JP5803536B2 - Electrocatalyst - Google Patents

Description

  The present invention relates to an electrode catalyst, particularly an electrode catalyst for an electrochemical device such as a fuel cell. More specifically, the present invention relates to an electrocatalyst for an electrochemical device that can improve the catalytic activity and the utilization rate of the catalyst component.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. In particular, a polymer electrolyte fuel cell (PEFC) is expected as a power source for electric vehicles because it operates at a relatively low temperature. The polymer electrolyte fuel cell generally has a structure in which an electrolyte membrane-electrode assembly is sandwiched between separators. The electrolyte membrane-electrode assembly is obtained by sandwiching a polymer electrolyte membrane between a pair of electrode catalyst layers and a gas diffusion layer (GDL).

In a polymer electrolyte fuel cell having an electrolyte membrane-electrode assembly (MEA) as described above, the following reaction formulas are used depending on the polarity of both electrodes (cathode and anode) sandwiching the polymer electrolyte membrane. Electric energy is obtained by advancing the electrode reaction indicated by. First, hydrogen contained in the fuel gas supplied to the anode (hydrogen electrode) side is oxidized by the catalyst component to become protons and electrons (2H ₂ → 4H ⁺ + 4e ⁻ : reaction 1). Next, the generated protons pass through the solid polymer electrolyte contained in the electrode catalyst layer and the solid polymer electrolyte membrane in contact with the electrode catalyst layer, and reach the cathode (oxygen electrode) side electrode catalyst layer. In addition, the electrons generated in the anode-side electrode catalyst layer include the conductive carrier constituting the electrode catalyst layer, the gas diffusion layer in contact with the side of the electrode catalyst layer different from the solid polymer electrolyte membrane, the separator, and the outside. The cathode side electrode catalyst layer is reached through the circuit. The protons and electrons that have reached the cathode-side electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode side to generate water (O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O: Reaction 2). . In the fuel cell, electricity can be taken out through the above-described electrochemical reaction.

In the electrochemical reaction, hydrogen ions (H ⁺ ) (hereinafter also referred to as “protons”) generated by the reaction 1 on the anode side permeate the solid polymer electrolyte membrane in a hydrated state (H ₃ O ⁺ ). (Spread. Protons that have passed through the membrane are supplied to the reaction 2 together with oxygen and electrons that have permeated (diffused) through the gas diffusion layer at the cathode. That is, the reaction at the anode and the cathode proceeds at the interface between the catalyst in the electrode catalyst layer and the solid polymer electrolyte, with the electrode catalyst layer in close contact with the electrolyte membrane as a reaction site. Therefore, if the interface between the catalyst and the polymer electrolyte increases and the formation of the interface becomes uniform, the above reactions 1 and 2 proceed more smoothly and actively.

  The polymer electrolyte fuel cell (PEFC) can be started at room temperature compared to other fuel cells such as phosphoric acid fuel cells (PAFC) and alkaline fuel cells (AFC), and the problem of electrolyte dissipation and retention There are few and maintenance is easy. However, in general, as the catalyst in the electrode catalyst layer, a conductive carrier (carbon black or the like) carrying platinum or a platinum alloy is used, but platinum as a catalyst component used for the electrode reaction is used. Has a problem in resource supply. Furthermore, platinum is expensive, and the cost of the platinum electrode accounts for about ¼ of the cost of the polymer electrolyte fuel cell system. Therefore, the amount of platinum catalyst is further reduced from the viewpoint of reducing the cost of the fuel cell system. Is needed. Therefore, further improvement in catalytic activity is required.

  In order to improve the oxygen reduction activity of the catalyst, for example, Patent Document 1 includes a Ni core, an Au underlayer covering the core, and a Pt outermost layer covering the underlayer. A nanoparticle electrocatalyst having a three-layer core-shell structure is disclosed. In the production of the electrode catalyst, first, Ni—Au / C in which an alloy of Ni and Au is supported on carbon is prepared, and then heat-treated at 600 ° C. to move Au to the surface. C is prepared. Next, the electrode catalyst is manufactured by a method of stacking Cu using an UPD (Under Potential Deposition) method and substituting Cu with Pt to obtain Pt / Au / Ni / C. Patent Document 1 describes that the catalyst thus produced exhibits higher catalytic activity than a Pt-supported carbon (Pt / C) catalyst.

US Patent Application Publication No. 2010/0197490

  However, in order to reduce the amount of platinum used and reduce the cost of the fuel cell system, further activation of the catalyst is necessary.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide electrode catalyst particles used as an electrode catalyst for an electrochemical device such as a fuel cell, which can provide high catalytic activity and reduce the amount of catalyst metal such as Pt. And

  The present inventors have intensively studied to solve the above problems. As a result, in the electrocatalyst particles having a three-layer core-shell structure of the metal particles, the first metal layer, and the second metal layer, the noble and base relationships between the metals constituting each layer satisfy a specific relationship. It has been found that electrode catalyst particles excellent in catalytic activity can be obtained by controlling to.

  That is, the present invention is an electrocatalyst particle having a three-layer structure in which a first metal layer is disposed on the surface of a metal particle, and a second metal layer is disposed on the surface of the first metal layer, Electrode catalyst particles, wherein the metal constituting the first metal layer is a base metal than the metal constituting the metal particle and the metal constituting the second metal layer.

  According to the electrode catalyst particles of the present invention, the catalytic activity per unit area of the metal (catalyst metal) constituting the second metal layer that is the outermost surface layer can be improved. Therefore, the catalytic activity per mass of the catalytic metal (mass specific activity) can be improved.

It is a schematic diagram which shows the structure of the electrode catalyst particle | grains of this invention. It is a schematic diagram which shows the outline of the manufacturing method of the electrode catalyst of this invention. It is a schematic sectional drawing of a polymer electrolyte fuel cell. It is a scheme which shows the preparation procedure of the electrocatalyst of Example 1,2. 2 is a TEM photograph of the electrode catalyst prepared in Example 1. 4 is a graph showing CV characteristics of the electrode catalysts prepared in Example 1 and Comparative Example 2. It is a figure showing the activity of the electrode catalyst prepared in Examples 1, 2 and Comparative Examples 1, 2. It is a figure showing the activity of the electrode catalyst prepared in Examples 1, 2 and Comparative Examples 1, 2.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from the actual ratios.

  The present invention is a three-layered electrocatalyst particle in which a first metal layer is disposed on the surface of a metal particle, and a second metal layer is disposed on the surface of the first metal layer, Electrode catalyst particles characterized in that the metal constituting the first metal layer is a base metal than the metal constituting the metal particle and the metal constituting the second metal layer.

  FIG. 1 is a schematic diagram showing a typical configuration of the electrode catalyst particles of the present invention. The electrode catalyst particle 10 of the present invention is a particle having a three-layer structure in which a first metal layer 12 and a second metal layer 13 are formed in this order on the surface of a metal particle 11. The metal constituting the second metal layer 13 acts as a catalyst metal.

The catalyst activity (mass specific activity) (A / g) per unit mass of the catalyst metal is expressed as follows: specific surface area (mass specific surface area) per unit mass of catalyst metal (m ² / g) It depends on the catalyst activity per unit area of the catalyst metal (area specific activity) (A / m ² ).

  In the electrocatalyst particles having a core-shell structure, the surface area per unit mass (mass specific surface area) of the catalyst metal can be improved as compared with particles made of a single catalyst metal. This is because the atoms of the catalyst metal exposed on the surface among the metals constituting the electrode catalyst particles are involved in the reaction. For example, in the case of an electrode catalyst (Pt / Au / C) in which core-shell particles composed of Au as a core and Pt as a shell are supported on a carbon support, the mass specific surface area is improved compared to Pt / C where Pt particles are supported. This is known to improve the mass specific activity.

