JP2009238577A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve downsizing of a fuel cell system, and at the same time to secure cooling function of a fuel cell. <P>SOLUTION: The fuel cell system equipped with an electrolyte film conducting cation, and an anode electrode and a cathode electrode as a pair of electrodes arranged at either side of the electrolyte film includes: a storage means storing fuel containing at least N and H in liquid to be supplied to the fuel cell; and a fuel supply system supplying liquid fuel stored in the storage means to the fuel cell after evaporating it. As fuel, ammonia or hydrazine, for instance, is used. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell system. More specifically, the present invention relates to a fuel cell system using an alkaline fuel cell in which a fuel containing N and H is used as the fuel.

  Various types of fuel cells such as an alkaline type and a solid polymer type are known. In general, in power generation of these fuel cells, hydrogen or a fuel that is a raw material for hydrogen is supplied to the anode electrode as fuel, and oxygen, air, or the like is supplied to the cathode electrode as an oxidant. When the reactant is supplied in this manner, hydroxide ions are generated from oxygen at the cathode electrode of the alkaline fuel cell, and the hydroxide ions pass through the electrolytic solution and reach the anode electrode. In the anode electrode, hydrogen atoms are generated from the supplied fuel, and water is generated by reacting with hydroxide ions moved from the cathode electrode side. For example, Patent Document 1 below discloses a fuel cell in which ammonia, hydrazine, monomethylhydrazine, or the like is used as a fuel.

JP 2003-346865 A

  By the way, in the electrochemical reaction of the fuel cell, reaction heat is generated, so that the fuel cell generates heat with its power generation. Therefore, in order to maintain the fuel cell at an appropriate operating temperature, a system for cooling the fuel cell during operation of the fuel cell is required. However, such a cooling system may hinder downsizing of the fuel cell, and is not preferable when downsizing of the fuel cell is desired.

  Accordingly, the present invention has been made to solve the above-described problems, and provides a fuel cell system improved to ensure the cooling function of the fuel cell while reducing the size of the fuel cell. Objective.

In order to achieve the above object, a first invention is a fuel cell system,
A fuel cell having an electrolyte membrane, and an anode electrode and a cathode electrode which are a pair of electrodes disposed on both sides of the electrolyte membrane;
A storage means for storing a fuel containing at least N and H as a liquid to be supplied to the fuel cell;
A fuel supply system for vaporizing and supplying the liquid fuel stored in the storage means to the fuel cell;
It is characterized by providing.

  According to a second invention, in the first invention, the fuel is ammonia or hydrazine.

According to a third invention, in the first or second invention,
Separation means for separating the fuel component and water from the exhausted fuel discharged from the anode electrode side;
And a circulation path for supplying the fuel component separated from the separation means to the fuel cell again.

  Here, the separation of the fuel component and the water from the exhaust fuel is not limited to the case where the fuel is completely separated from the exhaust fuel, but the fuel component is separated from the exhaust fuel so as to have a certain high concentration. Anything can be used. Therefore, for example, a certain amount of water may be mixed in the separated fuel component, and a certain amount of fuel component may be mixed in the separated water.

  According to the first aspect of the invention, the fuel cell system stores the fuel in a liquid state, while supplying the fuel to the fuel cell, the fuel can be vaporized and supplied. According to this system, the fuel cell in operation can be efficiently cooled by the vaporization heat lost when the fuel is vaporized. Therefore, the temperature increase of the fuel cell during operation can be suppressed and maintained at an appropriate operation temperature. In addition, in this system, since a device for cooling the fuel cell can be omitted, the fuel cell can be reduced in size.

  According to the second invention, ammonia or hydrazine is used as the fuel. Ammonia or hydrazine is easy to store because it becomes liquid at room temperature in the range of 1 to 10 atmospheres, and also has a great cooling effect because it takes away the heat of vaporization during vaporization. Moreover, since these fuels do not contain carbon, there is an advantage in that carbon dioxide is not generated during power generation.

