Cell control system

Abstract

A cell control system (1) controls the internal resistance of an electrochemical cell (2). The cell control system (1) has a deteriorated portion identification unit (31) and an operation determination unit (32). The deteriorated portion identification unit (31) performs deterioration diagnosis for identifying a deteriorated portion of the electrochemical cell (2). The operation determination unit (32) determines a reduction operation on the basis of the result of the deterioration diagnosis of the deteriorated portion identification unit (31). The reduction operation is an operation of the electrochemical cell (2) for reducing the internal resistance of the electrochemical cell (2), the internal resistance having been increased due to deterioration of the deteriorated portion. This cell control system (1) performs a control so that the internal resistance of the electrochemical cell (2), the voltage applied to the electrochemical cell (2), and the like reach specific target values by executing the reduction operation.

Description

[Cross Reference to Related Applications]

[0001] This application is based on and claims the benefit of priority from earlier Japanese Patent Application No. 2024-054509, filed in Japan on March 28, 2024, the entire contents of which are hereby incorporated by reference. [Technical Field]

[0002] The present disclosure relates to a cell control system. [Background Art]

[0003] For example, as described in PTL 1, a known hydrogen production system includes an electrolytic cell stack for electrolyzing a raw material to extract hydrogen. This hydrogen production system increases a temperature of the electrolytic cell stack when an internal resistance of the electrolytic cell stack increases due to degradation. Thereby, the hydrogen production system attempts to reduce the internal resistance of the electrolytic cell stack. [Citation List] [Patent Literature]

[0004] [PTL 1]: JP 6704998 B [Summary of Invention]

[0005] The hydrogen production system described in PTL 1 attempts to reduce the internal resistance by controlling the temperature of cells without identifying a degradation site of the cells constituting the electrolytic cell stack. Therefore, the hydrogen production system may not sufficiently reduce the internal resistance of the cell. That is, the cause of the increase in the internal resistance may differ depending on the part of the cell. Therefore, an operation content of the cell to efficiently reduce the internal resistance may differ for each degradation site of the cell. For this reason, the hydrogen production system may not sufficiently reduce the internal resistance only by controlling the temperature of the cell. The hydrogen production system described in PTL 1 has room for improvement from the viewpoint of efficiently reducing the internal resistance of the cell and suppressing the degradation of the cell.

[0006] The present disclosure provides a cell control system that can suppress degradation of an electrochemical cell by efficiently reducing an internal resistance of the electrochemical cell.

[0007] A cell control system according to a first aspect of the present disclosure is a system that controls an internal resistance of an electrochemical cell, including a cathode channel, an anode channel, and an electrolyte disposed between the anode channel and the cathode channel. The electrochemical cell is configured to produce hydrogen by electrolyzing a raw material using supplied electric power. The cell control system, according to the first aspect, includes: a degradation-site identifying unit that performs a degradation diagnosis to identify a degradation site of the electrochemical cell; and an operation determining unit that determines, based on a result of the degradation diagnosis by the degradation-site identifying unit, a lowering operation that is an operation of the electrochemical cell to reduce the internal resistance of the electrochemical cell, which has increased due to degradation of the degradation site identified by the degradation-site identifying unit. The cell control system, by performing the lowering operation determined by the operation determining unit, controls at least one of the internal resistance of the electrochemical cell, a voltage applied to the electrochemical cell, and a current flowing through the electrochemical cell to reach a predetermined target value.

[0008] A cell control system according to a second aspect of the present disclosure is a system that controls an internal resistance of an electrochemical cell, including a cathode channel, an anode channel, and an electrolyte disposed between the anode channel and the cathode channel. The electrochemical cell is configured to generate electricity by being supplied with a gas containing an oxidant to the cathode channel and being supplied with a gas containing fuel to the anode channel. The cell control system, according to the second aspect, includes: a degradation-site identifying unit that performs a degradation diagnosis to identify a degradation site of the electrochemical cell; and an operation determining unit that determines, based on a result of the degradation diagnosis by the degradation-site identifying unit, a lowering operation that is an operation of the electrochemical cell to reduce the internal resistance of the electrochemical cell, which has increased due to degradation of the degradation site identified by the degradation-site identifying unit. The cell control system, by performing the lowering operation determined by the operation determining unit, controls at least one of the internal resistance of the electrochemical cell, an output voltage of the electrochemical cell, and an output current of the electrochemical cell to reach a predetermined target value.

[0009] The cell control system includes the degradation-site identifying unit and the operation determining unit. Therefore, the cell control system can perform the resistance-lowering operation corresponding to the degradation site of the electrochemical cell. Hence, the cell control system can efficiently reduce the internal resistance of the electrochemical cell. As a result, degradation of the electrochemical cell can be suppressed because the cell control system can operate the electrochemical cell at a low internal resistance.

[0010] As described above, according to the above aspects, a cell control system of the present disclosure can suppress degradation of an electrochemical cell by efficiently reducing an internal resistance of the electrochemical cell. Note that reference signs in parentheses described in claims indicate correspondence with specific matters described in the embodiments described below, and do not limit the technical scope of the present disclosure. [Brief Description of Drawings]

[0011] The above object and other objects, features, and technical advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. In the drawings: [FIG. 1] FIG. 1 is a configuration diagram of a hydrogen production apparatus including a cell control system in a first embodiment; [FIG. 2] FIG. 2 is a diagram showing the cell control system in the first embodiment; [FIG. 3] FIG. 3 is a flowchart showing a degradation diagnostic process of an electrochemical cell and a lowering process for reducing an internal resistance of the electrochemical cell in the first embodiment; [FIG. 4] FIG. 4 is a diagram showing a timing to perform the degradation diagnosis of the electrochemical cell in the first embodiment; [FIG. 5] FIG. 5 is a diagram showing a relationship between an oxygen partial pressure and an electrolysis voltage when performing the degradation diagnosis of the electrochemical cell in the first embodiment; [FIG. 6] FIG. 6 is a diagram showing a relationship between the oxygen partial pressure and the electrolysis voltage when performing the lowering operation for the electrochemical cell in the first embodiment; [FIG. 7] FIG. 7 is a diagram showing a specific example of diagnostic items of each part of the electrochemical cell and the lowering operation for the electrochemical cell in the first embodiment; [FIG. 8] FIG. 8 is a diagram showing a relationship between a cell temperature and the electrolysis voltage when performing the degradation diagnosis of the electrochemical cell in the first embodiment; [FIG. 9] FIG. 9 is a diagram showing a relationship between the cell temperature and the electrolysis voltage when performing the lowering operation for the electrochemical cell in the first embodiment; [FIG. 10] FIG. 10 is a flowchart showing a degradation diagnostic process of an electrochemical cell and a lowering process for reducing an internal resistance of the electrochemical cell in a second embodiment; [FIG. 11] FIG. 11 is a configuration diagram of a hydrogen production apparatus including a cell control system in a third embodiment; [FIG. 12] FIG. 12 is a configuration diagram of a hydrogen production apparatus including a cell control system in a fourth embodiment; [FIG. 13] FIG. 13 is a configuration diagram of a hydrogen production apparatus including a cell control system in a fifth embodiment; [FIG. 14] FIG. 14 is a configuration diagram of a hydrogen production apparatus including a cell control system in a sixth embodiment; [FIG. 15] FIG. 15 is a configuration diagram of a hydrogen production apparatus including a cell control system in a seventh embodiment; [FIG. 16] FIG. 16 is a configuration diagram of a hydrogen production apparatus including a cell control system in an eighth embodiment; [FIG. 17] FIG. 17 is a diagram showing a cell control system in a ninth embodiment; [FIG. 18] FIG. 18 is a configuration diagram of a fuel cell including a cell control system in the ninth embodiment; [FIG. 19] FIG. 19 is a flowchart showing a degradation diagnostic process of an electrochemical cell and a lowering process for reducing an internal resistance of the electrochemical cell in the ninth embodiment; [FIG. 20] FIG. 20 is a diagram showing a relationship between an oxygen partial pressure and an output voltage when performing the degradation diagnosis of the electrochemical cell in the ninth embodiment; [FIG. 21] FIG. 21 is a diagram showing a relationship between the oxygen partial pressure and the output voltage when performing the lowering operation for the electrochemical cell in the ninth embodiment; [FIG. 22] FIG. 22 is a configuration diagram of a fuel cell including a cell control system in a tenth embodiment; and [FIG. 23] FIG. 23 is a configuration diagram of a hydrogen production apparatus including a cell control system in a case where a temperature adjustment unit is provided in a cathode supply channel or the like. [Description of Embodiments]

[0012] (First Embodiment) A cell control system according to a first embodiment will be described with reference to FIGs. 1 through 9. The cell control system 1 of the present embodiment controls an internal resistance of an electrochemical cell 2. As shown in FIG. 2, the electrochemical cell 2 is equipped with a cathode channel 21, an anode channel 22, and an electrolyte 23 disposed between the anode channel 22 and the cathode channel 21. In the present embodiment, the electrochemical cell 2 is configured to electrolyze a raw material 11 using supplied electric power to produce hydrogen.

[0013] As shown in FIG. 1, the cell control system 1 includes a degradation-site identifying unit 31 and an operation determining unit 32. The degradation-site identifying unit 31 performs a degradation diagnosis to identify a degradation site of the electrochemical cell 2. The operation determining unit 32 determines a lowering operation for the internal resistance of the electrochemical cell 2 (resistance-lowering operation) based on a result of the degradation diagnosis by the degradation-site identifying unit 31. The lowering operation for the internal resistance is an operation of the electrochemical cell 2 to reduce the internal resistance of the electrochemical cell 2, which has increased due to degradation of the degradation site identified by the degradation-site identifying unit 31. The cell control system 1 performs the lowering operation determined by the operation determining unit 32 to control at least one parameter among the internal resistance of the electrochemical cell 2, a voltage applied to the electrochemical cell 2, and a current flowing through the electrochemical cell 2 to reach a predetermined target value.

[0014] The cell control system 1 of the present embodiment can be used, for example, to control a hydrogen production apparatus that electrolyzes the raw material 11 using supplied electric power to produce hydrogen. In the present embodiment, a gas containing water vapor is supplied to the cathode channel 21 of the electrochemical cell 2 shown in FIG. 2, and air is supplied to the anode channel 22. The electrochemical cell 2 is configured to decompose water vapor with electric power supplied from a power supply 51 to generate hydrogen gas. That is, in the present embodiment, the raw material 11 is water. Further, the water as the raw material 11 is supplied to the cathode channel 21 in a state of water vapor.

[0015] As shown in FIG. 1, the cell control system 1 is equipped with a control device 3 that controls operating conditions of the electrochemical cell 2. The control device 3 has the degradation-site identifying unit 31 and the operation determining unit 32. The control device 3 is equipped with at least a processor and a memory (non-transitory tangible storage medium). The processor executes a program on data stored in the memory and stores the processed data back in the memory. Thereby, the control device 3 serves as the degradation-site identifying unit 31 and the operation determining unit 32.

[0016] Further, the cell control system 1 of the present embodiment is equipped with a cell stack 20 in which a plurality of the electrochemical cells 2 are stacked. In the cell stack 20, the electrochemical cells 2 are electrically connected to each other in series. In the cell stack 20, the electrochemical cells 2 are stacked in an arrangement direction Z (see FIG. 2) of the cathode channel 21, the electrolyte 23, and the anode channel 22 in the electrochemical cell 2. Further, each electrochemical cell 2 is sandwiched between a pair of end plates (not shown) disposed at both ends in the arrangement direction Z in the cell stack 20.

[0017] The cell stack 20 is accommodated in a housing 15 covered with a heat-insulating material. The housing 15 is provided to maintain the electrochemical cell 2 at a temperature suitable for electrolysis of the raw material 11. A temperature adjustment unit 151 that adjusts a temperature of the cell stack 20 is accommodated in the housing 15. The temperature adjustment unit 151 may be, for example, an electric heater, a heat exchanger, or the like. The control device 3 controls the temperature adjustment unit 151 to maintain a temperature of the electrochemical cell 2 at, for example, 600°C to 800°C.

[0018] The cell control system 1 is equipped with the power supply 51 that supplies electric power to the cell stack 20. The power supply 51 supplies electric power required for electrolysis of the raw material 11 to the electrochemical cell 2. In the present embodiment, the control device 3 controls the power supply 51 such that a magnitude of a current supplied from the power supply 51 to the electrochemical cell 2 is kept constant.

[0019] The cell control system 1 is equipped with a cathode supply channel 53 that supplies gas to the cathode channel 21 of the electrochemical cell 2, and an anode supply channel 54 that supplies gas to the anode channel 22 of the electrochemical cell 2. In the present embodiment, the cathode supply channel 53 supplies a gas containing water vapor of the raw material 11 to the cathode channel 21. The anode supply channel 54 supplies air to the anode channel 22. The cathode supply channel 53 is equipped with a flow-rate adjustment unit 531 that adjusts a flow rate of the gas supplied to the cathode channel 21. The flow-rate adjustment unit 531 may be, for example, a solenoid valve or the like. Further, the anode supply channel 54 is equipped with an air pump 541 to supply the pressurized air to the anode channel 22. The control device 3 controls the flow-rate adjustment unit 531 and the air pump 541 to adjust the flow rate of the gas supplied to the cathode channel 21 and the anode channel 22, as well as the pressure inside the cathode channel 21 and the anode channel 22.

