Pt targeted modified WO3 hierarchical structure hydrogen sensitive material, preparation method and application thereof, and preparation method of hydrogen sensor

Abstract

The invention provides a Pt targeted modified WO3 hierarchical structure hydrogen sensitive material, a preparation method and application thereof, and a preparation method of a hydrogen sensor, and belongs to the field of sensors. The morphology of the nanosheet hierarchical structure grown on the WO3 microsphere substrate is regulated and controlled by changing the tungsten source concentration in secondary solvothermal, and the WO3 nanosheet / microsphere hierarchical structure with the optimal hydrogen sensing performance is obtained; pt is loaded on a WO3 hierarchical structure through illumination deposition, Pt can be modified on nanosheets and microspheres in a targeted manner, the WO3 microspheres are formed by stacking nano-particles, many gaps exist among the particles, the WO3 microspheres have rich oxygen vacancies, and Pt is more easily enriched on the WO3 microspheres to form active sites for reaction of H atoms and O2 <->; due to the large specific surface area of the WO3 nanosheet, uniform Pt can be formed, H2 can be more favorably cracked into H atoms, and then the H atoms are transmitted to the microspheres to react with adsorbed O2 <->.

Description

Technical Field

[0001] This invention relates to the field of sensors, specifically to a Pt-targeted modified WO3 hierarchical hydrogen-sensitive material, its preparation method and application, and a method for preparing a hydrogen sensor. Background Technology

[0002] Hydrogen, as a clean and efficient new energy source, shows broad application prospects in energy transition, aerospace, fuel cells, and chemical production. However, hydrogen is flammable and explosive, making the development of highly sensitive, selective, and fast-response hydrogen sensors crucial for safe production and leak detection.

[0003] Among numerous gas-sensitive sensing technologies, resistive hydrogen sensors based on metal oxide semiconductors (such as WO3, SnO2, ZnO, etc.) have attracted much attention due to their simple fabrication process, low cost, and ease of miniaturization. Tungsten trioxide (WO3), as a typical n-type semiconductor, exhibits excellent gas-sensing activity towards hydrogen and is considered one of the most promising hydrogen-sensitive materials.

[0004] However, traditional WO3-based hydrogen-sensitive materials still face many challenges: for example, the limited specific surface area of ​​bulk or ordinary nanostructured WO3 results in insufficient adsorption and surface reaction sites for gas molecules, leading to low sensitivity; the slow response and recovery kinetics of the materials make it difficult to meet the needs of rapid detection; and the typically high operating temperature brings additional power consumption and stability issues. To overcome these shortcomings, researchers have conducted extensive research: increasing the specific surface area of ​​materials by constructing hierarchical micro / nanostructures (such as microspheres formed by the self-assembly of nanosheets) to provide more channels and active sites for gas diffusion and reaction has proven to be an effective strategy for improving sensitivity; in addition, surface modification of materials by loading noble metal (such as platinum and palladium) catalysts can utilize the "catalytic spillover effect" of noble metals to significantly reduce the reaction activation energy, thereby improving sensitivity, lowering the operating temperature, and accelerating the response speed.

[0005] However, existing methods for loading precious metals (such as impregnation and sputtering) often suffer from problems such as random modification sites, uneven distribution, and easy particle agglomeration, resulting in low utilization of precious metals and failure to fully realize their catalytic efficiency. Especially in hierarchical materials, if precious metals cannot be precisely loaded onto the most critical reactive sites (such as the edges and surfaces of nanosheets), their catalytic promoting effect will be greatly reduced. Summary of the Invention

[0006] This invention provides a Pt-targeted modified WO3 hierarchical hydrogen-sensitive material, its preparation method and application, and a method for preparing a hydrogen sensor. The Pt-targeted modified WO3 hierarchical hydrogen-sensitive material prepared by this invention enables the hydrogen sensor prepared from it to have a good catalytic promoting effect.

[0007] This invention provides a method for preparing a Pt-targeted modified WO3 hierarchical hydrogen-sensitive material, comprising the following steps: A first tungsten source is mixed with a first organic solvent to carry out a first solvothermal reaction, resulting in uncrystallized WO3 powder; The uncrystallized WO3 powder was subjected to a first annealing process to obtain WO3 microspheres; the WO3 microspheres were formed by the stacking of several crystalline WO3 nanoparticles. The WO3 microspheres, the second tungsten source, and the second organic solvent are mixed and subjected to a second solvothermal reaction to generate WO3 nanosheets loaded on the surface of the WO3 microspheres, thus obtaining the matrix; the mass ratio of the second tungsten source to the volume ratio of the second organic solvent is (0.03~0.06) mol:1L. The matrix is ​​subjected to a second annealing to obtain an annealed matrix; The annealed matrix, mixed solvent, and platinum-containing precursor solution were mixed and then photodeposited to obtain the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material.

[0008] Preferably, the mass ratio of the first tungsten source to the volume ratio of the first organic solvent is 0.02~0.04 mol:1L; The first tungsten source includes tungsten hexachloride; the first organic solvent includes glacial acetic acid; The temperature of the first solvothermal reaction is 150~200℃, and the time is 8~24h.

[0009] Preferably, the temperature of the first annealing and the second annealing are independently 300~600℃, and the time is independently 1~4h.

[0010] Preferably, the mass ratio of the WO3 microspheres to the second tungsten source is 1:2~4; The second tungsten source includes tungsten hexachloride; the second organic solvent includes ethanol; The temperature of the second solvothermal reaction is 150~200℃, and the time is 8~24h.

