MOF structure modification-based high-capacity magnesium-based composite material and preparation method thereof

Abstract

The invention discloses a preparation method of a high-capacity magnesium-based composite material based on MOF structure modification, and belongs to the technical field of hydrogen storage materials, the preparation method comprises the following steps: (1) preparing an M-MOF guest material; (2) modifying an aperture structure of the M-MOF guest material; and (3) preparing the MgH2 (at) S-M-MOF compound by a wet impregnation nano confinement method. Compared with a pure MgH2 hydrogen storage material, the MgH2 (at) S-M-MOF compound magnesium-based hydrogen storage material prepared by the nano confinement method has the advantages that the hydrogen absorption and desorption reaction temperature is obviously reduced, and the dynamics is greatly improved; compared with a traditional nano confinement hydrogen storage material preparation process, the preparation method has the advantages that the comprehensive hydrogen storage performance of a compound is enhanced by modifying a pore structure and introducing catalytic elements, the operability is high, the effective loading rate is high, the preparation period is short, and the yield is high; the required raw materials are cheap and easy to obtain, and the preparation process is low in cost, high in safety and suitable for industrial production and popularization.

Description

Technical Field

[0001] This invention relates to the field of hydrogen storage materials technology, and more specifically to a high-capacity magnesium-based composite material based on MOF structure modification and its preparation method. Background Technology

[0002] As one of the most anticipated new energy sources of the 21st century, hydrogen energy has garnered increasing attention. Its applications offer numerous advantages, such as a high calorific value of 142.351 kJ / kg, three times that of traditional gasoline, wide availability, and pure water as the combustion product with no pollutant emissions. However, efficient and safe hydrogen storage technology remains a critical issue hindering the rapid economic development of hydrogen energy. Currently, industrial and laboratory hydrogen storage technologies primarily rely on gaseous hydrogen storage in steel cylinders. These cylinders suffer from poor safety and low volumetric hydrogen storage capacity, with a capacity of only 1 wt% (15 MPa). Liquid hydrogen storage requires maintaining temperatures below liquid nitrogen, resulting in significant energy consumption and high costs, limiting its application to aerospace and limiting its practical civilian value. Compared to these two main methods, solid-state hydrogen storage technology is considered one of the most promising hydrogen storage solutions due to its safety and high storage density. Among various hydrogen storage materials, metal hydrides hold broad application prospects. For example, the theoretical hydrogen storage capacity of magnesium-based hydrogen storage material MgH2 can reach 7.6 wt%, exhibiting excellent reversible hydrogen absorption and desorption performance and remaining stable in air. Furthermore, magnesium is a common metallic element, abundant in reserves and inexpensive. However, due to the stable thermodynamic properties (enthalpy change of hydrogen absorption and desorption = ±75 kJ / mol H2) and poor hydrogen absorption and desorption kinetics of magnesium hydride materials, its hydrogen desorption temperature is above 623 K, which is unfavorable for its practical application.

[0003] Improving the hydrogen storage performance of magnesium-based solid-state hydrogen storage materials mainly involves addressing their thermodynamic and kinetic aspects. Kinetic regulation is relatively easy to achieve, commonly using the addition of noble metals, transition metals, specific oxides, and halides as catalysts to modify the reaction-diffusion nucleation kinetics. However, it has been found that existing catalytic technologies primarily focus on kinetic improvements, while thermodynamic performance alterations mainly rely on alloying and nano-sizing. Alloying and smelting generally lead to significant capacity loss, and traditional ball milling nano-sizing processes are energy-intensive, time-consuming, introduce impurities, and result in severe secondary agglomeration in later reactions. To address these technological challenges in nano-sizing, magnesium-based materials can be nano-sized using a "nano-confining" method. This involves wet impregnation of a magnesium-containing organic liquid into a highly porosity guest material, followed by drying and hydrogenation to prepare the composite. The advantage of nano-confining is that the guest framework material provides support for the magnesium nano-based material and prevents agglomeration during high-temperature reactions, thus ensuring that the overall hydrogen storage performance of the material does not degrade. The key to this method lies in the rational selection of suitable porous materials as the host material. Generally, porous silica and carbon materials (carbon nanotubes, graphene, porous carbon spheres, etc.) are expensive and do not possess catalytic properties themselves, only serving a structural support function. Among the host materials, the introduction of metal-organic frameworks (MOFs) is expected to introduce certain metal catalytic elements into the composite system, thereby achieving a dual improvement in thermodynamics and kinetics.

