A ductile n-type MOF-based high-performance thermoelectric foam and preparation method and application thereof

Abstract

The application relates to the field of MOF-based flexible thermoelectric materials, and discloses an n-type MOF-based high-performance thermoelectric foam with ductility and a preparation method and application thereof, which comprises the following steps: dissolving 1,3,5-benzene tricarboxylic acid and copper acetate in a mixed solution of N,N-dimethylformamide, ethanol and deionized water to prepare a precursor solution; immersing foamed nickel in the precursor solution for hydrothermal reaction, then taking out the foamed nickel material with uniformly grown nickel-copper MOF on the surface after cleaning and drying; and immersing the foamed nickel material in a mixed solution of polyaniline and DMF to graft a conductive polymer on the surface and channels of the nickel-copper MOF, so as to obtain a high-performance thermoelectric foam with ductility. The n-type MOF-based thermoelectric foam prepared by the application has excellent ductility and thermoelectric performance, and has the characteristics of metal plasticity, high-efficiency thermoelectric performance and sensitivity to temperature change. The excellent thermoelectric performance and wide application scenarios of the n-type MOF-based thermoelectric foam are far superior to the n-type MOF-based thermoelectric materials reported at present.

Description

Technical Field

[0001] This invention relates to the field of MOF-based flexible thermoelectric materials, specifically to a stretchable n-type MOF-based high-performance thermoelectric foam, its preparation method, and its applications. Background Technology

[0002] In the era of advancements in smart electronics, the development of self-powered flexible and wearable electronic products is inevitable. The human body, as a stable heat source, constantly radiates heat energy. The efficient collection of this waste heat could generate significant economic benefits. Based on the Seebeck effect, thermoelectric materials can effectively convert waste heat from the human body or other heat sources into electrical energy, potentially providing a new strategy for the development of self-powered electronic products. Currently, the most representative thermoelectric materials are inorganic semiconductor materials; however, the inherent rigid structure and toxicity of most inorganic thermoelectric materials make them difficult to meet the requirements of human safety and practical wearable applications. Therefore, to develop safe and reliable wearable thermoelectric devices, current research mainly focuses on the development of novel materials and the composite research of organic and inorganic thermoelectric materials.

[0003] Metal-organic framework (MOF) materials have shown great potential in the thermoelectric field due to their high porosity and tunable structure. Although most MOF materials are electrical insulators due to the low conjugation and poor orbital overlap between organic ligands and metal ions, the precise selection and arrangement of the metal center and organic ligands can effectively tune thermal and electrical properties. The combination of conjugated polymers with metal-organic coordination polymers enables them to achieve the electrical and thermal conductivity required for thermoelectric conversion. However, current research on MOF thermoelectric materials mainly focuses on p-type materials, and most MOF-based thermoelectric materials exist in powder form, with limited research reports on n-type flexible MOF composite thermoelectric materials. Therefore, there is a need to develop an n-type MOF-based thermoelectric foam with high Seebeck coefficient, high electrical conductivity, low thermal conductivity, high output power density, adaptability to various heat source surfaces, and ductility, which could potentially generate electricity through temperature response to drive low-power wearable sensing electronic devices. Summary of the Invention

[0004] Based on the above-mentioned technical problems, the present invention provides a high-performance thermoelectric foam with extensibility based on n-type MOF, its preparation method and application.

[0005] To achieve the above objectives, this invention provides a high-performance thermoelectric foam based on a flexible n-type MOF. The foam uses nickel foam (NF) as a matrix and is synthesized via hydrothermal method. Cu(II) ions and a small amount of free Ni(II) in the precursor solution are linked to four oxygen atoms of a 1,3,5-benzenetricarboxylic acid (BTC) ligand, forming a porous coordination polymer monomer with a face-centered cubic crystal structure on the nickel foam surface. This monomer is then impregnated in a mixed solution of polyaniline and N,N-dimethylformamide (DMF), where it cross-links and interpenetrates with polyaniline (PANI) molecules onto the MOF surface and pores, grafting conductive polymers. The specific preparation steps are as follows:

[0006] S1. Dissolve 1,3,5-benzenetricarboxylic acid (BTC) and copper acetate (Cu(OAc)2·H2O) in a mixed solution of N,N-dimethylformamide (DMF), ethanol (EtOH), and deionized water (DI) to prepare a precursor solution.

[0007] S2. Nickel foam (NF) is first immersed in the precursor solution of step S1 for hydrothermal reaction, and then taken out, cleaned and dried to obtain nickel foam material with uniform nickel-copper MOF growing on the surface.

