JP2007220543A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of maintaining activity of anode catalyst so as not to hinder power generation. <P>SOLUTION: During a period between stoppage and start-up of the fuel cell system, oxidant gas is mixed to inert gas as purge gas supplied to the anode so that an anode side potential is maintained at +0.4V to +0.5V (vs. SHE) against the standard hydrogen electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system suitable for, for example, consumer cogeneration.

  A polymer electrolyte fuel cell is a battery that generates electricity and heat simultaneously by electrochemically reacting a fuel gas such as hydrogen and an oxidant gas such as air at an anode and a cathode as gas diffusion electrodes. . FIG. 6 shows a unit cell which is a general basic configuration of such a fuel cell. As shown in FIG. 6, the unit cell 100 mainly includes a membrane electrode assembly (MEA) 105 and a pair of plate-like separators sandwiching the membrane electrode assembly 105, that is, an anode side separator 106 a and a cathode side. At least one unit cell including the separator 106b is provided.

  The membrane electrode assembly 105 has a configuration in which a polymer electrolyte membrane 101 that selectively transports cations (hydrogen ions) is disposed between an anode 104a and a cathode 104b. Furthermore, the anode 104a includes at least a catalyst layer 102a disposed in close contact with the polymer electrolyte membrane 101 side, and a gas diffusion layer 103a disposed between the catalyst layer 102a and the anode-side separator 106a. The cathode 104b includes at least a catalyst layer 102b disposed in close contact with the polymer electrolyte membrane 101 side and a gas diffusion layer 103b disposed between the catalyst layer 102b and the cathode-side separator 106b.

  The catalyst layers 102a and 102b are layers mainly composed of conductive carbon particles carrying an electrode catalyst (for example, platinum-based metal). The gas diffusion layers 103a and 103b are layers having both gas permeability and conductivity. The gas diffusion layers 103a and 103b include a conductive water repellent layer (not shown) including at least conductive carbon particles and a water repellent resin such as a fluororesin on a conductive porous substrate made of, for example, carbon. It is obtained by forming.

  The anode-side separator 106a and the cathode-side separator 106b have conductivity, mechanically fix the membrane electrode assembly 104, and adjacent membrane electrode assemblies 104 when a plurality of membrane electrode assemblies 104 are stacked. They are electrically connected to each other in series. The anode-side separator 106a and the cathode-side separator 106b are supplied with a reaction gas to the anode 104a and the cathode 104b, and a gas containing a product generated by the electrode reaction or an unreacted reactant is supplied to the outside of the membrane electrode assembly 104. The gas flow paths 107a and 107b for carrying away to the surface are formed on one surface (that is, the main surface of the anode separator 106a and the cathode separator 106b on the side in contact with the anode 104a and the cathode 104b, respectively).

  Further, cooling fluid flow paths 108a and 108b for introducing a cooling fluid (cooling water or the like) for adjusting the battery temperature to be substantially constant are formed on the other surfaces of the anode side separator 106a and the cathode side separator 106b. ing. By adopting a configuration in which the cooling fluid is circulated between the fuel cell and the heat exchanger disposed outside, the heat energy generated by the reaction can be used in the form of hot water or the like.

  The gas flow paths 107a and 107b are formed by providing grooves on the main surfaces of the anode-side separator 106a and the cathode-side separator 106b on the side in contact with the anode 104a and the cathode 104b, respectively, from the advantage that the manufacturing process can be simplified. The method is common. In general, the cooling fluid channels 108a and 108b are formed by providing grooves on the outer main surfaces of the anode side separator 106a and the cathode side separator 106b.

  In addition, a so-called stacked fuel cell (obtained by electrically stacking a plurality of membrane electrode assemblies 105 in series by interposing an anode side separator 106a and a cathode side separator 106b between a plurality of membrane electrode assemblies 105 ( In the fuel cell stack, manifolds (reactive gas supply manifolds provided on the anode side separator 106a and the cathode side separator 106b) for branching and supplying the reaction gas supplied to the fuel cell to the membrane electrode assemblies 105 are provided. A manifold (not shown) formed by combining holes and reactive gas discharge manifold holes in a continuously stacked state is provided. The manifold formed inside the fuel cell as described above is called an internal manifold, and such an “internal manifold type” fuel cell is generally used.

  Although not shown, in each unit cell 100 included in the stack, the inlet of the anode-side gas flow path communicates with the reaction gas supply manifold on the anode side, and the outlet of the anode-side gas flow path is on the anode side. It communicates with the reaction gas discharge manifold. That is, the fuel gas supplied to the reaction gas supply manifold on the anode side of the stack is distributed to each single cell 100 from the inlet of the gas flow path on the anode side, and the anode exhaust gas that has come out from each single cell 100 is It is mixed in the reaction gas discharge manifold on the anode side and discharged from the stack. Although not shown, the cathode side oxidant gas manifold and the cooling fluid manifold have the same configuration.

  Further, in the unit cell 100, gas leakage of the reaction gas (leakage of fuel gas to the cathode 104b side, leakage of the oxidant gas to the anode 104a side, leakage of the reaction gas to the outside of the membrane electrode assembly 105, etc.). In order to prevent this, between the anode-side separator 106a and the cathode-side separator 106b facing each other, the outer edge of the membrane electrode assembly 105 (outside the anode 104a and cathode 104b and the outer edge of the polymer electrolyte membrane 101). A pair of opposed gaskets having a gas sealing function, that is, an anode side gasket 109a and a cathode side gasket 109b are arranged.

  As the anode side gasket 109a and the cathode side gasket 109b, for example, an O-ring, a rubber sheet, a composite sheet of an elastic resin and a rigid resin, or the like is used. From the viewpoint of handling of the MEA 105, a composite material gasket having a certain degree of rigidity is often used in an integrated manner with the MEA 105.

  Here, pure hydrogen is suitable as the fuel to be supplied to the anode, but it is not necessarily suitable from the viewpoint of infrastructure and storage. Therefore, the fuel gas is often supplied to the fuel cell using a fuel processing unit that generates a fuel gas mainly composed of hydrogen from a hydrogen-containing compound (fossil fuel) such as hydrocarbon by a catalytic reaction. With such a fuel processing section, it is possible to generate a fuel gas containing hydrogen as a main component from hydrocarbons such as methane, butane or natural gas, alcohols such as methanol, dimethyl ether (DME), or gasoline.

Next, FIG. 7 is a diagram showing a configuration of a conventional fuel cell system using the fuel cell. This fuel cell system is used, for example, in a stationary cogeneration system.
In the stationary fuel cell cogeneration system, it is effective to reform the city gas (13A) for which infrastructure has already been developed, generate fuel gas mainly composed of hydrogen, and supply this to the fuel cell stack. is there. City gas is mainly composed of methane and contains ethane and propane.

