A method for preparing ultra-flexible, high-performance sulfur-doped silver selenide / nylon composite thermoelectric film

Abstract

The present invention relates to a method for preparing an ultra-flexible, high-performance, sulfur-doped silver selenide / nylon composite thermoelectric film, comprising the following steps: (1) reacting selenium nanowires with silver sulfide powder in ethylene glycol as a solvent to obtain a silver-selenium-sulfur ternary alloy powder; and (2) ultrasonically dispersing the silver-selenium-sulfur ternary alloy powder in anhydrous ethanol, vacuum filtering the powder using a nylon filter membrane as a substrate, drying the powder, and then hot pressing the powder to obtain the target product. Compared with the prior art, the composite film of the present invention has excellent flexibility and exhibits superior thermoelectric properties. High-output thermoelectric devices can be fabricated using the film, and are expected to serve as a new power source for wearable electronic devices.

Description

Technical Field

[0001] The invention belongs to the technical field of thermoelectric material preparation, and relates to a method for preparing an ultra-flexible, high-performance sulfur-doped silver selenide / nylon composite thermoelectric film. Background Art

[0002] Thermoelectric materials are a class of functional materials that directly convert heat and electricity through the transport of charge carriers within the material. Thermoelectric generators and cooling devices fabricated from these materials offer advantages such as simple structure, no moving parts, wear-free, noise-free, pollution-free, and compact size. As environmentally friendly materials, thermoelectric materials hold broad application prospects in the energy supply sector.

[0003] The general performance index of thermoelectric materials is the dimensionless thermoelectric figure of merit ZT, which is expressed as follows:

[0004] ZT=α 2 σT / κ Where: α is the Seebeck coefficient; σ is the electrical conductivity; κ is the thermal conductivity; T is the thermodynamic temperature. For thin film materials, the power factor PF (PF = α 2 σ) is used to measure its thermoelectric performance.

[0005] In recent years, flexible thermoelectric materials have attracted increasing attention from researchers and have made considerable progress, especially in organic and composite thermoelectric materials. Most previous research has focused on using conductive polymers as the matrix in composite thermoelectric materials, inorganic materials as fillers, and enhancing the thermoelectric performance of the composite material through the synergistic effect between the two phases. However, since conductive polymers are mostly p-type materials, are not easily n-type doped, and have relatively low thermoelectric performance, insulating polymers have the advantages of low price and good viscosity, and the method of using them as the matrix in composites has gradually attracted attention. In addition, due to the inherent rigidity of traditional inorganic thermoelectric materials, they cannot meet the requirements of flexibility on their own. In addition to composites with organic polymers, the method of using flexible materials as supporting substrates and inorganic thermoelectric materials as the phase providing thermoelectric performance is also receiving increasing attention.

[0006] Silver selenide is a narrow bandgap semiconductor (with a band gap of 0.07 eV at 273 K) and undergoes a phase transition from an orthorhombic phase to a cubic phase around 406 K. At low temperatures, silver selenide has an orthorhombic structure and exhibits semiconductor properties. At high temperatures, silver selenide has a cubic structure and is a superionic conductor. At low temperatures, the orthorhombic phase of silver selenide has high electrical conductivity, a high Seebeck coefficient, and low thermal conductivity, and exhibits excellent thermoelectric properties near room temperature (300 K). However, most of the silver selenide-based materials reported so far are non-flexible, which limits their application in flexible thermoelectric materials.

[0007] For example, CN109293962A discloses a method for preparing a silver selenide / nylon flexible composite film with high thermoelectric performance, comprising the following steps: (1) mixing a dispersion of selenium nanowires in ethylene glycol, silver nitrate, and ethylene glycol solvent, reacting, centrifuging, and washing to obtain silver selenide nanowires; (2) dispersing the silver selenide nanowires obtained in step (1) in anhydrous ethanol, using a nylon filter membrane as a sediment, and vacuum filtering to obtain a silver selenide / nylon flexible film; (3) finally, vacuum drying the silver selenide / nylon flexible film obtained in step (2), and then hot pressing to obtain the target product. This patent has poor flexibility and relatively high thermal conductivity. At the same time, it also performs poorly in terms of cost and toxicity. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for preparing ultra-flexible, high-performance sulfur-doped silver selenide / nylon composite thermoelectric film.

