JP6472004B2 - Core-shell type metal nanoparticles and method for producing core-shell type metal nanoparticles - Google Patents

Description

  The present invention relates to core-shell type metal nanoparticles and a method for producing the same.

  In recent years, metal nanoparticles with a particle size of 100 nm or less have physical properties different from those of the same kind of bulk metal, or have a very large surface area relative to the volume. There are great expectations for the use of features, and the possibility of use in the industrial field including catalysts is expected, and many improvements have been proposed. In the field of utilization using noble metals such as platinum, attention has been paid to the size of the surface area relative to the volume, and the utilization for catalysts has been promoted.

  In the case of industrial use of noble metal nanoparticles, high performance is expected and at the same time high cost becomes a problem. For example, attempts are being made to invent a substance that substitutes platinum as a substance for a catalyst that uses platinum, and reductions in cost are expected, such as reducing the amount of platinum used.

Patent Document 1 describes platinum supported on silica (silicon oxide) (SiO ₂ ) powder, titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), etc., used for automobile exhaust gas purification catalysts. . Platinum is supported by immersion.

  Patent Document 2 describes platinum nanoparticles supported on titanium oxide nanotubes or titanium oxide fine particles for a positive electrode material of a photoelectric conversion element such as a dye-sensitized solar cell. The platinum nanoparticle is obtained by reducing a platinum fine particle precursor using a reducing agent that is not particularly limited. Platinum is supported using one type of reducing agent.

  The positive electrode of the solid polymer fuel cell is particularly expected to improve the performance of the platinum fine particle catalyst. At the positive electrode, a reaction occurs in which oxygen molecules are reduced to water.

  Although the performance of the platinum fine particle catalyst has been evaluated, since the cost is high, many attempts have been made to reduce the amount of platinum used. As one of the researches, core-shell type PdPt nanoparticles in which palladium (Pd) nanoparticles are used as a core and platinum (Pt) nanoparticles are used as a shell around the core have been studied.

  However, the shape of the Pd nanoparticles as the core of the core-shell type PdPt nanoparticles is often a simple shape, the Pt shell layer is difficult to form uniformly, and a device for enhancing the catalytic performance of the PdPt nanoparticles is sufficiently provided. From the industrial point of view, there are many cases where improvement is necessary, such as increasing its performance and reducing manufacturing costs.

JP 2009-112961 A JP 2012-214373 A

  In view of the above circumstances, one of the problems to be solved by the present invention is that, as a catalyst used for a battery catalyst or the like, fine particles of a material different from platinum are used as base particles, the surface area of the base particles is increased, An object of the present invention is to provide a core-shell type metal nanoparticle and a method for producing the same, which can cover the periphery with nanoparticles having a uniform catalytic effect as much as possible and exhibit a high catalytic effect. As the catalyst nanoparticles as the shell, for example, platinum is particularly desirable, and when platinum is used as the shell, it is preferable to use, for example, palladium as the base, but it is not limited to this. It is also an object of the present invention to increase the catalytic effect by supporting the core-shell nanoparticles on a carrier such as carbon.

  One of the problems to be solved by the present invention is to provide core-shell type nanoparticles having a large catalytic effect at a low cost.

  The first invention of the present invention (hereinafter referred to as invention 1) made to solve the problem includes that the production process of the metal nanoparticles includes an evaporation process as a part of the production process of the produced nanoparticles. It is the manufacturing method of the metal nanoparticle characterized.

  A second invention of the present invention (hereinafter referred to as Invention 2) made by developing Invention 1 is characterized in that, in the method for producing metal nanoparticles according to Invention 1, the metal nanoparticles are core-shell nanoparticles. This is a method for producing metal nanoparticles.

A third invention of the present invention (hereinafter referred to as Invention 3) made by developing Invention 1 or 2 is the method for producing metal nanoparticles according to Invention 1 or 2, wherein the metal nanoparticles are at least Pd and Pt. It is a manufacturing method of the metal nanoparticle characterized by including one side.

  The fourth invention of the present invention (hereinafter referred to as invention 4) made by developing the invention 3 is the method for producing metal nanoparticles according to the invention 3, wherein the metal nanoparticles are PdPt core-shell nanoparticles. It is the manufacturing method of the metal nanoparticle characterized.

  According to a fifth invention of the present invention (hereinafter referred to as invention 5) made by developing the invention 4, in the method for producing metal nanoparticles according to the invention 4, an evaporation step is formed to form Pd core nanoparticles. A method for producing metal nanoparticles, which is a production process before forming Pt shell nanoparticles later.

The sixth invention of the present invention (hereinafter referred to as invention 6), which was developed by developing the invention 4 or 5, is the method for producing metal nanoparticles according to the invention 4 or 5, wherein an evaporation step is added. It is a manufacturing process after forming a shell nanoparticle, It is a manufacturing method of the metal nanoparticle characterized by the above-mentioned.

