Fuel cell system

Abstract

To provide technique enabling improvement of durability of a fuel cell system.SOLUTION: A fuel cell system comprises: a fuel cell stack generating power using chemical reaction between anode gas and cathode gas; a temperature measurement unit measuring temperature of the fuel cell stack; a pressure reduction unit; and an operation control unit controlling the fuel cell stack and the pressure reduction unit. The fuel cell stack comprises a cathode gas flow passage in which cathode gas flows. The pressure reduction unit can reduce the pressure of the cathode gas flow passage. When stopping operation of the fuel cell stack, the operation control unit controls the pressure reduction unit to reduce the pressure of the inside of the cathode gas flow passage until the pressure inside the cathode gas flow passage becomes lower than saturation water vapor pressure corresponding to the temperature of the fuel cell stack measured by the temperature measurement unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to fuel cell systems. [Background technology]

[0002] For example, Patent Document 1 discloses a fuel cell system in which residual water in the cathode gas flow path is removed by connecting the cathode gas flow path to a pressure reduction section that reduces the pressure to a level lower than atmospheric pressure when the fuel cell stack is stopped. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-97993 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent document 1 discusses a fuel cell system that can efficiently remove residual water from within the fuel cell stack and is free from the risk of freezing even when used in low-temperature environments, but does not consider how to improve the durability of the fuel cell system. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to one aspect of the present disclosure, there is provided a fuel cell system including: a fuel cell stack that generates electricity through a chemical reaction between an anode gas and a cathode gas; a temperature measurement unit that measures the temperature of the fuel cell stack; a pressure reduction unit; and an operation control unit that controls the fuel cell stack and the pressure reduction unit, wherein the fuel cell stack includes a cathode gas flow path through which the cathode gas flows, the pressure reduction unit is capable of reducing the pressure in the cathode gas flow path, and when operation of the fuel cell stack is stopped, the operation control unit controls the pressure reduction unit to reduce the pressure in the cathode gas flow path until the pressure in the cathode gas flow path becomes less than a saturated water vapor pressure corresponding to the temperature of the fuel cell stack measured by the temperature measurement unit. According to this type of fuel cell system, the amount of water contained in the membrane electrode assembly provided in the fuel cell stack can be reduced, thereby suppressing deterioration of the cathode catalyst layer contained in the membrane electrode assembly and improving the durability of the fuel cell system. (2) In the fuel cell system of the above aspect, the system may further include a pressure measuring unit that measures the pressure in the cathode gas flow path, and a target pressure setting unit that sets a reduced pressure target pressure, which is the pressure in the cathode gas flow path after being reduced by the pressure reducing unit, wherein the target pressure setting unit sets a pressure less than the saturated water vapor pressure as the reduced pressure target pressure, and the operation control unit, when stopping operation of the fuel cell stack, may control the pressure reducing unit to reduce the pressure in the cathode gas flow path until the pressure measured by the pressure measuring unit becomes the reduced pressure target pressure. According to this aspect of the fuel cell system, the pressure reduction operation of the cathode gas flow channel can be controlled using the pressure in the cathode gas flow channel as an index. (3) In the fuel cell system of the above aspect, the target pressure setting unit may set the reduced pressure target pressure to a value equal to or greater than 25% of the saturated water vapor pressure and less than 80% of the saturated water vapor pressure. According to this aspect of the fuel cell system, it is possible to reduce the amount of moisture contained in the membrane electrode assemblies provided in the fuel cell stack, and also to prevent the membrane electrode assemblies from becoming too dry due to reduced pressure. (4) In the fuel cell system of the above configuration, the system may further include a stack case that houses the fuel cell stack, the pressure reduction unit may be capable of reducing the pressure inside the stack case, and the operation control unit may control the pressure reduction unit to reduce the pressure inside the stack case when stopping operation of the fuel cell stack. According to this type of fuel cell system, the fuel cell stack can be kept warm by insulating it, and therefore the pressure in the cathode gas flow channel can be reduced efficiently. (5) The fuel cell system of the above aspect may further include a pressure measuring unit that measures the pressure in the cathode gas flow path, a membrane resistance measuring unit that measures a membrane resistance that is the electrical resistance of a membrane electrode assembly provided in the fuel cell stack, and a drive time setting unit that sets a drive time of the pressure reducing unit, wherein the drive time setting unit uses the membrane resistance measured by the membrane resistance measuring unit to set a planned drive time that is the drive time required to increase the value of the membrane resistance to a predetermined target resistance value, and the operation control unit, when stopping operation of the fuel cell stack, may control the pressure reducing unit to reduce the pressure in the cathode gas flow path from the time when the pressure measured by the pressure measuring unit falls below the saturated water vapor pressure until the planned drive time has elapsed. According to this aspect of the fuel cell system, the operation of depressurizing the cathode gas flow channel can be controlled using the driving time of the depressurizing unit as an index. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell system. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a fuel cell. [Figure 3] FIG. 4 is a process diagram of an operation shutdown process in the first embodiment. [Figure 4] Phase diagram of water. [Figure 5] FIG. 10 is a diagram showing the relationship between the pressure in the cathode gas flow channel, the membrane resistance, and the amount of oxidation of catalyst-supporting carbon. [Figure 6] FIG. 10 is an explanatory diagram showing a schematic configuration of a fuel cell system according to a second embodiment. [Figure 7] FIG. 10 is a process diagram of an operation shutdown process in the second embodiment. [Figure 8] FIG. 10 is an explanatory diagram showing a schematic configuration of a fuel cell system according to a third embodiment. [Figure 9] FIG. 11 is a process diagram of an operation shutdown process in the third embodiment. [Figure 10] FIG. 11 is a process diagram of an operation shutdown process in the third embodiment. [Figure 11] 10A and 10B are diagrams illustrating changes in membrane resistance with driving time of the pressure reducing unit. DETAILED DESCRIPTION OF THE INVENTION

