Electrode catalyst layer, membrane / electrode assembly, and electrochemical device using electrode catalyst

Abstract

An electrode catalyst according to the present invention includes: a mesoporous material; and catalyst metal particles that contain platinum and a metal other than platinum, and are carried at least inside of a mesoporous material. The mesoporous material has meso pores having a mode radius of 1-25 nm and a pore volume of 1.0-3.0 cm3 / g, and the carried meso catalyst metal particles have an L10 structure, the proportion of the L10 structure being greater than 0.25.

Description

[Technical Field]

[0001] The present disclosure relates to an electrode catalyst, an electrode catalyst layer including the electrode catalyst, a membrane / electrode assembly including the electrode catalyst layer, and an electrochemical device using the membrane / electrode assembly. [Background technology]

[0002] Fuel cells are known as an example of electrochemical devices. For example, a polymer electrolyte fuel cell includes a membrane / electrode assembly for causing an electrochemical reaction (power generation reaction) between a fuel gas containing hydrogen and an oxidant gas containing oxygen.

[0003] In general, the electrode catalyst layer that constitutes the membrane / electrode assembly is formed by dispersing a catalyst, which is a catalyst metal such as platinum supported on a conductive material such as carbon black, and a proton-conductive polymer electrolyte (hereinafter referred to as an ionomer) in a solvent such as water or alcohol to prepare a catalyst paste, and then coating and drying the catalyst paste on a polymer electrolyte membrane or other substrate.

[0004] The microstructure of the catalyst layer created in this way (hereinafter referred to as the three-phase interface structure) is a structure in which the catalyst is coated with an ionomer. In this three-phase interface structure, it has been thought that contacting the catalyst metal with the ionomer would lead to improved performance from the perspective of supplying protons to the catalyst metal surface. However, in recent years, it has been pointed out that the catalyst metal in contact with the ionomer is poisoned by the ionomer, and that this actually reduces catalytic performance.

[0005] To address this problem of reduced catalyst performance, a method has been proposed in which catalytic metal particles are supported inside a support such as mesoporous carbon, and the support carrying these particles is coated with an ionomer in order to prevent the poisoning of the catalytic metal by the ionomer (for example, Patent Document 1).

[0006] In addition, there are reports that the catalytic activity can be further improved by forming an ordered structure in the alloy catalyst. Normally, when the catalyst metal is an alloy of platinum and another metal, the crystalline structure of the alloy is an irregular structure in which the second metal is randomly dissolved in the platinum, but it has been reported that the catalytic activity improves when the L12 structure, which is one of the ordered structures, is formed (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6628867 [Patent Document 2] Patent No. 6352955 Summary of the Invention [Problem to be solved by the invention]

[0008] However, among the catalysts disclosed in Patent Documents 1 and 2, catalysts having high catalytic activity have not been sufficiently investigated.

[0009] The present disclosure has been made in view of the above-mentioned problems, and aims to improve the catalytic activity of a catalytic metal supported in a mesoporous material support compared to conventional methods. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, one embodiment of the electrode catalyst according to the present disclosure is an electrode catalyst comprising a mesoporous material and catalytic metal particles containing platinum and a metal other than platinum supported at least inside the mesoporous material, wherein the mesoporous material has a mode radius of 1-25 nm and a pore volume of 1.0-3.0 cm. 3 / g, the supported catalytic metal particles have an L10 structure, and the ratio of the L10 structure is greater than 0.25.

[0011] In order to solve the above-mentioned problems, one aspect of the electrode catalyst layer according to the present disclosure is an electrode catalyst layer comprising a mesoporous material and catalytic metal particles containing platinum and a metal other than platinum, which are supported at least inside the mesoporous material, wherein the mesoporous material has a mode radius of 1-25 nm and a pore volume of 1.0-3.0 cm. 3 / g, the supported catalytic metal particles have an L10 structure, and the ratio of the L10 structure is greater than 0.25, and an ionomer.

[0012] In order to solve the above-mentioned problems, one aspect of a membrane electrode assembly according to the present disclosure provides a membrane electrode assembly comprising a polymer electrolyte membrane, a fuel electrode provided on one main surface of the polymer electrolyte membrane, and a cathode provided on the other main surface of the polymer electrolyte membrane, wherein the cathode is an electrode catalyst comprising a mesoporous material and catalytic metal particles containing platinum and a metal other than platinum, the catalytic metal particles being supported at least inside the mesoporous material, and the mesoporous material has a mode radius of 1-25 nm and a pore volume of 1.0-3.0 cm. 3 The electrode catalyst layer includes an electrode catalyst having mesopores with a pore size of 0.1 / g, wherein the supported catalytic metal particles have an L10 structure and the ratio of the L10 structure is greater than 0.25, and an ionomer.

[0013] In order to solve the above-described problems, one aspect of the electrochemical device according to the present disclosure provides a polymer electrolyte membrane, an anode provided on one main surface of the polymer electrolyte membrane, and an cathode provided on the other main surface of the polymer electrolyte membrane, wherein the cathode is an electrode catalyst including a mesoporous material and catalytic metal particles containing platinum and a metal other than platinum, the catalytic metal particles being supported at least inside the mesoporous material, and the mesoporous material has a mode radius of 1-25 nm and a pore volume of 1.0-3.0 cm. 3 The present invention provides a membrane / electrode assembly including an electrode catalyst layer containing an ionomer and an electrode catalyst having mesopores with a pore size of 0.25 / g, wherein the supported catalytic metal particles have an L10 structure and the ratio of the L10 structure is greater than 0.25. [Effects of the Invention]

[0014] The present disclosure is configured as described above and has the effect of providing higher catalytic activity than conventional catalysts. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a schematic configuration of a membrane / electrode assembly included in an electrochemical device according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram schematically illustrating the general configuration of an electrode catalyst layer provided in the membrane / electrode assembly shown in FIG. [Figure 3] FIG. 1 shows X-ray diffraction (XRD) patterns of the electrode catalysts according to Examples 1 and 2 and Comparative Examples 1 to 3 of the present disclosure. [Figure 4] FIG. 1 shows XRD patterns of the electrode catalysts according to Examples 1 and 2 and Comparative Examples 1 to 3, their fitting values, and the (110) diffraction peak component and (020) diffraction peak component in the fitting values. [Figure 5] FIG. 2 is a diagram showing the relationship between catalytic activity and the proportion of the L10 structure in each of Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 in Table 1. DETAILED DESCRIPTION OF THE INVENTION

[0016] (How one embodiment of the present disclosure was achieved) The present inventors have conducted extensive research into the insufficient catalytic activity of the catalysts described in Patent Documents 1 and 2. As a result, they have focused on the ordered alloy phase of the catalytic metal supported on the mesoporous material. As a result, they have found that catalytic activity can be improved by ensuring that the catalytic metal particles supported on the mesoporous material have an L10 structure and that the ratio of the L10 structure is greater than 0.25.

