A MOF-derived carbon-confined magnesium-based nano-hydrogen storage material and its preparation method

Abstract

The present invention belongs to the technical field of solid-state hydrogen storage, and specifically discloses a MOF-derived carbon-confined magnesium-based nano hydrogen storage material and a preparation method thereof. The material comprises the following steps: dissolving a MOF ligand in a solvent, and adding a non-oxygen-containing magnesium salt to prepare a mixed solution a; selecting a transition metal salt and dissolving it in a solvent to prepare a mixed solution b, and adding the mixed solution b to the mixed solution a to prepare a mixed solution c; centrifugally collecting a precipitated product in the mixed solution c and vacuum drying it to prepare a precursor; and calcining the precursor at a high temperature so that carbon generated by decomposition of the MOF ligand is coated on Mg particles generated by decomposition of MgX in the precursor, while the carbon also reduces transition metal ions in the MOF to obtain a transition metal catalyst, thereby finally preparing carbon-confined magnesium-based composite nanoparticles. The material has the following advantages: the size of the carbon-confined magnesium nanoparticles is less than 10 nm, the type of transition metal catalyst can be controlled, the Mg loading rate can be effectively increased, and the hydrogen storage performance thereof can be improved. In addition, the preparation process of the present invention is simple, green and pollution-free.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state hydrogen storage, and in particular to a MOF-derived carbon-confined magnesium-based nano hydrogen storage material and a preparation method thereof. Background Art

[0002] Environmental pollution and climate problems caused by the use of fossil fuels have seriously affected human life and production. Hydrogen energy, as a clean energy, has a high weight energy density and is considered to be one of the most ideal alternative energy sources. However, due to the storage and safety issues of hydrogen, the practical application of hydrogen is greatly limited. Compared with low-temperature liquid hydrogen storage and high-pressure gaseous hydrogen storage, solid-state hydrogen storage has the advantages of safety and efficiency. Among many solid-state hydrogen storage materials, metallic Mg has a high theoretical hydrogen storage weight of 7.6wt% and a high storage capacity of 110kg·m -3 Mg's high volumetric hydrogen storage capacity has attracted widespread attention from researchers. Furthermore, magnesium is abundant, low-cost, pollution-free, and highly safe, making it a promising solid-state hydrogen storage material. Unfortunately, the high thermodynamic stability of Mg-based hydrogen storage materials, with a ΔHf of -76 kJ / molH2 and slow hydrogen absorption and desorption kinetics, results in high operating temperatures exceeding 573 K, limiting the practical application of magnesium hydrides.

[0003] Obtaining nanoscale Mg particles is an effective method to improve hydrogen storage performance. Generally speaking, nanostructured Mg has the characteristics of large specific surface area, rich grain boundaries / defects, and short hydrogen diffusion paths, which can significantly improve the hydrogen storage performance of Mg. For Mg nanoparticles, the higher surface energy will cause them to grow and agglomerate during the thermal dehydrogenation process, which inevitably leads to a decrease in hydrogen storage performance. Therefore, limiting Mg nanoparticles by confining framework materials is a feasible way to solve this problem. The current nanoconfinement process is mainly achieved through solution impregnation and metal melting methods. However, the Mg loading rate in the composite material prepared by this process is low, and it is not easy to add catalysts, which greatly reduces the hydrogen storage performance of the composite material. In addition, there are problems such as high raw material prices, complex preparation processes, and high overall costs.

[0004] To this end, a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material and a preparation method thereof are proposed to solve the above-mentioned problems. Summary of the Invention

[0005] The present invention aims to provide a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material and a preparation method thereof, so as to solve or improve at least one of the above-mentioned technical problems.

[0006] In view of this, a first aspect of the present invention is to provide a method for preparing a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material.

[0007] The second aspect of the present invention provides a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material.

