JPH0417385B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrochemical device that heats a solid electrolyte with a heater, and in particular, is composed of two stacked electrochemical cells using a flat solid electrolyte. It is related to the equipment used.

Conventionally, electrochemical devices using solid electrolytes, such as oxygen sensors for detecting the oxygen concentration in the exhaust gas of automobile internal combustion engines, have used oxygen ion conductive solid electrolytes such as zirconia porcelain.
2. Description of the Related Art Sensors and the like that determine oxygen concentration using the principle of an oxygen concentration battery are known. 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 such electrochemical devices have generally had a cylindrical shape with a bottom. In recent years, from the viewpoint of ease of assembling a structure, a stacked structure in which the solid electrolyte is made into a flat plate and predetermined electrodes are provided in contact with the surface of the solid electrolyte to constitute an electrochemical cell has been developed. It is being considered.

Therefore, in order for such an electrochemical device to operate effectively even when the temperature of the gas to be measured is relatively low, the solid electrolyte must be heated to a high temperature with an appropriate heater. However, according to the results of studies conducted by the present inventors, two electrochemical cells each consisting of a solid electrolyte and at least one pair of electrodes provided in contact with the solid electrolyte are connected through a predetermined cavity. In the case of the electrochemical device having an integrated structure, heating by such a heater tends to cause cracks or cracks in the solid electrolyte due to differences in thermal expansion, and the heater and electrodes tend to break. It became clear that there were inherent problems with poor reliability, such as short lifespan.

The present invention has been made against this background, and aims to improve reliability by effectively preventing the occurrence of cracks or cracks in the solid electrolyte due to differences in thermal expansion. Our goal is to provide an electrochemical device with a high level of integrated structure.
Another objective is to efficiently heat the two electrochemical cells that make up the device to their operating temperature, eliminate the temperature difference between them, and stabilize their operating characteristics. The objective is to provide a target device.

In order to achieve such an object, an electrochemical device according to the present invention includes two electrochemical cells each including a solid electrolyte and at least one pair of electrodes provided in contact with the solid electrolyte; a cavity sandwiched between two electrochemical cells, and a heater layer, one of the two electrochemical cells being an electrochemical pump cell;
The other one is an electrochemical detection cell, and one of the electrodes of the electrochemical pump cell and one of the electrodes of the electrochemical detection cell are each exposed to the cavity, while the heater layer is exposed to the cavity. surrounds the cavity on at least three sides,
Alternatively, the heater layer is disposed within the cavity so that at least a portion thereof is exposed.

Further, in the present invention, the heater layer interposed between the electrochemical pump cell and the electrochemical detection cell is composed of a heater and an insulating layer, and the electrochemical The pump cell is configured to be electrically insulated with respect to the electrochemical detection cell, and the insulating layer is formed of a porous ceramic layer such that the heater is surrounded by the porous ceramic layer. By doing so, it is possible to effectively absorb the difference in thermal expansion between the insulating layer and the solid electrolyte layer of each cell, thereby making it possible to more effectively prevent separation between them and, by extension, separation between cells. be.

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

First, FIG. 1 is a developed view of an element portion in an example of an oxygen concentration detector which is a specific example of an electrochemical device according to the present invention. That is, in this oxygen concentration detector, in other words, in this oxygen sensor, the oxygen pump cell 2 and the oxygen concentration detection cell 4 are connected to the heater layer 6.
and a spacer member 10 made of a solid electrolyte material such as zirconia porcelain for forming the cavity 8.
This is one of the so-called lean burn sensors that have a structure in which they are laminated and integrated through the two.

The oxygen pump cell 2 has a flat solid electrolyte 12 made of zirconia porcelain or the like, and has a porous layer made of, for example, platinum on one side of the solid electrolyte 12, that is, the side exposed to the gas to be measured such as exhaust gas. An outer pump electrode 14 is provided, and the outer pump electrode 14 can be electrically energized from the outside through a lead 16 thereof. On the other hand, the other surface (inner surface) of the solid electrolyte 12
is provided with an inner pump electrode 18 made of the same material as the outer pump electrode 14, that is, made of porous platinum, at a position corresponding to the outer pump electrode 14. It is designed to be connected to an external power source via an extending lead portion 20.

