JP2013231689A - Quantification method for coverage of core-shell particles, and manufacturing method for core-shell particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a more accurate quantification method for a shell coverage of core-shell particles, and a manufacturing method for core-shell particles to which the quantification method is applied.SOLUTION: An open-circuit potential of core-shell particles is measured, and for a mixed sample obtained by mixing particles of core metal material and particles of shell metal material, the sample having the same open-circuit potential as the measured value of the open-circuit potential of the core-shell particles, the ratio of the surface area of the particles of shell metal material to the sum of the surface area of the particles of core metal material and the surface area of the particles of shell metal material, is determined as a coverage of the core-shell particles.

Description

  The present invention relates to a method for determining the coverage of core-shell particles and a method for producing core-shell particles using the method.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Therefore, since the fuel cell is not subject to the Carnot cycle, it exhibits high energy conversion efficiency. A fuel cell is usually configured by laminating a plurality of single cells having a basic structure of a membrane electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes.

Conventionally, platinum catalysts and platinum alloy catalysts having high catalytic activity have been employed as electrode catalysts used in fuel cells. However, there is a problem that platinum is expensive and has a small amount of resources, and a reduction in the amount of platinum is required.
On the other hand, although the catalyst using platinum is very expensive, the catalytic reaction occurs only on the particle surface, and the inside of the particle hardly participates in the catalytic reaction. Therefore, the catalyst activity with respect to material cost in the catalyst using platinum was not necessarily high.

As one of the techniques aimed at solving the above problems, a platinum core-shell particle catalyst in which a platinum monoatomic layer (shell) is coated on a dissimilar metal (core metal) particle supported in a highly dispersed manner on a carrier has attracted attention. Yes. The “monoatomic layer” usually refers to a monoatomic layer, but includes a layer of several atoms in the thickness direction. In the core-shell particle, by using a relatively inexpensive material for the core metal material, the cost inside the particle that hardly participates in the catalytic reaction can be kept low.
Conventionally, as a method of forming a platinum shell, a metal monoatomic layer having a reduction potential lower than that of platinum such as copper is formed on the surface of the core metal particle (underpotential deposition method (UPD method)), and then platinum. Is generally used (substitution plating method).
However, at the time of mass production of the catalyst, there is a case where the platinum shell is not sufficiently coated due to the reason that electrons are not uniformly transmitted to the material and the reactant is not sufficiently supplied. If the platinum shell coating is not sufficient, the catalytic activity of the exposed portions of the core metal particles is low, leading to a decrease in catalyst performance. In addition, in an acidic atmosphere such as in a fuel cell, the core metal particles exposed on the catalyst surface are continuously eluted, which causes a problem in material durability.
For this reason, when manufacturing a platinum core-shell particle catalyst, the importance of accurately quantifying the coverage of the core-shell particles and selectively adopting the core-shell particles having a high coverage is increasing.
Here, the “coverage ratio of the core-shell particles” refers to the ratio (%) of the surface area of the core part covered by the shell part including the shell metal material to the total surface area of the core part including the core metal material.

As a method for measuring the surface area of an electrode catalyst, a method of calculating an electrochemical surface area based on a waveform measured by cyclic voltammetry (hereinafter sometimes referred to as CV) is widely known. The electrochemical surface area is a normalized surface area per unit mass (usually “cm ² / g”). Therefore, the total surface area of the electrode catalyst having a certain electrochemical surface area can be calculated by multiplying the value of the electrochemical surface area by the total mass of the electrode catalyst.
In addition, the particle size according to some definition such as the average particle diameter of the electrode catalyst is measured, and the surface area of the electrode catalyst is calculated based on the particle size.
In conventional platinum catalysts and platinum alloy catalysts, the entire catalyst has a uniform elemental composition. Therefore, the surface area of the catalyst could be calculated using the measurement results such as CV regardless of the presence or absence of unevenness on the catalyst surface.

JP 2011-212666 A

However, the outermost surface of the core-shell particle is composed of a portion covered by the shell and a defect portion of the shell, that is, a portion where the core is exposed. Therefore, the CV waveform measured when CV is performed on the core-shell particles is a combination of the waveform caused by the shell portion and the waveform caused by the portion where the core is exposed. Even if the electrochemical surface area is calculated based on the CV waveform of the core-shell particle itself, the surface area of only the shell portion of the core-shell particle cannot be calculated based on the electrochemical surface area. Therefore, there is a problem that the coverage of the core-shell particles cannot be quantified.
Further, when the surface area of the core-shell particle is measured or calculated by a method other than the electrochemical measurement method, it is impossible to measure the surface area of only the shell portion on the surface of the core-shell particle.

In paragraph [0018] of the specification of Patent Document 1, the following formula (A) is disclosed as a formula for obtaining a platinum coverage with respect to gold particles after platinum coating.
Coverage (%) = {[(Au peak area) − (Pt / Au peak area)] / (Au peak area)} × 100 Formula (A)
(In the above formula (A), “Au peak area” refers to the reduction peak area of gold oxide in the cyclic voltammogram for gold particles (Au) before platinum coating, “Pt / Au peak area”). Indicates the reduction peak area of the gold oxide in the cyclic voltammogram for the gold particles (Pt / Au) after platinum coating.
According to the above formula (A), the rate of change of the reduction peak area of the gold oxide in the cyclic voltammogram before and after the platinum coating is the platinum coating rate.
However, the method for determining the coverage ratio disclosed in Patent Document 1 calculates the reduction peak area of the gold oxide before platinum coating and the reduction peak area of the gold oxide after platinum coating, and before and after platinum coating. However, the exposed area of the core part and the area of the shell part are not directly calculated merely by determining the coverage based on the reduction peak area ratio of the gold oxide.
Therefore, this method can quantify the coverage only when a core metal material having a specific easily detectable peak area is used.

In addition, when the platinum core-shell particle catalyst is produced using the copper-underpotential deposition method (Cu-UPD method), the reason why the shell portion has a defect is that a defect has already occurred during the formation of the copper layer as a sacrificial material. In some cases, after the formation of the copper layer, the replacement of copper with platinum is not performed at the same position on the core metal, and platinum is segregated.
However, in the conventional coverage quantification method that does not rely on the coverage quantification method disclosed in Patent Document 1, the coverage cannot be easily quantified in the catalyst production process. The total coverage is estimated by XRD analysis, transmission electron microscope (TEM) observation, and catalyst performance evaluation.
Therefore, the analysis time required for non-defective product determination becomes longer by performing a plurality of types of measurements. Furthermore, since the coverage is comprehensively estimated from a plurality of types of measurement results, there is a problem that the accuracy of coverage determination is low, and there is a large variation in the activity performance and durability of the produced catalyst.
The present invention has been accomplished in view of the above-described circumstances, the analysis time required for non-defective product determination is short, the coverage quantification method in which the accuracy of coverage quantification is improved, and the method for producing core-shell particles using the quantification method The purpose is to provide.

