Hydrogen sensor and hydrogen detection system

Abstract

The present disclosure provides a hydrogen sensor comprising: a substrate; a sensitive film disposed on a first surface of the substrate and including tungsten oxide and a catalyst for dissociating hydrogen molecules; a pair of electrodes disposed on the first surface of the substrate and in contact with the sensitive film; and an IC tag connected to the pair of electrodes. The IC tag: includes an IC chip, an antenna connected to the IC chip, and a pair of sensor terminals connected to the IC chip and connected respectively to the pair of electrodes; and is of an open / short type in which the IC chip is determined as being in a high resistance state when the resistance value between the sensor terminals is less than or equal to a first threshold resistance value and in a low resistance state when the resistance value between the sensor terminals is equal to or smaller than a second threshold resistance value that is smaller than the first threshold resistance value. The resistance value between the sensor terminals becomes equal to or greater than the first threshold resistance value when the hydrogen concentration is zero, and becomes equal to or smaller than the second threshold resistance value when the hydrogen concentration is a set value.

Description

Hydrogen Sensor and Hydrogen Detection System

[0001] The present disclosure relates to hydrogen sensors and hydrogen detection systems.

[0002] In recent years, there has been a desire to utilize clean and recyclable energy sources from the perspective of protecting the global environment and preventing the depletion of fossil fuels. In particular, research into the use of hydrogen gas as an energy source has been actively conducted, focusing on fuel cells. However, hydrogen gas has a wide explosive limit concentration range, from 4% to 75%. Therefore, in order to popularize hydrogen gas as an energy source, it is essential to develop safety devices to prevent hydrogen leakage, as well as to handle hydrogen storage and transportation.

[0003] For example, odorization, which is used in city gas, can be considered, but in the case of hydrogen gas, problems such as poisoning of fuel cells and deterioration of gas turbines arise. Therefore, safety measures that replace odorization are required. Therefore, to ensure safety, hydrogen sensors that can detect hydrogen gas leaks have become extremely important.

[0004] Conventional hydrogen sensors mainly use the catalytic combustion or semiconductor method. Catalytic combustion hydrogen sensors use a heater to heat a catalytic metal such as platinum or palladium, and oxidize the hydrogen gas that comes into contact with the catalyst with oxygen in the air. The heat generated by this oxidation of the hydrogen gas is detected electrically as a change in the conductivity of the catalytic metal. Semiconductor hydrogen sensors detect changes in the electrical properties of the sensitive film due to the adsorption of hydrogen gas onto the sensitive film, i.e., changes in resistance value. Like catalytic combustion sensors, semiconductor hydrogen sensors are also used in a heated state. As such, conventional hydrogen sensors, such as those using catalytic combustion or semiconductor methods, involve heating, which poses a risk when used with hydrogen gas that requires explosion-proof measures.

[0005] Furthermore, gasochromic hydrogen sensors have been attracting attention in recent years. Gasochromic hydrogen sensors are equipped with a metal oxide such as tungsten trioxide, which changes color upon adsorbing hydrogen, and a catalyst such as platinum, which dissociates hydrogen gas into hydrogen atoms, and detect hydrogen gas optically. Because the electrical properties of metal oxides such as tungsten trioxide also change upon adsorbing hydrogen, gasochromic hydrogen sensors can also detect hydrogen gas electrically (see, for example, Patent Document 1).

[0006] Patent No. 4496204

[0007] In the wireless tag described in Patent Document 1, when the resonant circuit receives a wireless signal at the resonant frequency, it induces an AC current, which is stored as startup power and transmits data. Meanwhile, in a wireless tag, when hydrogen comes into contact with tungsten oxide, the tungsten oxide becomes conductive, shorting the antenna coil, causing a change in inductance and a change in the resonant frequency of the resonant circuit. As a result, even when a wireless signal is received, no AC current is induced, and data is not transmitted. In this way, the wireless tag determines the presence or absence of hydrogen based on the presence or absence of a response from the wireless tag in response to the transmitted wireless signal. However, the wireless tag can only detect the presence or absence of hydrogen.

[0008] The present disclosure has been made in consideration of the above-described circumstances, and has as its main object to provide a hydrogen sensor that can manage hydrogen concentration.

[0009] One embodiment of the present disclosure provides a hydrogen sensor including a substrate, a sensitive membrane disposed on a first surface of the substrate and containing a catalyst that dissociates hydrogen molecules and tungsten oxide, a pair of electrodes disposed on the first surface of the substrate in contact with the sensitive membrane, and an IC tag connected to the pair of electrodes, wherein the IC tag includes an IC chip, an antenna connected to the IC chip, and a pair of sensor terminals connected to the IC chip and respectively connected to the pair of electrodes, and the IC chip is an open-short type that determines a high resistance state when the resistance value between the sensor terminals is greater than or equal to a first threshold resistance value, and determines a low resistance state when the resistance value between the sensor terminals is less than or equal to a second threshold resistance value that is smaller than the first threshold resistance value, and wherein the resistance value between the sensor terminals when the hydrogen concentration is zero is greater than or equal to the first threshold resistance value, and the resistance value between the sensor terminals when the hydrogen concentration is a set value is less than or equal to the second threshold resistance value.

[0010] Another embodiment of the present disclosure provides a hydrogen detection system using the hydrogen sensor described above.

[0011] Another embodiment of the present disclosure provides a hydrogen pipeline using the hydrogen detection system described above.

[0012] The hydrogen sensor according to the present disclosure has the effect of being able to control the hydrogen concentration.

[0013] FIG. 1 is a schematic plan view illustrating a hydrogen sensor according to the present disclosure. FIG. 2 is a graph illustrating the relationship between hydrogen concentration and resistance between sensor terminals in a hydrogen sensor according to the present disclosure. FIG. 3 is a graph illustrating the relationship between hydrogen concentration and resistance between sensor terminals in a hydrogen sensor not corresponding to an embodiment of the present disclosure. FIG. 4 is a schematic plan view illustrating a hydrogen sensor according to the present disclosure. FIG. 5 is a schematic plan view illustrating a hydrogen sensor according to the present disclosure. FIG. 6 is a schematic plan view illustrating a hydrogen sensor according to the present disclosure. FIG. 7 is a schematic plan view illustrating a hydrogen sensor according to the present disclosure. FIG. 8 is a schematic plan view illustrating a hydrogen sensor according to the present disclosure. FIG. 9 is a schematic plan view illustrating a hydrogen sensor according to the present disclosure. FIG. 10 is a schematic plan view illustrating a hydrogen sensor according to the present disclosure. FIG. 11 is a schematic plan view illustrating a hydrogen sensor according to the present disclosure. FIG. 12 is a schematic plan view illustrating a hydrogen sensor according to the present disclosure. FIG. 13 is a schematic plan view illustrating a hydrogen sensor according to the present disclosure. FIG. 14 is a schematic plan view illustrating a hydrogen sensor according to the present disclosure. 1 is a graph showing the relationship between hydrogen concentration and resistance between sensor terminals in the hydrogen sensor of Example 1. 2 is a graph showing the relationship between hydrogen concentration and resistance between sensor terminals in the hydrogen sensors of Comparative Examples 1 and 2.

[0014] Below, embodiments of the present disclosure will be described with reference to the drawings and the like. However, the present disclosure can be implemented in many different forms, and should not be construed as being limited to the description of the embodiments exemplified below. Furthermore, to clarify the explanation, the drawings may schematically depict the width, thickness, shape, etc. of each component compared to the embodiments, but these are merely examples and do not limit the interpretation of the present disclosure. Furthermore, in this specification and each drawing, elements similar to those previously described with reference to the previous drawings will be designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0015] In this specification, when expressing an aspect in which another component is placed on a certain component, the term "on the surface side" or "on the surface" is used, unless otherwise specified, and includes both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component in between.

[0016] Furthermore, in this specification, terms such as "sheet," "film," and "plate" are not distinguished from one another solely based on differences in name. For example, the term "sheet" is used to include members also known as films and plates.

[0017] The hydrogen sensor and hydrogen detection system of the present disclosure will be described in detail below.

[0018] A. Hydrogen Sensor The hydrogen sensor disclosed herein utilizes the phenomenon in which a sensitive membrane containing a catalyst and tungsten oxide decreases in resistance upon reaction with hydrogen. The inventors of the present disclosure conducted extensive research into components for detecting changes in the resistance of the sensitive membrane in such hydrogen sensors and focused on an open-short type IC chip. An open-short type IC chip detects changes in resistance by determining a high-resistance state when the resistance between terminals is equal to or greater than a first threshold and a low-resistance state when the resistance between terminals is equal to or less than a second threshold. When applying an open-short type IC chip to such a hydrogen sensor, it is important to design the chip so that the resistance between terminals is equal to or greater than the first threshold in an air atmosphere and equal to or less than the second threshold when the hydrogen concentration in the atmosphere increases. This enables hydrogen leak detection. To provide an inexpensive hydrogen sensor, it is desirable to use a commercially available open-short type IC chip. However, in commercially available open-short type IC chips, the first and second thresholds are predetermined. Therefore, it was found that simply applying an open-short type IC chip to a hydrogen sensor may result in, for example, the resistance between the terminals falling below the second threshold, or the resistance between the terminals not falling below the second threshold even when the hydrogen concentration in the atmosphere increases. If the resistance between the terminals falls below the second threshold in both an air atmosphere and a hydrogen atmosphere, it is determined that hydrogen is leaking even in the air atmosphere. Furthermore, even when the hydrogen concentration in the atmosphere increases, a hydrogen leak cannot be detected unless the resistance between the terminals falls below the second threshold. The inventors of the present disclosure conducted further research and found that the resistance between the terminals depending on the hydrogen concentration can be adjusted by appropriately designing the sensitive film and the pair of electrodes, such as the thickness of the sensitive film and the spacing between the pair of electrodes, according to the first and second thresholds of the open-short type IC chip. That is, when an open-short type IC chip is applied to the above-described hydrogen sensor, it was found that the resistance between the terminals can be designed so that in an air atmosphere, the resistance between the terminals is above the first threshold, and as the hydrogen concentration in the atmosphere increases, the resistance between the terminals falls below the second threshold.The present disclosure is based on this finding.

