Hydrogen sensors and hydrogen detection systems

Abstract

Catalytic combustion and semiconductor-type hydrogen sensors require heating with a heater, which poses a risk to hydrogen gas, which requires explosion-proof measures. Therefore, we provide a hydrogen sensor that does not require heating with a heater and can manage hydrogen concentration. [Solution] The hydrogen sensor 1 consists of a substrate 2, a catalyst for dissociating hydrogen molecules, a sensitive film 3 containing tungsten oxide, and a pair of electrodes 4a and 4b positioned in contact with the sensitive film. An IC tag 5, which includes an IC chip 22 and an antenna 23 connected to the IC chip, is connected to the electrodes. The IC chip is of the open-short type, and a high-resistance state is determined when the resistance value between the pair of electrodes is greater than or equal to a first threshold resistance value, and a low-resistance state is determined when it is less than or equal to a second threshold resistance value, which is less than the first threshold resistance value. When the hydrogen concentration is zero, the resistance value is greater than or equal to the first threshold resistance value, and when the hydrogen concentration is at a set value, the resistance value between the sensor terminals is less than or equal to the second threshold resistance value.

Description

Technical Field

[0001] The present disclosure relates to a hydrogen sensor and a hydrogen detection system.

Background Art

[0002] In recent years, from the viewpoints of global environmental protection and prevention of depletion of fossil fuels, utilization of clean and recyclable energy has been desired. In particular, research for using hydrogen gas as an energy source has been actively conducted mainly centered around fuel cells. On the other hand, the explosion limit concentration of hydrogen gas is wide, ranging from 4% to 75%. Therefore, for hydrogen gas to be popularized as an energy source, handling such as storage and transportation of hydrogen, and safety devices against hydrogen leakage are indispensable.

[0003] For example, odor addition 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 occur. Therefore, safety measures alternative to odor addition are required. Thus, in order to ensure safety, hydrogen sensors for detecting leakage of hydrogen gas have become very important.

[0004] Conventional hydrogen sensors mainly use the catalytic combustion method or the semiconductor method. In a hydrogen sensor using the catalytic combustion method, a catalytic metal such as platinum or palladium is heated by a heater, and hydrogen gas in contact with the catalyst is oxidized by oxygen in the air. The heat generated by this oxidation action of hydrogen gas is electrically detected as a change in the conductivity of the catalytic metal. Also, a semiconductor-type hydrogen sensor detects a change in the electrical characteristics of a sensing film, that is, a change in resistance value, due to adsorption of hydrogen gas to the sensing film. This semiconductor-type hydrogen sensor is also used in a heated state, similar to the catalytic combustion type. Thus, in conventional hydrogen sensors such as the catalytic combustion method and the semiconductor method, heating is performed, which poses a risk for hydrogen gas that requires explosion-proof measures.

[0005] Furthermore, gasochromic hydrogen sensors have recently attracted attention. Gasochromic hydrogen sensors utilize a metal oxide such as tungsten trioxide, whose color changes upon hydrogen adsorption, and a catalyst such as platinum, which dissociates hydrogen gas into hydrogen atoms. They optically detect hydrogen gas. Since the electrical properties of metal oxides such as tungsten trioxide also change upon hydrogen adsorption, gasochromic hydrogen sensors can also electrically detect hydrogen gas. (See, for example, Patent Document 1) [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 4496204 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In the wireless tag described in Patent Document 1, when the resonant circuit receives a wireless signal at its resonant frequency, it induces an alternating current, which is stored as starting power and transmits data. On the other hand, in the wireless tag, when hydrogen comes into contact with tungsten oxide, the tungsten oxide becomes conductive, causing a short circuit in the antenna coil, which inductance changes and the resonant frequency of the resonant circuit also changes. As a result, even when a wireless signal is received, no alternating current is induced, and no data is transmitted. Thus, the presence or absence of hydrogen is determined by whether or not the wireless tag responds to the transmitted wireless signal. However, the wireless tag can only detect the presence or absence of hydrogen.

[0008] This disclosure is made in view of the above circumstances and primarily aims to provide a hydrogen sensor capable of managing hydrogen concentration. [Means for solving the problem]

[0009] One embodiment of the present disclosure provides a hydrogen sensor comprising a substrate, a sensitive film disposed on a first surface of the substrate and containing a catalyst for dissociating hydrogen molecules and tungsten oxide, a pair of electrodes disposed on the first surface of the substrate in contact with the sensitive film, 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 each connected to the pair of electrodes, and the IC chip is of 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 which is less than the first threshold resistance value, and provides a hydrogen sensor in which the resistance value between the sensor terminals is greater than or equal to the first threshold resistance value when the hydrogen concentration is zero, and the resistance value between the sensor terminals is less than or equal to the second threshold resistance value when the hydrogen concentration is a set value.

[0010] Other embodiments of this disclosure provide a hydrogen detection system using the hydrogen sensor described above.

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

[0012] The hydrogen sensor in this disclosure has the effect of being able to manage the hydrogen concentration. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic plan view illustrating a hydrogen sensor in this disclosure. [Figure 2] This graph illustrates the relationship between hydrogen concentration and the resistance value between the sensor terminals in the hydrogen sensor described herein. [Figure 3] This graph illustrates the relationship between hydrogen concentration and the resistance value between the sensor terminals in a hydrogen sensor that does not fall under the embodiments of this disclosure. [Figure 4] This is a schematic plan view illustrating a hydrogen sensor in this disclosure. [Figure 5] It is a schematic plan view illustrating the hydrogen sensor in the present disclosure. [Figure 6] It is a schematic plan view illustrating the hydrogen sensor in the present disclosure. [Figure 7] It is a schematic plan view illustrating the hydrogen sensor in the present disclosure. [Figure 8] It is a schematic plan view illustrating the hydrogen sensor in the present disclosure. [Figure 9] It is a schematic plan view illustrating the hydrogen sensor in the present disclosure. [Figure 10] It is a schematic plan view illustrating the hydrogen sensor in the present disclosure. [Figure 11] It is a schematic plan view illustrating the hydrogen sensor in the present disclosure. [Figure 12] It is a schematic plan view illustrating the hydrogen sensor in the present disclosure. [Figure 13] It is a schematic plan view illustrating the hydrogen sensor in the present disclosure. [Figure 14] It is a schematic plan view illustrating the hydrogen sensor in the present disclosure. [Figure 15] It is a schematic diagram illustrating the hydrogen detection system in the present disclosure. [Figure 16] It is a schematic diagram illustrating the hydrogen detection system in the present disclosure. [Figure 17] It is a schematic diagram illustrating the hydrogen detection system in the present disclosure. [Figure 18] In the hydrogen sensor of Example 1, it is a graph showing the relationship between the hydrogen concentration and the resistance value between the sensor terminals. [Figure 19] In the hydrogen sensors of Comparative Examples 1 to 2, it is a graph showing the relationship between the hydrogen concentration and the resistance value between the sensor terminals.

Embodiments for Carrying Out the Invention

[0014] Embodiments of this disclosure will be described below with reference to drawings and other figures. However, this disclosure can be implemented in many different ways and should not be interpreted as being limited to the embodiments described below. In addition, in order to make the explanation clearer, the drawings may schematically represent the width, thickness, shape, etc. of each component compared to the embodiments, but these are merely examples and should not limit the interpretation of this disclosure. Furthermore, in this specification and each figure, elements similar to those described above with respect to previously shown figures will be denoted by the same reference numerals, and detailed explanations may be omitted as appropriate.

