JP5655032B2 - Solid oxide fuel cell and cathode forming material of the fuel cell - Google Patents

Description

  The present invention relates to a material used for forming a cathode (air electrode) of a solid oxide fuel cell, and a solid oxide fuel cell constructed using the material.

A solid oxide fuel cell (SOFC; hereinafter simply referred to as “SOFC”) has high power generation efficiency among various types of fuel cells and can use various fuels. Development is progressing as a next-generation power generator with low environmental impact.
Such a SOFC (single cell) typically has a porous cathode (air electrode) formed on one surface of a dense solid electrolyte made of an oxygen ion conductor (for example, an oxygen ion conductive ceramic body). In this configuration, a porous anode (fuel electrode) is formed on the other surface. In use, an oxygen (O ₂ ) -containing gas (typically air) is present on the surface of the solid electrolyte on the side where the cathode is formed, and a fuel gas (typically on the surface of the solid electrolyte on the side where the anode is formed). Are each supplied with hydrogen (H ₂ )). When an electric current is applied to the SOFC supplied with the gas, oxygen is first oxidized at the cathode to become oxygen ions. Then, the oxygen ions reach the anode (via the solid electrolyte), react with the fuel gas, and emit electrons to generate electricity.

  The SOFC power generation is generally performed in a high temperature environment of about 800 ° C. to 1200 ° C. in order to achieve high power generation performance. However, since the constituent materials are likely to deteriorate under such a temperature environment, there has been a problem with the durability of the SOFC. In addition, there are also problems for practical use such as a long time for starting and stopping, and a limitation of materials that can be used in a high temperature environment, which tends to increase the manufacturing cost.

Therefore, in recent years, research for lowering the operating temperature of SOFC, for example, from 500 ° C. to 800 ° C. (hereinafter referred to as “medium temperature”) has been promoted from the viewpoints of improving durability, reducing costs, and expanding use applications. It has been. However, when the operating temperature is lowered, the resistance of the solid electrolyte is increased accordingly, and the power generation performance is lowered.
As a conventional technique for dealing with such a problem, for example, Patent Document 1 discloses that by controlling the anode structure (porosity), the reaction efficiency in the anode can be improved and the power generation performance of the SOFC can be improved. ing. Patent Document 2 discloses that the reaction efficiency in the anode can be improved and the power generation performance of SOFC can be improved by controlling the average particle diameter of the material (particles) constituting the anode.

JP 2004-200125 A JP 2007-103077 A

By the way, as a cathode material capable of exhibiting high reactivity (catalytic ability) even at medium and low temperatures, for example, a so-called electron − represented by a general formula: (LaSr) (CoFe) O ₃ (hereinafter referred to as “LSCF”) is used. Oxygen ion mixed conductors are known. However, since the LSCF has a larger thermal expansion than other cathode materials, the thermal shock (for example, the temperature at the time of stopping (typically normal temperature) and the temperature range during use (for example, 500 ° C. to 800 ° C.) Therefore, there is a demand for improvement in durability against repeated heating and cooling. In addition, since LSCF has a large reductive expansion compared to other cathode materials, for example, when fuel gas leaks and enters the cathode side, defects such as cracks may occur. In such a case, there is a possibility that the power generation performance is lowered or the power generation itself is not performed. Therefore, when LSCF is used as a cathode material, ceria (CeO ₂ ) is doped with gadolinia (Gd ₂ O ₃ ), and the general formula is CeGdO ₂ (Gadolinium doped Ceria; hereinafter referred to as “GDC”). Mixing and using the expressed materials is also under consideration. However, GDC is expensive, and it is preferable to reduce the amount of use as much as possible from the viewpoint of practical use and cost reduction.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an SOFC cathode-forming material that is excellent in durability and can improve electrode performance in a medium-low temperature range. Moreover, this invention provides SOFC provided with the cathode formed using the said material as another side surface.

In order to achieve the above object, the present invention provides a material for forming a cathode of a solid oxide fuel cell. Such a material is represented by the general formula: (La _1-x Sr _x ) (Co _y Fe _1-y ) O _3-δ (where x is a real number satisfying 0.1 ≦ x ≦ 0.5, and y is 0 0.1 ≦ y ≦ 0.5, and δ is a value determined so as to satisfy the charge neutrality condition), and perovskite-type oxide particles (LSCF) represented by the general formula: (La _{1 −x} Sr _x ) (Ti _y Fe _1−y ) O _3−δ (where x is a real number that satisfies 0.1 ≦ x ≦ 0.5, and y satisfies 0.1 ≦ y ≦ 0.5. This is a real number, and δ is a value determined so as to satisfy the charge neutrality condition.) Perovskite-type oxide particles (hereinafter referred to as “LSTF”), which are combined by mechanochemical treatment. Mainly composed of particles. Here, the mechanochemical treatment improves the electron conductivity as compared with the case where the oxide represented by the general formula (1) and the oxide represented by the general formula (2) are mixed. Done.

  The cathode material having the above configuration has suppressed thermal expansion and reductive expansion as compared with the case where LSCF is used alone, so that the exposed environment changes (for example, temperature change accompanying start / stop of SOFC) Also, when the gas atmosphere is changed to a reducing atmosphere, etc., the expansion and contraction are small, and the durability is excellent. In addition, since LSCF and LSTF have high chemical stability, the composite particles can be used stably without deterioration for a long time. Furthermore, since the material has improved electron conductivity and oxygen ion conductivity by mechanochemical treatment, it can exhibit excellent electrode performance as a cathode even in a medium to low temperature region (approximately 500 ° C. to 800 ° C.). Therefore, the power generation performance and reliability of the SOFC can be improved by using the cathode material having the above structure.

In a preferred embodiment of the material disclosed herein, the composite particle includes a core part formed of an oxide represented by the general formula (2) and the general formula formed on at least a part of the surface of the core part. And a covering portion made of an oxide represented by (1).
Since the particles of the above aspect use LSTF with little reductive expansion as a core part, expansion and contraction due to environmental changes such as temperature and gas atmosphere are further suppressed. Further, by arranging the LSCF near the surface (coating portion), a wide contact area with the oxygen-containing gas can be secured, and higher catalytic performance can be exhibited. For this reason, the effect of this invention can be exhibited more.

In a preferred embodiment of the material disclosed herein, the composite particle has a mass ratio of the oxide represented by the general formula (1) (LSCF) and the oxide represented by the general formula (2) (LSTF). LSCF: LSTF = 80: 20 to 30:70.
A material that satisfies the above-described mass ratio can exhibit even better electrode performance. Therefore, the effect of the present invention can be exhibited at a higher level.

In a preferred embodiment of the material disclosed herein, the composite particles have a thermal expansion coefficient (linear expansion) measured by thermomechanical analysis of 13 × 10 ⁻⁶ / K or more and 15 × 10 ⁻⁶ / K or less. The reduction expansion coefficient (linear expansion) is 1% or less.
By setting the thermal expansion coefficient of the cathode forming material within the above range, the difference in thermal expansion coefficient (thermal expansion coefficient) with other SOFC constituent materials (for example, members constituting a solid electrolyte or a power generation system) can be kept small. Can do. In addition, by setting the reductive expansion coefficient of the material to 1% or less, the reductive expansion can be kept low even in a reducing atmosphere having a low oxygen partial pressure (for example, in an atmosphere containing 1% by mass or more of hydrogen gas). Therefore, the cathode forming material is less prone to expansion and contraction due to environmental changes such as temperature and atmosphere, and can be excellent in long-term reliability and durability.

