JP2018048826A - Constant potential electrolytic type gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a constant potential electrolytic type gas sensor equipped with electrodes which are hardly susceptible to individual differences.SOLUTION: In a constant potential electrolytic type gas sensor X equipped with reaction electrodes 11 that, as gas electrodes to detect gas, cause detectable gas to electrochemically react, counter electrodes 12 to the reaction electrodes 11 and reference electrodes 13 that control the potentials of the reaction electrodes 11 so disposed as to come into contact with electrolyte 20 accommodated in an electrolyte tank 30, the reference electrodes 13 have a carrier caused to carry two kinds of precious metal different in immersion potential to the electrolyte 20, and the ratio between the two kinds of precious metal is so adjusted to make the set potential zero.SELECTED DRAWING: Figure 1

Description

  In the present invention, a reaction electrode for electrochemically reacting a gas to be detected as a gas electrode for detecting gas, a counter electrode with respect to the reaction electrode, and a reference electrode for controlling the potential of the reaction electrode are brought into contact with an electrolytic solution accommodated in an electrolytic cell. The present invention relates to a constant potential electrolysis gas sensor.

  A conventional constant potential electrolytic gas sensor is configured such that an electrode is provided facing an electrolytic solution storage part of an electrolytic cell in which an electrolytic solution is densely stored. For example, an electrode is detected as a gas electrode that detects gas. There are provided three electrodes, a working electrode for electrochemically reacting gas, a counter electrode for the working electrode, and a reference electrode for controlling the potential of the working electrode. A potentiostat circuit for setting the potential is connected. As the material of the three electrodes, a gas-permeable porous PTFE film having water repellency is coated with a noble metal catalyst such as platinum, gold, palladium, etc. As an electrolyte, an acidic aqueous solution such as sulfuric acid or phosphoric acid is used. Was used.

  In addition, the constant potential electrolytic gas sensor generates a current corresponding to a change in the surrounding environment between the working electrode and the counter electrode by controlling the potential of the working electrode to be constant with respect to a change in the surrounding environment. . Further, by utilizing the fact that the potential of the working electrode does not change and the oxidation-reduction potential varies depending on the gas type, the gas can be selectively detected depending on the set potential of the potentiostat circuit. Further, by changing the catalyst used for the gas electrode, it is possible to have high selectivity for the target gas.

  For example, carbon having a particle size of several tens of nm and noble metal fine particles of about several hundreds of nanometers are sometimes used. In order to support the noble metal fine particles on the carbon as described above, for example, an immersion support method may be used. When the noble metal particles are supported on the support by the immersion support method, the support is immersed in an aqueous solution of a metal salt, the metal component is adsorbed on the support surface, and drying, firing, and reduction are performed. After producing noble metal-carrying carbon by the dip-carrying method, it was applied to a porous PTFE film to produce an electrode.

  Note that the above-described constant potential electrolytic gas sensor, which is a conventional technique in the present invention, is a general technique, and therefore does not show any prior art documents such as patent documents.

  The noble metal-supported carbon produced by the above-mentioned method has a particle diameter of the noble metal fine particles larger than that of the carbon as the carrier and tends to aggregate in an aqueous solution, so it is difficult to uniformly disperse the noble metal fine particles. there were. When the noble metal-supported carbon prepared with the noble metal fine particles in a non-uniform state is used as a noble metal catalyst, there are cases where an individual difference in gas detection performance increases.

  Accordingly, an object of the present invention is to provide a constant potential electrolytic gas sensor including an electrode that hardly causes individual differences in gas detection performance.

  In order to achieve the above object, a constant potential electrolytic gas sensor according to the present invention controls a reaction electrode for electrochemically reacting a gas to be detected as a gas electrode for detecting gas, a counter electrode for the reaction electrode, and a potential of the reaction electrode. A constant potential electrolytic gas sensor provided with a reference electrode in contact with an electrolyte contained in an electrolytic cell, the first feature of which is that the reference electrode has two different immersion potentials with respect to the electrolyte It has the support | carrier which carry | supported the noble metal, and is the point which adjusted and comprised the said 2 types of noble metal so that the setting potential might be set to zero.