  The fuel processing unit for reforming city gas or the like is generally composed of a reforming unit 123, a shift unit 124, and a CO removing unit 125. In addition, flow control devices 26a, 26b, 26c and 26d are provided. Fossil fuels such as raw material gas containing hydrocarbons such as methane are supplied to the desulfurization section 22 where sulfur compounds contained in the odorant and the like are adsorbed and removed. The fossil fuel is reformed in the fuel processing unit to become a fuel gas mainly containing hydrogen, and is supplied to the anode of the fuel cell 121.

When methane is used as the raw material gas, in the reforming unit 123, a catalytic reaction occurs in accordance with the reaction formula: CH ₄ + 2H ₂ O → CO ₂ + 4H ₂ with water vapor, and several percent of CO is generated together with hydrogen. Thereafter, the generated CO is oxidized to carbon dioxide by the reaction formula: CO + H ₂ O → CO ₂ + H _{2 in the} CO conversion section 124 and is reduced to several thousand ppm. In the downstream CO remover 125, not only CO but also hydrogen of the fuel gas is oxidized, so that the CO concentration needs to be reduced as much as possible in the CO shift section 124. Further, the remaining CO is oxidized by the reaction formula: CO + 1 / 2O ₂ → CO ₂ in the CO removal section, and its concentration is reduced to about 20 ppm or less. Therefore, the total reaction in the fuel processing unit is represented by the reaction formula: CH ₄ + 2H ₂ O → CO ₂ + 4H ₂ .

  Here, CO has a property of adsorbing on the surface of Pt, and if CO is contained in the fuel gas supplied to the anode, it is adsorbed on Pt contained in the catalyst layer of the anode and is supposed to react with hydrogen. There is a problem that the smooth oxidation reaction on the Pt surface of the molecule is hindered and the output of the fuel cell is reduced (CO poisoning). As countermeasures against such CO poisoning, in addition to further improving the performance of the fuel processing section, it is possible to use a Pt—Ru alloy having CO poisoning resistance for the catalyst layer of the anode. CO poisoning cannot be avoided sufficiently.

On the other hand, in the stationary fuel cell cogeneration system, conventionally, the inert gas is purged and sealed to the anode and cathode when the operation of the fuel cell is stopped. For example, nitrogen or desulfurized source gas (13A) is used as the active gas. For example, in Patent Documents 1 and 2, the fuel is insufficient or deficient instantaneously and periodically during the operation of the fuel cell, with the intention of oxidizing and removing CO adsorbed on the poisoned catalyst at the anode. It has been proposed to increase the anodic potential by creating such a state.
Special Table 2002-500421 Japanese Patent No. 3536645

  However, as proposed in Patent Documents 1 and 2, it is very difficult to control the fuel cell system so that the fuel cell is in shortage or short of fuel instantaneously and periodically during operation of the fuel cell. It is difficult and voltage fluctuation must occur during operation, which is not preferable as a power supply system. Further, when the fuel gas supplied to the anode is deficient during the operation of the fuel cell, carbon in the catalyst layer is corroded or eluted. Furthermore, in the above-mentioned Patent Document 2, more specifically, it is proposed that the potential of the anode is set to a noble potential of +0.3 V or more with respect to the standard hydrogen electrode, but the CO adsorbed to Pt is more reliably detected. However, there was still room for improvement from the viewpoint of oxidizing and removing.

  In addition, in the conventional stationary fuel cell cogeneration system, when raw material gas such as city gas mainly composed of methane is used, it is stopped during the time period when electricity consumption is low in order to increase the utility cost. For example, DSS (Daily Start-up & DSS), which operates in the daytime and stops at midnight, is effective from the point of view that it is effective to operate in a time zone with a large amount of electricity consumption, and to increase the utility cost. Shut-down operation is preferred. That is, on the premise of DSS operation including such frequent start and stop, a method that can maintain the activity of the catalyst of the anode of the fuel cell system more easily and reliably has been desired.

  Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a fuel cell system capable of maintaining the activity of an anode catalyst so as not to hinder power generation. .

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies on reducing the poisoning of the anode catalyst in the fuel cell system. It has been found that CO adsorbed on the anode catalyst can be more reliably removed by supplying the desulfurized city gas as a purge gas and mixing the purge gas with air as an oxidant gas. More specifically, the present inventors produce a unit cell 10 having the configuration shown in FIG. 1, connect a potentiostat to the unit cell 10, and use an anode as a working electrode and a cathode as a reference electrode. When a test cell of the system was produced and intensive experiments were conducted, the following findings were found and the present invention was completed.

  As shown in FIG. 1, the unit cell 10 mainly includes a membrane electrode assembly 5 and a pair of plate-like separators sandwiching the membrane electrode assembly 5, that is, an anode side separator 6 a and a cathode side separator 6 b. The membrane electrode assembly 5 was configured by arranging the polymer electrolyte membrane 1 that selectively transports cations (hydrogen ions) between the anode 4a and the cathode 4b.

  The anode 4a includes a catalyst layer 2a disposed in close contact with the polymer electrolyte membrane 1, and a gas diffusion layer 3a disposed between the catalyst layer 2a and the anode separator 6a. Comprises a catalyst layer 2b disposed in close contact with the polymer electrolyte membrane 1 side, and a gas diffusion layer 3b disposed between the catalyst layer 2b and the cathode-side separator 6b.

  Moreover, the catalyst layers 2a and 2b were configured as layers mainly composed of conductive carbon particles carrying an electrode catalyst (platinum metal). Moreover, the gas diffusion layers 3a and 3b were configured as layers having both gas permeability and conductivity. The gas diffusion layers 3a and 3b were formed by forming a conductive water repellent layer containing conductive carbon particles and a fluororesin on a conductive porous substrate made of carbon.

  By providing grooves on one surface of the anode side separator 6a and the cathode side separator 6b (that is, the main surface of the anode side separator 6a and the cathode side separator 6b on the side in contact with the anode 4a and the cathode 4b, respectively), the anode 4a and the cathode The reaction gas was supplied to 4b, and the gas flow paths 7a and 7b for carrying away the product produced by the electrode reaction and the gas containing the unreacted reactant to the outside of the membrane electrode assembly 5 were formed. Further, a cooling fluid channel for introducing a cooling fluid (cooling water or the like) for adjusting the battery temperature to be substantially constant by providing a groove on the other surface of the anode side separator 6a and the cathode side separator 6b. 8a and 8b were formed.