In a preferred embodiment of the material disclosed herein, the composite particles are dispersed in at least one solvent and prepared in a paste form (including a slurry form and an ink form; the same applies hereinafter).
The materials disclosed herein are used to form the SOFC cathode (electrode). In such a case, a homogeneous cathode can be stably and efficiently produced by using a paste prepared by dispersing (or dissolving) the material in one or more solvents.

The present invention also provides a solid oxide fuel cell comprising an anode, a solid electrolyte, and a cathode. The cathode is formed mainly of the composite particles disclosed herein.
An SOFC including the cathode can exhibit high power generation performance (for example, the maximum power density at an operating temperature of 700 ° C. is 0.4 W / cm ² or more). In addition, since the cathode disclosed herein has suppressed expansion and contraction (for example, thermal expansion and reduction expansion) due to environmental changes, SOFCs equipped with such a cathode are excellent in reliability and durability and have a long-term life. It can be used stably. That is, the SOFC disclosed herein can achieve both power generation performance and durability at a high level.

In a preferred aspect of the SOFC disclosed herein, the cathode, the solid electrolyte, and the anode are laminated in layers, and the thickness of the cathode in the laminated structure is 10 μm or more and 100 μm or less.
Since the cathode disclosed here has a thermal expansion coefficient close to that of other SOFC constituent materials (for example, members constituting a solid electrolyte or a power generation system), problems associated with temperature changes (for example, generation of cracks in the cathode) occur. hard. In addition, since the reduction expansion coefficient is kept small, it is difficult for defects (for example, cathode warping) to occur even in a reducing atmosphere. For this reason, in such SOFC, even when the thickness of the electrode is relatively thick, excellent power generation performance can be stably exhibited over a long period of time.

In a preferred aspect of the SOFC disclosed herein, the cathode is formed directly without providing a reaction inhibiting layer on the solid electrolyte.
In general, when LSCF is used as a cathode forming material, a reaction inhibiting layer is formed between the cathode and a solid electrolyte (typically zirconia oxide) in order to inhibit the reaction between them. There is a need. However, since the cathode disclosed herein includes LSTF, such reactivity may be reduced. For this reason, it can be formed directly on the solid electrolyte and is efficient. In addition, since the structure of the SOFC is simplified, the internal resistance of the SOFC can be preferably reduced. For this reason, the SOFC disclosed herein can achieve both power generation performance and productivity at a high level.

Furthermore, the present invention provides a method for producing a cathode forming material for a solid oxide fuel cell. The manufacturing method provided here has a general formula: (La _1-x Sr _x ) (Co _y Fe _1-y ) O _3-δ (where x is a real number satisfying 0.1 ≦ x ≦ 0.5). Y is a real number satisfying 0.1 ≦ y ≦ 0.5, and δ is a value determined so as to satisfy the charge neutrality condition.), And perovskite-type oxide particles (LSCF) Formula: (La _1-x Sr _x ) (Ti _y Fe _1-y ) O _3-δ (where x is a real number satisfying 0.1 ≦ x ≦ 0.5, and y is 0.1 ≦ y ≦ A perovskite type oxide particle (LSTF) represented by the following formula: a real number satisfying 0.5, and δ is a value determined so as to satisfy the charge neutrality condition; the complexed by mechanochemical treatment, to obtain composite particles, wherein the Mekanokemi The cal treatment is performed so that an improvement in electronic conductivity is realized as compared with the case where the oxide represented by the general formula (1) and the oxide represented by the general formula (2) are mixed ; Using the particles to prepare a cathode forming material.
According to this manufacturing method, a cathode forming material having high electrode performance and excellent durability can be preferably manufactured.

In a preferred embodiment of the production method disclosed herein, the mechanochemical treatment is performed by a specific surface area B (m ² / g) after the treatment and a specific surface area A (m before the treatment) measured by a nitrogen adsorption method. ² / g), so that 10 ≦ (AB) / A ≦ 40. That is, the mechanochemical treatment is performed such that the specific surface area of the oxide is reduced by 10% or more and 40% or less by the treatment.
By performing a mechanochemical treatment so as to satisfy the above range, a cathode forming material having further excellent electron conductivity and oxygen ion conductivity can be obtained. Therefore, the effect of the present invention can be exhibited at a higher level.

In a preferred embodiment of the production method disclosed herein, the preparation of the oxide particles is performed by a mass ratio of the oxide represented by the general formula (1) and the oxide represented by the general formula (2). , (1) :( 2) = 80: 20 to 30:70.
By mixing LSCF and LSTF at the above mass ratio, both high electrode performance and durability can be achieved at a higher level.

FIG. 1 is a cross-sectional view schematically showing a power generation system including an SOFC according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing a SOFC manufacturing process according to an embodiment of the present invention, where (a) shows an anode as a support substrate (support), and (b) shows an anode-solid electrolyte laminate. (C) shows the anode-supported SOFC. FIG. 3 is an SEM photograph of the cathode surface according to Comparative Example 1. FIG. 4 is a result of SEM-EDX mapping showing the distribution of cobalt (Co) in the field of view of FIG. FIG. 5 is a result of SEM-EDX mapping showing the distribution of titanium (Ti) in the field of view of FIG. FIG. 6 is an SEM photograph in which a portion indicated by a broken line in FIG. 3 is enlarged. FIG. 7 is a chart showing the results of qualitative analysis at the points (S1 to S6) shown in FIG. FIG. 8 is an SEM photograph of the cathode surface according to Example 2. FIG. 9 is a result of SEM-EDX mapping showing the distribution of cobalt (Co) in the visual field of FIG. FIG. 10 is a result of SEM-EDX mapping showing the distribution of titanium (Ti) in the visual field of FIG. FIG. 11 is an SEM photograph in which a portion indicated by a broken line in FIG. 8 is enlarged. FIG. 12 is a chart showing the results of qualitative analysis at the points (S7 to S11) shown in FIG.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than the matters specifically mentioned in the present specification (for example, the configuration and manufacturing method of the power generation system) and the matters necessary for the implementation of the present invention are those of ordinary skill in the art based on the prior art in this field. It can be grasped as a design matter. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  In this specification, “mechanochemical treatment” means that physical materials are treated by applying mechanical energy such as compressive force, shearing force, frictional force, etc. to the objects to be treated (here, LSCF and LSTF). It is a treatment in which the specific surface area of the object to be processed is reduced by 10% or more (preferably 15% or more, for example, 15% or more and 30% or less). Further, in this specification, “composite particles” refers to particulate substances that are combined by such mechanochemical treatment.

In the present specification, the “specific surface area” refers to a surface area (BET specific surface area) obtained by analyzing a value measured by specific surface area measurement based on a constant capacity adsorption method using nitrogen gas by a BET method (for example, the BET one-point method). . In the present specification, the “average particle diameter” means a particle diameter corresponding to 50% cumulative from the fine particle side in a volume-based particle size distribution measured by particle size distribution measurement based on a general laser diffraction / light scattering method (D ₅₀ particle diameter, also called median diameter). In the present specification, the “average pore diameter” refers to a value obtained based on a general mercury intrusion measurement. Further, in this specification, the “porosity” is obtained by dividing the pore volume (Vb (cm ³ )) obtained by the measurement of the mercury intrusion method by the apparent volume (Va (cm ³ )). By multiplying, it means the calculated value (Vb / Va × 100 (%)).