In order to make the set potential zero, specifically, the potential of the reference electrode may be shifted by a mixed potential reaction that is a plurality of electrochemical reactions occurring on one electrode. Thus, for example, when gas detection is originally performed by applying a potential of +200 mV, gas detection can be performed by applying a potential of ± 0 mV.
By setting the set potential to zero in this way, the circuit voltage of the constant potential electrolysis gas sensor is stabilized and fluctuations in the zero point of the sensor can be suppressed, so that individual differences in gas detection performance are less likely to occur.

  In the constant potential electrolytic gas sensor according to the present invention, “the reference electrode has a carrier carrying two kinds of noble metals having different immersion potentials in the electrolytic solution” and “the set potential is zero. “The composition is adjusted by adjusting the ratio of the precious metal of the seed”, and the object is directly specified by the structure or characteristics thereof.

  The second characteristic configuration of the potentiostatic gas sensor according to the present invention is that the carrier is carbon and the two kinds of noble metals are gold and platinum.

  If the two kinds of noble metals are gold and platinum as in this configuration, it is possible to make the noble metal easily available out of the two kinds of noble metals having different immersion potentials with respect to the electrolytic solution.

  The third characteristic configuration of the constant potential electrolytic gas sensor according to the present invention is that a potentiostat circuit for setting the potential of each electrode is connected, and the potentiostat circuit is short-circuited.

  According to this configuration, since the potentiostat circuit is configured to be short-circuited, it is not necessary to provide a power source, and the constant potential electrolytic gas sensor can be configured simply.

It is the schematic which shows the constant potential electrolytic gas sensor of this invention. It is the schematic which shows a potentiostat circuit. It is sectional drawing and the principal part enlarged view of a reaction electrode. It is the graph which showed the result of having detected 1 ppm of germane using the constant potential electrolytic gas sensor of this invention. It is the graph which showed the result of having performed the electrochemical measurement of the reference electrode. It is the graph which showed the result of having put platinum of various content in the reference electrode of this invention, and adjusting the electric potential. It is the graph investigated about the sensitivity with respect to silane 0.5ppm. It is the graph investigated about the sensitivity with respect to 0.5 ppm of phosphine. It is the graph which investigated about the sensitivity with respect to germane 0.5ppm. It is the graph which investigated about the sensitivity with respect to arsine 0.5ppm.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the constant potential electrolytic gas sensor X controls a reaction electrode 11 that causes a gas to be detected to electrochemically react as a gas electrode 10 that detects gas, a counter electrode 12 with respect to the reaction electrode 11, and a potential of the reaction electrode 11. The reference electrode 13 is provided so as to be in contact with the electrolytic solution 20 accommodated in the electrolytic cell 30.

  The reaction electrode 11, the counter electrode 12, and the reference electrode 13 are formed by applying and baking a paste prepared from an electrode material described later on the surface of a porous gas-permeable film 14 having water repellency. The reaction electrode 11, the counter electrode 12, and the reference electrode 13 are disposed to face each other.

    The electrolytic cell 30 forms a gas conduction part 33 by forming an opening part 32 that opens to the side. Two gas permeable membranes 14 are provided, one gas permeable membrane 14 is provided with a reaction electrode 11, and the other gas permeable membrane 14 is provided with a counter electrode 12 and a reference electrode 13. The gas permeable membrane 14 disposed on the reaction electrode 11 side is attached to the electrolytic cell 30 so as to face the opening 32. The gas to be detected is introduced from the gas conduction part 33 and reacts on the reaction electrode 11.

  Each gas permeable membrane 14 and the O-ring 15 are fixed by a lid member 16. On the bottom surface of the electrolytic bath 30, an electrolytic solution injection port 34 for performing maintenance such as injection of the electrolytic solution 20 accommodated in the electrolytic solution accommodating unit 31 is formed.

  Such a constant potential electrolytic gas sensor X includes a potentiostat circuit (FIG. 2) for setting the potential of each electrode. The constant potential electrolytic gas sensor X of the present invention is used for detection of hydride gas such as silane, phosphine, germane, arsine, diborane.

  The reaction electrode 11 has a structure in which a thick film 3 having fluororesin particles 1 and noble metal-supporting carbon 2 is formed on the fluororesin film, and the noble metal-supporting carbon 2 is filled between the fluororesin particles 1 (FIG. 3). ).

