JP2019111510A - Supported metal catalyst and production method thereof - Google Patents

Abstract

To provide a supported metal catalyst capable of enhancing power generation performance.SOLUTION: The supported metal catalyst comprises a carrier powder being an aggregate of carrier fine particles, a metal fine particle 130 supported on the carrier powder and a coating layer 140 formed so as to cover the carrier fine particle. The coating layer 140 comprises a polymer having proton conductivity and when the average thickness of the coating layer 140 is d and the average particle size of the metal fine particle 130 is D, at least one of conditions (1) and (2) as given below are satisfied: (1) 0.18≤d/D≤0.32; and (2) 0.18≤d/D≤0.55 and 2.5 nm≤D≤4.9 nm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a supported metal catalyst and a method of producing the same. The supported metal catalyst of the present invention is suitably used as a cathode electrode catalyst of a fuel cell.

Patent Document 1 discloses a catalyst layer for a fuel cell, wherein the catalyst layer for a fuel cell is a catalyst composite in which platinum or a platinum alloy is supported on the surface of a SnO ₂ carrier, and a proton conductivity coating the catalyst composite. Wherein the ratio (I / MO) of the mass (I) of the ionomer to the mass (MO) of the SnO ₂ carrier is in the range of 0.10 to 0.12. A fuel cell catalyst layer is disclosed.

JP, 2017-188270, A JP 2017-157353 A

  Although the point which exhibits high electric power generation performance in a wide humidity environment is examined by patent document 1 by making I / MO into a specific range, it is demanded to further improve electric power generation performance.

  The present invention has been made in view of such circumstances, and provides a supported metal catalyst capable of enhancing the power generation performance.

According to the present invention, there is provided a carrier powder which is an aggregate of carrier fine particles, metal fine particles carried on the carrier powder, and a covering layer formed to cover the carrier fine particles, the covering layer being a proton It is made of a polymer having conductivity, and assuming that the average thickness of the coating layer is d and the average particle diameter of the metal fine particles is D, at least one of the following conditions (1) to (2) is satisfied: A supported metal catalyst is provided.
(1) 0.18 ≦ d / D ≦ 0.32
(2) 0.18 ≦ d / D ≦ 0.55, and 2.5 nm ≦ D ≦ 4.9 nm

  The inventors of the present invention conducted intensive studies and found that the power generation performance becomes very high when the condition (1) or (2) is satisfied, and the present invention has been completed.

FIG. 2 is a model view of a catalyst structure of a supported metal catalyst 100. It is the figure which extracted carrier fine particles 150 from FIG. It is a figure which shows the state of the branch 160 of the carrier fine particle 150 in FIG. It is a figure which shows the gas diffusion path in FIG. FIG. 5 is a conceptual view showing a state in which carrier fine particles 150 carrying metal fine particles 130 are covered with a coating layer 140. FIG. An example of distribution of the space | gap 110 contained in a carrier powder is shown. Fig. 1 shows a model of a fuel cell. 1 is a cross-sectional view through the center of a burner 2 of a production device 1 for producing a carrier powder. It is an enlarged view of the area | region X in FIG. It is AA sectional drawing in FIG. It is an enlarged view of the area | region Y in FIG. The TEM image of the sample which is I / S = 0.12 is shown.

  Hereinafter, embodiments of the present invention will be described using the drawings. The various features shown in the embodiments described below can be combined with one another. In addition, the invention is established independently for each feature.

1. Supported metal catalyst 100
As shown in FIGS. 1 to 5, the supported metal catalyst 100 is formed to cover the carrier powder which is an aggregate of the carrier fine particles 150, the metal fine particles 130 carried by the carrier powder, and the carrier fine particles 150. A covering layer 140 is provided. Each component will be described below.

1-1. Carrier fine particle 150 and carrier powder As shown in FIGS. 1 to 4, the carrier fine particle 150 is formed with a three-dimensional void 110 surrounded by the pores existing between the branches 160 and the plural branches thereof. There is. The branch 160 is a portion in which a chain-like portion formed by fusion bonding a plurality of crystallites 120 constituting the carrier fine particles 150 in a chain shape is divided as a branch. A gas diffusion path for diffusing oxygen as the oxidant and / or hydrogen as the fuel and transporting it to the supported metal catalyst 100 is formed by the configuration of the carrier fine particles 150 described above. Patent Document 2 discloses carrier fine particles 150 having such a structure.

