A MOF@MWCNTs composite catalyst modified magnesium-based hydrogen storage composite material and a preparation method thereof

Abstract

This invention discloses a magnesium-based hydrogen storage composite material modified with MOF@MWCNTs composite catalyst and its preparation method, belonging to the field of solid-state hydrogen storage material technology. The MOF@MWCNTs composite catalyst-modified magnesium-based hydrogen storage composite material includes magnesium powder as the matrix material and a composite modified catalyst. The composite modified catalyst is selected from any one of Ni-MOF@MWCNTs, Co-MOF@MWCNTs, or Ni-Co-MOF@MWCNTs. The composite catalyst uses MWCNTs as a support, and MOF materials containing Ni2+ and / or Co2+ metal active sites are grown in situ on the support surface. The mass percentage of the composite modified catalyst in the composite material is 5 wt.%~15 wt.%, solving the problems of thermodynamic instability, high reaction energy barrier, easy agglomeration during cycling, and rapid decay of hydrogen storage capacity in existing magnesium-based hydrogen storage materials.

Description

Technical Field

[0001] This invention relates to the field of solid-state hydrogen storage materials technology, specifically to a magnesium-based hydrogen storage composite material modified by MOF@MWCNTs composite catalyst and its preparation method. Background Technology

[0002] Existing magnesium-based hydrogen storage materials still face several technical bottlenecks hindering their large-scale application. First, MgH2 exhibits excessive thermodynamic stability, with a hydrogen release enthalpy ∆H as high as 75 kJ / mol H2 and an entropy ∆S of 135 J·K⁻¹·mol⁻¹. This means that MgH2 requires temperatures above 280 °C at 0.1 MPa to release hydrogen. Second, the hydrogen absorption / desorption kinetics are slow, and the strong interaction between HH bonds and Mg-H bonds results in a hydrogen release energy barrier of 145.08 for MgH2. The low hydrogen peroxide concentration (kJ / mol) directly leads to a slow hydrogen absorption / desorption reaction rate. Furthermore, the low diffusion coefficient of H in the MgH2 matrix further contributes to the long reaction time and incomplete hydrogenation and dehydrogenation. Third, poor surface passivation and cycling stability are significant issues. Magnesium's reactive chemical properties easily lead to the formation of a dense passivation layer on the particle surface during material preparation and repeated hydrogen absorption / desorption cycles. This passivation layer severely hinders the dissociation and recombination of H2, further deteriorating the material's hydrogen absorption / desorption kinetics. Simultaneously, magnesium-based particles are prone to severe agglomeration during hydrogen absorption / desorption cycles, resulting in rapid decay of hydrogen storage capacity and a significantly shortened cycle life. These core bottlenecks in thermodynamics, kinetics, and cycling stability severely restrict the large-scale and industrial application of magnesium-based hydrogen storage materials.

[0003] To address the thermodynamic and kinetic challenges of magnesium-based hydrogen storage materials, researchers have developed various modification strategies, including alloying, nano-sizing, and catalyst doping. Among these, synergistic modification through alloying and catalyst doping is currently a major research direction due to its significant modification effects and strong process adaptability. For example, Mg-Ni binary alloys can, to some extent, regulate the thermodynamic properties of magnesium-based materials and lower the reaction energy barrier. However, single alloying modification has limited effectiveness in improving hydrogen absorption / desorption kinetics and cycle stability, making it difficult to meet practical application requirements. In the field of catalyst modification, metal-organic framework (MOF) materials are widely used for the catalytic modification of magnesium-based hydrogen storage materials due to their ultra-high specific surface area, regular and tunable pore structure, and abundant metal active sites. For example, Chinese patent CN119929740A discloses a copper-based MOF-derived carbon-MgH2 composite solid hydrogen storage material and its preparation method. The copper-based MOF and MgH2 are mixed in a hydrogen atmosphere by high-energy ball milling to prepare a copper-based MOF-derived carbon-MgH2 composite solid hydrogen storage material. Although the metal active sites in the above MOF material can effectively reduce the reaction energy barrier between Mg and H2, and its pore structure can inhibit the agglomeration of magnesium-based particles to a certain extent, single MOF materials have the disadvantage of poor structural stability. During ball milling preparation and repeated hydrogen adsorption and desorption cycles, the framework is prone to collapse, resulting in the loss of active sites and rapid decay of catalytic performance. It is impossible to simultaneously achieve high catalytic activity and long-term cycle stability. In summary, among the existing magnesium-based hydrogen storage modification technologies, no composite catalytic system has yet been developed that can simultaneously achieve high catalytic activity, excellent structural stability, and cycle life. This makes it impossible to simultaneously improve the kinetic performance and cycle stability of magnesium-based hydrogen storage materials, which has become a key technical challenge restricting the industrialization of magnesium-based hydrogen storage materials. Summary of the Invention