[0008] The first aspect of the present invention provides a method for preparing a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material, comprising the following steps:

[0009] S1, under a protective atmosphere, dissolving a MOF ligand in a solvent by stirring to obtain a prefabricated solution, adding a certain amount of a non-oxygen-containing element magnesium salt to the prefabricated solution and stirring for 10 minutes to 120 minutes to obtain a mixed solution a;

[0010] S2, under a protective atmosphere, selecting a certain type of transition metal salt and dissolving it in a solvent by stirring, and stirring for 10 minutes to 120 minutes to prepare a mixed solution b;

[0011] S3, under a protective atmosphere, adding the mixed solution b to the mixed solution a at a certain speed and stirring for 10 minutes to 120 minutes, and letting it stand for 3 hours to 72 hours to obtain a mixed solution c;

[0012] S4, centrifuging the mixed solution c to collect the precipitated product, washing the precipitated product with a solvent, placing it in a vacuum container for vacuum drying for 1 h to 18 h, and removing the white solid on the surface to obtain the MgX@MOF precursor;

[0013] S5, placing the MgX@MOF precursor in a heat treatment furnace in a protective atmosphere environment, and calcining it at a high temperature to decompose the MOF ligand to produce carbon, which is in situ wrapped around the Mg particles produced by the decomposition of MgX in the MgX@MOF precursor. At the same time, the carbon will reduce the transition metal ions in MOF to obtain the transition metal catalyst M, thereby obtaining Mg@C or Mg-M@C composite nanoparticles.

[0014] The present invention provides a method for preparing a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material. Under a protective atmosphere at room temperature, a non-oxygen-containing magnesium salt (MgX) precipitated from a mixed solution is used as a crystal nucleus to in-situ grow a MOF material, thereby obtaining a MOF-encapsulated non-oxygen-containing magnesium salt precursor (MgX@MOF). The precursor is further heat-treated via a thermal decomposition-thermal reduction method, where MgX decomposes to produce metallic Mg. The carbon produced by the MOF decomposition reduces transition metal ions to a transition metal catalyst (M) at high temperature, and the metallic Mg and transition metal catalyst are then in-situ coated to obtain a carbon-confined magnesium-based nano-hydrogen storage material. This significantly improves the hydrogen storage performance of the Mg-based hydrogen storage material prepared by the present method.

[0015] By changing the metal type of transition metal salt during the MOF preparation process, the type of Mg catalyst can be adjusted to prepare Mg@C nanoparticles without catalyst or Mg-M@C composite nanoparticles containing single, binary or multi-element alloy metal catalysts, thereby optimizing and improving the hydrogen storage kinetics of composite nano hydrogen storage materials.

[0016] By varying the amount of non-oxygen magnesium salt added and controlling the thermal decomposition and reduction temperatures, size-controllable Mg or Mg-M nanoparticles with a particle size less than 10 nm can be prepared. By obtaining smaller Mg or Mg-M nanoparticles, the overall hydrogen storage performance of Mg@C or Mg-M@C composite nanoparticles can be improved.

[0017] The in situ generated transition metal catalyst in this method effectively improves the hydrogen storage kinetics of the Mg-M@C composite nanoparticles. The size of the skeleton carbon-confined Mg or Mg-M nanoparticles is less than 10 nm, which can effectively improve the hydrogen storage thermodynamics of the Mg@C or Mg-M@C composite nanoparticles.

[0018] Compared with traditional solution impregnation and metal melting methods, it is difficult to fully fill the pores in the skeleton with Mg particles, resulting in a low loading rate. The present invention can effectively increase the Mg loading rate by in-situ coating the surface of Mg or Mg-M nanoparticles with skeleton carbon, while inhibiting the growth and agglomeration of Mg or Mg-M nanoparticles, significantly improving the hydrogen absorption and desorption cycle performance of Mg@C or Mg-M@C composite nanoparticles;

[0019] The currently used solution impregnation method and metal melting method for preparing confined skeleton materials require chemicals such as resorcinol and furfural, which pollute the environment. The method of the present invention does not require the use of such chemicals, and the drugs and products used in the present invention are green and pollution-free to the environment.

