A nanostructure-based hydrogen sensor and a method of manufacturing the same

Abstract

The application relates to a nano-structure-based hydrogen sensor and a preparation method thereof, the hydrogen sensor is a hydrogen sensor with a detection lower limit of 10 ppb, the hydrogen sensor comprises a substrate and a PNP type three-section structure located on the substrate, the PNP type three-section structure comprises a hydrogen-sensitive film and conductive polymer (PEDOT) electrodes located on two sides of the hydrogen-sensitive film, the hydrogen-sensitive film is a semiconductor metal oxide nano-structure modified by noble metal particles, the diameter of the semiconductor metal oxide nano-structure is 50 nm-180 nm, and the thickness of the hydrogen-sensitive film is 1 mu m-500 mu m. The hydrogen sensor has the characteristics of small volume, low cost and simple structure, the response speed is very fast, the response time of the hydrogen sensor is less than 0.1 s when the hydrogen concentration is 200 ppb at a temperature of 180 DEG C, low-concentration hydrogen can be detected, and the lowest detection concentration of hydrogen is 10 ppb.

Description

Technical Field

[0001] This invention relates to the field of hydrogen sensing technology, specifically to a hydrogen sensor based on a nanostructure and its preparation method. Background Technology

[0002] In aerospace applications, hydrogen sensors need to operate under various environmental conditions. NASA's hydrogen safety specifications typically employ a combination of methods, including mass spectrometry, gas chromatography, and catalytic combustion hydrogen sensors, to detect hydrogen leaks. However, this approach has several inconveniences in practice. Spectroscopic analysis offers high resolution for hydrogen detection, but the required equipment is bulky and complex, and sampling times are long, making it unsuitable for the real-time, rapid hydrogen detection needs at launch sites in aerospace applications. Currently, portable and easily deployed hydrogen sensors suitable for real-time monitoring at rocket or missile launch sites mainly fall into five categories: electrochemical, catalytic combustion, metallic, surface acoustic wave (SAW), and metal oxide semiconductor (MOS) hydrogen sensors.

[0003] Although metal oxide semiconductors are currently a widely used material in resistive hydrogen sensors, the high-risk nature of space missions places higher demands on hydrogen detection. At present, hydrogen sensors are insufficient to meet the needs of future space missions in terms of detection sensitivity and reliability, especially the lower limit of sensor detection needs to be further reduced. Summary of the Invention

[0004] The purpose of this invention is to propose a small-sized, low-cost, simple-structured, and very fast-response hydrogen sensor based on nanostructures and its preparation method.

[0005] This invention discloses a hydrogen sensor based on a nanostructure, which has a detection limit of 10 ppb. The hydrogen sensor includes a substrate and a PNP-type three-segment structure on the substrate. The PNP-type three-segment structure includes a hydrogen-sensitive membrane and conductive polymer (PEDOT) electrodes located on both sides of the hydrogen-sensitive membrane. The hydrogen-sensitive membrane is a semiconductor metal oxide nanostructure modified with noble metal particles, with a diameter of 50 nm-180 nm and a thickness of 1 μm-500 μm. This application utilizes the fact that the PN junction contact barrier is modulated by the hydrogen concentration. The PNP structure amplifies the current change caused by resistance modulation, thus achieving a high response to ppb-level hydrogen concentrations in a very short time, with a detection limit of 10 ppb. Furthermore, the thickness of the hydrogen-sensitive membrane is 1 μm-500 μm; excessively large or small thicknesses will affect the sensing performance of the hydrogen sensor core to some extent. When the thickness is less than 1 μm, the stability of the device will deteriorate, and when the thickness is too thick, greater than 500 μm, the response to hydrogen will deteriorate.

[0006] Furthermore, the noble metal particles in the hydrogen-sensitive membrane described in this application are palladium or platinum, and the diameter of the noble metal particles is 5nm-20nm. When the diameter of the noble metal particles is less than 5nm, the particle spacing is too large, and the catalytic effect is weakened; when the particle diameter is greater than 20nm, the improvement in catalytic effect is not significant, and the particle spacing becomes smaller, resulting in competition and hindering the process of hydrogen desorbing oxygen on the surface.

[0007] Furthermore, the semiconductor metal oxide nanostructure described in this application is a zinc oxide, tin oxide, or a mixture of both. Zinc oxide and tin oxide nanostructures possess high specific surface areas and excellent photoelectric properties; for example, zinc oxide has a bandgap of 3.37 eV at room temperature, making it a direct wide bandgap material, and its exciton binding energy is also relatively large, at 60 meV. Therefore, using zinc oxide or tin oxide nanostructures as hydrogen sensing materials in this application can yield a heterostructure hydrogen sensor capable of rapidly detecting hydrogen concentration.

