JP7378888B2 - Electrocatalyst manufacturing device, electrode catalyst and manufacturing method thereof - Google Patents

Description

The present invention relates to an electrode catalyst manufacturing apparatus, an electrode catalyst and a manufacturing method thereof, and more particularly, an electrode catalyst manufacturing apparatus for efficiently manufacturing an electrode catalyst provided with alloy catalyst particles containing noble metal elements, and an electrode catalyst manufacturing apparatus therefor. The present invention relates to an electrode catalyst produced using the method and a method for producing the same.

A polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) in which electrodes containing a catalyst (a catalyst layer and a gas diffusion layer) are joined to both sides of an electrolyte membrane. Current collectors (separators) each having a gas flow path are further arranged on both sides of the MEA. A polymer electrolyte fuel cell usually has a structure (fuel cell stack) in which a plurality of single cells each made of such an MEA and a current collector are stacked.

Pt catalysts, Pt alloy catalysts, carbon alloy catalysts, oxide catalysts, and the like are used as electrode catalysts for polymer electrolyte fuel cells. Among these, it is widely known that Pt alloy catalysts can provide higher efficiency performance (under low current density and high voltage operating conditions) than pure Pt catalysts. Further, high performance may be obtained due to a special structure (for example, a hollow structure) obtained by eluting base metals from an alloy catalyst. Therefore, various proposals have been made regarding methods for producing Pt alloy catalysts.

For example, in Non-Patent Document 1,
(a) A precursor of Pt and Ni is reduced with NaBH ₄ at room temperature to obtain catalyst particles,
(b) A hollow PtNi/C nanocatalyst obtained by stirring catalyst powder in a 1M aqueous sulfuric acid solution at room temperature for 12 hours to elute the base metal as a core component is disclosed.

Patent Document 1 describes a method for producing a platinum core-shell catalyst, in which a platinum core-shell catalyst consisting of a Pd core/Pt shell is dispersed in an acidic sulfuric acid aqueous solution, metallic copper is allowed to coexist in the aqueous solution, and the aqueous solution is stirred while blowing air. is disclosed.
In the same document,
(a) When a platinum core-shell catalyst is repeatedly brought into contact with metallic copper and oxygen gas in an acidic sulfuric acid aqueous solution, oxidation and reduction of the platinum core-shell catalyst are repeated, and Pd is oxidized and eluted from the platinum core-shell catalyst, and
(b) It is described that this improves the oxygen reduction reaction (ORR) activity of the platinum core-shell catalyst.

It is known that a Pt alloy catalyst consisting of Pt and a base metal element exhibits higher performance than a pure Pt catalyst. However, when a Pt alloy catalyst containing a large amount of base metal elements is used in a fuel cell environment, there is a problem in that excess base metal elements are likely to be eluted. When the base metal element is eluted, not only the catalyst performance deteriorates, but also the fuel cell performance may deteriorate because the protons in the electrolyte exchange ions with the eluted base metal ions.

Furthermore, it is generally known that only atoms on the surface of catalyst particles function as catalysts for electrode reactions. Therefore, as described in Non-Patent Document 1 and Patent Document 1, when the catalyst particles have a hollow structure, the specific surface area of the catalyst particles increases, which improves the utilization rate of Pt, and reduces the amount of expensive Pt used. can be reduced.

However, as described in Non-Patent Document 1, the method of eluting the core base metal by simply stirring the catalyst in an acid requires a long processing time. Furthermore, since it is difficult to completely remove the core by simply stirring in an acid, the amount of base metals after acid treatment is also large.
On the other hand, as described in Patent Document 1, in the method of repeatedly bringing a catalyst into contact with metallic copper and oxygen gas, Cu may be mixed into the catalyst surface. When a catalyst containing Cu on the catalyst surface is used in a fuel cell environment, Cu ions are easily eluted from the catalyst surface, exchange ions with protons in the electrolyte, or precipitate on the anode catalyst, resulting in poor fuel cell performance. descend.

