JP2019171331A - Noble metal catalyst production method and noble metal catalyst - Google Patents

Abstract

Provided is a catalyst having high activity as a catalyst for a fuel cell and having excellent durability in catalytic performance.
A step of mixing a water-soluble noble metal compound, water, a base component, an organic solvent arbitrarily mixed with water, and a conductive oxide, a step of heating the mixed solution, and after the heating step, A method for producing a noble metal catalyst, comprising a step of firing in a reducing atmosphere or an inert gas atmosphere.
[Selection figure] None

Description

The present invention relates to a method for producing a noble metal catalyst and a noble metal catalyst. More specifically, the present invention relates to a method for producing a noble metal catalyst suitable as an electrode material for a fuel cell and a noble metal catalyst.

A fuel cell is a device that generates electric power by electrochemically reacting a fuel such as hydrogen or alcohol with oxygen, and depending on the electrolyte, operating temperature, etc., polymer electrolyte (PEFC), phosphoric acid (PAFC), It is divided into molten carbonate form (MCFC) and solid oxide form (SOFC). Among these, for example, a polymer electrolyte fuel cell is a fuel cell that uses an ion conductive polymer membrane (ion exchange membrane) as an electrolyte, but is used for stationary power sources and fuel cell vehicle applications, There is a need to maintain desired power generation performance over a long period of time.

In such fuel cells, carbon having a high conductivity (also referred to as electric conductivity) is used as a carrier, and a material in which fine platinum is supported thereon has high electrochemical characteristics, so that it is generally used as an electrode material. .
In addition, for catalyst materials in which a catalytic metal such as platinum is supported on a carbon support, methods for improving the catalytic function are also being studied. By using a reducing agent such as citric acid or sodium borohydride, the carbon is supported on carbon. Techniques for controlling the Pt diameter to be made are disclosed (see, for example, Patent Documents 1 and 2).

JP 2003-320249 A JP2013-085898A

As described above, as the electrode material, a material in which platinum is supported on a carbon support (hereinafter also referred to as “Pt / C”) is generally used. In general, the electrode material is advantageous when used at a high potential because the number of stacked electrodes is reduced. On the other hand, when the electrode material is used at a high potential, the oxidation reaction of the carbon support (C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻ ). May progress. For example, when the electrode potential exceeds 0.9 V, the oxidation reaction of the carbon support carrying platinum is likely to proceed. In this case, the supported platinum is aggregated or missing, and the effective electrode area is reduced. Will be significantly reduced. In addition, when the anode is deficient in hydrogen and used at a high potential, it is known that not only carbon oxidation reaction at Pt / C but also platinum is eluted. The eluted platinum often diffuses into the PEFC and precipitates in places such as the electrolyte membrane where it cannot perform its original catalytic function, which causes a decrease in power generation performance. In particular, when platinum is finely supported, all platinum is eluted only after being exposed to a high potential several times, which is a serious problem in terms of durability.

Among applications in which fuel cells are used, in automobile applications, large load fluctuations caused by starting and stopping occur, and accordingly, a high potential is easily applied to the electrode material. For this reason, electrode materials used in automotive applications are required to have materials that are less likely to cause the above problems even when used in environments where such load fluctuations occur. In reality, this is dealt with by separately installing a control device so that the potential of the electrode falls below 0.9V. Thus, the catalyst used in the fuel cell is not sufficient in terms of durability, and further improvement in durability is required.

In view of the above situation, an object of the present invention is to provide a catalyst having high activity as a catalyst for a fuel cell and having excellent durability in catalyst performance.

The present inventors examined a catalyst having high activity as a catalyst for a fuel cell and having excellent durability in catalytic performance, and focused on a conductive oxide as a support for an electrode material instead of carbon. And after mixing the inorganic salt and / or organic acid salt of noble metal, water, a base component, the organic solvent arbitrarily mixed with water, and a conductive oxide, and heating the obtained liquid mixture, it is further reduced atmosphere. Alternatively, when a catalyst is produced by calcination in an inert gas atmosphere, the catalyst activity is high, and when used as a catalyst for a fuel cell, it exhibits high electrochemical characteristics and the catalyst performance in an environment where a high potential is applied. The inventors have found that a noble metal catalyst having excellent durability can be obtained, and have completed the present invention.

That is, the present invention comprises a step of mixing a water-soluble noble metal compound, water, a base component, an organic solvent arbitrarily mixed with water, and a conductive oxide to obtain a mixed solution, a step of heating the mixed solution, And a step of firing in a reducing atmosphere or an inert gas atmosphere after the heating step.

The mixing step includes mixing a water-soluble noble metal compound with water and a base component to obtain an aqueous solution containing a noble metal hydroxide, mixing an organic solvent arbitrarily mixed with water and a conductive oxide. It is preferable to include a step of obtaining a conductive oxide dispersion and a step of mixing the aqueous solution containing the noble metal hydroxide and the conductive oxide dispersion to obtain a mixed solution.

In the mixing step of the aqueous solution containing the noble metal hydroxide and the conductive oxide dispersion, the amount of the organic solvent contained in the conductive oxide dispersion is 100 parts by volume of the aqueous solution containing the noble metal hydroxide. It is preferable that the step is a step of mixing the aqueous solution containing the noble metal hydroxide and the conductive oxide dispersion so as to be 0.1 to 10,000 parts by volume to obtain a mixed solution.

