JP2018004572A - Hydrogen gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen gas sensor which has excellent responsiveness to hydrogen gas even at low operating temperature of 200°C or less, and furthermore superior property of recovery of hydrogen gas detection capability after responding to hydrogen gas.SOLUTION: A hydrogen gas sensor for electrically detecting hydrogen gas is provided that comprises a substrate 10, a hydrogen sensing layer 20 provided on the substrate, and a pair of electrodes 40 provided in the hydrogen sensing layer. The hydrogen sensing layer includes a catalyst that dissociates hydrogen into protons and electrons, and a metal oxide whose electrical resistance is reduced by electrons generated by the dissociation of hydrogen gas by the catalyst, the metal oxide having a chloride concentration of 1.0×10atoms/cmor higher.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a hydrogen gas sensor.

  Since hydrogen does not emit carbon dioxide at the use stage, a low-carbon society can be realized by utilizing water splitting with renewable energy at the production stage. Hydrogen also has the convenience of being easy to store or transport as secondary energy from electricity. For this reason, the movement of hydrogen society is accelerating in Japan. For example, fuel cell vehicles that generate electricity using a chemical reaction between hydrogen and oxygen and run by rotating a motor have been developed. On the other hand, hydrogen gas, which is a gas that explodes in a wide range of 4 to 75% in the atmosphere, is colorless and transparent, does not smell, and is difficult to detect leakage. For this reason, interest in a hydrogen gas sensor for leak detection is increasing.

  There are various types of hydrogen sensor systems in practical use, such as a hot-wire semiconductor type, catalytic combustion type, and gas heat conduction type. The hot wire semiconductor type uses the change in electrical conductivity of the metal oxide semiconductor surface, the catalytic combustion type uses the temperature rise of the platinum wire coil due to catalytic combustion, and the gas thermal conduction type is the target gas. It uses the temperature change of the heating element due to the difference in thermal conductivity between standard gas and standard gas. Among them, as a sensor for detecting leakage, a contact combustion type capable of detecting low concentration hydrogen at a relatively high speed is often used. However, in the contact combustion type, since an operating temperature exceeding 200 ° C. (for example, about 300 to 400 ° C.) is necessary to realize a high-speed response, power consumption increases.

  Therefore, a gaschromic hydrogen sensor has attracted attention as one of novel detection methods that can realize a high-speed response even at a low operating temperature of 200 ° C. or lower. A gaschromic hydrogen sensor includes a metal oxide such as tungsten trioxide whose electrical characteristics change due to adsorption of hydrogen, and a catalyst such as platinum that dissociates hydrogen gas into protons and electrons. In addition to detecting hydrogen gas, it is also possible to electrically detect hydrogen gas (see, for example, Patent Document 1 below).

JP 2006-162365 A (Claim 1 and FIG. 12)

  However, the hydrogen gas sensor described in Patent Document 1 has room for improvement in terms of responsiveness to hydrogen gas and recoverability of hydrogen gas detection ability after response to hydrogen gas at an operating temperature of 200 ° C. or lower. Had.

  The present invention has been made in view of the above circumstances, and has excellent hydrogen gas detection ability after response to hydrogen gas while having excellent response to hydrogen gas even at an operating temperature of 200 ° C. or lower. An object of the present invention is to provide a hydrogen gas sensor having recoverability.

  As a result of repeated studies to solve the above problems, the present inventor has thought that the above problems can be solved by intentionally introducing chlorine as an impurity into the metal oxide of the hydrogen detection layer. As a result of further earnest research, the inventor has excellent responsiveness to hydrogen gas even when the operating temperature is 200 ° C. or lower when the chlorine concentration in the metal oxide exceeds a specific value. However, it has been found that it has excellent recoverability of hydrogen gas detection ability after response to hydrogen gas. Thus, the present inventor has completed the present invention.

That is, the present invention is a hydrogen gas sensor that electrically detects hydrogen gas, comprising a substrate, a hydrogen detection layer provided on the substrate, and a pair of electrodes provided on the hydrogen detection layer, The detection layer includes a catalyst for dissociating hydrogen gas into protons and electrons, and a metal oxide whose electrical resistance is reduced by electrons generated by dissociation of hydrogen gas by the catalyst, and the chlorine concentration in the metal oxide is It is a hydrogen gas sensor that is 1.0 × 10 ¹⁸ atoms / cm ³ or more.

