JP2021093270A - Alloy catalyst for solid polymer type fuel cell and manufacturing method thereof - Google Patents

Abstract

To provide a novel and improved alloy catalyst capable of improving durability of the alloy catalyst while maintaining high initial activity that the alloy catalyst has originally, and a manufacturing method thereof.MEANS FOR SOLVING THE PROBLEM: An alloy catalyst for a solid polymer type fuel cell comprises: compound metal particles including a noble metal element and a transition metal element; and a catalyst carrier carrying the compound metal particles. The compound metal particles contain the noble metal element and the transition metal element in a molar ratio of noble metal element:transition metal element=1:0.2 or more to 1:1 or less. In the case that X-ray diffraction analysis is performed on the compound metal particles, a diffraction peak is observed at 2θ=37° or larger to 42° or smaller. An alloying rate is 60% or more to 100% or less, and a crystallite diameter of the compound metal particle is 2 to 8 nm. In the case where a temperature rising desorption method is performed for temperature rising desorption of oxygen molecules adsorbed to the compound metal particles at 85K, an integration value of a desorption amount of the oxygen molecules is 1.0×10-6 mol or more per surface area 1 m2 of a noble metal portion exposed on a surface of the compound metal particle.SELECTED DRAWING: None

Description

The present invention relates to an alloy catalyst for a polymer electrolyte fuel cell and a method for producing the same.

As a kind of fuel cell, a polymer electrolyte fuel cell is known. The polymer electrolyte fuel cell has a pair of catalyst layers arranged on both sides of a solid polymer electrolyte membrane, a gas diffusion layer arranged outside each catalyst layer, and a separator arranged outside each gas diffusion layer. And. Of the pair of catalyst layers, one catalyst layer serves as the anode of the polymer electrolyte fuel cell, and the other catalyst layer serves as the cathode of the polymer electrolyte fuel cell. In a normal polymer electrolyte fuel cell, a plurality of unit cells having the above components are stacked in order to obtain a desired output.

As the catalyst used in the catalyst layer, a catalyst in which platinum, which is a catalyst particle, is supported on a catalyst carrier is widely used. However, polymer electrolyte fuel cells are required to have further cost reduction and higher performance, and from such a viewpoint, alloy catalysts using composite metal particles as catalyst particles are attracting attention. Composite metal particles are particles in which a transition metal element is alloyed with a noble metal element such as platinum. In the present specification, the "catalyst" such as "alloy catalyst" refers to a catalyst carrier on which catalyst particles having catalytic ability are supported, and the "catalyst particles" are individual particles supported on the catalyst carrier. That is, it refers to particles having catalytic ability.

Although such an alloy catalyst has high initial activity, it has a problem of low durability. As a method for increasing the durability of the alloy catalyst, for example, leaching disclosed in Patent Documents 1 to 3 and Non-Patent Document 1 is known. Reaching is generally a process of bringing an alloy catalyst into contact with an acidic aqueous solution. When the alloy catalyst is brought into contact with the acidic aqueous solution, the acidic aqueous solution may be heated.

One of the factors that lower the durability of the alloy catalyst is that the transition metal element exposed on the surface of the composite metal particles elutes into the polymer electrolyte membrane during use of the polymer electrolyte fuel cell. The purpose of leaching is to elute the transition metal element from the surface of the composite metal particles into an acidic aqueous solution. If the transition metal element can be eluted from the surface of the composite metal particles into the acidic aqueous solution, a skin layer composed of almost only the noble metal element can be formed on the surface of the composite catalyst particles. Such a skin layer makes it difficult for the transition metal element inside the skin layer to elute during use of the polymer electrolyte fuel cell. Therefore, it is expected that the durability of the alloy catalyst will be improved.

Japanese Unexamined Patent Publication No. 2010-0273664 JP-A-2016-054065 Japanese Unexamined Patent Publication No. 2001-052718

ACS Sustainable Chem. Eng. 2017, 5, 9809-9817

However, when the present inventor examined the conventional leaching, it was found that not only the durability cannot be increased by the conventional leaching, but also the initial activity may be rather decreased.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to maintain the durability of the alloy catalyst while maintaining the high initial activity inherent in the alloy catalyst. It is an object of the present invention to provide a new and improved alloy catalyst and a method for producing the same, which can be enhanced.

The present inventor investigated the cause of the decrease in the initial activity of the alloy catalyst and the cause of the durability not being improved by the conventional leaching. As a result, the present inventor found that the conventional leaching intensity (acid concentration, heating temperature, or contact time with an acidic aqueous solution) was too strong (for example, the acid concentration was too high, the heating temperature was too high, or the acidic aqueous solution). The contact time is too long, etc.), and I thought that the transition metal element might be eluted not only from the surface of the composite catalyst particles but also from the inside. That is, in the conventional leaching, as a result of eluting a large amount of transition metal elements, the composition of the composite metal particles after leaching deviates greatly from the prepared composition (the composition initially aimed at) (so-called “composition deviation”). .. As a result, it is considered that the initial activity of the alloy catalyst decreases. Further, it is considered that severe irregularities are formed on the surface of the composite metal particles by leaching, and the transition metal elements existing in the back of the composite metal particles are exposed on the surface due to such irregularities. Such transition metal elements elute into the polymer electrolyte membrane during use of the polymer electrolyte fuel cell. Therefore, it is considered that the durability is not improved.

Therefore, the present inventor leached the alloy catalyst by weakening the leaching strength (that is, lowering the acid concentration, lowering the heating temperature, or shortening the contact time with the acidic aqueous solution). As a result, although the initial activity of the alloy catalyst could be maintained, the durability was not improved. When the leaching strength was weak, it is considered that the durability was not improved because the transition metal element was not sufficiently eluted from the surface of the composite catalyst particles.

Therefore, the present inventor has investigated the leaching conditions capable of increasing the durability of the alloy catalyst while suppressing the composition deviation of the composite metal particles. By the way, as described above, the purpose of leaching is to form a skin layer on the surface of the composite metal particles. Such a skin layer makes it difficult for the transition metal element inside the skin layer to elute during use of the polymer electrolyte fuel cell. Therefore, the durability of the alloy catalyst is improved. However, if the transition metal element remains on the surface of the composite metal particles (that is, on the skin layer), the durability of the alloy catalyst is reduced. Therefore, the larger the abundance ratio of the noble metal element in the skin layer (conceptually, the ratio of the number of atoms of the noble metal element to the total number of atoms present on the surface of the composite metal particles, that is, the coverage ratio by the noble metal element), the more the skin layer It can be said that the durability of the alloy catalyst is improved. Therefore, when examining the leaching conditions, it is necessary to establish an evaluation method for quantitatively evaluating the abundance ratio of the noble metal element in the skin layer.

Conventionally, an electron microscope such as SEM-EDS (scanning electron microscope-energy dispersive X-ray analyzer) or XPS (X-ray photoelectron spectroscopy) has been used for observing composite metal particles. However, only local information can be obtained with an electron microscope such as SEM-EDS. In other words, only the composite metal particles of interest can be observed. Therefore, it is necessary to observe a certain number (N number) of composite metal particles, but it is very troublesome to observe a plurality of composite metal particles. Further, in the first place, with an electron microscope such as SEM-EDS, the region where the skin layer is formed cannot be selectively observed, and further quantitative evaluation cannot be performed. The analysis depth of XPS is about several nm, but the particle size of the composite metal particles is also about several nm. Therefore, XPS observes the entire composite metal particles, and cannot selectively observe the region where the skin layer is formed.

Therefore, the conventional observation method cannot quantitatively evaluate the abundance ratio of the noble metal element in the skin layer. Therefore, the present inventor first diligently studied a method for quantitatively evaluating the abundance ratio of noble metal elements in the skin layer.

Specifically, the present inventor has focused on the thermal desorption method. Precious metal elements and transition metal elements are present on the surface of the composite metal particles before leaching. Reaching increases the proportion of noble metal elements present on the surface of the composite metal particles. Here, oxygen molecules are not adsorbed on the noble metal element on the surface of the composite metal particles in the temperature range (about room temperature to several hundred ° C.) used in the usual temperature-temperature desorption method. However, if the temperature is very low (about 85K), oxygen molecules are physically adsorbed. On the other hand, since the transition metal element on the surface of the composite metal particles exists as an oxide, the oxygen molecule is not adsorbed on the transition metal element. Further, it is considered that the oxygen atom chemically bonded to the transition metal element interferes with the adsorption of the oxygen molecule to the noble metal element existing around the transition metal element. From these facts, the present inventor desorbs oxygen molecules adsorbed on the surface of composite metal particles at 85 K by raising the temperature, and if the amount of oxygen molecules desorbed at this time is evaluated, the noble metal occupying the skin layer. I thought that the abundance ratio of elements could be evaluated quantitatively. Hereinafter, such an evaluation method is also referred to as a "low temperature oxygen TPD measurement method".

That is, the larger the abundance ratio of the noble metal element in the skin layer, the more oxygen molecules are physically adsorbed on the surface of the composite metal particles. Since the oxygen molecules physically adsorbed on the surface of the composite metal particles are desorbed as the temperature rises, the larger the abundance ratio of the noble metal element in the skin layer, the larger the desorption amount of the oxygen molecules. Further, according to the low temperature oxygen TPD measurement method, all the composite metal particles to be measured can be evaluated.

Next, the present inventor investigated leaching conditions capable of increasing the durability of the alloy catalyst while suppressing the composition deviation of the composite metal particles. Simply increasing the leaching strength causes a composition shift of the composite metal particles and lowers the initial activity of the alloy catalyst. Further, severe irregularities are formed on the surface of the composite metal particles, and the irregularities expose the transition metal elements existing in the back of the composite metal particles to the surface. Therefore, the durability is not improved. On the other hand, when the leaching strength is weak, the abundance ratio of the noble metal element in the skin layer is not sufficiently high, and the durability is not improved.

Therefore, the present inventor has considered performing leaching a plurality of times with a weak leaching strength that is not conventionally performed. Furthermore, the present inventor has decided not only to perform leaching a plurality of times, but also to gradually weaken the leaching strength as the number of leachings increases. Then, when the produced alloy catalyst was evaluated by the above-mentioned low-temperature oxygen TPD measurement method, it was found that the desorption amount of oxygen molecules of the alloy catalyst produced under a specific leaching condition dramatically increased. Specifically, the integrated value of the desorption amount of oxygen molecules was 1.0 × ^10-6 mol or more ^{per 1 m 2} of the surface area of the noble metal portion exposed on the surface of the composite metal particles. Then, when the durability of the alloy catalyst obtained by obtaining such a desorption amount was evaluated, it was found that the alloy catalyst had sufficient durability. This indicates that the proportion of precious metal elements in the skin layer has increased significantly. Therefore, it was confirmed that the abundance ratio of the noble metal element in the skin layer can be quantitatively evaluated by the integrated value of the desorption amount of oxygen molecules. Furthermore, the present inventor has confirmed that there is no problem with the initial activity of the alloy catalyst produced by this production method. Therefore, it was confirmed that the composition deviation could be suppressed.

When the present inventor evaluated the alloy catalyst produced by the conventional leaching method by the low-temperature oxygen TPD measurement method, the amount of oxygen molecules desorbed was insufficient in each case. First, when the leaching strength is weak, many transition metal elements remain on the surface of the composite metal particles, so that the amount of oxygen molecules desorbed decreases. Therefore, if the leaching strength is increased, the transition metal element will eventually disappear from the surface of the composite metal particles, and the amount of oxygen molecules desorbed will increase. However, if the leaching strength is simply increased, the integrated value of the desorption amount of oxygen molecules is the above-mentioned value (1.0 × ^10-6 mol or more ^{per 1 m 2 of the surface area of the noble metal portion exposed on the surface of the composite metal particles).} Did not reach. When the leaching strength is increased, the surface of the composite metal particles is eroded by the acidic aqueous solution to form severe irregularities. Therefore, oxygen molecules can reach the transition metal elements existing in the back of the composite metal particles, and the oxygen molecules are not adsorbed on such transition metal elements. Therefore, it is considered that the amount of oxygen molecules desorbed is reduced. In addition, such transition metal elements are easily eluted during use of the fuel cell. Furthermore, as a result of the severe irregularities formed on the surface of the composite metal particles, the noble metal elements on the surface of the composite metal particles are not aligned. For these reasons, the durability of the alloy catalyst deteriorates. In order to solve such a problem, it is conceivable to anneal the composite metal particles to smooth the surface of the composite metal particles. However, when strong annealing (annealing at a high temperature) is performed to smooth the severe unevenness, the transition metal element existing in the back of the composite metal particles moves to the surface and is exposed. Therefore, the effect of leaching is offset, and the amount of oxygen molecules desorbed is also reduced. When the annealing strength is insufficient, the unevenness of the surface is not sufficiently smoothed, and the amount of oxygen molecules desorbed is also reduced.

When the leaching strength is increased, the problem of composition deviation also occurs. As a method for solving this problem, it is conceivable to prepare a large amount of transition metal elements in the composite metal particles in advance. However, when the leaching intensity is high, it is very difficult to predict how much the transition metal element is eluted by leaching. Therefore, it is very difficult to determine how much the transition metal element should be charged. Further, even if the composition after leaching happens to match the target composition, the above-mentioned problems (problems such as deterioration of durability due to the formation of severe irregularities on the surface) still remain.

From the above results, the present inventor has obtained the following findings. That is, the abundance ratio of the noble metal element in the skin layer can be quantitatively evaluated by the low temperature oxygen TPD measurement method. Furthermore, an alloy catalyst having excellent durability and initial activity can be produced by performing leaching multiple times with a weak leaching strength, which is not conventionally performed, and gradually reducing the leaching strength as the number of leachings increases. Can be done. The present invention has been made based on these findings.

That is, according to a certain viewpoint of the present invention, a composite metal particle containing a noble metal element and a transition metal element, and a catalyst carrier for supporting the composite metal particle are provided, and the noble metal element is a group consisting of Pt, Au, and Pd. Any one or more selected from the group, and the transition metal element is any one or more selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, and Ni, and the composite metal. The particles contain a noble metal element and a transition metal element in a molar ratio of noble metal element: transition metal element = 1: 0.2 or more and 1: 1 or less, and when the composite metal particles are subjected to X-ray diffraction analysis, 2θ = 37 ° or more. A diffraction peak is observed at 42 ° or less, and the lattice constant calculated based on the diffraction peak and the alloying ratio calculated based on the following equation (1) are 60% or more and 100% or less.
Alloying rate [%] = {(lattice constant of bulk noble metal)-(lattice constant of composite metal particles)} / {(lattice constant of bulk noble metal)-(lattice constant of maximum peak of bulk composite metal)} x 100 ( 1)
When the crystallite diameter of the composite metal particles calculated based on the diffraction peak is 2 to 8 nm and the temperature-temperature desorption method for heating and desorbing the oxygen molecules adsorbed on the composite metal particles at 85 K is performed, The temperature desorption curve of m / z = 32 corresponding to oxygen molecules has a desorption peak top in the range of 130K or more and 190K or less, and the desorption amount of oxygen molecules calculated based on the area of the desorption peak. Provided is an alloy catalyst for a solid polymer fuel cell, wherein the integrated value is 1.0 × ^{10-6 mol or more per 1 m 2} of the surface area of the noble metal portion exposed on the surface of the composite metal particles.

