JP6245066B2 - Catalyst particles for polymer electrolyte fuel cell, catalyst using the same, and polymer electrolyte fuel cell - Google Patents

Description

  The present invention relates to a catalyst particle for a polymer electrolyte fuel cell used in a polymer electrolyte fuel cell, a catalyst for a polymer electrolyte fuel cell formed using the catalyst particle, and a catalyst formed using the catalyst The present invention relates to a polymer electrolyte fuel cell.

  In a general polymer electrolyte fuel cell, a catalyst layer serving as an anode and a catalyst layer serving as a cathode are disposed with a proton conductive electrolyte membrane interposed therebetween, and a gas diffusion layer is disposed on the outside of the catalyst layer sandwiching these layers. And having a basic structure in which a separator is disposed outside the gas diffusion layer with these interposed therebetween, and in order to achieve a required output, the above basic structure is usually used as a unit cell, and a necessary number of units are provided. Cells are stacked to form a battery.

In order to take out the current from the solid polymer fuel cell having such a basic structure, oxygen or air or the like is provided on the cathode side through the gas diffusion layer from the gas flow path of the separator disposed on both electrodes of the anode and the cathode. Further, a reducing gas such as hydrogen is supplied to the catalyst layer on the anode side, and an electric current is taken out using a chemical reaction of the reducing gas and the oxidizing gas that occurs in each catalyst layer. For example, when the reducing gas is hydrogen gas and the oxidizing gas is oxygen gas, the following chemical reaction (1) that occurs on the catalyst particles of the anode side catalyst layer and on the catalyst particles of the cathode side catalyst layer: The electric current is taken out by utilizing the energy difference (potential difference) between the following chemical reaction (2) occurring in step (2).
H ₂ → 2H ⁺ + 2e ⁻ (E ₀ = 0V) (1)
O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (E ₀ = 1.23 V) (2)

  The anode-side and / or cathode-side catalyst layer used in the chemical reactions (1) and (2) has a catalytic metal having a function of promoting these necessary chemical reactions (1) and (2). Specifically, pure metals such as platinum, palladium, gold, tungsten, cobalt, nickel, tantalum, zirconium and molybdenum, and metal compounds such as carbides and nitrides can be used, but Pt is the highest as a pure metal. In general, platinum (Pt) or a Pt alloy containing Pt as a main component is used because of its reactive activity. Here, as the metal element used together with Pt, there are Co, Ni, Fe, Pd, Au, Ru, Rh, Ir and the like for the purpose of improving the activity as a catalyst metal. If the amount of the metal element other than Pt exceeds 50 at%, the ratio of the metal element other than Pt on the catalyst metal particle surface increases, and it dissolves under the operation of the fuel cell and the power generation performance may decrease. Therefore, the atomic composition percentage with respect to Pt is usually 50 at% or less.

  In a polymer electrolyte fuel cell, a perfluorosulfonic acid polymer that is a polymer electrolyte material is generally used as a proton conductive electrolyte membrane disposed between an anode side catalyst layer and a cathode side catalyst layer. Since the sulfonic acid group is present in the side chain of this polymer, the catalyst metal present in these catalyst layers is exposed to strong acidic conditions, and the potential fluctuates during continuous operation of the fuel cell. In addition, oxygen gas having oxidizing properties is supplied. For this reason, even when platinum having properties such as excellent acid resistance, oxidation resistance, and difficulty in dissolving under potential fluctuations compared to other catalytic metals is used as the catalytic metal, the aggregation of platinum particles gradually increases. Dissolution occurs, the surface area of the platinum particles involved in the power generation reaction is reduced, and the performance of the fuel cell is reduced.

  In addition, since platinum (Pt) has limited resource reserves and is expensive, the national industrial policy is to reduce the amount of platinum catalyst used (independent administrative agency). New Energy and Industrial Technology Development Organization Fuel Cell and Hydrogen Technology Development Roadmap 2010).

  Therefore, in order to achieve the low cost of the polymer electrolyte fuel cell and to promote the use thereof, the amount of platinum used in the catalyst particles for the fuel cell is reduced as much as possible, and the operating conditions of the fuel cell are reduced. It is possible to suppress aggregation and dissolution of catalyst particles even under strongly acidic conditions, high potential conditions, and potential fluctuations during continuous operation, thereby exhibiting stable power generation performance over a long period of time. It is essential to develop a catalyst that can be produced.

Thus, several attempts have been made in the past to reduce the amount of platinum used in the polymer electrolyte fuel cell and to improve the durability of the catalyst particles used.
For example, Non-Patent Document 1 and Patent Document 1 propose core-shell type catalyst fine particles in which palladium is used as the central metal particle and platinum is used for the metal catalyst coating layer covering the central metal particle. However, in such a core-shell type catalyst fine particle, palladium is used for the central metal particle, so that if a defect occurs in the platinum catalyst coating layer, palladium is easily eluted, and even if the initial characteristics are high, the core layer There is a problem that the central metal particles are eluted. This problem is inevitable that the elution of the central metal particles proceeds as long as palladium, which is easily dissolved under the operating conditions of the fuel cell with respect to platinum, is used.

  Moreover, in patent document 2, it is set as the 3 layer structure which consists of the metal particle located centering on a core-shell type electrocatalyst particle, the 1st metal layer located on the outer side, and the 2nd metal layer located further on the outer side. Electrocatalyst particles have been proposed in which a high catalytic activity is expressed by a combination of the three types of metal species. However, in the electrocatalyst particles having the three-layer structure, a base metal is used as the metal species in the first metal layer as compared with the metal in the second metal layer. Under the high potential conditions and during potential fluctuations during continuous operation, this base metal elution is inevitable, and as a result, the durability of the electrocatalyst particles is inevitably lowered.

  Further, Patent Document 3 proposes a carbon material-based catalyst that does not use platinum, and Patent Document 4 proposes a metal oxide-based catalyst that does not use platinum. However, such non-platinum catalysts have power generation performance that does not reach that of platinum catalysts. If the amount of catalyst used is increased in order to improve power generation characteristics, the thickness of the catalyst layer increases and the supplied oxidizing gas or reducing property The gas permeability deteriorates, and the oxidizing gas and reducing gas that can reach the catalyst layer are reduced. In this case, satisfactory power generation performance cannot be obtained. Furthermore, in the case of long-term power generation, hydrogen peroxide may be generated as a by-product with water as a product. This hydrogen peroxide chemically degrades the proton conductive electrolyte membrane, and the fuel cell. There is a concern that power generation performance will be adversely affected.

  Patent Documents 5 to 7 describe that by providing a ruthenium oxide or silicon oxide coating layer on the surface of the catalyst particles, aggregation and elution of the catalyst particles can be suppressed and a highly durable catalyst can be provided. However, since a coating layer of metal oxide is provided on the surface of the catalyst particles, the surface area of the catalyst particles that react when the oxidizing gas or reducing gas comes into contact is reduced, and a decrease in the activity of the catalyst particles is inevitable. is there.

