JP6326670B2 - Constant potential electrolytic gas sensor - Google Patents

Description

  The present invention provides a working electrode for electrochemically reacting a gas to be detected as a gas electrode for detecting a gas, a counter electrode for the working electrode, and a reference electrode for controlling the potential of the working electrode. The present invention relates to a constant potential electrolytic gas sensor provided facing a housing portion.

  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.

  As the noble metal catalyst applied to the electrode, for example, a carbon having a particle diameter of several tens of nanometers supported with gold fine particles of about several hundred nanometers may be used. In order to support the gold 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 preparing gold-supporting carbon by the immersion support method, an electrode was prepared by applying it to a porous PTFE membrane.

  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 gold-supported carbon produced by the above-described method has a particle diameter of the gold fine particles larger than that of the carbon as the carrier and tends to aggregate in an aqueous solution, so that it is difficult to uniformly disperse the gold fine particles. there were. When the gold-supported carbon produced in such a state that the gold fine particles are not uniform is used as a noble metal catalyst, there are cases where the gas detection performance varies.
In addition, although the firing temperature in the immersion support method may be about 600 ° C., when the carrier is carbon, if the firing temperature is such a high temperature, there is a risk that the carbon as the carrier will burn. there were.

  Accordingly, an object of the present invention is to provide a constant potential electrolytic gas sensor including a noble metal catalyst that is unlikely to vary in gas detection performance and that can keep the firing temperature low during production.

In order to achieve the above object, a constant potential electrolytic gas sensor according to the present invention controls a working electrode for electrochemically reacting a gas to be detected as a gas electrode for detecting gas, a counter electrode for the working electrode, and a potential of the working electrode. A constant potential electrolytic gas sensor provided with a reference electrode facing an electrolytic solution storage part of an electrolytic cell containing an electrolytic solution, wherein the first feature is that each electrode includes a noble metal catalyst, and the noble metal The catalyst is dried while adding a carbon powder to a solvent and stirring the carbon powder, adding a gold nanoparticle adding step of adding a colloidal solution in which gold nanoparticles are dispersed, and maintaining the temperature below the boiling point of the solvent. It is in the point produced by performing a drying process and the baking process which bakes the powder obtained by drying at 250-400 degreeC in air atmosphere .

  In the controlled potential electrolytic gas sensor of the present invention, gold-supported carbon supported in a state where gold nanoparticles are dispersed can be used as a noble metal catalyst. Since the gold-supporting carbon uses a colloidal solution in the production process, it can be supported on carbon as a carrier in a state in which the gold nanoparticles are dispersed, so the degree of dispersion of the gold nanoparticles is almost uniform. It can be in a state. Therefore, if such a gold-supported carbon is used as a noble metal catalyst, it is possible to prevent the gas detection performance from varying in the constant potential electrolytic gas sensor.

In addition, since the gold-supporting carbon according to the present configuration can be fired in an air atmosphere and the firing temperature can be suppressed to 250 to 400 ° C. during the production process, there is no possibility that carbon as a carrier will burn.

  The second characteristic configuration of the potentiostatic gas sensor according to the present invention is that a surfactant is added in the carbon powder addition step.

  According to this structure, the dispersibility of the carbon with respect to a solvent can be improved by adding surfactant.

It is sectional drawing which shows the constant potential electrolytic gas sensor of this invention. It is a flowchart which shows the outline | summary of preparation of gold carrying | support carbon. It is the graph which showed the particle size distribution of the gold nanoparticle. It is a photograph figure of the electron microscope of gold | metal | money carrying | support carbon (invention example). It is a photograph figure of the electron microscope of gold carrying carbon (comparative example). It is the graph which showed the result of having performed the gas sensitivity measurement with respect to phosphine gas 1ppm and 0.5ppm in a constant potential electrolytic gas sensor. It is the graph which showed the result of having performed the gas sensitivity measurement with respect to 1 ppm of silane, a phosphine, a germane, arsine, and diborane in a constant potential electrolytic gas sensor.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the constant potential electrolysis gas sensor X is a gas electrode for detecting a gas. A working electrode 11 for electrochemically reacting a gas to be detected, a counter electrode 12 for the working electrode 11, and a reference for controlling the potential of the working electrode. The electrode 13 is provided so as to face the electrolytic solution storage part 31 of the electrolytic bath 30 in which the electrolytic solution 20 is stored.

  The working electrode 11, the counter electrode 12, and the reference electrode 13 are formed by applying and baking a paste made of a known electrode material on the surface of a porous gas-permeable film 14 having water repellency. The working 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 working 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 working 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 working electrode 11.