[0004] While MOFs (Metal-Oxide-Factory) materials possess advantages such as low cost and regular structure, their internal pore sizes are very small, only at the nanoscale. The nanoscale effect of these pores makes it difficult for magnesium-containing organic liquids to completely penetrate the internal pores of MOFs and achieve maximum wetting during the nano-confined wet impregnation process. Taking a heptane solution of dibutylmagnesium as an example, in practice, the liquid tends to concentrate around the guest phase, making it difficult to impregnate all the MOFs in bulk. This poses a significant challenge to the implementation of this method and the preparation of high-capacity magnesium-based nanomaterials for hydrogen storage.

[0005] Therefore, those skilled in the art urgently need to propose a simple, safe, low-cost method for the mass production of high-performance magnesium-based nanoconfined hydrogen storage composite materials to solve the above problems. Summary of the Invention

[0006] In view of this, in order to address the shortcomings of existing nanoconfined synthesis technologies for magnesium-based hydrogen storage systems, such as difficulties in wet impregnation, low loading rates, and high operational complexity, this invention independently synthesizes low-cost MOF guest materials. By using alkali metal sulfides to control the passage time and temperature, the pore size of the guest materials is improved and the impregnation rate is controlled, thereby improving the nanoconfined loading efficiency, increasing the loading amount and bulk phase distribution of the corresponding magnesium-based nanocomposites, and ultimately achieving the efficient preparation of high-performance nanohydrogen storage materials.

[0007] This invention synthesizes MOF framework materials with specific morphologies using an aqueous solvent method. Subsequently, alkali metal sulfides are used to modify the pore size of the guest material through time and temperature control. Then, a high-loading-rate magnesium-based nanocomposite is prepared by wet impregnation. The MOF modification technology and the introduction of catalytic elements achieve dual regulation of magnesium-based hydrogen storage nanomaterials in terms of thermodynamics and kinetics, respectively, providing an effective improvement and feasible solution for the industrial application of this method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a high-capacity magnesium-based composite material based on MOF structure modification includes the following steps:

[0010] (1) Preparation of M-MOF guest materials

[0011] (11) Add the metal ion source to ethanol water to dissolve it and form solution A; in this step, the specific morphology and structure of the product are controlled by adjusting the mixing ratio of ethanol and water, and the mass ratio of ethanol in the mixed solvent is between 10-90%.

[0012] (12) Dissolve the surfactant in water and stir magnetically at 300-1000 rpm for 0.5-2 hours to form solution B;

[0013] (13) Add the organic ligand to ethanol water, stir magnetically at 400-1200 rpm, add anhydrous KOH at the same time, adjust the pH to neutral, until the organic ligand is completely dissolved to form solution C;

[0014] (14) Add solution B dropwise slowly to solution A and stir magnetically until the reactants are completely mixed to form solution D. Add solution D dropwise to solution C under magnetic stirring. During this process, a milky white M-MOF product is generated. Stir magnetically during this process. Finally, after the reaction precipitation is complete, collect the product, wash the product with a mixture of ethanol and water, centrifuge 5-8 times, and vacuum dry to obtain the M-MOF guest material.

[0015] (2) Modification of pore structure in nano-confined M-MOF guest materials:

[0016] (21) Add the M-MOF guest material to anhydrous ethanol, heat and stir to disperse it completely, and obtain a dispersion.

[0017] (22) Dissolve K2S in 15 mL of water to form a solution, then add the solution dropwise to the dispersion, keep it at 348-368 K and perform structural modification and sulfidation etching for 10-120 min, then cool to room temperature, centrifuge the obtained product, wash with excess anhydrous ethanol and repeat centrifugation and washing 8 times, and vacuum dry at 363-383 K for 24-48 h. The obtained product is denoted as SM-MOF.

[0018] (3) Preparation of MgH2@SM-MOF composites by wet impregnation nanoconfining method:

[0019] (31) Weigh the SM-MOF guest material and place it in a container. Heat it at 413-433K and keep it under vacuum for 24-48h to remove impurities, residual moisture and gas from the internal pore structure of SM-MOF.