  According to the hydrogen gas sensor of the present invention, it has excellent responsiveness to hydrogen gas even at an operating temperature of 200 ° C. or lower, and has excellent recoverability of hydrogen gas detection ability after response to hydrogen gas. Can be made possible.

  In addition, the inventor has inferred the reason why the above effect is obtained in the hydrogen gas sensor of the present invention as follows.

In the hydrogen gas sensor, in the hydrogen detection layer, protons and electrons generated from the hydrogen gas by the catalyst react with the metal oxide, so that the electric resistance of the metal oxide decreases. For this reason, the hydrogen gas sensor can detect hydrogen gas by measuring the change in electrical resistance at this time. Here, according to the hydrogen gas sensor of the present invention, by setting the chlorine concentration of the metal oxide of the hydrogen detection layer to 1.0 × 10 ¹⁸ atoms / cm ³ or more, protons in the metal oxide of the hydrogen detection layer can be obtained. The moving speed increases, and as a result, the oxygen sites in the metal oxide of the hydrogen detection layer and protons can react quickly. On the other hand, an increase in the proton transfer rate in the metal oxide of the hydrogen detection layer allows the oxygen sites in the metal oxide to remain after the response to the hydrogen gas, that is, after the hydrogen gas no longer exists around the metal oxide. The protons that have reacted with oxygen quickly react with oxygen outside the metal oxide and are easily released as carbon dioxide outside the metal oxide. Therefore, according to the hydrogen gas sensor of the present invention, even when the operating temperature is as low as 200 ° C. or less, the hydrogen gas sensor has excellent responsiveness to hydrogen gas, and excellent recoverability of hydrogen gas detection ability after response to hydrogen gas. It may be possible to have it.

In the hydrogen gas sensor, the carbon concentration in the metal oxide is preferably 2.5 × 10 ¹⁹ atoms / cm ³ or less.

In this case, compared with the case where the carbon concentration in the metal oxide is larger than 2.5 × 10 ¹⁹ atoms / cm ³ , the hydrogen gas sensor is superior to hydrogen gas even at an operating temperature of 200 ° C. or lower. In addition, it has excellent recoverability of hydrogen gas detection ability after response to hydrogen gas.

In the hydrogen gas sensor, the carbon concentration in the metal oxide is preferably 1.3 × 10 ¹⁸ atoms / cm ³ or less.

In this case, as compared with the case where the carbon concentration in the metal oxide is higher than 1.3 × 10 ¹⁸ atoms / cm ³ , the hydrogen gas sensor is much more resistant to hydrogen gas even at an operating temperature of 200 ° C. or lower. While having excellent responsiveness, it has even better recovery of hydrogen gas detection ability after response to hydrogen gas.

In the present invention, the chlorine concentration in the metal oxide or the carbon concentration in the metal oxide refers to the secondary ion mass spectrometry (hereinafter referred to as the following) under the following measurement conditions for the metal oxide in the hydrogen detection layer. The chlorine concentration or the carbon concentration obtained from the secondary ion intensity and time measured when “SIMS” is performed).

(Measurement condition)
Primary ion species: Cs ⁺
Primary ion acceleration energy: 3 keV
Secondary ion polarity: Negative
Oxygen leak: None Charging compensation means: Electron gun (E-gun)

  According to the present invention, there is provided a hydrogen gas sensor having excellent resilience of hydrogen gas detection ability after response to hydrogen gas while having excellent response to hydrogen gas even at an operating temperature of 200 ° C. or lower. Is done.

It is sectional drawing which shows one Embodiment of the hydrogen gas sensor of this invention.

  Hereinafter, an embodiment of the hydrogen gas sensor of the present invention will be described in detail with reference to FIG. FIG. 1 is a cross-sectional view showing an embodiment of the hydrogen gas sensor of the present invention.

  As shown in FIG. 1, the hydrogen gas sensor 100 is provided on a substrate 10, a hydrogen detection layer 20 provided on one surface 10 a of the substrate 10, and another surface 10 b on the opposite side of the substrate 10 from the one surface 10 a. A heater 30 that heats the detection layer 20 and a pair of electrodes 40 that are provided on the surface of the hydrogen detection layer 20 opposite to the substrate 10 and measure the electrical resistance of the hydrogen detection layer 20 are provided.