In the present invention, a method for quantifying the coverage of core-shell particles comprising a core part containing a core metal material and a shell part containing a shell metal material and covering the core part,
Measure the open circuit potential of the core-shell particles,
Surface area of the particles of the core metal material contained in the mixed sample formed by mixing the particles of the core metal material and the particles of the shell metal material having the same open circuit potential as the measured value of the open circuit potential of the core shell particle The ratio of the surface area of the particles of the shell metal material to the total surface area of the particles of the shell metal material is determined as the coverage of the core-shell particles.

In a typical embodiment of the present invention, the method comprises a step of measuring an open circuit potential of a core-shell particle, and a plurality of mixed samples having different mixing ratios expressed by masses of the core metal material particles and the shell metal material particles. In the mixed sample group, preparing a data group indicating the relationship between the mixing ratio and the open circuit potential;
Collating the measured value of the open-circuit potential of the core-shell particles with a data group, and identifying a mixed sample exhibiting the same open-circuit potential;
The ratio of the surface area of the particles of the core metal material to the total surface area of the particles of the core metal material and the shell metal material contained in the specified mixed sample is expressed as the area per unit mass of the core metal material particles, the shell metal Calculation is based on the area per unit mass of the particles of the material and the mixing ratio of the particles of the core metal material and the particles of the shell metal material, and the calculated value can be determined as the coverage of the core-shell particles.

In the present invention, the core metal material is preferably a metal material selected from the group consisting of palladium, copper, nickel, rhodium, silver, gold, iridium, and an alloy containing a metal selected from these.
In the present invention, the shell metal material is preferably a metal material selected from the group consisting of platinum, iridium, ruthenium, rhodium and gold and an alloy containing a metal selected from these.

In the present invention, a core portion containing palladium as a core metal material, and a method for quantifying the coverage of core-shell particles comprising platinum as a shell metal material and a shell portion covering the core portion,
Measuring the open circuit potential of the core-shell particles;
In a mixed sample group consisting of a plurality of mixed samples in which palladium particles and platinum particles having an average particle diameter of 4 nm to 10 nm and an average particle diameter difference of 1 nm or less are mixed at different mixing ratios represented by substance amounts, A step of preparing a data group indicating a relationship between a ratio of a substance amount of platinum particles to a sum of a substance amount of palladium particles and a substance amount of platinum particles contained in the mixed sample, and an open circuit potential;
Collating the measured value of the open circuit potential of the core-shell particles with the data group, and identifying a mixed sample exhibiting the same open circuit potential,
Coverage quantification of core-shell particles, characterized in that the ratio of the amount of platinum particles to the total amount of palladium particles and platinum particles contained in the specified mixed sample is determined as the core-shell particle coverage. Provide a method.

  In the present invention, a method for producing core-shell particles, in which a core portion containing a core metal material is coated with a shell portion containing a shell metal material, and then the coverage is quantified by the coverage quantification method. A method for producing core-shell particles is provided, wherein the shell metal material is additionally coated when is less than a predetermined value.

  According to the present invention, there is provided a core-shell particle coverage quantification method capable of improving the accuracy of core-shell particle coverage quantification and shortening the analysis time required for non-defective determination of core-shell particles, and the coverage quantification method. The manufacturing method of the used core-shell particle can be provided.

It is the isometric view schematic diagram which showed the electrochemical apparatus which performs open circuit electric potential measurement. It is the flowchart which showed the typical example of the manufacturing method of core-shell particle. FIG. 3 is a diagram showing a calibration curve in Example 1.

1. Core shell particle coverage quantification method The core shell particle coverage quantification method of the present invention includes a core portion including a core metal material, and a core shell particle coverage ratio including a shell metal material and a shell portion covering the core portion. A method of quantifying,
Measure the open circuit potential of the core-shell particles,
Surface area of the particles of the core metal material contained in the mixed sample formed by mixing the particles of the core metal material and the particles of the shell metal material having the same open circuit potential as the measured value of the open circuit potential of the core shell particle The ratio of the surface area of the particles of the shell metal material to the total surface area of the particles of the shell metal material is judged as the coverage of the core-shell particles.

The present invention is a method for quantitatively detecting the coverage of core-shell particles based on the principle that each metal has a specific redox potential in an acidic solution.
A metal immersed in an acidic solution is charged to a specific potential depending on the type and concentration of the acid and the temperature of the solution. In the case of the core-shell particles, the core portion is exposed at the defect portion of the shell portion, and the core-shell particles themselves are generally charged to a mixed potential of the oxidation-reduction potentials of the shell metal material and the core metal material.
The inventors of the present invention have a shell metal material that is in contact with the acidic solution with respect to the sum of the area of the shell metal material that is in contact with the acidic solution that is the measurement atmosphere and the area of the core metal material. It was found to be proportional to the ratio of.
According to this finding, when the open circuit potential measured for the core-shell particles and the open-circuit potential measured for the mixture of the core metal material particles and the shell metal material particles are equal, The result is that the ratio of the surface area of the particles of the core metal material and the ratio of the surface area of the particles of the shell metal material to the total surface area of the particles of the shell metal material contained in the mixture is the same value.
On the other hand, the ratio of the surface area of the particles of the shell metal material to the sum of the surface areas of the particles of the core metal material and the shell metal material contained in the mixture is the surface area per unit mass of the core metal material particles, the shell metal material The surface area per unit mass of the particles and the mixing ratio (mass ratio) represented by the mass of the core metal material particles and the shell metal material particles (for example, in grams) can be calculated. Further, the ratio of the surface area of the particles of the shell metal material to the sum of the surface areas of the particles of the core metal material and the shell metal material contained in the mixture may be known by methods other than those described above. .
Therefore, a mixed sample containing particles of a core metal material and particles of a shell metal material having the same open circuit potential as the measured value of the open circuit potential of the core-shell particles is measured in an acidic solution. And the ratio of the surface area of the shell metal material particles to the total surface area of the core metal material particles and the shell metal material particles contained in the mixed sample is calculated, and the calculated value is calculated as It can be determined that the coverage is due to the shell.

In the present invention, in order to easily specify a mixed sample having the same open circuit potential value as the measurement value of the open shell potential of the core shell particle that is the measurement target, the mixture of the core metal material particles and the shell metal material particles is mixed. Create a mixed sample group consisting of a plurality of mixed samples with different ratios, measure the open circuit potential of each mixed sample contained in the mixed sample group, and collate the measured values of the open circuit potential to correspond to the mixed sample It is preferable to use a data group that can specify
The data group used in the present invention can identify a mixed sample having the same open circuit potential as the measured value of the open circuit potential of the core-shell particles, and the surface area of the core metal material particles contained in the mixed sample and the shell metal Any data group can be used as long as it can be used to determine the ratio of the surface area of the particles of the shell metal material to the total surface area of the particles of the material.

By using the quantification method of the present invention, the coverage of the core-shell particles being produced can be accurately quantified and can be quantified efficiently in a short time.
The coverage of the core-shell particles is an index for determining the catalytic activity of the core-shell particles, and also is an index for determining the quality of the manufacturing method when manufacturing the core-shell particles.
Hereinafter, the present invention will be described in detail by taking typical embodiments of the present invention as examples.

