Long-term stable supercooling solar phase change heat storage material capable of controlling electric trigger heat emission and preparation method of long-term stable supercooling solar phase change heat storage material

Abstract

The invention belongs to the technical field of phase-change materials, and particularly relates to a long-term stable supercooling solar phase-change heat storage material capable of controlling electric trigger heat emission and a preparation method of the long-term stable supercooling solar phase-change heat storage material. The phase change heat storage material is composed of hydrogel serving as a framework material, hydrated salt fixed in a hydrogel framework through physical and chemical connection, a stably dispersed photo-thermal agent and an electrode embedded in the material. According to the invention, the spontaneous fluctuating effect of hydrated salt is obviously inhibited to reach a critical dimension and trigger crystallization, the long-term stable supercooled state of the material in a wide temperature range is realized, and by adjusting the proportion of the components, not only is the phase separation of the material effectively prevented, but also the photo-thermal conversion efficiency of the material can be obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of heat storage materials, and in particular to a long-term stable supercooled solar phase change heat storage material with controllable electrically triggered heat release and a preparation method thereof. Background Art

[0002] Against the backdrop of the rapid development of the global economy, the global demand for non-renewable energy is rising sharply. However, the exploitation and use of mineral energy poses a serious threat to the ecological environment. In the face of this challenge, optimizing energy acquisition methods, improving energy efficiency, and promoting the low-carbon transformation of the energy system have become core issues in the energy field.

[0003] As a sustainable and easily accessible energy source, solar energy is regarded as one of the most promising energy solutions due to its clean and renewable characteristics. However, the intermittent nature of solar radiation, low energy density, and restrictions on climate and terrain make the direct use of solar energy limited. Therefore, it is particularly important to convert solar energy into an energy form that is easy to store. The main conversion methods include photovoltaic effect into electrical energy and photothermal effect into thermal energy. Although photovoltaic technology has made progress in energy storage, its high cost and cycle stability issues still limit its widespread application.

[0004] In contrast, photothermal conversion technology directly stores thermal energy through a heat storage system and has better application prospects. The performance of the heat storage system depends largely on the heat storage materials used. Heat storage materials are mainly divided into three types: sensible heat, latent heat and chemical heat. Among them, latent heat storage materials have shown wide application potential in fields such as grid load balancing and solar heating due to their high heat storage density, flexible design and precise temperature control capabilities.

[0005] In particular, hydrated salt phase change materials have attracted extensive attention from researchers and the industry due to their high solid-liquid phase change latent heat, stable phase change temperature, economy and non-toxicity. However, existing hydrated salt phase change materials still face some key problems in practical applications, such as material leakage, low heat absorption efficiency and lack of controllable heat release mechanism.

[0006] In traditional research, in order to improve the photothermal performance of materials and reduce supercooling, researchers often improve them by adding nucleating agents. However, for cross-seasonal composite heat storage systems that require long-term energy storage, the ability of the material to maintain a stable supercooling during the heat storage stage is crucial. The main challenge currently faced is that metastable supercooled heat storage materials can easily cross thermodynamic and kinetic barriers under the thermal fluctuation mechanism, spontaneously form crystal nuclei and grow, resulting in a decrease in energy storage efficiency and a shortened energy storage cycle.

[0007] In addition, traditional supercooled phase change materials have significant problems in terms of stability. In a supercooled state, the material is easily affected by external disturbances or internal spontaneous fluctuation effects, resulting in spontaneous crystallization, which not only reduces the long-term heat storage time, but also reduces the heat storage efficiency. On the other hand, although some materials exhibit high stability, this stability often limits their ability to release energy when needed, that is, it is difficult to achieve effective crystallization exotherm, affecting the flexibility and controllability of the material in practical applications. Existing technologies usually rely on the addition of seed crystals to promote phase change, but this method has size limitations and is difficult to achieve large-scale controllable exotherm. At the same time, the addition of seed crystals may introduce impurities, affecting the purity and cycle stability of the material. Summary of the invention

[0008] The present application particularly and innovatively provides a long-term stable supercooled solar phase change heat storage material with controllable electrically triggered heat release and a preparation method thereof, which solves the problems of limited absorption of the solar spectrum by existing phase change heat storage materials, spontaneous crystallization heat release during long-term storage, and controllable triggered heat release.

