JP2009155122A - Method for manufacturing ruthenium oxide fine powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing high-quality ruthenium oxide fine powder without producing harmful octavalent ruthenium oxide (RuO<SB>4</SB>) and without leaving sodium which causes problems in characteristics of electrodes. <P>SOLUTION: After a ruthenium-nickel alloy having a ruthenium content of 10 to 50 mass% is subjected to heat treatment in vacuum or an inert atmosphere at 600 to 1,400°C for 1 to 10 hours and formed into a foil, nickel in the alloy is electrolyzed to collect fine particles of ruthenium oxide settling in the solution. The conditions of the electrolysis are preferably conditions in which temperature is 50 to 60°C, current density is 1 to 100 mA/cm<SP>2</SP>on the anode and an oxidation-reduction potential is 600 to 1,200 mV on the anode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a ruthenium oxide fine powder, and more particularly to a method for producing a ruthenium oxide fine powder suitable for an electrochemical capacitor electrode.

  Conventionally, typical electrochemical elements having a power storage function include secondary batteries, capacitors, and the like, and these have been put into practical use in applied devices that make use of their respective characteristics. All recently developed power storage devices utilize the electrochemical principle, and secondary batteries and electrochemical capacitors are typical.

  Secondary batteries are excellent in terms of the amount of energy (energy density) that can be stored per unit mass or unit volume, but are still large in terms of the usage period, charging time, and amount of energy that can be used per unit time (output density). There is a point that should be improved. On the other hand, the electrochemical capacitor has a lower energy density than the secondary battery, but exhibits characteristics superior to those of the secondary battery in terms of use time, charging time, and output density.

  There are two types of electrochemical capacitors. That is, an electric double layer capacitor that uses an electric double layer generated at the electrode / electrolyte interface for power storage, and a redox capacitor that uses a redox reaction (pseudo electric double layer capacitance) on the surface of a metal oxide or a conductive polymer. is there. In order to increase the volume energy density, a redox capacitor using a metal oxide is advantageous.

  Until now, as a metal oxide that has been developed as an electrode material for the redox capacitor, ruthenium oxide is known to exhibit excellent electrochemical characteristics. Here, “ruthenium oxide” includes ruthenium oxide and ruthenium oxide hydrate, as well as ruthenium oxide and ruthenium hydroxide that can be decomposed into water, and is widely used in the technical field as a generic term for these. .

  In general, ruthenium oxide having a size of several tens of nm suitable for a redox capacitor is produced by a thermal decomposition method or a sol-gel method using ruthenium chloride as a precursor. These methods are described in, for example, Japanese Patent Laid-Open No. 2-088432, B.E. Conway, Naoi, Nishino, Morimoto, “Electrochemical Capacitor”, Chapter 11, NTS, 2001, and J. Org. Electric Chem. Soc., Vol. 142, No. 8 and the like.

However, in the case of the above-described pyrolysis method, a toxic gas of octavalent ruthenium oxide (RuO ₄ ) that stimulates the mucous membrane is generated by heating in the atmosphere, so that the generated gas does not leak to the surroundings. Extra equipment with safety measures is required.

In the case of the above sol-gel method, there is almost no risk of the generation of toxic RuO ₄ , but a neutralization reaction is caused by adding an alkali metal hydroxide such as sodium hydroxide to ruthenium chloride. Sodium formation is inevitable. Since sodium chloride is difficult to remove completely even after repeated filtration and washing of ruthenium oxide fine powder, it remains several mass% as an impurity when used in an electrochemical capacitor electrode, adversely affecting its electrical properties and corrosion resistance. .

Japanese Patent Laid-Open No. 2-088432 B.E. Conway, Naoi, Nishino, Morimoto, "Electrochemical Capacitor", Chapter 11, NTS, 2001 J. et al. Electric Chem. Soc. , Vol.142, No8

The present invention has been made in view of the above-mentioned problems of the prior art, does not generate harmful and irritating octavalent ruthenium oxide (RuO ₄ ), and has an adverse effect on the characteristics of the electrode. It is an object of the present invention to provide a method for producing a high-quality ruthenium oxide fine powder that is excellent in safety and is simple and free from residual sodium.

