Heat-insulating moisture-proof thermoelectric device and preparation method thereof

Abstract

The invention discloses a heat-insulation moisture-proof thermoelectric device and a preparation method thereof, and relates to the technical field of thermoelectric materials, the thermoelectric device comprises a p-type Bi2Te3 galvanic couple arm and an n-type Bi2Te3 galvanic couple arm which are provided with moisture-proof layers on the surfaces and are connected with electrodes; the cellulose-based aerogel layer is filled between the adjacent galvanic couple arms; the porosity of the cellulose-based aerogel layer is 96%-99.5%, and the surface contact angle is larger than or equal to 150 degrees; the heat reflecting film covers the non-heat-conduction surface of the galvanic couple arm, and the reflectivity of the heat reflecting film at the wave band of 400-3000 nm is greater than or equal to 92%; the moisture-proof layer is made of a zinc-based zeolite imidazate framework material, the thickness of the moisture-proof layer is 50-200 nm, the porosity of the moisture-proof layer is 5%-10%, and the pore diameter is smaller than or equal to 0.34 nm. The preparation method of the heat-insulating and moisture-proof thermoelectric device comprises the following steps: S1, carrying out moisture-proof treatment on the galvanic couple arms; s2, filling the cellulose aerogel; s3, packaging a heat reflecting film; and S4, coating the conductive bonding layer. According to the invention, low-resistance, high-strength and moisture-proof connection between the galvanic couple arms and the electrodes is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric materials, and particularly to a heat-insulating and moisture-proof thermoelectric device and a preparation method thereof. Background Technique

[0002] Thermoelectric conversion technology utilizes the Seebeck effect to directly convert heat energy into electrical energy, and is widely applied in fields such as industrial waste heat recovery and heat dissipation power generation of electronic devices. In recent years, Bi2Te3-based materials have become the core materials of low-temperature thermoelectric modules due to their excellent thermoelectric performance (ZT value can reach 1.8) in the range from room temperature to 150 °C. However, these materials have encountered two major challenges in practical applications: one is the interface failure problem in a humid environment, and the other is the efficiency reduction caused by heat loss. These problems severely restrict the long-term stability and energy conversion efficiency of Bi2Te3-based thermoelectric devices.

[0003] To prevent the device from failing in a humid environment, traditional methods usually use polymers such as silica gel or epoxy resin as sealing materials. However, the molecular pore diameters of these materials are relatively large, and they cannot effectively block water molecules with a diameter of about 0.3 nanometers, resulting in problems such as oxidation on the surface of the thermocouple arms and electrode corrosion, which in turn increases the contact resistance and causes interface cracking. Although some studies have attempted to use metal barrier layers (such as nickel-based alloys) to enhance the moisture-proof effect, these methods are difficult to achieve molecular-level water vapor barrier due to their relatively thick thickness. Moreover, there is a large difference in the thermal expansion coefficient between the metal barrier layer and the Bi2Te3 material, which easily leads to heat stress concentration and further reduces the device life.

[0004] In the application of metal-organic framework materials (MOFs), although there has been some research in the field of moisture-proof, most of these studies focus on the surface treatment and coating application of moisture-proof materials, and have not yet involved the protection of thermoelectric materials. Analysis of the applications and limitations of MOFs in different fields: First, in the field of lithium battery separators, MOFs such as ZIF-8 are used to coat the surface of the separator to prevent trace moisture in the electrolyte from entering. However, the use of ZIF-8 particles results in uneven pore size distribution, and it is impossible to achieve an ideal molecular-level seal. Moreover, the thickness of the coating exceeds 5 micrometers, which increases the interface contact resistance by 15%. In addition, there is a large difference in the thermal expansion coefficient between ZIF-8 and the electrode material, which also becomes an obstacle in technology. In the field of electronic packaging, although the blending of MOFs and epoxy resin can effectively protect the PCB board, when the addition amount of MOFs exceeds 30%, it will significantly increase the thermal conductivity; and the coverage of MOFs on the irregular surface is incomplete, resulting in extremely low adhesion of the moisture-proof layer. Finally, in the field of gas separation, although the ZIF-8 membrane can efficiently separate CO2 and H2O, it needs to operate in a high-temperature environment, which does not match the working temperature of thermoelectric materials.

