Multifunctional composite phase change material, preparation method and application thereof

Abstract

The present application relates to a kind of multifunctional composite phase change material and its preparation method and application.Multifunctional composite phase change material is composed of graphene foam, MXene aerogel and phase change material;MXene aerogel is the sheet orientation structure coupled in the pore size of GF foam, and phase change material is encapsulated in multifunctional composite material, and multifunctional composite phase change material of GF foam-MXene aerogel double network collaborative support is formed.Heat conductivity reaches 11.39W m ‑1 K ‑1 ;Electromagnetic shielding effectiveness reaches 56.6dB, and energy storage density reaches 160.3J g ‑1 .It embodies higher strength and more perfect heat conduction network, and double encapsulation is carried out to molten state phase change material and heat transfer rate is strengthened, and the problems that current composite phase change material is generally low and easy to leak in surface thermal conductivity are overcome.In the application of electronic equipment cooling and energy storage / conversion device, it has excellent working performance, and application effect is outstanding.

Description

Technical Field

[0001] This invention relates to the technical field of phase change composite materials, and in particular to a multifunctional composite phase change material, its preparation method, and its applications. Background Technology

[0002] In the context of green and clean energy, thermal energy storage (TES) is considered an important energy technology for improving energy efficiency. Phase change energy storage utilizes the property of phase change materials (PCMs) to store and release energy by absorbing or releasing large amounts of heat during phase change. It has great application potential in the field of intermittent or unstable thermal energy management, such as periodic intermittent solar energy utilization, thermal management of high-power electronic devices / batteries, and industrial waste heat recovery. Organic PCMs (such as paraffin wax, polyethylene glycol, and fatty acids) have attracted considerable attention due to their advantages such as high energy density, small volume change, chemical stability, resistance to supercooling and phase separation, non-toxicity, non-corrosiveness, and low cost. However, organic PCMs suffer from melt leakage during solid-liquid phase transitions and inherently low thermal conductivity (generally between 0.15-0.5 W / m²). -1 K -1The long-term bottleneck of thermal management has led to a significant reduction in the thermal storage efficiency of PCM, which has severely restricted its application in the fields of energy storage and thermal management. To address the aforementioned problems with PCM, researchers have employed 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) to encapsulate the phase change material to prevent molten leakage; and have used carbon materials (diamond, carbon nanotubes, graphene, etc.) or metals and their oxides (silver, copper, aluminum oxide, etc.) to enhance the heat transfer process and improve the thermal conductivity of the phase change material. However, to achieve satisfactory shape stability and thermal conductivity in PCMs, current technologies rely on high loading of thermally conductive fillers, which inevitably reduces the proportion of PCM in the composite material, leading to a decrease in the overall energy storage density. Finding a balance between high thermal conductivity and high energy storage density, while simultaneously ensuring shape stability, is a key challenge that urgently needs to be addressed in PCM research. Furthermore, existing technologies produce phase change composites with limited functionality. For the thermal management of miniaturized and highly integrated electronic devices, electromagnetic shielding (EMI) performance must also be considered. On the one hand, high-frequency electromagnetic radiation not only reduces the operational accuracy of equipment and causes malfunctions but also threatens the health of operators. On the other hand, the EMI shielding performance of PCMs is closely related to efficient thermal management; EMI shielding directly converts most electromagnetic radiation into heat, ultimately triggering the PCM phase change process. Therefore, simultaneously improving the EMI shielding performance and thermal management capabilities of PCMs while ensuring high energy storage density is of great significance.

[0003] Researchers have proposed that constructing a three-dimensional interconnected thermally conductive framework within phase change composite materials could potentially improve the thermal conductivity of these materials while maintaining high energy density. Patent CN 112852386 A discloses a graphene aerogel phase change composite material prepared via a hydrothermal reduction method. However, the physical cross-linking of the graphene aerogel prepared from graphene oxide self-assembly under high temperature and pressure is mainly based on van der Waals forces, hydrogen bonds, and π-π interactions, and interfacial thermal resistance still exists between the two-dimensional graphene nanosheets. Therefore, the thermal conductivity of the prepared graphene aerogel phase change composite material is only increased to 0.727 W / m². -1 K -1 The performance falls far short of high-standard usage requirements (>10W m). -1 K -1 Compared to graphene aerogels (GA) prepared by self-assembly, graphene foams (GF) grown by chemical vapor deposition can more effectively improve the thermal conductivity of composite PCMs. This is because the cross-linking of GFs is mainly based on covalent bonds, which can form a high-quality three-dimensional interconnected graphene framework, providing a continuous path for phonon transport. However, the pore size of GFs is as high as several hundred micrometers, which is determined by the nickel (Ni) foam catalyst framework, resulting in poor shape stability, unsatisfactory electromagnetic shielding effectiveness, and limited improvement in thermal conductivity of the composite PCMs.

