JP2002097021A - High temperature conductive oxide, electrode for fuel cell and fuel cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric conductor usable at high temperature of 300 deg.C or more and, more particularly an electrochemical device and a sensor in high temperature environment and materials for electrode in a high temperature type fuel cell. SOLUTION: The high temperature conductive oxide is a perovskite-type compound oxide containing barium, cerium and zirconium and including at least either of manganese or bismuth and is preferably represented by the chemical formula: Ba2-w-x-y-zCewZrxMnyBizO3+δ(0<=w<=1.2, 0<=x<=1.2, 0<=y<=0.6, 0<=z<=0.6, 0.2<=w+x<=1.2, 0.01<=y+z, 0.8<=w+x+y+z<=1.2, |δ|<1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductor which can be used at a high temperature of 300.degree. C. or higher, and more particularly, to an electrochemical device and a sensor used in a high temperature environment, and an electrode material for a high temperature fuel cell. .

[0002]

2. Description of the Related Art In recent years, applications of various electrochemical devices using a solid oxide electrolyte have been studied, and applications to sensors and fuel cells are expected. As devices and sensors used at such a high temperature and electrodes for high-temperature fuel cells operated at a high temperature of 300 ° C. or more, materials used at room temperature cannot be used as they are in many cases. is important. In particular, the electrodes of a high-temperature fuel cell need to exchange electrons with the anode active material and the cathode active material, so they have electron conductivity, have high conductivity, and are used stably even in a high-temperature environment. There is a need for materials that can do this.

[0003] However, in a high-temperature oxidizing atmosphere, many metals and alloy materials except a part of noble metals such as platinum and gold are oxidized to oxides. Usually, most of these oxides have low conductivity, are close to insulators, and few exhibit stable conductivity at high temperatures. On the other hand, in a reducing atmosphere, since it is difficult for the oxide to be stably present, almost no oxide has stable conductivity.

[0004] By the way, among perovskite-type oxides composed of a composite oxide of barium and cerium or a composite oxide of barium and zirconium, those in which part of cerium or zirconium is replaced by a rare earth element exhibit high ionic conductivity. Have been reported. However, they show proton conductivity and little electron conductivity when a hydrogen source is present. Further, oxides containing lanthanum and manganese, oxides containing cobalt, or those doped with an alkaline earth element are known as those exhibiting electron conductivity at a high temperature of 600 ° C. or higher. These materials exhibit high electron (hole) conductivity in a high-temperature atmosphere and are used as cathode materials for solid oxide fuel cells. The lanthanum-chromium composite oxide is
It is known as a material exhibiting electron conductivity in both a high-temperature atmosphere and a high-temperature reducing atmosphere.

[0005]

SUMMARY OF THE INVENTION In a high-temperature oxidizing atmosphere,
Materials that exhibit high electrical conductivity under each high-temperature reducing atmosphere already exist. However, there are few known materials which are chemically stable both in a high-temperature oxidizing atmosphere and in a high-temperature reducing atmosphere and have high conductivity. Also, depending on the use conditions, it may be difficult to use depending on the material, for example, when it reacts with the target object. Therefore, it is necessary to prepare many materials so that usable materials can be selected depending on the environment.

Accordingly, an object of the present invention is to provide a material which is chemically stable both in a high-temperature oxidizing atmosphere and in a high-temperature reducing atmosphere, and has high conductivity.

[0007]

The above object is achieved by the present invention described below. That is, the high-temperature conductive oxide according to the present invention is a perovskite-type composite oxide containing barium and cerium, and further includes at least one of manganese and bismuth.

The high-temperature conductive oxide preferably has a crystal structure substantially showing a perovskite single phase by an X-ray diffraction method or the like. Here, the term “high temperature” refers to a temperature of approximately 300 ° C. or higher, preferably 550 ° C. or higher, more preferably 750 ° C. or higher, which is approximately the operating temperature of the high-temperature fuel cell.

