Hydrogen gas sensor and method for manufacturing same

Abstract

The present invention relates to a hydrogen gas sensor using multi-walled carbon nanotubes aligned in one direction. A hydrogen gas sensor according to an embodiment of the present invention includes carbon nanotubes aligned in one direction and a metal oxide, wherein, as hydrogen molecules are ionized, electrons are provided to the metal oxide, and a resistance value increases as the electrons of the metal oxide combine with holes of the carbon nanotubes, and the concentration of the hydrogen molecules is calculated by measuring a voltage corresponding to a change in the resistance value.

Description

Hydrogen gas sensor and method of manufacturing the same

[0001] The present invention relates to a hydrogen gas sensor. More specifically, it relates to a hydrogen gas sensor using unidirectionally aligned multi-walled carbon nanotubes. It also relates to a hydrogen gas sensor comprising a mixture of a carbon material and a metal oxide semiconductor material. Furthermore, it relates to a method for manufacturing a material that detects hydrogen gas and applying it to a hydrogen gas sensor.

[0002]

[0003] When using fossil fuels, nitrogen oxides (NOx) containing carbon dioxide and impurities x ), sulfur oxides (SO x ) is emitted, causing various environmental problems. For example, by-products from the use of fossil fuels can cause environmental problems such as acid rain, fine dust, and global warming.

[0004] To solve these environmental problems, there is an effort to replace fossil fuels with hydrogen. Hydrogen molecules can be obtained by utilizing solar reactions, reacting polymeric materials inside cells with sunlight in a photosynthetic bioreactor, electrolyzing nickel and iron electrodes at atmospheric pressure using an alkaline aqueous solution as an electrolyte, or separating hydrogen from hydrogen mixed gases generated during petrochemical industrial processes.

[0005] It has the advantages of emitting only water and no pollutants when hydrogen molecules are burned, facilitating easy energy storage and transportation, and enabling use across all industrial sectors.

[0006] However, hydrogen molecules pose an explosion risk due to their wide atmospheric concentration and low ignition point, and there is a problem in detecting reactions, particularly because they are colorless and odorless. Accordingly, the Hydrogen Safety Act, which mandates the installation of hydrogen gas sensors, has been enacted and is being implemented.

[0007] Conventional hydrogen gas sensors have the disadvantage of malfunctioning depending on the operating environment, frequent failures, and difficulty in predicting replacement timing and lifespan. Additionally, they can only detect up to 4% of the lower explosive concentration of hydrogen molecules, and there is a problem in that they cannot detect hydrogen molecule leakage when detecting low concentration ranges and cannot measure the purity of hydrogen molecules when detecting high concentration ranges.

[0008] Metal oxide semiconductors are a key component used in gas sensors, but due to their high operating temperatures, they can explode when exposed to hydrogen molecules in the atmosphere.

[0009]

[0010] [Prior Art Literature]

[0011] [Patent Literature]

[0012] Korean Patent Publication No. 10-0833835 (Publication Date: June 2, 2008)

[0013]

[0014] The objective of the present invention is to solve the above-mentioned problems by providing a hydrogen gas sensor capable of lowering the operating temperature.

[0015] And, it provides a hydrogen gas sensor using unidirectionally aligned multi-walled carbon nanotubes.

[0016] And it provides a hydrogen gas sensing layer mixed with carbon material and metal oxide semiconductor material.

[0017] And it provides a method for manufacturing hydrogen gas sensors.

[0018] To achieve the above objective, a hydrogen gas sensor according to one embodiment of the present invention comprises unidirectionally aligned carbon nanotubes and a metal oxide, wherein hydrogen molecules provide electrons to the metal oxide as they ionize, and as the electrons of the metal oxide combine with the holes of the carbon nanotubes, the resistance value increases, and the concentration of hydrogen molecules is calculated by measuring the voltage according to the change in the resistance value.

[0019] In one embodiment, the polydimethylsiloxane (PDMS) film is manufactured by aligning and attaching the carbon nanotube and the silicon platform chip.

[0020] In one embodiment, the carbon nanotubes are grown by chemical vapor deposition, and then a drawing process is performed to form carbon nanotube bundles aligned in one direction.

[0021] In one embodiment, the carbon nanotube bundle is placed over a hole formed in the PDMS film, and a portion of the carbon nanotube wire is suspended inside the hole.

[0022] In one embodiment, the silicon platform chip includes two electrodes separated from each other, and a groove is formed between the two electrodes.

[0023] In one embodiment, both ends of the carbon nanotube bundle located on the surface of the PDMS film are each attached by contacting one of the two electrodes of the silicon platform chip.

[0024] In one embodiment, the metal oxide is titanium dioxide (TiO2).

[0025] In one embodiment, a chamber is included, and the concentration of hydrogen gas inside the chamber is measured.

[0026] In one embodiment, the concentration of the hydrogen gas is 0.1% to 10%.

[0027] In one embodiment, the chamber includes an electric circuit, the electric circuit includes a first resistor located between a first node and a second node and a second resistor located between a second node and a third node, and the first resistor includes unidirectionally aligned carbon nanotubes and a metal oxide.

[0028] A method for manufacturing a hydrogen gas sensor according to one embodiment of the present invention comprises: a step A of grinding nanopowder of multi-walled carbon nanotubes and nanopowder of titanium dioxide in a mortar and pestle; a step B of mixing the powder ground in step A with an adhesive mixed with alpha-terpenol and ethyl cellulose to form a paste; a step C of coating the paste formed in step B onto an alumina sensor substrate or a silicon MEMS device and drying it; and a step D of heat-treating the alumina sensor substrate or silicon MEMS device dried in step C.

[0029] In one embodiment, in step D, heat treatment is performed for 1 hour in an electric furnace formed at a temperature of 400 to 500°C, and then cooled to sinter.

[0030] According to another embodiment of the present invention, a hydrogen gas sensor comprises: a substrate; a metal electrode formed on the substrate; and a sensing layer formed on the metal electrode; wherein the sensing layer comprises unidirectionally aligned carbon nanotubes and a metal oxide, and the sensing layer may be configured such that its resistance value changes according to the concentration of hydrogen in contact with hydrogen.

