Covalent organic framework-doped bismuth sulfide thermoelectric materials and methods of making the same

Abstract

The application discloses a kind of covalent organic framework doped bismuth sulfide thermoelectric material and preparation method thereof.The method is synthesized n-type Bi2S3 nanomaterial by solvothermal method, then mixed uniformly with BND-TFP COFs in ethylene glycol, high-performance BND-TFP COFs doped Bi2S3 thermoelectric material is prepared by using discharge plasma sintering technology.The application can improve electron concentration, enhance mobility, improve electrical conductivity, improve power factor by doping BND-TFP COFs, and uses discharge plasma sintering technology, Bi2S3 is combined with BND-TFP COFs at high temperature, lattice thermal conductivity is reduced, so as to realize the improvement of zT, power factor reaches 0.47 mW / m / K at 789 K 2 , thermoelectricity merit zT reaches 0.75 at most, and the thermoelectric performance of Bi2S3 nanomaterial is obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials and relates to a covalent organic framework (COFs) doped bismuth sulfide thermoelectric material and its preparation method. Background Technology

[0002] Thermoelectric energy conversion technology is a novel, green, and clean energy technology that directly converts electrical energy into heat energy, thus attracting widespread attention. Thermoelectric conversion technology achieves thermoelectric power generation through the Seebeck effect and thermoelectric cooling using the Peltier effect. It boasts advantages such as flexibility, safety, reliability, low cost, small size, simple structure, and environmental friendliness, and can be applied in fields such as environmental energy recovery, special power supplies, and refrigeration equipment. Thermoelectric materials are the carriers of electrical and heat energy conversion and are considered ideal alternatives to address the global fossil fuel crisis. However, the large-scale application of thermoelectric materials remains limited, mainly due to the relatively low efficiency of thermoelectric conversion and some unresolved scientific issues. Therefore, developing high-performance and environmentally friendly thermoelectric materials and studying the electroacoustic transport mechanisms of thermoelectric materials are of great significance.

[0003] The energy conversion efficiency of thermoelectric materials is expressed by the dimensionless thermoelectric figure of merit zT = (S 2 σ / κ)T=S 2 σT / (κ e +κ l The conductivity is measured by κ, where S is the Seebeck coefficient, σ is the electrical conductivity, and κ is the thermal conductivity (κ is usually determined by the lattice thermal conductivity κ). l and electronic thermal conductivity κ e Composition), T is absolute temperature. Therefore, to improve the performance of thermoelectric materials, the power factor (S) is generally increased. 2 σ) or by reducing thermal conductivity (κ) to continuously increase zT.

[0004] Bismuth sulfide (Bi2S3) is a typical rod-shaped material. Compared with traditional Bi2Te3 and PbTe-based inorganic thermoelectric materials and their alloys, which contain expensive, toxic, and scarce elements, Bi2S3 has advantages such as abundant reserves, low cost, and environmental friendliness. However, the relatively low thermoelectric performance of Bi2S3 limits its application. Currently, efforts are mainly made to improve the thermoelectric performance of Bi2S3 in two ways. One is to improve the power factor through strategies such as adjusting carrier concentration by doping, introducing impurities, and constructing core-shell structures. For example, Reference 1 uses the dopant MoCl5 to adjust the electrical properties of Bi2S3. By changing the amount of doping, the carrier concentration is increased, and higher thermoelectric performance is achieved. Among them, the product zT maxThe value is 0.7 (Wang,Y.;Feng,J.;Ge,Z.-H.,Enhancing powerfactor and ZT in non-toxic Bi2S3 bulk materials via band engineering and electronic structure modulation.Ceramics International 2023,49(14),23680-23688.). On the other hand, it is to reduce thermal conductivity and create multi-scale defects to scatter phonons of different wavelengths, such as dislocations, nanoprecipitations, alloying and high-density grain boundaries. For example, in reference 2, reduced graphene oxide (rGO) is doped into Bi2S3 samples, so that it is dispersed in the sample and tightly bound to the Bi2S3 sample. This not only significantly improves the electrical conductivity but also reduces the lattice thermal conductivity, thus increasing the product ZT. max is 0.22 (ai, Y.; Ouyang, T.; Li, X.; et al, Boosting the thermoelectric performance of n-type Bi2S3 by compositing rGO. Journal of Alloys and Compounds 2023, 933.). Summary of the Invention

[0005] The purpose of this invention is to provide a covalent organic framework-doped bismuth sulfide thermoelectric material and its preparation method. This method involves a one-step solvothermal synthesis of the bismuth sulfide thermoelectric material, followed by dispersion of bismuth sulfide and BND-TFPCOFs in ethanol, and sintering using spark plasma (SPS) to produce a dense, bulk covalent organic framework-doped bismuth sulfide thermoelectric material.