Here, the integrated value of the desorption amount of oxygen molecules may be 3.0 × ^10-6 mol or more ^{per 1 m 2 of the surface area of the noble metal element.}

Further, when the temperature-temperature desorption method is performed in which oxygen molecules adsorbed on composite metal particles are desorbed by temperature-temperature at 85 K, the temperature-temperature desorption curve of m / z = 44 corresponding to carbon dioxide molecules is 300 K or more. It has a desorption peak top in the range of 900K or less, and the integrated value of the desorption amount of carbon dioxide molecules calculated based on the area of the desorption peak is 1 m ^{2 of the surface area of the noble metal portion exposed on the surface of the composite metal particles.} It may be 3.0 × ^10-7 mol or less per hit.

Further, the integrated value of the desorption amount of carbon dioxide molecules may be 2.5 × ^10-7 mol or less ^{per 1 m 2} of the surface area of the noble metal portion exposed on the surface of the composite metal particles.

Further, the noble metal element is Pt, and the transition metal element may be any one or more selected from the group consisting of Fe, Co, and Ni.

According to another aspect of the present invention, the above-mentioned method for producing an alloy catalyst for a polymer electrolyte fuel cell, which comprises the following steps 0 to 10. A method for producing an alloy catalyst for a battery is provided.
(Step 0)
An untreated alloy catalyst comprising untreated composite metal particles containing a noble metal element and a transition metal element and a catalyst carrier supporting the untreated composite metal particles is prepared.
Here, the noble metal element is at least one selected from the group consisting of Pt, Au, and Pd, and the transition metal element is from Sc, Ti, V, Cr, Mn, Fe, Co, and Ni. Any one or more selected from the group.
(First step)
The untreated alloy catalyst is an inert gas composed of any one or more selected from the group consisting of argon, nitrogen, and helium, and hydrogen gas having a flow rate of 50% by volume or less with respect to the flow rate of the inert gas. In the including atmosphere, heat treatment is performed at a temperature of 500 ° C. or higher and 900 ° C. or lower for a time of 10 minutes or longer and 60 minutes or shorter.
(Second step)
^{The alloy catalyst obtained in the first step is 1.0 × 10 -3} mol / L or more of any one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and perchloric acid. It is brought into contact with an acidic aqueous solution containing a concentration of 5.0 × 10 ^-3 mol / L or less at a temperature of 30 ° C. or higher and 90 ° C. or lower for a time of 30 minutes or longer and 100 minutes or shorter.
(Third step)
The alloy catalyst obtained in the second step is washed and then dried.
(4th step)
The alloy catalyst obtained in the third step is an inert gas composed of any one or more selected from the group consisting of argon, nitrogen, and helium, and 10% by volume or less with respect to the flow rate of the inert gas. In an atmosphere containing the hydrogen gas of the above, heat treatment is performed at a temperature of 250 ° C. or higher and 550 ° C. or lower for a time of 10 minutes or longer and 60 minutes or lower.
(Fifth step)
^{The alloy catalyst obtained in the fourth step contains 1.0 × 10 -4} mol / L or more of any one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and perchloric acid. It is brought into contact with an acidic aqueous solution containing a concentration of 5.0 × 10 ^-4 mol / L or less at a temperature of 30 ° C. or higher and 70 ° C. or lower for a time of 10 minutes or longer and 60 minutes or shorter.
(6th step)
The alloy catalyst obtained in the fifth step is washed and then dried.
(7th step)
The alloy catalyst obtained in the sixth step is an inert gas composed of any one or more selected from the group consisting of argon, nitrogen, and helium, and 5% by volume or less with respect to the flow rate of the inert gas. In an atmosphere containing the hydrogen gas of the above, heat treatment is performed at a temperature of 200 ° C. or higher and 500 ° C. or lower for a time of 10 minutes or longer and 60 minutes or shorter.
(8th step)
^{The alloy catalyst obtained in the 7th step contains 1.0 × 10-5} mol / L or more of any one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and perchloric acid. It is brought into contact with an acidic aqueous solution containing a concentration of 5.0 × ^10-5 mol / L or less at a temperature of 30 ° C. or higher and 60 ° C. or lower for a time of 5 minutes or longer and 30 minutes or shorter.
(9th step)
The alloy catalyst obtained in the eighth step is washed and then dried.
(10th step)
The alloy catalyst obtained in the ninth step is used at a temperature of 200 ° C. or higher and 450 ° C. or lower in an inert gas atmosphere composed of any one or more selected from the group consisting of argon, nitrogen, and helium. Heat treatment is performed for a time of minutes or more and 30 minutes or less.

As described above, according to the present invention, it is possible to improve the durability of the alloy catalyst while maintaining the high initial activity inherent in the alloy catalyst.

Hereinafter, preferred embodiments of the present invention will be described in detail. The numerical range represented by using "~" means a range including the numerical values before and after "~" as the lower limit value and the upper limit value.

<1. About low temperature oxygen TPD measurement method>
In the present embodiment, the skin layer formed on the surface of the composite metal particles is quantitatively evaluated by performing the low temperature oxygen TPD measurement method. Hereinafter, an example of a specific procedure of the low temperature oxygen TPD measurement method will be described. Of course, the low temperature oxygen TPD measurement method according to the present embodiment is not limited to the following procedure.

The low temperature oxygen TPD measurement method according to the present embodiment can be performed using, for example, a quadrupole mass analyzer exhausted by a turbo molecular pump and a vacuum apparatus having a sample tube gas introduction system equipped with an oil diffusion pump. it can. The sample temperature is measured by a thermocouple thermometer attached to a quartz glass sample tube.

First, a predetermined amount (for example, about 0.05 g) of a sample of an alloy catalyst is placed in a sample tube, hydrogen reduction at 500 ° C. is performed for 5 minutes as a pretreatment, and the sample is exhausted at the same temperature. Hydrogen reduction is preferably performed a plurality of times (for example, about twice). The sample is then cooled to 85 K (-185 ° C.) with liquid nitrogen. Then, 1 kPa of oxygen is introduced into the sample tube and allowed to stand for 15 minutes. By this step, oxygen molecules are adsorbed on the sample.

Then, the sample tube is exhausted. After that, the sample tube is connected to the quadrupole analyzer. After allowing to stand for 20 minutes until the partial pressure of oxygen in the sample tube decreases, the temperature of the sample in the sample tube is raised at a heating rate of, for example, 10 K / min. At this time, a quadrupole mass spectrometer records a signal of m / z = 32, preferably further m / z = 44. Here, the signal of m / z = 32 corresponds to the oxygen molecule, and the signal of m / z = 44 corresponds to the carbon dioxide molecule. Each signal is calibrated for the specified amount of oxygen and carbon dioxide. Then, by plotting the measured values on the xy plane with the horizontal axis as the temperature and the vertical axis as mol / (s · g), the TPD spectrum of m / z = 32 corresponding to the oxygen molecule (temperature-rising elimination curve). , Preferably further obtain a TPD spectrum of m / z = 44 corresponding to the carbon dioxide molecule. When a catalyst carrier containing element C, for example, a porous carbon material, is used, a TPD spectrum of m / z = 44 may be obtained. The TPD spectrum of m / z = 32 has a desorption peak top in the range of 130K or more and 190K or less. The TPD spectrum of m / z = 44 may have a desorption peak top in the range of 300K or more and 900K or less. By acquiring the TPD spectrum of m / z = 44, the durability of the alloy catalyst can be evaluated more accurately. Details will be described later.

Then, the desorption peak is separated from each TPD spectrum, and the area of the desorption peak is calculated. Separation of the desorption peak can be performed, for example, by using the peak fit function of OriginPro 2018 (manufactured by Lightstone). The horizontal axis of the TPD spectrum is temperature, but the horizontal axis is converted to time based on the rate of temperature rise (for example, 10 K / min). Specifically, the value on the horizontal axis is converted into time by dividing the value on the horizontal axis of the desorption peak by the rate of temperature rise. Further, the unit of time on the horizontal axis is adjusted to the unit of time on the vertical axis (s, that is, seconds in the above example). After performing such conversion, the area of the desorption peak is calculated. The unit of the area of the desorption peak is mol / (s · g) × s = mol / g. Thereby, the area of the desorption peak having the unit of mol / g is calculated. The area of the desorption peak means the integrated value of the desorption amount of oxygen molecules or carbon dioxide molecules per 1 g of the sample.

As described above, the integrated value of the desorption amount of oxygen molecules is an index for quantitatively evaluating the abundance ratio of the noble metal element in the skin layer. Similarly, the integrated value of the desorption amount of carbon dioxide molecules is also an index for quantitatively evaluating the abundance ratio of the noble metal element in the skin layer. As shown in Examples described later, the larger the integrated value of the desorption amount of oxygen molecules (that is, the larger the abundance ratio of the noble metal element in the skin layer), the larger the integrated value of the desorption amount of carbon dioxide molecules. Tends to decrease. Therefore, it can be said that the smaller the integrated value of the desorption amount of carbon dioxide molecules, the larger the abundance ratio of the noble metal element in the skin layer. Although the cause of this is not clear, the present inventor believes that the carbon dioxide molecule is derived from the oxide of the transition metal element present on the surface of the composite metal particles. That is, it is considered that the C element in the catalyst carrier is bonded to oxygen chemically bonded to the transition metal element for some reason to become a carbon dioxide molecule and is desorbed from the alloy catalyst. As the abundance ratio of the noble metal element in the skin layer increases, the transition metal element present on the surface of the composite metal particles (that is, the skin layer) decreases, so that the integrated value of the desorption amount of carbon dioxide molecules also decreases.

However, the integrated value of the desorption amount of oxygen molecules or carbon dioxide molecules per 1 g of the sample may not accurately reflect the abundance ratio of the noble metal element in the skin layer. The measurement target of the low-temperature oxygen TPD measurement method is an alloy catalyst, which includes a catalyst carrier in addition to the composite metal particles as a constituent element. Further, although the details will be described later, the method for producing the alloy catalyst to be reached is not particularly limited. Therefore, the carrying ratio of the composite metal particles in the alloy catalyst (mass% of the composite metal particles with respect to the total mass of the alloy catalyst) can vary from alloy catalyst to alloy catalyst. In this case, even if the abundance ratio of the noble metal element in the skin layer is about the same, the area of the desorption peak may fluctuate depending on the loading ratio.

^{Therefore, the integrated value of the desorption amount of oxygen molecules or carbon dioxide molecules per 1 g of the sample is per 1 m 2} of the surface area of the noble metal portion exposed on the surface of the composite metal particles (hereinafter, also simply referred to as “the surface area of the noble metal portion”). Convert to a value. ^{Specifically, the surface area (m 2} / g) of the noble metal portion per 1 g of the sample is determined by the CO pulse injection chemisorption amount measurement method. Here, the CO pulse injection chemisorption amount measurement can be performed using, for example, a metal dispersion measuring device (BEL-METAL-3, manufactured by Microtrac Bell). Specifically, a predetermined amount (for example, 0.05 g) of a sample is placed in a sample tube. Then, as a pretreatment, the sample is heated to 500 ° C. under He gas flow and held for 5 minutes. Then, the He gas is switched to hydrogen gas, and the sample is held at 500 ° C. for 10 minutes under the flow of hydrogen gas. Then, the hydrogen gas is switched to Ar gas, and the sample is cooled to 40 ° C. under the flow of Ar gas. Then, while maintaining this temperature, 10% by volume CO gas pulse is injected into the sample tube every minute until CO adsorption is no longer observed. Then, the CO adsorption amount of the sample is calculated. ^{The surface area (m 2} / g) of the noble metal portion per 1 g of the sample is calculated based on the adsorbed amount of the obtained CO gas and the following formula (2). In equation (2), NA is Avogadro's constant.
The surface area of the noble metal portion ^{[m 2 / g] = (} CO adsorption amount [L] molecular area of ^{× NA × CO [m 2/} 1 molecule]) / (22.4 "L / mol" × sample weight [g] ) (2)

Then, by dividing the integrated value of the desorption amount of oxygen molecules or carbon dioxide molecules per 1 g of the sample by the surface area (m ² / g) of the noble metal portion per 1 g of the sample, the oxygen molecules per ^{1 m 2} of the surface area of the noble metal portion. Alternatively, the integrated value of the desorption amount of carbon dioxide molecules is obtained. ^{As described above, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal portion is an index for quantitatively evaluating the abundance ratio of the noble metal element in the skin layer. That is, the larger the abundance ratio of the noble metal element in the skin layer (in other words, the larger the surface area of the noble metal portion in the total surface area of the composite metal particles), the more oxygen molecules are physically adsorbed on the surface of the composite metal particles. Although details will be described later, in the present embodiment, the skin layer is firmly formed when the integrated value of the desorption amount of oxygen molecules per ^{1 m 2 of the surface area of the noble metal portion is 1.0 × 10-6 mol or more.} That is, it is judged that the durability of the alloy catalyst is sufficiently high. ^{The integrated value of the amount of carbon dioxide molecules desorbed per 1 m 2} of the surface area of the noble metal portion is also an index for quantitatively evaluating the abundance ratio of the noble metal element in the skin layer. That is, the larger the abundance ratio of the noble metal element in the skin layer, the smaller the integrated value of the desorption amount of carbon dioxide molecules.

<2. Alloy catalyst composition>
Next, the configuration of the alloy catalyst will be described. The alloy catalyst according to the present embodiment includes a large number of composite metal particles containing a noble metal element and a transition metal element, and a catalyst carrier supporting these composite metal particles. The catalyst carrier is a porous body, and composite metal particles are dispersed and supported on the surface of the catalyst carrier (including the wall surface of the inner pore portion).

(2-1. Composite metal particles)
Composite metal particles include noble metal elements and transition metal elements. The noble metal element is at least one selected from the group consisting of Pt, Au, and Pd. This improves the initial activity of the alloy catalyst. The noble metal element is preferably Pt. In this case, the initial activity of the polymer electrolyte fuel cell can be particularly improved. The transition metal element is at least one selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, and Ni. This improves the initial activity of the alloy catalyst. The transition metal element is preferably any one or more selected from the group consisting of Fe, Co, and Ni. In this case, the initial activity of the alloy catalyst can be particularly improved.