(1) First Embodiment A typical embodiment of the present invention includes the following procedure.
(1) measuring the open circuit potential of the core-shell particles;
(2) In a mixed sample group consisting of a plurality of mixed samples having different mixing ratios expressed by the mass (for example, in grams) of the core metal material particles and the shell metal material particles, the relationship between the mixing ratio and the open circuit potential is shown Preparing a data set;
(3) collating the measured value of the open circuit potential of the core-shell particles with a data group, and specifying a mixed sample exhibiting the same open circuit potential;
(4) The ratio of the surface area of the particles of the shell metal material to the total surface area of the particles of the core metal material and the particles of the shell metal material contained in the specified mixed sample is expressed as the area per unit mass of the core metal material particles. (For example, cm ² / g), the area per unit mass of the particles of the shell metal material, and the mixing ratio of the particles of the core metal material and the particles of the shell metal material. Judge as coverage.

(Core shell particles)
The core-shell particle that is a measurement target includes a core portion that includes a core metal material and a shell portion that includes the shell metal material and covers the core portion. The core-shell particles used in the present invention may be commercially available or may be produced in advance.
The method for coating the core portion with the shell portion is not particularly limited, and a known method can be used.

The core metal material constituting the core part is preferably a metal material that does not cause lattice mismatch with the shell metal material used for the shell part described later. Further, from the viewpoint of cost reduction, the core metal material that constitutes the core part is preferably a metal material that is less expensive than the shell metal material used for the shell part described later. Furthermore, it is preferable that the core metal material which comprises a core part is a metal material which can take electrical continuity.
From such a viewpoint, the core metal material included in the core portion is at least one metal material selected from the group consisting of palladium, copper, nickel, rhodium, silver, gold, iridium, and an alloy containing a metal selected from these. It is preferable that Of these metal materials, it is more preferable to use palladium or a palladium alloy containing the metal material as the core metal material, and palladium is particularly preferable.

The average particle diameter of the core metal material particles is not particularly limited as long as it is equal to or less than the average particle diameter of core-shell particles described later. The average particle size of the core metal material particles is preferably 30 nm or less, more preferably 2 to 10 nm.
In addition, the average particle diameter of the particle | grains used for this invention is computed by a conventional method. An example of a method for calculating the average particle size of the particles is as follows. First, in a TEM image of 400,000 times or 1,000,000 times, for one particle, the particle size when the particle is regarded as spherical is calculated. Such calculation of the particle diameter by TEM observation is performed for 200 to 300 particles of the same type, and the average value of the individual particle diameters of these particles is defined as the average particle diameter.

The core metal material may be supported on a carrier. In particular, when the core-shell particles in the present invention are used for an electrode catalyst layer of a fuel cell, the support is preferably a conductive material from the viewpoint of imparting conductivity to the electrode catalyst layer.
Specific examples of the conductive material that can be used as a carrier include Ketjen black (trade name: manufactured by Ketjen Black International Co., Ltd.), Vulcan (product name: manufactured by Cabot), Norit (trade name: manufactured by Norit), Carbon particles such as black pearl (trade name: manufactured by Cabot), acetylene black (trade name: manufactured by Chevron), and carbon fibers such as carbon nanotube (CNT), carbon nanohorn (CNH), and carbon nanofiber (CNF) And carbon materials; metal materials such as metal particles and metal fibers.
Conventionally used methods can be adopted as a method for supporting the core metal material on the carrier.

The shell metal material constituting the shell part preferably has a high catalytic activity.
From such a viewpoint, the shell metal material included in the shell portion is at least one metal material selected from the group consisting of platinum, iridium, ruthenium, rhodium, gold, and an alloy containing a metal selected from these. preferable.
Among these metal materials, the shell part particularly preferably contains platinum. Platinum is excellent in catalytic activity, in particular, oxygen reduction reaction (Oxygen Reduction Reaction; hereinafter referred to as ORR) activity. The lattice constant of platinum is 3.92３, whereas the lattice constant of palladium is 3.89Å, and the lattice constant of palladium is a value within a range of ± 5% of the lattice constant of platinum. Therefore, by using palladium as the core metal material and platinum as the shell metal material, there is no lattice mismatch between the core metal material particles and the shell metal material particles, and the core portion is sufficiently covered with platinum. Done.

The coating of the shell portion onto the core portion may be performed through a one-step reaction or may be performed through a multi-step reaction.
Hereinafter, an example in which the core portion is covered with the shell portion through a two-step reaction will be mainly described.

  As an example in which the core part is coated with the shell part through a two-step reaction, at least the process of coating the core part with a monoatomic layer, and replacing the monoatomic layer with a shell part containing a desired shell metal material The example which has the process to do is given.

As a specific example in which the core portion is coated with the shell portion through a two-step reaction, a monoatomic layer is previously formed on the core portion by an underpotential deposition method, and then the monoatomic layer is formed into a shell containing a desired shell metal material. The method of substituting for a part is mentioned. As the underpotential deposition method, it is preferable to use a Cu-UPD method. As the Cu-UPD method, a conventionally known method described in paragraphs [0036] to [0038] of the specification of JP2012-16684A can be used.
In particular, when a core made of palladium particles is used and platinum is coated as a shell, core-shell particles having a high platinum coverage and excellent durability can be produced by the Cu-UPD method.
The average particle diameter of the core-shell particles used in the present invention generally has a lower limit of 3 nm or more, preferably 4 nm or more, and an upper limit of 40 nm or less, preferably 10 nm or less.

(Measurement of open circuit potential)
In the present invention, the “open circuit potential” refers to a potential difference (unit mV or the like) between a working electrode and a reference electrode measured in a state where only a working electrode and a reference electrode are immersed in a solvent and no current is passed in electrochemical measurement. ).
The open circuit potential measuring method in the present invention is not particularly limited. Examples of the open circuit potential measurement method include a rotating disk electrode (hereinafter sometimes referred to as RDE), a rotating ring disk electrode (hereinafter sometimes referred to as RRDE), and the like. Is carried out by an electrochemical device using as a working electrode.