  On the other hand, in order to increase the mass specific activity of the catalyst metal, it is important to increase the mass specific surface area and increase the area specific activity.

  In Pt / Au / Ni / C (conventional example) described in Patent Document 1, a core shell having a three-layer structure in which an intermediate layer is provided between the core and the shell makes the area larger than Pt / Au / C. It is considered that specific activity is improved and high mass specific activity is exhibited. However, in order to reduce the amount of platinum used and to reduce the cost as an electrode catalyst for fuel cell automobiles, further improvement in catalytic activity is required.

  Therefore, the present inventors have found that in the catalyst particles having a three-layer structure, the area specific activity can be improved by controlling the relationship between the noble and base in the ionization row of the metal constituting each layer. In the embodiment shown in FIG. 1, the metal constituting the second metal layer 13 between the metal particles 11 (for example, made of Au) and the second metal layer 13 (for example, made of Pt). A first metal layer 12 made of a more basic metal (eg, made of Ni) is introduced. As a result, the electronic state of the metal (catalyst metal) constituting the second metal layer 13 is affected by the electronic state of the metal constituting the first metal layer 12, so the first metal layer 12 is not included. Compared to the case, the area specific activity of the catalytic metal can be improved. Furthermore, it has been found that by making the metal constituting the metal particles 11 a noble metal rather than the metal constituting the first metal layer 12, the area specific activity can be further improved. The reason why the area specific activity is improved by controlling the noble / base relationship in the ionization row of the metal constituting each layer as described above is not clear. However, the electronic state of the metal constituting the metal particle 11 changes the electronic state of the metal constituting the first metal layer 12, and this change in the electronic state is the electronic state of the metal constituting the second metal layer 13. That may ultimately give a high area specific activity. Furthermore, it is considered that the use of a metal that is more noble than the metal constituting the first metal layer 12 as the metal particle 11 has an effect of suppressing particle elution.

  The shape and size of the electrode catalyst particles of the present invention are not particularly limited, and the same shape and size as those of known metal catalysts used for the electrode catalyst can be used. For example, the smaller the average particle size of the electrode catalyst, the higher the effective electrode area where the electrochemical reaction proceeds, so that the oxygen reduction activity is also higher, which is preferable. Therefore, the average particle diameter of the electrode catalyst particles is, for example, 1 to 30 nm, preferably 1.5 to 20 nm, and more preferably 2 to 10 nm. It is preferably 1 nm or more from the viewpoint of ease of loading on the conductive support, and preferably 30 nm or less from the viewpoint of catalyst utilization. The average particle diameter of the electrocatalyst particles according to the present invention is measured by the crystallite diameter determined from the half width of the diffraction peak in X-ray diffraction or the average particle diameter of the electrocatalyst particles examined by a transmission electron microscope image. can do.

  Furthermore, the electrode catalyst particles of the present invention can be produced by chemical reduction that does not require energization. Therefore, the cost is low and large-scale preparation is possible.

In the above-mentioned Patent Document 1, a core-shell particle is prepared by annealing an alloy-containing nanoparticle, and a base metal monoatomic layer is further laminated on the core-shell particle using the UPD method. A method for producing an electrocatalyst that is substituted with a noble metal is disclosed. By this method, a nano-particle having a three-layer core-shell structure in which a monoatomic layer of a noble metal as a catalytic metal is further laminated on a core-shell particle composed of a base metal core and a noble metal shell. Specifically, Ni—Au / C in which an alloy of Ni as a base metal and Au as a noble metal is supported on carbon as a conductive carrier is prepared, and then heat-treated at 600 ° C. in an H ₂ atmosphere. Au is moved to the surface to prepare Au / Ni / C. Thereafter, a Cu monoatomic layer is formed on the surface using the UPD method to form Cu / Au / Ni / C, and immersed in a Pt solution to replace Cu with Pt to obtain Pt / Au / Ni / C. .

  However, since a heat treatment at 600 ° C. is necessary, the manufacturing process increases. In addition, it can be prepared only on the electrode because it includes electrochemical reduction that requires energization, such as Cu UPD. Furthermore, since the process of substituting Cu with Pt is also performed on the electrode, it is difficult to reduce the cost and mass production.

  On the other hand, the electrode catalyst particles of the present invention can be produced by chemical reduction that does not require energization. That is, no heat treatment is required, all the steps can be wet processes, and energization is not required. Therefore, cost reduction and mass production are possible.

  Hereinafter, each constituent member of the electrode catalyst particles of the present invention will be described.

(Metal particles)
A metal particle is a particle | grains which comprise the center part of the electrode catalyst particle of this embodiment. Although the particle diameter of a metal particle is not specifically limited, For example, it is 0.5-20 nm, Preferably it is 0.5-15 nm, More preferably, it is 0.5-10 nm.

  The metal constituting the metal particles is not particularly limited as long as it is noble than the metal constituting the first metal layer, and examples thereof include Au, Pt, Pd, Ir, Rh, Ru, Ag, and Cu. It is done. Of these, Au, Pt, and Pd are preferable, and Au and Pt are particularly preferable. High catalytic activity can be obtained by using these metals. Moreover, elution of particles can be suppressed. Moreover, cost reduction can be achieved by using a relatively inexpensive metal among the above metals. The metal particles may be composed of a single metal or a composite (alloy) composed of two or more kinds of metals. In the present specification, it is assumed that a metal having a smaller ionization tendency among the metals constituting each layer is noble and a larger metal is base. Further, in the present specification, when each layer constituting the electrode catalyst particles is composed of two or more kinds of metals, the noble and base relationship between the metals constituting each layer is determined between the metals as the main components of each layer. It means a noble relationship.

(First metal layer)
A 1st metal layer is formed in the surface of said metal particle, and forms an intermediate | middle layer between the 2nd metal layer mentioned later. The first metal layer can improve the catalytic activity by reducing the amount of the catalyst metal contained in the second metal layer and affecting the electronic state of the catalyst metal.

  The metal constituting the first metal layer is not particularly limited as long as it is lower than the metal constituting the metal particles and the metal constituting the second metal layer. For example, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag, etc. are mentioned, More preferably, it is Cr, Ag, Ni, Co, Most preferably, it is Ni. When the metal as described above is used, the area specific activity of the metal constituting the second metal layer can be further improved. In particular, regarding Ni, in the model electrode of the Pt thin film formed on the substrate, the area ratio activity of the Pt thin film is greatly improved by forming the Ni film as the base layer of the Pt thin film compared to the case where the base layer is not provided. Has been confirmed. The first metal layer may be composed of a single metal or a composite (alloy) composed of two or more kinds of metals.

  The thickness of the first metal layer is not particularly limited, but is preferably 50 atomic layers or less, more preferably 30 atomic layers or less, and even more preferably 10 atomic layers or less. If the thickness of the first metal layer is within the above range, the electronic state of the metal constituting the first metal layer is affected by the electronic state of the metal constituting the metal particles, and further the second metal layer It is preferable because it can change the electronic state of the metal and give high catalytic activity. In addition, if the thickness of the first metal layer is 50 atomic layers or less, the particle diameter of the electrode catalyst particles does not become too large, and a sufficient specific surface area can be secured, which is preferable. The thickness of the first metal layer is preferably 1 atomic layer or more.

(Second metal layer)
The second metal layer is the outermost surface layer and contains a metal (catalyst metal) that becomes a catalyst component.

