CN116855231A - Multifunctional composite phase change material and preparation method and application thereof - Google Patents

Abstract

The invention relates to a multifunctional composite phase change material, a preparation method and application thereof. The multifunctional composite phase-change material is formed by compounding graphene foam, MXene aerogel and a phase-change material; the MXene aerogel is a lamellar oriented structure coupled in the aperture of the GF foam, and the phase change material is encapsulated in the multifunctional composite material to form the GF foam-MXene aerogel double-network cooperatively supported multifunctional composite phase change material. The thermal conductivity reaches 11.39W m ^‑1 K ^‑1 The method comprises the steps of carrying out a first treatment on the surface of the The electromagnetic shielding efficiency reaches 56.6dB, and the energy storage density reaches 160.3J g ^‑1 . The composite phase-change material has higher strength and a more perfect heat conduction network, double packages the molten phase-change material and strengthens the heat transfer rate, and solves the problems of generally lower out-of-plane heat conductivity and easy leakage of the current composite phase-change material. Cooling and energy storage/conversion in electronic devicesThe device has excellent working performance and outstanding application effect when applied to the device.

Description

Multifunctional composite phase change materials and their preparation methods and applications

Technical field

The present invention relates to the technical field of phase change composite materials, and in particular to a multifunctional composite phase change material and its preparation method and application.

Background technique

In the context of green and clean energy, thermal energy storage (TES) is considered an important energy technology to improve energy efficiency. Phase change energy storage utilizes the large amount of heat absorption or heat release characteristics of phase change materials (PCM) during the phase change process to achieve the storage and release of energy. It has great application prospects in the field of intermittent or unstable thermal energy management. Such as periodic intermittent solar energy utilization, high-power electronic devices/battery thermal management, and industrial waste heat recovery and utilization. Organic PCM (such as paraffin, polyethylene glycol, fatty acids, etc.) has received great attention due to its advantages of high energy storage density, small volume change, stable chemical properties, not prone to supercooling and phase separation, non-toxic and non-corrosive, and low cost. s concern. However, organic PCM has long-term bottlenecks such as melt leakage and low inherent thermal conductivity during the solid-liquid phase transition process (generally between 0.15-0.5W m ^-1 K ^-1 ), which results in a significant reduction in the heat storage efficiency of PCM and severely restricts it. Its application in the fields of energy storage and thermal management. In response to the above problems of PCM, researchers use porous materials (Min Zhao, Yan Ye, Rui Yang. Absorption-polymerization method for synthesizing phase change composites with high enthalpy and thermal conductivity for efficient thermal energy storage [J]. Solar Energy Materials and Solar Cells, 248(2022)112027) or supporting materials (Yi-Cun Zhou, Jie Yang, Lu Bai, Rui-Ying Bao, Ming-Bo Yang, Wei Yang. Super-flexible phase change materials with a dual-supporting effect for solar thermoelectric conversion in the ocean environment[J].Journal of Materials Chemistry A,11(2023)341–351) Encapsulate phase change materials to prevent melt leakage; use carbon materials (diamond, carbon nanotubes, graphene, etc.) or metals and their oxidation Materials (silver, copper, alumina, etc.) strengthen the heat transfer process and improve the thermal conductivity of phase change materials. However, in order to achieve satisfactory shape stability and thermal conductivity of PCM, the existing technology needs to rely on a high load of thermally conductive fillers, which will inevitably significantly reduce the proportion of PCM in composite materials, resulting in the overall The energy storage density of the system decreases. Finding a balance between high thermal conductivity and high energy storage density while imparting shape stability is a key problem that needs to be solved in PCM research. In addition, the phase change composite materials prepared by the existing technology have single functionality. For thermal management of miniaturized and highly integrated electronic equipment, electromagnetic shielding (EMI) performance also needs to be considered. On the one hand, high-frequency electromagnetic radiation will not only reduce the operating accuracy of equipment and cause equipment failure, but also threaten the health of operators. On the other hand, the electromagnetic shielding performance of PCM is closely related to efficient thermal management. Electromagnetic shielding will directly convert most of the electromagnetic radiation into heat and ultimately trigger the PCM phase change process. Therefore, on the premise of ensuring high energy storage density of PCM, it is of great significance to simultaneously improve its electromagnetic shielding performance and thermal management capabilities.

The researchers proposed that constructing a three-dimensional interconnected thermally conductive skeleton inside the phase change composite material is expected to improve the thermal conductivity of the phase change composite material while maintaining a high energy storage density. Patent CN 112852386 A discloses a graphene aerogel phase change composite material prepared by hydrothermal reduction method. However, the physical cross-linking of graphene aerogel prepared by self-assembly of graphene oxide under high temperature and high pressure is mainly based on van der Waals force. , hydrogen bonds and π-π interactions, there is still interfacial thermal resistance between two-dimensional graphene nanosheets. Therefore, the thermal conductivity of the graphene airgel phase change composite prepared by it is only increased to 0.727W m ^-1 K ^-1 , and the performance is far from meeting the high standard usage requirements (>10W m ^-1 K ^-1 ). Compared with graphene aerogel (GA) prepared by self-assembly method, graphene foam (GF) grown by chemical vapor deposition can more effectively improve the thermal conductivity of composite PCM. This is because the cross-linking of GF is mainly based on covalent bonding, which can form a high-quality three-dimensional interconnected graphene skeleton and provide a continuous path for phonon transmission. However, the pore diameter of GF is as high as several hundred microns, which is determined by the nickel (Ni) foam catalyst skeleton, resulting in poor shape stability of the composite PCM, unsatisfactory electromagnetic shielding efficiency, and limited improvement in thermal conductivity.

