Electrode Catalyst

Abstract

The electrode catalyst of the present disclosure includes a mesoporous material and catalytic metal particles containing platinum and a metal different from platinum, the catalytic metal particles being supported at least inside the mesoporous material, and the mesoporous material has a mode radius of 1 nm or more and 25 nm or less and a pore surface area of 1.0 cm. 3 / g or more 3.0cm 3 / g or less, and the catalytic metal has the chemical formula Pt x Co 1-y Ni y wherein x of the catalytic metal ranges from 1 to 3, and y ranges from 0.20 to 0.47, and the catalytic metal particles contain an L10 phase.

Description

[Technical Field]

[0001] The present disclosure relates to electrocatalysts. [Background technology]

[0002] A polymer electrolyte fuel cell (PEFC) 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 an electrode catalyst, which is composed of a catalyst metal such as platinum supported on a catalyst support made of an electrically conductive material such as carbon black, and a polymer electrolyte (hereinafter referred to as an ionomer) having proton conductivity in a solvent such as water or alcohol, to prepare a catalyst paste, and then applying and drying the catalyst paste to a polymer electrolyte membrane or other substrate.

[0004] The microstructure of the electrode catalyst layer created in this way (hereinafter referred to as the three-phase interface structure) is a structure in which the electrode 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.

[0005] However, in recent years, it has been pointed out that catalytic metals that come into contact with ionomers are poisoned by the ionomers, and the catalytic activity is rather reduced.

[0006] To address this problem of decreased activity of electrode catalysts, a method has been proposed in which catalytic metal particles are supported inside a catalyst support such as mesoporous carbon, and the catalyst 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).

[0007] It has also been reported that the catalytic activity of an oxygen reduction reaction is improved by forming an ordered structure of a catalytic metal. For example, Patent Document 1 reports that when the catalytic metal is an alloy of platinum and cobalt, the formation of the L10 phase, which is one of the ordered structures of the catalytic metal, improves the catalytic activity of an electrode catalyst including the catalytic metal. That is, when the catalytic metal having the L10 phase is an alloy represented by the chemical formula "L10-PtCo," platinum atoms and cobalt atoms are strongly bonded in the c-axis direction of the crystal, and the c-axis length is shorter than in a disordered structure. This causes a lattice distortion effect, which changes the electronic state of platinum, thereby improving the catalytic activity of the electrode catalyst.

[0008] Furthermore, Non-Patent Document 1 reports that doping a catalytic metal represented by the chemical formula "L10-PtNi" with cobalt (Co) improves the catalytic activity of an electrode catalyst comprising such a catalytic metal. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2022 / 196404 [Non-patent literature]

[0010] [Non-Patent Document 1] Advanced Energy Materials,9(17),1803771.(2019) Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present disclosure is to provide, for example, an electrode catalyst that can improve the catalytic activity of a catalytic metal supported inside a mesoporous material compared to conventional methods. [Means for solving the problem]

[0012] In order to solve the above problems, an electrode catalyst according to one aspect of the present disclosure includes a mesoporous material and catalytic metal particles containing platinum and a metal different from platinum, the catalytic metal particles being supported at least inside the mesoporous material, the mesoporous material having a mode radius of 1 nm or more and 25 nm or less and a pore surface area of 1.0 cm. 3 / g or more 3.0cm 3 / g or less, and the catalytic metal has the chemical formula Pt x Co 1-y Ni y wherein x of the catalytic metal ranges from 1 to 3, and y ranges from 0.20 to 0.47, and the catalytic metal particles contain an L10 phase. [Effects of the Invention]

[0013] The electrode catalyst according to one embodiment of the present disclosure has the effect of improving the catalytic activity of the catalytic metal supported inside the mesoporous material compared to conventional methods. [Brief explanation of the drawings]

[0014] [Figure 1A] FIG. 1A is a schematic diagram of an L10 structure (binary system) in which catalytic metals (platinum and cobalt) are regularly arranged. [Figure 1B] FIG. 1B is a schematic diagram of an L10 structure (ternary system) in which catalytic metals (platinum, cobalt, and nickel) are regularly arranged. [Figure 2] FIG. 2 is a diagram illustrating an example of an electrode catalyst according to an embodiment of the present disclosure. [Figure 3] FIG. 3 shows examples of X-ray diffraction (XRD) patterns of the electrode catalysts in Experimental Examples 1-10 and Comparative Examples 1-4 of the present disclosure. [Figure 4] FIG. 4 is a graph showing an example of the catalytic activity of the electrode catalysts of Experimental Examples 1-10 and Comparative Examples 1-4 of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] Toward the widespread adoption of PEFCs, it is necessary to further improve the catalytic activity of electrode catalysts in order to reduce material costs by reducing the amount of platinum used in the electrode catalyst. Therefore, the present inventors have investigated, as one method, combining a mesoporous material such as mesoporous carbon with a catalyst metal with excellent catalytic activity in order to suppress poisoning of the catalyst metal by the ionomer.

[0016] However, Patent Document 1 discloses the relationship between the regularity of the catalytic metal represented by the chemical formula "L10-PtCo" and the catalytic activity of the electrode catalyst containing the catalytic metal. 1-y Ni y No consideration has been given to catalytic metals represented by the formula ".