[0008] A. First embodiment: 1 is an explanatory diagram showing a schematic configuration of a fuel cell system 100. The fuel cell system 100 is mounted on, for example, a fuel cell electric vehicle (FCEV). The fuel cell system 100 includes a fuel cell stack 30, a temperature measurement unit 40, a membrane resistance measurement unit 50, an anode gas supply / discharge system 60, a cathode gas supply / discharge system 70, a load 80, and a control unit 90.

[0009] The fuel cell stack 30 includes a plurality of fuel cell units 10 and a pair of end terminals 21, 22. Each of the plurality of fuel cell units 10 is plate-shaped and stacked in a stacking direction, which is the thickness direction. Each fuel cell unit 10 is a power-generating element that can generate power on its own. In this embodiment, the fuel cell unit 10 is configured as a polymer electrolyte fuel cell. The fuel cell unit 10 receives anode gas and cathode gas as reactant gases and generates power through an electrochemical reaction between them. For example, the anode gas is hydrogen and the cathode gas is air. The anode gas is also called fuel gas, and the cathode gas is also called oxidant gas.

[0010] 2 is a cross-sectional view showing a schematic configuration of a fuel cell 10. The fuel cell 10 includes a membrane electrode assembly (MEA) 11, an anode diffusion layer 15, a cathode diffusion layer 16, an anode separator 17, and a cathode separator 18.

[0011] The membrane electrode assembly 11 includes an electrolyte membrane 12, an anode catalyst layer 13, and a cathode catalyst layer 14. The electrolyte membrane 12 is a proton-conductive ion-exchange membrane formed from a solid polymer material, such as a fluororesin containing perfluorocarbon sulfonic acid, and exhibits good electrical conductivity in a wet state. The anode catalyst layer 13 and the cathode catalyst layer 14 are formed by coating conductive particles, such as carbon particles, carrying a catalyst such as platinum or a platinum alloy with a proton-conductive polymer electrolyte. The anode catalyst layer 13 is formed on one side of the electrolyte membrane 12, and the cathode catalyst layer 14 is formed on the other side of the electrolyte membrane 12.

[0012] The anode diffusion layer 15 and the cathode diffusion layer 16 are made of gas-permeable and conductive materials such as carbon cloth or carbon paper. The anode diffusion layer 15 is formed on the surface of the anode catalyst layer 13 opposite to the surface that contacts the electrolyte membrane 12. The cathode diffusion layer 16 is formed on the surface of the cathode catalyst layer 14 opposite to the surface that contacts the electrolyte membrane 12.

[0013] The anode separator 17 and the cathode separator 18 are made of gas-blocking and electrically conductive materials, such as dense carbon made by compressing carbon particles to make them gas-impermeable, or press-formed metal materials such as stainless steel or titanium steel. The anode separator 17 is disposed on the surface of the anode diffusion layer 15 opposite to the surface that contacts the anode catalyst layer 13. The anode separator 17 includes an anode gas flow channel 27 through which the anode gas flows. The cathode separator 18 is disposed on the surface of the cathode diffusion layer 16 opposite to the surface that contacts the cathode catalyst layer 14. The cathode separator 18 includes a cathode gas flow channel 28 through which the cathode gas flows.

