JPH05273175A - Electrochemical gas sensor - Google Patents

Abstract

PURPOSE:To improve the aging stability of gas sensitivity by providing an action electrode, a counter electrode, and a reference electrode on an insulating substrate, providing a polymer solid electrolyte film covering an electrode group and burying gaps between the electrodes, improving the polymer solid electrolyte film of an electrochemical gas sensor to be hardly polluted by a pollutant contained in the atmosphere, and preventing the reduction of gas permeability. CONSTITUTION:An electrochemical gas sensor is provided with an action electrode 2, a counter electrode 3, and a reference electrode 4 on an insulating substrate 1, and a series of air-permeable polymer solid electrolyte film 6 covering an electrode group 5 and burying gaps 7 between the electrodes is provided. A fluoric skin 8 is formed on the surface of the polymer solid electrolyte film 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrochemical gas sensor, and more particularly to a polymer solid electrolyte membrane in which a working electrode, a counter electrode and a reference electrode are provided on an insulating substrate, and these electrode groups are covered and the gaps between the electrodes are filled. The present invention relates to an electrochemical gas sensor provided with.

[0002]

2. Description of the Related Art Utilizing an electrochemical redox reaction,
Many electrochemical gas sensors have been proposed so far, which detect a specific gas in the atmosphere, for example, a test gas such as carbon monoxide, hydrogen, alcohol, or nitrogen oxide. Generally, this type of gas sensor can be used at room temperature and has high sensitivity, and is used in various fields such as industrial use, environmental protection, and fire alarms.
It can be expected to be used as a portable type and an installation type.

As an example of an electrochemical gas sensor, as disclosed in Japanese Patent Laid-Open No. 64-88354, a working electrode and a counter electrode are formed on an insulating substrate so as to face each other. Electrodes are arranged, and a solid electrolyte membrane that covers these electrode groups is further provided. When a constant potential is applied to the working electrode, the test gas is oxidized or reduced on the working electrode and generated at this time. Ions move in the solid polymer electrolyte membrane and are reduced or oxidized at the counter electrode. When the value of the current flowing between the working electrode and the counter electrode due to this electrochemical redox reaction is measured by an external device connected to this sensor, the concentration of the test gas can be known.

The electrochemical gas sensor having such a planar electrode structure can be applied to thin film forming technology, printed circuit forming technology, and photoengraving technology used in the field of semiconductor manufacturing, etc., so that it can be miniaturized and manufactured. It is possible to simplify.

However, although it has the advantages of the manufacturing method and the advantages of the performance as described above, there is a problem in the stability of the performance over time. That is, the gas sensitivity decreases with time, the gas concentration of the test gas cannot be accurately detected, and the life is short. One of the causes of the decrease in the gas sensitivity with time is that pollutants such as inorganic substances and organic substances existing in the air are mixed with and adhere to the polymer solid electrolyte membrane in various forms such as gas, dust, and the like. The gas permeability of the solid polymer electrolyte membrane becomes poor. This is because if the gas permeability of the solid polymer electrolyte membrane becomes poor, the amount of the test gas that reaches the working electrode will decrease, and a predetermined current will not flow.

[0006]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to improve the gas resistance by preventing the solid polymer electrolyte membrane from being easily contaminated by the pollutants contained in the atmosphere and preventing the decrease of gas permeability. An object of the present invention is to provide an electrochemical gas sensor having sensitivity stability over time.

[0007]

In the electrochemical gas sensor according to the present invention, a working electrode 2, a counter electrode 3 and a reference electrode 4 are provided on an insulating substrate 1, and these electrode groups 5 are covered with a space 7 between the electrodes. It is characterized in that a fluorinated skin 8 is formed on the surface of a series of air-permeable polymer solid electrolyte membranes 6 to be filled.

[0008]

According to the electrochemical gas sensor of the present invention, by forming the fluorinated skin 8 on the surface of the solid electrolyte membrane 6 covering the working electrode 2, the counter electrode 3 and the reference electrode 4 on the insulating substrate 1, The surface energy of the polymer solid electrolyte membrane 6 becomes small. Therefore, the contaminants are repelled by the skin 8 and are not mixed in the solid polymer electrolyte membrane 6,
In addition, since fluorine is chemically bonded to the polymer that constitutes the polymer solid electrolyte membrane 6, it is more stable over time than physical bonding and maintains the property of repelling contaminants for a long time. ..

