JP3926164B2 - Proton conductor gas sensor and gas detection method using the same - Google Patents

Description

[0001]
[Field of the Invention]
The present invention relates to a gas sensor using a proton conductor membrane, and more particularly to improvement of the water reservoir.
[0002]
[Prior art]
In a gas sensor using a proton conductor, for example, electrode films are stacked on both sides of a proton conductor film, one of which is a detection electrode and the other is a counter electrode. The detection electrode and the counter electrode are formed on, for example, hydrophobic carbon paper, and the carbon paper functions as a current collector from the electrode and as a gas channel for supplying detection target gas, oxygen, and water vapor to the entire electrode surface. A composite of the proton conductor film, the detection electrode, and the counter electrode is referred to as MEA (membrane electrode assembly). In principle, the MEA has carbon paper attached to both the detection electrode and the counter electrode. Then, water is stored in a metal can to form a water reservoir, a metal washer is attached to the metal can, a carbon paper on the counter electrode side of the MEA is disposed on the metal washer, and the counter electrode is conducted to the metal can through the metal washer. Place the upper metal plate in contact with the carbon paper on the detection electrode side, and attach the gasket between the metal can and the upper metal plate so that the upper metal plate is pressed to the MEA side. The continuity between the upper metal plate and the carbon paper on the detection electrode side is maintained, and at the same time, the continuity between the carbon paper on the counter electrode side and the metal washer, and between the metal washer and the metal can are maintained. At the same time, the gaskets block the ventilation between the water reservoir and the outside air, supply water vapor to the MEA from the pores provided in the metal washer, and supply the detection target gas from the upper metal plate to the detection electrode (US Pat. No. 5650054). .
[0003]
With such a gas sensor, when the ambient temperature suddenly increases with the metal can laid sideways, the air in the metal can expands, pressurizing the water in the water reservoir and pushing the water from the pores to the MEA side. Become. The characteristics of the MEA electrode may change when wetted with water. Such a problem occurs when water in the water pool moves around due to a change in temperature, a change in posture of the gas sensor, or the like.
[0004]
[Problems of the Invention]
A basic object of the present invention is to prevent water in a water reservoir from coming into contact with a sensor body (claims 1 to 6).
An additional object of the present invention is to prevent the water reservoir pack from colliding with the outer case and being torn when an impact is applied to the gas sensor.
Another object of the present invention is to control the moisture permeability of the sensor body by controlling the water vapor permeability of the water reservoir pack and to limit the water consumption of the water reservoir pack.
Another object of the present invention is to prevent the gas to be detected from flowing around to the counter electrode side and thereby reducing the output of the gas sensor (claim 6).
[0005]
[Structure of the invention]
The proton conductor gas sensor of the present invention supplies water vapor from water stored in a water reservoir to a sensor body having at least a detection electrode, a counter electrode, and a proton conductor film, and detects an object to be detected from an electrical output between the detection electrode and the counter electrode. In the sensor that detects gas, the water reservoir includes a water reservoir pack of a synthetic resin film that keeps water impermeable and allows water vapor to pass at a predetermined speed, and an outer case that holds the water reservoir pack. It is characterized by comprising (claim 1).
[0006]
Preferably, the synthetic resin film is a thermoplastic resin film (Claim 2), and particularly preferably a thermoplastic polyolefin resin film.
Preferably, means for restricting the movement of the water reservoir pack with respect to the outer case is provided so as to prevent the water reservoir pack from moving around with respect to the outer case. This means is, for example, an adhesive or a sticking material for fixing a foam, a sponge, or a water reservoir pack. Here, it is particularly preferable that the approximate position of the water reservoir is determined so that a gas space is generated between the water reservoir pack and the sensor body.
[0007]
In the gas detection method of the present invention, a water reservoir pack of a synthetic resin film for holding water impermeable and allowing water vapor to pass through is accommodated in the outer case, and at least a detection electrode and a counter electrode are provided in the outer case. A sensor main body having a proton conductor film is attached, the sensor main body is humidified with water vapor from the water reservoir pack, and a gas is detected from an electrical output between the detection electrode and the counter electrode.
[0008]
Preferably, the humidification rate of the sensor body from the water reservoir pack is controlled to a predetermined value by controlling the water vapor permeability of the water reservoir pack.
