JP2009028708A - Magnetic particle-deposited catalyst, method for manufacturing the same, electrode using the same for fuel cell, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic particle-deposited catalyst capable of achieving a high-output fuel cell having high catalyst efficiency. <P>SOLUTION: The first magnetic powder-deposited catalyst contains an electrically conductive particle and a catalyst particle deposited on the electrically conductive particle and haing magnetism, and has 4.0-79.8 kA/m coercivity and 1-20 Am<SP>2</SP>/kg saturation magnetized quantity. The second magnetic powder-deposited catalyst contains the electrically conductive particle, the catalyst particle deposited on the electrically conductive particle and a magnetic particle deposited on the electrically conductive particle, has 4.0-79.8 kA/m coercivity and preferably has 1-20 Am<SP>2</SP>/kg saturation magnetized quantity. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetic particle-supported catalyst having high catalytic efficiency, a method for producing the same, a fuel cell electrode using the same, and a fuel cell.

  Solid polymer electrolyte fuel cells have been developed as power sources for portable devices and automobiles because high current density can be obtained at low temperatures. A solid polymer electrolyte fuel cell has a structure in which an ion exchange membrane, which is a solid polymer electrolyte, is disposed between a fuel electrode (negative electrode) and an air electrode (positive electrode). Both the fuel electrode and the air electrode are composed of a mixture of a catalyst in which a noble metal having catalytic ability is supported on a conductive carrier such as carbon black and a polymer electrolyte. In this configuration, at the fuel electrode, a fuel such as hydrogen gas or methanol emits electrons by a reaction on the catalyst surface to generate hydrogen ions. Hydrogen ions reach the air electrode through the electrolyte and electrolyte membrane in the electrode. The emitted electrons flow through the catalyst carrier in the electrode to the external circuit, and reach the air electrode from the external circuit. On the other hand, at the air electrode, oxygen reaches the catalyst through the pores in the electrode and reacts with hydrogen ions and electrons generated at the fuel electrode.

  In the solid polymer electrolyte fuel cell, in order to promote the electrode reaction and improve the cell characteristics, it is first required that the activity of the catalyst constituting the electrode is high. For this reason, a catalyst in which a highly active noble metal, particularly platinum or a platinum alloy is supported on a conductive carrier such as carbon black is used as the catalyst.

  In order to make these platinum-supported catalysts highly active, it is effective to make the particle size of platinum particles deposited and supported on a carrier such as carbon black as small as possible. This is because the surface area of the platinum particles is increased by making the particles fine, and as a result, the reaction area is increased. However, when the platinum particle size is reduced in this way, high reactivity is exhibited in the initial stage. However, when used for a long period of time, there is a problem that the catalyst particles become coarse due to the fusion of the platinum particles and the catalytic activity decreases.

  Therefore, in order to increase the activity of the noble metal catalyst particles themselves and use them stably for a long period of time, alloy-based catalysts containing platinum as a main constituent element have been actively studied. Of these, platinum-ruthenium alloy catalysts are the most promising alloy-based catalysts, and research and development are actively conducted. Although the mechanism by which this alloy-based catalyst exhibits excellent catalytic performance even after long-term use has not been clarified, ruthenium decomposes carbon monoxide (CO), which is produced by catalytic reaction and becomes a catalyst poison. This is thought to be due to the effect of

  However, since ruthenium is an extremely expensive material like platinum, it is strongly required to replace ruthenium with another inexpensive material in terms of cost. In such a situation, a platinum-cobalt alloy catalyst in which a part of platinum is replaced with cobalt attracts attention. It is known that the platinum-cobalt alloy-based catalyst not only has a merit that a part of expensive platinum is replaced with cheaper cobalt than platinum, but also improves the catalytic performance itself by adding cobalt. Furthermore, a ternary alloy catalyst or a quaternary alloy catalyst in which elements such as nickel, chromium, vanadium, copper, and aluminum are added to the platinum-cobalt alloy has been studied (for example, see Patent Documents 1 to 7). .

  Platinum catalysts and platinum-cobalt alloy catalysts are used in both the fuel electrode and the air electrode because of their excellent catalytic ability. When these platinum-based catalysts are used for the fuel electrode, particularly when used for a fuel electrode using hydrogen as a fuel, a fuel electrode having sufficient performance can be obtained by using platinum as a catalyst supported on carbon particles. Has been obtained. On the other hand, when these platinum-based catalysts are used for the air electrode, there is a problem that the overvoltage becomes large and the performance of the air electrode is not sufficiently exhibited, and the catalyst efficiency is low.

  Further, since the oxygen source used for the air electrode is usually air, it contains a large amount of nitrogen in addition to oxygen necessary for the catalytic reaction. Therefore, as the electrode reaction proceeds, oxygen is consumed, and oxygen deficiency is likely to occur near the catalyst of the air electrode. In order to avoid such an oxygen-deficient state, for example, in Patent Documents 8 and 9, when forming a catalyst layer containing these platinum-based catalysts, a magnetic material such as a submillimeter-sized permanent magnet is further included in the catalyst layer. It has been proposed to increase the catalyst efficiency by attracting oxygen molecules by the magnetic force of the magnetic material.

JP-A-6-30001 JP-A-5-208135 JP-A-6-176766 JP-A-8-57317 JP-A-4-87260 JP-A-6-246163 Japanese Patent Laid-Open No. 9-17435 JP 2002-198057 A JP 2006-252966 A

  However, in the fuel cells described in Patent Documents 8 and 9, since the magnetic field is applied to the entire fuel cell or the entire catalyst layer when viewed from the catalyst particles, the particles having individual catalytic ability are used. On the other hand, it was found that oxygen could not be efficiently attracted and the expected performance improvement was not observed. That is, the fuel cells of Patent Documents 8 and 9 do not have a structure in which high concentration oxygen is attracted only in the vicinity of catalyst particles having catalytic ability.

  The present invention solves the above-described problem and effectively attracts oxygen to individual particles having catalytic ability, and improves the reactivity with oxygen to increase the substantial catalytic ability. A particle-supported catalyst is provided.

The first magnetic particle-supported catalyst of the present invention is a magnetic particle-supported catalyst comprising conductive particles and magnetized catalyst particles supported on the conductive particles, wherein the coercivity of the magnetic particle-supported catalyst is It is 4.0 to 79.8 kA / m, and the saturation magnetization is 1 to 20 A · m ² / kg.

  The first magnetic particle-supported catalyst production method of the present invention comprises a step of supporting two or more kinds of magnetic metal components on conductive particles, and the conductive particles supporting the magnetic metal components in a non-oxidizing atmosphere. And a step of heating at 250 to 600 ° C.

  The second magnetic particle-supported catalyst of the present invention includes conductive particles, catalyst particles supported on the conductive particles, and magnetic particles supported on the conductive particles.

  The method for producing a second magnetic particle-supported catalyst of the present invention comprises a step of supporting a catalyst metal component on conductive particles, and a conductive particle supporting the catalyst metal component at 250 to 600 ° C. in a non-oxidizing atmosphere. Heating the catalyst particles to carry the catalyst particles on the conductive particles, further supporting the conductive particles carrying the catalyst particles on the magnetic precursor, and the catalyst particles and the magnetic precursor. And a step of heating the conductive particles supporting.

  The electrode for a fuel cell according to the present invention includes the first or second magnetic particle-supported catalyst according to the present invention.

  The fuel cell of the present invention includes the fuel cell electrode of the present invention.

  The present invention can provide a magnetic particle-supported catalyst having high catalyst efficiency and capable of realizing a high output fuel cell.

