Air-cooled fuel cell system

Abstract

To remove an oxide film generated on a catalyst of an oxidant electrode while avoiding damage to a fuel cell caused by the high temperature of the fuel cell, in an air-cooling fuel cell system.SOLUTION: An electronic control unit alternately repeats an oxide film removal operation and a cell cooling operation when, after power generation of a fuel cell stack 12 is stopped, the fuel cell stack 12 is restarted. In the oxide film removal operation, the electronic control unit lowers the potential of an oxidant electrode 18 to a reduction potential Vr of an oxide film 182a or less by supplying fuel gas to a fuel electrode 20 while stopping the supply of cooling gas and allowing fuel battery cells 14 to generate electricity. On the other hand, in the cell cooling operation, the electronic control unit cools each of the fuel battery cells 14. Accordingly, the oxide film removal operation can be performed while the temperature rise of the fuel battery cells 14 is suppressed. Thus, the oxide film 182a generated on a catalyst of the oxidant electrode 18 can be removed while damage to a fuel cells 14 caused by high temperatures is avoided.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to an air-cooled fuel cell system in which a portion of a cooling gas for cooling a fuel cell is supplied to an oxidizer electrode of the fuel cell as an oxidizer gas. [Background technology]

[0002] Patent Document 1 describes a fuel cell system in which hydrogen is supplied to the anode of the fuel cell while the supply of air to the cathode is stopped, and the voltage of the fuel cell is adjusted to remove an oxide film formed on the cathode catalyst. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-185968 Summary of the Invention [Problem to be solved by the invention]

[0004] In an air-cooled fuel cell system, a portion of the cooling gas is supplied as an oxidant gas to the oxidant electrode (in other words, the cathode) of the fuel cell, so stopping the supply of the oxidant gas (e.g., air) also stops the cooling of the fuel cell by the cooling gas. Therefore, if the technology for removing the oxide film described in Patent Document 1 is applied directly to an air-cooled fuel cell system, the fuel cell may become too hot while the oxide film is being removed, which could damage the fuel cell, for example by accelerating its deterioration. The inventors have found the above as a result of detailed studies.

[0005] In view of the above, an object of the present invention is to remove an oxide film formed on a catalyst of an oxidizer electrode in an air-cooled fuel cell system while avoiding damage to the fuel cell due to high temperatures of the fuel cell. [Means for solving the problem]

[0006] In order to achieve the above object, the air-cooled fuel cell system according to claim 1 comprises: a fuel cell (14) including an electrolyte membrane (19), an oxidizer electrode (18) stacked on the electrolyte membrane and supplied with an oxidizer gas, and a fuel electrode (20) stacked on the side opposite the oxidizer electrode with respect to the electrolyte membrane and supplied with a fuel gas; a gas supply device (30) that supplies a cooling gas to the fuel cell for cooling the fuel cell; a control unit (40), A portion of the cooling gas is supplied to the oxidizer electrode as an oxidizer gas, The oxidizer electrode has a catalyst (182) on which an oxide film (182a) can be formed, When restarting the fuel cell after power generation by the fuel cell has stopped, the control unit alternately repeats a reduction process in which the supply of cooling gas from the gas supply device is stopped while fuel gas is supplied to the fuel electrode to cause the fuel cell to generate power, thereby lowering the potential of the oxidizer electrode to below the reduction potential (Vr) of the oxide film, and a cooling process in which the fuel cell is cooled after the reduction process is completed.

[0007] This makes it possible to extend the total time that the potential of the catalyst at the oxidizer electrode is equal to or less than the reduction potential of the oxide film while suppressing the temperature rise of the fuel cell, thereby avoiding damage to the fuel cell due to high temperatures and removing the oxide film that has formed on the catalyst at the oxidizer electrode, thereby achieving the effect of restoring the performance of the fuel cell.

[0008] In addition, in each section of the application documents, each element may be assigned a reference symbol in parentheses. In this case, the reference symbol merely indicates an example of the correspondence between the element and the specific configuration described in the embodiment described below. Therefore, the present invention is not limited in any way by the description of the reference symbol. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view showing a schematic configuration of a fuel cell system in a first embodiment. [Figure 2] 2 is a block diagram showing an input / output system of an electronic control device provided in the fuel cell system in the first embodiment. FIG. [Figure 3] FIG. 1 is an exploded perspective view showing a schematic configuration of a fuel cell unit that constitutes a fuel cell stack of a fuel cell system in a first embodiment. [Figure 4] FIG. 2 is a perspective view showing a schematic cross section of a part of a fuel cell in the first embodiment, with arrows indicating the flow of air blown by a blower. [Figure 5] FIG. 2 is a diagram showing a schematic view of a part of a catalyst layer that constitutes an oxidizer electrode of a fuel cell in the first embodiment. [Figure 6] FIG. 2 is a diagram showing a schematic diagram of a catalyst contained in a catalyst layer serving as an oxidizer electrode of a fuel cell in the first embodiment. [Figure 7] 4 is a flowchart showing a control process of an electronic control device provided in the fuel cell system of the first embodiment. [Figure 8] FIG. 5 is a perspective view corresponding to FIG. 4, in which arrows indicate the state in which air naturally diffuses to the oxidizer electrode while the blower is stopped, in the first embodiment. [Figure 9] FIG. 8 is a diagram showing an implementation count map used in the determination in step S04 of FIG. 7. [Figure 10] 8 is a time chart of the refresh operation performed in steps S02 to S06 in FIG. 7. [Figure 11] 8 is a flowchart showing the control process of an electronic control device of a fuel cell system of a comparative example, and corresponds to FIG. 7. [Figure 12] FIG. 8 is a diagram showing a first cell temperature map used for making the determination in step S03 of FIG. 7 in the second embodiment. [Figure 13] FIG. 8 is a diagram showing a second cell temperature map used for making the determination in step S06 of FIG. 7 in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, each embodiment will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

[0011] (First embodiment) In this embodiment, an example will be described in which the fuel cell system 10 of Fig. 1 is applied to an FCEV vehicle that obtains electric power to be supplied to a motor for driving the vehicle from a fuel cell stack 12. FCEV is an abbreviation for Fuel Cell Electric Vehicle.

[0012] 1 and 2, the fuel cell system 10 includes a fuel cell stack 12, a blower 30, a fuel gas supply pipe 32, a fuel gas discharge pipe 34, a fuel adjustment device 36, and an electronic control device 40. The fuel cell system 10 of this embodiment is an air-cooled fuel cell system in which the multiple fuel cell units 14 that make up the fuel cell stack 12 are air-cooled by the blower 30.

