JP2007323863A - Fuel cell system and shutdown method of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control an oxidation corrosion of a catalyst of a catalyst layer or a catalyst carrier and reduce a water content in the fuel cell efficiently as well when a fuel cell is shut down. <P>SOLUTION: When the fuel cell is shut down, a cathode gas and an anode gas supply is stopped, and after a cathode side is closed tight, cathode gas exhausted from the fuel cell is circulated in the fuel cell as cathode circulating gas, and a water content of the circulating gas in the circulating passage is removed and by controlling a circulation based on a water content in the cathode circulating gas, the oxidation corrosion of the catalyst of the catalyst layer or the catalyst carrier is controlled, and furthermore, the water content in the fuel cell can be efficiently reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system mounted on a vehicle or the like and a fuel cell stopping method.

  As one of the countermeasures against environmental problems and resource problems, chemical energy is converted into electric energy by electrochemical reaction using oxidizing gas such as oxygen and air and reducing gas (fuel gas) such as hydrogen and methane as raw materials. Fuel cells that generate electricity by conversion are drawing attention. The fuel cell is provided with an anode (anode catalyst layer) on one surface of the electrolyte membrane and a cathode (cathode catalyst layer) on the other surface with the electrolyte membrane sandwiched therebetween, and each of the electrolyte membranes sandwiched between them. A diffusion layer is further provided outside the catalyst layer, and these are sandwiched by separators provided with a raw material supply passage to form a battery. A raw material such as hydrogen or oxygen is supplied to each catalyst layer to generate electricity. Each catalyst layer includes catalyst-carrying particles in which a catalyst such as platinum (Pt) is supported on a carrier such as carbon.

  At the time of power generation of the fuel cell, when the raw material supplied to the anode is hydrogen gas and the raw material supplied to the cathode is air, hydrogen ions and electrons are generated from the hydrogen gas at the anode. Electrons reach the cathode from an external terminal through an external circuit. At the cathode, water is generated by oxygen in the supplied air, hydrogen ions that have passed through the electrolyte membrane, and electrons that have reached the cathode through an external circuit. In this way, a chemical reaction occurs at the cathode and the anode, and charges are generated to function as a battery. This fuel cell has been studied in various ways as a clean energy source due to the abundance of raw material gas and liquid fuel used for power generation and the fact that the substance discharged from the power generation principle is water. Has been.

  When stopping such a fuel cell, if hydrogen gas, air, or the like is left inside the fuel cell, hydrogen gas and air are mixed in the anode or cathode, an abnormal potential is generated, and the anode and cathode Oxidative corrosion of the catalyst or catalyst carrier occurs. When oxidative corrosion of such a catalyst or catalyst carrier occurs, the life of the fuel cell is shortened. Further, when the cathode side is closed and left, the water vapor remaining on the cathode condenses and becomes difficult to start the next battery due to a so-called flooding phenomenon.

  Thus, for example, Patent Document 1 describes purging by supplying an inert gas to the anode and cathode of the fuel cell when the fuel cell is stopped. Further, Patent Document 2 discloses that when the fuel cell is stopped, the cathode is sealed with the supply of the oxygen-containing gas to the cathode stopped, the cell is power-generated, oxygen in the cathode is consumed, and then the purge gas is used. Purge is described.

  Patent Document 3 describes purging with an inert gas generated by circulating and generating power in a cathode gas circulation system that is closed when the fuel cell is stopped.

JP-A-8-222259 JP 2002-93448 A Japanese Patent Laid-Open No. 2004-22487

  However, the methods as disclosed in Patent Documents 1 and 2 require an inert gas, and the system becomes large if an inert gas supply facility is provided.

  Further, in the method of Patent Document 3, a condenser is installed in the cathode gas circulation system, whereby moisture in the circulation gas is condensed and removed. However, the amount of residual moisture in the circulation gas is taken into account when stopping control of the fuel cell. Therefore, there is a possibility that the water inside the fuel cell is not sufficiently removed.

