Cobaltosic oxide / stannic oxide-based hydrogen sensor as well as preparation method and application thereof

Abstract

The invention discloses a cobaltosic oxide / stannic oxide-based hydrogen sensor as well as a preparation method and application thereof, relates to the technical field of gas sensors, and solves the problems of high detection lower limit and low sensitivity of a traditional hydrogen sensor. The preparation method of the hydrogen sensor provided by the invention comprises the following steps: preparing an Al2O3 ceramic substrate of which the surface is modified with a cobaltosic oxide / stannic oxide heterojunction nanorod by adopting an aerosol-assisted chemical vapor deposition method, and welding and packaging the Al2O3 ceramic substrate according to a general indirectly-heated gas sensitive element, the cobaltosic oxide / stannic oxide heterojunction hydrogen sensor is prepared. The cobaltosic oxide and stannic oxide synergistically act to form a heterojunction structure, electron migration is promoted, the charge separation efficiency is improved, the detection lower limit of the sensor is remarkably reduced, the response sensitivity and stability of the sensor are enhanced, and the sensor can be applied to chemical production operation and environmental gas detection.

Description

Technical Field

[0001] The present invention relates to the field of gas sensors, and particularly to a cobalt tetroxide / tin dioxide-based hydrogen sensor, a preparation method thereof, and an application thereof. Background Art

[0002] As a clean energy source with high energy density and zero carbon emissions, hydrogen has attracted much attention in the field of new energy vehicles. However, the high diffusion coefficient of hydrogen (0.61 cm 2 / s, about 6 times that of air) and the wide explosion limit range (4%-75%) make it extremely easy to leak and cause explosion accidents during storage, transportation, and use. Research shows that even in the initial stage of leakage, when the hydrogen concentration is only at the ppm or sub-ppm level, potential explosion risks may still be triggered. Therefore, developing a hydrogen sensor with a low detection limit and high sensitivity has important practical significance for realizing the safety management of hydrogen fuel and vehicle safety monitoring.

[0003] Tin dioxide has become an ideal sensitive material for hydrogen detection due to its excellent conductivity, high stability, and low cost. However, the use of pure tin dioxide in the sensing field is limited by its low sensitivity and limited ability to detect low-concentration gases. Metal-organic frameworks (MOFs), as a new type of crystalline porous material, are composed of metal ions and organic ligands, which are interconnected through self-assembly to form a porous structure with diverse network topologies. This unique structure endows MOF-derived metal oxides with rich pores, excellent crystallinity, and large specific surface area, thus effectively improving their gas adsorption and diffusion properties. In recent years, combining MOF-derived metal oxides with traditional metal oxides to form heterostructures has become a strategy with great potential for improving the performance of gas sensors. Currently, the methods for combining MOF-derived metal oxides with traditional metal oxides mainly include hydrothermal method, impregnation method, and solvothermal method, etc. However, the nanomaterials prepared by these methods usually exist in powder form and are difficult to form a uniform thin film, resulting in an increase in the complexity of experimental operations. Therefore, developing a new strategy for efficiently combining MOF-derived metal oxides with metal oxides is of great significance for the safety of hydrogen detection. Summary of the Invention

[0004] In order to solve the problems of high detection limit and low sensitivity of traditional hydrogen sensors, the present invention proposes a cobalt tetroxide / tin dioxide-based hydrogen sensor, a preparation method thereof, and an application thereof. The technical solution of the present invention is as follows:

[0005] A preparation method of a cobalt tetroxide / tin dioxide-based hydrogen sensor, comprising the following preparation steps:

[0006] S1: Add oxalic acid to the aqueous solution of stannic chloride pentahydrate and stir to obtain a precursor solution; place the Al2O3 ceramic substrate with interdigital electrodes in a tubular furnace, transfer the precursor solution to an ultrasonic humidifier to atomize it into an aerosol, use nitrogen as the carrier gas, and transport the aerosol to the central temperature zone of the tubular furnace for reaction; after the reaction, perform annealing to prepare an Al2O3 ceramic substrate with SnO2 nanorods modified on the surface;

[0007] S2: Place the Al2O3 ceramic substrate prepared in S1 into a tubular furnace, respectively place the cobalt nitrate hexahydrate methanol solution and 2-methylimidazole methanol solution in an ultrasonic humidifier to atomize them into aerosols, use air as the carrier gas, transfer the aerosols to the central temperature zone of the tubular furnace for reaction, and perform annealing after the reaction to prepare an Al2O3 ceramic substrate with cobalt cobalt oxide / tin dioxide heterojunction nanorods modified on the surface;

[0008] S3: Weld and package the Al2O3 ceramic substrate according to a general indirectly heated gas sensor to prepare a cobalt cobalt oxide / tin dioxide heterojunction hydrogen sensor;