[0014] 1 are arranged at both ends in the stacking direction of the fuel cell stack 30. Specifically, the first end terminal 21 is arranged at one end of the fuel cell stack 30, and the second end terminal 22 is arranged at the other end of the fuel cell stack 30. The first end terminal 21 has openings that connect to a cathode gas supply flow path 71 and a cathode gas discharge flow path 74, which will be described later. The second end terminal 22 has openings that connect to an anode gas supply flow path 62 and an anode gas discharge flow path 64, which will be described later.

[0015] The temperature measuring unit 40 measures the temperature of the fuel cell stack 30. In the example shown in Fig. 1, the temperature measuring unit 40 is connected to the second end terminal 22, but the temperature measuring unit 40 may be arranged in any location so as to be able to measure the temperature of the fuel cell stack 30. The temperature measuring unit 40 can transmit the measured temperature to the control unit 90.

[0016] The membrane resistance measuring unit 50 measures the membrane resistance, which is the electrical resistance of the membrane electrode assembly 11. In the example shown in Fig. 1, the membrane resistance measuring unit 50 is connected to one fuel cell 10, but the membrane resistance measuring unit 50 may be connected to each of a plurality of fuel cell cells 10, or may be connected so as to measure the resistance value of all of the plurality of fuel cell cells 10. The membrane resistance measuring unit 50 can transmit the measured membrane resistance value to the control unit 90.

[0017] The anode gas supply / discharge system 60 supplies anode gas to the fuel cell stack 30 and discharges anode off-gas from the fuel cell stack 30. The anode off-gas contains anode gas that was not used in the power generation of the fuel cell stack 30, moisture, and the like. The anode gas supply / discharge system 60 includes an anode gas tank 61, an anode gas supply flow path 62, an anode gas inlet valve 63, an anode gas discharge flow path 64, and an anode gas outlet valve 65.

[0018] The anode gas tank 61 is a container that stores the anode gas to be supplied to the fuel cell stack 30. The anode gas tank 61 stores, for example, high-pressure hydrogen gas.

[0019] The anode gas supply flow path 62 is a flow path that guides the anode gas from the anode gas tank 61 to the fuel cell stack 30. One end of the anode gas supply flow path 62 is connected to the anode gas tank 61, and the other end of the anode gas supply flow path 62 is connected to an opening of the second end terminal 22.

[0020] The anode gas inlet valve 63 adjusts the amount of anode gas supplied from the anode gas tank 61. The anode gas inlet valve 63 is provided in the anode gas supply passage 62.

[0021] The anode gas discharge flow path 64 is a flow path that discharges anode off-gas from the fuel cell stack 30. One end of the anode gas discharge flow path 64 is connected to an opening of the second end terminal 22. The other end of the anode gas discharge flow path 64 is open, and the anode off-gas is discharged through this opening.

[0022] The anode gas outlet valve 65 opens and closes the anode gas discharge passage 64. The anode gas outlet valve 65 is provided in the anode gas discharge passage 64.

[0023] The cathode gas supply / discharge system 70 supplies cathode gas to the fuel cell stack 30 and discharges cathode off-gas from the fuel cell stack 30. The cathode off-gas contains cathode gas not consumed in the power generation of the fuel cell stack 30 and moisture and the like produced in the power generation of the fuel cell stack 30. The cathode gas supply / discharge system 70 includes a cathode gas supply flow path 71, an air pump 72, a cathode gas inlet valve 73, a cathode gas discharge flow path 74, a cathode gas outlet valve 75, a cathode gas discharge branch flow path 76, a cathode gas branch outlet valve 77, a pressure reducing unit 78, and a pressure measuring unit 79.

[0024] The cathode gas supply flow path 71 is a flow path that introduces cathode gas to the fuel cell stack 30. One end of the cathode gas supply flow path 71 is open. Cathode gas can be taken in through this opening. The other end of the cathode gas supply flow path 71 is connected to an opening in the first end terminal 21. An air pump 72 and a cathode gas inlet valve 73 are provided in the cathode gas supply flow path 71.

[0025] The air pump 72 compresses the cathode gas and supplies the cathode gas to the fuel cell stack 30 via the cathode gas supply passage 71 .

