Metal composite material in which metal particles are supported on carbon material

Abstract

The present invention provides a metal composite material in which metal particles are supported on a carbon material, wherein crystal grains containing a metal element constitute at least a part of the surface of the metal particles.SOLUTION: A metallic composite material comprising a metallic material and metallic particles supported on the metallic material, wherein the metallic particles comprise nuclei containing two or more metallic elements and grains containing one or more metallic elements, the metallic elements contained in the grains are metallic elements having standard electrode potentials (25 °C., 1atm) higher than 0V and not higher than 50V, and the grains constitute at least part of the surfaces of the metallic particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a metal composite material in which metal particles are supported on a carbon material, a catalyst containing the same, and an electrode for a fuel cell. [Background technology]

[0002] Previously, fuel cell electrode catalysts that have been considered include Pt supported on a carbon material (Pt / C), but currently, catalysts in which an alloy of Pt and Co is supported on a carbon material (Pt-Co / C), which is 10 to 20 times more efficient than Pt / C, are primarily in practical use. In recent years, there has been a demand for catalysts with higher performance than Pt-Co / C (higher catalytic activity and durability), and high-entropy alloys such as those described in Patent Document 1 are being considered as one such catalyst. However, the high-entropy alloy described in Patent Document 1 has limitations on the metals that can form alloys with precious metal elements such as platinum, which limits the composition of the alloy. [Prior art documents] [Non-patent literature]

[0003] [Patent Document 1] International Publication No. 2021 / 020377 Brochure Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a metal composite material in which metal particles are supported on a carbon material, wherein the metal particles comprise a core containing two or more metal elements and crystal grains containing one or more metal elements, the metal elements contained in the crystal grains have a standard electrode potential (25°C, 1 atm) of more than 0 V and not more than 1.50 V, and the crystal grains constitute at least a portion of the surface of the metal particles. [Means for solving the problem]

[0005] As a result of extensive research to solve these problems, the present inventors have found that the above object can be achieved, and have arrived at the present invention.

[0006] The gist of the present invention is as follows. <1> A metal composite material in which metal particles are supported on a carbon material, wherein the metal particles comprise a core containing two or more metal elements and crystal grains containing one or more metal elements, the metal elements contained in the crystal grains have a standard electrode potential (25°C, 1 atm) of greater than 0 V and less than or equal to 1.50 V, and the crystal grains constitute at least a portion of the surface of the metal particles. <2> The core containing the metal element contains two or more metal elements selected from the group consisting of Cr, Fe, Co, Ni, and Mn. <1> The metal composite material according to claim 1. <3> The crystal grains containing the metal element contain precious metals. <1> or <2> The metal composite material according to any one of the preceding claims. <4> The crystal grains containing the metal element contain platinum. <1> ~ <3> The metal composite material according to claim 1. <5> <1> ~ <4> A catalyst comprising the metal composite material according to claim 1. <6> <5> An electrode for a fuel cell comprising the catalyst according to claim 1. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a metal composite material in which metal particles are supported on a carbon material, wherein the metal particles include a core containing two or more metal elements and crystal grains containing one or more metal elements, the metal elements contained in the crystal grains have a standard electrode potential (25°C, 1 atm) of more than 0 V and not more than 1.50 V, and the crystal grains constitute at least a part of the surface of the metal particles. The metal composite material of the present invention in which metal particles are supported on a carbon material can be suitably used as a catalyst or an electrode for a fuel cell because the crystal grains form at least a part of the surface of the metal particles. [Brief explanation of the drawings]