[0005] In terms of thermal insulation design, traditional materials such as fiberglass and foam plastics generally have relatively high room-temperature thermal conductivity, making it difficult to meet the requirements for the efficient utilization of low-grade thermal energy. In recent years, aerogels have received extensive attention due to their high porosity and low thermal conductivity. However, conventional silica aerogels have problems such as low mechanical strength and an increase in thermal conductivity after moisture absorption. Although some studies have proposed enhancing and composite-modifying aerogels with long aluminosilicate fibers, they still rely on surface coatings to achieve hydrophobicity, and the coatings are prone to peeling off during long-term use, resulting in the failure of moisture-proof performance. In addition, these aerogels do not solve the problem of the synergistic optimization of carrier transport and thermal insulation performance in material selection. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a heat-insulating and moisture-proof thermoelectric device and its preparation method, which solve the problems of moisture-proof, heat-insulating and reliability of Bi2Te3-based devices.

[0007] To achieve the above purpose, the technical scheme adopted by the present invention is as follows: Provide a heat-insulating and moisture-proof thermoelectric device, including a p-type Bi2Te3 thermocouple arm and an n-type Bi2Te3 thermocouple arm with a moisture-proof layer grown on the surface and connected to the electrode; a cellulose-based aerogel layer filled between adjacent p-type Bi2Te3 thermocouple arms and n-type Bi2Te3 thermocouple arms; the porosity of the cellulose-based aerogel layer is 96%-99.5%, and the surface contact angle ≥ 150°; a heat-reflecting film covering the non-thermally conductive surfaces of the p-type Bi2Te3 thermocouple arm and the n-type Bi2Te3 thermocouple arm, and the reflectivity of the heat-reflecting film in the 400-3000 nm band is ≥ 92%; the material of the moisture-proof layer is a zinc-based zeolitic imidazolate framework material, with a thickness of 50-200 nm, and the porosity of the moisture-proof layer is 5%-10%, and the pore diameter ≤ 0.34 nm.

[0008] Furthermore, the cellulose-based aerogel layer is a hydrophobic modified nano-cellulose aerogel, which is graft-modified by hexadecyltrimethoxysilane, and the loading amount of the modifier is 3-8 wt%, and Bi2Te3 quantum dots are uniformly dispersed in the hydrophobic modified nano-cellulose aerogel, and the particle size of the quantum dots is 2-5 nm, and the doping amount is 0.5-1.5 wt%.

[0009] Furthermore, the fibers of the hydrophobic modified nano-cellulose aerogel are vertically and directionally arranged, the degree of orientation ≥ 85%, and the fiber diameter is 5-20 nm, and the aspect ratio is 100:1 to 500:1.

[0010] Furthermore, ZnO nanoparticles are doped in the moisture-proof layer, and the doping amount is 2-5 wt%, and the size of the ZnO particles is 10-30 nm, and they are uniformly distributed on the inner wall of the pore channels of the moisture-proof layer.

[0011] Further, the heat-reflective film is a three-layer composite structure of TiO2 / Ag / TiO2, and the thickness of each layer is as follows: Inner layer TiO2: 30 - 50 nm, Ag layer: 80 - 120 nm, Outer layer TiO2: 30 - 50 nm.

[0012] Further, the joints of the p-type Bi2Te3 thermoelectric arms and the n-type Bi2Te3 thermoelectric arms with the electrodes are covered with a conductive adhesive layer. The conductive adhesive layer is a composite material of an epoxy resin matrix dispersed with Bi2Te3 nanosheets. The thickness of the Bi2Te3 nanosheets is 10 - 50 nm, and the volume fraction of the Bi2Te3 nanosheets in the composite material is 40 - 60 vol%.

