Aqueous aqueous precursor for the production of complex oxide nanoparticles and method for producing complex oxide nanoparticles

Abstract

To provide an aqueous precursor solution for producing composite oxide nanoparticles, that enables production of nanoparticles of lanthanum-calcium-iron composite oxide by firing at a low temperature.SOLUTION: A precursor aqueous solution for producing composite oxide nanoparticles comprises: at least one lanthanum compound selected from lanthanum carbonates, acetates, oxides, hydroxides, oxyhydroxides, and alkoxides; at least one calcium compound selected from calcium carbonate, acetate, citrate, oxide, peroxide, hydroxide, and alkoxide; at least one iron compound selected from iron carbonates, acetates, citrates, oxides, hydroxides, oxyhydroxides, and iron ammonium citrate; and a coordinating organic compound having a coordinating ability capable of coordinating with a metal ion, wherein the aqueous precursor solution has a pH greater than 2.7 to less than 8. Mass of the coordinating organic compound is more than twice the theoretical mass of produced lanthanum-calcium-iron composite oxide nanoparticles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aqueous precursor solution for producing nanoparticles of a complex oxide, And, Method for producing composite oxide nanoparticles using the aqueous precursor solution. In the law To relate to. [Background technology]

[0002] As a composite oxide used in the air electrode of a solid oxide fuel cell (SOFC), lanthanum calcium iron composite oxide (La) is used. 1-x Ca x ) y FeO3 (hereinafter sometimes simply referred to as lanthanum calcium iron composite oxide) is being considered. In the above chemical formula, x is greater than 0 and less than or equal to 0.4, and y is between 0.95 and 1.00. Since lanthanum calcium iron composite oxide does not contain strontium or cobalt, there is no risk of high-resistance phases such as SrCrO4 and SrZrO3 being formed by the reaction of zirconium and chromium with strontium and cobalt used in metal-supported solid oxide fuel cells. Therefore, if lanthanum calcium iron composite oxide is used as the air electrode in a solid oxide fuel cell, it is possible to manufacture a solid oxide fuel cell with excellent long-term durability. Non-patent document 1 proposes a manufacturing technology for lanthanum calcium iron composite oxide powder. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Journal of Power Sources,448,2020,227426 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, the technology disclosed in Non-Patent Document 1 uses lanthanum(III) nitrate and iron(III) nitrate as raw materials. Therefore, when producing lanthanum calcium iron complex oxide powder, it was necessary to calcine an aqueous solution containing lanthanum(III) nitrate and iron(III) nitrate at a high temperature of 900°C or higher. Calcination at a high temperature of 900°C or higher promotes particle growth, making it difficult to obtain nano-sized particles (nanoparticles) which are essential for the expression of high catalytic activity. Furthermore, when manufacturing metal-supported solid oxide fuel cells, firing at high temperatures of 900°C or higher accelerates the oxidation of the metal support, making it difficult to apply the technology disclosed in Non-Patent Document 1 to the manufacture of metal-supported solid oxide fuel cells.

[0005] The present invention aims to provide a precursor aqueous solution that enables the production of lanthanum calcium iron composite oxide nanoparticles by low-temperature calcination, and a method for producing lanthanum calcium iron composite oxide nanoparticles. 。 [Means for solving the problem]

[0006] A precursor aqueous solution for producing composite oxide nanoparticles according to one aspect of the present invention is a lanthanum calcium iron composite oxide (La 1-x Ca x ) yA precursor aqueous solution for producing composite oxide nanoparticles for producing nanoparticles of FeO3 (where x is greater than 0 and less than or equal to 0.4, and y is greater than or equal to 0.95 and less than or equal to 1.00), which contains at least one lanthanum compound selected from lanthanum carbonate, acetate, oxide, hydroxide, oxyhydroxide, and alkoxide, at least one calcium compound selected from calcium carbonate, acetate, citrate, oxide, peroxide, hydroxide, and alkoxide, at least one iron compound selected from iron carbonate, acetate, citrate, oxide, hydroxide, oxyhydroxide, and ammonium iron citrate, and a coordinating organic compound having a coordinating ability capable of coordinating with metal ions, with a pH greater than 2.7 and less than 8, and the mass of the coordinating organic compound contained in the precursor aqueous solution for producing the composite oxide nanoparticles is more than twice the theoretical mass of the nanoparticles of the lanthanum calcium iron composite oxide produced from the lanthanum compound, calcium compound, and iron compound contained in the precursor aqueous solution for producing the composite oxide nanoparticles.

[0007] The method for producing composite oxide nanoparticles according to another aspect of the present invention is a method for producing nanoparticles of lanthanum calcium iron composite oxide (La 1-x Ca x ) y FeO3 (where x is greater than 0 and less than or equal to 0.4, and y is greater than or equal to 0.95 and less than or equal to 1.00), which has a firing step of firing the precursor aqueous solution for producing composite oxide nanoparticles according to the above aspect. The solid oxide fuel cell single cell according to still another aspect of the present invention is a solid oxide fuel cell single cell having a laminated structure in which an air electrode, a solid electrolyte layer, and a fuel electrode are laminated in this order, and pores are open on the surface of the porous substrate constituting the air electrode, and nanoparticles of lanthanum calcium iron composite oxide (La 1-x Ca x ) y FeO3 (where x is greater than 0 and less than or equal to 0.4, and y is greater than or equal to 0.95 and less than or equal to 1.00) are arranged.

Advantages of the Invention

[0008] The precursor aqueous solution for producing composite oxide nanoparticles according to the present invention and the method for producing composite oxide nanoparticles can produce nanoparticles of lanthanum calcium iron composite oxide by firing at a low temperature. 。

Brief Description of the Drawings

[0009] [Figure 1] It is a schematic conceptual diagram for explaining an embodiment of the precursor aqueous solution for producing composite oxide nanoparticles according to the present invention. [Figure 2] It is a schematic conceptual diagram for explaining an embodiment of the method for producing composite oxide nanoparticles according to the present invention. [Figure 3] It is a diagram showing the results of analyzing the products generated during firing of the precursor aqueous solutions for producing composite oxide nanoparticles of Example 1-1 and Comparative Example 3-1 by X-ray diffraction method. [Figure 4] It is a schematic cross-sectional view for explaining the structure of a solid oxide fuel cell single cell used for evaluation in Examples and Comparative Examples.

Modes for Carrying Out the Invention

[0010] One embodiment of the present invention will be described below. Note that this embodiment shows an example of the present invention, and the present invention is not limited to this embodiment. Also, various changes or improvements can be made to this embodiment, and forms with such changes or improvements can also be included in the present invention.

[0011] The precursor aqueous solution for producing composite oxide nanoparticles of this embodiment is a precursor aqueous solution for producing nanoparticles of lanthanum calcium iron composite oxide (La 1-x Ca x ) y FeO3 (where x is greater than 0 and less than or equal to 0.4, and y is greater than or equal to 0.95 and less than or equal to 1.00), which contains a lanthanum compound, a calcium compound, an iron compound, and a coordinating organic compound.