[0026] The cathode gas inlet valve 73 adjusts the amount of cathode gas supplied from the air pump 72 .

[0027] The cathode gas discharge flow path 74 is a flow path that discharges cathode off-gas from the fuel cell stack 30. One end of the cathode gas discharge flow path 74 is connected to an opening of the first end terminal 21. The other end of the cathode gas discharge flow path 74 is open, and the cathode off-gas is discharged through this opening.

[0028] The cathode gas outlet valve 75 opens and closes the cathode gas discharge passage 74. The cathode gas outlet valve 75 is provided in the cathode gas discharge passage 74.

[0029] The cathode gas discharge branch channel 76 is a channel branching from the cathode gas discharge channel 74 between the fuel cell stack 30 and the cathode gas outlet valve 75. The end of the cathode gas discharge branch channel 76 is open.

[0030] The cathode gas branch outlet valve 77 opens and closes the cathode gas discharge branch passage 76. The cathode gas branch outlet valve 77 is provided in the cathode gas discharge branch passage 76. The cathode gas branch outlet valve 77 is closed while the fuel cell stack 30 is generating power.

[0031] The pressure reducing unit 78 is provided so as to be able to reduce the pressure in the cathode gas flow path 28, the cathode gas discharge flow path 74, and the cathode gas discharge branch flow path 76 within the fuel cell stack 30. The pressure reducing unit 78 is provided in the cathode gas discharge branch flow path 76. The pressure reducing unit 78 is, for example, a vacuum pump.

[0032] The pressure measuring unit 79 measures the pressure in the cathode gas flow channel 28. The pressure measuring unit 79 is provided in the cathode gas discharge flow channel 74 between the fuel cell stack 30 and the cathode gas outlet valve 75.

[0033] The load 80 is connected to the fuel cell stack 30 via an electric circuit (not shown) that includes a DC / DC converter. The load 80 is, for example, a drive motor of a vehicle equipped with the fuel cell system 100. The electric circuit is provided with a voltage measurement unit 81 and a current measurement unit 82. The voltage measurement unit 81 and the current measurement unit 82 are capable of measuring the output voltage and output current of the fuel cell stack 30 and transmitting the measurement values ​​to the control unit 90.

[0034] The control unit 90 is configured as a computer including a CPU 91 and a memory 92. The CPU 91 functions as an operation control unit 93 and a target pressure setting unit 94 by reading and executing a control program stored in the memory 92.

[0035] The operation control unit 93 controls each unit of the fuel cell system 100 to generate power in the fuel cell stack 30. Specifically, the operation control unit 93 controls the valves provided in the anode gas supply / discharge system 60 and the cathode gas supply / discharge system 70, the air pump 72, and the pressure reducing unit 78, thereby controlling the operation of the fuel cell stack 30.

[0036] The target pressure setting unit 94 sets a reduced pressure target pressure, which is the pressure inside the cathode gas flow channel 28 after being reduced by the pressure reducing unit 78 .

[0037] 3 is a process diagram of the operation stop process in the first embodiment. The operation stop process is a process for stopping the operation of the fuel cell stack 30. The operation stop process is executed when the control unit 90 receives an operation stop signal. The operation stop signal is received, for example, when a switch for starting a vehicle equipped with the fuel cell system 100 is turned off.

[0038] In step S10, the operation control unit 93 stops the air pump 72.

[0039] In step S20, the operation control unit 93 closes the anode gas inlet valve 63 and the cathode gas inlet valve 73.

[0040] In step S30, the operation control unit 93 closes the anode gas outlet valve 65 and the cathode gas outlet valve 75. By executing steps S20 and S30, the anode gas flow path 27 and the cathode gas flow path 28 are sealed.

[0041] In step S40, the temperature measurement unit 40 measures the temperature of the fuel cell stack 30. The temperature of the fuel cell stack 30 measured here is the temperature at the time when the operation of the fuel cell stack 30 is stopped.

[0042] In step S50, the target pressure setting unit 94 sets, as the depressurization target pressure, a pressure that is less than the saturated water vapor pressure that corresponds to the temperature of the fuel cell stack 30 measured in step S40. The target pressure setting unit 94 preferably sets, as the depressurization target pressure, a value that is 25% or more and less than 80% of the saturated water vapor pressure that corresponds to the temperature of the fuel cell stack 30 measured in step S40. It is more preferable that the target pressure setting unit 94 sets, as the depressurization target pressure, a value that is 25% or more and less than 50% of the saturated water vapor pressure that corresponds to the temperature of the fuel cell stack 30 measured in step S40.

