JP2017010738A - Electrode material for fuel cell, manufacturing method therefor, and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode material for a fuel cell not using a platinum group element, a method for producing the same, and a fuel cell.SOLUTION: Fuel cell electrode materials 2 and 3 of the embodiment are composed of a molded body not containing a platinum group element and containing at least a plurality of different transition metals as a metal material. In the molded body, the metal material is processed into a powder form. The molded body is formed such that the molded body is formed by mixing the respective powders so that hydrogen and oxygen used in the fuel cell 1 have voids dispersed in the molded body so that the hydrogen and oxygen can permeate the molded body.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrode material for a fuel cell, a manufacturing method thereof, and a fuel cell.

  In recent years, polymer electrolyte fuel cells have attracted attention, research and development as one of clean energy sources that do not generate carbon dioxide. In addition, it is used as a stationary electric and heat combined device, and is also being developed as a power source for driving vehicles such as electric vehicles. In particular, in a polymer electrolyte fuel cell, a catalyst in which a noble metal such as platinum or a platinum alloy is supported on carbon black is used as a cathode catalyst and an anode catalyst in order to activate a reaction process in an electrode.

  As a fuel cell catalyst, fuel cell catalyst fine particles such as Pt are supported on the surface of fullerenes, and fullerenes are used as a core, and the surface is a core-shell catalyst covered with fuel cell catalyst fine particles such as Pt. It is known that a catalytic action of hydrogen oxidation or oxygen reduction is exhibited on the surface (see, for example, Patent Document 1).

JP 2011-76828 A

  However, platinum (Pt) is a scarce resource and is a very expensive material because the amount of mining is limited. Therefore, development and commercialization of fuel cells that do not use platinum or other platinum group elements are desired.

FIG. 8 shows an example of a configuration (cross-sectional view) of a conventional polymer electrolyte fuel cell 100. In the polymer electrolyte fuel cell 100, as shown in FIG. 8, a fuel electrode 200 and an air electrode 300 are provided on both sides of the PEM membrane 4. The PEM film 4 is electrically insulated and blocks the movement of hydrogen gas (H ₂ ), oxygen gas (O ₂ ), water vapor (H ₂ O), etc. existing on both sides to the other side.

For the fuel electrode 200 and the air electrode 300, for example, carbon black carrying fine platinum (Pt) on the surface on the PEM film 4 side is used. This platinum promotes a reaction in which a hydrogen molecule (H ₂ ) releases an electron (e ⁻ ) and a reaction in which an oxygen molecule (O ₂ ) is bonded to a hydrogen ion (H ⁺ ) and an electron (e ⁻ ). Acts as a catalyst. In particular, in a low-temperature type fuel cell (for example, in the range of about 20 to 200 ° C.), the use of platinum in this way is an essential technology. Therefore, as described above, the solid polymer fuel cell 100 or the like is used. The challenge was how to use less platinum. What should be desired is the development and practical application of electrode materials for fuel cells that do not use platinum or other platinum group elements.

  However, the disclosed technology such as the above-mentioned patent document relates to a method for increasing the catalytic activity with a smaller amount of platinum, and a technology for increasing the catalyst performance with the same amount used, and as a low-temperature fuel cell, It is not a technology for fuel cells that do not use platinum group elements. Further, it does not disclose a technique for a fuel cell that does not use a platinum group element.

  Accordingly, the problem to be solved by the present invention is to provide a fuel cell electrode material that does not use a platinum group element, a manufacturing method thereof, and a fuel cell as a low temperature fuel cell.

  In order to solve the above-described problems, the fuel cell electrode material according to the present invention is a fuel cell electrode material that does not contain a platinum group element of Ru, Rh, Pd, Os, Ir, and Pt. The electrode material for a fuel cell is composed of a molded body containing at least a plurality of different transition metals as a metal material, and the molded body is a fuel used for a fuel cell, in which the metal material is processed into powder. Is characterized by being formed by mixing the respective powders so as to have voids dispersed in the molded body so as to be able to pass through the molded body.

  Further, in the electrode material for a fuel cell according to the present invention, the plurality of different transition metals include at least one of Fe, Ni, Mn, Cr, or Ti belonging to a 3d transition element, and the molded body further includes: The metal material other than the contained transition metal mainly includes any one of Cu, Zn, Al, or Mg, which has a higher electrical conductivity than the contained transition metal.

  Furthermore, the fuel cell electrode material according to the present invention is characterized in that the plurality of different transition metals include at least Ni and Fe, or Ni and Cu.

  Furthermore, in the fuel cell electrode material according to the present invention, the composition ratio of the metal material in the molded body is 1 to 3 mass% of Mg or Zn when the mass of the molded body is 100 mass%. The main feature is that it contains Ni, Fe, and Cr in a total of 2 to 3% by mass or 5 to 6% by mass of Al, and a mass% obtained by subtracting the mass% of the contained metal from 100% by mass. To do.

  In addition, the fuel cell electrode material according to the present invention is mainly characterized in that the porosity of the molded body is in a range of 20% to 40% with respect to the volume of the molded body.

  In addition, in the fuel cell electrode material according to the present invention, the powder is spherical or needle-shaped, or at least one type of the metal material is spherical and the other type of the metal material is needle-shaped. The main feature is that it has been processed.

  Furthermore, the fuel cell electrode material according to the present invention is mainly characterized in that a light-emitting substance that emits light by infrared rays or ultraviolet rays is supported on the molded body.