[0012] Lanthanum compounds are at least one selected from lanthanum carbonate, lanthanum acetate, lanthanum oxide, lanthanum hydroxide, lanthanum oxyhydroxide, and lanthanum alkoxide. Calcium compounds are at least one selected from calcium carbonate, calcium acetate, calcium citrate, calcium oxide, calcium peroxide, calcium hydroxide, and calcium alkoxide. Iron compounds are at least one selected from iron carbonate, iron acetate, iron citrate, iron oxide, iron hydroxide, iron oxyhydroxide, and ammonium iron citrate. Coordinating organic compounds are organic compounds that have coordinating ability to coordinate to metal ions.

[0013] Furthermore, the pH of the aqueous precursor solution for producing composite oxide nanoparticles in this embodiment is greater than 2.7 and less than 8. Furthermore, the mass of the coordinating organic compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles of this embodiment is more than twice the theoretical mass of the lanthanum calcium iron composite oxide nanoparticles produced from the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles of this embodiment.

[0014] The aqueous precursor solution for the production of composite oxide nanoparticles in this embodiment contains the above-mentioned mass of coordinating organic compound. Therefore, in the aqueous precursor solution for the production of composite oxide nanoparticles in this embodiment, the coordinating organic compound is coordinated to the lanthanum ions, calcium ions, and iron ions derived from the lanthanum compound, calcium compound, and iron compound, so the lanthanum ions, calcium ions, and iron ions are extremely uniformly dispersed in the aqueous precursor solution for the production of composite oxide nanoparticles.

[0015] Figure 1 schematically shows an example of a state in which lanthanum ions, calcium ions, and iron ions are uniformly dispersed in the aqueous precursor for the production of composite oxide nanoparticles according to this embodiment, due to the action of a coordinating organic compound. In Figure 1, the coordinating organic compound is indicated by a short dashed line.

[0016] Since lanthanum ions, calcium ions, and iron ions are uniformly dispersed in the aqueous precursor solution for the production of composite oxide nanoparticles, high temperatures of 900°C or higher are not required for calcination. Even if the calcination temperature of the aqueous precursor solution for the production of composite oxide nanoparticles in this embodiment is low, for example, 700°C or lower, it is possible to produce nanoparticles of lanthanum calcium iron composite oxide. In other words, instead of composite oxide particles on the micrometer order, extremely fine composite oxide nanoparticles on the nanometer order can be obtained.

[0017] In more detail, when nanoparticles of lanthanum calcium iron composite oxide are produced by calcining an aqueous precursor solution for the production of composite oxide nanoparticles, first, the solvent such as water in the aqueous precursor solution is removed, forming an amorphous gel in which lanthanum ions, calcium ions, and iron ions are uniformly distributed. After that, calcination is performed to produce nanoparticles of lanthanum calcium iron composite oxide.

[0018] Because this amorphous gel is amorphous, elemental segregation is suppressed, and lanthanum ions, calcium ions, and iron ions are uniformly distributed. Therefore, even when calcined at low temperatures below 700°C, for example, impurities such as unreacted materials and intermediate phases are less likely to be generated, and a high-purity lanthanum calcium iron composite oxide can be obtained.

[0019] Therefore, by using lanthanum calcium iron composite oxide nanoparticles obtained from the aqueous precursor solution for producing composite oxide nanoparticles of this embodiment to manufacture a solid oxide fuel cell single cell, a catalyst with a large surface area can be obtained, making it possible to manufacture a solid oxide fuel cell single cell with excellent catalytic activity at the air electrode. Furthermore, because it can be fired at low temperatures, firing can be carried out at low cost, and lanthanum calcium iron composite oxide nanoparticles, or solid oxide fuel cell single cells containing lanthanum calcium iron composite oxide nanoparticles, can be manufactured inexpensively.

[0020] Furthermore, with the aqueous precursor solution for the production of composite oxide nanoparticles of this embodiment, for example, a metal porous support used in a metal-supported solid oxide fuel cell single cell, or a porous substrate constituting the air electrode of a solid oxide fuel cell single cell, can be impregnated with the aqueous precursor solution for the production of composite oxide nanoparticles of this embodiment and fired to produce a metal-supported solid oxide fuel cell.

[0021] In other words, since nanoparticles of lanthanum calcium iron composite oxide can be produced by calcining the aqueous precursor solution for composite oxide nanoparticle production of this embodiment at a low temperature, it is possible to manufacture a metal-supported solid oxide fuel cell without causing high-temperature damage (e.g., oxidation or deformation) to the porous metal support or porous substrate constituting the air electrode. Therefore, the aqueous precursor solution for composite oxide nanoparticle production of this embodiment can be applied to the manufacture of a metal-supported solid oxide fuel cell.

[0022] Furthermore, since lanthanum calcium iron composite oxide does not contain strontium and cobalt, there is no risk of high-resistance phases such as SrCrO4 and SrZrO3 being formed by the reaction of zirconium and chromium with strontium and cobalt, which are used in metal-supported solid oxide fuel cells (a single-phase lanthanum calcium iron composite oxide is obtained). Therefore, if lanthanum calcium iron composite oxide nanoparticles obtained from the aqueous precursor solution for composite oxide nanoparticle production of this embodiment are used as the air electrode, it is possible to manufacture solid oxide fuel cell single cells with excellent long-term durability.

[0023] Here, the term "nanoparticles" in this invention means the following: In the case of nanoparticles of lanthanum calcium iron composite oxide obtained by calcination, it means particles with an average primary particle diameter of several tens of nanometers. The lower limit of the average primary particle diameter of nanoparticles of lanthanum calcium iron composite oxide obtained by calcination is preferably 10 nm or more, the upper limit is preferably less than 100 nm, and more preferably 50 nm or less.

[0024] The method for measuring the average primary particle diameter of lanthanum calcium iron composite oxide nanoparticles is not particularly limited, but for example, it can be measured using a transmission electron microscope (TEM). For example, a transmission electron microscope image of the nanoparticles may be acquired, and the average of the major axes of any 10 nanoparticles drawn on the acquired image may be calculated and this average value taken as the average primary particle diameter of the nanoparticles.

[0025] The aqueous precursor solution for the production of composite oxide nanoparticles, the method for producing composite oxide nanoparticles, and the solid oxide fuel cell single cell of this embodiment will be described in more detail below. (1) Regarding lanthanum calcium iron composite oxide nanoparticles The lanthanum calcium iron composite oxide of this embodiment is a composite oxide containing lanthanum, calcium, and iron, and has the chemical formula (La 1-x Ca x ) y It is represented as FeO3. In the above chemical formula, x is greater than 0 and less than or equal to 0.4, and y is between 0.95 and 1.00. An example of lanthanum calcium iron composite oxide in this embodiment is La 0.65 Ca 0.35 FeO3 is one example. As mentioned above, the average primary particle size of the lanthanum calcium iron composite oxide nanoparticles is around several tens of nanometers, preferably less than 100 nm, and more preferably 50 nm or less. As mentioned above, the small average primary particle size of the lanthanum calcium iron composite oxide nanoparticles results in excellent catalytic activity.

