JP2813424B2 - Electrochemical gas sensor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrochemical gas sensor device, and more particularly, to a gas sensor device 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 element are poor 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 one called Nafion (trade name, manufactured by DuPont).

The reason why the perfluorosulfonate polymer is preferable is that the degree of dissociation of the cation is large, that is, the impedance is small, or that 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 a green 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 scum sensor using a perfluorosulfonate polymer as an electrolyte as described above, the physical property value of the perfluorosulfonate polymer greatly varies 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 main body 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 body is incorporated, the structure of the control circuit and the like becomes complicated, and the external dimensions of the entire device become large, resulting in a high cost. There is. In addition, fluctuations in sensor sensitivity due to humidity can be corrected, but sensitivity cannot be corrected for temperature and other environmental conditions other than humidity.

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 device that can easily and reliably perform sensitivity correction with respect to changes in environmental conditions and aging.

[Means for solving the problem]

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

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 supported as a set by 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 by contacting the electrodes with a liquid or gel electrolyte. To form a gas sensor. The basic structure of these gas sensors can be the same as that of a conventional ordinary electrochemical gas sensor.

According to the present invention, a plurality of gas sensors as described above are provided in one device. First, as a reference gas sensor, a gas sensor 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-mentioned conditions and is preferable.However, air components other than oxygen gas can be used. The selected reference gas may be selected. In the reference gas sensor, an applied voltage or the like applied between the working electrode and the reference electrode is set so that the above-described reference gas can be detected. Next, a gas sensor for detecting a target gas to be detected is provided as a target gas sensor. The gas to be detected includes carbon monoxide, alcohol, hydrogen sulfide, and other various gases.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 sensitivity characteristics of the sensor for the reference gas and the sensor for the target gas are the same or substantially equal. 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 is connected to the sensor for the target gas and the sensor for the reference gas, similarly to a normal electrochemical gas sensor. You. These electronic circuits may be formed on a separate substrate from the insulating substrate forming the above-described sensor portion, and may be connected with a lead wire or the like,
Both the sensor portion and the electronic circuit portion may be formed on the same substrate.

A sensitivity correction means 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 sensor based on the output signal of the reference gas sensor. As sensitivity correction means, any electronic circuit or the like can be used 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 sensor, excluding the influence of environmental conditions and aging. Specifically, the sensitivity characteristics of the reference gas sensor and the target gas sensor are measured in advance, and the correlation between the sensitivity characteristics of the reference gas sensor and the target gas sensor is determined. 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, the sensitivity characteristics of the reference gas sensor can be made substantially equal to the sensitivity characteristics of the target gas sensor by making the configuration of the electrodes and the electrolyte substantially the same. In this manner, the sensor for the target gas and the sensor for the reference gas have the same change in the sensor sensitivity over time due to changes in various environmental conditions and aging. In other words, the target gas sensor and the reference gas sensor have a certain correlation with the change in sensor sensitivity.

Since the reference gas sensor detects a reference gas present at a constant concentration in the usage environment, if the output signal of the reference gas sensor for the reference gas having the constant concentration is continuously monitored, the reference gas sensor can be used. 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. As described above, since the change in the sensor sensitivity of the reference gas sensor is correlated with the change in the sensor sensitivity of the target gas sensor, the output of the target gas sensor is determined based on the output signal of the reference gas sensor. If the signal is corrected, accurate detection information on the target gas can be obtained from the output signal of the target gas sensor by removing the influence of changes in sensor sensitivity due to environmental conditions and aging.

〔Example〕

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

FIG. 1 and FIG. 2 show a schematic structure of an electrochemical gas sensor device, which includes two sets of gas sensors having exactly the same structure, a target gas sensor A and a reference gas sensor B. That is, in each of the gas sensors A and B, a plurality of sets of electrodes made of platinum, gold, and other electrode materials are formed on the surfaces of the insulating substrates 10 and 12. The electrodes consist of three rectangular electrodes, each of a working electrode 20, 50 for detecting a gas to be detected, counter electrodes 30, 60, and reference electrodes 40, 70. 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.

On the electrodes 20 to 40 and the electrodes 50 to 70 of both sensors A and B, solid electrolyte layers 80 and 82 made of perfluorosulfonate polymer or the like are formed so as to cover above and between them. 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 is extended and exposed to the outside of the solid electrolyte layers 80 and 82, and serves as a terminal portion 22, 32, 42, 52, 62, 72 for connection to an external circuit. In this way, the reference gas sensor B and the target gas sensor A having exactly the same electrode structure and electrolyte structure
Are provided side by side.

The sensor A for the target gas has a lead wire 10 connected to each terminal 22 to 42.
2 is connected to the detection circuit unit 100 via the detection circuit unit.
100 is connected to the sensitivity correction circuit unit 120. In the reference gas sensor B, a detection circuit section 110 is connected to each of the terminal sections 22 to 42 via a lead wire 104, and the detection circuit section 110 is connected to the sensitivity correction circuit section 120. Detection circuit 100, 110
Supplies power to the target gas sensor A and the reference gas sensor B as well as the normal gas sensor,
And the current flowing between the working electrode 50 and the working electrode 50 and the counter electrode 60, and the obtained detection signal is
Output to The sensitivity correction circuit section 120 corrects the output signal of the target gas sensor A based on the output signal from the reference gas sensor B, and removes the influence of the target gas excluding the influence of the sensor sensitivity fluctuation 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.