Therefore, this oxygen pump cell 2 constitutes an electrochemical cell with a solid electrolyte 12 and a pair of electrodes 14 and 18 provided in contact with each surface of the solid electrolyte 12,
As is well known, the voltage applied between these electrodes allows oxygen in the outer gas to be measured to be introduced into the cavity 8 provided in the inner spacer member 10, or Oxygen in 8 is released into the gas to be measured outside through solid electrolyte 12.

The oxygen concentration detection cell 4 has a structure similar to that of the oxygen pump cell 2, and has outer measurement electrodes 2 at corresponding positions on both sides of a flat solid electrolyte 22 made of zirconia porcelain or the like.
4 and the inner measuring electrode 26 are joined to constitute an electrochemical cell as an oxygen concentration battery. In addition, those measurement electrodes 24, 26
are guided to the outside by lead portions 28 and 30, respectively, and connected to a predetermined measuring device to measure the potential between these electrodes. That is, in this oxygen concentration detection cell 4, the oxygen concentration in these gases is measured between the outer measurement electrode 24 that is brought into contact with the gas to be measured and the inner measurement electrode 26 that is brought into contact with the atmospheric gas in the cavity 8. A predetermined superpower based on the difference will be measured.

Furthermore, the heater layer 6 has a U-shape as a whole, and the heater 3 is located at the base of the U-shape.
2 and its lead portion 34 are integrally sandwiched between upper and lower U-shaped insulating layers 36 and 38.

The oxygen pump cell 2 and the oxygen concentration detection cell 4 are stacked and integrated with the heater layer 6 and the spacer member 10 for forming the cavity 8 in between, thereby achieving the purpose. Thus, an electrochemical device will be constructed. At that time, the cavity 8 is formed by the notch hole of the spacer member 10 being surrounded and closed by the upper and lower solid electrolytes 12 and 22, and furthermore, the cavity 8 is formed on three sides by the heater layer 6. Heater 32 inside
The heater 32 and its lead portion 34 are surrounded by the solid electrolytes 12 and 2 above and below by insulating layers 36 and 38.
2 and is electrically insulated.

Further, the inner pump electrode 18 of the oxygen pump cell 2 is exposed through the space between the heater layers 6 in the cavity 8, and the inner measuring electrode 26 of the oxygen concentration detection cell 4 is also exposed in the cavity 8.
The inner pump electrode 18 is exposed inside the inner pump electrode 18 so as to face the inner pump electrode 18.

Therefore, in an electrochemical device having such a structure, a heater layer 6 is interposed between the oxygen pump cell 2 and the oxygen concentration detection cell 4, and the heater layer 6 allows The heater 32 is connected to the lead portion 3 of the cavity 8 formed between the cells, which is surrounded on three sides.
4 to an external power source (e.g. DC),
When a predetermined current is applied, the heater 32 generates heat due to the Joule heat, effectively heating the insulating layers 36 and 38 that are in close contact with the heater 32, as well as the solid electrolyte 12, the spacer member 10, and the solid electrolyte 22. Both cells 2, 4 are efficiently heated to their operating temperature.

Therefore, by effectively heating the oxygen pump cell 2 and oxygen concentration detection cell 4 on both sides by the heater layer 6 disposed in the center, the sharp temperature gradient in the cell stacking direction can be eliminated and the temperature can be reduced. By achieving this balance, the generation of large thermal stress between the solid electrolytes 12 and 22 of each stacked and integrated cell can be effectively eliminated, and the solid electrolytes 12 and 22 can be Cracks or cracks that occur can now be effectively prevented.

Furthermore, by interposing the heater layer 6 between the two cells, wasteful heat dissipation can be suppressed compared to the case where the heater is disposed outside the oxygen pump cell 2 or the oxygen concentration detection cell 4. Since the cells 2 and 4 can be efficiently heated up to the operating temperature, the heating efficiency by the heater layer 6 is good, and therefore the power consumption can be kept low, so disconnection of the heater and electrodes can be effectively suppressed.
It has also become possible to improve its lifespan.

In addition, by eliminating the temperature difference in the stacking direction of the oxygen pump cell 2 and the oxygen concentration detection cell 4, it is possible to stabilize the operating characteristics of each cell and, by extension, the sensor characteristics, thereby increasing its reliability. It became possible.

The oxygen sensor as an electrochemical device is used as a lean burn sensor.
This is suitably used to suppress an engine that generates exhaust gas in a lean atmosphere where the oxygen partial pressure is higher than the oxygen partial pressure of the stoichiometric air-fuel ratio.

