MXene-based aerogels and phase-change composite materials based on MXene

Abstract

The present invention belongs to the technical field of phase change composite materials. To solve the problem that the thermal management and electromagnetic shielding functions of phase change composite materials cannot be compatible, polyethyleneimine (PEI) and carboxymethyl cellulose (CMC) are added to the aqueous dispersion of titanium carbide (Ti3C2T x ), nanosheets (MXene) to obtain a uniformly dispersed mixed solution. The mixed solution is directionally frozen in liquid nitrogen and then vacuum freeze-dried to obtain an MXene-based aerogel framework MCP. The molten phase change material is adsorbed by vacuum impregnation to obtain a shape-stable phase change composite material, which not only has excellent thermal conductivity and electrical conductivity, but also has a stable electrothermal conversion energy storage capacity and good electromagnetic shielding performance, providing opportunities for meeting the multi-scenario response and practical applications of multifunctional composite materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of phase change composite materials, and relates to a phase change composite material with excellent thermal conductivity, electromagnetic interference shielding and electrothermal conversion energy storage performance, and in particular to a multifunctional phase change composite material based on a MXene-based aerogel skeleton and a preparation method thereof. Background Art

[0002] Fossil fuels have played an important role in the development of human beings and have promoted the significant development of human civilization. However, the consumption of fossil fuels has also caused many side effects and irreversible damage to the environment and climate. In the contradiction between energy consumption and environmental issues, the top priority is to reduce the pollution caused by existing fuels and develop more economical and efficient green energy.

[0003] Thermal energy storage (TES), as an important form of renewable energy, can effectively solve the spatial and temporal limitations of other renewable resources such as solar energy, wind energy and hydropower. Among them, the thermal energy storage of phase change material (PCM) is a form of energy storage with less temperature restrictions and high efficiency, mainly due to its characteristic of reversibly absorbing and releasing thermal energy during melting and freezing when phase change occurs. At present, many organic solid-liquid phase change materials (SLPCMs) have been widely used in the field of thermal energy storage as latent heat storage materials.

[0004] However, leakage, as an inherent property of phase change materials, has caused great limitations in their application. At the same time, the low thermal conductivity has also hindered the application of phase change materials to a certain extent.

[0005] At present, the shape skeleton or shape stabilization technology is mainly used to package and fix the phase change material. Although the effective packaging technology solves the key problem of easy leakage of phase change materials, it still faces the disadvantages of low thermal conductivity and poor electromagnetic shielding ability during application, resulting in limited application scenarios. Enhancing material performance and developing phase change composite materials (PCCs) with excellent properties such as thermal management and electromagnetic interference shielding or even more properties have become key problems to be overcome at this stage.

[0006] Nanomaterials have high electrical conductivity, wide absorption spectrum range and high thermal conductivity. Adding nanomaterials is a promising solution to the thermal conductivity and electromagnetic interference shielding problems of phase change materials. Titanium carbide (Ti3C2Tx) nanosheets (MXene) are a two-dimensional nanomaterial developed in 2011 with excellent electrical conductivity, flexible size adjustment, strong localized surface plasmon resonance effect and abundant surface functional groups.

[0007] Xie et al. (Yuqiong Xie, Minming Zou, Xiao Shikun, Wenjing Chen, Yichi Liu, Xiaowu Hu, Xiongxin Jiang, Yinshui He, Qinglin Li. MXene-modified bio-based pitaya peel foam / polyethylene glycol composite phase change material with excellent photo-thermal conversion efficiency, thermal energy storage capacity and thermal conductivity. Journal of energy storage . 2024, 78:https: / / doi.org / 10.1016 / j.est.2023.110089.) A novel multifunctional phase change composite material was prepared by encapsulating polyethylene glycol (PEG) into MXene-modified pitaya peel-based porous carbon using a simple vacuum impregnation method. The MXene-modified bio-based pitaya peel foam / PEG phase change composite material (PEG / BPC@M) exhibited a high loading ratio (95.4%) and a thermal conductivity of 0.566 W / m·K.

[0008] Jiang et al. (Lili Jiang, Wenqiang Zhang, Ruijia Zhang, Zhengbiao Hu,Jiahao Yang, Xiaoxu Ma, Jiaming Fan. High latent heat phase change materialscomposites based on MXene / biomass-derived cellulose nanocrystalline aerogel for solar-thermal energy conversion and storage. Ceramics International,2024. 50: 17428-17438. https: / / doi.org / 10.1016 / j.ceramint.2024.02.231) A novel tetradecylamine / MXene / cellulose nanocrystal phase change composite (TDA / MXene / CNC CPCM) was prepared by vacuum impregnation method, with a TDA loading rate of up to 90.6wt%. In addition, the thermal conductivity of TDA / MXene / CNC CPCM-5 was 0.491W / m·K.

[0009] Zheng et al. (Zhiheng Zheng, Huan Lui, Dezhen Wu, Xiaodong Wang. Polyimide / MXene hybrid aerogel-based phase-change composites for solar-driven seawater desalination. Chemical Engineering Journal , 2022, 440: https: / / doi.org / doi:10.1016 / J.CEJ.2022.135862.) A new phase change composite material was developed using polyimide (PI) / MXene hybrid aerogel as the supporting material and PEG as the phase change material. The material has a latent heat of 170 J / g and a thermal conductivity of 0.3533 W / m·K.

