A metal-carbon-based chemical heat storage composite material, its preparation method and application

Abstract

The present invention discloses a metal-carbon-based chemical heat storage composite material, a preparation method thereof and an application thereof. The composite material comprises a main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon and a compound represented by formula (I): MA (I) wherein M is selected from at least one of lithium, magnesium and aluminum; A is selected from at least one of hydroxide radical, sulfate radical and bromide anion. In the metal-carbon-based composite material of the present invention, a main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon is used as a support matrix, and is compounded with the compound represented by formula (I), so that the prepared composite material has excellent energy storage density, can efficiently store and utilize low-temperature heat energy and long-term heat energy storage across seasons, and can fully utilize low-temperature heat energy such as solar heat energy and industrial waste heat.

Description

Technical Field

[0001] The present invention belongs to the field of heat storage materials, and relates to a metal-carbon-based chemical heat storage composite material, a preparation method thereof, and an application thereof. Background Art

[0002] The contradiction between the substantial increase in energy demand caused by the rapid economic growth and the serious environmental pollution caused by the overuse of fossil fuels has become one of the most serious problems faced by mankind currently. Therefore, the development of new renewable energy sources (such as solar energy, wind energy, etc.) and energy conservation and emission reduction technologies has become a forefront hot topic in the field of energy research. However, these renewable energy sources have characteristics such as timeliness and uneven output. People need to use some energy storage systems to store this unstable energy and release the stored energy when needed, so as to solve the mismatch problem of energy between the supply side and the demand side in terms of time and space, and at the same time improve the energy utilization rate. For example, in summer, abundant solar heat energy can be stored, and the stored energy can be released in winter when solar heat energy is relatively scarce for building heating. Against this background, heat energy storage systems that can bridge the time and space gaps between energy supply and demand have received increasing attention worldwide. There are three common heat storage systems, namely sensible heat storage systems, latent heat storage systems, and chemical heat storage systems. Among them, chemical heat storage systems show great commercial value in future practical applications due to their advantages of long storage cycle, excellent heat storage performance, and extremely small heat loss.

[0003] Metal-organic frameworks, a kind of material formed by the coordination of metal ions and organic ligands, have received great attention in the fields of photocatalysis and energy storage due to their highly adjustable crystal structure and rich pore structure. However, compared with carbon materials, metal-organic frameworks usually show poor stability to heat and humidity, which greatly reduces their application scope. And metal-organic framework-derived porous carbon materials show great application potential in the fields of gas adsorption, catalysis, and energy due to their unique structures and properties. This kind of porous carbon material integrates the characteristics of high specific surface area, pore volume, adjustable pore size and structure of metal-organic frameworks, as well as the excellent stability and thermal conductivity of carbon materials, making it a rising star in the family of porous materials. However, the collapse inside the metal-organic framework crystal cannot be avoided during direct carbonization, so the desired good precursor structure after carbonization cannot be achieved, which limits its application. Although metal-organic framework-derived porous carbon materials have been widely used in many fields, they are rarely applied to the field of heat energy storage, and even less in the field of chemical heat storage.

[0004] Due to the characteristics of low cost, high safety and simplicity of system operation, inorganic hydrated salts stand out among numerous chemical heat storage systems. However, most salt hydrate heat storage materials cannot be applied to low-temperature heat energy storage due to their relatively high hydration temperature, resulting in the dilemma of being unable to fully utilize low-temperature heat energy such as industrial waste heat and solar heat energy, which greatly reduces the practical application value of such heat storage materials. Against this background, hydrated salt chemical energy storage composite materials with advantages such as low hydration temperature, outstanding storage capacity and non-toxicity have become a research hotspot in the field of low-temperature heat energy storage. In addition, although various hydrated salt chemical energy storage composite materials have made significant progress in terms of low-temperature heat energy storage and storage cycle, there is still great room for improvement in the heat storage performance of this kind of material in all aspects. Therefore, developing a hydrated salt chemical heat storage composite material that can effectively utilize and store low-temperature heat energy for a long time while maintaining excellent storage performance is still an urgent task to be solved. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a metal-carbon-based composite material, which includes a main porous carbon matrix composed of metal-organic-framework-derived graphene-based porous carbon and a compound represented by formula (I) compounded with the matrix:

[0006] MA (I)

[0007] Wherein, M is selected from at least one of lithium, magnesium, and aluminum;

[0008] A is selected from at least one of hydroxide, sulfate, and bromide anions.

