JPH0611478A - Electrochemical gas sensor and its manufacture - Google Patents

Abstract

PURPOSE:To provide an electrochemical gas sensor and a method of manufacture of the same, whose sensitivity is stable against secular change, by forming a solid electrolyte film which is free from exfoliation of or crack initiation in the solid electrolyte film and which is equipped with a surface having ion conductivity holding effect. CONSTITUTION:An electrochemical gas sensor concerned is equipped with a bunch 8 of electrodes installed on an insulative base board 1 and a solid electrolyte film 9 which covers this electrode bunch 8 in continuity, wherein the solid electrolyte film 9 consists in a gradient film in which the fluorine content is substantially incremental over the surfaces from the electrode bunch 8 to the solid electrolyte film 9. The solid electrolyte film 9 is plasma polymerized according to the rate at which fluoric monomers A are gradually incremental relative to monomers B having functional group giving ion conductivity from the electrode bunch 8.

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 a method for producing the same, more specifically, a plurality of electrodes including working electrodes are provided on an insulating substrate, and a solid electrolyte membrane is provided to cover these electrodes in series. Included in the atmosphere by utilizing the electrochemical reaction of gas that occurs on the working electrode and the counter electrode,
For example, the present invention relates to an electrochemical gas sensor that detects a test gas such as carbon monoxide, hydrogen, alcohol, and nitrogen oxide, and a manufacturing method thereof.

[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.

A conventional electrochemical gas sensor is shown in FIG. 3, which serves as a working electrode 2 on an insulating substrate 1, a counter electrode 3 through which a current flows between the working electrode 2, and a reference potential for the working electrode 2. The electrode group 8 is provided with a pole 4, and the electrode group 8 is covered with a solid electrolyte membrane 9. In order to retain the electrolyte of the solid electrolyte membrane 9 for a long period of time, the solid electrolyte membrane 9 is further covered with a protective film 10 having air permeability. There is. As a material of the solid electrolyte membrane 9, polystyrene sulfonate of an electrolyte,
Polyvinyl sulfonate, perfluoro sulfonate polymer, perfluoro carboxylate polymer and the like are known. Among them, perfluoro sulfonate polymer (trademark Nafion manufactured by DuPont) is practical and these materials are used on the insulating substrate 1. Then, the electrode group 8 is covered in series by casting. Protective film 1
As the material of 0, a film made of a fluorine-based polymer having water repellency is used. In this configuration, the solid electrolyte membrane 9
Since there is a difference in expansion coefficient between the protective film 10 and the protective film 10 with respect to changes in temperature and humidity, the protective film 10 is peeled or cracked from the solid electrolyte membrane 9, and the electrolyte of the solid electrolyte membrane 9 is retained by the protective film 10. However, the ionic conductivity of the solid electrolyte membrane 9 is unavoidably deteriorated over time, and as a result, the detection sensitivity of the electrochemical gas sensor is deteriorated.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is not to cause peeling or cracking and to have an effect of maintaining ion conductivity. An object of the present invention is to provide an electrochemical gas sensor having a time-dependent stability of detection sensitivity by forming a solid electrolyte membrane having a surface, and a method for producing the same.

[0005]

An electrochemical gas sensor according to claims 1 and 2 of the present invention comprises an electrode group 8 including a working electrode 2 and a counter electrode 3 provided on an insulating substrate 1, and an electrode group 8 of the electrode group 8.
And a solid electrolyte membrane 9 formed by covering the solid electrolyte membrane 9 in series, and the solid electrolyte membrane 9 is composed of a gradient membrane in which the fluorine content substantially increases from the electrode group 8 to the surface of the solid electrolyte membrane 9. Furthermore, the solid electrolyte membrane 9 is characterized by being composed of a fluorine-based polymer having ion conductivity.

In the method of manufacturing an electrochemical gas sensor according to a third aspect of the present invention, a fluorine-based monomer A that is plasma-polymerized alone in the electrode group 8 and a monomer B having a functional group that is polymerized with the fluorine-based monomer A are used. The solid electrolyte membrane 9 is formed of a polymer having ion conductivity, which is generated by plasma polymerization of the fluorine-based monomer A with respect to the monomer B in a sequentially increasing ratio.

[0007]

According to the present invention, the solid electrolyte membrane 9 is composed of an inclined membrane in which the content of fluorine increases substantially from the electrode group 8 to the surface, so that the electrode group 8 of the solid electrolyte membrane 9 is formed.
There is no boundary surface that causes a rapid composition change between the surface and the surface side. Therefore, the expansion coefficient due to changes in temperature and humidity is not significantly different in the thickness direction, so that peeling or cracking does not occur in the solid electrolyte membrane 9. Moreover, since the surface of the solid electrolyte membrane 9 is made of a water-repellent fluorine-based polymer, it has water repellency.