[0019] Conventionally, open / short type IC chips have been used to detect breaks in wiring or circuits. Other than the report by the inventors of the present disclosure, there have been no reports of using open / short type IC chips in hydrogen sensors.

[0020] The hydrogen sensor disclosed herein is a hydrogen sensor including a substrate, a sensitive membrane disposed on a first surface of the substrate and containing a catalyst that dissociates hydrogen molecules and tungsten oxide, a pair of electrodes disposed on the first surface of the substrate in contact with the sensitive membrane, and an IC tag connected to the pair of electrodes, wherein the IC tag includes an IC chip, an antenna connected to the IC chip, and a pair of sensor terminals connected to the IC chip and respectively connected to the pair of electrodes, and the IC chip is an open-short type that determines a high resistance state when the resistance value between the sensor terminals is greater than or equal to a first threshold resistance value, and determines a low resistance state when the resistance value between the sensor terminals is less than or equal to a second threshold resistance value that is smaller than the first threshold resistance value, and wherein the resistance value between the sensor terminals when the hydrogen concentration is zero is greater than or equal to the first threshold resistance value, and the resistance value between the sensor terminals when the hydrogen concentration is a set value is less than or equal to the second threshold resistance value.

[0021] FIG. 1 is a schematic plan view showing an example of a hydrogen sensor according to the present disclosure. As shown in FIG. 1, the hydrogen sensor 1 includes a substrate 2, a sensitive membrane 3 disposed on a first surface of the substrate 2 and containing a catalyst that dissociates hydrogen molecules and tungsten oxide, a pair of electrodes 4a, 4b disposed on the first surface of the substrate 2 in contact with the sensitive membrane 3, and an IC tag 5 connected to the pair of electrodes 4a, 4b. In FIG. 1, the pair of electrodes 4a, 4b are a pair of comb-shaped electrodes. The pair of electrodes 4a, 4b are alternately arranged at a distance d1 that allows detection of changes in the resistance value of the sensitive membrane 3. The IC tag 5 also includes a second substrate 21, an IC chip 22 disposed on the first surface of the second substrate 21, an antenna 23 disposed on the first surface of the second substrate 21 and connected to the IC chip 22, and a pair of sensor terminals 24a, 24b disposed on the first surface of the second substrate 21, connected to the IC chip 22, and connected to the pair of electrodes 4a, 4b, respectively. In the IC tag 5, the IC chip 22 is an open-short type, and is determined to be in a high resistance state when the resistance value between the sensor terminals 24a and 24b connected to the IC chip 22 is equal to or greater than a first threshold resistance value, and is determined to be in a low resistance state when the resistance value between the sensor terminals 24a and 24b is equal to or less than a second threshold resistance value.

[0022] The hydrogen sensor in the present disclosure utilizes the phenomenon that the resistance value decreases when a sensitive film containing a catalyst and tungsten oxide reacts with hydrogen. The operating principle of the hydrogen sensor in the present disclosure will be described.

[0023] Tungsten oxide (WO ３ ) has a high electrical resistance. Therefore, in an atmosphere without hydrogen, the sensitive film 3 has a high electrical resistance and is insulating. At this time, the pair of electrodes 4a, 4b are insulated and in a non-conductive state. Therefore, even when power is supplied to the IC tag 5 from the RFID reader / writer, no current flows through the pair of electrodes 4a, 4b via the sensitive film 3. In the IC chip 22, when the resistance value between the sensor terminals 24a, 24b is equal to or greater than the first threshold resistance value, the IC chip 22 enters a high resistance state, and flag information, for example, becomes "0." In the IC tag 5, the above information is transmitted to the RFID reader / writer via the antenna 23. In this case, it is determined that no hydrogen gas is leaking.

[0024] On the other hand, when hydrogen molecules come into contact with the catalyst, the hydrogen molecules are dissociated and adsorbed to generate hydrogen atoms. These hydrogen atoms are then adsorbed onto tungsten oxide (WO ３ ) is reduced to form a non-stoichiometric compound (H ｘ WO ３ (0<x<1)) is produced. ｘ WO ３ ) is W ５＋ and W ６＋ Since the tungsten oxide is in a mixed valence state, its electrical resistance is low. Therefore, in an atmosphere where hydrogen is present, the above-mentioned reduction reaction of tungsten oxide occurs, and the electrical resistance of the sensitive film 3 decreases, becoming conductive. At this time, the pair of electrodes 4a, 4b are short-circuited and become conductive. Therefore, when power is supplied to the IC tag 5 from the RFID reader / writer, current flows through the pair of electrodes 4a, 4b via the sensitive film 3. In the IC chip 22, if the resistance value between the sensor terminals 24a, 24b is equal to or less than the second threshold resistance value, the IC chip 22 enters a low resistance state, and flag information, for example, becomes "1." The IC tag 5 transmits the above information to the RFID reader / writer via the antenna 23. In this case, it is determined that hydrogen gas is leaking.

[0025] In this way, in the IC tag 5, hydrogen gas can be detected by detecting a change in the resistance value between the sensor terminals 24a and 24b.

[0026] FIG. 2 is a graph showing an example of the relationship between hydrogen concentration and resistance between the sensor terminals in a hydrogen sensor according to the present disclosure. In FIG. 2, T1 represents the first threshold resistance, T2 represents the second threshold resistance, and S represents the set value of hydrogen concentration. When the hydrogen concentration is zero, as described above, the electrical resistance of the sensitive membrane 3 is high, resulting in a non-conductive state between the pair of electrodes 4a and 4b. At this time, the resistance R1 between the sensor terminals 24a and 24b is equal to or greater than the first threshold resistance T1, resulting in a high resistance state, and for example, the flag information is set to "0." On the other hand, as the hydrogen concentration increases, the electrical resistance of the sensitive membrane 3 decreases, resulting in a conductive state between the pair of electrodes 4a and 4b. When the resistance between the sensor terminals 24a and 24b falls below the second threshold resistance T2, the sensor enters a low resistance state, and for example, the flag information is set to "1." When the hydrogen concentration is the set value S, the resistance R2 between the sensor terminals 24a and 24b is equal to or less than the second threshold resistance T2. Therefore, when the hydrogen concentration reaches or exceeds the set value S, a hydrogen leak is detected. Therefore, with the hydrogen sensor of the present disclosure, when the hydrogen concentration reaches or exceeds a predetermined concentration, a hydrogen leak can be accurately detected, and the hydrogen concentration can be managed. Furthermore, the inventors of the present disclosure have conducted research and found that the relationship between the hydrogen concentration and the resistance value between the sensor terminals follows a linear regression in a double logarithmic graph such as that shown in Figure 18 in the examples described below.

[0027] FIG. 3 is a graph showing an example of the relationship between hydrogen concentration and resistance between the sensor terminals in a hydrogen sensor that does not fall under the hydrogen sensor of the present disclosure. FIG. 3 shows an example in which the resistance between the sensor terminals when the hydrogen concentration is zero does not exceed the first threshold resistance value, and an example in which the resistance between the sensor terminals when the hydrogen concentration is a set value does not fall below the second threshold resistance value. In other words, FIG. 3 is an example that does not fall under the hydrogen sensor of the present disclosure. First, for the plots of black triangles, when the hydrogen concentration is zero, the resistance R3 between the sensor terminals 24a and 24b is greater than the first threshold resistance value T1, so the flag information is, for example, "0." On the other hand, when the hydrogen concentration is the set value S, the resistance R4 between the sensor terminals 24a and 24b is higher than the second threshold resistance value T2, so the flag information is not, for example, "1." Therefore, even when the hydrogen concentration is high and a hydrogen leak occurs, the hydrogen leak cannot be detected. Next, for the plot of black squares, when the hydrogen concentration is zero, the resistance value R5 between the sensor terminals 24a and 24b is equal to or less than the second threshold resistance value T2, so the flag information becomes "1", for example. Therefore, even if the hydrogen concentration is zero, it is determined that hydrogen is leaking. Therefore, in such a case, it is not possible to manage the hydrogen concentration.

[0028] Therefore, by using the hydrogen sensor of the present disclosure, it is possible to accurately detect hydrogen leaks and manage the hydrogen concentration.

[0029] Furthermore, as mentioned above, conventional hydrogen sensors, such as semiconductor and catalytic combustion sensors, require heating. Furthermore, conventional catalytic combustion and semiconductor hydrogen sensors detect hydrogen gas at the location where they are installed. Therefore, they can only detect hydrogen gas within a narrow range, such as a radius of approximately 10 cm around the hydrogen sensor. For example, with a suction nozzle-type hydrogen sensor, it is difficult to detect hydrogen gas unless the nozzle is precisely aimed at the hydrogen leak location, requiring the operator to become proficient.