  Oxygen used as an oxidant in the air electrode has a high magnetic susceptibility. This magnetic susceptibility indicates the ratio between the magnetic moment generated by applying a magnetic field to the magnetic material and the applied magnetic field, and the greater the magnetic susceptibility, the higher the sensitivity to the magnetic field. The magnetic susceptibility at normal temperature is +106.2 for oxygen, for example, nitrogen is -0.8, hydrogen is -1.97, and oxygen protrudes and has a high magnetic susceptibility. That is, oxygen has high sensitivity to a magnetic field, and if a magnetic material that generates a magnetic field exists in the vicinity of oxygen, this means that oxygen is attracted to this magnetic material.

  For example, as shown in FIG. 1, magnets 11 and 12 are arranged on both sides of a membrane electrode assembly 10 including an air electrode 13, a fuel electrode 14, and a solid polymer electrolyte membrane 15, and surrounds the entire membrane electrode assembly 10. If the magnetic field is generated in this way, it is considered that oxygen is attracted throughout the membrane electrode assembly 10. However, in this method, the effect of locally attracting oxygen only in the vicinity of the air electrode 13 cannot be expected. For this reason, unless a strong magnetic field of several Tesla or more is applied, the effect of attracting oxygen does not appear, and the effect is only a few percent improvement in output as a fuel cell, which is not realistic.

  Further, as shown in FIG. 2A, a method of kneading large magnetic particles 22 of several μ sizes or more together with the catalyst supporting particles 21 in the catalyst layer 20 is also conceivable. In this method, unlike in the case of FIG. 1, it is considered that the effect of attracting oxygen only to the catalyst layer 20 is enhanced. However, as shown in FIG. 2B, which is an enlarged view of the catalyst-carrying particles 21 in FIG. Oxygen cannot be locally attracted to the catalyst particles 23 having the individual catalytic ability. Rather, these coarse magnetic particles 22 hinder the electrical conduction between the conductive carriers 24 in the catalyst layer 20. Therefore, it is thought that the expected effect cannot be obtained.

  Therefore, the present inventors have supported a magnetic particle-supported catalyst in which catalyst particles having catalytic ability and specific magnetism are supported on a conductive support, or supported on a conductive support 31 as shown in FIG. The inventors have invented a magnetic particle-supported catalyst 30 in which magnetic particles 32 are arranged in the vicinity of the formed catalyst particles 33. And it discovered that a high output fuel cell was producible by manufacturing the electrode for fuel cells using these magnetic particle carrying catalysts.

  That is, the magnetic particle-supported catalyst of the present invention improves the catalytic reactivity with oxygen having a high magnetic susceptibility, particularly when used for an air electrode, without increasing the amount of expensive platinum used, resulting in a fuel cell. Can achieve higher performance.

  Embodiments of the present invention will be described below.

(Embodiment 1)
First, the first magnetic particle-supported catalyst of the present invention will be described. The first magnetic particle-supported catalyst of the present invention includes conductive particles and magnetized catalyst particles supported on the conductive particles, and the coercivity of the magnetic particle-supported catalyst is 4.0 to 79.8 kA. / M, and the saturation magnetization is 1 to 20 A · m ² / kg.

  Since the catalyst particles have magnetism, when the magnetic particle-supported catalyst is used as a catalyst for an air electrode of a fuel cell, for example, a magnetic field can be locally generated for each catalyst particle. Oxygen can efficiently react with hydrogen ions and electrons at the electrode, and the catalyst efficiency is improved. As a result, a high-power fuel cell can be provided without increasing the amount of expensive platinum catalyst used.

Regarding the magnetic strength of the magnetic particle-supported catalyst, considering that the magnetic susceptibility is +106.2, the magnetic particle-supported catalyst has a coercive force of 4.0 kA / m (50 oersted) or more, and its saturation. The amount of magnetization needs to be 1 A · m ² / kg (1 emu / g) or more. When the coercive force is less than 4.0 kA / m (50 oersted) and the saturation magnetization is less than 1 A · m ² / kg (1 emu / g), oxygen in the air is not sufficiently attracted, and a high output fuel cell It will be difficult to provide. On the other hand, the higher the coercive force and the saturation magnetization amount of the magnetic particle-supported catalyst, the better. However, in the current materials and production methods, the upper limit of the coercive force of the magnetic particle-supported catalyst is 79.8 kA / m, and the saturation magnetization amount thereof. It is sufficient to set the upper limit of 20 A · m ² / kg.

  In the present invention, the presence or absence of magnetism is confirmed by the shake of a magnetic needle, and the coercive force and the saturation magnetization are measured with a vibrating sample magnetometer.

The catalyst particles have magnetism that can impart 4.0 to 79.8 kA / m as the coercive force of the magnetic particle-supported catalyst that is the final product, and can impart 1 to 20 A · m ² / kg as the saturation magnetization. If it does, it will not specifically limit.

  Magnetic catalyst particles can be used as the catalyst particles, and the magnetic alloy particles preferably contain platinum and cobalt as alloy components. Platinum-cobalt alloy is a ferromagnetic material that can easily impart magnetism, and exhibits excellent catalytic ability when the magnetic particle-supported catalyst of the present invention is used as a platinum-cobalt alloy catalyst for fuel cell electrodes. Because it can.

The contents of platinum and cobalt in the magnetic alloy particles are preferably 40 to 98% by weight and 2 to 60% by weight, respectively, and more preferably 55 to 98% by weight and 2 to 45% by weight, respectively. Within the above range, the magnetic particle supported catalyst as the final product has a coercive force of 4.0 to 79.8 kA / m (50 to 1000 oersted) and a saturation magnetization of 1 to 20 A · m ² / kg (1 to 20 emu). / G) can be reliably imparted, and sufficient catalytic ability as a platinum-cobalt alloy catalyst can be exhibited. More specifically, when the platinum content is less than the above range, and the cobalt content is more than the above range, the platinum content is reduced, so the catalytic ability is reduced, and the platinum content is within the above range. When the content of cobalt is more than the above range, the content of cobalt is reduced, and sufficient magnetic properties for exhibiting the performance as a magnetic alloy catalyst cannot be obtained.

  The magnetic alloy particles may further include at least one element selected from the group consisting of nickel, iron, titanium, copper, manganese, aluminum, ruthenium, tungsten and molybdenum as an alloy component. That is, as long as the ferromagnetic material can be maintained, other alloy components can be contained in addition to platinum and cobalt to form ternary alloy particles or quaternary alloy particles. By using multi-component alloy particles, there are advantages such as reducing the amount of expensive platinum used while maintaining magnetic properties and catalytic ability, and improving the durability as a catalyst such as solubility and thermal stability. is there.

  The particle diameter of the magnetic alloy particles is preferably 1 to 10 nm, and more preferably 2 to 3 nm. When the particle size is smaller than 1 nm, the initial performance is excellent because the surface area of the particle is increased. However, when used for a long time, the particle dissolves and re-precipitates. As a result, grain growth occurs and the catalytic ability tends to decrease. On the other hand, when the particle size is larger than 10 nm, the surface area is reduced, and the catalytic ability is lowered. In the present invention, the particle diameter is determined by measuring the size of a particle in a transmission electron microscope (TEM) photograph.

  The supported amount of the catalyst particles is preferably 5 to 50% by weight with respect to the total weight of the magnetic particle-supported catalyst. If the amount is less than 5% by weight, the effective catalyst amount as a whole is reduced, so that the function tends to be difficult to be exhibited. If the amount is more than 50% by weight, the surface of the conductive particles is deposited as a single layer. Therefore, the catalyst particles are easily overlapped or aggregated.

  The conductive particles that serve as the carrier for the catalyst particles are not particularly limited. For example, carbon particles such as acetylene black, ketjen black, and furnace carbon are preferable. This is because they are highly conductive and stable against electrochemical reactions.

