TW201513935A - Noble metal catalyst and controlled potential electrolysis gas sensor - Google Patents

Abstract

A noble metal catalyst causing metal nanoparticles to be supported on carbon particles acting as a carrier, said metal nanoparticles having an average particle diameter of no more than the average particle diameter of the carbon particles. The noble metal catalyst is used for each electrode in a constant potential electrolyte gas sensor (X) comprising: a working electrode (11), as a gas electrode that detects gas, that causes detected gas to chemically react; a counter electrode (12) for the working electrode (11); and a reference electrode (13) controlling the potential of the working electrode. Said electrodes face an electrolyte housing section (31) of an electrolytic cell (30) housing electrolyte (20).

Description

Precious metal catalyst and constant potential electrolytic gas sensor

The present invention relates to a noble metal catalyst used in a constant potential electrolytic gas sensor, and the constant potential electrolytic gas sensor, in the constant potential electrolytic gas sensor, in an electrolytic cell containing an electrolyte The electrolyte storage portion is adjacent to each other, and includes: a working electrode for electrochemically reacting the gas to be detected as a gas electrode for detecting a gas; and a counter electrode opposite to the working electrode; and a reference electrode for controlling the potential of the working electrode.

A conventional constant-potential electrolytic gas sensor is configured such that an electrode is disposed adjacent to an electrolyte containing portion of an electrolytic cell in which an electrolytic solution is closely accommodated, and for example, as an electrode, a working electrode is provided to cause a gas to be detected An electrochemical reaction occurs as a gas electrode for detecting a gas; and a counter electrode is opposite to the working electrode; and a reference electrode controls the potential of the working electrode; and three electrodes are connected, and an electrolytic cell is also connected to accommodate the electrodes Contact with the electrolyte; and potentiostat circuit, set the potential of each electrode and so on. The material of the above three electrodes is coated with platinum, gold, palladium, etc. on a hydrophobic gas permeable porous PTFE film. A metal catalyst or the like is used, and an acidic aqueous solution such as sulfuric acid or phosphoric acid is used in the electrolyte.

Further, the constant-potential electrolytic gas sensor controls the potential of the working electrode to be constant with respect to changes in the surrounding environment, thereby generating a current equivalent to a change in the surrounding environment between the working electrode and the counter electrode. Further, the potential of the working electrode does not change, or the oxidation-reduction potential varies depending on the type of gas. By utilizing this characteristic, 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 to the target gas.

The noble metal catalyst applied to the electrode is, for example, a material in which gold fine particles of several hundreds of nm or so are supported on carbon having a particle diameter of several tens of nm. In order to hold the gold fine particles on the carbon as described above, for example, an immersion holding method is used. In the immersion holding method, when the noble metal particles are supported on the support, the support is immersed in an aqueous solution of the metal salt, and the metal component is adsorbed on the surface of the support, and dried, calcined, and reduced. . After the gold-adhering carbon was produced by the immersion-holding method, it was applied to a porous PTFE film to prepare an electrode.

Further, the above-described constant potential electrolytic gas sensor which is a conventional technique in the present invention is a general technique, and thus a conventional technical document such as a patent document is not disclosed.

The gold-attached carbon produced by the above method has a particle diameter larger than that of the carrier, that is, carbon, and tends to aggregate in an aqueous solution. Therefore, it is difficult to uniformly disperse the gold fine particles. When the gold-attached carbon produced by the gold fine particles in a non-uniform state is used as the noble metal catalyst, the gas detection performance may be inconsistent.

Further, in the immersion holding method, the firing temperature is set to about 600 ° C. However, when carbon is used as the carrier, if the firing temperature is so high, the carbon which is the carrier may be burned.

Therefore, the object of the present invention is to provide a noble metal catalyst which is inconsistent in gas detection performance when using a noble metal catalyst as the above-mentioned electrodes in a constant potential electrolytic gas sensor; and provides a precious metal contact The constant-potential electrolysis gas sensor of the medium is incapable of inconsistent gas detection performance, and can suppress the firing temperature to be low during production.

In order to achieve the above object, the noble metal catalyst of the present invention is characterized in that carbon powder as a support is used to hold gold nanoparticles, and the gold nanoparticles have an average particle diameter of the carbon powder or less. The average particle size.

In the noble metal catalyst of the present configuration, by holding the gold nanoparticles having an average particle diameter equal to or less than the average particle diameter of the carbon powder, the gold nanoparticles can be supported on the carbon which is a carrier in a dispersed state. Therefore, the degree of dispersion of the gold nanoparticles can be made to be substantially uniform. So if you like this Gold-supporting carbon, for example, can be used as a noble metal catalyst in a gas sensor to prevent inconsistencies in gas detection performance.

