JP2008201602A - Carbon carrying platinum-bridged nanowire particles and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new platinum-carbon complex carrying platinum controlled in its shape at a nanosize level on carbon which is usable as an electrode catalyst for a fuel cell or the like and its manufacturing method. <P>SOLUTION: In carbon carrying platinum nanoparticles, the platinum nanoparticle has a skeleton formed by platinum element and has a wire-like shape which consists of single crystals having an outer diameter of 5-100 nm in which cross-linked wire-like skeletons having a diameter of 1-5 nm are three-dimensionally bridged or microcrystals are connected. In a method for manufacturing carbon carrying platinum nanoparticles by preparing a reaction mixture consisting of a platinum complex compound, two kinds of non-ionic surfactants, water, and various kinds of carbon and reacting the reaction mixture by adding an aqueous solution of a reducer, platinum-bridged nanowire particles are formed by preparing the reaction mixture under a reduced pressure. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a catalyst used for various electrochemical reactions such as a fuel cell electrode catalyst utilizing the chemical and electrochemical characteristics of platinum, a catalyst used for various chemical reactions in industrial and environmental fields such as a catalyst for automobile exhaust gas treatment, Gas diffusion electrode for fuel cell, gas diffusion electrode for metal-air battery, gas diffusion electrode for salt electrolysis, gas diffusion electrode for electrolysis, microreactor constituent material, substance storage material, various sensors, paste, electrical wiring material, The present invention relates to a novel platinum-supported nanowire particle-supporting carbon used as a functional material such as an electric resistor, a capacitor, and a permanent magnet, and a method for producing the same.

  Various electrode catalysts and gas diffusion electrodes for energy conversion and substance conversion are generally used after introducing a metal component into a conductive support such as carbon using an aqueous solution or colloidal dispersion of a metal salt, followed by firing, hydrogen reduction, etc. It is prepared using a method of performing the above-described treatment (Non-patent Document 1) or a vapor phase method such as CVD. That is, the electrode catalyst is prepared in the form of composite particles in which metal particles are supported on the surface of a solid support, and its activity is not only the metal species but also the size of the supported metal fine particles, the type of crystal plane, the type of support. The control of the shape and size of the fine particles is particularly important.

  For this reason, as a method for preparing the platinum catalyst and the platinum electrode catalyst, in addition to devising the above general methods in various ways, a method of producing a platinum colloid by liquid phase reduction in the presence of a protective agent such as polyvinylpyrrolidone ( Non-patent document 2) has also been developed.

Recently, platinum nanowires have been obtained by photoreduction using mesoporous silica as a template, reduction using H ₂ gas and electrodeposition (Non-Patent Documents 3 and 4). Nanowires having a diameter and length corresponding to the pore diameter have been synthesized (Non-patent Document 5). In addition, by platinum reduction using mesoporous silica having a three-dimensional pore structure as a template, platinum wires are connected in a three-dimensional network, and porous platinum particles having pores with a diameter of about 3 nm corresponding to the thickness of the silica wall are obtained. Although it is obtained (Non-Patent Document 6), there is no mention of loading on carbon.

  On the other hand, the present inventors have developed a technique for reducing chloroplatinic acid using a liquid crystal composed of two kinds of surfactants as a template, and an outer diameter of 5 to 7 nm and an inner diameter of 2 to 4 nm depending on the kind of the reducing agent and the platinum salt. Of platinum, platinum nanotubes such as palladium, sponge-like platinum nanoparticles having a diameter of 1.5 to 4 nm and an outer diameter of 20 to 100 nm, and carbon carrying the sponge-like platinum nanoparticles (platinum nanosheet having a sponge-like form) were produced (patents) Literature 1, Patent Literature 2, Patent Literature 3).

  However, the platinum nanostructure disclosed in the above-mentioned document is a bulk ultrafine powder or sponge-like platinum nanoparticle (sheet) -supporting carbon that is independently generated. Absent.