  The present invention provides a fuel cell system and a fuel cell stop method that can suppress oxidative corrosion of a catalyst or catalyst support of a catalyst layer and efficiently reduce the amount of water inside the fuel cell when the fuel cell is stopped. is there.

  The present invention includes a fuel cell that generates electricity by supplying an anode gas to the anode and a cathode gas containing oxygen to the cathode, a sealing means for sealing the cathode side of the fuel cell, and a cathode discharged from the fuel cell. A circulation means for circulating gas as a cathode circulation gas to the cathode side of the fuel cell; a moisture removal means for removing moisture in the cathode circulation gas; and a moisture amount detection means for detecting the moisture content in the cathode circulation gas. Control means for controlling the circulation of the cathode circulation gas, and when the fuel cell is stopped, the supply of the anode gas and the cathode gas is stopped, and the cathode side of the fuel cell is sealed, and then the control means Circulates the cathode circulation gas while removing moisture in the cathode circulation gas, and performs the previous operation based on the detected amount of moisture. Controlling the circulation of the cathode circulating gas.

  In the fuel cell system, it is preferable that the control means stops the circulation of the cathode circulation gas when the detected moisture amount is equal to or less than a preset reference moisture amount when the fuel cell is stopped. .

  The fuel cell system further includes oxygen amount detection means for detecting an oxygen amount in the cathode circulation gas, and the control means is based on the detected water amount and oxygen amount when the fuel cell is stopped. It is preferable to control the circulation of the cathode circulation gas.

  In the fuel cell system, the control means may be configured such that, when the fuel cell is stopped, the cathode circulation is performed when the detected water amount and oxygen amount are equal to or less than a predetermined reference moisture amount and a reference oxygen amount, respectively. It is preferable to stop the gas circulation.

  Further, the present invention is a fuel cell stopping method for generating electricity by supplying anode gas to the anode and cathode gas containing oxygen to the cathode, the step of stopping the supply of the cathode gas and anode gas, Sealing the cathode side of the fuel cell; removing the moisture in the cathode circulation gas while circulating the cathode gas discharged from the fuel cell as the cathode circulation gas to the cathode side of the fuel cell; Detecting the amount of moisture in the cathode circulation gas, and controlling the circulation of the cathode circulation gas based on the detected amount of moisture.

  Further, in the step of controlling the fuel cell stopping method, it is preferable to stop the circulation of the cathode circulation gas when the detected moisture amount becomes equal to or less than a preset reference moisture amount.

  Preferably, in the step of controlling the fuel cell stopping method, the amount of oxygen in the cathode circulation gas is detected, and the circulation of the cathode circulation gas is controlled based on the detected amount of water and oxygen.

  Further, in the step of controlling the fuel cell stopping method, the circulation of the cathode circulation gas is stopped when the detected water amount and oxygen amount are less than or equal to a preset reference moisture amount and reference oxygen amount, respectively. It is preferable.

  In the present invention, when the fuel cell is stopped, the supply of the cathode gas and the anode gas is stopped, the cathode side is sealed, the cathode gas discharged from the fuel cell is circulated inside the fuel cell as the cathode circulation gas, and the circulation path The water in the circulating gas is removed and the circulation is controlled based on the amount of water in the cathode circulating gas, thereby suppressing the oxidative corrosion of the catalyst in the catalyst layer or the catalyst carrier when the fuel cell is stopped, and the fuel cell The amount of water inside can be reduced efficiently.

  Embodiments of the present invention will be described below.

  An example of a fuel cell system according to an embodiment of the present invention is schematically shown in FIG. The fuel cell system 1 includes a fuel cell 10, a cathode gas supply channel 12, a cathode gas discharge channel 14, a closing valve 16 that is a sealing means, a gas circulation channel 18 and a pump 20 that are circulation means, A condenser 22 that is a moisture removing unit, a humidity sensor 24 that is a moisture amount detecting unit, a channel switching valve 26 that is a channel switching unit, a control unit 28 that is a control unit, and oxygen that is an oxygen amount detecting unit. Sensor 42.

