JP5635386B2 - Composite particles for SOFC fuel electrode and method for producing the composite particles - Google Patents

Description

  The present invention relates to a method for producing composite particles used as a material for a fuel electrode of a solid oxide fuel cell (SOFC), composite particles obtained by the production method, and use of the composite particles.

A solid oxide fuel cell generally called “SOFC” has a high power generation efficiency, a low environmental load, and can use various fuels among various types of fuel cells. From this point, it is expected as a next-generation power generation device, and its development is in progress.
The basic structure (cell) of SOFC is that an air electrode (cathode) is formed on one surface of a dense solid electrolyte (eg, a dense membrane layer) made of an oxide ion conductor, and a fuel electrode (anode) is formed on the other surface. It is configured by being formed. Both the air electrode and the fuel electrode have a porous structure with good gas diffusibility. Fuel gas (typically H ₂ (hydrogen) gas or fuel gas such as methane) is supplied to the fuel electrode side of the solid electrolyte, and O ₂ (oxygen) -containing gas (typically air) is supplied to the air electrode side. ) Is supplied. At this time, O ₂ supplied to the air electrode side is converted into oxide ions (O ²⁻ ) by the air electrode, and supplied to the fuel electrode side through the solid electrolyte. On the fuel electrode side, power is generated by reacting the fuel gas with oxide ions supplied from the solid electrolyte and releasing electrons from the oxide ions. This reaction at the fuel electrode is made up of an interface of a solid electrolyte that supplies oxide ions to the fuel electrode side, an interface of pores to which fuel gas can be supplied, and an interface of a metal oxide that functions as a metal catalyst for the above reaction. Occurs at the constructed three-phase interface.

In recent years, in order to increase the number of three-phase interfaces in the fuel electrode, composite particles in which a metal oxide, a solid electrolyte, and the same type of oxide ion conductor are combined are used as the material of the fuel electrode. . When the composite particles are used for the fuel electrode, the oxide ions supplied from the solid electrolyte are supplied to the inside of the fuel electrode by the oxide ion conductor in the composite particles. Therefore, since the three-phase interface is formed not only in the interface with the solid electrolyte but also in the fuel electrode, the output characteristic of the SOFC is improved by increasing the field of the fuel electrode reaction.
Conventional examples of the composite particles are disclosed in, for example, Patent Documents 1 and 2, and conventional examples of secondary particles prepared from other metal fine particles are described in, for example, Patent Document 3.

JP 2010-6648 A JP 2006-4874 A JP 2008-195551 A

  By the way, in the technique disclosed in Patent Document 1, zirconia particles and nickel oxide particles are obtained by heat-treating a precipitate obtained by adding a dispersion containing zirconia particles and nickel ions to an alkaline solution in an oxidizing atmosphere. The composite particle which consists of is produced. Since the composite particles described in the document have improved distribution of the zirconia particles and nickel oxide particles constituting the composite particles, a portion where the zirconia particles and the nickel oxide particles are in contact (ZrO-NiO interface) is present. It has increased.

  However, although the number of ZrO—NiO interfaces is certainly increased in the composite particles disclosed in Patent Document 1, the three-phase interface is not present because the vacancies to which fuel gas can be supplied are not in contact with the ZrO—NiO interface. It is considered that there is a high possibility that a part that is not formed will occur.

  This invention is made | formed in view of the said problem, and it aims at providing the manufacturing method which can manufacture suitably the composite particle with many three-phase interfaces compared with the past. In addition, another object of the present invention is to provide composite particles provided by such a production method, and an SOFC produced using the composite particles.

In order to achieve the above object, the present invention provides a method for producing composite particles used as a material for a fuel electrode of a solid oxide fuel cell. The composite particles intended for production of the present invention include metal oxide particles that function as a catalyst and oxide ion conductor particles.
And the manufacturing method provided by this invention is:
Preparing a dispersion in which metal oxide particles and oxide ion conductor particles are dispersed in a dispersion medium together with polymer particles made of a predetermined organic polymer compound;
Spraying the dispersion into the chamber as droplets;
By heating the sprayed droplets in a chamber, the dispersion medium is removed from the dispersion, and the metal oxide particles, the oxide ion conductor particles, and the polymer particles are aggregated. Obtaining a collection;
Firing the agglomerates to remove the components constituting the polymer particles to obtain composite particles;
Is included.

In the manufacturing method having the above-described structure, composite particles are produced from a mist-like dispersion sprayed as droplets (that is, granulation is performed by a so-called spray drying method). Aggregation of the conductor particles can be suppressed. Therefore, according to the production method of the present invention, homogeneous composite particles can be produced over the whole in which the metal oxide particles and the oxide ion conductor particles are substantially evenly distributed.
Moreover, in this manufacturing method, polymer particles are dispersed in the dispersion. A component constituting the polymer particles (hereinafter referred to as “polymer component” as appropriate) is removed when the aggregate is fired. Since the part from which the polymer component has been removed is hollowed out in the composite particles obtained in this way, a plurality of micropores (or a hollow core part inside) are formed on the surface. For this reason, the number of vacancies to which fuel gas can be supplied is increased compared to conventional composite particles.
As described above, according to the production method of the present invention, the metal oxide particles and the oxide ion conductor particles are distributed almost evenly, and the pores to which the fuel gas can be supplied compared with the conventional method. Composite particles having an increased number can be easily produced. Compared to conventional composite particles, this composite particle has a three-phase interface composed of metal oxide particle interfaces, oxide ion conductor particle interfaces, and pore interfaces through which fuel gas can be supplied. Therefore, when it is used as a material for the fuel electrode of SOFC, the output characteristics of SOFC can be improved. In addition, since the mixed particles are homogeneous composite particles composed of metal oxide particles and oxide ion conductor particles, which are fine particles constituting the composite particles, distributed almost evenly. It can also contribute to stabilizing the operation of SOFC in the long term.

In the production method of a preferred embodiment disclosed herein, the pH of the dispersion is adjusted so that the signs of the zeta potentials of the metal oxide particles, the oxide ion conductor particles, and the polymer particles are equal, and the pH adjustment is performed. The dispersed liquid is sprayed into the chamber. At this time, the pH of the dispersion is preferably adjusted to pH 1 to pH 4.
If the signs of the zeta potentials of the three types of particles are the same in the dispersion, the particles repel each other. Thereby, since aggregation of each particle | grain can be suppressed, the composite particle in which the metal oxide particle and the oxide ion conductor particle were distributed substantially equally can be obtained more suitably.
In addition, according to this manufacturing method, since the polymer particles are distributed almost evenly in the aggregates of the particles formed after the dispersion medium is removed, the polymer component is removed from the aggregates to remove the polymer components. Composite particles in which a plurality of micropores are formed can be easily produced.

In the production method of a preferred embodiment disclosed herein, the pH of the dispersion is set such that the zeta potential of any one of the metal oxide particles, the oxide ion conductor particles, and the polymer particles is the other two types. The particle is adjusted to have a different sign from the zeta potential of the particles, and the pH adjusted dispersion is sprayed into the chamber. At this time, the pH of the dispersion is preferably adjusted to pH 7 to pH 10.
When the zeta potential of one kind of the three kinds of particles in the dispersion liquid is changed to a different sign, the other two kinds of particles are attracted to each other through the particles having the zeta potential having the different sign. . As a result, the polymer particles are arranged in the central part of the aggregate of the particles formed after the dispersion medium is removed. By removing the polymer component from the dispersion in this state, composite particles having hollow core portions formed inside the particles can be easily produced.

