JP2006297355A - Catalyst and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst which has excellent catalyst activity and durability by an inverse micelle method. <P>SOLUTION: The catalyst is formed by making the surface of a conductive carrier carry high dispersion compound noble metal particles having a composition of formula [Pt]<SB>a</SB>[Ir]<SB>b</SB>, wherein (a) is 0.7-0.99 atomic ratio of Pt, and (b) is 0.01-0.3 atomic ratio of Ir, and the sum of (a) and (b) is 1, and the average particle size is 3-8 nm. The compound noble metal particles are formed by adding reducing agents of water-soluble noble metal compounds into an inverse micelle solution formed by mixing an aqueous solution containing a water-soluble noble metal compound of platinum (Pt), and a water-soluble noble metal compound of iridium (Ir). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a catalyst and a method for producing the same. In particular, the present invention relates to an electrode catalyst having high catalytic activity and high power generation performance, in particular, an electrode catalyst for a fuel cell and a method for producing the same.

  In recent years, in response to social demands and trends against the background of energy and environmental issues, polymer electrolyte fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. . The solid polymer fuel cell is characterized by using an electrolyte layer made of a film-like solid polymer membrane.

  In such a polymer electrolyte fuel cell, the hydrogen gas of the fuel is converted into protons at the anode by the electrode catalyst, and oxygen is reduced at the cathode and combined with the protons that have passed through the electrolyte layer to become water. Thus, the polymer electrolyte fuel cell directly obtains electric energy from the reaction energy obtained by the chemical reaction.

  A fuel cell is required to exhibit high power generation performance over a long period of time, and is said to be 5000 hours for an automotive power source and 40,000 hours for a stationary power source. Therefore, the electrode catalyst is required to have high catalytic activity and durability. As the electrode catalyst, porous carbon particles carrying a catalyst metal such as a noble metal or base metal are used. For example, as a method for producing an electrode catalyst supported on carbon particles using a plurality of noble metals as catalyst metals, carbon particles are dispersed and mixed in an aqueous solution containing a plurality of noble metal compounds, and a reducing agent or a precipitating agent is added thereto. Thus, an adsorption method or the like in which precious metal particles are formed on carbon particles and then fired is generally used.

  However, in such a method, a plurality of noble metal particles formed by the insolubilizing agent are adsorbed randomly on other noble metal particles and on the surface of the support. For this reason, the composition of the composite noble metal particles formed by alloying by firing becomes non-uniform, and further, there is a problem that a large particle size is formed by sintering due to the addition of thermal energy. . Accordingly, there is a problem that the active surface area of the composite noble metal particles is reduced and the catalytic activity is lowered. Furthermore, when the adsorption method is used, composite noble metal particles are formed and supported in the fine pores of the carbon particles into which the electrolyte does not sufficiently permeate. Since the particles do not act as an active component of the electrode catalyst, there is a problem that the effective utilization rate of the supported composite noble metal particles is lowered.

  The reverse micelle method is used as a method for solving these problems. For example, an aqueous solution containing noble metal ions, or an aqueous solution containing noble metal ions and an aqueous solution containing transition metal ions are prepared as reverse micelles present as ultrafine droplets, and the noble metal ions and transition metal ions are precipitated or reduced. A method has been reported in which a noble metal or a noble metal and a transition metal are supported in a highly dispersed manner on the surface of a conductive carrier by insolubilization and dispersing and mixing the conductive carrier (carbon particles) therein (for example, Patent Document 1). .

According to such a reverse micelle method, a noble metal or the like can be supported in a highly dispersed manner on the carrier. Furthermore, since noble metals protected by reverse micelles are difficult to be supported in the pores of the carbon particles, they can be selectively and highly dispersed on the carbon particle surfaces.
JP-A-2005-34836

  However, although the method described in Patent Document 1 can produce composite noble metal particles having a uniform composition as compared to the adsorption method, a reducing agent is added to reverse micelles containing noble metal ions to make the noble metal ions noble metal particles. Since the process and the process of adding a precipitant to the reverse micelle solution containing transition metal ions to make the transition metal ions into transition metal particles are performed only once each, the composition is not sufficiently uniform and sufficient It was difficult to obtain a uniform solid solution, and the particle size distribution of the produced composite noble metal particles tended to be wide. In addition to the above problem, Patent Document 1 requires a high-temperature heat treatment (firing treatment) to form a solid solution (composite metal particles) of a noble metal and a transition metal. There has been a problem that the particle diameter increases and the specific activity decreases. Furthermore, when trying to use iridium (Ir), which is superior in corrosion resistance under strong acid compared to platinum, for the composite noble metal particles, the composition of the particles becomes non-uniform due to the firing treatment, so that Ir is improved. When the content is increased, there arises a problem that the power generation performance is lowered.

  Accordingly, the present invention has been made in view of the above circumstances, and aims to provide a catalyst having a higher catalytic activity, particularly an electrode catalyst, and has a particularly uniform composition and a narrow particle size distribution. By using / Ir-based composite noble metal particles, a catalyst exhibiting high catalytic activity and excellent stability (acid resistance) in an acidic electrolyte atmosphere even when the composition ratio of Ir is reduced, particularly an electrode catalyst The purpose is to provide.

  Another object of the present invention is to provide a catalyst having excellent durability, particularly an electrode catalyst, capable of suppressing a decrease in output even with respect to start / stop cycles and output fluctuation cycles that occur frequently over a long period of time (maintaining power generation performance). For the purpose.

  Another object of the present invention is to provide a method for producing a catalyst, particularly an electrode catalyst, which can form a uniform Pt—Ir solid solution without performing a heat treatment (firing treatment) at a high temperature.

  As a result of intensive studies to achieve the above object, the present inventor has obtained a Pt- having a uniform atomic composition (uniform solid solution) and a narrow particle size distribution of 3 to 8 nm by repeating the reverse micelle method a plurality of times. It has been found that Ir-based composite metal fine particles can be formed without being subjected to heat treatment (baking treatment) at a high temperature, and such Pt—Ir-based composite metal fine particles exhibit higher catalytic activity than before. In the above method, since the reverse micelle method is repeated a plurality of times, a catalyst having a uniform composition can be produced even if the composition ratio of Ir is reduced. Since a solid solution of Pt-Ir composite metal particles with a narrow diameter distribution can be firmly formed (alloyed) on the support, initial Pt elution due to fine Pt particles (1 nm or less) is suppressed even by potential cycling, and deterioration with time is suppressed. In addition, since the Pt—Ir based composite metal particles can be controlled to have a narrow particle size distribution of 3 to 8 nm, the surface energy of the particles themselves is lowered and stabilized. Therefore, such Pt—Ir composite metal particles are used. It has also been found that a fuel cell using an electrode catalyst can stably exhibit high power generation performance for a long period of time. Further, since the Pt—Ir composite metal particles use iridium (Ir) which is excellent in corrosion resistance under strong acidity, the electrode catalyst having such particles supported on a conductive carrier is used in an acidic electrolyte atmosphere. It has also been found that excellent stability (acid resistance) can be exhibited. Based on the above findings, the present invention has been completed.

That is, the above object is obtained by the formula: [Pt] _a [Ir] _b (where a represents the atomic ratio of Pt, 0.7 to 0.99, b represents the atomic ratio of Ir, and 0 Composite noble metal particles having a composition of .01 to 0.3 (the sum of a and b is 1) and having an average particle diameter of 3 to 8 nm is highly dispersed on the surface of the conductive carrier. The composite noble metal particles are supported by mixing an aqueous solution containing a water-soluble noble metal compound of platinum (Pt) and a water-soluble noble metal compound of iridium (Ir) in a solution in which a surfactant is dissolved in an organic solvent. This is achieved by a catalyst, particularly an electrode catalyst, which is formed by adding a reducing agent of the water-soluble noble metal compound to the reverse micelle solution thus formed.

Another object of the present invention is to provide a reverse micelle solution (A) containing a water-soluble noble metal compound of platinum (Pt) in a solution obtained by dissolving a surfactant in an organic solvent. After mixing with the reducing agent of the noble metal compound or the reverse micelle solution (A ′) containing the reducing agent, the reverse micelle solution (B) containing the water-soluble noble metal compound of iridium (Ir) is added, and further the water-soluble noble metal A step of mixing a compound reducing agent or a reverse micelle solution (B ′) containing a reducing agent; (b) containing a water-soluble noble metal compound of iridium (Ir) in a solution in which a surfactant is dissolved in an organic solvent. After the reverse micelle solution (B) is mixed with the reducing agent of the water-soluble noble metal compound or the reverse micelle solution (B ′) containing the reducing agent, the reverse micelle solution (A) containing the water-soluble noble metal compound of platinum (Pt) (A) ) And the water-soluble A step of mixing a metal compound reducing agent or a reverse micelle solution (A ′) containing a reducing agent; and (c) in a solution in which a surfactant is dissolved in an organic solvent, platinum (Pt) and iridium (Ir) At least two steps selected from the group consisting of a step of mixing a reverse micelle solution (C) containing a water-soluble noble metal compound with a reducing agent of the water-soluble noble metal compound or a reverse micelle solution (C ′) containing a reducing agent. The conductive support is dispersed in the mixed solution obtained in at least one step of (a) to (c) and the composite noble metal particles are supported on the support, and then the support on which the composite noble metal particles are supported. It is achieved by a method for producing a catalyst, characterized by having a step of forming a catalyst in which composite noble metal particles are supported on a carrier surface in a highly dispersed state by separating, washing and drying.