Cathode forming material of the solid oxide fuel cell disclosed herein has the general _{formula: (La 1-x Sr x} ) (Co y Fe 1-y) oxide particles of perovskite type represented by _{O 3-[delta]} (LSCF) and perovskite oxide particles (LSTF) represented by the general formula: (La _1-x Sr _x ) (Ti _y Fe _1-y ) O _3-δ are combined by mechanochemical treatment. It is characterized by mainly comprising composite particles (hereinafter, particles in which LSCF and LSTF are combined may be simply referred to as “composite particles”).
Whether the particles are composite particles or not is determined by using, for example, a general scanning electron microscope (SEM) -energy dispersive X-ray spectroscopy (EDX) method. Can be confirmed. More specifically, as shown in the examples described later, the determination can be made based on the observation image obtained by SEM observation and the distribution state of each element obtained by EDX analysis.

In the above general formula, “x” is a value indicating the ratio of “La element” to “Sr element” in the perovskite oxide. This x is within the range of 0.1 ≦ x ≦ 0.5 (preferably 0.1 ≦ x ≦ 0.4) as long as the structure can be maintained without destroying the perovskite structure. The real number may be taken.
Further, “y” in the above general formula is a value that determines the composition ratio between “Fe element” and “Co element (in the case of LSCF) or Ti element (in the case of LSTF)” in the perovskite oxide. This y may take any real number within the range of 0.1 ≦ y ≦ 0.5.

“Δ” in the above general formula is a value determined so as to satisfy the charge neutrality condition. That is, the number of oxygen atoms in the perovskite oxide can be 3 or less (typically less than 3). The value of δ is the type and substitution ratio of atoms (for example, “Sr element”, “(LSCF) Co element or (LSTF) Ti element)” in part of the perovskite structure. Depending on other conditions, the charge neutrality condition in the above general formula is satisfied. This δ is typically a positive number not exceeding 1 (0 ≦ δ <1).
As described above, since the δ value (that is, the number of oxygen atoms) can be changed depending on the conditions of other elements constituting the perovskite oxide, it is difficult to display accurately. Therefore, δ may be omitted for convenience. That is, (3-δ) in the above general formula is not intended to limit the technical scope of the present invention.

  LSCF is a so-called electron-oxygen ion mixed conductor and has higher electrode performance (power generation performance) than other perovskite oxides. Therefore, excellent performance can be exhibited even in a relatively low temperature range (for example, 500 ° C. to 800 ° C.). However, since the LSCF has a large thermal expansion and reduction expansion, when it is used alone as an SOFC electrode material (cathode forming material), defects (for example, electrode warpage or cracking) occur due to changes in the environment exposed to it. ) May occur. On the other hand, although LSTF is slightly inferior in power generation performance to LSCF, it is an electron-oxygen ion mixed conductor and has low heat expansion and reduction expansion. The cathode material disclosed herein can exhibit excellent electrode performance even in a relatively low temperature range (for example, 500 ° C. to 800 ° C.) by mixing the two, and the temperature, gas atmosphere, etc. Expansion and contraction due to environmental changes are suppressed and it has high durability. Furthermore, since LSCF and LSTF have low reactivity, the composite particles can be used stably without deteriorating for a long time.

  Furthermore, the cathode forming material disclosed here is mainly composed of composite particles obtained by mechanochemical treatment of LSCF and LSTF. Since the LSCF and the LSTF are physically combined (composited) by mechanochemical treatment, the composite particles are further excellent in electron conductivity and oxygen ion conductivity. For this reason, this material can exhibit the electrode performance which was excellent also in the medium-low temperature range.

In a preferred embodiment, the composite particle includes a core portion made of LSTF and a coating portion made of LSCF formed on at least a part of the surface of the core portion. In other words, the composite particle is a particle in a form in which LSCF particles (typically smaller in particle size than the LSTF) are dispersed and immobilized (composited) on the surface of the core LSTF particles. It is preferable. By using the LSTF with smaller thermal expansion and reductive expansion as the core, expansion / contraction associated with environmental changes such as temperature and gas atmosphere can be further suppressed. Further, by disposing LSCF in the vicinity of the surface of the composite particle, a wide contact area between the LSCF having high electrode performance and the oxygen-containing gas can be secured, and high catalytic performance can be exhibited. Therefore, the effect of the present invention can be exhibited at a higher level. Here, the above-mentioned “coating part” is sufficient if at least a part of the surface of the LSTF particles forming the core part is covered with the LSCF, and it is not always necessary to cover the entire surface of the core part. For example, it is preferable that 10% or more (typically 30% or more, preferably 50% or more, more preferably 70% or more) of the surface of the core part is coated, and substantially the entire surface of the core part ( More preferably, it is in the form of so-called core-shell particles coated with 90% or more, for example, 95% or more). In addition, it can be confirmed using the said SEM-EDX method whether it is a core-shell particle.
The proportion of the particles in the above-mentioned form in the total composite particles is preferably 10% or more (typically 30% or more, for example 50% or more, preferably 70% or more), and is substantially 100%. It is more preferable.

  The average particle size of LSCF and LSTF constituting the composite particle of the above aspect is typically LSCF <LSTF. The average particle diameter of the LSTF constituting the core portion can be, for example, 0.1 μm to 10 μm (typically 0.5 μm to 5 μm, preferably 1 μm to 3 μm). Moreover, the average particle diameter of LSCF which comprises a coating | coated part is less than 1 micrometer, for example (typically 0.001 micrometer-1 micrometer, Preferably 0.01 micrometer-0.5 micrometer, More preferably, 0.1 +/- 0.05 micrometer) It can be. When the above range is satisfied, the effect of the present invention can be exhibited at a higher level.

  Although the mass ratio of LSCF and LSTF in the composite particles is not particularly limited, for example, LSCF: LSTF = 80: 20 to 30:70 is preferable. A material satisfying the above mass ratio can exhibit the effects of the present invention at a higher level.

The cathode forming material disclosed herein preferably has a thermal expansion coefficient (linear expansion) close to other SOFC constituent materials (for example, members constituting a solid electrolyte or a power generation system). More specifically, the thermal expansion coefficient of the SOFC component materials can be a ^{9 × 10 -6 / K~18 × 10} -6 / K, for example, a solid thermal expansion coefficient of the electrolyte material generally ¹⁰ × 10 -6 / K It can be ˜13 × 10 ⁻⁶ / K. In such a case, the thermal expansion coefficient of the cathode forming material can typically be a ^{10 × 10 -6 / K~16 × 10} -6 / K, for example, 13 × ¹⁰ -6 / K~15 × was ^{10 -6 / K, 14 × 10} -6 / K~15 × 10 -6 / K in the examples described below, in particular ^{14.5 × 10 -6 / K~15 × 10} -6 / K It can be. A cathode satisfying the above thermal expansion coefficient is resistant to thermal shock, that is, the temperature rises and falls between a temperature during stopping (typically normal temperature) and a temperature range during use (for example, 500 ° C. to 800 ° C.). Even if it repeats, it is hard to produce the malfunction (for example, generation | occurrence | production of a crack) accompanying a temperature change. For this reason, an SOFC using such a cathode can exhibit stable power generation performance over a long period of time.
The thermal expansion coefficient is, for example, from room temperature (25 ° C.) to 500 ° C. or higher (for example, 500 ° C., 600 ° C., 700 ° C., 800 ° C.) using a thermomechanical analyzer (TMA) using a differential expansion method. An arithmetic average value of values (linear expansion) measured in a temperature range of 1000 ° C. can be employed. Specific measurement conditions will be described in Examples described later.

