MXene synergistic composite phase change heat storage material and preparation method thereof

Abstract

The invention provides an MXene synergistic composite phase change heat storage material and a preparation method thereof, and belongs to the technical field of phase change heat storage materials. Comprising the following steps: reacting graphite with mixed acid and potassium permanganate through an improved Hummers method, and carrying out centrifugal washing, dialysis and drying to obtain graphene oxide GO powder, dispersing MXene and the graphene oxide GO powder in deionized water, performing ultrasonic treatment, stirring and mixing, adding nanocellulose CNF and citric acid CA, continuing stirring, and performing directional freezing and freeze drying to obtain three-dimensional aerogel; the three-dimensional aerogel and molten paraffin are compounded through vacuum impregnation, and the MXene-based composite phase change heat storage material is obtained. The MXene-based composite phase change material prepared by the invention has high mechanical strength, can effectively prevent leakage during phase change of the organic PCMs, still keeps higher load rate and stable structure and shape after multiple cycles, and can be applied to the fields of microminiature thermal management and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of phase change heat storage materials, and in particular to a MXene synergistic composite phase change heat storage material and a preparation method thereof. Background Art

[0002] Phase change materials (PCMs) have broad application prospects in areas such as solar energy utilization, building energy conservation, and thermal management of electronic devices due to their excellent thermal energy storage properties. Organic PCMs, such as paraffin, are considered ideal thermal energy storage materials due to their high latent heat of phase change, wide temperature range, and excellent chemical stability. However, organic PCMs generally suffer from low thermal conductivity, large volume changes during phase change, and leakage, which severely limit their effectiveness in practical applications.

[0003] To solve the above problems, researchers have developed various forms of composite phase change materials. Among them, the method of encapsulating organic phase change materials in porous carriers to form composite phase change materials has attracted widespread attention. CN118344850A discloses a three-dimensional graphene-magnetic particle hybrid skeleton composite phase change material and its preparation method. The method adopts a "two-step" ice template technology to embed porous MXene-Co aerogel into a graphene array to obtain a three-dimensional graphene-magnetic particle hybrid skeleton with a complete heat conduction channel and rich electromagnetic hybrid heterogeneous interfaces. CN115612461A proposes a three-dimensional high thermal conductivity attapulgite / graphene oxide aerogel composite phase change material and its preparation method. By compounding attapulgite nanofibers and graphene oxide nanosheets to form a three-dimensional structured aerogel, and then vacuum impregnating it with a phase change material, high energy storage density, excellent anti-leakage performance and good thermal conductivity are achieved.

[0004] Graphene oxide (GO), a two-dimensional carbon material, is widely used as a carrier for composite phase-change materials due to its excellent mechanical and thermal properties. CN110205100B discloses a graphene oxide / expanded graphite aerogel phase-change composite material and its preparation method. This method involves mixing graphene oxide with expanded graphite to form a three-dimensional hydrogel. The aerogel is then freeze-dried and impregnated with paraffin to create a phase-change composite material with excellent thermal conductivity and high heat storage capacity.

[0005] In recent years, MXene, as a new type of two-dimensional transition metal carbide / nitride material, has shown great application potential in the field of composite phase change materials due to its excellent thermal conductivity, mechanical strength and large specific surface area. CN119505820A proposed a composite phase change heat storage material. By doping nitrogen quantum dots into porous carbon aerogel as a load carrier, using acidified paraffin as a phase change heat storage agent, and adding titanium dioxide-carbon nanotube composite materials, the phase change latent heat and thermal conductivity of the composite phase change heat storage material were effectively improved. CN117285909A introduced a mineral-based composite phase change heat storage aerogel. By chemically cross-linking the mineral-based composite phase change heat storage material with chitosan and bacterial cellulose, and then adding graphene oxide to form hydrogen bonds to form physical cross-links, a composite phase change heat storage aerogel with a double cross-linking system was constructed.