[0011] Preferably, the ratio of the mass of the annealed matrix, the volume of the mixed solvent, and the volume of the platinum-containing precursor solution is (0.2~0.5) g : (60~100) mL : (0.3~0.9) mL; The mixed solvent comprises methanol and water; the volume ratio of methanol to water is 1:(4~5); The concentration of the platinum-containing precursor solution is 5~20 g / L; the platinum-containing precursor solution includes chloroplatinic acid solution.

[0012] Preferably, the spectral range of the light source during photodeposition is the full spectrum.

[0013] The present invention also provides a Pt-targeted modified WO3 hierarchical hydrogen-sensitive material prepared by the preparation method described above, comprising a matrix and elemental Pt loaded on the matrix; the matrix comprises WO3 microspheres and WO3 nanosheets loaded on the surface of the WO3 microspheres; The WO3 microspheres are composed of several crystalline WO3 nanoparticles stacked together; The edge of the WO3 nanosheet is in contact with the surface of the WO3 microsphere.

[0014] Preferably, the diameter of the WO3 microspheres is 0.5~1.5μm; The WO3 nanosheets have a thickness of 10-50 nm, a length of 50-500 nm, and a width of 80-800 nm.

[0015] The present invention also provides the application of the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material described above in a hydrogen sensor.

[0016] This invention also provides a method for preparing a hydrogen sensor, comprising the following steps: The Pt-targeted modified WO3 hierarchical hydrogen-sensitive material described in the above technical solution is mixed with water and coated onto a MEMS device substrate for aging and drying to obtain the hydrogen sensor.

[0017] This invention prepares a hierarchical structure of WO3 nanosheets / microspheres through a secondary solvothermal reaction: The morphology of the hierarchical structure of nanosheets grown on the WO3 microsphere substrate is controlled by changing the tungsten source concentration in the secondary solvothermal reaction, resulting in a WO3 nanosheet / microsphere hierarchical structure with optimal hydrogen sensing performance. Pt is loaded onto the WO3 hierarchical structure via photodeposition, allowing for targeted modification of the nanosheets and microspheres. Since the WO3 microspheres are composed of stacked nanoparticles with numerous inter-particle gaps and abundant oxygen vacancies, Pt is more easily enriched on the WO3 microspheres to form H atoms and O2. - The active sites for the reaction; and the large specific surface area of ​​WO3 nanosheets will form uniform Pt, which is more conducive to the H2 splitting into H atoms, and then transporting them to the microspheres to react with the adsorbed O2. - The reaction. H2 pyrolysis on the nanosheets provides additional pyrolysis sites besides the microspheres, effectively improving hydrogen sensing performance.

[0018] The results of the examples show that the hydrogen sensor prepared by using Pt-targeted modified WO3 hierarchical hydrogen-sensitive material can detect hydrogen at 50°C, and has a high response value (1200ppmH2, response value 8372), fast response time (<1s) and good selectivity, repeatability and long-term stability. Attached Figure Description

[0019] Figure 1 SEM image of Pt / WO3; Figure 2 For Pt / W 0.05 SEM image of / WO3; Figure 3 For W 0.05 HRTEM plot of / WO3; Figure 4 For Pt / W 0.01 SEM image of / WO3; Figure 5 For Pt / W 0.07 SEM image of / WO3; Figure 6 For Pt / W 0.05 HRTEM plot of / WO3; Figure 7 For Pt / W 0.05 Platinum element distribution diagram of WO3 nanosheets and microspheres; Figure 8 For Pt / W 0.05 / WO3 response to 200~1200 ppm H2 at 50℃ and response comparison graph; Figure 9 For Pt / W 0.07 / WO3 response to 200~1200 ppm H2 at 50℃ and response comparison graph; Figure 10 For Pt / W 0.05 / WO3 response to 1200 ppm H2 at 50℃ and 100℃ and response time graph; Figure 11 The response of Pt / / WO3 to 200~1200 ppm H2 at 50℃ is shown in the graph and the response comparison diagram. Figure 12 For Pt / W 0.05 / WO3 response to 200~1200 ppm H2 at 100℃ and response comparison graph; Figure 13 The response of Pt / / WO3 to 200~1200 ppm H2 at 100℃ is shown in the graph and the response comparison diagram. Figure 14The response changes and response times of Pt / WO3 to 1200 ppm H2 at 50℃ and 100℃ are shown in the figure. Figure 15 For Pt / W 0.05 / WO3 response changes and response comparison at 50℃ to 200ppm H2, CO, NH3, CO2 and CH4. Detailed Implementation

[0020] This invention provides a method for preparing a Pt-targeted modified WO3 hierarchical hydrogen-sensitive material, comprising the following steps: A first tungsten source is mixed with a first organic solvent to carry out a first solvothermal reaction, resulting in uncrystallized WO3 powder; The uncrystallized WO3 powder was subjected to a first annealing process to obtain WO3 microspheres; the WO3 microspheres were formed by the stacking of several crystalline WO3 nanoparticles. The WO3 microspheres, the second tungsten source, and the second organic solvent are mixed and subjected to a second solvothermal reaction to generate WO3 nanosheets loaded on the surface of the WO3 microspheres, thus obtaining the matrix; the mass ratio of the second tungsten source to the volume ratio of the second organic solvent is (0.03~0.07) mol:1L. The matrix is ​​subjected to a second annealing to obtain an annealed matrix; The annealed matrix, mixed solvent, and platinum-containing precursor solution were mixed and then photodeposited to obtain the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material.

