Sodium alginate-assisted graphene-based molten salt phase change energy storage material and preparation method thereof

Abstract

The present application relates to the technical field of molten salt phase change energy storage materials, and discloses a sodium alginate-assisted graphene-based molten salt phase change energy storage material and a preparation method thereof. The preparation method comprises: preparing a few-layer graphene oxide; dispersing the few-layer graphene oxide and sodium alginate in a saturated or supersaturated sodium chloride solution, adding an inorganic cross-linking agent, and mixing evenly to obtain a composite hydrogel; freezing and freeze-drying the composite hydrogel to obtain a composite aerogel; and heat-treating the composite aerogel to obtain a sodium alginate-assisted graphene-based molten salt phase change energy storage material. In the phase change energy storage material of the present application, graphene oxide and the carbonized sodium alginate carbon skeleton form an aerogel matrix, which ensures the stability of the packaging structure while retaining a large number of NaCl crystals, thereby increasing the proportion of molten salt and the phase change stability. The molten salt is not easy to leak during the phase change energy storage process, which significantly improves the energy storage performance and thermal energy management efficiency, and has broad application prospects.

Description

Technical Field

[0001] The present application relates to the technical field of molten salt phase change energy storage materials, and in particular to a sodium alginate-assisted graphene-based molten salt phase change energy storage material and a preparation method thereof. Background Art

[0002] As renewable energy sources like wind and solar power rapidly increase their share in the global energy mix, their intermittent and unpredictable nature poses challenges to the stable operation of power grids. Therefore, developing high-efficiency, low-cost energy storage technologies is crucial to addressing this issue. Molten salt phase change energy storage, due to its unique performance advantages, has become a research hotspot.

[0003] Phase change energy storage technology is based on the principle that materials absorb or release a large amount of latent heat during the phase change process. Compared with traditional sensible heat energy storage, phase change energy storage has a higher energy density and can store more energy in a smaller volume or mass, making it particularly suitable for large-scale energy storage.

[0004] Molten salt as a phase change material is currently a hot topic of research due to its wide operating temperature range, good thermal and chemical stability, no overheating problems during operation, and longer service life and better cyclic stability. Extensive research has been conducted in the field of molten salt phase change energy storage. White et al. have studied and developed a phase change energy storage material (FSPCM) using a porous matrix prepared using freeze-casting technology as a matrix, specifically aluminum oxide-based composite materials. Freeze-casting allows for controlled porosity, the use of economical materials, and the ability to accommodate a variety of phase change materials. These FSPCMs have good thermal stability and thermal conductivity, especially in the direction parallel to the freeze-casting direction, where the thermal conductivity is high. However, the bonding stability between the matrix and the molten salt phase change material is poor, and the molten salt is prone to leakage during use. Summary of the Invention

[0005] The present application provides a sodium alginate-assisted graphene-based molten salt phase change energy storage material and a preparation method thereof, aiming to solve the problems of poor bonding stability between the matrix and the phase change energy storage material and easy leakage of molten salt in existing molten salt phase change energy storage materials.

[0006] In order to achieve the above objectives, this application adopts the following technical solutions.

[0007] In a first aspect of the present application, a method for preparing a sodium alginate-assisted graphene-based molten salt phase change energy storage material is provided, comprising:

[0008] S1, preparation of few-layer graphene oxide;

[0009] S2, dispersing the few-layer graphene oxide and sodium alginate in a saturated or supersaturated sodium chloride solution, adding an inorganic crosslinking agent, and mixing uniformly to obtain a composite hydrogel;

[0010] S3, freezing and freeze-drying the composite hydrogel to obtain a composite aerogel;

[0011] S4, heat-treating the composite aerogel to obtain a sodium alginate-assisted graphene-based molten salt phase change energy storage material.

[0012] In some embodiments, the inorganic crosslinking agent is calcium chloride.

[0013] In some embodiments, the freezing is a directional freezing of the hydrogel from bottom to top using liquid nitrogen.

[0014] In some embodiments, the freeze-drying temperature is -70 to -80°C, the vacuum degree is <15 Pa, and the freeze-drying time is 24 to 72 hours.

