JP2013164404A - Coverage calculation method of catalyst fine particle and catalyst fine particle evaluation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for more accurately calculating coverage of an outermost layer of catalyst fine particles for center particles than before, and a catalyst fine particle evaluation method applying the calculation method.SOLUTION: There is provided a method for calculating the coverage of the outermost layer for the center particles in the catalyst fine particles comprising the center particles and the outermost layer covering the center particles. The coverage calculation method includes the steps of: preparing the catalyst fine particles; calculating an electrochemical surface area of the catalyst fine particle; performing oxygen-reducing reaction measurement for the catalyst fine particle and calculating an amount of hydrogen peroxide generated through the measurement; and calculating the coverage from the electrochemical surface area value and the generation amount value of hydrogen peroxide.

Description

  The present invention relates to a method for calculating an accurate coverage of an outermost layer with respect to center particles in catalyst fine particles, and a method for evaluating catalyst fine particles to which the calculation method is applied.

  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. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle, and thus exhibit high energy conversion efficiency. A fuel cell is usually formed 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 and platinum alloy catalysts have been employed as anode and cathode electrode catalysts for fuel cells. However, platinum catalysts and platinum alloy catalysts required for electrodes in today's latest technology are still expensive to commercially realize mass production of fuel cells. The influence of the precious metal unit price on the catalyst price is large, and therefore further improvement in the catalyst activity per unit mass has been desired.
On the other hand, although the platinum catalyst and the platinum alloy catalyst are 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 catalytic activity for the material cost in the platinum catalyst and the platinum alloy catalyst is not necessarily high.
Further, when a platinum catalyst and a platinum alloy catalyst are used as electrodes, there is a problem that platinum ions are eluted under a high potential environment, while platinum ions are precipitated under a low potential environment. Therefore, when high potential discharge and low potential discharge are repeated alternately, aggregation of platinum fine particles occurs. Such agglomeration of platinum fine particles causes a decrease in the electrochemical surface area and contributes to a decrease in battery performance.

As one of the technologies aimed at solving the above-mentioned problems, a technology related to catalyst particles having a structure including a center particle and an outermost layer covering the center particle, that is, a so-called core-shell structure is known. In the catalyst fine particles, by using a relatively inexpensive material for the center particles, the cost inside the particles that hardly participate in the catalytic reaction can be kept low.
When the central particles are eluted in the catalyst fine particles having a core-shell structure, the battery performance is significantly deteriorated due to loss of catalytic activity of the catalyst fine particles themselves or contamination of the battery materials by the eluted ions. It has been known. In order to suppress such elution of the central particles, catalyst fine particles having a high ratio of the surface area of the central particles covered by the outermost layer to the total surface area of the central particles, that is, the coverage of the outermost layer with respect to the central particles is high. There is a need for catalyst particulates. Therefore, it is increasingly important to accurately calculate the coverage of catalyst fine particles in advance and selectively employ catalyst fine particles having a high coverage.

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.

JP 2011-212666 A

  Cyclic voltammetry (hereinafter sometimes referred to as CV) is widely used as a method for determining the electrochemical surface area of a general fuel cell electrode catalyst. However, when the CV is performed on the catalyst fine particles including the center particle and the outermost layer, the calculated electrochemical surface area includes the electrochemical surface area of the center particle not covered with the outermost layer in addition to the electrochemical surface area of the outermost layer. There is a problem that the surface area is also included. As a result, in the conventional method using CV, it was difficult to calculate the electrochemical surface area of only the outermost layer. Therefore, conventionally, the coverage of the catalyst fine particles cannot be accurately calculated, and it has been difficult to confirm the completeness of the produced catalyst fine particles.

Patent Document 1 discloses a method for calculating the coverage using the reduction peak area of gold oxide. However, since the method is limited to catalyst particles using gold, it is difficult to apply the method to catalyst particles using other metals. Further, according to paragraph [0029] of FIG. 4A and FIG. 4A, the reduction peak of gold oxide appears around 1.2 V (vs RHE). Application of such a high potential is likely to cause deterioration of the catalyst fine particles and the catalyst carrier.
The present invention has been accomplished in view of the above circumstances, and provides a method for calculating an accurate coverage of the outermost layer with respect to the center particle in the catalyst fine particles, and a method for evaluating the catalyst fine particles to which the calculation method is applied. With the goal.

  The catalyst fine particle coverage calculation method of the present invention is a method for calculating the coverage of the outermost layer with respect to the center particle in the catalyst fine particle including the center particle and the outermost layer covering the center particle, A step of preparing fine particles, a step of calculating an electrochemical surface area of the catalyst fine particles, a step of performing an oxygen reduction reaction measurement on the catalyst fine particles, and calculating an amount of hydrogen peroxide generated by the measurement, Calculating the coverage from the value and the value of the hydrogen peroxide generation amount.

  In the calculation method of the present invention, the coverage ratio calculating step includes at least one predetermined map representing a relationship between the coverage ratio of the outermost layer with respect to the center particle and the amount of hydrogen peroxide generated per unit electrochemical surface area of the catalyst fine particles. The step of calculating the coverage from the value of the electrochemical surface area and the value of the hydrogen peroxide generation amount may be employed.

  In the calculation method of the present invention, the predetermined map includes data on the amount of hydrogen peroxide generated per unit electrochemical surface area in the center particle, data on the amount of hydrogen peroxide generated per unit electrochemical surface area in the outermost layer, and A map including at least data on the amount of hydrogen peroxide generated per unit electrochemical surface area of a catalyst fine particle sample having the central particle and the outermost layer, and the covering ratio of the outermost layer to the central particle being n%, Also good.

In the calculation method of the present invention, the catalyst fine particle sample is a sample of catalyst fine particles in which a central particle is coated with an outermost layer by Cu-UPD, and the coverage ratio n% is a value obtained by the following formula (1). There may be.
Coverage n (%) = {C _Cu / (2 × C _H )} × 100 Formula (1)
(In the above formula (1), C _Cu is the copper adsorption charge amount (C) to the central particle during Cu-UPD, C _H is the proton adsorption charge amount (C) to the central particle, and 0 <n <100.)

