JP3221219B2 - Electrochemical element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrochemical device for electrochemically decomposing nitrogen oxides into nitrogen and oxygen in a gas atmosphere in which at least oxygen and nitrogen oxides coexist, and a method for producing the same.

[0002]

2. Description of the Related Art As a conventional apparatus for decomposing nitrogen oxides by an electrochemical method, for example, Japanese Patent Application Laid-Open No. 61-78421 discloses a decomposition apparatus shown in FIG. The device separates the space on the positive electrode film 5 side and the space on the negative electrode film 4 side via the solid electrolyte 13, and supplies the gas to be treated in the space on the negative electrode film 4 side and the atmosphere or reduced pressure gas in the space on the positive electrode film 5 side. Are brought into contact with each other. Platinum is used as a constituent material for both electrode films. In particular, it is disclosed that when the negative electrode film 4 is configured such that rhodium 4a is supported on the surface of the platinum electrode film, the decomposition reaction of nitrogen oxide proceeds even in an oxygen atmosphere.
In this decomposition device, nitrogen oxides are dissociated into nitrogen on the negative electrode film 4. The dissociated oxygen is taken into the solid electrolyte 13 as oxygen ions and moves toward the positive electrode film 5,
Reaching the positive electrode film 5, it is released to the atmosphere as oxygen molecules. On the other hand, the dissociated nitrogen remains on the negative electrode film 4 and is released into the gas to be treated as nitrogen molecules.

According to Japanese Patent Application Laid-Open No. 50-32092, as shown in FIG. 5, ZrO2-C is used as a decomposition device.
An apparatus in which a porous platinum positive electrode film 5 and a porous platinum negative electrode film 4 are formed on both surfaces of an eO-based solid electrolyte 13 is disclosed. It is described that the apparatus can decompose 50 to 5000 ppm of nitrogen oxides contained in air at a temperature of 500 to 950 ° C. by 90% or more.

Further, US DOE Report [NO.
DOE-PC-79855-T10 (1990)]
The nitrogen oxide decomposition characteristics of a device in which a porous ruthenium positive electrode film 5 and a porous ruthenium negative electrode film 4 are formed on both surfaces of a CeO2 based solid electrolyte 13 are described. According to this description, when decomposing 400 ppm of NOx at 459 ° C., about 84% of NOx is decomposed if the oxygen concentration is 0%, but only about 6% of NOx is decomposed when the oxygen concentration is increased to 1%. It is described as not.

[0005]

According to the conventional structure, for example, Japanese Patent Application Laid-Open No. 61-78421, the capability of decomposing nitrogen oxides in the presence of oxygen is not high. Operating temperature 7
Under the conditions of 00 ° C., an oxygen concentration of 1%, a NOx concentration of 1000 ppm, and a gas flow rate of 600 cc / min, the decomposition amount is as low as about 0.1 μmol / cm 2 per unit electrode film area. Moreover, at this time, a large current density is required for such an electrochemical device of 200 mA / cm 2. Also,
In Japanese Patent Application Laid-Open No. 50-32092, the oxygen concentration is not specifically specified, and some ambiguity remains in this regard.

[0006] The present onset Ming is to solve the above Symbol conventional issues, the oxygen concentration is high atmosphere, for example, 10% or higher temperature lower atmosphere can be decomposed efficiently nitrogen oxides at a low current density device ( The purpose is to provide (delete).

[0007]

The present invention has the following configuration to achieve the above object.

A hollow body made of a solid electrolyte having a hollow portion through which gas flows, and a pair of positive and negative electrode films provided on an outer surface and a hollow portion wall surface (hereinafter referred to as an inner surface) of the hollow body; At least the negative electrode film of the electrode film was composed of an electrode film made of a nitrogen oxide-adsorbing compound and a noble metal, and the pair of positive and negative electrode films contacted the gas to form an electrochemical device.

A hollow body made of an oxygen ion conductive solid electrolyte having a plurality of independent hollow portions through which gas flows, and a pair of positive and negative electrode films provided on the outer surface and the hollow portion wall surface of the hollow body. Wherein at least the negative electrode film of the electrode film is constituted by an electrode film containing a nitrogen oxide-adsorbing compound, and the pair of positive and negative electrode films is in contact with the gas.