Further, the high-temperature conductive oxide according to the present invention comprises:
The high-temperature conductive oxide, wherein the chemical formula is Ba _2-wyz C.
_{e w Mn y Bi z O 3+} δ (0.2 ≦ w ≦ 1.2,0 ≦ y ≦
0.6, 0 ≦ z ≦ 0.6, 0.01 ≦ y + z, 0.8 ≦
w + y + z ≦ 1.2, | δ | <1).

The high-temperature conductive oxide according to the present invention is a perovskite-type composite oxide containing barium and zirconium, and is characterized by containing at least one of manganese and bismuth.

Further, the high-temperature conductive oxide according to the present invention comprises:
The high-temperature conductive oxide, wherein the chemical formula is Ba _2-xyz Z.
_{r x Mn y Bi z O 3+} δ (0.2 ≦ x ≦ 1.2,0 ≦ y ≦
0.6, 0 ≦ z ≦ 0.6, 0.01 ≦ y + z, 0.8 ≦
x + y + z ≦ 1.2, | δ | <1).

The high-temperature conductive oxide according to the present invention is a perovskite-type composite oxide containing barium, cerium, and zirconium, and is characterized by containing at least one of manganese and bismuth.

Further, the high-temperature conductive oxide according to the present invention comprises:
The high-temperature conductive oxide, wherein the chemical formula is Ba _{2-wxyz
Ce w Zr x Mn y Bi z} O 3+ δ (0 ≦ w ≦ 1.2,0 ≦ x ≦ 1.2,0 ≦ y ≦ 0.6,
0 ≦ z ≦ 0.6, 0.2 ≦ w + x ≦ 1.2, 0.01 ≦
y + z, 0.8 ≦ w + x + y + z ≦ 1.2, | δ | <
It is characterized by being represented by 1).

Further, the high-temperature conductive oxide according to the present invention comprises:
The high-temperature conductive oxide, which has a conductivity of 1 S / S under an oxidizing atmosphere and a reducing atmosphere at a temperature of 750 ° C.
cm or more.

Further, the high-temperature conductive oxide according to the present invention has a conductivity of preferably 4 S / cm or more, more preferably 6 S / cm or more at a temperature of 750 ° C. under an oxidizing atmosphere and a reducing atmosphere. The high-temperature conductive oxide according to the present invention has a temperature of 300 ° C. or more, preferably 550 ° C.
As described above, more preferably, it has conductivity at a temperature of 750 ° C. or higher. Therefore, it can be used as an electrode for a high-temperature fuel cell operated at a temperature of 300 ° C. or higher.

The fuel cell electrode according to the present invention is characterized by comprising the high-temperature conductive oxide.

The fuel cell according to the present invention is characterized in that the fuel cell electrode is used for at least one of a fuel electrode and an air electrode.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A high-temperature conductive oxide according to an embodiment of the present invention will be described below with reference to the accompanying drawings.
This high-temperature conductive oxide can be obtained by various manufacturing methods, but is obtained here by a solid phase method as described below. First, predetermined amounts of barium, cerium, zirconium, manganese, and bismuth oxide powders are respectively weighed and ground and mixed in an agate mortar in an ethanol solvent. After this is sufficiently mixed for a predetermined time, the ethanol solvent is volatilized. Further, after pulverizing and mixing in an agate mortar, what was press-formed into a cylindrical shape was heated and fired at 1000 ° C. for 12 hours in an air atmosphere in an electric furnace. After this firing, the powder is roughly pulverized and pulverized in a benzene solvent with a planetary ball mill to obtain a powder having a particle size of about 3 μm. The obtained powder is vacuum-dried at a temperature of 150 ° C., and then subjected to isostatic pressing at a pressure of 2 ton / cm ² to form a column. Then, it is heated and fired at 1100 ° C. for 10 hours to obtain a sintered body.