  The method for evaluating catalyst fine particles according to the present invention is a method for evaluating catalyst fine particles comprising center particles and an outermost layer covering the center particles, the step of preparing the catalyst fine particles, and the electrochemical surface area of the catalyst fine particles. The step of calculating, the oxygen reduction reaction measurement for the catalyst fine particles, the step of calculating the amount of hydrogen peroxide generated by the measurement, the value of the electrochemical surface area and the value of the amount of hydrogen peroxide generated, and calculating the coverage And comparing the calculated coverage with a preset reference value, and determining that the catalyst fine particle is acceptable when the calculated coverage is equal to or greater than the reference value, and calculating the coating A step of determining that the catalyst fine particles are rejected when the rate is less than the reference value, and coating from the step of preparing the catalyst fine particles when it is determined to be rejected in the determination step. Which comprises carrying out again until the step of calculating the.

  In the evaluation method of the present invention, the coverage ratio calculating step is based on at least one predetermined map representing the relationship between the coverage ratio of the outermost layer with respect to the center particles and the amount of hydrogen peroxide produced per unit electrochemical surface area of the catalyst fine particles. The step of calculating the coverage from the value of the electrochemical surface area and the value of the hydrogen peroxide generation amount may be employed.

  In the evaluation method of the present invention, the predetermined map includes data on the amount of hydrogen peroxide generated per unit electrochemical surface area in the center particle, data on the amount of hydrogen peroxide generated per unit electrochemical surface area in the outermost layer, and A map including at least data on the amount of hydrogen peroxide generated per unit electrochemical surface area of a catalyst fine particle sample having the central particle and the outermost layer, and the covering ratio of the outermost layer to the central particle being n%, Also good.

  In the evaluation method of the present invention, the catalyst fine particle sample is a sample of catalyst fine particles in which a center particle is coated with an outermost layer by Cu-UPD, and the coverage n% is a value obtained by the above formula (1). There may be.

  According to the present invention, by using the calculated value of the electrochemical surface area and the value of the amount of hydrogen peroxide generated, it is possible to calculate the coverage of the outermost layer with respect to the center particle, which has been difficult in the past, and to improve the catalytic activity of the catalyst fine particles. It can be evaluated more accurately than before.

It is the perspective schematic diagram which showed the example of the electrochemical apparatus used suitably for this invention. It is the flowchart which showed the typical example of the evaluation method of the catalyst fine particle of this invention. It is the graph which showed the copper adsorption peak area in the cyclic voltammogram at the time of performing Cu-UPD in an Example. A cyclic voltammogram obtained by sweeping a potential at a sweep rate of 50 mV / s in a range of 0.05 to 1.2 V (vs RHE) for a catalyst fine particle sample, and a proton adsorption peak area in the cyclic voltammogram are hatched It is the graph represented by. It is the graph which showed the oxygen reduction wave in the oxygen reduction reaction measurement about a certain catalyst fine particle sample, and the graph which showed the hydrogen peroxide production amount in the oxygen reduction reaction measurement about the said catalyst fine particle sample. The vertical axis represents the amount of hydrogen peroxide produced per unit electrochemical surface area (A / C), and the horizontal axis represents the coverage n (%).

1. Catalyst fine particle coverage calculation method The catalyst fine particle coverage calculation method according to the present invention calculates the coverage of the outermost layer with respect to the center particle in the catalyst fine particle including the center particle and the outermost layer covering the center particle. A method of preparing the catalyst fine particles, calculating an electrochemical surface area of the catalyst fine particles, performing an oxygen reduction reaction measurement on the catalyst fine particles, and calculating an amount of hydrogen peroxide generated by the measurement; And the step of calculating the coverage from the value of the electrochemical surface area and the value of the hydrogen peroxide generation amount.

  In conventional platinum catalysts and platinum alloy catalysts, the entire catalyst has a uniform elemental composition. Therefore, the surface area of the catalyst calculated using CV or the like can be regarded as the electrochemical surface area of the catalyst as it is, regardless of whether the catalyst surface has irregularities.

On the other hand, the catalyst fine particle having a structure in which the center particle is covered with the outermost layer has a different element composition on the outermost surface of the catalyst fine particle and an element composition inside the catalyst fine particle. Therefore, a portion having an element composition different from that of the outermost layer, that is, the surface of the central particle is exposed on the surface of the catalyst fine particles having defects in the outermost layer. When CV or the like is performed on such catalyst fine particles, the exposed central particle surface also reacts. Therefore, the calculated electrochemical surface area is derived from the exposed central particle surface in addition to the electrochemical surface area derived from the outermost layer. Also included is an electrochemical surface area. As a result, it is impossible to accurately grasp the electrochemical surface area of the outermost layer that contributes to the catalytic activity. Therefore, it is difficult to calculate an accurate coverage of the outermost layer.
The presence of the outermost layer can also be confirmed by observation with a transmission electron microscope (Transmission Electron Microscope; hereinafter referred to as TEM). However, accurate values of electrochemical surface area and coverage cannot be obtained by TEM observation or the like.

The present inventors have found that there is a correlation between the amount of hydrogen peroxide generated per unit electrochemical surface area of the catalyst fine particles and the coverage of the outermost layer with respect to the central particles of the catalyst fine particles. As a result of diligent efforts, the present inventors have found that the coverage of catalyst fine particles can be calculated by quantifying the amount of hydrogen peroxide produced per unit electrochemical surface area of the catalyst fine particles, and completed the present invention.
The coverage of the catalyst fine particles is an index for determining the catalyst activity and the like of the catalyst fine particles, and is also an index for determining the quality of the manufacturing method when the membrane / electrode assembly is manufactured using the catalyst fine particles.

By the way, as shown in the formula (1) described later, the coverage of the catalyst fine particles produced by Cu-UPD theoretically represents the value of the copper adsorbed charge amount on the center particle during Cu-UPD and the center It can be calculated from the value of the proton adsorption charge amount on the particles. However, both the value of the copper adsorption charge amount and the value of the proton adsorption charge amount can be calculated only at the time of manufacture. Therefore, it is extremely difficult to calculate the coverage of the catalyst fine particles, which is a finished product, using Equation (1) described later.
The method for calculating the coverage of catalyst fine particles of the present invention has an advantage that the coverage of catalyst fine particles during production can be accurately calculated, and also for a finished product of catalyst fine particles having an unknown coverage per unit electrochemical surface area. There is an advantage that the coverage can be calculated by determining the amount of hydrogen peroxide produced, and it can be said that this is a new method completely different from the conventional method.

The present invention includes (1) a step of preparing catalyst fine particles, (2) a step of calculating an electrochemical surface area of the catalyst fine particles, (3) a step of calculating a hydrogen peroxide generation amount of the catalyst fine particles, and (4) catalyst fine particles. A step of calculating a coverage ratio of. The present invention is not necessarily limited to the above four steps.
Hereinafter, the steps (1) to (4) will be mainly described in order.

