JPH11228136A - Ion conductive oxide material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an ion conductive oxide material having high mechanical strength and to provide a fuel cell or the like high in durability. SOLUTION: In the ion conductive oxide material composed of La(1-x) Srx Ga(1-y-z) Mgy Alz O3 , the oxide ion conductive material is formed on the condition of 0<x<=0.2, 0<y<=0.2, and 0<z<=0.4. And an electrochemically acting member such as a cell is formed by laminating the oxide ion conductive material composed of La(1-x) Srx Ga(1-y-z) Mgy Alz O3 wherein 0<x<=0.2, 0<y<=0.2 and 0<z⊖0.4 and an electrode material through a prescribed intermediate layer. As a result, the oxide ion conductive material is increased in mechanical strength and the durability of electrochemical devices such as a solid electrolyte type fuel cell using the same is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide ion conductive material, and more particularly to an oxide ion conductive material having high mechanical strength, excellent durability and economic efficiency, and an electrochemical material formed using the same. Operative member.

[0002]

2. Description of the Related Art Zirconia and ceria-based oxide solid solutions having a fluorite-type crystal structure are known as the most common oxide ion conductive materials, and include fuel cells, high-temperature steam electrolysis, and oxygen sensors. Applications to a wide range of technical fields such as electrochemical reactors, gas separation membranes, and oxygen pumps have been attempted.

As zirconia-based oxide ion conductive materials, stabilized zirconia, ZrO ₂ -M ₂ O ₃ (M =
Y, Yb, Sc), ZrO ₂ -MO (M = Mg, Ca)
Are known as ceria, ceria solid solution, CeO ₂ -M ₂ O ₃ (M = Gd, Sm, Y), Ce
O ₂ -MO (M = Ca, Sr) and the like are known.

On the other hand, in recent years, solid solutions of perovskite-type oxide LaGaO ₃ having higher oxide ion conductivity than these materials have been proposed, and basic studies for application to various uses including fuel cells have been actively conducted. It is becoming.

In addition, as a newly proposed oxide ion conductive material, x = 0.1 to 0.2 and y = ₁₀ in La _(1-x) Sr _x Ga _(1-y) Mg _y O ₃ There is a composition with 0.2. It has a higher conductivity than the previous materials,
It is also reported that the effect increases as the temperature decreases, and basic research for application as an electrolyte material for a low-temperature operating solid oxide fuel cell is currently in progress.

[0006]

SUMMARY OF THE INVENTION However, LaG
The aO ₃ -based solid solution generally has high ionic conductivity, but has a problem of insufficient mechanical strength. Most of the methods of using the oxide ion conductive material are to cause a reaction by flowing and contacting gases having different compositions on the front and back surfaces, and temporarily cause cracks and communication holes in the oxide ion conductive material. Then, gas leaks on the front and back surfaces occur through it. If the gas leaks, it not only impairs the function of the device and significantly lowers the efficiency, but also may lead to damage to the entire device. Therefore, LaGaO
Improve mechanical strength of the oxide ion conducting material consisting of ₃ solid solution is required.

Further, electrode materials used in conventional zirconia-based or ceria-based electrochemically acting members, for example, unit cells in fuel cells, have high reactivity with LaGaO ₃ -based solid solutions, and have high reactivity with LaGaO ₃ -based solid solutions. In the case where is made of an oxide ion conductive material, there is a problem that it cannot be used as an electrode as in the related art.

Also, La _(1-x) Sr _x Ga _(1-y) Mg _y O
_In No. ₃ , there was a problem that the price of Ga was high, and the use of Ga increased the product price. Furthermore, L
The oxide ion conductive material made of the aGaO ₃ -based solid solution has a creep phenomenon at a high temperature, which is disadvantageous for long-term stable use.

An object of the present invention is to provide an inexpensive oxide ion conductive material which has high mechanical strength, is stable in shape and is inexpensive, and an electrochemically active member using the same. .

[0010]

Means for Solving the Problems In order to solve the above problems, the oxide ion conductive material is constituted as follows. That is, La _(1-x) Sr _x Ga _(1-yz) Mg _y Al _z O
_{In the} oxide ion conductive material composed of ₃ , 0 <x ≦
0.2, 0 <y ≦ 0.2, and 0 <z <0.4.