  Using the test cell including the unit cell 1 having the above-described configuration, the reformed gas (main component is hydrogen) obtained by reforming the city gas is supplied to the anode 4a and air is supplied to the cathode 4b. An electromotive force was generated. Since the reformed gas contains a small amount of CO, the voltage decreased. This was thought to be because CO was chemisorbed on the anode catalyst and the oxidation reaction of hydrogen was inhibited.

  In this way, after the unit cell 1 is operated for one cycle, before the operation is stopped and restarted, the desulfurized city gas is supplied to the anode as an inert gas (purge gas) and the city gas is supplied with an oxidant gas. The anode potential is gradually increased from about 50 mV to about +0.4 V to +0.5 V (vs. SHE) (hereinafter, +0.4 V to +0.5 V (vs. SHE)). It was also referred to as “potential E1”), and the current response was examined (second cycle).

  FIG. 2 shows the cyclic voltammogram obtained by the experiment as described above, that is, the relationship between the potential (mV) of the anode with respect to the standard hydrogen electrode and the current (A). As can be seen from the cyclic voltammogram shown in FIG. 2, in the first cycle, a current in the oxidation direction starts to flow from around +0.3 V to the hydrogen reference electrode, and the CO adsorbed on the surface is oxidized electrochemically. I can see that The oxidation of CO is complete above +0.5 V with respect to the hydrogen standard electrode.

  On the other hand, in the second cycle, an electric current caused by oxidation of adsorbed hydrogen, which was not recognized in the first cycle, was observed in the potential region of +0.3 V or less, and the activity against the hydrogen oxidation reaction was recovered. Further, it can be seen that the oxidation current due to the oxidation of CO disappears. From this result, CO adsorbed on the anode catalyst begins to oxidize at a potential higher than +0.3 V with respect to the hydrogen standard electrode, and when it exceeds +0.5 V, it is completely oxidized and removed, and once CO is oxidized. After the removal, it can be seen that the activity against hydrogen oxidation, which is the original function of the anode catalyst, is restored.

  Based on the experimental results as described above, the present inventors supply an inert gas as a purge gas to the anode between the time when the fuel cell is stopped and the time when the fuel cell is started, and the potential on the anode side becomes the standard hydrogen electrode. On the other hand, it has been found that CO adsorbed to the anode catalyst can be more reliably removed by mixing the oxidant gas with the purge gas so as to be maintained at +0.4 V to +0.5 V (vs. SHE). The present invention has been completed.

That is, the present invention
A fuel cell comprising an anode, a cathode and a membrane electrode assembly having a polymer electrolyte membrane disposed between the anode and the cathode;
A fuel gas supply section for supplying fuel gas obtained by reforming fossil fuel to the anode;
A first oxidant gas supply for supplying oxidant gas to the cathode;
A purge gas supply unit for supplying an inert gas as a purge gas to the anode during a period from when the fuel cell system is stopped to when it is started;
A second oxidant gas supply unit for mixing an oxidant gas with a purge gas supplied to the anode;
During the period from when the fuel cell system is stopped to when it is started, the potential supplied to the anode is maintained so that the potential on the anode side is maintained at +0.4 V to +0.5 V (vs. SHE) with respect to the standard hydrogen electrode. A control unit for mixing the oxidizing gas with the active gas;
A fuel cell power generation system is provided.

Here, the `` fossil fuel '' in the present invention is not particularly limited as long as it is a raw material for fuel supplied to the fuel cell. For example, hydrocarbons such as ethane, methane, propane and butane, ethane, methane, Examples include natural gas and city gas (including methane as a main component and including ethane, propane, and sulfur), alcohol such as methanol, dimethyl ether, gasoline, and the like including at least one of propane and butane.
The “inert gas” refers to the fossil fuel before reforming (for example, methane or city gas) in addition to nitrogen gas and argon gas, and the fossil fuel (for example, methane) before reforming and after desulfurization. And city gas). In particular, when city gas containing sulfur as an odorant is used as an inert gas, it is preferably used after desulfurization.

  As described above, during the period from when the fuel cell system is stopped to when it is started, the oxidant gas is mixed with the inert gas supplied to the anode so that the potential on the anode side is +0.4 V to +0 with respect to the standard hydrogen electrode. By maintaining the voltage at 5 V (vs. SHE), the CO adhering to the anode catalyst during operation of the fuel cell system can be more reliably oxidized and removed during the period from when the fuel cell system is stopped to when it is started. Therefore, the activity of the catalyst of the anode of the fuel cell system that performs DSS operation including starting and stopping can be maintained more easily and reliably.

  If the potential on the anode side is maintained at +0.4 V (vs. SHE) or higher with respect to the standard hydrogen electrode, CO adsorbed on the catalyst of the anode can be more reliably oxidized and removed, and +0.5 V (vs. SHE). ) If maintained below, elution of Ru, which is suitably used as one component of the anode catalyst, for example, can be more reliably prevented, which is preferable.

The present invention also provides:
A fuel cell comprising an anode, a cathode and a membrane electrode assembly having a polymer electrolyte membrane disposed between the anode and the cathode;
A fuel gas supply section for supplying fuel gas obtained by reforming fossil fuel to the anode;
A first oxidant gas supply unit for supplying an oxidant gas to the cathode;
An external power source connected to the anode and cathode;
Control for controlling the external power supply so that the anode side potential is maintained at +0.4 V to +0.5 V (vs. SHE) with respect to the standard hydrogen electrode during the period from when the fuel cell system is stopped to when it is started. Part;
There is also provided a fuel cell power generation system characterized by comprising:

  As described above, the potential on the anode side is maintained at +0.4 V to +0.5 V (vs. SHE) with respect to the standard hydrogen electrode by the external power source between the stop time and the start time of the fuel cell system. According to the above, it is possible to more reliably oxidize and remove CO adhering to the anode catalyst during the operation of the fuel cell system during the period from the stop of the fuel cell system to the start of the fuel cell system. The activity of the catalyst of the anode of the fuel cell system that performs the above can be maintained more easily and reliably.

  The fuel cell in the fuel cell system of the present invention can maintain the generation of high electromotive force, and as a result, the power generation energy efficiency can be improved. In addition, since poisoning and deactivation of the anode catalyst by CO can be continuously recovered, a fuel cell system that can be used maintenance-free for a longer period of time than before can be realized.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

[First Embodiment]
FIG. 3 is a diagram showing the configuration of the first embodiment of the fuel cell system of the present invention. First, the components of the fuel cell system 1 shown in FIG. 3 will be described. FIG. 1 is a schematic cross-sectional view showing a configuration of an example of a unit cell mounted on a fuel cell 21 used in the fuel cell system of the present embodiment. As shown in FIG. 3, the fuel cell system 1 of the present embodiment includes a fuel cell 21, a fuel gas supply unit 22, a first oxidant gas supply unit 24, a purge gas supply unit 23, a second oxidant gas supply unit 25, And a control unit 26.