[0009] The technical solution of the present invention is: a long-term stable supercooled solar phase change heat storage material with controllable electrically triggered heat release, which is composed of a hydrogel as a skeleton material, a hydrated salt fixed in the hydrogel skeleton by physical and chemical connection, a stably dispersed photothermal agent, and an electrode embedded in the material; the weight percentage of each component is: Hydrogel: 5-15 parts; Hydrated salt: 75-85 parts; Photothermal agent: 0.5-5 parts.

[0010] Among them, the hydrogel is a three-dimensional network structure with a large specific surface area and a surface rich in hydrophilic groups. It mainly ensures that there is no phase separation during the heat storage process of the phase change material and maintains that the hydrated salt does not leak before and after the phase change.

[0011] Preferably, the hydrogel is any one of polyacrylamide (PAM), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), polyisopropyl acrylamide (PNIPAM), polyacrylic acid (PAA), polyacrylate, polyethylene oxide (PEO), and sodium alginate.

[0012] Preferably, the hydrated salt is any one of sodium acetate trihydrate and disodium hydrogen phosphate.

[0013] Most preferably, the hydrated salt is sodium acetate trihydrate.

[0014] Furthermore, the photothermal agent is one or more materials with high photothermal conversion efficiency.

[0015] Preferably, the photothermal agent can be a carbon material. The carbon material has an extranuclear electron structure including sp 2 and sp 3 Hybridization, and its π electron cloud density is high and loosely distributed, the energy band width is small, and it has a large visible light absorption range. Most of the energy photons in visible light can be absorbed by electrons, making them excited; when the excited electrons fall back to the ground state, they release heat, thereby increasing the local temperature and diffusing it to the surrounding materials and environment. The photothermal agent can be polydopamine, dopamine-modified carbon nanotubes, hydroxylated carbon nanotubes, graphene oxide, functional group-modified expanded graphite, functional group-modified carbon fiber; it can also be a new type of material that can be chemically modified, specifically dopamine-modified carbon nanotubes, amino-functionalized metal organic frameworks (MOFs).

[0016] Preferably, the photothermal agent may also be a new type of material that can be chemically modified. The new type of material may be a carbon nanotube modified with dopamine.

[0017] Preferably, the electrode is a trigger electrode, which comprises a cathode and an anode. The cathode may be a graphite electrode, a copper electrode, a zinc electrode, an iron electrode, or an aluminum electrode, and the anode may be a silver electrode.

[0018] Most preferably, the trigger electrodes are a graphite cathode and a silver anode.

[0019] The present invention also provides a method for preparing the above-mentioned long-term stable supercooled solar phase change heat storage material, comprising: Step 1: Weigh the hydrogel monomer and the photothermal agent according to the formula ratio, and place them and ultrapure water in a magnetic stirrer until the hydrogel monomer is completely dissolved to obtain a hydrogel monomer solution and a photothermal agent slurry; Step 2: Weigh the hydrated salt according to the formula ratio, place it in a blender and stir it evenly. The blender speed is 400 r / s and the stirring time is 150-180 s to obtain a hydrated salt mixture; Step 3: Heat and melt the mixed hydrated salt mixture to obtain a molten mixture, add the photothermal agent and the hydrogel monomer solution into the molten mixture according to the formula, and stir evenly at a constant temperature of 30-90° C. for 120-180 s; Step 4: Weigh a certain amount of the mixture obtained in step 3 and pour it into a mold, add a crosslinking agent to the mixture, and let it stand at room temperature 20-30°C for 15-20 minutes; Step 5: Add the photothermal agent slurry to the shaped material obtained in step 4 and control the moisture content therein, and then embed the electrode to obtain a controllable electrically triggered long-term stable supercooled photothermal phase change material.