[0006] Although existing technologies have made some progress in improving the thermal conductivity and anti-leakage properties of organic phase change materials, the following problems still exist: First, although the existing three-dimensional porous framework can improve the packaging efficiency of organic PCMs, its mechanical properties in long-term use still need to be enhanced, especially after undergoing multiple phase change cycles, when structural damage is prone to occur, affecting the service life of the material; second, the thermal conductivity network construction method of existing composite phase change materials is relatively simple, making it difficult to simultaneously meet the requirements of high thermal conductivity and good mechanical properties; in addition, factors such as temperature fluctuations and mechanical shock faced by composite phase change materials in actual application environments place higher requirements on the structural stability of the material.

[0007] Therefore, developing a composite phase change heat storage material with excellent thermal conductivity, good mechanical strength and structural stability is of great significance for promoting the practical application of phase change materials in the field of thermal energy management. Summary of the Invention

[0008] In order to address the problems of low thermal conductivity, volume change and leakage during phase change of organic phase change materials (PCMs) in thermal energy storage applications, as well as the technical defects of insufficient mechanical properties of existing three-dimensional porous frameworks during long-term use, the present invention provides a MXene synergistic composite phase change thermal storage material and a preparation method thereof, so as to achieve the technical effects of improving the encapsulation efficiency of organic PCMs, enhancing thermal conductivity, preventing phase change leakage and maintaining long-term stability.

[0009] To achieve the above object, the present invention provides the following solutions: A method for preparing a MXene synergistic composite phase change thermal storage material comprises the following steps: S1. Preparing graphene oxide (GO) powder: reacting graphite with a mixed acid and potassium permanganate by a modified Hummers method, and obtaining the graphene oxide (GO) powder by centrifugal washing, dialysis, and drying; S2. Preparation of MXene / GO / CNF / CA aerogel: MXene and graphene oxide (GO) powder were dispersed in deionized water, stirred and mixed after ultrasonication, nanocellulose CNF and citric acid (CA) were added, and the mixture was further stirred and subjected to directional freezing and freeze-drying to obtain a three-dimensional aerogel; S3. Paraffin encapsulation: The three-dimensional aerogel is compounded with molten paraffin by vacuum impregnation to obtain a MXene-based composite phase change thermal storage material.

[0010] Preferably, in S1, the mixed acid is a mixture of concentrated sulfuric acid and phosphoric acid in a volume ratio of 9:1, the reaction temperature is not greater than 35°C, and after the potassium permanganate is dissolved, the mixture is stirred in a 50°C water bath for 12 hours.

[0011] Preferably, in S1, the reaction product is terminated by a 3% by mass hydrogen peroxide solution, wherein the ratio of hydrogen peroxide to ice-water mixture in the hydrogen peroxide solution is 1:9; then the mixture in S1 is centrifuged and washed three times each with deionized water, a 3% by mass hydrochloric acid solution, and anhydrous ethanol, at a centrifugal speed of 10,000 r / min.

[0012] Preferably, in S1, the mixture after centrifugal washing is placed in a dialysis bag and dialyzed for 7 days, and then vacuum dried at 50° C. for 2 hours to obtain the graphene oxide GO powder.

[0013] Preferably, in S2, the concentrations of the dispersions of MXene and graphene oxide (GO) powder are both 10 mg / ml, ultrasonication is performed in an ice bath for 30 min, and the two dispersions are mixed and stirred at 500 r / min for 30 min until they are uniformly mixed.

[0014] Preferably, in S2, the amount of the nanocellulose CNF added is 1 wt % of the reaction system. After the nanocellulose CNF is added to the mixed dispersion, the mixture is stirred at 1000 r / min for 2 h until uniform. The amount of the citric acid CA added is 10 mg.

[0015] Preferably, in S2, the directional freezing is carried out by liquid nitrogen treatment, and the freeze-drying time is 24 hours.

[0016] Preferably, in S3, the paraffin wax is melted in a vacuum drying oven at 80°C, and the vacuum impregnation time is 30 minutes.

[0017] The present invention also provides a MXene-based composite phase change thermal storage material prepared according to the above-mentioned preparation method of the MXene synergistic composite phase change thermal storage material, comprising a three-dimensional aerogel framework and paraffin encapsulated therein, wherein the aerogel framework is formed by cross-linking MXene, graphene oxide GO, nanocellulose CNF and citric acid CA.

