JP3100764B2 - 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 useful for detecting nitrogen oxides in the atmosphere or carbon monoxide in a fire.

2. Description of the Related Art An electrochemical gas sensor for detecting a specific gas in an atmosphere, for example, a gas to be detected such as carbon dioxide, carbon monoxide, hydrogen, alcohol, and nitrogen oxide by utilizing an electrochemical oxidation-reduction reaction is known. Many have been proposed so far. Here, a description will be given with reference to FIGS. 4 and 5 showing a known sensor element 10 constituting an electrochemical gas sensor.
As disclosed in Japanese Unexamined Patent Publication No. 4 (1994) -104, a working electrode 70 and a counter electrode 90 are formed on an insulating substrate 100 so as to face each other, and a reference electrode 80 is arranged next to the counter electrode 90 and the working electrode 70, and is further kept in a water-containing state. The electrodes are covered with a solid electrolyte membrane 110 to be formed, and when a voltage is applied between the working electrode 70 and the counter electrode 90, the gas to be detected causes an oxidation reaction or a reduction reaction on the working electrode 70, The ions generated by the reaction move in the solid electrolyte membrane 110 held in a water-containing state, and cause a reduction reaction or an oxidation reaction at the counter electrode 90. When the value of the current flowing between the counter electrode 90 and the working electrode 70 is measured by an external device such as an ammeter connected to the sensor element 10 by this electrochemical oxidation-reduction reaction,
The gas to be detected can be detected.

Referring to FIG. 3, which shows an example of an electrochemical gas sensor using this sensor element 10, this electrochemical gas sensor is composed of a housing 30 having an internal space 35, a water storage tank 40 attached to the housing 30, and an outside. 3 through which the gas to be detected is introduced into the internal space 35
4 and a communication port 36 formed in the partition wall 20 that divides the housing 30 and the water storage tank 40 and communicates with the internal space 35 and the water storage tank 40.
The above-described sensor element 10 is housed in the internal space 35 of the first embodiment.

However, in the electrochemical gas sensor as described above, the gas to be detected introduced into the internal space 35 containing the sensor element 10 from the vent hole 34 passes through the communication port 36 without staying in the internal space 35. Phase 4 of the water storage tank 40
As a result, the gas in the internal space 35 is diluted.
Therefore, it takes longer time to reach the existing gas concentration.
You. Therefore, the electrochemical reaction occurring in the sensor element 10
The current value flowing along with the
Indicates the applied current value and the current corresponding to the existing gas concentration
The problem is that it takes a long time to reach the value, and as a result, detection is delayed.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a water storage tank attached to a housing via a housing and a partition, wherein the housing is provided with a vent for introducing a gas to be detected and a gas to be detected introduced from the outside. The housing has a diffused internal space, a sensor element is accommodated in the internal space of the housing, and a communication port is formed in the partition wall for communicating the internal space with the water storage tank. Water-containing state covering the pole and counter electrode and this working electrode and counter electrode
Another object of the present invention is to provide an electrochemical gas sensor provided with a solid electrolyte membrane held in a sensor and to reduce the response time of detection by preventing dilution of the detection target gas in the internal space containing the sensor element.

[0006]

According to the present invention, there is provided an electrochemical method comprising:
The gas sensor has: (1) a water tank 40 attached to the housing 30 via the housing 30 and the partition wall 20;
(2) The housing 30 has a ventilation hole 34 for introducing the gas to be detected and an internal space 35 for diffusing the gas to be detected introduced from outside. (3) The sensor element 10 is provided in the internal space 35 of the housing 30. (4) A communication port 36 is formed in the partition wall 20 to communicate the internal space 35 with the water storage tank 40. (5) The sensor element 10 is provided with a working electrode 70 and a counter electrode 90, which are opposed to each other. The working electrode 70 and the counter electrode 90 are covered with a solid electrolyte membrane 110 maintained in a water-containing state. Further, (6) one end closes the communication port 36 and the other end is an aqueous phase in the water storage tank 40. immersed in part 46, when the water is caused air tightness, Bei <br/> example Rutotomoni the curtain 50 of absorbent, based on the (7) above curtain 50, the water tank
Breathability that closes the communication port 36 on the opposite side of the water phase part 46 in 40
And a water-tight porous layer 60 .