Therefore, developing new technologies to build a dense secondary thermal conductive network inside the large pores of GF can be used as an effective strategy to improve the shape stability of composite PCM and further enhance its thermal conductivity and electromagnetic shielding effectiveness. This is a problem that needs to be solved. .

Contents of the invention

According to the problems of the existing technology, the present invention provides a multifunctional composite phase change material supported by a GF foam-MXene (two-dimensional material) airgel dual network collaboratively and its preparation method and application. The multifunctional composite phase change material It can combine high out-of-plane thermal conductivity and high energy storage density, while showing excellent electromagnetic shielding performance and excellent shape stability. It overcomes the problems that traditional organic phase change materials are easy to leak, have low thermal conductivity, have single functionality, and are often unable to balance high thermal conductivity and high energy storage density. The multifunctional composite phase change material has an out-of-plane thermal conductivity as high as 6.72-11.39W m ^-1 K ^-1 at a lower filler content (9.06-13.78wt%), and the X-band electromagnetic shielding effectiveness is as high as 42.9- at a thickness of 3.0mm. 55.6dB, and has a high energy storage density of 160.3-166.9J g ^-1 and excellent leakage prevention capabilities.

The technical solution of the present invention is as follows:

A multifunctional composite phase change material; the multifunctional composite phase change material is composed of graphene foam (GF foam), MXene aerogel and phase change material; the MXene aerogel is coupled within the pore size of the GF foam With the lamellar orientation structure, the phase change material is encapsulated in a multifunctional composite material, forming a multifunctional composite phase change material supported by a GF foam-MXene aerogel dual network.

The thermal conductivity of the multifunctional composite phase change material reaches 6.72-11.39Wm ^-1 K ^-1 ; the electromagnetic shielding efficiency reaches 42.9-56.6dB, and the energy storage density reaches 160.3-166.9J g ^{- 1} .

The preparation method of the multifunctional composite phase change material of the present invention includes the following steps:

1): Deposit graphene foam on the nickel foam template through chemical vapor deposition, and then immerse it in hydrochloric acid to etch away the nickel foam to obtain self-supporting GF foam;

2): Use lithium fluoride and hydrochloric acid to etch titanium aluminum carbide to prepare a single layer or few layers of MXene;

3): Disperse MXene and binder in deionized water to obtain an aqueous slurry, then immerse GF in the slurry, and vacuum to achieve complete immersion;

4): Transfer GF and slurry liquid to a one-way freezing mold for directional freezing. After freeze-drying, a GF foam-MXene aerogel double network skeleton is obtained, in which the MXene aerogel is formed by coupling within the GF foam pores. Vertically oriented structure of lamellae;

5): Perform high-temperature heat treatment on the GF foam-MXene airgel double network skeleton under the protection of protective gas;

6): Composite the high-temperature heat-treated GF foam-MXene airgel double network skeleton with phase change materials through vacuum impregnation. 4. The method according to claim 3, wherein the chemical vapor deposition gas in step 1) is methane, the temperature is 800-1200°C, and the concentration of hydrochloric acid is 2-4 mol/l.

The mass ratio of lithium fluoride and titanium aluminum carbide in step 2) is 6:5~2:1; the concentration of hydrochloric acid is 8~12mol/l; the etching temperature is 30~40°C; the etching time is 18～30h; drying method is freeze drying; freeze drying temperature -80～-20℃; freeze drying time 24～72h.

The dispersion method in step 3) is one of ultrasonic dispersion, high-speed shear dispersion, ball mill dispersion or planetary gravity stirring dispersion; the binder is graphene oxide, polyvinyl alcohol, chitosan or carboxylic acid. One of the methyl celluloses; the total concentration of MXene and binder is 15~60mg mL ^-1 , the weight ratio of MXene and binder is 4:1~1:1; the vacuuming time is 4~8h.

The one-way freezing mold in step 4) is a polytetrafluoroethylene mold, and the bottom is a copper column soaked in a cold source. The cold source includes liquid nitrogen, dry ice or low-temperature ethanol. The cold source temperature is -196 ~-20℃; freeze-drying temperature -80~-20℃; freeze-drying pressure below 10Pa.

The protective gas in step 5) is argon or nitrogen; the high-temperature heat treatment is to raise the temperature to 600-1000°C at 3-10°C/min and maintain the temperature for 30-210 minutes.