  Furthermore, Non-Patent Document 2 describes that the use of a metal oxide as a carrier causes a strong interaction between the metal catalyst particles and changes the characteristics of the metal catalyst particles. By using tin oxide as the carrier and platinum particles as the metal catalyst particles, and precisely controlling the reducing atmosphere and the oxidizing atmosphere, the structure of the platinum particle surface changes, and the catalyst performance is optimized and deteriorated. It is said that the catalyst can be recovered. Further, in Patent Document 8, by using a support based on tin oxide as a catalyst support, there is no oxidative consumption of carbon observed when a carbon material is used as the catalyst support, and a highly durable result is obtained. Has been reported. Further, Patent Document 9 proposes a fuel cell catalyst that uses titanium carbide or titanium oxide as a catalyst carrier and has excellent catalytic activity and durability. Further, in Non-Patent Document 3, an effort is made to impart electronic conductivity to the metal oxide by using the oxygen deficiency of titanium oxide to impart conductivity.

  However, as in Non-Patent Document 2, Patent Document 8, and Non-Patent Document 3, when a metal oxide is used instead of a carbon material as a catalyst carrier, the oxidation of carbon observed in the case of a carbon material. Although the problem due to wear is resolved, the metal oxide has low electronic conductivity. Further, in the case of metal oxide using oxygen deficiency, the catalyst support is again formed due to the influence of oxygen gas supplied under the operation of the fuel cell. There is a possibility of being oxidized, and it cannot be said that the battery performance of the fuel cell is sufficiently improved. In the case of Patent Document 9, since the majority of platinum particles are present in titanium atoms (titanium carbide and titanium oxide), the operating conditions of the fuel cell (oxidizing gas atmosphere, acidic conditions, high It is expected that the platinum particles will be coated with titanium oxide at the potential), and in this case, as in the case of Patent Documents 5 to 7, the oxidizing gas and reducing gas that can reach the surface of the platinum particles are reduced, and the fuel There is concern about the long-term power generation performance of the battery.

  Further, in Patent Document 10, it is proposed that, in a tin oxide-modified carbon support obtained by adsorbing tin oxide on a carbon material, the oxidative consumption of the carbon support is suppressed by controlling the thickness of the tin oxide. However, the catalytic metal platinum is not selectively supported on tin oxide, and it cannot be said that the dissolution and aggregation of platinum can be sufficiently suppressed. Further, the particle size of tin oxide is about several tens of nm, and it is difficult to say that electron conductivity is sufficiently ensured.

JP 2013-239,331 JP 2013-080,683 JP JP 2007-207,662 A JP 2008-108,594 JP 2013-058,429 JP 2008-004,541 A JP 2012-022,960 WO09 / 060582 Publication JP 2013-127,869 JP 2012-000,525 JP

R.R.Adzic et al., J. Phys. Chem. B, 108, 10955 (2004) Eguchi et al., Microscope Vol. 46, No.1 (2011) T. Ioroi et al., Phys. Chem. Chem. Phys., 12 7529 (2010)

  Therefore, the inventors reduced the above-mentioned problem, that is, the amount of platinum used as much as possible, and the operating conditions of the fuel cell (strongly acidic conditions, high potential conditions, and potential fluctuations during continuous operation). As a result of intensive studies to develop new catalyst particles for fuel cells that can suppress agglomeration and dissolution in (b)), a predetermined center metal particle and a catalyst metal particle made of Pt or Pt alloy A barrier layer in which the metal oxide coating layer of the intermediate layer suppresses the elution of the central metal particles by using the core-shell type three-layer catalyst particles provided with the predetermined metal oxide coating layer for coating the central metal particles In addition to reducing the amount of platinum (Pt) used as catalyst metal particles, it can also function under the operating conditions of the fuel cell. It can suppress aggregation and dissolution Headlines, and completed the present invention.

  Therefore, the object of the present invention is to reduce the amount of platinum used as much as possible, and also under fuel cell operating conditions (strongly acidic conditions, high potential conditions, and under potential fluctuations during continuous operation). It is an object of the present invention to provide new catalyst particles for a polymer electrolyte fuel cell that can suppress aggregation and dissolution.

  In addition, another object of the present invention is for a polymer electrolyte fuel cell using catalyst particles in which the amount of platinum used is reduced and the aggregation and dissolution under the operating conditions of the fuel cell are suppressed. It is to provide a catalyst and to provide a polymer electrolyte fuel cell using the catalyst.

That is, the present invention is as follows.
(1) Catalyst particles for a polymer electrolyte fuel cell having a three-layer structure of central metal particles, a metal oxide coating layer covering the central metal particles, and catalytic metal particles supported on the metal oxide coating layer The central metal particle is a metal particle composed of at least one selected from Pd, Cu, Co, Ni, and Au, and has a particle size in the range of 5 to 10 nm, and The metal element of the metal oxide forming the metal oxide coating layer is a metal composed of at least one selected from Si, Ti, Sn, and Zr, and the thickness of the metal oxide coating layer is 1 to Solid polymer form, characterized in that it is in the range of 4 nm, and the catalyst metal particles are Pt or a Pt alloy containing Pt as a main component, and the particle size thereof is in the range of 1 to 3 nm. Catalyst particles for fuel cells.

(2) The center metal particle has a particle size in the range of 5 to 7 nm, and the catalyst metal particle has a particle size in the range of 1 to 2 nm. Catalyst particles for polymer electrolyte fuel cells.
(3) The catalyst particle for a polymer electrolyte fuel cell according to (1) or (2), wherein the metal element of the metal oxide coating layer is a metal composed of at least one selected from Si and Ti.

(4) A catalyst for a polymer electrolyte fuel cell, wherein the catalyst particles for a polymer electrolyte fuel cell described in any one of (1) to (3) above are supported on a carbon support .
(5) A polymer electrolyte fuel cell, characterized in that the catalyst for a polymer electrolyte fuel cell described in (4) is used for either or both of the positive electrode and the negative electrode.

  According to the present invention, the amount of platinum used is small, and the polymer electrolyte fuel cell does not aggregate or dissolve under the operating conditions of the fuel cell (strongly acidic condition, high potential condition, and potential fluctuation during continuous operation). Catalyst particles for solid polymer fuel cells that can provide stable power generation performance over a long period of time when used as a catalyst for solid polymer fuel cells Thus, the polymer electrolyte fuel cell can be provided, whereby the cost and spread of the polymer electrolyte fuel cell can be achieved.

FIG. 1 is a schematic view for explaining catalyst particles of the present invention. FIG. 2 is a STEM image showing the catalyst particles of Example 3 in which the central metal particles are Pd particles, the metal oxide coating layer is a SiO ₂ coating layer, and the catalyst metal particles are Pt particles. .

  As shown in the schematic diagram of FIG. 1, the catalyst particles for a polymer electrolyte fuel cell of the present invention include a central metal particle 3, a metal oxide coating layer 2 covering the central metal particle 3, As a barrier layer having a core-shell type three-layer structure composed of catalyst metal particles 1 supported on the metal oxide coating layer, the metal oxide coating layer 2 of the intermediate layer suppresses elution of the central metal particles 3 In addition to functioning and exhibiting a predetermined interaction with the catalytic metal particles 1, not only can the amount of platinum (Pt) used as the catalytic metal particles 1 be reduced, but also the operating conditions when used as a fuel cell. Suppresses aggregation and dissolution of catalyst particles underneath.

