JP2532334B2 - Galvanic battery gas sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a galvanic cell type gas sensor, and an object thereof is to provide a gas sensor which is not affected by carbon dioxide contained in a detection gas.

[0002]

2. Description of the Related Art Galvanic cell type gas sensors are generally used in a wide range of fields because they are easy and inexpensive and operate at room temperature.

The principle is that, for example, in the case of an oxygen sensor,
An oxygen-lead battery composed of a working electrode made of gold effective for an electrochemical reduction reaction of oxygen, a counter electrode made of lead, a diaphragm for limiting the permeation of an electrolyte and oxygen, and an oxygen diffusion-controlled region. This is based on the fact that the resistance end voltage is proportional to the oxygen concentration when discharged through a working resistor.

When an acidic electrolytic solution mainly containing an organic acid such as acetic acid or propionic acid is used for this sensor, the following reaction occurs. Working electrode: O ₂ + 4H ⁺ + 4e → 2H ₂ O Counter electrode: 2Pb + 2H ₂ O → 2PbO + 4H ⁺ + 4e

In this case, an alkali metal salt or an organic acid salt is usually added for the purpose of increasing the conductivity of the electrolytic solution or making the electrolytic solution a buffer solution.

In such a mixed acidic solution of an acid and a salt, charge transfer is not a hydrogen ion (H ⁺ ) flash but a cation dissociated from the salt, for example, a potassium ion (K ^{+ in} a mixed aqueous solution of acetic acid and potassium acetate). ), The surface of the positive electrode has a high potassium content, and although the offshore electrolytic solution is acidic, the vicinity of the working electrode may be locally alkaline.

At this time, when a relatively large amount of carbon dioxide gas is contained in the detection gas, insoluble lead carbonate or basic lead carbonate is deposited on the surface of the working electrode and the oxygen concentration cannot be measured.

In order to eliminate the influence of carbon dioxide gas as described above,
In order to prevent the vicinity of the working electrode from becoming alkaline, it is necessary to promptly diffuse potassium, which has finished supplying electric charges to the working electrode, into the offshore electrolytic solution to constantly update the electrolytic solution on the surface of the working electrode.

Therefore, generally, a continuous groove is provided on the surface of the working electrode so that the electrolyte or reaction product in the liquid film formed between the working electrode and the diaphragm diffuses into the offshore electrolytic solution. ing.

[0010]

As described above, in the conventional sensor, it is necessary to provide the working electrode with a continuous groove.
Since the working electrode is generally made of a metal or a metal oxide having a diameter of 1 to 5 mm, the groove is often formed by cutting, and it cannot be said that all the shapes and dimensions of the groove between the sensors are formed uniformly. Since the shape and size of the groove are greatly related to the working area of the working electrode, if these are varied, variations will occur among the individual sensor outputs. Further, since the liquid film in the groove becomes locally thick, the response performance of the sensor becomes worse than that of a sensor having a smooth working electrode surface.

According to the present invention, the galvanic cell type gas sensor, which does not have the above-mentioned groove on the surface of the working electrode, constantly updates the electrolytic solution on the surface of the working electrode, is not affected by carbon dioxide gas and has a high responsiveness. Is intended to be provided.

[0012]

Therefore SUMMARY OF THE INVENTION, and the working electrode for electrochemical oxidation or reduction gas, and that provided on the outside of a and the working electrode a diaphragm for limiting the permeation of gas , counter electrode and an electrolyte solution, consisting comprise, as that provided on the outside of the membrane a presser cover for keeping the thickness of the liquid film at a constant, which is formed between the working electrode and the membrane galvanic cell A galvanic cell type gas sensor is characterized in that in the gas sensor, a groove is formed on the diaphragm pressing surface of the holding lid to connect the electrolytic solution portion and the working electrode upper portion.

[0013]

By providing a groove for connecting the electrolytic solution portion and the working electrode upper part to the contact surface portion of the holding lid provided on the outside of the diaphragm, the contact pressure between the diaphragm and the working electrode is locally released at the groove portion. ,
The diffusion of the electrolyte solution in the diaphragm is facilitated, and the electrolyte solution on the surface of the working electrode is constantly updated. This can prevent the surface of the working electrode from becoming alkaline and being affected by carbon dioxide gas. Moreover, since no groove is formed on the surface of the working electrode,
The liquid film does not locally thicken, and the response characteristics of the sensor are not impaired.

[0014]

EXAMPLES The present invention will be described below with reference to preferred examples.

