JP4248162B2 - Proton conductor gas sensor - Google Patents

Description

[0001]
[Field of the Invention]
The present invention relates to a proton conductor gas sensor, and more particularly to a mounting structure thereof.
[0002]
[Prior art]
A proton conductor gas sensor using a metal can structure is known. The sensor body is obtained by sandwiching an organic synthetic resin proton conductor film with a pair of electrode films to form an MEA (membrane electrode composite), and further sandwiching the MEA with a carbon sheet or the like. And water is stored in a metal can, the 1st metal washer is arranged on the upper part of water, and a sensor main part is arranged on a metal washer. The upper part of the sensor body is covered with a second metal washer, and the second washer and the sensor body are pressed against the first washer side with an insulating gasket (US Pat. No. 6,200,493, Japanese Patent Laid-Open No. 2000-146908). The second washer is a terminal on the detection electrode side of the sensor, and a metal can that is conducted to the first washer is a terminal on the counter electrode side. The conduction between the MEA and the upper and lower washers is maintained by the pressure from the gasket. A gas sensor is usually provided with a filter such as activated carbon in order to prevent poisonous substances from entering the detection electrode. However, in the gas sensor, the filter mounting structure is not particularly studied.
[0003]
[Problems of the Invention]
A basic problem of the present invention is to provide a new attachment structure for a filter (claims 1 to 4).
An additional problem of the present invention is to prevent the atmosphere on the detection electrode side from flowing around to the counter electrode side through the side surface of the sensor body (claims 2 and 3).
Another additional problem of the present invention is to prevent the rot of the water in the water reservoir (claim 4).
[0004]
[Structure of the invention]
In the proton conductor gas sensor of the present invention, a lower metal body and a sensor body using an intermediate proton conductor film and an upper second metal member are provided in a metal can provided with a water reservoir in the lower portion. Attach a ring-shaped insulating gasket, introducing the measured ambient to the sensor unit from the second metal member side, in the sensor which is adapted to introduce water vapor into the sensor body from the first metal member, wherein The sensor body includes a proton conductor film, a counter electrode provided on the lower surface thereof, a detection electrode provided on the upper surface of the proton conductor film, and a porous conductive film having continuous pores provided on the detection electrode, and the sensor The main body is a disk-shaped member having an upper surface, a lower surface, and a side surface, and the second metal member is formed of a hollow container having a bottom plate and an upper plate and containing a filter material therein, and the bottom plate And the upper plate, So as not to overlap when viewed from a direction perpendicular to proton conductor film, characterized in that an opening for ventilation.
[0005]
Preferably, the gasket is in contact with the side surface of the sensor body so that no open space is generated between the gasket and the side surface of the sensor body.
[0006]
Also preferably, between the side surface of the gasket and the sensor body, by placing an insulating ring-shaped elastic member, so that the open space is not created between the side surface of the gasket and the sensor body.
[0007]
Preferably, the water in the water reservoir contains a preservative.
[0008]
[Operation and effect of the invention]
In this invention, a hollow container having a bottom plate and an upper plate and containing a filter material therein is used as a lid on the detection electrode side of the sensor body. A filter material such as activated carbon or silica gel is accommodated in the lid, and openings for ventilation are provided in the bottom plate and the top plate so as not to overlap each other when viewed from the direction perpendicular to the proton conductor membrane. The sensor body includes a proton conductor film, a counter electrode provided on the lower surface thereof, a detection electrode provided on the upper surface of the proton conductor film, and a porous conductor film having continuous pores provided on the detection electrode, and The sensor body is a disk-shaped member having an upper surface, a lower surface, and a side surface. In this way, the atmosphere to be measured diffuses through the filter material from the opening in the top plate and is guided from the opening in the bottom plate to the sensor body. Since the opening on the top plate and the opening on the bottom plate do not overlap in the direction perpendicular to the proton conductor membrane, a long and wide gas flow path can be obtained even with a small lid, and the sensor body can be deteriorated over a long period of time. Can be prevented. The lid is connected to the detection electrode and serves as one terminal of the sensor. Such lids are manufactured in large quantities as battery parts, and battery parts can be diverted to metal cans and gasket lids, so that a gas sensor can be manufactured at a low cost, and a battery can be used as a detector. Similarly, the sensor can be mounted (Claim 1).