  The hydrogen gas sensor 100 measures the electrical resistance value of the hydrogen detection layer 20 that changes when hydrogen gas is adsorbed by the hydrogen detection layer 20 by applying a voltage between the pair of electrodes 40, and The hydrogen gas is electrically detected by the change.

The hydrogen detection layer 20 includes a catalyst for dissociating hydrogen gas into protons and electrons, and a metal oxide whose electric resistance is reduced by electrons generated by dissociation of hydrogen gas by the catalyst. Chlorine in the metal oxide The concentration is 1.0 × 10 ¹⁸ atoms / cm ³ or more.

  According to the hydrogen gas sensor 100, it is possible to have excellent recoverability of hydrogen gas detection ability after response to hydrogen gas while having excellent response to hydrogen gas even at an operating temperature of 200 ° C. or lower. It becomes.

  Hereinafter, each of the substrate 10, the hydrogen detection layer 20, the heater 30, and the electrode 40 described above will be described in detail.

<Board>
As the substrate 10, an insulating substrate such as silicon, sapphire, glass, or alumina, a semi-insulating substrate such as SiC, or the like can be used.

  As the glass, alkali-free glass, quartz glass, or the like can be used.

<Hydrogen detection layer>
As described above, the hydrogen detection layer 20 includes a catalyst and a metal oxide.

(Metal oxide)
The metal oxide may be any metal oxide whose electric resistance is reduced by electrons generated by the dissociation of hydrogen gas by the catalyst. Examples of the metal oxide include molybdenum trioxide (MoO ₃ ), tungsten trioxide (WO ₃ ), titanium dioxide (TiO ₂ ), vanadium pentoxide (V ₂ O ₅ ), nickel oxide (NiO ₂ ), and the like. . These can be used alone or in combination of two or more. Among the metal oxides, tungsten trioxide and molybdenum trioxide are preferable, and tungsten trioxide is particularly preferable. In this case, the hydrogen gas sensor 100 can have more excellent responsiveness to hydrogen gas than when the metal oxide includes a metal oxide other than tungsten trioxide (for example, molybdenum trioxide). .

The chlorine concentration in the metal oxide is 1.0 × 10 ¹⁸ atoms / cm ³ or more. In this case, compared with the case where the chlorine concentration in the metal oxide is less than 1.0 × 10 ¹⁸ atoms / cm ³ , the hydrogen gas sensor 100 is more resistant to hydrogen gas even at a low operating temperature of 200 ° C. or lower. While having excellent responsiveness, it has excellent recoverability of hydrogen gas detection ability after response to hydrogen gas.

The chlorine concentration in the metal oxide is preferably 9.5 × 10 ¹⁸ atoms / cm ³ or more. In this case, compared with the case where the chlorine concentration in the metal oxide is less than 9.5 × 10 ¹⁸ atoms / cm ³ , the hydrogen gas sensor 100 is more resistant to hydrogen gas even at a low operating temperature of 200 ° C. or lower. It becomes possible to have excellent recoverability of hydrogen gas detection ability after response to hydrogen gas while having excellent response. However, the chlorine concentration in the metal oxide is preferably 1.0 × 10 ²⁰ atoms / cm ³ or less. In this case, the hydrogen gas sensor 100 can react with high sensitivity even to a low concentration of hydrogen gas. The chlorine concentration in the metal oxide is more preferably 2.0 × 10 ¹⁹ atoms / cm ³ or less.

The carbon concentration in the metal oxide is preferably 2.5 × 10 ¹⁹ atoms / cm ³ or less. In this case, even when the operating temperature is as low as 200 ° C. or less, the hydrogen gas sensor 100 has better responsivity for hydrogen gas, and more excellent recoverability of hydrogen gas detection ability after response to hydrogen gas. .

The carbon concentration in the metal oxide is more preferably 1.3 × 10 ¹⁸ atoms / cm ³ or less. In this case, compared with the case where the carbon concentration in the metal oxide is higher than 1.3 × 10 ¹⁸ atoms / cm ³ , the hydrogen gas sensor 100 is more resistant to hydrogen gas even at a low operating temperature of 200 ° C. or lower. Even more excellent responsiveness, and more excellent recovery of hydrogen gas detection ability after response to hydrogen gas.

