A graphene aerogel organic composite phase change material and its preparation method

Abstract

This invention discloses a graphene aerogel organic composite phase change material, comprising a graphene aerogel framework and an organic phase change material filling the voids in the graphene aerogel framework; wherein the density of the graphene aerogel framework is 240~340 kg / m³, and the mass of the organic phase change material accounts for 61%-66% of the composite material. This invention provides a graphene aerogel organic composite phase change material and its preparation method, resulting in a fully encapsulated phase change material that is not prone to leakage, has high thermal conductivity, and its preparation method is low-cost, easy to prepare, and has good reproducibility.

Description

Technical Field

[0001] This invention relates to the field of phase change energy storage materials technology, and in particular to a graphene aerogel organic composite phase change material and its preparation method. Background Technology

[0002] With rising living standards, population growth, and global urbanization, the demand for energy is increasing. As energy demand continues to climb, improving energy efficiency and reducing reliance on primary energy sources has become a major concern. Against this backdrop, phase change materials (PCMs) can store and release large amounts of energy during their melting and solidification processes at specific temperatures. Thermal energy storage not only reduces the mismatch between energy supply and demand but also improves the performance and reliability of energy systems, playing a crucial role in conserving energy resources.

[0003] Inorganic PCMs generally have higher latent heat storage capacity than organic PCMs. However, they suffer from several application problems, such as supercooling, phase segregation, and corrosivity. Compared to inorganic PCMs, organic PCMs exhibit negligible supercooling and lack phase segregation and corrosivity. Furthermore, organic phase change materials have lower thermal conductivity than inorganic phase change materials. Therefore, organic phase change materials may exhibit better performance in constructing applications. However, without a porous carrier or capsule, PCMs generally cannot be used directly because they tend to leak in a liquid state.

[0004] To address the leakage problem, the most popular method is to impregnate a phase change material into a porous carrier, forming a phase change composite material (PCC). Due to capillary action and surface tension, the molten or dissolved phase change material is firmly confined within the porous network of the carrier. Summary of the Invention

[0005] In view of the aforementioned deficiencies in the prior art, the technical problem to be solved by the present invention is the issues of "pore residue" and "difficulty in permeation by high-viscosity penetrants" in traditional vacuum impregnation methods. The present invention provides a graphene aerogel organic composite phase change material and its preparation method, which allows the phase change material to be fully encapsulated, resulting in a material that is not easily leaked, has a high thermal conductivity, and whose preparation method is low-cost, easy to prepare, and has good repeatability. The present invention combines vacuum equipment with an ultrasonic vibrator, a method that can significantly improve impregnation efficiency and depth, and is particularly suitable for the functional impregnation treatment of porous materials (such as ceramics, composite materials, and biological scaffolds).

[0006] To achieve the above objectives, the present invention provides a graphene aerogel organic composite phase change material, comprising a graphene aerogel framework and an organic phase change material filling the voids in the graphene aerogel framework; wherein the density of the graphene aerogel framework is 240~340 kg / m³. 3The organic phase change material accounts for 61%-66% of the mass of the composite material.

[0007] Furthermore, the organic phase change material includes one or a mixture of several of the following: sliced ​​paraffin, n-tetradecane, n-octadecane, lauryl alcohol, and octadecyl alcohol.

[0008] Furthermore, the graphene aerogel framework is formed by the self-assembly of graphene oxide through reduction with a reducing agent and assisted by an activating agent.

[0009] In a preferred embodiment of the present invention, a method for preparing a graphene aerogel organic composite phase change material is provided, comprising the following steps:

[0010] Dilute the graphene oxide dispersion to the specified concentration using deionized water;

[0011] The diluted graphene oxide dispersion was mixed with reducing agent and activator and stirred, then heated at 5~95℃ for 1~1.5h and refrigerated for 6~10h.

[0012] Continue heating at 85℃~95℃ for 6~9 hours, then wash and dry to obtain graphene aerogel;

[0013] The graphene aerogel is placed in a cylindrical mold and mechanically pressed to a set density to increase the aerogel density and enhance thermal conductivity.

[0014] The organic phase change material is heated to 10°C above the phase change temperature until it melts.

[0015] The graphene aerogel is placed in molten organic phase change material, and vacuum is repeatedly applied until the mass is constant. This ensures that the organic phase change material fully fills the graphene aerogel framework. No specific mold is required; once the mass is constant, it can be removed and allowed to cool naturally.