  In the fuel cell system 1 of FIG. 1, a cathode gas supply unit 30 serving as a cathode gas supply unit is connected to the suction side of the pump 20 via the channel switching valve 26 by the cathode gas supply channel 12, and the discharge side of the pump 20 is The cathode gas supply channel 12 is connected to the cathode gas inlet 32 of the fuel cell 10. The closing valve 16 is connected to the cathode gas outlet 34 of the fuel cell 10 by the cathode gas discharge channel 14. As a result, the cathode gas is supplied from the cathode gas supply unit 30 to the cathode side of the fuel cell 10 through the cathode gas supply channel 12, and the cathode gas used for power generation passes through the cathode gas discharge channel 14 and passes through the closing valve 16. To be discharged to the outside. Although omitted in FIG. 1, similarly, an anode gas supply section, which is an anode gas supply means, is connected to the anode gas inlet of the fuel cell 10 through an anode gas supply flow path. An anode gas discharge channel is connected to the outlet. As a result, the anode gas is supplied from the anode gas supply unit to the anode side of the fuel cell 10 through the anode gas supply flow path, and the anode gas used for power generation is discharged through the anode gas discharge flow path.

  On the other hand, the cathode gas discharge channel 14 between the cathode gas outlet 34 of the fuel cell 10 and the closing valve 16 and the channel switching valve 26 are connected by the gas circulation channel 18, and the condenser 22 is installed therebetween. ing. A valve 36 is installed between the connection portion between the cathode gas discharge channel 14 and the gas circulation channel 18 and the inlet side of the condenser 22. Further, a humidity sensor 24 is installed in the vicinity of the cathode gas outlet 34 of the cathode gas discharge channel 14, and an oxygen sensor 42 is installed in the fuel cell 10. A water storage tank 38 is connected to the condenser 22.

  Further, the control unit 28 is connected to the closing valve 16, the pump 20, the humidity sensor 24, the flow path switching valve 26, the valve 36, and the oxygen sensor 42. When the fuel cell system 1 is mounted on a vehicle or the like, the control unit 28 is, for example, an ECU.

  Next, the fuel cell stopping method and the operation of the fuel cell system 1 according to this embodiment will be described below.

  During normal operation of the fuel cell 10 in the fuel cell system 1, the flow path switching valve 26 is connected to the B side as shown in FIG. 1, the closing valve 16 is open, the valve 36 is closed, Cathode gas is supplied from the supply unit 30 to the cathode side of the fuel cell 10. In addition, anode gas is supplied from an anode gas supply unit (not shown) to the anode side of the fuel cell 10, and a cell reaction is performed in the fuel cell 10. The cathode gas used on the cathode side of the fuel cell 10 passes through the cathode gas discharge passage 14 and is discharged to the outside through the closing valve 16.

  The fuel cell 10 used in the present embodiment converts chemical energy into electric energy by an electrochemical reaction using an oxidizing gas such as oxygen or air as a cathode gas and a reducing gas (fuel gas) such as hydrogen or methane as an anode gas. There is no particular limitation on the power generation. FIG. 2 shows a schematic cross-sectional view of an example of a single cell constituting the fuel cell 10. In the fuel cell 50, for example, a catalyst layer containing catalyst-supporting particles such as carbon supporting platinum (Pt) on one surface of a solid polymer electrolyte membrane 52 such as a perfluorosulfonic acid type anode ( As the fuel electrode 54, a catalyst layer containing catalyst supporting particles such as carbon supporting platinum (Pt) on the other surface is provided as a cathode (air electrode) 56 so as to face each other with the electrolyte membrane 52 interposed therebetween. Yes. In addition, a diffusion layer 58 containing a porous conductor material such as a carbon material is further provided outside each catalyst layer (anode 54 and cathode 56) sandwiching the electrolyte membrane 52, and these provide a path for supplying raw materials. A battery is configured by being sandwiched between the separators 60, and a raw material gas such as hydrogen or oxygen is supplied to each catalyst layer to generate electricity. The hollow portion of the separator 60 having a comb-like cross section serves as raw material supply paths 62 and 64 for supplying anode gas such as hydrogen gas and cathode gas such as air to the anode 54 and the cathode 56, respectively.