In the production method of a preferred embodiment disclosed herein, polymer particles having an average particle diameter of 50 nm to 500 nm are used as the polymer particles.
In the present specification, the “average particle diameter” refers to D ₅₀ (median diameter) in the particle size distribution to be measured. Such D ₅₀ is, for example, can be easily measured by a conventionally known laser diffraction method, the particle size distribution measurement apparatus based on light scattering method or the like.
By using polymer particles having an average particle diameter of 50 nm or more, fine pores (or hollow core portions) having an appropriate size can be formed in the composite particles. In addition, composite particles having a small average particle diameter can be easily produced by using polymer particles having an average particle diameter of 500 nm or less.

  Moreover, in the manufacturing method of the preferable one aspect disclosed here, metal oxide particles having an average particle diameter of 1 nm to 50 nm are used as the metal oxide particles. By using metal oxide particles having an average particle size of 50 nm or less, composite particles having more increased number of interfaces of metal oxide particles can be produced. As a result, the opportunity for forming the three-phase interface in the composite particles can be increased.

  Moreover, in the manufacturing method of one preferable aspect disclosed here, oxide ion conductor particles having an average particle diameter of 1 nm to 50 nm are used as the oxide ion conductor particles. In this case, it is possible to produce composite particles in which the number of interfaces of oxide ion conductor particles is further increased, and to increase the chances of forming a three-phase interface.

In the manufacturing method of a preferable aspect disclosed herein, the dispersion is performed so that the mass ratio M / C of the metal oxide particles (M) to the oxide ion conductor particles (C) is in the range of 0.5 to 3. Prepare the solution.
By setting the mass ratio M / C of the metal oxide particles (M) to the oxide ion conductor particles (C) within the above numerical range, the metal oxide particles and the oxide ion conductor particles are evenly distributed. It becomes easy and the opportunity that a three-phase interface is formed in a composite particle can be increased.

  In the manufacturing method of one preferable mode disclosed here, nickel oxide particles are used as the metal oxide particles. As a result, composite particles that can provide good performance when used as a material for the SOFC fuel electrode can be produced at low cost.

  Moreover, in the manufacturing method of the preferable one aspect disclosed here, zirconia particles are used as the oxide ion conductor particles. Also in this case, composite particles suitable as a material for the SOFC fuel electrode can be produced at low cost.

Moreover, this invention provides the composite particle used for the fuel electrode of a solid oxide fuel cell as another aspect. The composite particles can be easily manufactured by performing the above-described manufacturing method.
Here, the composite particles include metal oxide particles and oxide ion conductor particles that function as a catalyst, and the metal oxide particles and the oxide ion conductor particles are distributed almost evenly. In addition, the composite particles have a plurality of micropores formed on the surface.
In such composite particles, the metal oxide particles and the oxide ion conductor particles are almost evenly distributed, so that the number of interfaces between the metal oxide particles and the oxide ion conductor particles is increased as compared with the prior art. Yes. Furthermore, since the composite particles have a plurality of micropores formed on the particle surface, the number of cavities interfaces to which fuel gas can be supplied is increased compared to the conventional case. Therefore, this composite particle is more likely to form more three-phase interfaces than conventional, and can be suitably used as a material for the fuel electrode of SOFC.

  The average pore diameter of the fine pores formed on the surface of the composite particle is preferably 10 nm to 500 nm. In the composite particles having an average pore diameter of 10 nm or more, a plurality of micropores having a pore size that is preferable as a cavity through which fuel gas can be supplied are formed, and thus the three-phase interface is easily formed. ing. On the other hand, in composite particles having an average pore diameter of 500 nm or less, the three-phase interface is likely to be formed because the fine pores, the metal oxide particles, and the oxide ion conductor particles are distributed almost evenly. ing.

  In the case of composite particles having fine pores formed on the surface, the porosity of the composite particles is preferably 50% to 95%. When the porosity is within the above numerical range, a suitable number of three-phase interfaces can be formed inside the composite particles.

In addition, the above-described production method can also produce composite particles having a mode different from the composite particles having fine pores formed on the surface. This composite particle includes metal oxide particles that function as a catalyst and oxide ion conductor particles, and includes a hollow core portion and a shell portion that surrounds the hollow core portion. Further, the metal oxide particles and the oxide ion conductor particles are distributed almost evenly in the shell part. Such a composite particle has the metal oxide particles and the oxide ion conductor particles substantially evenly distributed in the shell part. Due to the distribution, the number of interfaces between the metal oxide particles and the oxide ion conductor particles is increased as compared with the conventional case. Furthermore, since this composite particle has a hollow core portion, the number of interfaces of the cavities to which fuel gas can be supplied is increased compared to the conventional case. Therefore, this composite particle is more likely to form more three-phase interfaces than conventional, and can be suitably used as a material for the fuel electrode of SOFC.

  Moreover, it is preferable that the average diameter of the hollow core part of the said composite particle is 1 micrometer-5 micrometers. In the case of such composite particles, the porosity of the composite particles is preferably 70% to 95%. Even in these cases, a suitable number of three-phase interfaces can be formed inside the composite particles.

  The present invention also provides a solid oxide fuel cell (SOFC) using the composite particles described above as a fuel electrode. Since the above-mentioned composite particles have a suitable number of three-phase interfaces formed, an SOFC with improved battery characteristics can be constructed by using it as a material for the fuel electrode of the SOFC.

It is sectional drawing which shows typically SOFC which concerns on one Embodiment of this invention. It is a block diagram which shows an example of the apparatus for implementing suitably the manufacturing method of the composite particle of this invention. It is a SEM photograph of sample 1. 2 is a SEM photograph of Sample 2. 3 is a SEM photograph of Sample 3. 4 is a SEM photograph of Sample 4. It is a SEM photograph of sample 5. It is a graph which shows the relationship between pH in the dispersion liquid of each sample, and the zeta potential of each particle | grain in a dispersion liquid. 3 is an HR-TEM photograph of Sample 2. 5 is a logarithmic graph plotting the measurement results of Sample 2 by mercury porosimetry. The vertical axis on the right side in FIG. 10 indicates “differential pore volume” and corresponds to plot A in the graph. The vertical axis on the left side indicates “integrated pore diameter volume” and corresponds to plot B in the graph. It is a figure which shows the element which comprises the sample 2, and the result of having analyzed the distribution of this element, (a) in FIG. 11 is a SEM photograph, (b) is a TEM photograph, (c) is an energy dispersion | distribution X-ray spectrum analysis. As a result, (d) shows the result of elemental mapping of zirconium and nickel.

  Hereinafter, a preferred embodiment of the present invention will be described. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, devices and chambers used for the preparation and spraying of dispersions) are described in the prior art in this field. It can be grasped as a design matter of those skilled in the art based on. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  The production method disclosed herein is a method for producing composite particles used as a material for a fuel electrode of a solid oxide fuel cell. The composite particles include metal oxide particles that function as a catalyst and oxide ion conductor particles.

  In the production method disclosed herein, first, a dispersion liquid in which metal oxide particles, oxide ion conductor particles, and polymer particles are dispersed in a dispersion medium is prepared.

As the metal oxide particles, metal element oxide particles that have high catalytic activity and can be used as a metal catalyst can be preferably used. Examples of the metal oxide particles include nickel (Ni), iron (Fe), cobalt (Co), and the like, platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), etc., which are noble metal elements. The metal element oxide particles can be used. Among these, nickel oxide (NiO) which is an oxide of nickel can be particularly preferably used because it has high oxidation activity and hydrogenation activity and is relatively cheaper than noble metals.
As the metal oxide particles disclosed herein, particles having an average particle diameter of about 0.5 nm to 75 nm (preferably 1 nm to 50 nm, more preferably 5 nm to 10 nm) may be used.