  The fuel cell 21 is a unit cell including an anode 21a, a cathode 21b, and a membrane / electrode assembly having a polymer electrolyte membrane 21c having a cation (hydrogen ion) conductivity and disposed between the anode 21a and the cathode 21b. It is composed of a laminate (fuel cell stack). The configuration of the unit cell is as described above with reference to FIG.

  The fuel cell 21 in the first embodiment shown in FIG. 1 is mainly composed of a membrane electrode assembly 5 (hereinafter referred to as “MEA 5” as necessary) and a pair of plate-like conductive separators that sandwich the membrane electrode assembly 5. (That is, the anode side separator 6a and the cathode side separator 6b), the anode side gasket 9a arranged around the anode 4a of the membrane electrode assembly 5, and the cathode side arranged around the cathode 4b of the membrane electrode assembly 5 And a configuration including at least one unit cell including the gasket 9b.

  The polymer electrolyte membrane 1 is a solid electrolyte and has hydrogen ion conductivity that selectively transports hydrogen ions. In the membrane / electrode assembly 5 during power generation, hydrogen ions generated at the anode 4a move through the polymer electrolyte membrane 1 toward the cathode 4b. The polymer electrolyte membrane 1 is not particularly limited, and a polymer electrolyte membrane mounted on a normal solid polymer fuel cell can be used. For example, a polymer electrolyte membrane made of perfluorocarbon sulfonic acid (for example, Nafion (trade name) manufactured by DuPont, USA, Flemion (trade name) and Aciplex (trade name) manufactured by Asahi Glass Co., Ltd., Japan Gore-Tex Co., Ltd.) Manufactured by GSII, etc.).

  Preferred examples of the cation exchange group of the polymer electrolyte membrane 1 include those having a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, and a sulfonimide group. From the viewpoint of proton conductivity, the polymer electrolyte membrane 1 preferably has a sulfonic acid group.

  The resin constituting the polymer electrolyte membrane having a sulfonic acid group is preferably a dry resin having an ion exchange capacity of 0.5 to 1.5 meq / g. It is preferable that the ion exchange capacity of the polymer electrolyte membrane is 0.5 meq / g dry resin or more because an increase in the resistance value of the polymer electrolyte membrane during power generation can be more sufficiently reduced, and the ion exchange capacity is 1.5 meq / g. It is preferable that it is less than g dry resin, since it is easy to sufficiently ensure good gas diffusion characteristics in the catalyst layer while keeping the moisture content of the polymer electrolyte membrane appropriately. From the same viewpoint as described above, the ion exchange capacity is particularly preferably 0.8 to 1.2 meq / g dry resin.

_{Polyelectrolytes, CF 2 = CF- (OCF 2} CFX) m-Op- (CF 2) a perfluorovinyl compound represented by the n-SO ₃ H (m is an integer of 0 to 3, n is 1 An integer of ˜12, p is 0 or 1, and X is a fluorine atom or a trifluoromethyl group.) And a copolymer comprising a polymer unit based on tetrafluoroethylene. Is preferred.

Preferable examples of the fluorovinyl compound include compounds represented by the following formulas (1) to (3). However, in the following formula, q is an integer of 1 to 8, r is an integer of 1 to 8, and t is 1 to 8.
An integer of 3 is shown.
_{CF 2 = CFO (CF 2)} q-SO 3 H ··· (1)
_{CF 2 = CFOCF 2 CF (CF} 3) O (CF 2) r-SO 3 H ··· (2)
_{CF 2 = CF (OCF 2 CF} (CF 3)) tO (CF 2) 2 -SO 3 H ··· (3)
Moreover, the polymer electrolyte membrane 1 may be comprised with 1 type or multiple types of polymer electrolyte.

  The polymer electrolyte membrane 1 may include a reinforcing body (filler) disposed in a state in which hydrogen ion conduction can be ensured from the viewpoint of ensuring sufficient mechanical strength. Examples of the material constituting such a reinforcing body include polytetrafluoroethylene or polyfluoroalkoxyethylene. Examples of the reinforcing body include a porous body having pores that can be filled with a polymer electrolyte (having hydrogen ion conductivity) or a fibrillar fiber.

  Fibril-like fibers are fibers in which fibrils (small fibers) existing on the surface are fluffed (fibrillated), and there are fine air grooves (holes) between each fibril. It refers to the fibers that are formed. For example, all cellulosic fibers are bundles of many fibrils, and there are fine air grooves (holes) between the fibrils.

  As shown in FIG. 1, the cathode 4b is mainly composed of a catalyst layer 2b (cathode catalyst layer 2b) disposed on the main surface of the polymer electrolyte membrane 1, and a gas disposed further outside the catalyst layer 2b. And a diffusion layer 3b (cathode diffusion layer 3b).

  The structure of the catalyst layer 2b is not particularly limited as long as the effects of the present invention can be obtained, and may have the same structure as the catalyst layer of the gas diffusion electrode mounted on a known fuel cell. For example, the cathode catalyst layer 2b may have a configuration including conductive carbon particles carrying an electrode catalyst and a polymer electrolyte having cation (hydrogen ion) conductivity. You may have the structure containing water-repellent materials, such as polytetrafluoroethylene. In addition, as a polymer electrolyte, the same kind as the constituent material of the polymer electrolyte membrane 1 mentioned above may be used, and a different kind may be used. As a polymer electrolyte, what was described as a constituent material of the polymer electrolyte membrane 1 can be used.

  The cathode electrode catalyst is made of metal particles (for example, metal particles made of a noble metal) and used by being supported on conductive carbon particles (powder). The metal particles are not particularly limited and various metals can be used, but from the viewpoint of electrode reaction activity, platinum, gold, silver, ruthenium, rhodium, palladium, osmium, iridium, chromium, iron, titanium, manganese It is preferably at least one selected from the group consisting of cobalt, nickel, molybdenum, tungsten, aluminum, silicon, zinc and tin.

  The electrode catalyst particles more preferably have an average particle size of 1 to 5 nm. An electrode catalyst having an average particle diameter of 1 nm or more is preferable because it is easy to prepare industrially, and if it is 5 nm or less, the activity per mass of the electrode catalyst is more easily secured, thereby reducing the cost of the fuel cell. Connection is preferable.