The vacuum degree of vacuum impregnation in step 6) is less than 20 Pa, and the time is 6 to 18 hours; the phase change material is polyethylene glycol, paraffin, n-hexadecane, n-octadecane, and erythritol , myristic acid, fatty acid, lauric acid, polyol and at least one stearic acid.

The multifunctional composite phase change material of the present invention has applications in electronic equipment cooling, energy storage/conversion and related fields.

The advantages and excellent effects of the present invention are: the multifunctional composite phase change material prepared by the present invention is normally in a solid state, can still maintain good shape stability when it is higher than the melting temperature of the phase change material, and has high out-of-plane thermal conductivity, excellent Excellent electromagnetic shielding efficiency, high energy storage density and excellent cycle thermal stability. It overcomes the problems that traditional organic phase change materials are easy to leak, have low thermal conductivity, have single functionality, and are often unable to balance high thermal conductivity and high energy storage density.

The multifunctional composite phase change material obtained by the present invention contains a GF foam-MXene aerogel dual support network structure, and the oriented MXene aerogel formed by coupling within the GF foam pore has three functions: (1) Oriented MXene aerogel As a secondary thermal conductive network, glue can increase the density of the thermal conductive network and improve the thermal conduction path, which helps to promote directional transmission of phonons and reduce the thermal resistance of the system interface. (2) The dense porous structure of oriented MXene aerogel can provide strong capillary force and huge specific surface area for phase change material encapsulation, effectively preventing the melting leakage of phase change materials. (3) The porous honeycomb structure of oriented MXene aerogel can promote multiple reflection and absorption of electromagnetic waves and improve the electromagnetic shielding performance of the material. Therefore, the multifunctional composite phase change material prepared by the present invention has excellent comprehensive properties, the out-of-plane thermal conductivity is as high as 6.72-11.39W m ^-1 K ^-1 , the X-band electromagnetic shielding efficiency is as high as 42.9-55.6dB at a thickness of 3.0mm, and it has High energy storage density of 160.3-166.9J g ^-1 and excellent leakage prevention capabilities.

The GF foam-MXene aerogel dual network synergistic skeleton described in the present invention has higher strength and a more complete thermal conductive network than most single aerogels, and can double encapsulate molten phase change materials and enhance heat transfer. rate, overcoming the problems of generally low out-of-plane thermal conductivity (<10W m ^-1 K ^-1 ) and easy leakage of current composite phase change materials.

The multifunctional composite phase change material provided by the present invention is used in electronic equipment cooling and energy storage/conversion devices, and has excellent working performance and outstanding application effects.

Description of the drawings

Figure 1: Schematic diagram of the preparation process of the multifunctional composite phase change material in Examples 1-3

Figure 2: Scanning electron microscope image of the GF foam-MXene aerogel double network skeleton prepared in Example 2

Figure 3: Thermal conductivity properties of the multifunctional composite phase change materials prepared in Examples 1-3

Figure 4: Electromagnetic shielding effectiveness of the multifunctional composite phase change material prepared in Examples 1-3

Figure 5: Changes in energy storage density of the multifunctional composite phase change material prepared in Example 3 during 120 heating/cooling cycles

Figure 6: Infrared spectrum changes of the multifunctional composite phase change material prepared in Example 3 during 120 heating/cooling cycles

Figure 7: Comparative photos of the leakage of the multifunctional composite phase change material prepared in Example 3, polyethylene glycol and GF/polyethylene glycol during heating on the hot stage.

Figure 8: Thermal expansion curves of the multifunctional composite phase change material prepared in Example 3, polyethylene glycol and GF/polyethylene glycol.

Figure 9: Surface temperature changes of LED lamps when the multifunctional composite phase change material prepared in Example 3 and two commercially available silicone thermal pads (CP200 and HD90000) are used as thermal interface materials.

Figure 10: UV-visible-near infrared absorption spectra of the multifunctional composite phase change material prepared in Example 3, polyethylene glycol and GF/polyethylene glycol

Figure 11: When the multifunctional composite phase change material prepared in Example 3 is applied to a light-thermal-electric conversion device, the output voltage, output current and output power under different light intensities

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiment steps:

The invention proposes a multifunctional composite phase change material supported by a GF foam-MXene aerogel dual network, which is composed of graphene foam, MXene aerogel and a phase change material. The GF foam is composed of chemical vapor phase Deposited and grown three-dimensional interconnected high-quality graphene foam, the MXene aerogel is a lamellar oriented structure coupled within the GF foam pores, the phase change material is effectively encapsulated in a multifunctional composite, the GF foam- The thermal conductivity of the multifunctional composite phase change material collaboratively supported by the MXene airgel dual network is 6.72-11.39W m ^-1 K ^-1 ; the electromagnetic shielding efficiency is 42.9-56.6dB, and the energy storage density is 160.3-166.9J g ^-1 .

A method for preparing a multifunctional composite phase change material supported by a GF foam-MXene airgel dual network collaboratively, including the following steps:

1): Deposit graphene foam on the nickel foam template through chemical vapor deposition, and then immerse it in hydrochloric acid to etch away the nickel foam to obtain self-supporting GF foam;

2): Use lithium fluoride and hydrochloric acid to etch titanium aluminum carbide to prepare a single layer or few layers of MXene.