As the oxide ion conductor particles, particles of a metal compound having an elemental composition different from that of the metal oxide particles can be used. In particular, the same metal compound as that constituting the SOFC solid electrolyte may be used. Examples of the metal compound constituting the oxide ion conductor particle include oxides such as zirconium (Zr), cerium (Ce), lanthanum (La), and gallium (Ga). Zirconia (zirconium dioxide: ZrO ₂ ) can be preferably used. Furthermore, as the oxide ion conductor particles, stabilized zirconia particles in which the crystal structure is stabilized by dissolving a rare earth oxide in the zirconia can be preferably used. Among these stabilized zirconia, yttria-stabilized zirconia (YSZ) in which yttrium (Y) oxide is dissolved, scandia-stabilized zirconia (ScSZ) in which scandium (Sc) oxide is dissolved, and the like are particularly used. It can be preferably used.
The oxide ion conductor particles disclosed herein may be those having an average particle size of about 0.5 nm to 75 nm (preferably 1 nm to 50 nm, more preferably 1 nm to 10 nm).

As the polymer particles, particles mainly composed of an organic polymer compound that decomposes and evaporates by heating can be used. As the organic polymer compound constituting the polymer particles, for example, polystyrene, polyethylene oxide, polyolefin polymer compound (for example, polyethylene, polypropylene), or the like can be preferably used. Moreover, what is called latex particles provided by the system (latex) disperse | distributed to the predetermined | prescribed dispersion medium can be used suitably for a polymer particle. Latex particles are preferred because the particles in the dispersion medium have a substantially spherical shape and a small particle size distribution. Among these, latex particles made of polystyrene (also referred to as polystyrene latex beads, hereinafter referred to as “PSL”) can be used particularly preferably.
The polymer particles preferably have a larger average particle size than the metal oxide particles and the oxide ion conductor particles. Specifically, the average particle size is 50 nm to 700 nm (preferably (50 nm to 500 nm, more preferably 100 nm to 400 nm) may be used.

Any dispersion medium may be used as long as it can appropriately disperse the above-described particles (metal oxide particles, oxide ion conductor particles, and polymer particles), and a liquid that does not dissolve the particles is preferably used. . Here, examples of the dispersion medium include water, alcohols (for example, methanol (CH ₃ OH), ethanol (C ₂ H ₅ OH)), and the like. Among these, water is particularly preferably used in consideration of dispersibility of each particle and production cost.

  In the production method disclosed herein, the above-mentioned particles are dispersed in a dispersion medium to prepare a dispersion. When preparing the dispersion, a predetermined amount of each particle is added to the dispersion medium and mixed thoroughly. For this mixing treatment, a conventionally known method used for mixing liquids can be used. For example, it is possible to prepare a sol of each particle separately and stir and mix the sol while stirring. Examples of the method of stirring the dispersion by stirring and mixing include an ultrasonic homogenizer.

In preparing the dispersion, the mass ratio of the particles to be dispersed can be changed as appropriate. Although not particularly limited, the mass ratio (M / C) of the metal oxide particles (M) to the oxide ion conductor particles (C) is 0.5 to 3 (preferably 1 to 2, more preferably 1). The addition amount of the metal oxide particles and the oxide ion conductor particles may be determined so as to be within the range of .2 to 1.7). In this case, since the number of metal oxide particles and oxide ion conductor particles in the dispersion is approximate, composite particles in which each particle is evenly distributed can be easily produced.
Moreover, about addition amount of a polymer particle, mass ratio (P / (M + C)) of the polymer particle (P) with respect to the total mass (M + C) of a metal oxide particle (M) and an oxide ion conductor particle (C) is. It is good to determine so that it may become in the range of 1-3 (preferably 2-3, more preferably 2.2-2.7). In this case, since the number of metal oxide particles and oxide ion conductor particles in the dispersion is approximate, each particle can be evenly dispersed.

  Next, in the manufacturing method disclosed herein, the prepared dispersion is sprayed as droplets into the chamber. In order to spray the dispersion liquid as droplets, for example, a two-fluid nozzle, an ultrasonic sprayer or the like may be used. By using these devices, the dispersion can be sprayed as fine droplets of sub-micro to micro order. An example of the droplet diameter of the mist-like droplet at this time is 0.1 μm to 10 μm, preferably 1 μm to 6 μm, and more preferably about 2 μm to 5 μm. In this case, it is possible to easily produce composite particles having a small average particle diameter as compared with the case of manufacturing by a conventional manufacturing method.

  Next, the sprayed droplets are heated in the chamber to remove the dispersion medium from the dispersion. When the dispersion medium is removed from the dispersion, an aggregate in which metal oxide particles, oxide ion conductor particles, and polymer particles are aggregated is formed. In order to remove the dispersion medium from the sprayed droplets, granulation by a spray drying method can be used. The heating temperature at this time varies depending on the dispersion medium used, but is a temperature at which the dispersion medium can be removed (evaporated) from the dispersion (400 ° C. or less, for example, 100 ° C. to 400 ° C., typically 100 ° C. to 200 ° C. ).

  Next, in the production method disclosed herein, the agglomerates are baked to remove components constituting the polymer particles (hereinafter referred to as “polymer components” as appropriate) from the agglomerates. The conditions for heating the aggregate during firing vary depending on the components constituting the polymer particles, but may be set so that the polymer component can be removed from the aggregate. For example, when PSL particles are used as the polymer particles, the heating temperature is set to 400 ° C. or more and 1100 ° C. or less, preferably 500 ° C. or more and 1000 ° C. or less, for example, about 700 ° C. In addition, the heating time at this time may be set to 4 hours or less (preferably 30 minutes to 4 hours, more preferably 45 minutes to 2 hours, for example, about 1 hour).

The agglomeration may be performed in an atmosphere of an oxidizing gas (for example, an oxygen-containing gas (particularly preferably air)), or an inert gas (for example, nitrogen (N ₂ ), argon (Ar) ), Helium (He), etc.).
When firing in an oxidizing gas atmosphere, the oxidizing gas assists the removal (evaporation / decomposition) of the polymer component, so that the polymer component can be appropriately removed even when the heating temperature is relatively low. . Advantages of performing firing in a relatively low temperature range include that composite particles can be produced at low cost by preventing a decrease in durability of the firing furnace and reducing fuel costs required for temperature rise. Moreover, when air is used as the oxidizing gas, the manufacturing cost can be further reduced.
On the other hand, when the aggregate is fired in an inert gas atmosphere, the metal oxide particles and oxide ion conductor particles constituting the composite particles are oxidized more than necessary even when the heating temperature is relatively high. Can be prevented. That is, composite particles having excellent quality can be obtained stably.

  Composite particles are obtained through the above-described steps. An example of the phenomenon occurring at this time will be described below. Here, first, the dispersion liquid is sprayed into the chamber as droplets, and the dispersion medium is removed by heating the droplets. As a result, an agglomerate in which the metal oxide particles and the oxide ion conductor particles are almost uniformly distributed is obtained. When such an aggregate is fired, the polymer component is removed from the aggregate, and composite particles containing metal oxide particles and oxide ion conductor particles are obtained. Since this composite particle is produced by firing an aggregate in which metal oxide particles and oxide ion conductor particles are substantially evenly distributed, each particle is approximately evenly distributed. Furthermore, since the portion from which the polymer component has been removed by calcination is hollowed out, a plurality of micropores (or a hollow core portion inside the particle) are formed on the particle surface of the composite particle.