[0015] In some embodiments, the heat treatment is: heating the composite aerogel to 300° C. in an inert atmosphere and keeping the temperature for 1 to 3 hours.

[0016] In some embodiments, the inert atmosphere is an argon atmosphere.

[0017] In some embodiments, the mass ratio of the few-layer graphene oxide to sodium alginate is 1:(8-12);

[0018] And / or, the mass of the salt solution is 10 to 12 times the total mass of the few-layer graphene oxide and the sodium alginate;

[0019] And / or, the mass of the inorganic cross-linking agent is 0.125% to 0.25% of the mass of the sodium alginate.

[0020] In some embodiments, the method for preparing the few-layer graphene oxide comprises:

[0021] Mix graphite and sulfuric acid evenly, add sodium nitrate and phosphorus pentoxide, stir at 80-100°C for 12-24 hours, separate and collect the solid phase, wash and air-dry to obtain the precursor;

[0022] The precursor is dispersed in excess concentrated sulfuric acid, and potassium permanganate is slowly added thereto, stirred at -10 to 0°C, and then diluted with water. After that, the temperature is raised to 90°C, and hydrogen peroxide is added until the solution turns bright yellow to obtain a dispersion.

[0023] The dispersion is diluted with water, centrifuged at a speed of 5000-7000 r / min to remove multilayer graphene oxide, and then centrifuged at a speed of 10000-12000 r / min to remove impurities, and the concentrated solution obtained by centrifugation is freeze-dried to obtain few-layer graphene oxide;

[0024] The mass ratio of graphite, sulfuric acid, sodium nitrate and phosphorus pentoxide is (1-2):(18-20):(1.5-2):(1.5-2);

[0025] The mass ratio of the potassium permanganate to the graphite is 5:1.

[0026] In a second aspect of the present application, a sodium alginate-assisted graphene-based molten salt phase change energy storage material prepared by the above-mentioned preparation method is provided.

[0027] The third aspect of the present application provides the use of sodium alginate-assisted graphene-based molten salt phase change energy storage material prepared by the above preparation method in photothermal storage in solar thermal power stations.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] The present application realizes a sufficiently uniform distribution of sodium chloride solution and few-layer graphene oxide in the composite hydrogel through cross-linking and solidification of sodium alginate; a porous aerogel with uniformly distributed pores is obtained through freezing and freeze-drying preparation treatment, which is conducive to achieving thermal conductivity; the aerogel is then reduced and carbonized, and the graphene oxide and the carbonized sodium alginate carbon skeleton form an aerogel matrix, which ensures the stability of the packaging structure while retaining a large number of NaCl crystals, thereby increasing the proportion of molten salt and the phase change stability.

[0030] The sodium alginate-assisted graphene-based molten salt phase change energy storage material of the present application has good stability in combination with the graphene-based aerogel, and the molten salt is not easy to leak during the phase change energy storage process, which significantly improves the phase change stability, energy storage performance and thermal energy management efficiency, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some of the embodiments described in this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0032] Figure 1 This is a process flow chart of the preparation method of this application;

[0033] Figure 2 This is a physical picture of the porous composite aerogel prepared in Example 1;

[0034] Figure 3 This is a physical picture of the sodium alginate-assisted graphene-based molten salt phase change energy storage material prepared in Example 1;

[0035] Figure 4This is the SEM spectrum of the sodium alginate-assisted graphene-based molten salt phase change energy storage material prepared in Example 1. DETAILED DESCRIPTION

[0036] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0037] In the following description of this embodiment, the terms "include", "comprising", "having" and "containing" are open-ended terms, meaning including but not limited to.

[0038] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, B exists alone, and both A and B exist. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0039] In the following description of this embodiment, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0040] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0041] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0042] It will be understood by those skilled in the art that the numerical ranges in the examples of the present application are to be understood as specifically disclosing each intermediate value between the upper and lower limits of the range. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also included in the present application. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0043] Unless otherwise indicated, the technical / scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which this application belongs. Although this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict with any incorporated document, the content of this specification shall prevail.