Here, the present inventors consider the “interaction between the metal oxide coating layer 2 and the catalyst metal particles 1” as follows.
That is, oxygen atoms in the metal oxide of the metal oxide coating layer 2 in contact with the catalyst metal particles 1 are locally polarized to negative charges, while the catalyst metal particles 1 in contact with the metal oxide coating layer are locally positive. The surface of the catalytic metal particle 1 that is polarized to electric charge and is in contact with the oxidizing gas or reducing gas under the operating condition of the fuel cell is locally negatively charged, thereby suppressing fluctuations in the oxidation number of the catalytic metal particle. As a result, when the oxidizing gas or reducing gas supplied to the fuel cell comes into contact with the catalyst particles, the catalyst particles are aggregated without inhibiting the reaction on the surface of the catalyst metal particles 1. Dissolution can be suppressed.

  In the present invention, the metal oxide coating layer functions as a barrier layer that suppresses elution of the central metal particles as described above, and in order to express a desired interaction with the catalyst metal particles, Since this metal oxide coating layer may hinder electronic conductivity, the thickness of the metal oxide coating layer is ensured to function as a barrier layer and not to hinder electronic conductivity. It is necessary to control to the order of several nanometers.

  In the present invention, the central metal particle of the catalyst particle is a material that has electronic conductivity and is difficult to dissolve under the operating conditions of the fuel cell, and in order to increase its surface area, it is 5 nm to 10 nm, preferably It is selected from elements that can be synthesized as nanoparticles in the range of 5 nm to 7 nm, and specific examples include Pd, Cu, Co, Ni, and Au. Here, for example, Ag has excellent electron conductivity, is less soluble than Co, Ni, and Cu under the operating conditions of the fuel cell, and further, the synthesis of nanoparticles is easy. Has a melting point of 962 ° C., which is lower than that of Pd (1555 ° C.), Co (1495 ° C.), Ni (1455 ° C.), Cu (1085 ° C.), and Au (1064 ° C.). When there are many potential fluctuations, a complex solid solution with Pt and the metal oxide coating layer is likely to be formed, Pt is dissolved in Ag of the central metal particle, and the number of Pt atoms existing on the surface of the catalyst particle is reduced. The battery performance of the fuel cell is reduced.

  Further, when the particle diameter of the central metal particles is less than 5 nm, in the production process for producing the catalyst particles, when the central metal particles are coated with the metal oxide, the metal oxide is not contained in the reaction solution. Precipitation as particles takes precedence over precipitation on the surface, and it becomes difficult to form catalyst particles having a target core-shell three-layer structure.

On the other hand, when the particle diameter of the central metal particle is larger than 10 nm, the “surface area per weight of the central metal particle when used as a catalyst for a polymer electrolyte fuel cell” on which the catalyst particle is supported becomes small. However, satisfactory performance as a fuel cell cannot be obtained. “The surface area per weight of the central metal particles when used as a catalyst for a solid polymer fuel cell” is not an expression referring to one nano-order central metal particle, but a solid polymer fuel cell. Means the total surface area of a plurality of central metal particles per unit weight of the catalyst (for example, in the case of 1 g catalyst, the total surface area of about 10 ¹³ to 10 ¹⁶ central metal particles) .)

  In the present invention, the metal oxide coating layer serving as the intermediate layer of the catalyst particles has a function as a barrier layer that does not dissolve the central metal particles, in addition to not dissolving under the operating conditions of the fuel cell. In order to ensure good electronic conductivity between the central metal particles and the catalytic metal particles, the central metal particles must be capable of being coated with a dense coating layer. It is necessary to be able to form a coating layer, and furthermore, a metal alkoxide can be formed as a synthetic starting material for forming a metal oxide covering the central metal particle, and a metal having a relatively small atomic radius is required. It is. Specific examples of metal elements suitable for forming such a metal oxide coating layer include Si, Ti, Sn, and Zr. Preferably, Si and Ti are mentioned.

  The thickness of this metal oxide coating layer is usually in the range of 1 nm to 4 nm, preferably 1 nm to 2 nm. If this thickness is less than 1 nm, the target core-shell type three layers When catalyst particles having a structure cannot be obtained, on the contrary, when the thickness is larger than 4 nm, resistance of electron conduction by the metal oxide coating layer is increased, and in the catalyst obtained by supporting the catalyst particles on a carbon support, The conductivity of the electron conduction from the catalyst metal particles of the catalyst particles to the carbon support via the central metal particles is hindered, and the cell performance of the fuel cell is lowered.

  Here, regarding the metal elements constituting the metal oxide coating layer, the atomic radii are as follows: Si is 118 pm, Ti is 147 pm, Zr is 160 pm, Sn is 140 pm, while the atomic radius of oxygen atoms is 60 pm. Therefore, no matter how thin the metal oxide coating layer is, it becomes 0.2 nm or more. In addition, when the metal oxide coats the three-dimensional spherical central metal particles, the growth in the vertical direction to which the metal oxide film forming source is supplied is more than the planar direction of the surface area of the sphere. Prioritizing, the optimum thickness for coating the entire central metal particle is necessarily greater than 1 nm. When the thickness of the metal oxide coating layer is less than 1 nm, it becomes difficult to coat the entire central metal particles with the metal oxide coating layer, and the central metal particles are eluted under the operating conditions of the fuel cell. The battery performance of the battery may be reduced.

  Furthermore, in the present invention, the catalyst metal particles constituting the catalyst particles have the ability to promote the chemical reactions (1) and (2) described above, and in addition, are metals that are difficult to dissolve under the operating conditions of the fuel cell. Pt or a Pt alloy containing Pt as a main component is used. Here, the Pt alloy is an alloy containing metal elements such as Co, Ni, Fe, Pd, Au, Ru, Rh, and Ir added for the purpose of improving the activity of catalytic metal particles in addition to Pt. These additive metal elements are added to the catalyst metal particles at an atomic composition percentage of 50 at% or less, and when the addition amount is higher than 50 at%, the presence ratio of the additive elements on the surface of the catalyst metal particles increases. In addition, the catalytic metal particles are easily dissolved under the operating conditions of the fuel cell, and the battery performance is degraded.

  The catalyst metal particles usually have a particle size of 1 nm or more and 3 nm or less, preferably 1 nm or more and 2 nm or less. When the particle size is smaller than 1 nm, the catalyst metal particles are supported. The surface free energy of the catalyst metal particles is larger than the interaction from the metal oxide coating layer, the catalyst particles are aggregated during the operation of the fuel cell, the surface area of the catalyst particles is reduced, and the cell performance is lowered. On the contrary, when the particle size of the catalyst metal particles is larger than 3 nm, the number of catalyst metal particles (Pt) present per catalyst metal particle is up to about 1000, and each of the catalyst particles is composed of The catalytic metal particles (Pt) cannot enjoy the effect of local polarization, and as in the case of conventional general catalytic metal particles for fuel cells, the agglomeration and dissolution of the catalyst particles occur and the surface area becomes small. As a result, the battery performance of the fuel cell deteriorates.