Moreover, as a cathode forming material disclosed here, it is preferable that the reduction expansion coefficient (%) is suppressed. The reduction expansion coefficient is an index that quantitatively indicates a measure of reduction durability (that is, thermal expansion coefficient in a reducing atmosphere) based on a change in dimension (length) when heated in a reducing atmosphere. When the value of the reductive expansion coefficient is large, for example, when the fuel gas flowing on the anode side leaks and enters the cathode side, there is a possibility that problems such as warpage and cracks occur in the cathode. For this reason, the reduction expansion rate (%) can be, for example, less than 1.0, preferably 0.8 or less, and more preferably 0.7 or less. A cathode that satisfies the above reduction expansion coefficient has high durability and can exhibit stable power generation performance over a long period of time.
Note that in this specification, the “reducing atmosphere” means a state where the oxygen partial pressure is low, for example, a gas having reducibility such as hydrogen, carbon monoxide, and nitrogen monoxide is 0.1% by mass or more (typically 1% or more, for example, 4% or more). Further, in this specification, “reduction expansion coefficient (%)” is E _red (%) in a nitrogen atmosphere containing 5% by mass of reducing gas, and the thermal expansion coefficient in an air atmosphere is E _air. (%) Represents a value given by the following formula (3).
[{(1 + E _red / 100) − (1 + E _air / 100)} / (1 + E _air / 100)] × 100 (3)

Components other than the composite particles can be appropriately added to the cathode forming material disclosed herein as necessary. Examples of other components that can be optionally added include, but are not limited to, binders, thickeners, dispersants, pore formers, and the like, and are appropriately selected from conventionally known materials used for cathode formation, for example. Can be added. Examples of the binder include cellulose or a derivative thereof. More specifically, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, carboxyethylcellulose, carboxyethylmethylcellulose, cellulose, ethylcellulose, methylcellulose, ethylhydroxyethylcellulose, butyral and salts thereof can be mentioned.
The ratio of the optional additive component in the cathode forming material is not particularly limited, but is, for example, 20% by mass or less (typically 0.1% by mass to 20% by mass, 1% by mass to 10% by mass). Is preferred.

  The form of the material for forming a cathode disclosed herein is not particularly limited. For example, even if the material is a powder (particle) or a paste containing the particle and an arbitrary solvent, the paste is dried ( Alternatively, it may be a solid state fired. Among them, a material prepared by dispersing (or dissolving) the material disclosed herein in one or more arbitrary solvents and preparing it in a paste form can be preferably used. By using a paste-like material, a homogeneous cathode can be produced stably and efficiently.

As the solvent, one or two or more of those capable of suitably dispersing (or dissolving) the composite particles can be used without any particular limitation. Such solvents are roughly classified into organic solvents and inorganic solvents. Examples of the organic solvent include alcohol solvents, ether solvents, ester solvents, ketone solvents, cyclic ether solvents, aromatic hydrocarbon solvents, and other organic solvents. In particular, terpineol, isobutyl alcohol, ethylene glycol, octanol, butyl carbitol, butyl cellosolve (2-butoxyethanol), butyl diglycol acetate, isobornyl acetate and the like are preferably used. In addition, the inorganic solvent is preferably water or a mixed solvent mainly composed of water. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used.
The ratio of the solvent in the entire paste is not particularly limited, but can be, for example, 5% by mass to 35% by mass (preferably 10% by mass to 30% by mass).

Moreover, in this specification, the method of manufacturing suitably the cathode formation material mentioned above is provided. The manufacturing method provided here prepares LSCF and LSTF (preparation step); composites the LSCF and LSTF by mechanochemical treatment to obtain composite particles (composite step); To prepare a cathode forming material (preparation step). According to this manufacturing method, a cathode forming material having high electrode performance and excellent durability can be preferably manufactured.
Hereinafter, it demonstrates in order.

<Preparation process>
In the manufacturing method disclosed herein, first, LSCF and LSTF are prepared. Those purchased may be used, and for example, they can be produced from a raw material using a conventionally known method.
Although the properties of the oxide prepared here are not particularly limited, for example, the average particle size of LSCF is less than 2 μm (typically 0.001 μm to 2 μm, such as 0.01 μm to 1 μm, preferably 0.01 μm to 0.001 μm). 5 μm, more preferably 0.01 μm to 0.2 μm). The average particle size of the LSTF can be 0.1 μm to 20 μm (preferably 0.5 μm to 10 μm, more preferably 1 μm to 3 μm). By preparing the particle size of the oxide within the above range in advance before the compositing step described later, the form of the composite particles after mechanochemical treatment can be suitably adjusted, and the effects of the present application can be further improved. Can be demonstrated at a high level. The particle size can be adjusted by a conventionally known pulverization process, sieving, classification or the like.

  Here, as a preferable aspect, a mass ratio of LSCF and LSTF is prepared so that LSCF: LSTF = 80: 20 to 30:70. By using LSCF and LSTF at the above mass ratio, both high electrode performance and durability can be achieved at a higher level.

<Composite process>
In the production method disclosed herein, next, LSCF and LSTF weighed at a predetermined blending ratio (along with other additives as necessary) are put into a suitable mixer to perform mechanochemical treatment. Thereby, LSCF and LSTF can be compounded and composite particles can be obtained. In the mechanochemical treatment, one kind or two or more kinds of conventionally used grinding / mixing apparatuses can be used without any particular limitation. For example, non-medium type pulverizing and mixing machines such as jet mills, planetary mixers, homogenizers, and dispersers (one that does not require pulverizing media), and medium type pulverizing mixers such as ball mills and bead mills (one that requires pulverizing media) It is preferable to use a non-medium type pulverizing mixer. By using a non-medium type pulverizing mixer, the above-described compounding treatment can be suitably performed, and contamination (foreign matter contamination) due to contact with the medium can be reduced. More preferably, a dry non-medium type pulverizing mixer is used. By dry mixing, the particles can be prevented from being crushed more than necessary. Further, unintended alteration or change of the LSCF and LSTF as the raw materials and / or the composite particles as the object can be prevented. By appropriately adjusting the pulverization processing conditions (for example, pulverization strength and pulverization time) of the pulverizer, composite particles having a desired form (particle size, shape) can be obtained.
More specifically, for example, when performing mechanochemical treatment using “NOB-MINI” manufactured by Hosokawa Micron Corporation, output: 0.1 kW to 5 kW (typically 0.5 kW to 3 kW, for example, 1 kW to 3 kW) 1 to 30 minutes (typically 3 to 20 minutes, for example 5 to 15 minutes), the area after the treatment is 10% or more (typically 10% to 40%, preferably Can be reduced by 15% to 30%), and desired composite particles can be suitably obtained.

In such mechanochemical treatment, LSCF and LSTF are complexed, so that the specific surface area of the obtained composite particles is reduced as compared with that before the treatment. The specific surface area reduced by the treatment is 10% or more, typically 10% or more and 50% or less, such as 10% or more and 40% or less, preferably 15% or more and 35% or less, more preferably 15% or more and 30%. % Or less. That is, the relationship between the specific surface area B (m ² / g) after the mechanochemical treatment and the specific surface area A (m ² / g) before the treatment is 10 ≦ (AB) / A, typically 10 ≦ (A−B) / A ≦ 50, for example, 10 ≦ (A−B) / A ≦ 40, for example, 10 <(A−B) / A <40, preferably 15 ≦ (A−B) / A ≦ 35, more preferably 15 ≦ (A−B) / A ≦ 30. If the mechanochemical treatment is excessively performed, the particles are excessively crushed, which may cause a decrease in reactivity (catalytic ability) and an increase in resistance between particles. By performing the mechanochemical treatment so as to satisfy the above range, the contact resistance between particles is reduced, and a cathode forming material that is more excellent in electron conductivity and oxygen ion conductivity can be obtained.