  In order to achieve the above object, the method for producing fine ruthenium oxide powder provided by the present invention comprises electrolyzing nickel in an alloy of ruthenium and nickel, and collecting fine particles of ruthenium oxide that settle in the solution. Features.

In the present invention, “ruthenium oxide” refers to a tetravalent oxide of ruthenium oxide (RuO ₂ ), ruthenium oxide hydrate (RuO ₂ .nH ₂ O), and ruthenium hydroxide (Ru (OH)). ₄ ) means at least one selected from the above.

  In the manufacturing method of the ruthenium oxide fine powder according to the present invention, the ruthenium content in the ruthenium-nickel alloy is preferably 10 to 50% by mass. Moreover, it is preferable to heat-treat the ruthenium and nickel alloy at a temperature of 600 to 1400 ° C. for 1 to 10 hours in a vacuum or in an inert atmosphere before the electrolysis.

In the method for producing a ruthenium oxide fine powder according to the present invention, the electrolysis is performed under conditions of a temperature of 50 to 60 ° C., an anode current density of 1 to 100 mA / cm ² , and an anode oxidation-reduction potential of 600 to 1200 mV. It is preferable.

  Furthermore, in the method for producing a ruthenium oxide fine powder according to the present invention, it is preferable that the ruthenium oxide fine powder recovered from the solution after the electrolysis is further pulverized and dispersed.

According to the present invention, since no toxic RuO ₄ is generated, the safety of the process is high, and there is no residual sodium that adversely affects the characteristics of the electrode. A powder can be obtained.

  The ruthenium oxide fine powder obtained by the present invention can be suitably used for the production of an electrochemical capacitor electrode used for a hybrid power source in combination with a small memory backup power source or a solar cell.

  In the present invention, an alloy composed of ruthenium and nickel is preferably formed into a foil shape, and preferably after heat treatment under specific conditions, nickel is electrolyzed, and at the same time, fine particles that precipitate ruthenium oxide fine particles in the liquid are formed. By collecting, ruthenium oxide fine powder is obtained.

(1) Manufacture of an alloy of nickel and ruthenium An alloy of nickel and ruthenium as a starting material is generally manufactured by melting nickel and ruthenium by a method such as arc melting, plasma melting, or electron beam melting. it can. It can also be produced by melting by a high vacuum electron beam zone melting method.

  Here, nickel powder may be used as the raw material nickel, but normal electric nickel can be used. Moreover, as ruthenium used as a raw material, a commercially available ruthenium metal can be used, but it is also possible to use a used ruthenium sputtering target or chips generated during ruthenium machining. Since ruthenium is a very expensive rare metal, it is extremely advantageous to be able to effectively use the ruthenium scrap as described above.

  The ruthenium content in the nickel-ruthenium alloy is preferably 10 to 50% by mass, and more preferably 20 to 40% by mass. If the ruthenium content is less than 10% by mass, the strength of the porous layer structure made of the alloy ruthenium fine powder or the like cannot be maintained sufficiently, so that it falls off during the subsequent electrolysis process, and the yield decreases. It is not preferable. Further, if the ruthenium content is more than 50% by mass, a coarse ruthenium phase is formed in the solidified structure by any heat treatment, and coarse particles remain in the ruthenium oxide fine powder obtained after electrolysis. Therefore, a high capacity cannot be obtained when an electrochemical capacitor electrode is used.

(2) Heat treatment and alloy foil formation of nickel-ruthenium alloy Depending on the melting method at the time of alloy production, if the ruthenium concentration in the nickel-ruthenium alloy is high, solidification segregation is likely to occur, resulting in non-uniform ruthenium concentration. Cheap. If the concentration of ruthenium is nonuniform, the size of the ruthenium oxide fine particles generated when nickel is electrolyzed is not uniform, and coarse ruthenium oxide particles are likely to be generated.