[0044] First, as Figure 1 As shown, the present application provides a method for preparing a sodium alginate-assisted graphene-based molten salt phase change energy storage material, using graphene aerogel, sodium alginate and NaCl as raw materials, and adopting freeze drying and high temperature reduction methods to prepare aerogel molten salt composite material, specifically comprising:

[0045] S1, preparation of few-layer graphene oxide;

[0046] In this application, the few-layer graphene oxide is prepared by the following method:

[0047] Mix graphite and sulfuric acid evenly, add sodium nitrate and phosphorus pentoxide, stir at 80-100° C. for 12-24 hours, separate and collect the solid phase by suction filtration, and dry in the shade to obtain a precursor; wherein the graphite is preferably flake graphite;

[0048] Specifically, the mass ratio of the graphite, sulfuric acid, sodium nitrate and phosphorus pentoxide is preferably (1-2):(18-20):(1.5-2):(1.5-2).

[0049] The precursor is dispersed in excess concentrated sulfuric acid, and potassium permanganate is slowly added thereto, stirred at -10 to 0°C for 4 to 5 hours, then heated to 30 to 40°C, diluted with water, and then heated to 90°C. Hydrogen peroxide is added until the solution turns bright yellow to obtain a dispersion;

[0050] Wherein, the mass ratio of potassium permanganate to graphite is 5:1.

[0051] The dispersion is diluted with water, centrifuged at a speed of 5000-7000 r / min to remove multilayer graphene oxide, and then centrifuged at a speed of 10000-12000 r / min to remove impurities, and the concentrated liquid obtained by centrifugation is freeze-dried to obtain few-layer graphene oxide.

[0052] S2, dispersing the few-layer graphene oxide and sodium alginate in a saturated or supersaturated sodium chloride solution, adding an inorganic crosslinking agent, and mixing uniformly to obtain a composite hydrogel;

[0053] In this application, few-layer graphene oxide and sodium alginate are dispersed in a saturated or supersaturated sodium chloride solution and ultrasonically treated at 50-60°C for 5-7 hours to ensure that the few-layer graphene oxide and sodium alginate are evenly distributed in the sodium chloride solution and to remove bubbles in the mixture. An aqueous solution of an inorganic crosslinking agent is added dropwise to the mixture to cause the sodium alginate to self-crosslink into a hydrogel, thereby obtaining a composite hydrogel of graphene oxide / sodium alginate containing a saturated sodium chloride solution. The inorganic crosslinking agent is preferably calcium chloride, and the concentration of the calcium chloride solution is preferably 0.5wt%.

[0054] In the present application, the mass ratio of the few-layer graphene oxide to sodium alginate is preferably 1:(8-12); the mass of the saturated sodium chloride solution is preferably 10-12 times the total mass of the few-layer graphene oxide and sodium alginate; and the mass of the calcium chloride is preferably 0.125%-0.25% of the mass of sodium alginate.

[0055] S3, freezing and freeze-drying the composite hydrogel to obtain a composite aerogel;

[0056] In the present application, the composite hydrogel is directionally frozen from bottom to top by liquid nitrogen; the oriented freezing can make the composite hydrogel have a vertically oriented structure, and the vertically oriented structure can significantly improve the electrical conductivity, thermal conductivity and structural strength of the composite aerogel.

[0057] The frozen composite hydrogel is freeze-dried using a freeze dryer, preferably at a temperature of -70 to -80°C, a vacuum degree of <15 Pa, and a freeze-drying time of 24 to 72 hours. After freeze-drying, a composite aerogel with a porous structure is obtained.

[0058] S4, heat-treating the composite aerogel to obtain a sodium alginate-assisted graphene-based molten salt phase change energy storage material.

[0059] In this application, the composite aerogel is heated to 300°C in an inert atmosphere and held for 1-3 hours for reduction and carbonization. The graphene oxide and the carbonized sodium alginate carbon skeleton form an aerogel matrix. This aerogel matrix has a highly porous three-dimensional graphene network structure, which ensures the stability of the encapsulation structure while retaining a large number of NaCl crystals. The inert atmosphere is argon.

