JP6840314B2 - Carrier-supported palladium core platinum shell fine particle colloid, carrier-supported palladium core platinum shell fine particle catalyst, their manufacturing method, and battery - Google Patents

Description

The present invention relates to a carrier-supported palladium core platinum shell fine particle colloid, a carrier-supported palladium core platinum shell fine particle catalyst, a method for producing the same, and a battery, and more specifically, a carrier-supported palladium core and a carrier before forming a platinum shell. The present invention relates to core-shell type fine particles synthesized by using alkali metal hydroxide such as potassium hydroxide and microwave irradiation to form a platinum shell after synthesizing a supported palladium core. The fine particles referred to in the present invention have a primary particle size, and when referring to palladium core fine particles or palladium core platinum shell fine particles, they may mainly refer to nanoparticles, and in the case of a carrier carrying palladium core platinum shell fine particles. Often refers mainly to particles of several tens of μm or less.

Furthermore, the present invention also uses sodium hydroxide and microwave irradiation to synthesize a platinum shell after synthesizing a carrier-supported palladium core using sodium hydroxide and microwave irradiation. Regarding type fine particles.

The polymer electrolyte fuel cell (hereinafter referred to as PEFC) that uses hydrogen as fuel is considered to be an environment-friendly energy device that can be used by electric transportation vehicles. As the electrochemical catalyst for PEFC, metal nanoparticles, for example, binary metal-based metal particles such as palladium-core platinum sur-nanoparticles, exhibit higher oxygen reduction activity than catalysts using only platinum. It has attracted a great deal of attention because it reduces the amount of precious platinum used.

A catalyst containing metal nanoparticles using binary metal particles is dispersed in a porous carbon material having a high surface surface such as activated carbon, carbon nanotubes, and graphene in order to maximize the catalytic effect and ensure conductivity. It is generally fixed.

In recent years, it has become clear that metal nanoparticles composed of a plurality of types of metal elements exhibit different properties as compared with nanoparticles containing only one type of metal. For this reason, alloy nanoparticles obtained by alloying two types of metals, core-shell nanoparticles obtained by coating one metal nanoparticle with another metal, and the like have been actively studied, and various proposals have been made.

Core-shell nanoparticles are expected to be imparted with catalytic activity different from that of shell metal-only nanoparticles if the shell layer in contact with the outside can be uniformly formed. It is presumed that this is because the core particles serve as a base, which modifies the electronic properties of the shell layer and the geometrical arrangement of the crystal structure, and more effectively reduces the activation energy of the desired reaction. Has been done.

Further, when the metal having catalytic activity is very expensive, the core-shell structure is economical because the expensive metal can be effectively arranged in the shell layer in contact with the reactant. In addition, by uniformly coating the chemically stable noble metal as a shell, it is possible to indirectly participate in the reaction while shielding the base metal, which is easily oxidized and dissolved, from the outside, and to exhibit new catalytic properties. Will also be possible.

Further, when the metal having catalytic activity is very expensive, the core-shell structure is economical because the expensive metal can be effectively arranged in the shell layer in contact with the reactant. In addition, by uniformly coating the chemically stable noble metal as a shell, it is possible to indirectly participate in the reaction while shielding the base metal, which is easily oxidized and dissolved, from the outside, and to exhibit new catalytic properties. Will also be possible.

Attempts have been made to effectively use a small amount of platinum to obtain as good a catalytic ability as possible. In recent years, palladium core platinum shell metal nanoparticles have been used to reduce the cost of catalysts for fuel cells for households and automobiles. Is becoming more and more effective.

However, in the synthesis of core-shell type metal nanoparticles, it is very difficult to uniformly coat the shell layer, so the synthesis conditions are often limited in the laboratory, and the particle size is as small as a single nanometer. In that case, detailed observation with an electron microscope and analysis using an electron beam or X-ray become more difficult, so that the data demonstrating the core-shell structure often remain uncertain. Therefore, the process of mass-producing core-shell type metal nanoparticles having a uniform shell layer while maintaining stable quality at low cost has not yet been realized.

Non-Patent Document 1 asserts that palladium-core platinum-shell particles are promising mainly for fuel cell catalyst applications.

Patent Documents 1 and 2 describe an underpotential precipitation method in which a monoatomic layer of copper is formed on the surface of palladium particles by adjusting the potential on an electrode, and then a platinum salt is added to replace copper and platinum. Have been described. In principle, this method is excellent in that it can form a shell of a monoatomic layer, but platinum is used because electrons are not uniformly transferred to the material and the reactants are not uniformly supplied. The shell coating may not be sufficient. In addition, although it is a method that serves the purpose of forming a small amount of core-shell particles in the laboratory and analyzing the characteristics, it is a method that still has some drawbacks when considering productivity and automation during mass production.

On the other hand, a method of forming a shell by electroless plating without using an electrode has also been proposed. In Patent Document 3, a platinum shell layer is formed on palladium particles by examining the type of platinum salt, and the coverage is measured, but it is not satisfactory and it is also determined whether the shell layer has a uniform thickness. Not the target.

When using core-shell type metal fine particles as a catalyst, it is important to select conductive, high surface area fine particles or a coalition of fine particles as a carrier, and distribute the fine particles on the carrier at a density suitable for the purpose. , It is desirable that the particle size is as small as possible, and it is desirable that the particle size is the same in order to have the same characteristics. In the impregnation method currently used as a catalyst preparation method, there are problems that the supported particles are easily aggregated and it is difficult to uniformly make two or more kinds of metals into alloy fine particles or core-shell type fine particles. It has become.

As a means for heating the reaction solution, the reaction solution is irradiated with microwaves. In Patent Document 4, a semiconductor oscillator and a microwave resonance cavity are used, and the reaction tube of the continuous flow system is arranged at the largest position of the standing wave of the electric field for chemical reaction without impairing rapid heating or uniformity. Attempts have been made to heat the. This method, which combines a single-mode heating method and a continuous flow system, is extremely useful when the reaction is sufficiently promoted by microwave heating and completed in a short time.

Synthesizing core particles using the liquid phase reduction method facilitates subsequent modifications such as shell formation, but when trying to increase productivity using the batch method, nucleation occurs due to non-uniform heating and stirring. There was an adverse effect that the particles tended to be non-uniform and the particle sizes were not uniform. For this reason, at present, most of the metal nanoparticles that are said to have the same particle size are at the laboratory level, and it has been difficult to increase productivity without sacrificing quality in producing metal nanoparticles. ..
In particular, although palladium-core platinum-shell nanoparticles are expected to be used as catalysts, it is difficult to produce a uniform shell layer with stable quality and at low cost.

As a technique corresponding to this point, the method described in Patent Document 5 uses microwave heating for the synthesis of palladium core particles and adjusts the shell formation reaction by adding hydroxide ions to obtain a uniform platinum shell layer. The technology to form and achieve both stable quality and productivity improvement is described.

Various methods have been proposed as methods for producing core-shell fine particles for oxygen reduction catalysts in fuel cells, but it is difficult to continuously produce shell layers with stable quality and at low cost. is there. For example, the method described in Patent Document 5 aims to form a uniform platinum shell layer by adjusting the shell formation reaction by adding sodium hydroxide ion, but Patent Document 5 states that the quality is stable. Detailed conditions for achieving both improved productivity are not described. Further, Patent Document 5 describes that the addition of potassium hydroxide ion instead of sodium hydroxide ion may be used for the production of core-shell fine particles, but it is described as a possibility. However, no details are given.

Synthesis of carrier-supported palladium-core platinum-shell fine particles, especially in the case of a carrier exhibiting conductivity, is often unknown, and efficient synthesis of carrier-supported palladium-core platinum-shell fine particles is considered to be extremely difficult. There is.

Japanese Unexamined Patent Publication No. 2011-218278 JP2012-16684A Japanese Unexamined Patent Publication No. 2012-120949 Japanese Unexamined Patent Publication No. 2011-137226 Japanese Unexamined Patent Publication No. 2015-223535

NEDO Achievement Report: "Development of Practical Use Promotion Technology for Polymer Electrolyte Fuel Cell / Development of Basic Technology / Development of Low Platinum Technology" (FY2010-FY2012) Interim report for FY2010.

One of the problems of the present invention is a production method capable of providing core-shell type fine particles supported on a carrier exhibiting conductivity such as carbon, for example, carrier-supported palladium core platinum shell fine particles for a catalyst with high performance and low cost. Is to provide.

One of the problems of the present invention is a method for forming a shell for obtaining core-shell type fine particles supported on a carrier exhibiting conductivity such as carbon, for example, carrier-supported palladium core platinum shell fine particles for a catalyst with high performance and low cost. Is to provide.

One of the objects of the present invention is, for example, to provide high-performance and inexpensive carbon-supported palladium-core platinum-shell fine particles.

In order to solve the above problems and achieve the object, the embodiment of the invention according to the present invention includes, for example, the following configuration.

The first invention of the present invention (hereinafter referred to as Invention 1) made to solve the problem is a platinum raw material ion-containing solution in a colloid in which carrier-supported palladium fine particles are dispersed in a dispersion medium containing a glycol-based solvent. In a method of continuously forming a platinum shell on carrier-supported palladium core particles by microwave heating in a reaction raw material solution prepared by adding an alkali metal hydroxide solution, the platinum raw material solution and the alkali metal hydroxide solution were added. After that, it is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, wherein the concentration of hydroxide ions freed, coordinated, and adsorbed becomes 2 to 6 times the amount of the substance of the platinum raw material.