Japanese Patent Application Publication No. 2015-000398

Raphael, Chattot et al., Nano Lett. 2017, 17, 2447-2453

The problem to be solved by the present invention is to efficiently produce an electrode catalyst comprising alloy catalyst particles containing a noble metal element M ₁ and a metal element M ₂ that is less noble than the noble metal element M ₁ and having a small elution amount of the metal element M ₂ . An object of the present invention is to provide an apparatus for manufacturing an electrode catalyst.
Another problem to be solved by the present invention is to provide a method for manufacturing an electrode catalyst using such an apparatus for manufacturing an electrode catalyst.
Furthermore, another problem to be solved by the present invention is to provide an electrode catalyst manufactured using such a method.

In order to solve the above problems, the electrode catalyst manufacturing apparatus according to the present invention includes:
a container for containing an acidic aqueous solution in which an electrode catalyst precursor including an alloy catalyst particle precursor containing a noble metal element M ₁ and a metal element M ₂ less base than the noble metal element M ₁ is dispersed;
a working electrode and a counter electrode for electrically contacting the acidic aqueous solution;
a potential holding device for holding the working electrode at a potential lower than the reduction potential of the noble metal element M ₁ ;
a stirring device for stirring the acidic aqueous solution;
and a bubbling device for bubbling oxygen into the acidic aqueous solution.
however,
The “noble metal element M ₁ ” refers to at least one element selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os,
The "metal element M2 _" is an element to be eluted from the alloy catalyst particle precursor, and is an element other than the second noble metal element M21, the noble metal element M1, and the second _noble metal _element M21 _. Refers to at least one element selected from the group consisting of the metallic elements M22 _,
The “second noble metal element M ₂₁ ” is at least one element selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os, and is more preferable than the noble metal element M 1 _. Refers to something that is base.

The method for producing an electrode catalyst according to the present invention includes:
A first step of applying a potential cycle to an electrocatalyst precursor dispersed in an acidic aqueous solution to obtain an electrocatalyst using the electrocatalyst manufacturing apparatus according to the present invention;
and a second step of separating the electrode catalyst from the acidic aqueous solution and washing it.

Furthermore, the electrode catalyst according to the present invention has the following configuration.
(1) The electrode catalyst includes alloy catalyst particles.
(2) The alloy catalyst particles include a noble metal element M ₁ and a metal element M ₂ less noble than the noble metal element M ₁ , and the total content of the metal element M ₂ (excluding Cu) is 0.1 at%. The Cu content is less than 13 at%, and the Cu content is less than 6 at%.
however,
The “noble metal element M ₁ ” refers to at least one element selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os,
The “metal element M ₂ ” refers to at least one element selected from the group consisting of a second noble metal element M ₂₁ and a metal element M ₂₂ other than the noble metal element M ₁ and the second noble metal element M ₂₁ . good,
The “second noble metal element M ₂₁ ” is at least one element selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os, and is more preferable than the noble metal element M ₁ . I like things that are lowly,
The alloy catalyst particles exclude those in which the noble metal element M ₁ is Pd and the metal element M ₂ is Co.

An electrode catalyst precursor including an alloy catalyst particle precursor is dispersed in an acidic aqueous solution filled with oxygen, a working electrode is immersed in the acidic aqueous solution, and the potential of the working electrode is set to a potential lower than the reduction potential of the noble metal element _M1 . When the acidic aqueous solution is stirred while being held, the electrocatalyst precursor will be in a low potential state when it comes into contact with the working electrode. Further, when the electrode catalyst precursor is detached from the working electrode and comes into contact with oxygen in the acidic aqueous solution, it becomes in a high potential state.

That is, when such a method is used, a potential cycle can be efficiently applied to a relatively large amount of the electrode catalyst precursor. As a result, the metal element M ₂ can be eluted from the alloy catalyst particle precursor in a short time. Further, since a potential cycle can be applied to the alloy catalyst particle precursor without contacting it with metal copper, it is possible to obtain an electrode catalyst having alloy catalyst particles that do not contain Cu on the catalyst surface.

1 is a schematic diagram of an electrode catalyst manufacturing apparatus according to the present invention. 1 is a high-angle scattering annular dark-field scanning transmission electron microscope (HAAD-FTEM) image of the electrode catalyst obtained in Example 1.