[0009] Furthermore, the mass ratio of stannic chloride pentahydrate to oxalic acid is 97:1; the mass ratio of cobalt nitrate hexahydrate to 2-methylimidazole methanol solution is 29:66;

[0010] Furthermore, the stirring time in S1 is 5 min;

[0011] Furthermore, the resonance frequency of the ultrasonic humidifier is 1700 MHz;

[0012] Furthermore, the reaction temperature in S1 is 500 °C and the reaction time is 30 min;

[0013] Furthermore, the annealing in S1 is annealing at 500 °C for 2 h;

[0014] Furthermore, the reaction temperature in S2 is room temperature and the reaction time is 30 - 50 min;

[0015] Furthermore, the annealing in S2 is annealing at 350 °C for 1 h.

[0016] A cobalt cobalt oxide / tin dioxide-based hydrogen sensor is prepared by the above method.

[0017] An application of the above cobalt cobalt oxide / tin dioxide-based hydrogen sensor, which is applied to chemical production operations and environmental gas detection.

[0018] Compared with the prior art, the present invention solves the problems of high detection limit and low sensitivity of traditional hydrogen sensors. The specific beneficial effects are as follows:

[0019] 1. Low detection limit: The cobalt tetroxide / tin dioxide heterojunction sensitive material is prepared by the aerosol-assisted chemical vapor deposition method in the present invention. By adjusting the time of vapor deposition, cobalt tetroxide / tin dioxide heterojunction sensitive materials with different cobalt contents are obtained. The heterojunction structure inside the sensitive material can promote electron migration and improve the charge separation efficiency, enabling the cobalt tetroxide / tin dioxide-based hydrogen sensor to still produce obvious changes in electrical signals in a hydrogen environment with a concentration of 200 ppb, significantly reducing the detection limit of the sensor and effectively improving the detection performance of the sensor.

[0020] 2. High sensitivity: In the present invention, MOF-derived cobalt tetroxide is used to modify tin dioxide to construct a composite gas-sensitive material. Oxygen molecules can be adsorbed on the surface of tin dioxide, and these oxygen molecules capture electrons to form adsorbed oxygen species (O2 - 、O - 、O 2- ), resulting in a decrease in electron concentration and an increase in resistance; when hydrogen enters the sensor, it undergoes a redox reaction with the surface-adsorbed oxygen to generate water and release electrons back to tin dioxide, increasing the electron concentration in its conduction band, thereby reducing the resistance and generating a detectable signal; at the same time, the large specific surface area and porous structure characteristics of cobalt tetroxide provide rich active sites for the sensitive material, making it easier for hydrogen molecules to come into contact with and interact with the surface of the sensitive material, thus enhancing the response sensitivity of the sensor; in addition, the synergistic effect of cobalt tetroxide and tin dioxide forms a heterojunction structure, increasing the background resistance. When electrons are released during the hydrogen reaction, the depletion layer of the heterojunction becomes narrower, enhancing the resistance change and further improving the sensitivity, conductivity, and chemical stability of the sensor.

[0021] 3. Simple and efficient preparation process: In the present invention, the cobalt tetroxide / tin dioxide sensitive material is synthesized in situ in two steps, and it can be stably operated under vacuum, low pressure, or atmospheric environment. The sensitive material film layer is uniform and has high crystallinity, and the gas-sensitive performance is stable; the preparation process is simple and efficient, reducing the complexity and cost of operation, and enabling large-scale industrial application. Description of the Drawings

[0022] Figure 1 are the top view and bottom view of the structure of the cobalt tetroxide / tin dioxide semiconductor hydrogen sensor;

[0023] Figure 2 is the cyclic response curve of the hydrogen sensor at 310 °C and a hydrogen concentration of 10 ppm;

[0024] Figure 3 is the standard working curve of the sensitivity response of the hydrogen sensor at 310 °C and different hydrogen concentrations. Detailed Embodiments

[0025] To make the technical solution of the present invention clearer, the following will clearly and completely describe the technical solution in the embodiments of the present invention in conjunction with the accompanying drawings of the present invention. It should be noted that the following embodiments are only used to better understand the technical solution of the present invention and should not be construed as a limitation of the present invention.

[0026] Example 1.

[0027] S1: Add 36 mg of oxalic acid to 20 mL of an aqueous solution of stannous chloride pentahydrate at 175 g / L and stir to obtain a precursor solution; place the Al2O3 ceramic substrate with interdigital electrodes in a tubular furnace, transfer the precursor solution to an ultrasonic humidifier (resonant frequency 1700 MHz) to atomize it into an aerosol, and use nitrogen carrier gas at 500 sccm to transport the aerosol to the central temperature zone of the tubular furnace and react at 500 °C for 30 min; after the reaction, anneal the Al2O3 ceramic substrate at 500 °C for 2 h to prepare an Al2O3 ceramic substrate with SnO2 nanorods surface-modified.