The conductive carbon particles preferably have a specific surface area of 50 to 1500 m ² / g. If the specific surface area is 50 m ² / g or more, it is easy to increase the supporting rate of the electrode catalyst, preferably because it can more sufficiently ensure the output characteristics of the resulting cathode catalyst layer 2b, a specific surface area of 1500 m ² / It is preferable that the pore size is not more than g because sufficiently large pores can be secured more easily and coating with a polymer electrolyte becomes easier, and the output characteristics of the cathode catalyst layer 2b can be more sufficiently secured. From the same viewpoint as described above, the specific surface area is particularly preferably 200 to 900 m ² / g.

  The conductive carbon particles preferably have an average particle size of 0.1 to 1.0 μm. When the thickness is 0.1 μm or more, gas diffusibility in the cathode catalyst layer 2b is more easily secured, and flooding can be prevented more reliably. In addition, when the average particle diameter of the conductive carbon particles is 1.0 μm or less, it becomes easy to easily make the electrode catalyst covered with the polymer electrolyte in a good state, and the electrode catalyst covered area with the polymer electrolyte is more increased. Since it becomes easy to ensure enough, it becomes easy to ensure sufficient electrode performance more and is preferable.

  As the gas diffusion layer 3b, a conductive substrate having a porous structure, which is made using a high surface area carbon fine powder, a pore former, carbon paper, carbon cloth, or the like in order to give gas permeability. It may be used. Further, from the viewpoint of obtaining sufficient drainage, a water repellent polymer such as a fluororesin may be dispersed in the gas diffusion layer 3b. Furthermore, from the viewpoint of obtaining sufficient electron conductivity, the gas diffusion layer 3b may be made of an electron conductive material such as carbon fiber, metal fiber, or carbon fine powder.

  On the other hand, the anode 4a is mainly composed of a catalyst layer 2a (anode catalyst layer 2a) disposed on the main surface of the polymer electrolyte membrane 1 and a gas diffusion layer 3a (anode) further disposed outside the catalyst layer 2a. A diffusion layer 3a).

  The catalyst layer 2a includes a catalyst-supporting carbon obtained by supporting an electrode catalyst on carbon powder, and a polymer electrolyte having hydrogen ion conductivity. It does not specifically limit as an anode electrode catalyst, The electrode catalyst used for the anode of a well-known polymer electrolyte fuel cell can be used. For example, metal fine particles containing Pt constituent elements may be used, and metal fine particles containing Pt and Ru as constituent elements are preferably used in order to provide good durability against carbon monoxide.

  The configuration of the gas diffusion layer 3a is not particularly limited as long as the effects of the present invention can be obtained. Even if the gas diffusion layer 3a has the same configuration as the gas diffusion layer of a gas diffusion electrode mounted on a known fuel cell. Good. For example, it may have the same configuration as the gas diffusion layer 3b (cathode diffusion layer 3b) described above. The configuration of the gas diffusion layer 3a and the configuration of the gas diffusion layer 3b may be the same or different.

  As shown in FIG. 1, the MEA 5 has a main surface of the polymer electrolyte membrane 1 having a size of the anode 4a and the cathode 4b from the viewpoint of arranging the anode side gasket 9a and the cathode side gasket 9b for preventing gas leakage. And the entire outer edge portion of the polymer electrolyte membrane 1 protrudes outward from the outer edge ends of the anode 4a and the cathode 4b.

  Hereinafter, the anode side separator 6a and the cathode side separator 6b will be described. The anode-side separator 6a and the cathode-side separator 6b have conductivity, and when the MEA 5 is mechanically fixed and a plurality of unit cells are stacked and used, the adjacent MEAs 5 are electrically connected to each other in series. To connect.

  The anode 4a is provided with a gas flow path 7a for supplying a reaction gas (fuel gas) to the anode 4a and carrying a gas containing a product generated by the electrode reaction or an unreacted reactant to the outside of the MEA 5. That is, it is formed on the main surface on the side in contact with the MEA 5 of the anode separator 6a. A gas flow path 7b for supplying a reaction gas (oxidant gas) to the cathode 4b and carrying a product including an electrode reaction or a gas containing an unreacted reaction outside the MEA 5 is provided on one side ( That is, the cathode side separator 6b is formed on the main surface on the side in contact with the MEA 5.

  Further, a cooling fluid (cooling water or the like) for adjusting the battery temperature during power generation to a substantially constant level is introduced into the main surface opposite to the main surface where the gas flow path 7a of the anode separator 6a is formed. For this purpose, a cooling fluid flow path 8a is formed. Further, a cooling fluid (cooling water or the like) for adjusting the battery temperature during power generation to a substantially constant level is introduced into the main surface opposite to the main surface where the gas flow path 7b of the cathode separator 6b is formed. For this purpose, a cooling fluid flow path 8b is formed. By adopting a configuration in which the cooling fluid is circulated between the fuel cell and a heat exchanger (not shown) disposed outside, the heat energy generated by the reaction can be used in the form of hot water or the like.

  Due to the advantage that the manufacturing process can be simplified, the gas flow path 7a is formed by providing a groove on the main surface of the anode side separator 6a on the side in contact with the MEA 5. Further, for the same advantage as described above, the cooling fluid flow path 8a is also formed by providing a groove on the main surface opposite to the main surface where the gas flow path 7a of the anode separator 6a is formed. Furthermore, for the same advantages as described above, the gas flow path 7b is also formed by providing a groove on the main surface of the cathode separator 6b on the side in contact with the MEA 5. Further, for the same advantages as described above, the cooling fluid flow path 8b is also formed by providing a groove on the main surface opposite to the main surface where the gas flow path 7b of the cathode side separator 6b is formed. It is formed by providing a groove.

  Since the voltage value that can be output by one unit cell 10 is limited (theoretically, when hydrogen gas is used as the reducing agent and oxygen is used as the oxidizing agent, about 1.23 V), a desired output voltage is set according to the use environment. From the viewpoint of obtaining, for example, a fuel cell stack 30 shown in FIG. 4 is used in the fuel cell system of the present embodiment. In particular, in the case of the fuel cell stack 30 shown in FIG. 4, all the fuel cells constituting this are the single cells 10 shown in FIG.

  As shown in FIG. 4, the fuel cell stack 30 is obtained by interposing an anode-side separator 6a and a cathode-side separator 6b between a plurality of MEAs 5 and electrically stacking the plurality of MEAs 5 in series. In this case, in order to configure the fuel cell stack 30, the reaction gas supplied to the fuel cell stack 30 through an external gas line (not shown) is further branched and supplied to each MEA 5 from each MEA 5. A manifold for exhausting the exhausted gases collectively to the outside of the fuel cell stack 30, and an anode by branching the cooling fluid supplied to the fuel cell stack 30 to a required number through an external cooling fluid line (not shown) A manifold for supplying at least one of the side separator 6a and the cathode side separator 6b is required.

