JP2002050362A - Electrode member and solid electrolyte fuel cell using this electrode member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode member that has a high reliability and high generating performance and that is suitable for a solid electrolyte fuel cell air pole with low cost. SOLUTION: This is an electrode member which is expressed in the composition formula (Ln1-pAp)1-aMnO3, wherein Ln includes at least La, Ce, Pr, Nd, and Sm and the percentage of Nd in Ln is more than 1 mol % and less than 30 mol %, and A is made of an element of more than one kind as selected from a group of Sr, Ca, and Ba, and which does not have strength degradation before and after the heat cycle treatment between 1000 deg.C and the room temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic electrode member, and more particularly to a solid oxide fuel cell having high reliability and high power generation performance using the same as an air electrode and suitable for cost reduction.

[0002]

2. Description of the Related Art The prior art will be described by taking an air electrode or an air electrode support of a cylindrical cell type solid oxide fuel cell as an example. The solid oxide fuel cell is disclosed in Japanese Patent Publication No. 1-59705.
And the like. Solid oxide fuel cells are
It has a cylindrical cell consisting of an air electrode support-solid electrolyte-fuel electrode-interconnector-. Oxygen (air) is flowed to the air electrode side, and gas fuel (H ₂ , CO, CH ₄
), O ^2- ions move in this cell to cause chemical combustion, a potential is generated between the air electrode and the fuel electrode, and power is generated.

As a material for an air electrode of a solid oxide fuel cell, LaMnO _{3 is} disclosed in Japanese Patent Publication No.
In 8159, perovskite-type oxide ceramics such as La _1-x Sr _x MnO ₃ were proposed. Also, Proc. Of the 3
^rd Int. Symp. on SOFC, 1993
La _0.90 Sr _0.10 MnO ₃ is introduced. In addition, Japanese Patent Application Laid-Open
In 138069, (Ln
_1-x AE _x ) _1-y MnO ₃ -based perovskite solid solution as a main component, La is 74% by weight or more, Ce is 5% by weight or less,
A composition in which Pr is 20% by weight or less and Nd is 1% by weight or less is disclosed. In addition, the 8th SOFC Research Presentation Lecture Abstracts, In 79-80, La ₂ was used as a lanthanum raw material for lanthanum manganite in order to reduce cell cost.
O ₃ is 54.0 to 58.0%, and Nd ₂ O ₃ is 31.0 to ₃
An example using a lanthanum concentrate having a composition of 5.0%, Pr ₆ O ₁₁ of 9.0 to 12.0%, CeO ₂ of <0.3%, and Sm ₂ O ₃ of <1.0%. It has been disclosed.
On the other hand, in Japanese Patent Application No. 10-146579, as a cathode support for a solid oxide fuel cell, a radial crushing strength of 15MP
a or more and the gas permeability coefficient is 9.60 × 10 ⁻⁹ m ² · s ⁻¹
-It is required that it be Pa ^-1 or more. Further, the solid oxide fuel cell is operated at a temperature of about 1000 ° C., but undergoes a thermal cycle in which the temperature is lowered to around room temperature for maintenance of the system and the temperature is raised to 1000 ° C. again by restarting. The cell is required to have durability against a thermal cycle between 1000 ° C. and room temperature, and the support is required to have a strength not reduced by the thermal cycle treatment in order to prevent cell breakage.

[0004]

In the case of a cylindrical solid oxide fuel cell using an air electrode support, 90% of the cell material is used.
% Or more is constituted by the air electrode support, so that it is necessary to reduce the cost of the air electrode support for commercialization. In the case of lanthanum manganite prepared using a conventional high-purity raw material as a starting material, the cell cost is high due to the high price of the lanthanum raw material, and commercialization is difficult. As an example using a low-purity lanthanum raw material, see JP-A-7-1380.
69 discloses the above composition. For example, bastnaesite, which is a raw ore of a rare earth raw material, contains 1% by weight or more of Nd, and in order to reduce the cost, the number of purification steps is reduced or the purification method is simplified. It is preferable to use Nd at a content of 1% by weight or 1 mol% or more. However, in Japanese Patent Application Laid-Open No. 7-138069, the amount of Nd is limited to 1% by weight or less. If not, it is not appropriate. Also,
In the composition disclosed in the summary of the 8th SOCFC Research Presentation, the Nd content was 31.0 to 35.0.
Therefore, when the lanthanum manganite porous body is formed using the La raw material of the present composition as shown in the following Examples, the radial crushing strength and the gas permeability coefficient required for the solid oxide fuel cell are shown. Can not be compatible. The present invention has been made in order to solve the above problems, and an object of the present invention is to provide an electrode member having high reliability and high power generation performance, which is suitable for an air electrode of a low-cost solid oxide fuel cell. Is to provide.

