A phase change composite aerogel material for photothermal conversion and high-density thermal storage, its preparation method and application

Abstract

This invention provides a phase change composite aerogel material for photothermal conversion and high-density thermal storage. The material uses MXenes / CNTs modified aerogel as a three-dimensional porous continuous support framework and a phase change material as the filler. The phase change composite aerogel material, by mass percentage (100%), comprises 3.0-4.4% MXenes / CNTs modified aerogel and 95.6-97.0% phase change material. This invention also provides a method for preparing the above-mentioned phase change composite aerogel material. The MXenes / CNTs modified aerogel composite phase change material prepared by this invention is at the micron level, with MXenes and CNTs attached to its surface and interior. It has a large heat transfer area, good heat transfer performance, and good mechanical properties, making it suitable for a wide range of applications. The preparation method of this invention is simple, and the reaction time and conditions are easy to control. This invention also provides an application of the above-mentioned phase change composite aerogel material in solar photothermal conversion and thermal storage materials.

Description

Technical Field

[0001] This invention belongs to the field of solar thermal conversion and phase change material thermal storage technology, specifically relating to a phase change composite aerogel material for thermal conversion and high-density thermal storage, its preparation method and application. Background Technology

[0002] Renewable energy sources are gradually replacing most fossil fuels. Solar energy, as a representative of new renewable energy sources, is widely considered the most important renewable energy source due to its significant advantage of being inexhaustible. However, the spatiotemporal mismatch problem of solar energy limits its development. Phase change materials, capable of storing and releasing large amounts of heat energy during phase change processes, are considered ideal materials for solar thermal conversion and heat storage.

[0003] Phase change materials (PCMs), as energy storage media, can store or release large amounts of energy at near-constant temperatures during melting or solidification, achieving efficient energy utilization and thus reducing CO2 emissions. Common organic PCMs, such as paraffin wax (PW), polyethylene glycol (PEG), and fatty acids, are white substances. When sunlight shines on PCMs, light waves are reflected, resulting in poor sunlight capture capabilities. Therefore, photothermal conversion materials can be introduced into the field of phase change energy storage. Photothermal conversion materials are materials that can convert light energy into heat energy through their own photothermal conversion mechanism under illumination. The photon capture capability and the design and thermophysical properties of the heat storage material affect the photothermal conversion performance. Combining photothermal conversion materials with phase change materials allows the solar heat absorbed by the photothermal conversion materials to be stored in the phase change materials, achieving comprehensive performance such as high heat storage capacity, excellent photothermal conversion performance, and good thermal conductivity.

[0004] However, the flammability, volume expansion, leakage, poor thermal conductivity, and poor photothermal conversion performance of phase change materials (PCMs) during the phase change process are major obstacles to their development. Extensive research has focused on novel shape-stable PCM (ss-PCM) composite PCMs, such as preparing ss-PCMs by impregnating PCM within supporting materials (e.g., metal foams, microencapsulation). Aerogels, with their abundant pores, can provide capillary forces, restrict liquid flow, and prevent leakage, thus being widely used to adsorb liquid PCMs and form shape-stable composite PCMs. Two-dimensional transition metal carbides / carbonitrides (MXenes) show broad application prospects in energy conversion and storage. Previous studies have demonstrated that MXene nanosheets possess excellent light absorption properties and can spontaneously convert solar energy into thermal energy. Chinese patent document CN109852349A discloses a shape-stabilized phase change composite material for light-to-thermal energy conversion and thermal energy storage, and its preparation method. The composite material is composed of a supporting material and an organic phase change material. The supporting material is Ti2C, Ti3C2, Ti3CN, V2C, Nb2C, TiNbC, Nb4C3, Ta4C3, (Ti... 0.5 Nb 0.5 )2C or (V 0.5 Cr 0.5 The patented technology involves stacked MXene nanosheets (3C2), where the organic phase change material is paraffin, fatty acid, fatty acid ester, or alcohol compound. In this technology, MXene nanosheets and the phase change material are directly mixed. The improvement in the thermal conductivity of the phase change material is not ideal, and due to the large amount of MXene nanosheets added, the phase change enthalpy of the material also decreases dramatically. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a phase change composite aerogel material with good phase change performance and heat transfer performance and its preparation method, so as to solve the shortcomings of traditional organic phase change thermal storage materials such as low thermal conductivity, poor photothermal conversion performance and large decrease in phase change enthalpy.

[0006] To achieve the above objectives, the solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a phase change composite aerogel material for photothermal conversion and high-density heat storage, characterized in that it is a phase change composite aerogel material with MXenes / CNTs modified aerogel as a three-dimensional porous continuous support framework and phase change material as a filler material; wherein, based on 100% by mass, the mass percentage of MXenes / CNTs modified aerogel in the phase change composite aerogel material is 3.0-4.4%, and the mass percentage of phase change material is 95.6-97.0%.