[0020] Preferably, in step 3, the hydrated salt should be heated evenly by a constant temperature water bath or oil bath, the heating rate should be greater than 2K / min, and the heating melting temperature should be 15°C lower than the melting point of the hydrated salt.

[0021] Furthermore, in the preparation process, when the photothermal agent is a carbon nanotube modified with polydopamine or dopamine hydrochloride, the treatment method is as follows: Polydopamine: weigh dopamine hydrochloride in proportion, and simultaneously measure 0.1 mol / L sodium hydroxide solution to completely dissolve dopamine hydrochloride in the sodium hydroxide solution to obtain dopamine hydrochloride-sodium hydroxide solution; seal the solution and place it in a constant temperature oven to keep it warm; take out the solution after the reaction, measure acetic acid in an amount equivalent to that of sodium hydroxide, add acetic acid to the solution to neutralize the pH to neutral, and obtain a polydopamine solution.

[0022] Carbon nanotubes modified with dopamine hydrochloride: weigh 18.2 g of tris(hydroxymethyl)aminomethane and place it in a 100 mL beaker; add about 80 ml of deionized water and stir thoroughly to dissolve; adjust the pH value to 8.8 with concentrated hydrochloric acid and dilute to 100 mL to obtain tris(hydroxymethyl)aminomethane buffer. Weigh 0.02 g of carbon nanotubes and measure 20 mL of tris(hydroxymethyl)aminomethane buffer to completely disperse the carbon nanotubes in the tris(hydroxymethyl)aminomethane buffer and stir for 30-60 min; measure 5.5-6.5 mg of dopamine hydrochloride and add it to the solution, stir magnetically at room temperature 25°C for 12 hours; take the precipitate and wash it with water and ethanol several times to obtain dopamine-modified carbon nanotubes.

[0023] The technical principle of the present application is: the difference in free energy between the solid-liquid phases and the thermodynamic energy barrier of the phase change process are the two most important factors for maintaining the long-term supercooling of the system, and reducing the free energy of the supercooled state through hydrogen bonding is an innovative idea to maintain the stability of the system. Based on this, the long-term stable supercooled photothermal phase change material is obtained by selecting different hydrogels and photothermal agents according to the type of hydrated salt, and adopting physical mixing and monomer cross-linking polymerization. In the long-term stable supercooled photothermal phase change material thus obtained, the hydrated salt is fixed inside the hydrogel structure through physical and chemical connections, wherein the physical coating prevents the phase separation of the hydrated salt phase change process and reduces the cyclicity, and the chemical hydrogen bonding can effectively reduce the solid-liquid interface energy of the system, and prevent the hydrated salt from reaching the critical size through the spontaneous fluctuation effect and self-triggered crystallization and failure, thereby forming a stable composite hydrated salt system. On the other hand, through the innovative process of forming first and then adding the photothermal agent, the photothermal agent can be stably dispersed in the entire composite material formed by the hydrated salt and the hydrogel, and connected to the hydrated salt and the hydrogel through surface chemical groups. It will not trigger crystallization as a nucleation site, and can stably maintain the supercooled state and effectively improve the photothermal conversion efficiency of the composite material. In the electrical triggering stage, after power is turned on, the anodic elution phenomenon occurs on the surface of the silver anode, and cations appear in the solution to strengthen hydration, produce composition fluctuations in the supercooled hydrated salt, and induce crystallization exotherm. Under the condition that the material maintains its stable supercooled state, the trigger electrode, especially the anode, is activated by connecting a DC power supply, which triggers the directional migration of ions and the anodic elution effect. In this process, the release of cations enhances hydration, thereby changing the distribution of the supercooled hydrated salt and guiding the hydrated salt clusters to arrange in a specific direction. This orderly arrangement makes it easier for the hydrated salt clusters to grow to a critical size, thereby triggering crystallization. The latent heat released during the crystallization process realizes the heat release of the material. In addition, the entire heat release process can be precisely regulated by remotely controlling the power-on state of the electrodes, realizing intelligent management of energy release, thereby improving the system's response speed and operational flexibility.