Further, the composite metal particles contain a noble metal element and a transition metal element in a molar ratio of noble metal element: transition metal element = 1: 0.2 or more and 1: 1 or less. More specifically, the composite metal particles contain a transition metal element per 1 mol of the noble metal element at a ratio of 0.2 mol or more and 1.0 mol or less. This improves the initial activity of the alloy catalyst. Although the details will be described later, according to the method for producing an alloy catalyst according to the present embodiment, the composition deviation of the composite metal particles can be suppressed, and the composition of the composite metal particles is set to a value within the above range. be able to. Here, the molar ratio of the noble metal element and the transition metal element can be obtained by, for example, inductively coupled plasma emission spectroscopic analysis. Specifically, by inductively coupled plasma emission spectrometry (ICP-AES: Inductively Coupled Plasma-Atomic Emission Spectrum), the carrying ratio of noble metal elements in the alloy catalyst (% by mass of the noble metal elements with respect to the total mass of the alloy catalyst) and the transition metal. The element carrying ratio (mass% of the transition metal element with respect to the total mass of the alloy catalyst) is determined. Then, the molar ratio of the noble metal element and the transition metal element is obtained based on the carrying ratio of each of the noble metal element and the transition metal element. The measurement by inductively coupled plasma emission spectroscopy can be performed by, for example, ICPE-9800 manufactured by Shimadzu Corporation.

Further, when the composite metal particles are subjected to X-ray diffraction analysis, a diffraction peak is observed at 2θ = 37 ° or more and 42 ° or less, and the lattice constant calculated based on the diffraction peak and the following equation (1) are obtained. The alloying ratio calculated based on this is 60% or more and 100% or less. That is, the noble metal element and the transition metal element are alloyed at a high alloying rate. The alloying ratio is a value that conceptually indicates the degree of solid solution of the transition metal element in the composite metal particles, and the higher the alloying ratio, the more uniformly the transition metal element and the noble metal element are solid-solved in the composite metal particles. ing. By alloying the noble metal element and the transition metal element, the interatomic distance fluctuates and the initial activity is improved as compared with the catalyst particles consisting only of the noble metal element. In particular, when the alloying ratio is set to a value within the range of 60% or more and 100% or less, segregation of the transition metal element is suppressed and the initial activity is further improved. When the alloying ratio is low, that is, when the transition metal element is segregated in the composite metal particles, a large amount of the transition metal element may be eluted by leaching, and the composite metal particles may have a composition shift. This reduces the initial activity.
Alloying rate [%] = {(lattice constant of bulk noble metal)-(lattice constant of composite metal particles)} / {(lattice constant of bulk noble metal)-(lattice constant of maximum peak of bulk composite metal)} x 100
(1)

In the formula (1), the lattice constant of the composite metal particles is a value obtained by X-ray diffraction analysis. The lattice constant of the bulk precious metal is a lattice constant obtained by X-ray diffraction analysis of a standard sample of the noble metal element, and is stored in a database (for example, the International Center for Diffraction Date; a database distributed by ICDD). It is registered. When the composite metal particles contain a plurality of types of noble metal elements, the lattice constant of the noble metal element having the largest amount of substance in the composite metal particles can be used as the lattice constant of the bulk noble metal. The lattice constant of the maximum peak of the bulk composite metal is a lattice constant obtained by X-ray diffraction analysis of a standard sample having the same composition as the composite metal particles, and is a database (for example, International Center for Diffraction Date). It is registered in the database distributed by ICDD). In the examples described later, the alloying rate was calculated based on the database distributed by the International Center for Diffraction and Diffraction.

Further, the crystallite diameter of the composite metal particles calculated based on the diffraction peak is 2 to 8 nm. The crystallite diameter here is the so-called average crystallite diameter. By setting the crystallite diameter to a value within this range, the initial activity is improved. For example, when the crystallite diameter exceeds 8 nm, the total surface area of all composite metal particles becomes small. This means that the reaction field when the polymer electrolyte fuel cell is operated becomes narrow. Therefore, the initial activity becomes small. When the crystallite diameter is less than 2 nm, the total surface area of the composite metal particles is large, but the crystallite diameter is small, and aggregation due to Ostwald ripening is likely to occur in a fuel cell environment. Therefore, if the crystallite diameter is less than 2 nm, the composite metal particles are rapidly aggregated, so that the initial activity is rapidly reduced and the durability is lowered. The crystallite diameter here can be considered as the particle size of the composite metal particles, and there is no problem. This is because the particle size of the composite metal particles in the present embodiment is as small as several nm, and it is considered that the composite metal particles exist as a single crystal.

Further, when the low temperature oxygen TPD measurement is performed on the alloy catalyst, a TPD spectrum (heated desorption curve) of m / z = 32 corresponding to oxygen molecules can be obtained. This TPD spectrum has a desorption peak top in the range of 130K or more and 190K or less. The integrated value of the desorption amount of oxygen molecules calculated based on the area of the desorption peak is 1.0 × ^10-6 mol (mol / m ² ) or more ^{per 1 m 2 of the surface area of the noble metal portion. As described above, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal portion is an index for quantitatively evaluating the abundance ratio of the noble metal element in the skin layer. That is, the larger the abundance ratio of the noble metal element in the skin layer (in other words, the larger the surface area of the noble metal portion in the total surface area of the composite metal particles), the more oxygen molecules are physically adsorbed on the surface of the composite metal particles. Then, in the alloy catalyst according to the present embodiment, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2 of the surface area of the noble metal portion is 1.0 × 10-6} mol (mol / m ² ) or more. As a result, the skin layer is firmly formed, and the durability of the alloy catalyst is dramatically improved. Although it is assumed that a small amount of transition metal element remains in the skin layer, the integrated value of the amount of oxygen molecules desorbed per ^{1 m 2 of the surface area of the noble metal portion is 1.0 × 10-6} mol (mol). If it is / m ² ) or more, it can be judged that the abundance ratio of the noble metal element in the skin layer is sufficiently high and the durability is sufficiently high.

Here, the integrated value of the desorption amount of oxygen molecules is preferably 3.0 × ^10-6 mol (mol / m ² ) or more ^{per 1 m 2 of the surface area of the noble metal element.} In this case, the durability of the alloy catalyst is further improved. The upper limit is not particularly limited, but the integrated value of the desorption amount of oxygen molecules measured when it is assumed that the surface of the composite metal particles is entirely covered with the noble metal element can be a substantial upper limit.

Further, when low temperature oxygen TPD measurement is performed on the alloy catalyst, it is preferable to further obtain a TPD spectrum of m / z = 44 corresponding to carbon dioxide. This TPD spectrum may have a desorption peak top in the range of 300K or more and 900K or less. The integrated value of the desorption amount of carbon dioxide molecules calculated based on the area of the desorption peak is preferably 3.0 × ^10-7 mol (mol / m ² ) or less ^{per 1 m 2 of the surface area of the noble metal portion.} is there. As described above, the integrated value of the desorption amount of carbon dioxide molecules is also an index for quantitatively evaluating the abundance ratio of the noble metal element in the skin layer. That is, the larger the abundance ratio of the noble metal element in the skin layer, the smaller the integrated value of the desorption amount of carbon dioxide molecules. In the alloy catalyst according to the present embodiment, the integrated value of the desorption amount of carbon dioxide molecules per ^{1 m 2 of the surface area of the noble metal portion is preferably 3.0 × 10-7} mol (mol / m ² ) or less. In this case, the abundance ratio of the noble metal element in the skin layer becomes sufficiently high, and the durability of the alloy catalyst is improved. The integrated value of the amount of carbon dioxide molecules desorbed per ^{1 m 2} of the surface area of the noble metal portion ^{is more preferably 2.5 × 10 -7} mol (mol / m ² ) or less. In this case, the durability of the alloy catalyst is further improved. The lower limit of the integrated value of the desorption amount of carbon dioxide molecules is not particularly limited and may be ^{0 mol / m 2.}

(2-2. Catalyst carrier)
The type of the catalyst carrier is not particularly limited, and is not particularly limited as long as it is a porous material that can be used as a catalyst carrier for the polymer electrolyte fuel cell. Examples of the catalyst carrier include porous carbon materials (for example, activated carbon), silica, silica-alumina, silica-calcia, molecular sieve, alumina, zeolite, titania, clay, diatomaceous earth, silicon carbide and the like. Among the above-mentioned porous materials, porous carbon materials, silica, molecular sieves, alumina, zeolites, titania and the like are preferable because they have a relatively large pore capacity and are easily available and handled. When a carrier containing element C, for example, a porous carbon material, is used as the catalyst carrier, it may be possible to obtain a TPD spectrum of m / z = 44 corresponding to carbon dioxide molecules.

As described above, according to the alloy catalyst according to the present embodiment, the abundance ratio of the noble metal element in the skin layer can be increased, so that a strong skin layer can be formed on the surface of the composite metal particles. This improves the durability of the alloy catalyst. Further, the alloy catalyst according to the present embodiment can suppress the composition deviation of the composite metal particles, so that the initial activity is also improved.

<3. Alloy catalyst manufacturing method>
Next, a method for producing an alloy catalyst according to the present embodiment will be described. In the method for producing an alloy catalyst according to the present embodiment, it is generally said that leaching is performed a plurality of times with a weak leaching strength that is not conventionally performed, and the leaching strength is gradually weakened as the number of leachings increases. It is a thing. Specifically, the method for producing an alloy catalyst includes the 0th to 10th steps described below.

(3-0. 0th step)
In the 0th step, an untreated alloy catalyst comprising untreated composite metal particles containing a noble metal element and a transition metal element and a catalyst carrier supporting the untreated composite metal particles is prepared. That is, in the 0th step, an untreated alloy catalyst to be reached is prepared. The untreated alloy catalyst may be produced, for example, according to any of the following first to third production methods. Of course, the method for producing the untreated alloy catalyst is not limited to the following examples, and any production method may be used as long as it can produce the untreated alloy catalyst. Alternatively, a pre-made untreated alloy catalyst may be obtained.

(First manufacturing method)
The first method for producing an untreated alloy catalyst is a method in which a noble metal element and a transition metal element are separately supported on a catalyst carrier. In this method, one of the metal species is first supported on the catalyst carrier, and then the other metal species is further supported. Then, the catalyst carrier carrying the noble metal element and the transition metal element is heat-treated to alloy the noble metal element and the transition metal element.

Specific examples of the first manufacturing method are as follows. In this example, Pt—Co composite metal particles are supported on a porous carbon material that is a catalyst carrier. First, a porous carbon material as a catalyst carrier is dispersed in a solvent such as water, and an amount of platinum solution (for example, dinitrodiammine platinum nitrate solution) having a desired loading ratio and alcohol such as ethanol as a reducing agent are added thereto. , Heat in an oil bath. After heating, the solid content is recovered from the obtained mixed solution by filtration or the like, and the solid content is washed. Then, a solvent such as water is poured into the recovered solid content, and a cobalt solution (for example, an aqueous cobalt nitrate solution) having a desired loading ratio is added thereto and stirred. After stirring, the solvent is removed using a rotary evaporator or the like, and the solid content is dried. Then, the solid content is heat-treated in a reducing gas atmosphere to obtain the desired untreated alloy catalyst.

(Second manufacturing method)
The second method for producing an untreated alloy catalyst is a method in which a noble metal element and a transition metal element are simultaneously supported on a catalyst carrier. In this method, the noble metal element and the transition metal element are simultaneously reduced by adding a reducing agent to the solution containing the catalyst carrier, the noble metal element compound and the transition metal element compound.

Specific examples of the second manufacturing method are as follows. In this example, Pt—Co composite metal particles are supported on a porous carbon material that is a catalyst carrier. First, a porous carbon material as a catalyst carrier is dispersed in a solvent such as water, and an amount of a platinum solution (for example, dinitrodiammine platinum nitric acid solution) and a cobalt solution (for example, an aqueous solution of cobalt nitrate) having a desired loading ratio are dispersed therein. Add. At this time, an organic molecule such as polyvinylpyrrolidone may be added together for the purpose of improving the dispersibility of the catalyst metal particles. After stirring the mixed solution, a reducing agent such as sodium borohydride is added to the mixed solution, and the mixture is stirred. After stirring, the solid content is recovered from the mixed solution by filtration or the like, and the solid content is washed. Then, the recovered solid content is dried to obtain the desired alloy catalyst. The alloy catalyst after drying may be heat-treated for the purpose of increasing the alloying ratio of the Pt—Co composite metal particles.

(Third manufacturing method)
The third manufacturing method is an intermediate method between the first and second manufacturing methods described above. In this method, the catalyst carrier is impregnated with a solution containing a noble metal element compound and a transition metal element compound, dried, and the coagulated product is heat-treated in an atmosphere containing a reducing gas such as hydrogen. As a result, the noble metal element and the transition metal element are reduced at the same time.

Specific examples of the third manufacturing method are as follows. In this example, Pt—Co composite metal particles are supported on a porous carbon material that is a catalyst carrier. First, a porous carbon material as a catalyst carrier is dispersed in a solvent such as water, and an amount of a platinum solution (for example, dinitrodiammine platinum nitric acid solution) and a cobalt solution (for example, an aqueous solution of cobalt nitrate) having a desired loading ratio are dispersed therein. Add. The desired alloy catalyst can be obtained by stirring the mixed solution, removing the solvent using a rotary evaporator or the like, drying the mixture, and then performing heat treatment in a reducing gas atmosphere.

The untreated alloy catalyst obtained in the 0th step is not reached. Therefore, in addition to the noble metal element, a large number of transition metal elements may be present on the surface of the untreated composite metal particles. These transition metal elements are removed by a plurality of leachings described below, and the surface of the composite metal particles is smoothed by a subsequent annealing treatment. In addition, the alloying ratio of the untreated composite metal particles may not be sufficient, and this will be increased by the annealing treatment in the first step described below. Similar to the annealing treatment after leaching, the annealing treatment in the first step can also smooth the surface of the untreated composite metal particles.

(3-1. First step)
In the first step, the first annealing treatment is performed. Specifically, the untreated alloy catalyst is an inert gas composed of any one or more selected from the group consisting of argon, nitrogen, and helium, and 50% by volume or less with respect to the flow rate of the inert gas. Heat treatment is performed at a temperature of 500 ° C. or higher and 900 ° C. or lower for 10 minutes or longer and 60 minutes or lower in an atmosphere containing the hydrogen gas. The lower limit of the concentration of hydrogen gas may be 0% by volume. However, since hydrogen gas has an effect of increasing the alloying ratio of untreated composite metal particles, it is preferable to include hydrogen gas in the inert gas.

As is clear from the comparison with the second and subsequent annealing treatments described later, the strength of the first annealing treatment (hydrogen gas concentration, atmospheric gas temperature, or heat treatment time) is stronger than the strength of the second and subsequent annealing treatments. This is because the main purpose of the annealing treatment after leaching, which will be described later, is to smooth the surface irregularities of the composite metal particles generated by the leaching, whereas the main purpose of the annealing treatment in the first step is. This is because the alloying rate of the untreated alloy catalyst is increased. If it is desired to increase the alloying ratio as compared with smoothing, it is necessary to increase the strength of the annealing treatment. However, since both alloying and smoothing are possible by the annealing treatment, the alloying rate is increased even in the annealing treatment after leaching, and the smoothing also proceeds in the annealing treatment in the first step. If the alloying ratio of the composite metal particles after the tenth step remains low, the initial activity of the alloy catalyst decreases. Further, if large irregularities remain on the surface of the composite metal particles, ^{the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. To do. This is because the transition metal element existing in the back of the composite metal particles is exposed by the unevenness.