[0008] Furthermore, the noble metal in the hydrogen-sensitive membrane described in this application accounts for 0.01%-0.1% of the mass of zinc oxide, tin oxide, or a mixture of both. When the noble metal content is less than 0.01%, the coverage of the noble metal on the semiconductor material surface is low, resulting in poor catalytic effect. When the noble metal content is greater than 0.1%, the coverage is too large, and the effect on the desorption of oxygen by hydrogen is not significantly improved, or even a thin metal film is formed on the semiconductor surface, leading to a short circuit in the device. By using specific metals such as palladium, platinum, or gold loaded on zinc oxide or tin oxide nanostructures, a catalytic effect on hydrogen is achieved, which can decompose hydrogen into hydrogen atoms, lowering the reaction temperature. The hydrogen atoms react with adsorbed oxygen on the zinc oxide or tin oxide surface. Due to oxygen adsorption, the depletion layer width will decrease, and the potential barrier height at the heterojunction interface constructed with PEDOT will change, realizing the sensing function. A specific curve relationship exists between the change in current signal and the hydrogen concentration, thereby realizing the detection of the hydrogen environment.

[0009] Furthermore, the semiconductor metal oxide nanostructures described in this application are nanowires, nanoparticles, nanoflowers, nanotubes, or nanorods.

[0010] Furthermore, the thickness of the PEDOT electrode described in this application is 500nm-100μm. Excessive electrode thickness leads to waste of PEDOT material; excessively thin electrodes may prevent the device from conducting. In addition, the spacing between the electrodes also affects the performance of the hydrogen sensor. The spacing between the PEDOT electrodes is 100μm-500μm. Excessive spacing increases the number of nanowires between electrodes, requiring a higher bias voltage and increased power consumption; insufficient spacing results in fewer nanowires and fewer homogeneous junctions, which is detrimental to hydrogen sensing. The thickness and spacing of the PEDOT electrodes in this application, along with the thickness of the hydrogen-sensitive electrode, collectively affect the sensing performance of the hydrogen sensor.

[0011] A method for fabricating a hydrogen sensor based on a nanostructure as described above specifically includes the following steps:

[0012] 1) Preparation of semiconductor metal oxide nanostructures: Semiconductor metal oxide and carbon powder are uniformly mixed and then chemically vapor-deposited to obtain semiconductor metal oxide nanostructures, wherein the mass ratio of semiconductor metal oxide to carbon powder is 2:0.2-0.5;

[0013] 2) Modification of semiconductor metal oxide nanostructures: Noble metal particles are loaded onto the semiconductor metal oxide nanostructures using an ultraviolet reduction method;

[0014] 3) Fabrication of conductive polymer (PEDOT) electrodes:

[0015] 4) The noble metal-modified semiconductor metal oxide nanostructure is coated onto an insulating substrate with electrodes;

[0016] 5) Lead out the electrodes with copper wires to obtain the hydrogen sensor as described above.

[0017] Furthermore, the specific operation of step 1) of the preparation method described in this application is as follows: zinc oxide and carbon powder are mixed into a powder in an appropriate ratio and then anhydrous ethanol is added for grinding. The mass ratio of anhydrous ethanol to the mixed powder is 5:1-10:1. After grinding evenly, the powder is dried to obtain a gray-black sample. The gray sample is placed in a tube furnace for heating, heat preservation, and cooling to finally obtain a white semiconductor metal oxide nanostructure attached to the furnace wall.

[0018] Furthermore, step 2) of the preparation method described in this application includes the following specific operations: first, preparing a noble metal ion solution with a concentration of 0.6-0.7 mmol / L; then, placing the semiconductor metal oxide nanostructure obtained in step 1) into the noble metal ion solution in a dark environment, and using light with an intensity of 150-180 μw / cm². 2 The semiconductor metal oxide nanostructure was irradiated with ultraviolet light with a wavelength of 254-360nm for 110-130s; then the semiconductor metal oxide nanostructure was removed and washed with acetone, anhydrous ethanol and deionized water for 10-20min in sequence, and dried at 80-100℃ to obtain the noble metal modified semiconductor metal oxide nanostructure.

