JPH0827586A - Electrochemical element and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture an electrochemical element with which nitrogen oxides are efficiently decomposed at a low temp. through using a low current density by arranging a negative electrode contg. a multiple metal oxide and a positive electrode made of a noble metal opposite to each other through interposing an oxygen ion conductive electrolyte between them to form the element. CONSTITUTION:This element comprises a negative electrode 1 consisting of a multiple oxide (Fe2O3.Mn2O3.CuO) and Pt, an oxygen ion conductive electrolyte 2 consisting of ZrO2 stabilized with Y2O3 and a positive electrode 3 consisting of Pt. The element is manufactured by printing a pattern of a negative or positive conductive paste on either surface of the electrolyte 2, drying the resulting surface, thereafter, printing a pattern of another conductive paste having the reverse polarity to that of the former paste on the other surface of the electrolyte 2, drying the resulting latter surface, thereafter, firing the dried pastes at about 820 deg.C in the atmosphere to form a positive electrode 1 and a negative electrode 3 on the surfaces of the electrolyte 2 and further, bonding Pt lead wires to the ends of the electrodes 1 and 3. At this time, the firing temp. is not particularly limited to 820 deg.C and any temp. at which the sintering of the dried pastes occurs can be used as the firing temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element for electrochemically decomposing nitrogen oxide into nitrogen and oxygen in an atmosphere containing nitrogen oxide gas and a method for manufacturing the element.

[0002]

2. Description of the Related Art A conventional method for decomposing nitrogen oxides by an electrochemical method is disclosed in, for example, Japanese Unexamined Patent Publication No. 61-78421, in which a solid electrolyte 1 is used as a decomposition device as shown in FIG.
Both spaces of the positive electrode 12 and the negative electrode 13 through 1 are divided (platinum is used as the electrode material), and the gas to be treated is placed on the negative electrode side.
The positive electrode is configured to be brought into contact with the atmosphere other than the gas to be treated or a depressurized gas.

The above-mentioned decomposition apparatus dissociates nitrogen oxides into nitrogen and oxygen on the negative electrode, electrically disperses oxygen in the form of dissociated ions through the solid electrolyte, moves to the positive electrode side, and moves it into the atmosphere or reduced pressure gas. To release. On the other hand, nitrogen remains on the negative electrode side and is released into the gas to be treated. In this way, nitrogen oxides are decomposed.

[0004]

However, according to the above-mentioned conventional structure, for example, according to Japanese Patent Laid-Open No. 61-78421, the decomposition ability of nitrogen oxides is not so high. At an operating temperature of 700 ° C., NO concentration of 850 ppm, gas flow rate of 600 cc / min, current density of 20 mA / cm ² ,
NO decomposition amount per electrode unit area is 0.18 μmol / c
It was m ² / min.

In order to increase the decomposition rate, there are restrictions such as partitioning the positive and negative polar spaces. The present invention is to solve the above problems, and an object of the present invention is to provide an element or device that decomposes nitrogen oxides efficiently at low temperature and low current density, as compared with the prior art using a noble metal film negative electrode. is there.

[0006]

In order to achieve the above object, the present invention has the following constitution.

That is, the electrochemical device is arranged such that a negative electrode containing a composite oxide of iron oxide, manganese oxide and copper oxide, an oxygen ion conductive electrolyte, and the negative electrode via the electrolyte. And a positive electrode that has been formed.

The negative electrode is composed of at least a noble metal and the composite oxide. Further, the positive electrode is made of a noble metal.

Further, the electrolyte is made of stabilized ZrO ₂ . Further, on one surface of the oxygen ion conductive electrolyte, a conductive paste containing a complex oxide of iron oxide, manganese oxide and copper oxide as a negative electrode or a conductive paste containing a noble metal as a positive electrode is printed. After the drying, the positive or negative conductive paste having a polarity opposite to that of the already printed electrode was printed on the other surface of the electrolyte, dried, and then baked.