[0031] In another embodiment, the sensing layer is positioned such that the carbon nanotubes are dispersed within the metal oxide, and the carbon nanotubes can serve as conductive channels connecting the metal oxide particles.

[0032] In another embodiment, the carbon nanotube has p-type semiconductor characteristics and contains holes as majority carriers, the metal oxide has n-type semiconductor characteristics and contains electrons as majority carriers, and a pn junction may be formed between the carbon nanotube and the metal oxide.

[0033] In another embodiment, the titanium dioxide of the sensing layer comprises an anatase phase and a rutile phase, wherein the anatase phase may be composed of a higher proportion than the rutile phase.

[0034] In another embodiment, the sensing layer may be formed by grinding and mixing nanopowder of multi-walled carbon nanotubes and nanopowder of titanium dioxide, mixing them with an adhesive to form a paste, which is then coated onto the metal electrode and heat-treated.

[0035] In another embodiment, the sensing layer may include a multi-walled carbon nanotube layer coated on the metal electrode and a metal oxide thin film deposited by sputtering on the multi-walled carbon nanotube layer.

[0036] In another embodiment, the hydrogen sensing sensor operates at room temperature, and the resistance value can change linearly with respect to the concentration of hydrogen molecules.

[0037] In another embodiment, a sensing device for detecting hydrogen concentration includes a first resistor located between a first node and a second node and a second resistor located between a second node and a third node, wherein the first resistor comprises a substrate; a metal electrode formed on the substrate; and a sensing layer formed on the metal electrode; wherein the sensing layer comprises unidirectionally aligned carbon nanotubes and a metal oxide, and the sensing layer is configured to have a resistance value that changes according to the concentration of hydrogen in contact with hydrogen, and the hydrogen concentration can be measured by measuring the change in the voltage value of the second resistor according to the change in the first resistor.

[0038]

[0039] By implementing the present invention, the hydrogen gas sensor can be operated at room temperature. Additionally, the operating temperature can be adjusted to be linearly proportional to the concentration of hydrogen gas in the atmosphere.

[0040] According to one embodiment of the present invention, a hydrogen gas sensor incorporating a carbon nanotube bundle exhibits linear response characteristics in response to the concentration of hydrogen molecules across the entire concentration range. Additionally, the hydrogen gas sensing layer has a small volume, a large surface area, and a floating form, allowing for a driving power of less than 1 mW. Accordingly, the present invention can be applied to all cycles of hydrogen production, storage, transport, and consumption.

[0041]

[0042] Figure 1 shows the configuration of a hydrogen gas sensor according to one embodiment of the present invention.

[0043] Figure 2 shows the configuration of an electric circuit in one embodiment of the present invention.

[0044] FIG. 3 is a diagram showing the sensing mechanism of a hybrid sensor in one embodiment of the present invention.

[0045] Figure 4 shows the characteristic information of titanium dioxide.

[0046] Figure 5 shows the hydrogen sensing properties of a sensor composed solely of titanium dioxide.

[0047] Figure 6 shows the characteristics of a hybrid sensor composed of carbon and metal oxide in one embodiment of the present invention.

[0048] FIG. 7 shows the hydrogen sensing properties of a hybrid sensor in one embodiment of the present invention.

[0049] FIG. 8 is a graph showing gas sensitivity when mixing a carbon material and a metal oxide in one embodiment of the present invention.

[0050] FIG. 9 is a plan view showing the structure of a hydrogen gas sensor according to one embodiment of the present invention.

[0051] FIG. 10a is a diagram illustrating a method for manufacturing a hydrogen gas sensor according to a first embodiment of the present invention.

[0052] Fig. 10b is a conceptual diagram of Fig. 10a.

[0053] FIG. 11a is a flowchart of a method for manufacturing a hydrogen gas sensor according to a second embodiment of the present invention.

[0054] Fig. 11b is a conceptual diagram of Fig. 11a.

[0055] FIG. 12 shows an enlarged image of a multi-walled carbon nanotube and an enlarged image of a sensing layer prepared according to the first embodiment of the present invention.

[0056] FIG. 13 shows an enlarged image of a multi-walled carbon nanotube and an enlarged image of a sensing layer prepared according to a second embodiment of the present invention.

[0057] FIG. 14 illustrates the process of a hydrogen gas sensor detecting hydrogen molecules according to a first embodiment of the present invention.

[0058] FIG. 15 illustrates the process of a hydrogen gas sensor detecting hydrogen molecules according to a second embodiment of the present invention.

[0059] FIG. 16 shows the resistance and sensitivity of a hydrogen gas sensor in one embodiment of the present invention.

[0060] FIG. 17 shows the resistance of titanium dioxide and a hydrogen gas sensor manufactured according to one embodiment of the present invention.

[0061]

[0062] The present invention may be implemented with various modifications without departing from the spirit, and may have one or more embodiments. Furthermore, the embodiments described in the "specific details for implementing the invention" and "drawings," etc., in the present invention are examples for specifically explaining the present invention and do not limit or restrict the scope of the rights of the present invention.

[0063] Accordingly, anything that a person skilled in the art to which the present invention pertains can easily deduce from the "specific details for carrying out the invention" and "drawings," etc., of the present invention may be interpreted as falling within the scope of the present invention.

[0064] In addition, the size and shape of each component shown in the drawings may be exaggerated for the purpose of explaining the embodiments and do not limit the actual size and shape of the invention.

[0065] Unless specifically defined otherwise in the specification of the present invention, terms used therein may have the same meaning as generally understood by those skilled in the art to which the present invention pertains.

[0066] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0067]

[0068] Figure 1 shows the configuration of a hydrogen gas sensing system according to one embodiment of the present invention.

[0069] A system (100) according to one embodiment of the present invention includes a hydrogen gas flow controller (110), an atmospheric gas flow controller (120), a chamber (130), a power supply device (140), a data acquisition device (150), and a data inquiry device (160).

[0070] A hydrogen gas flow controller (110) is connected to a chamber (130) via a pipe and can control the flow rate of hydrogen gas (H2) supplied to the chamber (130). The concentration (or mass, volume) of the hydrogen gas flowing through the hydrogen gas flow controller (110) is measured by a sensor, and the hydrogen gas flow controller (110) can compare the measured value with a preset value. The hydrogen gas flow controller (110) can control a control valve (not shown) until the measured value becomes equal to the preset value. Alternatively, the control valve can be kept open if the measured value is less than (or less than) the preset value, and the control valve can be closed if the measured value is greater than (or exceeds) the preset value.

