JPS60259948A - Electrochemical apparatus - Google Patents

Abstract

PURPOSE:To upgrade the pump cell capacity by arranging a heater layer on the side of an electrochemical sensor cell while a fourth electrode exposed to a reference atmosphere is arranged in parallel with the third electrode exposed to a gas atmosphere to be measured as controlled through an airtight ceramic layer. CONSTITUTION:An oxygen pump cell which has a solid electrolytic layer 8 is equipped with an outer pump electrode 10 on the surface exposed to a gas to be measured such as exhaust gas while an inner pump electrode 12 is provided at the position corresponding to the electrode 10. A measuring electrode 18 of an oxygen concentration detection coil is placed between this electrode and the electrode 12 through a porous ceramic layer 22 and is brought into contact with the atmosphere of a gas to be measured which is formed in the perimeter of the electrode 12 and controlled. An airtight ceramic layer 24 is provided between the layer and the oxygen pump cell on the reference electrode 20 arranged side by side. The electrodes 18 and 20 are connected to a measuring device and a heat generating section 34 is formed on a ceramic layer 38 outside an oxygen concentration detection cell 4, that is, on the surface provided with none of the electrodes 18 and 20. Thus, the capacity of the pump cell can be upgraded while improving the heater life.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrochemical device formed by laminating an electrochemical pump cell and an electrochemical sensor cell, and particularly relates to an electrochemical device having such a laminated structure that efficiently heats This invention relates to a device that can be used to

Conventionally, electrochemical devices using solid electrolytes, such as oxygen concentration batteries using oxygen ion conductive solid electrolytes such as zirconia porcelain, have been used as oxygen sensors to detect the oxygen concentration in the exhaust gas of automobile internal combustion engines. Sensors that measure oxygen concentration using the principle are known. In addition, hydrogen, which uses the same concentration cell principle as the oxygen sensor
Electrochemical devices such as nitrogen, carbon dioxide, etc. detectors and pumps are also known. Until now, solid electrolytes used in such electrochemical devices have generally had a cylindrical shape with a bottom, but from the viewpoint of productivity and cost, it has also been difficult to In recent years, from the viewpoint of ease of assembling a complex structure, a layered structure has been developed 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. are being considered.

In order for such an electrochemical device to operate effectively even when the temperature of the gas to be measured is relatively low, the electrodes and solid electrolyte that make up the cell must be heated with a suitable heater. It is necessary to heat the cell to a high temperature, and for this purpose, in the past, a heater was placed around an electrochemical cell consisting of a solid electrolyte and an electrode with an insulating layer interposed between the heater and the heater. An indirectly heated structure has been disclosed in which the electrode and the cell are placed at different locations within the same plane.

By the way, as one of the above-mentioned electrochemical devices having a laminated structure, an electrochemical cell in which porous electrodes are provided on both sides of a porous solid electrolyte layer is used as a pump cell. There are sensor cells in which electrochemical cells each having a porous electrode are laminated and configured, and it is known that this is useful as a sensor with a wide measurement range. When a heater layer as described above is provided in an electrochemical device, it is generally placed in close contact with the sensor cell side. Barefoot,
When a heater layer is placed on the pump cell side, the heater pattern placed on the pump electrode of the pump cell for efficient heating causes the diffusion effect of the gas to be measured to be uneven locally, making the measurement difficult. There is a problem that accuracy decreases, and if the heater pattern is arranged so that it is not on the pump electrode and the pump electrode part is heated from the side, the temperature on the pump electrode may become unstable. This is because the pump current density becomes uniform, and the pump current density becomes non-uniform depending on the location, resulting in a problem of reduced measurement accuracy.

However, when a heater layer is placed on the electrochemical sensor cell side constituting such an electrochemical device, the heater pattern of such a heater layer is placed on the pump electrode of the pump cell via the sensor cell. Although it has the advantage of forming a heater layer with good temperature distribution and not interfering with the diffusion of the gas to be measured,
Since a sensor cell is interposed between the pump cell and the heater layer, it cannot be said that the heating effect of the heater layer is sufficiently exerted on the pump cell side, and this does not necessarily lead to an improvement in the pumping capacity of the pump cell. It could not be said that the For this reason, a measure can be considered to increase the amount of heat generated by the heater layer to improve its pumping ability, but such measures also lead to a reduction in the lifespan of the heater layer.