Hereinafter, one embodiment of the present invention will be described in detail.
[1. Electrocatalyst manufacturing equipment]
FIG. 1 shows a schematic diagram of an electrode catalyst manufacturing apparatus according to the present invention.
In FIG. 1, the electrode catalyst manufacturing apparatus 10 includes:
a container 16 for containing an acidic aqueous solution 14 in which an electrode catalyst precursor 12 is dispersed;
A working electrode 18 and a counter electrode 20 for electrically contacting the acidic aqueous solution 14;
a potential holding device (not shown) for holding the working electrode 18 at a potential lower than the reduction potential of the noble metal element M ₁ contained in the electrode catalyst precursor 12;
a stirring device (not shown) for stirring the acidic aqueous solution 14;
It is equipped with a bubbling device (not shown) for bubbling oxygen into the acidic aqueous solution 14.
The electrode catalyst manufacturing apparatus 10 may further include a reference electrode 22 for precisely controlling the potential of the working electrode 18.

[1.1. Electrocatalyst precursor]
The electrode catalyst precursor 12 is a processed object to which a potential cycle is applied by the electrode catalyst manufacturing apparatus 10. The electrode catalyst precursor 12 includes an alloy catalyst particle precursor containing a noble metal element M ₁ and a metal element M ₂ less noble than the noble metal element M ₁ . The electrode catalyst precursor 12 may be composed only of such an alloy catalyst particle precursor, or may be one in which the alloy catalyst particle precursor is supported on the surface of a carrier made of a conductive material.

“Noble metal element M ₁ ” refers to Au, Ag, Pt, Pd, Rh, Ir, Ru, or Os. The alloy catalyst particle precursor may contain any one of these as the first noble metal element _M1 , or may contain two or more thereof.

“Metal element M ₂ ” is an element to be eluted from the alloy catalyst particle precursor using the electrode catalyst manufacturing apparatus 10, and is a metal element that is less noble than the noble metal element M ₁ . M ₂ may be a noble metal element other than M ₁ as long as it is less base than M ₁ .
Examples of the metal element _M2 include Ni, Fe, Co, Mn, and Cu. The alloy catalyst particle precursor may contain any one of these metal elements _M2 , or may contain two or more of these metal elements.

The alloy catalyst particle precursor may be a solid particle in which the noble metal element M ₁ and the metal element M ₂ are uniformly dispersed.
Alternatively, the alloy catalyst particle precursor may be a core-shell particle comprising a core particle made of a metal element M ₂ and a shell made of a noble metal element M ₁ covering the surface of the core particle.

The carrier consists of an electrically conductive material. The material of the carrier is not particularly limited as long as it exhibits conductivity and can be used in the fuel cell operating environment. Examples of carrier materials include carbon black, carbon nanotubes, carbon nanohorns, activated carbon, natural graphite, mesocarbon microbeads, and glassy carbon powder.

When a potential cycle is applied to the electrode catalyst precursor 12 using the electrode catalyst manufacturing apparatus 10, the metal element _M2 is eluted from the alloy catalyst particle precursor. As a result, it is possible to obtain an electrode catalyst comprising alloy catalyst particles containing less metal element M ₂ than the alloy catalyst particle precursor before treatment.

[1.2. Acidic aqueous solution]
The acidic aqueous solution 14 is for eluting the metal element _M2 . The type of acidic aqueous solution 14 is not particularly limited as long as it can elute the metal element M ₂ . Examples of the acidic aqueous solution 14 include a sulfuric acid aqueous solution, a nitric acid aqueous solution, a perchloric acid aqueous solution, and a hydrochloric acid aqueous solution.
Further, the acidic aqueous solution 14 preferably has a pH of 3 or less. This is to promote oxidative elution of the metal element M ₂ .

[1.3. container]
The container 16 is for containing the acidic aqueous solution 14 in which the electrode catalyst precursor 12 is dispersed. The structure of the container 16 is
(a) It is possible to electrically contact the acidic aqueous solution 14 with the working electrode 18 and the counter electrode 20 (and, if necessary, the reference electrode 22),
(b) it is possible to bubble oxygen into the acidic aqueous solution 14, and
(c) There is no particular limitation as long as the electrode catalyst precursor 12 and the working electrode 18 can be brought into contact with each other efficiently.