[0017] Here, the catalytic metal represented by the chemical formula "L10-PtCo" has a structure in which layers containing cobalt (Co) and layers containing platinum (Pt) are alternately stacked, as shown in Figure 1A. 1-y Ni y In the catalytic metal represented by the formula "L10-PtCo", as shown in Figure 1B, nickel (Ni) is located in the same layer as cobalt (Co), and layers containing platinum (Pt) and layers containing nickel (Ni) and cobalt (Co) are alternately stacked. 1-y Ni y In a catalyst having a catalytic metal represented by the chemical formula "L10-PtCo," it is believed that by adding cobalt (Co) and appropriately adjusting the c-axis length and lattice distortion effect of nickel (Ni), the catalytic activity can be further improved compared to a catalyst having a catalytic metal represented by the chemical formula "L10-PtCo."

[0018] Furthermore, the catalytic metal particles disclosed in Non-Patent Document 1 are not particles supported inside a mesoporous material. Here, the growth of catalytic metal particles supported inside a mesoporous material is limited by the pore size and pore shape of the mesoporous material, so the shape of the catalytic metal particles and the distance between metal atoms in the catalytic metal particles are likely to be different from catalytic metals supported on support materials other than mesoporous materials. In other words, the invention described in Non-Patent Document 1 is directed to catalytic metal particles supported inside a mesoporous material and having the chemical formula "L10-PtCo 1-y Ni y The catalytic activity of an electrode catalyst comprising a catalytic metal represented by the formula "" has not been fully investigated.

[0019] Therefore, the present inventors have developed a Pt-based nanoparticle having the chemical formula "L10-PtCo" supported inside a mesoporous material. 1-y Ni y The present inventors focused on the relationship between the catalytic activity of an electrode catalyst comprising a catalytic metal represented by the formula "y" and the nickel composition ratio (y) of the catalytic metal. They then found that the catalytic activity of the electrode catalyst can be improved by setting the nickel composition ratio (y) of the catalytic metal supported inside the mesoporous material to 0.20 or more and 0.47 or less, and arrived at the following aspect of the present disclosure.

[0020] That is, the electrode catalyst of the first embodiment of the present disclosure includes a mesoporous material and catalytic metal particles containing platinum and a metal other than platinum, which are supported at least inside the mesoporous material, and the mesoporous material has a mode radius of 1 nm or more and 25 nm or less and a pore surface area of 1.0 cm 3 / g or more 3.0cm 3 / g or less, and the catalyst metal has the chemical formula Pt x Co 1-y Ni y wherein x of the catalytic metal ranges from 1 to 3, and y ranges from 0.20 to 0.47, and the catalytic metal particles contain an L10 phase.

[0021] According to this configuration, the electrode catalyst of this embodiment can improve the catalytic activity of the catalytic metal supported inside the mesoporous material compared to conventional methods. Specifically, when the nickel composition ratio (y) of the catalytic metal supported inside the mesoporous material is 0.20 or more and 0.47 or less, it has been found that the catalytic activity of the catalytic metal particles (hereinafter referred to as catalytic metal particles) containing the L10 phase can be appropriately improved due to the synergistic effect of two factors: the type of catalyst support (mesoporous material) and the nickel composition ratio (y) of the catalytic metal. Details will be explained later.

[0022] Furthermore, in the electrode catalyst of this embodiment, by supporting the catalytic metal particles inside the mesoporous material, it is possible to appropriately suppress contact between the catalytic metal particles and the ionomer even when the electrode catalyst layer is formed using an ionomer.

[0023] As described above, when a fuel cell is produced using the electrode catalyst of this embodiment, the fuel cell can achieve high power generation performance.

[0024] The electrode catalyst according to a second embodiment of the present disclosure may be the electrode catalyst according to the first embodiment, wherein the mode radius of the mesopores of the mesoporous material is 3 nm or more and 6 nm or less.

[0025] According to this configuration, the electrode catalyst of this embodiment has a smaller mode radius of mesopores than when the mode radius of the mesopores is greater than 6 nm, and therefore can suppress the penetration of ionomer into the mesopores of the mesoporous material.

[0026] Furthermore, the electrode catalyst of this embodiment has a larger mesopore mode radius than when the mesopore mode radius is less than 3 nm, making it possible to efficiently supply reactant gas to catalytic metal particles inside the mesoporous material. Furthermore, the electrode catalyst of this embodiment can more appropriately support catalytic metal particles within the mesopores than when the mesopore mode radius is less than 3 nm. As a result, poisoning of the catalytic metal by the ionomer can be reduced, and a decrease in the catalytic activity of the electrode catalyst can be suppressed.

[0027] The electrode catalyst according to a third aspect of the present disclosure may be the electrode catalyst according to the first or second aspect, in which the mesoporous material is mesoporous carbon.

[0028] According to this configuration, the electrode catalyst of this embodiment has excellent electrical conductivity and water repellency because the main constituent element of the mesoporous material is carbon. Therefore, when a fuel cell is fabricated using the electrode catalyst of this embodiment, the fuel cell can achieve high power generation performance.

[0029] Specific examples of the above-described aspects of the present disclosure will be described below with reference to the accompanying drawings. Each of the specific examples described below is an example of the above-described aspects of the present disclosure. Therefore, unless otherwise stated in the claims, the shapes, numerical values, components, and the positions of the components shown below do not limit the scope of the claims.

