Preparation method and application of PCN-doped MOF-derived nano-porous hydrogen storage composite material

Abstract

The invention is suitable for the technical field of solid hydrogen storage, and provides a preparation method and application of a PCN-doped MOF derived nano-porous hydrogen storage composite material. The preparation method comprises the following steps: firstly, synthesizing a cobalt-nickel bimetallic MOF material, and introducing melamine polyphosphate and pentaerythritol ester in the synthesis process; introducing metal vanadium ions to obtain an MOF derivative, and calcining the MOF derivative to obtain the PCN-doped MOF derivative nano-porous hydrogen storage material. And compounding with magnesium hydride to obtain the V-Ni-Co / PCN + MgH2 hydrogen storage composite material. The hydrogen storage capacity of the prepared material reaches 7.0 wt% or above, rapid hydrogen absorption can be started at 40 DEG C, the dehydrogenation starting temperature is reduced to about 150 DEG C, rapid hydrogen absorption / hydrogen desorption is completed within 30 min and 45 min respectively, and excellent hydrogen storage thermal / dynamic performance is shown; after 100 times of hydrogen absorption and desorption cycles, the hydrogen storage capacity retention rate of the material is as high as 97%, and the material shows excellent cycle stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state hydrogen storage, and particularly relates to a preparation method and application of a PCN-doped MOF-derived nanoporous hydrogen storage composite material. Background Art

[0002] In the context of the global energy pattern accelerating towards clean and sustainable transformation, hydrogen energy, as a highly potential clean energy carrier, is widely regarded as one of the key paths to solve energy and environmental problems due to its many advantages such as high energy density and zero pollution of combustion products. Solid-state hydrogen storage technology stands out among many hydrogen storage methods and becomes a research hotspot due to its high safety, large hydrogen storage density, and relatively simple operation. However, the current solid-state hydrogen storage technology still faces many challenges and cannot yet meet the needs of large-scale applications. The core element of solid-state hydrogen storage technology lies in the performance of solid-state hydrogen storage materials. Currently, commonly used solid-state hydrogen storage materials include metal hydrides (such as LiBH 4 , AlH 3 , NaAlH 4 , MgH 2 , etc.), metal alloys (such as LaNi 5 , TiFe, etc.), and some carbon materials, etc. Among them, metal hydrides have been widely studied due to their advantages of good safety, low cost, and high capacity. In particular, magnesium hydride (MgH 2 )-based hydrogen storage alloy composite materials have attracted much attention due to their relatively high mass hydrogen storage density (7.6 wt%). However, their poor kinetic performance and high thermodynamic stability severely limit their practical applications in industrial scenarios.

[0003] In the prior art, the Chinese invention patent with the publication number CN102191416A attempts to modify MgH 2 by alloying means to improve its hydrogen absorption / desorption kinetic performance, but the mass hydrogen storage density of the modified material has significantly decreased (3.0 wt%). The Chinese invention patents with the publication numbers CN119100333A and CN116101973A utilize the high carrier mobility and high thermal conductivity of graphene to reduce the hydrogen storage and release temperature, and MgH 2The activation energy of hydrogen desorption decreased from 122.7 kJ / mol to 63.8 kJ / mol, but the hydrogen storage capacity increased only slightly, making it difficult to meet the requirements of scenarios with high capacity requirements such as energy storage in hydrogen energy power stations. In addition, metal-organic framework (MOF) materials and their derivatives are also regarded as promising hydrogen storage materials. The Chinese invention patent with the publication number CN116618671A discloses a MOF-derived carbon-confined magnesium-based nano-hydrogen storage material and its preparation method, aiming to improve its hydrogen storage performance, but its mass hydrogen storage density is only about 4.0 wt%, and the technical advantages are not obvious. To sum up, the existing solid-state hydrogen storage materials still have deficiencies in terms of hydrogen storage capacity, hydrogen absorption / desorption kinetics, hydrogen absorption / desorption temperature, and cycle stability. Therefore, developing a hydrogen storage material with high hydrogen storage capacity, excellent hydrogen absorption / desorption kinetics, low operating temperature, and good cycle stability is of great significance for promoting the real industrial application of hydrogen energy in the future. For this reason, the present invention proposes a preparation method and application of a PCN-doped MOF-derived nanoporous hydrogen storage composite material. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method and application of a PCN-doped MOF-derived nanoporous hydrogen storage composite material, aiming to solve the problems raised in the above background technology.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A preparation method of a PCN-doped MOF-derived nanoporous hydrogen storage composite material, comprising the following steps:

[0007] Step S1: Synthesis of NiCo-MOF@MPP@PER, specifically including:

[0008] Step S11: Stir and dissolve Ni(NO 3 ) 2 ·6H 2 O and Co(NO 3 ) 2 ·6H 2 O in an organic solvent to obtain a metal salt solution A; add melamine polyphosphate and pentaerythritol ester to the metal salt solution A to obtain a mixed solution B;

[0009] Step S12: Weigh an organic ligand and stir it to dissolve in an organic solvent to obtain a ligand solution C; under magnetic stirring, add the ligand solution C to the mixed solution B, add a nucleating agent, and terminate the reaction after magnetic stirring to obtain a reaction product;

[0010] Step S13: Filter and wash the obtained product by suction, and then dry it to obtain NiCo-MOF@MPP@PER;

[0011] Step S2: Synthesis of VNiCo-MOF@MPP@PER, specifically including:

[0012] Step S21: Weigh NiCo-MOF@MPP@PER and a vanadium source and dissolve them in an organic solvent to obtain suspension D;

[0013] Step S22: Transfer suspension D to a high-pressure reactor for reaction to obtain a reaction product;

[0014] Step S23: Wash the reaction product repeatedly with absolute ethanol and deionized water, and then dry it to obtain VNiCo-MOF@MPP@PER;

[0015] Step S3: Preparation of V-Ni-Co / PCN;

[0016] Weigh the VNiCo-MOF@MPP@PER composite and grind it into powder in a mortar. Place the powder in a magnetic boat and perform high-temperature heat treatment in a tubular furnace to obtain the V-Ni-Co / PCN hydrogen storage material;

[0017] Step S4: Preparation of V-Ni-Co / PCN + MgH 2 Specifically including:

[0018] Step S41: Weigh V-Ni-Co / PCN and magnesium hydride, add anhydrous n-hexane as a dispersion medium, load the mixture into a stainless steel ball milling tank, and select steel balls with a mass of 0.1 - 1 g as the ball milling medium;

[0019] Step S42: Ball mill in a ball mill;

[0020] Step S43: After ball milling, transfer the mixture to a vacuum drying oven for drying to finally obtain the V-Ni-Co / PCN + MgH 2 hydrogen storage composite material.

[0021] Furthermore, the specific steps of step S1 are as follows:

[0022] Step S11: Stir and dissolve 2.0 - 30 g of Ni(NO 3 ) 2 ·6H 2 O and 2.0 - 30 g of Co(NO 3 ) 2 ·6H 2 O in 50 - 800 mL of an organic solvent to obtain a metal salt solution A; add 0 - 10 g of melamine polyphosphate and 0 - 10 g of pentaerythritol ester to the metal salt solution A to obtain a mixed solution B;

[0023] Step S12: Weigh 2.0 - 50 g of the organic ligand, stir and dissolve it in 50 - 800 mL of an organic solvent to obtain ligand solution C; under magnetic stirring, add ligand solution C to the mixed solution B, and add 0 - 5 g of a nucleating agent, and magnetically stir at 60 - 120 °C for 0.5 - 24 h, then terminate the reaction to obtain a reaction product;

[0024] Step S13: Filter the obtained product by suction and wash it 3 - 5 times, and dry it in an oven at 80 - 120 °C for 5 - 24 h to obtain NiCo-MOF@MPP@PER.