1-1. Step of Preparing Catalyst Fine Particles The catalyst fine particles used in the present invention are not particularly limited as long as they are provided with center particles and an outermost layer covering the center particles. The catalyst fine particles used in the present invention may be commercially available or may be produced in advance.

  Examples of the method for producing catalyst fine particles include a method in which center particles are prepared and the outermost layer is coated on the center particles. The method for coating the outermost layer on the center particle is not particularly limited, and a known method can be used.

The material constituting the central particle is preferably a metal material that does not cause lattice mismatch with the material used for the outermost layer described later. Further, from the viewpoint of cost reduction, the material constituting the center particle is preferably a metal material that is cheaper than the material used for the outermost layer described later. Furthermore, the material constituting the central particle is preferably a metal material that can be electrically connected.
From such a viewpoint, it is preferable that the material contained in the center particle contains a metal such as palladium, iridium, rhodium or gold, or an alloy made of two or more kinds of the metals. Of these metal materials, it is more preferable to use palladium or a palladium alloy containing the metal material as the central particle.

The average particle diameter of the center particles is not particularly limited as long as it is equal to or less than the average particle diameter of catalyst fine particles described later. In addition, from the viewpoint that the ratio of the surface area to the cost per one center particle is high, the average particle size of the center particle is preferably 30 nm or less, more preferably 5 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. The calculation of the particle size by such TEM observation is performed on 200 to 300 particles of the same type, and the average of these particles is defined as the average particle size.

The central particle may be supported on a carrier. In particular, when the catalyst fine particles according to the present invention are used in 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), Examples thereof include carbon particles such as black pearl (trade name: manufactured by Cabot), acetylene black (trade name: manufactured by Chevron), conductive carbon materials such as carbon fibers, and metal materials such as metal particles and metal fibers.

  Conventionally used methods can be adopted as a method for supporting the center particles on the carrier. When an alloy is used for the center particles, the synthesis of the alloy and the loading of the center particles on the support may be performed simultaneously.

The outermost layer may be coated on the center particle through a one-stage reaction or a multi-stage reaction.
Hereinafter, an example in which the outermost layer is coated on the center particle through a two-step reaction will be mainly described.

  As an example in which the outermost layer is coated on the center particle through a two-step reaction, at least the step of covering the center particle with a monoatomic layer and the step of replacing the monoatomic layer with a desired outermost layer Is mentioned.

As a specific example in which the outermost layer is coated on the center particle through a two-step reaction, a monoatomic layer is formed on the surface of the center particle in advance by an underpotential deposition method, and then the monoatomic layer is replaced with a desired outermost layer. A method is mentioned. As the underpotential deposition method, it is preferable to use a Cu-UPD method.
In particular, when palladium fine particles are used as the central particles and a platinum monoatomic layer is used as the outermost layer, catalyst fine particles having high platinum coverage and excellent durability can be produced by the Cu-UPD method. This is because copper can be deposited on the Pd {111} plane or the Pd {110} plane at a coverage of 100% by the Cu-UPD method.

  The amount of copper coated on the center particle by the Cu-UPD method can be calculated based on, for example, the amount of charge adsorbed on the center particle. The amount of charge adsorbed on copper is calculated from a cyclic voltammogram obtained by sweeping the potential of the central particles in the copper ion solution. Specifically, the adsorption charge amount of copper can be calculated from the area determined by determining the copper adsorption peak area in the reduction wave of the cyclic voltammogram. A specific example of the copper adsorption peak area is shown in FIG.

The copper adsorption peak area can be obtained by integrating a predetermined region of the reduction wave of the cyclic voltammogram with the potential. Here, the potentials that determine the integration interval are a start potential E ₀ and a stop potential E ₁ .
The starting potential E ₀ is preferably a potential at which copper deposition derived from Cu-UPD starts. For example, the start potential E ₀ can be determined as follows. In the reduction wave of the cyclic voltammogram, the slope of the tangent line of the reduction wave is 1.0 × 10 ^{−5 to} 0 (A / V), that is, almost 0 (A / V) at the beginning of the sweep, that is, at a relatively high potential portion. There is a range of potentials that can be considered as V). In this potential range, it is considered that the electrochemical reaction on the catalyst surface has not yet occurred, and charging / discharging occurs in a carrier such as carbon. Immediately after this sweep the early part, the potential to be a predetermined inclination with the tangent of the slope of the reduction wave, it is possible to determine a potential E _0. Here, the predetermined inclination is, for example, an inclination in a range of 5.0 × 10 ^{−4 to} 1.0 × 10 ⁻⁴ (A / V).
The start potential E ₀ may be a potential within a range of 0.6 to 0.7 V (vs RHE), for example.

The stop potential E ₁ is preferably a potential at which the amount of copper adsorbed charge is the largest and the ratio of the amount of copper adsorbed charge derived from Cu-UPD is the highest in the copper adsorbed charge amount. If you stop the sweeping at lower than the stop voltage E ₁ potential, the copper adsorption charge amount, the proportion of copper adsorption amount of charge derived from the Cu-UPD is lowered. On the other hand, when stopping the sweep at higher than the stop voltage E ₁ potential, copper adsorption charge amount itself is reduced.
Stop potential E ₁ is, for example, can be determined as follows. In the reduction wave of the cyclic voltammogram at the time of copper deposition, the potential at which the slope of the tangent line of the reduction wave exceeds −1.0 × 10 ⁻³ (A / V) at the later stage of the sweep, that is, at a relatively low potential portion. A range exists. In this potential range, it is considered that the copper adsorption charge amount derived from the bulk deposition of copper is larger than the copper adsorption charge amount by Cu-UPD. The potential having a predetermined slope with the slope of the tangent of the reduction wave can be determined as the potential E ₁ immediately before the potential range in the latter period of the sweep, that is, immediately before the bulk precipitation of copper becomes dominant. Here, the predetermined inclination is, for example, an inclination in a range of −1.0 × 10 ^{−3 to} 0 (A / V).
When the potential sweep rate is low, a maximum point or an inflection point may appear in the reduction wave immediately before copper bulk deposition becomes dominant. A potential corresponding to the maximum point or inflection point may stop potential E _1.
Stop potential _{E 1} is, for example, may be a potential within the range of 0.34~0.4V (vsRHE). Note that stop sweep potential at the stop potential E _1, the time the potential of a predetermined, it preferably secures 30-60 minutes.
Range of potential actually sweep the onset potential E ₀ may range from just wide potential and about 0.01~0.1V width including the scope to the stop potential E _1.