  The metal constituting the second metal layer is not particularly limited as long as it is noble than the metal constituting the first metal layer, but is preferably Pt or an alloy containing Pt. Pt exhibits high activity as an electrode catalyst for a fuel cell. By including Pt in the second metal layer, the activity per unit area of the metal constituting the second metal layer can be improved. The metal alloyed with Pt is not particularly limited as long as it has a function of promoting the electrode reaction in the arranged electrode. The metal to be alloyed is, for example, one or more selected from ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. The composition of the alloy depends on the type of metal to be alloyed, but Pt is preferably more than 50 atomic%, more preferably 70 atomic% or more.

  The thickness of the second metal layer is not particularly limited, but is preferably 50 atomic layers or less, more preferably 30 atomic layers or less, and even more preferably 10 atomic layers or less. By setting the number of atomic layers of the second metal layer to 50 atomic layers or less, the specific surface area per unit mass of the metal constituting the second metal layer is increased. Therefore, the catalytic activity per mass can be improved. The thinner the second metal layer, the larger the surface area per unit mass of the metal constituting the second metal layer, and most preferably all the metal particles constituting the second metal layer are exposed on the surface. In other words, it is a monoatomic layer. On the other hand, if it is the thickness more than the monoatomic layer in which the 1st metal layer is not exposed on the surface, it is preferable from a durable viewpoint.

  Furthermore, by setting the thickness of the second metal layer to 50 atomic layers or less, the electronic state of the metal constituting the second metal layer is easily affected by the electronic state of the metal constituting the first metal layer. It is considered that the area specific activity of the metal constituting the second metal layer is further improved. Therefore, the effect of improving the catalytic activity per mass is high.

  In addition, the thickness of each layer which comprises an electrode catalyst particle can be calculated | required from content of each component measured by a transmission electron microscope (TEM) or an inductively coupled plasma emission spectrometry (ICP).

  According to one embodiment of the present invention, an electrode catalyst is provided in which the electrode catalyst particles of the present invention are supported on a conductive carrier. The electrode catalyst in which the electrode catalyst particles are supported on a carrier can be taken out as a powder and an electrode catalyst layer for a fuel cell having a sufficient thickness can be formed. Therefore, it becomes possible to use the electrode catalyst at a high current density.

  The amount of the electrode catalyst particles supported is not particularly limited as long as the desired catalyst performance can be exhibited, but is preferably 5 to 60% by mass, and more preferably 10 to 50% by mass with respect to the total amount of the electrode catalyst. When the supported amount is 60% by mass or less, the aggregation of the electrode catalyst particles can be suppressed, the excellent dispersity on the conductive carrier can be effectively maintained, and the effect of improving the power generation performance is effectively expressed. There are advantages that can be made. Further, when the supported amount of the electrode catalyst particles is 5% by mass or more, the catalyst activity per unit mass is excellent, desired power generation performance according to the supported amount can be obtained, and the thickness of the electrode layer can be suppressed. Therefore, it is excellent in that the carrying amount design for ensuring the desired battery performance can be made relatively easily. The supported amount of the electrode catalyst particles (and their constituent components) can be examined by inductively coupled plasma emission spectrometry (ICP).

  The conductive carrier used in the electrode catalyst of the present invention is not particularly limited, and a known conductive carrier can be used. Preferably, it has a specific surface area for supporting the electrocatalyst particles in a desired dispersed state. The conductive carrier preferably has sufficient electronic conductivity as a current collector.

  As the material of the conductive carrier, a carbon-based material whose main component is carbon is desirable because it is stable in an acidic atmosphere, has a low electrical resistance, and can be controlled in length. Specific examples of the carbon-based material include carbon black, activated carbon, coke, graphite, high-temperature (graphitized) -treated carbon black, carbon nanotube, carbon nanohorn, carbon nanofiber, carbon fibril structure, and carbon-based material. A porous material etc. can be illustrated. The conductive carrier may be used alone or in the form of a mixture of two or more. In the present invention, “the main component is carbon” refers to containing a carbon atom as a main component, and is a concept including both a carbon atom only and a substantially carbon atom. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by mass or less is allowed.

  The shape of the conductive carrier is not particularly limited, but may be any of spherical, columnar, and tubular shapes. The size of the conductive carrier is not particularly limited. For example, when the conductive carrier is spherical, the average particle size of the conductive carrier is not particularly limited, and the existing average particle size can be adopted. From the viewpoint of controlling the ease of loading, the catalyst utilization rate, and the thickness of the electrode catalyst layer within an appropriate range, the average particle diameter is preferably about 5 to 200 nm, preferably about 10 to 100 nm.

The BET specific surface area of the conductive support may be sufficient as long as the electrode catalyst is supported in a highly dispersed manner. In the case of a spherical conductive carrier, the BET specific surface area of the conductive carrier is preferably 5 to 2000 m ² / g, more preferably 50 to 1500 m ² / g. When the specific surface area is 5 m ² / g or more, the dispersibility of the electrode catalyst and the polymer electrolyte on the spherical conductive carrier is improved, which is excellent in that sufficient power generation performance can be obtained. On the other hand, when it is 2000 m ² / g or less, it is excellent in that a high effective utilization rate of the electrode catalyst and the polymer electrolyte can be effectively maintained.

  Next, the manufacturing method of the electrode catalyst of this invention is demonstrated.

  The electrode catalyst of the present invention may be produced by any method, but a method as shown in FIG. 2 can be used as one embodiment of a typical production method. That is, another embodiment of the present invention is a three-layer electrode catalyst in which a first metal layer is disposed on the surface of metal particles, and a second metal layer is disposed on the surface of the first metal layer. A method for producing particles, comprising: adding a first reducing agent to a solution containing metal ions constituting the metal particles to obtain a colloidal dispersion containing metal particles; and A metal constituting the first metal layer, the metal constituting the metal particles and the metal ions which are lower than the metal constituting the second metal layer, and a second reducing agent, and the metal A metal ion constituting the second metal layer is further added to the solution obtained in the step of forming the first metal layer on the surface of the particle and the step of forming the first metal layer. And forming the second metal layer on the surface of the first metal layer to form an electrode catalyst Comprising the steps of obtaining a child, and to provide a manufacturing method of an electrode catalyst particles.

  According to this production method, electrode catalyst particles having a high mass specific surface area of the catalyst metal and a high area specific activity can be prepared by a wet process. Further, since the energization process is unnecessary and the manufacturing method is simplified, it is low in cost and suitable for mass production. Moreover, since no energization treatment is required, it is not necessary to perform the step of laminating the first metal layer and the second metal layer on a conductive carrier such as carbon, and after preparing the electrode catalyst particles having a core-shell structure, What is necessary is just to carry | support to an electroconductive support | carrier. Therefore, in the step of preparing the electrode catalyst particles, the particles do not come into contact with the conductive support, and each layer can be uniformly coated on the entire surface of the particles. In addition, since the conductive catalyst such as carbon is not included in the solution in the process of preparing the electrocatalyst particles, the progress of the reaction should be confirmed by observing the color change accompanying reduction deposition of the metal constituting each layer. Can do.

  Hereinafter, it demonstrates for every process. The following steps can be performed at room temperature, but are not limited thereto.

(A) Step of obtaining a colloidal dispersion containing metal particles by adding a first reducing agent to a solution containing metal ions constituting the metal particles First, a solution (solution A) containing the metal constituting the metal particles as ions ) Is prepared. The metal constituting the metal particles is as described above. Metal salts containing these metal elements as constituent elements are prepared and dissolved in a solvent. Such a metal salt is not particularly limited as long as it can be dissolved in a solvent and reduced by a reducing agent, and examples thereof include chloride, nitrate, sulfate, and metal chloride acid. Two or more of these may be used in combination.

