Ag2S-based composite thermoelectric material and preparation method thereof

Abstract

The invention discloses an Ag2S-based composite thermoelectric material and a preparation method thereof, and belongs to the technical field of thermoelectric material preparation. The method comprises the following steps: preparing an Ag2S cast ingot by adopting a melting method, preparing the Ag2S cast ingot into Ag2S powder in a low-temperature grinding manner, preparing Ti3AlC2 into Ti3C2Tx powder by adopting a lithium fluoride etching method, fully mixing the two kinds of powder in a grinding manner after the two kinds of powder are prepared, preparing a Ti3C2Tx / Ag2S composite material by adopting a die-casting method, and doping a proper amount of Ti3C2Tx into Ag2S to obtain the Ti3C2Tx / Ag2S composite material. The carrier transport can be optimized, the carrier concentration is improved to improve the conductivity, and finally the thermoelectric performance is improved. Practice proves that the method provides a brand new way for performance optimization of the thermoelectric material.

Description

Technical Field

[0001] The present invention relates to the technical field of nano material preparation, in particular to an Ag2S-based composite thermoelectric material and a preparation method thereof. Background Art

[0002] Thermoelectric materials are a class of materials that can harvest waste heat and convert electrical energy into thermal energy. Developing thermoelectric conversion technology has become one of the solutions to the current energy shortage problem. Thermoelectric materials have the advantages of being small, lightweight, noiseless, and pollution-free, and have great potential for development in heat collection and refrigeration systems. Thermoelectric figure of merit (ZT) is often used to measure the thermoelectric performance of a material. Generally speaking, the larger the ZT value of a material, the better its thermoelectric performance. The dimensionless ZT value is calculated using the following formula: S 2 σT / κ ,in S represents the Seebeck coefficient, σ represents conductivity, T is the absolute temperature, and κ is the thermal conductivity. Thermoelectric power factor PF= S 2 σ From the above formula, it can be seen that an excellent thermoelectric material must meet the characteristics of high Seebeck coefficient, high electrical conductivity and low thermal conductivity.

[0003] As a new type of inorganic semiconductor, Ag2S has attracted increasing attention in the field of thermoelectrics in recent years due to its low toxicity, high chemical stability, and low lattice thermal conductivity. In particular, at room temperature, Ag2S has a high Seebeck coefficient, which reflects the great development potential of Ag2S in the field of thermoelectrics. However, at room temperature, the Ag ions in the monoclinic structure of α-Ag2S are fixed in specific positions, making it difficult to migrate between different positions. Therefore, its electrical conductivity is extremely low, only 0.1-0.5 S m -1 This limits its development in room-temperature thermoelectric materials. Previous studies have shown that doping Ag2S with other elements or highly conductive substances is one of the effective strategies to improve its conductivity.

[0004] Theoretical studies have shown that combining highly conductive materials with Ag2S can improve the conductivity of Ag2S-based materials by optimizing carrier transport within the material, thereby enhancing their thermoelectric performance. MXene, a two-dimensional layered material with a graphene-like structure, offers advantages such as extremely high conductivity, diverse and tunable electronic properties, excellent mechanical properties, and strong affinity for water. However, the thermoelectric performance of composite materials prepared by doping MXene with Ag2S has not yet been reported. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides an Ag2S-based composite thermoelectric material and a preparation method thereof. Taking Ag2S as the research object, Ag2S powder and MXene powder are die-casted, and a high-performance two-dimensional composite thermoelectric film with a high power factor is prepared by changing the ratio of the two component powders.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: In one aspect, the present invention provides a method for preparing an Ag2S-based composite thermoelectric material, comprising the following steps: (1) Ag powder and sulfur powder are prepared into Ag2S ingots by a melting method, and the obtained ingots are ground into Ag2S powder by cryogenic grinding; the molar ratio of the Ag powder to the sulfur powder is 2:1; (2) preparing MXene powder from MAX material by hydrochloric acid / lithium fluoride etching method; the MAX material is Ti3AlC2; (3) Ag2S powder and MXene powder were cryogenically ground to obtain mixed powder, and then Ti3C2T was die-cast at room temperature. x / Ag2S composite material; in the mixed powder, the amount of Ag2S powder is 99.9wt%, and the amount of MXene powder is 0.1wt%.

