JP7150467B2 - Reducing gas detection material and reducing gas detection sensor - Google Patents

Description

The present invention relates to a reducing gas detection material and a reducing gas detection sensor using the same.

A reducing gas is a gaseous compound at room temperature that has a strong reducing action and has the property of reducing a compound that is easily reduced when it comes into contact with that compound. Specific examples of reducing gases include hydrogen, formaldehyde, carbon monoxide, and ethylene. In particular, hydrogen has begun to be used as a fuel for fuel cell vehicles and household fuel cells, and is expected as an energy source. While these reducing gases are widely used industrially, some of them are flammable, explosive, or have an effect on the human body. Therefore, in terms of safety management, it is required to detect leakage to the outside from tanks, cylinders, pipes, application equipment, etc. in which reducing gases are stored.

Patent Literature 1 describes an optical sensor that changes color upon reaction with hydrogen gas as a sensor for detecting reducing hydrogen gas. Specifically, a sensor is disclosed in which palladium oxide is used for the reaction layer that reacts with hydrogen, and palladium, platinum, gold, or the like is deposited thereon as a catalyst metal layer.

Non-Patent Document 1 describes a hydrogen gas detection sensor using a thin film of palladium oxide as a reaction site. In Non-Patent Document 1, reduction is performed by detecting a change in resistance (electrical conductivity) caused by a change in resistance (electrical conductivity) of a palladium oxide film due to an irreversible reduction reaction between palladium oxide and hydrogen gas. It is used as a gas detection sensor.

JP 2007-225299 A

Nanotechnology, 21, 165503 (5pp), 2010

In order to detect the reducing gas in the atmosphere, a sensor that detects the reducing gas with high sensitivity and accuracy is required.

However, the sensor of Patent Literature 1 includes uncertainties because the user visually determines the degree of discoloration of the coloring material. There is also a method of optically detecting color change, but in that case, there is a risk that the size of the sensor will increase. In addition, since the color change is used, there is a problem that it must be placed in a place where the user can visually recognize it.

In a reducing gas sensor that utilizes changes in electrical properties of a reaction layer, as described in Non-Patent Document 1, sensitivity is one of the important parameters that determine the power consumption of the sensor. In general, when the sensitivity of the sensor is high, the change in electrical conductivity caused by the contact of the reaction site with the reducing gas is large. can be done. Such a design makes it possible to reduce the power consumption of the sensor in a normal state in which no reducing gas is detected.

Non-Patent Document 1 describes that the sensitivity S of the hydrogen gas detection sensor obtained by the formula (1) is about 45, and the sensitivity of the sensor described in Non-Patent Document 1 cannot be said to be sufficient.
S=(G _H −G _N )/G _N (1)
( _GH : electrical conductivity in the presence of hydrogen, _GN : electrical conductivity in the absence of hydrogen)

In view of the above problems, the present invention provides a reducing gas detecting material reactive with reducing gas, a method for detecting reducing gas using the reducing gas detecting material, and a method for detecting reducing gas having improved sensitivity compared to conventional methods. An object of the present invention is to provide a reducing gas detection sensor with reduced power consumption.

The above objective is accomplished by the present invention. That is, one aspect of the present invention is a reducing gas detection material that contains a palladium compound and a carbon compound and is reactive with a reducing gas.

Another aspect of the present invention is a reducing gas detection sensor comprising the reducing gas detection material and means for measuring the electrical conductivity of the reducing gas detection material.
Furthermore, another aspect of the present invention is a moving object equipped with the reducing gas detection sensor.

Yet another aspect of the present invention is a method for producing a reducing gas sensing material, comprising the step of heat-treating a mixture of a palladium compound and a carbon compound.

Another aspect of the present invention is a method for detecting a reducing gas, characterized by detecting a change in electrical conductivity of the reducing gas detection material due to a reaction with the reducing gas.

As described above, according to the present invention, it is possible to provide a reducing gas detection material that can be used in a sensor that detects a reducing gas, thereby improving sensitivity and reducing power consumption compared to conventional materials. can be done.