The present invention is also a noble metal catalyst having a noble metal element and / or alloy supported on a conductive oxide support, the noble metal catalyst being obtained by electron microscope observation of the noble metal element and / or alloy supported on the support. It is also a noble metal catalyst characterized in that the average particle diameter (TEM diameter) is 6 nm or more and the utilization factor of the catalyst defined by the following formula is 45% or more.

The noble metal is preferably platinum.

The conductive oxide is preferably titanium suboxide.

The present invention is also an electrode material using the noble metal catalyst of the present invention.

The method for producing a noble metal catalyst of the present invention is a method capable of producing a noble metal catalyst having excellent electrochemical characteristics as well as excellent resistance to an environment where a high potential is applied.
Further, the noble metal catalyst of the present invention is a catalyst excellent in both resistance to an environment to which a high potential is applied and electrochemical characteristics, and can be suitably used as an electrode material for a fuel cell.

2 is an electron micrograph of the catalyst (powder 1) prepared in Example 1. 4 is an electron micrograph of the catalyst (powder 2) prepared in Example 2. 4 is an electron micrograph of the catalyst (powder 3) prepared in Example 3. 4 is an electron micrograph of the catalyst (powder 4) prepared in Example 4. 3 is an electron micrograph of a catalyst (powder 5) prepared in Comparative Example 1. 4 is an electron micrograph of a catalyst (powder 6) prepared in Comparative Example 2. 4 is an electron micrograph of a catalyst (powder 7) prepared in Comparative Example 3. 4 is an electron micrograph of a catalyst (powder 8) prepared in Comparative Example 4. The results of the catalyst durability test of the catalyst (powder 1) prepared in Example 1 and the catalyst (powder 8) prepared in Comparative Example 4 and 50% platinum-supported ketjen black EC manufactured by N.E. FIG.

Hereinafter, although the preferable form of this invention is demonstrated concretely, this invention is not limited only to the following description, In the range which does not change the summary of this invention, it can change suitably and can apply.

1. Method for producing noble metal catalyst The method for producing a noble metal catalyst of the present invention comprises a step of mixing a water-soluble noble metal compound, water, a base component, an organic solvent arbitrarily mixed with water, and a conductive oxide to obtain a mixed solution, It includes a step of heating the mixed solution and a step of baking in a reducing atmosphere or an inert gas atmosphere after the heating step.
The reason why a noble metal catalyst in which particles of a noble metal species having a large particle size (catalytically active species) are supported on a conductive oxide as a support is obtained by the production method as described above is not clear. It is considered as follows. That is, the amount of hydroxyl groups on the surface of the conductive oxide can be reduced by mixing not only water but also an organic solvent as a solvent for supporting the noble metal species on the conductive oxide as a carrier. As a result, the sites supporting the noble metal species are reduced, and the noble metal species are concentrated on the remaining support sites on the surface of the conductive oxide. As a result, a catalyst in which noble metal species having a large particle size are localized and supported is obtained. It is thought that. A catalyst loaded with a noble metal species having a large particle size is used as an electrode material for a fuel cell, and maintains catalytic activity by leaving at least a portion of the noble metal species without eluting even when exposed to a high potential multiple times. Can do.
The noble metal catalyst obtained by the method for producing a noble metal catalyst of the present invention uses the conductive oxide instead of carbon as a carrier, thereby causing the above-mentioned problem of aggregation and loss of noble metal species due to the oxidation reaction of the carbon carrier. In addition, since the particle size of the supported noble metal species is large, all of the noble metal species are not eluted even at a high potential, and at least a part of the noble metal species is retained on the support, so that the durability of the catalyst performance is excellent. . In addition, Patent Documents 1 and 2 described above disclose a technique for controlling the Pt diameter supported on carbon by using a reducing agent such as citric acid or sodium borohydride. When used as a catalyst having an oxide as a carrier, it has been confirmed that although the particle size of the noble metal can be increased, the activity of the obtained noble metal catalyst is lowered. This method is a method in which a noble metal reduced to large particles in a liquid is supported only by electrostatic attraction, and since the electronic conductivity from the conductive oxide to the noble metal is low, the catalytic performance of the noble metal can be obtained. It is possible that there is not. On the other hand, in the method for producing a noble metal catalyst of the present invention, since the noble metal species can be supported by a chemical bond on the conductive oxide whose outermost surface portion is oxidized, the catalytic activity is excellent and the durability thereof is improved. An excellent noble metal catalyst can be obtained.

<Mixing process>
The mixing step is a step of mixing a water-soluble noble metal compound, water, a base component, an organic solvent arbitrarily mixed with water, and a conductive oxide to obtain a mixed solution, which are mixed. As long as the order of mixing is not particularly limited, one kind may be mixed in order, or two or more kinds may be mixed simultaneously. Moreover, after preparing the mixture of some components among these and the mixture of the remaining components, you may make it mix mixtures.

In the mixing step, first, an aqueous solution containing a noble metal hydroxide is prepared by mixing a water-soluble noble metal compound, water and a base component (a step of obtaining an aqueous solution containing a noble metal hydroxide), and optionally with water. After preparing a conductive oxide dispersion by mixing an organic solvent to be mixed with a conductive oxide (a step of obtaining a conductive oxide dispersion), an aqueous solution containing a noble metal hydroxide and the conductive oxide It is preferable to mix the dispersion (a step of mixing an aqueous solution containing a noble metal hydroxide and a conductive oxide dispersion).
By mixing an organic solvent that is arbitrarily mixed with water and a conductive oxide in advance, the site of the conductive oxide surface where the noble metal species is supported can be sufficiently reduced, and then the noble metal hydroxide is contained. By mixing with the aqueous solution, the concentration of the noble metal species to the remaining specific supporting sites further proceeds, and therefore a catalyst supporting the noble metal species having a larger particle size can be produced.
In the present invention, the “noble metal hydroxide” means a component obtained by a reaction between a water-soluble noble metal compound and a base component, and includes those in which a noble metal and a base component form a complex. The aqueous solution containing the noble metal hydroxide may contain an unreacted water-soluble noble metal compound.