[0009] The purpose of the present invention can be achieved by the following technical solutions:

[0010] A method for preparing an ultra-flexible, high-performance sulfur-doped silver selenide / nylon composite thermoelectric film comprises the following steps:

[0011] (1) reacting selenium nanowires with silver sulfide powder in ethylene glycol as a solvent to obtain a silver-selenium-sulfur ternary alloy powder;

[0012] (2) The silver-selenium-sulfur ternary alloy powder is ultrasonically dispersed in anhydrous ethanol, and a nylon filter membrane is used as a substrate. The powder is vacuum filtered, dried, and then hot-pressed to obtain the target product.

[0013] Furthermore, in step (1), the molar ratio of selenium nanowires to silver sulfide is 0.6-0.8:1.

[0014] Furthermore, in step (1), the reaction temperature is 80-100° C. and the reaction time is 6-18 h.

[0015] Furthermore, in step (2), the ratio of anhydrous ethanol to the amount of silver sulfide used to prepare the silver-selenium-sulfur ternary alloy powder is (30-60) mL: 0.18 g.

[0016] Furthermore, in step (2), the pore size of the nylon filter membrane used is 0.22 μm.

[0017] Furthermore, in step (2), drying is carried out under vacuum conditions, the drying temperature is 60-70° C., and the drying time is 10-12 h.

[0018] Furthermore, in step (2), the process conditions of hot pressing are specifically: hot pressing at 200-250° C. and a pressure of 1-4 MPa for 30 minutes.

[0019] Furthermore, the silver sulfide powder used is produced by reacting silver nitrate with sulfur powder. Furthermore, the reaction temperature of the silver nitrate and sulfur powder is 120°C. The specific synthesis steps can be found in the following literature: "Ultralong Single-Crystalline Ag2S Nanowires: Promising Candidates for Photoswitches and Room-Temperature Oxygen Sensors" by D. Wang et al. Adv. Mater. 2008, 20, 2628–2632.

[0020] Furthermore, the selenium nanowires used were synthesized using selenium dioxide as a selenium source and ascorbic acid as a reducing agent. The specific synthesis steps of the selenium nanowires can be found in the following literature: "High-yield synthesis of selenium nanowires in water at room temperature" (Qing Li and Vivian Wing-Wah Yam, DOI: 10.1039 / b515025f).

[0021] The present invention relates to a method for preparing an ultra-flexible, high-performance, sulfur-doped silver selenide / nylon composite thermoelectric film. By using a simple wet chemical method, sulfur is doped into the silver selenide lattice. Taking advantage of the softness, non-toxicity, low cost, and low thermal conductivity of elemental sulfur, an ultra-flexible, high-performance, sulfur-doped silver selenide / nylon composite thermoelectric film with a unique core-shell structure is produced. Specifically, a predetermined ratio of selenium nanowires and silver sulfide powder are mixed and reacted at 90°C to produce a silver-selenium-sulfur ternary alloy powder. After filtration and film formation, the powder is hot-pressed to enhance performance. During the hot-pressing process, the alloy powder is in a viscous fluid state, and the affinity of silver for selenium is higher than that for sulfur. Therefore, silver and selenium first combine, forming nucleation and growth. Subsequently, silver combines with sulfur, which, together with unreacted amorphous sulfur, forms a shell surrounding the silver selenide. Furthermore, due to the poor fluidity of the viscous fluid, sulfur doping in the silver selenide and selenium doping in the silver sulfide are unavoidable. This results in a unique core-shell structure with selenium-doped silver sulfide and amorphous sulfur as the shell and sulfur-doped silver selenide as the core. Within this structure, the highly crystalline sulfur-doped silver selenide forms the primary conductive network, providing high electrical performance. The outer layer of selenium-doped silver sulfide and amorphous sulfur exhibits excellent plasticity, enhancing the film's flexibility and tensile strength. Furthermore, the outer layer's inherently low thermal conductivity, combined with the introduction of multiple heterogeneous interfaces, effectively reduces thermal conductivity, further enhancing the material's thermoelectric performance.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) This preparation process is convenient, simple, and easy to operate, with low reaction temperature, short reaction time, short heat treatment time, and energy saving;

