JPH0986934A - Production of nio/ysz complex powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production process of NiO/YSZ complex powder capable of contributing enhancement of power-generation characteristics and durability of a solid electrolyte type fuel cell and improved in powdery composition and organization. SOLUTION: This production process of NiO/YSZ(Y2 O3 -stabilized ZrO2 ) comprises (1) a solution preparation step in which a source solution containing Ni ion, Zr ion and Y ion in a predetermined ratio is prepared; (2) a coprecipitation step in which a solid material (a coprecipitated material) is coprecipitated by mixing a precipitation solution capable of precipitating the solid material containing at least one of above metals and oxygen from the above source solution and (3) a decomposition step in which the coprecipitated material is decomposed and powdery material (NiO/YSZ complex powder) containing each of the above metal oxides is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing NiO / YSZ composite powder used as a fuel electrode material for a solid oxide fuel cell (hereinafter also referred to as SOFC). In particular, NiO / YS with improved powder composition and uniformity of structure, which can contribute to improvement of power generation characteristics and durability of SOFC.
The present invention relates to a method for producing Z composite powder.

[0002]

2. Description of the Related Art A conventional technique will be described by taking an SOFC fuel electrode material as an example. As a fuel electrode material for SOFC, a sintered film of a composite powder in which NiO and Y ₂ O ₃ stabilized ZrO ₂ (YSZ) are mixed and composited is mainly used (Japanese Patent Laid-Open No. 61-1).
53280, JP-A-61-198570, etc.). In addition, Ni in the sintered film
O is reduced to Ni during operation of the SOFC.

N for such Ni / YSZ composite sintered film
The manufacturing method of the iO / YSZ composite powder is generally based on NiO.
A method is employed in which both the powder and the YSZ powder are mixed in a solid state, and then the temperature is raised and the powder is slightly sintered to form a composite. As a mixing method, a method using a ball mill or a method using mechanochemical mechanical mixing is known. The Ni / YSZ composite sintered film has various components (Ni and YSZ).
No. 1) has a cross-linked microstructure, but those in which Ni is connected like a mesh have good conductivity, and those in which the NiS mesh is cut due to agglomeration of YSZ grains have poor conductivity. If the conductivity of the SOFC fuel electrode is poor, the power generation efficiency of the SOFC decreases. Therefore, there is a demand for a NiO / YSZ composite powder that does not cause YSZ agglomeration and can firmly form a Ni network structure after firing of the coating film.

[0004]

The above-mentioned conventional manufacturing method has the following problems. Ball mill mixing method: Among the mixed powders, a component having a large specific gravity (NiO) or a component having a large particle size is precipitated, and the composition of the powder tends to be uneven. In particular, when wet mixing is performed using a liquid as a medium, such a sedimentation phenomenon is likely to occur in the drying step after the mixing process.

Mechanochemical mechanical mixing: In this method, for example, a rotary blade is installed in a container, and the powder mixing is promoted by centrifugal force and agitation by the rotation of the container or the rotary blade itself. At this time, the powders are mixed with each other in a state where the temperature is naturally raised by the heat generated naturally or the state where the temperature is forcibly raised. In other words, it is a major feature of the mechanochemical method that the bonding between the powders is promoted by heat. Then, this method is mainly used as a surface modification method in which a fine powder is adsorbed on the surface of the coarse powder in the mixing of the coarse powder and the fine powder to create a composite powder composed of a shell and a nucleus. It is becoming widely used today.

However, this mechanochemical surface modification method often utilizes a particle size difference such as sticking fine particles to the surface of coarse particles, so that the raw materials used are limited and the purpose is to mix the fine particles. On the other hand, the effect is difficult to be exhibited.

[0007] It is an object of the present invention to provide a method for producing a NiO / YSZ composite powder having improved composition and structure uniformity of the powder, which can contribute to improvement of power generation characteristics and durability of SOFC.

[0008]

In order to solve the above problems, a method for producing a NiO / YSZ composite powder according to the present invention is a solution for preparing a raw material solution containing Ni ions, Zr ions and Y ions in a desired ratio. Adjustment process and 1 of each metal
A coprecipitation step of coprecipitating a solid substance containing at least one species and oxygen from the above raw material solution; And powders (NiO / YS) containing oxides of the above respective metals.
Z composite powder) is obtained.