[0008] S3. The nickel foam material from step S2 is immersed in a mixed solution of polyaniline (PANI) and DMF to graft conductive polymers onto the surface and pores of the nickel-copper MOF, thereby obtaining a high-performance thermoelectric foam with ductility.

[0009] As a further preferred technical solution of the present invention, before step S2, the foamed nickel is further pretreated by soaking it in acetone, hydrochloric acid and ethanol respectively.

[0010] As a further preferred technical solution of the present invention, in the precursor solution of step S1, the amount of 1,3,5-pyromellitic acid added is 10.0-50.0 mmol / L, and the amount of copper acetate added is 0.1-50.0 mmol / L.

[0011] As a further preferred technical solution of the present invention, in step S1, the volume ratio of N,N-dimethylformamide, ethanol and deionized water is 1:1:1.

[0012] As a further preferred technical solution of the present invention, in step S2, a Teflon reactor is used for hydrothermal reaction.

[0013] As a further preferred technical solution of the present invention, in step S2, the temperature for hydrothermal reaction is 100-150℃ and the time is 10-20h.

[0014] As a further preferred technical solution of the present invention, in step S3, polyaniline is added to N,N-dimethylformamide at a concentration of 1.0-4.0 g / L, and the mixture is sonicated for 20-60 min to form a mixed solution.

[0015] As a further preferred technical solution of the present invention, in step S3, the soaking temperature is 50-80℃ and the soaking time is 2-6h.

[0016] According to another aspect of the present invention, the present invention also provides an n-type MOF-based high-performance thermoelectric foam, which is prepared by the above method.

[0017] According to another aspect of the present invention, the present invention also provides an application of n-type MOF-based high-performance thermoelectric foam as a flexible semiconductor material in thermoelectric conversion in the field of thermoelectric conversion in the thermoelectric power generation of heat source surfaces, and further applies it to wearable sensing devices or self-powered wearable electronic devices. Based on the plasticity of thermoelectric foam, it can be applied to any regular heat source surface.

[0018] This invention uses nickel foam as a matrix and employs a hydrothermal synthesis method to connect Cu(II) ions and a small amount of free Ni(II) in the precursor solution with four oxygen atoms of the BTC ligand, forming a porous coordination polymer monomer with a face-centered cubic crystal structure on the surface of the nickel foam. Then, it is immersed in a mixed solution of polyaniline and DMF, and after removal and washing, the ductile MOF-based thermoelectric foam described in this invention is obtained. This synthesis strategy allows for the customization of electrical and thermal properties through the tunability of the mixed materials, combining the superior properties of inorganic materials, nanostructure geometry, and organic materials, thus providing a powerful approach to enhancing thermoelectric performance.

[0019] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0020] 1) This invention employs a strategy of hydrothermal synthesis and polymer grafting, and its preparation method is simple and easy to implement, with the potential for mass production.

[0021] 2) The n-type MOF-based thermoelectric foam prepared by this invention exhibits excellent ductility and thermoelectric properties. The NCM@PANI / NF thermoelectric foam simultaneously possesses metallic plasticity, high-efficiency thermoelectric performance, and sensitivity to temperature changes. Its superior thermoelectric properties and wide range of applications far surpass those of currently reported n-type MOF-based thermoelectric materials. For example, the Seebeck coefficients of currently studied n-type Cu-MOF materials are concentrated between -10 and -30 μV / K, lower than those of this invention, and they lack plasticity, making them difficult to apply to complex heat source surfaces.

[0022] 3) The n-type MOF-based thermoelectric foam prepared by this invention has ductility, which enables the design of thermoelectric devices to be matched with heat sources of different specific shapes, thus improving their practicality.

[0023] 4) Based on n-type MOF-based thermoelectric foam, this invention can be used to prepare various ductile thermoelectric devices, which have good application prospects in the fields of thermoelectric power generation, intelligent thermal management, and thermoelectric wearables. Attached Figure Description

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0025] Figure 1 The images shown are optical photographs and magnified scanning electron microscope (SEM) images of the thermoelectric foams prepared in Example 1, where a is an optical photograph of the synthesized thermoelectric foams of different sizes; b is a magnified SEM image of NCM / NF; and c is a magnified SEM image of NCM@PANI / NF.

[0026] Figure 2 The energy dispersive X-ray spectrum of the NCM@PANI / NF thermoelectric foam prepared in Example 1;

[0027] Figure 3 The image shows the stretchable bending properties and thermoelectric properties of the thermoelectric foam prepared in Example 1, where a is an optical image of the stretchable bending of the thermoelectric foam, and b is the Seebeck coefficient for different degrees of folding and bending.

