Composite particles and methods for producing the same

Abstract

To provide a composite particle having excellent catalytic performance and durability while reducing costs.SOLUTION: A composite particle includes a first metal oxide particle and a second metal oxide particle. A particle diameter of the first metal oxide particle is smaller than a particle diameter of the second metal oxide particle. A plurality of first metal oxide particles cover at least a part of a surface of the second metal oxide particle so as to form a corona shape, and the first metal oxide particles are epitaxially grown on the surface of the second metal oxide particle.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to composite particles and a method for producing the same. [Background technology]

[0002] Electrolysis of water (also known as "water electrolysis") is a well-known technology that uses electrical energy to break down water and produce hydrogen.

[0003] For example, as disclosed in Non-Patent Document 1, typical water electrolysis methods include alkaline water electrolysis and solid polymer water electrolysis. In both methods, two catalysts are required: one for generating hydrogen and another for generating oxygen. In particular, the energy loss (overpotential) involved in the oxygen generation reaction (oxygen evolution reaction) is relatively large, and therefore, it is necessary to keep energy loss low.

[0004] Furthermore, because the electrodes in the oxygen evolution reaction are subjected to extremely harsh electrochemical conditions, the electrode catalyst also requires durability.

[0005] In solid polymer electrolyte water electrolysis systems, iridium oxide is known as a promising material as an electrode catalyst due to its durability and catalytic activity. However, iridium is scarce, which presents a challenge in terms of increasing the cost of water electrolysis.

[0006] On the other hand, in the alkaline water electrolysis method, electrode catalysts that are relatively inexpensive compared to iridium can be used as catalysts. In this regard, numerous electrode catalysts that can be used in alkaline water electrolysis reactions have been reported.

[0007] For example, Patent Document 1 discloses an oxygen evolution and oxygen reduction catalyst characterized by having a pyrochlore-type metal oxide as its main component, which contains aluminum, bismuth, ruthenium, and oxygen, and exhibits an oxygen ratio of 6.5 to 7.3 in TPR measurements.

[0008] Furthermore, Patent Document 2 discloses an air electrode for an air secondary battery that includes an air electrode mixture containing a mixed powder having catalytic function. In this case, the mixed powder having catalytic function in Patent Document 2 is an aggregate of mixed particles in which catalyst particles smaller than the core particles are combined with core particles, the core particles contain Ni, and the catalyst particles are formed from a pyrochlore-type metal oxide catalyst and are present on the surface of the core particles.

[0009] Furthermore, Patent Document 3 discloses a catalyst in which a catalyst made of a metal or metal oxide is formed on the surface of compound particles via epitaxial bonding. More specifically, the catalyst of Patent Document 3 is characterized in that it has compound particles (1) having a metastable surface (1a) which is a surface having a metastable plane orientation, and a catalyst (2) made of a metal or metal oxide is formed on the metastable surface (1a) of the compound particle (1) in a state that inherits the atomic arrangement state of the metastable plane orientation.

[0010] Furthermore, Patent Document 4 discloses fine particles on which a catalytic substance is uniformly supported on the surface. More specifically, the fine particles of Patent Document 4 are fine particles on which ultrafine particles or a thin film with a particle size smaller than the fine particles are coated on the surface by performing sputtering while stirring or rotating the fine particles inside a vacuum container having a polygonal cross-sectional shape, with the rotation axis being substantially perpendicular to the cross-section, and the ultrafine particles or the thin film consisting of at least one of a metal catalyst, an oxide catalyst, and a composite catalyst. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2019-195775 [Patent Document 2] Japanese Patent Publication No. 2021-077563 [Patent Document 3] Japanese Patent Publication No. 2007-105652 [Patent Document 4] Japanese Patent Application Laid-Open No. 2005-264297

Non-Patent Document

[0012]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0013] The present inventors have hitherto been engaged in the development of an electrode catalyst for a secondary battery using a reaction similar to the oxygen generation reaction of alkaline water electrolysis. According to the intensive research of the present inventors, it has been found that a metal oxide containing bismuth, ruthenium and oxygen (hereinafter also abbreviated as "BRO") has good catalytic performance for the oxygen generation reaction in an alkaline aqueous solution.

[0014] However, although ruthenium is not as expensive as iridium described above, its market price is relatively high, and in particular, in recent years, the upward trend of its price has become remarkable.