[0020] (32) The SM-MOF guest material under vacuum was transferred into a glove box along with a round-bottom flask. A heptane solution of dibutylmagnesium was injected into the flask and wet impregnated with stirring to obtain a mixture.

[0021] (33) The mixture was centrifuged to further increase the loading of dibutylmagnesium in the SM-MOF guest framework material, and then naturally dried in an Ar atmosphere until the heptane was completely evaporated and MgBu2 was completely crystallized to form a white solid. The resulting white solid was then transferred to a PCT device and hydrogen was introduced to carry out a hydrogenation reaction, finally obtaining the nano-confined MgH2@SM-MOF composite.

[0022] To avoid environmental pollution, all nano-confining steps of this invention are performed in an Ar atmosphere inside a glove box. The water and oxygen content inside the glove box is <1 ppm.

[0023] Furthermore, in step (1), the molar amount of the metal ion source and the mass ratio of the surfactant are 5 mmol: 0.02-0.05 g;

[0024] The molar ratio of the metal ion source to the organic ligand is 5:6.

[0025] Furthermore, the metal ion source is any one of the nitrate, sulfate, chloride, oxalate, bromide, phosphate, carbonate and acetate of the corresponding metal;

[0026] The metal is any one or a mixture of Ni, Fe, Co, Cu, Zn, Ag, La, Mn, Cr, Ti, Pt, Au, W, Cd, Pd, Mo, Ru, Rh, Nb, Zr, Y, Sc, V, Ce, Pr, Sm, Gd and Nd;

[0027] The surfactant is any one of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, hexadecylpyridine chloride, benzalkonium chloride, hexadecyltrimethylammonium chloride, dioctadecyldimethylammonium bromide, and hexadecyltrimethylammonium hydroxide;

[0028] The organic ligand is any one of terephthalic acid, pyromellitic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-bipyridine, 2-methylimidazolium, pyromellitic acid, porphyrin, sulfonic acid organic ligands (such as H2DSBDC), and phosphoric acid organic ligands (such as H4L).

[0029] Furthermore, in step (14), solution B is added dropwise at a rate of 2 ml / min.

[0030] The magnetic stirring speed is 500-1200 rpm, and the stirring time is 4-24 hours;

[0031] The volume ratio of ethanol to water in the ethanol-water mixture is 1:2.

[0032] The centrifugation is performed at a rate of 5000-8000 rpm for 5-8 centrifugations.

[0033] The vacuum drying temperature is 353-393K, and the vacuum drying time is 24-72h.

[0034] Furthermore, in step (2), the mass ratio of M-MOF to K2S is 1:0.02-0.08.

[0035] Furthermore, the heating and stirring method described in step (21) is to raise the temperature from room temperature to 358K at 10K / min and stir at 500rpm for 20min.

[0036] Furthermore, in step (3), the mass ratio of the SM-MOF guest material to the volume ratio of the heptane solution of dibutylmagnesium is 0.5 g: 11.5 mL;

[0037] The concentration of the heptane solution of dibutylmagnesium is 1M.

[0038] Furthermore, the stirring rate in step (32) is 500-1000 rpm for rapid stirring, and the wet impregnation time is 24-48 h.

[0039] Furthermore, in step (33), the centrifugation rate is 3000-8000 rpm and the centrifugation time is 1-8 h;

[0040] The hydrogenation reaction temperature is 453K, the hydrogen pressure is 3-5MPa H2, and the reaction time is 24-48h.

[0041] The beneficial effects of this invention are as follows:

[0042] Compared to pure MgH2 hydrogen storage materials, the MgH2@SM-MOF composite magnesium-based hydrogen storage material prepared by the nanoconfined method of this invention exhibits a significantly lower hydrogen absorption and desorption reaction temperature and greatly improved kinetics. Compared to traditional nanoconfined hydrogen storage material preparation processes, this invention enhances the comprehensive hydrogen storage performance of the composite through pore structure modification and the introduction of catalytic elements. It is highly operable, has a high effective loading rate, a short preparation cycle, and a high yield. The required raw materials are inexpensive and readily available, and the preparation process is low-cost and highly safe, making it suitable for industrial production and promotion. Attached Figure Description

[0043] Figure 1 This is a SEM image of the Zn-MOF guest precursor synthesized in Example 1 of the present invention;

[0044] Figure 2 The images show a TEM image of the Zn-MOF guest precursor synthesized in Example 1 of this invention and a high-resolution microscopic spectrum of the nano-MgH2 loaded thereon.

