathode diffusion resistance and the cathode diffusion capacitance are identified based on physical quantities correlated with the gas diffusion rate in the cathode, the difference in gas diffusion rate between the anode and the cathode is reflected in the equivalent circuit model. Use of such an equivalent circuit model makes it easier to understand the gas transport characteristics in the cathode separately from the gas transport characteristics in the anode, thereby enabling appropriate evaluation of the gas transport characteristics in the cathode.

[0012] According to another aspect of the present disclosure, a diagnostic device diagnoses a reaction device that outputs electric energy by an electrochemical reaction of a first gas that serves as an oxidant and a second gas that serves as a reductant, or that receives as input the first gas that serves as a reductant and the second gas that serves as an oxidant and electrolyzes the second gas with electric energy to output fuel, and includes: an impedance measurement unit that measures an internal impedance of the reaction device based on an AC signal including a plurality of frequencies that is output from the reaction device; a memory unit that stores an equivalent circuit model that simulates electrochemical characteristics of the reaction device; a parameter identification unit that compares the internal impedance measured by the impedance measurement unit with the equivalent circuit model to identify a plurality of parameters that constitute the equivalent circuit model; and a state diagnosis unit that diagnoses an internal state of the reaction device based on the equivalent circuit model that reflects the parameters identified by the parameter identification unit, wherein the equivalent circuit model includes one or more anode diffusion resistances and one or more anode diffusion capacitances as parameters that indicate gas transport characteristics of an anode of the reaction device, and one or more cathode diffusion resistances and one or more cathode diffusion capacitances as parameters that indicate gas transport characteristics of a cathode of the reaction device, The parameter identification unit identifies the parameter based on a first physical quantity that has a correlation with the gas diffusion rate in the anode and a second physical quantity that has a correlation with the gas diffusion rate in the cathode.

[0013] This makes it easier to understand the gas transport characteristics at the anode and the gas transport characteristics at the cathode separately, and therefore makes it possible to appropriately evaluate the gas transport characteristics at the anode and the cathode, respectively.

[0014] FIG. 1 is a schematic configuration diagram of a fuel cell system according to a first embodiment. FIG. 2 is an explanatory diagram illustrating an equivalent circuit model of a reaction device according to the first embodiment. FIG. 3 is a Cole-Cole plot diagram of internal impedance determined when an AC current is superimposed on a reaction device. FIG. 4 is an explanatory diagram illustrating gas diffusion characteristics of a fuel gas and an oxidant gas. FIG. 5 is a flowchart illustrating the flow of a diagnostic process performed by a diagnostic device. FIG. 6 is an explanatory diagram illustrating an anode diffusion resistance and a cathode diffusion resistance. FIG. 7 is a flowchart illustrating the flow of an abnormality countermeasure process performed by a control unit of a fuel cell system. FIG. 8 is an explanatory diagram illustrating an equivalent circuit model of a reaction device according to a first modified example of the first embodiment. FIG. 9 is an explanatory diagram illustrating an equivalent circuit model of a reaction device according to a second modified example of the first embodiment. FIG. 10 is an explanatory diagram illustrating an equivalent circuit model of a reaction device according to a third modified example of the first embodiment. FIG. 11 is a flowchart illustrating the flow of a diagnostic process performed by a control unit of a fuel cell system according to a second embodiment.

[0015] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, parts that are the same as or equivalent to those described in the preceding embodiments will be given the same reference numerals, and their description may be omitted. Furthermore, in the embodiments, when only some of the components are described, the components described in the preceding embodiments can be applied to the remaining components. The following embodiments can be partially combined with each other, even if not specifically stated, as long as there is no particular problem with the combination.

[0016] First Embodiment This embodiment will be described with reference to Figures 1 to 7. In this embodiment, an example will be described in which a diagnostic device 30 and an electrochemical reaction system according to the present disclosure are applied to a diagnostic device 30 for a fuel cell FC and a fuel cell system 1, as shown in Figure 1.

[0017] The fuel cell system 1 is configured as a system to be mounted on a mobile object such as a vehicle, and includes a fuel cell FC, an air supply unit SAP, a fuel supply unit SFP, and a control device 10 for the fuel cell FC, as shown in FIG.

[0018] The fuel cell FC outputs electrical energy through an electrochemical reaction of a fuel gas containing air as an oxidant and hydrogen as a reducing agent. The fuel cell FC of this embodiment outputs electrical energy through an electrochemical reaction between hydrogen and oxygen. In this embodiment, the fuel cell FC corresponds to the "reaction device." Also, in this embodiment, air corresponds to the "first gas" as an oxidant, and the fuel gas corresponds to the "second gas" as a reducing agent.

[0019] Specifically, the fuel cell FC is configured as a cell stack CS in which a plurality of polymer electrolyte fuel cells C are stacked. The polymer electrolyte fuel cells C are also called PEFCs (short for Polymer Electrolyte Fuel Cells).

[0020] As shown in the lower part of Fig. 2, each battery cell C includes an electrolyte membrane EM, a hydrogen electrode AN constituting the anode, an oxygen electrode CA constituting the cathode, and a separator SP forming an air flow path and a fuel flow path. The battery cell C outputs electrical energy to an external circuit (not shown) through the electrochemical reaction of hydrogen and oxygen shown in the following reaction formulas F1 and F2. The power output from each battery cell C is supplied to a load device or a battery via a power converter such as an inverter (not shown).

[0021] (Fuel electrode) 2H ２ →4H ＋ +4e － ...(F1) (oxygen electrode) 4H ＋ +O ２ +4e － →2H ２ O...(F2)

[0022] An air supply unit SAP including an air flow path and a fuel supply unit SFP including a fuel gas flow path are connected to the fuel cell FC. Air serving as an oxidizing agent and hydrogen serving as a reducing agent are supplied to the fuel cell FC through the air supply unit SAP and the fuel supply unit SFP.

[0023] The air supply unit SAP uses atmospheric air as a supply source and supplies the air from the supply source to the fuel cell FC using a blower or the like (not shown). The air supply unit SAP constitutes a "first gas supply unit" that controls the supply amount of a first gas, which serves as an oxidant, to the fuel cell FC, which is a reaction device.

[0024] The fuel supply unit SFP uses a hydrogen tank or the like as a fuel gas supply source, and supplies hydrogen from the supply source to the fuel cell FC using a blower or the like (not shown). The fuel supply unit SFP constitutes a "second gas supply unit" that controls the supply amount of a second gas, which serves as a reducing agent, to the fuel cell FC, which is a reaction device.

[0025] In a fuel cell FC, water produced by the electrochemical reaction between hydrogen and oxygen is discharged as off-gas. This off-gas may contain unreacted hydrogen in addition to water. For this reason, the fuel cell system 1 is designed so that the hydrogen concentration in the off-gas is reduced by recycling or by using a catalyst before it is discharged to the outside.

[0026] The control device 10 of the fuel cell FC is configured by a computer including a processor and a memory unit M. The memory unit M includes not only ROM and RAM but also auxiliary storage devices, etc. The memory unit M is a non-transitory tangible storage medium.

[0027] The control device 10 includes a control unit 20 that controls various devices in the fuel cell system 1 and a diagnostic device 30 that diagnoses the internal state of the fuel cell FC. The control unit 20 and the diagnostic device 30 may be configured using common hardware, or may be configured using separate hardware.

