JP2006012475A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system that does not cause a decrease in output due to long-term use.
In a normal power generation operation of a fuel cell main body 10, a valve V1 is opened and a valve V2 is closed so that a reformed gas is supplied from a hydrogen generator 20 through a fuel supply pipe 12 at a predetermined gas pressure. The fuel cell main body 10 is supplied. When the power generation amount of the fuel cell main body 10 measured by the voltage measuring device 22 is less than the reference value, the valve V2 is opened and hydrogen gas is supplied from the hydrogen gas tank 30 to the fuel cell main body 10. As a result, the organic matter that has contaminated the anode electrode in the fuel cell main body 10 is removed.
[Selection] Figure 1

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system that can be mounted on a vehicle such as a fuel cell electric vehicle.

  A conventional fuel cell electric vehicle is equipped with a fuel cell as a power source for obtaining a driving force of the vehicle, and hydrogen or a raw fuel for generating hydrogen as a fuel for generating electric power using the fuel cell. ing. In a fuel cell electric vehicle equipped with hydrogen, hydrogen is loaded with a cylinder filled with compressed hydrogen gas, or with a hydrogen storage alloy or hydrogen adsorption material that stores hydrogen. On the other hand, fuel cell electric vehicles equipped with raw fuel are equipped with hydrocarbons such as organic hydride as raw fuel and a hydrogen generator that generates hydrogen-rich reformed gas from this raw fuel through a dehydrogenation reaction. Yes.

  However, hydrogen storage alloys and hydrogen adsorption materials do not have sufficient hydrogen storage required for fuel cell electric vehicles, and it is difficult to control the release of hydrogen. On the other hand, a fuel cell electric vehicle equipped with raw fuel has an advantage that a distance that can be traveled by one refueling is longer than a fuel cell electric vehicle equipped with hydrogen. Raw fuel also has the advantage of being easy and safe to handle, such as transportation, compared to hydrogen gas.

Decalin (decahydronaphthalene), one of the hydrocarbons, has a vapor pressure at room temperature close to zero (boiling point is around 200 ° C) and is easy to handle. There are reports on a hydrogen generator using a fuel composed of decalin or a fuel mainly composed of decalin (for example, see Patent Document 1).
JP 2000-255503 A

  However, the hydrogen-rich reformed gas obtained from the hydrogen generator contains a small amount of organic hydride and reaction products (organic substances) generated by the dehydrogenation reaction. When such a reformed gas is used as a fuel, there has been a problem that the anode electrode of the fuel cell is contaminated with these trace amounts of organic substances and the amount of power generation is reduced.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a fuel cell system that does not cause a decrease in output due to long-term use.

  In order to achieve the above object, a fuel cell system of the present invention comprises a membrane electrode assembly comprising an anode electrode, a cathode electrode, and an electrolyte membrane sandwiched between the anode electrode and the cathode electrode, and the membrane A pair of separators that sandwich the electrode assembly and form a fuel flow path through which fuel passes between the anode electrode and an oxidizing gas flow path through which oxidizing gas passes between the cathode electrode are provided A fuel cell main body including a single cell; first fuel supply means for supplying reformed gas containing hydrogen obtained by dehydration reaction of organic hydride to the fuel flow path; and supplying hydrogen gas to the fuel flow path Second fuel supply means, oxidizing gas supply means for supplying oxidizing gas to the oxidizing gas flow path, first measuring means for measuring the power generation amount of the fuel cell main body, and the power generation amount being a reference value or more is there A reforming gas is supplied from the first fuel supply means to the fuel flow path, and when the power generation amount is less than a reference value, the second fuel supply means supplies the fuel. And a channel switching means for supplying hydrogen gas to the channel.

  In the present invention, hydrogen gas means a gas having a high purity of 3N (99.9%) or higher. The reformed gas refers to a hydrogen-rich gas obtained by a dehydrogenation reaction of organic hydride, and is distinguished from hydrogen gas. In the present invention, the gas obtained by removing organic substances in the reformed gas with a filter is included in the category of hydrogen gas.

  In the fuel cell system of the present invention, hydrogen in the reformed gas supplied from the first fuel supply means to the fuel flow path and oxygen in the oxidizing gas (air) supplied from the oxidizing gas supply means to the oxidizing gas flow path Causes an electrochemical reaction represented by the following formulas (1) to (3) and supplies electric power to the outside. Equation (1) shows the reaction on the anode electrode side, Equation (2) shows the reaction on the cathode electrode side, and Equation (3) shows the total reaction on the fuel cell main body.