<Preparation process>
Then, a cathode forming material is prepared using the composite particles. The form of the material may be in the form of powder, paste, solid or the like as described above. For example, the material and any of the above-described optional components (for example, binder or dispersant) are combined with one or more solvents (for example, terpineol). It is preferable that it is a paste-like composition mixed in. For the preparation of the paste, various conventionally known stirring / mixing devices such as a ball mill, a mixer, a disper, and a kneader can be appropriately used. Moreover, the kind of solvent which can be used, a mixing ratio, etc. may be the same as what was already mentioned above. For example, the powdery composite particles and other additives are kneaded at a stirring speed of 50 rpm to 300 rpm for 0.5 hour to 1 hour to form a paste-like cathode in which the powdery composite particles are suitably dispersed. Materials can be obtained.

  The present invention also provides a solid oxide fuel cell (SOFC) comprising an anode, a solid electrolyte, and a cathode. The cathode is formed mainly of the composite particles disclosed herein. The SOFC provided with the cathode can exhibit high power generation performance. Further, since the cathode expansion / contraction (for example, thermal expansion or reductive expansion) due to environmental changes is suppressed, such SOFC is excellent in reliability and durability and can be used stably over a long period of time.

  The SOFC disclosed herein has various structures, such as a conventionally known flat type (Planar), polygonal type, cylindrical type (Tubular), or a flat cylindrical type (Flat Tubular) in which the peripheral side surface of the cylinder is vertically crushed. The shape and size are not particularly limited. For example, the flat type has a feature that it has a high power density and is cheaper than the cylindrical type. In addition, the cylindrical type has a feature that it is easy to keep the gas flow rate constant and more stable power generation is possible. For this reason, it is preferable to select a preferable shape and size as appropriate according to the application. The flat SOFC includes an electrolyte-supported cell (ESC) with a thicker electrolyte, an anode-supported cell (ASC) with a thicker anode, and a cathode-supported (Cathode) with a thicker cathode. -Supported Cell: CSC). In addition, a metal-supported cell (MSC) in which a porous metal sheet is placed under the anode can be used.

An example will be described with reference to FIG. FIG. 1 is a diagram schematically illustrating a cross-sectional configuration of a power generation system including the SOFC 50 disclosed herein. The SOFC 50 having the structure shown here is an anode-supported SOFC, and is formed on a sheet-like anode (fuel electrode) 10 serving as a support (base material) and at least a part of the surface of the anode 10 (film-like). The solid electrolyte 20 and a sheet-like cathode (air electrode) 30 formed on the surface of the solid electrolyte 20 are laminated. The end 12 of the anode 10 and the joining surface of the gas pipe 60 that supplies fuel gas (typically H ₂ (hydrogen)) are joined by the connecting member 40 so that the gas does not flow out and / or flow in. Is sealed. The cathode 30 has a structure exposed to the outside air. When a current is applied to such a power generation system, oxygen atoms in the oxygen-containing gas (typically air) become oxygen ions at the cathode 30. The oxygen ions reach the anode 10 from the cathode 30 through the solid electrolyte 20 and are supplied to the anode 10. Then, electricity is generated by reacting with hydrogen (H ₂ ) in the fuel gas and releasing electrons.
Hereinafter, the components of the SOFC will be described in order.

  The anode (fuel electrode) 10 constituting the SOFC 50 disclosed herein has a porous structure that can permeate gas. The porosity of the anode 10 can be, for example, 10 volume% to 50 volume%, preferably 20 volume% to 40 volume%. The average pore diameter can be, for example, 10 μm or less, preferably 0.1 μm to 5 μm. When satisfying such a range, high mechanical strength and excellent gas permeability (that is, securing a sufficient gas contact area) can be achieved at a high level. Note that the shape of the anode only needs to be configured so as to be in contact with the fuel gas supplied to the SOFC, and can be appropriately selected according to the shape of the SOFC described above. In the SOFC 50 having the configuration shown in FIG. 1, the sheet-like anode 10 is formed relatively thick as a support for the SOFC 50. The thickness of the anode 10 as the support is typically about 0.1 mm to 10 mm, and preferably about 0.5 mm to 5 mm, but is not limited to this thickness. Further, for example, a structure in which two or more layers having different porous structures (porosities) are laminated may be used. In this case, it is possible to make the gas distribution uniform by increasing the porosity of the layer away from the solid electrolyte 20.

Examples of the material constituting the anode 10 include one or more metals or metal oxides. More specifically, titanium (Ti), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), strontium (Sr), zirconium (Zr), ruthenium (Ru), palladium (Pd) , Osmium (Os), iridium (Ir), platinum (Pt), lanthanum (La), gold (Au), or other metals, or cobalt oxide (CoO, Co ₂ O ₃ , Co ₃ O ₄ ), nickel oxide ( Examples thereof include metal oxides such as NiO, Ni ₂ O ₃ , Ni ₃ O ₄ ), zirconium oxide (ZrO ₂ ), and ruthenium oxide (RuO ₂ ). Among these, nickel is a particularly preferred metal species because it is cheaper than other metals and exhibits high activity. Moreover, the composite material which mixed these metals and metal oxides, and another material can also be used. More specifically, a composite in which the anode constituent material (metal or metal oxide) and a constituent material of the solid electrolyte 20 described later are mixed at an arbitrary ratio can be used. Preferred examples include nickel and stabilized zirconia (for example, Yttria stabilized zirconia (YSZ), calcia stabilized zirconia (CSZ), scandia stabilized zirconia (ScSZ), etc.). And cermet. By mixing with the constituent material of the solid electrolyte, the thermal expansion is matched and an SOFC having excellent durability can be constructed. Moreover, since sintering between nickel particles can also be prevented, it is preferable. The mixing ratio (mass ratio) of the metal and the solid electrolyte constituent material is not particularly limited, but is, for example, 90:10 to 40:60 (more preferably about 80:20 to 45:55). Can do.

  The solid electrolyte 20 constituting the SOFC 50 disclosed herein has a dense structure. The solid electrolyte 20 is laminated on the anode 10, and the shape thereof can be appropriately changed according to the shape of the anode 10. The thickness (film thickness) of the solid electrolyte 20 is typically about 5 μm to 100 μm, and preferably about 10 μm to 30 μm, but is not limited to this thickness.

As a material constituting the solid electrolyte 20, a compound having high oxygen ion conductivity is preferable. For example, magnesium (Mg), aluminum (Al), calcium (Ca), scandium (Sc), titanium (Ti), gallium (Ga), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb) ), Barium (Ba), lanthanum (La), cerium (Ce), samarium (Sm), gadolinium (Gd), tungsten (W), an oxide containing an element selected from bismuth (Bi), and the like. More specifically, the stability of yttria (Y ₂ O ₃ ), calcia (CaO), scandia (Sc ₂ O ₃ ), magnesia (MgO), ytterbia (Yb ₂ O ₃ ), erbia (Er ₂ O ₃ ), etc. Ceria (CeO ₂ ) doped with a dopant such as zirconia (ZrO ₂ ), yttria (Y ₂ O ₃ ), gadolinia (Gd ₂ O ₃ ), samaria (Sm ₂ O ₃ ), whose crystal structure is stabilized with an agent. ); And the like are preferable examples. In particular, yttria-stabilized zirconia (YSZ) in which an oxide of yttrium (Y) (for example, yttria (Y ₂ O ₃ )) is dissolved, oxide of scandium (Sc) (for example, scandia (Sc ₂ O ₃ )) Scandia-stabilized zirconia (ScSZ) in which is dissolved can be preferably used because it exhibits relatively high oxygen ion conductivity even at medium and low temperatures.