  Moreover, in order to solve the said subject, the manufacturing method of the electrode material for fuel cells which concerns on this invention is a manufacturing method of the electrode material for fuel cells for manufacturing the said electrode material for fuel cells. The manufacturing method includes a pulverization step of pulverizing the metal material used for the molded body to 200 μm or less as a powder, a mixing step of mixing the powder so as to be uniformly dispersed after the pulverization step, After the mixing step, the pressure step of pressing the uniformly dispersed powder at a pressure of 500 to 800 Mpa to form a molded body, and the sintering step of sintering the molded body after the pressing step, The main feature is to include.

  Furthermore, in the method for producing a fuel cell electrode material according to the present invention, in the sintering step, the sintering temperature is higher than the melting point of the metal having the highest electrical conductivity among the metal materials, and the most electrically conductive material. The main feature is that it is in a range lower than the melting point of a metal other than a high-rate metal.

  Furthermore, the fuel cell electrode material manufacturing method according to the present invention is mainly characterized in that it further includes a luminescent substance supporting step of supporting the luminescent substance emitting light by infrared rays or ultraviolet rays on the molded body.

  Furthermore, in order to solve the above-mentioned problems, the fuel cell according to the present invention is mainly characterized by using the above-mentioned electrode material for a fuel cell as an air electrode or a fuel electrode.

  Since the fuel cell electrode material according to the present invention can be used as a catalyst that does not use a platinum group element, the manufacturing cost of the low-temperature fuel cell can be reduced. In addition, since a metal that is not a scarce resource can be used, the problem of resource problems can be solved.

  Moreover, the fuel cell electrode material manufacturing method and the fuel cell according to the present invention can reduce the manufacturing cost of the low-temperature fuel cell by using the fuel cell electrode material that does not use a platinum group element. In addition, since a metal that is not a scarce resource can be used, the problem of resource problems can be solved.

The figure which shows an example of a structure of the fuel cell of embodiment which concerns on this invention. Diagram showing an example of the structure of the fuel electrode The figure which shows an example of a structure of the fuel cell of other embodiment. Diagram showing the appearance of the prototype fuel cell electrode material Exploded view for explaining prototype fuel cell and experimental comparison fuel cell List showing the outline of the prototype fuel cell electrode materials Diagram showing experimental data of fuel cell using prototype fuel cell electrode material The figure which shows an example of a structure of the conventional polymer electrolyte fuel cell

  Hereinafter, an electrode material for a fuel cell, a manufacturing method thereof, and a fuel cell according to an embodiment of the present invention will be specifically described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted. In the following embodiment described here, an example of a polymer electrolyte fuel cell will be described.

FIG. 1 shows an example of the configuration of a fuel cell 1 according to an embodiment of the present invention.
A fuel cell 1 shown in FIG. 1 is an example of a polymer electrolyte fuel cell. As shown in FIG. 1, the fuel cell 1 includes a fuel electrode 2, an air electrode 3, a PEM membrane 4, a hydrogen gas inlet 5, an oxygen gas inlet 6, a hydrogen gas supply connection 11, an oxygen gas supply connection 12, and A water discharge unit 13 is provided.

The fuel electrode 2 is an anode electrode having a fuel cell electrode material 21 that does not contain a platinum group element (Ru, Rh, Pd, Os, Ir, Pt). Hydrogen is supplied to the fuel electrode 2 through, for example, a hydrogen gas supply connection portion 11 connected to an external hydrogen supply source, and a hydrogen gas inlet portion 5 that takes in hydrogen gas supplied from the hydrogen supply source into the fuel cell 1. Gas (H ₂ ) is supplied. Note that fuel such as methanol (CH ₃ OH) may be supplied instead of hydrogen gas.

In the fuel electrode 2, the supplied hydrogen gas fuel is decomposed into hydrogen ions (H ⁺ ) and electrons (e ⁻ ) by a reaction of H ₂ → 2H ⁺ + 2e ⁻ . Thereafter, hydrogen ions pass through the inside of the PEM film 4, and electrons move to the air electrode 3 through the electrode connection terminals 14 and the load 15.

A PEM (Proton Exchange Membrane) film 4 is provided with a structure sandwiched between a fuel electrode 2 and an air electrode 3. The PEM membrane 4 is an electrolytic membrane that can carry hydrogen ions (H ⁺ ) that can be ionized by hydrogen gas from the fuel electrode 2 side to the air electrode 3 side.

The air electrode 3 is a cathode electrode having a fuel cell electrode material 31 that does not contain a platinum group element. For example, an oxygen gas supply connection unit 12 connected to an external oxygen supply source and an oxygen gas suction port 6 for taking oxygen gas supplied from the oxygen supply source into the fuel cell 1 are connected to the air electrode 3. Gas (O ₂ ) is supplied.

In the vicinity of the PEM film 4 side in the air electrode 3, hydrogen ions that have moved through the PEM film 4 and electrons that have passed through the load 15 and the electrode connection terminal 14 react with oxygen gas. That is, water (H ₂ O) is generated by the reaction of 4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O. For example, the generated water is discharged from the water discharge unit 13 to the outside of the fuel cell 1.

  FIG. 2 shows an example of the structure of the fuel electrode 2a (another embodiment of the fuel electrode 2). 2A is a cross-sectional view, and FIG. 2B is a plan view. FIG. 3 shows a configuration of a fuel cell 1a (another embodiment of the fuel cell 1) having the fuel electrode 2a and the air electrode 3a of FIG.

  The fuel electrode 2a is composed of a fuel cell electrode material 21 and a conductive material 22, as shown in FIG. The conductive material 22 is a well-known metal material that can conduct (conductive).