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

The electrochemical gas sensor according to the present invention is
As shown in FIGS. 1 and 2, a series of polymer solid electrolyte membranes in which a working electrode 2, a counter electrode 3 and a reference electrode 4 are provided on an insulating substrate 1 to cover the electrode group 5 and to fill the space 7 between the electrodes. 6 is provided. The polymer solid electrolyte membrane 6 is covered with the working electrode 2, the counter electrode 3, and the reference electrode 4 except for the ends thereof, and is covered with each other, and the terminals 2a, 2 used for connection with an external device are provided.
b, 2c are formed. Here, when the test gas comes into contact with the working electrode 2, an electrochemical reaction occurs, and at the same time as this reaction, a redox pairing with the reaction in the working electrode 2 occurs at the counter electrode 3, and a current flows through both electrodes. The reference electrode 4 functions as a reference potential for the redox reaction of the working electrode 2 and the counter electrode 3.
As the insulating substrate 1, a ceramic substrate such as alumina, a silicon substrate subjected to oxidation insulation treatment, or other cured resin substrate is used, and the working electrode 2, the counter electrode 3, and the reference electrode 4 are usually platinum or gold. As the polymer solid electrolyte membrane 6, polymers such as polystyrene sulfonate, polyvinyl sulfonate, perfluorosulfonate polymer, and perfluorocarboxylate polymer can be applied. Among them, the perfluorosulfonate polymer is preferable. Is most suitable as an electrolyte because of its high stability.

Then, a fluorinated skin 8 is formed on the surface of the polymer solid electrolyte membrane 6 to form an electrochemical gas sensor. This skin 8 is a thin layer having breathability, and 1500A to 5000A is sufficient,
There is no particular upper limit as long as the air permeability of the polymer solid electrolyte membrane 6 and the ionic conductivity between electrodes are not impaired. The fluorinated skin 8 is made of, for example, CF ₄ ,
Insulating substrate 1 in an atmosphere of a mixed gas prepared by diluting a fluorine compound gas such as SF ₄ with an inert gas such as nitrogen or helium
The solid polymer electrolyte membrane 6 covering the electrode group 5 is subjected to plasma treatment, and fluorine is introduced into the solid polymer electrolyte membrane 6. This plasma treatment is superior to other methods in that the skin 8 can be formed thin without impairing the air permeability of the polymer solid electrolyte membrane 6.

In the electrochemical gas sensor thus constructed, a current flows between the working electrode 2 and the counter electrode 3 due to the action of the electrolyte of the solid electrolyte membrane 6 due to the gas to be detected, and this current is detected. It is input to the above external device as an output signal for detecting gas. Then, the presence of the test gas is notified by the optical and audio means of this external device and other display means.

Hereinafter, the production of the skin 8 will be described with reference to a specific example. A solution of perfluorosulfonate polymer is applied to an insulating substrate 1 having a working electrode 2, a counter electrode 3 and a reference electrode 4 on one side, and dried to form a coating film on the insulating substrate 1 including the electrode group 5. Plasma treatment is performed in a chamber into which CF ₄ gas or SF ₄ gas is introduced to form a polymer solid electrolyte membrane 6 having a skin 8 whose surface is fluorinated with a coating film of perfluorosulfonate polymer. In this case, one example of plasma treatment is 1
With a high-frequency glow discharge of 3.65 MHz, fluorination can be easily performed at a pressure of 5 Torr in the chamber, a power of 50 W, and a treatment time of 10 minutes.

[0014]

According to the electrochemical gas sensor of the present invention, the polymer solid electrolyte membrane is less likely to be contaminated by the pollutants contained in the atmosphere, and the deterioration of gas permeability is prevented. Can be improved.

[Brief description of drawings]

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

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

[Explanation of symbols]

 1 Insulating Substrate 2 Working Electrode 3 Counter Electrode 4 Reference Electrode 5 Electrode Group 6 Polymer Solid Electrolyte Membrane 7 Between Electrodes 8 Skin

Claims (1)

[Claims] 1. A working electrode 2 and a counter electrode 3 on an insulating substrate 1.
And a reference electrode 4 are provided, and a fluorinated skin 8 is formed on the surface of a series of air-permeable polymer solid electrolyte membrane 6 that covers these electrode groups 5 and fills the gaps 7 between the electrodes. Electrochemical gas sensor.