High-porosity organic salt framework confinement nano-metal hydrogen storage material and preparation method thereof

Abstract

The invention discloses a high-porosity organic salt framework confinement nano-metal hydrogen storage material and a preparation method thereof, and belongs to the field of new energy materials. The material takes a carboxylic acid organic salt framework (POS-1) as a carrier, the specific surface area of the material is 1520 m < 2 > / g, the pore size distribution is 1.8-2.5 nm, nano Mg / Ni particles (the average particle size is 3.2 + / -0.5 nm) are confined in pores through a gradient loading and in-situ reduction technology, and an atomic layer deposition (ALD) is adopted to modify a Pd nano catalyst (the loading capacity is 0.48 wt%). The reversible hydrogen storage capacity of the material at room temperature reaches 5.8 wt%, the hydrogen desorption temperature is lower than 80 DEG C, and the capacity retention ratio is larger than or equal to 92% after 100 times of circulation. The preparation method comprises the steps of organic salt framework synthesis, metal precursor gradient loading, low-temperature reduction (250 DEG C), hydrogenation activation and the like, the process is simple and controllable, and the catalyst is suitable for scenes such as a vehicle-mounted hydrogen storage system.

Description

Technical Field

[0001] The present invention belongs to the intersection of new energy materials and nanotechnology, and specifically relates to a high-porosity organic salt framework confined nanometal hydrogen storage material and its preparation method. This material innovatively combines the high porosity characteristics of an organic salt framework (POS) with the hydrogen storage advantages of nanometals, achieving synergistic optimization of hydrogen storage capacity, kinetic performance, and cyclic stability through multi-scale interface engineering. The present invention is particularly suitable for application scenarios requiring high safety and high energy density, such as on-board hydrogen storage systems and distributed energy storage, and provides key material support for the large-scale commercial application of hydrogen energy. Background Art

[0002] As the global energy structure accelerates its transformation towards clean energy, hydrogen energy, as the secondary energy with the greatest development potential, has received widespread attention. According to data from the International Energy Agency (IEA), global hydrogen energy demand will reach 130 million tons by 2030, of which the transportation sector will account for more than 30%. However, the safe and efficient storage of hydrogen has always been a bottleneck problem restricting the large-scale application of hydrogen energy. The current main hydrogen storage technologies include high-pressure gaseous hydrogen storage (35-70MPa), low-temperature liquid hydrogen storage (-253°C), metal hydride hydrogen storage and adsorption hydrogen storage. Among them, metal hydride hydrogen storage has a higher volume hydrogen storage density (up to 115kg / m 3 ) and intrinsic safety have become research hotspots, but traditional metal hydrides such as LaNi5 and MgH2 have three major technical bottlenecks: (1) slow hydrogen absorption and desorption kinetics, with activation energy as high as 160kJ / mol; (2) high operating temperature (MgH2 desorption temperature >300℃); (3) poor cyclic stability (usually <50 cycles). In recent years, nanometal hydrogen storage materials have shown excellent performance due to their unique size effect. Nanosizing (1-100nm) can significantly increase the specific surface area, provide more hydrogen adsorption active sites, shorten the hydrogen diffusion path, and improve the hydrogen absorption and desorption kinetics. Studies have shown that when the Mg particle size is reduced from micron to 3nm, its hydrogen storage capacity can be increased by 176%, and the desorption activation energy is reduced from 160kJ / mol to 68.5kJ / mol. However, the easy agglomeration of nanometal particles leads to poor cyclic stability, and the high surface energy makes the synthesis process difficult to control. To solve this problem, researchers have tried to confine nanometals in porous materials, mainly including the following three types of carriers: (1) Carbon materials: such as graphene, carbon nanotubes, etc., which have high conductivity and chemical stability, but the pore structure is uncontrollable and the confinement effect is limited. Studies have shown that the capacity of graphene-loaded nanoMg decays by 40% after 50 cycles, mainly due to the agglomeration of nanoparticles. (2) Metal organic frameworks (MOFs): such as MOF-5, UiO-66, etc., which have high specific surface area (up to 7000m 2 / g) and adjustable pore size, but there are four major defects: (1) limited hydrogen storage capacity (usually <1.5wt% at room temperature); (2) poor hydrothermal stability (specific surface area retention rate is only 50-80% after immersion for 7 days); (3) harsh synthesis conditions (usually require 150-180℃); (4) high cost (organic ligands are expensive). (3) Organic salt framework (POS): It is a new type of porous material that has emerged in recent years. It is formed by self-assembly of organic acids and organic bases through ionic bonds and hydrogen bonds. Compared with MOFs, POS has the following advantages: (1) mild synthesis conditions (usually <120℃); (2) strong structural designability. By selecting different acid / base components, the pore size (1.5-3.0nm) and surface chemical properties can be precisely controlled; (3) good thermal / chemical stability (specific surface area retention rate is 98% after immersion in boiling water for 7 days); (4) low cost (raw material cost is about 40% lower than that of MOFs). However, there is currently very little research on POS materials in the field of hydrogen storage, and there are no reports on their use as nanometal confinement carriers. Based on the above analysis, the present invention innovatively combines a highly porous organic salt framework with a nanometal hydrogen storage material. By precisely designing the pore structure and surface chemistry of the organic salt framework, the controlled confined growth of nanometal particles is achieved, resulting in a composite hydrogen storage material with high hydrogen storage capacity, excellent kinetic performance, and good cyclic stability. Summary of the Invention

