JPH0518936A - Electrochemical gas sensor - Google Patents

Abstract

PURPOSE:To obtain an electrochemical type gas sensor with a function for self-diagnosing that its life expired by extending life and at the same time allowing the sensor itself to detect sensitivity characteristics constantly without requiring inspection. CONSTITUTION:A target gas detection portion A for detecting a target gas to be detected and a life-reporting means 110 which emits a signal when a detection output is below a certain value are connected and a reference gas detection portion B for detecting a reference gas which exists at a certain concentration within an environment of use is also provided. Protection films 90 and 92 for protecting solid electrolytes 80 and 82 are formed at both gas- detection portions A and B and a thickness on an operation pole 50 of the solid electrolyte 82 is thicker than that of other portions in the reference gas detection portion B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrochemical gas sensor, and more particularly to a gas sensor which detects gas in the atmosphere by utilizing an electrochemical reaction.

[0002]

2. Description of the Related Art As a basic structure of a gas sensor using an electrochemical reaction, a plurality of electrodes are connected by an ionic conductor, that is, an electrolyte to cause an electrochemical reaction. Conventionally, a liquid electrolyte or a gel electrolyte has been used as a material for the ionic conductor, but there is a problem in that the sensor is inferior in durability and reliability due to liquid leakage and solvent evaporation. In order to solve such a problem, development of a gas sensor using an inorganic or organic solid electrolyte has been advanced.

Examples of inorganic solid electrolytes include β-alumina, naconone, ricicon, and stabilized zirconia.
However, in a solid electrolyte made of these inorganic substances, the impedance is high at room temperature, and thus it is difficult for ions to conduct at room temperature. Therefore, in general, the inorganic solid electrolyte as described above is used by heating it to have a low impedance, which means that the gas sensor consumes a large amount of power, which is not preferable in practice.

As the organic solid electrolyte, there are polymers belonging to the cation exchange resin such as polystyrene sulfonate, polyvinyl sulfonate, perfluorosulfonate polymer, and pofluorocarboxylate polymer. Among these resins, perfluorosulfonate polymer is widely used as the most practically suitable one, and for example, Nafion (trade name: manufactured by DuPont)
There is something called.

The reason why the above-mentioned perfluorosulfonate polymer is preferable is that the degree of dissociation of cations is large, that is, the impedance is small, or that it is relatively stable thermally and electrochemically. Since the perfluorosulfonate polymer is soluble in the solvent, the solid electrolyte layer made of the perfluorosulfonate polymer can be easily formed on the insulating substrate or the electrode by casting the solution. This means that the gas sensor is easy to manufacture.

[0006]

In the electrochemical gas sensor using the above-mentioned perfluorosulfonate polymer as the electrolyte, the physical properties of the perfluorosulfonate polymer change with time, so that the sensitivity of the sensor changes with time. The sensor function cannot be exhibited at a certain point and the so-called life ends. It is important to extend the life of such an electrochemical gas sensor as much as possible, but there is a limit to extending the life. Further, the conventional electrochemical gas sensor has a problem that it cannot be easily known that the gas sensor in use has reached the end of its life.

More specifically, the physical properties such as impedance and gas permeability of the perfluorosulfonate polymer, which is the electrolyte connecting the electrodes, have a very large effect on the sensitivity of the gas sensor. The sensor sensitivity appears as it is with time. Then, when the sensor sensitivity decreases with time and becomes a sensitivity equal to or lower than the minimum value necessary for exhibiting the function as the sensor, the sensor has reached the end of its life. It is extremely dangerous to continue to use a gas sensor that has reached the end of its life, and it is necessary to promptly know that the life has come to the end.

In the conventional gas sensor, a gas to be detected having a constant concentration is periodically injected, and the sensor sensitivity to the gas is measured to determine whether or not the sensor has sufficient sensitivity. However, the inspection work of the sensor by such a method is very time-consuming and labor-intensive, and it cannot be known when the sensor has reached the end of its life during the inspection performed after a certain period of time. However, it was an inadequate method for knowing the sensor life quickly and reliably.