  Each gas permeable membrane 14 and the O-ring 15 are fixed by a lid member 16. An electrolytic solution inlet 34 for performing maintenance such as injection of the electrolytic solution 20 is formed on the bottom surface of the electrolytic bath 30.

  Such a constant potential electrolytic gas sensor X includes a current measuring unit capable of detecting a current based on electrons generated on the working electrode 11 by a reaction of the gas to be detected, and a potential control unit capable of controlling the potential of the working electrode 11. It is used as a gas detection device by connecting to a gas detection circuit (not shown). 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.

As shown in FIG. 2, each electrode 10 in the controlled potential electrolytic gas sensor X of the present invention includes a noble metal catalyst, and the noble metal catalyst includes a carbon powder addition step A in which carbon powder is added to a solvent and stirred. , A gold nanoparticle addition step B for adding a colloidal solution in which gold nanoparticles are dispersed, a drying step C for drying in a state maintained below the boiling point of the solvent, and a powder obtained by drying in an air atmosphere It is manufactured by performing a baking step D in which baking is performed at 250 to 400 ° C.

In the carbon powder addition step A, a predetermined amount of carbon powder is weighed, and water as a solvent is added and sufficiently stirred.
As the carbon powder, a known carbon powder such as carbon black (particle size of about 5 to 300 nm) can be used. In particular, acetylene black obtained by thermally decomposing acetylene gas is preferably used, but is not limited thereto. It is not something.

  This step may be performed by adding a surfactant. 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, in addition to adding a surfactant, for example, when the solvent is water, a surface treatment such as adding a hydroxyl group to the surface of carbon to increase hydrophilicity may be performed, Alternatively, ultrasonic treatment may be performed as pretreatment.

In the gold nanoparticle addition step B, a colloidal solution in which gold nanoparticles are dispersed in the solution obtained in the carbon powder addition step A is added.
The colloidal solution in which the gold nanoparticles are dispersed is in a state in which the gold nanoparticles having the above-described particle size 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.

  In the drying step C, the solution obtained in the gold nanoparticle addition step B 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 D, the powder obtained by drying is fired at 250 to 400 ° C. in an air atmosphere .
The firing temperature in the present embodiment is a temperature (250 to 400 ° C.) at which the organic substance 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 the baking process D may be complete | finished if it reaches predetermined temperature, without setting baking time.

  By the above method, gold-carrying carbon that carries gold nanoparticles in a dispersed state can be produced. That is, the controlled potential electrolytic gas sensor X of the present invention can use gold-supported carbon supported in a state where gold nanoparticles are dispersed as a noble metal catalyst. Since the gold-supporting carbon uses a colloidal solution in the production process, it can be supported on carbon as a carrier in a state in which the gold nanoparticles are dispersed, so the degree of dispersion of the gold nanoparticles is almost uniform. It can be in a state. Therefore, if such gold-supported carbon is used as a noble metal catalyst, it is possible to prevent the gas detection performance from varying in the constant potential electrolytic gas sensor X.

In addition, since the gold-supporting carbon according to the present configuration can be fired in an air atmosphere and the firing temperature can be suppressed to 250 to 400 ° C. during the production process, there is no possibility that carbon as a carrier will burn.

  Furthermore, in the gold-supported carbon produced by the above method, the gold nanoparticles can be dispersed with a particle size of about 5 to 50 nm. As a result, the amount of added gold fine particles in the gold-supported carbon produced by the conventional method is more than 50% by weight, whereas the amount of gold nanoparticles added in the gold-supported carbon produced by the above method is 5 to 50% by weight Can be reduced to a degree. Therefore, since the controlled potential electrolytic gas sensor X of the present invention can reduce the amount of gold nanoparticles added to the noble metal catalyst, the manufacturing cost of the sensor can be reduced.

[Example 1]
A gold-supporting carbon used as a noble metal catalyst in the electrode of the controlled potential electrolysis gas sensor X of the present invention was produced as follows. Each reagent was adjusted so that the content of the gold nanoparticles with respect to the gold-supported carbon was 25% by weight.