[0004] To alleviate or partially alleviate the above-mentioned technical problems, the solution of the present invention is as follows: A magnesium-based hydrogen storage composite material modified with MOF@MWCNTs composite catalyst, comprising magnesium powder as the matrix material and a composite modified catalyst; The composite modified catalyst is selected from any one of Ni-MOF@MWCNTs, Co-MOF@MWCNTs or Ni-Co-MOF@MWCNTs. The composite catalyst uses MWCNTs as a support, and MOF materials containing Ni2+ and / or Co2+ metal active sites are grown in situ on the surface of the support. The mass percentage of the composite modified catalyst in the composite material is 5 wt.%~15 wt.%.

[0005] To address the performance bottlenecks and shortcomings of existing magnesium-based hydrogen storage materials and modification technologies, this invention constructs a 'MOF@MWCNTs' two-component synergistic composite catalytic system: using structurally stable MWCNTs as a carrier, MOF materials containing Ni2+ and Co2+ active sites are grown in situ. This retains the advantages of MOF materials, such as ultra-high specific surface area and abundant metal active sites, while solving the problems of framework collapse and reduced active sites in single MOFs. Furthermore, it leverages the excellent structural stability and hydrogen transport capacity of MWCNTs to provide a rapid diffusion channel for hydrogen atoms, while also inhibiting the aggregation and surface passivation of magnesium particles during cycling. Ultimately, this achieves a balance between 'catalytic activity, structural stability, and cycle life,' simultaneously and significantly improving the hydrogen absorption / desorption kinetics and cycle stability of magnesium-based hydrogen storage materials.

[0006] Preferably, the mass percentage of the composite modified catalyst is 10 wt.%.

[0007] When the addition amount is less than 5 wt.%, there are insufficient catalytic active sites and the modification effect is limited; when the addition amount is more than 15 wt.%, the overall hydrogen storage capacity of the composite material will be reduced. 10 wt.% is the optimal ratio, which can achieve the optimal balance between catalytic activity and hydrogen storage capacity.

[0008] This solution also provides a method for preparing the above-mentioned MOF@MWCNTs composite catalyst modified magnesium-based hydrogen storage composite material, including the following steps; Step S1: Weigh out a metal nitrate and dissolve it in deionized water to obtain a metal salt solution; dissolve terephthalic acid in N,N-dimethylformamide to obtain an organic ligand solution; the metal nitrate is selected from at least one of nickel nitrate hexahydrate or cobalt nitrate hexahydrate; Step S2: Under stirring conditions, the organic ligand solution is added dropwise to the metal salt solution. After the addition is complete, the mixture is stirred continuously until homogeneous to obtain a mixed solution. Then, MWCNTs are added to the mixed solution, stirred first and then sonicated to make the MWCNTs uniformly dispersed in the mixed solution to obtain a uniformly dispersed MWCNTs mixture. Step S3: Add the above uniformly dispersed MWCNTs mixture into a hydrothermal reactor and carry out a solvothermal reaction under heating conditions; Step S4: After the reaction is complete, the product is naturally cooled to room temperature and the solid product is collected. Unreacted raw materials and reaction byproducts are removed by washing with DMF and anhydrous ethanol, respectively. The washed product is then vacuum dried to obtain the composite modified catalyst. Step S5: Under the protection of argon atmosphere, magnesium powder is mixed with the composite modified catalyst prepared above to obtain mixed powder; the mixed powder is ball-milled under the protection of argon atmosphere; after ball milling, the ball-milled product is taken out under the protection of argon atmosphere, thus obtaining the MOF@MWCNTs composite catalyst modified magnesium-based hydrogen storage composite material.

[0009] In step S1 above, when preparing Ni-MOF@MWCNTs, nickel nitrate hexahydrate is used as the metal nitrate; when preparing Co-MOF@MWCNTs, cobalt nitrate hexahydrate is used as the metal nitrate; and when preparing Ni-Co-MOF@MWCNTs, a mixture of nickel nitrate hexahydrate and cobalt nitrate hexahydrate is used as the metal nitrate. Mg+Ni-MOF@MWCNTs, Mg+Co-MOF@MWCNTs, and Mg+Ni-Co-MOF@MWCNTs composite materials are obtained for different catalysts.

[0010] Preferably, in step S1, the molar volume ratio of metal nitrate to deionized water is 10 mmol: 7 ml; the molar volume ratio of terephthalic acid to N,N-dimethylformamide is 10 mmol: 7 ml; and the volume ratio of metal salt solution to organic ligand solution is 1:1.

[0011] Preferably, in step S2, the mass-to-volume ratio of the amount of MWCNTs added to the mixed solution is 0.0225 g: 70 ml.

