JP5306276B2 - Electrochemical gas sensor - Google Patents

Description

The present invention relates to an electrochemical gas sensor .

  The inventors have developed a gas sensor as disclosed in Patent Document 1 (JP2004-226346A). This sensor supplies an atmosphere to be detected to the detection electrode side through a filter filled with a filter material such as activated carbon and a diffusion control plate. Further, these members are set in a metal can also serving as a water reservoir, and the filter is caulked to the metal can via a gasket. The detection electrode is electrically connected to the filter, the counter electrode is connected to a metal can, and the filter and the metal can serve as terminals of the gas sensor.

  In the gas sensor of Patent Document 1, there are holes in the side and bottom of the filter, and the atmosphere to be detected that has entered through the holes on the side is treated with activated carbon and exits from the hole on the bottom to the MEA side. Since it is difficult to accurately control the size of the hole in the bottom surface of the filter, a diffusion control plate having a diffusion control hole of a certain size is disposed between the bottom surface of the filter and the MEA by punching or the like. As a result, the amount of atmosphere diffusing into the MEA is made uniform among the gas sensors, and the gas sensitivity is made constant.

The inventor investigated the reliability of the above gas sensor and studied to find and solve a potential problem of the gas sensor. As a result, it has been found that if a gap is generated between the filter material in the filter and the metal plate on the detection electrode side, the detected atmosphere may be supplied to the detection electrode without passing through the filter material. If this happens, it may cause false alarms. Therefore, the inventor studied a filter that does not generate a flow path that does not pass through the filter material, and reached the present invention .

JP2004-226346A

The problem of the present invention is that the flow path that does not pass through the filter material does not occur, the detected atmosphere can be reliably treated with the filter material, and the filter material can be changed even if the container size or the filter material thickness varies. An object of the present invention is to provide a gas sensor provided with a filter that does not generate a gas flow path that does not pass through.

The present invention provides a gas sensor main body in which a detection electrode is provided on one surface of the front and back surfaces of a separator or proton conductor film that holds a liquid electrolyte , and a counter electrode is provided on the opposite surface;
In an electrochemical gas sensor comprising a filter that adsorbs unnecessary gas from the atmosphere to be detected supplied to the detection electrode,
The filter is a metal container in which two metal plates are joined together, a sheet-shaped or disk-shaped filter material accommodated in the metal container, a synthetic rubber, a synthetic resin elastomer, or a synthetic resin viscoelastic body. An elastic spacer made of
One of the two metal plates is provided with a hole for introducing the detected atmosphere into the container, and the other metal plate is provided with a hole for supplying the detected atmosphere that has passed the filter material to the detection electrode side,
The elastic spacer and the filter material are sandwiched between the two metal plates, the elastic spacer presses the filter material and fixes it in a metal container, and the filter material is placed in one of the holes. It is characterized by being in close contact.

In this invention, since the filter material is pressed and adhered to the hole provided in the metal container or the like by the elastic spacer , there is no gap for bypassing the filter material. Therefore, the gas does not pass through the filter without being treated with the filter material. Further, there is no generation of wear powder due to the filter material moving around in the metal container . Even if the thickness of the filter material or the inner diameter of the metal container varies, the filter material is pressed and fixed in the metal container , so that no gap is generated.

The elastic spacer includes at least one member of synthetic rubber, synthetic resin elastomer, and synthetic resin viscoelastic body , and can easily and uniformly press the filter material as compared with a case where the elastic spacer is pressed by a spring or the like.

In this specification, the filter material removes the target gas by adsorption . The filter material having a certain shape means that the filter material is molded into a disk shape or the like, or a sheet shape or the like, and means that the filter material does not have a certain shape. To do. Moreover, a container means an airtight container except a hole in principle.