Preferably, the sensor main body is arranged such that the detection electrode side is arranged on the ambient atmosphere side, the counter electrode side is arranged on the side close to the water reservoir pack, and the detection target gas that wraps around the counter electrode side of the sensor main body, A sensor main body is attached to the outer case so as to escape into the outer case, thereby preventing detection target gas from entering the counter electrode side (Claim 6).
[0009]
[Operation and effect of the invention]
In the present invention, since the water is sealed in the water reservoir pack, the sensor main body is not exposed to liquid water (claims 1 to 6). Here, when the water vapor transmission rate of the synthetic resin film of the water reservoir pack is controlled, the evaporation rate of the water is limited, and the time for which the water reservoir acts can be lengthened even when the airtightness of the outer case is low.
[0010]
The water retained in the sump pack is not limited to liquid water, but water that has been absorbed into a water-absorbing polymer or silica gel, gelled, anti-corrosive agent such as glycerin, or water added with a deliquescent agent such as calcium chloride. But it ’s okay. If the synthetic resin film used for the water reservoir pack is a thermoplastic resin film, the mouth of the pack can be easily fused and sealed (Claim 2).
[0011]
If the water pack collides with the outer case due to the gas sensor falling or periodic vibrations being applied to the gas sensor, the water pack may be broken. Therefore, if the movement of the water pool pack with respect to the outer case is restricted, it is possible to prevent the water pool pack from being torn by dropping or vibration (claim 3). Here, preferably, the approximate position of the water pool pack is limited so that a gap is formed in the outer case between the sensor body and the water pool pack. If it does in this way, this gap will serve as a buffer for supplying water vapor, and it will be possible to supply water vapor with a substantially predetermined relative humidity to the sensor body.
[0012]
The water vapor permeability of the water reservoir pack can be controlled in a wide range. For example, when a porous polyolefin resin is used, a very large water vapor transmission rate can be obtained, and the relative humidity in the outer case can be kept almost 100% even outside the water reservoir pack. On the other hand, when the thermoplastic resin material is a polyolefin resin having a low water vapor transmission rate such as vinyl chloride or vinylidene chloride, the relative humidity in the outer case can be maintained at, for example, about 60 to 80%. If the relative humidity outside the water pack in the outer case is lower than 100%, the life of the water pack is increased accordingly. Further, the part for supplying water vapor from the outer case to the sensor body can be made larger, and the sensor body can be humidified more uniformly than when the sensor body is humidified from a small part. For this reason, by controlling the water vapor permeability of the water reservoir pack, the humidification rate from the water reservoir pack to the sensor body can be controlled to a predetermined value.
[0013]
Since the water is sealed in the water reservoir pack, the air permeability between the outer case and the periphery on the counter electrode side of the sensor body can be enhanced. Then, the detection target gas that has circulated from the detection electrode side to the opposite side of the proton conductor film can escape into the outer case, and the outer case can be used as a buffer for the extra detection target gas. In this way, even when the detection target gas circulates on the opposite side of the detection electrode, it is possible to prevent or reduce the decrease in the output of the gas sensor (claim 6).
[0014]
【Example】
1 to 6 show a proton conductor gas sensor according to an embodiment. 1 to 3 show a first embodiment, 2 is a gas sensor using a proton conductor, 4 is a metal can using steel or stainless steel, and 6 is a water reservoir pack. A thermoplastic synthetic resin bag is used as the material of the water pool pack 6. For example, a bag having a high water vapor transmission rate includes a film bag made of a polyolefin film such as polypropylene or polyethylene that is made porous. Further, not only polyethylene and polypropylene but also a porous fluororesin polymer film or the like can be used to obtain the water reservoir pack 6 having high water vapor permeability. In order to reduce the evaporation rate of water from the water reservoir pack 6, a resin film having a low water vapor transmission rate such as polyvinyl chloride or polyvinylidene chloride may be used. In extreme cases, polyvinyl chloride, polyvinylidene chloride, etc. An aluminum film or the like may be laminated on this film. All of these resins are thermoplastic polyolefin resins. By storing the water in the water reservoir pack 6, the liquid water is prevented from touching the proton conductor membrane and its electrodes, preventing poisoning due to water and additives to the water, and water vapor from the water reservoir pack 6. Can control the evaporation rate. The fused portion 7 of the synthetic resin film of the water reservoir pack 6 is for closing the water reservoir pack 6. It should be noted that a waterless air space is not substantially left in the water reservoir pack 6 so that water does not move in the water reservoir pack 6 to break the pack film.