Hereinafter, a specific example of a method for measuring the open circuit potential of the core-shell particles will be described.
First, the powder of core-shell particles is added to a solvent containing at least water and dispersed. This dispersion is applied to the working electrode of the electrochemical cell and allowed to dry naturally.
The dispersion may be adhered to the working electrode using an electrolyte, for example, a perfluorosulfonic acid polymer electrolyte such as Nafion (registered trademark: manufactured by DuPont) as a binder. A solvent such as water or alcohol may be appropriately added to the dispersion.
As the working electrode, a material that can ensure conductivity, such as glassy carbon, can be used.
As the reference electrode, a reversible hydrogen electrode (hereinafter sometimes referred to as RHE) using hydrogen blown into platinum or a silver-silver chloride electrode is used. When converting the measured value of the silver-silver chloride electrode to the reversible hydrogen electrode, the potential difference between the RHE and the silver-silver chloride electrode is measured in advance and corrected later.
FIG. 1 is a schematic perspective view showing an electrochemical device that performs open circuit potential measurement. The working electrode 4 to which the electrolyte 2 is added and the dispersion 3 is further applied is provided in the glass cell 1. In the glass cell 1, the working electrode 4 and the reference electrode 5 are disposed so as to be sufficiently immersed in the electrolytic solution 2, and these two electrodes are electrically connected to the dual electrochemical analyzer. Further, the gas introduction pipe 6 is disposed so as to be immersed in the electrolytic solution 2, and oxygen is bubbled into the electrolytic solution 2 at room temperature for a certain period of time from an oxygen supply source (not shown) installed outside the cell. The oxygen is saturated inside. Bubbles 7 represent oxygen bubbles. Then, an open circuit potential between the working electrode 4 and the reference electrode 5 is measured.
When measuring the open circuit potential of core-shell particles using RDE as the working electrode, from the viewpoint of potential stability, RDE is immersed in an electrolytic solution, the RDE is rotated in the electrolytic solution, and the open circuit is opened several minutes after the immersion. It is preferable to measure the potential.
The open circuit potential measurement condition is preferably a condition that does not cause deterioration of the core-shell particles or carbon as the carrier. An example of specific conditions for open circuit potential measurement using RDE is shown below.
Electrolyte solution: 0.1M HClO ₄ aq (bubble oxygen)
・ Atmosphere: Under oxygen atmosphere ・ Rotation speed: 400-3,000 rpm
・ Reference electrode: Silver-silver chloride electrode

(Mixed sample)
As the particles of the core metal material used for the mixed sample, particles made of the same material as the core portion of the core-shell particles that are measurement targets can be used. Moreover, the particle | grains of the same material as the shell part of the core shell particle | grains which are measurement targets can be used for the particle | grains of the shell metal material used for a mixed sample.
The average particle diameters of the core metal material particles and the shell metal material particles are not particularly limited, but the lower limit similar to the average particle diameter of the core-shell particles is 3 nm or more, preferably 4 nm or more, and the upper limit is 40 nm or less, preferably 10 nm or less. Within the range, the open circuit potential of the mixed sample can be measured without any problem.
In order to specify a mixed sample having the same open circuit potential as that of the core-shell particles, usually, a plurality of mixed samples having different mixing ratios are prepared. The mixing ratio of the mixed sample is used to calculate the surface area of the particles of the core metal material and the surface area of the particles of the shell metal material contained in the mixed sample, and is a mixing ratio based on mass (usually in grams). It is represented by
The open circuit potential is measured for each mixed sample included in the mixed sample group, and a data group (data map) indicating the relationship between the mixing ratio and the open circuit potential is created. What is necessary is just to measure the open circuit potential of a mixed sample by the same method as a core-shell particle. In the present invention, the mixing ratio of the core metal material particles and the shell metal material particles is a direct comparison between the amount of the core metal material particles and the amount of the shell metal material particles contained in the mixture. The ratio of the amount of the shell metal material particles to the total amount of the core metal material particles and the shell metal material particles, for example, “mass%” This is a broad mixing ratio including a ratio.

(Data group and data verification)
As the data group, for example, it was derived from a simple data group consisting of a plot group in which the open circuit potential of the mixed sample and the mixing ratio correspond to each other, and from a plot group in which the open circuit potential of the mixed sample and the mixing ratio of the mixed sample correspond to each other. A data group expressed in the form of a relational expression is given.
The data group corresponds to the open circuit potential of the mixed sample and the ratio of the surface area of the core metal material particles contained in the mixed sample and the ratio of the surface area of the shell metal material particles to the total surface area of the shell metal material particles. A data group consisting of plotted plots, a data group in the form of a so-called calibration curve that graphs the relationship derived from the plot group that correlates the open circuit potential of the mixed sample and the surface area ratio as described above, etc. Thus, a data group that does not show the mixing ratio of the mixed sample in appearance. However, these modified examples are also obtained by further performing data processing on the data group consisting of plots corresponding to the open circuit potential of the mixed sample and the mixing ratio, thereby performing the data processing to be performed in the subsequent process. Only.

Data groups used in the present invention include, for example, (a) data on open circuit potential in particles of core metal material, (b) data on open circuit potential in particles of shell metal material, and (c) data on core metal material. It may be a data group including at least open circuit potential data in a plurality of mixed sample groups having different mixing ratios of particles and shell metal material particles.
The particles of the core metal material in (a) and the particles of the shell metal material in (b) are made of the same material as the core part and the shell part of the core-shell particle whose coverage is to be quantified, respectively. In addition, the mixed sample group in (c) refers to a mixed sample group including particles of the core metal material and particles of the shell metal material in an arbitrary ratio.
The data group used in the present invention will be specifically described. First, the open circuit potential V ₀ of the core metal material particles, the open circuit potential V _{100 of} the shell metal material particles, and the open circuit of a plurality of mixed sample groups having different mixing ratios of the core metal material particles and the shell metal material particles the potential _{V n,} is measured.
Next, the ratio n (wt%) of the shell metal material particles to the total of the core metal material particles and the shell metal material particles contained in the mixed sample is taken on the x axis, and the open circuit potential (V) of the mixed sample group is calculated. On the y-axis, a data group consisting of data (x, y) = (0, V ₀ ), (n, V _n ), (100, V ₁₀₀ ) is obtained.
By comparing the measured value of the open-circuit potential of the core-shell particle with such a data group, a mixed sample having the same open-circuit potential as the measured value of the open-circuit potential of the core-shell particle is identified, and the mixed sample is mixed. You can know the ratio.

(Surface area of core metal material particles and shell metal material particles)
After identifying a mixed sample having an open circuit potential equal to the measured value of the open circuit potential of the core-shell particles, the surface area of the particles of the core metal material and the surface area of the particles of the shell metal material contained in the mixed sample are calculated.
Here, the surface area of the particles of the core metal material in the mixed sample is the mass of the mixed sample, and the mixing ratio represented by the mass of the core metal material particles and the shell metal material particles contained in the mixed sample, Calculated from the area per unit mass of the core metal material particles. Moreover, the surface area of the particles of the shell metal material in the mixed sample is the mass of the mixed sample, the mixing ratio represented by the mass of the core metal material particles and the shell metal material particles contained in the mixed sample, and the shell It is calculated from the area per unit mass of the metal material particles.
Here, the mass of the mixed sample can be known by weighing the entire used mixed sample. Further, the mixing ratio represented by the mass of the core metal material particles and the shell metal material particles contained in the mixed sample is a value determined at the stage of preparing the mixed sample, and thus is known.