[0015] The present invention aims to improve the above circumstances, and its object is to provide composite particles having excellent catalytic performance and durability while reducing the amount of ruthenium used, that is, reducing the cost.

Means for Solving the Problems

[0016] The present invention for achieving the above object is as follows.

[0017] 〈Aspect 1〉 Composite particles containing first metal oxide particles and second metal oxide particles, where the particle diameter of the first metal oxide particles is smaller than the particle diameter of the second metal oxide particles, A plurality of the first metal oxide particles cover at least a portion of the surface of the second metal oxide particles to form a corona shape, and the first metal oxide particles are epitaxially grown on the surface of the second metal oxide particles. composite particles. <Aspect 2> A composite particle according to embodiment 1, for use as a catalyst. <Aspect 3> The first metal oxide particles are metal oxide particles containing bismuth, ruthenium, and oxygen, and The second metal oxide particles are metal oxide particles containing bismuth, titanium, and oxygen. The composite particle according to embodiment 1 or 2. <Aspect 4> The composite particle according to any one of embodiments 1 to 3, wherein the particle diameter of the first metal oxide particle is 1 / 2 or less of the particle diameter of the second metal oxide particle. <Aspect 5> A composite particle according to any one of embodiments 1 to 4, wherein the amount of the first metal oxide particles is 5.0 to 40 parts by mass per 100 parts by mass of the second metal oxide particles. <Pattern 6> A method for producing composite particles according to any one of embodiments 1 to 5, including the following steps: (i) preparing the second metal oxide particles, and (ii) Prepare a mixed solution containing a source of each element constituting the first metal oxide particles, the second metal oxide particles, and a basic compound, and epitaxially grow the first metal oxide particles on the surface of the second metal oxide particles in the mixed solution. <Aspect 7> The above step (i) includes a firing step at a temperature of 200°C or higher, The above step (ii) and the steps up to the production of the composite particles do not include a firing step at a temperature of 200°C or higher. The manufacturing method described in aspect 6. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide composite particles that have excellent catalytic performance and durability while reducing costs. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is a schematic diagram illustrating the unique structure of the composite particles of the present invention. [Figure 2] Figure 2 is a schematic diagram illustrating the core-shell structure of a conventional composite particle. [Figure 3] Figure 3 shows the X-ray diffraction patterns of composite particles BRO-BTO and BTO particles. [Figure 4] Figure 4 is a scanning electron microscope image of BTO particles. [Figure 5] Figure 5 shows a scanning electron microscope image of the composite particle BRO-BTO. [Figure 6] Figure 6 is a scanning electron microscope image of BTO particles. [Figure 7] Figure 7 shows a scanning electron microscope image of the composite particle BRO-BTO. [Figure 8] Figure 8 shows a scanning electron microscope image of the composite particle BRO-BTO. [Figure 9] Figure 9 shows the polarization curves for Example 1 and Comparative Example 1. [Figure 10] Figure 10 shows the results of Example 1 and Comparative Example 1 when electrolysis was performed at 1.6V, and the results of Comparative Example 2 when electrolysis was performed at 1.7V. [Figure 11] Figure 11 shows the results of Example 1, Comparative Example 1, and Comparative Example 2 when electrolysis was performed at 1.7V. [Figure 12] Figure 12 is a diagram for comparing the catalyst performance of Example 1 and Comparative Example 1. [Modes for carrying out the invention]

[0020] The embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below, and can be implemented with various modifications within the scope of the essence of the invention.

[0021] 《Composite particles》 The composite particles of the present invention are A composite particle comprising a first metal oxide particle and a second metal oxide particle, The particle size of the first metal oxide particle is smaller than the particle size of the second metal oxide particle. Multiple first metal oxide particles cover at least a portion of the surface of second metal oxide particles to form a corona shape, and the first metal oxide particles are epitaxially grown on the surface of the second metal oxide particles. composite particles That is the case.

[0022] Figure 1 is a schematic diagram illustrating the unique structure of the composite particles of the present invention. As shown in Figure 1, the composite particles 10 of the present invention include first metal oxide particles 1 and second metal oxide particles 2. The particle diameter of the first metal oxide particles 1 is smaller than the particle diameter of the second metal oxide particles 2. Multiple first metal oxide particles 1 cover at least a portion of the surface of the second metal oxide particles 2, forming a corona shape (figure to the right of the arrow). In addition, the first metal oxide particles 1 are epitaxially grown from the adhesive interface 1a on the surface of the second metal oxide particles 2.