[0028] Figure 4 The thermoelectric properties of the thermoelectric foam in Example 1 under different temperature differences are shown. Figure 4 The voltage-current density and output power density curves are shown under different temperature differences;

[0029] Figure 5 The Seebeck coefficient and conductivity variation curves of the thermoelectric foam prepared in Comparative Example 1 are shown in the precursor solutions with different contents of Cu(OAc)2·H2O.

[0030] Figure 6A comparison of Seebeck coefficients and electrical conductivity for NCM@PANI / NF, NCM / NF-0.5, NM / NF, and pure nickel foam;

[0031] Figure 7 The NCM@PANI / NF thermoelectric array device, fabricated using a surrounding tubular heat source with thermoelectric foam (1.7 mm thick) in Example 1, is shown in a diagram and an optical image, and its output voltage and power are shown in b.

[0032] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0033] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0034] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0035] The test methods involved in the following embodiments and comparative examples are as follows: The Seebeck coefficient of the thermoelectric foam was tested using a self-built testing device; the temperature difference between the left and right ends of the sample was controlled using a low-voltage power supply and a commercial Peltier heating module; the open-circuit voltage across the thermoelectric foam was measured using a Keithley 2450 data acquisition system; simultaneously, the real-time temperature of the left and right ends of the thermoelectric foam was measured using thermocouples to obtain the temperature difference, and the Seebeck coefficient was calculated. In the embodiments of this invention, the designed thermoelectric foam has an effective length of 40 mm and a width of 10 mm. Copper wires are used as electrodes connected to both ends of the thermoelectric foam. The resistance across the thermoelectric foam is measured using a Keithley 2450. Based on the length, resistance, and cross-sectional area of ​​the thermoelectric foam, its resistivity is calculated and converted into conductivity.

[0036] Example 1:

[0037] The method for preparing thermoelectric foam and devices provided in this embodiment is as follows:

[0038] (1) Cut the 1.7mm thick nickel foam material into small pieces of 2cm×2cm, soak them in acetone, hydrochloric acid and ethanol for 15min respectively, and remove the surface oil and oxide layer by ultrasonication.

[0039] (2) Dissolve 2.5 mmol of 1,3,5-tricarboxylic acid benzene (BTC) and 0.5 mmol of Cu(Ac)2·H2O in 75 mL of a mixed solution of DMF:DI:EtOH (1:1:1) and stir for 10 min to obtain the precursor solution;

[0040] (3) Immerse the pretreated nickel foam (2cm×2cm) from step (1) into the precursor solution from step (2), transfer the whole thing to a 100ml Teflon reactor, and react in a 120℃ oven for 16 hours, then cool to room temperature.

[0041] (4) The sample obtained in step (3) was rinsed with deionized water and anhydrous ethanol, and then dried overnight at 70°C in a vacuum drying oven to obtain nickel foam material, denoted as NCM / NF;

[0042] (5) The nickel foam material was immersed in 200 mL of 2 g / L PANI / DMF dispersion solution, stirred slowly at 60 °C for 4 h, cooled to room temperature, rinsed several times with DMF and ethanol, and dried at 50 °C to obtain thermoelectric foam, denoted as NCM@PANI / NF.

[0043] (6) Cut the thermoelectric foam into strips with dimensions of 40mm×10mm×1.7mm, and connect the left and right ends with copper wire as electrodes to obtain the corresponding thermoelectric foam device.

[0044] To further verify the feasibility of the present invention, based on Example 1, thermoelectric foams of different thicknesses were prepared using the same process, and the resulting samples are as follows. Figure 1 As shown. From Figure 1 As can be seen, thermoelectric foams can be synthesized using nickel foam substrates of different thicknesses (20mm, 10mm, 5.0mm, 1.7mm). Figure 1 As can be seen from b, a NiCu-MOF with a typical morphology is uniformly formed on the NCM / NF surface, with a lateral dimension between 5 and 10 μm and an octahedral structure. From Figure 1 As can be seen from c, NCM@PANI / NF is uniformly coated with polyaniline with a rough surface.

[0045] Figure 2 The energy-dispersive X-ray spectrum of NCM@PANI / NF in Example 1 is shown. Ni, Cu and C elements are uniformly distributed on NCM / NF, indicating that there is uniform substitution between Cu and Ni.

