JP2019067490A - Fuel cell system - Google Patents

Abstract

To provide a fuel cell system which is superior in power generation efficiency and durability.SOLUTION: A fuel cell system 2 comprises: a fuel cell 3 having an electrolyte layer 8, an anode electrode 9 and a cathode electrode 10; a fuel supplying unit 21 for supplying a liquid fuel to the anode electrode 9; and an air-supplying unit 24 for supplying oxygen to the cathode electrode 10. The air-supplying unit 24 includes a humidity regulator 50 for regulating a relative humidity of air. The liquid fuel contains hydrazine. The anode electrode includes a PtNi alloy and elemental Pt. The humidity regulator 50 regulates the relative humidity of air to 26% or under.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system provided with a liquid fuel supplied fuel cell.

  BACKGROUND Conventionally, a fuel cell system using a liquid fuel containing hydrazine is known as a fuel cell system mounted on a vehicle or the like.

  As such a fuel cell system, for example, a fuel cell provided with a membrane / electrode assembly in which an anode and a cathode are respectively joined to one surface and the other surface of an electrolyte membrane, a fuel supply path for supplying fuel to the anode An air supply path for supplying air to the cathode, and a humidifier for humidifying the air supplied to the cathode through the air supply path, the humidifier including the air supplied to the cathode at a relative humidity of at least 20% and A fuel cell system is known which humidifies to be in the range of 60% or less (see, for example, Patent Document 1).

  In such a fuel cell, the liquid fuel is supplied to the fuel side electrode and the air is supplied to the oxygen side electrode, whereby the electrochemical reaction shown in the following formulas (1) and (2) occurs, and the electromotive force Occurs.

(1) N ₂ H ₄ + ₄ OH ⁻ → N ₂ + 4 H ₂ O + 4 e ⁻ (Reaction at fuel side electrode)
(2) O ₂ + 2H ₂ O + 4 e ⁻ → 4 OH ⁻ (Reaction on the oxygen side electrode)

JP, 2015-185525, A

  On the other hand, as a fuel cell system, improvement in power generation efficiency is required, and further, improvement in durability is also required.

  The present invention is a fuel cell system excellent in power generation efficiency and durability.

  A first invention [1] is a fuel cell having an electrolyte layer capable of moving an anion component, an anode electrode disposed on one side of the electrolyte layer, and a cathode electrode disposed on the other side of the electrolyte layer A fuel supply unit for supplying liquid fuel to the anode electrode; and an oxygen supply unit for supplying air to the cathode electrode, the oxygen supply unit including humidity adjustment means for adjusting the relative humidity of the air; The liquid fuel includes hydrazines, the anode electrode includes a PtNi alloy, and Pt alone, and the humidity control unit includes a fuel cell system that adjusts the relative humidity of the air to 26% or less. There is.

A second invention [2] is a fuel cell having an electrolyte layer capable of moving an anion component, an anode electrode disposed on one side of the electrolyte layer, and a cathode electrode disposed on the other side of the electrolyte layer A fuel supply unit for supplying liquid fuel to the anode electrode; an oxygen supply unit for supplying air to the cathode electrode; and power extracting means for extracting electric power from the fuel cell, wherein the liquid fuel comprises hydrazines. The fuel cell system includes: the anode electrode includes a PtNi alloy; and Pt alone, and the power extracting means extracts power from the fuel cell at a current density of 170 to 180 mA / cm ² .

  In the fuel cell systems of the first and second inventions, the liquid fuel contains hydrazines, and the anode electrode contains PtNi alloy and Pt alone.

  In such a fuel cell system, when liquid fuel is supplied to the anode electrode, the PtNi alloy acts as a hydrazine decomposition catalyst at the anode electrode, and as shown in the following formula (3), hydrazines are nitrogen and hydrogen Disassemble.

(3) N ₂ H ₄ → N ₂ + 2H ₂
Next, at the anode electrode, Pt alone acts as a hydrogen oxidation catalyst to oxidize hydrogen generated by decomposition of hydrazine as shown in the following formula (4).

(4) 2H ₂ + 4 OH ⁻ → 4 H ₂ O + 4 e ⁻
The water thus generated permeates through the electrolyte layer and leaks to the cathode electrode to humidify the air supplied to the cathode electrode.

  Thereby, at the cathode electrode, an electrochemical reaction shown in the following formula (5) occurs.

(5) O ₂ + 2H ₂ O + 4 e ⁻ → 4 OH ⁻
That is, the reaction represented by the following formula (6) continuously occurs in the entire fuel cell, and an electromotive force is generated in the fuel cell.

(6) N ₂ H ₄ + O ₂ → N ₂ + 2H ₂ O
According to such an electrochemical reaction, electric power can be efficiently extracted as compared with the electrochemical reaction in which hydrazine is directly oxidized as represented by the above-mentioned formula (1) and the above-mentioned formula (2).

  In addition, in the first invention, the relative humidity of the air supplied to the cathode electrode is adjusted to 26% or less by the humidity adjusting means. Therefore, according to the first invention, the durability can be improved.

In the second aspect of the invention, the electric power is taken out of the fuel cell by the electric power taking means at a current density of 170 to 180 mA / cm ² . Therefore, according to the second invention, the durability can be improved.

FIG. 1 is a schematic block diagram of an electric vehicle equipped with an embodiment of the fuel cell system of the first invention. FIG. 2 is a schematic configuration view showing a unit cell of the fuel cell shown in FIG. FIG. 3 is a schematic block diagram of an electric vehicle equipped with an embodiment of the fuel cell system of the second invention. FIG. 4 is a graph showing the relationship between the relative humidity of air and the power density and operating time of the fuel cell. FIG. 5 is a graph showing the relationship between the current density when extracting power and the power density of the fuel cell and the operation time. FIG. 6 is a graph showing the relationship between current density and power density.

I. First Invention General Configuration of Fuel Cell System In FIG. 1, an electric vehicle 1 is a hybrid vehicle that selectively uses a fuel cell and a battery as a power source, and is equipped with a fuel cell system 2.

