JPH07138069A - Ceramic and cylindrical solid electrolyte-based fuel cell and flat-plate type solid electrolyte-based fuel cell - Google Patents

Abstract

PURPOSE:To raise the electrical conductivity of a lanthanum strontium manganite-based ceramic to be used for the basic body pipe for cylindrical solid electrolyte-based fuel cells or the substrate for flat-plate type solid electrolyte-based fuel cells. CONSTITUTION:The objective ceramic, a lanthanum strontium manganite consisting mainly of (Ln1-xAEx)1-yMnO3-based perovskite solid solution, is such that the chief constituents in Ln are composed of >=74wt.% of La, <=5wt.% of Ce, <=20wt.% of Pr and <=1wt.% of Nd, x and y satisfy the relationships: 0<x<=0.4 and 0<=y<0.1 and AE is Ca or Sr. presence of Ca or Sr and La, Ce, Pr and Nd raises the electrical conductivity of the aimed ceramic. This ceramic of the above composition can be suitably used for the basic body pipe for cylindrical solid electrolyte-based fuel cells or the substrate for flat-plate type solid electrolyte-based fuel cells.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic having a high electric conductivity and a cylindrical or flat plate type solid electrolyte fuel cell using the same. More specifically, the present invention relates to an improvement of a base tube of a cylindrical solid electrolyte fuel cell and a support portion of the flat plate solid electrolyte fuel cell which also serves as a current collector.

[0002]

2. Description of the Related Art A power generation method using a solid electrolyte fuel cell can obtain high power generation efficiency. Moreover, the operating temperature is 1000
Since the exhaust heat obtained from the battery is as high as 0 ° C. and is extremely high, the exhaust heat can be used in a steam turbine or an absorption refrigerating machine to further improve power generation efficiency and obtain cold heat for cooling. Therefore, solid electrolyte fuel cells are expected to have a wide range of applications from small power sources for cogeneration to large power sources for thermal power substitution.

Conventionally, in solid oxide fuel cells, research has been conducted on two types of structures, a cylindrical type and a flat type.

In the cylindrical solid electrolyte fuel cell, as shown in FIG. 17, an air electrode 2, a solid electrolyte 3 and a fuel electrode 4 are concentrically formed around a cylindrical substrate tube 1 to form a solid electrolyte 3 and a solid electrolyte 3. An interconnector 5 formed on the air electrode 2 so as to separate it from the fuel electrode 4 is provided so that a current on the air electrode 2 side can be taken out. The solid electrolyte (zirconia electrolyte membrane) 3 is exposed between the interconnector 5 and the fuel electrode 4, and plays a role of electrical insulation. In this cylindrical solid oxide fuel cell, air flows inside the substrate tube 1 and is supplied to the air electrode 2 through the porous substrate tube 1. This cylindrical solid oxide fuel cell is
Since it has a battery structure in which thermal stress is unlikely to occur and has a relatively high mechanical strength because it uses a porous substrate tube, research and development precedes the flat plate type.
This cylindrical solid oxide fuel cell has already succeeded in power generation of a 25 kW class module, and is now moving to the development of a 100 kW class module.

However, this cylindrical solid oxide fuel cell has a problem that the generated electricity is collected through a long collecting path, and thus the output density per unit volume is low.

Table 1 shows the electric resistance of each component in the cylindrical solid oxide fuel cell.

[Table 1] As is clear from Table 1, the air electrode and the fuel electrode are 10
The resistance value (resistivity) per unit length at 00 ° C. is two orders of magnitude smaller than that of the electrolyte, but the ratio of the internal resistance is large. This is because the electrical resistance of current collection is high.
Further, the electric resistance of the air electrode is higher than that of the fuel electrode because the lanthanum manganite oxide (La,
The electric resistance per unit length of Sr) MnO ₃ is nickel zirconia cermet (Ni-YS) which is the material of the fuel electrode.
This is because it is about 10 times larger than that of Z). From this, it is understood that the voltage drop due to the electric resistance of the air electrode, Joule heat, and the like are major causes of hindering the improvement of the output density of the battery.

Therefore, attempts have been made to reduce the internal resistance of electricity by making the air electrode thick to reduce the current collecting resistance of the air electrode during current collection. For example, a calcia-stabilized zirconia-based tube that does not contribute to current collection (it plays a role of increasing the mechanical strength of the battery)
Is proposed to be replaced with lanthanum manganit of the same quality as the air electrode. By changing the material, the thickness of the air electrode can be substantially increased to the thickness of the base tube, and the electric resistance of the air electrode can be reduced. The specific electric power of the air electrode during current collection can be maintained while maintaining the mechanical strength. This is because the resistance can be reduced and the energy loss can be reduced.

On the other hand, in the flat plate type solid oxide fuel cell, flat cells are stacked with a separator also serving as an interconnector interposed therebetween, and a space for flowing air and a space for flowing fuel between the separator and the single cell. And are formed. Lanthanum chromite has been conventionally used as a separator material (also serving as an interconnector for connecting single cells in series) of the flat plate type solid oxide fuel cell. It was also known that this lanthanum chromite was the only chemically stable compound in an oxidizing / reducing atmosphere at high temperature and had electron conduction. Also, the coefficient of thermal expansion can be matched with the battery material. From this, it has been considered until now that lanthanum chromite is suitable as a separator for a flat-plate solid electrolyte fuel cell.