Therefore, an object of the present invention is to extend the life of the electrochemical gas sensor as described above, and at the same time, the sensor itself is always operated without the troublesome work of the inspection work described above. An object of the present invention is to provide an electrochemical gas sensor having a function of self-diagnosing the end of its life by detecting the sensitivity characteristic.

[0010]

SUMMARY OF THE INVENTION An electrochemical gas sensor according to the present invention for solving the above-mentioned problems is an electrochemical gas sensor in which a plurality of electrodes on an insulating substrate are connected by a solid electrolyte to perform a detection action. In addition, the target gas detection unit for detecting the target gas to be detected and the reference gas detection unit for detecting the reference gas existing at a constant concentration in the operating environment are provided. A life notification means that outputs a signal when the output becomes a certain value or less is connected, and the target gas detection unit includes a pair of electrodes including a working electrode, a counter electrode, and a reference electrode, and a solid electrolyte covering the top and the space between the electrodes. , And a protective film for protecting the solid electrolyte, and the reference gas detection unit covers a pair of electrodes including a working electrode, a counter electrode, and a reference electrode, and covers each electrode above and between them, and on the working electrode. Thick solid electrolyte than the thickness of other portions thickness, and, a protective film for protecting the solid electrolyte.

First, the basic structure of the gas detector will be described. The electrodes are a set of a working electrode, a counter electrode, and a reference electrode, and are made of an electrode material such as gold, platinum, or the like, and are formed on an insulating substrate so as to have a shape or an arrangement structure corresponding to each function. .. Then, a solid electrolyte layer is formed so as to cover the electrodes and between the electrodes, so that the electrodes are connected to each other by the solid electrolyte. Further, in order to further reduce the change with time of the solid electrolyte, a protective film made of fluororesin or the like and covering the surface of the fixed electrolyte is formed. The specific material and manufacturing means of the protective film may be the same as those used in conventional electrochemical gas sensors and the like.

According to the present invention, two gas detectors as described above are provided in one element. First, the target gas detection part for detecting the target gas used as a detection target is provided. The gases to be detected are carbon monoxide, alcohol,
There are various gases such as hydrogen sulfide, and the voltage applied between the working electrode and the reference electrode is set according to the type of gas to be detected. Next, a reference gas detection unit for detecting a reference gas existing at a constant concentration in the use environment is provided. As the reference gas, for example, oxygen is preferable when used in the atmosphere, but if the use environment is different, a reference gas corresponding to the environment may be selected. In the reference gas detection unit, the voltage applied between the working electrode and the reference electrode is set so that the above reference gas can be detected.

The target gas detection unit and the reference gas detection unit have substantially the same shape and structure, but the reference gas detection unit has a thickness of the solid electrolyte covering the above and between each electrode different from that on the working electrode. It is thicker than the part. To make the thickness of the solid electrolyte different between the working electrode and other parts, form the working electrode and other electrodes on a flat insulating substrate, and place it on the upper surface of the solid electrolyte so that the solid electrolyte becomes thick only on the working electrode. It may be formed with steps, or a step may be formed on the insulating substrate so that only the working electrode formation portion is lower than other portions, and the solid electrolyte is formed so that the top surface is flat. You may keep it. Furthermore, a step may be provided on both the surface of the insulating substrate and the upper surface of the solid electrolyte.
The thickness of the solid electrolyte covering the working electrode of the reference gas detection unit is such that the reaction gas accompanying the electrochemical reaction of the reference gas does not accumulate in the working electrode, and the thickness of the reference gas can be suppressed from reaching the working electrode. The reference gas is set to be necessary and to a certain extent necessary to obtain a certain detection output so that it can reach the working electrode through the solid electrolyte. The specific thickness of the solid electrolyte depends on the structure of the entire sensor and the required performance.

The target gas detection unit and the reference gas detection unit are provided with a power supply for applying a voltage to the target gas detection unit and the reference gas detection unit, and an output signal detected by the target gas detection unit, as in a normal gas sensor. A signal processing circuit for processing, an external circuit and an external device for displaying the detected concentration of the target gas and for issuing a signal or warning when the target gas having a certain concentration or more is detected are connected.