[0017] The above-mentioned findings of the present inventors have not been disclosed until now, and have novel technical features that exhibit remarkable effects. Therefore, the present disclosure specifically provides the following aspects.

[0018] The electrode catalyst according to the first aspect of the present disclosure is an electrode catalyst comprising a mesoporous material and catalytic metal particles containing platinum and a metal other than platinum supported at least inside the mesoporous material, wherein the mesoporous material has a mode radius of 1-25 nm and a pore surface area of ​​1.0-3.0 m. 2 / g, the supported catalytic metal particles may have an L10 structure, and the ratio of the L10 structure may be greater than 0.25.

[0019] According to this configuration, the ratio of catalyst particles with an L10 structure, which have high catalytic activity, to all catalyst metal particles is greater than 0.25, so that the catalytic activity of the catalyst metal particles can be increased more than before.

[0020] Furthermore, by incorporating the above-mentioned catalytic metal particles in a mesoporous material, the electrode catalyst can suppress contact between the catalytic metal particles and the ionomer even when the catalyst layer is formed using an ionomer.

[0021] Therefore, the electrode catalyst according to the first aspect of the present disclosure has the effect of being able to obtain high catalytic activity. Furthermore, when this electrode catalyst is used to fabricate a fuel cell, for example, the fuel cell can obtain high power generation performance.

[0022] The electrode catalyst according to a second aspect of the present disclosure is the electrode catalyst of the first aspect described above, wherein the ratio of the L10 structure in the catalytic metal particles is 0.60 or more.

[0023] In the electrode catalyst according to a third aspect of the present disclosure, in the first or second aspect described above, the metal different from platinum may be cobalt.

[0024] According to this configuration, the catalytic metal particles can be made of an alloy containing platinum and cobalt, which has excellent catalytic activity and durability.

[0025] In the electrode catalyst according to the fourth aspect of the present disclosure, in any one of the first to third aspects described above, the mode radius of the mesopores may be 3 nm or more and 6 nm or less.

[0026] With this configuration, the mesopore size is sufficiently small compared to when the mode radius of the mesopores is 6 nm or more, so the ionomer prevents penetration into the pores of the mesoporous material, enabling efficient supply of reactant gas to the catalytic metal particles inside the mesoporous material. Furthermore, compared to when the mode radius of the mesopores is 3 nm or less, the mesopore size is sufficiently large, so the catalytic metal particles can be supported within the mesopores. As a result, poisoning of the catalytic metal by the ionomer is reduced, and a decrease in catalytic activity is suppressed.

[0027] An electrode catalyst according to a fifth aspect of the present disclosure is any one of the first to fourth aspects described above, wherein the mesoporous material may be mesoporous carbon.

[0028] With this configuration, since the mesoporous material is mesoporous carbon, the electrode catalyst can have excellent electrical conductivity and water repellency. Furthermore, when this electrode catalyst is used to fabricate a fuel cell, for example, the fuel cell can achieve high power generation performance.

[0029] An electrode catalyst layer according to a sixth aspect of the present disclosure is an electrode catalyst comprising a mesoporous material and catalytic metal particles containing platinum and a metal other than platinum supported at least inside the mesoporous material, wherein the mesoporous material has a mode radius of 1-25 nm and a pore volume of 1.0-3.0 m 2 / g, the supported catalytic metal particles have an L10 structure, and the ratio of the L10 structure is greater than 0.25, and an ionomer.

[0030] According to this configuration, the electrode catalyst layer can utilize the high proton conductivity of the ionomer. Furthermore, the electrode catalyst layer can suppress a decrease in activity caused by contact between the catalytic metal particles and the ionomer. Therefore, the electrode catalyst layer according to the sixth aspect of the present disclosure has the effect of being able to obtain a highly active electrode catalyst layer. Furthermore, when this electrode catalyst layer is used to fabricate a fuel cell, for example, the fuel cell can obtain high power generation performance.

[0031] The electrode catalyst layer according to a seventh aspect of the present disclosure is the electrode catalyst layer according to the sixth aspect described above, which may contain at least one of carbon black and carbon nanotubes.

[0032] The carbon particles that make up carbon black and carbon nanotubes are very fine, with an average particle size in the range of 10-100 nm. Therefore, electrode catalyst layers containing carbon particles can achieve high drainage due to capillary forces. On the other hand, electrode catalyst layers made solely of mesoporous materials can sometimes have issues with drainage.

[0033] With this configuration, the electrode catalyst layer contains at least one of carbon black and carbon nanotubes, which improves drainage compared to a catalyst layer made only of mesoporous material. Furthermore, when this electrode catalyst layer is used to fabricate a fuel cell, for example, the fuel cell can achieve high power generation performance.

[0034] An electrode catalyst layer according to an eighth aspect of the present disclosure is the electrode catalyst layer according to the seventh aspect described above, wherein the carbon black is Ketjen black.

[0035] With this configuration, the carbon black contained in the electrode catalyst layer is Ketjen black, so the electrode catalyst layer can have excellent electrical conductivity and drainage. Furthermore, when this electrode catalyst layer is used to fabricate a fuel cell, for example, the fuel cell can achieve high power generation performance.

[0036] A membrane electrode assembly according to a ninth aspect of the present disclosure includes a polymer electrolyte membrane, a fuel electrode provided on one main surface of the polymer electrolyte membrane, and a cathode provided on the other main surface of the polymer electrolyte membrane, wherein the cathode is an electrode catalyst including a mesoporous material and catalytic metal particles containing platinum and a metal other than platinum, the catalytic metal particles being supported at least inside the mesoporous material, and the mesoporous material has a mode radius of 1-25 nm and a pore volume of 1.0-3.0 cm. 3 The electrode catalyst layer includes an ionomer and a catalyst having mesopores with a pore size of 0.25 or more and wherein the supported catalytic metal particles have an L10 structure and the ratio of the L10 structure is greater than 0.25.

[0037] This configuration allows the electrode catalyst layer included in the air electrode of the membrane-electrode assembly to utilize the high proton conductivity of the ionomer. Furthermore, this electrode catalyst layer can suppress the decrease in activity caused by contact between the catalytic metal particles and the ionomer. Therefore, the membrane-electrode assembly can achieve high catalytic activity.

[0038] Therefore, when this membrane / electrode assembly is used to fabricate, for example, a fuel cell, the fuel cell can achieve high power generation performance.