[0015]
Reference numeral 8 denotes a foamed material such as expanded polystyrene, which is disposed on the sensor body side (upper side) when viewed from the water reservoir pack 6, and substantially fixes the position of the water reservoir pack 6 to the lower side of the metal can 4. Instead of substantially fixing the position of the water reservoir pack 6 with the foam 8, the bottom portion or side portion of the water reservoir pack 6 may be attached to the metal can 4 with an adhesive or an adhesive. Further, instead of the foam 8, a sponge-like cushion or the like may be arranged. The space occupied by the foam 8 at the top of the water pool pack 6 becomes a buffer for air humidified with water vapor evaporated from the water pool pack 6.
[0016]
A water vapor introduction hole 10 is provided in the upper part of the metal can 4, and 12 is an MEA, which corresponds to the sensor body. The structure of the MEA 12 is shown in FIG. 2. 14 is a proton conductor film, 15 is a detection electrode, 16 is a counter electrode, and 17 and 18 are carbon paper. The film thicknesses of the proton conductor film 14, the electrodes 15, 16 and the carbon paper 17, 18 are each 20 μm, for example, and SPE (solid polymer proton conductor) is used for the proton conductor film 14. The composition of the sensing electrode 15 and the counter electrode 16 is, for example, 60% by weight of carbon carrying Pt (weight ratio, Pt: carbon = 1: 4), 20% by weight of SPE, and 20% by weight of a binder fluororesin. And kneaded. The catalytic activity of the counter electrode 16 may be made lower than that of the detection electrode 15 so that the dissociation reaction of the detection target gas that has entered the counter electrode 16 side does not occur. The carbon papers 17 and 18 have a carbon fiber direction perpendicular to the thickness direction of the MEA 12 and high air permeability and conductivity in the direction perpendicular to the thickness direction of the MEA 12, and a small amount of fluororesin is added to the carbon fiber. Then, use a hydrophobized one. Preferably, a catalyst such as Pt is supported on the carbon paper 18 on the counter electrode side, and the detection target gas diffused into the metal can 4 is removed without causing proton transfer in the proton conductor film. Here, the detection electrode 15 is arranged on one side of the proton conductor film 14 and the counter electrode 16 is arranged on the opposite side, but three detection electrodes, a counter electrode, and a reference electrode may be provided.
[0017]
20 is a metal lid, 22 is a metal plate, 24 is a pore for introducing gas, 26 is a filter material such as activated carbon or zeolite, and is filled between the metal lid 20 and the metal plate 22, and 28 is a MEA 12. This is a gas introduction hole for introducing the detection target gas to the detection electrode 15 side. Reference numeral 30 denotes a gasket that secures airtightness between the metal lid 20 and the metal can 4, and 32 denotes a caulking portion that caulks and fixes the metal lid 20 to the metal can 4. 15, and the electrical connection between the counter electrode 16 and the metal can 4 is ensured. A gap 31 is likely to occur between the MEA 12 and the gasket 30 because it is difficult to accurately match the inner diameter of the gasket 30 and the outer diameter of the MEA 12.
[0018]
The operation of the embodiment will be described. A detection target gas such as CO passes through the gas introduction hole 28 from the pore 24 through the filter material 26, restricts air permeability through the gas introduction hole 28 or the pore 24, and supplies the gas to the MEA 12. For this reason, in the MEA 12, the supply of the detection target gas is diffusion-controlled. A plurality of pores 24 are provided in the side surface portion of the metal plate 22, and one gas introduction hole 28 is provided in the central portion of the MEA 12, or a plurality of gas introduction holes 28 are provided in the peripheral portion of the MEA 12, and the pores 24 are provided in the metal plate. By providing one at the top of 22 or the like, the gas to be detected passes through each part of the filter material 26 evenly, thereby extending the life of the filter material 26. For this reason, the fine holes 24 and the gas introduction holes 28 are arranged so as not to be aligned on the vertical direction (axial direction) of the gas sensor 2. The detection target gas that has reached the MEA 12 diffuses in the left-right direction (radial direction perpendicular to the axial direction) in FIG. 1 along the carbon paper 17 on the detection electrode 15 side, and is supplied to the detection electrode 15. Along with this, CO is oxidized by H 2 O at the detection electrode 15, and protons generated by the CO oxidation reaction move through the proton conductor film 14 and react with oxygen at the counter electrode 16 to be regenerated to H 2 O. When the metal can 4 and the metal plate 22 are connected via a small load resistance, the current flowing through the proton conductor film 14 flows through the load resistance, which is an output proportional to the CO concentration.