According to the manufacturing method of the present invention, the solid electrolyte membrane 9 comprises a fluorine-based monomer A which is plasma-polymerized alone and a monomer B which is polymerized with the fluorine-based monomer A and has a functional group imparting ion conductivity. The gradient film in which the fluorine content is substantially increased is formed by preparing the electrode group 8 by plasma polymerization so that the ratio of the fluorine-based monomer A to the monomer B is sequentially increased. Therefore, the ionic conductivity is high on the electrode group 8 side, and the surface is provided with water repellency, and the solid electrolyte membrane 9 in which the composition does not change suddenly can be obtained.

The present invention will be described in detail below. 1 is a cross-sectional view of an electrochemical gas sensor of the present invention, and FIG. 2 is FIG.
FIG.

As shown in FIGS. 1 and 2, this electrochemical gas sensor has an electrode group 8 formed on an insulating substrate 1 and including a working electrode 2, a counter electrode 3 and a working electrode 4. Working pole 2
Causes a redox reaction associated with the electrochemical reaction when the test gas comes into contact with the reaction gas. At the same time, a redox reaction paired with the reaction in the working electrode 2 occurs in the counter electrode 3, and the reference electrode 4 and the working electrode 2 counter electrode. It functions as a reference potential for the redox reaction of 3. Here, the insulating substrate 1 is a ceramic substrate such as alumina or a silicon substrate subjected to oxidation insulation treatment, and the working electrode 2, the counter electrode 3 and the reference electrode 4 are ordinary electrode materials such as platinum or gold. The electrode group 8 is a solid electrolyte except terminals 21 of the working electrode 2, a terminal 31 of the counter electrode 3 and a terminal 41 of the reference electrode 4 which are connected to an external device for signal processing and which are formed at each end of the electrodes. A series of coatings is provided by the membrane 9. The solid electrolyte membrane 9 is composed of an inclined membrane in which the content of fluorine increases substantially from the electrode group 8 to the surface. Here, the gradient film that substantially increases means that the fluorine content on the surface of the electrode group 8 of the solid electrolyte membrane 9 is relatively increased when it is compared, and is not necessarily continuous. It does not mean that the fluorine content increases. The solid electrolyte membrane 9 is made of, for example, a fluorinated polymer having ion conductivity. More specifically, a plasma polymer of a fluorine-based monomer A and a monomer B having a functional group that polymerizes with the fluorine-based monomer A and imparts ion conductivity is applied to the fluorine-based polymer.

Explaining the essential functions of the electrochemical gas sensor thus constructed, carbon monoxide, hydrogen,
When a test gas such as alcohol or nitrogen oxide 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. The current flowing between the working electrode 2 and the counter electrode 3 is input to the external device as an output signal for detecting the test gas. The presence of the test gas is notified by the optical and audio means of this external device and other display means.

The manufacturing method of the present invention will be described below by taking the above electrochemical gas sensor as an example.

The working electrode 2, the counter electrode 3 and the working electrode 4 are formed on the surface of the insulating substrate 1 by depositing an electrode material in a thin film by, for example, sputtering.
There is no limitation on the means for forming 3, 4 on the insulating substrate 1. The solid electrolyte membrane 9 that covers these electrode groups 8 is plasma-polymerized with a fluorine-based monomer A that is plasma-polymerized alone and a monomer B that has a functional group that imparts ion conductivity by polymerizing with the fluorine-based monomer A. It is composed of a gradient film.
The fluorine-based monomer A is not only a different monomer but also a monomer that deposits a fluorine-based polymer by plasma polymerization alone. As the fluorine-based monomer A,
Specifically, tetrafluoroethylene, hexafluoropropylene, trifluoromonochloroethylene or the like is used. As the monomer B, trifluoromethanesulfonic acid, benzenesulfonic acid, derivatives thereof, or the like are used. The solid electrolyte membrane 9 is prepared by adjusting the ratio of the liquid amounts of the fluorine-based monomer A and the monomer B so that the fluorine-based monomer A gradually increases with time from the electrode group 8 to the monomer B. , Plasma polymerization is performed.

