JPH0618475A - Electrochemical gas sensor - Google Patents

Abstract

PURPOSE:To provide an electrochemical gas sensor free from the influence of surrounding humidity and having the capability of keeping a solid electrolytic film 9 in a moisture-containing state suitable for maintaining electrolyte. CONSTITUTION:This sensor is constituted of a sensor element 6 and a sheet 8 having water absorptivity. In addition, the sensor element 6 is constituted of an electrode group 5 including a working electrode 2 and a counter electrode 3 arranged on an insulation substrate 1 having moisture permeability, and a solid electrolytic film 9 to become electrolyte in moisture content state. The sheet 8 having water absorptivity is laid at the opposite side of the film 9 via the substrate 1.

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 specifically, to an insulating substrate provided with a plurality of electrodes including a working electrode and a counter electrode, and further comprising a solid electrolyte membrane for coating these electrodes in series. The present invention relates to an electrochemical gas sensor for detecting a test gas, such as carbon monoxide, hydrogen, alcohol, or nitrogen oxide, contained in an atmosphere by utilizing an electrochemical reaction of gas occurring on a pole and a counter electrode.

[0002]

2. Description of the Related Art As disclosed in, for example, JP-A-53-115293 and JP-A-64-88354, a plurality of electrodes are formed on an insulating substrate and these electrodes are formed by a solid electrolyte membrane. The electrochemical gas sensor configured by coating detects the test gas in the atmosphere by using the test gas that occurs at the electrode, for example, the current that flows with the electrochemical reaction of carbon monoxide, hydrogen, alcohol, nitrogen oxides, etc. It can be used in a wide range of fields such as fire alarm, industrial, environmental protection.

Here, the conventional electrochemical gas sensor will be specifically described with reference to FIG. 3. In this electrochemical gas sensor, a working electrode 2 is provided on an insulating substrate 1, and a counter electrode in which a current flows between the working electrode 2 and the working electrode 2. 3 and a reference electrode 4 serving as a reference potential for the working electrode 2, and these electrode groups 5 are covered with a solid electrolyte membrane 9 serving as an electrolyte in a water-containing state, and carbon monoxide, hydrogen, alcohol, nitrogen oxidation When a test gas such as a substance passes through the solid electrolyte membrane 9 covering the working electrode 2 and reaches the working electrode 2, an electrochemical reaction occurs in the working electrode 2. In the counter electrode 3, a reaction that is paired with this reaction occurs, and as a result, the action of the electrolyte of the solid electrolyte membrane 9 causes a current to flow between the working electrode 2 to which a voltage is applied and the counter electrode 3. In this case, the reference electrode 4 maintains the set working electrode 2 at a constant potential. When the above-mentioned current flowing between the working electrode 2 and the counter electrode 3 is input to an external device connected to the electrochemical gas sensor as an output signal for detecting the gas to be detected, the optical and audio means of this external device and other The presence of the test gas is notified by the display means.

The electrochemical gas sensor using the above-mentioned solid electrolyte membrane 9 plays a role of ionic conductivity by the action of water contained in the solid electrolyte membrane 9. If the ambient humidity decreases, the water content of the solid electrolyte membrane 9 decreases, so the ion conductivity decreases, the sensitivity of the sensor decreases, and conversely, if the ambient humidity becomes abnormally high, the solid electrolyte membrane 9 decreases. Since the water content of (1) becomes excessively high, there is a drawback that the electrochemical gas sensor excessively reacts and causes a false alarm. Therefore, an example of the use of the conventional electrochemical gas sensor for eliminating this drawback is shown in FIG.
A water storage tank 20 is attached to the housing 10 for accommodating the water, and the water stored in the water storage tank 20 is used to replenish the housing 10 with steam to maintain the electrolyte of the solid electrolyte membrane 9 inside the housing 10. It is known to maintain the required water content. However, it cannot be said that the use mode of the electrochemical gas sensor is sufficient, and the effect of ambient humidity is further reduced by increasing the humidity control effect on the solid electrolyte membrane 9 to stabilize the solid electrolyte membrane 9 at an appropriate humidity. Therefore, the ability to hold it is required.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned facts, and its object is to reduce the influence of ambient humidity to a solid state in a water-containing state suitable for maintaining an electrolyte. An object is to provide an electrochemical gas sensor capable of holding the electrolyte membrane 9.

