JP2005331364A - Hydrogen gas sensing film and hydrogen gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen gas sensor using a hydrogen gas sensing film having high sensitivity and high speed response. <P>SOLUTION: The hydrogen gas sensor is constituted by providing a hydrogen gas sensing film 10 with a predetermined film thickness, which is changed in electric resistance when a proton formed by the dissociation of hydrogen gas is injected and reduced or the proton is eliminated to be oxidized, on a pair of the electrodes 20 provided on an insulating substrate. The hydrogen gas sensing film 10 is constituted of an aggregate of microcrystalline particles based on tungsten oxide and a catalyst metal in an oxidized state is provided on the surfaces of the microcrystalline particle tungsten oxide 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydrogen gas detection film and a hydrogen gas sensor in which electrical resistance changes by reducing a film made of an aggregate of fine particle tungsten oxide mainly composed of tungsten oxide by protons generated by dissociating hydrogen gas. It is.

Hydrogen gas sensors include semiconductor sensors, solid electrolyte sensors, contact heat conversion sensors, heat conduction sensors, light detection sensors, and other sensors that detect hydrogen optically in optical waveguides and optical fiber cladding. There are surface sensors with membranes. With the advent of gas liberation and the advent of a hydrogen fuel society, a hydrogen gas sensor capable of detecting gas containing hydrogen at ordinary temperatures from 23 ° C to 25 ° C, having high-speed response, high sensitivity, and high reliability is desired. ing. Conventional gas sensors containing hydrogen include a tin oxide (SnO ₂ ) sensor and an iron oxide (γ-Fe ₂ O ₃ ) sensor having various additives. These sensors have the problem that the operating temperature is as high as 350 ° C. and the power consumption accompanying the operating temperature is high, and a hydrogen gas sensor having sufficient sensitivity and responsiveness near room temperature has been desired.

A hydrogen gas sensor has been proposed and developed in which a tungsten oxide (WO ₃ ) thin film is formed by vacuum deposition on an insulating substrate made of quartz glass, silicon oxide, ceramics, or the like, and changes in electrical resistance due to a gas containing hydrogen. It is known that a change in electrical resistance occurs when a reducing gas contacts a semiconductor surface made of tungsten oxide.

Metal tungsten is vacuum-deposited on a quartz glass substrate, and then the metal tungsten is oxidized to form tungsten oxide. Further, a platinum thin film is formed on the tungsten oxide to produce a laminated thin film gas sensor. Using the laminated thin film gas sensor, a change in electrical resistance due to exposure to hydrogen gas is studied using a mixed gas containing 0.1% hydrogen gas in the air. However, this method has a problem that the detection sensitivity of hydrogen gas varies depending on the oxidation conditions of the metallic tungsten. This is because the structure of tungsten oxide is unstable due to the non-uniformity of tungsten oxide in the film thickness direction. In addition, this document did not describe the relationship between the structure of tungsten oxide and the detection sensitivity of hydrogen gas. (Non-Patent Document 1; APPLIED PHYSICS Letters, Vol. 11, No. 8, 1967, pages 255-257, P. J. Shaver)
In a thin film gas sensor using a sputtering deposition method in an inert gas atmosphere containing oxygen on an insulating substrate made of quartz glass, silicon oxide or ceramics, a thin film of tungsten oxide WO _3- δ (here, δ <0.2) is used. A thin film gas sensor is described. Furthermore, a selective thin film gas sensor is also described in which an activated film made of a noble metal or metal oxide is provided on the surface of the WO ₃ -δ thin film. However, these tungsten oxide films have low sensitivity to hydrogen gas. In this paper, the detailed structure of the noble metal or metal oxide as the active film is not mentioned. (Patent Document 1; JP-A-57-74648)

Regarding a hydrogen gas sensor, there is a disclosure of a hydrogen gas sensor in which an amorphous tungsten oxide thin film is provided over a pair of electrodes provided on the same substrate and platinum or palladium is further formed in an island shape thereon. In this structure, a hydrogen gas sensor using a tungsten oxide thin film is manufactured by using a resistance heating vapor deposition method so as to be an amorphous tungsten oxide thin film having a predetermined density, thereby increasing the detection sensitivity of hydrogen gas. However, the amorphous tungsten oxide thin film has a problem that density control is difficult, reliability is poor, and humidity is easily affected. This is due to the structural instability of the amorphous tungsten oxide thin film. In addition, the platinum thin film on the amorphous tungsten oxide thin film is easily affected by a flammable gas other than hydrogen gas, and the detection sensitivity of hydrogen gas varies. Palladium also has a problem that the detection sensitivity of hydrogen gas gradually deteriorates due to hydrogen vulnerability. (Patent Document 2; Patent Publication 1799658)
An n-type semiconductor such as tin oxide (SnO ₂ ) on a ceramic substrate in a gas sensor in which the electrical resistance of the sensitive layer changes according to the concentration of combustible gases such as carbon monoxide (CO), hydrogen (H ₂ ), and hydrocarbons A gas-sensitive layer based on a metal oxide, the sensitive film having a combination of sintered particles of a semiconductor metal oxide material, and covering the surface of the combination with gold and / or a gold alloy A combustible gas sensor is described. However, the sensitivity of hydrogen gas was low. (Patent Document 3; Japanese Translation of PCT International Publication No. 10-510919)

There is an attempt to attach a catalytic metal that adsorbs and dissociates hydrogen gas to tungsten oxide (WO ₃ ) for normal temperature operation. John E.M. Benson, H.M. W. Kohn and Michel Boudart et al. Kneaded tungsten oxide (WO ₃ ) powder with chloroplatinic acid (H ₂ PtCl ₆ ), screen-printed on a substrate, followed by atmospheric 600 ° C. for 10 hours at 425 ° C. A hydrogen gas detection film made of platinum mixed tungsten oxide is synthesized by calcining at 3 ° C. for 3 hours. As a result, the hydrogen gas detection film made of platinum mixed tungsten oxide was exposed to hydrogen gas at room temperature, and the hydrogen gas detection film increased in weight. doing. However, this paper does not mention the relationship between the structure of tungsten oxide and its crystal state, or the structure and crystal state of platinum and the detection sensitivity of hydrogen gas. This paper also does not describe changes in hue or electrical resistance due to hydrogen gas exposure. (Non-patent document 2, JOUNAL OF CATALYSIS Vol. 5, pp 307-313 (1966))

In addition, focusing on the crystalline state of the tungsten oxide thin film, the X-ray diffraction pattern (001) index X-ray diffraction intensity of the tungsten oxide thin film is increased, and the X-ray diffraction pattern (001) is realized. A highly sensitive photodetection type hydrogen sensor using a hue change, characterized in that it has a laminated structure of a tungsten oxide thin film with an increased index crystal plane and a catalytic metal, is disclosed. In this patent, the tungsten oxide thin film is formed as a crystal film having a high orientation in the X-ray diffraction pattern index (001), thereby reducing the variation in the amount of light absorption at the time of hydrogen gas detection. It is described that variation can be suppressed. However, the annealing temperature of the tungsten oxide (WO ₃ ) thin film in oxygen gas increases and the X-ray diffraction intensity of the crystal plane with index (001) increases, but the detection sensitivity of hydrogen gas increases monotonously. Decrease without. Further, this patent does not disclose the relationship between the detection sensitivity of hydrogen gas and the X-ray diffraction intensity of the crystal plane of the X-ray diffraction pattern index (001) of the tungsten oxide (WO ₃ ) thin film. Furthermore, as a catalyst metal disclosed in the above patent, in the case of a hydrogen sensor having a palladium thin film laminated on a tungsten oxide thin film, a hydrogen exposure cycle test results in hydrogen sensitivity due to the weakness of palladium due to hydrogenation. There is a problem of deterioration. On the other hand, in the case of a hydrogen sensor having a platinum thin film laminated on a tungsten oxide thin film as a catalyst metal according to another embodiment, it is easily affected by a gas other than hydrogen gas, resulting in variations in detection sensitivity of hydrogen gas. There's a problem. (See Patent Document 4; JP-A-62-257047)
P. J. et al. By Shaver, APPLIED PHYSICS Letters, Vol. 8, 1967, pages 255-257. John E.M. Benson, H.M. W. By Kohn and Michael Boudart, JOUNAL OF CATALYSIS, 5, 1966, 307-313. JP-A-57-74648 Japanese Patent No. 1799658 Japanese National Patent Publication No. 10-510919 JP-A-62-257047

  However, the conventional gas leak detection sensor containing hydrogen has a practical problem that the detection sensitivity of hydrogen gas near normal temperature is low, the response speed is very slow, and the long-term reliability is poor.