[0019] Furthermore, in step 1) of the preparation method described in this application, the gray sample is first placed in a ceramic boat and then placed in the central constant temperature zone of a tube furnace. Argon and oxygen are simultaneously introduced into the tube furnace, wherein the flow ratio of argon to oxygen is 240:25-30 sccm, the system pressure is atmospheric pressure, and the furnace is pre-ventilated for 20-30 minutes to remove air from the tube furnace. Then, the furnace temperature is raised to 1210-1230℃ at a heating rate of 25-35℃ / min and held for 40-60 minutes. After the holding period, the furnace is naturally cooled to room temperature to obtain the white semiconductor metal oxide nanostructures attached to the furnace wall.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] The nanostructure-based hydrogen sensor described in this invention features small size, low cost, and simple structure, exhibiting extremely fast response speed. At an optimal temperature of 180°C and a hydrogen concentration of 200 ppb, its response time can reach as fast as 0.1 seconds. Furthermore, it can detect low concentrations of hydrogen, with a minimum detection concentration of 10 ppb. This hydrogen sensor can be conveniently used to monitor leaks in all stages of hydrogen preparation, storage, transportation, and use, especially for early detection of even minute hydrogen leaks. Its rapid response characteristic holds promise for monitoring aerospace fuel leaks. On the other hand, the preparation method described in this invention has low equipment requirements, requires no high-precision instruments, and is simple and easy to understand, with readily available raw materials. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the hydrogen sensor described in this invention;

[0023] Figure 2 This is a graph showing the hydrogen response results of the hydrogen sensor described in Embodiment 1 of the present invention;

[0024] Figure 3 This is a SEM image of the hydrogen-sensitive membrane described in Embodiment 1 of the present invention;

[0025] Figure 4 This is a TEM image of the hydrogen-sensitive membrane described in Embodiment 1 of the present invention. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments.

[0027] Example 1:

[0028] like Figure 1As shown, the present invention discloses a hydrogen sensor based on a nanostructure with a detection limit of 10 ppb. The hydrogen sensor includes a substrate and a PNP-type three-segment structure located on the substrate. The substrate is a flexible insulating substrate with a resistivity of 1.8 × 10⁻⁶. 19 Ω / cm. The PNP-type three-segment structure includes a hydrogen-sensitive membrane and conductive polymer (PEDOT) electrodes located on both sides of the hydrogen-sensitive membrane. The hydrogen-sensitive membrane is a semiconductor metal oxide nanostructure modified with noble metal particles. The diameter of the semiconductor metal oxide nanostructure is 100-150 nm, and the thickness of the hydrogen-sensitive membrane is 100 μm-300 μm. In this embodiment 1, the noble metal particles in the hydrogen-sensitive membrane are palladium, and the diameter of the noble metal particles is 10 nm-15 nm. The semiconductor metal oxide nanostructure is zinc oxide nanowire, and the mass ratio of palladium to zinc oxide is 2:0.3. The thickness of the PEDOT electrodes is 10 μm-50 μm, and the spacing between the PEDOT electrodes is 200 μm-300 μm. In this application, the thickness and spacing of the PEDOT electrodes, as well as the thickness of the hydrogen-sensitive membrane, synergistically affect the sensing performance of the hydrogen sensor.

[0029] like Figure 2 As shown, the hydrogen sensor in Example 1 is connected to the test platform. The device is heated by a ceramic heating element. The gas flow rate and target gas concentration are controlled by a gas mass flow meter. A DC constant voltage is applied across the device. The current signal is collected by an electrometer. The test results show that at 180°C, in an atmosphere with a hydrogen concentration of 200 ppb, the response time is 0.1 s and the recovery time is 0.3 s.

[0030] Microscopic morphology analysis was performed on the hydrogen-sensitive membrane in Example 1, such as... Figure 3-4 As shown in the SEM image, the diameter of the zinc oxide nanowires is mainly distributed in the range of 50-180 nm, and the bright spots on them are modified palladium metal particles. The TEM image shows that the diameter of the zinc oxide nanowires is 70 nm, and the small black dots on them are modified palladium metal particles with a diameter of about 10 nm, which are uniformly distributed on the nanowires.

[0031] Example 2:

[0032] The only difference between Example 2 and Example 1 is that the noble metal particles in the hydrogen-sensitive membrane are platinum. Under the same conditions, the response time was 0.5 s and the recovery time was 2 s in an atmosphere with a hydrogen concentration of 200 ppb.

[0033] Example 3:

[0034] The only difference between Example 3 and Example 1 is that the thickness of the hydrogen-sensitive membrane is 400μm-500μm. At 180°C and in an atmosphere with a hydrogen concentration of 200ppb, the response time is 0.4s and the recovery time is 1.6s.