H ₂ → 2H ⁺ + 2e ⁻ (1)
(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)

  The power generation amount of the fuel cell main body is measured by the first measuring means at predetermined intervals, and the degree of contamination of the anode electrode by the organic matter is determined by determining whether or not the measured power generation amount is equal to or greater than a reference value. to decide. When the power generation amount is less than the reference value, the fuel supplied to the fuel flow path is switched from the reformed gas to the hydrogen gas by the flow path switching means. When hydrogen gas is supplied to the fuel flow path, organic substances that have contaminated the anode electrode are removed, and the power generation amount of the fuel cell main body increases. After the power generation amount of the fuel cell main body recovers to a reference value or more, the fuel supplied to the fuel flow path is switched from hydrogen gas to reformed gas by the flow path switching means. In this way, it is possible to realize a fuel cell system that does not cause a decrease in output due to long-term use.

  The fuel cell system of the present invention further includes second measuring means for measuring the supply amount of the reformed gas, and the reference value is determined based on the supply amount of the reformed gas measured by the second measuring means. You may do it. The power generation amount of the fuel cell main body varies depending on the supply amount of reformed gas (hydrogen). In the present invention, a fixed value may be used as the reference value, but the degree of contamination of the anode electrode can be accurately grasped by determining the reference value according to the supply amount of the reformed gas.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell system which does not produce the output fall by long-time use can be provided.

  Embodiments of a fuel cell system of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is provided to the member which has the same function throughout all drawings, and the description may be abbreviate | omitted.

  In the present embodiment, the fuel cell system according to the embodiment of the present invention is mounted on an electric vehicle that can be moved by a motor that drives the axle upon receipt of electric energy. In addition, the present embodiment provides a hydrogen generator capable of supplying a reformed gas by dehydrogenation of decalin which is a kind of organic hydride as the first fuel supply means (the reaction product when decalin is used is naphthalene). It is what was used.

(First embodiment)
FIG. 1 is a schematic view showing a fuel cell system according to a first embodiment of the present invention. A fuel cell system according to a first embodiment includes a membrane electrode assembly including an anode electrode, a cathode electrode, and an electrolyte membrane sandwiched between the anode electrode and the cathode electrode, and the membrane electrode assembly. A single cell comprising a pair of separators that sandwich and form a fuel channel through which fuel passes between the anode electrode and an oxidizing gas channel through which oxidizing gas passes between the cathode electrode is provided. A fuel cell main body portion 10 is provided that is stacked to form a stack structure.

  One end of a fuel supply pipe 12 is connected to the fuel cell main body 10 on the anode electrode side so as to communicate with a supply port of each fuel flow path of a single cell constituting a stack structure.

  The fuel supply pipe 12 is bifurcated, and one end of the other end of the fuel supply pipe 12 supplies a reformed gas containing hydrogen obtained by dehydrogenation of decalin, which is a kind of organic hydride. The other end of the fuel supply pipe 12 is connected to a hydrogen gas tank 30 which is a second fuel supply means for supplying hydrogen gas.

  The fuel supply pipe 12 is provided with a valve V1 and a valve V2, and the reformed gas is supplied from the hydrogen generator 20 to the fuel cell main body 10 by opening the valve V1 and closing the valve V2. On the other hand, hydrogen gas is supplied from the hydrogen gas tank 30 to the fuel cell main body 10 by closing the valve V1 and opening the valve V2. In this way, the valve V1 and the valve V2 are paired to constitute a flow path switching unit.

  In the vicinity of the connection portion of the fuel supply pipe 12 with the fuel cell main body 10, a flow meter 14 is provided as a second measuring means for measuring the supply amount of the reformed gas.

  A supply pipe 16 having a valve V3 for supplying hydrogen gas to the hydrogen gas tank 30 from an external hydrogen stand or the like is attached to the hydrogen gas tank 30.

  Further, one end of an exhaust pipe 18 provided with a valve V4 for discharging exhaust gas (anode off gas) is connected to the anode electrode side of the fuel cell main body 10. The valve V4 is normally in a closed state, and prevents the generation power of the fuel cell main body 10 from being deteriorated due to accumulation of generated water or nitrogen exhaust gas that has permeated through the electrolyte membrane constituting the single cell from the cathode electrode side. For this reason, the exhaust gas can be discharged in an open state every predetermined time. Since the hydrogen that has not been consumed remains in the anode off-gas, the exhaust pipe 18 can be branched, connected to the fuel supply pipe 12, and circulated to effectively use the hydrogen.