  In this embodiment, the gas permeable film 14 is a fluororesin film. For example, PTFE (polytetrafluoroethylene: Teflon), PFA (perfluoroalkoxyalkane), FEP (perfluoroethylene propene copolymer), or the like can be used as the fluororesin film 14, but it is not limited thereto. Absent.

  The fluororesin particles 1 are fine particles of the constituent material of the fluororesin film 14, and the particle size range thereof is, for example, 0.1 to 1.0 μm, preferably 0.1 to 0.5 μm. Moreover, the thickness of the thick film 3 is 5-50 micrometers, for example, Preferably it is 10-25 micrometers.

  The noble metal-supporting carbon 2 can be a carbon (carrier) b that supports a noble metal a such as gold or platinum. The precious metal-supporting carbon 2 can use a colloidal solution in the production process, and can be supported on the carbon as the carrier b in a state where the precious metal nanoparticles are dispersed, so that the degree of dispersion of the precious metal nanoparticles is almost uniform. It can be in a state. Therefore, if such a noble metal-supported carbon 2 is used as a noble metal catalyst, it is possible to prevent individual differences in gas detection performance from occurring in the potentiostatic gas sensor X. In this embodiment, a case where gold nanoparticles are used as noble metal nanoparticles will be described.

  As the carbon as the carrier b, a known carbon powder such as carbon black (particle size of about 5 to 300 nm) can be used, and in particular, acetylene black obtained by thermally decomposing acetylene gas is preferably used. It is not limited to.

  The particle size range of the noble metal-supporting carbon is, for example, 0.01 to 0.1 μm, preferably 0.01 to 0.05 μm.

  The noble metal-supported carbon 2 is dried in a state where the carbon powder is added to a solvent and stirred, a nanoparticle addition step in which a colloidal solution in which gold nanoparticles are dispersed is added, and the temperature is kept below the boiling point of the solvent. It is produced by performing a drying step to be performed and a firing step in which the powder obtained by drying is fired at 250 to 450 ° C.

  In the carbon powder addition step, a predetermined amount of carbon powder is weighed, and water as a solvent is added and sufficiently stirred (primary dispersion). This step may be performed by adding a surfactant such as sodium dodecylbenzenesulfonate. By adding the surfactant, the dispersibility of carbon in the solvent can be improved. As the surfactant, any of anionic, cationic, nonionic, and betaine surfactants can be used. In order to increase the dispersibility of carbon in the solvent, the water / surfactant / carbon suspension is agitated and dispersed by ultrasonic treatment such as an ultrasonic homogenizer. Disperse to the level (secondary dispersion).

  After the secondary dispersion of the water / surfactant / carbon suspension is defoamed with a rotary evaporator or the like, a nanoparticle addition step is performed in which a colloidal solution in which gold nanoparticles are dispersed is added.

The colloidal solution in which the gold nanoparticles are dispersed is in a state where the gold nanoparticles are dispersed in the solution. You may add additives, such as a protective agent, to the said colloid solution as needed.
The colloidal gold solution uses an in-solution reduction reaction in which metal ions are reduced to a colloid by adding a citrate solution as a reducing agent to a chloroauric acid solution such as tetrachloroauric acid (III) and heating. However, it is not limited to such a method. In this method, the size of colloidal gold particles can be changed by increasing or decreasing the amount of reducing agent added to chloroauric acid. The gold nanoparticles may be particles having a particle size of about 5 to 50 nm, but are not limited to this range. In this case, the particle size distribution is preferably such that the ratio of 5 to 50 nm particles is 90% by weight or more.

  After adding the colloidal solution, the carbon particles and the gold nanoparticles may be dispersed to the particle level by ultrasonic treatment such as an ultrasonic disperser (third-order dispersion). The tertiary-dispersed suspension is stirred with a rotary evaporator or the like, and dried under reduced pressure and heating at about 70 to 90 ° C.

  In the subsequent drying step, the obtained solution is dried in a state where the solution is kept below the boiling point of the solvent (water). Although the temperature set as below the boiling point of a solvent is not specifically limited, When a solvent is water, it is good to set it as about 80-100 degreeC. As a drying method, a known method such as reduced-pressure drying, vacuum drying, suction drying, or hot air drying can be applied. Known conditions may be applied as drying conditions in these drying methods.

