JP5251227B2 - Manufacturing method of alloy fine particles, alloy fine particles, catalyst for polymer electrolyte fuel cell containing the alloy fine particles, and metal colloid solution containing the alloy fine particles - Google Patents

Description

  The present invention relates to a method for producing alloy fine particles having a high degree of alloying and a nano-order average particle size. Further, the present invention relates to alloy fine particles produced by the method, a polymer electrolyte fuel cell catalyst containing the alloy fine particles, and a metal colloid solution containing the alloy fine particles.

  A fuel cell is required to exhibit high power generation performance over a long period of time, and is said to be 5000 hours for an automotive power source and 40,000 hours for a stationary power source. Therefore, the electrode catalyst is required to have high catalytic activity and durability. As the electrode catalyst, porous carbon particles carrying a catalyst metal such as a noble metal or base metal are used. For example, as a method for producing an electrode catalyst supported on carbon particles using a plurality of noble metals as catalyst metals, carbon particles are dispersed and mixed in an aqueous solution containing a plurality of noble metal compounds, and a reducing agent or a precipitating agent is added thereto. Thus, an adsorption method or the like in which precious metal particles are formed on carbon particles and then fired is generally used.

  However, in such a method, a plurality of noble metal particles formed by the insolubilizing agent are adsorbed randomly on other noble metal particles and on the surface of the support. For this reason, the composition of the composite noble metal particles formed by alloying by firing becomes non-uniform, and further, there is a problem that a large particle size is formed by sintering due to the addition of thermal energy. . Accordingly, there is a problem that the active surface area of the composite noble metal particles is reduced and the catalytic activity is lowered. Furthermore, when the adsorption method is used, composite noble metal particles are formed and supported in the fine pores of the carbon particles into which the electrolyte does not sufficiently permeate. Since the particles do not act as an active component of the electrode catalyst, there is a problem that the effective utilization rate of the supported composite noble metal particles is lowered.

  On the other hand, noble metals such as platinum and palladium are used as fuel cells and exhaust gas purification catalysts. However, since only a limited amount of noble metal elements exists on the earth, it is required to reduce the amount used as much as possible. Therefore, as a catalyst using a noble metal, for example, a catalyst in which fine particles of noble metal are supported on the surface of carrier particles made of carbon or an inorganic compound is generally used. In addition, since the catalytic action is mainly exerted on the surface of the noble metal, in order to reduce the amount of the noble metal used as much as possible while maintaining good catalytic action in the catalyst having the above structure, it is supported on the surface of the carrier particles. It is effective to make the noble metal fine particles to have a primary particle size as small as possible and a specific surface area as large as possible.

  Further, in recent years, for example, as conductive inks, fine particles of metal, particularly noble metals such as gold and silver, are dispersed in water or a mixed solvent of water and a water-soluble organic solvent. Is being considered. The fine particles of noble metal used in such applications are primary particles that are not as large as those for the above-mentioned catalysts in order to make the structure and conductivity of conductive wiring and conductive film formed using conductive ink uniform. It is required that the diameter is small, the particle size distribution is sharp, and the shape is spherical or granular.

  As a method for producing these fine metal fine particles, there are a high temperature treatment method called an impregnation method, a liquid phase reduction method, a gas phase method, and the like. The method, that is, a method in which metal ions to be deposited are reduced by the action of a reducing agent to deposit metal fine particles in a liquid phase reaction system is becoming widespread. In addition, the metal fine particles produced by the liquid phase reduction method have a spherical or granular shape, a sharp particle size distribution, and a small primary particle size. There is also an advantage of being.

  In order to produce alloy fine particles composed of an alloy of two or more kinds of metals by the above liquid phase reduction method, two or more kinds of metal ions that are the basis of the alloy are mixed in the reaction system. It is conceivable that both ions are reduced by the action of a reducing agent and precipitated as alloy fine particles.

  For example, in Patent Document 1 below, as a method for synthesizing fine particles composed of a monodispersed transition metal having a uniform particle size and a noble metal, Fe or At least one transition metal salt selected from Co or a complex thereof and at least one noble metal salt selected from Pt or Pd or a complex thereof are dissolved and heated under reflux with alcohol in an inert atmosphere. It is disclosed to produce a binary alloy composed of a transition metal and a noble metal by performing.

