Bi-cuseo / graphene composite thermoelectric material and preparation method and application thereof

Abstract

The application discloses a BiCuSeO / graphene composite thermoelectric material and a preparation method and application thereof, wherein the chemical expression of the BiCuSeO / graphene composite thermoelectric material is Bi 0.88 Pb 0.06 Ca 0.06 CuSeO / graphene. The BiCuSeO / graphene composite thermoelectric material has high electrical conductivity, low thermal conductivity and high thermoelectric performance, and has a wide application prospect. Specifically, the ZT value of the BiCuSeO / graphene composite thermoelectric material is not less than 1.13.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric ceramic materials, specifically relating to a BiCuSeO / graphene composite thermoelectric material, its preparation method, and its application. Background Technology

[0002] Energy and environmental issues are two major challenges facing human society. According to incomplete statistics, over 60% of energy is consumed as waste heat. The unique transport characteristics of microscopic charge carriers and phonons within thermoelectric materials enable direct and reversible conversion between thermal and electrical energy, holding significant application value in waste heat recovery and localized refrigeration. The conversion capability of thermoelectric materials between thermal and electrical energy is directly measured by their ZT value, which is closely related to the material's electrical conductivity, Seebeck coefficient, and thermal conductivity. However, since these three factors exhibit a certain degree of inverse coupling, synergistically regulating their relationship to improve the ZT value of thermoelectric materials has been one of the main problems that researchers have been trying to solve.

[0003] In recent years, with the successive proposals of strategies such as quantum confinement effect, band engineering, and full-scale phonon scattering, the ZT values ​​of some alloy thermoelectric systems (such as SnSe, PbTe, and GeTe) can exceed 2.0. However, on the one hand, the poor thermal and chemical stability of alloy systems makes it difficult to meet the requirements of real-world service environments; on the other hand, the preparation of alloy systems mostly requires harsh environmental conditions (vacuum / inert atmosphere), complex process steps, and lengthy preparation cycles, which greatly limits their practical application and industrialization. Compared with alloy systems, oxide systems not only have good high-temperature thermal and chemical stability, but also have simple preparation processes, showing broad application prospects.

[0004] Layered oxygen-containing compounds, such as BiCuSeO, have attracted widespread attention and research due to their intrinsically low thermal conductivity. Pb / Ca co-doping can effectively increase the carrier concentration of BiCuSeO, thereby improving its electrical conductivity; however, with increasing Pb / Ca doping concentration, the material's mobility deteriorates significantly, making further improvement in thermoelectric performance difficult. Furthermore, existing Pb / Ca co-doped BiCuSeO preparation processes are relatively complex, hindering large-scale industrial production.

[0005] Therefore, existing BiCuSeO thermoelectric materials need to be improved. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide a BiCuSeO / graphene composite thermoelectric material, its preparation method, and its applications. This BiCuSeO / graphene composite thermoelectric material exhibits high electrical conductivity, low thermal conductivity, and high thermoelectric performance. Specifically, the ZT value of this BiCuSeO / graphene composite thermoelectric material is not less than 1.13.

[0007] In one aspect, the present invention proposes a BiCuSeO / graphene composite thermoelectric material. According to an embodiment of the present invention, the chemical formula of the BiCuSeO / graphene composite thermoelectric material is Bi... 0.88 Pb 0.06 Ca 0.06 CuSeO / graphene.

[0008] The BiCuSeO / graphene composite thermoelectric material according to this invention, based on BiCuSeO, is doped with Pb and Ca, and the stoichiometric ratio of Bi, Pb, and Ca is controlled at 0.88:0.06:0.06. This effectively improves the electrical conductivity of the BiCuSeO thermoelectric material. Simultaneously, due to the high mobility of graphene, the BiCuSeO / graphene composite thermoelectric material formed by adding graphene not only exhibits high electrical performance but also low thermal conductivity, achieving synergistic regulation of electrical and thermal properties. Therefore, this BiCuSeO / graphene composite thermoelectric material possesses high electrical conductivity, low thermal conductivity, and high thermoelectric performance.