[0023] In contrast to the corona shape of the composite particle 10 of the present invention, for example, there are composite particles having a conventional core-shell shape. Figure 2 is a schematic diagram illustrating the core-shell structure of a conventional composite particle. As shown in Figure 2, in the composite particle 20, the first metal oxide particles 1, rather than being in the form of individual particles, cover the surface of the second metal oxide particles 2, which act as the core, as a first metal oxide particle layer 1'. When manufacturing such a core-shell composite particle 20, for example, the first metal oxide particles 1 covering the surface of the first metal oxide particles can be transformed into a first metal oxide particle layer 1' by a process such as firing.

[0024] Thus, the composite particles 10 of the present invention are fundamentally structurally different from conventional composite particles 20 having a core-shell shape. Furthermore, composite particles 20 having a core-shell shape have a relatively small surface area because they are a shell-shaped film on the surface, and are therefore considered undesirable as catalysts. In contrast, the composite particles 10 of the present invention have a relatively large surface area due to their unique corona shape. For this reason, the composite particles 10 of the present invention can be suitably used as a catalyst for the oxygen evolution reaction in alkaline water electrolysis described above, or as a catalyst for the oxygen evolution reaction or oxygen reduction reaction in secondary batteries. In other words, the composite particles 10 of the present invention offer excellent catalytic performance and durability while reducing costs.

[0025] The inventors have found that composite particles like those of the present invention (for example, composite particle 10 in Figure 1) can be obtained by manufacturing composite particles of the first metal oxide particles and the second metal oxide particles having substantially the same crystal structure and lattice constant, and by manufacturing these metal oxide particles in a specific manner.

[0026] With such composite particles, multiple first metal oxide particles cover at least a portion of the surface of the second metal oxide particles, thereby increasing the size of the composite particles to improve handling while increasing the specific surface area of ​​the first metal oxide. Furthermore, with such composite particles, the first metal oxide particles are epitaxially grown on the surface of the second metal oxide particles, thereby improving adhesion at the bonding interface between the first and second metal oxide particles while achieving high crystallinity of the first metal oxide particles.

[0027] <First metal oxide particle> In the present invention, the first metal oxide particles may be, for example, metal oxide particles containing bismuth, ruthenium, and oxygen, that is, bismuth-ruthenium oxide particles.

[0028] Furthermore, in the present invention, the first metal oxide particles may be, for example, a bismuth-containing ruthenium pyrochlore metal oxide. A bismuth-containing ruthenium pyrochlore metal oxide is, for example, one with the chemical formula "Bi x Ru y O z This is expressed as , where x is 1.5 to 2.5, especially 1.8 to 2.2, and more particularly 1.9 to 2.0, y is 1.5 to 2.5, especially 1.8 to 2.2, and more particularly 1.9 to 2.0, and z may be 6.5 to 7.5, especially 6.8 to 7.2, and more particularly 6.8 to 7.0. Bismuth ruthenium pyrochlore metal oxides can typically be represented as Bi2Ru2O7.

[0029] Furthermore, the first metal oxide particles according to the present invention may contain any other components (e.g., aluminum element) as long as they do not inhibit the catalytic action of the oxygen evolution reaction.

[0030] In the present invention, the particle size of the first metal oxide particles is not particularly limited as long as it is smaller than the particle size of the second metal oxide particles, which will be described later. For example, the particle size of the first metal oxide particles may be 1 / 2 or less, 1 / 5 or less, 1 / 10 or less, 1 / 50 or less, 1 / 100 or less, 1 / 200 or less, 1 / 300 or less, 1 / 400 or less, or 1 / 500 or less of the particle size of the second metal oxide particles, or it may be 1 / 2000 or more, or 1 / 1000 or more of the particle size of the second metal oxide particles.

[0031] The particle size of the first metal oxide particles according to the present invention may more specifically be, for example, 5 nm or more, 10 nm or more, or 15 nm or more, and may also be 50 nm or less, 30 nm or less, or 20 nm or less. In the present invention, unless otherwise specified, the particle size of the particles refers to the average particle size of the primary particles. More specifically, the particle size can be determined by measuring the particle size of 100 arbitrary (randomly selected) primary particles when observed at a magnification of 150,000 times using a scanning electron microscope (JSM-6701F, manufactured by JEOL Ltd.), and taking the average value.

