A method for preparing a thermoelectric device based on composite flame-retardant paper

Abstract

The present invention discloses a method for preparing a thermoelectric device based on composite flame-retardant paper, comprising: a. adding graphene oxide powder to water and stirring uniformly to form a colloidal suspension; b. dissolving hexaphenoxycyclotriphosphazene in ethanol and adding the dissolved solution to the colloidal suspension to obtain GO. ‑ @HPTCP suspension; c. Dissolve chitosan in acetic acid solution to obtain CS solution, and disperse carbon nanotubes in the CS solution to obtain CNTs@CS + Suspension; d. Immerse wood pulp paper in CNTs@CS + suspension, then rinsed and vacuum dried; e. Immerse the wood pulp paper treated in step d in GO ‑ @HPTCP suspension, then rinse and vacuum dry; f. Repeat steps d and e to obtain a composite flame retardant wood pulp paper; g. Cut the composite flame retardant wood pulp paper, and connect the cut composite flame retardant wood pulp paper in series, and then encapsulate it with a polyimide film to obtain a flexible thermoelectric device.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric materials, and more particularly to a method for preparing a thermoelectric device based on composite flame-retardant paper. Background Art

[0002] The research on thermoelectric materials can be traced back to the 18th century. In 1821, German physicist Seebeck discovered that the temperature difference between the two ends of a conductive material can generate a voltage, which in turn forms an electric current in an external circuit. This is the phenomenon of thermoelectric power generation, which is named the Seebeck effect. In 1834, Frenchman Peltier discovered that applying voltage to a conductive material can produce a temperature difference between the two ends of the material. This phenomenon is the reverse process of the Seebeck effect and is named the Peltier effect. Based on the huge application potential of these two effects in the energy field, thermoelectric materials have received increasing attention from academia and industry in recent years.

[0003] In recent years, in order to further enhance the thermoelectric performance of thermoelectric materials, research on polymer-based composite thermoelectric materials with conductive polymers as the matrix and inorganic semiconductor nanoparticles or nanocarbon materials as fillers has continued to increase. The polymer composite thermoelectric materials are highly flexible, which also lays the foundation for the preparation of flexible thermoelectric devices, thereby enabling efficient utilization of heat sources on curved or irregular surfaces (such as the heat energy of the human body itself). In addition, the Seebeck coefficient of the material is expected to be further improved through energy-filtering effects, and it can also better achieve the interfacial electrothermal synergistic transport effect of "continuous conductivity-discontinuous thermal conductivity". Therefore, polymer composite thermoelectric materials provide a solution for the preparation of high-performance flexible thermoelectric devices and show great potential in the field of flexible applications.

[0004] To further improve the thermoelectric performance of flexible composite thermoelectric materials, researchers have proposed combining carbon nanomaterials and organic polymers, which have synergistic effects in mechanical, electronic, and thermal properties, to assemble flexible thermoelectric devices. Currently, most of the flexible thermoelectric devices based on polymer composite thermoelectric materials reported in the literature use solid-state thin-film thermoelectric legs. Thin-film preparation methods generally include "template adsorption-in-situ polymerization" method, layer-by-layer self-assembly method, solution mixing method, etc. There are also a few reports on polymer composite inks suitable for inkjet printing and fiber-type polymer composite thermoelectric devices. Some studies have pointed out that paper materials with a three-dimensional network structure composed of one-dimensional fibers are low-cost and have unique flexibility and foldability. In addition, due to the presence of fiber pore structure, paper materials have excellent wettability, and can be precisely loaded with multiple carbon nanomaterials by layer-by-layer coating method to achieve specific electronic and thermal properties. However, the inherent flammability of paper materials is not conducive to their long-term application in the field of thermoelectric power generation. Therefore, how to prepare low-cost flexible thermoelectric devices that can be stably used in high-temperature environments remains a challenge. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a thermoelectric device based on composite flame-retardant paper, so as to prepare a thermoelectric device with good flexibility, low cost and stable application in high temperature environments.

