JPH0560727A - Electrochemical gas sensor - Google Patents

Abstract

PURPOSE:To obtain an electrochemical gas sensor of increased reliability by detecting that the sensitivity in detection of an object gas which is affected by a complex factor such as the electrical characteristic of a solid-electrolyte film or the gas permeability thereof is kept normal. CONSTITUTION:An electrochemical gas sensor has an object gas detecting element A which comprises an insulating substrate 10, an operating electrode 20, an opposite electrode 30 and a reference electrode 40 provided on this insulating substrate 10 and a solid-electrolyte film 80 covering these electrodes together and detects an object gas, a reference gas detecting element B which has the same construction as this object gas detecting element A and detects a reference gas existing in a prescribed concentration in an operating environment, and a lifetime notifying means which issues a signal when a detection output of this reference gas detecting element B becomes a prescribed value or below.

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 an electrochemical gas sensor comprising an insulating substrate provided with a plurality of electrodes including working electrodes, and a solid electrolyte membrane covering the electrodes in series. Relates to an electrochemical gas sensor that detects a specific gas in the atmosphere, for example, by utilizing an electrochemical reaction of a gas that occurs on an electrode.

[0002]

2. Description of the Related Art The basis of a gas sensor utilizing an electrochemical reaction is to connect a plurality of electrodes with an electrolyte to cause an electrochemical reaction at the electrodes. Here, although a liquid or gel electrolyte was used as the electrolyte, there is a problem that the sensor is inferior in durability and reliability because liquid leakage from the device and evaporation of the solvent occur. For this reason, inorganic or organic solid electrolytes have been adopted. As the inorganic substance, β-alumina, naconone, ricicone, stabilized zirconia, etc. are used. When these inorganic substances are used, the impedance at room temperature is high, so that ions are difficult to conduct at room temperature. Therefore, in general, the inorganic solid electrolyte as described above needs to be heated to keep the impedance low, and as a result,
Power consumption increases.

On the other hand, as the organic substance, polymers belonging to a cation exchange resin such as polystyrene sulfonate, polyvinyl sulfonate, perfluorosulfonate polymer, perfluorocarboxylate polymer and the like are used.
Since these resins have a large degree of cation dissociation at room temperature as compared with inorganic substances, they are advantageous in that they have a low impedance and therefore a low power consumption. Above all, the perfluorosulfonate polymer has a larger degree of cation dissociation than others, is thermally and electrochemically stable, and is soluble in a solvent. Therefore, it is formed on the insulating substrate and the insulating substrate. Since the film can be formed by casting on a plurality of electrodes, the manufacturing advantages cannot be overlooked.

By the way, an electrochemical gas sensor provided with a solid electrolyte membrane using an organic substance having such advantages is
Since the electrical characteristics or gas permeability of the solid electrolyte membrane changes over time, it causes a change in the sensitivity of the sensor over time, and there is a problem of lack of reliability.

[0005]

Therefore, the problem to be solved by the present invention is caused by complicated causes such as electric characteristics of solid electrolyte membranes or gas permeability.
An electrochemical gas sensor with improved reliability is provided by detecting that the sensitivity for detecting a target gas is normally maintained.

[0006]

An electrochemical gas sensor according to the present invention includes an insulating substrate 10, a working electrode 20, a counter electrode 30, a reference electrode 40 and electrodes 20, 30, 40 for these electrodes provided on the insulating substrate 10. A target gas detection unit A for detecting a target gas consisting of a solid electrolyte membrane 80 covering a series of
A reference gas detection unit B having the same configuration as the target gas detection unit A, which detects a reference gas existing at a constant concentration in the use environment, and a detection output of the reference gas detection unit B that is equal to or less than a certain value. It is characterized in that it is provided with a life notification means for emitting a signal.

