Composite oxide powder and its manufacturing method, air electrode material, and solid oxide fuel cell

Abstract

The present invention provides a composite oxide powder for air electrode materials that can suppress the decrease in conductivity while maintaining a high open porosity of the air electrode. [Solution] The composite oxide powder is a composite oxide powder having a perovskite-type structure, wherein the composition formula of the composite oxide powder is La x Sr 1-x The molecule is MnO3 (where x is between 0.6 and 0.9), and its average aspect ratio is 2.0 or greater.

Description

[Technical Field]

[0001] The present invention relates to a composite oxide powder having a perovskite-type structure, and more particularly to a composite oxide powder suitably used as an air electrode material for a solid oxide fuel cell (SOFC; hereinafter sometimes simply referred to as "SOFC"), and a method for producing the same. [Background technology]

[0002] SOFCs are being developed as a next-generation power generation device with low environmental impact due to their high power generation efficiency among various types of fuel cells and their ability to use a variety of fuels. An SOFC single cell has a structure in which a porous air electrode (cathode), a dense solid electrolyte containing oxide ion conductors, and a porous fuel electrode (anode) are stacked in this order (see Figure 5). When an SOFC is operating, an O2 (oxygen)-containing gas such as air is supplied to the air electrode, and a fuel gas such as H2 (hydrogen) is supplied to the fuel electrode. When an electric current is applied to the SOFC in this state, the O2 is reduced at the air electrode and O2 is produced. 2- It becomes an anion (oxygen ion). And this O 2- Anions pass through the solid electrolyte to the fuel electrode, where they oxidize H2 and release electrons. This generates electrical energy (i.e., electricity).

[0003] The reduction reaction of O2 at the air electrode occurs at the interface between the air electrode and the solid electrolyte. Therefore, to improve power generation efficiency, the air electrode must have many pores extending from its outer surface to this interface. Furthermore, the air electrode must also possess high conductivity. However, the open porosity and conductivity of the air electrode are conflicting properties; increasing the open porosity of the air electrode hinders the flow of current due to the pores, thus reducing conductivity. In other words, achieving both high open porosity and high conductivity in the air electrode has been a challenging task.

[0004] For example, Patent Document 1 describes a perovskite-type composite oxide powder, and Example 5 describes a powder with the compositional formula La xSr 1-x A perovskite-type composite oxide represented by MnO3(x=0.8) is disclosed. Patent document 2 discloses a perovskite-type composite oxide powder in which the volume-average particle size and crystallite size are within a specific range. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-162176 [Patent Document 2] Japanese Patent Publication No. 2020-113424 [Overview of the project] [Problems that the invention aims to solve]

[0006] While the aforementioned disclosed technology can be expected to improve the power generation efficiency of SOFCs to some extent, further improvements in power generation efficiency are desired. One method to increase the open porosity of an air electrode is to lower the firing temperature when obtaining the air electrode. However, when increasing the open porosity using this method when manufacturing an air electrode from a composite oxide powder, there is a problem in that the conductivity of the air electrode decreases. There is a need for a composite oxide that can obtain high conductivity when the open porosity of the air electrode is the same.

[0007] Therefore, the object of the present invention is to provide a composite oxide powder for air electrode material that can increase conductivity while maintaining the open porosity of the air electrode, a method for producing the same, an air electrode material using the composite oxide powder, and a solid oxide fuel cell using the air electrode material. [Means for solving the problem]

[0008] A composite oxide powder according to one embodiment of the present invention that achieves the above objective is a composite oxide powder having a perovskite-type structure, wherein the composition formula of the composite oxide powder is La x Sr 1-xThe compound is characterized by being MnO3 (where x is between 0.6 and 0.9) and having an average aspect ratio (major diameter of particles / minor diameter of particles) of 2.0 or higher. The aspect ratio of the composite oxide powder is measured by the measurement method described later.

[0009] Furthermore, the present invention provides an air electrode material for a solid oxide fuel cell, characterized by containing 10% to 100% by mass of the composite oxide powder having the above-mentioned configuration.

[0010] Furthermore, the present invention provides a solid oxide fuel cell comprising a fuel electrode, a solid electrolyte, and an air electrode, wherein the air electrode is composed of a calcined body of the air electrode material described above.