[0026] (2) Aqueous solutions of precursors for the production of complex oxide nanoparticles The aqueous precursor solution for the production of composite oxide nanoparticles of this embodiment is an aqueous precursor solution for the production of lanthanum calcium iron composite oxide nanoparticles, and contains a lanthanum compound, a calcium compound, an iron compound, and a coordinating organic compound. The solvent for the aqueous precursor solution for producing composite oxide nanoparticles in this embodiment may be water alone, but it may also be a mixture of water and an organic solvent, as long as the lanthanum compound, calcium compound, and iron compound are dissolved in it.

[0027] (3) Regarding lanthanum compounds The lanthanum compound is at least one selected from lanthanum carbonate, acetate, oxide, hydroxide, oxyhydroxide, and alkoxide, and is preferably at least one selected from lanthanum(III) carbonate (La2(CO3)3), lanthanum(III) acetate (La(CH3COO)3), lanthanum(III) oxide (La2O3), lanthanum(III) hydroxide (La(OH)3), lanthanum(III) oxyhydroxide (LaOOH), and lanthanum isopropoxide(III) (La(C3H7O)3).

[0028] (4) Regarding calcium compounds The calcium compound is at least one selected from calcium carbonates, acetates, citrates, oxides, peroxides, hydroxides, and alkoxides, and is preferably at least one selected from calcium carbonate (CaCO3), calcium acetate (Ca(CH3COO)2), calcium citrate (Ca3(C6H5O7)2), calcium oxide (CaO), calcium peroxide (CaO2), calcium hydroxide (Ca(OH)2), and calcium methoxide (Ca(CH3O)2).

[0029] (5) Regarding iron compounds The iron compound is at least one selected from iron carbonates, acetates, citrates, oxides, hydroxides, oxyhydroxides, and ammonium iron citrate, and is preferably at least one selected from iron(III) carbonate (Fe2(CO3)3), iron(III) acetate (Fe(CH3COO)3), iron(III) citrate (Fe(C6H5O7)), iron(III) oxide (Fe2O3), iron(III) hydroxide (Fe(OH)3), iron(III) oxyhydroxide (FeOOH), and ammonium iron citrate (III).

[0030] (6) The total concentration of lanthanum compounds, calcium compounds, and iron compounds The total concentration of the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for producing composite oxide nanoparticles in this embodiment can be 5% by mass or more and 15% by mass or less, but it is preferable to be 5% by mass or more and 14% by mass or less.

[0031] The total concentration is calculated by dividing the theoretical mass of lanthanum calcium iron composite oxide nanoparticles produced from a predetermined mass of a precursor aqueous solution for the production of composite oxide nanoparticles by the predetermined mass and multiplying by 100. Here, "theoretical mass" in this invention refers to the theoretically calculated mass of lanthanum calcium iron composite oxide nanoparticles that can be produced from a predetermined mass of a precursor aqueous solution for the production of composite oxide nanoparticles.

[0032] If the total concentration of the above is 5% by mass or more, lanthanum calcium iron composite oxide nanoparticles can be efficiently produced. For example, when a porous body is impregnated with an aqueous precursor solution for producing composite oxide nanoparticles, and the impregnated porous body is calcined to form lanthanum calcium iron composite oxide nanoparticles on the surface of the porous body, lanthanum calcium iron composite oxide nanoparticles can be produced with a small number of impregnation cycles.

[0033] On the other hand, if the total concentration is 14% by mass or less, the viscosity of the aqueous precursor solution for the production of composite oxide nanoparticles is suitable, and handling is excellent. For example, when the aqueous precursor solution for the production of composite oxide nanoparticles is impregnated into a porous body, and the impregnated porous body is calcined to form nanoparticles of lanthanum calcium iron composite oxide on the surface of the porous body, the impregnation of the aqueous precursor solution for the production of composite oxide nanoparticles into the porous body is easy.

[0034] (7) Regarding coordinating organic compounds The types of coordinating organic compounds are not particularly limited as long as they are organic compounds that have the ability to coordinate to metal ions such as lanthanum ions, calcium ions, and iron ions. Examples include chelating agents, polymer electrolytes, anionic surfactants, and amino acids.

[0035] Specific examples of chelating agents include citric acid, diammonium hydrogen citrate, triammonium citrate, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, L-glutamic acid diacetic acid, nitrilotriacetic acid, ethylenediamine, bipyridine, phenanthroline, porphyrin, and crown ethers. Specific examples of polymer electrolytes include polyacrylic acid, alginic acid, polyvinylamine, polyphosphate, and polystyrene sulfonic acid. Specific examples of anionic surfactants include sodium alkylbenzene sulfonate.

[0036] Among these coordinating organic compounds, chelating agents are preferred because they can further enhance the solubility and dispersibility of lanthanum ions, calcium ions, and iron ions. Among chelating agents, citric acid, diammonium hydrogen citrate, and triammonium citrate are more preferred. Furthermore, among citric acid, diammonium hydrogen citrate, and triammonium citrate, diammonium hydrogen citrate and triammonium citrate are even more preferred, and triammonium citrate is particularly preferred, because the stability of iron citrate, formed when these chelating agents coordinate with iron ions, is improved by the ammonium ion.

[0037] (8) Regarding the amount of coordinating organic compounds The mass of the coordinating organic compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles must be more than twice the theoretical mass of the lanthanum calcium iron composite oxide nanoparticles produced from the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles, preferably 3 to 10 times, and more preferably 3 to 5 times.

[0038] If the mass of the coordinating organic compound is more than twice the theoretical mass, lanthanum ions, calcium ions, and iron ions can be dispersed very uniformly in the aqueous precursor solution for the production of composite oxide nanoparticles. Furthermore, if the mass of the coordinating organic compound is three times or more the theoretical mass, the solubility and dispersibility of lanthanum ions, calcium ions, and iron ions are excellent, making it difficult for impurities to form, and single-phase lanthanum calcium iron composite oxide can be easily obtained by calcination at low temperatures.

[0039] Furthermore, if the mass of the coordinating organic compound is five times or less of the theoretical mass mentioned above, the viscosity of the aqueous precursor solution for the production of composite oxide nanoparticles is suitable, and handling is excellent. For example, when the aqueous precursor solution for the production of composite oxide nanoparticles is impregnated into a porous body, and the impregnated porous body is calcined to form nanoparticles of lanthanum calcium iron composite oxide on the surface of the porous body, the impregnation of the aqueous precursor solution for the production of composite oxide nanoparticles into the porous body is easy.