[0028] S2: Place the Al2O3 ceramic substrate prepared in S1 in a tubular furnace, transfer 20 mL of a cobalt nitrate hexahydrate methanol solution at 14.5 g / L and 20 mL of a 2-methylimidazole methanol solution at 33 g / L into two separate flasks respectively, place them in an ultrasonic humidifier (resonant frequency 1700 MHz) to atomize them into an aerosol, use air at a flow rate of 500 sccm as the carrier gas, transport the aerosol to the central temperature zone of the tubular furnace, react at room temperature for 30 min, and after the reaction, anneal the Al2O3 ceramic substrate at 350 °C for 1 h to prepare an Al2O3 ceramic substrate with cobalt tetroxide / tin dioxide heterojunction nanorods surface-modified.

[0029] S3: Weld and package the Al2O3 ceramic substrate according to a general indirectly heated gas sensor to prepare a cobalt tetroxide / tin dioxide-based hydrogen sensor.

[0030] As Figure 1 is a schematic diagram of the internal structure of a cobalt tetroxide / tin dioxide semiconductor hydrogen sensor. The left figure is a top view and the right figure is a bottom view. The sensor consists of an Al2O3 ceramic substrate, interdigital electrodes, a sensitive material covering between the interdigital electrodes, a heater, and a Pt wire for measurement. The working principle of the cobalt tetroxide / tin dioxide semiconductor hydrogen sensor is: using MOF-derived cobalt tetroxide to modify tin dioxide to construct a composite gas-sensitive material. Tin dioxide is an n-type semiconductor, and its surface adsorbs oxygen molecules in the air. These oxygen molecules capture electrons to form adsorbed oxygen species (O2 - 、O - 、O 2-) This results in a decrease in electron concentration and an increase in resistance. When hydrogen enters the sensor, it undergoes a redox reaction with the surface-adsorbed oxygen, generating water and releasing electrons back to tin dioxide, increasing the electron concentration in its conduction band, thereby reducing the resistance and producing a detectable signal. As for cobalt tetroxide, as a p-type semiconductor, it forms a p-n heterojunction with SnO, increasing the background resistance. When electrons are released during the hydrogen reaction, the depletion layer of the p-n heterojunction becomes narrower, further enhancing the resistance change and improving the sensor sensitivity.

[0031] Example 2.

[0032] The difference between this example and Example 1 is that the reaction time in S2 is 40 min, and the remaining preparation steps and conditions are the same as those in Example 1. A cobalt tetroxide / tin dioxide-based hydrogen sensor is prepared.

[0033] Example 3.

[0034] The difference between this example and Example 1 is that the reaction time in S2 is 50 min, and the remaining preparation steps and conditions are the same as those in Example 1. A cobalt tetroxide / tin dioxide-based hydrogen sensor is prepared.

[0035] Comparative Example 1.

[0036] S1: 36 mg of oxalic acid was added to 20 mL of a 175 g / L aqueous solution of tin tetrachloride pentahydrate and stirred to obtain a precursor solution; an Al2O3 ceramic substrate with interdigital electrodes was placed in a tube furnace, and the precursor solution was transferred to an ultrasonic humidifier (resonant frequency 1700 MHz) to be atomized into an aerosol. With a nitrogen carrier gas of 500 sccm, the aerosol was transported to the central temperature zone of the tube furnace and reacted at 500 °C for 30 min; after the reaction, the Al2O3 ceramic substrate was annealed at 500 °C for 2 h to prepare an Al2O3 ceramic substrate with SnO2 nanorods modified on its surface; the Al2O3 ceramic substrate was welded and encapsulated according to a general indirectly heated gas sensor element to obtain a tin dioxide nanorod hydrogen sensor.

[0037] Sensitivity test:

[0038] The cobalt tetroxide / tin dioxide-based hydrogen sensor was placed in a gas chamber, and the resistance value R of the sensor in air was measured a , and a micro syringe was used to inject hydrogen with concentrations of 200 ppb - 1000 ppm into the gas chamber, and the resistance values R of the sensor in hydrogen with different concentrations were measured g , according to the definition formula of sensitivity S = R a / R g , and the sensitivities of the sensor at different concentrations were obtained by calculation.

[0039] As Figure 2Cyclic response curves of the cobalt ferrite / tin dioxide-based hydrogen sensors prepared in Examples 1-3 and the tin dioxide nanorod hydrogen sensor prepared in Comparative Example 1 at 310 °C and a hydrogen concentration of 10 ppm. As can be seen from the figure, the cobalt ferrite / tin dioxide-based hydrogen sensors exhibit good consistency and stability within five cycles.