In the fuel cell 50, for example, when the anode gas supplied to the anode (fuel electrode) 54 is operated as hydrogen gas and the cathode gas supplied to the cathode (air electrode) 56 is operated as air,
2H ₂ → 4H ⁺ + 4e ⁻
Through the reaction formula (hydrogen oxidation reaction) shown in FIG. ₂ , hydrogen ions (H ⁺ ) and electrons (e ⁻ ) are generated from hydrogen gas (H ₂ ). Electrons (e ⁻ ) pass through an external circuit (not shown) from the diffusion layer 58 and reach the cathode 56 side from the other diffusion layer 58. In the cathode 56, oxygen (O ₂ ) in the supplied air, hydrogen ions (H ⁺ ) that have passed through the electrolyte membrane 52, and electrons (e ⁻ ) that have reached the cathode 56 side through an external circuit,
4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O
Water is produced through the reaction formula (oxygen reduction reaction) shown in FIG. In this way, a chemical reaction occurs in the anode 54 and the cathode 56, and electric charges are generated to function as a battery. And since the component discharged | emitted in a series of reaction is water, a clean battery is comprised.

  FIG. 3 shows a flowchart of a stopping method when the fuel cell 10 is stopped from the normal operation. First, in step S10, the flow control valve 26 is connected to the A side as shown in FIG. 4 by the control unit 28, and the supply of the cathode gas to the fuel cell 10 is stopped. Further, the supply of the anode gas to the fuel cell 10 is also stopped.

  Next, in step S12, the control unit 28 closes the closing valve 16 and opens the valve 36. As a result, the cathode gas discharge channel 14 is closed, and the cathode side of the fuel cell 10 is closed.

  In step S14, the operation of the pump 20 is continued by the control unit 28, and the cathode gas (air, etc.) is circulated through the gas circulation passage 18 as the cathode circulation gas in the cathode of the fuel cell 10 in the closed system. become. The cathode circulation gas flows into the condenser 22 along with the produced water generated by the cell reaction as described above when passing through the cathode portion of the fuel cell 10. In the condenser 22, the produced water contained in the cathode circulation gas is condensed and removed. The water separated in the condenser 22 is stored in a water storage tank 38, and when a predetermined amount of water is stored, the drain valve 40 is opened and discharged outside. On the other hand, the cathode circulation gas from which the water contained in the condenser 22 has been separated flows again into the cathode portion of the fuel cell 10 as a dry cathode gas, and the generated water in the cathode portion is further removed.

  A known condenser can be used as the condenser 22 which is a moisture removing means. A refrigerant such as cooling water is passed through the condenser 22, the cathode circulation gas is cooled by heat exchange, and the contained moisture is condensed. The cooling temperature in the condenser 22 is not particularly limited as long as moisture in the cathode circulation gas can be condensed. Since the normal operating temperature of the fuel cell is about 80 ° C., the water in the cathode circulation gas can be condensed if it is cooled to about 40 ° C. to 50 ° C., for example. The moisture removing means may be any means that can remove moisture in the gas, and is not limited to a condenser.