[0021] In this invention, a first tungsten source is mixed with a first organic solvent to carry out a first solvothermal reaction to obtain uncrystallized WO3 powder.

[0022] The present invention does not have any special limitations on the mixing operation of the first tungsten source and the first solvent, as long as the first tungsten source and the first solvent are mixed evenly.

[0023] In this invention, the mass ratio of the tungsten source to the volume ratio of the organic solvent is preferably 0.02~0.04 mol:1L. In specific embodiments of this invention, it can be 0.022 mol:1L, 0.024 mol:1L, 0.026 mol:1L, 0.028 mol:1L, 0.03 mol:1L, 0.032 mol:1L, 0.035 mol:1L, 0.036 mol:1L, or 0.038 mol:1L. The first tungsten source preferably includes tungsten hexachloride, and the first organic solvent preferably includes glacial acetic acid.

[0024] In this invention, the preferred temperature for the first solvothermal reaction is 150-200°C, and the preferred time is 8-24 hours. In specific embodiments of this invention, the temperature of the first solvothermal reaction can be 160°C, 170°C, 180°C, or 190°C, and the time can be 10 hours, 12 hours, 15 hours, 16 hours, 18 hours, 20 hours, or 22 hours. Limiting the temperature and time of the first solvothermal reaction to the above ranges in this invention can improve the catalytic performance of WO3 microsphere powder.

[0025] After the solvothermal reaction is completed, the present invention preferably performs post-processing on the product obtained from the solvothermal reaction.

[0026] In this invention, the post-processing preferably includes solid-liquid separation of the product obtained from the solvothermal reaction, followed by washing and drying of the obtained solid to obtain WO3 microspheres.

[0027] In this invention, the washing process is preferably performed 3 to 6 times; the washing solution used for each wash preferably includes water and / or anhydrous ethanol. In an embodiment of this invention, the washing involves three washes with water followed by three washes with anhydrous ethanol. In this invention, centrifugation is preferably performed after each wash; the centrifugation speed can be 4000 to 8000 rpm. This invention limits the number of washes, the type of washing solution used, and the centrifugation speed to the above ranges to sufficiently remove impurities from the WO3 powder.

[0028] After obtaining WO3 powder, the present invention performs a first annealing on the uncrystallized WO3 powder to obtain WO3 microspheres.

[0029] In this invention, the temperature of the first annealing is preferably 300~600℃, and the time is preferably 1~4h. In a specific embodiment of this invention, the temperature of the first annealing can be 350℃, 400℃, 450℃, 500℃ or 550℃, and the time can be 2h, 2.5h or 3h; the rate of heating to the first annealing temperature is preferably 3~5℃ / min.

[0030] In this invention, the first annealing is preferably carried out in air to remove lattice water and organic residues, repair oxygen vacancies, and obtain highly crystalline monoclinic WO3 microspheres.

[0031] The WO3 microspheres are composed of a stack of several crystalline WO3 nanoparticles.

[0032] After obtaining WO3 microspheres, the present invention mixes the WO3 microspheres, a second tungsten source, and a second organic solvent to carry out a second solvothermal reaction to generate WO3 nanosheets loaded on the surface of the WO3 microspheres, thus obtaining a matrix.

[0033] The present invention does not have any special limitations on the mixing operation, as long as the WO3 microspheres, the second tungsten source and the second organic solvent are mixed evenly.

[0034] In this invention, the mass ratio of the WO3 microspheres to the second tungsten source is preferably 1:2 to 4, and in specific embodiments of this invention, it can be 1:2.5, 1:3, or 1:3.5. The WO3 microspheres serve as the growth substrate for the nanosheets.

[0035] In this invention, the mass ratio of the second tungsten source to the volume ratio of the second organic solvent is (0.03~0.07) mol:1L. In specific embodiments of this invention, it can be 0.035 mol:1L, 0.04 mol:1L, 0.045 mol:1L, 0.05 mol:1L, 0.55 mol:1L, 0.6 mol:1L, or 0.065 mol:1L. The second tungsten source preferably includes tungsten hexachloride. The second organic solvent is preferably ethanol.

[0036] WCl6 is the core raw material for providing tungsten. Under the high temperature and pressure environment of a solvothermal reaction, WCl6 undergoes hydrolysis and alcoholysis to generate soluble tungstates or hydrated tungsten oxide intermediates. These intermediates eventually dehydrate and crystallize to form new WO3 crystals. WCl6 simultaneously provides an acidic environment and controls the nucleation rate. Ethanol, as a solvent, is responsible for dissolving WCl6 to form a homogeneous reaction system. Ethanol also acts as a reducing agent and structure-directing agent, directly reducing WCl6 under high temperature and pressure. 6 + To maintain electroneutrality, oxygen vacancies are forced to be generated in the lattice; selective adsorption inhibits the growth of specific crystal faces, directly promoting the nanosheet morphology.

[0037] In this invention, the preferred temperature for the second solvothermal reaction is 150-200°C, and the preferred time is 8-24 hours. In specific embodiments of this invention, the temperature of the second solvothermal reaction can be 160°C, 170°C, 180°C, or 190°C, and the time can be 10 hours, 12 hours, 15 hours, 16 hours, 18 hours, 20 hours, or 22 hours. Limiting the temperature and time of the second solvothermal reaction to the above ranges in this invention can improve the catalytic performance of the WO3 nanosheet structure.

[0038] After the second solvothermal reaction is completed, the present invention preferably separates the solid and liquid products obtained from the second solvothermal reaction, and then washes and dries the obtained solid products in sequence to obtain the matrix.