  The catalyst for a polymer electrolyte fuel cell of the present invention is a catalyst obtained by supporting the catalyst particles on a carbon support, and the carbon support for supporting the catalyst particles is not particularly limited. For example, porous carbon materials such as carbon black, graphite, carbon fiber, activated carbon and the like, pulverized products thereof, and carbon compounds such as carbon nanofiber can be used, and only one of them can be used alone. In addition, you may mix and use 2 or more types. Here, as a commercial product of carbon black, for example, Vulcan XC-72, Vulcan P, Black Pearls 880, Black Pearls 1100, Black Pearls 1300, Black Pearls 2000, Legal 400, etc. Ketjen Black EC, Oil Furnace Black such as # 3150 and # 3250 manufactured by Mitsubishi Chemical, Acetylene Black such as Denka Black manufactured by Denki Kagaku Kogyo, Ketjen EC and Ketjen EC-600Jd manufactured by Ketjen Black International Company Etc., Degussa's Printex XE2, Printex XE2-B, etc., Kuraray Chemical's YP, RP, and the like.

  In the present invention, the amount of catalyst particles supported in the catalyst (carbon support and catalyst particles) is not particularly limited, but the oxidizing gas or reducing gas is carbon under the operating conditions of the fuel cell. In order to efficiently diffuse and reach the surface of the catalyst particles through the carrier, the catalyst particles are usually 20% by mass or more and 80% by mass or less, preferably 20% by mass or more and 50% by mass or less in the catalyst. If the supported amount is less than 20% by mass, the thickness of the catalyst layer is increased and the permeability of the supplied oxidizing gas or reducing gas is deteriorated, so that the oxidizing gas or reducing agent that can reach the catalyst layer is reduced. In this case, there is a problem that satisfactory power generation performance cannot be obtained. On the other hand, if the amount exceeds 80% by mass, the catalyst layer becomes thin and the diffusibility of the oxidizing gas tends to be easy. There are metal catalyst particles As the distance between the particles becomes shorter, the catalyst particles tend to agglomerate, and the surface area of the catalyst particles decreases, which may cause a problem that the diffused oxidizing gas cannot react efficiently on the metal particle surface. is there.

  In the present invention, the method for preparing the central metal particles is not particularly limited. For example, a reducing agent is added to a solution containing metal ions selected from Pd, Cu, Co, Ni, and Au. Add a colloidal solution containing central metal particles (central metal particle colloidal solution). Here, the solution containing the metal ions is obtained by dissolving the metal chloride, nitrate, sulfate, metal chloride, etc. in a solvent such as water, alcohols, ketones or ethers. In addition, examples of the reducing agent include citric acids, ascorbic acids, carboxylic acids, hydrazine, hydrogen iodide, hydrogen sulfide, borohydride salts, and the like.

Further, the method of coating the surface of the central metal particle with the metal oxide coating layer is also particularly limited as long as the thickness of the metal oxide coating layer formed on the surface of the central metal particle can be adjusted. Instead, various known methods for coating metal particles with metal oxides can be applied. Specific examples include the methods described in Patent Document 6 (Japanese Patent Laid-Open No. 2008-004,541), GS News Technical Report 62 (2) pp46-53 (December 2003), and the like. For example, the central metal particle colloid solution prepared above is dispersed in an appropriate solvent such as water, a hydrophilic solvent, or a hydrophobic solvent to prepare a dispersion. For example, Si is used as the metal element of the metal oxide coating layer. In the case of selection, a surface treatment agent such as tetraethoxysilane (TEOS) or 3-aminopropylethoxysilane (APTE S) is added to the dispersion, and a hydrolysis / polymerization reaction is performed with stirring. After washing, separating and drying, firing at 200 to 1100 ° C. in an inert gas atmosphere, and further redispersing in an appropriate solvent such as a hydrophilic solvent or a hydrophobic solvent, a metal oxide coating layer There is a method of preparing a coated metal oxide coated central metal particle colloid.
In addition, the central metal particle colloid solution prepared above is dispersed in an appropriate solvent such as water, a hydrophilic solvent, or a hydrophobic solvent to prepare a dispersion, and the metal of the metal oxide coating layer is added to the dispersion. A metal compound such as a metal alkoxide of a metal selected from Si, Ti, Sn, and Zr can be added as an element, and a metal oxide-coated central metal particle colloid can be obtained by the same procedure as described above.

  Further, the method for supporting the catalyst metal particles on the metal oxide coating layer covering the central metal particles is not particularly limited, and various methods for supporting the conventionally known catalyst metal particles can be applied. . Specifically, for example, in the metal oxide-coated central metal particle colloid solution prepared above, an aqueous platinum precursor solution such as platinum chloride, nitrate, hydroxide and the like, citric acid, hydrazine, sodium borohydride A colloidal solution of catalyst particles is prepared by slowly dropping dropwise with stirring an aqueous solution of a reducing agent such as the above. Next, the catalyst particle colloidal solution is washed, separated, and dried to prepare core-shell type three-layer catalyst particles in which the catalyst metal particles are supported on the metal oxide coating layer covering the central metal particles. Etc. can be illustrated.

  Furthermore, the method for supporting the catalyst particles thus obtained on the carbon support is not particularly limited, and various methods for supporting the conventionally known catalyst metal particles can be applied. Specifically, for example, a predetermined carbon support is added to the catalyst particle colloid solution before separation prepared above, and maintained under a predetermined temperature and time under an inert gas atmosphere, and then washed. Examples thereof include a method of preparing a catalyst in which catalyst particles are supported on a carbon support by separating and drying.

  Hereinafter, based on an Example and a comparative example, the catalyst particle and catalyst for solid polymer fuel cells of this invention, and a solid polymer fuel cell are demonstrated concretely.

1. Preparation of catalyst particles In the following examples and comparative examples, catalyst particles were prepared by the following method.
(1) Synthesis of colloidal solution of central metal particles 7.0 g of 0.056 mol / L metal chloride aqueous solution (PdCl ₂ , CoCl ₂ , NiCl ₂ , AuCl ₃ , CuCl ₂ ) was measured in a three-necked flask and 30 g of distilled water. Is added to dilute to prepare a metal chloride aqueous solution, and 0.0879 g of polyvinylpyrrolidone (molecular weight 10000) is measured and diluted with 30 g of distilled water to prepare a polyvinylpyrrolidone aqueous solution. A polyvinylpyrrolidone aqueous solution was put into a three-necked flask containing and mixed to prepare a mixed aqueous solution containing a metal chloride and polyvinylpyrrolidone.

  Next, after stirring the mixed aqueous solution of the obtained metal chloride and polyvinylpyrrolidone for 5 minutes, 140 mL of ethylene glycol was added, and the resulting mixture was added at 160 ° C. and 180 ° C. under an argon flow atmosphere of 100 mL / min. After reacting under the condition of minutes, the mixture was allowed to cool to room temperature to obtain a central metal particle colloid.

When the colloidal solution of central metal particles of Co, Ni, and Cu was prepared, after completion of the above reaction, it was maintained at 25 ° C. for 30 minutes in a hydrogen flow atmosphere of 100 mL / min, and then the hydrogen was removed. For the purpose of gassing, it was kept for 30 minutes in an argon flow atmosphere of 100 mL / min.
Furthermore, in the case of Ni, 5 times the amount of N ₂ H ₄ · H ₂ O was added to the amount of NiCl ₂ , and it was confirmed that the central metal particle colloid solution turned from colorless to black.