[0009] In some embodiments of the present invention, in the BiCuSeO / graphene composite thermoelectric material, the graphene accounts for a proportion of the Bi... 0.88 Pb 0.06 Ca 0.06 The mass percentage of CuSeO is x%, where x ranges from 0.03 to 0.1. Therefore, this BiCuSeO / graphene composite thermoelectric material exhibits high thermoelectric performance.

[0010] In some embodiments of the present invention, x takes a value of 0.07 to 0.1. Therefore, the BiCuSeO / graphene composite thermoelectric material exhibits high thermoelectric performance.

[0011] In another aspect, the present invention provides a method for preparing the above-mentioned BiCuSeO / graphene composite thermoelectric material. According to an embodiment of the present invention, the method includes:

[0012] (1) Mix Bi powder, Bi2O3 powder, Se powder, Cu powder, PbO powder and CaO powder and compress them into tablets to obtain green blanks;

[0013] (2) The green blank is heated to induce a self-propagating reaction, so as to obtain Bi. 0.88 Pb 0.06 Ca 0.06 CuSeO bulk material;

[0014] (3) The Bi 0.88 Pb 0.06 Ca 0.06 CuSeO bulk material is ground into powder and mixed with graphene powder, then subjected to spark plasma sintering to obtain BiCuSeO / graphene composite thermoelectric material.

[0015] According to an embodiment of the present invention, the method for preparing the above-mentioned thermoelectric material involves mixing Bi powder, Bi₂O₃ powder, Se powder, Cu powder, PbO powder, and CaO powder, and then pressing them into tablets to ensure closer and more thorough contact between the powders, thereby facilitating the occurrence of a self-propagating reaction. The green compact is then subjected to heat treatment to induce a self-propagating reaction between the materials, resulting in the prepared Bi... 0.88 Pb 0.06 Ca 0.06 CuSeO bulk has high electrical conductivity, and finally Bi 0.88 Pb 0.06 Ca 0.06 The powder obtained by grinding CuSeO bulk material is mixed with graphene powder and then subjected to spark plasma sintering. Due to the high mobility of graphene, the resulting BiCuSeO / graphene composite thermoelectric material exhibits not only high electrical performance but also low thermal conductivity, achieving synergistic control of electrical and thermal properties. The method described in this application is simple, requires minimal experimental equipment and facilities, and is conducive to large-scale industrial production. Therefore, the BiCuSeO / graphene composite thermoelectric material prepared using this method exhibits high electrical conductivity, low thermal conductivity, and high thermoelectric performance.

[0016] Furthermore, the method for preparing BiCuSeO / graphene composite thermoelectric materials according to the above embodiments of the present invention also has the following additional technical features:

[0017] In some embodiments of the present invention, in step (1), the molar ratio of Bi powder, Bi₂O₃ powder, Se powder, Cu powder, PbO powder, and CaO powder is 0.294:0.293:1.03:1:0.06:0.06. This improves the electrical conductivity of the thermoelectric material.

[0018] In some embodiments of the present invention, in step (1), the pressure of the tablet is 4 to 6 MPa. This allows for a tighter and more complete contact between the materials, which is beneficial for the occurrence of a self-propagating reaction between the materials.

[0019] In some embodiments of the present invention, in step (2), the heating temperature is 400–600°C and the time is 30–90 seconds. This facilitates a self-propagating reaction between the materials.

[0020] In some embodiments of the present invention, in step (3), the discharge plasma sintering conditions are: sintering temperature of 873–923 K, pressure of 40–50 MPa, and holding time of 4–6 min. Thus, a BiCuSeO / graphene composite thermoelectric material with high electrical conductivity, low thermal conductivity, and high thermoelectric performance can be obtained.

[0021] In another aspect, the present invention provides a thermoelectric device. According to embodiments of the present invention, the thermoelectric device comprises the above-described BiCuSeO / graphene composite thermoelectric material or a BiCuSeO / graphene composite thermoelectric material prepared by the above method. Therefore, the thermoelectric device exhibits good thermoelectric performance and has broad application prospects in military aerospace, waste heat utilization, and waste incineration.