[0039] In this invention, the washing process is preferably performed 3 to 6 times; the washing solution for each wash preferably includes water and / or anhydrous ethanol. In an embodiment of this invention, the washing involves three washes with water followed by three washes with anhydrous ethanol. In this invention, centrifugation is preferably performed after each wash; the centrifugation speed can be 4000 to 8000 rpm. This invention limits the number of washes, the type of washing solution used, and the centrifugation speed to the above ranges to sufficiently remove impurities from the matrix.

[0040] After obtaining the substrate, the present invention performs a second annealing on the substrate to obtain an annealed substrate.

[0041] In this invention, the temperature of the second annealing is preferably 300~600℃, and the time is preferably 1~4h. In a specific embodiment of this invention, the temperature of the second annealing can be 350℃, 400℃, 450℃, 500℃ or 550℃, and the time can be 2h, 2.5h or 3h; the rate of heating to the second annealing temperature is preferably 3~5℃ / min.

[0042] In this invention, the second annealing is preferably carried out in air. The second annealing forms a stable structure with shared grain boundaries between microspheres and nanosheets, removes surface organic residues, and fine-tunes oxygen vacancies, resulting in a highly crystalline hierarchical WO3 support.

[0043] After obtaining the annealed matrix, the present invention mixes the annealed matrix, the mixed solvent and the platinum-containing precursor solution and performs photodeposition to obtain the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material.

[0044] The present invention does not have any particular limitation on the mixing operation, as long as the annealed matrix, mixed solvent and platinum-containing precursor solution are mixed evenly.

[0045] In this invention, the preferred ratio of the mass of the annealed matrix, the volume of the mixed solvent, and the volume of the platinum-containing precursor solution is (0.2~0.5) g : (60~100) mL : (0.3~0.9) mL. In specific embodiments of this invention, it can also be (0.2~0.4) g : (80~100) mL : (0.4~0.7) mL, or (0.2~0.3) g : (90~100) mL : (0.5~0.6) mL. In this invention, the mixed solvent preferably comprises methanol and water; the preferred volume ratio of methanol to water is 1 : (4~5), and in specific embodiments of this invention, it can be 1 : 4~4.5.

[0046] In this invention, the platinum-containing precursor solution preferably includes a chloroplatinic acid solution; the concentration of the platinum-containing precursor solution is preferably 5~20 g / L, and in specific embodiments of this invention, it can be 8 g / L, 10 g / L, 12 g / L, 13 g / L, 15 g / L or 18 g / L.

[0047] The present invention limits the mass of the annealed matrix, the volume ratio of the mixed solvent to the volume of the platinum-containing precursor solution, the type and proportion of the mixed solvent, and the type and concentration of the platinum-containing precursor solution to the above ranges, which can facilitate the uniform loading of Pt on the hierarchical structure of WO3 powder.

[0048] In this invention, the photodeposition is preferably performed in a protective atmosphere.

[0049] In this invention, the photodeposition is preferably carried out in a deposition bottle; the deposition bottle can be purged with N2 before use; the purging time can be 5-10 minutes. This invention removes all air from the deposition bottle by purging it.

[0050] In this invention, the spectral range of the light source during photodeposition is preferably full spectrum; the light source preferably includes a xenon arc lamp; the maximum operating current of the xenon arc lamp is preferably 15A; the power of the light source is preferably 200~500W, and in specific embodiments of this invention it can be 300W or 400W; the photodeposition time is preferably 30~60min, and in specific embodiments of this invention it can be 35min, 40min, 45min, 50min or 55min.

[0051] This invention enables the platinum precursor to undergo a photoreduction reaction to obtain elemental platinum by limiting the parameters in photodeposition to the above-mentioned range, and allows Pt to be uniformly loaded on WO3 nanosheet / microsphere hierarchical structure powder, which is beneficial to improving the hydrogen sensing performance of Pt-targeted modified WO3 hierarchical structure hydrogen-sensitive materials.

[0052] In this invention, after photodeposition, the product obtained by photodeposition is preferably separated into solid and liquid phases, and then the obtained solid is washed and dried.

[0053] In this invention, the washing is preferably performed 2 to 3 times; the washing solution for each wash can be water and / or anhydrous ethanol independently. In an embodiment of this invention, the washing involves washing once with water and then once with anhydrous ethanol. In this invention, centrifugation can be performed after each wash; the centrifugation speed can be 4000 to 8000 rpm. This invention limits the number of washes, the type of washing solution used, and the centrifugation speed to the above range to ensure thorough cleaning of the precipitate.

[0054] In this invention, the drying is preferably carried out in a vacuum drying oven; the drying temperature is preferably 80~120℃, and in a specific embodiment of this invention, it can be 100℃; the drying time is preferably 10~14h, and in a specific embodiment of this invention, it can be 11h or 12h. Limiting the drying temperature and time to the above ranges ensures the obtaining of dried Pt-targeted modified WO3 hierarchical hydrogen-sensitive materials.

[0055] This invention prepares WO3 nanosheet / microsphere hierarchical structure powder through two solvothermal reactions. By limiting the amount of tungsten source and the volume ratio of organic solvent in the second solvothermal reaction, the morphology of the WO3 powder can be effectively controlled to obtain the optimal hierarchical ratio of WO3 nanosheets and WO3 microspheres for H2 sensing. By loading Pt onto the WO3 nanosheet / microsphere hierarchical structure powder through photodeposition, Pt can be more enriched on the defects of WO3 microspheres, while Pt is uniformly distributed on the nanosheets, avoiding Pt agglomeration and improving the ability of Pt to crack H2 on the nanosheets and to carry out efficient gas reactions on the microspheres.