In FIG. 1, the container 16 includes a main container 16a, a first sub-container 16b, and a second sub-container 16c. The main container 16a is for accommodating the working electrode 18. Processing of the electrocatalyst precursor 12 is performed within the main container 16a.
The first sub-container 16b is for accommodating the counter electrode 20. The first sub-container 16b is connected to the main container 16a via a small-diameter first connecting pipe 16d. The reason why the counter electrode 20 is housed in the first sub-container 16b is to isolate the electrode catalyst precursor 12 from the counter electrode 20 when processing the electrode catalyst precursor 12, and to efficiently separate the electrode catalyst precursor 12 and the working electrode 18. This is to bring them into contact.

The second sub-container 16c is for electrically contacting the acidic aqueous solution 14 in the main container 16a and the reference electrode 22 via the salt bridge 24. The second sub-container 16c is connected to the main container 16a via a small-diameter second connecting pipe 16e.
One end of the salt bridge 24 is inserted into the acidic aqueous solution 14 in the second sub-container 16c. The salt bridge 24 is for electrically connecting the reference electrode 22 and the acidic aqueous solution 14 in the main container 16a. The salt bridge 24 is provided with a valve 26 for suppressing contamination of the electrode catalyst precursor 12 and the reference electrode 22 due to mutual contamination.

[1.3. Working electrode]
The working electrode 18 is an electrode for bringing the electrode catalyst precursor 12 floating in the acidic aqueous solution 14 into a low potential state. In other words, the working electrode 18 is an electrode for promoting the reaction of eluting the metal element M ₂ from the electrode catalyst precursor 12 by applying a potential cycle to the electrode catalyst precursor 12. One end of the working electrode 18 is immersed in the acidic aqueous solution 14 contained in the main container 16a. Further, the other end of the working electrode 18 is connected to a potential holding device (not shown).

The material and shape of the working electrode 18 are not particularly limited as long as they can cause such an electrochemical reaction.
Examples of materials for the working electrode 18 include noble metals, carbon, and conductive inorganic compounds. Examples of the shape of the working electrode 18 include a rod shape, a plate shape, a mesh shape, and a wire shape.

In the example shown in FIG. 1, the working electrode 18 consists of a noble metal mesh electrode. The noble metal mesh electrode is suitable as the working electrode 18 because it is difficult to dissolve in the acidic aqueous solution 14 and has high contact efficiency with the electrode catalyst precursor 12 floating in the acidic aqueous solution 14.

When a noble metal mesh electrode is used as the working electrode 18, the ratio of the pore diameter ( _d2 ) of the noble metal mesh electrode to the average particle diameter ( _d1 ) of the electrocatalyst precursor 12 (= _d2 / _d1 ) is 12 processing efficiency.
Here, the "average particle diameter (d ₁ ) of the electrode catalyst precursor 12" refers to the median diameter (d ₅₀ ) of the particle diameter of the powder measured by a laser diffraction scattering method.
"The pore diameter (d ₂ ) of the noble metal mesh electrode" refers to the opening of the mesh (the diameter between the lines).

If the d ₂ /d ₁ ratio becomes too small, the frequency of contact between the electrode catalyst precursor 12 and the working electrode 18 will decrease. Therefore, the d ₂ /d ₁ ratio needs to be greater than 1.
On the other hand, if the d ₂ /d ₁ ratio becomes too large, the frequency of contact between the electrode catalyst precursor 12 and the working electrode 18 will decrease. Therefore, the d ₂ /d ₁ ratio needs to be 1000 or less.

[1.4. Opposite]
The counter electrode 20 is an electrode paired with the working electrode 18 . One end of the counter electrode 20 is immersed in the acidic aqueous solution 14 contained in the first sub-container 16b. Further, the other end of the counter electrode 20 is connected to a potential holding device (not shown).

The material and shape of the counter electrode 20 are not particularly limited as long as they can cause the desired electrochemical reaction.
Examples of the material for the counter electrode 20 include noble metals, carbon, and conductive inorganic compounds. Examples of the shape of the counter electrode 20 include a rod shape, a plate shape, a mesh shape, and a wire shape.

