Flexible polymer composite thermoelectric material with multilevel structure and preparation method thereof

Abstract

The invention relates to the technical field of nano composite materials, and discloses a flexible polymer composite thermoelectric material with a multilevel structure and a preparation method thereof, the material is a flexible self-supporting film, and comprises an MOF matrix, a single-walled carbon nanotube and a conductive polymer coating layer; the material has a hierarchical pore structure of micropores, mesopores and macropores. A mesoporous / macroporous structure is regulated and controlled through a PS microsphere template, a micropore-mesoporous-macroporous hierarchical pore structure is constructed in combination with Cu3 (BTC) 2 intrinsic micropores, the pore size, the pore size distribution and the porosity are systematically regulated, the scattering effect on phonons with different wavelengths is enhanced, and accurate regulation and control of the thermal conductivity of the material are realized. According to the design, the limitation that the thermal conductivity of an existing MOFs thermoelectric material depends on an inherent structure is broken through, the problem that the thermal conductivity lacks an active regulation and control mechanism is solved, a basis is provided for subsequent optimization of the conductivity and the Seebeck coefficient, and implementation of a high power factor and a ZT value is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanocomposites, in particular to a flexible polymer composite thermoelectric material with a multi-level structure and a preparation method thereof. BACKGROUND

[0002] Thermoelectric materials are a kind of functional materials that can realize direct conversion between heat and electricity, and their performance is evaluated by ZT value. Ideal thermoelectric materials need to have high Seebeck coefficient, high electrical conductivity and low thermal conductivity at the same time to obtain high ZT value, promote waste heat recovery, thermoelectric generation and other practical applications. Metal organic frameworks (MOFs) have intrinsic microporous structure and low intrinsic thermal conductivity, and have become a research hotspot in the field of polymer composite thermoelectric materials. Constructing polymer / MOF composite thermoelectric materials has become an important direction to improve thermoelectric performance.

[0003] In the prior art, researchers often use the intrinsic microporous structure of MOFs to achieve low thermal conductivity, and construct conductive pathways by introducing electrically active guest molecules (such as conductive polymers) into the pores of MOFs to improve the electrical conductivity of the material. In the preparation process, solution mixing method is often used to mix MOFs and conductive polymers to form a composite material. Some studies adjust the ratio of metal salt to organic ligand during the synthesis of MOFs to control the intrinsic microporous structure, trying to optimize the thermal conductivity, and at the same time, by changing the amount of conductive guest molecules, the electrical conductivity of the material is adjusted.

[0004] The most critical deficiency in the prior art is that it is difficult to simultaneously optimize the Seebeck coefficient, electrical conductivity and thermal conductivity of polymer / MOF composite thermoelectric materials to obtain high ZT value. The three parameters are coupled with each other, and increasing the electrical conductivity (such as increasing the amount of conductive guest molecules) easily leads to the increase of carrier concentration, which in turn reduces the Seebeck coefficient. The low thermal conductivity of MOFs only depends on the intrinsic microporous structure, and lacks targeted control means, which cannot further reduce to match the optimization of electrical conductivity and Seebeck coefficient, ultimately leading to the difficulty of meeting the practical application requirements of the comprehensive thermoelectric performance of the material. In view of this, we propose a flexible polymer composite thermoelectric material with a multi-level structure and a preparation method thereof. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a flexible polymer composite thermoelectric material with a multi-level structure and a preparation method thereof, which solves the problem that the prior art cannot simultaneously optimize the Seebeck coefficient, electrical conductivity and thermal conductivity of polymer / MOF composite thermoelectric materials to obtain high ZT value.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a flexible polymer composite thermoelectric material with a multi-level structure and its preparation method, wherein the material is a flexible self-supporting thin film comprising a MOF matrix, single-walled carbon nanotubes, and a conductive polymer coating layer; the material has a multi-level porous structure of micropores, mesopores, and macropores; and the thermoelectric properties of the material satisfy the following: Seebeck coefficient ≥ 50. Electrical conductivity ≥750 S· Thermal conductivity ≤1.2 • ZT value ≥ 0.06; the MOF matrix is ​​Cu3(BTC)2, and the conductive polymer coating layer is polypyrrole (PPy).

[0007] Preferably, the amount of single-walled carbon nanotubes used is The PPy coating layer is formed on the surface of a Cu3(BTC)2 / single-walled carbon nanotube film via in-situ gas-phase oxidative polymerization. In the hierarchical porous structure, the micropores are intrinsic micropores of Cu3(BTC)2, while the mesopores and macropores are formed through polystyrene (PS) microsphere templates. The particle size of the polystyrene microspheres is [missing information]. The amount of PS microspheres used is .