[0014]

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

Example 1 A silicon substrate was used as an insulating substrate 1, and a working electrode 2 made of platinum, a counter electrode 3 and a reference electrode 4 made of gold were formed on this surface by sputtering to form an electrode group 8. In order to remove the water adhering to the electrode group 8 and the insulating substrate 1, it was exposed to plasma for 10 minutes in an argon atmosphere. Next, hexafluoropropylene is used as the fluorine-based monomer A, and trifluoromethanesulfonic acid having a sulfone group as a functional group is used as the monomer B to deposit a polymer by plasma polymerization, and the electrode group 8 is coated in series. The solid electrolyte membrane 9 was formed. The conditions for plasma polymerization of the solid electrolyte membrane 9 are as follows. The solid electrolyte membrane 9 is formed while changing the liquid amount of trifluoromethanesulfonic acid over time, and the fluorine content from the electrode group 8 to the surface is increased. Was ramped to increase substantially over -Radio frequency output: 25 W-Chamber pressure: 1.7 Pa-Plasma polymerization time: 180 minutes-Monomer flow rate: As shown below. Order Execution time Trifluoromethanesulfonic acid amount Hexafluoropropylene amount 1 60 minutes 0.50 cc / min 5.0 cc / min 2 10 minutes 0.45 cc / min 5.0 cc / min 3 10 minutes 0.40 cc / min 5.0 cc / min 4 10 minutes 0.30 cc / min 5.0 cc / min 5 10 minutes 0.20 cc / min 5.0 cc / min 6 10 minutes 0.10 cc / min 5.0 cc / min 7 10 minutes 0.05 cc / min 5. 0 cc / min 8 60 minutes 0 cc / min 5.0 cc / min The obtained electrochemical gas sensor was immersed in water at 70 ° C. for 1 hour, and the appearance of the solid electrolyte membrane 9 was visually confirmed. No peeling or cracking was observed at all.

Example 2 Example 1 was repeated except that, as in Example 1, the film was exposed to plasma in an argon atmosphere for 10 minutes to remove water, and then tetrafluoroethylene was used as the fluorine-based monomer A.
The solid electrolyte membrane 9 was formed by plasma polymerization under the same conditions as in.

The electrochemical gas sensor obtained was used in Example 1.
In the same manner as above, immersing in water at 70 ° C for 1 hour, the solid electrolyte membrane 9
When the appearance of the above was visually confirmed, neither peeling nor cracking in the solid electrolyte membrane 9 was observed at all.

Example 3 As in Example 1, except that trifluoromonochloroethylene was used as the fluorinated monomer A after exposure to plasma for 10 minutes in an argon atmosphere to remove water.
The solid electrolyte membrane 9 was formed by plasma polymerization under the same conditions as in Example 1.

The electrochemical gas sensor obtained was used in Example 1.
In the same manner as above, immersing in water at 70 ° C for 1 hour, the solid electrolyte membrane 9
When the appearance of the above was visually confirmed, neither peeling nor cracking in the solid electrolyte membrane 9 was observed at all.

Example 4 As in Example 1, after exposure to plasma for 10 minutes in an argon atmosphere to remove water, trifluoromonochloroethylene was used as the fluorine-based monomer A, and benzenesulfonic acid was used as the monomer B. The solid electrolyte membrane 9 was formed by plasma polymerization under the same conditions as in Example 1 except that the above was used.

The electrochemical gas sensor obtained was used in Example 1.
In the same manner as above, immersing in water at 70 ° C for 1 hour, the solid electrolyte membrane 9
When the appearance of the above was visually confirmed, neither peeling nor cracking in the solid electrolyte membrane 9 was observed at all.

Example 5 As in Example 1, the sample was exposed to plasma for 10 minutes in an argon atmosphere to remove water. Next, hexafluoropropylene was used as the fluorine-based monomer A, and trifluoromethanesulfonic acid was used as the monomer B. The conditions of the plasma polymerization for forming the solid electrolyte membrane 9 are as follows, and the solid electrolyte membrane 9 is formed while changing the liquid amount of trifluoromethanesulfonic acid with time, and the fluorine content is the electrode group 8: Was ramped so that it increased substantially over the surface. -Radio frequency output: 25W-Chamber pressure: 1.7Pa-Plasma polymerization time: 150 minutes-Monomer flow rate: As shown below. Order Execution time Trifluoromethanesulfonic acid amount Hexafluoropropylene amount 1 30 minutes 0.50 cc / min 5.0 cc / min 2 20 minutes 0.45 cc / min 5.0 cc / min 3 15 minutes 0.40 cc / min 5.0 cc / min 4 10 minutes 0.30 cc / min 5.0 cc / min 5 10 minutes 0.20 cc / min 5.0 cc / min 6 15 minutes 0.10 cc / min 5.0 cc / min 7 20 minutes 0.05 cc / min 5. 0 cc / min 8 30 minutes 0 cc / min 5.0 cc / min The obtained electrochemical gas sensor was used in the same manner as in Example 1 70
When the solid electrolyte membrane 9 was immersed in water at 0 ° C. for 1 hour and the appearance of the solid electrolyte membrane 9 was visually confirmed, no peeling or cracking in the solid electrolyte membrane 9 was observed.