3): Disperse MXene and binder in deionized water to obtain an aqueous slurry, then immerse GF in the slurry, and vacuum to achieve complete immersion;

4): Transfer GF and slurry liquid to a one-way freezing mold for directional freezing. After freeze-drying, a GF foam-MXene aerogel double network skeleton is obtained, in which the MXene aerogel is formed by coupling within the GF foam pores. Vertically oriented structure of lamellae;

5): Perform high-temperature heat treatment on the GF foam-MXene airgel double network skeleton under the protection of inert gas;

6): Composite the GF foam-MXene airgel double network skeleton that was subjected to high-temperature heat treatment in step 5 with the phase change material through vacuum impregnation.

Further, the gas of chemical vapor deposition described in step 1) is methane, the temperature is 800-1200°C; the concentration of hydrochloric acid is 2-4mol/l

Further, the mass ratio of lithium fluoride and titanium aluminum carbide described in step 2) is 6:5~2:1; the concentration of hydrochloric acid is 8~12mol/l; the etching temperature is 30~40°C; the etching time is 18～30h; the drying method is freeze drying; the freeze drying temperature is -80～-20℃; the freeze drying time is 24～72h.

Further, the dispersion method in step 3) is one of ultrasonic dispersion, high-speed shear dispersion, ball mill dispersion or planetary gravity stirring dispersion; the binder is graphene oxide, polyvinyl alcohol, chitosan or carboxylic acid. One kind of methylcellulose, preferably graphene oxide; the total concentration of MXene and binder is 15-60 mg mL ^~1 ; the weight ratio of MXene and binder is 4:1-1:1, preferably 2:1; vacuuming time is 4 to 8 hours.

Further, the one-way freezing mold in step 4) is a customized polytetrafluoroethylene mold, and the bottom is a copper column soaked in a cold source. Preferably, the cold source includes liquid nitrogen, dry ice or low-temperature ethanol. The source temperature is -196~-20℃. The freeze-drying temperature is -80~-20℃; the freeze-drying pressure is below 10Pa.

Further, the inert gas in step 5) is argon or nitrogen; the high-temperature heat treatment is to raise the temperature to 600-1000°C at 3-10°C/min and keep the temperature for 30-210 min.

Further, the vacuum degree of the vacuum impregnation in step 6) is less than 20 Pa, and the time is 6 to 18 hours; the phase change materials polyethylene glycol, paraffin, n-hexadecane, n-octadecane, erythritol, At least one of myristic acid, fatty acid, lauric acid, polyol and stearic acid is preferably polyethylene glycol.

Example 1:

1. Take 20×20×1.5mm nickel foam in a quartz tube furnace, in an atmosphere with a volume ratio of argon: hydrogen = 5:2, raise the temperature to 1000°C, and then introduce methane for the growth of graphene. And the sample was quickly cooled to room temperature under an argon/hydrogen atmosphere. The prepared nickel-GF was then dip-coated with 4wt% polymethylmethacrylate/anisole solution and baked at 180°C for 3h to form a thin layer of polymethylmethacrylate to prevent the nickel from etching. GF structure collapsed. Next, the nickel substrate was completely dissolved in 3 mol/l hydrochloric acid solution at 80°C overnight to obtain GF/polymethylmethacrylate. Finally, the polymethylmethacrylate layer was dissolved with acetone at 55°C to obtain GF.

2. Add 1.0g titanium aluminum carbide powder to 20mL etchant solution (containing 12mol/l hydrochloric acid and 1.6g lithium fluoride), and then stir continuously at 35°C for 24h. After the etching is completed, transfer the product to a centrifuge tube and centrifuge at 3500 rpm for 5 minutes to remove the upper acid solution, then add deionized water to wash the precipitate, and repeat centrifugation and washing until the pH value of the supernatant is close to 6. At this time, the precipitate gradually expanded and became viscous, similar to clay, and the supernatant liquid turned dark green, resulting in multi-layer MXene. Secondly, the multi-layer MXene was dispersed in water again, and ultrasonically peeled off in an argon atmosphere for 1 hour, followed by centrifugation at 3500 rpm for 1 hour, and the supernatant was collected, which is the few-layer MXene suspension. Finally, single-layer or few-layer MXene nanosheets were obtained by freeze-drying at -20°C for 24 hours.

3. Disperse MXene and binder graphene oxide with a weight ratio of 2:1 in deionized water through a planetary vacuum degassing mixer to obtain a uniform and stable slurry with a total concentration of MXene/graphene oxide of 15 mg mL ^-1 . Afterwards, GF was immersed in the MXene/graphene oxide slurry liquid and vacuumed for 6 h to achieve complete immersion.