[0015] In this specification, when describing a configuration in which one member is placed on top of another member, the terms "on the surface side" or "on the surface" include, unless otherwise specified, both cases in which the other member is placed directly above or below the other member so as to be in contact with it, and cases in which the other member is placed above or below the other member via yet another member.

[0016] Furthermore, in this specification, terms such as "sheet," "film," and "board" are not distinguished from each other solely based on differences in name. For example, "sheet" is used to include components that may also be called films or boards.

[0017] The hydrogen sensor and hydrogen detection system described in this disclosure will be explained in detail below.

[0018] A. Hydrogen sensor The hydrogen sensor in this disclosure utilizes the fact that when a sensitive film containing a catalyst and tungsten oxide reacts with hydrogen, its resistance decreases. The inventors of this disclosure have diligently studied components for detecting changes in the resistance of the sensitive film in such a hydrogen sensor and have focused on an open-short type IC chip. An open-short type IC chip is an IC chip that detects changes in resistance by determining that a high-resistance state is reached when the resistance between terminals exceeds a first threshold, and that a low-resistance state is reached when the resistance between terminals falls below a second threshold. When applying an open-short type IC chip to the above-described hydrogen sensor, it is important to design it so that in an air atmosphere, the resistance between terminals exceeds the first threshold, and when the hydrogen concentration in the atmosphere increases, the resistance between terminals falls below the second threshold. This makes it possible to detect hydrogen leaks. Here, in order 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 results in problems such as the resistance between terminals falling below the second threshold, or the resistance between terminals not falling below the second threshold even when the hydrogen concentration in the atmosphere increases. In both air and hydrogen atmospheres, if the resistance between terminals falls below the second threshold, it is incorrectly determined that hydrogen is leaking even in an air atmosphere. Furthermore, even if the hydrogen concentration in the atmosphere increases, if the resistance between terminals does not fall below the second threshold, hydrogen leakage cannot be detected. The inventors of this disclosure conducted further studies and found that the resistance between terminals can be adjusted according to the hydrogen concentration by appropriately designing the sensing film and the pair of electrodes, such as the thickness of the sensing film and the distance between the pair of electrodes, according to the first and second thresholds of the open-short type IC chip. In other words, it was found that when applying an open-short type IC chip to the hydrogen sensor as described above, the resistance between terminals can be designed to be above the first threshold in an air atmosphere, and below the second threshold when the hydrogen concentration in the atmosphere increases. This disclosure is based on these findings.

[0019] Conventionally, open-short type IC chips have been used to detect disconnections in wiring and circuits. Aside from the reports by the inventors of this disclosure, there are no other reported examples of open-short type IC chips being used in hydrogen sensors.

[0020] The hydrogen sensor in this disclosure includes a substrate, a sensitive film disposed on a first surface of the substrate and containing a catalyst for dissociating hydrogen molecules and tungsten oxide, a pair of electrodes disposed on the first surface of the substrate in contact with the sensitive film, 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 each connected to the pair of electrodes, and the IC chip is of 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 which is less than the first threshold resistance value, wherein the resistance value between the sensor terminals is greater than or equal to the first threshold resistance value when the hydrogen concentration is zero, and the resistance value between the sensor terminals is less than or equal to the second threshold resistance value when the hydrogen concentration is a set value.

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

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

[0023] Tungsten oxide (WO3) has high electrical resistance. Therefore, in an atmosphere without hydrogen, the sensing film 3 has high electrical resistance and acts as an insulator. In this state, the pair of electrodes 4a and 4b are insulated and non-conductive. Thus, even when power is supplied from the RFID reader / writer to the IC tag 5, no current flows through the sensing film 3 to the pair of electrodes 4a and 4b. In the IC chip 22, if the resistance value between the sensor terminals 24a and 24b is greater than or equal to the first threshold resistance value, a high-resistance state is entered, and for example, the flag information 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 one hand, when hydrogen molecules come into contact with the catalyst, the hydrogen molecules dissociate and adsorb to generate hydrogen atoms. These hydrogen atoms reduce tungsten oxide (WO3) to form a non-stoichiometric compound (H x WO3 (0 < x < 1)). The non-stoichiometric compound (H x WO3) is in a mixed valence state of W 5+ and W 6+ and thus has a low electrical resistance. Therefore, in an atmosphere where hydrogen is present, the reduction reaction of the above tungsten oxide occurs, and the sensing film 3 has a reduced electrical resistance and becomes conductive. At this time, the pair of electrodes 4a and 4b are short-circuited and enter a conductive state. Therefore, when power is supplied from the RFID reader / writer to the IC tag 5, a current flows through the pair of electrodes 4a and 4b via the sensing film 3. In the IC chip 22, when the resistance value between the sensor terminals 24a and 24b is below the second threshold resistance value, it enters a low-resistance state, and for example, the flag information becomes "1". 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 hydrogen gas is leaking.

[0025] Thus, 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] Figure 2 is a graph showing an example of the relationship between hydrogen concentration and the resistance value between the sensor terminals in the hydrogen sensor of this disclosure. In Figure 2, T1 is the first threshold resistance value, T2 is the second threshold resistance value, and S is the set value of the hydrogen concentration. When the hydrogen concentration is zero, as described above, the electrical resistance of the sensitive film 3 is high, so the pair of electrodes 4a and 4b are in a non-conductive state. At this time, the resistance value R1 between the sensor terminals 24a and 24b is greater than or equal to the first threshold resistance value T1, so it becomes a high-resistance state, and for example the flag information becomes "0". On the other hand, when the hydrogen concentration increases, the electrical resistance of the sensitive film 3 decreases, and the pair of electrodes 4a and 4b become conductive. Then, when the resistance value between the sensor terminals 24a and 24b becomes less than or equal to the second threshold resistance value T2, it becomes a low-resistance state, and for example the flag information becomes "1". When the hydrogen concentration is the set value S, the resistance value R2 between the sensor terminals 24a and 24b is less than or equal to the second threshold resistance value T2. Therefore, when the hydrogen concentration exceeds a set value S, hydrogen leakage is detected. Thus, the hydrogen sensor in this disclosure can accurately detect hydrogen leakage when the hydrogen concentration exceeds a predetermined concentration, and can manage the hydrogen concentration. Furthermore, the inventors of this disclosure have found that, in a log-log graph like Figure 18 in the embodiment described later, the relationship between the hydrogen concentration and the resistance value between the sensor terminals follows a linear regression.

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

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

[0029] Furthermore, conventional semiconductor and catalytic combustion type hydrogen sensors require heating, as mentioned above. Also, conventional catalytic combustion and semiconductor type hydrogen sensors detect hydrogen gas in the area where they are installed. Therefore, they can only detect hydrogen gas in a narrow range, such as within approximately 10 cm around the sensor. For example, with a suction nozzle type hydrogen sensor, detecting hydrogen gas is difficult unless the nozzle is precisely aimed at the hydrogen leak point, requiring operator skill.