[0023]

[Comparative example]

Comparative Example 1 As in Example 1, water was removed by exposing to plasma for 10 minutes in an argon atmosphere. Next, hexafluoropropylene was used as the fluorine-based monomer A, trifluoromethanesulfonic acid was used as the monomer B, and plasma polymerization was performed under the following conditions to form the solid electrolyte membrane 9.・ Radio frequency output: 25W ・ Trifluoromethanesulfonic acid flow rate: 0.5cc /
min ・ Hexafluoropropylene flow rate: 5.0 cc / mi
n. Chamber pressure: 1.7 Pa. Plasma polymerization time: 90 minutes Then, the protective film 10 was formed on the surface of the solid electrolyte membrane 9 by plasma polymerization under the following conditions.・ Radio frequency output: 25 W ・ Hexafluoropropylene flow rate: 5.0 cc / mi
n ・ Chamber pressure: 1.7 Pa ・ Plasma polymerization time: 90 minutes The electrochemical gas sensor thus obtained was used in the same manner as in Example 1
Immersion in water at ℃ for 1 hour, solid electrolyte membrane 9 and protective membrane 10
When the appearance of the above was visually confirmed, peeling was observed between the solid electrolyte membrane 9 and the protective film 10.

The electrochemical gas sensors according to Examples 1 to 4 are such that the solid electrolyte membrane 9 does not peel or crack in the solid electrolyte membrane 9 after being immersed in water at 70 ° C. for 1 hour, and is formed by plasma polymerization. The electrolyte membrane 9 also had the effect of improving the adhesion to the electrode group 8 as compared with the case where the electrolyte membrane 9 was formed by casting a conventional perfluorosulfonate polymer or the like.

[0025]

According to the production method of the present invention, the fluorine-based monomer A and the monomer B having a functional group imparting ion conductivity, which polymerizes with the fluorine-based monomer A, are added to the monomer B. The solid electrolyte membrane 9 in which the content of fluorine is substantially increased can be formed by preparing the electrode group 8 by plasma polymerization so that the proportion of A increases sequentially. According to the above-described manufacturing method, the electrode group 8 side has high ionic conductivity, the surface is given water repellency, and the solid electrolyte membrane 9 in which the composition does not change suddenly can be obtained.

In the electrochemical gas sensor of the present invention, the solid electrolyte membrane 9 is composed of an inclined membrane in which the content of fluorine increases substantially from the electrode group 8 to the surface, so that a rapid compositional change occurs. Since there is no boundary surface, the temperature,
Since the solid electrolyte membrane 9 does not peel or crack in response to changes in humidity and the surface is water repellent, the ion conductivity of the solid electrolyte membrane 9 on the electrode group 8 side is maintained. Therefore, the electrochemical gas sensor of the present invention has no deterioration in detection sensitivity and has stability over time.

[Brief description of drawings]

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

FIG. 2 is a plan view of the electrochemical gas sensor of FIG.

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

[Explanation of symbols]

 1 Insulating Substrate 2 Working Electrode 3 Counter Electrode 4 Reference Electrode 8 Electrode Group 9 Solid Electrolyte Membrane 21 Terminal 31 Terminal 41 Terminal

Claims (3)

[Claims] 1. An electrode group 8 including a working electrode 2 and a counter electrode 3 provided on an insulating substrate 1, and a solid electrolyte membrane 9 formed by coating the electrode group 8 in series, wherein the solid electrolyte membrane 9 is An electrochemical gas sensor characterized by comprising a gradient film in which the fluorine content is substantially increased from the electrode group 8 to the surface of the solid electrolyte membrane 9. 2. The electrochemical gas sensor according to claim 1, wherein the solid electrolyte membrane 9 is composed of a fluorine-based polymer having ion conductivity. 3. A fluorine-based monomer A that is plasma-polymerized alone in the electrode group 8 and a monomer B that is polymerized with the fluorine-based monomer A and has a functional group that imparts ion conductivity.
The solid electrolyte membrane 9 made of a polymer having ion conductivity, which is generated by plasma-polymerizing the fluorine-based monomer A with respect to the monomer B at a sequentially increasing rate. 1. The method for producing the electrochemical gas sensor according to 1 or 2.