[0008] Preferably, the phase change enthalpy of the phase change composite aerogel material is 195.2-210.0 J / g.

[0009] Preferably, the phase change material is selected from one or more of monohydric alcohol phase change materials, straight-chain alkane phase change materials, and fatty acid phase change materials. The monohydric alcohol phase change material is selected from one or more of dodecanol, tridecanol, tetradecanol, pentadecylol, and hexadecylol. The straight-chain alkane phase change material is selected from one or more of paraffin wax, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane, and n-eicosane. The fatty acid phase change material is selected from one or more of palmitic acid, stearic acid, lauric acid, myristic acid, and palmitic acid. Preferably, the phase change material is n-eicosane.

[0010] Preferably, the MXenes are selected from Ti2C MXenes, Ti3C2 MXenes, Ti3CN MXenes, V2C MXenes, Nb2C MXenes, TiNbC MXenes, Nb4C3 MXenes, Ta4C3 MXenes, (Ti 0.5 Nb 0.5 )2C MXenes and (V 0.5 Cr 0.5 One or more of 3C2 MXenes; preferably, the MXenes are Ti3C2 MXenes.

[0011] Preferably, the CNTs are selected from one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes, carboxylated carbon nanotubes, and aminated carbon nanotubes.

[0012] Secondly, the present invention also provides a method for preparing a phase change composite aerogel material with photothermal conversion and high-density heat storage as described above, comprising the following steps:

[0013] Step (1): Add boric acid and polyvinyl alcohol (PVA) to deionized water, stir and heat to obtain PVA mixture;

[0014] Step (2): PVA mixture, CNTs and MXenes dispersion are added to deionized water in proportion, stirred and heated to obtain a stable dispersion;

[0015] Step (3): The dispersion obtained in step (2) is transferred into a mold, pre-frozen, and then vacuum freeze-dried to obtain an aerogel material.

[0016] Step (4): The aerogel material obtained in step (3) is immersed in the phase change material in the molten state by vacuum impregnation to obtain the phase change composite aerogel material.

[0017] Preferably, in step (1), the mass ratio of boric acid to polyvinyl alcohol (PVA) is (1-5):(10-30), and the concentration of the PVA mixture is 30-50 mg / mL; in step (2), the concentration of MXenes dispersion is 3-7 mg / mL, the volume ratio of PVA mixture, MXenes dispersion and deionized water is 1:(0.01-0.47):(0.2-0.67), and the mass ratio of MXenes to CNTs is (1-7):6.

[0018] Preferably, in step (1), boric acid and polyvinyl alcohol (PVA) are first dissolved in deionized water, and then the boric acid solution and PVA solution are mixed and stirred at 80-100℃ for 5-15 min to form a homogeneous PVA mixture; in step (2), the mixture is stirred at 80-100℃ for 30-40 min; in step (3), the pre-freezing temperature is -20℃, the pre-freezing time is 5-7 h, the vacuum freeze-drying temperature is -50℃ to -60℃, the vacuum freeze-drying time is 45-55 h, and the vacuum degree is not greater than 15 Pa; in step (4), the vacuum degree of vacuum impregnation is not greater than 20 Pa, the time is 3-5 h, and the temperature is 60-80℃.

[0019] Thirdly, the present invention also provides a phase change composite aerogel material prepared by the preparation method described above.

[0020] Fourthly, the present invention also provides an application of the phase change composite aerogel material as described above in solar photothermal conversion and thermal storage materials.

[0021] According to the present invention, a phase change composite aerogel material is provided in which carbon nanotubes (CNTs) possess a unique one-dimensional tubular structure, high thermal conductivity, and mechanical stability, while two-dimensional transition metal carbides / carbonitrides (MXenes) exhibit excellent light absorption properties and can spontaneously convert solar energy into thermal energy. The present invention combines one-dimensional CNTs and two-dimensional MXenes in a PVA-formed aerogel through directional freezing and subsequent freeze-drying. The one-dimensional CNTs act as conductive "bridges" connecting the MXene nanosheets, constructing a conductive pathway network through line-to-surface contact. Strong π-π interactions improve the interactions between MXene nanosheets, and the interconnected network is synergistically enhanced by the CNTs. This method can produce materials with high thermal energy storage density, photothermal conversion efficiency, and excellent morphological stability, thermal stability, cycleability, and safety, making it widely applicable in solar energy conversion and thermal energy storage technologies.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) The MXenes / CNTs modified aerogel composite phase change material prepared by this invention is at the micron level. Its surface and interior are covered with MXenes and CNTs. It has a large heat transfer area, good heat transfer performance and good mechanical properties, and has a wide range of applications.