[0019]
The water vapor passes through the water storage pack 6, and at this time, the transmission speed is determined by the water vapor permeability of the synthetic resin film, enters the carbon paper 18 on the counter electrode 16 side from the water vapor introduction hole 10, and the inside of the carbon paper is in the thickness direction of the MEA 12. And is supplied to the counter electrode 16. Then, the water vapor diffuses from the counter electrode 16 to the proton conductor film 14 and the detection electrode 15 and is released from the gas introduction hole 28 to the outside air side according to the humidity difference from the outside air.
[0020]
The air permeability of the water vapor introduction hole 10 is made larger than the air permeability of the gas introduction hole 28. Further, the water vapor permeability of the water reservoir pack 6 may be determined so as to keep the relative humidity outside the water reservoir pack 6 near 100%, but the relative humidity outside the water reservoir pack 6 is maintained at about 60 to 80%. Thus, water vapor permeability can also be determined. Then, the relative humidity at the portion containing the foam 8 is also maintained at about 60 to 80%, and the relative humidity at the MEA 12 is also maintained at about 60 to 80%. Thus, the humidified air having a relative humidity lower than 100% can be uniformly supplied to the MEA 12 from the large water vapor introducing hole 10, and the consumption of water can be reduced accordingly. In any case, by using the water reservoir pack 6, the vaporization rate of the water vapor is reduced, and accordingly, the life acting as a water reservoir can be extended.
[0021]
As a problem in the proton conductor gas sensor, a detection target gas such as CO diffused in the carbon paper 17 on the detection electrode 15 side may diffuse from the gap 31 to the counter electrode 16 side. On the other hand, in the embodiment, since the water vapor introduction hole 10 can be enlarged, the detection target gas diffused from the gap 31 can be released to the space containing the foam 8 at the upper part of the water reservoir pack 6. For this reason, the space of the part of the foam 8 serves as a buffer for the extra detection target gas, and the extra detection target gas can be prevented from diffusing into the metal can 4 and lowering the output due to the gas that has entered the counter electrode. . The air in the space containing the foam 8 is also a buffer for humidified air to be supplied to the MEA 12 and supplies humidified air (water vapor) more uniformly than when the film of the water pool pack 6 is in direct contact with the water vapor introduction hole 10. it can.
[0022]
FIG. 3 shows the gas sensor 2 lying on its side. When water is stored directly in the metal can 4 without using the water reservoir pack 6, the water surface reaches above the water vapor introduction hole 10, and when the temperature of the gas sensor 2 suddenly rises, the air above the water surface Since it expands, water is pushed out from the water vapor introduction hole 10 toward the MEA 12 and the MEA 12 may get wet with water. This causes the activity of the detection electrode 15 and the counter electrode 16 to fluctuate and consumes water. However, if water is accommodated in the water reservoir pack 6, liquid water does not flow out from the water vapor introduction hole 10 to the MEA 12 side even if the gas sensor 2 is laid down. In addition, when the foam 8 is provided, it is possible to prevent the supersaturated water vapor from condensing on the MEA 12 even if it takes time for the water temperature in the water sump pack 6 to drop when the ambient temperature rapidly decreases.
[0023]
FIG. 4 shows a gas sensor 42 according to a modified example. 46 is a pore provided in the vicinity of the gap 31 for releasing the detection target gas that has entered the gap 31 from the MEA 12 to the buffer space above the water reservoir pack 6. It is. Reference numeral 44 denotes an adhesive portion using a double-sided tape or the like for substantially fixing the water reservoir pack 6 to the lower side of the metal can 4.