[0030] In contrast, the reduction reaction of tungsten oxide described above does not require an electric supply. Therefore, the hydrogen sensor in this disclosure can be made to cover a large area and can detect hydrogen gas over a relatively wide area at low cost. Consequently, by using the hydrogen sensor in this 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 Reference 1, the circuit configuration becomes complex and manufacturing costs are high in order to detect fluctuations in the resonant frequency of the resonant circuit. In contrast, in the hydrogen sensor in this disclosure, the circuit configuration can be simplified and manufacturing costs can be reduced by using the open-short type IC chip described above.

[0032] The hydrogen sensor in this disclosure will be described below for each component.

[0033] 1. Characteristics of the hydrogen sensor In the hydrogen sensor of this disclosure, if the IC chip is of an open-short type, where the resistance value between the sensor terminals changes to a high-resistance state when the resistance value between the sensor terminals is equal to or greater than a first threshold resistance value, and to a low-resistance state when the resistance value between the sensor terminals is less than or equal to a second threshold resistance value (less than the first threshold resistance value), then 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 the resistance value between the sensor terminals becomes less than or equal to the second threshold resistance value when the hydrogen concentration is a set value.

[0034] In the hydrogen sensor described 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 term "zero hydrogen concentration" includes cases where the hydrogen concentration is 0.00005% or less.

[0035] Furthermore, in the hydrogen sensor of this disclosure, the resistance value between the sensor terminals when the hydrogen concentration is at a set value is less than or equal to the second threshold resistance value. For example, when the set value of the hydrogen concentration is 1%, and the second threshold resistance value is set to 100%, the difference between the resistance value between the sensor terminals when the hydrogen concentration is at a set value and the second threshold resistance value is preferably 1% or more of the second threshold resistance value, more preferably 5% or more of the second threshold resistance value, and even more preferably 10% or more of the second threshold resistance value. Variations may occur in the characteristics of the IC chip. Therefore, considering safety, it is preferable that the above difference be within the above range. On the other hand, for example, when the set value of the hydrogen concentration is 1%, and the second threshold resistance value is set to 100%, the difference between the resistance value between the sensor terminals when the hydrogen concentration is at a set value and the second threshold resistance value is preferably 20% or less of the second threshold resistance value, more preferably 15% or less of the second threshold resistance value, and even more preferably 10% or less of the second threshold resistance value. If the above difference is too large, the resistance value between the sensor terminals when the hydrogen concentration is significantly lower than the set value may also fall below the second threshold resistance value, which could make it difficult to manage the hydrogen concentration. Specifically, when the set value of the hydrogen concentration is 1%, and the second threshold resistance value is set to 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 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 of the given hydrogen concentration, the impedance of the pair of electrodes connected to the pair of sensor terminals of 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. Five measurements are taken, and the average of the three measurements obtained by subtracting the maximum and minimum values ​​from the five measurements is taken as the resistance between the sensor terminals at the given hydrogen concentration.

[0037] As mentioned above, the hydrogen concentration in the air is approximately 0.00005%, and the term "zero hydrogen concentration" includes cases where the hydrogen concentration is 0.00005% or less. Therefore, when measuring the resistance between the sensor terminals when the hydrogen concentration is zero, the hydrogen sensor should be exposed to air.

[0038] Furthermore, when measuring the resistance value between the sensor terminals when the hydrogen concentration is at a set value, the hydrogen sensor is sealed in a sealed gas chamber connected to a gas mixing device via gas piping when exposed to an atmosphere of a predetermined hydrogen concentration. As the gas mixing device, for example, a flow meter-integrated gas mixing device manufactured by Kofloc Corporation is used. This allows hydrogen to be mixed with air at any desired concentration accurately, safely, and reproducibly. The reaction of the hydrogen sensor to hydrogen is very fast, but the process of the resistance value saturating takes time, so it is preferable to maintain an atmosphere of a predetermined hydrogen concentration for at least 10 minutes. The sealed gas chamber is preferably a metal sealed gas chamber, for example, having a transparent window made of glass or resin in part and equipped with a resin or rubber gasket, and having a structure that does not interfere with RFID communication. This makes it possible to evaluate not only IC tag-separated type hydrogen sensors, in which the IC tag, the sensing film and the substrate on which the pair of electrodes are arranged are separate, but also IC tag-integrated type hydrogen sensors, in which the IC tag, the sensing film and the substrate on which the pair of electrodes are arranged are integrated. Furthermore, a cylindrical sealed gas chamber with a diameter of 100 mm and a height of 20 mm can be used. For the transparent window, a glass plate with a thickness of 5 mm or an acrylic plate with a thickness of 5 mm can be used. For the packing, silicone rubber, fluororubber, or nitrile rubber can be used. The gas piping may be flexible piping made of resin or rubber, or fixed piping made of metal. The gas piping may be made of stainless steel or polypropylene. Also, for example, pipes with a diameter of 5 mm or more and a diameter of 10 mm or less can be used for the gas piping. 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 described herein, methods for adjusting the resistance between the sensor terminals when the hydrogen concentration is zero include, for example, adjusting the distance between a pair of electrodes, such as the distance between a pair of comb-tooth electrodes, and adjusting the thickness of the sensitive film. When the distance between the pair of comb-tooth electrodes is increased, the resistance between the sensor terminals when the hydrogen concentration is zero tends to increase, while when the distance between the pair of comb-tooth electrodes is decreased, the resistance between the sensor terminals when the hydrogen concentration is zero tends to decrease. Furthermore, when the thickness of the sensitive film is increased, the resistance between the sensor terminals when the hydrogen concentration is zero tends to increase, while when the thickness of the sensitive film is decreased, 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 the same as the method for adjusting the resistance between the sensor terminals when the hydrogen concentration is zero, as described above. When the distance between the pair of comb-tooth electrodes is increased, the resistance between the sensor terminals when the hydrogen concentration is at a set value tends to increase, while when the distance between the pair of comb-tooth electrodes is decreased, the resistance between the sensor terminals when the hydrogen concentration is at a set value tends to decrease. Also, when the thickness of the sensitive film is increased, the resistance between the sensor terminals when the hydrogen concentration is at a set value tends to increase, while when the thickness of the sensitive film is decreased, the resistance between the sensor terminals when the hydrogen concentration is at a set value tends to decrease.

[0041] As mentioned above, the explosive limit concentration of hydrogen gas is between 4% and 75%. Therefore, the set value for hydrogen concentration is less than 4%. For safety reasons, the set value for hydrogen concentration is preferably 2% or less, and more preferably 1% or less. On the other hand, if the set value for hydrogen concentration is too low, even extremely low concentrations that would not cause an explosion may be judged as a hydrogen leak. Therefore, the set value for hydrogen concentration is preferably 1% or more. In other words, the set value for hydrogen concentration is preferably 1% or more and less than 4%, more preferably 1% or more and 2%, and particularly preferably 1%.