Also, a hollow body made of an oxygen ion conductive solid electrolyte having a hollow portion through which a gas flows, a negative electrode film formed on an outer surface of the hollow body, and a negative electrode film formed on an inner surface of the hollow body. The negative electrode film is composed of an electrode film containing a nitrogen oxide-adsorbing compound, and the positive electrode film is made of an electrode film containing no nitrogen oxide-adsorbing compound. The electrochemical device is configured so that the positive electrode film and the negative electrode film are in contact with the gas.

Also, a hollow body made of an oxygen ion conductive solid electrolyte having a hollow portion through which gas flows, a negative electrode film formed on an outer surface of the hollow body, and a negative electrode film formed on an inner surface of the hollow body. The negative electrode film and the positive electrode film are composed of an electrode film containing a nitrogen oxide-adsorbing compound, and the positive electrode film and the negative electrode film are formed of the gas. The electrochemical element was brought into contact with.

Also, a hollow body made of an oxygen ion conductive solid electrolyte having a hollow portion through which gas flows, a positive electrode film formed on an outer surface of the hollow body, and a negative electrode film formed on an inner surface of the hollow body. A negative electrode film formed opposite to the electrode film, wherein the positive electrode film comprises an electrode film containing no nitrogen oxide-adsorbing compound, and the negative electrode film comprises an electrode film containing nitrogen oxide-adsorbing compound. The electrochemical device is configured so that the positive electrode film and the negative electrode film are in contact with the gas.

The hollow body is a hollow cylindrical body.

The nitrogen oxide-adsorbing compound is Ba.
The structure was an oxide having a 2YCu3O7 type structure.

The current density of the current flowing through the electrode film is 1 mA / cm 2 or more and 150 mA / cm 2 or less.

Further, the electrode film containing no nitrogen oxide-adsorbing compound is an electrode film containing a noble metal.

[0017]

The electrochemical device of the present invention uses a hollow body made of a solid electrolyte having a hollow portion through which gas flows, and has an electrode film on the inner surface and the outer surface thereof. At least the negative electrode film of the electrode film is nitrogen oxide. It is composed of electrode films containing a substance-adsorbing compound, and these electrode films come into contact with gas. The negative electrode film has a configuration including a nitrogen oxide adsorbing compound. Therefore, the nitrogen oxide-adsorbing compound can selectively adsorb a small amount of NOx at a low temperature of 500 ° C. or less even in an atmosphere containing 10% or more of oxygen.
x can be decomposed. This decomposition reaction starts from a process in which nitrogen oxide is adsorbed on the negative electrode film and dissociated into nitrogen and oxygen. The dissociated oxygen is taken into the oxygen ion conductive solid electrolytic chamber as oxygen ions, moves toward the positive electrode film, reaches the positive electrode film, and is released to the atmosphere as oxygen molecules. On the other hand, the dissociated nitrogen remains on the negative electrode film and is released into the gas to be treated as nitrogen molecules.

Further, since these electrode films come into contact with the gas, the gas to be processed flowing in the hollow space or the outer surface space of the hollow body comes into contact with the electrode film at the inner or outer peripheral portion of the hollow body. At this time, for example, since the electrode film is formed on the entire surface of the hollow body along the direction in which the gas to be processed flows, the gas to be processed can efficiently contact the electrode film as compared with the plate-like solid electrolyte. As a result, the decomposition reaction becomes efficient.

Further, since a plurality of independent hollow portions are provided in one electrochemical element, the processing of (deleted) gas to be processed can be more efficiently performed .

Further, since the hollow body is a hollow cylindrical body,
Manufacturing becomes very easy.

Further, Ba is used as a nitrogen oxide adsorbing compound.
Since the oxide having the 2YCu3O7 type structure is used, the nitrogen oxide adsorption performance is increased, and the processing efficiency can be improved.

Further, since the current density flowing through the electrode film is set to 1 to 150 mA / cm 2, nitrogen oxide can be treated more efficiently than before, without damaging the element.

