JP2022080741A - Constant potential electrolytic gas sensor - Google Patents

Abstract

To provide a constant potential electrolytic gas sensor that detects oxygen gas and toxic gas, and can be reduced in size despite its ability to be used in an environment in a wide humidity range.SOLUTION: A constant potential electrolytic gas sensor detects oxygen gas and toxic gas, and has an electrode lamination structure including a sheet-like electrolytic solution holding member that is impregnated with an electrolytic solution, a working electrode for oxygen gas and a working electrode for toxic gas that are arranged separate from each other on a top face of the electrolytic solution holding member, and a counter electrode and a reference electrode arranged separate from each other on an under surface of the electrolytic solution holding member. The ratio S2/S1 of the area S2 of the working electrode for toxic gas to the area S1 of the working electrode for oxygen gas is 1.5-13. The electrolytic solution holding member has the area covering the working electrode for oxygen gas and the working electrode for toxic gas. The ratio S4/S3 of the area S4 of the electrolytic solution holding member to the area S3 of the total of the area S1 of the working electrode for oxygen gas and the area S2 of the working electrode for toxic gas is 3.5 or less.SELECTED DRAWING: Figure 2

Description

There is an application for application of Article 30, Paragraph 2 of the Patent Law. February 25, 2nd year Asagoe Industry Co., Ltd. (557-4 Mishima, Minami-ku, Okayama-shi, Okayama), Sumitomo Metal Mine Co., Ltd. (5-11-3, Shimbashi, Minato-ku, Tokyo), Hitachi High-Tech Co., Ltd. (Yamaguchi Prefecture) Shimomatsu City Oaza Higashitoyoi 794) and J Mate. Delivered at Copper Products Co., Ltd. (2024-1 Dosokohama, Ogata-ku, Joetsu City, Niigata Prefecture).

The present invention relates to a constant potential electrolytic gas sensor capable of detecting oxygen gas and toxic gas.

When detecting oxygen gas or toxic gas, an electrolytic reaction is used because it has excellent selectivity of the target gas to be detected, and can detect the gas concentration with high sensitivity and high accuracy. The constant potential electrolytic gas sensor is widely used.

As this constant potential electrolytic gas sensor, in Patent Document 1, an electrode laminated structure in which a working electrode, a reference electrode, and a counter electrode are laminated via an electrolytic solution holding member made of a hydrophilic non-woven fabric impregnated with an electrolytic solution. Is disclosed. Further, Patent Document 1 discloses that it is possible to configure a gas sensor that detects a plurality of types of gas by providing a plurality of divided working electrodes.

Further, sulfuric acid is generally used as the electrolytic solution. Sulfuric acid absorbs water or evaporates water depending on the humidity of the environment in which the constant potential electrolytic gas sensor is used, and as a result, the volume of the electrolytic solution increases or decreases. Therefore, in the constant potential electrolytic gas sensor, the electrolytic solution is sufficiently impregnated over the entire electrolytic solution holding member even when used in a low humidity environment, and increases due to moisture absorption even when used in a high humidity environment. It is required that the obtained electrolytic solution can be accommodated in the electrolytic solution chamber.

Generally, in a constant potential electrolytic gas sensor that detects oxygen gas, the area of the working electrode mounted is smaller than that of a constant potential electrolytic gas sensor that detects toxic gas. Therefore, it is possible to use an electrolytic solution holding member having a small area, whereby the amount of electrolytic solution used may be small, and as a result, a small constant potential electrolytic gas sensor can be configured.

U.S. Pat. No. 7,608,177

However, when a constant-potential electrolytic gas sensor that detects oxygen gas and toxic gas is configured, as shown in FIG. 11, the area of the electrolytic solution holding member 93 that matches the size of the working electrode 92 that detects toxic gas. That is, the one having an area considerably larger than the total area of the working electrode 91 for detecting oxygen gas and the working electrode 92 for detecting toxic gas is used. Therefore, in order to use it in an environment with a wide humidity range, an excessive electrolyte solution and an excessive electrolyte chamber are required compared to the total area of the working electrodes 91 and 92, and as a result, a small constant potential is required. It is difficult to construct an electrolytic gas sensor.

The present invention has been made based on the above circumstances, and an object thereof is a constant potential electrolytic gas sensor for detecting oxygen gas and toxic gas, which can be used in an environment of a wide humidity range. However, it is an object of the present invention to provide a constant potential electrolytic gas sensor that can be miniaturized.

The constant potential electrolytic gas sensor of the present invention is a constant potential electrolytic gas sensor that detects oxygen gas and toxic gas.
A sheet-shaped electrolytic solution holding member impregnated with the electrolytic solution, an oxygen gas working electrode and a toxic gas working electrode arranged apart from each other on the upper surface of the electrolytic solution holding member, and the electrolytic solution holding member. A laminated electrode structure having counter electrode and reference electrode arranged at a distance from each other on the lower surface thereof.
The ratio S2 / S1 of the area S2 of the working electrode for toxic gas to the area S1 of the working electrode for oxygen gas is in the range of 1.5 to 13.
The electrolytic solution holding member has an area covering the oxygen gas working electrode and the toxic gas working electrode, and is the sum of the area S1 of the oxygen gas working electrode and the area S2 of the toxic gas working electrode. The ratio S4 / S3 of the area S4 of the electrolytic solution holding member to the area S3 is 3.5 or less.