[0013] The fuel cell stack 12 generates electric power by utilizing an electrochemical reaction between hydrogen and oxygen, which are reactant gases. The fuel cell stack 12 supplies electric power to power conversion devices, such as an inverter or a DC-DC converter (not shown). The inverter converts the direct current supplied from the fuel cell stack 12 into alternating current and supplies it to a traction motor or the like to drive the traction motor or the like.

[0014] The DC-DC converter is also connected to an electrical storage device such as a secondary battery, etc. The fuel cell system 10 is configured so that surplus power output from the fuel cell stack 12 is stored in the electrical storage device via the DC-DC converter.

[0015] The fuel cell stack 12 is configured as a cell stack in which a plurality of fuel cell units 14, which are the minimum units, are stacked together. The fuel cell units 14 may also be simply referred to as fuel cells, and correspond to the fuel cell of the present disclosure.

[0016] Each fuel cell 14 has a thickness in the cell stacking direction Ds in which the fuel cells 14 are stacked, and is formed so as to extend in a planar shape in a direction perpendicular to the cell stacking direction Ds. For example, in the fuel cell stack 12, multiple stacked fuel cells 14 are electrically connected in series. Therefore, the current output from the fuel cell stack 12 is the same as the current output from the fuel cell 14.

[0017] Specifically, the fuel cell 14 of this embodiment is configured as a solid polymer electrolyte fuel cell (so-called PEFC). As shown in Figures 3 and 4, the fuel cell 14 has an oxidant electrode-side separator 15, an oxidant gas diffusion layer 16, a membrane electrode assembly 17, a fuel gas diffusion layer 21, and a fuel electrode-side separator 22. These are stacked from one side in the cell stacking direction Ds in the following order: oxidant electrode-side separator 15, oxidant gas diffusion layer 16, membrane electrode assembly 17, fuel gas diffusion layer 21, and fuel electrode-side separator 22.

[0018] The membrane electrode assembly 17 also has an oxidizer electrode 18, an electrolyte membrane 19, and a fuel electrode 20. These are stacked from one side in the cell stacking direction Ds in the order of oxidizer electrode 18, electrolyte membrane 19, and fuel electrode 20. The oxidizer electrode 18 is an electrode to which an oxidizer gas (specifically, air) is supplied, and the fuel electrode 20 is an electrode to which a fuel gas (specifically, hydrogen) is supplied. The electrolyte membrane 19 has good proton conductivity. The oxidizer electrode 18 is also called a cathode electrode, and the fuel electrode 20 is also called an anode electrode.

[0019] In the fuel cell 14 configured in this manner, when fuel gas is supplied to the anode 20 and oxidizer gas is supplied to the oxidizer electrode 18, electrochemical reactions shown in the following reaction formulas F1 and F2 occur, generating electrical energy. In short, the fuel cell 14 generates electricity. Note that when each of the multiple fuel cell cells 14 generates electricity, the fuel cell stack 12 made up of the multiple fuel cell cells 14 generates electricity. ·Fuel electrode 20 side: H2 → 2H + +2e - ···(F1) Oxidant electrode 18 side: 2H + +1 / 2O2+2e - →H2O (F2)

[0020] The configuration of the oxidizer electrode 18 will now be described in detail. As shown in FIG. 5, the oxidizer electrode 18 is composed of a catalyst layer 180 including a plurality of carbon particles 181 supporting a catalyst 182 such as platinum that promotes electrochemical reactions. The carbon particles 181 are porous and may be, for example, carbon black. As shown in FIG. 6, an oxide film 182a may form on the surface of the catalyst 182. For example, if the catalyst 182 is exposed to air for a certain period of time after the fuel cell 14 stops generating electricity, the oxide film 182a will form.

[0021] The configuration of the fuel electrode 20 is the same as that of the above-described oxidizer electrode 18. That is, the fuel electrode 20 is made up of a catalyst layer containing a plurality of carbon particles supporting a catalyst such as platinum.

[0022] 1 and 3, the fuel cell 14 has an inlet-side through-manifold 141 provided at one end of the fuel cell 14, and an outlet-side through-manifold 142 provided at the other end of the fuel cell 14. The inlet-side through-manifold 141 has an inlet-side through passage 141a formed therein, which extends in the cell stacking direction Ds so as to form a passage that penetrates through all of the fuel cell cells 14 in the fuel cell stack 12. The inlet-side through passage 141a is connected to a fuel gas supply pipe 32 that supplies fuel gas (specifically, hydrogen) from the outside.

[0023] An outlet-side through passage 142a is formed in the outlet-side through manifold 142, and this outlet-side through passage 142a extends in the cell stacking direction Ds so as to become a passage that penetrates through all of the fuel cell cells 14 of the fuel cell stack 12. The outlet-side through passage 142a is connected to a fuel gas discharge pipe 34 that discharges fuel gas remaining after power generation to the outside.

[0024] 3 and 4, the oxidizer electrode-side separator 15 is formed with a plurality of oxidizer gas channels 15a and a plurality of cooling channels 15b. These channels 15a, 15b extend, for example, along the direction of air blown by the blower 30, and are configured to facilitate the circulation of air blown from the blower 30. Arrows Ara in Fig. 4 represent the flow of air blown by the blower 30 into the oxidizer gas channels 15a, and arrows Arb represent the flow of air blown from the blower 30 into the cooling channels 15b.

[0025] The air supplied from the blower 30 is supplied to the fuel cell units 14 as a cooling gas for cooling each of the fuel cell units 14. A portion of the cooling gas from the blower 30 flows through each of the oxidizing gas passages 15a, and some or all of the remaining cooling gas flows through each of the cooling passages 15b.

[0026] The oxidant gas channels 15a are open to the oxidant gas diffusion layer 16, and the cooling gas (specifically, air) flowing through the oxidant gas channels 15a is supplied as an oxidant gas to the oxidant electrode 18 via the oxidant gas diffusion layer 16. On the other hand, the cooling channels 15b are separated from the oxidant gas diffusion layer 16, and the cooling gas flowing through the cooling channels 15b absorbs heat from the fuel cell cells 14 as it flows, and is then discharged to the outside of the fuel cell stack 12. In this way, the fuel cell stack 12 is configured to be supplied with oxidant gas while being air-cooled by the operation of the blower 30.

[0027] A plurality of fuel gas channels 22a are formed in the fuel electrode side separator 22. These fuel gas channels 22a are channels through which supplied fuel gas (specifically, hydrogen) flows, and extend in a direction perpendicular to the extension directions of the oxidant gas channels 15a and the cooling channels 15b.

