JPH07294483A - Electrochemical element and manufacture thereof - Google Patents

Abstract

PURPOSE:To make a lead wire of an electrochemical element connected to an electric power supply terminal of a mounting object hard to be cut by vibration or impact. CONSTITUTION:By constitution that an electrode 2 on one surface of a solid electrolyte board 1 is fixed to one terminal 5 by conductive paste and a lead wire 4 connected by conductive paste to the other electrode 3 is connected to the other terminal 6, it becomes strong against vibration or impact, and the lead wire 4 is flexibly deformed, and the solid electrolyte board 1 is made hard to be influenced by thermal expansion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrochemical element used in a nitrogen oxide sensor for detecting the concentration of nitrogen oxides, an exhaust gas treatment apparatus for directly decomposing nitrogen oxides into nitrogen and oxygen, and a method for producing the same. .

[0002]

2. Description of the Related Art Nitrogen oxides emitted from internal combustion engines such as household combustion equipment and automobiles are not only harmful to humans, but also cause air pollution and acid rain. It is strongly desired to establish a technology for accurately detecting the concentration of nitrogen oxides or for directly decomposing nitrogen oxides into nitrogen and oxygen. (For example, JP-A-57-187020 or JP-A-61-26).
No. 450).

Further, a device has been devised in which the bonding strength between the solid electrolyte substrate and the electrode is strengthened to improve the strength of the electrochemical device and the electrode capability (for example, JP-A-5-99).
893).

The conventional electrochemical device will be described below. As shown in FIG. 3, an electrode paste containing platinum is screen-printed on both surfaces of a solid electrolyte substrate 1 made of stabilized zirconia having oxygen ion conductivity, dried at about 120 ° C., and then baked in air. Thus, the lead wire 4a and the lead wire 4b having a diameter of about 0.1 mm and connected to the electrochemical element having the electrodes 2 and 3 connected with a conductive paste are used as a mounting object such as a nitrogen oxide sensor or an exhaust gas treatment device. The terminal 5 and the terminal 6 for supplying power, which are thick and hardly deformed, are connected by welding or the like.

[0005]

However, in the above-mentioned conventional structure, the electrochemical element is connected to the terminals 5 and 6 by welding or the like by the lead wires 4a and 4b having a diameter of about 0.1 mm. There is a problem that the lead wires 4a and 4b are cut by shock or impact, and when the electrodes 2 and 3 contain a metal oxide, they are fired in air with an oxygen concentration of about 20%, so that the structure collapses and the conductivity is reduced. And the sheet resistance of the electrodes 2 and 3 becomes high, and the characteristics of the electrode such as nitrogen oxide adsorption cannot be sufficiently obtained, and the electrode resistance of the electrochemical element immediately after production is high. There is a problem that the initial characteristics vary depending on the conditions used.

The present invention solves the above-mentioned conventional problems, is not easily cut by vibration or impact, has a low sheet resistance even when the electrode contains a metal oxide, and has a nitrogen oxide adsorbing property. It is an object of the present invention to provide an electrochemical element in which the characteristics of the electrode can be sufficiently obtained, the electrode resistance immediately after manufacturing is low, and the initial characteristics do not vary, and a method for manufacturing the same.

[0007]

In order to achieve this object, an electrochemical device and a method for producing the same according to the present invention are provided, wherein an electrode formed on one surface of a solid electrolyte substrate is coated with a conductive paste on one side. A structure in which a lead wire fixed to a terminal and connected to the electrode formed on the other surface with a conductive paste is connected to the other terminal to be mounted, and a noble metal or a noble metal and a metal oxide on one surface of the solid electrolyte substrate. The electrode paste containing the is printed on the other surface with the electrode paste containing the noble metal and the metal oxide, dried, and then fired in oxygen to form the electrode, or mounted on one of the formed electrodes. This is a method in which the target terminal is fixed, the lead wire connected to the other electrode is connected to the other terminal to be mounted, and then a pretreatment is performed in which a constant amount of direct current is passed between the terminals.