[0012] Preferably, in step S3, the heating temperature is 140℃~180℃, and the solvothermal reaction time is 8-16 h.

[0013] Within this parameter range, the target MOF@MWCNTs composite catalyst can be successfully synthesized. Only the crystallinity and sheet size of the MOF material are slightly different, which does not affect the core catalytic performance.

[0014] Preferably, in step S5, the mass ratio of the composite modified catalyst to the magnesium powder is (1:19) to (3:17).

[0015] Preferably, in step S5, the mass ratio of the composite modified catalyst to the magnesium powder is 1:9.

[0016] Preferably, in step S6, the ball-to-material ratio is (15:1) to (30:1), the ball milling speed is 600 rpm to 1000 rpm, and the total ball milling time is 4 h to 8 h.

[0017] Within this parameter range, uniform dispersion of the catalyst in the magnesium matrix can be achieved, enabling alloying and composite modification, and adapting to the production needs of different industrial ball milling equipment.

[0018] Preferably, in step S6, the ball milling adopts an intermittent operation program, with a 15-minute pause for cooling after every 30 minutes of ball milling.

[0019] The technical solution of this invention has the following beneficial technical effects: The proposed method significantly improves the hydrogen absorption / desorption kinetics of the composite material. Experimental data show that under conditions of 350 °C and 3 MPa hydrogen pressure, the Mg+Co-MOF@MWCNTs composite material prepared in this invention can absorb 6.28 wt.% hydrogen within 5 min and reach 6.6 wt.% saturated hydrogen absorption within 50 min; while the pure magnesium sample only absorbs 3.20 wt.% hydrogen within 5 min and reaches 3.56 wt.% saturated hydrogen absorption. The hydrogen absorption rate and saturated hydrogen storage capacity of the material in this invention are both more than doubled, and the improvement in kinetic performance far exceeds that of single modification methods.

[0020] The preparation process of this solution is simple and controllable, and is suitable for large-scale industrial production. The solvothermal method and high-energy ball milling method used in this invention are both mature industrial preparation processes in the field of materials. They do not require complex production equipment and harsh production environments. The process parameters are stable and controllable, the raw materials are widely available and inexpensive, and it is easy to achieve large-scale production.

[0021] The dual-component synergistic modification has significant advantages. The abundant Ni2+ and Co2+ active sites in MOF materials can effectively reduce the reaction energy barrier between Mg and H2 and accelerate the dissociation of hydrogen molecules. MWCNTs not only provide support for MOF, but also provide a fast diffusion channel for hydrogen atoms. The synergistic effect of the two achieves the optimization of kinetic performance, and the modification effect is far superior to that of single MOF materials or single MWCNTs modification.

[0022] With good environmental compatibility and no environmental risks, the preparation process of this invention does not use toxic and harmful heavy metal raw materials or highly polluting organic solvents, and no toxic and harmful by-products are generated. It conforms to the green and low-carbon development concept of the hydrogen energy industry and has no environmental or application safety risks. Attached Figure Description

[0023] Figure 1 These are the XRD patterns of Ni-MOF@MWCNTs, Co-MOF@MWCNTs, and Ni-Co-MOF@MWCNTs; Figure 2 These are the Fourier transform infrared spectra of PTA, Ni-MOF@MWCNTs, Co-MOF@MWCNTs and Ni-Co-MOF@MWCNTs; Figure 3 This is a SEM microstructure image of the Ni-Co-MOF@MWCNTS catalyst; Figure 4 This is the XRD pattern of the composite material after high-energy ball milling; Figure 5 This is the hydrogen absorption kinetics curve. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] Existing magnesium-based hydrogen storage materials suffer from several key problems, including overly stable thermodynamic properties requiring high hydrogen desorption temperatures; slow hydrogen absorption / desorption kinetics with high reaction barriers, low hydrogen diffusion coefficients, slow reaction rates, and incomplete hydrogenation / dehydrogenation; and susceptibility to surface passivation and particle agglomeration during cycling, leading to rapid decay of hydrogen storage capacity and short cycle life, thus failing to meet the requirements for large-scale applications. While single MOF catalytic materials are rich in active sites, they are prone to framework collapse and loss of active sites during ball milling and hydrogen absorption / desorption cycling, resulting in rapid decline in catalytic performance. Although MWCNTs exhibit excellent structural stability and can suppress particle agglomeration, their inherent catalytic activity is limited, and individual modification is ineffective. Current technologies cannot construct composite catalytic systems that simultaneously achieve high catalytic activity, excellent structural stability, and long cycle life, and cannot simultaneously and significantly improve the hydrogen absorption / desorption kinetics and cycle stability of magnesium-based hydrogen storage materials, severely hindering their industrialization.

