JP2008066186A - Fuel cell system, its power generation shutdown method, and power generation shutdown storing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power generation shutdown method of a fuel cell system capable of restraining CO poisoning of catalyst at the time of power generation shutdown storage. <P>SOLUTION: Extraction of current from a fuel cell in a normal power generation state is stopped (a step 201), and a supply flow of air for CO oxidation is increased to adjust a density of the air for CO oxidation in a fuel electrode higher than that at the time of normal power generation. Or, by reducing a supply volume of fuel gas and increasing a density of the air in the fuel electrode, a supply ratio of the air for CO oxidation supplied to the fuel electrode is increased (a step 202). Further, a supply flow of air for CO oxidation is adjusted so that an amount of substance of a sum total of oxygen contained in the air for CO oxidation and air supplied to an oxidant electrode is not more than half of that of hydrogen contained in fuel gas supplied to the fuel electrode. Later, supply of the fuel gas to the fuel electrode and the air for CO oxidation is stopped, and at the same time, supply of air to the oxidant electrode is stopped (a step 203). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system in which fuel gas and oxidant gas are introduced to generate power by a chemical reaction, and in particular, improved to prevent CO poisoning of a fuel electrode catalyst when the fuel cell system is stopped from power generation. The present invention relates to a fuel cell system subjected to the above, a power generation stopping method thereof, and a power generation stop storage method.

  A fuel cell system supplies a fuel cell such as hydrogen and an oxidant such as air to a fuel cell and causes it to react electrochemically, thereby directly converting the chemical energy of the fuel into electrical energy and taking it out. It is. Despite its relatively small size, this fuel cell system is highly efficient and environmentally friendly, and can be applied as a cogeneration system by collecting the heat generated by power generation as hot water or steam. Therefore, it is expected to be used in a wide range of applications such as business use in factories and hospitals, general household use, and automobile use.

  The polymer electrolyte fuel cell includes a membrane electrode assembly in which a fuel electrode and an oxidant electrode are bonded to both sides of a polymer electrolyte membrane, and a fuel gas channel and an oxidant gas channel formed on both sides of the membrane electrode assembly. It has a structure sandwiched between. Further, the catalyst layer constituting part of the fuel electrode and the oxidant electrode is composed of a composite of a carbon support carrying a metal catalyst such as platinum or a platinum alloy and a polymer electrolyte. A fuel cell is generally composed of a stack in which a large number of single cells having such a structure are stacked.

As such a fuel cell system, there is an operation method using a reformed gas obtained by reforming a hydrocarbon gas such as a city gas in advance by a reformer as a fuel gas introduced into the fuel electrode. The reformed gas contains CO. Although this CO impairs the characteristics of the fuel cell system by poisoning the catalyst surface on the fuel electrode side, during the power generation operation of the fuel cell, an oxidant gas is supplied to the fuel electrode, and CO is converted into CO. There has been proposed a method of suppressing deterioration in characteristics during power generation operation of the fuel cell system due to CO poisoning by oxidizing and removing the gas to ₂ . (See Patent Document 1).
JP2004-241239

  However, the method disclosed in Patent Document 1 relates to the oxidation removal of CO poisoned by the catalyst of the fuel electrode during the power generation operation of the fuel cell system. This catalyst remains poisoned by CO.

  As a catalyst for this fuel electrode, an alloy catalyst of platinum and ruthenium is often used. However, if the alloy catalyst of platinum and ruthenium continues to be poisoned by CO, the state of the catalyst changes, so that the CO resistance of the catalyst is reduced. May be reduced. When the CO resistance of the catalyst is reduced in this way, during the power generation operation of the fuel cell system, even if the oxidant gas is supplied to the fuel electrode as described above, the oxidation removal of CO becomes insufficient, and as a result, the fuel There is a risk that the characteristics of the battery system will deteriorate and the fuel cell system cannot be operated.

  The present invention has been made to solve the above-described problems of the prior art, and its purpose is to remove CO oxidation from the fuel electrode during power generation stop operation and power generation stop storage of the fuel cell system. A fuel cell system that can promote and suppress CO poisoning of the catalyst at the time of power generation stop storage of the fuel cell system, and can suppress a decrease in the CO resistance of the catalyst of the fuel electrode, a power generation stop method thereof, and a power generation stop storage method Is to provide.