[0040] (9) pH of aqueous precursor solution for complex oxide nanoparticle production The pH of the aqueous precursor solution for the production of complex oxide nanoparticles must be greater than 2.7 and less than 8, but preferably between 3 and 7. If the pH of the aqueous precursor solution for the production of complex oxide nanoparticles is greater than 2.7 and less than 8, the solubility and dispersibility of lanthanum ions, calcium ions, and iron ions are excellent, making it difficult for impurities to form, and single-phase lanthanum calcium iron complex oxide can be easily obtained by calcination at low temperatures. The pH of the aqueous precursor solution for the production of complex oxide nanoparticles can be adjusted by adding a pH adjuster (e.g., tetramethylammonium hydroxide, ammonia, amine).

[0041] (10) Method for producing nanoparticles of lanthanum calcium iron composite oxide By calcining the aqueous precursor solution for the production of composite oxide nanoparticles according to this embodiment (calcination step), nanoparticles of lanthanum calcium iron composite oxide can be produced. Using the aqueous precursor solution for the production of composite oxide nanoparticles according to this embodiment, even if calcined at a low calcination temperature of, for example, 600°C or higher, nanoparticles of lanthanum calcium iron composite oxide with few impurities and high purity can be obtained. Furthermore, since calcination can be performed at a low temperature, calcination can be carried out at a low cost. The calcination temperature is preferably 600°C or higher, more preferably 610°C to 730°C, and even more preferably 660°C to 700°C.

[0042] When producing nanoparticles of lanthanum calcium iron composite oxide by calcining an aqueous precursor solution for the production of composite oxide nanoparticles, the calcination may be carried out with the aqueous precursor solution impregnated into a porous body. That is, the method for producing composite oxide nanoparticles in this embodiment may include an impregnation step of impregnating a porous body with an aqueous precursor solution for the production of composite oxide nanoparticles, and a calcination step of calcining the porous body that has been impregnated with the aqueous precursor solution for the production of composite oxide nanoparticles in the impregnation step. With such a production method, nanoparticles of lanthanum calcium iron composite oxide can be formed on the surface of the porous body.

[0043] A specific example of a method for producing nanoparticles of lanthanum calcium iron composite oxide will be explained with reference to Figure 2. First, in the impregnation step, an aqueous solution of the precursor for producing composite oxide nanoparticles is impregnated into a porous body. As a result, the aqueous solution of the precursor for producing composite oxide nanoparticles is retained inside the pores of the porous body. Next, in the drying step, the solvent such as water is removed from the aqueous solution of the precursor for producing composite oxide nanoparticles. As a result, an amorphous gel in which lanthanum ions, calcium ions, and iron ions are uniformly distributed is formed on the inner surface of the pores of the porous body. Next, in the firing step, the porous body is fired, and nanoparticles of lanthanum calcium iron composite oxide are generated and arranged on the inner surface of the pores of the porous body.

[0044] Furthermore, if the lanthanum compound contains lanthanum(III) carbonate and the calcium compound contains calcium carbonate, it is preferable to produce lanthanum calcium iron composite oxide nanoparticles in the following manner in order to prevent the precipitation of precipitates from the aqueous precursor solution for the production of composite oxide nanoparticles due to the coexistence of lanthanum(III) carbonate and calcium carbonate. Specifically, a calcium compound is dissolved in an aqueous solution containing a lanthanum compound, an iron compound, and a coordinating organic compound, and the temperature is 40°C or lower, to obtain an aqueous precursor solution for the production of composite oxide nanoparticles (aqueous solution preparation step), and the obtained aqueous precursor solution for the production of composite oxide nanoparticles is calcined (calcination step).

[0045] As described above, by preparing the aqueous precursor solution for the production of composite oxide nanoparticles in this manner, precipitates are less likely to form from the aqueous precursor solution, even if the lanthanum compound contains lanthanum(III) carbonate and the calcium compound contains calcium carbonate. Therefore, even if the aqueous precursor solution for the production of composite oxide nanoparticles is calcined at a low calcination temperature during the calcination process, high-purity lanthanum calcium iron composite oxide nanoparticles with few impurities can be obtained.

[0046] (11) Regarding solid oxide fuel cell single cells The solid oxide fuel cell single cell of this embodiment has a laminated structure in which an air electrode, a solid electrolyte layer, and a fuel electrode are stacked in that order. The surface of the porous substrate constituting the air electrode has pores, and nanoparticles of lanthanum calcium iron composite oxide are arranged on the inner surface of these pores. Because nanoparticles of lanthanum calcium iron composite oxide are arranged on the inner surface of the pores opening on the surface of the porous substrate constituting the air electrode, conductivity is increased and the catalytic activity of the air electrode is excellent.

[0047] Such an air electrode can be manufactured, for example, as follows: By impregnating a porous substrate constituting the air electrode with an aqueous precursor solution for producing composite oxide nanoparticles and then firing it, nanoparticles of lanthanum calcium iron composite oxide are formed on the inner surface of the pores opening on the surface of the porous substrate, thereby obtaining an air electrode having lanthanum calcium iron composite oxide nanoparticles.

[0048] Furthermore, the solid oxide fuel cell single cell of this embodiment may have a porous support further laminated on the fuel electrode side of the laminated structure. That is, the solid oxide fuel cell single cell of this embodiment may be a metal-supported solid oxide fuel cell single cell supported by a porous support, and the aqueous precursor solution for producing composite oxide nanoparticles of this embodiment can be applied to the production of a metal-supported solid oxide fuel cell. Furthermore, the solid oxide fuel cell single cell of this embodiment can be of the flat plate type or the cylindrical type. [Examples]

[0049] The present invention will be described in more detail below with reference to examples and comparative examples. [Example 1-1] First, we will describe the raw materials used in the production of the aqueous precursor solution for the manufacture of composite oxide nanoparticles in Example 1-1. Lanthanum(III) carbonate octahydrate was used as the lanthanum compound, calcium carbonate as the calcium compound, iron ammonium citrate as the iron compound, citric acid as the coordinating organic compound, and ultrapure water as the solvent.

[0050] Next, with reference to Table 1, the method for producing the aqueous precursor solution for composite oxide nanoparticles in Example 1-1 will be described. 0.508 g of lanthanum(III) carbonate octahydrate and 1.534 g of ammonium iron(III) citrate were added to an aqueous citric acid solution containing 4.0 g of citric acid, heated to 100°C, and stirred for 30 minutes to dissolve the lanthanum(III) carbonate octahydrate and ammonium iron(III) citrate in the aqueous solution.

[0051] Next, the aqueous solution was cooled to below 40°C, and then 0.168 g of calcium carbonate was added and stirred for 30 minutes to dissolve the calcium carbonate. Furthermore, 25% by mass aqueous ammonia was added to the aqueous solution containing the dissolved calcium carbonate to adjust the pH to 5. This yielded the aqueous precursor for the production of composite oxide nanoparticles of Example 1-1, in which lanthanum ions, calcium ions, and iron ions were uniformly dispersed.

[0052] Furthermore, as shown in Table 1, the mass of the coordinating organic compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles in Example 1-1 is three times the theoretical mass of the lanthanum calcium iron composite oxide nanoparticles produced from the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles in Example 1-1.