[0032] In the composite particles of the present invention, the amount of the first metal oxide particles is not particularly limited. From the viewpoint of reducing the amount of ruthenium used, the amount of the first metal oxide particles may be, for example, 40 parts by mass or less, 35 parts by mass or less, or 30 parts by mass or less per 100 parts by mass of the second metal oxide particles. Furthermore, from the viewpoint of improving conductivity and ensuring catalytic performance, the amount of the first metal oxide particles may be, for example, 5.0 mass or more, 10 mass or more, 15 mass or more, 20 mass or more, 25 mass or more, or 30 mass or more per 100 parts by mass of the second metal oxide particles.

[0033] <Second type of metal oxide particle> In the present invention, the second metal oxide particles may be, for example, metal oxide particles containing bismuth, titanium, and oxygen, that is, bismuth titanium oxide particles.

[0034] Furthermore, in the present invention, the second metal oxide particles may be bismuth-containing titanium pyrochlore metal oxide. Bismuth-containing titanium pyrochlore metal oxide is, for example, a metal with the chemical formula "Bi x Ti y O z This is expressed as , where x is 1.5 to 2.5, especially 1.8 to 2.5, and more particularly 1.8 to 2.2; y is 1.5 to 3.0, especially 2.0 to 2.8, and more particularly 2.4 to 2.8; and z may be 6.5 to 8.5, especially 7.5 to 8.5, and more particularly 7.8 to 8.4. Bismuth-containing titanium pyrochlore metal oxides can typically be represented as Bi2Ti2O7.

[0035] Furthermore, the second metal oxide particles according to the present invention may contain any other components (e.g., aluminum element) as long as they do not impair the effects of the present invention.

[0036] Furthermore, if the first metal oxide particles described above are Bi2Ru2O7, it is preferable that the second metal oxide particles be Bi2Ti2O7. This is because the crystal structure of Bi2Ru2O7 and the crystal structure of Bi2Ti2O7 are the same, and the theoretical value of the lattice constant of Bi2Ru2O7 is 10.3 Å, while the theoretical value of the lattice constant of Bi2Ti2O7 is 10.33 Å. Since the lattice constants of both are substantially the same, Bi2Ru2O7 can be epitaxially grown on the surface of Bi2Ti2O7.

[0037] In the present invention, the particle size of the second metal oxide particles is not particularly limited as long as it is larger than the particle size of the first metal oxide particles described above. The particle size of the second metal oxide particles can be appropriately adjusted, for example, by the amount used and by treatment such as firing.

[0038] In the composite particles of the present invention, the amount of the second metal oxide particles is not particularly limited and may be within the range of the ratio of parts by mass to the first metal oxide particles described above.

[0039] Method for manufacturing composite particles The present invention also provides a method for producing the composite particles of the present invention as described above (hereinafter also simply referred to as "the method of the present invention").

[0040] The method of the present invention includes the following steps: (i) preparing a second metal oxide particle, and (ii) Prepare a mixed solution containing a source of each element constituting the first metal oxide particles, the second metal oxide particles, and a basic compound, and epitaxially grow the first metal oxide particles on the surface of the second metal oxide particles in the mixed solution.

[0041] Conventionally, as described in Patent Document 3 above, epitaxial growth of metal particles relative to other metal particles is often carried out in the gas phase.

[0042] In contrast, through diligent research by the present inventors, the present invention has succeeded in epitaxially growing first metal oxide particles on the surface of second metal oxide particles in the liquid phase in step (ii). Furthermore, the composite particles of the present invention obtained in this way have a unique corona shape.

[0043] Process (i) In step (i), the second metal oxide particles are prepared. The preparation of the second metal oxide particles is not particularly limited; for example, commercially available second metal oxide particles may be used as is, or the second metal oxide particles may be manufactured using a coprecipitation method or the like.

[0044] Below, as an example, a method for producing second metal oxide particles using the coprecipitation method will be described. This method may include, for example, the following steps (a) to (f).

[0045] Process (a) In step (a), solutions of each source of each element constituting the second metal oxide particles are prepared.

[0046] If the second metal oxide particles are metal oxide particles containing bismuth, titanium, and oxygen, then a bismuth source and a titanium source may be used as the supply source.

[0047] Examples of bismuth sources include, but are not limited to, bismuth nitrate, bismuth sulfate, bismuth chloride, bismuth carbonate, bismuth alkoxide, or mixtures of two or more of these.

[0048] Examples of titanium sources include, but are not limited to, titanium chloride, titanium sulfate, titanium alkoxide, or mixtures of two or more of these.