[0008] A method for preparing a flexible polymer composite thermoelectric material with a multi-level structure includes the following steps: S1: To prepare a copper-based hydroxide nanowire suspension, a copper salt aqueous solution and an organic base aqueous solution were mixed and allowed to stand at room temperature for a preset time to obtain the copper-based hydroxide nanowire suspension. S2: Prepare a copper-based hydroxide composite film containing template and carbon nanotubes. Add PS microsphere template and SWCNT to the copper-based hydroxide nanowire suspension obtained in S1, mix evenly and filter onto a porous substrate to form a copper-based hydroxide composite film containing template and carbon nanotubes. S3: Prepare MOF / carbon nanotube hierarchical porous films. Peel the copper-based hydroxide composite film containing template and carbon nanotubes obtained in S2 from the porous substrate, immerse it in an organic ligand solution for a preset time, and then dissolve the PS microsphere template with a solvent to obtain MOF / carbon nanotube films with hierarchical porous structures. S4: In-situ gas-phase oxidative polymerization forms a conductive polymer coating layer. The MOF / carbon nanotube hierarchical porous film obtained in S3 is immersed in a mixed solution of oxidant and dispersant. After drying, it is placed in a sealed container containing conductive polymer monomers and reacted for a preset time under vacuum and low temperature to obtain a composite film coated with conductive polymer. S5: Annealing treatment regulates charge carrier performance. The composite film coated with conductive polymer obtained in S4 is annealed at a preset temperature for a preset time to obtain a flexible polymer composite thermoelectric material with a multi-level structure.

[0009] Preferably, in step S1, the copper salt is copper nitrate, the organic base is ethanolamine; the concentration of the copper nitrate aqueous solution is 2 mM, the concentration of the ethanolamine aqueous solution is 0.7 mM; the preset time for standing at room temperature is 24 hours; and the copper-based hydroxide is copper hydroxide.

[0010] Preferably, in step S2, the particle size of the PS microsphere template is [missing information]. The amount of PS microsphere template used is The dosage of SWCNT is The porous substrate is a porous polycarbonate (PC) substrate with a pore size of 200 nm; the vacuum degree of the filtration process is... .

[0011] Preferably, in step S3, the organic ligand is trimesic acid, the organic ligand solution is an ethanol-water solution of trimesic acid with a concentration of 10 mM, and the volume ratio of ethanol to water is 1:1; the preset soaking time is 1 hour; the solvent for dissolving the PS microsphere template is tetrahydrofuran; and the MOF / carbon nanotube film is a Cu3(BTC)2 / SWCNT film.

[0012] Preferably, in step S4, the oxidant is ferric chloride, and the dispersant is sodium dodecyl sulfonate; the concentration of ferric chloride is... The concentration of SDS is The conductive polymer monomer is pyrrole (Py), which is purified by rotary evaporation before use to remove polymerization inhibitors; the low-temperature environment is an ice bath environment with a temperature of The vacuum level of the vacuum environment is: The preset time for the reaction is... Hour.

[0013] Preferably, in step S4, the concentration of ferric chloride is... The temperature for the rotary evaporation purification is... The temperature of the ice bath environment is The preset time for the reaction is... Hour.

[0014] Preferably, in step S5, the preset annealing temperature is... The preset annealing time is The annealing atmosphere is air or an inert gas; after annealing, it is naturally cooled to room temperature to obtain a flexible, self-supporting composite thermoelectric material.

[0015] Preferably, in step S5, the preset annealing temperature is... The preset annealing time is Hours; the inert gas is nitrogen or argon; during annealing, the heating rate is... The cooling rate is .

[0016] This invention provides a flexible polymer composite thermoelectric material with a multi-level structure and its preparation method. It has the following beneficial effects: 1. This invention utilizes PS microsphere templates to control the mesoporous / macroporous structure, combining it with the intrinsic micropores of Cu3(BTC)2 to construct a multi-level pore structure of micropores-mesopores-macropores. The system adjusts pore size, pore size distribution, and porosity to enhance the scattering of phonons of different wavelengths, achieving precise control of the material's thermal conductivity. This design overcomes the limitation of existing MOF thermoelectric materials where thermal conductivity depends on the inherent structure, solving the problem of the lack of an active control mechanism for thermal conductivity. It provides a foundation for subsequent optimization of electrical conductivity and Seebeck coefficient, ensuring a core prerequisite for achieving high ZT values.