[0053] Furthermore, the total concentration of the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles in Example 1-1 is 10% by mass, as shown in Table 1. Here, the total concentration is calculated by dividing the theoretical mass of lanthanum calcium iron composite oxide nanoparticles produced from a predetermined mass of the aqueous precursor solution for the production of composite oxide nanoparticles in Example 1-1 by the predetermined mass and multiplying by 100.

[0054] [Table 1]

[0055] The aqueous precursor solution for the production of composite oxide nanoparticles obtained in this manner in Example 1-1 was subjected to various evaluations. (A) Dispersibility, solubility The dispersibility and solubility of the above raw materials in aqueous precursor solutions for the production of composite oxide nanoparticles were evaluated. Visual inspection of the aqueous precursor solution for the production of composite oxide nanoparticles in Example 1-1 revealed that it was transparent. Therefore, the dispersibility and solubility of the above raw materials in the aqueous precursor solution for the production of composite oxide nanoparticles in Example 1-1 were evaluated as good. The results are shown in Table 1. In Table 1, a circle (○) indicates that the aqueous precursor solution for the production of composite oxide nanoparticles is transparent, a triangle (△) indicates that it is turbid, and an X (×) indicates that it contains precipitate.

[0056] (B) Liquidity The fluidity of the aqueous precursor solution for the production of composite oxide nanoparticles was evaluated. When the container containing the aqueous precursor solution for the production of composite oxide nanoparticles of Example 1-1 was tilted, the precursor solution immediately began to flow, so the fluidity of the aqueous precursor solution for the production of composite oxide nanoparticles of Example 1-1 was evaluated as good. The results are shown in Table 1. In Table 1, a circle (○) indicates that the aqueous precursor solution for the production of composite oxide nanoparticles immediately begins to flow, a triangle (△) indicates that it does not immediately begin to flow but does flow, and an X (×) indicates that the aqueous precursor solution for the production of composite oxide nanoparticles has gelled.

[0057] (C) Impurities The aqueous precursor solution for the production of composite oxide nanoparticles in Example 1-1 was dried and then calcined in air to produce lanthanum calcium iron composite oxide La 0.65 Ca 0.35 FeO3 nanoparticles were produced. The drying conditions were a drying temperature of 150°C for 1 hour. The calcination conditions were a calcination temperature of 700°C for 0.5 hours. The average primary particle size of the lanthanum calcium iron composite oxide nanoparticles obtained by calcination was confirmed to be 50 nm or less.

[0058] The obtained lanthanum calcium iron composite oxide nanoparticles were analyzed by X-ray diffraction to check for the presence of impurities generated during calcination. The results are shown in Figure 3. Of the three X-ray diffraction charts drawn in Figure 3, the upper chart is the chart of lanthanum calcium iron composite oxide nanoparticles obtained by calcining the aqueous precursor solution for the production of composite oxide nanoparticles in Example 1-1. The lower chart is the chart of lanthanum calcium iron composite oxide La 0.65 Ca 0.35 This is a chart of standard FeO3 materials. The chart in the middle shows the composite oxide nanoparticles obtained by calcining the aqueous precursor solution for the production of composite oxide nanoparticles described in Comparative Example 3.

[0059] In Figure 3, the peaks marked with a circle are lanthanum calcium iron complex oxides (La). 0.65 Ca 0.35 The peaks originate from FeO3, the peaks marked with a triangle (△) originate from lanthanum(III) oxide, and the peaks marked with a diamond (◇) originate from Ca2Fe2O5. As can be seen from the upper chart in Figure 3, only lanthanum calcium iron complex oxide was identified, and no residual unreacted raw materials or impurities such as intermediate products were found. The results are shown in Table 1.

[0060] In Table 1, a circle (○) indicates that only lanthanum calcium iron complex oxide was detected and no residual unreacted raw materials or impurities such as intermediate products were found; a triangle (△) indicates that Ca2Fe2O5 was detected; and an X (×) indicates that residual unreacted raw materials or impurities such as intermediate products were found.

[0061] Next, a metal-supported solid oxide fuel cell single cell with a diameter of 30 mm was fabricated using the aqueous precursor solution for the production of composite oxide nanoparticles from Example 1-1. This will be explained with reference to Figure 4. A laminated structure was prepared having a laminated structure in which a fuel electrode 20, a solid electrolyte layer 30, and an air electrode 40 are stacked in this order on a porous support 10. The porous support 10 is made of a porous material made of stainless steel SUS, with a thickness of 300 μm and a porosity of 40%. The fuel electrode 20 is made of Sc 0.18Ce 0.01 Zr 0.81 O 1.91 A porous substrate consisting of Ni-Gd 0.1 Ce 0.9 An anode material consisting of O2 is attached, with a thickness of 20 μm. The solid electrolyte layer 30 is made of Sc 0.1 Zr 0.9 It consists of O2 and has a thickness of 10 μm. The air electrode 40 is made of Sc 0.1 Zr 0.9 It is a porous substrate made of O2, with a thickness of 20 μm.

[0062] Next, the laminated structure was impregnated with the aqueous solution of the composite oxide nanoparticle precursor from Example 1-1. When impregnating the laminated structure with the aqueous solution of the composite oxide nanoparticle precursor, the aqueous solution was dropped onto the air electrode 40. This dropping allowed the aqueous solution of the composite oxide nanoparticle precursor to permeate the air electrode 40. After the dropping of the aqueous solution of the composite oxide nanoparticle precursor was complete, it was held for 5 minutes, and any excess aqueous solution of the composite oxide nanoparticle precursor was removed after impregnation. Subsequently, the laminated structure was heated to 80°C on a hot plate and held for 10 minutes. Furthermore, after repeating the above dropping, holding, and heating process four times, the laminated structure was fired in air at a firing temperature of 700°C for a firing time of 30 minutes.

[0063] Through this procedure, the aqueous precursor for the production of composite oxide nanoparticles in Example 1-1 is converted to lanthanum calcium iron composite oxide La 0.65 Ca 0.35 FeO3 nanoparticles were generated, and lanthanum calcium iron composite oxide nanoparticles adhered to the inner surface of the pores opening on the surface of the porous substrate constituting the air electrode 40, thereby obtaining a solid oxide fuel cell single cell.

[0064] Various evaluations were performed on the solid oxide fuel cell single cell of Example 1-1 obtained in this manner. It was confirmed that the average primary particle size of lanthanum calcium iron composite oxide nanoparticles formed inside the solid oxide fuel cell single cell (i.e., on the inner surface of the pores formed on the surface of the porous substrate constituting the air electrode) was 50 nm or less.

[0065] (D) Ease of process The ease of the process was evaluated by the number of times the aqueous precursor solution for the production of composite oxide nanoparticles was impregnated into the air electrode 40 (porous substrate) and the ease of impregnation. The aqueous precursor solution for the production of composite oxide nanoparticles was impregnated into the laminated structure by the same operation as described above. The aqueous precursor solution for the production of composite oxide nanoparticles of Example 1-1 was easily impregnated into the laminated structure, and a sufficient amount of composite oxide nanoparticles could be formed in the laminated structure in less than 5 cycles of the above-mentioned dropping, holding, and heating operations, which constitute one cycle. Therefore, the aqueous precursor solution for the production of composite oxide nanoparticles of Example 1-1 was evaluated as having high process ease.

