JP7025636B2 - Supported metal catalyst and its manufacturing method - Google Patents

Description

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

Patent Document 1 describes 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 proton conductivity covering the catalyst composite. It is characterized by containing an ionomer which is a polymer having the above, and 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. The catalyst layer for a fuel cell is disclosed.

Japanese Unexamined Patent Publication No. 2017-188270 Japanese Unexamined Patent Publication No. 2017-157353

In Patent Document 1, it is studied that high power generation performance can be exhibited in a wide humidity environment by setting the I / MO in a specific range, but it is requested that the power generation performance be further improved.

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

According to the present invention, a carrier powder which is an aggregate of carrier fine particles, metal fine particles supported on the carrier powder, and a coating layer formed so as to cover the carrier fine particles are provided, and the coating layer is a proton. When the coating layer is made of a conductive polymer and the average thickness of the coating layer is d and the average particle size of the metal fine particles is D, at least one of the following conditions (1) and (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

As a result of diligent studies by the present inventors, it was found that the power generation performance becomes extremely high when the condition (1) or (2) is satisfied, and the present invention has been completed.

It is a model diagram of the catalyst structure of the supported metal catalyst 100. It is a figure which extracted the carrier fine particle 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. 1. It is a conceptual diagram which shows the state which the carrier fine particle 150 which carried the metal fine particle 130 is covered with a coating layer 140. An example of the distribution of voids 110 contained in the carrier powder is shown. A model diagram of a fuel cell is shown. It is sectional drawing which passes through the center of the burner 2 of the manufacturing apparatus 1 for manufacturing a carrier powder. It is an enlarged view of the region X in FIG. FIG. 8 is a cross-sectional view taken along the line AA in FIG. It is an enlarged view of the region Y in FIG. A TEM image of a sample with I / S = 0.12 is shown.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The various features shown in the embodiments shown below can be combined with each other. In addition, the invention is independently established for each characteristic item.

1. 1. Supported metal catalyst 100
As shown in FIGS. 1 to 5, the supported metal catalyst 100 is formed so as to cover the carrier powder, which is an aggregate of the carrier fine particles 150, the metal fine particles 130 supported on the carrier powder, and the carrier fine particles 150. A coating layer 140 is provided. Hereinafter, each configuration will be described.

1-1. Carrier fine particles 150 and carrier powder As shown in FIGS. 1 to 4, the carrier fine particles 150 are formed with a three-dimensional void 110 surrounded by a branch 160 thereof and holes existing between the plurality of branches thereof. There is. The branch 160 is a portion in which a chain 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. The gas diffusion path for diffusing oxygen as an oxidant and / or hydrogen as a fuel and transporting the gas onto the supported metal catalyst 100 is formed by the three-dimensional arrangement of the carrier fine particles 150 described above. The carrier fine particles 150 having such a structure are disclosed in Patent Document 2.

As shown in FIGS. 1 to 4 as an example of the structural model of the supported metal catalyst, the carrier fine particles 150 have branches connected to each other (branch point, sometimes simply referred to as branching point) b1, b2, b5, and so on. The first hole surrounded by b4, b1, the second hole surrounded by branch points b1, b2, b3, b1, and the second hole surrounded by branch points b2, b3, b6, b7, b5, b2. It is provided with a total of four holes, that is, a hole of 3 and a fourth hole surrounded by branch points b1, b3, b6, b7, b5, b4, and b1. Here, assuming that the surface surrounded by the branch points of each hole portion (first to fourth hole portions) is a hole surface, the void 110 is a three-dimensional space surrounded by these four hole surfaces. The carrier fine particles 150 are provided with a plurality of holes surrounded by a plurality of branch points connecting the plurality of branches in this way. The structure is such that three-dimensional spaces (voids) surrounded by a plurality of holes are continuously provided with each other. Therefore, this void becomes a gas diffusion path (gas diffusion path) such as oxygen and hydrogen. FIG. 4 is a diagram showing a gas diffusion route in FIG. FIG. 4 shows an example of a gas diffusion path (gas diffusion path) of the void 110. The flow of the oxidant (gas), fuel gas, etc. (gas diffusion path) 170 can flow in a desired direction through the void 110 as shown in FIG. That is, this void 110 becomes a gas diffusion route.