Another object of the present invention is to provide (a) a reverse micelle solution (A) containing a water-soluble noble metal compound of platinum (Pt) in a solution obtained by dissolving a surfactant in an organic solvent. After mixing the reducing agent of the noble metal compound or the reverse micelle solution (A ′) containing the reducing agent, the reverse micelle solution (B) containing the water-soluble noble metal compound of iridium (Ir) is added, and further the water-soluble noble metal compound A reducing agent or a reverse micelle solution (B ′) containing a reducing agent, and then dispersing a conductive carrier in the mixed solution to carry composite noble metal particles on the carrier;
(A) A reverse micelle solution (B) containing a water-soluble noble metal compound of iridium (Ir) in a solution obtained by dissolving a surfactant in an organic solvent contains a reducing agent or a reducing agent for the water-soluble noble metal compound. After mixing the reverse micelle solution (B ′), a reverse micelle solution (A) containing a water-soluble noble metal compound of platinum (Pt) is added, and a reverse micelle solution containing a reducing agent or a reducing agent for the water-soluble noble metal compound. (A ′) is then mixed, and then a conductive support is dispersed in the mixed solution, and composite noble metal particles are supported on the support; and (c) a solution in which a surfactant is dissolved in an organic solvent. Then, the reverse micelle solution (C ′) containing the water-soluble noble metal compound of platinum (Pt) and iridium (Ir) is mixed with the reverse micelle solution (C ′) containing the reducing agent or the reducing agent of the water-soluble noble metal compound. And then into the mixture By repeating the step selected from the group consisting of the step of dispersing the conductive support and supporting the composite noble metal particles on the support at least twice, separating, washing and drying the support supported by the composite noble metal particles It is also achieved by a method for producing an electrode, particularly an electrode catalyst, characterized in that it has a step of forming a catalyst in which composite noble metal particles are highly dispersed and supported on the surface of the support.

  The Pt—Ir alloy catalyst of the present invention exhibits high activity and excellent durability. Therefore, by using the highly active catalyst of the present invention particularly as a cathode electrode catalyst, reaction product water (product water of oxygen reduction reaction) or humidified water staying in the cathode electrode catalyst layer can be electrolyzed at a low potential. It can be degraded and reduced from around the active species. As a result, oxygen that has been electrolyzed under high potential in the active species can suppress the oxidative corrosion of the carbon support around the active species, and thus can significantly reduce the deformation of the electrode structure caused by the carbon corrosion, A decrease in diffusibility and a decrease in drainage of generated water can be suppressed, and an increase in concentration overvoltage can be reduced.

  Further, according to the method of the present invention, composite noble metal particles containing platinum and iridium having a uniform composition can be formed without being subjected to heat treatment at high temperature (firing treatment), so that fine Pt particles (1 nm or less) The initial Pt elution due to is suppressed, deterioration with time can be suppressed, and the durability is excellent. In addition to the above advantages, according to the method of the present invention, the average particle diameter of the Pt—Ir-based composite noble metal particles can be controlled in a narrow range of 3 to 8 nm, so that the surface energy of the particles themselves is reduced and stabilized. Stable and high power generation performance can be achieved for a long time.

The first of the present invention is the formula: [Pt] _a [Ir] _b (wherein a represents an atomic ratio of Pt, 0.7 to 0.99, b represents an atomic ratio of Ir, Composite noble metal particles having a composition of 0.01 to 0.3 (the sum of a and b is 1) and having an average particle diameter of 3 to 8 nm are formed on the surface of the conductive support. The composite noble metal particles, which are dispersed and supported, are mixed with an aqueous solution containing a water-soluble noble metal compound of platinum (Pt) and a water-soluble noble metal compound of iridium (Ir) in a solution in which a surfactant is dissolved in an organic solvent. An electrode, particularly an electrocatalyst, which is formed by adding a reducing agent of the water-soluble noble metal compound to the reverse micelle solution thus formed. Since the Pt—Ir based composite metal fine particles according to the present invention have a uniform composition and a narrow particle size distribution of 3 to 8 nm, the surface energy of the particles themselves is lowered and stabilized. For this reason, the electrocatalyst using the particles can suppress the elution of fine Pt particles of 1 nm or less even after the potential cycle, so that the deterioration of the catalytic activity due to the elution of Pt over time can be suppressed, and the power generation performance is significantly reduced. Can be prevented / suppressed. Furthermore, since the composite noble metal particles based on Pt—Ir contain iridium (Ir), which has excellent corrosion resistance under strong acid, in a homogeneous composition, excellent stability in an acidic electrolyte atmosphere even at a low Ir content. (Acid resistance) can be demonstrated. Therefore, a fuel cell using an electrode catalyst containing such Pt—Ir-based composite metal fine particles can stably exhibit high power generation performance for a long period of time and has excellent durability.

  In the present specification, the “reverse micelle solution” includes micelles formed by assembling the amphiphile by mixing an amphiphile such as a surfactant molecule in an organic solvent, and A solution containing a noble metal ion aqueous solution or the like in a micelle. In the organic solvent phase, the hydrophobic group is oriented to the outside, that is, the organic solvent phase side, the hydrophilic group is oriented to the inside, and the orientation of the hydrophobic group and the hydrophilic group is opposite to that in the aqueous solvent phase. Use reverse micelle solution. FIG. 1 schematically shows the reverse micelle solution. Such a reverse micelle solution can be prepared by adding an aqueous solution to a solution obtained by dissolving a surfactant in an organic solvent and stirring the solution. The portion where the hydrophilic groups are gathered has the ability to retain polar molecules such as water. The aqueous solution becomes very small water droplets having a diameter of several nanometers to several tens of nanometers and is stably dispersed in the organic solvent. However, the size of the microstructure of the reverse micelle is controlled by the molar ratio of the injected water and the surfactant. be able to.

  In the present specification, “composite noble metal particles” means composite particles of platinum particles, iridium particles, and if necessary, promoter metal particles, and platinum particles, iridium particles, and if necessary, promoter metal. Although it includes both alloy particles and particles, an alloyed form is preferred from the viewpoint of catalytic activity.

The composite noble metal particles according to the present invention contain platinum (Pt) and iridium (Ir) as essential metal atoms, that is, have a composition of the formula: [Pt] _a [Ir] _b . With such a composition, high catalytic activity and excellent durability (particularly corrosion resistance under strong acidity) are achieved. In the above formula, the sum of a and b is 1. Moreover, a represents the atomic ratio of Pt, which is 0.7 to 0.99, and b represents the atomic ratio of Ir, which is 0.01 to 0.3. At this time, if a is less than 0.7 or b is more than 0.3, there is Ir which does not dissolve in Pt, so that the catalytic activity of the composite noble metal particles may be reduced. When the value exceeds 0.99 or b is less than 0.01, the content of Ir is too small, and the durability of the composite noble metal particles (particularly, corrosion resistance under strong acidity) may be reduced. a is preferably 0.8 to 0.95, and b is preferably 0.05 to 0.2.

  The composite noble metal particles according to the present invention must have an average particle diameter of 3 to 8 nm. Thus, since the composite noble metal particles according to the present invention have a small particle size and a narrow particle size distribution, they can be highly dispersed on the surface of the conductive support, thereby increasing the active surface area effective for the electrode reaction. The performance when used as an electrode catalyst for a battery can be significantly improved. At this time, if the average particle diameter of the composite noble metal particles is less than 3 nm, the elution of small Pt particles occurs due to the potential cycle, and the catalytic activity tends to decrease with time. There is a possibility that the active surface area effective for the electrode reaction when dispersed on the surface of the carrier is reduced, resulting in a decrease in activity. The average particle diameter of the composite noble metal particles is preferably 4 to 6 nm.

  In the present invention, the average particle diameter of the catalyst metal such as platinum or iridium is the average of the crystallite diameter determined from the half-value width of the diffraction peak of the metal fine particles in X-ray diffraction or the average of the metal fine particles examined by a transmission electron microscope. The average particle size can be calculated.

  In the present invention, the water-soluble noble metal compound of iridium is not particularly limited, and examples thereof include halogens such as iridium nitrate, dinitrodiammine salt, sulfate, ammonium salt, amine, carbonate, bicarbonate, bromide, and chloride. Preferred examples include compounds capable of forming iridium ions in an aqueous solution, such as inorganic salts such as chloride, nitrite and oxalic acid, carboxylates such as formate and hydroxides, alkoxides and oxides. Of these, iridium halides, particularly iridium chloride, nitrates, and dinitrodiammine salts are preferably used, and iridium chloride is particularly preferred. This is because by using iridium chloride, iridium particles, which have been difficult in the past, can be deposited more easily. In the present invention, the iridium water-soluble noble metal compound may be a single compound or a mixture of two or more.

  The water-soluble noble metal compound of platinum is not particularly limited. For example, platinum nitrate, dinitrodiammine salt, sulfate, ammonium salt, amine, carbonate, bicarbonate, bromide, chloride and other halides, Preferable examples include inorganic salts such as nitrite and oxalic acid, carboxylates such as formate and hydroxides, alkoxides, oxides, and the like compounds capable of forming platinum ions in an aqueous solution. Of these, platinum halides, particularly platinum chlorides, nitrates, and dinitrodiammine salts are preferably used, and platinum chloride is particularly preferred. This is because platinum particles can be easily deposited by using platinum chloride. In the present invention, the water-soluble noble metal compound of platinum may be a single compound or a mixture of two or more.

In the present invention, the composite noble metal particles may contain a promoter metal in addition to the essential metal atoms of Pt and Ir. In this case, the promoter metal can be appropriately selected according to the desired properties, and is not particularly limited, but preferred examples include transition metals such as chromium, manganese, iron, cobalt and nickel, and base metals such as palladium and rhodium. This is because the catalytic activity and durability of the composite noble metal particles are further improved by using a promoter metal such as a transition metal and a base metal. In particular, when a transition metal is used, mass activity (activity per unit weight of metal) can be improved, which is advantageous. That is, the composite noble metal particles according to the present invention may have a composition of the formula: [Pt] _a [Ir] _b [X] _c . The sum of a, b and c is 1. X is at least one selected from the group consisting of Cr, Mn, Fe, Co, Ni, Pd, and Rh, and a represents an atomic ratio of Pt, preferably 0.7 to 0.99, preferably 0.8 to 0.95. B represents the atomic ratio of Ir and is 0.01 to 0.29, preferably 0.05 to 0.2. c represents the total atomic ratio of X, preferably 0.01 to 0.29, more preferably 0.05 to 0.2. In the above formula, considering catalyst performance and durability, (b + c) / (a + b + c) is in the range of 0.01 to 0.3. At this time, a + b + c = 1. (B + c) / (a + b + c) is preferably 0.05 to 0.2.