[0030] Furthermore, among the components described below, components that are not described in the independent claims that represent the highest concept of the present disclosure are described as optional components. Furthermore, in the drawings, components with the same reference numerals may not be described in detail. The drawings are schematic illustrations of each component for ease of understanding, and the shapes, dimensional ratios, and the like may not be accurately depicted.

[0031] (Embodiment) FIG. 2 is a diagram showing an example of an electrode catalyst according to an embodiment.

[0032] 2, the electrode catalyst 10 includes a mesoporous material 11 and catalytic metal particles 12 (hereinafter, catalytic metal particles 12). The electrode catalyst 10 may be used to catalyze the oxygen reduction reaction (ORR), the oxygen evolution reaction (OER), the formic acid oxidation reaction (FAOR), the methanol oxidation reaction (MOR), the ethanol oxidation reaction (EOR), and the like.

[0033] The electrode catalyst 10 can be used, for example, in a fuel cell or a metal-air cell, etc. Examples of fuel cells include a polymer electrolyte fuel cell (PEFC), a direct formic acid fuel cell, a direct methanol fuel cell (DMFC), and a direct ethanol fuel cell.

[0034] The electrode catalyst layer of the above electrochemical device may contain the above electrode catalyst 10 and an ionomer 20, as shown in FIG.

[0035] (mesoporous materials) Hereinafter, mesoporous carbon will be used as an example of the mesoporous material 11 of the electrode catalyst 10 as needed, but the mesoporous material 11 is not limited to mesoporous carbon. Other materials may be used as long as the mesoporous material 11 has the same mode radius and pore volume. Examples of mesoporous materials 11 other than mesoporous carbon include materials composed of oxides of titanium, tin, niobium, tantalum, zirconium, aluminum, silicon, and the like.

[0036] The mesoporous material 11 has a mesopore volume of 1.0 cm 3 / g or more 3.0cm 3 / g or less is suitable for the following reasons.

[0037] The pore volume of the mesopores in mesoporous material 11 is 1.0 cm 3 / g or more, the pore volume of the mesopores is 1.0 cm 3 / g, it becomes easier to support a large amount of catalytic metal particles 12 inside the mesoporous material 11. In addition, when the pore volume of the mesopores of the mesoporous material 11 is 3.0 cm3 / g or less, it becomes easier to support a large amount of catalytic metal particles 12 inside the mesoporous material 11. 3 / g or less, the pore volume of the mesopores is 3.0 cm 3 / g, the strength of the mesoporous material 11 as a structure can be improved.

[0038] The mesopore mode radius of the mesopores in the mesoporous material 11 may be 1 nm or more and 25 nm or less, and it is appropriate that the mesopore mode radius is 3 nm or more and 6 nm or less for the following reasons: The "mode radius" refers to the most frequent diameter (the diameter at the maximum value) in the pore size distribution of the mesoporous material 11.

[0039] When the mode radius of the mesopores of the mesoporous material 11 is 3 nm or more, the reactant gas is more easily supplied into the mesopores than when the mode radius of the mesopores is less than 3 nm. When the mode radius of the mesopores of the mesoporous material 11 is 6 nm or less, the ionomer 20 is less likely to penetrate into the mesopores than when the mode radius of the mesopores is greater than 6 nm.

[0040] Here, "the mode radius of the mesopores is 1 nm or more and 25 nm or less (preferably, 3 nm or more and 6 nm or less), and the pore volume of the mesopores is 1.0 cm 3 / g or more 3.0cm 3 / g or less” refers to the value at which the mesopores of the mesoporous material 11 are filled with the catalytic metal particles 12 before they are supported on the mesoporous material 11 .

[0041] The pore volume and mode radius of the mesopores of the mesoporous material 11 can be measured by nitrogen adsorption and derived by analysis using methods such as the Barrett-Joyner-Halenda (BJH) method, density functional theory (DFT) method, and quenched-solidified density functional theory (QSDFT) method.

[0042] Furthermore, the mesoporous material 11 may have an average particle size of 200 nm or more. The "average particle size" refers to the median diameter (d50) of the particle size distribution of the mesoporous material 11.

[0043] When the average particle size of the mesoporous material 11 is 200 nm or more, the proportion of the catalytic metal particles 12 that are affected by poisoning by the ionomer 20 can be reduced compared to when the average particle size is less than 200 nm, thereby improving the catalytic activity of the electrode catalyst.

[0044] The mesoporous material 11 may have an average particle size of 1000 nm or less. When the average particle size of the mesoporous material 11 is 1000 nm or less, the reactant gas is more easily supplied to the catalytic metal particles 12 supported inside the mesoporous material 11 than when the average particle size is greater than 1000 nm.

[0045] The average particle size of the mesoporous material 11 may be measured using a laser diffraction particle size distribution analyzer or the like while the mesoporous material 11 is dispersed in a solvent, or may be measured using images from a scanning electron microscope (SEM) or a transmission electron microscope (TEM). When measuring the particle size distribution while the mesoporous material 11 is dispersed in a solvent, it is necessary to prevent the mesoporous material 11 from aggregating. The solvent may be water, alcohol, or a mixture of water and alcohol.