The aqueous solution containing the noble metal hydroxide may contain an organic solvent arbitrarily mixed with water, and the conductive oxide dispersion may contain water. That is, the step of obtaining an aqueous solution containing a noble metal hydroxide by mixing a water-soluble noble metal compound, water and a base component may further include a step of mixing an organic solvent arbitrarily mixed with water. The step of mixing an organic solvent arbitrarily mixed with water and a conductive oxide to obtain a conductive oxide dispersion may further include a step of mixing water.

The mixing step, the step of obtaining an aqueous solution containing a noble metal hydroxide, the step of obtaining a conductive oxide dispersion, and the step of mixing an aqueous solution containing a noble metal hydroxide and a conductive oxide dispersion are appropriately performed. Although it can carry out stirring and the time to stir is not restrict | limited in particular, The process of obtaining the aqueous solution containing a noble metal hydroxide is preferably performed by stirring for 0.5 to 72 hours. By doing so, the reaction to the noble metal hydroxide proceeds. More preferably, the stirring is performed for 24 to 72 hours.
Further, in the step of obtaining the conductive oxide dispersion, the conductive oxide dispersion is sufficiently stirred or subjected to ultrasonic treatment in order to sufficiently reduce the supporting sites on the surface of the conductive oxide by the organic solvent. It is preferable. The time for stirring or sonication is preferably 10 to 120 minutes.

The content of the noble metal hydroxide in the aqueous solution containing the noble metal hydroxide is preferably such an amount that the mass of the noble metal atoms is 0.01 to 100 g / L. With such a content, the reaction from the water-soluble noble metal compound to the noble metal hydroxide tends to proceed. More preferably, the amount is such that the mass of the noble metal atom is 0.01 to 20 g / L, and still more preferably 0.01 to 5 g / L.

The amount of the base component used for the preparation of the aqueous solution containing the noble metal hydroxide is preferably 2 to 10 mol with respect to 1 mol of the noble metal atom contained in the aqueous solution containing the noble metal hydroxide. By using such an amount of the base component, the noble metal hydroxide can be prepared and the acid of the water-soluble noble metal compound used as a raw material can be sufficiently neutralized.

The conductive oxide content in the conductive oxide dispersion is preferably 0.1 to 50 g / L. With such a content, the noble metal species are easily supported uniformly on the conductive oxide. The content of the conductive oxide is more preferably 1 to 30 g / L, still more preferably 1 to 10 g / L.

In the mixing step of the aqueous solution containing the noble metal hydroxide and the conductive oxide dispersion, when these are mixed, the total amount of the aqueous solution containing the noble metal hydroxide and the total amount of the conductive oxide dispersion are used. It may be mixed at one time, the other may be added to one total amount little by little, and the aqueous solution containing the noble metal hydroxide and the conductive oxide dispersion may be mixed together little by little. It is preferable to add small amounts of an aqueous solution containing a noble metal hydroxide to the conductive oxide dispersion. By doing in this way, the obtained noble metal catalyst can have a noble metal species having a larger particle diameter, and the bond between the noble metal species and the conductive oxide carrier can be strengthened. In this case, the time required for the addition of the aqueous solution containing the noble metal hydroxide may be appropriately set depending on the amount of the aqueous solution containing the noble metal hydroxide or the conductive oxide dispersion, but it should be 1 to 72 hours. Is preferred. More preferably, it is 2 to 48 hours.

In the mixing step of the aqueous solution containing the noble metal hydroxide and the conductive oxide dispersion, the amount of the organic solvent contained in the conductive oxide dispersion is 100 parts by volume of the aqueous solution containing the noble metal hydroxide. The step is preferably a step of mixing an aqueous solution containing a noble metal hydroxide and a conductive oxide dispersion so as to be 0.1 to 10,000 parts by volume. By using the organic solvent in such a ratio, the conductive oxide supporting sites can be sufficiently reduced, and the resulting noble metal catalyst can have a noble metal species having a larger particle size.
The amount of the organic solvent contained in the conductive oxide dispersion is more preferably 10 to 1000 parts by volume, and still more preferably 100 to 400 parts by volume with respect to 100 parts by volume of the aqueous solution containing the noble metal hydroxide. Part.

When the aqueous solution containing the noble metal hydroxide and the conductive oxide dispersion are mixed, the conductivity contained in the conductive oxide dispersion with respect to 1 g of the noble metal atoms contained in the aqueous solution containing the noble metal hydroxide. It is preferable to mix the oxide in a ratio of 1 to 99 g. By mixing at such a ratio, the resulting catalyst tends to be excellent in catalyst performance. More preferably, the proportion of the conductive oxide contained in the conductive oxide dispersion is 2 to 29 g with respect to 1 g of the noble metal atom contained in the aqueous solution containing the noble metal hydroxide, and more preferably 4 to The ratio is 19 g.