[0020] In addition, the technical solution provided by the embodiment of the present invention may also have the following additional technical features:

[0021] In any of the above technical solutions, the transition metal salt is at least one selected from a preset range of species, and the preset range of species includes but is not limited to at least one of the following: cobalt nitrate, cobalt chloride, cobalt carbonate, nickel nitrate, nickel carbonate, nickel chloride, ferric nitrate, ferric carbonate and ferric chloride; wherein, by selecting the metal species contained in the transition metal salt of the mixed solution b prepared in S2, the type of transition metal catalyst of the Mg@C or Mg-M@C composite nanoparticles is adjusted to improve the hydrogen storage kinetics performance.

[0022] In this technical solution, by changing the metal type of the transition metal salt during the MOF preparation process, the catalyst type can be adjusted to prepare catalyst-free Mg@C composite nanoparticles or Mg-M@C composite nanoparticles containing mono-, binary- or multi-element alloy metal catalysts, thereby improving the hydrogen storage kinetics of the composite nano hydrogen storage material.

[0023] In any of the above technical solutions, the addition amount of the non-oxygen-containing element magnesium salt is in the range of 1 mmol to 50 mmol, and includes but is not limited to one of the following types: di-n-butyl magnesium, magnesium halide, magnesium sulfide, magnesium boride, magnesium borohydride, methylmagnesium bromide and magnesium porphyrin; wherein, the MgX@MOF precursor is prepared by selecting different types of non-oxygen-containing element magnesium salts, and calcining them at different temperatures of 500°C to 1000°C for 1h to 10h for thermal decomposition and thermal reduction to regulate the size of the obtained Mg or Mg-M@C composite nanoparticles, and controlling the Mg or Mg-M nanoparticles to be less than 10nm.

[0024] In this technical solution, the control of temperature during thermal decomposition and thermal reduction has an impact on the size of the final Mg-M@C composite nanoparticles, so calcination is carried out at different temperatures of 500°C to 1000°C to obtain Mg or Mg-M nanoparticles with different particle sizes.

[0025] In any of the above technical solutions, the MOF ligand includes but is not limited to one of the following types: 2-methylimidazole, terephthalic acid and trimesic acid.

[0026] In any of the above technical solutions, the molar ratio of the transition metal salt, the MOF ligand, and the non-oxygen-containing magnesium salt is 1:(1-5):(1-20).

[0027] In this technical solution, regulating the molar ratio of transition metal salts and non-oxygen-containing magnesium salts can control the catalyst content in Mg-M@C composite nanoparticles; regulating the molar ratio of MOF ligands and non-oxygen-containing magnesium salts can control the mass of skeleton carbon in Mg@C or Mg-M@C composite nanoparticles to increase the Mg loading rate.

[0028] In any of the above technical solutions, the inert gas is nitrogen, argon or hydrogen, and / or the solvent is N,N-dimethylformamide, pyridine or tetrahydrofuran.

[0029] In any of the above technical solutions, the skeleton carbon generated by the decomposition of the MOF ligand confines the Mg or Mg-M nanoparticles to inhibit the growth and agglomeration of the nanoparticles during the hydrogen absorption and desorption reaction.

[0030] In any of the above technical solutions, the skeleton carbon generated after the decomposition of MOF is in situ wrapped on the surface of Mg or Mg-M nanoparticles to form the skeleton carbon of Mg or Mg-M nanoparticles; the skeleton carbon is the confined skeleton material of Mg or Mg-M nanoparticles.

[0031] The second aspect of the present invention provides a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material, comprising: the Mg-M@C composite nanoparticles comprising Mg-M nanoparticles and an amorphous carbon layer; and the Mg@C comprising Mg and skeleton carbon; the skeleton carbon is used to prevent the growth and agglomeration between Mg or Mg-M nanoparticles, and the carbon decomposed by MOF is in situ wrapped around the nanoparticles to form; wherein the MOF-derived carbon-confined magnesium-based nano-hydrogen storage material is prepared by the preparation method described in any technical solution of the first aspect.

[0032] The present invention provides a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material. The composite nanomaterial comprises Mg or Mg-M nanoparticles and skeleton carbon. The skeleton carbon acts as a confining framework material, effectively limiting the growth and agglomeration of the Mg or Mg-M nanoparticles, ensuring that the size of the Mg or Mg-M nanoparticles is within the range of 1 to 100 nm. The Mg loading rate in the carbon-confined magnesium-based nano-hydrogen storage material can reach over 76%. This results in the Mg-based nano-hydrogen storage material prepared using the present invention having excellent hydrogen storage performance.