[0045] Figure 3 The Zn-MOF, S-Zn-MOF, and nano-confined materials prepared in Example 1 of this invention

[0046] XRD pattern of MgH2@S-Zn-MOF complex;

[0047] Figure 4 The automatic PCT hydrogen absorption and desorption curves at 613 K for MgH2@S-Zn-MOF prepared in Example 1 of this invention are shown.

[0048] Figure 5 The isothermal hydrogen absorption and desorption test results of the MgH2@S-Zn-MOF hydrogen storage material prepared in Example 1 of this invention at 593K after a single cycle of hydrogen absorption and desorption;

[0049] Figure 6 Dehydrogenation curves of the MgH2@S-Zn-MOF hydrogen storage material prepared in Example 1 of this invention at different test temperatures;

[0050] Figure 7 Fitting results of the dehydrogenation activation energy under the JMAK model for the MgH2@S-Zn-MOF hydrogen storage material prepared in Example 1 of this invention. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Example 1

[0053] A method for preparing a high-capacity magnesium-based composite material based on MOF(Zn) structure modification includes the following steps:

[0054] (1) Preparation of Zn-MOF guest materials

[0055] (11) Add 5 mmol Zn(NO3)2·6H2O (1.49 g) to 30 ml of ethanol water to dissolve and form solution A; in this step, the specific morphology and structure of the product are controlled by adjusting the mixing ratio of ethanol and water, and the mass ratio of ethanol in the mixed solvent is 50%.

[0056] (12) Dissolve 0.03g of CTAC (hexadecyltrimethylammonium chloride) surfactant in 20ml of water and stir magnetically at 800rpm for 1h to form solution B;

[0057] (13) Add 6 mmol of terephthalic acid (0.996 g) organic ligand to 150 ml of ethanol water, stir magnetically at 800 rpm, add anhydrous KOH at the same time, adjust the pH to 7, until the organic ligand is completely dissolved to form solution C.

[0058] (14) Add solution B dropwise to solution A at a rate of 2 ml / min and stir magnetically until the reactants are completely mixed to form solution D. Add solution D dropwise to solution C at a rate of 2 ml / min under magnetic stirring at 600 rpm. During this process, a milky white Zn-MOF product is generated. Stir magnetically for 8 hours. After the reaction precipitation is complete, collect the product, wash the product with a mixture of ethanol and water (ethanol to water volume ratio of 1:2), centrifuge at 6000 rpm 6 times, and dry under vacuum at 373 K for 48 hours to obtain Zn-MOF guest material.

[0059] (2) Pore structure modification of Zn-MOF guest materials:

[0060] (21) Add 1.0 g of Zn-MOF guest material to 100 mL of anhydrous ethanol, heat from room temperature to 358 K at 10 K / min, and stir at 500 rpm for 20 min to disperse it completely, and obtain a dispersion.

[0061] (22) Dissolve 0.04 g K2S in 15 mL of water to form a solution. Then add the solution dropwise to the dispersion and keep it at 358 K for 60 min for structural modification and sulfidation. Then cool it to room temperature, centrifuge the product, wash it with excess anhydrous ethanol and repeat the centrifugation and washing 8 times. Dry it under vacuum at 373 K for 36 h. The product is named S-Zn-MOF.

[0062] (3) Preparation of MgH2@S-Zn-MOF composites by wet impregnation nanoconfining method:

[0063] (31) Weigh 0.5g of S-Zn-MOF guest material and place it in a 100mL round-bottom flask connected by a T-connector. Heat at 423K and maintain vacuum for 36h to remove impurities, residual moisture and gas from the internal pore structure of S-Zn-MOF.

[0064] (32) The S-Zn-MOF guest material under vacuum was transferred into a glove box along with a round-bottom flask. 11.5 mL of dibutylmagnesium in heptane (MgBu2 concentration of 1 M) was injected into the flask and wet impregnated for 24 h with stirring at 600 rpm to obtain a mixture.

