JP4155562B2 - Electrochemical gas sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrochemical gas sensor in which a working electrode and a counter electrode are arranged with an electrolyte interposed therebetween.
[0002]
[Prior art]
In the electrochemical sensor, a conductive active substance layer is formed on a diaphragm having a water repellent property into which a gas to be detected can flow, and a distance that prevents the gas from reaching the working electrode and the counter electrode, usually 20 It is configured to be immersed in an electrolytic solution separated by 30 mm.
Thus, it is difficult to reduce the thickness of the test gas because it is necessary to prevent diffusion of the test gas to the counter electrode by the distance from the diaphragm.
[0003]
[Problems to be solved by the invention]
The present invention has been made in view of such problems, the purpose of which is to place a working electrode and a counter electrode sandwiching a water absorbent such as a filter paper without causing a decrease in detection accuracy, Thus, an electrochemical gas sensor that can be thinned is provided.
[0004]
[Means for Solving the Problems]
In order to solve such problems, in the present invention, a working electrode formed by forming a layer of a conductive active substance on a diaphragm capable of flowing a gas to be detected and having water repellency, and an electrolytic solution are impregnated. A first sheet, a membrane in which the test gas is substantially impermeable and capable of transmitting oxygen, a counter electrode, a second sheet impregnated with the electrolytic solution, and at least the second sheet And a support having a roughened surface facing each other are stacked and arranged in the above order, and are accommodated in a case so as to expose the diaphragm.
[0005]
[Action]
While the oxygen dissolved in the electrolytic solution reaches the counter electrode as much as possible, the sample gas is prevented from reaching the counter electrode by the membrane, and the sheet is surely impregnated by the rough surface of the support.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Therefore, details of the present invention will be described below based on the illustrated embodiment.
FIG. 1 shows an embodiment of an electrochemical gas sensor of the present invention, in which a gas to be detected can flow into a gas inlet 1a that opens at the center of a lid 1 constituting a sensor case. In addition, a working electrode 3 configured by forming a layer of a conductive active substance, for example, platinum black, on the diaphragm 2 having water repellency is disposed.
[0007]
The lower surface of the working electrode 3 is a sheet 4 impregnated with an electrolytic solution, in this embodiment a filter paper, and the lower surface thereof is a membrane 5 that is substantially impermeable to a test gas and is permeable to oxygen. In the example, an FEP film is arranged.
On the back surface of the film 5, a conductive counter electrode material layer is formed by vapor deposition or printing after the film 5 is subjected to an active rough surface treatment, and the counter electrode 6 is integrally formed.
[0008]
In this embodiment, the counter electrode 6 is covered with the second sheet 7 impregnated with the electrolytic solution, and the laminate is elastically held between the case lid 1 and the support 8. Is housed in.
[0009]
The case includes a lid body 1 having a gas inlet 1a in the center region, a cylindrical case body 9 having a through hole 9a in the center, and a bottomed cylindrical middle case 10 that can be inserted into the case body 9. The lid body 1 and the case main body 9 are fixed to each other.
[0010]
A stepped portion 10a is formed in the bottomed cylindrical middle case 10, and a support body 8 having at least three convex pieces 8a shown in FIG. It is comprised so that the edge part of the piece 8a may be supported. The support 8 is made of a material having a relatively small water repellency, such as vinyl chloride, and has at least a surface facing the counter electrode 6 as a rough surface as shown in FIG. Such roughening is possible by sandblasting, or by simultaneously forming a mesh or unevenness during injection molding.
[0011]
Further, as shown in FIG. 2B, an external terminal 12 to which a foil-like lead 11 is connected in advance is inserted on the back surface of the case body 9, and the lead 11 is inserted between the case body 9 and the middle case 10. Are inserted into the working electrode 3, and the other electrode is in contact with the counter electrode 6. The working electrode 3 and the counter electrode 6 are connected to the external terminals 12 and 12, respectively. In the figure, reference numeral 13 denotes a sealing ring-shaped packing, and reference numeral 14 denotes a dust removing filter.
[0012]
In this embodiment, when the test gas flows from the gas inlet 1a and passes through the diaphragm 2, a current corresponding to the concentration of the test gas is generated between the working electrode 3 and the counter electrode 6, and the terminals 12, An electric signal corresponding to the gas concentration can be taken out of the gas 12.
[0013]
On the other hand, the test gas and oxygen that have passed through the diaphragm 2 pass through the sheet 4 impregnated with the electrolyte and diffuse to the counter electrode 6, but the test gas is blocked by the membrane 5 that supports the counter electrode 6, Only oxygen passes through. As a result, although the working electrode 3 and the counter electrode 6 are separated only by a very short distance such as the thickness of the sheet 4, the arrival of the test gas to the counter electrode 6 is prevented as much as possible. The concentration of the test gas can be accurately detected.
[0014]
In this embodiment, since the support 8 is made of a material having a small water repellency and the surface is processed to be a rough surface, the electrolyte solution is also formed on the back surface of the film 5 together with the capillary phenomenon due to the rough surface. The electrolyte solution stored in the middle case 10 can be supplied to the sheet 7 to prevent drying.
[0015]
For comparison, the above-described sensor was configured using the support 8 that had not been roughened, and the internal resistance was measured to be 8.8Ω. On the other hand, in the above-described embodiment, the internal resistance was 7.3Ω, which was about 80% lower. Also from this fact, it was confirmed that roughening the support 8 had a great effect in spreading the electrolyte sufficiently.
[0016]
In addition, since the electrolyte stored in the middle case 10 is supplied from the surface of the support 8 to the sheet 4, the electrolyte 8 is reliably prevented from being impregnated and the support 8 is not roughened. The production yield can be improved as compared with the case using the above.
[0017]
In this embodiment, the FEP film is used as the film 5 which is substantially impermeable to the test gas and capable of transmitting oxygen. However, the polyethylene film has the same effect.
[0018]
Further, in the above-described embodiment, the counter electrode 6 is formed as a layer on the surface of the film 5 which is substantially impermeable to the test gas and capable of transmitting oxygen. Even if it is configured and the counter electrode 6 is disposed in close contact with the back surface of the film 5, the same effect is obtained.
[0019]
【The invention's effect】
As described above, according to the present invention, while the oxygen dissolved in the electrolytic solution reaches the counter electrode as much as possible, the test gas is prevented from reaching the counter electrode by the membrane, and the rough surface of the support is used. To provide an electrochemical gas sensor that can reliably impregnate an electrolyte solution into a sheet, is highly reliable, and can be thinned.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of an electrochemical gas sensor of the present invention.
FIGS. 2A and 2B are diagrams showing examples of a support body and an external terminal used in the sensor, respectively.
FIG. 3 is a view showing the state of the surface by enlarging the support body.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cover 1a Gas inlet 2 Diaphragm 3 Working electrode 4 Sheet 5 Membrane 6 Counter electrode 7 Sheet 8 Support body 8a Protruding piece 8b Through-hole 9 Case main body 10 Bottomed cylindrical middle case 10a Step part 11 Lead 12 External terminal