[0071] An atmospheric gas flow controller (120) is connected via a pipe and can control the flow rate of atmospheric gas (N2, O2, CO2, Ar) supplied to the chamber (130). The concentration (or mass, volume) of the atmospheric gas flowing through the atmospheric gas flow controller (120) is measured by a sensor, and the atmospheric gas flow controller (120) can compare the measured value with a preset value. The atmospheric gas flow controller (120) can control the control valve until the measured value becomes equal to the preset value. Alternatively, if the measured value is less than (or lower than) the preset value, the control valve can be kept open, and if the measured value is greater than (or exceeds) the preset value, the control valve can be closed.

[0072] Pipes connecting the hydrogen gas flow controller (110) and the atmospheric gas flow controller (120) to the chamber (130), respectively, can be connected to each other. For example, a first pipe between the hydrogen gas flow controller (110) and the chamber (130) and a second pipe between the atmospheric gas flow controller (120) and the chamber (130) can be connected to each other.

[0073] The hydrogen gas flow controller (110) and the atmospheric gas flow controller (120) may each be a thermal-mass flow controller or a Coriolis mass flow controller. In the case of a thermal-mass flow controller, a bypass sensor may be used, an inline measurement method using Constant Temperature Anemometry (CTA) may be used, or a Trough Chip Sensor (TCS) may be used.

[0074] The chamber (130) may be filled with hydrogen gas and atmospheric gas. The capacity of the chamber may be, for example, 180 ml. The concentration of hydrogen gas inside the chamber (130) may range from 0.1% to 10%. However, this is merely an example, and the scope of the invention is not limited by these figures.

[0075] A sensing device (131) is included to analyze the gas filled inside the chamber (130). The sensing device (131) includes a hydrogen gas sensor. The hydrogen gas sensor is a hybrid sensor composed of a carbon material and a metal oxide, and may contain 50 wt.% of the carbon material. Hereinafter, the hydrogen gas sensor may be referred to as a hybrid sensor. However, this is merely an example, and the scope of the invention is not limited by such figures. The carbon material may be unidirectionally aligned carbon nanotubes (CNT) or may include them.

[0076] A hybrid sensor can be manufactured by creating a PDMS (polydimethylsiloxane) film using carbon nanotubes and a silicon platform chip, and then aligning and attaching the two configurations.

[0077] The structure and manufacturing method of the hybrid sensor are described in detail as follows. Carbon nanotubes are grown by chemical vapor deposition (CVD), and then a drawing process is performed to form carbon nanotube bundles with a diameter of 40 μm to 60 μm that are aligned in one direction. By placing the carbon nanotube bundles over holes drilled in the PDMS film to allow gas passage, a portion of the carbon nanotube wires can be suspended inside the holes. The silicon platform chip has two separate electrodes, and a groove can be formed between the two electrodes. When both ends of the carbon nanotube bundles located on the surface of the PDMS film are attached to contact the two electrodes of the silicon platform chip, the grooves of the silicon platform chip located below and the holes of the PDMS film located above can be aligned. Consequently, the middle region of the carbon nanotube bundles can be suspended in the air. When current passes through carbon nanotubes, the temperature rises due to Joule heat, but heat transfer to the main body is minimized, so the responsiveness of the device can be improved by utilizing the self-heating effect. This allows the sensitivity of the device to be increased while minimizing driving power by increasing the surface-to-volume ratio of the sensing layer.

[0078] Inside the chamber (130), the characteristics of the device can be measured while changing the concentration of hydrogen molecules. Conventional hydrogen gas sensors operate only in some low-concentration or high-concentration ranges, but according to one embodiment of the present invention, a sensor with a carbon nanotube bundle exhibits linear response characteristics in response to the concentration of hydrogen molecules across the entire concentration range.

[0079] In addition, a sensor according to one embodiment of the present invention can be implemented such that the volume of the hydrogen sensing material is small, the surface area is large, and it is in a floating form, while the driving power is less than a preset power (e.g., 1 mW). Accordingly, the present invention can be applied in all cycles of hydrogen production, storage, transport, and consumption.

[0080] The power supply unit (140) can generate a voltage that meets the usage specifications and apply the voltage to the detection unit (131) and the data acquisition unit (150), respectively.

[0081] The data acquisition device (150) is connected to the sensing device (131) and can store information about the gas measured inside the chamber (130). For example, it can store the concentration of gases such as hydrogen gas, nitrogen, oxygen, carbon dioxide, or argon.

[0082] The data acquisition device (150) can receive an electrical signal from the detection device (131) and store electrical signal information by time.

[0083] The data inquiry device (160) can analyze information about the gas measured inside the chamber (130). The data inquiry device (160) is connected to the data acquisition device (150) and can retrieve stored information.

[0084] The data inquiry device (160) can analyze the characteristics of the metal oxide material, the hydrogen sensing properties of titanium dioxide (TiO2), the characteristics of carbon and metal oxide, and the hydrogen sensing properties of the hybrid sensor, respectively.

[0085] Figure 2 shows the configuration of an electric circuit in one embodiment of the present invention.

[0086] The sensing device (131) includes first to third nodes (N1 - N3), a first resistor (R1), and a second resistor (R2). The first resistor (R1) may be located between the first node (N1) and the second node (N1), and the second resistor (R2) may be located between the second node (N2) and the third node (N3).

[0087] The first node (N1) and the third node (N3) are connected to a power supply unit (140), and between the first node (N1) and the third node (N3), a voltage (Vin) set by the power supply unit (140) can be applied.

[0088] The first resistor (R1) may represent a hydrogen sensing sensor comprising titanium dioxide and a carbon material. The first resistor (R1) may have the properties of a variable resistor whose resistance value changes depending on the temperature or hydrogen gas concentration inside the chamber (130). The carbon material included in the hydrogen sensing sensor may be a carbon nanotube aligned in a unidirectional manner, or may be composed of carbon nanotubes and other materials.