[0043] 4 is a phase diagram of water. For example, the saturated water vapor pressure when the temperature of the fuel cell stack 30 is 60°C is 20 kPa. If the temperature of the fuel cell stack 30 measured in step S40 is 60°C, the target pressure setting unit 94 sets the reduced pressure target pressure to, for example, 10 kPa, which is 50% of the saturated water vapor pressure when the temperature of the fuel cell stack 30 is 60°C.

[0044] In step S60 of FIG. 3, the operation control unit 93 operates the pressure reducing unit 78.

[0045] In step S70, the operation control unit 93 opens the cathode gas branch outlet valve 77. As a result, the pressure inside the cathode gas flow channel 28 is reduced by the pressure reducing unit 78.

[0046] In step S80, the operation control unit 93 determines whether the pressure measured by the pressure measurement unit 79 is equal to or less than the target pressure reduction. If the pressure is equal to or less than the target pressure reduction, step S90 is executed. If the pressure is not equal to or less than the target pressure reduction, step S80 is repeated.

[0047] In step S90, the operation control unit 93 closes the cathode gas branch outlet valve 77.

[0048] In step S100, the operation control unit 93 stops the operation of the pressure reducing unit 78. The operation stopping process is performed as described above.

[0049] According to the fuel cell system 100 of the first embodiment described above, when the operation control unit 93 stops the operation of the fuel cell stack 30, it controls the pressure reducing unit 78 to reduce the pressure in the cathode gas flow channel 28 until the pressure in the cathode gas flow channel 28 becomes less than the saturated water vapor pressure corresponding to the temperature of the fuel cell stack 30 measured by the temperature measuring unit 40. By reducing the pressure in the cathode gas flow channel 28, the water in the cathode gas flow channel 28 is vaporized and discharged to the outside of the fuel cell stack 30. In addition, the amount of water contained in the membrane electrode assembly 11 can be reduced. If the amount of water contained in the membrane electrode assembly 11 is reduced, the oxidation corrosion reaction of the catalyst-supporting carbon particles represented by the following chemical formula (1) is less likely to occur in the cathode catalyst layer 14 at the next startup of the fuel cell stack 30. C+2H2O → CO2+4H + +4e - ···(1) This reduces the amount of oxidation of the catalyst-supported carbon particles contained in the cathode catalyst layer 14. This therefore makes it possible to suppress deterioration of the catalyst in the cathode catalyst layer 14 and improve the durability of the fuel cell system 100. Hereinafter, the carbon particles supporting the catalyst will be referred to as catalyst-supported carbon.

[0050] Furthermore, in this embodiment, when the operation of the fuel cell stack 30 is stopped, the operation control unit 93 controls the pressure reducing unit 78 to reduce the pressure inside the cathode gas flow channel 28 until the pressure measured by the pressure measuring unit 79 reaches the target pressure reduction. Therefore, the pressure reduction operation of the cathode gas flow channel 28 can be controlled using the pressure inside the cathode gas flow channel 28 as an index.

[0051] FIG. 5 is a diagram showing the relationship between the pressure in the cathode gas flow channel 28, the membrane resistance, and the amount of oxidation of catalyst-supported carbon contained in the cathode catalyst layer 14 during startup of the fuel cell stack 30. FIG. 5 shows the membrane resistance and the amount of oxidation of catalyst-supported carbon when the temperature of the fuel cell stack 30 is 60°C. As described above, the saturated water vapor pressure when the temperature of the fuel cell stack 30 is 60°C is 20 kPa. As shown in FIG. 5, when the pressure in the cathode gas flow channel 28 is reduced to a pressure lower than the saturated water vapor pressure corresponding to the temperature of the fuel cell stack 30, the amount of water contained in the membrane electrode assembly 11 decreases, and therefore the membrane resistance increases. However, if the membrane electrode assembly 11 dries out and the membrane resistance increases too much, the performance of the fuel cell stack 30 decreases.

[0052] In this embodiment, the target pressure setting unit 94 sets the reduced pressure target pressure to a value that is 25% or more and less than 80% of the saturated water vapor pressure corresponding to the temperature of the fuel cell stack 30. This makes it possible to reduce the amount of moisture contained in the membrane electrode assembly 11 and to prevent the membrane electrode assembly 11 from becoming too dry.