[0007]

According to the electrochemical gas sensor of the present invention, the working electrode 20, the counter electrode 30 provided on the insulating substrate 10,
A target gas detection unit A for detecting a target gas consisting of a reference electrode 40 and a solid electrolyte membrane 80 covering the electrodes 10, 20, 30 in series, and the same configuration as the target gas detection unit A. The reference gas detection unit B that detects the reference gas existing at a constant concentration in the environment, and the reference gas detection unit B are provided with a life notification means that emits a signal when the detection output becomes a certain value or less. The sensitivity characteristic of the reference gas detection unit B for detecting the reference gas existing at a constant concentration is the same as that of the target gas detection unit A for detecting the target gas. Since the change over time is the same as or equal to the sensitivity characteristic of the part A, it can be detected by the signal of the life notification means that emits a signal when the detection output of the reference gas detection part B becomes a certain value or less.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing the embodiments. FIG. 1 is a plan view schematically showing an electrochemical gas sensor according to an embodiment of the present invention, and FIG. 2 is a sectional view thereof.

In FIG. 1 and FIG. 2, the insulating substrate 10 is provided with a target gas detecting section A for detecting a target gas and a reference gas detecting section B forming a pair with the target gas detecting section A at intervals. The target gas detection unit A is a working electrode 20 formed on the insulating substrate 10 at a distance from each other, and the working electrode 20.
The counter electrode 30 and the reference electrode 40 are provided, and the electrodes 20, 30, 40 are further covered to form a solid electrolyte membrane 80 connected in series. The working electrode 20, the counter electrode 30 and the reference electrode 40 of the working electrode 20 are, for example, an electrode material such as platinum or gold on the insulating substrate 10 by means such as sputtering or vapor deposition, and one end thereof is a solid electrolyte. The terminal portion 2 exposed to the outside of the film 80 and used for connection with an external circuit
Solid electrolyte membrane 8 formed to have 2, 23, 24
0 is, for example, a polymer such as polystyrene sulfonate, polyvinyl sulfonate, perfluorosulfonate polymer, or perfluorocarboxylate polymer described above. It is practical. To form the solid electrolyte membrane 80, for example, simple casting or other suitable means is used.

A protective film 90 is further provided on the solid electrolyte membrane 80 for the purpose of preventing deterioration of the solid electrolyte membrane 80 with time, for example, change with time of electrical characteristics or change of permeability of a target gas. It is formed. This protective film 90
As an example, a fluorine-based resin can be used and can be formed by a vapor deposition method, a plasma method, or the like.

The reference gas detector B has the same structure as the target gas detector A described above. That is, a working electrode 50, which is formed on the insulating substrate 10 at a distance from each other, a counter electrode 60 and a reference electrode 70 of the working electrode 50, and these electrodes 50, 60, 70 are further covered to form a series. Like the working electrode 20, the counter electrode 30 and the reference electrode 40 of the working electrode 20, which are composed of the solid electrolyte membrane 82 to be connected,
One end is exposed to the outside of the solid electrolyte membrane 80, and the terminal portion 2
2, 23, 24, and further, the solid electrolyte membrane 82 is formed on the solid electrolyte membrane 82 that is the same as or equivalent to the deterioration over time of the solid electrolyte membrane 80 of the target gas detection unit A, and the solid electrolyte membrane 82 is attached to the working electrode 52. A protective film 92 having a shape substantially the same as that of the working electrode 52, which is sandwiched between and, is formed. Here, if the protective film 92 is formed only on the working electrode 52, the target gas detection unit A and the reference gas detection that have the same temporal characteristics such as temporal changes in electrical characteristics or changes in permeability of the target gas. Part B can be constructed. The reason is as follows. Since the reference gas detection unit B exists in the usage environment, and the electrochemical reaction is constantly occurring on the working electrode 52, for example, when the reference gas is oxygen,

[0012]

[Chemical 1]

Water continues to be generated by the reaction. When such a product stays in the solid electrolyte membrane 82, it exhibits a characteristic different from the aging characteristic of the target gas detection unit A. If the solid electrolyte membrane 82 is not covered with the protective film 92, most of such products are released into the environment of use, so that the solid electrolyte membrane 82 is not so affected, but the solid electrolyte membrane 82 does not affect the protective film 92. When it is coated with, it is difficult to be released. Therefore, if the entire surface of the solid electrolyte membrane 82 excluding the portion on the working electrode 50 is exposed, the release of the product is promoted.

