A near-room-temperature Ag2Se / MSe nanocomposite thermoelectric material and its preparation method

Abstract

The present invention discloses a near-room-temperature Ag2Se / MSe nanocomposite thermoelectric material and a preparation method thereof. The preparation method comprises the following steps: synthesizing a matrix Ag2Se particle by an aqueous solution method; mixing MO metal oxide powder with Se powder and adding the mixture to an amine-thiol mixed solution to obtain a MSe molecular ligand; then surface-modifying the matrix Ag2Se particle with the MSe molecular ligand and performing post-processing to obtain a near-room-temperature Ag2Se / MSe nanocomposite material, wherein the M is Cd or Zn, and the mole fraction of MSe in the Ag2Se / MSe nanocomposite material is 2% to 10%. The Ag2Se / MSe nanocomposite material is placed in a tubular furnace, annealed under a nitrogen atmosphere, and densified by plasma discharge sintering to obtain the Ag2Se / MSe nanocomposite thermoelectric material block. The present invention effectively reduces the excessively high carrier concentration of the Ag2Se material by surface functionalization, and simultaneously utilizes the MSe nanoprecipitate phase to enhance phonon scattering, thereby achieving an Ag2Se-based thermoelectric material with high thermoelectric performance at room temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of energy materials, and in particular to a near-room temperature Ag2Se / MSe nanocomposite thermoelectric material and a preparation method thereof. Background Art

[0002] Thermoelectric materials can convert heat energy into electrical energy and vice versa, and play a vital role in promoting compact cooling systems in 5G networks, seamless integration of the Internet of Things, and self-powered technologies based on body temperature. However, due to the insufficient performance of existing materials, complex manufacturing processes, and many challenges in integrating materials into functional devices, the potential of thermoelectric materials has not yet been fully explored. The ideal thermoelectric material needs to have both a high Seebeck coefficient (S) and high electrical conductivity (σ), as well as low thermal conductivity (κ tot ) to achieve excellent thermoelectric performance. However, due to the close relationship between carrier and phonon transport, improving the thermoelectric performance coefficient (zT=σS2T / κ tot ) faces great challenges. To address these issues, researchers have proposed a series of strategies, including adjusting the carrier concentration through doping or alloying, optimizing the electronic structure through bandgap engineering, and improving material properties through crystal structure modification. In addition, materials with naturally low lattice thermal conductivity have been explored, and multi-scale layered structures have been designed to scatter phonons across the entire spectrum, thereby further reducing the thermal conductivity κ. tot Therefore, the key to achieving high-performance thermoelectric materials lies in the fine engineering design of their composition and microstructure, which can not only optimize the thermoelectric performance but also improve the processability and feasibility of practical applications.

[0003] Currently, N-type thermoelectric materials near room temperature still rely primarily on Bi2Te3-based compounds as a performance benchmark. However, the scarcity of tellurium, the complex processing of Bi2Te3, and its poor mechanical properties significantly limit the widespread application and promotion of this type of material. In contrast, Ag2Se is considered a promising N-type thermoelectric material, with room-temperature performance comparable to, and potentially exceeding, that of Bi2Te3. At approximately 406K, Ag2Se undergoes a phase transition from the orthorhombic β-Ag2Se phase to the cubic α-Ag2Se phase. This first-order phase transition is accompanied by significant changes in the crystal structure and electronic structure, which directly affect its transport properties. Therefore, the excellent thermoelectric performance of Ag2Se is mainly reflected in the near-room temperature range before the phase transition. However, the performance stability of Ag2Se is significantly affected by the stoichiometric ratio and defect control. This is mainly due to the weak ionicity of the Ag-Se bond, which allows Ag ions to easily migrate to interstitial positions, providing additional free electrons. At the same time, the volatility of Se at high temperatures results in a high carrier concentration (>10 19 cm -3) is significantly higher than the range required to achieve optimal thermoelectric performance (~10 18 cm -3 ). Excessive carrier concentration not only affects the power factor (PF = σS2) of the material, but also increases the total thermal conductivity κ tot , further limiting its thermoelectric performance. In addition, the Ag2Se materials synthesized by the traditional solid-phase melting method have great difficulties in controlling the composition, and cannot effectively regulate the grain size and grain boundary phase of the bulk, resulting in significant differences in the transport parameters of samples with the same nominal composition, thereby causing a large range of fluctuations in the thermoelectric figure of merit (zT). On the other hand, although the solution method provides a certain degree of advantage, its mainstream methods (such as solvothermal and hydrothermal methods) usually require time-consuming and energy-consuming high-temperature reaction equipment, and the single output is limited, which seriously limits its economic and scalability potential for practical application. Therefore, developing a preparation method with high composition control accuracy, higher cost-effectiveness and easy scalability is the key to achieving widespread application of Ag2Se materials. Summary of the Invention

[0004] The purpose of the present invention is to provide a near-room temperature Ag2Se / MSe nanocomposite thermoelectric material and a preparation method thereof. The preparation method is simple, the synthesis conditions are mild and the energy consumption is low. It can realize large-scale rapid synthesis of high power factor Ag2Se-based nanocomposite thermoelectric materials near room temperature and has good practical application value.

