JP2988040B2 - Electrochemical gas sensor - Google Patents

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 a working electrode, and a solid electrolyte membrane covering these electrodes in series. The present invention relates to an electrochemical gas sensor that detects, for example, a specific gas in the atmosphere by utilizing an electrochemical reaction of a gas occurring on an electrode.

[0002]

2. Description of the Related Art The basic principle 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, as the electrolyte, a liquid or gel electrolyte is used, but there is a problem that the durability and reliability of the sensor are inferior because the liquid leaks from the device and the solvent evaporates. For this reason, inorganic or organic solid electrolytes have been adopted. As the inorganic substance, β-alumina, nasicon, lithicon, stabilized zirconia, or the like is 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, generally, the inorganic solid electrolyte as described above needs to be heated to maintain a low impedance state, and as a result,
Power consumption increases.

On the other hand, polymers belonging to cation exchange resins such as polystyrene sulfonate, polyvinyl sulfonate, perfluorosulfonate polymer and perfluorocarboxylate polymer are used as organic substances.
These resins are advantageous in that they have low impedance and therefore low power consumption because they have a high degree of cation dissociation at room temperature compared to inorganic substances. Among them, the perfluorosulfonate polymer has a higher degree of cation dissociation than others, and is thermally and electrochemically stable, and is soluble in a solvent. Since a film can be formed by casting on a plurality of electrodes, a manufacturing advantage cannot be overlooked.

By the way, an electrochemical gas sensor provided with a solid electrolyte membrane using an organic substance having such an advantage,
Since the electrical characteristics or gas permeability of the solid electrolyte membrane changes over time, the sensitivity of the sensor changes 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 factors such as the electrical characteristics of the solid electrolyte membrane or gas permeability.
An object of the present invention is to provide an electrochemical gas sensor with improved reliability by detecting that the sensitivity for detecting a target gas is normally maintained.

[0006]

An electrochemical gas sensor according to the present invention comprises an insulating substrate 10, a working electrode 20, a counter electrode 30, a reference electrode 40, and these electrodes 20, 30, 40 provided on the insulating substrate 10. A target gas detector A for detecting a target gas comprising the solid electrolyte membrane 80 to be coated in a series;
A reference gas detection unit B having the same configuration as the target gas detection unit A and detecting a reference gas present at a constant concentration in the use environment, and when the detection output of the reference gas detection unit B falls below a certain value. It is characterized by having a life notifying means for issuing a signal.

[0007]

According to the electrochemical gas sensor of the present invention, the working electrode 20, the counter electrode 30, and the
A target gas detecting section A for detecting a target gas comprising a reference electrode 40 and a solid electrolyte membrane 80 which covers these electrodes 10, 20, 30 in series, and has the same configuration as the target gas detecting section A. By providing a reference gas detection unit B that detects a reference gas present at a constant concentration in the environment, and a life notification unit that emits a signal when the detection output becomes equal to or less than a predetermined value, the reference gas detection unit B can be used in a usage environment. The sensitivity characteristic of the reference gas detection unit B that detects the reference gas existing at a constant concentration is the same as that of the target gas detection unit A that detects the target gas. Since the change with time is the same as or equivalent to the sensitivity characteristic of the portion A, it can be detected by the signal of the life notifying means which emits a signal when the detection output of the reference gas detection portion B falls below a certain value.

[0008]

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

In FIG. 1 and FIG. 2, an insulating substrate 10 is provided with a target gas detector A for detecting a target gas and a reference gas detector B paired with the target gas detector A at intervals. The target gas detector A includes a working electrode 20 formed on the insulating substrate 10 at a distance from each other,
And a solid electrolyte membrane 80 covering these electrodes 20, 30, and 40 and connecting them in series. One end of the working electrode 20, the counter electrode 30 of the working electrode 20, and the reference electrode 40 are connected to one end of a solid electrolyte as shown in the drawing by means of sputtering or vapor deposition of an electrode material such as platinum or gold on the insulating substrate 10. A terminal portion 2 exposed to the outside of the film 80 and used for connection to an external circuit
2, 32 , 42 , and the solid electrolyte membrane 8
0 is, for example, a polymer such as the above-mentioned polystyrene sulfonate, polyvinyl sulfonate, perfluorosulfonate polymer, or perfluorocarboxylate polymer. It is practical. To form the solid electrolyte membrane 80, for example, a simple casting or other appropriate means is used.

For the purpose of preventing the solid electrolyte membrane 80 from deteriorating with time, for example, a change in electrical characteristics with time or a change in the permeability of a target gas, a protective film 90 is further formed on the solid electrolyte membrane 80. It is formed. This protective film 90
Can be formed by a vapor deposition method or a plasma method using a fluorine-based resin.