[0024] (2) The preparation method of the present invention is simple, and the reaction time and reaction conditions are easy to control;

[0025] (3) The MXenes / CNTs modified aerogel composite phase change material prepared by the preparation method of the present invention has a small amount of MXenes added, and the mass percentage of MXenes / CNTs modified aerogel is only 3.0-4.4%, which can achieve excellent photothermal conversion efficiency. Moreover, the addition of CNTs improves the defect of significant decrease in phase change enthalpy caused by only adding MXenes to the modified aerogel composite phase change material.

[0026] (4) The MXenes / CNTs modified aerogel composite phase change material prepared by this invention is applied to solar energy storage materials. The composite phase change energy storage material exhibits high sensitivity to photothermal activity and has an extremely fast heating rate, which can quickly utilize solar energy to absorb heat, and the solar energy utilization rate is greatly improved. In addition, it can also solve the problems of volume expansion, significant flow, leakage oxidation and loss of high latent heat that occur during the solid-to-liquid phase conversion of phase change materials, and has broad application prospects in the field of phase change energy storage. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the preparation process of the MXenes / CNTs modified aerogel composite phase change material involved in this invention.

[0028] Figure 2 These are SEM images of the cross-section and longitudinal section of the aerogels prepared under the conditions of various embodiments of the present invention, as well as images of the aerogels after impregnation with phase change materials. The morphology of the samples was observed using a scanning electron microscope (SEM, Hitachi S-4800) at an accelerating voltage of 10.0 kV. Figure 2 (a1), 2(a2) and 2(a3) are SEM images of aerogels without CNTs and MXenes; Figure 2 (b1), 2(b1), and 2(b3) are SEM images of aerogels with added CNTs and 1 mL MXenes; Figure 2 (c1), 2(c2), and 2(c3) are SEM images of aerogels with added CNTs and 5 mL MXenes; Figure 2 (d1), 2(d2), and 2(d3) are SEM images of aerogels with added CNTs and 7 mL MXenes.

[0029] Figure 3The images show the XRD patterns of the aerogel composite phase change materials prepared under the conditions of various embodiments of the present invention. The crystal structure of the aerogel samples was analyzed by X-ray diffraction (XRD, D8 Advance) at a scanning angle (2θ) rate of 2° / min in the range of 5°-80°.

[0030] Figure 4 The images show the FT-IR spectra of the aerogel composite phase change materials prepared under the conditions of various embodiments of the present invention. The infrared spectra of the samples were measured using a Fourier transform infrared spectrometer (FT-IR, iS20).

[0031] Figure 5 The DSC curves of the aerogel composite phase change materials prepared under the conditions of various embodiments of the present invention are shown. The instrument used was a Diamond DSC differential scanning calorimeter manufactured by PerkinElmer Instruments Ltd. (heating and cooling range 15–55 °C, heating and cooling rate 5 °C / min, N2 flow rate 20 mL / min). The encapsulation efficiency of the aerogel composite phase change material can be calculated using the following formula (1):

[0032]

[0033] Figure 6 The graph shows the photothermal conversion curves of the aerogel composite phase change materials prepared under the conditions of various embodiments of the present invention.

[0034] Figure 7 The diagram shows the photothermal conversion efficiency of the aerogel composite phase change materials prepared under the conditions of various embodiments of the present invention. The photothermal conversion efficiency of the aerogel composite phase change materials can be calculated using the following formula (2):

[0035]

[0036] Where m is the mass of the composite phase change material, ΔHm is the enthalpy of melting of the composite phase change material, P is the light intensity, S is the surface area of ​​the composite phase change material, and Δt is the time difference from the start to the end of the phase change. Detailed Implementation

[0037] This invention provides an MXenes / CNTs modified aerogel composite phase change material for photothermal conversion, and the specific process of its preparation method is as follows: Figure 1 As shown, it includes the following steps:

[0038] Step 1: Add boric acid and PVA to deionized water at a mass ratio of (1-5):(10-30) (3:20 is used as an example in this embodiment of the invention), stir and heat to prepare a PVA mixture;

[0039] In a preferred embodiment, the process consists of three steps: First, 300 mg of boric acid is added to 50 mL of deionized water and stirred for 10 min to obtain a 6 mg / mL boric acid solution; second, 4000 mg of PVA is added to 100 mL of deionized water and stirred at 90°C for 30 min to obtain a 40 mg / mL PVA solution; third, the boric acid solution is added to the PVA solution and stirred at 90°C for 10 min to form a homogeneous PVA mixture.

[0040] Step 2: Add the PVA mixture, CNTs, MXenes dispersion, and deionized water from Step 1 to a beaker in the specified proportions, stir and heat to obtain a stable dispersion;

[0041] The concentration of the MXenes dispersion is 3-7 mg / mL (5 mg / mL is used as an example in this embodiment of the invention), the volume ratio of PVA mixture, MXenes dispersion and deionized water is 1:(0.01-0.47):(0.2-0.67), and the mass ratio of MXenes and CNTs is (1-7):6.