  As described above, in the production method disclosed herein, by removing the components constituting the polymer particles from the aggregate, a plurality of fine pores are formed on the surface of the composite particles, or a hollow core portion is formed inside the composite particles. Form. The shape of these pores can be controlled by adjusting the zeta potential of each particle in the dispersion. The zeta potential can be adjusted by adjusting the pH of the dispersion. Hereinafter, control of the shape of the holes by adjusting the zeta potential will be described.

Here, first, the case where the signs of the zeta potentials of the metal oxide particles, the oxide ion conductor particles, and the polymer particles are made equal will be described. In order to equalize the sign of the zeta potential of each particle, the pH of the dispersion may be adjusted within the range of pH 1 to pH 6.8 (preferably pH 1 to pH 4, more preferably pH 3 to pH 4). In order to adjust the pH of the dispersion within the numerical range, an acidic solution (for example, nitric acid, sulfuric acid, hydrochloric acid, etc.) generally used for pH adjustment is added to the dispersion. Thus, when the signs of the zeta potentials of the metal oxide particles, the oxide ion conductor particles, and the polymer particles are equalized, composite particles having a plurality of micropores formed on the surface can be obtained.
About obtaining composite particles in which micropores are formed, it is presumed as follows. When the signs of the zeta potentials of the particles become equal, the metal oxide particles, oxide ion conductor particles, and polymer particles repel each other in the dispersion. When the dispersion liquid droplets are heated in this state to remove the dispersion medium from the droplets, an aggregate in which the particles including the polymer particles are distributed almost evenly is formed. And when this aggregate is baked, the component which comprises the polymer particle distributed uniformly in the whole aggregate will come out of the aggregate, opening a fine hole in the surface of the aggregate. Thereby, it is considered that composite particles having a plurality of fine pores formed on the surface can be obtained.

The structure of the “composite particles having a plurality of fine pores formed on the surface” obtained as described above will be described.
The composite particles include metal oxide particles and oxide ion conductor particles, and the metal oxide particles and the oxide ion conductor particles are distributed almost evenly. Here, the metal oxide particles and the oxide ion conductor particles are “almost uniformly distributed” means that in the element mapping on the surface of the composite particle, the area where nickel is mapped is mapped to zirconium. The value (Ni / Zr) divided by the area is 0.5 to 1.5 (preferably 0.8 to 1.2, more preferably 0.9 to 1.1).

The average particle size of the composite particles may be 4 μm to 10 μm, preferably 5 μm to 8 μm, and more preferably 6 μm to 7 μm. The shape of the composite particle is typically a substantially spherical shape. Here, the “substantially spherical shape” in the present specification is a shape including a spherical shape, a rugby ball shape, a polygonal shape, etc., and its major axis / minor axis is preferably 2/1 to 1/1, typically Is 1.5 / 1 to 1/1, and can take a shape close to a true sphere (major axis / minor axis = 1/1).
Further, as described above, a plurality of fine holes are formed on the surface of the composite particle. Although not particularly limited, it is preferable that the fine pores are formed approximately 20 to 300, typically 50 to 250, for example, about 100 to 200 per particle.
The average pore diameter of the fine pores can be changed as appropriate by adjusting the average particle diameter of the polymer particles dispersed in the dispersion. Specifically, the average pore diameter of the micropores (average value calculated based on observation with an electron microscope; the same shall apply hereinafter) is 10 nm to 500 nm, preferably 50 nm to 200 nm, more preferably about 75 nm to 150 nm. .
The porosity of the composite particles is about 50% to 95% (preferably 55% to 80%, more preferably 55% to 70%). The porosity is a value based on the result measured by mercury porosimetry.

  Next, the pH of the dispersion is adjusted so that the zeta potential of any one of the metal oxide particles, oxide ion conductor particles, and polymer particles is different from the zeta potential of the other two particles. The case will be described. The particles whose zeta potential has a different sign from other particles may be any of the particles dispersed in the dispersion. In the following, for the convenience of explanation, the case where the pH of the dispersion is adjusted so that the zeta potential of the oxide ion conductor particles is different from the zeta potential of other particles (metal oxide particles, polymer particles) will be described. To do.

  In order to make the zeta potential of the oxide ion conductor particles different from the zeta potential of other particles, the pH of the dispersion is pH 7 to pH 14 (preferably pH 7 to pH 10, more preferably pH 8 to pH 9.5). Adjust within the range. In order to adjust the pH of the dispersion within the numerical range, an alkaline solution generally used for pH adjustment (for example, aqueous ammonia, aqueous sodium hydroxide, aqueous potassium hydroxide, etc.) is added to the dispersion. Thus, when the zeta potential of the oxide ion conductor particles is different from the zeta potential of the other particles, the oxide ion conductor particles are composed of a hollow core portion and a shell portion surrounding the hollow core portion. In the portion, composite particles in which the metal oxide particles and the oxide ion conductor particles are almost uniformly distributed are obtained.

About obtaining composite particles having a hollow core, it is presumed as follows.
When the zeta potential of any one kind of particles in the dispersion becomes different from the zeta potential of the other two kinds of particles, the other particles are attracted to the one kind of particles. When the dispersion medium is removed from the dispersion in this state, polymer particles are distributed in the center, and aggregates in which metal oxide particles and oxide ion conductor particles are distributed so as to surround the polymer particles are formed. When this aggregate is fired, the polymer particle components distributed in the central portion of the aggregate are released outside the aggregate while forming fine holes in the surface of the aggregate to form a hollow core portion. Thereby, composite particles composed of a hollow core part and a shell part surrounding the hollow core part are obtained. Although not particularly limited, when polymer particles having a larger average particle size than other particles (metal oxide particles, oxide ion conductor particles) are used, the polymer particles are distributed in the center of the aggregate. Therefore, composite particles in which a hollow core portion having a more suitable shape is formed can be easily obtained.

The structure of “composite particles composed of a hollow core part and a shell part” obtained as described above will be described.
In addition, regarding the composition other than the hollow core part and the shell part regarding the composite particles (distribution state of metal oxide particles and oxide ion conductor particles, average particle diameter, shape of the whole particle, etc.), already described above. Since it is equivalent to “composite particles in which a plurality of micropores are formed”, the description is omitted.

  The hollow core portion is an internal space formed inside the composite particle. Although the present invention is not particularly limited, the shape of the hollow core portion is preferably substantially spherical. When the shape of the hollow core part is substantially spherical, the average diameter of the hollow core part is about 1 μm to 5 μm, preferably about 3 μm to 4.5 μm, more preferably about 3.5 μm to 4 μm. The porosity of the composite particles is about 70% to 95% (preferably 75% to 90%, more preferably 75% to 80%). Here, the average diameter and porosity of the hollow core portion are calculated based on the result of measuring the pores formed in the composite particles by mercury porosimetry.

The shell part is formed so as to surround the hollow core part. The shell portion is composed of metal oxide particles and oxide ion conductor particles, and the metal oxide particles and oxide ion conductor particles are dispersed almost uniformly in the shell portion. In addition, the shell portion is formed with fine holes that allow the hollow core portion to communicate with the outside world. Further, a plurality of depressions are formed on the surface of the shell portion on the outside world side.
The thickness of the shell portion is about 1 μm to 9 μm, preferably about 2 μm to 5 μm, and more preferably about 2.5 μm to 4 μm.
The fine pores formed in the shell portion are preferably formed in a number of approximately 1 to 30, typically 1 to 20, for example, 1 to 10 per particle. The average pore diameter of the micropores formed in the shell portion is 10 nm to 500 nm, preferably 50 nm to 200 nm, more preferably about 75 nm to 150 nm.
In addition, the depressions formed in the shell portion may be formed approximately 20 to 300, typically 50 to 250, for example, about 100 to 200 per particle.