[0007]

[0008]

The sensor element constituting the electrochemical gas sensor according to the present invention is protected from contaminants in the atmosphere by being housed in the internal space of the housing. Since the housing 30 has a vent 34 for introducing the gas to be detected in the atmosphere into the internal space 35, when the gas to be detected is generated in the atmosphere, the gas to be detected enters the internal space 35 from the vent 34. Internal space 35 and water tank 40
The communication port 36 of the partition wall 20 that communicates with the
Immersed in the aqueous phase part 46 within 0, and when it contains water, airtightness occurs.
Since the water-absorbing curtain 50 is closed at one end, when the water vapor in the internal space 35 is in an unsaturated state, the water is sucked from the other end of the curtain 50 and the one end held in a saturated state. The water evaporates and passes through the communication port 36 to form the internal space 3
Spread into 5. Then, the water vapor in the internal space 35 is hydrogenated to the solid electrolyte membrane 110 of the sensor element 10 housed in the internal space 35 to maintain the solid electrolyte membrane 110 in a water-containing state, and the detection target introduced from the vent 34 When gas is generated, the inner space 35 is closed due to the airtightness caused by the saturated state of one end of the curtain 50 closing the communication port 36.
The detection target gas introduced into the inside is prevented from passing through the communication port 36 and diffusing into the water phase portion 46 in the water storage tank 40, and as a result, the detection target gas in the internal space 35 is prevented from being diluted.
That is, a decrease in the concentration of the detection target gas introduced into the internal space 35 is prevented.

Further , the electrochemical gas sensor of the present invention comprises:
The porous layer 60 that blocks the communication port 36 provided on the opposite side of the water phase portion 46 with respect to the curtain 50 has air permeability and water tightness, and thus has evaporated from the water phase portion 46 in the water storage tank 40. The water vapor passes through the porous layer 60, passes through the communication port 36, and diffuses into the internal space 35. However, the water in the water phase portion 46 in the water storage tank 40 passes through the porous layer 60 in a liquid state and communicates therewith. It is prevented from entering the internal space 35 through the mouth 36. That is, the sensor element 10 is protected from excessive water wetting, and the accompanying output abnormality of the sensor element 10 is prevented.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings according to embodiments.

As shown in FIG. 1, the electrochemical gas sensor of the present invention has a housing 30. The housing 30 has an internal space 35, and a water storage tank 40 is formed below the housing 30 via the partition wall 20.
The shapes of the housing 30 and the water tank 40 as a whole are rectangular parallelepiped, but are not particularly limited. The material of the entire housing 30 and the water tank 40 is made of various resins such as acrylic resin or SUS.
Such a metal can be used. This housing 30
A vent port 34 for introducing a gas to be detected communicating with the internal space 35 and a communication port 36 for communicating the water storage tank 40 with the housing 30 are provided above the partition wall 20.

Further, the electrochemical gas sensor according to the present invention has the sensor element 10 housed in the internal space 35 of the housing 30. The sensor element 10 is formed on an insulating substrate 100 such that a working electrode 70 and a counter electrode 90 face each other. Alumina,
A ceramic substrate such as aluminum nitride or silicon or a resin substrate such as epoxy resin or phenol resin is used.
The working electrode 70 and the counter electrode 90 use, for example, platinum electrodes. Next to the counter electrode 90 or the working electrode 70, the reference electrode 80
Are lined up. As the reference electrode 80, for example, a gold electrode is used. An ordinary thin film forming means such as vacuum evaporation or sputtering is used for electrode formation. Further, a solid electrolyte membrane 110 that covers the electrode group of the counter electrode 90, the working electrode 70, and the reference electrode 80 is provided. This solid electrolyte membrane 110
It has the property of becoming an electrolyte when it contains water. As the solid electrolyte membrane 110, a polymer compound composed of a perfluorosulfonate polymer or the like, or an inorganic compound is used. The solid electrolyte membrane made of a perfluorosulfonate polymer can be formed by, for example, applying it to the insulating substrate 100 in a molten state. When a constant potential is applied to the working electrode 70, the gas to be detected undergoes an oxidation reaction or a reduction reaction on the working electrode 70, and the ions generated at this time become solid.
After moving in the electrolyte membrane 110 , a reduction reaction or an oxidation reaction occurs at the counter electrode 90. By this electrochemical oxidation-reduction reaction, the gas to be detected is detected by the current value flowing between the counter electrode 90 and the working electrode 70, and the sensor element 10 responds. That is, the detection target gas is generated outside the sensor element 10, and the detection target gas flows into the internal space 35 of the housing 30.
And an output corresponding to the density. One end of the working electrode 70, the counter electrode 90, and one end of the reference electrode 80 of the sensor element 10 housed in the housing 30 is a terminal 5, and this terminal 5 is exposed to the outside of the housing 30 and is used for connecting an external device such as an ammeter. .