[0017] 2. This invention forms a PPy coating layer on the surface of a hierarchical porous MOF / SWCNT film through in-situ vapor-phase oxidation polymerization, achieving uniform low PPy loading and avoiding pore blockage and the introduction of "ineffective" guest molecules. At the same time, it coordinates the amount of SWCNT to control the conductive network, the FeCl3 concentration to adjust the PPy doping amount, and annealing to optimize the PPy crystallinity, precisely controlling the carrier mobility and carrier concentration. This improves conductivity while suppressing the decrease of Seebeck coefficient, effectively increasing the σ / κ ratio and solving the key problem of the difficulty in coordinating conductivity and Seebeck coefficient.

[0018] 3. This invention achieves decoupled control of thermal conductivity, electrical conductivity, and Seebeck coefficient through a multi-level porous structure construction, in-situ vapor-phase polymerization coating, and annealing regulation, thus preparing a flexible self-supporting composite thermoelectric thin film. This material possesses both high thermoelectric performance (ZT≥0.06) and excellent flexibility (electrical conductivity change rate after bending ≤4.5%). Flexible thermoelectric devices (10 thermoelectric legs connected in series) prepared based on this material achieve the required output power at a temperature difference of 30K, solving the problems of high brittleness and difficult device fabrication of traditional materials, and providing technical support for applications in the field of flexible thermoelectrics. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the preparation method of this flexible polymer composite thermoelectric material with a multi-level structure. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example: This invention provides a flexible polymer composite thermoelectric material with a multi-level structure. The material is a flexible self-supporting thin film comprising a MOF matrix, single-walled carbon nanotubes, and a conductive polymer coating layer. The material has a multi-level porous structure including micropores, mesopores, and macropores. The thermoelectric properties of the material satisfy the following condition: Seebeck coefficient ≥ 50. Electrical conductivity ≥750 S· Thermal conductivity ≤1.2W • ZT value ≥ 0.06; the MOF matrix is ​​Cu3(BTC)2, and the conductive polymer coating layer is polypyrrole (PPy).

[0022] The amount of single-walled carbon nanotubes used is The PPy coating layer is formed on the surface of a Cu3(BTC)2 / single-walled carbon nanotube film via in-situ gas-phase oxidative polymerization. In the hierarchical porous structure, the micropores are intrinsic micropores of Cu3(BTC)2, while the mesopores and macropores are formed through polystyrene (PS) microsphere templates. The particle size of the polystyrene microspheres is [missing information]. The amount of PS microspheres used is .

[0023] Please see the appendix Figure 1 A method for preparing a flexible polymer composite thermoelectric material with a multi-level structure includes the following steps: Example 1: Basic parameter set (parameters take the median value of the weight range) S1: Preparation of Cu(OH)2 nanowire suspension: 2mM copper nitrate aqueous solution and 0.7mM ethanolamine aqueous solution were mixed, magnetically stirred at 500rpm for 10 minutes, and allowed to stand at room temperature for 24 hours to obtain Cu(OH)2 nanowire suspension; S2: Preparation of PS / Cu(OH)2 / SWCNT composite film: PS microspheres (particle size 50nm, concentration 0.5mM) and SWCNT (10wt%) were added to the above suspension. After ultrasonic dispersion for 30 minutes, the mixture was magnetically stirred for 1 hour. The mixture was then filtered under a vacuum of 0.1MPa onto a porous polycarbonate substrate with a pore size of 200nm to form a PS / Cu(OH)2 / SWCNT composite film with a thickness of about 50μm. S3: Preparation of Cu3(BTC)2 / SWCNT hierarchical porous film: The film obtained in S2 was peeled off from the porous polycarbonate substrate and immersed in 10 mM pyromellitic acid in an ethanol-water solution (ethanol to water volume ratio 1:1) for 1 hour. After being taken out, it was soaked in tetrahydrofuran for 2 hours to dissolve the PS microspheres and dried under vacuum at 60°C for 2 hours to obtain Cu3(BTC)2 / SWCNT hierarchical porous film; S4: In-situ vapor-phase oxidative polymerization coating of PPy: The film obtained in S3 was immersed in a mixed solution of 1M ferric chloride and 0.03M sodium dodecyl sulfonate for 30 minutes and dried under vacuum at 40°C for 1 hour; it was then transferred to a sealed glass container, and 5 mL of pyrrole monomer purified by rotary evaporation at 70°C was added to the bottom of the container. The container was placed in an ice bath environment at 0-5°C and vacuumed to 0.095 MPa for 3 hours; after the reaction, the film was washed three times with deionized water and dried under vacuum at 60°C for 2 hours to obtain the PPy-coated composite film; S5: Annealing treatment: The composite film obtained in S4 is annealed in air at 180°C for 3 hours and then naturally cooled to room temperature to obtain a flexible polymer composite thermoelectric material with a multi-level structure.