4. Transfer the GF and slurry liquid to a one-way freezing mold (a custom-made polytetrafluoroethylene mold with a copper column soaked in liquid nitrogen at the bottom) for directional freezing. Next, freeze it in a freeze dryer (-50℃ , 0.1Pa; LGJ-20FG), freeze-dry the ice cube sample, remove the icicles through the sublimation effect, and obtain the GF foam-MXene aerogel double network skeleton, in which the MXene aerogel is formed by coupling within the GF foam pores Vertically oriented structure of lamellae.

5. The GF foam-MXene airgel double network skeleton was thermally annealed at 800°C for 2 hours in an argon environment, where the binder graphene oxide was thermally reduced to graphene.

6. Polyethylene glycol is melted in a vacuum oven at 90°C in advance, and the high-temperature heat-treated GF foam-MXene airgel double network skeleton is immersed in the polyethylene glycol melt, vacuum impregnated at 90°C for 12 hours, and then taken out Finally, oil-absorbing paper is used to remove the polyethylene glycol that is not stably adsorbed on the surface, and then the composite phase change material is obtained after natural cooling and solidification.

Example 2:

The difference between this embodiment and Example 1 is that the total concentration of MXene and binder graphene oxide in step 3 is 30 mg mL ^-1 , and other steps and parameters are the same as in Example 1.

Example 3:

The difference between this embodiment and Examples 1 and 2 is that the total concentration of MXene and binder graphene oxide in step 3 is 60 mg mL ^-1 , and other steps and parameters are the same as in Example 1.

Figure 1 is a schematic diagram of the preparation process of the multifunctional composite phase change material in Examples 1-3. As can be seen from Figure 1, the preparation process of the composite phase change material supported by the GF foam-MXene airgel dual network collaboratively is divided into four steps: (1) Preparation of MXene and binder graphene oxide slurry; (2) ) Directional freezing process of MXene and binder graphene oxide slurry liquid in GF foam; (3) Freeze drying and high-temperature heat treatment to obtain GF foam-MXene aerogel dual network skeleton; (4) Vacuum impregnation to prepare composite phase change Material.

Figure 2 is a scanning electron microscope image of the GF foam-MXene aerogel double network skeleton prepared in Example 2. As can be seen from Figure 2, MXene aerogel is a lamellar oriented structure coupled within the pore size of GF foam. The oriented MXene aerogel effectively increases the network density of GF foam. This densely porous GF foam-MXene airgel The gel double network skeleton is beneficial to the encapsulation of phase change materials and improves the thermal conductivity and electromagnetic shielding effectiveness of the material.

Figure 3 shows the thermal conductivity properties of polyethylene glycol, GF/polyethylene glycol and the multifunctional composite phase change materials prepared in Examples 1-3. As can be seen from Figure 3, the thermal conductivities of polyethylene glycol and GF/polyethylene glycol are 0.32 and 5.43W m ^-1 K ^-1 , while the polyethylene glycol prepared in Example 1, Example 2 and Example 3 The thermal conductivities of functional composite phase change materials are 6.72, 8.21 and 11.39W m ^-1 K ^-1 respectively, which are 23.8%, 51.2% and 109.8% higher than those of GF/polyethylene glycol, indicating that GF foam-MXene gas The gel double network skeleton has better thermal conductivity than single GF foam; in addition, the thermal conductivity of the material increases as the MXene airgel content increases, proving that the GF foam-MXene airgel double network skeleton in the present invention superiority.

Figure 4 shows the electromagnetic shielding effectiveness of polyethylene glycol, GF/polyethylene glycol and the multifunctional composite phase change material prepared in Examples 1-3. As can be seen from Figure 4, at 8.2~12.4GHz (X band), the electromagnetic shielding effectiveness of polyethylene glycol is less than 2.9dB, and the electromagnetic shielding effectiveness of GF/polyethylene glycol is less than 35.8dB; while Embodiment 1, Implementation The electromagnetic shielding effectiveness of the multifunctional composite phase change materials prepared in Example 2 and Example 3 were respectively greater than 44.5, 42.9 and 55.6dB, which were increased by 24.3%, 19.8% and 55.3% compared to GF/polyethylene glycol, indicating that It is found that the MXene aerogel coupled within the GF foam pores can promote the multiple reflection and absorption of electromagnetic waves and improve the electromagnetic shielding performance of the material, which proves the superiority of the GF foam-MXene aerogel dual network skeleton in the present invention.

Figure 5 and Table 2 show the changes in energy storage density of the multifunctional composite phase change material prepared in Example 3 during 120 heating/cooling cycles. It can be seen from Figure 5 that after 120 heating/cooling cycles of the multifunctional composite phase change material in Example 3, its phase change latent heat (melting enthalpy/crystallization enthalpy) and phase change temperature (melting point/crystallization point) are almost unchanged. changes, proving that the multifunctional composite phase change material provided by the present invention has excellent cycle thermal stability.

Figure 6 shows the infrared spectrum changes of the multifunctional composite phase change material prepared in Example 3 during 120 heating/cooling cycles. As can be seen from Figure 6, the molecular structure and functional groups of the multifunctional composite phase change material in Example 3 did not change after 120 heating/cooling cycles, proving that the multifunctional composite phase change material provided by the present invention has excellent cyclic thermal stability.