However, in recent years, lanthanum chromite (La, Ca) CrO ₃ and La (Cr, Mg) doped with an alkaline earth metal, which are most expected as a separate material, are used.
It was found that there is a big problem in the electric resistance of O ₃ and (La, Sr) CrO ₃ . Lantern chromite is shown in Figure 1.
As shown in FIG. 9, in a reducing atmosphere, that is, in an H ₂ atmosphere, the electric resistance is 10 times or more higher than the electric resistance in air, and in the lanthanum chromite, only the surface exposed to the oxidizing atmosphere has a small electric resistance. Other than the above, it was found that it was close to a reducing atmosphere with high electric resistance. Moreover, the mechanical strength of lanthanum chromite at high temperature is considerably lower than that of 8 mol% yttria-stabilized zirconia, which is the most effective electrolyte, and it may be only 3 kgf / mm ² at the operating temperature of 1000 ° C. all right. This is because the relationship between the measurement temperature shown in FIG. 20 and the three-point mechanical bending strength of 8 mol% yttria-stabilized zirconia, and FIG.
It is clear by comparing the measurement temperature shown in (3) and the relationship between the three-point mechanical bending strength of lanthanum chromite doped with various alkaline earth metals. Therefore, in order to obtain a separator material having a mechanical strength equivalent to that of the electrolyte plate, the separator plate needs to have a thickness eight times or more that of the electrolyte plate, and inevitably has a large electric resistance. This makes it difficult to develop a high performance flat plate solid oxide fuel cell.

Therefore, recently, as shown in FIG. 18, a support which also serves as a separator and a collector for blocking air and fuel to prevent their direct contact (a member for forming a space for passing air or a space for passing fuel). ) Are formed of different materials, and the same material as each electrode material of the unit cell 104 is used to form the collector / support body 103.
A structure sandwiching 5 is likely to be studied.

[0011]

However, at the present time,
Even with lanthanum manganite of the same quality as the air electrode that has been proposed as a material for the base tube of a cylindrical solid oxide fuel cell, there is a limit to the improvement of conductivity, and further development of a material with high conductivity is desired. ing. The same applies to the flat plate-type solid electrolyte, and a support that also serves as a current collector (in the present specification,
It is desired to improve the conductivity of a support that also serves as a current collector), particularly a support that also serves as a current collector and is made of the same material as the air electrode, which has an electric resistance 10 times or more higher than that of the fuel electrode.

In order to put the solid electrolyte fuel cell into practical use and its widespread use, it is indispensable to reduce the power generation cost, and the high performance of the fuel cell, that is, the high output density greatly influences it. Therefore, it is considered that the solid oxide fuel cell is being developed with the goal of achieving higher output. Then, in order to increase the output density, it is necessary to reduce the internal resistance. The solid electrolyte fuel cell has an internal resistance of 6 for the base tube in the case of the cylindrical type and 6 for the support in the case of the flat type.
Since it occupies 5%, it is important to reduce the internal resistance of the base tube of the cylindrical solid oxide fuel cell and the support of the flat solid oxide fuel cell in order to increase the output density of these solid oxide fuel cells. Is.

However, in the conventional solid electrolyte fuel cells, there is room for improvement in the reduction of the electric resistance in both the base tube of the cylindrical solid electrolyte fuel cell and the support of the flat plate solid electrolyte fuel cell. There is a limit to high power density and eventually to reduction of power generation cost.

It is an object of the present invention to provide a ceramic having high conductivity, a cylindrical solid electrolyte fuel cell using the same, and a flat plate solid electrolyte fuel cell.

[0015]

In order to achieve such an object, the ceramic of the present invention is (Ln _1-x AE _x ) _{1- y}
It is a lanthanum manganite whose main component is a MnO ₃ -based perovskite solid, and the main constituent of Ln is La 74 wt% or more, Ce 5 wt% or less, Pr 20 wt% or less, and Nd 1 wt% or less. , And the values of x and y are 0 <x ≦ 0.4, 0 ≦ y <0.1 and AE satisfies either Ca or Sr.

Further, in the solid oxide fuel cell of the present invention, this ceramic forms a base tube or a support which also serves as a current collector.

Here, the addition of Ca or Sr improves the conductivity of lanthanum manganite and adjusts the coefficient of thermal expansion. However, on the other hand, the addition of Ca or Sr in which the value of x exceeds 0.4 accelerates the sintering (densification) of the lanthanum manganite itself, and deteriorates the gas permeability, so that the gas diffusion function is required. It is not preferable because it impairs the practicality as a base tube of a cylindrical solid oxide fuel cell. Further, lanthanum manganite has a non-stoichiometry (y), but the range is suppressed to 0 ≦ y <0.1. This is because if the value of y is 0.1 or more, a single-phase perovskite crystal structure cannot be generated.

Substitution of lanthanum La with cerium Ce, praseodymium Pr, and neodymium Nd activates formation of complex conduction band with Mn and valence change of Mn to improve conductivity. However, Ce 5 wt%, Pr20
Substitution with lanthanum exceeding 1 wt% and Nd 1 wt% is because the ionic radius of these is smaller than that of lanthanum (La
³⁺ : 117.2 pm, Ce ³⁺ : 115 pm, Pr ³⁺ : 1
13 pm), the perovskite type crystal structure cannot be maintained, and a two-phase mixed phase is formed. As a result, the thermal expansion behavior changes microscopically, and the support, which also serves as the substrate tube and the current collector, may self-destruct in the thermal cycle.