[0046] It is appropriate to add a dispersant to the solvent to further improve the dispersibility of the mesoporous material 11. Examples of the dispersant that can be used include perfluorosulfonic acid resin, poly(oxyethylene) octylphenyl ether, and polyoxyethylene sorbitan monolaurate.

[0047] To further enhance the dispersibility of the mesoporous material 11, it is appropriate to carry out a dispersion treatment after mixing the mesoporous material with the solvent. Examples of the dispersion treatment device include an ultrasonic homogenizer, a wet jet mill, a ball mill, and a mechanical stirrer.

[0048] The method for producing the above-described mesoporous material 11 is not particularly limited, but for example, the method described in JP 2010-208887 A can be used. Mesoporous material 11 produced by this method has a large mesopore volume and a structure in which the mesopores are interconnected. This makes it easy to support catalytic metal particles 12 in the pores, and facilitates the supply of reaction gas to the supported catalytic metal particles 12.

[0049] In order to adjust the average particle size of the mesoporous material 11, 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 suitable because it is easy to pulverize to a fine particle size.

[0050] (Catalytic metal particles) The catalytic metal particles 12 contain platinum and a metal other than platinum, which are supported at least inside the mesoporous material 11. Specifically, the catalytic metal has the chemical formula Pt x Co 1-y Ni y where x of the catalytic metal is in the range of 1 or more and 3 or less, and y is in the range of 0.20 or more and 0.47 or less. The catalytic metal particles 12 contain the L10 phase. An alloy of platinum with cobalt and nickel is suitable because it has high catalytic activity for the oxygen reduction reaction (ORR) and good durability in the power generation environment of a fuel cell.

[0051] (ionomer) Ion exchange resins can be used as the ionomer 20 (proton-conductive resin). Perfluorosulfonic acid resins are particularly suitable because they have high proton conductivity and remain 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 is more likely to achieve high proton conductivity than an ion exchange capacity of less than 0.9 milliequivalents / g dry resin. An ion exchange capacity of 2.0 milliequivalents / g dry resin or less suppresses swelling of the resin due to water absorption, making it less likely to impair gas diffusion within the electrode catalyst layer than an ion exchange capacity greater than 2.0 milliequivalents / g dry resin. The weight ratio of the ionomer 20 to the total weight of the mesoporous material 11 and water-repellent material contained in the electrode catalyst layer is preferably 0.2 to 2.0.

[0052] (Method A for synthesizing platinum-cobalt alloy-supported mesoporous carbon) First, an explanation will be given of method A for synthesizing an electrode catalyst in the case where the catalyst metal is an alloy of platinum and cobalt.

[0053] 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 for 20 minutes at a peripheral speed of 12 m / s using a media-stirring wet bead mill (Ashizawa Finetech Co., Ltd., Labostar™ Mini). 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 11).

[0054] 1 g of the carbon support prepared above was placed in 400 mL of a 1:1 (weight ratio) water:ethanol mixed solvent 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.

[0055] The aggregates obtained above were ground in a mortar and heat-treated at 220°C for 2 hours in an atmosphere of nitrogen:hydrogen = 85:15 to produce platinum-supported mesoporous carbon (hereinafter referred to as "Pt / MPC").

[0056] 0.3 g of the Pt / MPC prepared above was placed in a conical beaker and left 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).

[0057] Next, 50 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 determined. After 15 minutes of ultrasonic dispersion, 50 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 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 2 hours. 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. During this time, a nitrogen / hydrogen mixed gas (nitrogen:hydrogen = 97:3) was flowed through the tube at a flow rate of 1 L / min to maintain a reducing atmosphere.

[0058] The powder obtained above was stirred in 100 mL of a 0.2 mol / L aqueous sulfuric acid solution at 80 °C for 2 hours, filtered, washed, and then stirred in 100 mL of a 0.2 mol / L aqueous nitric acid solution at 70 °C for 2 hours to pre-dissolve the excess cobalt on the outermost surface. The powder was then 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 an atmospheric tubular electric furnace and heated from room temperature to 120 °C over 10 minutes, then held at that temperature for 60 minutes. The temperature was then raised to 400 °C at a rate of 300 °C / hour and held at that temperature for 2 hours. The temperature was then lowered to 200 °C at a rate of 150 °C / hour, and then lowered to room temperature at a rate of 300 °C / hour. During this time, 100% hydrogen gas was flowed into the tube at a flow rate of 2 L / min to maintain a reducing atmosphere.

[0059] In this way, platinum-cobalt alloy-supported mesoporous carbon (hereinafter referred to as "PtCo / MPC") was prepared.

[0060] (Method B for synthesizing platinum-cobalt-nickel alloy-supported mesoporous carbon) Next, a method B for synthesizing an electrode catalyst in which the catalyst metal is an alloy of platinum, cobalt, and nickel will be described.

[0061] Synthesis method B for platinum-cobalt-nickel alloy-supported mesoporous carbon is similar to synthesis method A, except that nickel chloride hexahydrate is used in addition to cobalt chloride hexahydrate as a precursor, and the molar ratio of the sum of cobalt and nickel to the total amount of platinum, cobalt, and nickel is set to a predetermined amount.

[0062] (Method for calculating the ratio of metal elements contained in electrode catalyst) The element ratios of platinum and metals other than platinum contained in the electrode catalyst were measured by the following method.