In the firing step, the powder obtained by drying is fired at 250 to 450 ° C.
The firing temperature in the present embodiment is a temperature (250 to 450 ° C.) at which the organic matter such as the used surfactant evaporates at a temperature at which carbon oxidation does not proceed under an air atmosphere and atmospheric pressure.
The firing time may be set as appropriate until the surfactant, colloid protective agent, and the like are completely eliminated by evaporation, sublimation, and thermal decomposition. Therefore, the firing time can be shortened or extended each time depending on the amount of powder to be fired. However, in consideration of grain growth of gold nanoparticles, a decrease in activity due to sintering, etc., the upper limit of the firing time may be set to about 3 hours, for example. Moreover, you may set so that a baking process may be complete | finished if predetermined temperature is reached without setting baking time.

  In the present embodiment, the reaction electrode 11 is described on the case where the thick film 3 having the PTFE fine particles as the fluororesin particles 1 and the noble metal-supported carbon 2 (gold-supported carbon) is formed on the PTFE film as the fluororesin film 14. To do.

  That is, the reaction electrode 11 is obtained by printing an electrode material paste prepared by adding a kneaded colloidal solution containing PTFE fine particles 1 to a powder of gold-supporting carbon 2 on a PTFE sheet film 14, drying, and firing. Can be produced. In preparing the electrode material paste, a surfactant may be added.

  The counter electrode 12 may be formed by applying and baking a paste made of a known electrode material on the surface of the gas permeable film 14.

  The reference electrode 13 includes a carrier b carrying two kinds of noble metals having different immersion potentials with respect to the electrolytic solution 20, and the ratio of the two kinds of noble metals is adjusted so that the set potential becomes zero.

  The immersion potential is a potential measured when a metal material or the like is immersed in an aqueous solution, a redox reaction occurs on the surface of the metal material due to dissolved oxygen or ions, and the potential is measured with reference electrode 13 as a reference. It is. The two kinds of noble metals used in the reference electrode 13 of the present invention are not particularly limited as long as they have different immersion potentials, but the ratio of the two kinds of noble metals is adjusted so that the set potential becomes zero. For example, the carrier b is carbon, and the two noble metals are preferably gold and platinum.

  For example, when gold and platinum are used, the ratio of the two kinds of noble metals is 5 to 70% for gold, 1 to 10% for platinum, preferably 20 to 50% for gold, and 5 to 10% for platinum. It is good to do.

  In order to make the set potential zero, specifically, the potential of the reference electrode 13 may be shifted by a mixed potential reaction that is a plurality of electrochemical reactions occurring on one electrode. Thus, for example, when gas detection is originally performed by applying a potential of +200 mV, gas detection can be performed by applying a potential of ± 0 mV.

  By setting the set potential to zero in this way, the circuit voltage of the constant potential electrolytic gas sensor is stabilized and fluctuations in the zero point of the sensor can be suppressed.

  A method for producing carbon carrying two different kinds of noble metals is not particularly limited, and a known method such as an impregnation method or a coprecipitation method may be applied as appropriate. It can be produced according to the nanoparticle addition step, the drying step, and the firing step. At this time, in the nanoparticle addition step, a colloidal solution in which gold nanoparticles are dispersed and a colloidal solution in which platinum nanoparticles are dispersed may be used. The colloidal solution in which platinum nanoparticles are dispersed is in a state in which platinum nanoparticles are dispersed in the solution. The platinum nanoparticles may be any particles having a particle size of about 5 to 50 nm, similar to the gold nanoparticles described above, but are not limited to this range. In this case, the particle size distribution is preferably such that the ratio of 5 to 50 nm particles is 90% by weight or more.

  In this embodiment, since the set potential is set to zero, the potentiostat circuit is configured to be short-circuited.

  That is, in this configuration, since gas detection can be performed by applying a potential of 0 mV, it is not necessary to provide a power source.

[Example 1]
Examples of the present invention will be described.
A procedure for producing the reaction electrode 11 and the reference electrode 13 in the constant potential electrolytic gas sensor X of the present invention will be described below.