[0016] Further, this includes diluting the graphene oxide dispersion to a concentration of 4-8 mg / ml with deionized water.

[0017] Further, the diluted graphene oxide dispersion is mixed and stirred with a reducing agent and an activator, wherein the graphene oxide dispersion is 500 parts, the reducing agent is 1-5 parts, and the activator is 20-30 parts with a mass fraction of 5%.

[0018] Furthermore, the reducing agent is one or more of ascorbic acid, triethanolamine, diethanolamine, ammonia, and benzenesulfonic acid.

[0019] Furthermore, the activator is one or more of sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium lauryl polyoxyethylene ether sulfate, and sodium dioctyl sulfosuccinate.

[0020] Further, the material is heated at 85℃~95℃ for 6~9h, washed and dried to obtain graphene aerogel. The washing and drying process includes washing with anhydrous ethanol and then ultrasonically vacuum drying at 80~120℃ at a frequency of 20~40kHz for 6~24h.

[0021] In another preferred embodiment of the present invention, a graphene aerogel-n-octadecane composite phase change material is provided, which is prepared by the graphene aerogel-organic composite phase change material preparation method described above.

[0022] The present invention has the following technical effects:

[0023] 1. This invention solves the inherent problems of organic phase change materials in the solid-liquid conversion process. Graphene aerogel itself has good thermal stability. After mechanical pressing, the structure density is improved, which can provide physical support for organic phase change materials in high-temperature environments and prevent macroscopic leakage due to increased fluidity when the phase change temperature is exceeded.

[0024] 2. By optimizing the heating time (e.g., 1-1.5h at low temperature and 6-9h at high temperature) and drying parameters (6-24h), this invention shortens the preparation cycle while ensuring material performance. Compared with the reaction time of tens of hours in the traditional freeze-drying method, the reaction conditions are mild, the cost is low, it is easy to prepare, and it has good repeatability, making it more suitable for continuous industrial production.

[0025] 3. By replacing traditional water-based washing with anhydrous ethanol, the surface tension during drying is reduced. Combined with a gradient temperature control method of vacuum / blast drying at 80-120℃ (6-24h), the shrinkage and cracking of the aerogel during dehydration is reduced. This solves the problems of easy breakage and decreased porosity of graphene aerogel after drying, while retaining the material's high specific surface area advantage.

[0026] 4. The combination of "mechanical pressing to set density + repeated vacuuming" is adopted. Mechanical pressing can reduce the initial pore spacing of the aerogel, so that the negative pressure can be applied more evenly to the internal pores during subsequent vacuuming. This forces the molten phase change material (such as n-octadecane) to completely fill the micropores, overcoming the defects of the traditional soaking method, which has more adsorption on the material surface and less internal penetration, and ensuring the uniformity of the composite material composition.

[0027] 5. By combining vacuum impregnation with ultrasonic vibration at a specific frequency, the problems of "residual air in pores" and "difficulty in penetration of high-viscosity impregnation liquid" in traditional vacuum impregnation are solved, while the ultrasonic cavitation effect is used to enhance the interfacial bonding force.

[0028] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the preparation method of a preferred embodiment of the present invention;

[0030] Figure 2 This is a graph showing the thermal conductivity of materials with different densities in Embodiment 1 of the present invention;

[0031] Figure 3 These are before-and-after comparison images of Embodiment 1 of the present invention;

[0032] Figure 4 This is a scanning electron microscope image of Embodiment 1 of the present invention;

[0033] Figure 5 This is a differential scanning calorimetry test pattern of Embodiment 1 of the present invention. Detailed Implementation

[0034] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0035] In the following description, specific details, such as particular internal procedures and techniques, are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will appreciate that the invention may be practiced in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of the invention with unnecessary detail.