However, the carbon concentration in the metal oxide is preferably 1.0 × 10 ¹⁴ atoms / cm ³ or more. In this case, the responsiveness to hydrogen gas in the hydrogen gas sensor 100 is further improved. The carbon concentration in the metal oxide is more preferably 1.0 × 10 ¹⁶ atoms / cm ³ or more.

(catalyst)
The catalyst may be any catalyst that can dissociate the adsorbed hydrogen gas into protons and electrons. Examples of such a catalyst include platinum (Pt), palladium (Pd), iridium (Ir), nickel (Ni), rhodium (Rh), and ruthenium (Ru). You may use these individually by 1 type or in combination of 2 or more types. Of the above catalysts, platinum is particularly preferred.

  The catalyst may be supported on the metal oxide layer or may be attached to the surface of the metal oxide particles, but the catalyst is supported on the metal oxide layer. It is preferable. In this case, compared with the case where the catalyst is not supported on the metal oxide layer, the contact area between platinum and hydrogen is increased, so that the dissociation of hydrogen is performed with higher efficiency and the change in electric resistance is larger. Become.

  The method for reducing the carbon concentration in the metal oxide contained in the hydrogen detection layer 20 is not particularly limited, and examples thereof include heat treatment.

The method for reducing the carbon concentration in the metal oxide by heat treatment is a method in which carbon in the metal oxide is oxidized and discharged as carbon dioxide from the metal oxide, so it must be performed in the presence of oxygen gas. . The heat treatment is not particularly limited as long as it is in the presence of oxygen gas, but is preferably performed under conditions where the oxygen partial pressure is 2 × 10 ⁻¹ atm or more. In general, by increasing the oxygen partial pressure, the oxidation rate can be increased without increasing the heat treatment temperature. Therefore, it is more preferable to perform the heat treatment under conditions where the oxygen partial pressure is 4 × 10 ⁻¹ atm or more. .

  The temperature of the heat treatment is not particularly limited as long as it is a temperature at which oxygen and carbon in the metal oxide react, but 200 to 1500 ° C. is preferable. In this case, oxygen and carbon in the metal oxide easily react even in an air atmosphere.

  Although the time of heat processing is not specifically limited, It is preferable that it is 5 to 120 minutes. In this case, the growth of metal oxide particles can be suppressed.

<Heater>
Any heater 30 may be used as long as it can heat the hydrogen detection layer 20. Examples of the heater 30 include a ceramic heater and a bare heating element. Among these, a ceramic heater is preferable. In this case, since the heating element (resistor) is not in contact with the outside air, oxidation of the heating element can be suppressed, and disconnection and deterioration with time of the heating element can be more sufficiently suppressed.

<Electrode>
The electrode 40 is not particularly limited as long as it is a conductive material that does not exhibit catalytic activity against a reducing gas such as hydrogen gas, hydrocarbon-based gas, or carbon monoxide gas. Examples of the conductive material constituting such an electrode 40 include gold, silver, and an aluminum alloy. Of these, gold is particularly preferable as the conductive material constituting the electrode 40. The shape of the electrode 40 is not particularly limited, and examples of the shape of the electrode 40 include a circular shape, a square shape, and a comb shape. Especially, it is preferable that the shape of the electrode 40 is a comb-tooth shape, since the detection sensitivity with respect to hydrogen gas is high even if the electrode 40 is a microelectrode.

  Next, a method for manufacturing the hydrogen gas sensor 100 will be described.

  First, the substrate 10 is prepared.

  Next, the heater 30 is formed on the other surface 10 b of the substrate 10.

Next, the hydrogen gas detection layer 20 is formed on the one surface 10a of the substrate 10 so that the chlorine concentration in the metal oxide is 1.0 × 10 ¹⁸ atoms / cm ³ or more.

  The hydrogen gas detection layer 20 can be formed, for example, by first forming a metal oxide layer made of a metal oxide, performing a heat treatment, and then supporting a catalyst on the metal oxide layer after the heat treatment.

  The method for forming the metal oxide layer is not particularly limited. Examples of the method for forming the metal oxide layer include a sol-gel method, a CVD (chemical vapor deposition) method, and a PLD (pulse laser ablation). Law. Among these, the sol-gel method is preferably used because a metal oxide layer can be easily formed in the air.