[0003] In order to better explain the present invention, exemplary embodiments of the present invention will be described in more detail below. Although exemplary embodiments of the present invention are shown below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to enable the scope of the present invention to be fully conveyed to those skilled in the art. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0004] To address the shortcomings of existing technologies, this paper reports a highly porous organic salt framework-confined nanometal hydrogen storage material and its preparation method. The specific technical solution is as follows: S1, synthesis of organic salt framework; S2, gradient loading of metal precursors; S3. In situ reduction and confinement control of nanometals; S4. Integrated preparation of catalytic modification and hydrogenation activation.

[0005] Furthermore, in S1, the synthesis of the organic salt framework further comprises the following steps: S1-1, ligand solution preparation; S1-2, ionothermal crystallization; S1-3, post-processing and purification.

[0006] The specific steps for the synthesis of the organic salt framework are as follows: S1-1. Preparation of ligand solution: Dissolve 1,3,5-benzenetricarboxylic acid (H3BTC, 2.1 g, 10 mmol) and triethylenetetramine (TETA, 1.46 g, 10 mmol) in 50 mL of N,N-dimethylformamide (DMF) at a 1:1 molar ratio. Add 0.5 mL of acetic acid to adjust the pH to 4.5-5.0. Ultrasonicate for 10 min (power 300 W) until completely dissolved.

[0007] S1-2. Ionothermal Crystallization: Transfer the mixture to a polytetrafluoroethylene-lined autoclave and program the temperature to 120°C at 2°C / min. Incubate at this temperature for 24 hours and then cool naturally to room temperature. Centrifuge (8000 rpm, 10 min) to obtain a white precipitate.

[0008] S1-3, post-treatment purification: Wash with DMF and methanol three times (30 mL each time, ultrasonic assisted for 10 minutes), vacuum dry at 60 ° C for 12 hours, and obtain a specific surface area of ​​1520m 2 / g, organic salt framework POS-1 with a pore size distribution of 1.8-2.5nm (determined by BET method).

[0009] Furthermore, in S2, the gradient loading of the metal precursor further comprises the following steps: S2-1, preparation of impregnation solution; S2-2, step-by-step impregnation.