[0013] There is also provided a preparation method of the above heat-insulating and moisture-proof thermoelectric device, including the following steps: S1: Moisture-proof treatment of thermoelectric arms: Use liquid phase epitaxy to grow a moisture-proof layer on the surfaces of the p-type Bi2Te3 thermoelectric arms and the n-type Bi2Te3 thermoelectric arms. The concentration of 2-methylimidazole in the reaction solution is 0.1 - 0.3 mol / L, the concentration of zinc nitrate is 0.05 - 0.15 mol / L, the reaction temperature is 25 - 40 °C, and the time is 2 - 4 hours; conduct in-situ doping of ZnO on the moisture-proof layer, immerse the p-type Bi2Te3 thermoelectric arms and the n-type Bi2Te3 thermoelectric arms in a zinc acetate ethanol solution with a concentration of 0.1 - 0.5 wt%, and perform heat treatment at 80 °C for 1 - 2 hours; S2: Filling of cellulose aerogel: Disperse nanocellulose in a choline chloride and urea eutectic solvent with a molar ratio of 1:2, with a concentration of 5 - 10 wt%. After adding Bi2Te3 quantum dots, extrude them directionally through a microfluidic chip with a channel width of 200 - 500 μm, with an electric field strength of 50 - 100 V / cm; form by program freeze-drying combined with supercritical CO2 drying, with a freezing gradient of -40 °C → -20 °C → 0 °C, and supercritical conditions of a temperature of 45 °C and a pressure of 10 MPa; S3: Encapsulation of heat-reflective film: Use ALD atomic layer deposition method to deposit TiO2 / Ag / TiO2 composite film in sequence. The deposition temperature of TiO2 is 120 - 150 °C, the deposition temperature of Ag is 80 - 100 °C, the number of deposition cycles of TiO2 is 100 - 150 times, and the number of deposition cycles of Ag is 50 - 80 times; S4: Conductive adhesive layer coating: Bi2Te3 nanosheets and epoxy resin are mixed in proportion, wherein the volume fraction of Bi2Te3 nanosheets in the composite material formed by the mixture of Bi2Te3 nanosheets and epoxy resin is 40 - 60 vol%; the mixed material is dispersed by triple-roll grinding and then screen-printed on the electrode connection, and the curing conditions are first 120°C for 30 minutes and then 150°C for 15 minutes to obtain a thermoelectric device.

[0014] Furthermore, in step S1, after the moisture-proof layer is in-situ doped with ZnO, the moisture-proof porosity is reduced to 3%-8%.

[0015] Furthermore, in step S2, the choline chloride and urea low eutectic solvent is recycled, comprising the following steps: after supercritical CO2 drying is completed, the choline chloride and urea low eutectic solvent remaining in the aerogel forming process is collected, 0.1-0.3 wt% TiO2 nanoparticles are added as a photocatalyst, and ultraviolet light is used with a wavelength of 365 nm and an intensity of 50 mW / cm 2 , degrading the cellulose fragments remaining in the choline chloride and urea low eutectic solvent, the illumination time is 30-60 minutes; after filtering through a 0.22 μm filter membrane, it is reused in step S2.

[0016] Furthermore, in step S3, the ALD deposition of the TiO2 layer uses titanium tetraisopropoxide and water as precursors, the pulse time of titanium tetraisopropoxide is 0.1-0.3 s, the pulse time of water is 0.05-0.1 s, and the purge time is 5-10 s.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The zinc-based zeolite imidazolate framework material (ZIF-8)-based moisture-proof layer of the present invention achieves molecular-level water vapor barrier by precisely controlling the pore size and doping with ZnO. The moisture-proof ability of the layer is improved by more than 10 times compared with traditional sealing materials, and the oxidation of Bi2Te3 electric dipole arms and electrode corrosion are significantly inhibited, extending the device life to more than 5000 hours.

[0018] (2) The hydrophobically modified nanocellulose aerogel of the present invention combines oriented fiber structure with quantum dot doping, while maintaining ultra-low thermal conductivity, while increasing the compressive strength to 12 MPa, thus solving the problem of aerogel being "brittle and easy to absorb moisture", and is suitable for complex environments such as vibration and humidity.

[0019] (3) The heat reflective film of the present invention realizes the 400-3000 nm band through the TiO2 / Ag / TiO2 three-layer film structure, with a reflectivity of ≥92%, reducing the thermal radiation loss by more than 30%. In combination with the aerogel layer, the overall heat loss of the device is reduced by 40%, significantly improving the low-grade thermal energy conversion efficiency.

[0020] (4) The eutectic solvent recycling technology of the present invention is combined with photocatalytic degradation to avoid the pollution of traditional organic solvents; microfluidics and ALD technology achieve precise control of nanoscale structures, promoting the development of thermoelectric device preparation towards refinement and greenness. Description of the Drawings

[0021] Figure 1 is a schematic structural diagram of the heat-insulating and moisture-proof thermoelectric device of the present invention.

[0022] Figure 2 is a process flow chart for preparing the heat-insulating and moisture-proof thermoelectric device of the present invention.