  A seventh invention of the present invention (hereinafter referred to as invention 7) made by developing inventions 4 to 6 is the method for producing metal nanoparticles according to any one of inventions 4 to 6, wherein Pd nanoparticles are The method for producing metal nanoparticles is characterized in that the carrier is supported after the Pd core nanoparticles are formed.

  The eighth invention (hereinafter referred to as invention 8) of the present invention developed by developing the invention 7 is the method for producing metal nanoparticles according to the invention 7, in which the Pd nanoparticles are supported on the support. It is after manufacturing a nanoparticle, It is a manufacturing method of the metal nanoparticle characterized by the above-mentioned.

  A ninth invention of the present invention (hereinafter referred to as Invention 9) made to solve the problem is a core-shell type metal nanoparticle characterized by containing a multinucleated nanoparticle.

  The tenth invention of the present invention (referred to as invention 10) made by developing the invention 9 is a core-shell type metal nanoparticle according to the invention 9, in which at least one set of the multi-nucleated core-shell type metal nanoparticles are in contact with each other The core-shell type metal nanoparticles are characterized in that an element forming a shell is present between them.

  According to the present invention, a plurality of core particles and / or core-shell particles produced at the nano level are aggregated to exert the catalytic effect of the core-shell nanoparticles. The representative catalyst nanoparticles can be provided at low cost while maintaining the same effect level.

It is a figure which shows the example of the preparation procedure of Pd dispersion liquid. It is a figure explaining the preparation procedure of PdPt nanoparticle. It is a TEM image of PdPt nanoparticles before evaporation. It is a TEM image of PdPt nanoparticle after evaporation. It is a XRD measurement and peak splitting result of PdPt nanoparticles obtained in this experiment.

1: mononuclear PdPt nanoparticles 2: multinucleated PdPt nanoparticles 3: mononuclear nanoparticles constituting polynuclear PdPt nanoparticles 4: platinum peak 5: palladium peak

  Embodiments of the present invention will be described below with reference to the drawings. The drawings used for the description schematically show the dimensions, shapes, arrangement relationships, and the like of each component to the extent that an example of the present invention can be understood. For convenience of explanation of the present invention, there are cases where the enlargement ratio is partially changed for illustration, and the drawings used for explanation of the examples of the present invention may not necessarily be similar to actual objects and descriptions such as embodiments. Moreover, in each figure, about the same component, it attaches and shows the same number, and duplication of description may be avoided.

  The present inventors conducted various experiments for forming platinum (Pt) nanoparticles, which are well-established as catalyst particles, around the core nanoparticles, using palladium (Pd) as the core nanoparticles of the core-shell type nanoparticles. While examining the formation state of the particles using a transmission electron microscope (TEM) or other measuring means, the catalyst performance was also examined.

  As is well known, Pd also has catalytic performance. However, by adopting a core-shell structure of Pd core Pt shell, the catalyst performance is higher than that of Pd alone, and the material cost is lower than that of Pt alone. Focusing on this, various attempts were made to improve the catalyst performance in the core-shell structure.

  Various experiments for controlling the shape of the Pd nanoparticle as the core nanoparticle and the particle shape of the Pd-core Pt shell nanoparticle having the core-shell structure (hereinafter referred to as PdPt nanoparticle) are not normally used for such purposes. I also tried the method.

  Evaporation was performed on Pd nanoparticles and PdPt nanoparticles formed using the reduction reaction of metal salts and measured with a TEM. Multi-nuclearization of nanoparticles, which was not so noticeable before evaporation, caused evaporation. I found that it progressed by doing. When the catalytic action was measured, an improvement was seen compared to before the evaporation.

  For example, when used as a catalyst for a battery, there is a method of supporting it on a conductive carrier. A case where carbon is used as an example of the carrier will be described.

  There are various examples of how to perform evaporation. As a first example, a Pd nanoparticle as a core nanoparticle is prepared using a reaction action of a metal salt, and a Pt nanoparticle as a shell nanoparticle is formed around the Pd nanoparticle using a reaction action of the metal salt. There is a method of forming a substrate, evaporating it, and supporting it on carbon as a carrier.

  As a second example, Pd nanoparticles as core nanoparticles are produced using the reaction of metal salts, evaporated, and Pt nanoparticles as shell nanoparticles using the reaction of metal salts. Is formed around Pd nanoparticles and supported on carbon as a support.

  As a third example, Pd nanoparticles as core nanoparticles are produced using the reaction of metal salts, evaporated, and Pt nanoparticles as shell nanoparticles using the reaction of metal salts. Is formed around Pd nanoparticles, evaporated again, and supported on carbon as a support.