  Thus, in the state where supply of hydrogen gas to the anode side and air to the cathode side is stopped and air is circulated as the cathode circulation gas to the cathode side, in the fuel cell 10, a part of oxygen in the air is cathode. The electrolyte membrane permeates from the side to the anode side. Oxygen that has permeated the electrolyte membrane reacts with hydrogen remaining on the anode side to generate an electric current. Accordingly, oxygen in the cathode circulation gas is gradually consumed, and most of the cathode circulation gas becomes nitrogen, that is, an inert gas. Therefore, in step S <b> 16, the oxygen amount of the fuel cell 10 is measured by the oxygen sensor 42. A signal from the oxygen sensor 42 is transmitted to the control unit 28, and it is determined that the oxygen amount (oxygen concentration) is not more than a preset reference oxygen amount (reference oxygen concentration) (for example, below the detection limit), that is, oxygen on the cathode side has disappeared. Sometimes, the current of the fuel cell is stopped in step S18. If the current value does not fall below the reference oxygen amount, power generation by the fuel cell is continued in step S14.

  Here, the oxygen sensor 42 is used as the oxygen amount detection means, but is not limited to this.

  Next, in step S20, the humidity of the cathode circulation gas is detected by the humidity sensor 24 near the cathode gas outlet 34 of the fuel cell 10. When the humidity value signal is transmitted to the control unit 28 and it is determined that the humidity of the cathode circulation gas is equal to or lower than a preset value (reference humidity value), that is, the generated water on the cathode side has disappeared, the control unit 28 in step S22. The pump 20 is stopped and the stop of the fuel cell system 1 is completed. If the humidity does not fall below the reference humidity value, the circulation of the cathode circulation gas is continued in step S14. The reference humidity value may be determined according to the battery configuration of the fuel cell 10, the volume inside the fuel cell 10, and the like.

  Here, the circulation of the cathode circulation gas is controlled by the control unit 28 based on the humidity detected by the humidity sensor that detects the humidity of the cathode circulation gas discharged from the fuel cell 10. It is not limited to. Instead of the moisture amount detection means, the circulation of the cathode circulation gas may be controlled based on the time during which the cathode circulation gas is circulated.

  When the fuel cell 10 is started again, the flow control valve 26 is connected to the B side as shown in FIG. 1 by the control unit 28, the closing valve 16 is opened, and the valve 36 is closed. Cathode gas is supplied from the cathode gas supply unit 30 to the cathode side of the fuel cell 10. In addition, the anode gas is also supplied to the anode side, and a battery reaction is performed. At the time of startup, the drain valve 40 is opened until the water in the water storage tank 38 runs out, and the water is discharged to the outside. When the water in the water storage tank 38 runs out, the drain valve 40 is closed.

  When the produced water generated at the cathode stagnates in the catalyst layer or at the catalyst layer / diffusion layer interface, the so-called flooding phenomenon occurs in which the supply of cathode gas that has permeated the diffusion layer to the catalyst occurs. The output will drop. In this embodiment, the cathode side is sealed at the time of stop control of the fuel cell, the cathode side is purged with the cathode circulation gas, and a condenser is installed in the cathode gas circulation system to remove moisture in the cathode circulation gas, Furthermore, by detecting the amount of residual water in the cathode circulation gas and controlling the circulation of the cathode circulation gas, the water inside the fuel cell can be efficiently and sufficiently removed. Therefore, the occurrence of flooding can be suppressed. Further, since the fuel cell is hardly stopped while the generated water remains inside, the next fuel cell can be started without any problem.

  Further, in the fuel cell stopping method according to this embodiment, oxygen in the cathode circulation gas is consumed by circulating the cathode gas and generating power in the fuel cell, and the cathode circulation gas is mostly nitrogen, that is, an inert gas. It becomes. Therefore, the interior of the fuel cell 10 can be purged with an inert gas containing almost no oxygen without newly providing an inert gas supply means or the like. Further, by detecting the amount of residual oxygen in the cathode circulation gas and controlling the circulation of the cathode circulation gas, oxidative corrosion of the catalyst or catalyst carrier of the catalyst layer of the fuel cell can be prevented.