In the second invention of the present invention (hereinafter referred to as invention 2), which is a development of the invention 1, the carrier-supported palladium fine particles, which is one of the raw material components, is a glycol-based solvent in the method for producing a colloid according to the invention 1. , Carrier, palladium raw material, carrier-supported palladium, which is synthesized by microwave heating a reaction raw material solution containing an alkali metal hydroxide having a substance amount 4 to 7 times that of a carrier, a palladium raw material, and a palladium raw material atom. This is a method for producing a core platinum shell fine particle colloid.

In the third invention of the present invention (hereinafter referred to as invention 3), which is a development of the inventions 1 and 2, in the method for producing a carrier-supported palladium core platinum shell fine particle colloid according to the inventions 1 and 2, the carrier is carbon. Production of carbon-supported palladium-core platinum-shell fine particle colloid, which is a fine particle and is synthesized by a microwave continuous irradiation method in which a step of forming carbon-supported palladium fine particles and a step of forming a platinum shell are connected by a continuous flow path. The method.

The fourth invention of the present invention (hereinafter referred to as invention 4), which is a development of the inventions 1 to 3, is an alkali in the method for producing a carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 1 to 3. It is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, wherein the metal hydroxide is potassium hydroxide.

The fifth invention of the present invention (hereinafter referred to as Invention 5) made to solve the problem is a dispersion liquid in which a carrier is dispersed in a dispersion medium containing a glycol-based solvent, and a palladium raw material and a potassium hydroxide solution. In the method of continuously synthesizing carrier-supported palladium nanoparticles by microwave heating to prepare a reaction raw material solution, it is necessary to add potassium hydroxide in a substance amount 4 to 7 times the amount of the palladium raw material atom of the palladium raw material. It is a method for producing a carrier-supported palladium fine particle colloid.

The sixth invention of the present invention (hereinafter referred to as invention 6) made to solve the problem uses a colloid in which the fine particles described in invention 5 are dispersed in a dispersion medium containing a glycol-based solvent as a raw material, and hexachloro. In the method of forming a platinum shell on carrier-supported palladium core particles by adding a platinum (4) acid ion-containing solution and a potassium hydroxide solution at room temperature or heating, after adding the platinum raw material solution and the potassium hydroxide solution, A method for producing a carrier-supported palladium-core platinum-shell fine particle colloid, wherein the concentration of hydroxide ions freed, coordinated, and adsorbed is 2 to 6 times the amount of the substance of the platinum raw material. .. ..

In the seventh invention of the present invention (hereinafter referred to as invention 7), which is a development of the inventions 5 and 6, the carrier is carbon fine particles and the carbon-supported palladium nano is in the method for producing a colloid according to the inventions 5 and 6. It is a method for producing a carbon-supported palladium-core platinum-shell fine particle colloid, wherein the particle colloid and the subsequent method for forming a platinum shell are connected by a continuous flow path and are carried out by a continuous method.

In the eighth invention of the present invention (hereinafter referred to as invention 8), which is a development of the first invention, 2-aminoethanol is used as an additive in the method for producing a carrier-supported palladium-core platinum-shell fine particle colloid according to the first invention. It is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, which is characterized by being contained.

The ninth invention of the present invention (hereinafter referred to as invention 9) made by developing the inventions 1 to 3 and 8 is the production of the carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 1 to 3 and 8. In the method, it is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, wherein the alkali metal hydroxide is sodium hydroxide.

The tenth invention of the present invention (hereinafter referred to as invention 10) made by developing the inventions 1 to 3 and 8 is the production of the carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 1 to 3 and 8. In the method, it is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, wherein the alkali metal hydroxide is cesium hydroxide.

The eleventh invention of the present invention (hereinafter referred to as invention 11) made by developing the inventions 1 to 3 and 8 is the production of the carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 1 to 3 and 8. In the method, it is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, wherein the alkali metal hydroxide is lithium hydroxide.

The twelfth invention of the present invention (hereinafter referred to as invention 12), which is a development of the inventions 1 to 8, is an alkali in the method for producing a carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 1 to 8. It is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, which comprises adding tetramethylguanidine together with a metal hydroxide.

The thirteenth invention of the present invention (hereinafter referred to as invention 13), which is a development of the inventions 1 to 8, is an alkali in the method for producing a carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 1 to 8. It is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, which comprises adding hexamethylenetetramine together with a metal hydroxide.

The fourteenth invention of the present invention (hereinafter referred to as invention 14), which is a development of the inventions 1 to 8, is an alkali in the method for producing a carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 1 to 8. It is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, which comprises adding triethanolamine together with a metal hydroxide.

The fifteenth invention of the present invention (hereinafter referred to as invention 15), which is a development of the inventions 1 to 8, is an alkali in the method for producing a carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 1 to 8. It is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, which comprises adding choline together with a metal hydroxide.

The sixteenth invention of the present invention (hereinafter referred to as invention 16), which is a development of the inventions 1 to 15, is used in the method for producing a carrier-supported palladium-core platinum-shell fine particle colloid according to any one of the inventions 1 to 15. This is a method for producing a carrier-supported palladium-core platinum-shell fine particle colloid, wherein the glycol-based solvent used is ethylene glycol.

The seventeenth invention of the present invention (hereinafter referred to as invention 17), which is a development of the inventions 1 to 15, is the glycol in the method for producing a carrier-supported palladium-core platinum-shell fine particle colloid according to any one of the inventions 1 to 15. It is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, which comprises using glycerin mixed with a system solvent.

The eighteenth invention of the present invention (hereinafter referred to as invention 18), which is a development of the inventions 2 to 17, is the method for producing a carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 2 to 17. Palladium raw materials are palladium chloride (2) (PdCl ₂ ), sodium tetrachloropalladium (2) (Na ₂ [PdCl ₄ ]), potassium tetrachloropalladium (2) (K ₂ [PdCl ₄ ]), tetrachloro. Palladium (2) ammonium acid ((NH ₄ ) [PdCl ₄ ]), palladium acetate (2) (Pd (CH ₃ COOH) ₂ ), palladium oxalate (2) (PdC ₂ O ₄ ), palladium nitrate (2) Contains a salt raw material selected from (Pd (NO ₃ ) ₂ ), palladium sulfate (2) (Pd (SO ₄ )), palladium acetylacetonate, tetraammine palladium (2) salt, and dinitrodiammine palladium (2). It is a method for producing a carrier-supported palladium core platinum shell fine particle colloid.

The nineteenth invention of the present invention (hereinafter referred to as invention 19), which is a development of the inventions 2 to 18, is the method for producing a carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 2 to 18. It is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, wherein the palladium raw material is potassium tetrachloropalladium (2).

The twentieth invention of the present invention (hereinafter referred to as the invention 20), which is a development of the inventions 2 to 18, is the method for producing a carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 2 to 18. It is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, wherein the palladium raw material is sodium tetrachloropalladium (2).

The 21st invention of the present invention (hereinafter referred to as the invention 21), which is a development of the inventions 2 to 18, is the method for producing a carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 2 to 18. It is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, wherein the palladium raw material is palladium acetate (2).

The 22nd invention of the present invention (hereinafter referred to as invention 22), which is a development of the inventions 1 to 21, is the carrier-supported palladium core platinum shell fine particle colloid production method according to any one of the inventions 1 to 21. It is a method for producing a carrier-supported palladium core platinum shell fine particle colloid, which comprises moving to the next platinum shell forming step under the condition that the surface of the supported palladium core particle synthesis product is not contaminated.

The 23rd invention of the present invention (hereinafter referred to as invention 23), which is a development of the inventions 1 to 22, is the carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 1 to 22, and the majority of the shells. It is a carrier-supported palladium-core platinum-shell fine particle colloid characterized by having 5 or less layers.

In the 24th invention of the present invention (hereinafter referred to as the invention 24) developed by developing the invention 23, 90% or more of the shell layers are 5 or less in the carrier-supported palladium core platinum shell fine particle colloid according to the invention 23. It is a carrier-supported palladium core platinum shell fine particle colloid.

The 25th invention of the present invention (hereinafter referred to as invention 25), which is a development of the inventions 23 and 24, is a carrier-supported palladium core platinum shell fine particle colloid according to the inventions 23 and 24, wherein a majority of the palladium core platinum shell fine particles It is a carrier-supported palladium core platinum shell fine particle colloid, characterized in that the shell layer of the above covers 50% or more of the core layer.

The 26th invention of the present invention (hereinafter referred to as invention 26) made by developing the inventions 23 and 24 is a majority of palladium core platinum shell nanoparticles in the carrier-supported palladium core platinum shell fine particle colloid according to the inventions 23 and 24. It is a carrier-supported palladium core platinum shell fine particle colloid, characterized in that the shell layer of the above covers 90% or more of the core layer.

The 27th invention of the present invention (hereinafter referred to as invention 27), which is a development of the inventions 1 to 26, is when the carrier-supported palladium core platinum shell fine particle colloid according to any one of the inventions 1 to 26 is made into a dry powder. , A method for producing a carrier-supported palladium-core platinum-shell fine particle colloid, characterized in that alkali metal ions remain in the dry powder.

The 28th invention of the present invention (hereinafter referred to as the invention 28), which is a development of the inventions 1 to 27, uses the carrier-supported palladium core platinum shell fine particles produced by the method according to any one of the inventions 1 to 27 as a catalyst. The polymer electrolyte fuel cell used.