[0063] First, the electrode catalyst was weighed into a quartz beaker and heated in an electric furnace to burn off the carbon. After cooling, the material was heated by adding a small amount of nitric acid and hydrochloric acid to the beaker, diluted with pure water, and then introduced into an inductively coupled plasma-optical emission spectroscopy (ICP-OES) analyzer (Agilent Technologies "ICP-OES 710") for quantitative analysis of platinum and other metals. This allowed the elemental ratios of platinum and other metals contained in the electrode catalyst to be calculated.

[0064] (Example) Hereinafter, experimental examples 1-10 will be described, which were carried out using mesoporous carbon (MPC) as a catalyst support for supporting a catalytic metal.

[0065] <Experimental Example 1> The electrode catalyst of Experimental Example 1 was prepared by synthesis method A by adding 50 mL of pure water containing cobalt chloride hexahydrate dissolved in an amount such that the molar ratio of cobalt to the total amount of platinum and cobalt was 0.55 to a conical beaker containing Pt / MPC.

[0066] The composition of the catalytic metal in the electrode catalyst of Experimental Example 1 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 2.03 and y was 0.00.

[0067] <Experimental Example 2> The electrode catalyst of Experimental Example 2 was prepared by Synthesis Method B by adding 50 mL of pure water containing dissolved cobalt chloride hexahydrate and nickel chloride hexahydrate in amounts such that the molar ratio of the total amount of cobalt and nickel to the total amount of platinum, cobalt, and nickel was 0.55 to a conical beaker containing Pt / MPC.

[0068] The composition of the catalytic metal in the electrode catalyst of Experimental Example 2 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 1.85 and y was 0.08.

[0069] <Experimental Example 3 (Example)> The electrode catalyst of Experimental Example 3 was prepared in the same manner as the electrode catalyst of Experimental Example 2, except for the ratio of cobalt chloride hexahydrate and nickel chloride hexahydrate used as precursors.

[0070] The composition of the catalytic metal in the electrode catalyst of Experimental Example 3 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 1.85 and y was 0.20.

[0071] <Experimental Example 4 (Example)> The electrode catalyst of Experimental Example 4 was prepared in the same manner as the electrode catalyst of Experimental Example 2, except for the ratio of cobalt chloride hexahydrate and nickel chloride hexahydrate used as precursors.

[0072] The composition of the catalytic metal in the electrode catalyst of Experimental Example 4 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 1.68 and y was 0.30.

[0073] <Experimental Example 5 (Example)> The electrode catalyst of Experimental Example 5 was prepared in the same manner as the electrode catalyst of Experimental Example 2, except for the ratio of cobalt chloride hexahydrate and nickel chloride hexahydrate used as precursors.

[0074] The composition of the catalytic metal in the electrode catalyst of Experimental Example 5 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 1.95 and y was 0.35.

[0075] <Experimental Example 6 (Example)> The electrode catalyst of Experimental Example 6 was prepared in the same manner as the electrode catalyst of Experimental Example 2, except for the ratio of cobalt chloride hexahydrate and nickel chloride hexahydrate used as precursors.

[0076] The composition of the catalytic metal in the electrode catalyst of Experimental Example 6 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 2.07 and y was 0.41.

[0077] <Experimental Example 7 (Example)> The electrode catalyst of Experimental Example 7 was prepared in the same manner as the electrode catalyst of Experimental Example 2, except for the ratio of cobalt chloride hexahydrate and nickel chloride hexahydrate used as precursors.

[0078] The composition of the catalytic metal in the electrode catalyst of Experimental Example 7 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 1.92 and y was 0.43.

[0079] <Experimental Example 8 (Example)> The electrode catalyst of Experimental Example 8 was prepared in the same manner as the electrode catalyst of Experimental Example 2, except for the ratio of cobalt chloride hexahydrate and nickel chloride hexahydrate used as precursors.

[0080] The composition of the catalytic metal in the electrode catalyst of Experimental Example 8 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 1.66 and y was 0.47.

[0081] <Experimental Example 9> The electrode catalyst of Experimental Example 9 was prepared in the same manner as the electrode catalyst of Experimental Example 2, except for the ratio of cobalt chloride hexahydrate and nickel chloride hexahydrate used as precursors.

[0082] The composition of the catalytic metal in the electrode catalyst of Experimental Example 9 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 1.56 and y was 0.64.

[0083] <Experimental Example 10> The electrocatalyst of Experimental Example 10 was prepared in the same manner as the electrocatalyst of Experimental Example 2, except for the ratio of cobalt chloride hexahydrate and nickel chloride hexahydrate used as precursors.

[0084] The composition of the catalytic metal in the electrode catalyst of Experimental Example 10 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 1.70 and y was 0.70.

[0085] (Comparative Example) Comparative Examples 1-4, which were carried out using carbon black (KB) as the catalyst support for supporting the catalytic metal, will be described below.

[0086] <Comparative Example 1> The electrode catalyst of Comparative Example 1 was a platinum-cobalt alloy-supported carbon black (hereinafter referred to as "PtCo / KB") prepared in the same manner as the electrode catalyst of Experimental Example 1, except that carbon black was used as the catalyst support for supporting the catalytic metal. Specifically, a commercially available platinum-supported carbon black catalyst (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was used instead of the Pt / MPC that had been subjected to water vapor adsorption treatment.