[0049] If the bismuth source and titanium source are solids, it is preferable to dissolve each in a solvent. The solvent is not particularly limited, and for example, water or hydrochloric acid can be used.

[0050] Process (b) In step (b), the solutions from each prepared source are mixed in predetermined amounts to match the elemental ratio of the desired second metal oxide particles, thereby preparing a mixed solution.

[0051] For example, a titanium source solution may be added dropwise to a bismuth source solution and mixed by stirring or other means.

[0052] Process (c) In step (c), an aqueous solution of the basic compound is added to the mixed solution obtained above.

[0053] In this case, the pH of the mixed solution may be adjusted to about 8 to 14, preferably about 8 to 10. Examples of aqueous solutions of basic compounds include, but are not limited to, aqueous sodium hydroxide solution or potassium hydroxide.

[0054] Process (d) In step (d), the mixed solution after the addition of the alkaline aqueous solution is stirred, preferably vigorously, while being cooled in a local exhaust ventilation system. The equipment and operating conditions used for stirring are optional.

[0055] Furthermore, stirring can be performed while blowing in an oxygen-containing gas. Air, oxygen gas, etc., can be used as the oxygen-containing gas. In this case, the oxygen-containing gas may contain components other than oxygen (typically nitrogen, etc.) as long as they do not adversely affect the formation of the target oxide.

[0056] Process (e) In step (e), water and other substances are removed from the mixed solution to recover the solid matter (oxidation products).

[0057] Water removal can be carried out by any method, as long as it does not affect the recovered solids, and may include methods such as evaporation, drying, or filtration.

[0058] Process (f) In step (f), the recovered solid material (oxidation product) is calcined at a temperature of 200°C or higher. This yields the desired second metal oxide particles.

[0059] The firing may be carried out in air. The firing temperature may be 200°C or higher, for example, 250°C or higher, 300°C or higher, 350°C or higher, 400°C or higher, 450°C or higher, 500°C or higher, or 550°C or higher, or 700°C or lower, 650°C or lower, 600°C or lower, or 550°C or lower. The firing time is not particularly limited and may be, for example, 1 to 24 hours or 6 to 12 hours.

[0060] Furthermore, the compound after calcination may be washed (e.g., with water) to remove residual impurities and then dried before use. Washing to remove residual impurities may also be performed on the solid material recovered from the solution before calcination.

[0061] Process (ii) In step (ii), a mixed solution is prepared containing a source of each element constituting the first metal oxide particles, the second metal oxide particles, and a basic compound, and the first metal oxide particles are epitaxially grown on the surface of the second metal oxide particles in the mixed solution.

[0062] More specifically, in step (ii), first, an aqueous solution containing a source of each element constituting the first metal oxide particles, the second metal oxide particles, and a basic compound is prepared.

[0063] If the first metal oxide particles are metal oxide particles containing bismuth, ruthenium, and oxygen, then a bismuth source and a ruthenium source may be used as the supply source.

[0064] Since the bismuth source is the same as that used for the second metal oxide particles described above, we will omit the explanation here.

[0065] Examples of ruthenium sources include, but are not limited to, ruthenium chloride, water-soluble ruthenium complexes or ruthenium salts, or mixtures of two or more of these.

[0066] If the bismuth source and ruthenium source are solids, it is preferable to dissolve each in a solvent such as water.

[0067] Then, the solutions from each of the prepared first metal oxide particle sources are mixed in predetermined amounts according to the desired elemental ratio of the first metal oxide particles to prepare the first mixed solution.

[0068] A predetermined amount of the second metal oxide particles prepared above may be suspended in this first mixed solution, and then an aqueous solution of the basic compound may be added to prepare the second mixed solution. Alternatively, an aqueous solution of the basic compound may be added to this first mixed solution, and then a predetermined amount of the second metal oxide particles prepared above may be suspended in it to prepare the second mixed solution.

[0069] The predetermined amount of the second metal oxide particles here may be adjusted as appropriate to match the desired ratio of mass parts of the first metal oxide particles to the second metal oxide particles.

[0070] Next, the composite particles of the present invention are obtained by epitaxially growing the first metal oxide particles on the surface of the second metal oxide particles in a mixed solution (i.e., the second mixed solution described above) containing a source of each element constituting the obtained first metal oxide particles, the second metal oxide particles, and a basic compound.