The 29th invention of the present invention (hereinafter referred to as invention 29) made to solve the problem is
A 0.1 M aqueous solution of perchloric acid was added to a glass five-necked flask for convection voltammetry measurement having a width of 14.5 cm, a height of 12.5 cm, and a capacity of 300 ml or more.
Bubbling 3 L / min of nitrogen for 30 minutes to expel oxygen is used as the electrolyte.
To the glassy carbon rotating electrode with a diameter of 5 mm of the glassy carbon part coated with the catalyst ink so as to contain 0.96 μg of platinum,
At a temperature of 20 ° C
When a durability test was conducted in which a square wave with a potential of 0.6 V for 3 seconds and 1.0 V for 3 seconds was set as one cycle with a reversible hydrogen electrode as a reference electrode, and a potential cycle was applied.
A 0.1 M aqueous solution of perchloric acid was added to the flask.
Bubbling 3 L / min of oxygen for 30 minutes to expel nitrogen was used as the electrolyte.
Electrode rotation speed 1600 [rotation / minute],
Temperature 25 ° C,
Scanning speed to the high potential side of 20 [mV / sec],
Under the conditions of
In the mass activity calculation method in which the oxygen reduction current value at a potential of 0.9 V with the reversible hydrogen electrode as a reference electrode is derived from the Koutecky-Levic equation and the solution resistance is compensated for the calculation.
The mass activity of platinum as an oxygen reduction catalyst after 37,000 cycles, that is, the value obtained by dividing the current value in the mass activity calculation method by the amount of platinum applied 0.96 μg can maintain 75% of the mass activity before the durability test. It is a palladium core platinum shell fine particle colloid characterized by the above.

The thirtieth invention of the present invention (referred to as invention 30), which is a development of the inventions 1 to 27, is characterized in that the initial activity is 600 [A / g] or more in the mass activity calculation method in the invention 29. The palladium core platinum shell fine particle colloid according to any one of Inventions 1 to 27.

The 31st invention (referred to as Invention 31) of the present invention made by developing Inventions 1 to 27 is a carrier-supported palladium core platinum shell fine particle produced by the method according to any one of Inventions 1 to 27. It is a catalyst.

In the 32nd invention of the present invention (referred to as Invention 32) developed by developing Inventions 1 to 27, the initial activity of the catalyst calculated by the mass activity calculation method in Invention 29 is 600 [A / g] or more. It is a palladium core platinum shell fine particle catalyst characterized by.

If the hydroxide ion concentration and the like are appropriately adjusted by using a suitable additive such as potassium hydroxide for the synthesis of the carbon-supported palladium core particles in the core-shell type fine particles of the carbon-supported palladium core platinum shell by the method found in the present invention. When the fine particles are catalyst fine particles, core-shell type fine particles of a carbon-supported palladium-core platinum shell having high catalytic performance and excellent durability can be provided at low cost.

It is a figure explaining the carrier-supported palladium core platinum shell fine particle manufacturing method of this invention. It is a figure explaining the transmission electron microscope image of the carbon-supported palladium core platinum shell fine particles produced in the process of an Example. It is a graph which compared the mass activity of the oxygen reduction catalyst synthesized in Example and Comparative Example. It is a figure explaining the transition of the maintenance rate of mass activity with respect to the number of potential cycles in the durability test of the carbon-supported palladium core platinum shell fine particles synthesized by the method of an Example.

1: Raw material salt, dispersant, carrier, potassium hydroxide dissolved and dispersed in ethylene glycol and pump to send it 2: Microwave in a resonator structure that traps the electric field of the microwave Reaction system 3: A reaction system in which a standing wave is formed by irradiating the reaction solution circulating in the reaction tube arranged there with a microwave to heat the reaction solution 3: The high temperature reaction solution immediately after the microwave heating is placed outside the reaction tube. Equipment for cooling from 4: Potassium hydroxide ethylene glycol solution for adjusting the hydroxide ion concentration at the time of forming the platinum shell layer and a pump system for sending the solution 5: Dissolving the raw material salt for forming the platinum shell layer Raw material solution and pump system 6a, 6b for feeding the solution: Step using a mixer 7: Microwave irradiation reaction system for forming a platinum shell 8: Recovery tank 9: Carbon-supported palladium core Platinum shell catalyst 9a: Carbon carrier 9b: Palladium core platinum shell catalyst 10a: The initial activity in the load response durability test of Example 1 was represented as 100%. Point 10b: The retention rate of mass activity after 5000 cycles in the load response durability test of Example 1 was represented. Point 10c: Representing the retention rate of mass activity after 37,000 cycles in the load response durability test of Example 1 Point 10d: Representing the initial activity in the load response durability test of Example 2 as 100% Point 10e: Implementation Point 10f showing the retention rate of mass activity after 5000 cycles in the load response durability test of Example 2: Point showing the retention rate of mass activity after 37,000 cycles in the load response durability test of Example 2.

Hereinafter, examples of embodiments of the invention according to the present invention will be described in detail with reference to the drawings. It should be noted that each figure used for explanation schematically shows the dimensions, shapes, arrangement relationships, etc. of each component to the extent that an example of the present invention can be understood. In addition, for the convenience of the description of the present invention, the enlargement ratio may be partially changed in the illustration, and the figure may not necessarily be similar to the actual product such as the examples. Further, in each figure, the same number is assigned to the same configuration, and duplicate description is omitted. Further, in the following description, the description of the method for producing the metal fine particles may also serve as the description of the metal fine particles and the device for producing the metal fine particles, and vice versa, as long as no misunderstanding occurs.

Taking catalyst fine particles as an example, it is well known that palladium core platinum shell fine particles exhibit an excellent catalytic effect. Therefore, since platinum is expensive, many people skilled in the art are making great efforts to reduce the amount of platinum used as much as possible, enhance the catalytic effect as much as possible, and make a high-quality and inexpensive catalyst. The current situation. Further, with respect to the carrier, it is desired that the carrier can be supported and the core can be synthesized at the same time from the time of synthesizing the core fine particles.

In the process of synthesizing palladium fine particles by the liquid phase method in the coexistence of a carrier, it is considered that nucleation of palladium fine particles is likely to occur in functional groups and defects on the carrier such as carbon black. Therefore, by adjusting the type, number, density, etc. of the functional groups present in the carrier and appropriately adjusting the reaction conditions such as hydrogen ion concentration, hydroxide ion concentration, palladium raw material concentration, temperature, etc. at the time of reaction, the carrier Palladium fine particles can be supported at the same time as synthesis with the desired particle size and density.

_{Palladium chloride (2) (PdCl 2} ), sodium tetrachloropalladium (2) acid (Na ₂ [PdCl ₄ ]), potassium tetrachloropalladium (2) acid (K ₂ [PdCl ₄ ]) are suitable as raw materials for palladium. ), Palladium tetrachloropalladium (2) ((NH ₄ ) [PdCl ₄ ]), Palladium acetate (2) (Pd (CH ₃ COOH) ₂ ), Palladium oxalate (2) (PdC ₂ O ₄ ), Nitrate Raw material selected from palladium (2) (Pd (NO ₃ ) ₂ ), palladium sulfate (2) (Pd (SO ₄ )), palladium acetylacetonate, tetraammine palladium (2) salt, dinitrodiammine palladium (2) Can be mentioned.

It is known that the palladium core platinum shell structure is highly active and highly durable. However, the size of the catalyst fine particles is several nm, and the number is enormous even in a lot, and it is required that almost all of the catalyst fine particles have the above-mentioned highly active and highly durable structure. To. For convenience, this is referred to as catalyst quality.

In replacement plating and electroless plating, it is more difficult to form a shell structure on core metal particles supported on a conductive carrier. Since the carrier is conductive, electrons may flow through the carrier and the oxidation reaction and the reduction reaction may occur at distant positions, and side reactions such as the formation of single particles of shell metal on the carrier may occur. ..

It seems that a process similar to plating is required to form core-shell metal fine particles having a uniform shell structure, but the existing plating method cannot be applied as it is. However, in order to grow the shell layer uniformly over the entire surface of the fine particles without any side reaction in the particles or between the particles, the supply and reactivity of the shell raw material must be as uniform as possible.

Regarding the reactivity of shell layer formation, as much as possible, it is possible to proceed only the reaction in which the platinum shell layer is formed without pinholes on the surface of the palladium core particles, and control so that the reaction does not proceed after the shell layer formation is completed. desirable.
There is also a view that forming the shell layer as uniformly as possible is an important factor in controlling the characteristics of the core-shell type fine particles.
Uniformly form the shell layer, make the shell layer 5 or less, cover 50% or more of the core surface with the shell layer, cover 70% or more with the shell layer, cover 90% or more with the shell layer. It is also important to make a selection according to the application and purpose.
It is preferable in terms of characteristics that the shell layer is 5 layers or less and 50% or more of the core surface is covered with the shell layer, and it is further preferable to cover 90% or more with the shell layer.

For example, in order to suppress an unnecessary side reaction pathway, it is essential that the platinum salt is precipitated as a zero-valent metal only when it comes into contact with the palladium core particles or the surface of the platinum shell layer on which the palladium core particles are used as a base. In other words, it is necessary to suppress reactions such as extracting electrons from surrounding chemical species to form metal nuclei even though they are not in contact with the underlying core particles, or forming an excess shell layer on the existing platinum shell layer. It doesn't become. Also, the palladium (2) ions liberated in the solvent by substitution plating must not be reduced again in any way.

In order to realize such reaction control for all the palladium core particles and the platinum shell raw material salt present in the reaction solution, the reaction conditions tend to be non-uniform in the method of adding various kinds of additives. In particular, in PEFC using hydrogen as a fuel, adhesion of organic particles to the catalyst surface may reduce the activity, and a careful cleaning step is required.

Here, by synthesizing the core particles using the liquid phase reduction method, subsequent modifications such as shell formation become easy, but if the batch method is used to increase the productivity, the heating and stirring are non-uniform. As a result, nucleation tends to be non-uniform, causing adverse effects such as inconsistent particle sizes. Most of the currently known metal fine particles with uniform particle size are synthesized on a laboratory scale, and it is difficult to increase productivity without sacrificing quality in producing metal fine particles. Will also be proved.