  In the case of forming a metal oxide layer using a sol-gel method, for example, a metal alkoxide solution using metal chloride as a starting material is prepared, and this alkoxide solution is applied onto one surface 10a of the substrate 10 and then fired. Thus, the metal oxide layer may be formed by promoting the dehydration condensation reaction.

  The metal alkoxide solution can be obtained by dissolving a metal chloride in alcohol. As alcohol, methanol, ethanol, isopropanol etc. can be used, for example.

  The chlorine concentration in the metal oxide is controlled by controlling the substitution ratio of the chloro group to the alkoxy group in the metal chloride, or controlling the hydrolysis or dehydration condensation reaction of the metal alkoxide when obtaining the metal alkoxide solution. Can be adjusted. The substitution ratio of the chloro group to the alkoxy group of the metal chloride can be adjusted by controlling the addition amount of a catalyst comprising an acid catalyst or a base catalyst. The acid catalyst is not particularly limited, and examples of the acid catalyst include hydrochloric acid, sulfuric acid, nitric acid, acetic acid, and hydrofluoric acid. In addition, acid catalysts other than fluorine can cause polycondensation before the hydrolysis is completed, and are useful in the case of forming a low-density gel by suppressing the crosslinking reaction. The base catalyst is not particularly limited, and examples of the base catalyst include ammonia. In addition, ammonia is useful when it can be easily removed from the metal alkoxide solution by volatilization after the reaction, and the hydrolysis easily causes the Cl group of the metal chloride to be easily substituted with the alkoxy group. When the chlorine concentration in the metal oxide is adjusted by controlling the hydrolysis of the metal alkoxide, for example, the amount of water in the alcohol when the metal chloride is dissolved in the alcohol to alkoxide may be controlled. Alternatively, the alkoxide reacts with the moisture in the room to cause hydrolysis, so that the hydrolysis can also be controlled by reducing the humidity in the room. The chlorine concentration in the metal oxide by controlling the dehydration condensation reaction can be controlled by adjusting the temperature and reaction time of the metal alkoxide solution and suppressing indiscriminate reactions.

The method for reducing the carbon concentration in the metal oxide layer by the heat treatment is a method in which the carbon in the metal oxide layer is oxidized and discharged as carbon dioxide from the metal oxide layer. Therefore, the heat treatment is performed in an atmosphere containing oxygen gas. Need to do below. At this time, the partial pressure of oxygen gas in the atmosphere is not particularly limited, but is preferably 1 × 10 ⁻¹ atm or more. In this case, by increasing the oxygen partial pressure to 1 × 10 ⁻¹ atm or more, the oxidation can be accelerated without increasing the heat treatment temperature.

The oxygen partial pressure can be adjusted by mixing oxygen and non-oxygen such as nitrogen or a rare gas in a heat treatment furnace while adjusting them using a flow meter. The oxygen partial pressure can be measured using, for example, a zirconia (ZrO ₂ ) solid electrolyte.

  The temperature of the heat treatment is not particularly limited as long as oxygen and carbon in the metal oxide layer react with each other, but is preferably 200 to 1500 ° C. In this case, since the equilibrium oxygen partial pressure is lower than the oxygen partial pressure in the atmosphere, oxygen and carbon in the metal oxide layer can be reacted even by heat treatment in the air atmosphere.

  Note that the oxygen partial pressure and temperature required for reacting the metal and oxygen in the metal oxide can be calculated from the Ellingham diagram of the metal and oxygen in the metal oxide. The metal and oxygen Ellingham diagram in the metal oxide represents the standard production Gibbs energy of oxide per mole of oxygen as a function of temperature.

  Although the time of heat processing is not specifically limited, It is preferable that it is 5 to 120 minutes. In this case, the growth of metal oxide particles can be suppressed.

  Examples of the method for supporting the catalyst on the metal oxide layer include a spin coating method, a dip coating method, a spray coating method, a sputtering method, a CVD method, and a PLD method.

  Finally, a pair of electrodes 40 is formed on the surface of the hydrogen gas detection layer 20 opposite to the substrate 10. The pair of electrodes 40 can be formed, for example, by forming an electrode layer made of a conductive material on the surface of the hydrogen gas detection layer 20 opposite to the substrate 10 and performing photolithography on the electrode layer. it can.