[0042] The set value for hydrogen concentration is determined by the following method. As mentioned above, the hydrogen sensor may determine that there is no hydrogen gas leak or that there is a hydrogen gas leak. First, the hydrogen sensor is sealed in a sealed gas chamber connected to a gas mixing device via gas piping. The gas mixing device, sealed gas chamber, and gas piping are as described above. The IC tag may be installed inside the sealed gas chamber or 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 always set to 10 mL / min. Next, in the sealed gas chamber, the mixing ratio of hydrogen and air is set so that hydrogen is 0%, i.e., air is 100%. Subsequently, the hydrogen concentration in the sealed gas chamber is adjusted to the desired level. Initially, it is adjusted to a hydrogen concentration of 0.1%. As mentioned above, the hydrogen sensor's reaction to hydrogen is very fast, but the process of resistance saturating takes time, so it is preferable to maintain the atmosphere at that hydrogen concentration for at least 10 minutes. Next, a radio signal is transmitted from the RFID reader / writer to check whether the hydrogen sensor reacts to the hydrogen concentration in the atmosphere and detects hydrogen. Then, the sealed gas chamber is opened and maintained for 10 minutes to return to an air atmosphere. Next, the hydrogen concentration in the sealed gas chamber is increased by 0.1% increments, and the above procedure is repeated. The minimum hydrogen concentration at which a hydrogen gas leak is detected is then determined. Five measurements are taken, and the average of the minimum hydrogen concentrations is used as the set hydrogen concentration.

[0043] 2. IC tags The IC tag in this disclosure includes 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. The IC chip is of an open-short type, which determines that it is in 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 that it is in a low-resistance state when the resistance value between the sensor terminals is less than or equal to a second threshold resistance value which is less than the first threshold resistance value. The IC tag is also called an RF tag, RFID tag, electronic tag, wireless tag, etc. If it is an IC tag, hydrogen gas can be detected using RFID.

[0044] In an IC chip, the first and second threshold resistance values ​​are not particularly limited, except that 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 resistance may be detected frequently, which may lead to frequent misinterpretations of hydrogen leakage. Also, if the first threshold resistance value is too low, the difference between the first and second threshold resistance values ​​becomes small, making design difficult. The difference between the first and second threshold resistance values ​​is preferably, for example, 10 MΩ or more and 100 MΩ or less. If the above 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, prepare a fixed resistor with a known resistance value and a commercially available RFID reader / writer. Also, remove the IC tag from the hydrogen sensor. Connect the fixed resistor to the pair of sensor terminals on the IC tag, transmit a readout signal using the RFID reader / writer, and verify the value using the flag of the reflected signal. In an open-short type IC chip, "open" ideally means that the load (electrical resistance, impedance) connected to the IC chip is infinite, that is, the external load connection terminals of the IC chip are open. "Short" ideally means that the load (electrical resistance, impedance) connected to the IC chip is zero, that is, the external load connection terminals of the IC chip are short-circuited by a wire. However, in a normal electrical circuit, it is not possible to physically or mechanically disconnect the load, so it is common to determine that a resistance value above a certain level is open, and a resistance value below a certain level is short. The threshold resistance values ​​are set to be the resistance values ​​that can generally be considered as an insulating state in the case of an open circuit, and the resistance values ​​that can generally be considered as a conductive state in the case of a short circuit. In this disclosure, an open circuit is considered a high-resistance state, and a short circuit is considered a low-resistance state. Therefore, the first threshold resistance value is set to the resistance value that can be considered as an insulating state. Specifically, the minimum value among the resistance values ​​that can be considered as an insulating state is set as the first threshold resistance value. The second threshold resistance value is set to the resistance value that can be considered as a conductive state. Specifically, the maximum value among the resistance values ​​that can be considered as a conductive state is set as the second threshold resistance value. Although the first and second threshold resistance values ​​are published as characteristic data for commercially available IC chips, there are individual differences, so the above measurement method is adopted.

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

[0047] An 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. The configuration of an IC tag is the same as that of a typical IC tag.

[0048] IC tags come in two types: active tags, which have a built-in power source (battery), and passive tags, which do not. Of these, passive tags are preferred because they do not have their own power source (battery) and instead obtain power by receiving radio waves supplied from an external source via an antenna.

[0049] There is at least one IC tag. There may be one IC tag or more.

[0050] The IC tag may be integrated with the substrate on which the sensing film and pair of electrodes are arranged, or they may be separate. In Figure 1, the IC tag 5 and the substrate 2 on which the sensing film 3 and pair of electrodes 4a and 4b are arranged are separate. On the other hand, in Figure 4, the IC tag 5 is arranged on one side of the substrate 1, and the IC tag 5 and the substrate 2 on which the sensing film 3 and pair of electrodes 4a and 4b are arranged are integrated. When the IC tag is separate from the substrate on which the sensing film and pair of electrodes are arranged, the substrate on which the sensing film and pair of electrodes are arranged can be placed directly on the object to be detected for hydrogen leakage, while the IC tag can be placed in a state that is more conducive to transmitting and receiving radio waves, such as away from metals that have radio wave shielding properties, or with the antenna facing the RFID reader / writer. On the other hand, when the IC tag is integrated with the substrate on which the sensing film and pair of electrodes are arranged, the hydrogen sensor can be installed in a narrower space.

[0051] 3. Sensitive membrane The sensitive film in this disclosure comprises 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 it may contain, in order from the substrate side, a tungsten oxide layer containing tungsten oxide and a catalyst layer containing a catalyst.

[0053] If 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 include precious metals such as palladium, platinum, and iridium. The catalyst may be used alone or in combination of two or more types.

[0055] Tungsten oxide is tungsten trioxide (WO3).

[0056] The sensitive film only needs to be positioned in contact with the pair of electrodes, and its position is not particularly limited. For example, the pair of electrodes and the sensitive film may be arranged in this order on the first surface of the substrate, or the sensitive film and the pair of electrodes may be arranged in this order on the first surface of the substrate.

[0057] If 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 of the sensitive film, for example, between 100 nm and 3000 nm.

[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 thick enough to detect changes in the resistance of the tungsten oxide layer, for example, between 100 nm and 3000 nm. The thickness of the catalyst layer is appropriately selected depending on the method of forming the catalyst layer. When the catalyst layer is formed by vapor deposition, the thickness of the catalyst layer is, for example, between 1 nm and 10 nm. On the other hand, when the catalyst layer is formed by coating, the thickness of the catalyst layer is, for example, between 10 nm and 100 nm.

[0059] The area of ​​the sensing membrane in plan view is not particularly limited, for example, 1 cm². 2 9cm or more 2 The following applies:

[0060] When the sensitive film is a single layer containing a catalyst and tungsten oxide, one method for forming the sensitive film is the sol-gel method. For example, the sol-gel method for forming a sensitive film can be found in Japanese Patent Publication No. 5152797 and Japanese Patent Publication No. 5540248.

[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 includes, for example, the sol-gel method, vacuum deposition method, sputtering method, and ion plating method. The method for forming the catalyst layer is also not particularly limited and includes, for example, deposition methods such as vacuum deposition method, sputtering method, and ion plating method, and coating methods in which a resin composition containing a catalyst and a binder resin is applied.

[0062] 4. A pair of electrodes In this disclosure, the pair of electrodes are arranged on the first surface of the substrate in contact with the sensitive film. The pair of electrodes are typically arranged at an interval that allows for the detection of changes in the resistance of the sensitive film. In this specification, "an interval that allows for the detection of changes in the resistance of the sensitive film" means an interval at which the pair of electrodes can be short-circuited when the reduction reaction of tungsten oxide occurs and the resistance of the sensitive film decreases.