In addition, the term "holding" as used in the present specification is to attach gold nanoparticles having an average particle diameter below the average particle diameter of the carbon powder so as to distinguish the conventional gold-attached carbon from the average particle having a specific carbon powder. The gold nanoparticles with an average diameter of a large diameter are attached.

A second characteristic feature of the noble metal catalyst of the present invention is that the gold nanoparticles are supported by 5 to 50% by weight of 5 to 50% by weight.

According to this configuration, the gold nanoparticles can be supported on the carbon powder in a state of being well dispersed in the carbon powder.

Further, in the examples described later, the content of the gold nanoparticles in the gold-supporting carbon used in each electrode was changed from 5 to 50% by weight, and a constant potential electrolytic gas sensor was produced for each. As a result, as long as the amount of the gold nanoparticles added is 5% by weight or more, stable gas sensitivity can be obtained, and in view of the manufacturing cost of gold-supporting carbon, it is considered that the amount of gold nanoparticles in the gold-supporting carbon is preferably It is suppressed to 50% by weight.

A third characteristic feature of the noble metal catalyst of the present invention is that the particle diameter of the carbon powder is set to be in the range of 5 to 300 nm.

In the present configuration, the particle diameter of the carbon powder can be set to any particle diameter in the range of 5 to 300 nm, and the particle diameter of the gold nanoparticles can be set to be equal to or less than the arbitrary particle diameter. Specifically, for example, the particle size of carbon black can be adjusted to have such a particle size range and used.

The first special of the constant potential electrolytic gas sensor of the present invention In the constant potential electrolytic gas sensor, the electrolyte storage unit of the electrolytic cell containing the electrolytic solution is adjacent to each other, and includes a working electrode for electrochemically reacting the detected gas to serve as a gas electrode for detecting the gas. And the counter electrode is opposed to the working electrode; and the reference electrode controls the potential of the working electrode; and each of the electrodes includes the noble metal catalyst according to any one of the first to third features.

In the noble metal catalyst of the present configuration, the gold nanoparticles can be supported on the carbon which is a carrier in a dispersed state, so that the degree of dispersion of the gold nanoparticles can be made substantially uniform. Therefore, if such a gold-bearing carbon is used as a noble metal catalyst, it is possible to prevent the gas detection performance from being inconsistent in the constant-potential electrolytic gas sensor.

According to a second aspect of the present invention, in the constant-potential electrolytic gas sensor, the noble metal catalyst is produced by the following steps: a carbon powder addition process, adding carbon powder to a solvent and stirring; and gold Nanoparticle addition engineering, adding a colloid solution in which gold nanoparticles are dispersed; drying and drying, maintaining the boiling point of the solvent below the boiling point; and baking, drying and obtaining The carbon powder having the gold nanoparticles is fired at 250 to 450 °C.

In the constant potential electrolytic gas sensor of the present invention, carbon supported by gold nanoparticles in a dispersed state can be used as a noble metal catalyst. Since the gold-supporting carbon system uses a colloidal solution in the production process, the gold nanoparticles can be supported on the carbon which is a carrier in a dispersed state, so that the degree of dispersion of the gold nanoparticles can be made substantially uniform. Therefore, if such gold is used as a precious metal catalyst, then Inconsistent gas detection performance in a constant potential electrolytic gas sensor is prevented.

In addition, the gold of this structure can support the carbon, and the firing temperature can be suppressed to 250 to 450 ° C during the production process, so that the carbon, which is the support, does not burn.

A third feature of the constant potential electrolytic gas sensor of the present invention is that a surfactant is added to the carbon powder addition process.

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

A‧‧‧carbon powder addition project

B‧‧‧Ginnel Particle Addition Project

C‧‧‧Drying Engineering

D‧‧‧Burning Engineering

X‧‧‧Constant potential electrolytic gas sensor

11‧‧‧Working electrode

12‧‧‧ pole

13‧‧‧ reference electrode

20‧‧‧ electrolyte

30‧‧‧electrolyzer

31‧‧‧Electrolyte accommodation

Fig. 1 is a schematic cross-sectional view of a constant potential electrolytic gas sensor of the present invention.

[Fig. 2] A schematic flow chart showing the production of gold-bearing carbon.

[Fig. 3] Schematic diagram of particle size distribution of the gold nanoparticles.

Fig. 4 is an electron micrograph of gold-bearing carbon (an example of the present invention).

Fig. 5 is an electron micrograph of a gold-bearing carbon (comparative example).