As a simple configuration of the carrier fine particles 150, a single hole portion (for example, a first hole portion surrounded by branch points b1, b2, b5, b4, and b1) may be provided. In this case, the void 110 corresponding to the thickness of the crystallite grain of the crystallite 120 is provided. As a simpler configuration, the carrier fine particles 150 may have one or more branches. Even in this case, since there are branches between the carrier fine particles 150, they cannot be brought into close contact with each other, and a void 110 can be provided between them.

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

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

The aggregate of the carrier fine particles 150 is in the form of powder. Such an aggregate is referred to as "carrier powder".

The average particle size 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 device.

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

FIG. 6 shows an example of the distribution of the voids 110 contained in the carrier powder. The distribution of the voids 110 can be determined by measuring the volume of the three-dimensional voids of the carrier powder using a mercury porosimeter. In FIG. 6, the volume per void is obtained from the measured volume value and the number of voids, and the integrated value (the equivalent diameter of the sphere by the mercury intrusion method) converted into the diameter of the sphere having the same volume as the obtained volume is integrated. It shows the distribution. As shown in FIG. 6, it is preferable that the carrier powder has voids (primary pores) of 11 nm or less and voids (secondary pores) larger than 11 nm. 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, and more preferably 60% or more. The porosity is, for example, 50-80%, specifically, for example, 50, 55, 60, 65, 70, 75, 80%, within the range between any two of the numerical values exemplified here. There may be. The porosity can be determined by a mercury intrusion method, a FIB-SEM or a gas adsorption method.

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

The carrier fine particles 150 are preferably fine particles of an inorganic compound. Since the surface of the fine particles of the inorganic compound tends to be hydrophilic, there is an advantage that the coating layer 140 tends to be uniform when the coating layer 140 is formed by using an ink containing a hydrophilic solvent. The inorganic compound is preferably a rutile-type oxide, and more preferably contains tin oxide or titanium oxide. The ratio 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 within the range between any two of the numerical values exemplified here.

The carrier fine particles 150 are preferably doped, and are preferably doped with an element having a valence different from that of the metal contained in the inorganic compound. When the inorganic compound contains a tetravalent metal such as tin or titanium, it is preferably doped with an element other than tetravalent. As elements other than tetravalent, at least one of rare earth elements typified by yttrium, genus 5 elements typified by niobium and tantalum, genus 6 elements typified by tungsten, and genus 15 elements represented by antimony is at least one. To be elected. By doping with such an element, conductivity can be imparted to the carrier fine particles. Among such elements, a group 5 element represented by niobium and tantalum, or a group 6 element represented by 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. Specifically, the apparent density is, for example, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, and so on. 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 inside.

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

The carrier fine particle 150 has a branch 160 composed of a chain portion formed by fusion-bonding a plurality of crystallites 120 in a chain shape, and has a property of carrying electrons by itself. As shown in FIGS. 1 to 4, the carrier fine particles 150 have a plurality of branches 160, and the branches form a network through branch points (b1 to b7) where the branches are connected to each other. In between these, they will have an electrically conductive property. Therefore, the branch 160 of the carrier fine particles 150 shown by the dotted line from the point P0 in FIG. 1 itself constitutes the electron conduction path (electron conduction path) 140.