JP 2003-166040 A

  However, since the conventional method for producing fine alloy particles by the liquid phase reduction method is a synthesis method using a high-temperature reaction in an organic solvent, there are problems in that it is not simple and expensive.

  Then, this invention aims at providing the method of manufacturing the alloy fine particle which has a high alloying degree and an average particle diameter of nano order simply and at low cost.

  The present inventors have found that the above problems can be solved by adjusting the redox potential of each metal ion forming the alloy fine particles to produce the alloy fine particles, and have reached the present invention.

  That is, first, in the present invention, ions of two or more kinds of metals are reduced by the action of a reducing agent in a liquid phase reaction system, and precipitated as alloy fine particles made of an alloy of the two or more kinds of metals. An alloy fine particle manufacturing method according to the present invention is characterized in that the reduction and precipitation reactions are performed by adjusting the difference in reduction potential of the two or more metal ions to 110 mV or less. The difference in reduction potential between the two or more metal ions can be measured using, for example, a three-electrode oxidation / reduction potential measuring device.

  Means for adjusting the difference in reduction potential between two or more metal ions to 110 mV or less include (1) a combination of two or more metal salts or metal complex compounds as starting materials, (2) setting of the reduction temperature, and (3) The setting of the kind and density | concentration of a reducing agent is mentioned concretely. By using one or more of these means, the difference in reduction potential between two or more metal ions can be adjusted to 110 mV or less.

  According to the present invention, alloy fine particles comprising a combination of various elements are produced. For example, the case where two or more kinds of metal ions are Pt ions and Au ions and the alloy is a Pt—Au alloy is preferably exemplified.

  Second, the present invention is an alloy fine particle produced by the above method.

  Third, the present invention is a polymer electrolyte fuel cell catalyst containing alloy fine particles produced by the above method. The alloy fine particles produced in the present invention are widely used for various catalysts. Among them, it is suitably used as a fuel cell catalyst by taking advantage of the characteristics of alloy fine particles having a high degree of alloying and a nano-order average particle size.

  Fourthly, the present invention is a metal colloid solution containing alloy fine particles produced by the above method. Since the alloy fine particles produced in the present invention have a nano-order average particle size, the produced reaction solution is an excellent metal colloid solution. The metal colloid solution is widely used for applications such as conductive ink.

  By adjusting the oxidation-reduction potential of each metal ion forming the alloy fine particles to produce the alloy fine particles, it is possible to easily produce the alloy fine particles having a high degree of alloying and a nano-order average particle size at a low cost. It has become possible. Alloy fine particles having a high degree of alloying and a nano-order average particle diameter can be used in various applications including fuel cell catalysts. In particular, when used as a fuel cell catalyst, it exhibits high power generation performance.

  The liquid phase reaction system of the present invention dissolves a metal salt or complex salt, each of which is a metal compound, which serves as an ion source for two or more metals, and a reducing agent in a solvent common to each component, particularly water. Prepared. Therefore, any of various metal compounds that are soluble in a solvent such as water can be used as the metal salt or complex salt that is a metal compound serving as a metal ion source. However, if possible, the metal compound may be a halogen such as chlorine, which may cause abnormal nucleation as a starting point of nucleation during precipitation of alloy fine particles, or may deteriorate catalyst performance. It is preferable that an element and impurity elements, such as sulfur, phosphorus, and boron, are not included. Thereby, it is possible to produce alloy fine particles having a high degree of alloying, an average particle size of nano-order, a more uniform spherical shape or granular shape, and a sharp particle size distribution.