The fuel cell system 2 includes a fuel cell 3, a fuel supply and discharge unit 4, an air supply and discharge unit 5, a control unit 6, and a power unit 7.
(1) Fuel Cell The fuel cell 3 is a solid polymer fuel cell (anion exchange fuel cell) to which liquid fuel is directly supplied. The fuel cell 3 is disposed below the center of the electric vehicle 1.

  The fuel cell 3 is formed in a stack structure in which a plurality of fuel cells (unit cells) including the membrane electrode assembly 11, the fuel supply member 12, and the oxygen supply member 17 are stacked. In FIG. 2, only one of the plurality of unit cells is shown as the fuel cell 3, and the other unit cells are omitted.

  As shown in FIG. 2, the membrane electrode assembly 11 includes an electrolyte layer 8, an anode electrode 9, and a cathode electrode 10. The anode electrode 9 and the cathode electrode 10 are disposed opposite to each other with the electrolyte layer 8 interposed therebetween.

The electrolyte layer 8 is capable of moving an anion component, and is formed of an anion exchange membrane. The anion exchange membrane, anion component (e.g., a hydroxide ion (OH ^-), etc.) as long as the movable medium is not particularly limited, for example, quaternary ammonium groups, the anion-exchange group such as a pyridinium group The solid polymer membrane (anion exchange resin) which it has can be mentioned.

  The thickness of the electrolyte layer 8 is, for example, 5 μm or more, preferably 10 μm or more, and for example, 50 μm or less, preferably 30 μm or less.

  The anode electrode 9 is disposed on one side of the electrolyte layer 8. The thickness of the anode electrode 9 is, for example, 10 μm or more, preferably 20 μm or more, for example, 200 μm or less, preferably 100 μm or less. The details of the anode electrode 9 will be described later.

  The cathode electrode 10 is disposed on the other side of the electrolyte layer 8 (the opposite side of the anode electrode 9 with respect to the electrolyte layer 8). The cathode electrode 10 contains, for example, a cathode catalyst. The cathode electrode 10 is formed of, for example, a catalyst carrier (for example, a porous material such as carbon, etc.) supporting a cathode catalyst. Alternatively, the cathode catalyst may be formed directly as the cathode electrode 10 without using a catalyst carrier.

  As a cathode catalyst, a metal simple substance, a transition metal complex, etc. are mentioned, for example.

  Examples of the metal simple substance include platinum group elements (ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt)), iron group elements (iron (Fe) Periodic table group 8 to 10 (VIII) elements such as cobalt (Co) and nickel (Ni), for example, periodic table 11 (IB) such as copper (Cu), silver (Ag) and gold (Au) Group elements, furthermore, zinc (Zn) and the like. Such a single metal can be used alone or in combination of two or more.

  The transition metal complex is a metal complex in which an organic compound is coordinated to a transition metal element (central metal). As a transition metal element, for example, scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper ( Cu), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), lanthanum ( La), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au). Such transition metals can be used alone or in combination of two or more.

  Examples of the organic compound which coordinates to the transition metal element include pyrrole, porphyrin, tetramethoxyphenyl porphyrin, dibenzotetraazaannulene, phthalocyanine, choline, chlorin, phenanthroline, sarcomine, nicarbazin, pipemidic acid type compound, aminobenzimidazole, amino Antipyrine or polymers thereof are mentioned. Such organic compounds can be used alone or in combination of two or more.

  The thickness of the cathode electrode 10 is, for example, 0.1 μm or more, preferably 1 μm or more, for example, 100 μm or less, preferably 10 μm or less.

  The fuel supply member 12 is made of a gas impermeable conductive member, and one surface of the fuel supply member 12 is in opposite contact with the anode electrode 9. In the fuel supply member 12, a fuel side flow passage 13 for bringing the fuel into contact with the whole of the anode electrode 9 is formed as a creased groove which is recessed from one surface. Further, the fuel supply member 12 is formed with a supply port 15 and a discharge port 14 communicating with the fuel side flow path 13 at the upstream end and the downstream end.

  Similar to the fuel supply member 12, the oxygen supply member 17 is made of a gas-impermeable conductive member, and one surface of the oxygen supply member 17 is in opposite contact with the cathode electrode 10. In the oxygen supply member 17, an oxygen-side flow passage 18 for bringing oxygen (air) into contact with the whole of the cathode electrode 10 is formed as a creased groove recessed from one surface. A supply port 19 and a discharge port 20 communicating with the oxygen-side flow path 18 are formed in the upstream side end and the downstream side end of the oxygen-side flow path 18.

(2) Fuel Supply and Discharge Unit As shown in FIG. 1, the fuel supply and discharge unit 4 includes a fuel supply unit 21 as an example of a fuel supply unit, a fuel discharge line 31, a gas-liquid separator 23, and a reflux line 32. And have.

  The fuel supply unit 21 is configured to supply liquid fuel to the anode electrode 9. The fuel supply unit 21 includes a fuel tank 22, a fuel supply line 30, a fuel supply pump 33, and a fuel supply valve 34.

  The fuel tank 22 is disposed to the rear of the electric vehicle 1 and to the rear of the fuel cell 3. The fuel tank 22 stores liquid fuel. Liquid fuel includes hydrazines.

  Specifically, the liquid fuel contains hydrazines and water, and preferably comprises hydrazines and water. That is, the liquid fuel is an aqueous solution in which hydrazines are dissolved in water.

As the hydrazines, for example, hydrazine (NH ₂ NH ₂ ), hydrazine hydrate (NH ₂ NH ₂ · H ₂ O), hydrazine carbonate ((NH ₂ NH ₂ ) ₂ CO ₂ ), hydrazine hydrochloride (NH ₂ NH ₂₎ · HCl), hydrazine sulfate _{(NH 2 NH 2 · H 2} SO 4), monomethyl hydrazine _(CH 3 NHNH _2), dimethylhydrazine _{((CH 3) 2 NNH 2} , CH 3 NHNHCH 3), a carboxylic hydrazide ((NHNH _{2 2} ) CO) etc.

  The hydrazines can be used alone or in combination of two or more. Among hydrazines, preferably, non-carbon-containing hydrazines, that is, hydrazine, hydrazine hydrate, hydrazine sulfate and the like can be mentioned, and more preferably hydrazine hydrate can be mentioned.