[0026] To address the core issues of existing technologies, this invention proposes a MOF@MWCNTs composite catalyst-modified magnesium-based hydrogen storage composite material and its preparation method, through a core process route of "design and preparation of a carrier-supported composite catalyst - high-energy ball milling composite of catalyst and magnesium matrix". The MOF@MWCNTs composite catalyst modifies the magnesium-based hydrogen storage composite material, which includes magnesium powder as the matrix material and the composite modified catalyst. The composite modified catalyst is selected from any one of Ni-MOF@MWCNTs, Co-MOF@MWCNTs or Ni-Co-MOF@MWCNTs. The composite catalyst uses MWCNTs as a support, and MOF materials containing Ni2+ and / or Co2+ metal active sites are grown in situ on the surface of the support. The mass percentage of the composite modified catalyst in the composite material is 5 wt.% to 15 wt.%; for example, in the embodiment shown, the mass of the composite modified catalyst added is 10 wt.%, 5 wt.%, and 15 wt.% of the mass of the magnesium powder matrix material.

[0027] The specific steps for preparing the above-mentioned MOF@MWCNTs composite catalyst modified magnesium-based hydrogen storage composite material are as follows: I. Preparation of Ni / Co-MOF@MWCNTs composite catalysts (solvothermal method) This step can prepare three optional composite catalysts: Ni-MOF@MWCNTs, Co-MOF@MWCNTs, and Ni-Co-MOF@MWCNTs. The preparation process for all three is the same, with the only difference being the metal source. The detailed steps are as follows: Preparation of raw material solutions: Weigh 0.05 mol of metal nitrate and dissolve it in 35 mL of deionized water to obtain a metal salt solution; separately weigh 0.05 mol of terephthalic acid (PTA) and dissolve it in 35 mL of N,N-dimethylformamide (DMF) to obtain an organic ligand solution. In this process, nickel nitrate hexahydrate is used to prepare Ni-MOF@MWCNTs, cobalt nitrate hexahydrate is used to prepare Co-MOF@MWCNTs, and a mixture of nickel nitrate hexahydrate and cobalt nitrate hexahydrate is used to prepare Ni-Co-MOF@MWCNTs. The molar ratio of Ni2+ to Co2+ in the Ni-Co-MOF@MWCNTs composite catalyst is (1:3) to (3:1). For example, in the embodiment shown, the molar ratio of Ni2+ to Co2+ is 1:1. In addition, the molar ratio of Ni2+ to Co2+ can also be 1:3 or 3:1, etc. By adjusting the bimetallic ratio, the number and distribution of active sites of MOF material can be controlled to achieve excellent catalytic modification effect.

[0028] Mixing and Dispersion: Under magnetic stirring, the organic ligand solution was added dropwise to the metal salt solution. After the addition was completed, the magnetic stirring was continued for 20 min to ensure that the two components were fully mixed and homogeneous. Then, 0.0225 g of MWCNTs was added to the mixed solution, stirred for 10 min, and then sonicated for 20 min to ensure that the MWCNTs were uniformly dispersed in the system without obvious agglomeration.

[0029] Solvothermal reaction: The above uniformly dispersed mixture was transferred to a 100 mL hydrothermal reactor with a polytetrafluoroethylene liner, sealed, and placed in a forced-air drying oven for a solvothermal reaction at a constant temperature of 140℃~180℃ for 8 h~16 h.

[0030] Product post-processing: After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The solid product was collected and washed three times each with DMF and anhydrous ethanol to thoroughly remove unreacted raw materials and reaction byproducts. The washed product was placed in a vacuum drying oven and dried under vacuum at 60 °C for 12 h to obtain the target Ni / Co-MOF@MWCNTs composite modified catalyst.

[0031] II. Preparation of magnesium-based hydrogen storage composite materials (high-energy ball milling method) Inert atmosphere mixing: In a glove box protected by argon atmosphere, the composite modified catalyst prepared above is uniformly mixed with metallic magnesium powder to obtain a mixed powder. The mass ratio of the composite modified catalyst to magnesium powder can be adjusted between (1:19) and (3:17), wherein the amount of composite modified catalyst added is 5 wt.% to 15 wt.% of the total mass of magnesium powder and catalyst. For example, in the illustrated embodiment, when the mass ratio of the composite modified catalyst to magnesium powder is 10:90, the amount of composite modified catalyst added is 5 wt.% of the total mass of magnesium powder and catalyst; when the mass ratio of the composite modified catalyst to magnesium powder is 1:19, the amount of composite modified catalyst added is 5 wt.% of the total mass of magnesium powder and catalyst; when the mass ratio of the composite modified catalyst to magnesium powder is 3:17, the amount of composite modified catalyst added is 15 wt.% of the total mass of magnesium powder and catalyst.