In the constant potential electrolytic gas sensor of the present invention, the electrolytic solution holding member is for an oxygen gas working pole arrangement portion in which the oxygen gas working electrode is arranged and a toxic gas in which the toxic gas working electrode is arranged. It consists of a working pole arrangement part,
It is preferable that the ratio S5 / S1 of the area S5 of the oxygen gas working pole arrangement portion to the oxygen gas working pole area S1 is 5.5 or less.

Further, in the constant potential electrolytic gas sensor of the present invention, the electrode laminated structure in which a test gas introduction port for detecting oxygen gas and a test gas introduction port for detecting toxic gas are formed on the upper wall portion is accommodated. A casing and a support plate for supporting the electrode laminated structure in the casing are provided.
The support plate has an oxygen gas working pole arranging portion support portion that supports the oxygen gas working pole arranging portion in the electrolytic solution holding member, and is provided on the outer peripheral edge of the oxygen gas working pole arranging portion support portion. It is preferable that the upper surface tapered portion is formed so as to approach the upper wall portion from the peripheral edge of the support plate toward the outer peripheral edge of the oxygen gas action pole arrangement portion support portion.
Further, it is more preferable that the peripheral surface of the support plate following the upper surface tapered portion is formed with a peripheral surface tapered portion that approaches the center of the support plate from the upper surface to the lower surface of the support plate.

Further, in the constant potential electrolytic gas sensor of the present invention, the counter electrode and the reference electrode are formed on the upper surface of a pressure adjusting membrane made of a hydrophobic porous material.
The casing has a ventilation pipe portion that forms a ventilation hole and is provided so as to project inward from the lower wall portion and contact the lower surface of the pressure adjusting membrane.
An electrolytic solution chamber for accommodating the electrolytic solution, which leads to the space in which the electrode laminated structure is arranged, is formed around the ventilation pipe portion between the electrode laminated structure and the lower wall portion of the casing. It is preferable to have.
Further, a sealing resin material layer formed by curing the adhesive is formed on the inner surface of the lower wall portion of the casing, and the sealing resin material is formed on the upper surface of the sealing resin material layer. It is more preferable that a partition plate separating the layer and the electrolytic solution chamber is arranged.

In the present invention, "upper" and "lower" mean the constant potential when the constant potential electrolytic gas sensor of the present invention is arranged in a posture in which the surface of the casing on which the test gas inlet is formed faces upward. It indicates the direction in the electrolytic gas sensor. Therefore, for example, when the constant potential electrolytic gas sensor is arranged in a posture in which the surface of the casing on which the test gas inlet is formed faces downward, the "upper" and "lower" are actually in opposite directions, that is, "downward". When the constant potential electrolytic gas sensor is placed in a casing with the surface on which the test gas inlet is formed facing to the left, indicating the "down" and "up" directions, the "up" and "down" are actually Indicates the "left" and "right" directions, respectively.

According to the constant-potential electrolytic gas sensor of the present invention, it is a constant-potential electrolytic gas sensor that detects oxygen gas and toxic gas, and does not require an excessive electrolyte and an excessive electrolyte chamber, so that the environment has a wide humidity range. Although it can be used below, it can be miniaturized.

It is explanatory cross-sectional view which shows the outline of the structure in the example of the constant potential electrolysis type gas sensor of this invention. It is an exploded perspective view of the constant potential electrolytic oxygen sensor shown in FIG. It is a top view which shows the lower wall part in the constant potential electrolysis type gas sensor shown in FIG. It is explanatory cross-sectional view which expands and shows the working electrode for oxygen gas in the constant potential electrolysis type gas sensor shown in FIG. FIG. 3 is an explanatory cross-sectional view showing an enlarged working electrode for toxic gas in the constant potential electrolytic gas sensor shown in FIG. 1. It is a top view which shows the electrolytic solution holding member in the constant potential electrolysis type gas sensor shown in FIG. 1 together with the working electrode for oxygen gas and the working electrode for toxic gas. It is a top view which shows the electrode complex in the constant potential electrolysis type gas sensor shown in FIG. 1. It is a top view which shows the support plate in the constant potential electrolysis type gas sensor shown in FIG. It is a perspective view which shows the support plate in the constant potential electrolysis type gas sensor shown in FIG. It is explanatory cross-sectional view which shows the part of the support plate in the constant potential electrolysis type gas sensor shown in FIG. 1 in an enlarged manner. It is a top view which shows the electrolytic solution holding member in the conventional constant potential electrolysis type gas sensor together with the working electrode for oxygen gas and the working electrode for toxic gas.