  One end of an air supply pipe 37 provided with an air compressor 38 and a humidifier 39 is connected to the supply port of each oxidizing gas flow path of the single cell constituting the stack structure on the cathode electrode side of the fuel cell main body 10. It is connected to the. A filter 40 is attached to the other end of the air supply pipe 37, and the air supply pipe 37, the air compressor 38, the humidifier 39, and the filter 40 constitute an oxidizing gas supply means. The supply pressure and supply amount of air, which is an oxidizing gas, to the fuel cell main body 10 are controlled by the rotational speed of the air compressor 38.

  Further, one end of a discharge pipe 19 is connected to the cathode electrode side of the fuel cell main body 10 so that discharged air (cathode offgas) having a low oxygen concentration due to cell reaction and generated water can be discharged. The other end of the exhaust pipe 18 is connected to the discharge pipe 19. The other end of the discharge pipe 19 is connected to the muffler 36.

  Further, the fuel cell main body 10 is provided with a voltage measuring device 22 which is a first measuring means for measuring the amount of power generated by the fuel cell main body 10.

  Next, a single cell included in the fuel cell main body 10 will be described.

  FIG. 2 is a schematic cross-sectional view showing a configuration example of a single cell constituting the fuel cell main body 10. The fuel cell main body 10 is formed by laminating a plurality of single cells 10a configured as shown in FIG. 2 with a separator interposed therebetween. Each single cell 10 a includes a membrane electrode assembly 57 including an anode electrode 55, a cathode electrode 56, and a fluorine-based ion exchange resin membrane (electrolyte membrane) 50 sandwiched between the anode electrode 55 and the cathode electrode 56. In addition, the membrane electrode assembly 57 is sandwiched, and a fuel channel 60 through which fuel passes between the anode electrode 55 and an oxidizing gas channel 61 through which oxidizing gas passes between the cathode electrode 56 are formed. A pair of separators 58 and 59 are provided.

  The fuel cell main body 10 is supplied with reformed gas or hydrogen gas to the fuel flow path 60 and air is supplied to the oxidizing gas flow path 61, and is subjected to an electrochemical reaction represented by the above formulas (1) to (3). Supply power to the outside.

  The fluorine-based ion exchange resin membrane 50 can be composed of an electrolyte having ionic conductivity, and a perfluorosulfonic acid membrane or the like is generally used. In this embodiment, a Nafion membrane (manufactured by DuPont) is used. This membrane is usually in a wet state from the point of increasing ionic conductivity, and the hydrogen ions on the anode side obtained by supplying the reformed gas or hydrogen gas can conduct ions through the membrane well and move to the cathode side. Can do. This wet state can be formed by adding water (humidification) to air that is an oxidizing gas.

  The anode electrode 55 and the cathode electrode 56 are composed of a catalyst layer responsible for an electrochemical reaction and a diffusion layer functioning as a current collector. The anode electrode 55 is configured by laminating an anode catalyst layer 51 and a diffusion layer 53 in order from the fluorine ion exchange resin membrane 50 side, and the cathode electrode 56 is a cathode catalyst in order from the fluorine ion exchange resin membrane 50 side. The layer 52 and the diffusion layer 54 are laminated.

  The anode catalyst layer 51 and the cathode catalyst layer 52 are formed by applying platinum as a catalyst or an alloy made of platinum and another metal to the surface of the fluorine-based ion exchange resin film 50. For the coating, a carbon powder carrying platinum or an alloy composed of platinum and another metal is prepared, and the carbon powder is dispersed in a suitable organic solvent, and an electrolyte solution (for example, Aldrich Chemical Co., Nafion Solution) is added thereto. An appropriate amount can be added to form a paste, and screen printing can be performed on the fluorine-based ion exchange resin film 50. Alternatively, the paste containing the carbon powder may be formed into a sheet to form a sheet, and the sheet may be pressed onto the fluorinated ion exchange resin film 50. Alternatively, platinum or an alloy made of platinum and another metal may be applied to the surface of the diffusion layer facing the fluorine ion exchange resin film 50 instead of the fluorine ion exchange resin film 50.

  The diffusion layers 53 and 54 are both made of carbon cloth woven with yarns made of carbon fibers. In addition to the carbon cloth, the diffusion layer is preferably formed of carbon paper or carbon felt made of carbon fiber.

  The separators 58 and 59 are provided so as to further sandwich the membrane electrode assembly 57, and a fuel flow path 60 is formed between the anode electrode 55 constituting the membrane electrode assembly 57 and the cathode electrode 56. Between them, an oxidizing gas flow path 61 is formed. The separator can be composed of a gas-impermeable conductive member, for example, dense carbon that has been compressed by gas to be gas-impermeable.