[0004] Therefore, developing new technologies to construct a dense secondary thermally conductive network within the large aperture of a GF is an effective strategy to improve the shape stability of composite PCMs and further enhance their thermal conductivity and electromagnetic shielding effectiveness. This is a problem that needs to be solved. Summary of the Invention

[0005] To address the problems of existing technologies, this invention provides a multifunctional composite phase change material supported by a dual-network synergistic structure of GF foam-MXene (two-dimensional material) aerogel, along with its preparation method and applications. This multifunctional composite phase change material simultaneously possesses high out-of-plane thermal conductivity and high energy density, while exhibiting excellent electromagnetic shielding performance and outstanding shape stability. It overcomes the difficulties of traditional organic phase change materials, such as easy leakage, low thermal conductivity, limited functionality, and the often unattainable balance between high thermal conductivity and high energy density. The multifunctional composite phase change material achieves an out-of-plane thermal conductivity as high as 6.72-11.39 W / m² with relatively low filler content (9.06-13.78 wt%). -1 K -1 The X-band electromagnetic shielding effectiveness reaches 42.9-55.6 dB with a thickness of 3.0 mm, and has a strength of 160.3-166.9 J g. -1 It has high energy storage density and excellent leak-proof capabilities.

[0006] The technical solution of the present invention is as follows:

[0007] 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; MXene aerogel is a sheet-oriented structure coupled within the pore size of GF foam, and the phase change material is encapsulated in the multifunctional composite material to form a multifunctional composite phase change material with GF foam-MXene aerogel dual network synergistic support.

[0008] The thermal conductivity of the aforementioned multifunctional composite phase change material reaches 6.72-11.39 W / m². -1 K -1 The electromagnetic shielding effectiveness reaches 42.9-56.6 dB, and the energy storage density reaches 160.3-166.9 J g. -1 .

[0009] The preparation method of the multifunctional composite phase change material of the present invention includes the following steps:

[0010] 1): Graphene foam is deposited on a nickel foam template by chemical vapor deposition, and then the nickel foam is etched away by immersion in hydrochloric acid to obtain self-supporting GF foam;

[0011] 2): Single-layer or few-layer MXene is prepared by etching titanium aluminum carbide with lithium fluoride and hydrochloric acid;

[0012] 3): MXene and binder are dispersed in deionized water to obtain an aqueous slurry, and then GF is immersed in the slurry and vacuum is applied to achieve complete impregnation;

[0013] 4): GF and slurry were transferred to a unidirectional freezing mold for directional freezing. After freeze-drying, a GF foam-MXene aerogel dual network framework was obtained, in which MXene aerogel is a sheet-like vertically oriented structure coupled within the pore size of GF foam.

[0014] 5): The GF foam-MXene aerogel dual network framework is subjected to high-temperature heat treatment under protective gas protection;

[0015] 6): The GF foam-MXene aerogel dual-network framework, which has undergone high-temperature heat treatment, is composited with a phase change material via vacuum impregnation. 4. The method according to claim 3, characterized in that the gas used in the chemical vapor deposition in step 1) is methane, the temperature is 800-1200℃, and the concentration of hydrochloric acid is 2-4 mol / L.

[0016] In step 2), the mass ratio of lithium fluoride to titanium aluminum carbide is 6:5 to 2:1; the concentration of hydrochloric acid is 8 to 12 mol / L; the etching temperature is 30 to 40°C; the etching time is 18 to 30 h; the drying method is freeze drying; the freeze drying temperature is -80 to -20°C; and the freeze drying time is 24 to 72 h.

[0017] The dispersion method in step 3) is one of ultrasonic dispersion, high-speed shear dispersion, ball milling dispersion, or planetary gravity stirring dispersion; the binder is one of graphene oxide, polyvinyl alcohol, chitosan, or carboxymethyl cellulose; the total concentration of MXene and binder is 15–60 mg / mL. -1 The weight ratio of MXene to binder is 4:1 to 1:1; the vacuuming time is 4 to 8 hours.

[0018] In step 4), the unidirectional freezing mold is a polytetrafluoroethylene mold with a copper column at the bottom immersed in a cold source, including liquid nitrogen, dry ice, or low-temperature ethanol, with a temperature of -196 to -20°C; a freeze-drying temperature of -80 to -20°C; and a freeze-drying pressure below 10 Pa.

[0019] The protective gas in step 5) is argon or nitrogen; the high-temperature heat treatment is to raise the temperature to 600-1000℃ at a rate of 3-10℃ / min and hold it for 30-210min.

[0020] In step 6), the vacuum impregnation is performed with a vacuum degree of less than 20 Pa for 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, polyol, and stearic acid.

[0021] The multifunctional composite phase change material of the present invention has applications in electronic device cooling, energy storage / conversion and related fields.

[0022] The advantages and superior effects of this invention are: the multifunctional composite phase change material prepared by this invention is in a solid state under normal conditions, maintains good shape stability even above the melting temperature of phase change materials, and possesses high out-of-plane thermal conductivity, excellent electromagnetic shielding effectiveness, high energy storage density, and excellent cyclic thermal stability. It overcomes the problems of traditional organic phase change materials, such as easy leakage, low thermal conductivity, limited functionality, and the often inability to simultaneously achieve high thermal conductivity and high energy storage density.