[0087] The composition of the catalytic metal in the electrode catalyst of Comparative Example 1 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 1.53 and y was 0.00.

[0088] <Comparative Example 2> The electrode catalyst of Comparative Example 2 was a platinum-cobalt-nickel alloy-supported carbon black prepared in the same manner as the electrode catalyst of Experimental Example 2, except that carbon black was used as the catalyst support for supporting the catalytic metal. Specifically, a commercially available platinum-supported carbon black catalyst (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was used instead of the Pt / MPC that had been subjected to water vapor adsorption treatment.

[0089] The composition of the catalytic metal in the electrode catalyst of Comparative Example 2 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 1.26 and y was 0.19.

[0090] <Comparative Example 3> The electrode catalyst of Comparative Example 3 was prepared in the same manner as the electrode catalyst of Comparative Example 2, except for the ratio of cobalt chloride hexahydrate and nickel chloride hexahydrate used as precursors.

[0091] The composition of the catalytic metal in the electrode catalyst of Comparative Example 3 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 1.22 and y was 0.33.

[0092] <Comparative Example 4> The electrocatalyst of Comparative Example 4 was prepared in the same manner as the electrocatalyst of Comparative Example 2, except for the ratio of cobalt chloride hexahydrate and nickel chloride hexahydrate used as precursors.

[0093] The composition of the catalytic metal in the electrode catalyst of Comparative Example 4 is represented by the chemical formula "L10-Pt x Co 1-y Ni y ", x was 1.16 and y was 0.46.

[0094] (Evaluation of L10 structure in electrode catalysts of Experimental Examples 1-10 and Comparative Examples 1-4) The electrode catalysts of Experimental Examples 1-10 and Comparative Examples 1-4 were evaluated as follows.

[0095] [Calculation of the ratio R of the L10 structure] The ratio R of the L10 structure in the catalytic metal particles 12 of each of the electrode catalysts of Experimental Examples 1-10 and Comparative Examples 1-4 was calculated using the following formula (1) by performing the following X-ray diffraction measurement and fitting process of the XDR pattern.

[0096] X-ray diffraction (hereinafter referred to as XRD) measurements were performed using an X'pert Pro MPD manufactured by PANalytical.

[0097] First, the catalyst powder was spread on a sample holder with a recessed portion that had been ground 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. The incident light was CuKα, and the detector was a one-dimensional semiconductor detector. 2θ-θ measurements were performed in the range of 2θ = 20-60° using a focusing optical system.

[0098] Fig. 3 shows examples of XRD patterns for the electrode catalysts of Experimental Examples 1 to 10 and Comparative Examples 1 to 4. Each of the XRD patterns in Fig. 3 was subjected to fitting processing according to the following procedure.

[0099] First, the background of the data was removed using the pybeads library in the programming language Python.

[0100] The background-subtracted data curves were then subjected to multi-peak fitting in the range of 30–60° using the lmfit library in Python, where a symmetric pseudo-Voigt function was used to represent the shape of each peak.

[0101] Here, the peak at 2θ=40-45° corresponds to the (111) diffraction peak of the L10 structure, and the peak at 2θ=30-35° corresponds to the (110) diffraction peak of the L10 structure. The areas of these diffraction peaks are respectively referred to as "S 111 " and "S 110 When these are respectively expressed as "R", the ratio R of the L10 structure in the catalytic metal particle 12 (hereinafter referred to as the L10 ratio R) can be found by the following formula (1).

number

[0102] In addition, in formula (1), "S 110_thr " and "S 111_thr " are the theoretical intensities of the (110) diffraction peak and the (111) diffraction peak in the L10 structure, respectively, and the ratio thereof is 0.253 according to a diffraction intensity simulation using VESTA, a software capable of simulating X-ray diffraction. Since the denominator of formula (1) theoretically does not exceed 0.253, the L10 ratio R in formula (1) takes an appropriate value of "1" or less depending on the abundance ratio of the L10 structure in the catalytic metal particle 12.

[0103] [Diffraction angle of simulated diffraction peak] In Figure 3, the diffraction angles (2θ) of the diffraction peaks obtained by simulation using VESTA based on the structural data of "L10-PtCo" and "L10-PtNi" obtained from the Inorganic Crystal Structure Database (ICSD) are shown by black circles "●" and white squares "□", respectively.

[0104] [result] As shown in Table 1 (below), the L10 ratio R in the catalytic metal particles 12 of the electrode catalysts of Experimental Examples 1-10 and Comparative Examples 1-4 was all equal to or greater than 0.24, and it was found that all of these catalytic metal particles 12 contained the L10 phase.

[0105] 3, in the XDR patterns of the catalytic metal particles 12 of the electrode catalysts of Experimental Examples 1-10 and Comparative Examples 1-4, a diffraction peak corresponding to the diffraction angle (black circle) of "L10-PtCo" obtained by simulation and a diffraction peak corresponding to the diffraction angle (white square) of "L10-PtNi" obtained by simulation were observed. In particular, the diffraction peaks with diffraction angles between 30° and 40° are peaks derived only from ordered alloys having an L10 structure, and such diffraction peaks were clearly observed in the XDR patterns of FIG.