Hereinafter, embodiments of the constant potential electrolytic gas sensor of the present invention will be described.
FIG. 1 is an explanatory cross-sectional view showing an outline of the configuration in an example of the constant potential electrolytic gas sensor of the present invention, and FIG. 2 is an exploded perspective view of the constant potential electrolytic gas sensor shown in FIG.
This constant-potential electrolytic gas sensor detects oxygen gas and toxic gas, and has an oxygen gas working electrode 21 for detecting oxygen gas, a toxic gas working electrode 22 for detecting toxic gas, a counter electrode 26, and a reference electrode. It has an electrode laminated structure 20 having 27 and a casing 10 for accommodating the electrode laminated structure 20.
Here, examples of the toxic gas to be detected include carbon monoxide, hydrogen sulfide, sulfur dioxide, chlorine, ammonia, nitrogen dioxide, nitrogen monoxide, hydrogen cyanide, hydrogen gas, phosphine, ozone, and chlorine dioxide.

The casing 10 is composed of a cylindrical casing main body 11 having a closed lower end and a disk-shaped lid member 12 that closes an opening at the upper end of the casing main body 11 to form an upper wall portion 14. The casing body 11 and the lid member 12 are each made of a thermoplastic resin such as polypropylene. Further, the inner wall surface of the casing main body 11 is subjected to surface treatment such as corona treatment or plasma treatment in order to improve the affinity and adhesion with the adhesive forming the sealing resin material layer 45 described later. ing.

In the lid member 12 forming the upper wall portion 14, a test gas introduction port 13a for detecting oxygen gas and a plurality of test gas introduction ports 13a for detecting toxic gas penetrate the upper wall portion 14 in the thickness direction. It is formed to stretch. Further, a circular first recess 18 is formed on the upper surface of the lid member 12, and a circular second recess 19 is formed in the central region on the bottom surface of the first recess 18. A test gas introduction port 13a for detecting oxygen gas is formed in the central region on the bottom surface of the recess 19.

The internal space formed by the test gas introduction port 13a for detecting oxygen gas functions as a diffusion space for the test gas introduced through the pinhole 51 of the gas supply limiting means 50 described later.
The volume of the internal space formed by the test gas introduction port 13a is preferably, for example, about 0.1 to 10 mm ³ . With such a configuration, the introduced test gas can be sufficiently diffused, and the amount of oxygen gas remaining inside the sensor after the power is turned off can be reduced.

At the center position of the bottom wall portion of the casing main body 11, that is, the lower wall portion 15 of the casing 10, a ventilation pipe portion 16 having a circular cross section is upward (inwardly) from the lower wall portion 15 along the axial direction of the casing main body 12. It is formed so as to protrude and come into contact with the lower surface of the pressure adjusting film 28 described later. The ventilation pipe portion 16 forms a ventilation hole V that leads from the outer surface of the lower wall portion 15 to the lower surface of the pressure adjusting membrane 28.

As shown in FIG. 3, around the ventilation pipe portion 16 in the lower wall portion 15 of the casing 10, an oxygen gas working pole terminal 40, a toxic gas working pole terminal 41, a counter electrode terminal 42, and a reference pole terminal 43 are provided. They are arranged so as to be spaced apart from each other in the circumferential direction.
An electrolytic solution chamber S for accommodating the electrolytic solution is formed around the ventilation pipe portion 16 between the electrode laminated structure 20 and the lower wall portion 15 of the casing 10. The electrolytic solution chamber S leads to a space in which the electrode laminated structure 20 is arranged through a gap K between the peripheral wall portion 17 of the casing 10 and the support plate 30 described later.

Further, on the inner surface (upper surface) of the lower wall portion 15, a sealing resin material layer 45 formed by curing an adhesive such as an epoxy resin adhesive is provided as an oxygen gas working pole terminal 40 and a toxic gas working pole terminal. 41, it is formed so as to cover the counter electrode terminal 42 and the reference electrode terminal 43. By providing the sealing resin material layer 45, the electrolytic solution chamber S does not corrode the oxygen gas working electrode terminal 40, the toxic gas working electrode terminal 41, the counter electrode terminal 42, and the reference electrode terminal 43 by the electrolytic solution. It has a liquidtight sealing structure.

On the upper surface of the sealing resin material layer 45, a partition plate 46 that separates the sealing resin material layer 45 and the electrolytic solution chamber S is arranged. By arranging the partition plate 46, when the resin material layer 45 for sealing is formed, after the adhesive is filled in the casing main body 11, the adhesive is subjected to surface treatment such as corona treatment. It is prevented from rising along the inner wall surface of the casing main body 11, which makes it possible to reduce the amount of the adhesive used for forming the sealing resin material layer 45. If the amount of the adhesive used is small, the volume of the electrolytic solution chamber S increases relatively, so that it is possible to cope with a wider range of humidity environments.

In the second recess 19 of the lid member 12, a disk-shaped gas supply limiting means 50 that matches the shape of the second recess 19 is accommodated and arranged.
The gas supply limiting means 50 is formed so that a pinhole 51 extending in the thickness direction communicates with the gas introduction port 13 of the lid member 12. By passing the test gas through the pinhole 51, the supply amount of the test gas introduced into the casing 10 from the test gas introduction port 13 is limited.

The pinhole 51 has an inner diameter of a uniform size in the axial direction. The size of the inner diameter of the pinhole 51 is, for example, 1.0 to 200 μm. The length of the pinhole 51 is, for example, 0.1 mm or more.

