A method for preparing a hydrogen sensor and a sensitive element thereof for leak detection

Abstract

The present invention relates to a hydrogen sensor for leak detection and a preparation method of its sensitive element. The hydrogen sensor includes an air chamber with an air inlet and a measuring probe at one end and an air outlet and a heating probe at the other end, wherein a sensitive element is arranged in the air chamber, and the sensitive element includes a substrate and a measuring electrode and a heating electrode arranged on the front and back sides thereof, wherein the measuring electrode is connected to the measuring probe, the heating electrode is connected to the heating probe, and a shielding layer is covered on the heating electrode, and the measuring probe and the heating probe are also electrically connected to a signal circuit located outside the air chamber, respectively. The preparation method of the sensitive element is as follows: a multi-walled carbon nanotube loaded palladium-gold core-shell particle powder is plated on the front side of the substrate by a vacuum coating method, and a measuring electrode is formed after nanolithography; platinum powder is vacuum sputtered on the back side of the substrate, and a heating electrode is formed after nanolithography; a pulsed laser deposition method is used to form a silicon nitride film as a shielding layer covering the heating electrode. The hydrogen measurement sensitivity of the present invention is high, reaching the ppb level.

Description

Technical Field

[0001] The invention relates to a hydrogen sensor, and in particular to a hydrogen sensor for leak detection and a preparation method of a sensitive element thereof. Background Art

[0002] In the process of automated production, industrial leak detection has become an indispensable practical technology to ensure the sealing of components and systems, and can be widely used in aerospace, electronics, electric power, industrial refrigeration and other fields.

[0003] Traditional industrial leak detection methods include differential pressure method, water detection method, ultrasonic method and tracer gas method. The differential pressure method has a low detection rate and needs to be left for a certain period of time. Its detection sensitivity is comparable to that of the water detection method, and it can only detect 10 -1 Pa·m 3 / s. Ultrasonic method can detect 10 -2 Pa·m 3 The tracer gas method is the most sensitive method in the current industrial leak detection method and can detect leaks below 10 -5 Pa·m 3 / s leak rate. The tracer gases used in the tracer gas method include radioactive gases, halogen gases, helium and hydrogen. Among them, the helium leak detection method is the most sensitive leak detection method, but the cost of helium leak detection is relatively high. Helium is a rare resource in my country and has long been subject to import restrictions. In addition, the helium mass spectrometer leak detector needs to be implemented in conjunction with a vacuum system, which limits the application of high-precision leak detection technology in industrial leak detection.

[0004] Hydrogen leak detection is an emerging gas leak detection technology with a more reasonable gas detection cost. However, hydrogen detection cannot achieve the same sensitivity as helium detection, which makes hydrogen leak detection insignificant in micro-leakage and precision device applications. Therefore, in order to use low-cost hydrogen leak detection to replace the more expensive helium leak detection method, it is necessary to develop a high-sensitivity hydrogen sensor that reaches the ppb level. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a hydrogen sensor for leak detection and a method for preparing a sensitive element thereof. The sensitivity of the hydrogen sensor of the present invention reaches ppb level and can detect leaks below 10 -8 Pa·m 3 The leak rate of / s is consistent with the detection sensitivity of the helium mass spectrometer leak detector. It is suitable for industrial leak detection and can be used for micro-leakage and precision device detection.

[0006] The above technical problems of the present invention are mainly solved by the following technical solutions: A hydrogen sensor for leak detection of the present invention comprises an air chamber, an air inlet and two measuring probes are arranged on the top of the air chamber, an air outlet and two heating probes are arranged on the bottom of the air chamber, a sensitive element is arranged in the air chamber between the air inlet and the air outlet, the sensitive element comprises a substrate and a measuring electrode arranged on the front of the substrate, a heating electrode arranged on the back of the substrate, the two ends of the measuring electrode are respectively connected to the two measuring probes, the two ends of the heating electrode are respectively connected to the two heating probes, the heating electrode is covered with a shielding layer, and the measuring probe and the heating probe are also respectively electrically connected to the signal circuit located outside the air chamber. During operation, the gas to be measured flows into the air chamber from the air inlet, and after fully contacting the measuring electrode on the front of the substrate, it flows through the substrate and then flows out of the air chamber from the air outlet. The signal circuit outputs a fixed voltage to the heating electrode so that the sensitive element reaches the required operating temperature. At the same time, the signal circuit collects the signal of the measuring electrode through the measuring probe. After the measuring electrode comes into contact with the hydrogen in the gas, its electrical properties will change. The signal output by the measuring electrode represents the concentration of hydrogen in the gas. After being processed by the signal circuit, it is transmitted to the main control module of the hydrogen analyzer, thereby completing the leak detection of the equipment or components.