  As shown in FIGS. 1 to 4 as an example of the structural model of the supported metal catalyst, the carrier fine particles 150 are points (branch points, hereinafter sometimes simply referred to as branches) b1, b2, b5, b1 a first hole surrounded by b4 and b1, a second hole surrounded by branch points b1, b2, b3 and b1, a first hole surrounded by branch points b2, b3, b6, b7, b5 and b2 A total of four holes including a fourth hole surrounded by three holes and branch points b1, b3, b6, b7, b5, b4 and b1 are provided. Here, assuming that the surface surrounded by the branch points of the holes (first to fourth holes) is a hole surface, the air gap 110 is a three-dimensional space surrounded by these four hole surfaces. The carrier particle 150 includes a plurality of holes surrounded by a plurality of branch points where a plurality of branches are connected in this manner. A three-dimensional space (air gap) surrounded by a plurality of holes is provided continuously to one another. Therefore, this air gap becomes a gas diffusion path (gas diffusion path) of oxygen, hydrogen and the like. FIG. 4 is a view showing the gas diffusion path in FIG. FIG. 4 shows an example of the gas diffusion path (gas diffusion path) of the air gap 110. The flow (gas diffusion path) 170 of the oxidant (gas), fuel gas, etc. can flow in the desired direction through the air gap 110 as shown in FIG. That is, the air gap 110 becomes a gas diffusion path.

  In addition, as a simple configuration of the carrier fine particles 150, only one hole (for example, a first hole surrounded by branch points b1, b2, b5, b4, b1) may be provided. In this case, the void 110 is provided for the thickness of crystallite grains of the crystallite 120. As a simpler configuration, the carrier particles 150 may have one or more branches. Even in this case, since the carrier fine particles 150 are branched, they can not be in close contact with each other, and the air gap 110 can be provided therebetween.

  In addition, the place described as a hole above may be rephrased as a closed curve (closed loop). Alternatively, it can be rephrased to have the air gap 110 surrounded by a closed surface including a plurality of the above-described branch points (for example, branch points b1 to b7). The branch points b1 to b7 can be regarded as the center of gravity of the crystallite of the metal oxide constituting the carrier fine particle 150 in which the branches are connected to each other, or may be any one point on this crystallite.

  The size of the crystallite 120 is preferably 1 to 30 nm, and more preferably 5 to 15 nm. Specifically, the size is, for example, 1, 5, 10, 15, 20, 25, 30 nm, and may be in the range between any two of the numerical values exemplified here. The size (crystallite diameter) of the crystallite 120 can be determined from the half-width of the peak of the XRD pattern based on the Scherrer equation.

  The aggregate of carrier fine particles 150 is in the form of powder. Such an assembly is called "carrier powder".

  The average particle diameter of the carrier fine particles 150 in the carrier powder is 0.1 μm to 4 μm, preferably 0.5 μm to 2 μm. The average particle size of the carrier fine particles 150 can be measured by a laser diffraction / scattering type particle size distribution measuring apparatus.

The specific surface area of the carrier powder is preferably 12 m ² / g or more, and more preferably 25 m ² / g or more. The specific surface area, for example 12~150m ² / g, preferably in the 20~120m ² / g, specifically, for example, 12,15,20,25,30,35,40,45,50 , 100, 150 m ² / g, and may be in the range between any two of the numerical values exemplified here.

  An example of the distribution of the voids 110 contained in the carrier powder is shown in FIG. The distribution of the voids 110 can be determined by measuring the volume of the three-dimensional void of the carrier powder using a mercury porosimeter. FIG. 6 calculates the volume per void from the measured volume value and the number of voids, and integrates the value (sphere equivalent diameter by mercury intrusion method) converted to the diameter of a sphere of the same volume as the determined volume It shows the distribution. As shown in FIG. 6, in the carrier powder, it is preferable that voids (primary pores) of 11 nm or less and voids (secondary pores) larger than 11 nm exist. This secures a gas diffusion path in the catalyst layer of the fuel cell.

  The carrier powder preferably has a porosity of 50% or more, more preferably 60% or more. The porosity is, for example, 50 to 80%, specifically, for example, 50, 55, 60, 65, 70, 75, 80%, and the range between any two of the numerical values exemplified here. It may be. The porosity can be determined by mercury porosimetry or FIB-SEM or gas adsorption.

  The carrier powder preferably has a repose angle of 50 degrees or less, and more preferably 45 degrees or less. In this case, the carrier powder has the same fluidity as wheat flour and is easy to handle. The angle of repose is, for example, 20 to 50 degrees, specifically, for example, 20, 25, 30, 35, 40, 45, 50 degrees, and the range between any two of the numerical values exemplified here It may be The angle of repose can be determined by the drop volume method.

  The carrier fine particles 150 are preferably fine particles of an inorganic compound. The fine particles of the inorganic compound tend to be hydrophilic on the surface, and therefore, when forming the covering layer 140 using an ink containing a hydrophilic solvent, there is an advantage that the covering layer 140 tends to be uniform. The inorganic compound is preferably a rutile type oxide, and more preferably contains tin oxide or titanium oxide. The proportion of tin oxide or titanium oxide in the metal oxide contained in the carrier fine particles 150 is preferably 50 mol% or more. Specifically, this ratio is, for example, 50, 60, 70, 80, 90, 95, 100 mol%, and may be in the range between any two of the numerical values exemplified here.