<Heating process>
The method for producing a noble metal catalyst of the present invention includes a step of heating a mixture obtained by mixing a water-soluble noble metal compound, water, a base component, an organic solvent arbitrarily mixed with water, and a conductive oxide. In the heating step, as long as the mixed solution is to be heated, the timing for starting the heating is not particularly limited, and heating may be started after mixing of all the raw materials for preparing the mixed solution is completed. The heating may be started in parallel with the preparation of the mixed solution by starting the heating before the mixing of all the raw materials is completed.
The mixing step mixes a water-soluble noble metal compound, water and a base component to obtain an aqueous solution containing a noble metal hydroxide, and an organic solvent and a conductive oxide which are arbitrarily mixed with water to conduct electricity. A noble metal hydroxide in the case of including a step of obtaining a conductive oxide dispersion and a step of mixing the aqueous solution containing the noble metal hydroxide and the conductive oxide dispersion to obtain a mixed solution Heating is preferably performed in the step of mixing the aqueous solution and the conductive oxide dispersion to obtain a mixed solution. In this case, heating may be started at any time before the mixing of all of these amounts is completed.
Heating may be performed while refluxing, or may be performed while distilling the mixed solution and distilling off a solvent such as water.

The heating temperature in the heating step is preferably 50 to 180 ° C. With such a temperature, the amount of the noble metal species supported by the finally obtained noble metal catalyst can be increased. The heating temperature is more preferably 70 to 150 ° C, still more preferably 80 to 130 ° C.

Moreover, it is preferable that the heating time in a heating process is 0.5 to 72 hours. With such a heating time, it is possible to increase the amount of the noble metal species supported on the finally obtained noble metal catalyst. The heating time is more preferably 1 to 48 hours, still more preferably 3 to 36 hours.
In addition, when heating a mixed liquid prepared in parallel with the preparation of the mixed liquid, since at least a part of the mixed liquid is generated after the start of heating, the time from the start to the end of the heating operation and the actual mixed liquid However, the heating time here means the time during which the mixed liquid is actually heated.

<Solvent removal step>
It is preferable that the manufacturing method of the noble metal catalyst of this invention includes the process of removing a solvent from the liquid mixture obtained through the said mixing process and a heating process. By removing the solvent, the atmosphere in the firing step can be kept stable.
The solvent removal step may be performed by heating, but it is preferable that the temperature be 80 ° C. or lower even when heating. By setting it as such temperature, a solvent can be removed, without impairing the electroconductivity of a conductive oxide. The temperature of the solvent removal step is more preferably 10 to 60 ° C, still more preferably 20 to 40 ° C. Since it is low temperature, in order to remove a solvent efficiently, it is preferable to dry under reduced pressure.
The time of the solvent removal step is not particularly limited as long as the solvent is removed from the mixed solution, but it is preferably 8 to 24 hours in view of sufficient removal of the solvent and production efficiency.

<Baking process>
The method for producing a noble metal catalyst of the present invention includes a step of calcining a mixture obtained by performing the above-described mixing step, heating step, and solvent removal step as necessary in a reducing atmosphere or an inert gas atmosphere. The firing temperature in the firing step is preferably 300 to 1200 ° C. By firing at such a temperature, the reduction of the remaining water-soluble noble metal compound and / or noble metal hydroxide can proceed more sufficiently. In addition, the noble metal species supported by small particles of 3 nm or less can be combined with the noble metal species supported at the adjacent site to make a large particle. The firing temperature is more preferably 500 to 1100 ° C, and further preferably 500 to 1000 ° C.
The time for firing is preferably 0.5 to 24 hours in view of sufficiently firing the catalyst and the efficiency of production. More preferably, it is 1 to 6 hours.
The firing step is preferably a step of firing in a reducing atmosphere in order to exhibit the above effects more.

As a reducing atmosphere for performing the firing step, a hydrogen atmosphere or an atmosphere containing 5 to 100 vol% of a reducing gas such as hydrogen in an inert gas such as helium, nitrogen, or argon can be used.
As an inert gas atmosphere for performing the firing step, an atmosphere of an inert gas such as helium, nitrogen, or argon can be used.

<Other processes>
The method for producing a noble metal catalyst of the present invention may include the above-described solvent removal step and other steps as long as the above-described mixing step, heating step, and firing step are included. Examples of other processes include an aging process, a purification process, and a drying process. In the above heating step, when the heating is continued after the mixing step, it can be said that the aging step is being performed.

The method for producing a noble metal catalyst of the present invention includes a purification step of purifying the mixed solution before the solvent is removed from the mixed solution obtained through the mixing step, heating step (and aging step if necessary). Is preferred. The mixed solution contains a salt produced by the reaction of the water-soluble noble metal compound and the base component. The precious metal catalyst obtained by the production method of the present invention can be obtained by removing such a salt before the solvent is removed from the mixed solution obtained through the mixing step and heating step (and aging step if necessary). The impurity content can be reduced. The method for removing the salt is not particularly limited, but filtration is preferred.
In addition, the purification step may further include a step of washing the mixed solution with a solvent. The solvent used in the washing step is not particularly limited, but an aqueous solvent is preferable. By using an aqueous solvent, water-soluble impurities contained in the mixed solution can be removed.

As the aqueous solvent, water, methanol, ethanol or the like can be used, but it is preferable to use ethanol or a mixed solvent of ethanol and water. By using these, water-soluble impurities can be effectively removed while suppressing the influence on reducing the conductive oxide supporting sites by the organic solvent.

