JP2572912B2 - Method for manufacturing air electrode of solid oxide fuel cell - Google Patents

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 a self-supporting porous air electrode of a solid oxide fuel cell.

[0002]

2. Description of the Related Art Solid oxide fuel cells (SOFCs)
Recently, it has attracted attention as a very promising power generation device having features such as high power generation efficiency, diversification of fuels (such as naphtha, natural gas, methanol, and coal reformed gas), and low pollution.

[0003] In this solid oxide fuel cell, the thin-film electrode and the electrolyte, which are the main components, do not have sufficient strength to support themselves. For this reason, conventionally, an electrode film and a solid electrolyte film have been formed on a porous support by plasma spraying or slurry coating.

However, when the electrode film and the electrolyte film are formed on the porous support as described above, there is a problem that the output is reduced due to the gas diffusion resistance of the support, and the entire structure is complicated. Met. Therefore, if the porous electrode itself can be used as the support instead of providing the electrode on the porous support, the entire structure can be simplified, the manufacturing process can be simplified, and the cost can be reduced. The output can be improved without loss due to gas diffusion resistance. However, the conventional porous electrode itself did not provide sufficient strength and was not suitable as a structural support material.

In order to solve this problem, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 2-293384 a method of manufacturing a porous ceramic tube which can be used also as an air electrode. With this manufacturing method, it has become possible to stably manufacture a tube having much higher strength than before.

[0006]

However, as a result of further research, it has been newly found that problems still remain. That is, La ₂ O ₃ , MnO ₂ , and SrCO ₃ powders were used as starting materials, these raw material powders were weighed, wet-mixed in a ball mill to form a mixture, and the mixture was molded, dried, and fired. La _0.9 Sr _0.1 MnO ₃ was synthesized. The composite was once crushed into powder, water, an organic binder, and a pore-forming agent were added to the powder and kneaded, and the kneaded product was molded and fired to produce an air electrode tube.

Various contradictory requirements are imposed on the air electrode tube. First, since the air electrode tube is a structural support material of the cylindrical SOFC cell, it must have a predetermined radial crushing strength. Further, since the oxidizing gas diffuses, it must have an open porosity of 25% or more. However, if the open porosity is too large, the radial crushing strength of the air electrode tube becomes insufficient. Also, since the dimensions of the SOFC cell are determined by the dimensions of the air electrode tube, the dimensions of the air electrode tube need to be constant in order to assemble the cells and configure the assembled battery without any trouble. .

However, La ₂ O ₃ powder has extremely high hygroscopicity. For this reason, the La ₂ O ₃ powder was once roasted to remove as much moisture as possible, and then the La ₂ O ₃ powder was vacuum-packed and transported to a factory. However, at the stage of weighed La ₂ O ₃ powder and weighed by opening the vacuum pack, La ₂ O ₃ powder was found to absorb water this slight time. Specifically, even if it is intended to accurately measure the weight of the La ₂ O ₃ powder, the amount of La is actually reduced by the amount of water absorption, and the content ratio of Mn and Sr is relatively increased. Will be. It has been found that when the amount of Mn is increased, sintering proceeds too much in the subsequent sintering step, and the porosity of the final product is reduced.
In this case, the oxidizing gas hardly diffuses in the air electrode tube, and the output of the cell decreases. If the sintering of the air electrode tube proceeds too much as described above, the air electrode tube shrinks too much, and particularly its outer diameter becomes smaller than the range of tolerance. In this case, it cannot be used as a part.

Further, another problem has arisen because the La ₂ O ₃ powder has an extremely high hygroscopicity. That is, the weighed La ₂ O ₃ powder, MnO ₂ powder, and SrCO ₃ powder are wet-mixed in a ball mill. During this mixing process, La ₂ O ₃ rapidly absorbs water and generates heat violently. For this reason, the temperature of the mixture in the ball mill is 90
The temperature rapidly rose to over ℃ and the pressure in the ball mill increased, which could cause an explosion. For this reason, it was necessary to take some measures.

[0010] An object of the present invention is to prevent the porosity and size of the air electrode from being varied when producing a self-supporting porous air electrode of an SOFC comprising a lanthanum manganate-based composite oxide. It is an object of the present invention to improve the yield and eliminate the risk of explosion or the like when the raw materials of the lanthanum manganate-based composite oxide are wet-mixed.