[0046] Figure 3 This demonstrates the stretchable bending properties of the thermoelectric foam prepared in Example 1. From... Figure 3 It can be seen that the prepared thermoelectric foam can be twisted into different shapes. Figure 3b represents the folding and bending test of the plasticity and ductility of TE foam. After bending with different radii, the Seebeck coefficient of NCM@PANI / NF showed no significant change. The cross-linking protection of NiCu-MOF by the polyaniline polymer can suppress internal structural fracture caused by bending or folding. This means that the NCM@PANI / NF thermoelectric material has significant ductility and shape adaptability, allowing it to be molded into different shapes according to actual needs in its applications.

[0047] Figure 4 To optimize the thermoelectric performance of the thermoelectric foam under different temperature differences in Example 1, with temperature differences of 8K, 12K, 15K, 20K and 25K respectively, it can be seen that as the temperature difference increases, the maximum output power density of the thermoelectric foam also gradually increases, and the corresponding maximum output power density gradually increases from 205.83μW·m-2 to 696.04μW·m-2.

[0048] Comparative Example 1:

[0049] As a comparative experiment to Example 1, the differences are: the soaking step of the PANI / DMF dispersion solution was omitted, and the amount of Cu(Ac)₂·H₂O added was changed to 0.1 mmol, 0.5 mmol, 1 mmol, and 2 mmol respectively. The specific steps are as follows:

[0050] (1) Cut the nickel foam raw material into small pieces of 2cm×2cm, soak them in acetone, hydrochloric acid and ethanol for 15min respectively, and remove the surface oil and oxide layer by ultrasonication.

[0051] (2) Dissolve 2.5 mmol of 1,3,5-tristyric acid (BTC) and x mmol of Cu(Ac)2·H2O in 75 mL of a mixed solution of DMF:DI:EtOH (1:1:1) and stir for 10 min, where x is 0.1, 0.5, 1 or 2;

[0052] (3) Immerse the pretreated nickel foam (2cm×2cm) from step (1) into the mixture, transfer the whole thing to a 100ml Teflon reactor, and react in a 120℃ oven for 16 hours, then cool to room temperature.

[0053] (4) The sample obtained in step (3) was rinsed with deionized water and anhydrous ethanol, and then dried overnight at 70°C in a vacuum drying oven to obtain thermoelectric foam without grafted conductive polymer. The thermoelectric foam samples with different Cu(Ac)2·H2O addition amounts were labeled NCM-x, where x were 0.1, 0.5, 1 and 2 respectively.

[0054] (5) Cut the thermoelectric foam into strips with dimensions of 40mm×10mm×1.7mm, and connect the left and right ends with copper wire as electrodes to obtain the corresponding thermoelectric foam device.

[0055] Figure 5 The changes in Seebeck coefficient and conductivity of thermoelectric foam caused by using different amounts of Cu(OAc)₂·H₂O in Example 2 are shown. It can be seen that as the amount of Cu(OAc)₂·H₂O added to NCM / NF increases from 0.1 to 2 mmol, the Seebeck coefficient first increases and then decreases, while the conductivity increases from 136.7 to 179.71 S·m. -1 In Cu 2+ The concentration was 0.5 mmol (NCM / NF-0.5), and the Seebeck coefficient was -38.2 μV·K. -1 The conductivity is 158.83 S·m. -1 .

[0056] Comparative Example 2

[0057] The only difference from Comparative Example 1 is that the amount of Cu(Ac)₂·H₂O added is 0. The specific steps are as follows:

[0058] (1) Cut the nickel foam into small pieces of 2cm×2cm, soak them in acetone, hydrochloric acid and ethanol for 15min respectively, and then remove the surface oil and oxide layer by ultrasonication.

[0059] (2) Dissolve 2.5 mmol of 1,3,5-tristyric acid (BTC) in 75 mL of a mixed solution of DMF:DI:EtOH (1:1:1) and stir for 10 min;

[0060] (3) Immerse the pretreated nickel foam (2cm×2cm) from step (1) into the mixture, transfer the whole thing to a 100ml Teflon reactor, and react in a 120℃ oven for 16 hours, then cool to room temperature.

[0061] (4) The sample obtained in step (3) is rinsed with deionized water and anhydrous ethanol, and then dried overnight at 70°C in a vacuum drying oven to obtain thermoelectric foam, denoted as NM / NF.

[0062] (5) Cut the thermoelectric foam into strips with dimensions of 40mm×10mm×1.7mm, and connect the left and right ends with copper wire as electrodes to obtain the corresponding thermoelectric foam device.

[0063] The Seebeck coefficient of the NM / NF prepared in Comparative Example 2 was -33.7 μV·K⁻¹, the electrical conductivity was 136.7 S·m⁻¹, and the thermal conductivity was 0.070 W·m⁻¹K⁻¹.