[0005] In one aspect of the present invention, a method for preparing a near-room-temperature Ag2Se / MSe nanocomposite material is provided. According to an embodiment of the present invention, the method comprises the following steps:

[0006] (1) Synthesizing matrix Ag2Se particles by aqueous solution method;

[0007] (2) MO metal oxide powder and Se powder are mixed and added to an amine-thiol mixed solution to obtain MSe molecular ligands, and then the MSe molecular ligands are surface-modified on the matrix Ag2Se particles and post-treated to obtain a near-room temperature Ag2Se / MSe nanocomposite material, wherein the M is Cd or Zn, and the molar fraction of MSe in the Ag2Se / MSe nanocomposite material is 2% to 10%.

[0008] In addition, the method for preparing a near-room-temperature Ag2Se / MSe nanocomposite material according to the above embodiment of the present invention may also have the following additional technical features:

[0009] In some embodiments of the present invention, in step (1), the aqueous solution method is as follows: under argon protection, AgNO3 is added to deionized water to prepare an Ag source precursor; Se powder is slowly added to an aqueous solution of NaBH4 until the reaction is completely clarified to obtain a Se source precursor; the Se source precursor is added to a preheated boiling aqueous solution of the Ag source precursor to react, and after the reaction is completed, the solution is cooled to room temperature, washed, centrifuged, and vacuum dried to obtain Ag2Se particles.

[0010] In some embodiments of the present invention, the concentration of AgNO3 dissolved in deionized water is 0.3-0.5 mol·L -1 , the molar ratio of Se powder to NaBH4 is 1.0-1.1:2, and the molar ratio of Ag source precursor to Se source precursor is 2:0.9-1.2; the Se source precursor is added to the preheated boiling aqueous solution of Ag source precursor for reaction at a temperature of 100-101.3°C and a reaction time of 0.5-60min; the washing is performed by alternating washing with deionized water and ethanol for purification 2-5 times; the centrifugal speed is 5000-8000rpm, and the centrifugal time is 1-5min; the drying is performed by vacuum drying, the vacuum drying time is 6-8h, and the temperature is 60-80°C.

[0011] In some embodiments of the present invention, in step (2), the preparation method of the MSe molecular ligand is as follows: under a nitrogen atmosphere, MO metal oxide powder and Se powder are dissolved in ethylenediamine and 1,2-ethanedithiol solution, and stirred at room temperature until completely dissolved to obtain the MSe molecular ligand.

[0012] In some embodiments of the present invention, in step (2), the step of modifying the surface of the matrix Ag2Se particles with MSe molecular ligands is specifically as follows: adding N-methylformamide (MFA) solution to the Ag2Se solution, adding the MSe molecular ligand after uniform dispersion, stirring for a certain period of time, centrifuging and purifying it with acetone several times, and vacuum drying to obtain the Ag2Se@MSe nanocomposite thermoelectric material.

[0013] In some embodiments of the present invention, the molar ratio of Ag2Se to MSe is 1:x%, wherein 0<x≤10; the stirring time is not less than 24 hours; the centrifugal speed is 5000-10000 rpm, and the centrifugal time is 5-10 min; the drying is vacuum drying, the vacuum drying time is 6-8 h, and the temperature is 60-80°C.

[0014] In another aspect of the present invention, the present invention provides a near-room temperature Ag2Se / MSe nanocomposite material prepared according to the preparation method.

[0015] In another aspect of the present invention, a method for preparing an Ag2Se / MSe nanocomposite thermoelectric material is proposed. According to an embodiment of the present invention, the method includes the following steps: placing the Ag2Se / MSe nanocomposite material in a tubular furnace, annealing it in a nitrogen atmosphere, and densifying it by plasma discharge sintering to obtain the Ag2Se / MSe nanocomposite thermoelectric material block.

[0016] In addition, the method for preparing an Ag2Se / MSe nanocomposite thermoelectric material according to the above embodiment of the present invention may also have the following additional technical features:

[0017] In some embodiments of the present invention, the annealing temperature is 350-450°C, and the heating rate is 5-15°C·min -1 , annealing time is not less than 60min; the pressure of the plasma discharge sintering is 45-60MPa, the temperature is 350-450℃, and the time is not less than 5min.