In this step, the potential sweep rate is preferably 0.01 to 10 mV / sec. If the potential sweep rate is too slow, the synthesis takes a long time and the high potential holding time becomes long, so that the material constituting the center particle may be eluted. On the other hand, when the sweep rate of the potential is too fast, can not be sufficiently separate the CV waveforms derived from CV waveform and copper bulk precipitation derived from Cu-UPD, it is difficult to determine the stopping potential E ₁ There is a fear.

Hereinafter, specific examples of the Cu-UPD method will be described.
First, palladium (hereinafter referred to as Pd / C) powder supported on a conductive carbon material is dispersed in water, and a Pd / C paste obtained by filtration is applied to the working electrode of an electrochemical cell. The Pd / C paste may be adhered to the working electrode using an electrolyte such as Nafion (trade name) as a binder. A solvent such as water or alcohol may be appropriately added to the Pd / C paste. As the working electrode, a material such as platinum mesh or glassy carbon that can ensure conductivity can be used.

  FIG. 1 is a schematic perspective view showing an electrochemical apparatus for performing Cu-UPD. A working electrode 24 to which a copper ion solution 22 is added and a paste 23 is further applied is provided in the glass cell 21. In the glass cell 21, in addition to the working electrode 24, a counter electrode 26 and a reference electrode 27 are disposed so as to be sufficiently immersed in the copper ion solution 22, and these three electrodes are electrically connected to the dual electrochemical analyzer. . Further, the gas introduction tube 28 is disposed so as to be immersed in the copper ion solution 22, and nitrogen is bubbled into the copper ion solution 22 at room temperature for a certain period of time from a nitrogen supply source (not shown) installed outside the cell. The ion solution 22 is saturated with nitrogen. A circle 29 indicates a nitrogen bubble.

A copper monoatomic layer is deposited on the surface of the palladium fine particles by the Cu-UPD method. An example of specific conditions for the Cu-UPD method is shown below.
Copper ion solution: mixed solution of 0.05 mol / L CuSO ₄ and 0.05 mol / L H ₂ SO ₄ (nitrogen is bubbled)
Atmosphere: under a nitrogen atmosphere, sweep rate: 0.2~0.01mV / sec and potential: swept in the range of 0.3~0.75V (vsRHE), at the stop potential _E 1 = 0.35V (vsRHE) Fix the potential.
-Potential fixing time: 30-60 minutes

It is preferable that the material constituting the outermost layer has a high catalytic activity. The catalytic activity here refers to the activity when used as a fuel cell catalyst.
From such a viewpoint, the material included in the outermost layer is preferably at least one metal material selected from the group consisting of platinum, iridium, ruthenium, rhodium and gold.
Among these metal materials, the outermost layer 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 or a palladium alloy for the center particle and platinum for the outermost layer, lattice mismatch does not occur between the center particle and the outermost layer, and the center particle is sufficiently covered with platinum.

In the catalyst fine particles used in the present invention, the proportion of the monoatomic layer in the outermost layer may be large. Such catalyst fine particles have the advantage that the catalyst performance in the outermost layer is extremely high compared to the catalyst fine particles having the outermost layer of two atomic layers or more, and the advantage that the material cost is low because the coating amount of the outermost layer is small. There is.
The average particle diameter of the catalyst fine particles used in the present invention is 30 nm or less, preferably 5 to 10 nm.

Hereinafter, a specific example of a method for subjecting palladium fine particles coated with copper to substitution plating of platinum will be described.
After the potential fixing time in Cu-UPD is completed, the working electrode is immediately immersed in a platinum solution, and copper and platinum are replaced by plating using the difference in ionization tendency. The displacement plating is preferably performed in an inert gas atmosphere such as a nitrogen atmosphere, and it is more preferable to use a glove box or the like replaced with an inert gas atmosphere. By rapidly moving the working electrode from the copper ion solution to the platinum solution under an inert gas atmosphere, oxidation of copper after coating can be prevented.
The platinum solution is not particularly limited. For example, a 0.005M K ₂ PtCl ₄ solution can be used. It is preferable that the platinum solution is sufficiently stirred and nitrogen is bubbled in advance in the solution. The displacement plating time is preferably secured for 90 minutes or more.
By the substitution plating, copper atoms and platinum ions (Pt ²⁺ ) deposited by UPD are substituted on a one-to-one basis to obtain catalyst fine particles in which a platinum monoatomic layer is deposited on the surface of the fine palladium particles.

After the production of the catalyst fine particles, the catalyst fine particles may be washed and dried.
The filtering and washing of the catalyst fine particles is not particularly limited as long as it is a method that can remove impurities without impairing the coating structure of the produced catalyst fine particles. Examples of the filtration / washing include suction filtration using water, perchloric acid, dilute sulfuric acid, dilute nitric acid or the like.
The drying of the catalyst fine particles is not particularly limited as long as the method can remove the solvent and the like. As an example of the drying, a method of performing vacuum drying at room temperature for 0.5 to 2 hours and then drying under an inert gas atmosphere at a temperature of 60 to 80 ° C. for 1 to 4 hours can be given.

1-2. Step of calculating electrochemical surface area of catalyst fine particles The method of calculating the electrochemical surface area of catalyst fine particles in this step is not particularly limited.
Examples of the method for calculating the electrochemical surface area of the catalyst fine particles include a method of calculating from measurement results such as CV, CO adsorption, small angle X-ray scattering (hereinafter referred to as SAXS), and TEM. Since the average particle diameter of the catalyst fine particles can be calculated from the SAXS measurement result and the TEM observation result, the electrochemical surface area can be estimated from the average particle diameter.
The electrochemical surface area of the catalyst fine particles may be measured by, for example, a rotating disk electrode (hereinafter sometimes referred to as RDE) or a rotating ring disk electrode (hereinafter referred to as RRDE). ) Etc. for the working electrode. The convective voltammetry using RDE and RRDE is preferable from the viewpoints that the mass transport speed can be controlled with high reproducibility and the mass transport to the electrode can be made uniform.