[0028] The control unit 20 outputs control signals to various controlled devices such as the air supply unit SAP and the fuel supply unit SFP, thereby controlling the operation of the various controlled devices. Furthermore, when the diagnosis result of the internal state of the fuel cell FC by a diagnosis device 30 (described later) indicates an abnormal state, the control unit 20 performs recovery processing to recover from the abnormal state. The control unit 20 includes, as functional units for realizing various functions, a device control unit 21 that controls the operation of the various controlled devices, and a recovery execution unit 22 that executes recovery processing.

[0029] The diagnostic device 30 measures the internal impedance of the fuel cell FC and diagnoses the internal state of the fuel cell FC using an equivalent circuit model based on the measured internal impedance. The diagnostic device 30 includes an impedance measurement unit 32, a parameter identification unit 34, and a state diagnosis unit 36 ​​as functional units for realizing various functions.

[0030] The impedance measurement unit 32 measures the internal impedance of the fuel cell FC based on the electrochemical impedance method. Specifically, the impedance measurement unit 32 superimposes an AC current of a predetermined frequency on the fuel cell FC and measures the internal impedance of the fuel cell FC based on an AC signal containing multiple frequencies output from the fuel cell FC. The internal impedance measured by the impedance measurement unit 32 is used for fitting parameters of the equivalent circuit model ECM stored in the memory unit M. Note that the impedance measurement unit 32 may also be configured to superimpose an AC current of a predetermined frequency on each battery cell C and measure the internal impedance of each battery cell C based on the AC signal output from each battery cell C. In this case, the internal impedance of each battery cell C corresponds to the internal impedance of the fuel cell FC.

[0031] Here, the equivalent circuit model ECM is a circuit model that simulates the fuel cell FC, and is stored in advance in the storage unit M. The equivalent circuit model ECM includes parameters that indicate the gas transport characteristics of the anode and cathode of the fuel cell FC.

[0032] In the memory unit M of this embodiment, a circuit model is stored as an equivalent circuit model ECM, in which a membrane resistance Romh, a gas reaction component GR, an anode diffusion component AD, and a cathode diffusion component CD are connected in series, as shown in Fig. 2. The gas reaction component GR is a parameter indicating the reaction characteristics of the reaction gas in the catalyst, and is configured as a series circuit in which a reaction resistance Ract and a reaction capacity Cact are connected in parallel. The anode diffusion component AD is a parameter indicating the gas diffusion characteristics in the anode, and the anode diffusion resistance R Ｈ and anode diffusion capacitance C ＨThe cathode diffusion component CD is a parameter that indicates the gas diffusion characteristics in the cathode, and the cathode diffusion resistance R Ｏ and cathode diffusion capacitance C Ｏ and are configured as a series circuit connected in parallel.

[0033] The parameter identification unit 34 compares the internal impedance measured by the impedance measurement unit 32 with the equivalent circuit model ECM to identify a plurality of parameters that constitute the equivalent circuit model ECM. Upon completion of the parameter identification, the parameter identification unit 34 stores the equivalent circuit model ECM reflecting the parameters in the memory unit M.

[0034] Here, Fig. 3 is a Cole-Cole plot showing the behavior of the internal impedance of a fuel cell FC on a complex plane, measured based on the electrochemical impedance method. In Fig. 3, the behavior of the internal impedance when the gas transport properties inside the fuel cell FC are normal is shown by a solid line. In Fig. 3, the behavior of the internal impedance when the gas transport properties at the anode deteriorate is shown by a dashed-dotted line, and the behavior of the internal impedance when the gas transport properties at the cathode deteriorate is shown by a dashed-two-dotted line.

[0035] As shown in Figure 3, when the gas transport characteristics at the anode and cathode deteriorate, the internal impedance curve becomes larger on the right side of the complex plane compared to when the gas transport characteristics are normal. However, the frequency response frequency band of the gas transport characteristics at the anode is close to that of the gas transport characteristics at the cathode, making it difficult to distinguish between the gas transport characteristics at the anode and the gas transport characteristics at the cathode based on the internal impedance.

[0036] Therefore, even if a diffusion impedance, which is a parallel connection of a resistance component and a capacitance component, is simply incorporated into an equivalent circuit model ECM of a fuel cell FC, it is difficult to appropriately evaluate the gas transport characteristics at the anode or cathode. Note that the diffusion impedance is the impedance corresponding to the anode diffusion component AD and the cathode diffusion component CD.

[0037] In a fuel cell FC, the diffusion rate of gas at the anode differs from that at the cathode. Specifically, as shown in Figure 4, the diffusion rate of gas at the anode tends to be about four times faster than that at the cathode. This difference in diffusion rate is manifested as a difference in the cutoff frequency of the anode-diffused component AD and the cathode-diffused component CD.

[0038] Taking these factors into consideration, the parameter identification unit 34 is configured to identify parameters constituting the equivalent circuit model ECM based on a first physical quantity correlated with the gas diffusion rate in the anode and a second physical quantity correlated with the gas diffusion rate in the cathode. The parameter identification is performed by, for example, complex nonlinear least squares analysis, DRT analysis, or the like. DRT is an abbreviation for Distribution of Relaxation Times.

[0039] The parameter identifying unit 34 of this embodiment determines the cutoff frequency of the anode diffusion component AD as a first physical quantity having a correlation with the gas diffusion rate at the anode. The parameter identifying unit 34 also determines the cutoff frequency of the cathode diffusion component CD as a second physical quantity having a correlation with the gas diffusion rate at the cathode. The parameter identifying unit 34 may, for example, determine the cutoff frequency of the cathode diffusion component CD by using the formula "1 / (2π*R Ｈ *C Ｈ )" is calculated as the cutoff frequency of the anode diffusion component AD, and "1 / (2π*R Ｏ *C Ｏ )" is calculated as the cutoff frequency of the cathode diffusion component CD. Note that, hereinafter, the cutoff frequency of the anode diffusion component AD may also be referred to as "CF1," and the cutoff frequency of the cathode diffusion component CD may also be referred to as "CF2."

[0040] The parameter identification unit 34 then identifies the parameters that make up the equivalent circuit model ECM based on CF1 and CF2. Specifically, the parameter identification unit 34 sets predetermined constraints on CF1 and CF2 and identifies each parameter so that the constraints are met.

[0041] As the constraint, for example, at least one of the following conditions [LC1] to [LC6] is adopted.

[0042] [LC1] CF1 ≧ first threshold, CF2 ≧ second threshold (however, first threshold > second threshold) [LC2] CF1 is within the first range, CF2 is within the second range (however, first range > second range) [LC3] CF1-CF2 ≧ predetermined threshold [LC4] CF1-CF2 is within a predetermined range [LC5] CF1 / CF2 ≧ predetermined threshold [LC6] CF1 / CF2 is within a predetermined range

[0043] The above-mentioned constraint conditions are defined, for example, as relational expressions, functions, etc. Note that the constraint conditions are merely examples and may be different from those described above. Furthermore, the threshold values ​​and ranges in the constraint conditions are set based on CF1 and CF2 obtained through simulation, experimentation, on-board learning, etc. However, it is desirable that the threshold values ​​and ranges in the constraint conditions be changed in accordance with the battery temperature, battery voltage, battery load, deterioration over time, tightening force of the cell stack CS, etc.