As a means for heating the reaction solution in the liquid phase reduction method, the reaction solution is irradiated with microwaves as in the invention described in Patent Document 5. That is, here, by using a semiconductor oscillator and a microwave resonance cavity and arranging the reaction tube of the continuous flow system at the position where the standing wave of the electric field has the highest intensity, the chemistry that does not impair the uniformity by rapid heating. Heating for reaction is performed. Although not narrowly limited to this, the single mode heating method, which is a method of generating a single electromagnetic field mode in a cavity in which the dimensions and the resonance frequency are matched, is particularly preferable, and the reaction is sufficiently promoted by microwave heating for a short time. It is extremely useful when completing with. In addition, the non-uniformity of heating and reaction, which is a problem in the batch method, can be remarkably improved.

The effect of microwave irradiation varies depending on the frequency of the microwave irradiated to the reaction solution, the material of the reaction solution, the inner diameter of the reaction tube through which the reaction solution is circulated, the material of the reaction tube, and the like. In the case of Japan, various microwave frequencies such as 5.8 GHz and 0.9 GHz can be used in addition to the frequencies often used in microwave ovens (frequency band 2.4 to 2.5 GHz). In the study of the present invention, the frequency of 2.45 GHz was mainly used, and other frequency bands such as 5.8 GHz and 0.9 GHz were also used, although not narrowly limited thereto.

For example, when using a microwave oven in the frequency band 2.4 to 2.5 GHz, consider that any frequency in the frequency band 2.4 to 2.5 GHz can be within the standard. Therefore, the inner diameter of the reaction tube is not within 2.9 mm, which is the optimum dimension at 2.45 GHz, and the absorption intensity of standing waves is within the predetermined range even at 2.5 GHz, which is the highest frequency in the standard range. Therefore, it is preferable to set the inner diameter of the reaction tube at 2.5 GHz to an optimum value. From this point of view, the inner diameter of the reaction tube was set to 2.9 ÷ 2.5 × 2.45 = 2.8 mm or less when the microwave irradiation conditions were particularly strictly controlled.

Taking these things into consideration, the experiment of selecting a carrier was repeated using many materials and additives which have conductivity and are considered to be suitable for a carrier carrying palladium (Pd). As a result, we found the possibility of synthesizing core-shell fine particles of palladium-gore platinum shell by using carbon as the carrier and realizing a catalyst of good quality, and the following studies were conducted.

When synthesizing a palladium core platinum shell as catalyst fine particles, the method of synthesizing the fine particles and then supporting the fine particles has the difficulty that uniform support is difficult and there is a loss of precious metal fine particles, and the step of removing the dispersant is required. .. When the catalyst fine particles are mixed and supported with a carrier, it is difficult to adsorb and support the catalyst fine particles on the surface of the carbon carrier. On the other hand, if the catalyst fine particles are added in excess, aggregation occurs on the carbon carrier, which is effectively used. The noble metal raw material does not function effectively as a catalyst due to the formation of a catalyst surface that cannot be supported or the formation of free catalyst particles that are not supported. In PEFC, polymer dispersants and organic compounds that are not involved in the battery reaction adsorb to the surface of the catalyst and block active sites, or become carbon monoxide and cause poisoning of the catalyst, resulting in battery malfunction. It is necessary to remove such substances as much as possible because they cause causes. However, when carbon having a high surface area is used as a carrier, compounds having a hydrophobic group such as a polymer dispersant and a surfactant are easily adsorbed on the carbon carrier and difficult to remove. In order to completely remove it, it is necessary to repeat careful washing and firing in an inert atmosphere, which increases the number of steps and increases the cost. From this point of view, if the method of supporting the noble metal fine particles on the carbon carrier by microwave heating is used, the metal fine particle catalyst can be uniformly supported on the carrier, and if the conditions are met, almost all the noble metal raw materials can be converted as the catalyst. Yes, it is considered to be very useful.

By using a solvent that absorbs microwaves well, heating can be performed more rapidly and uniformly than normal heating of heaters, oil baths, etc., which has advantages such as completion of reaction in a short time and effective use of energy. Available.

Glycol-based solvents have a high boiling point and viscosity, dissolve various substances, are relatively safe for the human body, easily absorb microwaves, and often have a weak reducing ability, and are suitable for the technology of this patent. It is a solvent group. Specifically, there are ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, etc., but the present invention is not limited thereto. Absent. Further, polyols such as glycerin, glycol ethers such as ethylene glycol monobutyl ether, diethylene glycol monobutyl ether and diethylene glycol dimethyl ether, glycol esters and the like can be added to the glycol solvent as needed.

From these viewpoints, it is not narrowly limited to this, but in one of the embodiments of the present invention, it is a typical solvent that absorbs microwaves well, and it is heated to near its boiling point (196 ° C.) in a short time. I decided to use ethylene glycol that can be used.

When an ionomer for a fuel cell is used as a carbon dispersant, it is also important that it does not need to be completely removed by refining, firing, or the like. Polymer dispersants such as polyvinylpyrrolidone are widely used in the synthesis of metal nanoparticles, but these dispersants improve the dispersibility of metal nanoparticles and carbon, but are completely adsorbed on the surface of fine particles. It has been found that it is difficult to remove the polymer dispersant, and it is also known that the polymer dispersant remaining on the surface of the catalyst significantly impairs the catalytic performance. Since the ionomer for a fuel cell is one of the components of the battery added in the battery manufacturing process for the transfer of protons to the catalyst surface, even if a small amount remains, it does not significantly affect the fuel cell performance.

Further, in the embodiment of the present invention, metal nanoparticles are synthesized by reducing the raw metal salt. This reaction can be expressed by a chemical formula.
M ⁺ (metal ion) + e ^- (electron is supplied from the reducing agent) → M ⁰ (metal) (1)
Will be.
Metal fine particles are formed by gathering about several thousand zero-valent metals in the right section.

Various synthetic methods can be considered depending on what is used as the raw material for the above metal ions and the reducing agent for supplying electrons, but in the embodiment of the present invention, sodium tetrachloropalladium and chloride are used as the metal ions. Platinum acid was used, and ethylene glycol was used as a reducing agent.

Ethylene glycol becomes reducing when heated, and in the chemical formula,
Ethylene glycol → e ⁻ + ethylene glycol oxide product + hydrogen ion ・ ・ ・ (2)
It is expressed as.
By rapidly heating ethylene glycol containing a metal raw material salt with microwaves, a large amount of electrons are rapidly supplied from ethylene glycol, and the raw material metal salt is rapidly reduced, so that fine particles having a small particle size can be synthesized. ..

Gentle heating of ethylene glycol slows the nucleation and crystal growth of metal particles and tends to produce large nano or micron particles.

In equation (2), hydrogen ions are released along with the supply of electrons from ethylene glycol, but when these are accumulated, the reaction rate decreases and it becomes difficult to form fine particles with a small particle size. However, by adding a compound containing hydroxide ions, it is possible to suppress an increase in hydrogen ion concentration and maintain a high reaction rate, and as a result, nanoparticles with a small particle size are synthesized. be able to.

In the embodiment of the present invention, palladium core particles having a small particle size are synthesized by microwave heating, and for the platinum shell, platinum chloride is slowly reacted by microwave heating or at room temperature. It suppresses the formation of single fine particles and forms a shell of uniform thickness. In these cases, potassium hydroxide is used as an accelerator for the reduction reaction. By adding potassium hydroxide, the reduction reaction at high temperature becomes faster, and the reaction proceeds slowly even at room temperature, enabling delicate control of reactivity. Therefore, a shell having a uniform thickness can be formed, but by using potassium hydroxide in particular, the shell can be formed with higher quality.

Mines can be considered as compounds that suppress the increase in hydrogen ion concentration, but since amines have a strong tendency to form complexes with palladium raw materials and platinum raw materials and to be adsorbed on the surface of the generated fine particles, the reactivity of these raw materials and The state of particle growth changes in a complicated manner. Metal hydroxides are also considered sources of hydroxide ions, but must be well soluble in ethylene glycol. As described in detail in the present invention, as a result of many experiments, the inventor of the present invention uses potassium hydroxide as a hydroxide for the synthesis of palladium core particles in the core shell type catalyst fine particles of a carbon-supported palladium core platinum shell. Is particularly preferable, and the conditions have been found.
In the embodiment of the present invention, the above reaction is carried out in the coexistence of a carbon carrier. In this case, the palladium nanoparticles are generated in a state of being attached to the carbon, the platinum shell also grows on the surface of the palladium fine particles on the carbon, and the core shell structure is formed on the carbon carrier.

In Patent Document 5, palladium core particles and platinum shell particles are synthesized in an environment in which a carbon carrier does not coexist, but in the coexistence of a carbon carrier, carbon aggregation, blockage in a carbon reaction tube, and on the carrier of palladium core particles are performed. Unfavorable reaction pathways for the catalyst can occur, such as non-uniform distribution to the catalyst and the formation of platinum single particles on carbon. Therefore, there is known a production method of the present invention capable of synthesizing core particles and supporting them on carbon at the same time in a continuous reaction system, and then forming a uniform shell layer on the core particles supported on carbon. There wasn't.

The present inventors have found that the concentration of hydroxide ions in the reaction and the presence of potassium ions as counterions thereof are extremely important in the formation of the palladium core particles and the subsequent platinum shell. .. Then, as a result of a great deal of trial and error, a continuous synthesis method in which the reaction solution is irradiated with microwaves while suppressing the undesired reaction pathway and flowing the reaction solution is used to obtain high-performance carbon-supported palladium-core platinum-shell fine particles. The process of obtaining the catalyst could be completed.