[1.5. Reference pole]
The reference electrode 22 is an electrode that serves as a reference for the working electrode 18. In order to selectively elute the metal element M ₂ from the electrode catalyst precursor 12, it is necessary to maintain the working electrode 18 at a potential lower than the reduction potential of the noble metal element M ₁ contained in the electrode catalyst precursor 12. . The presence of the reference electrode 22 has the advantage of facilitating maintaining the working electrode 18 at such a potential.
However, the counter electrode 20 can also have a function as a reference electrode. In such a case, the reference pole 22 may be omitted.

In FIG. 1, the electrode catalyst manufacturing apparatus 10 includes a third sub-container 30 for accommodating the electrolytic solution 28. One end of the reference electrode 22 is immersed in the electrolytic solution 28 contained in the third sub-container 30. Further, the other end of the reference electrode 22 is connected to a potential holding device (not shown). Further, the other end of the salt bridge 24 is inserted into the electrolytic solution 28 in the third sub-container 30.

The material and shape of the reference electrode 22 are not particularly limited as long as they can cause the desired electrochemical reaction.
Examples of the reference electrode 22 include a noble metal electrode, a silver-silver chloride electrode, and a reversible hydrogen electrode. Examples of the shape of the reference electrode 22 include a rod shape, a plate shape, and a mesh shape. Examples of the electrolytic solution 28 include a sulfuric acid aqueous solution, a perchloric acid solution, and a nitric acid aqueous solution.

[1.5. Potential holding device]
The potential holding device (not shown) is for holding the working electrode 18 at a potential lower than the reduction potential of the noble metal element M ₁ contained in the electrode catalyst precursor 12. The potential holding device is not particularly limited as long as it can perform such a function.
Examples of the potential holding device include a potentiostat and a charging/discharging device.

[1.6. Stirring device]
The stirring device (not shown) is for stirring the acidic aqueous solution 14. The stirring device is not particularly limited as long as it can stir the acidic aqueous solution 14.
When the acidic aqueous solution 14 is stirred with the working electrode 18 immersed in the acidic aqueous solution 14, the frequency of contact between the electrode catalyst precursor 12 and the working electrode 18 increases. As a result, the elution rate of the metal element M ₂ from the electrode catalyst precursor 12 increases.

[1.7. Bubbling device]
The bubbling device (not shown) is for bubbling oxygen into the acidic aqueous solution 14. Further, oxygen is used to bring the electrode catalyst precursor 12 floating in the acidic aqueous solution 14 into a high potential state. The bubbling device is not particularly limited as long as it is capable of bubbling oxygen into the acidic aqueous solution 14.

[2. Manufacturing method of electrode catalyst]
The method for producing an electrode catalyst according to the present invention includes:
A first step of applying a potential cycle to an electrocatalyst precursor dispersed in an acidic aqueous solution to obtain an electrocatalyst using the electrocatalyst manufacturing apparatus according to the present invention;
and a second step of separating the electrode catalyst from the acidic aqueous solution and washing it.

[2.1. 1st process]
First, using the electrocatalyst manufacturing apparatus 10 according to the present invention, a potential cycle is applied to the electrocatalyst precursor 12 dispersed in the acidic aqueous solution 14 to obtain an electrocatalyst (first step). Specifically, the treatment of the electrode catalyst precursor 12 using the electrode catalyst device 10 is performed in the following procedure.

First, the acidic aqueous solution 14 is placed in the container 16, and the acidic aqueous solution 14 is filled with oxygen by bubbling the acidic aqueous solution 14 with oxygen using a bubbling device (not shown).
Next, an electrode catalyst precursor 12 including an alloy catalyst particle precursor containing a noble metal element M ₁ and a metal element M ₂ less noble than the noble metal element M ₁ is dispersed in the acidic aqueous solution 14 .
Further, the acidic aqueous solution 14 is stirred using a stirring device (not shown) while maintaining the potential of the working electrode 18 at a potential lower than the reduction potential of the noble metal element M ₁ using a potential holding device (not shown). do.
As a result, part or all of the metal element M ₂ is eluted from the alloy catalyst particle precursor, and an electrode catalyst including alloy catalyst particles containing less metal element M ₂ than the alloy catalyst particle precursor is obtained.