  The separators 58 and 59 each have a flow path formed only on one side of the single cell shown in FIG. 2, but when a single cell is stacked to form a stack structure, one separator has two membrane electrodes. A flow path is formed on both sides of each separator shared by the joined bodies. That is, recesses (ribs) are formed on both sides of one separator, a fuel flow path is formed between the anode electrode on one side, and a cathode electrode of an adjacent membrane electrode assembly is formed on the other side. An oxidizing gas flow path is formed between them. Thus, the separators 58 and 59 have a function of forming a flow path and separating the reformed gas or hydrogen gas and air between adjacent single cells.

  In addition, the ribs formed on both sides of the separator constituting the adjacent single cell may be formed in parallel with each other, or may be formed at a predetermined angle such as perpendicular to each surface. The rib shape is not limited as long as the reformed gas, hydrogen gas, or air can be supplied to the anode electrode or the cathode electrode, and can be formed into, for example, parallel grooves. When the stack structure is formed as described above, the two separators positioned at both ends of the stack structure may be formed with ribs only on the surface in contact with the membrane electrode assembly.

  When the fuel cell main body 10 is assembled, a plurality of sets of unit cells 10a (see FIG. 2) configured in the order of the separator 58, the anode electrode 55, the fluorine-based ion exchange resin membrane 50, the cathode electrode 56, and the separator 59 (this embodiment) In this case, a stack structure is formed by stacking. At this time, the separators 58 and 59 are shared between adjacent single cells.

  In the normal power generation operation of the fuel cell main body 10, the valve V1 is opened and the valve V2 is closed, and the reformed gas is supplied from the hydrogen generator 20 through the fuel supply pipe 12 at a predetermined gas pressure on the anode electrode side. Air (oxygen) supplied to the fuel flow path, sucked through the filter 40 on the cathode electrode side, compressed by the air compressor 38, and further humidified by the humidifier 39 is passed through the air supply pipe 37 to a predetermined level. This is performed by supplying the oxidizing gas flow path with a supply pressure. In each single cell, since the reaction rate increases and the power generation efficiency improves as the pressure of the reformed gas and air supplied generally increases, the reformed gas and air are preferably supplied under pressure. The anode off gas is exhausted to the outside through the exhaust pipe 18 and the exhaust pipe 19, and the cathode off gas is exhausted from the other end of the exhaust pipe 19 through the muffler 36. The produced water produced by the cell reaction in the fuel cell main body 10 is discharged through the discharge pipe 19 together with the cathode off gas. In a state where the power generation by the fuel cell main body 10 is being performed, the power generation amount of the fuel cell main body 10 is measured by the voltage measuring device 22, and it is determined whether or not the power generation amount is greater than or equal to a reference value.

  The fuel cell main body 10, the flow meter 14, the hydrogen generator 20, the voltage measuring device 22, the valve V1, the valve V2, and the like are electrically connected to the control unit 25, and the operation timing is controlled by the control unit 25. It is like that. The control unit 25 controls the normal power generation operation of the fuel cell that controls the output by adjusting the amounts of reformed gas and air according to the load of a motor (not shown) connected to the fuel cell main body 10. In addition, the power generation amount of the fuel cell main body 10 is taken in, and switching control of the hydrogen supply source (hydrogen generator 20 or hydrogen gas tank 30) is also performed based on a comparison between the taken power generation amount and the reference value.

  Next, a switching control routine of the hydrogen supply source (hydrogen generator 20 or hydrogen gas tank 30) by the control unit 25 of the fuel cell system according to the first embodiment of the present invention will be described with reference to FIG.

  In order to prevent the anode electrode from being contaminated with a small amount of organic substances contained in the reformed gas during the normal power generation operation of the fuel cell main body 10, the control unit 25 uses the power generation amount of the fuel cell main body 10 as a reference. When the value is less than the value, hydrogen gas is supplied as fuel, the organic matter that contaminated the anode electrode is removed, and the power generation amount of the fuel cell main body 10 is recovered.

  FIG. 3 shows a switching control routine when the reformed gas is supplied from the hydrogen generator 20. When this routine is executed, the supply amount of the reformed gas is taken from the flow meter 14 in step 100. Further, in step 110, a reference value for the power generation amount based on the supply amount of the reformed gas is determined. For example, a value of 90% of the theoretical value of the power generation amount based on the supply amount of the reformed gas can be used as the reference value for the power generation amount. In the present embodiment, the power generation amount reference value is determined in accordance with the supply amount of the reformed gas, but the power generation amount reference value may be a fixed value. Next, in step 120, the power generation amount of the fuel cell main body 10 is taken from the voltage measuring device 22.