[0065] (33) The mixture was centrifuged at 8000 rpm for 4 h to further increase the loading of dibutylmagnesium in the S-Zn-MOF guest framework material. Then it was naturally dried in an Ar atmosphere until the heptane was completely evaporated and the MgBu2 crystallized completely to form a white solid. The resulting white solid was then transferred to a PCT device and hydrogen was introduced. The hydrogenation reaction was carried out at 453 K and a hydrogen pressure of 4 MPa H2 for 24 h to finally obtain the nano-confined MgH2@S-Zn-MOF composite.

[0066] Figure 1 The image shows a SEM image of the self-prepared Zn-MOF guest precursor. It can be seen that by adjusting the ratio of polar solvent (deionized water) and non-polar solvent (ethanol) and adding the surfactant CTAC (hexadecyltrimethylammonium chloride), the microstructure of the monomer Zn-MOF can be effectively controlled. In this example, a hexahedral guest material precursor was successfully obtained with a particle size controlled at 0.5 μm and uniform morphology, which is beneficial for subsequent hydrogen storage material loading operations.

[0067] Figure 2These are TEM images of the Zn-MOF guest precursor synthesized in this invention and its high-resolution microscopic spectra of the nano-MgH2 loaded with the precursor. (ac) represent the TEM morphology characterization of Zn-MOF pore modification based on the Kirkendall effect after 10, 60, and 120 min under K2S etching. It can be seen that etching at 358K for 10 min did not significantly alter the internal structure or surface of the solid structure. At 60 min, pore structure modification was observed, and a rough surface morphology appeared. At 120 min, the pore structure modification under the Kirkendall effect was complete, revealing a central control structure. The surface shell provides structural anti-collapse stability, while the internal pore modification and hollow structure are beneficial for subsequent nano-confined experiments. The microstructure of the MgH2@S-Zn-MOF composite prepared using this guest for nano-confined experiments is shown below. Figure 2 As shown in (d), the distribution of Mg material inside and around the guest material and the complete preservation of the basic external structure can be clearly observed, indicating that the pore structure modification is beneficial to its wet impregnation effect and nano-confined operation. In the high-resolution image of Figure (e), it can be clearly seen that magnesium hydride nanoclusters with a diameter of about 5-10 nm are discretely distributed in the hollow S-Zn-MOF guest material. In Figure (f), the (200) crystal plane of MgH2 is observed, further proving the successful formation of magnesium-based hydrogen storage material.

[0068] Figure 3 The XRD patterns of the synthesized Zn-MOF, the pore-modified S-Zn-MOF guest material, and the nano-confined MgH2@S-Zn-MOF composite are shown. The synthesized Zn-MOF material exhibits good crystallinity. After 120 min of sulfidation modification, the material transforms into an amorphous peak, with no other crystalline material formed, indicating that sulfidation significantly alters its crystallinity. Pore modification increases its pore size, which is beneficial for subsequent nano-confined operation and improved loading rate. The XRD pattern of the MgH2@S-Zn-MOF composite shows that the main phase is magnesium hydride, confirming its ideal loading rate. A small amount of MgZn2 is also present, mainly due to the reaction between magnesium loaded into the guest material and Zn in the Zn-MOF, forming this alloy. MgZn2, as a nanocatalyst, can further enhance the kinetic properties of the composite material.

[0069] Figure 4The auto-PCT curves at 613 K for the MgH2@S-Zn-MOF composite hydride prepared by nanoconfinment show that the material possesses excellent reversible hydrogen absorption and desorption properties. The hydrogen absorption plateau pressure is 0.7 MPa, and the flat plateau pressure indicates good reaction kinetics. The maximum hydrogen absorption capacity is 4.17 wt%. Calculations show that the loading rate of this type of nanoconfined composite magnesium-based hydrogen storage material is as high as 55%, indicating that structural modification effectively improved the pore size and promoted the loading efficiency of wet impregnation.

[0070] Figure 5 The curves show the single hydrogen absorption and desorption cycles at 573K. It can be seen that the hydrogen absorption capacity is 4.24wt%, and the dehydrogenation performance is excellent, reaching 3.8wt% within 10 minutes. The reversible hydrogen absorption and desorption performance is also greatly improved due to the nano-effect and the catalytic effect of MgZn2.

[0071] Figure 6 The images show the isothermal dehydrogenation curves of the MgH2@S-Zn-MOF composite hydride at 573, 548, and 523 K. It can be seen that at 573 K, it can achieve a maximum dehydrogenation capacity of 4 wt% within 3600 s.