[0009] According to an embodiment of the present invention, the compound represented by formula (I) is selected from at least one of lithium hydroxide, magnesium sulfate, lithium bromide, and aluminum sulfate.

[0010] According to an embodiment of the present invention, the raw material of graphene in the main porous carbon matrix composed of metal-organic-framework-derived graphene-based porous carbon is graphene oxide or graphene.

[0011] Wherein, when the raw material of graphene in the main porous carbon matrix composed of metal-organic-framework-derived graphene-based porous carbon is graphene, it needs to be oxidized into graphene oxide.

[0012] According to an embodiment of the present invention, the main porous carbon matrix composed of metal-organic-framework-derived graphene-based porous carbon refers to a porous carbon material prepared by heat-treating and carbonizing a metal-organic framework and removing the metal components therein.

[0013] Preferably, the heat treatment refers to treatment under heating conditions, such as calcination treatment. The heating temperature can be 600-900 °C.

[0014] According to an embodiment of the present invention, the metal-organic framework contains a metal element and an organic ligand. Among them, the metal element is selected from at least one of zinc and cobalt, preferably zinc; the organic ligand is selected from at least one of 2-methylimidazole, terephthalic acid, benzimidazole, and 2-nitroimidazole, preferably 2-methylimidazole.

[0015] According to an embodiment of the present invention, in the composite material, the mass content of the compound shown in formula (I) is 20-80%, for example 30-70%, and exemplary values are 20%, 30%, 40%, 50%, 60%, 70%, 80%.

[0016] According to an embodiment of the present invention, the composite material is a low-temperature chemical heat storage composite material.

[0017] According to an embodiment of the present invention, the composite material can store thermal energy for a long time.

[0018] In the present invention, the composite material can store heat at a relatively high temperature and release heat at a relatively low temperature. For example, the composite material can store heat in summer with a relatively high temperature and release heat in winter with a relatively low temperature, and can store thermal energy across seasons. According to an embodiment of the present invention, the energy density of the metal-carbon composite material is not less than 1000 kJ / kg -1 , for example, the energy density is 1100-1700 kJ / kg -1 , and exemplary values are 1000 kJ / kg -1 , 1100 kJ / kg -1 , 1262.4 kJ / kg -1 , 1355.2 kJ / kg -1 , 1470.7 kJ / kg -1 , 1558.1 kJ / kg -1 , 1644.2 kJ / kg -1 , 1700 kJ / kg -1 .

[0019] According to an embodiment of the present invention, the peak heat release temperature of the metal-carbon composite material is 80-90 °C, for example 80-83 °C, and exemplary values are 80 °C, 80.2 °C, 80.8 °C, 81.3 °C, 82.5 °C, 82.8 °C, 83 °C, 85 °C, 87 °C, 90 °C.

[0020] The present invention also provides a method for preparing the above-mentioned metal-carbon composite material, which includes the following steps:

[0021] (1) React graphene oxide, polyvinylpyrrolidone, metal salt and organic ligand in a solvent to prepare a mixture;

[0022] (2) Heat the mixture in step (1) under an inert atmosphere, and then remove the metal salt in an acidic solution to prepare a main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon.

[0023] (3) Mix and react the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon in step (2) with the compound shown in formula (I) or the hydrate of the compound shown in formula (I) in water to prepare the metal-carbon-based composite material.

[0024] According to an embodiment of the present invention, the specific steps of step (1) are as follows:

[0025] (1-1) Disperse graphene oxide, polyvinylpyrrolidone, and metal salt evenly in a solvent to prepare a first mixture.

[0026] (1-2) Dissolve the organic ligand in a solvent and add it to the first mixture in step (1-1), and react to prepare a second mixture.

[0027] According to an embodiment of the present invention, the graphene oxide in step (1-1) or step (1) can be the product after graphene oxidation.

[0028] According to an embodiment of the present invention, the metal salt is selected from at least one of Zn(NO3)2·6H2O and Co(NO3)2·6H2O, and preferably Zn(NO3)2·6H2O.

