JPS6188138A - Electrochemical device - Google Patents

Abstract

PURPOSE:To obviate the staining of pumping electrodes and the deterioration of the electrode arising from a reducing gas by exposing the 2nd electrode of a pumping cell together with the reference electrode of a sensing cell into a space where a reference gas exists. CONSTITUTION:A DC voltage is impressed between the electrodes 12 and 14 of the electrochemical pumping cell 30, then oxygen in the gas to be measured in a cavity 8 or oxygen in the space 10 where the reference gas exists moves toward the other through a solid electrolyte 4. On the other hand, the electromotive force induced in accordance with the difference between the oxygen concn. in the atmosphere in the cavity 8 and the oxygen concn. in the reference gas in the space 10 is determined between the electrodes 22 and 24 of the electrochemical sensing cell 32. The detection of the oxygen concn. in the gas to be measured conducted to the underside of the prescribed diffused resistor through a gas vent hole 20 and the detection of the concn. of the unburned component are thus made possible.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an electrochemical device having a laminated structure, including an electrochemical cell using a flat solid electrolyte T in F. It relates to improvements in equipment.

(Prior Art and its Problems) Conventionally, electrochemical devices including electrochemical cells using solid electrolytes, such as zirconia porcelain etc., have been used as oxygen sensors for detecting the oxygen concentration in the exhaust gas of automobile internal combustion engines. 2. Description of the Related Art Sensors are known that use an oxygen ion conductive solid electrolyte to determine oxygen concentration using the principle of an oxygen concentration battery.

Further, detectors for hydrogen, nitrogen, carbon dioxide, etc., which utilize the same concentration cell principle as the oxygen sensor, and electrochemical devices such as pumps are also known. Until now, solid electrolytes used in electrochemical cells of such devices have generally had a cylindrical shape with a bottom, but from the viewpoint of productivity and In recent years, due to the ease of incorporating multiple speed structures into electrolytes,
An electrochemical device having a laminated structure has been studied, in which an electrochemical cell is constructed by forming such a solid electrolyte into a flat plate and predetermined electrodes are provided on the surface of the solid electrolyte. .

By the way, an electrochemical cell included in such a laminated structure device is generally constructed by combining a plate-shaped solid electrolyte and at least one pair of electrodes, and an electrochemical cell having such a cell structure Two target cells are stacked and integrated, and there is an internal cavity (cavity) that communicates with the external space where the gas to be measured exists and where the gas to be measured is introduced under a predetermined diffusion resistance. , are formed in the stacked structure, and one electrode of each cell is exposed in the internal cavity. Then, one of the electrochemical cells is used as a pumping cell, and by its pumping action, the concentration of a constant component (in the gas to be measured in the internal cavity) is controlled. is used as a sensing cell to measure the electromotive force generated based on the concentration difference of the component to be measured between the atmosphere in the internal space and a predetermined reference gas.

Therefore, in a device having such a structure in which one of the electrodes of the stacked electrochemical pumping cell and the electrochemical sensing cell is exposed to the internal cavity, With one electrode forming the electrode pair of the sensing cell, the other electrode forming the electrode pair of the sensing cell is exposed to a reference gas, or the other electrode forming the electrode pair of the pumping cell is covered with a suitable porous protection. It was placed in direct contact with the gas to be measured through the layer. Therefore, when the gas to be measured is a Lynch atmosphere, the other pumping electrode constituting the pair of electrodes in the pumping cell is a corrosive or reducing gas in the Lynch atmosphere, for example 0. There was a problem of deterioration due to hydrocarbons, etc. Furthermore, for example, in measuring automobile exhaust gas, the gases emitted from the engine are in a chemically non-equilibrium state and are active.
When touched, the electrode tends to be forced due to dissolution or precipitation of gas components, and the flow rate of the exhaust gas is extremely fast.
Deterioration due to evaporation of platinum, which is commonly used as an electrode, could not be ignored. Furthermore, even in the case of gases to be measured other than the Lynch atmosphere, there is an inherent problem in that the pumping electrode in contact with the gas to be measured becomes contaminated and deteriorates due to fine particles in the gas to be measured.