  The carrier fine particles 150 are preferably doped, and an element different in valence from the metal contained in the inorganic compound is preferably doped. When the inorganic compound contains a tetravalent metal such as tin or titanium, it is preferable that an element other than tetravalent be doped. As elements other than tetravalent elements, at least one of rare earth elements represented by yttrium, pentagonal elements represented by niobium and tantalum, hexavalent elements represented by tungsten and a group 15 element represented by antimony is preferred. To be elected. Conductivity can be imparted to the carrier fine particles by doping with such an element. Among such elements, a Group V element such as niobium and tantalum, or a Group 6 element such as tungsten is preferable.

When the carrier powder contains tin oxide, the apparent density is preferably 2 to 3.8 g / cm ³ . If the apparent density is too small, the rigidity of the carrier powder will be insufficient, and if it is too large, the surface area of the carrier powder will be too small. The apparent density is specifically, for example, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, It is 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8 g / cm ³ , and the range between any two of the numerical values exemplified here It may be within.

  The conductivity of the carrier powder is preferably 0.00001 S / cm or more, more preferably 0.0001 S / cm or more. The conductivity is, for example, 0.0001 to 1000 S / cm, and specifically, for example, 0.0001, 0.001, 0.01, 0.1, 1, 10, 100, 1000 S / cm, It may be in the range between any two of the numerical values exemplified here. The conductivity can be measured based on the JIS standard (JIS K 7194).

  The carrier fine particle 150 has a branch 160 composed of a chain-like portion formed by fusion bonding of a plurality of crystallites 120 in a chain-like manner, and has a property of causing electrons to flow. As shown in FIGS. 1 to 4, the carrier fine particles 150 have a plurality of branches 160, and the branches form a network via branch points (b1 to b7) at which the branches are connected to each other. In addition, between them, it has an electrically conductive property. Therefore, the branch 160 of the carrier fine particle 150 shown by a dotted line from the point P0 in FIG. 1 itself constitutes the electron conduction path (electron conduction path) 140.

1-2. Metal particles 130
The metal particles 130 are metal or alloy particles that can function as a catalyst. Assuming that the average particle diameter of the large number of metal particles 130 supported on the carrier powder is D, it is preferable that 2.5 ≦ D ≦ 9 nm, and more preferably 2.5 ≦ D ≦ 4.9 nm. The average particle diameter D is specifically, for example, specifically 2.5, 3, 3.5, 4, 4.5, 4.9, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9 nm, and may be in the range between any two of the numerical values exemplified here. If the average particle diameter of the metal particles 130 is 2.5 nm or more, the metal particles 130 are less likely to be buried in the coating layer 140. If it is 9 nm or less, the electrochemically active surface area is sufficiently large, and if it is 4.9 nm or less, the electrochemically active surface area is further reduced, and desired electrode performance is easily obtained. The average particle diameter D of the metal particles 130 is a transmission electron microscope, and a TEM image is taken at a magnification that enlarges the length of 10 nm to a size of 0.8 cm or more, and the crystallite 120 and the metal particles in the TEM image The minor axis S can be measured for each metal fine particle 130 where the contact surface with 130 can be observed, as shown in the schematic view of FIG. A TEM image can be taken with a tungsten filament at an acceleration voltage of 120 kV using, for example, a transmission electron microscope (HT7700 EXALENS mounting machine) manufactured by Hitachi High-Technologies. In general, the particles with the highest contrast in the TEM image are the metal particles 130. When the number of metal particles 130 in the TEM image is less than 500, data on 500 or more metal particles 130 is obtained by changing the imaging location and repeating the measurement of the short diameter of the metal particles 130. Then calculate the average. The minor diameter S of the metal particles 130 corresponds to the distance from the top of the metal particles 130 to the interface between the metal particles 130 and the carrier particles 150 in the schematic view of FIG. 5.

  The metal particles 130 are composed of any metal or alloy having a catalytic ability. The metal particles 130 are preferably made of only a noble metal or an alloy of a noble metal and a transition metal. The metal particles 130 may include a core and a skin layer covering the core. The core preferably comprises an alloy of a noble metal and a transition metal. The skin layer preferably contains a noble metal. As the noble metal, platinum is preferable, and as the transition element, cobalt (Co) or nickel (Ni) is preferable, and cobalt is particularly preferable.

  The amount of the metal fine particles 130 supported is preferably 1 to 50% by mass, and more preferably 5 to 25% by mass. Specifically, the supported amount is, for example, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50% by mass, and the range between any two of the numerical values exemplified here It may be within.