  For this reason, in order to homogenize and control the structure of the nickel-ruthenium alloy, it is desirable to heat-treat the alloy before electrolyzing the nickel. The heat treatment is preferably performed at a temperature of 600 to 1400 ° C. for about 1 to 10 hours in a vacuum or in an inert atmosphere. By heat-treating under the above conditions, the average primary particle diameter of the ruthenium oxide fine particles obtained during electrolysis can be reduced to about several tens of nanometers. Since the homogenization does not sufficiently proceed at a temperature of 600 ° C. or lower, the size of the obtained ruthenium fine particles is not uniform, and a temperature exceeding 1400 ° C. is not preferable because a melt may be generated.

  In order to obtain a shape suitable for electrolysis, for example, after the heat treatment, it is preferable to roll a nickel-ruthenium alloy into a foil. There is no problem even if it is cut out to an appropriate size. A homogeneous solid solution alloy has good plastic workability and can be made into a foil by cold rolling or the like. At this time, since the material is cured by cold working, annealing may be performed at 600 to 1300 ° C. in order to improve workability as necessary. Also, processing such as hot rolling can be performed.

(3) Nickel electrolysis from a nickel-ruthenium alloy By electrolyzing only nickel from a nickel-ruthenium alloy, at least one selected from ruthenium oxide fine particles, that is, ruthenium oxide, ruthenium oxide hydrate, and ruthenium hydroxide. Obtainable. That is, when electrolysis is performed using a nickel-ruthenium alloy as an anode, nickel is electrodeposited on the cathode, and ruthenium oxide fine particles settle in the electrolyte.

  As the electrolytic solution, an electrolytic solution used for usual electrolytic purification of nickel may be used. For example, a mixed solution of nickel sulfate and boric acid can be preferably used. The concentration of nickel in the electrolytic solution is preferably 40 to 50 g / l, and the concentration of boric acid is preferably 10 to 20 g / l. Moreover, a planar metal can be used as a cathode, and foils and plates, such as aluminum, nickel, and stainless steel, can be used.

  The temperature of the electrolytic solution is preferably 50 to 60 ° C. At a temperature lower than 50 ° C., nickel sulfate and boric acid, which are solutes of the electrolytic solution, are difficult to dissolve in water. On the other hand, when the temperature is higher than 60 ° C., water evaporates from the electrolytic solution, and it is necessary to replenish water frequently.

The current density of the anode is preferably 1 to 100 mA / cm ² . When the current density is less than 1 mA / cm ² , the amount of ruthenium oxide fine particles generated per unit time is reduced, so that the electrolysis time becomes long and is not practical. On the other hand, when it is larger than 100 mA / cm ² , the current efficiency is lowered and the cost is increased, which is not preferable.

  The oxidation-reduction potential of the anode during electrolysis is preferably 600 to 1200 mV (Ag / AgCl electrode is used as the reference electrode). When the oxidation-reduction potential is less than 600 mV, metal ruthenium is deposited, and the capacity is reduced when an electrochemical capacitor is formed. On the other hand, an oxidation-reduction potential greater than 1200 mV is not preferable because a toxic octavalent ruthenium oxide is generated.

  By electrolysis under the above-described electrolysis conditions, electrolysis of nickel from a nickel-ruthenium alloy can be performed in an electrolysis time of about 30 to 240 minutes. However, as the electrolysis time becomes longer, the ruthenium oxide fine particles that settle in the liquid are more likely to reaggregate and may not be used as a high-capacity capacitor electrode.

  During the electrolysis, fine particles of ruthenium oxide are formed on the surface of the nickel-ruthenium alloy, but the primary particle size may vary depending on the dispersion state of ruthenium and nickel in the alloy. When ruthenium is uniformly dispersed in the alloy, the average particle diameter of primary particles of ruthenium oxide fine particles obtained by electrolysis is reduced to about 40 nm. In addition, when solidification segregation of ruthenium occurs in the alloy, the average particle diameter of primary particles of ruthenium oxide fine particles obtained by electrolysis may be coarsened to about 100 nm at the maximum. The average primary particle diameter of the ruthenium oxide fine particles obtained by electrolysis is preferably 75 nm or less from the viewpoint of increasing the capacity per unit weight when formed into an electrochemical capacitor electrode.