 The present invention solves the conventional problems, and increases the detection sensitivity of a gas containing hydrogen at around room temperature, and at the same time provides a hydrogen gas detection film having high-speed response to hydrogen gas. An object of the present invention is to provide a hydrogen gas sensor using the hydrogen gas detection film.

  In order to solve the conventional problems, the hydrogen detection film of the present invention has an electric resistance that is changed by injecting protons generated by dissociating hydrogen gas and then reducing or oxidizing the protons. A hydrogen gas detection film, wherein the detection film is composed of an aggregate of crystalline fine particles mainly composed of tungsten oxide, and contains a catalytic metal in an oxidized state on a surface of the crystalline fine particle tungsten oxide. It is what you did.

  In addition, the present invention provides an electrical resistance in which protons generated by dissociating hydrogen gas are injected and reduced on a pair of electrodes provided on an insulating substrate, or reduced by being desorbed and oxidized. A hydrogen gas sensor having a detection film of a predetermined thickness that changes, wherein the detection film is composed of an aggregate of crystalline fine particles mainly composed of tungsten oxide, and is in an oxidized state on the surface of the crystalline fine particle tungsten oxide. It is characterized by containing a catalytic metal.

  In addition, the present invention has a predetermined film thickness in which electrical resistance is changed by injecting protons generated by dissociating hydrogen gas into an insulating substrate and then reducing or oxidizing the protons by desorption. A hydrogen gas sensor comprising a sensing film and a pair of electrodes on the sensing film, wherein the sensing film is composed of an aggregate of crystalline fine particles mainly composed of tungsten oxide and is oxidized on the surface of the crystalline fine particle tungsten oxide. The catalyst metal in a state is contained.

  As described above, according to the present invention, the detection sensitivity of hydrogen gas is increased near normal temperature, and a gas detection film containing hydrogen having a fast hydrogen gas responsiveness is provided. A hydrogen gas sensor having high sensitivity and high sensitivity can be realized.

  As a result of various investigations on the synthesis conditions of tungsten oxide, which is a detection film, for the purpose of improving the detection sensitivity of hydrogen gas, the tungsten oxide was made into fine particles, the crystalline state of the fine tungsten oxide, the average particle diameter of the fine tungsten oxide, the fine particle oxidation Ideal for oxygen defect state of tungsten, oxygen / tungsten atomic ratio of fine tungsten oxide, oxidation state of catalytic metal contained on fine tungsten oxide surface, type of catalytic metal, and average particle diameter of catalytic metal The inventors have found that there are conditions.

By bringing the catalytic metal into an oxidized state, the catalytic metal has an increased ability to withdraw electrons (electron acceptor), increasing the rate of adsorption and dissociation of hydrogen gas (H ₂ ) on the catalytic metal, and protons (H ⁺ ). By increasing the generation rate of hydrogen, both hydrogen gas detection speed and detection sensitivity are improved. Therefore, high-speed response and high sensitivity can be realized in hydrogen gas detection. Furthermore, in the fine particle tungsten oxide, by controlling the structure of the tungsten oxide, the number of oxygen defects (vacancy) in the fine particle tungsten oxide can be optimized, and the hydrogen detection sensitivity can be improved. This oxygen defect acts as a proton conduction channel and causes an increase in the electron carrier concentration. By both effects, the electric conductivity of the detection film is improved and the detection sensitivity of hydrogen gas is increased.

Protons and electrons generated on the catalytic metal move through oxygen vacancies of fine particle tungsten oxide, which is the main component of the hydrogen gas detection film, respectively. At this time, tungsten (W) of fine particle tungsten oxide is W ^6. Reduction from ⁺ to W ⁵⁺ forms tungsten bronze (H _x WO ₃ ). As a result, the electrical conductivity of the particulate tungsten oxide increases by several orders of magnitude. Therefore, leakage of hydrogen gas can be detected by a change in the electrical resistance of the thin film composed of the fine particle tungsten oxide. Note that, when tungsten bronze is formed from tungsten oxide, the color of the gas detection film changes from light yellow green to dark blue, so that hydrogen gas leakage detection due to hue change is also possible.

  Hereinafter, a hydrogen gas detection film and a hydrogen gas sensor using the same will be described in detail with reference to the drawings.

 1 is an enlarged cross-sectional view of the hydrogen gas detection film 10 of FIG. 2 according to the first embodiment of the present invention, and is an enlarged view of a cross-section A-A ′ of the hydrogen gas sensor of FIGS. 2 and 10.

  In FIG. 2, the structure of the hydrogen gas detection film 10 is represented by the hydrogen gas detection film 6 shown enlarged in FIG. 1. FIG. 1 is enlarged and emphasized in order to explain the cross-sectional structure of the hydrogen gas detection film 10 of the present invention. The film thickness of the hydrogen gas detection film 6 is 100 nm to 5 μm. The hydrogen gas detection film 6 is composed of an aggregate of fine particle tungsten oxide 1 having a particle diameter of 15 nm to 80 nm and has a gap 3. The gap 3 is formed by evaporating the solvent components of water and alcohol contained in a colloidal solution, which is a synthetic material of particulate tungsten oxide described later, when heat treatment is performed at 350 ° C. to 600 ° C. during manufacture of the hydrogen gas detection film. The The structure of the gap 3 of the fine particle tungsten oxide aggregate is related to gas adsorption. As the gap 3 increases, the hydrogen gas adsorption area increases and the detection sensitivity of hydrogen gas improves. The surface of the fine particle tungsten oxide 1 has a catalyst metal 2 having a particle diameter of 2 nm to 35 nm. The particle size of the fine particle tungsten oxide 1 is preferably larger than the particle size of the fine particle of the catalyst metal 2. The larger the area of the catalyst metal 2 exposed on the surface of the fine particle tungsten oxide, the greater the adsorption / dissociation action of hydrogen gas, Proton production increases. Although FIG. 1 shows that a plurality of metal catalysts 2 exist on the surface of the fine particle tungsten oxide, the number of catalyst metals on the surface of the fine particle tungsten oxide is not limited.

When the hydrogen gas detection film 10 composed of tungsten oxide aggregates and gaps is quantitatively expressed in terms of density, in the present invention, the filling density of the hydrogen gas detection film 10 made of particulate tungsten oxide is 4.0 g / cm ^3. ~12.0g / cm ^3, preferably is ^{4.2g / cm 3 ~6.5g / cm 3} , a high detection sensitivity of the hydrogen gas.

  A method for manufacturing the hydrogen gas sensor 70 having the structure of the hydrogen gas detection film 6 shown in FIG. 1 will be described below in detail with reference to the schematic diagram of the hydrogen gas sensor in FIG.

  In FIG. 2, the structure of the hydrogen gas detection film 10 is represented by the hydrogen gas detection film 6 shown enlarged in FIG. 1.

