JP2003206178A - Mixed conductive multiple oxide for oxygen separation and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an electron, oxygen ion mixed conductive oxide having low resistance against oxygen separation and capable of more rapidly separating oxygen than before, and a manufacturing method therefor. <P>SOLUTION: A CeO<SB>2</SB>-ZrO<SB>2</SB>solid solution having a composition expressed by Ce<SB>2-x</SB>Zr<SB>x</SB>O<SB>4-δ</SB>(x=0.125-1.9, δ=0-0.5) is used as the mixed conductive multiple oxide. In the mixed conductive multiple oxide, the main crystal system is a cubic system, Ce and Zr are regularly oriented and the diffraction pattern has peaks respectively in 2θ=13.8-14.6, 36.0-37.4 and 43.2-44.9. The mixed conductive multiple oxide is obtained by heating at ≥1000°C under an atmosphere of ≤10<SP>-8</SP>atm oxygen partial pressure. An electron, oxygen ion mixed conductor has high conductivity and exhibits high performance even when being used not only for the oxygen separation, but for a solid oxygen fuel cell (SOFC), and oxygen sensor, a co-catalyst, or the like, due to its high conductivity. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron / oxygen ion mixed conductive composite oxide used for separating oxygen from an oxygen-containing mixed gas, and a method for producing this composite oxide.

[0002]

2. Description of the Related Art Oxygen is used in large quantities in many industries such as iron making, metallurgy, chemistry, coal and pulp. At present, combustion of air is generally used for utilizing heat energy, but the thermal efficiency is poor because it contains a large amount of nitrogen that is unnecessary for combustion. In addition, there are many problems that enormous energy is required to generate nitrogen oxides and to recover harmful gases such as nitrogen oxides and carbon dioxide gas generated by being diluted with nitrogen. On the other hand, oxyfuel combustion using pure oxygen is expected to be more than twice as efficient as air combustion, and the amount of exhaust gas is small. Therefore, the recovery of carbon dioxide gas and other harmful gases can be performed easily and with a small device. It can be implemented at cost. It is also possible to suppress the generation of nitrogen oxides.

To meet the above demands, it is necessary to produce a large amount of inexpensive oxygen. Various methods are known for separating oxygen from a mixed gas such as air. For example, liquefaction separation method, pressure swing adsorption method (PS
A) and the like. These methods have advantages and disadvantages. For example, the liquefaction separation method is a method of distilling and separating by utilizing the difference in boiling point of each component of air, while high purity oxygen is obtained,
It requires a very low temperature and therefore requires a large amount of energy. On the other hand, the pressure swing adsorption method (PSA) is a method in which a pressurized raw material gas is passed through an adsorbent such as zeolite to adsorb and separate impurities to obtain a target gas of required purity, and the adsorbed impurity gas is atmospheric pressure or vacuum. This is a method of releasing by pressure. This method can save energy as compared with the liquefaction separation method, but it is difficult to obtain high-purity oxygen. In addition, since the adsorption and desorption of oxygen is repeated, there is a problem that the device becomes complicated.

In contrast to the above-mentioned oxygen separation technique, an oxygen separation method using an ion conductive substance has been proposed as a method of separating oxygen with higher efficiency and ease. This is a method of taking out only oxygen from a mixed gas by utilizing an ion conductive substance capable of selectively moving oxygen ions. The advantage of this method is that theoretically 100% pure oxygen can be obtained in a single stage treatment. Further, ideally, the energy required to separate oxygen from the mixed gas is only the energy corresponding to the change in free enthalpy of mixing. Therefore, it is highly efficient and energy saving compared to other methods.

[0005] There are several methods of different principles in the oxygen separation method using this ion conductive material. The method can be broadly classified into three methods: a direct current method, a concentration battery short circuit method, and a mixed conductor partition method.

The direct current method is a method in which an oxygen ion conductor such as stabilized zirconia is used as a partition wall, and electron conductors are attached to both sides of the partition wall to conduct electricity. By exposing one side to air and applying current to this air as a negative electrode, oxygen molecules in the air are reduced. Oxygen molecules become oxygen ions, which move in the electrolyte and are oxidized at the positive electrode to become oxygen again.