[0018] In another aspect of the present invention, the present invention provides an Ag2Se / MSe nanocomposite thermoelectric material prepared according to the Ag2Se / MSe nanocomposite thermoelectric material preparation method.

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

[0020] 1) Efficient, Controllable, and Precise Preparation: This invention proposes a novel, controllable, large-scale, and low-cost solution-based method for the rapid preparation of Ag2Se / MSe nanocomposites at near-room temperature. Compared to traditional solid-phase melting methods, this method utilizes a "bottom-up" aqueous solution synthesis strategy, enabling rapid material preparation at low temperatures. This method utilizes MSe molecular ligands to modify the Ag2Se matrix in aqueous solution, distinguishing it from conventional hydrothermal, solvothermal, and hot injection colloid methods. It effectively constructs near-room-temperature Ag2Se-based nanocomposite thermoelectric materials. Compared to traditional solid-phase synthesis and other liquid-phase synthesis methods (such as hydrothermal and solvothermal), this method offers significant advantages: the entire process eliminates the long, energy-intensive processing required for high-temperature (>1000K) processing required for solid-phase synthesis. Furthermore, it is not limited by the equipment and capacity of high-pressure reactors, making it suitable for the cost-effective, large-scale preparation of Ag2Se-based bulk materials. The process is simple, easy to operate, and does not require expensive or complex equipment. The preparation process is highly reproducible, demonstrating excellent potential for industrial application.

[0021] 2) Composition Control and Microstructure Optimization: In the synthesis method of Ag2Se materials, Ag precipitates are often observed, which is almost unavoidable. This is because the composition range of pure Ag2Se in the phase diagram is extremely narrow. However, the present invention uses molecular ligands prepared by the "amine-thiol" system to effectively eliminate the inevitable Ag second phase in the Ag2Se matrix. This improvement significantly reduces the excessive carrier concentration caused by the Ag second phase and accurately controls the stoichiometric ratio of Ag2Se, thereby achieving excellent electrical transmission performance with ultra-high power factor. During the sintering process, the MSe molecular ligands further crystallize to form nanocrystals, and the grain size and grain boundary structure of the material are precisely controlled through the "pinning effect."

[0022] 3) Significantly improve the near-room-temperature thermoelectric performance: During the sintering process of the present invention, the MSe molecular ligands further crystallize to form nanocrystals, and the grain size and grain boundary structure of the material are precisely controlled through the "pinning effect". At the same time, this method introduces more defect structures, greatly enhancing the phonon scattering ability, thereby providing a novel and efficient solution for the synergistic optimization of the electrical and thermal properties of Ag2Se-based thermoelectric materials. The Ag2Se / MSe nanocomposite material block finally prepared exhibits an almost constant high average thermoelectric figure of merit (zT avg ~1) and exhibits excellent thermal stability. These properties make it have great potential in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the process of preparing the Ag2Se / MSe nanocomposite thermoelectric material in Comparative Example 1 and Examples 1-8 of the present invention;

[0024] Figure 2 a) TEM image of Ag2Se nanoparticles without surface modification in Comparative Example 1 of the present invention, b) TEM image of Ag2Se@CdSe powder modified with 7% CdSe molecular ligands in Example 4 of the present invention, c) TEM image of Ag2Se@ZnSe modified with 4% ZnSe molecular ligands in Example 7 of the present invention;

[0025] Figure 3a) is the X-ray diffraction pattern (XRD) of the Ag2Se / x%CdSe (x=2, 4, 6, 7, 10) nanocomposite materials in Comparative Example 1 and Examples 1-5 of the present invention, b) is an enlarged view of the (112) peak and the (121) peak in the figure a), c) is the corresponding lattice parameters of the Ag2Se / x%CdSe nanocomposite materials in the a, b, and c directions calculated from the XRD pattern, d) is the X-ray diffraction pattern (XRD) of the Ag2Se / x%ZnSe (x=3, 4, 5) nanocomposite materials in Comparative Example 1 and Examples 6-8, and e) is an enlarged view of the (112) peak and the (121) peak in the figure d);

[0026] Figure 4 Figure 2. Temperature evolution of in situ XRD patterns of a) Ag2Se and b) Ag2Se / 7%CdSe bulk in the temperature range of 323–503 K, with two-dimensional plots of their intensity versus 2θ and temperature (T). c) Left: Temperature-dependent lattice parameters obtained by Rietveld refinement of XRD data. Right: Reversible phase transition of Ag2Se, characterized by different crystal structure transitions between β-Ag2Se and α-Ag2Se phases.

