JP2981039B2 - Electrochemical gas sensor - Google Patents

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 for detecting gas in the atmosphere using an electrochemical reaction.

[0002]

2. Description of the Related Art As a basic structure of a gas sensor utilizing an electrochemical reaction, a plurality of electrodes are connected with an ion 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 ion conductor. However, there has been a problem that the durability and reliability of the sensor are inferior due to liquid leakage and evaporation of the solvent. In order to solve such problems, development of a gas sensor using an inorganic or organic solid electrolyte has been promoted.

[0003] Examples of inorganic solid electrolytes include β-alumina, NASICON, lithicon, and stabilized zirconia.
However, solid electrolytes made of these inorganic substances have high impedance at room temperature, so that ions do not easily conduct at room temperature. Therefore, in general, the above-mentioned inorganic solid electrolyte is heated and used in a state of low impedance, which means that the power consumption of the gas sensor increases, which is not practically preferable.

[0004] Examples of organic solid electrolytes include polymers belonging to cation exchange resins such as polystyrene sulfonate, polyvinyl sulfonate, perfluorosulfonate polymer and perfluorocarboxylate polymer. Among these resins, perfluorosulfonate polymers are widely used as the most practically suitable ones, for example, Nafion (trade name, manufactured by DuPont)
There is something called.

[0005] The above-mentioned perfluorosulfonate polymer is preferred because the degree of dissociation of the cation is large, that is, the impedance is small, or it is relatively thermally and electrochemically stable. Further, since the perfluorosulfonate polymer is soluble in a solvent, a solid electrolyte layer made of the perfluorosulfonate polymer can be easily formed on an insulating substrate or an electrode by casting the solution. This means that the manufacture of the gas sensor is easy.

[0006]

In an electrochemical gas sensor using a perfluorosulfonate polymer as an electrolyte as described above, since the physical properties of the perfluorosulfonate polymer change with time, the sensitivity of the sensor increases with time. , And cannot function as a sensor for a certain period of time. However, the conventional electrochemical gas sensor has a problem that it is not easy to know that the gas sensor in use has reached the end of its life.

That is, physical properties such as impedance and gas permeability of a perfluorosulfonate polymer, which is an electrolyte connecting the electrodes, greatly affect the sensitivity of the gas sensor. It appears as a change in sensitivity over time. Then, when the sensor sensitivity decreases over time and becomes lower than the minimum value required to function as a sensor,
At this point, the life of the sensor has come. It is extremely dangerous to continue using the gas sensor whose life has expired, and it is required to know immediately that the life has expired.

In a conventional gas sensor, a gas to be detected having a constant concentration is periodically injected and the sensitivity of the sensor is measured to judge whether the sensor has sufficient sensitivity to function. However, the inspection work of the sensor by such a method is very time-consuming and labor-intensive, and when the life of the sensor comes at the time between the inspections to be performed after a certain period of time, it is possible to know that. It was not a sufficient method to quickly and reliably know the life of the sensor.

The life of the sensor due to the aging of the electrolyte is not limited to the case of using the above-mentioned perfluorosulfonate polymer, but is also the same when various solid electrolytes or liquid electrolytes are used. The problem existed. Therefore, an object of the present invention is to provide a function of detecting the sensitivity characteristic at all times and automatically performing a self-diagnosis of the end of the life without causing troublesome labor such as the inspection work described above, An object of the present invention is to provide an electrochemical gas sensor capable of quickly and accurately knowing the life of a sensor.

[0010]

In order to solve the above-mentioned problems, in an electrochemical gas sensor according to the present invention, in a structure including a gas detecting section in which a plurality of electrodes are connected by an electrolyte, the change in sensitivity with time is substantially the same. some gas detector two <br/> provided, the one gas detector a detection unit for measuring the detection target gas and the other gas detector of the reference gas existing at a constant concentration in the use environment The other gas detector is connected to the other gas detector with a life notifying unit that issues a signal when the detection output for the reference gas is out of a predetermined range.

Further, in order to quickly and accurately know the life of the sensor, one of the gas detection units is a detection unit dedicated to the target gas that constantly measures the detection target gas, and the other gas detection unit is other than the reference gas. The other gas detector is also connected to a measurement gas switching unit that normally performs measurement of the gas to be detected and intermittently performs measurement of the reference gas. Or
In particular, when the solid electrolyte is covered with a protective film, it is effective that the counter electrode and the working electrode are formed so as to enter each other in a comb shape.