  The solvent is not particularly limited as long as it can dissolve the ionic compound and the reducing agent, and examples thereof include water, alcohols, ketones, and ethers. Two or more of these may be used in combination. Examples of alcohols include methanol, ethanol, 1-propanol, and 2-propanol. Examples of ketones include methyl formate, methyl acetate, and ethyl acetate. Examples of ethers include methyl ethyl ether and diethyl ether. From the viewpoint of sufficiently dissolving the ionic compound, water is preferable as the solvent. It is particularly preferable to use pure water or ultrapure water.

  The concentration of metal ions contained in the solution containing metal ions constituting the metal particles (solution A) is not particularly limited, but is, for example, 50 mM or less, preferably 10 mM or less, more preferably 5 mM or less. More preferably, it is 2.5 mM or less. If it is the said range, it will become possible to prevent aggregation of the colloid particle formed at the time of colloid preparation.

  Next, a solution (solution B) containing the first reducing agent is prepared.

  Although it does not restrict | limit especially as a 1st reducing agent, The thing which melt | dissolves in water especially is preferable. For example, citric acids, ascorbic acids, carboxylic acids, hydrazine, hydrogen iodide, hydrogen sulfide, borohydride salts, and the like can be given. Two or more of these may be used in combination. Examples of the citric acids include citrates such as citric acid, sodium citrate, potassium citrate, or ammonium citrate. Examples of ascorbic acids include ascorbate such as ascorbic acid, sodium ascorbate, or potassium ascorbate. Examples of carboxylic acids include formic acid, acetic acid, fumaric acid, malic acid, succinic acid, aspartic acid, tannic acid, and carboxylic acid salts thereof. Examples of the borohydride salt include sodium borohydride, potassium borohydride, lithium aluminum hydride, lithium triborohydride, potassium triborohydride, sodium triethylborohydride and the like.

  As the solvent used for the solution containing the first reducing agent (solution B), the same solvent as the above solution A can be used.

  The amount of the first reducing agent added is not particularly limited as long as it is an amount sufficient to reduce metal ions in a solution (solution A) containing metal ions constituting the metal particles. Preferably it is 1-10 mol with respect to 1 mol, Preferably it is 1-5 mol, More preferably, it is 1-3 mol. When using 2 or more types of reducing agents, it is preferable that the total addition amount of these is within the above range. If the amount of the reducing agent added is in the above range, nano-sized metal particles can be suitably obtained.

  A colloidal dispersion of metal particles (solution C) can be obtained by adding a solution (solution B) containing the first reducing agent to a solution containing metal ions (solution A) constituting the metal particles and stirring. sell. At this time, if the color of the solution changes due to reduction of the metal ions, it can be visually confirmed that the reaction has progressed.

(B) The step of forming the first metal layer on the surface of the metal particles Next, the colloidal dispersion liquid (solution C) containing the metal particles obtained in the above (a) is added to the metal constituting the first metal layer. By adding ions and a second reducing agent, a first metal layer is formed on the surface of the metal particles by reduction deposition.

  At this time, preferably, a solution (solution D) containing a metal ion constituting the first metal layer and a second reducing agent dissolved in a solvent (solution D) containing the metal ion constituting the first metal layer and the first metal layer. A solution containing 2 reducing agents (solution E) is prepared, added in the order of solution D and solution E to the colloidal dispersion containing the metal particles (solution C) and stirred. As a result, metal ions constituting the first metal layer are reduced, the first metal layer is formed on the surface of the metal particles, and a solution (solution F) containing the core-shell particles having a two-layer structure can be obtained. At this time, it is possible to visually confirm that the color of the solution has changed due to reduction of metal ions constituting the first metal layer, and the reaction has progressed.

  According to this embodiment, the metal constituting the first metal layer is baser than the metal constituting the metal particles. Therefore, the first metal layer can be formed on the surface of the metal particles without dissolving the metal particles.

  The metal constituting the first metal layer is the same as described above. Although it does not restrict | limit especially as a metal salt, A chloride, nitrate, a sulfate, a chlorinated metal acid, etc. can be used. In addition, the reducing agent and the solvent can be the same as those described in the step (a) above. However, for the reducing agent, the metal constituting the first metal layer is the metal constituting the metal particles. Therefore, it is preferable to use one having a reducing power stronger than that used in the step (a) or to increase the amount of addition.

  Although it does not restrict | limit especially as a quantity of the metal which comprises the 1st metal layer to be used, Preferably it is 0.01-3000 mol with respect to 1 mol of metals which comprise a metal particle, More preferably, it is 0.1-3000 mol. It is 750 mol, More preferably, it is 0.1-50 mol. If it is the said range, the metal layer of 1 atomic layer-several atomic layers may be obtained.

  The temperature and time for stirring are not particularly limited. The stirring time is preferably 5 minutes to 3 hours, more preferably 10 minutes to 1 hour.

(C) Step of forming a second metal layer on the surface of the first metal layer to obtain electrode catalyst particles Next, a solution (solution G) containing metal ions constituting the second metal layer is prepared. The metal constituting the second metal layer is as described above. Examples of the metal salt include chloride, nitrate, sulfate, metal chloride acid, ammonium salt and the like. For example, the metal salt containing Pt as a constituent element is not particularly limited, but chloroplatinic acid (typically its hexahydrate; H ₂ [PtCl ₆ ] · 6H ₂ O), hexaammine platinum chloride ( [Pt (NH ₃ ) ₆ Cl ₄ ]), dinitrodiammine platinum (Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ), dichlorotetraammine platinum (typically its monohydrate; Pt (NH ₃ ) ₄ Cl ₂ · H ₂ O). Preferably, chloroplatinic acid can be used.

  Thereafter, the solution (solution G) containing the metal ions constituting the second metal layer is added to the solution (solution F) containing the core-shell particles having the two-layer structure obtained in the step (b) and stirred. To do. The temperature and time for stirring are not particularly limited. The stirring time is preferably 5 minutes to 3 hours, more preferably 10 minutes to 1 hour. In the present embodiment, since the metal constituting the second metal layer is noble than the metal constituting the second metal layer, the metal on the surface of the first metal layer constitutes the second metal layer. By replacing with metal, electrocatalyst particles having a three-layer structure can be obtained.

  Although it does not restrict | limit especially as a quantity of the metal which comprises the 2nd metal layer to be used, Preferably it is 0.01-20000 mol with respect to 1 mol of metals which comprise a metal particle, More preferably, it is 0.1-20,000 mol. It is 8500 mol, More preferably, it is 0.1-2000 mol. If it is the said range, the metal layer of 1 atomic layer-several atomic layers may be obtained.

  The control of the number of atomic layers of the first metal layer and the second metal layer described above can be performed, for example, by controlling the amount of the metal salt to be added.

  Specifically, when controlling the number of layers of the second metal layer, for example, the particle diameter of the particles in which the first metal layer is formed on the metal particles as the center is measured in a separate test. The particle diameter when the second metal layer having the number of layers is formed is calculated. When the second metal layer is formed, the metal constituting the first metal layer is eluted by a substitution reaction due to the difference in oxidation-reduction potential, and the necessary second metal layer is configured in consideration of this phenomenon. The amount of metal is calculated and a solution of metal salt containing this amount of metal is added.