Note that insulating layers 36 and 3 used to electrically insulate the heater 32 and its lead portion 34
8 is preferably a ceramic layer mainly composed of alumina or spinel, but other ceramics mainly composed of borosilicate glass, mullite, etc. may also be used without any support. and,
It is desirable that the thickness of such insulating layers 36 and 38 be as thin as possible as long as the electrical insulation properties thereof are not impaired, and the thickness is generally 100μ or less,
In particular, 50μ or less is suitable. In particular, in order to effectively relieve the stress caused by the difference in thermal expansion between the solid electrolyte 12 of the oxygen pump cell 2 and the spacer member 10, it is desirable that the insulating layers 36 and 38 be porous. Peeling between them can be prevented even more effectively.

In addition, when forming and laminating the oxygen pump cell 2, oxygen concentration detection cell 4, and heater layer 6, the solid electrolyte 12, which constitutes each cell,
Electrodes and their lead parts, insulating layers, heaters and their lead parts, etc. are sequentially printed on the raw material No. 22 by a screen printing method or the like, and together with the spacer member 10, the intended electrochemical device is constructed. Lay them on top of each other and sinter the whole thing,
Known methods such as integration are appropriately employed.

Furthermore, as the material of the heater in the present invention, fire-resistant metals such as nickel, silver, gold, platinum, rhodium, palladium, iridium, ruthenium, tungsten, molybdenum, etc., or alloys thereof are preferred due to their excellent durability. However, other than these, compounds such as ZnO, LaCrO ₃ , LaB ₆ , SiC, etc. can also be used. Further, in order to prevent the heater from peeling or breaking due to sintering during use, it is preferably employed to mix fine powder of zirconia, ittria, alimina, etc. into the heater.

Furthermore, in the present invention, as the solid electrolyte which is a central member constituting the electrochemical liquid pump cell and the electrochemical detection cell, in addition to the above-mentioned zirconia porcelain, β-alimina, aluminum nitride, NASICON, Examples include SrCeO ₈ , Bi ₂ O ₃ - rare earth oxide solid solution, La _1- 〓Ca〓YO _3- 〓, etc.

The electrochemical device according to the present invention is not limited to the above structure, but can be effectively applied to other structures or systems, and may also be used as a stacked element structure. For example, the structure shown in FIGS. 2 and 3 may be used.

That is, FIG. 2 shows that in the oxygen sensor shown in FIG.
A sensor having a structure filled with zeros is shown. By filling the cavity 8 with such porous ceramics 40, there is no space, the mechanical strength is increased, the volume of the cavity is made constant, the thermal conductivity is improved, etc. The porous ceramic 40 to be filled may be any material as long as it can allow gas to enter, and for example, porous zirconia or the like is preferably used.

The oxygen sensor shown in FIG. 3 is an example of an element used as a so-called lean burn sensor, and in this structure, a spacer is inserted through the oxygen pump cell 2 and through the heater layer 6. Two gas vents 42 and 44 are provided that reach the cavity 8 formed by the member 10. That is, the oxygen pump cell 2 includes a pump electrode 14 formed outside the solid electrolyte 12.
A porous electrode protective layer 46 is provided to cover the electrode, and a porous electrode having a predetermined size is formed so as to penetrate through the electrode protective layer 46, the outer pump electrode 14, the solid electrolyte 12, and the inner pump electrode 18. Gas vent holes 42 and 44 are formed therein.

Further, unlike the previous two examples, the heater layer 6 is formed by narrow and elongated plate-shaped insulating layers 36 and 38.
It is constructed integrally with the heater 32 and its lead portion 34 sandwiched therebetween, and gas vent holes 42 and 44 are provided to penetrate through the portion where the heater 32 is disposed.

By stacking the oxygen pump cell 2 and the heater layer 6 on the spacer member 10, the gas vents 42 and 44 communicate the cavity 8 with the outside atmosphere. The layer 6 is exposed on one side into the cavity 8 in the portion located above the inner pump electrode 18 . Note that such ventilation holes 42, 44
Instead of this communication method, it is also possible to communicate the cavity 8 with the outside atmosphere through a suitable gas permeable layer.