[0106] Note that no clear diffraction peaks corresponding to the diffraction angles slightly above 50° (white squares) or slightly below 50° (black circles) were observed in the XDR pattern in Figure 3. This is for the following reason.

[0107] The electrode catalysts synthesized in Experimental Examples 1-10 and Comparative Examples 1-4 are solid solutions of an alloy represented by "L10-PtCo" and an alloy represented by "L10-PtNi." Therefore, it is believed that the diffraction peaks are located between the diffraction angle slightly above 50° (open squares) and the diffraction angle slightly below 50° (filled circles). Furthermore, because the composition ratios of cobalt (Co) and nickel (Ni) in the solid solution are different in each of the electrode catalysts synthesized in Experimental Examples 1-10 and Comparative Examples 1-4, it is believed that the positions of the diffraction peaks shift slightly for each of the electrode catalysts synthesized in Experimental Examples 1-10 and Comparative Examples 1-4. In fact, when examining the XDR pattern in Figure 3, an asymmetric right shoulder is observed in the peak of the XDR pattern at a diffraction angle of around 50°. This asymmetric right shoulder is thought to be due to the diffraction peaks that exist between a diffraction angle slightly above 50° (open square) and a diffraction angle slightly below 50° (black circle).

[0108] As described above, the XDR patterns in FIG. 3 show that the electrode catalysts synthesized in Experimental Example 1-10 and Comparative Example 1-4 have the "L10-Pt x Co 1-y Ni y This data points to the formation of "

[0109] (Evaluation of the activity of the electrode catalysts in Experimental Examples 1-10 and Comparative Examples 1-4) In order to evaluate the performance of each of the electrocatalysts of Experimental Examples 1-10 and Comparative Examples 1-4, ring-disk electrodes (RDEs) equipped with electrocatalyst layers containing each of these electrocatalysts were fabricated as follows.

[0110] [Ink preparation] Each sample (5.0 mg) of the electrode catalysts of Experimental Examples 1-10 and Comparative Examples 1-4 was mixed with 7.92 μl of ionomer, 11.36 ml of pure water, and 8.87 ml of isopropanol (IPA), and then sonicated for 30 minutes using an ultrasonic homogenizer (Branson Digital Sonifier SFX 550) before use. The catalyst ink thus obtained was applied to the following glassy carbon disk.

[0111] [Evaluation equipment] For the electrochemical measurements, a potentiostat (ALS760E electrochemical analyzer manufactured by BAS), an electrode rotor and a standard three-electrode glass cell (manufactured by BAS), and a rotating ring-disk electrode apparatus (RRDE-3A manufactured by BAS) were used.

[0112] [Measurement method] The working electrode was a catalyst-coated glassy carbon disk, the counter electrode (CE) was a platinum-plated electrode, and the reference electrode (RE) was a reversible hydrogen electrode (RHE). The RE was isolated from the main cell compartment using a glass-fritted tube.

[0113] First, the catalytic metal surface was cleaned by 50 cycles of cyclic voltammetry (CV) at 0.05–1.15 V (100 mV / s) in 0.1 M HClO4 saturated with N2.

[0114] The ORR activity of the electrocatalysts was then evaluated by exchanging the electrolyte. Specifically, three cycles of cyclic voltammetry (CV) were performed in 0.1 M HClO saturated with O2 from 0.05 to 1.15 V (100 mV / s), followed by linear sweep voltammetry (LSV) in an O2-saturated electrolyte at 1600 rpm from 0.05 to 1.00 V (5 mV / s) to evaluate the ORR activity. The mass activity (MA) of each of the electrocatalysts in Experimental Examples 1-10 and Comparative Examples 1-4 was determined by normalizing the reaction current (ik) by the respective platinum content.

[0115] [result] Table 1 shows the composition of the catalyst metal for each of Experimental Examples 1-10 and Comparative Examples 1-4, with the chemical formula Pt x Co 1-y Ni y In the above formula, the platinum composition ratio (x = Pt / (Co + Ni)) and nickel composition ratio (y = Ni / (Co + Ni)) of the catalytic metal are listed. Table 1 also lists the L10 ratio R, catalytic activity of the electrode catalyst, and normalized catalytic activity of the electrode catalyst for each of Experimental Examples 1-10 and Comparative Examples 1-4.

[0116] The "normalized catalytic activity" is a value normalized by the catalytic activity of Experimental Example 1 (PtCo / MPC) for Experimental Examples 1-10, which were carried out using mesoporous carbon as the catalyst support for supporting the catalytic metal, and a value normalized by the catalytic activity of Comparative Example 1 (PtCo / KB) for Comparative Examples 1-4, which were carried out using carbon black as the catalyst support for supporting the catalytic metal. [Table 1]

[0117] Figure 4 shows an example of the relationship between the catalytic activity of each of the electrode catalysts of Experimental Examples 1-10 and Comparative Examples 1-4 and the range of the nickel composition ratio (y) of the catalytic metal of each of the electrode catalysts. Specifically, the vertical axis of Figure 4 represents the normalized catalytic activity of the electrode catalyst, and the horizontal axis of Figure 4 represents the nickel composition ratio (y) of the catalytic metal. In Figure 4, the data for each of the electrode catalysts of Experimental Examples 1-10 are represented by a black circle (●), and the data for each of the electrode catalysts of Comparative Examples 1-4 are represented by a white square (□).