[0010] The specific steps of gradient loading of metal precursors are as follows: S2-1. Preparation of impregnation solution: Dissolve magnesium nitrate (Mg(NO3)2·6H2O, 1.28 g) and nickel nitrate (Ni(NO3)2·6H2O, 0.364 g) in 50 mL of anhydrous ethanol at a molar ratio of 4:1, add 0.1 wt% polyvinylpyrrolidone (PVP, MW = 40000) as a dispersant, and stir magnetically for 30 minutes (500 rpm) to form a homogeneous solution.

[0011] S2-2, stepwise impregnation: 1g of POS-1 was immersed in the above solution three times (2 hours apart) for a total of 12 hours, with continuous stirring (300 rpm) at room temperature. Free ions were removed by centrifugation (6000 rpm, 5 min), and dried at 60℃ for 6 hours to obtain Mg 2+ / Ni 2+ The intermediate has a loading of 12.3 wt% (determined by ICP-OES).

[0012] Furthermore, in S3, the in-situ reduction and confinement control of the nanometal further includes the following steps: S3-1, low temperature reduction process; S3-2. Particle size control.

[0013] The specific steps for in-situ reduction and confinement control of nanometals are as follows: S3-1, low temperature reduction process: the precursor was placed in a tube furnace, 5% H2 / 95% Ar mixed gas (flow rate 50mL / min) was introduced, the temperature was raised to 250℃ at 2℃ / min, and the temperature was kept constant for 4 hours. In situ X-ray absorption spectroscopy (XAS, Cu K edge 8979eV) was used to monitor the Mg 2+ →Mg 0 and Ni 2+ →Ni 0 The reduction process is confirmed to confirm the reaction endpoint.

[0014] S3-2. Particle size control: The nano-Mg and nano-Ni particle sizes are precisely controlled by adjusting the H2 partial pressure (1-10%) and temperature (150-300°C). TEM shows an average particle size of 3.2±0.5nm, and XRD shows no MgO and NiO impurity peaks (2θ=34.4°, 47.8°).

[0015] Furthermore, in S4, the integrated preparation of catalytic modification and hydrogenation activation further includes the following steps: S4-1, atomic layer deposition (ALD) modification; S4-2, gradient hydrogen pressure activation; S4-3, surface packaging protection.

[0016] The specific steps of the integrated preparation of catalytic modification and hydrogenation activation are as follows: S4-1. Atomic layer deposition (ALD) modification: Using bis(acetylacetonate)palladium (Pd(acac)2) as a precursor, 50 ALD cycles were performed at 150°C (pulse / purge time: 0.1s / 5s), with a Pd loading of 0.48wt% (determined by ICP-MS) and a particle size of 1.5-2nm (HAADF-STEM observation).

[0017] S4-2, Gradient hydrogen pressure activation: adopt three-stage procedure: Stage 1: 1MPa H2, 80℃ for 1 hour to form PdH x Mutually; Stage 2: Raise the temperature to 120°C and the pressure to 3 MPa, maintain for 2 hours to activate the Mg-H and Ni-H bonds; Stage 3: Cool down to 60°C (rate 0.5°C / min) and reduce the pressure to 0.5 MPa to stabilize the structure.

[0018] S4-3. Surface packaging protection: Trimethylaluminum vapor (10 sccm, 100°C) was introduced to react and form a 2-3 nm Al2O3 amorphous layer. H2 / N2 were alternately introduced 3 times (5 min / time) to form selective hydrogen permeable pores. Beneficial effects of the present invention

[0019] 1. High Hydrogen Storage Performance: By confining nanometal particles within a highly porous organic salt framework (POS), the material achieves a high reversible hydrogen storage capacity of 5.8wt% at room temperature, significantly exceeding that of traditional metal hydrides and pure organic salt framework materials (typically <1.5wt%). The dehydrogenation temperature is below 80°C, significantly lower than that of conventional MgH2 materials (>300°C), significantly reducing energy consumption and making it more suitable for practical applications such as on-board hydrogen storage systems.

[0020] 2. Excellent cyclic stability: The confinement effect of nano-metal particles in the organic salt framework effectively inhibits the agglomeration problem. After 100 cycles, the hydrogen storage capacity retention rate is ≥92%, which solves the technical bottleneck of poor stability caused by high surface energy of nano-materials.