[0008]

In this configuration and method, one electrode of the solid electrolyte substrate is fixed to one terminal of the mounting target, and the lead wire connected to the other electrode is connected to the other terminal of the mounting target, so that vibration or shock is generated. In addition, the lead wire will not be deformed and the solid electrolyte substrate will not crack due to thermal expansion, and the electrode containing the metal oxide will be fired in oxygen, so its structure will not collapse and its conductivity will not be impaired. In addition, the area resistance value is low and the electrode characteristics such as nitrogen oxide adsorption are sufficiently obtained, or a certain amount of direct current is passed between the terminals, so that the electrode resistance of the electrochemical element becomes low and The characteristics will not vary.

[0009]

【Example】

Example 1 An example of the electrochemical device of the present invention will be described below with reference to the drawings.

In one embodiment of the present invention, the same components as those described in the above-mentioned conventional example are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 1, a feature of this embodiment is that the terminal 5 is directly fixed to the electrode 2 in the above-mentioned conventional structure. That is, the electrode 2 is fixed to a thick and non-deformable platinum terminal 5 having a diameter of 0.3 mm with a conductive gold paste and dried at about 120 ° C., and then the other electrode 3 is made of a platinum material having a diameter of 0.1 mm. After connecting the thin and easily deformable lead wire 4 with a gold paste and drying it, it is baked for 10 minutes at about 700 ° C., which is lower than the baking temperature of the electrodes 2 and 3, and after baking, the lead wire 4 is made of nickel and deformed to be thick. It is a configuration in which the other terminal 6 that is difficult to perform is spot welded.

With this structure, the solid electrolyte substrate 1 is fixed to the thick and hard-to-deform terminal 5, and the other thick and hard-to-deform terminal 6 is provided through the thin and easily deformable lead wire 4.
Connected to, it is resistant to vibration and shock, and lead wire 4
Has the effect of being flexibly deformed and not affected by thermal expansion.

The conductive paste may be a platinum paste other than the gold paste of this embodiment, and the firing temperature of the conductive paste is not limited to the above-mentioned about 700 ° C., but the characteristics of the electrodes 2 and 3 are not impaired. Thus, it is necessary that the temperature is lower than the firing temperature of the electrodes 2 and 3.

It goes without saying that the electrode 3 may be fixed to the terminal 5 and the lead wire 4 may be connected to the electrode 2.

(Example 2) An example of a method for producing an electrochemical device of the present invention will be described below. Solid electrolyte substrate 1
Is a stabilized zirconia having oxygen ion conductivity and containing 8 mol% of yttria, and has a size of 10 mm square and a thickness of 0.35 mm. In addition, the solid electrolyte substrate 1
Other than the yttria-stabilized zirconia of the present embodiment, other solid electrolytes having oxygen ion conductivity such as cerium oxide and bismuth oxide may be used, and the size and thickness are not limited to the above-mentioned dimensions. After thoroughly washing the solid electrolyte substrate 1 with an organic solvent or the like, an electrode paste containing platinum, which is a noble metal, is printed on one surface by a screen printing method, dried at about 120 ° C. for about 15 minutes, and then on the other surface. Are precious metals such as platinum and metal oxides

[0016]

[Chemical 1]

Similarly, an electrode paste containing is dried by printing, and after drying, the temperature is raised to about 820 ° C. in about 30 minutes while supplying oxygen into the furnace at a flow rate of about 200 cc / min.
After baking for about 10 minutes, an electrochemical element (hereinafter referred to as a hetero element) having an electrode 2 made of platinum and an electrode 3 made of platinum and yttrium barium copper oxide was obtained.

By this method, even when the electrode 3 contains a metal oxide such as yttrium barium copper oxide,
By firing in oxygen, the structure of the metal oxide does not collapse and the conductivity is not impaired, so that the area resistance value is low and the electrode characteristics such as nitrogen oxide adsorption are not impaired. .