  Thus, the hydrogen gas sensor 100 is obtained.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, the hydrogen gas sensor 100 includes the heater 30, but the hydrogen gas sensor of the present invention does not necessarily include the heater.

  In the above embodiment, the pair of electrodes 40 is provided on the surface of the hydrogen detection layer 20 opposite to the substrate 10, but is provided on the surface of the hydrogen detection layer 20 on the substrate 10 side. Also good.

  In addition, in order to reduce the environmental dependency of the measurement temperature in the hydrogen gas sensor 100, the hydrogen gas sensor 100 may incorporate a bridge circuit using a compensation element. In that case, a metal oxide that does not use a catalyst or a metal oxide that supports inert metal particles that do not act as a catalyst can be used as the compensation element.

  Hereinafter, the content of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

Example 1
First, a Si substrate having a thickness of 0.5 mm and a diameter of 25 mm was prepared, and a platinum heater was produced on the back surface of the Si substrate. Here, the platinum heater was produced using a sputtering method using a metal mask.

Next, a SiO ₂ film was formed as an insulating film on the platinum heater.

  Next, tungsten chloride was dissolved in ethanol under an argon atmosphere in a glove box to prepare a tungsten alkoxide solution. At this time, 10 ml of 13.8 mol / L aqueous ammonia was added as a catalyst to 100 ml of ethanol.

Next, the process of forming a film by applying a tungsten alkoxide solution to the surface of the Si substrate opposite to the insulating film and baking it at 80 ° C. for 1 hour is repeated until the thickness reaches 1 μm. Got the body. Thereafter, the obtained laminate was heat-treated in dry air under the following heat treatment conditions to produce a tungsten trioxide (WO ₃ ) film.

For the WO ₃ film, by SIMS, were measured chlorine concentration and the carbon concentration of WO ₃ film. The results are shown in Table 1. The SIMS measurement conditions were as follows. The chlorine concentration and carbon concentration in the WO ₃ film are values converted based on the sensitivity in HfO ₂ . The unit of chlorine concentration and carbon concentration is “atoms / cm ³ ”.

(Heat treatment conditions)
Heat treatment furnace: Atmospheric furnace heat treatment temperature: 400 ° C
Heat treatment time: 30 minutes Oxygen partial pressure: 2 × 10 ⁻¹ atm
Oxygen gas supply flow rate: 0.2 SLM
Nitrogen gas supply flow rate: 0.8 SLM

(SIMS measurement conditions)
Primary ion species: Cs ⁺
Primary ion acceleration energy: 3 keV
Secondary ion polarity: Negative
Oxygen leak: None Charging compensation means: E-gun (electron gun)

Subsequently, platinum particles as a catalyst were dispersed on the WO ₃ film by a sputtering method. Thus, a hydrogen detection layer was obtained on the Si substrate.

  Next, a pair of comb electrodes made of gold was formed on the hydrogen detection layer by vapor deposition. At this time, the length of the comb teeth was set to 3 mm in each comb electrode. The interval between the comb teeth of the pair of comb-teeth electrodes was 10 μm, and the number of comb-teeth pairs was 30.

  Thus, a hydrogen gas sensor was produced.

(Example 2)
When preparing an alkoxide solution of tungsten, 5 ml of 13.8 mol / L ammonia water was added as a catalyst to 100 ml of ethanol so that the chlorine concentration in the WO ₃ film was as shown in Table 1. A hydrogen gas sensor was fabricated in the same manner as in Example 1 except that the carbon concentration in the WO ₃ film was changed as shown in Table 1 by performing heat treatment under the heat treatment conditions.

(Heat treatment conditions)
Heat treatment furnace: Atmospheric furnace heat treatment temperature: 450 ° C
Heat treatment time: 30 minutes Oxygen partial pressure: 4 × 10 ⁻¹ atm
Oxygen gas supply flow rate: 4 SLM
Nitrogen gas supply flow rate: 6SLM

(Example 3)
When preparing an alkoxide solution of tungsten, 10 ml of 6 mol / L hydrochloric acid was added as a catalyst to 100 ml of ethanol so that the chlorine concentration in the WO ₃ film was as shown in Table 1, and the laminate was subjected to the following heat treatment conditions. A hydrogen gas sensor was produced in the same manner as in Example 1 except that the carbon concentration in the WO ₃ film was changed as shown in Table 1 by heat treatment.

