JPH04275923A - Multicomponent oxide powder and high-temperature electrode material, and production of the same - Google Patents

Abstract

PURPOSE:To offer a multicomponent oxide powder which can be used as the source material of new high-temp. electrode material for a fuel cell and has high electronic conductivity and almost same coefft. of thermal expansion as that of solid electrolyte zirconia, and to offer the high-temp. electrode material and production method of those. CONSTITUTION:This invention relates to a multicomponent oxide powder expressed by LaCo1-XFeXO3 (X=0.5 to 0.9) and high-temp. electrode material featuring in that it consists of this oxide. Moreover, this invention relates to the production method of the multicomponent oxide powder by preparing a mixture soln. of metal salt so that the compsn. of the mixture becomes LaCo1-XFeXO3 (X=0.5-0.9), dehydrating, drying to precipitate, thermally decomposing the precipitate and calcining the product at 800-1100 deg.C. Also this invention relates to the production method of the high-temp. electrode material by molding the obtd. multicomponent oxide powder and sintering at 1000-1500 deg.C.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The main uses of the present invention are composite oxide powders as raw materials for high-temperature electrode materials useful as air electrodes of solid electrolyte fuel cells, high-temperature electrode materials made of the composite oxides, and their use. Regarding the manufacturing method.

0002

2. Description of the Related Art Solid electrolyte fuel cells have high power generation efficiency and high output density, and are therefore being considered for various uses, such as in power generation plants. The properties required for an air electrode material in a solid electrolyte fuel cell are that it has high electronic conductivity, is stable in a high-temperature oxidizing atmosphere, does not react with the electrolyte, and has the ability to catalyze the charge transfer of oxygen.
The coefficient of thermal expansion is almost the same as that of the electrolyte. From this point of view, perovskite-type composite oxides, generally represented by the composition ABO3, are attracting attention, and among them, lanthanum-based transition metal oxides, which are stable in high-temperature air and have high electronic conductivity, are said to be promising. .

[0003] In the case of materials used together with various materials at high temperatures, it is necessary that the coefficients of thermal expansion among the materials be matched. In the case of metal materials, like potassium, 8.5 x 10
Some have a coefficient of thermal expansion as large as -5K-1, but most have a coefficient of thermal expansion of 1 to 2 x 10-5K-1. on the other hand,
In the case of oxides, it is often around 1 x 10-5K-1. In the case of solid electrolyte fuel cells, yttria-stabilized zirconia (YSZ) or tetragonal partially stabilized zirconia (TZP) used as the solid electrolyte has a thermal expansion coefficient of approximately 1 x 10-5 K in the temperature range of 0 to 1000°C. -1, but LaCoO3 has the highest electronic conductivity as an electrode material made of the lanthanum-based transition metal oxide mentioned above.
has a thermal expansion coefficient of 2 x 10-5K-1, which is significantly different from that of YSZ and TZP. Therefore, there is a risk that it will peel off from the solid electrolyte as the temperature of the battery rises and falls, and it is thought that it will be difficult to put it into practical use. In addition, LaNiO3 has a thermal expansion coefficient of 8.8 x 10-6K-1, which is YSZ and T
Although it is similar to ZP, due to its metallic nature, its electronic conductivity is lower than at low temperatures. Furthermore, La1-X SrX CoO3 doped with alkaline earth at the A site
, La1-X SrX MnO3, etc. have been actively studied, and currently, La1-X SrX MnO3, which is made by doping Sr into LaMnO3, which has slightly low electronic conductivity, is being actively studied.
is used. However, the coefficient of thermal expansion is LaM
1.1 x 10-5K-1 to 1.3 x 10-1 of nO3
It has increased to 5K-1 (X=0.3).

0004

[Problems to be Solved by the Invention] The above-mentioned conventional electrodes using lanthanum-based transition metal oxides sacrifice electronic conductivity in favor of matching thermal expansion coefficients. As a result, the overvoltage, which is a factor that impairs the characteristics of the fuel cell, is high, and the power generation efficiency is about 10% lower than the expected 60%. The present inventor conducted extensive research and discovered the present invention with the aim of solving this problem. An object of the present invention is to provide a novel high-temperature electrode material for use in fuel cells, which has high electronic conductivity and has a coefficient of thermal expansion almost the same as that of zirconia as a solid electrolyte, and a method for producing the same.