[0030] In contrast, the reduction reaction of tungsten oxide described above does not require the supply of electricity. Therefore, the hydrogen sensor according to the present disclosure can be made large-area and can detect hydrogen gas over a relatively wide area at low cost. Therefore, by using the hydrogen sensor according to the present disclosure, hydrogen gas leaks can be detected not only in small devices such as fuel cells, but also in large facilities such as hydrogen production facilities, hydrogen pipelines, transport tankers, storage tanks, hydrogen power generation facilities, and hydrogen stations.

[0031] Furthermore, in the wireless tag described in Cited Document 1, the circuit configuration is complicated in order to detect fluctuations in the resonant frequency of the resonant circuit, which increases manufacturing costs. In contrast, in the hydrogen sensor of the present disclosure, by using the open-short type IC chip described above, the circuit configuration can be simplified and manufacturing costs can be reduced.

[0032] Below, the hydrogen sensor according to the present disclosure will be described in detail for each component.

[0033] 1. Characteristics of the Hydrogen Sensor In the hydrogen sensor disclosed herein, if the IC chip is of an open-short type, which changes to a high resistance state when the resistance between the sensor terminals is equal to or greater than a first threshold resistance value, and a low resistance state when the resistance between the sensor terminals is equal to or less than a second threshold resistance value that is smaller than the first threshold resistance value, the resistance between the sensor terminals when the hydrogen concentration is zero will be equal to or greater than the first threshold resistance value, and the resistance between the sensor terminals when the hydrogen concentration is a set value will be equal to or less than the second threshold resistance value.

[0034] In the hydrogen sensor disclosed herein, the resistance between the sensor terminals when the hydrogen concentration is zero is equal to or greater than the first threshold resistance. Here, the hydrogen concentration in air is approximately 0.00005%. Therefore, in this specification, the concept of a hydrogen concentration of zero also includes a hydrogen concentration of 0.00005% or less.

[0035] Furthermore, in the hydrogen sensor disclosed herein, the resistance between the sensor terminals when the hydrogen concentration is at a set value is equal to or less than the second threshold resistance value. For example, when the set hydrogen concentration is 1%, and the second threshold resistance value is 100%, the difference between the resistance between the sensor terminals when the hydrogen concentration is at the set value and the second threshold resistance value is preferably equal to or more than 1% of the second threshold resistance value, more preferably equal to or more than 5% of the second threshold resistance value, and even more preferably equal to or more than 10% of the second threshold resistance value. Variations in IC chip characteristics may occur. Therefore, in consideration of safety, the difference is preferably within the above range. On the other hand, when the set hydrogen concentration is 1%, and the second threshold resistance value is 100%, the difference between the resistance between the sensor terminals when the hydrogen concentration is at the set value and the second threshold resistance value is preferably equal to or less than 20% of the second threshold resistance value, more preferably equal to or less than 15% of the second threshold resistance value, and even more preferably equal to or less than 10% of the second threshold resistance value. If the difference is too large, the resistance between the sensor terminals when the hydrogen concentration is significantly lower than the set value may also be equal to or lower than the second threshold resistance value, which may make it difficult to control the hydrogen concentration. Specifically, when the set value of the hydrogen concentration is 1%, and the second threshold resistance value is 100%, the difference between the resistance between the sensor terminals when the hydrogen concentration is the set value and the second threshold resistance value is preferably 1% to 20% of the second threshold resistance value, and more preferably 5% to 15% of the second threshold resistance value.

[0036] The resistance between the sensor terminals at a given hydrogen concentration is determined by the following method. First, the IC tag is removed from the hydrogen sensor. Next, while the hydrogen sensor is exposed to an atmosphere with a given hydrogen concentration, the impedance of a pair of electrodes connected to the pair of sensor terminals on the IC tag is measured at a frequency of 20 kHz using an LCR meter, and the resistance between the pair of electrodes is determined from the impedance. The measurement is performed five times, and the maximum and minimum values ​​are removed from the five measurements, and the average of the three measurements is used as the resistance between the sensor terminals at the given hydrogen concentration.

[0037] As mentioned above, the hydrogen concentration in air is approximately 0.00005%, and a hydrogen concentration of zero includes a hydrogen concentration of 0.00005% or less. Therefore, to measure the resistance between the sensor terminals when the hydrogen concentration is zero, the hydrogen sensor can be simply exposed to air.

[0038] Furthermore, when measuring the resistance between the sensor terminals when the hydrogen concentration is a set value, the hydrogen sensor is exposed to an atmosphere with a predetermined hydrogen concentration by enclosing it in a sealed gas chamber connected to a gas mixing device via a gas pipe. As the gas mixing device, for example, a gas mixing device with an integrated flow meter manufactured by Kofloc Corporation is used. This allows hydrogen to be mixed with air at a desired concentration with high accuracy, safety, and reproducibility. The hydrogen sensor responds very quickly to hydrogen, but since the process of saturating the resistance value takes time, it is preferable to maintain an atmosphere with a predetermined hydrogen concentration for at least 10 minutes. The sealed gas chamber is preferably a metal sealed gas chamber, for example, with a transparent glass or resin window in part and a resin or rubber gasket, and has a structure that does not interfere with RFID communication. This allows evaluation of not only hydrogen sensors with separate IC tags, in which the IC tag and the substrate on which the sensitive film and pair of electrodes are arranged are separate, but also hydrogen sensors with integrated IC tags, in which the IC tag and the substrate on which the sensitive film and pair of electrodes are arranged are integrated. The sealed gas chamber may be cylindrical, for example, with a diameter of 100 mm and a height of 20 mm. The transparent window may be, for example, a 5 mm thick glass plate or a 5 mm thick acrylic plate. The packing may be made of silicone rubber, fluororubber, or nitrile rubber. The gas piping may be flexible piping made of resin or rubber, or may be fixed piping made of metal. The gas piping may be stainless steel piping or polypropylene piping. The gas piping may be, for example, a pipe with a diameter of 5 mm or more and 10 mm or less. The LCR meter is installed outside the sealed gas chamber via electrical wiring and a packing. Details of the measurement conditions will be described in the Examples section below.

[0039] In the hydrogen sensor disclosed herein, methods for adjusting the resistance between the sensor terminals when the hydrogen concentration is zero include, for example, adjusting the spacing between a pair of electrodes, such as the spacing between a pair of comb-tooth electrodes, and adjusting the thickness of the sensitive film. As the spacing between the pair of comb-tooth electrodes increases, the resistance between the sensor terminals when the hydrogen concentration is zero tends to increase, while as the spacing between the pair of comb-tooth electrodes decreases, the resistance between the sensor terminals when the hydrogen concentration is zero tends to decrease. Furthermore, as the thickness of the sensitive film increases, the resistance between the sensor terminals when the hydrogen concentration is zero tends to increase, while as the thickness of the sensitive film decreases, the resistance between the sensor terminals when the hydrogen concentration is zero tends to decrease.

[0040] The method for adjusting the resistance between the sensor terminals when the hydrogen concentration is at a set value is similar to the method for adjusting the resistance between the sensor terminals when the hydrogen concentration is zero. As the spacing between the pair of comb-tooth electrodes increases, the resistance between the sensor terminals when the hydrogen concentration is at a set value tends to increase. Conversely, as the spacing between the pair of comb-tooth electrodes decreases, the resistance between the sensor terminals when the hydrogen concentration is at a set value tends to decrease. Furthermore, as the thickness of the sensitive film increases, the resistance between the sensor terminals when the hydrogen concentration is at a set value tends to increase. Conversely, as the thickness of the sensitive film decreases, the resistance between the sensor terminals when the hydrogen concentration is at a set value tends to decrease.

[0041] As mentioned above, the explosion limit concentration of hydrogen gas is between 4% and 75%. Therefore, the set value of the hydrogen concentration is less than 4%. In consideration of safety, the set value of the hydrogen concentration is preferably, for example, 2% or less, and more preferably 1% or less. On the other hand, if the set value of the hydrogen concentration is too low, even an extremely low concentration that does not lead to an explosion will be determined to be a hydrogen leak. Therefore, the set value of the hydrogen concentration is preferably, for example, 1% or more. In other words, the set value of the hydrogen concentration is preferably 1% or more and less than 4%, more preferably 1% or more and 2% or less, and particularly preferably 1%.

[0042] The set value of the hydrogen concentration is determined using the following method. As described above, the hydrogen sensor may determine that hydrogen gas is not leaking or that it is leaking. First, the hydrogen sensor is sealed in a sealed gas chamber connected to a gas mixing device via a gas pipe. The gas mixing device, sealed gas chamber, and gas pipe are as described above. The IC tag may be installed inside the sealed gas chamber, or it may be installed outside the sealed gas chamber via electrical wiring and a gasket. The set temperature is 25°C. The target fluids are hydrogen and air. The flow rate of the hydrogen and air mixed gas is set to a constant 10 mL / min. Next, the hydrogen and air mixture ratio in the sealed gas chamber is set to 0% hydrogen, i.e., 100% air. Next, the hydrogen concentration in the sealed gas chamber is adjusted to the desired value. Initially, the hydrogen concentration is adjusted to 0.1%. As described above, the hydrogen sensor responds very quickly to hydrogen, but it takes time for the resistance value to saturate. Therefore, it is preferable to maintain the atmosphere at that hydrogen concentration for at least 10 minutes. Next, radio waves are transmitted from the RFID reader / writer to confirm whether the hydrogen sensor reacts and detects hydrogen in an atmosphere of that hydrogen concentration. The sealed gas chamber is then opened and maintained for 10 minutes, returning to an air atmosphere. Next, the hydrogen concentration in the sealed gas chamber is increased by 0.1% each time, and the above procedure is repeated. The minimum hydrogen concentration at which it is determined that hydrogen gas is leaking is then determined. Measurements are performed five times, and the average of the minimum hydrogen concentrations is used as the set hydrogen concentration value.