[0060] The preparation method of the present application realizes a sufficiently uniform distribution of sodium chloride solution and few-layer graphene oxide in the composite hydrogel through cross-linking and solidification of sodium alginate; a porous aerogel with uniformly distributed pores is obtained through freezing and freeze-drying preparation treatment, which is conducive to achieving thermal conductivity; and the aerogel is then reduced and carbonized, and the graphene oxide and the carbonized sodium alginate carbon skeleton form an aerogel matrix, which ensures the stability of the packaging structure while retaining a large amount of NaCl crystals, thereby increasing the proportion of molten salt and the phase change stability.

[0061] Secondly, the present application provides a sodium alginate-assisted graphene-based molten salt phase-change energy storage material prepared by the above-mentioned preparation method. In the sodium alginate-assisted graphene-based molten salt phase-change energy storage material of the present application, the combination of sodium chloride and graphene-based aerogel has good stability, and the molten salt is not easily leaked during the phase-change energy storage process, which significantly improves the phase-change stability, energy storage performance, and thermal energy management efficiency, and has broad application prospects.

[0062] The sodium alginate-assisted graphene-based molten salt phase-change energy storage material of this application can be used for photothermal storage in solar thermal power plants or integrated photothermal air-conditioning systems in high-rise buildings. During the day, the heat energy collected by the solar collector heats the molten salt composite material. When the temperature (800°C) at which the molten salt inside undergoes a phase change is reached, the molten salt (phase change enthalpy ≈ 1348 J / g) undergoes a phase change to store thermal energy. At night or on cloudy days, the stored solar heat collected during the day is released to maintain the stability of power output, which can significantly reduce power consumption and achieve effective energy management and energy conservation and emission reduction.

[0063] The sodium alginate-assisted graphene-based molten salt phase change energy storage material of this application can also be used for heat energy storage and conversion in the metal smelting industry. For example, in steel producers, the waste heat released by high-temperature exhaust gas or cooling water is first transferred to these energy storage modules through a heat exchanger, prompting sodium chloride (phase change enthalpy ≈ 1348 J / g) to change from solid to liquid, storing a large amount of heat energy. Subsequently, when heat energy is needed in the production process, such as in the preheating stage of a heating furnace, the stored heat energy is released through the reverse phase change process and converted back into a usable heat source, reducing the need for direct combustion of fuel. This not only significantly improves the recovery rate of industrial waste heat, but also reduces energy costs for the factory.

[0064] The present application is further described below through examples.

[0065] Example 1

[0066] This embodiment provides a method for preparing a sodium alginate-assisted graphene-based molten salt phase change energy storage material, comprising:

[0067] S1. Preparation of few-layer graphene oxide: 2 g of graphite was mixed with 10 ml of 98% sulfuric acid and stirred at 80°C. 1.7 g of sodium nitrate and 1.7 g of phosphorus pentoxide were then added in sequence and stirred for 12 h. The mixture was filtered twice and dried in the shade at room temperature for 3 h to obtain a precursor.

[0068] 80ml of sulfuric acid and the precursor were added to a beaker. 10g of potassium permanganate was slowly added to the beaker at -10°C and stirred for 4.5 hours. The mixture was then placed in a 35°C water bath for 4 hours, diluted in 1000ml of water, and stirred for 15 minutes. The mixture was heated to 90°C and hydrogen peroxide was added until the solution turned bright yellow to obtain a dispersion. The dispersion was centrifuged at 11,000 rpm for 7 minutes, then at 6,000 rpm for 5 minutes to remove impurities, and then centrifuged again at 11,000 rpm for 15 minutes to obtain a concentrate. The concentrate was freeze-dried for 48 hours to obtain few-layer graphene oxide.

[0069] S2, dissolve 200 mg of few-layer graphene oxide and 2 g of sodium alginate in 20 mL of saturated NaCl solution, where the concentration of the saturated sodium chloride solution is 0.36 g / mL, and ultrasonically mix at 60°C for 6 h to ensure uniform distribution; take 0.5 ml of 0.5 wt% CaCl2 solution and add it dropwise to the saturated sodium chloride solution to cause the sodium alginate to self-crosslink and obtain a composite hydrogel.