[0027] Figure 5 Scanning tunneling microscope (SEM) images of Ag2Se / x%CdSe (x=0, 2, 4, 6, 7, 10) and Ag2Se / x%ZnSe (x=3, 4, 5) prepared in Examples 1-8 of the present invention;

[0028] Figure 6 In the figure, a) is the transmission electron microscopy (TEM) image of the Ag2Se matrix, bc) is the STEM-EDX element mapping of the square marked area in a); d) is the TEM image of Ag2Se / 7%CdSe nanoparticles; e) dislocation defect structure of Ag2Se / 7%CdSe nanoparticles; f) lattice strain defect structure of Ag2Se / 7%CdSe nanoparticles; g) dark field STEM images of Ag2Se / 7%CdSe at different magnifications, inset: STEM-EDX element mapping; h) high-resolution TEM image of Ag2Se / 7%CdSe nanoparticles; i) TEM image of Ag2Se / 4%ZnSe; j) TEM image of part of Ag2Se / 4%ZnSe; k) the boxed area is the STEM-EDX element mapping of Ag2Se / 4%ZnSe;

[0029] Figure 7 The thermoelectric performance diagram of the nanocomposite materials of Comparative Example 1 (Ag2Se matrix), Example 4 (Ag2Se / 7% CdSe) and Example 7 (Ag2Se / 4% ZnSe) of the present invention, a) electrical conductivity σ, b) thermal conductivity κ totFigure 2. c) Thermoelectric figure of merit zT value, d) Average thermoelectric figure of merit zT in the entire temperature test range of 300-390K ave value. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0031] Example 1

[0032] A method for preparing a near-room-temperature Ag2Se / 2%CdSe nanocomposite thermoelectric material comprises the following steps:

[0033] Step 1: Prepare Ag2Se matrix particles using an aqueous solution method. AgNO3 and Se powder are reacted according to the molar ratio of Ag:Se in Ag2Se = 2:1.1. This includes the following steps:

[0034] a. First, prepare a cationic Ag source precursor, AgNO3 solution, by mixing 60 mmol of AgNO3 (10.1922 g) powder with 150 mL of deionized water and stirring under nitrogen until completely dissolved. The solution is then heated to boiling (approximately 101.3°C) under reflux to obtain the cationic Ag source precursor.

[0035] b. Prepare a NaHSe solution, the precursor of the anionic Se source. Dissolve 60 mmol of NaBH4 (2.2698 g) in 150 mL of deionized water until completely dissolved. Slowly add 33 mmol of Se powder (2.6057 g) to the solution. This step will generate a large amount of hydrogen gas (avoid stirring). Once the bubbles disappear, stir under nitrogen until the solution becomes nearly colorless and transparent. This indicates that the Se powder has been completely reduced, resulting in the Se source precursor.

[0036] c. Rapidly inject the prepared Se source precursor into the boiling cationic Ag source precursor solution. The temperature then drops to 78°C. Once the reaction solution reaches a boil again, incubate for 30 minutes. After the reaction is complete, stop stirring, cool to room temperature in a water bath, and pour off the supernatant. Wash the remaining black precipitate three times with alternating centrifugation with deionized water and ethanol. The deionized water wash is centrifuged at 5000 rpm and 1 minute, respectively; the ethanol wash is centrifuged at 6000 rpm and 1 minute, respectively. Vacuum dry at 60°C for 6 hours to obtain Ag2Se matrix particles.

[0037] Step 2, preparation of CdSe molecular ligand, comprising the following steps:

[0038] d. 4 mmol of CdO and 4 mmol of Se powder were weighed at a molar ratio of Cd:Se = 1:1 and placed in a nitrogen-filled glass bottle. 8 mL of ethylenediamine and 0.8 mL of 1,2-ethanedithiol were injected into the above powder and stirred at room temperature for 5 minutes until completely dissolved, obtaining a CdSe molecular ligand with a concentration of 87 mg / mL.

[0039] Step 3: Preparation of Ag2Se / 2%CdSe nanocomposite thermoelectric material

[0040] e. In an inert gas glove box, weigh 0.3 mL of the CdSe molecular ligand solution obtained in step d and add a certain volume of N-methylformamide (MFA) solution under a nitrogen atmosphere to maintain its concentration at 50 μL / mL. Subsequently, this solution was mixed with 2.0 g of accurately weighed Ag2Se particles under nitrogen protection and stirred at room temperature for 24 hours to uniformly modify the CdSe molecular ligands on the surface of the Ag2Se particles. After completion, the mixture was purified and washed with acetone. Finally, it was dried in a vacuum drying oven at 60°C for 8 hours to obtain the Ag2Se / 2% CdSe nanocomposite thermoelectric material powder.