[0011] Furthermore, a method for producing a composite oxide powder according to one embodiment of the present invention that achieves the above objective comprises the steps of: dissolving La raw materials, Sr raw materials, and Mn raw materials in a solvent to prepare a solution; adding the prepared solution to an aqueous ammonia solution, blowing in carbon dioxide gas to precipitate a precursor of the composite oxide powder; separating and drying the precipitated precursor; calcining the dried precursor to obtain a calcined product; and pulverizing the obtained calcined product, characterized in that the amount (mol) of carbon dioxide gas blown into the solution is 2.0 times or more the total number of moles of La, Sr, and Mn in the raw materials. [Effects of the Invention]

[0012] When the composite oxide powder of the present invention is used as an air electrode material, the conductivity can be increased while maintaining the open porosity of the air electrode. Furthermore, the method for producing the composite oxide powder of the present invention allows for the efficient and reliable production of a composite oxide powder having a predetermined average aspect ratio. [Brief explanation of the drawing]

[0013] [Figure 1] This is an SEM image (20,000x magnification) of the composite oxide powder from Example 1. [Figure 2] This is an SEM image (20,000x magnification) of the composite oxide powder of Comparative Example 1. [Figure 3] SEM photograph (20,000 times magnification) of the composite oxide powder of Comparative Example 2. [Figure 4] Graph showing the change in conductivity with respect to the open porosity of the air electrode material using the composite oxide powders of Example 1 and Comparative Examples 1 and 2. [Figure 5] Cross-sectional configuration diagram schematically showing an example of a solid oxide fuel cell.

Mode for Carrying Out the Invention

[0014] (Composite Oxide Powder) One of the major features of the composite oxide powder having a perovskite-type structure according to the present invention (hereinafter sometimes referred to as "perovskite-type composite oxide powder") is that the average aspect ratio is 2.0 or more. When such a composite oxide powder is used as one of the air electrode materials, although the mechanism is unclear at present, the conductivity can be increased while maintaining the open porosity of the air electrode. The preferable average aspect ratio of the composite oxide powder is 2.3 or more.

[0015] The composite oxide powder according to the present invention has a perovskite-type structure, and its composition is La x Sr 1-x MnO3 (where x is 0.6 to 0.9). By setting x to be 0.6 or more and 0.9 or less, the application characteristics as an air electrode material can be satisfied.

[0016] The preferable volume average particle diameter of the composite oxide powder is 2.0 μm or less, more preferably 1.0 μm or less. On the other hand, the preferable lower limit value of the volume average particle diameter is 0.3 μm.

[0017] (Method for Producing Composite Oxide Powder) Next, the method for producing the composite oxide powder according to the present invention will be specifically described. In the production method according to the present invention, the composite oxide powder is produced through the following steps.

[0018] Step (a): Step of dissolving the raw materials of La, Sr, and Mn in a solvent to prepare a solution Step (b): After adding the prepared solution to an aqueous ammonia solution, carbon dioxide gas is blown in to precipitate the precursor of the complex oxide powder. Step (c): Step of separating and drying the precipitated precursor. Step (d): A step of firing the dried precursor to obtain a fired product. Step (e): Step of crushing the obtained calcined material.

[0019] The following provides further explanation of steps (a) through (e).

[0020] Process (a) The raw materials for La, Sr, and Mn are prepared by dissolving, for example, water-soluble nitrates in water to create raw material solutions. The raw materials for each element are preferably salts from which elements other than perovskite-type complex oxides are released as gas during calcination, in order to reduce the amount of impurities. These may be nitrates, oxides, carbonates, sulfates, chlorides, or organic acid salts of each element, but nitrates, sulfates, oxides, or carbonates are preferred. Furthermore, it is preferable to select the raw materials so that the weight of impurities in each component raw material is 100 ppm or less.

[0021] The concentration of each component raw material in the raw material solution is preferably between 0.01 mol / L and 0.60 mol / L, and more preferably between 0.01 mol / L and 0.50 mol / L. If this upper limit is not exceeded, the viscosity of the slurry obtained after neutralization with aqueous ammonia solution will not increase. Therefore, productivity can be maintained when the slurry is subjected to subsequent processes.

[0022] Process (b) The raw material solution is neutralized by adding it to an aqueous ammonia solution, thereby precipitating a precursor of the complex oxide. Then, the prepared solution is added to the aqueous ammonia solution, and carbon dioxide gas is blown in.