[0071] In this process, the first metal oxide particles can be epitaxially grown on the surface of the second metal oxide particles by, for example, stirring the mixed solution, blowing oxygen-containing gas into the mixed solution, or adding sodium hypochlorite. In the case of stirring, for example, vigorous stirring or stirring while blowing in oxygen-containing gas is also possible. Furthermore, when blowing oxygen-containing gas into the mixed solution, stirring can also be added. When adding sodium hypochlorite, either sodium hypochlorite powder or an aqueous solution of sodium hypochlorite may be used, but an aqueous solution of sodium hypochlorite is preferred. Sodium hypochlorite can also be added while stirring.

[0072] Thus, by step (ii), the first metal oxide particles are epitaxially grown on the surface of the second metal oxide particles to obtain the composite particles of the present invention.

[0073] As mentioned above, in order to maintain the unique corona shape of the composite particles of the present invention, it is preferable that step (ii) and the subsequent steps for manufacturing the composite particles of the present invention do not include a firing step at a temperature of 200°C or higher. Here, the steps for manufacturing the composite particles of the present invention after step (ii) are any steps from step (ii) until the composite particles of the present invention are obtained, and include, but are not limited to, a washing step (e.g., water washing) for the purpose of removing distillate impurities and / or a drying step at a temperature of less than 200°C. Of course, these optional steps are not required after step (ii). [Examples]

[0074] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0075] Example 1: Manufacturing of composite particles BRO-BTO In Example 1, a composite particle BRO-BTO of the present invention was manufactured in which multiple BRO particles covered at least a portion of the surface of a BTO particle to form a corona shape, and the BRO particles were epitaxially grown on the surface of the BTO particle.

[0076] (i) Synthesis of BTO particles In a local exhaust ventilation system, bismuth nitrate pentahydrate was dissolved in 120 mL of 1 M hydrochloric acid, and 8.32 mL of titanium chloride aqueous solution was slowly added dropwise while stirring. Then, 20 mL of 10 M sodium hydroxide aqueous solution was added dropwise, and the mixture was vigorously stirred in an ice bath. After the solution became opaque, it was stirred for 30 minutes, transferred to a plastic evaporating dish, and evaporated to dryness at 120°C to obtain a solid. The solid was then crushed in a mortar and washed with pure water. The washed solid was recovered by suction filtration and calcined at 550°C for 12 hours to obtain a white BTO particle powder.

[0077] (ii) Synthesis of composite particles BRO-BTO A predetermined amount of BTO particles prepared in (1) was added to a mixture prepared by dissolving 0.114 g of bismuth nitrate pentahydrate and 0.061 g of ruthenium chloride trihydrate in 125 mL of pure water. Here, the predetermined amount of BTO particles was determined by the mixing ratio of BTO particles to BRO particles. In this example, 0.2 g of BTO particles was added so that the amount of BRO particles was 30 parts by mass for every 100 parts by mass of BTO particles.

[0078] Next, 30 mL of 1.0 mol / L NaOH was added to the mixed aqueous solution, and the mixture was stirred for 72 hours while oxygen was flowed through it at a flow rate of 10 mL / min. After stirring, the water was evaporated from the mixture at 85°C to remove it, and the resulting solid was then dried at 120°C for 3 hours to produce the composite particle BRO-BTO.

[0079] <measurement> (Identification of composite particles) The identification of the composite particle BRO-BTO was performed by analysis using synchrotron radiation XRD diffraction (XRD), and the obtained diffraction pattern (actual salt) is shown in FIG. 3. For comparison, the diffraction pattern (dotted line) of the BTO particles synthesized above is also shown in FIG. 3.

[0080] In addition, by ICP analysis (high-frequency plasma spectroscopic analysis), in the composite particle BRO-BTO, the BRO part was found to be Bi 1.9~2.0 Ru 1.9~2.0 O 6.8~7.0 and the BTO part was found to be Bi 1.8~2.2 Ti 2.4~2.8 O 7.8~8.4

[0081] (Microscopic Observation) The synthesized BTO particles and the composite particle BRO-BTO were each observed with a scanning electron microscope. The respective observation results are shown in FIG. 4 (BTO particles) and FIG. 5 (composite particle BRO-BTO).

[0082] As shown in FIGS. 4 and 5, the surface of the BTO particles is very smooth. In contrast, the surface of the composite particle BRO-BTO is in a state with irregularities.