  Since the reference electrode 13 can be produced by a method according to the procedure for producing the reaction electrode 11 in Example 1, the procedure for producing the reaction electrode 11 will be described first.

  First, carbon black (average particle size 40 nm) and a surfactant (sodium dodecylbenzenesulfonate) were added to distilled water, stirred, and primarily dispersed (carbon powder addition step). This primary dispersion was subjected to sonication (20 kHz, 600 W, 15 minutes) with an ultrasonic homogenizer to be secondarily dispersed.

  This secondary dispersion was defoamed with a rotary evaporator (25 ° C., 10 hPa or less), and a colloidal solution (3 wt% aqueous solution of gold nanocolloid, average particle size of 10 nm) in which gold nanoparticles (particle size of about 50 nm) were dispersed was obtained. Added (nanoparticle addition step).

  After the colloidal solution was added, sonication (100 kHz, 300 W, 15 minutes) was performed with an ultrasonic disperser to disperse the carbon particles and gold nanoparticles to the particle level (tertiary dispersion).

  The tertiary-dispersed suspension is stirred by a rotary evaporator, depressurized and heated and dried (drying process) at 80 ° C., further pulverized and fired at 400 ° C. (firing process). Supported carbon).

  An electrode material paste prepared by adding and kneading a colloidal solution containing PTFE fine particles 1 (average particle size 0.2 μm) to the gold-supporting carbon 2 powder is printed on a PTFE sheet film (fluororesin film) 14, The reaction electrode 11 was produced by baking at 280 degreeC after drying at room temperature all day and night.

  A procedure for producing the reference electrode 13 in the constant potential electrolytic gas sensor X of the present invention will be described below. As described above, the reference electrode 13 can be produced by a technique according to the procedure for producing the reaction electrode 11 of Example 1.

  In the nanoparticle addition step, a colloidal solution in which gold nanoparticles were dispersed and a colloidal solution in which platinum nanoparticles were dispersed were used. That is, after adding the gold-supporting carbon prepared in Example 1 to a colloidal solution in which platinum nanoparticles are dispersed (3 wt% platinum nanocolloid aqueous solution, average particle diameter 10 nm), a drying step and a firing step were performed.

  An electrode material paste prepared by adding and kneading a colloidal solution containing PTFE fine particles 1 to the powder of carrier b carrying two kinds of precious metals having different immersion potentials is printed on a PTFE sheet film (fluororesin film) 14. The reference electrode 13 was produced by drying at room temperature for a whole day and night and firing at 280 ° C.

  That is, the ratio of the two kinds of noble metals used in the reference electrode 13 of this example was 45% gold and 10% platinum.

  Note that the firing temperature in the conventional immersion support method may be about 600 ° C., but when the carrier b is carbon as in the present invention, the firing temperature is such a high temperature. There was a risk that carbon b would burn. Therefore, in this embodiment, since the firing (firing process) is performed at 400 ° C., the firing temperature at the time of electrode preparation can be kept low without burning the carbon b as the carrier.

[Example 2]
FIG. 4 shows the result of detecting 1 ppm of germane using the constant potential electrolytic gas sensor X (four samples) of the present invention. As a comparative example (two samples), the result of detecting 1 ppm of germane using a conventional constant potential electrolytic gas sensor was also shown.

  As a result, the controlled potential electrolytic gas sensor X of the present invention exhibited a good (rapid) rise immediately after detecting germane, and then exhibited a sensor output showing a stable high output. On the other hand, in the controlled potential electrolytic gas sensor of the comparative example, the rising immediately after the detection of germane was gentle and exhibited a sensor output showing a low output. Thereby, it was recognized that the potentiostatic gas sensor X of the present invention had a sensitivity of about 2 to 3 times higher than that of the comparative potentiostatic gas sensor.

Example 3
It was examined how the detection sensitivity changes when the ratio of the two kinds of noble metals (gold and platinum) used in the reference electrode 13 of the present invention is changed.
In the reference electrode 13 of the present invention, the two noble metals are 5 wt. % Pt / [45 wt. % Au / C] (5PtAu / C: Invention Example 1), and 10 wt. % Pt / [45 wt. % Au / C] (10PtAu / C: Invention Example 2) was used. As a conventional reference electrode, gold-supported carbon (Au / C: Comparative Example 1) produced by an immersion support method was used.
These electrodes were subjected to electrochemical measurement using an ALS electrochemical analyzer. The measurement was performed by determining the ratio of these electrodes to NHE (normal hydrogen electrode). Measurement was performed 5 times for each electrode, and the measurement results are shown in Table 1.