  The concentration of hydrazines to the liquid fuel is, for example, 0.1% by volume or more, preferably 0.5% by volume or more, for example, less than 20% by volume, preferably 10% by volume or less, more preferably 5% by volume It is below.

  However, when the liquid fuel supplied to the anode electrode 9 permeates the electrolyte layer 8 and leaks to the cathode electrode 10, active species (strong In some cases, the output of the fuel cell 3 may be reduced.

  However, even if the liquid fuel passes through the electrolyte layer 8 and leaks to the cathode electrode 10 as the concentration of hydrazines to the liquid fuel is below the above-mentioned upper limit, the reaction between hydrazines and oxygen can be suppressed, and the fuel The output reduction of the battery 3 can be suppressed. Further, when the concentration of hydrazines with respect to the liquid fuel is above the lower limit, the amount of hydrogen necessary for the power generation reaction of the fuel cell 3 can be sufficiently ensured, and the output performance of the fuel cell 3 can be surely ensured.

  In addition, the liquid fuel preferably contains an alkali metal hydroxide as a supporting electrolyte. That is, the liquid fuel preferably comprises hydrazines, water and an alkali metal hydroxide.

  Examples of the alkali metal hydroxide include potassium hydroxide and sodium hydroxide. These can be used alone or in combination of two or more. As an alkali metal hydroxide, Preferably, potassium hydroxide is mentioned.

  The concentration of the alkali metal hydroxide relative to the liquid fuel is, for example, 1% by mass or more, preferably 1.5% by mass or more, more preferably 2% by mass or more, and still more preferably 2.5% by mass or more. For example, the content is 10% by mass or less, preferably 8% by mass or less, more preferably 7% by mass or less, and still more preferably 6% by mass or less.

  If the liquid fuel contains an alkali metal hydroxide in the above proportion, the power generation efficiency can be improved.

  The fuel supply line 30 is a pipe for transporting liquid fuel from the fuel tank 22 to the fuel cell 3 (specifically, the fuel side flow path 13). The upstream end of the fuel supply line 30 is connected to the fuel tank 22. The downstream end of the fuel supply line 30 is connected to the supply port 15 of the fuel side flow path 13 (see FIG. 2).

  The fuel supply pump 33 is provided on the fuel supply line 30 between the fuel tank 22 and the fuel cell 3. The fuel supply pump 33 is, for example, a known liquid supply pump.

  The fuel supply valve 34 is provided in the fuel supply line 30 between the fuel supply pump 33 and the fuel tank 22. The fuel supply valve 34 is a known on-off valve for opening and closing the fuel supply line 30.

  Then, the fuel supply valve 34 opens the fuel supply line 30 and the fuel supply pump 33 is driven, whereby liquid fuel is supplied from the fuel tank 22 to the fuel side flow path 13 of the fuel cell 3. The fuel supply unit 21 does not include a reformer for reforming the hydrazine contained in the liquid fuel supplied from the fuel tank 22 to the fuel cell 3 into hydrogen.

  The fuel discharge line 31 is a pipe for transporting the liquid fuel discharged from the fuel cell 3 (specifically, the fuel side flow passage 13). The upstream end of the fuel discharge line 31 is connected to the discharge port 14 of the fuel flow passage 13 (see FIG. 2). The downstream end of the fuel discharge line 31 is connected to the lower part of the gas-liquid separator 23.

  The gas-liquid separator 23 is interposed between the fuel discharge line 31 and the reflux line 32. The gas-liquid separator 23 comprises, for example, a hollow container. The downstream end of the fuel discharge line 31 is connected to the lower portion of the gas-liquid separator 23. In addition, a gas discharge pipe 26 is connected to the upper portion of the gas-liquid separator 23.

  The gas discharge pipe 26 is a pipe for discharging the gas (gas) separated by the gas-liquid separator 23 from the electric vehicle 1. The upstream end of the gas discharge pipe 26 is connected to the top of the gas-liquid separator 23. The downstream end of the gas discharge pipe 26 is open to the atmosphere. A gas discharge valve 27 is provided in the middle of the gas discharge pipe 26.

  The gas exhaust valve 27 is a valve for opening the gas exhaust pipe 26 to release the pressure in the gas-liquid separator 23. For example, a known on-off valve is used.

  The reflux line 32 is a pipe for transporting the liquid fuel separated by the gas-liquid separator 23 from the gas-liquid separator 23 to the fuel supply line 30. The upstream end of the reflux line 32 is connected to the lower part of the gas-liquid separator 23. The downstream end of the return line 32 is connected to the fuel supply line 30 between the fuel supply pump 33 and the fuel supply valve 34. Thus, the fuel supply line 30, the fuel cell 3 (fuel side flow path 13), the fuel discharge line 31, the gas-liquid separator 23, and the return line 32 form a closed line (closed flow path).

  The liquid fuel discharged from the fuel cell 3 flows into the gas-liquid separator 23 through the fuel discharge line 31, and then the gas is separated, and is returned to the fuel supply line 30 through the reflux line 32.

(3) Air Supply and Discharge Unit The air supply and discharge unit 5 includes an air supply unit 24 as an example of an oxygen supply unit, and an air discharge line 42.

  The air supply unit 24 is configured to supply oxygen (air) to the cathode electrode 10. The air supply unit 24 includes an air supply line 41, an air supply pump 43, an air supply valve 44, and a humidity adjustment device 50 as humidity adjustment means.

  The air supply line 41 is a pipe for sending air from the outside of the electric vehicle 1 to the fuel cell 3 (specifically, the oxygen-side flow path 18). The upstream end of the air supply line 41 is open to the atmosphere. The downstream end of the air supply line 41 is connected to the supply port 19 of the oxygen-side flow path 18 (see FIG. 2).

  The air supply pump 43 is provided in the middle of the air supply line 41. The air supply pump 43 is, for example, a known gas pump.

  The air supply valve 44 is provided in the air supply line 41 between the air supply pump 43 and the fuel cell 3. The air supply valve 44 is a known on-off valve for opening and closing the air supply line 41.