[0072] Figure 7 Based on isothermal dehydrogenation curve data, the activation energy of the dehydrogenation reaction kinetics was calculated using the JMAK model. The fitting results show that the dehydrogenation activation energy is 117.1 kJ / mol, which is significantly lower than that of the pure magnesium hydride system (184 kJ / mol). This indicates that the nanoclusters prepared by the nanoconfined method have excellent thermodynamic performance, while the MgZn2 catalyst further enhances its comprehensive hydrogen storage performance.

[0073] Comparative Example 1

[0074] According to the scheme in CN119929740A, MOF-MgH2 composites are prepared by ball milling, and the final magnesium-based material particle size is maintained between 2-10 μm. Due to the nano-confinement effect, the present invention can obtain magnesium-based hydrogen storage materials with a particle size of about 5 nm, thus having a better size advantage.

[0075] Comparative Example 2

[0076] The composite magnesium-based hydrogen storage material prepared by ball milling according to the scheme in CN119368238A mainly uses MOF as a catalyst. The particle size of the material is between 3-5 μm, and its hydrogen desorption rate within 10 min is only 1.2 wt%. In contrast, the MgH2@S-Zn-MOF composite prepared by the nanoconfining method in this invention has an effective particle size of 5 nm and can achieve 3.8 wt% hydrogen desorption within 10 min at 573 K, demonstrating superior thermodynamic and kinetic performance. This is mainly because the MOF material plays a dual synergistic role as a nanoconfined guest and a catalyst in this case. Therefore, compared with the comparative patent, it has a better design concept and methodological advancement.

[0077] Comparative Example 3

[0078] The magnesium-based material composite was prepared using a confined space method according to the scheme in CN116618671A. However, the actual particle size of the magnesium-based hydrogen storage material was not provided. According to Comparative Example 3, its average particle size is 10 nm, which is lower than the average Mg nanoparticle size of this invention. The XRD pattern in Comparative Example 3 shows that the composite contains a large amount of Co-based material, which has a significant impact on the overall hydrogen storage capacity of the composite. In this invention, the magnesium-based material loading rate is high, and the catalyst content is more precisely controlled, demonstrating the method's advancement.

[0079] Comparative Example 4

[0080] According to existing technical document 1 (YNLiu, JXZou, XQZeng, et al., Study on hydrogen storage properties of Mg nanoparticles confined in carbon aerogels, J. Hydrogen Energy 38(2013)5302-5308.), porous carbon gel was used as the guest material for nanoconfinement. Characterization revealed that the nanoconfined magnesium-based material had a particle size of 19.3 nm, an effective hydrogen storage capacity of 1.71 wt%, and a corresponding effective loading rate (mass of magnesium-based material / total mass of the composite) of 22.5%. In contrast, the loaded magnesium-based hydrogen storage material in this invention has a particle size of 5 nm. Due to pore structure modification, its effective hydrogen storage capacity reaches 4.17 wt%, and the corresponding loading rate is effectively increased to 55%. Therefore, compared to traditional nanoconfinement methods, this invention, through the introduction of MOF materials and pore structure modification, effectively improves the loading efficiency of the nanoconfined system while achieving the introduction of MOF basic catalytic elements.

[0081] Comparative Example 5

[0082] Based on prior art document 2 (ZWMa, QYZhang, S. Panda, In situ catalyzed and nanoconfined magnesium hydride nanocrystals in a Ni-MOF scaffold for hydrogenstorage, Sustainable Energy Fuels, 4(2020)4694-4703.), a magnesium-based composite material was synthesized using MOF material as the host material in a nanoconfined environment. The highest hydrogen storage capacity was 2.7 wt%, corresponding to a loading rate of 35.5%. The results indicate that the highest hydrogen storage capacity and loading rate of the product prepared in this invention are superior to those in prior art document 2. In this invention, the dehydrogenation activation energy of the composite is effectively reduced to 117.1 kJ / mol due to the nano-effect and the synergistic catalysis of the catalyst, which is a significant improvement compared to the 144.7 kJ / mol of the nanoconfined composite in prior art document 2.

[0083] Analysis of the reasons and results: In terms of phase composition, Mg and Zn are synthesized to prepare Mg-Zn intermetallic compounds in this invention, while MgH2@CoS-NBs in prior art document 2 produces the MgS system, and Mg-Co does not produce intermetallic compounds.