  The promoter metal (“X” in the formula) may be used alone or in combination of two or more, so that the resulting composite noble metal particles have desired characteristics. May be appropriately selected and used. Moreover, it does not specifically limit as a supply source of a promoter metal ion, What is necessary is just a compound containing an above-described transition metal ion or base metal ion, For example, a sulfate, ammonium salt, a halogen compound etc. are mentioned.

  The organic solvent used to form the reverse micelle solution is not particularly limited and can be appropriately selected depending on the kind of the precious metal Pt or Ir to be mixed or the promoter metal, and various substances can be used. Examples include cyclohexane, methylcyclohexane, cycloheptane, heptanol, octanol, dodecyl alcohol, cetyl alcohol, isooctane, n-heptane, n-hexane, n-decane, benzene, toluene, xylene, and preferably cyclohexane. These organic solvents can be used alone or in combination of two or more. Moreover, you may add alcohol etc. in order to adjust the magnitude | size of the water droplet in a reverse micelle solution. Examples of the alcohol that can be used in this case include methanol, ethanol, and the like, and these alcohols may be used alone or in the form of a mixture of two or more. Further, the organic solvent is prepared in the same manner as in the preparation of a reverse micelle solution including preparation of a reverse micelle solution containing iridium ions, preparation of a reverse micelle solution containing platinum ions, and preparation of a reverse micelle solution containing promoter metal ions. Further, when a reducing agent for iridium ions, platinum ions, and promoter metal ions is supplied as a reverse micelle solution, it can also be used for preparing these solutions. At this time, the organic solvent used for any reverse micelle solution and the organic solvent used for the other reverse micelle solution may be the same or different.

  The surfactant used for forming the reverse micelle solution is not particularly limited, and the same surfactants that are generally used for forming the reverse micelle solution can be used. Specifically, polyoxyethylene nonyl phenyl ether, magnesium laurate, zinc caprate, zinc myristate, sodium phenyl stearate, aluminum dicaprylate, tetraisoamyl ammonium thiocyanate, n-octadecyl Tri-n-butylammonium formate, n-amyltri-n-butylammonium iodide, sodium bis (2-ethylhexyl) succinate, sodium dinonylnaphthalene sulfonate, calcium cetyl sulfate, dodecylamine oleate, dodecylamine Propionate, cetyltrimethylammonium bromide, stearyltrimethylammonium bromide, cetyltrimethylammonium chloride, stearyltrimethylammonium chloride, dodecylto Methylammonium bromide, octadecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, didodecyldimethylammonium bromide, ditetradecyldimethylammonium bromide, didodecyldimethylammonium chloride, ditetradecyldimethylammonium chloride, (2-octyloxy -1-octyloxymethyl) polyoxyethylene ethyl ether and the like. Of these, polyoxyethylene nonylphenyl ether is preferably used as the surfactant. These surfactants can be used alone or in combination of two or more. In addition, the surfactant is used in the same manner as in the preparation of a reverse micelle solution including preparation of a reverse micelle solution containing iridium ions, preparation of a reverse micelle solution containing platinum ions, and preparation of a reverse micelle solution containing promoter metal ions. In addition, when a reducing agent for iridium ions, platinum ions, and promoter metal ions is supplied as a reverse micelle solution, it can also be used for preparing these solutions. In this case, the surfactant used for any reverse micelle solution and the surfactant used for the other reverse micelle solution may be the same or different.

  At this time, the addition amount of the surfactant is not particularly limited as long as it is an amount capable of satisfactorily forming a reverse micelle of a water-soluble noble metal compound such as platinum or iridium, but is preferably 10 to 300 with respect to 100 parts by mass of the organic solvent. Part by mass, more preferably 10 to 150 parts by mass. At this time, if the amount of the surfactant is less than 10 parts by mass, it may be difficult to form reverse micelles. On the other hand, if the amount exceeds 300 parts by mass, rod-like micelles are formed, and the particle size of the composite noble metal particles is reduced. There is a possibility that it cannot be controlled to a specific size of 3 to 8 nm as in the present invention.

The conductive carrier that can be used in the present invention is not particularly limited, but the same conductive carrier as that generally used for catalysts such as electrode catalysts, particularly electrode catalysts for fuel cells can be used. Carbon and oxide nanotubes are preferably used. The conductive carbon is not particularly limited as long as it has sufficient electronic conductivity as a current collector and a sufficient specific surface area for highly dispersing and supporting composite noble metal particles. As the specific surface area of conductive carbon, specifically, ^{80 m} 2 / g or more, 200 meters ² / g or more, preferably one having a BET specific surface area of 250~1,600m ² / g. As such conductive carbon, more specifically, acetylene black, Vulcan, Ketjen black, black pearl, graphitized acetylene black, graphitized Vulcan, graphitized Ketjen black, graphitized carbon, graphitized black pearl, Examples thereof include those containing as a main component at least one selected from carbon nanotubes, carbon nanofibers, carbon nanohorns, and carbon fibrils. Since the conductive carbon is highly dispersed in an organic solvent, it is advantageous in that micelles can be easily attached to the surface of carbon particles in a reverse micelle solution. In particular, BET specific surface area of 700~1,400m ² / g of Ketjen black, BET specific surface area of 200~600m ² / BET specific surface area graphitized part in Balkan and hot g is 100~600m ² / g Graphitized (graphitized) ketjen black, conductive carbon particle carrier called graphitized (graphitized) Vulcan or graphitized (graphitized) furnace black having a BET specific surface area of 80 to 200 m ² / g is also preferably used it can. Further, the shape of the conductive carrier is not particularly limited, and not only a general spherical shape, a substantially spherical shape, and an elliptical shape, but also a rectangular parallelepiped shape, a plate shape, a linear shape such as a fiber, a branched branch shape, and the like can be used. However, spherical and substantially spherical are preferable. The size in the case where the conductive support is spherical is not particularly limited, and the same size as that of a known support can be used. However, the composite noble metal particles are present uniformly, and the surface of the support supporting the particles and the solid surface In order to bring the contact state with the molecular electrolyte into a suitable state, the average particle diameter of the carrier is preferably 30 to 100 nm in the size of the primary particles. 1 μm particles may be formed. The conductive carbon particles are washed with an alkaline solution such as sodium hydroxide, potassium hydroxide, or calcium hydroxide solution to remove the deposits on the surface of the carrier to remove oils adhering to the manufacturing process and impurities. May be.

  In the present invention, it is desired that the conductive carbon has a large specific surface area, and generally, carbon having many pores is used. In particular, in an electrode catalyst for a fuel cell or the like, it is not possible to contribute to the electrode reaction. Therefore, it is desired to reduce the amount of catalytic metal supported in the pores as much as possible. On the other hand, in this invention, the size of a reverse micelle can be adjusted with the kind and addition amount of a solvent and surfactant to be used, and a micelle can adhere uniformly only to the surface of the said electroconductive support | carrier. Furthermore, in the conventional adsorption methods, aggregation of platinum and platinum alloys has occurred, and it has been difficult to control the particle size and particle distribution. The composite noble metal particles having a small particle size and a small particle size distribution can be highly dispersed and supported on the surface of the conductive support.

  According to the present invention, the composite noble metal particles can be highly dispersed only on the surface of the carrier, and the effective utilization rate of the composite noble metal particles is improved. According to the present invention, the ratio of the composite noble metal particles supported on the support surface to the composite noble metal particles supported in the support pores (composite noble metal particles supported on the support surface: composite supported in the support pores). (Mass ratio of the noble metal particles) can be 1: 1 to 9: 1, and the amount of the composite noble metal particles supported on the surface can be increased as compared with the conventional 1: 9 to 4: 6 such as an adsorption method. Is possible.

  In the catalyst of the present invention, the amount of the composite noble metal particles supported on the conductive carbon is 5 to 70% by mass, more preferably 10 to 50% by mass, as the total amount of platinum and iridium. If the supported amount of the composite noble metal particles is less than 5% by mass relative to the catalyst, there is a possibility that sufficient activity and durability cannot be obtained. Moreover, when it exceeds 70 mass%, it is difficult to disperse | distribute uniformly and there exists a possibility that the high dispersion | distribution support of a composite noble metal particle may become difficult. Further, when the promoter metal is further included, the total amount of platinum, iridium, and promoter metal may be in the above range.

  The catalyst of the present invention can be used for any application as described in detail below, but is preferably used for an electrode catalyst, particularly for an electrode catalyst for a fuel cell. When used for fuel cells, the electrocatalyst may be used on the cathode side or anode side, or on both the cathode side and anode side, but is preferably used on the cathode side. This is because reaction product water (oxygen reduction reaction product water) or humidification that stays in the cathode electrode catalyst layer by using the highly active Pt—Ir composite metal particle electrode catalyst according to the present invention as the cathode electrode catalyst. This is because water can be electrolyzed at a low potential and reduced from around the active species. As a result, the oxidative corrosion of the carbon support around the active species due to oxygen that has been electrolyzed at a high potential can be suppressed, and the deformation of the electrode structure caused by the carbon corrosion can be significantly reduced. It is possible to suppress the decrease and the drainage of the generated water and reduce the increase in concentration overvoltage.

  In the conventional reverse micelle method, in order to obtain a catalyst on which iridium and platinum are supported, an insolubilizing agent such as a reducing agent and a precipitant is added to a reverse micelle solution containing an aqueous solution containing platinum ions and iridium ions. Colloidal platinum particles and iridium particles are deposited, supported on a conductive carrier, and then fired. However, in the conventional method, a large amount of platinum particles may be precipitated, and iridium particles may hardly be precipitated. Even if an insolubilizing agent is further added to precipitate the iridium particles, the iridium particles are not precipitated, and the activity of the resulting catalyst may be lowered. The reason for this is that the platinum particles previously deposited by the excessively added insolubilizer are combined with other platinum particles to form a linearly connected state like a pearl necklace. Conceivable. When the platinum particles are connected, the effective reaction area is reduced, which leads to a decrease in catalytic activity. Therefore, in the past, it was difficult to deposit platinum and iridium with a uniform composition in the micelle, the ratio of platinum and iridium supported on the support was not stable, and the composition could not be made uniform. . In addition to the above problem, there was a problem that the particle size of the solid solution was increased and the specific activity was lowered by the firing treatment necessary for forming the composite metal particles.