[0035] Example 4:

[0036] The only difference between Example 4 and Example 1 is that the thickness of the PEDOT electrode is 50μm-100μm. At 180°C and in an atmosphere with a hydrogen concentration of 200ppb, the response time is 0.3s and the recovery time is 1.4s.

[0037] Example 5:

[0038] The only difference between Example 5 and Example 1 is that the noble metal particles are palladium, and the diameter of the noble metal particles is 15nm-20nm. The semiconductor metal oxide nanostructure is zinc oxide nanowire, and the mass ratio of palladium to zinc oxide is 0.05%. At 180°C, in an atmosphere with a hydrogen concentration of 200ppb, the response time is 0.6s, and the recovery time is 1.9s.

[0039] Comparative Example 1:

[0040] The only difference between Comparative Example 1 and Example 1 is that the hydrogen-sensitive membrane has a thickness of 600 μm, and at a test temperature of 180°C, in an atmosphere with a hydrogen concentration of 200 ppb, the response time is 2.1 s and the recovery time is 6.3 s.

[0041] Comparative Example 2:

[0042] The only difference between Example 2 and Example 1 is that the diameter of the palladium metal particles is 30-40 nm, and the mass ratio of palladium to zinc oxide in the hydrogen-sensitive membrane is 0.15%. At a test temperature of 180°C and in an atmosphere with a hydrogen concentration of 200 ppb, the response time is 2.6 s and the recovery time is 8.3 s.

[0043] Comparative Example 3:

[0044] The only difference between Comparative Example 3 and Comparative Example 1 is that the thickness of the PEDOT electrode is 400 nm. At a test temperature of 180°C, the device failed to work properly and did not conduct.

[0045] Comparative Example 4:

[0046] The only difference between Comparative Example 4 and Comparative Example 3 is that the spacing between the PEDOT electrodes is 50 μm, and the device cannot function properly.

[0047] Comparative Example 5:

[0048] The only difference between Comparative Example 5 and Example 1 is that the noble metal particles in the hydrogen-sensitive membrane are gold. Under an atmosphere with a hydrogen concentration of 200 ppb, the response time is 13 s and the recovery time is 42 s. This shows that gold has a poor catalytic effect on the modification of the hydrogen-sensitive membrane.

[0049] Example 6:

[0050] A method for fabricating a hydrogen sensor based on a nanostructure includes the following steps:

[0051] 1) First, add 2g of zinc oxide powder and 0.3g of graphite powder to a mortar, then add an appropriate amount of anhydrous ethanol to form a paste. Wet grind for one hour to ensure thorough mixing. Dry the mixture in an 80℃ forced-air oven until the sample turns grayish-black. Pour the dried powder into a ceramic boat and place it in the central constant-temperature zone of a tube furnace. Simultaneously, introduce 240sccm of argon and 27sccm of oxygen, maintaining atmospheric pressure. Pre-ventilate for 20 minutes to remove air from the tube furnace. Then, raise the furnace temperature to 1220℃ at a rate of 30℃ / min and hold for 40 minutes. After holding, allow the furnace to cool naturally to room temperature, then remove the white zinc oxide nanowires adhering to the furnace wall.

[0052] 2) Modification of semiconductor metal oxide nanostructures: 0.68 mM Pd was prepared using palladium acetate. 2+ Take 2 mL of the solution and place it in a 10 mL centrifuge tube. Take 0.03 g of the prepared zinc oxide nanowires for later use. Place the zinc oxide nanowires into Pd under dark conditions. 2+ The solution was irradiated with ultraviolet light at an intensity of 170 μw / cm² and a wavelength of 360 nm for 120 s. The zinc oxide nanowires were then removed and washed sequentially with acetone, anhydrous ethanol, and deionized water for 15 min each, before being dried in an oven at 80 °C.

[0053] 3) Preparation of conductive polymer (PEDOT) electrodes: Quartz sheets cut to 1.6cm × 1.6cm were sequentially cleaned with acetone, anhydrous ethanol, and deionized water for 15 minutes each, then dried in an 80℃ oven. Electrode masks were fixed onto the quartz sheets using Kapton tape. The electrode width was 1-10mm. PEDOT solution was repeatedly applied to achieve a suitable thickness, and then dried at room temperature.

[0054] 4) Coating the noble metal-modified semiconductor metal oxide nanostructure onto an insulating substrate with electrodes: The noble metal-modified semiconductor metal oxide nanostructure was ultrasonically dispersed in anhydrous ethanol at a ratio of 0.1 g of material per 10 mL of anhydrous ethanol. The dispersed nanostructure material was then transferred between the PEDOT electrodes by drop-coating or spray-coating, and then placed on a 60°C heating plate to allow the anhydrous ethanol to evaporate, ensuring device conductivity.