[0036] Example 1

[0037] Figure 1 This is a schematic diagram of the preparation process of Example 1 of the graphene aerogel organic composite phase change material of the present invention. Figure 1 As shown, this embodiment uses a chemical reduction self-assembly method to prepare graphene aerogel. Specifically, 25g of graphene oxide stock solution was taken and diluted with deionized water to 5mg / ml. 0.15g of ascorbic acid and 1.25g of 5% sodium dodecyl sulfonate were added, and the mixture was stirred with a magnetic stirrer for 10 minutes. The glass bottle was then sealed with plastic wrap and placed in a preheated drying oven at 90°C for 1 hour. After removal, it was allowed to cool naturally to room temperature, and then placed in a refrigerator for 8 hours. Next, the hydrogel was removed and allowed to melt naturally. It was then placed in a drying oven and heated again at 90°C for 6 hours. Finally, the sample was washed with anhydrous ethanol until the yellow liquid disappeared, and then dried in a drying oven at 50°C for 6 hours to obtain the desired graphene aerogel.

[0038] The graphene aerogel was placed in a cylindrical mold, and the pressure was controlled to achieve a final density of 300 kg / m³. 3 .

[0039] Using n-octadecane as the phase change material, graphene aerogels of different densities were impregnated with n-octadecane using an ultrasonic vacuum impregnation method. 10g of n-octadecane (phase change temperature 28℃) was added to a 100ml beaker. After complete melting, the graphene aerogel was impregnated. The ultrasonic frequency was set to 20Hz, and vacuum was repeatedly applied. The aerogel was then removed, dried, and weighed until its mass no longer changed. The resulting composite material contained four elements: C, H, O, and N, with a mass percentage of approximately 81:8.76:8.98:1.24. This method of the present invention does not require liquid nitrogen freezing to prepare the aerogel, making it safer and less costly. It also eliminates the need for freeze-drying, making it more suitable for industrial production, and yields a higher thermal conductivity.

[0040] Figure 2 This invention provides a comparison of the thermal conductivity of composite phase change materials with different densities, based on a graphene aerogel organic composite phase change material. Figure 3 This is a schematic diagram of an embodiment 1 of the graphene aerogel organic composite phase change material of the present invention. Figure 4 Scanning electron microscope image of Example 1, which is for the invention of a graphene aerogel organic composite phase change material. Figure 5 This is a DSC test chart of Example 1 of the graphene aerogel organic composite phase change material of the present invention. As can be seen from the chart, octadecane and graphene aerogel are in sufficient contact and are fully coated, with a latent heat of 225.5 J / g and a thermal conductivity of 22.5 W / mK.

[0041] Example 2

[0042] This embodiment is basically the same as embodiment 1, except that the raw material composition and amount added are changed in step (3).

[0043] In this embodiment, the composition and amount of each raw material are as follows: the reducing agent is replaced with 0.2g benzenesulfonic acid, the activator is replaced with 1g sodium lauryl polyoxyethylene ether sulfate, and the organic phase change material is replaced with n-tetradecane.

[0044] The performance of the composite phase change material was tested. The liquid phase of the composite phase change material leaked very little, its latent heat reached 188.2 J / g, and its thermal conductivity was 21.08 W / mk.

[0045] Example 3

[0046] This embodiment is basically the same as embodiment 1, except that the raw material composition and amount added are changed in step (3).

[0047] In this embodiment, the composition and amount of each raw material are as follows: the reducing agent is replaced with 1.5 ml of ammonia water, the activator is replaced with 0.8 g of sodium dioctyl sulfosuccinate, and the organic phase change material is replaced with octadecyl alcohol.

[0048] The performance of the composite phase change material was tested. The liquid phase of the composite phase change material leaked very little, its latent heat reached 210.5 J / g, and its thermal conductivity was 18.08 W / mk.

[0049] Example 4

[0050] This embodiment is basically the same as embodiment 1, except that the raw material composition and amount added are changed in step (3).

[0051] In this embodiment, the composition and amount of each raw material are as follows: the reducing agent is replaced with 0.4g triethanolamine, the activator is replaced with 1.2g sodium dodecyl sulfate, and the organic phase change material is replaced with sliced ​​paraffin.

[0052] The performance of the composite phase change material was tested. The liquid phase of the composite phase change material leaked very little, its latent heat reached 165.7 J / g, and its thermal conductivity was 20.98 W / mk.

[0053] Example 5

[0054] This embodiment is basically the same as embodiment 1, except that the raw material composition and amount added are changed in step (3).

[0055] In this embodiment, the composition and amount of each raw material are as follows: the reducing agent is replaced by a combination of 0.1g ascorbic acid and 0.05g benzenesulfonic acid; the activator is replaced by a combination of 0.6g sodium dodecyl sulfonate and 0.6g sodium dioctyl sulfosuccinate; and the organic phase change material is replaced by a combination of n-tetradecane and n-octadecane.

