JPH0634595A - Galvanic battery type combustible gas sensor - Google Patents

Abstract

PURPOSE:To obtain a galvanic batter type combustible gas sensor which can operate even in a combustible atmosphere containing no oxygen. CONSTITUTION:This apparatus has an electrolyte 4, a positive pole 2 which is arranged in the electrolyte 4 to reduce oxygen dissolved in the electrolyte 4 electrochemically and has at least one catalyst selected from a group comprising a gold catalyst, a carbon catalyst and a platinum catalyst and a negative pole 3 which functions as gas pole and has a catalyst effective for electrochemical oxidizing reaction of a combustible gas. In the positive pole 2, a reducing reaction alone of the oxygen dissolved in the electrolyte occurs and in the negative pole 3, an oxidizing reaction alone of the combustible gas occurs thereby enabling sufficient operation even in a combustible atmosphere containing no oxygen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor for measuring the concentration of combustible gases such as hydrogen and carbon monoxide dissolved in a gas phase or water, and more specifically, it is proportional to the concentration of the gas to be measured. The present invention relates to a galvanic battery type gas sensor that outputs by itself.

[0002]

2. Description of the Related Art Generally, a galvanic cell type gas sensor or a polaro type gas sensor, which is an electrochemical sensor, is used to measure the concentration of a specified gas in air or water. Both are basically composed of a diaphragm for limiting gas permeation, a working electrode that electrochemically oxidizes or reduces gas to act as a gas electrode, a counter electrode, an electrolytic solution, and a container that houses these. Has been done. Functionally, in the former, the working electrode and the counter electrode are always connected via a resistor and output in proportion to the concentration of the gas to be detected by itself, while the latter uses a constant potential applying device to externally output. The difference is that the output is proportional to the gas concentration only when a constant voltage is applied between both electrodes.

Comparing the usability of the two sensors, the galvanic cell type which outputs in proportion to the concentration of the gas to be detected by itself requires an expensive and difficult-to-handle constant potential applying device, and then outputs after applying the potential to the electrodes. Is superior to the polaro type, which requires a considerable amount of time to stabilize.

The electrochemical type flammable gas sensor currently in practical use is mainly of the polaro type, and both the positive electrode and the negative electrode are made of platinum or palladium which is effective for the electrochemical oxidation of the flammable gas and the electrochemical oxidation of oxygen. It is basically composed of a gas electrode. Therefore, a constant voltage is applied between both electrodes so that only the oxygen reduction reaction occurs in the positive electrode and only the flammable gas oxidation reaction occurs in the negative electrode. However, as described above, the polaro type has some problems in terms of usability.

[0005] Therefore, as a galvanic battery type combustible gas sensor, there is a sensor proposed in Japanese Patent Laid-Open No. 3-186753,186754,186755, which has not been put into practical use. These are a positive electrode which is made of a catalyst such as carbon or silver which is active for the reduction reaction of oxygen and which is inactive for the oxidation reaction of flammable gas and which acts as a gas electrode, and platinum and palladium which are active for the oxidation reaction of flammable gas. It is basically composed of a negative electrode which is a gas electrode composed of. In these flammable gas sensors, only the reduction reaction of oxygen takes place at the positive electrode and the oxidation reaction of the flammable gas takes place at the negative electrode due to the selective activity of the catalysts on both electrodes without applying a potential to the electrodes. Therefore, the galvanic battery type sensor can be driven.

[0006]

However, as described above, the galvanic cell type combustible sensor using the gas electrodes having different catalyst selectivities as the positive electrode and the negative electrode causes the positive electrode to carry out the reduction reaction of oxygen in the atmosphere. Therefore, there is a problem that it cannot be used in a flammable atmosphere containing no oxygen, for example, in 100% hydrogen gas or a mixed gas atmosphere of carbon monoxide and nitrogen.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a combustible gas sensor of the galvanic cell type which can sufficiently operate even in a combustible atmosphere containing no oxygen. .

[0008]

Therefore, there is provided an electrolytic solution and a positive electrode disposed in the electrolytic solution for electrochemically reducing dissolved oxygen in the electrolytic solution, which comprises a gold catalyst, a carbon catalyst and platinum. A catalyst having at least one catalyst selected from a catalyst group consisting of a catalyst, and a negative electrode functioning as a gas electrode and having a catalyst effective for an electrochemical oxidation reaction of a flammable gas. The above problem is solved by using a galvanic battery type combustible gas sensor provided.

[0009]

As described above, since the conventionally proposed combustible gas sensor for galvanic cells reduces oxygen in the atmosphere at the positive electrode, it cannot be used in a combustible gas atmosphere containing no oxygen. Therefore, the present invention focuses on the dissolved oxygen in the electrolytic solution, that the flammable gas in the atmosphere cannot easily enter the electrolytic solution whose external atmosphere is blocked by the sensor container, and the dissolved oxygen is reduced by the reduction reaction of the positive electrode. It takes advantage of the fact that it takes a considerable amount of time to be consumed.