Further, a life notification means is connected to the reference gas detecting section. The service life notification means monitors the detection signal of the reference gas, and when the detection signal falls below a certain value, the warning signal is issued or a warning is displayed to indicate that the gas sensor has reached the end of its life. The life of the can be announced. As the life notification means, not only visual and audible notifications such as warning sounds and warning lamps are used to notify the end of life, but also control signals are sent to external devices and devices that incorporate gas sensors to control the operation of external devices. Alternatively, the work of replacing the gas sensor or the like can be automatically performed.

The service life of the gas sensor is considered to be the service life when the sensor sensitivity falls below a certain rate, for example, when the sensor sensitivity becomes half of the initial value, or the sensor sensitivity decreases below a preset certain threshold value. The value of the sensor sensitivity for determining the end of life can be set freely according to the use and purpose of the gas sensor.

[0017]

In the electrochemical gas sensor, the gas component detects the gas component by causing an electrochemical reaction at the interface between the working electrode and the electrolyte. Therefore, the reason why the sensor sensitivity decreases with time is that the time for the gas component to reach the interface between the working electrode and the electrolyte is delayed with time, and the reaction rate of the electrochemical reaction is delayed with time. And the speed at which the product formed by the reaction moves to the counter electrode becomes slower with time. Each of these phenomena follows a fixed course depending on the sensor configuration. Therefore, by appropriately setting the configuration of the electrodes and the electrolyte of the reference gas detection unit, it is possible to form the reference gas detection unit having substantially the same temporal characteristics as the target gas detection unit.

As described above, if the target gas detecting section and the reference gas detecting section having the same sensitivity characteristics with time are used,
The decrease in sensitivity with time in the target gas detection unit and the reference gas detection unit will proceed in the same manner. Therefore, if you continuously monitor the detection output (sensitivity) of the reference gas detector for the reference gas that exists in a certain concentration in the operating environment,
It is possible to know the decrease in the sensitivity of the reference gas detector with time. The decrease in sensitivity in the reference gas detection unit also indicates the decrease in sensitivity in the target gas detection unit, as described above. In other words, when the sensor sensitivity in the reference gas detection unit falls below a certain ratio with respect to the initial value and falls below a certain threshold value, the life notification means connected to the reference gas detection unit is activated. For example, it is possible to notify that the target gas detection unit, that is, the gas sensor has reached the end of its life.

On the other hand, in order to prolong the life of the sensor, it is effective to protect the solid electrolyte of the target gas detecting portion with a protective film made of a fluorine resin or the like. This protective film is
It has the function of preventing harmful substances from entering the solid electrolyte from the external environment, and, on the contrary, stabilizing the characteristics of the solid electrolyte by preventing evaporation of water contained in the solid electrolyte, As a result, the life of the sensor can be extended. However, if the solid electrolyte of the target gas detection unit is covered with a protective film, the solid electrolyte of the reference gas detection unit must also be covered with a protective film so that the reference gas detection unit will have the same temporal characteristics as the target gas detection unit. I can't have it.

However, when the solid electrolytes of the target gas detection section and the reference gas detection section are covered with a protective film, the characteristics of the target gas detection section and the reference gas detection section with time are even if the protective film has exactly the same shape and structure. There will be a problem that will be greatly different. The cause is considered as follows. Since the reference gas detection unit is in contact with the reference gas that is always present at a constant concentration in the operating environment, the electrochemical reaction is constantly occurring on the working electrode, and the reaction products accompanying the electrochemical reaction are also generated. It will continue to be generated. For example, if the reference gas is oxygen, the reaction of O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O occurs on the working electrode of the reference gas detection unit, and water continues to be generated. When such reaction products accumulate in the solid electrolyte, the sensitivity of the reference gas detection unit is affected. On the other hand, in the target gas detection unit, unless a target gas such as carbon monoxide is generated in the environment, no electrochemical reaction occurs on the working electrode, and naturally no reaction product is generated.