Further, the manufacturing method is such that the conductive paste is printed and dried, and then fired in an oxidizing atmosphere. Furthermore, a negative electrode containing a composite oxide composed of iron oxide, manganese oxide, and copper oxide, an oxygen ion conductive electrolyte, and a positive electrode arranged facing the negative electrode via the electrolyte. Electrochemical device, a resistor for detecting a current as a voltage, a circuit means in which a DC variable power source for applying a voltage to the nitrogen decomposing element is connected in series, and a means for detecting the voltage across the resistor. A detector for comparing the output of the detecting means with a set value, and a heating means for heating the nitrogen oxide to an operating temperature, wherein the variable DC power supply is a nitrogen oxide decomposing device for varying the voltage by the output of the comparing means. .

Further, the treatment for removing water, particulate dust, or a substance inhibiting nitrogen oxide decomposition in the atmosphere before the atmosphere containing nitrogen oxides contacting the electrochemical element is brought into contact with the element. The nitrogen oxide decomposing apparatus is provided with means.

[0012]

According to the present invention, the composite oxide contained in the negative electrode enhances the reactivity of the negative electrode with respect to nitrogen oxides as compared with the negative electrode made of a noble metal, and has a low temperature (500).
It is possible to decompose nitrogen oxides into nitrogen and oxygen with higher efficiency than before even at low temperatures (° C. or less) and low current densities (about several mA / cm ² ).

The decomposition reaction of nitrogen oxides starts when the nitrogen oxide adsorbing compound fixes the nitrogen oxides on the negative electrode. On the negative electrode side of the electrochemical device, the nitrogen-oxygen bond of the nitrogen oxide is weakened in the vicinity of the contact interface between the complex oxide, the noble metal (for example, platinum), and the oxygen ion conductive electrolyte, and oxygen acts as oxygen ion in the electrolyte. Permeate through the negative electrode, move from the negative electrode side to the positive electrode side, and are discharged into the gas as oxygen molecules. On the other hand, nitrogen molecules are generated on the negative electrode side and are desorbed into the gas.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a schematic configuration diagram of an electrochemical device (hereinafter referred to as device A). 1 is a complex oxide (Fe ₂ O ₃
Mn ₂ O ₃ · CuO) and platinum negative electrode, 2 is Y ₂ O ₃
Oxygen ion conductive electrolyte 3 made of ZrO ₂ stabilized by means of 3 is a positive electrode made of platinum.

The above element A was prepared as follows. Electrolyte 2 Either positive or negative electrode conductive paste is printed and dried on one surface, and the opposite conductive paste is printed and dried on the other surface of Electrolyte 2 and then dried in air. And the positive and negative electrodes 3 and 1 were formed on the electrolyte 2. Further, a platinum wire serving as a lead wire was adhered to the end portion of each electrode (1, 3). The composition of the negative electrode conductive paste used was platinum vs. Fe ₂ O ₃ · Mn.
_The weight ratio of ₂ O ₃ .CuO is about 1: 1 but the composition is not necessarily limited to this. Also, the firing temperature is 8
The temperature is not limited to 20 ° C., but may be any temperature at which sintering occurs.

The electrolyte 2 is Y ₂ O ₃ 8 mol% -ZrO ₂
The length is 25 mm, the width is 12.5 mm, and the thickness is 0.5 mm. The electrodes 1 and 3 have a thickness of about 20 to 40 μm and an area of about 2.
It was set to 25 cm ² . These conditions are only one example, and are not limited thereto.

For comparison, an element having both positive and negative electrodes made of platinum (hereinafter referred to as element B) was also prepared. The electrolyte used for the platinum element is 1 cm x 1 cm, thickness 0.5 mm
However, the other conditions are the same as those of the element A.

Commercially available Fe ₂ O ₃ .Mn ₂ O ₃ .CuO and platinum conductive paste for the positive electrode were used. The conductive paste for the negative electrode is platinum conductive paste and Fe ₂ O ₃ · Mn ₂ O ₃ · C.
It was made by mixing uO.