[0063] Preferably, the pair of electrodes are a pair of comb-tooth electrodes. Specifically, as shown in Figure 5, the pair of electrodes 4a and 4b include 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, and preferably the plurality of first sensor electrodes and the plurality of second sensor electrodes are arranged on the first surface of the substrate in contact with the sensitive film and are arranged alternately with intervals that allow for detection of changes in the resistance value of the sensitive film. Electrode 4a includes a plurality of first sensor electrodes 11 and a first bus electrode 13 connected to the first sensor electrodes 11. Electrode 4b also 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 a pair of electrodes include carbon and metallic materials. Carbon is preferred among these. Carbon is inert to hydrogen gas and inexpensive. As described above, when the sensitive film and the pair of electrodes are arranged in that order on the first surface of the substrate, it is preferable that the conductive material used for the pair of electrodes is inert to hydrogen gas. On the other hand, when the pair of electrodes and the sensitive film are arranged in that order on the first surface of the substrate, the conductive material used for the pair of electrodes is not exposed to hydrogen gas, so it may be active or inert to hydrogen gas.

[0065] The thickness of the pair of electrodes is not particularly limited as long as it is a thickness that can function as an electrode, for example, between 0.1 μm and 2 μm.

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

[0067] Below, three embodiments of a pair of electrodes are illustrated.

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

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

[0070] The distance between the first and second sensor electrodes should be such that a change in the resistance of the sensitive film can be detected. The distance may be, for example, 100 μm or more, and may also be 500 μm or more. As mentioned above, if the distance is narrow, 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 fall below the first threshold resistance value. The distance may also be, for example, 10 mm or less, and may also be 5 mm or less. As mentioned above, if the distance is wide, the resistance between the sensor terminals when the hydrogen concentration is set to a certain value tends to increase. Therefore, if the distance is too wide, the resistance between the sensor terminals when the hydrogen concentration is set to a certain value may fall below the second threshold resistance value. That is, the distance may be, for example, 100 μm or more and 10 mm or less, and 500 μm or more and 5 mm or less.

[0071] The distance between the first and second sensor electrodes is the distance from the end of one adjacent first sensor electrode to the end of the second sensor electrode. For example, in Figure 6, the distance between the first sensor electrode 11 and the second sensor electrode 12 is shown by the shortest distance d1 of the line connecting the adjacent first and second sensor electrodes 11 and 12.

[0072] The widths of the first and second sensor electrodes should be such that they allow for the detection of changes in the resistance of the sensitive film. These widths may be, for example, 100 μm or more, or 500 μm or more. Alternatively, they may be, for example, 10 mm or less, or 5 mm or less. That is, for example, the widths may be between 100 μm and 10 mm, or between 500 μm and 5 mm. For example, in Figure 6, the width of the first sensor electrode 11 is shown by the length b1 in the direction perpendicular to the direction in which the first sensor electrode 11 extends. The width of the second sensor electrode 12 is shown by the length b2 in the direction perpendicular to the direction in which the second sensor electrode 12 extends.

[0073] The lengths of the first and second sensor electrodes should be such that they can detect changes in the resistance of the sensitive film. For example, the lengths may be 10 mm or more, and 50 mm or more. Alternatively, the lengths may be 500 mm or less, and 100 mm or less. That is, for example, the lengths may be 10 mm or more and 500 mm or less, and 50 mm or more and 100 mm or less. For example, in Figure 6, the length of the first sensor electrode 11 is shown by the length a1 in the direction in which the first sensor electrode 11 extends. The length of the second sensor electrode 12 is shown by the length a2 in the direction in which the second sensor electrode 12 extends.

[0074] The overlap length of the first sensor electrode and the second sensor electrode should be such that a change in the resistance value of the sensitive film can be detected. The overlap length may be, for example, 9 mm or more, and may be 45 mm or more. Alternatively, the overlap length may be, for example, 450 mm or less, and may be 90 mm or less. That is, the overlap length may be, for example, 9 mm or more and 450 mm or less, and 45 mm or more and 90 mm or less. For example, in Figure 6, the overlap length of 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 and second sensor electrodes is set appropriately according to the size of the hydrogen sensor, the arrangement of the first and second bus electrodes, and so on.

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

[0077] The first and second bus electrodes are arranged in a linear fashion that can be drawn in a single continuous line. In this specification, "linear fashion that can be drawn in a single continuous line" means that the line consists of a single continuous line and has no overlapping sections.

[0078] The linear arrangement that can be drawn in a single stroke is not particularly limited as long as the first bus electrode, second bus electrode, first sensor electrode, and second sensor electrode can be arranged evenly on the first surface of the substrate. Examples include a meandering linear arrangement as shown in Figures 6 and 7, and a spiral arrangement as shown in Figure 8. In particular, it is preferable that the first bus electrode and second bus electrode are arranged in a meandering linear arrangement. In this case, the first bus electrode and second bus electrode can be formed by a roll-to-roll method, 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 electrode and the second bus electrode are arranged so as to be aligned with each other.

[0080] The widths of the first and second bus electrodes are limited to widths that allow them to function as electrodes. The above widths may be, for example, 1 mm or more, and 5 mm or more. Alternatively, the above widths may be, for example, 50 mm or less, and 10 mm or less. That is, the above widths may be, for example, 1 mm or more and 50 mm or less, and 5 mm or more and 10 mm or less. For example, in Figure 6, the width of the first bus electrode 13 is shown by the length e1 in the direction perpendicular to the direction in which the first bus electrode 13 extends. The width of the second bus electrode 14 is shown by the length e2 in the 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, which face each other with the first sensor electrode and the second sensor electrode in between, is sufficient to allow the first sensor electrode and the second sensor electrode to be placed. The distance may be, for example, 11 mm or more, and may be 55 mm or more. Alternatively, the distance may be, for example, 550 mm or less, and may be 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 Figure 6, the distance between the first bus electrode 13 and the second bus electrode 14, which face each other with the first sensor electrode 11 and the second sensor electrode 12 in between, is shown by the shortest distance f of the line connecting the first bus electrode 13 and the second bus electrode 14, which face each other with the first sensor electrode 11 and the second sensor electrode 12 in between.

[0082] The distance between the first and second bus electrodes, which face each other without the first and second sensor electrodes in between, should be such that a change in the resistance of the sensitive film cannot be detected. The above distance may be, for example, 10 mm or more, and may be 50 mm or more. Alternatively, the above distance may be, for example, 100 mm or less, and may be 70 mm or less. That is, the above distance may be, for example, 10 mm or more and 100 mm or less, and 50 mm or more and 70 mm or less. If the above distance is too small, the reduction reaction of tungsten oxide may occur, and when the resistance of the sensitive film decreases, the first and second bus electrodes, which face each other without the first and second sensor electrodes in between, may become more conductive. The above distance is appropriately selected according to the thickness of the sensitive film. When the thickness of the sensitive film increases, the first and second bus electrodes, which face each other without the first and second sensor electrodes in between, tend to become less likely to short-circuit. Therefore, when the thickness of the sensitive film is relatively thick, the above distance may be relatively small within the above range. On the other hand, when the thickness of the sensitive film is reduced, the first bus electrode and the second bus electrode, which face each other without the first sensor electrode and the second sensor electrode in between, tend to short-circuit more easily. Therefore, when the thickness of the sensitive film is relatively thin, it is preferable that the above-mentioned distance is 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, which face each other without the first sensor electrode 11 and the second sensor electrode 12 in between, is indicated by the shortest distance g of the line connecting the first bus electrode 13 and the second bus electrode 14, which face each other without the first sensor electrode 11 and the second sensor electrode 12 in between.