In order to make the sensitivity of the one detecting unit and the other detecting unit uniform over time, the one gas detecting unit and the other gas detecting unit may have the same structure, or the one gas detecting unit and the other gas detecting unit may have the same structure. It is effective to provide the gas detection unit on the same substrate. It is also useful that the electrolyte is a solid electrolyte. Hereinafter, the present invention will be described specifically.

First, the electrodes constitute a set of electrodes called a working electrode, a counter electrode, a reference electrode, and the like.
Usually, it is made of gold, platinum or other ordinary electrode materials, and is formed on a supporting member such as an insulating substrate in a shape and an arrangement structure corresponding to each function. And, covering these electrodes and between them with a solid polymer electrolyte or inorganic solid electrolyte such as perfluorosulfonate polymer,
The gas detection unit is configured by bringing the electrodes into contact with a liquid or gel electrolyte and connecting the electrodes with the electrolyte.
With respect to the basic structure of these gas detection units, the same structure as that of a conventional ordinary electrochemical gas sensor can be employed.

[0014] In the sensor of the present invention, a gas detector having an electrode assembly which is connected with an electrolyte as described above usually comprises two in the same device. One of the two gas detectors (the target gas detector) measures the target gas to be detected. Gases to be detected include carbon monoxide,
There are alcohol, hydrogen sulfide, and other various gases, and the applied potential of the working electrode and the like are set according to the type of gas to be detected.

The other of the two gas detection units (reference gas detection unit) is a detection unit for measuring a reference gas existing at a constant concentration in the use environment, and is connected to a measurement gas switching unit. In some cases, the detection unit (intermittent reference gas detection unit) always measures the target gas and intermittently measures the reference gas. However, the measurement of the gas to be detected by the intermittent reference gas detection unit is not to obtain the target gas measurement signal, but to keep the detection unit in the same state as the target gas detection unit. Do not use. In the following, when simply referred to as the reference gas detection unit, the reference gas detection unit usually includes the intermittent reference gas detection unit.

As a reference gas, for example, when used in the atmosphere, oxygen gas satisfies the above conditions,
Although it is preferable, atmospheric components other than oxygen gas can be used, and if the use environment is different, a reference gas corresponding to the environment may be selected. In the reference gas detection unit, the applied potential of the working electrode is set so that the above-described reference gas can be detected. In the case of the intermittent reference gas detector, whether to measure the target gas or the reference gas can be set by simply changing the applied potential of the working electrode (the voltage applied between the working electrode and the reference electrode). Only a configuration for adding a circuit having a potential changing function is added.

The materials and structures of the electrodes and the electrolyte are set so that the target gas detecting section and the reference gas detecting section have the same or almost the same time-dependent change in sensitivity (temporal characteristics) as much as possible. For this purpose, the reference gas detection unit and the target gas detection unit must be made of exactly the same dimensions and material,
That is, it is sufficient to use the same structure, but if both sensitivity characteristics have a certain correlation and have substantially the same time-dependent characteristics, the function of each detection unit, the type of gas to be detected, etc. In accordance with this, an electrode having a partially different material or other structure may be used. In the present invention, the gas detectors having the same change over time in sensitivity include those having a certain correlation between both sensitivity characteristics and having substantially the same time characteristic, even if they are not completely the same configuration. It is done.

The target gas detecting section and the reference gas detecting section are provided with voltage applying means for applying a voltage to the target gas detecting section and the reference gas detecting section, similarly to a normal gas sensor, and an output signal detected by the target gas detecting section. , An external circuit for displaying the detected concentration of the target gas or issuing a signal or a warning when a target gas having a predetermined concentration or more is detected, and an external device.

When the solid electrolyte is covered with a protective film, the reference gas detector is preferably formed so that the counter electrode and the working electrode enter each other in a comb shape. This is because the counter electrode and the working electrode can be brought closer. It is preferable that the counter electrode and the working electrode face each other at an interval of about the thickness of the solid electrolyte. At this time, the target gas detection unit may be formed such that the solid electrolyte is covered with the protective film and the counter electrode and the working electrode enter each other in a comb shape, but this is not always necessary.

Further, according to the present invention, there is provided a life notifying means connected to the reference gas detecting section. The life notifying means monitors the detection signal of the reference gas, and, when the detection output is out of a predetermined range, assuming that the gas sensor has reached the end of its life, issues a warning signal or performs a warning display. And the life of the gas sensor can be notified. As the service life notification means, not only is it possible to notify the user of the service life by alerting the user visually or audibly with a warning sound or a warning lamp, but also by sending a control signal to an external device or device incorporating a gas sensor to control the operation of the external device. Alternatively, operations such as replacement of the gas sensor or the like can be automatically performed.