The concentration cell short-circuit method is the same device as the direct current method, but only short-circuits without energization from the outside. When one of the partition walls is exposed to air and the other is depressurized, an electromotive force is generated due to a difference in oxygen partial pressure, and an oxygen gas concentration battery having air as a positive electrode is formed. A current corresponding to the generated electromotive force flows in the external circuit, and oxygen ions move from the air electrode toward the decompression electrode in the electrolyte to become oxygen molecules on the decompression electrode surface.

Further, a mixed conductor partition wall method is a method in which, instead of the short circuit by the external circuit of the concentration battery short circuit method, the electrolyte itself has electronic conductivity to cause a short circuit. This method requires a mixed conducting oxide in which both oxygen ions and electrons can move. By separating the two chambers by using the mixed conductive oxide as a partition and flowing a mixed gas containing oxygen such as air into one of the chambers and sucking the other, a short-circuited oxygen concentration cell is formed and oxygen ions move. As described above, the mixed conductor partition method does not require a surface electrode or a lead wire of an external circuit, and only oxygen is moved only by providing a pressure difference between both sides of the partition, so that the oxygen separation device can be simplified. is there.

Unfortunately, however, oxygen separation by the mixed conductor partition wall method has not reached the level of the laboratory because the current mixed conductive materials do not provide satisfactory performance. The biggest problem with this is that a large current cannot flow due to insufficient conductivity of the mixed conductor.

At present, mixed conductor materials for oxygen separation membranes are roughly classified into three systems. First of all, for oxygen ion conductors such as stabilized zirconia,
An example is a composite in which a noble metal such as Pd is compounded, that is, mixed in a powder form and sintered densely to give pseudo mixed conductor material characteristics (Solid St).
ate Ionics, 86-88, 569-572
(1996), Solid State Ionic
s, 76, 23-28 (1995)). However, since the stabilized zirconia, which is an oxygen ion conductor, does not have a high ionic conductivity from the beginning, a large current cannot flow at a low temperature of 800 ° C. or less, so that a large amount of oxygen cannot be separated. difficult.

Next, La _x Sr _{1-x having} a perovskite structure
La- represented by CoO _3-y and SrCo _1-x FeO _3-y
Sr-Co-O-based oxide (Japanese Patent Laid-Open No. 2001-10653)
2, Solid State Ionics, 106,
189-195 (1998)), and the third is the Ce-Zr-MO system (M = Y,
There are oxides of Ca, Mg, etc. (J. Electroc
hem. Soc. , 131, 2407-2413 (19
84), Solid State Ionics, 86
-88, 739-744 (1996)).

The La-Sr-Co-O system and Ce-
The Zr-MO oxide is a mixed conductor that exhibits oxygen ion conductivity through oxygen ion vacancies. Both show higher oxygen ion conductivity than the stabilized zirconia. However, even with these substances, the resistance to oxygen gas separation is still high, and therefore, a device for extracting oxygen from a mixed gas on a large scale has not been put into practical use. The cause of this is considered to be the conductivity of oxygen ions in the mixed conductor, but the adsorption dissociation of oxygen molecules on the surface and ionization to oxygen ions, and vice versa, discharge of oxygen ions and generation and desorption of oxygen molecules. It has been pointed out that the separation process may be rate-determining (J. Appl. Electrochem., 24, 1).
222 (1994), Solid State Ion
ics, 53, 46 (1992)).

As described above, at the time of putting into practical use the mixed conductor partition wall method capable of oxygen separation by a highly efficient and simple device, at present, since the mixed conductor has a large resistance to oxygen separation, 800 ° C. The problem is that a large current cannot flow at the following low temperatures. The problem is that not only is the conductivity of oxygen ions in the mixed conductor insufficient, but the rate of reaction such as the ionization of oxygen molecules on the partition surface of the mixed conductor and the molecularization of oxygen ions is rate-limiting. It is considered.

Further, the electron / oxygen ion mixed conductive composite oxide is expected to be applied not only to an oxygen separation membrane but also to a solid oxygen fuel cell (SOFC), an oxygen sensor, etc., but this point is still sufficient. An electron / oxygen ion mixed conductive complex oxide capable of obtaining excellent performance has not been found.

[0015]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an electron / oxygen ion mixed conductive complex oxide having a low resistance to oxygen separation and capable of oxygen separation faster than ever before, and a method for producing the same. It is to be.