[0006]

An electrochemical gas sensor according to the present invention includes (1) an electrode group 5 including a working electrode 2 and a counter electrode 3 provided on an insulating substrate 1 having moisture permeability, and an electrode group 5 including the electrode group 5. The sensor element 6 is composed of a solid electrolyte membrane 9 which is coated and becomes an electrolyte in a water-containing state, and (2) a sheet 8 having water absorption formed integrally with the sensor element 6, and (3) It is characterized in that the water-absorbent sheet 8 is provided on the opposite side of the solid electrolyte membrane 9 with the insulating substrate 1 interposed therebetween.

[0007]

According to the present invention, when the ambient humidity decreases,
Since the insulating substrate 1 has moisture permeability, the moisture contained in the sheet 8 having water absorbency becomes water vapor, and the insulating substrate 1 permeates the insulating substrate 1 to reach the solid electrolyte membrane 9 so as to be in a proper water content state for maintaining an electrolyte. Become. When the solid electrolyte membrane 9 absorbs excessive moisture, the moisture of the solid electrolyte membrane 9 permeates the insulating substrate 1 and is absorbed by the sheet 8. In any case, moisture is reversibly transferred between the solid electrolyte membrane 9 and the sheet 8 through the insulating substrate 1, and the humidity control effect on the solid electrolyte membrane 9 is enhanced.

The present invention will be described in detail below. FIG. 1 is a sectional view showing an electrochemical gas sensor according to the present invention.

The electrochemical gas sensor of the present invention has a sensor element 6. The sensor element 6 includes an insulating substrate 1 having moisture permeability, a working electrode 2 and a counter electrode 3 provided on the insulating substrate 1.
And an electrode group 5 including the reference electrode 4, and a solid electrolyte membrane 9 which covers the electrode group 5 and serves as an electrolyte in a water-containing state. The moisture-permeable insulating substrate 1 is, for example,
A porous substrate having air holes that communicate with the front and back is used. This porous substrate may be a ceramic substrate made of alumina or the like, a silicon substrate that has been subjected to an oxidation treatment, or a substrate that is made by curing a resin, etc., with fine ventilation holes provided on the front and back sides by post processing, or may be a substrate such as cotton or paper. A substrate obtained by laminating a resin on a porous base material to the extent that the porosity does not disappear may be used. The electrode group 5 is made of an electrode material such as platinum or gold, and can be formed by various methods such as sputtering and vapor deposition. As the solid electrolyte membrane 9, polystyrene sulfonate, polyvinyl sulfonate, perfluorosulfonate polymer, perfluorocarboxylate polymer, or the like is used, and among them, a stable perfluorosulfonate polymer (trademark Nafion manufactured by DuPont) is suitable as an electrolyte. .

When a certain amount or more of the test gas that has passed through the solid electrolyte membrane 9 reaches the working electrode 2, the working electrode 2 and the counter electrode 3
An electrochemical reaction occurs at. As a result, a current flows through the working electrode 2 and the counter electrode 3 according to the applied voltage between the working electrode 2 and the reference electrode 4. This current is input to the external device as a signal of the sensor element 6. In order to prevent the deterioration of the solid electrolyte membrane 9 over time, which causes a decrease in sensitivity, a protective film such as a fluorine-based resin, for example, a plasma polymer of tetrafluoroethylene may be formed on the surface of the solid electrolyte membrane 9. Good.