[0018] Preferably, the MXene is Ti3C2T x , wherein 1<x<3; the mass ratio of the MXene to graphene oxide GO is 1:1.

[0019] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: (1) The present invention combines MXene with graphene oxide, and then crosslinks and reinforces it with nanocellulose (CNF) and citric acid (CA) to construct a three-dimensional aerogel framework. The synergistic effect of covalent bonds and hydrogen bonds is used to enhance the mechanical properties of the framework, so that the material can effectively disperse the load when subjected to external stress, inhibiting structural collapse and providing a stable support structure for the phase change material. This solves the problem of easy stacking and insufficient mechanical strength when constructing a framework using only MXene or graphene oxide.

[0020] (2) The three-dimensional aerogel framework provided by the present invention optimizes the heat transfer path and changes the heat transfer mode from relying on heat convection to mainly relying on heat conduction. At the same time, the high thermal conductivity of MXene and graphene oxide forms a continuous heat conduction channel, which reduces the interfacial thermal resistance and significantly improves the thermal conductivity of the composite phase change material, thereby improving the low heat transfer efficiency caused by the low thermal conductivity of the organic phase change material.

[0021] (3) The porous structure of the aerogel provided by the present invention achieves efficient encapsulation of paraffin through capillary action, and the framework structure can constrain the volume change of paraffin during the phase change process, effectively preventing leakage; at the same time, the synergistic effect of CNF and CA gives the material good cyclic stability, and it can still maintain structural integrity and high loading rate after multiple hot and cold cycles, expanding the practical value of organic phase change materials in fields such as thermal management. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 This is a flow chart of a method for preparing a MXene synergistic composite phase change thermal storage material of the present invention; Figure 2 Ti3C2T provided in Example 1 of the present invention x , GO, Ti3C2T x GO and Ti3C2T x SEM image of / GO / CA composite aerogel; among them, Figure 2 (a) is Ti3C2T x SEM images of Figure 2 (b) is the SEM image of GO. Figure 2 (c) in the figure is Ti3C2T x SEM image of / GO, Figure 2 (d) in the figure is Ti3C2T x SEM image of / GO / CA composite aerogel; Figure 3 Ti3C2T provided in Example 1 of the present invention x EDX images of different elements in / GO / CA composite aerogel; among them, Figure 3 (a) is Ti3C2T x Distribution of C elements in / GO / CA composite aerogels, Figure 3 (b) is Ti3C2T x Distribution of O element in / GO / CA composite aerogel, Figure 3 (c) in the figure is Ti3C2T x Distribution of Ti element in / GO / CA composite aerogel; Figure 4 XRD patterns of MXene, MGO, and MGOCA provided in Example 1 of the present invention; Figure 5 FTIR spectra of MXene, MGO, and MGOCA provided in Example 1 of the present invention; Figure 6 This is a high-resolution XPS spectrum of MXene, MGO, and MGOCA provided in Example 1 of the present invention; wherein, Figure 6 (a) is the XPS spectrum of O 1s. Figure 6 (b) is the XPS spectrum of C 1s. Figure 6 (c) in the figure is the XPS spectrum of Ti 2p; Figure 7 The stress-strain curves of MGO and MGOCA provided in Example 1 of the present invention; Figure 8 A cycle curve diagram of MGOCA / paraffin provided in Example 1 of the present invention; Figure 9 DSC curves of paraffin and MGOCA / paraffin provided in Example 1 of the present invention; Figure 10 This is a diagram of the solid-liquid thermal conductivity of paraffin and MGOCA / paraffin provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1 like Figure 1 As shown, the present invention provides a method for preparing a MXene synergistic composite phase change thermal storage material, comprising the following steps: S1. Preparing graphene oxide (GO) powder: reacting graphite with a mixed acid and potassium permanganate by a modified Hummers method, and obtaining the graphene oxide (GO) powder by centrifugal washing, dialysis, and drying; Specifically, a 500ml flask was placed on a magnetic stirrer filled with ice water. 360ml of concentrated sulfuric acid and 40ml of phosphoric acid were added and stirred. 3g of high-purity flake graphite was then added to the flask. Subsequently, 18g of potassium permanganate was slowly added to the flask while stirring continuously, maintaining the reaction temperature above 35°C. Once the potassium permanganate dissolved, the flask was stirred in a 50°C water bath for 12 hours. After the reaction was complete and cooled to room temperature, the resulting solution in the flask was slowly poured into 400ml of pre-chilled 3% hydrogen peroxide solution (a 1:9 ratio of hydrogen peroxide to ice water). The mixture was then centrifuged three times at 10,000 rpm with deionized water, 3% hydrochloric acid, and anhydrous ethanol. The mixture was then dialyzed in a dialysis bag for one week and finally vacuum-dried at 50°C for two hours to yield brown-yellow graphene oxide (GO) powder.