[0066] The results are shown in Table 1. In Table 1, if the aqueous precursor solution for the production of composite oxide nanoparticles is easily impregnated into the laminated structure and a sufficient amount of lanthanum calcium iron composite oxide nanoparticles can be formed within the laminated structure in fewer than 5 cycles, the process is considered easy to use and is indicated with a circle (○). If the aqueous precursor solution for the production of composite oxide nanoparticles is difficult to impregnate into the laminated structure, or if more than 5 cycles are required to form a sufficient amount of lanthanum calcium iron composite oxide nanoparticles within the laminated structure, the process is considered insufficiently easy to use and is indicated with a cross (×).

[0067] (E) Open circuit voltage The open-circuit voltage of the completed solid oxide fuel cell single cell was measured. The measurement conditions were as follows: Operating temperature: 600℃ Single-cell heating conditions: Heat from room temperature to 600°C at a heating rate of 5°C / min. Anode gas type: A mixture of 97% hydrogen gas and 3% water vapor. Anode gas flow rate: 200cc / min Type of cathode gas: Air Cathode gas flow rate: 200cc / min Cathode-side current collector: Platinum mesh

[0068] The open-circuit voltage of the solid oxide fuel cell single cell in Example 1-1 was measured and found to be in line with the theoretical value. The results are shown in Table 1. In Table 1, a circle (○) indicates that the measured open-circuit voltage was in line with the theoretical value, a triangle (△) indicates that it was slightly lower than the theoretical value, and an X (×) indicates that it was significantly lower than the theoretical value.

[0069] In addition, while the calcination temperature of the aqueous precursor for the production of composite oxide nanoparticles in Example 1-1 was 700°C, the aqueous precursor for the production of composite oxide nanoparticles was changed to 618°C, 663°C, or 694°C, and other aqueous precursors identical to those in Example 1-1 were also subjected to various evaluations in the same manner as in Example 1-1. The results are not shown in Table 1, but they were the same as those for Example 1-1.

[0070] [Examples 1-2, 1-3, 1-4, and Comparative Example 1-1] Except for changing the mass of the coordinating organic compound contained in the aqueous precursor for the production of composite oxide nanoparticles as shown in Table 1, aqueous precursors for Examples 1-2, 1-3, 1-4, and Comparative Example 1-1 were prepared in the same manner as in Example 1-1. Various evaluations were performed on the obtained aqueous precursors for Examples 1-2, 1-3, 1-4, and Comparative Example 1-1 in the same manner as in Example 1-1. The results are shown in Table 1.

[0071] [Example 2-1] First, we will describe the raw materials used in the production of the aqueous precursor solution for the manufacture of composite oxide nanoparticles in Example 2-1. Lanthanum(III) oxide was used as the lanthanum compound, calcium carbonate as the calcium compound, iron ammonium citrate as the iron compound, citric acid as the coordinating organic compound, and ultrapure water as the solvent. Because lanthanum(III) oxide was used as the lanthanum compound, lanthanum ions can be uniformly dispersed even with a smaller amount of coordinating organic compound compared to when lanthanum(III) carbonate was used.

[0072] Next, the method for producing the aqueous precursor solution for the manufacture of composite oxide nanoparticles in Example 2-1 will be described with reference to Table 1. 0.508 g of lanthanum(III) oxide, 0.168 g of calcium carbonate, and 1.534 g of ammonium iron(III) citrate were added to an aqueous citric acid solution containing 3.0 g of citric acid, and the pH was adjusted to 3 by adding 25% by mass aqueous ammonia. Then, the mixture was heated to 100°C and stirred for 30 minutes to dissolve the lanthanum(III) oxide, calcium carbonate, and ammonium iron(III) citrate in the aqueous solution. This yielded the aqueous precursor solution for the manufacture of composite oxide nanoparticles in Example 2-1, in which lanthanum ions, calcium ions, and iron ions were uniformly dispersed.

[0073] Furthermore, as shown in Table 1, the mass of the coordinating organic compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles in Example 2-1 is four times the theoretical mass of the lanthanum calcium iron composite oxide nanoparticles produced from the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles in Example 2-1.

[0074] Furthermore, the total concentration of lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles in Example 2-1 is 10% by mass, as shown in Table 1. The aqueous precursor solution for the production of composite oxide nanoparticles obtained in this manner in Example 2-1 was subjected to various evaluations in the same manner as in Example 1-1. The results are shown in Table 1.

[0075] [Examples 2-2, 2-3, 2-4, 2-5, and Comparative Examples 2-1, 2-2] Aqueous precursor aqueous solutions for the production of composite oxide nanoparticles for Examples 2-2, 2-3, 2-4, 2-5, and Comparative Examples 2-1 and 2-2 were prepared in the same manner as in Example 2-1, except that the pH was changed as shown in Table 1. Various evaluations were performed on the obtained aqueous precursor aqueous solutions for the production of composite oxide nanoparticles for Examples 2-2, 2-3, 2-4, 2-5, and Comparative Examples 2-1 and 2-2, in the same manner as in Example 1-1. The results are shown in Table 1.

[0076] [Example 3-1] First, we will describe the raw materials used in the production of the aqueous precursor solution for the manufacture of composite oxide nanoparticles in Example 3-1. Lanthanum(III) oxide was used as the lanthanum compound, calcium carbonate as the calcium compound, iron ammonium(III) citrate as the iron compound, triammonium citrate as the coordinating organic compound, and ultrapure water as the solvent. Since triammonium citrate was used as the coordinating organic compound, there was no need to add ammonia water as would be the case when citric acid was used.

[0077] Next, the method for producing the aqueous precursor solution for the production of composite oxide nanoparticles in Example 3-1 will be described with reference to Table 1. 0.508 g of lanthanum(III) oxide, 0.168 g of calcium carbonate, and 1.534 g of ammonium iron(III) citrate were added to an aqueous solution of triammonium citrate containing 3.798 g of triammonium citrate. The solution was then heated to 100°C and stirred for 30 minutes to dissolve the lanthanum(III) oxide, calcium carbonate, and ammonium iron(III) citrate in the aqueous solution. This yielded the aqueous precursor solution for the production of composite oxide nanoparticles in Example 3-1, in which lanthanum ions, calcium ions, and iron ions were uniformly dispersed. The pH of the aqueous precursor solution for the production of composite oxide nanoparticles in Example 3-1 was 4.

[0078] Furthermore, as shown in Table 1, the mass of the coordinating organic compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles in Example 3-1 is four times the theoretical mass of the lanthanum calcium iron composite oxide nanoparticles produced from the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles in Example 3-1.