1 is a schematic diagram illustrating the configuration of a first embodiment of a reducing gas detection sensor; FIG. FIG. 6 is a schematic diagram illustrating the configuration of a second embodiment of a reducing gas detection sensor; FIG. 2 is a schematic diagram illustrating the configuration of a fuel cell vehicle equipped with a reducing gas detection sensor;

EMBODIMENT OF THE INVENTION Below, the form and Example for implementing this invention are demonstrated. The present invention is not limited to the following embodiments and examples, and modifications can be made within the scope of the invention.

<Reducing gas detection material>
A reducing gas detection material according to an embodiment of the present invention is characterized by containing a palladium compound and a carbon compound and having reactivity with a reducing gas.

Formulas (a) and (b) show examples of the reaction between the palladium compound and the reducing gas in the reducing gas detecting material according to the embodiment of the present invention. Formula (a) shows an example in which palladium oxide is used as the palladium compound and hydrogen is used as the reducing gas. Formula (b) shows an example in which palladium oxide is used as the palladium compound and ethylene is used as the reducing gas. Hydrogen or ethylene, which is a reducing gas, reacts with palladium oxide to reduce a divalent palladium atom (Pd(II)) and generate a zerovalent palladium atom (Pd(0)).
Pd( _II )O+H2→Pd(0)+ _H2O (a)

When the palladium compound reacts with the reducing gas, the palladium atoms are reduced and the valence changes from divalent to zero. The reduction of the palladium atoms changes the color of the reducing gas sensing material from ocher to black, and the change in electrical conductivity of the palladium compound causes a large change in the electrical conductivity of the reducing gas sensing material. The reducing gas that can be detected by the reducing gas detection material according to the embodiment of the present invention is not limited to hydrogen and ethylene, and can also detect formaldehyde, carbon monoxide, hydrogen sulfide, sulfur dioxide, nitrous oxide, and the like. It is possible.

Japan Journal of Applied Physics, vol. 6, page 779 (1967) describes that the electrical conductivity of a palladium oxide film is about 1 Ω ⁻¹ cm ⁻¹ (at room temperature). A reducing gas detection sensor detects a change in conductivity due to a change of a divalent palladium atom to a zerovalent palladium atom. As a result of intensive studies, the present inventors have found that by mixing a carbon compound with a palladium compound, the reactivity of the palladium compound and the reducing gas and the sensitivity of the reducing gas detection material can be reduced without reducing exposure to the reducing gas. We have found that the electrical conductivity of the reducing gas sensing materials in the previous can be reduced.

Examples of palladium compounds that can be used in the reducing gas sensing material according to the embodiment of the present invention include inorganic salts, oxides, sulfides, and halogen compounds containing a divalent palladium atom (Pd(II)). Specific examples include palladium oxide, palladium sulfide, palladium chloride, palladium bromide, palladium sulfate, and palladium hydroxide.

Carbon compounds that can be used in the reducing gas detection material according to the embodiment of the present invention are compounds derived from carboxylic acids and alcohols. By mixing these carboxylic acids and alcohols with a palladium compound and heating them, they are converted to carbon compounds derived from carboxylic acids and alcohols. That is, carbon compounds in embodiments of the present invention are compounds in which carboxylic acids, alcohols, or mixtures thereof have been converted by reaction with palladium compounds. The carbon compound of the reducing gas sensing material is a compound or a mixture of multiple compounds having a C—C single bond, a C—H bond, a C=C double bond, and an OH group from XPS analysis and IR spectroscopy. is. The carbon compound may contain unreacted alcohol.

Examples of the carboxylic acid include monocarboxylic acids such as acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, pivalic acid, caproic acid, enanthic acid, caprylic acid, cyclohexylacetic acid, benzoic acid, and phenylacetic acid. , oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic acid, and dicarboxylic acids such as phthalic acid.

Examples of the alcohol include monohydric alcohols such as methanol, ethanol, propanol, isopropyl alcohol, butanol, s-butanol, t-butanol, pentanol, hexanol, cyclohexanol, phenol, benzyl alcohol, and phenethyl alcohol, ethylene glycol, Dihydric alcohols such as propylene glycol, diethylene glycol and catechol can be mentioned.

Hydroxy acids having a carboxyl group and a hydroxyl group, such as lactic acid, malic acid, citric acid, and hydroxybenzoic acid, can also be used.