[0039] An electrochemical device according to a tenth aspect of the present disclosure comprises a polymer electrolyte membrane, an anode provided on one main surface of the polymer electrolyte membrane, and an cathode provided on the other main surface of the polymer electrolyte membrane, wherein the cathode comprises an electrode catalyst including a mesoporous material and catalytic metal particles containing platinum and a metal other than platinum, the catalytic metal particles being supported at least inside the mesoporous material, and the mesoporous material has a mode radius of 1-25 nm and a pore volume of 1.0-3.0 cm. 3 The membrane / electrode assembly includes an electrode catalyst layer containing an ionomer and an electrode catalyst having mesopores with a pore size of 0.25 / g, wherein the supported catalytic metal particles have an L10 structure and the ratio of the L10 structure is greater than 0.25.

[0040] According to this configuration, the electrode catalyst layer included in the air electrode of the membrane / electrode assembly can utilize the high proton conductivity of the ionomer. Furthermore, this electrode catalyst layer can suppress a decrease in activity caused by contact between the catalytic metal particles and the ionomer. Therefore, an electrochemical device including this membrane / electrode assembly can achieve high catalytic activity. Therefore, for example, when the electrochemical device according to the tenth aspect of the present disclosure is a fuel cell, the fuel cell can achieve high power generation performance.

[0041] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that, in the following, identical or corresponding components throughout the drawings will be designated by the same reference numerals, and descriptions thereof may be omitted.

[0042] [Embodiment] An electrochemical device according to an embodiment of the present disclosure will be described. While a fuel cell will be described as an example of an electrochemical device according to an embodiment of the present disclosure, the electrochemical device is not limited to a fuel cell and may be, for example, a water electrolysis device that electrolyzes water to produce hydrogen and oxygen.

[0043] (membrane / electrode assembly) First, with reference to FIG. 1, the configuration of a membrane / electrode assembly 10 included in an electrochemical device according to the present invention will be described. FIG. 1 is a schematic diagram showing an example of the general configuration of a membrane / electrode assembly 10 included in an electrochemical device according to an embodiment of the present disclosure. As shown in FIG. 1, the membrane / electrode assembly 10 includes a polymer electrolyte membrane 11, a fuel electrode (anode) and an air electrode (cathode) each including an electrode catalyst layer 12 and a gas diffusion layer 13, and is configured such that the polymer electrolyte membrane 11 is sandwiched between the fuel electrode and the air electrode. That is, as shown in FIG. 1, a pair of electrode catalyst layers 12 are formed on both sides of the polymer electrolyte membrane 11, and a pair of gas diffusion layers 13 are further disposed so as to sandwich the pair of electrode catalyst layers 12.

[0044] (polymer electrolyte membrane) The polymer electrolyte membrane 11 conducts ions (protons) between the air electrode and the fuel electrode and must have both proton conductivity and gas barrier properties. Examples of the polymer electrolyte membrane 11 include an ion-exchange fluororesin membrane or an ion-exchange hydrocarbon-based resin membrane. Perfluorosulfonic acid resin membranes are particularly suitable because they have high proton conductivity and are stable even in the power generation environment of a fuel cell. The ion exchange capacity of the ion exchange resin is preferably 0.9 to 2.0 milliequivalents / g dry resin. An ion exchange capacity of 0.9 milliequivalents / g dry resin or more facilitates high proton conductivity, while an ion exchange capacity of 2.0 milliequivalents / g dry resin or less is suitable because it suppresses swelling of the resin due to water absorption and thus reduces dimensional changes in the polymer electrolyte membrane 11. The thickness of the polymer electrolyte membrane 11 is preferably 5 μm to 50 μm. When the membrane thickness is 5 μm or more, high gas barrier properties are obtained, and when it is 50 μm or less, high proton conductivity is obtained.

[0045] (gas diffusion layer) The gas diffusion layer 13 is a layer that combines current collection, gas permeability, and water repellency, and may be configured to include two layers: a substrate 13a and a coating layer 13b, as shown in Fig. 1. The substrate 13a may be made of a material that is highly conductive and permeable to gases and liquids, such as porous materials such as carbon paper, carbon fiber cloth, and carbon fiber felt. The coating layer 13b is interposed between the substrate 13a and the electrode catalyst layer 12 to reduce the contact resistance therebetween and improve liquid permeability (water repellency). The coating layer 13b is formed, for example, from a conductive material such as carbon black and a water-repellent resin such as polytetrafluoroethylene (PTFE) as its main components.

[0046] (electrode catalyst layer) The electrode catalyst layer 12 is a layer that accelerates the rate of electrochemical reactions of the electrodes. The electrode catalyst layer 12 according to an embodiment of the present disclosure will be described with reference to Fig. 2. Fig. 2 is a diagram that schematically illustrates the general configuration of the electrode catalyst layer 12 included in the membrane / electrode assembly 10 shown in Fig. 1.

[0047] As shown in Fig. 2, the electrode catalyst layer 12 according to the embodiment of the present disclosure includes an electrode catalyst 20 and an ionomer 30 (proton-conductive resin). The electrode catalyst 20 includes a mesoporous material 21 and catalytic metal particles 22 that contain platinum and a metal other than platinum and are supported at least inside the mesoporous material 21. The electrode catalyst 20 is an electrode catalyst for an electrochemical cell. Therefore, the electrode catalyst 20 can be used, for example, in fuel cells, electrochemical cells of water electrolysis devices, and electrochemical cells of electrochemical compressors.

[0048] Furthermore, a water-repellent material 31 may be added to the electrode catalyst layer 12 according to the embodiment of the present disclosure to improve drainage. For example, the electrode catalyst layer 12 may contain at least one of carbon black and carbon nanotubes as the water-repellent material 31. The carbon black may be Ketjenblack.

[0049] The electrode catalyst layer 12 according to the embodiment of the present disclosure can be formed by, for example, a method commonly used in fuel cells. For example, the electrode catalyst layer 12 can be formed by dispersing the above-described material in a solvent containing water or alcohol, applying the dispersion to a substrate such as the polymer electrolyte membrane 11, the gas diffusion layer 13, or various transfer films, and drying the dispersion.

[0050] The electrode catalyst layer 12 having the above-described configuration can be used as an electrode catalyst layer for an air electrode (cathode). It may also be used as an electrode catalyst layer for a fuel electrode (anode). Alternatively, the electrode catalyst layer for the fuel electrode may have a configuration similar to that of a conventional catalyst layer generally used in membrane electrode assemblies for fuel cells. In the membrane electrode assembly 10 according to an embodiment of the present disclosure, it is appropriate to use the electrode catalyst layer 12 having the above-described configuration at least as an electrode catalyst layer for the air electrode.

[0051] In the membrane / electrode assembly 10 according to the embodiment of the present disclosure, when the electrode catalyst layer of the fuel electrode has the same configuration as a conventional catalyst layer, it can be formed as follows: For example, platinum or a platinum alloy catalyst supported on carbon black and an ionomer are dispersed in a solvent containing water or alcohol, and the dispersion is applied to a substrate such as the polymer electrolyte membrane 11, the gas diffusion layer 13, or various transfer films, followed by drying.