Hiroo Tominaga et al., Chemical Review “Catalyst Design”, The Chemical Society of Japan, 1982, p.50-63 N. Toshima and 1 other person, Bull. Chem. Soc. Jpn., 65, 400 (1992) M. Sasaki and 6 others, Microporous Mesoporous Mater., 21, 597 (1998). Z. Liu and 7 others, Angew. Chem. Int. Ed., 39, 3107 (2000). K-. B. Lee and two others, Adv. Mater., 13, 7, 517 (2001). H. J. Shin and three others J. Am. Chem. Soc., 123, 1246-1247 (2001). Tsuyoshi Kijima, JP2004-034228 Takeshi Kijima and 1 other, JP2006-045582 Takeshi Kijima and one other, JP 2006-228450

  As described above, the conventional technique for supporting platinum and its alloys represented by platinum on carbon has a large number of spherical or amorphous ultrafine particles formed in a self-organized manner by adding a reducing agent and utilizing various reactions. In order to develop a large number of new physical properties and improve the performance of fuel cell electrodes, platinum is supported on carbon by controlling its shape at the nano-size level, which makes it a new platinum with different forms and properties. -Development of carbon composites is desired from various fields.

Further, as an electrode for a fuel cell, it is strongly desired to reduce the cathode overvoltage resulting from the low oxygen reduction activity.
It is an object of the present invention to provide a novel platinum-carbon composite that can be used as an electrode catalyst for a fuel cell, etc., supported on carbon by controlling the shape of platinum at a nanosize level, and a method for producing the same. To do.

  Therefore, in the present inventors, based on the conventional technology introduced above, the present inventors previously proposed and applied for a patent in order to develop a shape-controlled platinum catalyst having a form different from the conventional technology. As a result of further development of the template synthesis method based on the composite surfactant system described in Patent Literatures 1 to 3, a specific reaction mixture containing a platinum salt was prepared, and carbon powder was previously added to the reaction mixture under reduced pressure. After the mixture reaches a predetermined ratio, the platinum cross-linked nanowire particles are successfully deposited on the carbon powder by a reduction reaction, thereby providing a new form of platinum-carbon composite. I found out that I can do it. The present invention has been made on the basis of this finding, and the configuration thereof is as described in (1) to (9) below.

  That is, according to the first invention, (1) in carbon carrying platinum nanoparticles, the platinum nanoparticles are composed of a skeleton of platinum element, and a cross-bonded wire-like skeleton having a diameter of 1 to 5 nm is three-dimensional. It is a carbon carrying platinum nanoparticles, characterized in that it has a wire-like form consisting of a single crystal having an outer diameter of 5 to 100 nm cross-linked or having a crystallite connected thereto.

  The second invention presents the manufacturing method of the first invention. That is, (2) from the group consisting of platinum complex compounds and polyoxyethylene alkyl ethers, polyoxyethylene sorbitan esters, polyoxyethylene fatty acid esters, polyoxyethylene alkyl phenyl ethers, polyoxyethylene polyoxypropylene block polymers A method for producing carbon carrying platinum nanoparticles prepared by preparing a reaction mixture comprising two kinds of selected nonionic surfactants, water, and various carbons, and then adding an aqueous reducing agent solution to the reaction mixture for reaction. In the above, the reaction mixture is prepared under reduced pressure to form a skeleton of platinum element, and the cross-linked wire-like skeleton is composed of a three-dimensionally cross-linked single crystal or a wire-like form in which microcrystals are connected Producing platinum nanoparticles having Wherein a method for producing a carbon supporting platinum nanoparticles.

The third to sixth inventions show embodiments of the second invention.
That is, (3) hexachloroplatinic acid or a salt thereof is used as the platinum complex compound, and two types of nonionic surfactants are (4) nonaethylene glycol dodecyl ether as the polyoxyethylene alkyl ethers. (5) Polyoxyethylene sorbitan monostearate or the like is used as the polyoxyethylene sorbitan ester, and (6) A hydrazine aqueous solution or the like is used as the reducing agent aqueous solution (2) ) Is a method for producing carbon carrying platinum nanoparticles.

The seventh invention is (7) a functional material comprising the platinum-crosslinked nanowire particle-supporting carbon of the first invention and used for applications based on the physical properties thereof. The invention of No. 9 is used for a more specific application.
That is, the eighth invention is (8) the functional material of (7) provided and used as a catalyst material such as an electrode catalyst, and the ninth invention is (9) a fuel cell whose use is exclusively used. The functional material according to (7) is provided and used as a gas diffusion electrode for a metal-air battery or the like, or used as an electrode for electrolysis or the like. is there.
Furthermore, the functional material used exclusively as a microreactor constituting material, the functional material used, the functional material used exclusively as a material storage material, the functional material used, the application exclusively used for temperature, pressure, humidity, condensation Functional materials that are used as sensors for detecting or measuring flow rate, wind speed, light, gas, oxygen concentration, or displacement, or shape memory sensors, and that their applications are exclusively used as pastes. Functional materials that are characterized, functional materials that are used exclusively as electrical wiring materials, electrical resistors, or capacitors, functional materials that are used, and functional materials that are used exclusively as permanent magnets can do.