[0023] The amount of carbon dioxide blown in (mol) is 2.0 times or more the total number of moles of La, Sr, and Mn in the raw material solution. This yields a precursor of a complex oxide with an aspect ratio of 2.0 or higher. Here, the precursor refers to a metal hydroxide, metal oxide, metal carbonate, or a mixture thereof. A more preferable amount of carbon dioxide blown in (mol) is 3.0 times or more the total number of moles of La, Sr, and Mn in the raw material solution.

[0024] In this embodiment, it is preferable that the liquid temperature during the reaction is low in order to form this precursor. Specifically, it is preferable that the liquid temperature be 60°C or lower throughout step (b), and more preferably 45°C or lower. Since the reaction takes place in an aqueous solution, it is preferable to carry out the reaction at a temperature above the freezing point of water, i.e., 0°C or higher, in order to ensure the fluidity of the reaction system.

[0025] Furthermore, throughout step (b), the pH of the reaction solution is preferably 6 or higher, and more preferably alkaline.

[0026] Process (c) The generated and precipitated precursor should be separated into solid and liquid components by filtration, centrifugal sedimentation, decantation, etc., and washed with water to reduce the residue of impurity ions. The obtained precursor should be dried by methods such as natural drying, heat drying, or vacuum drying. After drying, grinding or classification should be carried out as needed.

[0027] Process (d) Next, the dried precursor is heat-treated (calcined) to obtain a composite oxide having a perovskite-type crystal structure. The calcination temperature is preferably 900 to 1600°C, and preferably 950°C or higher to improve the conductivity of the perovskite-type composite oxide. If the calcination temperature is too high, the particles will sinter and become difficult to dissolve, so it is preferable to keep it below 1500°C. Furthermore, to obtain a perovskite-type crystal structure from the dried powder of the perovskite-type composite oxide precursor, the temperature is preferably below 1300°C, and more preferably between 950 and 1300°C.

[0028] Process (e) Next, the perovskite-type composite oxide obtained in this way can be crushed as needed and then pulverized to obtain a perovskite-type composite oxide powder. For pulverization, a wet pulverization method using pulverizing beads in an aqueous solution or a wet crushing method using particle collisions in an aqueous solution is preferred.

[0029] (Air electrode material) The composite oxide powder described above is suitably used as an air electrode material for SOFCs. The content of the composite oxide powder in the air electrode material is preferably in the range of 10% to 100% by mass relative to the total air electrode material. By having a composite oxide powder content in the above range, it is possible to maintain a higher open porosity of the air electrode while increasing its conductivity. A more preferable composite oxide powder content is 30% to 100% by mass.

[0030] (Air pole) The air electrode material described above is suitable for use as an air electrode for SOFCs after being molded into a predetermined shape and then fired. Specifically, for example, first, the air electrode material of the present invention is mixed with a binder to create a slurry, and the cathode material is printed by screen printing. Then, heat treatment is performed to obtain the cathode electrode.

[0031] (Solid oxide fuel cell, SOFC) A solid oxide fuel cell will be described. Figure 5 is a schematic cross-sectional diagram showing an example of a solid oxide fuel cell. It has a structure in which a thin plate-shaped or sheet-shaped fuel electrode 1, which serves as a support, a solid electrolyte membrane 2 formed on the surface of the fuel electrode 1, and a thin plate-shaped or sheet-shaped air electrode 3 formed on the surface of the solid electrolyte membrane 2 are stacked.

[0032] Then, fuel gas (typically hydrogen (H2), but hydrocarbons such as methane (CH4) may also be used) is supplied to the fuel electrode 1, and a gas containing oxygen (O2) (air) is passed through the air electrode 3. When an electric current is applied to the fuel cell, the oxygen in the air at the air electrode 3 becomes oxide ions. These oxide ions are supplied from the air electrode 3 to the fuel electrode 1 via the solid electrolyte 2. At the fuel electrode 1, they react with the fuel gas to produce water (H2O), release electrons, and generate electricity.

[0033] SOFCs are manufactured by first creating a laminate of components such as a fuel electrode and a solid electrolyte membrane, and then forming an air electrode by forming a layer containing the air electrode material on top of the laminate using methods such as printing or vapor deposition, and then sintering it, although this process varies depending on the configuration and manufacturing process of the fuel cell to which the SOFC is applied.

[0034] The thickness of the air electrode can be appropriately determined according to the cell structure, etc., and is not particularly limited, but it is preferably 20 μm or more and 50 μm or less.