  In view of this, the present inventors examined various preparation conditions. As a result, when platinum and iridium were used as catalytic metals, when depositing platinum ions and iridium ions in reverse micelles, (a) A step of depositing iridium particles by adding iridium ions in the reverse micelles after depositing platinum particles in the reverse micelles comprising; (b) after depositing iridium particles in the reverse micelles containing iridium ions; Of the three steps of adding platinum ions into the reverse micelles to deposit platinum particles; or (c) depositing platinum particles and iridium particles in reverse micelles containing platinum ions and iridium ions, By repeating at least two steps, reverse micelles containing iridium particles and platinum particles in a uniform composition are obtained, and the resulting composite micelles are obtained. The noble metal particles have a uniform composition and an average particle size of 3 to 8 nm and a very narrow particle size distribution, and the composite noble metal particles can be stably and highly dispersedly supported on the conductive support without firing treatment. Further, it has been found that alloying is possible. Alternatively, (a) after depositing platinum particles in reverse micelles containing platinum ions, iridium ions are added to the reverse micelles to precipitate iridium particles, and the resulting composite noble metal particles are supported on a conductive carrier. (B) After iridium particles are precipitated in reverse micelles containing iridium ions, platinum ions are added to the reverse micelles to precipitate platinum particles, and the resulting composite noble metal particles are used as a conductive carrier. A step of supporting; or (c) depositing platinum particles and iridium particles in a reverse micelle containing platinum ions and iridium ions, and further supporting the obtained composite noble metal particles on a conductive carrier. By repeating at least two steps, a reverse micelle containing iridium particles and platinum particles with a uniform composition is obtained, and the resulting composite noble metal The particles have a uniform composition and a very narrow particle size distribution with an average particle diameter of 3 to 8 nm, and the composite noble metal particles can be stably and highly dispersedly supported on the conductive support without any firing treatment. It has also been found that alloying is possible. According to such a method, the composite noble metal particles having a stable and uniform composition ratio of platinum and iridium and an average particle diameter of 3 to 8 nm are firmly and stably dispersed on the conductive support. Supported. Further, according to the above two methods, a catalyst having a uniform Ir composition can be produced even if the composition ratio of Ir is reduced. Therefore, according to the above two methods, a catalyst excellent in catalytic activity and durability, particularly an electrode catalyst can be produced.

Accordingly, the second aspect of the present invention is that (a) a reverse micelle solution (A) containing a water-soluble noble metal compound of platinum (Pt) in a solution in which a surfactant is dissolved in an organic solvent is treated with the water-soluble noble metal. After mixing with the compound reducing agent or the reverse micelle solution (A ′) containing the reducing agent, the reverse micelle solution (B) containing a water-soluble noble metal compound of iridium (Ir) is added, and further the water-soluble noble metal compound Mixing the reducing agent or reverse micelle solution (B ′) containing the reducing agent;
(B) A reverse micelle solution (B) containing a water-soluble noble metal compound of iridium (Ir) in a solution in which a surfactant is dissolved in an organic solvent contains the water-soluble noble metal compound reducing agent or reducing agent. After mixing the reverse micelle solution (B ′), a reverse micelle solution (A) containing a water-soluble noble metal compound of platinum (Pt) is added, and a reverse micelle solution containing a reducing agent or a reducing agent for the water-soluble noble metal compound. A step of mixing (A ′); and (c) a reverse micelle solution (C) containing a water-soluble noble metal compound of platinum (Pt) and iridium (Ir) in a solution in which a surfactant is dissolved in an organic solvent. And a step selected from the group consisting of the step of mixing the reducing agent of the water-soluble noble metal compound or the reverse micelle solution (C ′) containing the reducing agent, and at least one of the steps (a) to (c). Obtained in one step The conductive noble metal particles are dispersed in the resulting mixed liquid and the composite noble metal particles are supported on the carrier, and then the carrier supported by the composite noble metal particles is separated, washed, and dried, so that the composite noble metal particles can be The present invention relates to a method for producing a catalyst, comprising a step of forming a dispersion-supported catalyst.

The third aspect of the present invention is (a) a reverse micelle solution (A) containing a water-soluble noble metal compound of platinum (Pt) in a solution in which a surfactant is dissolved in an organic solvent. After mixing the reducing agent or the reverse micelle solution (A ′) containing the reducing agent, the reverse micelle solution (B) containing the water-soluble noble metal compound of iridium (Ir) is added, and the reducing agent of the water-soluble noble metal compound or A step of mixing a reverse micelle solution (B ′) containing a reducing agent, and then dispersing a conductive support in the mixed solution to support composite noble metal particles on the support;
(A) A reverse micelle solution (B) containing a water-soluble noble metal compound of iridium (Ir) in a solution obtained by dissolving a surfactant in an organic solvent contains a reducing agent or a reducing agent for the water-soluble noble metal compound. After mixing the reverse micelle solution (B ′), a reverse micelle solution (A) containing a water-soluble noble metal compound of platinum (Pt) is added, and a reverse micelle solution containing a reducing agent or a reducing agent for the water-soluble noble metal compound. (A ′) is then mixed, and then a conductive support is dispersed in the mixed solution, and composite noble metal particles are supported on the support; and (c) a solution in which a surfactant is dissolved in an organic solvent. Then, the reverse micelle solution (C ′) containing the water-soluble noble metal compound of platinum (Pt) and iridium (Ir) is mixed with the reverse micelle solution (C ′) containing the reducing agent or the reducing agent of the water-soluble noble metal compound. And then into the mixture By repeating the step selected from the group consisting of the step of dispersing the conductive support and supporting the composite noble metal particles on the support at least twice, separating, washing and drying the support supported by the composite noble metal particles The present invention relates to a method for producing a catalyst, particularly an electrode catalyst, comprising a step of forming a catalyst in which composite noble metal particles are supported in a highly dispersed state on a support surface.

  The process according to the present invention will be described in detail particularly with respect to the process (b). First, when a reducing agent of iridium ions is added to a reverse micelle solution containing iridium ions inside the micelles, a reduction reaction proceeds in the micelles to form a stable complex, which is matured by about 0.5 to 5 nm. Of fine colloidal stable iridium particles. Next, when this is mixed with a reverse micelle solution containing platinum ions, the micelles are combined to form reverse micelles containing iridium particles and platinum ions. Furthermore, by adding a reducing agent of platinum ions, a stable complex containing platinum ions is formed by a reduction reaction in the micelle. By aging this, a fine complex of about 0.5 to 5 nm is formed on the iridium particles. Colloidal stable platinum particles can be deposited.

  Hereinafter, the second and third methods of the present invention will be described in detail. The overlapping portions of platinum (Pt) and iridium (Ir), such as water-soluble noble metal compounds and conductive carriers, will be described above unless otherwise specified. Therefore, the description is omitted here.

  In the second of the present invention, it is essential to repeat the steps (a) to (c) at least twice, and in the third of the present invention, it is essential to repeat the steps (a) to (c) at least twice. And By repeating the platinum and iridium precipitation steps at least twice as described above, heat treatment (for example, firing at 600 ° C. to 1100 ° C. in an inert gas atmosphere) required for stable support on the carrier and alloying is conventionally performed. ), It is possible to stably support / alloy composite noble metal particles (Pt—Ir alloy particles) having a uniform composition (uniform solid solution) and a narrow particle size distribution on a carbon support. . In general, the Ir alloy is superior in corrosion resistance under strong acidity to the Pt alloy, but has the disadvantage that the power generation performance is very low. According to the method of the present invention, the composite noble metal particles in which Ir is present uniformly Therefore, the composition ratio of Ir can be reduced, and the electrode catalyst using such particles exhibits excellent stability (acid resistance) in an acidic electrolyte atmosphere, and at the same time, Higher power generation performance can be exhibited.

  In the second method of the present invention, the conductive carrier is dispersed in the mixed solution obtained in at least two steps (a) to (c) and (d) at least one step of (a) to (c). Then, after the composite noble metal particles are supported on the carrier, the carrier on which the composite noble metal particles are supported is separated, washed, and dried, thereby forming a catalyst in which the composite noble metal particles are highly supported on the surface of the carrier. However, the step (d) for supporting the composite noble metal particles may be performed after all the steps (a) to (c) are performed, or the steps (a) to (c). However, it is preferably performed between the steps (a) to (c). According to the present invention, when a reducing agent is placed in a reverse micelle solution containing noble metal ions (or transition metal element ions), noble metal particles are formed in the reverse micelles, and this state is repeated several times. When the particles are stirred and held for a long time, the reverse micelles containing the noble metal particles collide with each other, and the noble metal particles may gradually aggregate. On the other hand, according to the latter method, the conductive support is dispersed in the reverse micelles on the way, so that it can be highly dispersed and supported on the support before aggregation of the noble metal particles occurs.

  In the second of the present invention, the steps (a) to (c) are preferably repeated 2 to 10 times, more preferably 2 to 5 times, and most preferably 2 times. In particular, when repeating twice, the order of (a) → (a), (a) → (c), (b) → (b), (b) → (c), (c) → (c) Although it is preferable, the steps (a), (b), and (c) can be arbitrarily combined. As described above, the supporting step (d) may be performed after the steps (a) to (c) are repeated two times, but is preferably performed between the two steps. Particularly preferred.

  In the third aspect of the present invention, the steps (a) to (c) are preferably repeated 2 to 10 times, more preferably 2 to 5 times, and most preferably 2 times. In particular, when repeating twice, (a) → (a), (a) → (c), (b) → (b), (b) → (c), (c) → (c) Although preferred, the steps (a), (b), and (c) can be arbitrarily combined.