  Moreover, it is preferable that the average particle diameter of the said electroconductive particle is 20-70 nm, and 30-50 nm is more preferable. Even if the average particle size is smaller than 20 nm, there is no problem in terms of the function as the magnetic catalyst of the present invention. However, since the particle size is small in the synthesis process, the particles are agglomerated and difficult to uniformly disperse. The average particle size of is preferably 20 nm or more. Further, even if the average particle diameter of the conductive particles is larger than 70 nm, the catalytic ability is not lost, but the specific surface area is reduced and the catalytic ability is lowered, so the average particle diameter of the conductive particles is 70 nm or less. Preferably there is.

  In the present invention, the average particle diameter is determined from the arithmetic average of the particle diameters of 100 particles observed from a transmission electron microscope (TEM) photograph.

  As the catalyst particles, oxide particles containing at least one element selected from the group consisting of iron, cobalt, nickel, zinc, manganese, and copper can also be used. This is because the oxide particles can be used as a catalyst for an alkaline fuel cell. The oxide particles preferably have a spinel structure or a perovskite structure. This is because the oxide particles having these structures are electrochemically stable.

  Next, the manufacturing method of the 1st magnetic particle carrying catalyst of this invention is demonstrated. The first magnetic particle-supported catalyst production method of the present invention is a production method in the case where magnetic alloy particles are used as the catalyst particles. The step of supporting two or more kinds of magnetic metal components on conductive particles, Heating the conductive particles carrying the metal component at 250 to 600 ° C. in a non-oxidizing atmosphere.

  The step of supporting the two or more kinds of magnetic metal components on the conductive particles, that is, the method of supporting the magnetic alloy precursor on the conductive particles is not particularly limited. For example, a metal salt of platinum or cobalt as a magnetic metal component is dissolved in a specific amount of water in advance, and conductive particles are dispersed in this aqueous metal ion solution. By depositing platinum or cobalt hydrate particles on the particles, followed by washing, filtering and drying, the conductive particles can carry the platinum component and the cobalt component. In addition, conductive particles are dispersed in a solution containing platinum or cobalt complex ions, and these metal complex ions are adsorbed on the conductive particles, followed by filtration and drying, whereby platinum components and cobalt are added to the conductive particles. Components can be supported.

In the state where two or more kinds of magnetic metal components are simply supported on the conductive particles as described above, the magnetic metal components are not alloyed with each other. It is necessary to heat at 250 to 600 ° C. in a non-oxidizing atmosphere. As a result, the magnetic metal component is alloyed and the alloy particles are supported on the conductive particles, and magnetism is imparted to the alloy particles. That is, the above process yields a magnetic particle-supported catalyst having a coercive force of 4.0 to 79.8 kA / m and a saturation magnetization of 1 to 20 A · m ² / kg.

  When the heating temperature is lower than 250 ° C., the magnetic metal component is not sufficiently alloyed, or even when alloyed, the coercive force and the saturation magnetization necessary for exhibiting sensitivity to oxygen are not exhibited. On the other hand, when the heating temperature is higher than 600 ° C., even if the magnetic metal component is alloyed, the alloy particles dispersed and precipitated on the conductive particles are fused and grown to increase the particle size, thereby reducing the catalytic ability.

  The reason for heating in a non-oxidizing atmosphere is that it becomes difficult to impart magnetism when the alloy particles are oxidized. In addition, examples of the non-oxidizing atmosphere include a reducing gas atmosphere such as hydrogen and an inert gas atmosphere such as argon and nitrogen. Furthermore, it is preferable to perform a two-stage process in which a heat treatment is performed in an inert gas and then a reduction process is performed by further heating in a reducing gas atmosphere.

  By heating the magnetic metal component in the above temperature range to form alloy particles, magnetism is imparted to the alloy particles. That is, for example, platinum has catalytic ability, but platinum alone has no magnetism. On the other hand, platinum becomes a magnetic material when it forms an alloy with cobalt. Therefore, for example, by using platinum-cobalt alloy particles, a magnetic alloy catalyst having both magnetism and catalytic ability can be obtained for the first time.

In any case, the coercive force is 4.0 to 79.8 kA / m (50 to 1000 oersted) by changing the heat treatment temperature according to the deposition method and the deposition state of platinum, cobalt, etc. on the support. , A magnetic particle-supported catalyst having a magnetic property in the range of 1-20 A · m ² / kg (1-20 emu / g) of saturation magnetization can be obtained, and by using the magnetic particle-supported catalyst for the air electrode The reactivity with oxygen becomes good and the performance of the fuel cell can be improved.

(Embodiment 2)
Next, the second magnetic particle-supported catalyst of the present invention will be described. The second magnetic particle-supported catalyst of the present invention is characterized by comprising conductive particles, catalyst particles supported on the conductive particles, and magnetic particles supported on the conductive particles.

The coercive force of the magnetic particle-supported catalyst is preferably 4.0 to 79.8 kA / m, and the saturation magnetization is preferably 1 to 20 A · m ² / kg.

  By supporting the magnetic particles together with the catalyst particles, when the magnetic particle-supported catalyst is used, for example, as a catalyst for an air electrode of a fuel cell, a magnetic field can be generated locally for each catalyst particle. Therefore, oxygen can efficiently react with hydrogen ions and electrons at the air electrode, and the catalyst efficiency is improved. As a result, a high-power fuel cell can be provided without increasing the amount of expensive platinum catalyst used.

Regarding the magnetic strength of the magnetic particle-supported catalyst, considering that the magnetic susceptibility is +106.2, the magnetic particle-supported catalyst has a coercive force of 4.0 kA / m (50 oersted) or more, and its saturation. The amount of magnetization is preferably 1 A · m ² / kg (1 emu / g) or more. If the coercive force is less than 4.0 kA / m (50 oersted) and the saturation magnetization is less than 1 A · m ² / kg (1 emu / g), the oxygen in the air may not be attracted sufficiently, resulting in high output. It becomes difficult to provide the fuel cell. On the other hand, the higher the coercive force and the saturation magnetization amount of the magnetic particle-supported catalyst, the better. However, in the current materials and production methods, the upper limit of the coercive force of the magnetic particle-supported catalyst is 79.8 kA / m, and the saturation magnetization amount thereof. It is sufficient to set the upper limit of 20 A · m ² / kg.

  In the present invention, the presence or absence of magnetism is confirmed by shake of a magnetic needle, and the coercive force and the saturation magnetization are measured by a vibrating sample magnetometer.

  The catalyst particles preferably contain platinum. This is because when the magnetic particle-supported catalyst of the present invention is used as a platinum-based catalyst for a fuel cell electrode, excellent catalytic ability can be exhibited. Therefore, the catalyst particles may be composed of platinum particles alone or platinum alloy particles. The platinum alloy particles can be composed of platinum and at least one element selected from the group consisting of nickel, iron, titanium, copper, manganese, aluminum, ruthenium, tungsten and molybdenum. However, the catalyst particles are not limited to platinum-based catalyst particles, and may be other than platinum-based catalyst particles as long as they have catalytic ability as a catalyst for a fuel cell electrode.

The magnetic particles have a magnetism capable of imparting 4.0 to 79.8 kA / m as a coercive force of a magnetic particle-supported catalyst as a final product, and imparting 1 to 20 A · m ² / kg as a saturation magnetization. For example, oxide particles or alloy particles that become a ferromagnetic material containing a transition metal element can be used.

  As the oxide particles, oxide particles containing at least one element selected from the group consisting of iron, cobalt, nickel, zinc, manganese and copper can be used. The oxide particles preferably have a spinel structure or a perovskite structure. This is because the oxide particles having these structures are electrochemically stable. Further, as the alloy particles, samarium-cobalt alloy, iron-platinum alloy, cobalt-platinum alloy and the like can be used.