[0023] The component numbers in the above-mentioned drawings are as follows: 1, p-type Bi2Te3 thermocouple arm; 2, n-type Bi2Te3 thermocouple arm; 3, cellulose-based aerogel layer; 4, heat-reflective film; 5, electrode; 6, conductive adhesive layer; 7, moisture-proof layer. Detailed Embodiments

[0024] The present invention will be further described below in conjunction with embodiments, and the embodiments of the present invention include but are not limited to the following embodiments.

[0025] Embodiment 1 As Figure 1 shown, a heat-insulating and moisture-proof thermoelectric device is provided, including a p-type Bi2Te3 thermocouple arm 1 and an n-type Bi2Te3 thermocouple arm 2 with a moisture-proof layer 7 grown on the surface and connected to the electrode 5. The material of the moisture-proof layer 7 is zinc-based zeolitic imidazolate framework material, with a thickness of 100 nm, and the porosity of the moisture-proof layer 7 is 8%, and the pore diameter is 0.32 nm. ZnO nanoparticles are doped in the moisture-proof layer 7, and the doping amount is 3 wt%, and the ZnO particle size is 20 nm, which are uniformly distributed on the inner wall of the pore channels of the moisture-proof layer 7. The thermocouple arms are made of commercial Bi2Te3-based thermoelectric materials. The p-type Bi2Te3 thermocouple arm 1 is doped with Sb, and the n-type Bi2Te3 thermocouple arm 2 is doped with Se. Both Bi2Te3 thermocouple arms are cut into cuboids with dimensions of 5 mm × 5 mm × 20 mm.

[0026] The cellulose-based aerogel layer 3 filled between adjacent p-type Bi2Te3 thermocouple arms 1 and n-type Bi2Te3 thermocouple arms 2 is a hydrophobic modified nanocellulose aerogel, which is grafted and modified by cetyltrimethoxysilane, and the loading amount of the modifier is 5 wt%. Bi2Te3 quantum dots are uniformly dispersed in the hydrophobic modified nanocellulose aerogel, and the quantum dot particle size is 3 nm, and the doping amount is 1 wt%. The fibers of the hydrophobic modified nanocellulose aerogel are vertically oriented, with an orientation degree of 88%, and the fiber diameter is 10 nm, and the aspect ratio is 300:1. The porosity of the cellulose-based aerogel layer 3 is 98%, and the surface contact angle ≥ 150°.

[0027] A thermal reflection film 4 covering the non-thermal conduction surfaces of the p-type Bi2Te3 thermoelectric couple arm 1 and the n-type Bi2Te3 thermoelectric couple arm 2, the reflectivity of the thermal reflection film 4 in the wavelength band of 400 - 3000 nm is 93%; the thermal reflection film 4 is a three-layer composite structure of TiO2 / Ag / TiO2, and the thicknesses of each layer are respectively: the inner layer TiO2: 40 nm, the Ag layer: 100 nm, and the outer layer TiO2: 40 nm. Specifically, the thermal reflection film 4 is arranged on the axial side surfaces of the p-type Bi2Te3 thermoelectric couple arm 1 and the n-type Bi2Te3 thermoelectric couple arm 2, that is, the two side surfaces along the length direction of the thermoelectric arm, and a coating-free area of 1 mm is maintained with the upper and lower end faces to ensure the smoothness of the heat flow channel. The TiO2 / Ag / TiO2 composite film is deposited on the axial side surface by magnetron sputtering to form a radiation shielding structure that surrounds the thermoelectric arm but does not cover the thermal conduction end face.

[0028] The connection parts of the p-type Bi2Te3 thermoelectric couple arm 1 and the n-type Bi2Te3 thermoelectric couple arm 2 with the electrode 5 are covered with a conductive adhesive layer 6, the conductive adhesive layer 6 is a composite material of an epoxy resin matrix dispersed with Bi2Te3 nanosheets, the thickness of the Bi2Te3 nanosheets is 20 nm, and the volume fraction of the Bi2Te3 nanosheets in the composite material is 50 vol%.