  The conductive material 22 is provided with a plurality of holes 23 penetrating from one flat surface to the other surface. Thereby, for example, the hydrogen gas taken into the hydrogen gas inlet 5 shown in FIG. 3 can reach the fuel cell electrode material 21 through the plurality of holes 23 of the conductive material 22. The conductive material 22 can be connected to the electrode connection terminal 14 and is arranged and connected so as to be conductive with the fuel electrode 2a.

  The air electrode 3a shown in FIG. 3 has the same structure as that of the fuel electrode 2a shown in FIG. 2, and includes a fuel cell electrode material 31 and a conductive material 32 having a plurality of holes 33. .

<Example of production of molded article>
Next, the fuel cell electrode materials 21 and 31 shown in FIG. 3 will be described. Conventionally, research and development related to transition metals and noble metals have been conducted on the catalytic action of fuel cell electrodes. In particular, an object of the present invention is to provide a fuel cell electrode material having a highly active catalytic action using different transition metals other than platinum group elements or a combination of these with other metals.

  The fuel cell electrode materials 21 and 31 are made of a metal material that does not contain a platinum group element (Ru, Rh, Pd, Os, Ir, Pt). The fuel cell electrode materials 21 and 31 are formed of a molded body containing at least a plurality of different transition metals as metal materials. In this molded body, each of a plurality of different transition metals is processed into a powder form, and the void used is dispersed in the molded body so that the fuel used in the fuel cell 1a can permeate the molded body. Each of these powders is formed by mixing.

  Preferably, the plurality of different transition metals include at least one of Fe, Ni, Mn, Cr, or Ti belonging to the 3d transition element. Further, the molded body contains any one of Cu, Zn, Al, or Mg, which is higher in electrical conductivity than the transition metal contained, as a metal material other than the contained transition metal.

  Therefore, as an example, an example of a material exhibiting a highly active catalytic action with a different transition metal other than the platinum group element or a combination thereof with another metal will be described and described. For example, examples are shown in which several different molded bodies are manufactured under the manufacturing conditions described below. FIG. 4 shows the appearance of the prototype fuel cell electrode materials 21 and 31 (prototypes).

<Fuel cell electrode material>
In the examples of the fuel cell electrode materials 21 and 31 of the present embodiment, for example, molded bodies containing a plurality of different transition metals described below are used.

  In terms of material cost, a material containing Ni and Fe or Ni and Cu as a plurality of different transition metals is preferable. For example, the embodiment shown in FIG. 4 contains a large amount of Ni as a 3d transition metal among different transition metals, and a small amount of Cu and a small amount of Fe by mass ratio than Ni as other 3d transition metals. It is a molded product.

  These transition metals or powders of these and other metals are mixed so as to be uniform throughout. Then, the mixed powder is pressed and sintered to form a molded body. The molded body thus produced has a large number of holes on the surface of the molded body so that hydrogen gas, oxygen gas, or a solution serving as a fuel can pass through the thickness direction of the molded body, and It has a structure (also referred to as a multiporous structure) in which many voids are provided inside the molded body.

  For example, when powder is filled in a mold having a certain shape and pressure is applied, the gap between the powders decreases as the pressure increases. Thus, the porosity of a molded object can be adjusted with the magnitude | size of a pressure. For this reason, in order to manufacture a molded object so that it may exist in the range of the desired porosity, the pressure to pressurize is controlled.

  Note that the porosity changes slightly depending on the sintering temperature and time during sintering after pressurization, so that the molded product that is finally produced can be obtained by adjusting and controlling these conditions as well. Manufactured to be in the range of porosity.

  The space provided in the molded body is a space surrounded by the surfaces of a plurality of different transition metals or other metals. In addition, on the surface, a plurality of holes that continue to the voids of the molded body are formed. As the plurality of transition metals contained in the molded body, 3d transition metals are preferable.

  For example, in the molded body of the example shown in FIG. 4, a plurality of different 3d transition metals contain, for example, mainly Ni and a small amount of Cu and Fe. Specifically, the molded body shown in FIG. 4 is provided with voids surrounded by metal at a ratio corresponding to the number of particles having the mass ratio Fe: Ni: Cu = 1: 48: 4. For example, in a molded body expressed as Fe-48Ni-4Cu, the composition ratio of Fe, Ni, and Cu is 1: 48: 4 in terms of mass ratio.

The effect of the space | gap provided in the above molded objects is demonstrated. For example, in the fuel cell electrode material 21 used for the fuel electrode 2a shown in FIG. 3, hydrogen gas (H ₂ ) that permeates through the voids surrounded by powder as described above passes through these voids. , (Formula 1) has a catalytic action that promotes the reaction on the right side.
(Fuel electrode) H ₂ → 2H ⁺ + 2e ⁻ (Expression 1)
And the hydrogen ion (H ^<+> ) produced | generated by (Formula 1) permeate | transmits the PEM film | membrane 4 which is an electrolytic membrane, and reaches | attains the air electrode 3a.

  That is, hydrogen molecules are adsorbed on the surfaces of the voids in the fuel cell electrode material 21 to weaken the bonds between hydrogen atoms, and act as a catalyst that promotes the reaction of releasing electrons and becoming hydrogen ions.