  Therefore, although not shown, the anode-side separator 6a and the cathode-side separator 6b are conventionally provided with a fuel gas supply manifold hole, a fuel gas discharge manifold hole, a cooling fluid supply manifold hole, a cooling fluid discharge manifold hole, an oxidation An agent gas supply manifold hole and an oxidant gas discharge manifold hole are provided.

  Further, in the anode side separator 6a of each unit cell 10, one end of the cooling fluid flow path 8a is connected to the cooling fluid supply manifold hole, and the other end is connected to the cooling fluid discharge manifold hole. Further, in the anode separator 6a of each fuel cell, one end of the gas flow path 7a is connected to the fuel gas supply manifold hole, and the other end is connected to the fuel gas discharge manifold hole.

  Further, in the cathode separator 6b of each fuel cell 10, one end of the cooling fluid flow path 8b is connected to the oxidant gas supply manifold hole and the other end is connected to the oxidant gas discharge manifold hole. Further, in the cathode separator 6b of each fuel cell, one end of the gas flow path 7b is connected to the oxidant gas supply manifold hole, and the other end is connected to the oxidant gas discharge manifold hole.

  As shown in FIG. 1, in the unit cell 10, the reaction gas leaks (fuel gas leaks to the cathode 4 b side, oxidant gas leaks to the anode 4 a side, reaction gas leaks to the outside of the MEA 5, etc.). In order to prevent gas from flowing between the anode-side separator 6a and the cathode-side separator 6b facing each other, gas is introduced into the outer edge of the MEA 5 (the outside of the anode 4a and the cathode 4b and the protruding portion P of the polymer electrolyte membrane 1). A pair of opposing gaskets having a sealing function, that is, an anode side gasket 9a and a cathode side gasket 9b are arranged.

  These anode side gasket 9a and cathode side gasket 9b have, for example, a continuous annular structure (ring-shaped structure) having a substantially rectangular cross-sectional shape, and the outer peripheral edge portion of the polymer electrolyte membrane 1 described above. Is sandwiched. The anode-side separator 6a, the polymer electrolyte membrane 1, and the anode-side gasket 9a form one closed space that encloses the anode 4a. The cathode-side separator 6b, the polymer electrolyte membrane 1, and the cathode-side gasket 9b form the cathode 4b. Another closed space is formed to envelop. These closed spaces prevent gas leakage of the reaction gas supplied to the anode 4a and the cathode 4b.

  The constituent material of the anode side gasket 9a and the cathode side gasket 9b is not particularly limited as long as it has an excellent gas sealing property, and those used for gaskets of known polymer electrolyte fuel cells are used. can do. For example, the anode side gasket 9a and the cathode side gasket 9b are conventionally known using O-rings, rubber-like sheets (sheets made of fluoro rubber, etc.), composite sheets of elastic resin and rigid resin, fluorine-based synthetic resin sheets, and the like. It can produce by this method.

In the case of the fuel cell stack 30 shown in FIG. 4, an end separator 6c is disposed outside the unit cell 10 disposed at the end. As shown in FIG. 4, when the outer separator of the unit cell 10 disposed at the end is the cathode separator 6b, the inner surface of the end separator 6c disposed further outside is cooled on the cathode separator 6b. A cooling fluid channel 8d is formed which is coupled to the fluid channel 8b over the entire region to define the cooling fluid channel 8e.
More specifically, the cooling fluid channel 8b and the cooling fluid channel 8d are mirror images of each other on the contact surface between the cathode separator 6b and the end separator 6c.

  By disposing the end separator 6c, the cooling fluid channel outside the separator outside the unit cell 10 disposed at the end can also be used as the cooling fluid channel. In addition, when the single cell 10 can be sufficiently cooled without using the cooling fluid channel outside the separator outside the single cell 10 disposed at the end, the cooling fluid channel (in the case of FIG. 4, the cooling fluid channel is used). A configuration may be adopted in which the cooling fluid does not flow through the fluid flow path 8e), and another end separator having a convex portion blocking the cooling fluid flow path outside the separator outside the fuel cell 10 disposed at the end may be disposed. Alternatively, only the separator outside the unit cell 10 arranged at the end may be provided with a cooling fluid channel (in the case of FIG. 4, the cooling fluid channel 8e), and an end separator may not be arranged. The end separator may also function as a current collector. Moreover, you may arrange | position the flat end separator which does not provide the cooling fluid flow path 8e instead of the end separator 6c of FIG.

  Further, the gas flow paths 7a and 7b and the cooling fluid flow paths 8a and 8b provided in the anode-side separator 6a and the cathode-side separator 6b may have a conventionally known shape. For example, in order to effectively use the main surface (for example, a substantially rectangular main surface) of the separator, the separator can be constituted by a continuous groove having a serpentine structure, for example.

Next, a method for manufacturing the unit cell 10 and the fuel cell stack 30 will be described.
First, the membrane electrode assembly 5 is manufactured. The manufacturing method of the membrane electrode assembly 5 is not particularly limited, and the membrane electrode assembly 5 can be manufactured using a thin film manufacturing technique that has been adopted again for manufacturing a membrane electrode assembly of a known polymer electrolyte fuel cell. . For example, the cathode catalyst layer 2b can be formed by preparing a cathode catalyst layer forming paste exemplified below. That is, for example, carbon particles supporting 50 wt% of Pt are used as a catalyst, and a cation exchange resin solution, for example, a fluorine-based sulfonic acid polymer resin solution having the same quality as the polymer electrolyte membrane 1 (for example, a solid content of 10 wt% of the resin) The mixture of ethanol and water is gradually added, and carbon particles supporting Pt are mixed until the solid content of the resin per unit area of the catalyst is, for example, 2 mg / m ^2, thereby forming the cathode catalyst layer. To paste for.

  The amount of the cation exchange resin solution contained in the cathode catalyst layer forming paste varies depending on the specific surface area, pore size, and dispersibility of the carbon particles. The greater the specific surface area and the better the dispersibility, the greater the amount of resin. For example, the optimum resin amount decreases when the specific surface area is large due to pores that are so small that the resin cannot enter. For example, in the case of ketjen black, the optimum resin amount per unit g is 1.4 g / g. Further, if the type of carbon used is crystallized or graphitized, it is more desirable because it can suppress the oxidation of carbon.

  The anode catalyst layer 2a can be formed by adjusting an anode catalyst layer forming paste exemplified below. In the case of using catalyst-carrying carbon in which the anode electrode catalyst is carried on carbon powder, the anode catalyst layer forming paste carries fine particles containing Pt and Ru as constituent elements instead of the carbon particles carrying Pt. What is necessary is just to prepare by the method similar to the paste for cathode catalyst layer formation mentioned above except using a carbon particle.