[0024] Example 2: The variable is the particle size of PS microspheres (the lower limit of the weight is used, and the rest is the same as in Example 1). Compared with Example 1, only the particle size of PS microspheres in step S2 was adjusted to 20 nm (the other parameters: PS concentration 0.5 mM, SWCNT dosage 10 wt%, ferric chloride concentration 1 M, annealing temperature 180 °C, etc. are the same as in Example 1). The specific steps are as follows: S1~S1: Same as in Example 1, to obtain Cu(OH)2 nanowire suspension; S2: PS microspheres (particle size 20nm, concentration 0.5mM) and SWCNTs (dosage 10wt%) were added to the suspension. The subsequent ultrasonic dispersion, stirring and filtration operations were the same as in Example 1 to form a PS / Cu(OH)2 / SWCNT composite film. S3~S5: exactly the same as in Example 1, finally obtaining a flexible polymer composite thermoelectric material with a multi-level structure.

[0025] Example 3: The variable is the usage of SWCNT (weighting should be based on the upper limit, otherwise the same as in Example 1). Compared with Example 1, only the amount of SWCNT in step S2 was adjusted to 20wt% (the other parameters: PS microsphere particle size 50nm, concentration 0.5mM, ferric chloride concentration 1M, annealing temperature 180℃, etc. are the same as in Example 1). The specific steps are as follows: S1: Same as in Example 1, a Cu(OH)2 nanowire suspension was obtained; S2: PS microspheres (50 nm in diameter, 0.5 mM in concentration) and SWCNTs (20 wt%) were added to the suspension. The subsequent ultrasonic dispersion, stirring and filtration were the same as in Example 1 to form a PS / Cu(OH)2 / SWCNT composite film. S3~S5: exactly the same as in Example 1, finally obtaining a flexible polymer composite thermoelectric material with a multi-level structure.

[0026] Example 4: The variables are ferric chloride concentration and annealing temperature (the upper limit of the weights is used, and the rest is the same as in Example 1). Compared with Example 1, only the ferric chloride concentration in step S4 was adjusted to 2M and the annealing temperature in step S5 was adjusted to 220℃ (the other parameters: PS microsphere particle size 50nm, SWCNT dosage 10wt%, annealing time 3 hours, etc. are the same as in Example 1). The specific steps are as follows: S1~S3: Completely the same as in Example 1, to obtain Cu3(BTC)2 / SWCNT hierarchical porous films; S4: The film obtained in S3 was immersed in a mixed solution of 2M ferric chloride and 0.03M sodium dodecyl sulfonate for 30 minutes. The subsequent drying and gas-phase polymerization operations were the same as in Example 1 to obtain a composite film coated with PPy. S5: The composite film obtained in S4 is annealed at 220°C in air for 3 hours and then naturally cooled to room temperature to finally obtain a flexible polymer composite thermoelectric material with a multi-level structure. Comparative Example 1: Lack of hierarchical porous structure (no PS microsphere template, unable to form mesopores / macropores) S1: Preparation of Cu(OH)2 nanowire suspension: exactly the same as in Example 1, to obtain Cu(OH)2 nanowire suspension; S2: Preparation of Cu(OH)2 / SWCNT composite film: Add only SWCNT (10wt%, without adding PS microspheres) to the suspension obtained in S1, disperse ultrasonically for 30 minutes, stir magnetically for 1 hour, filter under 0.1MPa vacuum onto a porous polycarbonate substrate with a pore size of 200nm to form Cu(OH)2 / SWCNT composite film; S3: Preparation of Cu3(BTC)2 / SWCNT film: The film obtained in S2 was peeled off from the porous polycarbonate substrate and immersed in an ethanol-water solution of 10 mM trimesic acid (ethanol to water volume ratio 1:1) for 1 hour without soaking in tetrahydrofuran (no PS microspheres are soluble). It was then vacuum dried at 60°C for 2 hours to obtain Cu3(BTC)2 / SWCNT film containing only intrinsic micropores of Cu3(BTC)2. S4~S5: exactly the same as in Example 1 (ferric chloride concentration 1M, annealing temperature 180℃), finally obtaining a Cu3(BTC)2 / SWCNT / PPy composite film without mesopores / macropores.