[0007] Preferably, the substrate is a silicon oxide substrate, and the measuring electrode is a hydrogen-sensitive film formed by coating a multi-walled carbon nanotube-loaded palladium-gold core-shell particle powder. The multi-walled carbon nanotube-loaded palladium-gold core-shell particle powder is a nanopowder. When there is hydrogen in the gas to be measured, the gas to be measured enters the gas chamber and fully contacts the measuring electrode. After the measuring electrode absorbs hydrogen, a palladium-hydrogen bond is formed, resulting in a change in the electron mobility of the measuring electrode. The change in the resistance of the measuring electrode reflects the amount of hydrogen adsorbed by the measuring electrode. Therefore, the concentration of hydrogen in the gas to be measured can be detected by detecting the resistance of the measuring electrode. The present invention forms a highly sensitive hydrogen-sensitive film by vacuum coating multi-walled carbon nanotube-loaded palladium-gold core-shell particle powder on the front side of a substrate. The gold core-palladium shell particles in the composite film have a crystal structure closest to palladium, so the hydrogen dissolution ratio is relatively high, and the hydrogen-sensitive performance of the measuring electrode is effectively improved. The skeleton structure is formed by multi-walled carbon nanotubes, and the gold core-palladium shell particles are dispersedly loaded, which reduces the occurrence of film microstructure fracture caused by particle expansion after hydrogen absorption, and at the same time increases the electron mobility, improves the hydrogen-sensitive response performance, and makes the hydrogen detection sensitivity of the sensitive element less than 5 ppb.

[0008] Preferably, the heating electrode is a platinum film formed by vacuum sputtering; and the shielding layer is a silicon nitride film formed by pulsed laser deposition. The shielding layer protects the heating electrode and prevents hydrogen from causing hydrogen embrittlement of the heating electrode and causing a change in the resistance of the heating electrode.

[0009] Preferably, the measuring electrode comprises a plurality of straight line segments arranged in parallel at equal intervals, and arc segments are staggered between the heads and tails of adjacent straight line segments, that is, the measuring electrode is arranged in a serpentine shape; the shape of the heating electrode is the same as that of the measuring electrode. The length of the measuring electrode and the heating electrode is extended as much as possible on a limited area, effectively increasing the contact area between the measuring electrode and the gas, further improving the hydrogen sensitivity of the measuring electrode, improving the heating efficiency of the heating electrode, ensuring that the sensitive element quickly reaches the working temperature, and the temperature distribution is uniform.

[0010] Preferably, two symmetrically arranged bosses are provided on the side wall of the air chamber, and two symmetrically arranged grooves are provided on the edge of the substrate, and the two grooves are respectively fixed on the two bosses, and there is a gap between the edge of the substrate and the side wall of the air chamber, so as to ensure that the substrate is firmly installed and there is a gap between the substrate and the air chamber to allow gas to flow through.

[0011] Preferably, the signal circuit includes a constant voltage output unit and an impedance conversion unit, a filtering unit, a three-stage amplification unit, an analog-to-digital conversion unit and a serial interface connected in sequence, the input end of the impedance conversion unit is connected to the measuring probe, and the output end of the constant voltage output unit is connected to the heating probe. The signal circuit outputs a fixed voltage to the heating electrode through the constant voltage output unit, so that the sensitive element reaches an operating temperature of 300°C, and at the same time, the signal of the measuring electrode is collected through the measuring probe. The signal output by the measuring electrode is demodulated into a set of serial binary codes and output to the serial interface after passing through the impedance conversion unit, the filtering unit, the three-stage amplification unit and the analog-to-digital conversion unit in sequence. The serial interface communicates with the main control module of the hydrogen analyzer and outputs the measured hydrogen concentration signal to the main control module.

[0012] The method for preparing a sensitive element of a hydrogen gas sensor for leak detection of the present invention is as follows: preparing the measuring electrode on the front side of the substrate and preparing the heating electrode on the back side of the substrate. The method for preparing the measuring electrode comprises the following steps:

[0013] ①Prepare a mixture of gold core seeds;

[0014] ②Preparing a free palladium ion solution;

[0015] ③Preparing gold core-palladium shell colloidal solution;

[0016] ④ Preparation of multi-walled carbon nanotube loaded palladium-gold core-shell particle powder;

[0017] ⑤ Use multi-walled carbon nanotube loaded palladium-gold core-shell particle powder as a sputtering target, and use a vacuum coating method to coat the multi-walled carbon nanotube loaded palladium-gold core-shell particle powder on a substrate to form a hydrogen-sensitive film, and use nanolithography technology to photolithograph the hydrogen-sensitive film to form a measuring electrode.

