JP2005294107A - Fuel cell and fuel cell system using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell which is capable of generating power stably for a long period by suppressing permeation of nitrogen through electrolyte membrane and has a high generating efficiency against hydrogen gas supply volume, and a fuel cell system using this. <P>SOLUTION: The fuel cell 10 has an anode electrode 12 which has a catalyst layer 12A having a catalyst and is supplied with hydrogen, a cathode electrode which has a catalyst layer 14A having a catalyst and is supplied with air, and an electrolyte membrane 16 clipped by the anode electrode 12 and the cathode electrode 14. An oxygen enrichment membrane 24 for separating oxygen selectively from the air is provided at the cathode electrode 14. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell and a fuel cell system using the same, and more particularly to a fuel cell suitable for a dead end system in which hydrogen gas is not circulated in an anode electrode and a fuel cell system using the same.

  In recent years, reserves of fossil fuels have drastically decreased, and development of alternative fuels has been demanded. As an alternative fuel for fossil combustion, hydrogen, which can be easily generated and has a low environmental impact, has attracted attention. As an energy source using hydrogen gas, a fuel cell which does not generate carbon dioxide during power generation and is a clean energy source has attracted attention, and various developments have been actively conducted.

  A polymer electrolyte fuel cell, which is a type of fuel cell, includes an anode electrode supplied with a fuel gas such as hydrogen, a cathode electrode supplied with an oxidant gas such as air, and an electrolyte membrane sandwiched between the electrodes. Each electrode is provided with a catalyst such as platinum. The polymer electrolyte fuel cell generates electricity by electrochemically reacting hydrogen and oxygen on a catalyst provided on an electrode.

  In the conventional polymer electrolyte fuel cell, in order to increase the utilization efficiency of hydrogen gas, surplus hydrogen gas or the like (anode offgas) that did not contribute to the electrochemical reaction at the anode electrode is mixed again into the hydrogen gas to the anode electrode. Many supply hydrogen gas circulation systems are adopted.

  On the other hand, air is supplied as an oxidant to the cathode electrode of the polymer electrolyte fuel cell. Usually, the air supplied to the cathode electrode contains a large amount of nitrogen gas together with oxygen gas. However, since nitrogen gas easily passes through the electrolyte membrane of the polymer electrolyte fuel cell, it passes through the electrolyte membrane and moves to the anode electrode. When the amount of nitrogen gas transferred increases, the reaction of hydrogen gas on the catalyst at the anode electrode is hindered, and the power generation efficiency of the fuel cell with respect to the amount of hydrogen gas supplied decreases.

  In a fuel cell employing the above hydrogen gas circulation system, since hydrogen gas is circulated, even if nitrogen gas has moved to the anode electrode, the hydrogen concentration in the circulation line is saturated, so that nitrogen permeation is prevented. It is suppressed.

  However, in such a state, it is necessary to supply more hydrogen gas than the consumption necessary for power generation of the fuel cell, and as a result, the utilization efficiency of hydrogen gas decreases.

  On the other hand, in recent years, a dead end system that does not circulate hydrogen gas in the anode electrode has attracted attention. According to such a dead end method, it is only necessary to supply hydrogen gas to the fuel cell in an amount necessary for power generation, the supply amount of hydrogen gas can be reduced to the required amount, and the utilization efficiency of hydrogen gas can be further increased. it can. Further, according to the dead end method, since it is not necessary to provide a circulation mechanism for supplying anode off gas to the anode electrode again, the fuel cell system can be simplified and miniaturized.

  However, in such a dead-end system, hydrogen gas is not circulated at the anode electrode, so the hydrogen concentration is less likely to be saturated on the hydrogen gas supply side of the anode electrode, and nitrogen gas permeation is suppressed compared to the hydrogen gas circulation system. There is a problem that it is difficult. For this reason, conventionally, when the nitrogen concentration in the anode electrode exceeds a certain level, it is necessary to release the shut valve for a certain period of time and to discharge hydrogen gas containing nitrogen gas out of the system.

  In order to prevent such permeation of nitrogen gas through the electrolyte membrane, a method has been proposed in which oxygen-enriched air enriched in advance with an oxygen concentration in the air is supplied to the fuel cell. As a technique for supplying oxygen-enriched air to the fuel cell in this way, an oxygen separator that concentrates oxygen in the air is installed on the cathode supply side of the fuel cell stack, and oxygen-enriched gas is supplied to the cathode side. At the same time, the use of nitrogen-enriched gas for reformer combustion gas, recovered water degassing gas, etc., aims to improve equipment power generation efficiency by reducing equipment costs, reducing plant size, and reducing power loss A fuel cell power generation system has been proposed (see, for example, Patent Document 1).