[0025] Furthermore, in step S1, the organic ligand is 2-methylimidazole, benzimidazole, terephthalic acid, 2-aminoterephthalic acid or trimesic acid; the organic solvent is methanol, ethanol, DMF, DMAc or deionized water; the nucleating agent is one or more of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, polyvinyl alcohol and sodium hydroxide.

[0026] Furthermore, the specific steps of step S2 are as follows:

[0027] Step S21: Weigh 5 - 60 g of NiCo-MOF@MPP@PER and 0 - 10 g of a vanadium source, dissolve them in 50 - 300 mL of an organic solvent to obtain suspension D;

[0028] Step S22: Transfer suspension D to a high-pressure reactor, react at 60 - 150 °C at a rotation speed of 300 - 1000 rpm for 6 - 24 h, then terminate the reaction to obtain a reaction product;

[0029] Step S23: Wash the reaction product repeatedly with absolute ethanol and deionized water 3 - 5 times, and dry it at 80 - 120 °C for 3 - 24 h to obtain VNiCo-MOF@MPP@PER.

[0030] Furthermore, in step S2, the vanadium source is one or more of ammonium vanadate, sodium orthovanadate, sodium metavanadate, vanadyl sulfate, vanadyl acetylacetonate and oxovanadium oxalate; the organic solvent is methanol, ethanol, DMF, DMAc or deionized water.

[0031] Furthermore, the specific process of step S3 is as follows:

[0032] Weigh 5 - 50 g of the VNiCo-MOF@MPP@PER composite, grind it into powder in a mortar, place the powder in a magnetic boat, and perform high-temperature heat treatment in a tube furnace; first in N 2Under protection, it is heated to 200 - 250 °C at a rate of 5 - 7.5 °C / min and held for 1 - 1.5 h; then heated to 300 - 400 °C at a rate of 7.5 - 10 °C / min and held for 2 - 4 h; then heated to 500 - 680 °C at a rate of 10 - 15 °C / min and held for 4 - 6 h; finally, it is naturally cooled to room temperature to obtain the V-Ni-Co / PCN hydrogen storage material.

[0033] Furthermore, the specific steps of step S4 are as follows:

[0034] Step S41: Weigh 0 - 50 g of V-Ni-Co / PCN and 0 - 50 g of magnesium hydride, add 5 - 100 mL of anhydrous n-hexane as a dispersion medium, put the mixture into a stainless steel ball milling tank, and select steel balls with a mass of 0.1 - 1 g as the ball milling medium;

[0035] Step S42: Ball mill in a ball mill at a speed of 300 - 800 rpm for 2 - 12 h, and pause for 10 - 30 min every 0.5 - 2 h to prevent overheating;

[0036] Step S43: After ball milling, transfer the mixture to a vacuum drying oven and dry it at 50 - 150 °C for 3 - 24 h to finally obtain the V-Ni-Co / PCN + MgH 2 hydrogen storage composite material.

[0037] Furthermore, in step S41, the mass ratio of the sample to the ball milling medium is 1:10 - 50, and the sample is V-Ni-Co / PCN and MgH 2 .

[0038] The PCN-doped MOF-derived nanoporous hydrogen storage composite material prepared according to the above-mentioned preparation method of the PCN-doped MOF-derived nanoporous hydrogen storage composite material.

[0039] The present invention has the following beneficial effects:

[0040] 1. High hydrogen storage capacity: The hydrogen storage capacity of the V-Ni-Co / PCN + MgH 2 hydrogen storage composite material prepared by the present invention can reach more than 7.0 wt%. This high hydrogen storage capacity benefits from the rich PCN network structure formed after calcination, which provides rich pore structures, specific surface areas, and relatively high electron densities, enhancing the interaction between hydrogen molecules and surface active sites. In addition, the presence of phosphorus and nitrogen elements optimizes the electronic environment of the material, enhances the electronic activity of the metal centers (nickel, cobalt), and further improves the adsorption ability of hydrogen molecules on the material surface. By combining V-Ni-Co / PCN with high adsorption ability for H 2 with MgH with high hydrogen storage capacity 2 in combination, the hydrogen storage performance of the composite material is further optimized.