Conventionally, when the fuel cell is stopped, it has been necessary to supply the cathode gas to the cathode side for several minutes to several tens of minutes to dry the cathode side while the supply of the anode gas is stopped in order to remove the generated water. At this time, oxygen slightly permeates the electrolyte membrane from the cathode side to the anode side, but in the state where residual hydrogen gas exists on the anode side, oxygen is immediately reduced to water, but hydrogen is not supplied. Therefore, hydrogen is gradually consumed, and a part where oxygen exists partially occurs. As a result, the anode potential rises and becomes an abnormal potential that exceeds the oxidation potential of carbon (about 1.2 mV), the carbon that is the catalyst support of the anode catalyst layer is oxidized to CO ₂ , and the catalyst is oxidized or desorbed. As a result, the catalyst layer deteriorated. According to the method for stopping a fuel cell according to the present embodiment, the amount of residual oxygen in the cathode circulation gas is detected, the circulation of the cathode circulation gas is controlled, and the cathode side is purged with an inert gas containing almost no oxygen. Therefore, such deterioration of the catalyst layer, that is, oxidative corrosion of the catalyst of the catalyst layer or the catalyst carrier can be prevented.

  The configuration of the fuel cell system 1 shown in FIG. 1 and FIG. 4 is an example, and the arrangement of each component device, for example, each valve 16, 26, 36, pump 20, humidity sensor 34, oxygen sensor 42, etc. is these. It is not limited to. Further, components of the fuel cell system 1, that is, the cathode gas supply channel 12, the cathode gas discharge channel 14, the closing valve 16, the gas circulation channel 18, the condenser 22, the pump 20, the humidity sensor 24, and the channel switching. Various known types of devices can be used for the valve 26, the control unit 28, the cathode gas supply unit 30, the valve 36, the water storage tank 38, the drain valve 40, the oxygen sensor 42, and the like. Not what you want.

  An outline of another example of the fuel cell system according to the embodiment of the present invention is shown in FIG. The fuel cell system 3 includes an expansion valve 44 in addition to the configuration of the fuel cell system 1 of FIGS. 1 and 3. As the expansion valve 44, various known types can be used, and the type and the like are not limited.

  In the fuel cell system 3 of FIG. 5, the cathode gas discharge channel 14 connects the suction side of the pump 20 to the cathode gas outlet 34 of the fuel cell 10, and the discharge side of the pump 20 is connected to the closing valve 16. An expansion valve 44 is installed on the outlet side of the condenser 22 in the gas circulation flow path 18.

  In the fuel cell system 3, when the fuel cell is stopped, the cathode gas (air or the like) in the fuel cell system 3 in a sealed system is sucked from the outlet side of the fuel cell 10 by the pump 20 in step S14. Is circulated through the gas circulation passage 18 as the cathode circulation gas. The cathode circulation gas flows into the condenser 22 along with the generated water generated by the cell reaction when passing through the cathode portion of the fuel cell 10. In the condenser 22, the produced water contained in the cathode circulation gas is condensed and removed. The cathode circulation gas from which the water contained in the condenser 22 has been separated is expanded by the expansion valve 44, is reduced in pressure, and flows again into the cathode portion of the fuel cell 10 as a dry cathode gas. That is, the gas circulation passage 18 between the expansion valve 44, the fuel cell 10, and the pump 20 inlet is in a reduced pressure state. As a result, the generated water in the cathode portion can be removed more quickly and efficiently by the cathode circulation gas.

  On the other hand, the gas circulation passage 18 between the outlet of the pump 20 and the inlet of the condenser 22 is in a pressurized state. Thereby, the temperature of the cathode circulation gas during this period is high, and it is easy to be cooled by the condenser 22, and water can be condensed and removed more efficiently.

  The fuel cell system according to the present embodiment is preferably used as, for example, a small power source for mobile devices such as a mobile phone and a portable personal computer, a power source for automobiles, a household power source, etc., particularly as a power source for automobiles and a household power source. it can.

