JP2813423B2 - Electrochemical gas sensor - Google Patents

Description

Description: 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 that detects an atmospheric gas or the like using an electrochemical reaction.

[Conventional technology]

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.

Examples of the inorganic solid electrolyte include β-alumina, NASICON, lithicon, and stabilized zirconia. However, a fixed electrolyte made of these inorganic substances has a 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.

Examples of the organic solid electrolyte include polymers belonging to a cation exchange resin such as polystyrene sulfonate, polyvinyl sulfonate, perfluorosulfonate polymer, and perfluorocarboxylate polymer. Of these resins, the perfluorosulfonate polymer is
It is widely used as the most practically suitable one, and for example, there is a so-called Nafion (trade name, manufactured by Dipon).

The reason why the above perfluorosulfonate polymer is preferable is that the degree of dissociation of the cation is large, that is, the impedance is small, or it is relatively stable thermally and electrochemically. 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.

[Problems to be solved by the invention]

In an electrochemical gas sensor using a perfluorosulfonate polymer as an electrolyte as described above, the physical property value of the perfluorosulfonate polymer greatly fluctuates depending on environmental conditions such as temperature and humidity, and also changes over time. . For this reason, there has been a problem that the sensitivity of the sensor also fluctuates due to environmental conditions and changes with time, and an accurate detection result cannot be obtained.

In other words, physical properties such as impedance and gas permeability of the perfluorosulfonate polymer, which is an electrolyte connecting the electrodes, have a great effect on the sensitivity of the gas sensor. It appears as a change.

However, as a gas sensor, accurate detection information cannot be obtained unless a constant sensitivity is exhibited for a gas of a constant concentration regardless of the fluctuation of the temperature and humidity or the passage of time as described above. Function cannot be performed sufficiently. Therefore, it has been desired to correct a change in sensor sensitivity due to environmental conditions and aging so as to obtain an accurate detection result.

Therefore, the present inventors have invented an electrochemical gas sensor in which a humidity sensor is incorporated in the sensor separately from the gas sensor element so that sensitivity can be corrected for a change in humidity. We have applied for a patent. However, in the case of this sensor, since a humidity sensor having a different structure and operation from the gas sensor element is incorporated, the structure of the control circuit and the like becomes complicated, the external dimensions of the entire sensor become large, and the cost becomes high. is there. In addition, fluctuations in sensor sensitivity due to humidity can be corrected, but sensitivity correction for temperature and other environmental conditions other than humidity is not performed.

In addition, if a sensor that detects the change of each environmental condition is installed for each different environmental condition, the sensitivity can be corrected for each environmental condition. Would be very complex and very expensive.

Further, in the conventional gas sensor, it is not possible to correct a change in sensitivity of the sensor element over time.

The need to correct the sensitivity of the sensor due to changes in the characteristics of the electrolyte due to fluctuations in environmental conditions or aging is not limited to the case where the above-described perfluorosulfonate polymer is used, and the same applies when various solid electrolytes or liquid electrolytes are used. .

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrochemical gas sensor that can easily and reliably perform sensitivity correction with respect to changes in environmental conditions and aging.

[Means for solving the problem]

In order to solve the above problems, an electrochemical gas sensor according to the present invention is an electrochemical gas sensor that performs a detection action by connecting a plurality of electrodes with an electrolyte. A reference gas detection unit including a set of electrodes and an electrolyte for detecting a gas; and a set for detecting a target gas to be detected which is a gas component contained in the same use environment as the reference gas and different from the reference gas. And a target gas detector comprising an electrolyte and a sensitivity correction means for correcting the output signal of the target gas detector based on the output signal of the reference gas detector.

The electrodes are made of gold, platinum and other common electrode materials,
A plurality of electrodes, which are called a working electrode, a counter electrode, a reference electrode, and the like and have a shape and an arrangement structure corresponding to each function, are set as a set to support a support member such as an insulating substrate. And
The electrodes are connected to each other by covering the electrodes and between them with a solid polymer electrolyte such as a perfluorosulfonate polymer or an inorganic solid electrolyte, or bringing the electrodes into contact with a liquid or gel electrolyte. To form a gas sensor element. The basic structure of these gas sensor elements can be the same as that of a conventional ordinary electrochemical gas sensor.