The electrochemically active surface area of the supported metal catalyst 100 is preferably 20 m ² / g or more. The surface area is, for example, 20 to 200 m ² / g, and specifically, for example, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, ²⁰⁰ m ² / g, and may be in the range between any two of the numerical values exemplified here. The electrochemically active surface area can be determined by cyclic voltammetry.

1-3. Coating layer 140
The covering layer 140 is made of a polymer having proton conductivity. An example of such a polymer is Nafion (Nafion, manufactured by DuPont), which is a copolymer of a fluorocarbon resin based on sulfonation tetrafluoroethylene.

  Assuming that the average thickness of the covering layer 140 is d, it is preferable that 0.18 ≦ d / D ≦ 0.55, and more preferably 0.18 ≦ d / D ≦ 0.32. It is further preferable that ≦ d / D ≦ 0.32. In this case, the supply of protons and the supply of oxygen to the metal fine particles 130 becomes smooth, and the cathode reaction that requires protons and oxygen can easily proceed. Specifically, d / D is, for example, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27. , 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0 .40, 0.41, 0.42, 0.43, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52 0.53, 0.54, 0.55, and may be in the range between any two of the numerical values exemplified here.

The average thickness d of the covering layer 140 can be calculated by the following method.
(A) First, with a transmission electron microscope, a TEM image is taken at a magnification that enlarges the length of 10 nm to a size of 0.8 cm or more. The imaging apparatus and conditions of the TEM image are the same as those described in "1-2. Metal fine particles 130". In general, the particle with the highest contrast in the TEM image is the fine metal particle 130, and the particle with the second highest contrast is the crystallite 120. The low contrast layer covering the crystallite 120 is the covering layer 140.
(B) The distance between the end points P1 and P2 of the contact surface between each metal particle 130 and the crystallite 120 for each metal particle 130 where the contact surface between the crystallite 120 and the metal particle 130 in the TEM image can be observed Then, distances T1 and T2 from the interface of crystallite 120 and covering layer 140 to the surface of covering layer 140 are measured at positions Q1 and Q2 separated from each of end points P1 and P2 by major axis L, respectively. The thickness is 140.
(C) Measure the thickness of the covering layer 140 at 100 or more places, and let the arithmetic mean be the average thickness of the covering layer 140.

2. Fuel cell 200
FIG. 7 shows a model of the fuel cell of the present invention. In FIG. 7, in the fuel cell (fuel cell) 200, the catalyst layer 220A on the anode 201 side, the gas diffusion layer 210A and the catalyst layer 220K on the cathode 202 side, and the gas diffusion layer 210K face each other across the electrolyte membrane 230. Configured The anode gas diffusion layer 210A, the anode catalyst layer 220A, the electrolyte membrane 230, the cathode catalyst layer 220K, and the cathode gas diffusion layer 210K are arranged in this order. The catalyst layer 220 K on the cathode side includes the supported metal catalyst 100. The catalyst layer 220A on the anode side may also include the supported metal catalyst 100, but may include another catalyst. By connecting the load 203 between the anode 201 and the cathode 202 of the polymer electrolyte fuel cell 200, power is output to the load 203.

3. Method of Manufacturing Carrier Powder First, the manufacturing apparatus 1 that can be used for manufacturing the carrier powder will be described with reference to FIGS. 8 to 11. The manufacturing apparatus 1 includes a burner 2, a raw material supply unit 3, a reaction cylinder 4, a recovery unit 5, and a gas storage unit 6. The raw material supply unit 3 includes an outer cylinder 13 and a raw material distribution cylinder 23.

  The burner 2 is cylindrical, and the raw material supply unit 3 is disposed inside the burner 2. The burner gas 2 a is circulated between the burner 2 and the outer cylinder 13. The burner gas 2 a is used to form a flame 7 at the tip of the burner 2 by ignition. The flame 7 forms a high temperature region of 1000 ° C. or higher. The burner gas 2a preferably contains a flammable gas such as propane, methane, acetylene, hydrogen or nitrous oxide. In one example, a mixed gas of oxygen and propane can be used as the burner gas 2a. The temperature of the high temperature region is, for example, 1000 to 2000 ° C., and specifically, for example, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000 ° C., the numerical values exemplified here It may be in the range between any two.