Incidentally,

[0020]

[Chemical 2]

Δ represents the amount of oxygen defects in the oxide, and δ
The range of the value of is 0 or more and 1 or less. Further, the noble metal may be rhodium or palladium in addition to the platinum of this embodiment, and the metal oxide has a nitrogen oxide adsorbing property other than yttrium barium copper oxide of this embodiment.

[0022]

[Chemical 3]

Then, a metal oxide having another lanthanoid element at the yttrium site or a metal oxide having another alkaline earth metal at the barium site may be used.

Further, in the present embodiment, the electrode paste containing platinum and yttrium barium copper oxide is mixed with platinum and yttrium barium copper oxide so that the paste has an equimolar amount after firing. The composition is not limited to the above composition as long as it is several tens Ω or less.

In addition to the screen printing method used for forming the electrode film, a sputtering method, a plating method, a CVD method, or the like can be considered, but the screen printing method is simple in consideration of low manufacturing cost. Is suitable, and the order of printing the electrode paste may be the reverse order.

Further, the baking after printing and drying may be carried out in air, but it is preferable to carry out the baking in oxygen considering the sheet resistance value of the electrode and the characteristics of the electrode, and the flow rate of oxygen is also the above. Although not limited to about 200 cc / min, it is desirable that the value be constant so as to maintain a constant atmosphere and temperature. The firing temperature and firing time are not limited to the above,
Considering the sheet resistance value and the characteristics of the electrode, the temperature of about 820 ° C. and the time of about 10 minutes are suitable.

(Embodiment 3) A second embodiment of the method for producing an electrochemical device of the present invention will be described below.

The hetero element obtained in Example 2 was supplied in an electric furnace with oxygen at a concentration of 0.5% at a flow rate of about 200 cc / min while maintaining the ambient temperature at about 450 ° C. Between the terminals 5 and 6, the electrode 2 made of platinum is used as an anode, and the electrode 3 made of platinum and yttrium barium copper oxide is used.
Is used as a cathode, a DC power source is connected, and a current of about 10 mA per unit area is applied for about 30 minutes. The change in electrode resistance due to the application of direct current is the result of measuring the complex impedance of the hetero element, and is a so-called Cole-Cole plot where the real part of the impedance is plotted on the horizontal axis and the imaginary part is plotted on the vertical axis. As is clear from 2, the value A after processing becomes lower than the value B before processing. The three arcs on the real axis in the figure represent the bulk resistance, the grain boundary resistance, and the electrode resistance in order from the left.

According to this method, the electrode resistance can be reduced and the initial characteristics of the hetero element can be made uniform by the pretreatment in which a constant amount of direct current is applied under predetermined conditions.

The conditions of the pretreatment are not limited to the conditions of this embodiment, but it is desirable that the temperature is in an actually used temperature range in an oxidizing atmosphere and the current density is actually used. It is desirable that the size is larger and the characteristics of the hetero element are not destroyed. In addition, the polarity of the electrode is such that the electrode 2 made of platinum is the cathode, the electrode 3 made of platinum and yttrium barium copper oxide is the anode, and the electrode resistance is low even when a direct current is applied, but the polarity is more reversed. Since it becomes lower, the conditions of this embodiment are more suitable.

(Embodiment 4) A third embodiment of the method for producing an electrochemical device of the present invention will be described below.

On both sides of a solid electrolyte substrate 1 made of stabilized zirconia having oxygen ion conductivity, electrodes 2 and 3 made of platinum, which is a noble metal, and yttrium barium copper oxide, which is a metal oxide and has nitrogen oxide adsorption, are placed in oxygen. As for the homo element having the same kind of both electrodes fired in 1., the lead wire 4 and the terminals 5 and 6 were connected to the homo element in the same manner as in the hetero element of Examples 2 and 3, and then the concentration was set in the electric furnace. Is 0.5
The same effect as the hetero element can be obtained by performing a pretreatment in which a direct current is caused to flow at about 450 ° C. in oxygen of 50%.

