JPH0758274B2 - 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 a gas concentration meter for measuring the concentration of a gas dissolved in a gas phase or in water, and more particularly to a galvanic cell type gas sensor which serves as a detector thereof.

[0002]

2. Description of the Related Art Generally, a galvanic battery type or polar type gas sensor which operates at room temperature and is easy to handle is used to detect a specified gas in air or water.

The galvanic cell type gas sensor has a working electrode composed of a catalytic electrode which causes an electrochemical oxidation or reduction reaction of a target gas, a working electrode located outside the catalytic electrode and a diaphragm for restricting the supply of the gas, and further reduction. Which is basically composed of a counter electrode composed of a conductive or oxidative active material, an electrolytic solution, and a container that stores them, and the target gas whose supply is limited by a diaphragm is electrochemically oxidized under the diffusion control. Alternatively, when the working electrode and the counter electrode are connected via a resistor selected so that a reduction reaction occurs and discharged, the current flowing between both electrodes is proportional to the gas concentration, and the gas concentration is known from the current value. Is.

Since the gas equilibrium potential differs depending on the type of gas, in the galvanic cell type gas sensor in which the potential of the working electrode greatly depends on the potential of the counter electrode, selection of the counter electrode becomes very important. This is because if the counter electrode is erroneously selected, not only the above diffusion-controlled region cannot be obtained, but also oxygen or hydrogen is generated from the working electrode and the current flows even though there is no target gas. Is. Therefore, when a plurality of gases are to be detected, it is necessary to prepare a sensor in which not only the counter electrode but also the electrolytic solution is changed for each detection gas.

On the other hand, the polaro type sensor has the same basic structure as the gas vane battery type sensor described above, but the working potential of the working electrode is largely different from the outside by using a constant potential applying device. Therefore, the potential of the working electrode can be freely selected so as to be diffusion-controlled, and oxygen or hydrogen is not generated, and one sensor can be used to detect a plurality of gases.

[0006]

Since the galvanic battery type gas sensor uses the battery reaction in principle, the sensor itself outputs the gas sensor, so that an external power source for driving the sensor is not necessary. However, in order to detect a plurality of gases as described above, a plurality of sensors having counter electrodes commensurate with the target gas are required. On the other hand, a polar gas sensor requires an expensive and difficult-to-handle low-potential application device such as a potentiostat and a power supply to drive it, but one sensor detects multiple gases by changing the potential of the working electrode. it can. The present invention is to provide a galvanic battery type gas sensor capable of detecting a plurality of gases by one sensor by taking advantage of the advantages of the galvanic battery type gas sensor and the polaro type gas sensor.

[0007]

The electric potential of the working electrode of the galvanic cell type gas sensor largely depends on the electric potential of the counter electrode. That is, in the galvanic cell type gas sensor, it is no exaggeration to say that the type of gas that can be detected is determined by what is selected for the counter electrode. Therefore, the present invention proposes a galvanic cell type gas sensor having a plurality of counter electrodes of different types for one working electrode and arbitrarily selecting the counter electrode according to the gas to be detected. According to the galvanic battery type gas sensor according to the present invention, it is possible to obtain a sensor compatible with a plurality of gases that does not require an external power source and is easy to handle. The reason why such an idea has not come out up to now is that the galvanic battery type gas sensor has a default concept that it detects a specific gas and that the potential of the counter electrode has not been considered so much.

[0008]

When the present invention is embodied, the equilibrium potential (VH) of hydrogen and the equilibrium potential (Vo) of oxygen in the electrolyte to be used are the equilibrium potentials (V1, V2) of the N electrodes serving as counter electrodes.
, ... Vn) and diffusion-controlled regions (V1'-VH, V2'-VH, ... Vn'-VH) at the working electrodes of N gases to be detected.
Or V1'~Vo, it is important to know the V2'~Vo ... Vn'~V _o). In order to simplify the description, a sensor that detects two types of gas, that is, a sensor that includes two types of counter electrodes will be described below.