In the method for producing the NiO / YSZ composite powder according to one aspect of the present invention, a solution based on an aqueous nitric acid solution is used as a raw material solution, and an oxalic acid aqueous solution is used as a coprecipitation solution. In this case, the following coprecipitation reaction occurs. Ni ²⁺ + (COOH) ₂ → Ni (COO) ₂ ↓ + 2H ⁺ Zr ⁴⁺ +2 (COOH) ₂ → Zr (COO) ₄ ↓ + 4H ⁺ 2Y ³⁺ +3 (COOH) ₂ → Y ₂ (COO) ₆ ↓ + 6H ⁺

In the method for producing the NiO / YSZ composite powder of the above aspect, the raw material solution and the coprecipitation solution are preliminarily mixed with each other.
It is preferable to raise the temperature to 0 ° C. to the boiling point and then mix.
Of the above reactions, the precipitation reaction of Ni oxalate is generally unlikely to occur at room temperature. Therefore, it is difficult to obtain a coprecipitated substance having a uniform composition. On the other hand, in the above temperature range, the above-mentioned three reactions occur almost uniformly, so that a coprecipitated substance having a uniform composition can be efficiently obtained.

The NiO / YSZ composite powder of the present invention is SOF
When used as a C fuel electrode material, NiO / YSZ
The weight ratio of NiO and YSZ in the composite powder is 30:
It is preferably 70 to 70:30. If the YSZ ratio exceeds 70, the conductivity of the powder fired film becomes low, which is not preferable. From such a viewpoint, it is more preferable that the ratio of the nickel oxide weight (converted value) to the YSZ weight (converted value) in the mixture is 50:50 to 70:30. However, for the graded layer between the solid electrolyte membrane and the fuel electrode, a low Ni one has a low electric conductivity of the membrane itself, but a stress caused by a difference in thermal expansion between the high Ni content layer and the electrolyte. Can be relaxed, which is preferable.

The NiO / YSZ composite powder of the present invention is SOF
When used as a C fuel electrode material, the particle size of the composite powder after calcination is preferably 0.1 to 10 μm. This is because the balance between gas permeability and conductivity is good. At this time, the upper layer of the fuel electrode may be formed using relatively coarse particles, and the lower layer may be formed using relatively fine particles.

[0013]

Embodiments of the present invention will be described below. FIG.
5 is a flowchart showing steps of a method for manufacturing NiO / YSZ composite powder according to a standard embodiment of the present invention. Description will be made with reference to this flowchart.

(1) Preparation of raw material solution: zirconium nitrate / yttrium aqueous solution (8 mol% Y ₂ O ₃ as a YSZ raw material)
Content, content in terms of oxide (23.4 wt%), nickel nitrate hexahydrate crystals as a NiO raw material, and pure water for adjusting the coprecipitating substance concentration are mixed in the composition shown in Table 1 and stirred well.

[0015]

[Table 1]

(2) Preparation of coprecipitation solution: In this example,
An oxalic acid aqueous solution was used as a coprecipitation solution. Pure water is taken into the container and heated to about 80 ° C. While stirring the warm water, oxalic acid dihydrate crystals were gradually added and dissolved.
It was kept at 0 ° C. Regarding the amount of the oxalic acid aqueous solution, it is preferable that the amount of oxalic acid is slightly in excess of the stoichiometric ratio so that the metal ions are completely precipitated in the coprecipitation step. The excess amount at this time was about 5 mol%, and the amount is shown in Table 1.

(3) Solution mixing → coprecipitation: Nickel oxalate crystals are difficult to form even when nickel nitrate and an aqueous solution of oxalic acid are reacted at room temperature. Therefore, the production rate of nickel oxalate is increased by adding nitric acid in a state where a nickel-containing aqueous solution such as nitrate is heated. The raw material solution (NiO / YSZ composite powder aqueous solution) is heated to 80 ° C to 90 ° C, and this is heated to 80 ° C to 9 ° C.
A precipitate was formed by the oxalic acid coprecipitation method by gradually adding it to an aqueous nitric acid solution which was heated and maintained at 0 ° C. with good stirring. Since powder is produced by the reaction, it is preferable to use a stirrer having a torque for stirring the solution.
Since the solution causes an exothermic reaction due to the coprecipitation reaction, the temperature of the solution usually rises by about 10 to 20 ° C. from the initial state after the reaction. After all the solutions were mixed, the solution was naturally cooled while continuing to stir to room temperature.