[0029] According to an embodiment of the present invention, in step (1), the mass ratio of polyvinylpyrrolidone to graphene oxide is 1:(0.6-2), such as 1:0.6, 1:0.67, 1:1, 1:1.5, 1:2.

[0030] According to an embodiment of the present invention, in step (1), the molar mass ratio of the metal salt to graphene oxide is 1(mmol):(5-10)(mg). For example, 1 mmol of Zn(NO3)2·6H2O corresponds to 5-10 mg of graphene oxide, or 1 mmol of Co(NO3)2·6H2O corresponds to 5-10 mg of graphene oxide. For example, 1 mmol of Zn(NO3)2·6H2O corresponds to 5 mg of graphene oxide, 1 mmol of Zn(NO3)2·6H2O corresponds to 6 mg of graphene oxide, 1 mmol of Zn(NO3)2·6H2O corresponds to 8 mg of graphene oxide, 1 mmol of Zn(NO3)2·6H2O corresponds to 10 mg of graphene oxide.

[0031] According to an embodiment of the present invention, in step (1), the molar ratio of the metal salt to the organic ligand is 1:(4-6), and examples are 1:4, 1:5, 1:6.

[0032] According to an embodiment of the present invention, in step (1), the concentration of graphene oxide is 0.3 - 0.6 mg / mL, preferably 0.4 mg / mL.

[0033] According to an embodiment of the present invention, in step (1), the concentration of the metal salt is 0.1 - 0.4 mmol / mL, preferably 0.13 - 0.33 mmol / mL.

[0034] According to an embodiment of the present invention, in step (1), the concentration of the organic ligand is 0.5 - 2 mmol / mL, preferably 0.8 - 1.33 mmol / mL.

[0035] According to an embodiment of the present invention, in step (1), ultrasonic dispersion can be used to make the dispersion uniform. The dispersion time can be 1 - 4 hours, such as 1 hour, 2 hours, 4 hours, preferably 2 h.

[0036] According to an embodiment of the present invention, the solvent is selected from at least one of methanol, water, ethanol, n - propanol, n - butanol, and 2 - butanol.

[0037] According to an embodiment of the present invention, in step (1 - 1), graphene oxide and polyvinylpyrrolidone can be first dispersed uniformly in the solvent, and then the metal salt or metal salt solution is added and dispersed uniformly to prepare the first mixture.

[0038] Among them, the metal salt solution can be prepared by dissolving the metal salt in methanol; for example, a methanol solution of Zn(NO3)2·6H2O is added to the mixed solution of graphene oxide and polyvinylpyrrolidone, and stirred at room temperature for 20 - 60 minutes, such as 30 minutes, 40 minutes, 60 minutes.

[0039] According to an embodiment of the present invention, in step (1 - 2), after the organic ligand is dissolved in the solvent, it is added dropwise to the first mixture.

[0040] According to an embodiment of the present invention, in step (1) or step (1 - 2), the temperature of the reaction is 20 - 40 °C, such as 20 °C, 30 °C, 40 °C. The reaction time is 3 - 7 h, for example 3 h, 4 h, 5 h, 6 h, 7 h.

[0041] According to an embodiment of the present invention, after the reaction in step (1) or step (1 - 2) is completed, the reaction product can also be purified. For example, the reaction product is centrifuged and washed with methanol at least 4 times, and then dried in a vacuum freeze dryer. The drying time is 24 - 60 hours, such as 24 hours, 48 hours, 60 hours. If atmospheric drying (such as drying in an oven) is used in the present invention, irreversible severe agglomeration of the prepared product will occur.

[0042] According to an embodiment of the present invention, in step (2), the inert atmosphere can be provided by any one of nitrogen, argon, helium, etc., and nitrogen or argon is preferred.

[0043] Furthermore, the heating temperature is 600 - 900 °C, and the heating time is 3 - 5 h; the heating temperature can be, for example, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C; preferably 600 °C; the heating time is, for example, 3 h, 3.5 h, 4 h, 4.5 h, 5 h.

[0044] According to an embodiment of the present invention, in step (2), during heating, the heating rate is 3 - 10 °C / min, such as 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min.

[0045] According to an embodiment of the present invention, in step (2), after heating, the product is cooled to room temperature, and the cooling rate is 3 - 10 °C / min, such as 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min.