The present invention was developed against this background, and its main purpose is to efficiently transmit heat from the heater layer to the pump cell side, improve pumping capacity, and The object of the present invention is to provide a configuration of an electrochemical device that can improve the life of a heater.

In order to achieve such an object, the present invention provides porous first solid electrolyte layers each having a predetermined diffusion resistance at opposing positions on both sides of the porous first solid electrolyte layer. An electrochemical pump cell in which a first electrode and a second electrode are arranged are respectively provided on the surface of a second solid electrolyte layer, and are juxtaposed in a projection view projected in a direction perpendicular to the surface. an electrochemical sensor cell in which porous third and fourth electrodes are disposed, and a heater layer disposed in close contact with the electrochemical sensor cell; the fourth electrode is exposed to substantially the same atmosphere in contact with the gas and the second electrode and the third electrode are in contact with the gas to be measured through the porous first solid electrolyte layer, and the fourth electrode The intended electrochemical device was constructed so that it was substantially separated from the gas to be measured by an airtight ceramic layer.

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 shows an expanded structure of an oxygen concentration detection element, which is a specific example of the electrochemical device according to the present invention, and FIG. 2 shows the structure of such an element. The cross-sectional form of the detection part in the longitudinal direction is shown enlarged more greatly in the thickness direction. That is, in this oxygen concentration detection element (oxygen sensor), an oxygen pump cell 2, an oxygen concentration detection cell (sensor cell) 4, and a heater layer 6 are stacked with the oxygen concentration detection cell 4 in between and are sintered together. It has a similar structure and is one of the so-called GW lean burn sensors.

The oxygen pump cell 2 constituting this element has a porous, flat, oxygen ion conductive solid electrolyte layer (first) 8 made of ittria-doped zirconia porcelain, etc., and one side thereof, i.e. An outer pump electrode (first electrode) 10 made of a porous layer made of, for example, platinum-zirconia is provided on the surface exposed to the gas to be measured such as exhaust gas,
The other surface (inner surface) of the porous solid electrolyte N8 is made of the same material as the outer pump electrode 10, that is, porous platinum, at a position corresponding to the outer pump electrode 10.
Inner pump electrode (second electrode) 12 made of zirconia
are provided, and the pump electrodes 10.12
is connected to the external power supply 14 (second
(see figure) so that a predetermined current is passed between these electrodes.

Note that the porous solid electrolyte N8 of the oxygen pump cell 2
has the function of a diffusion layer that allows the component to be measured (oxygen in this case) in the gas to be measured to diffuse from one surface to the other through its open pores with a predetermined diffusion resistance. ing. In an electrochemical cell composed of the solid electrolyte N8 and a pair of electrodes 10 and 12 provided in contact with the outer and inner surfaces of the solid electrolyte N8, respectively,
When a predetermined direct current is applied between the electrodes 10 and 12, it is guided toward the inner pump electrode 12 by diffusion as described above, as is well known and at a rate proportional to the current. Oxygen in the gas to be measured is moved to the outer pump electrode 10 side by electrochemical pumping action, and then released into the gas to be measured.

On the other hand, unlike the oxygen pump cell 2, the oxygen concentration detection cell 4 uses an airtight flat solid electrolyte N (second) 16 made of itria-doped zirconia porcelain or the like as its solid electrolyte layer. Then, on the inner surface of this airtight solid electrolyte layer 16, that is, the surface of the two oxygen pump cells, a porous measurement electrode (a third electrode) 18 and a reference electrode (fourth electrode) 20 separated from the gas to be measured by an airtight ceramic layer are juxtaposed such that the measurement electrode 18 and the inner electrode 12 of the oxygen pump cell 2 face each other. , respectively, and constitute an electrochemical cell as an oxygen concentration battery.

Note that a thin porous ceramic layer 22 made of porous alumina, zirconia, or the like is interposed between the measurement electrode 18 of the acidity concentration detection cell 4 and the inner pump electrode 12 of the oxygen pump cell 2. Through this porous ceramic layer 22, the electrodes 12.18 are brought into contact at the same time with the same atmosphere, in other words with the controlled gas atmosphere to be measured which is formed around the inner pump electrode 12 by the operation of the oxygen pump cell 2. It is now possible to In addition, a reference electrode 2 juxtaposed to the measurement electrode 18
0, an airtight ceramic layer 24 made of a material such as high resistance zirconia is provided to cover it and to be interposed between the oxygen pump cell 2 and the reference electrode 20. It is sandwiched between the ceramic N24 and the airtight solid electrolyte layer 16, and is airtightly provided.