[0070] In step S3, the composite hydrogel was poured into a 5-cm-diameter polyethylene mold and directionally frozen from the bottom up using liquid nitrogen for 15 minutes. After freezing, the mold was placed in a freeze dryer set to -70°C and a vacuum of <15 Pa for 48 hours to obtain a porous composite aerogel.

[0071] S4, placing the composite aerogel in a tubular furnace, then heating it to 300°C under an argon atmosphere and keeping it warm for 1 hour to obtain a sodium alginate-assisted graphene-based molten salt phase change energy storage material.

[0072] Example 2

[0073] This embodiment provides a method for preparing a sodium alginate-assisted graphene-based molten salt phase change energy storage material, comprising:

[0074] S1. Preparation of few-layer graphene oxide: 2 g of graphite was mixed with 10 ml of 98% sulfuric acid, stirred at 85°C, and then 1.7 g of sodium nitrate and 1.7 g of phosphorus pentoxide were added in sequence, and stirring was continued for 14 hours; the mixture was filtered three times and dried in the shade at room temperature for 24 hours to obtain a precursor.

[0075] Add 90 ml of sulfuric acid to a beaker, add the precursor, slowly add 10 g of potassium permanganate to the beaker at 0°C, stir for 6 hours, then place it in a 40°C water bath for 6 hours, dilute it in 2000 ml of water, and stir for 30 minutes; raise the temperature to 80°C and add hydrogen peroxide until the solution turns bright golden yellow to obtain a dispersion; centrifuge the dispersion at 12000 r / min for 10 minutes, then centrifuge at 8000 r / min for 8 minutes to remove impurities, and centrifuge again at 12000 r / min for 20 minutes to obtain a concentrate; freeze-dry the concentrate for 72 hours to obtain few-layer graphene oxide.

[0076] S2, dissolve 250 mg of few-layer graphene oxide and 3 g of sodium alginate in 30 mL of 0.4 g / mL NaCl solution, use an ultrasonic processor with an ice bath, and ultrasonically mix at 55°C for 8 h to ensure uniform distribution; take 1 ml of 0.7 wt% CaCl2 solution and add it dropwise to the above sodium chloride solution to cause the sodium alginate to self-crosslink and obtain a composite hydrogel.

[0077] In step S3, the composite hydrogel was poured into a 5-cm-diameter polyethylene mold and directionally frozen from the bottom up using liquid nitrogen for 15 minutes. After freezing, the mold was placed in a freeze dryer set to -70°C and a vacuum of <15 Pa for 72 hours to obtain a porous composite aerogel.

[0078] S4, placing the composite aerogel in a tubular furnace, then heating it to 400°C under an argon atmosphere and keeping it warm for 2 hours to obtain a sodium alginate-assisted graphene-based molten salt phase change energy storage material.

[0079] Example 3

[0080] This embodiment provides a method for preparing a sodium alginate-assisted graphene-based molten salt phase change energy storage material, comprising:

[0081] S1. Preparation of few-layer graphene oxide: 2 g of graphite was mixed with 10 ml of 95% sulfuric acid and stirred at 85°C. 1.7 g of sodium nitrate and 1.7 g of phosphorus pentoxide were then added sequentially and stirred for 14 hours. The mixture was filtered three times and air-dried in a 50°C constant temperature drying oven for 24 hours to obtain a precursor.

[0082] 85 ml of sulfuric acid was added to a beaker, and the precursor was added. 10 g of potassium permanganate was slowly added to the beaker at -5 ° C and stirred for 5 hours. The mixture was then placed in a 40 ° C water bath for 5 hours, diluted in 1200 ml of water, and stirred for 25 minutes. The temperature was raised to 85 ° C and hydrogen peroxide was added until the solution turned bright golden yellow to obtain a dispersion. The dispersion was centrifuged at a speed of 11000 r / min for 8 minutes, and then centrifuged at a speed of 6000 r / min for 6 minutes to remove impurities, and then centrifuged again at a speed of 11000 r / min for 10 minutes to obtain a concentrate. The concentrate was freeze-dried for 54 hours to obtain few-layer graphene oxide.