[0041] 2. Excellent hydrogen storage thermal / kinetic performance: The V-Ni-Co / PCN+MgH 2 hydrogen storage composite material prepared by the present invention can start rapid hydrogen absorption at 40 °C. The dehydrogenation starting temperature is reduced to about 150 °C, and rapid hydrogen absorption / hydrogen release is completed within 30 min and 45 min respectively, showing excellent hydrogen storage thermal / kinetic performance. This significant improvement in performance is closely related to the electron transfer ability of the material. Vanadium metal and its oxides (such as V, VO, V 2 O 3 ) provide an efficient electron transfer path through their multivalent state characteristics, promoting the activation and dissociation of hydrogen molecules. At the same time, the PCN network, with its high specific surface area, good electrical conductivity, and optimized pore structure, significantly improves the adsorption ability and migration rate of hydrogen molecules, thus achieving rapid adsorption and desorption during the hydrogen storage process.

[0042] 3. Good hydrogen storage cycle stability: After 100 hydrogen absorption and desorption cycles, the hydrogen storage capacity retention rate of the V-Ni-Co / PCN+MgH 2 hydrogen storage composite material prepared by the present invention is as high as 97%, showing excellent cycle stability. This stability stems from the porous support structure provided by the PCN network on the one hand. The strong chemical bonding between nitrogen, phosphorus elements and the carbon skeleton effectively enhances the thermal compression resistance of the overall structure, avoiding pore collapse and particle aggregation. On the other hand, during the hydrogen storage process, nitrogen and phosphorus elements form a stable electron network through their interaction with vanadium and magnesium, enhancing the electron transfer regulation ability within the material, thereby effectively resisting the electron environment fluctuations generated during multiple cycles. Description of the Drawings

[0043] Figure 1 For MgH 2 , V-Ni-Co / PCN, V-Ni-Co / PCN+MgH 2 (2:1), V-Ni-Co / PCN+MgH 2 (1:1) and V-Ni-Co / PCN+MgH 2 (1:2) sample hydrogen absorption / desorption performance; where (a) variable temperature hydrogen desorption curve, (b) constant temperature hydrogen desorption curve, (c) variable temperature hydrogen absorption curve, (d) constant temperature hydrogen absorption curve. Detailed Embodiments

[0044] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the implementable scope of the present invention.

[0045] The present invention provides a method for preparing a PCN-doped MOF-derived nanoporous hydrogen storage composite material, comprising the following steps:

[0046] Step S1: Synthesis of NiCo-MOF@MPP@PER, specifically including:

[0047] Step S11: Stir and dissolve 2.0 - 30 g of Ni(NO 3 ) 2 ·6H 2 O and 2.0 - 30 g of Co(NO 3 ) 2 ·6H 2 O in 50 - 800 mL of an organic solvent to obtain a metal salt solution A; add 0 - 10 g of melamine polyphosphate (MPP) and 0 - 10 g of pentaerythritol ester (PER) to the metal salt solution A to obtain a mixed solution B;

[0048] Step S12: Weigh 2.0 - 50 g of an organic ligand and stir and dissolve it in 50 - 800 mL of an organic solvent to obtain a ligand solution C; under magnetic stirring, add the ligand solution C to the mixed solution B, and add 0 - 5 g of a nucleating agent, and magnetically stir at 60 - 120 °C for 0.5 - 24 h and then terminate the reaction to obtain a reaction product;

[0049] Step S13: Filter the obtained product by suction and wash it 3 - 5 times, and dry it in an oven at 80 - 120 °C for 5 - 24 h to obtain NiCo-MOF@MPP@PER.