  According to such a fuel cell power generation system, oxygen-enriched air can be supplied to the fuel cell, so that it is estimated that nitrogen gas permeation of the electrolyte membrane can be suppressed to some extent. However, since it is necessary to provide an oxygen separation device that condenses the oxygen concentration in the air as an external device, it is necessary to increase the size of the device and increase the number of pipes and parts, and the oxygen separator has a resistance to passage. It increases, and the energy efficiency of the entire system decreases.

JP 2000-67891 A

  In order to solve the above-mentioned problems, the present invention can suppress the permeation of nitrogen gas through an electrolyte membrane and stably generate power over a long period of time, and has a high power generation efficiency with respect to the amount of hydrogen gas supplied. And it aims at providing a fuel cell system using the same.

  Means for solving the above problems are as follows.

  The fuel cell of the present invention includes an anode electrode having a catalyst layer having a catalyst and supplied with hydrogen gas, a cathode electrode having a catalyst layer having a catalyst and supplied with air, the anode electrode and the cathode A fuel cell comprising an electrolyte membrane sandwiched between electrodes, wherein the cathode electrode is provided with oxygen separation means for selectively separating oxygen from the air.

  According to the fuel cell of the present invention, the oxygen concentration can be increased by aggregating oxygen contained in the air reaching the electrolyte membrane by the oxygen separation means provided on the cathode electrode on the air supply side. As a result, the oxygen partial pressure in the air increases, and the nitrogen gas does not easily pass through the electrolyte membrane. Furthermore, according to the present invention, air having a high oxygen concentration (hereinafter sometimes referred to as “oxygen-enriched air”) can be supplied to the cathode electrode, so that the power generation efficiency of the fuel cell with respect to the amount of hydrogen gas supplied is improved. Can be made. Further, according to the present invention, since the oxygen enrichment means is provided inside the fuel cell, it is not necessary to separately install an oxygen enrichment device outside the device, and the system can be reduced in size and simplified.

  In the present invention, the “oxygen separation means” means a device capable of separating oxygen and nitrogen in the air and increasing the oxygen concentration in the air. The method for separating oxygen and nitrogen by the oxygen enrichment means is not particularly limited. For example, only oxygen is selectively utilized by utilizing the difference in the velocity of gas molecules between oxygen gas and nitrogen gas flowing in the porous membrane. An oxygen-enriched membrane that makes it difficult to permeate or permeate nitrogen, or to selectively permeate oxygen using the difference in solubility of gas molecules in a non-porous membrane (homogeneous membrane) and the diffusion rate in the membrane Examples thereof include an oxygen-enriched film component used for this, and an oxygen adsorbent that adsorbs only oxygen through pores using the molecular particle size difference between oxygen atoms and nitrogen atoms.

  The site for installing the oxygen separation means in the cathode electrode is not particularly limited as long as the oxygen and nitrogen in the air can be separated before the air supplied to the cathode electrode reaches the electrolyte membrane. The form of the oxygen separation means is not particularly limited, but it is preferable to block nitrogen reaching the electrolyte membrane using a film-like oxygen content means.

  As described above, the fuel cell of the present invention can use an oxygen-enriched membrane as the oxygen separation means. The fuel cell of the present invention can increase the oxygen partial pressure in the air reaching the electrolyte membrane and suppress the permeation of nitrogen gas by using the oxygen-enriched membrane as the oxygen separation means.

  As described above, as the oxygen-enriched film, as described above, a film that selectively transmits only oxygen using a difference in velocity between gas molecules of oxygen gas and nitrogen gas flowing in the porous film, or a non-porous film ( For example, oxygen can be selectively permeated using the difference in the solubility of gas molecules in the homogeneous membrane and the diffusion rate in the membrane. The oxygen-enriched membrane is installed on the air supply side of the catalyst layer from the viewpoint of improving power generation efficiency (if the gas diffusion layer is provided on the air supply side of the catalyst layer, the catalyst layer and the gas diffusion layer). Or in the gas diffusion layer or between the gas diffusion layer and the air supply means (for example, a separator). However, an oxygen-enriched membrane is provided between the electrolyte membrane and the catalyst layer. It can also be provided. The oxygen-enriched film is preferably provided with electrical conductivity by mixing a substance having electrical conductivity such as carbon particles in the film.

  In the fuel cell of the present invention, oxygen-adsorbing carbon is used as the oxygen separation means, and the catalyst layer of the cathode electrode can be configured to include the oxygen-adsorbing carbon. According to the fuel cell of the present invention, oxygen gas can be selectively collected in the catalyst layer by using oxygen-adsorbed carbon (catalyst layer including oxygen-adsorbed carbon) as the oxygen separation means. Thereby, it can suppress that nitrogen gas reaches | attains an electrolyte membrane, and can prevent the permeation | transmission.