[0032] Intermittent high-energy ball milling: The mixed powder is placed in a ball milling jar, sealed, and then subjected to high-energy ball milling under argon atmosphere protection. The core process parameters are: ball-to-material ratio 15:1~30:1, ball milling speed 600 rpm~1000 rpm, and total ball milling time 4 h~8 h.

[0033] Product collection: After ball milling, the ball milling product is taken out under the protection of argon atmosphere, thus obtaining the magnesium-based hydrogen storage composite material modified by the MOF@MWCNTs composite catalyst of the present invention. Mg+Ni-MOF@MWCNTs, Mg+Co-MOF@MWCNTs, and Mg+Ni-Co-MOF@MWCNTs composite materials are obtained for different catalysts.

[0034] III. Verification and Activation of Hydrogen Storage Performance of Materials Sample activation: The samples were activated using a Sieverts hydrogen storage performance testing device. Activation conditions were: activation temperature 300℃~400℃, activation hydrogen pressure set to 3 MPa~4 MPa. The samples underwent 2 to 5 hydrogen absorption / desorption cycles. Activation was complete when the sample's hydrogen absorption reached more than 90% of the theoretical value. By adjusting the activation process, the material can be rapidly activated under different conditions to achieve a stable hydrogen storage performance state.

[0035] Performance testing: After activation, the hydrogen absorption kinetics of the samples were tested at 350 ℃, 325 ℃, 300 ℃, and 275 ℃ under a hydrogen pressure of 3.0 MPa. The hydrogen desorption kinetics of the samples were tested at 350 ℃, 325 ℃, 300 ℃, and 275 ℃ under a hydrogen pressure of 0.01 MPa.

[0036] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0037] Example 1: 0.05 mol of nickel nitrate hexahydrate (Ni(NO3)2×6H2O) was dissolved in 35 mL of deionized water, and 0.05 mol of terephthalic acid (PTA) was dissolved in 35 mL of N,N-dimethylformamide (DMF). Under magnetic stirring, the PTA solution was added dropwise to the Ni(NO3)2×6H2O aqueous solution. After the addition was complete, magnetic stirring was continued for 20 min to ensure that the two components were thoroughly mixed. Then, 0.0225 g of multi-walled carbon nanotubes (MWCNTs) were added to the above mixed solution. The mixture was stirred for 10 min and then sonicated for 20 min to ensure that the MWCNTs were uniformly dispersed in the system. The resulting mixture was transferred to a 100 mL hydrothermal reactor with a polytetrafluoroethylene liner, sealed, and placed in a drying oven for solvothermal reaction at 160 °C for 12 h. After the reaction was completed and the mixture was allowed to cool naturally to room temperature, the product was collected and washed three times with DMF and anhydrous ethanol to remove unreacted raw materials and byproducts. Finally, the washed product was placed in a vacuum drying oven and dried under vacuum at 60 °C for 12 h to obtain the Ni-MOF@MWCNTs catalyst. Under an argon atmosphere, Mg powder and Ni-MOF@MWCNTs catalyst (10 wt.%) were uniformly mixed at a mass ratio of 9:1 and placed in a ball mill jar. High-energy ball milling was performed under experimental conditions of a ball-to-material ratio of 20:1, a rotation speed of 800 rpm, and a milling time of 6 h. Three types of grinding balls with diameters of 5 mm, 8 mm, and 10 mm were used. To reduce the temperature rise during ball milling, an intermittent operation program was adopted, specifically pausing for cooling for 15 minutes after every 30 minutes of milling. The final composite material Mg+Ni-MOF@MWCNTs was obtained.

[0038] Example 2: 0.05 mol of cobalt nitrate hexahydrate (Co(NO3)2×6H2O) was dissolved in 35 mL of deionized water, and 0.05 mol of terephthalic acid (PTA) was dissolved in 35 mL of N,N-dimethylformamide (DMF). Under magnetic stirring, the PTA solution was added dropwise to the Co(NO3)2×6H2O aqueous solution. After the addition was complete, magnetic stirring was continued for 20 min to ensure that the two components were thoroughly mixed. Then, 0.0225 g of multi-walled carbon nanotubes (MWCNTs) were added to the above mixed solution. The mixture was stirred for 10 min and then sonicated for 20 min to ensure that the MWCNTs were uniformly dispersed in the system. The resulting mixture was transferred to a 100 mL hydrothermal reactor with a polytetrafluoroethylene liner, sealed, and placed in a drying oven for solvothermal reaction at 140 °C for 16 h. After the reaction was completed and the mixture was allowed to cool naturally to room temperature, the product was collected and washed three times with DMF and anhydrous ethanol to remove unreacted raw materials and byproducts. Finally, the washed product was placed in a vacuum drying oven and dried under vacuum at 60 °C for 12 h to obtain the Co-MOF@MWCNTs catalyst. Under an argon atmosphere, Mg powder and Co-MOF@MWCNTs catalyst (5 wt.%) were uniformly mixed at a mass ratio of 19:1 and placed in a ball mill jar. High-energy ball milling was performed under experimental conditions of a ball-to-material ratio of 15:1, a rotation speed of 1000 rpm, and a milling time of 4 h. Three types of grinding balls with diameters of 5 mm, 8 mm, and 10 mm were used. To reduce the temperature rise during ball milling, an intermittent operation program was adopted, specifically pausing for cooling for 15 minutes after every 30 minutes of milling. The final composite material Mg+Co-MOF@MWCNTs was obtained.