[0008] [Figure 1]1 is a TEM image of the metal composite material of Example 2. Crystal grains can be seen in the area surrounded by the solid line on the surface of the metal particle in the image, and it can be confirmed that the crystal grains make up at least a part of the surface of the metal particle. [Figure 2] (1) STEM image of Example 2. (2) Mapping image (STEM-EDX image) of carbon element of Example 2. (3) Mapping image (STEM-EDX image) of cobalt element of Example 2. (4) Mapping image (STEM-EDX image) of chromium element of Example 2. (5) Mapping image (STEM-EDX image) of iron element of Example 2. (6) Mapping image (STEM-EDX image) of manganese element of Example 2. (7) Mapping image (STEM-EDX image) of nickel element of Example 2. (8) Mapping image (STEM-EDX image) of platinum element of Example 2. When comparing the STEM image with the mapping image of each element, cobalt, chromium, iron, manganese, and nickel are distributed evenly within the metal particles, forming a solid solution in which each metal is uniformly mixed. On the other hand, platinum element is distributed unevenly within the metal particles, and it can be confirmed that each is distributed as crystal grains. DETAILED DESCRIPTION OF THE INVENTION

[0009] The metal composite material of the present invention is a metal composite material in which metal particles are supported on a carbon material, wherein the metal particles include a core containing two or more metal elements and crystal grains containing one or more metal elements, the metal elements contained in the crystal grains have a standard electrode potential (25°C, 1 atm) of more than 0 V and not more than 1.50 V, and the crystal grains constitute at least a portion of the surface of the metal particles.

[0010] The metal element contained in the core is not particularly limited, but examples include lithium and beryllium from the second period of the periodic table, sodium, magnesium, and aluminum from the third period, potassium to gallium from the fourth period, rubidium to tin from the fifth period, cesium to polonium from the sixth period, and francium to hassium, copernicium, and flerovium from the seventh period. The metal element may contain a semimetal and be in an amorphous state, or may contain oxygen, fluorine, or the like and be in a ceramic or semiconductor state. The core preferably contains two or more elements from the group consisting of Cr, Fe, Co, Ni, and Mn, more preferably three or more elements, even more preferably four or more elements, and particularly preferably all five elements. The metal element contained in the crystal grains may be contained in the core, but its content is preferably low. If the core contains only one type of metal element, the metal element contained in the core and the element contained in the crystal grains may form an alloy, which may prevent the formation of crystal grains. When the nucleus is in a more stable solid solution state where multiple metal elements are randomly distributed, it becomes stronger against heat and corrosion and has improved durability. The entropy of mixing, which indicates the mixed state of metal elements in a solid solution state, can be calculated from the following formula (1), where R is the metal element gas constant, χi is the mole fraction of the metal components that form the nucleus, and n is the number of components. ΔS in the following formula (1) mix The larger the value, the more stable the polymer is. It is preferably 1.0R or more, more preferably 1.3R or more, and particularly preferably 1.5R or more.

[0011] Formula (1) JPEG2026009043000002.jpg24169

[0012] The average particle size of the crystal grains is preferably 5 nm or less, more preferably 4 nm or less from the viewpoint of obtaining higher catalytic activity, and even more preferably 3 nm or less. The crystal grains must contain one or more metal elements. From the viewpoint of the reduction rate during crystal grain formation, the metal elements must be metal elements having a standard electrode potential (25°C, 1 atm) of greater than 0 V and less than or equal to 1.50 V (e.g., Re (0.30 V), Cu (0.34 V), Ru (0.46 V), Rh (0.76 V), Os (0.90 V), Pd (0.95 V), Ir (1.16 V), Pt (1.18 V)). Noble metal elements (Ru, Rh, Os, Pd, Ir, Pt) are particularly preferred, with platinum being most preferred. Furthermore, the metal elements may be one type or two or more types.

[0013] The average particle size and crystallinity of the metal composite material of the present invention can be evaluated by measuring it with STEM and STEM-EDX.

[0014] The supported carbon material of the present invention is not particularly limited. Examples of the carbon material include activated carbon, carbon black, graphite, and carbon nanotubes, with carbon black being particularly preferred. From the viewpoint of obtaining higher catalytic activity, the amount of metal in the metal composite material supporting metal particles is preferably 10% by mass or more, and more preferably 30% by mass or more.