[0016]

According to the present invention, this mixed conductor composite oxide is added to Ce _2-x Zr _x O _4- δ (x = 0.125-
1.9, CeO having a composition represented by δ = 0 to 0.5)
It is characterized by using a _2- ZrO ₂ solid solution. Further, the mixed conductive complex oxide according to the present invention is characterized in that the main crystal system is a cubic crystal and Ce and Zr are regularly arranged. Here, whether or not Ce and Zr are regularly arranged is determined by powder X-ray diffraction measurement using Cu as a tube, and the diffraction pattern is 2θ = 13.8 to 14.6, 3 and 3.
This can be confirmed by exhibiting one peak at 6.0 to 37.4 and 43.2 to 44.9, respectively.

Further, it is preferable that the cubic crystal has a regular arrangement of Ce and Zr and also has a specific regular arrangement with oxygen deficiency. In the powder X-ray diffraction measurement using a sphere, the diffraction patterns are 2θ = 13.8 to 14.6, 36.0 to 3
It can be confirmed by adding a single peak at 7.4 and 43.2 to 44.9, and further exhibiting a peak at 2θ = 15.8 to 17.2. This regular array has a space group of F4-3m (No. 216),
The basic composition can be expressed as CeZrO _3.75 .

CeO ₂ --ZrO ₂ solid solution is Ce _2-x Zr _x
An atmosphere in which a composite oxide represented by O _4- δ (x = 0.125 to 1.9, δ = 0 to 0.5) is 1000 ° C. or more and an oxygen partial pressure P ₀₂ = 10 ⁻⁸ atm or less. It can be obtained by heat treatment in.

Further, this composite oxide is added in the range of 400 to 900.
It is possible to perform a heat treatment in which the oxygen partial pressure is maintained at 0 ° C. and the oxygen partial pressure is increased from a reducing atmosphere of 10 ⁻⁶ atm or less to an oxidizing atmosphere of 10 ⁻¹ atm or more for 4 hours or more.

Further, the oxygen partial pressure P _{02 is} added to the composite oxide.
= A 10 ^-6 ~10 ⁰ atm, 1~1 at 50 to 300 ° C.
It is also preferable to perform heat treatment for 200 hours.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION An electron / oxygen ion mixed conductive composite oxide of the present invention will be described.

As described above, Ce-Zr-M has been conventionally used.
-O-based (M = Y, Ca, Mg, etc.) fluorite-type related structure oxides have been investigated as mixed conductors. But Sol
idState Ionics, 98, 63-72 (1
997), CeO ₂ and ZrO ₂ do not form a solid solution,
Some materials are simply made into composite materials. Further, in the prior art, a third metal element (denoted by M in the above composition formula) other than Ce and Zr is always added. The third metal element is
It is added for the purpose of stabilizing the cubic crystal without distorting the crystal structure of the complex oxide into a tetragonal crystal, and improving the sintering density of the ceramic composed of the complex oxide. It is important to stabilize the cubic crystal in the complex oxide because the tetragonal distortion causes the oxygen ion conductivity to decrease.

The present invention is different from the above-mentioned prior art in that the cubic crystal is stabilized without adding a third metal element, and a specific heat treatment is applied so that oxygen is easily absorbed and released on the surface. It was a quality.

The present inventors have performed heat treatment at a high temperature of 1000 ° C. or higher and in a reducing atmosphere having an oxygen partial pressure of 10 ⁻⁸ atm or less, whereby Ce: Zr = 2-x: x (x =
In the range of 0.125 to 1.0), a mixed conductivity composed of CeO ₂ -ZrO ₂ solid solution with a small resistance to oxygen separation while forming a regular ordered arrangement of Ce and Zr and maintaining a perfect cubic crystal. It has been found that a composite oxide can be produced.

This peculiar ordered array can be easily confirmed by powder X-ray diffraction measurement. Specifically, C
In powder X-ray diffraction measurement using u as a tube, 2θ = 1
3.8-14.6, 36.0-37.4, 43.2-4
It is characterized by having one peak each at 4.9.