[0023] The multifunctional composite phase change material obtained by this invention contains a dual-support network structure of GF foam and MXene aerogel. The oriented MXene aerogel formed within the pores of the GF foam has three functions: (1) As a secondary thermally conductive network, the oriented MXene aerogel can increase the density of the thermally conductive network and improve the thermal conductivity path, which helps to promote phonon directional transport and reduce the interfacial thermal resistance of the system. (2) The dense porous structure of the oriented MXene aerogel can provide strong capillary forces and a large specific surface area for the encapsulation of the phase change material, effectively preventing the melting and leakage problem of the phase change material. (3) The porous honeycomb structure of the oriented MXene aerogel can promote the multiple reflection absorption of electromagnetic waves and improve the electromagnetic shielding performance of the material. Therefore, the multifunctional composite phase change material prepared by this invention has excellent comprehensive performance and an out-of-plane thermal conductivity as high as 6.72-11.39 W / m. -1 K -1 The X-band electromagnetic shielding effectiveness reaches 42.9-55.6 dB with a thickness of 3.0 mm, and has a strength of 160.3-166.9 J g. -1 It has high energy storage density and excellent leak-proof capabilities.

[0024] The GF foam-MXene aerogel dual-network synergistic framework described in this invention has higher strength and a more complete thermally conductive network than most single aerogels. It can dual-encapsulate molten phase change materials and enhance the heat transfer rate, overcoming the generally low out-of-plane thermal conductivity (<10 W / m²) of current composite phase change materials. -1 K -1 (and the issue of easy leakage.)

[0025] The multifunctional composite phase change material provided by this invention exhibits excellent performance and outstanding application effects in electronic device cooling and energy storage / conversion devices. Attached Figure Description

[0026] Figure 1 Schematic diagram of the preparation process of multifunctional composite phase change materials in Examples 1-3

[0027] Figure 2 Scanning electron microscope image of the GF foam-MXene aerogel dual network framework prepared in Example 2.

[0028] Figure 3 Thermal conductivity of the multifunctional composite phase change materials prepared in Examples 1-3

[0029] Figure 4 Electromagnetic shielding effectiveness of the multifunctional composite phase change materials prepared in Examples 1-3

[0030] Figure 5The change in energy storage density of the multifunctional composite phase change material prepared in Example 3 during 120 heating / cooling cycles.

[0031] Figure 6 Infrared spectral changes of the multifunctional composite phase change material prepared in Example 3 during 120 heating / cooling cycles.

[0032] Figure 7 Comparative photographs of the leakage of the multifunctional composite phase change material prepared in Example 3, polyethylene glycol, and GF / polyethylene glycol during heating on a hot stage.

[0033] Figure 8 Thermal expansion curves of the multifunctional composite phase change material prepared in Example 3, polyethylene glycol, and GF / polyethylene glycol.

[0034] Figure 9 The surface temperature change of the LED lamp 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.

[0035] Figure 10 The UV-Vis-NIR absorption spectra of the multifunctional composite phase change material prepared in Example 3, polyethylene glycol, and GF / polyethylene glycol.

[0036] Figure 11 When the multifunctional composite phase change material prepared in Example 3 is applied to a photo-thermal-electric conversion device, the output voltage, output current, and output power under different light intensities are observed. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0038] This invention proposes a multifunctional composite phase change material supported by a GF foam-MXene aerogel dual-network synergistic structure. The material is composed of graphene foam, MXene aerogel, and a phase change material. The GF foam is a three-dimensionally interconnected high-quality graphene foam grown by chemical vapor deposition. The MXene aerogel is a sheet-like oriented structure coupled within the pores of the GF foam. The phase change material is effectively encapsulated within the multifunctional composite material. The thermal conductivity of this GF foam-MXene aerogel dual-network synergistic multifunctional composite phase change material is 6.72-11.39 W / m². -1 K -1 The electromagnetic shielding effectiveness is 42.9-56.6 dB, and the energy storage density is 160.3-166.9 J g. -1 .

[0039] A method for preparing a multifunctional composite phase change material with GF foam-MXene aerogel dual-network synergistic support includes the following steps:

[0040] 1): Graphene foam is deposited on a nickel foam template by chemical vapor deposition, and then the nickel foam is etched away by immersion in hydrochloric acid to obtain self-supporting GF foam;

[0041] 2): Single-layer or few-layer MXene is prepared by etching titanium aluminum carbide with lithium fluoride and hydrochloric acid.

[0042] 3): MXene and binder are dispersed in deionized water to obtain an aqueous slurry, and then GF is immersed in the slurry and vacuum is applied to achieve complete impregnation;

[0043] 4): GF and slurry were transferred to a unidirectional freezing mold for directional freezing. After freeze-drying, a GF foam-MXene aerogel dual network framework was obtained, in which MXene aerogel is a sheet-like vertically oriented structure coupled within the pore size of GF foam.

[0044] 5): The GF foam-MXene aerogel dual network framework was subjected to high-temperature heat treatment under inert gas protection;

[0045] 6): The GF foam-MXene aerogel dual network skeleton, which underwent high-temperature heat treatment in step 5, is composited with phase change material by vacuum impregnation.