(Solution Means) The present invention has been made against the background of the above-mentioned circumstances, and has an improved structure that can improve the deterioration of the electrode due to contamination of the pumping electrode and reducing gas. It provides an electrochemical device, for which it has the following characteristics:

The electrochemical device according to the present invention includes (1) a first plate-shaped solid electrolyte and first and second electrodes provided in contact with the solid electrolyte; (b) an electrochemical sensing cell comprising a second plate-shaped solid electrolyte and third and fourth electrodes provided in contact with the solid electrolyte; and (c) an electrochemical sensing cell comprising: the electrification '-'i formed in an integral electrochemical element comprising a target pumping cell and the electrochemical sensing cell; a first electrode of the target pumping cell and the electrochemical sensing cell; an internal space in which the third electrode of the sensor cell is substantially exposed, communicates with an external space where the gas to be measured is present, and into which the gas to be measured is guided from the space where the gas to be measured is present under a predetermined diffusion resistance; and (d) a second electrode of the electrochemical pumping cell and a fourth electrode of the electrochemical sensing cell formed within the electrochemical element are each substantially exposed. 243 gas existing space.

That is, according to the present invention, the second electrode of the electrochemical pumping cell, together with the fourth electrode (reference electrode) of the electrochemical sensing cell, is capable of controlling the presence of gas in the base formed within the electrochemical element. Since a predetermined bombing action is performed between the first electrode exposed in the space and exposed in the internal space, the second electrode is not covered as in the conventional case. Since the second electrode is not exposed to the gas to be measured, the problem of contamination and deterioration of the second electrode due to the gas to be measured can be completely eliminated.

In addition, in the electrochemical device according to the present invention,
+iii Inner cavity In general, the first plate-shaped solid electrolyte and/or the second plate-shaped solid electrolyte 5! It is provided as a flat space extending in a direction parallel to the plate surface of the electrolyte, and is formed between the first and second plate-shaped solid electrolytes. Furthermore, in one embodiment of the present invention, the first electrode of the electrochemical pumping cell and the third electrode of the electrochemical sensing cell are integrated into an electrical unit including the cells. They are exposed to face each other in an internal cavity formed in the chemical element, and the base gas-existing space is communicated with the general atmosphere.

Also, according to a preferred embodiment of the present invention, an internal cavity )I51 is formed in an integrated electrochemical element comprising an electrochemical pumping cell and an electrochemical sensing cell, respectively. ) The Yugas existence space is arranged so as to be located on approximately the same plane, thereby greatly reducing the thickness of the electrochemical element (device).
(to reduce the temperature gradient in the thickness direction) 1)
C″6 because it can effectively suppress the destruction of the solid electrolyte due to thermal stress.

Furthermore, by making the element thinner, the element itself can be further miniaturized, and at the time of addition, it can be uniformly heated to the cell operating temperature in a short time. It can also be extremely advantageous in terms of thermal efficiency.

Furthermore, in the present invention, if the temperature of the gas to be measured is low and the solid electrolyte of the electrochemical cell is not maintained at a sufficient temperature, it will not be able to fully demonstrate its performance. The solid state electrode is heated by a heater;
1. It is desirable that the material is heated.
In such a case, one layer of a predetermined ceramic heater is generally provided in close contact with the solid electrolyte of the electrochemical cell.

(Example) Hereinafter, in order to clarify the present invention more specifically, the Ig configuration of the present invention will be explained in detail based on the Example shown in the drawings.

First, FIG. 1 is a developed view of an element portion having the most unusual structure in an example of an oxygen sensor which is a specific example of an electrochemical device according to the present invention. That is, this oxygen sensor has a laminated structure of three plate-shaped solid electrolytes such as zirconia molybdenum, first, second, and third solid electrolytes 2°4.6 mm. The internal cavity (xeviity) forming hole provided in the solid electrolyte 4 and the elongated notch extending in the longitudinal direction thereof are covered by the upper and lower first and third solid electrolytes 2 and 6, thereby forming an internal cavity. The cavity 8 and the reference gas existing space 10 are formed on substantially the same plane in the plane direction of the flat solid electrolyte. Note that the oxygen sensor having such a structure is one of those used as a so-called lean burn sensor or lean burn sensor.