  The cathode (air electrode) 30 that constitutes the SOFC disclosed herein has a porous structure that allows gas to permeate in the same manner as the anode 10. The porosity of the cathode 30 can be, for example, 10 volume% to 30 volume%, preferably 15 volume% to 25 volume%. The average pore diameter can be, for example, 10 μm or less, preferably 0.1 μm to 5 μm. The cathode 30 is laminated on the solid electrolyte 20, and the shape can be appropriately changed according to the shape of the solid electrolyte 20. The thickness (film thickness) of the cathode 30 is typically about 1 μm to 200 μm, preferably about 5 μm to 100 μm, more preferably 10 μm to 100 μm, but is not limited to this thickness.

  As a preferred embodiment of the SOFC disclosed herein, the cathode 30 is formed directly on the solid electrolyte 20 without providing a reaction inhibiting layer. In general, when LSCF is used as a cathode forming material, a reaction inhibiting layer is formed between the cathode and a solid electrolyte (typically zirconia oxide) in order to inhibit the reaction between them. There is a need. However, the cathode disclosed herein can include such LSTFs to reduce such reactivity. For this reason, it can form directly on the solid electrolyte 20, and the structure of SOFC can be simplified more. Therefore, it is excellent in productivity, and preferably the internal resistance of SOFC can be reduced. As the material constituting the cathode, the above-mentioned cathode forming material can be used.

  Moreover, in this specification, the method of manufacturing SOFC suitably is provided. The manufacturing method disclosed here is a method of manufacturing a solid oxide fuel cell having a laminated structure including a porous structure anode, a solid electrolyte composed of an oxygen ion conductor, and a porous structure cathode. is there. And the said cathode is comprised by the material for cathode formation disclosed here, It is characterized by the above-mentioned.

Such a manufacturing method includes preparing an anode-solid electrolyte laminate comprising the anode and a solid electrolyte formed on the anode, and forming a cathode disclosed herein on the surface of the laminate on the solid electrolyte side. Application material (typically, composite particles) and firing the laminate to which the material is applied to form the cathode. In the manufacturing method disclosed here, the difference in thermal expansion coefficient (thermal expansion coefficient) between the cathode and other constituent materials (for example, members constituting the solid electrolyte and the power generation system) is suppressed to be small. Inconveniences (for example, generation of cracks) due to Further, since the reactivity between the cathode material and the electrolyte is low, there is no need to provide a reaction inhibiting layer. Therefore, according to the manufacturing method disclosed herein, it is possible to easily manufacture an SOFC that can exhibit high power generation performance while having high durability.
A specific manufacturing method will be described in detail with reference to FIG.

<Preparation of anode-solid electrolyte laminate>
Here, the “anode-solid electrolyte laminate” indicates a state where the anode and the solid electrolyte are laminated, and there is no particular limitation on the method for preparing the anode-solid electrolyte laminate. Therefore, conventionally known anode and solid electrolyte production methods can be used in the SOFC production method.
For example, as shown in FIG. 2A, first, an anode 10 having a porous structure is formed as a support substrate (support). Here, a cermet material is prepared by mixing a group 8-10 metal element material (for example, nickel material) and a stabilized zirconia (for example, YSZ). Next, the cermet material, a binder (for example, a methacrylic ester polymer), a dispersant (for example, sorbitan trioleate), and a pore former (for example, carbon) are dispersed in a solvent (for example, xylene), and a paste is obtained. An anode forming material is prepared. The prepared anode forming material is molded by an appropriate molding method (for example, sheet molding), and the molded body is fired to form the sheet-like anode 10. The molded body can be fired, for example, by heating at a temperature of 1200 ° C. to 1500 ° C. for 1 hour to 5 hours. The firing of the anode forming material may be performed simultaneously with the firing of the solid electrolyte material described later.

  Then, as shown in FIG. 2 (b), the solid electrolyte 20 is formed on the anode 10. Here, the raw material (for example, YSZ) of the above-described solid electrolyte 20 is dispersed in a solvent (for example, xylene) together with a binder (for example, methacrylic ester-based polymer) and a dispersant (for example, sorbitan trioleate), and used for a paste-like solid electrolyte. Prepare the material. Next, the prepared solid electrolyte material is applied to the anode 10 (or a molded body of the anode forming material) by an arbitrary method (for example, printing molding) to form a molded body of the solid electrolyte material. And after drying the molded object which provided the material for solid electrolytes, it bakes in an atmospheric condition. The firing temperature at this time can be about 1200 to 1400 ° C., and the firing time can be about 1 to 5 hours. By such firing, a membrane-like solid electrolyte 20 is formed on the anode 10, and an anode-solid electrolyte laminate 110 including the anode 10 and the solid electrolyte 20 formed on the anode 10 can be obtained.

<Formation of cathode>
Next, as shown in FIG. 2C, the above-described cathode forming material is applied to the surface of the anode-solid electrolyte laminate 110 on the solid electrolyte 20 side. At this time, in order to stably produce a homogeneous electrode, a material prepared by dispersing (or dissolving) a constituent material in one or more solvents can be preferably used. Then, the paste-like composite particles are applied onto the solid electrolyte 20 using any method (for example, application). As a coating method, a doctor blade method, a dipping method, a screen printing method, a roll coating method, a spray method, or the like can be used. And the laminated body to which the material for cathode formation was provided is baked. Although a baking method is not specifically limited, For example, it can bake at the temperature of 700 to 900 degreeC (preferably 750 to 850 degreeC). Thereby, the cathode 30 is formed, and the SOFC 50 in which the anode 10, the solid electrolyte 20, and the cathode 30 are laminated can be obtained.

  Hereinafter, the present invention will be specifically described by way of examples. In this example, eight types of solid oxide fuel cells (SOFC) having different cathode forming materials were produced, and their characteristics and power generation performance were evaluated. Note that the examples described below are not intended to limit the present invention.

[Preparation of cathode forming material]
<Comparative Example 1>
LSCF oxide particles having an average particle diameter of 0.2 μm (here, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O _3-δ ) and LSTF having an average particle diameter of 1.0 μm Oxide particles (here, La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O _3-δ were used) were weighed at a mass ratio of LSCF: LSTF = 70: 30, and a mortar was prepared. A cathode forming material (Comparative Example 1) was obtained by using and mixing and dispersing.

<Example 1>
In Comparative Example 1 described above, the cathode forming material (Example) was obtained by performing mechanochemical treatment (dry mixing) for 10 minutes under the condition of 0.5 kW using “NOB-MINI” manufactured by Hosokawa Micron Corporation instead of mortar mixing. 1) was obtained.

<Example 2>
A cathode forming material (Example 2) was obtained in the same manner as in Example 1 except that the mechanochemical treatment was performed for 10 minutes under the condition of 1.0 kW.

<Example 3>
A cathode forming material (Example 3) was obtained in the same manner as in Example 1 except that the mechanochemical treatment was performed for 10 minutes under the condition of 3.0 kW.