The measuring electrode 18 and the reference electrode 20 are each guided to the outside by a lead part and installed in a predetermined measuring device (
It is connected to a potentiometer 26) to measure the potential between these electrodes. That is, in this oxygen concentration detection cell 4, there is a reference electrode 20 which is maintained at a high oxygen concentration potential by a separate pumping action, and an inner pump electrode of the oxygen pump cell 2 that contains a controlled amount of oxygen from the gas to be measured. A predetermined electromotive force based on the difference in acidity concentration is measured between the measuring electrode 18 and the measuring electrode 18 brought into contact with the atmosphere around the electrode 12 . In addition, in FIG. 1, 28 and 30 are a power supply and a resistor, respectively, incorporated in the electromotive force measuring circuit.

Furthermore, an electrode 18.2 is located outside the oxygen concentration detection cell 4, that is, on the opposite side to the side where the oxygen pump cell 2 is stacked.
The heater layer 6 is in close contact with the side where 0 is not provided.
It is placed in place. This heater layer 6 includes a heating section 34
A lead portion 36 thereof is formed on a ceramic N3B made of zirconia or the like, and is integrally joined to the outside of the oxygen concentration detection cell 4. It is powered by a power source and generates heat.

Therefore, in the electrochemical device (element) having the structure as shown in FIGS. 1 and 2, the heater N6 is placed in close contact with the oxygen concentration detection cell 4, which is the sensor cell, and the oxygen Since it is not directly provided in the pump cell 2, the diffusion effect of the oxygen pump cell 2 is
Of course, problems such as being affected by the heater pattern of the heater N6 are completely eliminated, and the heater pattern of the heater N6 can be formed over the entire surface without avoiding the pump electrodes 10 and 12 of the oxygen pump cell 2. This makes it possible to provide a heater pattern that provides a uniform temperature distribution on the pump electrodes 10.12.

The oxygen pump cell 2 is heated by the heater layer 6 via the oxygen concentration detection cell 4, but in the oxygen concentration detection cell 4, there are no electrodes that inhibit heat transfer from the heater layer 6. , that is, the reference electrode 20 is the measuring electrode 18
, such reference electrodes 2 are provided in a form that is juxtaposed so as not to overlap in the overlapping direction.
Since heat transfer from the heater layer 6 due to oxygen is not inhibited, the oxygen pump cell 2, particularly the portion where the pump electrodes 10, 12 are disposed, can be effectively heated. In other words, the heat of the heater layer 6 can be efficiently transferred to the oxygen pump cell 2 side, thereby effectively improving its pumping capacity and, in turn, improving the life of the heater.

In particular, when forming a predetermined space around the measurement electrode 18, by arranging the reference electrode 20 in parallel to the measurement electrode 18, this predetermined space will not inhibit heat transfer from the heater layer 6. The effect of juxtaposition is even greater.

Furthermore, in an electrochemical device with such a structure,
The porous solid electrolyte layer 8 of the oxygen pump cell 2 functions as a diffusion layer, so that oxygen in the outer gas to be measured passes through the fine pore structure of the porous solid electrolyte layer 8 to the inner pump electrode 12 side. Unlike the conventional structure in which the internal cavity is directly connected to the external gas to be measured through a diffusion hole such as a pinhole, it is possible to diffuse deposits such as soot. Changes in diffused resistance over time due to burial can be reduced.

In an electrochemical device with such a structure,
The oxygen partial pressure (concentration) in the atmosphere brought into contact with the measurement electrode 18 of the oxygen concentration detection cell 4 is controlled by the oxygen pump function of the oxygen pump cell 2 and the diffusion resistance of the porous solid electrolyte layer 8 as a diffusion layer. Since the oxygen partial pressure in the measurement atmosphere can be made lower than the actual oxygen partial pressure of the gas to be measured, 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. It is suitably used for this purpose.