[0009]
In the sensor body, a porous conductive film having continuous pores is disposed on the detection electrode . This is because the atmosphere to be measured is supplied to the widest possible range of the detection electrode. Here, the inventor found that if there is an open space between the sensor body and the surrounding gasket, the atmosphere to be measured circulates from the porous conductor film to the counter electrode side through the open space, and overshoot or underflow occurs in the sensor output. We found that a shoot occurred. In order to reduce overshoot and undershoot, this open space can be closed. For example, a gasket is brought into contact with the side surface of the disk-shaped sensor body to eliminate the open space.
[0010]
In order to close the open space, an insulating ring-shaped elastic member may be disposed between the gasket and the side surface of the sensor body, in addition to directly contacting the gasket with the side surface of the sensor body. This elastic member is deformed by the pressure applied to the lid, and closes the open space on the side surface of the sensor body.
[0011]
The inventor has found that mold or the like can occur in the water stored in the reservoir of the metal can. This is because even if metal ions and anions are removed in ion-exchanged water or the like, organic substances are not completely removed, and organisms such as fungi are generated using the organic substances as nutrients. Other sources of nutrients for fungi and the like include organic matter attached to the inside of the metal can, particularly organic matter such as dirt that has entered during the manufacture of the gas sensor. If mold or the like occurs in water, the water vapor passage from the water reservoir to the sensor body may be sealed, or the counter electrode may be deteriorated. In order to prevent this, a preservative may be added to the water in the water reservoir (claim 4).
[0012]
【Example】
1 and 2 show a gas sensor 2 of the embodiment. In these figures, reference numeral 4 denotes a sensor body, which comprises an MEA (membrane electrode assembly) 6 and a pair of carbon sheets 12 and 13 disposed on both upper and lower surfaces thereof, and the carbon sheets 12 and 13 may not be provided. The MEA 6 has a membrane-shaped detection electrode 10 disposed on one surface of the proton conductor film 8 and a film-shaped counter electrode 11 disposed on the other surface, and the MEA 6 itself is well known. The MEA has a diameter of about 5 to 13 mm, for example, and the proton conductor film 8 has a thickness of 10 to 200 μm, for example. In the following description, the detection electrode 10 and the carbon sheet 12 side are referred to as the upper side, and the counter electrode 11 and the carbon sheet 13 side are referred to as the lower side when viewed from the proton conductor film 8.
[0013]
A metal washer 14 is provided on the lower side of the sensor body 4, and 15 is an opening provided in the washer 14 and has a diameter of about 0.1 to 1.0 mm, for example. Reference numeral 16 denotes a lid on the upper side of the sensor main body 4, which has an opening 17 provided in the upper lid 19 and an opening 18 provided in the lower lid 20. The opening 18 of the lower lid 20 is, for example, a central portion of the sensor main body 4. Exists. A plurality of openings 17 of the upper lid 19 are arranged concentrically outside the opening 18 when viewed from the top to the bottom of FIG. The diameters of the openings 17 and 18 are, for example, about 0.1 to 1 mm. For example, granular activated carbon 21 is accommodated in the lid 16, but other filter materials such as silica gel may be used.
[0014]
22 is a ring-shaped electrically insulating gasket, 24 is a metal can, and 26 is a diaphragm. A metal ribbon 28 has one end welded to the metal washer 14 and the other end welded to the metal can 24. The gasket 22 is made of rubber such as insulating neoprene or butadiene, and the lid 16 and the metal washer 14 are pressurized toward the sensor body 4 by caulking the lid 16 with the metal can 24 through the gasket 22. Ensure electrical connection. The lower part of the metal can 24 is used as a water reservoir, for example, containing gelled water 30.
[0015]
FIG. 2 shows the flow of the atmosphere in the gas sensor 2, and the gas to be measured such as CO passes through the activated carbon 21 from the opening 17 provided in the upper lid 19 of the lid body 16 and from the opening 18 of the lower lid 20. It is supplied to the sensor body 4. Here, the opening 17 and the opening 18 do not overlap each other when viewed from the direction perpendicular to the sensor body 4. For this reason, the atmosphere that has entered the activated carbon 21 from the opening 17 arrives at the opening 18 while diffusing within the activated carbon 21 in a wide range. For this reason, since the gas flow path in the lid 16 can be widened and lengthened, the activated carbon 21 can be effectively used to prevent poisoning, deterioration, malfunction or the like of the sensor body 4.