(4) Recovery, pulverization and dispersion of fine ruthenium oxide powder The ruthenium oxide fine particles settle in the electrolytic solution by electrolysis of the nickel-ruthenium alloy. By separating the fine particle slurry from the solution by a method such as decantation, suction filtration or ultrafiltration, the ruthenium oxide fine powder can be recovered.

  The recovered ruthenium oxide fine powder can be used as an electrochemical capacitor electrode material in this state. Even if the recovered ruthenium oxide fine powder is used as it is, a high capacity can be obtained. However, in order to further increase the capacity, the fine powder is pulverized and dispersed by various mills to make the primary particles finer. It is preferable to disperse the agglomerated secondary particles to the primary particles. For the pulverization / dispersion of the powder, various pulverization methods such as a ball mill, an attritor and a sand mill can be used in addition to the bead mill.

[Example 1]
Electro-nickel 260.5g and ruthenium lump 64.9g cut out from the used sputtering target were melted by hydrogen plasma melting to form a button-like nickel-ruthenium alloy ingot having a diameter of about 75mm and a thickness of about 10mm. Produced.

  This nickel-ruthenium alloy ingot is cut into a size of 25 mm × 25 mm × 5 mm by wire cutting (made by Hitachi Via Mechanics Co., Ltd., 254Y), and is heated at 1300 ° C. in a vacuum with a high-temperature high vacuum furnace (made by Nemus Co., Ltd.). Heat treated for 6 hours. Thereafter, a nickel-ruthenium alloy foil having a thickness of 210 μm was formed by a rolling mill (manufactured by Ohno Roll Co., Ltd., 6-inch 2 / 4-stage DR rolling mill).

This nickel-ruthenium alloy foil was cut out to have an electrode area of 1.0 cm ² and used as an anode. In addition, an aluminum foil having a thickness of 30 μm was cut out so as to have an electrode area of 1.0 cm ² to form a cathode. A mixed solution of nickel sulfate and boric acid was used as the electrolytic solution, the nickel concentration in the electrolytic solution was 45 g / l, and the H ₃ BO ₃ concentration was 15 g / l.

The anode and the cathode were immersed in an electrolytic solution so as to face each other, and electrolysis was performed for 1 hour under conditions of an electrolytic solution temperature of 55 ° C., an anode current density of 50 mA / cm ² , and an anode oxidation-reduction potential of 750 mV. The ruthenium oxide fine powder precipitated by decantation was recovered from the solution after electrolysis and washed with nitric acid.

  The obtained ruthenium oxide fine powder was taken on a SEM photograph, two diagonal lines were drawn in the photograph, and the dimensions of all the ruthenium oxide primary particles in contact with the diagonal line were measured. ) Was 71 nm. The residual amount of sodium (Na) in the ruthenium oxide fine powder was quantified by ICP emission analysis, and was less than 0.1% by mass.

The recovered ruthenium oxide fine powder was applied to carbon paper (electrode area: 1 cm ² ) to produce a working electrode of an electrochemical capacitor. The counter electrode was a platinum plate, and an Ag / AgCl electrode (HS-201C, manufactured by Toa DK Corporation) filled with a saturated potassium chloride solution was used as the reference electrode. Cyclic voltammetry was measured using a potentiostat (Hokuto Denko, HA-501G) and a function generator (Hokuto Denko, HB-105).

The energized electricity amount when the potential is changed from V1 to V2 can be obtained by applying a piecewise quadrature method to the cyclic voltammogram. On the other hand, when it is assumed that the capacitance C is constant with respect to the potential V, the energization amount of electricity can be expressed by C × (V1−V2). From these, the capacity C of the working electrode produced from the ruthenium oxide fine powder of Example 1 was calculated and found to be 720 F / g. The electrode area of the working electrode was 1.0 cm ² , the electrolyte was a 0.5 mol / l sulfuric acid aqueous solution, and the scanning speed was 2 mV / s.