  The oxygen-adsorbing carbon is a kind of the above-mentioned oxygen adsorbing material, and utilizes an adsorption rate (easiness of adsorption) due to a molecular diameter difference between nitrogen and oxygen. The oxygen-adsorbed carbon has a plurality of micropores that are difficult for nitrogen molecules with a large molecular diameter to enter and oxygen molecules with a large molecular diameter easily enter, so that the oxygen gas in the air is adsorbed to separate the nitrogen gas. can do.

  In addition, by forming the catalyst layer of the cathode electrode with the oxygen-adsorbing carbon, a large amount of oxygen gas can be selectively present around the catalyst, and the power generation efficiency can be further improved.

  Furthermore, in the fuel cell of the present invention, an oxygen-enriched membrane component can be used as the oxygen separation means, and the oxygen-enriched membrane component can be contained in the catalyst layer. According to the fuel cell of the present invention, by containing an oxygen-enriched membrane component (component constituting the above-described oxygen-enriched membrane) in the catalyst layer, nitrogen gas can be prevented from moving in the catalyst layer. Therefore, permeation of nitrogen gas through the electrolyte membrane can be prevented. Furthermore, since a large amount of oxygen gas can selectively exist around the catalyst, the power generation efficiency of the fuel cell can be further improved.

  The fuel cell system of the present invention comprises the fuel cell of the present invention, a hydrogen gas supply means for supplying hydrogen gas to the anode electrode of the fuel cell, an air supply means for supplying air to the cathode electrode of the fuel cell, A cathode offgas discharging means for discharging the cathode offgas from the cathode electrode of the fuel cell. By providing the fuel cell system of the present invention, the fuel cell system of the present invention can supply stable power for a long time, and can further improve the power generation efficiency for the supplied hydrogen gas. Here, the “cathode off-gas” includes surplus air that has not contributed to the electrochemical reaction in the cathode electrode and water vapor generated in the cathode electrode. Further, the cathode off-gas is a nitrogen-enriched gas because it contains a large amount of nitrogen gas separated by the oxygen separation means.

  The fuel cell system of the present invention further includes an anode offgas discharge means for discharging anode offgas from the anode electrode of the fuel cell, and the anode offgas discharge means does not supply the anode offgas to the hydrogen gas supply means, An anode off gas can be configured to be discharged.

  Since the fuel cell system of the present invention includes the fuel cell of the present invention, the anode off-gas discharged from the anode electrode is not supplied again to the anode electrode, that is, the dead gas does not circulate hydrogen gas at the anode electrode. Even if it is configured as an end type fuel cell system, power generation efficiency does not decrease due to permeation of nitrogen gas, power can be supplied stably for a long time, and power generation efficiency with respect to hydrogen gas supply amount can be increased it can.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell which can suppress the permeation | transmission of the electrolyte membrane of nitrogen gas, can generate electric power stably over a long period of time, and has high electric power generation efficiency with respect to the supply amount of hydrogen gas, and a fuel cell using the same A system can be provided.

  Hereinafter, embodiments of the fuel cell system of the present invention will be described in detail with reference to the drawings.

(First embodiment)
The present embodiment is a fuel cell system including the fuel cell of the present invention, which supplies hydrogen gas stored in a hydrogen tank to the fuel cell and supplies air by a compressor for use in a power generation reaction. The fuel cell system adopts a dead-end system in which the anode off-gas discharged from the fuel is discharged out of the system together with the cathode off-gas without being supplied to the fuel cell again.

The fuel cell system according to the first embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram showing the configuration of the fuel cell system according to the first embodiment. As shown in FIG. 1, a fuel cell 10 according to the present invention includes an anode electrode 12 to which hydrogen gas as a fuel is supplied, a cathode electrode 14 to which air is supplied as an oxidant and provided with an oxygen-enriched film 24, and an electrolyte. The membrane 16 and the separators 18 and 20 are configured so that power can be supplied to the external device 48 through the external circuit 22 connected to the anode electrode 12 and the cathode electrode 14. In the fuel cell 10 of the present invention, the hydrogen gas supplied as fuel releases hydrogen ions and electrons (e ⁻ ) at the anode electrode 12, and the released electrons (e ⁻ ) pass through the external circuit 22 to the cathode electrode. Power is generated by moving to 14.

  Further, one end of a pipe 26 provided with a pump P1 and a pressure regulating valve V1 is connected to the hydrogen supply side of the separator 18 installed in the anode electrode 12, and the hydrogen gas stored in the hydrogen tank 28 is supplied to the pipe 26. To be supplied to the fuel cell 10.