[0043] 2. IC Tag The IC tag in the present disclosure includes an IC chip, an antenna connected to the IC chip, and a pair of sensor terminals connected to the IC chip and respectively connected to a pair of electrodes. The IC chip is an open-short type that determines a high resistance state when the resistance value between the sensor terminals is equal to or greater than a first threshold resistance value, and determines a low resistance state when the resistance value between the sensor terminals is equal to or less than a second threshold resistance value that is smaller than the first threshold resistance value. Note that IC tags are also referred to as RF tags, RFID tags, electronic tags, wireless tags, etc. An IC tag can detect hydrogen gas using RFID.

[0044] In the IC chip, the first threshold resistance value and the second threshold resistance value are not particularly limited as long as the second threshold resistance value is lower than the first threshold resistance value. The first threshold resistance value is preferably, for example, 1 MΩ or more and 20 MΩ or less, and more preferably 10 MΩ or more and 15 MΩ or less. If the first threshold resistance value is too low, changes in the resistance value may be detected frequently, which may result in frequent hydrogen leaks. Furthermore, if the first threshold resistance value is too low, the difference between the first threshold resistance value and the second threshold resistance value becomes small, making design difficult. The difference between the first threshold resistance value and the second threshold resistance value is preferably, for example, 10 MΩ or more and 100 MΩ or less. If the difference is too small or too large, design becomes difficult.

[0045] The first and second threshold resistance values ​​are determined by the following method. First, a fixed resistor with a known resistance value and a commercially available RFID reader / writer are prepared. The IC tag is then removed from the hydrogen sensor. The fixed resistor is connected to a pair of sensor terminals on the IC tag, and the RFID reader / writer transmits a read signal via radio waves. The signal is then confirmed by a flag indicating the reflected and transmitted radio waves. In an open-short type IC chip, an open state ideally refers to a state in which the load (electrical resistance, impedance) connected to the IC chip is infinite, i.e., a state in which the external load connection terminals of the IC chip are open. A short circuit ideally refers to a state in which the load (electrical resistance, impedance) connected to the IC chip is zero, i.e., a state in which the external load connection terminals of the IC chip are short-circuited by a conductor. However, since a load cannot be physically or mechanically disconnected in a typical electrical circuit, it is common to determine an open state when the resistance is above a certain level and a short state when the resistance is below a certain level. The threshold resistance value is set to a resistance value that is generally considered to be an insulating state in an open state, and a resistance value that is generally considered to be a conductive state in a short state. In the present disclosure, an open state is considered to be a high resistance state, and a short state is considered to be a low resistance state. Therefore, the first threshold resistance value is set to a resistance value that is generally considered to be an insulating state. Specifically, the first threshold resistance value is set to the minimum of the resistance values ​​that are considered to be an insulating state. Furthermore, the second threshold resistance value is set to the maximum of the resistance values ​​that are considered to be a conductive state. Note that, although the first threshold resistance value and the second threshold resistance value are published as characteristic data for commercially available IC chips, the above measurement method is adopted due to individual differences.

[0046] An example of an open-short type IC chip is UCODE G2iM+ manufactured by NXP.

[0047] The IC tag only needs to include an IC chip, an antenna connected to the IC chip, and a pair of sensor terminals connected to the IC chip and each connected to a pair of electrodes, and the configuration of the IC tag is the same as that of a general IC tag.

[0048] There are two types of IC tags: active tags that have a built-in power source (battery) and passive tags that do not. Of these, passive tags are preferred because they do not have their own power source (battery) but operate by receiving externally supplied radio waves via an antenna.

[0049] The number of IC tags is at least one. The number of IC tags may be one or more.

[0050] The IC tag may be integrated with or separate from the substrate on which the sensitive film and pair of electrodes are arranged. In FIG. 1 , the IC tag 5 is separate from the substrate 2 on which the sensitive film 3 and pair of electrodes 4a, 4b are arranged. On the other hand, in FIG. 4 , the IC tag 5 is arranged on one side of the substrate 1, and the IC tag 5 is integrated with the substrate 2 on which the sensitive film 3 and pair of electrodes 4a, 4b are arranged. When the IC tag is separate from the substrate on which the sensitive film and pair of electrodes are arranged, the substrate on which the sensitive film and pair of electrodes are arranged can be placed directly on the object to be detected for hydrogen leak detection, while the IC tag can be placed in a position that facilitates radio wave transmission and reception, such as by being away from metal or the like that blocks radio waves or by having the antenna directly facing the RFID reader / writer. On the other hand, when the IC tag is integrated with the substrate on which the sensitive film and pair of electrodes are arranged, the hydrogen sensor can be installed in a smaller space.

[0051] 3. Sensitive Film The sensitive film in the present disclosure contains a catalyst that dissociates hydrogen molecules and tungsten oxide.

[0052] The sensitive film may be a single layer containing a catalyst and tungsten oxide, or may include, in order from the substrate side, a tungsten oxide layer containing tungsten oxide and a catalyst layer containing a catalyst.

[0053] When the sensitive film includes a tungsten oxide layer and a catalyst layer, the catalyst layer may be a continuous film or a discontinuous film.

[0054] The catalyst is not particularly limited as long as it can dissociate hydrogen molecules into hydrogen ions (protons), and examples thereof include noble metals such as palladium, platinum, iridium, etc. The catalyst may be used alone or in combination of two or more.

[0055] Tungsten oxide is tungsten trioxide (WO ３ )

[0056] The position of the sensitive film is not particularly limited as long as it is disposed in contact with the pair of electrodes. For example, the pair of electrodes and the sensitive film may be disposed in this order on the first surface of the substrate, or the sensitive film and the pair of electrodes may be disposed in this order on the first surface of the substrate.

[0057] When the sensitive film is a single layer containing a catalyst and tungsten oxide, the thickness of the sensitive film is not particularly limited as long as it is thick enough to detect changes in the resistance value of the sensitive film, and is, for example, 100 nm or more and 3000 nm or less.

[0058] On the other hand, when the sensitive film includes a tungsten oxide layer and a catalyst layer, the thickness of the tungsten oxide layer is not particularly limited as long as it is a thickness that allows detection of changes in the resistance value of the tungsten oxide layer, and is, for example, 100 nm or more and 3000 nm or less. The thickness of the catalyst layer is also appropriately selected depending on the method for forming the catalyst layer. When the catalyst layer is formed by a vapor deposition method, the thickness of the catalyst layer is, for example, 1 nm or more and 10 nm or less. On the other hand, when the catalyst layer is formed by a coating method, the thickness of the catalyst layer is, for example, 10 nm or more and 100 nm or less.

[0059] The area of ​​the sensitive film in a plan view is not particularly limited, and may be, for example, 1 cm ２ Over 9cm ２ The following is the result.

[0060] When the sensitive film is a single layer containing a catalyst and tungsten oxide, the sensitive film can be formed by, for example, a sol-gel method. For examples of methods for forming sensitive films using the sol-gel method, see Japanese Patent Nos. 5,152,797 and 5,540,248.

[0061] On the other hand, when the sensitive film includes a tungsten oxide layer and a catalyst layer, the method for forming the tungsten oxide layer is not particularly limited, and examples thereof include a sol-gel method, a vacuum deposition method, a sputtering method, and an ion plating method.The method for forming the catalyst layer is also not particularly limited, and examples thereof include a deposition method such as a vacuum deposition method, a sputtering method, and an ion plating method, and a coating method in which a resin composition containing a catalyst and a binder resin is applied.

[0062] 4. Pair of Electrodes In the present disclosure, the pair of electrodes is disposed on the first surface of the substrate in contact with the sensitive film. The pair of electrodes is typically disposed at a distance that allows a change in the resistance value of the sensitive film to be detected. In this specification, the "distance that allows a change in the resistance value of the sensitive film to be detected" refers to a distance that allows the pair of electrodes to short-circuit when the reduction reaction of the tungsten oxide described above occurs and the resistance value of the sensitive film decreases.

[0063] The pair of electrodes is preferably a pair of comb-shaped electrodes. Specifically, as shown in FIG. 5 , the pair of electrodes 4a, 4b includes a plurality of first sensor electrodes 11 and a plurality of second sensor electrodes 12, a first bus electrode 13 connected to the first sensor electrodes 11, and a second bus electrode 14 connected to the second sensor electrodes 12. The plurality of first sensor electrodes and the plurality of second sensor electrodes are preferably arranged on the first surface of the substrate in contact with the sensitive film and alternately spaced at intervals that allow detection of changes in the resistance value of the sensitive film. The electrode 4a includes a plurality of first sensor electrodes 11 and a first bus electrode 13 connected to the first sensor electrodes 11. The electrode 4b includes a plurality of second sensor electrodes 12 and a second bus electrode 14 connected to the second sensor electrodes 12.

[0064] Examples of conductive materials used for the pair of electrodes include carbon and metal materials. Of these, carbon is preferred. Carbon is inactive to hydrogen gas and inexpensive. As described above, when the sensitive film and the pair of electrodes are arranged in this order on the first surface of the substrate, the conductive material used for the pair of electrodes is preferably inactive to hydrogen gas. On the other hand, when the pair of electrodes and the sensitive film are arranged in this order on the first surface of the substrate, the conductive material used for the pair of electrodes is not exposed to hydrogen gas, and therefore may be active or inactive to hydrogen gas.