[0083] The spacing between adjacent first bus electrodes and between adjacent second bus electrodes should be such that a change in the resistance of the sensitive film cannot be detected. The spacing may be, for example, 10 mm or more, and may be 50 mm or more. Alternatively, the spacing may be, for example, 100 mm or less, and may be 70 mm or less. That is, the spacing may be, for example, 10 mm or more and 100 mm or less, and 50 mm or more and 70 mm or less. If the spacing is too small, the reduction reaction of tungsten oxide may occur, and when the resistance of the sensitive film decreases, adjacent first bus electrodes or adjacent second bus electrodes may become more easily conductive. The spacing is appropriately selected according to the thickness of the sensitive film. When the thickness of the sensitive film increases, adjacent first bus electrodes or adjacent second bus electrodes tend to become less likely to short-circuit. Therefore, when the thickness of the sensitive film is relatively thick, the spacing may be relatively small within the above range. On the other hand, when the thickness of the sensitive film decreases, adjacent first bus electrodes or adjacent second bus electrodes tend to become more likely to short-circuit. Therefore, when the thickness of the sensitive film is relatively thin, it is preferable that the above-mentioned spacing be relatively large within the above-mentioned range. For example, in Figure 6, the spacing between adjacent first bus electrodes 13 is indicated by the shortest distance h1 of the line connecting adjacent first bus electrodes 13. Similarly, the spacing 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 usually one. However, if the first bus electrodes and the second bus electrodes form a pair, the number of first bus electrodes and the number of second bus electrodes may be two. For example, in Figure 9, the hydrogen sensor 1 includes two first bus electrodes 13a and 13b and two second bus electrodes 14a and 14b, with the first bus electrode 13a and the second bus electrode 14a forming a pair, and the first bus electrode 13b and the second bus electrode 14b forming a pair.

[0085] (2) Second aspect In this embodiment, a pair of electrodes consists of multiple first bus electrodes and multiple second bus electrodes connected to an IC tag via a flexible printed circuit board.

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

[0087] In this embodiment, the first bus electrode and the second bus electrode can be arranged in a straight line, thereby reducing the risk of wire breakage.

[0088] The distance between the first and second sensor electrodes should be such that a change in the resistance of the sensitive film can be detected. The distance may be, for example, 100 μm or more, and may also be 500 μm or more. As mentioned above, if the distance is narrow, 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 fall below the first threshold resistance value. The distance may also be, for example, 10 mm or less, and may also be 5 mm or less. As mentioned above, if the distance is wide, the resistance between the sensor terminals when the hydrogen concentration is set to a certain value tends to increase. Therefore, if the distance is too wide, the resistance between the sensor terminals when the hydrogen concentration is set to a certain value may fall below the second threshold resistance value. That is, the distance may be, for example, 100 μm or more and 10 mm or less, and 500 μm or more and 5 mm or less.

[0089] The distance between the first and second sensor electrodes is the distance from one end of the first sensor electrode to the other end of the second sensor electrode. For example, in Figure 10, the distance between the first sensor electrode 11 and the second sensor electrode 12 is shown by the shortest distance d1 of the line connecting the adjacent first and second sensor electrodes 11 and 12.

[0090] The widths of the first and second sensor electrodes should be such that they can detect changes in the resistance of the sensitive film. For example, the width may be 100 μm or more, or 500 μm or more. Alternatively, the width may be 10 mm or less, or 5 mm or less. That is, for example, the width may be 100 μm or more and 10 mm or less, or 500 μm or more and 5 mm or less. For example, in Figure 10, the width of the first sensor electrode 11 is shown by the length b1 in the direction perpendicular to the direction in which the first sensor electrode 11 extends. Similarly, the width of the second sensor electrode 12 is shown by the length b2 in the direction perpendicular to the direction in which the second sensor electrode 12 extends.

[0091] The lengths of the first and second sensor electrodes should be such that they can detect changes in the resistance of the sensitive film. For example, the lengths may be 10 mm or more, and 50 mm or more. Alternatively, the lengths may be 500 mm or less, and 100 mm or less. That is, for example, the lengths may be 10 mm or more and 500 mm or less, and 50 mm or more and 100 mm or less. For example, in Figure 10, the length of the first sensor electrode 11 is shown by the length a1 in the direction in which the first sensor electrode 11 extends. The length of the second sensor electrode 12 is shown by the length a2 in the direction in which the second sensor electrode 12 extends.

[0092] The overlap length of the first sensor electrode and the second sensor electrode should be such that a change in the resistance value of the sensitive film can be detected. The overlap length may be, for example, 9 mm or more, and may be 45 mm or more. Alternatively, the overlap length may be, for example, 450 mm or less, and may be 90 mm or less. That is, the overlap length may be, for example, 9 mm or more and 450 mm or less, and 45 mm or more and 90 mm or less. For example, in Figure 10, the overlap length of 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 and second sensor electrodes is set appropriately according to the size of the hydrogen sensor, the arrangement of the first and second bus electrodes, and so on.

[0094] The shape of the first sensor electrode and the shape of the second sensor electrode are not particularly limited and include, for example, a straight, bent, or curved shape.

[0095] The first bus electrode and the second bus electrode are paired and arranged alternately.

[0096] The widths of the first and second bus electrodes are limited to widths that allow them to function as electrodes. The above widths may be, for example, 1 mm or more, and 5 mm or more. Alternatively, the above widths may be, for example, 50 mm or less, and 10 mm or less. That is, the above widths may be, for example, 1 mm or more and 50 mm or less, and 5 mm or more and 10 mm or less. For example, in Figure 10, the width of the first bus electrode 13 is shown by the length e1 in the direction perpendicular to the direction in which the first bus electrode 13 extends. The width of the second bus electrode 14 is shown by the length e2 in the 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 placed. The distance may be, for example, 11 mm or more, and 55 mm or more. Alternatively, 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 Figure 10, the distance between the first bus electrode 13 and the second bus electrode 14 is shown by the shortest distance f of the line connecting the first bus electrode 13 and the second bus electrode 14 that face each other with the first sensor electrode 11 and the second sensor electrode 12 in between.

[0098] The number of first bus electrodes and the number of second bus electrodes can be multiple. The first bus electrodes and the second bus electrodes only need to be in pairs, and the number of first bus electrodes and the number of second bus electrodes can be the same or different. For example, in Figure 10, there are 4 first bus electrodes 13 and 5 second bus electrodes 14, so the number of first bus electrodes and the number of second bus electrodes are different.

[0099] Multiple first bus electrodes and multiple second bus electrodes are connected to the IC tag via a flexible printed circuit board (FPC). A standard FPC can be used.

[0100] (3) Third aspect In the pair of electrodes of this embodiment, a plurality of first bus electrodes are arranged along a first direction, and a plurality of second bus electrodes are arranged along a second direction perpendicular to the first direction. In this embodiment, 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 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.