[0033] In any of the above technical solutions, the size of the Mg or Mg-M nanoparticles is 1 to 100 nm to improve the hydrogen storage performance of the Mg@C or Mg-M@C composite nanoparticles; wherein the Mg@C composite nanoparticles do not contain a catalyst, and the catalyst M added to the Mg-M@C composite nanoparticles is a mono-, binary or multi-component alloy metal catalyst.

[0034] In this technical solution, the average particle size of the Mg or Mg-M nanoparticles is less than 10 nm, which can significantly shorten the diffusion distance of hydrogen molecules and reduce the diffusion energy barrier of hydrogen molecules, which is beneficial to reducing the kinetic activation energy and thermodynamic enthalpy change of the hydrogen absorption and desorption process, thereby making the Mg@C or Mg-M@C composite nanoparticles have a lower operating temperature and greater practical value.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] By changing the metal type of the transition metal salt during the MOF preparation process, the type of Mg catalyst can be adjusted to prepare catalyst-free Mg@C nanocomposite particles or Mg-M@C nanocomposite particles containing single, binary or multi-element alloy metal catalysts, thereby improving the hydrogen storage kinetics of composite nano hydrogen storage materials.

[0037] By varying the amount of non-oxygen-containing magnesium salt added and controlling the thermal decomposition and thermal reduction temperatures, Mg or Mg-M nanoparticles with a particle size less than 10 nm and adjustable size can be prepared. By obtaining smaller-sized nanoparticles, the comprehensive hydrogen storage performance of the material can be improved.

[0038] Adjust the catalyst type of Mg-M@C composite nanoparticles to effectively improve the hydrogen storage kinetics of the composite nanomaterials;

[0039] The size of the skeleton carbon-confined Mg or Mg-M nanoparticles is less than 10 nm, which effectively improves the hydrogen storage thermodynamic properties of the composite nanomaterials;

[0040] The skeleton carbon inhibits the growth and agglomeration of Mg or Mg-M nanoparticles, effectively improving the hydrogen absorption and desorption cycle performance of the composite nanomaterials;

[0041] The currently used solution impregnation method and metal melting method for preparing confined skeleton materials require chemicals such as resorcinol and furfural, which pollute the environment. These materials are suitable for generating confined skeletons of hydrogen storage materials, and are replaced by MOF ligand materials (such as 2-methylimidazole). The method of the present invention does not require the use of such chemicals, and the chemicals and products used in the present invention are green and pollution-free to the environment.

[0042] Additional aspects and advantages of embodiments according to the present invention will become apparent in the following description or may be learned through practice of embodiments according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0044] Figure 1 Schematic diagram of the preparation of Mg-M@C composite nanoparticles by in situ growth-solvothermal method and thermal decomposition-thermal reduction method of the present invention;

[0045] Figure 2 TEM (a) and particle size distribution diagram (b) of Mg-Co@C composite nanoparticles of Example 1 of the present invention;

[0046] Figure 3 This is an EDS elemental surface scan of the Mg-Co@C composite nanoparticles of Example 1 of the present invention;

[0047] Figure 4 This is the XRD pattern of the Mg-Co@C composite nanoparticles of Example 1 of the present invention;

[0048] Figure 5 This is the hydrogen absorption and desorption cycle curve of the Mg-Co@C composite nanoparticles in Example 1 of the present invention at 473K / 573K. DETAILED DESCRIPTION

[0049] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0050] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0051] See also Figure 1-5 The following describes a MOF-derived carbon-confined magnesium-based nano hydrogen storage material and a preparation method thereof according to some embodiments of the present invention. The preparation method specifically includes the following steps:

[0052] (1) Under a protective atmosphere, the MOF ligand is dissolved in a solvent by stirring; a certain amount of non-oxygen-containing magnesium salt is added, and the solution is stirred for 10 to 120 minutes to prepare a mixed solution a;