Of course, such an electrochemical device can be used not only as a lean burn sensor as described above, but also to measure gas such as exhaust gas in a neutral atmosphere where the oxygen partial pressure is approximately equal to the oxygen partial pressure of the stoichiometric air-fuel ratio. By reversing the direction of the current flowing through the oxygen sensor and pump cell 2, it can also be used as a rich burn sensor, etc., which uses exhaust gas in a lean atmosphere where the oxygen partial pressure is lower than the oxygen partial pressure of the stoichiometric air-fuel ratio as the gas to be measured. In either case, the oxygen (measurement component) concentration or excess fuel concentration of the target gas to be measured is determined according to a known measurement method.

Note that the oxygen pump cell 2 and oxygen concentration detection cell 4
As the solid electrolyte layers 8 and 16, in addition to the above-mentioned zirconia porcelain, which is suitably employed, aluminum nitride, 5
rCe03, B 1203-rare earth oxide solid solution,
The solid electrolyte layer 8 constituting the oxygen pump cell 2 is made of a porous material because it functions as a diffusion layer having a predetermined diffusion resistance, as described above. It needs to be a layer. Such a porous layer will have an appropriate porosity depending on the degree of diffusion resistance required, but the optimum open porosity will also vary depending on the manufacturing method of the porous layer. When using the deposition method, it is preferably about 2 to 30% as measured by the mercury porosimetry, and when using the plasma spraying method, it is preferably about 0.5 to 10% as measured by the mercury porosimetry.

The ceramic layer 22 interposed between the inner pump electrode 12 of the oxygen pump cell 2 and the measurement electrode 18 of the oxygen concentration detection cell 4 is porous because these electrodes need to be brought into contact with a common atmosphere. In addition to being a solid layer, it is preferably formed as a thin layer. Further, as the airtight ceramic layer 24 that airtightly sandwiches and surrounds the reference electrode 20 with the solid electrolyte layer 16, various known ceramics such as zirconia, alumina, mullite, spinel, titania, barium titanate, and calcium zirconate are used. It is possible to use
Among these, ceramics containing zirconia as a main component are preferably used in the present invention.

In addition, 3
It is preferable that the ceramic layer 38 forming the airtight ceramic layer 6 is an airtight layer made of the same material as the ceramic material forming the airtight ceramic layer 24, and furthermore, the heat generating part 34 and the lead part 36 are made of platinum, palladium, etc. It is composed of a mixed layer of platinum group metals such as rhodium, iridium, ruthenium, and osmium, and ceramics such as zirconia, yttoria, and alumina, and thereby constitutes a heater 34 and its lead portions 36,
Adhesion between the ceramic layers 16 and 38 surrounding them is improved.

The formation of such a heater mixed layer is achieved by mixing the ceramic fine powder into the platinum group metal powder,
It is effective to perform the firing.

In addition, in order to improve adhesion in a similar manner, the electrodes 10.12 of the oxygen pump cell 2, the electrodes 1B and 20 of the oxygen concentration detection cell 4, and their lead portions are connected to the heater N.
Similarly to the heater portions (34, 36) in No. 6, it is recommended that they be made of a mixture of platinum group metal and ceramics.

When forming an oxygen sensor as an electrochemical device in which the oxygen pump cell 2, the oxygen concentration detection cell 4, and the heater layer 6 are stacked, it is necessary to The electrodes and their lead portions are printed using a screen printing method or the like, and the porous ceramic layer 22 and the airtight ceramic layer 24 are printed on either side of the cell, while the back side of the solid electrolyte Ft16 constituting the oxygen concentration detection cell 4 is printed. , a heater (34°36), and a ceramic layer 38 are sequentially printed.
In order to improve the strength of the device, it is preferable to stack the cells 2 and 4 to form an electrochemical device using known techniques such as sintering and integrating the entire cell. After sintering the laminate except for the porous solid electrolyte layer, a porous solid electrolyte layer can be formed by a known plasma spraying method to produce an electrochemical device.

Incidentally, the electrochemical device according to the present invention has the structure shown in FIG.
The structure is not limited to the structure illustrated in FIG. 2, and various other structures may be adopted without departing from the spirit of the present invention. An example is shown.

That is, the electrochemical device shown in FIGS. 3 and 4 differs from the previous example in that it has two internal pump electrodes (second electrodes) 12 in two oxygen pump cells and a pH constant in four oxygen concentration detection cells. The third electrode (18) is a common electrode, which is structurally simple and economically advantageous.