[0044] The state diagnosis unit 36 ​​diagnoses the internal state of the fuel cell FC based on the equivalent circuit model ECM that reflects the parameters identified by the parameter identification unit 34. The state diagnosis unit 36 ​​of this embodiment diagnoses the internal state of the fuel cell FC based on the anode diffusion resistance R Ｈ Based on this, it is determined whether or not there is a shortage of fuel gas.

[0045] The state diagnosis unit 36 ​​uses, for example, one of the following conditions [JC1] to [JC3] as a determination condition, and determines that the fuel is insufficient when the determination condition is met.

[0046] [JC1]R Ｈ ≧ Abnormal threshold [JC2]R Ｈ is above the abnormal threshold multiple times in succession [JC3]R Ｈ exceeds the abnormal threshold multiple times within a specified period

[0047] Here, the determination of whether or not there is a lack of fuel is made by checking the anode diffusion resistance R Ｈ and the moving average value of the anode diffusion resistance R ＨThe abnormality threshold value in the determination conditions is preferably changed depending on the battery temperature, battery voltage, battery load, internal pressure of the fuel cell FC, stoichiometry on the anode side, etc.

[0048] Next, the operation of the fuel cell system 1 when diagnosing the internal state of the fuel cell FC will be described with reference to Figures 5 to 7. Figure 7 is a flowchart showing the flow of the abnormality countermeasure processing executed by the control unit 20. The control routine shown in Figure 5 is executed periodically or irregularly while the fuel cell FC is in a power generation state.

[0049] 5, in step S100, the diagnostic device 30 superimposes an AC current of a predetermined frequency on the fuel cell FC. The diagnostic device 30 changes the frequency of the AC current in a frequency range from low to high (for example, 0.01 Hz to 10 kHz).

[0050] Next, in step S110, the diagnostic device 30 measures the internal impedance of the fuel cell FC based on the electrochemical impedance method while changing the frequency of the alternating current superimposed on the fuel cell FC.

[0051] Next, in step S120, the diagnostic device 30 sets an equivalent circuit model ECM. Specifically, the diagnostic device 30 reads the equivalent circuit model ECM stored in the storage unit M in advance.

[0052] Next, in step S130, the diagnostic device 30 sets constraints for identifying the parameters constituting the equivalent circuit model ECM. These constraints are conditions for distinguishing between the gas diffusion characteristics of the anode and the cathode. In this embodiment, the constraints impose certain constraints on the cutoff frequencies of the anode diffusion component and the cathode diffusion component.

[0053] Next, in step S140, the diagnostic device 30 compares the internal impedance with the equivalent circuit model ECM to identify a plurality of parameters constituting the equivalent circuit model ECM. Specifically, the diagnostic device 30 sets predetermined constraints on the cutoff frequency of the anodic diffusion component AD and the cutoff frequency of the cathodic diffusion component CD, and identifies each parameter so that the constraints are met.

[0054] Here, FIG. 6 shows the anode diffusion resistance R identified by the diagnostic device 30. Ｈ and cathode diffusion resistance R Ｏ 6 is an explanatory diagram for explaining the above-mentioned Cole-Cole plot (proposed example) when each parameter is identified with constraints set, and the Cole-Cole plot (comparison example) when each parameter is identified without constraints set is shown in the upper left of FIG.

[0055] As shown in FIG. 6, the Cole-Cole plot of the comparative example behaves similarly to the Cole-Cole plot of the present invention. However, in the comparative example, the values ​​of the diffusion resistances R constituting the parameters of the equivalent circuit model ECM are different. Ｈ , R Ｏ There is a large variation in the two, making it difficult to distinguish between them.

[0056] In contrast to this, in the present invention, the diffusion resistances R constituting the parameters of the equivalent circuit model ECM are Ｈ , R Ｏ There is almost no variation in the resistance of each diffusion resistor R Ｈ , R Ｏ Since there is a significant difference between the two, it is possible to distinguish between them.

[0057] Next, in step S150, the diagnostic device 30 diagnoses the internal state of the fuel cell FC based on the equivalent circuit model ECM that reflects the parameters identified by the parameter identification unit 34. The diagnostic device 30 of this embodiment diagnoses the internal state of the fuel cell FC based on the anode diffusion resistance R Ｈ The diagnostic device 30 stores the diagnostic results of the internal state of the fuel cell FC in the memory unit M, and then ends the diagnostic process for the fuel cell FC.

[0058] Next, the control process executed by the control unit 20 based on the diagnosis results of the diagnosis device 30 will be described with reference to Fig. 7. The control routine shown in Fig. 7 is executed periodically or irregularly while the fuel cell FC is generating electricity.

[0059] 7, in step S200, the control unit 20 reads the diagnosis results of the internal state of the fuel cell FC by the diagnosis device 30 from the memory unit M. Then, in step S210, the control unit 20 determines whether the fuel cell FC is in a fuel shortage state.

[0060] If the fuel cell FC is in a fuel shortage state, the control unit 20 proceeds to step S220, and if the fuel cell FC is not in a fuel shortage state, the control unit 20 skips the process of step S220 and ends this process.

[0061] If the fuel cell FC is in a fuel-starved state, the control unit 20 executes recovery processing in step S220. Recovery processing is processing for recovering from an abnormal state when the diagnosis result of the internal state of the fuel cell FC by the diagnosis device 30 indicates an abnormal state. If the fuel cell FC is in a fuel-starved state, the control unit 20 of this embodiment executes recovery processing to restore the fuel-starved state to a normal state. If the fuel cell FC is in a fuel-starved state, the control unit 20 executes at least one of the processes shown below in [RP1] to [RP7] as recovery processing, for example.

[0062] [RP1] Suppress the accumulation of generated water at the anode by increasing the amount of fuel gas supplied. [RP2] Suppress the accumulation of generated water at the anode by reducing the humidity of the fuel gas. [RP3] Move the generated water from the anode to the cathode by reducing the pressure on the anode side and increasing the water vapor partial pressure on the cathode side. [RP4] Suppress the amount of generated water by increasing the temperature of the fuel gas and oxidant gas. [RP5] Suppress the amount of generated water by increasing the load on the fuel cell FC to raise the temperature of each battery cell C. [RP6] Suppress the amount of generated water by reducing the water vapor partial pressure on the cathode side. [RP7] Suppress the amount of generated water by lowering the upper limit of the sweep current from the fuel cell FC.

[0063] The abnormal state of the fuel cell FC is restored to a normal state by executing this recovery process in the control unit 20. The recovery process may be performed temporarily or permanently, but it is desirable to continue it until the diagnosis result of the diagnosis device 30 indicates a normal state.

[0064] The diagnostic device 30 described above identifies parameters constituting an equivalent circuit model based on a first physical quantity correlated with the gas diffusion rate at the anode and a second physical quantity correlated with the gas diffusion rate at the cathode. The diagnostic device 30 then diagnoses the internal state of the fuel cell FC based on the equivalent circuit model with the identified parameters. In this way, if the diagnostic device 30 is configured to identify parameters including the diffusion resistance and the diffusion capacitance based on the physical quantities correlated with the gas diffusion rates at the anode and the cathode, respectively, the difference in the gas diffusion rates at the anode and the cathode is reflected in the equivalent circuit model. Using such an equivalent circuit model makes it easier to understand the gas transport characteristics at the anode separately from the gas transport characteristics at the cathode, thereby enabling the gas transport characteristics at the anode to be appropriately evaluated.