[0101] In Figure 12, the multiple first bus electrodes 13 are arranged linearly in a first direction D1, and the multiple second bus electrodes 14 are arranged linearly 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 multiple first bus electrodes 13 and a fourth IC tag 5d connected to one end of the multiple 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 placed between the first bus electrodes 13 and the second bus electrodes 14.

[0102] In this embodiment, since it is not necessary to arrange the first bus electrode and the second bus electrode in a linear shape that can be drawn in a single stroke, the risk of wire breakage can be reduced. 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 kept constant, so the variation in the signal is reduced and the detection sensitivity is improved.

[0103] The distance between the first and second sensor electrodes should be such that a change in the resistance of the sensitive film can be detected. The distance may be, for example, 100 μm or more, and may also be 500 μm or more. As mentioned above, if the distance is narrow, 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 fall below the first threshold resistance value. The distance may also be, for example, 10 mm or less, and may also be 5 mm or less. As mentioned above, if the distance is wide, the resistance between the sensor terminals when the hydrogen concentration is set to a certain value tends to increase. Therefore, if the distance is too wide, the resistance between the sensor terminals when the hydrogen concentration is set to a certain value may fall below the second threshold resistance value. That is, the distance may be, for example, 100 μm or more and 10 mm or less, and 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 end of one adjacent first sensor electrode to the end of the second sensor electrode. For example, in Figure 12, the distance between the first sensor electrode 11 and the second sensor electrode 12 is shown by the shortest distance d1 of the line connecting the adjacent first and second sensor electrodes 11 and 12.

[0105] The widths of the first and second sensor electrodes should be such that they allow for the detection of changes in the resistance of the sensitive film. These widths may be, for example, 100 μm or more, or 500 μm or more. Alternatively, they may be, for example, 10 mm or less, or 5 mm or less. That is, these widths 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 Figure 12, the width of the first sensor electrode 11 is shown by the length b1 in the direction perpendicular to the direction in which the first sensor electrode 11 extends. The width of the second sensor electrode 12 is shown by the length b2 in the direction perpendicular to the direction in which the second sensor electrode 12 extends.

[0106] The lengths of the first and second sensor electrodes should be such that they can detect changes in the resistance of the sensitive film. For example, the lengths may be 10 mm or more, and 50 mm or more. Alternatively, the lengths may be 500 mm or less, and 100 mm or less. That is, for example, the lengths may be 10 mm or more and 500 mm or less, and 50 mm or more and 100 mm or less. For example, in Figure 12, the length of the first sensor electrode 11 is shown by the length a1 in the direction in which the first sensor electrode 11 extends. The length of the second sensor electrode 12 is shown by the length a2 in the direction in which the second sensor electrode 12 extends.

[0107] The overlap length of the first sensor electrode and the second sensor electrode should be such that a change in the resistance value of the sensitive film can be detected. The overlap length may be, for example, 9 mm or more, and may be 45 mm or more. Alternatively, the overlap length may be, for example, 450 mm or less, and may be 90 mm or less. That is, the overlap length may be, for example, 9 mm or more and 450 mm or less, and 45 mm or more and 90 mm or less. For example, in Figure 12, the overlap length of 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 and second sensor electrodes is set appropriately according to the size of the hydrogen sensor, the arrangement of the first and second bus electrodes, and so on.

[0109] The shapes of the first and second sensor electrodes are not particularly limited and include, for example, straight, bent, and curved shapes. Furthermore, the shapes of the first and second sensor electrodes may have branches. For example, in Figure 12, the shape of the first sensor electrode 11 is straight, and the shape of the second sensor electrode 12 has branches. Also, for example, in Figure 13, the shape of the first sensor electrode 11 is straight, and the shape of the second sensor electrode 12 is bent.

[0110] Multiple first bus electrodes are arranged along a first direction, and multiple second bus electrodes are arranged along a second direction perpendicular to the first direction.

[0111] The widths of the first and second bus electrodes are limited to widths that allow them to function as electrodes. The above widths may be, for example, 1 mm or more, and 5 mm or more. Alternatively, the above widths may be, for example, 50 mm or less, and 10 mm or less. That is, the above widths may be, for example, 1 mm or more and 50 mm or less, and 5 mm or more and 10 mm or less. For example, in Figure 12, the width of the first bus electrode 13 is shown by the length e1 in the direction perpendicular to the direction in which the first bus electrode 13 extends. The width of the second bus electrode 14 is shown by the length e2 in the direction perpendicular to the direction in which the second bus electrode 14 extends.

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

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

[0114] In this embodiment, the insulating film is placed between the first and second bus electrodes in the region where the first and second bus electrodes intersect. The material of the insulating film is not particularly limited as long as it is an insulating material, and examples 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 and second bus electrodes, 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 include a method of forming the insulating film and then patterning it, a mask deposition method, and a printing method. Examples of methods for forming the insulating film include vacuum deposition, sputtering, ion plating, and plating. Examples of patterning methods include etching and lift-off methods.

[0115] In this embodiment, regarding the position of the sensitive membrane, for example, the first sensor electrode and the second sensor electrode and the sensitive membrane may be arranged on the first surface of the substrate in this order, the sensitive membrane, the first sensor electrode and the second sensor electrode may be arranged on the first surface of the substrate in this order, the first sensor electrode, the sensitive membrane and the second sensor electrode may be arranged on the first surface of the substrate in this order, or the second sensor electrode, the sensitive membrane and the first sensor electrode may be arranged on the first surface of the substrate in this order.

[0116] In this embodiment, the IC tag includes a third IC tag connected to one end of a plurality of first bus electrodes and a fourth IC tag connected to one end of a 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 a 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 a 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 Figure 14, the IC tag includes a third IC tag 5c connected to one end of a plurality of first bus electrodes 13, a fourth IC tag 5d connected to one end of a plurality of second bus electrodes 14, and a fifth IC tag 5e connected to the other end of a plurality of first bus electrodes 13.

[0117] 5. Circuit board The substrate in this disclosure is an insulating component that supports the sensitive film and a pair of electrodes.

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

[0119] The thickness of the substrate is not particularly limited, for example, it can be between 10 μm and 2 mm.

[0120] 6. Other configurations In this disclosure, the sensitive film and the pair of electrodes may be arranged on the first surface of the substrate. The sensitive film and the pair of electrodes may be arranged on only one side of the substrate, or the sensitive film and the pair of electrodes may be arranged on both sides of the substrate.

[0121] B. Hydrogen detection system The hydrogen detection system in this disclosure uses the hydrogen sensor described above.

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

[0123] Figure 16 is a schematic diagram illustrating another example of a hydrogen detection system in this disclosure. In Figure 16, the hydrogen detection system 30 comprises 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 mounted on a hydrogen pipeline 41 installed underground. The RFID reader / writer 31 and antenna 32 are installed on a mobile unit 33 and are mobile.

[0124] Figure 17 is a schematic diagram illustrating another example of a hydrogen detection system in this disclosure. In Figure 17, the hydrogen detection system 30 is used in a hydrogen station. The hydrogen detection system 30 comprises 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 vehicles, etc. The RFID reader / writer 31 and antenna 32 are installed on a canopy (roof) 43 and are fixed in place.

[0125] In such a hydrogen detection system, the IC chip constituting the hydrogen sensor's IC tag is driven non-contact, and changes in the resistance value of the sensitive film can be detected, thereby enabling the detection of hydrogen gas.