  The humidity adjustment device 50 is provided downstream of the air supply pump 43 and the air supply valve 44 in the air supply line 41. The humidity adjustment device 50 may have a known configuration for adjusting the humidity of air, and includes, for example, a humidifier, a dehumidifier, a heater, a moisture meter, and the like.

  In the air supply / discharge unit 5 as described above, the air supply valve 44 opens the air supply line 41 and the air supply pump 43 is driven so that the air flows from the outside of the electric vehicle 1 to the oxygen side flow of the fuel cell 3. It is supplied to the passage 18.

  Further, although the details will be described later, the relative humidity of the air supplied to the oxygen-side flow passage 18 is adjusted by the humidity adjustment device 50.

  More specifically, in the air supply line 41, the air is adjusted to a predetermined temperature by the heater of the humidity adjusting device 50, and the relative humidity of the air at that temperature is measured by the moisture meter. Then, the humidifier or the dehumidifier is operated so that the relative humidity of the air becomes a preset value.

  The air discharge line 42 is a pipe for sending the air discharged from the fuel cell 3 (specifically, the oxygen-side flow passage 18). The upstream end of the air discharge line 42 is connected to the discharge port 20 of the oxygen-side flow passage 18. The downstream end of the air discharge line 42 is a drain.

  Then, the air discharged from the fuel cell 3 is discharged to the outside of the electrically powered vehicle 1 via the air discharge line 42.

(4) Control Unit The control unit 6 includes a control unit 29. The control unit 29 is a unit (for example, an ECU: Electronic Control Unit) that executes electrical control in the electrically powered vehicle 1, and is configured of a microcomputer including a CPU, a ROM, a RAM, and the like. The control unit 29 is electrically connected to each pump (the fuel supply pump 33 and the air supply pump 43) and each valve (the fuel supply valve 34, the gas discharge valve 27 and the air supply valve 44) (broken line in FIG. 1). reference). Thus, the control unit 29 appropriately controls the drive and stop of each pump and appropriately controls the opening and closing of each valve.

  In addition, the control unit 29 is electrically connected to the humidity adjustment device 50 (see a broken line in FIG. 1). Thus, the control unit 29 can control the humidity adjustment device 50, and can adjust the humidity of the air in the air supply line 41.

(5) Power Unit The power unit 7 includes a motor 37, an inverter 38, a battery 40, and a converter 36.

  The motor 37 converts the electrical energy output from the fuel cell 3 into mechanical energy as a driving force of the electric vehicle 1. The motor 37 is disposed on the front side of the electric vehicle 1 and in front of the fuel cell 3.

  The inverter 38 is a device for converting direct current power generated by the fuel cell 3 into alternating current power. The inverter 38 is disposed between the motor 37 and the fuel cell 3. The inverter 38 is electrically connected to the fuel cell 3 and the motor 37 by wiring.

  The battery 40 stores energy regenerated by the motor 37. The battery 40 is connected by a wire between the inverter 38 and the fuel cell 3. Thereby, the battery 40 can store the electric power from the fuel cell 3 and can supply the electric power to the motor 37.

  The converter 36 has a function of boosting and lowering the output voltage of the fuel cell 3 and has a function of adjusting the power of the fuel cell 3 and the input and output power of the battery 40. Converter 36 is disposed between battery 40 and fuel cell 3. Converter 36 is electrically connected to control unit 29 (see the broken line in FIG. 1), and thereby controls the output of fuel cell 3 in accordance with the input of the output control signal output from control unit 29. .

  The converter 36 is electrically connected to the fuel cell 3 and the battery 40 by wiring, and is electrically connected to the inverter 38 by branching of the wiring. Thus, the power from converter 36 to motor 37 is converted from DC power to AC power in inverter 38 and supplied to motor 37.

2. Details of Anode Electrode As shown in FIG. 2, the anode electrode 9 contains a PtNi alloy and a single Pt as an anode catalyst.

  The PtNi alloy is a hydrazine decomposition catalyst and is an alloy of platinum (Pt) and nickel (Ni).

  The content ratio of platinum in the PtNi alloy is, for example, 1 mol% or more, preferably 5 mol% or more, for example 70 mol% or less, preferably 60 mol% or less, based on the total number of moles of platinum and nickel. is there.

  The content ratio of nickel in the PtNi alloy is, for example, 30 mol% or more, preferably 40 mol% or more, for example 99 mol% or less, preferably 95 mol% or less, based on the total number of moles of platinum and nickel. is there.

  Such PtNi alloy is preferably supported on a catalyst support. That is, preferably, the anode electrode 9 contains a catalyst support carrying a PtNi alloy (hereinafter, referred to as a PtNi carrying support).

  Examples of the catalyst carrier include porous materials such as carbon. Examples of carbon include ketjen black, acetylene black, furnace black, channel black, thermal black, lamp black and the like. Among the carbon blacks, preferably ketjen black is mentioned. These carbon blacks can be used alone or in combination of two or more.

  The average primary particle diameter of the PtNi-supported carrier is, for example, 0.001 μm or more, preferably 0.005 μm or more, for example, 0.1 μm or less, preferably 0.05 μm or less. The average primary particle size can be measured by a transmission electron microscope.

The specific surface area of the PtNi-supported carrier is, for example, 100 m ² / g or more, preferably 300 m ² / g or more, for example, 1200 m ² / g or less, preferably 1000 m ² / g or less. In addition, a specific surface area is measured by the carrier gas method based on JISZ 8830 (2013).

  In order to prepare such a PtNi alloy, for example, a salt of nickel, a platinum complex and, if necessary, a catalyst support are mixed in the above proportions to prepare a catalyst raw material.

  Examples of the salt of nickel include inorganic salts (eg, sulfate, nitrate, chloride, phosphate etc.), organic acid salts (eg, acetate, oxalate etc.) and the like, preferably inorganic Salts, more preferably nitrates. The salts of nickel can be used alone or in combination of two or more.

  As a platinum complex, a hexachloro platinum (IV) acid, a dichloro platinum (II) acid, etc. are mentioned, for example, Preferably, a hexachloro platinum (IV) acid is mentioned. The platinum complexes can be used alone or in combination of two or more.