[0089] The second node (N2) is connected to a data acquisition device (150), and the data acquisition device (150) is connected to the voltage (V) of the second node (N2). out The voltage information can be stored for each time the ) was measured.

[0090] The data acquisition device (150) or data inquiry device (160) has a voltage (V) of a second node (N2) that varies by the temperature or hydrogen gas concentration inside the chamber (130). out From the information, the temperature or hydrogen gas concentration inside the chamber (130) can be calculated.

[0091] FIG. 3 is a diagram showing the detection mechanism of a hydrogen detection sensor in one embodiment of the present invention.

[0092] The detection mechanism is a process in which the resistance value changes according to the concentration of hydrogen gas in a hybrid sensor included in the first resistor (R1) of the detection device (131).

[0093] First, as shown in FIG. 3(a), a hybrid sensor composed of carbon material and titanium dioxide (TiO2) is located inside a chamber (130), and nitrogen molecules (N2), which are atmospheric gases, may be present. The carbon material may be unidirectionally aligned carbon nanotubes or may be configured to include carbon nanotubes and other materials together.

[0094] Next, hydrogen gas (H2) can be injected into the atmospheric gas as shown in Fig. 3 (b).

[0095] Then, as shown in Fig. 3 (c), hydrogen molecules are adsorbed on the surface of the hybrid sensor and ionized (H + Hydrogen molecules can provide electrons (-) to titanium dioxide as they ionize.

[0096] As shown in (d), electrons of titanium dioxide and holes of the carbon material combine, and accordingly, the resistance value of the first resistor (R1) can be increased. At this time, the holes of the carbon material act as major carriers of the carbon nanotube and combine with electrons, so that the conductivity can be lowered. As the resistance value of the first resistor (R1) increases, the output voltage (Vout) of the detection device (131) decreases, and the data inquiry device (160) can calculate the concentration of hydrogen gas in response to the output voltage (Vout).

[0097] Figure 4 shows characteristic information of titanium dioxide used in a sensor of one embodiment of the present invention.

[0098] (a) shows the X-ray diffraction (XRD) data of titanium dioxide, a metal oxide. Titanium dioxide can contain anatase and rutile phases depending on its crystal structure, and it can be seen that the intensity of anatase is higher than the intensity of rutile.

[0099] (b) shows the mass percentage of titanium dioxide powder, and it can be seen that anatase accounts for 91.6% and rutile accounts for 8.32%.

[0100] Accordingly, one embodiment of the present invention can achieve optimal hydrogen gas detection performance by implementing a hybrid sensor using titanium dioxide powder predominantly in the anatase phase.

[0101] Figure 5 shows the hydrogen sensing properties of titanium dioxide in one embodiment of the present invention.

[0102] A sensor using titanium dioxide alone can operate by receiving energy from an external source. In this case, energy must be supplied to the sensor through an external heater to raise the sensor's operating temperature and ensure sufficient sensitivity. As shown in the drawing, as the magnitude of the voltage applied to the heater increases and the energy supplied to the sensor increases, the sensitivity of hydrogen gas concentration measurement can be increased.

[0103] However, when operating the sensor at high temperatures using a heater, the risk of hydrogen gas explosion increases. Therefore, it is necessary to expose the sensor to atmospheric gases containing nitrogen molecules. If the volume ratio of hydrogen molecules in the sensor is 2.5 vol.% or higher than that of carbon materials and titanium dioxide, a heater may be required.

[0104] Figure 6 shows the characteristics of a hybrid sensor composed of carbon and metal oxide in one embodiment of the present invention.

[0105] Referring to Figure 6(a), it can be seen that in the hybrid sensor, the resistance value decreases as the mass proportion of carbon increases, and conversely, the resistance value increases as the mass proportion of carbon decreases. Figure 6(b) shows an image of the hybrid sensor taken with a scanning electron microscope (SEM), showing carbon nanotubes dispersed in titanium dioxide.

[0106] FIG. 7 illustrates the hydrogen detection properties of a hybrid sensor in one embodiment of the present invention. FIG. 7(a) shows the sensitivity corresponding to a hydrogen molecule concentration of 0% to 10% when the sensor is operated without a heater, and it can be seen that the sensitivity increases as the hydrogen molecule concentration increases. FIG. 7(b) and FIG. 7(c) show the voltage measured corresponding to the concentrations of nitrogen molecules and oxygen molecules over time, respectively. It can be seen that as time passes, the range of change in voltage corresponding to the concentration of nitrogen molecules increases, and the range of change in voltage corresponding to the concentration of oxygen molecules decreases.

[0107] FIG. 8 is a graph showing the gas sensitivity of various sensors in which the type and composition of the material combined with the carbon nanotube are configured differently in one embodiment of the present invention.

[0108] The drawings show the sensitivities corresponding to the concentration of hydrogen molecules for a sensor made of a thin film of carbon nanotubes and titanium dioxide (CNT / TiO2 Sputter), a sensor made of carbon nanotubes only (CNT 12V), a sensor made of a combination of carbon nanotubes and PDMS film (CNT / PDMS 12V), and a sensor made of powder of carbon nanotubes and titanium dioxide (CNT / TiO2 Milling). All were measured in an oxygen atmosphere.

[0109] The sensor composed of a thin film of carbon nanotubes and titanium dioxide (CNT / TiO2 Sputter) has the highest sensitivity. The sensor composed of carbon nanotubes and PDMS film (CNT / PDMS 12V) has low power consumption and noise, but the baseline is variable.

[0110] The mixing ratio of the sensor (CNT / TiO2 Milling) composed of carbon nanotubes and titanium dioxide powder is 1:99, it operates in a self-heating manner, and has the highest linearity.

[0111] Metal oxide semiconductors, such as tin oxide (SnO2), titanium dioxide (TiO2), zinc oxide (ZnO), indium oxide (In2O3), and tungsten oxide (WO3), can change their resistance values ​​as molecules within a gas are adsorbed or desorbed. Furthermore, the type and concentration of molecules within the gas can be determined by utilizing changes in resistance.

[0112] In order to increase the sensitivity and selectivity for gas detection using carbon materials such as carbon nanotubes or graphene, metal catalysts such as palladium (Pd) and platinum (Pt) are combined, or oxide mixtures are used to distinguish gases containing molecules other than hydrogen molecules.