[0084] In terms of loading efficiency of active material, the present invention effectively increases the loading of Mg material (corresponding to a comprehensive hydrogen storage capacity of 4.17 wt%) due to further structural modification. This is significantly higher than 3.5 wt% of MgH2@CoS-NBs and 2.7 wt% of MgH2@Ni-MOF, demonstrating its advanced hydrogen storage capacity after structural modification.

[0085] The results show that the MgH2@S-Zn-MOF composite system prepared in this invention finally achieved the nano-confined construction and uniform distribution of nano-sized magnesium-based materials under simple process conditions. By modifying the pore structure, the loading efficiency and catalytic efficiency were greatly improved, and the hydrogen storage capacity of the material under working conditions was effectively increased, creating the possibility for its industrial application.

[0086] The nanoscale Mg material in the composite prepared by the present invention enhances its thermodynamic properties, while the metal catalyst formed in situ inside the guest improves its kinetic properties. Ultimately, the material system achieves dual regulation of thermo / kinetic properties, and the guest material effectively inhibits the agglomeration and growth of nanomaterials during the reaction process, thus effectively maintaining its excellent hydrogen storage performance.

[0087] Example 2

[0088] The scheme is basically the same as that in Example 1, except that 5 mmol Zn(NO3)2·6H2O is replaced with 5 mmol Ni(NO3)2.

[0089] Example 3

[0090] The scheme is basically the same as that in Example 1, except that 5 mmol Zn(NO3)2·6H2O is replaced with 5 mmol Fe(SO4)2.

[0091] Example 4

[0092] The scheme is basically the same as that in Example 1, except that 5 mmol Zn(NO3)2·6H2O is replaced with 5 mmol Co(NO3)2.

[0093] Example 5

[0094] The scheme is basically the same as that in Example 1, except that 5 mmol Zn(NO3)2·6H2O is replaced with 5 mmol Cu(SO4)2.

[0095] Example 6

[0096] The scheme is basically the same as that in Example 1, except that 5 mmol Zn(NO3)2·6H2O is replaced with 5 mmol Zn(SO4)2.

[0097] Example 7

[0098] The scheme is basically the same as that in Example 1, except that 5 mmol Zn(NO3)2·6H2O is replaced with 5 mmol AgNO3.

[0099] Example 8

[0100] The scheme is basically the same as that in Example 1, except that 5 mmol Zn(NO3)2·6H2O is replaced with 5 mmol La(NO3)3.

[0101] Example 9

[0102] The scheme is basically the same as that in Example 1, except that 5 mmol Zn(NO3)2·6H2O is replaced with 5 mmol Mn(CH3COO)2.

[0103] Example 10

[0104] The scheme is basically the same as that in Example 1, except that 5 mmol Zn(NO3)2·6H2O is replaced with 5 mmol Cr(NO3)2.

[0105] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a high-capacity magnesium-based composite material based on MOF structure modification, characterized in that, Includes the following steps: (1) Preparation of M-MOF guest materials: (11) Add the metal ion source to ethanol water to dissolve it, forming solution A; (12) Dissolve the surfactant in water and stir magnetically to form solution B; (13) Add the organic ligand to ethanol water, stir magnetically, and add anhydrous KOH at the same time to adjust the pH to neutral until the organic ligand is completely dissolved to form solution C. (14) Add solution B dropwise slowly to solution A and stir magnetically until the reactants are completely mixed to form solution D. Add solution D dropwise to solution C under magnetic stirring. During this process, a milky white M-MOF product is generated. Stir magnetically during this process. Finally, after the reaction precipitation is complete, collect the product, wash the product with a mixture of ethanol and water, centrifuge, and vacuum dry to obtain the M-MOF guest material. (2) Modification of pore structure in M-MOF guest materials: (21) Add the M-MOF guest material to anhydrous ethanol, heat and stir to disperse it completely, and obtain a dispersion. (22) Dissolve K2S in 15 mL of water to form a solution, then add the solution dropwise to the dispersion, keep it at 348-368 K and perform structural modification and sulfidation etching for 10-120 min, then cool to room temperature, centrifuge the obtained product, wash with excess anhydrous ethanol and repeat centrifugation and washing 8 times, and vacuum dry at 363-383 K for 24-48 h. The obtained product is denoted as SM-MOF. (3) Preparation of MgH2@SM-MOF composites by wet impregnation nanoconfining method: (31) Weigh the SM-MOF guest material and place it in a container. Heat it at 413-433K and keep it under vacuum for 24-48h to remove impurities, residual moisture and gas from the internal pore structure of SM-MOF. (32) The SM-MOF guest material under vacuum was transferred into a glove box along with a round-bottom flask. A heptane solution of dibutylmagnesium was injected into the flask and wet impregnated with stirring to obtain a mixture. (33) The mixture was centrifuged and then naturally dried in an Ar atmosphere until the heptane was completely evaporated and the MgBu2 crystallized completely to form a white solid. The resulting white solid was then transferred to a PCT device and hydrogen was introduced to carry out a hydrogenation reaction, finally obtaining the nano-confined MgH2@SM-MOF composite.