Therefore, the alloying ratio of the untreated composite metal particles is increased by the first annealing treatment having a relatively strong strength, and the unevenness of the surface is smoothed. When the strength of the first annealing treatment is weaker than the above-mentioned strength, that is, when the heat treatment temperature is less than 500 ° C. and the heat treatment time is less than 10 minutes, the alloying ratio of the composite metal particles after the 10th step, The integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment, and the initial activity and the initial activity and Durability is reduced. More specifically, the alloying ratio of the composite metal particles after the first annealing treatment is very low. Therefore, the transition metal element is segregated in the composite metal particles. For this reason, it becomes difficult to control the elution amount of the transition metal element in the leaching after the second step, and the composition of the composite metal particles after the tenth step is the same as the composition of the untreated composite metal particles produced in the zeroth step. There is a large deviation (composition deviation). The composition of the resulting composite metal particles may satisfy the conditions of the present embodiment, but in any case, the composite metal particles are in a very unstable state. Therefore, the initial activity is low. Further, since the transition metal element is segregated, severe irregularities are formed on the surface of the composite metal particles by the leaching in the second and subsequent steps. Due to such unevenness, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Furthermore, the noble metal elements on the surface of the composite metal particles are not aligned. Therefore, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment. The durability of the alloy catalyst is reduced.

On the other hand, when the strength of the first annealing treatment is stronger than the above-mentioned strength, that is, when the hydrogen gas concentration exceeds 50% by volume, the heat treatment temperature exceeds 900 ° C., and the heat treatment time exceeds 60 minutes, the tenth step. The crystallite size of the later composite metal particles becomes too large, and the initial activity decreases. This is because the reaction field when the polymer electrolyte fuel cell is operated becomes narrow.

(3-2. Second step)
In the second step, the first leaching is performed. ^{Specifically, the alloy catalyst obtained in the first step is 1.0 × 10 −} one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and perchloric acid. ^{It is brought into contact with an acidic aqueous solution containing 3} mol / L or more and 5.0 × 10 ^-3 mol / L or less at a temperature of 30 ° C. or higher and 90 ° C. or lower for 30 minutes or longer and 100 minutes or shorter.

As is clear from the comparison with the second and subsequent leaching described later, the strength of the first leaching (acid concentration, heating temperature, or contact time with an acidic aqueous solution) is stronger than that of the second and subsequent leaching. However, the strength is weaker than that of the conventional leaching. For example, conventionally, the acid concentration is 0.01 mol / L at the lowest (Patent Document 2), but the acid concentration in the second step is 5.0 × 10 ^-3 mol / L at the highest. In the alloy catalyst obtained in the first step, many transition metal elements are present on the surface of the composite metal particles. Therefore, the transition metal element existing on the surface of the composite metal particles and at a relatively deep position from the surface is removed by the strongest leaching in this production method.

When the strength of the first leaching is weaker than the above-mentioned strength, that is, when the acid concentration is ^{less than 1.0 × 10 -3} mol / L, the heating temperature is less than 30 ° C., and the contact time is less than 30 minutes. , A large number of transition metal elements remain on the surface of the composite metal particles after the tenth step. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. When the strength of the first leaching is stronger than the above-mentioned strength, that is, when the acid concentration exceeds 5.0 × 10 ^-3 mol / L, the heating temperature exceeds 90 ° C., and the contact time exceeds 100 minutes. Large irregularities remain on the surface of the composite metal particles after the tenth step. Therefore, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Therefore, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment, and the alloy The durability of the catalyst is reduced. Further, as a result of removing a large amount of transition metal elements by leaching, the above-mentioned "composition deviation" occurs, and the composition of the composite metal particles does not satisfy the conditions of the present embodiment. Therefore, the initial activity of the alloy catalyst is lowered. In addition, the generated skin layer becomes excessively thick, and it becomes difficult to obtain the effect of the transition metal element inside the skin layer. In this respect as well, the initial activity of the alloy catalyst decreases.

(3-3. Third step)
In the third step, the alloy catalyst obtained in the second step is washed and then dried. The alloy catalyst can be washed with water, for example, but may be washed with another medium as long as the effects of the present embodiment are not impaired.

(3-4. Fourth step)
In the fourth step, the second annealing treatment is performed. Specifically, the alloy catalyst obtained in the third step is applied to an inert gas composed of at least one selected from the group consisting of argon, nitrogen, and helium, and the flow rate of the inert gas. In an atmosphere containing 10% by volume or less of hydrogen gas, heat treatment is performed at a temperature of 250 ° C. or higher and 550 ° C. or lower for 10 minutes or longer and 60 minutes or shorter. The lower limit of the concentration of hydrogen gas may be 0% by volume. However, since hydrogen gas has an effect of increasing the alloying ratio of untreated composite metal particles, it is preferable to include hydrogen gas in the inert gas.

The surface of the composite metal particles is smoothed by the second annealing treatment. However, as is clear from the comparison with the first annealing treatment described above, the strength of the second annealing treatment is weaker than the strength of the first annealing treatment. In the alloy catalyst that is the target of the second annealing treatment, the alloying rate of the composite metal particles is higher than that of the untreated alloy catalyst that is the target of the first annealing treatment, and the alloying rate of the composite metal particles is positively increased. This is because there is no need to increase it. However, since it is necessary to smooth the irregularities on the surface of the composite metal particles generated by the annealing treatment, a second annealing treatment is required.

When the strength of the second annealing treatment is weaker than the above-mentioned strength, that is, when the heat treatment temperature is less than 250 ° C. and the heat treatment time is less than 10 minutes, the surface irregularities of the composite metal particles are sufficiently smoothed. However, by the subsequent leaching, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Therefore, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2 of the surface area of the noble metal element and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element after the 10th step are the integrated values of the present embodiment. The conditions are not met and the durability of the alloy catalyst is reduced. When the strength of the second annealing treatment is stronger than the above-mentioned strength (for example, when the strength is equal to or stronger than the strength of the first annealing treatment), that is, the hydrogen gas concentration exceeds 10% by volume and the heat treatment temperature is 550 ° C. If the heat treatment time exceeds 60 minutes, alloying proceeds more than necessary, and many transition metal elements existing in the back of the composite metal particles move excessively to the surface. Therefore, the transition metal element on the surface of the composite metal particles cannot be sufficiently removed even if the second and subsequent leaching described later are performed. Therefore, in the alloy catalyst after the 10th step, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element and the integrated value of the desorption amount of carbon dioxide molecules per ^{1 m 2 of the surface area of the noble metal element are present.} The conditions of the embodiment are not satisfied, and the durability of the alloy catalyst is reduced. If the strength of the second annealing treatment is within the range of the present invention, even if the alloying proceeds with the smoothing of the surface of the composite metal particles and the transition metal element moves to the surface and its vicinity again, it will be described later. By performing the leaching after the first time, it is possible to sufficiently remove the transition metal element on the surface and its vicinity.

(3-5. 5th step)
In the fifth step, the second leaching is performed. ^{Specifically, the alloy catalyst obtained in the fourth step is 1.0 × 10 −} one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and perchloric acid. ^{It is brought into contact with an acidic aqueous solution containing 4} mol / L or more and 5.0 × 10 ^-4 mol / L or less at a temperature of 30 ° C. or more and 70 ° C. or less for 10 minutes or more and 60 minutes or less.

By the fourth step, the transition metal element moves to the surface of the composite metal particles and its vicinity. Therefore, the transition metal element existing on the surface of the composite metal particles and in the vicinity thereof is removed by the second leaching. However, as is clear from the comparison with the first leaching described above, the strength of the second leaching is weaker than the strength of the first leaching. This is because the number of atoms of the transition metal element existing on the surface of the composite metal particles and in the vicinity thereof is smaller than that of the alloy catalyst targeted for the first leaching. That is, in the second leaching, the transition metal element is removed from a position where the depth from the surface of the composite metal particle is shallower.

When the strength of the second leaching is weaker than the above-mentioned strength, that is, when the acid concentration is ^{less than 1.0 × 10 -4} mol / L, the heating temperature is less than 30 ° C., and the contact time is less than 10 minutes. , A large number of transition metal elements remain on the surface of the composite metal particles after the tenth step. Therefore, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment. The durability of the alloy catalyst is reduced. When the strength of the second leaching is stronger than the above-mentioned strength (for example, when it is as strong as or stronger than the strength of the first leaching), that is, when the acid concentration exceeds 5.0 × 10 ^-4 mol / L and the heating is performed. When the temperature exceeds 70 ° C. and the contact time exceeds 60 minutes, large irregularities remain on the surface of the composite metal particles after the tenth step. Therefore, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Therefore, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment, and the alloy The durability of the catalyst is reduced. Further, as a result of removing a large amount of transition metal elements by leaching, the above-mentioned "composition deviation" occurs, and the composition of the composite metal particles does not satisfy the conditions of the present embodiment. Therefore, the initial activity of the alloy catalyst also decreases. In addition, the generated skin layer becomes excessively thick, and it becomes difficult to obtain the effect of the transition metal element inside the skin layer. In this respect as well, the initial activity of the alloy catalyst decreases.

(3-6. 6th step)
In the sixth step, the alloy catalyst obtained in the fifth step is washed and then dried. The alloy catalyst can be washed with water, for example, but may be washed with another medium as long as the effects of the present embodiment are not impaired.

(3-7. 7th step)
In the seventh step, the third annealing treatment is performed. Specifically, the alloy catalyst obtained in the sixth step is applied to an inert gas composed of at least one selected from the group consisting of argon, nitrogen, and helium, and the flow rate of the inert gas. In an atmosphere containing 5% by volume or less of hydrogen gas, heat treatment is performed at a temperature of 200 ° C. or higher and 500 ° C. or lower for 10 minutes or longer and 60 minutes or shorter. The lower limit of the concentration of hydrogen gas may be 0% by volume. However, since hydrogen gas has an effect of increasing the alloying ratio of untreated composite metal particles, it is preferable to include hydrogen gas in the inert gas.

The surface of the composite metal particles is smoothed by the third annealing treatment. However, as is clear from the comparison with the second annealing treatment described above, the strength of the third annealing treatment is weaker than the strength of the second annealing treatment. Since the second leaching strength is weaker than the first leaching strength, the composite metal particles to be subjected to the third annealing treatment are transition metals as compared with the composite metal particles to be subjected to the second annealing treatment. The amount of elements eluted is small, and the surface irregularities of the composite metal particles are small. Therefore, since the surface of the composite metal particles to be subjected to the third annealing treatment is smoothed more than the composite metal particles to be subjected to the second annealing treatment, the strength of the annealing treatment is weaker. Do.

When the strength of the third annealing treatment is weaker than the above-mentioned strength, that is, when the heat treatment temperature is less than 200 ° C. and the heat treatment time is less than 10 minutes, the surface irregularities of the composite metal particles are sufficiently smoothed. However, by the subsequent leaching, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Therefore, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2 of the surface area of the noble metal element and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element after the 10th step are the integrated values of the present embodiment. The conditions are not met and the durability of the alloy catalyst is reduced. When the strength of the third annealing treatment is stronger than the above-mentioned strength (for example, when the strength is equal to or stronger than the strength of the second annealing treatment), that is, the hydrogen gas concentration exceeds 5% by volume and the heat treatment temperature is 500 ° C. When the heat treatment time exceeds 60 minutes, many transition metal elements existing in the back of the composite metal particles move to the surface. Therefore, the transition metal element on the surface of the composite metal particles cannot be sufficiently removed even if the third leaching described later is performed. Therefore, in the alloy catalyst after the 10th step, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element and the integrated value of the desorption amount of carbon dioxide molecules per ^{1 m 2 of the surface area of the noble metal element are present.} The conditions of the embodiment are not satisfied, and the durability of the alloy catalyst is reduced.

(3-8. 8th step)
In the eighth step, the third leaching is performed. ^{Specifically, the alloy catalyst obtained in the 7th step is 1.0 × 10 −} one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and perchloric acid. ^{It is brought into contact with an acidic aqueous solution containing 5} mol / L or more and 5.0 × ^10-5 mol / L or less at a temperature of 30 ° C. or more and 60 ° C. or less for a time of 5 minutes or more and 30 minutes or less.

By the seventh step, the transition metal element moves to the surface of the composite metal particles and its vicinity. Therefore, the transition metal element existing on the surface of the composite metal particles and in the vicinity thereof is removed by the third leaching. However, as is clear from the comparison with the second leaching described above, the strength of the third leaching is weaker than the strength of the second leaching. This is because the number of atoms of the transition metal element on or near the surface of the composite metal particles is smaller than that of the alloy catalyst targeted for the second leaching. That is, in the third leaching, the transition metal element is removed from a position where the depth from the surface of the composite metal particles is shallower.

When the strength of the third leaching is weaker than the above-mentioned strength, that is, when the acid concentration is ^{less than 1.0 × 10-5} mol / L, the heating temperature is less than 30 ° C., and the contact time is less than 5 minutes. , A large number of transition metal elements remain on the surface of the composite metal particles after the tenth step. Therefore, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment. The durability of the alloy catalyst is reduced. When the strength of the third leaching is stronger than the above-mentioned strength (for example, when the strength of the second leaching is equal to or stronger than that of the second leaching), that is, the acid concentration exceeds 5.0 × ^10-5 mol / L and heating When the temperature exceeds 60 ° C. and the contact time exceeds 30 minutes, large irregularities remain on the surface of the composite metal particles after the tenth step. Therefore, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Therefore, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment, and the alloy The durability of the catalyst is reduced. Further, as a result of removing a large amount of transition metal elements by leaching, the above-mentioned "composition deviation" occurs, and the composition of the composite metal particles does not satisfy the conditions of the present embodiment. Therefore, the initial activity of the alloy catalyst also decreases. In addition, the generated skin layer becomes excessively thick, and it becomes difficult to obtain the effect of the transition metal element inside the skin layer. In this respect as well, the initial activity of the alloy catalyst decreases.

(3-9. 9th step)
In the ninth step, the alloy catalyst obtained in the eighth step is washed and then dried. The alloy catalyst can be washed with water, for example, but may be washed with another medium as long as the effects of the present embodiment are not impaired.

(3-10. 10th step)
In the tenth step, the fourth annealing treatment is performed. Specifically, the alloy catalyst obtained in the ninth step is 200 ° C. or higher and 450 ° C. or lower in an inert gas atmosphere composed of any one or more selected from the group consisting of argon, nitrogen, and helium. Heat treatment is carried out at the same temperature for 5 minutes or more and 30 minutes or less.

The alloying ratio of the composite metal particles has been sufficiently increased up to the third annealing treatment, and the surface state of the composite metal particles is such that slight irregularities remain. Therefore, the fourth annealing treatment may smooth the unevenness slightly remaining on the surface of the composite metal particles. Therefore, as is clear from the comparison with the above-mentioned third annealing treatment, the strength of the fourth annealing treatment is weaker than the strength of the third annealing treatment. Further, in the fourth annealing treatment, not only is it not necessary to increase the alloying ratio, but if the alloying ratio is increased, the transition metal element moves again to the surface of the composite metal particles. Therefore, hydrogen gas is not used so as not to increase the alloying ratio.