The electrochemical gas sensor of the present invention comprises the sensor element 6 and a sheet 8 having a water absorbing property. The water-absorbent sheet 8 is attached to the opposite side of the solid electrolyte membrane 9 with the insulating substrate 1 interposed therebetween. The water-absorbing sheet 8 is formed by fixing, for example, a water-absorbing polymer on a base material. Examples of the water-absorbing polymer include polysaccharides such as starch and cellulose, polyacrylates,
Polymers such as polyvinyl alcohol and polyacrylamide are used, and as a base material for fixing these polymers, woven fabrics, non-woven fabrics, or mats made of inorganic fibers such as glass or organic synthetic fibers such as polyester or natural fibers are used. . The sheet 8 retains a large amount of water of several hundred to several thousand times in weight ratio with respect to the polymer contained in the sheet 8, and in order to enhance the water replenishing effect on the solid electrolyte membrane 9, the sheet is optionally used. It becomes possible by increasing the amount of the polymer contained in.

The operation of the water-absorbent sheet 8 will be described in more detail. When the humidity around the sensor element 6 decreases and the solid electrolyte membrane 9 lacks water, the insulating substrate 1 has moisture permeability, so The moisture contained in the sheet 8 having the property turns into water vapor, permeates the insulating substrate 1 and reaches the solid electrolyte membrane 9, and the solid electrolyte membrane 9 is in a water containing state suitable for maintaining the electrolyte. Further, when the humidity around the sensor element 6 becomes excessively high and the water content of the solid electrolyte membrane 9 is excessive, the water content of the solid electrolyte membrane 9 permeates the insulating substrate 1 to reach the sheet 8, and the solid electrolyte membrane 9 becomes It is kept at an appropriate humidity. In either case, the movement of water is reversibly performed between the solid electrolyte membrane 9 and the sheet 8 through the insulating substrate 1,
The humidity control effect on the solid electrolyte membrane 9 is enhanced. as a result,
The influence of ambient humidity is further reduced, and the solid electrolyte membrane 9 is stably maintained at an appropriate humidity.

An example of using the electrochemical gas sensor of the present invention is shown in FIG. The electrochemical gas sensor of the present invention is housed in the housing 10 and optimally exhibits the detection function of the test gas. In other words, the housing 10 prevents contaminants from the outside air from adhering to the solid electrolyte membrane 9, and the test gas is introduced through the ventilation hole 11 provided in the housing 10.
When this test gas reaches the working electrode 2, an electrochemical reaction occurs in the working electrode 2 and the counter electrode 3, and a current flows to the working electrode 2 and the counter electrode 3 according to the applied voltage between the working electrode 2 and the counter electrode 3 and the amount of the test gas. Flows. It is connected to the electrode group 5 via a lead wire 7, and this current is input to an external device including a report as an output signal of the electrochemical gas sensor. When it is necessary to artificially replenish the water-absorbent sheet 8 with water, for example, a water replenishing port provided in the housing 10 is used, or other various methods are adopted.

[0014]

EXAMPLES Examples and comparative examples of the present invention will be given below.

Example 1 A porous glass substrate is used as an insulating substrate 1, and a working electrode 2 made of platinum is formed on the insulating substrate 1 by sputtering.
A counter electrode 3 and a reference electrode 4 made of gold were formed to form an electrode group 5. On the electrode group 5, a solution containing 5% by weight of a perfluorosulfonate polymer was cast to cover the solid electrolyte membrane 9 in series to form a sensor element 6. As the water-absorbent sheet 8, the dispersed starch-based water-absorbing polymer was fixed on a glass non-woven fabric at about 1 mg / cm ² and contained about 1000 times as much water as the polymer. The water-absorbing sheet 8 is used as the solid electrolyte membrane 9 of the insulating substrate 1.
It was attached to the side opposite to the above, and was housed in the housing 10 as an electrochemical gas sensor.

