JPH0417384B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrochemical gas sensor that measures gas concentration by redoxing a gas with an electrode in contact with an electrolyte.

In a conventional electrochemical gas sensor, for example, an electrolyte chamber having two openings is formed in a case, each opening of the electrolyte chamber is closed with a gas permeable membrane having an electrode adhered to the inner surface, and Further, an electrolytic solution connected to and in contact with the electrode is housed in the electrolytic solution chamber, and one electrode oxidizes and reduces the gas, thereby measuring the gas concentration.

However, in such an electrochemical gas sensor, a gas permeable membrane with an electrode is provided at the opening of the electrolyte chamber, so water in the electrolyte becomes vapor and leaks outside from the gas permeable membrane. When the amount of electrolyte decreases, the contact area between the electrolyte and the electrode decreases, resulting in a problem that the output decreases over time even if the gas concentration is constant.

In order to solve these problems, it may be possible to use sulfuric acid, which has a hygroscopic function, as an electrolyte and prevent the amount of electrolyte from decreasing by releasing steam into the external environment or absorbing steam from the external environment. .

However, when doing this, the amount of electrolyte increases or decreases in response to changes in the humidity of the external environment, so the area of the electrolyte in contact with the electrode changes, and as a result,
There is a problem that the output changes even if the gas concentration is constant.

For this reason, it may be possible to provide an impregnated material made of paper or the like on the inner surface of each electrode and allow the electrolyte to rise in this impregnated material by capillary action, thereby expanding the contact area of the electrolyte with the electrode. Even with this method, if the electrolyte decreases significantly, the electrolyte rising through the impregnating material will not be able to reach the upper end of the electrode, and as a result, even if this impregnating material is used, the output will change. The problem is that it cannot be absorbed.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide an electrochemical gas sensor in which almost no error occurs in its output even if the humidity of the external environment changes or even if time passes. It is an object.

This purpose consists of a pair of storage chambers formed in the case, a gas permeable membrane that is housed in each storage chamber so as to close the opening of the storage chamber and has an electrode attached to its inner surface, and a gas permeable membrane formed inside the case. an electrolytic solution chamber whose lower end is located above the lower end of the storage chamber and stores the electrolytic solution; and a narrow passage formed within the case that connects the electrolytic solution chamber and the storage chamber and leads the electrolytic solution to the electrode. This can be achieved by having the following.

Hereinafter, a first embodiment of the present invention will be described based on the drawings.

In FIG. 1, 1 is a case, and this case 1 has a metal main body 4 with a pair of recesses 2 and 3 formed in its lower part. Side walls 5 and 6 are housed and fixed in the recesses 2 and 3, respectively, and these side walls 5,
6 and the main body 4 constitute the case 1. A working storage chamber 7 is formed between the inner surface of the side wall 5 and the bottom surface of the recess 2, and a pair storage chamber 7 is formed between the inner surface of the side wall 6 and the bottom surface of the recess 3. A chamber 8 is formed. Further, an opening 9 communicating with the action storage chamber 7 is formed in the side wall 5, and a gas to be detected such as carbon monoxide gas is introduced into the action storage chamber 7 through this opening 9. On the other hand, an opening 10 communicating with the storage chamber 8 is formed in the side wall 6, and air containing 21% oxygen gas is introduced into the storage chamber 8 through this opening 10. Reference numerals 11 and 12 indicate gas permeable membranes housed in the action storage chamber 7 and the counter storage chamber 8, respectively.
1 and 12 close the openings 9 and 10 by having their peripheral edges sandwiched between the side walls 5 and 6 and the main body 4, respectively. Both of these gas permeable membranes 11 and 12 are composed of porous membranes having gas permeability such as polyethylene film or fluororesin film. 12 allows permeation of oxygen gas in the air. A working electrode film 13 and a counter electrode film 14 as electrodes are deposited on the inner surfaces of the gas permeable membranes 11 and 12, respectively, and these working electrode film 13 and counter electrode film 14 are made of platinum, palladium,
It is made of a material selected from the group consisting of rhodium and other substances and alloys thereof, and is deposited by methods such as vapor deposition, sputtering, and ion plating. A working storage chamber 7 and a counter storage chamber 8 are formed on the inner surfaces of the working electrode film 13 and the counter electrode film 14.
Impregnated materials 15 and 16 made of paper or the like are provided inside. 17 is an electrolyte chamber formed in the case 1, and the lower end 1 of this electrolyte chamber 17 is
8 is located above the upper ends 19, 20 of the storage chambers 7, 8. As a result, the lower end 18 of the electrolyte chamber 17 is located above the lower ends 21 and 22 of the working storage chamber 7 and the counter storage chamber 8. The electrolyte chamber 17 contains an electrolyte 23 made of an aqueous solution of sulfuric acid, phosphoric acid, or the like. 24 is a narrow passage formed in the case 1, and one end of this narrow passage 24 is connected to the lower end 18 of the electrolyte chamber 17.
The other end is divided into two parts, and an operation storage chamber 7 is opened.
The other end is open to the storage chamber 8. As a result, the electrolyte chamber 17 and the working and pair storage chambers 7 and 8 are connected to each other by this narrow passage 24, so that the electrolyte 23 flows through this narrow passage 24 to the working and pairing storage chamber 7 and the pair of storage chambers 7 and 8. 8 and is impregnated with impregnating materials 15 and 16 to contact the inner surfaces of the working electrode membrane 13 and the counter electrode membrane 14. 25 and 26 are a pair of lead wires connected to the working electrode film 13 and the counter electrode film 14, and these lead wires 2
A constant voltage circuit 27 is connected to 5 and 26.