[0039] Example 3: 0.025 mol of nickel nitrate hexahydrate (Ni(NO3)2×6H2O) and 0.025 mol of cobalt nitrate hexahydrate (Co(NO3)2×6H2O) were weighed and dissolved in 35 mL of deionized water. Separately, 0.05 mol of terephthalic acid (PTA) was weighed and dissolved in 35 mL of N,N-dimethylformamide (DMF). Under magnetic stirring, the PTA solution was added dropwise to the Co(NO3)2×6H2O aqueous solution. After the addition was complete, magnetic stirring was continued for 20 min to ensure that the two components were thoroughly mixed. Then, 0.0225 g of multi-walled carbon nanotubes (MWCNTs) were added to the above mixed solution. The mixture was stirred for 10 min and then sonicated for 20 min to ensure that the MWCNTs were uniformly dispersed in the system. The resulting mixture was transferred to a 100 mL hydrothermal reactor with a polytetrafluoroethylene liner, sealed, and placed in a forced-air drying oven for a solvothermal reaction at 180 °C for 8 h. After the reaction was completed and the mixture was allowed to cool naturally to room temperature, the product was collected and washed three times with DMF and anhydrous ethanol to remove unreacted raw materials and byproducts. Finally, the washed product was placed in a vacuum drying oven and dried under vacuum at 60 °C for 12 h to obtain the Ni-Co-MOF@MWCNTs catalyst. Under an argon atmosphere, Mg powder and Ni-Co-MOF@MWCNTs catalyst (15 wt.%) were uniformly mixed at a mass ratio of 17:3 and placed in a ball mill jar. High-energy ball milling was performed under experimental conditions of a ball-to-material ratio of 30:1, a rotation speed of 600 rpm, and a milling time of 8 h. Three types of milling balls with diameters of 5 mm, 8 mm, and 10 mm were used. To reduce the temperature rise during ball milling, an intermittent operation program was adopted, specifically pausing for cooling for 15 minutes after every 30 minutes of milling. The final composite material Mg+Ni-Co-MOF@MWCNTs was obtained.

[0040] Example 4: X-ray diffraction (XRD) was performed on Ni-MOF@MWCNTs, Co-MOF@MWCNTs, and Ni-Co-MOF@MWCNTs to study the phase composition of the synthesized catalysts. Fourier transform infrared spectroscopy (FT-IR) was performed on Ni-MOF@MWCNTs, Co-MOF@MWCNTs, Ni-Co-MOF@MWCNTs, and PTA to study the changes in chemical bonds in the target catalysts. Scanning electron microscopy (SEM) was performed on Ni-Co-MOF@MWCNTs to observe the microstructure of the prepared catalysts. X-ray diffraction was performed on the composite material after high-energy ball milling to study the phase composition and crystal structure of the composite material after high-energy ball milling.

[0041] The hydrogen storage performance of the experimental samples was tested using a Sieverts-type device. First, the samples were activated three times under experimental conditions of 350 °C and 3.5 MPa hydrogen pressure. Activation was completed when the hydrogen absorption of the experimental samples reached more than 90% of the theoretical value.

[0042] Next, hydrogen absorption / desorption kinetics tests were performed on the samples. At a hydrogen pressure of 3.0 MPa, the hydrogen absorption kinetics were tested at 350 °C, 325 °C, 300 °C, and 275 °C. At a hydrogen pressure of 0.01 MPa, the hydrogen desorption kinetics were tested at the same temperatures.

[0043] Figure 1 of (a), Figure 1 (b) and Figure 1 (c) shows the XRD patterns of Ni-MOF@MWCNTs, Co-MOF@MWCNTs, and Ni-Co-MOF@MWCNTs, respectively. Each sample exhibits typical characteristic diffraction peaks of MOF materials in the low-angle range (2q = 5-20°). Furthermore, the XRD peak positions of the synthesized materials highly match the peak positions of the XRD patterns simulated based on single-crystal structure data of Ni-MOF (CCDC: 638866) and Co-MOF (CCDC: 905134), indicating that the target catalyst was successfully prepared.