[0065] The thickness of the pair of electrodes is not particularly limited as long as it is a thickness that allows the electrodes to function, and is, for example, 0.1 μm or more and 2 μm or less.

[0066] The method for forming the pair of electrodes is not particularly limited, and examples thereof include a method of forming a conductive film and patterning it, a mask vapor deposition method, and a printing method. Examples of the method for forming the conductive film include a vacuum vapor deposition method, a sputtering method, an ion plating method, and a plating method. Examples of the patterning method include an etching method and a lift-off method.

[0067] Three embodiments of the pair of electrodes will be described below.

[0068] (1) First Aspect In the pair of electrodes of this aspect, one first bus electrode and one second bus electrode are arranged in a line that can be drawn in one stroke, and one end of the first bus electrode and one end of the second bus electrode are connected to the IC tag.

[0069] 6 and 7 , first bus electrode 13 and second bus electrode 14 are arranged in a line that can be drawn in one stroke. Specifically, first bus electrode 13 and second bus electrode 14 are arranged in a meandering line. In Fig. 6 , one end of first bus electrode 13 and one end of second bus electrode 14 are connected to IC tag 5. In Fig. 7 , one end of first bus electrode 13 and one end of second bus electrode 14 are connected to first IC tag 5a, and the other end of first bus electrode 13 and the other end of second bus electrode 14 are connected to second IC tag 5b.

[0070] The distance between the first sensor electrode and the second sensor electrode may be any distance that allows detection of changes in the resistance value of the sensitive membrane. The distance may be, for example, 100 μm or more, or 500 μm or more. As described above, as the distance becomes narrower, the resistance between the sensor terminals when the hydrogen concentration is zero tends to decrease. Therefore, if the distance is too narrow, the resistance between the sensor terminals when the hydrogen concentration is zero may be lower than the first threshold resistance value. The distance may also be, for example, 10 mm or less, or 5 mm or less. As described above, as the distance becomes wider, the resistance between the sensor terminals when the hydrogen concentration is a set value tends to increase. Therefore, if the distance is too wide, the resistance between the sensor terminals when the hydrogen concentration is a set value may be higher than the second threshold resistance value. That is, the distance may be, for example, 100 μm or more and 10 mm or less, or 500 μm or more and 5 mm or less.

[0071] The distance between the first and second sensor electrodes refers to the distance from the edge of the adjacent first sensor electrode to the edge of the adjacent second sensor electrode. For example, in Fig. 6, the distance between the first and second sensor electrodes 11 and 12 is indicated by the shortest distance d1 between the adjacent first and second sensor electrodes 11 and 12.

[0072] The width of the first sensor electrode and the width of the second sensor electrode may be any width that allows detection of changes in the resistance value of the sensitive membrane. The width may be, for example, 100 μm or more and 500 μm or more. The width may be, for example, 10 mm or less and 5 mm or less. That is, the width may be, for example, 100 μm or more and 10 mm or less, or 500 μm or more and 5 mm or less. For example, in FIG. 6 , the width of the first sensor electrode 11 is indicated by a length b1 in a direction perpendicular to the extension direction of the first sensor electrode 11. The width of the second sensor electrode 12 is indicated by a length b2 in a direction perpendicular to the extension direction of the second sensor electrode 12.

[0073] The lengths of the first sensor electrode and the second sensor electrode may be any lengths that allow detection of changes in the resistance value of the sensitive membrane. The lengths may be, for example, 10 mm or more, or 50 mm or more. The lengths may be, for example, 500 mm or less, or 100 mm or less. That is, the lengths may be, for example, 10 mm or more and 500 mm or less, or 50 mm or more and 100 mm or less. For example, in FIG. 6 , the length of the first sensor electrode 11 is indicated by a length a1 in the direction in which the first sensor electrode 11 extends. The length of the second sensor electrode 12 is indicated by a length a2 in the direction in which the second sensor electrode 12 extends.

[0074] The overlap length between the first sensor electrode and the second sensor electrode may be any length that allows detection of changes in the resistance value of the sensitive membrane. The overlap length may be, for example, 9 mm or more, or 45 mm or more. The overlap length may be, for example, 450 mm or less, or 90 mm or less. That is, the overlap length may be, for example, 9 mm or more and 450 mm or less, or 45 mm or more and 90 mm or less. For example, in FIG. 6 , the overlap length between the first sensor electrode 11 and the second sensor electrode 12 is indicated by the length c of the portion where the first sensor electrode 11 and the second sensor electrode 12 face each other in the direction in which the first sensor electrode 11 and the second sensor electrode 12 extend.

[0075] The number of first sensor electrodes and the number of second sensor electrodes are set appropriately depending on the size of the hydrogen sensor, the arrangement of the first bus electrodes, the arrangement of the second bus electrodes, and the like.

[0076] The shapes of the first sensor electrode and the second sensor electrode are not particularly limited, and may be, for example, linear, polygonal, or curved. For example, in Fig. 6, the first sensor electrode 11 and the second sensor electrode 12 are linear. Also, in Fig. 8, the first sensor electrode 11 is linear and polygonal, and the second sensor electrode 12 is linear.

[0077] The first bus electrode and the second bus electrode are arranged in a linear shape that can be drawn in one stroke. In this specification, "linear shape that can be drawn in one stroke" means that the electrodes are formed of a single continuous line with no overlapping portions.

[0078] The linear shape that can be drawn in one stroke is not particularly limited as long as it allows the first bus electrode, second bus electrode, first sensor electrode, and second sensor electrode to be arranged over the entire first surface of the substrate, and examples thereof include meandering linear shapes as shown in Figures 6 and 7 and spiral shapes as shown in Figure 8. Of these, it is preferable that the first bus electrode and second bus electrode are arranged in a meandering linear shape. In this case, the first bus electrode and second bus electrode can be formed by a roll-to-roll process, allowing for efficient mass production of hydrogen sensors.

[0079] Since the multiple first sensor electrodes connected to the first bus electrode and the multiple second sensor electrodes connected to the second bus electrode are arranged alternately, the first bus electrodes and the second bus electrodes are arranged along each other.

[0080] The width of the first bus electrode and the width of the second bus electrode may be any width that allows them to function as electrodes. The width may be, for example, 1 mm or more, and may be 5 mm or more. The width may be, for example, 50 mm or less, and may be 10 mm or less. That is, the width may be, for example, 1 mm or more and 50 mm or less, and may be 5 mm or more and 10 mm or less. For example, in FIG. 6 , the width of the first bus electrode 13 is indicated by a length e1 in a direction perpendicular to the direction in which the first bus electrode 13 extends. The width of the second bus electrode 14 is indicated by a length e2 in a direction perpendicular to the direction in which the second bus electrode 14 extends.

[0081] The distance between the first bus electrode and the second bus electrode that face each other across the first sensor electrode and the second sensor electrode need only be sufficient to allow the first sensor electrode and the second sensor electrode to be arranged. The distance may be, for example, 11 mm or more and 55 mm or more. The distance may also be, for example, 550 mm or less and 110 mm or less. That is, the distance may be, for example, 11 mm or more and 550 mm or less and 55 mm or more and 110 mm or less. For example, in FIG. 6 , the distance between the first bus electrode 13 and the second bus electrode 14 that face each other across the first sensor electrode 11 and the second sensor electrode 12 is indicated by the shortest distance f of the line connecting the first bus electrode 13 and the second bus electrode 14 that face each other across the first sensor electrode 11 and the second sensor electrode 12.

[0082] The distance between the first and second bus electrodes facing each other without the first and second sensor electrodes sandwiched therebetween may be sufficient to prevent detection of changes in the resistance value of the sensitive membrane. The distance may be, for example, 10 mm or more, or 50 mm or more. The distance may also be, for example, 100 mm or less, or 70 mm or less. That is, the distance may be, for example, 10 mm or more, 100 mm or less, or 50 mm or more, 70 mm or less. If the distance is too small, the reduction reaction of tungsten oxide may occur, and when the resistance value of the sensitive membrane decreases, the first and second bus electrodes facing each other without the first and second sensor electrodes sandwiched therebetween may become more conductive. The distance is appropriately selected depending on the thickness of the sensitive membrane. As the thickness of the sensitive membrane increases, the first and second bus electrodes facing each other without the first and second sensor electrodes sandwiched therebetween tend to be less likely to short-circuit. Therefore, if the thickness of the sensitive membrane is relatively thick, the distance may be relatively small within the above range. On the other hand, as the thickness of the sensitive film becomes thinner, the first bus electrode and the second bus electrode that face each other without the first sensor electrode and the second sensor electrode sandwiched therebetween tend to be more likely to short-circuit. Therefore, when the thickness of the sensitive film is relatively thin, it is preferable that the above-mentioned distance be relatively large within the above-mentioned range. For example, in Figure 6, the distance between the first bus electrode 13 and the second bus electrode 14 that face each other without the first sensor electrode 11 and the second sensor electrode 12 sandwiched therebetween is represented by the shortest distance g of the line connecting the first bus electrode 13 and the second bus electrode 14 that face each other without the first sensor electrode 11 and the second sensor electrode 12 sandwiched therebetween.