[0041] f. The nanocomposite powder dried in step e was introduced into a tube furnace with high-purity N2 gas at 10 ° C. min. -1 The sample was heated to 400°C at a ramp rate of 100°C and annealed at 400°C for 60 minutes. After annealing, the sample was quickly transferred to a glove box. Subsequently, plasma spark sintering was performed at 400°C at a pressure of 45 MPa for 5 minutes to densify the sample, yielding a Ag2Se / 2%CdSe nanocomposite thermoelectric material block (8.6 mm in diameter and 1.5 mm in thickness).

[0042] Example 2

[0043] A method for preparing a near-room temperature Ag2Se / 4% CdSe nanocomposite thermoelectric material. This embodiment differs from Example 1 in that, in step e, 0.6 mL of the CdSe molecular complex solution obtained in step d is weighed in an inert gas glove box and then N-methylformamide (MFA) solution is added. Finally, in step f, a bulk Ag2Se / 4% CdSe nanocomposite thermoelectric material is obtained. The remaining steps are the same as in Example 1.

[0044] Example 3

[0045] A method for preparing a near-room temperature Ag2Se / 6% CdSe nanocomposite thermoelectric material. This embodiment differs from Example 1 in that, in step e, 0.9 mL of the CdSe molecular complex solution obtained in step d is weighed in an inert gas glove box and then N-methylformamide (MFA) solution is added. Finally, in step f, a bulk Ag2Se / 6% CdSe nanocomposite thermoelectric material is obtained. The remaining steps are the same as in Example 1.

[0046] Example 4

[0047] A method for preparing a near-room temperature Ag2Se / 7% CdSe nanocomposite thermoelectric material. This embodiment differs from Example 1 in that, in step e, 1.05 mL of the CdSe molecular complex solution obtained in step d is weighed in an inert gas glove box and then N-methylformamide (MFA) solution is added. Finally, in step f, a bulk Ag2Se / 7% CdSe nanocomposite thermoelectric material is obtained. The remaining steps are the same as in Example 1.

[0048] Example 5

[0049] A method for preparing a near-room temperature Ag2Se / 10% CdSe nanocomposite thermoelectric material. This embodiment differs from Example 1 in that, in step e, 1.5 mL of the CdSe molecular complex solution obtained in step d is weighed in an inert gas glove box and then N-methylformamide (MFA) solution is added. Finally, in step f, a bulk Ag2Se / 10% CdSe nanocomposite thermoelectric material is obtained. The remaining steps are the same as in Example 1.

[0050] Example 6

[0051] A method for preparing a near-room temperature Ag2Se / 3% ZnSe nanocomposite thermoelectric material comprises the following steps:

[0052] Step 1 is the same as step 1 of Example 1.

[0053] Step 2, preparation of ZnSe molecular ligand, comprising the following steps:

[0054] i. 4 mmol of ZnO and 4 mmol of Se powder were thoroughly mixed at a molar ratio of Zn:Se ​​= 1:1 under a nitrogen atmosphere. 12 mL of ethylenediamine and 1.2 mL of 1,2-ethanedithiol were then injected into the powder and stirred at room temperature for 5 minutes until completely dissolved, yielding a ZnSe molecular ligand concentration of 43.7 mg / mL.

[0055] Step 3: Preparation of Ag2Se / 3% ZnSe nanocomposite thermoelectric material

[0056] ii. In an inert gas glove box, weigh 0.67 mL of the ZnSe molecular complex solution obtained in step i and add a certain volume of N-methylformamide (MFA) solution under a nitrogen atmosphere to maintain its concentration at 50 μL / mL. Subsequently, these solutions were mixed with 2.0 g of accurately weighed Ag2Se particles under nitrogen protection and stirred at room temperature for 24 hours to uniformly modify the ZnSe molecular ligands on the surface of the Ag2Se particles. After completion, the mixture was purified and washed with acetone. Finally, the Ag2Se / 3% ZnSe nanocomposite thermoelectric material powder was obtained by drying in a vacuum drying oven at 60°C for 8 hours.

[0057] iii. The nanocomposite powder dried in step ii was introduced into a tube furnace with high-purity N2 gas at 10 ° C. min. -1 The sample was heated to 400°C at a ramp rate of 100°C and annealed at 400°C for 60 minutes. After annealing, it was quickly transferred to a glove box. Subsequently, plasma spark sintering was performed at 400°C at a pressure of 45 MPa for 5 minutes to obtain a Ag2Se / 3%ZnSe nanocomposite thermoelectric material block (8.6 mm in diameter and 1.5 mm in thickness).

[0058] Example 7

[0059] A method for preparing a near-room temperature Ag2Se / 4% ZnSe nanocomposite thermoelectric material. This embodiment differs from Example 6 in that, in step ii, 0.9 mL of the ZnSe molecular ligand solution obtained in step i is weighed in an inert gas glove box and then N-methylformamide (MFA) solution is added. Finally, in step iii, a bulk Ag2Se / 4% ZnSe nanocomposite thermoelectric material is obtained. The remaining steps are the same as in Example 1.