The electrochemical gas sensor according to the present invention further includes the curtain 50 described above. The curtain 50 has a water-absorbing property, and is made of a material that becomes airtight when it contains water. The curtain 50 includes a vertical piece 55 and a horizontal piece 56 extending horizontally from the upper end of the vertical piece 55. The lower end of the vertical piece 55 is immersed in the water phase portion 46 in the water tank 40, and the horizontal piece 56 is By contacting the lower surface and arranging the end of the horizontal piece 56 so as to close the communication port 36, the water-absorbing curtain 50 closes the communication port 36 at one end while the air-tightness is generated when water is contained. Is immersed in the water phase portion 46 in the water storage tank 40. That is, the water sucked from the lower end of the vertical piece 55 of the curtain 50 that is submerged in the water phase portion 46 in the water storage tank 40 travels along the horizontal piece 56 to make the other end saturated. Therefore, the communication port 36 is closed by the curtain 50 kept in a saturated state, and the air permeability between the internal space 35 and the water phase portion 46 in the water storage tank 40 is lost.

Hereinafter, the function of the electrochemical gas sensor of the present invention will be described. First, when a gas to be detected is generated in the atmosphere, the gas to be detected enters the internal space 35 from the vent 34. The gas to be detected diffuses into the internal space 35 and reaches the communication port 36 during that time. However, the water storage tank 4 is closed due to the airtightness caused by the saturated state of one end of the curtain 50 that closes the communication port 36.
It is prevented from diffusing into the aqueous phase portion 46 within the zero. That is, the detection target gas is diffused only in the internal space 35 and the internal space 3
The dilution of the gas to be detected introduced into 5 is prevented.
When the gas to be detected is diluted by the communication port 36, the detection
The sensor element 10 that obtains an output according to the concentration of the elephant gas is provided externally.
Response time is delayed due to longer time to reach gas concentration
However, since there is a curtain 50, there is no gas dilution and the response time
Can be shortened. When there is a response from the sensor element 10, the external device operates accordingly via the terminal 5.

As shown in FIG . 1 , the electrochemical gas sensor according to the present invention further includes an aqueous phase portion 4 based on the curtain 50 described above.
6, the porous layer 6 closing the communication port 36 provided on the opposite side of the porous layer 6.
0 is provided. This porous layer 60 has air permeability and water tightness. As an example of the porous layer 60, a nonwoven fabric of a polyfluorinated ethylene fiber is used. In addition, the porous layer 6
0 is a plasma chemical vapor deposit (plasma C) using tetrafluoroethylene (hereinafter abbreviated as TFE) monomer which is a kind of the above-mentioned polyfluoroethylene.
According to VD), those obtained by forming a TFE polymer on the surface of filter paper or cloth may be used. The porous layer 60 is sucked up from the lower end of the vertical piece 55 of the curtain 50,
The water that has reached the other end after passing through the liquid layer 6 is in a liquid state,
, Passing through the communication port 36, and is prevented from entering the internal space 35. The reason for preventing entry into the internal space 35 is that the porous layer 60 has water tightness. Also,
When the inside of the internal space 35 is in an unsaturated state, water is sucked up from the lower end of the vertical piece 55 of the curtain 50 from the water phase portion 46 in the water storage tank 40, and water reaching the other end through the horizontal piece 56 evaporates, The steam passes through the porous layer 60 and the communication port 36,
The vapor is diffused into the internal space 35. The vapor enters and diffuses into the internal space 35 because the porous layer 60 has air permeability. Therefore, the sensor element 10 housed in the internal space 35 is protected from excessive water wetting,
The accompanying destruction of the sensor element 10 and abnormal output are prevented.

[0016]

According to the electrochemical gas sensor of the present invention, it is possible to prevent the water in the water storage tank from evaporating due to long-term use or storage, thereby delaying the response time.
Further, the gas type to be detected can be used without limitation.

[Brief description of the drawings]

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

FIG. 2 is a sectional view of an electrochemical gas sensor according to a conventional example of the present invention .

FIG. 3 is a plan view of the electrochemical gas sensor element according to the present invention .
FIG.

FIG. 4 shows an X-Y electrochemical gas sensor element according to FIG .
It is sectional drawing cut | disconnected by.

Claims (1)

(57) [Claims] (1) A water storage tank (40) attached to the housing (30) via a housing (30) and a partition (20). (2) The housing (30) is provided with a ventilation hole (34) for introducing a gas to be detected and an externally introduced gas. (3) The sensor element 10 is housed in the inner space 35 of the housing 30. (4) The inner space 35 and the water storage tank 40 are provided in the partition 20. (5) The sensor element 10 includes a working electrode 70 and a counter electrode 90 that are opposed to each other, and a solid electrolyte membrane that covers the working electrode 70 and the counter electrode 90 and that is maintained in a water-containing state. consists 110., further (6) one end of closing the communication port 36, and the other end immersed in the water phase portion 46 of the water storage tank 40, when the water is caused air tightness, Ru comprises a curtain 50 of the water-absorbing along with the 7) based on the curtain 50, the water phase in the water tank 40
Breathable and water-tight porous that closes the communication port 36 on the opposite side of 46
An electrochemical gas sensor comprising a porous layer (60) .