[0083] The distance between adjacent first bus electrodes and the distance between adjacent second bus electrodes may be any distance that prevents detection of changes in the resistance value of the sensitive film. The distance may be, for example, 10 mm or more, or 50 mm or more. The distance may also be, for example, 100 mm or less, or 70 mm or less. That is, the distance may be, for example, 10 mm or more and 100 mm or less, or 50 mm or more and 70 mm or less. If the distance is too small, the reduction reaction of tungsten oxide may occur, and when the resistance value of the sensitive film decreases, adjacent first bus electrodes or adjacent second bus electrodes may become more likely to be electrically connected to each other. The distance is appropriately selected depending on the thickness of the sensitive film. As the thickness of the sensitive film increases, adjacent first bus electrodes or adjacent second bus electrodes tend to be less likely to short-circuit. Therefore, when the thickness of the sensitive film is relatively thick, the distance may be relatively small within the above range. On the other hand, as the thickness of the sensitive film decreases, adjacent first bus electrodes or adjacent second bus electrodes tend to be more likely to short-circuit to each other. Therefore, when the thickness of the sensitive film is relatively thin, it is preferable that the above-mentioned interval be relatively large within the above-mentioned range. For example, in Figure 6, the interval between adjacent first bus electrodes 13 is indicated by the shortest distance h1 of the line connecting adjacent first bus electrodes 13. Furthermore, the interval between adjacent second bus electrodes 14 is indicated by the shortest distance h2 of the line connecting adjacent second bus electrodes 14.

[0084] In this embodiment, the number of first bus electrodes and the number of second bus electrodes are typically 1. However, as long as the first bus electrode and the second bus electrode form a pair, the number of first bus electrodes and the number of second bus electrodes may be 2. For example, in Fig. 9, hydrogen sensor 1 includes two first bus electrodes 13a, 13b and two second bus electrodes 14a, 14b, where first bus electrode 13a and second bus electrode 14a form a pair, and first bus electrode 13b and second bus electrode 14b form a pair.

[0085] (2) Second Aspect In the pair of electrodes of this aspect, the plurality of first bus electrodes and the plurality of second bus electrodes are connected to the IC tag via a flexible printed circuit board.

[0086] 10, the plurality of first bus electrodes 13 and the plurality of second bus electrodes 14 are connected to IC tag 5 via flexible printed circuit board 9. In Fig. 11, one end of the plurality of first bus electrodes 13 and one end of the plurality of second bus electrodes 14 are connected to first IC tag 5a via flexible printed circuit board 9, and the other end of the plurality of first bus electrodes 13 and the other end of the plurality of second bus electrodes 14 are connected to second IC tag 5b via flexible printed circuit board 9.

[0087] In this embodiment, the first bus electrode and the second bus electrode can be arranged linearly, which reduces the risk of disconnection.

[0088] The distance between the first sensor electrode and the second sensor electrode may be any distance that allows detection of changes in the resistance value of the sensitive membrane. The distance may be, for example, 100 μm or more, or 500 μm or more. As described above, as the distance becomes narrower, the resistance between the sensor terminals when the hydrogen concentration is zero tends to decrease. Therefore, if the distance is too narrow, the resistance between the sensor terminals when the hydrogen concentration is zero may be lower than the first threshold resistance value. The distance may also be, for example, 10 mm or less, or 5 mm or less. As described above, as the distance becomes wider, the resistance between the sensor terminals when the hydrogen concentration is a set value tends to increase. Therefore, if the distance is too wide, the resistance between the sensor terminals when the hydrogen concentration is a set value may be higher than the second threshold resistance value. That is, the distance may be, for example, 100 μm or more and 10 mm or less, or 500 μm or more and 5 mm or less.

[0089] The distance between the first and second sensor electrodes refers to the distance from the edge of the adjacent first sensor electrode to the edge of the adjacent second sensor electrode. For example, in Fig. 10, the distance between the first and second sensor electrodes 11 and 12 is indicated by the shortest distance d1 between the adjacent first and second sensor electrodes 11 and 12.

[0090] The width of the first sensor electrode and the width of the second sensor electrode may be any width that allows detection of changes in the resistance value of the sensitive membrane. The width may be, for example, 100 μm or more and 500 μm or more. The width may be, for example, 10 mm or less and 5 mm or less. That is, the width may be, for example, 100 μm or more and 10 mm or less, or 500 μm or more and 5 mm or less. For example, in FIG. 10 , the width of the first sensor electrode 11 is indicated by a length b1 in a direction perpendicular to the extension direction of the first sensor electrode 11. The width of the second sensor electrode 12 is indicated by a length b2 in a direction perpendicular to the extension direction of the second sensor electrode 12.

[0091] The lengths of the first sensor electrode and the second sensor electrode may be any lengths that allow detection of changes in the resistance value of the sensitive membrane. The lengths may be, for example, 10 mm or more, or 50 mm or more. The lengths may be, for example, 500 mm or less, or 100 mm or less. That is, the lengths may be, for example, 10 mm or more and 500 mm or less, or 50 mm or more and 100 mm or less. For example, in FIG. 10 , the length of the first sensor electrode 11 is indicated by a length a1 in the direction in which the first sensor electrode 11 extends. The length of the second sensor electrode 12 is indicated by a length a2 in the direction in which the second sensor electrode 12 extends.

[0092] The overlap length between the first sensor electrode and the second sensor electrode may be any length that allows detection of changes in the resistance value of the sensitive membrane. The overlap length may be, for example, 9 mm or more, or 45 mm or more. The overlap length may be, for example, 450 mm or less, or 90 mm or less. That is, the overlap length may be, for example, 9 mm or more and 450 mm or less, or 45 mm or more and 90 mm or less. For example, in FIG. 10 , the overlap length between the first sensor electrode 11 and the second sensor electrode 12 is indicated by the length c of the portion where the first sensor electrode 11 and the second sensor electrode 12 face each other in the direction in which the first sensor electrode 11 and the second sensor electrode 12 extend.

[0093] The number of first sensor electrodes and the number of second sensor electrodes are set appropriately depending on the size of the hydrogen sensor, the arrangement of the first bus electrodes, the arrangement of the second bus electrodes, and the like.

[0094] The shapes of the first sensor electrode and the second sensor electrode are not particularly limited, and may be, for example, linear, polygonal, or curved.

[0095] The first bus electrode and the second bus electrode form a pair and are arranged alternately.

[0096] The width of the first bus electrode and the width of the second bus electrode may be any width that allows them to function as electrodes. The width may be, for example, 1 mm or more, and may be 5 mm or more. The width may be, for example, 50 mm or less, and may be 10 mm or less. That is, the width may be, for example, 1 mm or more and 50 mm or less, and may be 5 mm or more and 10 mm or less. For example, in FIG. 10 , the width of the first bus electrode 13 is indicated by a length e1 in a direction perpendicular to the direction in which the first bus electrode 13 extends. The width of the second bus electrode 14 is indicated by a length e2 in a direction perpendicular to the direction in which the second bus electrode 14 extends.

[0097] The distance between the first bus electrode and the second bus electrode may be any distance that allows the first sensor electrode and the second sensor electrode to be arranged. The distance may be, for example, 11 mm or more and 55 mm or more. The distance may also be, for example, 550 mm or less and 110 mm or less. That is, the distance may be, for example, 11 mm or more and 550 mm or less and 55 mm or more and 110 mm or less. For example, in FIG. 10 , the distance between the first bus electrode 13 and the second bus electrode 14 is indicated by the shortest distance f of the line connecting the first bus electrode 13 and the second bus electrode 14, which face each other across the first sensor electrode 11 and the second sensor electrode 12.

[0098] The number of first bus electrodes and the number of second bus electrodes are plural. The first bus electrodes and the second bus electrodes only need to form a pair, and the number of first bus electrodes and the number of second bus electrodes may be the same or different. For example, in Figure 10, there are four first bus electrodes 13 and five second bus electrodes 14, so the number of first bus electrodes and the number of second bus electrodes are different.

[0099] The plurality of first bus electrodes and the plurality of second bus electrodes are connected to the IC tag via a flexible printed circuit (FPC), which may be a general FPC.

[0100] (3) Third Aspect In the pair of electrodes of this aspect, the plurality of first bus electrodes are arranged along a first direction, and the plurality of second bus electrodes are arranged along a second direction perpendicular to the first direction. In this aspect, the IC tag includes a third IC tag connected to one end of the plurality of first bus electrodes and a fourth IC tag connected to one end of the plurality of second bus electrodes, and an insulating film is arranged between the first bus electrode and the second bus electrode in a region where the first bus electrode and the second bus electrode intersect.

[0101] 12 , the plurality of first bus electrodes 13 are linearly arranged in a first direction D1, and the plurality of second bus electrodes 14 are linearly arranged in a second direction D2 perpendicular to the first direction D1. The IC tag includes a third IC tag 5c connected to one end of the plurality of first bus electrodes 13 and a fourth IC tag 5d connected to one end of the plurality of second bus electrodes 14. In the region where the first bus electrodes 13 and the second bus electrodes 14 intersect, an insulating film 15 is arranged between the first bus electrodes 13 and the second bus electrodes 14.

[0102] In this embodiment, the first bus electrode and the second bus electrode do not need to be arranged in a linear manner that can be drawn in one stroke, thereby reducing the risk of disconnection. Also, as shown in Figure 12, the area of ​​the overlapping portion 10C of the first sensor electrode 11 and the second sensor electrode 12 can be made constant, thereby reducing signal variation and improving detection sensitivity.