[0050] Among them, the organic ligand is 2-methylimidazole, benzimidazole, terephthalic acid, 2-aminoterephthalic acid or trimesic acid; the organic solvent is methanol, ethanol, DMF, DMAc or deionized water; the nucleating agent is one or more of polyvinylpyrrolidone (PVP), sodium dodecylbenzenesulfonate (SDBS), polyvinyl alcohol (PVA) and sodium hydroxide (NaOH).

[0051] Step S2: Synthesis of VNiCo-MOF@MPP@PER, specifically including:

[0052] Step S21: Weigh 5 - 60 g of NiCo-MOF@MPP@PER and 0 - 10 g of a vanadium source and dissolve them in 50 - 300 mL of an organic solvent to obtain a suspension D;

[0053] Step S22: Transfer the suspension D to a high-pressure reactor, and react at 60 - 150 °C at a rotation speed of 300 - 1000 rpm for 6 - 24 h and then terminate the reaction to obtain a reaction product;

[0054] Step S23: Wash the reaction product repeatedly with absolute ethanol and deionized water for 3 - 5 times, and dry it at 80 - 120 °C for 3 - 24 h to obtain VNiCo-MOF@MPP@PER.

[0055] Among them, the vanadium source is one or more of ammonium vanadate (NH 4 VO 3 ), sodium orthovanadate (Na 3 VO 4 ), sodium metavanadate (NaVO 3 ), vanadyl sulfate (VOSO 4 ), vanadium acetylacetonate (V(acac) 3 ), and vanadyl oxalate (VOCzO 4 ); the organic solvent is methanol, ethanol, DMF, DMAc or deionized water.

[0056] Step S3: Preparation of V-Ni-Co / PCN;

[0057] Weigh 5 - 50 g of the VNiCo-MOF@MPP@PER composite and grind it into powder in a mortar. Place the powder in a magnetic boat and conduct high-temperature heat treatment in a tube furnace. First, under the protection of N 2 , heat it to 200 - 250 °C at a rate of 5 - 7.5 °C / min and hold at this temperature for 1 - 1.5 h; then heat it to 300 - 400 °C at a rate of 7.5 - 10 °C / min and hold at this temperature for 2 - 4 h; then heat it to 500 - 680 °C at a rate of 10 - 15 °C / min and hold at this temperature for 4 - 6 h; finally, cool it naturally to room temperature to obtain the V-Ni-Co / PCN hydrogen storage material.

[0058] Step S4: Preparation of V-Ni-Co / PCN + MgH 2 Specifically, it includes:

[0059] Step S41: Weigh 0 - 50 g of V-Ni-Co / PCN and 0 - 50 g of magnesium hydride (MgH 2 ), add 5 - 100 mL of anhydrous n-hexane as the dispersion medium, put the mixture into a stainless steel ball milling tank, select steel balls with a mass of 0.1 - 1 g as the ball milling medium, and add according to the mass ratio of the sample (V-Ni-Co / PCN and MgH 2 ) to the ball milling medium of 1:10 - 50;

[0060] Step S42: Ball mill in a ball mill at a speed of 300 - 800 rpm for 2 - 12 h, and pause for 10 - 30 min every 0.5 - 2 h to prevent overheating;

[0061] Step S43: After the ball milling is completed, transfer the mixture to a vacuum drying oven and dry it at 50-150 °C for 3-24 h to ensure that the dispersion medium is fully volatilized, and finally obtain V-Ni-Co / PCN+MgH 2 hydrogen storage composite material.

[0062] In the embodiment of the present invention, the present invention first synthesizes a cobalt-nickel bimetallic MOF material by a solvothermal method, and introduces melamine polyphosphate (MPP) and pentaerythritol ester (PER) during the synthesis process to enrich the content of carbon, nitrogen, and phosphorus elements; then introduces metal vanadium ions through an ion exchange strategy to obtain a MOF derivative; calcine this MOF derivative to obtain a PCN-doped MOF-derived nanoporous hydrogen storage material; finally, compound it with magnesium hydride by wet ball milling to obtain a PCN-doped MOF-derived nanoporous hydrogen storage composite material (V-Ni-Co / PCN+MgH 2 ).