Using a powder obtained by grinding a part of the sintered body, the crystal structure is identified by a powder X-ray method. Further, the conductivity of the sintered body is measured. When measuring the conductivity, a disc-shaped (thickness 0.5 mm, diameter 13 m
m), a platinum paste is applied to both surfaces thereof, and baked at 1200 ° C. in the air to form electrodes, thereby preparing a measurement sample. The measurement of the conductivity is performed at a temperature of 750 ° C. in an atmosphere in the air, a nitrogen atmosphere, and a hydrogen atmosphere.

The high-temperature conductive oxide is not limited to the one prepared by the solid-phase method. Also,
In addition to the solid phase method, it may be adjusted by a solution method such as a coprecipitation method or a sol-gel method, or a gas phase method such as a sputtering method or a CVD method.

For example, in the case of BaZr _0.4 Ce _0.4 Bi _0.2 O ₃ , the crystal structure was identified by a powder X-ray diffraction method, and as shown in FIG. 1, it was confirmed that the crystal structure was a single phase of a perovskite structure. are doing. It has a conductivity of 750 ° C., 10 S / c in air atmosphere, nitrogen atmosphere and hydrogen atmosphere.
It shows a high conductivity of m.

Accordingly, the composition is chemically stable and shows high conductivity in any of an oxidizing atmosphere, a reducing atmosphere, and an inert atmosphere in a high-temperature environment. Under the electrochemical device or
It can be used as an electrode for sensors, particularly as an electrode material for high-temperature fuel cells.

[0023]

EXAMPLES Hereinafter, more detailed examples of the high-temperature conductive oxide according to the present invention will be described.

Table 1 shows the conductivity of the composite oxide under various atmospheres at 750 ° C. when the composition of the constituent elements was variously changed.
And Table 2.

[0025]

[Table 1]

[0026]

[Table 2]

For each composition in Table 1, Ba
The ternary phase diagram of the —Ce—Mn—O system is shown in FIG.
-Bi-O ternary phase diagram is shown in FIG.
FIG. 4 shows a ternary phase diagram of the —O system, in which Ba—Zr—Bi
FIG. 5 shows the -O ternary phase diagram. Each number corresponds to the sample number for each system in Table 1. The hatched quadrilateral ABCD indicates a preferred composition range of the high-temperature conductive oxide according to the present invention. Each coordinate is, for example, Ba
In the —Ce—Mn—O system, A: Ba _1.2 Ce _0.79 Mn _0.01 O _{3- δ} B: Ba _0.8 Ce _1.19 Mn _0.01 O _{3- δ} C: Ba _0.8 Ce _0.6 Mn _0.3 O _{3- δ} D: Ba _1.2 Ce _0.3 Mn _0.3 O _{3 -δ} . In addition, Ba
CeO ₃ and BaZrO ₃ show a single phase of perovskite structure, but have no electronic conductivity, and their conductivity is less than 0.01 S / cm at 750 ° C., and is an electrode material for high-temperature fuel cells. Not suitable for use as Table 2 is not shown because it is a quaternary system that is difficult to show.

The preferred composition range of the high-temperature conductive oxide according to the present invention is represented by the following chemical formula: Ba-Ce-M
Ba- which combines the n-O system and the Ba-Ce-Bi-O system
As Ce-Mn-Bi-O _{system, Ba 2-wyz Ce w Mn} y Bi z O 3+ δ (0.2 ≦ w ≦ 1.2,0 ≦ y ≦ 0.6,0 ≦ z ≦ 0.
6, 0.01 ≦ y + z, 0.8 ≦ w + y + z ≦ 1.2,
| Δ | <1). Here, it is preferable to have 0.01 as the total amount (y + z) of manganese and bismuth. Further, (y + z) is further preferably 0.02 or more, more preferably 0.1 or more, as a lower limit value. Further, (y + z) is preferably 0.6 or less, more preferably 0.5 or less, as the upper limit. It is considered that the addition of manganese or bismuth imparts electron conductivity to the composite oxide. Further, the lower limit of w defining the amount of cerium is preferably 0.3 or more, more preferably 0.4 or more. The upper limit of w is preferably 1.1 or less, more preferably 1 or less. Also,
The reason why the oxygen content is represented by 3 + δ is that it can be variously changed depending on the ratio of the constituent elements. Here, δ is | δ | <
It can be a positive or negative value that satisfies 1.