When the strength of the fourth annealing treatment is weaker than the above-mentioned strength, that is, when the heat treatment temperature is less than 200 ° C. and the heat treatment time is less than 5 minutes, the surface irregularities of the composite metal particles after the 10th step become uneven. It is not sufficiently smoothed, and oxygen molecules are in a state where they can reach the transition metal element existing in the back of the composite metal particles from the surface. Therefore, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment. The durability of the alloy catalyst is reduced. When the strength of the fourth annealing treatment is stronger than the above-mentioned strength (for example, when the strength is equal to or stronger than the strength of the third annealing treatment), that is, the heat treatment temperature exceeds 450 ° C. and the heat treatment time exceeds 30 minutes. In some cases (or in addition to these, when the atmospheric gas contains hydrogen gas), many transition metal elements present in the back of the composite metal particles move to the surface. Therefore, in the alloy catalyst after the 10th step, the ^{integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element and the integrated value of the desorption amount of carbon dioxide molecules per ^{1 m 2} of the surface area of the noble metal element are calculated. The conditions of the present embodiment are not satisfied, and the durability of the alloy catalyst is lowered.

By the above steps, the alloy catalyst according to the present embodiment can be produced. That is, it is possible to produce an alloy catalyst capable of increasing the durability of the alloy catalyst while suppressing the composition deviation of the composite metal particles. It cannot be said unconditionally because each step is complicatedly related to each other, but by increasing the strength of the leaching or annealing treatment in each step within the above range, the integrated value of the desorption amount of oxygen molecules increases (this). The integrated value of the desorption amount of carbon dioxide molecules becomes smaller accordingly). However, as the intensity of the leaching or annealing treatment approaches the upper limit of the above range, the integrated value of the desorption amount of oxygen molecules starts to decrease (the integrated value of the desorption amount of carbon dioxide molecules increases accordingly). Will) tend to. In both the leaching and annealing treatments, it is preferable to gradually reduce the strength as the treatment progresses. That is, each leaching is preferably performed with a weaker strength than the previous leaching, and each annealing treatment is preferably performed with a weaker strength than the previous annealing treatment.

Next, an embodiment of the present embodiment will be described. In the examples, an experiment was conducted to confirm the effect of this embodiment. The details of the experiment will be described below.

<1. Measurement method>
(1-1. Low temperature oxygen TPD measurement method)
First, each measurement method used in this embodiment will be described. The low temperature oxygen TPD measurement method was performed as follows. First, a 0.05 g alloy catalyst sample was placed in a sample tube, hydrogen reduction at 500 ° C. was performed for 5 minutes as a pretreatment, and the sample was exhausted at the same temperature. Hydrogen reduction was performed twice. The sample was then cooled to 85 K (-185 ° C.) with liquid nitrogen. Then, 1 kPa of oxygen was introduced into the sample tube and allowed to stand for 15 minutes. By this step, oxygen molecules were adsorbed on the sample.

Then, the sample tube was exhausted. After that, the sample tube was connected to the quadrupole analyzer. After allowing to stand for 20 minutes until the partial pressure of oxygen in the sample tube decreased, the sample in the sample tube was linearly heated at a heating rate of 10 K / min. At this time, the signals of m / z = 32 and m / z = 44 were recorded by the quadrupole mass spectrometer, respectively. As described above, the signal of m / z = 32 corresponds to the oxygen molecule, and the signal of m / z = 44 corresponds to the carbon dioxide molecule. Each signal was calibrated for the specified amount of oxygen and carbon dioxide. Then, by plotting the measured values on the xy plane with the horizontal axis as the temperature and the vertical axis as mol / (s · g), the TPD spectrum of m / z = 32 corresponding to the oxygen molecule (temperature-rising elimination curve). , A TPD spectrum of m / z = 44 corresponding to a carbon dioxide molecule was obtained.

Then, the desorption peak was separated from each TPD spectrum, and the area of the desorption peak was calculated. Separation of the desorption peak was performed using the peak fit function of OriginPro 2018 (manufactured by Lightstone). The horizontal axis of the TPD spectrum is temperature, but the horizontal axis was converted to time based on the rate of temperature rise (10 K / min). As a result, the area of the desorption peak having the unit of mol / g was calculated. The area of the desorption peak means the integrated value of the desorption amount of oxygen molecules or carbon dioxide molecules per 1 g of the sample.

Then, the integrated value of the desorption amount of oxygen molecule or carbon dioxide molecule per 1 g of the sample was converted into the value per ^{1 m 2 of the surface area of the noble metal portion. Specifically, the surface area (m 2} / g) of the noble metal portion per 1 g of the sample was determined by the CO pulse injection chemisorption amount measurement method. Here, the CO pulse injection chemisorption amount was measured using a metal dispersion measuring device (BEL-METAL-3, manufactured by Microtrac Bell). Specifically, 0.05 g of a sample was placed in a sample tube. Then, as a pretreatment, the sample was heated to 500 ° C. under He gas flow and held for 5 minutes. Then, the He gas was switched to hydrogen gas, and the sample was held at 500 ° C. for 10 minutes under the flow of hydrogen gas. Then, the hydrogen gas was switched to Ar gas, and the sample was cooled to 40 ° C. under the flow of Ar gas. Then, while maintaining this temperature, a 10% by volume CO gas pulse was injected into the sample tube every minute until CO adsorption was no longer observed. Then, the CO adsorption amount of the sample was calculated. ^{The surface area (m 2} / g) of the noble metal portion per 1 g of the sample was calculated based on the adsorbed amount of the obtained CO gas and the above-mentioned formula (2).

Then, by dividing the integrated value of the desorption amount of oxygen molecules or carbon dioxide molecules per 1 g of the sample by the surface area (m ² / g) of the noble metal portion per 1 g of the sample, the oxygen molecules per ^{1 m 2} of the surface area of the noble metal portion. Alternatively, the integrated value (mol / m ² ) of the desorption amount of carbon dioxide molecules was determined.

(1-2. Method for measuring alloying ratio and crystallite diameter)
The alloying ratio of the composite metal particles was measured by an X-ray diffraction device (XRD, manufactured by Rigaku Corporation, Smart Lab). Specifically, a sample of the alloy catalyst was subjected to X-ray diffraction analysis by an X-ray diffractometer. Then, the lattice constant of the composite metal particles was calculated based on the diffraction peak observed at 2θ = 37 ° or more and 42 ° or less. Then, the alloying ratio of the composite metal particles was calculated based on the calculated lattice constant of the composite metal particles and the above-mentioned formula (1).

Further, the crystallite diameter of the composite metal particles was calculated based on the above-mentioned diffraction peak and the following equation (3) (Scherrer's equation).
Scherrer's equation: D = Kλ / βcosθ (3)
D: Crystallet diameter [nm], K: Scheller constant (0.94), λ: X-ray wavelength of CuKα [nm], β: Half width [rad], θ: Bragg angle [rad]

(1-3. Method for measuring the composition of composite metal particles)
The composition of the composite metal particles (more specifically, the composition of the composite metal particles after performing the first to tenth steps) was determined by inductively coupled plasma emission spectroscopy. Specifically, the ICPE-9800 manufactured by Shimadzu Corporation was used to support the noble metal element in the alloy catalyst (mass% of the noble metal element with respect to the total mass of the alloy catalyst) and the transition metal element (transition metal with respect to the total mass of the alloy catalyst). The mass% of the element) was calculated. Then, the composition of the composite metal particles, more specifically, the molar ratio of the noble metal element and the transition metal element was determined based on the carrying ratios of the noble metal element and the transition metal element.

<2. Fabrication of alloy catalyst>
(2-1. 1st process group)
The alloy catalysts were prepared in several groups. In the first process group, the conditions of the first process are set within and outside the range of the conditions of the present embodiment, and the conditions of the second to tenth steps are set so as to satisfy the conditions of the present embodiment. A catalyst was prepared (Comparative Example 1-1, Examples 1-2-1-7, Comparative Example 1-8).

(2-1-1. Comparative Example 1-1)
First, Comparative Example 1-1 will be described. In the 0th step of Comparative Example 1-1, a sample of the untreated alloy catalyst was prepared by the following steps. First, 1.0 g of Denka Black powder (manufactured by Denka) as a catalyst carrier was added to 120 mL of water, and Denka Black powder was dispersed in water for 2 minutes by an ultrasonic homogenizer. 2.01 g of a dinitrodiammine platinum nitric acid solution having a platinum concentration of 4.5% by mass and 30 mL of ethanol were added to the prepared dispersion, and the mixture was stirred in an oil bath set at 110 ° C. for 12 hours. The obtained mixed solution was filtered to wash the solid content, and then the solid content was recovered. 100 mL of water was poured into the recovered solid content, 0.054 g of titanium chloride was added thereto, and the mixture was stirred for 30 minutes. After stirring, the solvent was removed from the mixture using a rotary evaporator. Through the above steps, a sample of an untreated alloy catalyst was obtained. Then, the sample of the untreated alloy catalyst was vacuum dried.

Then, the above-mentioned first to tenth steps were performed on the sample of the untreated alloy catalyst. In the first step, the sample obtained in the 0th step was subjected to the first time under the conditions (atmospheric gas composition, atmospheric gas temperature, and heat treatment time) shown in Tables 1A to 1B (hereinafter abbreviated as Table 1). Annealing treatment was performed. In addition, in Table 1 and Tables 3A to 3B (hereinafter, abbreviated as Table 3), 5A to 5B (hereinafter, abbreviated as Table 5), 7A to 7B (hereinafter, abbreviated as Table 7), 9 which will be described later, " "%" In the item of "atmosphere" indicates "volume%", and "room temperature" indicates 25 ° C.

In the second step, 1.0 g of the sample after the first step was measured in an eggplant flask, and 100 mL of an acidic aqueous solution of the type and acid concentration shown in Table 1 was further added to the eggplant flask. Then, the eggplant flask containing the sample and the acidic aqueous solution was placed in an oil bath, and the first leaching was performed at the heating temperature and contact time shown in Table 1. During the leaching, the mixture of the sample and the acidic aqueous solution was stirred. In the third step, a sample was recovered from the mixed solution after the second step by filtration, and the recovered sample was washed with water. The sample was then vacuum dried. Then, the 4th to 10th steps were carried out in the same manner as the 1st to 3rd steps described above. The conditions of the 4th to 10th steps are as shown in Table 1. A sample of the alloy catalyst was prepared by the above steps. Then, <1. Measurement method> According to the measurement method shown in>, ^{the integrated value of the desorption amount of oxygen molecules or carbon dioxide molecules per 1 m 2} of the surface area of the noble metal portion, the alloying rate of the composite metal particles, the crystallite diameter of the composite metal particles, and the composite. The composition of the metal particles was measured. The results are shown in Table 2. The composition shows both the charged composition (composition of untreated composite metal particles) and the composition after leaching (composition after the first to tenth steps).

(2-1-2. Example 1-2)
The same treatment as in Comparative Example 1-1 is carried out except that 0.056 g of manganese chloride tetrahydrate is used instead of titanium chloride and the conditions of the first to tenth steps are the conditions shown in Table 1. Then, a sample of an untreated alloy catalyst was prepared. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 2.

(2-1-3. Example 1-3)
Perform the same treatment as in Comparative Example 1-1 except that 0.074 g of scandium chloride hexahydrate was used instead of titanium chloride and the conditions of the first to tenth steps were set as the conditions shown in Table 1. Then, a sample of an untreated alloy catalyst was prepared. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 2.

(2-1-4. Example 1-4)
Untreated by performing the same treatment as in Comparative Example 1-1 except that 0.045 g of vanadium chloride was used instead of titanium chloride and the conditions of the first to tenth steps were the conditions shown in Table 1. A sample of the alloy catalyst was prepared. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 2.

(2-1-5. Example 1-5)
The same treatment as in Comparative Example 1-1 is carried out except that 0.077 g of iron chloride hexahydrate is used instead of titanium chloride and the conditions of the first to tenth steps are the conditions shown in Table 1. Then, a sample of an untreated alloy catalyst was prepared. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 2.

(2-1-6. Example 1-6)
The same treatment as in Comparative Example 1-1 is carried out except that 0.076 g of chromium hexahydrate chloride is used instead of titanium chloride and the conditions of the first to tenth steps are the conditions shown in Table 1. Then, a sample of an untreated alloy catalyst was prepared. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 2.

(2-1-7. Example 1-7)
A sample of the untreated alloy catalyst was prepared by performing the same treatment as in Comparative Example 1-1 except that the conditions of the first to tenth steps were set to the conditions shown in Table 1. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 2.

(2-1-8. Comparative Example 1-8)
The same treatment as in Comparative Example 1-1 is carried out except that 0.076 g of chromium hexahydrate chloride is used instead of titanium chloride and the conditions of the first to tenth steps are the conditions shown in Table 1. Then, a sample of an untreated alloy catalyst was prepared. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 2.

(2-2. 2nd to 4th process groups)
In the 2nd to 4th process groups, the conditions of the 2nd to 4th steps are set within the range of the conditions of the present embodiment and outside, respectively, and the conditions of the 1st and 5th to 10th steps are the conditions of the present embodiment. An alloy catalyst was prepared so as to satisfy the conditions (Comparative Example 2-1 and Examples 2-2-2-4, Comparative Example 2-5).

(2-2-1. Comparative Example 2-1)
Except that 0.160 g of palladium nitrate was used instead of the dinitrodiammine platinum nitric acid solution, 0.094 g of iron chloride hexahydrate was used instead of titanium chloride, and the conditions of the first to tenth steps were set to the conditions shown in Table 3. Prepared a sample of an untreated alloy catalyst by performing the same treatment as in Comparative Example 1-1. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 4.

(2-2-2. Example 2-2)
The same treatment as in Comparative Example 2-1 is carried out except that 0.045 g of nickel chloride is used instead of iron chloride hexahydrate and the conditions of the first to tenth steps are the conditions shown in Table 3. Then, a sample of an untreated alloy catalyst was prepared. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 4.

(2-2-3. Example 2-3)
Similar to Comparative Example 2-1 except that 0.083 g of cobalt chloride hexahydrate was used instead of iron chloride hexahydrate and the conditions of the first to tenth steps were set to the conditions shown in Table 3. By performing the treatment, a sample of an untreated alloy catalyst was prepared. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 4.

(2-2-4. Example 2-4)
0.155 g of chloroauric acid tetrahydrate was used instead of the dinitrodiammine platinum nitric acid solution, 0.024 g of nickel chloride was used instead of titanium chloride, and the conditions of the first to tenth steps were set as the conditions shown in Table 3. A sample of an untreated alloy catalyst was prepared by performing the same treatment as in Comparative Example 1-1 except for the above. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 4.

(2-2-5. Comparative Example 2-5)
The same treatment as in Example 2-4 is carried out except that 0.051 g of iron chloride hexahydrate is used instead of nickel chloride and the conditions of the first to tenth steps are as shown in Table 3. Then, a sample of an untreated alloy catalyst was prepared. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 4.