And the first solid electrolyte in such a sensor ``2''
has a porous first electrode 1 made of platinum, for example, and a second electrode 1.1 on its inner surface, that is, the surface opposite to the side exposed to the gas to be measured such as exhaust gas. Predetermined route J
The first electrode 12 is exposed to the cavity 8 and the second electrode 14 is exposed to the reference gas existing space 10. In addition,
The first electrode 12 and the second electrode 14 are connected to an external pump power source via respective lead portions 16.18. Further, a gas vent hole 20 is provided as a diffusion rate controlling means, passing through the first solid type 6 material 2 and the first electrode 12 and having a hole diameter having a predetermined diffusion resistance.

On the other hand, on the inner surface of the third solid electrolyte 6, that is, on the side facing the second solid electrolyte 4, a third electrode 22 and a fourth electrode 24 are provided at a predetermined distance from each other. , and the third electrode 22 is exposed to the cavity 8, while the fourth electrode 24 is exposed to the reference gas existing space 10. In addition, these electrodes 2
2.21) are connected to a predetermined external device via the lead portions 26 and 28, respectively.

In short, the oxygen sensor of this embodiment includes an electrochemical pumping cell 30 consisting of a first solid electrolyte 2, a first electrode 12 and a second electrode 14, a third solid electrolyte 6 and a third electrode. 22 and a fourth electrode 24 have an integrated laminated structure with a second solid electrolyte 4 in between, and an electrochemical sensing cell made up of these cells A first electrode 1 is placed in a cavity 8 as an internal cavity formed in an electrochemical element.
The second and third electrodes 22 are exposed, and the reference gas existing space 10 in the electrochemical element has a structure in which the second electrode 14 and the fourth electrode 24 are exposed, respectively. There is.

Therefore, in an electrochemical device with such a structure,
As is well known, each time a predetermined direct current voltage is applied between the first electrode 12 and the second electrode 14 of the electrochemical pumping cell 30, a voltage proportional to the amount of electricity of the direct current is generated. In proportion, the oxygen in the gas to be measured in the cavity 8 is mainly moved through the second solid electrolyte 4 into the reference gas existence space 10 provided in the plane direction of the solid electrolyte, or vice versa, 4+
; 'f4ζ Oxygen is transferred from the gas existence space 10 to the cavity 8
It is made to move inside. On the other hand, between the third electrode 22 and the fourth electrode 24 of the electrochemical sensing cell 32, the oxygen concentration in the atmosphere in the cavity 8 and the reference gas in the gas presence space 10 are The electromotive force recalled is determined based on the difference between the oxygen depth and the oxygen depth, and thereby the oxygen depth in the gas to be measured under a predetermined diffusion resistance through the gas vent 20 can be detected.
Alternatively, the concentration of unburned components may be detected.

In addition, in an oxygen sensor having such a structure, since the cell part below -L has a symmetrical structure, here, the upper cell part (first solid state power i'' quality 2 and The lower cell part (consisting of the third solid electrolyte 6 and the third and fourth electrodes 22.24) is used as the pumping cell section 30, while the lower cell section (consisting of the third solid electrolyte 6 and the third and fourth electrodes 22.24) Although the sensing cell section 32 is used as the sensing cell section 32, it is also possible to use the upper cell section as the sensing cell section and the lower cell section as the pumping cell section.

In an electrochemical cell with this structure,
Due to the oxygen pumping function of the first and second electrodes 12.14, the gas to be measured, more specifically oxygen, which is the component to be measured therein, passes through the gas vent 20 and reaches the cavity 8, but the amount of gas passing through is It is controlled by the gas vent 20 and the oxygen partial pressure in the cavity 8 can be lower than the actual oxygen partial pressure of the gas to be measured, so that exhaust gas is in a lean atmosphere where the oxygen partial pressure is higher than the oxygen partial pressure of the stoichiometric air-fuel ratio. Controlling an engine that emits 4L of gas? 1) It is suitable for use in 1.

Of course, the electrochemical device manufactured in 1981 can also be used to detect the oxygen content of a neutral atmosphere such as exhaust gas obtained by combustion at a stoichiometric air-fuel ratio. It's something you get. In such a case, [r
Yumiko's first electricity (1) with 12 and the second 5ξ pole I4?
The electromotive force between the first electromotive force or the second electric current J'l<22 and the fourth electrode 24 is determined, and the oxygen pumping ability of the electrochemical pumping cell 30 is expressed by applying a predetermined DC voltage. Not done.