Furthermore, a carboxylic acid and/or alcohol complex of a divalent palladium atom may be used as a raw material for the reducing gas sensing material according to the embodiment of the present invention. Alternatively, after forming a coating film of a palladium complex having a specific structure, heat treatment is performed to convert the complex into a palladium compound and a carbon compound, thereby producing a reducing gas detection material.

（一般式（１）において、Ｒ_１は置換基を有してもよいアルキル基、置換基を有してもよいアリール基、または置換基を有してもよいアラルキル基を表す。）
Ｒ_１としては、例えば、メチル基、エチル基、プロピル基、イソプロピル基、ブチル基、ｓ－ブチル基、ｔ－ブチル基、ペンチル基、ヘキシル基、シクロヘキシル基、ペンチル基、オクチル基、フェニル基、トリル基、ベンジル基、フェネチル基などをあげることができる。 Specifically, a reducing gas detection material containing palladium oxide as a palladium compound and a carbon compound is formed by applying a palladium acetate analogue represented by the general formula (1) to form a coating film, followed by heat treatment. can be manufactured. The palladium acetate analogue represented by the general formula (1) may be a monomer, dimer, trimer or multimer.

(In general formula (1), R ₁ represents an optionally substituted alkyl group, an optionally substituted aryl group, or an optionally substituted aralkyl group.)
Examples of R ₁ include methyl group, ethyl group, propyl group, isopropyl group, butyl group, s-butyl group, t-butyl group, pentyl group, hexyl group, cyclohexyl group, pentyl group, octyl group, phenyl group, Tolyl group, benzyl group, phenethyl group and the like can be mentioned.

In the reducing gas detection material according to the embodiment of the present invention, the ratio R of the number of carbon atoms to the sum of the number P of atoms of palladium atoms contained in the palladium compound and the number of atoms C of carbon atoms contained in the carbon compound By setting (=C/(P+C)) to 0.50 or more and 0.95 or less, the electrical conductivity of the reducing gas detecting material before exposure to the reducing gas is significantly decreased.

Specifically, when the ratio R of the number of carbon atoms is within the above range, the electrical conductivity of the reducing gas sensing material is 1×10 ⁻⁸ to 1×10 ⁻¹¹ Ω ⁻¹ cm ⁻¹ at room temperature. becomes. This is 7 to 10 orders of magnitude smaller than the electrical conductivity (1Ω ⁻¹ cm ⁻¹ ) of a palladium oxide film described in Japan Journal of Applied Physics, vol.6, page 779 (1967). This extremely low electrical conductivity is considered to be due to the carbon compound inhibiting the electrical conductivity of the palladium compound. On the other hand, when the reducing gas sensing material according to the embodiment of the present invention is exposed to the reducing gas and the divalent palladium atoms in the palladium compound are reduced to zero valent palladium, the electrical conductivity of the reducing gas sensing material degree becomes very large. As described above, the reducing gas detection material according to the embodiment of the present invention has an extremely large difference in electrical conductivity before and after exposure to a reducing gas as compared with a conventional palladium oxide film. When used in a sensor, it can provide a highly sensitive sensor.

If the electrical conductivity of the reducing gas detection material before exposure to the reducing gas is small, the voltage applied in the standby state in the reducing gas detection sensor that detects the electrical conductivity of the reducing gas detection material from changes in the current value And the current value can be kept low. As a result, power consumption during operation of the reducing gas detection sensor can be suppressed, and the application range of the reducing gas detection sensor is widened. For example, a reducing gas detection sensor can be driven by a common small battery. Furthermore, the reducing gas detection sensor can be used for a long period of time without battery replacement. Therefore, the reducing gas detection sensor using the reducing gas detection material according to the embodiment of the present invention can be used not only in a reducing gas storage but also in a mobile object such as an electric vehicle.

(Method for producing reducing gas detection material)
An example of a method for producing a reducing gas sensing material according to an embodiment of the present invention has a step of heat-treating a divalent palladium complex. Another example further includes the step of obtaining a mixture of the palladium compound and the carbon compound, or heat-treating the obtained mixture. Specifically, a solution or dispersion of a divalent palladium complex is applied onto a substrate, and the resulting coating film is heat-treated to obtain a reducing gas detection material. Alternatively, a solution or dispersion of a palladium compound and a carbon compound is applied onto a substrate, and the resulting coating film is heat-treated as necessary to obtain a reducing gas detection material.