  The weight ratio of the catalyst particles to the magnetic particles is preferably 40:60 to 90:10. If the weight ratio of the catalyst particles is less than this range and the weight ratio of the magnetic particles is more than this range, the number of particles responsible for the catalyst activity decreases, so that the catalytic performance decreases, and the weight ratio of the catalyst particles falls within this range. If more and the weight ratio of the magnetic particles is less than this range, the number of magnetic particles existing in the vicinity of the individual catalyst particles is reduced, so that the local magnetic field for the individual catalyst particles is weakened, and oxygen at the air electrode is reduced. It becomes difficult to increase the reactivity with.

  Moreover, it is preferable that the load of the said catalyst particle and the said magnetic particle is 10 to 70 weight% with respect to the total weight of the said magnetic particle support catalyst. If the amount is less than 10% by weight, the effective catalyst amount as a whole is reduced, so that the function tends to be difficult to be exhibited. If the amount is more than 70% by weight, the surface of the conductive particles is deposited in a single layer. Therefore, the particles tend to overlap or aggregate.

  The particle diameters of the catalyst particles and the magnetic particles are each preferably 1 to 10 nm, and more preferably 2 to 3 nm. In the present invention, the particle diameter is determined by measuring the size of a particle in a transmission electron microscope (TEM) photograph.

  When the particle diameter of the catalyst particles is smaller than 1 nm, the initial performance is excellent because the surface area of the catalyst particles is increased. However, when used for a long time, the catalyst particles dissolve and reprecipitate, resulting in particle growth and reduced catalytic performance. It becomes easy to do. On the other hand, when the particle diameter of the catalyst particles is larger than 10 nm, the surface area is reduced and the catalytic ability is lowered.

  In addition, when the particle size of the magnetic particles is smaller than 1 nm, it is difficult to maintain magnetism in the case of alloy-based magnetic particles due to severe deterioration due to surface oxidation or the like, and in the case of oxide magnetic particles, such as deterioration due to oxidation. Since there is no problem, there is no problem if a magnetic field can be generated even if it is smaller than this. However, since the lattice constant of the oxide is about 0.5 nm, it is difficult to produce crystalline particles of 1 nm or less. It is. In addition, even if the particle size of the magnetic particles is larger than 10 nm, the effect of the magnetic field is not lost. However, in order to arrange the magnetic particles in the vicinity of the individual catalyst particles, the magnetic particles are equivalent to the catalyst particles. Since it preferably has a particle size, the particle size of the magnetic particles is preferably 10 nm or less. For example, when using platinum-based catalyst particles having a particle diameter of 2 to 3 nm, the particle diameter of the magnetic particles is preferably about 5 nm or less. In addition, when using non-conductive particles as magnetic particles, if the particle size of the non-conductive magnetic particles is too large, it becomes a factor that hinders electric conduction between the conductive particles that are conductive carriers, and oxygen This is not preferable because it can be a factor that deteriorates the performance as a fuel cell, even if there is no problem in terms of improving the reactivity.

  The conductive particles that serve as the carrier for the catalyst particles are not particularly limited. For example, carbon particles such as acetylene black, ketjen black, and furnace carbon are preferable. This is because they are highly conductive and stable against electrochemical reactions.

  Moreover, it is preferable that the average particle diameter of the said electroconductive particle is 20-70 nm, and 30-50 nm is more preferable. Even if the average particle size is smaller than 20 nm, there is no problem in terms of the function as the magnetic catalyst of the present invention. However, since the particle size is small in the synthesis process, the particles are agglomerated and difficult to uniformly disperse. The average particle size of is preferably 20 nm or more. Further, even if the average particle diameter of the conductive particles is larger than 70 nm, the catalytic ability is not lost, but the specific surface area is reduced and the catalytic ability is lowered, so the average particle diameter of the conductive particles is 70 nm or less. Preferably there is.

  In the present invention, the average particle diameter is determined from the arithmetic average of the particle diameters of 100 particles observed from a transmission electron microscope (TEM) photograph.

  Next, the manufacturing method of the 2nd magnetic particle carrying catalyst of this invention is demonstrated. The method for producing a second magnetic particle-supported catalyst of the present invention comprises a step of supporting a catalytic metal component on conductive particles and a conductive particle supporting the catalytic metal component at 250 to 600 ° C. in a non-oxidizing atmosphere. By heating the catalyst particles on the conductive particles, the step of further supporting the magnetic precursor on the conductive particles supporting the catalyst particles, the catalyst particles and the magnetic precursor Heating the conductive particles.

  The step of supporting the catalyst metal component on the conductive particles, that is, the method of supporting the catalyst particle precursor on the conductive particles is not particularly limited. For example, platinum salt alone or platinum salt and other metal salt as catalyst metal components are dissolved in a specific amount of water in advance, and conductive particles are dispersed in this aqueous metal ion solution. The catalyst metal component can be supported on the conductive particles by dropping and depositing catalyst metal hydrate particles on the conductive particles, followed by washing with water, filtration and drying. In addition, conductive particles are dispersed in a solution containing complex ions of catalytic metal, and these catalytic metal complex ions are adsorbed on the conductive particles, and then filtered and dried, whereby the catalytic metal component is added to the conductive particles. It can be supported.

  In the state where the catalyst metal component is simply supported on the conductive particles as described above, since the catalyst metal component is not metallized, the conductive particles supporting the catalyst metal component are then placed in a non-oxidizing atmosphere. It is necessary to heat at 250-600 degreeC in inside. As a result, the catalytic metal component is metallized and the catalytic metal particles are supported on the conductive particles. Further, when two or more kinds of catalyst metal components are supported on the conductive particles, the catalyst metal components are alloyed by the heating, and the catalyst alloy particles are supported on the conductive particles.

  When the heating temperature is lower than 250 ° C., the catalytic metal component may not be sufficiently metallized or alloyed. When the heating temperature is higher than 600 ° C., even if the catalytic metal component is metallized or alloyed, the catalyst particles dispersed and deposited on the conductive particles are fused and grown to increase the particle size, resulting in a decrease in catalytic performance. To do.

  The reason why heating is performed in a non-oxidizing atmosphere is that the catalytic ability decreases when the catalyst particles are oxidized. In addition, examples of the non-oxidizing atmosphere include a reducing gas atmosphere such as hydrogen and an inert gas atmosphere such as argon and nitrogen. Furthermore, it is preferable to perform a two-stage process in which a heat treatment is performed in an inert gas and then a reduction process is performed by further heating in a reducing gas atmosphere.

Subsequently, the conductive particles carrying the catalyst particles are further loaded with a magnetic precursor,
The magnetic precursor may be either a magnetic oxide precursor or a magnetic alloy precursor. For example, a compound containing a metal component that can be a magnetic substance such as a transition metal element can be used.

  In addition, after the magnetic precursor is supported on the conductive particles, heat treatment is performed to obtain magnetic particles. The heat treatment conditions at this time need to be appropriately selected according to the target magnetic particles. For example, if the magnetic particles are alloy particles, it is preferable to heat in a non-oxidizing atmosphere. This is because it becomes difficult to impart magnetism when the alloy particles are oxidized. If the magnetic particles are oxide particles, it is preferable to heat in an oxidizing atmosphere or an inert atmosphere. The heating temperature may be any temperature that is necessary and sufficient for the magnetic particles to crystallize. For example, in the case of an iron oxide such as magnetite, it may be heated at 200 ° C. or higher. However, in the case of these oxide magnetic bodies, if the heating temperature is too high, the particles are sintered and coarsened, so it is preferable to heat at 600 ° C. or lower.

As described above, the magnetic particle-supported catalyst supporting the catalyst particles and the magnetic particles is prepared. It is preferable to further magnetize the prepared magnetic particle-supported catalyst by applying a magnetic field. Magnetic properties with a coercive force of 4.0 to 79.8 kA / m (50 to 1000 oersted) and a saturation magnetization of 1 to 20 A · m ² / kg (1 to 20 emu / g) more reliably by magnetization. By using the magnetic particle-supported catalyst for the air electrode, the reactivity with oxygen is improved and the performance of the fuel cell can be improved.