[0027] S2. Preparation of MXene / GO / CNF / CA aerogel: MXene and graphene oxide (GO) powder were dispersed in deionized water, stirred and mixed after ultrasonication, nanocellulose CNF and citric acid (CA) were added, and the mixture was further stirred and subjected to directional freezing and freeze-drying to obtain a three-dimensional aerogel; Specifically, Ti3C2T xTi3C2T3 was prepared by mixing 10 ml of each dispersion and stirring at 500 r / min on a magnetic stirring table for 30 min. 1 wt% of CNF was added and stirred at 1000 r / min on a magnetic stirring table for 2 h. The resulting mixture was then directionally frozen in liquid nitrogen and placed in a freeze dryer for 24 h to obtain Ti3C2T3. x / GO aerogel (MGO). After adding CNF, 10 mg of citric acid CA was added during stirring, and after the aerogel was obtained, it was placed in a vacuum drying oven at 100 ° C for 3 h to form Ti3C2T x / GO / CA aerogel (MGOCA). The MXene is Ti3C2T x , wherein 1<x<3; the mass ratio of the MXene to graphene oxide GO is 1:1.

[0028] S3. Paraffin encapsulation: The three-dimensional aerogel is compounded with molten paraffin by vacuum impregnation to obtain a MXene-based composite phase change thermal storage material.

[0029] Specifically, paraffin was heated and melted in a vacuum drying oven at 80°C, and then the aerogel was placed in an alumina crucible filled with liquid paraffin. After vacuum pressure immersion in a vacuum drying oven at 80°C for 30 minutes, the aerogel was taken out to obtain a MXene-based composite phase change thermal storage material.

[0030] Furthermore, the present invention also provides a MXene-based composite phase change thermal storage material prepared according to the above-mentioned preparation method of the MXene synergistic composite phase change thermal storage material, comprising a three-dimensional aerogel framework and paraffin encapsulated therein, wherein the aerogel framework is formed by cross-linking MXene, graphene oxide GO, nanocellulose CNF and citric acid CA.

[0031] The obtained MXene-based composite phase change thermal storage material was then cooled to room temperature and tested. Figure 2 (a) After HCL / LiF etching and post-treatment, the Ti3C2T x In a single layer state. Figure 2 (b) shows that GO presents a large sheet-like structure. Figure 2 (c) in the figure is Ti3C2T x SEM image of / GO aerogel, showing the three-dimensional network structure without the addition of citric acid (CA). Figure 2(d) in the figure is the three-dimensional network structure after adding citric acid. It can be found that it has a more regular network structure and builds a better heat conduction channel. The implemented directional freezing method allows the nanosheets to grow in a direction perpendicular to the plane. This vertical design optimizes the heat transfer process, changing from relying mainly on heat convection to relying mainly on heat conduction, thereby increasing the heat transfer rate. Through scanning electron microscopy (SEM) analysis of paraffin vacuum impregnated 3D aerogels, it can be observed that paraffin is completely filled into the microporous structure of the 3D aerogel through capillary action, and this process does not damage the original directional structure. In addition, because MXene nanosheets have similar layers to GO, compared with pure Ti3C2T x Compared with Ti3C2T / GO aerogel x / GO+citric acid aerogel effectively reduces the stacking of nanosheets, thereby enhancing the heat transfer rate.