[0103] The distance between the first sensor electrode and the second sensor electrode may be any distance that allows detection of changes in the resistance value of the sensitive membrane. The distance may be, for example, 100 μm or more, or 500 μm or more. As described above, as the distance becomes narrower, the resistance between the sensor terminals when the hydrogen concentration is zero tends to decrease. Therefore, if the distance is too narrow, the resistance between the sensor terminals when the hydrogen concentration is zero may be lower than the first threshold resistance value. The distance may also be, for example, 10 mm or less, or 5 mm or less. As described above, as the distance becomes wider, the resistance between the sensor terminals when the hydrogen concentration is a set value tends to increase. Therefore, if the distance is too wide, the resistance between the sensor terminals when the hydrogen concentration is a set value may be higher than the second threshold resistance value. That is, the distance may be, for example, 100 μm or more and 10 mm or less, or 500 μm or more and 5 mm or less.

[0104] The distance between the first and second sensor electrodes refers to the distance from the edge of the adjacent first sensor electrode to the edge of the adjacent second sensor electrode. For example, in Fig. 12, the distance between the first and second sensor electrodes 11 and 12 is indicated by the shortest distance d1 between the adjacent first and second sensor electrodes 11 and 12.

[0105] The width of the first sensor electrode and the width of the second sensor electrode may be any width that allows detection of changes in the resistance value of the sensitive membrane. The width may be, for example, 100 μm or more and 500 μm or more. The width may be, for example, 10 mm or less and 5 mm or less. That is, the width may be, for example, 100 μm or more and 10 mm or less, or 500 μm or more and 5 mm or less. For example, in FIG. 12 , the width of the first sensor electrode 11 is indicated by a length b1 in a direction perpendicular to the extension direction of the first sensor electrode 11. The width of the second sensor electrode 12 is indicated by a length b2 in a direction perpendicular to the extension direction of the second sensor electrode 12.

[0106] The lengths of the first sensor electrode and the second sensor electrode may be any lengths that allow for detection of changes in the resistance value of the sensitive membrane. The lengths may be, for example, 10 mm or more, or 50 mm or more. The lengths may be, for example, 500 mm or less, or 100 mm or less. That is, the lengths may be, for example, 10 mm or more and 500 mm or less, or 50 mm or more and 100 mm or less. For example, in FIG. 12 , the length of the first sensor electrode 11 is indicated by a length a1 in the direction in which the first sensor electrode 11 extends. The length of the second sensor electrode 12 is indicated by a length a2 in the direction in which the second sensor electrode 12 extends.

[0107] The overlap length between the first sensor electrode and the second sensor electrode may be any length that allows detection of changes in the resistance value of the sensitive membrane. The overlap length may be, for example, 9 mm or more, or 45 mm or more. The overlap length may be, for example, 450 mm or less, or 90 mm or less. That is, the overlap length may be, for example, 9 mm or more and 450 mm or less, or 45 mm or more and 90 mm or less. For example, in FIG. 12 , the overlap length between the first sensor electrode 11 and the second sensor electrode 12 is indicated by the length c of the portion where the first sensor electrode 11 and the second sensor electrode 12 face each other in the direction in which the first sensor electrode 11 and the second sensor electrode 12 extend.

[0108] The number of first sensor electrodes and the number of second sensor electrodes are set appropriately depending on the size of the hydrogen sensor, the arrangement of the first bus electrodes, the arrangement of the second bus electrodes, and the like.

[0109] The shapes of the first sensor electrode and the second sensor electrode are not particularly limited, and may be, for example, linear, polygonal, or curved. The first sensor electrode and the second sensor electrode may also have a branched shape. For example, in FIG. 12 , the first sensor electrode 11 has a linear shape, and the second sensor electrode 12 has a branched shape. For example, in FIG. 13 , the first sensor electrode 11 has a linear shape, and the second sensor electrode 12 has a polygonal shape.

[0110] The plurality of first bus electrodes are arranged along a first direction, and the plurality of second bus electrodes are arranged along a second direction perpendicular to the first direction.

[0111] The width of the first bus electrode and the width of the second bus electrode may be any width that allows them to function as electrodes. The width may be, for example, 1 mm or more, and may be 5 mm or more. The width may be, for example, 50 mm or less, and may be 10 mm or less. That is, the width may be, for example, 1 mm or more and 50 mm or less, and may be 5 mm or more and 10 mm or less. For example, in FIG. 12 , the width of the first bus electrode 13 is indicated by a length e1 in a direction perpendicular to the direction in which the first bus electrode 13 extends. The width of the second bus electrode 14 is indicated by a length e2 in a direction perpendicular to the direction in which the second bus electrode 14 extends.

[0112] The distance between adjacent first bus electrodes and the distance between adjacent second bus electrodes may be any distance that allows the first sensor electrodes and the second sensor electrodes to be arranged. The distance may be, for example, 11 mm or more and 55 mm or more. The distance may be, for example, 550 mm or less and 110 mm or less. That is, the distance may be, for example, 11 mm or more and 550 mm or less and 55 mm or more and 110 mm or less. For example, in FIG. 12 , the distance between adjacent first bus electrodes 13 is indicated by the shortest distance k1 of the line connecting adjacent first bus electrodes 13. The distance between adjacent second bus electrodes 14 is indicated by the shortest distance k2 of the line connecting adjacent second bus electrodes 14.

[0113] The number of the first bus electrodes and the number of the second bus electrodes are plural.

[0114] In this embodiment, the insulating film is disposed between the first bus electrode and the second bus electrode in the region where the first bus electrode and the second bus electrode intersect. The material of the insulating film is not particularly limited as long as it is an insulating material, and examples thereof include inorganic oxides, inorganic nitrides, inorganic carbides, and resins. The thickness of the insulating film is not particularly limited as long as it is thick enough to insulate the first bus electrode and the second bus electrode, and is, for example, 0.1 μm or more and 2 μm or less. The method for forming the insulating film is not particularly limited, and examples thereof include a method of forming an insulating film and patterning it, a mask vapor deposition method, and a printing method. Examples of methods for forming the insulating film include a vacuum vapor deposition method, a sputtering method, an ion plating method, and a plating method. Examples of patterning methods include an etching method and a lift-off method.

[0115] In this aspect, with regard to the position of the sensitive film, for example, the first sensor electrode, the second sensor electrode, and the sensitive film may be arranged in this order on the first surface of the substrate; the sensitive film, the first sensor electrode, and the second sensor electrode may be arranged in this order on the first surface of the substrate; the first sensor electrode, the sensitive film, and the second sensor electrode may be arranged in this order on the first surface of the substrate; or the second sensor electrode, the sensitive film, and the first sensor electrode may be arranged in this order on the first surface of the substrate.

[0116] In this embodiment, the IC tag includes a third IC tag connected to one end of each of the plurality of first bus electrodes and a fourth IC tag connected to one end of each of the plurality of second bus electrodes. The IC tag may also include the third IC tag, the fourth IC tag, and a fifth IC tag connected to the other end of each of the plurality of first bus electrodes. The IC tag may also include the third IC tag, the fourth IC tag, and a sixth IC tag connected to the other end of each of the plurality of second bus electrodes. The IC tag may also include the third IC tag, the fourth IC tag, the fifth IC tag, and the sixth IC tag. For example, in FIG. 14 , the IC tag includes a third IC tag 5c connected to one end of each of the plurality of first bus electrodes 13, a fourth IC tag 5d connected to one end of each of the plurality of second bus electrodes 14, and a fifth IC tag 5e connected to the other end of each of the plurality of first bus electrodes 13.

[0117] 5. Substrate The substrate in the present disclosure is an insulating member that supports the sensitive membrane and the pair of electrodes.

[0118] The substrate is not particularly limited as long as it has insulating properties, and examples thereof include a glass substrate, a resin substrate, a ceramic substrate, and a silicon substrate having an insulating film on its surface.

[0119] The thickness of the substrate is not particularly limited, and is, for example, 10 μm or more and 2 mm or less.

[0120] 6. Other Configurations In the present disclosure, the sensitive film and the pair of electrodes may be disposed on the first surface of the substrate. The sensitive film and the pair of electrodes may be disposed on only one surface of the substrate, or the sensitive film and the pair of electrodes may be disposed on each of both surfaces of the substrate.

[0121] B. Hydrogen Detection System The hydrogen detection system of the present disclosure uses the hydrogen sensor described above.

[0122] Figure 15 is a schematic diagram showing an example of a hydrogen detection system according to the present disclosure. In Figure 15, a hydrogen detection system 30 includes multiple hydrogen sensors 1, an RFID reader / writer 31, and multiple antennas 32 connected to the RFID reader / writer 31. The hydrogen sensors 1 are attached to an underground hydrogen pipeline 41. The RFID reader / writer 31 and antenna 32 are fixed and installed at any location near the ground.

[0123] Figure 16 is a schematic diagram showing another example of a hydrogen detection system according to the present disclosure. In Figure 16, a hydrogen detection system 30 includes multiple hydrogen sensors 1, an RFID reader / writer 31, and an antenna 32 connected to the RFID reader / writer 31. The hydrogen sensors 1 are attached to an underground hydrogen pipeline 41. The RFID reader / writer 31 and antenna 32 are installed on a mobile object 33, making the system mobile.

[0124] Figure 17 is a schematic diagram showing another example of a hydrogen detection system according to the present disclosure. In Figure 17, the hydrogen detection system 30 is used in a hydrogen station. The hydrogen detection system 30 includes a plurality of hydrogen sensors 1, an RFID reader / writer 31, and an antenna 32 connected to the RFID reader / writer 31. The hydrogen sensors 1 are attached to a dispenser 42 that supplies hydrogen to automobiles and the like. The RFID reader / writer 31 and antenna 32 are fixedly installed in a canopy (roof) 43.