[0006] The technical solution for achieving the objective of this invention is as follows:

[0007] The preparation method of covalent organic framework-doped bismuth sulfide thermoelectric materials includes the following specific steps:

[0008] Bismuth nitrate pentahydrate and thiourea were added to ethylene glycol at a molar ratio of 1:5, heated and stirred until homogeneous, placed in a polytetrafluoroethylene liner, and subjected to a solvothermal reaction at 100–150 °C. After the reaction was completed, the mixture was cooled to room temperature, removed, centrifuged, washed to remove impurities, and vacuum dried. Then, bismuth sulfide and BND-TFPCOFs were dispersed in ethanol at a mass of 0.2%–0.7% of bismuth sulfide, vacuum dried, and finally subjected to discharge plasma sintering to obtain bulk BND-TFPCOFs-doped Bi2S3 thermoelectric material.

[0009] Preferably, the heating temperature is 30–40°C and the stirring time is 1–3 hours.

[0010] Preferably, the solvothermal reaction time is 14–24 h.

[0011] Preferably, the centrifugation speed is 6000–10000 r / min and the centrifugation time is 3–8 min.

[0012] Preferably, the washing method is to first wash twice with deionized water, and then wash once with anhydrous ethanol.

[0013] Preferably, the vacuum drying temperature is 50–70°C and the drying time is 6–10 hours.

[0014] Preferably, the stirring and dispersion time is 1 to 2 hours.

[0015] Preferably, the sintering temperature of the discharge plasma sintering is 400–550°C, the holding time is 10–15 min, and the sintering pressure is 20–40 MPa.

[0016] Preferably, the mass of BND-TFPCOFs is 0.5% of bismuth sulfide.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) This invention uses micro-covalent organic framework doped Bi2S3 material, which has a simple synthesis process, low raw material cost, abundant reserves, and is green and environmentally friendly. It also uses discharge plasma sintering technology, which has the characteristic of rapid sintering during the pressurization process. Compared with hot pressing and other molding technologies, it requires a lower temperature and the sample has better mechanical properties and density, which improves production efficiency and reduces synthesis energy consumption.

[0019] (2) This invention directly uses trace amounts of covalent organic frameworks doped into the product, and further performs discharge plasma sintering technology. Under the above-mentioned high-temperature sintering conditions, the product combines with BND-TFPCOFs, increasing the phonon scattering of the Bi2S3 thermoelectric material. At the same time, the non-stoichiometric synthesis of the product is conducive to the formation of vacancies, thus effectively improving the conductivity σ of the Bi2S3 thermoelectric material, from 149.63 S cm⁻¹ in the undoped sample Bi2S3. -1 The viscosity was increased to 164.49 Scm for Bi₂S₃ doped with 0.5 wt% COF. -1 The power factor PF showed a significant increase, from 0.43 mW / m / K. 2 Increased to 0.47mW / m / K 2 It significantly reduced the thermal conductivity κ from 0.65 W / m / K to 0.49 W / m / K, thereby comprehensively improving the thermoelectric figure of merit. Attached Figure Description

[0020] Figure 1 The graph shows the relationship between the thermoelectric figure of merit (zT) of the Bi2S3 samples prepared in Examples 1-3 and temperature changes.

[0021] Figure 2 The graph shows the relationship between the conductivity (σ) and temperature for samples of Bi2S3, Bi2S3-0.2wt%COFs, Bi2S3-0.5wt%COFs, and Bi2S3-0.7wt%COFs.

[0022] Figure 3 The Seebeck coefficient (S) of Bi2S3, Bi2S3-0.2wt%COFs, Bi2S3-0.5wt%COFs, and Bi2S3-0.7wt%COFs samples are plotted against temperature.

[0023] Figure 4 The power factor (S) of the samples Bi₂S₃, Bi₂S₃-0.2wt%COFs, Bi₂S₃-0.5wt%COFs, and Bi₂S₃-0.7wt%COFs. 2 σ) is related to temperature change.

[0024] Figure 5 The graph shows the relationship between thermal conductivity (κ) and temperature for Bi2S3, Bi2S3-0.2wt%COFs, Bi2S3-0.5wt%COFs, and Bi2S3-0.7wt%COFs samples.