(Heat treatment conditions)
Heat treatment furnace: Atmospheric furnace heat treatment temperature: 600 ° C
Heat treatment time: 30 minutes Oxygen partial pressure: 4 × 10 ⁻¹ atm
Oxygen gas supply flow rate: 4 SLM
Nitrogen gas supply flow rate: 6SLM

Example 4
When preparing an alkoxide solution of tungsten, 10 ml of 6 mol / L hydrochloric acid was added as a catalyst to 100 ml of ethanol so that the chlorine concentration in the WO ₃ film was as shown in Table 1, and the laminate was subjected to the following heat treatment conditions. A hydrogen gas sensor was produced in the same manner as in Example 1 except that the carbon concentration in the WO ₃ film was changed as shown in Table 1 by heat treatment.
(Heat treatment conditions)
Heat treatment furnace: Atmospheric furnace heat treatment temperature: 600 ° C
Heat treatment time: 30 minutes Oxygen partial pressure: 6 × 10 ⁻¹ atm
Oxygen gas supply flow rate: 6SLM
Nitrogen gas supply flow rate: 4SLM

(Example 5)
When preparing an alkoxide solution of tungsten, 30 ml of 6 mol / L hydrochloric acid was added as a catalyst to 100 ml of ethanol so that the chlorine concentration in the WO ₃ film was as shown in Table 1, and the laminate was subjected to the following heat treatment conditions. A hydrogen gas sensor was produced in the same manner as in Example 1 except that the carbon concentration in the WO ₃ film was changed as shown in Table 1 by heat treatment.

(Heat treatment conditions)
Heat treatment furnace: Atmospheric furnace heat treatment temperature: 600 ° C
Heat treatment time: 60 minutes Oxygen partial pressure: 1 atm
Oxygen gas supply flow rate: 10 SLM
Nitrogen gas supply flow rate: 0 SLM

(Comparative Example 1)
When preparing an alkoxide solution of tungsten, 20 ml of 13.8 mol / L ammonia water was added as a catalyst to 100 ml of ethanol so that the chlorine concentration in the WO ₃ film was as shown in Table 2. A hydrogen gas sensor was fabricated in the same manner as in Example 1 except that the carbon concentration in the WO ₃ film was changed as shown in Table 2 by heat treatment under the heat treatment conditions.

(Heat treatment conditions)
Heat treatment furnace: Atmospheric furnace heat treatment temperature: 350 ° C
Heat treatment time: 10 minutes Oxygen partial pressure: 2 × 10 ⁻² atm
Oxygen gas supply flow rate: 0.2 SLM
Nitrogen gas supply flow rate: 9.8 SLM

(Comparative Example 2)
When preparing an alkoxide solution of tungsten, 10 ml of 13.8 mol / L ammonia water was added as a catalyst to 100 ml of ethanol so that the chlorine concentration in the WO ₃ film was as shown in Table 2, and the laminate was formed as follows. A hydrogen gas sensor was fabricated in the same manner as in Example 1 except that the carbon concentration in the WO ₃ film was changed as shown in Table 2 by heat treatment under the heat treatment conditions.

(Heat treatment conditions)
Heat treatment furnace: Atmospheric furnace heat treatment temperature: 350 ° C
Heat treatment time: 10 minutes Oxygen partial pressure: 2 × 10 ⁻¹ atm
Oxygen gas supply flow rate: 2SLM
Nitrogen gas supply flow rate: 8 SLM

(Comparative Example 3)
When preparing an alkoxide solution of tungsten, 5 ml of 13.8 mol / L ammonia water was added as a catalyst to 100 ml of ethanol so that the chlorine concentration in the WO ₃ film was as shown in Table 2, and the laminate was formed as follows. A hydrogen gas sensor was fabricated in the same manner as in Example 1 except that the carbon concentration in the WO ₃ film was changed as shown in Table 2 by heat treatment under the heat treatment conditions.