[0125] In such a hydrogen detection system, the IC chip that constitutes the IC tag of the hydrogen sensor is driven in a non-contact manner, and changes in the resistance value of the sensitive film can be detected, thereby making it possible to detect hydrogen gas.

[0126] The hydrogen detection system of the present disclosure is not particularly limited as long as it is a system that uses a hydrogen sensor, but is preferably a system that uses RFID. Specifically, the hydrogen detection system of the present disclosure includes a hydrogen sensor, an RFID reader / writer, and an antenna connected to the RFID reader / writer.

[0127] The RFID reader / writer may be either fixed or mobile. When a fixed RFID reader / writer is used, continuous monitoring is possible. On the other hand, when a mobile RFID reader / writer is used, trace inspection can be performed, making the trace inspection more advanced, smarter, and less manpower-intensive.

[0128] The hydrogen detection system disclosed herein can be used not only in small devices such as fuel cells, but also in large facilities such as hydrogen production facilities, hydrogen pipelines, transport tankers, storage tanks, hydrogen power generation facilities, hydrogen stations, etc. As hydrogen pipelines, not only underground pipelines but also aerial pipelines can be used.

[0129] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure.

[0130] Hereinafter, the present disclosure will be described in more detail with reference to examples and comparative examples.

[0131] Example 1 A pair of electrodes was formed by printing on a 100 μm thick polyethylene terephthalate (PET) film. In the pair of electrodes, the length a1 of the first sensor electrode and the length a2 of the second sensor electrode were 5 mm, the width b1 of the first sensor electrode and the width b2 of the second sensor electrode were 0.5 mm, the distance d1 between the first sensor electrode and the second sensor electrode was 0.5 mm, and the width e1 of the first bus electrode and the width e2 of the second bus electrode were 0.5 mm. The thickness of the pair of electrodes was 0.15 μm.

[0132] Next, Tomoji Ohishi et al., Materials Sciences and Applications, "Low-Temperature Formation of a WO ３A sensitive film was formed on the PET film by the sol-gel method so as to cover the pair of electrodes, with reference to "Thin Film by the Sol-Gel Method Using Photo-Irradiation and Fabrication of a Flexible Hydrogen Sensor," 2020, 11, pp. 135-149. Specifically, tungsten hexachloride (WCl ) manufactured by Sigma-Aldrich was used as a raw material for tungsten oxide. ６ ), palladium (II) acetate manufactured by Kanto Chemical Co., Ltd. was used as the catalyst, and polystyrene (polymerization degree 2000) manufactured by Wako Pure Chemical Industries, Ltd. was used as the resin binder. The tungsten oxide raw material was dissolved in ethanol and applied to the PET film to form a precursor film. Next, the precursor film was irradiated with light at wavelengths of 254 nm and 185 nm and an illuminance of 12 mW / cm. ２ The film was irradiated with ultraviolet light at 100°C for 20 minutes. Next, the catalyst was added to a 10 wt% polystyrene toluene solution to prepare a 1 wt% Pd-containing solution. This Pd-containing solution was applied to the precursor film and heated at 100°C for 10 minutes. The sensitive film included, from the PET film side, a tungsten oxide layer and a catalyst layer, with the tungsten oxide layer being 600 nm thick and the catalyst layer being 90 nm thick.

[0133] Next, an IC tag was fabricated that included an IC chip (UCODE G2iM+ manufactured by NXP) and an antenna. Specifically, copper foil was attached to a glass epoxy substrate, and the copper foil was patterned according to a design drawing to form an antenna. The copper foil was patterned by etching or grinding with a grinder. Next, the IC chip was mounted so that the antenna terminal was connected to the antenna, and an IC tag was fabricated. The antenna was designed to be sensitive to UHF radio waves. Next, an IC tag was connected to a pair of electrodes to obtain a hydrogen sensor.

[0134] Comparative Example 1 A hydrogen sensor was fabricated in the same manner as in Example 1, except that the thickness of the tungsten oxide layer was set to 1.5 μm.

[0135] Comparative Example 2 A hydrogen sensor was fabricated in the same manner as in Example 1, except that the distance d1 between the first sensor electrode and the second sensor electrode was set to 1.0 mm.

[0136] [Evaluation] A UHF-band RFID reader / writer was used to transmit readout radio waves to the hydrogen sensor of Example 1, and it was confirmed that the reflected and transmitted radio waves could be detected. Furthermore, when radio waves were transmitted in the same manner as above while the hydrogen sensor was exposed to hydrogen gas, the signal level of the reflected and transmitted radio waves changed. This confirmed that hydrogen gas can be detected without the hydrogen sensor itself being equipped with a power source.

[0137] The resistance between the sensor terminals of the hydrogen sensor at a predetermined hydrogen concentration was determined using the following method. First, the gas mixing device and the sealed gas chamber were connected via gas piping. A Kofloc Corporation "GM-4B" gas mixing device with built-in flow meter was used as the gas mixing device. The sealed gas chamber was a metal sealed gas chamber with a partial glass transparent window and rubber gasket. The sealed gas chamber was cylindrical, with a diameter of 100 mm and a height of 20 mm. Stainless steel fixed piping was used as the gas piping. The IC tag was removed from the hydrogen sensor, and the hydrogen sensor was sealed in a sealed gas chamber connected to the gas mixing device. An LCR meter (Hiroki Corporation "IM3523") was connected to a pair of electrodes that were respectively connected to a pair of sensor terminals on the IC tag. The LCR meter was installed outside the sealed gas chamber via electrical wiring and gaskets. The set temperature was 25°C. The target fluids were hydrogen and air. The flow rate of the mixed gas of hydrogen and air was always set to 10 mL / min.

[0138] First, the hydrogen and air mixture ratio was set to 0% hydrogen, i.e., 100% air. Subsequently, the hydrogen concentration state was maintained for 10 minutes so that the predetermined hydrogen concentration was reached in the sealed gas chamber. Then, an LCR meter ("IM3523" manufactured by Hiroki) was used to measure the impedance at a frequency of 20 kHz for a pair of electrodes connected to a pair of sensor terminals of the IC tag, respectively, and the resistance value between the pair of electrodes was calculated from the impedance. The measurement was performed five times, and the average of the three measurements, excluding the maximum and minimum values, was used as the resistance value between the sensor terminals at the predetermined hydrogen concentration.

[0139] When changing the hydrogen concentration and determining the resistance value between the sensor terminals of the hydrogen sensor at a specified hydrogen concentration, the sealed gas chamber was opened and maintained for 10 minutes, then returned to an air atmosphere, and the above procedure was repeated.

[0140] The results for the hydrogen sensor of Example 1 are shown in Figure 18. The results for the hydrogen sensors of Comparative Examples 1 and 2 are shown in Figure 19.

[0141] In Example 1, when the hydrogen concentration was 0.00005%, which is the hydrogen concentration in air, the resistance between the sensor terminals was equal to or greater than the first threshold resistance value T1, and when the hydrogen concentration was 1%, which was the set value, the resistance between the sensor terminals was equal to or less than the second threshold resistance value T2. On the other hand, in Comparative Example 1, the thickness of the sensitive film was increased, so that when the hydrogen concentration was 0.00005%, which is the hydrogen concentration in air, the resistance between the sensor terminals was lower than the first threshold resistance value T1, as shown in Fig. 19. Furthermore, in Comparative Example 2, the distance d1 between the first and second sensor electrodes was increased, so that when the hydrogen concentration was 1%, which was the set value, the resistance between the sensor terminals was higher than the second threshold resistance value T2, as shown in Fig. 19.

[0142] REFERENCE SIGNS LIST 1 hydrogen sensor 2 substrate 3 sensitive film 4a, 4b pair of electrodes 5 IC tag 11 first sensor electrode 12 second sensor electrode 13 first bus electrode 14 second bus electrode 21 second substrate 22 IC chip 23 antenna 24a, 24b sensor terminals 30 hydrogen detection system

Claims

1. A hydrogen sensor comprising: a substrate; a sensitive membrane disposed on a first surface of the substrate and containing a catalyst that dissociates hydrogen molecules and tungsten oxide; a pair of electrodes disposed on the first surface of the substrate in contact with the sensitive membrane; and an IC tag connected to the pair of electrodes, wherein the IC tag comprises an IC chip, an antenna connected to the IC chip, and a pair of sensor terminals connected to the IC chip and respectively connected to the pair of electrodes, wherein the IC chip is an open-short type that determines a high resistance state when the resistance value between the sensor terminals is equal to or greater than a first threshold resistance value, and determines a low resistance state when the resistance value between the sensor terminals is equal to or less than a second threshold resistance value that is smaller than the first threshold resistance value, wherein the resistance value between the sensor terminals when the hydrogen concentration is zero is equal to or greater than the first threshold resistance value, and the resistance value between the sensor terminals when the hydrogen concentration is a set value is equal to or less than the second threshold resistance value.

2. The hydrogen sensor according to claim 1, wherein the set value of the hydrogen concentration is equal to or greater than 1% and less than 4%.

3. A hydrogen sensor as described in claim 1, wherein, when the second threshold resistance value is 100%, the difference between the resistance value between the sensor terminals when the hydrogen concentration is at the set value and the second threshold resistance value is greater than 1% and less than 20% of the second threshold resistance value.

4. A hydrogen detection system using the hydrogen sensor according to any one of claims 1 to 3.

5. A hydrogen pipeline using the hydrogen detection system according to claim 4.