[0065] The diagnostic device 30 of this embodiment also has the following features.

[0066] (1) The diagnostic device 30 determines the cutoff frequency of the anode diffusion component, which is determined using the anode diffusion resistance and the anode diffusion capacitance, as a physical quantity correlated with the gas diffusion rate at the anode. The diagnostic device 30 also determines the cutoff frequency of the cathode diffusion component, which is determined using the cathode diffusion resistance and the cathode diffusion capacitance, as a physical quantity correlated with the gas diffusion rate at the cathode. The diagnostic device 30 then identifies the parameters of the equivalent circuit model ECM based on the cutoff frequencies of the anode diffusion component and the cathode diffusion component. This makes it easier to separately understand the gas transport characteristics at the anode and the gas transport characteristics at the cathode.

[0067] (2) The fuel cell system 1 includes a diagnostic device 30 and a control unit 20 that performs recovery processing to recover from an abnormal state when the diagnosis result of the internal state of the fuel cell FC by the diagnostic device 30 indicates an abnormal state. This allows the abnormal state to be recovered from when the diagnosis result of the diagnostic device 30 indicates an abnormal state.

[0068] (3) Specifically, the diagnostic device 30 determines whether or not the fuel gas is insufficient, based on the anode diffusion resistance. If the fuel gas is insufficient, the control unit 20 performs a recovery process to restore the fuel gas insufficiency state to a normal state. If the fuel gas is insufficient, due to the accumulation of generated water inside the fuel cell FC or the like, the diffusion of fuel gas on the anode side is hindered, resulting in a fuel gas insufficiency state, which can cause a malfunction of the fuel cell FC. For this reason, as in this embodiment, it is desirable that the fuel cell system 1 be configured to be able to restore the fuel gas insufficiency state to a normal state.

[0069] (Modification of First Embodiment) The diagnostic device 30 of the first embodiment determines the cutoff frequencies of the anode diffusion component and the anode diffusion component, respectively, and identifies the parameters of the equivalent circuit model based on the cutoff frequencies, but is not limited to this. For example, the diagnostic device 30 may estimate the diffusion rates of the gas at the anode and the cathode using a map or the like that defines the relationship between the diffusion components and the diffusion rates of the gas at the anode and the cathode, and identify the parameters of the equivalent circuit model based on the estimation results.

[0070] The fuel cell system 1 is configured to determine whether or not a fuel gas shortage state occurs based on the magnitude of the anode diffusion resistance, but is not limited to this. The fuel cell system 1 may also be configured to determine whether or not a fuel gas shortage state occurs based on both the anode diffusion resistance and the anode diffusion capacity.

[0071] Furthermore, the fuel cell system 1 is configured to determine whether or not there is a lack of fuel gas based on the anode diffusion resistance, and if there is a lack of fuel gas, to restore the lack of fuel state to a normal state by performing a recovery process, but is not limited to this. For example, the fuel cell system 1 may be configured to determine whether or not there is a lack of air based on the cathode diffusion resistance, and if there is a lack of gas, to restore the lack of gas state to a normal state by performing a recovery process. Note that the recovery process is not essential in the fuel cell system 1. For example, the fuel cell system 1 may be configured to execute a process to notify of an abnormality instead of the recovery process. This also applies to the following embodiments.

[0072] (First Modification of Equivalent Circuit Model) In the first embodiment, the equivalent circuit model ECM is configured by a series circuit in which the anode diffusion component AD and the cathode diffusion component CD each have a diffusion resistance and a diffusion capacitance connected in parallel, but the equivalent circuit model ECM is not limited to this. For example, as shown in FIG. 8, the equivalent circuit model ECM may be configured by a nested circuit in which the cathode diffusion component CD is nested within the anode diffusion component AD.

[0073] (Second Modification of Equivalent Circuit Model) The equivalent circuit model ECM may include only the anode diffusion component AD, omitting the cathode diffusion component CD from the anode diffusion component AD and the cathode diffusion component CD. In this case, the diagnostic device 30 may be configured to, for example, determine the cutoff frequency of the anode diffusion component as a physical quantity correlated with the gas diffusion rate at the anode, and identify the parameters of the equivalent circuit model ECM based on the cutoff frequency of the anode diffusion component.

[0074] (Third Modification of Equivalent Circuit Model) The equivalent circuit model ECM may be configured to include only the cathodic diffusion component CD, omitting the anode diffusion component AD and the cathode diffusion component CD. In this case, the diagnostic device 30 may be configured to, for example, determine the cutoff frequency of the cathode diffusion component as a physical quantity correlated with the gas diffusion rate at the cathode, and identify the parameters of the equivalent circuit model ECM based on the cutoff frequency of the cathode diffusion component.

[0075] Second Embodiment Next, a second embodiment will be described with reference to Fig. 11. In this embodiment, differences from the first embodiment will be mainly described.

[0076] As described in the first embodiment, the gas diffusion resistance of fuel gas is smaller than that of air. If the gas diffusion resistance of fuel gas is too small, it may be difficult to evaluate the gas diffusion characteristics of the fuel gas. In this embodiment, fuel gas corresponds to a "low resistance gas" and air corresponds to a "high resistance gas."

[0077] In contrast, the diagnostic device 30 of this embodiment is configured to increase the gas diffusion resistance of fuel gas, which is a low-resistance gas, and to decrease the gas diffusion resistance of air, which is a high-resistance gas. The diagnostic process executed by the diagnostic device 30 of this embodiment will now be described with reference to FIG.

[0078] Here, the control process shown in Fig. 11 is based on the control process shown in Fig. 5. The processes of steps S100, S110, S120, S130, S140, and S150 shown in Fig. 11 are the same as those described in the first embodiment, and therefore description thereof will be omitted.

[0079] As shown in FIG. 11, the diagnostic device 30 proceeds to step S105 with an AC current superimposed on the fuel cell FC, and executes a gas diffusion control process to control the diffusion of gas supplied to the fuel cell FC.

[0080] The diagnostic device 30 of this embodiment executes a restriction process to restrict the diffusion of the low-resistance fuel gas inside the fuel cell FC so that the gas diffusion resistance of the low-resistance fuel gas increases. For example, the diagnostic device 30 restricts the diffusion of the low-resistance fuel gas inside the fuel cell FC by reducing the amount of fuel gas supplied to the fuel cell FC. In this case, the diagnostic device 30 reduces the amount of fuel gas supplied to the fuel cell FC within a range that does not result in a fuel shortage state.

[0081] Furthermore, the diagnostic device 30 executes a promotion process to promote the diffusion of air, which is a high-resistance gas, so as to reduce the gas diffusion resistance of air, which is a high-resistance gas. For example, the diagnostic device 30 promotes the diffusion of air, which is a high-resistance gas, inside the fuel cell FC by increasing the amount of air supplied to the fuel cell FC.