[0060] Example 8

[0061] A method for preparing a near-room temperature Ag2Se / 5% ZnSe nanocomposite thermoelectric material. This embodiment differs from Example 6 in that, in step ii, 1.12 mL of the ZnSe molecular complex solution obtained in step i is weighed in an inert gas glove box, followed by the addition of N-methylformamide (MFA) solution. Finally, in step iii, a bulk Ag2Se / 5% ZnSe nanocomposite thermoelectric material is obtained. The remaining steps are the same as in Example 1.

[0062] Comparative Example 1

[0063] The preparation method of the matrix Ag2Se thermoelectric block material is consistent with the preparation steps of the matrix Ag2Se in Examples 1-8, and mainly includes the following steps:

[0064] Take 2.0g of the Ag2Se matrix particles prepared in step 1 of Example 1, introduce high-purity N2 gas into a tube furnace at 10℃·min -1 The sample was heated to 400°C at a heating rate of 100°C and annealed at this temperature for 1 hour. After annealing, the sample was quickly transferred to a glove box. The annealed Ag2Se powder was then ground in an agate mortar and poured into an 8.6mm diameter graphite mold lined with 0.20mm carbon paper. This mold was then plasma-sintered at 400°C for 5 minutes at a pressure of 45MPa to obtain a block with a diameter of 8.6mm and a thickness of 1.5mm.

[0065] The particle micrographs and element distribution diagrams of the Ag2Se / MSe (M=Cd, Zn) nanocomposite powders prepared in Examples 1-8 and Comparative Example 1 were characterized using a German Zeiss field emission scanning electron microscope AurigaZeiss (SEM). The physical phases of the Ag2Se / MSe (M=Cd, Zn) composite materials in Examples 1-8 and the block in Comparative Example 1 were characterized using a German Bruker AXSD8 ADVANCE X-ray diffractometer (XRD). The electrical conductivity (σ) and Seebeck coefficient (S) of the samples were tested using a German Lindsay Seebeck coefficient / resistance analysis system LSR-3. The thermal diffusion rate (λ) of the samples was determined using a German Lindsay laser flash analyzer LFA 1000, and the final total thermal conductivity κ of the samples was calculated. tot .

[0066] Table 1 Parameters of the Ag2Se bulk matrix prepared in Comparative Example 1 and the Ag2Se / MSe (M=Cd, Zn) nanocomposite bulk prepared in Examples 1-8

[0067] sample <![CDATA[Ag2Se / x%MSe(M=Cd,Zn)]]> Required MSe molecular ligand (mL) <![CDATA[Density (g·cm -3 )]]> Relative theoretical density Comparative Example 1 x＝0 0 8.15 99.1％ Example 1 x=2%,M=Cd 0.3,M=Cd 8.01 97.4％ Example 2 x=4%,M=Cd 0.6,M=Cd 7.99 97.2％ Example 3 x=6%,M=Cd 0.9,M=Cd 7.87 96.5％ Example 4 x=7%,M=Cd 1.05,M=Cd 7.83 96.1％ Example 5 x=10%,M=Cd 1.5,M=Cd 7.85 95.5％ Example 6 x=3%,M=Zn 0.67,M=Zn 7.99 97.2％ Example 7 x=4%,M=Zn 0.90,M=Zn 7.92 96.3％ Example 8 x=5%,M=Zn 1.12,M=Zn 7.89 96.0％

[0068] The block density obtained in Comparative Example 1 and Examples 1-8 is within the theoretical density (8.22 g·cm -3 ) is between 95% and 99%.

[0069] The performance and structural morphology of the sintered samples and their cross sections were characterized by the following tests: 2 κ tot -1 (where T is the absolute temperature in thermodynamics; S is the Seebeck coefficient; σ is the electrical conductivity; κ tot is the thermal conductivity; where κ tot =λC p ρ, λ are thermal diffusivity, C p is the specific heat, ρ is the bulk density) and the thermoelectric figure of merit zT is calculated.

[0070] like Figure 1As shown, Ag2Se nanoparticles are synthesized in large quantities at near-room temperature and then added to a mixed solution of MSe (M=Cd, Zn) molecular ligands and N-methylformamide (MFA). After a series of precipitation, purification, and vacuum drying, surface-modified Ag2Se / MSe powder is obtained. Subsequently, annealing and densification sintering are performed to obtain a tightly bounded Ag2Se / MSe nanocomposite bulk, which contains numerous grain boundaries, dislocations, and MSe nanoprecipitates.