Ethyl acetate, butyl acetate, toluene, chloroform, dimethylformamide and the like are examples of solvents that can be used for the solution or dispersion of the palladium compound and the carbon compound.

Methods for applying the solution or dispersion of the palladium compound and the carbon compound include spin coating, dipping, casting, bar coating, and the like. In particular, when applying by spin coating, the thickness of the reducing gas detecting material can be adjusted by adjusting the rotation speed of spin coating, which is preferable.

The heat treatment is preferably performed at 60° C. or higher and 120° C. or lower. By heating the coating film in this range, the reaction between palladium and the carbon compound produces a suitable carbon compound. Due to the reaction between the palladium and the carbon compound, the number C of carbon atoms in the reducing gas detecting material becomes smaller than the number C of carbon atoms in the solution or dispersion of the palladium compound and the carbon compound. Therefore, so that the ratio R of the number of carbon atoms to the sum of the number P of palladium atoms and the number C of carbon atoms contained in the reducing gas detection material is 0.50 or more and 0.95 or less, Palladium compounds and carbon compounds are preferably used. In order to measure the ratio of the number of palladium atoms and the number of carbon atoms in the reducing gas detection material, for example, an X-ray photoelectron spectrometer or the like can be used.

The reducing gas detection material according to the embodiment of the present invention may have any shape, but a film shape is preferable because the contact area with the reducing gas is increased. When the reducing gas sensing material according to the embodiment of the present invention has a film shape, the film thickness is preferably 5 nm or more and 1000 nm or less, more preferably 10 nm or more and 500 nm or less.

(Method for detecting reducing gas using reducing gas detecting material)
A reducing gas detection material according to an embodiment of the present invention detects a reducing gas when a palladium compound reacts with a reducing gas to reduce palladium atoms and change the valence from divalent to zero. Detect reducing gases from changes in materials. Specifically, when the palladium compound reacts with the reducing gas, the reducing gas detecting material changes color from ocher to black, and the electric conductivity of the reducing gas detecting material greatly changes. Accordingly, a method of detecting reducing gas using a reducing gas sensing material according to embodiments of the present invention may utilize color change and/or conductivity change of a reducing gas detection sensor. In particular, in the reducing gas detection material according to the embodiment of the present invention, as described above, the conductivity changes greatly when the reducing gas is detected. It is preferable to use the change of As a means for measuring the conductivity of the reducing gas sensing material, a pair of electrodes in electrical contact with the reducing gas sensing material is used to measure the electrical conductivity of the reducing gas sensing material based on the change in electrical conductivity between the electrodes. It is possible to use a contact-type conductivity measurement method for measuring , or a non-contact-type conductivity measurement method for measuring the conductivity of a reducing gas detection material using microwaves.

<Reducing gas detection sensor>
A reducing gas detection sensor according to an embodiment of the present invention includes the reducing gas detection material described above and means for measuring the electrical conductivity of the reducing gas detection material. As a means for measuring the conductivity of the reducing gas sensing material, a pair of electrodes in electrical contact with the reducing gas sensing material is used to measure the electrical conductivity of the reducing gas sensing material based on the change in electrical conductivity between the electrodes. It is possible to use a contact-type conductivity measuring means for measuring the , or a non-contact-type conductivity measuring means for measuring the conductivity of the reducing gas detection material using microwaves.
An embodiment of a reducing gas detection sensor using contact conductivity measuring means will be described below.

(First embodiment)
In the present embodiment, a reducing gas detection sensor 100 (hereinafter also referred to as "sensor 100") using the above reducing gas detection material will be described with reference to FIG.

FIG. 1A is a schematic top view of the sensor 100 of this embodiment. The sensor 100 has a substrate 10 , a pair of electrodes 11 , a reducing gas sensing material 12 , a power source 13 and a measurement section (detection circuit) 14 .

As a material for the substrate 10, an insulator such as glass, quartz, or silicon can be used.
A pair of electrodes 11 are arranged on the surface of the substrate 10 so as to face each other. Conductors such as metals, metal oxides, and organic conductors can be used as materials for the pair of electrodes 11 . Specific examples include metals such as gold (Au) and aluminum (Al), metal oxides such as ITO, and organic conductors such as polyacetylene, polyparaphenylene, polythiophene, and PEDOT/PSS.