[0019]

The solid solution having a perovskite type crystal structure has a cerium (C
e), praseodymium (Pr), neodymium (Nd), and strontium (Sr) or calcium (Ca)
Is considered to have been replaced. Lanthanum has a valence of +3, which is a general property of rare earths, but C
e, Pr, etc. have a plurality of valences (Ce: +3, +4, Pr: +
(3, +4, etc.), when the above-mentioned addition amount is adjusted, a complex conduction band with manganese Mn is formed to improve conductivity while maintaining the perovskite type crystal structure, and Ce, Pr, etc. Is stimulated by the valence change of Mn to activate the valence change of Mn and improve the conductivity by hopping conduction.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described in detail below with reference to the embodiments shown in the drawings.

The lanthanum manganite-based ceramics of the present invention is a lanthanum strontium manganite or a lanthanum calcium manganite (A) containing (Ln _1-x AE _x ) _1-y MnO ₃ -based perovskite solid solution as a main component.
E is Ca or Sr), and the value of x is 0 <x ≦
0.4 preferably 0 <x ≦ 0.3 and the value of y is 0 ≦
It is adjusted so that y <0.1 is satisfied, and the main constituents in Ln satisfy the composition range conditions of La 74 wt% or more, Ce 5 wt% or less, Pr 20 wt% or less, and Nd 1 wt% or less. .

These powders can be synthesized by, for example, a powder mixing method, a coprecipitation method or a zolgel method.
In addition, La is Ce, Pr, which is originally removed as an impurity,
Since Nd is positively included, it is not necessary to prepare high-purity one. Therefore, low-purity lanthanum containing many impurities, for example, lanthanum manufactured by Daiden Co., Ltd. shown in Table 2 can be synthesized as a starting material.

[Table 2]

For example, as a starting material, Ln ₂ shown in Table 2 is used.
O ₃ , SrCO ₃ (99.9% made by Wako Pure Chemical Industries), and M
Using nCO ₃ (41-46% made by Nacalai Tesque),
After mixing for 30 minutes, it was calcined at 1000 ° C. for 6 hours. Then, they were mixed again and calcined at 1000 hours for 12 hours. After mixing this powder once again, at 12
The lanthanum strontium manganite of the present invention was synthesized by firing for a time. This lanthanum strontium manganite powder was pressure-molded at 20 to 30 MPa to obtain pellets of a predetermined size, which were further sintered at 1300 ° C. for 2 hours. Then, it was performed so that Sr was in the range of 0 <x ≦ 0.3.

To the powder of lanthanum strontium manganite, for example, a predetermined amount of a solvent, a plasticizer, a binder, a defoaming agent or other functional substance is added to prepare a slurry (mud) or a mud having a higher viscosity. Then, it can be obtained by forming it into a cylindrical body by extrusion molding or a doctor blade method, or forming a film on a green sheet having a uniform thickness.

The lanthanum manganite cylinders and membranes thus obtained have high electrical conductivity, gas permeability and a certain degree of mechanical strength, so that they can be used in various fields. For example, it can be suitably applied to a base tube of a cylindrical solid electrolyte fuel cell, a support that also serves as a collector of a flat plate solid electrolyte fuel cell, and the like.

FIG. 1 shows an embodiment of a cylindrical solid electrolyte fuel cell. In this cylindrical solid electrolyte fuel cell, a solid electrolyte 3 and a fuel electrode 4 are concentrically formed around a base tube 1 which also functions as an air electrode, and the solid electrolyte 3 and the fuel electrode 4 are separated from each other. The interconnector 5 formed above is provided so that the current on the air electrode side can be taken out from the portion of the base tube that functions as the air electrode. The solid electrolyte (zirconia electrolyte membrane) 3 is exposed between the interconnector 5 and the fuel electrode 4, and plays a role of electrical insulation.

In this cylindrical solid oxide fuel cell,
Since the base tube 1 plays a role of increasing the mechanical strength of the battery and also has conductivity, the whole body functions not only in the vicinity of contact with the solid electrolyte 3 but also as an air electrode, and the thickness of the air electrode is substantially equal to that of the base tube. The thickness is increased to 1 to reduce the electric resistance of the air electrode 2 and prevent the energy conversion efficiency from decreasing.

An embodiment of the flat plate type solid electrolyte fuel cell is shown in FIGS. 2 (A) and 2 (B). This flat-plate type solid oxide fuel cell has a stack 15 in which a single cell 11, gas diffusers 12 and 13 and a separator 14 that sandwich the single cell 11 from both front and back sides are stacked. The unit cell 11 has an air electrode 19 on the front surface side and the back surface side of the solid electrolyte 21.
And a fuel electrode 20 are formed. A pipe 18 having a fuel gas supply passage 16 and an air supply passage 17 communicating with the gas diffusers 12 and 13 is penetrated through the center of the stack 15. The gas supply passage 16 communicates with the gas diffuser 12 on the side of the fuel electrode 19, and the air supply passage 17 is connected to the air electrode 2
It communicates with the gas diffuser 13 on the 0 side. The gas diffusers 12 and 13 are, as shown in FIGS. 2A and 2B, a zigzag-shaped groove 22 that communicates with the disc in the radial direction.
And is configured to supply the fuel electrode 19 and the air electrode 20 through the fuel gas or the air in the groove 22. In the case of this embodiment, the gas diffusers 12 and 13 serve both as a current collector and a support, and are made of lanthanum manganite ceramics. Note that reference numerals 23 and 24 indicate an upper lid and a lower lid, respectively.