[0042] Step 3: Transfer the dispersion obtained in Step 2 into a mold and pre-freeze it;

[0043] In a preferred embodiment, the pre-freezing treatment is carried out in a freezer; the pre-freezing temperature is -20°C and the time is 6 hours.

[0044] Step 4: The sample that underwent pre-freezing treatment in Step 3 was subjected to vacuum freeze-drying to obtain the aerogel material;

[0045] In a preferred embodiment, the vacuum freeze-drying temperature is -50 to -60°C, the time is 48 hours, and the vacuum degree is not greater than 15 Pa.

[0046] Step 5: The aerogel material obtained in Step 4 is composited with a phase change material through vacuum impregnation;

[0047] In a preferred embodiment, the vacuum impregnation is performed at a vacuum level of no more than 20 Pa, for a duration of 3 to 5 hours, and at a temperature of 70°C.

[0048] In a preferred embodiment, the phase change material includes, but is not limited to, one or more of monohydric alcohol phase change materials, straight-chain alkane phase change materials, and fatty acid phase change materials. The monohydric alcohol phase change materials include, but are not limited to, one or more of dodecanol, tridecanol, tetradecanol, pentadecylol, and hexadecylol. The straight-chain alkane phase change materials include, but are not limited to, one or more of paraffin wax, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane, and n-eicosane. The fatty acid phase change materials include, but are not limited to, one or more of palmitic acid, stearic acid, lauric acid, myristic acid, and palmitic acid. In this embodiment of the invention, n-eicosane is used as an example of the phase change material.

[0049] In a preferred embodiment, the MXenes include, but are not limited to, Ti2C MXenes, Ti3C2 MXenes, Ti3CN MXenes, V2C MXenes, Nb2C MXenes, TiNbC MXenes, Nb4C3 MXenes, Ta4C3 MXenes, (Ti 0.5 Nb 0.5 )2C MXenes and (V 0.5 Cr 0.5 One or more of 3C2 MXenes; preferably, the MXenes are Ti3C2MXenes.

[0050] In a preferred embodiment, the CNTs include, but are not limited to, one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes, carboxylated carbon nanotubes, and aminated carbon nanotubes.

[0051] The present invention will be further illustrated below with reference to specific embodiments. The purpose of these embodiments is to provide a better understanding of the invention and to demonstrate its essential characteristics. Therefore, the examples given should not be considered as limitations on the scope of protection of the present invention. It is also specifically noted that, unless otherwise specified, the specific experimental methods and equipment involved in the embodiments are conventional methods or implemented according to the conditions recommended in the manufacturer's instructions, and the reagents involved are all commercially available unless otherwise specified.

[0052] Example 1:

[0053] Step 1: Weigh 300 mg of boric acid and add it to 50 mL of deionized water. Stir for 10 min to obtain a 6 mg / mL boric acid solution. Then add 4000 mg of PVA to 100 mL of deionized water and stir at 90°C for 30 min to obtain a 40 mg / mL PVA solution. Then add the boric acid solution to the PVA solution and stir at 90°C for 10 min to form a homogeneous PVA mixture.

[0054] Step 2: Take 15 mL of the PVA mixture obtained in Step 1 into a beaker, add 10 mL of deionized water, heat and stir at 90°C for 30 min to obtain a stable dispersion.

[0055] Step 3: Pour the dispersion obtained in Step 2 into a mold and pre-freeze it in a refrigerator at -10℃ for 6 hours.

[0056] Step 4: Take out the sample from Step 3 and place it in a freeze dryer for vacuum freeze drying to obtain aerogel material. The vacuum degree of this process is 19 Pa, the vacuum freeze drying temperature is -40℃, and the time is 48 hours.

[0057] Step 5: Composite the sample from Step 4 with the phase change material via vacuum impregnation. First, place n-eicosane in a beaker and heat to 70°C. After the n-eicosane has completely melted, place the prepared aerogel into the melted n-eicosane, then place the beaker in a vacuum oven at 70°C for 4 hours. Under negative pressure, the liquid n-eicosane fully permeates into the pores of the aerogel. After filling the aerogel with n-eicosane, filter off excess liquid n-eicosane from the surface using a ceramic funnel. The final product is the composite phase change material prepared from the aerogel.