  The composite particles produced by the above production method are used as a material for SOFC fuel electrodes. Hereinafter, an SOFC configured using the composite particles as a fuel electrode material will be described with reference to FIG. FIG. 1 is a cross-sectional view of an SOFC including an anode-supported cell and a gas pipe joined to the cell. In the drawings, members / parts having the same action are denoted by the same reference numerals, but the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect actual dimensional relationships.

  The SOFC 100 disclosed herein includes, for example, a fuel cell (hereinafter simply referred to as “cell”) 50 including a fuel electrode 10, an air electrode 20, and a solid electrolyte membrane 30. The cell 50 may be manufactured according to a conventional manufacturing method and does not require special processing. That is, the fuel electrode 10, the air electrode 20, and the solid electrolyte membrane 30 which are constituent members of the cell 50 disclosed here can be formed by various methods conventionally used.

  The fuel electrode 10 is a porous body containing a composite particle material composed of the above composite particles as a main component and a binder as another additive material. Note that the “composite particle material” includes a plurality of “composite particles having a plurality of fine pores formed on the surface” and “composite particles composed of a hollow core portion and a shell portion” (or its composite particles). Refers to a material that is a mixture of both. In the SOFC 100 disclosed herein, the solid electrolyte membrane 30 is laminated on the fuel electrode 10.

As described above, the solid electrolyte membrane 30 can be made of the same metal compound as the oxide ion conductor particles of the composite particles obtained by the above-described manufacturing method. As the metal compound, for example, oxides such as zirconium (Zr), cerium (Ce), lanthanum (La), gallium (Ga) can be used, and among these, zirconia (zirconium dioxide: ZrO) which is an oxide of zirconium. ₂ ) can be preferably used. Furthermore, as the oxide ion conductor particles, stabilized zirconia particles in which the crystal structure is stabilized by dissolving a rare earth oxide in the zirconia can be preferably used. Among these stabilized zirconia, yttria-stabilized zirconia (YSZ) in which yttrium (Y) oxide is dissolved, scandia-stabilized zirconia (ScSZ) in which scandium (Sc) oxide is dissolved, and the like are particularly used. It can be preferably used. Here, the solid electrolyte 20 is laminated on the fuel electrode 10, and the air electrode 20 is laminated on the solid electrolysis chamber 30.

The air electrode 20 may be the same as that used in a conventional fuel cell, and is not particularly limited. As the air electrode 20, a lanthanum cobaltate (LaCoO ₃ ) -based or lanthanum manganate (LaMnO ₃ ) -based perovskite oxide is preferably employed. Each of the porous bodies made of these materials can be used as the air electrode 20.

The cell 50 provided with the said structure can be constructed | assembled as follows, for example.
First, the fuel electrode 10 is produced as a support base (support). In order to produce the fuel electrode 10, first, the composite particle material and other additive materials (for example, a binder and a dispersant) are mixed together with a solvent to prepare a slurry-like fuel electrode molding material. Next, using this molding material, a molded body of the fuel electrode 10 is produced by, for example, extrusion molding. Here, the shape of the molded body of the fuel electrode 10 may be a sheet shape (or a flat plate shape), a hollow box shape having a hollow portion (gas flow path) for allowing fuel gas to flow into the fuel electrode, or Examples thereof include a hollow flat shape (flat tubular shape). In FIG. 1, a sheet-like fuel electrode 10 is formed.

  Next, a material for the solid electrolyte membrane 30 is prepared. That is, a predetermined material (for example, YSZ powder having an average particle size of about 0.1 μm to 10 μm, a binder, a dispersant, and a solvent) is mixed to prepare a molding material for the solid electrolyte membrane 30 in the form of a slurry (paste). The molding material for the solid electrolyte membrane 30 is printed and formed on the fuel electrode 10 at a film thickness of 100 μm or less (typically 1 μm to 100 μm, preferably 10 μm to 100 μm, for example, 10 μm to 50 μm). The solid electrolyte membrane 30 is formed. The solid electrolyte membrane 30 supported by the fuel electrode 10 is dried and then fired at a firing temperature of 1200 ° C. to 1400 ° C. in the atmosphere. As a result, a dense solid electrolyte membrane 30 is formed on the fuel electrode 10.

Next, a material for the air electrode 20 is prepared. That is, a slurry-like molding material for the air electrode 20 made of a predetermined material (for example, LaSrO ₃ powder having an average particle diameter of about 1 μm to 10 μm, a binder, a dispersant, and a solvent) is prepared. The molding material for the air electrode 20 is printed and formed on the surface of the solid electrolyte membrane 30 at a film thickness of 100 μm or less (typically 1 μm to 100 μm, preferably 10 μm to 100 μm, for example 10 μm to 50 μm). An air electrode layer (film) 20 is formed. After drying this, it is fired at a firing temperature of 1000 ° C. to 1200 ° C. in the air. In this way, the air electrode 20 is formed on the solid electrolyte membrane 30.
Through the above steps, the anode-supported cell 50 having a structure in which the fuel electrode 10, the solid electrolyte membrane 30, and the air electrode 20 are stacked in this order is formed.

Next, a gas pipe 40 for supplying fuel gas is connected to the cell 50. For example, the gas pipe 40 may be formed of a dense body made of the same material as the solid electrolyte membrane 30, or may be made of SUS430 metal commercially available for SOFC. The shape and size of the gas pipe 40 are appropriately set according to the size of the connected cell (stack) and the size of the joint portion.
When the gas pipe 40 is connected to the cell 50, as shown in FIG. 1, the connection is made in a state where one connecting surface 12 of the fuel electrode 10 and the end face 42 of the gas pipe 40 are in contact with each other. The bonding material 60 is applied so as to cover the contact surface (bonding surface). Furthermore, it is preferable to apply the bonding material 60 so as to extend beyond the contact surface to the end with the solid electrolyte membrane 30. At this time, the bonding material 60 is preferably applied so as to prevent the fuel electrode 10, which is a porous member, from being exposed to the outside by closing the gap between the gas pipe 40 and the solid electrolyte membrane 30. The same applies to the other connecting surface. By providing the bonding material 60 in this manner, a gap (that is, a part of the porous fuel electrode 10 that can be exposed) that may occur at the bonding portion between the solid electrolyte membrane 30 and the gas pipe 40 is completely formed by the bonding material 60. It is blocked. In such a state, the joining portion 62 is formed by firing in a temperature range (for example, about 800 ° C. to 900 ° C.) in which the joining material 60 does not flow out from the joining portion, and the gas pipe 40 and the cell 50 are joined and connected. By doing so, the SOFC 100 is constructed.