According to the present invention, two sets of detection units each including the above-described electrode set are provided in one element. First, as a reference gas detection unit, a set of electrodes for detecting a reference gas existing at a certain concentration in a use environment is provided. As the reference gas, for example, when used in the atmosphere, oxygen gas satisfies the above-described conditions and is preferable, but air components other than oxygen gas can be used, and if the use environment is different, The reference gas corresponding to the environment may be selected. In the reference gas detection unit, an applied voltage and the like applied between the working electrode and the reference electrode are set so that the above-described reference gas can be detected. Next, a set of electrodes for detecting a target gas to be detected is provided as a target gas detection unit. The gas to be detected is carbon monoxide, alcohol, hydrogen sulfide, and other various gases, and the voltage applied between the working electrode and the reference electrode is set according to the type of the gas to be detected. deep. It is preferable that the materials and structures of the electrodes and the electrolyte are set so that the reference gas detection unit and the target gas detection unit have the same or substantially the same sensitivity characteristics. For this purpose, the reference gas detection unit and the target gas detection unit may be made of exactly the same dimensions and material, but both have a certain correlation in their sensitivity characteristics and have substantially the same sensitivity. If the characteristics can be exhibited, it is also possible to adopt a material in which the materials of the electrodes are partially different in accordance with the function of each detection unit, the type of gas to be detected, and the like.

An electronic circuit including a power supply circuit for applying a voltage and a detection circuit for detecting a current flowing between the working electrode and the counter electrode are connected to the target gas detection unit and the reference gas detection unit, similarly to a normal electrochemical gas sensor. You. These electronic circuits are
The sensor part may be formed on a different substrate from the insulating substrate, and may be connected with a lead wire or the like, or both the sensor part and the electronic part may be formed on the same substrate.

A sensitivity correction unit is provided in a part of the electronic circuit, for example, by incorporating a sensitivity correction circuit for correcting the output signal of the target gas detection unit based on the output signal of the reference gas detection unit.
The sensitivity correction means may be configured with any electronic circuit or the like as long as the signal can be processed so that accurate detection information of the target gas can be output from the output signal of the target gas detection unit, excluding the influence of environmental conditions and aging. More specifically, the sensitivity characteristics of the target gas detector are measured in advance by the reference gas detector, and the correlation between the sensitivity characteristics of the reference gas detector and the target gas detector is obtained. The sensitivity correction circuit may be designed so that appropriate sensitivity correction is performed.

[Action]

In an electrochemical gas sensor, a gas component is detected by causing an electrochemical reaction at an interface between a working electrode and an electrolyte. Therefore, changes in sensor sensitivity include changes in the rate at which gas components reach the interface between the working electrode and the electrolyte, changes in the reaction rate of the electrochemical reaction, and the reaction products moving to the counter electrode. The occurrence and progress of these phenomena are determined by the configuration of the electrodes and the electrolyte. Therefore, it is possible to make the sensitivity characteristics of the reference gas detection unit substantially equal to the sensitivity characteristics of the target gas detection unit by making the configurations of the electrodes and the electrolyte substantially the same.
In this way, the target gas detection unit and the reference gas detection unit have the same change in sensor sensitivity over time due to changes in various environmental conditions and aging. In other words, the target gas detector and the reference gas detector have a certain correlation with the change in sensor sensitivity.

The reference gas detector detects a reference gas present at a constant concentration in the usage environment. Therefore, if the output signal of the reference gas detector for the constant concentration of the reference gas is continuously monitored, the reference gas detector detects the reference gas. The output signal indicates a change in the sensor sensitivity, and it is possible to know how the sensor sensitivity changes due to environmental conditions and aging. The change in sensor sensitivity in the reference gas detector is, as described above,
Since there is a correlation with the change in the sensor sensitivity of the target gas detector, if the output signal of the target gas detector is corrected based on the output signal of the reference gas detector, the output signal of the target gas detector will be By removing the influence of changes in sensor sensitivity due to conditions and aging, accurate detection information for the target gas can be obtained.

〔Example〕

Next, embodiments of the present invention will be described in detail below with reference to the drawings.

1 and 2 show a schematic structure of an electrochemical gas sensor, in which a plurality of sets of electrodes made of platinum, gold or other electrode materials are formed on the surface of an insulating substrate 10. FIG.
That is, a working electrode 20, a counter electrode 30, and a reference electrode 40 for detecting the detection target gas, an electrode set for the target gas including three rectangular electrodes, and are disposed so as to face the electrode set in contrast to each other, 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 oxygen as a reference gas is provided. 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.

Solid electrolyte layers 80 and 82 made of a perfluorosulfonate polymer or the like are formed on the two sets of electrodes 20 to 40 and electrodes 50 to 70 so as to cover above and between them. The solid electrolyte layers 80 and 82 are formed separately from each other. The materials and forming materials of the solid electrolyte layers 80 and 82 may be the same as those of a normal gas sensor. One end of each electrode 20-70 is a solid electrolyte layer
It is extended and exposed to the outside of 80 and 82, and serves as terminal portions 22, 32, 42, 52, 62 and 72 for connection to an external circuit.
In this manner, the reference gas detection unit B and the target gas detection unit A having exactly the same structure are provided side by side on one green substrate 10.