  As a fourth example, a Pd nanoparticle as a core nanoparticle is produced by utilizing the reaction action of a metal salt, evaporated on it, supported on carbon as a carrier, and the reaction action of the metal salt is There is a method of forming Pt nanoparticles as shell nanoparticles by using.

  When the catalytic effect was compared between these methods and the conventional method that does not perform evaporation, it was concluded that the respective methods that had evaporated at some stage had higher catalytic effects. .

An example will be described below with reference to the drawings.

(Preparation of palladium nanocolloid)
18 ml of ion-exchanged water and 12 ml of ethanol are weighed in a 30 ml screw tube, 0.228 g of PVP is added and dissolved therein, 0.028 g of palladium chloride PdCl ₂ is added, and dispersed with ultrasonic waves (frequency 38 kHz, 50 W), 80 ° C. For 3 hours to obtain 30 ml of palladium nanocolloid. The palladium concentration is 5.3 mM, PVPPd = 8: 1 (g / g). This process is shown in FIG.

(Preparation of chloroplatinic acid solution)
The ion-exchanged water 16ml was added to 36% hydrochloric acid 1.69 ml, 4% hydrochloric acid to prepare 17.69Ml, its inner 10.0 ml, dissolved chloroplatinic acid _{(H 2 PtCl 6 · 6H 2} O) 0.1g A chloroplatinic acid solution was prepared. The platinum concentration is 19.3 mM.

(Production of mononuclear and polynuclear mixed particles of palladium core platinum shell)
To 10 ml of the palladium nanocolloid prepared above, 0.84 ml of a 19.3 mM chloroplatinic acid solution and 9.14 ml of ion-exchanged water were added and stirred at 5 ° C. for 1 hour. To this solution, hydrazine monohydrate (NH ₂ NH ₂ .H ₂ O) as a reducing agent was added and reacted at a reaction temperature of 5 ° C. for 24 hours. The term “mononuclear” as used in the present invention does not mean a single crystal, but in the process of forming core-shell nanoparticles, the cores are grouped together and a shell is formed around them to form a group of core-shell nanocrystals. In the sense that it is formed into particles, “multinuclear” means that a set of core-shell nanoparticles is formed after each set of core-shell nanoparticles is formed. is there.

  FIG. 3 shows a TEM photograph before evaporation. PdPt nanoparticles surrounded by a dotted line denoted by reference numeral 1 are mononuclear nanoparticles, and PdPt nanoparticles surrounded by a solid line denoted by reference numeral 2 are examples of multinuclear nanoparticles. As can be seen from FIG. 3, it was confirmed that there were many mononuclear PdPt nanoparticles.

  After completion of the reaction, the solvent was removed by evaporation, the solvent was stopped immediately before drying, 20 ml of ethanol was added, and the mixture was centrifuged for 30 minutes at 24,000 rpm, and the resulting supernatant was removed. 20 ml of ethanol was added thereto and subjected to ultrasonic dispersion (42 kHz, 100 W), and then the solvent was distilled off by the second evaporation, and ethanol addition, ultrasonic dispersion and centrifugation were repeated. The evaporation conditions were a temperature setting of 40 ° C. and a degree of vacuum of 0.8 kPa. After removing the supernatant obtained by centrifugation, 20 ml of ethanol was added. Ultrasound was irradiated, dispersed, and centrifuged at 24,000 rpm for 30 minutes, and the resulting supernatant was removed to obtain a mixture of palladium core platinum shell mononuclear and polynuclear particles. An example of the procedure for producing PdPt nanoparticles is shown in FIG.

  FIG. 4 shows a TEM photograph after evaporation. Many mononuclear particles were confirmed along with mononuclear particles, and an increase in particle diameter was also confirmed. In the state where platinum nanoclusters are generated by the reducing agent hydrazine, evaporation under reduced pressure allows the mononuclear palladium core platinum shell particles to gather together with van der Waals forces, It is thought to become multinucleated. Many nuclei are aggregated from 2 to 6 mononuclear nanoparticles.

  As can be seen from FIG. 4, it can be seen that the number of multinucleated PdPt nanoparticles is larger in the area of the screen of the TEM image than the mononuclear PdPt nanoparticles. By supporting this on the carbon of the carrier, the surface area of the PdPt nanoparticles protruding from the surface of the carrier becomes larger than in the case of mononuclear PdPt nanoparticles, and a catalytic effect such as a battery solution of Pt nanoparticles is exhibited. The surface area in contact with the liquid to be increased. As an example of the loading method, for example, if the component part 3 of the multinucleated PdPt nanoparticles (mononuclear PdPt nanoparticles before composition) is loaded, the surface area of the Pt nanoparticles in contact with the liquid of the battery increases. It is expected.