[0063] The present invention will be further described below in conjunction with specific embodiments.

[0064] Example 1: The embodiment of the present invention provides a preparation method of a PCN-doped MOF-derived nanoporous hydrogen storage composite material, including the following steps:

[0065] Step 1: Synthesis of NiCo-MOF@MPP@PER, specifically including:

[0066] Step S11: Stir and dissolve 29.08 g of Ni(NO 3 ) 2 ·6H 2 O and 29.10 g of Co(NO 3 ) 2 ·6H 2 O in 500 mL of absolute ethanol to obtain a metal salt solution A; add 5.0 g of MPP and 2.5 g of PER to the metal salt solution A to obtain a mixed solution B;

[0067] Step S12: Weigh 49.26 g of 2-methylimidazole and stir and dissolve it in 500 mL of deionized water to obtain a ligand solution C; under magnetic stirring, add the ligand solution C to the mixed solution B, and add 2.5 g of PVP and 0.5 g of NaOH, and terminate the reaction after magnetic stirring at 80 °C for 8 h to obtain a reaction product;

[0068] Step S13: Filter the obtained product by suction and wash it 5 times, and dry it in an oven at 80 °C for 24 h to obtain NiCo-MOF@MPP@PER.

[0069] Step S2: Synthesis of VNiCo-MOF@MPP@PER, specifically including:

[0070] Step S21: Weigh 45 g of NiCo-MOF@MPP@PER and 5.85 g of NH 4 VO 3 Dissolve them in 250 mL of DMF to obtain suspension D;

[0071] Step S22: Transfer suspension D to a high-pressure reactor, react at 120 °C at a rotation speed of 600 rpm for 18 h, and then terminate the reaction to obtain a reaction product;

[0072] Step S23: Wash the reaction product repeatedly with absolute ethanol and deionized water 5 times, and then dry it at 80 °C for 24 h to obtain VNiCo-MOF@MPP@PER.

[0073] Step S3: Preparation of V-Ni-Co / PCN;

[0074] Weigh 40 g of the VNiCo-MOF@MPP@PER composite and grind it into powder in a mortar. Place the powder in a magnetic boat and perform high-temperature heat treatment in a tube furnace. First, heat it to 220 °C at a rate of 5 °C / min under the protection of N 2 , keep it at this temperature for 1.5 h; then heat it to 350 °C at a rate of 7.5 °C / min and keep it at this temperature for 2 h; then heat it to 625 °C at a rate of 10 °C / min and keep it at this temperature for 5 h, and finally cool it naturally to room temperature to obtain the V-Ni-Co / PCN hydrogen storage material.

[0075] Step S4: Preparation of V-Ni-Co / PCN + MgH 2 The preparation specifically includes:

[0076] Step S41: Weigh 25 g of V-Ni-Co / PCN and 12.5 g of magnesium hydride (MgH 2 ), add 75 mL of absolute n-hexane as a dispersion medium, put the mixture into a stainless steel ball milling tank, and select 750 g of steel balls with a mass of 0.1 g and 375 g of steel balls with a mass of 0.5 g as ball milling media;

[0077] Step S42: Ball mill at a speed of 600 rpm in a ball mill for 10 h, pause for 15 min every 1 h to prevent overheating;

[0078] Step S43: After ball milling, transfer the mixture to a vacuum drying oven and dry it at 120 °C for 6 h to ensure that the dispersion medium volatilizes fully, and finally obtain the V-Ni-Co / PCN + MgH 2 hydrogen storage composite material, denoted as V-Ni-Co / PCN + MgH 2 (2:1).

[0079] Example 2: Replace 25 g of V-Ni-Co / PCN in step S41 of Example 1 with 17.5 g of V-Ni-Co / PCN and 12.5 g of MgH 2 Replace with 17.5 g of MgH 2 , and keep other conditions unchanged. The obtained product is denoted as V-Ni-Co / PCN + MgH 2 (1:1).