The area per unit mass of the core metal material particles and the shell metal material particles is cyclic voltammetry (CV), CO adsorption, small angle X-ray scattering (hereinafter referred to as SAXS), TEM, and the like. Calculate from the appropriate measurement results. Since the average particle diameter of the metal material particles can be calculated from the SAXS measurement result and the TEM observation result, the area per unit mass of the particle can be calculated from the average particle diameter. Since the area per unit mass differs depending on the particle size even for particles made of the same material, it is necessary to calculate from the measurement results of the core metal material particles and the shell metal material particles actually used for preparing the mixed sample. is there.
The electrochemical surface area of the particles of the core metal material and the electrochemical surface area of the particles of the shell metal material calculated from the measurement results of cyclic voltammetry (CV) can be adopted as the area per unit mass of each particle. As for the electrochemical surface area of the core metal material particles, the cyclic voltammogram is obtained by performing CV measurement on the core metal material particles, and the hydrogen adsorption charge amount is calculated from the area of the hydrogen adsorption wave contained in the obtained cyclic voltammogram. It can calculate and can obtain | require from following Formula (1) using this hydrogen adsorption charge amount. Similarly, the electrochemical surface area of the particles of the shell metal material can be obtained from the equation (1).
[Formula (1)]
Electrochemical surface area (cm ² / g) = hydrogen adsorption charge amount (μC) of particle / [adsorption charge amount per unit active surface area of metal material constituting particle (μC / cm ² ) × particle weight (g)]
In addition, a known value can be used as the adsorption charge amount per unit active surface area of the metal material.
The electrochemical surface area is measured by, for example, an electrochemical apparatus using a rotating disk electrode, a rotating ring disk electrode, or the like as a working electrode. Convective voltammetry using RDE is preferable from the viewpoint that the mass transport speed can be controlled with high reproducibility and the mass transport to the electrode can be made uniform.
The measurement condition of the electrochemical surface area is preferably a condition that does not cause deterioration of the core-shell particles and deterioration of carbon as a carrier.

(Coverage)
After calculating the surface area of the core metal material particles included in the mixed sample and the surface area of the shell metal material particles, the total surface area of the core metal material particles and the shell metal material particles included in the mixed sample is calculated. The ratio of the surface area of the particles of the shell metal material is calculated, and the obtained calculated value is determined as the coverage of the core-shell particles corresponding to the mixed sample.
When the coverage of the core-shell particles is X, the surface area of the core metal material particles is A, and the surface area of the shell metal material particles is B, the coverage X is expressed by the following equation.
[Formula (2)]
Core shell particle coverage X (unit%)
= {Surface Metal B Particle Surface Area B (Unit cm ² ) / (Core Metal Material Particle Surface Area A (Unit cm ² ) + Shell Metal Material Particle Surface Area B (Unit cm ² ))} × 100

Further, the mass of the mixed sample is M, the mass of the core metal material particles contained in the mixed sample is Ma, the mass of the shell metal material particles contained in the mixed sample is Mb, and the unit mass of the core metal material particles per unit mass When the area is Sa, and the area per unit mass of the shell metal material particles is Sb, the mixed sample mass M, the mixing ratio R expressed by the mass of the core metal material particles and the shell metal material particles, The surface area A of the particles and the surface area B of the particles of the shell metal material are represented by the following equations, respectively.
[Formula (3)]
Mass M of the mixed sample (unit: g)
= Mass of core metal material particles Ma (unit: g) + Mass of shell metal material particles Mb (unit: g)
[Formula (4)]
Mixing ratio R expressed by mass of particles of core metal material and shell metal material
= Mass of core metal material particles Ma (unit g): Shell metal material particle mass Mb (unit g)

[Formula (5)]
Surface area A of the core metal material particles (unit cm ² )
= Area Sa per unit mass of core metal material particles (unit cm ² / g) × [Mass of mixed sample M (unit g) × {Ma (unit g) / (Ma + Mb (unit g))}]
When the above equation (3) is substituted into the above equation (5),
[Formula (6)]
Surface area A of the core metal material particles (unit cm ² )
= Area Sa (unit cm ² / g) per unit mass of the core metal material particles x mass Ma (unit g) of the core metal material particles

[Formula (7)]
Surface area B of shell metal material particles (unit cm ² )
= Area Sb per unit mass of shell metal material particles (unit cm ² / g) × [Mass of mixed sample M (unit g) × {Mb (unit g) / (Ma + Mb (unit g))}]
When the above equation (3) is substituted into the above equation (7),
[Formula (8)]
Surface area B of shell metal material particles (unit cm ² )
= Area Sb (unit cm ² / g) per unit mass of particles of shell metal material × mass Mb (unit g) of particles of shell metal material

Then, when the above formula (6) and the above formula (8) are substituted into the above formula (2),
[Formula (9)]
Core shell particle coverage X
= {B / (A + B)} × 100
= {Sb × Mb / (Sa × Ma + Sb × Mb)} × 100 (unit%)
In the above formula (9), the meaning of each symbol is as follows.
X: Coverage (unit%) of core-shell particles that are measurement targets
A: Surface area of the core metal material particles contained in the mixed sample (unit: cm ² )
B: Surface area of shell metal material particles contained in the mixed sample (unit: cm ² )
Sa: Area per unit mass of core metal material particles (unit: cm ² / g)
Sb: area per unit mass of particles of shell metal material (unit: cm ² / g)
Ma: Mass of core metal material particles contained in the mixed sample (unit: g)
Mb: mass of the shell metal material particles contained in the mixed sample (unit: g)
Here, according to the above formula (4), the mixing ratio R expressed by the mass of the core metal material particles and the shell metal material particles is equal to the mass Ma of the core metal material particles and the mass of the shell metal material particles. Since it is represented by the ratio of Mb (Ma: Mb), after all, the covering ratio X of the core-shell particles is the area Sa per unit mass of the core metal material particles, the area Sb per unit mass of the shell metal material particles, and , Based on the mixing ratio (Ma: Mb) represented by the mass of the core metal material particles and the shell metal material particles contained in the mixed sample.

(2) Second Embodiment The present inventors applied the first embodiment to quantify the coverage of core-shell particles composed of a core part containing palladium and a shell part containing platinum, and Under the limited condition that the palladium particles as the core metal material and the platinum particles as the shell metal material used for the preparation of the mixed sample have the same particle size distribution, the palladium particles contained in the mixed sample The mixing ratio (molar ratio) represented by the substance amount (mol) of the platinum particles can be identified with the ratio of the surface area of the palladium particles and the surface area of the platinum particles contained in the mixed sample. Or it discovered that a coverage could be quantified from the mixing ratio represented by the amount of substances.