Further, since the noble metal is included in the composition of the electrode film not containing the nitrogen oxide-adsorbing compound, the conductivity is stabilized and the reliability can be increased.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.
explain. The same parts as those in the conventional example are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 1 is a partially broken perspective view showing the structure of the electrochemical device of the present invention. On the outer surface of a hollow body 3 made of an oxygen ion conductive solid electrolyte having a hollow portion 2 through which gas flows from the open end, a negative electrode film 4 and a hollow portion wall surface (inner surface)
The positive electrode film 5 was formed thereon. The material of the oxygen ion conductive solid electrolyte is ZrO2 stabilized with 8 mol% of Y2O3, and its shape is 10 mm in inner diameter and 12 m in outer diameter.
m, a length of 100 mm, and a hollow cylindrical shape. The shape of the hollow body 3 is not limited to a hollow cylindrical shape, but may be any shape such as a hollow polygonal shape or a hollow elliptical shape as long as gas can flow therethrough. The cylindrical shape is excellent in that it is industrially easy to produce. I have.

Hereinafter, the case where nitrogen oxide is used as the gas will be specifically described.

(Embodiment 1) A case where the negative electrode film 4 is used on the outer surface of the hollow body 3 and the positive electrode film 5 is used on the inner surface of the hollow body 3 will be described.

As the negative electrode film 4, a mixed electrode film of platinum (Pt) and a nitrogen oxide-adsorbing compound was used. As the nitrogen oxide-adsorbing compound, MnOx.ZrO2, perovskite-type composite oxide and the like are known, but an oxide having a YBa2Cu3O7-.delta.-type structure is excellent. Although the detailed reason for this is unknown, it is considered that the oxide having the same structure has a relatively large cavity in the crystal structure and has electrical conductivity. Hereinafter, Pt and YBaCu3O7-δ
(Hereinafter, referred to as YBC). YBC
Is a nitrogen oxide adsorbing compound that adsorbs NOx even in an atmosphere in which oxygen is excessively present.

The positive electrode film 5 was an electrode film containing no nitrogen oxide adsorbing compound. As this kind of positive electrode film 5,
Noble metal electrode film such as Au, Ag, Pt, Pd, Ni, C
Although various types of electrode films such as a metal electrode film of u, Fe, etc. and a LaSrO3 based composite oxide electrode film are known, a noble metal electrode film is preferable because of its excellent stability. Hereinafter, a Pt electrode film was used. The negative electrode film 4 and the positive electrode film 5 are arranged to face each other with the hollow solid electrolyte 3 interposed therebetween.
And 2. A conventional electrode film configuration, that is, a negative electrode film 4 is formed by using a hollow body 3 made of another solid electrolyte having the same shape.
A platinum element composed of a Pt electrode film for both the positive electrode film and the positive electrode film was prepared, and the NOx decomposition reaction was compared.

The NOx decomposition reaction by the thus constructed electrochemical device of the present invention will be described below. The entire electrochemical element is arranged in the gas to be treated, that is, the negative electrode film 4 and the positive electrode film 5 are arranged so as to be in contact with the gas to be treated, and a DC voltage is applied to the electrochemical element from an external power supply. The current was passed. The gas to be treated is composed of about 500 ppm of NOx, about 10% of oxygen and about 90% of He, and has a flow rate of 200 c.
c / min. Before and after flowing into the electrochemical element, the concentration of NOx in the gas was measured by a chemiluminescent NOx meter, and N2 was measured by a gas chromatograph. When a current of about 240 mA (current density: 10 mA / cm 2) was passed, NOx after passing through the electrochemical element was reduced by about 30%, and an N2 increase corresponding to the NOx reduction was observed. The amount of NOx reduction or N2 increase was almost proportional to the current, but was about 12 mA.
At lower currents (current density 0.5 mA / cm 2 or less), NOx hardly decreased. Also, as the current density increased, it was observed that the proportional relationship between the current density and the processing amount was lost and the electrolyte white body was altered. Therefore, practically, the current density is 1 to 150 mA /
cm2 is preferred.

When the oxygen concentration was increased to about 20% (elimination) with the same NOx concentration, the NOx reduction amount was reduced to about 20%. The NOx reduction was measured under the same conditions for the above-mentioned platinum element, but no reduction was observed.