[0071] like Figure 2 As shown in the figures, a) the size distribution of the Ag2Se matrix particles is relatively wide, ranging from a few hundred nanometers to about 2 μm; bc) Ag2Se@MSe powders formed by surface treatment of Ag2Se matrix particles modified with MSe molecular ligands show that this surface modification causes the edges of the Ag2Se particles to soften slightly, making them appear more rounded. This phenomenon can be explained by the solubility of the "thiol-amine" solvent system, which can dissolve bulk inorganic materials, especially the high-energy atoms on the surface of the Ag2Se matrix.

[0072] like Figure 3 As shown in Figure a), it can be seen that all the characteristic peaks of the composite material block are the characteristic spectral lines of the matrix Ag2Se (standard card PDF 01-071-2410), indicating that the final prepared composite material is an Ag2Se-based compound, and its components correspond to the five different block samples of Ag2Se / 2%CdSe, Ag2Se / 4%CdSe, Ag2Se / 6%CdSe, Ag2Se / 7%CdSe, and Ag2Se / 10%CdSe in Examples 1-5, respectively, and are all consistent with the peaks of the pure phase of Ag2Se, and no impurity peaks appear. b) The enlarged (112) peak and (121) peak in the figure also verify this situation. c) The figure is the lattice parameters of all Ag2Se / x%CdSe samples in the a, b and c directions. The lattice parameters of all samples in each direction are consistent, which shows that the addition of CdSe molecular complexes will not change the lattice parameters. 2+ It is not doped into the orthorhombic β-Ag2Se lattice. d) Figure corresponds to three different bulk samples of Ag2Se / 3% ZnSe, Ag2Se / 4% ZnSe, and Ag2Se / 5% ZnSe in Examples 6-8, respectively. All of them are consistent with the characteristic peaks of pure Ag2Se, with no impurity peaks appearing. e) The magnified (112) and (121) peaks in the figure also confirm this.

[0073] like Figure 4 As shown, the Ag2Se thermoelectric block in Comparative Example 1 ( Figure 4 a) and the Ag2Se / 7%CdSe sample in Example 4 ( Figure 4b) Temperature-dependent in situ XRD patterns indicate that surface modification of the Ag2Se nanocomposite does not affect the phase transition temperature. At 403K, both samples undergo a phase transition from low-temperature orthorhombic β-Ag2Se to high-temperature cubic α-Ag2Se. c) Rietveld-refined XRD patterns indicate that CdSe ligand modification does not alter the lattice parameters of Ag2Se over the entire temperature range. This suggests that CdSe exists as a secondary phase within the Ag2Se matrix, forming the nanocomposite.

[0074] like Figure 5 As shown in the figure, the cross-section of the annealed and sintered Ag2Se nanomaterial is relatively flat and the grain size is large. The grain size of the Ag2Se / MSe bulk prepared by surface treatment with MSe molecular ligands gradually refines with increasing CdSe and ZnSe content, indicating that the cross-section of the Ag2Se / MSe nanocomposite material gradually densifies, with more stacking wrinkles and increased surface roughness.

[0075] like Figure 6 As shown in Figures ac) TEM images and STEM-EDX elemental mapping of the Ag2Se matrix reveal an enrichment of Ag nanosecond phases within its internal structure. dh) TEM images of Ag2Se / 7%CdSe nanoparticles reveal a significant enrichment of stress and dislocations, while the Ag second phase disappears. STEM-EDX elemental mapping and high-resolution electron microscopy (HRTEM) reveal the presence of the CdSe nanosecond phase. ik) Similarly, TEM images and STEM-EDX elemental mapping of Ag2Se / 4%ZnSe nanoparticles reveal a significant enrichment of nanoprecipitates, but no Ag second phase is observed. HRTEM confirms the presence of the ZnSe nanosecond phase.

[0076] like Figure 7 As shown in Figure 2, a) Compared with the Ag2Se matrix, the conductivity σ of the sample is significantly reduced after the introduction of MSe. This is because the introduction of MSe produces a large number of dislocations, which causes these Ag interstitial atoms to be partially captured, hindering their ionization into Ag. + And provide free electrons, Ag nanocrystals significantly reduced, and finally the sample was made of the intrinsic high carrier concentration of Ag2Se matrix (>10 19 cm -3 ) is gradually reduced to adjust to the most suitable level (~10 18 cm -3 b) the presence of MSe nanoprecipitates and the formation of a high-density grain boundary and dislocation defect structure in the Ag2Se / MSe sample, resulting in the thermal conductivity of all samples in Comparative Examples 1-8 κ totc) The final Ag2Se / 4%ZnSe sample has a higher peak zT at 369K max The Ag2Se / 7%CdSe sample has the highest zT at 380K, reaching 1.13. max The value reaches 1.05; d) it remains almost constant in the entire temperature range, and the average zT of Ag2Se / 4%ZnSe and Ag2Se / 7%CdSe samples in the temperature range of 300-390K is avg The value is more than 1, reaching zT avg =1.08 and zT avg =1.05, is the zT of Ag2Se matrix sample avg = more than twice that of 0.45, showing performance comparable to that of traditional room-temperature commercial Bi2Te3-based room-temperature thermoelectric materials.