This peculiar ordered array disappears when heat treatment is performed at 900 ° C. or higher in an oxidizing atmosphere.
At 00 ° C. or lower or in a reducing atmosphere, the unique regular array property can be maintained. That is, at a high temperature of 1000 ° C. or higher,
Further, even after the heat treatment in the reducing atmosphere having an oxygen partial pressure of 10 ^-10 atm or less, any heat treatment may be performed unless the heat treatment is performed at 900 ° C. or more in the oxidizing atmosphere.
For example, when a ceramic is obtained from a complex oxide solid solution powder, the temperature is higher than 1000 ° C. and the oxygen partial pressure is 10
This means that even if firing is performed in a reducing atmosphere of ^-10 atm or less, if the subsequent heat treatment is performed at 900 ° C or less, this specific ordered arrangement is maintained regardless of the atmosphere.

Further, Ce: Zr = 2-x: x (x = 1.
In the range of 0 to 1.9), a tetragonal phase may be partially precipitated depending on heat treatment conditions, particularly cooling conditions. When the cooling rate is high, the tetragonal phase is unlikely to precipitate, but when the cooling rate is slow and the oxygen partial pressure is relatively high, x is less than 10% at about 1.1, and x is 1. When it is about 9, tetragonal phase of less than 50% may be precipitated. But,
Even in this case, the main crystal phase is cubic and the obtained properties are superior to those in the past.

Although the correlation mechanism of the arrangement of Ce and Zr and the resistance reduction against oxygen separation is not clear, when the arrangement with Zr ions is formed, sites around which oxygen ions are easily absorbed and desorbed are formed. It is supposed to be one. That is, it is considered that a certain arrangement of Zr ions promotes adsorption and dissociation of oxygen molecules on the surface of the composite oxide and ionization of oxygen ions, and vice versa, discharge of oxygen ions and desorption process of molecules. .

Further, in Ce _2-x Zr _x O _4- δ, the value of δ is determined so that the electric charge of the composite oxide becomes electrically neutral. It is a value determined based on the composition before being subjected to oxygen separation, and when this composite oxide is actually used for oxygen separation, it may be slightly different from this value, but the value of δ is 0 to 0. 0.5
Is considered appropriate.

Electronic / oxygen ion mixed conductive composite of the present invention
Oxide is caused by the generation of oxygen vacancies in the crystal lattice.
And shows good electron conductivity and ionic conductivity. And C
e and Zr composition and oxygen deficiency satisfy certain conditions
If so, oxygen ions are regularly arranged. For example, Ce: Zr
= 1: 1 and oxygen deficiency is 1/8, Ce₂Zr₂O
₇And this regular arrangement is known as the pyrochlore structure.
Has been. Further, when Ce: Zr = 1: 1, the oxygen deficiency amount is
In the case of 1/16, the composition of the composite oxide is Ce ₂Zr₂O
_7.5(That is, CeZrO_3.75), And Pyrocro
(A) Oxygen deficiency, which is different from the structure, is regularly arranged.

The regular array property of this special oxygen deficiency can be easily confirmed by powder X-ray diffraction measurement as described above. Specifically, in powder X-ray diffraction measurement using Cu as a tube, 2θ = 13.8 to 14.6, 36.0.
In addition to the regular arrangement of Ce and Zr, each of which has one peak at 37.4 and 43.2 to 44.9, Ce
This can be confirmed by the peak at 2θ = 15.8 to 17.2 caused by the lack of regular arrangement of 1/16 oxygen of ZrO ₄ .

Further, the crystal structure of the mixed electron / oxygen ion conductive oxide having Ce: Zr = 1: 1 and the oxygen deficiency amount of 1/16 has a space group F4-3m (No. 216) (I
international Tables for C
It is a structure classified as rystallography: Volume A), and can be expressed as Ce ₂ Zr ₂ O _7.5 (that is, CeZrO _3.75 ).

Although the composition of the present invention does not include metal elements other than Ce and Zr, even if Ce or Zr is replaced by a metal element such as Y, Ti or Ca in a trace amount of 20% by weight or less, The advantages of the invention work without loss.

Of course, when actually used as a ceramic thin film for oxygen separation or a solid oxygen fuel cell (SOFC), a catalyst for promoting oxygen separation such as Pd or Pt may be provided on both sides of the thin film. Good.