Since the atomic diameters of platinum and palladium are approximately equal to 278 pm and 274 pm, respectively, when the platinum particles and the palladium particles have the same particle size distribution, the number of platinum atoms contained in one platinum particle and the palladium particles The number of palladium atoms contained in one is approximately equal. Further, when the platinum particles and the palladium particles have the same particle size distribution, the surface area of one platinum particle and the surface area of one palladium particle are substantially equal and exposed on the surface of one platinum particle. The number of platinum atoms and the number of palladium atoms exposed on the surface of one palladium particle are also substantially equal. Therefore, in the mixture of platinum particles and palladium particles, when the platinum particles and palladium particles have the same particle size distribution, the ratio of the surface area of the platinum particles to the surface area of the palladium particles is the amount of the platinum particles and the palladium particles. The mixing ratio is almost the same, and can be identified.
Further, when the open circuit potential of the core-shell particles composed of the core portion containing palladium and the shell portion containing platinum is equal to the open circuit potential measured for the mixed sample formed by mixing the palladium particles and the platinum particles, the former The ratio of the area of the core shell particle where the core part is exposed to the area of the part covered by the shell part is the ratio of the surface area of the palladium particles contained in the latter mixed sample to the surface area of the platinum particles. Consistent with the ratio. This fact is similar to other core-shell particles.
Accordingly, when the above-mentioned limited conditions are satisfied, the palladium particles contained in the mixed sample having an open circuit potential equal to the open circuit potential of the core-shell particles composed of the core portion containing palladium and the shell portion containing platinum. The ratio of the amount of platinum particles relative to the total amount of substances and the amount of platinum particles can be determined as the coverage of the core-shell particles.

The second embodiment of the present invention is a method capable of quantifying the covering ratio of the core-shell particles extremely efficiently when the above-mentioned limited conditions are satisfied, and includes the following procedure.
(1) a step of measuring an open circuit potential of a core-shell particle comprising a core part containing palladium as a core metal material and a shell part containing platinum as a shell metal material and covering the core part;
(2) A mixed sample composed of a plurality of mixed samples in which palladium particles and platinum particles having an average particle diameter of 4 nm to 10 nm and an average particle diameter difference of 1 nm or less are mixed at different mixing ratios represented by substance amounts. Preparing a data group indicating a relationship between a ratio of the amount of platinum particles contained in a mixed sample and a total amount of platinum particles contained in the mixed sample, and an open circuit potential;
(3) collating the measured value of the open circuit potential of the core-shell particles with the data group, and specifying a mixed sample exhibiting the same open circuit potential;
(4) The ratio of the substance amount of the platinum particles to the total of the substance amount of the palladium particles and the platinum substance contained in the specified mixed sample is determined as the coverage of the core-shell particles.
According to the second embodiment, it is not necessary to measure or calculate the area per unit mass of each of the particles of the core metal material and the shell metal material in the mixed sample by a method such as CV measurement. The quantitative procedure according to the invention can be greatly simplified.

In this embodiment, from the viewpoint of using palladium particles and platinum particles having an equivalent particle size distribution, a mixture of palladium particles and platinum particles having an average particle size of 4 nm to 10 nm and an average particle size difference of 1 nm or less. To prepare a mixed sample. By limiting the average particle diameter of palladium particles and platinum particles to 4 nm or more and 10 nm or less and the difference in average particle diameter to within 1 nm, quantitative results with particularly good reproducibility can be obtained.
Here, as the average particle diameter of the palladium particles and the platinum particles, a measurement value of the average particle diameter according to the definition of the X-ray diffraction method can be adopted. The average particle diameter according to such a definition can be measured, for example, by the following method.
The metal particles are irradiated with X-rays, the crystallite size is determined from the following Scherrer equation (10) from the diffraction image, and the obtained crystallite size is defined as the average particle size.
[Formula (10)]
D = (Kλ) / (βcosΘ)
In the above formula (10), the meaning of each symbol is as follows.
D: Crystallite size (nm)
K: Scherrer constant λ: Measurement X-ray wavelength (nm)
β: Half width (rad)
Θ: Bragg angle (rad) of diffraction line

In this embodiment, a data group indicating the relationship between the ratio of the amount of platinum particles contained in the mixed sample and the amount of platinum particles contained in the mixed sample and the open circuit potential is used. Here, the ratio of the substance amount of the platinum particles to the total of the substance amount of the palladium particles and the platinum particles contained in the mixed sample is defined as “mol%”, and the coverage ratio of the core-shell particles having the corresponding open circuit potential It is identified with the value of (Area%).
In this embodiment, when the coverage of the core-shell particles is X, the amount of palladium particles is C (unit mol), and the amount of platinum particles is D (unit mol), the coverage X is expressed by the following formula. .
[Formula (11)]
Core shell particle coverage X (unit%)
= {Substance amount of platinum particles D (unit mole) / (Substance amount of palladium particles C (unit mole) + Substance amount of platinum particles D (unit mole))} × 100
In the above formula (11), the meaning of each symbol is as follows.
X: Coverage (unit%) of core-shell particles that are measurement targets
C: Substance amount (unit mol) of palladium particles that are particles of the core metal material contained in the mixed sample exhibiting an open circuit potential equal to the open circuit potential of the core-shell particles
D: Substance amount (unit mol) of platinum particles, which are particles of the shell metal material contained in the mixed sample showing an open circuit potential equal to the open circuit potential of the core-shell particles
Therefore, in the second embodiment, the coverage X of the core-shell particles can be calculated based on the mixing ratio (C: D) expressed by the amount of palladium particles and platinum particles contained in the mixed sample.

2. Core-shell particle manufacturing method The core-shell particle manufacturing method of the present invention is a method in which a core part containing a core metal material is coated with a shell part containing a shell metal material, and then the coverage is quantified by the above-described core-shell particle coverage quantification method. When the quantitative value is less than a predetermined value, the shell metal material is additionally coated.

  The predetermined value in the present invention, that is, the target value of the coverage can be appropriately determined depending on the use of the core-shell particles. For example, when using core-shell particles for an electrode catalyst of a fuel cell, it is preferable to set the target value of the coverage to a value of 50% or more.

FIG. 2 is a flowchart showing a typical example of the method for producing core-shell particles of the present invention. In addition, this invention is not necessarily limited only to this typical example. Hereafter, the manufacturing method of this invention is demonstrated along FIG.
First, target core-shell particles are prepared (procedure 1). Next, an open circuit potential is measured for the core-shell particles (procedure 2). The method for measuring the open circuit potential is as described above. Subsequently, the coverage of the core-shell particles is quantified from the measured value of the open circuit potential (procedure 3). Next, the quantified coverage is compared with a predetermined value (procedure 4). When the coverage is equal to or higher than the predetermined value, the production of the core-shell particles is finished. On the other hand, when the coverage is less than the predetermined value, the shell metal material is additionally coated on the core-shell particles (procedure 5). As described above, when the predetermined value is not satisfied in the procedure 4, the shell metal material is additionally coated on the core-shell particles in the procedure 5, and the procedures 1 to 5 are repeated until the core-shell particles having a desired coverage are obtained. .