In addition, Ba-Zr-Mn-O system and Ba-Z
Ba-Zr-Mn-Bi- combined with r-Bi-O system
As O _{system, Ba 2-xyz Zr x Mn} y Bi z O 3+ δ (0.2 ≦ x ≦ 1.2,0 ≦ y ≦ 0.6,0 ≦ z ≦ 0.
6, 0.01 ≦ y + z, 0.8 ≦ x + y + z ≦ 1.2,
| Δ | <1). Here, the total amount of manganese and bismuth (y + z) is preferably 0.01. Further, (y + z) is further preferably 0.02 or more, more preferably 0.1 or more, as a lower limit value.
Further, (y + z) is preferably an upper limit of 0.1.
6 or less, more preferably 0.5 or less. further,
With respect to x defining the amount of zirconium, the lower limit is
It is preferably at least 0.3, more preferably at least 0.4. The upper limit of x is preferably 1.1 or less, more preferably 1 or less. The reason why the oxygen content is represented by 3 + δ is that it can be variously changed depending on the ratio of the constituent elements. Here, δ is | δ | <1
Can be positive or negative.

Further, Ba-Zr-Ce-Mn-Bi-
When integrally expressed as O _{system, Ba 2-wxyz Ce w Zr} x Mn y Bi z O 3+ δ (0 ≦ w ≦ 1.2,0 ≦ x ≦ 1.2,0 ≦ y ≦ 0.6,
0 ≦ z ≦ 0.6, 0.2 ≦ w + x ≦ 1.2, 0.01 ≦
y + z, 0.8 ≦ w + x + y + z ≦ 1.2, | δ | <
1). Here, the total amount of manganese and bismuth (y + z) is preferably 0.01. Further, (y + z) is further preferably 0.02 or more, more preferably 0.1 or more, as a lower limit value. Further, (y + z) is preferably 0.6 or less, more preferably 0.5 or less, as the upper limit. Further, w + x, which defines the total amount of cerium and zirconium, preferably has a lower limit of 0.3 or more, more preferably 0.4 or more. The upper limit of w + x is preferably 1.1 or less, more preferably 1 or less. Similarly, the lower limit and the upper limit of each of the cerium amount w and the zirconium amount x are preferably 0.3 or more, more preferably 0.4 or more. The upper limit is preferably 1.1 or less, more preferably 1 or less. In addition, the amount of oxygen is 3
+ Δ is because it can be variously changed depending on the ratio of the constituent elements. Here, δ can take a positive or negative value that satisfies | δ | <1.

The conductive stability of the high-temperature conductive oxides having the compositions shown in Tables 1 and 2 at high temperatures in an atmosphere in the air, an atmosphere in nitrogen, and an atmosphere in hydrogen is examined. Conductivity stability was measured at a temperature of 800 ° C. in each atmosphere at a current density of 1 mA / c.
A constant current is passed at m ² , and a change in output voltage after 1000 hours is detected and measured. As a result, in all samples, the change in the output voltage after 1000 hours was within 1% of that at the start of the measurement, and the current could be supplied very stably.

FIG. 6 shows the chemical formula of BaZr_0.4Ce_0.4Mn
_0.2O_ThreeAnd a chemical formula of BaZr _0.4Ce_0.4Bi
_0.2O_ThreeLogarithmic value lo of conductivity σ
g_TenIt is the graph which measured the relationship between (sigma) and temperature. these
Are 550 ° C. and 6
It shows high conductivity at 50 ° C. and 750 ° C. Ma
In FIG. 6, the logarithm of the conductivity σ increases as the temperature increases.
Value log_Tenσ increases almost linearly, and the conductivity σ
Exponentially rising, even at higher temperatures
It is considered to indicate conductivity.