[0046] Further, in step 1), the gas used for chemical vapor deposition is methane, and the temperature is 800-1200℃; the concentration of hydrochloric acid is 2-4 mol / L.

[0047] Further, in step 2), the mass ratio of lithium fluoride to aluminum titanium carbide is 6:5 to 2:1; the concentration of hydrochloric acid is 8 to 12 mol / L; the etching temperature is 30 to 40°C; the etching time is 18 to 30 h; the drying method is freeze drying; the freeze drying temperature is -80 to -20°C; and the freeze drying time is 24 to 72 h.

[0048] Further, the dispersion method described in step 3) is one of ultrasonic dispersion, high-speed shear dispersion, ball milling dispersion, or planetary gravity stirring dispersion; the binder is one of graphene oxide, polyvinyl alcohol, chitosan, or carboxymethyl cellulose, preferably graphene oxide; the total concentration of MXene and binder is 15–60 mg / mL. ～1 The weight ratio of MXene to binder is 4:1 to 1:1, preferably 2:1; the vacuuming time is 4 to 8 hours.

[0049] Further, the unidirectional freezing mold mentioned in step 4) is a customized polytetrafluoroethylene mold, with a copper pillar at the bottom immersed in a cold source. Preferably, the cold source includes liquid nitrogen, dry ice, or low-temperature ethanol, and the cold source temperature is -196 to -20°C. The freeze-drying temperature is -80 to -20°C; the freeze-drying pressure is below 10 Pa.

[0050] Further, the inert gas mentioned in step 5) is argon or nitrogen; the high-temperature heat treatment is to raise the temperature to 600-1000℃ at a rate of 3-10℃ / min and hold it for 30-210min.

[0051] Further, in step 6), the vacuum degree of vacuum impregnation is less than 20 Pa, and the time is 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, polyol and stearic acid, preferably polyethylene glycol.

[0052] Example 1:

[0053] 1. A 20×20×1.5mm nickel foam sample was placed in a quartz tube furnace and heated to 1000℃ in an atmosphere with an argon:hydrogen ratio of 5:2. Methane was then introduced for graphene growth, and the sample was rapidly cooled to room temperature under an argon / hydrogen atmosphere. The prepared nickel-GF was then dip-coated with a 4wt% polymethyl methacrylate / anisole solution and baked at 180℃ for 3 hours to form a thin polymethyl methacrylate layer to prevent GF structure collapse during nickel etching. Next, the nickel substrate was completely dissolved in a 3mol / L hydrochloric acid solution overnight at 80℃ to obtain GF / polymethyl methacrylate. Finally, the polymethyl methacrylate layer was dissolved in acetone at 55℃ to obtain GF.

[0054] 2. 1.0 g of titanium aluminum carbide powder was added to 20 mL of etchant solution (containing 12 mol / L hydrochloric acid and 1.6 g lithium fluoride), and then stirred continuously at 35 °C for 24 h. After etching, the product was transferred to a centrifuge tube and centrifuged at 3500 rpm for 5 min to remove the supernatant acid layer. The precipitate was then washed with deionized water, and repeated centrifugation and washing were performed until the pH of the supernatant was close to 6. At this point, the precipitate gradually swelled and became viscous, similar to clay, and the supernatant was dark green, yielding multilayer MXene. Next, the multilayer MXene was redispersed in water and ultrasonically exfoliated for 1 h under an argon atmosphere, followed by centrifugation at 3500 rpm for 1 h. The supernatant was collected, which is the few-layer MXene suspension. Finally, it was freeze-dried at -20 °C for 24 h to obtain monolayer or few-layer MXene nanosheets.

[0055] 3. MXene and graphene oxide binder at a weight ratio of 2:1 were dispersed in deionized water using a planetary vacuum degassing mixer to obtain a total MXene / graphene oxide concentration of 15 mg / mL. -1 A uniform and stable slurry was obtained. Then, GF was immersed in the MXene / graphene oxide slurry and vacuumed for 6 hours to achieve complete impregnation.

[0056] 4. Transfer the GF and slurry to a unidirectional freezing mold (a custom-made PTFE mold with a copper column immersed in liquid nitrogen at the bottom) for directional freezing. Next, freeze-dry the ice sample in a freeze dryer (-50℃, 0.1Pa; LGJ-20FG) to remove the ice column through sublimation, obtaining a GF foam-MXene aerogel dual network framework, where the MXene aerogel is a sheet-like vertically oriented structure coupled within the pores of the GF foam.

[0057] 5. The GF foam-MXene aerogel dual network framework was thermally annealed at 800℃ for 2 hours in an argon atmosphere, during which the binder graphene oxide was thermally reduced to graphene.

[0058] 6. Polyethylene glycol is pre-melted in a vacuum oven at 90°C. The GF foam-MXene aerogel double network skeleton after high-temperature heat treatment is immersed in the polyethylene glycol melt and vacuum impregnated at 90°C for 12 hours. After removal, the unadsorbed polyethylene glycol on the surface is removed with oil-absorbing paper. Then, after natural cooling and solidification, the composite phase change material is obtained.