Fig. 6 is a graph showing the results of gas sensitivity measurement of phosphine gas at 1 ppm and 0.5 ppm in a constant potential electrolytic gas sensor.

Fig. 7 is a graph showing the results of gas sensitivity measurement of 1 ppm of silane, phosphine, germane, arsine, and diborane in a constant potential electrolytic gas sensor.

Embodiments of the present invention will be described below based on the drawings.

The noble metal catalyst of the present invention uses a noble metal catalyst as each electrode in a constant potential electrolytic gas sensor.

In the noble metal catalyst, the carbon powder as the support is used to hold the gold nanoparticle, and the golden nanoparticle has an average particle diameter equal to or less than the average particle diameter of the carbon powder.

As shown in FIG. 1, in the constant-potential electrolytic gas sensor X, the electrolyte solution accommodating portion 31 of the electrolytic cell 30 containing the electrolytic solution 20 is adjacent to each other, and includes a working electrode 11 for electrochemically reacting the gas to be detected. As a gas electrode for detecting a gas; and a counter electrode 12 opposed to the working electrode 11, and a reference electrode 13, a potential of the working electrode is controlled.

The working electrode 11, the counter electrode 12, and the reference electrode 13 are formed by coating and baking a paste made of a known electrode material on the surface of the porous gas permeable membrane 14 having a hydrophobic property. The working electrode 11 is disposed to face the counter electrode 12 and the reference electrode 13 .

The electrolytic cell 30 is formed with an opening portion 32 that opens to the side to form a gas conducting portion 33. Two gas permeable membranes 14 are provided, one of the gas permeable membranes 14 is provided with the working electrode 11, and the other gas permeable membrane 14 is provided with the counter electrode 12 and the reference electrode 13. The gas permeable membrane 14 disposed on the side of the working electrode 11 is attached to the electrolytic cell 30 so as to be adjacent to the opening 32. The detected gas is introduced through the gas conduction portion 33 and reacted on the working electrode 11.

Each of the gas permeable membranes 14 and the O-ring 15 is fixed by the cover member 16. An electrolyte injection port 34 is formed on the bottom surface of the electrolytic cell 30 to perform maintenance such as injection of the electrolytic solution 20.

Such a constant potential electrolytic gas sensor X is connected to a gas detecting circuit (not shown) and used as a gas detecting device. The gas detecting circuit is provided with a current measuring unit, which is freely detectable due to being detected. The current caused by the electrons generated on the working electrode 11 by the reaction of the gas is measured; and the potential control unit can freely control the potential of the working electrode 11. The constant potential electrolytic gas sensor X of the present invention is used, for example, to detect a hydride gas such as decane, phosphine, decane, hydrazine or diborane.

As shown in Fig. 2, in the constant potential electrolytic gas sensor X of the present invention, each electrode 10 is provided with a noble metal catalyst, and the noble metal catalyst is produced by the following steps: carbon powder addition engineering A, a carbon powder is added to the solvent and stirred; and the gold nanoparticle is added to the engineering B to add a colloidal solution in which the gold nanoparticles are dispersed; and the drying process C is dried while maintaining the boiling point of the solvent; and burning In the process D, the carbon powder obtained by drying and holding the gold nanoparticles is baked at 250 to 450 °C.

In the carbon powder addition project A, the carbon powder was weighed to a predetermined amount, and water was added as a solvent, and the mixture was sufficiently stirred.

As the carbon powder, a known carbon powder such as carbon black (having a particle diameter of about 5 to 300 nm) can be used, and in particular, acetylene black obtained by thermally decomposing an acetylene gas is preferably used, but it is not limited thereto.

This project can also be carried out by adding a surfactant. By adding The addition of the surfactant enhances the dispersibility of the carbon for the solvent. As the surfactant, any of an anion type, a cation type, a nonion type, and a betaine type surfactant can be used. In order to improve the dispersibility of carbon to the solvent, in addition to adding a surfactant, for example, when the solvent is water, surface treatment may be performed by attaching a hydroxyl group to the carbon surface to improve hydrophilicity, or may also perform ultrasonic treatment. Processed as pre-processing.

In the gold nanoparticle addition engineering B, a colloidal solution in which gold nanoparticles are dispersed is added to a solution obtained by carbon powder addition engineering A.

The colloidal solution in which the gold nanoparticles are dispersed is in a state in which the gold nanoparticles having the above particle size are dispersed in the solution. In the colloidal solution, an additive such as a protective agent may be added as necessary.