1-2. Metal fine particles 130
The metal fine particles 130 are metal or alloy fine particles that can function as a catalyst. Assuming that the average particle size of the large number of metal fine particles 130 supported on the carrier powder is D, 2.5 ≦ D ≦ 9 nm is preferable, and 2.5 ≦ D ≦ 4.9 nm is more preferable. The average particle size D is specifically, for example, for example, 2.5, 3, 3.5, 4, 4.5, 4.9, 5, 5.5, 6, 6.5, It is 7, 7.5, 8, 8.5, 9 nm, and may be within the range between any two of the numerical values exemplified here. When the average particle size of the metal fine particles 130 is 2.5 nm or more, the metal fine particles 130 are less likely to be buried in the coating layer 140. Further, when it is 9 nm or less, the electrochemically active surface area is sufficiently large, and when it is 4.9 nm or less, the electrochemically active surface area is further reduced, and the desired electrode performance can be easily obtained. For the average particle size D of the metal fine particles 130, a TEM image was taken with a transmission electron microscope at a magnification of magnifying the length of 10 nm to a size of 0.8 cm or more, and the crystallites 120 and the metal fine particles in the TEM image were taken. For each metal fine particle 130 whose contact surface with the 130 can be observed, the minor axis S can be measured as shown in the schematic diagram of FIG. 5, and can be obtained by the arithmetic average thereof. The 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-equipped machine) manufactured by Hitachi High-Technologies Corporation. Usually, the particles having the highest contrast in the TEM image are the metal fine particles 130. When the number of metal fine particles 130 shown in the TEM image is less than 500, data on 500 or more metal fine particles 130 can be obtained by repeating the measurement of the minor axis of the metal fine particles 130 at different shooting locations. Then perform the calculated average. The minor axis S of the metal fine particles 130 corresponds to the distance from the apex of the metal fine particles 130 to the interface between the metal fine particles 130 and the carrier fine particles 150 in the schematic diagram of FIG.

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

The amount of the metal fine particles 130 supported is preferably 1 to 50% by mass, 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 is in the range between any two of the numerical values exemplified here. It may be inside.

The electrochemically active surface area of the supported metal catalyst 100 is preferably 20 m ² / g or more. This 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, It is 170, 180, 190, 200 m ² / g, and may be within 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 coating layer 140 is composed of a polymer having proton conductivity. Examples of such polymers include Nafion (Nafion, manufactured by DuPont), which is a copolymer of a fluororesin based on sulfonated tetrafluoroethylene.

Assuming that the average thickness of the coating layer 140 is d, it is preferably 0.18 ≦ d / D ≦ 0.55, more preferably 0.18 ≦ d / D ≦ 0.32, and 0.20. It is more preferable that ≦ d / D ≦ 0.32. In this case, the supply of protons and oxygen to the metal fine particles 130 becomes smooth, and the cathode reaction requiring protons and oxygen becomes easy to proceed. Specifically, d / D is, for example, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.25, 0.27, 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, 0.44, 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 within the range between any two of the numerical values exemplified here.

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

2. 2. Fuel cell 200
FIG. 7 shows a model diagram 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, the catalyst layer 220K on the cathode 202 side, and the gas diffusion layer 210K face each other with the electrolyte film 230 interposed therebetween. It is composed of. The anode-side gas diffusion layer 210A, the anode-side catalyst layer 220A, the electrolyte membrane 230, the cathode-side catalyst layer 220K, and the cathode-side gas diffusion layer 210K are arranged in this order. The catalyst layer 220K on the cathode side includes a supported metal catalyst 100. The catalyst layer 220A on the anode side may also contain the supported metal catalyst 100, but may also contain another catalyst. By connecting the load 203 between the anode 201 and the cathode 202 of the polymer electrolyte fuel cell 200, electric power is output to the load 203.

3. 3. Method for Producing Carrier Powder First, a production apparatus 1 that can be used for producing 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 tube 4, a recovery device 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 has a cylindrical shape, and the raw material supply unit 3 is arranged inside the burner 2. The burner gas 2a is circulated between the burner 2 and the outer cylinder 13. The burner gas 2a 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 in the high temperature region is, for example, 1000 to 2000 ° C., specifically, for example, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000 ° C., and the numerical values exemplified here. It may be within the range between any two of the above.

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

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 typified by tarpen. If the raw material solution 23a contains water, the fatty acid tin or titanium may be hydrolyzed and deteriorated. In order to prevent the hydrolysis of the fatty acid tin or titanium, the water content of the raw material solution 23a is preferably 100 ppm or less, more preferably 50 ppm or less.