  In the present invention, in the reverse micelle solution (A) containing the water-soluble noble metal compound of platinum, the amount of platinum water-soluble noble metal compound in the reverse micelle solution (A) is such that platinum fine particles are efficiently formed in the micelle. The amount may vary as appropriate depending on the amount of the water-soluble noble metal compound of iridium and the amount of the water-soluble noble metal compound of the promoter metal. Preferably, the amount is such that the concentration of platinum ions is 0.01 to 50% by mass, more preferably about 0.1 to 30% by mass in terms of metal in the reverse micelle solution (A).

  In the present invention, the reverse micelle solution (A) is mixed with a reducing agent of a water-soluble noble metal compound of platinum or a reverse micelle solution (A ′) containing the reducing agent, so that platinum particles are colloidally formed in the micelle. scatter. The reducing agent that can be used in this case is not particularly limited, and a known reducing agent can be used. Specific examples include hydrogen, hydrazine, sodium borohydride, sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, sodium borohydride, formaldehyde, methanol, ethanol, ethylene, carbon monoxide and the like. . What can be prepared as an aqueous solution of hydrazine or the like may be added directly to the reverse micelle solution as an aqueous solution having a concentration of 0.1 to 40% by mass, but a reverse micelle solution containing a reducing agent is prepared using the solution. The reverse micelle solution (A ′) may be added to the reverse micelle solution (A). The aqueous solution having a concentration of 0.1 to 40% by mass can be dispersed in the micelle in a colloidal form even when platinum ions become platinum particles in the micelle. Note that a powdered substance such as sodium borohydride can be supplied as it is. A gaseous substance at room temperature such as hydrogen can be supplied by bubbling. Of these, hydrazine (including an aqueous solution), sodium boride, and hydrogen are preferable, and sodium boride and hydrogen are particularly preferable. This is because stable iridium particles can be precipitated, and the composition in the micelle can be easily adjusted. The reduction with sodium boride is a reduction with hydrogen generated by the reaction with water, so that any reduction with hydrogen can be used effectively in the present invention. In addition, if the reduction rate of the platinum particles is too high, the precipitated platinum particles may be aggregated. However, by using a reducing agent as described above, platinum is easily precipitated, and the platinum particles can be obtained at an appropriate reduction rate. Aggregation can be prevented.

  The amount of addition of the reducing agent for the water-soluble noble metal compound of platinum is not particularly limited as long as platinum particles can be sufficiently formed from platinum ions, but it is 1 to 10 moles, preferably 3 times the number of moles of platinum ions. It should be ˜6 mole times. This is preferable because platinum particles having an average particle diameter of 0.5 to 5 nm, preferably 0.5 to 3 nm can be formed.

  In the present invention, in the reverse micelle solution (B) containing the water-soluble noble metal compound of iridium, the amount of the water-soluble noble metal compound of iridium in the reverse micelle solution (B) is such that the iridium fine particles are efficiently formed in the micelle. The amount may vary as appropriate depending on the amount of the water-soluble noble metal compound of platinum and the amount of the water-soluble noble metal compound of the promoter metal as described below. Preferably, the amount is such that the concentration of iridium ions is about 0.01 to 50% by mass, more preferably about 0.1 to 20% by mass in terms of the reverse micelle solution (B) and metal.

  In the present invention, the reverse micelle solution (B) is mixed with the reducing agent of the water-soluble noble metal compound of iridium or the reverse micelle solution (B ′) containing the reducing agent, so that the iridium particles are colloidally formed in the micelle. Disperse within the micelle. The reducing agent that can be used in this case is not particularly limited, and a known reducing agent can be used. Specific examples include hydrogen, hydrazine, sodium borohydride, sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, sodium borohydride, formaldehyde, methanol, ethanol, ethylene, carbon monoxide and the like. . What can be prepared as an aqueous solution of hydrazine or the like may be added directly to the reverse micelle solution as an aqueous solution having a concentration of 0.1 to 40% by mass, but a reverse micelle solution containing a reducing agent is prepared using the solution. The reverse micelle solution (B ′) may be added to the reverse micelle solution (B). An aqueous solution having a concentration of 0.1 to 40% by mass can be dispersed in the micelle in a colloidal form even when iridium ions become iridium particles in the micelle. Note that a powdered substance such as sodium borohydride can be supplied as it is. A gaseous substance at room temperature such as hydrogen can be supplied by bubbling. Of these, hydrazine (including an aqueous solution), sodium boride, and hydrogen are preferable, and sodium boride and hydrogen are particularly preferable. This is because stable iridium particles can be precipitated, and the composition in the micelle can be easily adjusted. The reduction with sodium boride is a reduction with hydrogen generated by the reaction with water, so that any reduction with hydrogen can be used effectively in the present invention. Further, if the reduction rate of the iridium particles is too high, the precipitated iridium particles may be aggregated. However, by using the reducing agent as described above, the iridium is easily precipitated, and the iridium particles are obtained at a suitable reduction rate. Aggregation can be prevented.

  The amount of the reducing agent added to the water-soluble noble metal compound of iridium is not particularly limited as long as iridium particles can be sufficiently formed from iridium ions, but it is 1 to 10 moles, preferably 3 times the number of moles of iridium ions. It should be ˜6 mole times. This is preferable because platinum particles having an average particle diameter of 0.5 to 5 nm, preferably 0.5 to 3 nm can be formed.

  In the conventional method, a precipitating agent such as ammonia is used in addition to the reducing agent as an insolubilizing agent for iridium ions and platinum ions. However, precipitates such as ammonium complexes precipitated thereby dissolve in the subsequent steps. There is a fear. For this reason, by using a reducing agent as an insolubilizing agent, stable composite noble metal particles can be deposited even in a later step.

  Further, as described above, the composite noble metal particles of the present invention may contain a promoter metal in addition to iridium and platinum, that is, the method of the present invention includes chromium, manganese, iron, cobalt, nickel, palladium, And at least one step of supporting at least one promoter metal selected from the group consisting of rhodium on the surface of the conductive support. In such a case, the step of adding the promoter metal is inserted before or after any of the steps (a) to (c) and (a) to (c) according to the present invention. It is preferable to insert the composite noble metal particles before the step of supporting the composite noble metal particles on the carrier. That is, in the second case of the present invention, (d) selected from the group consisting of chromium, manganese, iron, cobalt, nickel, palladium, and rhodium in a solution in which a surfactant is dissolved in an organic solvent. The reverse micelle solution (D) containing the water-soluble noble metal compound of at least one promoter metal is mixed with the reverse micelle solution (D ′) containing the reducing agent of the water-soluble noble metal compound or the reducing agent, and then the reverse micelle solution. The step of mixing (A ′) and the reverse micelle solution (B ′) or the reverse micelle solution (C ′) is combined with at least one of the steps (a) to (c) at least once. In the third case of the present invention, (d) selected from the group consisting of chromium, manganese, iron, cobalt, nickel, palladium, and rhodium in a solution in which a surfactant is dissolved in an organic solvent. The reverse micelle solution (D) containing the water-soluble noble metal compound of at least one promoter metal is mixed with the reverse micelle solution (D ′) containing the reducing agent of the water-soluble noble metal compound or the reducing agent, and then the reverse micelle solution. (A ′) and reverse micelle solution (B ′) or reverse micelle solution (C ′) are mixed, and then a conductive support is dispersed in the mixture to support composite noble metal particles on the support. Is combined at least once with at least one of the steps (a) to (c) above.

  In the step (d) or (d), the order in which the promoter metal is added is not particularly limited. For example, after depositing iridium particles and platinum particles, the promoter metal ions are added and precipitated. (I) adding a reducing agent of iridium ions to the reverse micelle solution (A) containing iridium ions inside the micelles, and then mixing the reverse micelle solution (B) containing platinum ions into the solution; A method of adding a reducing agent for platinum ions, mixing a reverse micelle solution (C) containing promoter metal ions with the solution, and adding a reducing agent for promoter metal ions can be used. Or (ii) adding a reducing agent of iridium ions to the reverse micelle solution (A) containing iridium ions inside the micelles, and then mixing the reverse micelle solution (C) containing promoter metal ions into the solution, A method in which a reducing agent for catalytic metal ions is added, a reverse micelle solution (B) containing platinum ions is further mixed with the solution, and a reducing agent for platinum ions is added; (iii) a promoter metal ion is contained inside the micelles A reverse micelle solution (C) is added with a promoter metal ion reducing agent, then mixed with the reverse micelle solution (A) containing iridium ions, added with an iridium ion reducing agent, and further added to the solution. A method of mixing a reverse micelle solution (B) containing platinum ions and adding a platinum ion reducing agent may be used.

  Next, in the method of the present invention, the composite noble metal particles are formed in micelles, and then the conductive noble metal particles are dispersed and mixed in the micelles, thereby supporting the composite noble metal particles on the carrier.

  The means for dispersing the conductive carrier that can be used at this time is not particularly limited, and known dispersing means can be used. Specifically, using a known stirring device such as an ultrasonic wave or a homogenizer, the conductive carrier is dispersed and mixed in the reverse micelle solution, and then the solution is mixed and stirred and reacted at 70 to 100 ° C. for 3 to 12 hours. The composite noble metal particles are preferably supported on a conductive carrier. According to these conditions, the composite noble metal particles can be reliably supported on the surface of the carrier without performing the firing treatment.

  It is preferable to add an alcohol such as methanol or ethanol after dispersing the conductive carrier. Thereby, a micelle can be destroyed and it can accelerate | stimulate that a composite noble metal particle is carry | supported by the support | carrier surface. Further, since there is a limit to the number of micelles that can be uniformly deposited on the outer surface of the conductive carrier, a high loading amount can be obtained in a highly dispersed state by loading composite noble metal particles while breaking the micelles with alcohol.

  The ratio of platinum to iridium supported on the conductive carrier is such that the atomic ratio is 0.7: 0.99 to 0.01: 0.3.