(2-3. 5th to 7th process groups)
In the 5th to 7th process groups, the conditions of the 5th to 7th steps are set within the range of the conditions of the present embodiment and outside, respectively, and the conditions of the 1st to 4th and 8th to 10th steps are the present. An alloy catalyst was prepared by setting so as to satisfy the conditions of the embodiment (Comparative Example 3-1 and Examples 3-2-3-4, Comparative Example 3-5).

(2-3-1. Comparative Example 3-1)
The amount of the dinitrodiammine platinum nitric acid solution used was changed from 2.01 g to 3.01 g, 0.034 g of cobalt chloride hexahydrate was used instead of titanium chloride, and the conditions of the first to tenth steps are shown in Table 5. A sample of the untreated alloy catalyst was prepared by performing the same treatment as in Comparative Example 1-1 except for the above. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 6.

(2-3-2. Example 3-2)
A sample of the untreated alloy catalyst was prepared by performing the same treatment as in Comparative Example 3-1 except that the conditions of the first to tenth steps were set to the conditions shown in Table 5. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 6.

(2-3-3. Example 3-3)
A sample of the untreated alloy catalyst was prepared by performing the same treatment as in Comparative Example 3-1 except that the conditions of the first to tenth steps were set to the conditions shown in Table 5. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 6.

(2-3-4. Example 3-4)
A sample of the untreated alloy catalyst was prepared by performing the same treatment as in Comparative Example 3-1 except that the conditions of the first to tenth steps were set to the conditions shown in Table 5. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 6.

(2-3-5. Comparative Example 3-5)
A sample of the untreated alloy catalyst was prepared by performing the same treatment as in Comparative Example 3-1 except that the conditions of the first to tenth steps were set to the conditions shown in Table 5. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 6.

(2-4. 8th to 10th process groups)
In the 8th to 10th process groups, the conditions of the 8th to 10th steps are set within and outside the range of the conditions of the present embodiment, and the conditions of the 1st to 7th steps satisfy the conditions of the present embodiment. To prepare an alloy catalyst (Comparative Example 4-1 and Examples 4-2 to 4-4, Comparative Example 4-5).

(2-4-1. Comparative Example 4-1)
The same treatment as in Comparative Example 3-1 was carried out except that 0.018 g of nickel chloride was used instead of 0.034 g of cobalt chloride hexahydrate and the conditions of the first to tenth steps were set to the conditions shown in Table 7. By doing so, a sample of an untreated alloy catalyst was prepared. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 8.

(2-4-2. Example 4-2)
A sample of the untreated alloy catalyst was prepared by performing the same treatment as in Comparative Example 4-1 except that the conditions of the first to tenth steps were set to the conditions shown in Table 7. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 8.

(2-4-3. Example 4-3)
A sample of the untreated alloy catalyst was prepared by performing the same treatment as in Comparative Example 4-1 except that the conditions of the first to tenth steps were set to the conditions shown in Table 7. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 8.

(2-4-4. Example 4-4)
A sample of the untreated alloy catalyst was prepared by performing the same treatment as in Comparative Example 4-1 except that the conditions of the first to tenth steps were set to the conditions shown in Table 7. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 8.

(2-4-5. Comparative Example 4-5)
A sample of the untreated alloy catalyst was prepared by performing the same treatment as in Comparative Example 4-1 except that the conditions of the first to tenth steps were set to the conditions shown in Table 7. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 8.

(2-5. Other groups)
(2-5-1. Comparative Example 5-1)
Comparative Example 5-1 is an example in which general leaching and annealing treatments that have been conventionally performed are performed. Specifically, in Comparative Example 5-1, the untreated alloy catalyst sample was subjected to the same treatment as in Comparative Example 3-1 except that the conditions of the first to fourth steps were set to the conditions shown in Table 9. Was produced. In Comparative Example 5-1, the fifth and subsequent steps were not performed. Further, as for the conditions of the first to fourth steps, Non-Patent Document 1 was referred to. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 10.

(2-5-2. Comparative Example 5-2)
In Comparative Example 5-2, the untreated alloy catalyst was subjected to the same treatment as in Comparative Example 5-1 except that the conditions of the fourth step of Comparative Example 5-1 (strength of the second annealing treatment) were strengthened. Samples were prepared. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 10.

(2-5-3. Comparative Example 5-3)
Comparative Example 5-3 is an example in which a large amount of transition metal elements are charged into the untreated composite metal particles in advance in anticipation of “composition deviation”. Specifically, in Comparative Example 5-3, 2.19 g of dinitrodiammine platinum nitric acid solution (same concentration) was used instead of 3.01 g of dinitrodiammine platinum nitric acid solution, and 0.034 g of cobalt chloride hexahydrate was replaced with chloride. A sample of an untreated alloy catalyst was subjected to the same treatment as in Comparative Example 3-1 except that 0.062 g of cobalt hexahydrate was used and the conditions of the first to fourth steps were set to the conditions shown in Table 9. Was produced. In Comparative Example 5-3, the fifth and subsequent steps were not performed. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 10.

(2-5-4. Comparative Example 5-4)
In Comparative Example 5-4, the untreated alloy was subjected to the same treatment as in Comparative Example 5-1 except that the conditions (strength of the first leaching) of the second step of Comparative Example 5-1 were made very weak. A catalyst sample was prepared. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 10.

(2-5-5. Comparative Example 5-5)
Comparative Example 5-5 is an example in which the example of Patent Document 1 is reproduced. Specifically, in Comparative Example 5-5, the untreated alloy catalyst sample was subjected to the same treatment as in Comparative Example 3-1 except that the conditions of the first to third steps were set to the conditions shown in Table 9. Was produced. In Comparative Example 5-5, the fourth and subsequent steps were not performed. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 10.

(2-5-6. Comparative Example 5-6)
Comparative Example 5-6 is an example of reproducing the example of Patent Document 2. Specifically, in Comparative Example 5-6, the untreated alloy catalyst sample was subjected to the same treatment as in Comparative Example 3-1 except that the conditions of the first to fourth steps were set to the conditions shown in Table 9. Was produced. In Comparative Example 5-6, the fifth and subsequent steps were not performed. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 10.

(2-5-7. Comparative Example 5-7)
Comparative Example 5-7 is an example in which the example of Patent Document 3 is reproduced. Specifically, in Comparative Example 5-7, the untreated alloy catalyst sample was subjected to the same treatment as in Example 1-4 except that the conditions of the first to fourth steps were set to the conditions shown in Table 9. Was produced. In Comparative Example 5-7, the fifth and subsequent steps were not performed. Furthermore, <1. The value of each parameter was measured by the measurement method shown in Measurement method>. The results are shown in Table 10.

<3. Preparation of test cell>
Next, test cells were prepared using the alloy catalysts of each group produced. The specific process is as follows.

(3-1. Preparation of coating ink)
A Nafion solution in which Nafion (Nafion manufactured by DuPont, registered trademark: Nafion, persulfonic acid-based ion exchange resin) to be an electrolyte resin was dissolved was prepared. Then, the alloy catalyst and the Nafion solution were mixed under an argon atmosphere. Here, the mass ratio of the solid content of the electrolyte resin was set to 1.0 times that of the alloy catalyst. Then, after lightly stirring the mixed solution, the alloy catalyst in the mixed solution was crushed by ultrasonic waves. Then, ethanol was further added to the mixed solution to adjust the total solid content concentration of the alloy catalyst and the electrolyte resin to 1.0% by mass with respect to the total mass of the mixed solution. As a result, a coating ink containing an alloy catalyst and an electrolyte resin was produced.

(3-2. Preparation of catalyst layer)
By further adding ethanol to the coating ink, the alloy catalyst concentration in the coating ink was set to 1.0% by mass with respect to the total mass of the coating ink. Here, the concentration of the alloy catalyst means the total concentration of all the components of the metal elements (here, the noble metal element and the transition metal element) constituting the alloy catalyst. The same applies to the basis weight amount described later. Then, the spray conditions were adjusted so that the mass per unit area of the catalyst layer of the alloy catalyst (hereinafter referred to as "catalyst basis weight") was 0.2 mg / cm ^2, and the coating ink was applied to a Teflon (registered trademark) sheet. Sprayed on top. Then, a catalyst layer was prepared by performing a drying treatment at 120 ° C. for 60 minutes in an argon atmosphere. Two of the same catalyst layers were prepared, one as a cathode and the other as an anode.

(3-3. Preparation of Membrane Electrode Assembly (MEA) A square electrolyte membrane having a side of 6 cm was cut out from a Nafion membrane (NR211 manufactured by DuPont), and on a Teflon (registered trademark) sheet. Each of the coated anode and cathode catalyst layers was cut out into a square shape with a side of 2.5 cm with a cutter knife. Between the anode and cathode catalyst layers cut out in this way, each catalyst layer was an electrolyte membrane. ^{The electrolyte membranes were sandwiched and pressed at 120 ° C. and 100 kg / cm 2} for 10 minutes so that they would be in contact with each other and not displaced from each other, and then the laminate was cooled to room temperature. Then, the anode and the anode and Only the Teflon (registered trademark) sheet was carefully peeled off for both the cathodes. By the above steps, the catalyst layers of the anode and the cathode were fixed to the electrolyte membrane.

Next, two square carbon papers having a side of 2.5 cm were cut out from the carbon paper (35BC manufactured by SGL Carbon Co., Ltd.) as the gas diffusion layer. Then, these carbon papers were laminated so that the anode and the cathode did not deviate from each other to prepare a laminated body. Then, the laminate was pressed at 120 ° C. and 50 kg / cm ² for 10 minutes to prepare MEA. The mass of the catalyst layer fixed on the Nafion film was obtained from the difference between the mass of the Teflon (registered trademark) sheet with a catalyst layer before pressing and the mass of the Teflon (registered trademark) sheet peeled off after pressing, and the composition of the catalyst layer was obtained. The amount of catalyst, the amount of alloy catalyst, and the amount of electrolyte resin were calculated from the mass ratio of. By this method, it was confirmed that the catalyst basis weight was 0.2 mg / cm ^2. Then, the prepared MEA was incorporated into the cell to prepare a test cell.

<4. Evaluation of initial activity and durability>
(4-1. Evaluation of initial activity)
The test cell was set in a fuel cell measuring device (AutoPEM manufactured by Toyo Corporation), and the initial activity of the alloy catalyst was evaluated by the following procedure.

Air was supplied to the cathode as a supply gas, and pure hydrogen was supplied to the anode as a supply gas under atmospheric pressure so that the utilization rates were 40% and 70%, respectively. The cell temperature was set to 80 ° C. In addition, both the cathode side and the anode side pass the supplied gas (that is, air or pure hydrogen) through the distilled water kept at 65 ° C. in the humidifier (that is, bubbling), so that the supplied gas is in the humidifier. Saturated water vapor corresponding to the water temperature of was applied. Then, the supply gas was supplied to the cathode or the anode.

Under such a setting, the initial power generation characteristics (that is, the initial activity of the alloy catalyst) were evaluated by gradually increasing the load while supplying the supply gas to the test cell. Specifically, the voltage between cell terminals (hereinafter referred to as cell voltage) at a current density of 0.2 A / cm ² was recorded, and the value of this cell voltage was used as an evaluation index of the initial activity of the alloy catalyst. Specifically, when the initial activity was 780 mV or more, the initial activity was regarded as a passing level. The evaluation results are summarized in Tables 2, 4, 6, 8 and 10.

(4-2. Evaluation of durability)
Subsequently, in order to evaluate the durability of the alloy catalyst, "the cell voltage was set to 0.6 V and held for 4 seconds, then the cell voltage was raised to 1.2 V and held for 4 seconds, and then the cell voltage was returned to the original value. The operation of "returning to 0.6V" was set as one cycle operation, and a durability test was conducted in which this cycle operation was repeated 300 times. After this endurance test, the cell voltage (cell voltage at a current density of 0.2 A / cm ² ) was measured by the same method as the above-mentioned initial activity evaluation test. The measured cell voltage (V) after the endurance test was subtracted from the cell voltage before the endurance test (that is, the cell voltage obtained in the above-mentioned initial activity evaluation test) to obtain the cell voltage drop width ΔV. Further, this decrease width ΔV was divided by the cell voltage before the pre-durability test to calculate the cell voltage decrease rate. Then, the cell voltage reduction rate was used as an evaluation index for durability. Specifically, if the rate of decrease is 15% or less, the pass level is set. If the rate of decrease is 5% or less, it can be said that the durability is particularly excellent. The evaluation results are summarized in Tables 2, 4, 6, 8 and 10. The cell voltage (V) after the durability test is shown as "after durability" in the table.

<5. Consideration of evaluation results>
(5-1. 1st process group)
Hereinafter, the evaluation results will be considered based on Tables 1 to 10. In Tables 1 to 10, values that do not meet the requirements of this embodiment or values that do not reach the passing level are underlined. In Examples 1-2 to 1-7, not only the conditions of the first step but also the conditions of the second to tenth steps satisfy the conditions of the present embodiment, so that the resulting alloy catalyst also satisfies the conditions of the present embodiment. That is, in Examples 1-2 to 1-7, since the transition metal element can be removed only from the surface of the composite metal particles and its vicinity by leaching, "composition deviation" can be suppressed, and the alloy catalyst can be used. The initial activity is high. In addition, the abundance ratio of the noble metal element in the skin layer is high, and a strong skin layer is formed. Therefore, the durability of the alloy catalyst is increased. Therefore, both the initial activity and durability were acceptable levels.

On the other hand, in Comparative Example 1-1, the strength of the first step, that is, the first annealing treatment is weaker than the conditions of the present embodiment. Specifically, the atmospheric gas temperature is lower than the condition of the present embodiment, and the heat treatment time is shorter than the condition of the present embodiment. Therefore, alloying of the composite metal particles after the tenth step, the integrated value of the amount of released oxygen molecules of the surface area 1 m ² per noble metal element, and elimination of carbon dioxide molecules in surface area 1 m ² per noble metal element The integrated value of was not satisfied with the conditions of the present embodiment, and the initial activity and durability were at the reject level.

More specifically, the alloying ratio of the composite metal particles after the first annealing treatment is very low. Therefore, the transition metal element is segregated in the composite metal particles. For this reason, it becomes difficult to control the elution amount of the transition metal element in the leaching after the second step, and the composition of the composite metal particles after the tenth step is the same as the composition of the untreated composite metal particles produced in the zeroth step. There is a large deviation (composition deviation). Therefore, the initial activity is reduced. Further, since the transition metal element is segregated, severe irregularities are formed on the surface of the composite metal particles by the leaching in the second and subsequent steps. Due to such unevenness, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Furthermore, the noble metal elements on the surface of the composite metal particles are not aligned. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced.

In Comparative Examples 1-8, the strength of the first annealing treatment is stronger than the conditions of the present embodiment. Specifically, the atmospheric gas temperature is higher than the condition of the present embodiment, and the heat treatment time is longer than the condition of the present embodiment. Further, the hydrogen gas concentration is higher than the condition of the present embodiment. Therefore, the crystallite diameter of the composite metal particles after the 10th step became too large, and the initial activity became a reject level. This is because the reaction field when the polymer electrolyte fuel cell is operated becomes narrow.