[0035] Examples of solid electrolyte layers include ceria-based solid oxide electrolytes and zirconia-based solid oxide electrolytes.

[0036] The thickness of the solid electrolytic layer is set to a balance between being thick enough to maintain the density of the solid electrolyte layer and thin enough to provide favorable conductivity for oxygen ions or hydrogen ions as a fuel cell, preferably between 0.1 μm and 50 μm, and more preferably between 1 μm and 20 μm.

[0037] As the fuel electrode, it only needs to have a porous structure and be configured to be able to contact the supplied fuel gas, and materials conventionally used in solid oxide fuel cells can be used. For example, metal oxides composed of one or more of metals and / or metal elements such as nickel (Ni), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), ruthenium (Ru) and other platinum group elements, cobalt (Co), lanthanum (La), strontium (Sr), titanium (Ti), etc. can be mentioned. These may be used alone or in combination of two or more.

[0038] From the viewpoints of durability, thermal expansion coefficient, etc., the film thickness of the fuel electrode is preferably 20 μm or more and 1 mm or less, and more preferably 20 μm or more and 250 μm or less.

[0039] In addition, the structure of the SOFC can be a conventionally known flat type, polygonal type, cylindrical type (Tubular), or flat cylindrical type (Flat Tubular) obtained by vertically crushing the peripheral side surface of a cylinder, etc., and the shape and size are not particularly limited. Further, as the flat SOFC, in addition to the anode-supported cell (ASC), for example, an electrolyte-supported cell (ESC) with a thick electrolyte, a cathode-supported cell (CSC) with a thick air electrode, etc. can be used. In addition, it can also be a metal-supported cell (MSC) in which a porous metal sheet is placed under the fuel electrode.

[0040] (Particle size distribution measurement method) Immediately after putting 0.15 g of the composite oxide powder into 60 mL of a 0.05 mass% aqueous sodium hexametaphosphate solution as a solvent and performing ultrasonic treatment, the particle size distribution of the obtained particles is measured by a Microtrac particle size distribution measuring device (MT3300EX manufactured by Nikkiso Co., Ltd.) (with a particle refractive index of 2.40, a solvent refractive index of 1.333, and a calculation mode of MT3000II). Then, the cumulative 50% particle size D 50 (Volume average particle diameter) is obtained.

[0041] (BET specific surface area) The BET specific surface area of ​​the composite oxide powder was measured using a BET specific surface area measuring device (Macsorb® HM model-1210, manufactured by Mountec Co., Ltd.) by the BET single-point method with nitrogen adsorption. The degassing conditions before measurement were 105°C for 20 minutes.

[0042] (Method for measuring the average aspect ratio) The composite oxide powder was observed at 20,000x magnification using a scanning electron microscope (SEM), and the aspect ratio was determined using the image analysis-based particle size distribution measurement software Mac-View. Specifically, for 50 particles whose contours could be confirmed, the aspect ratio, defined as the ratio of the major axis to the minor axis, was measured using the software, and the average of the measured values ​​was taken as the average aspect ratio. Here, the major and minor axes were defined as the longest side and shortest side of the circumscribing quadrilateral with the smallest area that circumscribes the selected particle.

[0043] (Open porosity) The measurement is performed in accordance with the Japanese Industrial Standard JIS R1634:1998, Method for Measuring Density and Porosity of Sintered Fine Ceramics. The air electrode material, processed into pellet form, is dried in a constant temperature oven at 110°C ± 5°C, cooled in a desiccator, and its mass is measured. This operation is repeated, and the mass when a constant weight is reached is taken as the dry mass W1. After measuring the dry mass, the sample is placed at the bottom of a vacuum container and suctioned under a vacuum of 2.0 kPa or less for 15 minutes to thoroughly remove air from the pores of the powder, and then water is injected. In this case, water is injected until the sample is completely submerged, then the stopcock is gradually opened to return to atmospheric pressure, and it is left for 30 minutes. The vacuum pump is kept running during the injection of the fluid and stopped after injection. The water mass of the saturated sample is measured while the saturated sample is suspended in water by a wire, and the water mass W2 is taken as the value corrected for the mass of the jig. The mass of the saturated sample is measured after removing it from the water, quickly wiping the surface with a damp gauze to remove water droplets, and then determining the saturated mass W3. Here, the gauze should be thoroughly soaked in water and then squeezed just enough to remove only the water droplets from the surface of the test specimen. The open porosity Po is calculated using the following formula and rounded to one decimal place in accordance with JIS Z 8401. Po = (W3 - W1) / (W3 - W2) × 100