  The magnetization may be performed at any stage after the magnetic particles are supported on the conductive particles, may be performed after the formation of the catalyst layer, or may be performed after the membrane electrode assembly is manufactured. Further, even after the magnetic particles are magnetized in this way, if the entire membrane electrode assembly is placed in a magnetic field, the catalyst efficiency can be improved over a longer period. When a magnetic field covering the entire membrane electrode assembly is used, the effect can be obtained with a weak magnetic field to the extent that a general-purpose magnet is disposed on both sides of the membrane electrode assembly as shown in FIG. This is because the magnetic field for attracting oxygen to the particles responsible for the catalytic activity is generated between the magnetic particles supported on the conductive particles, and the membrane electrode is used only to align the magnetic field direction of the magnetic particles in one direction. This is because the entire bonded body may be placed in a magnetic field. In the case of particles that are ferromagnetic materials, the magnetization of individual particles easily aligns in one direction in the presence of an external magnetic field. If magnetized, the magnetizations are aligned even in the absence of these external magnetic fields, but it is preferable to place them in an external magnetic field because the effect is more likely to appear.

(Embodiment 3)
Next, an example of the fuel cell electrode of the present invention will be described with reference to the drawings. In the present embodiment, a membrane electrode assembly (MEA), which is an example of a fuel cell electrode manufactured using the magnetic particle-supported catalyst of Embodiment 1 or Embodiment 2, will be described. By using the fuel cell electrode of the present embodiment, the magnetic particle-supported catalyst of Embodiment 1 or Embodiment 2 can be evaluated as a fuel cell catalyst.

  FIG. 4 is a schematic cross-sectional view showing an example of a membrane electrode assembly. In FIG. 4, the membrane electrode assembly 40 is disposed outside the air electrode 42, the air electrode 42 disposed on one side of the solid polymer electrolyte membrane 41 in the thickness direction, the fuel electrode 43 disposed on the other side, and the air electrode 42. The air electrode gas diffusion layer 44 and the fuel electrode gas diffusion layer 45 disposed outside the fuel electrode 43 are provided.

  Examples of the solid polymer electrolyte membrane 41 include a polyperfluorosulfonic acid resin membrane, specifically “Nafion” (trade name) manufactured by DuPont, “Flemion” (trade name) manufactured by Asahi Glass Co., Ltd., and Asahi Kasei Kogyo. A membrane such as “Aciplex” (trade name) manufactured by the company can be used. Further, as the gas diffusion layers 44 and 45, porous carbon cloth or carbon sheet can be used.

  The manufacturing method of the membrane electrode assembly 40 is not particularly limited, and the following general method can be applied. That is, the magnetic particle-supported catalyst of the first or second embodiment, the polymer material, and a binder or the like as necessary are mixed in a solvent mainly composed of a lower alcohol such as ethanol or propanol, and magnetically mixed. A catalyst paint is prepared by dispersing using a general dispersing device such as a stirrer, ball mill, ultrasonic disperser or the like. At this time, the amount of the solvent is adjusted so that the viscosity of the paint is optimized in accordance with the application method. The magnetic particle-supported catalyst of Embodiment 1 or Embodiment 2 may be used for either or both of the air electrode catalyst paint and the fuel electrode catalyst paint, but at least by being used as the air electrode catalyst paint. The original effect of the magnetic particle-supported catalyst of Embodiment 1 or Embodiment 2 can be evaluated. Conventionally used catalysts such as platinum-supported carbon particles can be used for the electrodes that do not use the magnetic particle-supported catalyst of Embodiment 1 or Embodiment 2.

  Next, the air electrode 42 or the fuel electrode 43 is formed using the obtained catalyst paint, and the following procedures generally include the following three methods (1) to (3). . Any of the evaluation means for the magnetic particle-supported catalyst of Embodiment 1 or Embodiment 2 may be used. However, when performing comparative evaluation, it is preferable to perform evaluation by unifying any one production method.

  (1) Using the obtained catalyst paint, a polytetrafluoroethylene (PTFE) film, a polyethylene terephthalate (PET) film, a polyimide film, a PTFE-coated polyimide film, a PTFE-coated silicon sheet, a PTFE-coated glass cloth, etc. An electrode film is formed on the releasable substrate by uniformly coating on the releasable substrate and drying. Next, the electrode film is peeled off and cut into a predetermined electrode size. A plurality of such electrode films are produced, and each is used as an air electrode and a fuel electrode. After that, the electrode membrane is bonded to both sides of the solid polymer electrolyte membrane by hot pressing or hot roll pressing, and then gas diffusion layers are arranged on both sides of the air electrode and the fuel electrode, and integrated by hot pressing. A membrane electrode assembly is produced.

  (2) The obtained catalyst paint is applied to the air electrode gas diffusion layer and the fuel electrode gas diffusion layer, respectively, and dried to form the air electrode and the fuel electrode. At this time, the coating method is a method such as spray coating or screen printing. Next, the solid polymer electrolyte membrane is sandwiched using the gas diffusion layer on which these electrode membranes are formed, and is integrated by hot pressing to produce a membrane electrode assembly.

  (3) The obtained catalyst paint is applied to both surfaces of the solid polymer electrolyte membrane by a method such as spray coating and dried to form an air electrode and a fuel electrode. Thereafter, gas diffusion layers are arranged on both sides of the air electrode and the fuel electrode and integrated by hot pressing to produce a membrane electrode assembly.

  In the membrane electrode assembly 40 obtained as described above, a current collector plate (not shown) is provided on each of the air electrode 42 side and the fuel electrode 43 side for electrical connection, and hydrogen is supplied to the fuel electrode 43. Can be operated as a fuel cell by supplying air (oxygen) to the air electrode 42, respectively.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited to a following example. The following Examples 1 to 3 relate to the magnetic particle-supported catalyst of Embodiment 1 described above, and the following Examples 4 and 5 relate to the magnetic particle-supported catalyst of Embodiment 2 described above.

Example 1
First, 4.5 g of chloroplatinic acid hexahydrate and 2.5 g of cobalt nitrate hexahydrate are dissolved in a mixed solution of 80 mL of water / 20 mL of ethanol, and 2.2 g of citric acid is added thereto, and platinum and cobalt are added. An aqueous solution containing citrate complex ions was prepared.

  Next, about 2 mL of the citrate complex ion aqueous solution was impregnated with 2 g of carbon black “Vulcan XC-72” (registered trademark, average particle diameter of 30 nm) manufactured by CABOT, which is conductive particles, and mixed in a mortar. . After drying this at 90 ° C., again impregnating with 2 mL of the above citric acid complex ion aqueous solution, mixing in a mortar, and then drying at 90 ° C., a total of 100 mL of the above aqueous citric acid complex ion solution was impregnated. Platinum and cobalt citrate complex ions were adsorbed on the surface of the carbon black. Then, it was dried for about 10 hours in an atmosphere having a relative humidity of 20% and a temperature of 90 ° C. to obtain carbon particles carrying a platinum compound and a cobalt compound.

  Subsequently, the carbon particles were heat-treated in argon gas at 550 ° C. for 4 hours. Thereafter, the temperature was lowered to 280 ° C. while flowing argon gas, the gas was switched from argon to hydrogen, reduction treatment was further performed for 2 hours, the temperature was lowered to room temperature while flowing hydrogen gas, and the hydrogen gas was replaced with air. Thereafter, by taking out into the air, platinum-cobalt alloy particle-supporting carbon particles in which platinum-cobalt alloy particles were precipitated as ferromagnetic particles on the carbon particles were obtained.