FIG. 7 shows the chemical formula of BaZr _0.4 Ce _0.4
The composite oxide of Bi _0.2 O ₃ at 750 ° C.
This is a relationship between an applied voltage and an output current under an oxygen atmosphere (in air), a hydrogen atmosphere, and a nitrogen atmosphere. This composite oxide shows high conductivity under any atmosphere.

The case where the high-temperature conductive oxide according to the present invention is used as the air electrode 1 of the small fuel cell 10 will be described. FIG. 8 is a sectional view of the small fuel cell 10.
Here, BaCe _0.8 Gd _0.2 O _{3 is used} as the solid electrolyte 2.
(Thickness 0.50 mm), a high-temperature conductive oxide represented by the chemical formula BaCe _0.8 Mn _0.2 O _{3 according} to the present invention is used as the air electrode 1, and Ni cermet is used as the fuel electrode 3. When the fuel cell 10 is operated, air 4 is supplied from the inner tube 9 on the side of the air electrode 1. The air 4 exits the fuel cell 10 from the inner tube 9, through the surface of the cathode 2, through the outer tube 8. On the other hand, hydrogen 5 is supplied from the inner pipe 9 on the fuel electrode 3 side. The hydrogen 5 exits the fuel cell 10 through the outer tube 8 through the surface of the anode 3. At this time, fuel electrode 3
In this case, the hydrogen 2 gives electrons to the fuel electrode 3 to be ionized, and moves toward the air electrode 1 via the solid electrolyte 2. On the other hand, in the air electrode 1, oxygen in the air 4 receives electrons from the air electrode 1 and is ionized, and reacts with the transferred hydrogen ions to generate water. Electric energy is generated by repeating such a cycle.

When using the high-temperature conductive oxide as the air electrode 1, the high-temperature conductive oxide is first pulverized by a planetary ball mill. Next, 4% by weight of polyvinyl butyral is added as a binder to the pulverized product, and further mixed with a mixed solvent of ethanol and toluene to form a paste. This paste is applied to the surface of the solid electrolyte 2 and baked at a temperature of 1200 ° C. to form the air electrode 1. The method for producing the air electrode 1 using the high-temperature conductive oxide is not limited to the method of baking after the above-mentioned pasting, and the air electrode 1 is formed by a vapor phase method such as a sputtering method or a vapor deposition method. You may. Further, the fuel electrode is not limited to the air electrode 1 but may be used as the fuel electrode 3. The fuel cell 10 uses the solid electrolyte 2 made of an oxide, but is not limited to this, and various solid electrolytes can be used. Further, another system may be used as the high-temperature fuel cell.

Next, a continuous discharge test of the small fuel cell 10 using this high-temperature conductive oxide as the air electrode 1 is performed. The discharge test is performed by supplying air at a temperature of 800 ° C. to the air electrode 1 at 200 ml / min and supplying humidified hydrogen to the fuel electrode 3 at 200 ml / min. This discharge test shows good discharge characteristics of 0.2 W / cm ² . In addition, constant current 100mA
In the continuous discharge test of / cm ^2, the discharge was stable for 1000 hours, and the voltage change was within 1% even after the lapse of 1000 hours.

[0037]

As described in detail above, according to the high-temperature conductive oxide of the present invention, the electronic conductive property can be obtained in any of an oxidizing atmosphere, a reducing atmosphere, and an inert atmosphere in a high-temperature environment. And exhibit high conductivity. Therefore, it is suitable as a conductor that can be used at a high temperature, particularly as an electrode material in an electrochemical device, a sensor, or a high-temperature fuel cell used in a high-temperature environment.

