Cu1.8 S and Cu1.96S composite thermoelectric material and preparation method thereof

Abstract

The invention discloses a preparation method of a Cu1.8S and Cu1.96S composite thermoelectric material, which comprises the following steps: adding CuCl powder and Na2S2O3 powder into deionized water to carry out hydrothermal reaction, and after the reaction is finished, carrying out suction filtration and drying to obtain Cu1.8S powder; and the Cu1.8 S powder is subjected to hot pressing sintering to obtain the Cu1.8 S and Cu1.96S composite thermoelectric material, the hot pressing sintering temperature is 700-900 DEG C, and the hot pressing time is 15-60 min. The Cu < 1.8 > S and Cu < 1.96 > S composite thermoelectric material prepared by the preparation method has relatively low thermal conductivity, and the ZT value is greatly improved compared with that of Cu < 1.8 > S.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermoelectric materials and specifically relates to a Cu 1.8 S and Cu 1.96 S composite thermoelectric material and preparation method thereof. Background Art

[0002] With the rapid growth of the world's population, economy and industrial production, limited fossil energy can no longer meet the growing energy demand of today's society. At the same time, the use of fossil energy is accompanied by increasingly prominent environmental problems, such as greenhouse effect, haze, etc. Therefore, finding an efficient clean energy and building a sustainable development society has become one of the themes of countries in the 21st century. According to incomplete statistics, about 60% of the world's energy is emitted in the form of waste heat. If the above waste heat can be effectively utilized, it will surely promote the further growth of global industry and economy.

[0003] Thermoelectric materials are a new type of energy conversion medium. Thermoelectric devices made of them can realize the mutual conversion of thermal energy and electrical energy. Thermoelectric devices have the advantages of no moving parts, no noise, reliability and flexibility, and have extremely broad application prospects in aerospace, national defense, automobiles, medical and other fields. The conversion efficiency η of thermoelectric devices is related to the thermoelectric figure of merit ZT of the material and the temperature T at both ends of the device. H , T C Generally speaking, η is proportional to the temperature difference and ZT value. However, the conversion efficiency of current thermoelectric devices is generally low, and the highest conversion efficiency reported in the literature is only 15%, which is far from the efficiency of traditional internal combustion engines.

[0004] Although thermoelectric materials have been studied for nearly 200 years, they (especially power generation devices) have not yet been industrialized on a large scale. The main reason is the low thermoelectric conversion efficiency. When the temperature difference between the hot and cold ends is determined, the thermoelectric conversion efficiency is only measured by ZT, which can be expressed as ZT = S 2 σT / κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity. κ is mainly composed of the electronic thermal conductivity κ e and lattice thermal conductivity κ l There is a complex coupling relationship between the three parameters S, σ, and κ. Breaking this interdependence to achieve independent regulation of electrons and phonons is the focus of current thermoelectric research.

[0005] Thermoelectric materials can realize the mutual conversion between thermal energy and electrical energy and are a new type of energy conversion medium. Thermoelectric devices constructed by thermoelectric materials can be used for temperature difference power generation and semiconductor refrigeration. 2-xM (M = S, Se, Te) based compounds have attracted great attention in the field of thermoelectrics due to their excellent thermoelectric properties, rich element reserves and high cost performance. 2-x S compounds are mostly found in natural minerals with abundant reserves. Cu and S are both non-toxic and environmentally friendly elements, which are consistent with today's environmental protection concept. The Cu2S-based thermoelectric materials with trace vacancies reported so far have extremely high thermoelectric performance. However, the material undergoes long-term current erosion during use, and Cu ions will migrate in a directional manner and eventually precipitate at one end of the material, resulting in device performance degradation. 1.8 S has an intrinsic high concentration of Cu vacancies and exhibits excellent current stability, but its thermal conductivity is slightly higher than that of Cu2S, resulting in its ZT being much lower than that of Cu2S. 1.8 The key to the application of this material is to improve the excellent electrical properties of S while reducing its thermal conductivity. Summary of the invention

[0006] The present invention provides a Cu 1.8 S and Cu 1.96 S composite thermoelectric material preparation method, the preparation method of Cu 1.8 S and Cu 1.96 S composite thermoelectric material has lower thermal conductivity, and its ZT value is lower than that of Cu 1.8 S has a big improvement.

[0007] The present invention provides a Cu 1.8 S and Cu 1.96 The preparation method of S composite thermoelectric material comprises:

[0008] CuCl powder and Na2S2O3 powder were added into deionized water for hydrothermal reaction. After the reaction, CuCl powder was filtered and dried to obtain 1.8 S powder;

[0009] Cu 1.8 S powder is hot pressed to obtain Cu 1.8 S and Cu 1.96 S composite thermoelectric material, the hot pressing sintering temperature is 700-900°C, and the hot pressing time is 15min-60min.