[0018] Preferably, the step ① is: adding 5 ml of 0.05M chloroauric acid to 50 ml of 0.2M hexadecyltrimethylammonium chloride solution, rapidly shaking for 3 minutes, then adding to 10 ml of 0.05M sodium borohydride solution, rapidly shaking again for 3 minutes, and after the solution turns brown, standing at 30°C for 2 hours to obtain a gold seed mixture;

[0019] The step ② is as follows: 3.54 g of palladium chloride is weighed and dissolved in 100 ml of concentrated hydrochloric acid solution, and the solution is heated and stirred in an air-tight manner to form a chloropalladic acid solution; the chloropalladic acid solution is diluted to a mass concentration of 0.01%, and then added to 50 ml of a 0.2 M hexadecyltrimethylammonium chloride solution, and stirred evenly to obtain a free palladium ion solution.

[0020] Preferably, the step ③ is: after uniformly mixing the gold core seed mixed solution obtained in step ① and the free palladium ion solution obtained in step ②, slowly dripping 30 ml of ascorbic acid with a burette, stirring for 30 minutes under an ice bath at 0° C. to obtain a gold core-palladium shell mixed solution, washing the gold core-palladium shell mixed solution with deionized water, centrifuging it several times on a centrifuge, and then removing the supernatant on the centrifuge tube to obtain a gold core-palladium shell colloidal solution on the lower layer;

[0021] The step ④ is as follows: 0.5 g of multi-walled carbon nanotubes are washed once with deionized water, 100 ml of ethylene glycol is added after filtering, ultrasonic dispersion is performed for 2 hours, 50 ml of the gold core-palladium shell colloidal solution obtained in step ③ is added, the mixture is stirred evenly and put into a ball mill, and the mixture is ground for 12 hours using a ball mill, and then the solution is taken out and centrifuged for washing, the supernatant on the centrifuge tube is removed, and the solution on the lower layer of the centrifuge tube is placed in a vacuum drying oven at 120° C. and dried for 6 hours, and nitrogen is used for protection during the drying process to obtain a multi-walled carbon nanotube-loaded palladium-gold core-shell particle powder.

[0022] Preferably, the preparation method of the heating electrode is: vacuum sputtering platinum powder on the back side of the substrate to form a platinum film, and using nano-lithography technology to photolithography the platinum film to form a heating electrode; then using pulsed laser deposition method, using α-Si3N4 single crystal silicon nitride as a target material, to deposit a silicon nitride film to form a shielding layer covering the heating electrode.

[0023] The beneficial effects of the present invention are as follows: a highly sensitive hydrogen-sensitive film is formed by vacuum coating multi-walled carbon nanotube-loaded palladium-gold core-shell particle powder as a measuring electrode, the gold core-palladium shell particles in the hydrogen-sensitive film have a crystal structure closest to palladium, so the hydrogen dissolving ratio is relatively high, and the hydrogen-sensitive performance of the measuring electrode is effectively improved. The skeleton structure is formed by multi-walled carbon nanotubes, and the gold core-palladium shell particles are dispersedly loaded, which reduces the occurrence of film microstructure fracture caused by particle expansion after hydrogen absorption, and increases the electron mobility, improves the hydrogen-sensitive response performance, and makes the detection sensitivity of the hydrogen-sensitive film less than 5ppb. The present invention prepares a measuring electrode and a heating electrode on the front and back sides of a substrate respectively, and uses a silicon nitride film as a shielding layer covering the heating electrode to prepare an integrated hydrogen-sensitive element, adopts an integrated signal circuit, reduces the volume of the hydrogen sensor, and achieves miniaturization, which is suitable for industrial leak detection, and is particularly suitable for leak detection of micro-leakage and precision devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the main structure of the hydrogen sensor used for leak detection of the present invention.

[0025] Figure 2 It is a main structural schematic diagram of the sensitive element in the present invention.

[0026] Figure 3 It is a schematic diagram of a top view structure of the sensitive element in the present invention.