[0028] One end of the fuel gas channel 22a is connected to the inlet-side through-passage 141a, and the other end of the fuel gas channel 22a is connected to the outlet-side through-passage 142a. Therefore, in the fuel gas channel 22a, the fuel gas flows from one end to the other end as shown by arrow Ah in Fig. 3. The fuel gas channel 22a is open to the fuel gas diffusion layer 21, and the fuel gas flowing through the fuel gas channel 22a is supplied to the anode 20 via the fuel gas diffusion layer 21.

[0029] As shown in FIG. 1, the blower 30 is a gas supply device that supplies cooling gas (specifically, air) to each of the fuel cell units 14 to cool the fuel cell units 14. For example, the blower 30 has a fan 301 and a fan motor that rotates the fan 301. The rotation of the fan 301 sends the cooling gas to the fuel cell units 14. The amount of air sent to the fuel cell stack 12 (i.e., the flow rate of the cooling gas) is increased or decreased in accordance with a control signal from the electronic control device 40. Note that the arrows Ar in FIGS. 1 and 3 indicate the flow of air sent by the blower 30.

[0030] The fuel gas supply pipe 32 is a pipe that supplies hydrogen to the fuel cell stack 12, and the fuel gas discharge pipe 34 is a pipe that discharges hydrogen off-gas (i.e., off-fuel) used in the fuel cell stack 12 to the outside of the fuel cell stack 12. A high-pressure hydrogen tank (not shown), which serves as a hydrogen supply source, is provided at the most upstream portion of the fuel gas supply pipe 32, and a fuel adjustment device 36 is provided midway along the fuel gas supply pipe 32. This fuel adjustment device 36 includes an on-off valve whose valve opening can be adjusted, and an electric actuator that increases or decreases the valve opening. The fuel adjustment device 36 operates in accordance with a control signal from the electronic control device 40, so that the electronic control device 40 can adjust the flow rate of hydrogen supplied to the fuel cell stack 12 using the fuel adjustment device 36.

[0031] The electronic control unit 40 shown in Fig. 2 is a control unit configured as an on-board microcomputer equipped with a CPU, RAM, ROM, non-volatile rewritable memory, etc. (not shown). That is, the electronic control unit 40 reads and executes a computer program stored in a ROM or non-volatile rewritable memory, which is a non-transitory tangible recording medium. Execution of this computer program results in the execution of a method corresponding to the computer program. That is, the electronic control unit 40 executes various control processes, such as the control process shown in Fig. 7 (described later), in accordance with the computer program.

[0032] Based on a computer program stored in a ROM or the like, the electronic control device 40 operates controlled devices connected to the output side of the electronic control device 40 to control the operation of the fuel cell stack 12. Specifically, controlled devices such as the blower 30 and fuel adjustment device 36 described above are connected to the output side of the electronic control device 40.

[0033] In the fuel cell system 10, for example, during normal operation of the fuel cell stack 12, the electronic control device 40 controls the operation of the controlled devices connected to the output side so that the fuel cell stack 12 outputs power according to the power required by load devices such as a traction motor. Specifically, a target current to be swept from the fuel cell stack 12 is set according to the load on the fuel cell stack 12, and the operation of the controlled devices is controlled so that the current swept from the fuel cell stack 12 is maintained at the target current.

[0034] A voltage detection device 41, a current detection device 42, a temperature detection device 43, and the like are connected to the input side of the electronic control device 40. The voltage detection device 41 is a voltage sensor that detects the operating voltage, which is the voltage output by the fuel cell stack 12. The voltage detection device 41 is provided between both terminals of the fuel cell stack 12. The current detection device 42 is a current sensor that detects the current extracted (i.e., swept) from the fuel cell stack 12.

[0035] The temperature detection device 43 is a temperature sensor that detects the temperature of the fuel cell stack 12. This temperature of the fuel cell stack 12 is a representative temperature of the temperatures Tc (i.e., cell temperatures Tc) of the individual fuel cell units 14 that make up the fuel cell stack 12. In this embodiment, unless otherwise specified, the cell temperatures Tc are treated as being equal to the temperature of the fuel cell stack 12 detected by the temperature detection device 43.

[0036] The signals output from each sensor, such as the voltage detector 41, the current detector 42, and the temperature detector 43, are input to the electronic control device 40. In other words, the electronic control device 40 obtains the operating voltage of the fuel cell stack 12 from the voltage detector 41, the current flowing from the fuel cell stack 12 from the current detector 42, and the cell temperature Tc from the temperature detector 43.

[0037] Next, a description will be given of the control process shown in Fig. 7, which is one of the various control processes executed by the electronic control device 40. The electronic control device 40 executes the control process shown in Fig. 7 when restarting the fuel cell stack 12 after power generation by the fuel cell stack 12 has stopped.

[0038] Note that "after power generation by the fuel cell stack 12 has stopped" specifically means after power generation by normal operation of the fuel cell stack 12 has stopped. That is, although power generation is also performed during the oxide film removal operation described below, "after power generation by the fuel cell stack 12 has stopped" does not mean after power generation by the oxide film removal operation has stopped. This is because, after the oxide film removal operation, for example, normal operation of the fuel cell stack 12 or a cell cooling operation described below is performed, and the fuel cell stack 12 is not restarted.

[0039] Furthermore, normal operation of the fuel cell stack 12 refers to operation in which the electronic control device 40 controls the operation of controlled devices so that the fuel cell stack 12 outputs power according to the power demanded of the fuel cell stack 12. For example, during normal operation, the operation of the blower 30, the amount of fuel gas supplied, the current output from the fuel cell stack 12, and the like are controlled in accordance with predetermined normal operating conditions.

[0040] 7, first, in step S01, the electronic control device 40 controls the fuel adjustment device 36 to start supplying hydrogen, which is fuel gas, to the fuel cell stack 12. At this time, hydrogen is supplied at a sufficient flow rate so that there is no shortage of hydrogen for power generation in the fuel cell stack 12. After step S01, the process proceeds to step S02.

[0041] In step S02, the electronic control device 40 performs an oxide film removal operation to remove the oxide film 182a from the surface of the catalyst 182 of the oxidizer electrode 18. In other words, this oxide film removal operation is a reduction process to reduce the oxide film 182a. Specifically, in the oxide film removal operation, the electronic control device 40 stops the supply of cooling gas by the blower 30 while supplying fuel gas to the fuel electrode 20 and causes the fuel cell stack 12 to generate power. As a result, in the oxide film removal operation, the electronic control device 40 puts the oxidizer electrode 18 in an oxygen-deficient (in other words, nitrogen-rich) state and reduces the potential of the oxidizer electrode 18 to or below the reduction potential Vr of the oxide film 182a.

[0042] The reason for this is that if the potential of the oxidizer electrode 18 falls below the reduction potential Vr of the oxide film 182a, the reduction of the oxide film 182a progresses, and the oxide film 182a is removed from the catalyst 182 of the oxidizer electrode 18. That is, in the oxide film removal operation, the electronic control device 40 removes the oxide film 182a from the catalyst 182 by lowering the potential of the oxidizer electrode 18 below the reduction potential Vr of the oxide film 182a.