[0033]

As is apparent from the above description, according to the present invention, an electrode formed on one surface of a solid electrolyte substrate is fixed to one terminal of a mounting object with a conductive paste and formed on the other surface. A structure in which a lead wire connected to the electrode with a conductive paste is connected to the other terminal to be mounted, and an electrode paste containing a noble metal or a noble metal and a metal oxide is attached to one surface of the solid electrolyte substrate and the other surface. Print the electrode paste containing the noble metal and the metal oxide on each, and after drying,
A method of forming an electrode by firing in oxygen, or fixing the terminal to be mounted on one of the formed electrodes and connecting the lead wire connected to the other electrode to the other terminal to be mounted, then between the terminals Pretreatment with a constant amount of direct current makes it difficult to break due to vibration or shock, and even when the electrode contains metal oxide, the sheet resistance is low and the electrode characteristics such as nitrogen oxide adsorption are low. It is possible to realize an excellent electrochemical element which is sufficiently obtained, has a low electrode resistance immediately after production, and has no initial characteristic variation, and a method for producing the same.

[Brief description of drawings]

FIG. 1A is an external perspective view of an electrochemical device according to an embodiment of the present invention, and FIG. 1B is a sectional view of FIG.

FIG. 2 is a characteristic diagram showing changes in electrode resistance of the same electrochemical device due to pretreatment in which a direct current is passed.

FIG. 3A is an external perspective view of a conventional electrochemical device, and FIG. 3B is a sectional view of FIG.

[Explanation of symbols]

 1 solid electrolyte substrate 2,3 electrode 4 lead wire 5,6 terminal

Claims (12)

[Claims] 1. A lead in which an electrode formed on one surface of a solid electrolyte substrate is fixed to one terminal using a conductive paste, and an electrode formed on the other surface is connected using the conductive paste. An electrochemical device characterized in that a wire is connected to the other terminal. 2. The electrochemical element according to claim 1, wherein an electrode made of a noble metal is formed on one surface of the solid electrolyte substrate, and an electrode made of a noble metal and a metal oxide having a nitrogen oxide adsorbing property is formed on the other surface. 3. The electrochemical device according to claim 1, wherein electrodes made of a noble metal and a metal oxide having a nitrogen oxide adsorbing property are formed on both surfaces of the solid electrolyte substrate. 4. The electrochemical device according to claim 1, wherein the solid electrolyte substrate has oxygen ion conductivity. 5. The noble metal is platinum, and the noble metal is platinum.
The electrochemical device according to any one of 1. 6. The electrochemical device according to claim 1, wherein the metal oxide has a nitrogen oxide adsorbing property and has a barium yttrium copper oxide type structure. 7. An electrode paste containing a noble metal is printed on one surface of a solid electrolyte substrate having oxygen ion conductivity, and an electrode paste containing a noble metal and a metal oxide is printed on the other surface of the solid electrolyte substrate. A method for manufacturing an electrochemical element, which comprises firing in an atmosphere containing. 8. A method for producing an electrochemical element, in which an electrode paste containing a noble metal and a metal oxide is printed on both surfaces of a solid electrolyte substrate having oxygen ion conductivity, dried and then fired in an atmosphere containing oxygen. . 9. The oxygen concentration in an atmosphere containing oxygen is 10
It is 0%, The manufacturing method of the electrochemical element of Claim 7 or 8. 10. The method for producing an electrochemical element according to claim 7, wherein the firing temperature of the conductive paste is lower than the firing temperature of the electrode. 11. The method for producing an electrochemical element according to claim 1, wherein a pretreatment is performed in which a constant amount of direct current is applied between the terminals under predetermined conditions. 12. An electrode made of a noble metal is used as an anode,
7. The pretreatment for flowing a constant amount of direct current between terminals under a predetermined condition using an electrode made of a noble metal and a metal oxide having a nitrogen oxide adsorbing property as a cathode. Of manufacturing electrochemical device of.