  A raw material solution 23 a for producing carrier powder is circulated in the raw material flow cylinder 23. As the raw material solution 23a, one containing a compound of a metal contained in the inorganic compound constituting the carrier fine particles 150 is used. When the inorganic compound is tin oxide or titanium oxide, one containing tin or a titanium compound is used. Examples of tin or titanium compounds include fatty acid tin or titanium. The carbon number of the fatty acid is, for example, 2 to 20, preferably 4 to 15, and more preferably 6 to 12. As fatty acid tin or titanium, tin octylate or titanium is preferred. The raw material solution 23 a may contain a metal compound for doping the carrier fine particles 150. As a metal compound, fatty acid metal (Nb, Ta, W etc.) salt is illustrated. The carbon number of the fatty acid is, for example, 2 to 20, preferably 4 to 15, and more preferably 6 to 12. Preferred fatty acid metal salts are niobium octylate, tantalum octylate and tungsten octylate. The molar ratio of tin or titanium compound: metal compound is appropriately determined in order to increase the conductivity of the carrier powder, but for example, 0.8: 0.2 to 0.99: 0.01 is preferable.

  In the raw material solution 23a, the tin or titanium compound is preferably dissolved or dispersed in a non-aqueous solvent. Examples of the non-aqueous solvent include organic solvents represented by terpene. If water is contained in the raw material solution 23a, fatty acid tin or titanium may be hydrolyzed and degraded. In order to prevent hydrolysis of fatty acid tin or titanium, the content of water of the raw material solution 23a is preferably 100 ppm or less, and more preferably 50 ppm or less.

  Between the outer cylinder 13 and the raw material flow cylinder 23, misting gas 13a used for mist formation of the raw material solution 23a is circulated. When the misting gas 13a and the raw material solution 23a are ejected together from the tip of the raw material supply unit 3, the raw material solution 23a is misted. The mist 23b of the raw material solution 23a is sprayed into the flame 7, and the tin or titanium compound in the raw material solution 23 is thermally decomposed in the flame 7 to form a chain formed by fusion bonding of the crystallites 120 in a chain. A carrier powder which is an aggregate of the carrier fine particles 150 having the shape-like portion is produced. The misting gas 13a is oxygen in one example.

  The reaction tube 4 is provided between the recovery unit 5 and the gas storage unit 6. A flame 7 is formed in the reaction tube 4. The recovery unit 5 is provided with a filter 5a and a gas discharge unit 5b. Negative pressure is applied to the gas discharge part 5b. For this reason, an air flow toward the gas discharge unit 5 b is generated in the recovery unit 5 and the reaction cylinder 4.

  The gas storage portion 6 is cylindrical, and includes a cooling gas introduction portion 6a and a slit 6b. Cooling gas 6 g is introduced into the gas storage unit 6 from the cooling gas introduction unit 6 a. Since the cooling gas introduction part 6a is directed in the direction along the tangent of the inner peripheral wall 6c of the gas storage part 6, the cooling gas 6g introduced into the gas storage part 6 through the cooling gas introduction part 6a is the inner peripheral wall Turn along 6c. A burner insertion hole 6 d is provided at the center of the gas storage portion 6. The burner 2 is inserted into the burner insertion hole 6d. The slit 6 b is provided at a position adjacent to the burner insertion hole 6 d so as to surround the burner insertion hole 6 d. For this reason, the slit 6 b is provided so as to surround the burner 2 in a state in which the burner 2 is inserted into the burner insertion hole 6 d. The cooling gas 6g in the gas storage unit 6 is driven by the negative pressure applied to the gas discharge unit 5b and discharged from the slit 6b toward the reaction cylinder 4. The cooling gas 6 g may be any one capable of cooling the produced tin oxide or titanium, and is preferably an inert gas, for example, air. The flow rate of the cooling gas 6 g is preferably twice or more the flow rate of the burner gas 2 a. The upper limit of the flow rate of the cooling gas 6 g is not particularly defined, but is, for example, 1000 times the flow rate of the burner gas 2 a. The flow rate of the cooling gas 6 g / the flow rate of the burner gas 2 a is, for example, 2 to 1000, and specifically, for example, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 100, 200, 500, 1000, and may be in the range between any two of the numerical values exemplified here. In the present embodiment, a negative pressure is applied to the gas discharge part 5b to flow the cooling gas 6g, but a positive pressure may be applied to the cooling gas introduction part 6a to flow the cooling gas 6g.

  In the present invention, since the cooling gas 6g is supplied around the flame 7 through the slit 6b, the cooling gas 6g flows in a laminar flow around the flame 7. For this reason, since the mist 23b, the crystallite 120 and the carrier fine particles 150 are not disturbed by the cooling gas 6g, they are sufficiently heated by the flame 7 while moving along the flame 7, and the reaction proceeds. Production. In addition, after the carrier fine particles 150 leave the flame 7, the carrier fine particles 150 are immediately cooled by the cooling gas 6g, so that a structure having a chain portion is maintained. The cooled carrier fine particles 150 are captured and collected by the filter 5a.

  In the present invention, the carrier powder which is an aggregate of the carrier fine particles 150 forms a high temperature region of 1000 ° C. or more at the tip of the burner 2 by the flame 7 using the manufacturing apparatus 1 and It can manufacture by thermally decomposing tin or a titanium compound in this high temperature area | region, supplying to the environment. The high temperature region may be formed by plasma or the like other than the flame 7.