[0032] In addition, this embodiment also tests Ti3C2T x / GO aerogel was characterized by EDX, and the distribution of different elements was shown in Figure 2. Figure 3 As shown in (a), (b) and (c), it can be seen that Ti3C2T x The main elements of GO (C, O, Ti) are evenly distributed in the aerogel. According to the analysis, the sample is mainly composed of carbon (C), oxygen (O) and titanium (Ti), with weight percentages of 41.39%, 42.39% and 16.22% respectively, and atomic percentages of 53.56%, 41.18% and 5.26%. The atomic percentage of carbon is significantly higher than the weight percentage, indicating that there may be lightweight carbon structure graphene or oxygen-containing functional groups in the material, which is similar to Ti3C2T x The characteristics of the MXene / GO composites are consistent. The high oxygen content (42 wt%) is mainly due to the hydroxyl and carboxyl functional groups of graphene oxide (GO), while the low atomic percentage of titanium (5.26%) may be due to the x / ) is covered or diluted by the GO layer, which is consistent with the characteristic of GO dominating the surface signal after the two are composited.

[0033] By Ti3C2T x 、Ti3C2T x XRD patterns of the / GO aerogel and the aerogel with added citric acid (CA) are shown in Figure 2. Figure 4 As shown in the figure, it can be seen that the characteristic peaks of GO become more obvious after the addition of CA, and the characteristic peaks of Ti3C2T x After mixing with GO, the (002) characteristic peak shifted from 6° to 5.8° and 5.5° with the addition of CA, indicating that the oxygen-containing functional groups of GO (such as hydroxyl, epoxy and carboxyl) and the carboxyl groups in citric acid reacted with Ti3C2T xThe surface interaction forms hydrogen bonds, which leads to an increase in the interlayer spacing, thus proving that Ti3C2T x The self-stacking situation is effectively reduced.

[0034] like Figure 5 As shown in the figure, the infrared spectral characteristics analysis of MXene and its composite materials show that the original MXene Ti3C2T x At 3435cm -1 The characteristic peak of OH stretching vibration of surface adsorbed water is shown at 1387 cm -1 and 550cm -1 The stretching vibrations of the CF bond and Ti-C bond correspond to the MXene / GO system at 3285 cm -1 The OH stretching vibration peak of GO is shown at 1682 cm -1 A significant C=O characteristic peak appears at 1314 cm, indicating the presence of carboxyl or carbonyl functional groups in GO. It is worth noting that the CF bond vibration peak of the MXene component shifts to 1314 cm -1 , while the characteristic vibration peak of GO is distributed at 1203cm -1 (CO), 1099cm -1 (COC) and 1032cm -1 (C-OH). Especially the Ti-C bond vibration peak at 593cm -1 The significant broadening at the interface confirms the strong interfacial interaction between MXene and GO.

[0035] After the introduction of citric acid, the MXene / GO+CA composite system showed an overall enhanced absorption peak, which was attributed to the superposition effect of the citric acid functional group. -1 The broadened OH peak at 2897 cm-1 can be attributed to the synergistic contribution of GO and hydroxyl groups in citric acid, while the peak at 2897 cm-1 can be attributed to the synergistic contribution of GO and hydroxyl groups in citric acid. -1 The newly appeared CH vibration peak at 1682cm -1 The C=O peak intensity at 1314 cm is weakened, which may be due to the fact that the abundant hydroxyl groups in GO and citric acid affect the vibration mode of the carboxyl group through hydrogen bonding. At the same time, this shift also confirms the uniform dispersion of the three-phase components. -1 (CF), 1203cm -1 (CO) and 1099cm -1 The positions of characteristic peaks such as (COC) remain stable, while 1032 cm -1 The peak shift at 556 cm reflects the superposition effect of C-OH and CH in-plane bending vibration in citric acid. Finally, the Ti-C bond vibration peak shifts to 556 cm -1Moreover, the peak shape maintains a broadening characteristic, which further supports the multiphase interface interaction mechanism in the composite system.