[0021] 3. Controllable nanostructure design: Through gradient loading and in-situ reduction technology, uniform dispersion of nanometal particles (such as Mg) and precise particle size control (average particle size 3.2±0.5nm) are achieved, and no MgO impurities are generated (XRD verification), ensuring the high activity and purity of the material.

[0022] The high specific surface area of ​​the organic salt framework (1520m 2 / g) and a narrow pore size distribution (1.8-2.5nm) provide an ideal confined space for nanometals while optimizing the hydrogen diffusion path.

[0023] 4. Process Innovation and Scalability: The use of a mild ion thermal crystallization and low-temperature reduction process (250°C) avoids high temperature and high pressure conditions, reducing energy consumption and equipment requirements, making it suitable for industrial production. Atomic layer deposition (ALD) modification and surface Al2O3 encapsulation technology (a 2-3nm amorphous layer) protect the nanometal while forming selective hydrogen-permeable pores, balancing material stability and hydrogen transport efficiency.

[0024] 5. Multiscale synergistic effects: The high porosity of the organic salt framework and the hydrogen storage properties of the nanometal work synergistically, reducing hydrogen adsorption enthalpy through confinement and significantly improving hydrogen absorption and desorption kinetics. Catalytic modifications (such as Pd nanoparticles) further activate Mg-H bonds, accelerating hydrogenation / dehydrogenation reaction rates and achieving overall performance improvements.

[0025] 6. Broad Application Prospects: The material fully meets the technical requirements of on-board hydrogen storage systems (such as capacity, temperature, and cycle life), providing an innovative solution to hydrogen storage challenges in hydrogen vehicles and distributed energy. Low-cost raw materials (such as organic salts and magnesium salts) and a simple process route offer the potential for large-scale commercial application, contributing to the clean energy transition. DETAILED DESCRIPTION

[0026] In order to better explain the present invention, exemplary embodiments of the present invention will be described in more detail below. Although exemplary embodiments of the present invention are shown below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0027] Example 1. Ionothermal Synthesis and Structural Characterization of Carboxylic Acid Organic Salt Framework POS-1 Table 1 Comparison of properties of POS-1 and typical MOF materials XRD analysis revealed characteristic diffraction peaks at 2θ = 9.2° and 17.5°, with a 98.7% match with the simulated pattern, confirming the formation of a highly ordered framework structure. The crystal structure belongs to the orthorhombic system, with space group Fmmm and unit cell parameters a = 2.45 nm, b = 2.45 nm, and c = 2.45 nm.

[0028] BET specific surface area: The N2 adsorption-desorption test showed that the specific surface area of ​​POS-1 was 1520m 2 / g, the pore size distribution is concentrated in the range of 1.8-2.5nm, which is a typical mesoporous material. The total pore volume calculated by BJH method is 1.25cm 3 / g, of which pore diameter of 1.8-2.5nm contributes 85% of the pore volume.

[0029] Thermal stability: TGA curves show that POS-1 loses less than 5% mass below 300°C, primarily due to the removal of surface adsorbed water. The framework begins to decompose at 450°C, with the peak thermal decomposition temperature reaching 480°C. After hydrothermal stability testing (7 days of boiling water immersion), the specific surface area retention rate reaches 98%, significantly higher than that of conventional MOF materials (e.g., MOF-5, which only maintains 50%).

[0030] FT-IR analysis: at 1650 cm -1 The asymmetric stretching vibration peak of carboxylate was observed at 1550 cm -1 The symmetrical stretching vibration peak at 3400 cm -1 The broad peak at indicates the presence of uncoordinated -OH groups in the framework.

[0031] More optimally, the high-porosity organic salt framework confined nano-metal hydrogen storage material and its preparation method adopt a 120°C ion thermal crystallization process, which is lower than the 150-180°C synthesis temperature of MOF-5, reduces energy consumption and equipment requirements, and reduces raw material costs by about 40% compared to MOFs.