[0113] A hydrogen gas sensor according to one embodiment of the present invention comprises a carbon nanotube composed of nanometer-sized carbon molecules configured in a tube shape. The carbon nanotube has a high surface area and conductivity, and when hydrogen molecules are adsorbed, its electrical resistance changes, thereby enabling the detection of hydrogen molecules. Based on this change in electrical resistance, the hydrogen gas sensor according to one embodiment of the present invention can generate a detection signal by adding a catalyst, such as palladium or platinum, to the surface of the carbon nanotube, thereby causing a change in conductivity when hydrogen molecules are adsorbed. The hydrogen gas sensor according to one embodiment of the present invention has a fast response speed, high sensitivity, can be miniaturized, and can operate at low power. In particular, the carbon nanotube possesses sensitivity capable of detecting trace amounts of hydrogen molecules. Such a hydrogen gas sensor can be utilized for real-time monitoring of vehicle hydrogen fuel cells, hydrogen refueling stations, batteries, etc.

[0114] According to another embodiment of the present invention, a hydrogen gas sensor may include graphene, which is a single carbon layer having a two-dimensional planar structure. Graphene possesses high electron mobility and a specific surface area. When hydrogen molecules are adsorbed onto the surface of graphene, the electrical properties change, allowing the concentration of hydrogen molecules to be detected. According to another embodiment of the present invention, the hydrogen gas sensor can measure the concentration of hydrogen molecules by detecting the change in conductivity that occurs when hydrogen molecules are adsorbed. Sensitivity may be further enhanced when palladium nanoparticles or other metal oxide catalysts are bonded to the graphene. Since graphene has higher electron mobility than carbon nanotubes and can react even to minute concentrations of hydrogen molecules, it can be used to fabricate ultra-high-sensitivity sensors. Therefore, according to another embodiment of the present invention, the hydrogen gas sensor can be used to monitor safety in hydrogen fuel cell vehicles, hydrogen production and storage facilities, etc.

[0115] FIG. 9 shows the structure of a hydrogen gas sensor according to one embodiment of the present invention.

[0116] As shown in FIG. 9(a), a hydrogen gas sensor (200) composed of a ‘thin film’ of carbon nanotubes and titanium dioxide is manufactured as follows. First, a metal electrode (220) of a specific pattern is prepared on a substrate (210). Then, carbon nanotubes aligned in a unidirectional manner are placed on the metal electrode (220), and a titanium dioxide thin film is deposited by sputtering. A sensing layer (230) composed of carbon nanotubes and titanium dioxide can be manufactured on the metal electrode by heat treatment at 500°C for 1 hour.

[0117] As shown in FIG. 9(b), a sensor composed of carbon nanotubes and titanium dioxide 'powder' can be manufactured as follows. A substrate (210) and a metal electrode (220) formed thereon are prepared. Titanium dioxide nanopowder and carbon nanotubes are mixed and milled, and a sensing layer (230) is formed on the electrode (220) using an ethylcellulose-based binder. Then, the sensing layer (230) can be completed by drying and then heat-treating at 500°C for 1 hour.

[0118] FIGS. 10a and FIGS. 10b respectively show a flowchart and a conceptual diagram of a method for manufacturing a hydrogen gas sensor (200) according to a first embodiment of the present invention, corresponding to the structure (b) of FIG. 9.

[0119] In the first embodiment of the present invention, a sensing layer (230) for detecting hydrogen gas is manufactured from a paste composed of carbon nanotube powder and titanium dioxide powder.

[0120] First, nanopowder of multi-walled carbon nanotubes (MWCNT) or single-walled carbon nanotubes (SWCNT) and nanopowder of titanium dioxide or other metal oxides are placed in an agate mortar and ground. (Step S1010)

[0121] Multiwalled carbon nanotubes are structures formed by stacking multiple layers of graphene sheets in a concentric pattern. Their diameter can range from a few nanometers to tens of nanometers, and their length can exceed several micrometers. Their bulk density is very low, at 0.1 g / cm³. 3 It can be less than, and the specific surface area is very large, hundreds of m² 2 It can be greater than / g. Multiwalled carbon nanotubes have the characteristic of strongly aggregating and clumping together. And sp 2 It exhibits a hexagonal lattice structure based on bonding and possesses high tensile strength and stiffness. Due to its metallic or semiconducting properties, it has high electrical conductivity, and its high thermal conductivity allows for rapid heat diffusion.

[0122] Single-walled carbon nanotubes are structures in which a single sheet of graphene is rolled into a cylindrical shape. Their diameter ranges from 0.4 nm to 2 nm, and their length can be from several hundred nm to several μm. As a single layer, they possess more flexible properties than multi-walled carbon nanotubes, but have higher strength. Due to their metallic or semiconducting properties, they have high electrical conductivity and thermal conductivity higher than that of diamond.

[0123] The mixing ratio (multi-walled carbon nanotube / titanium dioxide) of multi-walled carbon nanotube nanopowder and titanium dioxide nanopowder can be set according to the weight ratio of the multi-walled carbon nanotubes. For example, the mixing ratio can be determined by setting the weight ratio of the multi-walled carbon nanotubes to 0.25, 0.5, 1, 5, 20, 30, 50, or 100 wt%. However, this is merely an example, and the scope of the present invention is not necessarily limited thereto.

[0124] The average particle size of the titanium dioxide nanopowder can be 100 nm. The phase of the titanium dioxide nanopowder can be rutile or anatase. Rutile is a tetragonal phase and has the highest stability among the phases of titanium dioxide, making it suitable for high-temperature processes. Additionally, due to its high refractive index (n ≈ 2.7), it can be used in optical materials. Anatase is a tetragonal phase that is less stable than rutile and can transition to rutile upon heat treatment (600 to 700°C). Furthermore, it possesses excellent photocatalytic activity and UV absorption characteristics.

[0125] Next, the ground powder is added to a binder mixed with alpha-terpineol and ethyl cellulose, and mixed. (Step S1020) Both the grinding step (S1010) and the mixing step (S1020) can be performed for 2 hours, or each step can be performed for 2 hours.