[0036] Reference Figure 6 (a), (b) and (c) show the Ti3C2T x 、Ti3C2T x / GO、Ti3C2T x High-resolution C 1s, O 1s and Ti 2p XPS spectra of / GO+citric acid. It is observed that the C-Ti peak shifts to a higher binding energy, indicating that when Ti3C2T x When interacting with GO and citric acid, the oxygen-containing functional groups (such as hydroxyl, carboxyl or epoxy groups) in GO and citric acid react with Ti3C2T x This leads to the oxidation of titanium and changes in the binding environment. Due to these interactions, the electron density around the titanium atoms increases, causing the C-Ti peak to move to a higher binding energy. x The interlayer bonding between the nanosheets and GO improves the overall structural integrity. Also due to the presence of oxygen-containing functional groups, titanium atoms are more strongly bound to oxygen atoms, and the binding energy of the Ti-O peak increases. The CO peak corresponds to carbon atoms bound to oxygen, usually in the form of hydroxyl or epoxy groups, which exist in GO and citric acid. x The increase in oxygen-containing functional groups leads to a strengthening of the CO bond when interacting with GO and citric acid. This causes the CO peak to shift to higher binding energy. x The interaction with oxygen-containing groups in GO and citric acid forms stronger interlayer bonding, thereby reducing the possibility of interlayer delamination and improving the overall strength of the material. The oxidation of titanium and the formation of stable Ti-O and CO bonds improve the material's resistance to degradation.

[0037] This example also provides a stress-strain curve of the prepared 3D aerogel, as shown in FIG. Figure 7 As shown in Figure 2, the strength of 3D aerogel increases with the addition of CA. When CA is added, the maximum compressive strength can reach 24 kPa, which is a relative increase of about 8 kPa. x The functional groups on the surface of Ti3C2T / GO significantly improve its mechanical properties due to the presence of more covalent bonds. When an appropriate amount of CA is added, the synergistic effect between covalent bonds and ionic bonds enhances the mutual influence of the nanosheets, which makes the higher strength Ti3C2T x It is easier to be adsorbed on the surface of GO, thus giving it higher mechanical strength. At the same time, the introduction of CA effectively reduces the xThe stacking of nanosheets makes the overall structure more stable. Therefore, the ideal interaction between nanosheet layers plays a key role in affecting the mechanical properties of the prepared aerogel.

[0038] Reference Figure 8 and Figure 9 , which shows Ti3C2T x Experimental results show that GO / GO aerogels loaded with paraffin wax were subjected to alternating hot and cold cycles. Observations revealed that due to the aerogel's large specific surface area, the initial paraffin loading reached as high as 97% after vacuum impregnation and encapsulation. Remarkably, the paraffin loading remained above 90% after 300 cycles. Using DSC testing, the differences in specific heat capacity and phase transition temperature between pure and encapsulated paraffin wax were investigated. The phase transition temperatures were found to be very similar, differing by only 1.25°C, indicating that the aerogel has a relatively small effect on the paraffin phase transition temperature. The addition of GO and MXene also revealed a decrease in the latent heat of phase change. Since the heat storage process relies entirely on the phase transition of paraffin wax to store and release heat, GO and MXene do not play a key role in this regard. Therefore, a high loading is particularly crucial in the heat storage process.

[0039] Furthermore, CNF and CA play a synergistic role in enhancing the mechanical strength of MXene / GO composite three-dimensional aerogels. The mechanism can be attributed to the dual effects of multi-level cross-linking network construction and optimized stress dissipation. First, the carboxyl groups of CA undergo esterification with oxygen-containing groups (such as -Ti-O and -F) on the MXene surface and the epoxy (COC) and hydroxyl (-OH) groups of the GO sheets, forming covalent crosslinks that significantly strengthen the interfacial bonding between MXene and GO. Simultaneously, CA molecules connect to the hydroxyl network of CNF via hydrogen bonding, forming a MXene-GO-CNF heterogeneous interface bridge at the nanoscale and enhancing the compatibility of the components. Second, the three-dimensional continuous fiber network of CNF acts as a scaffold, encapsulating and anchoring the MXene and GO sheets within its network through physical entanglement and hydrogen bonding. This structure not only inhibits the stacking and agglomeration of the two-dimensional materials but also effectively distributes external loads through the fiber bridging effect. When the aerogel is subjected to compression or shear stress, the high aspect ratio and rigidity of CNF can induce crack deflection and fiber pullout mechanism, absorbing a large amount of fracture energy; while the dynamic covalent bond network formed by CA dissipates local stress through reversible fracture / reorganization, giving the material excellent elastic recovery ability.