The reference gas detector B has the same configuration as the target gas detector A described above. That is, a working electrode 50, a counter electrode 60 of the working electrode 50, and a reference electrode 70 are formed on the insulating substrate 10 at a distance from each other, and these electrodes 50, 60, and 70 are further covered to form a series. The working electrode 20 of the reference gas detection unit A, the counter electrode 30 of the working electrode 20 and the reference electrode 40 are configured as follows.
One end is exposed to the outside of the solid electrolyte membrane 82 so that the terminal 5
This solid electrolyte membrane 82 is formed to have the working electrode 50 on the solid electrolyte membrane 82 which is formed to have the same or equivalent deterioration over time as the solid electrolyte membrane 80 of the target gas detection section A. , A protective film 92 having substantially the same shape as the working electrode 50 is formed. Here, if the protective film 92 is formed only on the working electrode 50 , the target gas detection unit A and the reference gas detection unit having the same temporal characteristics such as a change in electric characteristics with time or a change in permeability of the target gas. The part B can be configured. The reason is as follows. In the reference gas detecting section B, since the electrochemical reaction is constantly occurring on the working electrode 50 because it is present in the use environment, for example, when the reference gas is oxygen,

[0012]

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Water continues to be generated due to the reaction. When such a product stays in the solid electrolyte membrane 82, it exhibits characteristics different from the temporal characteristics of the target gas detection unit A. If the solid electrolyte membrane 82 is not covered with the protective film 92, such products are largely released into the use environment and thus do not significantly affect the solid electrolyte film 82. When coated with, it is difficult to release. This is because exposing the entire surface of the solid electrolyte membrane 82 except for the portion on the working electrode 50 promotes the release of the product.

As described above, the electrodes 2 of the target gas detecting section A whose deterioration with time progresses in the same or equivalent manner with each other.
0, 30, 40 and the electrodes 50, 60,
Reference numeral 70 denotes each of the terminal portions 22, 32, 42 and 52, 6
At 2 and 72, the detection of the target gas via the lead wires 102 and 104 is performed by using the working electrode 20 and the counter electrode 3 of the target gas detection unit A.
It is connected to a signal processing circuit 100 performed by a current value flowing between 0 and a life notification circuit 110 for detecting deterioration with time of the reference gas detection unit B by a current value flowing between the working electrode 50 and the counter electrode 60 of the reference gas detection unit B. , This life notification circuit 11
0 constitutes a life notifying means for notifying the life by issuing a signal when the detection output determined by the value of the current flowing between the working electrode 50 and the counter electrode 60 falls below a certain value. Here, the signal for notifying the life is arbitrary such as generation of a warning sound and lighting of a warning lamp. In addition, the time when the life is announced can be the time when the initial current value flowing between the working electrode 50 and the counter electrode 60 becomes half or the time when the current value falls below a predetermined threshold value. It is necessary to set according to.

The target gas detected by the target gas detection section A can 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 40 is set according to these gas types. Similarly, as the reference gas of the reference gas detection unit B, in a normal use environment, oxygen existing in the atmosphere is appropriate. However, a gas type 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 70 is set.

[0016]

According to the electrochemical gas sensor according to the present invention, the working electrode 20 and the counter electrode 3 provided on the insulating substrate 10 are provided.
0, a target gas detector A for detecting a target gas comprising a reference electrode 40 and a solid electrolyte membrane 80 covering the electrodes 20, 30, 40 in series, and having the same configuration as the target gas detector. By providing a reference gas detector B for detecting a reference gas present at a certain concentration in the use environment, and a life notifying means for issuing a signal when the detection output becomes equal to or less than a certain value, the reference gas detector B is used. The sensitivity characteristic of the reference gas detection unit A for detecting the reference gas present at a constant concentration in the target gas is the same as that of the target gas detection unit A in which the reference gas detection unit B detects the target gas. Since the change over time is the same as or equivalent to the sensitivity characteristic of the detection unit A, it can be detected by the signal of the life notifying means that emits a signal when the detection output of the reference gas detection unit B falls below a certain value. As a result, by detecting that the sensitivity for detecting the target gas, which is caused by the electrical characteristics of the solid electrolyte membrane 80 of the target gas detection unit A or a complicated cause such as gas permeability, is normally maintained, the reliability is improved. An object of the present invention is to provide an electrochemical gas sensor with improved performance.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view of FIG. 1 according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION 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 detection part B Reference gas detection part

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-43950 (JP, A) JP-A-4-208849 (JP, A) JP-A-4-230843 (JP, A) 43951 (JP, A) JP-A-5-249075 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 27/416

Claims (2)

(57) [Claims] An insulating substrate (10), said insulating substrate (10)
In order to detect a target gas composed of a working electrode (20), a counter electrode (30), a reference electrode (40), and a solid electrolyte membrane (80) covering these electrodes in series,
The working electrode (20) and the reference electrode (40)
The target gas detector A to which the voltage to be applied is set , the same electrode configuration as the target gas detector A and these electrodes
Consists coated to the solid electrolyte membrane (82) made by, present at a constant concentration in a use environment, to detect the different reference gas and target gas, the working electrode in accordance with the type of gas reference gas
The voltage applied between (50) and the reference electrode (70) is set.
An electrochemical gas sensor, comprising: a reference gas detecting section B; and a life notifying means for issuing a signal when a detection output of the reference gas detecting section B becomes equal to or less than a predetermined value. 2. The solid electrolyte membrane of the target gas detection section A (80).
Protective film covering the entire surface (90), and on a solid electrolyte membrane (82) of the reference gas detector B, the solid electrolyte membrane (82) working electrode sandwiched between (50), the working electrode (50) The electrochemical gas sensor according to claim 1, further comprising a protective film (92) having substantially the same shape as the above.