The electrode 20 is made of a high melting point metal such as gold (Au) or a gold alloy, platinum (Pt) or a platinum alloy, molybdenum (Mo), tantalum (Ta), or niobium (Nb) on the insulating substrate 30 and is resistant to corrosion. The metal material is formed by vapor deposition. As the vapor deposition method, sputtering vapor deposition, electron beam vapor deposition, ion plating vapor deposition, or the like can be used. Thereafter, a pair of electrodes having an electrode width of 0.3 mm, an electrode interval of 0.1 mm, and an electrode length of 20 mm are formed by a known photolithography method.
Moreover, as an electrode formation method, you may form an electrode by the screen-printing method or the inkjet method. At this time, a material having heat resistance of 700 ° C. or higher is preferable.

The insulating substrate 30 only needs to be electrically insulative, such as a quartz substrate, a silicon substrate, a silicon carbide (SiC) substrate, or a ceramic substrate. Specifically, the electrical conductivity of the substrate is fine particle tungsten oxide. The electrical conductivity of the hydrogen gas detection film that is not exposed to the hydrogen gas should be less than 10 ⁻⁴ (Ω · cm) ⁻¹ and have heat resistance of 700 ° C. or higher. In a silicon substrate or silicon carbide (SiC) substrate, an insulating film such as a silicon oxide film (SiO _x ; where x is 1 to 2) or a nitrogen silicon film (SiN _x ; where x is 1.0 to 1.33) is used. Then, a hydrogen gas detection film 6 or 10 made of particulate tungsten oxide is formed on the insulating film by a sol-gel method. Details of the method for producing fine-particle tungsten oxide by the sol-gel method are shown below.

Dissolve 2.5 g of tungstic acid (H ₂ WO ₄ ) in 31 ml of methanol, stir at room temperature for 30 minutes, add 18 ml of pure water, and then add a predetermined amount of aqueous catalyst metal salt solution to add tungstic acid (H ₂ WO ₄ ). To obtain a colloidal solution. For example, when platinum is used as the catalyst metal, a chloroplatinic acid aqueous solution (H ₂ [PtCl ₆ ] · xH ₂ O) is added to the colloidal solution of tungstic acid in a proportion of 0.3 to 30 mol% with respect to tungsten. To obtain a tungstic acid colloidal solution containing a catalytic metal.

  In the above sol-gel synthesis, methanol was used as the reducing agent, but it is not limited to methanol, and various reducing agents such as ethanol, propanol, and glucose can be used. Can be controlled. Here, the hydrogen of the tungstic acid and the hydroxyl group of the reducing agent react with each other to cause dehydration condensation, and the tungsten oxide starts to gel. Stabilization of the sol-gel state of tungsten oxide can be controlled by utilizing the difference in the dissociation rate of hydroxyl groups depending on each reducing agent.

Further, as a precursor of tungstic acid, an aqueous solution of sodium tungstate (Na ₂ WO ₄ ) may be used, and tungstic acid may be obtained by H ⁺ ion exchange resin.

  Further, alkoxide tungsten may be used as a precursor of tungstic acid.

A colloidal solution of tungstic acid (H ₂ WO ₄ ) can be obtained from anhydrous chlorotungsten (WCl ₆ ) and anhydrous ethanol.

  Furthermore, the catalyst metal salt may be an inorganic salt or an organic salt. For example, inorganic salts include chloride salts, nitrate salts, sulfate salts, etc., and organic salts include carboxylate salts, dicarboxylate salts, and acetylacetone complex salts.

  Next, a method for manufacturing the hydrogen gas sensor 70 will be described.

  A colloidal solution of tungstic acid containing a catalytic metal is applied onto a pair of electrodes 20 provided in advance on an insulating substrate by spin coating to form a hydrogen gas detection film 10 made of particulate tungsten oxide with a thickness of 100 nm to 5 μm, preferably A film thickness of 200 nm to 3 μm is formed.

  Note that the method of applying tungsten oxide is not limited to the above spin coating, and it is sufficient if it can be formed so as to cover a pair of electrodes, and a screen printing method or an ink jet method may be used.

  After that, by calcining for 5 hours at a calcining temperature of 350 ° C. to 700 ° C. in a flow state of air of 50 ml / min, tungsten catalyst is crystallized by partially containing a platinum catalyst metal on the surface. A hydrogen gas sensor 70 having a detection film 10 having a film thickness of 100 nm to 3 μm made of a hydrogen gas detection film 6 in which fine particles of tungsten oxide were assembled was produced. In addition, water and alcohol components, which are solvents contained in the colloidal solution, are evaporated by the calcination treatment, and the film thickness of the hydrogen gas detection film 10 after baking is approximately 40% to the film thickness before baking. Reduce to 60%. Further, the hydrogen gas detection film 6 has a gap 3.

  Then, one end of each of the pair of electrodes 20 is exposed to form the lead wire 40, the lead wire 40 is formed with Ag paste, and an electric field strength of about 10 V / cm is applied by the DC power source 60. In order to measure the electrical resistance value or electrical conductivity between the pair of electrodes 20, a microammeter 50 is connected to measure the hydrogen gas detection sensitivity and responsiveness.

  An AC impedance measuring device may be used instead of the microammeter, and the present invention is not limited to the measuring method. The hydrogen gas detection layer 10 may cover the pair of electrodes 20.

  The detection sensitivity of hydrogen gas is measured using the measurement system shown in FIG. 2 under the conditions of an operating temperature of 25 ° C., a hydrogen gas concentration of 1% in air, and a relative humidity of 50%.

Here, the detection sensitivity of the hydrogen gas, expressed by the ratio of the electric resistance R _e of the resistance value R ₀ and hydrogen gas concentration of 1% exposure state in air at state not exposed to hydrogen gas (= R ₀ / R _e) . That is, the detection sensitivity of hydrogen gas = R ₀ / _Re .

As the hydrogen gas detection sensitivity, in consideration of sensitivity variations and / or response speed variations, R ₀ / _Re is 10 or more, preferably 100 or more, as a hydrogen gas sensor.

  When the hydrogen gas is detected, the hydrogen gas detection film 10 absorbs and dissociates the hydrogen gas on the catalyst metal to generate protons, and the protons are injected into the fine particle tungsten oxide, thereby reducing the fine particle tungsten oxide, A hydrogen gas detection film made of an aggregate of fine particles mainly composed of tungsten oxide exhibits a hue change from light green to blue, and at the same time, the electric resistance of the hydrogen gas detection film 10 is reduced by hydrogen gas.

  The inventor conducted the following investigation on the structure of the hydrogen gas detection film that achieves this hydrogen gas detection sensitivity.

  First, the relationship between the amount of catalytic metal contained on the surface of fine particle tungsten oxide and the detection sensitivity of hydrogen gas was examined below.

A predetermined amount of the catalyst metal is added as an aqueous solution of a catalyst metal salt to the above-described tungstic acid colloid solution during the sol-gel synthesis. For example, when platinum is used as a catalyst metal, 0.0125 mol / l of a chloroplatinic acid aqueous solution (H ₂ [PtCl ₆ ] · xH ₂ O) is added to a colloidal solution of tungstic acid in 4 ml, 8 ml, 24 ml, 48 ml, and 80 ml. Is added to obtain a colloidal solution of tungstic acid containing platinum catalysts with a platinum catalyst to tungsten molar ratio of 0.5%, 1%, 3%, 6% and 10%, respectively. These colloidal solutions are applied by spin coating so as to cover a pair of pre-formed electrodes, and then calcined for 5 hours at a calcining temperature of 350 ° C. to 700 ° C. in a flow state of air 50 ml / min. By doing this, the gas sensor shown in FIG. 2 is produced. Note that the method of applying tungsten oxide is not limited to the above spin coating, and any method such as a screen printing method or an ink jet method can be applied as long as it can be formed so as to cover a pair of electrodes.