[0020] Further, the cell control system 1 is equipped with a cathode discharge channel 57 through which the gas discharged from the cathode channel 21 flows, and an anode discharge channel 58 through which the gas discharged from the anode channel 22 flows.

[0021] The cell control system 1 of the present embodiment is equipped with an inert gas supply channel 55 that supplies an inert gas to the electrochemical cell 2. The inert gas supply channel 55 is connected to the cathode supply channel 53 and the anode supply channel 54. Accordingly, the inert gas supply channel 55 is configured to supply the inert gas to each of the cathode channel 21 and the anode channel 22. The inert gas supply channel 55 is equipped with flow-rate adjustment units 551 and 552 that adjust a flow rate of the inert gas supplied to the cathode channel 21 or the anode channel 22. The flow-rate adjustment units 551 and 552 may be, for example, solenoid valves or the like. The control device 3 controls the flow-rate adjustment units 551 and 552 to adjust the flow rate of the inert gas supplied to the cathode channel 21 or the anode channel 22.

[0022] The cell control system 1 of the present embodiment is equipped with a hydrogen supply channel 56 that supplies hydrogen gas to the cathode channel 21. The hydrogen supply channel 56 is connected to the cathode supply channel 53. Further, the hydrogen supply channel 56 is equipped with a flow-rate adjustment unit 561 that adjusts a flow rate of the hydrogen gas supplied to the cathode channel 21. The flow-rate adjustment unit 561 may be, for example, a solenoid valve or the like. The hydrogen supply channel 56 supplies the hydrogen gas to the cathode channel 21 as necessary. Accordingly, the cell control system 1 suppresses oxidation of a cathode diffusion layer 242 and a cathode reaction layer 241, which will be described later, thereby preventing degradation of the diffusion layer and the reaction layer. The control device 3 controls the flow-rate adjustment unit 561 to adjust the flow rate of hydrogen gas supplied to the cathode channel 21.

[0023] The cell control system 1 is equipped with a recirculation channel 571 that branches from a cathode discharge channel 57 and connects the cathode discharge channel 57 and the cathode supply channel 53. The recirculation channel 571 supplies water vapor and hydrogen, which have been discharged to the cathode discharge channel 57 without being decomposed by the electrochemical cell 2, back to the cathode channel 21. The recirculation channel 571 is equipped with a pump 572 to supply the gas in the cathode discharge channel 57 to the cathode channel 21 via the cathode supply channel 53. The control device 3 controls the pump 572 to adjust a recirculation flow rate of the gas supplied back from the cathode discharge channel 57 to the cathode channel 21 via the recirculation channel 571.

[0024] The cell control system 1 is equipped with a temperature measurement unit (not shown) that measures the temperature of the electrochemical cell 2. Data of the temperature measured by the temperature measurement unit (temperature measurement data) is transmitted to the control device 3. The temperature measurement unit may be, for example, a thermocouple, a resistance temperature detector, or the like. When the temperature measurement unit is a sheathed thermocouple, for example, the cell control system 1 can measure the temperature of the electrochemical cell 2 by inserting and arranging the sheathed thermocouple inside the pair of end plates (not shown) disposed at both ends in the arrangement direction Z in the cell stack 20.

[0025] The cell control system 1 is equipped with a pressure measurement unit (not shown) that measures respective pressures in the cathode channel 21 and the anode channel 22. The pressure measurement unit can directly measure the respective pressures in the cathode channel 21 and the anode channel 22, for example, by being mounted to the electrochemical cell 2. Data of the pressures measured by the pressure measurement unit (pressure measurement data) is transmitted to the control device 3. Further, the pressure measurement unit may also be mounted, for example, to the cathode supply channel 53, the cathode discharge channel 57, the anode supply channel 54, the anode discharge channel 58, or the like. In this case, the control device 3 can perform control such as the degradation diagnosis by, for example, regarding a magnitude of the pressure in the cathode supply channel 53 or the cathode discharge channel 57 as a magnitude of the pressure in the cathode channel 21, and regarding a magnitude of the pressure in the anode supply channel 54 or the anode discharge channel 58 as a magnitude of the pressure in the anode channel 22. Further, the control device 3 may calculate the magnitude of the pressure in the cathode channel 21 based on the magnitude of the pressure in the cathode supply channel 53. The control device 3 may calculate the magnitude of the pressure in the anode channel 22 based on the magnitude of the pressure in the anode supply channel 54.

[0026] The cell control system 1 is equipped with a flow-rate measurement unit (not shown) that measures respective flow rates of gases flowing through the cathode channel 21 and the anode channel 22. Data of the flow rates of the gases measured by the flow-rate measurement unit (flowrate measurement data) is transmitted to the control device 3. The flow-rate measurement unit may be provided, for example, in the cathode supply channel 53 and the anode supply channel 54. In this case, the control device 3 can also regard a flow rate of the cathode supply channel 53 as the flow rate of the cathode channel 21, and regard a flow rate of the anode supply channel 54 as the flow rate of the anode channel 22. Further, the control device 3 may calculate the flow rate of the cathode channel 21 based on the flow rate of the cathode supply channel 53. The control device 3 may calculate the flow rate of the anode channel 22 based on the flow rate of the anode supply channel 54. The flow-rate measurement unit may be, for example, a mass flow meter, a volumetric flow meter, or the like. Further, a volumetric flow rate of the gas containing water vapor 11 flowing through the cathode channel 21 varies easily with the temperature and pressure. Therefore, when the volumetric flow meter is used as the flow-rate measurement unit, the cell control system 1 preferably converts the volumetric flow rate into a mass flow rate to use the mass flow rate for controlling the electrochemical cell 2. That is, the cell control system 1 preferably converts the volumetric flow rate, which is measurement data of the volumetric flow meter, into the mass flow rate based on measurement data of the temperature measurement unit or the pressure measurement unit, to use the mass flow rate for controlling the electrochemical cell 2.

[0027] As shown in FIGs. 1 and 2, the cell control system 1 is equipped with a voltage measurement unit 52 that measures a magnitude of a voltage applied to the electrochemical cell 2. Data of the voltage measured by the voltage measurement unit 52 (voltage measurement data) is transmitted to the control device 3. Further, the cell control system 1 is also equipped with a current measurement unit (not shown) that measures a magnitude of a current flowing through the electrochemical cell 2. Data of the current measured by the current measurement unit (current measurement data) is transmitted to the control device 3.

[0028] Next, the electrochemical cell 2 will be described with reference to FIG. 2. In the present embodiment, the electrochemical cell 2 is a solid oxide cell. That is, in the present embodiment, the electrochemical cell 2 is a solid oxide electrolysis cell (SOEC). The electrolyte 23 is made of a solid oxide ceramic and has oxide-ion (O2-) conductivity. The electrolyte 23 may be composed of, for example, yttria-stabilized zirconia, a perovskite-type oxide, yttria-partially-stabilized zirconia, or similar materials.

[0029] The electrochemical cell 2 is equipped with a porous cathode reaction layer 241 provided on one side of the electrolyte 23 in the arrangement direction Z, and a porous cathode diffusion layer 242 provided between the cathode reaction layer 241 and the cathode channel 21. In the present embodiment, the cathode reaction layer 241 contains a catalyst, such as nickel, to promote a decomposition reaction of the water vapor 11. The cathode diffusion layer 242 functions to diffuse the water vapor 11 from the cathode channel 21 into the cathode reaction layer 241. Furthermore, the cathode diffusion layer 242 functions to diffuse hydrogen gas generated by electrolysis from the cathode reaction layer 241 into the cathode channel 21. The cathode reaction layer 241 and the cathode diffusion layer 242 may be composed of, for example, a metal, a metal compound, or similar materials.

[0030] Further, the electrochemical cell 2 is equipped with a porous anode reaction layer 251 provided on the other side of the electrolyte 23 in the arrangement direction Z, and a porous anode diffusion layer 252 provided between the anode reaction layer 251 and the anode channel 22. In the present embodiment, the anode reaction layer 251 contains a catalyst to promote the generation of oxygen gas. The anode diffusion layer 252 functions to diffuse oxygen gas generated in the anode reaction layer 251 from the anode reaction layer 251 into the anode channel 22. The anode reaction layer 251 and the anode diffusion layer 252 may be composed of, for example, a metal or a metal compound, or similar materials. Further, the anode reaction layer 251 may contain, for example, a perovskite-type oxide or the like as a catalyst.

[0031] Next, the electrolysis of the water vapor 11 in the electrochemical cell 2 will be described. In the present embodiment, the water vapor 11 supplied to the cathode channel 21 reaches the cathode reaction layer 241 through the cathode diffusion layer 242. As a result, an electrolytic reaction [H2O + 2e_ ^ H2 + O2-] occurs in the cathode reaction layer 241. Further, a reaction [O2- ^ I / 2O2 + 2e_] occurs in the anode reaction layer 251. That is, in the cathode reaction layer 241, the water vapor 11 is electrolyzed, and hydrogen gas and oxide ions (O2-) are generated. The hydrogen gas diffuses into the cathode channel 21. The oxide ions move through the electrolyte 23 toward the anode channel 22, and are oxidized in the anode reaction layer 251 to become oxygen gas. The oxygen gas diffuses into the anode channel 22. The hydrogen gas generated by the electrolytic reaction is discharged from the cathode channel 21 to the cathode discharge channel 57. Further, the oxygen gas generated by the electrolytic reaction is discharged from the anode channel 22 to the anode discharge channel 58.

[0032] Next, control of the electrochemical cell 2 by the control device 3 will be described with reference to a flowchart of FIG. 3. First, in step S1, the control device 3 determines whether the electrochemical cell 2 is in a state capable of operating at a predetermined rated output. That is, the control device 3 determines whether the temperature or the like of the electrochemical cell 2 is a predetermined temperature or the like at which operation at the rated output is possible. In step S1, when the control device 3 determines that the electrochemical cell 2 is in the state capable of operating at the rated output (YES), the control device 3 proceeds to step S2. On the other hand, in step S1, when the control device 3 determines that the electrochemical cell 2 is not in the state capable of operating at the rated output (NO), the control device 3 determines again whether the electrochemical cell 2 is in the state capable of operating at the rated output.

[0033] Next, in step S2, the control device 3 measures a voltage applied to the electrochemical cell 2 by the voltage measurement unit 52 (see FIGs. 1 and 2). Thereafter, in step S3, the control device 3 determines whether a voltage value of the electrochemical cell 2 is equal to or greater than a predetermined threshold value. That is, in the present embodiment, whether the electrochemical cell 2 has degraded is determined based on a magnitude of a voltage of the electrochemical cell 2 when a current having a constant magnitude is controlled to flow through the electrochemical cell 2. Then, as shown in FIG. 4, when the control device 3 determines that an electrolysis voltage, which is the voltage applied to the electrochemical cell 2, exceeds a predetermined target value and an electrolysis voltage value is equal to or greater than the threshold value (YES), the control device 3 proceeds to step S4, and performs the degradation diagnosis and the lowering operation in accordance with a predetermined condition. On the other hand, in step S3, when the control device 3 determines that the electrolysis voltage value of the electrochemical cell 2 is less than the threshold value (NO), the control device 3 proceeds to step S5. That is, as shown in FIG. 4, as an operating time of the electrochemical cell 2 elapses, the electrochemical cell 2 gradually degrades, and the electrolysis voltage gradually increases from the target value. Therefore, when the electrolysis voltage reaches or exceeds the threshold value, the control device 3 performs the degradation diagnosis and the lowering operation in accordance with the predetermined condition described later. Thereby, the electrolysis voltage, which is the voltage applied to the electrochemical cell 2, is reduced to the target value. The threshold value can be, for example, a voltage value that is 5% greater than the target value of the voltage. Further, the target value can be, for example, an electrolysis voltage value of the electrochemical cell 2 that has not degraded during a rated operation.

[0034] Further, in step S5 in the flowchart of FIG. 3, the control device 3 determines whether a predetermined period (certain period) has elapsed since a degradation site was identified previously (since the degradation site was identified by the degradation-site identifying unit 31). When the control device 3 determines that the predetermined period has elapsed since the previous identification of the degradation site (YES), the control device 3 proceeds to step S4 even when the electrolysis voltage value is less than the threshold value. On the other hand, when the control device 3 determines that the predetermined period has not elapsed since the previous identification of the degradation site (NO), the control device 3 returns to step S1, and performs determination in each step again. That is, as shown in FIG. 4, when, for example, one week of the operating time has elapsed since the previous identification of the degradation site, the control device 3 performs the degradation diagnosis even when the electrolysis voltage value is less than the threshold value.