[0083] S2, dissolve 250 mg of few-layer graphene oxide and 2.2 g of sodium alginate in 25 mL of 0.4 g / mL NaCl solution, use an ultrasonic processor with an ice bath, and ultrasonically mix at 50°C for 7 h to ensure uniform distribution; take 0.6 ml of 0.6 wt% CaCl2 solution and add it dropwise to the above sodium chloride solution to cause the sodium alginate to self-crosslink and obtain a composite hydrogel.

[0084] In step S3, the composite hydrogel was poured into a 5-cm-diameter polyethylene mold and directionally frozen from the bottom up using liquid nitrogen for 15 minutes. After freezing, the mold was placed in a freeze dryer set to -70°C and a vacuum of <15 Pa for 72 hours to obtain a porous composite aerogel.

[0085] S4, placing the composite aerogel in a tubular furnace, heating it to 320°C under an argon atmosphere, and keeping it warm for 1.5 hours to obtain a sodium alginate-assisted graphene-based molten salt phase change energy storage material.

[0086] In the process of preparing sodium alginate-assisted graphene-based molten salt phase change energy storage material in Example 1, the physical object of the porous structure composite aerogel is as follows: Figure 2 As shown, from Figure 2 It can be seen that with the assistance of sodium alginate, the dispersion of graphene oxide was not affected by the introduction of NaCl, and aerogel was successfully formed.

[0087] Sodium alginate assisted graphene-based molten salt phase change energy storage material Figure 3 As shown, from Figure 3 It can be seen that the aerogel structure composed of reduced graphene oxide and carbonized sodium alginate was combined with NaCl to successfully prepare graphene-based molten salt phase change energy storage materials.

[0088] Figure 4 This is the SEM spectrum of the sodium alginate-assisted graphene-based molten salt phase change energy storage material prepared in Example 1. Figure 4It can be seen that the prepared graphene aerogel has a uniform pore structure and a large number of pores. In the enlarged image, it can be seen that the pores are interconnected. The combination of the two can greatly improve the filling degree of the molten salt.

[0089] The sodium alginate-assisted graphene-based molten salt phase change energy storage material prepared in the examples of this application combines the high thermal conductivity of graphene with the phase change energy storage characteristics of phase change materials, solving the shortcomings of phase change energy storage materials, such as weak thermal conductivity and low energy storage efficiency. During the heat storage-release process, the highly porous three-dimensional mesh graphene structure of the sodium alginate-assisted graphene-based molten salt phase change energy storage material provides high thermal conductivity, significantly improving the transfer rate of thermal energy, shortening the time of energy storage and release, and improving the response speed and energy storage efficiency of the overall system. It also increases the phase change conversion rate of the molten salt, significantly improving the thermal energy management efficiency, and providing an innovative solution for high-performance thermal management systems.

[0090] The sodium alginate-assisted graphene-based molten salt phase-change energy storage material prepared in Example 1 can be combined with an efficient solar thermal collection system for use in large-scale solar thermal power plants. During the day, the heat collected by the solar collector heats the molten salt composite material. When the temperature reaches 800°C, which causes the molten salt inside to undergo a phase change, the sodium chloride molten salt (phase change enthalpy ≈ 1348 J / g) undergoes a phase change and stores the heat. At night or on cloudy days, the solar heat collected during the day is released to maintain the stability of the power output.

[0091] The sodium alginate-assisted graphene-based molten salt phase change energy storage material prepared in Example 2 can be used in the photothermal integrated air-conditioning system of high-rise buildings. The system uses sunlight to directly heat the energy storage module containing sodium alginate-assisted graphene-based molten salt phase change energy storage material by installing a high-efficiency photothermal conversion heat collecting panel on the roof of the building. The introduction of sodium alginate-assisted graphene greatly enhances the thermal conductivity of the material, allowing sodium chloride (phase change enthalpy ≈ 1348 J / g) to quickly complete the phase change energy storage process and store excess heat energy during the day. At night or in rainy weather, this stored heat energy is released and used for heating buildings or driving absorption refrigeration systems for summer cooling, thereby greatly reducing the consumption of traditional electricity and achieving effective energy management and energy conservation and emission reduction. In addition, the miniaturized design of the system makes it easy to promote in urban environments, promoting the development of green buildings.