  In the method of the present invention, after the composite noble metal particles are supported (attached) on the surface of the support, the support is separated from the solution, and the support is washed and dried. In this case, the cleaning liquid that can be used for cleaning is not particularly limited, but an organic solvent such as methanol and ethanol and pure water can be used to effectively remove the surfactant. As the drying method, for example, natural drying, evaporation to dryness, rotary evaporator, spray dryer, drying with a drum dryer, or the like can be used. The drying time may be appropriately selected according to the method to be used, but the drying time is not particularly limited because it varies depending on the amount of composite noble metal particles prepared, but about 180 to 720 minutes is sufficient.

  According to the method of the present invention, the composite noble metal particles supported on the conductive support have a predetermined particle size, a narrow particle size distribution, can be arbitrarily adjusted, and have a uniform composition. The composite noble metal particles can be reliably and highly supported on the conductive support without firing. Therefore, the Pt—Ir alloy fine particles having a uniform atomic composition (uniform solid solution) and a narrow particle size distribution of 3 to 8 nm are formed on the conductive carrier by the above drying without performing a heat treatment (firing treatment) at a high temperature. It can be supported stably and firmly. Further, the catalyst thus obtained, particularly an electrode catalyst, can stably exhibit high power generation performance for a long period of time and is excellent in stability (acid resistance) in an acidic electrolyte atmosphere.

  The obtained catalyst, particularly the electrode catalyst, can be obtained by changing the type of reducing agent used in the above-described method and the order of preparation to obtain composite noble metal particles having an average particle diameter of 3 to 8 nm. By setting the average particle size within this range, a surface area sufficient for catalyst activity can be secured, and the amount of catalyst activity per unit mass of metal can be increased.

  As described above, according to the method of the present invention, it is possible to obtain a catalyst in which composite noble metal particles having a uniform composition and a narrow particle size distribution are supported on a support in a highly dispersed manner. Accordingly, such a catalyst can exhibit high catalytic activity over a long period of time. The application of such an electrode catalyst is not particularly limited, and examples thereof include electrode catalysts for fuel cells. In particular, the cathode of a fuel cell is in a noble potential state of 0.7 V or higher in a strongly acidic electrolyte, and the composite noble metal particles supported on the surface of the carrier are easily released and cause sintering, which hinders the efficiency of the fuel cell. There is a case. However, since the catalyst obtained by the method of the present invention has the above-mentioned various characteristics, it is particularly suitably used for such a cathode.

  The use of the catalyst of the present invention described above is only an embodiment and is not limited thereto. That is, as long as the catalyst obtained by the method of the present invention is effectively used, it can be applied to any application.

  Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples.

Example 1
Using 22 g of polyoxyethylene (5) nonylphenyl ether as a surfactant, cyclohexane was added to 1.0 L (0.05 mol / L), and this was mixed and stirred. To this, 7.15 g of an aqueous platinum chloride solution (Pt concentration: 25% by mass) was added and stirred for 1 hour until it became transparent to prepare a reverse micelle solution A.

  Using 22 g of polyoxyethylene (5) nonylphenyl ether as a surfactant, cyclohexane was added to 1.0 L (0.05 mol / L), mixed and stirred. To this was added 6.2 g of an iridium chloride aqueous solution (Ir concentration 5 mass%), and the mixture was stirred for 1 hour to prepare a reverse micelle solution B.

  To reverse micelle solution A, 0.5 g of sodium borohydride was added and stirred for 1 hour until it became transparent. To this, reverse micelle solution B was added and further stirred for 1 hour.

Next, 4.2 g of carbon black (Ketjen Black EC: Ketjen Black EC: BET specific surface area = 800 m ² / g manufactured by Ketjen Black International Co., Ltd.) was mixed with the mixed solution of the reverse micelle solutions A and B and stirred for 1 hour. Then, 0.5 g of sodium borohydride (NaBH ₄ ) was added and stirred for 1 hour.

After stirring for a predetermined time, reverse micelle solution A was further added and stirred for 1 hour, and then 0.5 g of sodium borohydride (NaBH ₄ ) was added and stirred for 1 hour.

Further, reverse micelle solution B was added and stirred for 1 hour, and then 0.5 g of sodium borohydride (NaBH ₄ ) was added and stirred for 1 hour.

  To this mixed solution of reverse micelle solution A, reverse micelle solution B and carbon black, 1.4 g of sodium borohydride was further added and stirred for 1 hour.

Then, it centrifuged for 6 hours using the centrifuge (Hitachi CENTRIFUGE05P-20B), and isolate | separated precipitation, Then, this was wash | cleaned with ethanol and water. The obtained solid was dried under reduced pressure at 85 ° C. for 12 hours and pulverized in a mortar to obtain an electrode catalyst (Pt _0.85 Ir _0.15 ).

Example 2
Reverse micelle solutions A and B were prepared in the same manner as in Example 1.

  Using 44 g of polyoxyethylene (5) nonylphenyl ether as a surfactant, cyclohexane was added to 1.0 L (0.05 mol / L), and this was mixed and stirred. To this, 7.15 g of an aqueous platinum chloride solution (Pt concentration: 25% by mass) and 6.2 g of an iridium chloride aqueous solution (Ir concentration: 5% by mass) were added and stirred for 1 hour until it became transparent to prepare a reverse micelle solution C.

  To reverse micelle solution A, 0.5 g of sodium borohydride was added and stirred for 1 hour until it became transparent. The reverse micelle solution B was added to this and further stirred for 1 hour.

Carbon black (Ketjen Black International Ketjen Black EC: BET specific surface area = 800 m ² / g) 4.2 g was mixed with the mixed solution of reverse micelle solutions A and B, and the mixture was stirred for 1 hour. Sodium borohydride 0.5g was added and it stirred for further 1 hour.

After stirring for a predetermined time, reverse micelle solution C and 1.4 g of sodium borohydride (NaBH ₄ ) were further added, and the mixture was further stirred and aged for 24 hours.

Then, it centrifuged for 6 hours using the centrifuge (Hitachi CENTRIFUGE05P-20B), and isolate | separated precipitation, Then, this was wash | cleaned with ethanol and water. The obtained solid was dried under reduced pressure at 85 ° C. for 12 hours and pulverized in a mortar to obtain an electrode catalyst (Pt _0.85 Ir _0.15 ).

Example 3
Reverse micelle solutions A and B were prepared in the same manner as in Example 1.

  To reverse micelle solution B, 0.5 g of sodium borohydride was added and stirred for 1 hour until it became transparent. Reverse micelle solution A was added thereto, and the mixture was further stirred for 1 hour.

After 4.2 g of carbon black (Vulcan XC-72: BET surface area = 280 m ² / g manufactured by Cabot) was mixed in the mixed solution of reverse micelle solutions A and B and stirred for 1 hour, sodium borohydride was further added in an amount of 0. 5 g was added and stirred for 1 hour.

After stirring for a predetermined time, 0.5 g of reverse micelle solution B and sodium borohydride (NaBH ₄ ) were further added and stirred for 1 hour until it became transparent. The reverse micelle solution A was added thereto and stirred for another hour, then 1.4 g of sodium borohydride was added, and the mixture was further stirred and aged for 24 hours.

Then, it centrifuged for 6 hours using the centrifuge (Hitachi CENTRIFUGE05P-20B), and isolate | separated precipitation, Then, this was wash | cleaned with ethanol and water. The obtained solid was dried under reduced pressure at 85 ° C. for 12 hours and pulverized in a mortar to obtain an electrode catalyst (Pt _0.85 Ir _0.15 ).

Example 4
Reverse micelle solutions A and B were prepared in the same manner as in Example 1, and reverse micelle solution C was prepared in the same manner as in Example 2.

To reverse micelle solution B, 0.5 g of sodium borohydride was added and stirred for 1 hour until it became transparent. The reverse micelle solution A was added thereto, and the mixture was further stirred for 1 hour, and then 4.2 g of carbon black (Acetlenblack: BET surface area = 120 m ² / g manufactured by Cabot) was mixed with the mixed solution of the reverse micelle solutions A and B. After stirring for 1 hour, 0.5 g of sodium borohydride (NaBH ₄ ) was added and stirred for 1 hour.

  After stirring for a predetermined time, the reverse micelle solution C was further added and stirred for 1 hour, and then 1.4 g of sodium borohydride was further added to the mixed solution of the reverse micelle solutions A, B and C, and the mixture was further stirred for 24 hours. Aged.

Then, it centrifuged for 6 hours using the centrifuge (Hitachi CENTRIFUGE05P-20B), and isolate | separated precipitation, Then, this was wash | cleaned with ethanol and water. The obtained solid was dried under reduced pressure at 85 ° C. for 12 hours and pulverized in a mortar to obtain an electrode catalyst (Pt _0.85 Ir _0.15 ).

Example 5
Reverse micelle solution C was prepared in the same manner as in Example 2.

To reverse micelle solution C, 0.5 g of sodium borohydride was added and stirred for 1 hour until it became transparent. Graphitized carbon black (graphitized ketjen black EC: BET specific surface area = 800 m ² / g manufactured by Ketjen Black International Co., Ltd.) was graphitized at 2,500 to 2,800 ° C. (Processed Ketjenblack: BET surface area = 125 m ² / g) 4.2 g was mixed and stirred for 1 hour, 0.5 g of sodium borohydride was added, and the mixture was further stirred for 1 hour.
The reverse micelle solution C was added again thereto and stirred for another hour, then 1.4 g of sodium borohydride was added, and the mixture was further stirred and aged for 24 hours.

Then, it centrifuged for 6 hours using the centrifuge (Hitachi CENTRIFUGE05P-20B), and isolate | separated precipitation, Then, this was wash | cleaned with ethanol and water. The obtained solid was dried under reduced pressure at 85 ° C. for 12 hours and pulverized in a mortar to obtain an electrode catalyst (Pt _0.85 Ir _0.15 ).

Example 6
Reverse micelle solution C was prepared in the same manner as in Example 2.