A circular buffer film 55 is housed and arranged in the first recess 18.
The buffer film 55 of this example is composed of a laminate having a gas diffusion layer 56 into which the test gas flows from the outer peripheral surface and a protective layer 57 having gas impermeableness and water repellency, and the whole is circular. It is formed in a plate shape.

The gas diffusion layer 56 is adhered and fixed to the bottom surface of the first recess 18 of the lid member 12 and the upper surface of the gas supply limiting means 50 by a double-sided adhesive tape 58 having a through hole 58a formed in the pinhole 51. ing.
The gas diffusion layer 56 can be made of a fluororesin film such as a PTFE film.
The gas diffusion layer 56 preferably has an air permeability of 0.15 to 1.5 L / day, and the thickness, outer diameter dimension, void ratio, and other specific configurations are such that the air permeability is within the above numerical range. Can be set to be.

The size of the inner diameter of the through hole 58a of the double-sided adhesive tape 58 is preferably 0.05 to 3 mm, for example. The thickness of the double-sided adhesive tape 58 is preferably 0.05 to 1 mm, for example.
With such a configuration, it is possible to obtain sufficient durability against the external environment without significantly deteriorating the gas responsiveness, and it is possible to surely obtain a stable indicated value.

The protective layer 57 is adhered and fixed to the upper surface of the gas diffusion layer 56 with a double-sided adhesive tape 59. The protective layer 57 may be fixed to the upper surface of the gas diffusion layer 56 by using an adhesive layer made of an adhesive instead of the double-sided adhesive tape 59.
The protective layer 57 can be made of a composite film in which an aluminum foil is laminated on a resin film such as PET.

The electrode laminated structure 20 is a sheet-shaped electrolyte holding member 23 impregnated with an electrolytic solution, and a circular sheet-shaped working electrode 21 for oxygen gas arranged on the upper surface of the electrolytic solution holding member 23 so as to be separated from each other. It is composed of a semicircular sheet-shaped working electrode 22 for toxic gas, and an electrode composite 25 having a counter electrode 26 and a reference electrode 27 arranged apart from each other on the upper surface of the electrolytic solution holding member 23. The separation distance between the working pole 21 for oxygen gas and the working pole 22 for toxic gas is, for example, 0.3 to 4 mm. The distance between the counter electrode 26 and the reference electrode 27 is, for example, 0.3 to 8 mm.

The oxygen gas working pole 21 has an area smaller than the area of the toxic gas working pole 22. Specifically, the ratio S2 / S1 of the area S2 of the toxic gas working electrode 22 to the area S1 of the oxygen gas working electrode 21 is in the range of 1.5 to 13, preferably in the range of 2 to 8.

As shown in FIG. 4, the oxygen gas working electrode 21 is configured by forming an electrode catalyst layer 21b on a gas permeable film 21a having hydrophobicity, and the electrode catalyst layer 21b is an electrolytic solution holding member 23. It is arranged so as to be in contact with. Further, the gas permeable film 21a in the oxygen gas working electrode 21 is arranged so as to close the test gas introduction port 13. Further, the upper surface of the gas permeable film 21a is heat-welded to the lower surface (inner surface) of the upper wall portion 14 so as to surround the test gas introduction port 13a. Since the gas permeable film 21a is heat-welded to the upper wall portion 14, it is possible to prevent the electrolytic solution from leaking from between the gas permeable film 21a and the upper wall portion 14.

As shown in FIG. 5, the action electrode 22 for toxic gas is configured by forming an electrode catalyst layer 22b on a gas permeable film 22a having hydrophobicity, and the electrode catalyst layer 22b is an electrolytic solution holding member 23. It is arranged so as to be in contact with. Further, each of the gas permeable films 22a in the working electrode 22 for toxic gas is arranged so as to close the test gas introduction port 13b. Further, the upper surface of the gas permeable film 22a is heat-welded to the lower surface (inner surface) of the upper wall portion 14 so as to surround the test gas introduction port 13b. Since the gas permeable film 22a is heat-welded to the upper wall portion 14, it is possible to prevent the electrolytic solution from leaking from between the gas permeable film 22a and the upper wall portion 14.

As the gas permeable films 21a and 22a, for example, a porous membrane made of a fluororesin such as polytetrafluoroethylene (PTFE) can be used.
The porous membrane preferably has a Garley number of 3 to 3000 seconds. The thickness and porosity of the porous membrane can be set so that the number of garleys is within the above numerical range. For example, the porosity is 10 to 70% and the thickness is 0.01 to 1 mm. Is preferable.

The electrode catalyst layers 21b and 22b are formed of catalyst fine particles such as catalyst metal fine particles insoluble in an electrolytic solution, catalyst metal oxide fine particles, catalyst metal alloy fine particles, or a mixture of these fine particles. ing. As the catalyst metal insoluble in the electrolytic solution, for example, platinum (Pt), gold (Au), ruthenium (Ru), palladium (Pd), iridium (Ir) and the like can be used. Such an electrode catalyst layer 21b can be formed by preparing a paste containing catalyst fine particles and a binder, applying the paste to the surface of the gas permeable film 21a by screen printing or the like, and firing the paste. ..