The mist-ized gas 13a used for mist-forming the raw material solution 23a is distributed between the outer cylinder 13 and the raw material distribution cylinder 23. When the mistified 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 converted into mist. 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 23a undergoes a thermal decomposition reaction in the flame 7, and the crystallites 120 are fused and bonded in a chain shape. A carrier powder which is an aggregate of carrier fine particles 150 having a shaped portion is produced. The mistified gas 13a is, in one example, oxygen.

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

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

In the present invention, since 6 g of the cooling gas is supplied around the flame 7 through the slit 6b, the cooling gas 6 g becomes a laminar flow and flows around the flame 7. For this reason, the mist 23b, the crystallite 120, and the carrier fine particles 150 are not disturbed by the cooling gas 6 g, and are sufficiently heated by the flame 7 while moving along the flame 7, so that the carrier fine particles 150 are efficient. Can be manufactured. Further, after the carrier fine particles 150 are discharged from the flame 7, the carrier fine particles 150 are immediately cooled by 6 g of the cooling gas, so that the structure having the chain portion is maintained. The cooled carrier fine particles 150 are captured and recovered by the filter 5a.

In the present invention, the carrier powder, which is an aggregate of the carrier fine particles 150, uses the manufacturing apparatus 1 to form a high temperature region of 1000 ° C. or higher by the flame 7 at the tip of the burner 2, and 6 g of the cooling gas is applied to the high temperature region through the slit 6b. It can be produced by thermally decomposing a tin or titanium compound in this high temperature region while supplying it to the surroundings. The high temperature region may be formed by plasma or the like in addition to the flame 7.

4. Method for Producing Supported Metal Catalyst 100 The method for manufacturing the supported metal catalyst 100 includes a supporting step, a reduction step, and a mixing step. These steps may be performed in order, 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 in advance.

<Supporting process>
In the supporting step, the metal fine particles 130 are supported on the carrier powder. This support can be performed by using a method such as a reverse micelle method, a colloid method, or an impregnation method. In the colloidal method, the supporting step includes an adsorption step and a heat treatment step.

In the adsorption step, the metal colloidal particles are adsorbed on the carrier powder. More specifically, a dispersion liquid in which metal colloidal particles synthesized by the colloidal method are dispersed in an aqueous solution is prepared, and the colloidal particles are added to and mixed with the dispersion liquid to prepare the colloidal particles on the surface of the carrier powder. To adsorb. The carrier powder on 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 change the metal colloidal particles into metal fine particles 130. This heat treatment varies depending on the type of the inorganic compound constituting the carrier fine particles, but when the inorganic compound contains tin oxide, it is preferably performed at 300 to 1000 ° C. When the inorganic compound contains titanium oxide, it is preferably carried out at 800 to 1500 ° C.

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 within the range between any two of the above.

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

<Reduction process>
In the reduction step, the reduction treatment of the metal fine particles 130 is performed after the heat treatment step. The reduction treatment can be performed by performing a 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., and is exemplified here. It may be within 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. It may be within 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 even 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 are used. It may be within 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 supporting step and the reducing step (a structure in which the metal fine particles 130 are supported on the carrier powder) and the ink containing the polymer having proton conductivity are mixed. As a result, 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 and the volume I of the polymer, the I / S is appropriately adjusted according to the size of the metal fine particles 130. By setting the 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 the carrier powder and the polymer by the density, respectively.

The I / S is not particularly limited, but for example, 0.01 ≦ I / S <0.2, and 0.07 ≦ I / S ≦ 0.18 is preferable. Specifically, the 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 within the range between the two.

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

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 hydrophilic treatment, the abundance of water and OH groups on the surface of the carrier powder is increased, the hydrophilicity of the carrier powder is improved, and the thickness of the coating layer 140 is likely to be more uniform.