[0040] MXene nanosheets have weak interlayer interactions, making it challenging to construct aerogels alone. GO itself can form a hydrogel that serves as the primary framework for aerogels. Furthermore, CNFs have chemically modified or functionalized surfaces, as readily available hydroxyl groups can hydrogen bond with the surface terminals of MXene. The resulting negatively charged surface of the MXene / nanocellulose hybrid helps prevent restacking caused by electrostatic repulsion. CA, on the other hand, can react with CNFs and form irreversible covalent bonds between cellulose chains, helping to form a cross-linked network structure and produce aerogels with high mechanical strength. Simultaneously, the plasticizing effect of CA reduces the van der Waals forces between GO sheets, promoting their uniform dispersion within the CNF backbone. The high-modulus sheets of MXene act as rigid fillers embedded within the flexible network, forming a "rigid and flexible" composite structure.

[0041] Finally, if Figure 10 As shown, it can be found that the average thermal conductivity of solid paraffin (25°C) is 0.2536 W·m -1 ·K -1 (corresponding to Figure 10 The thermal conductivity of the composite phase change material after packaging can reach 0.7549W·m -1 ·K -1 (corresponding to Figure 10 The horizontal axis in 2) is 0.1458 W·m -1 ·K -1 (corresponding to Figure 10 The thermal conductivity of the composite phase change material after packaging can reach 0.6851W·m -1 ·K -1 (corresponding to Figure 10 From the above test results, we can see that due to the Ti3C2T x The regular three-dimensional structure of / GO aerogel, its high specific surface area and better thermal conductivity channel greatly improve the thermal properties of the encapsulated composite phase change material.

[0042] According to the above content, this embodiment combines Ti3C2T x MXene nanosheets and graphene oxide nanosheets to enhance Ti3C2T x Mechanical properties of MXene three-dimensional aerogels. Ti3C2T xMXene, due to its excellent electrical conductivity and mechanical strength, has become a research hotspot in materials science. Graphene oxide, with its outstanding mechanical properties and good chemical stability, provides strong support for improving the performance of composite materials. Citric acid, a non-toxic organic acid, can effectively improve the compatibility between MXene and graphene, thereby enhancing the overall performance of the composite. Paraffin wax was successfully encapsulated into the prepared three-dimensional aerogel structure through vacuum impregnation, forming a composite phase-change thermal storage material. Testing of the composite phase-change thermal storage material revealed that paraffin wax combined with the MXene / GO / CNF / CA three-dimensional aerogel, with a 1:1 MXene to GO ratio and the addition of 10mg of CA, achieved optimal mechanical properties for the three-dimensional framework as the structural support material. The mechanical properties of the three-dimensional framework and paraffin wax leakage were systematically analyzed using a dynamic mechanical analyzer and infrared thermal imaging. The results show that when 10mg of citric acid is added, the hydrogen bond crosslinking between CA and MXene and GO significantly enhances the mechanical properties of the three-dimensional framework, increasing the compressive strength from 18kPa to 24kPa, an increase of 33%. Cyclic storage and release heat cycles revealed that the framework exhibited excellent performance in mechanical structure and paraffin loading. After 300 cycles of testing, the three-dimensional structure remained stable, with only 10% paraffin leakage. At the same time, leakage tests were conducted using an infrared thermal imager, revealing that the load changes of the three-dimensional framework at different temperatures revealed that the three-dimensional framework can effectively prevent leakage during the paraffin phase transition, and that the structure of the three-dimensional framework can ensure that it is not affected during the paraffin phase transition.