The shape of the pair of electrodes 11 can be appropriately designed according to the type of reducing gas to be detected, the required sensitivity, and the like. For example, FIG. 1A shows a trapezoidal electrode in which the opposing portions of a pair of electrodes 11 facing each other are linear. However, the shape of the electrode 11 is not limited to such a shape, and may be various shapes such as a rectangle and a square. Also, the shape of the opposing portions of the electrodes is not limited to a linear shape, and may be, for example, a comb-tooth shape like the electrode 15 in FIG. 1(b). In the case of a pair of electrodes 15 having a comb-shaped facing portion, the effective length (electrode length) of the facing electrodes 15 is defined as an electrode having a linear shape at the facing portion. 11, the current value can be measured even with a substance having low electrical conductivity, and the sensitivity of the reducing gas detection sensor 100 can be increased.

The distance between the electrodes 11 and 15 is preferably 0.05 μm or more and 100 μm or less, more preferably 0.05 μm or more and 30 μm or less, and still more preferably 0.1 μm or more and 10 μm or less. Here, the electrode interval is defined as the shortest distance among the distances between the electrodes in the portion where the pair of electrodes are opposed to each other.

A reducing gas sensing material 12 is disposed on the surface of the substrate 10 . The reducing gas sensing material 12 is arranged on the pair of electrodes 11 (15) so as to be in contact with each of the pair of electrodes 11 (15). Further, the reducing gas detection material 12 must be arranged so as to be in contact with the reducing gas to be detected. Therefore, the reducing gas detection material 12 is formed by applying a coating film of a solution or dispersion of a mixture of a palladium compound and a carbon compound to the surface of the substrate 10 having the electrode 11 (15) on the side of the electrode 11 (15) by the coating method described above. can be formed by heat treatment. FIG. 1(c) is a cross-sectional view taken along line A-A' in FIG. 1(b). The reducing gas sensing material 12 is arranged on the substrate 10 so as to cover the pair of electrodes 15 facing each other. Therefore, the reducing gas sensing material 12 can contact the reducing gas on the surface opposite to the substrate 10 .

A power supply 13 and a detection circuit 14 are electrically connected to each of the pair of electrodes 11 (15) to supply a voltage to the pair of electrodes 11 (15). The detection circuit 14 detects changes in conductivity of the reducing gas sensing material 12 by measuring changes in conductivity between the pair of electrodes 11 . In addition, since the detection circuit 14 only needs to be able to measure changes in the electrical conductivity of the reducing gas sensing material 12, it is possible to measure at least one change in resistance between the pair of electrodes 11 and electrical conductivity between the pair of electrodes 11. may be configured.

As described above, the electrical conductivity of the reducing gas detection material is suppressed before exposure to the reducing gas. It becomes possible to use it as a detection sensor.

Further, while some conventional hydrogen gas sensors require a heater when used, the reducing gas detection sensor 100 of the present embodiment can detect reducing gas at room temperature. Therefore, since the reducing gas detection sensor 100 does not require a heater, the structure of the reducing gas detection sensor 100 is simple, and the reducing gas detection sensor can be made to achieve both miniaturization and cost reduction.

(Second embodiment)
In this embodiment, the configuration of the reducing gas detection sensor 200 will be described with reference to FIG. FIG. 2 is a schematic cross-sectional view illustrating the configuration of the reducing gas detection sensor 200 of this embodiment. The reducing gas detection sensor 200 has the same configuration as that of the first embodiment except that the arrangement of the substrate 20, the pair of electrodes 21 and the reducing gas detection material 22 is different from that of the first embodiment.

In this embodiment, the reducing gas sensing material 22 is arranged on the surface of the substrate 20 so as to be sandwiched between the pair of electrodes 21 in the direction perpendicular to the surface of the substrate 20 .

With this configuration, the reducing gas detection sensor 200 can have higher sensitivity than the conventional reducing gas detection sensor. Moreover, the power consumption can be reduced more than the reducing gas detection sensor 100 in the first embodiment, and can be driven with a simple power source such as a battery. Therefore, the reducing gas detection sensor 200 can be used in various applications.