The elution of the metal element M ₂ is promoted by such a method due to the low potential state when the alloy catalyst particle precursor and the working electrode 18 come into contact with each other in the acidic aqueous solution 14 and the alloy catalyst particle precursor and the working electrode 18 . This is because the high potential state when in contact with oxygen is repeated, that is, a pseudo potential cycle acts on the alloy catalyst particle precursor.

[2.2. 2nd process]
Next, the electrode catalyst is separated from the acidic aqueous solution and washed (second step). Thereby, the electrode catalyst according to the present invention is obtained. The method for separating and washing the electrode catalyst is not particularly limited, and an optimal method can be selected depending on the purpose.

[3. Electrode catalyst]
The electrode catalyst according to the present invention includes alloy catalyst particles. The electrode catalyst may be composed only of alloy catalyst particles, or may be one in which alloy catalyst particles are supported on the surface of a carrier made of a conductive material.

[3.1. Alloy catalyst particles]
Alloy catalyst particles are
Noble metal element M ₁ and
The metal element M ₂ is less noble than the noble metal element M ₁ .

[3.1.1. composition]
[A. Noble metal element M ₁ , metal element M ₂ ]
The details of the noble metal element M ₁ and the metal element M ₂ are as described above, so a description thereof will be omitted.

[B. Total content of metal elements _M2 other than Cu]
The total content of metal elements M ₂ (excluding Cu) influences the performance of the electrocatalyst. Generally, the efficiency point performance (low current density/high voltage operating conditions) improves as the total content of the metal element M ₂ increases. In order to obtain such an effect, the total content of the metal element M ₂ is preferably more than 0.1 at%.

On the other hand, when the total content of the metal element M ₂ becomes excessive, M ₂ is eluted in the fuel cell environment, resulting in a decrease in activity and output. Therefore, the content of the metal element _M2 is preferably less than 13 at%.

[C. Cu content]
If Cu is contained in a noble metal-based alloy catalyst, Cu may be eluted during use in a fuel cell and then deposited on the anode, resulting in a decrease in performance. Therefore, the smaller the Cu content, the better.
The method according to the present invention does not use Cu when applying potential cycles to the electrocatalyst precursor. Therefore, an electrode catalyst substantially free of Cu can be obtained. Specifically, when the method according to the present invention is used, the Cu content is less than 6 at%, less than 3 at%, or less than 1%.

[3.1.2. Structure of alloy catalyst particles]
The alloy catalyst particles may be solid particles or may be core-shell particles in which the surface of a core particle is covered with a shell.
Furthermore, the alloy catalyst particles may be hollow nanoparticles obtained by eluting cores from core-shell particles.

By using the method according to the present invention, it is possible to obtain an electrode catalyst comprising alloy catalyst particles having a hollow nanoparticle structure with an average particle size of 5 nm or more and 15 nm or less.
Here, the "particle size" of the alloy catalyst particles refers to the maximum dimension of the particles measured under electron microscopy.
The "average particle size" of the alloy catalyst particles refers to the average value of the particle sizes of 50 or more randomly selected alloy catalyst particles.

[3.2. Carrier]
The carrier consists of an electrically conductive material. Since the details of the carrier are as described above, the explanation will be omitted.

[3.3. Use]
The fuel cell catalyst according to the present invention is suitable as a cathode catalyst of a polymer electrolyte fuel cell, but can also be used as an anode catalyst.

[4. Effect]
An alloy catalyst containing a noble metal element M ₁ and a metal element _{M 2 less} noble than the noble metal element M _{1 exhibits higher performance than a catalyst containing only the noble metal element M 1} . However, when such an alloy catalyst is used in a fuel cell environment, excess metal element M ₂ contained in the alloy catalyst tends to be eluted. As a result, the performance of the alloy catalyst itself deteriorates, or the ions of the eluted metal element _M2 undergo ion exchange with the protons of the electrolyte, resulting in a deterioration of the battery performance.

On the other hand, an electrode catalyst precursor containing an alloy catalyst particle precursor is dispersed in an acidic aqueous solution filled with oxygen, a working electrode is immersed in the acidic aqueous solution, and the potential of the working electrode is set to be lower than the reduction potential of the noble metal element _M1 . When the acidic aqueous solution is stirred while also being held at a low potential, the electrocatalyst precursor will be in a low potential state when it comes into contact with the working electrode. Further, when the electrode catalyst precursor is detached from the working electrode and comes into contact with oxygen in the acidic aqueous solution, it becomes in a high potential state.