[0046] According to an embodiment of the present invention, in step (2), the acidic solution is an acidic aqueous solution, and the concentration of the acidic solution is 1 - 4 mol / L, such as 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L. Furthermore, the acidic solution is selected from any one of nitric acid solution, sulfuric acid solution, and hydrochloric acid, and hydrochloric acid is preferred.

[0047] According to an embodiment of the present invention, in step (2), after removing the metal salt, the solution is filtered, the product is washed to neutrality, and then vacuum freeze-dried; the drying time is 4 - 10 h; for example, the drying time is 4 h, 6 h, 8 h, 10 h. For example, deionized water can be used for washing.

[0048] According to an embodiment of the present invention, in step (3), the hydrate of the compound shown in formula (I) is selected from at least one of lithium hydroxide monohydrate, magnesium sulfate heptahydrate, lithium bromide monohydrate, and aluminum sulfate octadecahydrate.

[0049] According to an embodiment of the present invention, in step (3), the mass ratio of the main porous carbon matrix composed of the metal-organic-framework-derived graphene-based porous carbon to the compound represented by formula (I) or the hydrate of the compound represented by formula (I) is 1:(0.5 - 2.8), preferably 1:(0.5 - 2.4), such as 1:(0.6 - 2.3), and exemplarily 1:0.5, 1:0.6, 1:0.67, 1:1.0, 1:1.5, 1:2.3, 1:1.5, 1:1.6, 1:1.8, 1:2, 1:2.3, 1:2.8.

[0050] As a preferred embodiment, the mass of the main porous carbon matrix carrier composed of the metal-organic-framework-derived graphene-based porous carbon is 50 - 100 mg, preferably 100 mg.

[0051] According to an embodiment of the present invention, in step (3), the main porous carbon matrix composed of the metal-organic-framework-derived graphene-based porous carbon and the compound represented by formula (I) or the hydrate of the compound represented by formula (I) are stirred and mixed evenly in water at room temperature, and the stirring time is 1 - 5 hours, preferably 2 hours.

[0052] According to an embodiment of the present invention, in step (3), the reaction temperature is 120 - 180 °C, preferably 150 °C; the reaction time is 10 - 20 h, for example, it can be 10 h, 12 h, 14 h, 15 h, 16 h, 18 h, 20 h, and preferably 12 - 18 h.

[0053] According to an embodiment of the present invention, in step (3), after the reaction is completed, the reaction product is dried to obtain a composite material. For example, the drying temperature is 90 - 100 °C, preferably 100 °C; the drying time is 3 - 7 h, preferably 5 h.

[0054] According to a preferred embodiment of the present invention, the preparation method of the metal-carbon-based chemical energy storage composite material specifically includes the following steps:

[0055] (1-1) Polyvinylpyrrolidone is added to the methanol solution of graphene oxide (the concentration of graphene oxide is 0.4 mg / mL) in proportion and ultrasonicated to disperse it evenly; then the methanol solution of Zn(NO3)2·6H2O is added to the mixed solution of graphene oxide and polyvinylpyrrolidone, and stirred at room temperature to prepare a first mixture;

[0056] (1-2) Then, the methanol solution of 2-methylimidazole is dropped into the first mixture in step (1-1) for reaction; after the reaction is completed, the reaction product is centrifuged, washed with methanol at least 4 times, and vacuum freeze-dried to prepare a second mixture;

[0057] (3) Heat the obtained grey powder (i.e., the second mixture) under nitrogen atmosphere; after heating, cool it down to room temperature, then immerse the obtained black powder into HCl solution and stir to remove the zinc component in the sample; finally, filter the crude product, wash it with deionized water until neutral, and then freeze-dry it under vacuum to prepare the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon.

[0058] (4) Prepare the metal-carbon composite: Add the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon described in step (3) and the compound shown in formula (I) or the hydrate of the compound shown in formula (I) into 60 mL of deionized water, and stir at room temperature; then transfer the mixture to a stainless-steel hydrothermal autoclave lined with a polytetrafluoroethylene inner liner, heat it in an oven, and after the stainless-steel hydrothermal autoclave cools down to room temperature, vacuum-dry the obtained black solution at 90 °C for 3 hours to prepare the metal-carbon composite.