[0027] In the figure, 1. shell, 2. air chamber, 3. air inlet pipe, 4. air inlet, 5. air outlet pipe, 6. air outlet, 7. measuring probe, 8. heating probe, 9. signal circuit, 10. sensitive element, 11. substrate, 12. measuring electrode, 13. heating electrode, 14. groove, 15. boss, 16. shielding layer, 17. lead area. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0029] Embodiment: A hydrogen sensor for leak detection in this embodiment, such as Figure 1As shown, it includes a cylindrical shell 1, which encloses an air chamber 2, the diameter of the air chamber is less than 20mm, and the height of the air chamber is less than 10mm. The shell is made of stainless steel, with low adsorption rate and high temperature resistance. An air inlet pipe 3 connected to the air chamber is installed at the center of the top of the shell to form an air inlet 4, and two measuring probes 7 are also installed on the top of the shell, and the two measuring probes are located on both sides of the air inlet pipe. An air outlet pipe 5 connected to the air chamber is installed at the center of the bottom of the shell to form an air outlet 6, and two heating probes 8 are also installed at the bottom of the shell, and the two heating probes are located on both sides of the air outlet pipe. The measuring probe and the heating probe are respectively connected to the signal circuit 9 located outside the shell through wires. The signal circuit includes a constant voltage output unit, an impedance conversion unit, a filtering unit, a three-stage amplification unit, an analog-to-digital conversion unit and a serial interface. The measuring probe is connected to the input end of the impedance conversion unit, and the impedance conversion unit is connected to the filtering unit, the three-stage amplification unit, the analog-to-digital conversion unit and the serial interface in sequence. The output end of the constant voltage output unit is connected to the heating probe.

[0030] There is a sensitive element 10 in the middle of the air chamber, which is parallel to the top and bottom of the shell. The sensitive element is like a baffle between the air inlet and the air outlet, but there is a gap between the edge of the sensitive element and the inner wall of the shell for gas to flow through. Figure 2 As shown, the sensitive element includes a substrate 11, a measuring electrode 12 and a heating electrode 13. The substrate is a circular silicon oxide substrate, the diameter of which is 2 mm smaller than the diameter of the gas chamber. The edge of the substrate has two symmetrically arranged grooves 14, and the side wall of the gas chamber has two symmetrically arranged bosses 15. The two grooves are fixed on the two bosses respectively, and there is a gap between the edge of the substrate and the side wall of the gas chamber. Figure 3As shown, there is a measuring electrode 12 on the front of the substrate 11, and the measuring electrode is opposite to the air inlet. The measuring electrode is a hydrogen-sensitive film formed by coating multi-walled carbon nanotubes with palladium-gold core-shell particle powder by vacuum coating method, and then photolithography is used to form a serpentine curved arrangement, that is, the measuring electrode includes a plurality of straight line segments arranged in parallel at equal intervals, and the heads and tails of adjacent straight line segments are staggered with 180° arc segments, and the two ends of the measuring electrode have a 0.5mm×0.5mm lead area 17, which is respectively connected with leads connected to the measuring probe. In this embodiment, the thickness of the measuring electrode is 30nm, the width is 0.2mm, and the length is 65mm. There is a heating electrode 13 on the back of the substrate 11, and the heating electrode is opposite to the air outlet. The heating electrode is a platinum film formed by vacuum sputtering, and then photolithography is used to form a serpentine curved arrangement by nanolithography, that is, the heating electrode includes a plurality of straight line segments arranged in parallel at equal intervals, and the heads and tails of adjacent straight line segments are staggered with 180° arc segments. The shape of the heating electrode is the same as that of the measuring electrode, and the position of the heating electrode corresponds to that of the measuring electrode. There is a 0.5 mm × 0.5 mm lead area at both ends of the heating electrode, which is connected to the heating probe respectively. In this embodiment, the thickness of the heating electrode is 100 nm, the width is 0.2 mm, and the length is 65 mm. The heating electrode is covered with a shielding layer 16, which is a dense silicon nitride film formed by pulsed laser deposition, and the thickness of the silicon nitride film is 20 nm.