Now, the oxidizing gases to be measured are A and B,
When each gas is energized while making contact with the working electrode, the potential of the working electrode changes as shown in FIG. Here, VH is the equilibrium potential of hydrogen, and hydrogen is generated from the working electrode at a potential lower than VH. For gas A, between Va 'and VH, and for gas B, Vb'
It is shown that each gas diffusion region is between VH and VH, and if the sensor is operated during this region, the gas concentration and the current have a proportional relationship. Therefore, when selecting the counter electrode,
When the equilibrium potential is gas A, the electrode must be nobler than VH and less base than Va ', and in the case of gas B, the electrode must be nobler than VH and less base than Vb'. Further, since gases A and B may coexist, it is better to set the counter electrode of gas A to have a noble potential higher than Vb ″, which is not affected by gas B. Thus, for gas A, Va, For gas B, counter electrodes 5a and 5b having an equilibrium potential of Vb are selected,
When detecting the gas A, the working electrode and the counter electrode 5a are
When detecting the, the working electrode and the counter electrode 5b are connected via a resistor. At this time, the potentials of the working electrodes are respectively Va + i
Since R and Vb + iR, it is necessary to select Va so that it does not exceed Va ′ and Vb ′ when selecting the resistance. In some cases, the detection resistance R which is different between the counter electrodes 5a and 5b.
Of course, it is possible to use. As described above, one sensor can detect a plurality of gases.

The present invention will be described below with reference to preferred embodiments. FIG. 1 is a sectional structural view of a galvanic cell type gas sensor according to an embodiment of the present invention. This sensor comprises a container body 1 made of ABS resin, a catalyst electrode 2 in which platinum is electrodeposited on a porous carbon, and tetrafluoroethylene provided outside thereof.
A working electrode 4 composed of a diaphragm 3 made of a propylene hexafluoride copolymer, a counter electrode 5a made of lead, a counter electrode 5b made of lead dioxide, and an electrolytic solution 7 made of a mixed aqueous solution of acetic acid, lead acetate and potassium acetate. And the working electrode 4 and the counter electrode 5a or 5b are closed via the detection resistor 8,
The selection of the counter electrode 5a or 5b at that time is performed by the changeover switch 9
Performed by. FIG. 3 shows the relationship between the equilibrium potentials Va and Vb of the counter electrodes 5a and 5b and the equilibrium potentials Vo and VH of oxygen and hydrogen, and changes in the potential when oxygen or hydrogen is energized while contacting the working electrode. .

As shown in FIG. 3, the diffusion-controlled regions of oxygen and hydrogen are Va 'to _VH = Va and Vb' to Vo = respectively.
It is Vb, and the equilibrium potentials of the counter electrode 5a for enzyme detection and the counter electrode 5b for hydrogen detection are within the above diffusion-controlled region. Further, it can be seen that the potential of the working electrode 4 changes to Va + iR or Vb-iR due to the current i flowing through the detection resistor 8, but does not deviate from the diffusion rate-controlled region of each gas. In this galvanic battery type sensor, the counter electrode 5a made of lead is selected by the changeover switch 9 so that the concentration of oxygen (O ₂ ) is 20, 6
It is left in 0, 100% nitrogen and the output voltage detected at both ends of the detection resistor 8 and the counter electrode 5b made of lead dioxide are selected by the changeover switch 9 to detect the hydrogen (H ₂ ) which is a heatable gas. Fig. 2 shows the electric power voltage detected at both ends of the detection resistor 8 when left in the air having a concentration of 20, 60 or 100%.
Plotted on. It can be seen from FIG. 2 that the galvanic cell sensor according to the present invention can detect different gases simply by switching the counter electrodes.

[0012]

The galvanic cell type gas sensor according to the present invention can detect different gases simply by switching the counter electrodes. By using this sensor, it is possible to provide a gas concentration meter that is easy to handle and is capable of detecting a plurality of gases with one sensor, and it is very important to contribute to the industry.

[Brief description of drawings]

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

FIG. 2 is a diagram showing the relationship between the oxygen concentration in nitrogen or the hydrogen concentration in air and the output voltage of the sensor.

FIG. 3 is a diagram showing a relationship between electrode potential and current.

FIG. 4 is a diagram showing a relationship between an electrode potential and a current.

[Explanation of symbols]

 1 container 2 catalyst electrode 3 diaphragm 4 working electrode 5a counter electrode 5b counter electrode 7 electrolyte 8 detection resistor 9 changeover switch

Claims (1)

[Claims] 1. A working electrode (2) for causing an electrochemical oxidation or reduction reaction of a gas, a counter electrode (5) made of a reducing or oxidizing active material, an electrolytic solution (7), and a container (there for accommodating them). In the galvanic battery gas sensor basically composed of 1) and 1), one working electrode (4) and two or more counter electrodes (5
a, 5b) and a counter electrode (5) combined with the working electrode (4).
A galvanic electric gas sensor, characterized in that a, 5b) can be arbitrarily selected according to the type of gas to be detected.