[0016]
The gas diffused from the opening 18 to the carbon sheet 12 is diffused in the carbon sheet 12 and supplied to the detection electrode 10 side of the MEA 6 in a wide range as indicated by the black arrows in FIG. On the other hand, water vapor and oxygen in the metal can 24 are supplied from the opening 15 to the carbon sheet 13, and similarly diffuse in the carbon sheet 13 as indicated by the white arrow in FIG. 2 and supply to the counter electrode 11 in a wide range. Is done. For this reason, the sensor body 4 can be used in a wide range, a large output can be taken out, and the life of the sensor can be extended.
[0017]
When the gas diffused in the carbon sheet 12 flows from the outside of the side surface of the sensor body 4 to the counter electrode 11 side, overshoot or undershoot occurs in the sensor output. In order to prevent this, an open space between the side surface of the sensor body 4 and the gasket 22 may be eliminated. In the case of FIG. 2, the open space is removed by making the gasket 22 substantially contact the side surface of the sensor body 4. ing.
[0018]
FIG. 3 shows the structure of the gas sensor 3 in which liquid water is stored. The gas sensor 3 is the same as the gas sensor of FIGS. 1 and 2 except that liquid water is stored instead of the gelled water 30. In the field of batteries, the gasket 22 is usually hermetically sealed in a metal can 24 with a pitch or the like. By the way, when liquid water instead of the gel water 30 is held in the metal can 24 and the gas sensor 3 is used on its side, when the air in the water reservoir expands in summer or the like, the water is pushed out from the opening 15 to the sensor body 4 side. Sometimes. This shortens the life of the gas sensor.
[0019]
Therefore, the gasket 22 is not fixed to the inner surface of the metal can 24, that is, the gasket 22 is not adhered to the metal can 24 with an adhesive such as a pitch. In this way, when the air in the metal can 24 is pressurized, the pressurized air can escape from the gap between the gasket 22 and the metal can 24. Since the gasket 22 is hydrophobic and the gap between the gasket 22 and the metal can 24 is small, liquid water does not escape from here.
[0020]
The gelled water 30 and the water 31 may be moldy. This is because in the case of inexpensive ion-exchanged water, organic substances are not completely removed, and there remains a nutrient source for mold. In addition to this, if the cleaning of the metal can 24 and the management at the time of manufacture are insufficient, the nutrient source may get into the water. Therefore, a preservative is preferably added to the gelled water 30 and the water 31. As the preservative, for example, glycerin, pentanol, ethylene glycol or the like is used, and those containing no cation or anion are preferable. And the addition amount shall be 1-30 weight% with respect to 100 weight% of the gelatinized water 30 or the water 31, for example, Preferably it is about 10 weight%.
[0021]
FIG. 4 shows a modified gas sensor 42. In addition, except the part pointed out especially below, it is the same as that of the gas sensor 2 of FIG. 1, FIG. 2, and the same code | symbol represents the same thing. Reference numeral 44 denotes a new gasket. Since the metal washer 14 is not sandwiched between the gaskets 44, the metal washer 14 can be directly connected to the metal can 24. An O-ring 46 is disposed in the gap between the sensor body 4 and the ring-shaped gasket 44 to seal this gap. The O-ring 46 is made of an insulating and elastic material such as neoprene or isoprene. The O-ring 46 is deformed by a pressure applied from the gasket 44 through the lid body 16 to close the gap on the outer periphery of the side surface of the sensor body 4. Like that.
[0022]
FIG. 5 shows a gas sensor 52 of a comparative example. The gas sensor 52 is for examining the effect of the open space 56 on the outer periphery of the side surface of the sensor body 4. The gas sensor 52 is the same as the gas sensor 2 of FIGS. 1 and 2 except that the structure of the gasket 54 is changed so that the open space 56 is generated. It is the same.
[0023]
We examined overshoot and undershoot with and without open space. 6 shows a response waveform with respect to CO 0 to 1000 ppm when the gas sensor 42 of the embodiment of FIG. 4 is used, and FIG. 7 shows a response waveform when the gas sensor 52 of FIG. 5 is used. None of the gas sensors uses gelled water 30 or water. However, as long as the atmosphere is not extremely dry, the sensor body 4 operates without storing water in the water reservoir.
[0024]
A vertical axis in FIGS. 6 and 7 shows a case where the lid 16 is one pole, the metal can 24 is the other pole, and a load resistance of about 100Ω is arranged therebetween to amplify the flowing current. The horizontal axis is time, and the CO concentration was increased stepwise from 0 to 1000 ppm, and then CO was removed. In the case of FIG. 6, no overshoot is observed from CO 30 to 300 ppm, and a slight overshoot occurs at CO 1000 ppm. Excluding CO, the sensor output returns to the initial value. In FIG. 6, the output in CO 0 ppm is not 0, but this is due to the offset of the amplifier circuit.