[0055] 5) Lead copper wires from the two PEDOT electrodes and connect the copper wires to the electrodes using high-temperature conductive adhesive. Finally, place the device in a 60℃ oven to dry and age for 6 hours to obtain the hydrogen sensor described in this application.

Claims

1. A hydrogen sensor based on a nanostructure, characterized in that, The hydrogen sensor is a hydrogen sensor with a detection concentration lower limit of 10 ppb. The hydrogen sensor includes a substrate and a PNP-type three-segment structure on the substrate. The PNP-type three-segment structure includes a hydrogen-sensitive membrane and conductive polymer (PEDOT) electrodes on both sides of the hydrogen-sensitive membrane. The hydrogen-sensitive membrane is a semiconductor metal oxide nanostructure modified with noble metal particles. The diameter of the semiconductor metal oxide nanostructure is 50 nm-180 nm, and the thickness of the hydrogen-sensitive membrane is 1 μm-500 μm. The mass fraction of noble metal in the hydrogen-sensitive membrane is between 0.01% and 0.1%.

2. The hydrogen sensor according to claim 1, characterized in that, The noble metal particles in the hydrogen-sensitive membrane are palladium or platinum, and the diameter of the noble metal particles is 5nm-20nm.

3. The hydrogen sensor according to claim 2, characterized in that, The semiconductor metal oxide nanostructure is a nanostructure of zinc oxide, tin oxide, or a mixture of both.

4. The hydrogen sensor according to claim 3, characterized in that, The semiconductor metal oxide nanostructures are nanowires, nanoparticles, nanoflowers, nanotubes, or nanorods.

5. The hydrogen sensor according to claim 4, characterized in that, The thickness of the PEDOT electrode is 500nm-100μm.

6. A method for fabricating a hydrogen sensor based on a nanostructure as described in any one of claims 1 to 5, characterized in that, Specifically, the steps include the following: 1) Preparation of semiconductor metal oxide nanostructures: Semiconductor metal oxide and carbon powder are uniformly mixed and then chemically vapor-deposited to obtain semiconductor metal oxide nanostructures, wherein the mass ratio of semiconductor metal oxide to carbon powder is 2:0.2-0.5; 2) Modification of semiconductor metal oxide nanostructures: Noble metal particles are loaded onto the semiconductor metal oxide nanostructures using an ultraviolet reduction method; 3) Fabrication of conductive polymer (PEDOT) electrodes; 4) The precious metal-modified semiconductor metal oxide nanostructure is coated onto an insulating substrate with electrodes; 5) Lead out the electrodes with copper wires to obtain the hydrogen sensor according to any one of claims 1 to 5.

7. The preparation method according to claim 6, characterized in that, The specific operation of step 1) is as follows: zinc oxide and carbon powder are mixed into a powder in an appropriate ratio and then anhydrous ethanol is added for grinding. The mass ratio of anhydrous ethanol to the mixed powder is 5:1-10:

1. After grinding evenly, the powder is dried to obtain a gray-black sample. The gray sample is placed in a tube furnace for heating, heat preservation, and cooling to finally obtain a white semiconductor metal oxide nanostructure attached to the furnace wall.

8. The preparation method according to claim 7, characterized in that, The specific operation of step 2) includes: first, preparing a noble metal ion solution with a concentration of 0.6-0.7 mmol / L; placing the semiconductor metal oxide nanostructure obtained in step 1) into the noble metal ion solution in a dark environment; irradiating it with ultraviolet light with an intensity of 150-180 μw / cm2 and a wavelength of 254-360 nm for 110-130 s; then taking out the semiconductor metal oxide nanostructure and washing it sequentially with acetone, anhydrous ethanol and deionized water for 10-20 min; and drying it at 80-100℃ to obtain the noble metal modified semiconductor metal oxide nanostructure.

9. The preparation method according to claim 8, characterized in that, In step 1), the gray sample is first placed in a ceramic boat and then placed in the central constant temperature zone of a tube furnace. Argon and oxygen are simultaneously introduced into the tube furnace, with an argon to oxygen flow rate ratio of 240:25-30 sccm and a system pressure of atmospheric pressure. The furnace is pre-ventilated for 20-30 minutes to remove air from the tube furnace. Then, the furnace temperature is raised to 1210-1230℃ at a heating rate of 25-35℃ / min and held for 40-60 minutes. After the holding period, the sample is allowed to cool naturally to room temperature, resulting in a white semiconductor metal oxide nanostructure attached to the furnace wall.

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