[0053] Dosage: 10 mmol of MOF ligand requires 10 mL to 100 mL of solvent, and the amount of non-oxygen element magnesium salt added is 1 to 50 mmol;

[0054] (2) dissolving the transition metal salt in the solvent by stirring under a protective atmosphere, and stirring the solution for 10 to 120 minutes to prepare a mixed solution b;

[0055] Dosage: 5 mmol of transition metal salt requires 10 mL to 100 mL of solvent;

[0056] (3) Under a protective atmosphere, slowly add the mixed solution b obtained in step (2) to the mixed solution a obtained in step (1), stir for 10 to 120 minutes, and let it stand at room temperature for 3 to 72 hours to obtain a mixed solution c;

[0057] (4) The mixed solution c obtained in step (3) was centrifuged, repeatedly washed with tetrahydrofuran, placed in a vacuum container, and vacuum treated for 1 h to 18 h, and then the white solid on the surface was removed to obtain a MgX@MOF precursor.

[0058] Centrifugation conditions: centrifugation time 3 to 30 minutes, centrifugation speed 3000 to 9000 rpm.

[0059] (5) The MgX@MOF precursor obtained in step (4) is subjected to two-stage programmed temperature increase in a heat treatment furnace in a protective atmosphere environment: first calcining at 120°C to 200°C for 1h to 2h, and then calcining at 500°C to 1000°C for 1h to 10h to obtain Mg@C or Mg-M@C composite nanoparticles.

[0060] Mg@C or Mg-M@C composite nanoparticles include: Mg or Mg-M nanoparticles and skeleton carbon;

[0061] The framework carbon is used to inhibit the growth and agglomeration of Mg or Mg-M nanoparticles and is formed by the decomposed carbon in situ wrapping around the Mg or Mg-M nanoparticles.

[0062] By changing the type of transition metal salt added in step (2), the type of composite nanoparticles obtained after heat treatment under the temperature conditions of step (5) will also be different. If a transition metal salt corresponding to a low-melting-point metal element, such as a Zn metal salt, is added, the transition metal Zn will volatilize during the heat treatment process, and the final product will be Mg@C composite nanoparticles; if a transition metal salt corresponding to a high-melting-point metal element, such as a Ni, Co metal salt, is added, the transition metal element will not volatilize during the heat treatment process, and the final product will be Mg-M@C composite nanoparticles; if a low-melting-point metal salt and a high-melting-point transition metal salt are added at the same time, the low-melting-point transition metal will volatilize during the heat treatment process, leaving only the high-melting-point transition metal, and the final product will be Mg-M@C composite nanoparticles.

[0063] In the case of adding a transition metal salt, by setting the temperature in step (5), when the melting point of the corresponding metal element contained in the transition metal salt is lower than the maximum value of the set temperature, the setting time of the maximum value is controlled so that the metal element in the transition metal salt is volatilized, so that the final product is Mg@C; or the setting time of the maximum value is controlled so that the metal element in the transition metal salt is completely retained, so that the final product is Mg-M@C; or the setting time of the maximum value is controlled so that the metal element in the transition metal salt is partially retained, so that the final products are Mg@C and Mg-M@C;

[0064] Example 1

[0065] The method for preparing the Mg-Co@C composite nano hydrogen storage material of the present invention comprises the following steps:

[0066] (1) Under Ar atmosphere, 10 mmol of 2-methylimidazole was dissolved in 30 mL of N,N-dimethylformamide solvent by stirring; 10 mL of di-n-butylmagnesium (1.0 M heptane) solution was added, and the solution was stirred for 30 min to prepare a mixed solution a;

[0067] (2) Under Ar atmosphere, 5 mmol of CoCl2 was dissolved in 30 mL of N,N-dimethylformamide solvent by stirring, and the solution was stirred for 30 min to prepare a mixed solution b;

[0068] (3) Under Ar environment, the mixed solution b obtained in step (2) was slowly added to the mixed solution a obtained in step (1), stirred for 30 minutes, and allowed to stand at room temperature for 24 hours to obtain a mixed solution c;

[0069] (4) The mixed solution c obtained in step (3) was centrifuged, repeatedly washed with tetrahydrofuran, placed in a vacuum container, and vacuum treated for 6 hours, and the white solid on the surface was removed to obtain a MgBu2@ZIF-67 precursor.