<Use of the reducing gas detection sensor according to the embodiment of the present invention>
The reducing gas detection sensor according to the embodiment of the present invention can be used in reducing gas storage facilities and reducing gas supply facilities. Further, as described in the first embodiment or the second embodiment, the reducing gas detection sensor according to the embodiment of the present invention can be driven with low power consumption, so that it can be used in a fuel cell using reducing gas. It can also be used by being mounted on a moving object using Examples of such moving bodies include cars, motorcycles, and drones equipped with fuel cells. A vehicle 300 equipped with a fuel cell that utilizes hydrogen gas (hereinafter referred to as a "fuel cell vehicle") will be described below with reference to FIG.

As for the configuration of the fuel cell vehicle 300, a generally known configuration of a fuel cell vehicle can be adopted, and includes a vehicle interior 31, reducing gas detection sensors 32 and 34, a hydrogen fuel tank 33, a fuel cell 35, and a motor 36. have. Note that the fuel cell vehicle 300 may be configured to have only one of the reducing gas detection sensors 32 and 34 .

The hydrogen fuel tank 33 and the fuel cell 35 are each arranged in a space separated from the vehicle interior 31 . The fuel cell 35 generates electricity using oxygen and hydrogen gas supplied from the hydrogen fuel tank 33 . Electric power generated by the fuel cell 35 is transmitted to the motor 36 and used as driving force for driving the fuel cell vehicle 300 .

Reducing gas detection sensors 32 and 34 are provided close to the same space of hydrogen fuel tank 33 and fuel cell 35 to detect hydrogen gas, respectively. As the reducing gas detection sensors 32 and 34, the reducing gas detection sensors described in the first embodiment and the second embodiment can be used, respectively.

The reducing gas detection sensors 32 and 34 are capable of detecting hydrogen with lower power consumption than conventional reducing gas detection sensors. Therefore, hydrogen gas can always be detected even when the fuel cell 35 in the fuel cell vehicle 300 is not generating power. As a result, hydrogen gas, which was conventionally detectable only when the fuel cell 35 was generating power, can now be detected even when the fuel cell 35 is not generating power. Therefore, it is possible to more reliably manage the safety of the fuel cell vehicle.

EXAMPLES The present invention will be described below using examples, but the present invention is not limited to the following examples.

(Example 1)
A 1% by weight ethyl acetate solution of palladium acetate (manufactured by Aldrich Co., Ltd.) is prepared, and the ethyl acetate solution is spin-coated on comb-shaped electrodes patterned on a glass substrate to form a coating film. did. The conditions for spin coating were 1000 rpm for 30 seconds, and the thickness of the coating film after spin coating was 50 nm. The electrode interval between electrodes was 5 μm, and the electrode length of the electrodes was 80 cm. After the film formation, annealing was performed at 60° C. for 2 hours to prepare a reducing gas detection material, and a reducing gas detection sensor having the configuration of the reducing gas detection sensor 100 shown in FIG. 1(b) was prepared. .

(1) Identification of Components in Reducing Gas Detecting Material X-ray photoelectron spectroscopy (XPS) was performed in order to identify the components in the reducing gas detecting material prepared above. As a measuring apparatus, Quntera SXM manufactured by ULVAC-PHI was used, and as measuring conditions, Al monoKα as an X-ray source, a sample angle of 45°, a beam of 100 µmΦ, 1.25 W, and 15 kV were used. In the XPS spectrum of the reducing gas sensing material prepared above, peaks corresponding to carboxyl groups present in palladium acetate disappeared when compared with a sample not subjected to annealing treatment. On the other hand, there was a peak in the spectrum (285.0 eV) corresponding to carbon 1s electrons derived from C—C single bond, C—H bond or C═C double bond. The presence of this spectrum confirmed the presence of carbon compounds with C--C single bonds, C--H bonds or C=C double bonds in the reducing gas sensing material.
Focusing on the spectrum corresponding to palladium 3d electrons, the presence of palladium oxide was confirmed by the presence of a spectrum corresponding to palladium oxide (binding energy=337.4 eV).
Further, the ratio R of the number of carbon atoms to the sum of the number of palladium atoms and the number of carbon atoms calculated from the spectral area intensity of palladium 3d electrons and carbon 1s electrons was 78%.