[0005]

[Means for Solving the Problems] The present invention provides LaCo1-
The present invention relates to a composite oxide powder characterized by being represented by XFeXO3 (X=0.5 to 0.9). The present invention further relates to a high temperature electrode material comprising the oxide. Further, the present invention has a composition of LaCo1-X FeX O3
Prepare a mixed aqueous solution of salts of each metal so that The present invention relates to a method for producing a composite oxide powder, and further relates to a method for producing a high-temperature electrode material, which is characterized in that the obtained composite oxide powder is molded and sintered at 1000 to 1500°C. The present invention will be explained in detail below.

[0006] The present inventor used Fe as the transition metal ion in a method of replacing the B site of LaCoO3 with a transition metal ion to control its coefficient of thermal expansion and electronic conductivity. When the value of X is 0.5 to 0.9, preferably 0.6 to 0.8
By setting it in the range of 5, the coefficient of thermal expansion is small and can reach 700℃.
We have discovered a new composite oxide that can be used as an excellent electrode material with high electronic conductivity in the above high temperature range.

When a metal other than Fe, such as Ni, is used as the transition metal ion, a coefficient of thermal expansion similar to that of YSZ and TZP can be obtained, but the electronic conductivity in the high temperature region of 700° C. or higher is low. Unsatisfactory results cannot be obtained. Moreover, if the value of the above-mentioned X is smaller than 0.5, the coefficient of thermal expansion becomes too large, which is not preferable. Furthermore,
If the value of X above is greater than 0.9, 700℃
The electronic conductivity in the above high temperature range becomes too low, which is not preferable.

The electrode material of the present invention satisfies the condition that the coefficient of thermal expansion is approximately equal to that of the solid electrolyte between room temperature and operating temperature (up to about 1000°C), and the electronic conductivity is
In the temperature range of about 850℃, about 2/2 of LaCoO3
It has an excellent property of reaching up to 3. Furthermore, it is stable even in high-temperature oxidizing atmospheres, making it useful as an electrode for solid electrolyte fuel cells.

[0009] The electronic conductivity of the electrode material obtained in the present invention can be determined by a normal AC measurement method using a sample powder that is pressure-formed into a pellet shape and then sintered, with Ag electrodes baked on both sides. can. Further, the coefficient of thermal expansion is determined by measuring the lattice constant of the sample using a normal heating X-ray diffraction method. The method for producing a composite oxide powder of the present invention has a composition of LaCo1-X FeX O3 (X=0.
5 to 0.9), dehydrate and dry the resulting product, thermally decompose it at 350°C or higher, and calcinate it at 800 to 1100°C. It will be done. Examples of the salts of each metal include hydrochloride, acetate, nitrate, oxalate, and the like. Dehydration and drying methods include conventional methods such as evaporation by heating (reduced pressure), azeotropic distillation using lower alcohols to remove water and solvent, spray drying, and the like. The thermal decomposition temperature is 3
The temperature is 50°C to 1000°C, preferably 400 to 600°C. The time for thermal decomposition is not particularly limited, but may be about 1 to 10 hours. Next, the thermal decomposition product is subjected to a solid phase reaction by calcining to obtain the desired composite oxide. At this time, if the pyrolysis product is not in powder form, it is preferable to crush it into powder. Calcining temperature is 800-1100℃, preferably 900-1100℃
The temperature is 1000°C. The calcination time is not particularly limited, but it is 8 to 1
About 5 hours is enough. Then, the obtained powder sample is molded and sintered at 1000 to 1500°C to obtain an electrode material. The molding method may be any conventional method, such as press molding,
Examples include cast molding, sheet molding, injection molding, and extrusion molding. At this time, a commercially available binder may be used as the binder, if necessary.

The electrode material of the present invention thus obtained has a coefficient of thermal expansion of 1.25 to 1.25, as shown in the following examples.
6×10-5K-1, which is close to yttria-stabilized zirconia, that is, the difference in thermal expansion coefficient with the electrolyte material is small.
Since it does not break due to thermal cycles and has a resistivity of 0.18 to 0.5 Ω·cm at 850°C, it becomes an electrode material with low overvoltage and can increase power generation efficiency. The present invention will be explained in more detail with reference to Examples below.