A gold colloid solution, for example, can be added to a chlorinated gold acid solution such as hydrogen tetrachloroaurate (III) to be used as a reducing agent and heated, thereby reducing metal ions and forming a colloid It is produced by a reduction reaction in a solution, but is not limited to such a method. In this method, the size of the gold colloidal particles can be changed by increasing or decreasing the amount of the reducing agent added to the gold chloride acid. The gold nanoparticles may be particles having a particle diameter of about 5 to 50 nm, but are not limited to this range. In this case, the particle size distribution can be made into a ratio of 5 to 50 nm particles of 90% by weight or more.

In the drying process C, the gold nanoparticle is added to the solution obtained in the engineering B, and the solution is maintained at a temperature lower than the boiling point of the solvent (water). dry. The temperature below the boiling point of the solvent is not particularly limited, but when the solvent is water, it can be set to about 80 to 100 °C. The drying method can be, for example, a known method such as vacuum drying, vacuum drying, air drying, or hot air drying. Known conditions can be applied to the drying conditions in the drying methods.

In the firing process D, the dried powder is fired at 250 to 450 °C.

The firing temperature in the present embodiment is a temperature (250 to 450 ° C) at which the temperature at which carbon oxidation does not occur in an air atmosphere or atmospheric pressure is promoted, and an organic substance such as a surfactant used is evaporated.

The firing time can be appropriately set to a time required for the surfactant, the protective agent for the colloid, and the like to completely disappear by evaporation, sublimation, or thermal decomposition. Therefore, it is possible to shorten and extend the firing time at any time by the amount of powder to be fired. However, considering the growth of the crystal grains of the gold nanoparticles and the decrease in activity due to sintering, for example, the upper limit of the firing time may be set to about 3 hours. Further, instead of setting the firing time, it is also possible to set the firing process D to be completed when the predetermined temperature is reached.

According to the above method, it is possible to produce gold-supporting carbon which allows the gold nanoparticles to be held in a dispersed state. In other words, the constant potential electrolytic gas sensor X of the present invention can hold carbon as a gold metal supported by the gold nanoparticles in a dispersed state, and can be used as a noble metal catalyst. Since the gold-supporting carbon system uses a colloidal solution in the production process, the gold nanoparticles can be supported on the carbon which is a carrier in a dispersed state, so that the degree of dispersion of the gold nanoparticles can be made substantially uniform. Therefore, if such a gold-bearing carbon is used as a noble metal catalyst, a constant potential electrolytic gas sensor can be used. Inconsistent gas detection performance in X prevents this from happening.

In addition, the gold of this structure can support the carbon, and the firing temperature can be suppressed to 250 to 450 ° C during the production process, so that the carbon, which is the support, does not burn.

Further, in the gold-supporting carbon produced by the above method, the gold nanoparticles can be dispersed in a particle diameter of about 5 to 50 nm. As a result, the amount of gold nanoparticles supported by gold by the above-mentioned method is more than 50% by weight, and the amount of gold nanoparticles which can be produced by the above-mentioned method is high. Reduce it to about 5~50% by weight. Therefore, the constant potential electrolytic gas sensor X of the present invention can reduce the amount of gold nanoparticles added to the noble metal catalyst, thereby reducing the manufacturing cost of the sensor.

[Examples] [Example 1]

The electrode of the constant potential electrolytic gas sensor X of the present invention is used as a gold-supporting carbon as a noble metal catalyst, and is produced in the following manner. Each of the reagents was adjusted so that the content of the gold nanoparticles was 25% by weight for the gold-supporting carbon.

3 g of acetylene black powder and 2 mL of a surfactant (sodium dodecylbenzenesulfonate) were added to 600 mL of water and stirred well (carbon powder addition engineering A).

To the stirring solution, 33.3 g of a colloidal aqueous solution (3 wt%) in which gold nanoparticles were dispersed was added (Gold Nanoparticle Addition Engineering B).

Thereafter, the mixture was kept at 80 ° C while stirring, and then dried under reduced pressure (100 hPa, 80 ° C) (drying process C).

After drying, the sample powder to be taken out was fired at 400 ° C for 1 hour under atmospheric pressure and in an air atmosphere (baking engineering D) to obtain a gold-bearing carbon powder (Inventive Example 1).

The particle size distribution of the gold nanoparticle powder of Example 1 of the present invention (measured by a small angle X-ray scattering method) is shown in Fig. 3, and an electron micrograph of the gold-bearing carbon is shown in Fig. 4 . An electron micrograph of a conventional gold-bearing carbon (comparative example) is shown in Fig. 5 for comparison.

It is confirmed from Fig. 3 that the powder of the gold nanoparticles has a particle diameter of about 5 to 50 nm. Further, in the gold-supporting carbon of Example 1 of the present invention, it was confirmed that the gold nanoparticles were dispersed and supported on carbon (Fig. 4). On the other hand, in the gold of the comparative example, it was confirmed that the gold fine particles were aggregated (Fig. 5).