[0058] Test results: The mass ratio of the obtained composite phase change material aerogel was 3.0%, and the mass ratio of n-eicosane was 97.0%. SEM images showed that the aerogel was well-arranged, exhibiting continuous wrinkles and a bridge-like structure, forming a continuous and interconnected 3D network. There were no obvious boundaries between the wrinkles in the aerogel after filling with the phase change material, indicating that n-eicosane had completely filled the microporous structure. XRD and FT-IR spectra showed that no new peaks appeared besides the characteristic peaks of CNTs and PVA, indicating that PVA had no effect on the crystal structure of n-eicosane. DSC analysis showed that the melting and crystallization phase change enthalpies of this phase change aerogel material reached 209.1 J / g and 205.7 J / g, respectively, with melting and crystallization temperatures of 37.5℃ and 31.4℃, respectively, corresponding to an encapsulation efficiency of 92.4%. The photothermal conversion efficiency was calculated to be 21.51% using the photothermal conversion efficiency formula.

[0059] Example 2:

[0060] Step 1: Weigh 300 mg of boric acid and add it to 50 mL of deionized water. Stir for 10 min to obtain a 6 mg / mL boric acid solution. Then add 4000 mg of PVA to 100 mL of deionized water and stir at 90°C for 30 min to obtain a 40 mg / mL PVA solution. Then add the boric acid solution to the 40 mg / mL PVA solution and stir at 90°C for 10 min to form a homogeneous PVA mixture.

[0061] Step 2: Take 15 mL of the PVA mixture obtained in Step 1 into a beaker, add 30 mg of CNTs and 1 mL of MXenes solution (MXenes solution concentration is 5 mg / mL), and finally add 9 mL of deionized water. Heat and stir at 90 °C for 30 min to obtain a stable dispersion.

[0062] Step 3: Pour the dispersion obtained in Step 2 into a mold and pre-freeze it in a refrigerator at -10℃ for 6 hours.

[0063] Step 4: Take out the sample from Step 3 and place it in a freeze dryer for vacuum freeze drying to obtain aerogel material. The vacuum degree of this process is 15 Pa, the vacuum freeze drying temperature is -55℃, and the time is 48 hours.

[0064] Step 5: Composite the sample from Step 4 with the phase change material via vacuum impregnation. First, place n-eicosane in a beaker and heat to 70°C. After the n-eicosane has completely melted, place the prepared aerogel into the melted n-eicosane, then place the beaker in a vacuum oven at 70°C for 4 hours. Under negative pressure, the liquid n-eicosane fully permeates into the pores of the aerogel. After filling the aerogel with n-eicosane, filter off excess liquid n-eicosane from the surface using a ceramic funnel. The final product is the composite phase change material prepared from the aerogel.

[0065] Test results: The mass ratio of the obtained composite phase change material aerogel was 3.6%, and the mass ratio of n-eicosane was 96.4%. SEM images showed that the aerogel was well-arranged, exhibiting continuous wrinkles and a bridge-like structure, forming a continuous and interconnected 3D network. There were no obvious boundaries between the wrinkles of the aerogel after filling with the phase change material, indicating that n-eicosane had completely filled the microporous structure. XRD and FT-IR spectra showed that no new peaks appeared besides the characteristic peaks of CNTs and PVA, indicating that PVA had no effect on the crystal structure of n-eicosane. DSC images showed that the melting phase transition enthalpy and crystallization phase transition enthalpy of this phase change aerogel material reached 210.0 J / g and 207.4 J / g, respectively, with melting temperature and crystallization temperature of 37.3℃ and 31.4℃, respectively, corresponding to an encapsulation efficiency of 92.9%. The photothermal conversion efficiency of Example 2 was improved by 315.6% compared to the sample of Example 1, reaching 89.39%.

[0066] Example 3:

[0067] Step 1: Weigh 300 mg of boric acid and add it to 50 mL of deionized water. Stir for 10 min to obtain a 6 mg / mL boric acid solution. Then add 4000 mg of PVA to 100 mL of deionized water and stir at 90°C for 30 min to obtain a 40 mg / mL PVA solution. Then add the boric acid solution to the 40 mg / mL PVA solution and stir at 90°C for 10 min to form a homogeneous PVA mixture.

[0068] Step 2: Take 15 mL of the PVA mixture obtained in Step 1 into a beaker, add 30 mg of CNTs and 3 mL of MXenes solution (MXenes solution concentration is 5 mg / mL), and finally add 7 mL of deionized water. Heat and stir at 90 °C for 30 min to obtain a stable dispersion.

[0069] Step 3: Pour the dispersion obtained in Step 2 into a mold and pre-freeze it in a refrigerator at -10℃ for 6 hours.

[0070] Step 4: Take out the sample from Step 3 and place it in a freeze dryer for vacuum freeze drying to obtain aerogel material. The vacuum degree of this process is 15 Pa, the vacuum freeze drying temperature is -55℃, and the time is 48 hours.

[0071] Step 5: Composite the sample from Step 4 with the phase change material via vacuum impregnation. First, place n-eicosane in a beaker and heat to 70°C. After the n-eicosane has completely melted, place the prepared aerogel into the melted n-eicosane, then place the beaker in a vacuum oven at 70°C for 4 hours. Under negative pressure, the liquid n-eicosane fully permeates into the pores of the aerogel. After filling the aerogel with n-eicosane, filter off excess liquid n-eicosane from the surface using a ceramic funnel. The final product is the composite phase change material prepared from the aerogel.