[0070] Centrifugation conditions: centrifugation time 3 min, centrifugal speed 8000 rpm.

[0071] (5) The MgBu2@ZIF-67 precursor obtained in step (4) was placed in a horizontal tube furnace in an Ar atmosphere and subjected to two-stage programmed temperature increase: first calcined at 200°C for 2h, and then calcined at 800°C for 2h to obtain Mg-Co@C composite nanoparticles.

[0072] The Mg-Co@C composite nanoparticles prepared in Example 1 were observed under a transmission electron microscope (TEM). Figure 2 、 Figure 3 As shown in the figure, the size of the prepared Mg-Co composite nanoparticles ranges from 2 to 30 nm, with an average particle size of 9.5 nm. Except for the enrichment of Co on the surface of some Co particles, the other elements are evenly distributed on the sample surface.

[0073] The Mg-Co@C composite nanoparticles prepared in Example 1 were subjected to X-ray diffraction (XRD) test, and the results were as follows: Figure 4 As shown in the figure, the XRD pattern of the Mg-Co@C composite nanoparticles shows only diffraction peaks of Mg and Co. Compared with standard diffraction charts (Mg: JCPDS65-3365; Co: JCPDS88-2325), no other impurities are found, indicating that the purity of Mg and Co in the Mg-Co@C composite nanoparticles is very high. In addition, the diffraction peaks between 15° and 35° indicate the formation of an amorphous carbon layer.

[0074] The Mg-Co@C composite nanoparticles prepared in Example 1 were tested for hydrogen storage performance and cyclic stability in a Sievert-type device: the sample was activated once at 673K, cooled to 473K under vacuum conditions, and then subjected to a 30-min hydrogen absorption test. After heating to 573K under a hydrogen atmosphere, a 30-min hydrogen release test was performed. A total of 20 cyclic hydrogen storage tests were performed. The results are as follows: Figure 5 As can be seen from the figure, the amount of hydrogen absorbed and released by the Mg-Co@C composite nanoparticles did not decrease significantly after 20 cycles, indicating that the sample has good cyclic hydrogen storage stability. In summary, the excellent hydrogen storage performance of the Mg-Co@C composite nanoparticles can be attributed to the synergistic effect of the carbon skeleton on the confinement of the Mg particle size and the catalytic effect of Co.

[0075] Example 2

[0076] The method for preparing the Mg-Ni@C composite nano hydrogen storage material of the present invention comprises the following steps:

[0077] (1) Under Ar atmosphere, 6 mmol of 2-methylimidazole was dissolved in 30 mL of N,N-dimethylformamide solvent by stirring; 10 mL of di-n-butylmagnesium (1.0 M heptane) solution was added dropwise, and the solution was stirred for 30 min to prepare a mixed solution a;

[0078] (2) Under Ar atmosphere, 1.5 mmol of Ni(NO3)2 and 1.5 mmol of Zn(NO3)2 were dissolved in 30 mL of N,N-dimethylformamide solvent by stirring, and the solution was stirred for 30 min to prepare a mixed solution b;

[0079] (3) Under Ar environment, the mixed solution b obtained in step (2) was slowly added to the mixed solution a obtained in step (1), stirred for 30 minutes, and allowed to stand at room temperature for 24 hours to obtain a mixed solution c;

[0080] (4) The mixed solution c obtained in step (3) was centrifuged, repeatedly washed with tetrahydrofuran, placed in a vacuum container, and vacuum treated for 6 hours, and then the white solid on the surface was removed to obtain a MgBu2@Ni-ZIF precursor.

[0081] Centrifugation conditions: centrifugation time 3 min, centrifugal speed 8000 rpm.

[0082] (5) The MgBu2@Ni-ZIF precursor obtained in step (4) was placed in a horizontal tube furnace in an Ar atmosphere and subjected to two-stage programmed temperature increase: first calcined at 200°C for 2h, and then calcined at 800°C for 2h to obtain Mg-Ni@C composite nanoparticles.