FIG. 1 is a structural sectional view of a galvanic cell type oxygen sensor according to an embodiment of the present invention. This sensor is A
A container 1 made of BS resin, a working electrode 2 having a diameter of 5 mm and made of platinum having a smooth surface, and a working electrode 2 located on the outer side thereof.
As a known structure described in 15058,
Vessel 1 of tetrafluoroethylene-hexafluoropropylene copolymer Polymerization film of diaphragm 3 is provided on the inner surface, from ABS resin provided outside of the membrane 3 for joining the working electrode 2 and the diaphragm 3 at a constant pressure And a counter electrode 5 made of lead, and an electrolytic solution 6 made of a mixed aqueous solution of acetic acid, potassium acetate, and lead acetate. The working electrode 2 and the counter electrode 5 are externally closed via a resistor 7. In addition, the diaphragm 3 is adhered to prevent leakage of the electrolytic solution,
It is obvious that it can be attached to the container 1 by welding.
It

FIG. 2 schematically shows the groove 8 provided on the diaphragm contact surface of the pressing lid 4. The groove 8 is for communicating the electrolytic solution portion and the working electrode upper portion. The groove (a) is an example in which a relatively large groove is provided, (b) is an example in which a relatively small groove is provided radially from the center, and (c) is an example in which a relatively small groove is provided in a lattice pattern. is there.

By providing such a groove 8 on the contact surface of the holding lid 4, the pressing of the diaphragm 3 against the working electrode 2 is locally released, so that the electrolyte in the liquid film is offshore along the groove. Can freely diffuse with the electrolyte solution.

Next, in order to confirm the effect of the present invention, in the oxygen sensor as shown in FIG. 1, a large number of radial electrolytic solution passage grooves are provided in the contact surface portion of the holding lid as shown in FIG. 2 (b). (A), and (B) is the one in which an electrolytic solution passage groove similar to that of the above-mentioned pressing lid is provided on the surface of the working electrode as in the conventional case.
A smooth cover and working electrode were prepared as (C).

When these were placed in a mixed gas of oxygen 20%, carbon dioxide gas 10%, and nitrogen 70%, aging characteristics as shown in FIG. 3 were obtained.

In the case of the sensor (C) in which both the holding lid and the working electrode are smooth, the oxygen concentration is constant at 20%,
The sensor output decreases with time and is obviously affected by carbon dioxide gas, whereas the product (A) of the present invention is not affected by carbon dioxide gas at all as in the conventional product (B). I understand from.

Further, FIG. 4 shows the response characteristics when the product (A) of the present invention and the conventional product (B) were exposed to 100% nitrogen atmosphere from the atmosphere. From this figure, the product (A) of the present invention in which the surface of the working electrode is smooth is more It can be seen that the response performance is excellent.

[0021]

As described above, the galvanic cell type gas sensor according to the present invention comprises a working electrode for electrochemically oxidizing or reducing gas, and a diaphragm for limiting gas permeation. One provided on the outside of the working electrode, the counter electrode, the electrolytic solution, and a holding lid for keeping the thickness of the liquid film formed between the working electrode and the diaphragm constant, and provided on the outside of the diaphragm. In the galvanic cell type gas sensor, the groove for connecting the electrolytic solution portion and the working electrode upper portion is formed in the diaphragm pressing surface of the pressing lid.

With this structure, the contact pressure between the diaphragm and the working electrode in the groove is locally released, and the electrolytic solution that reaches the surface of the working electrode through the diaphragm is constantly renewed. The influence of gas can be prevented, and since no groove is formed on the surface of the working electrode, the liquid film does not locally thicken, and good response characteristics of the sensor can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional structural view of a galvanic cell type oxygen sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of an electrolyte solution passage groove of a holding lid according to the present invention.

FIG. 3 is a diagram showing a result of an output characteristic comparison test.

FIG. 4 is a diagram showing a response characteristic comparison test result.

[Explanation of symbols]

 1 Container 2 Working Electrode 3 Diaphragm 4 Holding Cap 5 Counter Electrode 6 Electrolyte 7 Resistance 8 Groove

Claims (1)

(57) [Claims] 1. A working electrode for electrochemically oxidizing or reducing gas, a diaphragm for limiting gas permeation, which is provided outside the working electrode, a counter electrode, and an electrolytic solution. When, in the galvanic cell type gas sensor a pressing lid becomes comprise, as that provided on the outside of the diaphragm for maintaining the thickness of the liquid film at a constant, which is formed between the working electrode and the membrane, pressing the lid A galvanic cell type gas sensor, characterized in that a groove that connects the electrolytic solution portion and the working electrode upper portion is formed on the diaphragm pressure contact surface.