The life of the gas sensor is considered to be the life when the sensor sensitivity falls below a certain ratio, for example, when the sensor sensitivity becomes half of the initial value, or the sensor sensitivity drops below a predetermined threshold value. The life of the gas sensor may be determined when the gas sensor is used. The value of the sensor sensitivity for determining that the life is reached can be freely set according to the use and purpose of the gas sensor.

[0022]

The electrochemical gas sensor detects the gas component by causing an electrochemical reaction at the interface between the working electrode and the electrolyte. Therefore, taking as an example the case where the sensor sensitivity decreases over time, the cause is that the speed at which the gas component reaches the interface between the working electrode and the electrolyte decreases over time, and the electrochemical reaction Reaction time slows down over time, and the speed at which the product of the reaction moves to the counter electrode slows down over time, etc. It depends on the sensor configuration. Therefore, by appropriately setting the electrodes and electrolyte of the reference gas detection unit, it is possible to provide the same time-dependent characteristics as the target gas detection unit in terms of gas sensitivity.

As described above, by using a reference gas detector having the same gas sensitivity over time as that of the target gas detector,
In the target gas detection unit and the reference gas detection unit, a change in characteristics over time, that is, a decrease in sensitivity proceeds similarly. The reference gas detector detects a reference gas present at a constant concentration in the operating environment. Therefore, if the detection output of the reference gas detector for the constant concentration of the reference gas is continuously monitored, the reference gas detector can detect the reference gas. The detection output indicates a change with time of the sensor sensitivity, and it is possible to know how much the sensor sensitivity has decreased. This is because the decrease in the sensor sensitivity in the reference gas detection unit also indicates the decrease in the sensor sensitivity in the target gas detection unit, as described above.

Therefore, when the sensor sensitivity of the reference gas detecting section falls below a certain ratio with respect to the initial value or falls below a certain threshold value, the life notifying means connected to the reference gas detecting section. By operating, it is possible to accurately notify that the sensor sensitivity in the target gas detection unit has decreased and the life of the gas sensor has come. In the electrochemical gas sensor of the present invention, in particular, the sensitivity of the target gas detector and that of the intermittent reference gas detector decrease in the same manner, and the life of the intermittent reference gas detector matches the life of the target gas detector very well. And the announcement of the Sanza life is very accurate.

In the case of the intermittent reference gas detector, the measurement of the reference gas is intermittent and short, and the measurement of the target gas is performed at other times, which leads to more accurate life announcement. Now, assuming that the reference gas is constantly measured in the intermittent reference gas detection unit, since the reference gas is always present in the use environment, the electrochemical reaction constantly occurs on its working electrode, Reaction products continue to be produced.

For example, when the reference gas is oxygen gas,
The reaction O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O occurs, and the generation of water continues. When such a reaction product accumulates in the electrolyte, the sensitivity of the intermittent reference gas detection unit appears, and the aging characteristic differs from that of the target gas detection unit. In view of this, the intermittent reference gas detection unit only measures the reference gas intermittently and suppresses the generation of reaction products. The measurement of the target gas is performed at other times, but this is not for the purpose of detecting the target gas, but for keeping the same operation state as the target gas detection unit including the applied potential. In the meantime, the reaction product generated while detecting the reference gas is spontaneously released to the outside of the electrolyte.
Therefore, the intermittent reference gas detection unit maintains a normal function for a long time, and the temporal characteristics match well with the target gas detection unit.

When the counter electrode and the working electrode of the reference gas detecting portion are formed so as to enter each other in a comb shape, more accurate life notification can be expected. The solid electrolyte of the target gas detection unit is often covered with a coating film (protective film) for protection.
In this case, if the solid electrolyte of the reference gas detecting section is also covered with the protective film, the characteristics over time can be made uniform. However, when the solid electrolyte of the reference gas detection unit is covered with the protective film, reaction products such as water are hardly released and easily accumulate. However, at the working electrode of the reference gas detection unit, a reaction that generates water as described above occurs, but at the counter electrode, a reaction of 2H ₂ O → O ₂ + 4H ⁺ + 4e ⁻ occurs, and water is consumed. When the working electrode and the counter electrode are formed so as to enter each other in a comb shape, the working electrode and the counter electrode are close to each other and face each other, so that water generated at the working electrode easily reaches the counter electrode, and water consumption is promoted. Will not collect. If the working electrode and the counter electrode are far apart, water generated at the working electrode will not easily reach the counter electrode, and water consumption at the counter electrode will not proceed, and water will accumulate.