  The detection sensitivity of hydrogen gas was measured under the conditions of room temperature of 25 ° C., hydrogen gas concentration in air of 1%, and relative humidity of 50%. At the same time, the relationship between the crystallinity and surface state of the fine particle tungsten oxide of the gas sensor element, the detection sensitivity of hydrogen gas, the amount of catalyst metal, and the oxidation state of the catalyst metal was investigated.

  The calcining treatment conditions such as the heat treatment temperature and time are not limited to the above production conditions, but the fine tungsten oxide, which is the structure of the tungsten oxide detection film of the present invention, is used as the main component. If the catalyst metal in the oxidized state is contained on the surface of the metal, the adsorption and dissociation of hydrogen gas is facilitated. If the catalyst metal in the oxidized state is contained, the oxidized catalyst metal acts as an electron acceptor. The detection sensitivity of hydrogen gas according to the reduction potential can be realized.

  FIG. 3 shows an X-ray diffraction pattern of the hydrogen gas detection film 10 composed of an aggregate of fine particle tungsten oxide containing the catalytic metal of the present invention. Here, the catalyst metal is platinum and the ratio to tungsten is 3 mol%, and the legend of each X-ray diffraction pattern is the calcining temperature at the time of manufacturing the hydrogen gas detection film. When observing the X-ray diffraction pattern, an X-ray diffraction main peak of tungsten oxide is observed at an X-ray diffraction angle 2θ = 20 ° to 30 °, and higher-order X is observed at a wider angle than the X-ray diffraction angle 2θ = 30 °. From the fact that a line diffraction peak is observed, it can be seen that the hydrogen gas detection film 10 has a crystal structure. In particular, 2θ = 24.2 ° corresponds to the triclinic main diffraction peak crystal lattice plane index (200) of tungsten oxide, and 2θ = 23.1 ° is a monoclinic system of tungsten oxide. The main diffraction peak crystal lattice plane index (001). FIG. 3 also shows another triclinic peak (020) of tungsten oxide.

  Further, the diffraction intensity of the X-ray diffraction main peak of tungsten oxide decreases as the ratio of the catalytic metal to tungsten increases, but when the ratio of the catalytic metal to tungsten is 0.3 to 30 mol%, the X-ray diffraction of tungsten oxide. The presence of a crystal phase can be confirmed from the peak (not shown).

  On the other hand, according to the observation of the hydrogen gas detection film of a scanning electron microscope (SEM), it is confirmed that the hydrogen gas detection film is an aggregate of tungsten oxide fine particles, and the average particle diameter of the fine particle tungsten oxide is determined by SEM. As a result of calculating from the particle size frequency distribution of about 100 particles, the average particle size of the fine particle tungsten oxide was 15 nm to 100 nm. Therefore, from observation of an X-ray diffraction pattern and a scanning electron microscope (SEM), the hydrogen gas detection film is an aggregate of fine particle tungsten oxide having an average particle diameter of 15 nm to 100 nm, and each fine particle tungsten oxide is crystallized. It was confirmed.

  FIG. 4 shows the ratio of triclinic and monoclinic X-ray diffraction main peaks of tungsten oxide obtained from the X-ray diffraction pattern of tungsten oxide in FIG. 3 (= (001) / ( 200) and hydrogen gas detection sensitivity dependence in Fig. 4. In Fig. 4, the sol-gel method is used for the synthesis method of the hydrogen gas detection film, and the catalyst metal at the time of sol-gel synthesis is platinum and platinum relative to tungsten. The molar ratio of the catalyst was 3% The calcining conditions were calcining conditions at a temperature of 350 ° C. to 700 ° C. for 5 hours with air 50 ml / min, and returned to room temperature after the calcining treatment. The X-ray diffraction pattern of the gas detection film 10 was measured, and the hydrogen gas detection sensitivity was measured using the hydrogen gas sensor 70 having the measurement system of Fig. 2. The measurement conditions were an operating temperature of 25 ° C and in the air. And 1% oxygen gas concentration, relative humidity is 50% for.

As shown in FIG. 4, the ratio of the main peak (= (001) / (200)) increases as the calcining temperature rises. For the detection sensitivity of the hydrogen gas, the ratio of the main peak (= (001) / (200)), by 0.53 from 0.94, the detection sensitivity R ₀ / R _e of the hydrogen gas is 10 or more and A hydrogen gas sensor 70 can be realized. The mechanism for increasing the sensitivity of this hydrogen gas detection is that when the tungsten oxide hydrogen detection film has two crystal phases, a shift defect layer (shear defect) is formed at the interface between the crystal phases. In the altered layer, oxygen defects are easily formed, the electron concentration is increased, and a proton transfer path is easily formed. Therefore, it is considered that proton mobility with high mobility is obtained and electric conductivity is increased. Here, the detection sensitivity of hydrogen gas is increased when the two crystal phases have a ratio of the main peak of the triclinic and monoclinic X-ray diffraction patterns. In the present invention, the triclinic main diffraction peak crystal lattice index (200) and the monoclinic main diffraction peak crystal of the tungsten oxide hydrogen detection film 6 are described. It is not limited to the lattice plane index (001).

FIG. 5 shows the relationship between the average particle diameter of fine tungsten oxide and the detection sensitivity of hydrogen gas. The average particle diameter of the fine particle tungsten oxide is controlled by the treatment temperature and the treatment time in the sol-gel synthesis when forming the fine particle tungsten oxide. The fine particle tungsten oxide used for the measurement of the gas sensitivity characteristics in FIG. 5 was prepared by dissolving 2.5 g of tungstic acid (H ₂ WO ₄ ) in 31 ml of methanol at the time of sol-gel synthesis and stirring at room temperature for 30 minutes. 18 ml was added to prepare a colloidal solution. Platinum is used as the catalyst metal, and 8 ml of 0.0125 mol / l of chloroplatinic acid aqueous solution is added to the colloidal solution of tungstic acid, and the colloid is placed on the insulating substrate 30 so as to cover the pair of electrodes 20 formed in advance. The solution was applied by spin coating, and was calcined under a flow condition of 50 ml / min of air as calcining conditions, and each was calcined at a temperature of 300 ° C. to 800 ° C. for 5 hours, and then naturally cooled to 25 ° C.

  The average particle size of the fine particle tungsten oxide 1 was calculated from the frequency distribution of the particle size of about 100 fine particle tungsten oxides using a scanning electron microscope (SEM) in each calcining condition sample. The hydrogen gas detection sensitivity was measured using a hydrogen gas sensor 70 in which a hydrogen gas detection film was produced under each calcining condition using the evaluation system shown in FIG.

  The hydrogen gas detection film has the same structure in FIGS. 1, 2, and 10. As can be seen from FIG. 5, the fine particle tungsten oxide 1 constituting the hydrogen gas detection film 6 or 10 of the present invention has an average particle size. When the diameter (shorter length) is 15 nm to 80 nm, a hydrogen gas detection sensitivity of 10 or more is obtained. The reason for this improvement in detection sensitivity of hydrogen gas is that the surface area on which the catalytic metal can be adsorbed can be increased by increasing the average particle size of the fine particle tungsten oxide from 15 nm to 80 nm, thereby realizing high sensitivity of hydrogen gas. . On the other hand, when the average particle size of the fine particle tungsten oxide is smaller than 15 nm, the surface area on which the catalytic metal can be adsorbed is reduced, and the proton and electron scattering in the tungsten oxide is increased and the electric conductivity is lowered. Decrease.