Next, the method for producing the electron-oxygen ion mixed conduction composite oxide and ceramics of the present invention will be described.

The electron-oxygen ion mixed conductive composite oxide and ceramics of the present invention can be prepared basically by a method including heat treatment. For example, a compound containing a metal atom such as Ce or Zr, which can be converted into an oxide in a heat treatment process such as sintering, such as CeO ₂ or ZrO ₂
Oxides such as, or nitrates, carbonates, and other C
Inorganic acid salts such as eCl ₃ and ZrCl ₄ , organic acid salts such as alkoxides, halides such as CeF ₃ , or Ce
There is a method in which hydroxides such as (OH) ₄ and Zr (OH) ₄ are mixed in a desired ratio and heat treatment is performed.

Further, the mixed aqueous solution of each metal salt described above is hydrolyzed with an alkaline aqueous solution such as ammonia water, and the precipitate obtained by a so-called coprecipitation method is heat-treated to obtain a desired complex oxide. Good. Further, a mixture of respective metals or an alloy may be heat-treated to be oxidized.

To obtain ceramics from the CeO ₂ -ZrO ₂ solid solution powder of the present invention, the following method is used. That is, A
Pressurized pressure 50 to 500 k in an inert gas atmosphere such as r
gf / cm ² , preferably 100 to 250 kgf / c
m ² , heating temperature 1100 to 1500 ° C., preferably 12
Pressure sintering is performed at 00 to 1400 ° C. for a heating time of 0.1 to 15 hours, preferably 2 to 5 hours. The temperature rising rate at this time is preferably 1 to 20 ° C./min. Pressurized pressure is 5
If it is 0 kgf / cm ² or less, there is a risk of gas leakage due to insufficient sintered density of ceramics.
When it is 0 kgf / cm ² or more, the restrictions on the apparatus become large, which is not desirable. If the heating temperature is 1100 ° C. or lower, a dense sintered body cannot be obtained, and if it is 1500 ° C. or higher, the crystal system may change. If the heating time is 0.1 hours or less, a dense ceramic cannot be obtained, and if the heating time is 15 hours or more, the crystal grains become coarse and the strength of the ceramic decreases.

Next, the oxygen partial pressure is controlled to 10 ^-8 atm or less, preferably 10 ^-8 to 10 ^-16 atm, and 1000 to 1000 ° C., preferably 1100 to 1200 ° C., 0.1 to 24.
Bake for hours. The oxygen partial pressure can be controlled by, for example, introducing a CO ₂ —H ₂ mixed gas into the furnace. When the oxygen partial pressure is 10 ^-8 atm or more, a crack occurs due to a volume change due to oxygen absorption, and when the firing temperature is 1000 ° C. or less, the crystal arrangement peculiar to the present invention may be insufficient, so that the desired ceramic Can't get

Further, in order to prevent the occurrence of cracks in the ceramics, it is desirable to cool to room temperature by the following method. The temperature was lowered to 400 to 900 ° C. at a temperature lowering rate of 0.1 to 3 ° C./min without changing the mixing ratio of the CO ₂ —H ₂ mixed gas, and the oxygen partial pressure was adjusted to 10 while keeping this temperature.
^The oxygen partial pressure is gradually increased from a reducing atmosphere of ^-6 atm or less to an oxidizing atmosphere of 10 ^-1 atm over 4 hours or more, preferably 6 to 72 hours, and finally firing is performed in an oxygen stream. Then, it is further gradually cooled at a rate of 0.1 to 3 ° C./min. When the holding temperature is 900 ° C or higher, the impurity phase precipitates,
Further, if the temperature is 400 ° C. or lower, oxygen absorption becomes insufficient. The holding time depends on the holding temperature and the rising rate of the oxygen partial pressure, but is preferably 6 hours or more. If the holding time is 6 hours or less, there is a risk of cracks. Also, cracks may occur even if the temperature decrease rate after holding is 3 ° C./min or more. On the other hand, when the temperature lowering rate is 0.1 ° C./min or less, productivity is remarkably impaired, which is not realistic.

The above is a method for obtaining ceramics from the CeO ₂ --ZrO ₂ solid solution powder of the present invention.
The following method is desirable to obtain ceramics in which and are regularly arrayed, and further, oxygen deficiency is regularly arrayed.