(2) Formation of metal oxide coating layer For the formation process of the metal oxide coating layer covering the central metal particles, refer to Patent Document 6 (Japanese Patent Laid-Open No. 2008-004,541), and the metal oxide coating layer is the central metal. The metal oxide coating layer described in Examples 1 to 53, 103 to 106, 119, and 122 (where the metal element of the metal oxide is a metal oxide) is a method that is partially improved so that the particles can be coated. (In the case of Si) is described as an example. The same applies when the metal element of the metal oxide is a metal element other than Si.
That is, while confirming the central metal particle colloid solution synthesized in the above step (1) so that the central metal particle colloidal particles do not aggregate and precipitate under an argon flow atmosphere, An aqueous ammonia solution was added to the solution to adjust the pH of the central metal particle colloid solution to basic. Next, the three-necked flask containing the basic metal particle colloid solution adjusted to the basicity is transferred to a 60 ° C. hot bath, and the substance amount ratio (center of the Si metal element to the central metal element of the central metal particle colloid is calculated. Add 3-aminopropylethoxysilane (APTES) at a drop rate of 0.01 mL / min for 80 minutes under stirring conditions of 600 rpm or more in an argon flow atmosphere so that the ratio of (metal element: Si element) is 1: 1. did. Further, 60 minutes after the end of dropping of APTES, 1000 rpm in an argon flow atmosphere so that the substance amount ratio (central metal element: Si element) is 1: 1 in terms of Si element with respect to the central metal element of the central metal colloidal particle. Under the above stirring conditions, tetraethoxysilane (TEOS) was added at a dropping rate of 0.02 mL / min for 30 minutes, and after completion of the dropping, the stirring was continued for 1 hour to conduct hydrolysis and polymerization reaction. . If stirring is not sufficient when forming the metal oxide coating layer, the central metal particles are easily aggregated and precipitated, and the metal oxide-coated central metal colloid cannot be obtained, which is incompatible.

Thereafter, the resulting mixed solution after completion of the hydrolysis / polymerization reaction is filtered through a membrane filter, and the solvent is removed to recover the SiO ₂ -coated central metal particle component, and the temperature rise rate is 10 in an inert gas atmosphere. The temperature was raised to 600 ° C at a rate of ° C / min, and firing was performed at 600 ° C for 1 hour. Next, the recovered SiO ₂ -coated central metal particles are placed in a three-necked flask and separately redispersed in a mixed solvent of polyvinyl pyrrolidone aqueous solution and ethylene glycol prepared at the same rate as in the above step (1). The mixture was stirred for 10 minutes at a rotational speed of 1000 rpm or higher under sonic irradiation, and the generated aggregate was removed by centrifugation, and only the supernatant component was collected to obtain a colloidal solution of SiO ₂ coated center metal particles.

(3) Loading of catalyst metal particles on the metal oxide coating layer First, when the catalyst metal particles are Pt, the central metal particle colloidal solution (metal oxidation) coated with the metal oxide coating layer obtained above. The metal oxide-coated central metal particle in the central metal particle colloid solution is 0.0020 mol / L in terms of the amount of metal in the central metal particle while cooling the metal-coated central metal particle colloid solution) to 10 ° C. 0.05 mol / L H ₂ PtCl ₆ aqueous solution and 1.0 mol / L L (+) ascorbic acid aqueous solution at a dropping rate of 0.08 mL / min for H ₂ PtCl ₆ aqueous solution, The (+) ascorbic acid aqueous solution was dropped at a dropping rate of 0.152 mL / min at the same time for 60 minutes while stirring to prepare a catalyst particle colloid solution in which catalyst metal particles were supported on the metal oxide coating layer.

When the catalyst metal particles are a Pt alloy, the additive elements (Co, Ni, Fe, Pd, Au, Ru, Rh, etc.) are added when the 0.05 mol / L H ₂ PtCl ₆ aqueous solution is added. (Ir) chloride is added after adjusting the concentration so that the atomic composition ratio of the target catalytic metal particles is reached (for example, when Pt: Co = 50: 50, H ₂ PtCl ₆ aqueous solution and CoCl ₂ The amount of the aqueous solution added was adjusted so that the substance amounts of Pt and Co were equal to each other.) In the same manner as described above, a catalyst particle colloid solution in which catalyst metal particles were supported on the metal oxide coating layer was prepared.

2. Preparation of catalyst 0.179g of carbon support [Lion Corporation product name: EC600JD] was added to the catalyst particle colloid solution obtained above (0.0018 mol / L in terms of the amount of metal in the central metal particle). The catalyst particles were supported on a carbon support under an argon flow atmosphere at 90 ° C. for 1 hour. Next, after allowing to cool to room temperature, suction filtration is performed with a membrane filter, and the obtained powder is redispersed in 500 mL of ethanol, stirred for 1 hour, and then suction filtered with a membrane filter again to support the catalyst particles on the carbon support. A catalyst for a polymer electrolyte fuel cell was obtained. In addition, about the load of the catalyst particle in a catalyst, it adjusted so that it might become 40 mass% in all the following examples and comparative examples.

Here, in Examples 1 to 45 shown in Table 1, Pd is used as the central metal particle, Si is used as the metal element of the metal oxide coating layer, and Pt is used as the catalyst metal particle. Was prepared.
In Examples 1 to 18, the center metal particle Pd has a particle size of 5 to 7 nm, the metal oxide coating layer has a thickness of 1 to 4 nm, and the catalyst metal particle Pt has a particle size of 1 to 2 nm. In Examples 19 to 27, the particle diameter of the central metal particle Pd is 5 to 7 nm, the thickness of the metal oxide coating layer is 2 to 4 nm, the particle diameter of the catalyst metal particle Pt is 3 nm, In Examples 28 to 45, the particle diameter of the central metal particle Pd was 8 to 10 nm, the thickness of the metal oxide coating layer was 2 to 4 nm, and the particle diameter of the catalyst metal particle Pt was 1 to 2 nm.