  The mixing method is not particularly limited, and examples thereof include known methods such as wet mixing and dry mixing, and preferably include wet mixing.

  In order to wet-mix the nickel salt and the platinum complex, the nickel salt and the platinum complex are dissolved and stirred in water where the catalyst support is dispersed, if necessary.

  The mixing time (stirring time) is, for example, 5 hours or more, preferably 10 hours or more, for example, 50 hours or less, preferably 40 hours or less.

  Next, the catalyst raw material is dried if necessary and then calcined. Specifically, the catalyst raw material is fired, for example, under an atmosphere of an inert gas (for example, nitrogen gas, argon gas or the like) or a reducing gas (for example, a mixed gas of nitrogen gas and hydrogen gas). Preferably, the catalyst raw material is calcined under an inert gas atmosphere.

  As the firing conditions, the firing temperature is, for example, 400 ° C. or more, preferably 500 ° C. or more, for example, 1500 ° C. or less, preferably 1000 ° C. or less, more preferably 900 ° C. or less.

  However, in the decomposition reaction of hydrazine, it may be decomposed into ammonia or may be decomposed into nitrogen and hydrogen. When the calcination temperature is in the above range, the selectivity for decomposition to nitrogen and hydrogen can be improved in the decomposition reaction of hydrazine, and hydrogen can be efficiently generated.

  The baking time is, for example, 15 minutes or more, preferably 30 minutes or more, for example, 5 hours or less, preferably 3 hours or less. The catalyst raw material can be calcined in one step or in multiple steps.

  By this, the catalyst raw material is calcined to prepare a PtNi alloy (PtNi-supported carrier).

  Pt alone is a hydrogen oxidation catalyst and is a platinum single metal.

  The content ratio of the single Pt is, for example, 0.1 parts by mass or more, preferably 0.5 parts by mass or more, for example, 10 parts by mass or less, preferably 5 parts by mass or less with respect to 1 part by mass of the PtNi alloy. is there.

  The content ratio of the single Pt is, for example, 9% by mass or more, preferably 33% by mass or more, for example 90% by mass or less, preferably 83% by mass or less based on the total mass of the PtNi alloy and the single Pt .

  The content ratio of Pt alone is, for example, 5% by mass or more, preferably 25% by mass or more, for example, 80% by mass or less, preferably 70% by mass or less, based on the total mass of the anode electrode 9.

  Such Pt alone is preferably supported on the above catalyst support. That is, preferably, the anode electrode 9 contains a catalyst support (hereinafter, referred to as a Pt-supporting support) supporting the Pt-supporting unit.

  The average primary particle diameter of the Pt-supported single carrier is, for example, 0.001 μm or more, preferably 0.003 μm or more, for example, 0.1 μm or less, preferably 0.05 μm or less.

The specific surface area of the single Pt-supporting carrier is, for example, 100 m ² / g or more, preferably 300 m ² / g or more, for example, 1200 m ² / g or less, preferably 1000 m ² / g or less.

  In order to prepare a Pt single-support carrier, the platinum complex and the catalyst carrier described above are mixed in the same manner as described above and then fired.

  The anode electrode 9 may further contain an ionomer. Examples of the ionomer include hydrocarbon-based ionomers, fluorine-based ionomers, urethane-based ionomers and the like, preferably hydrocarbon-based ionomers. The ionomers can be used alone or in combination of two or more.

  In addition, the content ratio of the ionomer is, for example, 0.1 parts by mass or more, preferably 0.3 parts by mass or more, for example, 1.0 part by mass, with respect to 1 part by mass of the anode catalyst (a mixture of PtNi alloy and Pt alone). It is not more than mass part, preferably not more than 0.8 mass part.

  In order to prepare such an anode electrode 9, first, a PtNi alloy (preferably, a PtNi-supported carrier) and a Pt simple substance (preferably, a Pt single-supported carrier) are mixed in the above ratio.

  The mixing method is not particularly limited, and examples thereof include known methods such as wet mixing and dry mixing, and preferred examples include dry mixing. As a mixing apparatus, well-known mixers, such as a ball mill, are mentioned, for example.

  Thus, a cathode catalyst containing PtNi alloy and Pt alone is prepared.

  Then, a cathode catalyst and, if necessary, an ionomer are dispersed in a solvent to prepare a dispersion (cathode electrode ink).

  Examples of the solvent include organic solvents such as alcohols (for example, methanol, ethanol, 1-propanol, 2-propanol and the like), ethers (for example, tetrahydrofuran and the like) and the like, for example, water and the like. These solvents can be used alone or in combination of two or more.

  Then, the dispersion is applied to one surface of the electrolyte layer 8 and dried. Thus, the anode electrode 9 fixed on one surface of the electrolyte layer 8 is prepared.

3. Power Generation by Fuel Cell System In the fuel cell system 2 described above, the fuel supply valve 34 is opened by the control of the control unit 29, and the liquid fuel stored in the fuel tank 22 is driven by driving the fuel supply pump 33. The fuel is supplied to the fuel side flow passage 13 via the fuel supply line 30. Further, the air supply valve 44 is opened and the air supply pump 43 is driven, whereby air is supplied to the oxygen-side flow passage 18 through the air supply line 41.

  Then, the liquid fuel passes through the fuel channel 13 while being in contact with the anode electrode 9. As a result, electrochemical reactions shown in the following (A) and (B) occur at the anode electrode 9.

(A) N ₂ H ₄ → N ₂ + 2H ₂ (reaction at the anode electrode 9)
(B) 2H ₂ + 4 OH ⁻ → 4 H ₂ O + 4 e ⁻ (Reaction at the anode electrode 9)
In addition, when the liquid fuel passes through the fuel side flow path 13, a part of the liquid fuel passes through the electrolyte layer 8 and leaks to the cathode electrode 10. The liquid fuel contains water produced by the reaction shown in the above (B). Therefore, the water contained in the liquid fuel leaked to the cathode electrode 10 humidifies the air passing through the oxygen-side flow passage 18.

  Then, the humidified air passes through the oxygen-side flow passage 18 while being in contact with the cathode electrode 10. Thereby, in the cathode electrode 10, an electrochemical reaction shown in the following (C) occurs.