[0056] The present invention also provides a Pt-targeted modified WO3 hierarchical hydrogen-sensitive material prepared by the preparation method described above, comprising a matrix and elemental Pt loaded on the matrix; the matrix comprises WO3 microspheres and WO3 nanosheets loaded on the surface of the WO3 microspheres; The WO3 microspheres are composed of several crystalline WO3 nanoparticles stacked together; The edge of the WO3 nanosheet is in contact with the surface of the WO3 microsphere.

[0057] In this invention, the diameter of the WO3 microspheres is preferably 0.5~1.5μm, and in specific embodiments of this invention, it can be 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm or 1.4μm.

[0058] In this invention, the thickness of the WO3 nanosheet is preferably 10-50 nm, the length is preferably 50-500 nm, and the width is preferably 80-800 nm. In specific embodiments of this invention, the thickness of the WO3 nanosheet can be 20 nm, 30 nm, or 40 nm, the length can be 100 nm, 200 nm, 300 nm, or 400 nm, and the width can be 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, or 700 nm.

[0059] The present invention also provides the application of the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material described above in a hydrogen sensor.

[0060] The present invention also provides a hydrogen sensor, wherein the hydrogen-sensitive material in the hydrogen sensor is the Pt-targeted modified WO3 hierarchical structure hydrogen-sensitive material described in the above technical solution.

[0061] This invention also provides a method for preparing a hydrogen sensor, comprising the following steps: A hydrogen sensor was obtained by mixing Pt-targeted modified WO3 hierarchical hydrogen-sensitive material with water and coating it onto a MEMS device substrate for aging.

[0062] In this invention, the mass ratio of the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material to the volume ratio of water can be (5~20) mg:(0.5~2) mL. In specific embodiments of this invention, it can be (5~15) mg:(0.5~1.5) mL, (5~10) mg:(0.5~1.0) mL, or (5~8) mg:(0.5~0.8) mL. Limiting the mass ratio of the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material to the volume ratio of water within the above range allows for better coating of the mixture of Pt-targeted modified WO3 hierarchical hydrogen-sensitive material and water onto the MEMS device substrate.

[0063] In this invention, the mixing of the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material with water is preferably carried out under ultrasonic conditions; the ultrasonication time is preferably 20-60 minutes, and in specific embodiments of this invention, it can be 30 minutes, 40 minutes, or 50 minutes. This invention does not have a specific limitation on the ultrasonic frequency; any ultrasonic frequency commonly used by those skilled in the art can be used. This invention uses ultrasound to make the mixing of the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material with water more uniform.

[0064] In this invention, the coating preferably includes drop coating; the coating amount is preferably 1~5 μL / mm. 2 In a specific embodiment of the present invention, it can be 2 μL / mm 2 3μL / mm 2 or 4μL / mm 2 By limiting the coating method and coating amount to the above-mentioned range, this invention ensures that the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material can be uniformly distributed in MEMS devices and maintain an appropriate thickness.

[0065] In this invention, the coating process may further include drying; the drying temperature is preferably 80~100℃, and in a specific embodiment of this invention it may be 890℃; the drying time is preferably 10~14h, and in a specific embodiment of this invention it may be 11h or 12h.

[0066] In this invention, the aging temperature is preferably 200~300℃, and in a specific embodiment of this invention, it can be 250℃; the aging time is preferably 1~5 days, and in a specific embodiment of this invention, it can be 2 days, 3 days, or 4 days. Limiting the aging temperature and time to the above ranges in this invention can further improve the performance of the hydrogen sensor.

[0067] In this invention, the aging is preferably carried out in air.

[0068] The purpose of aging is to remove water molecules and other substances adsorbed on the sensor surface, stabilize the surface state of the material, allow the sensitive material to undergo thermal expansion matching with the MEMS micro hot plate substrate and electrodes, and promote stable interface contact. It can also allow the concentration of active sites such as oxygen vacancies in the material to reach a dynamic equilibrium at the operating temperature. In addition, after a period of aging, the initial resistance of the device (resistance in air) will tend to a relatively stable value, which is beneficial to the long-term stable sensing of the device.

[0069] The following detailed descriptions, in conjunction with embodiments, illustrate the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material, its preparation method, its application, and the preparation method of a hydrogen sensor provided by this invention. However, these descriptions should not be construed as limiting the scope of protection of this invention.