[0024] The beneficial effects of the present invention are: The long-term stable supercooled solar phase change thermal storage material with controllable electrically triggered heat release provided in the present application has the remarkable characteristics of long-term stable supercooling, high photothermal conversion efficiency, and controllable triggered heat release. It has the potential to be widely used in large-scale residential winter heating, building photothermal storage, industrial waste heat recovery and other fields.

[0025] 1) In addition to its conventional physical coating function as a skeleton, hydrogel can also chemically connect with hydrated salts to reduce the solid-liquid interface energy of the system, and then form a composite material system with stable photothermal shape by post-loading photothermal agents.

[0026] 2) While effectively improving the photothermal conversion efficiency, the photothermal agent can change its hydrophilicity through physical and chemical processes, interconnect with the hydrated salt to maintain a stable supercooled state of the system during cooling and long-term heat storage, and will not serve as a nucleation site to trigger crystallization.

[0027] 3) By regulating the hydrogen bond interaction between the functional groups of the hydrated salt and the hydrogel and photothermal agent, it can maintain stable supercooling during the low-temperature heat storage process, solving the problem of material failure caused by self-crystallization during the seasonal heat storage of composite phase change materials; 4) Through electrically triggered crystallization, precise control of the exothermic process is achieved, overcoming the size limitations of traditional technologies. Intelligent management of energy release is achieved, improving the response speed and flexibility of the system.

[0028] 5) The overall preparation process adopts a mixing-before-curing method, which can be filled into the phase change material container and then cured during the application stage, which is better adapted to the phase change material container and has great application value in the application of heat storage devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 The working process and physical structure diagram of the long-term stable supercooled solar phase change heat storage material with controllable electrically triggered heat release of the present invention.

[0031] Figure 2 This is a scanning electron microscope image of the long-term stable supercooled solar phase change thermal storage material with controllable electrically triggered heat release obtained in Example 1 of the present invention.

[0032] Figure 3 This is a scanning electron microscope image of the long-term stable supercooled solar energy phase change heat storage material hydrogel network coated phase change material with controllable electrically triggered heat release obtained in Example 1 of the present invention.

[0033] Figure 4 This is a scanning electron microscope image of the long-term stable supercooled solar phase change thermal storage material hydrogel network loaded with a photothermal agent with controllable electrically triggered heat release obtained in Example 1 of the present invention.

[0034] Figure 5 The supercooling conditions of the long-term stable supercooled solar phase change thermal storage material with controllable electrically triggered heat release obtained in Example 1 of the present invention are compared with those of hydrated salt and hydrated salt-hydrogel.

[0035] Figure 6 This is a differential scanning calorimetry data diagram of the long-term stable supercooled solar phase change thermal storage material with controllable electrically triggered heat release obtained in Example 1 of the present invention.

[0036] Figure 7 This is a spectrum diagram of the long-term stable supercooled solar phase change thermal storage material with controllable electrically triggered heat release obtained in Example 1 of the present invention.

[0037] Figure 8 This is a synchronous thermal analysis mass spectrometry data diagram of the long-term stable supercooled solar phase change heat storage material with controllable electrically triggered heat release obtained in Example 1 of the present invention.

[0038] Fig. 9 Schematic diagram and actual picture of the electrically triggered heat release of the long-term stable supercooled solar phase change thermal storage material with controllable electrically triggered heat release obtained in Example 1 of the present invention, as well as the temperature changes during the process. DETAILED DESCRIPTION

[0039] The embodiments of the present invention provide a long-term stable supercooled solar phase change heat storage material with controllable electrically triggered heat release and a preparation method, which can solve the problem that the phase change material has limited solar spectrum absorption and is prone to spontaneous crystallization and failure during the seasonal heat storage process.