(C) O ₂ + 2H ₂ O + 4 e ⁻ → 4 OH ⁻ (Reaction at cathode electrode 10)
That is, a reaction represented by the following formula (D) continuously occurs in the entire fuel cell 3, and an electromotive force is generated in the fuel cell 3.

(D) N ₂ H ₄ + O ₂ → N ₂ + 2H ₂ O (reaction in the entire fuel cell 3)
4. Adjustment of Humidity On the other hand, in the above-mentioned electrochemical reaction (the above formulas (A) to (D)), sufficient durability can not be obtained depending on the relative humidity of the air supplied to the cathode electrode 10. The output may decrease with the continuous operation of.

  Therefore, in the fuel cell system 2 described above, by operating the humidity adjustment device 50, the air is humidified and / or dehumidified in the air supply line 41, and adjusted to a predetermined relative humidity.

  More specifically, in the fuel cell system 2, when liquid fuel and air are supplied to the fuel cell 3, the humidity adjustment device 50 is operated by the control of the control unit 29.

  When the humidity adjustment device 50 operates, the heater adjusts the air in the air supply line 41 to a predetermined temperature, and the relative humidity of the air at that temperature is measured by the moisture meter. Then, the humidifier or the dehumidifier is operated so that the relative humidity of the air becomes a preset value.

  The relative humidity adjusted by the humidity adjusting device 50 is 26% or less, preferably 25% or less, more preferably 20% or less, still more preferably 16% or less, and usually 0% or more.

  If the relative humidity of the air exceeds the upper limit, moisture contained in the air is deposited on the oxygen-side flow path 18 to inhibit the diffusion of oxygen, as described later, resulting in poor durability.

  On the other hand, if the relative air humidity is adjusted to the above range, an excellent output can be obtained, and a decrease in the output when the fuel cell system 2 is continuously operated can be suppressed, and the excellent durability You can get sex.

5. Operation and Effect of the First Invention In the fuel cell system 2 described above, the liquid fuel contains hydrazines. Further, the anode electrode 9 contains a PtNi alloy and a single Pt.

  In such a fuel cell system 2, when liquid fuel is supplied to the anode electrode 9, the PtNi alloy acts as a hydrazine decomposition catalyst at the anode electrode 9 and, as shown in the above formula (A), hydrazines are nitrogen And hydrogen. Therefore, the fuel cell system 2 does not need a reformer for reforming hydrazines to hydrogen.

  Next, at the anode electrode 9, Pt alone acts as a hydrogen oxidation catalyst to oxidize hydrogen generated by the decomposition of hydrazine as shown in the above-mentioned formula (B).

  Further, the liquid fuel contains water produced by the reaction shown in the above (B). Therefore, when the liquid fuel leaks to the cathode electrode 10, the water contained in the liquid fuel humidifies the air passing through the oxygen-side flow passage 18.

  Thereby, in the cathode electrode 10, an electrochemical reaction shown in the above-mentioned formula (C) occurs.

  That is, the reaction represented by the above-mentioned formula (D) continuously occurs in the entire fuel cell 3 and an electromotive force is generated in the fuel cell.

  According to such an electrochemical reaction, electric power can be efficiently extracted as compared with the electrochemical reaction in which hydrazine is directly oxidized as represented by the following formula (E) and the following formula (F).

(E) N ₂ H ₄ + ₄ OH ⁻ → N ₂ + 4 H ₂ O + 4 e ⁻ (reaction at the anode electrode 9)
(F) O ₂ + 2H ₂ O + 4 e ⁻ → 4 OH ⁻ (Reaction at cathode electrode 10)
In addition, in the fuel cell system 2 described above, the relative humidity of the air supplied to the cathode electrode 10 is adjusted to 26% or less by the humidity adjustment device 50. Therefore, it is possible to obtain excellent power generation efficiency and to improve durability.

  More specifically, conventional electrochemical reactions represented by the above formulas (E) to (F) require the use of a relatively high concentration of liquid fuel in order to directly oxidize hydrazines.

  However, if a relatively high concentration of liquid fuel is used, the reaction between hydrazines and oxygen may generate active species (strongly attacking species), which may damage the electrolyte layer 8. Therefore, it is necessary to improve durability by using a relatively thick electrolyte layer 8.

Furthermore, in the conventional electrochemical reaction represented by the above formulas (E) to (F), a predetermined amount of H ₂ O is required in the reaction at the cathode electrode 10, so the relative humidity of air is relatively high. You need to keep it.

  However, if the relative humidity of the air is relatively high, the moisture may be deposited in the oxygen-side flow path 18 and may inhibit the diffusion of the air, which reduces the power generation efficiency with long-term use, resulting in durability. It is inferior.

  On the other hand, in the electrochemical reactions shown by the above formulas (A) to (D), the hydrazine concentration of the liquid fuel is sufficient if it is a concentration that can cause the decomposition reaction of the hydrazine shown by the above formula (A) is there. Therefore, liquid fuel with a low concentration can be used compared with the electrochemical reaction shown by the said Formula (E)-(F).

  And when using low concentration liquid fuel, compared with using high concentration liquid fuel, generation of active species and damage to the electrolyte layer 8 can be suppressed, so high concentration liquid fuel is used The electrolyte layer 8 can be thinned compared to the case where

  When the electrolyte layer 8 is thinned, as described above, a sufficient amount of liquid fuel passes through the electrolyte layer 8 and leaks to the cathode electrode 10. Therefore, air is humidified by water contained in the liquid fuel, and The reaction shown in (C) (reaction at the cathode electrode 9) can be triggered.

Therefore, excellent power generation efficiency can be obtained without excessively humidifying by the humidity adjustment device 50. Moreover, since it is not necessary to humidify excessively, it can suppress that a water | moisture content accumulates on the oxygen side flow path 18, and can also acquire the outstanding durability.
II. Second Invention General Configuration of Fuel Cell System In FIG. 3, the electric vehicle 1 is a hybrid vehicle that selectively uses a fuel cell and a battery as a power source, and is equipped with the fuel cell system 2.