[0070] Example 1 A method for preparing a Pt-targeted modified WO3 hierarchical hydrogen-sensitive material: (1) 0.395 g of tungsten hexachloride and 35 mL of glacial acetic acid (the molar ratio of tungsten source to solvent volume is 0.028 mol: 1 L) were mixed and subjected to a solvothermal reaction at 180 °C for 12 h. The precipitate obtained by the solvothermal reaction was washed three times with water and then three times with anhydrous ethanol (centrifuged after each washing at 8000 rpm). After drying at 80 °C for 12 h, non-crystallized WO3 powder was obtained. (2) The uncrystallized WO3 powder obtained in step (1) was annealed in air at 500°C for 1 hour to obtain crystallized WO3 microsphere powder; (3) 0.2g of the crystallized WO3 microsphere powder obtained in step (2) was used as a growth substrate and added to 0.595g of tungsten hexachloride and 30mL of ethanol (the molar ratio of tungsten source to solvent volume is 0.05mol:1L). The mixture was then subjected to a solvothermal reaction at 180℃ for 12h. The precipitate obtained by the solvothermal reaction was washed three times with water and then three times with anhydrous ethanol (centrifuged after each washing at a speed of 8000rpm). The mixture was then dried at 80℃ for 12h to obtain WO3 nanosheet / microsphere hierarchical structure powder. (4) Anneal the WO3 hierarchical structure powder obtained in step (3) at 500°C in air for 1 hour to obtain annealed WO3 nanosheet / microsphere hierarchical structure powder (denoted as W). 0.05 / WO3); (5) The annealed WO3 hierarchical structure powder obtained in step (4), a mixed solvent (a mixed solvent of methanol and water, with a volume ratio of methanol to water of 1:4), and a 10 g / L chloroplatinic acid solution (the ratio of the mass of the annealed WO3 hierarchical structure powder, the volume of the mixed solvent, and the volume of the platinum-containing precursor solution is 0.2 g: 100 mL: 0.6 mL) are mixed and deposited in a deposition bottle (the deposition bottle is purged with N2 for 5 min before use) using a 15 A xenon arc lamp (the spectral range of the light source is the full spectrum, and the power of the light source is 300 W) for 30 min. Then the supernatant is discarded, and the precipitate is washed once with water and then once with anhydrous ethanol (centrifuged after each wash at a speed of 8000 rpm). The precipitate is then dried in a vacuum drying oven at 80 °C for 12 h to obtain the Pt-targeted modified WO3 hierarchical structure hydrogen-sensitive material (denoted as Pt / W). 0.05 / WO3).

[0071] The Pt-targeted modified WO3 hierarchical hydrogen-sensitive material prepared in Example 1 consists of a hierarchical structure composed of a WO3 microsphere substrate and WO3 nanosheets grown vertically on its surface, and Pt elemental loaded onto the WO3 nanosheets / microspheres by photodeposition. The diameter of the WO3 microspheres is 0.6 μm, and the thickness of the nanosheets is 20 nm, the length is 400 nm, and the width is 600 nm.

[0072] Example 2 The difference between Example 2 and Example 1 is that the volume ratio of the tungsten source to the solvent in step (3) is 0.04 mol: 1 L. Everything else is the same as in Example 1. The resulting hydrogen-sensitive material is denoted as Pt / W. 0.04 / WO3.

[0073] Example 3 The difference between Example 3 and Example 1 is that the volume ratio of the tungsten source to the solvent in step (3) is 0.06 mol: 1 L. Everything else is the same as in Example 1. The resulting hydrogen-sensitive material is denoted as Pt / W. 0.06 / WO3.

[0074] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that steps (3) and (4) are not included. Otherwise, they are the same as in Example 1. The resulting hydrogen-sensitive material is denoted as Pt / WO3.

[0075] Comparative Example 2 The difference between Comparative Example 2 and Comparative Example 1 is that the volume ratio of the tungsten source to the solvent in step (3) is 0.03 mol: 1 L, while the rest is the same as Comparative Example 1. The resulting hydrogen-sensitive material is denoted as Pt / W. 0.03 / WO3.

[0076] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the volume ratio of the tungsten source to the solvent in step (3) is 0.07 mol: 1 L, while the rest is the same as Comparative Example 1. The resulting hydrogen-sensitive material is denoted as Pt / W. 0.07 / WO3.

[0077] Application Example 1 A hydrogen sensor, consisting of a MEMS micro-heating plate and a hydrogen-sensitive material; The hydrogen-sensitive material is the Pt-targeted modified WO3 hierarchical structure hydrogen-sensitive material described in Example 1; The hydrogen sensor is prepared using the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material described in Example 1: The Pt-targeted WO3 hierarchical hydrogen-sensitive material was mixed with water (the mass ratio of Pt-targeted WO3 hierarchical hydrogen-sensitive material to water volume was 5 mg: 0.5 mL) and then drop-coated (the coating amount was 1 μL / mm). 2 After drying at 80°C for 12 hours on a MEMS device substrate, the hydrogen sensor is aged at 300°C for 2 hours to obtain the hydrogen sensor.

[0078] Comparative Application Example 1 A hydrogen sensor, consisting of a MEMS micro-heating plate and a hydrogen-sensitive material; The hydrogen-sensitive material is the Pt-targeted modified WO3 hierarchical structure hydrogen-sensitive material described in Comparative Example 3; The hydrogen sensor is prepared using the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material described in Comparative Example 3, and the preparation method is the same as in Application Example 1.

[0079] Comparative Application Example 2 A hydrogen sensor, consisting of a MEMS micro-heating plate and a hydrogen-sensitive material; The hydrogen-sensitive material is the hydrogen-sensitive material described in Comparative Example 1; The hydrogen sensor is prepared using the hydrogen-sensitive material described in Comparative Example 1, and the preparation method is the same as in Application Example 1.

[0080] The hydrogen-sensitive materials obtained in Example 1 and Comparative Example 1 were observed using a scanning electron microscope. The SEM image of Comparative Example 1 is shown below. Figure 1 As shown, the SEM image of Example 1 is as follows. Figure 2 As shown.

[0081] Figure 1 SEM image of Pt / WO3; Figure 2 For Pt / W 0.05 SEM image of / WO3.

[0082] from Figure 1 and Figure 2 It can be seen that after the second solvothermal treatment, nanosheet structures grew on the surface of the WO3 microspheres.

[0083] Figure 3 For W 0.05 HRTEM plot of / WO3.