[Example 2]
The ruthenium oxide fine powder obtained in Example 1 was mixed with pure water so that the concentration of the powder was 10% by mass, and 0.03 mm beads were used with a bead mill (manufactured by Ashizawa Finetech, Minizea). For 60 minutes. When the dimensions of the primary particles of the obtained ruthenium oxide fine powder were measured in the same manner as in Example 1, the average value (SEM diameter) was 60 nm. The residual amount of sodium (Na) in this ruthenium oxide fine powder was less than 0.1% by mass as determined by ICP emission analysis.

  The obtained slurry of ruthenium oxide fine powder was applied to carbon paper and dried in the atmosphere at 60 ° C. for 30 minutes to produce a working electrode coated with the ruthenium oxide fine powder. The capacity C of this working electrode was measured in the same manner as in Example 1 and was 795 F / g.

[Comparative Example 1]
A ruthenium oxide hydrate fine powder was prepared by a conventional sol-gel method. That is, ruthenium (III) chloride hydrate was dissolved in distilled water to obtain a precursor solution. A sodium hydroxide aqueous solution was slowly added to the precursor solution to maintain the pH of the solution at about 7, and a black powder was precipitated in the solution.

  The precipitated powder was filtered through a filter having an aperture of about 8 μm and washed. The washing operation was repeated 5 times by pouring an appropriate amount of distilled water into a container containing the powder, stirring for about 30 minutes, and filtering. The powder obtained after the washing was heat-treated at 60 ° C. for 8 hours in a vacuum to obtain a ruthenium oxide fine powder.

  About this ruthenium fine powder, the average value (SEM diameter) of the primary particles measured in the same manner as in Example 1 was 107 nm. The residual amount of sodium (Na) in the ruthenium oxide fine powder was 2.0% by mass as determined by ICP emission analysis.

  A working electrode was prepared in the same manner as in Example 1 using the ruthenium oxide fine powder of Comparative Example 1, and the capacity C was determined in the same manner as in Example 1. The result was 705 F / g. . The results of Examples 1-2 and Comparative Example 1 are summarized in Table 1 below.

As can be seen from this result, by using the method of the present invention, sodium as an impurity could be remarkably reduced as compared with the conventional sol-gel method. In addition, since the method of the present invention does not require heat treatment in the atmosphere, generation of toxic RuO ₄ could be prevented.

  In addition, the working electrode using the ruthenium oxide fine powder of the present invention has an example when compared with the ruthenium oxide hydrate of Comparative Example 1 by the sol-gel method which has been conventionally considered to have a high capacity. 1, it was found that almost the same capacitance was obtained and it was effective as a capacitor electrode. Further, in Example 2, which was further pulverized and dispersed by a bead mill, the capacity of the working electrode was 795 F / g, which was higher than that of the comparative example.

Claims (5)

  A method for producing a fine powder of ruthenium oxide comprising at least one of ruthenium oxide, ruthenium oxide hydrate and ruthenium hydroxide, and electrolyzing nickel in an alloy of ruthenium and nickel, and ruthenium oxide precipitated in a solution A method for producing fine ruthenium oxide powder, comprising collecting fine particles of a product.   2. The method for producing fine ruthenium oxide powder according to claim 1, wherein the ruthenium content in the alloy of ruthenium and nickel is 10 to 50 mass%.   The ruthenium oxide according to claim 1 or 2, wherein the ruthenium and nickel alloy is heat-treated at a temperature of 600 to 1400 ° C for 1 to 10 hours in a vacuum or in an inert atmosphere before the electrolysis. A method for producing fine powder. The electrolysis is performed under conditions of a temperature of 50 to 60 ° C, an anode current density of 1 to 100 mA / cm ² , and an anode oxidation-reduction potential of 600 to 1200 mV. Method for producing ruthenium oxide fine powder.   The method for producing a ruthenium oxide fine powder according to any one of claims 1 to 4, wherein the ruthenium oxide fine powder recovered from the solution after the electrolysis is further pulverized and dispersed.