As an apparatus provided with RDE, the electrochemical apparatus shown in FIG. 1 mentioned above is mentioned, for example. In the electrochemical device, RDE with a tachometer is used as the working electrode 24.
The electrochemical measurement conditions are preferably conditions that do not cause deterioration of the catalyst fine particles and deterioration of carbon as a carrier. An example of specific conditions for CV using RDE is shown below.
Electrolyte solution: 0.1M HClO ₄ aq (nitrogen is bubbled)
-Atmosphere: Under nitrogen atmosphere-Sweep speed: 10-100 mV / sec-Potential: 0-1.1 V (vs RHE)

  As will be described later, FIG. 4B is a graph in which the area corresponding to the proton adsorption charge amount of the catalyst fine particles is represented by diagonal lines. In FIG. 4B, the point corresponding to the potential at which proton adsorption on the surface of the catalyst fine particles starts is indicated by a white circle, and the point corresponding to the potential at which proton adsorption on the surface of the catalyst fine particle ends is indicated by a black circle. The electrochemical surface area of the catalyst fine particles is calculated by a known method using the proton adsorption charge amount.

1-3. Step of calculating hydrogen peroxide generation amount of catalyst fine particles This step is a step of performing oxygen reduction reaction (ORR) measurement on the catalyst fine particles and calculating the amount of hydrogen peroxide generated by the measurement.
In the cathode of a fuel cell, it is ideal that only the four-electron reduction reaction shown in the following formula (I) usually occurs.
O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O Formula (I)
However, in practice, the two-electron reduction reaction represented by the following formulas (II) and (III) proceeds simultaneously with the four-electron reduction reaction.
O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O ₂ formula (II)
H ₂ O ₂ + 2H ⁺ + 2e ⁻ → 2H ₂ O Formula (III)
It is considered that the ORR activity of the catalyst fine particles can be evaluated by each contribution of the 4-electron reduction reaction (formula (I)) and the 2-electron reduction reaction (formula (II) and formula (III)) in the entire ORR. In this step, the ORR activity of the catalyst fine particles used in the measurement can be quantitatively evaluated by quantifying hydrogen peroxide (H ₂ O ₂ ), which is an intermediate product of the two-electron reduction reaction.

The ORR measurement method in this step is not particularly limited. Examples of the ORR measurement method include the above-described CV.
The ORR measurement is performed by, for example, an electrochemical device using the above-described RRDE or the like as a working electrode. Convective voltammetry using RRDE has the advantage that the product produced at the disk electrode can be detected at the ring electrode in addition to the advantages of using RDE as described above. In the ring electrode, the reverse reaction of the above formula (III) occurs, and the amount of hydrogen peroxide produced can be determined from the detected current (A). In RRDE, the oxygen reduction current is detected by the disk electrode, and at the same time, the generated hydrogen peroxide can be quantified by the ring electrode.

As an apparatus provided with RRDE, the electrochemical apparatus shown in FIG. 1 mentioned above is mentioned, for example. In the electrochemical apparatus, an RRDE attached with a tachometer is used as the working electrode 24. As the RRDE, for example, one having a glassy carbon electrode as a disk electrode and a platinum electrode as a ring electrode can be used.
The electrochemical measurement conditions are preferably conditions that do not cause deterioration of the catalyst fine particles and deterioration of carbon as a carrier. An example of specific conditions for CV using RRDE is shown below.
Electrolyte solution: 0.1M HClO ₄ aq (bubble oxygen)
-Atmosphere: oxygen atmosphere-Sweep speed: 10-100 mV / sec-Potential: 0.05-1.1 V (vs RHE)
・ Rotation speed: 400-3,000 rpm

The current value indicating the generation of hydrogen peroxide depends on the size of the electrochemical surface area and the composition of elements appearing on the surface of the catalyst fine particles. For example, when palladium fine particles and platinum fine particles having substantially the same electrochemical surface area are compared with each other, palladium fine particles are more likely to undergo a two-electron reduction reaction than platinum fine particles, and thus generate a larger amount of hydrogen peroxide.
In the present invention, the current value (A) derived from hydrogen peroxide detected by the ring electrode may be regarded as the amount of hydrogen peroxide produced, and the catalyst fine particles may be compared relatively.

1-4. Step of calculating the coverage of the catalyst fine particles This step is a step of calculating the coverage from the value of the electrochemical surface area and the value of the hydrogen peroxide generation amount. In this step, first, the value of the amount of hydrogen peroxide produced is divided by the value of the electrochemical surface area to obtain the amount of hydrogen peroxide produced per unit electrochemical surface area of the catalyst fine particles. It is preferable to calculate the coverage of catalyst fine particles from the amount of hydrogen peroxide produced per unit electrochemical surface area.
In the present invention, the coverage of the outermost layer with respect to the center particles refers to the ratio (%) of the surface area of the center particles covered by the outermost layer to the total surface area of the center particles.

  The method for calculating the coverage of the catalyst fine particles from the amount of hydrogen peroxide produced per unit electrochemical surface area is not particularly limited. As a method for calculating the coverage of the catalyst fine particles, for example, a relational expression between the coverage of the catalyst fine particles and the amount of hydrogen peroxide generated per unit electrochemical surface area is prepared, and from the amount of hydrogen peroxide generated per unit electrochemical surface area, A method for uniquely calculating the coverage; peroxidation per unit electrochemical surface area by using one or more predetermined maps representing the relationship between the coverage of catalyst fine particles and the amount of hydrogen peroxide generated per unit electrochemical surface area A method for calculating the coverage from the amount of hydrogen produced; a program capable of calculating the coverage from the amount of hydrogen peroxide produced per unit electrochemical surface area of the catalyst fine particles is prepared in advance and incorporated in the electrochemical device, before and after electrochemical measurement, or electrochemical And a method of calculating the coverage of the catalyst fine particles simultaneously with the measurement.

The relational expression, map, and program (hereinafter sometimes referred to as relational expression etc.) may be obtained empirically or may be theoretically obtained. As a method of empirically obtaining the relational expression, for example, a method of collecting data on catalyst fine particles with known coverage and the amount of hydrogen peroxide generated per unit electrochemical surface area and reflecting the accumulation result in the relational expression etc. Is mentioned. On the other hand, as a method for theoretically obtaining a relational expression or the like, for example, there is a method of performing a simulation based on the material or shape used for the catalyst fine particles and taking the simulation result into the relational expression or the like. The relational expression or the like may be obtained empirically and theoretically.
Hereinafter, the map used for this invention is demonstrated.