As described above, when the sensitivity of the target gas detector and the reference gas detector are changed over time and the decrease in sensitivity proceeds in the same manner, the decrease in sensitivity of the reference gas detector with respect to the reference gas does not occur. This also indicates a decrease in the sensitivity of the target gas detector to the target gas. Therefore, when the sensor sensitivity (detection output) of the reference gas detection unit with respect to the reference gas falls below a certain threshold value, the sensor sensitivity of the target gas detection unit with respect to the target gas is regarded as correspondingly reduced. There is no mistake. Therefore, the difference between the notification time notified by the service life notification unit connected to the reference gas detection unit and the true service life is small, and the fact that the service life of the sensor has come is accurately notified.

Further, when the reference gas detecting section and the target gas detecting section are provided in the same element, the reference gas detecting section can be manufactured simultaneously in the same manufacturing process as the target gas detecting section, and the gas sensor and the target gas detecting section can be manufactured simultaneously. Compared with providing a service life detecting means separately, there are added advantages that the structure is much simpler, the manufacturing is easy, the manufacturing cost can be reduced, and the entire gas sensor can be downsized.

[0030]

Next, embodiments of the present invention will be described in detail with reference to the drawings. 1 and 2
1 schematically shows a structural example of an electrochemical gas sensor. In this sensor, first, two sets of electrodes made of platinum, gold, or another electrode material are formed on the surface of one insulating substrate 10. That is, the working electrode 20, the counter electrode 30, and the reference electrode 40 for detecting the gas to be detected, an electrode set for the target gas including three rectangular electrodes, and are disposed so as to face symmetrically with the electrode set, An electrode set for a reference gas including three rectangular electrodes of a working electrode 50, a counter electrode 60, and a reference electrode 70 for detecting a reference gas is provided on the insulating substrate 10.
It is formed on the surface. The electrodes are formed by a normal electrode forming means such as sputtering or vapor deposition, and the structure of each electrode may be the same as that of a normal gas sensor.

Two sets of electrodes 20 to 40 and electrodes 50 to 7
0, the solid electrolyte layers 80 and 8 made of perfluorosulfonate polymer or the like are covered over and between the layers.
2 are formed. The solid electrolyte layers 80 and 82 are formed separately from each other. The materials and forming means of the solid electrolyte layers 80 and 82 may be the same as those of a normal gas sensor. One end of each of the electrodes 20 to 70 extends to the outside of the solid electrolyte layers 80 and 82 and is exposed, and serves as a connection terminal portion 22, 32, 42, 52, 62, 72 for connection to an external circuit.
As described above, on one insulating substrate 10, the target gas detection unit A and the intermittent reference gas detection unit B having exactly the same structure are provided side by side. That is, the target gas detector A and the intermittent reference gas detector B are provided in the same element.

Each of the electrodes 20 to 40 of the target gas detector A is
It is connected to the signal processing circuit unit 100 via the lead wire 102 connected to the terminal units 22 to 42, and the detection signal of the target gas detected by the target gas detection unit A can be taken out and used. It has become. Each of the electrodes 50 to 70 of the intermittent reference gas detection unit B normally measures the target gas and intermittently measures the reference gas via the lead wires 104 connected to the terminal portions 52 to 72. The measuring gas switching means 105 and the life notifying means 110 are connected. The measurement gas switching means 105 alternately changes the potential of the working electrode 50 between a potential for target gas measurement and a potential for reference gas measurement at certain intervals. In addition, the life notifying means 110 monitors the detection output of the reference gas of the intermittent reference gas detection unit B, emits a signal when the detection output becomes less than a certain value, emits a warning sound or turns on a warning lamp. In this way, the user can be notified that the sensor has reached the end of its life. Measurement gas switching means 105 having such a function
And the life notifying means 110 are constituted by the same ordinary electronic circuits as those used in various apparatus and the like.

The sensor operation in the target gas detection section A of the gas sensor having the above structure will be described. The gas component of the gas to be detected penetrates through the surface of the solid electrolyte layer 80 and reaches the working electrode 20, where an electrochemical reaction occurs. At the counter electrode 30, a reaction that forms a pair with the working electrode 20 occurs. As a result, a detection current flows between the working electrode 20 and the counter electrode 30, and detection and quantification of gas components can be performed. The reference electrode 40 functions as a reference for maintaining the potential of the working electrode 20 constant. That is, the potential of the working electrode 20 is maintained at a constant potential corresponding to the gas component to be detected. Such sensor action is
This is exactly the same as in the case of a normal gas sensor.