[0022] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0023] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0024] Figure 1 This is a schematic flowchart of a method for preparing BiCuSeO / graphene composite thermoelectric materials according to an embodiment of the present invention;

[0025] Figure 2 Bi prepared in proportion 0.88 Pb 0.06 Ca 0.06 XRD pattern of CuSeO;

[0026] Figure 3 The graph shows the change in electrical conductivity of the BiCuSeO / graphene composite materials of the comparative examples and Examples 1-4 as a function of temperature.

[0027] Figure 4 The Seebeck curve for BiCuSeO / graphene composites in comparative examples and Examples 1-4 is shown as a function of temperature.

[0028] Figure 5 The graph shows the power factor of the BiCuSeO / graphene composite materials in the comparative examples and Examples 1-4 as a function of temperature.

[0029] Figure 6The graph shows the change in thermal conductivity of the BiCuSeO / graphene composite materials of the comparative examples and Examples 1-4 as a function of temperature.

[0030] Figure 7 This is a graph showing the ZT value of the BiCuSeO / graphene composite materials in the comparative examples and Examples 1-4 as a function of temperature. Detailed Implementation

[0031] The embodiments of the present invention are described in detail below, and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0032] In one aspect of the present invention, a BiCuSeO / graphene composite thermoelectric material is proposed. According to an embodiment of the present invention, the chemical formula of the BiCuSeO / graphene composite thermoelectric material is Bi. 0.88 Pb 0.06 Ca 0.06 CuSeO / graphene.

[0033] The inventors discovered that doping BiCuSeO with Pb and Ca, and controlling the stoichiometric ratio of Bi, Pb, and Ca to be 0.88:0.06:0.06, can effectively improve the electrical conductivity of the BiCuSeO thermoelectric material. Simultaneously, due to the high mobility of graphene, the BiCuSeO / graphene composite thermoelectric material formed by adding graphene not only exhibits high electrical performance but also low thermal conductivity, achieving synergistic regulation of electrical and thermal properties. Therefore, this BiCuSeO / graphene composite thermoelectric material possesses high electrical conductivity, low thermal conductivity, and high thermoelectric performance. Specifically, the ZT value of this BiCuSeO / graphene composite thermoelectric material is not less than 1.13.

[0034] In some embodiments of the present invention, in the above-mentioned BiCuSeO / graphene composite thermoelectric material, graphene accounts for a certain proportion of Bi... 0.88 Pb 0.06 Ca 0.06 The mass percentage of CuSeO is x%, where x ranges from 0.03 to 0.1, for example, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, and 0.10. The inventors discovered that when the amount of graphene added is low, i.e., x is less than 0.03, the high mobility of graphene is difficult to fully utilize, resulting in poor thermoelectric properties of the obtained thermoelectric material. When the amount of graphene added is high, i.e., x is greater than 0.1, the relative density of the thermoelectric material decreases, leading to deterioration in mechanical properties. Therefore, when x is set to a value of 0.03 to 0.1 as described in this application, the obtained thermoelectric material exhibits better thermoelectric and mechanical properties. Preferably, the value of x is 0.07 to 0.1.

[0035] In another aspect, the present invention provides a method for preparing the above-mentioned BiCuSeO / graphene composite thermoelectric material, according to embodiments of the present invention, referring to... Figure 1 The method includes:

[0036] S100: Bi powder, Bi2O3 powder, Se powder, Cu powder, PbO powder and CaO powder are mixed and then compressed into tablets.