[0024] (2) This preparation process introduces a certain amount of non-toxic and low-cost sulfur element, which reduces the cost and toxicity of the preparation and reduces pollution. In addition, sulfur-doped silver selenide materials are successfully synthesized by wet chemical methods. After hot pressing at a relatively low hot pressing temperature and pressure, a microstructure is obtained in which a shell layer containing selenium-doped silver sulfide and amorphous sulfur is relatively evenly wrapped around the inner sulfur-doped silver selenide grains.

[0025] (3) The selenium-doped silver sulfide and amorphous sulfur in the shell of the prepared special core-shell structure have excellent flexibility, which makes the entire inorganic film have good flexibility, and ultimately makes the composite film have excellent flexibility and greatly improved tensile properties;

[0026] (4) The selenium-doped silver sulfide and amorphous sulfur in the prepared special core-shell structure have very low thermal conductivity. At the same time, the introduction of multiple heterogeneous interfaces enhances the scattering of phonons, reduces the thermal conductivity of the material, and comprehensively improves the thermoelectric performance of the composite film;

[0027] (5) The flexible thermoelectric device prepared using this film has excellent performance, low contact resistance, low power loss, high power density under low temperature difference, and high device stability. It can be used for heat collection of wearable electronic devices in different usage scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 XRD patterns of sample films (film 1 and film 2) with selenium nanowire / silver sulfide molar ratios of 0.7 and 0.6, respectively, prepared in the present invention.

[0029] Figure 2 XRD patterns of sample powder (powder 1) and film (film 1) with a selenium nanowire / silver sulfide molar ratio of 0.7 prepared in the present invention.

[0030] Figure 3 This is the SEM image of sample film 1 prepared in the present invention.

[0031] Figure 4 This is a TEM image of powder 1 of the sample prepared in the present invention.

[0032] Figure 5 TEM image of sample film 1 prepared in the present invention.

[0033] Figure 6 This is a temperature-dependent thermoelectric performance diagram of sample film 1 prepared in the present invention.

[0034] Figure 7 The figure shows the flexibility test results of the sample film 1 prepared in the present invention. DETAILED DESCRIPTION

[0035] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0036] In the following examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0037] Example 1:

[0038] A method for preparing an ultra-flexible, high-performance, sulfur-doped silver selenide / nylon flexible composite thermoelectric film comprises adding 20 ml of ethylene glycol dispersion (25.7 mmol / L) of selenium nanowires, 0.18 g of silver sulfide (in an amount sufficient to achieve a molar ratio of selenium nanowires to silver sulfide of 0.7), and 20 ml of ethylene glycol to a beaker. The mixture is stirred at 90°C for 15 hours and then centrifuged at 3000 rpm. The resulting black precipitate is extracted and washed with anhydrous ethanol at 3000 rpm for 1 minute to remove impurities. After centrifugation, the carefully washed black target product is dispersed in 45 ml of anhydrous ethanol and ultrasonically dispersed for 15 minutes. The resulting film is then vacuum-filtered using a nylon filter membrane as a substrate to obtain a silver-selenium-sulfur ternary alloy nylon flexible film. The resulting film is then dried in a vacuum drying oven at 60°C for 12 hours. The film is then removed and hot-pressed at 230°C and 1 MPa for 30 minutes to obtain an ultra-flexible, sulfur-doped silver selenide / nylon composite thermoelectric film.

[0039] Figure 1 The following are XRD patterns of sample films (film 1 and film 2) obtained with a selenium nanowire / silver sulfide molar ratio of 0.7 and 0.6, respectively. As can be seen from the figure, when the selenium / silver sulfide molar ratio is 0.7 (film 1), the resulting film is primarily composed of silver selenide (JCPDS#24-1041); when the selenium / silver sulfide molar ratio is 0.6 (film 2), the resulting film is primarily composed of silver sulfide (JCPDS#14-0072). Since this patent primarily studies the thermoelectric properties of silver selenide-based materials, other characterizations of the selenium / silver sulfide molar ratio of 0.6 (film 2) will not be described below.