[0035] Further, the cell control system 1 of the present embodiment is configured to prohibit performing at least one operation of the degradation diagnosis and the lowering operation in accordance with a predetermined prohibition condition. Therefore, in step S4, the control device 3 determines whether the prohibition condition for diagnosis is not satisfied (not applicable). The prohibition condition for diagnosis is a condition for determining that at least one operation of the degradation diagnosis and the lowering operation should not be executed in processes after step S6, which will be described later. In step S4, when the control device 3 determines that the prohibition condition for diagnosis is not satisfied (not applicable) (YES), the control device 3 proceeds to step S6. On the other hand, when the control device 3 determines that the prohibition condition for diagnosis is satisfied (NO), the control device 3 proceeds to step S7. In the present embodiment, an example of the prohibition condition for diagnosis can be that a remaining capacity of a hydrogen storage tank (not shown) for storing the hydrogen gas produced by the electrochemical cell 2 is equal to or less than a predetermined value. By performing the degradation diagnosis, a production amount of the hydrogen gas in the electrochemical cell 2 may decrease, or the production of the hydrogen gas may temporarily stop. Therefore, in the present embodiment, a condition in which the production of hydrogen gas is prioritized over the degradation diagnosis is set as the prohibition condition for diagnosis, and the degradation diagnosis is not performed as necessary.

[0036] In step S7, because the prohibition condition for diagnosis is satisfied, the control device 3 determines whether a period during which the degradation diagnosis or the lowering operation is prohibited is equal to or greater than a predetermined period. When the control device 3 determines that the period during which the degradation diagnosis or the like is prohibited is equal to or greater than the predetermined period (YES), the control device 3 proceeds to step S6 even when the prohibition condition for diagnosis is satisfied. On the other hand, in step S7, when the control device 3 determines that the period during which the degradation diagnosis or the like is prohibited is less than the predetermined period (NO), the control device 3 returns to step S1. That is, when the prohibition on performing at least one of the degradation diagnosis and the lowering operation continues for the predetermined period or longer, the cell control system 1 of the present embodiment performs the degradation diagnosis and the lowering operation even when the prohibition condition is satisfied. In step S7, the predetermined period can be, for example, one week.

[0037] Next, in steps S6, S8, S9, and S10, the control device 3 performs the degradation diagnosis by the degradation-site identifying unit 31. Specifically, the degradation-site identifying unit 31 sets the temperature of the electrochemical cell 2, the pressure in the cathode channel 21, the pressure in the anode channel 22, a partial pressure of the water vapor 11 in the gas supplied to the cathode channel 21, a partial pressure of oxygen in the gas supplied to the anode channel 22, the flow rate of the gas flowing through the cathode channel 21, and the flow rate of the gas flowing through the anode channel 22, as a plurality of diagnostic items for degradation. At this time, the degradation-site identifying unit 31 identifies the degradation site of the electrochemical cell 2 by changing a value of at least one diagnostic item among the plurality of diagnostic items.

[0038] Further, the degradation-site identifying unit 31 measures an amount of change in a state of the electrochemical cell 2 when the value of the diagnostic item (diagnostic parameter) is changed, and acquires a measured amount of change. Then, the degradation-site identifying unit 31 compares the measured amount of change with a predetermined reference value (reference amount of change) of the amount of change in the state of the electrochemical cell 2. Thereby, the degradation-site identifying unit 31 identifies a degradation site of the electrochemical cell 2 based on a comparison result. Further, in the present embodiment, the amount of change in the state is an amount of change in a magnitude of a voltage applied to the electrochemical cell 2 when a current flowing through the electrochemical cell 2 (an input current to the electrochemical cell) is controlled to be a constant current. In the present embodiment, the degradation-site identifying unit 31 identifies the degradation site of the electrochemical cell 2 by changing, in addition to the temperature of the electrochemical cell 2, at least one value of diagnostic items other than the temperature of the electrochemical cell 2.

[0039] In the present embodiment, the degradation-site identifying unit 31 changes the values of the plurality of diagnostic items one by one, rather than changing them simultaneously. Further, in the present embodiment, the degradation-site identifying unit 31 performs the degradation diagnosis by changing the values of all the diagnostic items among the plurality of diagnostic items. In step S6, the control device 3 changes the value of one diagnostic item (one diagnostic parameter) among the plurality of diagnostic items, and proceeds to step S8. Next, in step S8, the control device 3 measures an amount of change between the electrolysis voltage value of the electrochemical cell 2 before changing the value of the diagnostic item and the electrolysis voltage value of the electrochemical cell 2 after changing the value of the diagnostic item in step S6, as the measured amount of change. After executing the process of step S8, the control device 3 proceeds to step S9 and determines whether the values of all the diagnostic items have been changed. When the control device 3 determines that the values of all the diagnostic items have been changed (YES), the control device 3 proceeds to step S10, and identifies the degradation site of the electrochemical cell 2 based on the measured amount of change. On the other hand, in step S9, when the control device 3 determines that the values of all the diagnostic items have not been changed (NO), the control device 3 returns to step S6 and changes the value of the diagnostic item to a value of a next diagnostic item. Then, the control device 3 repeatedly executes the processes from step S6 to step S9 until the values of all the diagnostic items are changed.

[0040] As a specific example, when the diagnostic item is the "oxygen partial pressure in the gas supplied to the anode channel 22", details of the degradation diagnosis by the degradation-site identifying unit 31 will be described with reference to a graph of FIG. 5. In the graph of FIG. 5, a horizontal axis represents a magnitude of the oxygen partial pressure in the anode channel 22, and a vertical axis represents a magnitude of the electrolysis voltage of the electrochemical cell 2. In the graph of FIG. 5, "initial operation" refers to a normal rated operation of the electrochemical cell 2 immediately before performing the degradation diagnosis. Further, in the graph of FIG. 5, filled circles are plot results of data obtained when testing was performed in the past using the electrochemical cell 2 that has not degraded, showing a relationship between the oxygen partial pressure and the electrolysis voltage. Open circles are plot results of data showing a relationship between the oxygen partial pressure and the electrolysis voltage of the degraded electrochemical cell 2 when the degradation diagnosis up to step S10 is performed. In the graph of FIG. 5, during the initial operation, comparing the data for the degraded electrochemical cell 2 with that for the electrochemical cell 2 that has not degraded, the electrolysis voltage of the degraded electrochemical cell 2 is increased. That is, it can be seen that the electrolysis voltage increases due to degradation. Further, a characteristic line L1 is an approximate straight line based on data of past test results, and is a line showing characteristics of the electrochemical cell 2 that has not degraded.

[0041] Further, in performing the degradation diagnosis, the degradation-site identifying unit 31 first changes a value of the oxygen partial pressure in the anode channel 22 from a value C0 during the initial operation. In the present embodiment, the value of the oxygen partial pressure is decreased from the value C0 during the initial operation to a value C1. Then, the degradationsite identifying unit 31 measures an electrolysis voltage V1b corresponding to the oxygen partial pressure C1 by the voltage measurement unit 52. Furthermore, the degradation-site identifying unit 31 measures a difference (voltage difference) AV1 between an electrolysis voltage Via corresponding to the oxygen partial pressure C0 during the initial operation and the electrolysis voltage Vib corresponding to the oxygen partial pressure C1. That is, the voltage difference AV 1 is the measured amount of change.

[0042] Further, in the present embodiment, the reference value of the amount of change in the state of the electrochemical cell 2 is a difference in a magnitude of the electrolysis voltage (voltage difference) AV0 when the oxygen partial pressure was changed under similar conditions using the electrochemical cell 2 that has not degraded. That is, as shown in FIG. 5, the voltage difference AV0 is a difference between an electrolysis voltage V0a corresponding to the oxygen partial pressure C0 during the initial operation and an electrolysis voltage V0b corresponding to the oxygen partial pressure C1 when the electrochemical cell 2 that has not degraded is used. Then, the degradation-site identifying unit 31 compares the voltage difference AV1, which is the measured amount of change, with the voltage difference AV0, which is the reference value of the amount of change in the state. When the voltage difference AV1 (amount of change) is greater than a predetermined value with respect to the voltage difference AV0 (reference value), the degradation-site identifying unit 31 determines that the anode reaction layer 251 has degraded, thereby identifying the degradation site. Here, the degradation of the anode reaction layer 251 corresponds to, for example, a state in which oxide ions are less likely to be oxidized due to a decrease in a reaction area of the anode reaction layer 251 caused by structural change resulting from a high temperature or adhesion of a foreign matter contained in the gas supplied to the anode channel 22 to the anode reaction layer 251. Then, due to the degradation of the anode reaction layer 251, an overvoltage of the anode reaction layer 251 during operation of the electrochemical cell 2 increases. As shown in FIG. 5, by decreasing the oxygen partial pressure in the anode channel 22 through the degradation diagnosis, oxidation capability of the oxide ions in the anode reaction layer 251 is recovered. As a result, the electrolysis voltage of the electrochemical cell 2 decreases. That is, the reaction in the anode reaction layer 251 is more sensitive to a change in the oxygen partial pressure in the anode channel 22 than reactions in the electrolyte 23, the cathode reaction layer 241, and the like. Therefore, the degradation-site identifying unit 31 can identify that the anode reaction layer 251 among the respective sites of the electrochemical cell 2 has degraded based on the result of the degradation diagnosis using the oxygen partial pressure in the anode channel 22.

[0043] Next, as described above, after identifying the degradation site in step S10, the control device 3 proceeds to step S11 in the flowchart of FIG. 3, and performs the lowering operation for the electrochemical cell 2 such that the electrolysis voltage of the electrochemical cell 2 becomes the predetermined target value. Thereafter, the control device 3 proceeds to step S1 again and performs a similar process.

[0044] In the present embodiment, the lowering operation is an operation of changing at least one value among the temperature of the electrochemical cell 2, the pressure in the cathode channel 21, the pressure in the anode channel 22, the partial pressure of the water vapor 11 in the gas supplied to the cathode channel 21, the partial pressure of oxygen in the gas supplied to the anode channel 22, the flow rate of the gas in the cathode channel 21, and the flow rate of the gas in the anode channel 22.

[0045] Specifically, based on the degradation diagnosis result (identified degradation site) shown in FIG. 5, the operation determining unit 32 determines a lowering operation corresponding to the identified degradation site as the lowering operation for the electrochemical cell 2 (operation to reduce the internal resistance increased due to the degradation), as shown in FIG. 6. In the graph of FIG. 6, a characteristic line L2 is an approximate straight line based on data obtained when the degradation diagnosis was performed on the degraded electrochemical cell 2, and is a line showing characteristics of the degraded electrochemical cell 2.

[0046] In the present embodiment, the operation determining unit 32 determines the oxygen partial pressure at which a target voltage V0 (predetermined target value) is obtained based on the characteristic line L2. Then, as the lowering operation, the operation determining unit 32 decreases the oxygen partial pressure in the gas supplied to the anode channel 22 to the determined value C2. Here, in the present embodiment, the anode channel 22 is configured such that air flows therethrough. The cell control system 1 changes the oxygen partial pressure in the anode channel 22 by causing the gas other than the air to further flow through the anode channel 22. Specifically, the cell control system 1 decreases the oxygen partial pressure in the anode channel 22 by, for example, causing nitrogen gas, helium gas, or the like other than the air to flow through the anode channel 22. That is, the cell control system 1 flows the inert gas from the inert gas supply channel 55 (see FIG. 1) into the anode channel 22 via the anode supply channel 54. As a result, an oxygen concentration of the gas supplied to the anode channel 22 becomes lower than 21%, which is an oxygen concentration of air. This allows the oxygen gas generated in the anode reaction layer 251 to be easily dispersed into the anode channel 22 and more readily discharged to the outside via the anode channel 22. As a result, the overvoltage of the electrochemical cell 2 decreases. Therefore, the electrolysis voltage of the electrochemical cell 2 is set to the predetermined target value.

[0047] Further, in the present embodiment, a parameter used during the lowering operation is the same as a parameter (diagnostic item) used during the diagnostic operation for degradation. That is, for example, the diagnostic operation for identifying the degradation of the anode reaction layer 251 and the lowering operation for decreasing the overvoltage of the anode reaction layer 251 are both based on a change in the oxygen partial pressure in the gas supplied to the anode channel 22 (a common parameter).

[0048] Further, as shown in FIG. 7, the cell control system 1 of the present embodiment can change, for example, the flow rate of gas flowing through the anode channel 22 (flow rate of a fluid), the temperature of the cell stack 20, or the like, in addition to the oxygen partial pressure described above in the degradation diagnosis and the lowering operation. Thereby, the cell control system 1 can identify the anode reaction layer 251 and the anode diffusion layer 252 as the degradation site, and can reduce the overvoltage of the anode reaction layer 251 and the anode diffusion layer 252 by improving an oxygen discharge property and the like. Similarly, in a case of the cathode reaction layer 241, the cell control system 1 can identify the cathode reaction layer 241 as the degradation site by, for example, changing the partial pressure of the water vapor 11 in the gas supplied to the cathode channel 21 (partial pressure of a raw material), the temperature of the cell stack 20, or the like. By changing the partial pressure of the water vapor 11 and the like, the cell control system 1 can improve reactivity to the water vapor 11 and reduce an overvoltage of the cathode reaction layer 241. Further, in a case of the cathode diffusion layer 242, the cell control system 1 can identify the cathode diffusion layer 242 as the degradation site by, for example, changing the flow rate of the gas flowing through the cathode channel 21 (flow rate of a fluid), the temperature of the cell stack 20, or the like, and can reduce an overvoltage of the cathode diffusion layer 242. That is, when diffusion efficiency of the water vapor 11 or hydrogen gas decreases due to degradation of the cathode diffusion layer 242, the cell control system 1 increases, for example, the flow rate of the gas flowing through the cathode channel 21. Accordingly, the cell control system 1 can improve the diffusion efficiency of hydrogen gas and reduce the electrolysis voltage and the like. Further, in a case of the electrolyte 23, the cell control system 1 can identify the electrolyte 23 as the degradation site by changing the temperature of the cell stack 20 as the temperature of the electrochemical cell 2, for example, and can decrease an internal resistance or an electrolysis voltage of the electrolyte 23 to a target value. Hereinafter, identification of the electrolyte 23 as the degradation site and a lowering operation for the electrolyte 23 will be described.