[0052] (mesoporous materials) Hereinafter, mesoporous carbon will be used as an example of the mesoporous material 21 contained in the electrode catalyst 20 according to an embodiment of the present disclosure, but the mesoporous material 21 is not limited to mesoporous carbon. Other materials may be used as long as they have the same mode radius and pore volume. Examples of materials other than mesoporous carbon include mesoporous materials 21 made of oxides of titanium, tin, niobium, tantalum, zirconium, aluminum, silicon, and the like.

[0053] The mesoporous material 21 according to the embodiment of the present disclosure has a mesopore mode radius of 1-25 nm and a mesopore volume of 1.0-3.0 cm 3 / g. The mesopore volume is preferably 1.0 cm 3 / g or more is preferable because many catalytic metal particles 22 can be supported inside the mesoporous material 21. 3 / g or less is appropriate because it increases the strength of the mesoporous material 21 as a structure. 3 / g” is the value at which the mesopores of the mesoporous material 21 are filled before the catalytic metal particles 22 are supported on the mesoporous material 21 .

[0054] Furthermore, in the mesoporous material 21 according to the embodiment of the present disclosure, if the mode radius of the mesopores is 3 nm or more, it is preferable because this facilitates the supply of reaction gas into the pores, and if it is 6 nm or less, it becomes difficult for the ionomer 30 to penetrate into the pores.

[0055] Furthermore, the mesoporous material 21 according to the embodiment of the present disclosure may have an average particle size of 200 nm or more. If the average particle size is 200 nm or more, the proportion of catalytic metal particles 22 that are affected by poisoning by the ionomer 30 is reduced, thereby improving catalytic activity. Furthermore, the average particle size of the mesoporous material 21 may be 1000 nm or less. If the average particle size is 1000 nm or less, the reactant gas is more easily supplied to the catalytic metal particles 22 supported inside the mesoporous material 21.

[0056] The average particle size of the mesoporous material 21 may be measured using a laser diffraction particle size distribution analyzer or the like while the mesoporous material 21 is dispersed in a solvent, or may be observed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). When measuring the particle size distribution by dispersing the mesoporous material 21 in a solvent, it is necessary to prevent the mesoporous material 21 from agglomerating. Therefore, water, alcohol, or a mixture of water and alcohol can be appropriately used as the solvent. To further improve dispersibility, it is appropriate to add a dispersant to the solvent. Examples of dispersants include perfluorosulfonic acid resin, poly(oxyethylene)octylphenyl ether, and polyoxyethylenesorbitan monolaurate. To further improve dispersibility, it is appropriate to perform a dispersion treatment after mixing the solvent and mesoporous material. Examples of dispersion treatment devices include an ultrasonic homogenizer, a wet jet mill, a ball mill, and a mechanical stirrer.

[0057] Furthermore, the method for producing the mesoporous material 21 according to the embodiment of the present disclosure is not particularly limited, but for example, the method described in Japanese Patent Application Laid-Open No. 2010-208887 can be appropriately used.

[0058] The mesoporous material 21 produced by this method has a structure in which the mesopores have a large pore volume and are interconnected. This makes it easy to support catalytic metal particles 22 in the pores, and facilitates the supply of reaction gas to the supported catalytic metal particles 22. Furthermore, in order to adjust the average particle size of the mesoporous material 21, a pulverization treatment may be performed after synthesis. Examples of pulverization methods include a wet bead mill, a dry bead mill, a wet ball mill, a dry ball mill, a wet jet mill, and a dry jet mill. Among these, a wet bead mill is preferred because it facilitates pulverization to a fine particle size.

[0059] (Catalytic metal particles) The catalytic metal particles 22 supported at least inside the mesoporous material 21 according to an embodiment of the present disclosure contain platinum and a metal other than platinum. Examples of metals other than platinum include cobalt, nickel, manganese, titanium, aluminum, chromium, iron, molybdenum, tungsten, ruthenium, palladium, rhodium, iridium, osmium, copper, and silver. Among these, an alloy of platinum and cobalt is suitable because it has high catalytic activity for the oxygen reduction reaction and good durability in the power generation environment of a fuel cell.

[0060] (water repellent material) Typically, an electrode catalyst layer containing carbon particles with an average particle size of 10 to 100 nm exhibits high water repellency due to capillary forces. However, because the mesoporous material 21 used in the electrode catalyst layer 12 according to an embodiment of the present disclosure has an average particle size of 200 nm or more, issues with drainage may arise. Therefore, at least one of carbon black and carbon nanotubes may be added to the electrode catalyst layer 12 as a water repellent material. This configuration can improve the drainage properties of the electrode catalyst layer 12. Therefore, when the membrane / electrode assembly 10 according to an embodiment of the present disclosure is used in a fuel cell, the power generation performance of the fuel cell can be improved.

[0061] Examples of carbon black include Ketjenblack, acetylene black, Vulcan, and Black Pearl. Examples of carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes. Ketjenblack is particularly suitable because its aggregates develop linearly, allowing effective drainage paths to be formed in the electrode catalyst layer 12 even with a small amount added.

[0062] (ionomer) Ion exchange resins can be used as the ionomer 30 (proton conductive resin) according to the embodiment of the present disclosure. Perfluorosulfonic acid resins are particularly suitable because they have high proton conductivity and are stable even in the power generation environment of a fuel cell. The ion exchange capacity of the ion exchange resin may be 0.9 to 2.0 milliequivalents / g dry resin. An ion exchange capacity of 0.9 milliequivalents / g dry resin or greater facilitates high proton conductivity. An ion exchange capacity of 2.0 milliequivalents / g dry resin or less suppresses swelling of the resin due to water absorption, thereby minimizing the inhibition of gas diffusion within the electrode catalyst layer 12. The weight ratio of the ionomer 30 to the total weight of the mesoporous material 21 and water-repellent material 31 contained in the electrode catalyst layer 12 is preferably 0.2 to 2.0.

[0063] [Example] Hereinafter, a method for synthesizing the electrode catalysts (hereinafter sometimes abbreviated as catalysts) provided in Examples 1 and 2 and Comparative Examples 1 to 3 according to the present disclosure will be described.

[0064] (Catalyst synthesis) [Example 1] The mesoporous material used was commercially available mesoporous carbon (CNovel, manufactured by Toyo Tanso Co., Ltd.) with a designed pore size of 10 nm. This mesoporous carbon was added to a mixed solvent containing equal amounts of water and ethanol to prepare a slurry with a solids concentration of 1 wt%. Zirconia beads with a diameter of 0.5 mm were added to this slurry and milled using a media-stirring wet bead mill (Labstar Mini, manufactured by Ashizawa Finetech Co., Ltd.) at a peripheral speed of 12 m / s for 20 minutes. The zirconia beads were removed from the milled slurry, the solvent was evaporated, and the resulting aggregates were ground in a mortar to produce a carbon support (mesoporous material 21).