[Example 2]

The electrodes of the constant potential electrolytic gas sensor X were produced in the following manner. In the gold-supporting carbon used for each electrode, the content of the gold nanoparticles is changed from 5 to 50% by weight, and a constant potential electrolytic gas sensor X is produced for each.

Add 0.1g of gold-supported carbon powder, 0.1mL of surfactant (sodium dodecylbenzenesulfonate), PTFE (polytetrafluoroethylene; Teflon) dispersion (colloidal solution containing PTFE microparticles, specific gravity 1.5 0.35 mL was kneaded to prepare an electrode material paste. The obtained electrode material paste was printed on a PTFE sheet, dried, and fired at 280 ° C for 8 hours. Each electrode 10 is obtained. Each of the obtained electrodes 10 was used as the working electrode 11, the counter electrode 12, and the reference electrode 13, and the electrolytic solution 20 was set to a 42% by weight sulfuric acid aqueous solution to prepare a constant potential electrolytic gas sensor X.

In each of the obtained constant potential electrolytic gas sensors X, gas sensitivity measurement was performed for phosphine gas at 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 such as decane, phosphine, decane, hydrazine or diborane (Fig. 7).

Further, the gas sensitivity is defined as the magnitude of the current flowing from the working electrode 11 to the gas detecting circuit 40 in the target gas atmosphere.

As a result, it was confirmed that the reactivity of the gas is sufficient as long as it is a fixed potential electrolytic gas sensor X in which the amount of gold nanoparticles in the gold is 5 wt% or more, particularly 20 wt% or more. High acting electrode. Further, in view of the manufacturing cost of the carbon-supporting carbon, it is preferred to suppress the addition amount of the gold-bearing gold nano-particles in the gold-supporting carbon to at most 50% by weight, preferably 30% by weight. Therefore, considering the gas sensitivity and the manufacturing cost, the amount of gold nanoparticles in the gold-bearing carbon can be set to about 5 to 50% by weight.

[Industry Utilization]

The present invention can be utilized in a noble metal catalyst used in a constant potential electrolytic gas sensor, and the constant potential electrolytic gas sensor, in the electrolytic cell containing the electrolyte in the constant potential electrolytic gas sensor of The electrolyte storage portion is adjacent to each other, and includes: a working electrode for electrochemically reacting the gas to be detected as a gas electrode for detecting a gas; and a counter electrode opposite to the working electrode; and a reference electrode for controlling the potential of the working electrode.

X‧‧‧Constant potential electrolytic gas sensor

10‧‧‧ electrodes

11‧‧‧Working electrode

12‧‧‧ pole

13‧‧‧ reference electrode

14‧‧‧ gas permeable membrane

15‧‧‧O-ring

16‧‧‧Caps

20‧‧‧ electrolyte

30‧‧‧electrolyzer

31‧‧‧Electrolyte accommodation

32‧‧‧ openings

33‧‧‧Gas Conduction

34‧‧‧ electrolyte injection port

Claims (6)

A noble metal catalyst characterized in that carbon powder as a support is used to hold gold nanoparticles, and the gold nanoparticles have an average particle diameter of not less than an average particle diameter of the carbon powder. The noble metal catalyst according to claim 1, wherein the gold nanoparticles are supported by 5 to 50% by weight of 5 to 50% by weight. The noble metal catalyst according to claim 1 or 2, wherein the carbon powder has a particle diameter of 5 to 300 nm. A constant potential electrolytic gas sensor characterized in that: in an electrolyte storage portion of an electrolytic cell containing an electrolyte, a working electrode is provided to electrochemically react a gas to be detected as a gas electrode for detecting a gas And the counter electrode, opposite to the working electrode; and the reference electrode, controlling the potential of the working electrode; the constant potential electrolytic gas sensor, as the above-mentioned respective electrodes, having any one of the first to third patent claims The precious metal catalyst described in the item. The constant potential electrolytic gas sensor according to claim 4, wherein the noble metal catalyst is produced by the following steps: carbon powder addition engineering, adding carbon powder to the solvent and stirring a gold nanoparticle addition process, adding a colloid solution in which gold nanoparticles are dispersed; drying work, drying it while maintaining the boiling point of the solvent; and In the firing process, the carbon powder obtained by drying and holding the gold nanoparticles is baked at 250 to 450 °C. The constant potential electrolytic gas sensor according to claim 5, wherein in the carbon powder addition engineering, a surfactant is added.