When the SOFC 100 generates power, air (oxygen gas) is supplied around the air electrode 20, and fuel gas (hydrogen, methane, ethane, etc.) is supplied to the fuel electrode 10 through the gas pipe 40. Thereby, on the air electrode 20 side, the supplied oxygen reaches the vicinity of the interface with the solid electrolyte membrane 30 through the air electrode 20 and is ionized into oxide ions (O ²⁻ ). The oxide ions move to the fuel electrode 10 side through the solid electrolyte membrane 30. In the fuel electrode 10, the interface of the metal oxide particles constituting the composite particles, the interface of the oxide ion conductor particles (or the solid electrolyte membrane 30), and the vacancies (composites in the composite particle material) to which fuel gas can be supplied. Oxide ions and fuel gas react at a three-phase interface composed of a gap between particles or an interface of a fine particle or a hollow core part of the composite particle). By this reaction, electrons are emitted while reaction products (H ₂ O, CO _2, etc.) are generated on the fuel electrode 10 side. Electrons generated by this electrode reaction are taken out as an electromotive force at an external load on another route. In the SOFC 100 disclosed here, the output characteristics are improved because the three-phase interface in the fuel electrode 10 is increased as compared with the conventional one.

Hereinabove, the composite particle and the manufacturing method thereof according to an embodiment of the present invention have been described. The above manufacturing method can be easily implemented by using an apparatus 1000 as shown in FIG. The following configuration of the apparatus 1000 does not limit the present invention.
Broadly speaking, the apparatus 1000 includes a spray unit 110 that sprays the dispersion liquid L, a chamber 120 that removes the dispersion medium from the droplets by heating the droplets of the dispersion liquid, and the dispersion medium is removed. The collection part 130 which collects the aggregate formed by this, and the baking furnace 140 which bakes the aggregate collected by the collection part 130 are comprised.

The spray unit 110 is a member for spraying the dispersion liquid L in the chamber 120 as mist droplets. The spray unit 110 shown in FIG. 2 includes a two-fluid nozzle 112 that sprays the dispersion L by blowing out carrier gas at a high pressure, and a gas supply unit 114 that supplies the carrier gas to the two-fluid nozzle 112. . As the two-fluid nozzle 112, a conventionally known device (for example, mini spray dryer B-290 manufactured by BUCHI) can be used. For example, a nozzle having a nozzle tip diameter of 200 μm to 600 μm (for example 400 μm) is preferable. . The gas supply unit 114 is preferably capable of supplying the carrier gas at a flow rate of 3 L / min to 10 L / min, for example. The carrier gas supplied from the gas supply unit 114 is an inert gas (eg, nitrogen (N ₂ ), argon (Ar), helium (He), etc.) or an oxidizing gas (eg, oxygen gas (particularly preferably). Air)). The spray unit 110 is connected to the chamber 120 so that droplets sprayed by the two-fluid nozzle 112 can be supplied into the chamber 120.

  The chamber 120 is a member for heating the sprayed droplets inside. The chamber 120 shown in FIG. 2 is a cylindrical part having an internal cavity, and one end in the longitudinal direction is connected to the two-fluid nozzle 112 and the other end is connected to a collection unit 130 described later. . Although not particularly limited, it is appropriate that the chamber 120 has a capacity of about 0.4 L to 3 L as a whole. For example, a chamber having a capacity of about 0.9 L is preferably used. Can do. Moreover, the diameter of the transport pipe 122 is suitably about 5 mm to 20 mm, and more preferably about 13 mm.

  A heated carrier gas is supplied into the chamber 120. Here, a gas supply line 122 is attached to the chamber 120, and the gas supply line 122 is connected to the gas supply unit 114 without going through the two-fluid nozzle 112. In addition, a heater 124 is attached to the gas supply line 122, and the carrier gas passing through the gas supply line 122 is heated by the heater 124 and then supplied into the chamber 120. A conventionally known electric heating device or the like can be used for the heater 124. The heater 124 can heat the carrier gas to a temperature range of 100 ° C. to 400 ° C. (typically 100 ° C. to 200 ° C.).

  Furthermore, in the apparatus 1000 disclosed here, the collection unit 130 is provided downstream of the chamber 120. The collection unit 130 includes a dust collector 132 and a drain separator 134. The dust collector 132 is provided to collect a relatively small particle size of the aggregates formed in the chamber 120. On the other hand, the drain separator 134 is provided to collect a relatively large particle size among the aggregates. In the apparatus 1000 disclosed herein, aggregates collected by the dust collector 132 and the drain separator 134 are stored in the containers 132a and 134a, respectively.

The firing furnace 140 is a member for firing the aggregate obtained by the collection unit 130. The firing furnace 140 accommodates and heats the aggregate in the interior. The temperature in the firing furnace 140 at this time is 400 to 1100 ° C., preferably 500 to 1000 ° C., for example, about 700 ° C. The firing furnace 140 is connected to the heating gas supply unit 142, and the atmosphere in the firing furnace 140 can be adjusted by the type of heating gas supplied from the heating gas supply unit 142. As the heating gas, an inert gas (eg, nitrogen (N ₂ ), argon (Ar), helium (He), or the like) or an oxidizing gas (eg, oxygen gas (particularly preferably air)) can be used.

A procedure for performing the above-described manufacturing method using the apparatus 1000 will be described. First, the dispersion liquid L and the carrier gas are supplied to the two-fluid nozzle 112 of the spray unit 110. Thus, in the two-fluid nozzle 112, the dispersion liquid L collides with the high-pressure carrier gas, and the dispersion liquid L is sprayed into the chamber 120 as mist-like droplets. At this time, a high-temperature carrier gas heated by the heater 124 is supplied into the chamber 120 through the gas supply line 122. Thereby, the droplets of the dispersion liquid pass through the chamber 122 while being heated by the high-temperature carrier gas. As a result, the dispersion medium is removed from the droplets of the dispersion to form an aggregate. The aggregate is transferred to the collection unit 130 while staying in the chamber 122. Among the formed aggregates, a large particle size is collected by the drain separator 134, and a small particle size is collected by the dust collector 132.
Next, the aggregates collected by the drain separator 134 and / or the dust collector 132 are accommodated in the firing furnace 140 and fired. At this time, in order to obtain composite particles having a relatively large particle size, the aggregate collected by the drain separator 134 may be used, and in order to obtain composite particles having a small particle size, the dust collector 132 may be used. The collected aggregate may be used.
When the aggregate is fired in the firing furnace 140, the polymer component is removed from the aggregate. As a result, composite particles in which the metal oxide particles and the oxide ion conductor particles are substantially evenly distributed and a plurality of micropores (or hollow core portions inside) are formed on the surface are obtained. Thus, if the apparatus 1000 is used, the above-described method for producing composite particles can be easily performed.

  EXAMPLES Next, examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the following examples. In the following examples, composite particles (samples 1 to 5) prepared by different processes were prepared.

Nickel oxide (NiO) having an average particle diameter of 7 nm was prepared as metal oxide particles, and the nickel oxide was suspended in pure water to prepare a 5 mass% NiO suspension. Then, yttria-stabilized zirconia (YSZ) having an average particle diameter of 2 nm was prepared as oxide ion conductor particles, and the YSZ was suspended in pure water to prepare a 5 mass% YSZ suspension.
Next, polystyrene latex particles (PSL particles) having an average particle size of 300 nm were prepared as polymer particles. The PSL particles were prepared by adding 27 ml of styrene to 120 ml of pure water heated to 80 ° C. in a nitrogen atmosphere, adding 2-methylpropinoamidine to the mixture, and adding nitrogen until the average particle size became 0.3 μm. It was produced by allowing the reaction to proceed under an atmosphere. Then, the PSL particles were suspended in pure water to prepare a 10 mass% PSL suspension.
Here, in sample 1, nitric acid (HNO ₃ ) was added to the suspension of each particle (NiO, YSZ, PSL particle) to adjust the pH of each suspension to 1.7.