[0005]

Means for Solving the Problems] claims To achieve the above object 1 is represented by a composition formula _{(Ln 1-p A p)} 1-a MnO 3, Ln is at least La, Ce, Pr, Nd , Sm, and the ratio of Nd in Ln exceeds 1 mol% and is 30 mol
less than 1%, and A is at least one element selected from the group consisting of Sr, Ca, and Ba;
To provide an air electrode that is an electrode member that does not decrease in strength before and after thermal cycling between 0 ° C. and room temperature, has high reliability and high power generation characteristics, and is suitable for a low-cost solid oxide fuel cell. Is possible.

[0006] Claim 2 in order to achieve the above object, expressed by a composition formula _{(Ln 1-p A p)} 1-a MnO 3, Ln includes at least La, Ce, Pr, Nd, and Sm, Ln N in
the ratio of d is more than 1 mol% and less than 30 mol%,
A first phase A is composed of at least Sr, Ca, 1 or more elements selected from the group consisting of _{Ba, (Ln 1-p A} p)
An electrode member which is a mixture of _1-a MnO ₃ and a second phase having a composition different from that of the first phase, and having no strength reduction before and after a heat cycle treatment at 1000 ° C. and room temperature. It is possible to provide an air electrode having high reliability and high power generation characteristics and suitable for a low-cost solid oxide fuel cell.

[0007] 3. In order to achieve the above object, expressed by a composition formula _{(Ln 1-p A p)} 1-a MnO 3, Ln includes at least La, Ce, Pr, Nd, and Sm, Ln N in
the ratio of d is more than 1 mol% and less than 30 mol%,
A first phase in which the A consists of one or more elements selected from the group consisting of at least Sr, Ca, Ba, (Ln 1- p
A _p ) an electrode member comprising a mixture of _1-a MnO ₃ constituent elements and a second phase having a composition different from that of the first phase, wherein the proportion of the second phase is 10% by weight or less. It is possible to provide an air electrode having high reliability and high power generation characteristics and suitable for a low-cost solid oxide fuel cell.

According to a fourth aspect of the present invention, there is provided a solid electrolyte having high reliability, high power generation characteristics and low cost, wherein the second phase is CeO _2. It is possible to provide an air electrode suitable for a fuel cell.

According to a fifth aspect of the present invention, there is provided a solid oxide fuel cell using the electrode member of the first to fourth aspects as an air electrode or an air electrode support. It is possible to provide a low-cost solid oxide fuel cell having reliability and high power generation performance.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The electrode member of the present invention is used for an air electrode support of a solid oxide fuel cell.
It has the property that the strength does not decrease before and after the thermal cycle treatment between 000 ° C. and room temperature.

The electrode member of the present invention has a composition formula (Ln
_1- pA _p ) _1-a MnO ₃ , wherein Ln is at least La;
Including Ce, Pr, Nd, and Sm, wherein A is at least Sr,
It is composed of one or more elements selected from the group consisting of Ca and Ba, the ratio of Nd in Ln exceeds 1 mol%,
Desirably less than 30 mol%, 20 mol%
It is more desirable that: When used as an air electrode support for a solid oxide fuel cell, the radial crushing strength of the air electrode support is 15 MPa in order to improve the production yield in the cell production process and prevent the cell from being damaged during power generation.
Or more, more preferably 20 MPa or more, and an output density of 0.2 W · cm.
To ensure ^-2 or more, the gas permeability coefficient is 9.60 × 1
It is desirable that it be 0 ^-9 m ² · s ^-1 · Pa ^-1 or more.
This is because when the ratio of Nd in Ln is less than 30 mol%, this can be satisfied. In addition, in order to reduce the cost of the lanthanum raw material, it is preferable that the ratio of Nd in Ln exceeds 1 mol%.