  Furthermore, one end of a pipe 30 provided with a shut valve V2 is connected to the anode off gas discharge side of the separator 18, and the anode off gas is connected via a pipe 32 connected to the other end of the pipe 30 by opening and closing the shut valve V2. Can be discharged out of the system.

  One end of a pipe 36 including a compressor 34 is connected to the separator 20 installed on the cathode side of the fuel cell 10, and the air sent by the compressor is supplied to the fuel cell 10 through the pipe 36. Has been.

  Further, one end of a pipe 32 provided with a purification device 38 is provided on the cathode off gas discharge side of the separator 20 so that the cathode off gas discharged from the fuel cell 10 can be discharged out of the system.

  First, the configuration of the fuel cell 10 will be described. As shown in FIG. 1, the fuel cell 10 of the present invention is provided such that the anode electrode 12 and the cathode electrode 14 are in close contact with both surfaces of the electrolyte membrane 16. Further, separators 18 and 20 that form gas flow paths for hydrogen gas and air are installed outside the anode electrode 12 and the cathode electrode 14, respectively.

  As shown in FIG. 1, the cathode electrode 14 includes a gas diffusion layer 14B formed of a catalyst layer 14A in which a platinum-based metal catalyst is supported on oxygen-adsorbed carbon, an oxygen-enriched film 24, and a porous member having pores. The catalyst layer 14 </ b> A is disposed so as to be in close contact with one surface of the electrolyte membrane 16.

  An oxygen-enriched film 24 is installed between the catalyst layer 14A and the gas diffusion layer 14B, and is contained in the air supplied via the gas diffusion layer 14B from a gas flow path formed by the separator 20 described later. Of oxygen gas and nitrogen gas, only oxygen gas is selectively permeated. The air that has passed through the oxygen-enriched membrane 24 reacts with hydrogen ions and electrons in the catalyst layer 14A to generate water.

  The oxygen-enriched film 24 is mainly formed of a polyimide porous film, and further, carbon black is mixed as a conductor. The oxygen-enriched film 24 can selectively (preferentially) permeate oxygen only by using the difference in velocity between gas molecules of oxygen gas and nitrogen gas flowing in the polyimide porous film, and enters the catalyst layer 14A. Nitrogen can be separated from the air. Further, polytetrafluoroethylene (PTFE) or the like can be added to the oxygen-enriched film 24.

  The thickness of the oxygen-enriched film 24 is not particularly limited as long as the effect of the present invention can be exhibited, but is preferably about 5 to 100 μm, and more preferably about 5 to 10 μm. The oxygen-enriched film 24 can be formed by adding a conductor or the like to a polyimide porous film manufactured by Ube Industries.

  The catalyst layer 14A is composed of oxygen-adsorbed carbon and an electrolyte membrane component, and further includes a metal catalyst supported on a support such as activated carbon (may be oxygen-adsorbed carbon powder). Since the catalyst layer 14A is formed using oxygen-adsorbed carbon, oxygen gas is adsorbed by the catalyst layer 14A, and therefore the oxygen concentration in the air entering the porous structure of the catalyst layer 14A is the supplied air. It is higher than As the oxygen concentration of the air entering the catalyst layer 14A increases, the nitrogen concentration in the air decreases in proportion to this, and nitrogen gas can be prevented from permeating the electrolyte membrane 16. Further, when oxygen-enriched air having a high oxygen concentration of air enters the catalyst layer 14A, the amount of oxygen per unit time passing over the catalyst provided in the catalyst layer 14A increases, so that hydrogen ions and oxygen in the catalyst layer 14A The reaction efficiency can be improved.

  The oxygen adsorption action of the catalyst layer 14A will be described with reference to FIG. FIG. 2 is a schematic view for explaining the oxygen adsorption action of the catalyst layer in the first embodiment. As shown in FIG. 2, the oxygen-adsorbing carbon forming the catalyst layer 14A has a plurality of micropores, and the difference in molecular diameter between oxygen molecules and nitrogen molecules (oxygen molecules: 3.8 × 2. Oxygen molecules and nitrogen molecules can be separated (adsorbed oxygen molecules) using 8Å, nitrogen molecules: 4.2 × 3.0Å).

  In the pores provided in the catalyst layer 14A, oxygen molecules 40 having a small molecular diameter can easily enter, and nitrogen molecules 42 having a large molecular diameter compared to oxygen molecules are difficult to enter. That is, the oxygen molecules 40 can enter the pores of the catalyst layer 14A without harmful effects, but the nitrogen molecules 42 having a large molecular diameter cannot enter the pores.