[0079] Furthermore, the total concentration of the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor for the production of composite oxide nanoparticles in Example 3-1 is 1% by mass, as shown in Table 1. The aqueous precursor for the production of composite oxide nanoparticles obtained in this manner in Example 3-1 was subjected to various evaluations in the same manner as in Example 1-1. The results are shown in Table 1.

[0080] [Examples 3-2, 3-3, 3-4, 3-5] Examples 3-2, 3-3, 3-4, and 3-5 were prepared in the same manner as Example 3-1, except that the total concentrations of lanthanum compounds, calcium compounds, and iron compounds contained in the aqueous precursor for the production of composite oxide nanoparticles were changed as shown in Table 1. Various evaluations were performed on the obtained aqueous precursor for the production of composite oxide nanoparticles of Examples 3-2, 3-3, 3-4, and 3-5 in the same manner as in Example 1-1. The results are shown in Table 1.

[0081] In Examples 3-1, 3-2, 3-3, 3-4, and 3-5, the mass of the coordinating organic compound contained in the aqueous precursor for the production of composite oxide nanoparticles was four times the theoretical mass of the lanthanum calcium iron composite oxide nanoparticles produced from the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor for the production of composite oxide nanoparticles. However, the aqueous precursor for the production of composite oxide nanoparticles was exactly the same as in Examples 3-1, 3-2, 3-3, 3-4, and 3-5, except that this mass was 3 times or 5 times. Various evaluations were performed on these aqueous precursors, similar to those in Example 1-1. The results are not shown in Table 1, but they were the same as those for Examples 3-1, 3-2, 3-3, 3-4, and 3-5.

[0082] Furthermore, in Examples 3-1, 3-2, 3-3, 3-4, and 3-5, the pH of the aqueous precursor for the production of composite oxide nanoparticles was 4, but the aqueous precursor for the production of composite oxide nanoparticles was exactly the same as in Examples 3-1, 3-2, 3-3, 3-4, and 3-5, except that the pH was set to 3, 5, 6, or 7. Various evaluations were also performed on these aqueous precursors, similar to those in Example 1-1. The results are not shown in Table 1, but they were similar to those in Examples 3-1, 3-2, 3-3, 3-4, and 3-5.

[0083] Furthermore, in Examples 3-1, 3-2, 3-3, 3-4, and 3-5, the calcination temperature of the aqueous precursor for the production of composite oxide nanoparticles was 700°C, but in Examples 3-1, 3-2, 3-3, 3-4, and 3-5, the calcination temperature was changed to 729°C. These aqueous precursors were also subjected to various evaluations, similar to those in Example 1-1. Although the results are not shown in Table 1, they were similar to those in Examples 3-1, 3-2, 3-3, 3-4, and 3-5.

[0084] [Example 4-1] First, we will describe the raw materials used in the production of the aqueous precursor solution for the manufacture of composite oxide nanoparticles in Example 4-1. Lanthanum(III) acetate 1.5-hydrate was used as the lanthanum compound, calcium acetate monohydrate as the calcium compound, iron(III) acetate as the iron compound, triammonium citrate as the coordinating organic compound, and ultrapure water as the solvent. Since triammonium citrate was used as the coordinating organic compound, there is no need to add ammonia water as would be the case when citric acid is used. Note that the ligands of the lanthanum ions, calcium ions, and iron ions in the aqueous precursor solution for the manufacture of composite oxide nanoparticles in Example 4-1 are replaced from acetate ions to citrate ions.

[0085] Next, the method for producing the aqueous precursor solution for the manufacture of composite oxide nanoparticles in Example 4-1 will be described with reference to Table 1. 1.070 g of lanthanum(III) acetate 1.5 hydrate, 0.296 g of calcium acetate monohydrate, and 0.836 g of iron(III) acetate were added to an aqueous solution of triammonium citrate containing 3.798 g of triammonium citrate. The mixture was then heated to 100°C and stirred for 30 minutes to dissolve the lanthanum(III) acetate 1.5 hydrate, calcium acetate monohydrate, and iron(III) citrate in the aqueous solution. This yielded the aqueous precursor solution for the manufacture of composite oxide nanoparticles in Example 4-1, in which lanthanum ions, calcium ions, and iron ions were uniformly dispersed. The pH of the aqueous precursor solution for the manufacture of composite oxide nanoparticles in Example 4-1 was 4.

[0086] Furthermore, as shown in Table 1, the mass of the coordinating organic compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles in Example 4-1 is four times the theoretical mass of the lanthanum calcium iron composite oxide nanoparticles produced from the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles in Example 4-1.

[0087] Furthermore, the total concentration of lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles in Example 4-1 is 10% by mass, as shown in Table 1. The aqueous precursor for the production of composite oxide nanoparticles obtained in this manner in Example 4-1 was subjected to various evaluations in the same manner as in Example 1-1. The results are shown in Table 1.

[0088] In Example 4-1, the mass of the coordinating organic compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles was four times the theoretical mass of the lanthanum calcium iron composite oxide nanoparticles produced from the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for the production of composite oxide nanoparticles. However, the aqueous precursor solution for the production of composite oxide nanoparticles was exactly the same as in Example 4-1, except that the mass was three times or five times the theoretical mass. Various evaluations were performed on these aqueous precursor solutions in the same manner as in Example 1-1. The results are not shown in Table 1, but they were the same as those for Example 4-1.

[0089] Furthermore, in Example 4-1, the pH of the aqueous precursor for the production of composite oxide nanoparticles was 4, but in Example 4-1, the pH of the aqueous precursor for the production of composite oxide nanoparticles was set to 3, 5, 6, or 7, and other aqueous precursors identical to those in Example 4-1 were also subjected to various evaluations, similar to those in Example 1-1. The results are not shown in Table 1, but they were the same as those for Example 4-1.

[0090] [Comparative Example 3-1] First, we will describe the raw materials used in the production of the aqueous precursor solution for the manufacture of composite oxide nanoparticles in Comparative Example 3-1. Lanthanum(III) nitrate was used as the lanthanum compound, calcium nitrate as the calcium compound, iron(III) nitrate as the iron compound, citric acid as the coordinating organic compound, and ultrapure water as the solvent. Lanthanum(III) nitrate, calcium nitrate, iron(III) nitrate, and citric acid were mixed and heated to dissolve them. This yielded the aqueous precursor solution for the manufacture of composite oxide nanoparticles in Comparative Example 3-1, in which lanthanum ions, calcium ions, and iron ions were dispersed.

[0091] The aqueous precursor solution for the production of composite oxide nanoparticles obtained in this manner was subjected to various evaluations in the same manner as in Example 1-1. The results are shown in Table 1. When the aqueous precursor solution for the production of composite oxide nanoparticles of Comparative Example 3-1 is calcined at a low temperature of 700°C, impurities tend to be generated. As a result, nanoparticles of lanthanum calcium iron composite oxide with low catalytic activity are obtained.

