JP3042616B2 - Constant potential electrolytic 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 potentiostatic gas sensor for measuring gas concentration, and more particularly to a potentiostatic gas sensor for measuring high-concentration gas of% level.

[0002]

2. Description of the Related Art A gas sensor is a device that responds to a specific gas contained in a gas, converts the gas into an electric signal, and detects and quantitatively detects the gas. As such a gas sensor,
Various types such as a semiconductor sensor, a solid electrolyte sensor, a contact combustion sensor, and an electrochemical sensor are currently known. Among them, the potentiostatic gas sensor belonging to the electrochemical sensor is for quantifying the gas concentration from the electrolytic current when the gas is subjected to potentiostatic electrolysis by an electrochemical cell.

More specifically, this potentiostatic gas sensor comprises three electrodes, a working electrode, a counter electrode and a reference electrode, an electrolyte and a container for accommodating the same, and the three electrodes are a gas-permeable porous membrane. , Which are in contact with the electrolyte. The measurement gas is supplied to the working electrode side,
The gas passes through the gas-permeable porous membrane to which the working electrode is connected, reaches the working electrode, and is oxidized or reduced on the surface of the working electrode. At this time, a current corresponding to the gas concentration flows between the counter electrode and the gas concentration is measured, and the gas concentration is measured by keeping the potential of the working electrode constant with respect to the reference electrode in advance. Is characterized by being able to measure the gas selectively and stably.

As described above, the potentiostatic gas sensor is small and lightweight, operates at room temperature, consumes little power, and has high sensitivity and can discriminate a gas having a concentration of ppm level. , H ₂ S, etc., are widely used as portable detectors for measuring allowable concentrations and sensors for measuring instruments.

[0005]

As described above, the potentiostatic electrolytic gas sensor is conventionally used for measuring a gas having a particularly low concentration, for example, for detecting a gas leak. However, this conventional potentiostatic electrolytic gas sensor,
CO as reducing gas in process control, concentration measurement, etc. H _2, H ₂ S gas concentration check in tanker crude oil tanker, or volcanic like in such H ₂ S gas concentration measurement of a gas, the percent level high It could not be used to measure the concentration of gas. That is, in the conventional potentiostatic gas sensor, the working electrode is bonded to the gas-permeable porous membrane, so that the introduced measurement target gas permeates the porous membrane without being controlled, and Current flows between the counter electrode and the counter electrode. However, since it is designed to detect the concentration of ppm level, if the gas of the concentration of% level is introduced as the gas to be measured, the flowing current becomes too large. There is a problem that the measurement is saturated and measurement cannot be performed.

It is an object of the present invention to provide a potentiostatic gas sensor which can be applied to such a high concentration gas of% level.

[0007]

In order to solve the above-mentioned problems, a constant potential electrolytic gas sensor according to the present invention comprises a working electrode, a counter electrode and a reference electrode, an electrolyte, and a container body containing the electrolyte. Do Ri, the three electrodes are gas permeable multi
A porous membrane, which is bonded to an inner side in contact with the electrolytic solution,
A gas-permeable non-porous membrane is disposed on the gas supply side of the working electrode opposite to the surface in contact with the electrolyte.

In the galvanostatic gas sensor of the present invention, the gas permeable non-porous membrane is disposed on the measurement gas supply side of the working electrode, so that the amount of the gas to be measured reaching the working electrode is extremely limited. As a result, even if a high-concentration measurement gas is supplied, the current generated by the reaction does not become excessive,
Measurement of high-concentration gas becomes possible.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a constant-potential electrolytic gas sensor according to the present invention. FIG. 1 is a sectional view showing an embodiment of a potentiostatic gas sensor according to the present invention, and FIG. 2 is an exploded perspective view of the galvanostatic gas sensor. Reference numeral 1 denotes a cylindrical container body having two openings 21 and 22 at both ends. One opening 21
Is provided with a semicircular counter electrode 4 and a reference electrode 5 coupled to a gas-permeable porous membrane 10, and the other opening 22 has
A circular working electrode 6 is provided which is coupled to a gas permeable porous membrane 11, and leads 7, 8 and 9 are connected to each electrode.