The hydrogen ions (H ⁺ ) that have reached the air electrode 3a are connected to an oxygen gas (O ₂ ), an external load 15 and the like in the vicinity of the boundary where the PEM membrane 4 and the fuel cell electrode material 31 are in contact with each other. Water (H ₂ O) is generated by a chemical reaction with electrons (e ⁻ ) supplied from the terminal 14 as shown in (Formula 2).
(Air electrode) 1 / 2.O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (Formula 2)
That is, the catalytic action that promotes the reaction between oxygen molecules, hydrogen ions, and electrons is exerted on the surface of the void in the electrode material 31 for the fuel cell and the surface near the boundary with the PEM 4. Conventionally, as a catalyst material for a low-temperature fuel cell, a material in which a platinum catalyst is supported on a carbon black carrier has been used. Instead, a fuel cell electrode material 31 can be used.

<Example of production of molded article>
For example, an example in which several different molded bodies are manufactured under the manufacturing conditions described below will be shown. Here, FIG. 4 shows an external appearance of the prototype. FIG. 6 is a list showing an outline of the prototypes (fuel cell electrode materials 21 and 31) that have been experimentally produced.

  The compacts shown in FIG. 4 are fuel cell electrode materials 21 and 31 for use in the fuel cell 1a. The fuel cell electrode materials 21 and 31 shown in FIG. 4 have a large number of holes (not holes of a size visible to the naked eye) on the disk-shaped surface. Many of the holes are formed by continuous many voids (not having a size that can be seen with the naked eye) inside the molded body. Further, the void inside the molded body is formed so that the fuel used in the fuel cell 1a can pass through the molded body. For example, when a water droplet is dropped on the fuel cell electrode materials 21 and 31 shown in FIG. 4 and the surface is rubbed by hand with the surface immersed in the water droplet, the water droplet is absorbed into the molded body.

  As an example of this embodiment, prototypes No. 1, No. 2, No. 3, and No. 4 shown in FIG. 6 were prototyped for use in the fuel cell electrode materials 21 and 31 of the fuel cell 1a. As production conditions for the prototypes No. 1 to No. 4, the respective materials, sintering temperature, sintering time, pressure during sintering, and other conditions are as shown below.

<Material of molded body>
The metal materials of trial production No1, No2, No3, and No4 are all Fe-48Ni-4Cu. That is, the metal material contains Fe (iron), Ni (nickel), and Cu (copper) metals in a mass ratio of approximately 1: 48: 4.

<Powder shape>
Preferably, the powder to be mixed for manufacturing the molded body is spherical or acicular, or at least one type of metal material is processed into a spherical shape and another type of metal material is processed into an acicular shape.
Further, preferably, among the metals contained in the compact, at least the metal having the lowest melting point is spherical, and the other metal having the highest melting point is a needle-like powder.

  When needle-shaped powder is used, when the mixed powder is pressure-molded, it is easy to form a void having good permeability in the finished molded body. Further, if the metal having the lowest melting point is a spherical powder, the surface area when joining to another metal can be increased.

  Each transition metal or metal, or an alloy containing the transition metal or the like is pulverized by a pulverizer so as to be equal to or smaller than a predetermined average particle diameter to obtain powder. The average particle diameter of the powder (for example, the length of the longitudinal portion of the longitudinal shape or the outer diameter of the sphere) is 200 (μm) or less. For example, the pulverized powder is passed through a mesh that allows a pore diameter of about 200 (μm) or less to pass through, for example, in a processing step, and sieved. This is because if the average particle diameter exceeds 200 (μm), the strength becomes difficult due to warpage or cracks of the molded article to be produced.

  Preferably, the average particle size is 10 to 200 (μm). When the average particle diameter of many powders is less than 10 (μm), voids (pores) are likely to close during pressing and sintering, and the manufactured compact has a permeability of oxygen, hydrogen, etc. It is because it falls. In some cases, the average particle diameter may be less than 10 (μm) in a small part of the powder by treatment with a pulverizer or the like, but there is no practical problem when a very small amount is contained.

<Pressing pressure>
Each transition metal or metal powder is mixed so as to be uniformly dispersed by a mixer or the like, and the mixed powder is put into a mold for molding and pressed at a predetermined pressure. The pressure at the time of pressurization is about 5 to 8 (t / cm ² ), in other words, about 500 to 800 (Mpa).

  As a guide, if the pressure during pressurization is less than 500 (Mpa), the voids are slightly too large (the void ratio is too high), and the molded body is likely to be cracked or warped. The strength of is reduced. Moreover, it is because the space | gap of the manufactured molded object will become a little too small (the porosity will become low too much) when the pressure at the time of pressurization exceeds 800 (Mpa).

  On the other hand, the voids (also referred to as pores) provided in the molded body are in the above-described range and have voids as much as possible because they affect the transmittance of the fuel electrode 2 through which hydrogen passes and the air electrode 3 through which oxygen passes. A higher rate is preferred.

<Sintering conditions>
Next, after the mixed powder is put into a mold and subjected to pressure molding, the compact is sintered. For example, sintering at the time of sintering a compact (Fe-48Ni-4Cu) containing a metal whose composition ratio of Fe (iron), Ni (nickel), and Cu (copper) is approximately 1: 48: 4 by mass ratio. The conclusion conditions are as follows.

(1) Sintering temperature 1100-1400 ° C
As a guideline, when the sintering temperature is below 1100 ° C., the melting point of Cu contained in the molded body is 1084 ° C., particularly on the inner side of the molded body. In this case, since Cu having high electrical conductivity does not melt, it is difficult to closely bond to other transition metal powders. On the other hand, when the sintering temperature exceeds 1400 ° C., especially when the melting point of Ni contained in the compact is higher than 1455 ° C., a certain amount of voids are provided in the pressure-molded state. Since melting of Ni starts by heating, the formed voids are extremely deformed, and problems such as closing the voids arise. Moreover, it becomes difficult to adjust a desired porosity.