  In addition, the fuel cell stopping method according to the present embodiment can be suitably used particularly in a fuel cell system for automobile power sources and household power sources.

It is the schematic which shows an example of a structure of the fuel cell system which concerns on embodiment of this invention. It is the schematic which shows an example of a structure of the fuel cell concerning embodiment of this invention. It is a flowchart which shows an example of the stop method of the fuel cell which concerns on embodiment of this invention. It is the schematic which shows an example of a structure of the fuel cell system which concerns on embodiment of this invention. It is the schematic which shows the other example of a structure of the fuel cell system which concerns on embodiment of this invention.

Explanation of symbols

  1,3 Fuel cell system, 10 Fuel cell, 12 Cathode gas supply channel, 14 Cathode gas discharge channel, 16 Block valve, 18 Gas circulation channel, 20 Pump, 22 Condenser, 24 Humidity sensor, 26 Channel switching Valve 28 control unit 30 cathode gas supply unit 32 cathode gas inlet 34 cathode gas outlet 36 valve 38 storage tank 40 drain valve 42 oxygen sensor 44 expansion valve 50 fuel cell 52 electrolyte membrane 54 Anode (fuel electrode), 56 Cathode (air electrode), 58 Diffusion layer, 60 Separator, 62, 64 Raw material supply path.

Claims (8)

A fuel cell that generates electricity by supplying an anode gas to the anode and a cathode gas containing oxygen to the cathode; and
Sealing means for sealing the cathode side of the fuel cell;
A circulation means for circulating the cathode gas discharged from the fuel cell as a cathode circulation gas to the cathode side of the fuel cell;
Moisture removing means for removing moisture in the cathode circulation gas;
Water content detection means for detecting the water content in the cathode circulation gas;
Control means for controlling circulation of the cathode circulation gas;
With
When the supply of the anode gas and the cathode gas is stopped when the fuel cell is stopped and the cathode side of the fuel cell is sealed, the control means removes the water in the cathode circulation gas while the cathode circulation gas is removed. And the circulation of the cathode circulation gas is controlled based on the detected water content. The fuel cell system according to claim 1,
The control means stops the circulation of the cathode circulation gas when the detected moisture amount becomes equal to or less than a preset reference moisture amount when the fuel cell is stopped. The fuel cell system according to claim 1,
An oxygen amount detecting means for detecting the amount of oxygen in the cathode circulation gas;
The control means controls the circulation of the cathode circulation gas based on the detected water content and oxygen content when the fuel cell is stopped. The fuel cell system according to claim 3,
The control means stops the circulation of the cathode circulation gas when the detected water amount and oxygen amount are equal to or less than a preset reference moisture amount and a reference oxygen amount, respectively, when the fuel cell is stopped. A fuel cell system. A method for stopping a fuel cell that generates electricity by supplying an anode gas to an anode and a cathode gas containing oxygen to the cathode,
Stopping the supply of the cathode gas and the anode gas;
Sealing the cathode side of the fuel cell;
Removing the moisture in the cathode circulation gas while circulating the cathode gas discharged from the fuel cell as a cathode circulation gas to the cathode side of the fuel cell;
Detecting the amount of water in the cathode circulation gas, and controlling the circulation of the cathode circulation gas based on the detected amount of water;
A method for stopping a fuel cell, comprising: A fuel cell stopping method according to claim 5,
The method of stopping a fuel cell, wherein, in the controlling step, the circulation of the cathode circulation gas is stopped when the detected moisture amount becomes equal to or less than a preset reference moisture amount. A fuel cell stopping method according to claim 5,
In the controlling step, the amount of oxygen in the cathode circulation gas is detected, and the circulation of the cathode circulation gas is controlled based on the detected moisture amount and oxygen amount. A method for stopping a fuel cell according to claim 7,
In the control step, the cathode circulation gas circulation is stopped when the detected water amount and oxygen amount are equal to or less than a preset reference moisture amount and a reference oxygen amount, respectively. How to stop.

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