[0015] The method for synthesizing the metal particles and supporting them on the carbon material is not particularly limited, but it is preferable to synthesize the metal particles in the presence of the carbon material, as this makes it easier to control the generation of nuclei and crystal grains, and it is particularly preferable to perform the wet synthesis described below.

[0016] Examples of wet synthesis include a method (first method) in which a carbon material to be a support and solution A containing metal ions that will become the metal particle nuclei of the metal particles, solution B containing metal ions that will become crystal grains, and solution C containing a reducing agent, a method (second method) in which the metal element that will become the crystal grains is protected with a chelating agent, mixed with other metal ions, and reduced with a reducing agent, and a method (third method) that uses a standard electrode potential difference. Among these, method 1 is preferred because of its ease of control. Below, method 1 will be explained.

[0017] It is preferable to mix the carbon material with Solution A, which contains metal ions that will become the nuclei of the metal particles. Although the reason for this is unclear, it is presumed that by supporting the metal ions that will become the nuclei on the carbon material in advance, it becomes difficult for crystal grains to be directly supported on the carbon material, and they are more likely to form on the nuclei surface.

[0018] The carbon material is preferably pretreated to improve its ability to adsorb metal particles, for example by applying ultrasonic waves under acidic conditions.

[0019] As the raw material for the metal particles, metal ions obtained by dissolving a metal salt in a solvent such as water can be used. The metal salt is not particularly limited as long as it can be dissolved in the reaction solvent used and can supply metal ions in a reducible state.

[0020] The concentration of each metal ion in solutions A and B is preferably 5 to 1000 mmol / L, more preferably 30 to 300 mmol / L, and even more preferably 50 to 200 mmol / L, because this improves the yield of the resulting metal composite material in which metal particles are supported on a carbon material and tends to increase the specific surface area. Furthermore, the concentration of each metal ion does not need to be constant and can be increased or decreased as needed.

[0021] The mass of the carbon material in Solution A is preferably 0.1 to 1.0 times, and more preferably 0.2 to 0.5 times, the total mass of the metal ions in the solution.

[0022] The reducing agent is not particularly limited, and examples thereof include reducing agents containing boron atoms such as sodium borohydride, potassium borohydride, and dimethylamine borane, hydrazines such as hydrazine and phenylhydrazine, alcohols such as isopropyl alcohol and ethylene glycol, amines such as octylamine and triethylamine, organic acids such as ascorbic acid and formic acid, and phosphorus-based reducing agents such as sodium hypophosphite. Among these, it is preferable to use reducing agents containing boron atoms such as sodium borohydride, potassium borohydride, and dimethylamine borane, and it is more preferable to use sodium borohydride.

[0023] The concentration of the reducing agent in solution C is not particularly limited, but it is preferable to use a reducing agent in an amount 1.2 to 2.0 mol times the total amount of metal ions, and therefore the concentration is preferably 30 to 10,000 mmol / L, more preferably 180 to 3,000 mmol / L, and even more preferably 300 to 2,000 mmol / L.

[0024] In wet synthesis, from the viewpoint of crystal grain formation, it is preferable to mix solution A with solution B, and then mix it with solution C. Although the reason for this is not clear, it is presumed that by including a carbon material and metal ions that will serve as nuclei in solution A, the metal ions that will serve as nuclei are supported on the carbon material in advance, and by subsequently mixing solutions B and C, the resulting crystal grains are less likely to be supported directly on the carbon material and are more likely to form on the nuclei surfaces.

[0025] The temperature at which the wet synthesis is carried out is preferably 5 to 40°C from the viewpoint of controlling the rate of the reduction reaction and controlling the average particle size of the crystal grains.

[0026] Purification after the synthesis reaction can be carried out by centrifugation, filtration, or the like.

[0027] The metal composite material in which the recovered metal particles are supported on a carbon material is preferably fired at a temperature equal to or higher than the temperature at which it is to be used, so that it can be used suitably at the temperature at which it is actually used. The firing time is preferably 3 hours or more.