[0007] Furthermore, the step (1) includes the following steps: (11) The Ag powder and sulfur powder are sealed in a quartz tube and prepared into an Ag2S ingot by a melting method; (12) Take the prepared Ag2S ingot and grind it into powder at low temperature.

[0008] Preferably, the step (11) is specifically as follows: after sealing the Ag powder and the sulfur powder in a quartz tube, the quartz tube is placed in a heating furnace for melting, and the melting process is specifically as follows: slowly heating to 1050°C over 7 hours, then keeping the temperature at 1050°C for 8 hours, and then cooling to room temperature with the furnace.

[0009] Preferably, the step (12) is specifically as follows: taking the prepared Ag2S ingot, placing it in a mortar, pouring liquid nitrogen into the mortar several times, and continuously pounding for 4 hours until it is crushed into Ag2S powder.

[0010] Furthermore, the step (2) includes the following steps: (21) MAX is placed in hydrochloric acid and lithium fluoride for etching to obtain a crude MXene product after etching; the mass ratio of the MAX to the lithium fluoride is 1:1; the mass volume ratio of the lithium fluoride to the hydrochloric acid is 1g:10mL; (22) The crude MXene product is washed, centrifuged, and dried to obtain MXene powder.

[0011] Preferably, during the etching process in step (21), the oil bath is heated and stirred at a temperature of 40-45°C, a stirring speed of 1000 rpm, and a reaction time of 18-30 h; the concentration of the concentrated hydrochloric acid is 9 mol / L, and the particle size of the MAX material is 300 mesh.

[0012] Preferably, the step (22) is specifically as follows: the crude MXene product is placed in a centrifuge tube and mixed with deionized water, shaken at a speed of 5000 rpm, centrifuged for 5 min, and the above washing process is repeated 5-6 times; finally, the precipitate after centrifugation is collected and dried in a vacuum heating drying oven at a heating temperature of 60°C and a drying time of 24 h to finally obtain MXene powder.

[0013] Furthermore, the step (3) is specifically as follows: Ag2S powder and MXene powder are put into a mortar and ground for 30 minutes to mix the two evenly; the above powders are die-casted through a mold at room temperature to obtain a composite material, the die-casting pressure is 20 MPa, and the die-casting time is 30 minutes.

[0014] On the other hand, the present invention also provides an Ag2S-based composite thermoelectric material prepared by the above method.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The Ag2S-based composite thermoelectric material prepared by the present invention has a Seebeck coefficient of -455.56 μV / K and a power factor of 0.0524 μW m -1 K -2 The Ag2S-based composite thermoelectric material prepared in the present invention has excellent thermoelectric performance, and its electrical conductivity is increased by 2.5 times compared with pure Ag2S.

[0016] The preparation process of the present invention is simple, easy to operate, has low environmental requirements, and does not require expensive and complex experimental equipment. Practice has proven that this method can prepare Ag2S-based composite thermoelectric materials. This method has important theoretical and practical significance for further expanding the application range of Ag2S-based composite thermoelectric materials at room temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the preparation process of Ag2S-based composite thermoelectric material in Example 1; Figure 2 The electrical conductivity diagram, Seebeck coefficient diagram, and power factor diagram of composite materials with different MXene powder contents; Figure 3 (a) is a SEM image of the material prepared in Comparative Example 1; (b) is a SEM image of the composite material prepared in Example 1 of the present invention; (c)-(f) are EDS images of Example 1; Figure 4 This is the XRD comparison diagram of the powder in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0018] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0019] Unless otherwise specified, all materials and reagents used in this invention are commercially available. The MAX used in this invention is Ti3AlC2 with a particle size of 300 mesh; the concentrated hydrochloric acid used has a concentration of 9 mol / L; the Ag used has a purity of 99.99%; and the S used has a purity of 99.99%.