That is, after the above CeO ₂ --ZrO ₂ solid solution powder was pressure-sintered, the oxygen partial pressure P ₀₂ was 10 ^-6 -10.
And ⁰ atm, subjected to a heat treatment of 1 to 1200 hours at 50~300 ℃. When the oxygen partial pressure P ₀₂ is less than 10 ⁻⁶ atm, it takes 1200 hours or more for heat treatment to manufacture, which is not realistic. Further, when the oxygen partial pressure P ₀₂ is 10 ⁰ atm (that is, 1 atm) or more, pressurization is required, which results in cost reduction. Is increased, which is not preferable. If the treatment temperature is lower than 50 ° C., the production rate of the target ordered array is slow and the productivity is greatly impaired, which is not suitable, and if it exceeds 300 ° C., oxygen vacancies may disappear, which is not preferable.

In the present invention, in order to obtain a desired cubic crystal, preferable sintering conditions and firing conditions are specified as described above. This is because, under conditions other than the above-specified conditions, the cubic system does not become a cubic system, or other crystal systems coexist, and the oxygen ion conductivity decreases, and cracks or cracks occur, which is desirable. This is because ceramics cannot be obtained.

The composite oxide and ceramics obtained as described above are prepared from an oxygen-containing mixed gas such as air.
It can be suitably used as an oxygen separation membrane for separating oxygen. Further, this composite oxide can be used as a co-catalyst as an oxygen storage material, and is suitable for use in a device utilizing an electrochemical mechanism such as an oxygen sensor and a fuel cell.

[0045]

EXAMPLES The present invention will now be described in more detail with reference to examples. (Example 1) As Example 1, CeZrO ₄ was synthesized.
That is, this is the case where x = 1 and δ = 0. Cerium nitrate (Ce (NO ₃ ) ₃ ) and zirconium nitrate (Zr (N
An aqueous solution was prepared by mixing O ₃ ) ₃ ) in a molar ratio of Ce / Zr = 5/5, and ammonia water was added dropwise with stirring to neutralize to form a precipitate. Subsequently, a hydrogen peroxide solution containing hydrogen peroxide in a mole number of 1/2 of the cerium ion contained in this mixed aqueous solution, and 1 of the obtained composite oxide.
An aqueous solution containing 0% by weight of alkylbenzene sulfonic acid was added and mixed and stirred. The obtained slurry is charged with gas 40
The complex oxide solid solution powder was prepared by spraying in an atmosphere of 0 ° C. and an outlet gas of 250 ° C., drying by a spray drying method, and evaporating and decomposing coexisting ammonium nitrate.
Further, this powder was subjected to stationary Ar gas substitution using a graphite heater heating type atmospheric pressure sintering furnace, and then, using a graphite press die, at 1400 ° C. under a pressure of 500 kgf / cm ^2.
Pressure sintering for 2 hours, φ150mm, height about 5mm
A sintered body of was obtained.

The sintered body is further placed in an atmosphere sintering furnace, and a CO ₂ -H ₂ mixed gas (CO ₂ / H ₂ = 9.5) is flown to reduce the oxygen partial pressure P ₀₂ in the furnace. Firing was performed at 1200 ° C. for 12 hours while controlling at 10 ⁻⁹ atm. further,
Without changing the CO ₂ -H ₂ mixing ratio, the temperature was lowered to 800 ° C., the oxygen partial pressure was gradually increased over 48 hours while maintaining the temperature at 800 ° C., and finally firing was performed in an oxygen stream. . Then, it was gradually cooled at a temperature decrease rate of 1 ° C./min to obtain a target ceramic sample. This multi-step heat treatment is a heat treatment necessary to obtain a sample having the composition and structure specified in the present invention without cracks. The obtained ceramic sample is cut into a disk-shaped thin piece with a diameter of 20 mm and a thickness of 1 mm,
The sample was used for oxygen separation.

Further, this ceramic sample was pulverized and subjected to powder X-ray diffraction measurement. The results are shown in Fig. 1. All the peaks of the obtained diffraction pattern were assigned to cubic crystals and 1
C near 4.5 °, 37.1 °, 44.7 ° (▼ in the figure)
A peak indicating that e and Zr were regularly arranged was observed.