[0049] A graph of FIG. 8 shows a result of the degradation diagnosis when the diagnostic item is the "temperature of the electrochemical cell 2". In the graph of FIG. 8, a horizontal axis represents a magnitude of the temperature of the electrochemical cell 2 (hereinafter referred to as a cell temperature), and a vertical axis represents a magnitude of the electrolysis voltage of the electrochemical cell 2. In performing the degradation diagnosis, the degradation-site identifying unit 31 first changes the cell temperature from a temperature C0 during the initial operation. In the present embodiment, the cell temperature is increased from the temperature C0 during the initial operation to a value C3. Then, the degradation-site identifying unit 31 measures an electrolysis voltage at the cell temperature C3 by the voltage measurement unit 52. Furthermore, in the degraded electrochemical cell 2, the degradation-site identifying unit 31 measures a difference (voltage difference) AV 1 between an electrolysis voltage V1 c corresponding to the cell temperature C0 during the initial operation and an electrolysis voltage V1d corresponding to the cell temperature C3. Note that in the graph of FIG. 8, a characteristic line L3 is an approximate straight line based on data of past test results, and is a line showing characteristics of the electrochemical cell 2 that has not degraded.

[0050] Further, in the present embodiment, the reference value of the amount of change in the state of the electrochemical cell 2 is a difference in a magnitude of the electrolysis voltage (voltage difference) AV0 when the cell temperature is changed under similar conditions using the electrochemical cell 2 that has not degraded. That is, the voltage difference AV0 is a difference between an electrolysis voltage V0c corresponding to the cell temperature C0 during the initial operation and an electrolysis voltage V0d corresponding to the cell temperature C3 when the electrochemical cell 2 that has not degraded is used. Then, the degradation-site identifying unit 31 compares the voltage difference AV1, which is the measured amount of change, with the voltage difference AV0, which is the reference value of the amount of change in the state. Then, when the voltage difference AV1 (amount of change) is greater than a predetermined value with respect to the voltage difference AV0 (reference value), the degradation-site identifying unit 31 determines that the electrolyte 23 has degraded, thereby identifying the degradation site. Here, the degradation of the electrolyte 23 corresponds to, for example, a state in which oxide ions are less likely to pass through the electrolyte 23 due to structural change resulting from a high temperature. Then, due to the degradation of the electrolyte 23, an overvoltage of the electrolyte 23 during operation of the electrochemical cell 2 increases.

[0051] Next, as shown in FIG. 9, the operation determining unit 32 determines the lowering operation for the electrochemical cell 2 based on the degradation diagnosis result shown in FIG. 8. In the graph of FIG. 9, a characteristic line L4 is an approximate straight line based on data obtained when the degradation diagnosis was performed on the degraded electrochemical cell 2, and is a line showing characteristics of the degraded electrochemical cell 2.

[0052] Specifically, the operation determining unit 32 determines the cell temperature at which a target voltage V0 (predetermined target value) is obtained based on the characteristic line L4. Then, as the lowering operation, the operation determining unit 32 increases a value of the cell temperature to the determined value C4. Specifically, in the cell control system 1, the control device 3 controls the temperature adjustment unit 151 to increase the cell temperature. This allows the oxide ions generated in the cathode reaction layer 241 to easily pass through the electrolyte 23. As a result, the overvoltage of the electrolyte 23 decreases. Therefore, the electrolysis voltage of the electrochemical cell 2 is set to the predetermined target value.

[0053] Next, advantageous effects of the present embodiment will be described. The cell control system 1 of the present embodiment includes the degradation-site identifying unit 31 and the operation determining unit 32. Therefore, the cell control system 1 can perform the resistance-lowering operation corresponding to the degradation site of the electrochemical cell 2. Hence, the cell control system 1 can efficiently reduce the internal resistance of the electrochemical cell 2. As a result, degradation of the electrochemical cell 2 can be suppressed because the cell control system 1 can operate the electrochemical cell 2 at a low internal resistance.

[0054] Electrolysis of water is performed by reactions at respective sites of an electrochemical cell. Further, for a reaction process in the electrochemical cell to proceed, an overvoltage is required in addition to a theoretical voltage. Then, the overvoltage of the electrochemical cell increases due to degradation of each site of the electrochemical cell. When the electrochemical cell is operated at a high overvoltage, there is a possibility that the degradation of the electrochemical cell may be promoted. Furthermore, without identifying the degradation site of the electrochemical cell, for example, when an attempt is made to reduce an internal resistance or the overvoltage only by controlling a cell temperature, there is a possibility that the internal resistance or the overvoltage cannot be sufficiently reduced if an operation required to reduce the internal resistance or the like is other than changing the cell temperature. Furthermore, if the temperature of the electrochemical cell is increased excessively, there is a possibility that agglomeration of a catalyst or the like may occur, and as a result, degradation of the electrochemical cell may be promoted. In this regard, the cell control system 1 of the present embodiment performs the degradation diagnosis and the lowering operation. Accordingly, the cell control system 1 can identify the degradation site and further perform the resistance-lowering operation corresponding to each degradation site. Hence, the cell control system 1 can efficiently reduce the internal resistance of the electrochemical cell 2, and further can also efficiently reduce the overvoltage. Therefore, the cell control system 1 can operate the electrochemical cell 2 at a low overvoltage, thereby suppressing degradation of the electrochemical cell 2. As a result, the cell control system 1 can extend the service life of the electrochemical cell 2.

[0055] In the cell control system 1 of the present embodiment, the lowering operation is an operation of changing at least one value among the temperature of the electrochemical cell 2, the pressure in the cathode channel 21, the pressure in the anode channel 22, the partial pressure of the water vapor 11 in the gas supplied to the cathode channel 21, the partial pressure of oxygen in the gas supplied to the anode channel 22, the flow rate of the gas flowing through the cathode channel 21, and the flow rate of the gas flowing through the anode channel 22. Hence, in the cell control system 1, the internal resistance and the overvoltage of the electrochemical cell 2 are easily reduced. Furthermore, the cell control system 1 can perform the lowering operation for the electrochemical cell 2 using an apparatus or the like for water electrolysis, without providing a new apparatus or the like for performing the lowering operation. As a result, the cell control system 1 can achieve structural simplification and downsizing.

[0056] In the cell control system 1 of the present embodiment, the degradation-site identifying unit 31 identifies the degradation site of the electrochemical cell 2 by changing the value of at least one diagnostic item among the plurality of diagnostic items described above. Further, the degradation-site identifying unit 31 identifies the degradation site of the electrochemical cell 2 by comparing the measured amount of change acquired by measuring the amount of change in the state of the electrochemical cell 2 with the reference value of the amount of change in the state of the electrochemical cell 2. Hence, in the cell control system 1, the degradation site is easily identified. As a result, in the cell control system 1, the internal resistance and the overvoltage of the electrochemical cell 2 are easily reduced. Furthermore, the cell control system 1 can identify the degradation site by acquiring the measured amount of change of the diagnostic item. Therefore, the cell control system 1 can perform the degradation diagnosis for the electrochemical cell 2 using an apparatus or the like for water electrolysis, without providing a new apparatus or the like for performing the degradation diagnosis. As a result, the cell control system 1 can achieve structural simplification and downsizing.

[0057] In the cell control system 1 of the present embodiment, the degradation-site identifying unit 31 identifies the degradation site of the electrochemical cell 2 by changing values of the plurality of diagnostic items. Hence, the cell control system 1 can identify the degradation site more accurately. As a result, the cell control system 1 can sufficiently reduce the overvoltage, thereby further suppressing degradation of the electrochemical cell 2.

[0058] In the cell control system 1 of the present embodiment, the anode channel 22 is configured such that air flows therethrough. The cell control system 1 changes the oxygen partial pressure in the anode channel 22 by causing the gas other than the air to further flow through the anode channel 22. Hence, the cell control system 1 can easily and sufficiently adjust the oxygen partial pressure in the anode channel 22. As a result, the cell control system 1 can accurately and easily perform the lowering operation and the degradation diagnosis for the electrochemical cell 2.

[0059] In the cell control system 1 of the present embodiment, the amount of change in the state of the electrochemical cell 2 is the amount of change in the magnitude of the voltage of the electrochemical cell 2 when the current flowing through the electrochemical cell 2 is controlled to be the constant current. Hence, the cell control system 1 can accurately identify the degradation site of the electrochemical cell 2, and can easily perform the degradation diagnosis. Further, the cell control system 1 can perform the degradation diagnosis for the electrochemical cell 2 without providing a new apparatus or the like for performing the degradation diagnosis. As a result, the cell control system 1 can achieve structural simplification and downsizing.

[0060] In the cell control system 1 of the present embodiment, the electrochemical cell 2 is the solid oxide cell. Hence, in the cell control system 1, power-generation efficiency can be easily improved.

[0061] The cell control system 1 of the present embodiment is configured to prohibit performing at least one operation of the degradation diagnosis and the lowering operation for the electrochemical cell 2 in accordance with the predetermined prohibition condition. Hence, the cell control system 1 can suppress a decrease in the production amount of hydrogen gas or the like, for example, when the remaining capacity of the hydrogen storage tank for storing the hydrogen gas produced by the electrochemical cell 2 is equal to or less than the predetermined value. As a result, in the cell control system 1, the production amount of hydrogen gas is easily and sufficiently secured.

[0062] The cell control system 1 of the present embodiment performs the degradation diagnosis and the lowering operation for the electrochemical cell 2 when the prohibition on performing at least one operation of the degradation diagnosis and the lowering operation continues for the predetermined period or longer, even when the prohibition condition is satisfied. Hence, the cell control system 1 can sufficiently reduce the overvoltage of the electrochemical cell 2. As a result, the cell control system 1 can extend the service life of the electrochemical cell 2. Further, the cell control system 1 can easily maintain a production capacity of hydrogen gas over a long period.

[0063] Furthermore, in the cell control system 1 of the present embodiment, the details of the lowering operation are the same as those of the diagnostic operation (diagnostic items). That is, the lowering operation can be performed using the same parameter (diagnostic item) used during the diagnostic operation for degradation. Hence, the cell control system 1 can more easily reduce the overvoltage of the electrochemical cell 2 based on the degradation diagnosis result.

[0064] As described above, according to the present embodiment, it is possible to provide the cell control system 1 that suppresses the degradation of the electrochemical cell 2 by efficiently reducing the internal resistance of the electrochemical cell 2.

[0065] In the present embodiment, the temperature measurement unit measures the temperature of the cell stack 20 in which the plurality of electrochemical cells 2 are stacked. However, the temperature measurement unit may be configured to measure, for example, a temperature of gas in a cathode discharge channel or an anode discharge channel, and set the measured temperature as a representative temperature of the electrochemical cell. Further, the temperature measurement unit may be configured to measure, for example, a temperature of an end portion in a stacking direction of a cell stack, a temperature of a center portion of the cell stack, a temperature of an end portion located at a gas supply side or an end portion located at a gas discharge side of a cathode channel or an anode channel of an electrochemical cell, or the like, and set the measured temperature as the representative temperature of the electrochemical cell.

[0066] In the present embodiment, the voltage measurement unit 52 measures a voltage applied to the cell stack 20 in which the plurality of electrochemical cells 2 are stacked. However, the voltage measurement unit can also measure a voltage of a specific electrochemical cell, for example. That is, the voltage measurement unit may be configured to measure, for example, a voltage of an electrochemical cell whose temperature is relatively higher than that of other electrochemical cells constituting a cell stack, so that reactivity is high and degradation proceeds easily. Further, the voltage measurement unit may be configured to measure, for example, a voltage of an electrochemical cell in which a flow rate of gas flowing through a cathode channel or an anode channel is relatively smaller than that of other electrochemical cells constituting the cell stack. Furthermore, the voltage measurement unit can also be configured to measure a voltage of a power supply terminal to which the power supply 51 is connected.

[0067] In the present embodiment, the control device 3 may be configured to decrease an internal resistance or an electrolysis voltage of the electrochemical cell 2 to a target value by simultaneously performing a plurality of lowering operations.

[0068] (Second Embodiment) A cell control system 1 of the present embodiment is configured to control a voltage applied to an electrochemical cell 2 to be constant.

[0069] In the present embodiment, an amount of change in a state of the electrochemical cell 2 is an amount of change in a magnitude of a current flowing through the electrochemical cell 2 when a voltage applied to the electrochemical cell 2 (an input voltage) is controlled to be a constant voltage. That is, a power supply 51 applies the constant voltage to a cell stack 20.