[0011] Further, in the electrochemical action member constituted by combining the oxide ion conductive material and the electrode material, an intermediate layer is provided between the oxide ion conductive material and the electrode material. The intermediate layer was formed from a CeO ₂ -based oxide solid solution.

Further, the operating temperature of the electrochemical action member using the oxide ion conductive material is set to 900 ° C. or less. Further, a solid oxide fuel cell was constructed using the electrochemically acting member satisfying the above conditions.

As a result, it is possible to provide an oxide ion conductive material having high mechanical strength, durability and low cost, an electrochemically active member using the same, and a product comprising the same.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below.

Oxide ion conductive material La _(1-x) Sr _x
In Ga _(1-yz) Mg _y Al _z O ₃ , an aqueous nitrate solution of each metal component was added at x = 0.2, y = 0.2, z = 0,.
The powders were mixed so as to be 05, 0.1, 0.2, 0.3, and 0.4, and six kinds of raw material powders having different components were synthesized by a spray pyrolysis method. The obtained powder was formed into a plate by uniaxial pressure molding using a mold, then subjected to isostatic pressing at a pressure of 2500 kgf / cm ² , and then fired in air at 1350 ° C. to 1450 ° C. for 3 to 12 hours. .

4 mm × 3 mm × 40 from the formed sintered body
mm test piece was cut out at room temperature according to JIS160.
A four-point bending test according to No. 1 was performed, and the bending strength and the elastic modulus were measured. The results are shown in FIG. As shown in FIG. 1, by partially replacing Ga with Al, it can be seen that the average four-point bending strength at room temperature is higher than that of the conventional product at z = 0 in any range.

Further, a sample of 4 mm square × 25 mm length is cut out from the sintered body of z = 0, 0.05, 0.10 and
_{In a} mixed gas of ₂ / Ar and a mixed gas of CO / CO ₂ , the conductivity was measured at 800 ° C. by a DC four-terminal method. As shown in FIG. 2, the conductivity showed a constant value independent of the oxygen partial pressure in a wide oxygen partial pressure range from 10 −22 atm to 1 atm. From this, it is considered that the conductivity is governed by the conduction of oxide ions. Further, when a part of Ga is replaced by Al, a slight decrease in the conductivity value is observed, but this does not hinder the application to various electrochemical working members.

If the value of x is set to 0 or more, a part of La is replaced by Sr, and oxygen in the crystal lattice is released according to the amount of the replacement, so that the oxide ion conductivity is improved. On the other hand, if the value of x is 0.2 or more, it is not preferable to set the value of x to 0.2 or more since Sr cannot enter the perovskite-type crystal lattice and generates a second phase having low conductivity. .

If the value of y is set to 0 or more, part of Ga is replaced by Mg, and oxygen in the crystal lattice is released according to the amount of replacement, so that the oxide ion conductivity is improved. On the other hand, if the value of y is 0.2 or more, Mg does not fit into the perovskite-type crystal lattice, and a second phase having low conductivity is generated.

Further, even if the value of z is increased, the decrease in conductivity or the like is hardly a problem. However, if the value of z is 0.4 or more, the amount of substitution by Al increases, and the decrease in conductivity decreases. It is not practical because it becomes large.

Further, a mixture of a powder of a composition with z = 0 (conventional product, hereinafter referred to as LSGM) in a molar ratio of 1: 1 in a combination shown in FIG.
Annealing was performed at ４００1400 ° C. for 12 hours, and the presence or absence of a reaction product and the like was analyzed by powder X-ray diffraction. as a result,
LSGM is an LSM (La _0.85 Sr) which has been generally used as an air electrode material of a solid oxide fuel cell.
_0.15 MnO ₃ ) and LSC (La _0.9 Sr _0.1 CoO ₃ )
Does not react, which means that a conventional product can be used as a cathode material.

On the other hand, conventionally used N
Regarding iO / 8YSZ-based fuel electrode materials, NiO, 8Y
_{SZ (8mol% Y 2 O 3} -ZrO 2) none of the LS
Remarkably reacted with GM and produced another compound,
They could not be used as they were as electrodes for LaGaO ₃ -based materials.