That is, when such a method is used, a potential cycle can be efficiently applied to a relatively large amount of the electrode catalyst precursor. As a result, the metal element M ₂ can be eluted from the alloy catalyst particle precursor in a short time. Further, since a potential cycle can be applied to the alloy catalyst particle precursor without contacting it with metal copper, it is possible to obtain an electrode catalyst having alloy catalyst particles that do not contain Cu on the catalyst surface.

(Example 1, Comparative Examples 1 to 3)
[1. Preparation of sample]
[1.1. Preparation of electrode catalyst precursor]
A Pt precursor, a Ni precursor, and a carrier were dispersed in a water/alcohol mixed solvent and stirred. NaBH ₄ was added dropwise to this dispersion as a reducing agent. After the dropping of the reducing agent was completed, stirring was performed for 55 minutes. The solid content recovered from the dispersion was washed and filtered, and dried at 100°C to obtain core-shell particles/C catalyst (electrode catalyst precursor).

[1.2. Preparation of electrode catalyst]
[1.1. Example 1]
Core-shell particles/C catalyst (electrode catalyst precursor) was processed using the electrode catalyst manufacturing apparatus 10 shown in FIG. That is, a 1M sulfuric acid aqueous solution (acidic aqueous solution 14) was placed in a container 16. The temperature of the sulfuric acid aqueous solution was maintained at 60° C., and oxygen was bubbled to fill the sulfuric acid aqueous solution with oxygen. Thereafter, the potential of the working electrode 18 was maintained at 0 V (vs. RHE), and the sulfuric acid aqueous solution was stirred for 3 hours. Thereafter, filtration, washing with ultrapure water, and drying were performed to obtain an electrode catalyst.

[1.2. Comparative example 1]
A 1M aqueous sulfuric acid solution (aqueous acidic solution 14) was placed in a container 16 shown in FIG. 1, and the temperature of the aqueous sulfuric acid solution was maintained at 60°C. Thereafter, core-shell particles/C catalyst (electrode catalyst precursor) was added and stirred for 3 hours. Thereafter, filtration, washing with ultrapure water, and drying were performed to obtain an electrode catalyst.

[1.3. Comparative example 2]
An electrode catalyst (hollow PtNi/C nanocatalyst) was produced using the method described in Non-Patent Document 1. That is, core-shell particles/C catalyst (electrode catalyst precursor) were added to a 1M sulfuric acid solution at room temperature and stirred for 12 hours. Furthermore, the solid portion recovered from the treatment liquid was washed and filtered to obtain a hollow PtNi/C nanocatalyst.

[1.4. Comparative example 3]
An electrode catalyst was produced using the method described in Patent Document 1. That is, a 1M sulfuric acid aqueous solution was placed in a container. The temperature of the sulfuric acid aqueous solution was maintained at 60° C., and oxygen was bubbled to fill the sulfuric acid aqueous solution with oxygen. Thereafter, a copper mesh was placed in the solution, and the sulfuric acid aqueous solution was stirred for 3 hours. Thereafter, filtration, washing with ultrapure water, and drying were performed to obtain an electrode catalyst.

[2. Test method]
[2.1. Composition analysis]
ICP analysis was performed on each electrode catalyst.
[2.2. HAADF-STEM observation]
Each electrode catalyst was observed using a high-angle scattering annular dark field scanning transmission electron microscope (HAAD-FTEM).

[3. result]
[3.1. Composition analysis]
Table 1 shows the ICP analysis results of each catalyst. From Table 1, the following can be seen.
(1) Example 1 has the smallest amount of Ni. Further, the Ni/Pt ratio in Example 1 was about 1/7.
(2) Comparative Example 3 was able to reduce Ni, but had Cu contamination. The Ni/Pt ratio of Comparative Example 3 is about 1/6, and Ni is relatively larger than that of Example 1.