  The outline of the production method of the present invention is specified by reducing platinum salt using a structure obtained by mixing at least two kinds of surfactants, an aqueous solution of platinum salt and carbon under appropriate conditions under reduced pressure as a template. The size of the nanoparticles is induced on the carbon, and the optimum temperature and mixing conditions for constructing the template are the target platinum type, the characteristics of the surfactant used, the characteristics of the carbon used, and the reducing agent. Varies depending on the type of

Hexachloroplatinic acid (H ₂ PtCl ₆ ) is used as a platinum complex compound (platinum salt), and nonaethylene glycol dodecyl ether and polyoxyethylene (20) sorbitan monostearate are used as two types of nonionic surfactants. In such a case, the following conditions can be adopted.
1 to 10 mol of nonaethylene glycol dodecyl ether and 1 to 600 mol of water are added to 2 mol of hexachloroplatinic acid, and the mixture is shaken and mixed at 60 to 70 ° C. for 10 to 30 minutes, and then cooled to obtain an aqueous solution A. Next, 1 to 10 mol of polyoxyethylene (20) sorbitan monostearate and 1 to 600 mol of water are added at 50 to 70 ° C., mixed for 10 to 30 minutes, and then cooled to obtain an aqueous B solution. The aqueous B solution was added to the aqueous A solution, and after stirring for 10 to 30 minutes, carbon was added thereto so that the total weight ratio of Pt was 10 to 70 wt%, and the mixture was stirred under reduced pressure until an arbitrary molar ratio was obtained. While removing the water. Cool sufficiently to 0 to 30 ° C., preferably 0 to 10 ° C., and drop hydrazine in an amount of 1 to 700 mol, preferably 350 to 600 mol per mol of hexachloroplatinic acid, and hold at that temperature for 1 minute to 24 hours. It is made to dry through ethanol washing and water to obtain platinum-crosslinked nanowire particle-supporting carbon.

  The decompression conditions that characterize the present invention are not limited, but preferably 0.01 to 0.0001 atm. As described in Patent Document 3, when the reaction mixture is adjusted at normal pressure, carbon carrying platinum nanoparticles having a wire-like form as shown in the present invention cannot be obtained.

  As the carbon, carbon black such as furnace black, carbon nanotube, and the like can be used.

  The present invention has the above-described features, but the present invention will be specifically described below with reference to the embodiments and the accompanying drawings. However, these examples merely disclose one aspect of the present invention, and are not intended to limit the present invention. The metal species and the manufacturing method constituting the present invention should not be limited by this example.

  FIG. 1 is a transmission electron microscope observation photograph of cross-bonded wire-like platinum nanoparticle-supported carbon obtained in Example 1 of the present invention described below. According to this, the platinum structure of the present invention is It is observed that it exhibits a cross-bonded wire-like structure and is supported on carbon.

A platinum-bridged nanowire particle-supporting carbon containing platinum as a platinum component was produced as follows.
To 2 mol of hexachloroplatinic acid (H ₂ PtCl ₆ ), 2 mol of nonaethylene glycol dodecyl ether (C ₁₂ EO ₉ ) and 300 mol of water were added, and the mixture was shaken at 60 ° C. for 10 minutes, then cooled, did. Next, 2 mol of polyoxyethylene (20) sorbitan monostearate (Tween 60; trade name of Atlas Powder, USA) was added at 60 ° C. and 300 mol of water were mixed for 15 minutes, followed by cooling to obtain an aqueous B solution. The aqueous B solution was added to the aqueous A solution, and after stirring for 10 minutes, furnace black (VXC72R; trade name of Cabot Corp., USA) was added thereto so that the total weight ratio of Pt was 46 wt%, and H ₂ PtCl ₆ : C Water was removed while stirring under reduced pressure (0.0008 atm) until ₁₂ EO ₉ : Tween 60: H ₂ O = 2: 2: 2: 30. After sufficiently cooling to 4 ° C., 481 mol of hydrazine was added dropwise per 1 mol of hexachlorochloroplatinic acid, kept at that temperature for 10 minutes, and then dried through ethanol washing and water washing to obtain a black powder.