4. Method of Producing Supported Metal Catalyst 100 The method of producing the supported metal catalyst 100 includes a supporting step, a reducing step, and a mixing step. These steps may be sequentially performed, or only the mixing step may be performed after preparing a structure in which the metal fine particles 130 are supported on the carrier powder.

<Supporting process>
In the supporting step, the metal powder 130 is supported on the carrier powder. This loading can be carried out using a reverse micelle method, a colloid method, an impregnation method or the like. In the colloid method, the loading step comprises an adsorption step and a heat treatment step.

  In the adsorption step, metal colloid particles are adsorbed to the carrier powder. More specifically, a dispersion liquid in which metal colloid particles synthesized by a colloid method are dispersed in an aqueous solution is prepared, and the metal colloid particles are added to and mixed with the dispersion liquid to form the colloid particles on the carrier powder surface. Adsorb. The carrier powder to which the colloidal particles are adsorbed can be separated from the dispersion medium through filtration and drying.

  In the heat treatment step, after the adsorption step, heat treatment is performed to convert the metal colloid particles into metal fine particles 130. Although this heat processing changes with kinds of inorganic compound which constitutes carrier particulates, when an inorganic compound contains tin oxide, it is preferred to carry out at 300-1000 ° C. When an inorganic compound contains a titanium oxide, it is preferable to carry out at 800-1500 degreeC.

  The heat treatment time is, for example, 0.1 to 20 hours, preferably 0.5 to 5 hours. Specifically, this time is, for example, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20 hours, and the numerical values exemplified here It may be in the range between any two.

  The heat treatment can be performed under an inert gas atmosphere such as nitrogen or under an inert gas atmosphere containing 1 to 4% hydrogen.

<Reduction process>
In the reduction step, a reduction treatment of the metal fine particles 130 is performed after the heat treatment step. The reduction treatment can be performed by heat treatment in a reducing atmosphere containing a reducing gas such as hydrogen.

  The temperature of this heat treatment is, for example, 70 to 300 ° C, preferably 100 to 200 ° C. This temperature is, for example, specifically, for example, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, 300 ° C., as exemplified here. It may be in the range between any two of the numerical values.

  The time of this heat treatment is, for example, 0.01 to 20 hours, preferably 0.1 to 5 hours. Specifically, this time is, for example, 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20 hours. And may be in the range between any two of the numerical values exemplified here.

  When the reducing gas is hydrogen, its concentration is, for example, 0.1 to 100% by volume, preferably 0.2 to 10% by volume, and more preferably 0.5 to 3% by volume. Specifically, this concentration is, for example, 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 10, 100% by volume, and the numerical values exemplified here It may be in the range between any two.

  The metal fine particles 130 after the heat treatment in the supporting step may be in an oxidized state, in which case the metal fine particles 130 may not exhibit catalytic activity. In this case, the catalytic activity can be enhanced by reducing the metal fine particles 130.

<Mixing process>
In the mixing step, the structure obtained by the loading step and the reduction step (a structure in which the metal fine particles 130 are supported on the carrier powder) is mixed with an ink containing a polymer having proton conductivity. Thus, the coating layer 140 can be formed on the carrier fine particles 150 constituting the carrier powder.

  Since the thickness of the coating layer 140 can be adjusted by changing the ratio (I / S) of the volume S of the carrier powder to the volume I of the polymer, the I / S should be appropriate according to the size of the metal fine particles 130. By setting the value to a value, the supported metal catalyst 100 described in “1. Supported metal catalyst 100” can be obtained. S and I can be calculated by dividing the dry weight of carrier powder and polymer by density, respectively.

  Although I / S is not particularly limited, for example, 0.01 ≦ I / S <0.2, and preferably 0.07 ≦ I / S ≦ 0.18. Specifically, I / S is, for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10. 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.195, and any of the numerical values exemplified here It may be in the range between or two.

  The ink preferably contains a hydrophilic solvent. As a hydrophilic solvent, water, alcohol, or these mixed solvents are mentioned. Examples of the alcohol include methanol, ethanol and isopropanol. Since the surface of the inorganic compound constituting the carrier fine particles 150 tends to be hydrophilic, the thickness of the coating layer 140 can be obtained by forming the coating layer 140 of a polymer having proton conductivity using an ink containing a hydrophilic solvent. Can be made uniform.

  A hydrophilization treatment may be performed before mixing the structure and the ink. Examples of the hydrophilization treatment include a method of mixing a structure and a hydrophilic solvent. The description of the hydrophilic solvent is as described above. By performing the hydrophilization treatment, the amount of water and OH groups present on the carrier powder surface is increased, the hydrophilicity of the carrier powder is improved, and the thickness of the coating layer 140 tends to be more uniform.