<Example 4>
A cathode forming material (Example 4) was obtained in the same manner as in Example 1 except that the mechanochemical treatment was performed for 20 minutes under the condition of 3.0 kW.

<Comparative example 2>
The case where only the LSCF oxide was used (that is, the case where the LSTF oxide was not used) was used as the cathode forming material (Comparative Example 2).

<Comparative Example 3>
Cathode forming material (comparison) as in Comparative Example 1 except that GDC was used instead of LSTF oxide and dry mixing was performed so that the mass ratio of LSCF oxide to GDC was LSCF: GDC = 50: 50. Example 3) was obtained.

<Comparative Example 4>
A cathode forming material (Comparative Example 4) was obtained in the same manner as Comparative Example 3 except that the dry mixing was performed so that the mass ratio of the LSCF oxide to GDC was LSCF: GDC = 40: 60.
The particle conditions are summarized in Table 1.

[Measurement of specific surface area]
The specific surface area of the obtained cathode forming material was measured under the following conditions. The results are shown in Table 1 together with the materials used for production and the dry mixing conditions. In Table 1, “−” in the column of mechanochemical treatment conditions indicates that no mechanochemical treatment was performed.
Measuring device: Nippon Bell Co., Ltd., automatic specific surface area / pore distribution measuring device “BELSORP ™ -18PLUS”
Measurement method; Constant volume adsorption method Adsorption gas; Nitrogen Analysis method; BET one-point method

  As shown in Table 1, the specific surface area after the treatment tended to decrease as the output was increased and / or the treatment time was increased in the mechanochemical treatment. This indicates that LSCF and LSTF have been combined by mechanochemical treatment.

[Electron microscope observation]
The properties of the obtained cathode forming material were observed with a scanning electron microscope (SEM). As representative results, the observation results of Comparative Example 1 and Example 2 are shown in FIGS. 3 and 8, respectively. FIG. 3 is an SEM observation photograph of particles according to Comparative Example 1, that is, mixed particles not subjected to mechanochemical treatment. FIG. 8 is a SEM observation photograph of particles according to Example 2, that is, composite particles subjected to mechanochemical treatment. In addition, energy dispersive X-ray spectroscopic analysis (EDX) was performed within the limited visual field, and the distribution states of cobalt (Co) and titanium (Ti) were mapped. The obtained results are shown in FIG. 4 (Co (Kα) distribution in Comparative Example 1), FIG. 5 (Ti (Kα) distribution in Comparative Example 1), and FIG. 9 (Co (Kα) distribution in Example 2). FIG. 10 (distribution of Ti (Kα) in Example 2), respectively.

  From the mapping result of SEM-EDX, in FIG. 4 and FIG. That is, in Comparative Example 1, it was found that LSCF and LSTF were partially aggregated and not uniformly dispersed. On the other hand, in FIGS. 9 and 10 according to Example 2, Co and Ti were more uniformly dispersed as compared with Comparative Example 1. Therefore, it was shown that the mechanochemical treatment can obtain not only a mechanical combination but also a uniform dispersion effect.

Furthermore, the SEM photograph which expanded the part shown with the broken line in FIG.3 and FIG.8 is shown in FIG. 6 (comparative example 1) and FIG. 11 (Example 2). As a result, compared to Comparative Example 1 (FIG. 6), in Example 2 (FIG. 11), there are many small particles of submicron order (for example, about 0.1 μm), and these small particles are 0.5 μm to 1 μm. A state of being bound (complexed) to larger particles was observed.
Therefore, in order to clarify the types of the observed particles, qualitative analysis was performed using the EDX method at the points shown in FIG. 6 (S1 to S6) and FIG. 11 (S7 to S11). The results are shown in the charts of FIG. 7 (Comparative Example 1) and FIG. 12 (Example 2). Table 2 shows the results of quantitative analysis of each element.
7 and Table 2 show that in Comparative Example 1, LSTF and LSCF are mixed in an independent state. On the other hand, from the results shown in FIG. 11 and Table 2, in Example 2, the LSTF particles of about 0.5 μm to 1 μm were used as the core, and a large number of submicron LSCFs adhered (physically bonded) to the surface of the core part. It was shown that the structure was formed with parts.

(Thermal characteristics evaluation)
Further, the eight types of cathode forming materials obtained above were subjected to thermomechanical analysis (TMA) under the following conditions to measure the thermal expansion coefficient and the reduction expansion coefficient. In the corresponding column of Table 3, the arithmetic average value in the measurement temperature range is shown.
Measuring device: Model “CN8098F1” manufactured by Rigaku Corporation
Measurement method; differential expansion method Measurement temperature range: room temperature (25 ° C.) to 1000 ° C., rate of temperature increase: 5 ° C./min (When measuring reduction expansion coefficient)

As shown in Table 3, the cathode forming material of Comparative Example 2 composed only of LSCF had the highest thermal expansion coefficient. For this reason, it is considered that the durability against temperature changes such as thermal shock is low. Further, in Comparative Examples 3 and 4 in which LSCF and GDC were mixed, the thermal expansion coefficient was suppressed as compared with Comparative Example 2, but the reductive expansion coefficient showed a large value exceeding 1%. For this reason, when the cathode is formed of such a material, the cathode may be peeled off or the structure may be broken in a reducing atmosphere. In comparison with this, the cathode forming materials of Examples 1 to 4 according to the present invention have a small reduction expansion coefficient of 0.7%, and the thermal expansion coefficient of a typical material used for SOFC cells is also low. The value was close to the coefficient (10-13 (× 10 ⁻⁶ / K)). From the above results, it has been shown that the cathode forming material disclosed here has little deterioration due to environmental changes and can be excellent in reliability and durability.

[Construction of SOFC]
Using the above 8 types of composite particles for cathode formation, SOFC was constructed in the following procedure.
Specifically, first, yttria-stabilized zirconia (YSZ) powder having an average particle diameter of 1 μm and nickel oxide (NiO) powder having an average particle diameter of 3 μm are mixed at a mass ratio of YSZ: NiO = 40: 60, and further manufactured. Carbon as a pore material was added to obtain a mixed powder. The mixed powder, a binder (methacrylic ester polymer), and a dispersant (sorbitan trioleate) were kneaded in a solvent (xylene) to prepare a paste-like anode forming material. The anode forming material was formed into a sheet by a doctor blade method to prepare an anode molded body having a diameter of about 20 mm and a thickness of about 1 mm.
Next, a yttria-stabilized zirconia (YSZ) powder having an average particle diameter of 1 μm, a binder (methacrylic acid ester polymer), and a dispersant (sorbitan trioleate) are kneaded in a solvent (xylene) to obtain a paste. A solid electrolyte material was prepared. The solid electrolyte material was screen-printed on the anode molded body to form a solid electrolyte having a diameter of 20 mm and a thickness of 10 μm. And after drying the molded object which consists of the said laminated | stacked 2 layer, the anode-solid electrolyte laminated body was obtained by baking at the temperature of 1400 degreeC for 3 hours.