  According to the third invention, the fuel component can be extracted from the exhausted fuel and recycled again. Thereby, it can circulate and use, maintaining a high fuel concentration, and can improve a fuel utilization rate.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

Embodiment.
FIG. 1 is a schematic diagram for explaining a fuel cell according to an embodiment of the present invention. The fuel cell system shown in FIG. 1 has an alkaline fuel cell 2 using anions as a conductor. The fuel cell 2 has an anion exchange membrane 10 (electrolyte membrane) which is a solid polymer electrolyte membrane. An anode 12 and a cathode 14 are formed on both sides of the anion exchange membrane 10, respectively.

  The anion exchange membrane 10 is a medium that can move hydroxide ions generated by the electrode catalyst of the cathode electrode 14 to the anode electrode 12 side. As the anion exchange membrane 10, for example, a solid polymer membrane having an anion exchange group such as a primary to tertiary amino group, a quaternary ammonium group, a pyridyl group, an imidazole group, a quaternary bilidium group, and a quaternary imidazolium group is used. be able to. Examples of the solid polymer film include hydrocarbon-based and fluorine-based resins.

  Each of the anode electrode 12 and the cathode electrode 14 has an electrode catalyst layer configured by mixing catalyst particles in an electrolyte solution (or ionomer) and applying the mixture to the anion exchange membrane 10. The catalyst particles of the electrodes 12 and 14 have a function of catalyzing a reaction at each electrode described later. Specific catalyst particles include, for example, those formed of iron (Fe), platinum (Pt), cobalt (Co), nickel (Ni), or any one of these metals supported on a carrier such as carbon. And organometallic complexes having these metal atoms as the central metal, or those having such an organometallic complex supported on a carrier.

  Referring to FIG. 1, a separator 16 is provided in contact with the anode electrode 12. The separator 16 is formed with a fuel flow path through which fuel flows, and a fuel inflow hole and a fuel discharge hole formed in communication with the upstream and downstream sides of the fuel flow path, respectively. A separator 18 is provided in contact with the cathode electrode 14. The separator 18 is formed with an oxygen flow path through which air flows, and an oxygen inflow hole and an oxygen discharge hole formed in communication with the upstream and downstream sides of the oxygen flow path, respectively. Moreover, both separators 16 and 18 are each formed with a metal, and have a part which has a function as a current collecting plate. The separators 16 and 18 are connected to an external circuit 20 provided outside the fuel cell 2.

  In FIG. 1, only one set of the power generation unit including the anion exchange membrane 10, the anode electrode 12, and the cathode electrode 14 configured as described above and the pair of separators 16 and 18 disposed on both sides thereof is illustrated. The fuel cell 2 has a stack structure in which a plurality of power generation units are stacked with separators interposed therebetween. When a plurality of power generation units are stacked via separators as described above, the fuel inflow hole and the fuel discharge hole of the separator 16 on the anode electrode 12 side are connected to one to connect the fuel supply manifold 22 and the fuel discharge manifold 24, respectively. Configure. Similarly, the oxygen inflow hole and the oxygen exhaust hole of the separator 18 on the cathode electrode 14 side are connected in series to form an oxygen supply manifold (not shown) and an oxygen discharge manifold (not shown).

A fuel supply path 30 is connected to the fuel inlet of the fuel supply manifold 22 of the fuel cell 2. The fuel supply path 30 is connected to a fuel supply source 32. The fuel supply source 32 stores ammonia (NH ₃ ) as a fuel as a liquid in a state compressed to about 10 atmospheres. A regulator 34 is attached to the fuel supply path 30 so that the compressed fuel supplied from the fuel supply source 32 is adjusted to have a predetermined fuel supply pressure in the fuel supply path 30.

  On the other hand, one end of a circulation path 36 is connected to the fuel discharge port of the fuel discharge manifold 24 of the fuel cell 2. A gas-liquid separator 38 and a stripping device 40 are installed in the circulation path 36. An exhaust passage 42 is connected to the gas-liquid separator 38.