<Comparative Example 1> Ln ₂ (CO ₃ ) was used as a starting material.
₃ · 8H ₂ O, was used MnCO _3. Ln ₂ (CO ₃ )
₃ · 8H ₂ O is, 1000 ° C., 6 hours, further pulverized in a mortar, 1300 ° C., by baking 12 hours, Ln ₂ O ₃
Used as. According to the composition ratio of these, Ln ₂ O ₃
Is 5.8900 g, and MnCO ₃ · xH ₂ O is 4.110 g.
0 g was dry mixed in a mortar. When these compositions are compared with the actual weighed composition ratios, they are slightly larger. The reason is that the purity of MnCO ₃ is 91% by weight with respect to the substance as a result of ICP analysis, and Ln ₂ O ₃ is 0.0% as a result of ICP analysis.
This is because it was found that impurities and water content of 2% by weight or less were included and these were subtracted. The composition of each rare earth element present in Ln ₂ O ₃ as a result of ICP analysis, when set to 1 by weight of _{Ln 2 O 3, La 2 O} 3 ( lanthanum oxide) is 7
9.4 wt%, CeO ₂ (cerium oxide) 4.9 wt%, Pr ₆ O ₁₁ (praseodymium oxide) 19.2 wt%, Nd ₂ O ₃ (neodymium oxide) <0.1 wt% And Ln: Mn = 1 as a whole.
The moles were mixed so as to satisfy the composition ratio of 1 mole. These mixtures were calcined at 1000 ° C. for 6 hours and further at 1000 ° C. for 12 hours while pulverizing and mixing. This is 1300 ℃,
A sample of LnMnO ₃ was synthesized by firing for 12 hours.

<Example 1> Ln ₂ (CO ₃ ) was used as a starting material.
₃ · 8H ₂ O were obtained from _{Ln 2 O 3, SrCO 3,} MnC
O ₃ · xH ₂ O was used. Matching these to the composition ratio,
Ln ₂ O ₃ 5.3300 g, SrCO ₃ 0.5
300 g and MnCO ₃ .xH ₂ O 4.6000 g were dry mixed using a mortar. 1000 of these mixtures
Calcination was carried out for 6 hours at 1000 ° C. and for 12 hours at 1000 ° C. while mixing and pulverizing. This was baked at 1300 ° C. for 12 hours to obtain a Ln _0.9 Sr _0.1 MnO ₃ based solid solution sample.

<Example 2> As a starting material, Ln ₂ (CO
_{3) 3 · 8H 2 O,} MnCO 3 · xH 2 O, SrCO 3
Was used. These are Ln: Sr: Mn = 0.8: 0.
Ln ₂ O ₃ 4.7 according to the composition ratio of 2: 1.0.
700 g, SrCO ₃ 1.0600 g, MnCO
The ₃ · xH ₂ O _4.6300g were dry mixed in a mortar. Add these mixtures at 1000 ° C. for 6 hours and then 100
Calcination was carried out at 0 ° C. for 12 hours while mixing and pulverizing. This is baked at 1300 ° C. for 12 hours, and Ln _0.8 Sr _0.2
A MnO ₃ based solid solution sample was obtained.

<Example 3> As a starting material, the above-mentioned Ln ₂ (CO
_{3) 3 · 8H 2 O,} MnCO 3 · xH 2 O, SrCO 3
Was used. These are Ln: Sr: Mn = 0.7: 0.
Ln ₂ O ₃ 4.2 in accordance with the composition ratio of 3: 1.0
000g, SrCO ₃ 1.6100g, MnCO
The ₃ · xH ₂ O _4.6600g were dry mixed in a mortar. Add these mixtures at 1000 ° C. for 6 hours and then 100
Calcination was carried out at 0 ° C. for 12 hours while mixing and pulverizing. This was baked at 1300 ° C. for 12 hours to give Ln _0.7 Sr _0.3
A MnO ₃ based solid solution sample was obtained.

Example 4 Ln ₂ (CO ₃ ) was used as the starting material.
_{3 · 8H 2 O, MnCO 3} · xH 2 O, was used CaCO _3. These are Ln: Ca: Mn = 0.9: 0.1:
Ln ₂ O ₃ 5.42 in accordance with the composition ratio of 1.0
g, CaCO ₃ 0.37 g, MnCO ₃ 4.68
g was dry mixed using a mortar. 10 of these mixtures
The mixture was calcined at 00 ° C. for 6 hours and further at 1000 ° C. for 12 hours while mixing and pulverizing. This was baked at 1300 ° C. for 12 hours to obtain a Ln _0.9 Ca _0.1 MnO ₃ based solid solution sample.