[0053] B. Second embodiment: 6 is an explanatory diagram showing a schematic configuration of a fuel cell system 100b according to the second embodiment. The fuel cell system 100b further includes a stack case 110 and a stack case discharge flow path 111.

[0054] The stack case 110 accommodates the fuel cell stack 30. The stack case 110 is made of a material, such as metal, that allows the pressure inside to be reduced.

[0055] The stack case exhaust flow path 111 is a flow path that exhausts gas from inside the stack case 110. One end of the stack case exhaust flow path 111 is connected to the stack case 110. The other end of the stack case exhaust flow path 111 is connected to the cathode gas exhaust branch flow path 76 between the cathode gas branch outlet valve 77 and the pressure reducing unit 78. In other words, the pressure reducing unit 78 can reduce the pressure inside the stack case 110.

[0056] 7 is a process diagram of the operation shutdown process in the second embodiment. In the second embodiment, steps S30 to S70 are executed in the order of step S30, step S60, step S40, step S50, and step S70. In the second embodiment, when the pressure reducing unit 78 is operated in step S60, the pressure inside the stack case 110 is reduced.

[0057] According to the fuel cell system 100b of the second embodiment described above, when the operation control unit 93 stops the operation of the fuel cell stack 30, it controls the pressure reducing unit 78 to reduce the pressure inside the stack case 110. Therefore, by insulating the fuel cell stack 30, it is possible to keep the fuel cell stack 30 warm.

[0058] The following description will be given by taking as an example a case where the temperature of the fuel cell stack 30 is 60°C when step S60 is executed, and the target pressure setting unit 94 sets the pressure reduction target pressure to 50% of the saturated water vapor pressure corresponding to the temperature of the fuel cell stack 30 measured in step S40. In this embodiment, execution of step S60 keeps the fuel cell stack 30 warm. If the temperature of the fuel cell stack 30 does not drop from 60°C, the depressurization target pressure set in step S50 is 10 kPa. However, if the fuel cell system 100 does not include a stack case 110, the temperature of the fuel cell stack 30 will drop before the depressurization target pressure is calculated. For example, if the temperature of the fuel cell stack 30 drops to 40°C, the depressurization target pressure will be 4 kPa. Therefore, the power of the depressurization unit 78 is increased compared to when the fuel cell stack 30 is kept warm. In this embodiment, since the fuel cell stack 30 is kept warm, the power of the depressurization unit 78 can be reduced, and the depressurization unit 78 can be made smaller. Furthermore, the pressure inside the cathode gas flow path 28 can be efficiently reduced.

[0059] C. Third embodiment: 8 is an explanatory diagram showing a schematic configuration of a fuel cell system 100c according to the third embodiment. A control unit 90c of the fuel cell system 100c does not include a target pressure setting unit 94, but includes a drive time setting unit 95. The configuration of each unit of the fuel cell system 100c other than the control unit 90c is the same as that of the first embodiment.

[0060] The drive time setting unit 95 sets the drive time of the pressure reducing unit 78. The drive time setting unit 95 is realized by the CPU 91 reading out and executing a control program stored in the memory 92.

[0061] 9 and 10 are process diagrams of the operation shutdown process in the third embodiment. In Fig. 9 and 10, the same reference numerals as in Fig. 3 are used for steps in which the same processes as in Fig. 3 are executed, and the description thereof will be omitted.

[0062] In step S5, the membrane resistance measuring unit 50 measures the membrane resistance.

[0063] In step S55, the drive time setting unit 95 sets a planned drive time using the membrane resistance value measured in step S5. The planned drive time is the drive time of the pressure reducing unit 78 required to increase the membrane resistance value to a predetermined target resistance value. The target resistance value is a value greater than the membrane resistance value when the pressure in the cathode gas flow channel 28 is the saturated water vapor pressure corresponding to the temperature of the fuel cell stack 30. The target resistance value is preferably the membrane resistance value when the pressure in the cathode gas flow channel 28 is 25% or more and less than 80% of the saturated water vapor pressure corresponding to the temperature of the fuel cell stack 30.