  An air introduction path 44 for supplying air from the outside and a drainage path 46 for discharging treated water to the outside are connected to the lower part of the stripping device 40 (separating means). Inside the stripping device 40, a perforated plate 48 and a downcomer 50 are provided. At the downstream side of the stripping device 40, the end of the circulation path 36 is connected to the fuel supply path 30.

  On the other hand, although not shown, an air supply path for introducing air from the outside is connected to the oxygen inlet of the oxygen supply manifold of the fuel cell 2. A humidifier is installed in the middle of the air supply path, so that the air is humidified to some extent before being supplied to the cathode electrode 14. On the other hand, an air discharge path is connected to the oxygen discharge port of the oxygen discharge manifold of the fuel cell 2. The air discharge path is open to the outside, and the air off-gas discharged from the cathode 14 side is released to the outside through this air discharge path.

  In this system, ammonia as fuel is supplied to the fuel flow path of each separator 16 through the fuel supply manifold 22 in the fuel cell 2 via the fuel supply path 30 and used for the reaction at the anode electrode 12. Exhaust fuel including unreacted fuel and products is discharged to the circulation path 36 via the fuel discharge manifold 24. On the other hand, air is taken into the air supply path from outside by a blower, a compressor (not shown), or the like and is sent under pressure. The pressure-fed air is humidified in a humidifier and is supplied from the oxygen supply manifold in the fuel cell 2 to the oxygen flow path of the cathode electrode 14. The air off-gas containing unreacted oxygen discharged from the cathode electrode 14 is discharged to the outside from the oxygen discharge manifold via the air discharge path.

Here, the fuel supplied to the anode electrode 12 is decomposed by the function of the electrode catalyst of the anode electrode 12 to become hydrogen atoms, and the hydroxide ions (OH ⁻ ) that have passed through the anion exchange membrane 10 react to react with water. (H ₂ O) is produced. At this time, the emitted electrons pass from the separator 16 through the external circuit 20 and move to the cathode 14 side. When ammonia is supplied to the anode electrode 12 as fuel and decomposed, as a result, a reaction represented by the following formula (1) occurs at the anode electrode 12.
2NH ₄ ⁺ + 8OH ⁻ → 8H ₂ O + N ₂ + 6e ⁻ (1)

On the other hand, when air is supplied to the cathode electrode 14, hydroxide ions are generated from oxygen molecules (O ₂ ) and water through several stages due to the function of the electrode catalyst of the cathode electrode 14. The hydroxide ions pass through the anion exchange membrane 10 and move to the anode electrode 12 side. The reaction at the cathode electrode 14 is represented by the following equation (2).
1 / 2O ₂ + H ₂ O + 2e ⁻ → 2OH ⁻ (2)

  Summarizing the reactions on the anode electrode 12 side and the cathode electrode 14 side as described above, the water generation reaction occurs in the entire fuel cell 2, and the electrons move between the two electrodes via the external circuit 20. The work is performed on the load, and energy is extracted.

As described above, in the electrochemical reaction during power generation of the fuel cell 2, water and nitrogen (N ₂ ) are generated from the fuel at the anode 12 as shown in the formula (1). Accordingly, the exhausted fuel discharged from the fuel cell 2 contains a large amount of moisture and nitrogen in addition to unused fuel. That is, unused fuel is in a state diluted with a large amount of moisture. Therefore, in order to circulate and use the exhaust fuel, it is desirable to remove nitrogen and water contained in the exhaust fuel to some extent, so that the fuel concentration can be kept high.

  Therefore, the fuel cell system of this embodiment has a gas-liquid separator 38 and a stripping device 40. The gas-liquid separator 38 separates the exhaust fuel into a liquid ammonia aqueous solution and a gas nitrogen, and removes nitrogen from the exhaust fuel. The separated nitrogen is released into the air through the exhaust passage 42 or is processed by another appropriate method depending on the use environment of the fuel cell 2.