Moreover, in this embodiment, the reference electrode 20 is an airtight reference gas formed from the airtight solid electrolyte jif 16 of the oxygen concentration detection cell 4, the spacer member 42 made of an airtight ceramic material, and the plate-shaped lid member. aisle 46
It is characterized in that it is exposed to the atmosphere and is brought into contact with the atmosphere introduced from one open end of the reference gas passage 46. That is, the spacer member 42 has a notch (slit) 48 in its longitudinal direction.
The notch 48 is covered with the lid member 44 and stacked from the oxygen pump cell 2 side to cover the oxygen pump cell 2, thereby creating an airtight seal as shown in FIG. Therefore, a reference gas passage 46 is formed. The reference gas passage 46 is opened at the end of the notch 48 of the spacer member 42 and communicated with the atmosphere. Therefore, in this device, the reference atmosphere brought into contact with the reference electrode 20 is
Unlike the previous example, the electromotive force based on the oxygen concentration difference between the measuring electrode 18 which is exposed to the atmosphere and the controlled gas atmosphere to be measured is measured as in the previous example. It becomes.

In addition, in this embodiment, a spacer member 42 and a lid member 4 corresponding to the outer pump electrode 10 of the oxygen pump cell 2 are used.
A gas introduction hole 50 through which the gas to be measured is introduced is provided in the 4 portion, and the gas to be measured is introduced into the porous structure from the direction perpendicular to the electrode surface of the outer pump electrode 10 through the gas introduction hole 50. It is adapted to be guided through an electrode protection layer 52 such as an alumina layer. In other words, by providing the gas introduction direction control layer made of an airtight ceramic layer around the outer pump electrode 10, the gas to be measured is prevented from entering from the side, and the gas introduced perpendicularly to the electrode surface is prevented from entering from the side. The gas to be measured passes through the outer pump electrode 10 from only one direction.
The gas to be measured can be diffused within the porous solid electrolyte layer 8 as a diffusion layer, thereby making it possible to advantageously control the amount of the gas to be measured.

Furthermore, in this embodiment, the heater layer 6 is
4 and its lead portion 36 are sandwiched between airtight ceramic layers 38 and 40 made of high-resistance zirconia or the like, and are integrated with the outside of the oxygen concentration detection cell 4 via an insulating layer 32 made of porous alumina or the like. They are connected to each other and are supplied with power from an external DC power supply. Note that 54. in this example.
Reference numerals 56 and 58 are insulating layers made of porous alumina or the like, which together with the electrode protective layer 52 electrically insulate the lead portions of the respective electrodes.

In the electrochemical device shown in this embodiment, the reference electrode 20 exposed to the reference atmosphere in the airtight reference gas passage 46 is arranged so that it does not overlap with the measurement electrode 18 in the overlapping direction. By juxtaposing the reference electrodes 18, the reference gas passage 46 does not enter between the pump electrodes i10, 12 and the heater layer 6 and impede heat transfer, so the effect of juxtaposing the reference electrodes 18 is even more remarkable.

Furthermore, in the specific examples illustrated above, the measurement electrode 18 and the reference electrode 20 constituting the oxygen concentration detection cell 4 are both on the same side surface (on the inner surface) of the airtight solid electrolyte layer 16.
However, it is also possible to provide the two electrodes 18, 20 on different surfaces of the solid electrolyte layer 16, an example of which is shown in FIG.

That is, in the embodiment shown in FIG. 5, a reference electrode 20 is provided outside the solid electrolyte layer 16 of the oxygen concentration detection cell 4, and a heater layer is provided around the reference electrode 20. The airtight ceramic layer 38.
A reference gas passage 46 similar to the previous example is provided, surrounded by 40. In other words, the ceramic layer 40 on the inside of the heater N6 has a notch (slit) similar to the spacer member 42 in the previous example, and the ceramic layer 38 on the outside has a flat plate shape similar to the lid member 44. The insulating layer 32 has the same shape as the ceramic layer 42, and by stacking them, a reference gas passage 46 with one end open is formed around the reference electrode 20. are substantially separated from the gas to be measured by airtight ceramic layers 38 and 40.

It should be noted that other parts of this embodiment have the same functions as those of each of the embodiments described above, and therefore are given the same numbers and detailed explanations will be omitted.