(2) Measurement of current value While applying a voltage of 0.1 V to the pair of electrodes of the reducing gas detection sensor prepared above, a mixed gas of 1 vol% hydrogen gas / 99 vol% argon (hereinafter referred to as "1% hydrogen mixed gas ” was introduced near the reducing gas detection sensor, and the current value was measured. 200 seconds after the introduction of the 1% hydrogen mixed gas, the current value began to change abruptly, and 20 seconds after that, the current value became constant. The current value was 2×10 ⁻¹³ A before the mixed gas was introduced, and the current value was 3×10 ⁻³ A after the mixed gas was introduced. When the sensitivity S was calculated from the formula (1) using these current values, the sensitivity S was 1×10 ¹⁰ . It was confirmed that the color of the reducing gas detection material in the reducing gas detection sensor changed from ocher to black before and after exposure to the 1% hydrogen mixed gas.

(Example 2)
A reducing gas detection sensor was produced in the same manner as in Example 1, except that the temperature of the annealing treatment in Example 1 was changed to 85°C. As in Example 1, X-ray photoelectron spectroscopy and current value measurement were performed on the produced reducing gas detection sensor, and the sensitivity of the reducing gas detection sensor was calculated from the obtained current value. Table 1 shows the results. It was confirmed that the color of the reducing gas detection material in the reducing gas detection sensor changed from ocher to black before and after exposure to the 1% hydrogen mixed gas.

(Example 3)
A reducing gas detection sensor was produced in the same manner as in Example 1, except that the annealing treatment in Example 1 was performed at 100° C. for 2 hours. X-ray photoelectron spectroscopy and current value measurement were performed in the same manner as in Example 1, and the sensitivity of the reducing gas detection sensor was calculated from the obtained current value. Table 1 shows the results. It was confirmed that the color of the reducing gas detection material in the reducing gas detection sensor changed from ocher to black before and after exposure to the 1% hydrogen mixed gas.

(Example 4)
A reducing gas detection sensor was produced in the same manner as in Example 1, except that the annealing treatment in Example 1 was performed at 120° C. for 2 hours. X-ray photoelectron spectroscopy and current value measurement were performed in the same manner as in Example 1, and the sensitivity of the reducing gas detection sensor was calculated from the obtained current value. Table 1 shows the results. It was confirmed that the color of the reducing gas detection material in the reducing gas detection sensor changed from ocher to black before and after exposure to the 1% hydrogen mixed gas.

(Example 5)
Regarding the reducing gas detection sensor created in Example 1, in measuring the current value, a 1% hydrogen mixed gas was a mixed gas of 1% vol hydrogen gas/99 vol% argon (hereinafter referred to as "1% ethylene mixed gas"). The current value was measured in the same manner, except that it was changed to Table 1 shows the results. Before and after exposure to the 1% ethylene mixed gas, it was confirmed that the color of the reducing gas detection material in the reducing gas detection sensor changed from ocher to black.

(Example 6)
For the reducing gas detection sensor produced in Example 2, the current value was measured in the same manner, except that the 1% hydrogen gas mixture was changed to the 1% ethylene gas mixture. Table 1 shows the results. Before and after exposure to the 1% ethylene mixed gas, it was confirmed that the color of the reducing gas detection material in the reducing gas detection sensor changed from ocher to black.

(Comparative example)
A reducing gas detection sensor was produced in the same manner as in Example 1, except that the temperature of the annealing treatment in Example 1 was changed to a temperature lower than 60°C. However, when the current value of the obtained reducing gas detection sensor was measured in the same manner as in Example 1, stable data could not be obtained. This is probably because annealing at a temperature lower than 60° C. does not sufficiently generate palladium compounds and carbon compounds.

The reducing gas detection sensors having the reducing gas detection materials containing palladium oxide and carbon compounds of Examples 1 to 6 have a sensitivity of about 1×10 ¹⁰ , and the sensitivity described in Non-Patent Document 1 is 45. It was found to have extremely high sensitivity compared to the gas detection sensor.