[0006] To solve the above technical problems, the present invention provides a method for preparing a thermoelectric device based on composite flame-retardant paper, comprising:

[0007] a. Add graphene oxide powder to water and stir evenly to form a colloidal suspension;

[0008] b. Dissolve hexaphenoxycyclotriphosphazene in ethanol and add the dissolved solution to the colloidal suspension obtained in step a to obtain GO - @HPTCP suspension;

[0009] c. Dissolve chitosan in acetic acid solution to obtain CS solution, and disperse carbon nanotubes in the CS solution to obtain CNTs@CS + suspension;

[0010] d. Immerse wood pulp paper in CNTs@CS + suspension, then rinsed and vacuum dried;

[0011] e. Immerse the wood pulp paper treated in step d into GO - @HPTCP suspension, then rinsed and vacuum dried;

[0012] f. Repeat steps d and e to obtain a composite flame retardant wood pulp paper with the desired carbon nanomaterial loading amount;

[0013] g. Cut the composite flame-retardant wood pulp paper, connect the cut composite flame-retardant wood pulp paper in series, and then encapsulate it with a polyimide film to obtain a flexible thermoelectric device.

[0014] A further technical solution is: in step a, the graphene oxide powder is dispersed by probe-type ultrasonic stirring, and the ultrasonic time is 15 minutes, 30 minutes or 1 hour.

[0015] A further technical solution is as follows: in the step b, the weight of hexaphenoxycyclotriphosphazene is 25 mg, 50 mg, 100 mg or 200 mg.

[0016] A further technical solution is: in step c, the weight of the carbon nanotubes is 25 mg, 50 mg, 100 mg or 200 mg.

[0017] The further technical solution is as follows: in the step c, the pH value of the CS solution obtained by dissolving chitosan in the acetic acid solution is 4.

[0018] The further technical solution is: in step d, the wood pulp paper is immersed in CNTs@CS + The soaking time of the suspension is 1 min, 3 min or 5 min; the vacuum drying temperature is 60° C., 80° C. or 100° C.

[0019] Its further technical solution is: in the step e, the wood pulp paper treated in the step d is immersed in GO - The immersion time of the HPTCP suspension is 1 min, 3 min or 5 min; the vacuum drying temperature is 60°C, 80°C or 100°C.

[0020] A further technical solution is: in step g, the shape of the cut composite flame-retardant wood pulp paper is rectangular, square or circular.

[0021] Its further technical solution is: in the step g, when the shape of the cut composite flame retardant wood pulp paper is rectangular, the size is 8mm×32mm or 10mm×30mm; when the shape of the cut composite flame retardant wood pulp paper is square, the size is 16mm×16mm; when the shape of the cut composite flame retardant wood pulp paper is circular, the diameter is 18.05mm.

[0022] A further technical solution is as follows: in step g, copper wires and conductive silver paste are used to connect the cut composite flame-retardant wood pulp paper in series.

[0023] Compared with the prior art, the preparation method of the present invention alternately immerses wood pulp paper into CNTs@CS + Suspension and GO -@HPTCP suspension, an alternating multilayer coating of functionalized graphene oxide and carbon nanotubes was constructed, that is, a multilayer coating of graphene oxide and carbon nanotubes was obtained by simple layer-by-layer assembly of suspensions with opposite charges. Compared with other methods or general layer-by-layer assembly coating methods, this method is more efficient and convenient, and the structure and dosage of the resulting carbon nanomaterial coating are also more controllable. The prepared composite flame-retardant wood pulp paper has significantly enhanced electrical conductivity and a high Seebeck coefficient, while retaining the mechanical flexibility of the carbon nanotubes. During the combustion process, the physical carbon layer produced by the functionalized graphene oxide and carbon nanotubes is coated by the chemical carbon layer produced by the carbonization of the wood pulp paper catalyzed by hexaphenoxycyclotriphosphazene. After combustion, it can still maintain its original shape, exhibiting excellent mechanical and flame-retardant properties. The prepared composite flame-retardant wood pulp paper can be easily cut into any shape and assembled into a planar thermoelectric device. The resulting thermoelectric device has good mechanical flexibility, low cost, and can be stably used in high-temperature environments, with high practical value. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to more clearly understand the objectives, technical solutions and advantages of the present invention, the present invention is further described below with reference to the following embodiments.