(5-2. 2nd to 4th process groups)
In Examples 2-2-2-4, not only the conditions of the second to fourth steps but also the conditions of the first and fifth to tenth steps satisfy the conditions of the present embodiment, so that the resulting alloy catalyst is also present. The conditions of the embodiment are satisfied. That is, in Examples 2-2-2-4, since the transition metal element can be removed only from the surface of the composite metal particles and its vicinity by leaching, "composition deviation" can be suppressed, and the alloy catalyst can be used. The initial activity is high. In addition, the abundance ratio of the noble metal element in the skin layer is high, and a strong skin layer is formed. Therefore, the durability of the alloy catalyst is increased. Therefore, both the initial activity and durability were at the acceptable level.

On the other hand, in Comparative Example 2-1 the strength of the second step, that is, the strength of the first leaching is weaker than the condition of the present embodiment. Specifically, the acid concentration and the heating temperature are lower than the conditions of the present embodiment, and the contact time with the acidic aqueous solution is shorter than the conditions of the present embodiment. Further, the conditions of the fourth step, that is, the second annealing treatment, are weaker than the conditions of the present embodiment. Specifically, the atmospheric gas temperature is lower than the condition of the present embodiment, and the heat treatment time is shorter than the condition of the present embodiment. Hydrogen gas is not contained in the atmospheric gas. Therefore, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2 of the surface area of the noble metal element and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element after the 10th step are the integrated values of the present embodiment. The conditions were not met and the durability was at a reject level.

More specifically, many transition metal elements remain on the surface of the composite metal particles after the first leaching. Further, since it can be said that the strength of the second annealing treatment is weaker than the conditions of the present embodiment, large irregularities remain on the surface of the composite metal particles after the second annealing treatment. Due to such unevenness, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Although the other steps satisfy the conditions of the present embodiment, these steps do not solve these problems either. Therefore, many transition metal elements remain on the surface of the composite metal particles after the tenth step, and large irregularities remain. Furthermore, the noble metal elements on the surface of the composite metal particles are not aligned. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced.

In Comparative Example 2-5, the strength of the first leaching is stronger than the condition of the present embodiment. Specifically, the acid concentration and the heating temperature are higher than the conditions of the present embodiment, and the contact time with the acidic aqueous solution is longer than the conditions of the present embodiment. Further, the conditions of the fourth step, that is, the second annealing treatment, are stronger than the conditions of the present embodiment. Specifically, the atmospheric gas temperature is higher than the condition of the present embodiment, and the heat treatment time is longer than the condition of the present embodiment. Further, the hydrogen gas concentration is higher than the condition of the present embodiment. Therefore, the composition of the composite metal particles after the tenth step does not satisfy the conditions of the present embodiment. Further, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment. Therefore, the initial activity and durability were at the reject level.

More specifically, large irregularities are formed on the surface of the composite metal particles after the first leaching. Therefore, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Further, as a result of removing a large amount of transition metal elements by leaching, the above-mentioned "composition deviation" occurs. Further, the second annealing treatment proceeds more than necessary for alloying, and many transition metal elements existing in the back of the composite metal particles move to the surface and are exposed. Although the other steps satisfy the conditions of the present embodiment, these steps do not solve these problems either. Therefore, many transition metal elements remain on the surface of the composite metal particles after the tenth step, and large irregularities remain. Furthermore, the noble metal elements on the surface of the composite metal particles are not aligned. It is considered that the unevenness is alleviated by the second annealing treatment, but even if the unevenness is alleviated, a large number of transition metal elements remain on the surface. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced. Further, the initial activity is also lowered due to the “composition deviation”.

(5-3. 5th-5th process group)
In Examples 3-2-3-4, not only the 5th to 7th steps but also the conditions of the 1st to 4th and 8th to 10th steps satisfy the conditions of the present embodiment, and thus the alloy is a result. The catalyst also satisfies the conditions of the present embodiment. That is, in Examples 3-2-3-4, since the transition metal element can be removed only from the surface of the composite metal particles and its vicinity by leaching, "composition deviation" can be suppressed, and the alloy catalyst can be used. The initial activity is high. In addition, the abundance ratio of the noble metal element in the skin layer is high, and a strong skin layer is formed. Therefore, the durability of the alloy catalyst is increased. Therefore, both the initial activity and durability were at the acceptable level. In particular, in Example 3-3, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{is 3.0 × 10-6} mol / m ² or more, which is a preferable condition of the present embodiment. The integrated value of the desorption amount of carbon dioxide molecules per ^{1 m 2} of the surface area of the noble metal element ^{is 2.5 × 10 -7} molmol / m ² or less, which is a preferable condition of the present embodiment. Therefore, the durability is particularly excellent (the reduction rate is 5.0% or less).

On the other hand, in Comparative Example 3-1 the strength of the fifth step, that is, the strength of the second leaching is weaker than the condition of the present embodiment. Specifically, the acid concentration and the heating temperature are lower than the conditions of the present embodiment, and the contact time with the acidic aqueous solution is shorter than the conditions of the present embodiment. Further, the conditions of the seventh step, that is, the third annealing treatment, are weaker than the conditions of the present embodiment. Specifically, the atmospheric gas temperature is lower than the condition of the present embodiment, and the heat treatment time is shorter than the condition of the present embodiment. Hydrogen gas is not contained in the atmospheric gas. Therefore, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2 of the surface area of the noble metal element and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element after the 10th step are the integrated values of the present embodiment. The conditions were not met and the durability was at a reject level.

More specifically, many transition metal elements remain on the surface of the composite metal particles after the second leaching. Furthermore, since it can be said that the strength of the third annealing treatment is weaker than the conditions of the present embodiment, large irregularities remain on the surface of the composite metal particles after the third annealing treatment. Due to such unevenness, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Although the other steps satisfy the conditions of the present embodiment, these steps do not solve these problems either. Therefore, many transition metal elements remain on the surface of the composite metal particles after the tenth step, and large irregularities remain. Furthermore, the noble metal elements on the surface of the composite metal particles are not aligned. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced.

In Comparative Example 3-5, the strength of the second leaching is stronger than the condition of the present embodiment. Specifically, the acid concentration and the heating temperature are higher than the conditions of the present embodiment, and the contact time with the acidic aqueous solution is longer than the conditions of the present embodiment. Further, the strength of the seventh step, that is, the third annealing treatment is stronger than the condition of the present embodiment. Specifically, the atmospheric gas temperature is higher than the condition of the present embodiment, and the heat treatment time is longer than the condition of the present embodiment. Further, the hydrogen gas concentration is higher than the condition of the present embodiment. Therefore, the composition of the composite metal particles after the tenth step does not satisfy the conditions of the present embodiment. Further, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment. Therefore, the initial activity and durability were at the reject level.

More specifically, large irregularities are formed on the surface of the composite metal particles after the second leaching. Therefore, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Further, as a result of removing a large amount of transition metal elements by leaching, the above-mentioned "composition deviation" occurs. Further, the alloying proceeds more than necessary by the third annealing treatment, and many transition metal elements existing in the back of the composite metal particles move to the surface and are exposed. Although the other steps satisfy the conditions of the present embodiment, these steps do not solve these problems either. Therefore, many transition metal elements remain on the surface of the composite metal particles after the tenth step, and large irregularities remain. Furthermore, the noble metal elements on the surface of the composite metal particles are not aligned. It is considered that the unevenness is alleviated by the third annealing treatment, but even if the unevenness is alleviated, a large number of transition metal elements remain on the surface. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced. Further, the initial activity is also lowered due to the “composition deviation”.

(5-4. 8th to 10th process groups)
In Examples 4-2 to 4-4, not only the 8th to 10th steps but also the conditions of the 1st to 7th steps satisfy the conditions of the present embodiment, so that the resulting alloy catalyst is also the same as that of the present embodiment. Satisfy the conditions. That is, in Examples 4-2 to 4-4, since the transition metal element can be removed only from the surface of the composite metal particles and its vicinity by leaching, "composition deviation" can be suppressed, and the alloy catalyst can be used. The initial activity is high. In addition, the abundance ratio of the noble metal element in the skin layer is high, and a strong skin layer is formed. Therefore, the durability of the alloy catalyst is increased. Therefore, both the initial activity and durability were at the acceptable level. In particular, in Examples 4-3 and 4-4, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element is ^{a preferable condition of the present embodiment of 3.0 × 10-6} mol (mol / mol /). m ² ) or more, and the integrated value of the desorption amount of carbon dioxide molecules per ^{1 m 2} of the surface area of the noble metal element is ^{a preferable condition of the present embodiment 2.5 × 10-7} mol (mol / m ² ). It is as follows. Therefore, the durability is particularly excellent (the reduction rate is 5.0% or less).

On the other hand, in Comparative Example 4-1 the strength of the eighth step, that is, the third leaching is weaker than the condition of the present embodiment. Specifically, the acid concentration and the heating temperature are lower than the conditions of the present embodiment, and the contact time with the acidic aqueous solution is shorter than the conditions of the present embodiment. Further, the conditions of the tenth step, that is, the fourth annealing treatment are weaker than the conditions of the present embodiment. Specifically, the atmospheric gas temperature is lower than the condition of the present embodiment, and the heat treatment time is shorter than the condition of the present embodiment. Therefore, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2 of the surface area of the noble metal element and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element after the 10th step are the integrated values of the present embodiment. The conditions were not met and the durability was at a reject level.

More specifically, many transition metal elements remain on the surface of the composite metal particles after the third leaching. Further, large irregularities remain on the surface of the composite metal particles after the fourth annealing treatment. Due to such unevenness, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Although the other steps satisfy the conditions of the present embodiment, these steps do not solve these problems either. Therefore, many transition metal elements remain on the surface of the composite metal particles after the tenth step, and large irregularities remain. Furthermore, the noble metal elements on the surface of the composite metal particles are not aligned. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced.

In Comparative Example 4-5, the strength of the third leaching is stronger than the condition of the present embodiment. Specifically, the acid concentration and the heating temperature are higher than the conditions of the present embodiment, and the contact time with the acidic aqueous solution is longer than the conditions of the present embodiment. Further, the condition of the tenth step, that is, the fourth leaching is stronger than the condition of the present embodiment. Specifically, the atmospheric gas temperature is higher than the condition of the present embodiment, and the heat treatment time is longer than the condition of the present embodiment. Further, the hydrogen gas concentration is higher than the condition of the present embodiment. Therefore, the composition of the composite metal particles after the tenth step does not satisfy the conditions of the present embodiment. Further, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment. Therefore, the initial activity and durability were at the reject level.

More specifically, large irregularities are formed on the surface of the composite metal particles after the third leaching. Therefore, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Further, as a result of removing a large amount of transition metal elements by leaching, the above-mentioned "composition deviation" occurs. Further, the alloying proceeds more than necessary by the fourth annealing treatment, and many transition metal elements existing in the back of the composite metal particles move to the surface and are exposed. Although the other steps satisfy the conditions of the present embodiment, these steps do not solve these problems either. Therefore, many transition metal elements remain on the surface of the composite metal particles after the tenth step, and large irregularities remain. Furthermore, the noble metal elements on the surface of the composite metal particles are not aligned. It is considered that the unevenness is alleviated by the fourth annealing treatment, but even if the unevenness is alleviated, a large number of transition metal elements remain on the surface. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced. Further, the initial activity is also lowered due to the “composition deviation”.

(5-5. Other groups)
Comparative Example 5-1 is an example in which general leaching and annealing treatments that have been conventionally performed are performed. In Comparative Example 5-1, the strength of the first step, that is, the strength of the first annealing treatment satisfies the conditions of the present embodiment. However, the leaching is performed only once in the second step, and the strength of the leaching is stronger than the condition of the present embodiment. Specifically, the acid concentration is higher than the condition of the present embodiment, and the contact time with the acidic aqueous solution is longer than the condition of the present embodiment. Therefore, in Comparative Example 5-1, the alloying ratio and the crystallite diameter of the composite metal particles satisfy the conditions of the present embodiment, but the composition of the composite metal particles does not satisfy the conditions of the present embodiment. Further, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment. Therefore, the initial activity and durability were at the reject level.

More specifically, since the strength of the first step, that is, the first annealing treatment satisfies the conditions of the present embodiment, the alloying ratio and the crystallite diameter satisfy the conditions of the present embodiment. However, since the leaching strength is stronger than the conditions of the present embodiment, large irregularities are formed on the surface of the composite metal particles after leaching. Therefore, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Further, as a result of removing a large amount of transition metal elements by leaching, the above-mentioned "composition deviation" occurs. The strength of the fourth step, that is, the strength of the second annealing treatment satisfies the condition of the present embodiment, but the unevenness cannot be sufficiently smoothed by this annealing treatment. Therefore, many transition metal elements remain on the surface of the composite metal particles produced in Comparative Example 5-1 and large irregularities remain. Furthermore, the noble metal elements on the surface of the composite metal particles are not aligned. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced. Further, the initial activity is also lowered due to the “composition deviation”.

Comparative Example 5-2 is an example in which the conditions (strength of the second annealing treatment) of the fourth step of Comparative Example 5-1 are strengthened. Even in Comparative Example 5-2, the initial activity and durability were at the failing level. Also in Comparative Example 5-2, the reaching strength of the second step is stronger than the condition of this embodiment. Further, in Comparative Example 5-2, the atmospheric gas temperature of the second annealing treatment is higher than the condition of the present embodiment, and the heat treatment time is longer than the condition of the present embodiment. Therefore, the composition and crystallite diameter of the composite metal particles produced in Comparative Example 5-2 do not satisfy the conditions of the present embodiment. Further, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment. Therefore, the initial activity and durability were at the reject level.

More specifically, in Comparative Example 5-2, since the leaching strength is stronger than the condition of the present embodiment, large irregularities are formed on the surface of the composite metal particles after leaching. Therefore, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Further, as a result of removing a large amount of transition metal elements by leaching, the above-mentioned "composition deviation" occurs. Therefore, the initial activity is reduced. The surface irregularities of the composite metal particles are smoothed to some extent by the annealing treatment in the fourth step. However, since the strength of the annealing treatment is stronger than the conditions of the present embodiment, the composite metal particles are aggregated and coarsened, and the crystallite diameter becomes large. As a result, the crystallite diameter does not satisfy the conditions of the present embodiment, and the initial activity also decreases in this respect. This is because the reaction field when the polymer electrolyte fuel cell is operated becomes narrow. Further, the annealing treatment in the fourth step proceeds more than necessary for alloying, and many transition metal elements existing in the back of the composite metal particles move to the surface and are exposed. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced.