[0080] Example 3: Replace 25 g of V-Ni-Co / PCN in step S41 of Example 1 with 12.5 g of V-Ni-Co / PCN and 12.5 g of MgH 2 Replace with 25 g of MgH 2 , and keep other conditions unchanged. The obtained product is denoted as V-Ni-Co / PCN + MgH 2 (1:2).

[0081] Comparative Example 1: Use pure MgH 2 as the hydrogen storage material

[0082] Comparative Example 2: Use pure V-Ni-Co / PCN as the hydrogen storage material.

[0083] Structure characterization and performance testing;

[0084] 1. Specific surface area and pore size test analysis;

[0085] Use a Belsorp MAXⅡ analyzer to test the BET surface area and pore structure gas adsorption of the material at -195 °C by the method of N 2 adsorption and desorption. Use the Brunauer-Emmett-Teller (BET) equation to determine the total surface area. The specific surface area and pore volume test results are shown in Table 1.

[0086] Table 1 Specific surface area and pore volume test results

[0087] Sample <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Average pore diameter (nm) V-Ni-Co / PCN 3246.28 1.461 0.67 <![CDATA[V-Ni-Co / PCN+MgH 2 (2:1)]]> 2367.69 1.052 0.66 <![CDATA[V-Ni-Co / PCN+MgH 2 (1:1)]]> 1702.45 0.847 0.68 <![CDATA[V-Ni-Co / PCN+MgH 2 (1:2)]]> 1309.23 0.668 0.67 <![CDATA[MgH 2 > 29.76 - -

[0088] As can be seen from the data in Table 1, the samples of Examples 1 to 3 all have a high specific surface area and pore volume. The specific surface area and pore volume of the sample of Example 1 are 2367.69 m 2 / g and 1.052 cm 3 / g respectively. The samples of Example 2 are 1702.45 m 2 / g and 0.847 cm 3 / g respectively. The samples of Example 3 are 1309.23 m 2 / g and 0.668 cm 3 / g respectively, and with H 2Pores with a molecular dynamic diameter comparable to that of the material. These physical properties provide a structural basis for the high hydrogen storage capacity of the material.

[0089] 2. Hydrogen storage kinetic performance test;

[0090] (1) Variable-temperature hydrogen absorption / desorption performance test: The Sievert-type equipment was used to test the variable-temperature hydrogen absorption / desorption performance of the samples of Examples 1-3, and Comparative Examples 1 and 2. During the hydrogen absorption process, the hydrogen pressure was kept constant at 5 MPa, and the temperature was gradually increased to 350 °C at a rate of 1 °C / min; during the hydrogen desorption process, the hydrogen pressure was kept constant at 0.1 MPa, and the temperature was gradually increased to 400 °C at a rate of 1 °C / min. The changes in temperature and pressure were recorded, and the hydrogen absorption / desorption amount of the samples was calculated using the ideal gas state equation (PV = nRT).

[0091] (2) Constant-temperature hydrogen absorption / desorption performance test: The Sievert-type equipment was used to test the constant-temperature hydrogen absorption / desorption performance of the samples of Examples 1-3, and Comparative Examples 1 and 2. During the hydrogen absorption process, the temperature was kept constant at 175 °C, and high-pressure hydrogen was rapidly charged, and the change in pressure with time was recorded; during the hydrogen desorption process, the temperature was kept constant at 250 °C, and the hydrogen pressure was rapidly reduced, and the change in pressure with time was recorded. The constant-temperature hydrogen absorption / desorption amount of the samples was calculated using the ideal gas state equation (PV = nRT).