[0040] The following examples are used to further illustrate the present invention, but they do not constitute a limitation or restriction on the scope of the present invention. It should be additionally noted that the raw materials mentioned in the following examples can be purchased directly from the market. For materials that cannot be purchased directly, their processing methods will be described in the examples. Example

[0041] (1) Preparation of hydrogel monomer solution: Weigh the hydrogel monomer and ultrapure water according to the formula ratio, dissolve 25.0 g of acrylamide in 125 mL of ultrapure water, and then purge with nitrogen to eliminate dissolved oxygen. Stir and mix evenly in a stirrer. The stirrer speed is 400 r / s and the stirring time is 150-180 s. Stir until the hydrogel monomer is completely dissolved to obtain a hydrogel monomer solution.

[0042] (2) Preparation of molten hydrated salt mixture: Weigh 85 parts by weight of sodium acetate trihydrate, place it in a constant temperature water bath and heat it at 70°C for 25 minutes to obtain molten hydrated salt.

[0043] (3) Material molding: Pour the molten mixture into a heat storage material container, then add 0.048 g of a cross-linking agent, methylenebisacrylamide, and 2 mL of a cross-linking accelerator, tetramethylethylenediamine. Let it stand at room temperature (20-30 °C) for 15-20 min to obtain a long-term stable supercooled phase change material.

[0044] (4) Weigh 3 parts by weight of the photothermal agent polydopamine, take an appropriate amount of ultrapure water, place in a constant temperature water bath at 75°C and magnetically stir at 120 r / min to obtain a polydopamine solution, and then add it into the above-mentioned long-term stable supercooled phase change material in proportion. The water content in the composite material can be controlled by a drying oven, and finally a long-term stable supercooled photothermal phase change material with photothermal capacity is obtained.

[0045] The preparation method of polydopamine is as follows: weigh 2g of dopamine hydrochloride, measure 20-40mL, 0.1mol / L sodium hydroxide solution, and completely dissolve dopamine hydrochloride in the sodium hydroxide solution to obtain dopamine hydrochloride-sodium hydroxide solution; seal the solution and place it in a constant temperature oven at 45-65°C for 30-60min; take out the solution after the reaction, measure acetic acid in an amount equivalent to that of sodium hydroxide, add acetic acid to the solution to neutralize the pH to neutral, and obtain a polydopamine solution. At the same time, sodium acetate in the solution can be used as a phase change material to complete heat storage after adding the composite material.

[0046] (5) Embedding the trigger electrode: inserting the trigger electrode comprising a graphite cathode and a silver anode into the composite material, and connecting the power supply to the trigger electrode to obtain a long-term stable supercooled solar phase change thermal storage material with controllable electrically triggered heat release. Example

[0047] Except for step (4), steps (1), (2), (3), and (5) are the same as the corresponding steps in Example 1.

[0048] (4) Weigh 5 parts by weight of carbon nanotubes modified with photothermal agent dopamine, take an appropriate amount of ultrapure water, place in a constant temperature water bath at 75°C and magnetically stir at 120 r / min to obtain a dopamine-modified carbon nanotube slurry, and then add it into the above-mentioned long-term stable supercooled phase change material in proportion. The water content in the composite material can be controlled by a drying oven, and finally a long-term stable supercooled photothermal phase change material with photothermal capacity is obtained.

[0049] The preparation method of the dopamine hydrochloride modified carbon nanotubes is as follows: weigh 18.2 g of tris(hydroxymethyl)aminomethane and place it in a 100 mL beaker; add about 80 ml of deionized water and stir thoroughly to dissolve; adjust the pH value to 8.8 with concentrated hydrochloric acid, and dilute to 100 mL to obtain tris(hydroxymethyl)aminomethane buffer. Weigh 0.02 g of carbon nanotubes, measure 20 mL of tris(hydroxymethyl)aminomethane buffer, and completely disperse the carbon nanotubes in the tris(hydroxymethyl)aminomethane buffer, and stir for 30-60 min; measure 5.5-6.5 mg of dopamine hydrochloride and add it to the solution, and stir magnetically for 12 h at room temperature of 25 degrees Celsius; take the precipitate and wash it with water and ethanol several times to obtain dopamine modified carbon nanotubes. Example

[0050] Except for step (2), steps (1), (3), (4) and (5) are the same as the corresponding steps in Example 1.