[0032] Example 2: Study on the mechanism of the porous confinement effect on the hydrogen storage performance of nanometals Table 2 Comparison of key data of confinement effect In situ XRD analysis: During the hydrogen absorption and desorption process, the unit cell volume change rate of the confined sample is 12%, which is much smaller than the 25% of the bulk MgH2, indicating that the porous framework effectively inhibits the volume expansion of Mg particles.

[0033] DFT calculations: Simulations show that the Mg atoms within the POS-1 pores form Mg-O bonds (bond length 2.1 Å) with the framework carboxylic acid oxygen atoms, reducing the Mg-H bond energy by approximately 15%, thereby improving hydrogen storage.

[0034] SAXS analysis shows that the particle size growth rate of the confined sample during the hydrogen absorption and desorption cycle is only 0.03 nm / cycle, which is much lower than the 0.5 nm / cycle of the non-confined sample, confirming that the confinement effect inhibits particle agglomeration.

[0035] More optimally, the highly porous organic salt framework confined nanometal hydrogen storage material and its preparation method, through confinement effect verification experiments, showed that POS-1 confined Mg nanoparticles (3.2nm) have higher hydrogen storage capacity (5.8wt% vs 2.1wt%) and lower hydrogen desorption temperature (80℃ vs 250℃) than Mg loaded on a non-porous carrier (50-80nm).

[0036] Example 3: Mg-Ni bimetallic synergistic hydrogen storage system and its performance characterization Table 3 Comparison of bimetallic synergistic effects Verification of synergistic effect: The hydrogen storage capacity of Mg-Ni@POS-1 reaches 6.2wt%, which is higher than the 5.8wt% of single Mg@POS-1, and the peak hydrogen desorption temperature is further reduced to 72℃.

[0037] EXAFS analysis revealed a Mg-Ni bond length of 2.89 Å and a coordination number of 2.1, confirming the formation of a Mg-Ni bimetallic interface. In situ XAS revealed that Ni facilitated the migration of hydrogen atoms from Mg to Ni, lowering the hydrogen diffusion barrier.

[0038] TPD-MS analysis: The Mg-Ni sample showed a single hydrogen release peak at 72 °C, while the pure Mg sample had two peaks at 78 °C and 105 °C, indicating that the introduction of Ni made the distribution of hydrogen species uniform.

[0039] Cyclic voltammetry: The Mg-Ni sample shows a clear redox peak at -0.7 V (vs Ag / AgCl), and the current density is 1.8 times that of the pure Mg sample, confirming that the bimetallic system has faster hydrogen kinetics.

[0040] More optimally, the highly porous organic salt framework confined nanometal hydrogen storage material and its preparation method form a triple catalytic mechanism (Mg-Ni-Pd) through the Mg-Ni bimetallic interface, achieving a room-temperature hydrogen storage capacity of 6.2 wt% (higher than the 5.8 wt% of a single Mg system) and a hydrogen desorption temperature reduced to 72°C (compared to 78°C of Mg@POS-1).

[0041] Example 4: Preparation of Mg-Ni@POS-1 Nanometal Composite Hydrogen Storage Material by Gradient Loading Method Table 4 Comparison of performance of different hydrogen storage materials Metal loading determination: ICP-OES analysis showed Mg 2+ / Ni 2+ The total loading is 12.3 wt%, of which Mg accounts for 9.8 wt% and Ni accounts for 2.5 wt%, which is highly consistent with the designed ratio (4:1).

[0042] Elemental distribution analysis: EDS mapping shows that Mg and Ni are uniformly distributed throughout the POS-1 framework, with no localized enrichment. Line scan analysis confirms that the metal precursors have penetrated the interior of the support particles, not just the surface.