[0029] There is also provided a preparation method of the above heat insulation and moisture-proof thermoelectric device, and the process flow chart is as Figure 2 shown, and the preparation method includes the following steps: S1: Moisture-proof treatment of the thermoelectric couple arm: First, the p-type Bi2Te3 thermoelectric couple arm 1 and the n-type Bi2Te3 thermoelectric couple arm 2 (5 mm×5 mm×20 mm) are ultrasonically cleaned with acetone and ethanol for 15 minutes each in sequence, and dried with nitrogen. Then, a moisture-proof layer 7 is grown on the surfaces of the p-type Bi2Te3 thermoelectric couple arm 1 and the n-type Bi2Te3 thermoelectric couple arm 2 by liquid phase epitaxy. Specifically, a 2-methylimidazole solution of 0.2 mol / L and a zinc nitrate solution of 0.1 mol / L are configured, mixed and added to a reaction kettle, and stirred at a constant temperature of 25 °C for 2 hours to obtain a reaction solution. Then, the p-type Bi2Te3 thermoelectric couple arm 1 and the n-type Bi2Te3 thermoelectric couple arm 2 are immersed in the reaction solution, and a ZIF-8 layer is grown on the surface by liquid phase epitaxy; Then, in-situ doping of ZnO is carried out on the moisture-proof layer 7. An ethanol solution of zinc acetate with a concentration of 0.3 wt% is configured, and the p-type Bi2Te3 thermoelectric couple arm 1 and the n-type Bi2Te3 thermoelectric couple arm 2 are immersed and heat-treated at 80 °C for 1.5 hours, and ZnO nanoparticles are in-situ deposited on the inner wall of the ZIF-8 pore channels; after the in-situ doping of ZnO on the moisture-proof layer 7, the moisture-proof porosity is reduced to 4%.

[0030] S2: Cellulose aerogel filling: Disperse nanocellulose with a concentration of 8 wt% in a choline chloride and urea eutectic solvent with a molar ratio of 1:2. After adding 1 wt% Bi2Te3 quantum dots, extrude them directionally through a microfluidic chip with a channel width of 300 μm under an electric field strength of 80 V / cm to achieve vertical and directional alignment of the fibers. Through programmed freeze-drying, the freezing gradient is -40°C → -20°C → 0°C, and the freeze-drying program is to hold at -40°C for 2 hours → hold at -20°C for 1 hour → hold at 0°C for 1 hour, and then transfer it to a supercritical CO2 drying equipment. The supercritical conditions are a temperature of 45°C and a pressure of 10 MPa, and hold for 4 hours.

[0031] S3: Encapsulation of the heat-reflective film 4: Use an atomic layer deposition equipment to deposit a TiO2 / Ag / TiO2 composite film successively by ALD atomic layer deposition method. The deposition temperature of TiO2 is 130°C, the deposition temperature of Ag is 85°C. The number of deposition cycles of TiO2 is 120 times, and the number of deposition cycles of Ag is 60 times. When depositing the TiO2 layer by ALD, titanium tetraisopropoxide (TTIP) and water are used as precursors. The pulse time of titanium tetraisopropoxide is 0.2 s, the pulse time of water is 0.1 s, and the purge time is 10 s.

[0032] S4: Coating of the conductive adhesive layer 6: Mix Bi2Te3 nanosheets and epoxy resin E44 in a ratio of 50 vol%, disperse the mixed material by three-roll grinding, and then screen-print it at the connection of the electrode 5. The rotation speed of the three-roll grinder is 500 rpm, and the grinding cycle is 3 times. The curing conditions are to cure at 120°C for 30 minutes first, and then cure at 150°C for 15 minutes to form a conductive layer with a thickness of 100 μm, and finally obtain a thermoelectric device.

[0033] Example 2 Different from Example 1, the thickness of the moisture-proof layer 7 of the thermoelectric device in this example is 50 nm.

[0034] Example 3 Different from Example 1, the thickness of the moisture-proof layer 7 of the thermoelectric device in this example is 200 nm.

[0035] Example 4 Different from Example 1, the porosity of the cellulose-based aerogel layer 3 of the thermoelectric device in this example is 96%.

[0036] Example 5 Different from Example 1, the porosity of the cellulose-based aerogel layer 3 of the thermoelectric device in this example is 99.5%.

[0037] Example 6 Different from Example 1, the thicknesses of each layer of the heat-reflective film 4 in this example are as follows: inner layer TiO2: 30 nm, Ag layer: 80 nm, outer layer TiO2: 30 nm.

[0038] Example 7 Different from Example 1, the thicknesses of each layer of the heat-reflective film 4 in this example are as follows: inner layer TiO2: 50 nm, Ag layer: 120 nm, outer layer TiO2: 50 nm.