[0065] 1 g of the obtained carbon support was added to 400 mL of a mixed solvent of water:ethanol = 1:1 (weight ratio) and ultrasonically dispersed for 15 minutes. After dispersion, a 14 wt% dinitrodiamine platinum nitrate solution was added dropwise while stirring under a nitrogen atmosphere so that the platinum content relative to the carbon support was 50 wt%, and the mixture was heated and stirred at 80°C for 6 hours. After cooling, the mixture was filtered, washed, and dried at 80°C for 15 hours. The obtained aggregates were ground in a mortar and pestle and heat-treated at 220°C for 2 hours under a nitrogen:hydrogen atmosphere of 85:15 to produce platinum-supported mesoporous carbon (hereinafter referred to as Pt / MPC).

[0066] 0.3 g of the obtained Pt / MPC was placed in a conical beaker and allowed to stand at 30° C. / 90% RH (relative humidity) for 12 hours to allow water vapor to be adsorbed onto the Pt / MPC (water vapor adsorption treatment step).

[0067] Furthermore, 30 mL of pure water containing cobalt chloride hexahydrate was added to the conical beaker containing the Pt / MPC, with the molar ratio of cobalt to the total amount of platinum and cobalt being 0.48. After ultrasonic dispersion for 15 minutes, 30 mL of 1 wt% sodium borohydride solution was slowly added dropwise, followed by stirring at room temperature for 10 minutes to reduce the cobalt. The mixture was filtered, washed, and dried at 80°C for 15 hours. The resulting powder was ground in a mortar, sealed in an alumina crucible, and heat-treated in a reducing atmosphere. Specifically, the alumina crucible containing the powder was placed in a Tammann tube-type atmospheric electric furnace (Motoyama, S6T-2035D). The temperature was first raised from room temperature to 120°C over 10 minutes, then held at that temperature for 60 minutes. The temperature was then raised to 1000°C at a rate of 150°C / hour and held at that temperature for 30 minutes. The tube was then heated to 1100°C at a rate of 100°C / hour and held at that temperature for 2 hours. The tube was then cooled to 1000°C at a rate of 100°C / hour and held at that temperature for 30 minutes. The tube was then cooled to room temperature at a rate of 150°C / hour. A 97:3 nitrogen / hydrogen mixed gas was flowed through the tube at a flow rate of 1 L / min to maintain a reducing atmosphere. The resulting powder was then stirred in 100 mL of a 0.2 mol / L aqueous sulfuric acid solution at 80°C for 2 hours, filtered, and washed. The powder was then stirred in 100 mL of a 0.2 mol / L aqueous nitric acid solution at 70°C for 2 hours to dissolve the excess cobalt on the outermost surface. This was filtered, washed, and dried at 80°C for 15 hours. The resulting powder was ground in a mortar to produce platinum-cobalt alloy-supported mesoporous carbon (hereinafter referred to as PtCo / MPC) as the catalyst of Example 1.

[0068] [Example 2] The catalyst (PtCo / MPC) of Example 2 was prepared in the same manner as the catalyst of Example 1, except for the heat treatment conditions for alloying.

[0069] Specifically, in the heat treatment for alloying, the temperature was first raised from room temperature to 120°C over 10 minutes and then held at that temperature for 60 minutes. The temperature was then raised to 1000°C at a rate of 150°C / hour and held at that temperature for 30 minutes. The temperature was then raised to 1100°C at a rate of 100°C / hour and held at that temperature for 30 minutes. The temperature was then lowered to 1000°C at a rate of 100°C / hour and held at that temperature for 30 minutes. The temperature was then lowered to room temperature at a rate of 150°C / hour.

[0070] [Comparative Example 1] The catalyst (PtCo / MPC) of Comparative Example 1 was prepared in the same manner as the catalyst of Example 1, except for the amount of cobalt chloride hexahydrate and the heat treatment conditions for alloying.

[0071] Specifically, after water vapor was adsorbed onto Pt / MPC, the amount of cobalt chloride hexahydrate added to the conical beaker containing Pt / MPC was adjusted so that the molar ratio of cobalt to the total amount of platinum and cobalt was 0.28. Furthermore, during the heat treatment for alloying, the temperature was first raised from room temperature to 120°C over 10 minutes and then held at that temperature for 60 minutes. The temperature was then raised to 700°C at a rate of 150°C / hour and held at that temperature for 30 minutes. The temperature was then raised to 800°C at a rate of 100°C / minute and held at that temperature for 30 minutes. The temperature was then lowered to 700°C at a rate of 100°C / hour and held at that temperature for 30 minutes. The temperature was then lowered to room temperature at a rate of 150°C / minute.

[0072] Comparative Example 2 The catalyst (PtCo / MPC) of Comparative Example 2 was prepared in the same manner as the catalyst of Comparative Example 1, except for the heat treatment conditions for alloying.

[0073] Specifically, in the heat treatment for alloying, the temperature was first raised from room temperature to 120°C over 10 minutes and then held at that temperature for 60 minutes. The temperature was then raised to 800°C at a rate of 150°C / hour and held at that temperature for 30 minutes. The temperature was then raised to 900°C at a rate of 100°C / minute and held at that temperature for 30 minutes. The temperature was then lowered to 800°C at a rate of 100°C / hour and held at that temperature for 30 minutes. The temperature was then lowered to room temperature at a rate of 150°C / minute.

[0074] Comparative Example 3 The catalyst of Comparative Example 3 was prepared in the same manner as the catalyst of Comparative Example 2, except for the supported carbon black.

[0075] Specifically, a commercially available platinum-supported carbon black catalyst (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E) was used instead of the Pt / MPC that had been subjected to water vapor adsorption treatment. In the heat treatment for alloying, the temperature was first raised from room temperature to 120°C over 10 minutes and then held at that temperature for 60 minutes. The temperature was then raised to 800°C at a rate of 150°C / hour and held at that temperature for 30 minutes. The temperature was then raised to 900°C at a rate of 100°C / minute and held at that temperature for 30 minutes. The temperature was then lowered to 800°C at a rate of 100°C / hour and held at that temperature for 30 minutes. The temperature was then lowered to room temperature at a rate of 150°C / minute.

[0076] Comparative Example 4 The catalyst of Comparative Example 4 was prepared in the same manner as the catalyst of Example 1, except for the supported carbon black.