[0010] Preferably, the hot pressing sintering temperature is 800-900° C. By further controlling the hot pressing sintering temperature, a larger amount of the second phase Cu 1.96 The introduction of S significantly reduces the thermal conductivity. The composite material provided by the present invention and Cu 1.8 Compared with S thermoelectric materials, the conductivity does not change much, so the ZT value is significantly improved.

[0011] Preferably, the hot pressing sintering pressure is 50-100 MPa.

[0012] Preferably, the molar ratio of the CuCl powder to the Na2S2O3 powder is greater than or equal to 0.5. Using the hydrothermal method provided by the present invention, sufficient Na2S2O3 powder can be provided to form Cu 1.8 S powder, the preparation method is simple and efficient.

[0013] Further preferably, the molar ratio of the CuCl powder to the Na2S2O3 powder is 0.5-2.

[0014] Preferably, the reaction temperature of the hydrothermal reaction is 120-240° C., and the reaction time is 6-24 h.

[0015] In another aspect, the present invention provides a Cu 1.8 S and Cu 1.96 S composite thermoelectric material, through the Cu 1.8 S and Cu 1.96 The S composite thermoelectric material is prepared by the preparation method.

[0016] Preferably, the Cu 1.8 S and Cu 1.96 The Seebeck coefficient of S composite thermoelectric material is 50-200 μV / K at 200-600 K, and the conductivity is 4×10 4 ~1.3×10 5 S / m, thermal conductivity is 1.5~3.0W / m K, and thermoelectric performance figure of merit ZT is 0.6~0.9.

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

[0018] The present invention controls the temperature and time of hot pressing sintering to obtain a Cu 1.8 In-situ formation of a suitable amount of second phase Cu on S 1.96 S, and at high temperatures Cu 1.8 S grains are broken to form multiple grain boundaries and pores. Therefore, in the Cu with lower thermal conductivity 1.96 S, and the synergistic effect of the formed multiple grain boundaries and pores on the heat conduction, significantly reducing the intrinsic thermal conductivity. At the same time, the present invention also ensures that the appropriate amount of Cu 1.8 S to maintain a high conductivity, thereby making the Cu 1.8 S and Cu 1.96 S composite thermoelectric material has a higher ZT value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The Cu prepared in Example 1 of the present invention 1.8XRD and SEM images of S, where Figure 1 (a) is the Cu prepared in Example 1 1.8 XRD pattern of S, Figure 1 (b) and Figure 1 (c) is the Cu obtained in Example 1 1.8 SEM image of S.

[0020] Figure 2 XRD diagrams of the composite thermoelectric materials prepared in Examples 1 to 3 of the present invention and the thermoelectric material prepared in Comparative Example 1;

[0021] Figure 3 The electrical conductivity, Seebeck coefficient, power factor (PF), thermal conductivity (k), lattice thermal conductivity (K) of the composite thermoelectric materials prepared in Examples 1 to 3 of the present invention and the thermoelectric material prepared in Comparative Example 1 are shown in FIG. L ) and ZT curves, where Figure 3 (a) is the conductivity curve. Figure 3 (b) is the Seebeck curve diagram, Figure 3 (c) is the power factor (PF) curve, Figure 3 (d) is the thermal conductivity (k) curve, Figure 3 (e) is the lattice thermal conductivity (K L ) curve graph, Figure 3 (f) is the ZT curve diagram. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to the accompanying drawings.

[0023] Example 1

[0024] Step 1: Weigh 6g of CuCl powder with a purity greater than 99% and 8g of Na2S2O3 powder, put the powder into a 50ml polytetrafluoroethylene-lined reactor, and add 30ml of deionized water.

[0025] Step 2: Seal the reactor and place it in an oven at 200°C for 10 hours.

[0026] Step 3: After the reaction is completed, blue Cu is obtained by filtration. 1.8 S powder, such as Figure 1 (a)- Figure 1 As shown in (c), the powder obtained by filtration in this embodiment is Cu 1.8 S powder.

[0027] Step 4: Dry the powder in an oven at 60°C for 3 h.

[0028] Step 5: Use a hot pressing sintering furnace to hot press the dried powder to obtain Cu 1.8S-Cu 1.96 S composite bulk thermoelectric material, first pour the powder into a mold with a diameter of 12.7, and hot press sintering at a temperature of 700°C, a pressure of 75MPa, and a hot pressing time of 30min.

[0029] Example 2

[0030] The difference from Example 1 is that the hot pressing sintering temperature is 800°C.

[0031] Example 3

[0032] The difference from Example 1 is that the hot pressing sintering temperature is 900°C.