  On the other hand, the stripping device 40 is a device that extracts ammonia from an aqueous ammonia solution by an ammonia stripping method. Specifically, from the circulation path 36 connected to the upper part of the stripping device 40, an aqueous ammonia solution as exhaust fuel after nitrogen is removed is introduced. The aqueous ammonia solution is dammed to the perforated plate 48, but gradually moves downward from the downcomer 50. From the lower part of the stripping device 40, a part of the air of the radiator fan is introduced as a carrier gas via the air introduction path 44. The introduced air passes through the holes of the porous plate 48 of the stripping device 40, flows in the aqueous ammonia solution blocked by the porous plate 48, and moves from the lower stage toward the upper stage.

  In this process, ammonia moves to the gas phase by gas-liquid contact of the aqueous ammonia solution. Thereby, ammonia is gradually removed from the aqueous ammonia solution. The remaining moisture flows from the upper stage to the lower stage through the downcomer 50 and moves downward, and is finally drained from the drainage channel 46 installed at the lower part of the stripping device 40. Here, the ammonia that has moved to the gas phase is joined again into the fuel supply path 30 through the circulation path 36, mixed with the fuel newly supplied from the fuel supply source 32, and supplied to the fuel cell 2.

  Here, the power generation of the fuel cell is accompanied by heat generation due to the reaction heat in the electrochemical reaction. However, in order to suppress the deterioration of the fuel cell and perform effective power generation, it is desirable to maintain the operating temperature of the fuel cell within an appropriate temperature range. Accordingly, it is necessary to cool the fuel cell during operation of the fuel cell in order to suppress a temperature rise due to reaction heat. In general, for example, a method of cooling the fuel cell by circulating cooling water to the reaction part of the fuel cell is used.

  In this fuel cell system, it is desirable that the operating temperature of the fuel cell 2 be 100 [° C.]. However, this is determined in consideration of the activation of the catalyst, durability of the anion exchange membrane 10, activation energy, water vaporization of the water, the size of the radiator (not shown), and the like. Not what you want.

  In the fuel cell system of this embodiment, ammonia compressed to about 10 atmospheres is stored in the fuel supply source 32 as a liquid. When the fuel is supplied into the fuel cell 2, the fuel is reduced to a predetermined supply pressure by the regulator 34 and supplied. Ammonia gradually vaporizes from the liquid to the gas while passing through the fuel supply passage 30 and the fuel supply manifold 22. Ammonia once becomes a gas in the fuel supply manifold 22, but when introduced into the fuel flow path of the anode electrode 12, the ammonia dissolves in the water existing in the vicinity and flows through the fuel flow path as ammonia water. It becomes.

  By the way, when ammonia vaporizes, it takes 22.3 [KJ / mol] heat of vaporization. Therefore, when ammonia is vaporized in the fuel supply path 30 and the fuel supply manifold 22, the vicinity of the fuel supply path 30 and the fuel supply manifold 22 is cooled by the heat of vaporization. Since the separators 16 and 18 constituting the fuel supply manifold 22 are made of metal, the thermal conductivity is high. Therefore, when the inside of the fuel supply manifold 22 is cooled by the vaporization of ammonia, the temperature is efficiently transmitted to the entire separator 16 and eventually the entire power generation unit of the fuel cell 2 to cool the entire fuel cell 2. Therefore, the inside of the fuel cell 2 is inevitably cooled by the supply of liquid ammonia, and the temperature rise of the fuel cell 2 is suppressed.

  As described above, according to the system of the first embodiment, it is possible to cool the fuel cell 2 without providing a particularly large cooling system by vaporizing and supplying liquid ammonia. That is, according to the system of this embodiment, the cooling system including the cooling water and the cooling fan for cooling the cooling water can be omitted, and the fuel cell can be simplified and downsized.