[0059] Example 2:

[0060] The difference between this embodiment and Example 1 is that the total concentration of MXene and the binder graphene oxide in step 3 is 30 mg / mL. -1 The other steps and parameters are the same as in Example 1.

[0061] Example 3:

[0062] The difference between this embodiment and Examples 1 and 2 is that the total concentration of MXene and the binder graphene oxide in step 3 is 60 mg / mL. -1 The other steps and parameters are the same as in Example 1.

[0063] Figure 1 This is a schematic diagram illustrating the preparation process of the multifunctional composite phase change materials in Examples 1-3. Figure 1It can be seen that the preparation process of the composite phase change material supported by the GF foam-MXene aerogel dual network consists of four steps: (1) preparation of MXene and binder graphene oxide slurry; (2) directional freezing process of MXene and binder graphene oxide slurry in GF foam; (3) freeze drying and high temperature heat treatment to obtain the GF foam-MXene aerogel dual network skeleton; (4) vacuum impregnation to prepare the composite phase change material.

[0064] Figure 2 This is a scanning electron microscope (SEM) image of the GF foam-MXene aerogel dual-network framework prepared in Example 2. From... Figure 2 It can be seen that MXene aerogel is a sheet-oriented structure coupled within the pore size of GF foam. The oriented MXene aerogel effectively increases the network density of GF foam. This dense and porous GF foam-MXene aerogel dual network skeleton is beneficial for the encapsulation of phase change materials and for improving the thermal conductivity and electromagnetic shielding effectiveness of the materials.

[0065] Figure 3 The thermal conductivity of polyethylene glycol, GF / polyethylene glycol, and the multifunctional composite phase change materials prepared in Examples 1-3 is described. Figure 3 It can be seen that the thermal conductivity of polyethylene glycol and GF / polyethylene glycol is 0.32 W / m and 5.43 W / m, respectively. -1 K -1 The thermal conductivity of the multifunctional composite phase change materials prepared in Examples 1, 2, and 3 were 6.72, 8.21, and 11.39 W / m, respectively. -1 K -1 Compared to GF / polyethylene glycol, the thermal conductivity was increased by 23.8%, 51.2%, and 109.8%, indicating that the GF foam-MXene aerogel dual network skeleton has better thermal conductivity than single GF foam. In addition, the thermal conductivity of the material increases with the increase of MXene aerogel content, proving the superiority of the GF foam-MXene aerogel dual network skeleton in this invention.

[0066] Figure 4 The electromagnetic shielding effectiveness of polyethylene glycol, GF / polyethylene glycol, and the multifunctional composite phase change materials prepared in Examples 1-3 is described. Figure 4It can be seen that in the 8.2–12.4 GHz (X-band), the electromagnetic shielding effectiveness of polyethylene glycol is less than 2.9 dB, and that of GF / polyethylene glycol is less than 35.8 dB. However, the electromagnetic shielding effectiveness of the multifunctional composite phase change materials prepared in Examples 1, 2, and 3 is greater than 44.5, 42.9, and 55.6 dB, respectively, which is 24.3%, 19.8%, and 55.3% higher than that of GF / polyethylene glycol. This indicates that the MXene aerogel coupled within the pores of the GF foam can promote the absorption of multiple reflections of electromagnetic waves and improve the electromagnetic shielding performance of the material, demonstrating the superiority of the GF foam-MXene aerogel dual-network framework in this invention.

[0067] Figure 5 Table 2 shows the change in energy storage density of the multifunctional composite phase change material prepared in Example 3 during 120 heating / cooling cycles. Figure 5 It can be seen that after 120 heating / cooling cycles, the latent heat of phase change (enthalpy of melting / enthalpy of crystallization) and phase change temperature (melting point / crystallization point) of the multifunctional composite phase change material in Example 3 hardly changed, proving that the multifunctional composite phase change material provided by the present invention has excellent cyclic thermal stability.

[0068] Figure 6 The infrared spectral changes of the multifunctional composite phase change material prepared in Example 3 during 120 heating / cooling cycles are shown. Figure 6 As can be seen, the multifunctional composite phase change material in Example 3 showed no change in its molecular structure and functional groups after 120 heating / cooling cycles, proving that the multifunctional composite phase change material provided by the present invention has excellent cyclic thermal stability.

[0069] Figure 7 These are comparative photographs showing the leakage of the multifunctional composite phase change material prepared in Example 3, polyethylene glycol, and GF / polyethylene glycol during heating on a hot plate. Figure 7 As can be seen, when polyethylene glycol, GF / polyethylene glycol, and the multifunctional composite phase change material in Example 3 are heated to 100°C on a hot plate, polyethylene glycol completely melts, GF / polyethylene glycol shows slight leakage, while the sample in Example 3 shows no leakage and excellent shape stability, which confirms that the multifunctional composite phase change material provided by the present invention has excellent leak-proof performance and shape stability.

[0070] Figure 8 The figures show the thermal expansion curves of the multifunctional composite phase change material prepared in Example 3, polyethylene glycol, and GF / polyethylene glycol. Figure 8It can be seen that when the temperature is above 70℃, the size of polyethylene glycol will change dramatically, and the size of GF / polyethylene glycol will change significantly. However, the size of the sample in Example 3 remains almost constant, which confirms that the multifunctional composite phase change material provided by the present invention has excellent shape stability.