The working pole 21 for oxygen gas and the working pole 22 for toxic gas are each electrically connected to one end of a lead member for working pole (not shown). An oxygen gas working pole terminal 40 is electrically connected to the other end of the working pole lead member to which the oxygen gas working pole 21 is connected. Further, a toxic gas working pole terminal 41 is electrically connected to the other end of the toxic gas working pole 22 working pole lead member.
As a material constituting the lead member for the working electrode, metals such as gold (Au), tungsten (W), niobium (Nb) and tantalum (Ta) can be used. Further, as the lead member 46 for the working electrode, a resin-coated platinum (Pt) wire can also be used. Among these, tantalum (Ta) wire is used as the lead member for the working electrode connected to the working pole 21 for oxygen gas, and platinum (Pt) wire is used as the lead member for the working pole connected to the working pole 22 for toxic gas. It is preferable to use.

The electrolytic solution holding member 23 has an area covering the oxygen gas working electrode 21 and the toxic gas working electrode 22, and is the total area S3 of the oxygen gas working electrode area S1 and the toxic gas working electrode area S2. The ratio S4 / S3 of the area S4 of the electrolytic solution holding member 23 to the above is 3.5 or less, preferably 2.8 or less. When the ratio S4 / S3 is excessive, an excessive amount of electrolytic solution is required, which makes it difficult to reduce the size. Further, the working pole 21 for oxygen gas and the working pole 22 for toxic gas are arranged so that the entire lower surface thereof is in contact with the electrolytic solution holding member 23.

As shown in FIG. 6, in the electrolytic solution holding member 23, the oxygen gas working pole arrangement portion 23a in which the oxygen gas working pole 21 is arranged and the toxic gas working pole 22 in which the toxic gas working pole 22 is arranged are arranged. It is composed of an arrangement portion 23b. Here, the boundary between the oxygen gas working pole arranging portion 23a and the toxic gas working pole arranging portion 23b is that the distances to the oxygen gas working pole arranging portion 23a and the toxic gas working pole arranging portion 23b are equal to each other. Identified by the connecting line.
In the electrolytic solution holding member 23 of the illustrated example, a substantially semicircular working pole arrangement portion 23b for toxic gas having a radius larger than that of the working pole 22 for toxic gas is formed, and the working pole arrangement portion 23b for toxic gas is formed. The oxygen gas action pole arrangement portion 23a is formed so as to project vertically from the diameter portion. The ratio S5 / S1 of the area S5 of the oxygen gas working pole arrangement portion 23a to the area S1 of the oxygen gas working pole 21 is preferably 5.5 or less, and more preferably 4.0 or less. When the ratio S5 / S1 is excessive, an excessive amount of electrolytic solution is required, which may make it difficult to reduce the size.

The thickness of the electrolytic solution holding member 23 is such that the volume of the electrolytic solution holding member 23 can be as small as possible while being able to impregnate a sufficient amount of the electrolytic solution. It is 0.1 to 2 mm. With such a configuration, highly reliable gas detection can be performed even in a high humidity environment.
As the electrolytic solution holding member 23, for example, a glass fiber filter paper, a silica filter paper, or a non-woven fabric made of glass fiber, PP fiber, PP / PE composite fiber, or ceramic fiber can be used.

As also shown in FIG. 7, the electrode complex 25 is a hydrophobic porous material that holds a counter electrode 26 and a reference electrode 27 each composed of a catalyst layer, and a counter electrode 26 and a reference electrode 27, which are arranged apart from each other. It is composed of a pressure adjusting film 28 and the like. The pressure adjusting film 28 in the electrode complex 25 is arranged so as to close the ventilation hole V on the upper end surface of the ventilation pipe portion 16 in the casing 10. As a result, the internal space of the casing 10 is opened to the outside atmosphere through the pressure adjusting membrane 28 and the ventilation holes V. Further, the lower surface of the pressure adjusting membrane 28 is heat-welded to the upper end surface of the ventilation pipe portion 16 so as to surround the ventilation hole V. Since the pressure adjusting membrane 28 is heat-welded to the upper end surface of the ventilation pipe portion 16, it is possible to prevent the electrolytic solution from leaking from between the pressure adjusting membrane 28 and the upper end surface of the ventilation pipe portion 16. ..

The catalyst layer constituting the counter electrode 26 and the reference electrode 27 may be fine particles of a catalyst metal insoluble in an electrolytic solution, fine particles of an oxide of the catalyst metal, fine particles of an alloy of the catalyst metal, or a mixture of these fine particles. It is formed by catalyst fine particles. As the catalyst metal insoluble in the electrolytic solution, for example, platinum (Pt), gold (Au), ruthenium (Ru), palladium (Pd), iridium (Ir) and the like can be used. The catalyst layer constituting the counter electrode 26 and the reference electrode 27 is formed by preparing a paste containing catalyst fine particles and a binder, applying the paste to the surface of the pressure adjusting film 28 by screen printing or the like, and firing the paste. be able to.
Further, the electrode catalyst layer constituting the counter electrode 26 and the reference electrode 27 may be made of the same material or different materials, but both the counter electrode 26 and the reference electrode 27 may be used in a single process. From the viewpoint that they can be formed, they are preferably made of the same material.