  In order to achieve the above object, the present invention is characterized by promoting oxidation removal of CO existing in the fuel electrode during power generation stop operation and power generation stop storage of the fuel cell system.

  That is, the invention according to claim 1 is a fuel cell, fuel gas supply means for supplying fuel gas to the fuel electrode of the fuel cell, and oxidant gas for supplying oxidant gas to the oxidant electrode of the fuel cell. In a fuel cell system including a supply means, a CO oxidation gas supply means for supplying a CO oxidation gas to the fuel electrode of the fuel cell is provided, and a flow rate of the CO oxidation gas supplied to the fuel electrode is controlled. When the fuel cell system stops generating power, the control means determines that the supply ratio of the CO oxidizing gas to the amount of CO contained in the fuel gas on the fuel electrode side is the CO oxidizing gas during normal power generation. It is characterized by controlling so that it may become higher than the supply ratio.

  According to the first aspect of the present invention having the above-described configuration, when the power generation of the fuel cell system is stopped, the supply ratio of the CO oxidizing gas with respect to the CO amount contained in the fuel gas on the fuel electrode side is determined during normal power generation. By making it higher than this, the oxidation removal of CO in the fuel gas can be promoted more than during normal power generation. As a result, since CO poisoning of the catalyst of the fuel electrode during power generation stop storage of the fuel cell system is suppressed, it is possible to suppress a decrease in the CO resistance of the catalyst.

  The invention described in claim 2 is a fuel cell, a fuel gas supply means for supplying fuel gas to the fuel electrode of the fuel cell, and an oxidant gas supply means for supplying oxidant gas to the oxidant electrode of the fuel cell. In the fuel cell system, a CO oxidizing gas supply means for supplying a CO oxidizing gas to the fuel electrode of the fuel cell is provided, and a fuel gas flow rate supplied to the fuel electrode and an oxidant electrode are supplied. Control means for controlling the oxidant gas flow rate and the CO oxidizing gas flow rate supplied to the fuel electrode is provided, and when the power generation of the fuel cell system is stopped, the control means includes the amount of CO contained in the fuel gas on the fuel electrode side. The ratio of supplying the CO oxidizing gas to the fuel is controlled to be higher than the supplying ratio of the CO oxidizing gas during normal power generation, and oxygen contained in the CO oxidizing gas on the fuel electrode side The fuel gas flow rate and the oxidant are set so that the total amount of oxygen contained in the oxidant gas on the oxidant electrode side is not more than half the amount of hydrogen contained in the fuel gas on the fuel electrode side. The gas flow rate and the CO oxidation gas flow rate are controlled.

  According to the second aspect of the invention having the above-described configuration, when the fuel cell system stops generating power, the supply ratio of the CO oxidizing gas to the amount of CO contained in the fuel gas on the fuel electrode side is higher than that during normal power generation. The total amount of oxygen contained in the air supplied to the CO oxidizing gas and the oxidant electrode is less than half of the amount of hydrogen supplied to the fuel electrode. By adjusting the supply flow rate, even when oxygen is excessive in the fuel cell when storing the power generation system in the fuel cell system, the oxygen is consumed by reacting with hydrogen. It is possible to prevent the catalyst from being held at a high potential, and it is possible to suppress a decrease in CO resistance due to the catalyst being held at a high potential.

  According to a third aspect of the present invention, there is provided a fuel cell, fuel gas supply means for supplying fuel gas to the fuel electrode and oxidant electrode of the fuel cell, and oxidant gas to the fuel electrode and oxidant electrode of the fuel cell. Supplying oxidant gas supply means, reaction gas supply switching means for switching the supply destination of the fuel gas and oxidant gas between the fuel electrode and oxidant electrode, and control means for controlling the reaction gas supply switching means The fuel cell system is controlled to supply fuel gas to the fuel electrode and to supply oxidant gas to the oxidant electrode during normal power generation of the fuel cell system. When stopping, the fuel gas is supplied to the oxidant electrode, and the oxidant gas is controlled to be supplied to the fuel electrode.