[0028] The metal composite material of the present invention in which metal particles are supported on a carbon material can be suitably used as a catalyst or a fuel cell catalyst electrode, since the crystal grains constitute at least a part of the surface of the metal particles. [Example]

[0029] EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. The metal composite materials were evaluated by the following methods. (1) Molar fraction of metal and metalloid elements in metal particles The obtained metal composite material was baked in vacuum at 70°C for 1 hour and at 200°C for 4 hours, and then the mole fraction of each detected metal and metalloid element was determined by ICP-AES.

[0030] Let R be the gas constant and x be the mole fraction of component i. i , the number of components is n, and from the above equation (1), ΔS mix was calculated. (2) Loading rate in carbon material As in (1), the amount of metal (metal + metalloid) in the obtained metal particles supported on a carbon material was measured by ICP-AES, and this was taken as the support rate. (3) Average particle size of metal particles in carbon materials, and characteristic values ​​of core and surface crystal grains The metal composite material in which the obtained metal particles were supported on a carbon material was photographed using STEM-EDX, and the distribution of metal elements in the metal composite material supported on the carbon material was confirmed from the field of view, and the crystallinity of the core particles and the presence or absence of crystal grains were evaluated. (4) Average grain size Ten crystal grains were randomly selected from the TEM image of the obtained metal composite material, and the average value of the length of their major axes was taken as the average particle size of the crystal grains.

[0031] Example 1 Solution A was prepared by adding 5 g of carbon black (Cabot Vulcan XC-72R) to 200 g of water and adjusting the pH to 2 with hydrochloric acid. Subsequently, 6.65 g (25 mmol) of chromium(III) chloride hexahydrate, 4.95 g (25 mmol) of manganese(II) chloride tetrahydrate, 4.95 g (25 mmol) of iron(II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, and 5.95 g (25 mmol) of nickel chloride hexahydrate were added and sonicated for 5 minutes. (The ratio of chromium(III) chloride hexahydrate: manganese(II) chloride tetrahydrate: iron(II) chloride tetrahydrate: cobalt chloride hexahydrate: nickel chloride hexahydrate was 20 mol%:20 mol%:20 mol%:20 mol%:20 mol%). Solution B was prepared by dissolving 12.95 g (25 mmol) of chloroplatinic acid hexahydrate in 100 g of ethanol. As solution C, 9.66 g (256 mmol) of sodium borohydride was dissolved in 200 g of water. Solutions A and B were mixed at room temperature, and then solution C was added dropwise over 15 minutes. The mixture was then allowed to stand for another 10 minutes. The reaction solution was poured into 200 parts by mass of water and diluted. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water, and then calcined in a vacuum at 70°C for one hour and at 200°C for four hours to obtain a metal composite material of the present invention in which metal particles are supported on a carbon material. It has been confirmed that the metal composite material of the present invention contains Cr, Mn, Fe, Co, and Ni as metal elements in the core, and Pt as crystal grains on the surface of the metal particles.

[0032] Example 2 To prepare Solution A, 5 g of carbon black (Vulcan XC-72R, manufactured by Cabot Corporation) was added to 200 g of water, and the pH was adjusted to 2 with hydrochloric acid. Subsequently, 6.65 g (25 mmol) of chromium (III) chloride hexahydrate, 4.95 g (25 mmol) of manganese (II) chloride tetrahydrate, 4.95 g (25 mmol) of iron (II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, 5.95 g (25 mmol) of nickel chloride hexahydrate, and 12.95 g (25 mmol) of chloroplatinic acid hexahydrate were further added, and the mixture was treated with ultrasound for 5 minutes. (Chromium(III) chloride hexahydrate: manganese(II) chloride tetrahydrate: iron(II) chloride tetrahydrate: cobalt chloride hexahydrate: nickel chloride hexahydrate: chloroplatinic acid hexahydrate = 16.7 mol%: 16.7 mol%: 16.7 mol%: 16.7 mol%: 16.7 mol%,). As solution C, 9.66 g (256 mmol) of sodium borohydride was dissolved in 200 g of water. Solution C was added dropwise to Solution A over 15 minutes, and then allowed to stand for an additional 10 minutes. The reaction solution was poured into 200 parts by mass of water and diluted. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water and three times with methanol, and calcined under vacuum at 70°C for one hour and at 200°C for four hours to obtain a metal composite material of the present invention in which metal particles are supported on a carbon material. It has been confirmed that the metal composite material of the present invention contains Cr, Mn, Fe, Co, and Ni as metal elements in the core, and Pt as crystal grains on the surface of the metal particles.