[0064] FIG. 11 is a diagram illustrating the change in membrane resistance over time for the pressure reducing unit 78. In FIG. 11, the change in membrane resistance in a wet state is indicated by a solid line, and the change in membrane resistance in a dry state is indicated by a dashed line. The wet state is a state in which liquid water is present in the cathode gas flow path 28 when the anode gas flow path 27 and the cathode gas flow path 28 are sealed. The dry state is a state in which liquid water is not present in the cathode gas flow path 28 when the anode gas flow path 27 and the cathode gas flow path 28 are sealed. In other words, the wet state is a state in which the membrane resistance is equal to or less than a reference resistance value when the anode gas flow path 27 and the cathode gas flow path 28 are sealed, and the dry state is a state in which the membrane resistance exceeds the reference resistance value when the anode gas flow path 27 and the cathode gas flow path 28 are sealed. Here, the reference resistance value is the membrane resistance value in a state where liquid water is present in the cathode gas flow channel 28, i.e., a state where the water content of the electrolyte membrane 12 is at its maximum, and the water vapor pressure in the cathode gas flow channel 28 has reached the saturated water vapor pressure corresponding to the temperature of the fuel cell stack 30. Whether the state is wet or dry is determined using the membrane resistance value measured in step S5. Note that the saturated water vapor pressure depends on the temperature of the fuel cell stack 30, and therefore the relationship between the operation time of the pressure reducing unit 78 and the membrane resistance depends on the temperature of the fuel cell stack 30. For the sake of explanation, in FIG. 11, the pressure reduction start times in the dry state and the wet state are shown shifted from each other.

[0065] In the dry state, pressure reduction begins at time T1, and the membrane resistance reaches the target resistance value at time T2. The drive time setting unit 95 sets the time from time T1 to time T2 as the planned drive time for the dry state. In the wet state, pressure reduction begins at time T0, the pressure in the cathode gas flow path 28 falls below the saturated water vapor pressure at time T1, and the membrane resistance reaches the target resistance value at time T3. The drive time setting unit 95 sets the time from time T1 to time T3 as the planned drive time for the wet state. The relationship between the drive time of the pressure reduction unit 78 and the change in membrane resistance shown in Figure 11 is stored in advance in the memory 92.

[0066] 9, the operation control unit 93 determines whether the value of the membrane resistance measured by the membrane resistance measurement unit 50 is equal to or less than the reference resistance value. If the membrane resistance is equal to or less than the reference resistance value, step S82 is executed. If the membrane resistance is not equal to or less than the reference resistance value, step S83 is executed. That is, step S82 is executed in the case of a wet state, and step S83 is executed in the case of a dry state.

[0067] In step S82, the operation control unit 93 determines whether the pressure in the cathode gas flow channel 28 measured by the pressure measurement unit 79 is less than the saturated water vapor pressure corresponding to the temperature of the fuel cell stack 30 measured by the temperature measurement unit 40 in step S40. If the pressure is less than the saturated water vapor pressure, step S83 is executed. If the pressure is not less than the saturated water vapor pressure, step S82 is executed repeatedly. That is, in a wet state, the pressure in the cathode gas flow channel 28 is reduced until the pressure in the cathode gas flow channel 28 becomes less than the saturated water vapor pressure.

[0068] In step S83, the operation control unit 93 starts counting the driving time of the pressure reducing unit 78. In other words, the operation control unit 93 counts the elapsed time from the point in time when it is determined in step S82 that the pressure is less than the saturated water vapor pressure.

[0069] In step S84, the operation control unit 93 determines whether the scheduled drive time has elapsed since it was determined that the pressure was less than the saturated water vapor pressure. If the scheduled drive time has elapsed, step S90 is executed. If the scheduled drive time has not elapsed, step S84 is repeatedly executed.

[0070] According to the fuel cell system 100c of the third embodiment described above, the drive time setting unit 95 sets the expected drive time using the membrane resistance measured by the membrane resistance measuring unit 50, and when stopping the operation of the fuel cell stack 30, the operation control unit 93 controls the decompression unit 78 to decompress the cathode gas flow channel 28 from the point when the pressure measured by the pressure measuring unit 79 falls below the saturated water vapor pressure until the expected drive time has elapsed. Therefore, the decompression operation of the cathode gas flow channel 28 can be controlled using the drive time of the decompression unit 78 as an index.

[0071] D. Other Embodiments: (D-1) In the first and second embodiments, the fuel cell systems 100, 100b include a membrane resistance measuring unit 50. In contrast, the fuel cell systems 100, 100b do not necessarily need to include a membrane resistance measuring unit 50.