[0083] To make it easier to observe, the observation image of the BTO particles in FIG. 4 is enlarged and shown in FIG. 6. Also, the observation image of the composite particle BRO-BTO in FIG. 5 is enlarged and shown in FIG. 7.

[0084] As shown in FIGS. 6 and 7, the surface of the BTO particles is very smooth. In contrast, in the composite particle BRO-BTO, a plurality of BRO particles cover at least a part of the surface of the BTO particles and form a corona shape. It is also clear that the particle diameter of the BRO particles is smaller than that of the BTO particles.

[0085] Then, the observation image of the composite particle BRO-BTO in FIG. 5 is further enlarged and shown in FIG. 8.

[0086] ​As is clear from Figure 8, it was found that BRO particles were epitaxially grown on the surface of BTO particles.

[0087] Comparative Example 1 In Comparative Example 1, BRO particles were synthesized as follows.

[0088] More specifically, ruthenium chloride crystals (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., 6-07-11-01) 0.979g (3.74 x 10⁻⁶) -3 (mol), and the same amount of bismuth(III) nitrate pentahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 028-02002) 1.814 g (3.74 × 10⁻¹⁴) -3 The mol(s) were weighed and dissolved in approximately 60 ml of ultrapure water in separate beakers. The two solutions were mixed in a 1 L TPX beaker, and more ultrapure water was added to make a 500 ml mixed solution. 60 mL of 2 mol / L NaOH was added to this. The mixture was then stirred for 24 hours while oxygen was flowed through it at a flow rate of 10 mL / min. After stirring, the water was evaporated from the mixture at 85°C to remove it, and the resulting solid was then dried at 120°C for 3 hours. The dried solid was crushed in a mortar and calcined in air at 500°C for 3 hours. The calcined product was washed with ultrapure water at 75°C and then dried at 120°C for 3 hours to obtain the final product, BRO particles. The obtained BRO particles were analyzed by ICP (Infrared Plasma Spectroscopy) to determine Bi 1.9~2.0 Ru 1.9~2.0 O 6.8~7.0 It turned out that this was the case.

[0089] 《Catalyst Performance Evaluation》 The catalytic performance of the oxygen evolution reaction was evaluated for both the BRO-BTO composite particles of Example 1 and the BRO particles of Comparative Example 1 using the rotating electrode method.

[0090] More specifically, the composite particles BRO-BTO from Example 1 or the BRO particles from Comparative Example 1 were placed on a gold disc electrode so that the ruthenium weight per unit area of ​​the gold disc electrode was 1.78 μg, and measurements were taken in a 0.1 M potassium hydroxide aqueous solution. The reference electrode was Hg / HgO, and the counter electrode was a Ni mesh. The electrode was rotated at a speed of 2500 rpm. The scanning speed was 5 mV / s. The polarization curves obtained from these measurements are shown in Figure 9. In Figure 9, Example 1 is represented by a solid line, and Comparative Example 1 is represented by a dotted line.

[0091] As is clear from Figure 9, in both Example 1 and Comparative Example 1, a current began to flow from approximately 1.4V. This suggests that the reaction initiation potential of the BTO-BRO composite particles in Example 1 is similar to that of the BRO particles in Comparative Example 1.

[0092] Furthermore, the Tafel gradient obtained from Figure 9 was 34 mV / dec for the composite particle BRO-BTO in Example 1, and 34 mV / dec for the BRO particle in Comparative Example 1, indicating that both were the same.

[0093] 《Evaluation of catalyst performance and durability》 In this test, the composite particles BRO-BTO from Example 1, the BRO particles from Comparative Example 1, and the commercially available RuO2 particles from Comparative Example 2 were used. More specifically, electrolysis (oxygen evolution reaction) was performed at 1.6V or 1.7V for 5 minutes, followed by an open circuit state (no current flow) for 5 minutes. Then, the electrodes were removed, any bubbles (oxygen) adhering to the electrodes were removed, and the electrodes were immersed in a 0.1M potassium hydroxide aqueous solution. The electrolysis process was repeated at 1.6V or 1.7V for 5 minutes.

[0094] The results of electrolysis performed at 1.6V are shown in Figure 10, and the results of electrolysis performed at 1.7V are shown in Figure 11. In Figures 10 and 11, the amount of electricity during electrolysis is divided by the weight of ruthenium and plotted on the horizontal axis. Since this amount of electricity is the product of current and time, moving to the right on the horizontal axis indicates that more electricity flows. The vertical axis represents the potential at which a current of 100A flows per weight of ruthenium. Note that the theoretical potential for water splitting is 1.23V, so it is desirable to approach this theoretical value on the vertical axis. For the sake of comparison, Figure 10 also shows the results of Comparative Example 2, which was performed at 1.7V.