[0010] The gas-permeable porous membrane to which each electrode is bonded is defined as having a larger mean free path of gas molecules.
Refers to a membrane having a pore size of about 50 ° to 1 μm, and thus refers to a membrane that is permeable to gas but impermeable to liquid. As such a film, for example, a material such as tetrafluoroethylene resin (PTFE) is used. The counter electrode 4 and the reference electrode 5 are made of platinum, and are bonded to the gas-permeable porous membrane 10 by a binder. The working electrode 6 is made of a noble metal such as platinum or gold, and is bonded to the gas-permeable porous film 11 by a binder, or has a gas-permeable property by a method such as vacuum deposition, sputtering, plating, or electroless plating. Porous membrane 11
Is combined with Which of these methods is used is mainly selected depending on the gas to be measured.

A non-porous gas-permeable membrane 12 is arranged outside the gas-permeable porous membrane 11 to which the working electrode 6 is connected, that is, on the measurement gas supply side. The gas-permeable non-porous membrane has a pore diameter extremely small as compared with the above-mentioned porous membrane, and therefore is not only impermeable to liquid but also freely permeable to gas. A membrane that cannot be gasified and restricts gas permeation. As the gas-permeable non-porous membrane 12, a polymer membrane generally used as a gas separation membrane, for example, a fluororesin, a polyalkylene resin, a polydimethylsiloxane resin, or the like is used. Among these, from the viewpoints of chemical resistance, solvent resistance, weather resistance and the like, fluororesins, for example, ethylene tetrafluoride-propylene hexafluoride copolymer (FEP), polyvinyl fluoride (PVF), polyvinylidene fluoride ( PVDF), perfluoroalkoxy fluororesin (PFA), ethylene-
It is preferable to use tetrafluoroethylene copolymer (ETFE), polychloroethylene trifluoride (PCTFE), or the like. The gas permeable non-porous membrane 12 may be a single membrane, or may be combined with other materials in addition to a single resin, such as a plasticized membrane, a graft membrane, or a multilayer membrane. A composite film may be used.

The gas permeable non-porous membrane 12 may be simply superimposed on the gas permeable porous membrane 11 to which the working electrode 6 is connected, or may be used as a single body by hot pressing or the like. Good. The gas permeable porous membrane 11
Alternatively, the working electrode 6 may be directly coupled to the gas-permeable non-porous membrane 12.

The side plate 15 on the side of the opening 21 is provided with an air hole 17 for supplying air to the counter electrode 4 and the reference electrode 5, and the side plate 16 on the side of one opening 22 is provided with a measurement hole. A gas chamber 18 for supplying gas is provided, and the gas chamber 18 is connected to outside air by an air supply path 19 and an exhaust path 20. Reference numerals 2, 3, 13 and 14 denote seal packings, all of which are assembled by crimping and fixing, and the container body 1 is filled with the electrolytic solution 23. As the electrolytic solution 23, an aqueous solution of sulfuric acid, phosphoric acid, potassium hydroxide, sodium hydroxide, potassium chloride or the like is used.

When a gas to be measured is introduced from the air supply path 19 into the thus-configured constant potential electrolytic gas sensor of the present invention, the gas to be measured enters the gas chamber 18. However,
Since the gas chamber 18 and the working electrode 6 are separated by the gas permeable non-porous membrane 12, the gas entering the gas chamber 18 depends on the gas permeability of the gas permeable non-porous membrane 12. Only the accumulated gas reaches the working electrode 6 and is oxidized or reduced to generate a current between the gas and the counter electrode.