  When the platinum and cobalt contents in the platinum-cobalt alloy particle-supported carbon particles were measured by fluorescent X-ray analysis, they were 28.2% by weight and 8%, respectively, based on the total weight of the platinum-cobalt alloy particle-supported carbon particles. .4% by weight.

Further, when a magnetic needle was brought close to the platinum-cobalt alloy particle-carrying carbon particles, the magnetic needle was shaken, so that it was confirmed that the platinum-cobalt alloy particle-carrying carbon particles had magnetism. Subsequently, when the coercive force and saturation magnetization of the platinum-cobalt alloy particle-supporting carbon particles were measured with a vibrating sample magnetometer, they were 19.2 kA / m (240 oersted) and 11.3 A · m ² / kg ( 11.3 emu / g). Here, as a measurement condition using the vibrating sample magnetometer, the maximum applied magnetic field was set to 1274 kA / m (16 kilo-Oersted).

  Furthermore, the average particle diameter of the platinum-cobalt alloy particles deposited and supported on the carbon particles was measured using a high-resolution transmission electron microscope (TEM) and found to be 2.8 nm.

(Example 2)
In Example 1, platinum-cobalt alloy particle-supported carbon particles were produced in the same manner as in Example 1 except that the heat treatment conditions in argon gas were changed to 2 hours at 510 ° C. in argon gas.

When the platinum and cobalt contents in the platinum-cobalt alloy particle-supported carbon particles were measured in the same manner as in Example 1, they were 28.6% by weight based on the total weight of the platinum-cobalt alloy particle-supported carbon particles. And 8.7% by weight. The coercive force and saturation magnetization of the platinum-cobalt alloy particle-supported carbon particles measured after confirming that they had magnetism in the same manner as in Example 1 were 14.4 kA / m (180 oersted) and 8. It was 8 A · m ² / kg (8.8 emu / g). Furthermore, the average particle diameter of the platinum-cobalt alloy particles deposited and supported on the carbon particles measured in the same manner as in Example 1 was 2.4 nm.

(Example 3)
In place of the carbon particles carrying the platinum compound and the cobalt compound prepared in Example 1, a fuel cell catalyst “TEC36E52” (trade name) manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. was prepared. This fuel cell catalyst comprises platinum-cobalt-supported carbon particles, and the contents of platinum and cobalt are 46.8% by weight and 4.7% by weight, respectively.

  Next, the carbon particles were heat-treated at 550 ° C. for 4 hours in argon gas. Thereafter, the temperature was lowered to 280 ° C. while flowing argon gas, the gas was switched from argon to hydrogen, reduction treatment was further performed for 2 hours, the temperature was lowered to room temperature while flowing hydrogen gas, and the hydrogen gas was replaced with air. Thereafter, by taking out into the air, platinum-cobalt alloy particle-supporting carbon particles in which platinum-cobalt alloy particles were precipitated as ferromagnetic particles on the carbon particles were obtained.

The coercive force and saturation magnetization of the platinum-cobalt alloy particle-supported carbon particles measured after confirming that they had magnetism in the same manner as in Example 1 were 12.8 kA / m (160 oersted) and 10.6 A · s, respectively. m ^{2 /} kg (10.6 emu / g). Furthermore, the average particle diameter of the platinum-cobalt alloy particles deposited and supported on the carbon particles measured in the same manner as in Example 1 was 2.7 nm.

(Comparative Example 1)
The carbon particles carrying the platinum compound and the cobalt compound prepared in Example 1 were used as platinum-cobalt-carrying carbon particles without subsequent heat treatment and reduction treatment.

  When a magnetic needle was brought close to the platinum-cobalt-carrying carbon particles in the same manner as in Example 1, it was confirmed that the platinum-cobalt-carrying carbon particles had no magnetism because the magnetic needle did not shake at all.

(Comparative Example 2)
The fuel cell catalyst “TEC36E52” (trade name) manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. used in Example 3 was used as platinum-cobalt-supported carbon particles without subsequent heat treatment and reduction treatment.

  When a magnetic needle was brought close to the platinum-cobalt-carrying carbon particles in the same manner as in Example 1, it was confirmed that the platinum-cobalt-carrying carbon particles had no magnetism because the magnetic needle did not shake at all.

  Next, in order to evaluate the catalytic characteristics of the platinum-cobalt-supported carbon particles obtained in Examples 1 to 3 and Comparative Examples 1 and 2, membrane electrode assemblies (MEA) for fuel cells were prepared and used. The output characteristics of the fuel cell were investigated. In the following, an electrode film using the platinum-cobalt-supported carbon particles was used for the air electrode, and a standard electrode film shown below was used for the fuel electrode.

<Preparation of electrode film used for air electrode>
“Nafion” manufactured by Aldrich, which is a 5% by weight solution of polyperfluorosulfonic acid resin, was added 1 part by weight of the platinum-cobalt-supported carbon particles of Examples 1 to 3 and Comparative Examples 1 and 2. (Trade name, EW = 1000) 9.72 parts by weight and “Nafion” (trade name) 2.52 parts by weight manufactured by DuPont, which is a 20% by weight solution of polyperfluorosulfonic acid resin, and Each catalyst paint was prepared by adding the mixture to 1 part by weight of water and sufficiently stirring the mixed solution so as to disperse uniformly. Next, each catalyst paint was applied onto the PTFE film so that the platinum loading was 0.5 mg / cm ² and dried, and then peeled off to obtain a platinum-cobalt supported carbon particle electrode film.

<Preparation of standard electrode film for fuel electrode>
A catalyst coating was prepared in the same manner as described above using a platinum-supported carbon “10E50E” (trade name) manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., on which 50% by weight of platinum was supported, and then the amount of platinum supported was 0 on the PTFE film. After coating and drying so as to be ² mg / cm ² , it was peeled off to obtain a standard electrode film.

<Preparation of membrane electrode assembly>
As the solid polymer electrolyte membrane, a polyperfluorosulfonic acid resin membrane “Nafion 112” (trade name) manufactured by DuPont was cut into a predetermined size and used. The previously prepared platinum-cobalt-supported carbon particle electrode film and the standard electrode film are superposed on both sides of the solid polymer electrolyte membrane, and hot pressing is performed at a temperature of 160 ° C. and a pressure of 4.4 MPa, and these are joined. did. Next, a carbon nonwoven fabric “TGP-H-120” (trade name) manufactured by Toray Industries, Inc., which has been subjected to water repellency treatment in advance, is bonded to both surfaces of the solid polymer electrolyte membrane on which the electrode membrane is formed by hot pressing. Thus, a membrane electrode assembly was produced.

<Evaluation of output characteristics>
The IV characteristics were measured using the membrane electrode assembly obtained as described above. In the measurement, the measurement system including the membrane electrode assembly is held at 60 ° C., 60 ° C. humidified / heated hydrogen gas is supplied to the fuel electrode side, and 60 ° C. humidified / heated is supplied to the air electrode side. The measurement was performed with the supplied air supplied. From the IV characteristics, the maximum power density (mW / cm ² ) was measured as the output characteristics of the fuel cell. The results are shown in Table 1. In Table 1, the relative value when the maximum output density of Example 1 is 1.00 is shown as the output density ratio. Table 1 also shows the coercive force, saturation magnetization, platinum content, and cobalt content.

  As is clear from Table 1, the maximum output density of the fuel cells using the magnetic alloy particle-supporting carbon particles of Examples 1 to 3 is Comparative Examples 1 and 2 using platinum-cobalt-supporting carbon particles having no magnetism. It is clear that it is clearly higher than This is because the platinum-cobalt alloy particles supported on the magnetic alloy particle-supported carbon particles of Examples 1 to 3 are made ferromagnetic and have a specific coercive force and saturation magnetization, and therefore, by the magnetic field generated from the carbon particles, This is considered to be because oxygen having a high magnetic susceptibility was attracted to the vicinity of the carbon particles, and as a result, the catalytic reaction proceeded more efficiently.