[0025] Figure 6 The graph shows the relationship between the thermoelectric figure of merit (zT) and temperature for the samples Bi2S3, Bi2S3-0.2wt%COFs, Bi2S3-0.5wt%COFs, and Bi2S3-0.7wt%COFs. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings. In the present invention, the BND-TFPCOFs used are synthesized with reference to existing literature (Evans, AM; Ryder, MR; Flanders, NC; et al, Buckling of Two-Dimensional Covalent Organic Frameworks under Thermal Stress. Industrial & Engineering Chemistry Research 2019, 58(23), 9883-9887.).

[0027] Example 1

[0028] Bismuth nitrate pentahydrate and thiourea were added to 60 ml of deionized water at a molar ratio of 1:4. The mixture was stirred until homogeneous and subjected to a solvothermal reaction at 150 °C for 20 h. After the reaction was completed, the mixture was cooled to room temperature, and the product was washed twice with deionized water and once with anhydrous ethanol. The product was centrifuged at 10000 r / min for 5 min and then vacuum dried at 60 °C for 12 h. The sample was then removed, ground into powder, and placed in a specially made graphite mold with an inner diameter of 10 mm for discharge plasma sintering at a temperature of 500 °C for 15 min and a sintering pressure of 40 MPa.

[0029] Example 2

[0030] This embodiment is basically the same as Embodiment 1, except that the molar ratio of bismuth nitrate pentahydrate to thiourea is 1:5.

[0031] Example 3

[0032] This embodiment is basically the same as Embodiment 1, except that the molar ratio of bismuth nitrate pentahydrate to thiourea is 1:6.

[0033] Comparative Example 1

[0034] This comparative example is basically the same as Example 1, except that the molar ratio of bismuth nitrate pentahydrate to thiourea is 2:3, which is the ratio under which Bi2S3 cannot be synthesized.

[0035] Table 1

[0036]

[0037] Since the sample synthesized in Comparative Example 1 with a Bi:S feed ratio of 2:3 was not Bi2S3, we directly compared it with the Bi2S3 synthesized in Examples 1-3. Figure 1 As shown, their dimensionless thermoelectric properties (zT) are 0.62, 0.65, and 0.59, respectively. It can be seen that the sample prepared when the Bi:S feed ratio is 1:5 has the best performance. Therefore, in the following examples, Bi2S3 prepared when the Bi:S molar ratio is 1:5 is used as raw material to dope COFs.

[0038] Example 4

[0039] Using the Bi2S3 sample prepared in Example 2 as raw material, 0.2% of BND-TFPCOFs by mass of the sample were weighed. The Bi2S3 sample and BND-TFPCOFs were stirred and dispersed in ethanol, vacuum dried, ground into powder, and then placed in a specially made graphite mold with an inner diameter of 10 mm for discharge plasma sintering. The sintering temperature was 500℃, the holding time was 15 minutes, and the sintering pressure was 40 MPa to obtain Bi2S3-0.2wt%COFs.

[0040] Example 5

[0041] This embodiment is basically the same as Example 4, except that the amount of BND-TFPCOFs added is 0.5% of the Bi2S3 sample, thus obtaining Bi2S3-0.5wt%COFs.

[0042] Example 6

[0043] This embodiment is basically the same as Example 4, except that the amount of BND-TFPCOFs added is 0.7% of the Bi2S3 sample, thus obtaining Bi2S3-0.7wt%COFs.

[0044] Table 2

[0045]

[0046] Figure 2 The graph shows the relationship between the conductivity (σ) and temperature for Bi₂S₃, Bi₂S₃-0.2wt%COFs, Bi₂S₃-0.5wt%COFs, and Bi₂S₃-0.7wt%COFs samples. It can be seen that the conductivity of the undoped bismuth sulfide material is relatively low, at 149.6 S cm⁻¹ at 786 K. -1 It is significantly lower than the conductivity of Bi₂S₃-0.2wt%COFs and Bi₂S₃-0.5wt%COFs (164.48 Scm, respectively). -1 171.50S cm -1 However, when micro-doped with COFs (Bi₂S₃ - 0.2 wt% COFs), a high conductivity of 164.48 S cm⁻¹ was achieved at 786 K. -1 This indicates that trace amounts of COFs can improve the electrical conductivity of the material.