[0027] Comparative Example 2: Alternative in-situ gas-phase polymerization (using traditional solution mixing polymerization, which leads to PPy agglomeration) S1~S3: Completely the same as in Example 1, to obtain Cu3(BTC)2 / SWCNT hierarchical porous films; S4: Solution-coated PPy by mixed polymerization: Prepare a mixed aqueous solution containing 1M ferric chloride, 0.03M sodium dodecyl sulfonate and 5mL pyrrole monomer. Immerse the film obtained in S3 in this mixed solution and stir magnetically at room temperature for 3 hours (replacing gas-phase polymerization). After the reaction, wash the film three times with deionized water and dry it under vacuum at 60℃ for 2 hours to obtain a PPy-coated composite film (PPy is prone to agglomeration in the pores). S5: Completely the same as in Example 1 (annealing at 180°C for 3 hours), finally obtaining Cu3(BTC)2 / SWCNT / PPy composite film prepared by solution polymerization.

[0028] Comparative Example 3: Missing annealing step (unable to optimize PPy crystallinity and carrier mobility) S1~S4: Completely the same as in Example 1 (PS microspheres with a particle size of 50nm, SWCNT dosage of 10wt%, and ferric chloride concentration of 1M), to obtain a composite film coated with PPy; The S5 annealing step is omitted: the PPy coated composite film obtained in S4 after cleaning and drying is directly used as the final product without annealing at 180℃, and finally an unannealed Cu3(BTC)2 / SWCNT / PPy composite film is obtained.

[0029] Comparative Example 4: The amount of PS microspheres used exceeded the required range (concentration 2mM, exceeding the range of 0.1-1mM, resulting in abnormal pore structure). S1: The same as in Example 1, a Cu(OH)2 nanowire suspension was obtained; S2: Preparation of high PS content composite film: PS microspheres (particle size 50nm, concentration 2mM, beyond the essential range) and SWCNT (10wt%) were added to the suspension obtained in S1. After ultrasonic dispersion for 30 minutes, the mixture was magnetically stirred for 1 hour. The mixture was then filtered under a vacuum of 0.1MPa onto a porous polycarbonate substrate with a pore size of 200nm to form a PS / Cu(OH)2 / SWCNT composite film with excess PS. S3: Preparation of hierarchical porous films: The film obtained in S2 was peeled off from the porous polycarbonate substrate, immersed in 10 mM pyromellitic acid in an ethanol-water solution (ethanol to water volume ratio 1:1) for 1 hour, immersed in tetrahydrofuran for 4 hours (if PS is in excess, the dissolution time needs to be extended), and vacuum dried at 60°C for 2 hours to obtain Cu3(BTC)2 / SWCNT hierarchical porous films with dense pore structure. S4~S5: exactly the same as in Example 1, finally obtaining Cu3(BTC)2 / SWCNT / PPy composite film with PS dosage exceeding the range.

[0030] Experimental objective: By testing key parameters in four sets of examples (controlling a single variable) and four sets of comparative examples (missing / deviating from the key features of the invention), the influence of variables such as "PS microsphere particle size, SWCNT dosage, FeCl3 concentration-annealing temperature" on the thermoelectric properties of the material in this invention was verified.

[0031] Experimental subjects Example groups: Example 1 (basic parameters: PS particle size 50nm, SWCNT 10wt%, FeCl3 1M, annealing 180℃), Example 2 (variable: PS particle size 20nm), Example 3 (variable: SWCNT 20wt%), Example 4 (variable: FeCl3 2M + annealing 220℃); Comparative examples: Comparative example 1 (missing PS template, no mesopores / macropores), Comparative example 2 (solution mixing polymerization instead of in-situ gas phase polymerization), Comparative example 3 (missing annealing step), Comparative example 4 (PS concentration 2 mM, exceeding the range of 0.1-1 mM). Experimental protocol (a) Testing of core thermoelectric performance parameters (Seebeck coefficient, electrical conductivity, thermal conductivity, ZT value) 1. Testing Principles Seebeck coefficient (S): Characterizes the thermoelectric power generation capability of a material, measured in μV·K. -1 The test is based on the ratio of the potential difference generated at both ends of the material under temperature difference to the temperature difference; Electrical conductivity (σ): Characterizes the charge transport capability of a material, measured in S·cm. -1 The test is based on Ohm's law and is performed directly using the four-probe method. Thermal conductivity (κ): Characterizes the thermal conductivity of a material, measured in W·m. -1 ・K -1 The test is based on the laser flare method, and calculations are made by measuring the thermal diffusivity, density, and specific heat capacity. α is the thermal diffusivity, ρ is the material density, and c is the thermal diffusivity. p (specific heat capacity); ZT value: A comprehensive evaluation of thermoelectric performance, calculated using the formula: (T is the absolute temperature, taken as 300K, i.e., room temperature).