Furthermore, an electrochemical device of such structure has a rich region,
In other words, if the fuel is burned in an excess state, 14
The measurement target gas is exhaust gas in a region where the oxygen partial pressure is lower than the oxygen partial pressure of the stoichiometric air-fuel ratio and where a large amount of unburned components are present. It can also be suitably used as a so-called rich burn sensor, which is a sensor that knows the combustion state of an engine that generates combustion, and the effects of the present invention can be exhibited even more effectively.

In this case, unlike in the case of the lean burn sensor, a direct current is caused to flow from the first electrode 12 side to the second electrode 14 side, thereby causing the Q, I;, '<4.3 Substances, for example, oxygen in the atmosphere with which the spaces 10 are communicated, are moved to the cavity 8 side. Therefore, in the vicinity of the first electrode 12, the unburned components in the i=I constant gas that have diffused while counteracting the diffusion of the sludge pores 20 are transferred to the second electrode 14 side. The atmosphere inside the cavity 8, which is combusted and reacted by the oxygen transferred from the ion to the first electrode 12 side, and the atmosphere inside the cavity 8 changed by such reaction is transferred to the two electrodes of the electrochemical sensing cell 32, namely the third electrode. electrode 22 and fourth electrode 2
4, the combustion state (A/F value) that provides the desired amount of unburned components and the amount of unburned components is detected.

In particular, when used as such a rich burn sensor, the external gas to be measured is a corrosive or reducing gas such as CO2 hydrocarbons, or the second electrode 14 of the electrochemical pumping cell is is not exposed to such a reducing gas and is exposed in the reference gas existence space 10, so is it caused by such a gas? The problem of η wear or deterioration is not caused at all. Moreover, the first electrode 12 of the electrochemical pumping cell 30 and the electrochemical sensing cell 32
Although the space inside the cavity 8 where the third electrode 22 is exposed is communicated with the external space where the gas to be measured exists through the gas vent 20, the space inside the cavity 8 is exposed through the gas vent 20. , the first and third electrodes 12, 22 will not deteriorate if they are maintained in a substantially neutral atmosphere that is neither rich nor lean.

Furthermore, even if the inside of the cavity 8 is not maintained in a neutral atmosphere, the first electrode 12 and the third electrode 22 are connected to the internal cavity where the gas to be measured moves at a velocity M through a predetermined diffusion resistance. (cavity), and the gas in this internal space is in a chemically normal state due to collisions with walls, etc. or 4J collisions between gas molecules, and gas flow. Since there is almost no deterioration of the electrode due to dissolution/precipitation of gas components or evaporation of the electrode, the deterioration of the electrode is extremely small.

In addition, in such an electrochemical element, it is +1·v
As the solid electrolyte 2.4.6, which is the central component of the structure, in addition to the above-mentioned zirconia porcelain, aluminum nitride, 5rCeO:+, BizOl-dilute upper oxide solid solution, Lad-xCa i YO4 etc. will be used.

In addition, when laminating and forming such an electrochemical device,
Electrodes 12, 14, 22.24 and their lead portions 16, 18, 26.28 are printed on the solid power Y quality 2 or 6 green substrate by screen printing method, and the second space forming member is printed. A publicly known method such as stacking the raw materials of the solid electrolyte 4 in between to form the desired electrochemical cell (element), and sintering and integrating the whole, or a method adopted as appropriate. It is.

When forming a desired electrochemical element (cell) by such simultaneous integral sintering method,
Each electrode 12.14, 22.24 and their lead portion 16
, 18, 26, and 28 are preferably fired at the same time, and in that case, their electrodes and leads are mainly made of platinum group metals such as platinum, palladium, rhodium, iridium, ruthenium, and osmium. It is desirable that the electrodes or lead portions be formed by printing using some type of material and firing the printed material.

In order to prevent such peeling and disconnection of the electrodes and leads, fine ceramic powder such as zirconia, ittria, alumina, etc. is mixed into the electrodes and leads, and the powder is heated during firing. It is desirable to improve integration with adjacent layers.

It should be noted that the electrochemical device according to the present invention is not limited to the structure described above, and can be effectively applied to a pond structure, for example, as shown in FIGS. 2 and 3. It may have a structure as shown.