(2) Sintering time About 4-6 hours At the set sintering temperature, a sufficient heating time is provided, and the compact is sintered at about normal pressure (atmospheric pressure). The sintering time of 4 to 6 hours is data based on experience. Further, an inert gas is used in the atmosphere so that the metal is not oxidized during sintering.

  (3) After sintering, natural cooling is performed. Moreover, although it may cool by a cooling fan or water cooling, it is not necessary to cool rapidly in time. This is because rapid cooling tends to cause cracks and warpage in the molded body.

<Manufacturing method>
Hereinafter, an example of the manufacturing method of the electrode materials 21 and 31 for fuel cells of this embodiment is demonstrated.

  As a basic process, a plurality of different transition metals other than platinum group elements or powders of these and other metals are mixed so as to be uniform overall, and the mixed powder is pressed and sintered, It is a manufacturing method including the process of manufacturing a molded object (electrode materials 21 and 31 for fuel cells). For example, the method for manufacturing the fuel cell electrode materials 21 and 31 includes the following steps.

(Crushing process)
First, a 1st process is a grinding | pulverization process grind | pulverized to 200 micrometers or less as a powder for every transition metal or those and another metal.
Preferably, the pulverizing step further includes a shape processing step in which the powder is processed into a spherical shape or a needle shape, or at least one type of metal material is processed into a spherical shape and another type of metal material is processed into a needle shape.

(Mixing process)
Next, the second step is a mixing step in which powders containing different transition metals are mixed so as to be uniformly dispersed after the pulverization step.
(Pressure process)
Next, the third step is a pressurization step in which the uniformly dispersed powder is put into a mold after the mixing step and is pressed at a pressure of about 500 to 800 MPa to form a molded body.

(Sintering process)
Next, a 4th process is a sintering process which sinters a molded object at high temperature after a pressurization process. Preferably, the sintering time is about 4 to 6 hours at the sintering temperature set in the sintering step.
Preferably, in the sintering step, the sintering temperature is in a range higher than the melting point of the metal having the highest electrical conductivity among the metal materials and lower than the melting point of the metal other than the metal having the highest electrical conductivity. .

  The reason for the above sintering temperature is that when heating is started in the sintering process, the powders are joined by surface diffusion, and the heating temperature is the melting point of the metal having the highest electrical conductivity among the included metals. As a result, the internal diffusion also occurs inside the powder of the molded body, and the powders are bonded to each other. As a result, a metal having high electrical conductivity is closely bonded to other powders in the sintered compact.

  For example, the metal material of the molded body made of Fe-48Ni-4Cu includes Fe and Ni belonging to the 3d transition element, and the metal material has a higher electrical conductivity than the 3d transition metal Fe and Ni contained therein. The case of the example containing Cu will be described. Cu is also a 3d transition metal.

For example, at an atmospheric pressure of 1 atm, the melting point of Cu is 1084 ° C., the melting point of Fe is 1536 ° C., and the melting point of Ni is 1455 ° C. (see Science Chronology, Vol. 88, 2015). Further, where the term high electric conductivity and is, for example, when compared with the value of the electrical resistivity (and 0 ℃ ^{reference), Fe: 8.9 (10 -8} Ωm), Ni: 6.2 (10 - Compared with 3d transition metals such as ⁸ Ωm), Al: 2.50 (10 ⁻⁸ Ωm), Cu: 1.55 (10 ⁻⁸ Ωm), Mg: 3.94 (10 ⁻⁸ Ωm), etc. It is a metal having electrical resistance characteristics (see Science Chronology, Vol.88, 2015).

  In this case, in the sintering process of the compact including the powders of Fe, Ni, and Cu (when the pressure is 1 atm), the sintering temperature is the melting point of the metal Cu having the highest electrical conductivity among the metal materials. The range is higher than 1084 ° C. and lower than the melting point of the metal other than the metal having the highest electrical conductivity (Ni melting point: 1455 ° C.). That is, the sintering temperature is in the range of 1100 to 1400 ° C., for example.

<Experimental data>
Hereinafter, the measurement result of the electromotive force of the fuel cell comparing the prototype fuel cell and the experimental comparison fuel cell will be described. Here, in FIG. 5, as the prototype fuel cell and the experimental comparison fuel cell used for the comparative measurement, FIG. 5A shows a state in which the prototype fuel cell is disassembled for each component material, and FIG. Shows a state in which the experimental fuel cell is disassembled for each component material.

The prototype fuel cell shown in FIG. 5A is a prototype based on the configuration of the fuel cell 1a of the present embodiment shown in FIG. Specifically, the fuel cell 1a using each of the prototypes No. 1, No. 2, No. 3, and No. 4 shown in FIG. 6 as the fuel cell electrode materials 21 and 31 shown in FIG. 3 is made into four types of prototype fuel cells. It is. When the fuel cell electrode materials 21 and 31 shown in FIG. 5A are calculated on the basis of a substantially disk-shaped average outer shape in each of the prototypes No. 1, No. 2, No. 3, and No. 4 shown in FIG. = About 8.4 to 8.9 (cm ² ).

Further, the experimental comparison fuel cell shown in FIG. 5B is based on the configuration of the fuel cell 100 of the present embodiment shown in FIG. Specifically, a commercially available structure using the electrode catalysts 201 and 301 (referred to as a comparative sample (B)) in which platinum is supported on a carbon carrier on the fuel electrode 200a and the air electrode 300a shown in FIG. 5B. This is a fuel cell. Note that the electrode catalysts 201 and 301 shown in FIG. 5B have a surface area S on one side of 4 cm × 4 cm (width) of about 16 (cm ² ) and platinum on the surface has a thickness of about 1 to 10 μm. It is supported.