  Then, the composite particles produced above and a binder (ethyl cellulose) were added to a solvent (terpineol) and kneaded for 0.5 hour by a roll mill to obtain paste-like composite particles. The paste-like composite particles were screen-molded on the solid electrolyte layer to form a φ16 mm cathode molded body on the solid electrolyte layer. In addition, the thickness of the molded object for cathodes at this time was about 10 micrometers-50 micrometers. And the cathode was formed by baking the molded object which consists of the laminated | stacked two layers at the temperature of 800 degreeC for 1 hour. As a result, an anode-supported SOFC in which the anode, the solid electrolyte, and the cathode were laminated in this order was obtained. In addition, as shown in the corresponding column of Table 3, the porosity of the cathode was in the range of 15% by volume to 20% by volume, and was a suitable value from the viewpoint of mechanical strength and gas permeation.

[Power generation test]
The produced SOFC was operated at a temperature of 500 ° C. to 800 ° C., and power generation characteristics were evaluated. As a representative value of “power generation performance”, the value of the maximum power density (W / cm ² ) at a temperature of 700 ° C. is shown in the corresponding column of Table 3.

As shown in Table 3, the highest power density was shown with the cathode forming material of Comparative Example 2 composed only of LSCF. In the cathode forming material of Comparative Example 1 in which LSCF and LSTF were simply mixed at a ratio of 70:30, the maximum power density was reduced to about half that of Comparative Example 2. On the other hand, in Examples 1 to 4 in which mechanochemical treatment was applied to Comparative Example 1, the power generation performance was higher than that of Comparative Example 1, and the maximum output at 700 ° C. was 0.4 W / cm ² or more (preferably 0.45 W / cm ² or more). This is presumably because the particles can be combined by mechanochemical treatment of LSCF and LSTF, and the conduction path of electrons and oxygen ions is increased. That is, by performing mechanochemical treatment so that the specific surface area decreases at a rate of 10% to 40% (preferably 15% to 30%), the cathode is further excellent in electron conductivity and oxygen ion conductivity. It has been shown that it can be a forming material.

[Electron microscope observation]
Moreover, the SOFC after the power generation test was disassembled, and the surface of the anode (the surface of the molded body) was observed with a scanning electron microscope (SEM) to confirm the state of the electrode surface. Then, in Comparative Examples 2 and 3 in which the thermal expansion coefficient was higher than 15 × 10 ⁻⁶ / K, occurrence of cracks was observed on the cathode electrode surface. Therefore, in this example, it is preferable that the thermal expansion coefficient is 15 × 10 ⁻⁶ / K or less.

  From the above results, it was shown that by using the cathode forming material of the present invention, a thermal expansion and a reduction expansion can be suppressed and a cathode having excellent electrode performance can be formed. In addition, it was shown that SOFCs using the cathode can achieve both power generation performance (power density) and durability at a high level in a low temperature range.

  According to the material of the present invention, an SOFC cathode having excellent electrode performance and improved durability can be formed. Therefore, the present invention can contribute to the construction of a high-performance SOFC (or power generation system). By using such a material, it is possible to construct an SOFC that can exhibit high power generation performance even in a medium / low temperature region. Furthermore, since the cathode disclosed herein can be directly formed on a solid electrolyte, the operation is simple, and preferably battery characteristics can be improved (for example, resistance can be reduced).

10 Anode (fuel electrode)
20 Solid electrolyte 30 Cathode (Air electrode)
40 Joining member 50 SOFC
60 Gas Pipe 110 Anode-Solid Electrolyte Laminate

Claims (11)

A material for forming a cathode of a solid oxide fuel cell;
The following general formula (1):
_{(La 1-x Sr x)} (Co y Fe 1-y) O 3-δ (1)
(Where x is a real number satisfying 0.1 ≦ x ≦ 0.5, y is a real number satisfying 0.1 ≦ y ≦ 0.5, and δ is a value determined to satisfy the charge neutrality condition. is there.)
Perovskite-type oxide particles represented by
The following general formula (2):
_{(La 1-x Sr x)} (Ti y Fe 1-y) O 3-δ (2)
(Where x is a real number satisfying 0.1 ≦ x ≦ 0.5, y is a real number satisfying 0.1 ≦ y ≦ 0.5, and δ is a value determined to satisfy the charge neutrality condition. is there.)
Perovskite-type oxide particles represented by
Is mainly composed of composite particles composited by mechanochemical treatment ,
The mechanochemical treatment is performed so that an improvement in electronic conductivity is realized as compared with the case where the oxide represented by the general formula (1) and the oxide represented by the general formula (2) are mixed. A material for forming a cathode of a solid oxide fuel cell.   The composite particle includes a core portion made of an oxide represented by the general formula (2) and a coating portion made of an oxide represented by the general formula (1) formed on at least a part of the surface of the core portion. The material for forming a cathode of a solid oxide fuel cell according to claim 1, comprising:   In the composite particles, the mass ratio of the oxide represented by the general formula (1) and the oxide represented by the general formula (2) is (1) :( 2) = 80: 20 to 30:70. The material for forming a cathode of a solid oxide fuel cell according to claim 1 or 2, wherein The composite particles have a thermal expansion coefficient of 13 × 10 ⁻⁶ / K or more and 15 × 10 ⁻⁶ / K or less as measured by thermomechanical analysis, and a reductive expansion coefficient of 1% or less. The material for forming a cathode of a solid oxide fuel cell according to any one of the above.   The material for forming a cathode of a solid oxide fuel cell according to any one of claims 1 to 4, wherein the composite particles are dispersed or dissolved in at least one solvent and prepared in a paste form. A solid oxide fuel cell comprising an anode, a solid electrolyte and a cathode,
The solid oxide fuel cell, wherein the cathode is formed mainly of the composite particles according to any one of claims 1 to 5. The cathode, the solid electrolyte, and the anode are formed in a layered manner,
The solid oxide fuel cell according to claim 6, wherein the thickness of the cathode in the laminated structure is 10 μm or more and 100 μm or less.   The solid oxide fuel cell according to claim 7, wherein the cathode is formed directly on the solid electrolyte without providing a reaction inhibiting layer. A method for producing a cathode forming material for a solid oxide fuel cell;
The following general formula (1):
_{(La 1-x Sr x)} (Co y Fe 1-y) O 3-δ (1)
(Where x is a real number satisfying 0.1 ≦ x ≦ 0.5, y is a real number satisfying 0.1 ≦ y ≦ 0.5, and δ is a value determined to satisfy the charge neutrality condition. is there.)
Perovskite-type oxide particles represented by
The following general formula (2):
_{(La 1-x Sr x)} (Ti y Fe 1-y) O 3-δ (2)
(Where x is a real number satisfying 0.1 ≦ x ≦ 0.5, y is a real number satisfying 0.1 ≦ y ≦ 0.5, and δ is a value determined to satisfy the charge neutrality condition. is there.)
Perovskite-type oxide particles represented by
Preparing
The oxide represented by the general formula (1) and the oxide represented by the general formula (2) are composited by mechanochemical treatment to obtain composite particles , wherein the mechanochemical treatment is performed by the general formula Compared with the case where the oxide represented by (1) and the oxide represented by the general formula (2) are mixed, an improvement in electronic conductivity is achieved.
Preparing a cathode-forming material using the composite particles;
A method for producing a material for forming a cathode of a solid oxide fuel cell. In the mechanochemical treatment, the relationship between the specific surface area B (m ² / g) after the treatment measured by the nitrogen adsorption method and the specific surface area A (m ² / g) before the treatment is 10 ≦ (A The production method according to claim 9, which is performed so that −B) / A ≦ 40.   Preparation of the oxide particles is such that the mass ratio of the oxide represented by the general formula (1) and the oxide represented by the general formula (2) is (1) :( 2) = 80: 20 to The manufacturing method according to claim 9 or 10, wherein 30:70 is prepared.