That is, FIG. 2 shows an oxygen sensor having a structure in which a ceramic heater layer 34 is provided in addition to the one illustrated in FIG. This ceramic heater single layer 34 is formed by sandwiching a heater element 36 between electrically insulating materials 38 and 40, and is laminated so as to be in close contact with the first solid type 5W material 2 constituting the pumping cell 30. It is integrated. And this ceramic heater single layer 34
A gas vent 20 having a predetermined diffusion resistance is also formed in the ceramic heater layer 34 and the pumping cell 30.
Through the gas vent 20 passing through the cavity 8 , the measured component (oxygen) in the measured gas, more specifically the cough measured gas, is introduced into the cavity 8 in a controlled proportion.
They are now focused on themselves.

By forming the heater layer 34 in this manner, the oxygen sensor as an electrochemical device can be used when the temperature of the gas to be measured is low.
It has the advantage of being able to effectively heat the sensor to a desired temperature, and in addition, by making the sensor thinner, it is possible to reach the sensor operating temperature in a short time even during such heating.

The insulating layers 38 and 40 used to electrically insulate the heater element 36 and its lead portions are preferably ceramic layers made of alumina or spinel, or other materials such as borosilicate glass or mullite. There is no problem even if ceramics whose main components are And such one color 8.1 layer 3
8.40, it is desirable to make its thickness as thin as possible as long as it does not impede its electrical insulation properties, and -J
'G' has a thickness of 300 μm or less, particularly about 10 to 200 μm. In particular, such an insulating layer 38.
In order to effectively relieve the stress due to the difference in thermal expansion between the insulating layer 38.4 and the first solid electrolyte 2, it is necessary to
It is desirable that ZJ be porous, so that peeling between them can be more effectively prevented.

FIG. 3 also shows a structure in which the first electrode 12 of the electrochemical pumping cell 30 and the third electrode 22 of the electrochemical sensing cell 32 in the oxygen sensor shown in FIG. sensors are shown. In such a sensor, by applying a predetermined pump voltage between the first electrode 12 and the second electrode 14,
Oxygen in the gas to be measured in the cavity 8 is taken out to the reference gas existing space 10 side through the first solid electrolyte 2,
Or, on the contrary, in the electrochemical sensing cell 32, the atmosphere in the cavity 8 and the reference gas existing space are transferred into the cavity 8 from the base gas existing space 10. An electromotive force based on the difference in oxygen concentration between the reference gas and the reference gas in the gas is measured between the third electrode 22 (12) and the fourth electrode 24. That is, Here, a pump cell 30 is constructed from the first electrode 12, the second electrode 14, and the first solid electrolyte 2, with the first electrode 12 as a common electrode. electrode 22), a fourth electrode 24, and first, second and third solid electrolytes 2,
The sensing cell 32 is constructed from 4.6.

In addition, an oxygen sensor (electrochemical device) with this structure
Also, the first electrode 12 and the second electrode 14 of the pumping cell 30 and the third electrode 2 of the sensing cell 32
The second and fourth electrodes 24 are arranged in the cavity 8 and the JJ g-gas existence space 10, respectively, and have a structure that prevents them from coming into direct contact with the external gas to be measured. , the useful effects according to the present invention can be enjoyed. Also in this embodiment, the cavity 8 and the gas existence space 10 are arranged in the direction of the plate surface of the solid electrolyte to be stacked, and are juxtaposed on substantially the same plane. This feature also allows the cell thickness to be reduced and effective heating to be performed.

Although not shown in the drawings, the present invention is disclosed in Japanese Patent Application Laid-Open No. 58-1
As shown in Japanese Patent Application No. 53155, etc., the thickness of a flat internal cavity formed in an electrochemical element is controlled so that the internal cavity itself has a diffusion resistance function. It can also be advantageously applied to an electrochemical device having a structure in which the diffusion control means itself is used. In that case, the internal cavity having a predetermined diffusion resistance is communicated directly or indirectly with the external space in which the gas to be measured exists, and such an internal cavity The first electrode of the electrochemical pumping cell and the third electrode of the electrochemical sensing cell are arranged in such a way that they can be exposed at the inner part of the cell.