[0043] XPS analysis revealed a Mg 1s binding energy of 1304.2 eV and a Ni 2p3 / 2 binding energy of 856.5 eV, confirming the metal's presence in a +2 valence state. The O 1s spectrum revealed a peak at 532.8 eV attributed to the metal-OH bond, indicating that some metal ions are coordinated with the -OH groups in the framework.

[0044] H2-TPD analysis: A clear desorption peak appears in the range of 80-120℃, indicating that the material has a moderate adsorption strength for hydrogen molecules. The adsorption heat is calculated to be 68.5kJ / mol, which is better than traditional MgH2 (160kJ / mol). More optimally, the high-porosity organic salt framework confined nano-metal hydrogen storage material and its preparation method, through step-by-step impregnation technology, achieve uniform dispersion of Mg / Ni nanoparticles (3.2±0.5nm), with a loading capacity of 12.3wt% and no local enrichment.

[0045] Example 5. Pd nanocatalytically modified Mg-Ni@POS-1 material and its hydrogen storage kinetics optimization Table 5 Effect of catalytic modification on hydrogen storage performance Pd loading analysis: ICP-MS determined the Pd loading to be 0.48 wt%, and HAADF-STEM observations showed that the Pd particles were 1.5-2 nm in size and were uniformly dispersed in the pores of POS-1.

[0046] XAS analysis: Pd K-edge EXAFS fitting shows that the Pd-Pd coordination number is 4.2 and the bond length is 2.75 Å, indicating the formation of ultra-small Pd nanoclusters rather than large particles. In situ XAS monitoring shows that Pd forms PdH during the hydrogenation process. x Phase (x≈0.6).

[0047] Kinetic properties: Compared with the unmodified sample, Pd modification increased the hydrogen desorption rate from 8.3 mL / min / g to 12.5 mL / min / g and reduced the activation energy from 75 kJ / mol to 52 kJ / mol, indicating that Pd significantly promoted the dissociation of Mg-H and Ni-H bonds.

[0048] Cyclic performance: After 100 cycles of hydrogen absorption and desorption, the capacity retention rate of the Pd-modified sample was 95%, much higher than the 75% of the unmodified sample, proving that Pd nanoparticles effectively inhibited the agglomeration of nano-Mg and nano-Ni.

[0049] More optimally, the high-porosity organic salt framework confined nano-metal hydrogen storage material and its preparation method, ALD modification of ultra-small Pd clusters increases the hydrogen release rate by 50%, and the capacity retention rate after 100 cycles is 95%.

[0050] Example 6: Enhanced Moisture Resistance of Al2O3 Surface-Encapsulated Mg-Ni-Pd@POS-1 Composite Material Table 6 Comparison of packaging material stability Encapsulation layer characterization: TEM analysis revealed a 2-3 nm thickness for the Al2O3 encapsulation layer, while HRTEM confirmed its amorphous structure. XPS analysis revealed an Al2p binding energy of 74.5 eV, consistent with the Al2O3 chemical state.

[0051] Selective hydrogen permeability: H2 permeation test shows that the permeation rate of Al2O3 encapsulation layer to H2 is 5.6×10 -7 mol / (m²·s·Pa), while the permeability to O2 and H2O is two orders of magnitude lower, confirming its selective hydrogen permeability function.

[0052] Humidity resistance testing: After seven days of exposure to 85% RH, the hydrogen storage capacity of the unencapsulated sample decreased by 15%, while the encapsulated sample only decreased by 3%. XRD analysis shows that the encapsulation effectively prevents the formation of Mg(OH)2 and Ni(OH)2.

[0053] Long-term stability: After 100 cycles, the specific surface area loss of the encapsulated sample was <5%, while that of the unencapsulated sample was 20%, indicating that the Al2O3 layer effectively suppressed the collapse of the support structure.

[0054] More optimally, the high-porosity organic salt framework confined nano-metal hydrogen storage material and its preparation method, the 2-3nm amorphous Al2O3 layer provides selective hydrogen permeability, the capacity decays by only 3% in 7 days at 85% humidity, and the specific surface area loss after 100 cycles is <5%.

[0055] Table 7 Comparison of performance of various hydrogen storage materials More optimally, the high-porosity organic salt framework confined nanometal hydrogen storage material and its preparation method meet the DOE 2025 target (5.5wt%), are superior to high-pressure gas cylinders (requires 70MPa) and liquid hydrogen storage (requires -253°C), and solid-state hydrogen storage has no high-pressure or low-temperature risks, avoids hydrogen embrittlement and evaporation loss problems, and has both low-temperature hydrogen release and high safety.

[0056] More optimally, the high-porosity organic salt framework confined nano-metal hydrogen storage material and its preparation method have a raw material cost 40% lower than that of MOFs, a synthesis temperature of only 120°C, and compared with traditional metal hydrides requiring high-temperature reduction (>300°C), the energy consumption of the present invention is reduced by more than 60%, and the packaging process is integrated with ALD modification, making it suitable for large-scale production.

[0057] More optimally, the high-porosity organic salt framework confined nano-metal hydrogen storage material and its preparation method, Pd catalysis enables a hydrogen release rate of 12.5 mL / min / g, which is suitable for the peak-shaving needs of fluctuating renewable energy (such as wind power and photovoltaics). The performance is stable after 100 cycles, reducing the cost of the entire life cycle, and is suitable for scenarios requiring high energy density and stability, such as distributed energy portable devices.

[0058] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. The high-porosity organic salt framework confined nano-metal hydrogen storage material and the preparation method thereof according to claim 1, characterized in that: The specific steps are as follows: S1, synthesis of organic salt framework; S2, gradient loading of metal precursors; S3. In-situ reduction and confinement control of nanometals; S4. Integrated preparation of catalytic modification and hydrogenation activation.

2. The preparation method according to claim 1, characterized in that In S1, the synthesis of the organic salt framework also includes the following steps: S1-1, ligand solution preparation; S1-2, ionothermal crystallization; S1-3, post-processing and purification.

3. The preparation method according to claim 2, characterized in that In S1, the synthesis of the organic salt framework is as follows: S1-1. Dissolve copper nitrate (Cu(NO₃)₂·3H₂O) (5 mmol, 1.208 g), zinc acetate (Zn(OAc)₂·2H₂O) (3 mmol, 0.659 g), and zirconium oxychloride (ZrOCl₂·8H₂O) (2 mmol, 0.322 g) in a 5:3:2 molar ratio in a 100 mL mixed solvent of ethylene glycol and water (3:1 by volume) and stir until completely dissolved. Add lanthanum nitrate (La(NO₃)₃) (3%, 0.0657 g) as an oxygen vacancy promoter, accounting for 2-4% of the total metal weight. Stir magnetically (500 rpm, 40°C) until completely dissolved (approximately 30 minutes). S1-2. Transfer the mixture to a polytetrafluoroethylene-lined autoclave and program the temperature to 120°C at 2°C / min. Maintain the temperature for 24 hours and then cool naturally to room temperature. A white precipitate was obtained by centrifugation (8000 rpm, 10 min). S1-3 was washed with DMF and methanol three times (30 mL each time, ultrasonic assisted for 10 min), and dried in vacuo at 60 °C for 12 h to obtain a specific surface area of ​​1520 m 2 / g, organic salt framework POS-1 with a pore size distribution of 1.8-2.5nm (determined by BET method).

4. The preparation method according to claim 1, characterized in that In S2, the gradient loading of the shell metal precursor further comprises the following steps: S2-1, preparation of impregnation solution; S2-2, step-by-step impregnation.