[0025] The present invention provides a method for preparing a thermoelectric device based on composite flame-retardant paper, comprising:

[0026] a. Add graphene oxide powder (GO) to water and stir evenly to form a colloidal suspension.

[0027] In this step, the graphene oxide powder is dispersed by probe-type ultrasonic stirring, and the ultrasonic time can be 15 minutes, 30 minutes or 1 hour. In the present invention, the graphene oxide powder can be added to deionized water, and the amount of graphene oxide powder can be 100 mg. Correspondingly, the amount of deionized water is 100 mL.

[0028] b. Dissolve hexaphenoxycyclotriphosphazene (HPCTP) in ethanol and add the dissolved solution to the colloidal suspension obtained in step a to obtain GO - @HPTCP suspension.

[0029] In this step, the weight of hexaphenoxycyclotriphosphazene can be 25 mg, 50 mg, 100 mg or 200 mg, preferably 100 mg, and the amount of ethanol used can be 15 mL. Preferably, in the present invention, HPCTP is dissolved in 15 mL of ethanol, and the dissolved solution is slowly added to the colloidal suspension obtained in step a under constant stirring.

[0030] c. Dissolve chitosan (CS) in acetic acid solution to obtain CS solution, and disperse carbon nanotubes (CNTs) in the CS solution to obtain CNTs@CS + suspension.

[0031] In this step, the weight of the carbon nanotubes can be 25 mg, 50 mg, 100 mg or 200 mg, preferably 100 mg; the carbon nanotubes (CNTs) can be dispersed in the CS solution and then immersed in an ultrasonic water bath.

[0032] In the present invention, the amount of chitosan used can be 100 mg, the amount of acetic acid solution used can be 100 mL, and when dissolving chitosan (CS) in the acetic acid solution, the concentration of acetic acid can be adjusted so that the pH value of the CS solution is 4.

[0033] d. Immerse wood pulp paper (WPP) in CNTs@CS + The suspension was then rinsed and dried under vacuum.

[0034] In this step, wood pulp paper is immersed in CNTs@CS + The suspension can be immersed in the solution for 1 minute, 3 minutes, or 5 minutes; then it can be rinsed in deionized water for 2 minutes, and the vacuum drying temperature is 60°C, 80°C, or 100°C. Among them, the immersion time is preferably 3 minutes, the vacuum drying temperature is preferably 80°C, and the vacuum drying time can be 15 minutes.

[0035] e. Immerse the wood pulp paper treated in step d into GO - @HPTCP suspension, then rinsed and vacuum dried.

[0036] In this step, the wood pulp paper treated in step d is immersed in GO - The soaking time of the @HPTCP suspension can be 1 min, 3 min, or 5 min, followed by rinsing in deionized water for 2 minutes. The vacuum drying temperature can be 60°C, 80°C, or 100°C. The soaking time is preferably 3 min, the vacuum drying temperature is preferably 80°C, and the vacuum drying time can be 15 min.

[0037] f. Repeat steps d and e to obtain a composite flame-retardant wood pulp paper (GO / CNTs@WPP) that meets the required carbon nanomaterial loading amount.

[0038] In the present invention, steps d and e can be cyclically repeated 10 times, 20 times, 30 times, 50 times, 75 times or 100 times, preferably 50 times.

[0039] g. Cut the composite flame-retardant wood pulp paper, connect the cut composite flame-retardant wood pulp paper in series, and then encapsulate it with a polyimide film to obtain a flexible thermoelectric device.

[0040] In this step, the cut composite flame-retardant wood pulp paper is shaped like a rectangle, square, or circle. If the cut composite flame-retardant wood pulp paper is rectangular, the dimensions can be 8mm x 32mm or 10mm x 30mm; if the cut composite flame-retardant wood pulp paper is square, the dimensions can be 16mm x 16mm; if the cut composite flame-retardant wood pulp paper is circular, the diameter can be 18.05mm. Furthermore, copper wire and conductive silver paste can be used to connect the cut composite flame-retardant wood pulp paper end to end in series.