That is, the sensitivity characteristics of the reference gas detection unit in which the reaction products are always generated and the target gas detection unit in which the reaction products are not always generated differ with time. However, if the surface of the solid electrolyte is exposed without being covered by the protective film, the reaction product generated in the reference gas detection unit is easily released from the surface of the solid electrolyte into the environment, so the reference gas detection The reaction product is less likely to accumulate in the part, and the difference in characteristics over time between the target gas detection part and the reference gas detection part is relatively small.

However, when the surface of the solid electrolyte is covered with the protective film, the reaction product generated in the reference gas detection section is hard to be released from the solid electrolyte into the environment and accumulates in the solid electrolyte. is there. Therefore, when the protective film is used, it becomes very difficult to match the time characteristics of the reference gas detection unit with the time characteristics of the target gas detection unit. Therefore, in the present invention, by making the thickness of the solid electrolyte covering the working electrode of the reference gas detection portion thicker than the thickness of the other portion, the reaction product is accumulated in the working electrode of the reference gas detection portion. prevent. That is, if the solid electrolyte covering the working electrode of the reference gas detection unit is thick, the amount of the reference gas that passes through the solid electrolyte from the environment to reach the working electrode is reduced,
The electrochemical reaction and the formation of reaction products on the working electrode are also reduced. As a result, the sensitivity of the reference gas detection unit does not change, and the temporal characteristics equivalent to those of the target gas detection unit can be maintained. Moreover, even if the solid electrolyte is thick, a small amount of reference gas reaches the working electrode.Therefore, the reference gas detection unit should always output the reference gas detection signal and monitor its change over time. Is possible. Further, the difference in the thickness of the solid electrolyte covering the working electrode of the reference gas detection unit and the working electrode of the target gas detection unit means that the reference gas detection unit and the target gas detection unit have structural differences. However, this has little effect on the sensitivity with time. In addition, such a difference in sensitivity characteristics based on the difference in the thickness of the solid electrolyte can be known at the time of manufacturing the sensor in advance.Therefore, if appropriate sensitivity correction is performed, the time-dependent characteristics of the reference gas detection unit can be used for the target gas. It is easy to match the characteristics of the detector with time.

As described above, in the electrochemical gas sensor according to the present invention, by forming the protective film, it is possible to prolong the life or improve the performance, and at the same time,
By setting the thickness of the solid electrolyte on the working electrode of the reference gas detection unit as described above, it is possible to prevent the target gas detection unit and the reference gas detection unit from having different sensitivity aging characteristics.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 to 3 show a schematic structure of an electrochemical gas sensor according to the present invention. First, the entire surface of the insulating substrate 10 made of a silicon substrate or the like having an insulating film formed thereon is substantially flat, and, as is clear from FIG. 2, only a portion 12 is dug low to leave the remaining surface. There is a step between the part and it. On the surface of such an insulating substrate 10, two sets of electrodes made of an electrode material such as platinum or gold are formed. That is, the working electrode 2 for detecting the gas to be detected
0, a counter electrode 30, and a reference electrode 40, a target gas detection electrode set composed of three rectangular electrodes, and a working electrode 50 for detecting a reference gas, which is arranged symmetrically opposite to the electrode set. It is a reference gas detection electrode set including three rectangular electrodes of a counter electrode 60 and a reference electrode 70. Of these, the working electrode 50 for detecting the reference gas is formed on the lower portion 12 of the insulating substrate 10 described above. For forming each electrode, a normal electrode forming means such as sputtering or vapor deposition is used.

The two sets of electrodes 20-40 and 50-70 are covered with a solid electrolyte layer 80, 82 made of a perfluorosulfonate polymer or the like so as to cover the above and between the electrodes.
However, the reference gas detection target gas and target gas detection target are formed separately from each other. Solid electrolyte layer 80, 82
Has a flat upper surface. Therefore, as shown in FIG. 2, the thickness T ₁ of the solid electrolyte layer 82 on the working electrode 50 for reference gas detection is larger than the thickness T ₀ of the solid electrolyte layer 82 in other portions of the insulating substrate 10. It is thicker for the difference in level. The material and forming means of the solid electrolyte layers 80 and 82 may be the same as in the case of a normal gas sensor.