  The supported metal catalyst was manufactured by the method shown below, and various evaluations were performed.

1. Production of Supported Metal Catalyst 100 (Production of Carrier Powder)
The carrier powder was manufactured using the manufacturing apparatus 1 shown in FIGS. As the burner gas 2a, a gas obtained by mixing 5 L / min of oxygen and 1 L / min of propane gas was used, and this gas was ignited to form a flame (chemical flame) 7 of 1600 ° C. or more at the tip of the burner 2. As the raw material solution 23a, a solution obtained by mixing and dissolving tin octylate and niobium octylate in a molar ratio of 0.95: 0.05 in a mineral split terpene was used. Oxygen was used as the misting gas 13a. 9 L / min of misting gas 13a and 3 g / min of raw material solution 23a are mixed and sprayed from the tip of raw material supply unit 3 which is a spray nozzle (atomizer) to the flame center to burn and aggregate carrier fine particles 150 A body of carrier powder was produced. At that time, by making the gas discharge part 5b negative pressure, air was sucked from the slit 6b at a flow rate of 170 L / min, and the generated carrier powder was collected in the collection device 5 (with the filter 5a). The raw material supply unit 3 has a double pipe structure (total length 322.3 mm) and is supplied with oxygen gas from the outer cylinder 13, the raw material solution 23 a is supplied to the raw material circulation cylinder 23, and a fluid nozzle and an air nozzle are provided at the tip of the raw material circulation cylinder 23. There, the raw material solution 23a was turned into mist 23b. The amount of carrier powder recovered was 10 g or more after 60 minutes of operation.

(Support and reduction of metal particles 130)
Next, the metal fine particles 130 were supported on the carrier powder according to the following procedure.

  First, 0.57 mL of chloroplatinic acid hexahydrate aqueous solution was dissolved in 38 ml of ultrapure water, and 1.76 g of sodium carbonate was further added and stirred.

  The solution was diluted with 150 ml of water and the pH of the solution was adjusted to 5 with NaOH. Thereafter, 25 ml of hydrogen peroxide was added and the pH was readjusted to 5 with NaOH.

A dispersion obtained by dispersing 0.50 g of the carrier powder in 15 mL of ultrapure water was added to the dispersion, and the mixture was stirred at 90 ° C. for 3 hours. After cooling to room temperature, filtration, washing with ultrapure water and alcohol, drying at 80 ° C. overnight, heat treatment at 800 ° C. in air for 2 hours to support metal fine particles 130 on carrier powder Then, heat treatment was performed at 150 ° C. for 2 hours in 1% hydrogen to reduce the metal fine particles 130. Through the above steps, a structure (Pt / Nb-SnO ₂ catalyst) in which the metal fine particles 130 are supported on the carrier powder was obtained.

(Formation of covering layer 140)
1.0 g of the structure obtained in the above process, 1.820 g of water, and 1.789 g of ethanol were weighed, and planetary ball mill mixing was performed. The mixing was performed at 270 rpm for 30 minutes under the conditions of 45 ml zirconia pots and 10 pieces of 5 mm diameter zirconia balls.

  Next, an alcohol-water mixed solution containing 5% by mass of Nafion (hereinafter referred to as "Nafion solution") was added to the above zirconia pot, and planetary ball mixing was carried out at 270 rpm for 30 minutes. It added so that the value of I / S might differ for every.

2. Various evaluations <BET specific surface area>
It was 31 m < ² > / g when the specific surface area by BET was measured about the said carrier powder.

<Apparent density>
It was 3.6 g / cm < ³ > when the apparent density of the sample shape | molded by the uniaxial pressurization method (press pressure: 20 kg / cm < ² >) was measured about the said carrier powder.

<XRD pattern>
When the XRD pattern was measured about the said carrier powder, the peak resulting from a rutile phase was observed. In addition, the average particle diameter of the crystallites was 15 nm.

<Analysis by TEM image>
For the sample with I / S = 0.12, a TEM image was taken with a transmission electron microscope at a magnification that enlarged the length of 10 nm to a size of 0.8 cm or more. The TEM image was taken with a tungsten filament at an accelerating voltage of 120 kV using a transmission electron microscope (HT7700 EXALENS mounting machine) manufactured by Hitachi High-Technologies Corporation. This TEM image is shown in FIG. A large number of TEM images similar to FIG. 12 are taken, and based on these TEM images, the average particle diameter D of the metal particles 130, and the coating layer, according to the method described in “1-1. The average thickness d of 140 was calculated.

  Moreover, the average particle diameter D of the metal microparticle 130 and the average thickness d of the coating layer 140 were computed by the same method also about another sample from which I / S differs. The results are shown in Table 1.