A description will be given of the sensor operation of the target gas sensor A of the gas sensor device having the above-described structure. The gas component of the gas to be detected penetrates the inside from 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. Reference electrode 40 is the working electrode
Serves as a reference to keep the potential of 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 sensor A includes the influence of fluctuations 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 reference gas sensor B will be described. In the reference gas detector B, the solid electrolyte layer
Oxygen as a reference gas reaches the working electrode 50 through the inside of the surface 82 and reaches the working electrode 50, where an electrochemical reaction occurs. Counter electrode 60
As a result, 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 detecting section B, the potential of the working electrode 50 is
Is maintained at a constant potential corresponding to oxygen, so that only oxygen can be detected. That is,
In the target gas sensor A and the reference gas sensor B, the working electrode
The only difference between the potential settings of 20 and 50 is that the principle of the flow of the electrochemical reaction and detection current is exactly the same. The output signal of the reference gas sensor B obtained in this manner also includes the influence of changes 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 the sensor sensitivity does not change, the reference gas sensor 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 sensor B changes with environmental conditions and aging, the output signal also changes. That is, this reference gas sensor B
The change of the output signal in the above indicates the change of the sensor sensitivity as it is. Therefore, the output signal of the reference gas sensor B is constantly monitored, and the output signal of the target gas sensor A is corrected based on the output signal of the reference gas sensor 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 sensor A. Specifically, for example, the output value of the reference gas sensor B is subtracted from the output value of the target gas sensor A, or the output value of the reference gas sensor B is multiplied by an appropriate coefficient before the output value of the target gas sensor A. 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, a description will be given of a result of manufacturing an electrochemical gas sensor device having the above-described structure and measuring a change in environmental conditions and a change in sensitivity over time.

-Example 1-10 mm square glass plates were used as the materials of the insulating substrates 10 and 12, respectively. 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 by sputtering, counter electrodes 30 and
Reference electrodes 40 and 70 made of 60 and gold, respectively, were produced.
Thereafter, 5% by weight of perfluorosulfonate polymer was added.
Containing solution, each electrode 20-40, 50-70 and insulating substrate 10,12
The solid electrolyte layers 80 and 82 having a thickness of 3 μm were formed by casting on the substrate.

In order to confirm that the sensor device combining the target gas sensor A and the reference gas sensor B manufactured in this way has a sensor function and a sensitivity correction function for the target gas, carbon monoxide and carbon monoxide were used. The change in sensor sensitivity to oxygen was measured.

For the measurement, a test device shown in FIG. 3 was used. The sensor device was housed in the measurement chamber 90, and the terminal portions 22 of the electrodes 20 were connected to the potentiostats 92 and 93 of the target gas sensor and the reference gas sensor 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 between the working electrode 20 and the reference electrode 40 of the target gas sensor A for detecting carbon monoxide is set to 0.45 V, and the reference gas sensor B for detecting oxygen is set. The applied voltage between the working electrode 50 and the reference electrode 70 was set to -0.4V. The working electrode 50 and the counter electrode 60 of the reference gas sensor B
The oxygen detection current flowing between them is constantly monitored by the recorder 95. Further, the atmosphere in the chamber 90 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 sensor A at this time is recorded. Measured at 94. In the chamber 90, carbon monoxide is supplied at regular intervals,
The measurement was repeated with various changes in humidity and temperature.

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. In each case, the sensor for the target gas was used. The sensitivity characteristic to carbon monoxide in A and the sensitivity characteristic to oxygen in the reference gas sensor B show a similar tendency, and it is understood 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 ratio of the sensitivity of the target gas sensor A and the reference gas sensor 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 sensor A is corrected based on the output signal of the reference gas sensor B, an accurate detection of the target gas, excluding the influence of the sensitivity change due to temperature, humidity, and aging, is performed. It was demonstrated that detection information could be obtained.

-Example 2 A sensor device 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 sensor B for reference gas.

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

〔The invention's effect〕

According to the electrochemical gas sensor device according to the present invention described above, in addition to a target gas sensor similar to a normal gas sensor, a reference gas sensor that detects a reference gas present at a certain concentration in a use environment is provided. By providing the sensor, the sensitivity of the output signal of the target gas sensor is corrected, and the effects of changes in sensor sensitivity over time and environmental conditions are removed.
Accurate detection information of the target gas can be obtained. In addition, sensitivity correction can be performed simultaneously and automatically for all environmental conditions having a correlation between the sensitivity characteristics of the reference gas sensor and the target gas sensor. as a result,
Always has a certain sensitivity regardless of the use environment and time lapse,
A highly reliable gas sensor device that does not depend on the environment or change over time can be provided.

Furthermore, since the basic structure of the sensor for reference gas and the sensor for target gas are the same, they can be manufactured in a common manufacturing process, and operation and control during use can be performed in common. Is much simpler to manufacture, easier to manufacture, lowers manufacturing costs,
It is possible to reduce the size of the entire sensor device.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a sensor device showing an embodiment of the present invention, FIG. 2 is an end view of a sensor portion, FIG. 3 is a schematic configuration diagram of a sensor sensitivity test device, and FIG. FIG. 5 is a graph showing the result of measurement with respect to temperature change, FIG. 6 is a graph showing the result of measurement with respect to humidity change of another embodiment, and FIG. 7 is a graph showing the result of measurement with respect to temperature change. 8 and 9 are graphs showing measurement results with time. A: Target gas sensor, B: Reference gas sensor, 1
0,12 …… insulating substrate, 20,30,40,50,60,70 …… electrodes, 80,82
…… Solid electrolyte, 100,110 …… Detection circuit part, 120 …… Sensitivity correction circuit part

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 27/26

Claims (1)

(57) [Claims] 1. An apparatus provided with an electrochemical gas sensor for performing a detecting action by connecting a plurality of electrodes with an electrolyte,
A reference gas sensor for detecting a reference gas present at a certain concentration in a use environment, and a target 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. An electrochemical gas sensor device comprising: a gas sensor; and sensitivity correction means for correcting the output signal of the target gas sensor based on the output signal of the reference gas sensor.