[0020] The present invention provides an Ag2S-based composite thermoelectric material and a preparation method thereof, and specific embodiments are as follows. Example 1

[0021] A method for preparing Ag2S-based composite thermoelectric materials, the process is as follows Figure 1 , including the following steps: (1) After Ag powder (99.99%) and S (99.99%) with a molar ratio of 2:1 were sealed in a quartz tube, the quartz tube was placed in a heating furnace for melting. The melting process included heating to 1050 °C for 7 h, maintaining at 1050 °C for 8 h, and then cooling to room temperature in the heating furnace. Take the prepared Ag2S ingot, put it into a mortar, pour liquid nitrogen into the mortar several times, and pound it continuously for 4 h until it is crushed into Ag2S powder; (2) Add 1g MAX (Ti3AlC2), 1g LiF, and 10ml concentrated hydrochloric acid into a 50ml tetrafluoroethylene crucible, place the tetrafluoroethylene crucible in an oil bath, heat and stir to react, the stirring temperature is 45°C, the reaction time is 24h, and then the crude MXene product is obtained; The crude MXene product was transferred from the tetrafluoroethylene crucible to a centrifuge tube for cleaning, then mixed with deionized water and shaken, and then centrifuged at a speed of 5000 rpm for 5 minutes. The cleaning process was repeated five times. After cleaning, the solid MXene at the bottom of the centrifuge tube was collected and dried in a vacuum oven at 60°C for 24 hours to obtain MXene powder. (3) The total mass of MXene powder and Ag2S sample was fixed at 0.3 g, of which MXene powder mass was 0.1 wt% and the rest was Ag2S powder. The two were placed in a mortar, and liquid nitrogen was poured into the mortar several times. The mixture was continuously cryogenically ground for 30 min to mix the two evenly. Finally, the powder was die-cast into a composite material (Ti3C2T x / Ag2S), the die casting pressure was 20 MPa, and the die casting time was 30 min.

[0022] In order to further illustrate the beneficial effects of the present invention, the following comparative examples are constructed. Comparative Example 1

[0023] A method for preparing an Ag2S thermoelectric material, comprising: The preparation method of Ag2S powder is the same as steps (1)-(2) of Example 1; The powder was then die-cast into Ag2S thermoelectric material through a mold at room temperature with a die-casting pressure of 20 MPa and a die-casting time of 30 min. Comparative Example 2

[0024] In step (3) of this comparative example, the total mass of the MXene powder and the Ag2S sample was fixed at 0.3 g, the amount of MXene powder was 0.3 wt%, and the amount of Ag2S powder was 99.7 wt%. The other conditions were the same as those in Example 1. Comparative Example 3

[0025] In step (3) of this comparative example, the total mass of the MXene powder and the Ag2S sample was fixed at 0.3 g, the amount of MXene powder was 0.5 wt%, and the amount of Ag2S powder was 99.5 wt%. The other conditions were the same as those in Example 1. Comparative Example 4

[0026] In step (3) of this comparative example, the total mass of the MXene powder and the Ag2S sample was fixed at 0.3 g, the amount of MXene powder was 0.7 wt %, and the amount of Ag2S powder was 99.3 wt %. The other conditions were the same as those in Example 1. Comparative Example 5

[0027] In step (3) of this comparative example, the total mass of the MXene powder and the Ag2S sample was fixed at 0.3 g, the amount of MXene powder was 1 wt%, and the amount of Ag2S powder was 99 wt%. The other conditions were the same as those in Example 1.

[0028] The thermoelectric performance test was conducted using the composite materials prepared in Example 1 and Comparative Examples 1-5, and the results are as follows.

[0029] Figure 2The conductivity, Seebeck coefficient, and power factor of the prepared thermoelectric materials with different MXene powder contents are shown in the figure. The results show that when the MXene content is 0.1wt%, the power factor PF reaches a maximum value of 0.0524 μW m -1 K -2 , which is about 140% of the original Ag2S.

[0030] The results of scanning electron microscopy test on Comparative Example 1 and Example 1 are as follows: Figure 3 As shown in (a) and (b), the results show that compared with the pure Ag2S sample, Ti3C2T x The / Ag2S composite sample is more tightly bound. This may be beneficial to the transport of carriers, thereby making the composite sample have higher conductivity. Figure 3 As shown in (c)-(f), the results show that Ag, S, Ti and C elements exist in the composite sample, and Ti3C2T x The above results prove that Ti3C2T x MXene and A g2 S compound.

[0031] The thermoelectric materials in Example 1 and Comparative Example 1 were subjected to XRD testing, and their diffraction spectra were as follows: Figure 4 As shown. The results show that the XRD spectrum of the prepared Ag2S has obvious sharp diffraction peaks at 2q=26.3°, 28.9°, 31.4°, 37.1° and 37.6°. These diffraction peaks correspond to the (012), (111), (-112), (013) and (-103) diffraction planes of monoclinic Ag2S, respectively. These diffraction peaks are consistent with the standard monoclinic Ag2S diffraction peaks, indicating that the monoclinic Ag2S sample was successfully prepared in this experiment, and the prepared Ag2S has good crystallinity. In addition, in the prepared Example 1 sample, its diffraction peak is consistent with the original Ag2S sample, and no obvious impurities and secondary phases are found, which may be due to the Ti3C2T x It can be concluded that the appropriate amount of Ti3C2T x The addition of will not destroy the original crystal structure of Ag2S.