[Brief description of the drawings]

FIG. 1 shows BaZr _0.4 Ce according to an embodiment of the present invention.
_{4 is} a powder X-ray diffraction pattern of _0.4 Bi _0.2 O _{3+ δ} .

FIG. 2 shows B of a high-temperature conductive oxide according to an example of the present invention.
FIG. 3 is a ternary phase diagram illustrating a composition range of an a-Ce—Mn—O-based composite oxide.

FIG. 3 shows B of a high-temperature conductive oxide according to an example of the present invention.
FIG. 3 is a ternary phase diagram showing a composition range of an a-Ce-Bi-O-based composite oxide.

FIG. 4 shows B of the high-temperature conductive oxide according to the example of the present invention.
FIG. 3 is a ternary phase diagram illustrating a composition range of an a-Zr—Mn—O-based composite oxide.

FIG. 5 shows B of the high-temperature conductive oxide according to the example of the present invention.
FIG. 3 is a ternary phase diagram illustrating a composition range of an a-Zr—Bi—O-based composite oxide.

FIG. 6 is a graph showing a relationship between temperature and conductivity of a high-temperature conductive oxide according to an example of the present invention.

FIG. 7 shows a high-temperature conductive oxide 7 according to an embodiment of the present invention.
It is a graph which shows the relationship between the applied voltage and output current under each atmosphere at 50 degreeC.

FIG. 8 is a cross-sectional view showing an internal structure of a high-temperature fuel cell using an electrode for a high-temperature fuel cell according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Air electrode 2 Solid electrolyte 3 Fuel electrode 4 Air 5 Hydrogen 6 Gas packing 7a, 7b Lead 8 Outer tube 9 Inner tube 10 Fuel cell

Claims (9)

[Claims] 1. A high-temperature conductive oxide, which is a perovskite-type composite oxide containing barium and cerium, further comprising at least one of manganese and bismuth. 2. A chemical formula _{Ba 2-wyz Ce w Mn y} Bi z O 3+
_δ (0.2 ≦ w ≦ 1.2, 0 ≦ y ≦ 0.6, 0 ≦ z ≦
0.6, 0.01 ≦ y + z, 0.8 ≦ w + y + z ≦ 1.
2. The high-temperature conductive oxide according to claim 1, which is represented by | δ | <1). 3. A high-temperature conductive oxide which is a perovskite-type composite oxide containing barium and zirconium, wherein the oxide contains at least one of manganese and bismuth. 4. A chemical formula _{Ba 2-xyz Zr x Mn y} Bi z O 3+
_δ (0.2 ≦ x ≦ 1.2, 0 ≦ y ≦ 0.6, 0 ≦ z ≦
0.6, 0.01 ≦ y + z, 0.8 ≦ x + y + z ≦ 1.
4. The high-temperature conductive oxide according to claim 3, wherein | δ | <1). 5. A high-temperature conductive oxide, which is a perovskite-type composite oxide containing barium, cerium, and zirconium, comprising at least one of manganese and bismuth. 6. formula _{Ba 2-wxyz Ce w Zr x} Mn y B
_{i z O 3+ δ (0 ≦} w ≦ 1.2,0 ≦ x ≦ 1.2,0 ≦ y
≦ 0.6, 0 ≦ z ≦ 0.6, 0.2 ≦ w + x ≦ 1.2,
0.01 ≦ y + z, 0.8 ≦ w + x + y + z ≦ 1.2,
| Δ | <1), wherein the high-temperature conductive oxide according to claim 5 is represented by | δ | <1). 7. The high-temperature conductive oxidation according to claim 1, wherein the conductivity is 1 S / cm or more under an oxidizing atmosphere and a reducing atmosphere at a temperature of 750 ° C. object. 8. An electrode for a fuel cell, comprising the high-temperature conductive oxide according to any one of claims 1 to 7. 9. A fuel cell, wherein the fuel cell electrode according to claim 8 is used for at least one of a fuel electrode and an air electrode.