In Examples 46 to 53 and Comparative Examples 1 and 2 shown in Table 2, in Examples 46 to 53, Au, Cu, Ni, or Co is used as the metal element of the central metal particle, and the metal oxide coating is used. The catalyst particles are prepared using Si as the metal element of the layer and Pt as the catalyst metal particles. In Comparative Examples 1 and 2, Ag is used as the center metal particle, and the metal oxide coating layer Catalyst particles were prepared using Si as the metal element and Pt as the catalyst metal particles.
Here, in Example 46, the particle diameter of the central metal particle Au is 7 nm, the thickness of the metal oxide coating layer is 3 nm, the particle diameter of the catalyst metal particle Pt is 2 nm, and in Example 47, the central metal particle is The particle size of Cu is 7 nm, the thickness of the metal oxide coating layer is 4 nm, the particle size of the catalytic metal particles Pt is 1 nm, and in Example 48, the particle size of the central metal particles Ni is 7 nm. The thickness of the material coating layer is 4 nm, the particle size of the catalytic metal particles Pt is 2 nm, and in Example 49, the particle size of the central metal particles Co is 7 nm, and the thickness of the metal oxide coating layer is 4 nm. In Example 50, the particle size of the central metal particle Au is 10 nm, the thickness of the metal oxide coating layer is 4 nm, and the particle size of the catalytic metal particle Pt is 2 nm. In Example 51, the central metal particle Cu has a particle diameter of 10 nm, and the thickness of the metal oxide coating layer is 4 nm, the particle size of the catalyst metal particles Pt is 2 nm, and in Example 52, the particle size of the center metal particles Ni is 10 nm, the thickness of the metal oxide coating layer is 4 nm, and the particles of the catalyst metal particles Pt In Example 53, the diameter of the central metal particle Co was 10 nm, the thickness of the metal oxide coating layer was 4 nm, and the diameter of the catalyst metal particle Pt was 2 nm. In Comparative Example 1, the central metal particle Ag has a particle size of 7 nm, the metal oxide coating layer has a thickness of 4 nm, and the catalytic metal particle Pt has a particle size of 1 nm. In Comparative Example 2, the central metal particle Ag has a particle size of 1 nm. The particle size of the catalyst was 10 nm, the thickness of the metal oxide coating layer was 4 nm, and the particle size of the catalyst metal particles Pt was 2 nm.

Further, in Comparative Examples 3 to 24 shown in Table 3, Pd is used as the metal element of the central metal particle, Si is used as the metal element of the metal oxide coating layer, and Pt is used as the catalyst metal particle. Catalyst particles were prepared.
Here, in Comparative Examples 3 to 10, the center metal particle Pd has a particle size of 5 to 6 nm, the metal oxide coating layer has a thickness of 5 to 6 nm, and the catalyst metal particle Pt has a particle size of 1 to 2 nm. In Comparative Examples 11 to 14, the center metal particle Pd has a particle size of 5 nm, the metal oxide coating layer has a thickness of 4 nm, the catalyst metal particle Pt has a particle size of 4 nm, and Comparative Examples 15 to 18 In this case, the particle diameter of the central metal particle Pd is 5 nm, the thickness of the metal oxide coating layer is 5 nm, the particle diameter of the catalyst metal particle Pt is 4 nm, and in Comparative Examples 19 to 24, the particle diameter of the central metal particle Pd is Was 11 nm, the thickness of the metal oxide coating layer was 2 to 4 nm, and the particle size of the catalyst metal particles Pt was 1 to 2 nm.
Comparative Example 25 is a commercially available catalyst [TEC1040E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.], and Comparative Example 26 is a core-shell type catalyst prepared according to the production method of Non-Patent Document 1 (central metal particles: Pd and Furthermore, Comparative Example 27 is a catalyst prepared according to the production method of Patent Document 7 (a catalyst in which tin oxide and a carbon carrier are combined and Pt catalyst particles are supported thereon).

In Examples 54 to 98 shown in Table 4, Pd is used as the metal element of the central metal particle, Zr is used as the metal element of the metal oxide coating layer, and further Pt is used as the catalyst metal particle. Was prepared.
Here, in Examples 54 to 71, the particle diameter of the central metal particle Pd is 5 to 7 nm, the thickness of the metal oxide coating layer is 2 to 4 nm, the particle diameter of the catalyst metal particle Pt is 1 to 2 nm, In Examples 72 to 80, the particle diameter of the central metal particle Pd is 5 to 7 nm, the thickness of the metal oxide coating layer is 2 to 4 nm, the particle diameter of the catalyst metal particle Pt is 3 nm, and Example 81 In .about.98, the particle size of the central metal particle Pd was 8 to 10 nm, the thickness of the metal oxide coating layer was 2 to 4 nm, and the particle size of the catalyst metal particle Pt was 1 to 2 nm.

In Examples 99 to 102 shown in Table 5, Pd is used as the metal element of the central metal particle, Ti and Sn are used as the metal element of the metal oxide coating layer, and Pt is used as the catalyst metal particle. Catalyst particles were prepared.
Here, in Example 99, the central metal particle Pd has a particle diameter of 7 nm, the metal oxide coating layer has a thickness of 2 nm, and the catalytic metal particle Pt has a particle diameter of 2 nm. In Example 100, the central metal particle Pd has a particle diameter of 2 nm. The particle size of Pd is 7 nm, the thickness of the metal oxide coating layer is 2 nm, the particle size of the catalyst metal particles Pt is 2 nm, and in Example 101, the particle size of the central metal particles Pd is 10 nm. The thickness of the material coating layer is 3 nm, the particle size of the catalytic metal particles Pt is 2 nm, and in Example 102, the particle size of the central metal particles Pd is 10 nm, and the thickness of the metal oxide coating layer is 3 nm. The particle size of the catalyst metal particles Pt was 2 nm.

In Examples 103 to 106 and Comparative Examples 28 and 29 shown in Table 6, Pd is used as the metal element of the central metal particle, Si is used as the metal element of the metal oxide coating layer, and further, as the catalyst metal particle Catalyst particles were prepared using a Pt alloy containing Pt as a main component.
Here, in Examples 103 and 104, a Pt alloy with Co added as catalyst metal particles is used, and in Examples 105 and 106, a Pt alloy with Ni added as catalyst metal particles is used. Then, a Pt alloy containing Co as the main component was used as the catalyst metal particles, and a Pt alloy containing Ni as the main component was used as the catalyst metal particles in Comparative Example 29.
Table 6 also shows the catalyst particles of Example 1.

In Examples 107 to 118 shown in Table 7, Au, Cu, Ni, and Co are used as the metal elements of the central metal particles, Ti, Sn, and Zr are used as the metal elements of the metal oxide coating layer. Catalyst particles were prepared using Pt as catalyst metal particles.
Here, in Example 107, the central metal particle Au has a particle diameter of 10 nm, the metal oxide coating layer has a thickness of 4 nm, and the catalytic metal particle Pt has a particle diameter of 3 nm. In Example 108, the central metal particle Au The particle size of Cu is 10 nm, the thickness of the metal oxide coating layer is 4 nm, the particle size of the catalyst metal particles Pt is 3 nm, and in Example 109, the particle size of the central metal particles Ni is 10 nm. The thickness of the material coating layer is 4 nm, the particle size of the catalyst metal particles Pt is 3 nm, the particle size of the central metal particles Co is 10 nm in Example 110, and the thickness of the metal oxide coating layer is 4 nm. In Example 111, the particle diameter of the catalyst metal particles Pt is 3 nm, the particle diameter of the central metal particles Au is 10 nm, the thickness of the metal oxide coating layer is 4 nm, and the particle diameter of the catalyst metal particles Pt is 3 nm. In Example 112, the central metal particle Cu has a particle diameter of 10 nm, and gold The thickness of the metal oxide coating layer is 4 nm, the particle size of the catalyst metal particles Pt is 3 nm, and in Example 113, the particle size of the central metal particles Ni is 10 nm, and the thickness of the metal oxide coating layer is 4 nm. In Example 114, the particle diameter of the central metal particle Co is 10 nm, the thickness of the metal oxide coating layer is 4 nm, and the particle diameter of the catalytic metal particle Pt is In Example 115, the central metal particle Au has a particle diameter of 10 nm, the metal oxide coating layer has a thickness of 4 nm, and the catalytic metal particle Pt has a particle diameter of 3 nm. The particle size of the metal particle Cu is 10 nm, the thickness of the metal oxide coating layer is 4 nm, the particle size of the catalyst metal particle Pt is 3 nm, and in Example 117, the particle size of the central metal particle Ni is 10 nm. The thickness of the metal oxide coating layer is 4 nm, and the particle size of the catalyst metal particles Pt is 3 nm. Further, the particle diameter of the central metal particles Co in Example 118 and 10 nm, the thickness of the metal oxide coating layer is 4 nm, the particle diameter of the catalyst metal particles Pt was 3 nm.