<Example 5> As a starting material, the above Ln ₂ (CO
_{3) 3 · 8H 2 O,} MnCO 3 · xH 2 O, CaCO 3
Was used. These are Ln: Ca: Mn = 0.8: 0.
Ln ₂ O ₃ 4.9 according to the composition ratio of 2: 1.0.
400g, CaCO ₃ 0.7500g, MnCO
The ₃ · xH ₂ O _4.7900g were dry mixed in a mortar. Add these mixtures at 1000 ° C. for 6 hours and then 100
Calcination was carried out at 0 ° C. for 12 hours while mixing and pulverizing. This is baked at 1300 ° C. for 12 hours, and Ln _0.8 Ca _0.2
A MnO ₃ based solid solution sample was obtained.

<Example 6> As a starting material, Ln ₂ (CO
_{3) 3 · 8H 2 O,} MnCO 3 · xH 2 O, CaCO 3
Was used. These are Ln: Ca: Mn = 0.9: 0.
Ln ₂ O ₃ 4.4 in accordance with the composition ratio of 1: 1.0
300g, CaCO ₃ 1.1600g, MnCO
₃ 4.9100 g was dry mixed using a mortar. These mixtures are heated at 1000 ° C. for 6 hours, then 1000 ° C., 12
It was calcined while adding time, mixing and crushing. This is 130
It was baked at 0 ° C. for 12 hours to obtain a Ln _0.7 Ca _0.3 MnO ₃ based solid solution sample.

<Comparative Example 2> As a starting material, Ln ₂ (CO
_{3) 3} · 8H ₂ O, was used MnCO ₃ · xH ₂ O. According to the composition ratio of Ln: Mn = 0.95: 1.0, Ln ₂ O ₃ 11.5225 g, MnCO ₃ x
9.4195 g of H ₂ O was dry mixed using a mortar.
These mixtures were calcined at 1000 ° C. for 12 hours while mixing and pulverizing. This was baked at 1300 ° C. for 12 hours to obtain a Ln _0.95 MnO ₃ based solid solution sample.

Example 7 Ln ₂ (CO ₃ ) was used as a starting material.
_{3 · 8H 2 O, MnCO 3} · xH 2 O, was used CaCO _3. These are Ln: Ca: Mn = (0.9 × 0.9
5): (1.0 × 0.95): in accordance with the composition ratio of 1.0, Ln ₂ O ₃ 10.6094 g, CaCO ₃
0.7175 g and MnCO ₃ 9.6368 g were dry mixed using a mortar. 1000 ° C. of these mixtures,
The mixture was calcined for 6 hours while mixing and pulverizing. This is 13
Baking at 00 ° C for 12 hours, (Ln _0.9 Ca _0.1 ) _0.95
A MnO ₃ based solid solution sample was obtained.

Comparative Example 3 Ln ₂ (CO ₃ ) was used as the starting material.
_{3 · 8H 2 O, MnCO 3} · xH 2 O, was used CaCO _3. These are Ln: Ca: Mn = (0.8 × 0.9
5) :( 0.2 × 0.95): 1.0 according to the composition ratio of Ln ₂ O ₃ 9.6533 g, CaCO ₃
1.4689G, were dry mixed in a mortar MnCO ₃ 9.8643g. 1000 ° C. of these mixtures,
The mixture was calcined for 6 hours, further at 1000 ° C. for 12 hours while mixing and pulverizing. This is baked at 1300 ° C. for 12 hours,
(Ln _0.8 Ca _0.2 ) _0.85 MnO ₃ based solid solution sample was obtained.

Comparative Example 4 Ln ₂ (CO ₃ ) was used as the starting material.
_{3 · 8H 2 O, MnCO 3} · xH 2 O, was used CaCO _3. These are Ln: Ca: Mn = (0.7 × 0.9
5) :( 0.3 × 0.95): 1.0 according to the composition ratio of Ln ₂ O ₃ 8.650 g, CaCO ₃ 2.
2566 g and 10.1028 g of MnCO ₃ were dry mixed using a mortar. Mix these mixtures at 1000 ° C, 6
The mixture was calcined for an additional 12 hours at 1000 ° C. while being mixed and ground. This is baked at 1300 ° C. for 12 hours,
(Ln _0.7 Ca _0.3 ) _0.95 MnO ₃ based solid solution sample was obtained.

Comparative Example 5 Ln ₂ (CO ₃ ) was used as the starting material.
_{3 · 8H 2 O, MnCO 3} · xH 2 O, was used CaCO _3. These are Ln: Ca: Mn = (0.9 × 0.
9) :( 0.1 × 0.9): 1.0 according to the composition ratio of Ln ₂ O ₃ 10.598g, CaCO ₃
0.7006 g and MnCO ₃ 9.9328 g were dry-mixed using a mortar. 1000 ° C. of these mixtures,
The mixture was calcined for 6 hours, further at 1000 ° C. for 12 hours while mixing and pulverizing. This is baked at 1300 ° C. for 12 hours,
A (Ln _0.8 Ca _0.1 ) _0.9 MnO ₃ based solid solution sample was obtained.