Next, the life detecting operation of the intermittent reference gas detecting section B will be described. In the intermittent reference gas detection unit B, the same state as that of the target gas detection unit A is normally maintained. However, when the potential of the working electrode 50 is at the potential for measuring the reference gas, oxygen as the reference gas is not used. Then, the solid electrolyte layer 82 passes through the inside from the surface and reaches the working electrode 50, where an electrochemical reaction occurs. At the counter electrode 60, a reaction that forms a pair with the working electrode 50 occurs, and an oxygen detection current flows between the working electrode 50 and the counter electrode 60. The intermittent reference gas detector B can detect oxygen when the potential of the working electrode 50 is maintained at a constant potential corresponding to oxygen with reference to the reference electrode 70. That is, the target gas detection and the reference gas detection are
Only the potential setting at the working electrode is different, and the principle of the flow of the electrochemical reaction and the detection current is exactly the same. As described above, since the measurement of the reference gas is intermittent, water does not accumulate in the solid electrolyte 82 of the intermittent reference gas detector B.

Since oxygen always exists at a constant concentration in the atmosphere, a constant oxygen detection current should always be obtained in the intermittent reference gas detection section B unless the sensor sensitivity changes over time. However, as described above, since the sensor sensitivity of the intermittent reference gas detection unit B decreases with time, the oxygen detection current gradually decreases. The same phenomenon as the temporal change of the detection current (that is, the sensor sensitivity) in the intermittent reference gas detection unit B occurs simultaneously in the target gas detection unit A. Therefore, the detection current (sensor sensitivity) in the intermittent reference gas detection unit B is monitored at appropriate intervals, and if the detection current becomes equal to or less than a predetermined value, it is determined that the life of the sensor, that is, the target gas detection unit A is reached. I just need.

FIGS. 5 and 6 schematically show other structural examples of the electrochemical gas sensor. Even with this sensor,
Two sets of electrodes made of platinum, gold, or another electrode material are formed on the surface of one insulating substrate 10. That is, the working electrode 20, the counter electrode 30, and the reference electrode 40 for detecting the gas to be detected, an electrode set for the target gas including three rectangular electrodes, and are disposed so as to face symmetrically with the electrode set, Working electrode 150, counter electrode 1 for detecting reference gas
60 and electrode sets for the reference gas consisting of three electrodes the reference electrode 170 is what is formed on the surface of the insulating substrate 10.

The working electrode 150 and the counter electrode 160 are respectively
The teeth 150b, 160b are formed in a comb shape including the bases 150a, 160a and the teeth 150b, 160b so as to enter each other, and face closely. 2
Solid electrolyte layers 80 and 82 made of perfluorosulfonate polymer or the like are formed on the pair of electrodes 20 to 40 and electrodes 150 to 170 so as to cover the upper and lower portions, respectively. The solid electrolyte layers 80 and 82 are formed separately from each other. The materials and forming means of the solid electrolyte layers 80 and 82 may be the same as those of a normal gas sensor.

Then, a protective film 181, made of, for example, a fluorine-based resin is covered so as to cover the solid electrolyte layers 80, 82.
182 are formed. The protective films 181 and 182 are formed by a vapor deposition method or a plasma polymerization method. Each electrode 20 to 170
Are connected to the solid electrolyte layers 80 and 82 and the protective film 18.
1, 182, which are extended and exposed to the outside, and have connection terminal portions 22, 32, 42, 152, 16 for connection to an external circuit.
2,172. Thus, the target gas detection unit C and the reference gas detection unit D are provided side by side on one insulating substrate 10. That is, the target gas detector C and the reference gas detector D are provided in the same element.

Each of the electrodes 20 to 40 of the target gas detector C is
It is connected to the signal processing circuit unit 100 via the lead wire 102 connected to the terminal units 22 to 42, and the detection signal of the target gas detected by the target gas detection unit C is taken out and used. It has become. Each of the electrodes 150 to 170 of the reference gas detection unit D is connected to the terminal unit 152 to 172 via a lead wire 104, and the life notification unit 110
Connected to The life notifying means 110 monitors the detection output of the reference gas of the reference gas detection unit D, and emits a signal when the detection output becomes equal to or less than a predetermined value to emit a warning sound or turn on a warning lamp. In addition, it is possible to notify that the sensor has reached the end of its life. The life notifying unit 110 having such a function is configured by a normal electronic circuit or the like similar to that used in various types of equipment.