[0072] Test results: The mass ratio of the obtained composite phase change material aerogel was 4.0%, and the mass ratio of n-eicosane was 96.0%. SEM images showed that the aerogel was well-arranged, exhibiting continuous wrinkles and a bridge-like structure, forming a continuous and interconnected 3D network. There were no obvious boundaries between the wrinkles in the aerogel after filling with the phase change material, indicating that n-eicosane had completely filled the microporous structure. XRD and FT-IR spectra showed that no new peaks appeared besides the characteristic peaks of CNTs and PVA, indicating that PVA had no effect on the crystal structure of n-eicosane. DSC images showed that the melting enthalpy and crystallization enthalpy of this phase change aerogel material reached 203.6 J / g and 194.0 J / g, respectively, with melting and crystallization temperatures of 37.0℃ and 31.3℃, respectively, corresponding to an encapsulation efficiency of 89.8%. The photothermal conversion efficiency of Example 3 was improved by 338.6% compared to the sample in Example 1, reaching 94.35%.

[0073] Example 4:

[0074] Step 1: Weigh 300 mg of boric acid and add it to 50 mL of deionized water. Stir for 10 min to obtain a 6 mg / mL boric acid solution. Then add 4000 mg of PVA to 100 mL of deionized water and stir at 90°C for 30 min to obtain a 40 mg / mL PVA solution. Then add the boric acid solution to the 40 mg / mL PVA solution and stir at 90°C for 10 min to form a homogeneous PVA mixture.

[0075] Step 2: Take 15 mL of the PVA mixture obtained in Step 1 into a beaker, add 30 mg of CNTs and 5 mL of MXenes solution (MXenes solution concentration is 5 mg / mL), and finally add 5 mL of deionized water. Heat and stir at 90 °C for 30 min to obtain a stable dispersion.

[0076] Step 3: Pour the dispersion obtained in Step 2 into a mold and pre-freeze it in a refrigerator at -10℃ for 6 hours.

[0077] Step 4: Take out the sample from Step 3 and place it in a freeze dryer for vacuum freeze drying to obtain aerogel material. The vacuum degree of this process is 15 Pa, the vacuum freeze drying temperature is -55℃, and the time is 48 hours.

[0078] Step 5: Composite the sample from Step 4 with the phase change material via vacuum impregnation. First, place n-eicosane in a beaker and heat to 70°C. After the n-eicosane has completely melted, place the prepared aerogel into the melted n-eicosane, then place the beaker in a vacuum oven at 70°C for 4 hours. Under negative pressure, the liquid n-eicosane fully permeates into the pores of the aerogel. After filling the aerogel with n-eicosane, filter off excess liquid n-eicosane from the surface using a ceramic funnel. The final product is the composite phase change material prepared from the aerogel.

[0079] Test results: The mass ratio of the obtained composite phase change material aerogel was 4.4%, and the mass ratio of n-eicosane was 95.6%. SEM images showed that the aerogel was well-arranged, exhibiting continuous wrinkles and a bridge-like structure, forming a continuous and interconnected 3D network. There were no obvious boundaries between the wrinkles of the aerogel after filling with the phase change material, indicating that n-eicosane had completely filled the microporous structure. XRD and FT-IR spectra showed that no new peaks appeared besides the characteristic peaks of CNTs and PVA, indicating that PVA had no effect on the crystal structure of n-eicosane. DSC images showed that the melting phase transition enthalpy and crystallization phase transition enthalpy of this phase change aerogel material reached 200.9 J / g and 194.4 J / g, respectively, with melting temperature and crystallization temperature of 37.2℃ and 31.3℃, respectively, corresponding to an encapsulation efficiency of 88.5%. The photothermal conversion efficiency of Example 4 was improved by 340.4% compared to the sample of Example 1, reaching 94.73%.

[0080] Example 5:

[0081] Step 1: Weigh 300 mg of boric acid and add it to 50 mL of deionized water. Stir for 10 min to obtain a 6 mg / mL boric acid solution. Then add 4000 mg of PVA to 100 mL of deionized water and stir at 90°C for 30 min to obtain a 40 mg / mL PVA solution. Then add the boric acid solution to the 40 mg / mL PVA solution and stir at 90°C for 10 min to form a homogeneous PVA mixture.

[0082] Step 2: Take 15 mL of the PVA mixture obtained in Step 1 into a beaker, add 30 mg of CNTs and 7 mL of MXenes solution (MXenes solution concentration is 5 mg / mL), and finally add 3 mL of deionized water. Heat and stir at 90 °C for 30 min to obtain a stable dispersion.