[0070] Next, control of the electrochemical cell 2 by a control device 3 will be described with reference to a flowchart of FIG. 10. In step S11A of the present embodiment, a process similar to that in step S1 of the first embodiment described above is performed. In step S12, the control device 3 measures the magnitude of the current flowing through the electrochemical cell 2. After measuring the magnitude of the current in step S12, the control device 3 determines in step S13 whether a value of the current flowing through the electrochemical cell 2 (current value) is equal to or less than a predetermined threshold value. That is, in the present embodiment, whether the electrochemical cell 2 has degraded is determined based on the magnitude of the current flowing through the electrochemical cell 2 when a voltage having a constant magnitude is controlled to be applied to the electrochemical cell 2. Then, when the control device 3 determines that the current value of the electrochemical cell 2 is equal to or less than the threshold value (YES), the control device 3 proceeds to step S14. On the other hand, in step S13, when the control device 3 determines that the current value of the electrochemical cell 2 is greater than the threshold value (NO), the control device 3 proceeds to step S15. That is, as an operating time of the electrochemical cell 2 elapses, the electrochemical cell 2 gradually degrades, and an overvoltage increases. Thereby, the current of the electrochemical cell 2 gradually decreases from a predetermined target value. Therefore, when the current value becomes equal to or less than the threshold value, the control device 3 performs a degradation diagnosis and a lowering operation in accordance with a predetermined condition. Thereby, the current flowing through the electrochemical cell 2 increases to the target value. In steps S14, S15, and S17 of the present embodiment, processes similar to those in steps S4, S5, and S7 of the first embodiment are executed. Therefore, description thereof will be omitted.

[0071] Next, in step S16, the control device 3 changes a value of one diagnostic item among a plurality of diagnostic items, and proceeds to step S18. Next, in step S18, the control device 3 measures an amount of change between the current value flowing through the electrochemical cell 2 before changing the value of the diagnostic item and the current value flowing through the electrochemical cell 2 after changing the value of the diagnostic item in step S16, as a measured amount of change. That is, a degradation-site identifying unit 31 of the present embodiment measures the amount of change in the magnitude of the current flowing through the electrochemical cell 2 when the value of the diagnostic item is changed, as the measured amount of change. After executing the process of step S18, the control device 3 proceeds to step S19 and determines whether values of all the diagnostic items have been changed. When the control device 3 determines that the values of all the diagnostic items have been changed (YES), the control device 3 proceeds to step S110, and identifies a degradation site of the electrochemical cell 2 based on the measured amount of change. On the other hand, in step S19, when the control device 3 determines that the values of all the diagnostic items have not been changed (NO), the control device 3 returns to step S16 and changes the value of the diagnostic item to a value of a next diagnostic item. Then, the control device 3 repeatedly executes the processes from step S16 to step S19 until the values of all the diagnostic items are changed.

[0073] Next, after identifying the degradation site in step S110, the control device 3 proceeds to step S111 and performs the lowering operation for the electrochemical cell 2 such that the current flowing through the electrochemical cell 2 becomes the predetermined target value. Thereafter, the control device 3 proceeds to step S11A again and performs a similar process. Other technical matters are similar to the matters described in the first embodiment. Note that among reference signs used in the present embodiment and subsequent embodiments, reference signs identical to those used in the preceding embodiment represent components similar to the components in the preceding embodiment unless otherwise specified.

[0074] In the present embodiment, the amount of change in the state is the amount of change in the magnitude of the current flowing through the electrochemical cell 2 when the voltage applied to the electrochemical cell 2 is controlled to be the constant voltage. Hence, the cell control system 1 of the present embodiment can accurately identify the degradation site, and can easily perform the degradation diagnosis. Further, the cell control system 1 can perform the degradation diagnosis for the electrochemical cell 2 using an apparatus or the like used for electrolysis of water, without providing a new apparatus or the like for performing the degradation diagnosis. The cell control system 1 of the present embodiment has, in addition to the advantageous effects described above, advantageous effects similar to those of the first embodiment.

[0075] (Third Embodiment) A cell control system 1 of the present embodiment is configured to supply carbon dioxide to a cathode channel 21, as shown in FIG. 11.

[0076] The cell control system 1 of the present embodiment is equipped with a carbon dioxide supply channel 59 that supplies a gas containing carbon dioxide to the cathode channel 21 via a cathode supply channel 53. The carbon dioxide supply channel 59 is connected to the cathode supply channel 53. The carbon dioxide supply channel 59 is provided with a flow-rate adjustment unit 591. The control device 3 controls the flow-rate adjustment unit 591 to adjust a flow rate of the gas containing carbon dioxide supplied to the cathode channel 21.

[0077] That is, carbon dioxide gas is supplied to the cathode channel 21 in addition to water vapor. The electrochemical cell 2 produces hydrogen and carbon monoxide from the water vapor and the carbon dioxide by co-electrolysis. Then, a gas containing the produced hydrogen and carbon monoxide is discharged to a cathode discharge channel 57. Here, the co-electrolysis is an electrolytic reaction in which electrolysis of water and electrolysis of carbon dioxide are simultaneously performed, and a reaction [3H2O + CO2 ^ CO + 3H + 2O2] occurs in the electrochemical cell 2. Other technical matters are similar to the matters described in the first embodiment.

[0078] In the present embodiment, the electrochemical cell 2 produces hydrogen and carbon monoxide from water vapor and carbon dioxide by co-electrolysis. Hence, the cell control system 1 of the present embodiment can use the gas containing the produced hydrogen and carbon monoxide to produce methane, for example. The cell control system 1 of the present embodiment has, in addition to the advantageous effects described above, advantageous effects similar to those of the first embodiment.

[0079] (Fourth Embodiment)

[0080] As shown in FIG. 12, a cell control system 1 of the present embodiment is equipped with an anode recirculation channel 581 that branches from an anode discharge channel 58 and connects the anode discharge channel 58 and an anode supply channel 54.

[0081] The anode recirculation channel 581 supplies a gas flowing through the anode discharge channel 58 back to an anode channel 22 via the anode supply channel 54 by driving a pump 582 provided in the anode recirculation channel 581. Further, the control device 3 controls the pump 582 to adjust a recirculation flow rate of the gas supplied back from the anode discharge channel 58 to the anode channel 22 via the anode recirculation channel 581. Other technical matters are similar to the matters described in the first embodiment.

[0082] The cell control system 1 of the present embodiment includes the anode recirculation channel 581. Hence, the cell control system 1 can supply a gas at a relatively high temperature that flows through the anode discharge channel 58 back to the anode channel 22. Accordingly, the cell control system 1 can recover waste heat of the gas flowing through the anode discharge channel 58. As a result, the cell control system 1 can improve energy efficiency. The cell control system 1 of the present embodiment has, in addition to the advantageous effects described above, advantageous effects similar to those of the first embodiment.

[0083] (Fifth Embodiment) A cell control system 1 of the present embodiment is configured to supply air to an anode channel 22 using a high-pressure gas, as shown in FIG. 13. In the present embodiment, a high-pressure gas from a factory or a high-pressure gas from a cylinder is supplied to an inert gas supply channel 55. An internal pressure in the inert gas supply channel 55 is higher than an internal pressure in an anode supply channel 54. In the present embodiment, the internal pressure in the anode supply channel 54 is equivalent to atmospheric pressure. A pressure in the gas supplied to the inert gas supply channel 55 can be, for example, several hundred kPaG or less.

[0085] As shown in FIG. 13, the inert gas supply channel 55 is provided with an ejector 62. Further, the anode supply channel 54 is connected to the ejector 62. Then, the ejector 62 uses the high-pressure inert gas in the inert gas supply channel 55 as a motive fluid to suck air flowing through the anode supply channel 54, and supplies the sucked air to the electrochemical cell 2 together with the inert gas. With this configuration, the anode supply channel 54 is not provided with an air pump 541.

[0086] The inert gas supply channel 55 is provided with a flow-rate adjustment unit 551 at a portion located upstream of the ejector 62. The control device 3 controls the flow-rate adjustment unit 551 to adjust a flow rate of the inert gas flowing into the ejector 62. Other technical matters are similar to the matters described in the first embodiment.

[0087] The cell control system 1 of the present embodiment supplies the gas from the anode supply channel 54 to the anode channel 22 using the ejector 62. Hence, the cell control system 1 can supply air to the electrochemical cell 2 without providing an air pump in the anode supply channel 54. As a result, the cell control system 1 can simplify facilities and reduce costs. That is, when the inert gas is supplied to the anode channel 22 for a purpose of a normal operation of the electrochemical cell 2, a lowering operation for an internal resistance, or the like, air can be supplied to the anode channel 22 using a pressure of the inert gas without using the air pump. The cell control system 1 of the present embodiment has, in addition to the advantageous effects described above, advantageous effects similar to those of the first embodiment.

[0088] (Sixth Embodiment) A cell control system 1 of the present embodiment is configured to adjust respective pressures in a cathode channel 21 and an anode channel 22 by adjusting back pressure in an electrochemical cell 2.

[0089] As shown in FIG. 14, in the present embodiment, a cathode discharge channel 57 and an anode discharge channel 58 are provided with pressure adjustment units 573 and 583, respectively. The pressure adjustment unit 573 adjusts the pressure inside the cathode channel 21 by adjusting a flow channel resistance of the cathode discharge channel 57. The pressure adjustment unit 583 adjusts the pressure inside the anode channel 22 by adjusting a flow channel resistance of the anode discharge channel 58. The pressure adjustment units 573 and 583 may be, for example, solenoid valves or the like. The control device 3 controls the pressure adjustment unit 573 to adjust the pressure inside the cathode channel 21. The control device 3 controls the pressure adjustment unit 583 to adjust the pressure inside the anode channel 22. Other technical matters are similar to the matters described in the first embodiment.

[0090] The cell control system 1 of the present embodiment adjusts the pressure inside the cathode channel 21 or the anode channel 22 by controlling the pressure adjustment unit 573 or 583. Hence, in the cell control system 1, the pressure inside the cathode channel 21 or the anode channel 22 can be easily adjusted. Accordingly, in the cell control system 1, a degradation diagnosis and a lowering operation for the electrochemical cell 2 using the pressure inside the cathode channel 21 or the anode channel 22 can be easily performed. As a result, the cell control system 1 can more effectively reduce an overvoltage of the electrochemical cell 2. The cell control system 1 of the present embodiment has, in addition to the advantageous effects described above, advantageous effects similar to those of the first embodiment.

[0091] (Seventh Embodiment) A cell control system 1 of the present embodiment is equipped with a plurality of cell stacks 20, as shown in FIG. 15.

[0092] The cell control system 1 of the present embodiment is equipped with a plurality of cell stacks 20, a plurality of temperature adjustment units 151, and a plurality of housings 15. In the present embodiment, two housings 15 are provided, and two cell stacks 20 are accommodated in each housing 15. Temperature adjustment is performed for each cell stack 20 by a separate temperature adjustment unit 151. Further, a cathode discharge channel 57 and an anode discharge channel 58 are connected to each housing 15. Each cathode discharge channel 57 is provided with a pressure adjustment unit 573, and each anode discharge channel 58 is provided with a pressure adjustment unit 583. Accordingly, the cell control system 1 of the present embodiment can adjust pressures in a cathode channel 21 and an anode channel 22 for each housing 15.

[0093] A cathode supply channel 53, an anode supply channel 54, and the like are connected to each housing 15. Further, the cell control system 1 is configured such that an inert gas flows into each anode supply channel 54 from an inert gas supply channel (not shown). Each of the cathode supply channel 53, the anode supply channel 54, and the inert gas supply channel is provided with a flow-rate adjustment unit (not shown). Accordingly, the cell control system 1 of the present embodiment can adjust each flow rate, each oxygen partial pressure, or the like of the cathode channel 21 and the anode channel 22 of the electrochemical cell 2 for each housing 15. Other technical matters are similar to the matters described in the sixth embodiment.

[0094] The cell control system 1 of the present embodiment is equipped with the plurality of cell stacks 20. Hence, the cell control system 1 can further improve a production capacity of hydrogen gas.

[0095] Further, the cell control system 1 of the present embodiment is equipped with the plurality of housings 15, and at least one cell stack 20 is accommodated in each housing 15. Hence, the cell control system 1 can adjust, for each housing 15, a temperature of the cell stack 20, and each flow rate, each pressure, each oxygen partial pressure, or the like in the cathode channel 21 and the anode channel 22. Accordingly, the cell control system 1 can perform a degradation diagnosis, a lowering operation, and the like for each housing 15 at different timings and under different operation conditions. The cell control system 1 of the present embodiment has, in addition to the advantageous effects described above, advantageous effects similar to those of the sixth embodiment. (Eighth Embodiment) As shown in FIG. 16, a cell control system 1 of the present embodiment is equipped with one or more heat shields 16 between a plurality of cell stacks 20.

[0096] In the cell control system 1 of the present embodiment, the plurality of cell stacks 20 is accommodated in a housing 15. Specifically, two cell stacks 20 are accommodated in the housing 15. Further, to separately adjust a temperature of each cell stack 20, a separate temperature adjustment unit 151 is provided for each cell stack 20. In the present embodiment, adjustment temperatures of the respective cell stacks 20 are different from each other.