[0041] Because graphene has a single-layer two-dimensional carbon atom lattice, it has excellent mechanical and electrical properties, while carbon nanotubes are considered to be graphene cylinders curled at a certain angle. They have many similar properties to graphene, including excellent chemical / thermal stability and excellent electronic and optical properties. Benefiting from their one-dimensional structure, CNTs also have a high aspect ratio and high surface area. The present invention focuses on the integration of these two types of carbon nanomaterials, using a layer-by-layer assembly method of suspensions with opposite charges to combine graphene (two-dimensional structure) and CNTs (one-dimensional structure) to form a GO / CNTs hybrid coating, which improves the mechanical and thermoelectric properties of wood pulp paper and well preserves the mechanical flexibility of the latter. In addition, the physical carbon layer produced by functionalized graphene oxide and carbon nanotubes during the combustion process is coated by the chemical carbon layer produced by the carbonization of wood pulp paper catalyzed by hexaphenoxycyclotriphosphazene. After combustion, it can still maintain its original shape and exhibit excellent flame retardant properties.

[0042] The preparation method of the thermoelectric device based on the composite flame-retardant paper of the present invention is described below with reference to specific examples.

[0043] Example 1

[0044] (1) 100 mg of graphene oxide (GO) powder was dispersed in 100 mL of deionized water and ultrasonically dispersed for 30 min using a probe ultrasonicator to form a stable colloidal suspension;

[0045] (2) Dissolve 100 mg of hexaphenoxycyclotriphosphazene (HPCTP) in 15 mL of ethanol and slowly add the dissolved solution to the colloidal suspension obtained in (1) under constant stirring to obtain GO - @HPTCP suspension;

[0046] (3) 100 mg of chitosan (CS) was dissolved in 100 mL of acetic acid solution to obtain CS solution. The acetic acid concentration was adjusted to make the pH value of the solution 4. 100 mg of CNTs was dispersed in the CS solution and immersed in an ultrasonic water bath for 20 minutes to obtain CNTs@CS solution. + suspension;

[0047] (4) Immersing wood pulp paper (WPP) into CNTs@CS+ suspension for 3 min, then rinsed in deionized water for 2 min and dried under vacuum at 80 °C for 15 min;

[0048] (5) Immerse the WPP treated in step (4) into GO - @HPTCP suspension for 3 min, then rinsed in deionized water for 2 min and dried in vacuum at 80 °C for 15 min;

[0049] (6) Repeat steps (5) and (6) 50 times each to obtain a composite flame-retardant wood pulp paper having a desired carbon nanomaterial loading amount.

[0050] (7) Each obtained composite flame-retardant wood pulp paper (GO / CNTs@WPP) was cut into five rectangles of specified size (8 mm × 32 mm), and copper wire and conductive silver paste were used to connect each five GO / CNTs@WPP rectangles end to end in series, and then encapsulated with polyimide film to assemble a flexible thermoelectric device.

[0051] As we all know, the evaluation index of the thermoelectric performance of materials is the dimensionless thermoelectric figure of merit ZT = S 2 σT / κ, where S, σ, T and κ are the Seebeck coefficient, electrical conductivity, absolute temperature and thermal conductivity of the material respectively. It can be seen that the material needs to have a large Seebeck coefficient, high electrical conductivity and low thermal conductivity to obtain excellent thermoelectric performance. For organic polymers and their composite materials, due to their low thermal conductivity, the power factor PF is often used. 2 σ is used to measure the quality of the thermoelectric performance of the material.

[0052] The thermoelectric properties of the composite flame-retardant wood pulp paper and thermoelectric device prepared according to the parameters of this embodiment are as follows: The electrical conductivity of the composite flame-retardant wood pulp paper (GO / CNTs@WPP) is 97.80S cm -1 , the Seebeck coefficient is 33.50μVK -1 , the power factor is 10.98μWm -1 K -2 The planar flexible thermoelectric device prepared based on this GO / CNTs@WPP has a maximum output power of 1.14μW at a temperature difference of 80K.