[0059] The present invention also provides a heat storage device comprising the above composite material.

[0060] The present invention also provides the application of the above metal-carbon composite material in low-temperature heat energy storage devices, preferably the application of the composite material in fields such as solar heat energy and industrial waste heat treatment.

[0061] Advantages of the present invention:

[0062] In the metal-carbon composite material of the present invention, the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon is used as the supporting matrix, and is compounded with the compound shown in formula (I), so that the prepared composite material has excellent energy storage density and can efficiently store and utilize low-temperature heat energy and long-term heat energy storage across seasons. Moreover, the composite material prepared by the present invention can make full use of low-temperature heat energy such as solar heat energy and industrial waste heat. Description of the Drawings

[0063] Figure 1 It is the scanning electron microscope image of the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon prepared in Example 3 of the present invention.

[0064] Figure 2 It is the scanning electron microscope image of the metal-carbon chemical energy storage composite material prepared in Example 3 of the present invention.

[0065] Figure 3 It is the X-ray diffraction characterization pattern of the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon, the metal-carbon chemical energy storage composite material, and pure lithium hydroxide prepared in Example 3 of the present invention.

[0066] Figure 4Differential scanning calorimetry spectrum of the metal carbon-based chemical energy storage composite material prepared in Example 3 of the present invention. Detailed implementation manners

[0067] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only for illustrative explanation of the present invention and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0068] Unless otherwise specified, the raw materials and reagents used in the following embodiments are commercially available products or can be prepared by known methods.

[0069] The energy density test method for the composite materials in the following Examples 1-4 is as follows:

[0070] First, the metal carbon-based chemical energy storage composite materials prepared in Examples 1-4 are respectively fully hydrated and then stored. The hydration and storage time is 60 min. After the storage is completed, the test is carried out by DSC. First, set the initial temperature of the DSC to 30 °C and stabilize for 15 minutes, and then heat it to 200 °C at a heating rate of 5 °C / min to test its energy storage.

[0071] Example 1

[0072] (1) Add 30 mg of polyvinylpyrrolidone to 50 mL of a methanol solution of graphene oxide (0.4 mg / mL) and ultrasonicate for 2 hours to disperse it evenly; then dissolve 4 mmol of Zn(NO3)2·6H2O and 24 mmol of 2-methylimidazole in 30 mL of methanol respectively for standby. Then, first add the methanol solution of Zn(NO3)2·6H2O to the mixed solution of graphene oxide and polyvinylpyrrolidone and stir at room temperature for 30 minutes to prepare a first mixture.

[0073] (2) Then, drop the methanol solution of 2-methylimidazole into the above first mixture and react at 30 °C for 5 hours; after the reaction is completed, centrifuge the mixture and wash it with methanol at least 4 times, and then vacuum freeze-dry for 48 hours to prepare a second mixture;

[0074] (3) Heat the obtained gray powder (i.e., the second mixture) to 600 °C at a heating rate of 3 °C / min under nitrogen atmosphere and hold for 3 hours. Then cool it to room temperature at a cooling rate of 3 °C / min, immerse the obtained black powder in HCl solution (2 mol / L) and stir to remove the zinc component in the sample. Finally, filter the crude product, wash it with deionized water until neutral, and then vacuum freeze-dry for 8 hours to finally obtain a main porous carbon matrix composed of graphene-based porous carbon derived from metal-organic frameworks.

[0075] (4) Preparation of metal-carbon-based chemical energy storage composite material: 100 mg of the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon and 66.6 mg of lithium hydroxide monohydrate were added to 60 mL of deionized water, and after stirring at room temperature for 2 hours, the mixture was then transferred to a stainless-steel hydrothermal autoclave lined with a polytetrafluoro inner liner and maintained in an oven at 150 °C for 12 hours. After the stainless-steel hydrothermal autoclave was cooled to room temperature, the resulting black solution was dried at 90 °C for 3 hours to obtain the metal-carbon-based chemical energy storage composite material. The mass content of lithium hydroxide in the composite material is 40%, and the energy storage density reaches 1355.2 kJ·kg -1 。

[0076] Example 2

[0077] (1) 45 mg of polyvinylpyrrolidone was added to 75 mL of a methanol solution of graphene oxide (0.4 mg / mL) and sonicated for 2 hours to disperse it evenly. Then, 6 mmol of Zn(NO3)2·6H2O and 30 mmol of 2-methylimidazole were separately dissolved in 30 mL of methanol and set aside. Then, the methanol solution of Zn(NO3)2·6H2O was first added to the mixed solution of graphene oxide / polyvinylpyrrolidone and stirred at room temperature for 30 minutes to prepare the first mixture.