[0011]

SUMMARY OF THE INVENTION The present invention is a method for producing a self-supporting porous air electrode of a solid oxide fuel cell, which comprises producing a lanthanum manganate-based composite oxide having a predetermined composition after firing. Lanthanum hydroxide powder and other metal compound powder are weighed, and the weighed lanthanum hydroxide powder and other metal compound powder are wet-mixed, and the mixed powder is molded and fired to form a lanthanum manganese powder. A powder obtained by synthesizing a carbonate-based composite oxide and pulverizing the synthesized product,
Knead with at least binder, water and pore-forming agent,
This kneaded product is molded, and the molded body thus obtained is dried and fired to produce an air electrode,
It relates to a manufacturing method.

In the above, the lanthanum manganate-based composite oxide has the following chemical formula. La _1-x Ax MnO ₃ A: Sr, Ca, Mg, Zn or Ce X: preferably 0.5 or less, more preferably 0.2 or less. In the above chemical formula, the site occupied by the metal A may be partially missing.

The air electrode of the SOFC is required to have conductivity, durability against oxidizing gas, and heat resistance.

The powder obtained by pulverizing the above synthesized product is kneaded with at least a binder, water and a pore-forming agent. Examples of such pore formers include acrylic powder and carbon powder. The kneaded material is molded, and the molded body thus obtained is dried and fired to produce a self-supporting air electrode. This firing temperature is preferably set to 1400 to 1600 ° C.

In the step of synthesizing the lanthanum manganate-based composite oxide, the lanthanum hydroxide powder and the other metal compound powder are weighed so as to have the stoichiometric ratio shown in the above chemical formula. The other metal compound powder is the element A
And a compound powder containing manganese. Preferred examples are shown below. Compound powder containing element A: SrCO ₃ , CaCO ₃ , MgCO ₃ Compound powder containing manganese: MnO ₂ , Mn ₃ O ₄

[0016]

The present inventor has made various attempts to accurately measure the La ₂ O ₃ powder, but this has been very difficult. Therefore, I completely changed the idea and changed the type of raw material powder itself. As a result, it was found that the amount of lanthanum can be measured very accurately using the lanthanum hydroxide powder. This may be due to the property that crystallization water and attached water do not adhere to the dry powder of lanthanum hydroxide (La (OH) ₃ ).

As a result, the lanthanum hydroxide powder is wet-mixed with the other metal compound powder, and then the S
Even when the OFC component was manufactured, there was almost no variation in important characteristics such as porosity and dimensional accuracy of the component. As a result, a stable quality SOFC component can be always obtained, and the number of defective SOFC components is reduced, thereby improving the yield. Moreover, even if the lanthanum hydroxide powder is wet-mixed, no heat is generated at this stage, so that there is no danger that the temperature in the container such as a ball mill will rise rapidly or explode.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example in which an air electrode tube for SOFC is manufactured will be described. This composition was La _0.9 Sr _0.1 MnO ₃ . (Example of the present invention) First, 31.9% by weight of MnO ₂ powder and 5.
4% by weight of SrCO ₃ powder and 62.7% by weight of lanthanum hydroxide powder were weighed. Of these, the lanthanum hydroxide powder was produced as follows. First, 33% by weight of pure water was put in a plastic container, and 67% by weight of lanthanum oxide powder was gradually added to the pure water to form a gel, which was left for 1 hour. After that, the inside of the plastic container is heated to 100 ° C to evaporate the attached water,
A powder of lanthanum hydroxide was obtained. X about this dry powder
A line diffraction analysis was performed to confirm that it was 100% La (OH) ₃ .