[0051] (2) Preparation of molten hydrated salt mixture: Weigh 85 parts by weight of binary water and salt (sodium thiosulfate pentahydrate and sodium acetate trihydrate 4:1), place it in a constant temperature water bath at 70°C, stir at 200 r / min and heat for 25 min to obtain molten hydrated salt.

[0052] Except for step (4), steps (1), (2), (3), and (5) are the same as the corresponding steps in Example 1.

[0053] (4) Weigh 5 parts by weight of photothermal agent carbon nanotubes, measure an appropriate amount of ultrapure water, and mix in a constant temperature water bath at 75°C with magnetic stirring at 120 r / min to obtain a carbon nanotube slurry, which is then added to the above-mentioned long-term stable supercooled phase change material in proportion. The water content in the composite material can be controlled by a drying oven, and finally a long-term stable supercooled photothermal phase change material with photothermal capacity is obtained.

[0054] Except for step (2), steps (1), (3), (4) and (5) are the same as the corresponding steps in Example 1.

[0055] (2) Preparation of molten hydrated salt mixture: Weigh 80 parts by mass of binary water and salt (sodium carbonate decahydrate and disodium hydrogen phosphate dodecahydrate in a ratio of 1:9), place it in a constant temperature water bath at 70°C, stir it at 200 r / min and heat it for 25 min to obtain molten hydrated salt.

[0056] The parameters of the above embodiments and comparative examples are listed below: Table 1

[0057] Comparative Example 1-3 shows that different mass fractions of hydrated salts are selected, or different hydrated salt types are selected, different latent heats of phase change will be brought. When the mass fraction of selected hydrated salt as sodium acetate trihydrate is larger, the latent heat of phase change is larger. Meanwhile, the results of embodiment 1-3 for long-term stable supercooling for 24 months all show that when polydopamine and dopamine-modified carbon nanotubes are selected as photothermal agents, hydrogen bonds can be effectively formed, and free energy can be reduced to maintain a stable supercooled state. It can be seen from this that when the mass fraction of hydrogel is selected as 12-15 parts, the mass fraction of hydrated salt is selected as 80-85 parts of sodium acetate trihydrate, and the mass fraction of photothermal agent is selected as 2-5 parts, a relatively reasonable controllable electric triggering heat release long-term stable supercooled solar energy phase change heat storage material can be formed.

[0058] Table 2 shows the triggering conditions of the long-term stable supercooled solar phase change thermal storage material with controllable electrically triggered heat release obtained in Example 1 through different triggering electrodes.

[0059] Table 2

[0060] Figure 1 This is a structural diagram of the controllable electrically triggered heat release and long-term stable supercooled solar phase change heat storage material of the present invention. Figure 2 and Figure 3 Scanning electron microscope (SEM) images of hydrogel networks and long-term stable supercooled photothermal phase change materials. It can be seen that the hydrated salt is completely wrapped in the hydrogel three-dimensional network. The hydrated salt changes from solid to liquid after heating. The three-dimensional network pores prevent the flow of liquid through physical adsorption and chemical bonding. After crystallization, the composite material maintains the same morphology before and after, and no leakage is found. Figure 4 This is the differential scanning calorimetry (DSC) diagram of Example 1. The thermal differential analysis results consist of two curves: heat charging and heat storage. During the heating process, a melting peak began to appear at 36.4°C, with a melting temperature of 224.2 J / g. No solidification peak appeared during the cooling process, indicating that the material was in a stable supercooled state. During the heat storage stage, the material of Example 1 was scanned, and no endothermic or exothermic peaks appeared in its heating and cooling curves, indicating that the material of Example 1 can maintain a stable supercooled state for a long time and has good stability. Figure 5 This is the ultraviolet visible light absorption spectrum of Example 1. The figure shows that the composite material after adding the photothermal agent has a high absorption rate in the infrared and visible light bands. In the visible light range, its absorption rate is 92.66%, which can realize the photothermal charging process faster. In summary, this material is an excellent long-term stable supercooled heat storage material. Figure 6 The simultaneous thermal analysis and mass spectrometry showed that the composite material had good high-temperature stability, with water evaporation completed at 155°C and decomposition to produce carbon dioxide at 450°C. Figure 7 Physical picture of electrically triggered long-term stable supercooled solar phase change thermal storage material with controllable electrically triggered heat release.