  In a comparative experiment of the prototype fuel cell shown in FIG. 5 (a) and the experimental comparison fuel cell shown in FIG. 5 (b), hydrogen gas having a purity of 99.99% was used as hydrogen supplied to the fuel electrodes 2a and 200a. Air was used as oxygen supplied to the air electrodes 3a and 300a. The atmospheric temperature during the experiment is about room temperature.

  As an example of the present embodiment, as shown in FIG. 6, prototypes No. 1, No. 2, No. 3, and No. 4 used for the fuel cell electrode materials 21 and 31 were prototyped by the manufacturing method as described above. FIG. 6 is a list showing an outline of these prototypes. In particular, it shows characteristics such as the external shape and density of the prototype.

  In FIG. 6, for each prototype No. (prototype type) of the molded body used as the fuel cell electrode materials 21 and 31, the electrode material, the substantially disk-shaped average outer shape, the average thickness, the density, the relative density, and the sintering temperature are shown. Show. In addition, as manufacturing conditions of trial manufacture No1-No4, each sintering temperature, sintering time, sintering conditions, such as the pressure at the time of sintering, and other conditions are as having mentioned above, Here, trial manufacture No1 mainly , No. 2, No. 3, and No. 4 will be described in terms of differences in trial production conditions.

<Material of molded body>
The metal materials of trial production No1, No2, No3, and No4 are all Fe-48Ni-4Cu. Here, the notation of Fe-48Ni-4Cu indicates that the composition ratio of Fe (iron), Ni (nickel), and Cu (copper) contained as a metal material is 1: 48: 4 in mass ratio. It is. In this material, each metal is easily available, and the material cost is low.

<Density of molded body>
After the sintering, as shown in FIG. 6, the average outer shape and the average thickness of the molded body were measured for each of prototype Nos. 1 to 4. Further, the volume of the molded body was calculated from the average outer shape and the average thickness, and the mass for each prototype No. was measured, and the measured mass was divided by the calculated volume to calculate each density.

<Relative density of molded body>
The relative density of the molded body shown in FIG. 6 is calculated as follows.
In the known technology, if the particle diameter of the close-packed particles is combined (the smaller particles are filled in the gaps between the particles and the particles are mixed and adjusted), the theoretical porosity can be filled to about 4%. Are known. Therefore, the relative density of the molded body is calculated by setting such a metal plate that is closest packed (filled with 96% of particles) to 100% relative density.

For example, the density ρ at a relative density of 100% of the reference Fe-48Ni-4Cu was calculated using the following data (see Science Chronology, 2015, Vol. 88).
Fe density: 7.874 (g / cm ³ ), 20 ° C.
Ni density: 8.902 (g / cm ³ ), 25 ° C.
Cu density: 8.96 (g / cm ³ ), 20 ° C.
Here, when the composition ratio of Fe, Ni, and Cu is 1: 48: 4 by mass ratio, for example, when the mass and volume of the metal are simply added at these ratios, the volume per 53 (g) is 5. Since 9654 (cm ³ ), 53 (g) /5.9654 (cm ³ ) = 8.885 (g / cm ³ ).

Therefore, when it is a metal plate that is closest packed with Fe, Ni, Cu powder as particles,
ρ = 8.885 (g / cm ³ ) × 0.96 = 8.53 (g / cm ³ )
Calculate as The relative density shown in FIG. 6 was calculated using the above density ρ = 8.53 (g / cm ³ ) as a comparison standard with a relative density of 100%.

As described above, as shown in FIG. 6, the relative density of each of the prototypes No. 1 to No. 4 is approximately 65%, 70%, and 75 based on ρ = 8.53 (g / cm ³ ) where the relative density is 100%. % And 80%.

<Calculation of porosity of molded body>
The metal plate used as the closest packing described above is defined as 100% relative density, and the relative porosity at this time is defined as 0%, and the porosity of the molded body is defined as (Equation 3). To do.
Porosity = 100−relative density (%) (Formula 3)

Based on the results of the relative density shown in FIG.
(Prototype No. 1) Relative density 65%, porosity 35%
(Prototype No2) 70% relative density, 30% porosity
(Prototype No. 3) Relative density 75%, porosity 25%
(Prototype No. 4) Relative density 80%, porosity 20%
The result is as described above. In addition to this, regarding the calculation of the porosity, there may be a method of calculating by measuring the amount of water or oil (liquid with a small contact angle) impregnated into the molded body.

<Differences in sintering temperature under prototype conditions>
・ Sintering temperature Temperature a = 1100-1300 ° C. (center temperature around 1200 ° C.)
Temperature b = 1000 to 1200 ° C. (center temperature about 1100 ° C.)
The sintering temperature of the prototype No. 1 is the above-mentioned temperature a and is in the range of the central temperature 1200 ° C. that is sufficiently higher than the melting point 1084 ° C. of Cu. On the other hand, the sintering temperature of the prototypes Nos. 2, 3, and 4 is the temperature b, which is about a central temperature of about 1100 ° C. near the melting point of 1084 ° C. of Cu.

  Therefore, in the range of 1200 ° C., which is sufficiently higher than the melting point of 1084 ° C., the Cu solid powder transitions to the liquid state. That is, in the sintering process, which is the sintering temperature of the prototype No. 1, Cu has a lower melting point than other transition metals and has a high conductivity (high electrical conductivity) if the sintering temperature is 1100 to 1300 ° C. Melts and is in a state of being closely bonded to Ni and Fe powder having a high melting point (melting point higher than that of one metal).