  Next, in the first metal layer, the target number of layers is determined, the number of layers that elute when the metal constituting the second metal layer is precipitated is obtained, and the number of layers that are eluted is combined with the target number of layers It can be controlled by calculating the amount of the metal giving the number and adding a solution of the metal salt containing this amount of metal.

(D) Step of supporting electrode catalyst particles on a conductive carrier The step of supporting electrode catalyst particles on a conductive carrier is not particularly limited, and a carbon carrier (carbon Various production methods in which electrode catalyst particles are supported on a black carrier or the like can be appropriately used. That is, the method for supporting the electrode catalyst particles on the conductive carrier is not particularly limited. For example, the electrode catalyst particles prepared in advance are attached to the conductive carrier and then fired to support (fix) the metal particles. May be. Alternatively, for example, there is a method in which a conductive carrier is added to a solution containing electrode catalyst particles, mixed and stirred, and the electrode catalyst particles are supported on the conductive carrier.

  For example, a conductive support is added to the solution (solution H) containing the electrode catalyst particles obtained as described in (a) to (c) above, for example, at 0 to 90 ° C. for 1 to 120 hours, Stir and mix. The mixture is then filtered and washed. At this time, it is preferable to repeatedly wash with pure water. Thereafter, the filtrate is dried, for example, at room temperature to 90 ° C., for example, for 30 minutes or longer, preferably for 4 hours or longer.

  The electrocatalyst produced by the above-described method has a high mass specific activity. For this reason, the electrode catalyst according to the present embodiment is a fuel cell, a secondary battery, a water electrolysis device, a hydrohalic acid electrolysis device, a salt electrolysis device, an oxygen and / or hydrogen concentrator, a humidity sensor, a gas sensor, and other various electric devices. It can be used as an oxygen reduction catalyst used in chemical devices. In particular, an electrolyte membrane-electrode assembly including an electrode catalyst according to the present embodiment and a fuel cell using the same can obtain excellent performance and reduce the amount of catalyst metal used. Furthermore, the polymer electrolyte fuel cell using the electrode catalyst according to the present invention can be used for an in-vehicle power source, a stationary small power generator, a cogeneration system, and the like.

  The invention therefore also provides an electrochemical device comprising an electrocatalyst according to the invention.

  The electrolyte membrane-electrode assembly (MEA) for electrochemical devices of this embodiment includes an electrode catalyst layer containing the electrode catalyst according to the present invention on at least one surface of the electrolyte membrane. Here, the electrode catalyst according to the present invention may be used for the cathode side electrode catalyst layer and the anode side electrode catalyst layer. Hereinafter, a fuel cell including the electrode catalyst of the present embodiment will be described.

  FIG. 3 is a schematic cross-sectional view schematically showing the basic configuration (single cell configuration) of the fuel cell. In FIG. 3, the fuel cell (single cell) 20 has an anode-side electrode catalyst layer 22 a and a cathode-side electrode catalyst layer 22 b facing each other on both sides (front and back surfaces) of the electrolyte membrane 21. The fuel cell 20 of the present invention is characterized in that the electrode catalyst of the present invention is used for at least one of the anode side electrode catalyst layer 22a and the cathode side electrode catalyst layer 22b. However, since the reduction reaction at the cathode is slower than the oxidation reaction of hydrogen at the anode and the valence voltage is large, the form used at least for the cathode-side electrode catalyst layer 22b is highly effective and preferable.

Furthermore, an anode side gas diffusion layer (GDL) 23a and a cathode side GDL 23b are respectively arranged on both sides (outside) of the anode side electrode catalyst layer 22a and the cathode side electrode catalyst layer 22b so as to face each other. , Also referred to as MEA). Anode and cathode palators 25a and 25b are arranged on both sides (outside) of the GDLs 23a and 23b. Gas flow paths (grooves) 26a and 26b are provided inside the separators 25a and 25b. Through the gas flow paths (grooves) 26a and 26b, the hydrogen-containing gas (for example, H ₂ gas) and the oxygen-containing gas (for example, Air) pass through the anode-side and cathode-side GDLs 23a and 23b and the electrode catalyst layers 22a and 22b. Are supplied respectively. Further, in order to prevent gas from leaking to the outside, gaskets 27 are respectively disposed between the outer peripheral region of the electrolyte membrane 21 and the separators 25a and 25b.

  Hereinafter, the fuel cell of the present invention will be described for each component.

(A) Electrolyte membrane The electrolyte membrane which can be used for the fuel cell of this invention should just have high proton conductivity. Examples of the membrane having high proton conductivity include a polymer or copolymer of a monomer having an ion exchange group such as —SO ₃ H group; or a polymer of a monomer having an ion exchange group and another monomer. A film made of a material can be used. Specific examples of the material of the electrolyte membrane 21 include an electrolyte having a fluorinated resin in which all or part of the polymer skeleton is fluorinated and having an ion exchange group, or an aromatic that does not contain fluorine in the polymer skeleton. An electrolyte having an ion exchange group, which is a group hydrocarbon resin.

Examples of the ion-exchange group is not particularly _{limited, -SO 3 H, -COOH, -PO} (OH) 2, -POH (OH), - SO 2 NHSO 2 -, - Ph (OH) (Ph represents a phenyl group A cation exchange group such as —NH ₂ , —NHR, —NRR ′, —NRR′R ″ ⁺ , —NH ₃ ^{+ and the} like (R, R ′, R ″ represent an alkyl group, cycloalkyl Anion exchange groups such as a group, an aryl group, and the like.

  Specific examples of the electrolyte having a fluorine resin and having an ion exchange group include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, Asahi Glass). Perfluorocarbon sulfonic acid polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylenetetrafluoroethylene-g-styrene sulfonic acid polymer, Suitable examples include ethylene-tetrafluoroethylene copolymer, polytetrafluoroethylene-g-polystyrene sulfonic acid polymer, and polyvinylidene fluoride-g-polystyrene sulfonic acid polymer.

  Specific examples of the electrolyte that is an aromatic hydrocarbon resin and includes an ion exchange group include a polysulfone sulfonic acid polymer, a polyether ether ketone sulfonic acid polymer, a polybenzimidazole alkyl sulfonic acid polymer, Preferred examples include benzimidazole alkylphosphonic acid polymers, cross-linked polystyrene sulfonic acid polymers, polyethersulfone sulfonic acid polymers, and the like.

  The polymer electrolyte preferably contains a fluorine atom because it is excellent in heat resistance, chemical stability, and the like. Among these, fluorine electrolytes such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) and the like are preferable. In particular, in the present invention, when a polymer electrolyte having a sulfonic acid group such as Nafion (registered trademark, manufactured by DuPont) is used, it is preferable to use one having an EW of about 600 to 1100. In addition, EW (Equivalent Weight) represents the dry membrane weight per 1 mol of sulfonic acid groups, and means that the specific gravity of the sulfonic acid groups is larger as it is smaller.

Further, the amount of the polymer electrolyte is not particularly limited. The ratio (Ionomer / Carbon; I / C) of the polymer electrolyte mass (I) to the conductive carrier mass (C) is 0.5 to 2.0, more preferably 0.7 to 1.6. It is preferable that the amount is small. In such a range, sufficient proton conductivity and gas diffusivity can be achieved. The I / C ratio is determined by measuring the conductive carrier mass and electrolyte solid content contained in the electrode catalyst layer to be mixed in advance when preparing the catalyst ink (slurry) described in detail below. It can be calculated and controlled by adjusting the mixing ratio. Further, the mass (C) of the conductive carrier when the electrode catalyst layer is analyzed to determine the I / C is the mass of the electrode catalyst minus the mass of the catalyst metal particles. The mass of the catalytic metal particles can be quantified by inductively coupled plasma emission spectroscopy (ICP). When the electrode catalyst layer is analyzed to determine the I / C, the mass (I) of the polymer electrolyte in the electrode catalyst layer is calculated from the structure analysis of the polymer electrolyte by ¹⁹ F-NMR and the S atom by coulometric titration. It can be quantified by combining the two.