  According to the third aspect of the invention having the above-described configuration, when the power generation of the fuel cell system is stopped, the oxidant gas is supplied to the fuel electrode of the fuel cell, so that the fuel electrode potential is increased, and the fuel electrode By oxidizing and removing CO poisoned by the catalyst, CO poisoning on the catalyst at the time of fuel cell power generation stop storage can be suppressed. In addition, by switching the supply destination of the fuel gas and the oxidant gas, each gas supply is stopped, and then the reverse current is taken out from the fuel cell, thereby consuming oxygen in the fuel electrode and lowering the fuel electrode potential. It is possible to prevent a decrease in the CO resistance of the catalyst due to maintaining the high potential of the fuel electrode when the fuel cell system is stopped during power generation.

  The invention described in claims 4 to 10 captures the invention described in claims 1 to 3 from the viewpoint of a power generation stopping method of the fuel cell system, and claims 11 to 10. The invention described in No. 12 is taken from the viewpoint of the power generation stop storage method of the fuel cell system.

  According to the present invention as described above, the CO oxidation removal of the fuel electrode is promoted during the power generation stop operation and the power generation stop storage of the fuel cell system, and the catalyst is poisoned with CO during the power generation stop storage of the fuel cell system. It is possible to provide a fuel cell system, a power generation stop method thereof, and a power generation stop storage method that can suppress the reduction in the CO resistance of the fuel electrode catalyst.

  Hereinafter, embodiments of a fuel cell system, a power generation stopping method thereof, and a power generation stop storage method according to the present invention (hereinafter referred to as embodiments) will be specifically described with reference to the drawings.

(1) First Embodiment (1-1) Configuration As shown in FIG. 1, the fuel cell system 1 of the present embodiment is roughly divided to supply fuel gas to the fuel cell 10 and the fuel electrode 10 a of the fuel cell 10. The fuel gas supply means 20 for performing the above, the oxidant gas supply means 30 for supplying the oxidant gas to the oxidant electrode 10b of the fuel cell 10, and the air for oxidizing and removing CO to the fuel electrode 10a of the fuel cell 10 are supplied. It comprises CO oxidizing gas supply means 40.

  The fuel cell 10 is a solid polymer fuel cell. This polymer electrolyte fuel cell is composed of a membrane electrode assembly in which a fuel electrode and an oxidant electrode are bonded to both sides of a polymer electrolyte membrane, and a separator in which a fuel gas channel and an oxidant gas channel are formed on both sides. It has a sandwiched structure. Further, the catalyst layer constituting part of the fuel electrode and the oxidant electrode is composed of a composite of a carrier carrying a catalyst and a polymer electrolyte. The fuel cell 10 generally uses a stack in which a large number of single cells having such a structure are stacked.

  The fuel gas supply means 20 includes a fuel gas supply source 21 that supplies a reformed gas that is a fuel gas, a fuel gas supply pipe 22 that supplies the reformed gas to the fuel electrode 10a of the fuel cell 10, and a fuel cell. The reformed gas supplied from the fuel gas supply source 21 passes through the fuel gas supply pipe 22 to the fuel electrode 10a of the fuel cell 10. It is configured to be supplied and discharged from the fuel gas discharge pipe 23.

  The oxidant gas supply means 30 includes an oxidant gas supply source 31 for supplying air as an oxidant gas, an oxidant gas supply pipe 32 for supplying air to the oxidant electrode 10b of the fuel cell 10, and a fuel. An oxidant gas discharge pipe 33 for discharging the oxidant gas from the oxidant electrode 10 b of the battery 10 is configured. The air supplied from the oxidant gas supply source 31 is supplied to the oxidant electrode 10b of the fuel cell 10 through the oxidant gas supply line 32 and discharged from the oxidant gas discharge line 33. Has been.

  Further, in the present embodiment, as the CO oxidizing gas supply means 40, a CO oxidizing gas supply pipe 42 connected to the fuel gas supply pipe 22 and a CO oxidizing gas supply source 41 connected thereto are provided. Is provided. The flow rate of each gas supplied from the fuel gas supply source 21, the oxidant gas supply source 31, and the CO oxidation gas supply source 41 is controlled by the control device 50. In the figure, arrows indicated by dotted lines indicate control by the control device 50. Air was used as the CO oxidizing gas.

(1-2) Fuel Cell System Power Generation Stop Method Next, a power generation stop method of the fuel cell system of the present embodiment having the above-described configuration will be described. FIG. 2 is a flowchart showing a power generation stop procedure of the fuel cell system in the present embodiment.