[0078] (2) Then, the methanol solution of 2-methylimidazole was dropped into the above first mixture, and the reaction was carried out at 30 °C for 4 hours; after the reaction was completed, the mixture was centrifuged and washed with methanol at least 4 times, and then freeze-dried in vacuo for 48 hours to prepare the second mixture;

[0079] (3) The resulting gray powder (i.e., the second mixture) was heated to 700 °C at a heating rate of 3 °C / min under nitrogen and maintained for 4 hours. Then, it was cooled to room temperature at a cooling rate of 3 °C / min, and the resulting black powder was immersed in an HCl solution (2 mol / L) and stirred to remove the zinc component in the sample. Finally, the crude product was filtered, washed with deionized water until neutral, and then freeze-dried in vacuo for 8 hours to finally obtain the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon.

[0080] (4) Preparation of metal-carbon-based chemical energy storage composite material: 100 mg of the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon and 100 mg of lithium hydroxide monohydrate were added to 60 mL of deionized water and stirred at room temperature for 2 hours. Then the mixture was transferred to a stainless-steel hydrothermal autoclave lined with a polytetrafluoro inner liner and maintained in an oven at 150 °C for 15 hours. After the stainless-steel hydrothermal autoclave was cooled to room temperature, the resulting black solution was dried at 90 °C for 3 hours to obtain the metal-carbon-based chemical energy storage composite material. The mass content of lithium hydroxide in the composite material is 50%, and the energy storage density reaches 1470.7 kJ·kg -1 .

[0081] Example 3

[0082] (1) 60 mg of polyvinylpyrrolidone was added to 100 mL of a methanol solution of graphene oxide (0.4 mg / mL) and sonicated for 2 hours to disperse it evenly. Then 8 mmol of Zn(NO3)2·6H2O and 32 mmol of 2-methylimidazole were respectively dissolved in 30 mL of methanol and set aside. Then, the methanol solution of Zn(NO3)2·6H2O was first added to the mixed solution of graphene oxide / polyvinylpyrrolidone and stirred at room temperature for 30 minutes to prepare the first mixture.

[0083] (2) Then, the methanol solution of 2-methylimidazole was added dropwise to the above first mixture, and the reaction was carried out at 30 °C for 5 hours; after the reaction was completed, the mixture was centrifuged and washed with methanol at least 4 times, and vacuum freeze-dried for 48 hours to prepare the second mixture;

[0084] (3) The obtained gray powder (i.e., the second mixture) was heated to 800 °C at a heating rate of 3 °C / min under nitrogen atmosphere and maintained for 5 hours. Then, it was cooled to room temperature at a cooling rate of 3 °C / min, and the obtained black powder was immersed in HCl solution (2 mol / L) and stirred to remove the zinc component in the sample. Finally, the crude product was filtered and washed with deionized water until neutral, and then vacuum freeze-dried for 8 hours to finally obtain the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon.

[0085] (4) Preparation of metal-carbon-based chemical energy storage composite material: 100 mg of the main porous carbon matrix composed of graphene-based porous carbon derived from metal-organic framework and 150 mg of lithium hydroxide monohydrate were added to 60 mL of deionized water and stirred at room temperature for 2 hours. Then the mixture was transferred to a stainless-steel hydrothermal autoclave lined with a polytetrafluoroethylene inner liner and kept in an oven at 150 °C for 16 hours. After the stainless-steel hydrothermal autoclave was cooled to room temperature, the obtained black solution was dried at 90 °C for 3 hours to obtain the metal-carbon-based chemical energy storage composite material. The mass content of lithium hydroxide in the composite material is 60%, and the energy storage density reaches 1644.2 kJ·kg -1 .