  The map used in the present invention includes, for example, (a) data on the amount of hydrogen peroxide generated per unit electrochemical surface area in the center particle, (b) data on the amount of hydrogen peroxide generated per unit electrochemical surface area in the outermost layer, And (c) a map including at least data on the amount of hydrogen peroxide produced per unit electrochemical surface area in a catalyst fine particle sample with a coverage of n%. The central particles in (a) and the outermost layer in (b) are the same materials as the central particles or outermost layers of catalyst fine particles (hereinafter, sometimes referred to as target catalyst fine particles) whose coverage is to be calculated. Consists of. In addition, the catalyst fine particle sample in (c) includes a central particle and an outermost layer like the target catalyst fine particle, and the central particle and the outermost layer are made of the same material as the central particle and the outermost layer of the target catalyst fine particle. And a sample with a known coverage. In addition, since it is difficult to directly calculate the data of (b), preparing particles consisting only of the elements constituting the outermost layer, calculating the amount of hydrogen peroxide generated per unit electrochemical surface area for the particles, The calculated data may be regarded as the data (b). The data (c) may be data relating to only one type of catalyst fine particle sample, or may be data relating to two or more types of catalyst fine particle samples having different coverages.

The map will be described in detail, taking as an example catalyst fine particles in which the central particles are palladium fine particles and the outermost layer is a platinum monoatomic layer. First, hydrogen peroxide generation amount P ₀ per unit electrochemical surface area of palladium fine particles (= center particle), hydrogen peroxide generation per unit electrochemical surface area of platinum fine particles (= particles composed only of elements constituting the outermost layer) A hydrogen peroxide production amount P _n per unit electrochemical surface area of the catalyst fine particle sample having an amount P ₁₀₀ and a coverage of n% is calculated. The amount of hydrogen peroxide produced per unit electrochemical surface area is a value obtained by dividing the value of hydrogen peroxide produced by the value of electrochemical surface area. The electrochemical surface area can be calculated by the method described in the section “1-2. Step for calculating electrochemical surface area of catalyst fine particles”. The amount of hydrogen peroxide produced can be calculated by the method described in the section “1-3. Step of calculating the amount of hydrogen peroxide produced by the catalyst fine particles”.

Next, assuming that palladium fine particles (= center particles) are catalyst fine particles with a coverage of 0% and platinum fine particles (= particles composed only of elements constituting the outermost layer) are catalyst fine particles with a coverage of 100%, P ₀ is The amount of hydrogen peroxide generated per unit electrochemical surface area of catalyst fine particles with a coverage of 0%, and the P ₁₀₀ can be regarded as the amount of hydrogen peroxide generated per unit electrochemical surface area of catalyst fine particles with a coverage of 100%. Therefore, when the coverage (%) of the catalyst fine particles is taken on the x axis and the amount of hydrogen peroxide generated per unit electrochemical surface area (A / C) of the catalyst fine particles is taken on the y axis, (x, y) = (0, A map composed of data of (P ₀ ), (n, P _n ), (100, P ₁₀₀ ) is obtained.
The amount of hydrogen peroxide produced depends on the potential during ORR measurement. Therefore, if the potential V ₀ (V) during ORR measurement is taken on the z axis, the above data is (x, y, z) = (0, P ₀ , V ₀ ), (n, P _n , V ₀ ). , (100, P ₁₀₀ , V ₀ ). A three-dimensional map can also be obtained by using the electric potential during ORR measurement as a variable.

  There may be only one map used in this step, or two or more maps. Alternatively, one or more optimum maps may be selected from maps prepared in advance of two or more and used for calculating the coverage.

As described above, the catalyst fine particle sample with a coverage of n% is a sample of catalyst fine particles with a known coverage that is different from the target catalyst fine particles. For example, when the catalyst fine particle sample is a sample of catalyst fine particles in which the outermost layer is coated on the center particle with Cu-UPD, the coating rate n% is obtained by the following formula (1).
Coverage n (%) = {C _Cu / (2 × C _H )} × 100 Formula (1)
In the above formula _{(1), C Cu} is copper adsorption charge amount to the central particles during _{Cu-UPD (C), C} H is a proton adsorption charge amount to the central particles (C). Also, 0 <n <100. The reason why the denominator is multiplied by 2 in the above formula (1) is to correct the difference in valence because the valence of the cation is different between the copper (II) ion and the proton.

  As described above, according to the present invention, the coverage of the catalyst fine particles can be accurately calculated by using a relational expression or the like prepared in advance. Further, according to the present invention, the upper limit of the potential in the oxygen reduction reaction measurement is about 1 V, so that there is little possibility that the structure of the catalyst fine particles is damaged or the center particles are eluted. The coverage calculated according to the present invention can be used to determine the quality of the catalyst fine particles, as will be described later.

2. Method for evaluating catalyst fine particles The method for evaluating catalyst fine particles according to the present invention is a method for evaluating catalyst fine particles comprising center particles and an outermost layer covering the center particles, the step of preparing the catalyst fine particles, the catalyst fine particles The step of calculating the electrochemical surface area of the catalyst, the step of performing an oxygen reduction reaction measurement on the catalyst fine particles, the step of calculating the amount of hydrogen peroxide generated by the measurement, the value of the electrochemical surface area and the value of the hydrogen peroxide generation amount The step of calculating the coverage, and comparing the calculated coverage with a preset reference value, if the calculated coverage is greater than or equal to the reference value, determine that the catalyst fine particles are acceptable, And having a step of determining that the catalyst fine particles are rejected when the calculated coverage is less than the reference value, and determining that the catalyst fine particles have failed in the determination step, It is characterized by carrying out again from the step of preparing to the step of calculating the coverage.

  The present invention includes (1) a step of preparing catalyst fine particles, (2) a step of calculating an electrochemical surface area of the catalyst fine particles, (3) a step of calculating a hydrogen peroxide generation amount of the catalyst fine particles, and (4) And (5) a determination step of catalyst fine particles. Among these, the steps (1) to (4) are the same as the steps (1) to (4) in the method for calculating the coverage of the catalyst fine particles described above.

The determination step of the catalyst fine particles in the present invention is calculated by comparing the calculated coverage with a preset reference value, and determining that the catalyst fine particles are acceptable when the calculated coverage is equal to or higher than the reference value. In this step, the catalyst fine particles are judged to be rejected when the coverage is less than the reference value.
The reference value serving as a determination criterion can be determined as appropriate depending on the application of the catalyst fine particles. For example, when using catalyst fine particles as an electrode catalyst for a fuel cell, the reference value is preferably set to a value of 90% or more, more preferably a value of 95% or more.