[0044] (conductivity) To measure the conductivity of the air electrode, the air electrode material is pelletized, and its conductivity is measured using a source meter (Series 2400 Source Meter, manufactured by Keithley Instruments, Inc.). Specifically, a 0.2 mm diameter platinum wire is wrapped around a pellet-shaped air electrode at four locations, at both ends and on the inside, with a spacing of 3.5 mm between them. The sample surface and the platinum wire are joined using silver paste. This pellet is heated from 25°C to 500°C using an electric heater. While maintaining the temperature at 500°C, current is applied to the terminals at both ends using the four-terminal method of a source meter, varying the current value from 30 mA to -30 mA in 10 mA increments, and the voltage value generated at the inner terminal is measured. The resistance value is calculated from the relationship between the voltage and current at the six obtained points. Then, the conductivity σ is calculated from the following formula. Conductivity σ=L / (R×b×d) (In the formula, L: distance between voltage terminals, b × d: cross-sectional area, R: resistance) [Examples]

[0045] Example 1 Lanthanum nitrate (La), strontium nitrate (Sr), and manganese nitrate (Mn) were dissolved in pure water to obtain a molar ratio of La:Sr:Mn of 0.8:0.2:1.0, and 0.75 kg of raw material aqueous solution was prepared with a total molar concentration of La, Sr, and Mn of 0.6 mol / L. Next, 2.0 kg of pure water was added to the reaction vessel and stirring with a stirring blade was started. This stirring continued until the injection of CO2 gas (carbon dioxide), which will be described later, was completed. Next, nitrogen gas was injected into the reaction vessel at a flow rate of 180 mL / min, and 0.25 kg of 22% by mass ammonia aqueous solution was added. After the entire raw material aqueous solution was added to the reaction vessel in one go, the injection of nitrogen gas was stopped, and air was injected at a flow rate of 150 mL / min for 120 minutes. Next, the air injection was stopped, and nitrogen gas at a flow rate of 180 mL / min and CO2 gas at a flow rate of 540 mL / min were injected for 120 minutes to obtain a slurry containing a precursor of perovskite-type complex oxide. Here, the flow rate of CO2 gas was set to an amount such that the total amount injected was 4.78 times the total amount of La, Sr, and Mn in molar ratio. Furthermore, from the time the aqueous raw material solution was added all at once until the injection of CO2 gas was stopped, the temperature of the reaction solution was below 60°C, and the pH of the reaction solution was alkaline. Next, the obtained slurry was filtered, and the solid components were washed with water to obtain a wet cake. Next, the wet cake was formed into cylindrical pellets and dried in air at 250°C for 2 hours to obtain a black dried powder. Next, the obtained dried powder was placed in a crucible and calcined in an electric muffle furnace (Toyo Seisakusho Co., Ltd., model name: KM-160) at 1125°C in air for 2 hours to obtain calcined powder. The obtained calcined powder was subjected to a sample mill grinding device (Kyōritsu Riko Co., Ltd., model name: SK-M10) and the grinding operation was repeated twice with a rotation scale of 60 and an operating time of 30 seconds to obtain dry-ground powder. The obtained dry-ground powder was subjected to wet grinding using a bead mill (Aimex Corporation, model name: 4TSG-1 / 16), 1.00 mm diameter ZrO2 beads, and water (liquid medium) to obtain the perovskite-type composite oxide powder according to Example 1. The specific surface area, average particle diameter, and average aspect ratio of the obtained composite oxide powder were measured using the aforementioned measurement method, and the specific surface area was found to be 3.68 m². 2 The particle size was 1.02 μm and the average aspect ratio was 2.32. The number of particles measured at the time of the average aspect ratio measurement was 50. Figure 1 shows an SEM image of the composite oxide powder of Example 1.

[0046] (Air electrode materials and fabrication of air electrodes) 10 g of composite oxide powder was weighed, 3.7 g of 10% polyvinyl alcohol was added and kneaded, and dried at 110°C for 2 hours. The resulting dried material was crushed in a mortar to obtain the air electrode material. 1.7 g of the obtained air electrode material was weighed and placed in a mold having a rectangular cross-sectional shape with a width of 5 mm and a depth of 20 mm. It was molded using a uniaxial molding machine under a load of 12.2 kN, and then compacted using a CIP molding machine under a pressure of 290 MPa. The resulting pellets were fired in air at 800°C, 900°C, and 1000°C (firing temperature) for 2 hours. The open porosity and conductivity of the obtained pelletized air electrodes were measured using the method described above. The measurement results are shown in Table 1 and Figure 4.