  The thickness of the electrolyte membrane can be appropriately determined in consideration of the characteristics of the obtained fuel cell, but is preferably 5 to 300 μm, more preferably 10 to 200 μm, and particularly preferably 15 to 150 μm. The thickness of the electrolyte membrane is preferably 5 μm or more from the viewpoint of strength during film formation and durability during operation of the fuel cell, and is preferably 300 μm or less from the viewpoint of output characteristics during operation of the fuel cell.

  In the present invention, the constituent member containing the electrolyte component interposed between the anode and cathode electrodes of the fuel cell is referred to as an electrolyte membrane, but the name is never limited. In view of the purpose of use used in the fuel cell, for example, even when it is referred to as an electrolyte layer or an electrolyte, it may be included in the electrolyte membrane referred to in the present invention. The same applies to the other component requirements, and the identity is not limited to the name, but the identity may be determined in light of the purpose of use.

(B) Electrode catalyst layer At least one of the anode side electrode catalyst layer 22a and the cathode side electrode catalyst layer 22b that can be used in the fuel cell of the present invention is characterized in that the electrode catalyst of the present invention is used. Is. The electrode catalyst of the present invention is preferably used for the cathode side electrode catalyst layer 22b, more preferably for both the anode side electrode catalyst layer 22a and the cathode side electrode catalyst layer 22b.

  Although the thickness of the electrode catalyst layer by this embodiment is not specifically limited, 0.1-100 micrometers is preferable, More preferably, it is 1-20 micrometers. When the thickness of the electrode catalyst layer is 0.1 μm or more, it is preferable in that a desired power generation amount can be obtained, and when it is 100 μm or less, it is preferable in that a high output can be maintained.

(C) Gas diffusion layer (GDL)
The gas diffusion layers (GDL) 23a and 23b may be included in the constituent members of the MEA 24, or may be constituent members of the fuel cell 20 other than the MEA 24. Although it does not specifically limit as GDL23a, 23b, The porous base material etc. which use the sheet-like material which has electroconductivity and porosity, such as a carbon fabric, a paper-like paper body, a felt, and a nonwoven fabric, etc. are mentioned. Similarly to the electrode catalyst layers 22a and 22b, the GDLs 23a and 23b may be subjected to water repellency treatment on the GDLs 23a and 23b using known means in order to increase water repellency and prevent flooding. A layer composed of a carbon particle aggregate may be formed.

  In the polymer electrolyte fuel cell having the MEA configuration of the present invention, the electrode catalyst layer 22, the GDL 23, and the electrolyte membrane 21 are desirably thin to improve the diffusibility of the fuel gas, but are too thin. A sufficient electrode output cannot be obtained. Accordingly, the MEA 24 having the desired characteristics, and further, the solid polymer fuel cell may be determined as appropriate.

(D) Separator The anode and cathode separators 25a and 25b are not particularly limited, such as carbon paper, carbon cloth, dense carbon graphite, carbon such as carbon plate, or metal such as stainless steel. A well-known thing can be used. The separators 25a and 25b have a function of separating air and fuel gas, and gas flow paths (grooves) 26a and 26b processed into a desired shape in order to secure the flow paths are provided. It is desirable that it is formed, and conventionally known techniques can be used as appropriate. The thicknesses and sizes of the separators 25a and 25b, the shapes of the gas flow channel grooves 26a and 26b, and the like are not particularly limited, and may be appropriately determined in consideration of output characteristics of the obtained fuel cell.

(E) Gasket The gasket 27 may be impermeable to gas, particularly oxygen or hydrogen gas, but generally includes a single impermeable portion such as an O-ring made of a gas impermeable material. It only has to be done. Further, if necessary, a composite such as a gas seal tape with an adhesive, which is provided with an adhesive portion for adhesion to the electrolyte membrane 21 and the edges of the oxygen electrode and the fuel electrode catalyst layers 22a and 22b. It is good also as a simple structure. There are no particular limitations on the material that forms the impervious portion of the O-ring or gas seal tape as long as it is impervious to oxygen and hydrogen gas in a state where a predetermined pressure is applied after installation.

  Among the materials constituting the impervious portion, examples of the material constituting the O-ring include rubber materials such as fluorine rubber, silicon rubber, ethylene propylene rubber (EPDM), polyisobutylene rubber, and polytetrafluoroethylene (PTFE). , Fluorine polymer materials such as polyvinylidene fluoride (PVDF), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and thermoplastic resins such as polyolefin and polyester.

  On the other hand, examples of the material constituting the impermeable portion such as a gas seal tape include polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVdF). . In addition, the material constituting the bonding portion such as a gas seal tape is not particularly limited as long as the electrolyte membrane 21, the oxygen electrode and the fuel electrode catalyst layers 22a and 22b, and the gasket 27 can be closely bonded. For example, hot melt adhesives such as polyolefin, polypropylene, and thermoplastic elastomer, acrylic adhesives, olefin adhesives such as polyester and polyolefin, and the like can be used.

  The method for forming the gasket 27 is not particularly limited, and a known method can be used. For example, the adhesive is applied on the electrolyte membrane 21 or on the electrolyte membrane 21 while covering the edge of the electrode catalyst layer 22 so as to have a thickness of 5 to 30 μm. Thereafter, a method of applying the gas-impermeable material as described above to a thickness of 10 to 200 μm and curing it by heating at 25 to 150 ° C. for 10 seconds to 10 minutes can be used. Alternatively, after a gas-impermeable material is formed into a sheet shape in advance, an adhesive is applied to the impermeable film to form a gasket 27, which is then placed on the electrolyte membrane 21 or a part of the gasket 27. You may affix on the electrolyte membrane 21, covering. At this time, the thickness of the impermeable portion is not particularly limited, but is preferably 15 to 40 μm. The thickness of the adhesive part is not particularly limited, but is preferably 10 to 25 μm.

  About the said gasket 27, you may purchase and use a commercially available thing. The commercial items mentioned here include ordered items or custom-made items manufactured by the manufacturer according to the specifications (size, shape, material, characteristics, etc.) on the purchaser side.

  In the fuel cell having the configuration of the MEA 24 of the present invention, the electrode catalyst layer 22, the GDL 23, and the electrolyte membrane 21 are desirably thin to improve the diffusibility of the fuel gas. The electrode output cannot be obtained. Therefore, it may be determined as appropriate so as to obtain an MEA (fuel cell) having desired characteristics.

  In the fuel cell of the present invention, the electrode catalyst layer 22 is inside, the GDL 23 is outside, the electrolyte membrane 21 is used, and the electrolyte membrane 21 is sandwiched between the electrode catalyst layers 22 from both sides and appropriately hot pressed. Thus, the MEA 24 can be manufactured.

  As such hot press conditions, it is desirable to set appropriate temperature and pressure. Specifically, it is desirable to heat to 130 to 200 ° C., preferably 140 to 160 ° C., and hot press at 1 MPa to 5 MPa, preferably 2 MPa to 4 MPa for 1 to 10 minutes, preferably 3 to 7 minutes. If the hot press temperature is 130 ° C. or higher (the film is softened and bonding is easy. If the hot press temperature is 200 ° C. or lower, the film can be prevented from being decomposed. Also, the hot press pressure is 1 MPa or higher. If the hot press pressure is 5 MPa or less, problems such as film perforation can be prevented, and if the hot press time is 1 minute or longer, joining is easy. In addition, if the hot press time is 10 minutes or less, it is possible to prevent defects such as film perforations, etc. The atmosphere during hot pressing is preferably an atmosphere that does not affect the MEA, such as in nitrogen. It is desirable to carry out in an atmosphere.