[3.2. HAADF-STEM observation]
FIG. 2 shows a HAAD-FTEM image of the electrode catalyst obtained in Example 1. The brightness is weak in the center of many particles, suggesting that the inside of the particles is hollow. Further, the particle size of these particles was 5 to 15 nm.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

The electrode catalyst manufacturing apparatus according to the present invention can be used for manufacturing an electrode catalyst for a polymer electrolyte fuel cell.
The electrode catalyst according to the present invention can be used as an electrode catalyst for the air electrode of a polymer electrolyte fuel cell used in a power source for an automobile, a small stationary generator, and the like.

Claims (8)

a container for containing an acidic aqueous solution in which an electrode catalyst precursor including an alloy catalyst particle precursor containing a noble metal element M ₁ and a metal element M ₂ less base than the noble metal element M ₁ is dispersed;
a working electrode and a counter electrode for electrically contacting the acidic aqueous solution;
a potential holding device for holding the working electrode at a potential lower than the reduction potential of the noble metal element M ₁ ;
a stirring device for stirring the acidic aqueous solution;
and a bubbling device for bubbling oxygen into the acidic aqueous solution.
however,
The “noble metal element M ₁ ” refers to at least one element selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os,
The “metal element M ₂ ” is an element to be eluted from the alloy catalyst particle precursor, and includes the second noble metal element M ₂₁ , the noble metal element M ₁ and the second noble metal element M ₂₁ Refers to at least one element selected from the group consisting of metallic elements other than M22 _,
The “second noble metal element M ₂₁ ” is at least one element selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os, and is more preferable than the noble metal element M 1 _. Refers to something that is base. The electrode catalyst manufacturing apparatus according to claim 1, further comprising a reference electrode for precisely controlling the potential of the working electrode. The electrocatalyst manufacturing apparatus according to claim 1 or 2, wherein the working electrode is a noble metal mesh electrode. The electrode catalyst according to claim 3, wherein the ratio (= _{d 2 /} d ₁ ) of the pore diameter (d ₂ ) of the noble metal mesh electrode to the average particle diameter (d 1 ) of the electrode catalyst precursor is more than 1 and 1000 or less. Manufacturing equipment. A first step of applying a potential cycle to an electrocatalyst precursor dispersed in an acidic aqueous solution using the electrocatalyst manufacturing apparatus according to any one of claims 1 to 4 to obtain an electrocatalyst;
A method for producing an electrode catalyst, comprising a second step of separating the electrode catalyst from the acidic aqueous solution and washing it. The first step is
Filling the acidic aqueous solution with oxygen by placing the acidic aqueous solution in the container and bubbling the acidic aqueous solution with oxygen using the bubbling device,
Dispersing in the acidic aqueous solution an electrode catalyst precursor comprising an alloy catalyst particle precursor _containing the noble metal element _M1 and a metal element _M2 less noble than the noble metal element M1,
Stirring the acidic aqueous solution using the stirring device while maintaining the potential of the working electrode at a potential lower than the reduction potential of the noble metal element M ₁ using the potential holding device,
6. The method for producing an electrode catalyst according to claim 5, wherein the electrode catalyst is thereby obtained having alloy catalyst particles having a lower content of the metal element _M2 than the alloy catalyst particle precursor. An electrode catalyst with the following configuration.
(1) The electrode catalyst includes alloy catalyst particles.
(2) The alloy catalyst particles include a noble metal element M ₁ and a metal element M ₂ less noble than the noble metal element M ₁ , and the total content of the metal element M ₂ (excluding Cu) is 0.1 at%. The Cu content is less than 13 at%, and the Cu content is less than 6 at%.
however,
The “noble metal element M ₁ ” refers to at least one element selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os,
The “metal element M ₂ ” refers to at least one element selected from the group consisting of a second noble metal element M ₂₁ and a metal element M ₂₂ other than the noble metal element M ₁ and the second noble metal element M ₂₁ . good,
The “second noble metal element M ₂₁ ” is at least one element selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os, and is more preferable than the noble metal element M ₁ . I like things that are lowly,
The alloy catalyst particles exclude those in which the noble metal element M ₁ is Pd and the metal element M ₂ is Co. The electrode catalyst according to claim 7, wherein the alloy catalyst particles have a hollow nanoparticle structure with an average particle size of 5 nm or more and 15 nm or less.

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