[0043] When there is sufficient hydrogen at the fuel electrode 20, the potential of the oxidizer electrode 18 becomes a cell voltage Vc, which is the potential difference between the oxidizer electrode 18 and the fuel electrode 20 in the fuel cell 14. The reduction potential Vr of the oxide film 182a is the maximum potential of the oxidizer electrode 18 at which reduction of the oxide film 182a occurs.

[0044] During the oxide film removal operation, the electronic control device 40 does not gradually increase the current output from the fuel cell stack 12, but rather causes the fuel cell stack 12 to generate electricity so that the current output from the fuel cell stack 12 immediately reaches a predetermined current target value. For example, the current target value is determined in advance so that the oxygen consumption rate is greater than the oxygen diffusion rate during power generation during the oxide film removal operation.

[0045] The oxygen consumption rate is the amount of oxygen consumed per unit time by the power generation of the fuel cell 14, and the oxygen diffusion rate is the amount of oxygen per unit time diffusing from the outside of the oxidizer electrode 18 of the fuel cell 14 to the oxidizer electrode 18. Just to be clear, during the oxide film removal operation, the amount of cooling gas supplied by the blower 30 becomes zero, but the oxygen diffusion rate does not become zero because air naturally diffuses from the atmosphere around the fuel cell stack 12 to the oxidizer electrode 18 as shown by arrow Ax in Figure 8.

[0046] For example, the target current value can be determined by previously conducting a test operation of the fuel cell stack 12. Specifically, during the test operation, the blower 30 is stopped and the fuel gas supply rate is the same as in the oxide film removal operation. Under these test operation conditions, the fuel cell stack 12 is caused to generate power by outputting a constant current of a certain magnitude. If the operating voltage (i.e., the terminal voltage) of the fuel cell stack 12 decreases over time, it can be determined that the oxygen consumption rate is greater than the oxygen diffusion rate during power generation. In other words, the current of this certain magnitude can be set as the target current value for the oxide film removal operation.

[0047] During the oxide film removal operation, the flow rate of the fuel gas supplied to the fuel cell stack 12 does not need to be constant. However, in this embodiment, for example, a preset constant flow rate of fuel gas is supplied to the fuel cell stack 12 so as to promote the reduction of the oxide film 182a. During the oxide film removal operation, the fuel cell stack 12 generates power in an oxygen-deficient state, and as the power generation proceeds, each fuel cell 14 generates heat, causing the cell temperature Tc to rise over time. Note that if the oxide film removal operation has already started in step S02, the oxide film removal operation continues. After step S02, the process proceeds to step S03.

[0048] In step S03, the cell temperature Tc is detected. In this embodiment, the cell temperature Tc is detected by the temperature detection device 43.

[0049] Then, in step S03, the electronic control device 40 determines whether the detected cell temperature Tc is less than a predetermined first temperature determination value T1. The first temperature determination value T1 is experimentally set in advance so as to allow the oxide film removal operation to continue for a long time while avoiding damage to the fuel cell 14 due to high temperatures.

[0050] In step S03, if it is determined that the cell temperature Tc is less than the first temperature determination value T1, the process proceeds to step S04. On the other hand, if it is determined that the cell temperature Tc is equal to or greater than the first temperature determination value T1, the process proceeds to step S05.

[0051] In step S04, the electronic control unit 40 determines whether or not the oxide film 182a has been removed from the catalyst 182 of the oxidizer electrode 18 to a predetermined extent or more.

[0052] Here, the longer the power generation stop elapsed time PD, which is the time elapsed from when the fuel cell stack 12 stops generating power until the fuel cell stack 12 is restarted, the longer the time the oxidizer electrode 18 is exposed to a high potential, resulting in the formation of a larger oxide film 182a on the catalyst 182. The point at which the fuel cell stack 12 is restarted is, for example, the point at which the control process shown in FIG. 7 is started. In the control process shown in FIG. 7, the oxide film removal operation is intermittently performed multiple times. For these reasons, in this embodiment, the number of times the oxide film removal operation is performed required to remove a predetermined amount of the oxide film 182a or more from the catalyst 182 of the oxidizer electrode 18 is experimentally determined in advance. The relationship between the required number of times the oxide film removal operation is performed and the power generation stop elapsed time PD is preset as an execution count map MPn shown in FIG. 9. Specifically, the execution count map MPn is set so that the execution count judgment value Nx, which is the number of times the oxide film removal operation is performed and obtained from the execution count map MPn, increases as the power generation stop elapsed time PD increases.

[0053] Since the execution count map MPn in Figure 9 is set in this way, the electronic control unit 40 knows the power generation stop elapsed time PD in advance. Then, in step S04 in Figure 7, the electronic control unit 40 determines the execution count judgment value Nx based on the power generation stop elapsed time PD using the execution count map MPn in Figure 9. For example, as shown in Figure 9, when the power generation stop elapsed time PD is PD1, the execution count judgment value Nx becomes Nx1.

[0054] After determining the execution count judgment value Nx from the execution count map MPn in Fig. 9, the electronic control device 40 determines whether the actual execution count of the oxide film removal operation started in step S02 in Fig. 7 is equal to or greater than the execution count judgment value Nx. If the result of the determination is that the actual execution count of the oxide film removal operation is equal to or greater than the execution count judgment value Nx, the electronic control device 40 determines that a predetermined amount of the oxide film 182a or more has been removed from the catalyst 182 of the oxidizer electrode 18.

[0055] 9 is set so that the oxide film removal operation started in step S02 and the cell cooling operation started in step S05 (described later) are alternately repeated at least once. In other words, the execution count map MPn is set so that the oxide film removal operation and the cell cooling operation are each performed at least once, and therefore the execution count determination value Nx obtained from the execution count map MPn is 2 or more.

[0056] If it is determined in step S04 that the oxide film 182a equal to or greater than the predetermined amount has been removed from the catalyst 182 of the oxidizer electrode 18, i.e., if the number of times the oxide film removal operation has actually been performed is equal to or greater than the execution count judgment value Nx, the process proceeds to step S07. On the other hand, if it is determined that the oxide film 182a equal to or greater than the predetermined amount has not been removed from the catalyst 182 of the oxidizer electrode 18, i.e., if the number of times the oxide film removal operation has actually been performed is less than the execution count judgment value Nx, the process proceeds to step S02. If the loop of steps S02, S03, and S04 continues in the control process of FIG. 7, the oxide film removal operation continues to be performed.