  As shown in FIG. 2, when stopping the power generation of the fuel cell system, first, the extraction of the current from the fuel cell 10 in the normal power generation state is stopped (step 201). Then, the supply ratio of the CO oxidizing air supplied to the fuel electrode 10a of the fuel cell 10 is increased (step 202).

  In addition, as a method of increasing the supply ratio of the CO oxidation air, for example, the supply flow rate of the CO oxidation air is increased, and the concentration of the CO oxidation air in the fuel electrode 10a is changed to the CO during normal power generation of the fuel cell. It is possible to use a method of increasing the concentration of CO oxidation air in the fuel electrode 10a by adjusting the concentration to be higher than the concentration of oxidation air or by reducing the amount of fuel gas supplied.

  After increasing the supply ratio of the CO oxidation air in this way, the amount of oxygen in the total of oxygen contained in the air supplied to the CO oxidation air and the oxidant electrode is further supplied to the fuel electrode 10a. It is preferable to adjust the supply flow rate of the CO oxidizing air so that the amount of hydrogen contained in the gas is half or less. The reason is that if the supply ratio of the CO oxidizing air is excessively increased, oxygen is left in the fuel cell when the fuel cell is stopped and stored, and the fuel electrode may be held at a high potential by this oxygen. Therefore, excess oxygen is consumed by reacting with hydrogen.

  Thereafter, the supply of fuel gas and CO oxidation air to the fuel electrode 10a is stopped, and the supply of air to the oxidant electrode 10b is stopped (step 203). Further, a shutoff valve may be provided at the fuel gas inlet / outlet of the fuel electrode 10a and the air inlet / outlet of the oxidant electrode 10b, and leakage of gas and outside air inside the fuel cell may be shut off by this shutoff valve.

  According to the power generation stop method described above, before the supply of the fuel gas supplied to the fuel cell 10 is stopped, it is included in the fuel gas by a method such as increasing the supply flow rate of the CO oxidizing air than during normal power generation. By increasing the ratio of the supply flow rate of the CO oxidizing air to the amount of CO generated, the oxidation removal of CO in the fuel gas is promoted more than during normal power generation. As a result, CO poisoning of the fuel electrode catalyst during power generation stop storage of the fuel cell system is suppressed. In this way, by suppressing the CO poisoning of the catalyst during the power generation stop storage of the fuel cell system, it is possible to suppress a decrease in the CO resistance of the catalyst.

  In addition, the supply flow rate of CO oxidation air is set so that the total amount of oxygen contained in the air supplied to the CO oxidation air and the oxidant electrode is less than half of the amount of hydrogen supplied to the fuel electrode. By adjusting, even when the oxygen in the fuel cell becomes excessive when the fuel cell system stops generating power, the oxygen is consumed by reacting with hydrogen, so the fuel electrode potential is increased by oxygen. It is possible to prevent the decrease in CO resistance due to the high potential holding of the catalyst.

(1-3) Test Example FIGS. 3A and 3B show a single cell held in a state where CO is removed from the fuel electrode and a single cell held in a state where CO is not removed from the fuel electrode. This shows the relative ratio of CO resistance reduction.

  As is apparent from FIG. 3, the degree of reduction in CO resistance of a single cell held with CO removed from the fuel electrode is compared to the degree of CO resistance reduction of a single cell held without CO removed from the fuel electrode. It was shown to be about 10%. That is, it was shown that the CO resistance reduction of the fuel electrode catalyst can be suppressed to about 10% by removing CO poisoned by the fuel electrode catalyst.

(1-4) Actions / Effects As described above, according to the present embodiment, the amount of CO oxidation air supplied to the fuel electrode is changed to the fuel gas on the fuel electrode side when power generation of the fuel cell system is stopped. By controlling so that the supply ratio of the CO oxidation air with respect to the amount of CO contained is higher than the supply ratio of the CO oxidation air during the normal power generation operation of the fuel cell system, It is possible to promote the oxidation removal of CO poisoning to the fuel electrode catalyst during stop storage, and to suppress the reduction of the CO resistance due to CO poisoning of the catalyst, so that the battery durability can be drastically improved. it can.