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 The present invention may be implemented in forms with various changes, modifications, improvements, etc. based on the knowledge of those skilled in the art, as long as the invention does not deviate from the above, and the present invention includes such embodiments. , it goes without saying.

Further, the electrochemical device according to the present invention can be used not only as an example of a lean burn sensor but also as a rich burn sensor as described above, and as a device that measures a gas to be measured such as exhaust gas that is combusted at a stoichiometric air-fuel ratio. It can be advantageously applied to oxygen sensors such as sensors, and can also be applied to detectors or controllers of components other than oxygen that are involved in electrode reactions in fluids such as nitrogen, carbon dioxide, and hydrogen. It is something.

As is clear from the above description, the electrochemical device according to the present invention has a structure in which an electrochemical pump cell and an electrochemical sensor cell are stacked, and a predetermined heater layer is provided on the electrochemical sensor cell side. A fourth electrode exposed to a predetermined reference atmosphere of the electrochemical sensor cell is placed in close contact with the third electrode exposed to a controlled gas atmosphere to be measured in a direction perpendicular to the laminated surface. They have structures that are juxtaposed in a projected view, whereby the heat transfer from the heater layer to the electrochemical pump cell side is carried out within the fourth electrode or a predetermined space around the fourth electrode. As a result, the pump cell can be heated efficiently without being inhibited by the heating process, and the pump cell can be heated efficiently, thereby achieving excellent effects such as improving the pump capacity and further improving the heater life. This is where the great industrial significance of the present invention lies.

[Brief explanation of the drawing]

FIG. 1 is a perspective explanatory view showing one of the oxygen concentration detection devices according to an example of the electrochemical device according to the present invention in an expanded state, and FIG. 2 is a schematic diagram showing the nn cross section in FIG. 1. , FIG. 3 is a diagram corresponding to FIG. 1 showing another example of the oxygen concentration detection device according to the present invention, FIG. 4 is a diagram corresponding to FIG. 2, and FIG. 5 is a diagram corresponding to FIG. FIG. 2 is a diagram corresponding to FIG. 2 showing another embodiment of the oxygen concentration detection device according to the present invention. 2: Oxygen pump cell 4: Oxygen concentration detection cell 6: Heater layer 8: Porous solid electrolyte layer 10: Outer pump electrode 12: Inner pump electrode 16: Airtight solid electrolyte layer 18: Measuring electrode - 20 = Reference electrode 22: Porous Quality ceramic layer 24: Airtight ceramic layer 32: Electrical insulation N 34: Heat generating part 36: Lead part 38.40: Ceramic layer 42 spacer member 44: Lid member 46: Reference gas passage 50: Gas introduction hole Applicant: Nippon Insulator Co., Ltd. Figure 1 Figure 2 Figure 5

Claims (6)

[Claims] (1) An electrochemical pump cell in which a porous first electrode and a second porous electrode are respectively disposed at opposing positions on both sides of a porous first solid electrolyte layer having a predetermined diffusion resistance; A porous third electrode and a fourth porous electrode are respectively provided on the surface of the second solid electrolyte layer and arranged so as to appear juxtaposed in a projection view projected in a direction perpendicular to the surface. an electrochemical sensor cell;
a heater layer disposed in close contact with the electrochemical sensor cell, the first electrode being in contact with the gas to be measured, and the second electrode. and the third electrode are exposed to substantially the same atmosphere in contact with the gas to be measured through the porous first solid electrolyte layer, and the fourth electrode is exposed to the gas to be measured through the airtight ceramic layer. An electrochemical device characterized in that it is substantially separated from a gas. (2) The electrochemical device according to claim 1, wherein the second electrode and the third electrode are common. (3) A predetermined space is formed around the fourth electrode by the airtight ceramic layer, and the space is communicated with the atmosphere through a passageway with one end open. 2. Electrochemical device according to item 2. (4) The electrochemical device according to claim 1 or 2, wherein the fourth electrode is sandwiched between airtight ceramic layers from both sides and embedded in the ceramic layers. (5) The third electrode and the fourth electrode are provided on the same surface of the second solid electrolyte layer, according to any one of claims 1 to 4. electrochemical device. (6) According to any one of claims 1 to 4, wherein the third electrode and the fourth electrode are provided on different surfaces of the second solid electrolyte layer. electrochemical device.