Further, in the oxygen concentration detection cell 4, an inner measuring electrode 26 is provided on the solid electrolyte 22, while an outer electrode is provided as a reference electrode 48 on a single plate-shaped solid electrolyte 50, By stacking these with a U-shaped solid electrolyte 52 in between, an electrochemical cell is constructed. Note that a space 54 is formed by sandwiching the U-shaped solid electrolyte 52 between the upper and lower solid electrolytes 22 and 50, and a standard gas, such as the atmosphere, enters the space 54. The electrode 48 is adapted to be brought into contact with the standard gas introduced into this cavity 54.

In this structure, unlike the previous sensor, the gas to be measured reaches the cavity 8 through the gas vents 42 and 44, but the oxygen partial pressure in the cavity 8 is reduced by the operation of the oxygen pump cell 2. Since the oxygen partial pressure can be lower than the actual oxygen partial pressure of the gas to be measured, similarly to the two sensors described above, the engine is controlled to generate exhaust gas in a lean atmosphere where the oxygen partial pressure is higher than the oxygen partial pressure of the stoichiometric air-fuel ratio. Therefore, it is suitably used.

Even with this type of oxygen, the heater layer 6 according to the present invention is interposed between the oxygen pump cell 2 and the oxygen concentration detection cell 4, so that the same effects as in the previous example can be achieved. It can be done.

Although several embodiments of the present invention have been described above, the electrochemical device of the present invention is by no means limited to such illustrative specific structures, and does not depart from the spirit of the present invention. It goes without saying that the present invention may be implemented in various forms with various modifications, modifications, improvements, etc. based on the knowledge of those skilled in the art, and the present invention also includes such embodiments. By the way.

Further, in the present invention, the heating current applied to the heater 32 of the heater layer 6 may be either alternating current or direct current, but it is particularly effective in the case of direct current, where it is preferable to arrange an insulating layer between the heater and the solid electrolyte. It is something that can be used. On the other hand, when using alternating current, it is also possible to have a structure in which the insulating layers 36 and 38 do not exist.

As is clear from the above description, the electrochemical device of the present invention is constructed by laminating an electrochemical pump cell and an electrochemical detection cell in an integrated manner via a predetermined heater layer. According to
It aims to improve the efficiency and uniformity of heating, effectively prevent the occurrence of cracks or cracks in the solid electrolyte due to thermal stress, reduce power consumption, prevent disconnection of heaters and electrodes, and further improve the direction of cell stacking. It is possible to achieve excellent effects such as eliminating the temperature difference between the two and stabilizing the sensor characteristics, and this is where the present invention has great industrial significance.

[Brief explanation of drawings]

FIG. 1 is a perspective explanatory view showing the developed structure of a sensor element part showing an example of an oxygen concentration detector which is one of the electrochemical devices according to the present invention, and FIGS. 2 and 3 are respectively The first example shows another example of
FIG. 2... Oxygen pump cell, 4... Oxygen concentration detection cell, 6... Heater layer, 8... Cavity, 10
... Spacer member, 12 ... Solid electrolyte, 14
...Outer pump electrode, 18...Inner pump electrode,
22...Solid electrolyte, 24...Outer measurement electrode, 2
6...Inner measurement electrode, 32...Heater, 36,
38... Insulating layer, 40... Porous ceramics,
42, 44... Gas vent, 46... Electrode protective layer, 48... Reference electrode, 50, 52... Solid electrolyte, 54... Vacant space.

Claims (1)

[Claims] 1. Two electrochemical cells each comprising a solid electrolyte and at least one pair of electrodes provided in contact with the solid electrolyte, a cavity sandwiched between the two electrochemical cells, and a heater. one of the two electrochemical cells is an electrochemical pump cell, the other one is an electrochemical detection cell, and one of the electrodes of the electrochemical pump cell and one of the electrodes of the electrochemical detection cell are each exposed to the cavity;
The heater layer is composed of a heater and an insulating layer made of a ceramic porous layer surrounding the heater, and the heater is electrically insulated from the electrochemical cell via the insulating layer. and the heater layer surrounds the cavity on at least three sides, or the heater layer is arranged in the cavity so that at least a portion thereof is exposed. . 2. The electrochemical device according to claim 1, wherein the cavity is communicated with an external atmosphere via a gas vent or a gas permeable layer. 3. The electrochemical device according to claim 1 or 2, wherein the cavity is filled with porous ceramics. 4. The electrochemical device according to any one of claims 1 to 3, wherein the solid electrolyte is zirconia porcelain.