10 substrate 11 electrode 12 reducing gas detection material 13 power supply 14 measurement part (detection circuit)
15 Electrode 20 Substrate 21 Electrode 22 Reducing gas detection material 31 Vehicle interior 32 Reducing gas detection sensor 33 Hydrogen fuel tank 34 Reducing gas detection sensor 35 Fuel cell 36 Motor 100 Reducing gas detection sensor 200 Reducing gas detection sensor 300 Fuel battery car

Claims (20)

Consists of a palladium compound and a carbon compound,
The ratio of the number of carbon atoms to the sum of the number of palladium atoms contained in the palladium compound and the number of carbon atoms contained in the carbon compound is 0.50 or more and 0.95 or less. A reducing gas detection material characterized by: A reducing gas sensing material comprising a palladium compound and a carbon compound,
The ratio of the number of carbon atoms to the sum of the number of palladium atoms contained in the reducing gas detecting material and the number of carbon atoms contained in the reducing gas detecting material is 0.50 or more. .95 or less. The electrical conductivity of the reducing gas sensing material before the reducing gas sensing material reacts with the reducing gas is 1×10 at room temperature. ^-8 ～1×10 ^-11 Ω ^-1 cm ^-1 The reducing gas sensing material according to claim 1 or 2, characterized in that: A reducing gas sensing material comprising a palladium compound and a carbon compound,
A reducing gas detecting material, wherein the electrical conductivity of the reducing gas detecting material before reaction with the reducing gas is 1×10 ⁻⁸ to 1×10 ⁻¹¹ Ω ⁻¹ cm ⁻¹ at room temperature. . The reducing gas detecting material reacts with the reducing gas, thereby reducing palladium atoms contained in the reducing gas detecting material and increasing the electrical conductivity of the reducing gas detecting material. Item 5. The reducing gas sensing material according to any one of Items 1 to 4. 6. The reducing gas detecting material according to any one of claims 1 to 5, wherein the reducing gas detecting material reacts with the reducing gas to change the color of the reducing gas detecting material. . The reducing gas sensing material according to any one of claims 1 to 6, wherein the reducing gas is hydrogen gas. The reducing gas sensing material according to any one of claims 1 to 7, wherein the palladium compound is palladium oxide. 9. The carbon compound of claims 1 to 8 , wherein the carbon compound is a compound or a mixture of a plurality of compounds having a C--C single bond, a C--H bond, a C=C double bond, and an OH group. The reducing gas sensing material according to any one of claims 1 to 3. The reducing gas sensing material according to any one of claims 1 to 9 ;
and detection means for detecting a change in the electrical conductivity of the reducing gas detection material caused by the reaction of the reducing gas detection material with the reducing gas. The detection means is
a pair of electrodes in electrical contact with the reducing gas sensing material;
means for supplying a voltage to the pair of electrodes;
a detection circuit for detecting a change in conductivity of the reducing gas sensing material by measuring a change in conductivity between the pair of electrodes;
The reducing gas detection sensor according to claim 10 , comprising: 12. The reducing gas detection sensor according to claim 11 , wherein the shortest distance between the electrodes in the portion where the pair of electrodes face each other is 0.05 [mu]m or more and 100 [mu]m or less. 13. The reducing gas detection sensor according to claim 11 or 12 , wherein each of said pair of electrodes has a comb shape. 14. The reducing gas detection sensor according to any one of claims 10 to 13 , wherein the reducing gas detection material has a film shape. 15. The reducing gas detection sensor according to claim 14 , wherein the film thickness of the reducing gas detection material having a film shape is 5 nm or more and 1000 nm or less. 16. The reducing gas detection sensor according to any one of claims 10 to 15, wherein the reducing gas can be detected at room temperature. The reducing gas detection sensor according to any one of claims 10 to 16 , wherein the reducing gas is hydrogen gas. A moving body comprising the reducing gas detection sensor according to any one of claims 10 to 17 . A hydrogen fuel tank and a fuel cell are provided in the moving object,
19. The moving body according to claim 18 , wherein the reducing gas detection sensor is arranged near at least one of the hydrogen fuel tank and the fuel cell. A method for detecting a reducing gas, which comprises detecting a change in conductivity of the reducing gas detecting material according to any one of claims 1 to 9 due to a reaction with the reducing gas.

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