  On the other hand, since the sintering temperature of the prototypes Nos. 2, 3, and 4 is 1100 ° C., many portions on the inner side of the molded body, in particular, have a sintering temperature of 1000 to 1084 lower than the melting point of Cu of 1084 ° C. It is considered to be in the range of ° C., and in the sintering process, since it remains a Cu solid powder at the time of pressure forming, it is not in a state where it is sufficiently bonded to Ni and Fe powder. Conceivable.

  The validity of the above can be inferred from the experimental results described below and shown in FIG. FIG. 7 is a diagram showing experimental data of a fuel cell using a prototype fuel cell electrode material. Here, the experimental results shown in FIG. 7 show that in the configuration of FIG. 3, a voltage tester was connected to the electrode connection terminal 14 instead of the load 15, and the interelectrode voltage of the prototype fuel cell (corresponding to the fuel cell 1a) was measured. Data is shown. Further, in the configuration of FIG. 8, similarly, data obtained by measuring the interelectrode voltage of the experimental comparison fuel cell (corresponding to the fuel cell 100) is shown. Note that the ambient temperature during measurement is about room temperature.

  In FIG. 7, the horizontal axis indicates the measurement time (minutes), and the vertical axis indicates the interelectrode voltage (V). The interelectrode voltage is a voltage between the electrode connection terminals 14 shown in FIG. Further, since the voltage tester has a high resistance, a slight current flows during measurement of the prototype fuel cell and the experimental fuel cell. For this reason, since the open circuit voltage is measured at the initial stage of measurement (between a little before 1 minute from the start of measurement), it is slightly higher than the measured terminal voltage after the initial stage of measurement.

  Referring to the graph shown in FIG. 7, in the comparative sample (B) using platinum as a catalyst, the terminal voltage of the experimental comparative fuel cell was measured around 1.2 (V).

  On the other hand, in the prototype No. 1, the terminal voltage of the experimental fuel cell was an average voltage lower by about 0.2V than the comparative sample (B) using platinum as a catalyst. In the other prototypes No. 2 to No. 4, the terminal voltages of the prototype fuel cells were 0.6V, 0.8V, and 1.0V lower than those of the comparative sample (B).

  From this result, prototype No. 1 is fuel cell electrode materials 21 and 31 that are sufficiently practical, though somewhat inferior to the comparative sample (B) using platinum as a catalyst. However, in the prototype No. 2 to the prototype No. 4, the fuel cell electrode materials 21 and 31 have insufficient electrical characteristics for use in the fuel cell 1a. This may be due to the following reasons.

  If FIG. 6 is referred, the sintering temperature in trial manufacture No1 is the molded object sintered at the temperature a higher than the temperature b. As described above, at a high temperature a (sintering temperature 1100 to 1300 ° C .: center temperature of about 1200 ° C.), Cu powder having a high electric conductivity melts and has a high melting point (a melting point higher than that of one transition metal). ) And Ni and Fe powders.

  On the other hand, at the temperature b (sintering temperature 1000 to 1200 ° C .: center temperature about 1100 ° C.), the sintering temperature is lower than the melting point 1084 ° C. of the Cu, particularly on the inner side of the compact. In this case, since Cu does not melt, it is difficult to closely bond to other transition metal powders. That is, it can be said that the superiority or inferiority of the prototype No. 1 and the prototype Nos. 2 to 4 as the fuel cell electrode material depends on the setting of the sintering temperature range during sintering.

  Although the number of samples in FIG. 7 is not large, as for the correlation between the porosity of the molded body and the terminal voltage of the fuel cell 1a, the porosity of the molded body is within a certain range of porosity (20 to 40%). As the rate increases, the terminal voltage of the fuel cell 1a tends to be closer to the terminal voltage of the experimental comparison fuel cell.

  Preferably, the porosity of the molded body is in the range of 20% to 40% with respect to the volume of the molded body (or 100% relative density of the metal plate that is the closest packed). This is because when the porosity is less than 20%, the permeability of fuel such as hydrogen gas or oxygen gas is decreased, and the surface area ratio of the void is also decreased. On the other hand, if the porosity exceeds 40%, the strength of the molded body becomes weak in the structural aspect of the molded body, and it is difficult to maintain sufficient strength.

  As shown in the results of FIG. 7, in the fuel cell electrode material 21 containing a transition metal other than the platinum group element, it was confirmed that the catalytic action promotes the reaction of releasing electrons and becoming hydrogen ions. Moreover, in the fuel cell electrode material 31 containing a transition metal other than the platinum group element, it was possible to confirm a catalytic action having an oxygen reduction ability approaching that of a platinum catalyst.

In addition to the above examples, as the metal material in the molded body, when the mass of the molded body is 100 mass%, Mg is 1 to 3 mass%, Zn is 2 to 3 mass%, or Al is 5 to 5 mass%. It is preferable to include at least 6% by mass, including Ni, Fe, and Cr, with a total of mass% obtained by subtracting mass% of the contained metal from 100% by mass.
Other Examples 1) Ni, Fe, Cr, Mg: Other Examples including 1 to 3% by mass of Mg 2) Ni, Fe, Cr, Zn: Other Examples including 2 to 3% by mass of Zn 3) Ni, Fe, Cr, Al: A combination of a 3d transition metal containing 5 to 6% by mass of Al and the above metal has been found to be promising as a fuel cell electrode material.