[0032] 2. Test equipment and conditions Equipment: Thermoelectric performance testing system (model LSR-3), four-probe resistance tester (model RTS-8), laser flare thermal conductivity meter (model LFA-467), electronic density meter (model MD-300S), differential scanning calorimeter (model DSC-60). Environmental conditions: Room temperature (300K), relative humidity 40% 60%, no vibration interference; Sample pretreatment: All samples were cut into standard specimens of 10mm×10mm×50μm (length×width×thickness), and the surface was wiped clean with anhydrous ethanol to ensure that no impurities adhered.

[0033] 3. Testing Procedures Seebeck coefficient test: The sample was fixed on the sample stage of the thermoelectric performance testing system. The hot end temperature was set to 310K and the cold end temperature to 300K (temperature difference 10K). After the temperature stabilized, the potential difference ΔV between the two ends was recorded. According to the formula Calculate the Seebeck coefficient, repeat the test 3 times, and take the average value; Conductivity test: Press the probes of the four-probe tester vertically onto the sample surface (probe spacing 1 mm), apply a constant current (10 mA), and record the voltage drop ΔU between the probes; According to the formula (I is the current, d is the sample thickness) Calculate the conductivity, repeat the test 3 times, and take the average value; Thermal conductivity test: The sample density ρ was measured using an electronic densitometer, and the sample specific heat capacity c was measured using a differential scanning calorimeter. p (Test range 298) 302K); The sample was placed in a laser flash thermal conductivity meter, a laser pulse (energy 5J) was emitted, the temperature change curve of the back side of the sample over time was recorded, and the thermal diffusivity α was calculated. According to the formula Calculate the thermal conductivity, repeat the test 3 times, and take the average value; Power factor ( PF Calculation: Substitute the average values ​​of S and σ above into the formula. The power factor is obtained.

[0034] ZT value calculation: Substitute the average values ​​of S, σ, and κ above, and T=300K into the formula. The ZT value is obtained.

[0035] (ii) Flexibility test (rate of change of conductivity after bending) 1. Testing Principles Based on the application requirements of flexible materials, the actual processing / use scenarios are simulated by repeated bending, and the flexibility is evaluated by the rate of change of electrical conductivity before and after bending (the smaller the rate of change, the better the flexibility).

[0036] 2. Test equipment and conditions Equipment: Four-probe resistance tester (same as before), custom bending fixture (can fix the bending radius to 5mm); Sample specifications: 10mm×50mm×50μm (length×width×thickness), matching the dimensions of the device's thermoelectric legs; Bending conditions: bending radius 5mm, bending angle 180° (bending from the plane until the two ends coincide), single bending time 10s, 100 cycles in total.

[0037] 3. Testing Procedures Test the initial conductivity σ0 (test method is the same as before); Fix the sample to the bending fixture and bend it repeatedly 100 times according to the set conditions; Test the conductivity σ1 immediately after bending; According to the formula Calculate the rate of change of conductivity η, repeat the test 3 times, and take the average value.

[0038] (III) Output power test of flexible thermoelectric devices 1. Testing Principles The output power was tested at a temperature difference of 30K to verify the actual application performance of the material. The higher the output power, the stronger the application value of the device.

[0039] 2. Test equipment and conditions Equipment: Temperature difference controller (model TC-1000), precision power meter (model PM-200), silver paste (conductive electrode), polyimide substrate (encapsulation); Device fabrication: Each sample was cut into 1cm×5cm×50μm thermoelectric legs (10 pieces / device), and the thermoelectric legs were connected in series and soldered to a polyimide substrate with silver paste to form a flexible device; Test conditions: hot end temperature 330K, cold end temperature 300K (temperature difference 30K), load resistance range 0~10kΩ (adjusted to maximum power point).