[0077] Specifically, a commercially available platinum-supported carbon black catalyst (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E) was used instead of the Pt / MPC that had been subjected to water vapor adsorption treatment. In the heat treatment for alloying, the temperature was first raised from room temperature to 120°C over 10 minutes and then held at that temperature for 60 minutes. The temperature was then raised to 1000°C at a rate of 150°C / hour and held at that temperature for 30 minutes. The temperature was then raised to 1100°C at a rate of 100°C / minute and held at that temperature for 120 minutes. The temperature was then lowered to 1000°C at a rate of 100°C / hour and held at that temperature for 30 minutes. The temperature was then lowered to room temperature at a rate of 150°C / minute.

[0078] The heat treatment conditions for the catalysts of Examples 1 and 2 and Comparative Examples 1 to 4 are summarized in Table 1 below for easy comparison with other examples.

[0079] (Calculation of catalyst loading rate) The overall catalyst loading rate of platinum and cobalt for the catalysts of Examples 1 and 2 and Comparative Examples 1-4 was determined as follows. First, the catalyst was weighed into a quartz beaker and heated in an electric furnace to burn off the carbon. After cooling, a small amount of nitric acid and hydrochloric acid was added to the beaker and heated, followed by dilution with pure water. The catalyst was then introduced into an inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyzer (Spectro CIROS-1200) for quantitative analysis of platinum and cobalt.

[0080] The weights of platinum and cobalt in the catalyst were determined in this manner, and the catalyst loading rate was calculated from the ratio of the weight of platinum and cobalt to the total weight of the catalyst.

[0081] (Calculation of the ratio of L10 structure) The ratio of the L10 structure (L10 ordered alloy structure) for the catalysts of Examples 1 and 2 and Comparative Examples 1-3 was determined as follows. X-ray diffraction (XRD) measurements were performed using a Spectris X'pert Pro MPD. First, catalyst powder was spread on a sample holder with a polished recess so that the catalyst powder surface was aligned with the edge of the sample holder, and then the sample holder was set in the instrument. CuKα incident light was used, and a one-dimensional semiconductor detector was used as the detector. 2θ-θ measurements were performed in the range of 2θ = 10-90° using a focusing optical system. Figure 3 shows the XRD patterns for the catalysts of Examples 1 and 2 and Comparative Examples 1-4.

[0082] The obtained XRD patterns were subjected to fitting processing using the analysis software HighScore Plus provided with the instrument, following the procedure below. First, the data background was determined using a Cubic Spline curve and subtracted. Next, the data curve after background subtraction was subjected to multi-peak fitting across the entire angle range. A symmetric pseudo-Voigt function was used to represent each peak shape. In particular, the data curve in the 2θ = 45-50° range was considered to be a superposition of two peaks. If the areas of these two peaks, i.e., the peak corresponding to the L10 structure (110) diffraction on the low angle side and the peak corresponding to the (020) diffraction on the low angle side, are designated S1 and S2, respectively, the ratio R of the L10 structure is expressed by the following equation (1):

number

[0083] Figure 4 shows the XRD pattern measurements (dots) in the 45-50° range when the multi-peak fitting was performed on the measured XRD patterns of Examples 1 and 2 and Comparative Examples 1-4. The fitted values ​​(solid lines) show the components of the (110) diffraction peak P1 (dotted lines) and the (020) diffraction peak P2 (dashed lines) in the fitted values. In other words, S1 in Equation (1) corresponds to the integral of the counts on the vertical axis for the (110) diffraction peak P1. S2 in Equation (1) corresponds to the integral of the counts on the vertical axis for the (020) diffraction peak P2. However, in Figure 4, the (110) diffraction peak P1 and the (020) diffraction peak P2 are shifted downwards because they would overlap with the fitted values ​​and be difficult to distinguish if shown as they are.

[0084] (Catalytic activity evaluation) In order to evaluate the performance of each of the catalysts of Examples 1 and 2 and the catalysts of Comparative Examples 1 to 4, a single fuel cell having an electrode catalyst layer 12 containing each of these catalysts was fabricated as follows.

[0085] First, the catalyst layers for the air electrodes of Examples 1 and 2 and Comparative Examples 1 and 2 were fabricated using the following procedure. The catalysts of Examples 1 and 2 and Comparative Examples 1 and 2, along with Ketjen Black (EC300J, manufactured by Lion Specialty Chemicals) in an amount half the weight of the mesoporous carbon contained in the catalyst, were added to a mixed solvent containing equal amounts of water and ethanol and stirred. An ionomer (Nafion, manufactured by DuPont) was added to the resulting slurry so that the weight ratio of the ionomer to the total carbon (mesoporous carbon + Ketjen Black) was 1.2, and a dispersion process was performed. The resulting catalyst ink was spray-coated onto a polymer electrolyte membrane 11 (Nafion, manufactured by DuPont) to fabricate the catalyst layer for the air electrode.

[0086] Meanwhile, the catalyst layers for the air electrodes of Comparative Examples 3 and 4 were prepared by the following procedure. The catalysts of Comparative Examples 3 and 4 were introduced into a mixed solvent containing equal amounts of water and ethanol and stirred. An ionomer (Nafion, manufactured by DuPont) was introduced into the resulting slurry so that the weight ratio of the ionomer to the carbon support was 0.8, and a dispersion treatment was carried out. The catalyst ink thus obtained was applied by spraying onto a polymer electrolyte membrane 11 (Nafion, manufactured by DuPont) to prepare the catalyst layers for the air electrodes.

[0087] Next, a catalyst layer for the anode was formed in the following manner: The catalyst layer for the anode was the same as that in Examples 1 and 2 and Comparative Examples 1-4.

[0088] First, a commercially available platinum-supported carbon black catalyst (TEC10E50E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was added to a mixed solvent containing equal amounts of water and ethanol and stirred. An ionomer (Nafion manufactured by DuPont) was added to the resulting slurry so that the weight ratio of the ionomer to the carbon support was 0.8, and the mixture was subjected to ultrasonic dispersion treatment. The catalyst ink thus obtained was applied by spraying to the main surface of the polymer electrolyte membrane 11 opposite to the main surface on which the air electrode catalyst layer was formed, to prepare a catalyst layer for the fuel electrode.

[0089] A gas diffusion layer 13 (GDL25BC manufactured by SGL Carbon Japan Co., Ltd.) was placed on each of the thus-prepared air electrode catalyst layers and fuel electrode catalyst layers of Examples 1 and 2 and Comparative Examples 1 to 4, and the gas diffusion layer 13 was heated to a high temperature of 140° C. with a pressure of 7 kgf / cm 2 A pressure of 100 MPa was applied for 5 minutes to prepare a membrane / electrode assembly 10.

[0090] The obtained membrane / electrode assembly was sandwiched between separators having serpentine-shaped flow channels, and this was assembled into a predetermined jig to fabricate a single cell of a fuel cell.