Next, the operation of the first embodiment of the present invention will be explained.

First, when a test gas such as carbon monoxide gas is introduced into the opening 9, the test gas passes through the gas permeable membrane 11 and the working electrode film 13, and then passes through the working electrode film 13 and the electrolyte 2.
An oxidation reaction occurs at the interface with the impregnated material 15 impregnated with No. 3. On the other hand, oxygen gas in the air supplied to the opening 10 passes through the gas permeable membrane 12 and the counter electrode membrane 14.
, and a reduction reaction occurs at the interface between the counter electrode membrane 14 and the impregnated material 16 impregnated with the electrolytic solution 23. As a result, the working electrode film 13 and the counter electrode film 14
An electrolytic current corresponding to the carbon monoxide gas concentration flows between the two. Then, by measuring this electrolytic current, the concentration of the gas to be detected is measured. When the concentration of the gas to be detected is measured over a long period of time in this way, the water in the electrolyte 23 turns into vapor and moves in and out of the gas permeable membranes 11 and 12, causing the electrolyte 23 to increase, decrease, or unilaterally decrease. . However, while the volume of the narrow passage 24 is extremely small, the electrolyte chamber 1
Since the volume of 7 is extremely large, even if the amount of electrolyte 23 fluctuates or decreases considerably, the narrow passage 24
This means that the inside is filled with electrolyte 23. Moreover, since the lower end 18 of the electrolyte chamber 17 is located above the upper ends 19 and 20 of the storage chambers 7 and 8, if the electrolyte 23 is
Even if the electrolytic solution 23 decreases to around 8, the electrolytic solution 23 always reaches the upper ends 19 and 20 of the storage chambers 7 and 8 due to Pascal's principle, and as a result, the impregnated material 1
5 and 16 are constantly immersed in the electrolytic solution 23 over the entire area. Thus, in this example,
No matter how the electrolyte 23 increases or decreases in the electrolyte chamber 17, as long as a small amount of the electrolyte 23 remains, sufficient to fill the narrow passages 24, the working, counter electrode membrane 13,
Since the contact area of 14 with electrolyte 23 is always constant, it is possible to obtain an output that accurately corresponds to the gas concentration.

FIG. 2 is a diagram showing a second embodiment of the invention. In this embodiment, the lower end 32 of the electrolyte chamber 31 is connected to the lower end 21, 22 of the storage chamber 7, 8.
It is located higher than the upper ends 19 and 20. The lower end of this electrolyte chamber 31 and the paired storage chambers 7 and 8 are connected by a pair of narrow passages 33 and 34. As a result, the liquid level of the electrolyte 35 in the storage chambers 7 and 8 is lowered by the lower end 32 of the electrolyte chamber 31 and the lower end 21 and 2 of the storage chamber 7 and 8.
As a result, even if the amount of electrolyte 35 increases or decreases, the amount of electrolyte 3
5, the variation in the contact area with the counter electrode films 13 and 14 becomes smaller. Furthermore, in this embodiment, the electrolyte chamber 31 is located lower than the electrolyte chamber 17 in the first embodiment, so that the overall size can be reduced. Thus, in this example, the electrolyte 3
This makes it possible to reduce the overall size while suppressing fluctuations in output due to increases and decreases in the amount of 5 to a practical range. Note that the other configurations and operations are the same as those in the first embodiment.

In the above embodiment, the case where two electrodes, a working electrode and a counter electrode, were used was explained. Stationary electrodes may be provided that are not affected by the gas being detected and measured. Furthermore, in the above-mentioned embodiments, the present invention was applied to a constant potential electrolysis type gas sensor, but the present invention also applies to a galvanic cell type gas sensor.
It can also be applied to polarographic, coulometric, and solution conductivity type gas sensors.

As described above, according to the present invention, almost no error occurs in the output even if the humidity of the external environment changes or even if time passes.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing a first embodiment of the invention, and FIG. 2 is a schematic sectional view showing a second embodiment of the invention. 1... Case, 7, 8... Storage room, 9, 10...
...Opening, 11, 12...Gas permeable membrane, 13, 14
... Electrode, 17, 31 ... Electrolyte chamber, 23, 35
...Electrolyte, 24, 33, 34...Narrow path.

Claims (1)

[Claims] 1 A pair of storage chambers formed in a case, a gas permeable membrane stored in each storage chamber so as to close the opening of the storage chamber and having an electrode adhered to its inner surface, and a gas permeable membrane formed in the case whose lower end is The electrolyte chamber is located above the lower end of the storage chamber and contains the electrolyte, and the narrow path is formed in the case and connects the electrolyte chamber and the storage chamber to lead the electrolyte to the electrode. An electrochemical gas sensor featuring: