A high polymer composite graphene aerogel and a composite phase change material prepared by the same

Abstract

The application discloses a kind of high polymer composite graphene aerogel and preparation composite phase change material thereof.Preparation process is as follows:(1) polymer matrix is added to the oxidized graphene suspension obtained by electrochemical method, magnetic stirring is carried out, then it is transferred to reaction kettle, and high polymer composite graphene hydrogel is obtained after hydrothermal reaction;(2) high polymer graphene composite hydrogel is freeze-dried, and high polymer composite graphene aerogel is obtained, which is carbonized and graphitized to obtain nitrogen-hydrogen-oxygen co-doped graphene aerogel;(3) high polymer composite graphene aerogel or nitrogen-hydrogen-oxygen co-doped graphene aerogel is used to absorb molten paraffin, which is completely and uniformly dispersed, to obtain high polymer composite graphene aerogel / paraffin composite phase change material or nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material.The application has the advantages of simple preparation method, high thermal conductivity, excellent electromagnetic shielding and absorbing performance, good stability, good heat dissipation effect, etc.

Description

Technical Field

[0001] This invention belongs to the field of graphene-based polymer composite phase change materials, specifically relating to a method for preparing a composite phase change material with graphene aerogel as the thermal conductivity enhancement material, organic paraffin as the phase change material, and polyester formed by combining polyvinyl alcohol with polyacrylic acid as the carrier. This composite material is expected to be applied to efficient heat dissipation and electromagnetic interference shielding in power electronic equipment. Background Technology

[0002] With the rapid development of electronic technology and portable electronic devices (such as mobile phones, tablets, laptops, or other smart hardware), higher demands are placed on their multi-functionality, lightness, thinness, and even flexibility. Therefore, modern power electronic devices are developing towards miniaturization, high integration, high power density, and multi-functionality. The heat generated per unit area of ​​electronic components is constantly increasing. Furthermore, electromagnetic coupling, electromagnetic induction, or conduction in electronic devices causes electromagnetic signal interference, resulting in serious electromagnetic pollution that affects human health. During the operation of electronic devices, some electrical energy is converted into heat. If this heat is not dissipated in time, the local temperature of the electronic components increases sharply. Overheating and unavoidable electromagnetic waves can lead to the formation of "hot spots," decreased system efficiency and reliability of electronic devices, increased failure rates, shortened lifespan, and in severe cases, even safety hazards. Therefore, effectively dissipating excess heat from high-power electronic devices to the external environment and effectively shielding against electromagnetic interference have become major factors in ensuring device performance and lifespan. Typically, when a heat sink directly contacts a heat-generating element (device), the interfacial thermal resistance is very high because the interfacial gaps are filled with non-flowing air, resulting in very low thermal conductivity. To eliminate high interfacial thermal resistance, thermal interface materials are typically used to fill micro-gaps to maximize the effective contact area of ​​mating surfaces. Generally, phase change materials (PCMs) are naturally viscous materials that can serve as alternatives to thermal greases. When they reach their melting point (50-62°C), PCMs become at least partially liquid, filling all the gaps between the heat source and the heat sink. Dissipating large amounts of heat quickly is a key issue in the thermal management of electronic devices. Traditional thermal management methods such as air cooling and water cooling have many drawbacks, including high cost and large space requirements, making them unsuitable for increasingly miniaturized and micro-sized electronic products such as smartphones and laptops. In recent years, PCMs with high in-plane thermal conductivity have played a crucial role in effective heat dissipation, influencing the lifespan and reliability of electronic devices. Specifically, PCMs regulate the ambient temperature by storing and releasing heat during the phase change process. However, current PCM applications in electronic device thermal management suffer from low thermal conductivity, severe metal corrosion, and leakage problems during the phase change process. Furthermore, the low thermal conductivity of phase change materials currently limits the power density output of phase change material-based solar thermoelectric generators. With the development of modern science and technology, metal products are used in all aspects of our lives. Increased oxygen, moisture, and humidity in the atmosphere exacerbate the corrosion of metal products. Traditional epoxy anti-corrosion coatings inevitably contain porosity, and the large molecular weight of epoxy resin results in a hard texture after curing, making it prone to cracking in hot and cold environments and easily oxidized under acid and ultraviolet light, leading to poor coating performance. Additionally, polyurethane anti-corrosion coatings also have drawbacks such as poor acid and alkali resistance and salt resistance.

[0003] Nanomaterials with extremely high thermal conductivity are ideal fillers for enhancing interfacial thermal conductivity. These include zero-dimensional diamond, one-dimensional carbon nanotubes, two-dimensional graphite nanosheets, expanded graphite, graphene or graphene oxide, and three-dimensional graphene aerogels. Theoretically, graphene's thermal conductivity can reach as high as 5000 W·m. -1 ·K -1 Among the thermally conductive materials reported to date, graphene stands out. Due to its excellent mechanical, thermal, optical, electrical, chemical stability and molecular impermeability (barrier properties), graphene or graphene derivatives can be used as functional fillers to achieve multiple functions such as high thermal conductivity, high electromagnetic shielding, efficient energy storage, and electrostatic discharge and corrosion protection.

[0004] Graphene aerogels are three-dimensional graphene networks formed by cross-linking graphene nanosheets. They possess an interconnected porous structure, high thermal and electrical conductivity, and environmentally friendly properties. Therefore, 3D graphene aerogels have a richer thermal conductivity network, exhibiting faster thermal response and heat transfer rates, and superior thermal conductivity compared to graphene itself, making them a more ideal thermally conductive filler for polymer-based composite phase change materials. In this invention, the intermediate formed between polyvinyl alcohol, polyacrylic acid, and graphene uses carboxyl groups to connect graphene and paraffin, establishing a delocalized conjugated system. On the other hand, for example, paraffin-phase organic materials exhibit very low thermal conductivity (0.1-0.5 W·m). -1 ·K -1 However, it has the advantages of chemical stability, a well-defined phase transition temperature and no tendency to separate, and is non-toxic, inexpensive, has low supercooling and high energy density.

[0005] The preparation, structure, construction, and properties of graphene have a significant, even dominant, impact on the performance and applications of graphene-based thermal management materials. Using graphite as a raw material offers the advantage of abundant and inexpensive raw materials; however, the preparation methods and processing engineering for graphene exfoliation have a crucial influence on the structure and properties of graphene. Different stages of controlling graphene defects and surface functionality also significantly affect its performance and cost. Typically, the preparation, processing, and specific application methods and processes for graphene lack a unified design, resulting in high costs and poor compatibility.

[0006] With the rapid development of electronic information technology and the continuous upgrading of electronic products, the 5G communication era has arrived. The introduction of high frequencies has exacerbated electromagnetic interference between electronic devices, while simultaneously increasing device power and energy consumption, leading to a rapid rise in heat generation. This has become a key factor affecting the development of high-frequency, high-power electronic products. To address this issue, electronic products must incorporate multifunctional material components with high thermal conductivity and electromagnetic interference shielding properties during the design phase.

[0007] This invention aims to provide a method for the assembly and preparation of graphene aerogels, polymer composites, modification of defects and hydrophilicity, and continuous processing of graphene aerogels co-doped with hetero-elements and their composites with different phase change materials. This method achieves process compatibility and continuity, reduces costs, and enables products to have excellent performance and diverse functions. Summary of the Invention

[0008] This invention proposes a composite phase change material based on graphene containing oxide functional groups, graphene aerogel, and nitrogen-hydrogen-oxygen co-doped graphene aerogel, which adsorbs the organic phase change material paraffin to enhance its thermal conductivity. This addresses the key bottleneck issues of current phase change materials in thermal management and electromagnetic pollution of electronic devices. During the phase change process, heat is absorbed or released through latent heat pathways. Compared to traditional phase change materials with low thermal conductivity, the addition of nitrogen-hydrogen-oxygen co-doped graphene aerogel filler, through its interaction with the organic phase change material paraffin, combines the advantages of graphene (high thermal conductivity, high electrical conductivity, high carrier mobility, low density, strong mechanical properties) with paraffin (high specific heat capacity, high latent heat of phase change, and no supercooling). This significantly improves the heat transfer efficiency and magnetic permeability of the composite phase change material in heat storage / release and electromagnetic interference shielding processes. The graphene aerogel composite phase change material combines the high latent heat of phase change materials with the significant thermal conductivity of additives, ensuring efficient and stable operation of solar thermoelectric generators. It represents a forward-looking solution to the aforementioned thermal management and severe electromagnetic pollution problems.

[0009] The principle of this invention is as follows: A polymer matrix and an oxidized graphene suspension are first subjected to solution polymerization, followed by self-assembly at room temperature or with mild heating until fully mixed. Then, after a high-temperature and high-pressure reaction with a polytetrafluoroethylene liner, the mixture is freeze-dried. This allows the free radicals of the polymer chains and the oxygen-containing functional groups of graphene to combine through covalent bonds, hydrogen bonds, and van der Waals interactions, constructing a three-dimensional porous interconnected, highly efficient thermally conductive network structure, resulting in a polymer composite graphene aerogel. After carbonization and graphitization, a high thermal conductivity nitrogen-hydrogen-oxygen co-doped graphene aerogel is obtained. Then, the nitrogen-hydrogen-oxygen co-doped graphene aerogel and solid paraffin are dispersed in a small amount of constant-temperature water bath, allowing the liquid paraffin to completely and uniformly fill the interconnected pores of the high thermal conductivity nitrogen-hydrogen-oxygen co-doped graphene aerogel, avoiding the problem of uneven dispersion of phase change materials naturally immersed in the thermally conductive filler under vacuum conditions. The graphene aerogel and its composite phase change materials, prepared and regulated by continuous processes, provided by this invention exhibit efficient heat dissipation and electromagnetic interference shielding capabilities as their thermal and electrical conductivity improves. This broadens their application and development prospects in building energy conservation, heat dissipation and thermal management of battery electronic devices, and electromagnetic interference shielding. It is of great significance for the development and utilization of novel high thermal conductivity composite phase change materials in the thermal management and attenuation of electromagnetic pollution in integrated circuits.

[0010] The purpose of this invention is to address the problems of low thermal conductivity, severe metal corrosion, and easy leakage in current phase change materials (PCMs) for thermal management, as well as poor heat transfer and dissipation, significant electromagnetic interference, and short service life in the operating environment of high-frequency, high-power electronic devices. Therefore, this invention provides a continuous method for preparing and controlling the production of polymer composite graphene aerogels and their composite PCMs. Specifically, a polymer composite graphene hydrogel is prepared from hydrophilic oxygen-containing functional group graphene, which is then freeze-dried to obtain a polymer composite graphene aerogel. This aerogel is then subjected to high-temperature heat treatment to obtain an oleophilic nitrogen-hydrogen-oxygen co-doped graphene aerogel, which is then combined with organic paraffin to prepare a nitrogen-hydrogen-oxygen co-doped graphene aerogel with high thermal conductivity and high electromagnetic interference shielding effectiveness, and a multifunctional advanced material for phase change heat storage / dissipation. This continuous preparation and control method for polymer composite graphene aerogels and their composite PCMs offers advantages such as good thermal conductivity and dissipation, high thermal conductivity, high electrical conductivity, excellent thermal stability and electromagnetic interference shielding, as well as a simple preparation method and a green and environmentally friendly process.

[0011] In this invention, the polymer composite graphene aerogel or nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material has multifunctionality, including high thermal conductivity, excellent electromagnetic interference shielding effectiveness, high energy storage and conversion efficiency, and superior comprehensive performance. It meets the needs of various applications (such as heat dissipation and electromagnetic shielding of 5G electronic products, corrosion protection and heat dissipation and electromagnetic shielding of flexible electronics), such as thermal conductivity and heat dissipation, heat dissipation shielding, thermal conductivity and wave absorption, thermal conductivity and energy storage, and electrostatic discharge and corrosion protection.

[0012] To achieve the objectives of this invention, the following technical solutions are provided: A polymer matrix is ​​added to an oxidized graphene suspension obtained by an electrochemical method, magnetically stirred, and then transferred to a reaction vessel for hydrothermal reaction to obtain a polymer composite graphene hydrogel; the polymer composite graphene hydrogel is freeze-dried to obtain a polymer composite graphene aerogel, which is then carbonized and graphitized to obtain a nitrogen-hydrogen-oxygen co-doped graphene aerogel; the polymer composite graphene aerogel or the nitrogen-hydrogen-oxygen co-doped graphene aerogel is adsorbed with molten paraffin wax and completely and uniformly dispersed to obtain a polymer composite graphene aerogel / paraffin composite phase change material or a nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material.

[0013] The process for preparing polymer composite graphene aerogels and composite phase change materials described above is further explained below.

[0014] This invention provides a method for preparing polymer composite graphene aerogel, comprising the following steps:

[0015] A) Take 50-150 mL of oxidized graphene suspension and stir continuously in 5-15 mL of high-concentration alkaline medium for 6-48 h to achieve preliminary reduction; add polymer matrix to oxidized graphene suspension in a ratio of 1-2 parts polymer matrix to 30-90 parts oxidized graphene; stir magnetically for 3-18 h, then transfer to a high-temperature and high-pressure reactor for hydrothermal reaction at 110-120℃ for 24-48 h to obtain polymer composite graphene hydrogel through hydrothermal reduction reaction.

[0016] B) The obtained polymer composite graphene hydrogel is first frozen at -80 to -40°C for 2 to 6 hours or directly frozen with liquid nitrogen for 2 to 6 hours, and then vacuum dried for 1 to 3 days to obtain polymer composite graphene aerogel.

[0017] Furthermore, the polymer composite graphene aerogel prepared above is further processed: the obtained polymer composite graphene aerogel is subjected to carbonization and graphitization treatment to obtain nitrogen, hydrogen, and oxygen co-doped graphene aerogel. The specific operation process of the carbonization and graphitization treatment is as follows: during the continuous passage of high-purity argon gas, the temperature is increased at a rate of about 25°C / min, and the carbonization treatment is carried out at 2000°C for 2 hours. Then, the temperature is heated from room temperature to 1000°C at maximum power, and then increased to 2000°C at a rate of 25°C / min. Next, the temperature is increased to 2500°C at a rate of 10°C / min, and then increased to 2800°C at a rate of 5°C / min and held for 1 hour for graphitization post-treatment.

[0018] Specifically, the oxidized graphene suspension described in step A) is prepared by an electrochemical method, and its mass concentration is 1 to 40.88 mg / mL; the reaction effect is optimal when the mass concentration is 1.5 to 10 mg / mL.

[0019] The reaction in step A) includes one or more preparation methods combined, such as solution polymerization, hydrothermal method, chemical reduction method, freeze drying method, and high-temperature heat treatment.

[0020] Furthermore, when the polymer matrix is ​​subjected to solution polymerization, heating at 100–120°C for 12–48 h or stirring at room temperature for 6–18 h, adding one or two drops of acid as a catalyst, dehydration condensation, and forming more abundant functional groups, including hydroxyl, amino, carboxyl, ester or carbonyl (amide) groups, effectively realizing the functionalization of graphene;

[0021] When using the hydrothermal method, the reaction temperature is 110–120℃ and the reaction time is 12–48 h;

[0022] The polymer matrix is ​​composed of polyols and polyacids, selected from a group consisting of polyvinyl alcohol and polyacrylic acid, polypropylene alcohol and polyacetic acid, polyethylene glycol and polyethylene glycol, and polybutenol and polypropionic acid; the mass ratio of polyol to polyacid in the polymer matrix is ​​1.5~9:3. By adjusting the ratio of the polymer matrix, the hydrophilicity and oleophilicity or partially hydrophilic and oleophilicity of polymer composite graphene aerogels or nitrogen-hydrogen-oxygen co-doped graphene aerogels can be controlled, and the density can be adjusted; however, by introducing different proportions of polyols and polyacids, heteroatoms of nitrogen, oxygen, and hydrogen are doped into the graphene sheets. Polyvinyl alcohol and graphene sheets, and polyacrylic acid and graphene sheets are bonded together through hydrogen bonds, van der Waals forces, and π-π conjugation, forming a three-dimensional graphene network structure, thereby controlling the band gap structure and making it exhibit semiconductor characteristics such as thermosensitivity, doping, and photosensitivity. Taking polyvinyl alcohol and polyacrylic acid as an example, the polyester generated by the reaction between the two and between oxygen-containing graphene and polyacrylic acid contains abundant π-π conjugated structures, which can directly realize the functionalization of 3D graphene aerogel without introducing defects, thereby regulating and improving the interfacial interaction between polymer composite graphene aerogel and the matrix, reducing interfacial thermal resistance, optimizing impedance matching, and improving electromagnetic wave attenuation loss capability.

[0023] Furthermore, the alkaline medium is one of concentrated ammonia, hydrazine hydrate, sodium hydroxide, ethylenediamine, or sodium borohydride.

[0024] This invention provides a polymer composite graphene aerogel prepared by the above-described method, which is in the form of blocks, discs, frustums, or cylinders. The graphene aerogel is very lightweight, with a density of 0.027~1.37 g·cm³. -3 Its thermal conductivity and electrical conductivity are 7.6~9.33 W·m, respectively. -1 ·K -1 and 28.59~83.29 S·cm -1 The electromagnetic interference (EMI) shielding effectiveness (EMI) of the sample ranged from 43.2 to 70.5 dB in the X-band (8.2–12.4 GHz) and from 49.3 to 77.4 dB in the K-band (18–26.5 GHz). The sample thickness ranged from 100 to 420 micrometers. The thermal conductivity and electrical conductivity of the nitrogen-hydrogen-oxygen co-doped graphene aerogel after high-temperature heat treatment were 60–85.4 W·m, respectively. -1 ·K -1 and 350~470 S·cm -1 Its electromagnetic interference shielding effectiveness in the X-band is 37.9~68dB, and its electromagnetic interference shielding effectiveness in the K-band reaches 57~107.8dB. The sample thickness is between 100~420 micrometers.

[0025] This invention also provides a composite phase change material made from the above-mentioned polymer composite graphene aerogel and nitrogen-hydrogen-oxygen co-doped graphene aerogel. The preparation method is as follows: The polymer composite graphene aerogel or nitrogen-hydrogen-oxygen co-doped graphene aerogel and solid paraffin are dispersed in ultrapure water, heated and stirred at 60-80°C for 12-24 hours, and then dried to obtain a sheet-like solid material with completely uniform paraffin adsorption. 0.05-0.3g of the obtained product is poured into a mold, and a pressure of 120-380 Psi (or 10-40 MPa) is applied to obtain a polymer composite graphene aerogel / paraffin composite phase change film or a nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change film with a thickness of 100-420 μm.

[0026] The raw material ratio is as follows: graphene aerogel: 20~90 parts, paraffin: 5~340 parts, water: 3~7 parts.

[0027] The polymer composite graphene aerogel / paraffin composite phase change material and the nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material use polymer composite graphene aerogel and highly thermally conductive nitrogen-hydrogen-oxygen co-doped graphene aerogel as thermally conductive fillers, respectively, and solid paraffin as the phase change material. The preparation of composite phase change materials with enhanced thermal conductivity by polymer composite graphene aerogel or nitrogen-hydrogen-oxygen co-doped graphene aerogel cleverly applies organic phase change, inorganic salt phase change, physical phase change and mixed phase change.

[0028] In the composite phase change materials prepared by the above method, the mass fraction of graphene aerogel is 3wt%–96.5wt%; the thermal conductivity of the polymer composite graphene aerogel / paraffin composite phase change material is 1.4–8.3 W·m. -1 ·K -1 The electromagnetic interference (EMI) shielding effectiveness in the X-band is 34.1–72 dB, and in the K-band it reaches 42.5–110 dB; the thermal conductivity of the carbonized and graphitized nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material is 8.5–79.6 W·m. -1 ·K -1 Its conductivity is 3~288.6 S·cm -1 The electromagnetic interference (EMI) shielding effectiveness in the X-band is 40–61.3 dB, and in the K-band it reaches 61.9–115 dB. When the content of high-temperature heat-treated graphene aerogel in the phase change material is 75.7 wt%, the thermal conductivity of the composite phase change material can reach 76.4 W·m. -1 ·K -1 The electrical conductivity of the polymer-polymer composite graphene aerogel / paraffin composite phase change material is 1.9–101.2 S·cm. -1The electrical conductivity of nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change materials treated at high temperatures ranges from 3 to 288.6 S·cm. -1 .

[0029] Furthermore, applying a certain pressure during the preparation of the composite phase change film can improve the thermal conductivity of the composite phase change material. The graphene aerogel / paraffin composite phase change material is formed by pressing with a hot press. For the phase change material prepared by combining polymer composite graphene aerogel and paraffin, the applied pressure is 120-210 Psi, with the best effect achieved by applying pressure 1-3 times at a pressure of 150 Psi. For the phase change material composed of high thermal conductivity nitrogen-hydrogen-oxygen co-doped graphene aerogel and paraffin after high-temperature heat treatment, the applied pressure is 200-380 Psi, with the best effect achieved by applying pressure once or twice at a pressure of 300 Psi.

[0030] The composite phase change material made of polymer composite graphene aerogel in this invention has adjustable oleophilic and hydrophilic properties, adjustable amount of organic paraffin added, adjustable thickness and density of aerogel, adjustable electromagnetic shielding band and effectiveness, and also has anti-corrosion and heat dissipation functions.

[0031] Graphene aerogels possess a large macroscopic aspect ratio and a continuous, orderly, anisotropic porous structure. The primary reason for the formation of graphene aerogels is the strong self-assembly effect of covalent bonds, van der Waals forces, π-π stacking, and hydrogen bonds, which allows graphene sheets to tightly aggregate into orderly, continuous thin layers. The 3D porous network structure of graphene aerogels is typically connected by weak physical interactions between graphene nanosheets, such as electrostatic interactions, hydrogen bonds, and π-π interactions. Therefore, it avoids the inevitable collapse or deformation of porous structures. Compared to aerogels formed through weak physical interactions, chemical crosslinking enhances the structural stability of graphene aerogels by harmonizing strong covalent bonds and weak non-covalent bonds.

[0032] The key to this invention lies in the fact that the oxidized graphene suspension used is obtained through an electrochemical method. The oxidized graphene itself carries a large number of oxygen-containing functional groups, primarily hydroxyl groups. These hydroxyl groups, combined with polyacids and polyols to form polyesters, enable the polymer composite graphene aerogel and the nitrogen-hydrogen-oxygen co-doped graphene aerogel to form a flexible framework with the paraffin matrix during the cross-linking and blending process, thus constructing a highly efficient thermal conductivity pathway. Furthermore, the significantly increased number of hydrophobic groups on the surface of the polymer-doped graphene aerogel exhibits higher lipophilicity, contributing to good interfacial compatibility between the paraffin / graphene aerogel. This is because paraffin molecules and the graphene aerogel surface have similar chemical compositions and the same polarity, thereby reducing interfacial thermal resistance. Paraffin wax is filled into the interconnected porous structure of graphene aerogel to create a graphene composite phase change material with a complete lattice structure. This not only endows the graphene composite phase change material with excellent mechanical properties but also enhances the "maze" effect of the graphene composite phase change coating against corrosive media, effectively isolating the metal from the corrosive media, increasing the path curvature of the corrosive media to the metal, and improving corrosion resistance. The prepared polymer composite graphene aerogel and nitrogen-hydrogen-oxygen co-doped graphene aerogel not only possess a highly heat-transferring, interconnected, three-dimensional (3D) porous network structure, exhibiting excellent multifunctional characteristics such as thermal conductivity and heat dissipation, electromagnetic absorption and shielding, thermal conductivity and wave absorption, thermal conductivity and energy storage, and corrosion resistance, but also the hydrogen bonds in the polymer composite graphene aerogel or nitrogen-hydrogen-oxygen co-doped graphene aerogel enhance interfacial coupling, improve the compatibility of the organic paraffin phase, and thus achieve micro-encapsulation of the phase change material, effectively preventing paraffin leakage during the phase change process.

[0033] The beneficial effects of this invention are:

[0034] 1) The polymer composite graphene aerogel and nitrogen-hydrogen-oxygen co-doped graphene aerogel obtained in the production process of this invention synergistically realize the covalent and non-covalent functionalization of graphene. Its rich porous three-dimensional network structure effectively enhances the thermal conductivity, heat transfer and electromagnetic wave absorption and multiple reflection loss capabilities of the composite phase change material. At the same time, it can adsorb a large amount of phase change material, improve energy storage efficiency, and reduce phase change leakage rate.

[0035] 2) The polymer composite graphene aerogel or nitrogen-hydrogen-oxygen co-doped graphene aerogel composite phase change material provided by the present invention not only has high in-plane thermal conductivity and excellent electromagnetic interference shielding performance, but also has high energy storage density, high latent heat value, efficient heat dissipation capacity, excellent thermal stability and electrical conductivity.

[0036] 3) The polymer composite graphene aerogel or nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material described in this invention provides a new way for the effective functionalization of graphene aerogel, and the hydrophilicity and oleophilicity of graphene aerogel can be regulated by controlling the ratio of basic polymers.

[0037] 4) The production process of the polymer composite graphene aerogel and nitrogen-hydrogen-oxygen co-doped graphene aerogel described in this invention is simple, easy to operate, requires few experimental equipment, and has low cost for large-scale production.

[0038] 5) The polymer composite graphene aerogel and nitrogen-hydrogen-oxygen co-doped graphene aerogel provided by this invention ingeniously utilize organic phase transition, physical phase transition and mixed phase transition.

[0039] 6) The preparation of the polymer composite graphene aerogel and its composite phase change material described in this invention achieves a very low aerogel density of 0.027 g·cm³. -3 1.37 g·cm -3 The transformation provides a method for adjusting density to meet the needs of different applications.

[0040] 7) The preparation of the polymer composite graphene aerogel and its composite phase change material described in this invention provides a new solution for achieving efficient electromagnetic interference shielding and electromagnetic wave absorption by controlling the amount of adsorbed organic paraffin.

[0041] 8) The nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material provided by this invention has multifunctionality, especially excellent thermal conductivity and electromagnetic interference shielding performance, with an in-plane thermal conductivity of up to 79.6 W·m. -1 ·K -1 Compared to pure paraffin (0.21 W·m -1 ·K -1 It is about 378 times higher than that of other electromagnetic interference shielding devices. In the X-band (8-12.4GHz), its electromagnetic interference shielding effectiveness reaches 61.3 dB, with an electromagnetic interference shielding efficiency of over 99.995%. Moreover, it has excellent electromagnetic interference shielding effectiveness in the K-band (18-26.5GHz), reaching up to 115 dB, with an electromagnetic interference shielding efficiency of 100% in the entire band.

[0042] 9) The polymer composite graphene aerogel or nitrogen-hydrogen-oxygen co-doped graphene aerogel composite phase change material of the present invention can be used for heat dissipation and shielding of electromagnetic interference in building energy conservation, highly intelligent and integrated electronic devices, and thermal insulation or shielding and absorbing electromagnetic wave composite materials in military and aerospace thermal management engineering. Attached Figure Description

[0043] Figure 1 The images show actual photos of the polymer composite graphene aerogel from Example 1 and Example 2.

[0044] Figure 2 FTIR images of oxidized graphene exfoliated by electrochemical method and the polymer composite graphene aerogel of Example 4;

[0045] Figure 3 XRD patterns of electrochemically intercalated oxidized graphene and polymer composite graphene aerogel of Example 3 (left) and XRD patterns of paraffin, polymer composite graphene aerogel / paraffin composite phase change material (right).

[0046] Figure 4 This is a schematic diagram of the contact angles of the polymer composite graphene aerogel and the nitrogen-hydrogen-oxygen co-doped graphene aerogel before and after graphitization in Example 5.

[0047] Figure 5 SEM images of the polymer composite graphene aerogel and the polymer composite graphene aerogel / paraffin composite phase change material in Example 5.

[0048] Figure 6 Raman diagrams of oxidized graphene exfoliated by electrochemical method, polymer composite graphene aerogel of Example 6 and its polymer composite graphene aerogel / paraffin composite phase change material.

[0049] Figure 7 XPS full spectrum of polymer composite graphene aerogel and polymer composite co-doped graphene aerogel / paraffin composite phase change material in Example 7;

[0050] Figure 8 The XPS N1s plots for the polymer composite co-doped graphene aerogel and the polymer composite graphene aerogel / paraffin composite phase change material of Example 7 are shown.

[0051] Figure 9 TGA curves of pure paraffin, polymer composite graphene aerogel of Example 1, and polymer composite graphene aerogel / paraffin composite phase change material.

[0052] Figure 10 A comparison of the thermal conductivity and electrical conductivity of electrochemically exfoliated oxidized graphene, the polymer composite graphene aerogel of Example 8, and its graphitized nitrogen-hydrogen-oxygen co-doped graphene aerogel.

[0053] Figure 11 The DSC curves of the polymer composite graphene aerogel / paraffin composite phase change material of Example 9 are pure paraffin, and the DSC test results of the polymer composite graphene aerogel / paraffin composite phase change material of Example 10 before and after the heating-cooling cycle are shown.

[0054] Figure 12 Tensile test results of polymer composite graphene aerogel / paraffin composite phase change materials in Examples 6 and 8, which are pure paraffin wax;

[0055] Figure 13The curves showing the temperature change over time during heating and cooling of the polymer composite graphene aerogel / paraffin composite phase change materials of Examples 7 and 11 (pure paraffin) are provided.

[0056] Figure 14 The images show actual photos of polymer composite graphene aerogel / paraffin composite phase change materials with different thermally conductive filler mass fractions as shown in Example 12.

[0057] Figure 15 The thermal conductivity and electrical conductivity of the graphene aerogel / paraffin composite phase change material before and after graphitization with different loadings of nitrogen-hydrogen-oxygen co-doped graphene aerogel as thermally conductive filler in Example 12 are tested.

[0058] Figure 16 The results of in-plane thermal conductivity, through-plane thermal conductivity, and electrical conductivity tests of the nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material used as thermally conductive filler in Example 5 are as follows:

[0059] Figure 17 Electromagnetic interference shielding effectiveness of electrochemically exfoliated oxidized graphene, polymer composite graphene aerogel of Example 1, polymer composite graphene aerogel / paraffin composite phase change material of Example 2, and nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material of Example 12 in the X-band (8.2-12.4 GHz) and K-band (18-26.5 GHz).

[0060] Figure 18 Electromagnetic interference shielding efficiency diagrams for oxidized graphene exfoliated by electrochemical method, polymer composite graphene aerogel of Example 1, polymer composite graphene aerogel / paraffin composite phase change material of Example 2, and nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material of Example 12 in X-band and K-band.

[0061] Figure 19 The diagram shows the energy storage and conversion effects of the polymer composite graphene aerogel of Example 13, the polymer composite graphene aerogel / paraffin composite phase change material of Example 14, the polymer composite graphene aerogel / paraffin composite phase change material of Example 2, and the nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material of Example 12.

[0062] Figure 20 The diagram shows the principle of energy storage and conversion of composite phase change materials, and the current-time curve of the polymer composite graphene aerogel / paraffin composite phase change material in Example 14. Detailed Implementation

[0063] To further illustrate the purpose, technical features, and effects of the present invention, the following embodiments are provided. These embodiments will help those skilled in the art to better understand the present invention and are not limited to the specific implementations disclosed.

[0064] Example 1

[0065] Take 50 mL of electrochemically intercalated and exfoliated oxidized graphene suspension (7 mg / mL), add 5 mL of hydrazine hydrate, 0.0242 g of polyvinyl alcohol and 0.0366 g of polyacrylic acid, stir at room temperature for 1 h, and then react at 110 °C for 24 h in a high-pressure autoclave lined with polytetrafluoroethylene to form a polymer composite graphene hydrogel; freeze at -68 °C using a freeze dryer and dry for three days to obtain a polymer composite graphene aerogel; take 0.5 g of polymer composite graphene aerogel, 0.08 g of paraffin and 40 mL of ultrapure water, heat at 80 °C for 24 h to make it completely homogenized, then filter under vacuum through a carboxymethyl cellulose membrane with a pore size of 0.22 μm and freeze dry.

[0066] Graphene oxide was reduced using a chemical reduction method, with hydrazine hydrate selected as the reducing agent, to obtain high-quality reduced graphene oxide. A polymer composite graphene aerogel was synthesized by adding a polymer matrix, achieving surface modification of the reduced graphene oxide. Compared with Example 3 or Example 4, the amounts of polyvinyl alcohol and polyacrylic acid in the polymer matrix of this example were doubled, resulting in a cylindrical graphene aerogel with a diameter of 3.5 cm and a height of 3 cm, with a density of 0.729 g·cm³. -3 The polymer composite graphene aerogel prepared in this embodiment is a porous, sponge-like structure. Compared to Example 2, the pores of the polymer composite graphene aerogel in this embodiment are smaller. Figure 1 As shown. Both the polymer composite graphene aerogel and the polymer composite graphene aerogel / paraffin composite phase change material in this embodiment exhibit excellent thermal stability. At 600℃, the polymer composite graphene aerogel loses approximately 10% of its weight, and the polymer composite graphene aerogel / paraffin composite phase change material loses approximately 14% of its weight. Figure 9 As shown. The polymer composite graphene aerogel film has a thickness of approximately 233 μm. Its total electromagnetic interference (EMI) shielding effectiveness (MEI) in the X-band (8.2–12.4 GHz) is 44.8–63.5 dB, with an MEI shielding efficiency exceeding 99.996%; in the K-band (18–26.5 GHz), its MEI shielding effectiveness is 50.8–61.6 dB, with an MEI shielding efficiency exceeding 99.999%. See Figure 17 and Figure 18 In this embodiment, the polymer-polymer composite graphene aerogel has a mass fraction of 87.1 wt% in the composite phase change material, and its thermal conductivity is calculated to be 6.5 W·m based on the thermal conductivity formula. -1 ·K-1 The measured conductivity was 61.48 S·cm. -1 .

[0067] The thermal conductivity of the polymer composite graphene aerogel and its composite phase change material described in this invention is calculated using the following formula:

[0068] λ=α·Cp·ρ

[0069] λ: Thermal conductivity, also known as thermal conductivity

[0070] α: Thermal diffusivity

[0071] Cp: ​​Specific heat

[0072] ρ: density

[0073] The thermal diffusivity of the polymer composite graphene aerogel or nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material is obtained by laser scintillation with an LFA467. The specific heat is measured by differential scanning calorimetry (DSC). The density is obtained, but is not limited to physical methods and measurement with an XS-300W fully automatic solid density meter. When measuring the thermal diffusivity of the graphene aerogel / paraffin composite phase change material sample, the composite phase change material is a disc with a diameter of 23-25 ​​mm and a thickness of 40-420 μm, wherein 70% of the sample has a thickness of 50-260 μm.

[0074] The electromagnetic interference shielding effectiveness of the aforementioned polymer composite graphene aerogel, polymer composite graphene aerogel / paraffin composite phase change material, and nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material is mainly based on absorption loss effectiveness, which is 2 to 3 times that of reflection loss effectiveness. Figure 17 Reflective shielding effectiveness can cause secondary electromagnetic pollution, making it urgent to develop electromagnetic interference shielding materials that primarily absorb losses.

[0075] Example 2

[0076] Take 50 mL of oxidized graphene suspension (8.74 mg / mL), add 5 mL of hydrazine hydrate, stir at room temperature for 7.5 h, add 0.0361 g of polyvinyl alcohol and 0.0546 g of polyacrylic acid, stir for 3 h, then transfer to a high-pressure reactor lined with 100 mL of polytetrafluoroethylene and react for 24 h to form a polymer composite graphene hydrogel. Freeze at -70 °C for 2 h using a freeze dryer, then vacuum dry for three days to obtain a polymer composite graphene aerogel. Take 0.2 g of the graphene aerogel, 0.077 g of paraffin wax and 40 mL of ultrapure water, heat at 80 °C for 24 h to make it completely homogenized, then vacuum filter through a carboxymethyl cellulose membrane with a pore size of 0.22 μm and freeze dry.

[0077] Compared with Example 3 or Example 4, the amounts of polyvinyl alcohol and polyacrylic acid in the polymer matrix of this example are increased by two times, resulting in a frustum-shaped polymer composite graphene aerogel with a bottom diameter of 4.8 cm, a top diameter of 3.5 cm, and a height of 2.9 cm, and a density of 1.37 g·cm³. -3 The polymer composite graphene aerogel prepared in this example is porous and cotton-like, with larger pores than that in Example 1, attributed to the increased amount of polymer. Figure 1 As shown. In this embodiment, the mass ratio of polyvinyl alcohol to polyacrylic acid is 2:3, the mass fraction of graphene aerogel in the composite phase change material is 72.2 wt%, and the thermal conductivity is 5.8 W·m. -1 ·K -1 The conductivity is 47.76 S·cm. -1 In this embodiment, when the thickness of the polymer composite graphene aerogel / paraffin composite phase change material sample is approximately 290 μm, its total electromagnetic interference (EMI) shielding effectiveness (TEE) in the X-band (8–12.4 GHz) is 53.7–62.3 dB, and its EMI shielding efficiency in the X-band is close to 100%. In the K-band (18–26.5 GHz), it exhibits excellent TEE, reaching 65–100 dB, with EMI shielding efficiency of 100% across the entire band. (See [reference needed]). Figure 17 and Figure 18 In the electrothermal conversion process of the polymer composite graphene aerogel / paraffin composite phase change material of this embodiment, voltages of 2V, 2.5V, and 3V were applied respectively. A clear plateau appeared between 300 and 1200 seconds, indicating that the composite phase change material converts electrical energy into heat energy for storage. After the power supply was turned off at 1200 seconds, the sample rapidly cooled between 1200 and 1700 seconds, releasing heat energy. Moreover, in the energy storage and conversion process, the heating and cooling slopes of Example 2 were greater than those of Example 14, indicating that the heat absorption and release rates of the polymer composite graphene aerogel / paraffin composite phase change material of this embodiment were faster, attributed to its higher thermal conductivity. See Figure 19 .

[0078] Example 3

[0079] Take 50 mL of an electrochemically prepared oxidized graphene suspension (23.18 mg / mL) with a mass concentration of 16.5 mg / mL, add 0.0128 g of polyvinyl alcohol, 0.0188 g of polyacrylic acid and 0.0158 g of cetyltrimethylammonium bromide (CTAB), and simultaneously add 20 μL of concentrated sulfuric acid as a catalyst. After heating in an oil bath at 120 °C for 2 h, react in a high-pressure autoclave lined with polytetrafluoroethylene at 110 °C for 10 h to form a polymer composite graphene hydrogel. Wash three times with ultrapure water, freeze-dry at -60 °C for three days, and obtain a polymer composite graphene aerogel. Take 0.4516 g of the graphene aerogel, add 2.236 g of paraffin and 25 mL of ultrapure water, heat at 100 °C for 27 h to completely and uniformly disperse it, and then dry in a vacuum oven at 60 °C for 13 h.

[0080] Crosslinking agents promote the gelation of graphene oxide sheets by significantly enhancing the bonding force between them. Several crosslinking agents are available, including polyvinyl alcohol (PVA), oxygen-containing polymers (hydroxypropyl cellulose (HPC), polyethylene oxide (PEO), etc.), or nitrogen-containing functional groups (polyamines, ethylenediamine). These polymers form hydrogen bonds with the surrounding graphene oxide sheets, providing stronger bonding during gelation. In addition, several relatively small quaternary ammonium salts, such as hexadecyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), tetramethylammonium chloride (TMAC), and melamine, can be used to promote the formation of graphene hydrogels. In this embodiment, hexadecyltrimethylammonium bromide is selected as the surfactant to promote the formation of the polymer composite graphene hydrogel. In this embodiment, the mass ratio of polyvinyl alcohol to polyacrylic acid is 2:3, the graphene aerogel has a diameter of 4.3 cm, a height of 2.7 cm, and a density of 0.454 g / cm³. 3 Compared to oxidized graphene exfoliated by electrochemical methods, the polymer composite graphene aerogel of this embodiment exhibits a very weak graphite peak, and paraffin is completely and uniformly filled into the voids of the graphene aerogel. The characteristic peaks of the paraffin crystalline phase are clearly visible in the XRD pattern. See [link / reference]. Figure 3 The content of polymer-polymerized graphene aerogel in the composite phase change material is 25 wt%. The melting point of the polymer-polymerized graphene aerogel / paraffin composite phase change material is 61.02℃, the enthalpy of fusion (endothermic) in the latent heat of phase change is 92.29 J / g, the crystallization temperature is 56.67℃, and the enthalpy of crystallization (exothermic) is 96.88 J / g. The thermal conductivity is calculated to be 2.7 W·m based on the thermal conductivity formula. -1 ·K -1 The measured conductivity was 18.32 S·cm. -1The content of polymer-polymerized graphene aerogel in the composite phase change material is 25 wt%. The melting point of the polymer-polymerized graphene aerogel / paraffin composite phase change material is 61.02℃, the enthalpy of fusion (endothermic) in the latent heat of phase change is 92.29 J / g, the crystallization temperature is 56.67℃, and the enthalpy of crystallization (exothermic) is 96.88 J / g. The thermal conductivity is calculated to be 2.7 W·m based on the thermal conductivity formula. -1 ·K -1 The measured conductivity was 18.32 S·cm. -1 The polymer composite graphene aerogel / paraffin composite phase change material film of this embodiment has a thickness of 220 μm, and its electromagnetic shielding performance in the X-band is 35.8~49.5 dB, and its electromagnetic shielding effectiveness in the K-band is 43.4~57 dB.

[0081] Example 4

[0082] Take 200 mL of an electrochemically prepared oxidized graphene suspension (30.57 mg / mL) with a mass concentration of 20.79 mg / mL, add 0.0189 g of polyacrylic acid and 0.0128 g of polyvinyl alcohol, add one drop of concentrated sulfuric acid, heat and stir at 120 °C for 48 h, then add 1 mL of ethylenediamine, transfer to a high-pressure reactor lined with polytetrafluoroethylene, and react at 110 °C for 6 h to form a graphene hydrogel; freeze-dry the graphene hydrogel to obtain a graphene aerogel; weigh 99.67 g of white sliced ​​paraffin wax and place it in a vacuum oven at 80 °C for 4 h until the paraffin wax is completely melted, then remove it. Mix the graphene aerogel with the molten paraffin wax, heat and stir at 80 °C for 36 h to ensure complete mixing, and then dry in a vacuum oven at 60 °C overnight.

[0083] A small amount of acid was added to initiate a dehydration condensation reaction. Ethylenediamine was used as a crosslinking agent to modify the functional groups of the graphene aerogel, enriching it with oxidized, amidated, iminated, and hydrogenated compounds. In this embodiment, sulfuric acid was used for acid catalysis. The mass ratio of polyvinyl alcohol to polyacrylic acid was 2:3, and the density of the graphene aerogel was 0.215 g / cm³. 3 The polymer composite graphene aerogel film of this embodiment has a thickness of 150 μm, and its electromagnetic shielding performance in the X-band is 47.6~68.5 dB, while its electromagnetic shielding effectiveness in the K-band is 52~65.3 dB. Compared with oxidized graphene exfoliated by electrochemical methods, the polymer composite graphene aerogel of this embodiment contains more oxygen-containing functional groups such as hydroxyl and carboxyl groups, more chemical interactions such as nitrogen-hydrogen bonds, carbon-oxygen double bonds in amides, and π-π conjugated structures, effectively functionalizing it and crosslinking the graphene sheets to construct a porous three-dimensional interconnected network. Its functional group structure information is as follows: Figure 2As shown, the content of polymer-polymer composite graphene aerogel in the composite phase change material is 3 wt%. The melting point of the polymer-polymer composite graphene aerogel / paraffin composite phase change material is 59.34℃, the enthalpy of fusion (endothermic) in the latent heat of phase change is 163.5 J / g, the melting point is 56.4℃, and the enthalpy of crystallization (exothermic) is 161.8 J / g. The thermal conductivity is calculated to be 1.896 W·m based on the thermal conductivity formula. -1 ·K -1 The measured conductivity was 2.4 S·cm. -1 .

[0084] Example 5

[0085] Take 50 mL of an electrochemically prepared oxidized graphene suspension (10.35 mg / mL), add 5 mL of hydrazine hydrate, 0.0242 g of polyvinyl alcohol, and 0.0366 g of polyacrylic acid. After stirring at room temperature for 1 h, react in a high-pressure autoclave lined with polytetrafluoroethylene at 110 °C for 24 h to form a polymer composite graphene hydrogel. Freeze at -71 °C using a freeze dryer and dry for three days to obtain a polymer composite graphene aerogel. Take 0.5 g of the graphene aerogel, 0.252 g of paraffin wax, and 40 mL of ultrapure water, heat at 100 °C for 24 h to make it completely homogenized, then filter under vacuum through a carboxymethyl cellulose membrane with a pore size of 0.22 μm and freeze-dry.

[0086] Graphene oxide was reduced using a chemical reduction method, with hydrazine hydrate used as the reducing agent to form reduced graphene oxide. A polymer matrix was then added to synthesize graphene aerogel, achieving surface modification of the graphene. Compared to Example 3 or Example 4, the amounts of polyvinyl alcohol and polyacrylic acid in the polymer matrix of this example were doubled, resulting in a polymer composite graphene aerogel with a density of 0.657 g·cm³. -3 The freeze-dried polymer composite graphene aerogel of this embodiment was subjected to high-temperature heat treatment at 1000℃, 1500℃, 2000℃, and 2500℃ respectively to further obtain a nitrogen-hydrogen-oxygen co-doped graphene aerogel with high thermal conductivity. The polymer composite graphene aerogel of this embodiment is hydrophilic with a contact angle of 34.2°. After high-temperature heat treatment, the obtained nitrogen-hydrogen-oxygen co-doped graphene aerogel becomes oleophilic with a contact angle of 114.2~115.3°, achieving the control of the hydrophilicity and oleophilicity of the graphene aerogel. Figure 4As shown. The highly thermally conductive nitrogen-hydrogen-oxygen co-doped graphene aerogel was mixed with paraffin in equal amounts according to the above process. The mass fraction of the carbonized highly thermally conductive graphene aerogel was 66.5 wt%, resulting in a composite phase change material. The electrical conductivity, in-plane thermal conductivity, and thermal conductivity across the plane all increased with increasing heat treatment temperature. The porous morphology of the polymer composite graphene aerogel in this embodiment and the relatively smooth morphology of the polymer composite graphene aerogel / paraffin composite phase change material obtained by adsorbing and uniformly filling paraffin are shown in the figure. Figure 5 As shown, the composite phase change material, after high-temperature heat treatment at 2500℃, exhibits excellent thermal and electrical conductivity, with a thermal conductivity reaching 63.63 W·m. -1 ·K -1 Its electrical conductivity is as high as 123.9 S·cm. -1 ,like Figure 16 As shown.

[0087] Example 6

[0088] Take 50 mL of oxidized graphene suspension with a mass concentration of 1.5 mg / mL, add a mixed solution of concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 1:3, where 300 μL of concentrated sulfuric acid and 900 μL of concentrated nitric acid are used. After ultrasonic dispersion for 30 min, heat in an oil bath at 120 °C for 12 h. Wash several times with ultrapure water to remove excess acid until neutral. Add 1 mL of ethylenediamine to adjust the pH of the solution to alkaline. After ultrasonication for 15 min, add 0.0127 g of polyvinyl alcohol and 0.0189 g of... Polyacrylic acid was stirred at room temperature for 1 hour, then transferred to a high-pressure autoclave lined with polytetrafluoroethylene and reacted at 110°C for 24 hours to form a polymer composite graphene hydrogel. After freezing at -76°C using a freeze dryer, it was dried for three days to obtain a polymer composite graphene aerogel. 0.2 g of the graphene aerogel, 0.05 g of paraffin wax, and 40 mL of ultrapure water were taken and heated at 75°C for 24 hours to make it completely homogenized. Then, it was vacuum filtered through a carboxymethyl cellulose membrane with a pore size of 0.22 μm and freeze-dried.

[0089] First, the oxidized graphene suspension is acidified with a strong acid, then the pH of the solution is adjusted with a weak base, ethylenediamine, to better expand the stacked oxidized graphene sheets into high-quality large sheets of oxidized graphene. Due to the lack of mutual repulsion, the oxidized graphene suspension is unstable in concentrated acid. When the pH decreases, the electrostatic repulsion weakens, while the hydrogen bonds are strengthened due to the protonation of the carboxyl groups. Therefore, stable GO gelation can be achieved by increasing the bonding force or weakening the repulsion force. In this embodiment, nitrogen-containing functional group ethylenediamine is selected as a crosslinking agent to further promote the gelation between oxidized graphene sheets. The mass ratio of polyvinyl alcohol to polyacrylic acid is 2:3, and the density of the polymer composite graphene aerogel is 0.036 g / cm³. 3Compared to oxidized graphene exfoliated by electrochemical methods, the polymer composite graphene aerogel of this embodiment contains more defects. However, after adsorbing paraffin, the defects in the resulting polymer composite graphene aerogel / paraffin composite phase change material are significantly reduced. See [link / reference]. Figure 6 The composite phase change material sample has a thickness of 240 μm and a supported graphene aerogel mass fraction of 80.3 wt%. The thermal conductivity, calculated using the thermal conductivity formula, is 6 W·m. -1 ·K -1 The measured conductivity was 55.67 S·cm. -1 Its electromagnetic shielding performance in the X-band is 52~61.8dB, and its electromagnetic shielding effectiveness in the K-band reaches 63~105.7dB. The composite phase change material prepared in this embodiment has good mechanical properties, with a tensile strength of 6.17MPa. Figure 12 .

[0090] Example 7

[0091] 100 mL of electrochemically intercalated graphene suspension (1.5 mg / mL) was soaked in a suitable amount of 3 mol / L sodium hydroxide solution for 58 h. The solution was then vacuum filtered, washed with water until neutral, and 5 mL of hydrazine hydrate was added, followed by stirring for 8.5 h. 0.012 g of polyvinyl alcohol and 0.0189 g of polyacrylic acid were added, and the mixture was stirred at room temperature for 17 h. The mixture was then transferred to a high-pressure reactor lined with polytetrafluoroethylene and hydrothermally reacted at 110 °C for 48 h to form a polymer composite graphene hydrogel. The hydrogel was washed twice with ultrapure water and once with a mixture of ethanol and ultrapure water (volume ratio 1:1). After freezing at -73 °C for 2 h, it was vacuum dried for 89 h to obtain a polymer composite graphene aerogel. Take 0.2g of the graphene aerogel, 0.013g of paraffin and 40mL of ultrapure water, heat at 80℃ for 24h to make it completely homogenized, then filter it under vacuum through a carboxymethyl cellulose membrane with a pore size of 0.22μm and freeze-dry it.

[0092] An electrochemically prepared graphene oxide suspension was soaked in a strong alkali solution to further remove the solid electrolyte remaining on the graphene oxide sheets during the electrochemical exfoliation process, thereby obtaining higher quality graphene oxide. The polymer composite graphene aerogel of this embodiment contains significantly more effective nitrogen and oxygen doping compared to electrochemically exfoliated graphene oxide. Figure 7 The polymer composite graphene aerogel of this embodiment has a high content of graphitic nitrogen and pyrrole nitrogen. After adsorbing paraffin, the graphitic nitrogen content decreases significantly, while the pyrrole nitrogen and pyridine nitrogen content increases. See Figure 8 The graphene aerogel in this composite phase change material has a mass fraction of 94 wt% and a thermal conductivity of 8 W·m. -1 ·K -1 The conductivity is 85.47 S·cm. -1The sample, with a thickness of 130 μm, exhibited electromagnetic shielding performance of 55.2–69.8 dB in the X-band and 67.4–107 dB in the K-band. During isothermal heating at 50 °C, the surface temperature of the polymer-polymer composite graphene aerogel / paraffin composite phase change material in this embodiment rose rapidly, demonstrating a faster thermal response and indicating excellent thermal responsiveness, attributed to its high thermal conductivity. Pure paraffin absorbed heat more slowly than the polymer-polymer composite graphene aerogel / paraffin composite phase change material, due to its low thermal conductivity. Furthermore, at the initial heating stage, the temperature of the polymer-polymer composite graphene aerogel / paraffin composite phase change material in this embodiment was lower than that in Example 11, indicating that it provided more thermal pathways. During the temperature rise and cooling process after the heat source was turned off for 60 seconds, its heating and cooling rates were also faster than those of the polymer composite graphene aerogel / paraffin composite phase change material in Example 11. This is because the thermal conductivity of the polymer composite graphene aerogel / paraffin composite phase change material in this example is higher than that in Example 11. See Figure 13 .

[0093] Example 8

[0094] 100 mL of electrochemically intercalated graphene suspension (1.5 mg / mL) was soaked in a suitable amount of 3 mol / L sodium hydroxide solution for 58 h. After vacuum filtration, the solution was washed with water until neutral, 10 mL of hydrazine hydrate was added, and the mixture was sonicated for 15 min and stirred for 9.5 h. 0.0241 g of polyvinyl alcohol and 0.0364 g of polyacrylic acid were added, and the mixture was stirred at room temperature for 2 h. After adding 1 mL of ethanol, the mixture was transferred to a high-pressure reactor lined with polytetrafluoroethylene and hydrothermally reacted at 110 °C for 48 h to form a polymer composite graphene hydrogel. The hydrogel was washed three times with ultrapure water, frozen at -78 °C for 2 h using a freeze dryer, and then vacuum dried for 89 h to obtain a graphene aerogel. 0.2 g of the polymer composite graphene aerogel, 0.345 g of paraffin wax, and 40 mL of ultrapure water were heated at 80 °C for 24 h to ensure complete homogenization. The mixture was then vacuum filtered through a carboxymethyl cellulose membrane with a pore size of 0.22 μm and freeze-dried.

[0095] An electrochemically prepared graphene oxide suspension was soaked in a strong alkali solution. To further remove the solid electrolyte remaining on the graphene oxide sheets during the electrochemical exfoliation process, thereby obtaining higher quality graphene oxide, a polymer matrix was added to synthesize graphene aerogel, achieving surface modification of the reduced graphene oxide. Compared with Example 3 or Example 4, the amounts of polyvinyl alcohol and polyacrylic acid in the polymer matrix of this example were doubled, resulting in a cylindrical polymer composite graphene aerogel with a diameter of 3.5 cm and a height of 3 cm, and a density of 1.281 g·cm³. -3The prepared polymer composite graphene aerogel was first carbonized at 2000℃ for 2 hours, and then graphitized at 2800℃ for 1 hour to obtain nitrogen, hydrogen, and oxygen co-doped graphene aerogel. The thermal conductivity and electrical conductivity of the polymer composite graphene aerogel described in this example are 7.6~9.33 W·m, respectively. -1 ·K -1 and 28.59~83.29 S·cm -1 Compared to the original oxidized graphene (4.2 W·m), -1 ·K-1 and 28.6S·cm -1 The thermal conductivity and electrical conductivity of the nitrogen-hydrogen-oxygen co-doped graphene aerogel after carbonization and graphitization were 66.4 W·m⁻¹, respectively. -1 ·K -1 and 383 S·cm -1 This is 15.8 and 13.4 times higher than the original oxidized graphene. See Figure 10 In this embodiment, the composite phase change material contains 36.8 wt% graphene aerogel with a thermal conductivity of 2.7 W·m. -1 ·K -1 The conductivity is 19.54 S·cm. -1 The polymer-polymer composite graphene aerogel / paraffin composite phase change material of this embodiment possesses certain mechanical properties, with a tensile strength of 5.52 MPa. Figure 12 As shown.

[0096] Example 9

[0097] 125 mL of an electrochemically prepared oxidized graphene suspension (1.5 mg / mL) was soaked in an appropriate amount of concentrated ammonia for two days, washed three times with distilled water, 10 mL of hydrazine hydrate was added, and the mixture was stirred for 11 h. Then, 0.365 g of polyvinyl alcohol and 0.0247 g of polyacrylic acid were added, and the mixture was stirred at room temperature for 2 h. The mixture was then reacted at 110 °C for 48 h in a high-pressure reactor lined with polytetrafluoroethylene to form a polymer composite graphene hydrogel. After freezing at -75 °C using a freeze dryer, the hydrogel was dried for four days to obtain a polymer composite graphene aerogel. 0.5 g of the graphene aerogel, 1.5 g of paraffin wax, and 40 mL of ultrapure water were heated at 100 °C for 24 h to make it completely homogenized. The mixture was then vacuum filtered through a carboxymethyl cellulose membrane with a pore size of 0.22 μm and freeze-dried.

[0098] Reduced graphene oxide was formed by reducing oxidized graphene using a chemical reduction method with hydrazine hydrate as the reducing agent. A polymer matrix was then added to synthesize graphene aerogel, achieving surface modification of the graphene. The mass ratio of polyvinyl alcohol to polyacrylic acid was 3:2. The prepared graphene aerogel had a diameter of 4.9 cm, a height of 6.2 cm, and a density of 0.056 g / cm³. 3The polymer-polymer composite graphene aerogel has a mass fraction of 16.8 wt% in the composite phase change material. The melting point of the polymer-polymer composite graphene aerogel / paraffin composite phase change material is 58.12℃, the enthalpy of fusion (endothermic) in the latent heat of phase change is 146.2 J / g, the crystallization temperature is 55.6℃, and the enthalpy of crystallization (exothermic) is 145.6 J / g. The relatively large latent heat indicates that this polymer-polymer composite graphene aerogel / paraffin composite phase change material has good heat storage and release capabilities. Figure 11 As shown. The thermal conductivity, calculated using the thermal conductivity formula, is 1.64 W·m. -1 ·K -1 The measured conductivity was 1.94 S·cm. -1 The sample has a thickness of 245 μm and its electromagnetic shielding performance in the X-band is 34.4~45.7 dB, while its electromagnetic shielding effectiveness in the K-band is 42.8~49.5 dB.

[0099] Example 10

[0100] Take 50 mL of an electrochemically prepared oxidized graphene suspension with a mass concentration of 6.06 mg / mL, add a mixed solution of concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 1:3, where 20 μL of concentrated sulfuric acid and 60 μL of concentrated nitric acid are used. After ultrasonic dispersion for 30 min, heat in an oil bath at 120 °C for 12 h. Wash several times with ultrapure water to remove excess acid until neutral. Add 2 mL of hydrazine hydrate solution, 0.0127 g of polyvinyl alcohol, and 0.0189 g of polyacrylic acid. Stirred at room temperature for 1 hour, then transferred to a high-pressure autoclave lined with polytetrafluoroethylene and reacted at 110°C for 24 hours to form a polymer composite graphene hydrogel. After freezing at -76°C using a freeze dryer, it was dried for three days to obtain a polymer composite graphene aerogel. 0.2 g of the graphene aerogel, 0.69 g of paraffin wax and 40 mL of ultrapure water were taken and heated at 75°C for 24 hours to make it completely homogenized. Then, it was vacuum filtered through a carboxymethyl cellulose membrane with a pore size of 0.22 μm and freeze-dried.

[0101] First, the oxidized graphene suspension was acidified with a strong acid, and then the pH of the solution was adjusted with a weak base, hydrazine hydrate, to better expand the stacked oxidized graphene sheets into high-quality large sheets of oxidized graphene. Due to the lack of mutual repulsion, the oxidized graphene suspension is unstable in concentrated acid. When the pH decreases, the electrostatic repulsion weakens, while the hydrogen bonds are strengthened due to the protonation of the carboxyl groups. Therefore, stable GO gelation can be achieved by increasing the bonding force or weakening the repulsion force. The density of this polymer composite graphene aerogel is 0.676 g / cm³. 3The graphene aerogel in the composite phase change material has a mass fraction of 22.7 wt%. The melting point of the graphene aerogel / paraffin composite phase change material is 60.02℃, the enthalpy of fusion (endothermic) in the latent heat of phase change is 110.79 J / g, the crystallization temperature is 54.37℃, and the enthalpy of crystallization (exothermic) is 110.6 J / g. The thermal conductivity, calculated using the thermal conductivity formula, is 2 W·m. -1 ·K -1 The measured conductivity was 2.6 S·cm. -1 In this embodiment, the polymer-polymer composite graphene aerogel completely and uniformly adsorbs the organic paraffin melt, exhibiting good compatibility between the two. This effectively reduces interfacial thermal resistance, improves impedance matching, and demonstrates excellent multifunctionality, integrating heat dissipation, shielding, electrostatic discharge, and corrosion protection. The electromagnetic shielding performance of this graphene aerogel / paraffin composite phase change material is 35.6~47.2 dB in the X-band and 43.3~54.8 dB in the K-band (sample thickness 163 μm). During the heating-cooling cycle, the enthalpy of melting during the first heating cycle is 110.79 J / g, and the enthalpy of crystallization during cooling is 110.6 J / g; after the 20th cycle, the enthalpy of melting becomes 108.88 J / g, and the enthalpy of crystallization becomes 112.08 J / g. After heating-cooling cycles, the latent heat (endothermic) decreases by 1.7%, and the latent heat (exothermic) increases by 1.3%, indicating good cyclic thermal stability. See [link to relevant documentation]. Figure 11 .

[0102] Example 11

[0103] 125 mL of graphene suspension (1.5 mg / mL) was soaked in concentrated ammonia for 72 h, washed three times with distilled water, and 10 mL of hydrazine hydrate was added. After stirring for 3.5 h, 0.0244 g of polyvinyl alcohol and 0.0246 g of polyacrylic acid powder were added, and the mixture was stirred at room temperature for 4 h. The mixture was then transferred to a high-pressure reactor lined with polytetrafluoroethylene and reacted at 110 °C for 48 h to form a polymer composite graphene hydrogel. The hydrogel was then frozen at -76 °C for 2 h using a freeze dryer and vacuum dried for three days to obtain a polymer composite graphene aerogel. 0.2 g of graphene aerogel, 0.3609 g of paraffin wax, and 40 mL of ultrapure water were heated at 80 °C for 24 h to ensure complete homogenization. The mixture was then vacuum filtered through a carboxymethyl cellulose membrane with a pore size of 0.22 μm and freeze-dried.

[0104] In this embodiment, concentrated ammonia was used to soak the electrochemically prepared graphene oxide suspension to remove the solid electrolyte remaining on the graphene oxide sheets during the electrochemical exfoliation process, thereby obtaining graphene oxide with higher purity. Compared with Example 3 or Example 4, the amount of polyvinyl alcohol in the polymer matrix was doubled, while the amount of polyacrylic acid was the same as that of polyvinyl alcohol. The resulting polymer composite graphene aerogel had a diameter of 4.7 cm, a height of 5.7 cm, and a density of 0.1 g / cm³. 3The graphene aerogel in the composite phase change material has a mass fraction of 35.7 wt% and a thermal conductivity of 2.93 W·m. -1 ·K -1 The measured conductivity was 19.84 S·m. -1 Its electromagnetic shielding performance in the X-band is 40.7~57.8dB, and its electromagnetic shielding effectiveness in the K-band is 46.5~60dB (sample thickness is 300 μm). During the isothermal heating process at 50℃, when the surface temperature change of the sample was captured and recorded using an infrared thermometer, the surface temperature of the polymer composite graphene aerogel / paraffin composite phase change material in this embodiment rose relatively quickly. During the cooling process after the heat source was turned off for 60 seconds, the slope was slightly larger than that of paraffin, indicating that it cooled down faster than paraffin, which is attributed to its higher thermal conductivity than pure paraffin. Figure 13 As shown.

[0105] Example 12

[0106] Take 100 mL of electrochemically intercalated and exfoliated oxidized graphene suspension (7 mg / mL), add 5 mL of hydrazine hydrate, 0.0246 g of polyvinyl alcohol and 0.0368 g of polyacrylic acid, stir at room temperature for 1 h, then react in a high-pressure reactor lined with polytetrafluoroethylene at 110 °C for 24 h to form a polymer composite graphene hydrogel; freeze-dry at -68 °C for three days to obtain a polymer composite graphene aerogel; the polymer composite... Graphene aerogels were carbonized by continuously passing high-purity argon gas through them and heating at a rate of approximately 25°C / min to 2000°C for 2 hours. Then, they were heated from room temperature to 1000°C at maximum power, and then heated to 2000°C at a rate of 25°C / min. After that, they were heated to 2500°C at a rate of 10°C / min and then to 2800°C at a rate of 5°C / min. They were then carbonized at 2800°C for 1 hour to obtain nitrogen-hydrogen-oxygen co-doped graphene aerogels with higher thermal conductivity. 0.2 g of the high thermal conductivity nitrogen-hydrogen-oxygen co-doped graphene aerogel was heated with different masses of paraffin in a 40 mL constant temperature water bath at 80 °C for 24 h to ensure complete and uniform adsorption of the nitrogen-hydrogen-oxygen co-doped graphene aerogel and paraffin. The mixture was then vacuum filtered through a 0.22 μm pore size carboxymethyl cellulose membrane and freeze-dried to obtain GA / Paraffin composite phase change materials with thermally conductive filler contents of 22.7 wt%, 50 wt%, 66.5 wt%, 75.7 wt%, 94 wt%, and 96.5 wt%. In this example, the polymer composite graphene aerogel / composite phase change material films prepared with different thermally conductive fillers showed a gradual change in film surface color from a dark black to a grayish-black as the amount of thermally conductive filler increased. Figure 14 As shown.

[0107] Graphene oxide was reduced using a chemical reduction method, with hydrazine hydrate used as the reducing agent, to obtain high-quality reduced graphene oxide. A graphene aerogel was synthesized by adding a polymer matrix to achieve surface modification of the reduced graphene oxide. Compared with Example 3 or Example 4, the amounts of polyvinyl alcohol and polyacrylic acid in the polymer matrix of this example were doubled, resulting in a cylindrical nitrogen-hydrogen-oxygen co-doped graphene aerogel with a diameter of 3.5 cm and a height of 3 cm, and a density of 1.22 g·cm³. -3 .

[0108] In this embodiment, the graphene aerogel content in the phase change material ranges from 22.7 wt% to 96.5 wt%, and the thermal conductivity of the polymer composite graphene aerogel / paraffin composite phase change material ranges from 1.4 to 8.3 W·m. -1 ·K -1 The thermal conductivity of the carbonized and graphitized nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material is 8.5~76.6 W·m. -1 ·K -1 When the content of high-temperature heat-treated graphene aerogel in the phase change material is 75.7 wt%, the thermal conductivity of the composite phase change material can reach up to 76.4 W·m. -1 ·K -1 Compared with pure paraffin (thermal conductivity 0.21 W·m), -1 ·K -1 Compared to the previous example, this represents a 363.8-fold improvement. The electrical conductivity of the polymer composite graphene aerogel / paraffin composite phase change material described in this embodiment is 1.9–101.2 S·cm. -1 The electrical conductivity of the nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material treated with carbonization and graphitization is 3~288.6 S·cm. -1 When the content of graphitized nitrogen-hydrogen-oxygen co-doped graphene aerogel in the phase change material is 75.7 wt%, the electrical conductivity of the composite phase change material can reach up to 218.5 S cm⁻¹. -1 Superior to metal oxides (~102S cm⁻¹) -1 The thermal conductivity of polymer-coated graphene aerogel / paraffin composite phase change materials increases with increasing graphene aerogel loading; while the thermal conductivity of nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change materials increases first and then decreases. The electrical conductivity of both polymer-coated graphene aerogel / paraffin composite phase change materials and nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change materials increases with increasing thermally conductive filler content. (See...) Figure 15 .

[0109] In this embodiment, when the thickness of the nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material film is 100~420μm, the total electromagnetic interference (EMI) shielding effectiveness (MEI) is 43.1~51.3 dB in the X-band (8–12.4 GHz), with an MEI shielding efficiency of over 99.995% in the X-band; it also exhibits excellent MEI shielding effectiveness in the K-band (18–26.5 GHz), reaching 72~115 dB, with an MEI shielding efficiency of 100% across the entire band. See Figure 17 and Figure 18 .

[0110] During the electrothermal conversion process, voltages of 2V, 2.5V, and 3V were applied to the nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material of this embodiment, respectively. A significant broad plateau appeared between 300 and 1200 s, indicating that the composite phase change material converts electrical energy into heat energy for storage. After the power supply was turned off at 1200 s, the sample rapidly cooled down between 1200 and 1700 s, releasing heat energy. In the energy storage and conversion process, the heat energy storage plateau of the nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material of this embodiment was significantly wider than that of Examples 2 and 14, indicating that it can store more energy. Furthermore, the heating and cooling slopes of this embodiment were also greater than those of Examples 2 and 14, indicating that the polymer composite graphene aerogel / paraffin composite phase change material of this embodiment has a faster rate of heat absorption and release, attributed to its higher thermal conductivity. See [link to relevant documentation]. Figure 19 .

[0111] Example 13

[0112] 50 mL of electrochemically intercalated graphene suspension (3 mg / mL) was soaked in an appropriate amount of concentrated ammonia water for 48 h. After soaking, it was washed three times with distilled water and vacuum filtered through a 0.22 μm carboxymethyl cellulose membrane. 2 mL of hydrazine hydrate was added, and the mixture was sonicated for 5 min. 0.242 g of polyvinyl alcohol and 0.0187 g of polyacrylic acid were added, and the mixture was stirred at room temperature for 1 h. The mixture was then reacted in a high-pressure autoclave lined with polytetrafluoroethylene at 110 °C for 24 h to form a polymer composite graphene hydrogel. After freezing at -68 °C using a freeze dryer, the hydrogel was dried for three days to obtain a polymer composite graphene aerogel. 0.5023 g of the graphene aerogel, 0.508 g of paraffin wax, and 40 mL of ultrapure water were heated at 75 °C for 24 h to make it completely homogenized, and then dried in a vacuum oven at 60 °C for 12 h.

[0113] Graphene oxide was reduced using a chemical reduction method, with hydrazine hydrate as the reducing agent, to form reduced graphene oxide. A polymer matrix was then added to synthesize graphene aerogel, achieving surface modification of the reduced graphene oxide. Compared to Example 3 or Example 4, the amount of polyvinyl alcohol in the polymer matrix was doubled, while the amount of polyacrylic acid remained unchanged. The resulting polymer composite graphene aerogel had a diameter of 4.4 cm, a height of 2 cm, and a density of 0.645 g / cm³. 3 The polymer-polymer composite graphene aerogel in the composite phase change material has a mass fraction of 50 wt% and a thermal conductivity of 3.9 W·m. -1 ·K -1 The measured conductivity was 23 S·cm. -1 The electromagnetic shielding performance in the X-band was 48.5~62.9dB, and the electromagnetic shielding effectiveness in the K-band was 51.7~70dB (sample thickness was 280 μm). Electrothermal conversion tests were performed on the polymer composite graphene aerogel film of this embodiment by applying voltages of 2V, 2.5V, and 3V respectively. When the voltage was 2.5V or 3V, the sample temperature rapidly reached 120~137℃ in about 300s without a significant buffer plateau, indicating that the polymer composite graphene aerogel did not store energy. Figure 19 As shown.

[0114] Example 14

[0115] 100 mL of oxidized graphene suspension (3 mg / mL) was mixed with 10 mL of hydrazine hydrate and stirred for 8.5 h. Then, 0.012 g of polyvinyl alcohol and 0.0189 g of polyacrylic acid were added, and the mixture was stirred at room temperature for 17 h. The mixture was then transferred to a high-pressure autoclave lined with polytetrafluoroethylene and hydrothermally reacted at 110 °C for 48 h to form a polymer composite graphene hydrogel. This hydrogel was then frozen at -73 °C for 2 h using a freeze dryer and vacuum dried for 87 h to obtain a polymer composite graphene aerogel. 0.2 g of the graphene aerogel, 0.27 g of paraffin wax, and 40 mL of ultrapure water were heated at 80 °C for 24 h to ensure complete homogenization. The mixture was then vacuum filtered through a carboxymethyl cellulose membrane with a pore size of 0.22 μm and freeze-dried.

[0116] In this embodiment, the mass ratio of polyvinyl alcohol to polyacrylic acid is 2:3. The frustum-shaped polymer composite graphene aerogel has a top diameter of 3.5 cm, a bottom diameter of 3.9 cm, a height of 4.3 cm, and a density of 0.712 g / cm³. 3 The graphene aerogel in the composite phase change material has a mass fraction of 42.6 wt%. The melting point of the phase change composite material is 57.51℃, with a latent heat (endothermic) of 116.8 J / g. The crystallization temperature is 57.13℃, with a latent heat (exothermic) of 119.8 J / g. Its thermal conductivity is 2.5 W·m. -1 ·K -1The conductivity is 20.7 S·cm. -1 The phase change composite film has a thickness of 190 μm and exhibits electromagnetic shielding performance of 43.5–60.9 dB in the X-band and 43–67.4 dB in the K-band. During the electrothermal conversion process of the polymer-composite graphene aerogel / paraffin composite phase change material in this embodiment, voltages of 2, 2.5, and 3 V were applied. A clear plateau appeared between 450 and 1200 s, indicating that the composite phase change material converts electrical energy into heat energy for storage. After the power supply was turned off at 1200 s, the sample rapidly decreased in temperature between 1200 and 1700 s, releasing the heat energy. See [link to relevant documentation]. Figure 19 In the energy storage and conversion process of this embodiment, an electrochemical workstation was used to apply working voltages of 2V, 2.5V, and 3V, and the current-time curves of the polymer composite graphene aerogel / paraffin composite phase change material were measured. Initially, the current gradually increased, and then stabilized after 100-200 seconds. See [link to relevant documentation]. Figure 20 .

[0117] The energy storage and conversion test methods described in Examples 2, 12, 13, and 14 involve placing the sample in an insulated environment, providing voltage with a DC power supply, measuring the temperature change of the sample with a temperature sensor, recording the data using a data recording system, and then transmitting the data to a computer. Figure 20 As shown.

Claims

1. A method for preparing a polymer composite graphene aerogel, characterized in that... Includes the following steps: A) Take 50-150 mL of oxidized graphene suspension and stir continuously in 5-15 mL of high-concentration alkaline medium for 6-48 h to achieve preliminary reduction; add polymer matrix to oxidized graphene suspension in a ratio of 1-2 parts polymer matrix to 30-90 parts oxidized graphene; stir magnetically for 3-18 h, then transfer to a high-temperature and high-pressure reactor for hydrothermal reaction at 110-120℃ for 24-48 h to obtain polymer composite graphene hydrogel through hydrothermal reduction reaction. The alkaline medium is one of concentrated ammonia, hydrazine hydrate, or ethylenediamine. The polymer matrix is ​​a polyol and a polyacid, selected from a group consisting of polyvinyl alcohol and polyacrylic acid, polypropylene alcohol and polyacetic acid, polyethylene glycol and polyethylene glycol, and polybutenol and polypropionic acid; the polymer matrix undergoes a polymerization reaction in the system, and then the polymer chain free radicals and graphene oxygen-containing functional groups combine through covalent bonds, hydrogen bonds and van der Waals interactions to construct a three-dimensional interconnected porous network structure; B) The obtained polymer composite graphene hydrogel is first frozen at -80 to -40℃ for 2 to 6 hours or directly frozen with liquid nitrogen for 10 to 30 minutes, and then vacuum dried for 1 to 3 days to obtain polymer composite graphene aerogel. The obtained polymer composite graphene aerogel was subjected to carbonization and graphitization treatment to obtain nitrogen, hydrogen and oxygen co-doped graphene aerogel. The specific operation process of the carbonization and graphitization treatment is as follows: during the continuous passage of high-purity argon gas, the temperature is increased at a rate of 25℃ / min, and the carbonization treatment is maintained at 2000℃ for 2 hours. Then, the temperature is rapidly increased from room temperature to 1000℃, and then increased to 2000℃ at a rate of 25℃ / min. After that, the temperature is increased to 2500℃ at a rate of 10℃ / min, and then increased to 2800℃ at a rate of 5℃ / min for 1 hour for graphitization post-treatment.

2. The method for preparing polymer composite graphene aerogel according to claim 1, characterized in that: The oxidized graphene suspension described in step A) is prepared by an electrochemical method, and its mass concentration is 1–40.88 mg / mL. Polymerization reactions include solution polymerization self-assembly, hydrothermal methods, chemical reduction methods, freeze drying methods, high-temperature heat treatment, and one or more preparation methods combined.

3. The method for preparing polymer composite graphene aerogel according to claim 2, characterized in that: When the polymer matrix is ​​subjected to solution polymerization, heating at 100-120℃ for 12-48 hours or stirring at room temperature for 6-18 hours, adding one or two drops of acid catalysis, dehydration condensation, and forming more abundant functional groups, including hydroxyl, amino, carboxyl, ester, carbonyl or amide, effectively realizes the functionalization of graphene, enhances interfacial compatibility, and optimizes impedance matching. When using the hydrothermal method, the reaction temperature is 110–120℃ and the reaction time is 12–48 h; The mass ratio of polyol to polyacid in the polymer matrix is ​​1.5 to 9:

3.

4. A polymer composite graphene aerogel prepared by the method according to any one of claims 1 to 3, characterized in that: The polymer-composite graphene aerogel is in the form of blocks, discs, frustums, or cylinders; the graphene aerogel is very lightweight, with a density of 0.027~1.37 g·cm³. -3 ; The thermal conductivity and electrical conductivity of the polymer composite graphene aerogel are 7.6~9.33 W·m, respectively. -1 ·K -1 and 28.59~83.29 S·cm -1 When the thickness of the sample is between 100 and 420 micrometers, its electromagnetic interference shielding effectiveness is 43.2 to 70.5 dB in the X-band of 8.2–12.4 GHz and 49.3 to 77.4 dB in the K-band of 18–26.5 GHz. The thermal conductivity and electrical conductivity of the nitrogen-hydrogen-oxygen co-doped graphene aerogel after carbonization and graphitization treatment are 60~85.4 W·m, respectively. -1 ·K -1 and 350~470 S·cm -1 When the sample thickness is between 100 and 420 micrometers, its electromagnetic interference shielding effectiveness in the X-band is 37.9 to 68 dB, and its electromagnetic interference shielding effectiveness in the K-band reaches 57 to 107.8 dB.

5. A composite phase change material made from the polymer-graphene aerogel as described in claim 4, characterized in that: Polymer composite graphene aerogel or nitrogen-hydrogen-oxygen co-doped graphene aerogel are used as thermally conductive fillers, and solid paraffin is used as a phase change material. The weight proportions of each raw material are as follows: graphene aerogel: 20~90 parts, solid paraffin: 5~340 parts, water: 3~7 parts; The obtained composite phase change materials contained graphene aerogel with a mass fraction of 3 wt%–96.5 wt%, and the sample thickness ranged from 100 to 420 μm. The thermal conductivity of the polymer-polymer composite graphene aerogel / paraffin composite phase change materials ranged from 1.4 to 8.3 W·m. -1 ·K -1 The electromagnetic interference (EMI) shielding effectiveness in the X-band is 34.1–72 dB, and in the K-band it reaches 42.5–110 dB; the thermal conductivity of the carbonized and graphitized nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material is 8.5–79.6 W·m. -1 ·K -1 The electromagnetic interference shielding effectiveness in the X-band is 40~61.3dB, and the electromagnetic interference shielding effectiveness in the K-band reaches 61.9~115dB. By adjusting the amount of organic paraffin added, the thickness and density of the phase change material can be adjusted, thereby achieving adjustable electromagnetic shielding band and effectiveness of the composite phase change material, while also providing corrosion resistance and heat dissipation.

6. A method for preparing a composite phase change material made from polymer-composite graphene aerogel as described in claim 5, characterized in that: Polymer composite graphene aerogel or nitrogen-hydrogen-oxygen co-doped graphene aerogel and solid paraffin are dispersed in ultrapure water, heated to 60~80℃, stirred for 12~24h and then dried to obtain a sheet-like solid material that has completely and uniformly adsorbed paraffin; this is the polymer composite graphene aerogel / paraffin composite phase change material or nitrogen-hydrogen-oxygen co-doped graphene aerogel / paraffin composite phase change material.

7. The application of a composite phase change material made from polymer composite graphene aerogel as described in claim 5 in the efficient shielding of electromagnetic interference in electronic devices.

8. The application of a composite phase change material made from the polymer composite graphene aerogel as described in claim 5 in thermal conductivity and energy storage.

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