[0083] Step 3: Pour the dispersion obtained in Step 2 into a mold and pre-freeze it in a refrigerator at -10℃ for 6 hours.

[0084] Step 4: Take out the sample from Step 3 and place it in a freeze dryer for vacuum freeze drying to obtain aerogel material. The vacuum degree of this process is 15 Pa, the vacuum freeze drying temperature is -55℃, and the time is 48 hours.

[0085] Step 5: Composite the sample from Step 4 with the phase change material via vacuum impregnation. First, place n-eicosane in a beaker and heat to 70°C. After the n-eicosane has completely melted, place the prepared aerogel into the melted n-eicosane, then place the beaker in a vacuum oven at 70°C for 4 hours. Under negative pressure, the liquid n-eicosane fully permeates into the pores of the aerogel. After filling the aerogel with n-eicosane, filter off excess liquid n-eicosane from the surface using a ceramic funnel. The final product is the composite phase change material prepared from the aerogel.

[0086] Test results: The mass ratio of the obtained composite phase change material aerogel was 3.5%, and the mass ratio of n-eicosane was 96.5%. SEM images showed that the aerogel was well-arranged, exhibiting continuous wrinkles and a bridge-like structure, forming a continuous and interconnected 3D network. There were no obvious boundaries between the wrinkles of the aerogel after filling with the phase change material, indicating that n-eicosane had completely filled the microporous structure. XRD and FT-IR spectra showed that no new peaks appeared besides the characteristic peaks of CNTs and PVA, indicating that PVA had no effect on the crystal structure of n-eicosane. DSC images showed that the melting phase transition enthalpy and crystallization phase transition enthalpy of this phase change aerogel material reached 195.2 J / g and 192.0 J / g, respectively, with melting temperature and crystallization temperature of 37.0℃ and 31.4℃, respectively, corresponding to an encapsulation efficiency of 86.3%. Example 5 showed a 354.3% improvement in photothermal conversion efficiency compared to Example 1, reaching 97.71%, making it the most efficient sample among all examples.

[0087] Comparative Example 1 (with only MXenes added):

[0088] Step 1: Weigh 300 mg of boric acid and add it to 50 mL of deionized water. Stir for 10 min to obtain a 6 mg / mL boric acid solution. Then add 4000 mg of PVA to 100 mL of deionized water and stir at 90°C for 30 min to obtain a 40 mg / mL PVA solution. Then add the boric acid solution to the 40 mg / mL PVA solution and stir at 90°C for 10 min to form a homogeneous PVA mixture.

[0089] Step 2: Take 15 mL of the PVA mixture obtained in Step 1 into a beaker, add 7 mL of MXenes solution (MXenes solution concentration is 5 mg / mL), and finally add 10 mL of deionized water. Heat and stir at 90℃ for 30 min to obtain a stable dispersion.

[0090] Step 3: Pour the dispersion obtained in Step 2 into a mold and pre-freeze it in a refrigerator at -10℃ for 6 hours.

[0091] Step 4: Take out the sample from Step 3 and place it in a freeze dryer for vacuum freeze drying to obtain aerogel material. The vacuum degree of this process is 15 Pa, the vacuum freeze drying temperature is -55℃, and the time is 48 hours.

[0092] Step 5: Composite the sample from Step 4 with the phase change material via vacuum impregnation. First, place n-eicosane in a beaker and heat to 70°C. After the n-eicosane has completely melted, place the prepared aerogel into the melted n-eicosane, then place the beaker in a vacuum oven at 70°C for 4 hours. Under negative pressure, the liquid n-eicosane fully permeates into the pores of the aerogel. After filling the aerogel with n-eicosane, filter off excess liquid n-eicosane from the surface using a ceramic funnel. The final product is the composite phase change material prepared from the aerogel.

[0093] The melting phase transition enthalpy and crystallization phase transition enthalpy of this phase change aerogel material reach 184.1 J / g and 183.0 J / g, respectively, and the melting temperature and crystallization temperature are 37.5℃ and 31.1℃, respectively.

[0094] As can be seen from Examples 1-5 and Comparative Example 1 above:

[0095] (1) The MXenes / CNTs modified aerogel composite phase change materials prepared according to Examples 2 to 5 above, based on a mass percentage of 100%, have a mass percentage of 3.0-4.4% for MXenes / CNTs modified aerogel and a mass percentage of 95.6-97.0% for phase change materials. The photothermal conversion efficiency increased from 21.51% in Example 1 (without MXenes and CNTs) to 89.13%-97.71%, indicating that the addition of CNTs and MXenes significantly improved the photothermal conversion efficiency of the phase change composite material.