[0118] Based on the data indicated by black circles in Figure 4, we investigated the effect of the nickel composition ratio (y) of the catalytic metal on the catalytic activity of the electrocatalyst when mesoporous carbon is used as the catalyst support. The results showed that the normalized catalytic activity of the electrocatalyst increased as the nickel composition ratio (y) of the catalytic metal increased up to 0.35, after which the normalized catalytic activity began to decrease. In other words, the normalized catalytic activity of the electrocatalyst reached its maximum value (2.58) when the nickel composition ratio (y) of the catalytic metal was 0.35. Furthermore, the normalized catalytic activity of the electrocatalyst decreased as the nickel composition ratio (y) of the catalytic metal increased beyond 0.35.

[0119] Based on the data indicated by the white squares in Figure 4, we investigated the effect of the nickel composition ratio (y) of the catalytic metal on the catalytic activity of the electrode catalyst when carbon black is used as the catalyst support. As a result, we found that the normalized catalytic activity of the electrode catalyst increases as the nickel composition ratio (y) of the catalytic metal increases up to a range of 0.33, after which the normalized catalytic activity of the electrode catalyst begins to decrease. In other words, we found that the normalized catalytic activity of the electrode catalyst reaches its maximum value (1.71) when the nickel composition ratio (y) of the catalytic metal is 0.33.

[0120] From the above investigation results, it was found that the nickel composition ratio (y) of the catalytic metal is a factor that can be involved in improving the catalytic activity of the electrode catalyst, regardless of the type of catalyst support that supports the catalytic metal.

[0121] Next, we compared the change in catalytic activity of the electrode catalyst caused by differences in the nickel composition ratio (y) of the catalytic metal when mesoporous carbon is used as the catalyst support for supporting the catalytic metal with the change in catalytic activity of the electrode catalyst caused by differences in the nickel composition ratio (y) of the catalytic metal when carbon black is used as the catalyst support for supporting the catalytic metal.

[0122] If we assume that the improvement in catalytic activity of an electrode catalyst is determined solely by the nickel composition ratio (y) of the catalytic metal, the normalized catalytic activity of the electrode catalyst when mesoporous carbon is used as the catalyst support for supporting the catalytic metal (black circles in Figure 4) should be approximately the same as the normalized catalytic activity of the electrode catalyst when carbon black is used as the catalyst support for supporting the catalytic metal (white squares in Figure 4). This is because the normalized catalytic activities of both are normalized by the data of Experimental Example 1 (PtCo / MPC) and Comparative Example 1 (PtCo / KB), respectively, and therefore it is thought that the effects of improving the catalytic activity of the electrode catalyst due to the difference in catalyst support are canceled out.

[0123] However, according to the data indicated by the black circles and white squares in Figure 4, the normalized catalytic activity of the electrode catalyst when mesoporous carbon is used as the catalyst support for supporting the catalytic metal is greater than the normalized catalytic activity of the electrode catalyst when mesoporous carbon is used as the catalyst support for supporting the catalytic metal when the nickel composition ratio (y) of the catalytic metal is in the range of 0.20 to 0.47. This means that when the nickel composition ratio (y) of the catalytic metal is in the range of 0.20 to 0.47, the catalytic activity of the electrode catalyst is improved by the synergistic effect of the two factors, mesoporous carbon (a type of catalyst support) and the nickel composition ratio (y) of the catalytic metal.

[0124] As described above, the electrode catalyst of this embodiment can improve the catalytic activity of the catalytic metal supported inside the mesoporous carbon compared to conventional methods. Specifically, when the nickel composition ratio (y) of the catalytic metal supported inside the mesoporous carbon is 0.20 or more and 0.47 or less, the catalytic activity of the electrode catalyst in which the catalytic metal particles 12 contain the L10 phase can be appropriately improved due to the synergistic effect of two factors: the type of catalyst support (mesoporous material) and the nickel composition ratio (y) of the catalytic metal.

[0125] Furthermore, in the electrode catalyst of this embodiment, by supporting the catalytic metal particles 12 inside the mesoporous carbon, it is possible to appropriately suppress contact between the catalytic metal particles 12 and the ionomer even when the electrode catalyst layer is formed using an ionomer.

[0126] As described above, when a fuel cell is fabricated using the electrode catalyst of this embodiment, the fuel cell can achieve high power generation performance.

[0127] From the above description, many modifications 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]

[0128] One aspect of the present disclosure can be used, for example, in an electrode catalyst that can improve the catalytic activity of a catalytic metal supported inside a mesoporous material compared to conventional methods. [Explanation of symbols]

[0129] 10:Electrode catalyst 11: Mesoporous materials 12:Catalytic metal particles 20: Ionomer R:L10 ratio

Claims

1. a mesoporous material; and catalytic metal particles containing platinum and a metal different from platinum supported at least inside the mesoporous material, The mesoporous material has a mode radius of 1 nm or more and 25 nm or less and a pore surface area of 1.0 cm ３ / g or more 3.0cm ３ / g or less mesopores, The catalytic metal has the formula Pt ｘ Co １－ｙ Ni ｙ and the range of x of the catalytic metal is 1 or more and 3 or less, and the range of y is 0.20 or more and 0.47 or less, and the particles of the catalytic metal are represented by L1 ０ phase, the electrocatalyst.

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

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

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