Figure 7 is a photograph comparing the leakage of the multifunctional composite phase change material prepared in Example 3, polyethylene glycol and GF/polyethylene glycol during the heating process on the hot stage. It can be seen from Figure 7 that after polyethylene glycol, GF/polyethylene glycol and the multifunctional composite phase change material in Example 3 are heated to 100°C on the hot table, polyethylene glycol is completely melted, and GF/polyethylene glycol is completely melted. The diol showed slight traces of leakage, but the sample of Example 3 did not have any leakage and had excellent shape stability, which confirmed that the multifunctional composite phase change material provided by the present invention has excellent leakage prevention performance and shape stability.

Figure 8 is the thermal expansion curve of the multifunctional composite phase change material prepared in Example 3, polyethylene glycol and GF/polyethylene glycol. As can be seen from Figure 8, after the temperature is higher than 70°C, the size of polyethylene glycol will change dramatically, and the size of GF/polyethylene glycol will change greatly, while the sample size of Example 3 remains almost constant. , confirming that the multifunctional composite phase change material provided by the invention has excellent shape stability.

Table 1. DSC heating/cooling data of multifunctional composite phase change materials in Example 1, Example 2 and Example 3

Among them, T _m /T _c is the melting point/crystallization point; ΔH _m /ΔH _c is the melting enthalpy/crystallization enthalpy.

Table 2. DSC data of the multifunctional composite phase change material in Example 3 during 120 heating/cooling cycles

Among them, T _m /T _c is the melting point/crystallization point; ΔH _m /ΔH _c is the melting enthalpy/crystallization enthalpy.

Example 4:

1. Take 20×20×1.5mm nickel foam in a quartz tube furnace, in an atmosphere with a volume ratio of argon: hydrogen = 5:2, raise the temperature to 800°C, and then introduce methane for the growth of graphene. And the sample was quickly cooled to room temperature under an argon/hydrogen atmosphere. The prepared nickel-GF was then dip-coated with 4wt% polymethylmethacrylate/anisole solution and baked at 180°C for 3h to form a thin layer of polymethylmethacrylate to prevent the nickel from etching. GF structure collapsed. Next, the nickel substrate was completely dissolved in 2 mol/l hydrochloric acid solution at 80°C overnight to obtain GF/polymethylmethacrylate. Finally, the polymethylmethacrylate layer was dissolved with acetone at 55°C to obtain GF.

2. Add 1.0g titanium aluminum carbide powder to 20mL etchant solution (containing 8mol/l hydrochloric acid and 1.2g lithium fluoride), and then stir continuously at 40°C for 18h. After the etching is completed, transfer the product to a centrifuge tube and centrifuge at 3500 rpm for 5 minutes to remove the upper acid solution, then add deionized water to wash the precipitate, and repeat centrifugation and washing until the pH value of the supernatant is close to 6. At this time, the precipitate gradually expanded and became viscous, similar to clay, and the supernatant liquid turned dark green, resulting in multi-layer MXene. Secondly, the multi-layer MXene was dispersed in water again, and ultrasonically peeled off in an argon atmosphere for 1 hour, followed by centrifugation at 3500 rpm for 1 hour, and the supernatant was collected, which is the few-layer MXene suspension. Finally, single-layer or few-layer MXene nanosheets were obtained by freeze-drying at -50°C for 48 hours.

3. Ultrasonically disperse MXene and the binder polyvinyl alcohol in a weight ratio of 4:1 in deionized water to obtain a uniform and stable slurry with a total concentration of MXene/polyvinyl alcohol of 20 mg mL ^-1 . Afterwards, GF was immersed in the MXene/polyvinyl alcohol slurry liquid and vacuumed for 4 h to achieve complete immersion.

4. Transfer the GF and slurry liquid to a one-way freezing mold (a custom-made polytetrafluoroethylene mold with a copper column soaked in -78°C dry ice at the bottom) for directional freezing. Next, freeze it in a freeze dryer (- The ice cube sample is freeze-dried at 80°C, 10 Pa), and the icicles are removed through the sublimation effect to obtain a GF foam-MXene aerogel double network skeleton, in which the MXene aerogel is a vertical lamellar layer formed by coupling within the pores of the GF foam. Straight orientation structure.

5. The GF foam-MXene airgel double network skeleton was thermally annealed at 600°C for 210 minutes in an argon environment, in which the binder polyvinyl alcohol was sintered into carbon.

6. Paraffin wax is melted in a vacuum oven at 70°C in advance. The high-temperature heat-treated GF foam-MXene aerogel double network skeleton is immersed in the paraffin melt and vacuum-immersed at 70°C for 6 hours. After taking it out, use oil-absorbing paper to remove the surface. The paraffin that is not stably adsorbed is then naturally cooled and solidified to obtain a composite phase change material.