  For this reason, only the oxygen molecules 40 enter the pores one after another and are separated from the remaining nitrogen molecules 42. Thus, the catalyst layer 14A adsorbs only the oxygen molecules 40, whereby the oxygen concentration of the air entering the catalyst layer 14A can be increased.

  Further, as the catalyst provided in the catalyst layer 14A, a known catalyst can be appropriately used. For example, a noble metal-based catalyst such as Pt, Pt—Rh, Pt—Ir, Pt—Re, Pt—W, Pt—Ru, etc. A carbon-supported Pt catalyst using a metal, a carbon-supported Pt-Ir composite metal catalyst, a carbon-supported Pt-Re composite metal catalyst, a carbon-supported Pt-W composite metal catalyst, a catalyst using a nickel-based metal, or the like can be used. .

  The catalyst layer 14A is, for example, bonded to oxygen-absorbing carbon powder such as “Bellfine” manufactured by Kanebo Co., Ltd., a catalyst supported on activated carbon, and a polymer membrane (electrolyte) solution used for the electrolyte membrane 16. It can be formed by mixing an agent or the like.

  As shown in FIG. 1, a gas diffusion layer 14B is installed outside the oxygen-enriched membrane 24 (the side not in close contact with the catalyst layer 14A), and diffuses the air supplied from the separator 20, The catalyst layer 14A is supplied uniformly. The gas diffusion layer 14B is composed of a porous member having pores, and examples of the porous member include carbon paper, carbon nonwoven fabric, and carbon cloth.

  In the present embodiment, an oxygen-enriched film 24, which is an oxygen separating means, is provided between the catalyst layer 14A and the gas diffusion layer 14B. For example, the gas diffusion layer 14B includes two or more gas diffusion layers 14B. And an oxygen-enriched film may be provided between the gas diffusion layers. In addition, an oxygen-enriched film component such as powder may be added to the gas diffusion layer 14B, whereby air having a higher oxygen concentration can be supplied to the catalyst layer 14A.

  A separator 20 is installed outside the gas diffusion layer 14B (the side not in close contact with the oxygen-enriched film 24) to supply air to the gas diffusion layer 14B and discharge the cathode off-gas after the power generation reaction. A gas flow path is formed for this purpose.

  As shown in FIG. 1, one end of a pipe 36 including a compressor 34 and a humidifier 44 is connected to the air supply side (left side of the paper) of the separator 20, and the air supplied through the filter 46 is supplied. Is supplied to the fuel cell 10 by the compressor 34 while being humidified by the humidifier 44.

  Further, one end of a pipe 32 is connected to the cathode off-gas discharge side (right side of the drawing) of the separator 20, and water, excess air, etc. generated by the power generation reaction in the cathode electrode 14 are systemized as a cathode off-gas via the purification device 38. Discharged outside.

  Further, as shown in FIG. 1, the anode electrode 12 includes a catalyst layer 12A mainly composed of carbon powder carrying a platinum-based metal catalyst, a gas diffusion layer 12B formed of a porous member having pores, The catalyst layer 12 </ b> A is disposed so as to be in close contact with one surface of the electrolyte membrane 16. The hydrogen gas supplied through the gas flow path formed by the separator 18 reaches the catalyst layer 12A through the gas diffusion layer 12B.

  As the catalyst provided in the catalyst layer 12A, the catalyst used in the catalyst layer 14A described above can be used. The catalyst layer 12A can be formed by mixing a catalyst supported on carbon powder or the like, a polymer membrane (electrolyte) solution used for the electrolyte membrane 16, and a binder.

  Furthermore, the gas diffusion layer 12B disposed outside the catalyst layer 12A (the side not in close contact with the electrolyte membrane 16) can be formed of a porous member having pores in the same manner as the gas diffusion layer 14B.

  A separator 18 is installed outside the gas diffusion layer 12B (side not in close contact with the catalyst layer 12A), and a gas flow path for supplying hydrogen gas to the gas diffusion layer 12B and discharging excess hydrogen gas is provided. Is formed. Further, one end of a pipe 26 provided with a pump P1 and a pressure regulating valve V1 is connected to the gas supply side (left side of the paper) of the separator 18, and the hydrogen gas stored in the hydrogen tank 28 is supplied to the pump P1. Is configured to be supplied to the fuel cell 10.

  Furthermore, one end of a pipe 30 is connected to the anode off-gas discharge side (right side of the paper) of the separator 18, and surplus hydrogen gas that has not contributed to the reaction at the anode electrode 12 is discharged to the anode off-gas and the system through the pipe 32. It has become so.