[0083] Example 3

[0084] The method for preparing the Mg-CoNi@C composite nano hydrogen storage material of the present invention comprises the following steps:

[0085] (1) Under Ar atmosphere, 10 mmol of 2-methylimidazole was dissolved in 30 mL of N,N-dimethylformamide solvent by stirring; 10 mL of di-n-butylmagnesium (1.0 M heptane) solution was added, and the solution was stirred for 30 min to prepare a mixed solution a;

[0086] (2) Under an Ar atmosphere, 2.5 mmol of CoCl2 and 2.5 mmol of NiCl2 were dissolved in 30 mL of N,N-dimethylformamide solvent by stirring, and the solution was stirred for 30 min to prepare a mixed solution b;

[0087] (3) Under Ar environment, the mixed solution b obtained in step (2) was slowly added to the mixed solution a obtained in step (1), stirred for 30 minutes, and allowed to stand at room temperature for 24 hours to obtain a mixed solution c;

[0088] (4) The mixed solution c obtained in step (3) was centrifuged, repeatedly washed with tetrahydrofuran, placed in a vacuum container, and vacuum treated for 6 hours, and then the white solid on the surface was removed to obtain a MgBu2@CoNi-ZIF precursor.

[0089] Centrifugation conditions: centrifugation time 3 min, centrifugal speed 8000 rpm.

[0090] (5) The MgBu2@CoNi-ZIF precursor obtained in step (4) was placed in a horizontal tube furnace in an Ar atmosphere and subjected to two-stage programmed temperature increase: first calcined at 200°C for 2h, and then calcined at 800°C for 2h to obtain Mg-CoNi@C composite nanoparticles.

[0091] Example 4

[0092] The method for preparing the Mg@C composite nano hydrogen storage material of the present invention comprises the following steps:

[0093] (1) Under Ar atmosphere, 10 mmol of 2-methylimidazole was dissolved in 30 mL of N,N-dimethylformamide solvent by stirring; 10 mL of di-n-butylmagnesium (1.0 M heptane) solution was added, and the solution was stirred for 30 min and then allowed to stand at room temperature for 24 h to prepare a mixed solution a;

[0094] (2) Under Ar atmosphere, 3 mmol of Zn(NO3)2 was dissolved in 30 mL of N,N-dimethylformamide solvent by stirring, and the solution was stirred for 30 min to prepare a mixed solution b;

[0095] (3) Under Ar environment, the mixed solution b obtained in step (2) was slowly added to the mixed solution a obtained in step (1), stirred for 30 minutes, and allowed to stand at room temperature for 24 hours to obtain a mixed solution c;

[0096] (4) The mixed solution obtained in step (3) was centrifuged, washed repeatedly with tetrahydrofuran, placed in a vacuum container, and vacuum treated for 6 hours to obtain a white precursor;

[0097] Centrifugation conditions: centrifugation time 3 min, centrifugal speed 8000 rpm;

[0098] (5) The white precursor obtained in step (4) was placed in a horizontal tube furnace in an Ar atmosphere and subjected to two-stage programmed temperature increase: first calcined at 200°C for 2h, and then calcined at 800°C for 2h to obtain Mg@C composite nanoparticles.

[0099] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0100] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A method for preparing a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material, characterized in that: The steps include: S1, under a protective atmosphere, dissolving a MOF ligand in a solvent by stirring to obtain a prefabricated solution, adding a certain amount of a non-oxygen-containing element magnesium salt to the prefabricated solution and stirring for 10 min to 120 min to obtain a mixed solution a; S2, under a protective atmosphere, selecting a certain type of transition metal salt and dissolving it in a solvent by stirring, and stirring for 10 minutes to 120 minutes to prepare a mixed solution b; S3, under a protective atmosphere, adding the mixed solution b to the mixed solution a at a certain speed and stirring for 10 min to 120 min, and letting it stand for 3 h to 72 h to obtain a mixed solution c; S4, centrifuging the mixed solution c to collect the precipitated product, washing the precipitated product with a solvent, placing it in a vacuum container for vacuum drying for 1 h to 18 h, and removing the white solid on the surface to obtain the MgX@MOF precursor; S5, placing the MgX@MOF precursor in a heat treatment furnace in a protective atmosphere environment, and calcining it at a high temperature to decompose the MOF ligand to produce carbon, which is in situ wrapped around the Mg particles produced by the decomposition of MgX in the MgX@MOF precursor. At the same time, the carbon will reduce the transition metal ions in MOF to obtain the metal catalyst M, thereby obtaining Mg@C or Mg-M@C composite nanoparticles.