In the gas sensor of the present invention, the filter material is pressed by the elastic spacer so as to be in close contact with the hole of one of the metal plates, so that the detected atmosphere does not reach the detection electrode without passing through the filter material. Therefore, the risk of misinformation is reduced. Further, since the filter material is fixed when pressed by the elastic spacer, even if the filter material is formed from fine powder, for example, the filter material is not rubbed and fine powder is not generated. Be further varied thickness, etc. of the size or filter material of the filter material, a spacer of elastic can be pressed toward the filter material to ensure that the sensing electrode side or the like of the metal plate. Preferably, the elastic spacer is disposed between the filter material and the opposite metal plate. If it does in this way, a filter material can be pressed easily and reliably so that it may contact | adhere with the hole of metal plates, such as a detection pole side .

Sectional view of the electrochemical gas sensor of the example Diffusion control hole in embodiment and enlarged sectional view around it Expanded sectional view of the filter of the embodiment Enlarged sectional view of the filter in the conventional example Cross-sectional view of a modified filter Sectional view of the filter of the reference example Block diagram of a gas detector using the gas sensor of the embodiment

  In the following, an optimum embodiment for carrying out the present invention will be shown.

With reference to FIGS. 1-6, an Example is described for the electrochemical gas sensor 2 as an example . FIG. 1 shows the overall configuration of the electrochemical gas sensor 2, and FIGS. 2 and 3 show the configuration of each part of the electrochemical gas sensor 2. Hereinafter, the electrochemical gas sensor 2 may be simply referred to as the gas sensor 2. In each figure, 4 is a metal can such as stainless steel, titanium, etc., in which water 6 is sealed with the inside as a water reservoir. Reference numeral 8 denotes a filter, which is circular in plan view, in which two circular metal plates 8a and 8b are joined together at the circumferential portion, and a space is provided between the metal plates 8a and 8b. There are holes 10 in several places on the side of the upper metal plate 8a, and there are holes 12 in, for example, the center of the lower metal plate 8b. For example, a two-layer activated carbon sheet 14 is accommodated inside the filter 8, and the activated carbon sheet 14 is pressed by an elastic spacer 16 so as to be in close contact with the hole 12 at the bottom.

The elastic spacer 16 is made of an elastic material made of synthetic rubber, synthetic resin elastomer, or synthetic resin viscoelastic body. When a spring such as a synthetic resin washer is used for the elastic spacer 16 , it is difficult to press the activated carbon sheet 14 uniformly, and when the elastic spacer 16 comes into contact with the sheet 14, fine powder of activated carbon may be generated. The elastic spacer 16 is preferably made of a material that has high heat resistance and does not emit gas at a high temperature so that the gas sensor 2 does not adversely affect even if the gas sensor 2 experiences a high temperature. A particularly preferable material for the elastic spacer 16 is EPDM (ethylene propylene rubber) or CR (chloroprene rubber). In the embodiment, EPDM is used. As an example of the size in the embodiment, the gap between the metal plates 8 a and 8 b is 4 mm, the activated carbon sheet 14 is 3 mm in total thickness, and the thickness of the elastic spacer 16 is in a state before being set in the filter 8. For example, 3 mm. In addition, instead of the activated carbon sheet 14, sheet-like zeolite or sheet-like silica gel may be used, and the number of sheets 14 is arbitrary, such as one, two, and three. That is, other than the activated carbon sheet 14 can be used as long as it is a filter material that adsorbs a gas molded into a fixed shape.

  18 is a gasket for fixing the filter 8 to the top of the metal can 4 by caulking the top of the metal can 4, insulating between them, and keeping the metal can 4 and the filter 8 airtight.

  In FIG. 2, reference numeral 20 denotes a diffusion control plate made of a thin stainless steel plate or the like, and includes a diffusion control hole 22 that communicates with the hole 12 on the bottom surface of the filter 8, that is, overlaps in plan view. A gas sensor main body 24 includes, for example, a porous separator holding a liquid electrolyte, detection electrodes and a counter electrode on the front and back sides thereof, and a hydrophobic carbon sheet that distributes gas to the detection electrode and the counter electrode. A metal washer 25 has a hole 26 and supplies water vapor and air from the inside of the metal can 4 to the counter electrode side. Reference numeral 28 denotes a recess provided in the metal can 4 and supports the washer 25.