[0010] It can be seen that the performance of the above-mentioned phase change composite materials is not outstanding due to the serious stacking tendency of MXene nanosheets and the weak interconnection between adjacent nanosheets. Even though MXene in the form of three-dimensional aerogel can better adsorb phase change materials and encapsulate them in porous skeletons to prevent leakage during the phase change process, the intermolecular interaction force of the phase change material is weak due to the inability to form an interconnected structure, and heat is not easily transferred. Due to its short chain structure and dispersed arrangement, the thermal conductivity cannot be better improved, resulting in the thermal conductivity coefficients of the above-mentioned phase change composite materials not being too high.

[0011] At the same time, none of the above documents mentions the electromagnetic shielding performance of phase change composite materials. Phase change materials themselves do not have electromagnetic shielding performance. Even with the support of functional materials such as MXene, it is difficult to ensure the electromagnetic shielding performance of composite materials because it cannot form a regular arrangement in the aerogel structure. Summary of the invention

[0012] The purpose of the present invention is to solve the serious problem of MXene stacking and provide a MXene-based aerogel that can be regularly arranged to form a continuous three-dimensional interconnected network structure.

[0013] Another purpose of the present invention is to provide a phase change composite material based on the MXene-based aerogel as a skeleton to solve the problem that the current phase change composite materials are difficult to stably exert thermal management and electromagnetic shielding performance.

[0014] The present invention first provides a MXene-based aerogel, which is a MXene-based aerogel skeleton MCP obtained by adding PEI and CMC to a MXene aqueous dispersion to disperse evenly to obtain a mixed solution, directionally freezing in liquid nitrogen, and vacuum freeze-drying.

[0015] Furthermore, in the MXene-based aerogel skeleton MCP described in the present invention, the mass ratio of MXene to PEI and CMC is preferably 1:(1-3.5):(1-3.5).

[0016] Furthermore, the concentration of the MXene aqueous dispersion is preferably 5 to 10 mg / mL.

[0017] In the present invention, PEI and CMC are added to the MXene aqueous dispersion and stirred for not less than 30 minutes to obtain a mixed solution by uniform dispersion.

[0018] Specifically, the present invention is to put the mixed solution into a polytetrafluoroethylene mold with a copper plate at the bottom, and immerse it in liquid nitrogen for directional freezing.

[0019] The directional freezing described in the present invention is accomplished with the aid of a specific mold. The entire mold is made of polytetrafluoroethylene, with only the bottom being set as a copper plate, so that the heat of the mixed solution can only be exchanged with liquid nitrogen in a directional and rapid manner through the bottom copper plate, thereby forming an ice crystal structure from bottom to top.

[0020] If MXene is directly freeze-dried, although a three-dimensional aerogel structure can be obtained, the supporting force of the aerogel structure is very weak. Not only can it not adsorb phase change materials, but it will also cause serious stacking, affecting the basic performance of the aerogel.

[0021] Therefore, in order to give full play to the characteristics of MXene nanosheets and ensure their excellent mechanical properties, the present invention first uses a polymer or nanomaterial carboxymethyl cellulose (CMC) containing oxygen polar groups to assemble a high-strength functional nanocomposite material with MXene through hydrogen bonding interactions. Based on the unique one-dimensional filamentous macrostructure of CMC, the insulating contact between the two-dimensional materials of the aerogel constructed by the hydrogen bonding interaction between CMC and MXene is reduced, similar to the "brick and tile" toughening mechanism to support the arrangement of MXene nanosheets. However, due to the weak interaction force between the interfaces of the two, the aerogel structure formed is not sufficient to support more MXene, the functional filler is too little, and the overall performance of the aerogel is still not ideal.

[0022] Furthermore, the present invention further enhances the interfacial interaction between CMC and MXene by adding PEI (polyethyleneimine). Through hydrogen bonding, PEI and CMC achieve a "mortar"-like effect and are firmly interlocked with the MXene "bricks", ultimately forming a strong aerogel structure that can be well used for adsorbing phase change materials.

[0023] In the process of liquid nitrogen freezing to form aerogel, if the ordinary direct quick freezing process is adopted, the temperature is not low enough to quickly and directly form ice crystals. Although the formed aerogel can adsorb phase change materials, the MXene therein is severely stacked and cannot be arranged regularly to form a three-dimensional interconnected structure.

[0024] Therefore, the present invention further adopts a directional freezing method so that MXene can be gradually firmly supported by PEI and CMC. At the same time, by taking advantage of the difference in thermal conductivity between copper and polytetrafluoroethylene, the ice crystals are oriented to induce them to be regularly arranged to form a continuous three-dimensional arrangement network. This can not only construct an aerogel structure with a high loading rate, but also have more properties such as thermal management and electromagnetic shielding.

[0025] Secondly, the present invention also uses the MXene-based aerogel to prepare a multifunctional phase-change composite material. Specifically, the MXene-based aerogel is used as a skeleton, and it also acts as a thermal conductor and a conductive filler. The molten phase-change material is adsorbed by vacuum impregnation to obtain a shape-stable phase-change composite material.

[0026] Furthermore, in the phase change composite material prepared by the MXene-based aerogel of the present invention, the loading amount of the phase change material can reach 90 to 98% of the total mass of the phase change composite material.

[0027] Wherein, the phase change material can be any one of polyethylene glycol (PEG), polymethyl methacrylate (PMMA) or polystyrene (PS).

[0028] Furthermore, the phase change material of the present invention is preferably PEG.

[0029] The phase change composite material prepared by the present invention not only has excellent thermal conductivity and electrical conductivity, but also has stable electrothermal conversion energy storage capacity and good electromagnetic interference shielding performance, integrating multiple functions into one, and is a new type of phase change composite material.

[0030] The present invention maximizes the excellent performance of MXene, prevents the stacking of its nanosheets, and forms a regular arrangement of nanosheets in the process of converting two-dimensional materials to construct three-dimensional aerogel, thereby forming a continuous three-dimensional interconnected network, and finally compounding it with a phase change material through a vacuum impregnation method to obtain a phase change composite material with both excellent properties of thermal management and electromagnetic interference shielding.

[0031] The phase change composite material prepared by the present invention has a thermal conductivity of up to 1.43 W / m·K, and an electromagnetic interference shielding effectiveness (EMI SE) of up to 53.7 dB, which is much higher than the commercial standard of 20 dB. It can not only further protect the human body and electronic equipment from electromagnetic pollution other than thermal runaway, but also has broad application prospects in electrothermal energy storage and thermal management of electronic equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 These are the SEM images and EDS spectra of the aerogel skeleton MCP-2 and the phase change composite material MCP-2@PEG.

[0033] Figure 2 This is the XPS energy spectrum of the aerogel skeleton MCP-1 and the phase change composite material MCP-1@PEG.

[0034] Figure 3 It is the Fourier transform infrared spectrum of phase change composite materials and raw materials.

[0035] Figure 4 It is the XRD diagram of phase change composite materials and raw materials.

[0036] Figure 5 It is the DSC curve diagram of different phase change composite materials.

[0037] Figure 6 It is the result of shape stability measurement of different phase change composite materials.

[0038] Figure 7 It is the EMI SE test diagram of different phase change composite materials.

[0039] Figure 8 It is a diagram of the EMI SE mechanism of different phase change composites.

[0040] Fig. 9 It is a graph of thermal conductivity of different phase change composite materials.

[0041] Fig.10 It is a diagram of the electrical conductivity of different phase change composite materials.

[0042] Fig.11 This is a test diagram of the electrothermal conversion capability of the phase change composite material MCP-2@PEG. Implementation

[0043] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solution of the present invention so that those skilled in the art can well understand and utilize the present invention, rather than limiting the scope of protection of the present invention.

[0044] The production processes, experimental methods or detection methods involved in the embodiments of the present invention, unless otherwise specified, are all conventional methods in the prior art, and their names and / or abbreviations are all conventional names in the field, and are very clear and unambiguous in the relevant application fields. Technical personnel in the field can understand the conventional process steps based on the names and apply the corresponding equipment, and implement them according to conventional conditions or the conditions recommended by the manufacturer.

[0045] The various instruments, equipment, raw materials or reagents used in the embodiments of the present invention are not particularly limited in terms of their sources, and are all conventional products that can be purchased through regular commercial channels, or can be prepared according to conventional methods well known to those skilled in the art.

[0046] The raw material MXene solution used in the embodiment of the present invention is prepared by etching Ti3AlC2 MAX phase precursor with LiF. Specifically, 2g LiF is added to 30mL of 12M HCl solution, stirred continuously for 30min, 2g Ti3AlC2 MAX phase precursor is added, stirred at 35°C for 24h, and the Al layer is etched away; deionized water is added to the solution after etching, centrifuged at 8000 rpm for 10min, the supernatant is discarded, deionized water is continued to be added, and the above operation is repeated 6 to 7 times until the pH value of the supernatant is 6, and the washing is completed; the product is placed in low-temperature ethanol at 0 to 30°C, and ultrasonicated at 40kHz for 10 min under an inert atmosphere, during which ice bags or ice cubes are used for cooling, and the dark green supernatant containing layered MXene nanosheets is collected as the raw material of the MXene solution.

[0047] After freeze-drying the prepared MXene solution raw material at -40°C for 48 hours, solid Ti3C2Tx nanosheets can be obtained. After weighing, the concentration of the MXene solution is calculated to be 12.15 mg / mL.

[0048] The above MXene solution, PEI and CMC were used as raw materials, and the mixed solution was evenly dispersed with water, placed in a polytetrafluoroethylene mold with a copper plate at the bottom, immersed in liquid nitrogen for directional freezing, vacuum dried, and taken out to obtain a MXene / CMC / PEI (MCP) aerogel skeleton. PEG-8000 was then used as a phase change material and adsorbed into the MCP aerogel skeleton by vacuum impregnation to obtain a shape-stable phase change composite material MCP@PEG. Example

[0049] Example 1

[0050] Add 7.5 ml of MXene solution to a beaker containing 10 ml of deionized water, and then add 0.3 g of PEI and 0.3 g of CMC solid powder. Stir evenly in a magnetic stirrer for 30 min to obtain a mixed solution after uniform dispersion.

[0051] The mixed solution was loaded into a polytetrafluoroethylene mold with a copper plate at the bottom, immersed in liquid nitrogen for directional freezing, and then the mold was placed in a vacuum freeze dryer for 48 hours to prepare an aerogel skeleton MXene / CMC / PEI, which was recorded as MCP-1.

[0052] The MCP-1 prepared above was placed in a beaker containing excess PEG by vacuum impregnation method and placed in a vacuum oven at 70°C to allow MCP-1 to fully absorb the molten PEG. After repeated vacuum adsorption three times, the excess PEG on the surface of MCP-1 was removed with filter paper to obtain a shape-stable phase change composite material, which was recorded as MCP-1@PEG.

[0053] Example 2

[0054] Add 7.5 ml of MXene solution to a beaker containing 10 ml of deionized water, and then add 0.2 g of PEI and 0.2 g of CMC solid powder. Stir evenly in a magnetic stirrer for 30 min to obtain a mixed solution after uniform dispersion.

[0055] The mixed solution was loaded into a polytetrafluoroethylene mold with a copper plate at the bottom, immersed in liquid nitrogen for directional freezing, and then the mold was placed in a vacuum freeze dryer for 48 hours to prepare an aerogel skeleton MXene / CMC / PEI, which was recorded as MCP-2.

[0056] PEG was adsorbed into the MCP-2 prepared above by vacuum impregnation at 70°C. After repeated vacuum adsorption three times, excess PEG on the surface of MCP-2 was removed with filter paper to obtain a shape-stable phase change composite material, which was recorded as MCP-2@PEG.

[0057] Example 3

[0058] Add 7.5 ml of MXene solution to a beaker containing 10 ml of deionized water, and then add 0.1 g of PEI and 0.1 g of CMC solid powder. Stir evenly in a magnetic stirrer for 30 min to obtain a mixed solution after uniform dispersion.

[0059] The mixed solution was loaded into a polytetrafluoroethylene mold with a copper plate at the bottom, immersed in liquid nitrogen for directional freezing, and then the mold was placed in a vacuum freeze dryer for 48 hours to prepare an aerogel skeleton MXene / CMC / PEI, which was recorded as MCP-3.

[0060] PEG was adsorbed into the MCP-3 prepared above by vacuum impregnation at 70°C. After repeated vacuum adsorption three times, excess PEG on the surface of MCP-3 was removed with filter paper to obtain a shape-stable phase change composite material, which was recorded as MCP-3@PEG.

[0061] Comparative Example 1

[0062] A mixed solution was prepared according to Example 1, loaded into a polytetrafluoroethylene mold without a copper plate at the bottom, immersed in liquid nitrogen for non-directional freezing, and dried in a vacuum freeze dryer for 48 hours to prepare a MXene-based aerogel skeleton MXene / CMC / PEI, recorded as MCP-4.

[0063] The MCP-4 prepared above was placed in a beaker containing excess PEG by vacuum impregnation method and placed in a vacuum oven at 70°C to allow MCP-4 to fully absorb the molten PEG. After repeated vacuum adsorption three times, the excess PEG on the surface of MCP-4 was removed with filter paper to obtain a shape-stable phase change composite material, which was recorded as MCP-4@PEG.

[0064] Comparative Example 2

[0065] Take a certain amount of MXene solution, stir it evenly in a magnetic stirrer for 30 minutes to make the solution evenly dispersed, put it into a polytetrafluoroethylene mold with a copper plate at the bottom, immerse it in liquid nitrogen for directionally freezing, and then put the mold into a vacuum freeze dryer for 48 hours to prepare a MXene aerogel skeleton.

[0066] The prepared MXene was placed in a beaker containing PEG and placed in a vacuum oven at 70°C. An attempt was made to adsorb the molten PEG into the interior of the MXene by vacuum impregnation. As a result, the MXene aerogel skeleton collapsed directly and the molten PEG could not be adsorbed to obtain a phase change composite material.

[0067] This is because the supporting force of the pure MXene aerogel skeleton is very weak. Not only can it not adsorb molten PEG in a vacuum environment, but it will also cause serious stacking due to the vacuum conditions, affecting its basic performance.

[0068] Comparative Example 3

[0069] 7.5 ml of MXene solution and 0.3 g of CMC solid powder were added to a beaker containing 10 ml of deionized water, and the mixture was stirred evenly in a magnetic stirrer for 30 min to obtain a mixed solution.

[0070] The mixed solution was loaded into a polytetrafluoroethylene mold with a copper plate at the bottom, immersed in liquid nitrogen for directional freezing, and then the mold was placed in a vacuum freeze dryer for 48 hours to prepare a MXene-based aerogel skeleton MXene-CMC.

[0071] It can be clearly observed that the prepared aerogel skeleton not only has too large pores, but also has extremely uneven pore size distribution, and even has large vacancies. When PEG is vacuum adsorbed by MXene-CMC, the molten PEG cannot be adsorbed and encapsulated in the aerogel skeleton to obtain a phase change composite material.

[0072] The aerogel skeleton MXene-CMC supports the arrangement of MXene nanosheets through the hydrogen bond interaction between CMC and MXene, similar to the "brick and tile" toughening mechanism. However, due to the weak interfacial interaction between the two, CMC is not sufficient to support more MXene, and ultimately cannot form a three-dimensional aerogel skeleton structure, and cannot achieve the adsorption of PEG.

[0073] Comparative Example 4

[0074] 7.5 ml of MXene solution and 0.3 g of PEI were added to a beaker containing 10 ml of deionized water, and the mixture was stirred evenly in a magnetic stirrer for 30 min to obtain a mixed solution after being evenly dispersed.

[0075] The mixed solution was loaded into a polytetrafluoroethylene mold with a copper plate at the bottom, immersed in liquid nitrogen for directionally freezing, and then the mold was placed in a vacuum freeze dryer for 48 hours. The prepared MXene-PEI could not form a basic three-dimensional aerogel structure, but directly shrank into a ball. No pores were found, and the aerogel skeleton could not be obtained.

[0076] Due to the lack of CMC support and the extensive aggregation of MXene by PEI, serious agglomeration occurred during the aggregation process of MXene, resulting in the inability to form a three-dimensional aerogel structure, and it could not serve as a skeleton for adsorbing PEG.

[0077] Application Example 1

[0078] Firstly, the microstructures of aerogel skeleton MCP-2 and phase change composite material MCP-2@PEG were characterized by scanning electron microscopy.

[0079] Figure 1(a) and (a') are SEM images of the aerogel skeleton MCP-2 at different magnifications. It can be observed that the aerogel skeleton has a highly interconnected porous three-dimensional structure. The reason for the formation of this three-dimensional framework is mainly due to the use of directional freezing, which makes the ice crystals generated during the freezing process grow in a vertical direction and form a unidirectional void channel during the freeze-drying process. During the directional freezing and freeze-drying process, the interaction between molecules purposefully resists the expansion resistance brought by the ice crystal growth process and overcomes the capillary tension during the ice crystal sublimation process, so that the final MCP aerogel skeleton has a stable structure and can more effectively adsorb phase change materials. At the same time, because the MXene sheets are arranged vertically along the ice crystals and grow in an orderly and directional manner, they form a continuous structure and a continuous path, which can play a great role in the thermal conductivity and electromagnetic shielding properties of the formed phase change composite material.

[0080] Figure 1 (b) and (b') are SEM images of the phase change composite material MCP-2@PEG after the aerogel skeleton MCP-2 is loaded with PEG at different magnifications. It can be clearly seen that PEG is fully infiltrated into the porous structure of the MCP aerogel skeleton, and the gap between MCP and PEG is very small, with almost no obvious boundary line, indicating that PEG and the MCP aerogel skeleton can be well compatible and PEG is fully filled into the aerogel skeleton. This is mainly due to the interconnected pathways of the aerogel skeleton. During the melting process of PEG, it can easily penetrate into the aerogel skeleton through these pathways, and accompanied by the blessing of vacuum conditions, through the hydrogen bonds and capillary tension provided by the PEG molecules, it is targeted and fixed in the pore wall of the aerogel skeleton, so that the porous aerogel skeleton can effectively encapsulate PEG and overcome its disadvantage of easy leakage during the solid-liquid phase change process, thereby successfully forming a MCP@PEG phase change composite material with stable shape and high adsorption rate.

[0081] Furthermore, the energy dispersive spectroscopy (EDS) elemental mapping of the aerogel skeleton MCP-2 and the phase change composite material MCP-2@PEG was obtained using field emission scanning electron microscopy.

[0082] Depend on Figure 1 As can be seen in (c), due to the presence of MXene nanosheets and PEI in the aerogel skeleton MCP-2, a series of signals corresponding to the elements C, O, N, F, and Ti appear in the elemental mapping diagram, and they show a uniform and dense distribution in the aerogel skeleton. Figure 1 (d) After the MCP aerogel skeleton adsorbs PEG, it can be seen that the C and O signals in the mapping diagram are strong, almost covering the other element signals from PEI and MXene nanosheets, indicating that the aerogel skeleton has been completely impregnated with PEG and the proportion of PEG in the overall phase change composite material is relatively large.

[0083] Figure 2 The X-ray photoelectron spectroscopy (XPS) of the aerogel skeleton MCP-1 and the phase change composite material MCP-1@PEG is further provided. In the XPS broad spectrum of (a), no Al was detected in MCP-1 in the 200-1350 eV measurement region, proving that the Al in the MAX phase has been completely corroded by HF. Common peaks of C 1s, O 1s, F 1s and Ti 2p were found, indicating the presence of =O, -OH, and -F groups in MXene. The extra N 1s peak further proves that PEI was successfully introduced into the aerogel skeleton. In the MCP-1@PEG spectrum in contrast, due to the high PEG content, the C 1s and O 1s peaks are more prominent, and the other peaks are relatively weakened, indicating that the vacuum impregnation method can encapsulate PEG in the aerogel skeleton.

[0084] Figure 2 (b), (c), and (d) are high-resolution XPS spectra of Ti 2p, C 1s, and N 1s of MCP-1, respectively. The Ti 2p energy level in the Ti 2p XPS spectrum can be deconvoluted into four pairs of 2p 3 / 2 / 2p 1 / 2 Dual lines, 2p at the same time 3 / 2 It can be divided into Ti-C (454.86eV), Ti 2+ (455.86eV), Ti 3+ (456.46eV) and Ti-O (458.22eV). In the XPS deconvoluted spectrum of C 1s, the six separated sub-peaks correspond to C-Ti (281.55eV), C-Ti-O (282.46eV), C-C (284.6eV), C-O (286.11eV) and C-F (288.56eV) bonds. For the N 1s region, the peaks centered at 400.12eV and 398.35eV are attributed to C-NH3 + and C-NH2, showing characteristic peaks corresponding to the charged and uncharged primary amine moieties in PEI.

[0085] The Fourier transform infrared spectroscopy (FT-IR) used to identify the functional groups in the prepared phase change composite materials and raw materials is shown in the figure Figure 3 As shown, the characteristic peak of MXene appears at 1060 cm -1 、2960cm -1 and 3450cm -1 , corresponding to CO, CH and -OH, respectively, while 1056 cm -1 Corresponding to COC, 1382cm -1 and 1670cm -1The corresponding positions are CN and NH in PEI, respectively, which proves the formation of hydrogen bonds between MXene, CMC and PEI. -1 and 2885cm -1 The absorption peaks at 1360 cm-1 belong to the stretching vibration of COC and -CH2, while the absorption peaks at 1360 cm-1 belong to the stretching vibration of COC and -CH2, respectively. -1 and 1470cm -1 The absorption peak at belongs to the CH bond; all MCP@PEG have the PEG characteristic peak, and no obvious new peak is found in the spectrum, which confirms that there is only physical adsorption between the raw materials and no chemical reaction occurs.

[0086] In order to explore the phase composition and crystallinity of phase change composite materials, X-ray diffractometer was used to test the XRD patterns of relevant materials. Figure 4 As shown. The characteristic peak (002) position of MXene at 7.4° becomes 7.1° in MCP, and a larger interlayer spacing is formed between MXene layers, proving that PEI and CMC are successfully embedded in MXene nanosheets to form a denser structure. PEG presents two main characteristic peaks, located at 19.0° and 23.5°, corresponding to the (120) and (032) planes of PEG crystals, showing good crystallization ability. No new characteristic peaks appear in all phase change composites, which mainly show the combination of composite components, leaving only the peaks of the corresponding fillers, indicating that all components are physically combined, not chemically combined.

[0087] Application Example 2

[0088] In order to further understand the heat absorption and release capacity of the phase change composite material prepared by the present invention, the phase change composite materials prepared in Examples 1 to 3 and Comparative Example 1 and the single phase change material PEG were tested by differential scanning calorimetry. The phase change latent heat and temperature of the material were obtained by analyzing the DSC measurement results to characterize the latent heat storage capacity of the material. All materials were tested in a nitrogen atmosphere with a flow rate of 20 mL / min, a temperature range of 20 to 100 ° C, and a heating rate of 10 ° C / min.

[0089] Figure 5 The DSC curves of PEG, MCP-1@PEG, MCP-2@PEG, MCP-3@PEG and MCP-4@PEG are given respectively. All materials in the figure show obvious endothermic and exothermic peaks during the phase change process, and show similar trends to the phase change material PEG during melting and solidification, indicating that PEG and the aerogel skeleton are combined through physical adsorption and no chemical changes occur.

[0090] The DSC thermal performance parameters of the above materials are given in detail in Table 1. The melting temperature (T m ) and crystallization temperature (Tc ) are 68.4 and 53.9 °C, respectively, and the relative melting enthalpy (ΔH m ) and crystallization enthalpy (ΔH c ) are 182.1 and 173.2 J / g, respectively, with high melting latent heat values, showing excellent thermal energy storage and thermal management capabilities. Correspondingly, the ΔH m Between 173.7 and 176.8 J / g, ΔHc is between 168.3 and 164.2 J / g. Compared with pure PEG, the value of the phase change composite material is slightly reduced. The main reason is that the phase change enthalpy is related to the proportion of the phase change material. The addition of the aerogel skeleton in the phase change composite material slightly reduces the phase change enthalpy data. At the same time, due to the adsorption of the skeleton, the direction and penetration behavior of the PEG molecules are subject to certain restrictions, and the phase change process is delayed. However, thanks to the aerogel skeleton's adsorption efficiency of PEG is as high as 96% or more, its excellent adsorption maintains PEG's outstanding ability in thermal energy adjustment and management. At the same time, it can be seen that although Comparative Example 1 also has good adsorption capacity, its aerogel skeleton does not form an interconnected structure, so the adsorption performance is somewhat different from that of other embodiments.

[0091]

[0092] Application Example 3

[0093] The aerogel skeleton provides strong surface tension and strong capillary force. In the molten state, PEG can easily penetrate into the aerogel through the interconnected channels of the aerogel, and then anchor on the pore walls of the aerogel through hydrogen bonds and capillary forces under vacuum conditions. There are no obvious boundaries between them, and PEG is well adsorbed. At the same time, PEG is also fully impregnated into the aerogel skeleton, indicating that the two have good compatibility and bonding. The phase change composite material of the present invention has good shape stability and excellent PCM packaging ability.

[0094] Figure 6 The shape stability test results of PEG, MCP-1@PEG, MCP-2@PEG, MCP-3@PEG and MCP-4@PEG in the temperature range of 20 to 80°C are shown. Figure 6 It can be seen from the state change picture in (a) that PEG begins to phase change at 60°C, and at 80°C it can be clearly observed that PEG cannot effectively maintain its shape stability during the solid-liquid phase change, and becomes liquid, resulting in serious leakage. In comparison, no liquid leakage was observed in the three phase change composite materials of Examples 1 to 3 during each temperature period. Therefore, the MCP aerogel skeleton of the present invention can effectively encapsulate PEG, thereby obtaining an MCP@PEG phase change composite material with good shape stability and anti-leakage performance.

[0095] At the same time, as the temperature rises, it can be observed that the boundary line of the phase change composite material MCP-4@PEG in Comparative Example 1 gradually becomes blurred, and a small amount of PEG is adsorbed on the filter paper, indicating that the shape stability of MCP-4@PEG is poor, its aerogel skeleton cannot adsorb PEG well, and leakage occurs during the phase change process.

[0096] The mass of the phase change composite material at 20°C before heating and at 80°C after heating was weighed, and the leakage rate of the phase change composite material was calculated by the mass change before and after heating. The results are as follows: Figure 6 As shown in (b), it can be seen that although the MCP aerogel skeleton of Comparative Example 1 can also adsorb PEG, due to the fact that its aerogel has no directional freezing growth, the aerogel skeleton cannot effectively block the leakage of PEG during the phase change process, resulting in a mass loss of at least 20%, while the mass loss of the phase change composite materials of Examples 1 to 3 is almost negligible, which verifies the adsorption effect of the pores formed by its directional freezing growth.

[0097] Application Example 4

[0098] Electromagnetic wave radiation (EMW) generated by electronic products not only affects the performance of electronic devices, but also harms human health. Therefore, it is crucial to prepare multifunctional phase change composites with electromagnetic interference shielding effect while meeting thermal management requirements. According to Xu et al. (Dengji Xu, Que Huang, Likai Yang, Yanjun Chen, Zhumao Lu, Huijuan Liu, Peijie Han, Li Guo, Chao Wang, Changcheng Liu. Experimental design of composite films with thermal management and electromagnetic shielding properties based on polyethylene glycol and MXene. Carbon , 2023,202: 1-12. https: / / doi.org / 10.1016 / j.carbon.2022.11.010) reported that the EMI SE commercial level of typical electromagnetic interference shielding materials should be >20dB.

[0099] This application example tests the electromagnetic interference shielding performance of the phase change material PEG and the phase change composite materials prepared in Examples 1 to 3 and Comparative Example 1 in the frequency range of 12.4 to 18 GHz. The relevant tests are performed using a vector network analyzer VNA. The results are shown in the figure. Figure 7As shown in the figure, the EMI SE values ​​of MCP-1@PEG, MCP-2@PEG and MCP-3@PEG are about 37.6dB, 53.7dB and 38.8dB respectively. The EMI SE value of MCP-2@PEG is the highest. The main reason is that the MXene sheets are arranged in a regular pattern, forming a flowing conductive network. In addition, the CMC and PEI double networks promote the combination of hydrogen bonds and enhance the interface interaction between adjacent MXenes, making the insulation gap smaller, thus forming a more complete and tight three-dimensional porous conductive network, so that the phase change composite material has a relatively excellent electromagnetic shielding performance. The EMI SE value of MCP-3@PEG is reduced, which may be mainly due to the agglomeration of MXene, which affects the performance.

[0100] but Figure 7 The EMI SE value of the phase change composite material MCP-4@PEG prepared in Comparative Example 1 is close to that of PEG, and has no electromagnetic shielding effect at all. By comparing Example 1 with Comparative Example 1, it is proved that directional freezing is the key to ensure that the MXene sheets grow in an orderly manner vertically along with the ice column. Although Comparative Example 1 does not use directional freezing, it also prepares a three-dimensional aerogel and can greatly adsorb PEG, but it cannot form a continuous structure, so it does not have electromagnetic shielding performance.

[0101] Figure 8 The SE total (SE T )、SE absorption(SE A ) and SE reflection (SE R ) on the EMI SE mechanism, it can be observed that the SE of MCP@PEG A Much higher than the corresponding SE R , S.E. A / SE T The value is about 94%, SE A It occupies an absolute dominant position, indicating that the mechanism by which the phase change composite material of the present invention achieves electromagnetic wave radiation attenuation is mainly through absorption rather than reflection.

[0102] With the effective continuous network of MXene, SE T and SE A It shows an upward trend, while SE R However, it always remains at a low level below 3dB. The enhanced impedance matching allows electromagnetic waves to enter the phase change composite material in the form of incident instead of direct reflection, and the main electromagnetic waves are absorbed through phase change. It not only has excellent electromagnetic shielding performance, but also reduces the generation of secondary pollution.

[0103] Application Example 5

[0104] Thermal conductivity is closely related to heat transfer capacity and heat storage density. It is an important performance parameter that reflects the heat transfer capacity of phase change materials, evaluates phase change composite materials, and is a core parameter that reflects the thermal management application of phase change composite materials. The MCP aerogel skeleton, due to its porous and continuous three-dimensional structure, not only provides a good impregnation platform for PEG, but also provides a continuous pathway for heat transfer.

[0105] Using the transient plane heat source method, PEG, MCP-1@PEG, MCP-2@PEG, MCP-3@PEG and MCP-4@PEG were pressed into cylinders with a diameter of 28 mm and a height of 7 mm, respectively. The thermal conductivity of the materials was evaluated using a thermal constant analyzer and a 5501 PI-coated probe (R=6.403 mm).

[0106] The results of the test are as follows Fig. 9 , the thermal conductivities of PEG, MCP-4@PEG, MCP-1@PEG, MCP-2@PEG, and MCP-3@PEG are 0.32, 0.45, 0.87, 1.06, and 1.43 W / m·K, respectively.

[0107] Due to the short chain structure of PEG, its thermal conductivity is low. However, the thermal conductivity of the three phase change composite materials of Examples 1 to 3 increased significantly, and showed a trend of increasing with the increase of MXene content. The thermal conductivity of MCP-3@PEG increased to 1.43W / m·K, which was 343% higher than that of pure PEG, thus verifying that the MCP aerogel skeleton has excellent thermal conductivity and interconnected skeleton structure, which promotes the formation of effective heat transfer pathways inside the phase change composite material, and can effectively improve the thermal conductivity of the phase change composite material. The interconnected three-dimensional structure of the MCP aerogel constructed based on the present invention can not only efficiently adsorb PEG, but also has a significant improvement effect in thermal conductivity.

[0108] The thermal conductivity of the phase change composite material in Comparative Example 1 is only 0.45 W / m·K, which proves again that the MCP aerogel skeleton constructed by it cannot form a continuous three-dimensional structure and an effective heat transfer path because the MXene is not stably arranged through directional freezing, resulting in a small improvement in the overall thermal conductivity. However, it is still a small improvement compared with PEG due to the participation of MXene.

[0109] Similarly, the electrical conductivity of the phase change composite material of the present invention also has a similar law. Fig.10In the conductivity measurement results, PEG and MCP-4@PEG have basically no conductivity, but the conductivity of MCP-1@PEG, MCP-3@PEG and MCP-2@PEG increases significantly with the formation of the porous three-dimensional structure of the MCP aerogel skeleton. The conductivity of MCP-2@PEG is the highest, rising to 11.62S / m.

[0110] Application Example 6

[0111] In the latent heat storage process, the first thing to do is the conversion and transmission of energy, including photothermal, electrothermal, magnetic thermal conversion and heat conduction. Electric energy and thermal energy are the largest supply and consumption ends in life and production, and the conversion, storage and utilization between the two occupy an important link in the energy system. By converting valley electricity into latent heat energy for storage, and releasing it during peak electricity consumption for heating, production or thermal power generation, the high efficiency of Joule heat conversion and the high energy density of latent heat storage are fully utilized, which makes electrothermal phase change materials have unique application value in power peak regulation and thermal energy storage.

[0112] This application example takes the phase change composite material MCP-2@PEG as an example. The phase change composite material is connected to different DC voltage circuits, and the temperature change of the material is monitored using an infrared thermal imaging temperature measuring device. The real-time temperature, average temperature, temperature difference and other values ​​of the material under different working environments are obtained, and its electrothermal conversion performance is tested to characterize the electrothermal conversion ability of the phase change composite material. The results are as follows: Fig.11 shown.

[0113] The voltage conditions were set to 5V, 7V and 9V respectively. When the power was on for 300s, the temperature of the phase change composite material reached about 66.7, 76.5 and 96.9℃ respectively (a). After the power was turned off for 300s, the material temperature dropped to about 25.1, 26.7 and 35.9℃ respectively. MCP-2@PEG showed agile electrothermal response performance under different voltages. Fig.11 In the infrared thermal image of MCP-2@PEG during the electrothermal conversion process (c), the electrothermal path of the material can be clearly observed.

[0114] CP-2@PEG has good electrothermal conversion capability, heat storage performance and management performance, and has good application prospects in the field of intelligent temperature control of electronic equipment.

[0115] The above embodiments of the present invention do not describe all the details in detail, nor limit the present invention to the above embodiments. Various changes, modifications, substitutions and variations made by ordinary technicians in this field without departing from the principles and purpose of the present invention should be included in the protection scope of the present invention.

Claims

1. A MXene-based aerogel is prepared by adding PEI and CMC to a MXene aqueous dispersion to obtain a mixed solution, which is then evenly dispersed into a polytetrafluoroethylene mold with a copper plate at the bottom, immersed in liquid nitrogen for directionally freezing, and vacuum freeze-dried to obtain a MXene-based aerogel skeleton MCP.

2. The MXene-based aerogel according to claim 1, characterized in that The mass ratio of MXene to PEI and CMC is 1:(1~3.5):(1~3.5).

3. The MXene-based aerogel according to claim 1, characterized in that The concentration of the MXene aqueous dispersion is 5 to 10 mg / mL.

4. The MXene-based aerogel according to claim 1, characterized in that Add PEI and CMC into the MXene aqueous dispersion and stir for no less than 30 min to disperse evenly to obtain a mixed solution.

5. The phase change composite material prepared using the MXene-based aerogel according to claim 1 is a phase change composite material with a stable shape obtained by vacuum impregnation and adsorption of molten phase change material using the MXene-based aerogel as a skeleton.

6. The phase change composite material according to claim 5, characterized in that The loading amount of the phase change material is 90-98% of the total mass of the phase change composite material.

7. The phase change composite material according to claim 5, characterized in that The phase change material is any one of polyethylene glycol, polymethyl methacrylate or polystyrene.

8. The phase change composite material according to claim 7, characterized in that The phase change material is polyethylene glycol.

Images