[0097] Further, during operation, the cell stack 20 is at a high temperature of about 700°C, and heat thereof is released to the outside as radiant heat. Therefore, in the present embodiment, the heat shield 16 that blocks the radiant heat radiated from the respective cell stack 20 is provided between the two cell stacks 20. The heat shield 16 may be, for example, a heat shield plate or the like. Other technical matters are similar to the matters described in the first embodiment. In the cell control system 1 of the present embodiment, the heat shield 16 is provided between the two cell stacks 20. Hence, the cell control system 1 can suppress heat transfer from the cell stack 20 having a relatively high temperature to the cell stack 20 having a relatively low temperature. Therefore, in the cell control system 1, even if two or more cell stacks 20 are accommodated in the housing 15, the temperature of each cell stack 20 can be easily adjusted to a desired temperature. As a result, the cell control system 1 can easily manage the temperature of each cell stack 20. The cell control system 1 of the present embodiment has, in addition to the advantageous effects described above, advantageous effects similar to those of the first embodiment.

[0099] (Ninth Embodiment) As shown in FIGs. 17 through 21, a cell control system 1 of the present embodiment is configured to control an electrochemical cell 2 that functions as a fuel cell. In the present embodiment, the electrochemical cell 2 is a solid oxide fuel cell (SOFC). The electrochemical cell 2 is electrically connected to an external load 18.

[0100] In the present embodiment, as shown in FIG. 17, the electrochemical cell 2 is configured to generate electricity by being supplied with a gas containing an oxidant 12 to a cathode channel 21 and being supplied with a gas containing fuel 13 to an anode channel 22. In the present embodiment, by performing a lowering operation determined by an operation determining unit 32, control is executed such that at least one parameter among an internal resistance of the electrochemical cell 2, a voltage applied to the external load 18 from the electrochemical cell 2 (hereinafter referred to as "an output voltage of the electrochemical cell"), and a current flowing to the external load 18 from the electrochemical cell 2 (hereinafter referred to as "an output current of the electrochemical cell") becomes a predetermined target value.

[0101] In the present embodiment, a cathode supply channel 53 supplies air to the cathode channel 21. An anode supply channel 54 supplies a gas containing the fuel 13 to the anode channel 22. In the present embodiment, the oxidant 12 is oxygen. The fuel 13 is hydrogen gas. Further, in the present embodiment, a gas having a low oxygen partial pressure flows from the electrochemical cell 2 to a cathode discharge channel 57. A gas containing a large amount of water vapor generated by the electrochemical cell 2 flows through an anode discharge channel 58. That is, air after the oxygen 12 is consumed by the electrochemical cell 2 flows through the cathode discharge channel 57.

[0102] As shown in FIG. 18, the cathode supply channel 53 is provided with an air pump 532 to supply air to the cathode channel 21. The anode supply channel 54 is provided with a flow-rate adjustment unit 542 that adjusts a flow rate of the gas containing the fuel 13 supplied to the anode channel 22. The flow-rate adjustment unit 542 may be, for example, a solenoid valve or the like. The control device 3 controls the air pump 532 and the flow-rate adjustment unit 542 to adjust a supply amount of air to the cathode channel 21, a supply amount of the fuel 13 to the anode channel 22, the partial pressure of the fuel 13 in the anode channel 22, or the like.

[0103] As shown in FIG. 17, in a cathode reaction layer 241, oxide ions are generated by reducing the oxygen 12. In an anode reaction layer 251, a reaction occurs in which protons and electrons are generated from the hydrogen gas of the fuel 13. Then, the generated electrons flow to the external load 18. The protons react with the oxide ions that have moved toward the anode reaction layer 251 through the electrolyte 23. As a result, water vapor is generated. The generated water vapor is diffused by an anode diffusion layer 252, moves to the anode channel 22, and is discharged to the anode discharge channel 58. Further, the cathode reaction layer 241 and the anode reaction layer 251 contain a catalyst to promote the reaction in each reaction layer.

[0104] Next, control of the electrochemical cell 2 by a control device 3 will be described with reference to a flowchart of FIG. 19. In step S21 of the present embodiment, a process similar to that in step S1 of the first embodiment described above is executed. In the present embodiment, in step S22, the control device 3 measures a magnitude of an output voltage from the electrochemical cell 2 to the external load 18. After measuring the magnitude of the output voltage in step S22, the control device 3 determines in step S23 whether a value of the output voltage of the electrochemical cell 2 (output voltage value) is equal to or less than a predetermined threshold value. That is, in the present embodiment, degradation of the electrochemical cell 2 is determined based on the output voltage from the electrochemical cell 2 to the external load 18. Then, when the control device 3 determines that the output voltage value of the electrochemical cell 2 is equal to or less than the threshold value (YES), the control device 3 proceeds to step S24. On the other hand, when the control device 3 determines in step S23 that the output voltage value of the electrochemical cell 2 is greater than the threshold value (NO), the control device 3 proceeds to step S25. That is, as an operating time of the electrochemical cell 2 elapses, the electrochemical cell 2 gradually degrades, and an overvoltage increases. Thereby, the output voltage of the electrochemical cell 2 gradually decreases from a predetermined target value. Therefore, when the output voltage becomes equal to or less than the threshold value, the control device 3 performs a degradation diagnosis and a lowering operation in accordance with a predetermined condition. Thereby, the output voltage of the electrochemical cell 2 increases to the target value. In steps S25 and S27 of the present embodiment, processes similar to those in steps S5 and S7 of the first embodiment are executed. Therefore, description thereof will be omitted.

[0105] In step S24, the control device 3 determines whether a prohibition condition for diagnosis is not satisfied (not applicable). In the present embodiment, the prohibition condition for diagnosis can be, for example, a condition that an amount of power required to be generated by the electrochemical cell 2 is equal to or greater than a predetermined value.

[0106] Next, in step S26, the control device 3 changes a value of one diagnostic item among a plurality of diagnostic items, and proceeds to step S28. Next, in step S28, the control device 3 measures an amount of change between the output voltage value of the electrochemical cell 2 before changing the value of the diagnostic item and the output voltage value after changing the value of the diagnostic item in step S26, as a measured amount of change. That is, a degradationsite identifying unit 31 measures the amount of change in the magnitude of the output voltage of the electrochemical cell 2 when the value of the diagnostic item is changed, as the measured amount of change.

[0107] In the present embodiment, the degradation-site identifying unit 31 sets a temperature of the electrochemical cell 2, a pressure in the cathode channel 21, a pressure in the anode channel 22, the partial pressure of the oxygen 12 in the gas supplied to the cathode channel 21, the partial pressure of the fuel 13 in the gas supplied to the anode channel 22, the flow rate of the gas in the cathode channel 21, and the flow rate of the gas in the anode channel 22 as the diagnostic items for degradation.

[0108] After executing the process of step S28, the control device 3 proceeds to step S29 and determines whether the values of all the diagnostic items have been changed. When the control device 3 determines that the values of all the diagnostic items have been changed (YES), the control device 3 proceeds to step S210, and identifies a degradation site of the electrochemical cell 2 based on the measured amount of change. On the other hand, in step S29, when the control device 3 determines that the values of all the diagnostic items have not been changed (NO), the control device 3 returns to step S26 and changes the value of the diagnostic item to a value of a next diagnostic item. Then, the control device 3 repeatedly executes the processes from step S26 to step S29 until the values of all the diagnostic items are changed.

[0109] Next, after identifying the degradation site in step S210, the control device 3 proceeds to step S211 and performs the lowering operation for the electrochemical cell 2 such that the output voltage of the electrochemical cell 2 becomes the predetermined target value. Thereafter, the control device 3 proceeds to step S21 again and performs a similar process.

[0110] In the present embodiment, the lowering operation is an operation of changing at least one value among the temperature of the electrochemical cell 2, the pressure in the cathode channel 21, the pressure in the anode channel 22, the partial pressure of the fuel 13 in the gas supplied to the anode channel 22, the partial pressure of the oxygen 12 in the gas supplied to the cathode channel 21, the flow rate of the gas in the cathode channel 21, and the flow rate of the gas in the anode channel 22.

[0111] Next, as a specific example, when the diagnostic item is the "oxygen partial pressure in the gas supplied to the cathode channel 21", details of the degradation diagnosis by the degradation-site identifying unit 31 will be described with reference to a graph of FIG. 20. In the graph of FIG. 20, a horizontal axis represents a magnitude of the oxygen partial pressure in the cathode channel 21, and a vertical axis represents a magnitude of the output voltage of the electrochemical cell 2. In the graph of FIG. 20, filled circles are plot results of data obtained when testing was performed in the past using the electrochemical cell 2 that has not degraded, showing a relationship between the oxygen partial pressure and the output voltage. Further, open circles are plot results of data showing a relationship between the oxygen partial pressure and the output voltage of the degraded electrochemical cell 2 when a degradation diagnosis up to step S210 is performed. In the graph of FIG. 20, during an initial operation, comparing the data for the degraded electrochemical cell 2 with that for the electrochemical cell 2 that has not degraded, the output voltage of the degraded electrochemical cell 2 is decreased. That is, it can be seen that the output voltage of the electrochemical cell 2 decreases due to degradation. Further, a characteristic line L5 is an approximate straight line based on data of past test results, and is a line showing characteristics of the electrochemical cell 2 that has not degraded. Further, in performing the degradation diagnosis, the degradation-site identifying unit 31 first changes a value of the oxygen partial pressure in the cathode channel 21 from a value C0 during the initial operation. In the present embodiment, the value of the oxygen partial pressure is increased from the value C0 during the initial operation to a value C5. Then, the degradationsite identifying unit 31 measures an output voltage V1h corresponding to the oxygen partial pressure C5 by the voltage measurement unit 52. Furthermore, the degradation-site identifying unit 31 measures a voltage difference AV1 (measured amount of change), which is a difference between an output voltage V1g corresponding to the oxygen partial pressure C0 during the initial operation and the output voltage V1h corresponding to the oxygen partial pressure C5.

[0113] Further, in the present embodiment, a reference value of an amount of change in a state of the electrochemical cell 2 is a difference in the magnitude of the output voltage (voltage difference) AV0 when the oxygen partial pressure was changed under similar conditions using the electrochemical cell 2 that has not degraded. That is, the voltage difference AV0 is a difference between an output voltage V0e corresponding to the oxygen partial pressure C0 during the initial operation and an output voltage V0f corresponding to the oxygen partial pressure C5 when the electrochemical cell 2 that has not degraded is used. Then, the degradation-site identifying unit 31 compares the voltage difference AV1, which is the measured amount of change, with the voltage difference AV0, which is the reference value of the amount of change in the state. When the voltage difference AV1 (amount of change) is greater than a predetermined value with respect to the voltage difference AV0 (reference value), the degradation-site identifying unit 31 determines that the cathode reaction layer 241 has degraded, thereby identifying the degradation site. Here, the degradation of the cathode reaction layer 241 corresponds to, for example, a state in which the oxygen 12 is less likely to be reduced due to a decrease in a reaction area of the cathode reaction layer 241 caused by structural change resulting from a high temperature or adhesion of a foreign matter contained in the gas supplied to the cathode channel 21 to the cathode reaction layer 241. Then, due to the degradation of the cathode reaction layer 241, an overvoltage of the cathode reaction layer 241 during operation of the electrochemical cell 2 increases.

[0114] Next, after identifying the degradation site in step S210, the control device 3 proceeds to step S211. Based on the degradation diagnosis result (identified degradation site), the operation determining unit 32 determines the lowering operation for the electrochemical cell 2 as shown in FIG. 21. In a graph of FIG. 21, a characteristic line L6 is an approximate straight line based on data obtained when the degradation diagnosis was performed on the degraded electrochemical cell 2, and is a line showing characteristics of the degraded electrochemical cell 2.

[0115] In the present embodiment, the operation determining unit 32 determines the oxygen partial pressure at which a target voltage V0 (predetermined target value) is obtained based on the characteristic line L6. Then, as the lowering operation, the operation determining unit 32 increases the oxygen partial pressure in the gas supplied to the cathode channel 21 to the determined value C6. Specifically, the cell control system 1 increases the oxygen partial pressure in the cathode channel 21 by, for example, causing a gas having a high oxygen partial pressure to flow through the cathode channel 21. As a result, an oxygen concentration of the gas supplied to the cathode channel 21 becomes higher than 21%, which is an oxygen concentration of air. This allows the oxygen 12 to be easily reduced in the cathode reaction layer 241, and an overvoltage of the cathode reaction layer 241 decreases. Therefore, the output voltage of the electrochemical cell 2 is set to the predetermined target value.