  The arrangement of the diffusion control hole 22 and the gas sensor main body 24 will be described with reference to FIG. For example, the hole 12 provided in the filter 8 has a diameter of about 1 mm, and the metal plates 8a and 8b have a thickness of about 1 mm. In contrast, the diffusion control plate 20 is a thin metal plate having a thickness of about 0.1 mm, and the diffusion control hole 22 is a small hole having a diameter of about 0.1 mm. The gas sensor main body 24 includes, for example, a central porous separator, front and back detection electrodes 31 and counter electrodes 32, and hydrophobic carbon sheets 33 and 34 outside the detection electrodes 31 and the counter electrodes 32. The hydrophobic carbon sheets 33 and 34 may be omitted. The porous separator 30 holds an aqueous solution of an electrolyte, and the separator 30 is unnecessary when a proton conductor membrane is used instead of the liquid electrolyte. The detection electrode 31 and the counter electrode 32 are obtained by supporting an electrode catalyst such as Pt or Pt-Ru on a carrier such as carbon powder, and may be attached to the front and back of the separator 30, or may be a hydrophobic carbon sheet 33, 34 may be brought into contact with the separator 30.

  The hydrophobic carbon sheets 33 and 34 are porous and hydrophobic carbon sheets. The hydrophobic carbon sheet 33 on the diffusion control hole 22 side distributes the detected atmosphere uniformly to the detection electrode 31 and electrically connects the detection electrode 31 and the diffusion control plate 20. The hydrophobic carbon sheet 34 uniformly distributes water vapor and air from the inside of the metal can 4 to the counter electrode 32, and prevents liquid water inside the metal can 4 from overflowing from the hole 26 to the counter electrode 32 side. Further, the counter electrode 32 is electrically connected to the washer 25.

  Here, the electrical connection of the gas sensor 2 will be described. The detection electrode 31 is connected in the order of the hydrophobic carbon sheet 33, the diffusion control plate 20, and the filter 8, and the filter 8 serves as an external terminal. The counter electrode 32 is connected in the order of the hydrophobic carbon sheet 34, the washer 25, and the metal can 4, and the metal can 4 serves as an external terminal. The filter 8 and the metal can 4 are insulated by a gasket 18.

  The significance of the elastic spacer 16 will be described with reference to FIGS. As described above, the elastic spacer 16 is made of ethylene propylene rubber or the like, and the shape thereof is, for example, a disk shape as shown on the right side of FIG. 3, and the activated carbon sheet 14 is pressed toward the hole 12 side. 14 so that no gap remains. The activated carbon sheet 14 may be a single layer or three or more layers. If the gap between the activated carbon sheet 14 and the hole 12 is not generated, the atmosphere entering from the hole 10 does not reach the hole 12 unless it passes through the activated carbon sheet 14. Further, since the spacer 16 is elastic, the activated carbon sheet 14 can be brought into close contact with the hole 12 even if the thickness of the activated carbon sheet 14 varies or the size of the inside of the filter 8 varies. Since the elastic spacer 16 fixes the activated carbon sheet 14, the activated carbon sheet 14 does not move and fine particles of activated carbon are not generated.

FIG. 4 shows a filter 9 in the conventional example, which is the same as the filter 8 in the example except that the elastic spacer 16 is not provided. In this case, since the thickness of the activated carbon sheet 14 varies and the size of the inside of the filter 9 also varies, for example, when the gas sensor is laid sideways as shown in FIG. There is a possibility that a flow path that reaches the hole 12 without passing through may occur. Then, there is a possibility that gases such as alcohol, hydrogen sulfide, and SO _x that interfere with detection of the target gas may reach the gas sensor main body 24 without being processed by the filter material 14, and this may cause, for example, false alarms.

  Gas sensor 2 using elastic spacer 16 made of EPDM is sealed one by one in a polyethylene bag, stored in a humid atmosphere at 60 ° C for one month, taken out from the bag, returned to room temperature, and waited for one day to measure the characteristics. did. There is no difference in the characteristics of the gas sensor 2 from that before standing at high temperature, which indicates that the gas that poisons the gas sensor main body 24 is not released from the elastic spacer 16 or the gasket 18. Further, the gas sensor 2 was disassembled, the appearance of the elastic spacer 16 was inspected, and the elastic modulus was measured, but no change due to high temperature experience was observed.