[0031] During operation, the gas to be measured flows into the gas chamber from the gas inlet, and after fully contacting the front of the substrate, it flows through the gap between the substrate and the side wall of the gas chamber, and finally flows out of the gas chamber from the gas outlet. The signal circuit outputs a fixed voltage to the heating electrode through the constant voltage output unit, so that the sensitive element reaches an operating temperature of 300°C. The gas to be measured flows into the gas chamber, and the measuring electrode adsorbs the hydrogen in the gas to be measured to form a palladium-hydrogen bond, which causes the electron mobility of the measuring electrode to change. The change in its resistance reflects the concentration of hydrogen in the gas to be measured. The signal circuit collects the resistance of the measuring electrode through the measuring probe, and after passing through the impedance conversion unit, the filtering unit, the three-stage amplification unit and the analog-to-digital conversion unit in sequence, a set of serial binary codes is demodulated and output to the serial interface. The serial interface communicates with the main control module of the hydrogen analyzer and outputs the measured hydrogen concentration signal to the main control module.

[0032] The method for preparing a sensitive element of a hydrogen sensor for leak detection in this embodiment is as follows: preparing a measuring electrode on the front side of a substrate and preparing a heating electrode on the back side of the substrate.

[0033] The method for preparing the measuring electrode comprises the following steps:

[0034] ① Preparation of gold seed mixture: add 5 ml of 0.05 M chloroauric acid to 50 ml of 0.2 M hexadecyltrimethylammonium chloride solution, shake rapidly for 3 minutes, then add to 10 ml of 0.05 M sodium borohydride solution, shake rapidly again for 3 minutes, and after the solution turns brown, stand at 30°C for 2 hours to obtain the gold seed mixture;

[0035] ②Preparing a free palladium ion solution: Weigh 3.54 g of palladium chloride and dissolve it in 100 ml of concentrated hydrochloric acid solution, isolate it from air, heat and stir to form a chloropalladic acid solution; dilute the chloropalladic acid solution to a concentration of 0.01% (ω), add it to 50 ml of a 0.2 M hexadecyltrimethylammonium chloride solution, stir evenly, and obtain a free palladium ion solution;

[0036] ③Preparing a gold core-palladium shell colloidal solution: after uniformly mixing the gold core seed mixed solution obtained in step ① and the free palladium ion solution obtained in step ②, slowly dripping 30 ml of ascorbic acid with a burette, stirring for 30 minutes under an ice bath at 0° C. to obtain a gold core-palladium shell mixed solution, washing the gold core-palladium shell mixed solution with deionized water, centrifuging it several times in a centrifuge, and then removing the supernatant in the centrifuge tube to obtain a gold core-palladium shell colloidal solution in the lower layer;

[0037] ④ Preparation of multi-walled carbon nanotube-loaded palladium-gold core-shell particle powder: 0.5 g of multi-walled carbon nanotubes was washed once with deionized water, filtered, and then 100 ml of ethylene glycol was added, ultrasonically dispersed for 2 h, and then 50 ml of the gold core-palladium shell colloidal solution obtained in step ③ was added, stirred evenly, and then put into a polytetrafluoroethylene ball mill, and ground with a ball mill for 12 hours, and then the solution was taken out for centrifugal washing, the upper clear liquid of the centrifuge tube was removed, and the lower solution of the centrifuge tube was placed in a vacuum drying oven at 120° C. for 6 h. During the drying process, 99.999% pure nitrogen was used for protection to obtain multi-walled carbon nanotube-loaded palladium-gold core-shell particle powder;

[0038] ⑤ Take a circular silicon oxide substrate as a substrate, clean it with distilled water and ethylene glycol ultrasonically for 15 minutes, and then dry it at 100°C. Use the multi-walled carbon nanotube loaded palladium-gold core-shell particle powder obtained in step ④ as a sputtering target, and use a vacuum coating method to coat the multi-walled carbon nanotube loaded palladium-gold core-shell particle powder on the substrate. The vacuum degree is less than 5×10 -5 Pa started plating, the temperature was 500℃, the sputtering power was 150W, and the sputtering rate was After the film coating is completed, it is heat treated at 300℃ for 6 hours to form a hydrogen-sensitive film with a thickness of 30nm. The hydrogen-sensitive film is then photolithographically processed using nanolithography technology to form a serpentine-shaped measuring electrode.

[0039] The preparation method of the heating electrode is as follows: the material of the heating electrode is a pure platinum film, platinum powder is vacuum sputtered on the back of the substrate to form a platinum film with a thickness of 100nm, and then the platinum film is photolithographically processed using nanolithography technology to form a serpentine-shaped heating electrode; then a pulsed laser deposition method is used, with high-purity α-Si3N4 single crystal silicon nitride as the target material, a substrate temperature of 200°C, a nitrogen pressure of 5Pa, and a pulse energy of 200mJ to deposit a silicon nitride film with a thickness of 20nm, and finally, in a nitrogen atmosphere, heat treated at 300°C for 1h to form a shielding layer covering the heating electrode.