  In addition, it has been confirmed that the CO resistance of the fuel electrode catalyst decreases even when the fuel electrode potential is maintained at a high potential, but according to the present embodiment, when the fuel cell system stops generating power. The amount of oxygen in the CO oxidizing air is the sum of the amount of oxygen in the CO oxidizing air and the amount of oxygen in the air supplied to the oxidizer electrode, which is half the amount of hydrogen supplied to the fuel electrode. By adjusting so as to be as follows, oxygen in the fuel cell is consumed by reacting with hydrogen at the time of power generation stop storage of the fuel cell system. As a result, since it is possible to prevent the fuel electrode potential from being held at a high potential by oxygen, it is possible to suppress a decrease in CO resistance due to the high potential holding of the catalyst.

(2) Second Embodiment This embodiment is characterized in that the CO oxidation removal operation in the first embodiment is a potential operation of the fuel electrode, and the other embodiments are the same as in the first embodiment. Therefore, explanation is omitted.

(2-1) Power Generation Stop Method for Fuel Cell System Next, a power generation stop method for the fuel cell system according to the present embodiment will be described. FIG. 4 is a flowchart showing a power generation stop procedure of the fuel cell system in the present embodiment.

  As shown in FIG. 4, when stopping the power generation of the fuel cell system, first, adjustment of the supply flow rate of the fuel gas to the fuel cell in the normal power generation state and the current value taken out from the fuel cell are adjusted. Thus, the voltage of the fuel cell is set to 0 V (step 401). When the voltage reaches 0 V (step 402), the extraction of current from the fuel cell is stopped, and the supply of fuel gas and air to the fuel cell is stopped (step 403). Further, a shutoff valve may be provided at the fuel gas inlet / outlet of the fuel electrode 10a and the air inlet / outlet of the oxidant electrode 10b, and leakage of gas and outside air inside the fuel cell may be shut off by this shutoff valve.

  As described above, in the present embodiment, the fuel electrode potential is increased by extracting the current from the fuel cell while reducing the supply amount of the fuel gas supplied to the fuel cell. As the fuel electrode potential rises, the CO poisoned by the fuel electrode catalyst is oxidized and removed, thereby suppressing the CO poisoning of the fuel electrode catalyst during the power generation stop storage of the fuel cell system.

(2-2) Test Example FIG. 5 shows the fuel electrode potential with respect to the hydrogen electrode potential at each current density when the fuel electrode catalyst is CO poisoned. As is apparent from the figure, the fuel electrode potential increases as the current density increases. This is due to an increase in reaction polarization due to CO poisoning of the fuel electrode catalyst. When the current density is further increased, it can be seen that the fuel electrode potential approaches 0.3 V with respect to the hydrogen electrode potential. This is because CO poisoning the catalyst is oxidized and removed when the fuel electrode potential is around 0.3V. Therefore, it is understood that CO poisoning to the fuel electrode catalyst can be oxidized and removed by raising the fuel electrode potential to 0.3 V or more with respect to the hydrogen electrode potential.

  In this case, in order to prevent a decrease in the CO resistance due to a change in the state of the catalyst due to a further increase in the fuel electrode potential, while monitoring the voltage of the fuel cell so as not to reverse the polarity of the fuel cell, The flow rate and the current value are adjusted, and when the voltage of the fuel cell 10 becomes 0V, the current value is set to zero.

(2-3) Action / Effect As described above, according to the present embodiment, the catalyst in the fuel electrode can be simply obtained without supplying the CO oxidizing air to the fuel electrode when the power generation of the fuel cell system is stopped. It is possible to oxidize and remove CO poisoned. The effect of this embodiment is the same as that of the first embodiment, and a description thereof will be omitted.

(3) Third Embodiment The present embodiment is characterized in that the CO oxidation removal operation is performed at the time of power generation stop storage of the fuel cell system, and the other aspects are the same as those in the first embodiment. Omitted.

(3-1) Power Generation Stop Storage Method of Fuel Cell System Next, an operation at the time of power generation stop storage of the fuel cell system will be described.
In other words, air is additionally supplied to the fuel electrode when the fuel cell system is stored and stopped. At this time, the oxygen in the air to be additionally supplied is the total amount of oxygen in the air and oxygen in the air supplied to the oxidizer electrode when the power generation of the fuel cell system is stopped. Adjust so that it is less than half of the amount of hydrogen supplied to the fuel electrode when it is stopped.

(3-2) Actions / Effects As described above, when the fuel cell system is stopped from generating power, by supplying additional air to the fuel electrode, CO poisoning to the fuel electrode catalyst can be easily oxidized and removed. Can do. Further, even if the CO oxidation removal at the time of stopping the power generation of the fuel cell system according to the first and second embodiments is insufficient, an additional operation can be performed according to the present embodiment.