[0056] The performance of the composite phase change material was tested. The liquid phase of the composite phase change material leaked very little, its latent heat reached 203.4 J / g, and its thermal conductivity was 23.12 W / mk.

[0057] Therefore, the present invention employs the above-mentioned preparation method of graphene aerogel organic composite phase change material and composite phase change material, which can effectively solve the problems of leakage and low thermal conductivity during phase change of organic phase change materials.

[0058] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A graphene aerogel organic composite phase change material, characterized in that, The composite material comprises a graphene aerogel framework and an organic phase change material filling the voids in the graphene aerogel framework; wherein the density of the graphene aerogel framework is 240~340 kg / m³, and the mass of the organic phase change material accounts for 61%-66% of the composite material. The preparation steps include the following: Dilute the graphene oxide dispersion to the specified concentration using deionized water; The diluted graphene oxide dispersion was mixed with reducing agent and activator and stirred, then heated at 5~95℃ for 1~1.5 h and refrigerated for 6~10 h. Continue heating at 85℃~95℃ for 6~9 hours, then wash and dry to obtain graphene aerogel; The graphene aerogel was placed in a cylindrical mold and mechanically pressed to a set density, with the final density controlled to 300 kg / m³. 3 ; The organic phase change material is heated to 10°C above the phase change temperature until it melts. The graphene aerogel was placed in molten organic phase change material and subjected to repeated vacuuming using an ultrasonic vacuum impregnation method until the material mass was constant.

2. The graphene aerogel organic composite phase change material as described in claim 1, characterized in that, Organic phase change materials include one or a mixture of several of the following: sliced ​​paraffin, n-tetradecane, n-octadecane, lauryl alcohol, and octadecyl alcohol.

3. The graphene aerogel organic composite phase change material as described in claim 1, characterized in that, The graphene aerogel framework is formed by the self-assembly of graphene oxide through reduction with a reducing agent and assisted by an activator.

4. A method for preparing a graphene aerogel organic composite phase change material as described in any one of claims 1-3, characterized in that, Includes the following steps: Dilute the graphene oxide dispersion to the specified concentration using deionized water; The diluted graphene oxide dispersion was mixed with reducing agent and activator and stirred, then heated at 5~95℃ for 1~1.5 h and refrigerated for 6~10 h. Continue heating at 85℃~95℃ for 6~9 hours, then wash and dry to obtain graphene aerogel; The graphene aerogel was placed in a cylindrical mold and mechanically pressed to a set density, with the final density controlled to 300 kg / m³. 3 ; The organic phase change material is heated to 10°C above the phase change temperature until it melts. The graphene aerogel was placed in molten organic phase change material and subjected to repeated vacuuming using an ultrasonic vacuum impregnation method until the material mass was constant.

5. The method for preparing a graphene aerogel organic composite phase change material as described in claim 4, characterized in that, This includes diluting the graphene oxide dispersion with deionized water to a concentration of 4-8 mg / ml.

6. The method for preparing a graphene aerogel organic composite phase change material as described in claim 4, characterized in that, The diluted graphene oxide dispersion is mixed and stirred with a reducing agent and an activator, wherein the graphene oxide dispersion is 500 parts, the reducing agent is 1-5 parts, and the activator is 20-30 parts with a mass fraction of 5%.

7. The method for preparing a graphene aerogel organic composite phase change material as described in claim 6, characterized in that, The reducing agent is one or more of ascorbic acid, triethanolamine, diethanolamine, ammonia, and benzenesulfonic acid.

8. The method for preparing a graphene aerogel organic composite phase change material as described in claim 6, characterized in that, The activator is one or more of sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium lauryl polyoxyethylene ether sulfate, and sodium dioctyl sulfosuccinate.

9. The preparation method of a graphene aerogel organic composite phase change material as described in claim 4, characterized in that, Continue heating at 85℃~95℃ for 6~9h, then wash and dry to obtain graphene aerogel. The washing and drying process includes washing with anhydrous ethanol followed by vacuum drying or forced-air drying at 80~120℃ for 6~24h.

10. A graphene aerogel-n-octadecane composite phase change material obtained by the method for preparing graphene aerogel-organic composite phase change material according to any one of claims 4-9.

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