[0053] Example 2

[0054] The method is similar to that of Example 1, except that the cutting shape in step (7) is changed to a square with a size of 16 mm × 16 mm. The thermoelectric properties of the composite flame-retardant wood pulp paper and thermoelectric device finally prepared in this example are as follows: The electrical conductivity of the composite flame-retardant wood pulp paper (GO / CNTs@WPP) is 97.80 S cm -1, the Seebeck coefficient is 33.50μVK -1 , the power factor is 10.98μWm -1 K -2 ; The planar flexible thermoelectric device prepared based on this GO / CNTs@WPP has a maximum output power of 0.91μW at a temperature difference of 80K.

[0055] Example 3

[0056] The method is similar to that of Example 1, except that the cutting shape in step (7) is changed to a circle with a diameter of 18.05 mm. The thermoelectric properties of the composite flame-retardant wood pulp paper and thermoelectric device finally prepared in this example are as follows: The electrical conductivity of the composite flame-retardant wood pulp paper (GO / CNTs@WPP) is 97.80 S cm -1 , the Seebeck coefficient is 33.50μVK -1 , the power factor is 10.98μWm -1 K -2 ; The planar flexible thermoelectric device prepared based on this GO / CNTs@WPP has a maximum output power of 0.94μW at a temperature difference of 80K.

[0057] Example 4

[0058] The method is similar to that of Example 1, except that the weight of CNTs in step (3) is replaced by 25 mg. The thermoelectric properties of the composite flame-retardant wood pulp paper and thermoelectric device finally prepared in this example are as follows: The electrical conductivity of the composite flame-retardant wood pulp paper (GO / CNTs@WPP) is 38.45 S cm -1 , the Seebeck coefficient is 35.60μVK -1 , the power factor is 4.87μWm -1 K -2 ; The planar flexible thermoelectric device prepared based on this GO / CNTs@WPP has a maximum output power of 0.40μW at a temperature difference of 80K.

[0059] Example 5

[0060] The method is similar to that of Example 1, except that the wood pulp paper (WPP) in step (4) is immersed in CNTs@CS + The suspension time was changed from 3 minutes to 5 minutes, and the WPP treated in step (4) was immersed in GO in step (5). - The time in the HPTCP suspension was also changed from 3 minutes to 5 minutes. The thermoelectric properties of the composite flame-retardant wood pulp paper and thermoelectric device finally prepared in this embodiment are as follows: The electrical conductivity of the composite flame-retardant wood pulp paper (GO / CNTs@WPP) is 186.80S cm -1, the Seebeck coefficient is 22.40μVK -1 , the power factor is 9.37μWm -1 K -2 ; The planar flexible thermoelectric device prepared based on this GO / CNTs@WPP has a maximum output power of 0.92μW at a temperature difference of 80K.

[0061] Example 6

[0062] The method is similar to that of Example 1, except that the number of repetitions in step (6) is changed from 50 to 100 times. The thermoelectric properties of the composite flame-retardant wood pulp paper and thermoelectric device finally prepared in this example are as follows: The electrical conductivity of the composite flame-retardant wood pulp paper (GO / CNTs@WPP) is 218.30S cm -1 , the Seebeck coefficient is 21.30μVK -1 , the power factor is 9.90μWm -1 K -2 ; The planar flexible thermoelectric device prepared based on this GO / CNTs@WPP has a maximum output power of 1.06μW at a temperature difference of 80K.

[0063] In summary, the present invention combines paper materials with two carbon nanomaterials at a low load to assemble a planar flexible thermoelectric device with excellent flexibility and high flame retardancy, providing a new method for preparing flexible thermoelectric devices with low preparation cost, green and environmentally friendly, and stable application in high-temperature environments. That is, by layer-by-layer dip coating of a carbon nanomaterial suspension with opposite charges, a functionalized alternating multilayer coating of graphene oxide and carbon nanotubes is constructed, and after rinsing and drying, a composite flame-retardant wood pulp paper with excellent mechanical flexibility, conductivity and flame retardancy is obtained, and the composite flame-retardant wood pulp paper is assembled in series into a thermoelectric device. Compared with other methods or general layer-by-layer assembly coating methods, this layer-by-layer dip coating method is more efficient and convenient. The structure and dosage of the obtained carbon nanomaterial coating are also more controllable, and the prepared composite flame-retardant wood pulp paper has significantly enhanced electrical conductivity and a higher Seebeck coefficient, while retaining the mechanical flexibility of carbon nanotubes. During the combustion process, the physical carbon layer produced by functionalized graphene oxide and carbon nanotubes is coated by the chemical carbon layer produced by the carbonization of wood pulp paper catalyzed by hexaphenoxycyclotriphosphazene. After combustion, it can still maintain its original shape, showing excellent mechanical properties and flame retardant properties; and the prepared composite flame-retardant wood pulp paper can be easily cut into any shape and assembled into a planar thermoelectric device. The obtained thermoelectric device has good mechanical flexibility, low cost, and can be stably used in high-temperature environments, and has high practical value.