  In addition, the amount of oxygen in the additionally supplied air is the total amount of oxygen in the CO oxidation air in the fuel electrode and the oxygen in the air supplied to the oxidizer electrode when the fuel cell system stops power generation. By adjusting the fuel cell system so that it is less than half the amount of hydrogen supplied to the fuel electrode when power generation is stopped, it is possible to prevent the high potential of the fuel electrode potential from being maintained when the fuel cell system is stopped. Therefore, it is possible to suppress a decrease in CO resistance due to the high potential holding of the catalyst.

  In the present embodiment, the CO oxidation removal operation is performed by additionally supplying air to the fuel electrode during the power generation stop storage of the fuel cell system. However, by increasing the fuel electrode potential as in the second embodiment. The CO poisoned by the fuel electrode catalyst may be removed by oxidation.

  The fuel electrode potential is preferably raised to 0.3 V or higher with respect to the standard hydrogen electrode potential. In that case, the current value taken out from the fuel cell is controlled, and the current value is controlled so that the potential of the fuel cell becomes 0V. At this time, the current value is controlled so that the fuel cell does not reverse and the deterioration of the CO resistance due to the high potential holding of the fuel electrode catalyst does not proceed.

(4) Fourth Embodiment (4-1) Configuration As shown in FIG. 6, the fuel cell system 2 of the present embodiment includes a fuel cell 10 and both the fuel electrode 10 a and the oxidant electrode 10 b of the fuel cell 10. Fuel gas supply means 25 for supplying fuel gas, oxidant gas supply means 35 for supplying oxidant gas to both the fuel electrode 10a and the oxidant electrode 10b of the fuel cell 10, and supply of fuel gas and oxidant gas The reaction gas supply switching unit 60 switches between the fuel electrode 10a and the oxidant electrode 10b, and the control unit 70 controls the switching operation by the reaction gas supply switching unit 60.

(4-2) Power Generation Stop Method for Fuel Cell System Next, a power generation stop method for the fuel cell system according to the present embodiment will be described. FIG. 7 is a flowchart showing a power generation stop procedure of the fuel cell system. Further, in the fuel cell system 2, during normal power generation, the control means 70 controls the reaction gas supply switching means 60 so that fuel gas is supplied to the fuel electrode 10a and air is supplied to the oxidant electrode 10b. Is configured to do.

  As shown in FIG. 7, when the power generation of the fuel cell system 2 is stopped, first, the extraction of the current from the fuel cell 10 is stopped (step 701), and the control means 70 controls the reaction gas supply switching means 60. Then, the fuel gas is supplied to the oxidant electrode 10b and the air is supplied to the fuel electrode 10a (step 702).

  When the fuel gas and air are supplied to the oxidant electrode 10b and the fuel electrode 10a, respectively, and the voltage of the fuel cell becomes less than 0 V (step 703), the supply of the fuel gas and air is stopped (step 704). Thereafter, the reverse current is taken out from the fuel cell (step 705), the current is adjusted so that the voltage of the fuel cell does not exceed 0V, and when the voltage becomes 0V (step 706), the taking out of the reverse current is stopped, The supply of fuel gas and air is stopped (step 707). Further, a shutoff valve may be provided at the fuel gas inlet / outlet of the fuel electrode 10a and the air inlet / outlet of the oxidant electrode 10b, and leakage of gas and outside air inside the fuel cell may be shut off by this shutoff valve.

  As described above, FIG. 5 shows the fuel electrode potential with respect to the hydrogen electrode potential at each current density when the fuel electrode catalyst is poisoned with CO. From this, the fuel electrode potential is expressed as the hydrogen electrode potential. It can be seen that the CO poisoning to the fuel electrode catalyst can be oxidized and removed by raising the voltage to 0.3 V or more.

(4-3) Action / Effect According to the present embodiment, by supplying air to the fuel electrode of the fuel cell, the potential of the fuel electrode rises, and CO poisoning to the catalyst of the fuel electrode is oxidized and removed. As a result, CO poisoning on the catalyst during fuel cell power generation stop storage can be suppressed. The fuel electrode potential is preferably raised to 0.3 V or higher with respect to the standard hydrogen electrode potential.