[0044] Figure 2 The Fourier transform infrared (FTIR) spectra of PTA, Ni-MOF@MWCNTs, Co-MOF@MWCNTs, and Ni-Co-MOF@MWCNTs are shown. The characteristic absorption peak of PTA at 1674.6 cm⁻¹ belongs to the carbonyl stretching vibration. At this peak position, the conjugation effect between the benzene ring and the carboxyl group weakens the carbonyl bond order, resulting in a lower carbonyl stretching vibration frequency and a redshift of the absorption wavenumber. In the FTIR spectra of Ni-MOF@MWCNTs, Co-MOF@MWCNTs, and Ni-Co-MOF@MWCNTs, the original single carbonyl characteristic peak of PTA (1674.6 cm⁻¹) is split into two independent absorption peaks (1579.6 cm⁻¹ and 1502.2 cm⁻¹). This phenomenon indicates that the carbonyl group has coordinated with Ni²⁺ or Co²⁺, further confirming the successful synthesis of the target catalysts.

[0045] Figure 3 SEM microstructure of the catalyst Ni-Co-MOF@MWCNTS, from Figure 3The catalyst morphology is clearly observed to be an irregular flake-like structure, approximately 100 nm thick, with relatively uniform size and no obvious agglomeration. During high-energy ball milling, these nanosheets can be uniformly dispersed on the surface of Mg particles, providing numerous diffusion channels for the dissociation of H2 into H and the diffusion transport of H, while also hindering particle growth. Therefore, nanoscale catalysts can optimize the hydrogen absorption / desorption kinetics of materials.

[0046] Figure 4 The XRD patterns of the composite materials Mg+Ni-MOF@MWCNTs, Mg+Co-MOF@MWCNTs and Mg+Ni-Co-MOF@MWCNTs after high-energy ball milling are shown. It can be observed that the Mg phase is the main diffraction peak in the composite material at 2q=32.13°, 34.38°, 36.63°, 47.86°, with corresponding crystal plane indices of (100), (002), (101), and (102). No diffraction peak of MgO was found. Figure 4 (b) is Figure 4 (a) The enlarged view of the red box shows that after ball milling for 6 h, diffraction peaks of Ni-MOF@MWCNTs were found in Mg+Ni-MOF@MWCNTs, diffraction peaks of Co-MOF@MWCNTs were found in Mg+Co-MOF@MWCNTs, and diffraction peaks of Ni-MOF@MWCNTs were found in Mg+Ni-Co-MOF@MWCNTs. The results indicate that the catalyst was successfully introduced into Mg powder by high-energy ball milling, confirming that the composite materials Mg+Ni-MOF@MWCNTs, Mg+Co-MOF@MWCNTs and Mg+Ni-Co-MOF@MWCNTs were successfully prepared.

[0047] Figure 5The hydrogen absorption kinetics curves for Mg, Mg+Ni-MOF@MWCNTs, Mg+Co-MOF@MWCNTs, and Mg+Ni-Co-MOF@MWCNTs under experimental conditions of 350 ℃ and 3 MPa hydrogen pressure are shown. It can be observed that Mg absorbs only 3.20 wt.% hydrogen within 5 min, reaching saturation at 3.56 wt.% after 50 min; Mg+Ni-MOF@MWCNTs absorbs 5.59 wt.% hydrogen within 5 min, reaching saturation at 5.81 wt.% after 50 min; Mg+Co-MOF@MWCNTs absorbs 6.28 wt.% hydrogen within 5 min, reaching saturation at 6.6 wt.% after 50 min; and Mg+Ni-Co-MOF@MWCNTs absorbs 5.66 wt.% hydrogen within 5 min, reaching saturation at 5.99 wt.% after 50 min. The results show that the experimental samples doped with Co-MOF@MWCNTs exhibit superior hydrogen absorption performance compared to samples doped with other catalysts. This is because the catalyst provides a large number of active sites, accelerates the dissociation of H2 into H atoms, and provides numerous diffusion channels, thereby accelerating the hydrogen absorption kinetics of the experimental samples.

[0048] The magnesium-based hydrogen storage composite material prepared by this invention can be widely used in the storage and transportation links of the entire hydrogen energy industry chain. The core compatible products and application scenarios include: stationary hydrogen energy storage power stations, hydrogen fuel cell vehicle on-board hydrogen storage systems, distributed hydrogen energy supply systems, industrial by-product hydrogen recovery and long-distance storage and transportation equipment, portable hydrogen emergency power supplies, and hydrogen storage units for marine hydrogen power systems. It is especially suitable for large-scale commercial hydrogen energy application scenarios with high requirements for hydrogen storage density, hydrogen absorption and desorption rate, cycle life, operational safety and cost control.