[0064] Figure 6The graph shows a comparison of the thermal and electrical properties of the three thermoelectric foams prepared in Example 1, Comparative Example 1, and Comparative Example 2, as well as pure nickel foam, illustrating the Seebeck coefficient and conductivity variation curves of the four materials. This is achieved by combining... Figure 5 It can be seen that the introduction of 0.5 mmol Cu(OAc)₂·H₂O into the precursor solution significantly improves the Seebeck coefficient and conductivity of the thermoelectric foam. Furthermore, the grafting of polyaniline greatly enhances the Seebeck coefficient and conductivity of the thermoelectric foam; the Seebeck coefficient of NCM@PANI / NF is -53.1 μV·K. -1 The conductivity is 872.39 S·m. -1 Moreover, its overall performance is far superior to that of MOF-based n-type thermoelectric materials reported to date.

[0065] Figure 7 An NCM@PANI / NF thermoelectric array device was fabricated using the thermoelectric foam prepared in Example 1. The thermoelectric foam was bent into a semi-circular shape and fixed to the surface of a flexible Ecoflex strip. Then, the cylindrical device was wrapped around a tubular heat source, with one side of the cylindrical thermoelectric array directly contacting the heat source as the hot side, and the other side exposed to air as the cold side. Hot water at different temperatures was circulated inside a steel pipe with good thermal conductivity, maintaining the pipe surface temperature at approximately 30, 50, 70, and 90°C. The electrical signals generated by the thermoelectric array device at different temperature differences were measured using a digital multimeter (Keithley 2450 system). Under the final stable conditions, when the pipe surface temperature was approximately 30, 50, 70, and 90°C, the corresponding maximum output power was 0.21, 1.33, 3.55, and 6.43 μW, respectively. These results further demonstrate the significant advantages of NCM@PANI / NF thermoelectric foam in terms of ductility and shape consistency in the fields of heat harvesting and flexible electronics.

[0066] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A method for preparing a stretchable n-type MOF-based high-performance thermoelectric foam, characterized in that, Includes the following steps: S1. Dissolve 1,3,5-pyromellitic acid and copper acetate in a mixed solution of N,N-dimethylformamide, ethanol and deionized water to prepare a precursor solution. S2. The nickel foam is first immersed in the precursor solution of step S1 for hydrothermal reaction, and then taken out, cleaned and dried to obtain nickel foam material with uniform nickel-copper MOF growing on the surface. S3. The nickel foam material from step S2 is immersed in a mixed solution of polyaniline and N,N-dimethylformamide to graft conductive polymers onto the surface and pores of the nickel-copper MOF, thereby obtaining a high-performance thermoelectric foam with ductility.

2. The method for preparing ductile n-type MOF-based high-performance thermoelectric foam according to claim 1, characterized in that, Before step S2, the process includes a pretreatment step of soaking the nickel foam in acetone, hydrochloric acid, and ethanol respectively.

3. The method for preparing ductile n-type MOF-based high-performance thermoelectric foam according to claim 1, characterized in that, In the precursor solution of step S1, the amount of 1,3,5-pyromellitic acid added is 10.0-50.0 mmol / L, and the amount of copper acetate added is 0.1-50.0 mmol / L.

4. The method for preparing ductile n-type MOF-based high-performance thermoelectric foam according to claim 1, characterized in that, In step S1, the volume ratio of N,N-dimethylformamide, ethanol, and deionized water is 1:1:

1.

5. The method for preparing a stretchable n-type MOF-based high-performance thermoelectric foam according to claim 1, characterized in that, In step S2, a Teflon reactor is used for the hydrothermal reaction.

6. The method for preparing ductile n-type MOF-based high-performance thermoelectric foam according to claim 1, characterized in that, In step S2, the hydrothermal reaction is carried out at a temperature of 100-150℃ for 10-20 hours.

7. The method for preparing a stretchable n-type MOF-based high-performance thermoelectric foam according to claim 1, characterized in that, In step S3, polyaniline is added to N,N-dimethylformamide at a concentration of 1.0-4.0 g / L, and the mixture is sonicated for 20-60 min to form a mixed solution.

8. The method for preparing a stretchable n-type MOF-based high-performance thermoelectric foam according to claim 1, characterized in that, In step S3, the soaking temperature is 50-80 ℃ and the soaking time is 2-6 h.

9. A type n MOF-based high-performance thermoelectric foam, characterized in that, It is prepared by the method described in any one of claims 1-8.

10. The n-type MOF-based high-performance thermoelectric foam of claim 9 is used as a flexible semiconductor material for thermoelectric conversion in the field of thermoelectric conversion for thermoelectric power generation on the surface of any regular heat source.

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