[0040] As Figure 3 is the standard working curve of the sensitivity response of the hydrogen sensor at 310 °C and different hydrogen concentrations. As can be seen from the figure, the gas-sensing performance of the sensor can be effectively adjusted by adjusting the time of aerosol-assisted chemical vapor deposition. When the time of chemical vapor deposition is 40 min, a hydrogen concentration of 200 ppb can be clearly detected. It is proved that by adjusting the deposition time of MOF-derived cobalt ferrite during the chemical vapor deposition process, cobalt ferrite / tin dioxide heterojunction sensitive materials with different cobalt contents can be obtained. The MOF-derived materials have a large specific surface area and a highly ordered porous structure. This characteristic provides rich active sites for the sensitive materials, making it easier for hydrogen molecules to come into contact with and interact with the surface of the sensitive materials, thereby enhancing the response sensitivity of the sensor. In addition, there is a heterojunction structure inside the cobalt ferrite / tin dioxide heterojunction material, and the energy level difference at the material interface can promote electron migration and improve the charge separation efficiency, enabling the sensor to still produce obvious changes in electrical signals in a low-concentration hydrogen environment, thereby significantly reducing the detection limit of the sensor.

[0041] The present invention uses the aerosol-assisted chemical vapor deposition method to prepare the cobalt ferrite / tin dioxide heterojunction sensitive material, which significantly reduces the detection limit of the sensor and effectively improves the sensitivity and long-term reliability of the sensor; at the same time, the preparation process of the present invention is simple and efficient, reducing the complexity and cost of operation, and enabling large-scale industrial application.

[0042] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0043] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of a cobalt tetroxide / tin dioxide-based hydrogen sensor, characterized in that, It includes the following preparation steps: S1: Add oxalic acid to the aqueous solution of stannic chloride pentahydrate and stir to obtain a precursor solution; place the Al2O3 ceramic substrate with interdigital electrodes in a tubular furnace, transfer the precursor solution to an ultrasonic humidifier to atomize it into an aerosol, use nitrogen as the carrier gas, and transport the aerosol to the central temperature zone of the tubular furnace for reaction; after the reaction, perform annealing to prepare an Al2O3 ceramic substrate with SnO2 nanorods modified on the surface; S2: Place the Al2O3 ceramic substrate prepared in S1 into a tubular furnace, respectively atomize the cobalt nitrate hexahydrate methanol solution and the 2-methylimidazole methanol solution into aerosols in an ultrasonic humidifier, use air as the carrier gas, transfer the aerosol to the central temperature zone of the tubular furnace for reaction, and perform annealing after the reaction to prepare an Al2O3 ceramic substrate with cobalt oxide spinel / tin dioxide heterojunction nanorods modified on the surface; S3: Weld and package the Al2O3 ceramic substrate prepared in S2 according to a general indirectly heated gas sensor to prepare a cobalt oxide spinel / tin dioxide heterojunction hydrogen sensor.

2. The preparation method of the cobalt tetroxide / tin dioxide-based hydrogen sensor according to claim 1, characterized in that, The mass ratio of the stannic chloride pentahydrate to the oxalic acid is 97:1; the mass ratio of the cobalt nitrate hexahydrate to the 2-methylimidazole methanol solution is 29:

66.

3. The preparation method of the cobalt tetroxide / tin dioxide-based hydrogen sensor according to claim 1, characterized in that, The stirring time in S1 is 5 min.

4. The preparation method of the cobalt ferrite / tin dioxide-based hydrogen sensor according to claim 1, wherein, The resonant frequency of the ultrasonic humidifier is 1700 MHz.

5. The preparation method of the cobalt tetroxide / tin dioxide-based hydrogen sensor according to claim 1, characterized in that The reaction temperature in S1 is 500 °C and the reaction time is 30 min.

6. The preparation method of the cobalt tetroxide / tin dioxide-based hydrogen sensor according to claim 1, characterized in that, The annealing in S1 is annealing at 500 °C for 2 h.

7. The preparation method of the cobalt tetroxide / tin dioxide-based hydrogen sensor according to claim 1, wherein, The reaction temperature in S2 is room temperature and the reaction time is 30 - 50 min.

8. The preparation method of the cobalt ferrite / tin dioxide-based hydrogen sensor according to claim 1, characterized in that, The annealing in S2 is annealing at 350 °C for 1 h.

9. A cobalt tetroxide / tin dioxide-based hydrogen sensor, characterized in that, Prepared by the method according to any one of claims 1 - 8.

10. Use of the cobalt tetroxide / tin dioxide-based hydrogen sensor as described in claim 9, characterized in that, Applied to chemical production operations or environmental gas detection.

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