The sensor operation in the target gas detection section C of the gas sensor having the above-described structure is the same as that shown in FIG. 1 except that the target detection gas passes through the protective film 181 and the solid electrolyte layer 80 and reaches the working electrode 20. The description is omitted because it is the same as the example. The life detecting operation of the reference gas detecting unit D is basically the same as that of the structure example of FIG. 1, but is specifically as follows.

In the reference gas detector D, oxygen as a reference gas permeates through the solid electrolyte layer 82 from the surface of the protective film 182 and reaches the working electrode 150, where an electrochemical reaction occurs. At the counter electrode 160, a reaction that forms a pair with the working electrode 150 occurs, and an oxygen detection current flows between the working electrode 150 and the counter electrode 160. In the reference gas detector D, the working electrode 1
Since the potential of 50 is maintained at a constant potential corresponding to oxygen with reference to the reference electrode 170, oxygen can be detected. That is, the detection of the target gas and the detection of the reference gas are different from each other only in the potential setting at the working electrode. The working electrode 15
As described above, water does not accumulate in the solid electrolyte 82 of the reference gas detector D because the 0 and the counter electrode 160 are comb-shaped and enter each other.

Since oxygen is always present at a constant concentration in the atmosphere, a constant oxygen detection current should always be obtained in the reference gas detection section D if the sensor sensitivity does not change over time. However, as described above, since the sensor sensitivity of the reference gas detection unit D decreases with time, the oxygen detection current gradually decreases. The same phenomenon as the temporal change of the detection current (that is, the sensor sensitivity) in the reference gas detection unit D occurs simultaneously in the target gas detection unit C. Therefore, the detection current (sensor sensitivity) in the reference gas detection unit D is monitored at appropriate intervals, and if the detection current becomes equal to or less than a predetermined value, it is determined that the life of the sensor, that is, the target gas detection unit C is reached. Good.

Next, the results of manufacturing an electrochemical gas sensor having the above-described structure and examining the change over time in the gas detection action will be described. -Example 1-Example 1 corresponds to the structural example of FIG. Insulating substrate 10
A glass plate of 10 mm square was used as a material for. However, in order to increase the adhesion between the substrate and the electrode, a polysilicon layer having a thickness of about 2000 mm was formed on the glass plate by sputtering. Working electrodes 20 and 50 made of platinum, counter electrodes 30 and 60, and reference electrodes 40 and 70 made of gold were formed on the insulating substrate 10 by sputtering. Thereafter, a solution containing 5% by weight of a perfluorosulfonate polymer is cast on each of the electrodes 20 to 40, 50 to 70 and the insulating substrate 10, so that a solid electrolyte layer 80 made of a perfluorosulfonate polymer having a thickness of 3 μm is formed.
82 was formed.

In order to confirm that the gas sensor combined with the target gas detector A and the intermittent reference gas detector B thus manufactured has a sensor function for the target gas and a life detecting function, The change over time in sensor sensitivity to carbon monoxide and oxygen was measured. At this time, the intermittent reference gas detection unit B
According to 5, the measurement of oxygen for 1 hour and the measurement of carbon monoxide for 23 hours were repeated.

For the measurement, a test apparatus shown in FIG. 3 was used.
A gas sensor is accommodated in the measurement chamber 120, and the terminal portions 22 of the electrodes 20 are connected via lead wires 121 to respective potentiostats 122 for the target gas detection unit and the intermittent reference gas detection unit. , 123.
Note that the potentiostat 123 is connected to a measurement gas switching unit 105 so that the intermittent reference gas detector B normally measures the target gas and intermittently measures the reference gas. By the measurement gas switching means 105, the voltage between the working electrode and the reference electrode of the intermittent reference gas detection unit B is set to 0.40 V when measuring the target gas and −0.6 V when measuring the reference gas.
V. In addition, each potentiostat 122, 123
Are connected to recorders 124 and 125, respectively.

Using the test apparatus as described above, the working electrode 20 and the reference electrode 40 of the target gas detector A for detecting carbon monoxide are used.
Is set to 0.40 V, and the applied voltage between the working electrode 50 and the reference electrode 70 of the intermittent reference gas detector B is 0.40 V when measuring the target gas, and − when measuring the reference gas.
The test was performed with the voltage set to 0.6V. The oxygen detection current flowing between the working electrode 50 and the counter electrode 60 of the intermittent reference gas detection unit B was constantly monitored by the recorder 125. Further, the atmosphere in the chamber 120 is replaced with air containing 1000 ppm of carbon monoxide from the state of only air, and at that time, a carbon monoxide detection current flowing between the working electrode 20 and the counter electrode 30 of the target gas detection part A is recorded. Measured at 124. Chamber 1
The measurement was repeated by supplying air containing carbon monoxide at regular time intervals into 20.