  Moreover, the graph which plotted the average, maximum, and minimum data in each electrode was shown in FIG.

  As a result, Examples 1 and 2 of the present invention and Comparative Example 1 were recognized as having different electrochemical properties. In addition, even when the ratio of the two kinds of noble metals (gold and platinum) used in the reference electrode 13 was changed, it was recognized as having the same good electrochemical properties. As a result, it was recognized that individual differences in the gas detection performance are less likely to occur because fluctuations in the zero point of the sensor can be suppressed.

Example 4
Regarding two kinds of noble metals (gold and platinum) used in the reference electrode 13 of the present invention, the potential was adjusted by putting platinum of various contents into the reference electrode (45 wt% Au / C). The platinum content was variously adjusted from 0 to 10%. The potentiostat HA-151A (manufactured by Hokuto Denko Co., Ltd.) was used for measuring the potential (V). The measurement was performed 5 times for each electrode, and the results are shown in Table 2 and FIG.

  As a result, when the platinum content is 0% (Example 3: Comparative Example 1), the platinum content is 0.73 μA, whereas when the platinum content is 1 to 10%, the platinum content is 0.80. It was 0.93 μA. As a result, it was recognized that the reference electrode 13 of the present invention example and Comparative Example 1 have different electrochemical properties (gas sensitivity characteristics).

Example 5
The sensitivity to each gas was examined by a constant potential electrolytic gas sensor X using the reference electrode 13 of the present invention. The sensitivity to each gas was also used for the conventional constant potential electrolytic gas sensor used in Example 2. The gases used were silane (SiH ₄ ), phosphine (PH ₃ ), germane (GeH ₄ ), and arsine (AsH ₃ ). All gases were 0.5 ppm.

  For the reference electrode 13 of the present invention, as shown in Example 4, the platinum content was variously adjusted from 0 to 10%. The current value was measured at each platinum content. The measurement results are shown in Table 3.

  Table 4 shows the current values measured for the conventional constant potential electrolytic gas sensor.

  Further, the current amount of the constant potential electrolytic gas sensor X using the reference electrode 13 of the present invention in each gas and the current amount of the conventional constant potential electrolytic gas sensor are graphed for each gas, and FIG. 7 (silane), The results are shown in FIG. 8 (phosphine), FIG. 9 (germane), and FIG. 10 (arsine).

  As a result, the constant potential electrolysis gas sensor X using the reference electrode 13 of the present invention example and the conventional constant potential electrolysis gas sensor are recognized to have different electrochemical properties (gas sensitivity characteristics) in each gas. It was.

  In the present invention, a reaction electrode for electrochemically reacting a gas to be detected as a gas electrode for detecting gas, a counter electrode with respect to the reaction electrode, and a reference electrode for controlling the potential of the reaction electrode are brought into contact with an electrolytic solution accommodated in an electrolytic cell. It can utilize for the constant potential electrolytic gas sensor provided.

X constant potential electrolytic gas sensor b carrier 11 reaction electrode 12 counter electrode 13 reference electrode 20 electrolyte 30 electrolytic cell

Claims (3)

As a gas electrode for detecting gas, a reaction electrode for electrochemically reacting a gas to be detected, a counter electrode for the reaction electrode, and a reference electrode for controlling the potential of the reaction electrode were provided so as to come into contact with an electrolytic solution contained in an electrolytic cell. A constant potential electrolytic gas sensor,
The reference electrode has a support on which two kinds of noble metals having different immersion potentials in the electrolytic solution are supported, and is configured by adjusting the ratio of the two kinds of noble metals so that the set potential becomes zero. Potential electrolysis gas sensor.   The constant potential electrolytic gas sensor according to claim 1, wherein the carrier is carbon, and the two kinds of noble metals are gold and platinum.   The potentiostatic gas sensor according to claim 1 or 2, wherein a potentiostat circuit for setting the potential of each electrode is connected, and the potentiostat circuit is short-circuited.

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