Particularly big issues in producing carrier-supported palladium-core platinum-shell fine particles, for example, carbon-supported palladium-core platinum-shell fine particles for catalysts for batteries, are cost reduction, performance, and quality improvement. A synthetic method that has as high a catalytic performance as possible, has excellent durability, and can be manufactured at low cost is desired.

As a result of many experiments, it was found that it is effective to use an alkali metal hydroxide as an additive for the reaction in order to effectively proceed with the reaction for solving the problem of the present invention. We decided to investigate the relationship between the type of oxide and the quality of the catalyst in detail.

Specifically, lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide and the like can be used as the alkali metal hydroxide. Further, for the purpose of increasing the hydroxide ions involved in the reaction, basic substances such as amines and guanidines can be added as long as they do not induce an undesired side reaction. Specifically, ammonia, 2-aminoethanol, diethanolamine, triethanolamine, choline, butylamine, taurine, glucosamine, trishydroxymethylaminomethane, pyridine, triethylamine, guanidine, tetramethylguanidine, hexamethylenetetramine, N, N- There are diisopropylethylamine, triisopropylamine, diazabicycloundecene, diazabicyclononen, triethylenediamine and the like.

Although the mechanism is not clear, as a result of experiments, potassium hydroxide has an important effect on improving catalyst quality if the concentration to be added is appropriately selected among alkali metal hydroxides as additives for promoting the reaction. I found out that I would do it and decided to investigate in detail.

Since it is important to adjust the potassium hydroxide concentration in the reaction solution, it is considered that potassium ions and hydroxide ions in the reaction system play important roles. Substances that produce these two species, such as potassium acetate, potassium carbonate, potassium phosphate, etc., and mixtures of substances that produce these two species, such as sodium hydroxide and potassium chloride, but also potassium ions and hydroxide. It is believed that the above-mentioned favorable effects are produced in the formation of the potassium shell because the product ions are generated. However, in the coexistence of a carrier, ions other than potassium ion and hydroxide ion may cause aggregation of the carrier, and potassium hydroxide was the most suitable additive in a reaction system using ethylene glycol as a solvent.

Potassium ions are thought to have the effect of depositing [PtCl4] 2-ions and / or [PtCl6] 2-ions in ethylene glycol, and may suppress the formation of free platinum particles. Further, while the hydroxide ion is adsorbed on the surface of the palladium core particles, it also interacts with the alkali metal ion, and the above-mentioned [PtCl4] 2-ion and / or [PtCl6] 2-ion is placed on the palladium particles instead of on the carrier. It seems to have the effect of selectively depositing.

Sodium ions also strongly attract hydroxide ions and are present on the surface of palladium, but their adsorption is strong and tends to inhibit uniform shell formation, and Na2 [PtCl6] is soluble in ethylene glycol. It is considered difficult to form a high-quality platinum shell with sodium ions alone because of the high concentration and difficulty in forming a deposited structure of the platinum raw material. On the other hand, potassium ions are not as strong as sodium ions in attracting hydroxide ions, so it is considered that the effect of inhibiting shell formation is not as strong as that of sodium ions. In the shell forming step, when the reaction was carried out slowly at room temperature without using microwave heating, there was a remarkable difference in the activity of the catalyst between the case of using sodium hydroxide and the case of using potassium hydroxide.

Even when sodium hydroxide is used instead of potassium hydroxide, if the platinum shell is formed by selecting the coexisting hydroxide ion concentration and temperature under favorable conditions and using the microwave continuous heating method, the shell is slowly formed at room temperature. It was also found that catalyst particles having higher mass activity than when formed can be synthesized.

By adjusting the potassium hydroxide concentration, in the platinum shell forming step, a deposit composed of platinum chloride ion and potassium ion is adsorbed on the carrier-supported palladium core particles with moderate strength and rapidly heated by microwaves. As a result, the shell forming reaction proceeds only on the surface of the palladium core particles, and there is a possibility that a platinum shell having a uniform thickness or as close as possible to the same thickness is preferably formed.

It is preferable that the shell layer of fine particles such as nanoparticles covers the core particles in a complete layer, but the actual synthesized shell layer covers the core particles in a perfect layer and the core particles. There are many forms, such as when it is partially attached to the surface. Further, as a matter of course, it is no wonder that the shell layer is not arranged on the portion of the core particles supported on the carrier. In the production of core-shell type fine particles, those in which at least a part of the performance of the intended use in the application is improved are referred to as core-shell type fine particles in the present invention.

By using the microwave continuous heating method, the present inventors have also solved the trade-offs of maintaining quality within lots, suppressing variation between lots, and simplifying the process. Rapid heating by microwave heating enables rapid heating as compared with normal heating using an oil bath or steam, and is used in various organic synthesis and inorganic synthesis processes. In addition, if the volume of the object to be heated is reduced to some extent, the energy of the electric field can be concentrated to further increase the heating rate, and only the solvent can be heated uniformly. Therefore, the timing of nucleation and growth of nanoparticles and the like is important. Suitable for reaction. In addition, by constructing the heating process using microwaves by a continuous method using a flow path, it was possible to eliminate variations between lots and trade-offs in productivity. Microwave heating can also be performed by the batch method, but if the volume of the object to be heated is increased in order to increase productivity, the uniformity is impaired and the quality within the lot varies. On the other hand, in the continuous microwave irradiation method, the synthetic product is always obtained under the same conditions, so that automation is easy. Further, even if a trouble occurs, it is only necessary to switch the flow path to separate defective products, and unlike the batch method, a situation in which the entire tank is wasted of precious precious metal raw materials does not occur.

In addition, the advantage of connecting the palladium fine particle forming step and the subsequent platinum shell forming step with a continuous reaction tube to form a continuous method is also important. Immediately after synthesis, it is thought that coexisting hydroxide ions and chloride ions are adsorbed on the surface of the palladium fine particles, but if left in the air, an oxide layer may be formed on the surface or sulfur may be formed from the outside. It is considered that the surface is contaminated due to strong adsorption of impurity atoms such as. Such surface contamination is considered to hinder the formation of a uniform platinum-coated structure, and if the two steps are separated by a batch method or the like, it causes variation. Therefore, it is ideal to coat the palladium fine particles with platinum atoms as quickly as possible, and the synthesis by the continuous method satisfies this requirement.

In the field of plating, it is widely practiced to use additives to suppress unwanted side reactions and abnormal growth of precipitated metal layers. Considering that the same method can be applied to form a platinum shell on palladium core particles in the presence of a carrier, the inventors repeated a large number of experiments and added additives and reaction conditions capable of forming a high-quality platinum shell layer. However, no effective additive could be found in the reaction at least at room temperature. It is thought that most of the cause was that the additive was strongly adsorbed on the surface of the palladium core particles and inhibited the formation of the platinum shell. Even if it is heated to allow the reaction to proceed, if it is heated at a high temperature for a long time in the presence of a carrier, the palladium core particles will aggregate on the carrier and the surface area of the catalyst will decrease. However, it was difficult to find the optimum conditions when a reaction-suppressing additive was used.

However, it has been found that a high-quality platinum shell can be formed even in the presence of reaction-suppressing additives by appropriately selecting the reaction conditions and rapidly heating with microwaves in a short time. .. In the microwave continuous heating method, in which the core synthesis step and the shell synthesis step are continued, and microwave irradiation is performed in both steps, the raw material liquid can be uniformly heated only for the time required for forming the platinum shell. , It has become possible to form a shell in which agglomeration of particles on a carrier is significantly suppressed. Additives are thought to play an important role in controlling the shape, surface irregularities, and crystal planes of metal fine particle catalysts, and may also be an important control factor when forming core-shell structures with binary metal species. There is. For this reason, the microwave continuous method is a very excellent technique in that it realizes only the effect of the reaction-suppressing additive, suppresses side reactions, and enables the production of a more highly controlled metal fine particle catalyst. ..

When the two-step reaction is carried out by the microwave continuous heating method, there is a problem that the residue of the first step does not hinder the second step in the second step. The residue in the palladium fine particle synthesis step was overcome by selecting raw materials and reaction conditions that do not adversely affect the platinum shell forming step, and using the residue for deposition such as the use of potassium hydroxide.

In performing the microwave continuous heating method in the coexistence of a carrier, a pump capable of transporting the slurry without pulsation is required. Appropriate use of MONO pumps, precision diaphragm pumps, etc. has also been found to be useful in conductive carbon carriers, which are most commonly used as fuel cell catalyst carriers. By connecting the raw material and the carrier slurry to a pump and continuously heating them with microwaves, we were able to create an ideal process in which a high-quality catalyst slurry supported can be produced.

By performing the reaction of forming and supporting the palladium particles in the coexistence of the carrier and then the reaction of forming the platinum shell layer, it was possible to significantly reduce the amount of platinum used and improve the productivity. As described above, the method of adsorbing the catalyst particles on the carrier after the synthesis of the catalyst particles is not suitable for actual production due to the poor support rate and the non-uniformity of the support. Moreover, in the case of a catalyst using a noble metal as in the present invention, a fine particle catalyst such as a core-shell structure, which requires a lot of time and effort, is lost at the final stage of synthesis, resulting in an inefficient process. After extensive experiments and studies, the present inventors have formed a palladium-platinum composite catalyst on the carrier without using any polymer or surfactant that is not contained in the final product and without intervening the purification process in the middle. I found a way. Only the process of removing water-soluble salts and solvent residues by washing with water is performed after the synthesis. No repeated cleaning to remove the dispersant or firing to remove organic matter is required.

According to electron microscopic observation, a small amount of platinum single particles may be observed, but the number can be greatly reduced by appropriately selecting the synthesis conditions.