[0040] 3. Testing Procedures Fix the device to the temperature difference controller, set the hot end to 330K and the cold end to 300K, and wait for the temperature to stabilize for 30 minutes; Connect the precision power meter to the device, adjust the load resistance, and record the output voltage U and current I under different resistances; According to the formula Calculate the output power and find the maximum power value. Repeat the test 3 times and take the average value. Table of Key Parameter Test Results for Multi-Level Flexible Polymer Composite Thermoelectric Materials

[0041] Experimental conclusions The core parameter range set in this invention (PS microsphere particle size 20–200 nm, SWCNT dosage 1–20 wt%, FeCl3 concentration 0.1–2 M, annealing temperature 120–220 °C) is reasonable and effective. Within this range, stable optimization of the composite thermoelectric material's performance can be achieved through single-variable control. Test results from Examples 1–4 show that all samples meet the Seebeck coefficient ≥ 50 μV·K. -1 Electrical conductivity ≥750 S·cm -1 Thermal conductivity ≤ 1.2 W·m -1 ・K -1 The core performance indicators, such as ZT value ≥ 0.06, conductivity change rate ≤ 4.5% after bending, and device output power ≥ 14.8 μW, indicate that the material has both excellent thermoelectric properties and flexible processing performance within this parameter range.

[0042] The effect of single-variable regulation on material properties is clearly directional: reducing the particle size of PS microspheres (20 nm) can enhance phonon scattering and reduce thermal conductivity to 0.9 W·m. -1 ・K -1 Increasing the amount of SWCNT (20wt%) strengthens the conductive network, increasing the conductivity to 820.5 S·cm. -1 Furthermore, because the increase in carrier concentration is controllable, the Seebeck coefficient only decreases slightly by 1.7 μV·K. -1 When the FeCl3 concentration (2M) and annealing temperature (220℃) are increased to their upper limits, the carrier mobility and concentration can be synergistically improved by optimizing the PPy doping amount and crystallinity, thereby increasing the conductivity to 810.3 S·cm. -1 Furthermore, the decrease in the Seebeck coefficient was controlled within 2.3 μV·K. -1 Ultimately, the ZT value of all embodiments remained stable at 0.07, achieving a synergistic balance of thermal conductivity, electrical conductivity, and Seebeck coefficient.

[0043] "Hierarchical porous structure (PS microsphere template), in-situ vapor-phase polymerization, annealing treatment, and PS microsphere dosage of 0.1–1 mM" are key technical characteristics that ensure the excellent performance of composite thermoelectric materials. The absence or deviation of any of these characteristics will lead to a significant deterioration in material performance: without the PS microsphere template, the thermal conductivity of the material soars to 1.8 W·m -1 ・K -1 The ZT value dropped to 0.04, and the device output power was halved; when conventional solution-mixed polymerization was used instead of in-situ gas-phase polymerization, the Seebeck coefficient of the material dropped to 39.5 μV·K. -1 The conductivity decreased to 645.3 S·cm -1 The ZT value is only 0.03; when the annealing step is omitted, the conductivity drops to 698.7 S·cm. -1 The Seebeck coefficient dropped to 44.8 μV·K. -1 The ZT value decreased to 0.04; when the amount of PS microspheres exceeded the range of 0.1–1 mM (2 mM), the rate of change of electrical conductivity after bending increased to 14.5%, and the thermal conductivity increased to 1.6 W·m. -1 ・K -1 The ZT value dropped to 0.03, and both the flexibility and the device output power decreased significantly.

[0044] In summary, by employing a synergistic technical approach of "constructing a multi-level porous structure using PS microsphere templates + achieving uniform PPy coating through in-situ vapor-phase polymerization + optimizing carrier performance through annealing," and combining this with precise control of core parameters within a set range, composite thermoelectric materials with both high thermoelectric performance (ZT≥0.06) and good flexibility (conductivity change rate after bending ≤4.5%) can be stably prepared. Furthermore, flexible thermoelectric devices based on this material have an output power ≥14.8μW at a temperature difference of 30K, demonstrating potential for practical applications.

[0045] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A flexible polymer composite thermoelectric material with a multi-level structure, characterized in that, The material is a flexible, self-supporting thin film comprising a MOF matrix, single-walled carbon nanotubes, and a conductive polymer coating layer; the material possesses a hierarchical porous structure including micropores, mesopores, and macropores; the thermoelectric properties of the material satisfy the following: Seebeck coefficient ≥ 50. Electrical conductivity ≥750 S· Thermal conductivity ≤1.2W • ZT value ≥ 0.06; the MOF matrix is ​​Cu3(BTC)2, and the conductive polymer coating layer is polypyrrole (PPy).

2. The flexible polymer composite thermoelectric material with a multi-level structure according to claim 1, characterized in that, The amount of single-walled carbon nanotubes used is The PPy coating layer is formed on the surface of a Cu3(BTC)2 / single-walled carbon nanotube film via in-situ gas-phase oxidative polymerization. In the hierarchical porous structure, the micropores are intrinsic micropores of Cu3(BTC)2, while the mesopores and macropores are formed through polystyrene (PS) microsphere templates. The particle size of the polystyrene microspheres is [missing information]. The amount of PS microspheres used is .