[0037] In this step, commercially available Bi, Se, and Cu elemental powders with a purity greater than 99.5% and Bi2O3, PbO, and CaO oxide powders are weighed as raw material powders according to the molar ratio of Bi powder, Bi2O3 powder, Se powder, Cu powder, PbO powder, and CaO as 0.294:0.293:1.03:1:0.06:0.06. Se powder is added in excess at a ratio of 3%. The appropriate excess of Se powder can replenish the Se lost in the heating reaction in the air. After the above materials are mixed evenly, they are compressed into tablets under a pressure of 4-6 MPa to obtain green tablets. The inventors discovered that doping BiCuSeO with Pb and Ca, and controlling the stoichiometric ratio of Bi, Pb, and Ca to be 0.88:0.06:0.06, can effectively improve the electrical conductivity of the BiCuSeO thermoelectric material. They also found that if the pressing pressure is too low, the resulting block is not dense enough, leading to insufficient self-propagating reaction during subsequent heating; conversely, if the pressing pressure is too high, the block is prone to breakage during demolding. Therefore, pressing at a pressure of 4–6 MPa not only ensures closer and more complete contact between the powders but also promotes subsequent self-propagating reactions and facilitates demolding.

[0038] S200: Heating the green body to induce a self-propagating reaction.

[0039] In this step, the green body obtained in step S100 is heated to cause a self-propagating reaction at high temperature. The reaction begins with ignition at the bottom of the green body, and the combustion wave rapidly spreads from the bottom to the top throughout the entire green body. The reaction process is intensely exothermic, and during this process, the raw material powder fully contacts and reacts to generate Bi. 0.88 Pb 0.06 Ca 0.06 The CuSeO phase was obtained. After the reaction was complete, it was allowed to cool naturally to yield Bi. 0.88 Pb 0.06 Ca 0.06 CuSeO bulk material. It should be noted that the specific heating method described above is not particularly limited, and those skilled in the art can choose according to actual needs; for example, heating with an alcohol lamp can be used.

[0040] Furthermore, the heating temperature is 400–600°C, and the time is 30–90 seconds. The inventors discovered that if the heating temperature is too low or the time is too short, the self-propagating reaction is unlikely to occur; while if the heating temperature is too high or the time is too long, the Se powder volatilization loss is significant, and the self-propagating reaction has already been completed, further heating would reduce efficiency. Therefore, the heating conditions described in this application not only reduce Se powder volatilization loss but also promote the occurrence of the self-propagating reaction.

[0041] S300: Bi 0.88 Pb 0.06 Ca 0.06 CuSeO bulk material was ground and mixed with graphene powder, then subjected to spark plasma sintering.

[0042] In this step, the Bi obtained in step S200 is... 0.88 Pb 0.06 Ca 0.06 CuSeO bulk material is ground into powder, mixed with graphene powder, and then subjected to spark plasma sintering (SPCS). During SPCS, the instantaneous discharge plasma generated when a DC pulse current is applied to the electrodes causes uniform Joule heating within each particle of the sintered body, activating the particle surface. Simultaneously, under high pressure, the powder is rapidly sintered and densified to obtain a BiCuSeO / graphene composite bulk material. Due to the high mobility of graphene, the resulting BiCuSeO / graphene composite thermoelectric material not only possesses high electrical properties but also low thermal conductivity, achieving synergistic control of electrical and thermal properties.

[0043] Furthermore, the aforementioned spark plasma sintering conditions are: sintering temperature of 873–923 K, pressure of 40–50 MPa, and holding time of 4–6 min. This yields a BiCuSeO / graphene composite thermoelectric material with high electrical conductivity, low thermal conductivity, and high thermoelectric performance.

[0044] Therefore, the method of this application is simple and has low requirements for experimental equipment and site, which is conducive to the large-scale and industrial production of the BiCuSeO / graphene composite thermoelectric material. The BiCuSeO / graphene composite thermoelectric material prepared by this method has high electrical conductivity, low thermal conductivity and high thermoelectric performance.

[0045] In another aspect, the present invention provides a thermoelectric device. According to embodiments of the present invention, the thermoelectric device comprises the above-described BiCuSeO / graphene composite thermoelectric material or a BiCuSeO / graphene composite thermoelectric material prepared by the above-described method. Therefore, the thermoelectric device exhibits good thermoelectric performance. Those skilled in the art will understand that the features and advantages described above for the BiCuSeO / graphene composite thermoelectric material and its preparation method are also applicable to this thermoelectric device, and will not be repeated here.