  In the present embodiment, the hydrogen gas stored in the hydrogen tank 28 is supplied to the fuel cell 10 through the pipe 26 by driving the pump P1. At this time, the pressure of the hydrogen gas is controlled by the pressure regulating valve V1.

  Note that since the fuel cell system in the present embodiment employs the dead end method, the hydrogen gas once discharged from the anode electrode 12 is not supplied to the anode electrode 12 again, so that the pressure regulating valve V1 is opened. It is not necessary to adjust the degree for each supply, and the opening degree of the pressure regulating valve V1 may be kept constant.

  Further, the hydrogen gas supplied to the fuel cell 10 is supplied to the anode electrode 12 from a gas flow path formed by the separator 18. The hydrogen gas supplied to the anode electrode reaches the catalyst layer 12A via the gas diffusion layer 12B, and generates hydrogen ions and electrons by the action of the catalyst provided in the catalyst layer 12A.

  Hydrogen ions generated in the catalyst layer 12A pass through the electrolyte membrane 16 and move to the cathode electrode 14 to be used for reaction with oxygen molecules. On the other hand, electrons that cannot pass through the electrolyte membrane 16 move to the cathode electrode 14 via the external circuit 22. The fuel cell 10 of the present invention can supply electric power to the external device 48 by this movement of electrons.

  Further, the air that has passed through the filter 46 is supplied to the cathode electrode 14 by the compressor 34 while being humidified by the humidifier 44 provided in the pipe 36.

  After the air supplied to the cathode electrode 14 is diffused by the gas diffusion layer 14B, nitrogen is separated by the oxygen-enriched membrane 24 and supplied to the catalyst layer 14A as oxygen-enriched air.

  The oxygen-enriched air supplied to the catalyst layer 14A receives and reacts with the hydrogen ions that have moved to the cathode electrode 14 through the electrolyte membrane 16 and the electrons that have moved through the external circuit 22 on the catalyst. Generate. Water generated by the reaction between hydrogen ions and oxygen does not contribute to the reaction, and is discharged out of the system through the purification device 38 through the piping 32 together with the cathode off gas containing a large amount of the separated nitrogen gas.

  According to the present embodiment, since the oxygen-enriched film 24 is provided between the catalyst layer 14A and the gas diffusion layer 14B of the cathode electrode 14, it is possible to suppress the nitrogen gas from reaching the electrolyte film 16 and to prevent the anode electrode. The amount of nitrogen gas moving to 12 can be reduced, and the reaction efficiency in the catalyst layer 14A can be increased by supplying air having a high oxygen concentration to the catalyst layer 14A.

  Further, according to the present embodiment, the catalyst layer 14A is formed using oxygen-adsorbed carbon, and by increasing the oxygen concentration of the air that enters the catalyst layer 14A, the nitrogen gas that reaches the electrolyte membrane 16 is increased. The amount of oxygen passing through the catalyst can be increased by increasing the oxygen concentration of the air entering the catalyst layer 14A, and the reaction efficiency of oxygen molecules, hydrogen ions, and electrons can be increased. Can be increased.

(Second Embodiment)
Next, a fuel cell system using another example of the fuel cell of the present invention will be described with reference to FIG. FIG. 3 is a schematic diagram showing the configuration of the fuel cell system according to the second embodiment. As shown in FIG. 3, the fuel cell 50 used in the present embodiment has the cathode electrode 14 in the first embodiment not disposed outside the gas diffusion layer 52B (between the separator 20 and the gas diffusion layer 52B). An oxygen-enriched film 54 having a porous film (homogeneous film) as a main component is provided. Further, the catalyst layer 52A contains a granular polyimide porous body (hereinafter sometimes simply referred to as “polyimide”) as an oxygen-enriched film component. Constituent elements common to the fuel cell 50 in the present embodiment and the fuel cell 10 in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 3, the cathode electrode 52 includes a catalyst layer 52A in which a platinum-based metal catalyst is supported on oxygen-adsorbing carbon, a gas diffusion layer 52B formed of a porous member having pores, and an oxygen-enriched film 54. The catalyst layer 52A is arranged so as to be in close contact with one surface of the electrolyte membrane 16.

  An oxygen-enriched film 54 is provided outside the gas diffusion layer 52B (between the gas diffusion layer 52B and the separator 20), and air supplied from a gas flow path formed by the separator 20 described later. Of the oxygen gas and nitrogen gas contained in the gas, only the oxygen gas is selectively permeated. The air that has passed through the oxygen-enriched film 54 is shared with the catalyst layer 52A via the gas diffusion layer 52B, and reacts with hydrogen ions and electrons to generate water.

