JPS60211351A - Electrochemical type gas sensor - Google Patents

Abstract

PURPOSE:To prevent the change in the humidity of external environment from affecting an electrode reaction by passing an electrolyte through a fine path from an electrolyte chamber so as to contact with a pair of electrode-gas permeable membranes and filling the electrolyte in the fine path even if the quantity of the electrolyte increases or decreases. CONSTITUTION:A combination of a pair of gas permeable membrane-electrodes 11-13; 12-14 is provided in the lower part of a case 1. A gas to be detected, for example, gaseous CO is introduced through an aperture 9 and is permeated through the gas permeable membrane 11. On the other hand, air (O2) is introduced through the aperture 10 and is permeated through the gas permeable membrane 12. The electrolyte is passed through the fine path 24 from the electrolyte chamber 23 provided in the upper part of a case 1 and is brought into contact with the electrode 13 and the electrode 14 so that oxidation reaction is effected on one side and a reduction reaction on the other. The potential of the electrode reaction is detected by a voltage circuit 27. The quantity of the electrolyte in the electrolyte chamber is extremely larger than the quantity in the fine path and therefore the electrolyte is always filled in the fine path and the potential is stably and accurately measured without the influence of the change in the humidity of the external environment on the electrode reaction.

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.

Conventional electrochemical gas sensors, for example, have two
An electrolytic solution chamber having several openings is formed, each opening of the electrolytic solution chamber is closed with a gas permeable membrane having an electrode adhered to the inner surface thereof, and an electrolytic solution is provided in the electrolytic solution chamber in contact with the electrode. The device houses a liquid and uses one electrode to oxidize and reduce 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 moisture 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, resulting in a change in output even if the gas concentration is constant. There is a problem.

For this reason, it is conceivable to provide an impregnating material made of paper or the like on the inner surface of each electrode and allow the electrolyte to rise through this impregnating material by capillary action, thereby expanding the contact area of the electrolyte with the electrode. However, if the electrolyte decreases significantly, the electrolyte rising through the impregnating material will not be able to reach the top of the electrode, and as a result, even if this impregnating material is used, it will not be able to absorb changes in output. The problem is that it cannot be done.

This invention was made by focusing on the above-mentioned problems.
It is an object of the present invention to provide an electrochemical gas sensor that causes almost no error in its output even if the humidity of the external environment changes or even if time passes.

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 Figure 1, l is a case, and this case l
is a metal body 4 with a pair of recesses 2.3 formed at the bottom.
has. Side walls 5, 6 are housed and fixed in the recesses 2, 3, respectively, and these side walls 5.8 and the main body 4 constitute the case 1. The inner surface of the side wall 5 and the recess 2
A working storage chamber 7 is formed between the inner surface of the side wall 6 and the bottom surface of the recess 3, and a paired storage chamber 8 is formed as a pair with the working storing chamber 7. Further, an opening 8 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 8. On the other hand, an opening 10 is formed in the side wall 6 and communicates with the storage chamber 8.
Air containing oxygen gas at a concentration of 1% is introduced into the storage chamber 8. 11.12 is the action storage chamber 7. These gas permeable membranes 1 are housed in respective storage chambers 8.
1.12 closes the openings 8.10 by having their peripheral edges sandwiched between the side wall 5.8 and the main body 4. And these gas permeable membranes 11. = 12 are both composed of porous membranes having gas permeability such as polyethylene films and fluororesin films, and as a result, the gas permeable membrane 11 is impermeable to the test gas, and the gas permeable membrane 12 is impermeable to the oxygen gas in the air. Allows transmission. Gas permeable membranes 11 and 1
A working electrode film 13 and a counter electrode film 14 as electrodes are deposited on the inner surface of the electrode 2, respectively. It is made of a material selected from the above, and is deposited by methods such as vapor deposition, sputtering, and ion blasting. These working electrode membranes 13
On the inner surface side of the counter electrode membrane 14, impregnating materials 15 and 1B made of paper or the like are provided in the action housing chamber 7 and the counter housing chamber 8. 17 is an electrolyte chamber formed in the case 1, and the lower end 18 of this electrolyte chamber 17 is located above the upper end 18.20 of the storage chamber 7.8. As a result, the lower end 18 of the electrolyte chamber 17 is located above the lower ends 21, 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. Reference numeral 24 denotes a narrow passage formed in the case 1. One end of this narrow passage 24 opens at the lower end 18 of the electrolyte chamber 17, and the other end is bifurcated into two, leading to the action storage chamber 7 and the counter storage chamber 8. The other end is open. As a result, the electrolyte chamber 17
The working storage chambers 7 and 8 are connected to each other by this narrow passage 24, so that the electrolyte 23 is led to the working storage chamber 7 and the paired storage chamber 8 through this narrow passage 24, and is impregnated. The material 15.18 is impregnated into contact with the inner surfaces of the working electrode membrane 13 and the counter electrode membrane 14. 25.2e is a pair of lead wires connected to the working electrode film 13 and the counter electrode film 14, and a constant voltage circuit 27 is connected to these lead wires 25.28.