[0040] Figure 2The XRD patterns of the prepared sample powder (powder 1) and film (film 1) with a selenium nanowire / silver sulfide molar ratio of 0.7 are shown. As can be seen from the figure, when the selenium / silver sulfide molar ratio is 0.7, silver selenide is already the main phase in the powder state. After hot pressing, the XRD diffraction peak of film 1 becomes sharper, indicating that the crystallinity of the film is improved. Compared with the diffraction peak of powder 1, the secondary peak of film 1 diffraction peak changes, indicating that hot pressing also affects the orientation of the grains in the film. From the local magnified diffraction pattern at 30-35°, it can be seen that the diffraction peak of film 1 is shifted to the right to a certain extent compared with the standard card. This is mainly due to the doping of sulfur in silver selenide, because the atomic radius of sulfur is 0.109nm, which is significantly smaller than the atomic radius of selenium, which is 7.896nm. This also proves that this patent successfully incorporates sulfur into silver selenide.

[0041] Figure 3 This is a SEM image of sample film 1. As can be seen, after hot pressing, the film becomes relatively dense, containing a small amount of pores with a pore size of approximately 50-500 nm. This dense film improves the material's electrical conductivity.

[0042] Figure 4 The following is a TEM image of the powder 1. Four points were selected for elemental analysis, and the results are shown in Table 1. The powder was found to be a silver-selenium-sulfur ternary alloy powder (the percentages of silver-selenium-sulfur elements corresponding to the four selected points).

[0043] Table 1

[0044] point 1 2 3 4 S(％) 4.6 3.7 4.7 1.4 Se(%) 13.8 15.0 30.7 36.0 Ag(%) 81.6 81.3 60.6 62.6

[0045] Figure 5 TEM image of the prepared sample film 1. Figure 5 a is a typical HRTEM image of film 1, showing a porous network structure. Figure 5 Figure b is an enlarged view of the area within the yellow box in Figure a. As can be seen from Figure b, film 1 has an interesting "core-shell" structure, with an inner layer consisting of well-crystalline sulfur-doped silver selenide and an outer layer consisting of a shell approximately 15 nm thick, which includes selenium-doped silver sulfide and amorphous sulfur. The well-crystalline sulfur-doped silver selenide forms the primary conductive pathway, through which carriers can migrate smoothly, ensuring high conductivity. The selenium-doped silver sulfide and amorphous sulfur in the outer layer have excellent plasticity and can wrap around the inner layer, improving the material's flexibility and tensile strength to a certain extent. In addition, due to their intrinsically low thermal conductivity and the introduction of multiple interface-scattered phonons of different wavelengths, they effectively reduce the material's thermal conductivity.

[0046] Figure 6 The temperature-dependent thermoelectric performance diagram of the prepared sample film 1. At 300K, the conductivity of the film is 849.1S·cm -1 , has high conductivity; Seebeck coefficient is -106μV·K -1 , indicating that the film is an n-type thermoelectric material. As the temperature increases, the conductivity of the film increases in the range of 300-380K and reaches a maximum of about 1486.8S·cm near 380K. -1 ; At 380-420K, it shows a downward trend. As the temperature rises, the absolute value of the Seebeck coefficient of the film gradually decreases until it shows an upward trend around 350K. After 380K, it continues to decrease until 420K. This is related to the phase transition of silver selenide around 407K (from monoclinic phase to cubic phase). The power factor value calculated from this shows a change pattern of first increasing and then decreasing as the temperature rises, from 954.7μW·m at room temperature to 100μW·m -1 ·K -2 The maximum value is 1208.6μW·m at 380K -1 ·K -2 .

[0047] Figure 7 The flexibility test results of the prepared sample film 1 are shown below. After being bent around a round rod with a radius of 4 mm 1000 times, the conductivity of film 1 remained at 96.2% of the initial value. After being bent 2000 times, the conductivity remained at 94.4% of the initial value, demonstrating excellent flexibility.