In the electrode member of the present invention, the composition formula (Ln _1-p
A _p ) _1-a MnO ₃ , wherein Ln is at least La, C
e, Pr, Nd, and Sm, and the ratio of Nd in Ln is 1
less than 30 mol% exceed mol%, wherein A is at least Sr, Ca, a first phase consisting of one or more elements selected from the group consisting of _{Ba, (Ln 1-p A} p) 1-a Mn
An electrode member composed of a constituent element of O ₃ and a second phase having a composition different from that of the first phase.
It is desirable that the content be not more than weight%. This is because, if the content exceeds 10% by weight, the strength is reduced due to a thermal shock such as a thermal cycle under use conditions.

The second phase in the present invention is (Ln
_1-p A _p) consists constituent elements of _1-a MnO _3, there compounds of different composition to be first phase _{(Ln 1-p A p)} 1-a MnO 3 perovskite oxide composition For example, Ce
O ₂ and the like.

[0014]

EXAMPLES _{((La 1-xyzw Ce x} Pr y Nd z Sm w) 0.75 Sr 0.25)
A powder having a target composition of _0.99 MnO ₃ was synthesized, and an electrode material composed of a porous sintered body was prepared therefrom. Measurement of radial crushing strength, gas permeability coefficient, and identification of a generated phase by XRD were performed. For Examples 1 to 6 and Comparative Examples 1 to 5, L
_{a 2 O 3, CeO 2,} Pr 6 O 11, Nd 2 O 3, Sm 2 O 3, M
nO ₂ and SrCO ₃ were used as starting materials, weighed so as to have the composition shown in Table 1, and wet-mixed with a ball mill.
By calcining at 00 ° C., a powder was synthesized to prepare an electrode material. In Comparative Example 6, lanthanum nitrate, strontium nitrate, and manganese nitrate were used as raw materials, which were weighed, mixed, and thermally decomposed.
And heat-treated to synthesize a powder. Synthetic powder 100
Parts, 10 parts of organic binder, 3 parts of glycerin, 10 parts of water
After the addition, the mixture was mixed in a mixer and kneaded using a kneader. This kneaded material was molded using an extrusion molding machine, and dried and degreased. Then, in a gas firing furnace,
1. Baking at 500 ° C. for 10 hours, outer diameter 22 mm, wall thickness 2.
An electrode member made of a 0 mm porous sintered body was produced.

The radial crushing strength and gas permeability of the produced electrode members were evaluated by the following methods. 20 samples of 50 mm length
9.8 × 10 ³ between the inner and outer surfaces of the sample.
A differential pressure of Pa (N ₂ gas) was applied, and the gas permeation coefficient was calculated by measuring the amount of N ₂ gas permeating the sample under this differential pressure. The radial crushing strength is determined by placing a sample between the compression jigs of the testing machine, breaking it by applying pressure from above and below, and using the load value at that time to obtain σ _γ = P (D-
d) was calculated from / ld ^2. Here sigma _gamma is radial crushing strength, P is breaking load, D is the outer diameter of the sample, d is thickness, l indicates the sample length.

As a result of measuring the gas permeability coefficient of the fabricated electrode member, as shown in Table 1, the gas permeability coefficient required as an air electrode support for a solid oxide fuel cell was 9 for all samples. .60 × 10 ^-9 m ² · s ^-1
-It is satisfied that it is Pa ^-1 or more. On the other hand, the radial crushing strength of Comparative Examples 1 to 5 was 15 MPa or less, which proved to be inappropriate. As shown in FIG. 1, when the Nd content in the Ln site is 30 mol% or more, the radial crushing strength becomes less than 15 MPa, and in order to make the radial crushing strength 15 MPa or more, the Nd content in the Ln site is 30 mol%.
% Has been found to be necessary.