[0033] Example 3 Solution A was prepared by adding 5 g of carbon black (Cabot Vulcan XC-72R) to 200 g of water and adjusting the pH to 2 with hydrochloric acid. Subsequently, 6.65 g (25 mmol) of chromium(III) chloride hexahydrate, 4.95 g (25 mmol) of manganese(II) chloride tetrahydrate, 4.95 g (25 mmol) of iron(II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, and 5.95 g (25 mmol) of nickel chloride hexahydrate were added and sonicated for 5 minutes. (The ratio of chromium(III) chloride hexahydrate:manganese(II) chloride tetrahydrate:iron(II) chloride tetrahydrate:cobalt chloride hexahydrate:nickel chloride hexahydrate was 20 mol%:20 mol%:20 mol%:20 mol%:20 mol%). Solution B was prepared by dissolving 25.90 g (50 mmol) of chloroplatinic acid hexahydrate in 100 g of ethanol. To prepare solution C, 15.19 g (375 mmol) of sodium borohydride was dissolved in 200 g of water. Solutions A and B were mixed, and Solution C was added dropwise over 15 minutes, after which the mixture was allowed to stand for another 10 minutes. The reaction solution was poured into 200 parts by mass of water and diluted. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water and three times with methanol, and calcined under vacuum at 70°C for one hour and at 200°C for four hours to obtain a metal composite material of the present invention in which metal particles are supported on a carbon material. It has been confirmed that the metal composite material of the present invention contains Cr, Mn, Fe, Co, and Ni as metal elements in the core, and Pt as crystal grains on the surface of the metal particles.

[0034] Example 4 Solution A was prepared by adding 5 g of carbon black (Cabot Vulcan XC-72R) to 200 g of water and adjusting the pH to 2 with hydrochloric acid. Subsequently, 6.65 g (25 mmol) of chromium(III) chloride hexahydrate, 4.95 g (25 mmol) of manganese(II) chloride tetrahydrate, 4.95 g (25 mmol) of iron(II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, and 5.95 g (25 mmol) of nickel chloride hexahydrate were added and sonicated for 5 minutes. (The ratio of chromium(III) chloride hexahydrate:manganese(II) chloride tetrahydrate:iron(II) chloride tetrahydrate:cobalt chloride hexahydrate:nickel chloride hexahydrate was 20 mol%:20 mol%:20 mol%:20 mol%:20 mol%). As solution B, 25.90 g (50 mmol) of hydrogen hexachloroiridate hexahydrate was dissolved in 100 g of ethanol. To prepare solution C, 15.19 g (375 mmol) of sodium borohydride was dissolved in 200 g of water. Solutions A and B were mixed, and Solution C was added dropwise over 15 minutes, after which the mixture was allowed to stand for another 10 minutes. The reaction solution was poured into 200 parts by mass of water and diluted. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water and three times with methanol, and calcined under vacuum at 70°C for one hour and at 200°C for four hours to obtain a metal composite material of the present invention in which metal particles are supported on a carbon material. It has been confirmed that the metal composite material of the present invention contains Cr, Mn, Fe, Co, and Ni as metal elements in the core, and Pt as crystal grains on the surface of the metal particles.