  Since the hole 10 was provided in the inclined surface of the side part of the metal plate 8a in the Example, the elastic spacer 16 was arrange | positioned at the metal plate 8a side, and the activated carbon sheet 14 was pressed to the metal plate 8b side. However, as shown in FIG. 5, the activated carbon sheet 14 may be pressed by the ring-shaped elastic spacer 17 into the hole 10 'on the metal plate 8a side.

In the embodiment, application to the gas sensor 2 is shown. An example of using a filter as an arbitrary filter is shown in FIG. 6, but this is not included in the scope of the present invention. 50 is a new filter, 51 is an airtight container of metal or plastic, and here, two upper and lower plastic pieces are fitted together, 52 is a hole on the gas inlet side, and 53 is a hole on the gas outlet side. A filter material 54 formed of activated carbon, silica gel, zeolite, hydrogen storage alloy or the like is held in the container 51, and a gas adsorbent such as activated carbon or silica gel or a gas sorbent such as zeolite is used for the filter material 54. In this case, an unnecessary gas may be decomposed by supporting an oxidation catalyst such as Pt. Reference numeral 56 denotes, for example, a ring-shaped elastic spacer, which presses the filter material 54 to either side of the holes 52 and 53 so as to be in close contact therewith. Such a filter 50 can be used as a filter for removing unnecessary gas from the air to be sampled, for example, in a measuring instrument. Further, it can be used as a gas mask or a filter for removing harmful gas from the air circulating through electronic devices, chemical devices, and the like.

FIG. 7 shows a gas detector using the electrochemical gas sensor 2 of the embodiment, and the current flowing between both electrodes of the gas sensor 2 is defined as the current between the metal can 4 and the filter 8 by the current measuring means 70 with a high amplification factor. Take out. This current is proportional to the concentration of CO, which is the detection target gas, and is compared with a predetermined threshold by the gas detection determination means 72 and the detection result is displayed by the display means 74. Since the activated carbon sheet 14 in the filter 8 is fixed by the elastic spacers 16 and 17 and the like, the activated carbon sheet 14 can be mounted even if the gas detector is installed sideways or a vibration or impact is applied to the gas detector. There is no detouring airflow and stable gas detection can be performed.

2 Electrochemical gas sensor 4 Metal can 6 Water 8 Filter 8a, 8b Metal plate 10, 12 Hole 14 Activated carbon sheet 16, 17 Elastic spacer 18 Gasket 20 Diffusion control plate 22 Diffusion control hole 24 Gas sensor body 25 Washer 26 Hole 28 Recess 30 Porous Separator 31 Detection electrode 32 Counter electrode 33, 34 Hydrophobic carbon sheet 50 Filter 51 Airtight container 52 Gas inlet side hole 53 Gas outlet side hole 54 Filter material 56 Elastic spacer

Claims (1)

A gas sensor body in which a detection electrode is provided on one surface of the separator or proton conductor film holding the liquid electrolyte, and a counter electrode is provided on the opposite surface;
  In an electrochemical gas sensor comprising a filter that adsorbs unnecessary gas from the atmosphere to be detected supplied to the detection electrode,
  The filter is a metal container in which two metal plates are joined together, a sheet-shaped or disk-shaped filter material accommodated in the metal container, a synthetic rubber, a synthetic resin elastomer, or a synthetic resin viscoelastic body. An elastic spacer made of
  One of the two metal plates is provided with a hole for introducing the detected atmosphere into the container, and the other metal plate is provided with a hole for supplying the detected atmosphere that has passed the filter material to the detection electrode side,
  The elastic spacer and the filter material are sandwiched between the two metal plates, the elastic spacer presses the filter material and fixes it in a metal container, and the filter material is placed in one of the holes. An electrochemical gas sensor characterized by being in close contact.

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