[0082] In step S110, the diagnostic device 30 measures the internal impedance of the fuel cell FC while controlling the gas diffusion resistance of the fuel gas, which is a low-resistance gas, to be large and the gas diffusion resistance of the air, which is a high-resistance gas, to be small.

[0083] The other points are the same as those in the first embodiment. The fuel cell system 1 of this embodiment can obtain the same effects as those in the first embodiment that are achieved by the configuration common to or equivalent to that of the first embodiment.

[0084] The fuel cell system 1 of this embodiment also has the following features.

[0085] (1) The fuel cell system 1 includes a diagnostic device 30, an air supply unit SAP that controls the amount of air supplied to the fuel cell FC, and a fuel supply unit SFP that controls the amount of fuel gas supplied to the fuel cell FC. When identifying the parameters of the equivalent circuit model ECM, the diagnostic device 30 executes a restriction process that restricts the diffusion of low-resistance gas in the fuel cell FC and a promotion process that promotes the diffusion of high-resistance gas in the fuel cell FC. In this way, restricting the diffusion of low-resistance gas to increase the diffusion resistance of low-resistance gas, or promoting the diffusion of high-resistance gas to reduce the diffusion characteristics of high-resistance gas, has the advantage of making it easier to evaluate the gas diffusion characteristics of the fuel gas.

[0086] (Modification of the Second Embodiment) The diagnostic device 30 of the second embodiment is configured to execute both the restriction process and the acceleration process as the gas diffusion control process, but is not limited to this. The diagnostic device 30 may execute either the restriction process or the acceleration process as the gas diffusion control process. Furthermore, the contents of the restriction process and the acceleration process may be different from those described above.

[0087] Third Embodiment Next, a second embodiment will be described with reference to Fig. 12 and Fig. 13. In this embodiment, differences from the first embodiment will be mainly described.

[0088] In this embodiment, as shown in FIG. 12, an example will be described in which a diagnostic device 30A and an electrochemical reaction system according to the present disclosure are applied to a diagnostic device 30A for an electrolysis device EC and a water electrolysis system 1A.

[0089] The water electrolysis system 1A is configured as a system for producing fuel by electrolysis of water. As shown in Fig. 12, the water electrolysis system 1A includes an electrolysis device EC, an air supply unit SAP, a water supply unit SWP, and a control device 10A for the electrolysis device EC.

[0090] The electrolysis device EC receives air as a reducing agent and steam as an oxidizing agent as input, electrolyzes the steam using electrical energy, and outputs fuel. In this embodiment, the electrolysis device EC corresponds to a "reaction device." In this embodiment, air corresponds to a "first gas" as a reducing agent, and steam corresponds to a "second gas" as an oxidizing agent.

[0091] Specifically, the electrolysis device EC is configured as a cell stack CS in which multiple solid polymer electrolytic cells are stacked. Although not shown, each solid polymer electrolytic cell includes an electrolyte membrane, an anode, a cathode, and separators that form air and steam flow paths. When power is supplied from a power source (not shown), the electrolytic cell separates and outputs hydrogen and oxygen through electrolysis of steam as shown in the following reaction formulas F3 to F5.

[0092] (anode) 2O ２－ →O２ +4e － …(F3)

[0093] (Cathode) H ２ O + 2e － →H ２ +O ２－ …(F4)

[0094] (Overall) 2H ２ O → 2H ２ +O ２ ...(F5) An air supply unit SAP including an air flow path and a water supply unit SWP including a water vapor flow path are connected to the electrolysis device EC. Air and hydrogen serving as reducing agents are supplied to the electrolysis device EC through the air supply unit SAP and the water supply unit SWP.

[0095] The air supply unit SAP uses atmospheric air as a supply source and supplies the air from the supply source to the electrolysis device EC using a blower or the like (not shown). The air supply unit SAP constitutes a "first gas supply unit" that controls the supply amount of a first gas, which serves as a reducing agent, to the electrolysis device EC, which is a reaction device.

[0096] The water supply unit SWP supplies water vapor generated in a vaporizer (not shown) to the electrolysis device EC using a blower (not shown) or the like. The water supply unit SWP constitutes a "second gas supply unit" that controls the supply amount of a second gas, which serves as an oxidizing agent, to the electrolysis device EC, which is a reaction device.

[0097] In the electrolysis device EC, oxygen and hydrogen are separated and produced by electrolysis of water vapor and discharged as off-gas. The hydrogen output from the electrolysis device EC is stored as fuel in a hydrogen tank HT or the like.

[0098] The control device 10A of the electrolysis device EC is configured by a computer including a processor and a memory unit M. The control device 10A of this embodiment is equipped with a control unit 20A that controls various devices of the fuel cell system 1 and a diagnostic unit 30A that diagnoses the internal state of the fuel cell FC. The control unit 20A and the diagnostic unit 30A may be configured by common hardware or may be configured by separate hardware.

[0099] The control unit 20A outputs control signals to various controlled devices such as the air supply unit SAP and the water supply unit SWP to control the operation of the various controlled devices. Furthermore, when the diagnosis result of the internal state of the electrolysis apparatus EC by the diagnosis device 30A indicates an abnormal state, the control unit 20A performs recovery processing to recover from the abnormal state. The control unit 20A includes, as functional units for realizing various functions, a device control unit 21A that controls the operation of the various controlled devices and a recovery execution unit 22A that executes recovery processing.

[0100] The diagnostic device 30A measures the internal impedance of the electrolytic device EC and diagnoses the internal state of the electrolytic device EC using an equivalent circuit model based on the measured internal impedance. The diagnostic device 30A includes an impedance measurement unit 32A, a parameter identification unit 34A, and a state diagnosis unit 36A as functional units for realizing various functions.

[0101] The impedance measurement unit 32A measures the internal impedance of the electrolysis device EC based on the electrochemical impedance method. Specifically, the impedance measurement unit 32A superimposes an AC current of a predetermined frequency on the electrolysis device EC, and measures the internal impedance of the electrolysis device EC based on the AC signal containing multiple frequencies output from the electrolysis device EC. The internal impedance measured by the impedance measurement unit 32A is used to fit the parameters of the equivalent circuit model ECM stored in the memory unit M.

[0102] Here, the equivalent circuit model ECM is a circuit model that simulates the electrolysis device EC, and is stored in advance in the storage unit M. As described in the first embodiment, the equivalent circuit model ECM includes parameters that indicate the gas transport characteristics of the anode and cathode of the electrolysis device EC. Note that, as in the modified example of the first embodiment, the equivalent circuit model ECM may have a circuit configuration that includes parameters that indicate the gas transport characteristics of one of the anode and cathode of the electrolysis device EC.

[0103] The parameter identification unit 34A compares the internal impedance measured by the impedance measurement unit 32A with the equivalent circuit model ECM to identify a plurality of parameters that constitute the equivalent circuit model ECM. Upon completion of the parameter identification, the parameter identification unit 34A stores the equivalent circuit model ECM reflecting the parameters in the memory unit M.

[0104] As in the first embodiment, the parameter identification unit 34A identifies the parameters that constitute the equivalent circuit model ECM based on a first physical quantity that is correlated with the gas diffusion rate in the anode and a second physical quantity that is correlated with the gas diffusion rate in the cathode.