The measurement results are approximately as shown in the graph of FIG. 4. The change over time in the sensor sensitivity of the target gas detecting section A for carbon monoxide and the sensor sensitivity of the intermittent reference gas detecting section B for oxygen are almost the same. It turns out that it shows the tendency. Therefore, assuming that the time until the target gas detection unit A reaches the sensor sensitivity at which the function of the sensor cannot be fulfilled is the life, the sensor sensitivity of the intermittent reference gas detection unit B corresponds to the life time of the target gas detection unit A. It has been proved that the sensor life can be detected quickly and reliably by determining that the sensor has reached the end of its life when the sensor sensitivity falls below a certain level and issuing an appropriate warning signal.

Embodiment 2 Embodiment 2 corresponds to the structural example of FIG. Insulating substrate 10
A glass plate of 10 mm square was used as a material for. However, in order to increase the adhesion between the substrate and the electrode, a polysilicon layer having a thickness of about 2000 mm was formed on the glass plate by sputtering. Working electrodes 20 and 150 made of platinum, counter electrodes 30 and 160, and reference electrodes 40 and 170 made of gold were formed on the insulating substrate 10 by sputtering. In order to form the working electrode 150 and the counter electrode 160 in a comb shape, a method of patterning a metal film formed by sputtering by ion milling was used. The interval between the working electrode 150 and the counter electrode 160 is 5 μm, and the width of the tooth portions 150b and 160b is also 5 μm.
m.

Thereafter, a solution containing 5% by weight of the perfluorosulfonate polymer was applied to each of the electrodes 20 to 40, 150 to
The solid electrolyte layers 80 and 82 made of a perfluorosulfonate polymer having a thickness of 3 μm were formed by casting on the substrate 170 and the insulating substrate 10. Subsequently, protective films 181 and 182 made of a polymer of tetrafluoroethylene were formed by plasma polymerization so as to cover the solid electrolyte layers 80 and 82.

In order to confirm that the gas sensor combining the target gas detector C and the reference gas detector D thus manufactured has a sensor function for the target gas and a life detecting function, The change over time of the sensor sensitivity to carbon oxide and oxygen was measured. The test device shown in FIG. 7 was used for the measurement. Measurement chamber 1
A gas sensor is accommodated in the terminal 20, and the terminal portions 22 of the electrodes 20 are connected to the respective potentiostats 122 and 123 for the target gas detecting section and the reference gas detecting section via lead wires 121. did. The potentiostats 122 and 123 have recorders 124 and 1 respectively.
25 are connected.

Using the test apparatus as described above, the working electrode 20 and the reference electrode 40 of the target gas detector C for detecting carbon monoxide are used.
Is set to 0.40 V, and the applied voltage between the working electrode 150 and the reference electrode 170 of the reference gas detector D is set to −
The test was performed with the voltage set to 0.6V. The oxygen detection current flowing between the working electrode 150 and the counter electrode 160 of the reference gas detection unit D was constantly monitored by the recorder 125. Further, the atmosphere in the chamber 120 is replaced with air containing 1000 ppm of carbon monoxide from the state of only air, and at this time, a carbon monoxide detection current flowing between the working electrode 20 and the counter electrode 30 of the target gas detection part C is recorded. Measured at 124. Chamber 1
The measurement was repeated by supplying air containing carbon monoxide at regular time intervals into 20.

The measurement result is also approximately as shown in the graph of FIG.
It can be seen that the sensor sensitivity of the reference gas detection unit D and the sensor sensitivity of the reference gas detection unit D to oxygen with time show almost the same tendency. Therefore, assuming that the time until the target gas detection unit C reaches the sensor sensitivity at which the function of the sensor cannot be fulfilled is the life, the sensor sensitivity of the reference gas detection unit D corresponds to the life time of the target gas detection unit C. It has been proved that the life of the sensor can be detected quickly and reliably by determining that the life of the sensor has expired when the sensor sensitivity falls below a certain level and issuing an appropriate warning signal.

Example 3 Example 3 also corresponds to the structural example of FIG. 5, and is the same as Example 2 except that the protective films 181 and 182 are made of Teflon, which is a fluororesin. The measurement results are also approximately as shown in the graph of FIG. 9. The temporal changes in the sensor sensitivity of the target gas detection unit C for carbon monoxide and the sensor sensitivity of the reference gas detection unit D for oxygen show almost the same tendency. It turns out that it shows.