As described above, according to the electrode film configuration of the electrochemical device of the present invention, even when oxygen is excessively present, trace NOx
Can be decomposed. Further, since the electrochemical element has a configuration in which the negative electrode film 4 is formed on the outer surface of the cylindrical hollow body 3, when the gas to be processed flows in the axial direction of the cylinder, the entire surface of the outer surface is processed. The gas can contact the negative electrode film 4. This allows for efficient disassembly.

(Embodiment 2) The present embodiment has the same hollow body structure as that of Embodiment 1 except that the positive electrode film 5 also uses a mixed electrode film of Pt and YBC, that is, the negative electrode film 4 and the positive electrode film 4 have the same structure. The electrode film 5 is made of both Pt and YBC
This is the point that the mixed electrode film was used. An experiment was performed under the same conditions as in Example 1 and the same measurement was performed. As a result, the reduction amount of NOx was reduced to 1/4 as compared with the electrochemical device having the structure of Example 1.

However, even if excess oxygen is present, a small amount of N
It was observed that Ox could be decomposed. It is clear that this reduction is large without any problem compared to the platinum element. Since the negative electrode film 4 and the positive electrode film 5 are made of the same material, this electrode film configuration is excellent in that the electrode film forming operation is easy.

(Embodiment 3) The present embodiment has the same hollow body structure as that of Embodiment 1, except that a positive electrode film 5 is formed on the outer surface and a negative electrode film 4 is formed on the inner surface. An experiment was performed under the same conditions as in Example 1 and the same measurement was performed. As a result, almost the same result as the electrochemical device having the configuration of Example 1 was obtained.

Although the electrochemical devices described in the first to third embodiments have been described with reference to the case of the hollow body 3 having one hollow portion 2 through which gas flows, the number of hollow portions is not necessarily limited to one. There may be more than one. Further, the cross-sectional areas of the plurality of hollow portions may be variously different.
By providing a plurality of hollow portions or changing the cross-sectional area in this manner, the contact area between the gas to be treated and the electrochemical element increases, so that the gas to be treated can be treated more efficiently.

Further, in order to increase the chance of contact between the gas to be treated and the solid electrolyte having oxygen ion conductivity, the surface of the hollow body is provided with irregularities or the like to increase the contact area or to make turbulence more likely to occur. Or you may.

Although the embodiment of the present invention has been described with respect to the case where an oxygen ion conductive solid electrolyte is used as the solid electrolyte, the present invention is not limited to this. For example, strontium cerium oxide may be used as the solid electrolyte. Hydrogen ion conductive solid electrolyte or the like.
Even when a solid electrolyte other than the oxygen ion conductive solid electrolyte is used, the same effect as in the above embodiment can be obtained.

[0039]

As described above, according to the electrochemical device of the present invention, the following effects can be obtained.

(1) A pair of positive and negative electrode films are provided on the inner and outer surfaces of a hollow body made of a solid electrolyte, the negative electrode contains a nitrogen oxide adsorbing compound, and the pair of positive and negative electrode films is a gas to be treated. Since the gas to be treated flows in the length direction of the hollow solid electrolyte, it has good nitrogen oxide adsorption performance, and efficiently decomposes nitrogen oxide at low temperature and low current density even in an atmosphere with a high oxygen concentration. be able to.

(2) Since a plurality of independent hollow portions are provided in one electrochemical element, the contact area between the gas to be treated and the electrochemical element increases. Therefore, the processing of the gas to be processed can be performed more efficiently.

[0042] (3) If the inner and outer front surface of the hollow body constituting the electrode film made of a nitrogen oxide adsorbing compound of the same material, which facilitates the electrode film forming operations.

(4) Since the hollow body is formed in a hollow flame shape, it is industrially easy to produce.

(5) Ba as a nitrogen oxide adsorbing compound
Since it has a 2YCu3O7 type structure, it has good adsorption performance of nitrogen oxides and can efficiently decompose nitrogen oxides even in an atmosphere having a high oxygen concentration.

(6) The density of the current flowing through the electrode film is 1 to 1
Since it is 50 mA / cm 2, nitrogen oxides can be efficiently decomposed and the electrode film is not damaged.