  FIG. 6 shows the ratio of the number of oxygen atoms and the number of tungsten atoms constituting the fine-particle tungsten oxide determined by X-ray photoelectron spectroscopy (XPS) measurement | O | / | W | and the detection sensitivity dependence of hydrogen gas. Indicates. The ratio between the number of oxygen atoms and the number of tungsten atoms is 15 KV, 300 W using an X-ray electron spectrometer (model number AXIS-HSU) manufactured by Shimadzu, and MgKα: 1253.6 eV is used as the X-ray source. The hydrogen gas detection film 6 is synthesized by the following sol-gel method.

Specifically, 2.5 g of tungstic acid (H ₂ WO ₄ ) is melted in 31 ml of methanol, stirred at room temperature for 30 minutes, and 18 ml of pure water is added to prepare a colloidal solution. Platinum is employed as the catalyst metal, and 1.8 ml, 3.6 ml, 11 ml, and 23 ml of 0.1 mol / l chloroplatinic acid aqueous solution are added to the colloidal solution of tungstic acid, and the ratio of the platinum catalyst to tungsten is 1. Tungstic acid colloidal solutions containing 8 mol%, 3.6 mol%, 11 mol%, 23 mol% platinum catalyst are synthesized. The calcination conditions were such that the calcination temperature was 350 ° C. to 700 ° C. for 5 hours in a flow state of air of 50 ml / min.

  After calcination, the mixture was naturally cooled to room temperature of 25 ° C., hydrogen gas concentration in air was set to 1%, relative humidity was set to 50%, and hydrogen gas detection sensitivity was measured.

  As shown in FIG. 6, the ratio of the number of oxygen atoms and the number of tungsten atoms constituting the fine particle tungsten oxide | O | / | W | is increased from 350 ° C. to 700 ° C. without depending on the molar ratio of the platinum catalyst. Increase with increasing

  In FIG. 6, especially when the ratio of the platinum catalyst to tungsten is 1.8 mol%, the ratio of the number of oxygen atoms to the number of tungsten atoms | O | / | W | When | O | / | W | is 2.60, the hydrogen gas detection sensitivity reaches a maximum value 320, and the hydrogen gas detection sensitivity tends to decrease slightly as | O | / | W | increases. When | O | / | W | = 2.63, the hydrogen gas detection sensitivity is 80. Therefore, when the ratio of the platinum catalyst to tungsten is 1.8 mol%, the ratio of the number of oxygen atoms to the number of tungsten atoms | O | / | W | is 2.54 to 2.63. A detection sensitivity of hydrogen gas of 10 or more is obtained, which is preferable as a detection film for a hydrogen gas sensor. More preferably, when | O | / | W | is 2.56 to 2.62, a hydrogen gas detection sensitivity of 100 or more can be realized.

  When the ratio of platinum catalyst to tungsten is 3.6 mol%, the ratio of the number of oxygen atoms to the number of tungsten atoms | O | / | W | is 2.54 to 2.63, and the detection sensitivity of hydrogen gas is 10 or more. Particularly, when | O | / | W | is in the range of 2.55 to 2.63, a hydrogen gas detection sensitivity of 100 or more can be obtained.

  When the ratio of the platinum catalyst to tungsten is increased to 11 mol% or more, the detection sensitivity of hydrogen gas decreases.

  At a platinum catalyst ratio of 23 mol% with respect to tungsten, the hydrogen gas detection sensitivity was 10 or less. The inventors speculate that this is because as the ratio of the platinum catalyst to tungsten increases, the platinum particles agglomerate, the particles become huge, and the surface area of the catalytic metal adsorbed by hydrogen gas decreases.

  The improvement in hydrogen gas detection sensitivity due to the above oxygen defects increases the electron carrier concentration by increasing the oxygen defects of the fine particle tungsten oxide, increases the electrical conductivity, and increases the gap 3 into which the protons of the fine particle tungsten oxide enter, This is because a proton conduction channel is effectively formed in each fine particle tungsten oxide. Therefore, there exists an optimal ratio of oxygen atoms to tungsten atoms | O | / | W |. The reason why the hydrogen gas detection sensitivity decreases in a region where there are many oxygen defects, that is, where | O | / | W | is small, is that the particle size of tungsten oxide is too small due to the low calcining temperature, and the grain boundary of tungsten oxide is reduced. It is believed that the proton and electron scattering at this point becomes more dominant than the conduction, and the electric conductivity is lowered and the hydrogen gas detection sensitivity is lowered.

  On the other hand, when | O | / | W | is increased, the detection sensitivity of hydrogen gas decreases. When | O | / | W | is 2.60 or more, the calcining temperature is heated to 550 ° C. or more. At the calcining temperature within that range, the increase in the calcining temperature, the effect of increasing the electrical resistance because the oxygen defects decrease and the electron carrier concentration decreases, Since the average particle diameter increases, it is interpreted that the aggregation of tungsten oxide occurs and the surface area of tungsten oxide decreases, thereby reducing the amount of catalytic metal adsorbed on the tungsten oxide surface.

  FIG. 7 shows the relationship between the oxidation state of the platinum metal catalyst contained on the surface of the particulate tungsten oxide and the detection sensitivity of hydrogen gas. The measurement of the oxidation state of platinum was evaluated by the aforementioned X-ray photoelectron spectroscopy (XPS) measurement.

As shown in FIG. 8, it has an electronic state 4f _2/7 peak (Pt ⁰ ) of metallic platinum that is not oxidized to a binding energy of 70.9 eV in X-ray photoelectron spectroscopy of a platinum metal catalyst. Oxidized platinum chemically shifts to a higher energy side by bonding with oxygen, and exhibits a bivalent oxidized platinum (PtO) peak at a binding energy of 73.7 eV. Further, oxidation progresses, and a peak appears at a binding energy of 74.5 eV in platinum (PtO ₂ ) in a tetravalent oxidation state.

In the X-ray photoelectron spectroscopy measurement of the fine particle tungsten oxide containing the synthesized platinum catalyst, as shown in FIG. 8, at the platinum peak with a binding energy of 65 eV to 80 eV, the metal state (Pt ⁰ ), divalent oxidation state (PtO), 4 Peak separation is performed in the valence oxidation state (PtO ₂ ). An example of each peak separation is shown by dotted lines in FIG. Here, as the definition of the oxidation state of the platinum catalyst, the peak area appearing at the binding energy position 70.9 eV of the electronic state 4f _2/7 of platinum in FIG. 1 and the peak area of the binding energy 73.7 eV of the divalent oxidation state platinum are shown. And the sum of the peak areas appearing at 74.5 eV of the binding energy of tetravalent oxidation state platinum, that is, using the expression (XPS (1) / XPS (2)) × 100 (%), Calculate the percentage.

  Here, XPS (1) = XPS peak area in the platinum oxidation state, XPS (2) = XPS platinum metal state peak area + XPS oxidation state peak area.

The hydrogen gas detection layer was prepared by using a sol-gel synthesis method. Specifically, 2.5 g of tungstic acid (H ₂ WO ₄ ) was melted in 31 ml of methanol, stirred at room temperature for 30 minutes, and 18 ml of pure water was added. Add colloidal solution. Platinum is used as the catalyst metal, 4 ml of a chloroplatinic acid (H ₂ (PtCl ₆ )) aqueous solution having a concentration of 0.1 mol / l is added to the colloidal solution of tungstic acid, and the ratio of the platinum catalyst to tungsten is 4 mol%. Tungstic acid colloidal solution containing platinum catalyst was synthesized. In particular, the calcination treatment is performed in a flow state of 50 ml / min of air at a calcining temperature of 350 ° C. to 700 ° C. for 5 hours, and by optimizing oxygen defects of the fine particle tungsten oxide by the calcining temperature, The oxidation state of some platinum was controlled.

  The hydrogen gas sensor sensitivity was measured at the measurement temperature of 25 ° C., the hydrogen gas concentration in the air of 1%, and the relative humidity of 50% using the hydrogen gas sensor shown in FIG.