[0039] Comparative Example 1 Different from Example 1, in step S1 of this comparative example, the reaction solution is prepared as follows: 2-methylimidazole (0.2 mol / L) and zinc nitrate (0.1 mol / L) are mixed at a volume ratio of 1:1 and stirred at 25 °C for 2 hours. The p-type Bi2Te3 thermocouple arm 1 and the n-type Bi2Te3 thermocouple arm 2 are immersed in the reaction solution and left standing at 25 °C for 4 hours to grow a pure ZIF-8 layer with a thickness of 100 nm on the surface. Finally, it is rinsed 3 times with deionized water and vacuum dried at 60 °C for 2 hours to obtain a thermoelectric device with an unmodified ZIF-8 moisture-proof layer.

[0040] Comparative Example 2 Different from Example 1, in this comparative example, silicone coating is used. Dow Corning DC 1-2577 silicone with a viscosity of 5000 mPa·s and a solid content of 98% is selected. The silicone is diluted to a solid content of 50% (using ethyl acetate as the solvent) and sprayed on the surfaces of the p-type Bi2Te3 thermocouple arm 1 and the n-type Bi2Te3 thermocouple arm 2, with a wet film thickness of 200 μm. After baking at 80 °C for 2 hours, a silicone sealing layer with a thickness of about 50 μm is formed to obtain a thermoelectric device using a traditional silicone sealing material.

[0041] Comparative Example 3 Different from Example 1, in this comparative example, only a single-layer Ag film is deposited. A magnetron sputtering device (background vacuum ≤ 5×10 -4 Pa) is used, with an Ar gas flow rate of 20 sccm and a sputtering power of 150 W. A single-layer Ag film with a thickness of 100 nm is deposited on the axial side surface of the thermocouple arm. Finally, it is left standing at room temperature for 24 hours under nitrogen protection to obtain a thermoelectric device using a single-layer Ag film.

[0042] Comparative Example 4 Different from Example 1, in this comparative example, only the cleaning step of Example 1 (ultrasonic cleaning with acetone and ethanol) is performed, and the surface of the thermocouple arm remains in the original Bi2Te3 material state to obtain an uncoated thermocouple arm.

[0043] Based on the above examples, the following experiments were conducted: I. Water vapor transmission rate test Verify the molecular-level water vapor barrier ability of the ZIF-8 / ZnO composite moisture barrier through water vapor transmission rate tests, taking the samples prepared in Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2 as examples.

[0044] Using the ASTM E96 standard, test the water vapor transmission rate (WVTR) of different moisture barrier thicknesses (50 / 100 / 200 nm) at 85% RH. The test equipment uses a PERMATRAN-W 3 / 33 water vapor transmission rate tester, and the sample size is 20 mm × 20 mm (the surface of the Bi2Te3 thermocouple arm including Moisture Barrier 7); the test temperature is 25°C, the humidity gradient is 85% RH (high humidity side) → 50% RH (low humidity side), and the steady-state transmission amount is measured for 24 hours. The test results are shown in Table 1: Table 1 Water vapor transmission rates of different samples Experimental conclusion: The WVTR of the ZIF-8 / ZnO composite moisture barrier is reduced by 10 - 50 times compared with traditional silica gel, and reaches the lowest value of 0.005 g / (m 2 ·day) when the thickness is 200 nm, verifying the molecular-level water vapor barrier effect with pore size ≤ 0.34 nm. The doping of ZnO reduces the porosity of the moisture barrier from 8% to 4%, significantly reducing the water vapor penetration channels. The WVTR of Example 1 (0.008) is 78% lower than that of Comparative Example 1 (0.035).

[0045] II. Testing of the thermal conductivity and mechanical properties of aerogels Verify the ultra-low thermal conductivity and high compressive strength of the hydrophobic modified nanocellulose aerogel through the testing of the thermal conductivity and mechanical properties of the aerogel, taking the samples prepared in Example 1, Example 4, and Example 5 and traditional silica aerogel as examples.

[0046] Thermal conductivity test: Use a Hot Disk TPS 2500S thermal conductivity meter to test the thermal conductivity of aerogels with different porosities (96% / 98% / 99.5%), the test temperature is 25°C, and the pressure is 0.1 MPa Mechanical property test: Use an INSTRON 5967 universal testing machine to test the compressive strength in the vertical direction, and the compression rate is 1 mm / min. The test results are shown in Table 2: Table 2 Test data of the thermal conductivity and fiber orientation degree of different samples Experimental conclusion: When the porosity is 99.5%, the thermal conductivity is the lowest (0.018 W / m·K), which is 44% lower than that of traditional aerogels (0.032). However, the compressive strength decreases to 9.8 MPa due to the high porosity. The fiber orientation degree of 88% in Example 1 enables the balance of thermal conductivity of 0.021 W / m·K and compressive strength of 14.2 MPa at a porosity of 98%. The doping of Bi2Te3 quantum dots (1 wt%) further reduces the heat conduction path.