The X-ray diffraction pattern of the product obtained by adjusting H ₂ PtCl ₆ : C ₁₂ EO ₉ : Tween 60: H ₂ O = 2: 2: 2: 30 shows a peak reflecting the crystal structure of platinum. It was confirmed that the obtained product was carbon carrying platinum (FIG. 3).

  Observation by a transmission electron microscope shows that a platinum product supported on carbon is formed of a single crystal having an outer diameter of 5 to 100 nm in which a cross-bonded wire-like skeleton having a diameter of 1 to 5 nm is three-dimensionally connected. And it confirmed that it had the wire-like form which the microcrystal connected (FIG. 1, FIG. 2). As a result, it was confirmed that carbon carrying wire-like platinum nanoparticles having a porous single crystal structure or crystallites according to the present invention was obtained.

  As described above, the present invention is very useful in electrode catalysts for fuel cells, gas diffusion electrodes for fuel cells, gas diffusion electrodes for metal-air cells, gas diffusion electrodes for salt electrolysis, gas diffusion electrodes for electrolysis and the like. It is expected that a device having a significant activity and thus using a very expensive platinum or platinum material will exhibit a high level of properties and functions as well as a material saving effect. Gas diffusion electrodes and their constituent materials used in fuel cells, metal-air batteries, salt electrolysis, etc. are positioned as important technologies in the near future, and are one of the most important technical issues from the viewpoint of energy and environment. It is. The significance of the carbon material carrying platinum having a peculiar form of the present invention and a peculiar gap is extremely great.

2 is an observation view of platinum-supported nanowire particle-supported carbon obtained in Example 1 with a transmission electron microscope. FIG. FIG. 2 is an observation view (enlarged view of FIG. 1) of the platinum-bridged nanowire particle-supported carbon obtained in Example 1 with a transmission electron microscope. 2 is an X-ray diffraction pattern of platinum-bridged nanowire particle-supported carbon obtained in Example 1. FIG.

Claims (9)

  In carbon carrying platinum nanoparticles, the platinum nanoparticles are formed of a single element having an outer diameter of 5 to 100 nm in which a skeleton is formed by platinum element and a cross-linked wire-like skeleton having a diameter of 1 to 5 nm is three-dimensionally crosslinked. A carbon carrying platinum nanoparticles, characterized in that it has a wire-like form made of crystals or connected with microcrystals.   Two types selected from the group consisting of platinum complex compounds and polyoxyethylene alkyl ethers, polyoxyethylene sorbitan esters, polyoxyethylene fatty acid esters, polyoxyethylene alkyl phenyl ethers, polyoxyethylene polyoxypropylene block polymers In the method for producing carbon carrying platinum nanoparticles, a reaction mixture comprising a nonionic surfactant, water, and various carbons is prepared, and then an aqueous reducing agent solution is added to the reaction mixture for reaction. Is prepared under reduced pressure to form a platinum nanoparticle having a wire-like form in which a skeleton is formed of platinum element and a cross-bonded wire-like skeleton is made of a single crystal three-dimensionally cross-linked or a microcrystal is connected White, characterized by generating Carbon manufacturing method of carrying nanoparticles.   The method for producing carbon carrying platinum nanoparticles according to claim 2, wherein the platinum complex compound is hexachloroplatinic acid or a salt thereof.   The method for producing carbon carrying platinum nanoparticles according to claim 2 or 3, wherein the polyoxyethylene alkyl ether is nonaethylene glycol dodecyl ether or nonaethylene glycol monohexadecyl ether.   The method for producing carbon carrying platinum nanoparticles according to any one of claims 2 to 4, wherein the polyoxyethylene sorbitan ester is polyoxyethylene sorbitan monostearate.   The method for producing carbon carrying platinum nanoparticles according to any one of claims 2 to 5, wherein the aqueous reducing agent solution is an aqueous hydrazine solution.   A functional material comprising carbon carrying the platinum nanoparticles according to claim 1.   The functional material according to claim 7, wherein the functional material is a catalyst material.   The functional material according to claim 7, wherein the functional material is an electrode material.

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