[0092] The sodium alginate-assisted graphene-based molten salt phase change energy storage material prepared in Example 3 can be used in the field of industrial waste heat recovery, such as waste heat recovery in the steel industry. The waste heat released by high-temperature exhaust gas or cooling water is first transferred to the energy storage module containing sodium alginate-assisted graphene-based molten salt phase change energy storage material through a heat exchanger, prompting sodium chloride (phase change enthalpy ≈ 1348 J / g) to change from solid to liquid, storing a large amount of thermal energy. Subsequently, when heat energy is needed in the production process, such as in the preheating stage of a heating furnace, the stored heat energy is released through the reverse phase change process and converted back into a usable heat source, reducing the need for direct combustion of fuel.

[0093] Although this specification has been used to fully describe the present application using general descriptions and specific embodiments, it is obvious to those skilled in the art that modifications or improvements may be made based on the present application. Therefore, such modifications or improvements made without departing from the spirit of the present application are within the scope of protection claimed in this application.

Claims

1. A method for preparing a sodium alginate-assisted graphene-based molten salt phase change energy storage material, characterized in that: include: S1, preparation of few-layer graphene oxide; S2, dispersing the few-layer graphene oxide and sodium alginate in a saturated or supersaturated sodium chloride solution, adding an inorganic crosslinking agent, and mixing uniformly to obtain a composite hydrogel; S3, freezing and freeze-drying the composite hydrogel to obtain a composite aerogel; S4, heat-treating the composite aerogel to obtain a sodium alginate-assisted graphene-based molten salt phase change energy storage material; The inorganic cross-linking agent is calcium chloride; The mass ratio of the few-layer graphene oxide to sodium alginate is 1:(8-12); The mass of the sodium chloride solution is 10 to 12 times the total mass of the few-layer graphene oxide and sodium alginate; The mass of the inorganic cross-linking agent is 0.125% to 0.25% of the mass of sodium alginate.

2. The preparation method according to claim 1, characterized in that The freezing is to perform directional freezing on the hydrogel from bottom to top using liquid nitrogen.

3. The preparation method according to claim 1, characterized in that The freeze-drying treatment temperature is -70 to -80°C, the vacuum degree is less than 15 Pa, and the freeze-drying time is 24 to 72 hours.

4. The preparation method according to claim 1, characterized in that The heat treatment comprises heating the composite aerogel to 300° C. in an inert atmosphere and keeping the temperature for 1 to 3 hours.

5. The preparation method according to claim 4, characterized in that The inert atmosphere is an argon atmosphere.

6. The preparation method according to claim 1, characterized in that The preparation method of the few-layer graphene oxide comprises: Mix graphite and sulfuric acid evenly, add sodium nitrate and phosphorus pentoxide, stir at 80-100°C for 12-24 hours, separate and collect the solid phase, wash and air-dry to obtain the precursor; The precursor is dispersed in excess concentrated sulfuric acid, and potassium permanganate is slowly added thereto. The mixture is stirred at -10 to 0°C, and then diluted with water. The mixture is then heated to 90°C and hydrogen peroxide is added until the solution turns bright yellow to obtain a dispersion. The dispersion is diluted with water, centrifuged at a speed of 5000-7000 r / min to remove multilayer graphene oxide, and then centrifuged at a speed of 10000-12000 r / min to remove impurities, and the concentrated solution obtained by centrifugation is freeze-dried to obtain few-layer graphene oxide; The mass ratio of graphite, sulfuric acid, sodium nitrate and phosphorus pentoxide is (1-2):(18-20):(1.5-2):(1.5-2); The mass ratio of the potassium permanganate to the graphite is 5:

1.

7. Sodium alginate-assisted graphene-based molten salt phase change energy storage material prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the sodium alginate-assisted graphene-based molten salt phase change energy storage material prepared by the preparation method according to any one of claims 1 to 6 in photothermal storage in a solar thermal power station.

Images