  FIG. 5 shows the results of XRD measurement and peak splitting of the PdPt nanoparticles obtained in this experiment. The function used for curve fitting is a Gaussian function. In the figure on the left side of FIG. 5, the black circle indicates Pd and the white circle indicates Pt. In the diagram on the right side of FIG. 5, reference numerals 4 and 5 indicate XRD patterns obtained by fitting Pt and Pd, respectively. Diffraction peaks are seen around 40, 46 and 68 °. These peaks are considered to be the (111), (200) and (220) faces of the cubic metal Pt (ICSD card No. 01-071-3757), but the lattice constants of Pt and Pd are very close. The attribution could not be determined. Therefore, Gaussian function analysis was performed. According to the Gaussian function analysis around 40 °, it was divided into 39.8 ° and 40.1 ° peaks. These are due to metal Pt and metal Pd, respectively. Therefore, formation of metal Pt and metal Pd was confirmed.

  On the other hand, there is also a possibility of producing a Pt—Pd alloy. According to the Scherrer equation, the crystallite diameters of metal Pd and metal Pt were 3.8 and 5.0 nm, respectively. Since this value almost coincided with the particle diameter (3.8 and 4.8 nm) obtained from the TEM image, the particle obtained in this experiment was regarded as a single crystal. From the above, formation of metal Pt and metal Pd, or Pt—Pd alloy was confirmed in this experiment.

(Palladium core platinum shell mononuclear and polynuclear mixed particles supported on carbon)
To a mixed solvent of 0.1% Vulcan XC-72 (carbon) / H ₂ O: isopropanol (volume ratio 19: 6), 5 mg of mixed particles of mononuclear and polynuclear palladium core platinum shell were added. After ultrasonic irradiation, the mixture was allowed to stand for 20 minutes and supported on carbon. next. The supernatant was removed by centrifugation, and suspended in 0.01% Nafion / H2O, after centrifugation again, H ₂ O: was dispersed in IPA mixed solvent to obtain a catalyst ink for electrochemical measurements.

The obtained catalyst ink had high oxidation-reduction catalytic activity.
(Comparative Example 1)

Palladium core platinum shell particles were produced in the same process as in Example 1 except that the evaporation operation was not performed. Multinuclear particles could not be made.
(Comparative Example 2)

  Instead of evaporation, palladium core platinum shell particles were produced in the same process as Example 1 except that the mixture was stirred for 2 hours while being heated to 40 ° C. However, multinuclear particles were not formed.

  After producing the palladium nanocolloid of Example 1, the evaporation operation was repeated twice, and a platinum shell was attached in the same manner as in Example 1. Mixed particles with many nuclei were produced together with the single core of the palladium core platinum shell. The particles were supported on carbon and subjected to electrochemical measurement.

  Although it synthesize | combined like Example 2, it did not evaporate after attaching a platinum shell. Mononuclear and polynuclear mixed particles of palladium core platinum shell were synthesized. The obtained particles were supported on carbon in the same manner as in Example 1 and subjected to electrochemical measurement.

  After producing the palladium nanocolloid of Example 1, the evaporation operation was repeated twice, and the obtained palladium particles were supported on carbon, and then a platinum shell was formed. Mononuclear and polynuclear mixed particles of palladium core platinum shell were synthesized. The obtained particles were supported on carbon in the same manner as in Examples, and electrochemical measurements were performed.

  The method of putting an evaporation process in the manufacturing process of core-shell type nanoparticles is not limited to this. The evaporation process as described above was introduced into the manufacturing processes described in the second example, the third example, and the fourth example, respectively. Each confirmed the effect of multinucleation.

  As mentioned above, although embodiment of this invention was described using drawing, this invention is not limited narrowly to this, Many variations are possible.

  INDUSTRIAL APPLICABILITY The present invention provides a catalyst at a low cost to industrial fields that require a catalytic effect such as batteries, and greatly contributes to the development of the industry.

Claims (3)

In the production process of core-shell type metal nanoparticles of palladium (Pd) core / platinum (Pt) shell, after synthesizing Pd particles, the synthetic solution is evaporated, and then the solution is added and ultrasonic dispersion is performed at least once. A core-shell type metal nanoparticle production method, comprising: forming a core shell on a carrier, and forming a platinum shell on the core particle carried on the carrier. In the production process of the core-shell type metal nanoparticles of palladium (Pd) core / platinum (Pt) shell, after synthesizing Pd particles, a Pt shell is formed around the Pd core, and then the synthetic solution is evaporated. A method for producing core-shell type metal nanoparticles, wherein a core-shell particle formed by adding a solution to the core-shell particle and performing ultrasonic dispersion at least once is supported on a carrier. It has at least one set of multinucleated palladium (Pd) core particles, a carrier supporting the Pd core particles, and a platinum (Pt) shell formed around the Pd core particles supported on the carrier. Core-shell type metal nanoparticles.