However, LSGM and SDC (Ce _0.8 S
In combination with m _0.2 O _1.9 ), solid solution was observed between some components, but no reaction product was observed. From this result and the fact that the fuel electrode for a solid oxide fuel cell manufactured by mixing SDC, NiO and 8YSZ is functioning normally, the NiO / 8YSZ-based It can be determined that the material is applicable as an electrode for a LaGaO ₃ -based material. SDC is LS
Since no reaction product is generated between M and LSC, it can also be used as an intermediate layer on the air electrode side.
That is, the intermediate layer may be provided only on one side of the electrolyte material, or may be provided on both sides.

Further, in the above example, z = 0, that is, Al
Has been described, but z is 0 or more, that is, Al
The same effect can be obtained even when the substitution is made by

Also, x = 0.2, y = 0.2, z = 0,
A sintered body of each composition of 0.10 and 0.40 was formed by the method described in the above embodiment, and a 4 mm square × 2
The sample was cut to a length of 0 mm, and three types of samples were manufactured. This sample was set on a differential dilatometer using sintered alumina as a standard sample, and a constant weight of 30 grams was applied in the length direction. Was measured.

As a result, when the temperature was set to 1000 ° C., the shrinkage of 0.18% occurred in the conventional product, but z = 0.1
At 0, it is 0.11%, and when z = 0.40,
It was 0.05%. Furthermore, when the experimental temperature was 900 ° C., almost no shrinkage occurred in any of the samples.

From this, even when used at 1000 ° C., when Al contains 10% or more, deformation is small, and
When the temperature is 900 ° C or lower, no deformation is observed in any case. Therefore, by operating the electrochemically acting member composed of these oxide ion conductive materials at 900 ° C or lower, the mechanical reliability is greatly reduced. Can be improved.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will be given of a solid oxide fuel cell constituted by using an electrochemically acting member constituted by the above oxide ion conductive material.

In the fuel cell, the above-mentioned oxide ion conductive material is used as an electrolyte material, the electrodes are used as the electrodes used in conventional NiO / 8YSZ-based materials, and CeO is placed between these oxide ion conductive materials and the electrodes. It was composed of an electrochemically active member having a _two- system intermediate layer interposed, and was operated at about 800 ° C. This fuel cell had a good power generation effect at a relatively low operating temperature and exhibited excellent durability.

[0030]

According to the oxide ion conductive material of the present invention, the mechanical strength can be improved without deteriorating the electrochemical properties and the amount of Ga can be reduced, so that the cost can be reduced. In addition, by using the intermediate layer, a conventionally used electrode can be used.

By operating at 900 ° C. or lower, it is possible to provide a solid oxide fuel cell capable of suppressing the occurrence of creep and achieving stable operation for a long time.

[Brief description of the drawings]

FIG. 1 is a view showing experimental results of an oxide ion conductive material of the present invention.

FIG. 2 is a view showing experimental results of the oxide ion conductive material of the present invention.

FIG. 3 is a view showing experimental results of the oxide ion conductive material of the present invention.

[Explanation of symbols]

Claims (5)

[Claims] 1. La _(1-x) Sr _x Ga _(1-yz) Mg _y Al
_In an oxide ion conductive material composed of zO ₃ , 0 <
An oxide ion conductive material, wherein x ≦ 0.2, 0 <y ≦ 0.2, and 0 <z <0.4. 2. La _(1-x) Sr _x Ga _(1-yz) Mg _y A
l _z O ₃ and 0 <x ≦ 0.2, 0 <y ≦ 0.2, 0 ≦
In an electrochemical action member formed by laminating an electrode material on an oxide ion conductive material with z <0.4, a predetermined intermediate layer is provided between the oxide ion conductive material and the electrode material. An electrochemically acting member, wherein the member is provided. 3. The electrochemically active member according to claim 2, wherein the intermediate layer is formed of a CeO ₂ -based oxide solid solution. 4. The method according to claim 1, wherein the oxide ion conductive material is 900 ° C.
4. The electrochemically acting member according to claim 2, which is operated as follows. 5. A power generating operation by supplying a predetermined oxidizing gas and a reducing gas to the electrochemically active member using the electrochemically active member according to any one of claims 2 to 4. A solid oxide fuel cell, characterized in that the fuel cell is configured to be operated.