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

[0127] RFID reader / writers may be fixed or mobile. Using a fixed RFID reader / writer allows for continuous monitoring. On the other hand, using a mobile RFID reader / writer enables traceability inspection, making the traceability inspection more sophisticated, smarter, and less labor-intensive.

[0128] The hydrogen detection system described in this disclosure can be used not only in small devices such as fuel cells, but also in large-scale facilities such as hydrogen production facilities, hydrogen pipelines, transport tankers, storage tanks, hydrogen power generation facilities, and hydrogen stations. In addition to underground pipelines, aerial pipelines can also be used as hydrogen pipelines.

[0129] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure. [Examples]

[0130] The present disclosure will be further described below with reference to examples and comparative examples.

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

[0132] Next, referring to Tomoji Ohishi et al., Materials Sciences and Applications, “Low-Temperature Formation of a WO3Thin Film by the Sol-Gel Method Using Photo-Irradiation and Fabrication of a Flexible Hydrogen Sensor,” 2020, 11, pp. 135-149, a sensitive film was formed on the PET film by the sol-gel method to cover a pair of electrodes. Specifically, tungsten hexachloride (WCl6) manufactured by Sigma-Aldrich was used as the raw material for tungsten oxide, palladium(II) acetate manufactured by Kanto Chemical Co., Ltd. was used as the catalyst, and polystyrene (degree of polymerization 2000) manufactured by Wako Pure Chemical Industries, Ltd. was used as the resin binder. The tungsten oxide raw material was dissolved in ethanol and coated onto the PET film to form a precursor film. Subsequently, the precursor film was exposed to wavelengths of 254 nm and 185 nm and an irradiance of 12 mw / cm². 2 The sample 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 consisted of a tungsten oxide layer and a catalyst layer, in that order from the PET film side. The tungsten oxide layer was 600 nm thick, and the catalyst layer was 90 nm thick.

[0133] Next, an IC tag including an IC chip (NXP's UCODE G2iM+) and an antenna was fabricated. Specifically, copper foil was bonded to a glass epoxy substrate, and the antenna was formed by patterning the copper foil according to the design. The copper foil patterning was done by etching and grinding. Next, the IC chip was mounted so that the antenna terminals and antenna were connected, and the IC tag was fabricated. The antenna was designed to be sensitive to UHF band waves. Finally, the 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 and second sensor electrodes was set to 1.0 mm.

[0136] [evaluation] In Example 1, a readout radio wave was transmitted to the hydrogen sensor using a UHF band RFID reader / writer, and it was confirmed that the reflected radio wave could be detected. Furthermore, when the hydrogen sensor was exposed to hydrogen gas and radio waves were transmitted in the same manner as above, the signal level of the reflected radio wave changed. This confirmed that hydrogen gas can be detected without the hydrogen sensor itself having a power supply.

[0137] Furthermore, the resistance value between the sensor terminals of the hydrogen sensor at a predetermined hydrogen concentration was determined using the following method. First, a gas mixing device and a sealed gas chamber were connected via gas piping. The gas mixing device used was a Kofloc GM-4B flow meter-integrated gas mixing device. The sealed gas chamber was a metal sealed gas chamber with a transparent glass window in part and a 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 for the gas piping. The IC tag was removed from the hydrogen sensor, and the hydrogen sensor was sealed inside the sealed gas chamber connected to the gas mixing device. An LCR meter (Hiroki IM3523) was connected to the pair of electrodes that were connected to the pair of sensor terminals of the IC tag. The LCR meter was installed outside the sealed gas chamber via electrical wiring and a gasket. The set temperature was 25°C. The target fluids were hydrogen and air. The flow rate of the hydrogen and air mixed gas was always set to 10 mL / min.

[0138] First, the mixture ratio of hydrogen and air was set to 0% hydrogen, i.e., 100% air. Next, the hydrogen concentration in the sealed gas chamber was maintained at a predetermined level for 10 minutes. Then, the impedance of a pair of electrodes connected to the pair of sensor terminals of the IC tag was measured at a frequency of 20 kHz using an LCR meter (Hiroki IM3523), and the resistance value between the pair of electrodes was determined from the impedance. Five measurements were taken, and the average of the three measurements (excluding the maximum and minimum values) was taken as the resistance value between the sensor terminals at the predetermined hydrogen concentration.

[0139] When determining the resistance value between the sensor terminals of the hydrogen sensor at a predetermined hydrogen concentration by changing the 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 of the hydrogen sensor in Example 1 are shown in Figure 18. The results of the hydrogen sensors in Comparative Examples 1 and 2 are shown in Figure 19.

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

[0142] 1… Hydrogen sensor 2… Circuit board 3. Sensitive membrane 4a, 4b... A pair of electrodes 5… IC tags 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. circuit board and A sensitive film is provided on the first surface of the substrate, comprising a catalyst that dissociates hydrogen molecules and tungsten oxide, A pair of electrodes are arranged on the first surface of the substrate in contact with the sensitive film, An IC tag connected to the pair of electrodes, A hydrogen sensor including, 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 each connected to the pair of electrodes. The IC chip has two threshold values ​​pre-set, and when one of the two threshold values ​​is designated as the first threshold resistance value and the other threshold value smaller than the first threshold resistance value is designated as the second threshold resistance value, the IC chip determines that it is in a high resistance state when the resistance value between the sensor terminals is equal to or greater than the first threshold resistance value, and the flag information indicates a first value, and determines that it is in a low resistance state when the resistance value between the sensor terminals is equal to or less than the second threshold resistance value, and the flag information indicates a second value. In the IC tag, the flag information is transmitted via the antenna. When the hydrogen concentration is zero, the resistance between the sensor terminals becomes equal to or greater than the first threshold resistance value, and when the hydrogen concentration is a set value, the resistance between the sensor terminals becomes equal to or less than the second threshold resistance value. A hydrogen sensor in which power is constantly supplied to the IC tag from an external source when the hydrogen sensor is in use, and the IC tag communicates with the external source regardless of the hydrogen concentration.

2. The hydrogen sensor according to claim 1, wherein the antenna is a non-coiled antenna.

3. The hydrogen sensor according to claim 2, wherein the IC tag communicates in the UHF band.

4. The pair of electrodes are a pair of comb-shaped electrodes, The hydrogen sensor according to claim 1, wherein the spacing between the pair of comb-tooth electrodes and the thickness of the sensitive film are adjusted such that the resistance between the sensor terminals when the hydrogen concentration is zero is 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 is equal to or less than the second threshold resistance value.

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

6. The hydrogen sensor according to claim 1, wherein, when the second threshold resistance value is set to 100%, the difference between the resistance value between the sensor terminals when the hydrogen concentration is the set value and the second threshold resistance value is 1% or more and 20% or less of the second threshold resistance value.

7. The hydrogen sensor according to claim 1, wherein the difference between the first threshold resistance value and the second threshold resistance value is 10 MΩ or more and 100 MΩ or less.

8. A hydrogen detection system using a hydrogen sensor according to any one of claims 1 to 7.

9. A hydrogen pipeline using the hydrogen detection system described in claim 8, A hydrogen pipeline in which the hydrogen sensor is arranged along the outer surface of the hydrogen pipeline.

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