Various compounds can be used as a metal salt or complex salt which is a metal compound suitable as a metal ion source. For example, in the case of silver, silver nitrate (I) (AgNO ₃ ), silver methanesulfonate (CH ₃ SO ₃ Ag), and the like can be given. In the case of platinum, dinitrodiammine platinum (II) (Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ), hexachloroplatinum (IV) acid hexahydrate (H ₂ (PtCl ₆ ) · 6H ₂ O), etc. Is mentioned. In the case of gold, tetrachloroauric (III) acid tetrahydrate (HAuCl ₄ .4H ₂ O) and the like can be mentioned. In the case of palladium, palladium nitrate (II) nitric acid solution (Pd (NO ₂ ) ₂ / H ₂ O), palladium chloride (II) solution (PdCl ₂ ) and the like can be mentioned. In the case of iridium, hexachloroiridium (III) hexahydrate (2 (IrCl ₆ ) · 6H ₂ O), in the case of rhodium, rhodium (III) chloride solution (RhCl ₃ · 3H ₂ O), in the case of ruthenium Includes a ruthenium (III) nitrate solution (Ru (NO ₃ ) ₃ ). Furthermore, in the case of copper, copper nitrate (II) (Cu (NO ₃ ) ₂ ), copper sulfate (II) pentahydrate (CuSO ₄ .5H ₂ O) and the like can be mentioned.

  As the reducing agent, any of various reducing agents that can be precipitated as alloy fine particles by reducing two or more kinds of metal ions in a liquid phase reaction system can be used. Examples of the reducing agent include sodium borohydride, sodium hypophosphite, hydrazine, and transition metal element ions (trivalent titanium ions, divalent cobalt ions, and the like). However, in order to make the primary particle diameter of the alloy fine particles to be precipitated as small as possible, it is effective to reduce the reduction and precipitation rate of ions of two or more metals, and to reduce the reduction and precipitation rate, It is preferable to select and use a reducing agent having a reducing power as weak as possible.

  Examples of the reducing agent having a weak reducing power used include alcohols such as methanol, ethanol and isopropyl alcohol, ascorbic acid, and the like, as well as ethylene glycol, glutathione, organic acids (citric acid, malic acid, Tartaric acid, etc.), reducing sugars (glucose, galactose, mannose, fructose, sucrose, maltose, raffinose, stachyose, etc.) and sugar alcohols (sorbitol, etc.).

  The concentration of the reducing agent in the liquid phase reaction system is not particularly limited, but in general, the lower the reducing agent concentration, the slower the reduction and precipitation rate of two or more metal ions, and the individual formed Since the primary particle size of the alloy fine particles tends to be reduced, it is preferable to set a suitable concentration range according to the intended primary particle size range. Further, the pH of the liquid phase reaction system is preferably 7 to 13 as described above in consideration of producing alloy fine particles having a primary particle size as small as possible. As described above, as a pH adjuster for adjusting the pH of the reaction system to the above range, impurities such as alkali metals, alkaline earth metals, halogen elements such as chlorine, sulfur, phosphorus, boron, etc. Ammonia and ammonium carboxylate containing no element are preferred.

Hereinafter, examples of the present invention and comparative examples will be shown to describe a method for producing alloy fine particles.
[Example 1]
Hexahydroxo platinum nitric acid containing 4.8 g of platinum was added to pure water to make the total amount 1.0 L. Gold ammonium sulfite containing 0.5 g of gold was added to pure water to make the total amount 1.0 L. 1 g of ammonium citrate was added to each and stirred sufficiently. To this platinum and gold solution, 100 g of a 5 wt% ethanol solution was dropped at a rate of 1 g / min and reduced at 90 ° C. At this time, the potential was measured using a three-electrode type oxidation-reduction potential measuring device, and the difference in potential between the platinum solution and the gold solution was determined. Then, hexahydroxo platinum nitric acid containing 4.8 g of platinum and gold ammonium sulfite containing 0.5 g of gold were added to pure water to make a total amount of 1.0 L. To this, 1 g of ammonium citrate was added and stirred sufficiently. 100 g of a 5 wt% ethanol solution was added dropwise at a rate of 1 g / min and reduced at 90 ° C.

[Example 2]
Hexahydroxo platinum nitric acid containing 4.8 g of platinum was added to pure water to make the total amount 1.0 L. Gold ammonium sulfite containing 0.5 g of gold was added to pure water to make the total amount 1.0 L. 1 g of ammonium citrate was added to each and stirred sufficiently. To this platinum and gold solution, 100 g of a 5 wt% ethanol solution was added dropwise at a rate of 1 g / min and reduced at 60 ° C. At this time, the potential was measured using a three-electrode type oxidation-reduction potential measuring device, and the difference in potential between the platinum solution and the gold solution was determined. Then, hexahydroxo platinum nitric acid containing 4.8 g of platinum and gold ammonium sulfite containing 0.5 g of gold were added to pure water to make a total amount of 1.0 L. To this, 1 g of ammonium citrate was added and stirred sufficiently. 100 g of a 5 wt% ethanol solution was added dropwise at a rate of 1 g / min and reduced at 60 ° C.