[0071] Table 1. DSC heating / cooling data of the multifunctional composite phase change materials in Examples 1, 2 and 3

[0072]

[0073]

[0074] Among them, T m / T c Melting point / crystallization point; ΔH m / ΔH c It refers to the enthalpy of melting / enthalpy of crystallization.

[0075] Table 2. DSC data of the multifunctional composite phase change material in Example 3 during 120 heating / cooling cycles.

[0076]

[0077] Among them, T m / T c Melting point / crystallization point; ΔH m / ΔH c It refers to the enthalpy of melting / enthalpy of crystallization.

[0078] Example 4:

[0079] 1. A 20×20×1.5mm nickel foam sample was placed in a quartz tube furnace and heated to 800℃ in an atmosphere with an argon:hydrogen ratio of 5:2. Methane was then introduced for graphene growth, and the sample was rapidly cooled to room temperature under an argon / hydrogen atmosphere. The prepared nickel-GF was then dip-coated with a 4wt% polymethyl methacrylate / anisole solution and baked at 180℃ for 3 hours to form a thin polymethyl methacrylate layer to prevent GF structure collapse during nickel etching. Next, the nickel substrate was completely dissolved in a 2mol / L hydrochloric acid solution overnight at 80℃ to obtain GF / polymethyl methacrylate. Finally, the polymethyl methacrylate layer was dissolved in acetone at 55℃ to obtain GF.

[0080] 2. 1.0 g of titanium aluminum carbide powder was added to 20 mL of etchant solution (containing 8 mol / L hydrochloric acid and 1.2 g lithium fluoride), and then stirred continuously at 40 °C for 18 h. After etching, the product was transferred to a centrifuge tube and centrifuged at 3500 rpm for 5 min to remove the supernatant acid. The precipitate was then washed with deionized water, and repeated centrifugation and washing were performed until the pH of the supernatant was close to 6. At this point, the precipitate gradually swelled and became viscous, similar to clay, and the supernatant was dark green, yielding multilayer MXene. Next, the multilayer MXene was redispersed in water and ultrasonically exfoliated under an argon atmosphere for 1 h, followed by centrifugation at 3500 rpm for 1 h. The supernatant was collected, which is the few-layer MXene suspension. Finally, it was freeze-dried at -50 °C for 48 h to obtain monolayer or few-layer MXene nanosheets.

[0081] 3. MXene and polyvinyl alcohol (polyvinyl alcohol) at a weight ratio of 4:1 were ultrasonically dispersed in deionized water to obtain an MXene / polyvinyl alcohol total concentration of 20 mg / mL. -1 A uniform and stable slurry was obtained. Then, GF was immersed in the MXene / polyvinyl alcohol slurry and vacuumed for 4 hours to achieve complete impregnation.

[0082] 4. Transfer the GF and slurry to a unidirectional freezing mold (a custom-made PTFE mold with a copper column at the bottom immersed in -78℃ dry ice) for directional freezing. Next, freeze-dry the ice sample in a freeze dryer (-80℃, 10Pa) to remove the ice column through sublimation, obtaining a GF foam-MXene aerogel dual network framework, where the MXene aerogel is a sheet-like vertically oriented structure coupled within the pores of the GF foam.

[0083] 5. The GF foam-MXene aerogel double network skeleton was thermally annealed at 600℃ for 210 min in an argon atmosphere, during which the binder polyvinyl alcohol was sintered into carbon.

[0084] 6. The paraffin wax is pre-melted in a vacuum oven at 70°C. The GF foam-MXene aerogel double network skeleton after high-temperature heat treatment is immersed in the paraffin wax melt and vacuum impregnated at 70°C for 6 hours. After removal, the unadsorbed paraffin wax on the surface is removed with oil-absorbing paper. Then, after natural cooling and solidification, the composite phase change material is obtained.

[0085] Example 5:

[0086] 1. A 20×20×1.5mm nickel foam sample was placed in a quartz tube furnace and heated to 1200℃ in an atmosphere with an argon:hydrogen ratio of 5:2. Methane was then introduced for graphene growth, and the sample was rapidly cooled to room temperature under an argon / hydrogen atmosphere. The prepared nickel-GF was then dip-coated with a 4wt% polymethyl methacrylate / anisole solution and baked at 180℃ for 3 hours to form a thin polymethyl methacrylate layer to prevent GF structure collapse during nickel etching. Next, the nickel substrate was completely dissolved in a 4mol / L hydrochloric acid solution overnight at 80℃ to obtain GF / polymethyl methacrylate. Finally, the polymethyl methacrylate layer was dissolved in acetone at 55℃ to obtain GF.