  More specifically, an anode electrode catalyst is obtained by supporting fine particles containing Pt and Ru as constituent elements as an electrode catalyst on carbon, and this is used as a cation exchange resin solution, for example, a fluorine-based sulfone having the same quality as the polymer electrolyte membrane 1. An acid polymer resin solution (for example, a solution in which a solid content of 10 wt% of the resin is mixed in a mixed solution of ethanol and water) is gradually added to prepare. When the catalyst-supported carbon in which the anode electrode catalyst is supported on carbon powder is used, the amount of the cation exchange resin solution contained in the anode catalyst layer forming paste is the same as that of the cathode catalyst layer forming paste described above. Can be used.

  Next, the cathode catalyst layer forming paste or the anode catalyst layer forming paste prepared by the manufacturing method described above is applied to a synthetic resin film such as a PP film by a bar coater and then dried. After drying, it is cut into a desired electrode size and transferred to the polymer electrolyte membrane by hot pressing to form the cathode catalyst layer 2b and the anode catalyst layer 2a. The method of forming the catalyst layer is not limited to this method, and a method of printing the catalyst layer paste on the film, a method of spraying the catalyst layer paste on the film, or the like may be used. At that time, the polymer electrolyte membrane used is not particularly limited, and as described above, a polymer electrolyte exchange membrane having a sulfonic acid group can be used.

  Further, the gas diffusion layer 3a and the gas diffusion layer 3b are laminated on the outside of the anode catalyst layer 2a or the cathode catalyst layer 2b so as to be in the state shown in FIG. 1 by using a conventionally known thin film laminate manufacturing method. . Next, the polymer electrolyte membrane 1 is disposed between the anode 4a and the cathode 4b. At this time, the gasket 9a and the gasket 9b are disposed around the anode 4a and the cathode 4b. Next, the anode-side separator 6a and the cathode-side separator 6b are arranged on the outside of the membrane electrode assembly 9 as shown in FIG. Next, the fuel cell stack 30 as shown in FIG. 4 is manufactured by stacking a plurality of unit cells 10.

Next, components other than the fuel cell 21 in the fuel cell system of the present embodiment will be described.
First, the fuel gas supply unit 22 supplies fuel gas obtained by reforming fossil fuel to the anode 21 a side of the fuel cell 21. Here, as described above, the “fossil fuel” is not particularly limited as long as it is a raw material of the fuel supplied to the fuel cell. For example, hydrocarbons such as ethane, methane, propane and butane, ethane, Natural gas and city gas (including methane as a main component and including ethane, propane, and sulfur), alcohol such as methanol, dimethyl ether, gasoline, and the like including at least one of methane, propane, and butane .

  As the fuel gas supply unit 22, for example, a unit having a reformer, a shift unit, and a CO oxidation unit in the order of the reformer, the shift unit, and the CO oxidation unit from the upstream side to the downstream side can be used. Moreover, conventionally well-known thing can be used as a modification part, a modification part, and a CO oxidation part. In the reforming section, several percent of CO is generated together with hydrogen by the catalytic reaction of fossil fuel accompanied by water vapor. Thereafter, the generated CO is oxidized to carbon dioxide at the metamorphic part and reduced to several thousand ppm. Further, the remaining CO is oxidized in the most downstream CO oxidation section, and the concentration thereof is reduced to about 20 ppm or less. Although not shown, the fuel gas supply unit 22 is provided with a flow rate control device such as an electromagnetic valve.

  Next, the first oxidant gas supply unit 24 supplies an oxidant gas (for example, air) to the cathode 21 b side of the fuel cell 21. As the first oxidant gas supply unit 24, one having the same configuration as the conventional one can be used. Although not shown, the first oxidant gas supply unit 24 is provided with a flow rate control device such as an electromagnetic valve.

  The purge gas supply unit 23 supplies an inert gas as a purge gas to the anode 21a side of the fuel cell 21 during the period from when the fuel cell system 1 is stopped to when it is started. As used herein, the term “inert gas” refers to the fossil fuel (for example, methane and city gas) before reforming, as well as nitrogen gas and argon gas, as well as before reforming and after desulfurization. Any of the fossil fuels (for example, methane and city gas) may be used. In particular, when a city gas containing sulfur as an odorant is used as the fossil fuel, the city gas can also be used as an inert gas. In this case, the city gas is desulfurized and then used as a purge gas. It is preferable to use it.

  Therefore, although not shown, the purge gas supply unit 23 preferably includes a desulfurization unit. As a desulfurization part, the thing similar to the past can be used. Although not shown, the purge gas supply unit 23 is provided with a flow rate control device such as an electromagnetic valve.

  Further, the fuel gas supply unit 22 may also serve as the purge gas supply unit 23. For example, when the fuel gas supply unit 22 reforms, transforms, and removes CO to generate fuel gas, and supplies the fuel gas to the anode 21a side of the fuel cell 21, the city gas is used as the fuel gas. The city gas from the supply unit 22 may be supplied as it is to the anode 21a as an inert gas and a purge gas. Therefore, in this case, although not shown, it is preferable that the fuel gas supply unit 22 includes the desulfurization unit.

  Next, the second oxidant gas supply unit 25 mixes an oxidant gas (for example, air) with the purge gas supplied to the anode 21a. The second oxidant gas supply unit 25 only needs to have the same configuration as the first oxidant gas supply unit 24, and the first oxidant gas supply unit 24 corresponds to the second oxidant gas supply unit 25. It may also serve as. Although not shown, the second oxidant gas supply unit 25 is provided with a flow rate control device such as an electromagnetic valve.

  The control unit 26 is connected to the fuel cell 21, the fuel gas supply unit 22, the first oxidant gas supply unit 24, the purge gas supply unit 23, and the second oxidant gas supply unit 25, and controls them. It is. Specifically, the control unit 26 determines that the potential on the anode 21a side is +0.4 V to +0.5 V with respect to the standard hydrogen electrode between the stop time and the start time of the fuel cell system 1 (particularly the fuel cell 21). The oxidant gas is mixed with the inert gas supplied to the anode 21a so as to be held at (vs. SHE).

  As described above, the oxidant gas is mixed with the inert gas supplied to the anode 21a during the period from when the fuel cell system 1 is stopped to when it is started, so that the potential on the anode 21a side is +0 with respect to the standard hydrogen electrode. By holding at 4 V to +0.5 V (vs. SHE), the CO adhering to the catalyst of the anode during the operation of the fuel cell system 1 is more reduced between the time when the fuel cell system 1 is stopped and the time when it is started. Oxidation and removal can be reliably performed, and the activity of the catalyst of the anode of the fuel cell system that performs DSS operation including starting and stopping can be more easily and reliably maintained.