[0084] Depend on Figures 2-3 It can be seen that, compared with W without load Pt, 0.05 Compared to WO3, Pt deposition largely maintains the hierarchical structure of nanosheets / microspheres.

[0085] Figure 4 For Pt / W 0.01 SEM image of / WO3; Figure 5 For Pt / W 0.07 SEM image of / WO3.

[0086] from Figure 4 and Figure 5 It can be seen that when the tungsten source concentration in the second solvothermal reaction decreases to 0.01 mol / L, almost no nanosheets form on the surface, and the microspheres gradually granulate, but still retain a microsphere structure. When the tungsten source concentration in the second solvothermal reaction increases to 0.07 mol / L, excessive nanosheets stack on the surface. The increase in tungsten source concentration in the second solvothermal reaction leads to the gradual granulation of microspheres, forming a microsphere structure composed of particle stacking, while simultaneously forming nanosheets in situ, creating a hierarchical structure.

[0087] The Pt-targeted modified WO3 hierarchical hydrogen-sensitive material obtained in Example 1 was observed using transmission electron microscopy (HRTEM), and the resulting HRTEM images are shown below. Figure 6 As shown.

[0088] Figure 6 For Pt / W 0.05 HRTEM plot of / WO3.

[0089] Depend on Figure 6 It can be seen that the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material has a black granular morphology, which is Pt nanoparticles after photodeposition, and is mostly distributed on the microspheres assembled from the nanoparticles. Figure 7 For Pt / W 0.05 Platinum element distribution diagram of / WO3 nanosheets and microspheres.

[0090] Depend on Figure 7 It can be seen that Pt with strong and concentrated signals is more easily formed on microspheres, while Pt formed on nanosheets is more uniform.

[0091] The hydrogen sensor obtained using the gas-sensitive detection system corresponding to Application Example 1 and Comparative Application Example 1 was tested for hydrogen responsiveness under conditions of 50℃ and 200~1200ppm H2. The hydrogen response change and response value graph obtained from Application Example 1 are shown below. Figure 8 As shown in the figure, the hydrogen response change and response value obtained in Application Example 1 are compared. Figure 9 As shown.

[0092] Figure 8 For Pt / W 0.05 / WO3 response to 200~1200 ppm H2 at 50℃ and response comparison graph; Figure 9 For Pt / W 0.07 The response of / WO3 to 200~1200 ppm H2 at 50℃ and the response comparison graph.

[0093] Depend on Figure 9 It can be seen that Pt / W 0.05 / WO3 compared to Pt / W 0.07 / WO3 exhibits superior hydrogen response. In a 1200ppm H2 environment, Pt / W 0.05 The / WO3 response value (Ra / Rg) is 8372, approximately Pt / W. 0.07 / WO3 response value is 4 times that of the previous value.

[0094] In this invention, the response value in a reducing gas is defined as the ratio of resistance (R0). a / R g) , where R a R represents the resistance value in air. g This indicates the resistance value in hydrogen gas. The test process uses a dynamic test system, in which the device is placed in a 100mL chamber, and air is introduced into it as background gas. The hydrogen concentration is adjusted by controlling the ratio of air to hydrogen carrier gas through a gas flow meter.

[0095] The hydrogen sensor obtained using the gas-sensitive detection system corresponding to Case 1 was tested for response to a 1200 ppm H2 concentration at 50℃ and 100℃. The hydrogen response changes and response times are as follows: Figure 10 As shown.

[0096] Figure 10 For Pt / W 0.05 The response changes and response time of / WO3 to 1200 ppm H2 at 50℃ and 100℃.

[0097] from Figure 10 It can be seen that Pt / W 0.05 / WO3 exhibits extremely fast response times at both 50℃ and 100℃, with response times of less than 1 second.

[0098] The hydrogen sensor obtained in Comparative Application Example 2 was tested using a gas-sensitive detection system under conditions of 50°C and 200~1200ppm H2. The hydrogen response comparison graph is shown below. Figure 11 As shown.

[0099] Figure 11 The graph shows the response of Pt / / WO3 to 200~1200 ppm H2 at 50℃ and the comparison of responses.

[0100] from Figure 11 It can be seen that without nanosheets, the response of Pt / WO3 to 1200ppmH2 is only 928, and the response value is reduced to that of Pt / WO3. 0.05 / WO3 11%. It can be seen that the synergistic effect of nanosheets and microspheres is the key to improving the H2 response at 50℃.

[0101] The hydrogen sensors obtained using the gas-sensitive detection system corresponding to Case 1 and Comparative Application Example 2 were tested for hydrogen responsiveness under conditions of 100℃ and 200~1200ppm H2. The resulting hydrogen response comparison graphs are shown below. Figure 12 and Figure 13 As shown.

[0102] Figure 12 For Pt / W 0.05 / WO3 response to 200~1200 ppm H2 at 100℃ and response comparison graph; Figure 13 The graph shows the response of Pt / / WO3 to 200~1200 ppm H2 at 100℃ and the comparison of responses.

[0103] from Figures 12-13 It can be seen that the response of Pt / WO3 to 1200ppmH2 is 2885, and the response of Pt / WO3 to 1200ppmH2 is 2885. 0.05 / WO3 has a response of 5167 to 1200ppmH2, and the response value of Pt / WO3 is reduced to Pt / W 0.05 The / WO3 response value is 55.8%. This shows that regardless of 50℃ or 100℃, Pt / W 0.05 / WO3 has a higher hydrogen response than Pt / WO3.