Then, the solid electrolyte layer 80 as described above,
Protective films 90 and 92 made of fluorine resin are formed so as to cover the entire surface of 82. In FIG. 1, the protective film 90,
The formation location of 92 is represented by hatching. Protective film 9
0 and 92 are formed by a vapor deposition method, a plasma polymerization method, or the like. One end of each of the electrodes 20 to 70 has a solid electrolyte layer 80, 8
2 and the protective films 90 and 92 are extended to the outside to be exposed to the outside, and are connected to external circuits.
2, 52, 62, 72. In this way
The target gas detection unit A and the reference gas detection unit B are provided side by side on one insulating substrate 10.

The electrodes 20 to 40 of the target gas detector A are
The detection signal of the target gas, which is connected to the signal processing circuit 100 and is detected by the target gas detection unit A, is connected to the signal processing circuit 100 via the lead wires 102 connected to the terminal portions 22 to 42 so that the detection signal can be used outside. Is becoming Reference gas detector B
The respective electrodes 50 to 70 are connected to the life notification means 110 via the lead wires 104 connected to the terminals 52 to 72.

The life notification means 110 is a reference gas detection unit B.
The sensor output can be monitored, and when the detected output falls below a certain value, a signal is emitted and a warning sound is emitted or a warning lamp is turned on to notify that the sensor has reached the end of its life. Is becoming The life notification means 110 having such a function is composed of an ordinary electronic circuit or the like similar to that used in various devices.

In the gas sensor having the above structure, the sensor function of the target gas detection unit A will be described. The gas component of the gas to be detected passes through the protective film 90 and the solid electrolyte layer 80 from the surface of the protective film 90 and reaches the working electrode 20, where an electrochemical reaction occurs. Counter electrode 3
At 0, a reaction pairing with the working electrode 20 occurs. As a result, a detection current flows between the working electrode 20 and the counter electrode 30,
Can detect and quantify gas components. The reference electrode 40 functions as a reference for keeping the potential of the working electrode 20 constant. That is, by keeping the potential of the working electrode 20 at a constant potential corresponding to the gas component to be detected, the gas component to be detected causes an electrochemical reaction in the working electrode 20. Such a sensor action is similar to that of a normal electrochemical gas sensor.

Next, the life detecting operation in the reference gas detecting section B will be described. In the reference gas detection unit B, oxygen as the reference gas is transferred from the surface of the protective film 92 to the protective film 92.
And, it penetrates through the solid electrolyte layer 82 and reaches the working electrode 50, where an electrochemical reaction occurs. However, since the thickness T ₁ of the solid electrolyte layer 82 on the working electrode 50 is large, the amount of oxygen reaching the working electrode 50 is small and the reaction amount is extremely small. In the counter electrode 60, a reaction to form a pair with the working electrode 50 occurs, and an oxygen detection current flows between the working electrode 50 and the counter electrode 60. In the reference gas detection unit B, the working electrode 5
Since the potential of 0 is maintained at a constant potential corresponding to oxygen with reference to the reference electrode 70, oxygen can be detected. That is, the reference gas detector B and the target gas detector A
Then, only the potential settings of the working electrodes 20 and 50 are different, but the basic electrochemical reaction and the principle action through which the detection current flows are the same.

Since oxygen is always present in the atmosphere at a constant concentration, a constant detection current should always be obtained in the reference gas detection section B unless the sensitivity changes with time. However, as described above, the sensitivity of the reference gas detection unit B decreases over time, so the detection current gradually decreases. The same phenomenon as the change in the detected current in the reference gas detection unit B, that is, the sensitivity, with time also occurs in the target gas detection unit A at the same time. Therefore, the reference gas detector B
The detection current (sensitivity) in (1) is constantly monitored, and when the detection current becomes a predetermined value or less, it may be determined that the sensor, that is, the target gas detection unit A has reached the end of its life.