[0032] In summary, the present invention successfully utilizes MXene (Ti3C2T x) and Ag2S to prepare a high-performance Ag2S-based composite thermoelectric material. The doping of highly conductive MXene alters the carrier transport pathway within the material, improving the electrical conductivity of the composite thermoelectric film and, in turn, its thermoelectric performance. This invention provides new insights into optimizing the thermoelectric performance of Ag2S-based composite thermoelectric materials and broadens their application.

[0033] The above is a preferred embodiment of the present invention. For ordinary technicians in this technical field, making several improvements and modifications without departing from the principles of the present invention should also be considered as the scope of protection of the present invention.

Claims

1. A method for preparing an Ag2S-based composite thermoelectric material, characterized in that: The following steps are involved: (1) Ag powder and sulfur powder are prepared into Ag2S ingots by a melting method, and the obtained ingots are ground into Ag2S powder by cryogenic grinding; the molar ratio of the Ag powder to the sulfur powder is 2:1; (2) preparing MXene powder from MAX material by hydrochloric acid / lithium fluoride etching method; the MAX material is Ti3AlC2; (3) Ag2S powder and MXene powder were cryogenically ground to obtain mixed powder, and then Ti3C2T was die-cast at room temperature. x / Ag2S composite material; in the mixed powder, the amount of Ag2S powder is 99.9wt%, and the amount of MXene powder is 0.1wt%.

2. The preparation method according to claim 1, characterized in that The step (1) comprises the following steps: (11) The Ag powder and sulfur powder are sealed in a quartz tube and prepared into an Ag2S ingot by a melting method; (12) Take the prepared Ag2S ingot and grind it into powder at low temperature.

3. The preparation method according to claim 2, wherein The step (11) is specifically as follows: after sealing the Ag powder and the sulfur powder in a quartz tube, the quartz tube is placed in a heating furnace for melting. The melting process is specifically as follows: slowly heating to 1050°C over 7 hours, then keeping the temperature at 1050°C for 8 hours, and then cooling to room temperature with the furnace.

4. The preparation method according to claim 2, wherein The step (12) is specifically as follows: taking the prepared Ag2S ingot, placing it in a mortar, pouring liquid nitrogen into the mortar several times, and continuously pounding for 4 hours until it is crushed into Ag2S powder.

5. The preparation method according to claim 1, characterized in that The step (2) includes the following steps: (21) MAX is placed in hydrochloric acid and lithium fluoride for etching to obtain a crude MXene product after etching; the mass ratio of the MAX to the lithium fluoride is 1:1; the mass volume ratio of the lithium fluoride to the hydrochloric acid is 1g:10mL; (22) The crude MXene product is washed, centrifuged, and dried to obtain MXene powder.

6. The preparation method according to claim 5, wherein During the etching process of step (21), the oil bath is heated and stirred at a temperature of 40-45°C, a stirring speed of 1000 rpm, and a reaction time of 18-30 h; the concentration of the concentrated hydrochloric acid is 9 mol / L, and the particle size of the MAX material is 300 mesh.

7. The preparation method according to claim 5, wherein The step (22) is specifically as follows: the crude MXene product is placed in a centrifuge tube and mixed with deionized water, shaken at a speed of 5000 rpm, centrifuged for 5 min, and the above washing process is repeated 5-6 times; finally, the precipitate after centrifugation is collected and dried in a vacuum heating drying oven at a heating temperature of 60°C and a drying time of 24 hours to finally obtain MXene powder.

8. The preparation method according to claim 1, wherein The step (3) is specifically as follows: Ag2S powder and MXene powder are put into a mortar and ground for 30 minutes to mix the two evenly; the above powders are die-casted through a mold at room temperature to obtain a composite material, the die-casting pressure is 20 MPa, and the die-casting time is 30 minutes.

9. An Ag2S-based composite thermoelectric material, characterized in that: The method is prepared by any one of claims 1 to 8.

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