FIG. 2 is a flowchart showing a typical example of the catalyst fine particle evaluation method of the present invention. In addition, this invention is not necessarily limited only to this typical example. Hereinafter, the evaluation method of the present invention will be described with reference to FIG.
First, catalyst fine particles to be evaluated are prepared (S1). Next, with respect to the catalyst fine particles, an electrochemical surface area and a hydrogen peroxide generation amount are calculated (S2). The method for calculating the electrochemical surface area and the method for calculating the hydrogen peroxide generation amount are as described above. Subsequently, the coverage of the catalyst fine particles is calculated from the value of the electrochemical surface area and the value of the amount of hydrogen peroxide generated (S3). In calculating the coverage, for example, as described above, a relational expression, a map, a program, or the like can be used. Next, as a determination step, the calculated coverage ratio n (%) is compared with a preset reference value n ₀ (%) (S4). If n ≧ n ₀ , the catalyst fine particle is determined to be acceptable (S5), and the evaluation of the catalyst fine particle is terminated. On the other hand, in the case of n <n ₀ determines the fine catalyst particles fail and, to prepare the catalyst particles again (S1). The catalyst fine particles prepared in this case may be catalyst fine particles different from the catalyst fine particles determined to be rejected, or may be regenerated by coating the outermost layer again with the catalyst fine particles determined to be rejected. Fine catalyst particles may be used. Thus, when it determines with disqualification in determination process (S4), it implements again from the process of preparing catalyst fine particles, and repeatedly evaluates until the catalyst fine particles which have a desired coverage are obtained.

  Thus, by using the calculated coverage for determining the quality of the catalyst fine particles, only excellent catalyst fine particles can be used for the catalytic reaction. In the case where the catalyst fine particles determined to be acceptable in the evaluation method of the present invention are used for, for example, an electrode for a fuel cell, there is no possibility that the voltage will decrease due to elution of the center particle, and a fuel cell having excellent discharge performance is provided It becomes possible. Moreover, even if the catalyst fine particles are rejected by the evaluation method of the present invention, high-quality catalyst fine particles can be provided without waste by performing the step of coating the outermost layer again.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited only to the examples.

1. 1. Synthesis of carbon-supported catalyst fine particles 1-1. Formation of copper monoatomic layer First, carbon-supported palladium fine particle powder (manufactured by Basf, 20% Pd / C) was prepared.
Next, copper single atoms were coated on the palladium fine particles by the Cu-UPD method. Specifically, first, 0.5 g of carbon-supported palladium fine particle powder and 0.2 g of Nafion (trade name) were dispersed in an alcohol aqueous solution, and a catalyst ink obtained by filtration was applied to a glassy carbon electrode.
The electrochemical apparatus which performed Cu-UPD is as showing in FIG. The details of the electrochemical device are as follows.
Copper ion solution: mixed solution of 0.05 mol / L CuSO ₄ and 0.05 mol / L H ₂ SO ₄ (nitrogen was previously bubbled)
・ Electrode: Electrode with glassy carbon ・ Counter electrode: Platinum electrode (manufactured by Hokuto Denko)
Reference electrode: Silver-silver chloride electrode (manufactured by Cypress)
Dual electrochemical analyzer: ALS700C manufactured by BAS

FIG. 3 is a graph showing a copper adsorption peak area in a cyclic voltammogram when Cu-UPD is performed. In FIG. 3, white circles indicate points corresponding to the start potential E ₀ , and black circles indicate points corresponding to the stop potential E ₁ .
In this example, first, the potential was swept from 0.29 V to 0.73 V (vs RHE). Next, the potential is swept from 0.73 V (vsRHE) to a stop potential E ₁ (a potential corresponding to the black circle in FIG. 3), and the potential is maintained at the stop potential E ₁ for a predetermined time. A copper monoatomic layer was deposited on the surface.

1-2. Formation of Platinum Monoatomic Layer First, a 0.005M K ₂ PtCl ₄ solution was prepared, and nitrogen was bubbled into the solution in advance. After the copper monoatomic layer is deposited on the surface of the palladium fine particles by the method described in the section “1-1. Formation of the copper monoatomic layer”, the electrode including the glassy carbon is placed in a glove box under a nitrogen atmosphere. And immediately immersed in a K ₂ PtCl ₄ solution for a predetermined time. By the immersion, copper atoms and platinum ions precipitated by Cu-UPD were substituted one-on-one, and carbon-supported catalyst fine particles in which a platinum monoatomic layer was deposited on the surface of palladium fine particles were produced.

2. Creation of a map A map showing the relationship between the coverage and the amount of hydrogen peroxide produced per unit electrochemical surface area of the catalyst fine particles was created.
First, four types of catalyst fine particle samples having carbon-supported palladium fine particles, carbon-supported platinum fine particles, and a core-shell structure and different coverages (5-95%) were prepared. The four types of catalyst fine particle samples are catalyst fine particles produced under different conditions using Cu-UPD, and the coverage is a value calculated in advance by the above-described equation (1).

2-1. Calculation of Electrochemical Surface Area First, carbon-supported palladium fine particles, carbon-supported platinum fine particles, and the above four kinds of catalyst fine particle samples (hereinafter, these six kinds of fine particles may be referred to as six kinds of catalysts), respectively. An ink was prepared. Specifically, 0.5 g of catalyst powder and 0.2 g of Nafion (trade name) were dispersed in an alcohol aqueous solution, and the filtrate was used as catalyst ink.
Next, the catalyst ink was applied to a glassy carbon electrode. The glassy carbon electrode was installed in the electrochemical device shown in FIG. The details of the apparatus are the same as the apparatus shown in FIG. 1 except that the electrolytic solution is changed to 0.1 mol / L HClO ₄ .
Subsequently, CV was performed by sweeping the potential at a sweep speed of 50 mV / s in the range of 0.05 to 1.2 V (vs RHE). FIG. 4A is a cyclic voltammogram obtained by the CV for a certain catalyst fine particle sample. FIG. 4B is a graph in which the area corresponding to the proton adsorption peak charge amount in the cyclic voltammogram is represented by hatching.
The electrochemical surface area was calculated from the proton adsorption peak area obtained from FIG.

2-2. Next, the catalyst ink used in “2-1. Calculation of electrochemical surface area” was applied to a glassy carbon electrode portion of a glassy carbon electrode (RRDE) provided with a platinum ring electrode. The RRDE was installed in the electrochemical apparatus shown in FIG. The details of the apparatus are the same as the apparatus shown in FIG. 1 except that the electrolytic solution is changed to 0.1 mol / L HClO ₄ and the nitrogen bubbling is changed to oxygen bubbling.
Subsequently, ORR measurement was performed while rotating RRDE at 1600 rpm. FIG. 5A is a graph showing the oxygen reduction wave in the ORR measurement for a certain catalyst fine particle sample, and FIG. 5B is a graph showing the amount of hydrogen peroxide produced in the ORR measurement for the catalyst fine particle sample. From FIG. 5B, the value of the hydrogen peroxide generation amount at a voltage of 0.1 V was calculated.