The drying step is a step of drying the solid content after removing the solvent from the mixed solution obtained through the mixing step and heating step (and aging step if necessary) before being subjected to the firing step, and is obtained. From the viewpoint of increasing the purity of the noble metal catalyst, it is preferable to dry the solid content after the purification step. The drying step may be performed by heating as long as the solid content is dried, but it is preferably performed without heating from the viewpoint of preventing the carrier from being oxidized.

<Raw material>
In the method for producing a noble metal catalyst of the present invention, an inorganic salt and / or an organic acid salt of a noble metal is used as a water-soluble noble metal compound.
Examples of the noble metal include platinum, iridium, ruthenium, rhodium, and palladium. Among these, platinum is preferable.
Although it does not restrict | limit especially as an inorganic salt, A sulfate, nitrate, a chloride, a phosphate etc. are mentioned.
Although it does not restrict | limit especially as an organic acid salt, An organic carboxylic acid complex etc. are mentioned.
Of these, chloroplatinic acid is most preferred from the viewpoint of reactivity.

The base component used in the method for producing a noble metal catalyst of the present invention is not limited as long as it generates a noble metal hydroxide by reacting with the inorganic salt and / or organic acid salt of the noble metal, lithium, sodium, Examples thereof include hydroxides of Group 1 elements of the periodic table such as potassium, or Group 2 elements of the periodic table such as magnesium, calcium and strontium. Among these, sodium hydroxide is preferable.

Examples of the organic solvent arbitrarily mixed with water used in the method for producing a noble metal catalyst of the present invention include amide solvents such as dimethylformamide and dimethylacetamide; alcohols such as methanol, ethanol, propanol and ethylene glycol.
Among these, dimethylformamide, ethanol, or ethylene glycol is preferable. More preferred is dimethylformamide.

As the conductive oxide used in the method for producing the noble metal catalyst of the present invention, suboxides such as titanium, tin, zinc and tungsten, and other elements such as niobium and tantalum are introduced together with these elements to impart conductivity. And oxides.
Among these, titanium suboxide is preferable. Titanium suboxide has high conductivity and high acid resistance, and the noble metal catalyst obtained by using titanium suboxide is excellent in strong acid resistance, making it more suitable as an electrode material for batteries. . More preferably, it is Ti ₄ O ₇ among titanium suboxides.

The conductive oxide preferably has a specific surface area of 10 m ² / g or more. When a material having such a specific surface area is used, the resulting catalyst becomes more excellent in catalytic activity. More preferably, the specific surface area is 13 m ² / g or more.
The conductive oxide preferably has a volume resistance of 5 × 10 ² Ω · cm or less and 1 × 10 ⁻⁶ Ω · cm or more. When such a material having a volume resistance is used, the obtained catalyst is suitable as an electrode material. More preferably, the volume resistance is 1 × 10 ² Ω · cm or less, and still more preferably, the volume resistance is 5 × 10 ¹ Ω · cm or less.

In the present invention, the water-soluble noble metal compound, the base component, the organic solvent arbitrarily mixed with water, and the conductive oxide may be used singly or in combination of two or more.

2. Noble metal catalyst The present invention is also a noble metal catalyst in which a noble metal element and / or alloy is supported on a conductive oxide support, and the noble metal catalyst is an electron microscope of the noble metal element and / or alloy supported on a support. It is also a noble metal catalyst characterized in that the average particle diameter (TEM diameter) by observation is 6 nm or more and the utilization factor of the catalyst defined by the following formula is 45% or more.

The geometric specific surface area of the noble metal simple substance and / or alloy is the specific surface area of the noble metal simple substance and / or alloy particles observed with an electron microscope or the like, and the electrochemical effective specific surface area is the surface area of the noble metal catalyst surface. Of these, it means the area that actually exhibits catalytic action. The utilization rate calculated by the above formula is the ratio of the area that exhibits catalytic action among the specific surface area of the single noble metal and / or alloy particles, and the higher the utilization rate, the higher the activity as a catalyst. To do.
The noble metal catalyst of the present invention is a highly active catalyst having a utilization rate of 45% or more, and the average particle diameter (TEM diameter) of the noble metal alone and / or alloy observed with an electron microscope is 6 nm or more. Therefore, when used as an electrode material of a battery, even when exposed to a high potential, at least a part of the catalyst remains in the electrolyte solution of the noble metal and / or the alloy without being eluted, so that the durability is excellent. Is.
The specific surface area and the electrochemically effective specific surface area of the noble metal simple substance and / or alloy particles can be determined by the method described in Examples described later.

The noble metal catalyst of the present invention has a utilization rate of 45% or more, but the utilization rate is preferably 80% or more, and more preferably 90% or more.

The noble metal catalyst of the present invention has an average particle diameter (TEM diameter) of 6 nm or more of a noble metal simple substance and / or alloy observed by an electron microscope, but the noble metal simple substance and / or alloy has an average particle diameter of 8 nm or more. It is preferable that More preferably, it is 10 nm or more. The average particle diameter is preferably 100 nm or less, and more preferably 50 nm or less.

Examples of the noble metal of the noble metal catalyst of the present invention include platinum, iridium, ruthenium, rhodium, and palladium, and platinum is particularly preferable.
Examples of noble metal alloys include platinum ruthenium alloys.