In the microwave continuous heating method, the reaction tube can be thickened and scaled up within the range where microwaves can be uniformly heated and rapidly heated. In the batch method, there are various items to be examined such as heat transfer and stirring when the reaction is carried out in a large tank, etc. by scale-up, but in the microwave continuous method, it is relatively easy to produce by controlling the input energy and residence time. The amount can be increased.

The above method can be applied not only to the formation of a platinum shell structure using palladium fine particles as a base, but also to uniformly form a platinum thin film having a thickness of several nm or less on the palladium thin film as a base. In addition, the method of depositing the platinum raw material salt is applied not only to the carbon carrier but also to form a platinum thin film on various substrates such as ceramics and a substrate in which carbon, metal, and ceramics are combined. be able to. Therefore, this method is extremely useful in that it can be widely applied not only to the formation of a palladium core platinum shell structure but also to the formation of platinum composite fine particles having a platinum thin film structure and a platinum composite structure.

As described above, various trade-offs related to production that have existed up to now could be solved by an appropriate combination of the elemental technologies of deposition, microwave continuous method, and synthesis in the coexistence of carriers of the present invention. INDUSTRIAL APPLICABILITY According to the present invention, palladium-platinum composite fine particles having both quality, cost and productivity can be produced, and it can be said that this is a great progress toward widespread practical use of polymer electrolyte fuel cells.

An example of an embodiment of the present invention based on the above will be specifically described below.

FIG. 1 is a diagram schematically showing a configuration of a carbon-supported palladium-core platinum-shell fine particle manufacturing apparatus as an example of an embodiment of the present invention.

In FIG. 1, reference numeral 1 is composed of a raw material salt of palladium core particles, an ionomer, a carbon carrier, a reaction raw material solution in which a potassium hydroxide raw material is dissolved and dispersed in a solvent, and a pump for feeding the reaction raw material solution. Specifically, a reaction raw material solution in which potassium tetrachloropalladium (2) acid (K2PdCl4), solvent (registered trademark), Vulcan (registered trademark) XC72, potassium hydroxide aqueous solution, and EG (ethylene glycol) are mixed is fed by a liquid feed pump. The process of sending liquid to the next process is shown.

Reference numerals 2 and 7 are resonator structures for confining the electric field of microwaves and irradiating and heating the liquid in the reaction tube. Specifically, the reaction liquid prepared and sent in the reaction raw material liquid preparation process. Is a resonator structure such as a cavity that circulates a microwave in a reaction tube that passes through the inside of the microwave resonator structure and irradiates the reaction raw material liquid that flows in the reaction tube with microwaves, and constitutes a microwave irradiation system. Reference numeral 3 is a device for cooling or retaining heat of the reaction solution heated by reference numeral 2, and a double tube or a Peltier element capable of flowing a refrigerant can be used.

Reference numeral 4 is composed of a potassium hydroxide solution and a pump that feeds the solution, and reference numeral 6a is a potassium hydroxide solution fed by reference numeral 4 and a carbon-supported palladium nanoproduced by reference numeral 2 and cooled by reference numeral 3. The step of mixing the particle dispersion liquid with a mixer is shown.

Reference numeral 5 is composed of a solution in which the raw material salt for forming the platinum shell layer is dissolved and a pump for feeding the solution, and reference numeral 6b is a dispersion liquid in which the platinum raw material solution sent by reference numeral 5 and the raw material solution of reference numeral 6a are mixed. The process of mixing and with a mixer is shown. The carbon-supported palladium particle dispersion mixed with the platinum raw material solution is heated by microwave irradiation in the cavity of reference numeral 7, and a platinum shell is formed. Reference numeral 8 is a tank for recovering the produced carbon-supported palladium-core platinum-shell particles. When the platinum shell formation is allowed to proceed slowly at room temperature, it is also possible to carry out the shell formation reaction in the tank of reference numeral 8 without heating in reference numeral 7.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not narrowly limited thereto.

(Example 1)
When potassium hydroxide is added and microwave heating is used to form the shell.
Vulcan® XC72 is mixed with ethylene glycol so as to be 0.1% by weight and Nafion® (DE520 CS type) is 0.03%, and ultrasonic waves are applied to make Vulcan XC72 a uniform dispersion. To be. Potassium tetrachloropalladium (2) acid was added to this dispersion so as to be 2 mM and potassium hydroxide was added to 13 mM to completely dissolve the dispersion, and this was used as a reaction raw material solution. This reaction raw material liquid is sent by a pump that can handle the carbon dispersion liquid.

As a result of repeated detailed experiments by the present inventors, it is desirable to add potassium hydroxide to the reaction raw material solution in an amount of 4 to 7 times the amount of the substance of potassium tetrachloropalladium (2) to be added. Clarified. If the hydroxide ion concentration is low, nucleation is slowed down and the particle size becomes large, and unreacted palladium ions may remain. If the hydroxide ion concentration is high, the reduction rate is too fast and agglomerates of free particles and palladium nanoparticles that are not supported are generated.

The reaction raw material solution was sent in a PFA (Perfluoroalcoxy alkane) reaction tube having an inner diameter of 2 mm at a flow rate of 6 ml / min and heated at 100 ° C. The reaction tube was arranged along the cylindrical central axis of a microwave cavity having a cylindrical space having an inner diameter of 90 mm and a height of 10 cm. The cavity was heated by irradiating the cavity with a microwave having a frequency at which a standing wave in TM010 mode was formed, and the temperature of the reaction raw material solution was measured at the center of the reaction tube by a radiation thermometer. Further, the frequency at which the standing wave of the TM010 mode is formed changes depending on the temperature of the reaction raw material liquid, but the frequency of the irradiated microwave is adjusted so as to always match the frequency. The frequency range at this time was 2.45 GHz.

To the carbon-supported palladium particle dispersion synthesized by the above method, the potassium hydroxide ethylene glycol solution required for the platinum shell formation reaction was added by finely adjusting the concentration by the mixer (mixer in the pipe junction flow path) of 6a. It was done. In this example, a 0.5 M potassium hydroxide ethylene glycol solution was added so that the potassium concentration increased by 3 mM.

The carbon-supported palladium particle dispersion synthesized by the above method is added with a potassium hydroxide ethylene glycol solution, and then 100 mM with a 6b mixer so that the molar ratio of palladium to platinum in the mixed solution is 1: 1. Chloroplatinic acid (4) It was mixed with an ethylene glycol solution.

Since the hydroxide ion added in the step indicated by reference numeral 4 in FIG. 1 reacts with the hydrogen ion generated from the platinum raw material added in the step indicated by reference numeral 5, the amount of the added hydroxide ion is all the shell formation reaction. Is not involved in. However, it is considered that the free hydroxide ions still remaining after the neutralization reaction, the hydroxide ions forming a complex with the platinum ions, and the hydroxide ions adsorbed on the surface of the palladium particles are involved in the shell formation reaction. Be done. As a result of repeated detailed experiments, the inventors found that the concentration of these hydroxide ions was 2 to 6 times the amount of substance of hexachloroplatinum (4) acid ion, which is a precursor of platinum shell formation as a raw material. It was clarified that it is desirable to be a degree. If the hydroxide concentration in the shell formation reaction is low, the reaction rate slows down and the platinum raw material becomes unreacted. If the hydroxide concentration is too high, platinum is generated as particles instead of shells on the carbon carrier or palladium core surface. Or, free platinum particles are likely to be produced as a by-product. When the platinum raw material salt is a salt obtained by neutralizing chloroplatinic acid, when the palladium core particles are formed by another method, or when the palladium core particles are purified before the shell formation reaction, the hydroxide ion is described above. It is necessary to adjust the concentration of sodium hydroxide to be added so as to be within the range of.

The carbon-supported palladium particle dispersion and the ethylene glycol chloride (4) acid solution mixed with the mixer of reference numeral 6b are sent to a reaction tube arranged in the microwave cavity of 7 at a flow rate of 7 ml / min to reach 80 ° C. Was heated. The synthesized carbon-supported palladium-core platinum-shell colloid was recovered in 8 tanks.

(Example 2)
When potassium hydroxide is added and microwave heating is not used for shell formation.
Carbon-supported palladium particles were synthesized in the same manner as in Example 1, mixed with a potassium hydroxide ethylene glycol solution and an ethylene glycol chloride (4) acid solution, and then the mixed solution was collected in a recovery container without heating at 7. , It was left at room temperature for 72 hours for complete reaction at room temperature.

(Example 3)
When sodium hydroxide is added and microwave heating is used to form the shell.
Palladium core particles were synthesized and a platinum shell was formed by using sodium hydroxide instead of potassium hydroxide in Example 1 and using sodium tetrachloropalladium (2) instead of potassium tetrachloropalladium (2). .. Specifically, to prepare the reaction raw material solution of 1, a 5 M aqueous sodium hydroxide solution was added so as to be 13 mM. In No. 4, a 0.5 M aqueous sodium hydroxide solution was added so as to increase the sodium concentration by 3 mM, and the mixture was mixed with a mixer of 6a. Except for the above, the same raw material concentration and heat treatment as in Example 1 were carried out, and the product was recovered.

(Example 4)
Vulcan® XC72 is mixed with ethylene glycol to 0.1% by weight and Nafion® (DE520CS) to 0.03%, and ultrasonic waves are applied to make Vulcan XC72 a uniform dispersion. To. Potassium tetrachloropalladium (2) acid was added to this dispersion to 3 mM, potassium hydroxide to 20 mM, and monoethanolamine to 6 mM to completely dissolve the dispersion, which was used as a reaction raw material solution. After flowing the reaction raw material solution and heating with microwaves in the same manner as in Example 1, the concentration after mixing the ethylene glycol solution of hexachloroplatinic acid (4) acid and monoethanolamine in reference numeral 5 is platinum (4) acid chloride. 2 mM and monoethanolamine were mixed at reference numeral 6b so as to be 24 mM, and heated at reference numeral 7 at 160 ° C.