(Method of additionally coating shell metal material)
In the present invention, the method of additionally coating the core-shell particles with the shell metal material is not particularly limited, and examples include potential cycle treatment, acid cleaning treatment, UPD method, and chemical reduction treatment.
The potential cycle treatment is not particularly limited, but the core shell particle is subjected to a potential cycle (for example, 1.1 V to 0.6 V vs. RHE rectangular wave) to partially elute the core metal material of the core portion, and the shell portion that is difficult to melt For example, a method of suppressing the exposed core part by promoting the self-healing effect. In this case, although the particle diameter of the core-shell particles is slightly reduced, core-shell particles with few defects in the shell portion can be obtained.
The acid cleaning treatment is not particularly limited, but the core shell particles are immersed in an acid such as nitric acid, and the core metal material in the core portion is partially eluted in the same manner as the potential cycle treatment, and the self-healing effect of the shell portion that is difficult to dissolve is obtained. Examples of the method include a method of suppressing the exposed core part by promoting it. In this case as well, as with the potential cycle treatment, the core-shell particle size is slightly reduced, but core-shell particles with few defects in the shell portion can be obtained.
The UPD method is not particularly limited, but copper may be used, or substitution plating with other metals may be performed. In the case of the Cu-UPD method, the required amount of copper layer can be formed by controlling the deposition end point with the potential.
The chemical reduction treatment is not particularly limited, but chemical reduction using a metal salt of a shell metal material using alcohols or hydrogen may be performed.

In this way, by applying the core shell particle coverage determination method of the present invention to the core shell particle manufacturing method, it is easy to determine the quality of the catalyst, the accuracy of the coverage determination is improved, and excellent core shell particles Only can be subjected to catalytic reaction.
When the core-shell particles obtained by the production method of the present invention are used for, for example, an electrode of a fuel cell, there is no fear that the voltage is lowered due to elution of the particles of the core metal material, and a battery having excellent discharge performance is provided. Is possible. In addition, the production method of the present invention can provide high-quality core-shell particles without waste.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples.

Example 1
1. Synthesis of core-shell particles supported on carbon (Pt / Pd / C) 0.5 g of 30 wt% palladium-supported carbon powder (hereinafter referred to as Pd / C) is placed in a graphite container, and 1.0 L of 0.05 M sulfuric acid aqueous solution is added. It was.
A graphite vessel was set as a working electrode (hereinafter referred to as WE), a platinum mesh as a counter electrode (hereinafter referred to as CE), and a silver-silver chloride electrode as a reference electrode (hereinafter referred to as RE), and each was immersed in a sulfuric acid aqueous solution.
The vessel was sealed, and nitrogen was bubbled into the sulfuric acid aqueous solution in which Pd / C was suspended at 50 cc / min for 30 minutes. Thereafter, hydrogen was bubbled at 50 cc / min for 30 minutes.
WE, RE, and CE were connected to a potentiostat (HZ-5000, manufactured by Hokuto Denko Corporation), and CV was rotated 360 cycles between 0.40 to 0.45 V vs. RHE. The potential sweep rate was 5 mV / s.
A solution prepared by dissolving 14.6 g of copper sulfate pentahydrate in 66 mL of 0.05 M aqueous sulfuric acid solution was added to the container, and the WE potential was kept constant at 0.40 V vs RHE for 2 hours. A monoatomic layer was deposited.
A solution prepared by dissolving 161.3 mg of potassium platinum chloride and 4.5 g of citric acid monohydrate in 140 mL of 0.05 M aqueous sulfuric acid solution was added to the vessel over about 80 minutes, and then the suspension was added for 1 hour. The mixture was stirred to deposit a platinum monoatomic layer on the surface of the palladium particles.
Thereafter, about 15 mL of suspension was extracted and filtered. It was washed with 300 mL of ultrapure water and vacuum dried for 3 hours to obtain carbon-supported core-shell particles.

2. Creation of data group Palladium particles having an average particle diameter of 4.5 nm and platinum particles having an average particle diameter of 5.4 nm were supported on the same kind of carbon, respectively, to prepare palladium particle-supporting carbon and platinum particle-supporting carbon.
The ratio of the amount of platinum particles to the total amount of platinum particles and palladium particles is 0 mol%, 20 mol%, 40 mol%, 60 mol%, 80 mol%, 100 mol. %, And each mixed sample was applied on a glassy carbon electrode as a working electrode, and rotated at 1600 rpm in an oxygen-saturated 0.1 M perchloric acid aqueous solution. The circuit potential was measured. FIG. 3 shows the open circuit potential (mV) of each mixed sample with respect to the ratio (mol%) of the amount of platinum particles to the total amount of platinum particles and palladium particles contained in each mixed sample. It is a calibration curve showing the relationship.

3. Evaluation of core-shell particles before additional coating For core-shell particles before additional coating, open circuit potential measurement, coverage quantification, measurement of catalyst activity per unit mass of platinum, and elution rate of palladium core, Measured with
(1) Open circuit potential and coverage The powder of core-shell particles obtained by drying was ground in a mortar. This powder was added to a mixed solution of 6.0 mL of ultrapure water, 1.5 mL of isopropanol, and 35 μL of 5% perfluorosulfonic acid polymer electrolyte (Nafion (registered trademark: manufactured by DuPont)) dispersion, and dispersed. I let you. This solution was applied to RDE and air dried.
The dried RDE was rotated (1600 rpm) in a 0.1 M aqueous solution of perchloric acid saturated with oxygen (30 mL / min for 30 minutes or more in advance), and the open circuit potential was measured 3 minutes after immersion.
The measured value of the open circuit potential was compared with the calibration curve of FIG. 3, and the numerical value of the ratio (mol%) of the corresponding substance amount was determined as the coverage of the core-shell particles. The coverage was calculated based on the open circuit potential measured for a control sample of 100% platinum particles (0% palladium particles).

(2) Catalyst activity per unit mass of platinum A solution of core-shell particles prepared by a method similar to the method described in “(1) Open circuit potential and coverage” was applied to RDE and air dried.
The dried RDE was rotated (1600 rpm) in a 0.1 M aqueous solution of perchloric acid saturated with oxygen (30 mL / min for 30 minutes in advance) and the potential was changed from 1.05 V to 0.05 V (vsRHE). In the range of 10 mV / sec. The sweep is repeated until the values of 0.95 V and 0.35 V are stabilized, the current value of 0.9 V is the oxygen reduction current (I _0.9 ), the current value of 0.35 V is the diffusion limit current (I _lim ), The activation dominant current (Ik) was determined from the following equation (12). And Ik (A) was remove | divided by the amount (g) of platinum apply | coated on RDE, and the catalyst activity per unit mass of platinum (A / g-Pt) was computed.
[Formula (12)]
Ik = (I _lim × I _0.9 ) / (I _lim −I _0.9 )
In the above formula (12), the meaning of each symbol is as follows.
Ik: Activation dominant current (A)
I _lim : diffusion limit current (A)
I _0.9 : Oxygen reduction current (A)

(3) Elution rate of palladium core The powder of the core-shell particles used for the determination of the coverage was ground in a mortar.
This powder was immersed in 0.1 mol / L sulfuric acid at 80 ° C. After 1 hour, sulfuric acid was filtered, and the palladium element eluted in sulfuric acid was quantified by inductively coupled plasma mass spectrometry (ICP-MS). The elution amount was expressed as an elution mass per hour (wt% / hr) with respect to the total amount of the palladium core.