(4) Drying: The reaction product was allowed to stand in a dryer for 1
Hot air at 20 ° C. was sent to evaporate the water content of the precipitate. (5) Pyrolysis: The dried sample was heat-treated at 500 ° C. for 5 hours to remove nitric acid components and residual oxalic acid. The reaction at that time is estimated as follows. Ni (COO) ₂ → NiO + CO + CO ₂ Zr (COO) ₄ → ZrO ₂ + 2CO + 2CO ₂ Y ₂ (COO) ₆ → Y ₂ O ₃ + 3CO + 3CO ₂

(6) Ball mill grinding: PSZ of 2φ and 3φ
Wet grinding using balls was performed. This aims at crushing and homogenizing the secondary particles. However, according to the wet laser diffraction particle size distribution measurement, the powder obtained by this coprecipitation method was 1
Since the particles having a size of less than or equal to μm occupy about 80% of the whole, and even the large secondary particles have a particle size of 10 to 20 μm, it is possible to omit the ball milling treatment.

(7) Coarse pulverization: A lump sample obtained by drying the slurry after the ball mill treatment was crushed. According to wet laser diffraction particle size distribution measurement, this powder had a maximum diameter of 10 μm even for secondary particles.

(8) Calcination: For the purpose of investigating the influence of the calcination conditions on the powder characteristics, the obtained powder was heated at 900 ° C. for 10 hours,
1000 ° C x 3hr, 1100 ° C x 2hr, 1100 ° C
X10hr, 1150 ° C x 5hr, 1200 ° C x 5h
Calcination (heat treatment) was performed under each condition of r, 1250 ° C. × 5 hr. The purpose of calcination is to optimize the properties of the fired film (conductivity, air permeability, durability, etc.) by adjusting the sinterability of the powder during main firing after film formation to an appropriate range. is there. During calcination, the fine powder of NiO mainly coalesces with other NiO powder due to the sintering phenomenon. Further, Y ₂ O ₃ is gradually solid-dissolved in ZrO ₂ and crystallized.

(9) Preparation of sintered body: 10 wt% PVA (polyvinyl alcohol) based on the powder obtained in the above process
The aqueous solution was added as a binder. This powder was press-molded and then fired at 1400 ° C. for 2 hours. Next, this sintered body was heated to 1000 ° C. in a nitrogen atmosphere containing 3% hydrogen,
A reduction treatment was performed for 40 hours to obtain a Ni / YSZ composite sintered body.

The porosity of this sintered body was evaluated by the Archimedes method, and the conductivity was evaluated by the four-terminal method. For comparison,
Powders were synthesized from the NiO / YSZ composite powder aqueous solution used in the coprecipitation method of this example by the evaporation dry method, and their characteristics were also examined. As a result, the porosity of the sintered body of the comparative example was about 30% or more, while the porosity of the sintered body of the example was 90%.
In the case of 0 to 1000 ° C, it was 22 to 24%. Therefore, a dense sintered body or a fired film can be obtained.
In addition, when the calcination temperature is 1100 ° C. or higher, the porosity is 27 to 34.
%. In addition, the electrical conductivity of the raw material obtained by the evaporation-drying method was around 1700 S / cm, whereas the electrical conductivity of the raw material prepared by the coprecipitation method powder was 2500-3000 S / cm.
It was confirmed to be extremely high as cm.

When the calcination temperature is increased, the particles grow large and the surface activity of the powder decreases due to the calcination, so that it becomes difficult for the sintering to proceed and the porosity tends to increase (data example, Calcination temperature 900 ° C: 21.9%, 1
000 ° C: 22.5%, 1100 ° C: 23.9%). Further, as the porosity increases, the conductivity also tends to decrease (data example, calcination temperature 900 ° C .: 2975 S / c).
m, 1000 ° C .: 2972 S / cm, 1100 ° C .: 26
60 S / cm). However, these values show greater conductivity than the conventional sample.

Further, in the SEM observation of the fracture surface of the sintered body, as shown in FIG. 2, in the conventional product, Ni and YS were used.
In contrast to the fact that the Z particles were aggregated, it was confirmed that the main body invention product had a uniform structure with a uniform particle size. In addition, N ₂ ; 85, H ₂ ; 15% of these samples
After a long-time reduction treatment in the atmosphere at 1050 ° C. for 100 hours, the conductivity further increased due to the progress of reduction of Ni, and no change was observed in the microstructure. Therefore, the powder produced in this experiment can produce a fuel electrode having higher performance and durability.