Example 5:

1. Take 20×20×1.5mm nickel foam in a quartz tube furnace, in an atmosphere with a volume ratio of argon: hydrogen = 5:2, raise the temperature to 1200°C, and then introduce methane for the growth of graphene. And the sample was quickly cooled to room temperature under an argon/hydrogen atmosphere. The prepared nickel-GF was then dip-coated with 4wt% polymethylmethacrylate/anisole solution and baked at 180°C for 3h to form a thin layer of polymethylmethacrylate to prevent the nickel from etching. GF structure collapsed. Next, the nickel substrate was completely dissolved in 4 mol/l hydrochloric acid solution at 80°C overnight to obtain GF/polymethylmethacrylate. Finally, the polymethylmethacrylate layer was dissolved with acetone at 55°C to obtain GF.

2. Add 1.0g titanium aluminum carbide powder to 20mL etchant solution (containing 10mol/l hydrochloric acid and 2.0g lithium fluoride), and then stir continuously at 30°C for 30h. After the etching is completed, transfer the product to a centrifuge tube and centrifuge at 3500 rpm for 5 minutes to remove the upper acid solution, then add deionized water to wash the precipitate, and repeat centrifugation and washing until the pH value of the supernatant is close to 6. At this time, the precipitate gradually expanded and became viscous, similar to clay, and the supernatant liquid turned dark green, resulting in multi-layer MXene. Secondly, the multi-layer MXene was dispersed in water again, and ultrasonically peeled off in an argon atmosphere for 1 hour, followed by centrifugation at 3500 rpm for 1 hour, and the supernatant was collected, which is the few-layer MXene suspension. Finally, single-layer or few-layer MXene nanosheets were obtained by freeze-drying at -80°C for 72 h.

3. Disperse MXene and binder chitosan in a 2wt% acetic acid aqueous solution by ball milling with a weight ratio of 1:1 to obtain a uniform and stable slurry with a total concentration of MXene/chitosan of 40 mg mL ^-1 . Afterwards, GF was immersed in the MXene/chitosan syrup solution and vacuumed for 8 h to achieve complete immersion.

4. Transfer the GF and slurry liquid to a one-way freezing mold (a custom-made polytetrafluoroethylene mold with a copper column soaked in low-temperature ethanol at -20°C at the bottom) for directional freezing. Next, freeze it in a freeze dryer ( Freeze-dry the ice cube sample at -20°C, 5 Pa), remove the icicles through the sublimation effect, and obtain the GF foam-MXene aerogel double network skeleton, in which the MXene aerogel is a lamellar layer formed by coupling within the pores of the GF foam. Vertically oriented structure.

5. The GF foam-MXene airgel double network skeleton was thermally annealed at 1000°C for 30 minutes in a nitrogen environment, in which the binder chitosan was sintered into carbon.

6. N-octadecane is melted in a vacuum oven at 70°C in advance, and the high-temperature heat-treated GF foam-MXene aerogel double network skeleton is immersed in the n-octadecane melt, vacuum immersed at 70°C for 18 hours, and then taken out Finally, oil-absorbing paper is used to remove n-octadecane that is not stably adsorbed on the surface, and then the composite phase change material is obtained after natural cooling and solidification.

Test example 1

The multifunctional composite phase change material obtained in Example 3 and two commercial silicone thermal pads CP200 (2.0W m ^-1 K ^-1 , DOBON, China) and HD90000 (7.5W m ^-1 K ^-1 , Laird Tflex, USA ) as the thermal management performance of thermal interface materials, the method is as follows:

The multifunctional composite phase change material obtained in Example 3 and two commercial silicone thermal pads CP200 and HD90000 were cut into sizes of 20×20×1.5mm3, and then assembled with 10W ^LED lamps and aluminum block radiators respectively. Infrared heat was used to The imager records the surface temperature change within 1000s after the LED is lit, and the results are shown in Figure 9. From the comparison in Figure 9, it can be seen that when the multifunctional composite phase change material of the present invention is used as a thermal interface material, the rise in surface temperature of the LED lamp within 1000 seconds is much lower than that of the two commercial silicone thermal pads when the LED is used as a thermal interface material. The surface temperature of the lamp proves that the multifunctional composite phase change material of the present invention has excellent heat dissipation performance when used as a thermal interface material.

Test example 2

The light absorption performance of the multifunctional composite phase change material obtained in Example 3 was tested. Polyethylene glycol and GF/polyethylene glycol were used as comparisons. The test method was ultraviolet-visible light absorption spectroscopy. The results are shown in Figure 10. It can be seen that implementation The multifunctional composite phase change material obtained in Example 3 has excellent light absorption performance because the GF foam-MXene aerogel double network skeleton can serve as an effective photon capture agent.