[0096] (2) The phase transition enthalpy of the aerogel phase change material in Example 1 (without MXenes and CNTs) was 209.1 J / g. The phase transition enthalpy of the phase change composite aerogel material obtained by adding only MXenes in Comparative Example 1 was 184.1 J / g, showing a significant decrease. The phase transition enthalpy of the MXenes / CNTs modified aerogel composite phase change materials prepared according to Examples 2 to 5 showed a gradient decreasing trend, ranging from 195.2 to 210.0 J / g. This indicates that the addition of CNTs improved the defect of significant decrease in phase transition enthalpy caused by the addition of only MXenes in the modified aerogel composite phase change material.

[0097] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A phase change composite aerogel material for light-heat conversion and high-density heat storage, characterized in that, The phase change composite aerogel material is prepared by using MXenes / CNTs modified aerogel as a three-dimensional porous continuous support skeleton and using a phase change material as a filling material; wherein, according to 100% by mass, the mass percentage of the MXenes / CNTs modified aerogel is 3.0-4.4%, and the mass percentage of the phase change material is 95.6-97.0%. The phase change material is selected from one or more of monohydric alcohol phase change materials, straight-chain alkane phase change materials and fatty acid phase change materials; the monohydric alcohol phase change material is selected from one or more of dodecanol, tridecanol, tetradecanol, pentadecanol and hexadecanol; the straight-chain alkane phase change material is selected from one or more of paraffin, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane and n-eicosane; and the fatty acid phase change material is selected from one or more of soft fat acid, stearic acid, lauric acid, myristic acid and palmitic acid. the MXenes are selected from one or several of Ti2C MXenes, Ti3C2 MXenes, Ti3CN MXenes, V2C MXenes, Nb2C MXenes, TiNbC MXenes, Nb4C3 MXenes, Ta4C3 MXenes, (Ti 0.5 Nb 0.5 )2C MXenes and (V 0.5 Cr 0.5 )3C2 MXenes; The mass ratio of MXenes to CNTs is (1-7):

6. 2.The phase change composite aerogel material of light thermal conversion and high-density heat storage of claim 1, wherein, The phase change enthalpy value of the phase change composite aerogel material is 195.2-210.0 J / g, and the encapsulation rate is greater than 85%. 3.The phase change composite aerogel material of light thermal conversion and high-density heat storage of claim 1, wherein, The phase change material is n-eicosane. 4.The phase change composite aerogel material of light thermal conversion and high-density heat storage of claim 1, wherein, The MXenes are Ti3C2 MXenes. 5.The phase change composite aerogel material of light thermal conversion and high-density heat storage of claim 1, wherein, The CNTs are selected from one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes, carboxylated carbon nanotubes and aminated carbon nanotubes.

6. A method for preparing the phase change composite aerogel material for light-heat conversion and high-density heat storage according to any one of claims 1-5, characterized in that, The method comprises the following steps: Step (1), boric acid and polyvinyl alcohol (PVA) are added to deionized water, and stirring and heating are performed to obtain a PVA mixed solution; Step (2), the PVA mixed solution, a CNTs dispersion liquid and a MXenes dispersion liquid are added to deionized water in a certain proportion, and stirring and heating are performed to obtain a stable dispersion liquid; Step (3), the dispersion liquid obtained in Step (2) is transferred to a mold, pre-freezing treatment is performed first, and then vacuum freeze-drying is performed to obtain an aerogel material; Step (4), the aerogel material obtained in Step (3) is immersed in a phase change material in a molten state by a vacuum immersion method to obtain a phase change composite aerogel material.

7. The production method according to claim 6, wherein In Step (1), the mass ratio of boric acid to polyvinyl alcohol (PVA) is (1-5):(10-30), and the concentration of the PVA mixed solution formed is 30-50 mg / mL; in Step (2), the concentration of the MXenes dispersion liquid is 3-7 mg / mL, the volume ratio of the PVA mixed solution, the MXenes dispersion liquid and deionized water is 1:(0.01-0.47):(0.2-0.67), and the mass ratio of MXenes to CNTs is (1-7):

6.

8. The preparation method according to claim 6, characterized in that, In step (1), boric acid and polyvinyl alcohol (PVA) are respectively dissolved in deionized water, and then the boric acid solution and the PVA solution are mixed, stirred at 80-100℃ for 5-15 min to form a uniform PVA mixture; in step (2), the mixture is stirred at 80-100℃ for 30-40 min; in step (3), the pre-freezing temperature is-20℃, the pre-freezing time is 5-7 h, the vacuum freeze-drying temperature is-50℃ to-60℃, the vacuum freeze-drying time is 45-55 h, and the vacuum degree is not more than 15 Pa; in step (4), the vacuum degree of vacuum impregnation is not more than 20 Pa, the time is 3-5 h, and the temperature is 60-80℃.

9. A phase change composite aerogel material prepared by the preparation method of any one of claims 6-8.

10. Application of the phase change composite aerogel material of claim 9 to solar light-heat conversion and heat storage materials.

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