[Example 3]
Tetraamminedichloroplatinum containing 4.8 g of platinum was added to pure water to make the total amount 1.0 L. Gold ammonium sulfite containing 0.5 g of gold was added to pure water to make the total amount 1.0 L. 1 g of ammonium citrate was added to each and stirred sufficiently. To this platinum and gold solution, 100 g of a 5 wt% ethanol solution was dropped at a rate of 1 g / min and reduced at 90 ° C. At this time, the potential was measured using a three-electrode type oxidation-reduction potential measuring device, and the difference in potential between the platinum solution and the gold solution was determined. Thereafter, tetraamminedichloroplatinum containing 4.8 g of platinum and gold ammonium sulfite containing 0.5 g of gold were added to pure water to make the total amount 1.0 L. To this, 1 g of ammonium citrate was added and stirred sufficiently. 100 g of a 5 wt% ethanol solution was added dropwise at a rate of 1 g / min and reduced at 90 ° C.

[Example 4]
Tetraamminedichloroplatinum containing 4.8 g of platinum was added to pure water to make the total amount 1.0 L. Gold ammonium sulfite containing 0.5 g of gold was added to pure water to make the total amount 1.0 L. 1 g of ammonium citrate was added to each and stirred sufficiently. To this platinum and gold solution, 100 g of a 5 wt% ethanol solution was added dropwise at a rate of 1 g / min and reduced at 60 ° C. At this time, the potential was measured using a three-electrode type oxidation-reduction potential measuring device, and the difference in potential between the platinum solution and the gold solution was determined. Then, tetraamminedichloroplatinum containing 4.8 g of platinum and gold ammonium sulfite containing 0.5 g of gold were added to pure water to make the total amount 1.0 L. To this, 1 g of ammonium citrate was added and stirred sufficiently. 100 g of a 5 wt% ethanol solution was added dropwise at a rate of 1 g / min and reduced at 60 ° C.

[Example 5]
Chloroplatinic acid containing 4.8 g of platinum was added to pure water to make the total amount 1.0 L. Gold water sodium sulfite containing 0.5 g of gold was added to pure water to make the total amount 1.0 L. 1 g of ammonium citrate was added to each and stirred sufficiently. To this platinum and gold solution, 100 g of a 5 wt% ethanol solution was dropped at a rate of 1 g / min and reduced at 90 ° C. At this time, the potential was measured using a three-electrode type oxidation-reduction potential measuring device, and the difference in potential between the platinum solution and the gold solution was determined. Thereafter, chloroplatinic acid containing 4.8 g of platinum and sodium gold sulfite containing 0.5 g of gold were added to pure water to make the total amount 1.0 L. To this, 1 g of ammonium citrate was added and stirred sufficiently. 100 g of a 5 wt% ethanol solution was added dropwise at a rate of 1 g / min and reduced at 90 ° C.

[Comparative Example 1]
Chloroplatinic acid containing 4.8 g of platinum was added to pure water to make the total amount 1.0 L. Gold ammonium sulfite containing 0.5 g of gold was added to pure water to make the total amount 1.0 L. 1 g of ammonium citrate was added to each and stirred sufficiently. To this platinum and gold solution, 100 g of a 10 wt% ethanol solution was dropped at a rate of 1 g / min and reduced at 60 ° C. At this time, the potential was measured using a three-electrode type oxidation-reduction potential measuring device, and the difference in potential between the platinum solution and the gold solution was determined. Thereafter, chloroplatinic acid containing 4.8 g of platinum and gold ammonium sulfite containing 0.5 g of gold were added to pure water to make the total amount 1.0 L. To this, 1 g of ammonium citrate was added and stirred sufficiently. 100 g of a 10 wt% ethanol solution was added dropwise at a rate of 1 g / min and reduced at 60 ° C.