[0047] III. Spectral Reflectance Test of Thermal Reflection Film The spectral reflectance test of the thermal reflection film verifies that the reflectance of the TiO2 / Ag / TiO2 three-layer composite structure is ≥92% in the 400 - 3000 nm band, taking the samples prepared in Example 1, Example 6, Example 7, Comparative Example 3, and Comparative Example 4 as examples.

[0048] The test equipment uses a UV-Vis-NIR spectrophotometer equipped with a 150 mm integrating sphere to test the reflection spectra of different samples. The test range is 400 - 3000 nm, the incident angle is 8°, and the resolution is 5 nm; the thermal reflection film is peeled off and tested separately to avoid substrate interference. The test results are shown in Table 3: Table 3 Spectral Reflectance of Thermal Reflection Films of Different Samples Experimental conclusion: The TiO2 / Ag / TiO2 three-layer structure enhances broadband reflection through the interference effect. Example 7 (50 / 120 / 50 nm) achieves the highest average reflectance of 94.1%, which is 7.7% higher than that of the single-layer Ag film (87.4%). The outer layer of TiO2 (50 nm) has a reflectance of 97.3% in the infrared band, verifying the technical effect of "reflectance ≥92%". Thermal imaging shows that the surface temperature of the coated area is 12°C lower than that of the uncoated area (under the condition of ΔT = 50K), and the heat radiation loss is reduced by 35%.

[0049] In summary, through material modification and process innovation, the present invention significantly improves the moisture resistance, heat insulation, and reliability of thermoelectric devices. All performance indicators are superior to the prior art and have industrial application value.

[0050] The above embodiments are only one of the preferred embodiments of the present invention and should not be used to limit the protection scope of the present invention. Any meaningless modifications or polishing made on the main design concept and spirit of the present invention, as long as the technical problems solved are still the same as those of the present invention, should be included in the protection scope of the present invention.

Claims

1. A heat-insulating and moisture-proof thermoelectric device, characterized in that: It includes a p-type Bi2Te3 thermocouple arm (1) with a moisture-proof layer (7) grown on its surface and connected to an electrode (5), and an n-type Bi2Te3 thermocouple arm (2); a cellulose-based aerogel layer (3) filled between adjacent p-type Bi2Te3 thermocouple arms (1) and n-type Bi2Te3 thermocouple arms (2); the porosity of the cellulose-based aerogel layer (3) is 96% - 99.5%, and the surface contact angle ≥ 150°; a heat-reflective film (4) covering the non-thermally conductive surfaces of the p-type Bi2Te3 thermocouple arm (1) and n-type Bi2Te3 thermocouple arm (2), and the reflectivity of the heat-reflective film (4) in the 400 - 3000 nm band ≥ 92%; the material of the moisture-proof layer (7) is a zinc-based zeolitic imidazolate framework material, with a thickness of 50 - 200 nm, and the porosity of the moisture-proof layer (7) is 5% - 10%, and the pore diameter ≤ 0.34 nm.

2. The heat insulation and moisture-proof thermoelectric device according to claim 1, characterized in that: The cellulose-based aerogel layer (3) is a hydrophobic modified nano-cellulose aerogel, which is graft-modified by cetyltrimethoxysilane, the loading amount of the modifier is 3 - 8 wt%, and Bi2Te3 quantum dots are uniformly dispersed in the hydrophobic modified nano-cellulose aerogel, the particle size of the quantum dots is 2 - 5 nm, and the doping amount is 0.5 - 1.5 wt%.

3. The heat insulation and moisture-proof thermoelectric device according to claim 2, wherein: The fibers of the hydrophobic modified nano-cellulose aerogel are vertically oriented, the orientation degree ≥ 85%, and the fiber diameter is 5 - 20 nm, and the aspect ratio is 100:1 to 500:

1.

4. The heat insulation and moisture-proof thermoelectric device according to claim 1, characterized in that: ZnO nanoparticles are doped in the moisture-proof layer (7), the doping amount is 2 - 5 wt%, and the size of the ZnO particles is 10 - 30 nm, which are uniformly distributed on the inner wall of the pore channels of the moisture-proof layer (7).