[0126] The alpha-terpenol component in the adhesive lowers viscosity and provides flowability, and allows for working time to be secured by slow evaporation. The ethylcellulose component can fix solid particles, form a film, and increase viscosity. Alpha-terpenol may be present in an amount of about 80 to 90 wt%, and ethylcellulose may be present in an amount of about 5 to 10 wt%.

[0127] Next, the paste formed in the mixing step (S1020) is coated onto a substrate (210) on which a metal electrode is formed or a silicon MEMS (micro electro mechanical system) device, and then dried. (Step S1030)

[0128] The substrate (210) is made of aluminum oxide (Al2O3) and supports the structure of the sensor, allowing it to operate stably in environments of temperature change or chemical reaction. The crystal structure is α-Al2O3, and since the melting point is high at about 2050°C, the sensor can operate in high-temperature environments. The silicon MEMS device may have a configuration such as a beam, a capacitor plate, a diaphragm, and a spring.

[0129] Paste or solution can be coated onto the sensing area to a thickness ranging from a few micrometers to several hundred micrometers. Coating can be performed using methods such as blade coating, screen printing, drop casting, dispenser coating, spin coating, slot die coating, and spray coating. In the blade coating method, paste is applied to the substrate or device and spread flat using a doctor blade. This method is simple and allows for uniform thickness control. It also offers the characteristics of rapid coating over a large area and low cost. In the screen printing method, a desired pattern is created on a mesh, and a solution or paste is pressed through using a squeegee. This method enables pattern coating and allows for mass production through precise, repetitive printing. In the drop casting method, the solution is dropped and spread out like droplets. This method is simple and requires no additional equipment, making it suitable for small-batch processes. In the dispenser coating method, a precise nozzle dispenses a quantitative amount of solution to a designated location. This method enables automation and the formation of fine patterns. It also allows for more precise quantitative control and has the characteristic of being applicable to irregular substrates.

[0130] In the spin coating method, a paste or solution is applied to a substrate or device and rotated at high speed. This method is characterized by its ability to uniformly coat nanometer-scale thin films. In the slot die coating method, a solution is continuously applied onto the substrate through slots, which are uniform gaps. This method is suitable for roll-to-roll processes and is characterized by its ability to form thin films over large areas at high speeds. In the spray coating method, fine particles are sprayed using an airbrush or nozzle. This method is characterized by its ability to be applied to substrates that are complexly formed, have large areas, or are curved surfaces.

[0131] Drying can be performed at approximately 80°C for 10 minutes.

[0132] Next, the dried substrate or device is heat-treated. (Step S1040) The substrate or device coated with paste can be heat-treated for 1 hour in an electric furnace formed at a temperature of 400 to 500°C, and then slowly cooled to sinter. The sintered material can form the first resistor (R1) shown in FIG. 2 as a material that detects hydrogen gas.

[0133] FIGS. 11a and FIGS. 11b respectively show a flowchart and a conceptual diagram of a method for manufacturing a hydrogen gas sensor (200) according to a second embodiment of the present invention, corresponding to the structure of FIG. 9 (a).

[0134] In the second embodiment of the present invention, a sensing layer (230) is manufactured using a drop-cast of carbon nanotubes and a thin film of titanium dioxide.

[0135] First, the powder of multi-walled carbon nanotubes is placed in deionized water (DI-water) or a binder mixed with alpha-terpenol and ethylcellulose and dispersed. (Step S2010) The deionized water contains cations (Ca 2+ , Mg 2+, Na + (etc.) and anions (Cl - , S04 2- , NO 3- Water from which (etc.) has been removed has low electrical conductivity. The weight of the multi-walled carbon nanotube can be about 0.1g, and the volume of the solution can be about 100ml.

[0136] Dispersion can be achieved using high-frequency vibration energy generated by ultrasound. Ultrasound can be used to break down aggregates in multi-walled carbon nanotubes and disperse them uniformly in deionized water. When high frequencies of 20 kHz or higher are transmitted to a solution, microbubbles are generated and burst, creating localized high temperature, high pressure, and strong shear forces that can break the bonds between particles and disperse them. Dispersants or surfactants can be added before ultrasound irradiation. For example, Triton X-100, SDS (sodium dodecyl sulfate), or PVP (polyvinylpyrrolidone) can be added. Dispersants or surfactants can prevent re-aggregation between particles.

[0137] Ultrasonic waves of 500W can be applied to the solution for 1 to 30 minutes. To prevent heat generation, cooling may be performed after the ultrasonic waves are applied. Additionally, ultrasonic waves may be applied at regular intervals. For example, ultrasonic waves may be applied for 10 seconds, and then the application may be stopped for 10 seconds. When storing the solution after ultrasonic wave application, stirring may be maintained or a dispersant may be added to prevent aggregation.

[0138] Next, the dispersed solution is drop-cast onto an alumina sensor substrate or silicon MEMS device on which a metal electrode is formed. (Step S2020) Three drops of the dispersed solution can be drop-cast onto a hot plate dried at 80°C. Then, the substrate or device can be dried.

[0139] Next, the dried substrate or device is heat-treated. (Step S2030) The dried substrate or device can be heat-treated at 300°C for 1 hour. For example, it can be heat-treated at 300°C for 1 hour in an electric furnace.

[0140] Next, a thin film of titanium dioxide or another metal oxide is deposited on the heat-treated substrate or device. (Step S2040) A metal mask with a fine pattern formed on a metal plate can be fixed to the top of the substrate or device, and a thin film can be deposited through the opening of the metal mask. After fixing the metal mask in close contact with the top of the substrate or device or at a certain distance, atoms of the target material, titanium dioxide or another metal oxide, can be ejected using ionized gas in a vacuum chamber, and the atoms can be deposited on the top of the substrate or device through the opening. Alternatively, an RF magnetron sputtering process can be performed. Argon (Ar) gas can be injected into a vacuum chamber to generate plasma under vacuum conditions, and then an RF power source can be activated to eject atoms of the target material, titanium dioxide or another metal oxide, and the atoms can be deposited on the top of the substrate or device. At this time, a high frequency of 13.56 MHz can be used for the RF power source.