3. The method for preparing the flexible polymer composite thermoelectric material with a multi-level structure according to claim 1, characterized in that, Includes the following steps: S1: To prepare a copper-based hydroxide nanowire suspension, a copper salt aqueous solution and an organic base aqueous solution were mixed and allowed to stand at room temperature for a preset time to obtain the copper-based hydroxide nanowire suspension. S2: Prepare a copper-based hydroxide composite film containing template and carbon nanotubes. Add PS microsphere template and SWCNT to the copper-based hydroxide nanowire suspension obtained in S1, mix evenly and filter onto a porous substrate to form a copper-based hydroxide composite film containing template and carbon nanotubes. S3: Prepare MOF / carbon nanotube hierarchical porous films. Peel the copper-based hydroxide composite film containing template and carbon nanotubes obtained in S2 from the porous substrate, immerse it in an organic ligand solution for a preset time, and then dissolve the PS microsphere template with a solvent to obtain MOF / carbon nanotube films with hierarchical porous structures. S4: In-situ gas-phase oxidative polymerization forms a conductive polymer coating layer. The MOF / carbon nanotube hierarchical porous film obtained in S3 is immersed in a mixed solution of oxidant and dispersant. After drying, it is placed in a sealed container containing conductive polymer monomers and reacted for a preset time under vacuum and low temperature to obtain a composite film coated with conductive polymer. S5: Annealing treatment regulates charge carrier performance. The composite film coated with conductive polymer obtained in S4 is annealed at a preset temperature for a preset time to obtain a flexible polymer composite thermoelectric material with a multi-level structure.

4. The method for preparing a flexible polymer composite thermoelectric material with a multi-level structure according to claim 1, characterized in that, In step S1, the copper salt is copper nitrate, the organic base is ethanolamine, the concentration of the copper nitrate aqueous solution is 2 mM, the concentration of the ethanolamine aqueous solution is 0.7 mM, the preset time for standing at room temperature is 24 hours, and the copper-based hydroxide is copper hydroxide.

5. The method for preparing a flexible polymer composite thermoelectric material with a multi-level structure according to claim 1, characterized in that, In S2, the particle size of the PS microsphere template is... The amount of PS microsphere template used is The dosage of SWCNT is ; The porous substrate is a porous polycarbonate (PC) substrate with a pore size of 200 nm; the vacuum degree of the filtration process is... .

6. The method for preparing a flexible polymer composite thermoelectric material with a multi-level structure according to claim 1, characterized in that, In step S3, the organic ligand is trimesic acid, the organic ligand solution is an ethanol-water solution of trimesic acid with a concentration of 10 mM, and the volume ratio of ethanol to water is 1:1; the preset soaking time is 1 hour; the solvent for dissolving the PS microsphere template is tetrahydrofuran; and the MOF / carbon nanotube film is a Cu3(BTC)2 / SWCNT film.

7. The method for preparing a flexible polymer composite thermoelectric material with a multi-level structure according to claim 1, characterized in that, In step S4, the oxidant is ferric chloride, and the dispersant is sodium dodecyl sulfonate; the concentration of ferric chloride is... The concentration of SDS is The conductive polymer monomer is pyrrole (Py), which is purified by rotary evaporation before use to remove polymerization inhibitors; the low-temperature environment is an ice bath environment with a temperature of The vacuum level of the vacuum environment is: The preset time for the reaction is... Hour.

8. The method for preparing a flexible polymer composite thermoelectric material with a multi-level structure according to claim 7, characterized in that, In S4, the concentration of ferric chloride is: The temperature for the rotary evaporation purification is... The temperature of the ice bath environment is The preset time for the reaction is... Hour.

9. The method for preparing a flexible polymer composite thermoelectric material with a multi-level structure according to claim 3, characterized in that, In step S5, the preset annealing temperature is... The preset annealing time is The annealing atmosphere is air or an inert gas; after annealing, it is naturally cooled to room temperature to obtain a flexible, self-supporting composite thermoelectric material.

10. The method for preparing a flexible polymer composite thermoelectric material with a multi-level structure according to claim 9, characterized in that, In step S5, the preset annealing temperature is... The preset annealing time is Hours; the inert gas is nitrogen or argon; during annealing, the heating rate is... The cooling rate is .

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