[0061] Comparative Examples 1-3 and Comparative Examples 1-2 show that when carbon nanotubes are directly used as photothermal agents, or a combination of sodium carbonate decahydrate and disodium hydrogen phosphate dodecahydrate is selected as a hydrated salt, Comparative Examples 1 and Comparative Examples 2 begin to spontaneously crystallize at 26°C and 20.2°C, respectively. In Comparative Example 1, this is because there are no surface chemical groups between such photothermal agents that can form hydrogen bonds with hydrated salts, and thus the free energy of the system cannot be reduced. Not only can it not play a role in reducing the degree of supercooling, but the newly added photothermal agent also becomes an impurity particle in the crystallization as a nucleation site, making the system more prone to spontaneous crystallization. In Comparative Example 2, the photothermal agent is polydopamine, which can form hydrogen bonds with hydrated salts, but this type of composite hydrated salt system sodium carbonate decahydrate and disodium hydrogen phosphate dodecahydrate are completely clear and transparent in the molten state. As the temperature decreases, this cannot form a stable supercooled state, and the system free energy barrier is small, thereby spontaneously crystallizing. Therefore, the supercooling degree of Comparative Examples 1 and 2 is relatively small, and it is not recommended to use them as long-term stable supercooling phase change energy storage materials.

[0062] The present invention effectively reduces the interfacial tension between the liquid hydrated salt and the additive in the system through the hydrogen bond formed by the hydrogel, the photothermal agent and the surface of the hydrated salt, and reduces the solid-liquid interface energy. This design significantly suppresses the spontaneous fluctuation effect of the hydrated salt to reach the critical size and trigger crystallization, and realizes the long-term stable supercooled state of the material in a wide temperature range. In addition, by adjusting the ratio of each component, not only the phase separation of the material is effectively prevented, but also the photothermal conversion efficiency of the material can be improved by the addition of the photothermal agent, and the energy of sunlight or other light sources can be converted into thermal energy, thereby improving the thermal performance of the material. The present invention also specially designs a controllable trigger electrode to realize the controllable heat release of the supercooled material, which enhances the practicality and intelligence level of the material. The prepared composite phase change material exhibits excellent long-term stable supercooling characteristics, efficient photothermal conversion ability and excellent cycle stability, indicating that it has huge application potential and market prospects in many fields such as solar thermal energy storage, building energy saving, and industrial waste heat utilization.

[0063] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A long-term stable supercooled solar phase change heat storage material with controllable electrically triggered heat release, characterized in that: It is composed of a hydrogel as a skeleton material, a hydrated salt fixed in the hydrogel skeleton by physical and chemical connection, a stably dispersed photothermal agent, and an electrode embedded in the material; the weight percentage of each component is: Hydrogel: 5-15 parts; Hydrated salt: 75-85 parts; Photothermal agent: 0.5-5 parts.

2. The long-term stable supercooled solar phase change heat storage material with controllable electrically triggered heat release according to claim 1, characterized in that: The hydrogel is any one of polyacrylamide, polyvinyl alcohol, polyvinyl pyrrolidone, polyisopropylacrylamide, polyacrylic acid, polyacrylate, polyethylene oxide and sodium alginate.

3. The long-term stable supercooled solar phase change heat storage material with controllable electrically triggered heat release according to claim 1, characterized in that: The hydrated salt used is sodium acetate trihydrate or disodium hydrogen phosphate dodecahydrate.