2. The method for preparing a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material according to claim 1, wherein the transition metal salt is at least one selected from a preset range of species, and the preset range of species is: Cobalt nitrate, cobalt chloride, cobalt carbonate, nickel nitrate, nickel carbonate, nickel chloride, ferric nitrate, ferric carbonate, and ferric chloride; in, By selecting the metal species contained in the transition metal salt of the mixed solution b prepared in S2, the type of transition metal catalyst of the Mg@C or Mg-M@C composite nanoparticles is changed to improve the hydrogen storage kinetics performance.

3. The method for preparing a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material according to claim 1, characterized in that: The amount of the non-oxygen-containing element magnesium salt added is in the range of 1 mmol to 50 mmol, and the non-oxygen-containing element magnesium salt is one of the following types: Di-n-butylmagnesium, magnesium halides, magnesium sulfide, magnesium boride, magnesium borohydride, methylmagnesium bromide, and magnesium porphyrin; Among them, MgX@MOF precursors made from different types of non-oxygen-containing magnesium salts were selected and calcined at different temperatures of 500℃~1000℃ for 1 h~10 h for thermal decomposition and thermal reduction to regulate the size of the obtained Mg or Mg-M@C composite nanoparticles, and the Mg or Mg-M nanoparticles were controlled to be less than 10 nm.

4. The method for preparing a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material according to claim 1, characterized in that: The MOF ligand is one of the following types: 2-Methylimidazole, terephthalic acid and trimesic acid.

5. The method for preparing a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material according to any one of claims 1 to 4, characterized in that: The molar ratio of the transition metal salt, the MOF ligand, and the non-oxygen-containing magnesium salt is 1:(1-5):(1-20).

6. The method for preparing a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material according to claim 1, characterized in that: The protective atmosphere is nitrogen, argon or hydrogen, and / or the solvent is N, N-dimethylformamide, N, N-dimethylacetamide or pyridine or tetrahydrofuran.

7. The method for preparing a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material according to claim 1, characterized in that: The skeleton carbon generated by the decomposition of the MOF ligand confines the Mg or Mg-M nanoparticles, thereby inhibiting the growth and agglomeration of the nanoparticles during the hydrogen absorption and desorption reaction.

8. The method for preparing a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material according to claim 1, characterized in that: The skeleton carbon generated after the decomposition of MOF is in situ wrapped on the surface of Mg or Mg-M nanoparticles to form the skeleton carbon of Mg or Mg-M nanoparticles; The skeleton carbon is a confined skeleton material of Mg or Mg-M nanoparticles.

9. A MOF-derived carbon-confined magnesium-based nano-hydrogen storage material, characterized in that: The Mg-M@C composite nanoparticles include Mg-M nanoparticles and an amorphous carbon layer; and the Mg@C includes Mg and skeleton carbon; The skeleton carbon is used to prevent the growth and agglomeration of Mg or Mg-M nanoparticles, and the carbon decomposed from MOF is in situ wrapped around the nanoparticles; Wherein, the MOF-derived carbon-confined magnesium-based nano hydrogen storage material is prepared by the preparation method according to any one of claims 1, 2, 4, 6, 7 or 8.

10. The MOF-derived carbon-confined magnesium-based nano-hydrogen storage material according to claim 9, wherein: The size of the Mg or Mg-M nanoparticles is 1 to 100 nm to improve the hydrogen storage performance of the Mg@C or Mg-M@C composite nanoparticles; The Mg@C composite nanoparticles do not contain a catalyst, and the catalyst M added to the Mg-M@C composite nanoparticles is a monovalent, binary or multivalent alloy metal catalyst.

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