Next, the NOx decomposition behavior of element A and element B was measured in a gas flow system. Gas flow rate is 200cc / mi
It was fixed at n. The gas composition was mixed and adjusted with NO as NOx and He as a balance gas, and a chemiluminescence type NOx meter and a gas chromatograph were used for composition analysis. The peak of N ₂ O considered as a by-product was not observed above the detection limit level in the gas chromatograph. The above gases were each supplied from a gas cylinder whose concentration was adjusted.

The concentration resolution of the gas chromatograph is ± 10 considering the reproducibility of measurement data and the stability of equipment.
It is about ppm.

FIG. 2 shows a typical relationship between the gas composition and the element current value when NO is decomposed by the element A in a schematic pattern.

From FIG. 2, when a current flows through the element A, NO
It can be seen that the nitrogen and oxygen concentrations increase as the concentration decreases.

Specific values of NO decomposition by the elements A and B are shown in (Table 1).

[0025]

[Table 1]

In Table 1, ΔNO is the NO concentration difference obtained from (outlet concentration)-(supply concentration), and ΔN ₂ is also the nitrogen concentration difference obtained from (outlet concentration)-(supply concentration). A minus sign indicates a decrease in density. From (Table 1), it is clear that element A decomposes NO, which is about twice that of element B.

Further, the ratio of the NO reduction amount and the produced nitrogen amount is about 2: 1, which is equal to the stoichiometric ratio when considering the decomposition reaction of the formula-1.

2NO → N ₂ + O ₂ (1) N ₂ O, which is considered as a by-product, was not detected by gas chromatography, and the ratio of the NOx reduction amount to the produced nitrogen amount was
Since it is 2: 1, it is considered that there is almost no side reaction other than the formula (1) in the elements A and B. This is a great advantage in NOx decomposition.

FIG. 3 shows the NO decomposition amount-current curve of the elements A and B. The test conditions are the same as in (Table 1).
Obviously, element A is excellent.

In element A, the positive and negative electrode compositions are different, but the positive electrode may have the same composition as the negative electrode material. This is because the negative electrode also contains platinum and sufficiently functions as a positive electrode.

The manufacturing method of each element described above is the printing method as described in the description of FIG. The formation of electrodes in each device is an important process affecting NO decomposition. As the method, a sputtering method, a vapor deposition method, a CVD method, a PVD method, and the like can be considered in addition to the printing method, but the printing method is preferable in consideration of cost and simplicity. The firing atmosphere is preferably an oxidizing atmosphere in consideration of the use environment and the structural stability of the obtained electrode.

Next, a schematic structure of an embodiment of the nitrogen oxide decomposing apparatus will be described with reference to FIG. In FIG. 4, 4 is an electrochemical element (hereinafter referred to as an element), 5 is a resistor for detecting an element current as a voltage, 6 is a DC variable power source for applying a voltage to the element, and 7 is the element 4 and a resistor. 5 is a circuit means for electrically connecting the DC variable power supply 6 in series, 8 is a detection means for detecting the voltage across the resistor 5, 9 is a means for comparing the output value of the detection means 8 with a set value, and 10 is the element. Is a heating means for heating to the operating temperature.

In the above nitrogen oxide decomposing apparatus, the element 4
Is exposed to a gas containing NO, and the heating means 10 causes about 4
Hold at 50 ° C. When a voltage is applied to the element 4 by the DC variable power source 6, NO decomposition occurs, and an ionic current flows due to the generated oxygen ions.

This ionic current is used as a device current for the resistor 5
The detection means 8 detects the voltage across the voltage. If the element current is abnormally changed due to deterioration of the electrode of the element 4 or some other influence, the comparison means 9 compares the preset value with the detection value of the detection means 8. Because
By this comparison, the abnormality of the element current can be detected. The DC variable power supply 6 controls the voltage across the element based on the detection of abnormality by the comparison unit 9 so as to reduce the abnormality.

In this way, the nitrogen oxide decomposing apparatus of FIG. 4 shows a stable decomposing operation of NO contained in the gas, and discharges nitrogen and oxygen into the gas.