  In this embodiment, the case where ammonia is used as the fuel has been described. However, in the present invention, the fuel for the fuel cell is not limited to ammonia. As the fuel, any fuel can be used as long as it is liquid at room temperature of about 1 to 10 atm, becomes gas at the fuel supply pressure, and takes heat of vaporization upon vaporization. Specifically, for example, hydrazine can be used.

  Further, in this embodiment, a case has been described in which nitrogen is removed from the exhausted fuel by passing the gas-liquid separator 38 before the exhausted fuel is introduced into the stripping device 40. However, the present invention is not limited to the one having the gas-liquid separator 38 as described above.

  Moreover, in this embodiment, the case where the separators 16 and 18 were formed with the metal was demonstrated. Thereby, the heat conductivity of the separators 16 and 18 can be made high, and cooling by vaporization heat can be performed effectively. However, the present invention is not limited to this, and the separator may be formed of another member. Further, the present invention is not limited to the one that cools the fuel cell by the heat conduction of the separator. For example, as in the past, a cooling medium such as cooling water is circulated in the separator to cool the fuel cell, and the cooling medium is cooled in a portion where the temperature drop due to vaporization heat is large. It can also be.

Further, when the fuel cell 2 is mounted on a vehicle and used as a main power source, a large amount of hydrogen is required per unit time. In order to effectively decompose ammonia into N and H so as to generate a large amount of hydrogen in this way, after heating to 600 [° C.] or higher and performing high decomposition through the catalyst, H ₂ is further decomposed at the anode electrode. Such a method is conceivable. However, in this case, it is conceivable that the system for the decomposition is complicated and complicated. Therefore, considering the miniaturization of the space in the fuel cell and the system in which the fuel cell is mounted, for example, when mounted on a vehicle, an auxiliary power source for driving an auxiliary machine such as an air conditioner is used as a relatively power It is desirable to apply to small things. In addition, this fuel cell system is not limited to being mounted on a vehicle, and is suitable for use as a small power source of 10 kW or less, such as an electric wheelchair, a nursing care and an attraction robot, and the like.

  In addition, in this embodiment, when the number of each element, quantity, quantity, range, etc. is mentioned, the number mentioned unless it is clearly specified or the number is clearly specified in principle. It is not limited to. The structures described in the embodiments are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

  The fuel supply source 32 in this embodiment corresponds to the “storage means” of the present invention, the fuel supply path 30, the regulator 34, and the fuel supply manifold 22 correspond to the “fuel supply system”, and the stripping device 40. Corresponds to “separation means”, and the circulation path 36 corresponds to “circulation path”.

It is a schematic diagram for demonstrating the fuel cell system of embodiment of this invention.

Explanation of symbols

2 Fuel Cell 10 Anion Exchange Membrane 12 Anode Electrode 14 Cathode Electrode 16, 18 Separator 20 External Circuit 22 Fuel Supply Manifold 24 Fuel Discharge Manifold 30 Fuel Supply Path 32 Fuel Supply Source 34 Regulator 36 Circulation Path 38 Gas-Liquid Separator 40 Stripping Device 42 Exhaust passage 44 Air introduction passage 46 Drainage passage 48 Perforated plate 50 Downcomer

Claims (3)

A fuel cell having an electrolyte membrane, and an anode electrode and a cathode electrode which are a pair of electrodes disposed on both sides of the electrolyte membrane;
A storage means for storing a fuel containing at least N and H as a liquid to be supplied to the fuel cell;
A fuel supply system for vaporizing and supplying the liquid fuel stored in the storage means to the fuel cell;
A fuel cell system comprising:   The fuel cell system according to claim 1, wherein the fuel is ammonia or hydrazine. Separation means for separating the fuel component and water from the exhausted fuel discharged from the anode electrode side;
The fuel cell system according to claim 1, further comprising a circulation path for supplying the fuel component separated from the separation unit to the fuel cell again.

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