3 g of acetylene black powder and 2 mL of a surfactant (sodium dodecylbenzenesulfonate) were added to 600 mL of water and sufficiently stirred (carbon powder addition step A).
To this stirring solution, 33.3 g of a colloidal aqueous solution (3% by weight) in which gold nanoparticles were dispersed was added (gold nanoparticle addition step B).
Then, it kept at 80 degreeC, continuing stirring, and also made it dry under reduced pressure (100 hpa, 80 degreeC) (drying process C).
After drying, the sample powder taken out was baked at 400 ° C. for 1 hour under atmospheric pressure and air atmosphere to obtain gold-supported carbon powder (Invention Example 1).

  The particle size distribution (measured by the X-ray small angle scattering method) of the gold nanoparticle powder of Invention Example 1 is shown in FIG. 3, and the electron micrograph of the gold-supporting carbon is shown in FIG. FIG. 5 shows an electron micrograph of a conventional gold-supporting carbon (comparative example) for comparison.

  From FIG. 3, it was recognized that the powder of the said gold nanoparticle has a particle size of about 5-50 nm. In the gold-supported carbon of Invention Example 1, it was recognized that the gold nanoparticles were dispersed and supported on the carbon (FIG. 4). On the other hand, in the gold-supporting carbon of the comparative example, it was recognized that the gold fine particles were aggregated (FIG. 5).

[Example 2]
Each electrode of the potentiostatic gas sensor X was produced as follows. In the gold-supporting carbon used in each electrode, the content of the gold nanoparticles was variously changed from 5 to 50% by weight, and a potentiostatic gas sensor X was produced in each.

  0.1 g of gold-supported carbon powder, 0.1 mL of surfactant (sodium dodecylbenzenesulfonate), PTFE (polytetrafluoroethylene: Teflon) dispersion (a colloidal solution containing fine particles of PTFE, specific gravity 1.5). 35 mL of each was added and kneaded to prepare an electrode material paste. The obtained electrode material paste was printed on a PTFE sheet, dried, and baked at 280 ° C. for 8 hours to obtain each electrode 10. Each of the obtained electrodes 10 was used as a working electrode 11, a counter electrode 12, and a reference electrode 13, and a potentiostatic gas sensor X was prepared in which the electrolytic solution 20 was a 42% by weight sulfuric acid aqueous solution.

In each of the obtained potentiostatic gas sensors X, gas sensitivity was measured for phosphine gas 1 ppm and 0.5 ppm in an environment of 20 ° C. and 50% RH (FIG. 6). Similarly, gas sensitivity measurement was performed for 1 ppm of each gas of silane, phosphine, germane, arsine, and diborane (FIG. 7).
The gas sensitivity was defined by the magnitude of the current value flowing from the working electrode 11 to the gas detection circuit 40 in the target gas atmosphere.

  As a result, the potentiostatic gas sensor X in which the amount of added gold nanoparticles in the gold-supported carbon is 5% by weight or more, particularly 20% by weight or more is recognized as a working electrode having a sufficiently high reactivity to gas. It was. In view of the production cost of the gold-supported carbon, the amount of gold nanoparticles added to the gold-supported carbon should be suppressed to 50% by weight, preferably 30% by weight. Therefore, in consideration of gas sensitivity and production cost, the amount of gold nanoparticles added to the gold-supported carbon is preferably about 5 to 50% by weight.

  The present invention provides a working electrode for electrochemically reacting a gas to be detected as a gas electrode for detecting a gas, a counter electrode for the working electrode, and a reference electrode for controlling the potential of the working electrode. The present invention can be used for a constant potential electrolytic gas sensor provided facing a housing portion.

A Carbon powder addition process B Gold nanoparticle addition process C Drying process D Firing process X Constant potential electrolytic gas sensor 11 Working electrode 12 Counter electrode 13 Reference electrode 20 Electrolytic solution 30 Electrolytic tank 31 Electrolytic solution container

Claims (2)

As a gas electrode for detecting gas, a working electrode for electrochemically reacting a gas to be detected, a counter electrode for the working electrode, and a reference electrode for controlling the potential of the working electrode are faced to an electrolytic solution housing part of an electrolytic cell containing an electrolytic solution. A constant potential electrolytic gas sensor provided in
Each electrode includes a noble metal catalyst, and the noble metal catalyst is:
Adding carbon powder to the solvent and stirring the carbon powder;
A gold nanoparticle addition step of adding a colloidal solution in which gold nanoparticles are dispersed;
A drying step of drying in a state maintained below the boiling point of the solvent;
A constant potential electrolytic gas sensor produced by performing a baking step of baking powder obtained by drying at 250 to 400 ° C. in an air atmosphere .   The constant potential electrolytic gas sensor according to claim 1, wherein a surfactant is added in the carbon powder addition step.