  Next, the most common platinum particles (non-magnetic particles) were used as catalyst particles, and a magnetic particle-supported catalyst supporting the catalyst particles and magnetic particles was prepared.

Example 4
First, 4.4 g of chloroplatinic acid hexahydrate was dissolved in a mixed solution of 80 mL of water / 20 mL of ethanol, and 2.2 g of citric acid was added thereto to prepare an aqueous solution containing platinum citrate complex ions.

  Next, about 2 mL of the citrate complex ion aqueous solution was impregnated with 2 g of carbon black “Vulcan XC-72” (registered trademark, average particle diameter of 30 nm) manufactured by CABOT, which is conductive particles, and mixed in a mortar. . After drying this at 90 ° C., again impregnating with 2 mL of the above citric acid complex ion aqueous solution, mixing in a mortar, and then drying at 90 ° C., a total of 100 mL of the above aqueous citric acid complex ion solution was impregnated. Platinum citrate complex ions were adsorbed on the surface of the carbon black. Thereafter, it was dried for about 10 hours in an atmosphere having a relative humidity of 20% and a temperature of 90 ° C. to obtain carbon particles carrying a platinum compound.

  Subsequently, the carbon particles were heat-treated in hydrogen gas at 280 ° C. for 2 hours, cooled to room temperature in a state where hydrogen gas was flown, and after replacing the hydrogen gas with nitrogen gas, the platinum particles were taken out into the air. The platinum particle carrying | support carbon particle which carry | supported 46 weight% was obtained.

  Next, 2.56 g of iron (III) nitrate nonahydrate was dissolved in 20 mL of ethanol to prepare an ethanol solution containing iron ions. To this ethanol solution, 2 g of the previously obtained platinum particle-supporting carbon particles were added, and 1 g of citric acid was quickly added and dissolved, and then completely dried at 60 ° C. in air to obtain precursor particles. . The precursor particles were heat-treated in nitrogen gas at 500 ° C. for 2 hours to obtain platinum particles / iron oxide particle-supported carbon particles.

  Finally, the platinum particles / iron oxide particle-supporting carbon particles were magnetized by applying a magnetic field of 1.6 ESL.

As a result of measuring the powder X-ray diffraction spectrum of the above platinum particles / iron oxide particle-supported carbon particles, it is very broad at about 25 degrees with clear peaks of platinum (Pt) and magnetite (Fe ₃ O ₄ ). A peak derived from carbon was confirmed.
When the platinum and magnetite contents in the platinum particle / magnetite particle-supported carbon particles were measured by fluorescent X-ray analysis, the weight ratio of platinum particles to magnetite particles was 65:35, and the platinum particles and magnetite particles were supported. The amount was 57% by weight based on the total weight of platinum particles / magnetite particle-supporting carbon particles.

Further, when a magnetic needle was brought close to the platinum particle / magnetite particle-carrying carbon particle, the magnetic needle was shaken, so that it was confirmed that the platinum particle / magnetite particle-carrying carbon particle had magnetism. Subsequently, the coercive force and the saturation magnetization of the platinum particles / magnetite particle-supported carbon particles were measured with a vibrating sample magnetometer, and found to be 6.8 kA / m (85 Oersted) and 9.2 A · m ² / kg ( 9.2 emu / g). Here, as a measurement condition using the vibrating sample magnetometer, the maximum applied magnetic field was set to 1274 kA / m (16 kilo-Oersted).

  Furthermore, when the average particle diameter of platinum particles and magnetite particles deposited and supported on the carbon particles was measured using a high-resolution transmission electron microscope (TEM), the average particle diameter was 2.3 nm and 4.2 nm, respectively. there were. A TEM photograph of platinum particles / magnetite particle-supporting carbon particles of this example is shown in FIG.

(Example 5)
In the same manner as in Example 4, platinum particle-supporting carbon particles were obtained. Next, precursor particles were obtained in the same manner as in Example 4 except that the amount of iron nitrate nonahydrate used was 1.0 g using the platinum particle-supporting carbon particles. The precursor particles were heat-treated in air at 250 ° C. for 30 minutes to obtain platinum particles / iron oxide particle-supported carbon particles. Finally, the platinum particles / iron oxide particle-supporting carbon particles were magnetized by applying a magnetic field of 1.6 ESL.

As a result of measuring the powder X-ray diffraction spectrum of the platinum particles / iron oxide particles-supported carbon particles, about 25 degrees with clear peaks of platinum (Pt) and γ iron oxide (γ-Fe ₂ O ₃ ). A peak derived from very broad carbon was confirmed.

  When the content of platinum and γ iron oxide in the platinum particle / γ iron oxide particle-supported carbon particles was measured by fluorescent X-ray analysis, the weight ratio of platinum particles to γ iron oxide particles was 82:18. The supported amount of particles and γ iron oxide particles was 51% by weight with respect to the total weight of platinum particles / γ iron oxide particle-supported carbon particles.

The coercive force and saturation magnetization of the platinum particles / γ iron oxide particle-supported carbon particles measured after confirming that they had magnetism in the same manner as in Example 4 were 4.6 kA / m (58 oersted) and It was 5.4 A · m ² / kg (5.4 emu / g). Furthermore, the average particle sizes of platinum particles and γ iron oxide particles deposited and supported on the carbon particles measured in the same manner as in Example 1 were 2.3 nm and 3.1 nm, respectively.

(Comparative Example 3)
Platinum particles / magnetite particle-carrying carbon particles were obtained in the same manner as in Example 4 except that magnetization was not performed.

  When the magnetic needle was brought close to the platinum particle / magnetite particle-carrying carbon particle in the same manner as in Example 4, it was confirmed that the platinum particle / magnetite particle-carrying carbon particle had no magnetism. It was.

(Comparative Example 4)
Platinum particles / γ iron oxide particle-carrying carbon particles were obtained in the same manner as in Example 5 except that magnetization was not performed.

  In the same manner as in Example 4, when the magnetic needle was brought close to the platinum particle / γ iron oxide particle-supporting carbon particle, the magnetic needle did not shake at all, so the platinum particle / γ iron oxide particle-supporting carbon particle did not have magnetism. I was able to confirm.

(Comparative Example 5)
Precursor particles were produced in the same manner as in Example 4. Thereafter, using this precursor particle, instead of heat treatment at 500 ° C. for 2 hours in nitrogen gas, heat treatment was performed at 280 ° C. for 1 hour in air, and the sample was not further magnetized. Thus, carbon particles carrying platinum particles / iron oxide particles were obtained.

As a result of measuring the powder X-ray diffraction spectrum of the platinum particles / iron oxide particle-supported carbon particles, about platinum (Pt) and a non-magnetic hematite (α-Fe ₂ O ₃ ) were clearly observed. A peak derived from very broad carbon was observed around 25 degrees.

  When the platinum and hematite contents in the platinum particle / hematite particle-supported carbon particles were measured by fluorescent X-ray analysis, the weight ratio of platinum particles to hematite particles was 65:35, and the platinum particles and hematite particles were supported. The amount was 57% by weight based on the total weight of platinum particles / hematite particle-supporting carbon particles.

  Further, when the magnetic needle was brought close to the platinum particle / hematite particle-supporting carbon particle in the same manner as in Example 4, the magnetic needle did not shake at all. It could be confirmed. Furthermore, the average particle sizes of platinum particles and hematite particles deposited and supported on the carbon particles measured in the same manner as in Example 1 were 2.3 nm and 3.4 nm, respectively.

Next, in order to evaluate the catalyst characteristics of the platinum particles / oxide particle-supported carbon particles obtained in Examples 4 and 5 and Comparative Examples 3 to 5, the platinum support amount of the electrode film used for the air electrode was 0.5 mg / A membrane electrode assembly (MEA) for a fuel cell was prepared in the same manner as in Examples 1 to 3 and Comparative Examples 1 and 2 except that cm ² to 0.4 mg / cm ^2. Similarly, the IV characteristics were measured. From the IV characteristics, the maximum power density (mW / cm ² ) was measured as the output characteristics of the fuel cell. When measuring the IV characteristics, a small magnet of 4 cm × 2 cm × 1 cm was placed on both sides of the measurement cell in the measurement of Examples 4 and 5, and measurement was performed in a weak magnetic field. The results are shown in Table 2. In Table 2, the relative value when the maximum output density when the magnetic field is not present at the time of measurement of Example 4 is 1.00 is shown as the output density ratio. Table 2 also shows the coercivity, the saturation magnetization, and the presence or absence of magnetization.

  As is clear from Table 2, the maximum output density of the fuel cell using the platinum particles / oxide particle-supported carbon particles of Examples 4 and 5 is platinum particles / oxide particle-supported carbon particles having no magnetism. It can be seen that it is clearly higher than Comparative Examples 3-5. This is because the platinum particles / oxide particle-carrying carbon particles of Examples 4 and 5 have a specific coercive force and saturation magnetization, so that oxygen having a high magnetic susceptibility is generated in the vicinity of the carbon particles by a magnetic field generated from the carbon particles. This is considered to be because the catalytic reaction proceeded more efficiently as a result.

  In addition, it has been found that the effects of Examples 4 and 5 become more prominent as the amount of air flowing to the air electrode side is smaller. Even when the oxygen concentration is low, the effect of the catalyst can be effectively attracted by the less oxygen. It can be expressed. It can also be seen that if an external magnetic field is applied during measurement, a further output improvement effect can be obtained as compared with the case where there is no external magnetic field.

  On the other hand, magnetite particles and γ iron oxide particles are microscopically magnetized but not magnetized when they are not exposed to a magnetic field after the particles have been produced. Since it cannot be made as a whole, it has no magnetism, and it is considered that oxygen cannot be efficiently attracted. Therefore, as shown in Comparative Examples 3 and 4, even when exactly the same magnetic particles are used, an output difference of about 30% appears depending on the presence or absence of magnetization. Further, in Comparative Example 5 in which no magnetic particles were carried, the output value was further lowered.

  From the above, it can be seen that oxygen can be more efficiently induced in the vicinity of platinum particles having catalytic ability by a micro local magnetic field, and as a result, characteristics as a fuel cell can be improved.

  As described above, the magnetic particle-supported catalyst of the present invention can exhibit excellent catalytic ability as an electrode catalyst, and can provide a high-power fuel cell electrode using the catalyst.

It is a schematic diagram which shows the case where the membrane electrode assembly of a fuel cell is placed in a magnetic field. 2A is a schematic view showing a case where magnetic particles are included in the catalyst layer, and FIG. 2B is an enlarged view of the catalyst-carrying particles in FIG. 2A. It is a schematic diagram showing a magnetic particle-supported catalyst of the present invention in which catalyst particles and magnetic particles are supported on conductive particles. It is a schematic cross section which shows an example of the membrane electrode assembly which is an electrode for fuel cells of this invention. 6 is a diagram showing a TEM photograph of a magnetic particle-supported catalyst obtained in Example 4. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Membrane electrode assembly 11, 12 Magnet 13 Air electrode 14 Fuel electrode 15 Solid polymer electrolyte membrane 20 Catalyst layer 21 Catalyst supported particle 22 Magnetic particle 23 Catalyst particle 24 Conductive carrier 30 Magnetic particle supported catalyst 31 Conductive carrier 32 Magnetic particle 33 catalyst particles 40 membrane electrode assembly (MEA)
41 solid polymer electrolyte membrane 42 air electrode 43 fuel electrode 44 gas diffusion layer for air electrode 45 gas diffusion layer for fuel electrode

Claims (21)

A magnetic particle-supported catalyst comprising conductive particles and catalyst particles having magnetism supported on the conductive particles,
A magnetic particle-supported catalyst having a coercive force of 4.0 to 79.8 kA / m and a saturation magnetization of 1 to 20 A · m ² / kg.   The magnetic particle-supported catalyst according to claim 1, wherein the catalyst particles are magnetic alloy particles.   The magnetic particle-supported catalyst according to claim 2, wherein the magnetic alloy particles include platinum and cobalt as alloy components.   4. The magnetic particle-supported catalyst according to claim 3, wherein the content of platinum and cobalt in the magnetic alloy particles is 40 to 98 wt% and 2 to 60 wt%, respectively.   The magnetic particle-supported catalyst according to claim 3, wherein the magnetic alloy particles further include at least one element selected from the group consisting of nickel, iron, titanium, copper, manganese, aluminum, ruthenium, tungsten, and molybdenum as an alloy component.   The magnetic particle-supported catalyst according to claim 1, wherein the catalyst particles have a particle diameter of 1 to 10 nm.   2. The magnetic particle-supported catalyst according to claim 1, wherein the supported amount of the catalyst particles is 5 to 50 wt% with respect to the total weight of the magnetic particle-supported catalyst.   2. The magnetic particle-supported catalyst according to claim 1, wherein the catalyst particles are oxide particles containing at least one element selected from the group consisting of iron, cobalt, nickel, zinc, manganese, and copper. A method for producing a magnetic particle-supported catalyst according to any one of claims 2 to 7,
A step of supporting two or more kinds of magnetic metal components on conductive particles;
And heating the conductive particles carrying the magnetic metal component at 250 to 600 ° C. in a non-oxidizing atmosphere.   A magnetic particle-supported catalyst comprising conductive particles, catalyst particles supported on the conductive particles, and magnetic particles supported on the conductive particles. The magnetic particle-supported catalyst according to claim 10, wherein the magnetic particle-supported catalyst has a coercive force of 4.0 to 79.8 kA / m and a saturation magnetization of 1 to 20 A · m ² / kg.   The magnetic particle-supported catalyst according to claim 10, wherein the catalyst particles include platinum.   The magnetic particle-supported catalyst according to claim 10, wherein the magnetic particles are oxide particles containing at least one element selected from the group consisting of iron, cobalt, nickel, zinc, manganese and copper.   The magnetic particle-supported catalyst according to claim 13, wherein the oxide particles have a spinel structure or a perovskite structure.   11. The magnetic particle-supported catalyst according to claim 10, wherein a weight ratio of the catalyst particles to the magnetic particles is 40:60 to 90:10.   11. The magnetic particle-supported catalyst according to claim 10, wherein the supported amount of the catalyst particles and the magnetic particles is 10 to 70 wt% with respect to the total weight of the magnetic particle-supported catalyst.   11. The magnetic particle-supported catalyst according to claim 10, wherein each of the catalyst particles and the magnetic particles has a particle diameter of 1 to 10 nm. A method for producing a magnetic particle-supported catalyst according to any one of claims 10 to 17,
A step of supporting a catalytic metal component on conductive particles;
Heating the conductive particles carrying the catalytic metal component in a non-oxidizing atmosphere at 250 to 600 ° C. to carry the catalyst particles on the conductive particles;
A step of further supporting a magnetic precursor on the conductive particles supporting the catalyst particles;
And a step of heating the conductive particles supporting the catalyst particles and the magnetic precursor.   19. The method for producing a magnetic particle-supported catalyst according to claim 18, further comprising a step of magnetizing by applying a magnetic field after heating the conductive particles supporting the catalyst particles and the magnetic precursor.   A fuel cell electrode comprising the magnetic particle-supported catalyst according to any one of claims 1 to 8 and 10 to 17.   A fuel cell comprising the fuel cell electrode according to claim 20.

Images