The amount of gas permeating the gas permeable non-porous membrane 12 is expressed by the following equation. Q = (P / L) (p ₁ −p ₂ ) At In the above equation, Q is the gas permeation amount, P is the gas permeation coefficient, p ₁ and p ₂ are the partial pressure of the gas supplied to the membrane and the pressure of the membrane, respectively. The partial pressure of the gas on the permeation side, L is the film thickness, A is the permeation area, and t is the time. The gas permeability coefficient is a unique value depending on the combination of the material of the membrane and the gas. Therefore, the material of the gas-permeable non-porous membrane 12 may be selected according to the gas to be measured and according to the concentration to be measured. Further, the concentration range that can be measured can be adjusted by changing the film thickness, the area of the film, and the supply pressure of the gas to be measured.

In any case, since the gas permeability of the gas-permeable non-porous membrane 12 is very low, the amount of gas reacting on the surface of the working electrode 6 depends on the gas-permeable non-porous membrane 12. Is 1/1000 compared to the case where
It can be 0 or less. That is, it is possible to measure the concentration at the% level using a sensor for measuring the concentration at the ppm level in the related art.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a gas-permeable nonporous membrane 12, a thickness of 1
In a potentiostatic gas sensor (reaction area of the working electrode of about 5 cm ² ) constructed as shown in FIG. 1 using FEP films of 2.5 μm, 25 μm and 50 μm, the output current of this sensor with respect to 10% H ₂ S was obtained. Was measured, and the results are shown in Table 1 below. As a comparison, Table 1 also shows the output current of this conventional constant-potential-electrolysis gas sensor with respect to 10 ppm of H ₂ S in which the gas-permeable nonporous membrane 12 is not provided.

[0018]

[Table 1]

As is clear from Table 1, in the galvanostatic gas sensor of the present invention, by arranging a gas-permeable non-porous membrane, the gas to be measured having a concentration of% level can be conventionally used. Can be detected with the same level of current as when measuring the concentration at the ppm level. Further, by changing the thickness of the gas-permeable non-porous membrane, the measurement current can be arbitrarily set, and can be adjusted according to the concentration of the measurement gas.

In a galvanostatic gas sensor using a 12.5 μm-thick FEP film as the gas-permeable nonporous film 12, the output current of this sensor with respect to the H ₂ S gas concentration (0 to 30%) is measured. Was measured, and the results are shown in FIG.

As is clear from the graph of FIG. 3, in the constant potential electrolytic gas sensor of the present invention, the output current changes in a correlated manner according to the concentration of the measured gas, similarly to the conventional constant potential electrolytic gas sensor. It turns out that it is effective in measuring the concentration of the measurement gas.

[0022]

The potentiostatic electrolytic gas sensor of the present invention has a p
By using a gas sensor for measuring the concentration at the pm level, the gas concentration at the high concentration at the% level can be measured.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a potentiostatic gas sensor of the present invention.

FIG. 2 is an exploded perspective view of the potentiostatic gas sensor of the present invention.

FIG. 3 is a graph showing the output current of this sensor against the concentration of H ₂ S gas measured using the potentiostatic gas sensor of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container main body 2, 3, 13, 14 ... Seal packing 4 ... Counter electrode 5 ... Comparative electrode 6 ... Working electrode 7, 8, 9 ... Lead wire 10, 11 ... Gas permeable porous membrane 12 ... Gas permeable Non-porous membrane 15, 16 ... Side plate 17 ... Air hole 18 ... Gas chamber 19 ... Gas supply path 20 ... Gas exhaust path 21, 22 ... Opening 23 ... Electrolyte liquid

Claims (1)

(57) [Claims] 1. A constant potential electrolytic gas sensor comprising a working electrode, a counter electrode, and a reference electrode, an electrolytic solution, and a container body for storing the electrolytic solution, wherein the three electrodes are gas permeable.
Bonded to the inside of the transient porous membrane in contact with the electrolyte.
And a non-porous gas-permeable membrane disposed on the gas supply side of the working electrode opposite to the surface in contact with the electrolytic solution.