Claims (5)

  A working electrode formed by forming a layer of a conductive active material on a diaphragm capable of flowing a gas to be detected and having water repellency, a first sheet impregnated with an electrolytic solution, and the gas to be tested are substantially A membrane that is impervious to oxygen and capable of permeating oxygen, a counter electrode, a second sheet impregnated with the electrolytic solution, and a support having a roughened surface at least facing the second sheet. The electrochemical gas sensor is configured to be stacked and arranged in the above order and accommodated in a case so as to expose the diaphragm.   2. The electrochemical gas sensor according to claim 1, wherein the counter electrode is formed as a layer on the surface of a film that allows the gas to be detected to be substantially impermeable and allows oxygen to pass therethrough.   The case includes a lid body having an opening in a central region, a cylindrical case body, and a bottomed cylindrical middle case that can be inserted into the case body, and the bottomed cylindrical middle case has an outer periphery. The electrochemical gas sensor according to claim 1, wherein the working electrode, the counter electrode, and the sheet are sandwiched between the supported elastic frame and the lid. External connection terminals provided on the bottom surface of the case body before Symbol cylindrical body, and is connected via an insertion has been read in and the counter electrode and the working electrode between the case body and the bottomed cylindrical in case The electrochemical gas sensor according to claim 3 .   The electrochemical gas sensor according to claim 1, wherein a through hole is formed in a central portion of the support.

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