In Comparative Examples 30 to 41 shown in Table 8, Au, Cu, Ni, and Co are used as the metal elements of the central metal particles, Ti, Sn, and Zr are used as the metal elements of the metal oxide coating layer. Catalyst particles were prepared using Pt as catalyst metal particles.
Here, in Comparative Example 30, the particle diameter of the central metal particle Au is 11 nm, the thickness of the metal oxide coating layer is 4 nm, the particle diameter of the catalytic metal particle Pt is 3 nm, and in Comparative Example 31, the central metal particle is The particle size of Cu is 11 nm, the thickness of the metal oxide coating layer is 4 nm, the particle size of the catalyst metal particles Pt is 3 nm, and in Comparative Example 32, the particle size of the central metal particles Ni is 10 nm. The thickness of the material coating layer is 6 nm, the particle size of the catalyst metal particles P is 3 nm, the particle size of the central metal particles Co is 10 nm in Comparative Example 33, and the thickness of the metal oxide coating layer is 6 nm. In the comparative example 34, the particle size of the central metal particle Au is 10 nm, the thickness of the metal oxide coating layer is 6 nm, and the particle size of the catalyst metal particle Pt is 3 nm. In Comparative Example 35, the central metal particle Cu has a particle diameter of 10 nm, The thickness of the layer is 4 nm, the particle size of the catalyst metal particles Pt is 4 nm, and in Comparative Example 36, the particle size of the central metal particle Ni is 11 nm, and the thickness of the metal oxide coating layer is 4 nm. In the comparative example 37, the particle size of the central metal particle Co is 11 nm, the thickness of the metal oxide coating layer is 4 nm, and the particle size of the catalyst metal particle Pt is 3 nm. In Comparative Example 38, the central metal particle Au has a particle diameter of 10 nm, the thickness of the metal oxide coating layer is 6 nm, and the catalytic metal particle Pt has a particle diameter of 3 nm. In Comparative Example 39, the central metal particle The particle size of Cu is 10 nm, the thickness of the metal oxide coating layer is 4 nm, the particle size of the catalyst metal particles Pt is 4 nm, and in Comparative Example 40, the particle size of the central metal particles Ni is 12 nm. The thickness of the material coating layer was 4 nm, the particle size of the catalytic metal particles Pt was 3 nm, and Comparative Example 41 The particle size of the central metal particles Co and 11 nm, the thickness of the metal oxide coating layer is 4 nm, the particle diameter of the catalyst metal particles Pt was 3 nm.

In Examples 119 to 123 and Comparative Examples 42 to 44 shown in Table 9, Au, Cu, Ni, and Co are used as the metal elements of the central metal particles, and Si, Ti, and the like are used as the metal elements of the metal oxide coating layer. Catalyst particles were prepared using Sn and Zr, and further using a Pt alloy containing Pt as a main component as catalyst metal particles.
Here, in Example 119, the central metal particle Au has a particle diameter of 5 nm, the thickness of the metal oxide coating layer is 2 nm, and Pt alloy to which Co is added is used as the catalyst metal particle. In Example 120, The central metal particle Cu has a particle size of 5 nm, the metal oxide coating layer has a thickness of 2 nm, and a Pt alloy to which Co is added is used as the Pt alloy of the catalyst metal particle. The particle size of the metal oxide coating layer is 2 nm, the catalyst metal particles are made of Pt alloy having Ni as the main component, and in Example 121, the particle size of the central metal particles Co is 5 nm. The thickness of the metal oxide coating layer is set to 2 nm, and a Pt alloy to which Co is added is used as the catalyst metal particles. In Example 122, the central metal particle Au has a particle size of 5 nm. The thickness is 2 nm and Ni is added as catalyst metal particles In Example 123, the center metal particle Cu has a particle diameter of 9 nm, the metal oxide coating layer has a thickness of 4 nm, and Ni is added as a catalyst metal particle. In Comparative Example 43, the central metal particle Ni has a particle diameter of 5 nm, the thickness of the metal oxide coating layer is 2 nm, and a Pt alloy whose main component is Ni is used as the catalyst metal particle. In this example, the central metal particle Co has a particle size of 5 nm, the thickness of the metal oxide coating layer is 2 nm, and a Pt alloy whose main component is Ni is used as the catalyst metal particle.

3. Physical property evaluation of catalyst particles
(1) The particle size of the central metal particles the particle size of the central metal particles in the catalyst particle (d ₃₎ in the catalyst particles (d _3), TEM image observed by a transmission electron microscope (FEI Inc. Tecnai) ( (Bright field image).
That is, 1 mL of the colloidal solution of the central metal particles obtained at the time of preparation of the catalyst particles was measured with a dropper, diluted with 10 mL of ethanol, dispersed with an ultrasonic wave for 1 minute, and dropped onto a copper mesh grid. This was vacuum-dried overnight, then set in a sample holder, and an arbitrary visual field having a size of 20 nm × 20 nm was measured at an acceleration voltage of 200 kV. The central metal particle is observed as a black spot of several nm, 10 black spots are measured from a visual field having a size of 20 nm × 20 nm, and the same measurement is repeated for another arbitrary visual field having a size of 20 nm × 20 nm for a total of 10 The average value of the diameters of 100 particles (10 measurements x 10 measurement points at each time), which is the total number of particles obtained by these 10 measurements, is obtained. The average value was defined as the particle size (d ₃ ) of the central metal particles.

(2) The thickness of the metal oxide coating layer in the catalyst particles (d ₂₎ for the metal oxide coating layer in the catalyst grain thickness about (d ₂₎ is observed by a transmission electron microscope (FEI Inc. Tecnai) It calculated using the STEM image.
That is, 1 mL of the metal oxide-coated central metal particle colloid solution obtained at the time of preparation of the catalyst particles was measured with a dropper, diluted with 10 mL of ethanol, dispersed with ultrasound for 1 minute, and dropped onto a copper mesh grid. This was vacuum-dried overnight, set in a sample holder, measured at an accelerating voltage of 200 kV and an arbitrary visual field of size 20 nm × 20 nm, and from the light / dark contrast of the STEM image, a thin coating covering the surface of the central metal particle The contrast interval was measured. The distance of 10 points is measured from a visual field of size 20 nm × 20 nm, and the same measurement is repeated for another arbitrary visual field of size 20 nm × 20 nm, for a total of five measurements. An average value of intervals of 50 measurement points in total (10 points × 5 times) was obtained, and this average value was defined as the thickness (d ₂ ) of the metal oxide coating layer.