[Comparative Example 2]
Chloroplatinic acid containing 4.8 g of platinum was added to pure water to make the total amount 1.0 L. Gold ammonium sulfite containing 0.5 g of gold was added to pure water to make the total amount 1.0 L. 1 g of ammonium citrate was added to each and stirred sufficiently. To this platinum and gold solution, 100 g of a 20 wt% ethanol solution was added dropwise at a rate of 2 g / min and reduced at 60 ° C. At this time, the potential was measured using a three-electrode type oxidation-reduction potential measuring device, and the difference in potential between the platinum solution and the gold solution was determined. Thereafter, chloroplatinic acid containing 4.8 g of platinum and gold ammonium sulfite containing 0.5 g of gold were added to pure water to make the total amount 1.0 L. To this, 1 g of ammonium citrate was added and stirred sufficiently. 100 g of a 20 wt% ethanol solution was added dropwise at a rate of 2 g / min and reduced at 60 ° C.

[Comparative Example 3]
Chloroplatinic acid containing 4.8 g of platinum was added to pure water to make the total amount 1.0 L. Chloroauric acid containing 0.5 g of gold was added to pure water to make the total volume 1.0 L. 1 g of ammonium citrate was added to each and stirred sufficiently. To this platinum and gold solution, 100 g of a 5 wt% ethanol solution was dropped at a rate of 1 g / min and reduced at 90 ° C. At this time, the potential was measured using a three-electrode type oxidation-reduction potential measuring device, and the difference in potential between the platinum solution and the gold solution was determined. Thereafter, chloroplatinic acid containing 4.8 g of platinum and chloroauric acid containing 0.5 g of gold were added to pure water to make the total amount 1.0 L. To this, 1 g of ammonium citrate was added and stirred sufficiently. 100 g of a 5 wt% ethanol solution was added dropwise at a rate of 1 g / min and reduced at 90 ° C.

[Comparative Example 4]
Cyanated platinic acid containing 4.8 g of platinum was added to pure water to make the total amount 1.0 L. Chloroauric acid containing 0.5 g of gold was added to pure water to make the total volume 1.0 L. 1 g of ammonium citrate was added to each and stirred sufficiently. To this platinum and gold solution, 100 g of a 5 wt% ethanol solution was dropped at a rate of 1 g / min and reduced at 90 ° C. At this time, the potential was measured using a three-electrode type oxidation-reduction potential measuring device, and the difference in potential between the platinum solution and the gold solution was determined. Thereafter, chloroplatinic acid containing 4.8 g of platinum and cyanogenated gold acid containing 0.5 g of gold were added to pure water to make the total amount 1.0 L. To this, 1 g of ammonium citrate was added and stirred sufficiently. 100 g of a 5 wt% ethanol solution was added dropwise at a rate of 1 g / min and reduced at 90 ° C.

[Comparative Example 5]
A colloidal solution containing 4.8 g of 2 nm platinum and a colloidal solution containing 0.5 g of 2 nm gold were mixed with a dispersion containing 5 g of carbon, and platinum and gold were supported on the carbon. After stirring for 1 hour, the platinum, gold, and carbon mixture was filtered, and the resulting solid was heat treated at 900 ° C.

[Comparative Example 6]
A colloidal solution containing 4.8 g of 2 nm platinum and a colloidal solution containing 0.5 g of 2 nm gold were mixed with a dispersion containing 5 g of carbon, and platinum and gold were supported on the carbon. After stirring for 1 hour, the platinum, gold, and carbon mixture was filtered, and the resulting solid was heat treated at 700 ° C.

[Test method]
For the Pt—Au alloy particles obtained in Examples 1 to 5 and Comparative Examples 1 to 6, a small-angle wide-angle diffractometer (RINT2000) manufactured by Rigaku was used, and “NANO-Solver (ver. 3.1) manufactured by Rigaku was used for analysis. ”Was used to determine the average particle size. The degree of alloying was measured from the XRD measurement results. The Pt lattice constant a was obtained from the diffraction peak of the Pt (111) plane, and the degree of Pt—Au alloying was calculated according to the following equation according to the Vegard law.
Degree of alloying = (Pt lattice constant a−measured value of lattice constant a) × 100 / (Pt lattice constant a−Au lattice constant a)
Here, JCPDS card data was used for Pt and Au lattice constant a.