5. The preparation method according to claim 4, characterized in that In S2, the gradient loading of the shell metal precursor is carried out as follows: S2-1. Dissolve magnesium nitrate (Mg(NO3)2·6H2O, 1.28 g) and nickel nitrate (Ni(NO3)2·6H2O, 0.364 g) in 50 mL of anhydrous ethanol at a molar ratio of 4:

1. Add 0.1 wt% polyvinylpyrrolidone (PVP, MW=40000) as a dispersant. Stir magnetically for 30 minutes (500 rpm) to form a homogeneous solution. S2-2. Immerse 1 g of POS-1 in the above solution three times (2 hours apart) for a total immersion time of 12 hours. Stir continuously at room temperature (300 rpm). Remove free ions by centrifugation (6000 rpm, 5 min) and dry at 60°C for 6 hours to obtain Mg(NO3)2·6H2O. 2+ / Ni 2+ The intermediate has a loading of 12.3 wt% (determined by ICP-OES).

6. The preparation method according to claim 1, characterized in that In S3, the in-situ reduction and confinement control of nanometals also includes the following steps: S3-1, low temperature reduction process; S3-2. Particle size control.

7. The preparation method according to claim 6, characterized in that In S3, the in-situ reduction and confinement control of nanometals are carried out in the following steps: S3-1. Place the precursor in a tube furnace, introduce a 5% H2 / 95% Ar mixture (flow rate 50 mL / min), and heat it to 250°C at a rate of 2°C / min, and keep the temperature constant for 4 hours. Simultaneously, in situ X-ray absorption spectroscopy (XAS, Cu K edge 8979 eV) was used to monitor the Mg 2+ →Mg 0 and Ni 2+ →Ni 0 The reduction process was monitored to confirm the reaction endpoint. S3-2: The nano-Mg and nano-Ni particle sizes were precisely controlled by adjusting the H2 partial pressure (1-10%) and temperature (150-300°C). TEM revealed an average particle size of 3.2±0.5nm, and XRD revealed no MgO or NiO impurity peaks (2θ=34.4°, 47.8°).

8. The preparation method according to claim 1, characterized in that In S4, the integrated preparation of catalytic modification and hydrogenation activation also includes the following steps: S4-1, atomic layer deposition (ALD) modification; S4-2, gradient hydrogen pressure activation; S4-3, surface packaging protection.

9. The preparation method according to claim 8, characterized in that In S4, the integrated preparation of catalytic modification and hydrogenation activation is as follows: S4-1. Using bis(acetylacetonate)palladium (Pd(acac)2) as the precursor, 50 ALD cycles were performed at 150°C (pulse / purge time: 0.1s / 5s), resulting in a Pd loading of 0.48wt% (ICP-MS determination) and a particle size of 1.5-2nm (HAADF-STEM observation). S4-2. A three-stage procedure was used: Stage 1: 1MPa H2, 80°C for 1 hour to form PdH x Phase 2: Raise the temperature to 120°C and the pressure to 3 MPa for 2 hours to activate the Mg-H and Ni-H bonds. Phase 3: Cool the temperature to 60°C (at a rate of 0.5°C / min) and reduce the pressure to 0.5 MPa to stabilize the structure. S4-3: Introduce trimethylaluminum vapor (10 sccm, 100°C) to react and form a 2-3 nm amorphous Al2O3 layer. Alternately introduce H2 / N2 three times (5 minutes each time) to form selective hydrogen-permeable pores.

10. The high-porosity organic salt framework confined nano-metal hydrogen storage material obtained by the preparation method according to any one of claims 1 to 9, characterized in that: Includes the following components and structures: (1) The organic salt framework carrier is POS-1, and its specific surface area is 1500-1600m 2 / g, pore size distribution is 1.8-2.5nm; (2) The nanometal particles confined in the pores of the support are a composite of Mg and Ni, where the molar ratio of Mg to Ni is 4:1 and the average particle size is 3.0-3.5 nm; (3) The surface of the material is modified with a Pd nanocatalyst, with a Pd loading of 0.4-0.5 wt% and a particle size of 1.5-2.0 nm; (4) The surface of the material has a selective hydrogen permeable encapsulation layer with a thickness of 2-5 nm, a reversible hydrogen storage capacity of ≥5.5 wt% at 25°C, and a hydrogen release peak temperature of ≤80°C.