4. The long-term stable supercooled solar phase change heat storage material with controllable electrically triggered heat release according to claim 1, characterized in that: The photothermal agent is polydopamine, dopamine-modified carbon nanotubes, hydroxylated carbon nanotubes, graphene oxide, functional group-modified expanded graphite, functional group-modified carbon fiber, dopamine-modified Ti3C2T x , any of the amino-functionalized metal-organic frameworks.

5. The long-term stable supercooled solar phase change heat storage material with controllable electrically triggered heat release according to claim 1, characterized in that: The electrode comprises a cathode and an anode, the cathode is any one of a graphite electrode, a copper electrode, a zinc electrode, an iron electrode and an aluminum electrode, and the anode is a silver electrode.

6. A method for preparing the long-term stable supercooled solar phase change thermal storage material according to any one of claims 1 to 5, comprising the following steps: Step 1: Weigh the hydrogel monomer and the photothermal agent according to the formula ratio, and place them and ultrapure water in a magnetic stirrer until the hydrogel monomer is completely dissolved to obtain a hydrogel monomer solution and a photothermal agent slurry; Step 2: Weigh the hydrated salt according to the formula ratio, place it in a blender and stir and mix it evenly to obtain a hydrated salt mixture; Step 3: Heat and melt the mixed hydrated salt mixture to obtain a molten mixture, add the photothermal agent and the hydrogel monomer solution into the molten mixture according to the formula, and stir evenly at a constant temperature of 30-90°C; Step 4: Weigh a certain amount of the mixture obtained in step 3 and pour it into a mold, add a crosslinking agent to the mixture, and let it stand at 20-30°C; Step 5: Add the photothermal agent slurry to the shaped material obtained in step 4 and control the moisture content therein, and then embed the electrode to obtain a controllable electrically triggered long-term stable supercooled photothermal phase change material.

7. The method for preparing the long-term stable supercooled solar phase change thermal storage material according to claim 6, characterized in that: The heating method is a constant temperature water bath or oil bath heating, the heating rate should be greater than 2 K / min, and the heating melting temperature should be 15°C lower than the melting point of the hydrated salt.

8. The method for preparing the long-term stable supercooled solar phase change thermal storage material according to claim 6, characterized in that: When polydopamine is selected as the photothermal agent, the specific treatment method of the polydopamine is as follows: weigh 2 g of dopamine hydrochloride, measure 20-40 mL of 0.1 mol / L sodium hydroxide solution, and completely dissolve the dopamine hydrochloride in the sodium hydroxide solution to obtain a dopamine hydrochloride-sodium hydroxide solution; seal the solution and place it in a constant temperature oven at 45-65° C. for 30-60 min; take out the solution after the reaction, measure acetic acid in an amount equivalent to that of sodium hydroxide, and add acetic acid to the solution to neutralize the pH to neutrality to obtain a polydopamine solution.

9. The method for preparing a long-term stable supercooled solar phase change thermal storage material according to claim 6, characterized in that: When carbon nanotubes modified with dopamine hydrochloride are selected as the photothermal agent, the specific processing method of the carbon nanotubes modified with dopamine hydrochloride is: weigh tris(hydroxymethylaminomethane) and place it in a beaker; add deionized water and stir and dissolve it thoroughly; adjust the pH value with concentrated hydrochloric acid to obtain a tris(hydroxymethylaminomethane) buffer solution; weigh the carbon nanotubes, measure the tris(hydroxymethylaminomethane) buffer solution, make the carbon nanotubes completely dispersed in the tris(hydroxymethylaminomethane) buffer solution, and stir for 30-60 minutes; measure 5.5-6.5 mg of dopamine hydrochloride and add it to the solution, stir it magnetically; take the precipitate and wash it with water and ethanol for multiple times to obtain the dopamine-modified carbon nanotubes.

10. The method for preparing a long-term stable supercooled solar phase change thermal storage material according to claim 6, characterized in that: The overall preparation process adopts the method of mixing first and then curing, that is, in the application stage, the phase change material container is first filled and then cured.

Images