[0025]
On the other hand, in the case of FIG. 7, a remarkable overshoot is observed when CO is 300 ppm or more, and a significant undershoot is observed when CO is excluded. The difference between the sensor in FIG. 6 and FIG. 7 is that the sensor 2 used in FIG. 6 has no open space around the sensor body 4 and the sensor 52 used in FIG. Therefore, the occurrence of overshoot and undershoot can be estimated as follows. When the open space 56 exists, CO wraps around from the detection electrode side to the counter electrode side. This wraparound is slow. Immediately after the introduction of CO, since CO is not diffused on the counter electrode side, a large output is obtained, and then CO gradually diffuses on the counter electrode side, resulting in a decrease in output. In this way, overshoot occurs. When CO is excluded, the CO concentration first decreases on the detection electrode side, and the decrease in CO concentration on the counter electrode side is delayed, so undershoot occurs.
[0026]
As another cause of overshoot and undershoot, oxygen supply to the counter electrode may be delayed. If a high concentration of CO is supplied and the supply of oxygen to the counter electrode is slow, the output may drop apparently. However, in the case of FIG. 6, even if such a phenomenon occurs in 1000 ppm of CO, it is slight. In order to speed up the supply of oxygen to the counter electrode, the air permeability of the carbon sheet 13 on the counter electrode side may be increased, or the air permeability of the counter electrode 11 may be increased more than the air permeability of the detection electrode 10.
[0027]
As described above, in the embodiment, it is possible to manufacture a gas sensor easily and inexpensively by using substantially commercially available battery components for a package. The gas sensor can be attached to the detection device in the same manner as a normal battery. And the gas flow path in the cover body 16 can be made wide and long, and the deterioration of the sensor can be prevented. Further, it is possible to prevent gas from flowing from the detection electrode side to the counter electrode side, and to reduce overshoot and undershoot. Furthermore, it is possible to prevent the water in the water pool from decaying.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of the gas sensor of the embodiment. FIG. 2 is an enlarged cross-sectional view of the main part of the gas sensor of the embodiment. FIG. 3 is a modified gas sensor in which liquid water is held in a water reservoir. FIG. 4 is a cross-sectional view of a modified gas sensor. FIG. 5 is a cross-sectional view of a gas sensor of a comparative example. FIG. 6 is a waveform diagram showing the response of the gas sensor of the example to CO 30 to 1000 ppm. Waveform diagram showing the response of the gas sensor of FIG. 5 to CO 30 to 1000 ppm [Explanation of symbols]
2, 3, 42, 52 Gas sensor 4 Sensor body 6 MEA (membrane electrode composite)
8 Proton conductor film 10 Detecting electrode 11 Counter electrode 12, 13 Carbon sheet 14 Metal washer 15, 17, 18 Opening 16 Lid 19 Upper lid 20 Lower lid 21 Activated carbon 22, 44, 54 Gasket 24 Metal can 26 Diaphragm 28 Metal ribbon 30 Gel Chemical water 31 Water 46 O-ring 56 Open space

Claims (4)

The lower first metal member and the sensor body using the intermediate proton conductor film and the upper second metal member are attached to a metal can provided with a water reservoir with a ring-shaped insulating gasket. In the sensor, the atmosphere to be measured is introduced into the sensor body from the second metal member side, and water vapor is introduced into the sensor body from the first metal member side.
The sensor body includes a proton conductor film, a counter electrode provided on the lower surface thereof, a detection electrode provided on the upper surface of the proton conductor film, and a porous conductive film having continuous pores provided on the detection electrode, and The sensor body is a disk-shaped member having an upper surface, a lower surface, and a side surface, and the second metal member is a hollow container having a bottom plate and an upper plate and containing a filter material therein, and A proton conductor gas sensor, wherein an opening for ventilation is provided on each of a bottom plate and an upper plate so as not to overlap each other when viewed from a direction perpendicular to the proton conductor film. By the gasket is in contact with the side surface of the sensor body, the gasket and the open space between the side surface of the sensor body is so no, and wherein the proton conductor gas sensor as claimed in claim 1. An insulating ring-shaped elastic member is disposed between the gasket and the side surface of the sensor body so that an open space does not occur between the gasket and the side surface of the sensor body. Item 1. The proton conductor gas sensor according to Item 1.   The proton conductor gas sensor according to any one of claims 1 to 3, wherein a preservative is contained in the water of the water reservoir.

Images