  Also, by switching the fuel gas and air and stopping the supply of each gas, the reverse current is taken out from the fuel cell, thereby consuming oxygen in the fuel electrode and lowering the fuel electrode potential. A decrease in the CO resistance of the catalyst due to holding the high potential of the fuel electrode during stop storage can be prevented.

  As described above, CO poisoning to the fuel electrode catalyst can be completely oxidized and removed by switching the supply of fuel gas and air and controlling the current extraction. The effect of this embodiment is the same as that of the first embodiment, and a description thereof will be omitted.

(5) Other Embodiments The present invention is not limited to the above-described embodiments, and includes other embodiments exemplified below. For example, in the above embodiment, an example in which air is used as the oxidizing gas and the CO oxidizing gas has been described. However, oxygen may be used as the oxidizing gas and the CO oxidizing gas.

  In addition, the present invention is suitable for a fuel cell system including a solid polymer fuel cell, but these techniques are used in a phosphoric acid fuel cell, a molten carbonate fuel cell, a solid electrolyte fuel cell, The present invention can be similarly applied to a fuel cell system including an alkaline fuel cell.

The figure which shows the whole structure of 1st Embodiment of the fuel cell system by this invention. The flowchart which shows the electric power generation stop procedure of the fuel cell system in 1st Embodiment. The figure which shows the comparison of the CO-resistant fall degree by the presence or absence of CO removal operation in 1st Embodiment. The flowchart which shows the electric power generation stop procedure of the fuel cell system in 2nd Embodiment. The figure which shows the relationship between the fuel electrode potential in the case of CO poisoning, and current density. The figure which shows the whole structure of 4th Embodiment of the fuel cell system by this invention. The flowchart which shows the electric power generation stop procedure of the fuel cell system in 4th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Fuel cell system 10 ... Fuel cell 10a ... Fuel electrode 10b ... Oxidant electrode 20, 25 ... Fuel gas supply means 21 ... Fuel gas supply source 30, 35 ... Oxidant gas supply means 31 ... Oxidant gas supply source 40 ... CO oxidation gas supply means 41 ... CO oxidation gas supply source 50 ... control means 60 ... reactive gas supply switching means 70 ... control means

Claims (12)