[0057] 7 proceeds from step S04 to step S07, the oxide film removal operation ends, and the alternating execution of the oxide film removal operation and the cell cooling operation described below also ends. Therefore, the electronic control device 40 determines the execution count judgment value Nx from the execution count map MPn in Figure 9, and thereby increases the number of times the oxide film removal operation is executed as the elapsed time PD of the fuel cell stack 12 that has stopped power generation is longer.

[0058] In step S05, the electronic control device 40 performs a cell cooling operation to cool each fuel cell 14. At this time, if an oxide film removal operation is being performed, the electronic control device 40 starts the cell cooling operation after finishing the oxide film removal operation. If the cell cooling operation has already been started, the cell cooling operation continues.

[0059] In other words, the cell cooling operation performed in step S05 is a cooling process for cooling the fuel cell units 14. Specifically, in the cell cooling operation, the electronic control device 40 operates the blower 30 and supplies air as a cooling gas from the blower 30 to each fuel cell unit 14, thereby cooling each fuel cell unit 14. In short, in the cell cooling operation of this embodiment, each fuel cell unit 14 is forcibly air-cooled by air blown from the blower 30. For example, in the cell cooling operation, it is preferable that each fuel cell unit 14 be cooled in as short a time as possible, so the blower 30 is operated to blow the maximum amount of air.

[0060] In the cell cooling operation, the purpose is to cool the fuel cell 14, so in this embodiment, power generation in each fuel cell 14 is temporarily stopped. That is, the electronic control device 40 sets the current output from the fuel cell 14 to zero. The current output from the fuel cell 14 is adjusted, for example, by the electronic control device 40 controlling a load device electrically connected to the load side of the fuel cell stack 12.

[0061] Furthermore, during the cell cooling operation, fuel gas may be supplied to the fuel cell stack 12, but in this embodiment, the supply of fuel gas to the fuel cell stack 12 is stopped during the cell cooling operation. After step S05, the process proceeds to step S06.

[0062] In step S06, the cell temperature Tc is detected. In this embodiment, the cell temperature Tc is detected by the temperature detection device 43.

[0063] In step S06, the electronic control device 40 determines whether the detected cell temperature Tc is equal to or lower than a predetermined second temperature determination value T2. The second temperature determination value T2 is experimentally set in advance so as to shorten the duration of the cell cooling operation while allowing the oxide film removal operation, which is started after the cell cooling operation is completed, to continue for a long time. The second temperature determination value T2 is set to a temperature lower than the first temperature determination value T1.

[0064] In step S06, if it is determined that the cell temperature Tc is equal to or lower than the second temperature determination value T2, the process proceeds to step S02. On the other hand, if it is determined that the cell temperature Tc is higher than the second temperature determination value T2, the process proceeds to step S05.

[0065] The cell cooling operation continues when the loop of steps S05 and S06 continues in the control process of Fig. 7. On the other hand, when the control process of Fig. 7 proceeds from step S06 to step S02, the cell cooling operation ends and the oxide film removal operation starts in step S02.

[0066] In step S07, the electronic control device 40 starts the blower 30 to perform normal operation of the fuel cell stack 12. By starting the blower 30, air is supplied as a cooling gas from the blower 30 to the oxidant gas passage 15a and the cooling passage 15b (see FIG. 4) of each fuel cell 14. For example, the blower 30 started in step S07 continues to operate until it is stopped in step S10, which will be described later. After step S07, the process proceeds to step S08.

[0067] In step S08, the electronic control device 40 performs normal operation of the fuel cell stack 12, causing the fuel cell stack 12 to generate power. This normal operation of the fuel cell stack 12 continues, for example, until the electronic control device 40 receives a stop command to stop power generation by the fuel cell stack 12. When the electronic control device 40 receives the stop command, the control process in FIG. 7 proceeds from step S08 to step S09.

[0068] In step S09, the electronic control device 40 stops power generation by the fuel cell stack 12. Stopping power generation by the fuel cell stack 12 specifically means that the electronic control device 40 controls the load devices electrically connected to the load side of the fuel cell stack 12 to reduce the current output from the fuel cell stack 12 to zero. After step S09, the process proceeds to step S10.

[0069] In step S10, the electronic control device 40 stops the blower 30. After step S10, the process proceeds to step S11.

[0070] In step S11, the electronic control device 40 controls the fuel regulator 36 to stop the supply of fuel gas to the fuel cell stack 12. This ends the normal operation of the fuel cell stack 12 that began in step S07.

[0071] The processing in each step of FIG. 7 described above implements the respective functions and constitutes the functional units provided in the electronic control unit 40.

[0072] 7 are steps for performing a refresh operation in which an oxide film removal operation and a cell cooling operation are alternately performed before the start of normal operation of the fuel cell stack 12. During this refresh operation, for example, the cell voltage Vc, the battery output current Ibt, which is the current output from the fuel cell stack 12, and the cell temperature Tc each change as shown in FIG.

[0073] Specifically, at time ta1 in the time chart of Figure 10, the control process of Figure 7 shifts from step S06 to step S02, and the oxide film removal operation is started at time ta1. The oxide film removal operation is then continuously performed from time ta1 to time ta2 in Figure 10. Therefore, from time ta1, the battery output current Ibt is controlled to a predetermined current target value greater than zero. As this battery output current Ibt increases, the cell voltage Vc drops to or below the reduction potential Vr of the oxide film 182a. Furthermore, from time ta1, the fuel cell 14 generates heat as it generates electricity, and the cell temperature Tc rises from time ta1 to time ta2.

[0074] At time ta2 in Fig. 10, it is determined in step S03 in Fig. 7 that the cell temperature Tc is equal to or higher than the first temperature determination value T1. As a result, the oxide film removal operation ends at time ta2 in Fig. 10, and the cell cooling operation starts. The cell cooling operation is then carried out continuously from time ta2 to time ta3.

[0075] During this cell cooling operation, power generation by the fuel cell 14 is stopped, so the cell output current Ibt drops sharply from time ta2 and remains zero until time ta3. At this time, hydrogen is not supplied to the anode 20, but the hydrogen that was supplied up to time ta2 remains in the anode 20, so the cell voltage Vc during the cell cooling operation is higher than the cell voltage Vc during the oxide film removal operation. Furthermore, during the cell cooling operation, each fuel cell 14 is air-cooled by the blower 30, so the cell temperature Tc gradually decreases toward time ta3 and becomes equal to or less than the second temperature judgment value T2 at time ta3. In other words, the cell cooling operation lowers the cell temperature Tc from the start of the cell cooling operation to equal to or less than the second temperature judgment value T2.