[0105] The state diagnosis unit 36A diagnoses the internal state of the electrolysis device EC based on the equivalent circuit model ECM that reflects the parameters identified by the parameter identification unit 34 A. The state diagnosis unit 36A of this embodiment is configured to determine whether or not the electrolysis device EC is in a gas shortage state where there is a shortage of water vapor, based on the cathode diffusion resistance.

[0106] The state diagnosis unit 36A uses, for example, one of the following [JC4] to [JC6] as a determination condition, and determines that the vehicle is out of gas when the determination condition is met.

[0107] [JC4] Cathode diffusion resistance ≧ abnormal threshold [JC5] Cathode diffusion resistance is greater than or equal to the abnormal threshold multiple times in succession [JC6] Cathode diffusion resistance is greater than or equal to the abnormal threshold multiple times within a specified period

[0108] Here, the determination of whether or not the gas is out of state may be performed using the moving average value of the cathode diffusion resistance, the slope of an approximation curve showing the trend of the cathode diffusion resistance, etc. Note that it is desirable that the abnormality threshold value in the determination conditions be changed depending on the temperature, voltage, internal pressure of the electrolysis device EC, stoichiometry on the cathode side, etc.

[0109] Next, the abnormality countermeasure processing executed by the control unit 20A based on the diagnosis results of the diagnosis device 30A will be described with reference to Fig. 13. The control routine shown in Fig. 13 is executed periodically or irregularly during operation of the electrolysis device EC.

[0110] 13, in step S300, the control unit 20A reads the diagnosis result of the internal state of the electrolysis device EC by the diagnosis device 30A from the memory unit M. Then, in step S310, the control unit 20A determines whether the electrolysis device EC is out of gas.

[0111] If the electrolysis device EC is out of gas, the control unit 20A proceeds to step S320, and if the electrolysis device EC is not out of gas, the control unit 20A skips the process of step S320 and ends this process.

[0112] If the electrolysis device EC is out of gas, the control unit 20A executes a recovery process in step S320. The recovery process is a process for recovering from an abnormal state when the diagnosis result of the internal state of the electrolysis device EC by the diagnosis device 30A indicates an abnormal state. In this embodiment, the control unit 20A executes a recovery process to recover from the out-of-gas state to a normal state when the electrolysis device EC is out of gas. When the electrolysis device EC is out of gas, the control unit 20A executes the recovery process, for example, by increasing the amount of water vapor supplied to suppress the accumulation of produced water at the cathode. This restores the abnormal state of the electrolysis device EC to a normal state. The recovery process may be executed temporarily or permanently, but is preferably continued until the diagnosis result of the diagnosis device 30A indicates a normal state.

[0113] The water electrolysis system 1A of this embodiment is otherwise similar to that of the first embodiment. Similar to the first embodiment, the water electrolysis system 1A of this embodiment can obtain the same effects as those of the first embodiment, which are achieved by a configuration common to or equivalent to that of the first embodiment.

[0114] The water electrolysis system 1A of this embodiment also has the following features.

[0115] (1) The diagnostic device 30A determines whether or not the vehicle is in a gas shortage state due to a lack of water vapor based on the cathode diffusion resistance. If the vehicle is in a gas shortage state, the control unit 20A performs a recovery process to restore the gas shortage state to a normal state.

[0116] A gas-out state in which the second gas is depleted due to impeded diffusion on the cathode side can cause a malfunction of the electrolysis device EC. Therefore, it is desirable that the water electrolysis system 1A be configured to be able to restore a normal state from a gas-out state.

[0117] (Variation of the Third Embodiment) In the third embodiment, the electrolysis device EC that electrolyzes water vapor and outputs hydrogen as fuel has been described, but the gases and the like supplied to the electrolysis device EC are not limited to those described above. For example, the electrolysis device EC may be configured to electrolyze a mixed gas of water vapor and carbon dioxide and output methane as fuel. In this case, the mixed gas of water vapor and carbon dioxide corresponds to the "second gas."

[0118] In the third embodiment, air is supplied as a reducing agent to the electrolysis device EC, but the gases supplied to the electrolysis device EC are not limited to those described above. For example, the electrolysis device EC may be configured so that nitrogen is supplied to the anode as a purge gas instead of air. In this case, nitrogen corresponds to the "first gas."

[0119] The diagnostic device 30 of the third embodiment is preferably configured to execute the gas diffusion control process described in the second embodiment when identifying the parameters of the equivalent circuit model ECM.

[0120] Other Embodiments Although typical embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be modified in various ways, for example, as follows.

[0121] The fuel cell system 1 described above is preferably configured to perform recovery processing to recover from the abnormal state when the diagnosis result of the internal state of the fuel cell FC by the diagnosis device 30 indicates an abnormal state, but it does not have to be configured in this way. The same applies to the water electrolysis system 1A.

[0122] In the above-described embodiment, an example has been described in which the diagnostic device 30A of the present disclosure is applied to a solid oxide fuel cell FC or an electrolysis device EC, but the application of the diagnostic device 30A is not limited to this. The diagnostic device 30A can also be applied to other reaction devices, such as a polymer electrolyte fuel cell FC or an electrolysis device EC.

[0123] In the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential unless they are specifically stated as essential or are clearly considered essential in principle.

[0124] In the above-described embodiments, when numerical values ​​such as the number, values, amounts, ranges, etc. of components of the embodiments are mentioned, they are not limited to the specific numbers unless they are specifically stated as essential or are clearly limited to a specific number in principle.

[0125] In the above-described embodiments, when referring to the shapes, positional relationships, etc. of components, etc., the shapes, positional relationships, etc. are not limited to those unless otherwise specified or when they are fundamentally limited to specific shapes, positional relationships, etc.

[0126] The controller and method of the present disclosure may be implemented on a special-purpose computer by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. The controller and method of the present disclosure may be implemented on a special-purpose computer by configuring a processor with one or more dedicated hardware logic circuits. The controller and method of the present disclosure may be implemented on one or more special-purpose computers configured with a processor and memory programmed to perform one or more functions in combination with a processor configured with one or more hardware logic circuits. The computer program may also be stored on a computer-readable non-transitory tangible storage medium as instructions executed by a computer.

[0127] [Aspects of the present disclosure]

[0128] [First Aspect] A diagnostic device for diagnosing a reaction device (FC, EC) that outputs electric energy by an electrochemical reaction of a first gas that serves as an oxidant and a second gas that serves as a reductant, or that receives as input a first gas that serves as a reductant and a second gas that serves as an oxidant and electrolyzes the second gas with electric energy to output fuel, the diagnostic device comprising: an impedance measurement unit (32, 32A) that measures an internal impedance of the reaction device based on an AC signal including a plurality of frequencies that is output from the reaction device; a memory unit (M) that stores an equivalent circuit model that simulates electrochemical characteristics of the reaction device; a parameter identification unit (34, 34A) that compares the internal impedance measured by the impedance measurement unit with the equivalent circuit model to identify a plurality of parameters that constitute the equivalent circuit model; and a state diagnosis unit (36, 36A) that diagnoses an internal state of the reaction device based on the equivalent circuit model in which the parameters identified by the parameter identification unit are reflected, wherein the equivalent circuit model includes one or more anode diffusion resistances and one or more anode diffusion capacitances as the parameters that indicate gas transport characteristics of an anode of the reaction device, The parameter identification unit identifies the parameters including the anode diffusion resistance and the anode diffusion capacitance based on a physical quantity that has a correlation with a gas diffusion rate in the anode of the reactor.