In a fuel cell system comprising a fuel cell, a fuel gas supply means for supplying a fuel gas to a fuel electrode of the fuel cell, and an oxidant gas supply means for supplying an oxidant gas to an oxidant electrode of the fuel cell,
A CO oxidizing gas supply means for supplying a CO oxidizing gas to the fuel electrode of the fuel cell, and a control means for controlling the flow rate of the CO oxidizing gas supplied to the fuel electrode;
When the power generation of the fuel cell system is stopped, the control means causes the supply ratio of the CO oxidizing gas to be higher than the supply ratio of the CO oxidizing gas during the normal power generation, with respect to the amount of CO contained in the fuel gas on the fuel electrode side. A fuel cell system that is controlled to be In a fuel cell system comprising a fuel cell, a fuel gas supply means for supplying a fuel gas to a fuel electrode of the fuel cell, and an oxidant gas supply means for supplying an oxidant gas to an oxidant electrode of the fuel cell,
A CO oxidizing gas supply means for supplying a CO oxidizing gas to the fuel electrode of the fuel cell is provided, a fuel gas flow rate supplied to the fuel electrode, an oxidant gas flow rate supplied to the oxidant electrode, and a fuel electrode A control means for controlling the flow rate of the supplied CO oxidation gas;
When the power generation of the fuel cell system is stopped, the control means causes the supply ratio of the CO oxidizing gas to be higher than the supply ratio of the CO oxidizing gas during the normal power generation, with respect to the amount of CO contained in the fuel gas on the fuel electrode side. As well as controlling
The total amount of oxygen contained in the CO-oxidizing gas on the fuel electrode side and oxygen contained in the oxidant gas on the oxidant electrode side is equal to the amount of hydrogen contained in the fuel gas on the fuel electrode side. The fuel cell system, wherein the fuel gas flow rate, the oxidant gas flow rate, and the CO oxidation gas flow rate are controlled to be less than half. A fuel cell;
Fuel gas supply means for supplying fuel gas to the fuel electrode and oxidant electrode of the fuel cell;
An oxidant gas supply means for supplying an oxidant gas to the fuel electrode and the oxidant electrode of the fuel cell;
Reactive gas supply switching means for switching the supply destination of the fuel gas and the oxidant gas between the fuel electrode and the oxidant electrode;
Control means for controlling the reaction gas supply switching means,
By the control means, during normal power generation of the fuel cell system, the fuel gas is supplied to the fuel electrode and the oxidant gas is supplied to the oxidant electrode.
A fuel cell system, wherein when the power generation of the fuel cell system is stopped, the fuel gas is supplied to the oxidant electrode and the oxidant gas is supplied to the fuel electrode. In a fuel cell system power generation stopping method comprising a fuel cell, a fuel gas supply means for supplying a fuel gas to the fuel cell, and an oxidant gas supply means for supplying an oxidant gas to the fuel cell.
Control is performed so that the CO concentration of the fuel electrode when the supply of the fuel gas to the fuel electrode is stopped is equal to or less than the CO concentration of the fuel electrode when the fuel gas is supplied to the fuel electrode. A method for stopping power generation in a fuel cell system. In a fuel cell system power generation stopping method comprising a fuel cell, a fuel gas supply means for supplying a fuel gas to the fuel cell, and an oxidant gas supply means for supplying an oxidant gas to the fuel cell.
An operation of stopping the extraction of current from the fuel cell;
CO oxidation removal operation for oxidizing and removing CO present in the fuel electrode;
A method for stopping power generation of a fuel cell system, comprising: an operation of stopping the supply of the fuel gas to the fuel cell and the supply of the oxidant gas.   6. The method for stopping power generation of a fuel cell system according to claim 5, wherein the CO oxidation removal operation is an operation of supplying a CO oxidation gas to the fuel electrode.   The CO oxidation removal operation makes the supply ratio of the CO oxidation gas to the amount of CO contained in the fuel gas on the fuel electrode side higher than the supply ratio of the CO oxidation gas during normal power generation of the fuel cell system. 6. The method for stopping power generation of a fuel cell system according to claim 5, wherein the operation is an operation.   The CO oxidation removal operation makes the supply ratio of the CO oxidation gas to the amount of CO contained in the fuel gas on the fuel electrode side higher than the supply ratio of the CO oxidation gas during normal power generation of the fuel cell system. In addition, the total amount of oxygen contained in the CO-oxidizing gas on the fuel electrode side and oxygen contained in the oxidant gas on the oxidant electrode side is the amount of hydrogen contained in the fuel gas on the fuel electrode side. 6. The method of stopping power generation of a fuel cell system according to claim 5, wherein the operation is performed to be half or less of the fuel cell system.   6. The fuel cell system according to claim 5, wherein the CO oxidation removal operation is a fuel electrode potential operation that raises the fuel electrode potential of the fuel cell to 0.3 V or more with respect to the hydrogen electrode potential. Power generation stop method. A fuel cell;
Fuel gas supply means for supplying fuel gas to the fuel electrode and oxidant electrode of the fuel cell;
An oxidant gas supply means for supplying an oxidant gas to the fuel electrode and the oxidant electrode of the fuel cell;
In the fuel cell system power generation stopping method comprising a reactive gas supply switching means for switching the supply destination of the fuel gas and the oxidant gas between the fuel electrode and the oxidant electrode,
An operation of stopping the extraction of current from the fuel cell;
An operation of switching the supply destination of the fuel gas and the oxidant gas between the fuel electrode and the oxidant electrode by the reaction gas supply switching unit;
A method for stopping power generation of a fuel cell system, comprising: an operation of stopping the fuel gas supply and the oxidant gas supply of the fuel cell. In a fuel cell system power generation stop storage method comprising a fuel cell, a fuel gas supply means for supplying fuel gas to the fuel cell, and an oxidant gas supply means for supplying oxidant gas to the fuel cell.
A power generation stop storage method for a fuel cell system, wherein CO oxidation gas is additionally supplied to the fuel electrode of the fuel cell during power generation stop storage of the fuel cell system.   The additionally supplied CO oxidizing gas includes oxygen in the additionally supplied CO oxidizing gas, oxygen contained in the CO oxidizing gas on the fuel electrode side when power generation of the fuel cell system is stopped, and the oxidant electrode. 12. The control according to claim 11, wherein the total amount of oxygen contained in the side oxidant gas is controlled to be less than or equal to half of the amount of hydrogen contained in the fuel gas on the fuel electrode side. Power storage stop method of the fuel cell system.

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