  In addition, the method for producing the fuel cell of the present invention is not particularly limited, and can be assembled using a conventionally known production technique. For example, a catalyst ink is applied and dried on an electrolyte membrane, followed by hot pressing, the electrode catalyst layer is joined to the electrolyte membrane, and the resulting joined body is sandwiched between gas diffusion layers to form MEA; Ink may be applied to the gas diffusion layer and dried to form an electrode catalyst layer, which may be joined to the electrolyte membrane by hot pressing, or any other known technique may be used as appropriate.

  The type of the fuel cell is not particularly limited. In the above description, the polymer electrolyte fuel cell has been described as an example, but in addition to this, an alkaline fuel cell, a direct methanol fuel cell, a micro fuel A battery etc. are mentioned. Among them, a polymer electrolyte fuel cell (PEFC) is preferable because it is small and can achieve high density and high output. The fuel cell is useful as a stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. However, the fuel cell is particularly useful for an automobile application in which system start / stop and output fluctuation frequently occur. It can be particularly preferably used.

  The application of the fuel cell is not particularly limited, but it is preferably applied to a vehicle. The electrolyte membrane-electrode assembly described above is excellent in power generation performance and durability, and can be downsized. For this reason, a fuel cell using this is particularly advantageous when the fuel cell is applied to a vehicle from the viewpoint of in-vehicle performance.

  In particular, the polymer electrolyte fuel cell is useful as a power source for a mobile body such as an automobile in which a mounting space is limited in addition to a stationary power source. In particular, it is particularly preferable to be used as a power source for a mobile body such as an automobile that requires a high output voltage after a relatively long time of operation stop.

  The effect of this embodiment will be described using the following examples. However, the technical scope of this embodiment is not limited to the following examples.

  First, the outline of the preparation procedure of the electrode catalyst of Example 1, 2 is shown in FIG.

<Example 1 (Pt / Ni / Au / C)>
0.968 g of chloroauric acid aqueous solution (9.26 wt%) was weighed in a beaker for catalyst preparation, and 300 mL of ultrapure water cooled to 10 ° C. or lower was added thereto, and solution A (0.435 mM, 500 mL) and did.

  In another beaker, 0.31 g of trisodium citrate dihydrate was weighed, 50 mL of ultrapure water was added, and it was completely dissolved by ultrasonic waves. Thereafter, 0.1 g of sodium borohydride was added and dissolved to obtain a solution B. When 25 mL of this solution B was weighed and added to the above solution A, the color of the solution immediately changed from yellow to reddish purple. This solution was continuously stirred for 30 minutes to obtain a solution C.

  Next, 0.6 g of trisodium citrate dihydrate was weighed into another beaker, 50 mL of ultrapure water was added, and the solution was completely dissolved by ultrasonic waves. Thereafter, 0.2 g of sodium borohydride was added and dissolved to obtain a solution E. Further, 11 mL (0.105 M) of nickel chloride / hexahydrate aqueous solution (solution D) was weighed and added to the red-purple solution C. Subsequently, the whole amount of the solution E was added, and stirring was continued for 30 minutes. By the above procedure, the color of the solution changed to black (solution F).

  Next, 6.3 mL of chloroplatinic acid aqueous solution (30 mM) (solution G) was added, and stirring was continued for 30 minutes (solution H).

  Thereafter, a dispersion of 0.1 g of ketjen black (average particle size 50 nm) was added to the solution H, and stirring was continued for about 60 hours to support the catalyst metal on the surface of the carbon support.

  Thereafter, filtration was performed, the plate was thoroughly washed with ultrapure water three times, and dried at 60 ° C. for 4 hours or more. The obtained substance was used as an electrode catalyst.

<Example 2 (Pt / Co / Au / C)>
0.968 g of chloroauric acid aqueous solution (9.26 wt%) was weighed in a beaker for catalyst preparation, and 300 mL of ultrapure water cooled to 10 ° C. or lower was added thereto, and solution A (0.435 mM, 500 mL) and did.

  In another beaker, 0.31 g of trisodium citrate dihydrate was weighed, 50 mL of ultrapure water was added, and it was completely dissolved by ultrasonic waves. Thereafter, 0.1 g of sodium borohydride was added and dissolved to obtain a solution B. When 25 mL of this solution B was weighed and added to the above solution A, the color of the solution immediately changed from yellow to reddish purple. This solution was continuously stirred for 30 minutes to obtain a solution C.

  Next, 0.6 g of trisodium citrate dihydrate was weighed into another beaker, 50 mL of ultrapure water was added, and the solution was completely dissolved by ultrasonic waves. Thereafter, 0.2 g of sodium borohydride was added and dissolved to obtain a solution E. Further, 11 mL (0.105 M) of cobalt chloride hexahydrate aqueous solution (solution D) was weighed and added to the red-purple solution C. Subsequently, the whole amount of the solution E was added, and stirring was continued for 30 minutes. By the above procedure, the color of the solution changed to black (solution F).

  Next, 6.3 mL of chloroplatinic acid aqueous solution (30 mM) (solution G) was added, and stirring was continued for 30 minutes (solution H).

  Thereafter, a dispersion of 0.1 g of ketjen black (average particle size 50 nm) was added to the solution H, and stirring was continued for about 60 hours to support the catalyst metal on the surface of the carbon support.

  Thereafter, filtration was performed, the plate was thoroughly washed with ultrapure water three times, and dried at 60 ° C. for 4 hours or more. The obtained substance was used as an electrode catalyst.

<Comparative Example 1 (Pt / C)>
Add 1.0 g of ketjen black and 40 mL of methanol as a reducing agent to a separable flask for catalyst preparation, add 200 g of 0.5 wt% diaminedinitroplatinum nitrate aqueous solution to the solution, heat to 85 ° C., 6 hours Stirring was performed. At this time, the upper part of the separable flask was connected to a reflux tube, and the reaction was carried out under reflux conditions. Thereafter, filtration was performed, the plate was thoroughly washed with ultrapure water three times, and dried at 60 ° C. for 4 hours or more. The obtained substance was used as an electrode catalyst.

<Comparative Example 2 (Pt / Au / C)>
Solution C was prepared in the same procedure as in Example 1 above.

  The reducing agent was weighed in another beaker, ultrapure water was added, and it was completely dissolved by ultrasonic waves to prepare a reducing agent solution. Next, 6.3 mL of chloroplatinic acid aqueous solution (30 mM) was added to Solution C, then the above reducing agent solution was added, and stirring was continued for 30 minutes.

  Thereafter, a dispersion of 0.1 g of ketjen black (average particle size 50 nm) was added, and stirring was continued for about 60 hours to support the catalyst metal on the surface of the carbon support.

  Thereafter, filtration was performed, the plate was thoroughly washed with ultrapure water three times, and dried at 60 ° C. for 4 hours or more. The obtained substance was used as an electrode catalyst.

<Observation using transmission electron microscope (TEM)>
FIG. 5 is a photograph showing a TEM measurement result of the electrode catalyst prepared in Example 1. The measurement was performed using a field emission type transmission electron microscope HF-2000 manufactured by Hitachi, Ltd. The acceleration voltage was 200 kV. The pretreatment was performed by a suspension method. From FIG. 5, it was confirmed that the electrode catalyst particles of Example 1 were particles having an average particle diameter of about 5 nm.