(Comparative Example 1)
When carbon-supported platinum particles are synthesized by the microwave continuous method.
As Comparative Example 1, a carbon-supported platinum catalyst was synthesized by a continuous microwave method, and the catalytic activity of the oxygen reduction reaction was compared. The manufacturing method will be described below. Vulcan® XC72 as a carbon carrier and Nafion® (DE520 CS type) as a dispersant were mixed with ethylene glycol and sufficiently irradiated with ultrasonic waves to disperse carbon well. Hexachloroplatinum (4) ethylene glycol solution and potassium hydroxide ethylene glycol solution are added to the dispersion, and finally carbon is 0.1 g / L, Nafion (registered trademark) is 0.03 g / L, and hexachloroplatinum (2). ) The raw material solution was prepared so that the concentration of acid was 2 mM and the concentration of potassium hydroxide was 20 mM. The raw material liquid was flown through a PFA reaction tube having an inner diameter of 2 mm arranged on the central axis of the cylinder of the microwave cavity at a flow rate of 2 ml / min, and heated so that the temperature of the raw material liquid became 85 ° C. ..

(Comparative Example 2)
When sodium hydroxide is added and microwave heating is not used to form the shell.
Carbon-supported palladium core particles were synthesized in the same manner as in Example 3 except that the microwave heat treatment was not performed in No. 7, and mixed with an aqueous sodium hydroxide solution and a platinum (4) ethylene glycol solution. The shell formation reaction was carried out by leaving it in a recovery container at room temperature for 72 hours.

(Comparative Example 3)
When a highly active catalyst cannot be obtained by adding sodium hydroxide and irradiating with microwaves.
Vulcan® XC72 is mixed with ethylene glycol to 0.1% by weight and Nafion® (DE520CS) to 0.03%, and ultrasonic waves are applied to make Vulcan XC72 a uniform dispersion. To. Sodium tetrachloropalladium (2) acid was added to this dispersion so as to be 3 mM and sodium hydroxide was added to 20 mM to completely dissolve the dispersion, and this was used as a reaction raw material solution. This reaction raw material liquid was sent by a pump capable of handling a carbon dispersion liquid, and heated at a flow velocity of 6 ml / min and 100 ° C. in a microwave cavity of reference numeral 2 in the same manner as in Example 1. Subsequently, in reference numeral 5, a 100 mM chloroplatinic acid (4) ethylene glycol solution was mixed by a mixer of reference numeral 6b so that the molar ratio of palladium to platinum in the mixed solution was 3: 2. Next, heating was performed in the microwave cavity of reference numeral 7 at 130 ° C. and a flow rate of 7 ml / min.

The formed carbon-supported palladium-core platinum shell particles and carbon-supported platinum particles are purified by centrifugation, and TEM (transmission electron microscopy) and STEM (scanning electron microscopy) are used using an electron microscope (JEM-2200FS manufactured by JEOL Ltd.). Observation by electron microscopy) and analysis by EDS (energy dispersive X-ray analysis) were performed.

Measurement and loading of oxygen reduction catalytic activity with reference to the standard method proposed by the FCCJ (Fuel Cell Practical Use Promotion Council) (the method described in "Proposals for goals, R & D issues and evaluation methods for solid high-division fuel cells") A response potential cycle endurance test was carried out, and the catalysts of Examples and Comparative Examples were compared.
The detailed method will be described below.

The catalyst particles obtained in the above Examples and Comparative Examples were repeatedly purified by centrifugation to remove ethylene glycol and water-soluble salts, and finally had a carbon concentration of 0.0123% by weight and Nafion®. ) A catalyst ink having a concentration of 0.0125% by weight was prepared. As the solvent of the catalyst ink, a mixed solvent of water and IPA (isopropanol) (weight ratio 3: 1) was used. 20 mg of this catalyst ink was applied to a polished glassy carbon rotating electrode having a diameter of 5 mm, dried, and used for electrochemical measurement. A 0.1 M perchloric acid was used as the electrolytic solution, and a reversible hydrogen electrode was used as a reference electrode. The surface of the catalyst is cleaned by potential scanning in the range of 0.05 to 1.2 V (hereinafter, the potential value is expressed with reference to the reversible hydrogen electrode) in an electrolytic cell in which oxygen is expelled by bubbling 3 L / min of nitrogen. Then, the electrochemically active surface area was measured from the shape of the hydrogen adsorption / desorption peak. Subsequently, oxygen was dissolved in the electrolytic solution by bubbling with 3 L / min of oxygen, and the rotating electrode was rotated at 1600 rpm to perform convection voltammetry, and the oxygen reduction activity was measured. The scanning speed was 20 mV / sec from the low potential side to the high potential side, the value of the oxygen reduction current at 0.9 V was recorded, and the oxygen reduction activity of the catalyst was produced by the Koutecky-Levich equation. The temperature of the electrolytic solution at the time of activity measurement was 25 ° C. The oxygen reduction activity was calculated in the form of an oxygen reduction current (mass activity) per weight of platinum used as a raw material.
The unit of mass activity is gram [A / g] per ampere. However, in Example 4, platinum quantified from the results of EDS analysis after purification by centrifugation was used in the calculation of mass activity.
The flow rate of nitrogen and oxygen gas and the setting conditions of the sample in the bubbling with nitrogen and the bubbling with oxygen can be appropriately changed depending on the purpose of the sample test, etc., but as a guideline for the test result, as an example. As an example of comparing the performance of the fine particles of the present invention under the above conditions, the initial activity of the catalyst calculated by the mass activity calculation method of the fine particles of the present invention is 500 [A / g] or more. It was confirmed that 600 [A / g] or more can be achieved by setting more preferable production conditions, and 700 [A / g] or more can be achieved by setting particularly preferable conditions.

The potential cycle in the load response durability test is a square wave of 0.6 V for 3 seconds and 1.0 V for 3 seconds as one cycle using the above electrolytic solution and rotating electrode, and nitrogen is bubbled and saturated in the electrolytic solution. Under the above conditions, potentials of 5,000 and 37,000 cycles were applied at 20 ° C., and the surface area and oxygen reduction activity were measured before and after the potential cycle by the same method as described above.

FIG. 2 is an observation image of the carbon-supported palladium-core platinum-shell catalyst synthesized by the method of Example 1 by STEM. The carbon carrier 9a and the palladium-core platinum-shell catalyst fine particles 9b supported therein constitute the carbon-supported palladium-core platinum-shell catalyst synthesized in Example 1. As illustrated by reference numeral 9b, particles having a diameter of 3 to 4 nm are supported substantially uniformly on the carbon carrier. Moreover, according to the result of EDS, the distributions of palladium and platinum were uniform and consistent over a wide range, and the ratio was almost the same as the ratio of the charged amount at the time of synthesis. From this, it can be said that the synthesis method proposed by the present inventors is used so as to significantly reduce the waste of precious metals, and the high surface area required for the oxygen reduction catalyst can be achieved.

FIG. 3 is a graph comparing the mass activity of the oxygen reduction catalyst before the durability test of Examples and Comparative Examples. The mass activity values of Examples 1, 2, 3 and 4 are 696, 643, 548 and 637 [A / g], respectively, and the mass activity values of Comparative Examples 1, 2 and 3 are 241, 394 and 100 [A, respectively. / G]. The catalyst synthesized by the method of Example had several times the activity of the carbon-supported platinum catalyst synthesized by the microwave of Comparative Example 1, and potassium hydroxide and microwave heating were not used for shell formation. The activity was higher than that of the carbon-supported palladium-core platinum-shell catalyst of Comparative Example 2. From these facts, it can be seen that the catalyst synthesized by the method of the example can effectively utilize expensive and rare platinum as a catalyst.

First, the effect of forming a platinum shell by heating with microwaves will be described. When a platinum shell is synthesized by microwave heating, the synthesis rate is clearly faster than when the shell is slowly formed at room temperature, which can contribute to the improvement of productivity. Further, by combining with the continuous method, it is possible to achieve the problems of the present invention, such as variation between lots and simplification of the process. What about the quality of the catalyst in which the platinum shell is synthesized by microwave heating? Examples 1 and 2 have the same conditions except that microwave heating is used to form the platinum shell. Comparing the mass activity values of Example 1 and Example 2 of FIG. 3, Example 1 has the same or slightly higher mass activity than Example 2, and even if the platinum shell formation time is short, it is gentle at room temperature. It was found that the performance was equal to or better than that in the case of reaction. Further, Example 3 and Comparative Example 2, which are reaction systems in which potassium ions do not exist, have the same conditions except for the microwave heat treatment in shell formation. Example 3 showed higher activity than Comparative Example 2, demonstrating the effectiveness of microwave heating in platinum shell formation.

However, as in Comparative Example 3, a highly active catalyst may not be obtained even if microwaves are used for shell formation. When the reaction temperature is high and the nucleation rate is high, platinum does not form a shell and becomes free particles, which are lost in the purification process and thus become a catalyst with low activity. In order to improve productivity by using the microwave continuous method for shell formation in the coexistence of carriers, the hydroxide ions coexisting in the reaction process, the paired cations, and the reaction temperature must be appropriately adjusted.