[0064] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Those skilled in the art may make various equivalent changes and improvements based on the above embodiment. Any equivalent changes or modifications made within the scope of the claims shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a thermoelectric device based on composite flame-retardant paper, characterized in that: include: a. Add graphene oxide powder to water and stir evenly to form a colloidal suspension; b. Dissolve hexaphenoxycyclotriphosphazene in ethanol and add the dissolved solution to the colloidal suspension obtained in step a to obtain GO - @HPTCP suspension; c. Dissolve chitosan in acetic acid solution to obtain CS solution, and disperse carbon nanotubes in the CS solution to obtain CNTs@CS + suspension; d. Immerse wood pulp paper in CNTs@CS + suspension, then rinsed and vacuum dried; e. Immerse the wood pulp paper treated in step d into GO - @HPTCP suspension, then rinsed and vacuum dried; f. Repeat steps d and e to obtain a composite flame retardant wood pulp paper with the desired carbon nanomaterial loading amount; g. Cut the composite flame-retardant wood pulp paper, connect the cut composite flame-retardant wood pulp paper in series, and then encapsulate it with a polyimide film to obtain a flexible thermoelectric device.

2. The method for preparing a thermoelectric device based on composite flame-retardant paper according to claim 1, characterized in that: In the step a, the graphene oxide powder is dispersed by probe-type ultrasonic stirring, and the ultrasonic time is 15 minutes, 30 minutes or 1 hour.

3. The method for preparing a thermoelectric device based on composite flame-retardant paper according to claim 1, characterized in that: In the step b, the weight of hexaphenoxycyclotriphosphazene is 25 mg, 50 mg, 100 mg or 200 mg.

4. The method for preparing a thermoelectric device based on composite flame-retardant paper according to claim 1, wherein: In the step c, the weight of the carbon nanotubes is 25 mg, 50 mg, 100 mg or 200 mg.

5. The method for preparing a thermoelectric device based on composite flame-retardant paper according to claim 1, wherein: In the step c, the pH value of the CS solution obtained by dissolving chitosan in the acetic acid solution is 4.

6. The method for preparing a thermoelectric device based on composite flame-retardant paper according to claim 1, wherein: In the step d, the wood pulp paper is immersed in CNTs@CS + The soaking time of the suspension is 1 min, 3 min or 5 min; the vacuum drying temperature is 60° C., 80° C. or 100° C.

7. The method for preparing a thermoelectric device based on composite flame-retardant paper according to claim 1, characterized in that: In the step e, the wood pulp paper treated in step d is immersed in GO - The immersion time of the HPTCP suspension is 1 min, 3 min or 5 min; the vacuum drying temperature is 60°C, 80°C or 100°C.

8. The method for preparing a thermoelectric device based on composite flame-retardant paper according to claim 1, wherein: In the step g, the shape of the cut composite flame-retardant wood pulp paper is rectangular, square or circular.

9. The method for preparing a thermoelectric device based on composite flame-retardant paper according to claim 8, characterized in that: In step g, when the shape of the cut composite flame retardant wood pulp paper is rectangular, the size is 8mm×32mm or 10mm×30mm; when the shape of the cut composite flame retardant wood pulp paper is square, the size is 16mm×16mm; when the shape of the cut composite flame retardant wood pulp paper is circular, the diameter is 18.05mm.

10. The method for preparing a thermoelectric device based on composite flame-retardant paper according to claim 8, characterized in that: In the step g, the cut composite flame-retardant wood pulp paper is connected in series end to end using copper wire and conductive silver paste.