[0091] The temperature of the resulting single fuel cell was maintained at 65°C. Hydrogen with a dew point of 65°C was supplied to the fuel electrode at a flow rate of 70% utilization, and air with a dew point of 65°C was supplied to the air electrode at a flow rate of 40% utilization. The voltages of the fuel cell were measured during constant current operation using an electronic load device (Kikusui Electronics Co., Ltd. PLZ-664WA). The fuel cell's electrical resistance was also measured in situ during the measurements using a low-resistance meter with a fixed frequency of 1 kHz. The current value at 0.9 V was read from the current-voltage curve, corrected for the fuel cell's electrical resistance. This was normalized by the amount of platinum contained in the cathode catalyst layer to provide an index of catalytic activity. This is called mass activity at 0.9 V (A / g-Pt) and is commonly used as an index of fuel cell catalytic activity.

[0092] The production methods, physical properties, etc. of the catalysts of Examples 1 and 2 and the catalysts of Comparative Examples 1 to 4 prepared as described above are summarized in Table 1 below.

[0093] [Table 1] Table 1 summarizes the production methods (production conditions), physical properties, and catalytic activity for the catalysts of Examples 1 and 2 and Comparative Examples 1-4. In other words, for each of Examples 1 and 2 and Comparative Examples 1-4 listed in the horizontal columns, Table 1 lists the type of catalyst before alloying, the molar ratio of charged cobalt to the total amount of platinum and cobalt, and heat treatment programs 1-5, which are examples of heat treatment conditions for each of the catalysts. These heat treatment programs 1-5 are executed continuously.

[0094] Heat treatment program 1 shows the time (10 minutes) corresponding to the rate at which the catalyst is heated from the initial temperature (room temperature) to 120° C., and the holding time (60 minutes) for holding the catalyst at 120° C. The conditions for heat treatment program 1 are the same for Examples 1 and 2 and Comparative Examples 1-4.

[0095] Heat treatment program 2 indicates the rate (°C / hour) for raising the temperature of the catalyst from the above temperature (120°C) to a first temperature higher than this temperature, and the holding time (minutes) for holding the catalyst at the first temperature. For example, in Example 1, in heat treatment program 2, the catalyst was raised in temperature from 120°C to 1000°C at a heating rate of 150°C / hour, and the catalyst was held at the catalyst temperature of 1000°C for 30 minutes.

[0096] Heat treatment program 3 indicates the rate (°C / hour) for raising the temperature of the catalyst from a first temperature to a second temperature higher than the first temperature, and the holding time (minutes) for holding the catalyst at the second temperature. For example, in Example 1, in heat treatment program 3, the catalyst was raised in temperature from 1000°C to 1100°C at a heating rate of 100°C / hour, and the catalyst was held at the catalyst temperature of 1100°C for 120 minutes.

[0097] Heat treatment program 4 indicates the rate (°C / hour) for lowering the catalyst temperature from the second temperature to the third temperature and the holding time (minutes) for holding the catalyst at the third temperature. In Heat Treatment Program 4 of this example, in Examples 1 and 2 and Comparative Examples 1-4, the third temperature was set to the same temperature as the first temperature in Heat Treatment Program 2, and the holding time was set to the same time as the holding time in Heat Treatment Program 2. For example, in Example 1, Heat Treatment Program 4 lowered the catalyst temperature from 1100°C to 1000°C at a temperature drop rate of 100°C / hour, and the catalyst was held at 1000°C for 30 minutes. The following Heat Treatment Program 5 was then performed.

[0098] Heat treatment program 5 indicates the rate (°C / hour) for cooling the catalyst from the first temperature to room temperature. Note that in all of Examples 1 and 2 and Comparative Examples 1-4, the catalyst was held at room temperature for zero time. For example, in Example 1, heat treatment program 5 caused the catalyst to cool from 1000°C to room temperature at a rate of 150°C / hour. This marked the end of the heat treatment of the catalyst of Example 1.

[0099] Furthermore, in Table 1, for each of Examples 1 and 2 and Comparative Examples 1 to 4 listed in each horizontal column, each vertical row shows the physical properties and power generation performance in terms of the catalyst loading rate (combined platinum and cobalt), the ratio of the L10 structure, and catalytic activity.

[0100] First, we compared Comparative Examples 1 and 2 with Comparative Example 3 to examine the differences in the ratio of the L10 structure due to differences in the carbon support and heat treatment conditions. As shown in Table 1, in Comparative Example 3, in which Ketjen black (KB) was used as the carbon support, the ratio of the L10 structure was 0.02. On the other hand, in Comparative Example 1, in which mesoporous carbon (MPC) was used as the carbon support, the ratio of the L10 structure was 0.15. Furthermore, in Comparative Example 2, in which the maximum temperature was even higher than in Comparative Example 1, the ratio of the L10 structure was 0.20. This is thought to reflect the fact that the use of mesoporous carbon, which has a larger pore surface area than Ketjen black and can support catalytic metal particles in a highly dispersed manner, prevented the aggregation of catalytic metal particles. In addition, the sufficiently long total heat treatment time allowed cobalt to diffuse until it reached an energetically stable atomic site, resulting in the formation of a thermodynamically more stable alloy phase with the L10 structure. However, the catalytic activity of fuel cells using the catalysts of Comparative Examples 1 and 2 as the catalysts for the air electrode was almost the same as that of Comparative Example 3, in which the L10 structure was hardly formed.

[0101] In Comparative Examples 1 to 3, the cobalt molar ratios in the feed were the same and the catalyst loading rates were almost the same, as shown in Table 1. Although significant differences occurred in the L10 structure ratio by changing the total history time of the heat treatment, the catalytic activity was almost the same. This suggests that within the range of the L10 structure ratio of these catalysts, there is no significant impact on the catalytic activity.

[0102] Next, Examples 1 and 2 will be compared with Comparative Examples 1-3. In Examples 1 and 2, the maximum temperature during the heat treatment was 1100°C. In Example 2, the holding time at the maximum temperature was 30 minutes, while in Example 1, the holding time at the maximum temperature was 120 minutes (2 hours). Comparing the XRD patterns of the catalysts of Examples 1 and 2 with those of Comparative Examples 1-3, as shown in Figure 4, the peaks near 45-50° in Examples 1 and 2 are asymmetric with a shoulder on the high-angle side, whereas those in Comparative Example 2 are nearly symmetric. This corresponds to the fact that, in the disordered phase, only one peak appears in this angle range, whereas in the L10 structure, another diffraction peak is formed due to the long-range order structure associated with the formation of the L10 structure. When the peaks were resolved by peak fitting and the ratio of the L10 structure was calculated according to formula (1), the results were 0.61 for Example 1 and 0.65 for Example 2, while the results were 0.15, 0.20, and 0.02 for Comparative Examples 1-3, respectively, confirming that Examples 1 and 2 indeed had a larger ratio of the L10 structure than Comparative Examples 1-3. Furthermore, as shown in Table 1, the catalytic activity (hereinafter sometimes abbreviated as catalytic activity) of a single cell of a fuel cell using the catalysts of Examples 1 and 2 as the air electrode catalyst was significantly improved compared to the catalytic activity of a single cell of a fuel cell using the catalysts of Comparative Examples 1-3 as the air electrode catalyst.