The thickness (d ₂ ) of the metal oxide coating layer of the catalyst particles may be determined by the following method.
That is, 1 mg of a catalyst obtained by supporting catalyst particles on a carbon support is measured in a plastic container of about 1 cm × 2 cm, and an epoxy resin is poured into the container and cured overnight to prepare a cured product. Next, for this cured product, using a microtome, sliced with a diamond cutter to a predetermined thickness within a range of 20 to 60 nm, the cut measurement sample was supported on a copper mesh grid, You may calculate using the STEM image observed with a transmission electron microscope (Tecnai by FEI).

(3) The particle diameter of the catalyst metal particle diameter of the catalyst metal particles in the catalyst particle for (d ₁₎ in the catalyst particles (d _1), a STEM image observed by a transmission electron microscope (FEI Inc. Tecnai) Used to calculate.
That is, 1 mL of the catalyst particle colloid solution obtained at the time of preparation of the catalyst particles was measured with a dropper, diluted with 10 mL of ethanol, dispersed with ultrasound for 1 minute, and dropped onto a copper mesh grid. After this was vacuum dried overnight, it was set in a sample holder, an arbitrary visual field of size 20 nm × 20 nm was measured at an acceleration voltage of 200 kV, and a bright spot on the metal oxide coating layer was measured as catalyst metal particles. Ten bright spots are measured from a 20 nm × 20 nm field of view, and the same measurement is repeated for another arbitrary field of 20 nm × 20 nm, for a total of five measurements. These five measurements The average value of the bright spots of a total of 50 measurement points (10 points × 5 times) obtained in the above was obtained, and this average value was taken as the particle size (d ₁ ) of the catalyst metal particles.

Example 1 catalyst particles (center metal particles: Pd particles, metal oxide coating layer: SiO ₂ coating layer, catalyst metal particles: Pt particles) taken using the transmission electron microscope (Tecnai manufactured by FEI) The STEM image of is shown in FIG.
In the STEM image of this catalyst particle, the bright part indicated by the dotted line with reference numeral 1 is platinum particles, and the part indicated by the dotted line with reference numeral 2 is a metal oxide coating layer covering the central metal particles.

4). Preparation of catalyst layer and membrane electrode assembly (MEA) The catalysts for polymer electrolyte fuel cells prepared in each of the above Examples and Comparative Examples were used, and a 5% by mass Nafion solution ( Using DuPont DE521), the ionomer solution was added so that the mass of Nafion solids was 1.2 times the mass of the catalyst in an argon stream, and after gently stirring, the catalyst was pulverized with ultrasonic waves, Under stirring, butyl acetate was added so that the solid content concentration of the catalyst and Nafion was 2% by mass to prepare a catalyst layer slurry for preparing the catalyst layer.

The catalyst layer slurry thus prepared was applied to one side of a Teflon (registered trademark) sheet by a spray method, dried in an argon stream at 80 ° C. for 10 minutes, and then in an argon stream at 120 ° C. for 1 hour. A catalyst layer sheet for a molecular fuel cell was obtained. When preparing each catalyst layer sheet, conditions such as spraying are set so that the amount of Pt or Pt alloy used is 0.10 mg / cm ^{2. The} amount of Pt or Pt alloy used is the same as before and after spray coating. The dry mass of the Teflon (registered trademark) sheet was measured and calculated from the difference.

Next, two 2.5 cm square catalyst layers are cut out from the catalyst layer sheet prepared using the catalyst of each Example and Comparative Example so that each catalyst layer contacts the electrolyte membrane (Nafion 112). An electrolyte membrane was sandwiched between the two catalyst layers, and hot pressing was performed for 10 minutes at 130 ° C. and 90 kg / cm ² . After cooling to room temperature, only the Teflon (registered trademark) sheet was carefully peeled off to fix the anode and cathode catalyst layers to the electrolyte membrane. In addition, two 2.5 cm square carbon cloths were cut from a commercially available carbon cloth (Electro-Chem EC-CC1-060), and placed so that the anode and cathode catalyst layers fixed on the electrolyte membrane were sandwiched between them. Then, hot pressing was performed for 10 minutes under the conditions of 130 ° C. and 50 kg / cm ² to fabricate an MEA.

5). Performance Evaluation of Polymer Electrolyte Fuel Cell Catalysts For each of the Examples and Comparative Examples produced as described above, the MEA was assembled in a cell and set in a fuel cell measurement device. evaluated.
Air was supplied to the cathode side, pure hydrogen was supplied to the anode side, and the amount of gas necessary for power generation of 1000 mA / cm ² was set to 100% so that the utilization rates were 40% and 70%, respectively. The gas pressure was 0.1 MPa, and the cell temperature was 80 ° C.

First, the supplied air and pure hydrogen were bubbled and humidified in distilled water kept at 80 ° C., respectively. Then, after supplying gas to the cell under the above conditions, 1000 mA / cm ² until gradually increasing the load to secure the load when it reaches 1000 mA / cm ^2, the voltage between cell terminals after the elapse of 60 minutes Was measured as the cell performance of the fuel cell before the durability test.

Next, as a durability test, a durability test was performed by repeating a cycle of holding the voltage at 0.6 V for 4 seconds and then holding at 1.0 V for 4 seconds, and then repeating the battery performance as before the durability test. It was measured.
About the performance of the catalyst for polymer electrolyte fuel cells, it evaluated by the cell voltage after an endurance test. Therefore, the higher the cell voltage after the durability test, the higher the durability of the catalyst, that is, the catalyst particles, and the better the battery performance.
The results are shown in Tables 1-9.

Claims (5)

Catalyst particles for a polymer electrolyte fuel cell having a three-layer structure of central metal particles, a metal oxide coating layer covering the central metal particles, and catalytic metal particles supported on the metal oxide coating layer, ,
The central metal particle is a metal particle composed of at least one selected from Pd, Cu, Co, Ni, and Au, and has a particle size in the range of 5 to 10 nm;
The metal element of the metal oxide forming the metal oxide coating layer is a metal composed of at least one selected from Si, Ti, Sn, and Zr, and the thickness of the metal oxide coating layer is 1 to 4 nm. In addition,
Catalyst particles for a polymer electrolyte fuel cell, wherein the catalyst metal particles are Pt or a Pt alloy containing Pt as a main component, and the particle diameter thereof is in the range of 1 to 3 nm.   2. The solid polymer form according to claim 1, wherein the central metal particles have a particle size in the range of 5 to 7 nm, and the catalyst metal particles have a particle size in the range of 1 to 2 nm. Catalyst particles for fuel cells.   The catalyst particles for a polymer electrolyte fuel cell according to claim 1 or 2, wherein the metal element of the metal oxide coating layer is a metal composed of at least one selected from Si and Ti.   A catalyst for a polymer electrolyte fuel cell, wherein the catalyst particles for a polymer electrolyte fuel cell according to any one of claims 1 to 3 are supported on a carbon support. 5. A polymer electrolyte fuel cell, wherein the catalyst for a polymer electrolyte fuel cell according to claim 4 is used in one or both of a positive electrode and a negative electrode.