[0076] At time ta3 in Figure 10, it is determined in step S06 in Figure 7 that the cell temperature Tc is equal to or lower than the second temperature determination value T2. As a result, at time ta3 in Figure 10, the cell cooling operation ends, and the oxide film removal operation starts. The oxide film removal operation has been performed continuously since time ta3. The changes in the cell voltage Vc, battery output current Ibt, and cell temperature Tc during the oxide film removal operation from time ta3 onwards are the same as those during the oxide film removal operation performed from time ta1 to time ta2.

[0077] In this embodiment, as described above, a refresh operation is performed before the start of normal operation of the fuel cell stack 12. For comparison with this embodiment, FIG. 11 shows a flowchart of a comparative example in which normal operation of the fuel cell stack 12 is started without performing the refresh operation. The content of each of steps S01, S07, S08, S09, S10, and S11 shown in FIG. 11 is the same as the content of the steps with the same numbers shown in FIG. 7. As can be seen from a comparison between FIG. 7 and FIG. 11, in the operation of the fuel cell stack 12 in this embodiment, the processing of steps S02 to S06 is added to that of the comparative example.

[0078] 7 and 10, when restarting the fuel cell stack 12 after power generation by the fuel cell stack 12 has stopped, the electronic control device 40 alternately repeats an oxide film removal operation and a cell cooling operation. In the oxide film removal operation, the electronic control device 40 stops the supply of cooling gas while supplying fuel gas to the anode 20 to cause the fuel cells 14 to generate power, thereby lowering the potential of the oxidizer electrode 18 to below the reduction potential Vr of the oxide film 182a. On the other hand, in the cell cooling operation, the electronic control device 40 cools each of the fuel cell cells 14.

[0079] Therefore, it is possible to extend the total time during which the catalyst 182 of the oxidizer electrode 18 is at a potential equal to or lower than the reduction potential Vr of the oxide film 182a while suppressing a rise in temperature of the fuel cell 14. As a result, it is possible to remove the oxide film 182a formed on the catalyst 182 of the oxidizer electrode 18 while avoiding damage to the fuel cell 14 due to an increase in temperature of the fuel cell 14, and it is possible to achieve the effect of restoring the performance of the fuel cell 14 by removing the oxide film 182a.

[0080] (1) Furthermore, according to this embodiment, as shown in Fig. 9, the longer the elapsed time PD from when power generation by the fuel cell stack 12 stops until the fuel cell stack 12 is restarted, the more frequently the electronic control device 40 performs the oxide film removal operation. This makes it possible to perform the refresh operation, which alternates between the oxide film removal operation and the cell cooling operation, for an appropriate required time that is neither too long nor too short.

[0081] (2) Furthermore, according to this embodiment, as shown in Figures 7 and 10, if the cell temperature Tc becomes equal to or higher than a predetermined first temperature judgment value T1 during the oxide film removal operation, the electronic control device 40 ends the oxide film removal operation and starts the cell cooling operation. If the cell temperature Tc becomes equal to or lower than a predetermined second temperature judgment value T2 during the cell cooling operation, the electronic control device 40 ends the cell cooling operation and starts the oxide film removal operation. Therefore, the oxide film removal operation can be repeatedly performed while avoiding damage to the fuel cell 14 due to high temperatures.

[0082] (3) Furthermore, according to this embodiment, the electronic control device 40 obtains the cell temperature Tc from the temperature detection device 43 that detects the temperature of the fuel cell stack 12. Therefore, it is possible to alternate between the oxide film removal operation and the cell cooling operation at an appropriate timing according to changes in the cell temperature Tc.

[0083] (4) Furthermore, according to this embodiment, during cell cooling operation, the electronic control device 40 activates the blower 30 to supply air as a cooling gas to each fuel cell 14, thereby cooling each fuel cell 14. This reduces the time required for the cell cooling operation compared to, for example, stopping the blower 30 and cooling the fuel cell 14 by natural heat dissipation. As a result, it is possible to reduce the time required for the refresh operation, which alternates between the oxide film removal operation and the cell cooling operation.

[0084] (5) Furthermore, according to this embodiment, during the oxide film removal operation, the electronic control device 40 causes each fuel cell 14 to generate power so that the current output from the fuel cell 14 reaches a predetermined current target value.

[0085] Therefore, compared to, for example, a case where the current output from the fuel cell 14 is gradually increased from the start of the oxide film removal operation, the potential of the oxidizer electrode 18 can be reduced to or below the reduction potential Vr of the oxide film 182a earlier. This lengthens the time during which the potential of the oxidizer electrode 18 remains below the reduction potential Vr of the oxide film 182a during the oxide film removal operation, thereby facilitating the removal of the oxide film 182a.

[0086] (6) Furthermore, according to this embodiment, the current target value is determined in advance so that the amount of oxygen consumed per unit time by power generation in the fuel cell 14 during the oxide film removal operation is greater than the amount of oxygen per unit time diffusing from the outside of the oxidizer electrode 18 to the oxidizer electrode 18. Therefore, once the current output from the fuel cell 14 reaches the current target value, removal of the oxide film 182a can immediately proceed.

[0087] (Second embodiment) Next, a second embodiment will be described. In this embodiment, differences from the first embodiment will be mainly described. Furthermore, parts that are the same as or equivalent to the first embodiment will be omitted or simplified.

[0088] In this embodiment, the determination method in step S03 in the control process of FIG. 7 is different from that in the first embodiment, and the determination method in step S06 is also different from that in the first embodiment.

[0089] Specifically, in order to make the determination in step S03 in Fig. 7, a first relationship is experimentally determined, which is the relationship between the elapsed time during the oxide film removal operation and the cell temperature Tc that increases as the oxide film removal operation is performed, as shown in Fig. 12. Then, this first relationship is stored and set in advance in the electronic control device 40 as a first cell temperature map MP1.

[0090] Furthermore, in order to make the determination in step S06 in Fig. 7, a second relationship, which is the relationship between the elapsed time during which the cell cooling operation is being performed and the cell temperature Tc that decreases as the cell cooling operation is being performed, is experimentally obtained as shown in Fig. 13. Then, this second relationship is stored and set in advance in the electronic control device 40 as a second cell temperature map MP2.

[0091] The control process of FIG. 7 of this embodiment is executed after these first and second cell temperature maps MP1, MP2 are set in advance.

[0092] In step S02 of FIG. 7, the electronic control device 40 obtains from the temperature detection device 43 the temperature Tcr at the start of the removal operation, which is the cell temperature Tc at the start of the oxide film removal operation.

[0093] Then, in step S03, the electronic control device 40 estimates a first arrival time TM1, which is the time required for the cell temperature Tc to reach the first temperature judgment value T1 from the start of the oxide film removal operation, based on the removal operation start temperature Tcr from the first cell temperature map MP1 of Fig. 12. In detail, the first arrival time TM1 is determined to be the time difference between the time TM1a corresponding to the removal operation start temperature Tcr and the time TM1b corresponding to the first temperature judgment value T1 in the first cell temperature map MP1.