Next, the results of manufacturing the electrochemical gas sensor having the above-mentioned structure and testing the gas detecting action with time will be described. -Example 1-As the material for the insulating substrate 10, a 10 mm square and 1 mm thick silicon substrate was used. Of the surface of the silicon substrate, only a part 12 is stepped by 0.1 mm lower than the other parts, and the entire surface is oxidized. Further, in order to enhance the adhesion between the substrate and the electrode, a polysilicon layer having a thickness of about 2000 Å was formed on the surface of the silicon substrate by sputtering. Working electrodes 20, 50 and counter electrode 3 made of platinum are formed on the insulating substrate 10 by sputtering.
Reference electrodes 40 and 70 made of 0 and 60 and gold were formed. However, the working electrode 50 was formed on the portion 12 of the surface of the insulating substrate 10 which was lower than the other portions.
Then, 5% by weight of perfluorosulfonate polymer
The solution containing was cast on each of the electrodes 20-40, 50-70 and the insulating substrate 10 around the electrodes to form solid electrolyte layers 80, 82 made of perfluorosulfonate polymer having a thickness of 3 μm. Since the upper surfaces of the solid electrolyte layers 80 and 82 are flat, the working electrode 50 formed on the lower portion 12 of the insulating substrate 10 is covered with the solid electrolyte layer 82 with a thickness of about 0.1 mm. Become. Further, a protective film 9 covering the entire surfaces of the solid electrolyte layers 80 and 82 and made of a polymer of tetrafluoroethylene
0, 92 were formed by plasma polymerization.

In order to confirm that the gas sensor in which the target gas detection unit A and the reference gas detection unit B thus manufactured have a sensor function for the target gas and a life notification function, Gas detector A
The time-dependent changes in the sensitivity of the reference gas detection unit B and the sensitivity to carbon monoxide and oxygen were measured. The test apparatus shown in FIG. 4 was used for the measurement. The gas sensor is housed in the measurement chamber 120, and the terminal portions 22 of the electrodes 20 are connected to the potentiometers 122 for the target gas detection portion A and the reference gas detection portion B via the lead wires 121.
Connected to 23. Recorders 124 and 125 are connected to the potentiostats 122 and 123 for the target gas detection unit A and the reference gas detection unit B, respectively.

Using the test apparatus as described above, the working electrode 20 and the reference electrode 40 of the target gas detecting section A for detecting carbon monoxide are used.
The test was conducted by setting the applied voltage between 0.4 and 5V and the applied voltage between the working electrode 50 and the reference electrode 70 of the standard gas detection unit B for detecting oxygen to -0.6V. The oxygen detection current flowing between the working electrode 50 and the counter electrode 60 of the reference gas detection unit B was constantly monitored by the recorder 125. Also,
The atmosphere in the chamber 120 is replaced with air containing 1000 ppm of carbon monoxide from the state of only air, and the carbon monoxide detection current flowing between the working electrode 20 and the counter electrode 30 of the target gas detection unit A is recorded by the recorder 124. It was measured. The measurement was repeated by supplying air containing carbon monoxide into the chamber 120 at regular intervals.

FIG. 5 shows the measurement result. As is clear from this graph, it can be seen that the temporal changes in the sensitivity of the target gas detection unit A to carbon monoxide and the sensitivity of the reference gas detection unit B to oxygen show almost the same tendency. Therefore, if the time until the sensitivity at which the target gas detection unit A cannot function as a sensor becomes the life, the sensitivity of the reference gas detection unit B is less than or equal to the sensitivity at the elapsed time corresponding to the life of the target gas detection unit B. If the sensor life is judged to have expired and an appropriate warning signal is issued, the sensor life can be detected quickly and reliably.

Example 2 A gas sensor is manufactured through the same manufacturing process as in Example 1 except that Teflon is used as the material of the protective films 90 and 92 and the vapor deposition method is used as the forming method in Example 1. Manufactured. With respect to the gas sensor manufactured in this manner, the same measurement as in Example 1 was performed. The measurement results are shown in FIG. In the case of Example 2, as compared with Example 1,
Although the sensitivity deterioration rate is high, the behaviors of the target gas detection unit A and the reference gas detection unit B with respect to changes in sensitivity with time are similar. In the case of this gas sensor as well, from the detection output of the reference gas detection unit B, It turns out that the life can be detected.