[0017]

[Table 1]

Further, in Examples 3 and 4, which have the same gas permeability coefficient as Comparative Example 6 produced as a conventional high-purity product comparative sample, the radial crushing strength is increased by 1.2 to 1.6 times.
Although the detailed cause of the increase in strength is unknown, it has been found that the use of lanthanum concentrate at the Ln site has an effect of increasing the strength.

As a result of identifying the formed phases of the samples prepared by XRD, Examples 3, 4, 6, and Comparative Examples 3 and 4 showed a lanthanum manganite perovskite type oxide as the first phase and a second phase. A CeO ₂ peak was detected as two phases. From these results, it was found that these samples were not a single phase but a mixture with CeO ₂ . In the case of a mixture, there is a concern that the strength may be reduced due to thermal shock, so the following experiment was conducted. To the powder synthesized in Example 1, CeO ₂ powder was added at an internal ratio of 5, 10, and 12% by weight, respectively, and porous sintered bodies were produced in the same manner. Comparative Example 7
And For Examples 1, 7, 8 and Comparative Example 7,
The temperature was raised to 1000 ° C in an electric furnace
After holding at 00 ° C. for 1 hour, the temperature was lowered to room temperature,
A thermal cycle treatment in which the temperature was raised to 00 ° C. was performed, and a change in strength before and after the treatment was measured. The temperature rise / fall rate in the heat cycle treatment was 300 ° C./hour, and the number of repetitions was 10 times. As a result, as shown in Table 2, no change in strength was observed in Examples 1, 7, and 8 due to the heat cycle treatment, but the strength was reduced in Comparative Example 7. Although the detailed cause of the decrease in strength after the heat cycle treatment in Comparative Example 7 is unknown, it is desirable that the proportion of the second phase be 10% by weight or less in order to prevent the strength decrease due to the heat cycle treatment. I understood.

[0020]

[Table 2]

[0021]

According to the present invention, the following effects are exhibited by the above configuration. The electrode member of the present invention has high reliability and high power generation characteristics, and can provide an air electrode or an air electrode support suitable for a low-cost solid oxide fuel cell.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of Nd in Ln and radial crushing strength in a sample composition of the present invention.

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Claims (5)

[Claims] Represented by 1. A composition formula _{(Ln 1-p A p)} 1-a MnO 3, Ln includes at least La, Ce, Pr, Nd, and Sm, the ratio of Nd in Ln is exceed 1 mol% 30mo
less than 1%, and A is at least one element selected from the group consisting of Sr, Ca, and Ba;
An electrode member characterized in that there is no decrease in strength before and after a heat cycle treatment between 0 ° C. and room temperature. 2. A expressed by a composition formula _{(Ln 1-p A p)} 1-a MnO 3, Ln includes at least La, Ce, Pr, Nd, and Sm, the ratio of Nd in Ln is exceed 1 mol% 30mo
less than l%, A is at least Sr, Ca, a first phase consisting of one or more elements selected from the group consisting of Ba, from the constituent elements of the _{(Ln 1-p A p)} 1-a MnO 3 An electrode member comprising: a mixture comprising a first phase and a second phase having a composition different from that of the first phase, wherein there is no decrease in strength before and after a heat cycle treatment between 1000 ° C. and room temperature. 3. A expressed by a composition formula _{(Ln 1-p A p)} 1-a MnO 3, Ln includes at least La, Ce, Pr, Nd, and Sm, the ratio of Nd in Ln is exceed 1 mol% 30mo
less than 1%, wherein A is at least Sr, Ca, Ba
A first phase consisting of one or more elements selected from the group consisting of a second phase having a first phase and different composition consists constituent elements of _{(Ln 1-p A p)} 1-a MnO 3, Wherein the proportion of the second phase is 10% by weight or less. 4. The electrode member according to claim 3, wherein the second phase is CeO ₂ . 5. A solid oxide fuel cell using the electrode member according to claim 1 as an air electrode or an air electrode support.