  If the potential on the anode side is maintained at +0.4 V (vs. SHE) or higher with respect to the standard hydrogen electrode, CO adsorbed on the catalyst of the anode can be more reliably oxidized and removed, and +0.5 V (vs. SHE). ) If maintained below, elution of Ru, which is suitably used as one component of the anode catalyst, for example, can be more reliably prevented, which is preferable. Although not particularly illustrated, the control unit 26 includes a storage unit, a central processing unit (CPU), and the like. A program relating to the operation of each component of the fuel cell system 1 is stored in advance in the storage unit of the control unit 26, and the control unit 26 controls the fuel cell system 1 based on the program stored in the storage unit. Is appropriately controlled.

  As described above, according to this embodiment, during the period from when the fuel cell system is stopped to when it is started, the oxidant gas is mixed with the inert gas supplied to the anode so that the potential on the anode side becomes the standard hydrogen electrode. On the other hand, by holding at + 0.4V to + 0.5V (vs. SHE), CO adhering to the catalyst of the anode during operation of the fuel cell system is reduced between the time when the fuel cell system is stopped and the time when it is started. Oxidation can be removed more reliably, and the activity of the catalyst of the anode of the fuel cell system that performs DSS operation including start and stop can be more easily and reliably maintained.

[Second Embodiment]
Next, a second embodiment of the fuel cell system of the present invention will be described. The fuel cell system of the second embodiment is provided with an external power source except for the purge gas supply unit and the second oxidant gas supply unit in the fuel cell system 1 of the first embodiment shown in FIG. Other configurations are the same as those of the fuel cell system 1 of the first embodiment.

  The control unit 26 in the present embodiment is detachably connected to the fuel cell 21, the fuel gas supply unit 22, the first oxidant gas supply unit 24, and the external power source 27, and controls them. Specifically, the control unit 26 determines that the potential on the anode 21a side is +0.4 V to +0.5 V with respect to the standard hydrogen electrode between the stop time and the start time of the fuel cell system 1 (particularly the fuel cell 21). The external power supply 27 is controlled so as to be held at (vs. SHE). As this external power supply 27, the thing of the structure similar to the past can be used.

  As described above, during the period from when the fuel cell system 1 is stopped to when it is started, the potential on the anode 21a side is set to +0.4 V to +0.5 V (vs. SHE) with respect to the standard hydrogen electrode by the external power source 27. By holding, CO attached to the anode catalyst during operation of the fuel cell system 1 can be more reliably oxidized and removed during the period from when the fuel cell system 1 is stopped to when it is started. The activity of the catalyst of the anode of the fuel cell system that performs the DSS operation including can be more easily and reliably maintained.

  As described above, according to this embodiment, during the period from when the fuel cell system is stopped to when it is started, the oxidant gas is mixed with the inert gas supplied to the anode so that the potential on the anode side becomes the standard hydrogen electrode. On the other hand, by holding at + 0.4V to + 0.5V (vs. SHE), CO adhering to the catalyst of the anode during operation of the fuel cell system is reduced between the time when the fuel cell system is stopped and the time when it is started. Oxidation can be removed more reliably, and the activity of the catalyst of the anode of the fuel cell system that performs DSS operation including start and stop can be more easily and reliably maintained.

The fuel cell system of the present invention can be suitably used for, for example, a stationary fuel cell system that performs DSS operation in which start and stop are frequently performed.

It is a schematic sectional drawing which shows the structure of an example of the single cell mounted in the fuel cell used for the fuel cell system of this invention. FIG. 2 is a diagram (cyclic voltammogram) showing a relationship between an anode versus standard hydrogen electrode potential (mV) and current (A) as an experiment using the test cell using the single battery shown in FIG. 1. It is a figure which shows the structure of 1st Embodiment of the fuel cell system of this invention. It is a schematic sectional drawing which shows the structure of an example of the fuel cell used for the fuel cell system of this invention. It is a figure which shows the structure of 2nd Embodiment of the fuel cell system of this invention. It is a schematic sectional drawing which shows the single cell which is the general basic composition of the conventional fuel cell. It is a figure which shows the structure of the conventional fuel cell system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101 ... Polymer electrolyte membrane, 2a, 102a ... Anode catalyst layer, 2b, 102b ... Cathode catalyst layer, 3a, 103a ... Anode gas diffusion layer, 3b, 103b ... Cathode gas diffusion Layer, 4a, 104a ... Anode, 4b, 104b ... Cathode 5, 105 ... Membrane electrode assembly, 6a, 106a ... Anode side separator, 6b, 106b ... Cathode side separator, 7a 7b, 107a, 107b ... gas flow path, 8a, 8b, 108a, 108b ... cooling fluid flow path, 21, 121 ... fuel cell, 21a ... anode, 21b ... cathode, 22 ... Fuel gas supply unit, 23 ... Purge gas supply unit, 24 ... First oxidant gas supply unit, 25 ... Second oxidant gas supply unit, 26 ... Control unit, 122 ..Desulfurization section, 123 ... reforming section, 124 ... transforming section, 125 ... CO oxidation section, 126a, 126b, 126c, 126d ... flow rate control section, 27, 127 ... external power source .

Claims (2)

A fuel cell comprising an anode, a cathode, and a membrane electrode assembly having a polymer electrolyte membrane disposed between the anode and the cathode;
A fuel gas supply unit for supplying fuel gas obtained by reforming fossil fuel to the anode;
A first oxidant gas supply unit for supplying the oxidant gas to the cathode;
A purge gas supply unit for supplying an inert gas as a purge gas to the anode during a period from when the fuel cell system is stopped to when it is started;
A second oxidant gas supply unit for mixing an oxidant gas with the purge gas supplied to the anode;
Supplied to the anode so that the potential on the anode side is maintained at +0.4 V to +0.5 V (vs. SHE) with respect to the standard hydrogen electrode during the period from the stop to the start of the fuel cell system A controller for mixing the oxidant gas with the inert gas;
A fuel cell power generation system comprising: A fuel cell comprising an anode, a cathode, and a membrane electrode assembly having a polymer electrolyte membrane disposed between the anode and the cathode;
A fuel gas supply unit for supplying fuel gas obtained by reforming fossil fuel to the anode;
A first oxidant gas supply unit for supplying the oxidant gas to the cathode;
An external power source connected to the anode and the cathode;
The external power supply is set so that the anode side potential is maintained at +0.4 V to +0.5 V (vs. SHE) with respect to the standard hydrogen electrode during the period from when the fuel cell system is stopped to when it is started. A control unit to control;
A fuel cell power generation system comprising:

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