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

First, when a gas to be detected such as -carbon oxide gas is introduced into the opening 9, this gas to be detected passes through the gas permeable membrane 11 and the working electrode membrane 13, and the impregnated working electrode membrane 13 and the electrolyte 23 are impregnated. An oxidation reaction occurs at the interface with the material 15. On the other hand, the oxygen gas in the air supplied to the opening 1O is transferred to the gas permeable membrane 12.
, passes through the counter electrode membrane 14, and a reduction reaction occurs at the interface between the counter electrode membrane 14 and the impregnated material IB impregnated with the electrolytic solution 23. As a result, an electrolytic current corresponding to the carbon monoxide gas concentration flows between the working electrode film 13 and the counter electrode film 14. 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 becomes vapor and enters and exits the gas permeation 11911.12, and the electrolyte 23
increases or decreases or decreases unilaterally. However, while the volume of the narrow passage 24 is extremely small, the electrolyte chamber 17
Since the volume of the electrolyte 23 is extremely large, even if the amount of the electrolyte 23 fluctuates or decreases considerably, the electrolyte 23 remains in the narrow passage 24.
3 is full. Moreover, since the lower end 18 of the electrolyte chamber 17 is located above the upper end 18.20 of the working and storage chambers 7 and 8, even if the electrolyte 23 decreases to near the lower end 18 of the electrolyte chamber 17, Also, action, storage room 7
．． The electrolytic solution 23 always reaches the upper end 18.2o of 8 due to Pascal's principle, and as a result, the impregnating material 15.1
6 is constantly immersed in the electrolytic solution 23 over the entire area. In this way, in this embodiment, no matter how the electrolyte 23 increases or decreases in the electrolyte chamber 17, as long as a small amount of electrolyte 23 remains, sufficient to fill the narrow passage 24, action,
Since the contact area of the counter electrode membranes 13, 14 with the 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 arranged above the lower end 21.22 of the working and storage chamber 7.8 and the upper end 18.
It is located below 20. A pair of narrow passages 3 connects the lower end of the electrolyte chamber 31 and the working and storage chambers 7 and 8.
It is connected by 3.34. As a result, the liquid level of the electrolyte 35 in the storage chambers 7 and 8 is higher than before by the amount that the lower end 32 of the electrolyte chamber 31 is higher than the lower end 21.22 of the storage chambers 7 and 8. As a result, even if the amount of the electrolyte 35 increases or decreases, the action of the electrolyte 35 and the counter electrode 119
The variation in contact area for 13.14 will be smaller. Furthermore, in this embodiment, the electrolyte chamber 31 is lowered from the position of the electrolyte chamber 17 in the first embodiment, so that the overall size can be reduced. In this way, this embodiment can reduce the overall size while suppressing fluctuations in output due to increases and decreases in the amount of electrolyte 35 to a practical range.

Note that the other configurations and operations are the same as those in the first embodiment.

Note that in the above-mentioned embodiment, two electrodes, an action electrode and a counter electrode, are used.
Although we have explained the case where two electrodes are used, a static electrode that is not affected by the gas to be detected is provided on the inner surface of one gas permeable membrane (gas permeable H12) to accurately display and measure the static potential of the counter electrode. It's okay. Furthermore, in the above embodiment,
Although the present invention has been described in the case where it is applied to a constant potential electrolysis type gas sensor, the present invention can also be applied to a galvanic cell type, polarographic type, coulometric type, and solution type conductivity type gas sensor.

As explained below, according to the present invention, even if the humidity of the external environment changes or even if time passes, there is almost no error in the humidity.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing a first embodiment of the present invention, and FIG.
The figure is a schematic sectional view showing a second embodiment of the invention. 1...Case? , 8...Storage chamber 8.10...Opening 11.12...Gas permeable membrane 13
．． 14... Electrode 17.31... Electrolyte chamber 23.3
5... Electrolyte 24.33.34... Hosoji Patent Applicant Riken Keiki Co., Ltd. Agent Patent Attorney Ta 1) Toshio Figure 2

Claims (1)

[Claims] a pair of storage chambers formed in the case; a gas permeable membrane that is stored in each storage chamber so as to close the opening of the storage chamber and has an electrode adhered to its inner surface; The electrolyte chamber is located above the lower end of the chamber and contains the electrolyte, and the narrow passage is formed in the case and connects the electrolyte chamber and the storage chamber to lead the electrolyte to the electrode. Characteristic electrochemical gas sensor.