  To reverse micelle solution C, 0.5 g of sodium borohydride was added and stirred for 1 hour until it became transparent. The reverse micelle solution C was added again thereto, and the mixture was further stirred for 1 hour.

To this mixed solution of reverse micelle solution C, graphitized carbon black (graphitized ketjen black EC: BET specific surface area = 800 m ² / g manufactured by Ketjen Black International Co., Ltd.) at 2,500 to 2,800 ° C. Graphite-treated graphitized Ketjenblack: BET surface area = 125 m ² / g) was mixed and stirred for 1 hour, and then added with 1.4 g of sodium borohydride, and further stirred and aged for 24 hours.

Then, it centrifuged for 6 hours using the centrifuge (Hitachi CENTRIFUGE05P-20B), and isolate | separated precipitation, Then, this was wash | cleaned with ethanol and water. The obtained solid was dried under reduced pressure at 85 ° C. for 12 hours and pulverized in a mortar to obtain an electrode catalyst (Pt _0.85 Ir _0.15 ).

Example 7
Reverse micelle solutions A and B were prepared in the same manner as in Example 1.

  To reverse micelle solution A, 0.5 g of sodium borohydride was added and stirred for 1 hour until it became transparent. The reverse micelle solution B was added to this and further stirred for 1 hour.

To the mixed solution of the reverse micelle solutions A and B, graphitized carbon black (graphitized ketjen black EC: BET specific surface area = 800 m ² / g manufactured by Ketjen Black International Co., Ltd.) After mixing 2.1 g of graphitized Ketjenblack: BET surface area = 125 m ² / g) graphitized at ° C. and stirring for 1 hour, 0.7 g of sodium borohydride was added, and the mixture was further stirred and aged for 24 hours. .

  Next, reverse micelle solution A and 0.5 g of sodium borohydride were added and stirred for 1 hour until it became transparent, then reverse micelle solution B was added and stirred for another hour.

To the mixed solution of the reverse micelle solutions A and B, graphitized carbon black (graphitized ketjen black EC: BET specific surface area = 800 m ² / g manufactured by Ketjen Black International Co., Ltd.) After mixing 2.1 g of graphitized Ketjenblack: BET surface area = 125 m ² / g) graphitized at ° C. and stirring for 1 hour, 0.7 g of sodium borohydride was added, and the mixture was further stirred and aged for 24 hours. .

Then, it centrifuged for 6 hours using the centrifuge (Hitachi CENTRIFUGE05P-20B), and isolate | separated precipitation, Then, this was wash | cleaned with ethanol and water. The obtained solid was dried under reduced pressure at 85 ° C. for 12 hours and pulverized in a mortar to obtain an electrode catalyst (Pt _0.85 Ir _0.15 ).

Example 8
Reverse micelle solutions A and B were prepared in the same manner as in Example 1.

  To reverse micelle solution B, 0.5 g of sodium borohydride was added and stirred for 1 hour until it became transparent. Reverse micelle solution A was added thereto, and the mixture was further stirred for 1 hour.

To the mixed solution of the reverse micelle solutions A and B, graphitized carbon black (graphitized ketjen black EC: BET specific surface area = 800 m ² / g manufactured by Ketjen Black International Co., Ltd.) After mixing 2.1 g of graphitized Ketjenblack: BET surface area = 125 m ² / g) graphitized at ° C. and stirring for 1 hour, 0.7 g of sodium borohydride was added, and the mixture was further stirred and aged for 24 hours. .

  Next, reverse micelle solution B and 0.5 g of sodium borohydride were added and stirred for 1 hour until it became transparent, then reverse micelle solution A was added and stirred for another 1 hour.

To the mixed solution of the reverse micelle solutions A and B, graphitized carbon black (graphitized ketjen black EC: BET specific surface area = 800 m ² / g manufactured by Ketjen Black International Co., Ltd.) After mixing 2.1 g of graphitized Ketjenblack: BET surface area = 125 m ² / g) graphitized at ° C. and stirring for 1 hour, 0.7 g of sodium borohydride was added, and the mixture was further stirred and aged for 24 hours. .

Then, it centrifuged for 6 hours using the centrifuge (Hitachi CENTRIFUGE05P-20B), and isolate | separated precipitation, Then, this was wash | cleaned with ethanol and water. The obtained solid was dried under reduced pressure at 85 ° C. for 12 hours and pulverized in a mortar to obtain an electrode catalyst (Pt _0.85 Ir _0.15 ).

Example 9
Reverse micelle solution C was prepared in the same manner as in Example 2.

0.5 g of sodium borohydride was added to the reverse micelle solution C and stirred for 1 hour, and graphitized carbon black (graphitized ketjen black EC manufactured by Ketjen Black International Co., Ltd .: BET specific surface area = 800 m ² / g was graphitized at 2,500 to 2,800 ° C., 2.1 g of graphitized Ketjenblack (BET surface area = 125 m ² / g) was mixed and stirred for 1 hour, and then 0.7 g of sodium borohydride was added. In addition, the mixture was further stirred and aged for 24 hours.

Next, reverse micelle solution C and 0.5 g of sodium borohydride were added again thereto, and the mixture was stirred for 1 hour. Graphitized carbon black (graphitized ketjen black EC: BET manufactured by Ketjen Black International Co., Ltd.) was added thereto. Specific surface area = 800 m ² / g, graphitized at 2,500 to 2,800 ° C. Graphitized Ketjenblack: BET surface area = 125 m ² / g) was mixed and stirred for 1 hour, then hydrogenated Sodium boron (0.7 g) was added, and the mixture was further stirred and aged for 24 hours.

  Then, it centrifuged for 6 hours using the centrifuge (Hitachi CENTRIFUGE05P-20B), and isolate | separated precipitation, Then, this was wash | cleaned with ethanol and water. The obtained solid was dried at 85 ° C. under reduced pressure for 12 hours and pulverized in a mortar to obtain an electrode catalyst (Pt0.85Ir0.15).

Comparative Example 1
To 250 g of chloroplatinic acid aqueous solution containing 0.4% by mass of Pt, 1.0 g of conductive carbon black carbon black (Ketjen Black International Co., Ltd .: Ketjen Black EC: BET specific surface area = 800 m ^{2 /} g) is added, After sufficiently dispersing using a homogenizer, 3 g of sodium citrate was added thereto, and the mixture was heated to 80 ° C. using a reflux reactor to carry out reduction loading of Pt. And after standing to cool to room temperature, the carbon by which Pt was carry | supported was separated by filtration, and the electrode catalyst of carbon carrying | support Pt (Pt carrying amount 50 mass%) was obtained.

Comparative Example 2
Add conductive carbon black (Cabot's VulcanXC-72, BET surface area = 280 m ^{2 /} g) 1.0 g to 250 g of chloroplatinic acid aqueous solution containing 0.4% by mass of Pt, and thoroughly disperse using a homogenizer. Thereafter, 3 g of sodium citrate was added thereto, and the mixture was heated to 80 ° C. using a reflux reactor to carry out reduction loading of Pt. And after standing to cool to room temperature, the carbon by which Pt was carry | supported was separated by filtration, and the electrode catalyst of carbon carrying | support Pt (Pt carrying amount 50 mass%) was obtained.

Experiment 1: Performance Evaluation of Electrocatalyst MEA (Membrane Electrode Assembly) using each of the electrode catalysts obtained in Examples 1 to 9 and Comparative Examples 1 and 2 as a cathode catalyst was prepared. The cell performance was measured.

  The MEA was produced according to the following procedure.

1. Preparation of Anode Catalyst As a conductive carbon material, 4.0 g of carbon black (Ketjen Black TMEC manufactured by Ketjen Black International Co., Ltd., BET surface area = 800 m ^{2 /} g) was prepared, and dinitrodiammine platinum aqueous solution (Pt concentration: 1. 0%) was added and stirred for 1 hour. Furthermore, 50 g of methanol was mixed as a reducing agent and stirred for 1 hour. Thereafter, the mixture was heated to 80 ° C. in 30 minutes, stirred at 80 ° C. for 6 hours, and then cooled to room temperature in 1 hour. After filtering the precipitate, the obtained solid was dried under reduced pressure at 85 ° C. for 12 hours, pulverized in a mortar, and catalyst a1 (average particle diameter of Pt particles 2.6 nm, Pt supported concentration 45.7% by mass) Got.

2. Preparation of anode electrode catalyst layer 5 times the amount of purified water was added with respect to the mass of the anode catalyst (a1) produced in Step 1, and a vacuum degassing operation was added for 5 minutes. To this, 0.5 times the amount of n-propyl alcohol was added, and a solution containing a proton conductive polymer electrolyte (containing 20 wt% Nafion (registered trademark) manufactured by DuPont) was added. The content of the polymer electrolyte in the solution was such that the mass ratio of the solid content to the carbon mass of the electrode catalyst (a1) was Carbon / Ionomer = 1.0 / 0.9.

The obtained mixed slurry was well dispersed with an ultrasonic homogenizer, and a catalyst slurry was prepared by applying a vacuum degassing operation. An amount of the catalyst slurry corresponding to the desired thickness was printed on one side of the polytetrafluoroethylene sheet by screen printing and dried at 60 ° C. for 24 hours. The size of the formed anode catalyst layer was 5 cm × 5 cm. Further, the coating layer on the polytetrafluoroethylene sheet was adjusted so that the amount of Pt was 0.1 mg / cm ² .

3. Preparation of Cathode Electrocatalyst Layer 5 times the amount of purified water was added to the mass of each electrode catalyst (c1) obtained in Examples 1 to 9 and Comparative Examples 1 and 2, and vacuum degassing operation was performed 5 times. Added for a minute. To this, 0.5 times the amount of n-propyl alcohol was added, and a solution containing a proton conductive polymer electrolyte (containing 20 wt% Nafion (registered trademark) manufactured by DuPont) was added. The content of the polymer electrolyte in the solution was such that the solid content mass ratio with respect to the carbon mass of the electrode catalyst (c1) was Carbon / Ionomer = 1.0 / 0.9.

The obtained mixed slurry was well dispersed with an ultrasonic homogenizer, and a catalyst slurry was prepared by applying a vacuum degassing operation. An amount of the catalyst slurry corresponding to the desired thickness was printed on one side of the polytetrafluoroethylene sheet by screen printing and dried at 60 ° C. for 24 hours. The size of the formed cathode catalyst layer was 5 cm × 5 cm. Further, the coating layer on the polytetrafluoroethylene sheet was adjusted so that the amount of Pt was 0.4 mg / cm ² .

4). Bonding with a solid polymer electrolyte membrane As a solid polymer electrolyte membrane, Nafion ^™ 111 (film thickness 25 µm) and an electrode catalyst layer formed on the previously prepared polytetrafluoroethylene sheet were superposed. At that time, the anode catalyst layer, the solid polymer electrolyte membrane, and the cathode catalyst layer were laminated in this order. Thereafter, hot pressing was performed at 130 ° C. and 2.0 MPa for 10 minutes.

The cathode catalyst layer had a thickness of about 10 μm, the Pt loading was 0.4 mg per 1 cm ² apparent electrode area, and the electrode area was 25 cm ² . The anode catalyst layer had a thickness of about 2 μm, the amount of Pt supported was 0.1 mg per 1 cm ² apparent electrode area, and the electrode area was 25 cm ² .

5. MEA Performance Evaluation After joining the catalyst layer and the solid polymer electrolyte membrane, a gas diffusion layer (GDL) was placed outside thereof to produce a membrane electrode assembly (MEA). A gas separator with a gas flow path was disposed on both surfaces of the MEA, and was further sandwiched between gold-plated stainless steel current collector plates to form a single cell for evaluation. In the evaluation unit cell, hydrogen was supplied as a fuel to the anode side, and air was supplied as an oxidant to the cathode side. The supply pressure of both gases was atmospheric pressure, hydrogen was set to 58.6 ° C. and relative humidity 60%, air was set to 54.8 ° C. and relative humidity 50%, and the cell temperature was set to 70 ° C. The hydrogen utilization rate was 67% and the air utilization rate was 40%. Under this condition, the cell voltage when power was generated at a current density of 1.0 A / cm ² was measured as the initial cell voltage.

Subsequently, after generating power for 60 seconds, power generation was stopped. After stopping, the supply of hydrogen and air was stopped, the single cell was replaced with air, and the system was on standby for 50 seconds. Thereafter, hydrogen gas was supplied to the anode side for 10 seconds at 1/5 of the above utilization rate. Thereafter, hydrogen gas was supplied to the anode side and air was supplied to the cathode side under the same conditions as described above, and power was generated again at a current density of 1.0 A / cm ² for 60 seconds. The load current at this time was increased from 0 A / cm ² to 1 A / cm ² in 30 seconds. This power generation / stop operation was performed, the cell voltage was measured, and the power generation performance was evaluated. The number of cycles when the cell voltage at a current density of 1.0 A / cm ² was 0.45 V was used as the durability evaluation value.

  These results are shown in Table 1 below.

  From the results of Table 1 above, it is shown that the electrode catalyst of the present invention is very excellent in durability.

Claims (15)

Formula: [Pt] _a [Ir] _b (wherein, a represents an atomic ratio of Pt and is 0.7 to 0.99, b represents an atomic ratio of Ir, and 0.01 to 0.3 Wherein the total of a and b is 1), and the composite noble metal particles having an average particle diameter of 3 to 8 nm are highly dispersed and supported on the surface of the conductive support, The composite noble metal particle is a reverse micelle solution formed by mixing an aqueous solution containing a water-soluble noble metal compound of platinum (Pt) and a water-soluble noble metal compound of iridium (Ir) in a solution in which a surfactant is dissolved in an organic solvent. And a catalyst formed by adding a reducing agent for the water-soluble noble metal compound.   2. The catalyst according to claim 1, wherein the water-soluble noble metal compound of iridium (Ir) is at least one selected from the group consisting of iridium chloride, nitrate and dinitrodiammine salt.   The catalyst according to claim 1 or 2, wherein the water-soluble noble metal compound of platinum (Pt) is at least one selected from the group consisting of platinum chloride, nitrate and dinitrodiammine salt.   The conductive carrier is acetylene black, vulcan, ketjen black, black pearl, graphitized acetylene black, graphitized vulcan, graphitized ketjen black, graphitized black pearl, carbon nanotube, carbon nanofiber, carbon nanohorn, and carbon. The catalyst according to any one of claims 1 to 3, comprising as a main component at least one selected from the group consisting of fibrils.   The catalyst according to claim 4, wherein the conductive carrier contains at least one selected from the group consisting of acetylene black, vulcan, ketjen black, and black pearl as a main component.   The catalyst according to any one of claims 1 to 5, wherein the composite noble metal particles further include at least one promoter metal selected from the group consisting of chromium, manganese, iron, cobalt, nickel, palladium, and rhodium. . The composite noble metal particles have the formula: [Pt] _a [Ir] _b [X] _c (where X is at least one selected from the group consisting of Cr, Mn, Fe, Co, Ni, Pd, Rh, a represents an atomic ratio of Pt, b represents an atomic ratio of Ir, and c represents a total atomic ratio of X, where (b + c) / (a + b + c) is 0.01 to 0.3. And a + b + c = 1). 7. The catalyst of claim 6 having a composition of:   The catalyst according to any one of claims 1 to 7, wherein the composite noble metal particles have an average particle size of 4 to 6 nm. (A) In a solution in which a surfactant is dissolved in an organic solvent, a reverse micelle solution (A) containing a water-soluble noble metal compound of platinum (Pt) is added to the water-soluble noble metal compound reducing agent or the reducing agent. After mixing with the reverse micelle solution (A ′) containing, the reverse micelle solution (B) containing the water-soluble noble metal compound of iridium (Ir) is added, and the reverse micelle further containing the reducing agent or reducing agent of the water-soluble noble metal compound Mixing the solution (B ′);
(B) A reverse micelle solution (B) containing a water-soluble noble metal compound of iridium (Ir) in a solution in which a surfactant is dissolved in an organic solvent contains the water-soluble noble metal compound reducing agent or reducing agent. After mixing the reverse micelle solution (B ′), a reverse micelle solution (A) containing a water-soluble noble metal compound of platinum (Pt) is added, and a reverse micelle solution containing a reducing agent or a reducing agent for the water-soluble noble metal compound. A step of mixing (A ′); and (c) a reverse micelle solution (C) containing a water-soluble noble metal compound of platinum (Pt) and iridium (Ir) in a solution in which a surfactant is dissolved in an organic solvent. And a step selected from the group consisting of the step of mixing the reducing agent of the water-soluble noble metal compound or the reverse micelle solution (C ′) containing the reducing agent, and at least one of the steps (a) to (c). Obtained in one step The conductive noble metal particles are dispersed in the resulting mixed liquid and the composite noble metal particles are supported on the carrier, and then the carrier supported by the composite noble metal particles is separated, washed, and dried, so that the composite noble metal particles can be A method for producing a catalyst, comprising a step of forming a dispersion-supported catalyst. (A) A reverse micelle solution (A) containing a water-soluble noble metal compound of platinum (Pt) in a solution in which a surfactant is dissolved in an organic solvent contains the water-soluble noble metal compound reducing agent or reducing agent. After mixing the reverse micelle solution (A ′), the reverse micelle solution (B) containing the water-soluble noble metal compound of iridium (Ir) is added, and the water-soluble noble metal compound reducing agent or the reverse micelle solution containing the reducing agent is further added. (B ′) is mixed, and then a conductive support is dispersed in the mixed solution to support composite noble metal particles on the support;
(A) A reverse micelle solution (B) containing a water-soluble noble metal compound of iridium (Ir) in a solution obtained by dissolving a surfactant in an organic solvent contains a reducing agent or a reducing agent for the water-soluble noble metal compound. After mixing the reverse micelle solution (B ′), a reverse micelle solution (A) containing a water-soluble noble metal compound of platinum (Pt) is added, and a reverse micelle solution containing a reducing agent or a reducing agent for the water-soluble noble metal compound. (A ′) is then mixed, and then a conductive support is dispersed in the mixed solution, and composite noble metal particles are supported on the support; and (c) a solution in which a surfactant is dissolved in an organic solvent. Then, the reverse micelle solution (C ′) containing the water-soluble noble metal compound of platinum (Pt) and iridium (Ir) is mixed with the reverse micelle solution (C ′) containing the reducing agent or the reducing agent of the water-soluble noble metal compound. And then into the mixture By repeating the step selected from the group consisting of the step of dispersing the conductive support and supporting the composite noble metal particles on the support at least twice, separating, washing and drying the support supported by the composite noble metal particles A method for producing a catalyst, comprising the step of forming a catalyst in which composite noble metal particles are supported in a highly dispersed state on a support surface.   The method according to claim 9 or 10, wherein the water-soluble noble metal compound of iridium (Ir) is at least one selected from the group consisting of iridium chloride, nitrate and dinitrodiammine salt.   The method according to any one of claims 9 to 11, wherein the water-soluble noble metal compound of platinum (Pt) is at least one selected from the group consisting of platinum chloride, nitrate and dinitrodiammine salt.   The conductive carrier is acetylene black, vulcan, ketjen black, black pearl, graphitized acetylene black, graphitized vulcan, graphitized ketjen black, graphitized black pearl, carbon nanotube, carbon nanofiber, carbon nanohorn, and carbon. The method of any one of Claims 9-12 containing at least 1 type chosen from the group which consists of fibrils as a main component.   The method according to claim 13, wherein the conductive carrier contains at least one selected from the group consisting of acetylene black, vulcan, ketjen black, and black pearl as a main component.   The method according to any one of claims 9 to 14, further comprising at least one step of supporting at least one promoter metal selected from the group consisting of chromium, manganese, iron, cobalt, nickel, palladium, and rhodium on the surface of the conductive support. 2. The method according to item 1.