It was confirmed by a scanning electron microscope (SEM) that the powder obtained in this experiment was a fine powder in which all the temporary particle diameters after pyrolysis were in the submicron range. However, in the laser diffraction particle size distribution measuring method, since secondary particles are measured, particle diameters of 1 μm or more are also measured.

Using the powder calcined at 900 ° C. for 10 hours, a slurry and a film were formed as follows, and a power generation test cell was prepared and evaluated. That is, the powder was mixed with an organic solvent containing alcohol as a main component to form a slurry. This is coated on a base tube consisting of an air electrode and an electrolyte, dried, and 1400
The product was calcined at 0 ° C. and reduced in a 3% H ₂ atmosphere. fuel;
11% H ₂ O, 89% H ₂ , oxidizer; 4 times equivalent amount of air, fuel utilization rate of 40%, power generation evaluation under operating conditions of temperature 1000 ° C. As a result, high output of maximum output 0.48 W / cm ² was obtained. It was confirmed that it was higher than the maximum output (about 0.42 W / cm ² ) of the cell manufactured using the powder obtained by the conventional powder mixing.

[0028]

As is apparent from the above description, the method for producing NiO / YSZ composite powder of the present invention exhibits the following effects. The conductivity of the SOFC fuel electrode can be improved, and thereby the power generation performance of the SOFC can be improved. Since the conductivity is higher than that of the conventional powder of the same composition, S
The OFC fuel electrode can be thinned, and thereby the power generation performance of the SOFC can be improved. Since the texture of the sintered body and the fired film are excellent in dispersibility, YSZ does not agglomerate even in a high temperature environment, so that deterioration of the conductive characteristics with time can be prevented and reliability can be improved. It is possible to provide a powder manufacturing method which is excellent in mass productivity because the manufacturing department stays well and the reactor is simple.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a manufacturing process of NiO / YSZ composite powder according to an example of the present invention.

FIG. 2 is an SEM photograph of a fractured surface of a Ni / YSZ sintered body obtained by using powders according to Examples of the present invention and Comparative Examples as raw materials.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Akinaga 2-47 Shiobara, Minami-ku, Fukuoka City Kyushu Electric Power Co., Inc. Research Institute (72) Kimiyasu Tachibana 2- 1-47 Shiobara, Minami-ku, Fukuoka City Kyushu Electric Power Co., Inc. Research Institute (72) Hiroyuki Nagayama, Inventor Hiroyuki Nagayama 2-1-1 Nakajima, Kokurakita-ku, Kitakyushu, Fukuoka Totoki Equipment Co., Ltd. (72) Masanobu Aizawa 2 Nakajima, Kokurakita-ku, Kitakyushu, Fukuoka 1st-1st Totoki Equipment Co., Ltd.

Claims (5)

[Claims] 1. A solution adjusting step of adjusting a raw material solution containing Ni ions, Zr ions and Y ions in a desired ratio, and a co-precipitation method of coprecipitating a solid substance containing one or more of each metal and oxygen from the raw material solution. A coprecipitation step of mixing a precipitation solution with the above raw material solution to coprecipitate the solid substance (coprecipitation substance), and a powder or granular material (NiO / YSZ) that decomposes the coprecipitation substance and contains an oxide of each metal. And a decomposition step of obtaining a composite powder), and a manufacturing method of the NiO / YSZ composite powder. 2. The method for producing NiO / YSZ composite powder according to claim 1, wherein the raw material solution is a nitric acid aqueous solution-based solution, and the coprecipitation solution is an oxalic acid aqueous solution. 3. The NiO / YS according to claim 2, wherein the respective aqueous solutions are preheated to 60 ° C. to the boiling point and then mixed.
Method for producing Z composite powder. 4. The method further comprises a calcining step of calcining the NiO / YSZ composite powder to adjust the NiO particle size.
~ The method for producing the NiO / YSZ composite powder as described in 3 above. 5. The NiO / YOZ composite powder according to claim 4, wherein the particle size after calcination is 0.1 to 10 μm.
Method for producing YSZ composite powder.