[0035] Example 5 Solution A was prepared by adding 5 g of carbon black (Cabot Vulcan XC-72R) to 200 g of water and adjusting the pH to 2 with hydrochloric acid. Subsequently, 6.65 g (25 mmol) of chromium(III) chloride hexahydrate, 4.95 g (25 mmol) of manganese(II) chloride tetrahydrate, 4.95 g (25 mmol) of iron(II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, and 5.95 g (25 mmol) of nickel chloride hexahydrate were added and sonicated for 5 minutes. (The ratio of chromium(III) chloride hexahydrate:manganese(II) chloride tetrahydrate:iron(II) chloride tetrahydrate:cobalt chloride hexahydrate:nickel chloride hexahydrate was 20 mol%:20 mol%:20 mol%:20 mol%:20 mol%). Solution B was prepared by dissolving 12.95 g (25 mmol) of chloroplatinic acid hexahydrate in 100 g of ethanol. As solution C, 12.80 g (256 mmol) of hydrazine monohydrate was dissolved in 200 g of water. The mixture was heated to 85°C for liquid A, 50°C for liquid B, and 90°C for liquid C. Solutions A and B were mixed, and liquid C was added dropwise over 15 minutes, after which the mixture was allowed to stand for another 10 minutes. The reaction solution was poured into 200 parts by mass of water for dilution. The resulting black solid was recovered by filtration using a PTFE filter (T100A090C), washed three times with water and three times with methanol, and calcined under vacuum at 70°C for one hour and at 200°C for four hours to obtain a metal composite material of the present invention in which metal particles are supported on a carbon material. It has been confirmed that the metal composite material of the present invention contains Cr, Mn, Fe, Co, and Ni as metal elements in the core, and Pt as crystal grains on the surface of the metal particles.

[0036] Example 6 Solution A was prepared by adding 2 g of carbon black (Cabot Vulcan XC-72R) to 200 g of water and adjusting the pH to 2 with hydrochloric acid. Subsequently, 6.65 g (25 mmol) of chromium(III) chloride hexahydrate, 4.95 g (25 mmol) of manganese(II) chloride tetrahydrate, 4.95 g (25 mmol) of iron(II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, and 5.95 g (25 mmol) of nickel chloride hexahydrate were added and sonicated for 5 minutes. (The ratio of chromium(III) chloride hexahydrate:manganese(II) chloride tetrahydrate:iron(II) chloride tetrahydrate:cobalt chloride hexahydrate:nickel chloride hexahydrate was 20 mol%:20 mol%:20 mol%:20 mol%:20 mol%). Solution B was prepared by dissolving 25.90 g (50 mmol) of chloroplatinic acid hexahydrate in 100 g of ethanol. To prepare solution C, 15.19 g (375 mmol) of sodium borohydride was dissolved in 200 g of water. Solutions A and B were mixed, and Solution C was added dropwise over 15 minutes, after which the mixture was allowed to stand for another 10 minutes. The reaction solution was poured into 200 parts by mass of water and diluted. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water and three times with methanol, and calcined under vacuum at 70°C for one hour and at 200°C for four hours to obtain a metal composite material of the present invention in which metal particles are supported on a carbon material. It has been confirmed that the metal composite material of the present invention contains Cr, Mn, Fe, Co, and Ni as metal materials in the core, and Pt as crystal grains on the surface of the metal particles.

[0037] Comparative Example 1 To prepare Solution A, 5 g of carbon black (Vulcan XC-72R manufactured by Cabot Corporation) was added to 200 g of water, and the pH was adjusted to 2 with hydrochloric acid. Subsequently, 29.75 g (125 mmol) of nickel chloride hexahydrate was further added, and the mixture was treated with ultrasound for 5 minutes. Solution B was prepared by dissolving 12.95 g (25 mmol) of chloroplatinic acid hexahydrate in 100 g of ethanol. To prepare Solution C, 9.66 parts by mass (256 mmol) of hydrazine monohydrate was dissolved in 200 g of water. Solution A heated to 90°C and solution B at room temperature were added dropwise to solution C heated to 90°C over 15 minutes, and then allowed to stand for another 10 minutes. The reaction solution was poured into 200 parts by mass of water and diluted. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water and three times with methanol, and calcined in air at 70°C for one hour and at 300°C for four hours to obtain a metal composite material in which metal particles were supported on a carbon material. In the metal composite material, the core contained Ni as the metallic material, but no crystal grains were observed.