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

1. 1. Production of supported metal catalyst 100 (Production of carrier powder)
The carrier powder was produced using the production apparatus 1 shown in FIGS. 8 to 11. As the burner gas 2a, a gas in which oxygen 5 L / min and propane gas 1 L / min were mixed was used, and this gas was ignited to form a flame (chemical flame) 7 having a temperature of 1600 ° C. or higher at the tip of the burner 2. As the raw material solution 23a, tin octylate and niobium octylate were mixed with a mineral split tarpen at a molar ratio of 0.95: 0.05 and dissolved. Oxygen was used as the mistified gas 13a. 9 L / min mistified gas 13a and 3 g / min raw material solution 23a are mixed, sprayed from the tip of the raw material supply unit 3 which is a spray nozzle (atomizer) to the center of the flame, and burned to aggregate the carrier fine particles 150. The carrier powder, which is the body, was produced. At that time, the produced carrier powder was recovered in the collector 5 (with the filter 5a) by sucking air from the slit 6b at a flow rate of 170 L / min by setting the gas discharge portion 5b to a negative pressure. The raw material supply unit 3 has a double pipe structure (total length 322.3 mm), oxygen gas is supplied from the outer cylinder 13, the raw material solution 23a is supplied to the raw material distribution cylinder 23, and a fluid nozzle and an air nozzle are supplied to the tip of the raw material distribution cylinder 23. Therefore, the raw material solution 23a was made into a mist 23b. The recovered amount of the carrier powder was 10 g or more after 60 minutes of operation.

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

First, 0.57 mL of an aqueous solution of platinum chloride hexahydrate 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. Then, 25 ml of hydrogen peroxide was added, and the pH was readjusted to 5 with NaOH.

A dispersion in which 0.50 g of the carrier powder was dispersed 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, and then heat-treating at 800 ° C. for 2 hours in air to support the metal fine particles 130 on the carrier powder. Then, heat treatment was performed in 1% hydrogen at 150 ° C. for 2 hours 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 were supported on the carrier powder was obtained.

(Formation of coating layer 140)
1.0 g of the structure obtained in the above step, 1.820 g of water and 1.789 g of ethanol were weighed and mixed with a planetary ball mill. Mixing was carried out at 270 rpm for 30 minutes under the conditions of a 45 ml zirconia pot and 10 5 mmφ zirconia balls.

Next, an alcohol-water mixture solution containing 5% by mass of Nafion (hereinafter referred to as "Nafion solution") was added to the above zirconia pot, and a planetary ball mill mixture was performed at 270 rpm for 30 minutes. The Nafion solution was a sample. It was added so that the value of I / S was different for each.

2. 2. Various evaluations <BET specific surface area>
When the specific surface area of the carrier powder was measured by BET, it was 31 m ² / g.

<Apparent density>
The apparent density of the sample molded by the uniaxial pressure method (press pressure: 20 kg / cm ² ) for the carrier powder was measured and found to be 3.6 g / cm ³ .

<XRD pattern>
When the XRD pattern was measured for the carrier powder, a peak due to the rutile phase was observed. The average particle size of the crystallites was 15 nm.

<Analysis by TEM image>
For the sample having I / S = 0.12, a TEM image was taken with a transmission electron microscope at a magnification of magnifying the length of 10 nm to a size of 0.8 cm or more. The TEM image was taken with a tungsten filament using a transmission electron microscope (HT7700 EXALENS-equipped machine) manufactured by Hitachi High-Technologies Corporation at an acceleration voltage of 120 kV. This TEM image is shown in FIG. A large number of TEM images similar to those in FIG. 12 were taken, and based on these TEM images, the average particle size D of the metal fine particles 130 and the coating layer were taken according to the method described in "1-1. Carrier fine particles 150 and carrier powder". The average thickness d of 140 was calculated.

Further, for another sample having a different I / S, the average particle size D of the metal fine particles 130 and the average thickness d of the coating layer 140 were calculated by the same method. The results are shown in Table 1.