4). Additional coating treatment The additional coating treatment was performed by (A) potential cycle treatment, (B) acid cleaning treatment, and (C) Cu-UPD treatment.
(A) Potential cycle treatment The suspension was filtered to collect core-shell particles. The core-shell particle powder was washed with 3 L of ultrapure water.
The powder of the core-shell particles was press-pressed on a graphite plate at room temperature and fixed.
The core-shell particles immobilized on graphite were immersed in an oxygen-saturated 0.1M perchloric acid aqueous solution. This graphite plate was added to the same system as WE, platinum mesh as CE, and silver-silver chloride electrode as RE. The potential of WE was cycled 80 times at 0.2 V to 1.1 V vs. RHE and 50 mV / s to elute and remove unnecessary palladium particles.
The core-shell particles were peeled off from the graphite, dispersed using ultrasonic waves, and filtered to collect the core-shell particles. The powder of the core-shell particles was washed with 3 L of ultrapure water and vacuum dried at 50 ° C. for 6 hours.
(B) Acid washing treatment The suspension was filtered to collect core-shell particles. The core-shell particle powder was washed with 3 L of ultrapure water.
The core-shell particle powder was suspended in 0.8 L of oxygen-saturated 1.0 M nitric acid aqueous solution and stirred for 60 minutes.
The suspension was filtered, and the powder of the core-shell particles was washed and vacuum-dried at 50 ° C. for 6 hours.
(C) Cu-UPD treatment The WE of the container containing the suspension of core-shell particles was again set to 0.4 V vs RHE, and the potential was kept constant for 60 minutes. In addition, since Cu originally exists in a solution excessively, addition of Cu is unnecessary.
Potassium chloride chloride and 1.0 g of citric acid were dissolved in 0.05 M sulfuric acid and added to the suspension of core-shell particles. For platinum potassium chloride, 1.2 times the platinum deficiency estimated from the calibration curve was added. The suspension was stirred for 60 minutes.
The suspension was filtered to collect the core-shell particles. The powder of the core-shell particles was washed with 3 L of ultrapure water and vacuum dried at 50 ° C. for 6 hours.

5. Evaluation of core-shell particles after additional coating The open-circuit potential of the powder of core-shell particles obtained by the potential cycle treatment of (A) above was measured, and the coverage was quantified. Moreover, about the said core-shell particle, the catalyst activity per unit mass of platinum and the elution rate of the palladium core were measured.

(Comparative Example 1)
With respect to the palladium-supported carbon powder used for the synthesis of the core-shell particles in Example 1, the open circuit potential was measured, the coverage was quantified, and the elution rate of the palladium core was measured in the same manner as in Example 1.

(Evaluation results)
Table 1 shows the measurement results of the open-circuit potential, the coverage, the catalytic activity per mass of platinum, and the palladium elution rate of the core-shell particles before and after the additional coating of Example 1 and the core-shell particles of Comparative Example 1. Show.

By creating a calibration curve as shown in FIG. 3 above, the coverage could be quantified by measuring the open circuit potential of core-shell particles with unknown coverage.
In Comparative Example 1, the open circuit potential was measured for palladium particles that had not been subjected to any coating treatment, and was compared with a calibration curve. As a result, the coverage was determined to be 0%.
On the other hand, in Example 1, the coating amount of the core-shell particles was first determined by the method of the present invention, and the second determination was performed after the additional coating. As a result, as shown in Table 1, the mass of platinum Per catalytic activity was improved from 450 (A / g-Pt) to 730 (A / g-Pt), and the variation in activity value was reduced from ± 25% to ± 10%. After the additional coating, the palladium elution rate from the core-shell particles was also significantly reduced.
In addition, the analysis time required for non-defective product determination was conventionally about 3 weeks, but in Example 1, the analysis time was shortened to 0.5 days and the analysis determination procedure was simplified.

DESCRIPTION OF SYMBOLS 1 Glass cell 2 Electrolytic solution 3 Dispersion liquid 4 Working electrode 5 Reference electrode 6 Gas introduction tube 7 Bubble

Claims (6)

A method for quantifying the coverage of core-shell particles comprising a core part containing a core metal material and a shell part containing a shell metal material and covering the core part,
Measure the open circuit potential of the core-shell particles,
Surface area of the particles of the core metal material contained in the mixed sample formed by mixing the particles of the core metal material and the particles of the shell metal material having the same open circuit potential as the measured value of the open circuit potential of the core shell particle The ratio of the surface area of the particles of the shell metal material to the total surface area of the particles of the shell metal material is determined as the coverage of the core-shell particles. Measuring the open circuit potential of the core-shell particles;
In a mixed sample group consisting of a plurality of mixed samples having different mixing ratios represented by the mass of the core metal material particles and the shell metal material particles, preparing a data group indicating the relationship between the mixing ratio and the open circuit potential;
Collating the measured value of the open-circuit potential of the core-shell particles with a data group, and identifying a mixed sample exhibiting the same open-circuit potential;
The ratio of the surface area of the particles of the core metal material to the total surface area of the particles of the core metal material and the shell metal material contained in the specified mixed sample is expressed as the area per unit mass of the core metal material particles, the shell metal It is calculated based on the area per unit mass of the particles of the material and the mixing ratio of the particles of the core metal material and the particles of the shell metal material, and the obtained calculated value is judged as the coverage of the core shell particles The coverage quantification method according to claim 1.   The coverage quantification according to claim 1 or 2, wherein the core metal material is a metal material selected from the group consisting of palladium, copper, nickel, rhodium, silver, gold, iridium, and an alloy containing a metal selected from these. Method.   The coverage according to any one of claims 1 to 3, wherein the shell metal material is a metal material selected from the group consisting of platinum, iridium, ruthenium, rhodium and gold and an alloy containing a metal selected from these. Quantitation method. A method of quantifying the coverage of core-shell particles comprising a core part containing palladium as a core metal material and a shell part containing platinum as a shell metal material and covering the core part,
Measuring the open circuit potential of the core-shell particles;
In a mixed sample group consisting of a plurality of mixed samples in which palladium particles and platinum particles having an average particle diameter of 4 nm to 10 nm and an average particle diameter difference of 1 nm or less are mixed at different mixing ratios represented by substance amounts, A step of preparing a data group indicating a relationship between a ratio of a substance amount of platinum particles to a sum of a substance amount of palladium particles and a substance amount of platinum particles contained in the mixed sample, and an open circuit potential;
Collating the measured value of the open circuit potential of the core-shell particles with the data group, and identifying a mixed sample exhibiting the same open circuit potential,
Coverage quantification of core-shell particles, characterized in that the ratio of the amount of platinum particles to the total amount of palladium particles and platinum particles contained in the specified mixed sample is determined as the core-shell particle coverage. Method.   It is a manufacturing method of core-shell particle | grains, Comprising: After coat | covering the core part containing a core metal material with the shell part containing a shell metal material, a coverage is measured by the fixed_quantity | quantitative_assay method as described in any one of the said Claims 1 thru | or 5. A method for producing core-shell particles, characterized in that when the amount is quantitatively determined and the quantitative value is less than a predetermined value, the shell metal material is additionally coated.