Next, the above MnO ₂ powder, SrCO ₃ powder and lanthanum hydroxide powder were wet-mixed in a ball mill. At this time, the weight ratio of water was set to 50% by weight, and zirconia cobblestone was used as the cobblestone. After mixing for 1 hour in this state, the temperature of the mixture increased only to about 20 to 30 ° C. After completion of the mixing, the mixture was dried in an electric furnace until the water content became 0% by weight, and the dried product was fired at 1400 ° C. for 5 hours to synthesize La _0.9 Sr _0.1 MnO ₃ . This synthesized product was pulverized, and 3 parts by weight of cellulose (a pore-forming agent) and polyvinyl alcohol (organic binder) were added to 100 parts by weight of the pulverized powder, and 18 parts by weight of water was further added. These were kneaded in a kneader for 2 hours. This kneaded material is extruded,
A cylindrical molded body having an outer diameter of 33 mm and a thickness of 2 mm was obtained. The cylindrical molded body was conditioned and dried by an electric dryer to reduce the water content of the cylindrical molded body to 10% by weight. After drying the cylindrical molded body
It was fired at 1600 ° C. to obtain an air electrode tube. The porosity and outer diameter of the thus obtained air electrode tubes (batch Nos. 1 to 5) were measured. Table 1 shows the measurement results.

[0020]

[Table 1]

Thus, according to the present invention,
The average porosity is the target value of 25.0%,
The deviation σ also became smaller. With such an air electrode tube,
The diffusion of oxidizing gas is sufficient and the conductivity is
Not optimized, both are optimized and power generation output is improved
I do. Also, the average value of the outer diameter is close to the target value (20.00mm).
The standard deviation was 0.03 mm. This air electrode tube
The tolerance of the outer diameter of
Hateful. In addition, the porosity and outer diameter are stable in this way.
As a result, the mechanical strength of the air electrode tube was also stabilized. [Comparative Example 1] Next, a batch was prepared in the same manner as in the above embodiment.
 No. 1 to 5 air electrode tubes were manufactured. However,
La instead of tin powder_TwoO_ThreePowder was used. Also, La
_0.9Sr _0.1MnO_Three To match the stoichiometric ratio of_TwoO_Three
The amount of powder was 45.3% by weight, and SrCO_Three8.0 weight of powder
% And MnO_TwoThe amount of powder was 46.8% by weight. La_TwoO_Three
For powder, remove from vacuum pack and in air
Weighed as quickly as possible. The air electrode tube thus obtained
The porosity and the outer diameter were measured. The results are shown in Table 2.
You.

[0022]

[Table 2]

As can be seen from the results, the porosity is far from the target value of 25%, and the standard deviation is close to 1%. For this reason, the mechanical strength and electrical conductivity of the air electrode tube decrease. Further, since the standard deviation of the outer diameter dimension is very large, defective products increase. [Comparative Example 2] Batch Nos.
5 air electrode tubes were manufactured. However, after taking out the La ₂ O ₃ powder from the vacuum pack, it was roasted by holding at 900 ° C. for 3 hours.
It was then cooled and weighed. The porosity and the outer diameter of the air electrode tube were measured. Table 3 shows the results.

[0024]

[Table 3]

In this example as well, although somewhat improved over Comparative Example 1, the porosity still deviates considerably from the target value, and there is considerable variation in both the porosity and the outer diameter. In addition, when the time for raising the temperature to 900 ° C. and the time for lowering the temperature from 900 ° C. are included, the roasting process takes one day, and energy consumption is very wasteful.

[0026]

As described above, according to the present invention, S
The porosity and dimensional accuracy of the self-supporting porous air electrode of the OFC do not vary. As a result, the quality of the air electrode can be kept constant, defective products can be reduced, and the yield can be improved. In addition, there is no excessive heat generation at the stage of wet mixing with the raw material powder at first, and there is no fear that the temperature in the mixing container such as a ball mill rises rapidly or explodes.

Claims (1)

(57) [Claims] 1. A method for producing a self-supporting porous air electrode of a solid oxide fuel cell, comprising the steps of: forming a lanthanum manganate-based composite oxide having a predetermined composition after firing; And the other metal compound powders are weighed respectively, and the weighed lanthanum hydroxide powder and the other metal compound powder are wet-mixed, and the mixed powder is molded and fired to synthesize the lanthanum manganate-based composite oxide. Then, the powder obtained by pulverizing the composite is kneaded with at least a binder, water and a pore-forming agent, the kneaded product is molded, and the molded body thus obtained is dried and fired to produce the air electrode. A method of manufacturing an air electrode of a solid oxide fuel cell.