Comparative Example 6 Ln ₂ (CO ₃ ) was used as the starting material.
_{3 · 8H 2 O, MnCO 3} · xH 2 O, was used CaCO _3. Ln: Ca: Mn = (0.8 × 0.
9) :( 0.2 × 0.9): 1.0 according to the composition ratio of Ln ₂ O ₃ 9.4209 g, CaCO ₃
1.4335 g and MnCO ₃ 10.1617 g were dry mixed using a mortar. 1000 of these mixtures
Calcination was carried out for 6 hours at 1000 ° C. and for 12 hours at 1000 ° C. while mixing and pulverizing. This was fired at 1300 ° C. for 12 hours to obtain a (Ln _0.8 Ca _0.2 ) _0.9 MnO ₃ based solid solution sample.

Comparative Example 7 Ln ₂ (CO ₃ ) was used as the starting material.
_{3 · 8H 2 O, MnCO 3} · xH 2 O, was used CaCO _3. Ln: Ca: Mn = (0.8 × 0.
9) :( 0.3 × 0.9): 1.0 according to the composition ratio of Ln ₂ O ₃ 8.4377 g, CaCO ₃
2.2010 g and 10.4014 g of MnCO ₃ were dry mixed using a mortar. 1000 of these mixtures
Calcination was carried out for 6 hours at 1000 ° C. and for 12 hours at 1000 ° C. while mixing and pulverizing. This was baked at 1300 ° C. for 12 hours to obtain a (Ln _0.7 Ca _0.3 ) _0.9 MnO ₃ based solid solution sample.

<Example 8> As a starting material, the above Ln ₂ (CO
_{3) 3 · 8H 2 O,} MnCO 3 · xH 2 O, SrCO 3
Was used. These are Ln: Sr: Mn = (0.9 × 0.
95) :( 0.1 × 0.95): 1.0, Ln ₂ O ₃ 10.4317 g, SrCO ₃
1.0404 g, MnCO ₃ · xH ₂ O 9.47
5 g was dry mixed using a mortar. 1 of these mixtures
000 ° C, 6 hours, further 1000 ° C, 12 hours, mixing,
It was calcined while adding crushing. This was baked at 1300 ° C. for 12 hours to obtain a (Ln _0.9 Sr _0.1 ) _0.95 MnO ₃ based solid solution sample.

<Example 9> As a starting material, Ln ₂ (CO
_{3) 3 · 8H 2 O,} MnCO 3 · xH 2 O, SrCO 3
Was used. These are Ln: Sr: Mn = (0.8 × 0.
95) :( 0.2 × 0.95): 1.0, Ln ₂ O ₃ 9.3280 g, SrCO ₃
2.0932 g, MnCO ₃ · xH ₂ O 9.532
0 g was dry mixed using a mortar. 1 of these mixtures
000 ° C, 6 hours, further 1000 ° C, 12 hours, mixing,
It was calcined while adding crushing. This was baked at 1300 ° C. for 12 hours to obtain a (Ln _0.8 Sr _0.2 ) _0.95 MnO ₃ based solid solution sample.

<Comparative Example 8> As the starting material, Ln ₂ (CO
_{3) 3 · 8H 2 O,} MnCO 3 · xH 2 O, SrCO 3
Was used. These are Ln: Sr: Mn = (0.7 × 0.
95) :( 0.3 × 0.95): 1.0 according to the composition ratio of Ln ₂ O ₃ 8.2110 g, SrCO _{3
3.1587g, MnCO 3 · xH 2 O} 9.589
2 g was dry mixed using a mortar. 1 of these mixtures
000 ° C, 6 hours, further 1000 ° C, 12 hours, mixing,
It was calcined while adding crushing. This was baked at 1300 ° C. for 12 hours to obtain a (Ln _0.7 Sr _0.3 ) _0.95 MnO ₃ based solid solution sample.

<Comparative Example 9> As the starting material, Ln ₂ (CO
_{3) 3 · 8H 2 O,} MnCO 3 · xH 2 O, SrCO 3
Was used. These are Ln: Sr: Mn = (0.9 × 0.
9) :( 0.1 × 0.9): 1.0 according to the composition ratio of Ln ₂ O ₃ 10.1904 g, SrCO ₃
1.0163 g, MnCO ₃ · xH ₂ O 9.770
3 g was dry mixed using a mortar. 1 of these mixtures
000 ° C, 6 hours, further 1000 ° C, 12 hours, mixing,
It was calcined while adding crushing. This was baked at 1300 ° C. for 12 hours to obtain a (Ln _0.9 Sr _0.1 ) _0.9 MnO ₃ based solid solution sample.

<Comparative Example 10> Ln ₂ (C
_{O 3) 3 · 8H 2 O} , MnCO 3 · xH 2 O, SrCO
₃ was used. These are Ln: Sr: Mn = (0.8 ×
0.9) :( 0.2 × 0.9): 1.0 according to the composition ratio of Ln ₂ O ₃ 9.1109 g, SrCO ₃
2.0444 g, MnCO ₃ · xH ₂ O 9.827
3 g was dry mixed using a mortar. 1 of these mixtures
000 ° C, 6 hours, further 1000 ° C, 12 hours, mixing,
It was calcined while adding crushing. This was baked at 1300 ° C. for 12 hours to obtain a (Ln _0.8 Sr _0.2 ) _0.9 MnO ₃ based solid solution sample.