The target gas detection unit A has a detection circuit unit 100 connected to each of the terminals 22 to 42 via a lead wire 102.
Is connected to the sensitivity correction circuit unit 120. In the reference gas detection section B, a detection circuit section 110 is connected to each terminal section 22 to 42 via a lead wire 104, and the detection circuit section 110 is connected to the sensitivity correction circuit section 120. The detection circuit units 100 and 110
Similarly to a normal gas sensor, power is supplied to the target gas detection unit A and the reference gas detection unit B, and the working electrode 20 and the counter electrode 30 are supplied.
Alternatively, a current flowing between the working electrode 50 and the counter electrode 60 is detected, and the obtained detection signal is output to the sensitivity correction circuit unit 120. The sensitivity correction circuit section 120 corrects the output signal of the target gas detection section A based on the output signal from the reference gas detection section B, and removes the influence of the fluctuation of the sensor sensitivity due to environmental conditions and aging. Output accurate detection information. The sensitivity correction circuit 120 is configured by an appropriate electronic circuit similar to that used in various measuring devices and sensor devices.

The sensor operation of the gas sensor having the above structure will be described. The gas component of the detection target gas passes through the inside from the surface of the solid electrolyte layer 80 to the working electrode in the target gas detection section A.
20 is reached, where the electrochemical reaction takes place. 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, by maintaining the potential of the working electrode 20 at a constant potential corresponding to the gas component to be detected, only the target gas of interest can be detected. Such a sensor operation is exactly the same as that of a normal gas sensor. However, the output signal of the target gas detection unit A includes the influence of changes in environmental conditions such as temperature and humidity or changes in sensor sensitivity over time, and cannot be said to be accurate detection information of the target gas as it is. .

Next, the sensitivity correction operation of the sensor will be described. In the reference gas detection section B, oxygen as a reference gas reaches the working electrode 50 through the surface of the solid electrolyte layer 82 and reaches the working electrode 50, where an electrochemical reaction occurs. In 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. In the reference gas detection unit B, the potential of the working electrode 50 is maintained at a constant potential corresponding to oxygen with reference to the reference electrode 70, so that only oxygen can be detected. That is, in the target gas detection unit A and the reference gas detection unit B, only the potential settings of the working electrodes 20 and 50 are different, and the electrochemical reaction and the principle of the flow of the detection current are exactly the same. The output signal of the reference gas detection unit A thus obtained also includes the influence of fluctuations in environmental conditions such as temperature and humidity or changes in sensor sensitivity over time.

Oxygen is always present at a constant concentration in the atmosphere,
If there is no change in the sensor sensitivity, the reference gas detector B should always obtain a constant detection current, that is, an output signal. However, as described above, since the sensor sensitivity of the reference gas detector B changes with environmental conditions and aging, the output signal also changes. That is, the change in the output signal in the reference gas detection unit B directly indicates the change in the sensor sensitivity. Therefore, if the output signal of the reference gas detection unit B is constantly monitored and the output signal of the target gas detection unit A is corrected based on the output signal of the reference gas detection unit B, that is, the amount of change in the sensor sensitivity. In addition, only the influence of the change in the sensor sensitivity can be removed from the output signal of the target gas detection unit A. Specifically, for example, the output value of the reference gas detection unit B is subtracted from the output value of the target gas detection unit A, or the output value of the reference gas detection unit B is multiplied by an appropriate coefficient. Appropriate arithmetic processing such as dividing or subtracting the output value may be performed, and such arithmetic processing may be performed by the sensitivity correction circuit 120.

Next, the results of manufacturing an electrochemical gas sensor having the above-described structure and measuring a change in environmental conditions and a change in sensitivity over time will be described.

-Example 1-A 10 mm square glass plate was used as a material of the insulating substrate 10.
However, in order to increase the adhesion between the substrate and the electrode, a polysilicon layer having a sputtering thickness of about 2000 mm was formed on the glass plate. Working electrodes 20, 50 made of platinum, counter electrodes 30, 60, and reference electrodes 40, 70 made of gold were formed on the insulating substrate 10 by sputtering. Thereafter, a solution containing 5% by weight of a perfluorosulfonate polymer was cast on each of the electrodes 20 to 70 and the insulating substrate 10 to form solid electrolyte layers 80 and 82 having a thickness of 3 μm.

In order to confirm that the sensor manufactured in this way has a sensor function for a target gas and a sensitivity correction function, a change in sensor sensitivity to carbon monoxide and oxygen was measured.

For the measurement, a test device shown in FIG. 3 was used. The gas sensors were accommodated in the measuring chamber 90, and the terminal portions 22 of the electrodes 20 were connected to the respective potentiostats 92 and 93 for the target gas detecting portion and the reference gas detecting portion via lead wires 91. . Recorders 94 and 95 are connected to the potentiostats 92 and 93, respectively.