[0046] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0047] Comparative Example

[0048] (1) Using Bi powder, Bi2O3 powder, Se powder, Cu powder, PbO powder, and CaO powder as raw materials, 11g of raw material powder was weighed according to the molar ratio of 0.294:0.293:1.03:1:0.06:0.06. The powder was ground in an agate mortar for 20 minutes. After mixing evenly, the powder was taken out and placed in a metal mold (12.5mm in diameter) and compressed into tablets in a tablet press at a pressure of 5MPa. The compacted block was placed in an alumina crucible and heated in the outer flame of an alcohol lamp (600℃). After about 30 seconds, a self-propagating reaction occurred. The alcohol lamp was removed, and the mixture was allowed to cool naturally to obtain Bi. 0.88 Pb 0.06 Ca 0.06 CuSeO bulk material;

[0049] (2) The Bi prepared in step (1) 0.88 Pb 0.06 Ca 0.06 The CuSeO bulk material was ground into a uniform and fine powder, placed in a graphite mold, and subjected to discharge plasma sintering at a temperature of 923 K and a pressure of 40 MPa for 5 minutes to obtain Bi. 0.88 Pb 0.06 Ca 0.06 CuSeO thermoelectric material.

[0050] Bi prepared in the comparative example 0.88 Pb 0.06 Ca 0.06 XRD phase characterization was performed on the CuSeO thermoelectric material sample, and its XRD pattern was referenced. Figure 2 It can be found that it is a BiCuSeO single-phase material, indicating that the method used in this invention can prepare pure-phase Bi. 0.88 Pb 0.06 Ca 0.06 CuSeO sample.

[0051] Bi prepared in the comparative example 0.88 Pb 0.06 Ca 0.06 Thermoelectric properties of CuSeO were tested, and the results are attached. Figure 3 , 4 As shown in Figures 5, 6, and 7, its conductivity at 923 K is 217 S cm⁻¹. -1 The Seebeck coefficient is 191 μV. -1 K -1 The power factor is 789 μWm -1 K -2 Thermal conductivity is 0.70 W / m -1 K -1 The ZT value is 1.03.

[0052] Example 1

[0053] Step (1) of Example 1 is the same as step (1) of Comparative Example;

[0054] (2) The Bi prepared in step (1) 0.88 Pb 0.06 Ca 0.06 CuSeO bulk material was ground into a uniform, fine powder and mixed evenly with 0.0033 g of graphene powder. The mixture was then placed in a graphite mold and subjected to discharge plasma sintering at 923 K and 40 MPa for 5 min to obtain Bi0. 0.88 Pb 0.06 Ca 0.06 CuSeO / 0.03wt% graphene composite thermoelectric material.

[0055] Bi prepared in Example 1 0.88 Pb 0.06 Ca 0.06 Thermoelectric properties of CuSeO / 0.03wt% graphene were tested, and the results are attached. Figure 3 , 4 As shown in Figures 5, 6, and 7, its conductivity at 923 K is 197 S cm⁻¹. -1 The Seebeck coefficient is 203 μV. -1 K -1 The power factor is 813 μW / m. -1 K -2 The thermal conductivity is 0.66 W / m. -1 K -1 The ZT value is 1.13.

[0056] Example 2

[0057] The difference between Example 2 and Example 1 is that in step (2), 0.0055g of graphene powder and Bi are weighed.0.88 Pb 0.06 Ca 0.06 The CuSeO powder was mixed evenly. Bi was then prepared. 0.88 Pb 0.06 Ca 0.06 CuSeO / 0.05wt% graphene composite thermoelectric material.

[0058] Bi prepared in Example 2 0.88 Pb 0.06 Ca 0.06 Thermoelectric properties of CuSeO / 0.05wt% graphene were tested, and the results are attached. Figure 3 , 4 As shown in Figures 5, 6, and 7, its conductivity at 923 K is 197 S cm⁻¹. -1 The Seebeck coefficient is 204 μV. -1 K -1 The power factor is 818 μW / m. -1 K -2 The thermal conductivity is 0.61 W / m. -1 K -1 The ZT value is 1.24.