Test example 3

The energy storage and conversion performance of the multifunctional composite phase change material obtained in Example 3 was tested as follows:

The multifunctional composite phase change material obtained by cutting and polishing Example 3 is size, it is applied to a self-made light-thermal-electric energy conversion device, which consists of a xenon lamp (AM 1.5), a multifunctional composite phase change material for efficient sunlight collection, and a commercial thermoelectric power generation sheet (40× 40mm ² ,TEC2-25408) and liquid cooling radiator. Adjusting the light intensity to 150, 250, 400, 600, 800 and 1000mW cm ^-2 , the output voltage, output current and output power of the light-thermal-electric energy conversion device are shown in Figure 11. It can be seen from Figure 11 that after using the multifunctional composite phase change material obtained in Example 3, the output voltage, output current and output power of the light-thermal-electric energy conversion device under the light intensity of 1000mW cm ^-2 are as high as 1046.5mV. , 190.6mA and 124.7W m ^-2 , proving that the multifunctional composite phase change material of the present invention has excellent energy storage and conversion properties.

The technical solutions disclosed and proposed by the present invention can be realized by those skilled in the art by drawing lessons from the contents of this article and appropriately changing the conditional routes and other links. Although the method and preparation technology of the present invention have been described through preferred implementation examples, relevant technical personnel can obviously The methods and technical routes described herein can be modified or recombined without departing from the content, spirit and scope of the present invention to achieve the final preparation technology. It should be noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are deemed to be included in the spirit, scope and content of the present invention.

Claims (10)

1. A multifunctional composite phase change material; the multifunctional composite phase change material is characterized by being formed by compounding graphene foam (GF foam), MXene aerogel and a phase change material; the MXene aerogel is a lamellar oriented structure coupled in the aperture of the GF foam, and the phase change material is encapsulated in the multifunctional composite material to form the GF foam-MXene aerogel double-network cooperatively supported multifunctional composite phase change material.

2. The multifunctional composite phase change material of claim 1; the multifunctional composite phase-change material is characterized in that the thermal conductivity of the multifunctional composite phase-change material reaches 6.72-11.39W m ^-1 K ^-1 The method comprises the steps of carrying out a first treatment on the surface of the The electromagnetic shielding efficiency reaches 42.9-56.6dB, and the energy storage density reaches 160.3-166.9J g ^-1 。

3. A method of preparing the multifunctional composite phase change material of claim 1; the method is characterized by comprising the following steps of:

1): depositing graphene foam on a foam nickel template through chemical vapor deposition, and then immersing the graphene foam in hydrochloric acid to etch out foam nickel, so as to obtain self-supporting GF foam;

2): etching titanium aluminum carbide by using lithium fluoride and hydrochloric acid to prepare single-layer or less-layer MXene;

3): dispersing MXene and a binder in deionized water to obtain aqueous slurry, immersing GF in the slurry, and vacuumizing to realize complete impregnation;

4): transferring GF and slurry into a unidirectional freezing mold for directional freezing, and freeze-drying to obtain a GF foam-MXene aerogel double-network framework, wherein the MXene aerogel is a lamellar vertical orientation structure formed by coupling in GF foam pore diameters;

5): carrying out high-temperature heat treatment on the GF foam-MXene aerogel double-network framework under the protection of protective gas;

6): and compounding the GF foam-MXene aerogel double-network framework subjected to high-temperature heat treatment with a phase-change material through a vacuum impregnation method.

4. The method of claim 3, wherein the chemical vapor deposition gas in step 1) is methane at a temperature of 800-1200 ℃; the concentration of hydrochloric acid is 2-4mol/l.

5. A method according to claim 3, wherein the mass ratio of lithium fluoride to titanium aluminium carbide in step 2) is from 6:5 to 2:1; the concentration of hydrochloric acid is 8-12 mol/l; the etching temperature is 30-40 ℃; etching time is 18-30 h; the drying mode is freeze drying; freeze drying temperature is-80 to-20 ℃; the freeze drying time is 24-72 h.

6. The method of claim 3, wherein the dispersion in step 3) is one of ultrasonic dispersion, high-speed shear dispersion, ball mill dispersion or planetary gravity stirring dispersion; the binder is one of graphene oxide, polyvinyl alcohol, chitosan or carboxymethyl cellulose; the total concentration of the MXene and the binder is 15-60 mg mL ^-1 The weight ratio of the MXene to the binder is 4:1-1:1; the vacuumizing time is 4-8 h.

7. The method of claim 3, wherein the unidirectional freezing mold in the step 4) is a polytetrafluoroethylene mold, the bottom is a copper column immersed in a cold source, the cold source comprises liquid nitrogen, dry ice or low-temperature ethanol, and the temperature of the cold source is between-196 ℃ and-20 ℃; freeze drying temperature is-80 to-20 ℃; the freeze-drying pressure is below 10 Pa.

8. A method according to claim 3, wherein the shielding gas in step 5) is argon or nitrogen; the high-temperature heat treatment is to heat up to 600-1000 ℃ at 3-10 ℃/min, and the temperature is kept for 30-210 min.

9. A method according to claim 3, wherein the vacuum degree of the vacuum impregnation in step 6) is less than 20Pa for a period of 6 to 18 hours; the phase change material is at least one of polyethylene glycol, paraffin, n-hexadecane, n-octadecane, erythritol, myristic acid, fatty acid, lauric acid, polyalcohol and stearic acid.

10. The multifunctional composite phase change material of claim 1, wherein the application fields comprise electronic device cooling, energy storage/conversion and related fields.