[0037]

As described above, according to the electrochemical gas sensor of the present invention, in addition to the target gas detecting section similar to the normal gas sensor, the reference gas existing at a constant concentration in the use environment is detected. Since the reference gas detection unit is provided, the life of the gas sensor can be detected quickly and reliably. That is, the gas sensor itself has a function of self-diagnosing whether or not the life has expired. As a result, it is possible to save a great deal of labor and time required for the inspection work for confirming the function of the sensor, and it is possible to significantly reduce the maintenance cost. Further, it is possible to provide a highly reliable gas sensor that can reliably avoid a dangerous situation that occurs when a gas sensor that has reached the end of its life is used as it is.

In particular, by providing the protective layer for protecting the solid electrolyte, it is possible to prevent the sensitivity of the sensor from being lowered due to the change in physical properties of the solid electrolyte layer with time, and to extend the life of the sensor. Further, since the thickness of the solid electrolyte layer is thicker than the other portions on the working electrode of the reference gas detection unit, even if the protective layer as described above is formed, the reaction product accompanying the electrochemical reaction of the reference gas Is less likely to accumulate on the working electrode, the time-dependent characteristics of the reference gas detection unit can be reliably matched with the time-dependent characteristics of the target gas detection unit, and the life notification function of the reference gas detection unit can be exhibited well.

As a result of the above, the electrochemical gas sensor according to the present invention can satisfy both contradictory requirements, which have heretofore been unrealizable, of a long service life and quick and reliable notification of the service life. This will greatly contribute to improving the functions of various types of gas sensors or expanding their applications.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a gas sensor showing an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a reference gas detection unit.

FIG. 3 is an enlarged sectional view of a target gas detection unit.

FIG. 4 is a schematic configuration diagram of a sensor sensitivity test device.

[Fig. 5] Diagram showing sensitivity measurement results

FIG. 6 is a diagram showing the sensitivity measurement results of another example.

[Explanation of symbols]

 A target gas detection unit B reference gas detection unit 10 insulating substrate 12 low part 20, 50 working electrode 30, 60 counter electrode 40, 70 reference electrode 80, 82 solid electrolyte 90, 92 protective film 110 life notification means

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[Procedure amendment]

[Submission date] November 9, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

Then, the solid electrolyte layer 80 as described above,
Protective films 90 and 92 made of fluorocarbon resin are formed so as to cover the entire surface of 82. In FIG. 1, the protective film 90,
The formation location of 92 is represented by hatching. Protective film 9
0 and 92 are vapor deposition method, plasma polymerization method , casting
It is formed by the method . One end of each of the electrodes 20 to 70 is extended to the outside of the solid electrolyte layers 80, 82 and the protective films 90, 92 and exposed to the outside, and the terminal portions 22, 32, 42, 52 for connecting to an external circuit are provided. 62 and 72.
In this way, the target gas detection unit A and the reference gas detection unit B are provided side by side on one insulating substrate 10.

Claims (1)

Claim: What is claimed is: 1. An electrochemical gas sensor for detecting a gas by connecting a plurality of electrodes on an insulating substrate with a solid electrolyte, for detecting a target gas to be detected on the same substrate. A target gas detection unit and a reference gas detection unit for detecting a reference gas that exists at a constant concentration in the operating environment, and the reference gas detection unit issues a signal when the detection output falls below a certain value. Are connected, the target gas detection unit is a pair of electrodes consisting of a working electrode, a counter electrode, and a reference electrode, a solid electrolyte covering the above and between the electrodes, and
The reference gas detection unit is composed of a protective film for protecting the solid electrolyte, and the reference gas detection unit covers a pair of electrodes including a working electrode, a counter electrode, and a reference electrode, and covers each electrode over and between the electrodes, and has a thickness on the working electrode at other portions. An electrochemical gas sensor characterized by comprising a solid electrolyte thicker than the thickness of the solid electrolyte and a protective film for protecting the solid electrolyte.