[0094] In step S03, after estimating the first arrival time TM1, the electronic control device 40 determines whether the elapsed time from the start of the oxide film removal operation (in other words, the execution time from the start of the oxide film removal operation) is shorter than the first arrival time TM1.

[0095] If the result of this determination is that the time elapsed since the start of the oxide film removal operation is shorter than the first arrival time TM1, the electronic control device 40 estimates that the cell temperature Tc has not yet reached the first temperature determination value T1. Conversely, if the time elapsed since the start of the oxide film removal operation is equal to or greater than the first arrival time TM1, the electronic control device 40 estimates that the cell temperature Tc is equal to or greater than the first temperature determination value T1.

[0096] That is, if the elapsed time from the start of the oxide film removal operation is shorter than the first arrival time TM1, it is determined that the cell temperature Tc is less than the first temperature judgment value T1, and the process proceeds from step S03 to step S04. On the other hand, if the elapsed time from the start of the oxide film removal operation is equal to or greater than the first arrival time TM1, it is determined that the cell temperature Tc is equal to or greater than the first temperature judgment value T1, and the process proceeds from step S03 to step S05. When proceeding to step S05, the oxide film removal operation is terminated, and the cell cooling operation is started instead. In this way, the electronic control device 40 of this embodiment determines the timing to terminate the oxide film removal operation and start the cell cooling operation based on the preset first cell temperature map MP1 of FIG. 12.

[0097] 7. Furthermore, the electronic control device 40 obtains from the temperature detection device 43 the cooling operation start temperature Tcc, which is the cell temperature Tc at the start of the cell cooling operation, in step S05 of FIG.

[0098] Then, in step S06, the electronic control device 40 estimates a second arrival time TM2, which is the time required for the cell temperature Tc to reach the second temperature judgment value T2 from the start of the cell cooling operation, based on the cooling operation start temperature Tcc from the second cell temperature map MP2 of Figure 13. In detail, the time difference between the time TM2a corresponding to the cooling operation start temperature Tcc and the time TM2b corresponding to the second temperature judgment value T2 in the second cell temperature map MP2 is set to be the second arrival time TM2.

[0099] In step S06, when the electronic control device 40 estimates the second reaching time TM2, it determines whether the elapsed time from the start of the cell cooling operation (in other words, the execution time from the start of the cell cooling operation) is equal to or longer than the second reaching time TM2.

[0100] If the result of this determination is that the elapsed time from the start of the cell cooling operation is equal to or greater than the second arrival time TM2, the electronic control device 40 estimates that the cell temperature Tc is equal to or less than the second temperature determination value T2. Conversely, if the elapsed time from the start of the cell cooling operation is shorter than the second arrival time TM2, the electronic control device 40 estimates that the cell temperature Tc is still higher than the second temperature determination value T2.

[0101] That is, if the elapsed time since the start of the cell cooling operation is equal to or greater than the second arrival time TM2, it is determined that the cell temperature Tc is equal to or less than the second temperature judgment value T2, and the process proceeds from step S06 to step S02. When proceeding to step S02, the cell cooling operation is terminated, and the oxide film removal operation is started instead. On the other hand, if the elapsed time since the start of the cell cooling operation is shorter than the second arrival time TM2, it is determined that the cell temperature Tc is higher than the second temperature judgment value T2, and the process proceeds from step S06 to step S05, and the cell cooling operation continues. In this way, the electronic control device 40 of this embodiment determines the timing to terminate the cell cooling operation and start the oxide film removal operation based on the preset second cell temperature map MP2 of FIG. 13.

[0102] (1) As described above, according to this embodiment, the electronic control device 40 determines the timing to end the oxide film removal operation and start the cell cooling operation using the preset first cell temperature map MP1 in Figure 12. Then, the electronic control device 40 determines the timing to end the cell cooling operation and start the oxide film removal operation using the preset second cell temperature map MP2 in Figure 13. Therefore, it is possible to easily determine the timing to alternate between the oxide film removal operation and the cell cooling operation.

[0103] Except for the points described above, this embodiment is the same as the first embodiment. In this embodiment, the same effects as those of the first embodiment can be obtained from the configuration common to the first embodiment.

[0104] (Other embodiments) (1) In the above-described embodiments, the fuel cell 14 shown in FIG. 1 is configured as a solid polymer electrolyte cell, but it may be a cell other than a solid polymer electrolyte cell.

[0105] (2) In each of the above-described embodiments, in step S04 of Fig. 7, whether or not a predetermined amount of the oxide film 182a or more has been removed from the catalyst 182 of the oxidizer electrode 18 is determined using the execution count map MPn of Fig. 9, but this is just one example. For example, the determination may be made by operating the fuel cell stack 12 under predetermined operating conditions in which the current output from the fuel cell stack 12 is constant, without using the execution count map MPn.

[0106] In this case, if the cell voltage Vc of each fuel cell 14 operated under the predetermined operating conditions is equal to or greater than a predetermined voltage threshold, it is determined that a predetermined amount of the oxide film 182a or more has been removed from the catalyst 182 of the oxidizer electrode 18. For example, the voltage threshold is preferably determined according to the cell temperature Tc.

[0107] (3) In each of the above-described embodiments, in the cell cooling operation performed as the cooling process in step S05 of Fig. 7, each fuel cell 14 is forcibly air-cooled by air blown from the blower 30, but this is just one example. In the cooling process, each fuel cell 14 may be cooled by natural heat dissipation from the fuel cell 14 without operating the blower 30.

[0108] For example, as a modified example of the second embodiment, consider a case where the blower 30 is not operated during the cooling process and each fuel cell 14 is cooled by natural heat dissipation. In this case, in order to estimate the second arrival time TM2, the natural heat dissipation map MPr of Figure 13 is used in place of the second cell temperature map MP2. This natural heat dissipation map MPr corresponds to the second relationship of the present disclosure, and in the natural heat dissipation map MPr, the cell temperature Tc decreases more gradually over time than in the second cell temperature map MP2.

[0109] (4) In each of the above-described embodiments, the processing of each step shown in the flowchart of FIG. 7 is implemented by a computer program, but it may also be implemented by hardware.

[0110] (5) The present invention is not limited to the above-described embodiments and can be practiced in various modified forms. Furthermore, in each of the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential unless they are specifically stated as essential or are considered to be clearly essential in principle.