  The fuel cell system 2 includes a fuel cell 3, a fuel supply and discharge unit 4, an air supply and discharge unit 5, a control unit 6, and a power unit 7 as a power extraction unit.

  In FIG. 3, the fuel cell system 2 has the same configuration as the fuel cell system 2 shown in FIG. 1 except that the fuel cell system 2 is not provided with the humidity adjusting device 50.

  Also, the electrochemical reaction that occurs during power generation of the fuel cell system 2 shown in FIG. 3 is the same as the electrochemical reaction that occurs during power generation of the fuel cell system 2 shown in FIG. 1 (the above formulas (A) to (D)). is there.

2. Adjustment of current density In the above-mentioned electrochemical reaction (the above formulas (A) to (D)), depending on the current density of the power extracted by the power unit 7, sufficient durability can not be obtained. The output may decrease with the operation.

  Therefore, in the fuel cell system 2 described above, when liquid fuel and air are supplied to the fuel cell 3 and power is taken out from the fuel cell 3, the converter 36 is operated by the control of the control unit 29, and the current density of the power taken out Adjust the

Current density of power drawn is at 170 mA / cm ² or more and 180 mA / cm ² or less.

  When the current density is less than the above lower limit, the obtained output is not sufficient, and when the current density exceeds the above upper limit, the liquid fuel having permeated through the electrolyte layer 8 is the oxygen side flow path 18 as described later. It is less durable because it blocks the diffusion of oxygen.

  On the other hand, if the current density is adjusted to the above range, an excellent output can be obtained, and a decrease in output when the fuel cell system 2 is continuously operated can be suppressed, and excellent durability is obtained. You can get

3. Operation and Effect of the Second Invention In the fuel cell system 2 described above, the liquid fuel contains hydrazines. Further, the anode electrode 9 contains a PtNi alloy and a single Pt.

  In such a fuel cell system 2, when liquid fuel is supplied to the anode electrode 9, the PtNi alloy acts as a hydrazine decomposition catalyst at the anode electrode 9 and, as shown in the above formula (A), hydrazines are nitrogen And hydrogen. Therefore, the fuel cell system 2 does not need a reformer for reforming hydrazines to hydrogen.

  Next, at the anode electrode 9, Pt alone acts as a hydrogen oxidation catalyst to oxidize hydrogen generated by the decomposition of hydrazine as shown in the above-mentioned formula (B).

  Further, the liquid fuel contains water produced by the reaction shown in the above (B). Therefore, when the liquid fuel leaks to the cathode electrode 10, the water contained in the liquid fuel humidifies the air passing through the oxygen-side flow passage 18.

  Thereby, in the cathode electrode 10, an electrochemical reaction shown in the above-mentioned formula (C) occurs.

  That is, the reaction represented by the above-mentioned formula (D) continuously occurs in the entire fuel cell 3 and an electromotive force is generated in the fuel cell.

  According to such an electrochemical reaction, electric power can be efficiently extracted as compared with the electrochemical reaction in which hydrazine is directly oxidized as represented by the following formula (E) and the following formula (F).

(E) N ₂ H ₄ + ₄ OH ⁻ → N ₂ + 4 H ₂ O + 4 e ⁻ (reaction at the anode electrode 9)
(F) O ₂ + 2H ₂ O + 4 e ⁻ → 4 OH ⁻ (Reaction at cathode electrode 10)
In addition, in the fuel cell system 2 described above, power is taken from the fuel cell 3 at a current density of 170 to 180 mA / cm ² by the converter 36 of the power unit 7. Therefore, while being able to obtain the outstanding power generation efficiency, durability improvement can also be aimed at.

  More specifically, in the fuel cell system 2 described above, when the current density of the power extracted from the fuel cell is excessively low, a sufficient output can not be obtained.

  On the other hand, when the current density of the power extracted from the fuel cell is excessively high, an excessive amount of liquid fuel may leak through the electrolyte layer 8 to the cathode electrode 10 side.

  In such a case, the leaked liquid fuel is accumulated in the oxygen-side flow passage 18 to inhibit the diffusion of air, so that the power generation efficiency is lowered with long-term use, and the durability is poor.

On the other hand, when electric power is taken out from the fuel cell 3 at a current density of 170 to 180 mA / cm ² , it is possible to suppress an excessive amount of liquid fuel from passing through the electrolyte layer 8 while obtaining excellent output. .

  As a result, since an appropriate amount of liquid fuel passes through the electrolyte layer 8 and leaks to the cathode electrode 10, air contained in the liquid fuel is sufficiently humidified by air, and the reaction represented by the above formula (C) 9) can be triggered.

  Therefore, according to the fuel cell system 2 described above, excellent power generation efficiency can be obtained. In addition, since the liquid fuel can be prevented from depositing in the oxygen-side flow passage 18, excellent durability can also be obtained.

  Although an example is shown below and the present invention is explained still more concretely, the present invention is not limited to them. Specific numerical values such as blending ratios (content ratios), physical property values, parameters, etc. used in the following description are the blending ratios (content ratios) corresponding to those described in the above-mentioned "embodiments for carrying out the invention" ), Physical property values, parameters, etc. may be substituted for the upper limit (numerical values defined as “below”, “less than”) or lower limit (numerical values defined as “above”, “exceed”), etc. it can.

Preparation Example 1
0.5 g of carbon (Ketjen black, trade name: ECP 600 JD, manufactured by Lion Corporation) was dispersed in 0.4 L of pure water. Then, to the dispersion, nickel nitrate _{(Ni (NO 3) 2 ·} 6H 2 O, manufactured by Kishida Chemical Co., Ltd.) and, hexachloroplatinic (IV) acid _{(H 2 (PtCl 6) ·} 6H 2 O, manufactured by Kishida Chemical Co., Ltd. Were added such that the atomic ratio of Ni to Pt was 1: 1, and the metal mass was 20% by mass with respect to the total mass of the catalyst, and stirred for 24 hours.

  Then, it was separated into a filtrate and a catalyst raw material by filtration. The catalyst raw material contained carbon, nickel nitrate and hexachloroplatinum (IV) acid.