  Further, as the metal material used for the powder, not only a single metal but also an alloy of two or more metals, for example, an alloy of Ni and Fe, may be used as a powder. Moreover, you may use the powder below a predetermined particle diameter.

<Authentication judgment function>
Preferably, the fuel cell electrode materials 21 and 31 support a luminescent material that emits light by infrared or ultraviolet light in a part between the gaps of the molded body, and when a counterfeit product of the product is produced, Provide a function that can determine the authenticity of the presence or absence.

  For example, the luminescent material or the like may be physically fitted in a part of the plurality of voids in the molded body, or may be fixed in the void by an adhesive or the like, and is embedded in a part of the surface of the molded body. You may do it.

  When an adhesive is used, the adhesive is not particularly limited, and a well-known one can be used. For example, the luminescent material can be fixed to the surface of the sintered molded body by a phenol resin adhesive, an epoxy resin adhesive, or the like.

  Further, the step of supporting the luminescent material (luminescent material supporting step) is performed at a certain low temperature or less (a temperature not impairing the characteristics of the luminescent material), for example, in a cooling step after sintering or after completion of cooling. Addition and adhesion.

The luminescent substance is a substance that emits light by infrared rays, ultraviolet rays, or the like. For example, a light-emitting substance that emits light by ultraviolet rays or the like contains BaMg ₂ Al ₁₆ O ₂₇ : Eu, BaMg ₂ Al ₁₆ O ₂₇ : Eu, Mn, or the like as a main component.

  As described above, the present invention shows a technique related to an electrode material for a fuel cell having oxygen reduction ability without using a platinum group element. Further, as an example of the present embodiment, in the present invention, an electrode material for a fuel cell having an electrode catalytic action, a manufacturing method thereof, and a fuel cell can be provided without using a platinum group element.

[Other Embodiments]
As mentioned above, although embodiment of this invention was described, this embodiment is shown as an example and is not intending limiting the range of invention. Further, for example, this embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. For example, when an electrode catalyst using platinum is used, the fuel cell electrode material according to the present invention is used in order to reduce the amount of platinum used. This embodiment and its modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and their equivalents.

  DESCRIPTION OF SYMBOLS 1, 1a, 100 ... Fuel cell 2, 2a, 200, 200a ... Fuel electrode 3, 3a, 300, 300a ... Air electrode, 4 ... PEM membrane, 5 ... Hydrogen gas inlet part, 6 ... Oxygen gas inlet part, DESCRIPTION OF SYMBOLS 11 ... Hydrogen gas supply connection part, 12 ... Oxygen gas supply connection part, 13 ... Water discharge part, 14 ... Electrode connection terminal, 15 ... Load, 21, 31 ... Electrode material for fuel cells, 22, 32 ... Conductive material, 23 33, holes, 201, 301 ... catalyst for electrodes

Claims (11)

A fuel cell electrode material containing no platinum group elements of Ru, Rh, Pd, Os, Ir and Pt,
The electrode material for a fuel cell comprises a molded body containing at least a plurality of different transition metals as a metal material,
Each of the molded bodies has a void dispersed in the molded body so that the metal material is processed into a powder and fuel used in a fuel cell can pass through the molded body. An electrode material for a fuel cell, which is formed by mixing powder. The plurality of different transition metals include at least one of Fe, Ni, Mn, Cr, or Ti belonging to the 3d transition element,
Furthermore, the molded body includes any one of Cu, Zn, Al, or Mg, which is higher in electrical conductivity than the transition metal included, as the metal material other than the transition metal included. The electrode material for fuel cells according to claim 1. The electrode material for a fuel cell according to claim 2, wherein the plurality of different transition metals include at least Ni and Fe, or Ni and Cu. The composition ratio of the metal material in the molded body is 1 to 3 mass% for Mg, 2 to 3 mass% for Zn, or 5 to 6 mass% for Al when the mass of the molded body is 100 mass%. 4. The fuel cell electrode material according to claim 3, comprising at least Ni, Fe, and Cr, which includes at least 100% by mass and subtracts mass% of the metal contained from 100% by mass. 5. The electrode material for a fuel cell according to claim 1, wherein the porosity of the molded body is in a range of 20% to 40% with respect to the volume of the molded body. . 6. The powder according to claim 1, wherein the powder is spherical or needle-shaped, or at least one kind of the metal material is spherical and other kinds of the metal material are processed into a needle shape. The electrode material for fuel cells according to any one of the above. The electrode material for a fuel cell according to any one of claims 1 to 6, wherein a luminescent material that emits light by infrared rays or ultraviolet rays is supported on the molded body. A method for producing an electrode material for a fuel cell for producing the electrode material for a fuel cell according to any one of claims 1 to 6,
Crushing step of crushing and processing the metal material used for the molded body as a powder to 200 μm or less;
A mixing step of mixing the powder so as to uniformly disperse after the pulverization step;
After the mixing step, pressurizing the uniformly dispersed powder at a pressure of 500 to 800 Mpa to form a molded body; and
And a sintering step of sintering the compact after the pressurizing step. A method for producing an electrode material for a fuel cell. In the sintering step, the sintering temperature is in a range higher than the melting point of the metal having the highest electrical conductivity among the metal materials and lower than the melting point of the metal other than the metal having the highest electrical conductivity. The method for producing a fuel cell electrode material according to claim 8. The method for producing an electrode material for a fuel cell according to claim 8 or 9, further comprising a luminescent substance supporting step of supporting a luminescent substance that emits light by infrared rays or ultraviolet rays on the molded body. A fuel cell comprising the fuel cell electrode material according to any one of claims 1 to 7 as an air electrode or a fuel electrode.