[0047] Figure 3The graph shows the relationship between the Seebeck coefficient (S) and temperature for Bi2S3, Bi2S3-0.2wt%COFs, Bi2S3-0.5wt%COFs, and Bi2S3-0.7wt%COFs samples. At 786K, the Seebeck coefficients of Bi2S3-0.2wt%COFs and Bi2S3 are -162.49uV / K, -169.22uV / K, -153.9uV / K, and -168.93uV / K, respectively. Since the Seebeck coefficient and conductivity are mutually constrained, the Seebeck coefficient of Bi2S3 materials with trace amounts of COFs doped has a relatively small change.

[0048] Figure 4 The power factor (S) of the samples Bi₂S₃, Bi₂S₃-0.2wt%COFs, Bi₂S₃-0.5wt%COFs, and Bi₂S₃-0.7wt%COFs. 2 The graph shows the relationship between σ and temperature. At 786 K, the concentrations of Bi₂S₃-0.2wt%COFs, Bi₂S₃-0.5wt%COFs, Bi₂S₃-0.7wt%COFs, and Bi₂S₃ are 0.38 mW / m / K. 2 0.47mW / m / K 2 0.41mW / m / K 2 0.42mW / m / K 2 It can be seen that the power factor of the Bi2S3 material doped with 5wt% COFs is significantly improved compared with the undoped ethylene glycol material.

[0049] Figure 5 The graph shows the relationship between thermal conductivity (κ) and temperature for Bi2S3, Bi2S3-0.2wt%COFs, Bi2S3-0.5wt%COFs, and Bi2S3-0.7wt%COFs samples. At 786K, the κ values ​​for Bi2S3-0.2wt%COFs, Bi2S3-0.5wt%COFs, Bi2S3-0.7wt%COFs, and Bi2S3 are 0.60mW / m / K, 0.49mW / m / K, 0.64mW / m / K, and 0.65mW / m / K, respectively. It can be observed that the thermal conductivity of Bi2S3 materials doped with COFs decreases.

[0050] Figure 6The graph shows the relationship between the thermoelectric figure of merit (zT) and temperature for Bi2S3, Bi2S3-0.2wt%COFs, Bi2S3-0.5wt%COFs, and Bi2S3-0.7wt%COFs samples. At 786K, the zT values ​​for Bi2S3-0.2wt%COFs, Bi2S3-0.5wt%COFs, Bi2S3-0.7wt%COFs, and Bi2S3 are 0.64, 0.75, 0.64, and 0.65, respectively. It can be seen that when 0.5wt%COFs is doped, the highest zT of 0.80 is achieved at 786K. Compared with the Bi2S3 sample with the same feed ratio but without COFs, the thermoelectric performance is improved by about 66%.

Claims

1. A method for preparing covalent organic framework-doped bismuth sulfide thermoelectric materials, characterized in that, The specific steps are as follows: Bismuth nitrate pentahydrate and thiourea were added to ethylene glycol at a molar ratio of 1:5, heated and stirred until homogeneous, placed in a polytetrafluoroethylene liner, and subjected to a solvothermal reaction at 100-150 °C. After the reaction was completed, the mixture was cooled to room temperature, removed, centrifuged, washed to remove impurities, and vacuum dried. Then, bismuth sulfide and BND-TFP COFs were dispersed in ethanol at a mass of 0.2%-0.7% of bismuth sulfide, vacuum dried, and finally subjected to discharge plasma sintering to obtain bulk BND-TFP COFs-doped Bi2S3 thermoelectric material.

2. The preparation method according to claim 1, characterized in that, The heating temperature is 30~40 ℃, and the stirring time is 1~3 h.

3. The preparation method according to claim 1, characterized in that, The solvothermal reaction time is 14~24 h.

4. The preparation method according to claim 1, characterized in that, Centrifugation speed is 6000~10000 r / min, centrifugation time is 3~8 min.

5. The preparation method according to claim 1, characterized in that, The washing method is to wash twice with deionized water, and then wash once with anhydrous ethanol.

6. The preparation method according to claim 1, characterized in that, The vacuum drying temperature is 50–70 °C, and the drying time is 6–10 h.

7. The preparation method according to claim 1, characterized in that, The stirring and dispersion time is 1~2 hours.

8. The preparation method according to claim 1, characterized in that, The sintering temperature of the discharge plasma sintering is 400~550 ℃, the holding time is 10~15 min, and the sintering pressure is 20~40 MPa.

9. The preparation method according to claim 1, characterized in that, The mass of BND-TFP COFs is 0.5% of bismuth sulfide.

10. A covalent organic framework-doped bismuth sulfide thermoelectric material prepared by any one of the preparation methods according to claims 1 to 9.

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