  In FIG. 7, the oxidation state of the platinum catalyst metal contained in the tungsten oxide obtained by the sol-gel synthesis method and the dependence on detection sensitivity of hydrogen gas are indicated by symbols ●.

  As can be seen from FIG. 7, at a calcination temperature of 400 ° C., the oxidation state of the platinum catalyst contained on the surface of the fine particle tungsten oxide is 18%, and the hydrogen gas detection sensitivity 36 at that time is obtained. Since the gas sensor is required to have a detection sensitivity of 10 or more for hydrogen gas, it is performed for 5 hours at a calcining condition where the oxidation state of the platinum catalyst is 10% or more, that is, calcining temperature 400 ° C. and air flow condition 50 ml / min. preferable.

  Further, the calcining temperature is raised to 500 ° C. or higher, and an oxidation state of 30% of the platinum catalyst is obtained. The gas sensor element mainly composed of fine particle tungsten oxide having the platinum catalyst in this oxidation state has a hydrogen gas detection sensitivity of 250. Can be realized. This satisfies the gas sensitivity of 100 or more required for a highly sensitive hydrogen gas sensor element. In the above-described colloidal solution of tungstic acid containing chloroplatinic acid, the calcining temperature is increased from 450 ° C. to 650 ° C., and the oxidation state of the platinum catalyst is increased from 30% to 78%. The detection sensitivity of hydrogen gas takes a maximum value of about 1000 when the oxidation state of the platinum catalyst is about 60%. However, when the oxidation state of the platinum catalyst exceeds about 60%, the detection sensitivity of hydrogen gas decreases.

As another sol-gel synthesis method, 26.6 g of Na ₂ WO ₄ .2H ₂ O is taken and pure water is added to adjust to 200 ml. At a liquid temperature of 60C, ultrasonic waves are irradiated for 30 minutes to stir and dissolve to obtain a colorless and transparent Na ₂ WO ₄ aqueous solution (0.4 mol / l). Thereafter, sodium and hydrogen atoms are exchanged using a cation exchange resin (trade name; Diaiion SK1B, manufactured by Mitsubishi Chemical) to prepare a tungstic acid (H ₂ WO ₄ ) colloidal solution. A 125 mol / l chloroplatinic acid (H ₂ (PtCl ₆ )) aqueous solution (64 ml) was added to prepare a colloidal solution of tungstic acid (H ₂ WO ₄ ) containing a platinum catalyst. The calcining conditions and the hydrogen gas detection sensitivity measurement are the same as in the case of the colloidal solution containing the tungstic acid (H ₂ WO ₄ ) as a precursor. The relationship between the oxidation state of the metal catalyst and the dependence on the detection sensitivity of hydrogen gas is also indicated by symbol ◯ in FIG. As can be seen from FIG. 7, it hardly depends on the sol-gel synthesis method of a tungstic acid (H ₂ WO ₄ ) colloidal solution, and a hydrogen gas detection sensitivity of 10 or more is obtained when the oxidation state of the platinum catalyst is 20% to 90%. It is done. Furthermore, a hydrogen gas detection sensitivity of 100 or more is obtained when the oxidation state of the platinum catalyst is 30% to 78%.

  The additive as the catalyst metal is not limited to the chloride salt as in Examples 1 and 2, but may be an inorganic salt such as nitrate or sulfate, or an organic salt. Organic salts include carboxylates, dicarboxylates and acetylacetone complex salts. Furthermore, the additive as the catalyst metal is preferably one that dissolves in the tungstic acid colloid solution.

In the case of palladium, palladium hydrate is added to a colloidal solution of tungstic acid (H ₂ WO ₄ ). Specifically, 2.5 g of tungstic acid (H ₂ WO ₄ ) is melted in 31 ml of methanol, stirred at room temperature for 30 minutes, and 18 ml of pure water is added to prepare a colloidal solution of tungstic acid. As a catalytic metal, 2 ml of dinitrodiamine palladium nitrate aqueous solution Pd (NH ₃ ) 2 (NO ₂ ) at a concentration of 0.0125 mol / l was added to a colloidal solution of tungstic acid, and a colloid of tungstic acid containing palladium catalytic metal. The solution is applied by spin coating on the insulating substrate 30 so as to cover the pair of electrodes 20 shown in FIG. 2, and is heated and held at a calcining temperature range of 400 ° C. to 600 ° C. for 5 hours at 50 ml / min. Thereafter, it was naturally cooled and the detection sensitivity of hydrogen gas was measured at room temperature of 25 ° C. The detection sensitivity of hydrogen gas is improved with the palladium catalyst compared with the platinum catalyst. Also, the detection speed of hydrogen gas is increased.

In the case of iridium (Ir) as the catalyst metal, a hydrogen gas sensor element was prepared in the same manner except that 8 ml of a solution having a concentration of 0.0125 mol / l iridium nitrate Ir (NO ₃ ) ₄ was added. The detection sensitivity was evaluated. Alternatively, 8 ml of a 0.0125 mol / l chlorinated iridium acid (H ₂ [IrCl ₆ ] · 6H ₂ O) aqueous solution may be added.

  In the case of osmium (Os) as the catalyst metal, an element was prepared in the same manner except that 8 ml of an osmium oxide (VIII) aqueous solution having a concentration of 0.0125 mol / l was added.

  In the case of rhodium (Rh) as the catalyst metal, a device was prepared in the same manner except that 8 ml of a rhodium nitrate solution (III) aqueous solution having a concentration of 0.0125 mol / l was added.

  In the case of ruthenium (Ru) as the catalyst metal, a device was produced in the same manner except that 8 ml of a ruthenium (III) nitrate aqueous solution having a concentration of 0.0125 mol / l was added.

  As described above, the platinum group metals have substantially the same electronegativity, and have almost the same effect on hydrogen adsorption / dissociation although there are differences in the detection sensitivity and speed of hydrogen gas. The hydrogen gas sensor shown in FIG. When measured at 0 ° C., a hydrogen gas concentration in air of 1%, and a relative humidity of 50%, a hydrogen gas detection sensitivity of 10 or more can be obtained.

  Metals as dopants added to tungsten oxide have a work function, which is the minimum energy required to extract one electron from the crystal surface of a metal or semiconductor to the outside, because the ionic radius is close to that of tungsten. Vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), Ni (nickel), copper (Cu), niobium (Nb), molybdenum (Mo), rhenium, close to tungsten (Re) and titanium (Ti) can also be used. By adding a proportion of 0.25 mol% to 5 mol% with respect to tungsten, minute distortion occurs in tungsten oxide and oxygen defects are generated in tungsten oxide. Therefore, the proton conductivity and the electron carrier concentration can be increased, and the electrical conductivity can be improved.

  In the case of vanadium (V) as the catalyst metal, a device was prepared in the same manner except that 2 ml of 0.0125 mol / l ammonium metavanadate aqueous solution was added to the colloidal solution of tungstic acid.

  Further, in the case of chromium (Cr) as the catalyst metal, a device was fabricated in the same manner except that 2 ml of 0.0125 mol / l concentration chromium nitrate (III) nonahydrate was added. The addition amount of chromium (Cr) is preferably 0.25 mol% to 2 mol% with respect to tungsten.

  In the case of manganese (Mn) as the catalyst metal, a device was prepared in the same manner except that 2 ml of 0.0125 mol / l aqueous manganese nitrate solution was added.

In the case of iron (Fe) as the catalyst metal, a device was fabricated in the same manner except that 2 ml of 0.0125 mol / l ferrous chloride (FeCl ₂ (H ₂ O)) 4 aqueous solution was added.