[0086] Example 4

[0087] (1) 75 mg of polyvinylpyrrolidone was added to 125 mL of a methanol solution of graphene oxide (0.4 mg / mL) and sonicated for 2 hours to disperse it evenly. Then 10 mmol of Zn(NO3)2·6H2O and 40 mmol of 2-methylimidazole were respectively dissolved in 30 mL of methanol and kept for later use. Then, the methanol solution of Zn(NO3)2·6H2O was first added to the mixed solution of graphene oxide / polyvinylpyrrolidone and stirred at room temperature for 30 minutes to prepare the first mixture.

[0088] (2) Then, after the methanol solution of 2-methylimidazole was added dropwise to the above first mixture, the reaction was carried out at 30 °C for 3 hours; after the reaction was completed, the mixture was centrifuged and washed with methanol at least 4 times, and then vacuum freeze-dried for 48 hours to prepare the second mixture;

[0089] (3) The obtained gray powder (i.e., the second mixture) was heated to 800 °C at a heating rate of 3 °C / min under nitrogen atmosphere and kept for 5 hours. Then it was cooled to room temperature at a cooling rate of 3 °C / min, and the obtained black powder was immersed in HCl solution (2 mol / L) and stirred to remove the zinc component in the sample. Finally, the crude product was filtered, washed with deionized water until neutral, and then vacuum freeze-dried for 8 hours to finally obtain the main porous carbon matrix composed of graphene-based porous carbon derived from metal-organic framework.

[0090] (4) Preparation of metal-carbon-based chemical energy storage composite material: 100 mg of the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon and 233.2 mg of lithium hydroxide monohydrate were added to 60 mL of deionized water and stirred at room temperature for 2 hours. Then the mixture was transferred to a stainless-steel hydrothermal autoclave lined with a polytetrafluoroethylene inner liner and maintained in an oven at 150 °C for 18 hours. After the stainless-steel hydrothermal autoclave was cooled to room temperature, the obtained black solution was dried at 90 °C for 3 hours to obtain the metal-carbon-based chemical energy storage composite material. The mass content of lithium hydroxide in the composite material is 70%, and the energy storage density reaches 1558.1 kJ·kg -1 .

[0091] Figure 1 and Figure 2 are the scanning electron microscope images of the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon and the metal-carbon-based chemical energy storage composite material prepared in Example 3, respectively. It can be seen from Figure 1 that the surface of the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon is uniformly covered with carbonized metal-organic frameworks, and no other particles are observed; while it can be clearly seen from Figure 2 that obvious lithium hydroxide particles exist on the surface of the metal-carbon-based chemical energy storage composite material; this indicates the successful compounding of lithium hydroxide with the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon.

[0092] Figure 3 are the X-ray diffraction characterization patterns of the main porous carbon matrix (i.e., porous carbon main matrix) composed of metal-organic framework-derived graphene-based porous carbon, the metal-carbon-based chemical energy storage composite material, and pure lithium hydroxide prepared in Example 3. It can be clearly seen from Figure 3 that the metal-carbon-based chemical energy storage composite material and lithium hydroxide have consistent characteristic diffraction peaks, and an amorphous carbon diffraction peak attributed to the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon can also be clearly observed at 24.3 degrees, further proving the successful preparation of the metal-carbon-based chemical energy storage composite material.

[0093] Figure 4 is the differential scanning calorimetry spectrum of the metal-carbon-based chemical energy storage composite material of Example 3. It can be seen from the figure that the peak exothermic temperature of the material is 80.2 °C, and the obtained energy storage density reaches 1644.2 kJ kg -1 . These results show that the metal-carbon-based chemical energy storage composite material of the present invention has excellent performance in efficient storage and utilization of low-temperature heat energy and energy storage density, which is beneficial to further fully utilize low-temperature heat energy such as solar energy and industrial waste heat for heat energy storage.

[0094] In the present invention, the molar ratio of Zn(NO3)2·6H2O to 2-methylimidazole, or the heating temperature, or the heating rate, or the heating time, or the concentration of the acidic solution, or the mass ratio of the main porous carbon matrix composed of the metal-organic framework-derived graphene-based porous carbon to the compound shown in formula (I), or the reaction temperature of each step, etc. are adjusted within the scope of the present application, and the preparation of the metal-carbon-based chemical energy storage composite material can be achieved, and it exhibits a heat storage density and heat release substantially consistent with those of Example 3.