[0048] Example 2:

[0049] Compared with Example 1, most of the steps are the same except that the amount of sulfur added is adjusted so that the molar ratio of selenium nanowires to silver sulfide is 0.5.

[0050] Example 3:

[0051] Compared with Example 1, most of the steps are the same except that the amount of silver sulfide added is adjusted so that the molar ratio of selenium nanowires to silver sulfide is 0.8:1.

[0052] Example 4:

[0053] Compared with Example 1, most of the steps are the same, except that the reaction temperature of selenium nanowires and silver sulfide is controlled to be 80° C. and the reaction time is controlled to be 18 h.

[0054] Example 5:

[0055] Compared with Example 1, most of the steps are the same, except that the reaction temperature of the selenium nanowires and the silver sulfide is controlled to be 100° C. and the reaction time is controlled to be 12 h.

[0056] Example 6:

[0057] Compared with Example 1, most of the conditions are the same, except that the process conditions for controlling the hot pressing are specifically: hot pressing at 200° C. and a pressure of 1 MPa for 30 minutes.

[0058] Example 7:

[0059] Compared with Example 1, most of the conditions are the same, except that the process conditions for controlling the hot pressing are specifically: hot pressing at 250° C. and a pressure of 4 MPa for 30 minutes.

[0060] Example 3:

[0061] Compared with Example 1, most of the steps are the same except that the amount of silver sulfide added is adjusted so that the molar ratio of selenium nanowires to silver sulfide is 0.6:1.

[0062] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing ultra-flexible, high-performance sulfur-doped silver selenide / nylon composite thermoelectric film, characterized in that: The following steps are involved: (1) reacting selenium nanowires with silver sulfide powder in ethylene glycol as a solvent to obtain a silver-selenium-sulfur ternary alloy powder; (2) taking silver, selenium and sulfur ternary alloy powder and ultrasonically dispersing it in anhydrous ethanol, using a nylon filter membrane as a substrate, vacuum filtering, drying, and then hot pressing to obtain the target product; In step (1), the molar ratio of selenium nanowires to silver sulfide is 0.6 to 0.8:1; In step (1), the reaction temperature is 80-100° C. and the reaction time is 6-18 hours.

2. The method for preparing an ultra-flexible, high-performance sulfur-doped silver selenide / nylon composite thermoelectric film according to claim 1, characterized in that: In step (2), the ratio of anhydrous ethanol to the amount of silver sulfide used to prepare the silver-selenium-sulfur ternary alloy powder is (30-60) mL: 0.18 g.

3. The method for preparing an ultra-flexible, high-performance sulfur-doped silver selenide / nylon composite thermoelectric film according to claim 1, characterized in that: In step (2), the pore size of the nylon filter membrane used is 0.22 μm.

4. The method for preparing an ultra-flexible, high-performance sulfur-doped silver selenide / nylon composite thermoelectric film according to claim 1, characterized in that: In step (2), drying is carried out under vacuum conditions, the drying temperature is 60-70° C., and the drying time is 10-12 h.

5. The method for preparing an ultra-flexible, high-performance sulfur-doped silver selenide / nylon composite thermoelectric film according to claim 1, characterized in that: In step (2), the hot pressing process conditions are specifically: hot pressing at 200-250° C. and a pressure of 1-4 MPa for 30 minutes.

6. The method for preparing an ultra-flexible, high-performance sulfur-doped silver selenide / nylon composite thermoelectric film according to claim 1, characterized in that: The silver sulfide powder used is produced by reacting silver nitrate with sulfur powder.

7. The method for preparing an ultra-flexible, high-performance sulfur-doped silver selenide / nylon composite thermoelectric film according to claim 6, characterized in that: The temperature for the reaction of silver nitrate and sulfur powder is 120℃.

8. The method for preparing an ultra-flexible, high-performance sulfur-doped silver selenide / nylon composite thermoelectric film according to claim 1, characterized in that: The selenium nanowires are synthesized by using selenium dioxide as a selenium source and ascorbic acid as a reducing agent.

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