[0092] The composite oxide nanoparticles obtained by calcining the aqueous precursor solution for composite oxide nanoparticle production of Comparative Example 3-1 were analyzed by X-ray diffraction to check for the presence of impurities generated during calcination. The results are shown in Figure 3. Of the three X-ray diffraction charts drawn in Figure 3, the middle chart is the chart for the composite oxide nanoparticles obtained by calcining the aqueous precursor solution for composite oxide nanoparticle production of Comparative Example 3-1. As can be seen from the middle chart in Figure 3, the presence of unreacted raw materials and the generation of impurities were confirmed. [Explanation of Symbols]

[0093] 10...Porous support 20...Fuel electrode 30...Solid electrolyte layer 40...Air pole

Claims

1. Lanthanum calcium iron complex oxide (La 1-x Ca x ) y FeO 3 A precursor aqueous solution for producing composite oxide nanoparticles for producing nanoparticles (where x is greater than 0 and less than or equal to 0.4, and y is between 0.95 and 1.00), At least one lanthanum compound selected from lanthanum carbonates, acetates, oxides, hydroxides, oxyhydroxides, and alkoxides, At least one calcium compound selected from calcium carbonates, acetates, citrates, oxides, peroxides, hydroxides, and alkoxides, At least one iron compound selected from iron carbonates, acetates, citrates, oxides, hydroxides, oxyhydroxides, and ammonium iron citrate, Coordinating organic compounds having coordinating ability to coordinate to metal ions, It contains, The pH is greater than 2.7 but less than 8. The aqueous precursor solution for producing complex oxide nanoparticles is such that the mass of the coordinating organic compound contained in the aqueous precursor solution is three times or more and five times or less the theoretical mass of the nanoparticles of the lanthanum calcium iron complex oxide produced from the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for producing complex oxide nanoparticles.

2. The lanthanum compound is at least one selected from lanthanum carbonate (III), lanthanum acetate (III), lanthanum oxide (III), lanthanum hydroxide (III), lanthanum oxyhydroxide (III), and lanthanum isopropoxide (III). The calcium compound is at least one selected from calcium carbonate, calcium acetate, calcium citrate, calcium oxide, calcium peroxide, calcium hydroxide, and calcium methoxide. The aqueous precursor aqueous solution for producing composite oxide nanoparticles according to claim 1, wherein the iron compound is at least one selected from iron(III) carbonate, iron(III) acetate, iron(III) citrate, iron(III) oxide, iron(III) hydroxide, iron(III) oxyhydroxide, and ammonium iron(III) citrate.

3. The aqueous precursor aqueous solution for producing composite oxide nanoparticles according to claim 1 or claim 2, wherein the coordinating organic compound is a chelating agent.

4. The aqueous precursor aqueous solution for producing composite oxide nanoparticles according to claim 3, wherein the chelating agent is at least one of citric acid, diammonium hydrogen citrate, and triammonium citrate.

5. The total concentration of the lanthanum compound, the calcium compound, and the iron compound contained in the aqueous aqueous precursor for the production of composite oxide nanoparticles is 5% by mass or more and 14% by mass or less. The aqueous precursor solution for producing composite oxide nanoparticles according to any one of claims 1 to 4, wherein the total concentration is calculated by dividing the theoretical mass of the lanthanum calcium iron composite oxide nanoparticles produced from a predetermined mass of the aqueous precursor solution for producing composite oxide nanoparticles by the predetermined mass and multiplying by 100.

6. An aqueous precursor solution for producing composite oxide nanoparticles according to any one of claims 1 to 5, wherein the pH is 3 or higher and 7 or lower.

7. A precursor aqueous solution for producing composite oxide nanoparticles for producing nanoparticles of lanthanum calcium iron composite oxide (La 1-x Ca x) y FeO 3 (where x is greater than 0 and 0.4 or less, and y is 0.95 or more and 1.00 or less), At least one lanthanum compound selected from lanthanum carbonates, oxides, hydroxides, oxyhydroxides, and alkoxides, At least one calcium compound selected from calcium carbonates, citrates, oxides, peroxides, hydroxides, and alkoxides, At least one iron compound selected from iron carbonates, citrates, oxides, hydroxides, oxyhydroxides, and ammonium iron citrate, Coordinating organic compounds having coordinating ability to coordinate to metal ions, It contains, The pH is greater than 2.7 but less than 8. The aqueous precursor solution for producing complex oxide nanoparticles is such that the mass of the coordinating organic compound contained in the aqueous precursor solution is more than twice the theoretical mass of the nanoparticles of the lanthanum calcium iron complex oxide produced from the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for producing complex oxide nanoparticles.

8. A precursor aqueous solution for producing composite oxide nanoparticles for producing nanoparticles of lanthanum calcium iron composite oxide (La 1-x Ca x) y FeO 3 (where x is greater than 0 and 0.4 or less, and y is 0.95 or more and 1.00 or less), At least one lanthanum compound selected from lanthanum carbonates, acetates, oxides, hydroxides, oxyhydroxides, and alkoxides, At least one calcium compound selected from calcium carbonates, acetates, citrates, oxides, peroxides, hydroxides, and alkoxides, At least one iron compound selected from iron carbonates, acetates, citrates, oxides, hydroxides, oxyhydroxides, and ammonium iron citrate, Coordinating organic compounds having coordinating ability to coordinate to metal ions, It contains, The coordinating organic compound is a chelating agent, and the chelating agent is at least one of diammonium hydrogen citrate and triammonium citrate. The pH is greater than 2.7 but less than 8. The aqueous precursor solution for producing complex oxide nanoparticles is such that the mass of the coordinating organic compound contained in the aqueous precursor solution is more than twice the theoretical mass of the nanoparticles of the lanthanum calcium iron complex oxide produced from the lanthanum compound, calcium compound, and iron compound contained in the aqueous precursor solution for producing complex oxide nanoparticles.

9. Lanthanum calcium iron complex oxide (La 1-x Ca x ) y FeO 3 A method for producing nanoparticles (where x is greater than 0 and 0.4 or less, and y is 0.95 or more and 1.00 or less), comprising a calcination step of calcining an aqueous solution of a precursor for producing composite oxide nanoparticles according to any one of claims 1 to 8.

10. A method for producing composite oxide nanoparticles according to claim 9, wherein the firing temperature is 600°C or higher.

11. A method for producing composite oxide nanoparticles according to claim 9 or 10, wherein, if the lanthanum compound contains lanthanum (III) carbonate and the calcium compound contains calcium carbonate, the method includes, before the calcination step, an aqueous solution preparation step to obtain an aqueous precursor solution for producing composite oxide nanoparticles by dissolving the calcium compound in an aqueous solution containing the lanthanum compound, the iron compound, and the coordinating organic compound and having a temperature of 40°C or lower.

12. A method for producing composite oxide nanoparticles according to any one of claims 9 to 11, comprising an impregnation step of impregnating a porous body with the aqueous solution of the precursor for producing composite oxide nanoparticles, wherein the porous body impregnated in the impregnation step is calcined in the calcination step.

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