Next, the effect of coexisting potassium ions will be described. In the process of Example 1, the sodium ion was not contained in the reaction system, and the cation contained in the palladium raw material and the hydroxide was potassium ion. In contrast, in the process of Example 3, potassium ions were not contained in the reaction system, and the cations contained in the palladium raw material and the hydroxide were sodium ions. Example 1 and Example 3 are equivalent in other conditions, and when these are compared, it can be seen that Example 1 has higher mass activity. In addition, Example 2 and Comparative Example 2 are also in contrast, and Example 2 contains only potassium ions, and Comparative Example 2 contains only sodium ions in the reaction system. Comparing Example 2 and Comparative Example 2, it can be seen that Example 2 has higher mass activity. From these results, it can be seen that when the reaction conditions are the same, a catalyst having higher activity tends to be synthesized when the cation of the pair of the palladium raw material and the hydroxide to be added is potassium rather than sodium.

The details of the action of potassium and sodium ions in the process of forming a palladium core and a platinum shell in the presence of a carrier are not clear, but the phenomenon is as described. One of the clear differences is the solubility of the raw metal salt, where potassium tetrachloropalladium (2) and potassium hexachloroplatinum (4) are from the corresponding sodium tetrachloropalladium (2) and sodium hexachloroplatinum (4). Low solubility in ethylene glycol solvent. This difference in solubility may be related to the formation of free palladium particles and platinum particles that are lost during the purification process.

Another clear difference is the ability of hydroxide ions to form ion pairs. Sodium ions have a smaller ionic radius than potassium ions and strongly attract surrounding water, polar solvents, and hydroxide ions. On the other hand, potassium ions are weaker than sodium ions in attracting them. Since the surface of the palladium nanoparticles adsorbs hydroxide ions and is negatively charged in the coexistence of hydroxide ions, it is considered that cations are wrapped around the surface. Sodium ions are thought to interact more strongly with hydroxide ions on the surface of palladium nanoparticles than potassium ions, and the strong coexistence of sodium ions on the surface of palladium nanoparticles leads to the growth of palladium core nanoparticles and the subsequent formation of platinum shells. May be affecting.

It is difficult to observe these processes in-situ, and it is difficult to directly prove the difference in the functions of sodium and potassium ions in platinum shell formation. There is no doubt that the above differences have an effect, but there may be unknown effects, and they may have complex effects with other factors such as reaction temperature. However, in spite of such difficulties, the inventors have found the influence of sodium ion and potassium ion, and have achieved the improvement of the performance and productivity of palladium core platinum shell fine particle catalyst synthesis in the coexistence of a carrier. ..

In Example 4, palladium core particles and a platinum shell are formed in the presence of monoethanolamine in the presence of a carrier. Since primary amines such as monoethanolamine and ammonia form stable complexes with palladium and platinum ions, they have the effect of suppressing the reduction reaction of these raw materials. Therefore, when monoethanolamine is added, the particle size of the palladium core particles becomes slightly larger, and the platinum shell hardly reacts at room temperature. It is possible to proceed with the platinum shell formation reaction even in the presence of monoethanolamine by heating by a batch method using a normal heating means such as an electric heater, an oil bath, or steam. However, in order to form a uniform shell, it is necessary to suppress the reaction rate and allow the reaction to react slowly for a long time, and as described above, heat transfer and diffusion tend to be non-uniform when scaled up in order to increase productivity in batches. There is a problem. As described above, the type of additive that suppresses the reaction rate and controls particle growth and shell formation is incompatible with the usual heating method.
However, when microwave heating is used, uniform heating can be performed rapidly, and there is a possibility that the reaction can proceed in a short time even in the presence of a reaction-suppressing additive. In addition, in the case of a reaction in which the crystallinity of nanoparticles and the diffusion of raw material atoms on the surface are important factors, it is necessary to react at a high temperature. The method of combining is effective. In Example 4, it was possible to form a platinum shell even under the condition that the primary amino group was present several times as much as the platinum raw material. It was found that some of the platinum added as a raw material was not incorporated into the catalyst, but the mass activity based on the platinum contained in the catalyst showed a high value. Further, in Example 4, the mass activity of 98% or more of the initial activity is maintained even after the load response durability test of 5000 cycles, and the additives and temperature in the shell forming process may have an important influence on the durability. Understand. Synthesis of such a catalyst is difficult with the conventional batch method, and the effectiveness of the microwave continuous heating method has been clarified.

FIG. 4 shows the transition of the maintenance rate of mass activity with respect to the number of potential cycles in the durability test of the carbon-supported palladium-core platinum-shell catalyst of Example 1 and Example 2. Here, the maintenance rate is a 100% representation of the activity after the durability test with respect to the initial activity, and is an index showing the maintenance rate of the activity by increasing the number of potential cycles, with the initial activity as 100%. Assuming that the initial activity of Example 1 with reference numeral 10a is 100%, the activity with reference numeral 10b after 5000 cycles was 84%, and the activity with reference numeral 10c after 37,000 cycles was 80%. In Example 2, assuming that the code 10d of the initial activity is 100%, the code 10e which is the activity after 5000 cycles is 93%, and the code 10f which is the activity after 37,000 cycles is 84%. From this, it was found that the carbon-supported palladium-core platinum-shell catalyst of the present invention maintained an activity of 80% or more of the initial activity even after the potential cycle of 37,000 cycles, which is an important property in the practical use of the fuel cell. It turned out to be very good at some durability.

As described above, by using potassium hydroxide in the synthesis of the carbon-supported palladium core platinum shell catalyst fine particles of the present invention in the presence of the core and the carrier of the shell, and effectively using microwave heating for the shell formation reaction, It is possible to obtain carbon-supported palladium-core platinum-shell catalyst fine particles having high catalyst performance and little deterioration in performance in durability tests.

Although the present invention has been described above with reference to the drawings with reference to Examples and Comparative Examples, the present invention is not narrowly limited to this, and many variations are possible based on the technical idea of the present invention. It is clear that it is a thing. For example, as microwaves, the present invention has described a lot about single-mode microwave irradiation, but the present invention is not limited to this, and includes the use of multi-mode microwave irradiation, and the microwave irradiation is irradiated. The intensity distribution range of the microwave applied to the body and the method of applying the microwave are determined by the purpose of applying the microwave to the irradiated object.

In the present invention, the carbon-supported palladium core platinum shell fine particle catalyst synthesized by the method using potassium hydroxide and microwave heating for the synthesis of the core and the shell in the coexistence of the carrier has high catalytic efficiency and excellent durability. , Can be used as a catalyst for chemical reactions and fuel cells.

Claims (5)

Carrier-supported palladium is continuously added to a reaction raw material solution prepared by adding a platinum raw material-containing solution and an alkali metal hydroxide solution to a colloid in which carrier-supported palladium fine particles are dispersed in a dispersion medium containing a glycol-based solvent by microwave heating. In the method of forming a platinum shell on core particles, the solution is freed, coordinated, and adsorbed at the ratio of the amount of the substance contained in the reaction raw material solution after adding and mixing the platinum raw material-containing solution and the alkali metal hydroxide solution. A carrier characterized in that the addition of the platinum raw material-containing solution and / or the alkali metal hydroxide solution is controlled so that the amount of the hydroxide ion contained in the material is 2 to 6 times the amount of the platinum raw material atom. A method for producing a supported palladium core platinum shell fine particle colloid. In the method for producing a carrier-supported palladium core platinum shell fine particle colloid according to claim 1, the carrier-supported palladium fine particles, which are one of the raw material components, are 4 to 7 times as much as the glycol-based solvent, the carrier, the palladium raw material, and the palladium raw material atom. A method for producing a carrier-supported palladium-core platinum-shell fine particle colloid, which is synthesized by microwave-heating a reaction raw material solution containing an amount of alkali metal hydroxide. In the method for producing a carrier-supported palladium core platinum shell fine particle colloid according to claim 1 or 2, the carrier is carbon fine particles, and the carbon-supported palladium fine particle forming step and the platinum shell forming step are connected by a continuous flow path. A method for producing a carbon-supported palladium-core platinum-shell fine particle colloid, which is synthesized by a continuous microwave irradiation method. The method for producing a carrier-supported palladium-core platinum-shell fine particle colloid according to any one of claims 1 to 3, wherein the carrier-supported palladium-core platinum-shell fine particle colloid is produced, wherein the alkali metal hydroxide is potassium hydroxide. Method. Bubbling 3 L / min of nitrogen in a 0.1 M perchloric acid aqueous solution for 30 minutes to expel oxygen is used as an electrolytic solution.
A glassy carbon rotating electrode coated with catalyst ink so that 0.96 μg of platinum is contained in the glassy carbon portion having a diameter of 5 mm.
When a durability test is performed at a temperature of 20 ° C. with a square wave of 0.6 V for 3 seconds and 1.0 V for 3 seconds as one cycle with a reversible hydrogen electrode as a reference electrode.
In a 0.1M perchloric acid aqueous solution,
Bubbling 3 L / min of oxygen for 30 minutes to expel nitrogen was used as the electrolyte.
Electrode rotation speed 1600 [rotation / minute],
Temperature 25 ° C,
Scanning speed to the high potential side of 20 [mV / sec],
Under the conditions of
When applying the oxygen reduction current value compensated for the solution resistance at a potential of 0.9 V with the reversible hydrogen electrode as the reference electrode and the mass activity calculation method using the Koutecky-Levic equation,
Platinum mass activity as an oxygen reduction catalyst after 37,000 cycles, that is, i in the activation dominant current value (Koutecky-Levich equation 1 / i = 1 / (ik) + 1 / (il) in the mass activity calculation method: measured current , Ik: Activation dominant current, il: From limit diffusion current) is divided by the amount of coated platinum of 0.96 μg, and 80% of the mass activity before the durability test can be maintained, and the initial stage before the durability test. A carrier-supported palladium-core platinum-shell fine particle catalyst having an activity of 600 A / g or more.