  As shown in Table 1, the mass activity is high when 0.18 ≦ d / D ≦ 0.55, and particularly high when 0.18 ≦ d / D ≦ 0.32. The mass activity was higher when 0.20 ≦ d / D ≦ 0.32.

1: Manufacturing device 2: Burner 2a: Burner gas 3: Raw material supply unit 4: Reaction tube 5: Recovery device 5a: Filter 5b: Gas discharge unit 6: Gas storage unit 6a: Cooling gas introduction unit 6b: Slit 6c: Inner peripheral wall 6d: burner insertion hole 6g: cooling gas 7: flame 13: outer cylinder 13a: mist forming gas 23: raw material flow cylinder 23a: raw material solution 23b: mist 100: supported metal catalyst 110: void 120: crystallite 130: metal fine particles 140 A: Coating layer 150: Carrier fine particles 160: Branch 200: solid polymer fuel cell 201: Anode 202: Cathode 203: Load 210A: Anode side gas diffusion layer 210K: Cathode side gas diffusion layer 220A: Anode side catalyst layer 220K: Cathode side catalyst layer 230: electrolyte membrane

Claims (22)

A carrier powder which is an aggregate of carrier fine particles, metal fine particles carried on the carrier powder, and a covering layer formed to cover the carrier fine particles,
The covering layer is composed of a polymer having proton conductivity,
A supported metal catalyst satisfying at least one of the following conditions (1) to (2), where d is an average thickness of the coating layer and D is an average particle diameter of the metal fine particles.
(1) 0.18 ≦ d / D ≦ 0.32
(2) 0.18 ≦ d / D ≦ 0.55, and 2.5 nm ≦ D ≦ 4.9 nm A supported metal catalyst according to claim 1, wherein
Supported metal catalyst, wherein 0.20 ≦ d / D ≦ 0.32. The supported metal catalyst according to claim 1 or 2, wherein
Supported metal catalyst, wherein 2.5 nm ≦ D ≦ 9 nm. A supported metal catalyst according to claim 3, wherein
Supported metal catalyst, wherein 2.5 nm ≦ D ≦ 4.9 nm. The supported metal catalyst according to any one of claims 1 to 4, wherein
The carrier fine particle is a fine particle of an inorganic compound, which is a supported metal catalyst. The supported metal catalyst according to claim 5, wherein
The inorganic compound is doped, supported metal catalyst. A supported metal catalyst according to claim 5 or claim 6, wherein
The inorganic compound is a supported metal catalyst comprising tin oxide. A supported metal catalyst according to claim 6 or claim 7, wherein
The said support powder is a supported metal catalyst whose apparent density is 2-3.8 g / cm < ³ >. A supported metal catalyst according to any one of the preceding claims, wherein
The carrier powder has a specific surface area of 12 m ² / g or more. The supported metal catalyst according to any one of claims 1 to 9, wherein
The carrier powder has a porosity of 50% or more. The supported metal catalyst according to any one of claims 1 to 10, wherein
The carrier powder is a supported metal catalyst having a repose angle of 50 degrees or less. The supported metal catalyst according to any one of claims 1 to 11, wherein
The carrier powder has a conductivity of 0.00001 S / cm or more. The supported metal catalyst according to any one of claims 1 to 12, wherein
The carrier fine particle comprises a chain-like portion formed by fusion bonding a plurality of crystallites in a chain-like manner. 14. The supported metal catalyst according to claim 13, wherein
The supported metal catalyst, wherein the crystallites are 1-30 nm in size. A supported metal catalyst according to claim 13 or claim 14, wherein
The chain includes a plurality of branches, a hole existing between the plurality of branches, and a void.
The supported metal catalyst, wherein the void is surrounded by the plurality of branches and the holes. The supported metal catalyst according to claim 15, wherein
The carrier powder comprises a plurality of the voids, and the voids have a void having a sphere equivalent diameter of 11 nm or less and a void larger than 11 nm according to a mercury intrusion method. A method of producing a supported metal catalyst, comprising a mixing step, comprising:
In the mixing step, a method of mixing a structure in which metal fine particles are supported on a carrier powder, and an ink containing a polymer having proton conductivity. The method according to claim 17, wherein
Assuming that the volume of the polymer is I and the volume of the carrier powder is S,
The method, wherein the mixing step is performed such that 0.01 ≦ I / S <0.2. Method according to claim 18, wherein
The method, wherein the mixing step is performed such that 0.07 ≦ I / S ≦ 0.18. The method according to any one of claims 17-19, wherein
The carrier powder is an aggregate of carrier fine particles,
The carrier fine particles are fine particles of an inorganic compound,
The method wherein the ink comprises a hydrophilic solvent. 21. The method of claim 20, wherein
The method wherein the inorganic compound is doped. 22. A method according to claim 20 or 21, wherein
The method, wherein the inorganic compound comprises tin oxide.