Claims

1. A method for preparing a sensitive element of a hydrogen sensor for leak detection, the hydrogen sensor for leak detection comprising an air chamber, an air inlet and two measuring probes are arranged on the top of the air chamber, an air outlet and two heating probes are arranged on the bottom of the air chamber, a sensitive element is arranged in the air chamber between the air inlet and the air outlet, the sensitive element comprises a substrate and a measuring electrode arranged on the front side of the substrate, and a heating electrode arranged on the back side of the substrate, the two ends of the measuring electrode are respectively connected to the two measuring probes, the two ends of the heating electrode are respectively connected to the two heating probes, the heating electrode is covered with a shielding layer, and the measuring probe and the heating probe are also respectively electrically connected to a signal circuit located outside the air chamber; characterized in that The measuring electrode is prepared on the front side of the substrate, and the heating electrode is prepared on the back side of the substrate. The method for preparing the measuring electrode comprises the following steps: ①Prepare a mixture of gold core seeds; ②Preparing a free palladium ion solution; ③Preparing gold core-palladium shell colloidal solution; ④ Preparation of multi-walled carbon nanotube loaded palladium-gold core-shell particle powder; ⑤ Use multi-walled carbon nanotube loaded palladium-gold core-shell particle powder as a sputtering target, and use a vacuum coating method to coat the multi-walled carbon nanotube loaded palladium-gold core-shell particle powder on a substrate to form a hydrogen-sensitive film, and use nanolithography technology to photolithograph the hydrogen-sensitive film to form a measuring electrode.

2. The method for preparing a sensitive element of a hydrogen sensor for leak detection according to claim 1, characterized in that The step ① is as follows: 5 ml of 0.05M chloroauric acid is added to 50 ml of 0.2M hexadecyltrimethylammonium chloride solution, and the mixture is rapidly shaken for 3 minutes, and then added to 10 ml of 0.05M sodium borohydride solution, and the mixture is rapidly shaken for 3 minutes again. After the solution turns brown, the mixture is kept at a constant temperature of 30° C. for 2 hours to obtain a gold seed mixture; The step ② is as follows: 3.54 g of palladium chloride is weighed and dissolved in 100 ml of concentrated hydrochloric acid solution, and the solution is heated and stirred in an air-tight manner to form a chloropalladic acid solution; the chloropalladic acid solution is diluted to a concentration of 0.01%, and then added to 50 ml of a 0.2 M hexadecyltrimethylammonium chloride solution, and stirred evenly to obtain a free palladium ion solution.

3. A method for preparing a sensitive element of a hydrogen sensor for leak detection according to claim 1 or 2, characterized in that The step ③ is: after the gold core seed mixed solution obtained in step ① and the free palladium ion solution obtained in step ② are uniformly mixed, 30 ml of ascorbic acid is slowly added dropwise with a burette, and stirred for 30 minutes under an ice bath at 0° C. to obtain a gold core-palladium shell mixed solution, the gold core-palladium shell mixed solution is washed with deionized water, centrifuged multiple times on a centrifuge, and then the upper clear liquid of the centrifuge tube is removed to obtain a gold core-palladium shell colloidal solution in the lower layer; The step ④ is as follows: 0.5 g of multi-walled carbon nanotubes are washed once with deionized water, 100 ml of ethylene glycol is added after filtering, ultrasonic dispersion is performed for 2 hours, 50 ml of the gold core-palladium shell colloidal solution obtained in step ③ is added, the mixture is stirred evenly and put into a ball mill, and the mixture is ground for 12 hours using a ball mill, and then the solution is taken out and centrifuged for washing, the supernatant on the centrifuge tube is removed, and the solution on the lower layer of the centrifuge tube is placed in a vacuum drying oven at 120° C. and dried for 6 hours, and nitrogen is used for protection during the drying process to obtain a multi-walled carbon nanotube-loaded palladium-gold core-shell particle powder.

4. The method for preparing a sensitive element of a hydrogen sensor for leak detection according to claim 1, characterized in that The preparation method of the heating electrode is as follows: platinum powder is vacuum sputtered on the back of the substrate to form a platinum film, and the platinum film is photolithographically processed using nano-lithography technology to form a heating electrode; then a pulsed laser deposition method is used to deposit a silicon nitride film using α-Si3N4 as a target material to form a shielding layer covering the heating electrode.

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