[0103] Finally, Comparative Example 4 will be compared with Comparative Examples 1-3 and Examples 1-2. In Comparative Example 4, the maximum temperature and holding time of the heat treatment were the same as in Example 1: 1100°C and 120 minutes (2 hours). Looking at the XRD pattern of the catalyst of Comparative Example 4, as shown in Figure 4, the peak near 45-50° has an asymmetric shape with a shoulder on the high-angle side, similar to Examples 1 and 2. Peak fitting was used to resolve this peak, and the L10 structure ratio was calculated according to equation (1). This resulted in 0.52, confirming that the L10 structure ratio was higher than that of Comparative Examples 1-3. Furthermore, as shown in Table 1, the catalytic activity of a single fuel cell using the catalyst of Comparative Example 4 as the air electrode catalyst was 269 A / g-Pt, which was improved compared to the catalytic activity of a single fuel cell using the catalyst of Comparative Examples 1-3 as the air electrode catalyst. However, the difference between these values ​​was smaller than the difference in catalytic activity obtained in Examples 1 and 2.

[0104] Thus, the inconsistency in the improvement in catalytic activity relative to the increase in the proportion of the L10 structure is thought to reflect the difference in the carbon support used in Examples 1 and 2 and Comparative Example 4. That is, in Comparative Example 4, Ketjen Black is used as the carbon support, so the catalytic activity of the catalytic metal decreases due to contact with the ionomer, and the inherent performance of the L10 structure cannot be fully exhibited. On the other hand, in Examples 1 and 2, mesoporous carbon is used as the carbon support, so the catalytic metal does not come into contact with the ionomer, and it is thought that the inherent catalytic performance of the L10 structure is exhibited.

[0105] Therefore, the relationship between catalytic activity and the ratio of the L10 structure was examined for Comparative Example 3 and Comparative Example 4, in which a Ketjen Black carrier (hereinafter, KB carrier) was used as the catalyst carrier, and for Comparative Example 2 and Example 1, in which a mesoporous carbon carrier (hereinafter, MPC carrier) was used as the catalyst carrier.

[0106] Fig. 5 shows the relationship between catalytic activity and the ratio of the L10 structure in each of Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4. The horizontal axis of Fig. 5 represents the ratio of the L10 structure, and the vertical axis represents catalytic activity (A / g-Pt).

[0107] As can be easily seen from Figure 5, the rate of increase in catalytic activity with respect to changes in the ratio of the L10 structure when an MPC support is used as the catalyst support is greater than the rate of increase in catalytic activity with respect to changes in the ratio of the L10 structure when a KB support is used as the catalyst support. This means that when two factors, the type of catalyst support and the ratio of the L10 structure, are involved in improving catalytic activity, a synergistic effect can be obtained.

[0108] Specifically, as shown in Fig. 5, the gradient of the straight line (solid line) passing through the data positions (coordinates) in Fig. 5 for Comparative Example 2 and Example 1 is greater than the gradient of the straight line (dotted line) passing through the data positions (coordinates) in Fig. 5 for Comparative Example 3 and Comparative Example 4. If the two factors, namely, the type of catalyst support and the ratio of the L10 structure, each only showed their own independent effects in improving catalytic activity, the gradients of the solid line and the dotted line would be approximately equal. However, in reality, when these factors act simultaneously, as described above, the rate of increase in catalytic activity indicated by the solid line was greater than the rate of increase in catalytic activity indicated by the dotted line.

[0109] Therefore, when the ratio of the L10 structure at the intersection point where the solid line and the dotted line intersect was calculated, it was found to be approximately 0.25, as shown in Figure 5. Therefore, it is believed that when an MPC support is used as a catalyst support, the catalytic activity-enhancing effect inherent to the L10 structure can be appropriately exerted when the ratio of the L10 structure is in the range of more than 0.25.

[0110] As described above, when an MPC support is used as a catalyst support, it is found that the ratio of the L10 structure can be increased by increasing the maximum temperature reached in the heat treatment process in a reducing atmosphere. In addition, it was found that by setting the ratio of the L10 structure within the above range when an MPC support is used as a catalyst support, a synergistic effect in improving catalytic activity due to the two factors of the type of catalyst support and the ratio of the L10 structure can be appropriately exerted.

[0111] From the above description, many improvements and other embodiments of the present disclosure will be apparent to those skilled in the art. Therefore, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present disclosure. Details of the structure and / or function thereof can be substantially changed without departing from the spirit of the present disclosure. [Industrial Applicability]

[0112] The present disclosure is useful, for example, in electrode catalysts used in membrane / electrode assemblies that constitute electrochemical devices such as fuel cells. [Explanation of symbols]

[0113] 10 Electrode assembly 11 Polymer electrolyte membrane 12 Electrode catalyst layer 13 Gas diffusion layer 13a Base material 13b Coating layer 20 Electrocatalyst 21 Mesoporous Materials 22 Catalytic metal particles 30 Ionomer 31 Water-repellent material

Claims

1. a mesoporous material; and catalytic metal particles containing platinum and cobalt supported at least inside the mesoporous material, The mesoporous material has a mode radius of 1-25 nm and a pore surface area of ​​1.0-3.0 cm 3 / g of mesopores, The supported catalytic metal particles are L1 0 and L1 0 an electrocatalyst having a structure ratio greater than 0.25; Ionomer and An electrode catalyst layer comprising:

2. L1 in the catalytic metal particles 0 The electrode catalyst layer according to claim 1 , wherein the ratio of the structure is 0.60 or more.

3. 3. The electrode catalyst layer according to claim 1, wherein the mesopores of the mesoporous material have a mode radius of 3 nm or more and 6 nm or less.

4. The electrode catalyst layer according to claim 1 , wherein the mesoporous material is mesoporous carbon.

5. The electrode catalyst layer according to claim 1 , which contains at least one of carbon black and carbon nanotubes.

6. The electrode catalyst layer according to claim 5 , wherein the carbon black is Ketjen black.

7. a polymer electrolyte membrane; a fuel electrode and a cathode, each of which is provided on either side of the polymer electrolyte membrane and includes an electrode catalyst layer and a gas diffusion layer; A membrane / electrode assembly, wherein the electrode catalyst layer of at least the air electrode comprises the electrode catalyst layer according to claim 1 .

8. An electrochemical device comprising the membrane / electrode assembly according to claim 7.

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