[0095] In the BRO particle results for Comparative Example 1, as shown in Figure 10, 10 8 It was found that the potential (vertical axis) increased when the value exceeded C / g. This indicates that the electrode began to deactivate due to the total amount of electricity passed through it. This is thought to be mainly due to the leaching of ruthenium. In addition, in the BRO particle results for Comparative Example 1, as shown in Figure 11, 7 × 10 7 It was found that the reaction started to rise from around C / g. This suggests that increasing the potential during electrolysis by 0.1V to 1.7V accelerated the deactivation of BRO particles.

[0096] In contrast, the results for the composite particle BRO-BTO in Example 1, as shown in Figures 10 and 11, showed that the potential (vertical axis) increased when a larger amount of electricity flowed compared to Comparative Example 1. The ability to pass a larger amount of electricity indicates higher electrode durability, so it is clear that the composite particle BRO-BTO in Example 1 is approximately 2.5 to 3 times more durable than the BRO particle in Comparative Example 1. Furthermore, this increased durability is thought to be due to the effect of the composite with BTO.

[0097] Furthermore, in the results for the RuO2 particles of Comparative Example 2, as shown in Figures 10 and 11, the RuO2 particles were 10 5 ~10 6 It was found that the potential increases with C / g, leading to deactivation.

[0098] Therefore, in terms of durability evaluation, it was found that Example 1 had the best durability, and while Comparative Example 1's durability was inferior to Example 1, it was better than Comparative Example 2.

[0099] From the viewpoint of catalytic performance, the potentials of Example 1, Comparative Example 1, and Comparative Example 2 at the start of the test were compared.

[0100] As is clear from Figures 10 and 11, the RuO2 particles of Comparative Example 2 showed a potential of 1.55V at the start of the test, which was higher than that of Example 1 and Comparative Example 1. This indicates that the RuO2 particles of Comparative Example 2 had the highest potential required to pass a current of 100A / g, meaning that their catalytic performance for the oxygen evolution reaction was inferior to that of Example 1 and Comparative Example 1.

[0101] Furthermore, to facilitate comparison between Example 1 and Comparative Example 1, the potentials at the start of the test are summarized in Figure 12.

[0102] As is clear from Figure 12, in both the 1.6V and 1.7V electrolysis cases, the potential of Example 1 was found to be lower than that of Comparative Example 1, and closer to the theoretical value of 1.23V for water splitting. In other words, the composite particle BRO-BTO of Example 1 was found to have excellent catalytic performance. [Explanation of Symbols]

[0103] 1. First metal oxide particles 2. Second metal oxide particles 1a Adhesive interface 1' First metal oxide particle layer 10. Composite particles of the present invention 20 Composite particles with a core-shell structure

Claims

1. A composite particle comprising a first metal oxide particle and a second metal oxide particle, The particle size of the first metal oxide particle is smaller than the particle size of the second metal oxide particle. A plurality of the first metal oxide particles, in particle shape, cover at least a portion of the surface of the second metal oxide particles to form a corona shape, and the first metal oxide particles are epitaxially grown on the surface of the second metal oxide particles. The first metal oxide particles are metal oxide particles containing bismuth, ruthenium, and oxygen, and The second metal oxide particles are metal oxide particles containing bismuth, titanium, and oxygen, and It is for catalytic use. composite particles.

2. The composite particle according to claim 1, wherein the particle diameter of the first metal oxide particle is 1 / 2 or less of the particle diameter of the second metal oxide particle.

3. The composite particle according to claim 1, wherein the amount of the first metal oxide particles is 5.0 to 40 parts by mass per 100 parts by mass of the second metal oxide particles.

4. A method for producing composite particles according to any one of claims 1 to 3, comprising the following steps: (i) preparing the second metal oxide particles, and (ii) Prepare a mixed solution containing a source of each element constituting the first metal oxide particles, the second metal oxide particles, and a basic compound, and epitaxially grow the first metal oxide particles on the surface of the second metal oxide particles in the mixed solution.

5. The above step (i) includes a firing step at a temperature of 200°C or higher, The above step (ii) and the steps up to the production of the composite particles do not include a firing step at a temperature of 200°C or higher. The manufacturing method according to claim 4.

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