[0141] Next, the deposited substrate or device is heat-treated. (Step S2050) The deposited substrate or device can be heat-treated at 400°C or lower to crystallize the thin film. In order to avoid damaging or destroying the structure of the multi-walled carbon nanotube, the heat treatment is performed at 400°C or lower.

[0142] FIG. 12 shows an image of a multi-walled carbon nanotube and an enlarged image of a sensing layer (230) manufactured according to the first embodiment of the present invention.

[0143] The two images are images taken with a scanning electron microscope. (a) is an image of a material composed solely of multi-walled carbon nanotubes, showing that the multi-walled carbon nanotubes are intertwined. (b) is an image of a hydrogen gas sensing layer (230) manufactured according to the first embodiment of the present invention, showing a form in which multi-walled carbon nanotubes are dispersed within titanium dioxide. Molecules of hydrogen or other gases can penetrate into the sensing layer (230) to increase sensitivity. Also, since the multi-walled carbon nanotubes have high conductivity and reduce the overall resistance of the sensing layer (230), they can be used at room temperature.

[0144] FIG. 13 shows an image of a multi-walled carbon nanotube and an image of a hydrogen gas sensing layer (230) manufactured according to a second embodiment of the present invention.

[0145] The two images were taken using a scanning electron microscope. (a) shows the top of an alumina substrate coated with a solution in which multi-walled carbon nanotubes are dispersed. (b) shows a sensing layer (230) manufactured according to the second embodiment of the present invention, illustrating a form in which a thin film of titanium dioxide is deposited on top of the multi-walled carbon nanotubes. A metal oxide thin film formed in the same way as a coating of a carbon material is deposited, allowing the large specific surface area characteristics of the carbon material to be utilized. For example, if the specific surface area characteristics of the sensing layer (230) are large, the number of gas molecules adsorbed on the surface increases, thereby increasing sensitivity. The specific surface area range of the carbon nanotubes is 100 to 1000 m² 2 With internal and external surfaces at 1 / g, it has a large specific surface area and is easy to store or capture hydrogen.

[0146] FIG. 14 illustrates the process of a hydrogen gas sensor detecting hydrogen molecules in the first embodiment of the present invention.

[0147] Multiwalled carbon nanotubes are conductive, but they can exhibit semiconductor properties if defects are formed on their surface. Multiwalled carbon nanotubes with semiconductor properties can have a resistance of 10 kΩ or more, but this resistance may decrease as the temperature increases. Additionally, multiwalled carbon nanotubes can exhibit p-type semiconductor characteristics where the majority of carriers are holes. Titanium dioxide or other metal oxides can exhibit n-type semiconductor characteristics where the majority of carriers are electrons.

[0148] Materials made of carbon materials have high electrical conductivity compared to metal oxides, and in a hydrogen gas sensor manufactured according to the first embodiment of the present invention, multi-walled carbon nanotubes, which are p-type semiconductors, can act as a conductive channel connecting titanium dioxide (or other metal oxides), which are n-type semiconductors.

[0149] As illustrated in FIG. 14 (a), the sensing layer (230) is assumed to be composed of a paste in which titanium dioxide is positioned around multi-walled carbon nanotubes. The multi-walled carbon nanotubes contain holes that act as carriers, and oxygen molecules are attached to the titanium dioxide.

[0150] Subsequently, hydrogen molecules may appear around the hydrogen sensing layer (230) as shown in Fig. 14 (b). As shown in Fig. 14 (c), hydrogen molecules react with oxygen molecules attached to titanium dioxide to form water molecules, and the water molecules can be removed from the titanium dioxide. At this time, electrons captured by the oxygen molecules are released into the titanium dioxide, and the electrons can recombine with holes, which are the majority carriers of the multi-walled carbon nanotubes. As electrons and holes recombine, the resistance of the hydrogen gas sensor (200) may increase. At this time, if the range of voltage drop due to the increase in resistance is measured, the concentration of hydrogen can be calculated.

[0151] FIG. 15 illustrates the process of a hydrogen gas sensor detecting hydrogen molecules in a second embodiment of the present invention. FIG. 15 (a) shows a conceptual diagram (left) and an energy band diagram (right) of a hydrogen gas sensing layer (230) before electrons and holes recombine, and FIG. 15 (b) shows a conceptual diagram (left) and an energy band diagram (right) of a hydrogen gas sensing layer (230) after electrons and holes recombine.

[0152] A pn junction is formed between a multiwalled carbon nanotube and titanium dioxide (or other metal oxide), and a space charge layer can be formed at the junction.

[0153] A space charge region is an area where the charge distribution becomes neural due to a local electric field formed by the redistribution of charge carriers; it can be triggered by external stimuli such as junctions, potential differences, and impurities. In a pn junction, when holes from the p-type semiconductor and electrons from the n-type semiconductor diffuse into each other and combine at the interface, free charges disappear, leaving only stationary ions, which can form a space charge region. An electric field forms within the space charge region, preventing further carrier diffusion and maintaining equilibrium.

[0154] When oxygen molecules are adsorbed on the surface of titanium dioxide (or other metal oxide), electrons from titanium dioxide (or other metal oxide) can move to the oxygen. As shown in FIG. 15 (a), electrons are deficient near the surface of titanium dioxide (or other metal oxide), which can form a space charge region.

[0155] And as shown in Fig. 15 (b), if hydrogen molecules are present in the surrounding atmosphere of titanium dioxide (or other metal oxide), they react with oxygen molecules adsorbed on the surface of titanium dioxide (or other metal oxide) to form water molecules, and the water molecules can be removed from the surface of titanium dioxide (or other metal oxide).

[0156] Electrons captured by oxygen molecules can be emitted into titanium dioxide (or other metal oxides). The emitted electrons move to multi-walled carbon nanotubes, which act as conductive channels, and can recombine with holes, which are majority carriers. When electrons and holes recombine, the electron density decreases, causing the band to bend upward and the space charge region to expand. Consequently, the electron pathway narrows, leading to an increase in resistance. When comparing the conceptual diagram shown in (b) with that shown in (a), it can be observed that the space charge region has expanded and the p-type region has contracted. Additionally, the height of the barrier can be seen to have increased in the energy diagram. At this point, the concentration of hydrogen gas can be calculated by measuring the voltage drop at the output terminal as the variable resistance increases.