<ICP analysis>
Table 1 shows the results of ICP analysis of the electrode catalyst prepared in Example 1. ICP analysis was measured using an inductively coupled plasma emission spectrometer SPS-3500 manufactured by SII Nanotechnology. The pretreatment was performed by a melting method.

  From Table 1 above, it can be seen that the supported amount of Ni is significantly reduced from the charged amount. From this, it can be confirmed that the precipitation of Pt is due to a substitution reaction between Ni and Pt ions. Further, from the TEM observation (not shown) of Au particles prepared on the ketjen black (Au / C) prepared by the same method as the metal particles of Example 1, the average particle diameter of Au is about 3 nm. It was confirmed that. From the average particle diameter of this Au and the results of elemental analysis in Table 1, it was found that there was approximately 1 atomic layer of Ni and approximately 2 atomic layers of Pt.

  Further, from the CV characteristics of the electrode catalyst Pt / Ni / Au / C of Example 1 shown in FIG. 6A, a peak due to Au in the vicinity of 1.15 V (vs. RHE) is shown in Comparative Example 2 in FIG. 6B. It was confirmed that it was reduced as compared with Pt / Au / C. From this, it was found that in the electrode catalyst of Example 1, the area of Au exposed on the surface was small, and the Pt coverage was significantly improved.

<Oxygen reduction activity evaluation>
A three-electrode electrochemical cell was used, and Hokuto Denko's electrochemical system HZ-5000 was used as a potentiostat. As a working electrode, a glassy carbon rotating electrode (GC-RDE) was used, and an electrode obtained by coating and drying an ink in which the electrode catalyst prepared in Examples and Comparative Examples was dispersed in a dispersion medium was used. The electrode area was 0.196 cm ² . A platinum wire was used as the counter electrode, and a reversible hydrogen electrode was used as the reference electrode. The electrolyte was saturated with O ₂ using 0.1 M perchloric acid. The measurement was performed at 25 ° C.

The catalytic effective surface area (ECA) was calculated by cyclic voltammetry (CV). Prior to the measurement, a 20-cycle potential scan was performed in a potential range of 0 to 1.2 V at a potential sweep rate of 500 mV / s (catalyst surface cleaning treatment). Thereafter, a potential range of 0 to 1.2 V was measured for 3 cycles at a potential sweep rate of 50 mV / s. Using the data of the third cycle at this time, the effective surface area of the catalyst was calculated using the amount of electricity of hydrogen adsorption 210 μC / cm ² .

The oxygen reduction activity evaluation was calculated using the Koutecky-levich equation. Here, by subtracting the current in the N ₂ atmosphere from the result in O ₂ , a current not resulting from the oxygen reduction reaction was subtracted.

Table 2 and FIGS. 7 and 8 show the catalytic activities of the electrode catalysts prepared in the examples and comparative examples. FIG. 7 is a graph showing a comparison of mass specific activities of the respective electrode catalysts. FIG. 8 is a diagram in which the mass specific surface area (m ² / g) and the area specific activity (μA / cm ² ) of platinum of each electrode catalyst are plotted, and the mass specific activity increases toward the upper right of the graph. Represents high performance. In addition, the mass specific activity of the electrode catalyst of a prior art example is the value calculated | required by calculation from the result of the cited reference 1. FIG.

  From the results of Table 2 and FIGS. 7 and 8, the electrocatalyst prepared in the examples of the present application has a higher mass compared to Pt / C, Pt / Au / C, and Pt / Au / Ni / C that are conventionally used. It became clear to show specific activity.

10 electrocatalyst particles,
11 metal particles,
12 first metal layer,
13 second metal layer,
20 fuel cells,
21 electrolyte membrane,
22 Fuel cell electrode catalyst layer,
22a Anode side electrocatalyst layer,
22b cathode catalyst layer,
23 Gas diffusion layer,
23a Anode gas diffusion layer,
23b cathode gas diffusion layer,
24 Electrolyte membrane-electrode assembly (MEA),
25a anode separator,
25b cathode separator,
26a Anode side gas flow path (groove),
26b cathode side gas flow path (groove),
27 Gasket.

Claims (10)

Electrocatalyst particles having a three-layer structure in which a first metal layer is disposed on the surface of the metal particles, and a second metal layer is disposed on the surface of the first metal layer,
The metal constituting the first metal layer, base metal der Ri than the metal constituting the metal and the second metal layer constituting the metal particles,
The metal constituting the metal particles is Au,
The metal constituting the first metal layer includes Co, Ni, or a composite of these metals,
Electrocatalyst particles characterized in that the metal constituting the second metal layer contains platinum .   The electrode catalyst particle according to claim 1, wherein the second metal layer has a thickness of 50 atomic layers or less. An electrode catalyst comprising the electrode catalyst particles according to claim 1 or 2 supported on a conductive carrier. An electrochemical device comprising the electrode catalyst according to claim 3 . The electrochemical device according to claim 4 , which is a fuel cell. A method for producing electrocatalyst particles having a three-layer structure in which a first metal layer is disposed on the surface of a metal particle, and a second metal layer is disposed on the surface of the first metal layer,
Adding a first reducing agent to a solution containing metal ions constituting the metal particles to obtain a colloidal dispersion containing metal particles;
In the colloid dispersion liquid, ions of the metal constituting the first metal layer, the metal constituting the metal particles and the metal constituting the second metal layer, and the second reduction. Adding an agent to form the first metal layer on the surface of the metal particles;
Further, ions of a metal constituting the second metal layer are further added to the solution obtained in the step of forming the first metal layer, and the second metal layer is formed on the surface of the first metal layer. Forming and obtaining electrocatalyst particles;
Only including,
The metal constituting the metal particles is Au,
The metal constituting the first metal layer includes Co, Ni, or a composite of these metals,
The method for producing electrode catalyst particles, wherein the metal constituting the second metal layer contains platinum . The method for producing electrocatalyst particles according to claim 6 , wherein the metal ion concentration of the metal constituting the metal particle at the time of preparing the colloidal dispersion containing the metal particle is 2.5 mM or less. The method for producing electrode catalyst particles according to claim 6 or 7 , wherein the first metal layer has a thickness of 50 atomic layers or less. The electrocatalyst particles having a three-layer structure in which the first metal layer is disposed on the surface of the metal particles and the second metal layer is disposed on the surface of the first metal layer are supported on the conductive carrier. A method for producing an electrode catalyst, comprising:
Adding a first reducing agent to a solution containing metal ions constituting the metal particles to obtain a colloidal dispersion containing metal particles;
In the colloid dispersion liquid, ions of the metal constituting the first metal layer, the metal constituting the metal particles and the metal constituting the second metal layer, and the second reduction. Adding an agent to form the first metal layer on the surface of the metal particles;
Further, ions of a metal constituting the second metal layer are further added to the solution obtained in the step of forming the first metal layer, and the second metal layer is formed on the surface of the first metal layer. Forming and obtaining electrocatalyst particles;
Supporting the electrocatalyst particles on a conductive carrier;
Only including,
The metal constituting the metal particles is Au,
The metal constituting the first metal layer includes Co, Ni, or a composite of these metals,
The method for producing an electrode catalyst, wherein the metal constituting the second metal layer contains platinum . The method for producing an electrode catalyst according to claim 9 , wherein the amount of the electrode catalyst particles supported on the conductive carrier is 5 to 60% by mass.