[0116] The cell control system 1 of the present embodiment is configured such that air flows through the cathode channel 21. The cell control system 1 changes the oxygen partial pressure in the cathode channel 21 by causing the gas other than air to further flow through the cathode channel 21. As shown in FIG. 18, the cell control system 1 is equipped with an oxygen-enriched gas supply channel 61 that supplies an oxygen-enriched gas containing a large amount of oxygen to the cathode channel 21. The oxygen-enriched gas has an oxygen partial pressure higher than that of air. The oxygen-enriched gas supply channel 61 is connected to the cathode supply channel 53, and supplies the oxygen-enriched gas to the cathode channel 21 via the cathode supply channel 53. Accordingly, the oxygen partial pressure in the cathode channel 21 is increased. Further, the oxygen-enriched gas supply channel 61 is provided with a flow-rate adjustment unit 611 that adjusts a flow rate of the oxygen-enriched gas supplied to the cathode channel 21. Then, the control device 3 controls the flow-rate adjustment unit 611 to control the oxygen partial pressure in the cathode channel 21. The flow-rate adjustment unit 611 may be, for example, a solenoid valve or the like. Other technical matters are similar to the matters described in the first embodiment.

[0117] Also in the present embodiment, the cell control system 1 includes the degradation-site identifying unit 31 and the operation determining unit 32. Therefore, the cell control system 1 can perform the resistance-lowering operation corresponding to the degradation site of the electrochemical cell 2. As a result, the cell control system 1 can suppress degradation of the electrochemical cell 2.

[0118] In the cell control system 1 of the present embodiment, the lowering operation is an operation of changing at least one value among the temperature of the electrochemical cell 2, the pressure in the cathode channel 21, the pressure in the anode channel 22, the partial pressure of the fuel 13 in the gas supplied to the anode channel 22, the partial pressure of the oxygen 12 in the gas supplied to the cathode channel 21, the flow rate of the gas in the cathode channel 21, and the flow rate of the gas in the anode channel 22. Hence, in the cell control system 1, the internal resistance and the overvoltage of the electrochemical cell 2 are easily reduced. As a result, the cell control system 1 can sufficiently secure the output voltage and the output current of the electrochemical cell 2. Further, the cell control system 1 can perform the lowering operation for the electrochemical cell 2 using an apparatus or the like for power generation, without providing a new apparatus or the like for performing the lowering operation. As a result, the cell control system 1 can achieve structural simplification and downsizing.

[0119] Also in the cell control system 1 of the present embodiment, the degradation-site identifying unit 31 identifies the degradation site of the electrochemical cell 2 by changing the value of at least one diagnostic item among the plurality of diagnostic items described above. Hence, in the cell control system 1, the degradation site is easily identified. Further, the cell control system 1 can identify the degradation site by measuring the measured amount of change of the diagnostic item. Therefore, the cell control system 1 can perform the degradation diagnosis for the electrochemical cell 2 using an apparatus or the like for power generation, without providing a new apparatus or the like for performing the degradation diagnosis. As a result, the cell control system 1 can achieve structural simplification and downsizing.

[0120] The cell control system 1 of the present embodiment changes the oxygen partial pressure in the cathode channel 21 by causing the gas other than air to further flow through the cathode channel 21. Hence, the cell control system 1 can easily and sufficiently adjust the oxygen partial pressure in the cathode channel 21. As a result, the cell control system 1 can accurately and easily perform the lowering operation and the degradation diagnosis for the electrochemical cell 2.

[0121] The cell control system 1 of the present embodiment is equipped with the oxygen-enriched gas supply channel 61. Hence, in the cell control system 1, the oxygen partial pressure in the gas flowing through the cathode channel 21 is easily adjusted. Thereby, the cell control system 1 can easily perform the degradation diagnosis and the lowering operation for the electrochemical cell 2 based on the oxygen partial pressure in the cathode channel 21. As a result, the cell control system 1 can efficiently reduce the overvoltage of the electrochemical cell 2, and can efficiently suppress degradation of the electrochemical cell 2. The cell control system 1 of the present embodiment has, in addition to the advantageous effects described above, advantageous effects similar to those of the first embodiment.

[0122] As in the present embodiment, in a case of a cell control system that controls the electrochemical cell 2 functioning as a fuel cell, an amount of change in a state may be, for example, an amount of change in an output voltage of the electrochemical cell 2 when an output current of the electrochemical cell 2 is controlled to be a constant current. Further, in the case of the cell control system that controls the electrochemical cell 2 functioning as the fuel cell, the amount of change in the state may be, for example, an amount of change in the output current of the electrochemical cell 2 when the output voltage of the electrochemical cell 2 is controlled to be a constant voltage. In these cases, the cell control system 1 can easily identify a degradation site, and can easily perform a degradation diagnosis. Further, the cell control system 1 can perform the degradation diagnosis for the electrochemical cell 2 without providing a new apparatus or the like for performing the degradation diagnosis. As a result, the cell control system 1 can achieve structural simplification and downsizing.

[0123] (Tenth Embodiment) A cell control system 1 of the present embodiment is configured to use fuel 13 discharged without being utilized by an electrochemical cell 2 for temperature adjustment of the electrochemical cell 2.

[0124] In the cell control system 1 of the present embodiment, as shown in FIG. 22, a cathode discharge channel 57 and an anode discharge channel 58 merge with each other to form a merging channel 17. The merging channel 17 is provided with an off-gas burner 152, which will be described later. Further, a cathode supply channel 53 is provided with a branch channel 533 that branches from a channel for supplying air to a cathode channel 21 and is connected to the cathode discharge channel 57. The branch channel 533 is provided with a flow-rate adjustment unit 534 that adjusts a flow rate of air supplied to the cathode discharge channel 57. The control device 3 controls the flow-rate adjustment unit 534 to adjust the flow rate of air supplied to the cathode discharge channel 57. The flow-rate adjustment unit 534 may be, for example, a solenoid valve or the like.

[0125] A gas flowing through the anode discharge channel 58 contains hydrogen that has not been utilized by power generation of the electrochemical cell 2. The off-gas burner 152 burns oxygen contained in a gas flowing into the merging channel 17 from the branch channel 533 and the cathode discharge channel 57, and remaining hydrogen in a gas flowing into the merging channel 17 from the anode discharge channel 58. High-temperature gas burned by the off-gas burner 152 flows into a temperature adjustment unit 151 through the merging channel 17. In the present embodiment, the temperature adjustment unit 151 is configured to be heated by the high-temperature gas burned by the off-gas burner 152, and to adjust a temperature of a cell stack 20 by heating. Other technical matters are similar to the matters described in the ninth embodiment.

[0126] The cell control system 1 of the present embodiment includes the temperature adjustment unit 151 that adjusts the temperature of the electrochemical cell 2 using the high-temperature gas generated by combustion in the off-gas burner 152. Hence, the cell control system 1 can use energy (the high-temperature gas) in the fuel 13 contained in the gas discharged from the electrochemical cell 2 for temperature adjustment of the electrochemical cell 2. As a result, the cell control system 1 can further improve energy efficiency. The cell control system 1 of the present embodiment has, in addition to the advantageous effects described above, advantageous effects similar to those of the ninth embodiment.

[0127] In the present embodiment, the electrochemical cell 2 is heated using the high-temperature gas generated by combustion in the off-gas burner 152. Further, in the cell control system 1, the heat generated by the off-gas burner 152 may also be used to adjust the temperature of other facilities in addition to the electrochemical cell 2.

[0128] Further, the cell control system 1 in which the electrochemical cell 2 is utilized as a fuel cell, as in the ninth and tenth embodiments described above, can integrate with the cell control system 1 in which the electrochemical cell 2 is utilized as a hydrogen production apparatus, as in the first to eighth embodiments described above. According to this configuration, the cell control system can introduce a gas containing a large amount of water vapor and a gas having a low oxygen partial pressure, which are discharged from the electrochemical cell constituting the fuel cell, into a cathode channel or an anode channel of the electrochemical cell constituting the hydrogen production apparatus to produce hydrogen. Furthermore, the cell control system can be configured to temporarily store, in a storage facility, the gas having a low oxygen partial pressure or the like discharged from the electrochemical cell constituting the fuel cell, and to utilize the gas for hydrogen production by the electrochemical cell constituting the hydrogen production apparatus at a predetermined timing.

[0129] Further, a cell control system may be configured to supply a gas having a high oxygen partial pressure and a gas containing a large amount of hydrogen, which are discharged from an electrochemical cell constituting a hydrogen production apparatus, to an electrochemical cell constituting a fuel cell. In this case as well, a gas having a high oxygen partial pressure or the like may be temporarily stored in a storage facility. According to this configuration, the cell control system can directly utilize the gas stored in the storage facility, or adjust a ratio or the like between the gas stored in the storage facility and air to utilize the gas for performing a degradation diagnosis or a lowering operation for the electrochemical cell. Furthermore, in this case, after the electrochemical cell is utilized as the hydrogen production apparatus, the utilized electrochemical cell can also be utilized as the fuel cell. That is, the cell control system can also be utilized for control of an electrochemical cell that can be operated by switching between power generation and hydrogen production. In this case, the cell control system can easily and flexibly respond to fluctuations in demand for hydrogen gas and power generation.

[0130] Further, when an electrochemical cell is utilized as a fuel cell, carbon monoxide can be used as fuel in addition to hydrogen. In this case, the cell control system may be configured to include, for example, a reformer (not shown). The reformer reforms methane gas, a gas containing methane as a main component, or the like, through a reaction by a catalyst to generate a fuel gas containing hydrogen and carbon monoxide. The cell control system supplies the fuel gas generated by the reformer to an anode channel via an anode supply channel. In this case, the electrochemical cell outputs electric energy by water being generated through a reaction between hydrogen gas and oxide ions, and carbon dioxide being generated through a reaction between carbon monoxide and oxide ions. Further, in a case of the cell control system 1 of the third embodiment, by using the generated carbon dioxide, hydrogen, and carbon monoxide can be generated by co-electrolysis to produce methane.

[0131] In the first embodiment and the like described above, the temperature of the electrochemical cell 2 is adjusted by the temperature adjustment unit 151. The cell control system 1 may be configured to adjust the temperature of the electrochemical cell 2, for example, without using the temperature adjustment unit 151, by utilizing Joule heat generated by a voltage or electric power applied to the cell stack 20, or heat generated by a reaction between an oxidant and fuel during power generation. That is, although a reaction of electrolysis of water vapor is an endothermic reaction, Joule heat due to an internal resistance of an electrochemical cell is generated by energization of the electrochemical cell. Therefore, the control device 3 adjusts an amount of generation of the Joule heat by controlling a power supply 51 (controlling the energization of the electrochemical cell 2). Accordingly, the cell control system 1 can also adjust the temperature of the electrochemical cell 2.

[0132] In the first embodiment and the like described above, the temperature of the cell stack 20 is adjusted by the temperature adjustment unit 151 provided inside the housing 15. As shown in FIG. 23, the temperature adjustment unit 151 may be configured to be provided outside the housing 15 to heat the cathode supply channel 53 and the anode supply channel 54, for example, rather than being provided inside the housing 15. In this case, the cell control system 1 can supply gas heated to a desired temperature to the anode channel 22 and the cathode channel 21, thereby adjusting the temperature of the electrochemical cell 2.

[0133] Further, in the case of the cell control system 1 of the ninth embodiment, for example, the oxygen partial pressure in the cathode channel 21 can be changed by causing a dry gas having low humidity (a low partial pressure of water vapor) and a high oxygen partial pressure to flow into the electrochemical cell 2.

[0134] Further, the degradation-site identifying unit 31 can identify the degradation site of the electrochemical cell 2 also by using, for example, a measurement result of AC impedance, a current interruption method, a current sweep method, or the like. Specifically, when using the measurement result of AC impedance, the degradation-site identifying unit 31 causes a plurality of alternating currents having different frequencies from each other to flow through the electrochemical cell 2, and compares a response of a voltage at that time with a predetermined reference value. Accordingly, the degradation-site identifying unit 31 can identify the degradation site. That is, the degradation-site identifying unit 31 can identify the degradation site based on the response speed of the voltage or the like when the alternating current of each frequency is caused to flow. When using the current interruption method, the degradation-site identifying unit 31 compares a response of a voltage when a current flowing through the electrochemical cell 2 is turned off in a phased manner with a predetermined reference value. Accordingly, the degradation-site identifying unit 31 can identify the degradation site. That is, the degradation-site identifying unit 31 can identify the degradation site based on a decrease in the voltage, a voltage waveform, the response speed of the voltage, or the like when the current is turned off. When using the current sweep method, the degradation-site identifying unit 31 sweeps a current density flowing through the electrochemical cell 2, and can identify the degradation site based on voltage characteristics measured at that time. Further, the degradation-site identifying unit 31 may identify the degradation site by combining the measurement result of AC impedance, the current interruption method, and the current sweep method. Furthermore, the degradationsite identifying unit 31 may identify the degradation site by combining the measurement result of AC impedance, the current interruption method, or the current sweep method with the diagnostic items described above.

[0135] If a temperature of an electrochemical cell is too low, the electrochemical cell easily degrades due to a high voltage. Further, if the temperature of the electrochemical cell is too high, the electrochemical cell easily degrades due to a high temperature. Therefore, a temperature measurement unit measures, for example, a temperature of an end portion of a cell stack where the temperature easily becomes low, or a temperature of a center portion of the cell stack where the temperature easily becomes high. The temperature measurement unit can set the measured temperature as the temperature of the electrochemical cell that serves as a reference when performing a degradation diagnosis or a lowering operation.