<Comparative Example 11> As a starting material, Ln ₂ (C
_{O 3) 3 · 8H 2 O} , MnCO 3 · xH 2 O, SrCO
₃ was used. These are Ln: Sr: Mn = (0.7 ×
0.9) :( 0.3 × 0.9): 1.0 according to the composition ratio of Ln ₂ O ₃ 8.0188 g, SrCO ₃
3.0847 g, MnCO ₃ · xH ₂ O 9.885
0 g was dry mixed using a mortar. 1 of these mixtures
000 ° C, 6 hours, further 1000 ° C, 12 hours, mixing,
It was calcined while adding crushing. This was baked at 1300 ° C. for 12 hours to obtain a (Ln _0.7 Sr _0.3 ) _0.9 MnO ₃ based solid solution sample.

<X-ray Diffraction Measurement Test> The sample was identified by an X-ray diffraction measurement device (trade name MXP-1 manufactured by Mac Science Co., Ltd.).
8) was used to perform an X-ray powder diffraction method under the following conditions. X-ray source CuKα monochromated with a monochromator,
CuKβ X-ray voltage 40KV X-ray tube current 150mA Diffraction angle range 2θ = 20 to 80 °

The results of the X-ray diffraction measurement of the lanthanum strontium manganite or the lanthanum calcium manganite synthesized in Comparative Example 1 and Examples 1 to 6 are shown in FIGS. 3 to 9. These X-ray diffraction patterns include CeO ₂ , Pr ₅ O
_We could not find a diffraction peak for the second-order component such as ₁₁ . That is, it can be seen that it is lanthanum manganite without impurities. Further, all the diffraction peaks shown in FIGS. 3 to 9 correspond to those of the orthorhombic perovskite, and the lanthanum strontium manganite or the lanthanum calcium manganite synthesized in Examples 1 to 7 are single perovskite. I could judge it as a phase. In addition, changes in the lattice constant of lanthanum strontium manganite due to changes in strontium components in the lanthanum strontium manganite synthesized this time, and changes in lattice constants of lanthanum calcium manganite due to changes in calcium components in lanthanum calcium manganite are shown in FIGS. 12 and 1, respectively.
3 shows. From this figure, it can be seen that the added Ca and Sr are incorporated in the crystal.

Lanthanum manganites are known to have nonstoichiometry. The influence of this nonstoichiometry on the perovskite crystal structure was examined in Examples 7 to 9 and Comparative Examples 2 to 11 in addition to the above Examples 1 to 6.
As a result, it was found that Comparative Examples 2 to 11 could not obtain a single-phase perovskite crystal structure, and had nonstoichiometry in the regions shown in FIGS. Therefore, when the composition range of the present invention is adopted, a single-phase perovskite crystal structure can be formed without impurities and the operating temperature is 1000 or less.
It can be seen that there is no possibility of causing self-destruction due to the change of the crystal structure at around ° C.

<Conductivity Measurement Experiment> Conductivity measurement was carried out by pellets obtained by sintering the compositions of Comparative Examples and Examples 1 to 6 at 1300 ° C. for 12 hours in a size of 2 mm in length and width and 15 mm in length. It was cut out with a diamond cutter and performed by a four-terminal method.

After winding four platinum wires around the sample, a platinum paste (Pla, manufactured by NE Chemcat Co., Ltd., was used).
It was fixed with tinum Ink A-3444), baked for 1 hour, and then measured. 500-1000 ℃ in air
Was carried out in the temperature range up to. The conductivity of the lanthanum strontium manganite and the lanthanum calcium manganite synthesized in Comparative Examples and Examples 1 to 6 is shown in FIGS. 14 and 15.
Shown in. 22 and 23 show the conductivity of lanthanum strontium manganite and lanthanum calcium manganite, which are prior arts. The conductivity of lanthanum manganite having a nonstoichiometric composition is shown in FIG. As is clear from this comparison, the lanthanum strontium manganite and lanthanum calcium manganite of the present invention have a conductivity about 1.5 times higher than that of the prior art lanthanum strontium manganite and lanthanum calcium manganite. Moreover, it is clear that even in the nonstoichiometric composition, the conductivity is improved by adding Ca or Sr.

[0054]

As is apparent from the above description, the lanthanum manganite-based ceramics of the present invention have higher conductivity than conventional lanthanum manganite-based ceramics and can form a single-phase perovskite crystal structure.
When used as a base tube of a cylindrical solid electrolyte fuel cell or as a support for a flat plate solid electrolyte fuel cell, the internal density of the cell can be significantly reduced to increase the output density and achieve high performance. Then, by increasing the output density, it is possible to reduce the power generation cost and promote the practical application and widespread use of the solid oxide fuel cell.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part of an embodiment of a cylindrical solid electrolyte fuel cell of the present invention.

FIG. 2 is a view showing a main part of an embodiment of a flat plate type solid electrolyte fuel cell of the present invention, (A) is a longitudinal sectional view, and (B) is a support (gas diffuser) also serving as a current collector. It is a top view.

FIG. 3 shows lanthanum manganites (Ln
_{3 is} an X-ray diffraction pattern of MnO ₃ ).

4 is an X-ray diffraction pattern of lanthanum strontium manganite (Ln _0.9 Sr _0.1 MnO ₃ ) synthesized in Example 1. FIG.

5 is an X-ray diffraction pattern of lanthanum strontium manganite (Ln _0.8 Sr _0.2 MnO ₃ ) synthesized in Example 2. FIG.