[0111] Furthermore, in each of the above embodiments, when numerical values ​​such as the number, values, amounts, and ranges of components of the embodiments are mentioned, they are not limited to the specific numbers, except when it is particularly clearly stated that they are essential or when they are clearly limited to a specific number in principle, etc. Furthermore, in each of the above embodiments, when the material, shape, positional relationship, etc. of components are mentioned, they are not limited to the material, shape, positional relationship, etc., except when it is particularly clearly stated or when they are clearly limited to a specific material, shape, positional relationship, etc. in principle, etc.

[0112] (Features of the present invention) [Claim 1] 1. An air-cooled fuel cell system, comprising: a fuel cell (14) including an electrolyte membrane (19), an oxidizer electrode (18) stacked on the electrolyte membrane and supplied with an oxidizer gas, and a fuel electrode (20) stacked on the side of the electrolyte membrane opposite to the oxidizer electrode and supplied with a fuel gas; a gas supply device (30) that supplies a cooling gas for cooling the fuel cell to the fuel cell; a control unit (40), a portion of the cooling gas is supplied to the oxidizer electrode as the oxidizer gas; The oxidizer electrode has a catalyst (182) on which an oxide film (182a) can be formed, an air-cooled fuel cell system in which, when restarting the fuel cell after power generation by the fuel cell has stopped, the control unit alternately repeats a reduction process in which the supply of the cooling gas by the gas supply device is stopped while the fuel gas is supplied to the fuel electrode to cause the fuel cell to generate power, thereby lowering the potential of the oxidizer electrode to a value equal to or lower than the reduction potential (Vr) of the oxide film, and a cooling process in which the fuel cell is cooled after the reduction process is completed. [Claim 2] 2. The air-cooled fuel cell system according to claim 1, wherein the control unit increases the number of times the reduction process is performed as the elapsed time (PD) from when the power generation of the fuel cell stops until the fuel cell is restarted becomes longer. [Claim 3] 3. The air-cooled fuel cell system of claim 1, wherein the control unit terminates the reduction process and starts the cooling process when the temperature (Tc) of the fuel cell becomes equal to or higher than a predetermined first temperature judgment value (T1) during the reduction process, and terminates the cooling process and starts the reduction process when the temperature (Tc) of the fuel cell becomes equal to or lower than a predetermined second temperature judgment value (T2) that is lower than the first temperature judgment value during the cooling process. [Claim 4] 4. The air-cooled fuel cell system according to claim 3, wherein the control unit obtains the temperature of the fuel cell from a temperature sensor (43) that detects the temperature of the fuel cell. [Claim 5] 4. An air-cooled fuel cell system as described in any one of claims 1 to 3, wherein the control unit determines the timing to terminate the reduction process from a predetermined first relationship (MP1) between the elapsed time during the reduction process and the temperature of the fuel cell, and determines the timing to terminate the cooling process from a predetermined second relationship (MP2, MPr) between the elapsed time during the cooling process and the temperature of the fuel cell. [Claim 6] 6. The air-cooled fuel cell system according to claim 1, wherein the control unit, in the cooling process, operates the gas supply device to supply the cooling gas to the fuel cell, thereby cooling the fuel cell. [Claim 7] 7. The air-cooled fuel cell system according to claim 1, wherein the control unit causes the fuel cell to generate electricity in the reduction process so that the current output from the fuel cell becomes a predetermined current target value. [Claim 8] 8. The air-cooled fuel cell system according to claim 7, wherein the current target value is predetermined so that, in the reduction process, the amount of oxygen consumed per unit time by power generation in the fuel cell is greater than the amount of oxygen per unit time diffusing from outside the oxidizer electrode to the oxidizer electrode. [Explanation of symbols]

[0113] 10. Fuel Cell System 14 Fuel Cell (Fuel Cell) 18 Oxidant electrode 19 Electrolyte membrane 20 Fuel electrode 30 Blower (gas supply device) 40 Electronic control unit (control unit) 182 Catalyst 182a Oxide film

Claims

1. 1. An air-cooled fuel cell system, comprising: a fuel cell (14) including an electrolyte membrane (19), an oxidizer electrode (18) stacked on the electrolyte membrane and supplied with an oxidizer gas, and a fuel electrode (20) stacked on the side of the electrolyte membrane opposite to the oxidizer electrode and supplied with a fuel gas; a gas supply device (30) that supplies a cooling gas for cooling the fuel cell to the fuel cell; a control unit (40), a portion of the cooling gas is supplied to the oxidizer electrode as the oxidizer gas; The oxidizer electrode has a catalyst (182) on which an oxide film (182a) can be formed, When restarting the fuel cell after power generation by the fuel cell has stopped, the control unit alternately repeats a reduction process in which the supply of the cooling gas by the gas supply device is stopped while the fuel gas is supplied to the fuel electrode to cause the fuel cell to generate power, thereby lowering the potential of the oxidizer electrode to a reduction potential (Vr) of the oxide film or less, and a cooling process in which the fuel cell is cooled after the reduction process is completed.

2. 2. The air-cooled fuel cell system according to claim 1, wherein the control unit alternately repeats the reduction process and the cooling process more frequently the longer the elapsed time (PD) from when the fuel cell stops generating power until the fuel cell is restarted.

3. 3. The air-cooled fuel cell system of claim 1, wherein the control unit terminates the reduction process and starts the cooling process when the temperature (Tc) of the fuel cell becomes equal to or higher than a predetermined first temperature judgment value (T1) during the reduction process, and terminates the cooling process and starts the reduction process when the temperature (Tc) of the fuel cell becomes equal to or lower than a predetermined second temperature judgment value (T2) that is lower than the first temperature judgment value during the cooling process.

4. 4. The air-cooled fuel cell system according to claim 3, wherein the control unit obtains the temperature of the fuel cell from a temperature sensor (43) that detects the temperature of the fuel cell.

5. 3. The air-cooled fuel cell system of claim 1, wherein the control unit determines the timing to terminate the reduction process from a predetermined first relationship (MP1) between the elapsed time during the reduction process and the temperature of the fuel cell, and determines the timing to terminate the cooling process from a predetermined second relationship (MP2, MPr) between the elapsed time during the cooling process and the temperature of the fuel cell.

6. 3. The air-cooled fuel cell system according to claim 1, wherein the control unit, in the cooling process, operates the gas supply device to supply the cooling gas to the fuel cell, thereby cooling the fuel cell.

7. 3. The air-cooled fuel cell system according to claim 1, wherein the control unit, during the reduction process, causes the fuel cell to generate electricity so that the current output from the fuel cell becomes a predetermined current target value.

8. 8. The air-cooled fuel cell system according to claim 7, wherein the current target value is predetermined so that, in the reduction process, the amount of oxygen consumed per unit time by power generation in the fuel cell is greater than the amount of oxygen per unit time diffusing from outside the oxidizer electrode to the oxidizer electrode.

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