[0136] The electrochemical cell 2 of the cell control system 1 may be, for example, a polymer electrolyte cell or the like, instead of a solid oxide cell.

[0137] The present disclosure is not limited to the embodiments described above and can be applied to various embodiments without departing from its essence.

[0138] The present disclosure has been described in accordance with the embodiments. However, the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and variations within the equivalent scope. In addition, the scope and spirit of the present disclosure include various combinations and forms, and further include other combinations and forms including only one element, more, or less, thereto.

[0139] < Supplementary Note > Structures of the present disclosure are described below. [Structure 1] A cell control system (1) that controls an internal resistance of an electrochemical cell (2), including a cathode channel (21), an anode channel (22), and an electrolyte (23) disposed between the anode channel and the cathode channel, the electrochemical cell being configured to produce hydrogen by electrolyzing a raw material (11) using supplied electric power, the cell control system including: a degradation-site identifying unit (31) that performs a degradation diagnosis to identify a degradation site of the electrochemical cell; and an operation determining unit (32) that determines, based on a result of the degradation diagnosis by the degradation-site identifying unit, a lowering operation that is an operation of the electrochemical cell to reduce the internal resistance of the electrochemical cell, which has increased due to degradation of the degradation site identified by the degradation-site identifying unit, in which, by performing the lowering operation determined by the operation determining unit, at least one of the internal resistance of the electrochemical cell, a voltage applied to the electrochemical cell, and a current flowing through the electrochemical cell is controlled to reach a predetermined target value. [Structure 2] The cell control system according to Structure 1, in which: the raw material is water; and the lowering operation is an operation of changing at least one of a temperature of the electrochemical cell, a pressure in the cathode channel, a pressure in the anode channel, a partial pressure of water vapor in a gas supplied to the cathode channel, a partial pressure of oxygen in a gas supplied to the anode channel, a flow rate of the gas in the cathode channel, and a flow rate of the gas in the anode channel. [Structure 3] The cell control system according to Structure 1 or 2, in which: the raw material is water; in a case where a plurality of diagnostic items of the degradation-site identifying unit includes a temperature of the electrochemical cell, a pressure in the cathode channel, a pressure in the anode channel, a partial pressure of water vapor in a gas supplied to the cathode channel, a partial pressure of oxygen in a gas supplied to the anode channel, a flow rate of the gas in the cathode channel, and a flow rate of the gas in the anode channel, the degradation-site identifying unit identifies the degradation site of the electrochemical cell by changing a value of at least one diagnostic item among the plurality of diagnostic items; and the degradation-site identifying unit acquires a measured amount of change by measuring an amount of change in a state of the electrochemical cell when the value of the diagnostic item is changed, and identifies the degradation site of the electrochemical cell by comparing the measured amount of change with a predetermined reference value of the amount of change in the state of the electrochemical cell. [Structure 4] The cell control system according to Structure 2 or 3, in which: the anode channel is configured such that air flows therethrough; and the oxygen partial pressure in the anode channel is changed by causing a gas other than the air to further flow through the anode channel. [Structure 5] The cell control system according to Structure 3, in which the amount of change in the state is an amount of change in a magnitude of a voltage applied to the electrochemical cell when a current flowing through the electrochemical cell is controlled to a constant current. [Structure 6] The cell control system according to Structure 3, in which the amount of change in the state is an amount of change in a magnitude of a current flowing through the electrochemical cell when a voltage applied to the electrochemical cell is controlled to a constant voltage. [Structure 7] A cell control system (1) that controls an internal resistance of an electrochemical cell (2), including a cathode channel (21), an anode channel (22), and an electrolyte (23) disposed between the anode channel and the cathode channel, the electrochemical cell being configured to generate electricity by being supplied with a gas containing an oxidant to the cathode channel and being supplied with a gas containing fuel to the anode channel, the cell control system including: a degradation-site identifying unit (31) that performs a degradation diagnosis to identify a degradation site of the electrochemical cell; and an operation determining unit (32) that determines, based on a result of the degradation diagnosis by the degradation-site identifying unit, a lowering operation that is an operation of the electrochemical cell to reduce the internal resistance of the electrochemical cell, which has increased due to degradation of the degradation site identified by the degradation-site identifying unit, in which, by performing the lowering operation determined by the operation determining unit, at least one of the internal resistance of the electrochemical cell, an output voltage of the electrochemical cell, and an output current of the electrochemical cell is controlled to reach a predetermined target value. [Structure 8] The cell control system according to Structure 7, in which: the oxidant is oxygen; and the lowering operation is an operation of changing at least one of a temperature of the electrochemical cell, a pressure in the cathode channel, a pressure in the anode channel, a partial pressure of the fuel in the gas supplied to the anode channel, a partial pressure of the oxygen in the gas supplied to the cathode channel, a flow rate of the gas in the cathode channel, and a flow rate of the gas in the anode channel. [Structure 9] The cell control system according to Structure 7 or 8, in which: the oxidant is oxygen; in a case where a plurality of diagnostic items of the degradation-site identifying unit includes a temperature of the electrochemical cell, a pressure in the cathode channel, a pressure in the anode channel, a partial pressure of the oxygen in a gas supplied to the cathode channel, a partial pressure of the fuel in a gas supplied to the anode channel, a flow rate of the gas in the cathode channel, and a flow rate of the gas in the anode channel, the degradation-site identifying unit identifies the degradation site of the electrochemical cell by changing a value of at least one diagnostic item among the plurality of diagnostic items; and the degradation-site identifying unit acquires a measured amount of change by measuring an amount of change in a state of the electrochemical cell when the value of the diagnostic item is changed, and identifies the degradation site of the electrochemical cell by comparing the measured amount of change with a predetermined reference value of the amount of change in the state of the electrochemical cell. [Structure 10] The cell control system according to Structure 8 or 9, in which: the cathode channel is configured such that air flows therethrough; and the oxygen partial pressure in the cathode channel is changed by causing a gas other than the air to further flow through the cathode channel. The cell control system according to Structure 9, in which the amount of change in the state is an amount of change in a magnitude of the output voltage of the electrochemical cell when the output current of the electrochemical cell is controlled to a constant current. [Structure 12] The cell control system according to Structure 9, in which the amount of change in the state is an amount of change in a magnitude of the output current of the electrochemical cell when the output voltage of the electrochemical cell is controlled to a constant voltage. [Structure 13] The cell control system according to any one of Structures 1 to 12, in which the electrochemical cell is a solid oxide cell. [Structure 14] The cell control system according to any one of Structures 1 to 13, in which the cell control system is further configured to prohibit performing at least one operation of the degradation diagnosis and the lowering operation in accordance with a predetermined prohibition condition. [Structure 15] The cell control system according to Structure 14, in which the cell control system is further configured to perform the degradation diagnosis and the lowering operation, when the prohibition on performing at least one operation of the degradation diagnosis and the lowering operation continues for a predetermined period or longer, even when the prohibition condition is satisfied.

Claims

[CLAIMS]

1. 1. A cell control system (1) that controls an internal resistance of an electrochemical cell (2), including a cathode channel (21), an anode channel (22), and an electrolyte (23) disposed between the anode channel and the cathode channel, the electrochemical cell being configured to produce hydrogen by electrolyzing a raw material (11) using supplied electric power,the cell control system comprising:a degradation-site identifying unit (31) that performs a degradation diagnosis to identify a degradation site of the electrochemical cell; andan operation determining unit (32) that determines, based on a result of the degradation diagnosis by the degradation-site identifying unit, a lowering operation that is an operation of the electrochemical cell to reduce the internal resistance of the electrochemical cell, which has increased due to degradation of the degradation site identified by the degradation-site identifying unit,wherein, by performing the lowering operation determined by the operation determining unit, at least one of the internal resistance of the electrochemical cell, a voltage applied to the electrochemical cell, and a current flowing through the electrochemical cell is controlled to reach a predetermined target value.

2. 2. The cell control system according to claim 1, wherein:the raw material is water; andthe lowering operation is an operation of changing at least one of a temperature of the electrochemical cell, a pressure in the cathode channel, a pressure in the anode channel, a partial pressure of water vapor in a gas supplied to the cathode channel, a partial pressure of oxygen in a gas supplied to the anode channel, a flow rate of the gas in the cathode channel, and a flow rate of the gas in the anode channel.

3. 3. The cell control system according to claim 1, wherein:the raw material is water;in a case where a plurality of diagnostic items of the degradation-site identifying unit includes a temperature of the electrochemical cell, a pressure in the cathode channel, a pressure in the anode channel, a partial pressure of water vapor in a gas supplied to the cathode channel, a partial pressure of oxygen in a gas supplied to the anode channel, a flow rate of the gas in the cathode channel, and a flow rate of the gas in the anode channel, the degradation-site identifying unit identifies the degradation site of the electrochemical cell by changing a value of at least one diagnostic item among the plurality of diagnostic items; andthe degradation-site identifying unit acquires a measured amount of change by measuring an amount of change in a state of the electrochemical cell when the value of the diagnostic item is changed, and identifies the degradation site of the electrochemical cell by comparing the measured amount of change with a predetermined reference value of the amount of change in the state of the electrochemical cell.

4. 4. The cell control system according to claim 2 or 3, wherein:the anode channel is configured such that air flows therethrough; andthe oxygen partial pressure in the anode channel is changed by causing a gas other than the air to further flow through the anode channel.

5. 5. The cell control system according to claim 3, whereinthe amount of change in the state is an amount of change in a magnitude of a voltage applied to the electrochemical cell when a current flowing through the electrochemical cell iscontrolled to a constant current.

6. 6. The cell control system according to claim 3, whereinthe amount of change in the state is an amount of change in a magnitude of a current flowing through the electrochemical cell when a voltage applied to the electrochemical cell is controlled to a constant voltage.

7. 7. A cell control system (1) that controls an internal resistance of an electrochemical cell (2), including a cathode channel (21), an anode channel (22), and an electrolyte (23) disposed between the anode channel and the cathode channel, the electrochemical cell being configured to generate electricity by being supplied with a gas containing an oxidant to the cathode channel and being supplied with a gas containing fuel to the anode channel,the cell control system comprising:a degradation-site identifying unit (31) that performs a degradation diagnosis to identify a degradation site of the electrochemical cell; andan operation determining unit (32) that determines, based on a result of the degradation diagnosis by the degradation-site identifying unit, a lowering operation that is an operation of the electrochemical cell to reduce the internal resistance of the electrochemical cell, which has increased due to degradation of the degradation site identified by the degradation-site identifying unit,wherein, by performing the lowering operation determined by the operation determining unit, at least one of the internal resistance of the electrochemical cell, an output voltage of the electrochemical cell, and an output current of the electrochemical cell is controlled to reach a predetermined target value.

8. 8. The cell control system according to claim 7, wherein:the oxidant is oxygen; andthe lowering operation is an operation of changing at least one of a temperature of the electrochemical cell, a pressure in the cathode channel, a pressure in the anode channel, a partial pressure of the fuel in the gas supplied to the anode channel, a partial pressure of the oxygen in the gas supplied to the cathode channel, a flow rate of the gas in the cathode channel, and a flow rate of the gas in the anode channel.

9. 9. The cell control system according to claim 7, wherein:the oxidant is oxygen;in a case where a plurality of diagnostic items of the degradation-site identifying unit includes a temperature of the electrochemical cell, a pressure in the cathode channel, a pressure in the anode channel, a partial pressure of the oxygen in a gas supplied to the cathode channel, a partial pressure of the fuel in a gas supplied to the anode channel, a flow rate of the gas in the cathode channel, and a flow rate of the gas in the anode channel, the degradation-site identifying unit identifies the degradation site of the electrochemical cell by changing a value of at least one diagnostic item among the plurality of diagnostic items; andthe degradation-site identifying unit acquires a measured amount of change by measuring an amount of change in a state of the electrochemical cell when the value of the diagnostic item is changed, and identifies the degradation site of the electrochemical cell by comparing the measured amount of change with a predetermined reference value of the amount of change in the state of the electrochemical cell.

10. 10. The cell control system according to claim 8 or 9, wherein:the cathode channel is configured such that air flows therethrough; andthe oxygen partial pressure in the cathode channel is changed by causing a gas other than the air to further flow through the cathode channel.

11. 11. The cell control system according to claim 9, whereinthe amount of change in the state is an amount of change in a magnitude of the output voltage of the electrochemical cell when the output current of the electrochemical cell is controlled to a constant current.

12. 12. The cell control system according to claim 9, whereinthe amount of change in the state is an amount of change in a magnitude of the output current of the electrochemical cell when the output voltage of the electrochemical cell is controlled to a constant voltage.

13. 13. The cell control system according to claim 1 or 7, whereinthe electrochemical cell is a solid oxide cell.

14. 14. The cell control system according to claim 1 or 7, whereinthe cell control system is further configured to prohibit performing at least one operation of the degradation diagnosis and the lowering operation in accordance with a predetermined prohibition condition.

15. 15. The cell control system according to claim 14, whereinthe cell control system is further configured to perform the degradation diagnosis and the lowering operation, when the prohibition on performing at least one operation of the degradation diagnosis and the lowering operation continues for a predetermined period or longer, even when5 the prohibition condition is satisfied.

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