(Heat treatment conditions)
Heat treatment furnace: Atmospheric furnace heat treatment temperature: 400 ° C
Heat treatment time: 30 minutes Oxygen partial pressure: 2 × 10 ⁻¹ atm
Oxygen gas supply flow rate: 2SLM
Nitrogen gas supply flow rate: 8 SLM

<Characteristic evaluation>
≪Response to hydrogen gas≫
In the hydrogen gas sensors of Examples 1 to 5 and Comparative Examples 1 to 3, the temperature of the hydrogen detection layer was set to 100 ° C. by passing an electric current through the platinum heater, and 1% hydrogen gas (99% dry air gas) was supplied in this state. The 90% response speed was calculated by measuring the resistance value while spraying for 5 minutes. The results are shown in Tables 1 and 2. The response to hydrogen gas was evaluated based on this 90% response speed.
The 90% response speed is the difference ΔR (= R0) between the resistance value (initial resistance value) R0 immediately after being left for 30 minutes after passing the current through the heater and the resistance value R1 after 5 minutes from blowing hydrogen gas. -R1) is defined as 100%, and the time from when the hydrogen gas is blown until the change in resistance value reaches 90% of ΔR. The acceptance criterion 1 was as follows based on ISO26142.
(Acceptance criteria 1)
90% response speed when 1% hydrogen gas is blown is 30 seconds or less

≪Resilience after response to hydrogen gas≫
After stopping the blowing of 1% hydrogen, the resistance value was continuously measured to calculate the 90% recovery rate. The results are shown in Tables 1 and 2. The recoverability after response to hydrogen gas was evaluated based on this 90% recovery rate.
Note that the 90% recovery rate was obtained by setting the difference ΔR ′ (= R0−R2) between the resistance value R2 immediately after stopping the hydrogen gas blowing and the initial resistance value R0 to 100%, and stopping the hydrogen gas blowing. This is the time until the change in resistance value reaches 90% of ΔR ′. The results are shown in Tables 1 and 2. The acceptance criterion 2 was as follows based on ISO26142.
(Acceptance criteria 2)
90% recovery speed when blowing 1% hydrogen gas is 60 seconds or less

≪Pass / fail judgment≫
In Tables 1 and 2, when any one of the acceptance criteria 1 and 2 is not satisfied, “x” is indicated, and when both the acceptance criteria 1 and 2 are satisfied, “◯” is indicated. In particular, when both of the acceptance criteria 1 and 2 were satisfied and the 90% recovery rate when 1% hydrogen gas was blown was 30 seconds or less, “◎” was indicated.

  From the results shown in Table 1, the hydrogen gas sensors of Examples 1 to 5 reached the acceptance standard in terms of responsiveness to hydrogen gas and recoverability after response to hydrogen gas. On the other hand, from the results shown in Table 2, the hydrogen gas sensors of Comparative Examples 1 to 3 did not reach the acceptance standard in terms of responsiveness to hydrogen gas or recoverability after response to hydrogen gas.

  From the above, according to the hydrogen gas sensor of the present invention, the hydrogen gas detection capability is excellent after response to hydrogen gas while having excellent response to hydrogen gas even at an operating temperature of 200 ° C. or lower. It was confirmed to have recoverability.

DESCRIPTION OF SYMBOLS 10 ... Board | substrate 20 ... Hydrogen detection layer 30 ... Heater 40 ... Electrode 100 ... Hydrogen gas sensor

Claims (4)

A hydrogen gas sensor that electrically detects hydrogen gas,
A substrate,
A hydrogen detection layer provided on the substrate;
A pair of electrodes provided on the hydrogen detection layer,
The hydrogen detection layer includes a catalyst for dissociating hydrogen gas into protons and electrons, and a metal oxide whose electrical resistance is reduced by electrons generated by dissociation of hydrogen gas by the catalyst,
The hydrogen gas sensor whose chlorine concentration in the said metal oxide is 1.0 * 10 < ¹⁸ > atoms / cm < ³ > or more. 2. The hydrogen gas sensor according to claim 1, wherein a carbon concentration in the metal oxide is 2.5 × 10 ¹⁹ atoms / cm ³ or less. ^3. The hydrogen gas sensor according to claim 1, wherein a carbon concentration in the metal oxide is 1.3 × 10 ¹⁸ atoms / cm ³ or less.   The hydrogen gas sensor according to any one of claims 1 to 3, wherein the metal oxide includes tungsten trioxide.

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