[0038] Comparative Example 2 Solution A was prepared by adding 5 g of carbon black (Cabot Vulcan XC-72R) to 200 g of water and adjusting the pH to 2 with hydrochloric acid. Subsequently, 6.65 g (25 mmol) of chromium(III) chloride hexahydrate, 4.95 g (25 mmol) of manganese(II) chloride tetrahydrate, 4.95 g (25 mmol) of iron(II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, and 5.95 g (25 mmol) of nickel chloride hexahydrate were added and ultrasonically treated for 5 minutes. (chromium(III) chloride hexahydrate: manganese(II) chloride tetrahydrate: iron(II) chloride tetrahydrate: cobalt chloride hexahydrate: nickel chloride hexahydrate = 20 mol%:20 mol%:20 mol%:20 mol%:20 mol%). As solution B, 10.30 g (25 mmol) of tetrachloroauric acid tetrahydrate was dissolved in 100 g of ethanol. As solution C, 9.66 g (256 mmol) of sodium borohydride was dissolved in 200 g of water. Solutions A and B were mixed, and then solution C was added dropwise over 15 minutes, after which the mixture was allowed to stand for another 10 minutes. The reaction solution was poured into 200 parts by mass of water and diluted. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water and three times with methanol, and calcined under vacuum at 70°C for one hour and at 200°C for four hours to obtain a metal composite material in which metal particles were supported on a carbon material. In the metal composite material, the core contained Cr, Mn, Fe, Co, and Ni as metal materials, but no crystal grains were observed.

[0039] Tables 1 and 2 show the compositions and evaluation results of the metal composite materials in which metal particles are supported on a carbon material in Examples 1 to 5 and Comparative Examples 1 and 2.

[0040] [Table 1]

[0041] [Table 2]

[0042] The metal composite materials of Examples 1 to 5 comprised a core containing two or more metal elements and crystal grains containing one or more metal elements, the metal elements contained in the crystal grains having a standard electrode potential (25°C, 1 atm) of greater than 0 V and less than or equal to 1.50 V, and the crystal grains constituted at least a portion of the surface of the metal particles. In particular, in the metal composite materials of Examples 1 and 3 to 5, by adding a carbon material and metal ions that would serve as cores to Solution A, the metal ions that would serve as cores were pre-supported on the carbon material, and then mixing Solutions B and C, the resulting crystal grains were less likely to be directly supported on the carbon material and more likely to be formed on the core surface, resulting in a ΔS of greater than 1.5.

[0043] In Comparative Example 1, nickel was the only metal element used as the nucleus, so nickel formed an alloy with platinum during the reduction reaction, and platinum crystal grains were not formed.In Comparative Example 2, the standard electrode potential of gold (standard electrode potential 1.52 V) was too high, so gold, which would become crystal grains, was reduced at a high speed and separated as coarse particles.

Claims

1. A metal composite material in which metal particles are supported on a carbon material, the metal particles include a core containing two or more metal elements and a crystal grain containing one or more metal elements, the metal element contained in the crystal grains is a metal element having a standard electrode potential (25°C, 1 atm) of more than 0 V and not more than 1.50 V, A metallic composite material, characterized in that the crystal grains constitute at least a part of the surface of the metallic particles.

2. 2. The metallic composite material according to claim 1, wherein the core containing a metallic element contains two or more metallic elements selected from the group consisting of Cr, Fe, Co, Ni, and Mn.

3. 3. The metal composite material according to claim 1, wherein the crystal grains containing a metal element contain a noble metal.

4. 3. The metal composite material according to claim 1, wherein the crystal grains containing a metal element contain platinum.

5. A catalyst comprising the metal composite material according to claim 1 or 2.

6. An electrode for a fuel cell comprising the catalyst according to claim 5 .

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