2. The method for preparing a high-capacity magnesium-based composite material based on MOF structure modification according to claim 1, characterized in that, In step (1), the molar amount of the metal ion source and the mass ratio of the surfactant are 5 mmol: 0.02-0.05 g. The molar ratio of the metal ion source to the organic ligand is 5:

6.

3. The method for preparing a high-capacity magnesium-based composite material based on MOF structure modification according to claim 1 or 2, characterized in that, The metal ion source is any one of the nitrate, sulfate, chloride, oxalate, bromide, phosphate, carbonate and acetate of the corresponding metal; The metal is any one or a mixture of Ni, Fe, Co, Cu, Zn, Ag, La, Mn, Cr, Ti, Pt, Au, W, Cd, Pd, Mo, Ru, Rh, Nb, Zr, Y, Sc, V, Ce, Pr, Sm, Gd and Nd; The surfactant is any one of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, hexadecylpyridine chloride, benzalkonium chloride, hexadecyltrimethylammonium chloride, dioctadecyldimethylammonium bromide, and hexadecyltrimethylammonium hydroxide; The organic ligand is any one of terephthalic acid, pyromellitic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-bipyridine, 2-methylimidazolium, pyromellitic acid, porphyrin, sulfonic acid organic ligands, and phosphoric acid organic ligands.

4. The method for preparing a high-capacity magnesium-based composite material based on MOF structure modification according to claim 1, characterized in that, In step (14), solution B is added dropwise at a rate of 2 ml / min. The magnetic stirring speed is 500-1200 rpm, and the stirring time is 4-24 hours; The volume ratio of ethanol to water in the ethanol-water mixture is 1:

2. The centrifugation is performed at a rate of 5000-8000 rpm for 5-8 centrifugations. The vacuum drying temperature is 353-393K, and the vacuum drying time is 24-72h.

5. The method for preparing a high-capacity magnesium-based composite material based on MOF structure modification according to claim 1, characterized in that, In step (2), the mass ratio of M-MOF to K2S is 1:0.02-0.

08.

6. The method for preparing a high-capacity magnesium-based composite material based on MOF structure modification according to claim 1 or 5, characterized in that, The heating and stirring method described in step (21) is to raise the temperature from room temperature to 358K at 10K / min and stir at 500rpm for 20min.

7. The method for preparing a high-capacity magnesium-based composite material based on MOF structure modification according to claim 1, characterized in that, In step (3), the mass ratio of the SM-MOF guest material to the volume ratio of the dibutylmagnesium heptane solution is 0.5 g: 11.5 mL; The concentration of the heptane solution of dibutylmagnesium is 1M.

8. The method for preparing a high-capacity magnesium-based composite material based on MOF structure modification according to claim 1 or 7, characterized in that, The stirring rate in step (32) is 500-1000 rpm for rapid stirring, and the wet impregnation time is 24-48 h.

9. The method for preparing a high-capacity magnesium-based composite material based on MOF structure modification according to claim 1 or 7, characterized in that, In step (33), the centrifugation rate is 3000-8000 rpm and the centrifugation time is 1-8 h; The hydrogenation reaction temperature is 453K, the hydrogen pressure is 3-5MPa H2, and the reaction time is 24-48h.

10. A high-capacity magnesium-based composite material based on MOF structure modification, characterized in that, It is prepared by the method described in any one of claims 1-9.

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