[0087] 2. Add 1.0 g of titanium aluminum carbide powder to 20 mL of etchant solution (containing 10 mol / L hydrochloric acid and 2.0 g of lithium fluoride), and then stir continuously at 30 °C for 30 h. After etching, transfer the product to a centrifuge tube and centrifuge at 3500 rpm for 5 min to remove the supernatant acid. Then add deionized water to wash the precipitate, and repeat centrifugation and washing until the pH of the supernatant is close to 6. At this time, the precipitate gradually expands and becomes viscous, similar to clay, and the supernatant is dark green, which yields multilayer MXene. Next, disperse the multilayer MXene again in water and sonicate it under an argon atmosphere for 1 h, followed by centrifugation at 3500 rpm for 1 h. Collect the supernatant, which is the few-layer MXene suspension. Finally, freeze-dry at -80 °C for 72 h to obtain monolayer or few-layer MXene nanosheets.

[0088] 3. MXene and chitosan binder in a weight ratio of 1:1 were ball-milled and dispersed in a 2wt% acetic acid aqueous solution to obtain a total MXene / chitosan concentration of 40 mg / mL. -1 A uniform and stable slurry solution was obtained. Then, GF was immersed in the MXene / chitosan slurry solution and vacuumed for 8 hours to achieve complete impregnation.

[0089] 4. Transfer the GF and slurry to a unidirectional freezing mold (a custom-made polytetrafluoroethylene mold with a copper column at the bottom immersed in -20°C ethanol) for directional freezing. Next, freeze-dry the ice sample in a freeze dryer (-20°C, 5Pa) to remove the ice column through sublimation, obtaining a GF foam-MXene aerogel dual network framework, where the MXene aerogel is a sheet-like vertically oriented structure coupled within the pores of the GF foam.

[0090] 5. The GF foam-MXene aerogel dual network skeleton was thermally annealed at 1000℃ for 30 min under nitrogen atmosphere, during which the binder chitosan was sintered into carbon.

[0091] 6. Octadecylene is pre-melted in a vacuum oven at 70°C. The GF foam-MXene aerogel double network skeleton after high-temperature heat treatment is immersed in the octadecylene melt and vacuum impregnated at 70°C for 18 hours. After removal, the unadsorbed octadecylene on the surface is removed with oil-absorbing paper. Then, after natural cooling and solidification, the composite phase change material is obtained.

[0092] Experimental Example 1

[0093] The multifunctional composite phase change material obtained in Example 3 and two commercial silicone thermal pads, CP200 (2.0W m), were used together. -1 K -1 (DOBON, China) and HD90000 (7.5W m -1 K -1 The thermal management properties of Laird Tflex (USA) as a thermal interface material are determined by the following method:

[0094] The multifunctional composite phase change material obtained in Example 3, along with two commercial silicone thermal pads, CP200 and HD90000, were cut into 20×20×1.5mm pieces. 3 The dimensions were then determined, and the components were assembled with a 10W LED light and an aluminum heat sink. An infrared thermal imager was used to record the surface temperature change of the LED within 1000 seconds after it was turned on. The results are as follows: Figure 9 As shown. (Through) Figure 9 The comparison shows that when the multifunctional composite phase change material of the present invention is used as a thermal interface material, the surface temperature rise of the LED lamp within 1000 seconds of being lit is much lower than that of the LED lamp when two commercial silicone thermal pads are used as thermal interface materials, which proves that the multifunctional composite phase change material of the present invention has excellent heat dissipation performance when used as a thermal interface material.

[0095] Experimental Example 2

[0096] The light absorption performance of the multifunctional composite phase change material obtained in Example 3 was tested, with polyethylene glycol and GF / polyethylene glycol as comparisons. The test method was ultraviolet-visible absorption spectroscopy, and the results are as follows: Figure 10 As shown, the multifunctional composite phase change material obtained in Example 3 exhibits excellent light absorption performance because the GF foam-MXene aerogel dual network framework can serve as an effective photon trap.

[0097] Experimental Example 3

[0098] The energy storage and conversion performance of the multifunctional composite phase change material obtained in Example 3 was tested using the following method:

[0099] The multifunctional composite phase change material obtained in Example 3 by cutting and grinding is The dimensions were used in a self-made light-thermal-electric energy conversion device, which consisted of a xenon lamp (AM 1.5), a multifunctional composite phase change material for efficient solar energy collection, and a commercial thermoelectric generator (40×40mm). 2 (TEC2-25408) and liquid cooling radiator. Adjust the light intensity to 150, 250, 400, 600, 800 and 1000 mW cm⁻¹. -2 The output voltage, output current, and output power of this photo-thermal-electric energy conversion device are as follows: Figure 11 As shown. (Through) Figure 11 It can be seen that, after using the multifunctional composite phase change material obtained in Example 3, the photo-thermal-electric energy conversion device achieves a performance of 1000mW / cm². -2 Under light intensity, the output voltage, output current, and output power reach 1046.5mV, 190.6mA, and 124.7W, respectively. -2 This demonstrates that the multifunctional composite phase change material of the present invention has excellent energy storage and conversion performance.

[0100] The technical solutions disclosed and proposed in this invention can be implemented by those skilled in the art by appropriately modifying the conditions and routes, etc. Although the methods and preparation techniques of this invention have been described through preferred embodiments, those skilled in the art can obviously modify or recombine the methods and technical routes described herein without departing from the content, spirit, and scope of this invention to achieve the final preparation technique. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the spirit, scope, and content of this invention.