[0024]
5 and 6 show a gas sensor 52 of the second embodiment. Reference numeral 54 denotes a non-moisture permeable pack, for example, as shown in FIG. 6, which is a film bag in which an aluminum film 56 or the like is laminated on a thermoplastic film 55 such as polyethylene or polypropylene to extremely reduce water vapor permeability. The water reservoir pack 6 is accommodated inside the moisture-impermeable pack 54. The moisture-impermeable pack 54 has low water vapor permeability, but still has slight water vapor permeability when in direct contact with liquid water, which prevents water vapor from escaping through the small pores in the aluminum film 56. This is because it is difficult to do. For this reason, when, for example, 5 cm ³ of water is directly held in the moisture-impermeable pack 54, water may be lost within three years in a dry atmosphere such as a desert. Therefore, the water reservoir pack 6 is accommodated in the moisture-impermeable pack 54, the water vapor permeability of the water reservoir pack 6 is limited, and the life as a water reservoir is extended.
[0025]
The water reservoir pack 6 is attached to the inner lower portion of the moisture-impermeable pack 54 with the adhesive portion 44, and a gap 60 remains in the upper portion thereof. Reference numeral 62 denotes a moisture permeable portion, which includes an opening 63 obtained by cutting the aluminum film 56 and an opening 64 of the thermoplastic film 55 communicating therewith as shown in FIG. The openings 63 and 64 may have the same diameter, or the opening 64 may not be provided by utilizing the water vapor permeability of the thermoplastic film 55 itself.
[0026]
Reference numeral 66 denotes a sensor body. Leads 67 and 68 are arranged on both sides of the MEA 12 as shown in FIG. 6, and these are sandwiched between heat shrink films 72 and 73. In addition, conductivity between the lead 68 and the MEA 12 is obtained. The contact portions 74 and 76 are, for example, plates having the same size as the MEA 12 and are portions for obtaining electrical contact between the leads 67 and 68 and the MEA 12. The sensor body 66 is attached by, for example, fusing or adhering the heat shrink film 73 on the moisture-impermeable pack 54 side to the thermoplastic film 55. The heat-shrink films 72 and 73 are for securing the contact between the lead 68 and the MEA 12 and the contact between the MEA 12 and the lead 67 and restricting the introduction path of gas and water vapor. If it is obtained by this method, it may not be provided. A filter 70 is made of activated carbon, silica gel, zeolite, or the like, and removes toxic gases and interference gases such as ethanol and NOx.
[0027]
The contact portion 74 has a small-diameter gas introduction hole 78 and introduces the detection target gas so that the MEA 12 is diffusion-controlled. The contact portion 76 has, for example, a plurality of water vapor introduction holes 79 and introduces uniformly humidified air into the MEA 12. Instead of providing the plurality of water vapor introduction holes 79 in the peripheral part of the MEA 12, a water vapor introduction hole having a diameter larger than that of the gas introduction hole 78 may be provided in the central part of the MEA 12. Reference numeral 80 denotes a pore, which communicates with the gas introduction hole 78, and the pore 81 communicates with the water vapor introduction hole 79. The sensor main body 66 may be disposed above the water reservoir 6 inside the non-moisture permeable pack 54 as indicated by a chain line in FIG.
[0028]
The operation of the second embodiment will be described. The impermeable pack 54 has a slight water vapor permeability, and if the water storage pack 6 is not used, water may be consumed in a short time. On the other hand, if the water vapor permeability is limited by the water reservoir pack 6, the life as the water reservoir can be extended to, for example, 3 years or more. The detection target gas may contact the MEA 12 from the filter 70 through the pore 80 and the gas introduction hole 78 and may flow from the side surface of the MEA 12 to the counter electrode side. Therefore, the detection target gas flowing into the counter electrode is caused to flow from the opening 64 into the gap 60 of the moisture-impermeable pack 54, and this portion is used as a buffer.