(7) Since the electrode film containing no nitrogen oxide adsorbate is an electrode film containing a noble metal, a stable electrode film can be obtained.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view of an electrochemical device according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view of a conventional nitrogen oxide decomposition apparatus.

FIG. 3 is a cross-sectional view of another conventional nitrogen oxide decomposition apparatus.

[Explanation of symbols]

 2 Hollow part 3 Hollow body 4 Negative electrode film 5 Positive electrode film 6 Delete 7 Delete 8, 9 Delete 10, 11 Delete

Continuation of the front page (56) References JP-A-61-78421 (JP, A) JP-A-61-242622 (JP, A) JP-A-2-299167 (JP, A) JP-A-4-131429 (JP) , U) Surface Science, 9 [7] (1988) Shimada, p. 489-494 “Chemical Dictionary 9” (edited by the Chemical Dictionary Editors Committee) (49-3-10), Kyoritsu Shuppan Co., Ltd. p. 78 (58) Field surveyed (Int.Cl. ⁷ , DB name) B01D 53/32 B01D 53/56 B01D 53/74 F01N 3/08

Claims (9)

(57) [Claims] 1. A solid electrolytic device having a hollow portion through which a gas flows.
A hollow body made of quality, the outer surface and a hollow wall surface in said empty body (hereinafter, an inner surface denoted) provided with a pair of positive and negative electrode film provided on the at least the negative electrode layer of the electrode film is a nitrogen acid
An electrochemical device comprising an electrode film containing a compound adsorbing compound and a noble metal, wherein the pair of positive and negative electrode films contact the gas. 2. A plurality of independent hollow portions through which a gas flows.
Body made of oxygen ion conductive solid electrolyte
And a positive electrode provided on the outer surface of the hollow body and the wall surface of the hollow portion.
A pair of negative electrode films, and at least a negative
The electrode film is composed of an electrode film containing a nitrogen oxide-adsorbing compound.
Wherein the pair of positive and negative electrode films contact the gas . 3. An oxygen ion having a hollow portion through which a gas flows.
A hollow body made of a non-conductive solid electrolyte;
A negative electrode film formed on the outer surface, and an inner surface of the hollow body;
The negative electrode film and a positive electrode film formed facing the negative electrode film;
The negative electrode film is an electrode film containing a nitrogen oxide-adsorbing compound.
And the positive electrode film contains no nitrogen oxide adsorbing compound.
The positive electrode film and the negative electrode film
Is an electrochemical device contacting the gas . 4. An oxygen ion having a hollow portion through which a gas flows.
A hollow body made of a non-conductive solid electrolyte;
A negative electrode film formed on the outer surface, and an inner surface of the hollow body;
The negative electrode film and a positive electrode film formed facing the negative electrode film;
The negative electrode film and the positive electrode film
The positive electrode film and the negative electrode
An electrochemical device in which an electrode film contacts the gas . 5. An oxygen ion having a hollow portion through which a gas flows.
A hollow body made of a non-conductive solid electrolyte;
A positive electrode film formed on the outer surface and an inner surface of the hollow body
A negative electrode film formed opposite to the positive electrode film;
Electrode whose positive electrode film does not contain a nitrogen oxide-adsorbing compound
The negative electrode film contains a nitrogen oxide-adsorbing compound.
The positive electrode film and the negative electrode film
Is an electrochemical device contacting the gas . 6. The hollow body is a hollow cylindrical body.
The electrochemical device according to any one of claims 1 to 7 . 7. The nitrogen oxide-adsorbing compound is Ba2Y.
An oxide having a Cu3O7 type structure.
The electrochemical device according to any one of claims 7 to 14 . 8. The current density of a current flowing through the electrode film is 1
Claims: It is mA / cm2 or more and 150 mA / cm2 or less.
The electrochemical device according to any one of claims 1 to 5 . 9. The method according to claim 1 , which does not contain a nitrogen oxide-adsorbing compound.
4. The electrode film according to claim 1, wherein the electrode film is an electrode film containing a noble metal.
Or the electrochemical device according to any one of claims 5 to 7 .