  The oxygen-enriched film 54 is mainly formed of an organic non-porous polymer film that is a non-porous film (homogeneous film), and further, carbon black is mixed as a conductor. The oxygen-enriched film 54 can selectively (preferentially) permeate oxygen only by utilizing the difference in the solubility of gas molecules in the non-porous film and the diffusion rate in the film, and allows the gas diffusion layer 52B to pass through. Nitrogen can be separated from the supplied air. Further, polytetrafluoroethylene (PTFE) or the like can be added to the oxygen-enriched film 54.

  Examples of the organic non-porous polymer film constituting the oxygen-enriched film 54 include cellulose acetate, polysulfone, polyamide, polyimide, porphyrin film, and the like.

  The thickness of the oxygen-enriched film 54 is not particularly limited as long as the effect of the present invention can be exhibited, but is preferably about 0.1 to 100 μm, and more preferably 0.1 to 1 μm.

  The catalyst layer 52A is composed of powdered activated carbon or the like, polyimide that is an oxygen-enriched membrane component, and an electrolyte membrane component, and further includes a metal catalyst supported on a carrier such as activated carbon. . Since the catalyst layer 52A contains polyimide, which is an oxygen-enriched membrane component, even when nitrogen gas enters the catalyst layer 52A, the catalyst layer 52A moves by the oxygen-enriched membrane component before reaching the electrolyte membrane 16. Can be suppressed.

  Further, as the catalyst provided in the catalyst layer 52A, a catalyst similar to the catalyst layer 14A in the first embodiment can be appropriately used.

  Further, the catalyst layer 52A is a mixture of a catalyst supported on carbon powder or the like, a solution of a polymer film (electrolyte) used for the electrolyte membrane 16, polyimide as an oxygen-enriched membrane component, a binder, and the like. Can be formed.

  As shown in FIG. 3, a gas diffusion layer 52B is provided outside the catalyst layer 52A (side not in close contact with the electrolyte membrane 16), and air supplied from the separator 20 through the oxygen-enriched membrane 54 is provided. Can be diffused and uniformly supplied to the catalyst layer 52A. The gas diffusion layer 52B is composed of a porous member having pores, and examples of the porous member include carbon paper, carbon nonwoven fabric, or carbon cloth.

  In the present embodiment, the catalyst layer 52A contains polyimide, which is an oxygen-enriched film component. For example, the gas diffusion layer 52B can contain the polyimide. In the present invention, the oxygen-enriched film component is not limited to polyimide, and components used for the oxygen-enriched film can be appropriately selected and used within a range not impairing the effects of the present invention.

  A separator 20 is installed outside the oxygen-enriched film 54 (on the side not in close contact with the gas diffusion layer 52B) for supplying air to the oxygen-enriched film 54 and discharging the cathode off-gas after the power generation reaction. A gas flow path is formed.

  As shown in FIG. 3, one end of a pipe 36 including a compressor 34 and a humidifier 44 is connected to the air supply side (left side of the paper) of the separator 20, and the air supplied through the filter 46 is supplied. However, it is supplied to the fuel cell 50 while being humidified by the compressor 34 in the humidifier 44.

  Further, one end of a pipe 32 is connected to the cathode offgas discharge side (right side of the drawing) of the separator 20, and water, surplus air, and the like generated by the power generation reaction in the cathode electrode 52 are systemized via the purifier 38 as cathode offgas. Discharged outside.

  In the present embodiment, the hydrogen gas stored in the hydrogen tank 28 is supplied to the fuel cell 10 through the pipe 26 by driving the pump P1. At this time, the pressure of the hydrogen gas is controlled by the pressure regulating valve V1. Note that since the fuel cell system in the present embodiment employs the dead end system, the hydrogen gas once discharged from the anode electrode 12 is not supplied to the anode electrode 12 again. There is no need to adjust the opening for each supply.

  Further, the hydrogen gas supplied to the fuel cell 10 is supplied to the anode electrode 12 from a gas flow path formed by the separator 18. The hydrogen gas supplied to the anode electrode reaches the catalyst layer 12A via the gas diffusion layer 12B, and generates hydrogen ions and electrons by the action of the catalyst provided in the catalyst layer 12A.

  Hydrogen ions generated in the catalyst layer 12A pass through the electrolyte membrane 16 and move to the cathode electrode 14 to be used for reaction with oxygen molecules. On the other hand, electrons that cannot pass through the electrolyte membrane 16 move to the cathode electrode 14 via the external circuit 22. The fuel cell 10 of the present invention can supply electric power to the external device 48 by this movement of electrons.

  Further, the air that has passed through the filter 46 is supplied to the cathode electrode 52 by the compressor 34 while being humidified by the humidifier 44 provided in the pipe 36.