5. The heat insulation and moisture-proof thermoelectric device according to claim 1, characterized in that: The heat-reflective film (4) is a TiO2 / Ag / TiO2 three-layer composite structure, and the thickness of each layer is respectively: Inner layer TiO2: 30 - 50 nm, Ag layer: 80 - 120 nm, Outer layer TiO2: 30 - 50 nm.

6. The heat insulation and moisture-proof thermoelectric device according to claim 1, wherein: The joints of the p-type Bi2Te3 thermocouple arm (1) and n-type Bi2Te3 thermocouple arm (2) with the electrode (5) are covered with a conductive adhesive layer (6), the conductive adhesive layer is a composite material of an epoxy resin matrix dispersed with Bi2Te3 nanosheets, the thickness of the Bi2Te3 nanosheets is 10 - 50 nm, and the volume fraction of the Bi2Te3 nanosheets in the composite material is 40 - 60 vol%.

7. A preparation method of the heat insulation and moisture-proof thermoelectric device according to any one of claims 1-6, characterized in that: It includes the following steps: S1: Moisture-proof treatment of the thermocouple arm: Use liquid phase epitaxy to grow a moisture-proof layer (7) on the surfaces of the p-type Bi2Te3 thermocouple arm (1) and n-type Bi2Te3 thermocouple arm (2), the concentration of 2-methylimidazole in the reaction solution is 0.1 - 0.3 mol / L, the concentration of zinc nitrate is 0.05 - 0.15 mol / L, the reaction temperature is 25 - 40 °C, and the time is 2 - 4 hours; conduct in-situ doping of ZnO on the moisture-proof layer (7), immerse the p-type Bi2Te3 thermocouple arm (1) and n-type Bi2Te3 thermocouple arm (2) in a zinc acetate ethanol solution with a concentration of 0.1 - 0.5 wt%, and heat-treat at 80 °C for 1 - 2 hours; S2: Cellulose aerogel filling: Disperse nanocellulose in a choline chloride and urea eutectic solvent with a molar ratio of 1:2 at a concentration of 5 - 10 wt%. After adding Bi2Te3 quantum dots, extrude them directionally through a microfluidic chip with a channel width of 200 - 500 μm under an electric field strength of 50 - 100 V / cm. Form it by program-controlled freeze-drying combined with supercritical CO2 drying. The freezing gradient is -40°C → -20°C → 0°C, and the supercritical conditions are a temperature of 45°C and a pressure of 10 MPa. S3: Thermal reflection film encapsulation: Deposit a TiO2 / Ag / TiO2 composite film successively by ALD atomic layer deposition. The deposition temperature of TiO2 is 120 - 150°C, the deposition temperature of Ag is 80 - 100°C. The number of cycles for depositing TiO2 is 100 - 150 times, and the number of cycles for depositing Ag is 50 - 80 times. S4: Coating of conductive adhesive layer: Mix Bi2Te3 nanosheets and epoxy resin in proportion. In the composite material formed after mixing Bi2Te3 nanosheets and epoxy resin, the volume fraction of Bi2Te3 nanosheets is 40 - 60 vol%. After dispersing the mixed material by three-roll grinding, screen-print it at the electrode connection. The curing conditions are curing at 120°C for 30 minutes first, and then curing at 150°C for 15 minutes to obtain a thermoelectric device.

8. The preparation method according to claim 7, characterized in that: In step S1, after in-situ doping of ZnO on the moisture-proof layer (7), the moisture-proof porosity is reduced to 3% - 8%.

9. The preparation method according to claim 7, characterized in that: In step S2, the recycling of the choline chloride and urea eutectic solvent includes the following steps: after the supercritical CO2 drying is completed, the choline chloride and urea eutectic solvent remaining during the aerogel forming process is collected, 0.1-0.3 wt% TiO2 nanoparticles are added as a photocatalyst, and ultraviolet light with a wavelength of 365 nm and an intensity of 50 mW / cm 2 is used to degrade the residual cellulose fragments in the choline chloride and urea eutectic solvent, and the illumination time is 30-60 minutes; after filtration through a 0.22 μm filter membrane, it is recycled to step S2.

10. The preparation method according to claim 7, characterized in that: In step S3, when depositing the TiO2 layer by ALD, titanium isopropoxide and water are used as precursors. The pulse time of titanium isopropoxide is 0.1 - 0.3 s, the pulse time of water is 0.05 - 0.1 s, and the purge time is 5 - 10 s.

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