[0047] (Comparative Example 1) A perovskite-type composite oxide powder according to Comparative Example 1 was obtained using the same procedure as in Example 1, except that the flow rate of CO2 gas was set to an amount such that the total amount of injected CO2 was 0.88 times the molar ratio of the total amount of La, Sr, and Mn. The specific surface area, average particle diameter, and average aspect ratio of the obtained composite oxide powder were measured using the measurement method described above, and the specific surface area was found to be 3.50 m². 2 The particle size was 0.99 μm and the average aspect ratio was 1.78. The number of particles measured at the time of the average aspect ratio measurement was 40. Figure 2 shows an SEM image of the composite oxide powder of Comparative Example 1. The obtained perovskite-type composite oxide powder was used as the air electrode material and air electrode in the same procedure as in Example 1. The open porosity and conductivity of the obtained air electrode were measured using the method described above. The measurement results are shown in Table 1 and Figure 4.

[0048] (Comparative Example 2) A perovskite-type composite oxide powder according to Comparative Example 2 was obtained by the same procedure as in Example 1, except that the flow rate of CO2 gas was adjusted so that the total amount of injected material was 1.73 times the molar ratio of the total amount of La, Sr, and Mn. When the specific surface area, average particle diameter, and average aspect ratio of the obtained composite oxide powder were measured, the specific surface area was 3.80 m². 2 The particle size was 0.86 μm and the average aspect ratio was 1.59. The number of particles measured at the time of the average aspect ratio measurement was 40. Figure 3 shows an SEM image of the composite oxide powder of Comparative Example 2. The obtained perovskite-type composite oxide powder was used as the air electrode material and air electrode in the same procedure as in Example 1. The open porosity and conductivity of the obtained air electrode were measured using the method described above. The measurement results are shown in Table 1 and Figure 4.

[0049] [Table 1]

[0050] As is clear from Table 1 and Figure 4, even with perovskite-type composite oxide powders of the same composition, the air electrode using the composite oxide powder of Example 1, which had an average aspect ratio of 2.0 or higher, exhibited higher conductivity at the same open porosity than the air electrodes using the composite oxide powders of Comparative Examples 1 and 2, which had an average aspect ratio of less than 2.0. Furthermore, perovskite-type composite oxide powders with an average aspect ratio of 2.0 or higher were effectively produced by adding the raw material solution to an aqueous ammonia solution during the manufacturing process, followed by blowing in carbon dioxide in a number of moles equal to or greater than 2.0 times the total number of moles of La, Sr, and Mn in the raw materials. [Industrial applicability]

[0051] When the composite oxide powder of the present invention is used as an air electrode material, the conductivity can be increased while maintaining the open porosity of the air electrode. [Explanation of Symbols]

[0052] 1 Fuel electrode 2 Solid electrolyte membrane 3. Air electrode

Claims

1. A composite oxide powder having a perovskite-type structure, The composition formula of the aforementioned composite oxide powder is La ｘ Sr １－ｘ MnO ３ (In the formula, x is between 0.6 and 0.9) And, The average aspect ratio is 2.0 or higher. A composite oxide powder characterized by the following features.

2. An air electrode material for a solid oxide fuel cell, characterized by containing 10% by mass or more and 100% by mass or less of the composite oxide powder described in claim 1.

3. A solid oxide fuel cell comprising a fuel electrode, a solid electrolyte, and an air electrode, A solid oxide fuel cell characterized in that the air electrode is composed of a fired body of the air electrode material described in claim 2.

4. A method for producing a composite oxide powder according to claim 1, The process involves dissolving raw materials for La, Sr, and Mn in a solvent to prepare a solution, The process involves adding the prepared solution to an aqueous ammonia solution, then blowing in carbon dioxide to precipitate a precursor of the complex oxide powder, A step of separating and drying the precipitated precursor, A step of firing the dried precursor to obtain a fired product, The process of crushing the resulting calcined material and It has, A method for producing a composite oxide powder, characterized in that the amount (mol) of carbon dioxide blown into the solution is 2.0 times or more the total number of mol of La, Sr, and Mn in the raw materials.

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