[0129] [Second Aspect] A diagnostic device for diagnosing a reaction device (FC, EC) that outputs electric energy by an electrochemical reaction of a first gas that serves as an oxidant and a second gas that serves as a reductant, or that receives as input a first gas that serves as a reductant and a second gas that serves as an oxidant and electrolyzes the second gas with electric energy to output fuel, the diagnostic device comprising: an impedance measurement unit (32, 32A) that measures an internal impedance of the reaction device based on an AC signal including a plurality of frequencies that is output from the reaction device; a memory unit (M) that stores an equivalent circuit model that simulates electrochemical characteristics of the reaction device; a parameter identification unit (34, 34A) that compares the internal impedance measured by the impedance measurement unit with the equivalent circuit model to identify a plurality of parameters that constitute the equivalent circuit model; and a state diagnosis unit (36, 36A) that diagnoses an internal state of the reaction device based on the equivalent circuit model in which the parameters identified by the parameter identification unit are reflected, wherein the equivalent circuit model includes one or more cathode diffusion resistances and one or more cathode diffusion capacitances as the parameters that indicate gas transport characteristics of the cathode of the reaction device, The parameter identification unit identifies the parameters including the cathode diffusion resistance and the cathode diffusion capacitance based on a physical quantity that has a correlation with a gas diffusion rate in the cathode of the reaction device.

[0130] [Third Aspect] A diagnostic device for diagnosing a reaction device (FC, EC) that outputs electric energy by an electrochemical reaction of a first gas that serves as an oxidant and a second gas that serves as a reductant, or that receives as input a first gas that serves as a reductant and a second gas that serves as an oxidant, and electrolyzes the second gas with electric energy to output fuel, comprising: an impedance measurement unit (32, 32A) that measures an internal impedance of the reaction device based on an AC signal including a plurality of frequencies that is output from the reaction device; a memory unit (M) that stores an equivalent circuit model that simulates electrochemical characteristics of the reaction device; a parameter identification unit (34, 34A) that compares the internal impedance measured by the impedance measurement unit with the equivalent circuit model to identify a plurality of parameters that constitute the equivalent circuit model; and a state diagnosis unit (36, 36A) that diagnoses an internal state of the reaction device based on the equivalent circuit model in which the parameters identified by the parameter identification unit are reflected, the equivalent circuit model includes one or more anode diffusion resistances and one or more anode diffusion capacitances as the parameters indicating the gas transport characteristics of the anode of the reactor, and one or more cathode diffusion resistances and one or more cathode diffusion capacitances as the parameters indicating the gas transport characteristics of the cathode of the reactor, and the parameter identification unit identifies the parameters based on a first physical quantity correlating with the gas diffusion rate in the anode of the reactor and a second physical quantity correlating with the gas diffusion rate in the cathode of the reactor.

[0131] [Fourth Aspect] The diagnostic device according to the first or third aspect, wherein, in the equivalent circuit model, a circuit formed by the anode diffusion resistance and the anode diffusion capacitance is defined as an anode diffusion component, the parameter identification unit determines a cutoff frequency of the anode diffusion component specified using the anode diffusion resistance and the anode diffusion capacitance as a physical quantity correlated with a gas diffusion rate in the anode, and identifies the parameter based on the cutoff frequency of the anode diffusion component.

[0132] [Fifth Aspect] The diagnostic device according to the second or third aspect, wherein, in the equivalent circuit model, a circuit formed by the cathode diffusion resistance and the cathode diffusion capacitance is defined as a cathode diffusion component, the parameter identification unit determines a cutoff frequency of the cathode diffusion component specified using the cathode diffusion resistance and the cathode diffusion capacitance as a physical quantity correlated with a gas diffusion rate in the cathode, and identifies the parameter based on the cutoff frequency of the cathode diffusion component.

[0133] [Sixth Aspect] In the equivalent circuit model, when a circuit formed by the anode diffusion resistance and the anode diffusion capacitance is defined as an anode diffusion component, and a circuit formed by the cathode diffusion resistance and the cathode diffusion capacitance is defined as a cathode diffusion component, the parameter identification unit determines a cutoff frequency of the anode diffusion component specified using the anode diffusion resistance and the anode diffusion capacitance as a physical quantity correlating with a gas diffusion rate at the anode of the reactor, and determines a cutoff frequency of the cathode diffusion component specified using the cathode diffusion resistance and the cathode diffusion capacitance as a physical quantity correlating with a gas diffusion rate at the cathode, and identifies the parameters based on the cutoff frequencies of the anode diffusion component and the cathode diffusion component, respectively.

[0134] [Seventh Aspect] An electrochemical reaction system comprising: the diagnostic device (30, 30A) according to any one of the first to sixth aspects; the reaction device; a first gas supply unit (SAP) that controls the amount of a first gas supplied to the reaction device; and a second gas supply unit (SFP, SWP) that controls the amount of a second gas supplied to the reaction device, wherein, when, of the first gas and the second gas, a gas that has a low gas diffusion resistance in the reaction device is defined as a low-resistance gas and a gas that has a low gas diffusion resistance in the reaction device is defined as a high-resistance gas, the diagnostic device executes at least one of a restriction process that restricts diffusion of the low-resistance gas in the reaction device and a promotion process that promotes diffusion of the high-resistance gas in the reaction device through control of at least one of the first gas supply unit and the second gas supply unit when identifying the parameters using the parameter identification unit.

[0135] [Eighth Aspect] An electrochemical reaction system comprising: a diagnostic device (30, 30A) according to any one of the first to sixth aspects; the reaction device; and a control unit (20, 20A) that performs recovery processing to recover from an abnormal state when a diagnosis result of the internal state of the reaction device by the diagnostic device indicates an abnormal state.

[0136] [Ninth Aspect] The electrochemical reaction system according to the eighth aspect, wherein the reaction device is a fuel cell (FC) that outputs electric energy by the electrochemical reaction, the diagnostic device (30) determines whether or not the reaction device is in a state of lack of fuel due to a shortage of the second gas based on the gas diffusion characteristics of the anode of the reaction device, and the control unit (20) restores the state of lack of fuel to a normal state by the restoration process if the state of lack of fuel is present.

[0137] [Tenth Aspect] The electrochemical reaction system according to the eighth aspect, wherein the reaction device is an electrolysis device (EC) that outputs fuel by the electrolysis, the diagnosis device (30A) determines whether or not a gas shortage state occurs due to a shortage of a second gas based on gas diffusion characteristics of a cathode of the reaction device, and the control unit (20A) restores the gas shortage state to a normal state by the recovery process if the gas shortage state occurs.