[0077] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a near-room-temperature Ag2Se / MSe nanocomposite material, characterized in that: The following steps are involved: (1) Synthesizing matrix Ag2Se particles by aqueous solution method; (2) MO metal oxide powder and Se powder are mixed and added to an amine-thiol mixed solution to obtain MSe molecular ligands, and then the MSe molecular ligands are surface-modified on the matrix Ag2Se particles and post-treated to obtain a near-room temperature Ag2Se / MSe nanocomposite material, wherein the M is Cd or Zn, and the molar fraction of MSe in the Ag2Se / MSe nanocomposite material is 2% to 10%.

2. The method for preparing a near-room-temperature Ag2Se / MSe nanocomposite material according to claim 1, wherein: In step (1), the aqueous solution method is as follows: under argon protection, AgNO3 is added to deionized water to prepare an Ag source precursor; Se powder is slowly added to an aqueous solution of NaBH4 until the reaction is completely clarified to obtain a Se source precursor; the Se source precursor is added to a preheated boiling aqueous solution of the Ag source precursor to react, and after the reaction is completed, it is cooled to room temperature, washed, centrifuged, and vacuum dried to obtain Ag2Se particles.

3. The method for preparing a near-room-temperature Ag2Se / MSe nanocomposite material according to claim 2, wherein: The concentration of AgNO3 dissolved in deionized water is 0.3-0.5 mol·L -1 , the molar ratio of Se powder to NaBH4 is 1.0-1.1:2, and the molar ratio of Ag source precursor to Se source precursor is 2:0.9-1.2; The Se source precursor is added to the preheated boiling aqueous solution of the Ag source precursor for reaction at a temperature of 100-101.3°C and a reaction time of 0.5-60 min; The washing is performed by alternately washing with deionized water and ethanol for 2-5 times; The centrifugal speed is 5000-8000 rpm, and the centrifugal time is 1-5 min; The drying is performed by vacuum drying, the vacuum drying time is 6-8 hours, and the temperature is 60-80°C.

4. The method for preparing a near-room-temperature Ag2Se / MSe nanocomposite material according to claim 1, wherein: In step (2), the preparation method of the MSe molecular ligand is as follows: under a nitrogen atmosphere, MO powder and Se powder are dissolved in ethylenediamine and 1,2-ethanedithiol solution, and stirred at room temperature until completely dissolved to obtain the MSe molecular ligand.

5. The method for preparing a near-room-temperature Ag2Se / MSe nanocomposite material according to claim 1, characterized in that: In step (2), the steps of modifying the surface of the matrix Ag2Se particles with MSe molecular ligands are specifically as follows: adding N-methylformamide solution to the Ag2Se solution, adding MSe molecular ligands after uniform dispersion, stirring for a certain period of time, centrifuging and purifying it with acetone several times, and vacuum drying to obtain Ag2Se@MSe nanocomposite thermoelectric material.

6. The method for preparing a near-room-temperature Ag2Se / MSe nanocomposite material according to claim 5, characterized in that: The molar ratio of Ag2Se to MSe is 1:x%, wherein 0<x≤10; The stirring time is not less than 24 hours; The centrifugal speed is 5000-10000 rpm, and the centrifugal time is 5-10 min; The drying is performed by vacuum drying, the vacuum drying time is 6-8 hours, and the temperature is 60-80°C.

7. A near-room temperature Ag2Se / MSe nanocomposite material prepared according to the preparation method according to any one of claims 1 to 6.

8. A method for preparing Ag2Se / MSe nanocomposite thermoelectric material, characterized in that: The method comprises the following steps: placing the Ag2Se / MSe nanocomposite material according to claim 7 in a tube furnace, annealing the material in a nitrogen atmosphere, and densifying the material by plasma discharge sintering to obtain the Ag2Se / MSe nanocomposite thermoelectric material block.

9. The method for preparing an Ag2Se / MSe nanocomposite thermoelectric material according to claim 8, characterized in that: The annealing temperature is 350-450°C, and the heating rate is 5-15°C·min -1 , annealing time is not less than 60min; The plasma spark sintering is performed under a pressure of 45-60 MPa, a temperature of 350-450° C., and a time of not less than 5 minutes.

10. An Ag2Se / MSe nanocomposite thermoelectric material prepared according to the preparation method according to claim 9.

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