[0029]
In the embodiment, a catalyst such as Pt is supported on the carbon paper 18 on the counter electrode side, and the detection target gas that has entered the counter electrode side is removed. However, the catalyst for removing the detection target gas may be provided in the space above the water pool pack 6 or the like. In the embodiment, it is possible to prevent liquid water from moving around and coming into contact with the MEA 12, and to control (select) the water vapor permeability of the water storage pack 6, as in the non-moisture permeable pack 54 of FIGS. 5 and 6. Even when the airtightness of the water is insufficient, the life of the water reservoir can be extended. Moreover, the relative humidity of the water vapor supplied to the MEA 12 can be lower than 100%, and air having a relative humidity of, for example, about 60 to 80% can be uniformly supplied to the MEA 12 from a wider range, so that the entire MEA 12 can be uniformly humidified. The impact applied to the water reservoir pack 6 is absorbed by the foam 8 or the water reservoir pack 6 is fixed by the adhesive portion 44 to prevent the water reservoir pack 6 from being damaged. The detection target gas that wraps around to the counter electrode side due to the gap 31 or the like can escape to the space of the foam 8 above the water reservoir pack 6 or the gap 60 or the like, and can prevent a decrease in output due to the detection target gas wrapping around the counter electrode side. . Since water is accommodated in the water reservoir pack 6, the MEA 12 can be prevented from getting wet with liquid water.
[Brief description of the drawings]
FIG. 1 is a vertical sectional view of a gas sensor of an embodiment. FIG. 2 is a sectional view of an MEA used in the embodiment. FIG. 3 is a sectional view showing a state when the gas sensor of the embodiment is laid down. ] Cross-sectional view in the vertical direction of the gas sensor according to the modified example [FIG. 5] Cross-sectional view in the horizontal direction of the gas sensor according to the second embodiment [FIG. 6] Enlarged cross-sectional view of the main part of the gas sensor according to the second embodiment
2 Gas Sensor 4 Metal Can 6 Water Reservoir Pack 7 Fusion Portion 8 Foam 10 Water Vapor Introduction Hole 12 MEA
14 Proton conductor film 15 Detection electrode 16 Counter electrode 17, 18 Carbon paper 20 Metal lid 22 Metal plate 24 Pore 26 Filter material 28 Gas introduction hole 30 Gasket 31 Clearance 32 Caulking part 42 Gas sensor 44 Adhesive part 46 Pore 52 Gas sensor 54 Non Moisture permeable pack 55 Thermoplastic film 56 Aluminum film 60 Gap 62 Moisture permeable portion 63, 64 Opening 66 Sensor body 67, 68 Lead 70 Filter 72, 73 Heat shrink film 74, 76 Contact portion 78 Gas introduction hole 79 Water vapor introduction hole 80, 81 pores

Claims (6)

In a sensor that supplies water vapor from water stored in a water reservoir to a sensor body having at least a detection electrode, a counter electrode, and a proton conductor film, and detects a detection target gas from an electrical output between the detection electrode and the counter electrode. ,
The water reservoir is composed of a water reservoir pack of a synthetic resin film for keeping water impermeable and allowing water vapor to pass through at a predetermined speed, and an outer case holding the water reservoir pack. Body gas sensor. 2. The proton conductor gas sensor according to claim 1, wherein the synthetic resin film is a thermoplastic resin film. 3. The proton conductor gas sensor according to claim 1, further comprising means for restricting movement of the water reservoir pack relative to the outer case so as to prevent the water reservoir pack from moving around with respect to the outer case. While holding the water impermeable and allowing the water vapor to permeate, the synthetic resin film reservoir pack is housed in the outer case,
A sensor body having at least a detection electrode, a counter electrode, and a proton conductor film is attached to the outer case, and the sensor body is humidified with water vapor from the water reservoir pack,
And the gas detection method which detects gas from the electrical output between the said detection electrode and a counter electrode. 5. The gas detection method according to claim 4, wherein the humidification rate of the sensor body from the water pack is controlled to a predetermined value by controlling the water vapor permeability of the water pack. The sensor body is arranged so that the detection electrode side is arranged on the ambient atmosphere side and the counter electrode side is arranged on the side close to the water reservoir pack,
In addition, the sensor main body is attached to the outer case so that the detection target gas that has entered the counter electrode side of the sensor body escapes into the outer case, thereby preventing the detection target gas from entering the counter electrode side. The gas detection method according to claim 4 or 5.

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