The present invention is not limited to the above embodiment. For example, in FIG. 1, a structure in which the working electrode and the counter electrode of the intermittent reference gas detection unit are comb-shaped as shown in FIG. 5 is given as another embodiment. In FIG. 5, the reference gas detection unit D shown in FIG. As another embodiment, the structure in which the measurement gas switching means is also connected as described above.

[0055]

According to the above-described electrochemical gas sensor according to the present invention, in addition to the target gas detecting section similar to the ordinary gas sensor, the sensitivity for detecting the reference gas present at a constant concentration in the use environment is detected. The provision of the reference gas detection unit whose change with time is substantially the same as that of the target gas detection unit enables quick and accurate detection of the life of the gas sensor. That is, the gas sensor itself has a function of correctly performing self-diagnosis as to whether or not the life has expired.
As a result, a great deal of labor and time required for inspection work for checking the function of the sensor can be saved, and the cost for maintenance can be greatly reduced. In addition, it is possible to provide a highly reliable gas sensor that can reliably avoid a dangerous situation that occurs when a gas sensor whose life has expired is used as it is.

When the electrolyte is a solid electrolyte, there is an additional advantage that there is no problem of liquid leakage or solvent evaporation.
Also, the reference gas detector is usually connected to measurement gas switching means for measuring the gas to be detected and intermittently measuring the reference gas, or the counter electrode and the working electrode of the reference gas detector are connected. In the case where the electrodes are formed in a comb shape so as to penetrate each other, there is an additional advantage that the reaction product is not accumulated in the working electrode, and the life is more accurately notified.

Further, if the target gas detecting section and the reference gas detecting section have the same structure, there is an advantage that the life can be notified more accurately because the sensitivity change characteristics with time are excellent.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a structural example of an electrochemical gas sensor according to the present invention.

FIG. 2 is a cross-sectional view of a gas detector in the electrochemical gas sensor of FIG.

FIG. 3 is a schematic explanatory view showing a state when a sensor sensitivity is tested in the first embodiment.

FIG. 4 is a graph showing test results of the sensor of Example 1.

FIG. 5 is an overall configuration diagram of another structural example of the electrochemical gas sensor of the present invention.

FIG. 6 is a cross-sectional view of a gas detection unit in the electrochemical gas sensor of FIG.

FIG. 7 is a schematic explanatory view showing a state when a sensor sensitivity is tested in Examples 2 and 3.

FIG. 8 is a graph showing test results of the sensor of Example 2.

FIG. 9 is a graph showing test results of the sensor of Example 3.

[Explanation of symbols]

 A Target gas detector B Intermittent reference gas detector C Target gas detector D Reference gas detector 10 Insulating substrate 20 Working electrode 30 Counter electrode 40 Reference electrode 50 Working electrode 60 Counter electrode 70 Reference electrode 80 Solid electrolyte 82 Solid electrolyte 105 Solid gas switching 105 Means 110 Life notification means 150 Working electrode 160 Counter electrode 170 Reference electrode 181 Protective film 182 Protective film

Continuing from the front page (72) Inventor Noriyuki Yamaga 1048 Kadoma, Kazuma, Osaka Prefecture Matsushita Electric Works, Ltd. (56) References JP-A-5-60727 (JP, A) JP-A-4-43950 (JP, A) JP-A-4-208849 (JP, A) JP-A-4-230843 (JP, A) JP-A-4-43951 (JP, A) JP-A-4-43952 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G01N 27/416

Claims (4)

(57) [Claims] 1. A electrochemical gas sensor having a gas detector comprising connecting a plurality of electrodes in the electrolyte, the gas detector aging of sensitivity is substantially equal two with, one gas detector is the detection target Target gas for continuous gas measurement
A detecting unit for scan-only, other measurement and reference gas of the reference gas and the other gas detector which is present in certain concentration in a use environment
Detection measurement of the target gas is also a detection unit for performing, wherein the other gas detector, the detection output with respect to a reference gas lifetime notification means for issuing an outside a signal from the range defined is connected, further other gases The detection unit always has
Measurement of the reference gas intermittently.
An electrochemical gas sensor to which a measurement gas switching means to be connected is also connected . 2. The electrochemical gas sensor according to claim 1 , wherein the counter electrode and the working electrode of the other gas detecting portion are formed so as to enter each other in a comb shape. 3. One of the electrochemical gas sensor according to claim 1 or 2 gas detector and the other gas detector have the same structure. 4. The method according to claim 1, wherein the electrolyte is a solid electrolyte.
The electrochemical gas sensor of the mounting come to any one of up to three.