As the pressure adjusting film 28, for example, a porous film made of a fluororesin such as polytetrafluoroethylene (PTFE) can be used.
The porous membrane preferably has a Garley number of 3 to 3000 seconds. The thickness and porosity of the porous membrane can be set so that the number of garleys is within the above numerical range. For example, the porosity is 10 to 70% and the thickness is 0.01 to 1 mm. Is preferable.

The pressure adjusting film 28 has a circular electrode forming portion 28a on which the counter electrode 26 and the reference electrode 27 are formed, and three or more extending radially outward from the outer peripheral edge of the electrode forming portion 28a, respectively (4 in the illustrated example). It is composed of a rectangular tongue piece portion 28b. Each of the tongue piece portions 28b is formed so as to be arranged at equal intervals in the circumferential direction of the electrode forming portion 28a.

The counter electrode 26 and the reference pole 27 are electrically connected to one end of the counter electrode lead member (not shown) and the reference pole lead member (not shown), and to the other ends of the counter electrode lead member and the reference pole lead member. , The counter electrode terminal 42 and the reference electrode terminal 43 are electrically connected, respectively.
As a material constituting the counter electrode lead member and the reference electrode lead member, metals such as gold (Au), platinum (Pt), tungsten (W), niobium (Nb) and tantalum (Ta) can be used.

A support plate 30 for supporting the electrode laminated structure 20 is provided at the upper end portion of the ventilation pipe portion 16. A top view of the support plate 30 is shown in FIG. 8, and a perspective view of the support plate 30 is shown in FIG.
The support plate 30 is an action for oxygen gas in the electrode forming portion supporting portion 31 that supports the electrode forming portion 28a in the pressure adjusting film 28 and the electrolytic solution holding member 23 formed around the electrode forming portion supporting portion 31. A plurality of (three in the illustrated example) toxic gas working pole arranging part support 34b, which support the oxygen gas working pole arranging part 34a supporting the pole arranging part 23a and the toxic gas working pole arranging part 23b, It has 34c and 34d, and a tongue piece support portion 35 that supports the tongue piece portion 28b formed corresponding to each of the tongue piece portions 28b in the pressure adjusting film 28.

Further, as shown in an enlarged manner in FIG. 10, the support plate 30 has an oxygen gas working pole arranging portion support portion 34a on the outer peripheral edge of the oxygen gas working pole arranging portion supporting portion 34a from the peripheral edge of the support plate 30. An upper surface tapered portion 33 is formed that approaches the upper wall portion 14 toward the outer peripheral edge of the surface. By forming the upper surface tapered portion 33 on the support plate 30, the electrolytic solution easily collects from the peripheral edge of the support plate 30 toward the oxygen gas working pole arranging portion support portion 34a, so that the size of the oxygen gas working pole arranging portion 23a Even if the size is small, a sufficient amount of electrolytic solution can be impregnated in the oxygen gas working electrode arrangement portion 23a.

Further, on the peripheral surface of the support plate 30 following the upper surface tapered portion 33, a peripheral surface tapered portion 37 that approaches the center of the support plate 30 from the upper surface to the lower surface of the support plate 30 is formed. By forming the peripheral surface tapered portion 37 on the support plate 30, the electrolytic solution tends to collect toward the upper surface tapered portion 33 via the peripheral surface tapered portion 37 due to the capillary phenomenon. A sufficient amount of electrolytic solution can be impregnated more reliably. Further, as a result of the electrolytic solution easily flowing along the circumferential direction of the peripheral surface tapered portion 37, the electrolytic solution is easily supplied to the toxic gas acting pole arrangement portion 23b.

In the illustrated example, on the upper surface of the support plate 30, there is a step between the electrode forming portion support portion 31, the oxygen gas working electrode arrangement portion support portion 34a, and the toxic gas working pole arrangement portion supporting portion 34b, 34c, 34d. The part is formed. As a result, a substantially circular recess R in the pressure adjusting film 28 that receives and supports the electrode forming portion 28a is formed on the electrode forming portion supporting portion 31.

At the center position of the electrode forming portion support portion 31, a through hole 32 for the ventilation pipe portion having an inner diameter suitable for the outer diameter of the ventilation pipe portion 16 in the casing 10 is formed. The tip portion of the ventilation pipe portion 16 is fitted into the through hole 32 for the ventilation pipe portion.

The angle θ1 formed by the plane perpendicular to the thickness direction of the support plate 30 and the surface of the upper surface tapered portion 33 is preferably 5 to 30 °. When this angle θ1 is too small, the difference between the distance from the upper wall portion 14 on the inner peripheral edge of the upper surface tapered portion 33 and the distance from the upper wall portion 14 on the outer peripheral edge of the upper surface tapered portion 33 is too small. It becomes difficult for the electrolytic solution to collect in the center of the support plate 30, and there is a possibility that the electrolytic solution will not be supplied to the oxygen gas acting electrode arranging portion 23a in the electrolytic solution holding member 23. On the other hand, when this angle θ1 is excessive, the electrolytic solution becomes difficult to move in a region where the distance between the support plate 30 and the upper wall portion 14 is large, and the electrolytic solution can be effectively used. It will be difficult.