[0033] Comparative Example 1

[0034] The difference from Example 1 is that the hot pressing sintering temperature is 600°C to obtain Cu 1.8 S thermoelectric material.

[0035] Performance Analysis:

[0036] like Figure 2 As shown, by comparing the PDF cards, it can be seen that the thermoelectric material prepared in Example 1 to Example 3, that is, the HP is 700-800°C is Cu 1.8 S and Cu 1.96 S composite thermoelectric material, while in Comparative Example 1, the thermoelectric material prepared at HP of 600°C is Cu 1.8 S.

[0037] The performance of the thermoelectric material provided by the specific embodiment of the present invention is characterized by a dimensionless thermoelectric figure of merit ZT, where ZT=S 2 σT / κ, where S 2 σ represents the power factor (σ is the electrical conductivity, S is the Seebeck coefficient), T is the absolute temperature, and κ is the thermal conductivity (lattice thermal conductivity κ l and the electronic thermal conductivity κ e sum).

[0038] The electrical transmission performance testing method provided by the specific embodiment of the present invention is to cut the block obtained by hot pressing into 2*2*10mm strips for testing the electrical conductivity and Seebeck coefficient.

[0039] like Figure 3 (a)- Figure 3 As shown in (c), the electrical conductivity and Seebeck coefficient of the composite electric heating materials prepared in Examples 1 to 3 and the composite electric heating material prepared in Comparative Example 1 have almost no change above 300 degrees, and the power factor obtained by calculation does not change much.

[0040] The thermal conductivity test method provided in the specific embodiment of the present invention is to cut the bulk thermoelectric material prepared in the embodiment into The disc with a thickness of 2 mm is used to detect the thermal conductivity, and the test is performed using a laser thermal conductivity meter.

[0041] like Figure 3 (d)- Figure 3 As shown in (e), since Examples 1 to 3 introduce Cu 1.96 S, thermal conductivity is significantly reduced, the above formula S 2 The σT / κ calculation can give the ZT value, such as Figure 3 As shown in (f), the thermoelectric merit ZT of the composite materials prepared in Examples 1 to 3 is significantly higher than that of the Cu prepared in Comparative Example 1. 1.8 S thermoelectric material, when the hot pressing sintering temperature reaches 900℃, the corresponding maximum ZT value of the composite thermoelectric material reaches 1.1.

[0042] For those skilled in the art, several modifications and improvements can be made without departing from the technical solution of the present invention, which should also be regarded as the protection scope of the present invention. These will not affect the effect of the implementation of this patent and the practicality of the patent.

Claims

1. A Cu 1.8 S and Cu 1.96 The preparation method of S composite thermoelectric material is characterized in that: include: CuCl powder and Na2S2O3 powder were added into deionized water for hydrothermal reaction. After the reaction, CuCl powder was filtered and dried to obtain 1.8 S powder; Cu 1.8 S powder is hot pressed to obtain Cu 1.8 S and Cu 1.96 S composite thermoelectric material, the hot pressing sintering temperature is 700-900°C, and the hot pressing time is 15-60min.

2. The Cu according to claim 1 1.8 S and Cu 1.96 The preparation method of S composite thermoelectric material is characterized in that: The temperature of the hot pressing sintering is 800-900°C.

3. Cu according to claim 1 1.8 S and Cu 1.96 The preparation method of S composite thermoelectric material is characterized in that: The hot pressing sintering pressure is 50-100Mpa.

4. The Cu according to claim 1 1.8 S and Cu 1.96 The preparation method of S composite thermoelectric material is characterized in that: The molar ratio of the CuCl powder to the Na2S2O3 powder is greater than or equal to 0.

5.

5. The Cu according to claim 4 1.8 S and Cu 1.96 The preparation method of S composite thermoelectric material is characterized in that: The molar ratio of the CuCl powder to the Na2S2O3 powder is 0.5-2.

6. The Cu according to claim 1 1.8 S and Cu 1.96 The preparation method of S composite thermoelectric material is characterized in that: The reaction temperature of the hydrothermal reaction is 120-240° C., and the reaction time is 6-24 hours.

7. A kind of Cu 1.8 S and Cu 1.96 S composite thermoelectric material, characterized in that By the Cu according to any one of claims 1-6 1.8 S and Cu 1.96 The S composite thermoelectric material is prepared by the preparation method.

8. The Cu according to claim 7 1.8 S and Cu 1.96 S composite thermoelectric material, characterized in that The Cu 1.8 S and Cu 1.96 The Seebeck coefficient of S composite thermoelectric material is 50-200 μV / K at 200-600 K, and the conductivity is 4×10 4 ~1.3×10 5 S / m, thermal conductivity is 1.5~3.0W / m K, and thermoelectric performance figure of merit ZT is 0.6~0.9.

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