With respect to the ceramic sample cut out as described above, the oxygen permeation rate was evaluated using the evaluation apparatus shown in FIG. 20 cc / min of dry air from the gas 1 inlet
Was introduced at the rate of, and the high oxygen concentration side was set. Further, high-purity helium gas (oxygen partial pressure of 10 ⁻³ atm or less) was introduced from the gas 2 inlet at a rate of 20 cc / min to make the low oxygen concentration side. The produced ceramic sample was adhered to an alumina tube by a glass seal to completely separate the high oxygen concentration side and the low oxygen concentration side. Gas 1 outlet and gas 2
The gas discharged from the outlet was analyzed using a quadrupole mass spectrometer and an oxygen sensor, respectively. The amount of oxygen passing through the ceramic sample was determined from the oxygen concentration of the gas released from the gas outlet 2 and the flow rate of the helium gas. The separation between the high oxygen concentration side and the low oxygen concentration side was confirmed by not detecting helium gas in the gas released from the gas 1 outlet.

The experiment of oxygen permeation was carried out by heating this apparatus with an electric furnace, under the conditions of 750 ° C., an inlet oxygen partial pressure of 0.2 atm, and an outlet oxygen partial pressure of 10 ⁻⁶ atm. As a result, the oxygen permeability was 2.3 cc · min ⁻¹ cm ⁻² . (Comparative Example 1) As a comparative example, La _0.6 Sr _0.4 Co ₀ O _{3 −} which is a conventionally known electron and oxygen ion conductor.
δ was synthesized. Lanthanum oxide, strontium carbonate, and cobalt trioxide were weighed so that the above composition had a molar ratio, and these mixtures were well mixed in an automatic mortar. This mixture was calcined in air at 850 ° C. for 12 hours. This calcined body was pressure-molded by a hydrostatic press into a disk shape having a thickness of about 2 mm, and the molded body was fired in air at 1300 ° C. for 6 hours to be sintered. This sintered body was φ20 m in the same manner as in Example 1.
The sample was cut into a disc-shaped thin piece having a thickness of 1 mm and a thickness of 1 mm to obtain a sample for oxygen separation.

An oxygen permeation test was carried out under the same conditions as in Example 1. As a result, the oxygen permeability is 1.2 cc · m.
It was in ^-1 cm ^-2 . (Example 2) As Example 2, CeZrO _3.75 was synthesized. That is, this is the case where x = 1 and δ = 0.25.

First, a mixed solution of cerium nitrate (Ce (NO ₃ ) ₃ ) and zirconium nitrate (Zr (NO ₃ ) ₃ ) was treated in the same manner as in Example 1 to prepare a composite oxide solid solution powder. Further, this solid solution powder was subjected to pressure sintering in the same manner as in Example 1 to obtain a sintered body having a diameter of 150 mm and a height of about 5 mm.

Next, this sintered body was further fired in an atmosphere firing furnace at 200 ° C. for 4 hours with oxygen gas, and then,
The target sintered body was obtained by cooling at a rate of 5 ° C./min.
From this sintered body, the same φ20 mm as in Example 1 and a thickness of 1 m
A disk-shaped thin piece of m was cut out and used as a sample for oxygen separation.

Also, a sample of this sintered body was crushed to obtain powder X.
A line diffraction measurement was performed. The results are shown in Fig. 3. All the peaks of the obtained diffraction pattern were assigned to cubic crystals and were 14.4.
Peaks indicating that Ce and Zr were regularly arranged were observed at 3 °, 36.7 °, and 44.2 ° (in the figure). Furthermore, the peak (∇ in the figure) caused by the lack of regular arrangement of 1/16 oxygen of CeZrO ₄ is 16.
It appears at 6 °.

An oxygen permeation test was carried out using the evaluation apparatus shown in FIG. 2 as in Example 1. For the oxygen permeation test, this equipment was heated to 200 ° C. in an electric furnace to obtain an oxygen partial pressure of 0.2 a
It was carried out under the conditions of tm and outlet oxygen partial pressure of 10 ⁻⁶ atm.
As a result, the oxygen permeability is 0.1 cc · min ⁻¹ cm
It was ^-2 . This is because the oxygen permeation performance obtained under the same conditions using La _0.6 Sr _0.4 Co ₀ O _{3 −} δ (Comparative Example 1), which is a conventionally known electron and oxygen ion conductor, is 0c.
While it was c · min ⁻¹ cm ⁻² , it can be said that this example has an extremely excellent oxygen permeability.