  In step 130, it is determined whether or not the power generation amount of the fuel cell main body 10 is equal to or greater than a reference value. When it is determined that the power generation amount is greater than or equal to the reference value, the supply of the reformed gas is maintained as it is, and this routine ends.

  On the other hand, when it is determined in step 130 that the power generation amount is less than the reference value, it is determined that the anode electrode is contaminated with an organic substance, and hydrogen gas is supplied to the anode electrode in step 140. At this time, only the hydrogen gas may be supplied to the anode electrode by closing the valve V1 and opening the valve V2, or by opening the valve V2 while the valve V1 remains open, Hydrogen gas and reformed gas may be supplied simultaneously.

  When hydrogen gas is supplied to the anode electrode, organic substances that have contaminated the anode electrode are volatilized and removed. In this case, it is preferable to open the valve V4 so that the volatile organic substance is quickly removed from the fuel flow path.

  In a state where hydrogen gas is supplied to the anode electrode, the power generation amount of the fuel cell main body 10 is taken in from the voltage measuring device 22 in step 150. In step 160, it is determined whether or not the power generation amount of the fuel cell main body 10 is greater than or equal to a reference value. The reference value in step 160 may be a fixed value, or the reference value determined in step 110 may be used. Further, the supply amount of hydrogen gas (when hydrogen gas and reformed gas are supplied at the same time, the total supply amount of hydrogen gas and reformed gas) is taken from the flow meter 14, and the hydrogen gas supply amount (hydrogen When the gas and the reformed gas are supplied at the same time, a power generation reference value based on the sum of the supply amounts of the hydrogen gas and the reformed gas may be determined.

  When it is determined that the power generation amount is equal to or greater than the reference value, it is determined that the organic matter adhering to the anode electrode has been removed, the supply of hydrogen gas is stopped in step 170, and this routine ends. On the other hand, when it is determined in step 160 that the power generation amount is less than the reference value, it is determined that the removal of organic substances attached to the anode electrode is insufficient, and the process returns to step 150 and the hydrogen gas is discharged until the power generation amount exceeds the reference value. Supply continues.

  The hydrogen supply source switching control routine is executed at predetermined intervals (for example, every 30 minutes).

(Second Embodiment)
FIG. 4 is a schematic view showing a fuel cell system according to the second embodiment of the present invention. The fuel cell system according to the second embodiment is configured such that excess organic substances in the reformed gas generated by the hydrogen generator 20 are removed by the filter 21 and can be stored in the hydrogen gas tank 30. The hydrogen generator 20 is connected to a hydrogen gas tank 30 via a pipe 23 including a valve V5 and a filter 21. A pump may be provided between the filter 21 and the hydrogen gas tank 30 in the pipe 23 so that the hydrogen gas obtained from the surplus reformed gas can be stored in the hydrogen gas tank 30 at a high pressure.

1 is a schematic diagram showing a fuel cell system according to a first embodiment. It is a schematic sectional drawing which shows the structural example of the single cell which comprises a fuel cell main-body part. It is a figure which shows the switching control routine of a hydrogen supply source. It is the schematic which shows the fuel cell system which concerns on 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fuel cell main-body part 12 Fuel supply pipe 14 Flowmeter 18 Exhaust pipe 19 Exhaust pipe 20 Hydrogen generator 22 Voltage measuring device 25 Control part 30 Hydrogen gas tank

Claims (2)

A membrane electrode assembly comprising an anode electrode, a cathode electrode, and an electrolyte membrane sandwiched between the anode electrode and the cathode electrode, and sandwiching the membrane electrode assembly and between the anode electrode A fuel cell main body including a single cell having a pair of separators forming a fuel flow path through which fuel passes and an oxidizing gas flow path through which oxidizing gas passes between the cathode electrode;
First fuel supply means for supplying a reformed gas containing hydrogen obtained by dehydrogenation of organic hydride to the fuel flow path;
Second fuel supply means for supplying hydrogen gas to the fuel flow path;
An oxidizing gas supply means for supplying an oxidizing gas to the oxidizing gas flow path;
First measuring means for measuring the power generation amount of the fuel cell main body,
Determination means for determining whether or not the power generation amount is a reference value or more;
The reformed gas is supplied from the first fuel supply means to the fuel flow path, and the hydrogen gas is supplied from the second fuel supply means to the fuel flow path when the power generation amount is less than a reference value. Road switching means;
A fuel cell system comprising: A second measuring means for measuring the supply amount of the reformed gas;
2. The fuel cell system according to claim 1, wherein the reference value is determined based on a supply amount of reformed gas measured by the second measuring unit.

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