[0104] The hydrogen sensor obtained in Comparative Application Example 2 was tested using a gas-sensitive detection system at 50°C and 100°C to respond to a 1200 ppm H2 concentration. The hydrogen response changes and response times are as follows: Figure 14 As shown.

[0105] Figure 14 The graph shows the response changes and response times of Pt / WO3 to 1200 ppm H2 at 50℃ and 100℃.

[0106] from Figure 14 It can be seen that Pt / WO3 exhibits extremely fast response times at both 50℃ and 100℃, with response times of less than 1 second. Pt / WO3 and Pt / W 0.05 Like / WO3, it has an extremely fast response time, which is related to the efficient cracking of H2 by Pt, which speeds up the response time.

[0107] Using the hydrogen sensor obtained from test case 1 of the gas-sensitive detection system, selective tests were performed at 50°C on 200 ppm H2, 200 ppm CO, 200 ppm NH3, 200 ppm CO2, and 200 ppm CH4, respectively. The obtained response changes and response values ​​are as follows: Figure 15 As shown.

[0108] Figure 15 For Pt / W 0.05 / WO3 response changes and response comparison at 50℃ to 200ppm H2, CO, NH3, CO2 and CH4.

[0109] from Figure 15 It can be seen that Pt / W 0.05 / WO3 showed a response of 156.1 to 200 ppm H2, 2.15 to 200 ppm CO, 6.39 to 200 ppm NH3, no response to 200 ppm CO2, and 2.08 to 200 ppm CH4. Pt / W 0.05 / WO3 exhibits excellent selectivity.

[0110] The Pt-targeted modified WO3 hierarchical hydrogen-sensitive material prepared by the preparation method provided by this invention has a hierarchical structure of nanosheets and microspheres assembled together. The Pt-targeted modified WO3 hierarchical hydrogen-sensitive material is used as a hydrogen sensor to detect hydrogen at 50°C. It has an extremely fast response time (<1s), an extremely high response value (>8372~1200ppm), and excellent selectivity, and has good hydrogen sensing performance.

[0111] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a Pt-targeted modified WO3 hierarchical hydrogen-sensitive material, characterized in that, Includes the following steps: A first tungsten source is mixed with a first organic solvent to carry out a first solvothermal reaction, resulting in uncrystallized WO3 powder; The uncrystallized WO3 powder was subjected to a first annealing process to obtain WO3 microspheres; the WO3 microspheres were formed by the stacking of several crystalline WO3 nanoparticles. The WO3 microspheres, the second tungsten source, and the second organic solvent are mixed and subjected to a second solvothermal reaction to generate WO3 nanosheets loaded on the surface of the WO3 microspheres, thus obtaining the matrix; the mass ratio of the second tungsten source to the volume ratio of the second organic solvent is (0.03~0.06) mol:1L. The matrix is ​​subjected to a second annealing to obtain an annealed matrix; The annealed matrix, mixed solvent, and platinum-containing precursor solution were mixed and then photodeposited to obtain the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the first tungsten source to the volume ratio of the first organic solvent is 0.02~0.04 mol:1L; The first tungsten source includes tungsten hexachloride; the first organic solvent includes glacial acetic acid; The temperature of the first solvothermal reaction is 150~200℃, and the time is 8~24h.

3. The preparation method according to claim 1, characterized in that, The temperature of the first annealing and the second annealing are independently 300~600℃, and the time is independently 1~4h.

4. The preparation method according to claim 1, characterized in that, The mass ratio of the WO3 microspheres to the second tungsten source is 1:2~4; The second tungsten source includes tungsten hexachloride; the second organic solvent includes ethanol; The temperature of the second solvothermal reaction is 150~200℃, and the time is 8~24h.

5. The preparation method according to claim 1, characterized in that, The ratio of the mass of the annealed matrix, the volume of the mixed solvent, and the volume of the platinum-containing precursor solution is (0.2~0.5) g : (60~100) mL : (0.3~0.9) mL; The mixed solvent comprises methanol and water; the volume ratio of methanol to water is 1:(4~5); The concentration of the platinum-containing precursor solution is 5~20 g / L; the platinum-containing precursor solution includes chloroplatinic acid solution.

6. The preparation method according to claim 1, characterized in that, The light source used for photodeposition has a full spectrum.

7. The Pt-targeted modified WO3 hierarchical hydrogen-sensitive material prepared by the preparation method according to any one of claims 1 to 6, characterized in that, It includes a matrix and elemental Pt loaded on the matrix; the matrix includes WO3 microspheres and WO3 nanosheets loaded on the surface of the WO3 microspheres; The WO3 microspheres are composed of several crystalline WO3 nanoparticles stacked together; The edge of the WO3 nanosheet is in contact with the surface of the WO3 microsphere.

8. The Pt-targeted modified WO3 hierarchical hydrogen-sensitive material according to claim 7, characterized in that, The diameter of the WO3 microspheres is 0.5~1.5μm; The WO3 nanosheets have a thickness of 10-50 nm, a length of 50-500 nm, and a width of 80-800 nm.

9. The application of the Pt-targeted modified WO3 hierarchical hydrogen-sensitive material according to any one of claims 7 to 8 in hydrogen sensors.

10. A method for preparing a hydrogen sensor, characterized in that, Includes the following steps: The Pt-targeted modified WO3 hierarchical hydrogen-sensitive material according to any one of claims 7-8 is mixed with water and coated onto a MEMS device substrate for aging and drying to obtain the hydrogen sensor.

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