Although several embodiments of the present invention have been described above, the electrochemical device of the present invention is by no means to be interpreted as being limited to such illustrative specific structures, and the gist of the present invention Without departing from the above, the present invention may be implemented in forms with various modifications, modifications, improvements, etc. based on the knowledge of those skilled in the art, and the present invention includes such embodiments. , it goes without saying.

Further, the electrochemical device according to the present invention can be particularly suitably applied to a rich burn sensor, but as described above, it can be applied to a sensor whose measured gas is exhaust gas obtained by combustion near the stoichiometric air-fuel ratio. Of course, the present invention can also be suitably applied to a lean burn sensor that uses exhaust gas in a lean region as the gas to be measured, and can also be applied to oxygen sensors having other structures. Furthermore, the present invention can also be applied to a detector or controller for components involved in electrode reactions in fluids such as nitrogen, carbon dioxide, and hydrogen other than oxygen.

(Effects of the Invention) As is clear from the above description, the electrochemical device according to the present invention includes an electrochemical device including an electrochemical pumping cell and an electrochemical sensing cell. The electrochemical The second electrode of the pumping cell and the fourth electrode of the sensing cell are arranged in a reference gas existing space formed in the target element, and in particular, the second electrode of the pumping cell Since the second electrode is not exposed to the external gas to be measured as in the conventional case, it is possible to effectively prevent the second electrode from being contaminated or deteriorated by the gas to be measured. It has great industrial significance.

Further, in the present invention, in particular, the internal space in which the first electrode and the third electrode are exposed and the reference gas presence space in which the second electrode and the fourth electrode are exposed are formed of a plate-shaped solid body. A structure in which each cell is formed so that they are located on substantially the same plane in the plane direction of the electrolyte is preferably adopted, but in that case, the cell thickness must be effectively adjusted. While the cell can be made thinner and the cell can be further miniaturized, the temperature gradient in the cell thickness direction due to the thinner wall is reduced, which prevents the solid electrolyte and, by extension, the cell (device) from being destroyed due to thermal stress. Moreover, during heating, excellent effects such as being able to reach the cell operating temperature in a short time can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a perspective explanatory view showing an expanded structure of a sensor element portion without showing an example of the oxygen sensor, which is one of the electrochemical devices according to the present invention, and FIGS. 2 and 3 are respectively views of the present invention. 2 is a diagram corresponding to FIG. 1 showing different examples of oxygen sensors as electrochemical devices according to the following. 2: First solid electrolyte 4: Second solid electrolyte 6 Second solid electrolyte 8: Cavity 10: Reference gas presence space 12: First electrode 14: Second electrode 20: Gas vent 22: Third electrode 24: Fourth electrode 30: Electrochemical pumping cell 32: Electrochemical sensing cell 34: Ceramic heater single layer 36: heater element 38.40: insulation layer 1) Fig. 2 Fig. 3

Claims (6)

[Claims] (1) An electrochemical pumping cell including a first plate-shaped solid electrolyte and first and second electrodes provided in contact with this solid electrolyte, a second plate-shaped solid electrolyte, and this solid electrolyte. an electrochemical sensing cell including third and fourth electrodes provided in contact with the electrochemical pumping cell and the electrochemical sensing cell; The first electrode of the electrochemical pumping cell and the third electrode of the electrochemical sensing cell, formed in an inner cavity through which a measurement gas is guided from the gas-to-be-measured space under a predetermined diffusion resistance; a second electrode of the electrochemical pumping cell formed in the electrochemical element; an electrochemical device comprising: a fourth electrode of a reference sensing cell; and a reference gas presence space, each of which is substantially exposed. (2) The internal space is a flat space that extends in a direction parallel to the plate surface of the first plate-shaped solid electrolyte and/or the second plate-shaped solid electrolyte. Electrochemical device according to item 1. (3) The electrochemistry according to claim 1 or 2, wherein the internal space is formed between the first plate-shaped solid electrolyte and the second plate-shaped solid electrolyte. device. (4) The electrochemistry according to any one of claims 1 to 3, wherein the first electrode and the third electrode are exposed to face each other in the internal space. device. (5) Claim 1, wherein the internal space and the reference gas existing space are located on substantially the same plane.
5. The electrochemical device according to any one of Items 4 to 4. (6) The electrochemical device according to any one of claims 1 to 5, wherein the reference gas existing space is communicated with the atmosphere.