The noble metal catalyst of the present invention has the above-mentioned characteristics, and the production method thereof is not particularly limited as long as it has such characteristics, but the above-mentioned method for efficiently producing the noble metal catalyst of the present invention is described above. The method for producing a noble metal catalyst of the present invention is suitable.

As described above, the noble metal catalyst of the present invention is highly active, and when used as an electrode material for a battery, even when it is exposed to a high potential, all of the noble metal simple substance and / or alloy are electrolyte solution. Can be suitably used as a battery electrode material. An electrode material using such a noble metal catalyst is also one aspect of the present invention, and an electrode configured using the electrode material of the present invention and a battery configured using the electrode are also included in the present invention. It is one of.

In order to describe the present invention in detail, specific examples are given below, but the present invention is not limited to these examples. Unless otherwise specified, “%” and “wt%” mean “wt% (mass%)”.

Production Example 1
Rutile type titanium oxide (trade name “STR-100N”, manufactured by Sakai Chemical Industry Co., Ltd., specific surface area 100 m ^{2 /} g) 2.0 g and metal titanium (trade name “titanium, powder” manufactured by Wako Pure Chemical Industries, Ltd.) After 3 g of dry mixing, the temperature was raised to 700 ° C. over 70 minutes in a hydrogen atmosphere, held at 700 ° C. for 6 hours, cooled to room temperature, and the titanium oxide whose crystal phase was represented by Ti ₄ O ₇ A carrier was obtained. The specific surface area of titanium suboxide measured by the following method was 16.5 m ² / g, and the volume resistance was 5.0 × 10 ¹ Ω · cm.

<Specific surface area measurement of titanium suboxide>
Specific surface area (BET-SSA)
In accordance with the provisions of JIS Z8830 (2013), the sample was heat-treated at 200 ° C. for 60 minutes in a nitrogen atmosphere, and then the specific surface area was measured using a specific surface area measuring device (trade name “Macsorb HM-1220” manufactured by Mountec Co., Ltd.). (BET-SSA) was measured.
<Measurement of volume resistance (also called volume resistivity) of titanium suboxide>
For the measurement of volume resistance, a powder resistance measurement system MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd. was used.
The powder resistance measurement system includes a hydraulic powder press unit, a four-point probe, and a high resistance measurement device (manufactured by the same company, Lorestar GX MCP-T700).
The value of volume resistance (Ω · cm) was determined according to the following procedure.
1) Put the sample powder into a press jig (diameter 20 mm) equipped with a four-probe probe on the bottom, and set it in the pressurizing part of the powder resistance measurement system. Connect the probe and the high resistance measuring device with a cable.
2) Pressurize to 20 kN using a hand press. The powder thickness is measured with a digital caliper, and the resistance value is measured with a high resistance measuring device.
3) From the bottom area, thickness, and resistance value of the powder, the volume resistivity (Ω · cm) is obtained based on the following formula (i).

Example 1
A hexachloroplatinic acid aqueous solution (15.343 wt% concentration by weight of platinum atom, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was diluted to prepare 256 ml of a 2 mM platinum solution. To this was added 3.44 ml of a 1 mol / L sodium hydroxide solution (amount to neutralize excess hydrochloric acid in addition to 4 times the amount of platinum) and stirred at room temperature for 24 hours to obtain a platinum hydroxide complex. A containing aqueous solution was obtained.
To the four-necked flask, 0.9 g of the titanium suboxide (Ti ₄ O ₇ ) support obtained in Production Example 1 and 256 ml of dimethylformamide (DMF) were added, and this was subjected to ultrasonic treatment for 30 minutes. While this was put into an oil bath and stirred with a magnetic stirrer, the platinum hydroxide-containing aqueous solution was dropped over 2 hours with a tube pump while refluxing. After completion of the dropwise addition, the reaction was carried out under reflux conditions for 24 hours. The temperature at reflux was 120 ° C.
After completion of the reaction, according to a conventional method, filtration, washing with ethanol, and drying at 35 ° C. under reduced pressure, 1 g of powder was obtained. 0.5 g of the obtained powder was heated to 550 ° C. in a 100% hydrogen atmosphere, held at 550 ° C. for 1 hour, and then cooled to room temperature to obtain Powder 1.

Example 2
To a four-necked flask, 0.9 g of titanium suboxide (Ti ₄ O ₇ ) carrier and 256 ml of dimethylformamide were added, and this was subjected to ultrasonic treatment for 30 minutes. While this was put in an oil bath and refluxed, a platinum hydroxide-containing aqueous solution prepared by the same method as in Example 1 was dropped over 48 hours with a tube pump. Otherwise, a powder 2 was obtained in the same manner as in Example 1.

Example 3
Powder 3 was obtained in the same manner as in Example 1 except that the organic solvent was changed from dimethylformamide to ethanol and the temperature at reflux was 81 ° C.

Example 4
Powder 4 was obtained in the same manner as in Example 1 except that the carrier was reduced to 0.4 g, the organic solvent was changed from dimethylformamide to ethylene glycol, and the temperature at reflux was 125 ° C.

Comparative Example 1
Powder 5 was obtained in the same manner as in Example 1 except that the organic solvent was changed from dimethylformamide to butyl acetate and the temperature at reflux was 90 ° C.