As described above, the electrode 2 of the target gas detection portion A having the same or equivalent progressing deterioration over time.
0, 30, 40 and the electrodes 50, 60 of the reference gas detector B,
70 designates the respective terminal portions 22, 32, 42 and 52, 6
2 and 72, the target gas is detected via the lead wires 102 and 104, and the working electrode 20 and the counter electrode 3 of the target gas detection unit A are detected.
It is connected to a signal processing circuit 100 that performs a current value flowing between zero and a life notification circuit 110 that detects aged deterioration of the reference gas detecting unit B by a current value flowing between the working electrode 50 and the counter electrode 60 of the reference gas detecting unit B. , This life notification circuit 11
0 constitutes a life notification means for issuing a signal and notifying the life when the detection output determined by the current value flowing between the working electrode 50 and the counter electrode 60 is below a certain value. Here, the signal notifying the end of life is arbitrary such as generation of a warning sound and lighting of a warning lamp. The life may be notified at a time when the initial current value flowing between the working electrode 50 and the counter electrode 60 becomes half, or when it falls below a preset threshold value. Need to be set accordingly.

The target gas detected by the target gas detection unit A may be various gases such as carbon monoxide, alcohol, hydrogen sulfide and the like. That is, the voltage applied between the working electrode 20 and the reference electrode 30 is set according to these gas species. Similarly, as the reference gas of the reference gas detection unit B, oxygen present in the atmosphere is suitable in a normal use environment, but a gas species is selected according to the use environment and the working electrode 5 is selected according to the selected gas.
The voltage applied between 0 and the reference electrode 60 is set.

[0016]

According to the electrochemical gas sensor of the present invention, the working electrode 20 and the counter electrode 3 provided on the insulating substrate 10 are provided.
0, a reference electrode 40, and a target gas detection unit A for detecting a target gas consisting of a solid electrolyte membrane 80 covering the electrodes 10, 20, 30 in series, and the same configuration as the target gas detection unit. By using a reference gas detection unit B that detects a reference gas existing at a constant concentration in the use environment, and a life notification unit that issues a signal when the detection output falls below a certain value, the reference gas detection unit B is used. The sensitivity characteristic of the reference gas detection unit A for detecting the reference gas existing at a constant concentration in the target gas is the same as that of the target gas detection unit A for detecting the target gas in the reference gas detection unit B. Since the sensitivity characteristics of the detection unit A are the same as or equal to those of the sensitivity characteristics of the detection unit A, the detection output of the reference gas detection unit B can be detected by the signal of the life notifying unit that emits a signal when the detection output becomes a certain value or less. , By detecting that the sensitivity for detecting the target gas is normally maintained, which is caused by a complicated cause such as the electrical characteristics of the solid electrolyte membrane 80 of the target gas detection unit A or gas permeability. It is intended to provide an electrochemical gas sensor having improved temperature.

[Brief description of drawings]

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

FIG. 2 is a sectional view of FIG. 1 according to an embodiment of the present invention.

[Explanation of symbols]

 10 Insulating Substrate 20 Working Electrode 30 Counter Electrode 40 Reference Electrode 80 Solid Electrolyte Membrane 82 Solid Electrolyte Membrane 90 Protective Film 92 Protective Film A Target Gas Detector B Reference Gas Detector

Claims (2)

[Claims] 1. A target gas for detecting a target gas comprising an insulating substrate 10, a working electrode 20, a counter electrode 30, a reference electrode 40 provided on the insulating substrate 10 and a solid electrolyte membrane 80 which covers these electrodes in series. The detection unit A, the reference gas detection unit B having the same configuration as the target gas detection unit A, which detects the reference gas existing at a constant concentration in the use environment, and the detection output of the reference gas detection unit B is a constant value. An electrochemical gas sensor, characterized in that it is provided with a life notification means that emits a signal when: 2. The solid electrolyte membrane 82 is provided on the protective film 90 which covers the entire surface of the solid electrolyte membrane 50 of the target gas detecting section A and the solid electrolyte membrane 82 of the reference gas detecting section B.
The electrochemical gas sensor according to claim 1, further comprising a protective film 92 that is substantially the same as the working electrode 50 that is sandwiched between 0 and 0.