In the case of cobalt (Co) as the catalyst metal, a device was fabricated in the same manner except that 2 ml of 0.0125 mol / l concentration cobalt chloride (CoCl ₂ .6H ₂ O) aqueous solution was added.

In the case of nickel (Ni) as the metal catalyst, a device was fabricated in the same manner except that 2 ml of 0.0125 mol / l nickel hydrated oxide (Ni ₂ O ₃ .2H ₂ O) aqueous solution was added. .

In addition, in the case of copper (Cu) as the metal catalyst, the same except that 2 ml of 0.0125 mol / l copper acetate (II) hydrate (Cu (CH ₃ COO) 2 .H ₂ O) aqueous solution is added. Thus, an element was produced.

  In the case of niobium (Nb) as the metal catalyst, a device was produced in the same manner except that 2 ml of 0.0125 mol / l niobium chloride aqueous solution was added.

  In the case of molybdenum (Mo) as the metal catalyst, a device was fabricated in the same manner except that 2 ml of 0.0125 mol / l concentration molybdenum (I) hydrate aqueous solution was added.

  In the case of rhenium (Re) as the metal catalyst, a device was fabricated in the same manner except that 2 ml of 0.0025 mol / l concentration rhenium oxide hydrate solution was added.

Further, when a metal catalyst titanium (Ti) is an element in the same manner except that the addition of 0.0025 mol / l concentration titanate alkoxide 2ml ethanol 5 X 10- ⁵ moles diethanolamine 4X 10- ⁶ moles Produced.

  In any of the above cases, the hydrogen gas sensor shown in FIG. 2 measured at a measurement temperature of 25 ° C., an air hydrogen gas concentration of 1%, and a relative humidity of 50%. It was.

FIG. 9 shows the dependence of the average particle size of platinum catalyst metal as the catalyst metal on the detection sensitivity of hydrogen gas. The fine particle tungsten oxide of the hydrogen gas detection film is produced by a sol-gel method. Specifically, 2.5 g of tungstic acid (H ₂ WO ₄ ) is melted in 31 ml of methanol, stirred at room temperature for 30 minutes, and 18 ml of pure water is added to prepare a colloidal solution of tungstic acid (H ₂ WO ₄ ). A platinum catalyst is used as a catalyst metal, and 0.1 mol / l of a chloroplatinic acid aqueous solution (H ₂ (PtCl ₆ )) is added in 1.8 ml, 3.6 ml, 11 ml, and 23 ml to a tungstic acid colloidal solution. Using a platinum amount as a parameter, a colloidal solution of tungstic acid containing a catalyst metal with a molar ratio of platinum catalyst to tungsten of 1.8%, 3.6%, 11%, and 23% is synthesized. Thereafter, a colloidal solution of tungstic acid each having a platinum catalyst was spin-coated on the insulating substrate 30 so as to cover the pair of electrodes 20 as shown in FIG. Thereafter, calcination treatment was performed for 5 hours at a temperature of 350 ° C. to 600 ° C. with air at 50 ml / min. The film thickness of the hydrogen gas detection film 10 after calcination was about 500 nm.

  After calcination, the mixture was naturally cooled to room temperature of 25 ° C., and the hydrogen gas detection sensitivity was measured at an air hydrogen gas concentration of 1% and a relative humidity of 50%. In addition, the average particle diameter of a platinum catalyst is about 100 platinum catalysts using the scanning electron microscope (SEM) in the sample produced | generated on the conditions of each calcining temperature similarly to the measurement of the average particle diameter of fine particle tungsten oxide. The average particle size was calculated from the frequency distribution of the particle size.

  As the molar ratio of platinum catalyst to tungsten increases, the average particle size of the platinum catalyst particles increases.

  From FIG. 9, when the molar ratio of platinum to tungsten | Pt | / | W | is 0.036 to 0.11 and the platinum average particle diameter is 2 nm to 35 nm, the hydrogen gas detection sensitivity is 10 or more. It is done. In addition, as for the data of each molar ratio, the average particle diameter of a platinum catalyst increases with a raise of calcination temperature.

  When | Pt | / | W | = 0.23, the detection sensitivity of hydrogen gas is 10 or less, and the average particle diameter of the platinum catalyst is 22 nm to 78 nm. This is thought to be because with the increase in platinum catalysts, the generation of water by the complete oxidation of protons generated from hydrogen gas on the platinum catalyst and oxygen in the air becomes more dominant than the formation of tungsten bronzes.

  From the above results, it is preferable that the catalyst metal contained on the surface of the fine particle tungsten oxide containing tungsten oxide as a main component as the hydrogen gas detection film has an average particle diameter of 5 nm to 20 nm.

 FIG. 10 shows a hydrogen gas sensor structure according to another embodiment 2. Example 2 is the same as Example 1 except that the pair of electrodes 20 is formed on the hydrogen gas detection layer 10. A line A-A ′ represents a cross section, and an enlarged view of the cross section A-A ′ has the same structure as FIG. 1. In FIG. 10, a colloidal solution of tungstic acid containing the above catalytic metal is calcined on an insulating substrate 30 such as a quartz substrate, an insulating substrate having an insulating film on a silicon substrate or a silicon carbide substrate, or a ceramic substrate such as alumina. It is applied by spin coating so that the film thickness afterwards becomes 300 nm to 1 μm, heated and maintained at a calcining temperature range of 400 ° C. to 600 ° C. for 5 hours with air 50 ml / min, and then naturally cooled to detect hydrogen gas A film 10 is formed. Thereafter, a pair of electrodes 20 is formed. Compared to Example 1, since the pair of electrodes are formed after the calcination treatment of the hydrogen gas detection film, the electrode material is gold (Au) or gold alloy, platinum (Pt) or platinum alloy, or molybdenum of Example 1. In addition to high melting point metal materials such as (Mo), tantalum (Ta), or niobium (Nb), low melting point metal materials such as copper (Cu) and aluminum (Al) can be used. Since the electrode material can be manufactured by a printing method or an inkjet method, the degree of freedom of the electrode material and the electrode manufacturing method is increased, and the manufacturing cost can be reduced.

  Furthermore, in order to reduce the influence of sensor ambient temperature and humidity in the measurement environment, or to improve the detection sensitivity and response speed of hydrogen gas, a heater is provided to include a hydrogen gas detection film sandwiched between a pair of electrodes. Preferably (not shown). As the heater, nickel (Ni), chromium (Cr) or an alloy thereof, platinum, or a platinum alloy, or the like can be used. As a structure of a heater, it can also provide in the other side of a hydrogen gas detection film | membrane through an insulating substrate. In addition, a heater is formed in advance on the insulating substrate, and then an electric insulating film is formed on the heater. Further, a hydrogen gas detection film is formed on the electrical insulating film.

  By using a hydrogen gas sensor equipped with a heater and changing the temperature of the detection film of the hydrogen gas sensor with the heater, it is possible to obtain desired values for the hydrogen gas detection sensitivity and responsiveness. Although the response time of the detection film is improved depending on the method of manufacturing the hydrogen gas detection film, the operation temperature of the hydrogen gas sensor may be set higher than the normal temperature at the time of leakage monitoring. For example, the operating temperature is preferably 50 ° C to 300 ° C. Although the hydrogen gas detection speed increases, the hydrogen gas detection sensitivity tends to decrease as the operating temperature increases. Therefore, it is possible to provide a desired hydrogen gas sensor by changing the operating temperature of the hydrogen gas detection film depending on whether responsiveness is important when detecting hydrogen gas or sensitivity is important.

  The hydrogen gas detection film according to the present invention provides a hydrogen gas detection film that increases the detection sensitivity of hydrogen gas and at the same time improves the detection speed, and easily leaks gas containing hydrogen using the gas detection film. A hydrogen gas sensor can be realized.