Comparative Example 2
0.48 g of citric acid anhydride and 500 ml of ion-exchanged water were added to a 1 L four-necked flask, and the mixture was refluxed for 30 minutes in an oil bath while stirring with a magnetic stirrer. 1.27 g of hexachloroplatinic acid aqueous solution (15.343 wt% concentration by weight of platinum atom) was added, and the mixture was further stirred under reflux for 1 hour. After cooling this, 0.5 g of the titanium suboxide (Ti 4 O 7) support obtained in Production Example 1 was added to the cooled liquid, stirred for 1 hour at room temperature, filtered, washed with water, dried in the same manner as in Example 1. And it fired and the powder 6 was obtained.

Comparative Example 3
After stirring 0.668 g of titanium suboxide (Ti ₄ O ₇ ) in 128 ml of water, 6 g of dilute hexachloroplatinic acid (2.2 wt% concentration by weight of platinum atoms) aqueous solution was added, and pH 7 was added thereto at room temperature. PH 7 was maintained for 2 hours while adding a 1 mol / L sodium borohydride aqueous solution so as to maintain the pH. The total amount of sodium borohydride aqueous solution added was 4.5 ml. Then, after stirring at room temperature for 1 hour, it filtered, washed with water, dried and baked similarly to Example 1, and the powder 7 was obtained.

Comparative Example 4
After diluting 0.57 g of hexachloroplatinic acid aqueous solution (15.343% concentration by weight of platinum atom, Tanaka Kikinzoku Kogyo Co., Ltd.) with 3.4 g of ion-exchanged water, hydrazine chloride (manufactured by Tokyo Chemical Industry Co., Ltd., product) 0.024 g (name “Hydrazine Dihydrochloride”) was added and stirred and mixed (prepared as “mixed aqueous solution”).
While stirring the titanium suboxide support slurry prepared by stirring 0.668 g of titanium suboxide (Ti ₄ O ₇ ) in 128 ml of water, 4.0 g of the above mixed aqueous solution prepared in another beaker was added, The mixture was stirred and mixed while maintaining the liquid temperature at 70 ° C. Further, 3.2 ml of a 1 mol / L sodium hydroxide aqueous solution was added, and the mixture was heated and held at a liquid temperature of 70 ° C. for 1 hour with stirring and mixed, and then filtered, washed with water, dried and fired as in Example 1. Powder 8 was obtained.

<Physical property evaluation>
The physical properties and the like of each powder obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were evaluated by the following procedure. Various evaluation results other than the durability test are shown in Table 1, and the results of the durability test are shown in FIG. Moreover, the electron micrograph of each powder obtained in Examples 1-4 and Comparative Examples 1-4 is shown in FIGS.
1. Electrochemical surface area (ECSA)
(1) Production of working electrode A 5 wt% perfluorosulfonic acid resin solution (manufactured by Sigma Aldrich Japan Co., Ltd.), isopropyl alcohol (manufactured by Wako Pure Chemical Industries, Ltd.) and ion-exchanged water are added to the sample to be measured. A paste was prepared by dispersing with sonic waves. The paste was applied to a rotating glassy carbon disk electrode and thoroughly dried. The rotating electrode after drying was used as a working electrode.
(2) Cyclic voltammetry measurement
A rotating electrode device (trade name “HR-301”, manufactured by Hokuto Denko Co., Ltd.) was connected to the Automatic Polarization System (Hokuto Denko Co., Ltd., product name “HZ-5000”), and the working electrode was obtained as described above. An electrode with a measurement sample was used, and a platinum electrode and a reversible hydrogen electrode (RHE) electrode were used for the counter electrode and the reference electrode, respectively.
In order to clean the electrode with the measurement sample, it was subjected to cyclic voltammetry from 1.2 V to 0.05 V at 25 ° C. while bubbling argon gas into the electrolyte (0.1 mol / l perchloric acid aqueous solution). Thereafter, the current value was measured at 25 ° C. while sweeping from 1.2 V to 0.05 V with an electrolyte solution saturated with argon gas (0.1 mol / l perchloric acid aqueous solution) at a sweep rate of 50 mV / sec. .
Then, the electrochemical effective specific surface area (ECSA) is calculated using the following formula (ii) from the area of the hydrogen adsorption wave (charge amount at the time of hydrogen adsorption: QH (μC)) obtained during the sweep, and the electrochemical characteristics It was used as an index. In the formula (ii), “210 (μCcm ² )” is an adsorption charge amount per unit active area of platinum (Pt), and the unit of weight of Pt is g. The weight of Pt was calculated using the following formula (iii).
Electrochemical effective specific surface area (ECSA)
= (-QH / 210) × 10 ⁴ × (1 / Pt weight) (ii)
Pt weight on working electrode (g)
= (Pt carrying amount (%) / 100) × 6 μl (paste amount to be applied to working electrode) × 5 × 10 ⁻⁶ g / μl (catalyst concentration in ink) (iii)

2. Electron micrograph observation Observation was carried out using a field emission type transmission electron microscope JEM-2100F (manufactured by JEOL Ltd.).

3. Platinum content was measured using a fluorescent X-ray analyzer ZSX Primus II (manufactured by Rigaku Corporation) to calculate the platinum content in the sample.

4). Average primary particle diameter of supported platinum First, in a transmission electron micrograph (also referred to as a TEM image or TEM photograph), the major axis and minor axis of the platinum particle are measured with a ruler, and the average value of the major axis and minor axis is calculated. The primary particle size was determined by dividing by the photographing magnification. Furthermore, 80 platinum particles in the TEM image were randomly extracted, and the primary particle size of all particles was measured by the above method. The maximum primary particle size among the measured values was the maximum, and the minimum value among the measured values was the minimum. The average primary particle size was determined by averaging the measured values as the primary particle size. The TEM image photographing magnification may be any magnification, but a preferable range is 20,000 times to 500,000 times.