[0049] To better illustrate the present invention, numerous specific details have been provided in the detailed embodiments described above. Those skilled in the art should understand that the present invention can be practiced even without certain specific details. In some instances, methods, means, components, and circuits well known to those skilled in the art have not been described in detail in order to highlight the main points of the present invention.

[0050] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A magnesium-based hydrogen storage composite material modified with MOF@MWCNTs composite catalyst, characterized in that, This includes the matrix material magnesium powder and composite modified catalysts; The composite modified catalyst is selected from any one of Ni-MOF@MWCNTs, Co-MOF@MWCNTs, or Ni-Co-MOF@MWCNTs. The composite catalyst uses MWCNTs as a support, and Ni-containing compounds are grown in situ on the surface of the support. 2+ and / or Co 2+ MOF materials with metal active sites; The mass percentage of the composite modified catalyst in the composite material is 5 wt.%~15 wt.%.

2. The MOF@MWCNTs composite catalyst modified magnesium-based hydrogen storage composite material according to claim 1, characterized in that, The mass percentage of the composite modified catalyst is 10 wt.%.

3. The preparation method of a magnesium-based hydrogen storage composite material modified by MOF@MWCNTs composite catalyst as described in any one of claims 1-2, characterized in that, Includes the following steps; Step S1: Weigh out a metal nitrate and dissolve it in deionized water to obtain a metal salt solution; dissolve terephthalic acid in N,N-dimethylformamide to obtain an organic ligand solution; the metal nitrate is selected from at least one of nickel nitrate hexahydrate or cobalt nitrate hexahydrate; Step S2: Under stirring conditions, the organic ligand solution is added dropwise to the metal salt solution. After the addition is complete, the mixture is stirred continuously until homogeneous to obtain a mixed solution. MWCNTs were then added to the mixed solution, stirred and then sonicated to ensure that the MWCNTs were uniformly dispersed in the mixed solution, resulting in a uniformly dispersed MWCNTs mixture. Step S3: Add the above uniformly dispersed MWCNTs mixture into a hydrothermal reactor and carry out a solvothermal reaction under heating conditions; Step S4: After the reaction is complete, the product is naturally cooled to room temperature and the solid product is collected. Unreacted raw materials and reaction byproducts are removed by washing with DMF and anhydrous ethanol, respectively. The washed product is then vacuum dried to obtain the composite modified catalyst. Step S5: Under the protection of argon atmosphere, magnesium powder is mixed with the composite modified catalyst prepared above to obtain mixed powder; the mixed powder is ball-milled under the protection of argon atmosphere; after ball milling, the ball-milled product is taken out under the protection of argon atmosphere, thus obtaining the MOF@MWCNTs composite catalyst modified magnesium-based hydrogen storage composite material.

4. The preparation method of the MOF@MWCNTs composite catalyst modified magnesium-based hydrogen storage composite material according to claim 3, characterized in that, In step S1, the molar volume ratio of metal nitrate to deionized water is 10 mmol: 7 ml; the molar volume ratio of terephthalic acid to N,N-dimethylformamide is 10 mmol: 7 ml; and the volume ratio of metal salt solution to organic ligand solution is 1:

1.

5. The preparation method of the MOF@MWCNTs composite catalyst modified magnesium-based hydrogen storage composite material according to claim 3, characterized in that, In step S2, the mass-volume ratio of the amount of MWCNTs added to the mixed solution is 0.0225 g: 70 ml.

6. The preparation method of the MOF@MWCNTs composite catalyst modified magnesium-based hydrogen storage composite material according to claim 3, characterized in that, In step S3, the heating temperature is 140℃~180℃, and the solvothermal reaction time is 8-16 h.

7. The preparation method of the MOF@MWCNTs composite catalyst modified magnesium-based hydrogen storage composite material according to claim 3, characterized in that, In step S5, the mass ratio of the composite modified catalyst to magnesium powder is (1:19) - (3:17).

8. The preparation method of the MOF@MWCNTs composite catalyst modified magnesium-based hydrogen storage composite material according to claim 3, characterized in that, In step S5, the mass ratio of the composite modified catalyst to magnesium powder is 1:

9.

9. The preparation method of a magnesium-based hydrogen storage composite material modified by MOF@MWCNTs composite catalyst according to claim 3, characterized in that, In step S6, the ball-to-material ratio is (15:1) to (30:1), the ball milling speed is 600 rpm to 1000 rpm, and the total ball milling time is 4 h to 8 h.

10. The preparation method of a magnesium-based hydrogen storage composite material modified by MOF@MWCNTs composite catalyst according to claim 3, characterized in that, In step S6, the ball mill adopts an intermittent operation program, pausing for cooling for 15 minutes every 30 minutes of ball milling.

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