  Next, the 5 mass% NiO suspension, the 5 mass% YSZ suspension, and the 10 mass% PSL suspension were mixed, and 125 ml of pure water was further added while performing ultrasonic homogenization to prepare a dispersion L.

  Next, the dispersion liquid was sprayed into the chamber 120 as mist droplets using an apparatus 1000 as shown in FIG. At this time, the carrier gas supplied to the two-fluid nozzle 112 is set to air (flow rate: 5 L / min), and the dispersion is sprayed into the chamber 120 so as to form mist droplets having a droplet diameter of 2 μm to 5 μm. did.

  Next, the dispersion liquid droplets were heated in the chamber 120. Here, granulation is performed by a so-called spray drying method in which the sprayed droplets are heated by supplying the carrier gas (air) heated by the heater 124 into the chamber 120. As a result, the dispersion medium in the droplets was removed, and an aggregate containing NiO, YSZ, and PSL particles was obtained. And the said aggregate was collected with the dust collector 132 of the collection part 130. FIG. Next, the aggregates collected by the collection unit 130 were accommodated in the firing furnace 140 and fired at 700 ° C. for 1 hour. As a result, the PSL particles were removed from the aggregate, and composite particles composed of NiO and YSZ were obtained. Hereinafter, the composite particle obtained here is referred to as “sample 1”.

<Sample 2>
Here, composite particles were obtained through the same process as Sample 1 except that nitric acid (HNO ₃ ) was added to the suspension of each particle to adjust the pH to 3.7. The composite particle obtained here is referred to as “Sample 2”.

<Sample 3>
Here, composite particles were obtained through the same process as Sample 1 except that nitric acid (HNO ₃ ) was added to the suspension of each particle to adjust the pH to 5.7. The composite particle obtained here is referred to as “Sample 3”.

<Sample 4>
Here, composite particles were obtained through the same process as Sample 1 except that the dispersion L (pH 7.7) was adjusted without adjusting the pH of the suspension of each particle. The composite particle obtained here is referred to as “Sample 4”.

<Sample 5>
Here, ammonia water (HH ₄ ⁺ ) was added to the suspension of each particle, and the pH of the suspension of each particle was adjusted to 9.7. Composite particles were obtained. The composite particle obtained here is referred to as “Sample 5”.

  The production conditions of Samples 1 to 5 are summarized in Table 1 below.

<SEM observation of samples 1 to 5>
Samples 1 to 5 were observed with a scanning electron microscope (FE-SEM, Hitachi, S3100H, S5000). SEM photographs of the observation results are shown in FIGS. 3 is an SEM photograph of Sample 1, FIG. 4 is Sample 2, FIG. 5 is Sample 3, FIG. 6 is Sample 4, and FIG.

  When the particle shapes of Samples 1 to 5 were compared, in the composite particles (Samples 1 to 3) in which the pH of the dispersion L was adjusted to be low, a large number of micropores were formed on the particle surface. On the other hand, in the composite particles (samples 4 and 5) produced from the dispersion L having a relatively high pH, a depression was formed on the particle surface (shell portion) instead of the fine holes. When these Samples 4 and 5 were observed with TEM, FE-SEM, or the like, it was confirmed that the inside of the particles was hollow and a hollow core portion was formed.

<Measurement of zeta potential of samples 1 to 5>
In addition, for each sample 1 to 5, an appropriate amount of a suspension of each particle before the dispersion L is prepared, and the zeta of NiO, YSZ, and PSL particles dispersed in the suspension of each particle. The potential was measured. Here, the surface charge of the particles in each suspension was measured using a zeta potential measuring device (Malvern Instruments Ltd, Zetasizer, Nano series, ZEN2600), and the zeta potential was measured using laser Doppler electrophoresis. Laser Doppler electrophoresis is the measurement of particle mobility, electric field strength, dispersion viscosity, and dielectric constant when an electric field is applied to a dispersion of particles to be measured. It is a method of measuring. The result of the measurement is shown in FIG.

As shown in FIG. 8, in samples 1 to 3 whose pH was adjusted to be acidic, the sign of the zeta potential of each particle in the dispersion was +, and the value was also approximate. On the other hand, in the samples 4 and 5 adjusted to be neutral to alkaline, the sign of the zeta potential of YSZ was −.
From the above, when the pH of the dispersion before being provided for spray drying is adjusted to acidic (here, pH 1 to pH 4), the sign of the zeta potential of each particle in the dispersion becomes equal, and there are many fine pores on the surface. It was found that formed composite particles were obtained. On the other hand, when the pH of the dispersion was adjusted to neutral to alkaline (here, pH 7 to pH 10), only the zeta potential of the YSZ particles became (−) in the dispersion, resulting in a different sign from the other two types of particles. It was found that composite particles composed of a hollow core part and a shell part surrounding the hollow core part were obtained.

<HR-TEM observation of sample 2>
Next, sample 2 was observed with a high-resolution transmission electron microscope (HR-TEM) in order to observe the composite particles further enlarged than the above-described SEM. The observation results are shown in FIG.

  As shown in FIG. 9, the sample 2 was formed with elliptical micropores having a major axis of about 140 nm. In addition, nickel particles and zirconia particles were distributed almost uniformly around the micropores. That is, it can be seen that a number of three-phase interfaces where nickel, zirconia, and fuel gas are in contact are formed around the micropores of sample 2.

Next, a mercury porosimeter was applied to sample 2, and the pore diameter of the micropores formed in sample 2 and the porosity in sample 2 were measured. The measurement results are shown in FIG. The vertical axis on the right side of this graph represents “differential pore volume” and corresponds to plot A. The vertical axis on the left side indicates “integrated pore diameter volume” and corresponds to plot B.
According to the plot A (differential pore volume) of this graph (FIG. 10), the composite particles of sample 2 have many fine pores having a pore diameter of 0.3 μm to 7.0 μm, and in particular, the pore size is 0.8. It was found that many 3 μm fine holes were formed. From this, it was found that in sample 2, a large number of micropores having the same pore size as the average particle size (0.3 μm) of the PSL particles added to the dispersion were formed.
As a result of calculation based on the “integrated pore diameter volume” of plot B, the porosity of sample 2 was 70% or more. From this, it was found that a large number of micropores were formed in the sample 2 as in the above-described observation results by TEM and FE-SEM.

<Distribution of constituent elements of sample 2>
Next, the distribution of elements constituting Sample 2 was examined. Here, a TEM photograph of sample 2 was taken, energy dispersive X-ray spectrum analysis, and elemental mapping of zirconium and nickel were performed. The measurement results are shown in FIG. 11A is an SEM photograph, FIG. 11B is a TEM photograph, FIG. 11C is a result of energy dispersive X-ray spectrum analysis, and FIG. 11D is a result of element mapping.
As shown in FIG. 11C, when energy dispersive X-ray spectrum analysis was performed on sample 2, it was found that sample 2 contained a large amount of nickel element and zirconium element. It can be inferred that the nickel element is derived from nickel oxide (NiO) as metal oxide particles, and the zirconium element is derived from yttria-stabilized zirconia (YSZ) as oxide ion conductor particles.

Next, from the result of element mapping (see FIG. 11D), in Sample 2, the nickel element and the zirconium element were distributed almost uniformly throughout the particle. From this, it was found that in the composite particles of Sample 2, NiO and YSZ were distributed almost evenly.
Moreover, as a result of calculating a value (Ni / Zr) obtained by dividing the area where the nickel element is distributed by the area where the zirconium element is distributed, the Ni / Zr value of the composite particle of Sample 2 is 0.8 to It was within the range of 1.2.