[0072] (D-2) In the first embodiment, the fuel cell system 100 includes a target pressure setting unit 94. However, the fuel cell system 100 does not necessarily need to include the target pressure setting unit 94. In this case, step S50 of the operation stop processing shown in FIG. 3 is not executed. Also, in step S80, the operation control unit 93 may determine whether the pressure measured by the pressure measurement unit 79 is less than the saturated water vapor pressure corresponding to the temperature of the fuel cell stack 30 measured by the temperature measurement unit 40, and execute step S90 if the pressure is less than the saturated water vapor pressure.

[0073] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0074] 10... fuel cell, 11... membrane electrode assembly, 12... electrolyte membrane, 13... anode catalyst layer, 14... cathode catalyst layer, 15... anode diffusion layer, 16... cathode diffusion layer, 17... anode separator, 18... cathode separator, 21... first end terminal, 22... second end terminal, 27... anode gas flow path, 28... cathode gas flow path, 30... fuel cell stack, 40... temperature measurement unit, 50... membrane resistance measurement unit, 60... anode gas supply / discharge system, 61... anode gas tank, 62... anode gas supply flow path, 63... anode gas inlet valve, 64... anode gas discharge flow path, 65... anode gas outlet valve Lube, 70... cathode gas supply and discharge system, 71... cathode gas supply flow path, 72... air pump, 73... cathode gas inlet valve, 74... cathode gas discharge flow path, 75... cathode gas outlet valve, 76... cathode gas discharge branch flow path, 77... cathode gas branch and outlet valve, 78... pressure reduction unit, 79... pressure measurement unit, 80... load, 81... voltage measurement unit, 82... current measurement unit, 90, 90c... control unit, 91... CPU, 92... memory, 93... operation control unit, 94... target pressure setting unit, 95... drive time setting unit, 100, 100b, 100c... fuel cell system, 110... stack case, 111... stack case discharge flow path

Claims

1. 1. A fuel cell system, comprising: a fuel cell stack that generates electricity through a chemical reaction between an anode gas and a cathode gas; a temperature measurement unit that measures the temperature of the fuel cell stack; a pressure reducing section; an operation control unit that controls the fuel cell stack and the pressure reducing unit, the fuel cell stack includes a cathode gas flow path through which the cathode gas flows, the pressure reducing unit is capable of reducing the pressure in the cathode gas flow channel, when stopping operation of the fuel cell stack, the operation control unit controls the pressure reduction unit to reduce the pressure in the cathode gas flow channel until the pressure in the cathode gas flow channel becomes less than the saturated water vapor pressure corresponding to the temperature of the fuel cell stack measured by the temperature measurement unit. Fuel cell system.

2. 2. The fuel cell system according to claim 1, a pressure measuring unit that measures the pressure in the cathode gas flow channel; a target pressure setting unit that sets a reduced pressure target pressure, which is the pressure in the cathode gas flow channel after being reduced by the pressure reducing unit, the target pressure setting unit sets a pressure less than the saturated water vapor pressure as the reduced pressure target pressure, when stopping operation of the fuel cell stack, the operation control unit controls the pressure reduction unit to reduce the pressure in the cathode gas flow channel until the pressure measured by the pressure measurement unit reaches the reduced pressure target pressure. Fuel cell system.

3. 3. The fuel cell system according to claim 2, the target pressure setting unit sets a value that is equal to or greater than 25% of the saturated water vapor pressure and less than 80% of the saturated water vapor pressure as the reduced pressure target pressure. Fuel cell system.

4. 2. The fuel cell system according to claim 1, a stack case that houses the fuel cell stack; the pressure reducing section is capable of reducing the pressure inside the stack case, the operation control unit controls the pressure reducing unit to reduce the pressure inside the stack case when stopping the operation of the fuel cell stack. Fuel cell system.

5. 2. The fuel cell system according to claim 1, a pressure measuring unit that measures the pressure in the cathode gas flow channel; a membrane resistance measuring unit for measuring a membrane resistance, which is the electrical resistance of a membrane electrode assembly provided in the fuel cell stack; a drive time setting unit that sets a drive time of the pressure reducing unit, the drive time setting unit sets a planned drive time, which is the drive time required to increase the value of the membrane resistance to a predetermined target resistance value, using the membrane resistance measured by the membrane resistance measuring unit; when stopping operation of the fuel cell stack, the operation control unit controls the pressure reducing unit to reduce the pressure in the cathode gas flow channel from the time when the pressure measured by the pressure measuring unit falls below the saturated water vapor pressure until the expected operation time has elapsed. Fuel cell system.

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