[0157] FIG. 16 shows the resistance and sensitivity of a hydrogen gas sensor in one embodiment of the present invention.

[0158] Sensitivity indicates how much the resistance changes with changes in hydrogen gas concentration. Sensitivity can be calculated according to the following mathematical formula.

[0159] [Mathematical Formula 1]

[0160] S = (R2-R1) / R1

[0161] (S: Sensitivity, R1: Resistance in the atmosphere, R2: Resistance when exposed to a specific concentration of hydrogen gas)

[0162] Each graph shows the reactivity at a hydrogen gas concentration of 0 to 100%. The graphs shown in (a) and (b) respectively show the resistance and sensitivity of the hydrogen sensing layer (230) manufactured according to the first embodiment. It can be seen that as time passes, the transfer of electrons becomes smoother and the range of change in resistance increases. It can also be seen that as the concentration of hydrogen molecules increases, the sensitivity increases proportionally.

[0163] The graphs shown in (c) and (d) represent the resistance and sensitivity of the hydrogen sensing layer (230) manufactured according to the second embodiment, respectively. It can be seen that the range of change in resistance decreases over time. Also, it can be seen that the degree to which sensitivity increases gradually decreases as the concentration of hydrogen molecules increases.

[0164] FIG. 17 shows the resistance of titanium dioxide and a hydrogen gas sensor manufactured according to one embodiment of the present invention.

[0165] In the graph shown in (a), it can be seen that the resistance of a material composed solely of titanium dioxide decreases when the concentration of surrounding hydrogen molecules is high. This is due to hydrogen molecules (H2) and oxygen ions (O2) adsorbed on titanium dioxide. - ) react to become water molecules (H2O), and electrons (e - The resistance decreases rapidly as it returns ).

[0166] In the graph shown in (b), it can be seen that the resistance of the mixture of multiwalled carbon nanotubes and titanium dioxide prepared according to the first embodiment of the present invention increases when the concentration of hydrogen molecules in the surroundings is high. This is due to hydrogen molecules (H2) and oxygen ions (O2) adsorbed on titanium dioxide. - ) react to become water molecules (H2O) and electrons (e - It returns ), but electrons recombine with holes, causing conductivity to decrease and resistance to increase.

[0167] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. Various modifications may be made within the scope of the detailed description of the invention and the attached drawings, provided that such modifications do not depart from the spirit of the invention and do not impair its effects. Furthermore, it is obvious that such embodiments fall within the scope of the present invention.

[0168]

[0169] [Explanation of the symbol]

[0170] 100 : System

[0171] 110: Hydrogen gas flow controller

[0172] 120 : Atmospheric gas flow controller

[0173] 130 : Chamber

[0174] 140 : Power supply

[0175] 150: Data acquisition device

[0176] 160 : Data retrieval device

[0177] 200 : Substrate

[0178] 210: Metal electrode

[0179] 220 : Detection layer

Claims

1. Substrate; A metal electrode formed on the substrate; and A sensing layer formed on the metal electrode; comprising The above sensing layer is, It includes unidirectionally aligned carbon nanotubes and metal oxides, and A hydrogen gas sensor in which the above-mentioned sensing layer is configured such that the resistance value changes according to the concentration of hydrogen in contact with hydrogen.

2. In claim 1, the metal oxide is titanium dioxide (TiO2). Hydrogen gas sensor.

3. In Claim 1, The above carbon nanotube is a multi-walled carbon nanotube. Hydrogen gas sensor.

4. In Claim 2, The above sensing layer A hydrogen gas sensor in which the carbon nanotubes are dispersed and located within the metal oxide, and the carbon nanotubes act as conductive channels connecting the metal oxide particles.

5. In claim 2, in the sensing layer, The above carbon nanotubes have p-type semiconductor characteristics and contain holes as majority carriers, The above metal oxide has n-type semiconductor characteristics and contains electrons as majority carriers, A pn junction is formed between the carbon nanotube and the metal oxide. Hydrogen gas sensor.

6. In Claim 2, The titanium dioxide of the above sensing layer includes an anatase phase and a rutile phase, The anatase phase is composed of a higher proportion than the rutile phase, Hydrogen gas sensor.

7. In Claim 2, The above sensing layer is, A paste formed by grinding and mixing nanopowder of multi-walled carbon nanotubes and nanopowder of titanium dioxide, mixing with an adhesive, coating on the metal electrode, and heat-treating to form Hydrogen gas sensor.

8. In Claim 2, The above sensing layer is, A multi-walled carbon nanotube layer coated on the metal electrode and a metal oxide thin film deposited by sputtering on the multi-walled carbon nanotube layer Hydrogen gas sensor.

9. In Claim 2, The above hydrogen detection sensor operates at room temperature, and Resistance value changes linearly with respect to the concentration of hydrogen molecules Hydrogen gas sensor.

10. Includes a first resistor located between a first node and a second node, and a second resistor located between a second node and a third node, The first resistor comprises a substrate; a metal electrode formed on the substrate; and a sensing layer formed on the metal electrode; wherein the sensing layer comprises unidirectionally aligned carbon nanotubes and a metal oxide, and the sensing layer is configured such that its resistance value changes according to the concentration of hydrogen in contact with hydrogen. The hydrogen gas sensor is configured such that the first resistor comes into contact with hydrogen. A sensing device for detecting hydrogen concentration that measures the change in the voltage value of the second resistance according to the change in the first resistance.

11. Step A, in which nanopowder of multi-walled carbon nanotubes and nanopowder of titanium dioxide are placed in an agate mortar and ground; Step B, in which the powder ground in Step A above is added to an adhesive mixture of alpha-terpenol and ethylcellulose and mixed to form a paste; Step C, which involves coating and drying the paste formed in Step B above onto an alumina sensor substrate or a silicon MEMS device; and Step D, which involves heat-treating the alumina sensor substrate or silicon MEMS device dried in Step C above. Method for manufacturing a hydrogen gas sensor.

12. In Claim 11, In the above step D, heat treatment is performed for 1 hour in an electric furnace formed at a temperature of 400 to 500°C, and then cooled to sinter. Method for manufacturing a hydrogen gas sensor.

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