An electrolytic solution, a positive electrode using gold, carbon, or platinum as a catalyst, which is provided in the electrolytic solution, and a catalytic electrode effective for an electrochemical oxidation reaction of a flammable gas are provided. A galvanic cell type combustible gas sensor consisting of a diaphragm made of an organic polymer film provided on the outside of the catalyst electrode, a container accommodating these, and a resistor connecting the positive electrode and the negative electrode is used in a combustible gas or combustible gas. When placed in a mixed gas of a reactive gas and an inert gas or a heatable gas and oxygen, only a reduction reaction of dissolved oxygen in the electrolytic solution occurs at the positive electrode and an oxidation reaction of the flammable gas occurs at the negative electrode.

These reactions are shown below using oxygen monoxide as an example of a flammable gas. [When the electrolyte is acidic] Positive electrode reaction 1/2 O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O Negative electrode reaction CO + H ₂ O → CO ₂ + 2H ⁺ + 2e
^- total reaction O ₂ + CO → CO ₂ [when the electrolyte is alkaline positive electrode reaction _{O 2 + H 2 O + 2e} - → 2OH - anode reaction _{^{CO + 2OH - → CO 2 +}} H 2 O + 2
e ^- Whole reaction O ₂ + CO → CO ₂

As described above, the inventor of the present invention has noticed that oxygen is dissolved in the electrolytic solution, and only the oxygen reduction reaction takes place in the positive electrode and the flammable gas oxidation reaction does not occur. The reason is that the combustible gas cannot easily enter because it is shielded from the external atmosphere by the sensor container, and that it takes a considerable time for the dissolved oxygen to be consumed by the reduction reaction of the positive electrode. In particular, since the electrode using gold or carbon as a catalyst is used for the positive electrode,
Even if some flammable gas is dissolved in the electrolytic solution by leaving it in a heatable gas for a long time, the gas selectivity of these catalysts causes
After all, only the reduction reaction of oxygen occurs. As the electrons move from the negative electrode to the positive electrode through the resistor in accordance with the above reaction, the voltage across the resistor is measured to determine the amount of electricity flowing between the two electrodes, in other words, the concentration of flammable gas. I can know.

[0013]

EXAMPLES The present invention will be described below with reference to preferred examples. FIG. 1 is a schematic sectional view of a galvanic cell type combustible gas sensor according to an embodiment of the present invention. In this embodiment, A
A container body 1 made of BS resin, a positive electrode 2 in which a gold catalyst is vapor-deposited on carbon, a negative electrode 3 in which platinum is electrodeposited on porous carbon, and an electrolysis consisting of a mixed aqueous solution of acetic acid and potassium acetate. The liquid 4 and the diaphragm 5 made of a tetrafluoroethylene-6-fluoropropylene copolymer film provided outside the negative electrode are provided, and the positive electrode 2 and the negative electrode 3 are connected via the detection resistor 6. There is.

This galvanic cell type combustible gas sensor is provided with a combustible gas such as hydrogen (H ₂ ) or carbon monoxide (CO).
2 was left in a nitrogen gas containing 2, 6, 10%, and the output voltage detected by both electrodes of the detection resistor 6 was plotted in FIG.
From FIG. 2, it was confirmed that the galvanic cell type combustible gas sensor according to the present invention has an excellent linearity with respect to the concentration of hydrogen or carbon monoxide, and it was confirmed that the galvanic cell type combustible gas sensor operates sufficiently even in a combustible atmosphere containing no oxygen. .

[0015]

As described above, the galvanic cell type combustible gas sensor according to the present invention is an electrolytic solution and a positive electrode disposed in the electrolytic solution, which electrochemically removes dissolved oxygen in the electrolytic solution. Characterized in that it comprises a catalyst having a gold catalyst or carbon catalyst for reduction or a platinum catalyst, and a negative electrode functioning as a gas electrode and having a catalyst effective in the electrochemical oxidation reaction of a combustible gas. To do. Therefore, it is not necessary to use a constant potential applying device, and the combustible gas concentration in any atmosphere can be immediately detected. By using this sensor, it is possible to provide a heatable gas concentration meter and an alarm device that are inexpensive, consume less power, and are easy to handle, which is a great contribution to industrial development.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a galvanic cell type combustible gas sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the concentration of hydrogen or carbon monoxide in nitrogen and the sensor output.

[Explanation of symbols]

 2 Positive electrode 3 Negative electrode 4 Electrolyte

Claims (1)

[Claims] 1. An electrolytic solution (4) and a positive electrode (2) disposed in the electrolytic solution (4) for electrochemically reducing dissolved oxygen in the electrolytic solution (4), the positive electrode (2) being gold. A catalyst having at least one catalyst selected from a catalyst group consisting of a catalyst, a carbon catalyst and a platinum catalyst, and a negative electrode (3) functioning as a gas electrode, which is used for electrochemical oxidation reaction of combustible gas. A galvanic cell type combustible gas sensor comprising: an effective catalyst.