The circuit means 7 is a conducting wire, but since the element is at 450 ° C. and the gas containing NO may be high in temperature, a noble metal wire such as a platinum wire is preferable in such a high temperature portion.

When the NOx-containing gas contains dust or the like, it is considered that it may induce a side reaction in the decomposition element as an inhibitor of NOx decomposition, or may poison or contaminate the electrode surface. Therefore, it is preferable to remove such NOx decomposition inhibiting substances in advance before the gas reaches the device. In order to solve this problem, a pretreatment unit such as a filter or a dehumidifier may be provided.

According to the constitution of the above-mentioned embodiment, it is possible to obtain an electrochemical device exhibiting a NOx decomposition rate superior to the conventional one and an inexpensive manufacturing method thereof. Further, a nitrogen oxide decomposing apparatus showing a stable NOx decomposing operation can be obtained by using the electrochemical element.

[0039]

As described above, according to the present invention, it is possible to obtain an electrochemical device exhibiting an excellent NOx decomposition rate at a lower temperature and a lower current density than ever before, and an inexpensive manufacturing method thereof. In addition, when the electrochemical device of the present invention is used, stable N
A nitrogen oxide decomposing device having an Ox decomposing operation is obtained.
Therefore, there is an effect of reducing the destruction of the natural environment and the adverse effects on the human body due to NOx.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an electrochemical device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a schematic change in gas composition and device current during NOx decomposition.

FIG. 3 is a diagram showing the same NO decomposition amount-current characteristic.

FIG. 4 is a schematic configuration diagram of the nitrogen oxide decomposing apparatus.

FIG. 5 is a block diagram of a conventional NOx decomposing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Negative electrode 2 Electrolyte 3 Positive electrode 4 Electrochemical element (element) 5 Resistance 6 DC variable power source 7 Circuit means 8 Detection means 9 Comparison means 10 Heating means

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C25B 1/00 Z F01N 3/08

Claims (8)

[Claims] 1. A negative electrode containing a composite oxide composed of iron oxide, manganese oxide and copper oxide, an oxygen ion conductive electrolyte, and a positive electrode arranged to face the negative electrode via the electrolyte. An electrochemical device composed of and. 2. The electrochemical device according to claim 1, wherein the negative electrode comprises at least a noble metal and a composite oxide. 3. The electrochemical device according to claim 1, wherein the positive electrode is made of a noble metal. 4. The electrochemical device according to claim 1, wherein the electrolyte is stabilized ZrO ₂ . 5. A conductive paste containing a composite oxide of iron oxide, manganese oxide and copper oxide as a negative electrode or a conductive paste containing a noble metal as a positive electrode on one surface of an oxygen ion conductive electrolyte. After printing or drying,
Further, a method for producing an electrochemical element, in which after printing the positive or negative conductive paste having a polarity opposite to that of the electrode already printed on the other surface of the electrolyte, drying and then firing in an oxidizing atmosphere . 6. The method for producing an electrochemical element according to claim 5, wherein the firing atmosphere after printing and drying the conductive paste is an oxidizing atmosphere. 7. A negative electrode containing a composite oxide composed of iron oxide, manganese oxide and copper oxide, an oxygen ion conductive electrolyte, and a positive electrode arranged to face the negative electrode via the electrolyte. And an electrochemical element, a resistor for detecting a current as a voltage, a circuit means in which a DC variable power source for applying a voltage to the nitrogen decomposing element is connected in series, and a voltage across the resistor is detected. Means, a means for comparing the output of the detecting means with the set value, and a heating means for heating the nitrogen oxide to an operating temperature, and the direct current variable power source changes the voltage by the output of the comparing means. Decomposing device. 8. A pretreatment for removing water, particulate dust, or a substance inhibiting nitrogen oxide decomposition in the atmosphere, before the atmosphere containing nitrogen oxides in contact with the electrochemical device is in contact with the device. The nitrogen oxide decomposing apparatus according to claim 7, which is provided with means.