2-3. Next, a map representing the relationship between the coverage and the amount of hydrogen peroxide produced per unit electrochemical surface area was created. A value obtained by dividing the value of the amount of hydrogen peroxide produced by the value of the electrochemical surface area was defined as the amount of hydrogen peroxide produced P _n per unit electrochemical surface area of the catalyst. The amount of hydrogen peroxide generated per unit electrochemical surface area of the carbon-supported palladium fine particles was P _0, and the amount of hydrogen peroxide generated per unit electrochemical surface area of the carbon-supported platinum fine particles was P ₁₀₀ .
FIG. 6 shows the hydrogen peroxide production amount P _n (A / C) per unit electrochemical surface area on the vertical axis and the coverage n (%) on the horizontal axis based on the data of the above six types of catalysts. It is a map. In FIG. 6, the coverage of the carbon-supported palladium fine particles was 0%, and the coverage of the carbon-supported platinum fine particles was 100%.
As shown in FIG. 6, it can be seen that the data of the above six types of catalysts are arranged substantially in a straight line. From FIG. 6, the relationship between P _n and n can be expressed by the following formula (2).
P _n = − (2 × 10 ⁻⁴ ) × n + 0.0181 Formula (2)

  From the above, it can be seen that the amount of hydrogen peroxide produced per unit electrochemical surface area in the catalyst fine particles and the coverage of the catalyst fine particles show a strong correlation. Therefore, as shown in FIG. 6 above, a map is created using catalyst fine particles having a known coverage in advance, or the catalyst fine particle coverage per unit electrochemical surface area and the catalyst fine particle coverage per unit electrochemical surface area as in the above equation (2). By preparing a relational expression with the amount of hydrogen peroxide produced, the amount of hydrogen peroxide produced per unit electrochemical surface area can be quantified even for catalyst fine particles with unknown coverage. It can be seen that

21 Glass cell 22 Copper ion solution 23 Paste 24 Working electrode 26 Counter electrode 27 Reference electrode 28 Gas introduction tube 29 Bubble

Claims (8)

In a catalyst fine particle having an outermost layer covering the center particle and the center particle, a method for calculating a coverage of the outermost layer with respect to the center particle,
Preparing the catalyst fine particles,
Calculating an electrochemical surface area of the catalyst fine particles,
Performing an oxygen reduction reaction measurement on the catalyst fine particles, calculating the amount of hydrogen peroxide generated by the measurement, and
A method for calculating the coverage of catalyst fine particles, comprising the step of calculating the coverage from the value of the electrochemical surface area and the value of the hydrogen peroxide generation amount.   In the covering ratio calculation step, the value of the electrochemical surface area is determined by at least one predetermined map representing the relationship between the covering ratio of the outermost layer with respect to the center particle and the amount of hydrogen peroxide generated per unit electrochemical surface area of the catalyst fine particles. 2. The method for calculating the coverage of catalyst fine particles according to claim 1, wherein the coverage is calculated from the value of the hydrogen peroxide generation amount. The predetermined map is:
Data on the amount of hydrogen peroxide produced per unit electrochemical surface area in the central particle,
Data of hydrogen peroxide production per unit electrochemical surface area in the outermost layer, and
The map includes at least data on the amount of hydrogen peroxide generated per unit electrochemical surface area of a catalyst fine particle sample including the central particle and the outermost layer, and the coverage of the outermost layer with respect to the central particle is n%. Item 3. A method for calculating the coverage of catalyst fine particles according to Item 2. The catalyst fine particle sample is a sample of catalyst fine particles in which a center particle is coated with an outermost layer by Cu-UPD,
The method according to claim 3, wherein the coverage n% is a value obtained by the following formula (1).
Coverage n (%) = {C _Cu / (2 × C _H )} × 100 Formula (1)
(In the above formula (1), C _Cu is the copper adsorption charge amount (C) to the central particle during Cu-UPD, C _H is the proton adsorption charge amount (C) to the central particle, and 0 <n <100.) A method for evaluating catalyst fine particles comprising a center particle and an outermost layer covering the center particle,
Preparing the catalyst fine particles,
Calculating an electrochemical surface area of the catalyst fine particles,
Performing an oxygen reduction reaction measurement on the catalyst fine particles, and calculating the amount of hydrogen peroxide generated by the measurement,
Calculating the coverage from the electrochemical surface area value and the hydrogen peroxide generation value, and
The calculated coverage is compared with a preset reference value, and when the calculated coverage is equal to or greater than the reference value, the catalyst fine particles are determined to be acceptable, and the calculated coverage is the reference value. Having a step of judging that the catalyst fine particles are rejected when it is less than
When it is determined that the determination step is unsuccessful, the catalyst fine particle evaluation method is performed again from the step of preparing the catalyst fine particles to the step of calculating the coverage.   In the covering ratio calculation step, the value of the electrochemical surface area is determined by at least one predetermined map representing the relationship between the covering ratio of the outermost layer with respect to the center particle and the amount of hydrogen peroxide generated per unit electrochemical surface area of the catalyst fine particles. The method for evaluating catalyst fine particles according to claim 5, which is a step of calculating the coverage from the value of the hydrogen peroxide generation amount. The predetermined map is:
Data on the amount of hydrogen peroxide produced per unit electrochemical surface area in the central particle,
Data of hydrogen peroxide production per unit electrochemical surface area in the outermost layer, and
The map includes at least data on the amount of hydrogen peroxide generated per unit electrochemical surface area of a catalyst fine particle sample including the central particle and the outermost layer, and the coverage of the outermost layer with respect to the central particle is n%. Item 7. The method for evaluating catalyst fine particles according to Item 6. The catalyst fine particle sample is a sample of catalyst fine particles in which a center particle is coated with an outermost layer by Cu-UPD,
8. The method for evaluating catalyst fine particles according to claim 7, wherein the coverage ratio n% is a value obtained by the following formula (1).
Coverage n (%) = {C _Cu / (2 × C _H )} × 100 Formula (1)
(In the above formula (1), C _Cu is the copper adsorption charge amount (C) to the central particle during Cu-UPD, C _H is the proton adsorption charge amount (C) to the central particle, and 0 <n <100.)

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