[0055]

According to the present invention, a mixed conductor having high conductivity for both electrons and oxygen ions can be manufactured. Therefore, it is possible to provide a mixed conductive complex oxide having a performance that can be practically used for an oxygen separation device by the mixed conductor partition wall method. In addition, as a result, it is possible to provide a technique that consumes less energy than before and that enables oxygen production at low cost.

Further, the electron / oxygen ion mixed conductor of the present invention, due to its high conductivity, is used not only for the oxygen separation membrane but also for other applications such as a solid oxygen fuel cell (SOF).
Even when applied to C), oxygen sensor, co-catalyst, etc., high performance can be exhibited.

[Brief description of drawings]

FIG. 1 is a powder X-ray diffraction pattern of CeZrO _{4 according to} the present invention, showing a regular arrangement of Ce and Zr (▼ in the figure).

FIG. 2 is a schematic diagram of an evaluation apparatus for evaluating the oxygen permeation rate of a sintered body made of the mixed conductive complex oxide of the present invention.

FIG. 3 shows CeZrO _3.75 (Ce ₂ Zr ₂ O according to the present invention).
_{It is} a powder X-ray diffraction pattern of _7.5 ), and shows that Ce and Zr are regularly arrayed and that 1/16 oxygen is regularly arrayed (∇ in the figure).

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 8/02 H01M 8/02 K 8/12 8/12 F term (reference) 4G031 AA07 AA12 BA02 BA03 BA07 CA01 GA16 GA17 4G048 AA03 AB02 AC04 AD03 AE07 5G301 CA02 CA28 CA30 CD01 5H026 AA06 BB01 CX04 EE13 HH00 HH05 HH08 HH09 HH10

Claims (8)

[Claims] 1. Ce _2-x Zr _x O _4- δ (x = 0.125-
1.9, δ = 0 to 0.5), and a major crystal system is a cubic crystal, which is an electron / oxygen ion mixed conductive complex oxide. 2. The cubic crystal is 2θ = 13.8 to 14.6, 36.36 in powder X-ray diffraction measurement using Cu as a tube.
The electron-oxygen mixed conductive complex oxide according to claim 1, which has one peak each at 0-37.4 and 43.2-44.9. 3. The mixed electron-oxygen ion conductive complex oxide according to claim 1, wherein Ce and Zr are regularly arranged in the cubic crystal, and oxygen vacancies are also regularly arranged. 4. The cubic crystal is 2θ = 13.8 to 14.6, 36.36 in powder X-ray diffraction measurement using Cu as a tube.
The electron-oxygen ion mixture according to claim 3, which has a peak at 2θ = 15.8 to 17.2 in addition to one peak at 0 to 37.4 and 43.2 to 44.9, respectively. Conductive complex oxide. 5. The electron-oxygen ion mixed conductive complex oxide according to claim 3 or 4, wherein the space group is F4-3m (No. 216) and the basic composition is CeZrO _3.75 . 6. Ce _2-x Zr _x O _4- δ (x = 0.125-
1.9, δ = 0 to 0.5) 1
6. The method for producing an electron / oxygen ion mixed conductive complex oxide according to claim 1, wherein the heat treatment is performed in an atmosphere having a temperature of 000 ° C. or more and an oxygen partial pressure P ₀₂ = 10 ⁻⁸ atm or less. . 7. The composite oxide is kept at 400 to 900 ° C.
Hold, oxygen partial pressure 10 ^-61 from reducing atmosphere below atm
0^-1It takes 4 hours or more to oxidize the atmosphere above atm
The electron or oxygen ion according to claim 6, which includes a heat treatment for raising the temperature.
Method for producing mixed conductive complex oxide. 8. The oxygen partial pressure P ₀₂ = 10 ^{−6 in the} composite oxide.
To 10 ⁰ atm and then, electrons of claim 6 including the heat treatment of 1 to 1200 hours at 50 to 300 ° C., the manufacturing method of the oxygen ion mixed conductive composite oxide.