Comparative Example 5-3 is an example in which a large amount of transition metal elements are charged into the untreated composite metal particles in advance in anticipation of “composition deviation”. However, even in Comparative Example 5-3, the initial activity and durability were at the rejected level. In Comparative Example 5-3, the composition of the composite metal particles certainly satisfies the conditions of the present embodiment. However, it is the same as Comparative Example 5-1 in that the strength of the second step, that is, the leaching is stronger than the condition of the present embodiment. Therefore, a large number of transition metal elements are eluted not only from the surface of the composite metal particles but also from the inside, and severe irregularities are formed on the surface of the composite metal particles. In addition, a large number of pores are formed inside the composite metal particles. Therefore, the composite metal particles become unstable and the initial activity decreases. Further, such unevenness exposes the transition metal element inside. Furthermore, the noble metal elements on the surface of the composite metal particles are not aligned. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced.

Comparative Example 5-4 is an example in which the conditions (strength of the first leaching) of the second step of Comparative Example 5-1 are made very weak. In Comparative Example 5-4, the initial activity reached the pass level, but the durability was still at the fail level. In Comparative Example 5-4, the strength of the first step, that is, the strength of the first annealing treatment satisfies the conditions of the present embodiment. Therefore, the alloying ratio and the crystallite diameter satisfy the conditions of the present embodiment. However, the strength of leaching is weaker than the condition of this embodiment. Specifically, the acid concentration is lower than the condition of the present embodiment, and the contact time with the acidic aqueous solution is shorter than the condition of the present embodiment. Therefore, "composition deviation" is suppressed and the initial activity is high. However, a large number of transition metal elements remain on the surface of the composite metal particles. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced.

Comparative Example 5-5 is an example in which the example of Patent Document 1 is reproduced. Even in Comparative Example 5-5, the initial activity and durability were at the failing level. In Comparative Example 5-5, the strength of the first step, that is, the first annealing treatment is stronger than the condition of the present embodiment. Specifically, the atmospheric gas temperature is higher than the conditions of the present embodiment. Further, the strength of the second step, that is, the leaching is stronger than the condition of the present embodiment. Specifically, the acid concentration is higher than the condition of the present embodiment, and the contact time with the acidic aqueous solution is longer than the condition of the present embodiment. Therefore, the composition and crystallite diameter of the composite metal particles produced in Comparative Example 5-5 do not satisfy the conditions of the present embodiment. Further, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment. Therefore, the initial activity and durability were at the reject level.

More specifically, since the strength of the first annealing treatment is stronger than the conditions of the present embodiment, the composite metal particles are aggregated and coarsened, and the crystallite diameter is increased. As a result, the crystallite diameter of the composite metal particles does not satisfy the conditions of the present embodiment, and the initial activity is lowered. This is because the reaction field when the polymer electrolyte fuel cell is operated becomes narrow. Further, since the leaching strength is stronger than the condition of the present embodiment, a large amount of transition metal elements are removed by the leaching, and the above-mentioned "composition deviation" occurs. Therefore, the composition of the composite metal particles does not satisfy the conditions of the present embodiment. In this respect as well, the initial activity decreases. Further, since the leaching strength is stronger than the condition of the present embodiment, severe unevenness is formed on the surface of the composite metal particles. In Comparative Example 5-5, since the annealing treatment is not performed after the leaching, such unevenness is not smoothed. Therefore, the transition metal element existing in the back of the composite metal particles is exposed on the surface due to the unevenness. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced.

Comparative Example 5-6 is an example of reproducing the example of Patent Document 2. Even in Comparative Example 5-6, the initial activity and durability were at the failing level. In Comparative Example 5-6, the strength of the first step, that is, the first annealing treatment is stronger than the condition of the present embodiment. Specifically, the heat treatment time is longer than the conditions of the present embodiment. Further, the strength of the second step, that is, the leaching is stronger than the condition of the present embodiment. Specifically, the acid concentration is higher than the condition of the present embodiment, and the contact time with the acidic aqueous solution is longer than the condition of the present embodiment. Although the heating temperature is lower than the conditions of the present embodiment, it can be said that the leaching strength is strong as a whole. Further, the strength of the fourth step, that is, the second annealing treatment is stronger than the condition of the present embodiment. Specifically, the atmospheric gas temperature is higher than the condition of the present embodiment, and the heat treatment time is longer than the condition of the present embodiment. Therefore, the composition and crystallite diameter of the composite metal particles produced in Comparative Example 5-6 do not satisfy the conditions of the present embodiment. Further, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment. Therefore, the initial activity and durability were at the reject level.

More specifically, in Comparative Example 5-6, since the strength of the first annealing treatment is stronger than the condition of the present embodiment, the composite metal particles are aggregated and coarsened, and the crystallite diameter is increased. As a result, the crystallite diameter of the composite metal particles does not satisfy the conditions of the present embodiment, and the initial activity is lowered. This is because the reaction field when the polymer electrolyte fuel cell is operated becomes narrow. Further, the strength of the second step, that is, the leaching is stronger than the condition of the present embodiment. Therefore, a large amount of transition metal elements are removed by leaching, and the above-mentioned "composition deviation" occurs. Therefore, the composition of the composite metal particles does not satisfy the conditions of the present embodiment. In this respect as well, the initial activity decreases. Further, since the leaching strength is stronger than the condition of the present embodiment, severe unevenness is formed on the surface of the composite metal particles. Due to such unevenness, the transition metal element existing in the back of the composite metal particles is exposed on the surface. Further, the strength of the fourth step, that is, the second annealing treatment is stronger than the condition of the present embodiment. Therefore, the alloying proceeds more than necessary by the second annealing treatment, and many transition metal elements existing in the back of the composite metal particles move to the surface and are exposed. The crystallite diameter of the composite metal particles is also coarsened by the second annealing treatment. Therefore, many transition metal elements remain on the surface of the composite metal particles produced in Comparative Example 5-6, and large irregularities remain. Furthermore, the noble metal elements on the surface of the composite metal particles are not aligned. It is considered that the unevenness is alleviated by the second annealing treatment, but even if the unevenness is alleviated, a large number of transition metal elements remain on the surface. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced.

Comparative Example 5-7 is an example in which the example of Patent Document 3 is reproduced. Even in Comparative Example 5-7, the initial activity and durability were at the failing level. In Comparative Example 5-7, the strength of the first step, that is, the first annealing treatment is stronger than the condition of the present embodiment. Specifically, the heat treatment time is longer than the conditions of the present embodiment. Further, the strength of the second step, that is, the leaching is stronger than the condition of the present embodiment. Specifically, the acid concentration and the heating temperature are higher than the conditions of the present embodiment, and the contact time with the acidic aqueous solution is longer than the conditions of the present embodiment. Therefore, the crystallite diameter of the composite metal particles produced in Comparative Example 5-7 does not satisfy the conditions of the present embodiment. Further, the integrated value of the desorption amount of oxygen molecules per ^{1 m 2} of the surface area of the noble metal element ^{and the integrated value of the desorption amount of carbon dioxide molecules per 1 m 2} of the surface area of the noble metal element do not satisfy the conditions of the present embodiment. Therefore, the initial activity and durability were at the reject level.

More specifically, in Comparative Example 5-7, since the strength of the first annealing treatment is stronger than the condition of the present embodiment, the composite metal particles are aggregated and coarsened, and the crystallite diameter is increased. As a result, the crystallite diameter of the composite metal particles does not satisfy the conditions of the present embodiment, and the initial activity is lowered. This is because the reaction field when the polymer electrolyte fuel cell is operated becomes narrow. Further, the strength of the second step, that is, the leaching is stronger than the condition of the present embodiment. Therefore, a large amount of transition metal elements are removed by leaching, and the above-mentioned "composition deviation" occurs. However, since the molar ratio of the transition metal elements to be charged is large, the composition of the composite metal particles satisfies the conditions of the present embodiment. On the other hand, leaching forms severe irregularities on the surface of the composite metal particles. In addition, a large number of pores are formed inside the composite metal particles. Therefore, the composite metal particles are in an unstable state. Therefore, the composite metal particles become unstable and the initial activity decreases. Further, such unevenness exposes the transition metal element existing in the back of the composite metal particles to the surface. The strength of the fourth step, that is, the strength of the second annealing treatment satisfies the condition of the present embodiment, but the unevenness cannot be sufficiently smoothed by this annealing treatment. Therefore, many transition metal elements remain on the surface of the composite metal particles produced in Comparative Example 5-7, and large irregularities remain. Furthermore, the noble metal elements on the surface of the composite metal particles are not aligned. ^{Therefore, the integrated value of the desorption amount of oxygen molecules per 1 m 2} of the surface area of the noble metal element does not satisfy the conditions of the present embodiment, and the durability of the alloy catalyst is lowered. In addition, since many transition metal elements (more specifically, oxides of transition metal elements) are exposed on the surface of the composite metal particles, an integrated value of the amount of desorption of carbon dioxide molecules due to the oxides. Becomes large and does not satisfy the conditions of the present embodiment. In this respect as well, the durability of the alloy catalyst is reduced.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical idea described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

Claims (6)

Composite metal particles containing noble metal elements and transition metal elements,
A catalyst carrier that supports the composite metal particles, and
The noble metal element is at least one selected from the group consisting of Pt, Au, and Pd.
The transition metal element is at least one type selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, and Ni.
The composite metal particles contain the noble metal element and the transition metal element in a molar ratio of noble metal element: transition metal element = 1: 0.2 or more and 1: 1 or less.
When the composite metal particles are subjected to X-ray diffraction analysis, a diffraction peak is observed at 2θ = 37 ° or more and 42 ° or less, and the lattice constant calculated based on the diffraction peak is based on the following equation (1). The alloying rate calculated by the above is 60% or more and 100% or less.
Alloying rate [%] = {(lattice constant of bulk noble metal)-(lattice constant of the composite metal particles)} / {(lattice constant of bulk noble metal)-(lattice constant of maximum peak of bulk composite metal)} × 100 (1)
The crystallite diameter of the composite metal particles calculated based on the diffraction peak is 2 to 8 nm.
When the temperature-temperature desorption method is performed in which the oxygen molecules adsorbed on the composite metal particles are desorbed by heating at 85K, the temperature-temperature desorption curve of m / z = 32 corresponding to the oxygen molecules is 130K or more and 190K. It has a desorption peak top in the following range, and the integrated value of the desorption amount of the oxygen molecule calculated based on the area of the desorption peak is 1 m ^{2 of the surface surface of the noble metal portion exposed on the surface of the composite metal particles.} An alloy catalyst for a solid polymer fuel cell, characterized in that it is 1.0 × ^{10-6 mol or more per unit.} The alloy for a polymer electrolyte fuel cell according to claim 1, wherein the integrated value of the desorption amount of oxygen molecules is 3.0 × ^{10-6 mol or more per 1 m 2 of the surface area of the noble metal element.} catalyst. When the temperature-temperature desorption method is performed in which oxygen molecules adsorbed on the composite metal particles are desorbed by temperature-temperature at 85K, the temperature-temperature desorption curve of m / z = 44 corresponding to carbon dioxide molecules is 300K or more and 900K. It has a desorption peak top in the following range, and the integrated value of the desorption amount of the carbon dioxide molecule calculated based on the area of the desorption peak is 1 m on the surface surface of the noble metal portion exposed on the surface of the composite metal particles. ^The alloy catalyst for a solid polymer fuel cell according to claim 1 or 2, wherein the amount is 3.0 × ^{10-7 mol or less per 2 of the catalyst.} The third aspect of claim 3, wherein the integrated value of the desorption amount of the carbon dioxide molecule is 2.5 × 10 ^{-7 mol or less per 1 m 2} of the surface area of the noble metal portion exposed on the surface of the composite metal particles. Alloy catalyst for polymer electrolyte fuel cells. The precious metal element is Pt,
The solid polymer fuel cell according to any one of claims 1 to 4, wherein the transition metal element is at least one selected from the group consisting of Fe, Co, and Ni. Alloy catalyst for batteries. The method for producing an alloy catalyst for a solid polymer fuel cell according to any one of claims 1 to 5, wherein the solid polymer type includes the following 0th to 10th steps. A method for manufacturing an alloy catalyst for a fuel cell.
(Step 0)
An untreated alloy catalyst comprising untreated composite metal particles containing a noble metal element and a transition metal element and a catalyst carrier supporting the untreated composite metal particles is prepared.
Here, the noble metal element is at least one selected from the group consisting of Pt, Au, and Pd, and the transition metal element is Sc, Ti, V, Cr, Mn, Fe, Co, and. Any one or more selected from the group consisting of Ni.
(First step)
The untreated alloy catalyst is an inert gas composed of any one or more selected from the group consisting of argon, nitrogen, and helium, and a hydrogen gas having a flow rate of 50% by volume or less based on the flow rate of the inert gas. Heat treatment is performed at a temperature of 500 ° C. or higher and 900 ° C. or lower for 10 minutes or longer and 60 minutes or lower in an atmosphere containing.
(Second step)
^{The alloy catalyst obtained in the first step is 1.0 × 10 -3} mol / L of any one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and perchloric acid. The acidic aqueous solution contained at a concentration of 5.0 × 10 ^-3 mol / L or less is brought into contact with the acidic aqueous solution at a temperature of 30 ° C. or higher and 90 ° C. or lower for 30 minutes or longer and 100 minutes or shorter.
(Third step)
The alloy catalyst obtained in the second step is washed and then dried.
(4th step)
The alloy catalyst obtained in the third step is an inert gas composed of any one or more selected from the group consisting of argon, nitrogen, and helium, and 10 volumes with respect to the flow rate of the inert gas. Heat treatment is performed at a temperature of 250 ° C. or higher and 550 ° C. or lower for 10 minutes or longer and 60 minutes or shorter in an atmosphere containing% or less of hydrogen gas.
(Fifth step)
^{The alloy catalyst obtained in the fourth step is 1.0 × 10 -4} mol / L of any one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and perchloric acid. The acidic aqueous solution contained at a concentration of 5.0 × 10 ^-4 mol / L or less is brought into contact with the acidic aqueous solution at a temperature of 30 ° C. or higher and 70 ° C. or lower for a time of 10 minutes or longer and 60 minutes or shorter.
(6th step)
The alloy catalyst obtained in the fifth step is washed and then dried.
(7th step)
The alloy catalyst obtained in the sixth step is an inert gas composed of any one or more selected from the group consisting of argon, nitrogen, and helium, and 5 volumes with respect to the flow rate of the inert gas. Heat treatment is performed at a temperature of 200 ° C. or higher and 500 ° C. or lower for 10 minutes or longer and 60 minutes or shorter in an atmosphere containing% or less of hydrogen gas.
(8th step)
^{The alloy catalyst obtained in the seventh step is 1.0 × 10-5} mol / L of any one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and perchloric acid. The acidic aqueous solution contained at a concentration of 5.0 × ^10-5 mol / L or less is brought into contact with the acidic aqueous solution at a temperature of 30 ° C. or higher and 60 ° C. or lower for a time of 5 minutes or longer and 30 minutes or shorter.
(9th step)
The alloy catalyst obtained in the eighth step is washed and then dried.
(10th step)
The alloy catalyst obtained in the ninth step is used at a temperature of 200 ° C. or higher and 450 ° C. or lower in an inert gas atmosphere composed of any one or more selected from the group consisting of argon, nitrogen, and helium. Heat treatment is performed for 5 minutes or more and 30 minutes or less.