The angle θ2 formed by the thickness direction of the support plate 30 and the surface of the peripheral surface tapered portion 37 is preferably 3 to 30 °. When this angle θ2 is too small, for example, when used in a low humidity environment, when the amount of the electrolytic solution decreases, the electrolytic solution does not collect toward the upper surface tapered portion 33, and the electrolytic solution is used for oxygen gas. It may be difficult to sufficiently supply the working electrode arrangement portion 23a. On the other hand, when this angle θ2 is excessive, the action of the capillary phenomenon is small, so that the electrolytic solution does not collect toward the upper surface tapered portion 33, and the electrolytic solution is sufficiently supplied to the oxygen gas action pole arrangement portion 23a. Can be difficult.

Each of the tongue piece support portions 35 is formed by a groove G extending in the radial direction from the recess R toward the outer peripheral surface of the support plate 30.
In the tongue piece support portion 35, a through hole 36 for the tongue piece is formed at each bottom surface position of the groove G. Each of the tongue piece portions 28b in the pressure adjusting membrane 28 enters the tongue piece portion through hole 36, and the tip portion of the tongue piece portion 28b is formed so as to be located in the electrolytic solution chamber S. According to such a configuration, regardless of the posture of the constant potential electrolytic gas sensor, the internal pressure of the casing 10 can be kept constant by the ventilation of the outside air to the inside of the casing 10.

In this constant-potential electrolytic gas sensor, the working pole 21 for oxygen gas, the working pole 22 for toxic gas, and the reference pole 27 are kept at a constant potential by, for example, a potentiostat circuit (not shown).
Then, the test gas introduced from the test gas introduction port 13a of the casing 10 permeates the gas permeable film 21a in the oxygen gas working electrode 21, and the oxygen (O ₂ ) contained in the test gas is an electrode. Upon contact with the catalyst layer 21b, a reduction reaction of oxygen (O ₂ ) occurs in the electrode catalyst layer 21b, and a decomposition reaction of water (H ₂ O) occurs in the counter electrode 26.

On the other hand, when the toxic gas to be detected is contained in the test gas, the test gas introduced from the test gas introduction port 13b of the casing 10 has gas permeability in the toxic gas working electrode 22. When the film 22a permeates and comes into contact with the electrode catalyst layer 22b, an oxidation reaction occurs in the electrode catalyst layer 22b and a reduction reaction occurs in the counter electrode 26.

For example, when the toxic gas to be detected is carbon monoxide (CO) ^, an oxidation reaction of CO + H ₂ O → CO ₂ + 2H ⁺ + 2e- occurs in the electrode catalyst layer 22b in the working electrode 22 for the toxic gas, while , 1 / 2O ₂ + 2H ⁺ + ^2e- → H ₂ O reduction reaction occurs at the counter electrode 26.
Further, for example, when the toxic gas to be detected is hydrogen sulfide (H2 S), H ₂ S + 4H ₂ O → H ₂ SO ₄ + 8H ⁺ + 8e ^- in the electrode catalyst layer 21b in the working electrode 22 for the toxic gas. An oxidation reaction occurs, while a reduction reaction of 2O ₂ + 8H ⁺ + ^8e- → 4H _2O occurs at the counter electrode 26.

At this time, the value of the current generated between the working pole 21 for oxygen gas and the working pole 22 for toxic gas and the counter electrode 26 is proportional to the concentration of the oxygen gas or toxic gas to be detected, and therefore the working pole for oxygen gas. By measuring the current flowing between the 21 and the working electrode 22 for toxic gas and the counter electrode 26, the concentration of the detection target gas in the test gas can be measured.
Further, in the counter electrode 26, oxygen (O ₂ ) is generated by the electrolysis of water, and the pressure inside the casing 10 is adjusted by the pressure adjusting membrane 28.

As described above, according to the constant potential electrolytic gas sensor of the present invention, the area S4 of the electrolytic solution holding member 23 with respect to the total area S3 of the area S1 of the working electrode 21 for oxygen gas and the area S2 of the working electrode 22 for toxic gas. Since the ratio S4 / S3 of S4 / S3 is 3.5 or less, an excessive electrolytic solution and an excessive electrolytic solution chamber are not required, so that it can be used in an environment with a wide humidity range, but it is downsized. Can be planned.
Further, the ratio S5 / S1 of the area S5 of the oxygen gas working electrode arrangement portion 23a in the electrolytic solution holding member 23 to the area S1 of the oxygen gas working electrode is 5.5 or less, so that the amount of the electrolytic solution used can be further increased. It can be reduced, and further miniaturization can be achieved.
Further, since the support plate 30 having the upper surface tapered portion 33 is provided, the electrolytic solution easily collects from the peripheral edge of the support plate 30 toward the oxygen gas action electrode arrangement portion support portion 34a, so that the size of the support plate 30 is small. Even if the electrolytic solution holding member 23 having the working electrode arrangement portion support portion 34a is used, a sufficient amount of electrolytic solution can be impregnated over the entire electrolytic solution holding member 23, and therefore, so-called liquid withering is for oxygen gas. It is possible to prevent it from occurring locally on the working electrode arrangement portion support portion 34a.