Using the test apparatus as described above, the applied voltage is set to 0.45 V between the working electrode 20 and the reference electrode 40 of the target gas detection section A for detecting carbon monoxide, and the reference gas detection section B for detecting oxygen. The applied voltage between the working electrode 50 and the reference electrode 70 was set to -0.4V. 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 95.
In addition, the atmosphere in the chamber 90 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 94. The measurement was repeated while supplying carbon monoxide to the chamber 90 at regular intervals and changing the humidity and temperature variously.

FIG. 4 shows the measurement results when the humidity was changed, FIG. 5 shows the measurement results when the temperature was changed, and FIG. 8 shows the measurement results showing the change over time. A
And the sensitivity characteristic for oxygen in the reference gas detector B show a similar tendency, and it can be seen that there is a certain correlation. The sensitivity correction circuit unit 120 was designed by determining the sensitivity correction coefficient and other conditions from the sensitivity ratio of the target gas detection unit A and the reference gas detection unit B in the above test. A constant output signal was always obtained for carbon monoxide. From this, if the output signal of the target gas detection unit A is corrected based on the output signal of the reference gas detection unit B, accurate detection of the target gas, excluding the effects of sensitivity changes due to temperature, humidity, and aging, can be performed. It was demonstrated that detection information could be obtained.

-Example 2-A gas sensor was manufactured through the same steps as in Example 1 except that gold was used as the material of the working electrode 50 in the reference gas detection unit B.

The same measurement as in Example 1 was performed on the gas sensor manufactured as described above. FIG. 6, FIG. 7, and FIG. 9 show the measurement results. In the case of the second embodiment, although the sensor sensitivity of the reference gas detection unit B to oxygen is lower than that of the first embodiment, the behavior of the sensitivity change is the same as that of the sensitivity change of the sensor sensitivity to carbon monoxide in the target gas detection unit. Similarly, in the case of this gas sensor, it can be seen that the sensitivity can be corrected based on the detection output of the reference gas detection unit B.

〔The invention's effect〕

According to the electrochemical gas sensor according to the present invention described above, in addition to the target gas detection unit similar to a normal gas sensor, the reference gas detection unit that detects a reference gas present at a certain concentration in the use environment is provided. By doing so, it is possible to correct the sensitivity of the output signal of the target gas detection unit, remove the effects of changes in sensor sensitivity over time and environmental conditions, and obtain accurate detection information of the target gas. In addition, it is possible to simultaneously and automatically perform sensitivity correction for all environmental conditions having a correlation between the sensitivity characteristics of the reference gas detection unit and the target gas detection unit. As a result, it is possible to provide a highly reliable gas sensor that has a constant sensitivity regardless of the use environment and the passage of time, and does not depend on the environment or change with time.

Furthermore, since the reference gas detection unit is provided in the same element as the target gas detection unit, the reference gas detection unit can be manufactured simultaneously in the same manufacturing process as the target gas detection unit, and separately from the gas sensor. Compared to incorporating a humidity sensor or the like, the structure becomes much simpler, the manufacturing becomes easier, the manufacturing cost is reduced, and the entire sensor device can be downsized.

[Brief description of the drawings]

1 is an overall configuration diagram of a gas sensor showing an embodiment of the present invention, FIG. 2 is a cross-sectional view of a detection unit, FIG. 3 is a schematic configuration diagram of a sensor sensitivity test apparatus, and FIG. , FIG. 5 is a graph showing a measurement result with respect to a temperature change, FIG. 6 is a graph showing a measurement result with respect to a humidity change of another embodiment, and FIG. 7 is a graph showing a measurement result with respect to a temperature change. FIG. 8, FIG. 8 and FIG. 9 are graphs showing measurement results with respect to the change with time. A: Target gas detector, B: Reference gas detector, 10
Insulating substrate, 20, 30, 40, 50, 60, 70 ... electrodes, 80, 82 ... solid electrolyte, 100, 110 ... detection circuit section, 120 ... sensitivity correction circuit section

Continuation of the front page (72) Inventor Shigemasa Kusanagi 1048 Oji Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works, Ltd. (56) References JP-A-60-200160 (JP, A) (58) Fields investigated .Cl. ⁶ , DB name) G01N 27/26

Claims (1)

(57) [Claims] In an electrochemical gas sensor for performing a detecting action by connecting a plurality of electrodes with an electrolyte, a set of electrodes and an electrolyte for detecting a reference gas present at a certain concentration in a use environment in one element. A reference gas detector,
A target gas detector comprising a set of electrodes and an electrolyte for detecting a target gas to be detected, which is a gas component contained in the same use environment as the reference gas and different from the reference gas, further comprising: An electrochemical gas sensor comprising sensitivity correction means for correcting an output signal of a target gas detection unit based on an output signal of a detection unit.