Claims

1. A multifunctional composite phase change material; characterized in that, The multifunctional composite phase change material is composed of graphene foam (GF foam), MXene aerogel, and a phase change material. The MXene aerogel is a sheet-like oriented structure coupled within the pores of the GF foam. The phase change material is encapsulated within the multifunctional composite material, forming a multifunctional composite phase change material with synergistic support from a GF foam-MXene aerogel dual network. The preparation method includes the following steps: 1): Graphene foam is deposited on a nickel foam template by chemical vapor deposition, and then the nickel foam is etched away by immersion in hydrochloric acid to obtain self-supporting GF foam; 2): Single-layer or few-layer MXene is prepared by etching titanium aluminum carbide with lithium fluoride and hydrochloric acid; 3): Disperse MXene and binder in deionized water to obtain an aqueous slurry, then immerse GF in the slurry and apply vacuum to achieve complete impregnation; 4): GF and slurry are transferred to a unidirectional freezing mold for directional freezing. After freeze-drying, a GF foam-MXene aerogel dual network framework is obtained, in which MXene aerogel is a sheet-like vertically oriented structure coupled within the pore size of GF foam. 5): The GF foam-MXene aerogel dual network framework is subjected to high-temperature heat treatment under protective gas protection; 6): The GF foam-MXene aerogel dual network framework, which has undergone high-temperature heat treatment, is composited with a phase change material by vacuum impregnation. Multifunctional composite phase change materials exhibit out-of-plane thermal conductivity of 6.72-11.39 W / m at filler contents of 9.06-13.78 wt%. -1 K -1 The X-band electromagnetic shielding effectiveness reaches 42.9-55.6 dB with a thickness of 3.0 mm, and the energy storage density reaches 160.3-166.9 J g. -1 .

2. The method for preparing the multifunctional composite phase change material according to claim 1; characterized in that, Includes the following steps: 1): Graphene foam is deposited on a nickel foam template by chemical vapor deposition, and then the nickel foam is etched away by immersion in hydrochloric acid to obtain self-supporting GF foam; 2): Single-layer or few-layer MXene is prepared by etching titanium aluminum carbide with lithium fluoride and hydrochloric acid; 3): Disperse MXene and binder in deionized water to obtain an aqueous slurry, then immerse GF in the slurry and apply vacuum to achieve complete impregnation; 4): GF and slurry are transferred to a unidirectional freezing mold for directional freezing. After freeze-drying, a GF foam-MXene aerogel dual network framework is obtained, in which MXene aerogel is a sheet-like vertically oriented structure coupled within the pore size of GF foam. 5): The GF foam-MXene aerogel dual network framework is subjected to high-temperature heat treatment under protective gas protection; 6): The GF foam-MXene aerogel dual network framework, which has undergone high-temperature heat treatment, is composited with phase change material by vacuum impregnation.

3. The method as described in claim 2, characterized in that, The gas used in the chemical vapor deposition in step 1) is methane, and the temperature is 800–1200 °C; the concentration of hydrochloric acid is 2–4 mol / L.

4. The method as described in claim 2, characterized in that, In step 2), the mass ratio of lithium fluoride to aluminum titanium carbide is 6:5 to 2:1; the concentration of hydrochloric acid is 8 to 12 mol / L; the etching temperature is 30 to 40 °C; the etching time is 18 to 30 h; the drying method is freeze drying; the freeze drying temperature is -80 to -20 °C; and the freeze drying time is 24 to 72 h.

5. The method as described in claim 2, characterized in that, The dispersion method described in step 3) is one of ultrasonic dispersion, high-speed shear dispersion, ball milling dispersion, or planetary gravity stirring dispersion; the binder is one of graphene oxide, polyvinyl alcohol, chitosan, or carboxymethyl cellulose; the total concentration of MXene and binder is 15–60 mg / mL. -1 The weight ratio of MXene to binder is 4:1 to 1:1; the vacuuming time is 4 to 8 hours.

6. The method as described in claim 2, characterized in that, The unidirectional freezing mold mentioned in step 4) is a polytetrafluoroethylene mold with a copper column at the bottom immersed in a cold source, including liquid nitrogen, dry ice or low-temperature ethanol, with a cold source temperature of -196 to -20 ℃; a freeze-drying temperature of -80 to -20 ℃; and a freeze-drying pressure of less than 10 Pa.

7. The method as described in claim 2, characterized in that, The protective gas mentioned in step 5) is argon or nitrogen; the high-temperature heat treatment is to raise the temperature to 600-1000 ℃ at a rate of 3-10 ℃ / min and hold it for 30-210 min.

8. The method as described in claim 2, characterized in that, The vacuum degree of the vacuum impregnation in step 6) is less than 20 Pa, and the time is 6 to 18 h; the phase change material is at least one of paraffin, n-hexadecane, n-octadecane, fatty acid and polyol.

9. The method as described in claim 2, characterized in that, The phase change material mentioned in step 6) is erythritol, polyethylene glycol, Myristic acid, lauric acid, or stearic acid.

10. The multifunctional composite phase change material according to claim 1, whose application fields include electronic device cooling and energy storage / conversion.

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