Claims

1. A diagnostic device for diagnosing a reaction device (FC, EC) that outputs electric energy by an electrochemical reaction of a first gas serving as an oxidant and a second gas serving as a reductant, or that receives a first gas serving as a reductant and a second gas serving as an oxidant as input and electrolyzes the second gas using electric energy to output fuel, the diagnostic device comprising: an impedance measurement unit (32, 32A) that measures the internal impedance of the reaction device based on an AC signal including a plurality of frequencies output from the reaction device; a memory unit (M) that stores an equivalent circuit model that simulates the electrochemical characteristics of the reaction device; a parameter identification unit (34, 34A) that compares the internal impedance measured by the impedance measurement unit with the equivalent circuit model to identify a plurality of parameters that constitute the equivalent circuit model; and a condition diagnosis unit (36, 36A) that diagnoses the internal condition of the reaction device based on the equivalent circuit model in which the parameters identified by the parameter identification unit are reflected, wherein the equivalent circuit model includes one or more anode diffusion resistances and one or more anode diffusion capacitances as the parameters that indicate the gas transport characteristics of the anode of the reaction device, The parameter identification unit identifies the parameters including the anode diffusion resistance and the anode diffusion capacitance based on a physical quantity that has a correlation with a gas diffusion rate in the anode of the reaction device.

2. A diagnostic device for diagnosing a reaction device (FC, EC) that outputs electric energy by an electrochemical reaction of a first gas that serves as an oxidant and a second gas that serves as a reductant, or that receives a first gas that serves as a reductant and a second gas that serves as an oxidant and electrolyzes the second gas with electric energy to output fuel, the diagnostic device comprising: an impedance measurement unit (32, 32A) that measures the internal impedance of the reaction device based on an AC signal including a plurality of frequencies output from the reaction device; a memory unit (M) that stores an equivalent circuit model that simulates the electrochemical characteristics of the reaction device; a parameter identification unit (34, 34A) that compares the internal impedance measured by the impedance measurement unit with the equivalent circuit model to identify a plurality of parameters that constitute the equivalent circuit model; and a condition diagnosis unit (36, 36A) that diagnoses the internal condition of the reaction device based on the equivalent circuit model that reflects the parameters identified by the parameter identification unit, wherein the equivalent circuit model includes one or more cathode diffusion resistances and one or more cathode diffusion capacitances as the parameters that indicate the gas transport characteristics of the cathode of the reaction device, The parameter identification unit identifies the parameters including the cathode diffusion resistance and the cathode diffusion capacitance based on a physical quantity that has a correlation with a gas diffusion rate in the cathode of the reaction device.

3. A diagnostic device for diagnosing a reaction device (FC, EC) that outputs electrical energy through an electrochemical reaction between a first gas that serves as an oxidant and a second gas that serves as a reductant, or that receives a first gas that serves as a reductant and a second gas that serves as an oxidant and electrolyzes the second gas with electrical energy to output fuel, comprising: an impedance measurement unit (32, 32A) that measures the internal impedance of the reaction device based on an AC signal containing multiple frequencies output from the reaction device; a memory unit (M) that stores an equivalent circuit model that simulates the electrochemical characteristics of the reaction device; a parameter identification unit (34, 34A) that compares the internal impedance measured by the impedance measurement unit with the equivalent circuit model to identify multiple parameters that constitute the equivalent circuit model; and a condition diagnosis unit (36, 36A) that diagnoses the internal condition of the reaction device based on the equivalent circuit model in which the parameters identified by the parameter identification unit are reflected. the equivalent circuit model includes one or more anode diffusion resistances and one or more anode diffusion capacitances as the parameters indicating the gas transport characteristics of the anode of the reactor, and one or more cathode diffusion resistances and one or more cathode diffusion capacitances as the parameters indicating the gas transport characteristics of the cathode of the reactor, and the parameter identification unit identifies the parameters based on a first physical quantity correlating with the gas diffusion rate in the anode of the reactor and a second physical quantity correlating with the gas diffusion rate in the cathode of the reactor.

4. The diagnostic device according to claim 1 or 3, wherein, in the equivalent circuit model, when a circuit formed by the anode diffusion resistance and the anode diffusion capacitance is defined as an anode diffusion component, the parameter identification unit determines a cutoff frequency of the anode diffusion component specified using the anode diffusion resistance and the anode diffusion capacitance as a physical quantity correlated with the gas diffusion rate at the anode of the reaction device, and identifies the parameter based on the cutoff frequency of the anode diffusion component.

5. A diagnostic device according to claim 2 or 3, wherein, in said equivalent circuit model, when a circuit formed by said cathode diffusion resistance and said cathode diffusion capacitance is defined as a cathode diffusion component, said parameter identification unit determines a cutoff frequency of said cathode diffusion component specified using said cathode diffusion resistance and said cathode diffusion capacitance as a physical quantity correlating with the gas diffusion rate in said cathode, and identifies said parameter based on the cutoff frequency of said cathode diffusion component.

6. The diagnostic device of claim 3, wherein, in the equivalent circuit model, a circuit formed by the anode diffusion resistance and the anode diffusion capacitance is defined as an anode diffusion component, and a circuit formed by the cathode diffusion resistance and the cathode diffusion capacitance is defined as a cathode diffusion component, the parameter identification unit determines a cutoff frequency of the anode diffusion component specified using the anode diffusion resistance and the anode diffusion capacitance as a physical quantity correlated with the gas diffusion rate at the anode of the reactor, and determines a cutoff frequency of the cathode diffusion component specified using the cathode diffusion resistance and the cathode diffusion capacitance as a physical quantity correlated with the gas diffusion rate at the cathode of the reactor, and identifies the parameters based on the cutoff frequencies of the anode diffusion component and the cathode diffusion component, respectively.

7. An electrochemical reaction system comprising: a diagnostic device (30, 30A) according to any one of claims 1 to 3; the reaction device; a first gas supply unit (SAP) that controls the amount of a first gas supplied to the reaction device; and a second gas supply unit (SFP, SWP) that controls the amount of a second gas supplied to the reaction device, wherein, when, of the first gas and the second gas, a gas that has a low gas diffusion resistance in the reaction device is defined as a low-resistance gas and a gas that has a low gas diffusion resistance in the reaction device is defined as a high-resistance gas, the diagnostic device, when identifying the parameters using the parameter identification unit, executes at least one of a restriction process that restricts the diffusion of the low-resistance gas in the reaction device and a promotion process that promotes the diffusion of the high-resistance gas in the reaction device through control of at least one of the first gas supply unit and the second gas supply unit.

8. An electrochemical reaction system comprising: a diagnostic device (30, 30A) according to any one of claims 1 to 3; the reaction device; and a control unit (20, 20A) that performs recovery processing to recover from an abnormal state when the diagnosis result of the internal state of the reaction device by the diagnostic device indicates an abnormal state.

9. The electrochemical reaction system according to claim 8, wherein the reaction device is a fuel cell (FC) that outputs electric energy through the electrochemical reaction, the diagnostic device (30) determines whether or not the reaction device is in a state of lack of fuel due to a shortage of the second gas based on the gas diffusion characteristics of the anode of the reaction device, and the control unit (20) restores the state of lack of fuel to a normal state by the restoration process if the state of lack of fuel is present.

10. The electrochemical reaction system according to claim 8, wherein the reaction device is an electrolysis device (EC) that outputs fuel by electrolysis, the diagnostic device (30A) determines whether or not the reaction device is in a gas-out state where the second gas is insufficient based on the gas diffusion resistance of the cathode of the reaction device, and the control unit (20A) restores the gas-out state to a normal state by the recovery process if the gas-out state is present.

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