[0011]

[Example] Examples 1 to 4 and Comparative Examples 1 to 4 Fe acetate and Co, La nitrate were mixed into LaCo1-X FeX O3
The mixture was mixed so that each composition had a substitution ratio of X=0.5, 0.67, and 0.85, then dissolved in pure water, and water was evaporated under reduced pressure in a rotary evaporator. The obtained precipitate was thermally decomposed in a furnace at 450 to 500°C with air flowing for about 5 hours to obtain a mixed oxide. After adding ethanol to this mixed oxide and mixing well in a mortar, the ethanol was evaporated and calcined for 12 hours at the reaction temperature shown in Table 1 to perform a solid phase reaction.

When the crystal structure of the obtained powder sample was measured by X-ray diffraction, it was confirmed that it was a velopskite type oxide. When the substitution ratio X was 0.50, it had a rhombohedral structure, and when X was 0.67 or more, it was an orthorhombic structure. X is 0.67
The lattice constants at room temperature are a=5.512 Å, b=5.
526 Å, c=7.795 Å. Next, after grinding the powder sample in a mortar, 10 m
Pressure molded into a disk shape of mφ and heated at 1100℃ in air for 5 minutes.
Sintered for hours. After baking silver paste electrodes on both sides of the obtained disc pellet, the resistivity of the sintered body was measured from room temperature to 850°C by an alternating current method, and the results at 850°C are shown in Table 1.

[0013] In addition, a sample was prepared by mixing platinum black for calibration with a powder sample, and a high-temperature X-ray diffraction device was used to measure the
The thermal expansion coefficient was calculated by measuring the lattice constant up to 00°C. The above results are listed in Table 1. As comparative examples, the substitution rate X was 0 (LaCoO3), 0.33, and 1 (LaFe
Composite oxide powder was obtained in the same manner as in the example, pressure molded and sintered. Also, nitrates of Mn and La are converted into LaMnO
3 and the same procedure was carried out. The measurement results are also listed in Table 1.

[0014]

[Table 1]
Table 1──────────────
────────────────────
Fe placement Calcination Thermal expansion Resistivity Electron conduction Crystal form
Temperature
Coefficient (850℃) Degrees (850℃
) (room temperature) x
℃ K −1 Ω・c
m Ω-1・cm-1 ──
──────────────────────────
─────── Example 1 0.5
1000 1.6 ×10-5 0.1
8 5.56 Rhombohedral crystal Example
2 0.67 1000 1.5
×10-5 0.23 4.35
Orthorhombic Example 3 0.67
900 1.55×10-5 0.2
8 3.57 Orthorhombic Example 4 0.85 1000 1.2
5×10-5 0.50 2.00
Orthorhombic comparative example 1 0
1000 2.15×10-5 0.
13 7.69 Rhombohedral Comparative Example 2 0.33 1000 1.8
×10-5 0.17 5.88
Rhombohedral Comparative Example 3 1.0
1000 1.05×10-5 2.5
0.40 Orthorhombic Comparative Example 4 LaMnO3 1050 1.1
×10-5 2.0 0.5
─── ──────────────────
──────────────────── As shown in Table 1, Example 4 (X=0.85), that is, LaCo0.
15Fe0.85O3 is LaMnO3 of Comparative Example 4
In addition to having a coefficient of thermal expansion close to , the resistivity is 1/5 of that, making it possible to significantly reduce overvoltage, that is, ohmic loss. Therefore, if the high temperature electrode material according to the present invention is used in a solid electrolyte fuel cell, a fuel cell with high power generation efficiency can be obtained.

Claims (4)

[Claims] [Claim 1] LaCo1-X FeX O3 (X
=0.5 to 0.9). [Claim 2] LaCo1-X FeX O3 (X
=0.5-0.9) A high-temperature electrode material comprising a composite oxide represented by the formula: =0.5-0.9). [Claim 3] Composition is LaCo1-X FeX O3
Prepare a mixed aqueous solution of salts of each metal so that Characteristic method for producing composite oxide powder. [Claim 4] Composition is LaCo1-X FeX O3
(X = 0.5 to 0.9), a mixed aqueous solution of metal salts was prepared, dehydrated and dried, and the resulting precipitate was thermally decomposed and calcined at 800 to 1100°C. A method for producing a high-temperature electrode material, which comprises molding powder and sintering it at 1000 to 1500°C.