<Evaluation of SOFC battery performance using Sample 2>
Next, a test SOFC cell A was constructed using the composite particles of Sample 2 as the fuel electrode material, and the battery characteristics were examined. Here, cells B and C were also constructed as comparative examples for cell A, and the battery characteristics were examined.

<Cell A>
Here, 10 g of sample 2 and 0.6 g of methylcellulose binder were dispersed in 4 ml of water to prepare a slurry-like molding material for fuel electrode. And after printing the said molding material for fuel electrodes on the surface of the yttria stabilized zirconia (8YSZ disk: 25mm * 1mm) as a solid electrolyte using a screen printing method, it baked in air | atmosphere (1100 degreeC, 2 hours) ) To form a fuel electrode.

In addition, a slurry-like air electrode molding material composed of LaSrO ₃ powder (LSM) having an average particle size of about 1 μm to 10 μm, a binder, a dispersant, and a solvent) is printed on the back side of the solid electrolyte, and then fired in an air atmosphere. The air electrode was formed by performing (1000 degreeC, 4 hours). Thus, a test SOFC cell A composed of a fuel electrode, an air electrode, and a solid electrolyte membrane was constructed.

<Cell B>
In the cell B, instead of using the sample 2 as the material for the fuel electrode, a powder obtained by mixing NiO powder (average particle size 3 μm) and YSZ powder (average particle size 0.3 μm) at 6: 4 was used. In constructing the cell B, the same process as the cell A was performed except that the above-mentioned powder was used as the material of the fuel electrode.

<Cell C>
In cell C, a powder obtained by mixing NiO powder (average particle size 3 μm) and scandia-stabilized zirconia (10ScSZ) powder (average particle size 0.6 μm) at a ratio of 6: 4 was used instead of sample 2. The 10ScSZ powder has a higher ionic conductivity than the above-described YSZ powder and can increase the output density of SOFC, but has a feature that it is inferior in cost compared to the YSZ powder. The cell C is also constructed by the same process as the cell A except that the above powder is used as the material for the fuel electrode.

<Measurement of relative power density of cells A to C>
The power density of each of the SOFC cells A to C constructed as described above was measured. Specifically, while maintaining the cell temperature at 800 ° C., fuel gas (humidified hydrogen gas) was supplied to the fuel electrode and air was supplied to the air electrode to generate power in each of the cells A to C. Then, the current value when the voltage was 0.7 V was measured, and the maximum output density when the current value when the voltage was 0.7 V was used as a reference. Next, cell B was selected as a reference cell, and the maximum output densities of cells A and C relative to the maximum output density of cell B were relatively compared. The value at this time was defined as “relative output density”, the “relative output density” of cell B was set to 100, and the “relative output density” of cells A and C was calculated. Table 2 shows the calculation results.

As shown in Table 2, the cell A had a relatively higher power density than the cell B. Therefore, even when the same kind of metal oxide particles (NiO particles) and oxide ion conductor particles (YSZ particles) are used as the material for the fuel electrode, the composite particles disclosed here are used. It was found that higher power density can be obtained.
When cell A and cell C are compared, cell C uses oxide ion conductor particles (10 ScSZ) having higher ionic conductivity than cell A as the material for the fuel electrode. However, the power density was higher than that of the cell C. From this, it was found that when the fuel electrode is constituted by using the composite particles disclosed herein, the output density of SOFC can be greatly improved without using a high-cost oxide ion conductor.

  The composite particles produced by the production method disclosed herein can be used as a fuel electrode material for SOFC. At this time, the number of three-phase interfaces in the fuel electrode can be increased, and the output characteristics of the SOFC can be greatly improved.

DESCRIPTION OF SYMBOLS 10 Fuel electrode 20 Air electrode 30 Solid electrolyte membrane 40 Gas pipe 50 Cell 100 Solid oxide fuel cell (SOFC)
DESCRIPTION OF SYMBOLS 110 Spray part 112 Two-fluid nozzle 114 Gas supply unit 120 Chamber 122 Gas supply line 124 Heater 130 Collection part 132 Dust collector 134 Drain separator 140 Firing furnace 142 Heating gas supply unit

Claims (13)

A method for producing composite particles comprising metal oxide particles functioning as a catalyst and oxide ion conductor particles and used as a material for a fuel electrode of a solid oxide fuel cell,
Preparing a dispersion in which the metal oxide particles and the oxide ion conductor particles are dispersed in a dispersion medium together with polymer particles mainly composed of organic polymer compounds that are decomposed and evaporated by heating ;
Spraying the dispersion into the chamber as droplets;
Aggregates formed by heating the droplets in the chamber to remove the dispersion medium from the dispersion and agglomerating the metal oxide particles, the oxide ion conductor particles, and the polymer particles. To obtain;
Firing the agglomerates to remove the components constituting the polymer particles to obtain composite particles;
It encompasses,
Here, the pH of the dispersion is adjusted so that the signs of the zeta potentials of the metal oxide particles, the oxide ion conductor particles, and the polymer particles are equal, and the pH-adjusted dispersion is adjusted in the chamber. The manufacturing method characterized by spraying . The pH of the dispersion is adjusted to PH1～pH4, The method according to claim 1. A method for producing composite particles comprising metal oxide particles functioning as a catalyst and oxide ion conductor particles and used as a material for a fuel electrode of a solid oxide fuel cell,
Preparing a dispersion in which the metal oxide particles and the oxide ion conductor particles are dispersed in a dispersion medium together with polymer particles mainly composed of organic polymer compounds that are decomposed and evaporated by heating;
Spraying the dispersion into the chamber as droplets;
Aggregates formed by heating the droplets in the chamber to remove the dispersion medium from the dispersion and agglomerating the metal oxide particles, the oxide ion conductor particles, and the polymer particles. To obtain;
Firing the agglomerates to remove the components constituting the polymer particles to obtain composite particles;
Including
Here, the pH of the dispersion is different from the zeta potential of any one of the metal oxide particles, the oxide ion conductor particles, and the polymer particles. adjusted to, characterized by spraying the pH adjusted dispersion into the chamber method. The manufacturing method of Claim 3 which adjusts pH of the said dispersion liquid to pH7-pH10. The production method according to any one of claims 1 to 4 , wherein polymer particles having an average particle diameter of 50 nm to 500 nm are used as the polymer particles. The manufacturing method according to any one of claims 1 to 5 , wherein metal oxide particles having an average particle diameter of 1 nm to 50 nm are used as the metal oxide particles. The manufacturing method as described in any one of Claims 1-6 which uses the oxide ion conductor particle whose average particle diameter is 1 nm-50 nm as said oxide ion conductor particle. The dispersions are prepared wherein such mass ratio M / C of the metal oxide particles to oxide ion conductor particles (C) (M) is within the range of 0.5 to 3, claim 1-7 The manufacturing method as described in any one of these. The manufacturing method according to any one of claims 1 to 8 , wherein nickel oxide particles are used as the metal oxide particles. The manufacturing method according to any one of claims 1 to 9 , wherein zirconia particles are used as the oxide ion conductor particles. Composite particles used for a fuel electrode of a solid oxide fuel cell,
Including metal oxide particles and oxide ion conductor particles that function as a catalyst,
The metal oxide particles and the oxide ion conductor particles are distributed almost evenly,
A composite particle in which a plurality of micropores are formed on a surface, and the porosity of the composite particle is 50% to 95% . The composite particles according to claim 11 , wherein the average pore diameter of the micropores is 10 nm to 500 nm. A solid oxide fuel cell comprising the composite particle according to claim 11 as a fuel electrode.