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

1: Manufacturing equipment 2: Burner 2a: Burner gas 3: Raw material supply part 4: Reaction tube 5: Recovery device 5a: Filter 5b: Gas discharge part 6: Gas storage part 6a: Cooling gas introduction part 6b: Slit 6c: Inner peripheral wall 6d: Burner insertion hole 6g: Cooling gas 7: Flame 13: Outer cylinder 13a: Mistified gas 23: Raw material distribution cylinder 23a: Raw material solution 23b: Mist 100: Supported metal catalyst 110: Void 120: Crystallite 130: Metal fine particles 140 : Coating layer 150: Carrier fine particles 160: Branches 200: Solid polymer fuel cell 201: Abox 202: Cathode 203: Load 210A: Anode side gas diffusion layer 210K: Cathode side gas diffusion layer 220A: Abox side catalyst layer 220K: Catalyst layer 230 on the cathode side: Electrolyte film

Claims (19)

It comprises a carrier powder which is an aggregate of carrier fine particles, metal fine particles supported on the carrier powder, and a coating layer formed so as to cover the carrier fine particles.
The coating layer is composed of a polymer having proton conductivity, and is composed of a polymer.
Assuming that the average thickness of the coating layer is d and the average particle size of the metal fine particles is D,
A supported metal catalyst for a catalyst layer of a fuel cell, in which 0.22 ≦ d / D ≦ 0.51 and 2.5 nm ≦ D ≦ 4.9 nm . The supported metal catalyst according to claim 1 .
The carrier fine particles are supported metal catalysts that are fine particles of an inorganic compound. The supported metal catalyst according to claim 2 .
The inorganic compound is a supported metal catalyst that is doped. The supported metal catalyst according to claim 2 or 3.
The inorganic compound is a supported metal catalyst containing tin oxide. The supported metal catalyst according to claim 3 or 4.
The carrier powder is a supported metal catalyst having an apparent density of 2 to 3.8 g / cm ³ . The supported metal catalyst according to any one of claims 1 to 5 .
The carrier powder is a supported metal catalyst having a specific surface area of 12 m ² / g or more. The supported metal catalyst according to any one of claims 1 to 6 .
The carrier powder is a supported metal catalyst having a porosity of 50% or more. The supported metal catalyst according to any one of claims 1 to 7 .
The carrier powder is a supported metal catalyst having an angle of repose of 50 degrees or less. The supported metal catalyst according to any one of claims 1 to 8 .
The carrier powder is a supported metal catalyst having a conductivity of 0.00001 S / cm or more. The supported metal catalyst according to any one of claims 1 to 9 .
The carrier fine particles are a supported metal catalyst having a chain portion formed by fusion-bonding a plurality of crystallites in a chain shape. The supported metal catalyst according to claim 10 .
The crystallite is a supported metal catalyst having a size of 1 to 30 nm. The supported metal catalyst according to claim 10 or 11.
The chain portion comprises a plurality of branches, holes existing between the plurality of branches, and voids.
The void is a supported metal catalyst surrounded by the plurality of branches and the pores. The supported metal catalyst according to claim 12 .
The carrier powder is a supported metal catalyst having a plurality of the voids, and the voids have voids having a sphere equivalent diameter of 11 nm or less and voids larger than 11 nm by a mercury intrusion method. The method for producing a supported metal catalyst according to any one of claims 1 to 13.
A method for producing a supported metal catalyst, which comprises a mixing step.
In the mixing step, a method of mixing a structure composed of fine metal particles supported on a carrier powder and an ink containing a polymer having proton conductivity. The method according to claim 14 .
Let I be the volume of the polymer and S be the volume of the carrier powder.
The method in which the mixing step is carried out so that 0.01 ≦ I / S <0.2. The method according to claim 15 .
The method in which the mixing step is carried out so that 0.07 ≦ I / S ≦ 0.18. The method according to any one of claims 14 to 16 .
The carrier powder is an aggregate of carrier fine particles and is an aggregate.
The carrier fine particles are fine particles of an inorganic compound and are
The method, wherein the ink comprises a hydrophilic solvent. The method according to claim 17 .
The method in which the inorganic compound is doped. 17. The method according to claim 17 or claim 18 .
The method, wherein the inorganic compound comprises tin oxide.

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