[0059] Example 3

[0060] The difference between Example 3 and Example 1 is that in step (2), 0.0077g of graphene powder and Bi are weighed. 0.88 Pb 0.06 Ca 0.06 The CuSeO powder was mixed evenly. Bi was then prepared. 0.88 Pb 0.06 Ca 0.06 CuSeO / 0.07wt% graphene composite thermoelectric material.

[0061] Bi prepared in Example 3 0.88 Pb 0.06 Ca 0.06 Thermoelectric properties of CuSeO / 0.07wt% graphene were tested, and the results are attached. Figure 3 , 4 As shown in Figures 5, 6, and 7, its conductivity at 923 K is 195 S cm⁻¹. -1 The Seebeck coefficient is 207 μV. -1 K -1 The power factor is 838 μW / m. -1 K -2 The thermal conductivity is 0.61 W / m. -1 K -1 The ZT value is 1.27.

[0062] Example 4

[0063] The difference between Example 4 and Example 1 is that in step (2), 0.0110g of graphene powder and Bi are weighed. 0.88 Pb 0.06 Ca 0.06 The CuSeO powder was mixed evenly. Bi was then prepared. 0.88 Pb 0.06 Ca 0.06 CuSeO / 0.1wt% graphene composite thermoelectric material.

[0064] Bi prepared in Example 4 0.88 Pb 0.06 Ca 0.06 Thermoelectric properties of CuSeO / 0.1wt% graphene were tested, and the results are attached. Figure 3 , 4 As shown in Figures 5, 6, and 7, its conductivity at 923 K is 200 S cm⁻¹. -1 The Seebeck coefficient is 201 μV. -1 K -1 The power factor is 811 μW m. -1 K -2 The thermal conductivity is 0.53 W / m. -1 K -1 The ZT value is 1.41.

[0065] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0066] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A BiCuSeO / graphene composite thermoelectric material, characterized in that, The chemical formula of the BiCuSeO / graphene composite thermoelectric material is Bi 0.88 Pb 0.06 Ca 0.06 CuSeO / graphene; In the composite thermoelectric material, the graphene accounts for x% of the Bi 0.88 Pb 0.06 Ca 0.06 x% of the mass of CuSeO, wherein x is 0.03-0.

1.

2. The composite thermoelectric material according to claim 1, characterized in that, x takes values ​​from 0.07 to 0.

1.

3. The composite thermoelectric material according to claim 1, characterized in that, The composite thermoelectric material ZT The value is not less than 1.

13.

4. A method for preparing the composite thermoelectric material according to any one of claims 1-3, characterized in that, include: (1) Mix Bi powder, Bi2O3 powder, Se powder, Cu powder, PbO powder and CaO powder and compress them into tablets to obtain green blanks; (2) The green blank is heated to cause a self-propagating reaction in order to obtain Bi. 0.88 Pb 0.06 Ca 0.06 CuSeO bulk material; (3) The Bi 0.88 Pb 0.06 Ca 0.06 CuSeO bulk material is ground into powder and mixed with graphene powder, then subjected to spark plasma sintering to obtain BiCuSeO / graphene composite thermoelectric material.

5. The method according to claim 4, characterized in that, In step (1), the molar ratio of Bi powder, Bi2O3 powder, Se powder, Cu powder, PbO powder and CaO powder is 0.294:0.293:1.03:1:0.06:0.

06.

6. The method according to claim 4 or 5, characterized in that, In step (1), the pressure of the tablet is 4~6 MPa.

7. The method according to claim 4, characterized in that, In step (2), the heating temperature is 400~600℃ and the time is 30~90 s.

8. The method according to claim 4, characterized in that, In step (3), the discharge plasma sintering conditions are: sintering temperature of 873~923 K, pressure of 40~50 MPa, and holding time of 4~6 min.

9. A thermoelectric device, characterized in that, The thermoelectric device comprises the BiCuSeO / graphene composite thermoelectric material according to any one of claims 1-3 or the BiCuSeO / graphene composite thermoelectric material prepared by the method according to any one of claims 4-8.

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