[0095] As described above, the embodiments of the present invention have been described by way of example. However, the protection scope of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A metal carbon-based composite material, characterized in that, The composite material includes a main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon and a compound represented by formula (I) compounded with the matrix: MA(I) wherein M is selected from at least one of lithium, magnesium, and aluminum; A is selected from at least one of hydroxide, sulfate, and bromide anions; The metal-organic framework contains a metal element and an organic ligand; wherein, the metal element is selected from at least one of zinc and cobalt; the organic ligand is selected from at least one of 2-methylimidazole, terephthalic acid, benzimidazole, and 2-nitroimidazole; The preparation method of the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon is as follows: (1) React graphene oxide, polyvinylpyrrolidone, metal salt, and organic ligand in a solvent to prepare a mixture; (2) Heat the mixture in step (1) under an inert atmosphere, and then remove the metal salt in an acidic solution to prepare the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon.

2. The composite material according to claim 1, characterized in that, The compound represented by formula (I) is selected from at least one of lithium hydroxide, magnesium sulfate, lithium bromide, and aluminum sulfate.

3. The composite material according to claim 1, characterized in that, The raw material of graphene in the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon is graphene oxide or graphene.

4. The composite material according to claim 1, characterized in that, In the composite material, the mass content of the compound represented by formula (I) is 20-80%.

5. The composite material according to claim 1, wherein The composite material is a low-temperature chemical heat storage composite material.

6. The composite material according to claim 1, characterized in that, The energy density of the composite material is not less than 1000 kJ / kg -1 .

7. The composite material according to claim 6, characterized in that, The energy density of the composite material is 1100 - 1700 kJ / kg -1 .

8. The composite material according to claim 1, characterized in that, The peak heat release temperature of the composite material is 80-90 °C.

9. The method for preparing the composite material according to any one of claims 1-8, characterized in that, The method includes the following steps: (1) React graphene oxide, polyvinylpyrrolidone, metal salt, and organic ligand in a solvent to prepare a mixture; (2) Heat the mixture in step (1) under an inert atmosphere, and then remove the metal salt in an acidic solution to prepare the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon; (3) Mix and react the main porous carbon matrix composed of metal-organic framework-derived graphene-based porous carbon in step (2) with the compound represented by formula (I) or the hydrate of the compound represented by formula (I) in water to prepare the metal-carbon-based composite material.

10. The preparation method according to claim 9, characterized in that, The specific steps of step (1) are: (1-1) Disperse graphene oxide, polyvinylpyrrolidone, and metal salt evenly in a solvent to prepare a first mixture; (1-2) Dissolve the organic ligand in the solvent and add it to the first mixture in step (1-1), and react to prepare a second mixture.

11. The preparation method according to claim 9, characterized in that, The metal salt is selected from at least one of Zn(NO3)2·6H2O and Co(NO3)2·6H2O.

12. The preparation method according to claim 9, characterized in that, In step (1), the mass ratio of polyvinylpyrrolidone to graphene oxide is 1:(0.6-2).

13. The preparation method according to claim 9, characterized in that, In step (1), the molar mass ratio of the metal salt to graphene oxide is 1 (mmol):(5-10) (mg); In step (1), the molar ratio of the metal salt to the organic ligand is 1:(4-6); In step (1), the concentration of graphene oxide is 0.3-0.6 mg / mL.

14. The preparation method according to claim 9, characterized in that, In step (2), the heating temperature is 600-900 °C.

15. The preparation method according to claim 9, wherein In step (2), the concentration of the acidic solution is 1-4 mol / L; the acidic solution is any one of nitric acid solution, sulfuric acid solution, and hydrochloric acid solution.

16. The preparation method according to claim 9, wherein In step (3), the mass ratio of the main porous carbon matrix composed of the metal-organic framework-derived graphene-based porous carbon to the compound shown in formula (I) or the hydrate of the compound shown in formula (I) is 1:(0.5-2.8).

17. A heat storage device, characterized in that, Comprising the composite material according to any one of claims 1-8.

18. Application of the composite material according to any one of claims 1-8 in a low-temperature thermal energy storage device.

19. The application according to claim 18, wherein Application in the fields of solar energy and industrial waste heat treatment.

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