[0043] Therefore, the above-mentioned MXene synergistic composite phase change heat storage material and its preparation method are adopted. The MXene-based composite phase change material prepared by the above method has high mechanical strength, can effectively prevent leakage during phase change of organic PCMs, and still maintains a high load rate, stable structure and shape after multiple cycles, and can be applied to fields such as micro-scale thermal management.

[0044] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A method for preparing a MXene synergistic composite phase change thermal storage material, characterized in that: The following steps are involved: S1. Preparing graphene oxide (GO) powder: reacting graphite with a mixed acid and potassium permanganate by a modified Hummers method, and obtaining the graphene oxide (GO) powder by centrifugal washing, dialysis, and drying; S2. Preparation of MXene / GO / CNF / CA aerogel: MXene and graphene oxide (GO) powder were dispersed in deionized water, stirred and mixed after ultrasonication, nanocellulose CNF and citric acid (CA) were added, and the mixture was further stirred and subjected to directional freezing and freeze-drying to obtain a three-dimensional aerogel; S3. Paraffin encapsulation: The three-dimensional aerogel is compounded with molten paraffin by vacuum impregnation to obtain a MXene-based composite phase change thermal storage material.

2. The method for preparing a MXene synergistic composite phase change thermal storage material according to claim 1, characterized in that: In S1, the mixed acid is a mixture of concentrated sulfuric acid and phosphoric acid in a volume ratio of 9:1, the reaction temperature is not higher than 35°C, and after the potassium permanganate is dissolved, the mixture is stirred in a 50°C water bath for 12 hours.

3. The method for preparing a MXene synergistic composite phase change thermal storage material according to claim 1, characterized in that: In S1, the reaction product was terminated by adding a 3% by mass hydrogen peroxide solution, wherein the ratio of hydrogen peroxide to ice water mixture in the hydrogen peroxide solution was 1:9; then the mixture in S1 was washed by centrifugation three times with deionized water, 3% by mass hydrochloric acid solution, and anhydrous ethanol, at a centrifugal speed of 10,000 r / min.

4. The method for preparing a MXene synergistic composite phase change thermal storage material according to claim 3, characterized in that: In S1, the mixture after centrifugal washing is placed in a dialysis bag and dialyzed for 7 days, and then vacuum dried at 50° C. for 2 hours to obtain the graphene oxide GO powder.

5. The method for preparing a MXene synergistic composite phase change thermal storage material according to claim 1, characterized in that: In S2, the concentrations of the MXene and graphene oxide (GO) powder dispersions were both 10 mg / ml, ultrasonication was performed in an ice bath for 30 min, and the two dispersions were mixed and stirred at 500 r / min for 30 min until they were uniformly mixed.

6. The method for preparing a MXene synergistic composite phase change thermal storage material according to claim 1, characterized in that: In S2, the amount of the nanocellulose CNF added is 1 wt % of the reaction system. After the nanocellulose CNF is added to the mixed dispersion, the mixture is stirred at 1000 r / min for 2 h until uniform. The amount of the citric acid CA added is 10 mg.

7. The method for preparing a MXene synergistic composite phase change thermal storage material according to claim 1, characterized in that: In S2, the directional freezing is carried out by liquid nitrogen treatment, and the freeze drying time is 24 hours.

8. The method for preparing a MXene synergistic composite phase change thermal storage material according to claim 1, characterized in that: In S3, the paraffin wax is melted in a vacuum drying oven at 80°C, and the vacuum impregnation time is 30 minutes.

9. A MXene-based composite phase change thermal storage material prepared according to the method for preparing a MXene synergistic composite phase change thermal storage material according to any one of claims 1 to 8, characterized in that: The invention comprises a three-dimensional aerogel framework and paraffin encapsulated therein, wherein the aerogel framework is formed by cross-linking MXene, graphene oxide GO, nanocellulose CNF and citric acid CA.

10. The MXene-based composite phase change thermal storage material prepared by the method for preparing a MXene synergistic composite phase change thermal storage material according to claim 9, characterized in that: The MXene is Ti3C2T x , wherein 1<x<3; the mass ratio of the MXene to graphene oxide GO is 1:1.

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