  Table 1 below shows reduction in reduction potential, degree of alloying, and average particle diameter of the Pt—Au alloy particles obtained in Examples 1 to 5 and Comparative Examples 1 to 6.

  FIG. 1 shows the relationship between the reduction potential reduction and the degree of alloying. FIG. 2 shows the relationship between the reduction potential reduction and the average particle size. Further, FIG. 3 shows the relationship between the degree of alloying and the average particle size.

  In Comparative Examples 1 to 4, since the particles are synthesized in a state where the difference in reduction potential between the alloy types is higher than 110 mv, the noble Au is first reduced to generate Au particles. Au particles are easy to aggregate and the particles become coarse. Thereafter, Pt particles are produced, but Pt-Au alloy is not formed because Pt particles and Au particles are produced separately. That is, as shown in Table 1 and FIG. 1, the degree of alloying decreases when the reduction potential shift is 110 mV or more due to the relationship between the reduction potential deviation and the degree of alloying. As shown in Table 1 and FIG. The average particle size is increased from the relationship between the deviation and the average particle size.

  Comparative Examples 5 and 6 were obtained by alloying separately carrying Pt and Au fine particles by heat treatment at 700 ° C. and 900 ° C., respectively, but the degree of alloying increased by the heat treatment, but the particle diameter increased. Comparative examples 5 and 6 in the relationship between the degree of alloying and the average grain size in FIG. 3 show this.

  On the other hand, in Examples 1 to 5, since the reduction potential difference is close, Pt particles and Au particles are generated at the same time and formed in an alloyed state with fine particles.

  In FIG. 4, the image of alloy fine particle production | generation of Examples 1-5 is shown. In Examples 1 to 5, alloy particles are generated in the alloy preparation process.

  In FIG. 5, the image of the fine particle production | generation of Comparative Examples 1-4 is shown. In Comparative Examples 1 to 4, Au particles are first generated. Au particles are aggregated and coarsened. Thereafter, the Pt particles are also reduced but produced as separate particles. For this reason, the degree of alloying is extremely low.

  FIG. 6 shows an image of fine particle generation in Comparative Examples 5 and 6. In Comparative Examples 5 and 6, the alloy particles are coarsened in the heat treatment step.

  Alloy fine particles having a high degree of alloying and a nano-order average particle diameter obtained by the method for producing alloy fine particles of the present invention can be used for various applications including fuel cell catalysts. In particular, when used as a fuel cell catalyst, it exhibits high power generation performance.

The relationship between the reduction | restoration potential of a reduction potential and an alloying degree is shown. The relationship between the reduction | restoration potential of a reduction potential and an average particle diameter is shown. The relationship between an alloying degree and an average particle diameter is shown. The image of alloy fine particle production | generation of Examples 1-5 is shown. The image of the fine particle production | generation of Comparative Examples 1-4 is shown. The image of the fine particle production | generation of the comparative examples 5 and 6 is shown.

Claims (5)

A method for producing alloy fine particles in which ions of two or more kinds of metals are reduced by the action of a reducing agent in a liquid phase reaction system and precipitated as alloy fine particles comprising an alloy of the two or more kinds of metals,
Adjusting the difference in reduction potential between the two or more metal ions to 110 mV or less, and carrying out the reduction and precipitation reactions;
Performing the reduction by adding a reducing agent to the solution containing the two or more metal ions,
That said reducing agent is at least one selected from ethanol and ammonium citrate, and
The method for producing fine alloy particles, wherein the two or more kinds of metal ions are Pt ions and Au ions, and the alloy is a Pt-Au alloy . In order to adjust the difference in reduction potential between the two or more metal ions to 110 mV or less, (1) a combination of two or more metal salts or metal complex compounds as starting materials, (2) setting of the reduction temperature, and ( 3) The method for producing fine alloy particles according to claim 1 , wherein at least one means selected from setting of the concentration of the reducing agent is used. Alloy fine particles produced by the method according to claim 1 or 2 . A catalyst for a polymer electrolyte fuel cell comprising alloy fine particles produced by the method according to claim 1 or 2 . Metal colloid solution containing alloy fine particles produced by the method according to claim 1 or 2.

Images