Although the embodiment of the constant potential electrolytic gas sensor of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made.
For example, a plurality of action electrodes for toxic gas that detect different types of toxic gas can be arranged on the upper surface of the electrolytic solution holding member.
Further, in the support plate, even if a peripheral surface taper portion that approaches the center of the support plate from the upper surface to the lower surface of the support plate is formed on the peripheral surface following the support portion of the action pole arrangement portion for toxic gas. good.

10 Casing 11 Case sink body 12 Lid member 13 Test gas inlet 14 Upper wall part 15 Lower wall part 16 Ventilation pipe part 17 Peripheral wall part 18 First recess 19 Second recess 20 Electrode laminated structure 21 Working electrode for oxygen gas 21a Gas permeable film 21b Electrocatalyst layer 22 Working pole for toxic gas 22a Gas permeable film 22b Electrolytic solution holding member 23a Working pole arrangement for oxygen gas 23b Working pole arrangement for toxic gas 25 Electrode composite 26 Counter electrode 27 Reference pole 28 Pressure adjustment film 28a Electrode forming part 28b Tongue piece part 30 Support plate 31 Electrode forming part Support part 32 Through hole for ventilation pipe part 33 Top taper part 34a Working pole arrangement part for oxygen gas Support part 34b, 34c, 34d Toxic gas working pole arrangement support 35 Tongue piece support 36 Tongue piece through hole 37 Peripheral taper 40 Oxygen gas working pole terminal 41 Toxic gas working pole terminal 42 Counter electrode terminal 43 Reference pole terminal 45 Sealing resin material layer 46 partition plate 50 gas supply limiting means 51 pinhole 55 buffer film 56 gas diffusion layer 57 protective layer 58a through hole 58 double-sided adhesive tape 59 double-sided adhesive tape 91,92 working electrode 93 electrolyte holding member G groove K Gap R Recess S Electrolyte chamber V Vent

Claims (6)

A constant-potential electrolytic gas sensor that detects oxygen gas and toxic gas.
A sheet-shaped electrolytic solution holding member impregnated with the electrolytic solution, an oxygen gas working electrode and a toxic gas working electrode arranged apart from each other on the upper surface of the electrolytic solution holding member, and the electrolytic solution holding member. A laminated electrode structure having counter electrode and reference electrode arranged at a distance from each other on the lower surface thereof.
The ratio S2 / S1 of the area S2 of the working electrode for toxic gas to the area S1 of the working electrode for oxygen gas is in the range of 1.5 to 13.
The electrolytic solution holding member has an area covering the oxygen gas working electrode and the toxic gas working electrode, and is the sum of the area S1 of the oxygen gas working electrode and the area S2 of the toxic gas working electrode. A constant-potential electrolytic gas sensor characterized in that the ratio S4 / S3 of the area S4 of the electrolytic solution holding member to the area S3 is 3.5 or less. The electrolytic solution holding member is composed of an oxygen gas working pole arrangement portion in which the oxygen gas working electrode is arranged and a toxic gas working pole arrangement portion in which the toxic gas working electrode is arranged.
The constant potential electrolytic gas sensor according to claim 1, wherein the ratio S5 / S1 of the area S5 of the oxygen gas working electrode arrangement portion to the area S1 of the oxygen gas working electrode is 5.5 or less. A casing accommodating the electrode laminated structure in which a test gas introduction port for detecting oxygen gas and a test gas introduction port for detecting toxic gas are formed on an upper wall portion, and the electrode laminated structure in the casing. Equipped with a support plate to support
The support plate has an oxygen gas working pole arranging portion support portion that supports the oxygen gas working pole arranging portion in the electrolytic solution holding member, and is provided on the outer peripheral edge of the oxygen gas working pole arranging portion support portion. 2. The constant potential electrolytic gas sensor described in 1. 3. The peripheral surface of the support plate following the upper surface tapered portion is formed with a peripheral surface tapered portion that approaches the center of the support plate from the upper surface to the lower surface of the support plate. The constant potential electrolytic gas sensor described in 1. The counter electrode and the reference electrode are formed on the upper surface of a pressure adjusting membrane made of a hydrophobic porous material.
The casing has a ventilation pipe portion that forms a ventilation hole and is provided so as to project inward from the lower wall portion and contact the lower surface of the pressure adjusting membrane.
An electrolytic solution chamber for accommodating the electrolytic solution, which leads to the space in which the electrode laminated structure is arranged, is formed around the ventilation pipe portion between the electrode laminated structure and the lower wall portion of the casing. The constant potential electrolytic gas sensor according to claim 3 or 4, wherein the gas sensor is characterized by the above. A sealing resin material layer formed by curing the adhesive is formed on the inner surface of the lower wall portion of the casing, and the sealing resin material layer and the sealing resin material layer are formed on the upper surface of the sealing resin material layer. The constant potential electrolytic gas sensor according to claim 5, wherein a partition plate separating the electrolytic solution chamber is arranged.

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