5. Geometric specific surface area of platinum From the following formula (iv), the geometric specific surface area of platinum was calculated from the average primary particle diameter. The calculation was performed assuming that the platinum density was 21.45 (g / cm ³ ), the circumferential ratio was 3.14, and platinum was a true sphere.
Geometric specific surface area of platinum = (average primary particle size / 2) ² × 4 × 3.14 / {(average primary particle size / 2) ³ × (4/3) × 3.14 × 21.45} Formula (iv)

6). Effective platinum ratio (utilization rate)
Using the following formula (v) using the electrochemical effective specific surface area (ECSA) of Pt obtained from the above formula (i) and the geometric specific surface area of platinum obtained by the above formula (iv), the proportion of effective platinum (Utilization rate) was obtained.
Utilization rate (%) = electrochemical effective specific surface area (ECSA) × 100 (%) / geometric specific surface area of platinum Formula (v)

7. Durability Test A working electrode was produced in the same manner as the electrochemical effective specific surface area measurement described above. Thereafter, the initial cyclic voltammogram was measured and ECSA was determined in the same manner as the cyclic voltammogram measurement described above. Then, after holding at 0.6 V for 30 seconds, 1600 cycles were carried out with 1.0 V for 3 seconds and 0.6 V for 3 seconds for 6 seconds, and cyclic voltammograms were measured in the same manner. This test was repeated up to 17600 cycles.
The durability test was performed on the catalysts obtained in Example 1 and Comparative Example 4, and as a comparison target, 50% platinum-supported ketjen black EC (denoted as Pt / C in the graph) manufactured by N.E. A similar test was conducted.

In Table 1, ECSA-Pt diameter is the particle diameter of Pt calculated from the electrochemical effective specific surface area (ECSA) calculated by the following formula (vi).
ECSA-Pt diameter = 3 × 2 / (ECSA × 0.001 × 21.45) Formula (vi)

When comparing Examples 1 to 4 and Comparative Example 4, in Comparative Example 4 prepared using a precipitation method using only ion-exchanged water as a solvent, the obtained catalyst had a high utilization rate but was an average particle of Pt. Whereas the diameter was about 5 nm, the catalysts prepared by the methods of Examples 1 to 4 using DMF, ethanol, and ethylene glycol all had an average particle diameter of Pt as large as 7 nm or more, and the utilization rate was 49. It was high with more than%.
In Comparative Example 1 using butyl acetate having low water solubility, although the platinum was large, the utilization rate was so bad that it could not be measured. Therefore, the resulting catalyst is considered to have poor binding properties between the support and platinum.
Moreover, the catalyst prepared by the method of Comparative Examples 2 and 3 using only ion-exchanged water as a solvent has a lower utilization rate, and Comparative Example 3 using the base component is more in comparison with Comparative Example 2 using no base component. The average particle size of Pt was also small. From this, it was confirmed that there is technical significance in the combination of the use of an organic solvent arbitrarily mixed with water and the use of a base component.
Further, from the results of the durability test, the catalyst supporting platinum on carbon had ECSA decreased for each cycle test. However, the platinum catalyst supported on the oxide support had a high ECSA retention rate. In particular, the catalyst of Example 1 was a comparative example. 4 shows higher durability than the fine platinum-supported product.
From the above results, it was confirmed that a catalyst having high activity as a catalyst of a fuel cell and excellent in durability of catalyst performance can be produced by the production method of the present invention.

1: Noble metal catalyst 10: Titanium suboxide 20: Platinum

Claims (7)

Mixing a water-soluble noble metal compound, water, a base component, an organic solvent arbitrarily mixed with water, and a conductive oxide to obtain a mixed solution;
Heating the mixture;
A method for producing a noble metal catalyst, comprising a step of calcining in a reducing atmosphere or an inert gas atmosphere after the heating step. The mixing step is a step of mixing a water-soluble noble metal compound, water and a base component to obtain an aqueous solution containing a noble metal hydroxide;
Mixing an organic solvent arbitrarily mixed with water and a conductive oxide to obtain a conductive oxide dispersion;
The method for producing a noble metal catalyst according to claim 1, further comprising a step of mixing the aqueous solution containing the noble metal hydroxide and the conductive oxide dispersion to obtain a mixed solution. In the mixing step of the aqueous solution containing the noble metal hydroxide and the conductive oxide dispersion, the amount of the organic solvent contained in the conductive oxide dispersion is 100 parts by volume of the aqueous solution containing the noble metal hydroxide. The aqueous solution containing a noble metal hydroxide and a conductive oxide dispersion are mixed to obtain a mixed solution so as to be 0.1 to 10,000 parts by volume. A method for producing a noble metal catalyst. A noble metal catalyst in which a single noble metal and / or alloy is supported on a conductive oxide support,
The noble metal catalyst has an average particle diameter (TEM diameter) of 6 nm or more by observation with an electron microscope of a noble metal alone and / or an alloy supported on a carrier, and a utilization rate of a catalyst defined by the following formula is 45%. A noble metal catalyst characterized by the above.
The noble metal catalyst according to claim 4, wherein the noble metal is platinum. The noble metal catalyst according to claim 4 or 5, wherein the conductive oxide is titanium suboxide. The electrode material using the noble metal catalyst in any one of Claims 4-6.