In addition, since the hydrogen gas detection film and the hydrogen gas sensor of the present invention utilize changes in physical properties due to protons (H ⁺ ), hydrogen sulfide gas (H ₂ S), ammonia (NH ₃ ), and nitrogen oxides that are flammable gases (NO _x), it can be applied to the gas sensing film or a gas sensor for carbon monoxide (CO). Furthermore, by using the hue change of tungsten oxide, it can be used for a gas detection paint, a gas detection tape, or a light detection type gas sensor.

  Further, the hydrogen gas sensor can be used for a chemical sensor such as a pH (pH) sensor for detecting a proton amount.

Moreover, since the hydrogen gas detection film | membrane concerning this invention utilizes the physical property change by a proton (H ^<+> ), it can apply also as ink materials for electronic books, such as an electromic (EC) display material and e-ink.

The figure for demonstrating typically the hydrogen gas detection film | membrane in Example 1 of this invention (enlarged sectional drawing of the detection film | membrane 10 of the hydrogen gas sensor in FIG.2 and FIG.10) The figure which shows the structure of the hydrogen gas sensor in Example 1 of this invention. The figure for demonstrating the calcination temperature dependence at the time of the sol-gel synthesis | combination of the fine particle tungsten oxide X-ray diffraction pattern which comprises the hydrogen gas detection film | membrane in Example 1 of this invention The figure which shows the detection sensitivity dependence of the ratio (= (001) / (200)) of the X-ray crystal plane index main peak of the fine particle tungsten oxide in Example 1 of this invention, and hydrogen gas. The figure which shows the relationship between the average particle diameter of particulate tungsten oxide and the detection sensitivity of hydrogen gas in Example 1 of this invention The figure which shows hydrogen sensitivity dependence with ratio | O | / | W | of oxygen atom number and tungsten atom number of the fine particle tungsten oxide in Example 1 of this invention. The figure which shows the relationship between the oxidation state of platinum in the platinum metal catalyst as a catalyst metal contained in the surface of the fine particle tungsten oxide in Example 1 of this invention, and the detection sensitivity of hydrogen gas The figure which shows the X-ray photoelectron spectroscopy spectrum of platinum contained in the fine particle tungsten oxide in Example 1 of this invention. The figure which shows the detection sensitivity dependence of the average particle diameter of the platinum catalyst metal contained in the fine-particle tungsten oxide in Example 1 of this invention, and hydrogen gas The figure which shows the structure of the hydrogen gas sensor in Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tungsten oxide 2 Catalytic metal 3 Crevice 4 Particulate tungsten oxide containing catalyst metal on the surface 5 Insulating substrate 6 Hydrogen gas detecting film 10 Hydrogen gas detecting film 20 Electrode 30 Insulating substrate 40 Lead wire 50 Microammeter 60 DC power supply 70 Hydrogen gas sensor element

Claims (21)

A hydrogen gas detection membrane in which electric resistance is changed by injecting protons generated by dissociating hydrogen gas and being reduced or desorbing and oxidizing the protons,
2. The hydrogen gas detection film according to claim 1, wherein the detection film is composed of an aggregate of crystal fine particles containing tungsten oxide as a main component, and a catalytic metal in an oxidized state is contained on a surface of the crystal fine particle tungsten oxide. The hydrogen gas detection film according to claim 1, wherein the crystalline fine particle tungsten oxide has an average particle diameter of 15 nm to 80 nm. 2. The hydrogen gas detection film according to claim 1, wherein the crystalline fine particle tungsten oxide has a predetermined ratio of oxygen defects. 2. The hydrogen gas detection film according to claim 1, wherein the ratio of the number of oxygen atoms and the number of tungsten atoms in the fine crystalline tungsten oxide is 2.54 to 2.63. 2. The hydrogen gas detection film according to claim 1, wherein the crystalline fine particle tungsten oxide includes at least a triclinic crystal system and an orthorhombic crystal structure. 3. In the fine particle tungsten oxide, vanadium (V), chromium (Cr),
Manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu),
Any metal of niobium (Nb), molybdenum (Mo), rhenium (Re), titanium (Ti), or a mixture of these metals is 0.25 mol% to 5 mol with respect to tungsten. 2. The hydrogen gas detection film according to claim 1, wherein the hydrogen gas detection film is doped with a concentration of about 1%. 2. The hydrogen gas detection film according to claim 1, wherein the catalyst metal is in an oxidized state of 18% to 90% of the total amount of the catalyst metal contained in the fine particle tungsten oxide. 2. The hydrogen gas detection film according to claim 1, wherein the catalyst metal has a ratio of 1.8 mol% to 11 mol% with respect to tungsten. 2. The hydrogen gas detection film according to claim 1, wherein the catalyst metal has an average particle diameter of 2 nm to 35 nm. The catalyst metal is any one of platinum, (Pt), iridium (Ir), osmium (Os), palladium (Pd), rhodium (Rh), ruthenium (Ru), or any of these metals. It is a mixture, The hydrogen gas detection film | membrane of Claim 1 characterized by the above-mentioned On a pair of electrodes provided on an insulating substrate, protons generated by dissociating hydrogen gas are injected and reduced, or a predetermined film whose electric resistance is changed by desorption and oxidation of the protons A hydrogen gas sensor having a thickness detection film,
2. The hydrogen gas sensor according to claim 1, wherein the detection film is composed of an aggregate of crystal fine particles containing tungsten oxide as a main component, and contains a catalytic metal in an oxidized state on a surface of the crystal fine particle tungsten oxide. A detection film having a predetermined thickness whose electrical resistance is changed by injecting and reducing protons generated by dissociating hydrogen gas on an insulating substrate and reducing or oxidizing the protons. A hydrogen gas sensor comprising a pair of electrodes on a membrane,
2. The hydrogen gas sensor according to claim 1, wherein the detection film is composed of an aggregate of crystal fine particles containing tungsten oxide as a main component, and contains a catalytic metal in an oxidized state on a surface of the crystal fine particle tungsten oxide. The hydrogen gas sensor according to claim 11 or 12, wherein the crystalline fine particle tungsten oxide has an average particle diameter of 15 nm to 80 nm. 13. The hydrogen gas sensor according to claim 11, wherein the crystalline fine particle tungsten oxide includes at least a triclinic crystal structure and an orthorhombic crystal structure. 13. 13. The hydrogen gas sensor according to claim 11, wherein the crystalline fine particle tungsten oxide has oxygen defects at a predetermined ratio. 13. The hydrogen gas sensor according to claim 11, wherein a ratio between the number of oxygen atoms and the number of tungsten atoms in the crystalline fine particle tungsten oxide is 2.54 to 2.63. In the fine particle tungsten oxide, vanadium (V), chromium (Cr),
Manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu),
Any metal of niobium (Nb), molybdenum (Mo), rhenium (Re), titanium (Ti), or a mixture of these metals is 0.25 mol% to 5 mol with respect to tungsten. 13. The hydrogen gas sensor according to claim 11, wherein the hydrogen gas sensor is doped at a concentration of%. 13. The hydrogen gas sensor according to claim 11, wherein the catalyst metal is in an oxidized state in an amount of 18% to 90% of the total amount of the catalyst metal contained in the particulate tungsten oxide. The catalyst metal is any one of platinum, (Pt), iridium (Ir), osmium (Os), palladium (Pd), rhodium (Rh), ruthenium (Ru), or any of these metals. It is a mixture, The hydrogen gas sensor in any one of Claim 11 or Claim 12 characterized by the above-mentioned. The hydrogen gas sensor according to claim 11, wherein the catalyst metal has a ratio of 1.8 mol% to 11 mol% with respect to tungsten. 13. The hydrogen gas sensor according to claim 11, wherein the catalyst metal has an average particle diameter of 2 nm to 35 nm.

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