  In the air supplied to the cathode electrode 52, nitrogen is separated by the oxygen-enriched film 54 to become oxygen-enriched air and supplied to the gas diffusion layer 52B. The oxygen-enriched membrane air supplied to the gas diffusion layer 52B is diffused and then supplied to the catalyst layer 52A.

  The oxygen-enriched air supplied to the catalyst layer 52A receives and reacts with the hydrogen ions that have moved to the cathode electrode 52 via the electrolyte membrane 16 and the electrons that have moved via the external circuit 22 on the catalyst. Generate. Water generated by the reaction between hydrogen ions and oxygen does not contribute to the reaction, and is discharged out of the system through the purification device 38 through the piping 32 together with the cathode off gas containing a large amount of the separated nitrogen gas.

  According to the present embodiment, since the oxygen-enriched film 54 is provided between the gas diffusion layer 52B and the separator 20, the nitrogen gas is prevented from reaching the electrolyte film 16 and moves to the anode electrode 12. The amount of nitrogen gas can be reduced. Furthermore, since air with a high oxygen concentration can be supplied to the catalyst layer 52A, the reaction efficiency in the catalyst layer 52A can be increased.

  Further, according to the present embodiment, since the catalyst layer 52A contains polyimide as an oxygen-enriched film component, even if nitrogen gas remains in the air that enters the catalyst layer 52A. Since the movement of the catalyst layer 52A can be inhibited, the amount of nitrogen gas reaching the electrolyte membrane 16 can be suppressed.

  In the present invention, the catalyst layer formed using the oxygen-adsorbing carbon in the first embodiment can contain an oxygen-enriched film component such as polyimide.

  As described above, the fuel cell of the present invention and the fuel cell system using the same can effectively suppress the movement of nitrogen gas to the anode electrode by the oxygen separation means provided in the cathode electrode, and the amount of hydrogen gas supplied can be reduced. Power generation efficiency can be increased. Furthermore, according to the fuel cell of the present invention and the fuel cell system using the same, electric power can be stably supplied over a long time.

  In addition, since the fuel cell of the present invention can supply oxygen-enriched air to the catalyst of the cathode electrode, the amount of oxygen passing over the catalyst provided in the cathode electrode can be increased. The reaction efficiency between hydrogen ions and electrons can be increased.

  Further, since the fuel cell system of the present invention does not require an external device to obtain oxygen-enriched air, the system can be reduced in size and simplified, such as a fuel cell system mounted on a vehicle. Can be suitably used.

  Furthermore, in the present embodiment, the fuel cell having a single cell structure has been described as an example. However, the present invention is not limited to this, and can be configured as a fuel cell in which a plurality of cells are stacked.

It is the schematic which shows the structure of the fuel cell system in 1st Embodiment. It is the schematic for demonstrating the oxygen adsorption effect | action of the catalyst layer in 1st Embodiment. It is the schematic which shows the structure of the fuel cell system in 2nd Embodiment.

Explanation of symbols

10, 50 Fuel cell 12 Anode electrode 12A Catalyst layer 12B Gas diffusion layer 14, 52 Cathode electrodes 14A, 52A Catalyst layer 14B, 52B Gas diffusion layer 16 Electrolyte membrane 18, 20 Separator 22 External circuit 24, 54 Oxygen enriched membrane

Claims (6)

  An anode electrode having a catalyst layer having a catalyst and supplied with hydrogen gas, a cathode electrode having a catalyst layer having a catalyst and supplied with air, and an electrolyte sandwiched between the anode electrode and the cathode electrode And a membrane, wherein the cathode electrode is provided with oxygen separation means for selectively separating oxygen from the air.   The fuel cell according to claim 1, wherein the oxygen separation means is an oxygen-enriched membrane.   The fuel cell according to claim 1 or 2, wherein the oxygen separation means is oxygen-adsorbed carbon, and the catalyst layer of the cathode electrode includes the oxygen-adsorbed carbon.   The fuel cell according to any one of claims 1 to 3, wherein the oxygen separation means is an oxygen-enriched membrane component, and the oxygen-enriched membrane component is contained in a catalyst layer of the cathode electrode.   A fuel cell according to any one of claims 1 to 4, a hydrogen gas supply means for supplying hydrogen gas to the anode electrode of the fuel cell, an air supply means for supplying air to the cathode electrode of the fuel cell, And a cathode offgas discharging means for discharging cathode offgas from the cathode electrode of the fuel cell.   An anode offgas discharge means for discharging anode offgas from the anode electrode of the fuel cell, wherein the anode offgas discharge means discharges the anode offgas without supplying the anode offgas to the hydrogen gas supply means. 6. The fuel cell system according to 5.

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