The potential of the working electrode 2 is set to 0.40 V with respect to the reference electrode 4, and the relative humidity is 20%, 40%, 60%.
%, 80%, and 95% of CO gas 1
The sensitivity to 00 ppm was measured by the potentiostatic electrolysis method. The results are shown in Table 1, and the maximum between the working electrode 2 and the counter electrode 3 is 9
A current value of 1.6 nA to a minimum of 88.4 nA was shown.

Example 2 A porous alumina substrate was used as the insulating substrate 1, and Example 1 was used.
A sensor element 6 was manufactured in the same manner as in. As the water-absorbent sheet 8, the dispersed polyacrylate polymer was fixed on a glass non-woven fabric at about 2.5 mg / cm ² and contained about 300 times as much water as the polymer. Thereafter, as in Example 1, a sheet 8 having water absorbency was attached to the opposite side of the insulating substrate 1 from the solid electrolyte membrane 9, and this was housed in a housing 10 as an electrochemical gas sensor. Furthermore, the potential of the working electrode 2 is set to 0.40 V with respect to the reference electrode 4, and the sensitivity to 100 ppm of CO gas is determined for 5 points of relative humidity 20%, 40%, 60%, 80%, and 95%. It was measured by the potential electrolysis method. The results are shown in Table 1, and the maximum between the working electrode 2 and the counter electrode 3 is 93.8 nA to the minimum 89.5 nA.
The current value of A is shown.

[0018]

[Comparative example]

Comparative Example 1 The same porous alumina substrate as in Example 2 was used as the insulating substrate 1, and a sensor element 6 was produced in the same manner as in Example 1. The sensor element 6 is housed in the housing 10 as an electrochemical gas sensor, the potential of the working electrode 2 is set to 0.40 V with respect to the reference electrode 4 as in the first embodiment, and the relative humidity is 20.
%, 40%, 60%, 80%, and 95%, the sensitivity to 100 ppm of CO gas was measured by the potentiostatic electrolysis method. As a result, as shown in Table 1, a current value between the working electrode 2 and the counter electrode 3 was 120.4 nA at maximum and 10.5 nA at minimum.

As is clear from Examples 1 and 2 and the comparative example, the sensitivity of the electrochemical gas sensor according to the comparative example was greatly influenced by the high and low of the surrounding humidity.
The sensitivity of the electrochemical gas sensor according to the present invention was stable because the influence of ambient humidity was mitigated.

[0020]

[Table 1]

[0021]

According to the present invention, the sensor element 6 is additionally provided with the water-absorbing sheet 8 so that the influence of ambient humidity is mitigated and the solid electrolyte membrane 9 is held in a water-containing state suitable for maintaining the electrolyte. I was able to.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an electrochemical gas sensor according to the present invention.

FIG. 2 is a cross-sectional view showing an example of use of an electrochemical gas sensor according to the present invention.

FIG. 3 is a cross-sectional view showing a conventional electrochemical gas sensor.

FIG. 4 is a cross-sectional view showing a conventional usage example of the electrochemical gas sensor of FIG.

[Explanation of symbols]

 1 Insulating Substrate 2 Working Electrode 3 Counter Electrode 4 Reference Electrode 5 Electrode Group 6 Sensor Element 7 Lead Wire 8 Sheet 9 Solid Electrolyte Membrane 10 Housing 11 Vent

Claims (2)

[Claims] (1) An electrode group 5 including a working electrode 2 and a counter electrode 3 provided on an insulating substrate 1 having moisture permeability, and this electrode group 5.
And a solid electrolyte membrane 9 serving as an electrolyte in a water-containing state, and (2) this sensor element 6
And a water-absorbing sheet 8 integrally formed with the sheet, and (3) the water-absorbing sheet 8 is attached to the opposite side of the solid electrolyte membrane 9 with the insulating substrate 1 interposed therebetween. Electrochemical gas sensor. 2. The electrochemical gas sensor according to claim 1, wherein (1) the water-absorbent sheet 8 comprises a base material and a water-absorbing polymer fixed to the base material.