6 is an X-ray diffraction pattern of lanthanum strontium manganite (Ln _0.7 Sr _0.3 MnO ₃ ) synthesized in Example 3. FIG.

FIG. 7 is an X-ray diffraction pattern of the lanthanum calcium manganite (Ln _0.9 Ca _0.1 MnO ₃ ) synthesized in Example 4.

8 is an X-ray diffraction pattern of lanthanum calcium manganite (Ln _0.8 Ca _0.2 MnO ₃ ) synthesized in Example 5. FIG.

FIG. 9 is an X-ray diffraction pattern of lanthanum calcium manganite (Ln _0.7 Ca _0.3 MnO ₃ ) synthesized in Example 6.

FIG. 10 is a graph showing the effect of the nonstoichiometry of (Ln _1-y Ca _x ) _1-y MnO _{3 and} the amount of Ca substitution on the perovskite crystals. Here, the abscissa represents the amount of Ca substitution (x) and the abscissa represents the amount of A site deficiency (y), which represents the region where the perovskite single phase was present. A: rhombohedral system, B: tetragonal system, C: orthorhombic system, ◯: single phase, x: mixed phase of Mn ₃ O ₄ .

FIG. 11 is a graph showing the influence of the nonstoichiometry of (Ln _1-y Sr _x ) _1-y MnO _{3 and} the amount of Ca substitution on the perovskite crystals. Here, the abscissa shows the substitution amount of Sr (x) and the abscissa shows the amount of A site deficiency (y), which represents the region where the perovskite single phase was present. A: rhombohedral system, B: tetragonal system, C: orthorhombic system, ◯: single phase, x: mixed phase of Mn ₃ O ₄ .

FIG. 12 Lanthanum Strontium Manganite (La
It is a graph showing a lattice constant change due Strontium amount of _{1-x Sr x MnO 3)} .

FIG. 13: Lanthanum calcium manganite (Ln _1-x
Ca _x MnO _3, it is a graph showing a lattice constant change due to the amount of calcium 0 ≦ x ≦ 0.3).

FIG. 14 is a graph showing the temperature dependence of the electrical conductivity of the lanthanum calcium manganites of the present invention.

FIG. 15 is a graph showing the temperature dependence of the electrical conductivity of the lanthanum strontium manganite of the present invention.

FIG. 16 is a graph showing the temperature dependence of the electrical conductivity of the lanthanum manganite of the present invention in the case of a nonstoichiometric composition for lanthanum calcium manganite {(Ln _1-x Ca _x ) 0.90MnO ₃ }.

FIG. 17 is a perspective view of a main part of a conventional cylindrical solid oxide fuel cell.

FIG. 18 is an exploded perspective view of a conventional flat plate solid electrolyte fuel cell in which a current collector / support is made of the same material as an electrode material of a single cell, and a separator plate is sandwiched between them.

FIG. 19 is a graph showing the conductivity dependence of lanthanum chromite doped with alkaline earth metal on oxygen partial pressure at 1000 ° C.

FIG. 20: 8 mol% at room temperature, 500 ° C. and 1000 ° C.
3 is a graph showing the three-point bending mechanical strength of yttria-stabilized zirconia.

FIG. 21 is a graph showing the three-point bending mechanical strength of lanthanum chromite doped with alkaline earth metal at room temperature, 500 ° C. and 1000 ° C.

FIG. 22 is a graph showing the temperature dependence of the electrical conductivity of lanthanum strontium manganite (La _1-x Sr _x MnO ₃ ) which is a prior art.

FIG. 23 is a graph showing the temperature dependence of the electrical conductivity of lanthanum calcium manganite (La _1-x Ca _x MnO ₃ ) which is a prior art.

[Explanation of symbols]

1 Base tube of cylindrical solid electrolyte fuel cell 12, 13 Gas diffuser of flat plate solid electrolyte fuel cell (support also used as current collector)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hibiki Ito 2-6-1, Nagasaka, Yokosuka City, Kanagawa Prefectural Institute of Electric Power, Yokosuka Research Center (72) Inventor, Toshio Abe 2-6, Nagasaka, Yokosuka City, Kanagawa Prefecture 1 Foundation Hosei Electric Power Central Research Institute Yokosuka Research Institute (72) Inventor Shinichiro Muraji 3330 Nakatsukuma, Kitamoge-cho, Sanyogi-gun, Saga Daiden Co., Ltd. Saga Factory (72) Keiichiro Yamashita Nakatsu, Kitamoge-cho, Sanyogi-gun, Saga Kuma 3330 Daiden Co., Ltd. Saga Factory

Claims (3)

[Claims] 1. A lanthanum manganite containing a (Ln _1-x AE _x ) _1-y MnO ₃ type perovskite solid solution as a main component, and the main constituent in Ln is La 74% by weight or more and Ce 5% by weight. It is composed of Pr 20 wt% or less and Nd 1 wt% or less, and x and y values are 0 <x ≦ 0.4, O ≦ y <0.1, and AE satisfies either Ca or Sr. Ceramics characterized by being. 2. A cylindrical solid electrolyte fuel cell, characterized in that a cylindrical body is formed from the ceramic according to claim 1 and is used as a base tube for supporting a single cell. 3. A flat plate type solid electrolyte fuel cell, characterized in that a support also serving as a current collector is formed by the ceramic according to claim 1 to support a unit cell.