  Then, the catalyst raw material was washed with pure water and then dried at 100 ° C. for 10 hours. Thereafter, the dried catalyst raw material was calcined at 600 ° C. for 2 hours under an argon atmosphere.

  Thus, a catalyst support (PtNi supported support) supporting a PtNi alloy was prepared. The content ratio of platinum in the PtNi alloy was 50 mol% with respect to the total number of moles of platinum and nickel. The content ratio of nickel in the PtNi alloy was 50 mol% with respect to the total number of moles of platinum and nickel.

Preparation Example 2
0.5 g of carbon (Ketjen black, trade name: ECP 600 JD, manufactured by Lion Corporation) was dispersed in 0.4 L of pure water. Then, hexachloroplatinum (IV) acid (H ₂ (PtCl ₆ ) · 6H ₂ O, manufactured by Kishida Chemical Co., Ltd.) is added to the dispersion so that the metal mass is 20 mass% with respect to the total mass of the catalyst. Stir for 24 hours.

  Then, it was separated into a filtrate and a catalyst raw material by filtration. The catalyst raw material contained carbon and hexachloroplatinum (IV) acid.

  Then, the catalyst raw material was washed with pure water and then dried at 100 ° C. for 10 hours. Thereafter, the dried catalyst raw material was calcined at 600 ° C. for 2 hours under an argon atmosphere.

  In this way, a catalyst carrier supporting Pt alone (Pt single carrier) was prepared.

Production Example 1
An anode catalyst was prepared by mixing 0.5 g of the PtNi-supported carrier of Preparation Example 1 and 0.5 g of the Pt-only supported carrier of Preparation Example 2. Then, the anode catalyst, ionomer (trade name: Tokuyama AS 4), and 2-propanol (organic solvent) are mixed so that the ratio of ionomer mass / catalyst mass is 50% by mass, and the total amount of ink of 30 g is obtained. It was prepared and dispersed to prepare an anode electrode ink.

  Further, 1 g of the Pt-supported carrier of Preparation Example 2, an ionomer (trade name: Tokuyama A201), and 2-propanol (organic solvent) are mixed so that the ratio of ionomer mass / catalyst mass is 50 mass%. A total of 30 g of ink was prepared and dispersed to prepare a cathode electrode ink.

Next, the amount of the anode catalyst (PtNi alloy and Pt alone) is 3.2 mg / cm ² on one surface of the anion exchange electrolyte membrane (trade name: Tokuyama A201), and the surface area after drying is 4 cm ² The anode electrode ink was applied so that

In addition, the cathode electrode ink is applied to the other surface of the anion exchange electrolyte membrane so that the amount of cathode catalyst (Pt alone) is 1.0 mg / cm ² and the area of the surface after drying is 4 cm ^2. Thereafter, the solvent was evaporated in the air at normal temperature, and the membrane electrode assembly was pressurized for 2 minutes with a hydraulic press at a pressure of 12 MPa to produce a membrane electrode assembly.

Evaluation method 1. Adjustment of Humidity The membrane electrode assembly obtained in Production Example 1 was set in a fuel cell evaluation cell (Labcell, manufactured by Daihatsu Kogyo Co., Ltd.), and a liquid fuel (1.5% by mass hydrazine hydrate, 5. 3% by mass potassium hydroxide was supplied at a flow rate of 6.3 cc / min.

  Also. Air was supplied to the cathode electrode at a flow rate of 300 cc / min.

  At this time, the relative humidity of air was set to 15.52%, 25.96%, and 41.94%.

Then, the power density and the operation time were measured while taking out the power at a current density of 200 mA / cm ² . The results are shown in FIG.

Moreover, measurement conditions (cell temperature and back pressure) are shown below.
Cell temperature: 80 ° C
Back pressure; anode: 0 kPa, cathode: 0 kPa
2. Adjustment of current density The membrane electrode assembly obtained in Production Example 1 is set in a fuel cell evaluation cell (Labcell, manufactured by Daihatsu Kogyo Co., Ltd.), and a liquid fuel (1.5 mass% hydrazine hydrate, 5 .3 mass% potassium hydroxide) was supplied at a flow rate of 6.3 cc / min.

  Also. Air was supplied to the cathode electrode at a flow rate of 300 cc / min.

  At this time, the relative humidity of air was set to 41.94%.

^Then, while drawing power at each current density of ^{170mA / cm 2, 180mA / cm} 2, 190mA / cm 2, 200mA / cm 2, to measure the output density and operating time. The results are shown in FIG.

  Further, FIG. 6 shows the relationship between the current density and the output density at the 0th hour from the operation (the characteristic at the beginning of the operation).

Moreover, measurement conditions (cell temperature and back pressure) are shown below.
Cell temperature: 80 ° C
Back pressure; anode: 0 kPa, cathode: 0 kPa

Reference Signs List 2 fuel cell system 3 fuel cell 8 electrolyte layer 9 anode electrode 10 cathode electrode 21 fuel supply unit 24 air supply unit 50 humidity adjustment device

Claims (2)

A fuel cell comprising an electrolyte layer capable of moving an anion component, an anode electrode disposed on one side of the electrolyte layer, and a cathode electrode disposed on the other side of the electrolyte layer;
A fuel supply unit for supplying liquid fuel to the anode electrode;
And an oxygen supply unit for supplying air to the cathode electrode,
The oxygen supply unit includes humidity adjusting means for adjusting the relative humidity of the air;
The liquid fuel includes hydrazines,
The anode electrode contains PtNi alloy and Pt alone,
The fuel cell system, wherein the humidity adjusting means adjusts the relative humidity of the air to 26% or less. A fuel cell comprising an electrolyte layer capable of moving an anion component, an anode electrode disposed on one side of the electrolyte layer, and a cathode electrode disposed on the other side of the electrolyte layer;
A fuel supply unit for supplying liquid fuel to the anode electrode;
An oxygen supply unit for supplying air to the cathode electrode;
Power extraction means for extracting power from the fuel cell;
The liquid fuel includes hydrazines,
The anode electrode contains PtNi alloy and Pt alone,
The fuel cell system according to claim 1, wherein the power extracting means extracts power from the fuel cell at a current density of 170 to 180 mA / cm ² .

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