[0092] From Figure 1 the results, it can be seen that the V-Ni-Co / PCN+MgH 2 hydrogen storage composite material exhibits excellent performance in terms of hydrogen storage kinetics and thermodynamics. As Figure 1 shown in (c) below, during the hydrogen absorption process, the samples of Examples 1-3 all started to absorb hydrogen at 40 °C, while the initial hydrogen absorption temperature of pure MgH 2 was as high as about 130 °C, which reflects the low-temperature and rapid hydrogen absorption ability of the V-Ni-Co / PCN+MgH 2 hydrogen storage composite material prepared by the present invention. As Figure 1 shown in (d) below, in the constant-temperature hydrogen absorption test, the samples of Examples 1-3 reached 50% of the maximum hydrogen absorption amount within 5 minutes and reached the maximum hydrogen storage capacity within 30 minutes, while the hydrogen absorption mass of pure MgH 2 within 60 minutes was 2.16 wt%. As Figure 1 shown in (a) below, during the hydrogen desorption process, compared with pure MgH 2 , the dehydrogenation start temperatures of the samples of Examples 1-3 were reduced from 310 °C to 152 °C, 161 °C, and 169 °C respectively, while the dehydrogenation start temperature of V-Ni-Co / PCN in Comparative Example 2 was only about 140 °C. As Figure 1 shown in (b) below, in the constant-temperature hydrogen desorption test, the samples of Examples 1-3 almost reached the maximum hydrogen desorption amount within 45 minutes, while pure MgH2 The hydrogen release amount in 60 min is only 0.24 wt%. Generally speaking, compared with pure MgH 2 , the V-Ni-Co / PCN+MgH 2 hydrogen storage composite material prepared by the present invention exhibits excellent properties such as low hydrogen absorption / release temperature, high hydrogen absorption / release rate, and high hydrogen storage capacity.

[0093] 3. Cycling stability test;

[0094] The cycling stability of the samples of Examples 1 to 3, Comparative Examples 1 and 2 was tested using a Sievert-type device. The hydrogen absorption temperature was selected according to the variable temperature performance of each sample, the hydrogen pressure was maintained at 5 MPa, and the mass percentage (wt%) of hydrogen absorption of the material was recorded each time; the hydrogen release temperature was also selected according to the variable temperature performance of each sample, the hydrogen pressure was maintained at 0.1 MPa, and the mass percentage (wt%) of hydrogen release of the material was recorded each time. After hydrogen absorption / release was completed, the residual gas was removed and the next cycle was entered. The hydrogen absorption / release amount of the sample in each cycle was recorded and compared with the initial hydrogen storage amount (the maximum hydrogen absorption amount before cycling), and the hydrogen storage capacity retention rate after each cycle was calculated. The test results of the hydrogen storage capacity (wt%) cycling stability are shown in Table 2, and the calculated hydrogen storage capacity retention rates are shown in Table 3.

[0095] Table 2 Test results of hydrogen storage capacity (wt%) cycling stability

[0096] Sample 1st 5th 10th 20th 40th 80th 100th V-Ni-Co / PCN 6.67 6.65 6.63 6.59 6.57 6.54 6.49 <![CDATA[V-Ni-Co / PCN+MgH 2 (2:1)]]> 7.01 7.00 6.97 6.92 6.89 6.86 6.82 <![CDATA[V-Ni-Co / PCN+MgH 2 (1:1)]]> 7.26 7.25 7.22 7.19 7.14 7.09 7.05 <![CDATA[V-Ni-Co / PCN+MgH 2 (1:2)]]> 7.62 7.64 7.61 7.55 7.50 7.47 7.42 <![CDATA[MgH 2 > 7.61 7.38 7.14 6.69 6.25 5.71 5.28

[0097] Table 3 Hydrogen storage capacity retention rate

[0098] Sample Retention rate of hydrogen storage capacity after 100 cycles (%) V-Ni-Co / PCN 97.3 <![CDATA[V-Ni-Co / PCN+MgH 2 (2:1)]]> 97.3 <![CDATA[V-Ni-Co / PCN+MgH 2 (1:1)]]> 97.1 <![CDATA[V-Ni-Co / PCN+MgH 2 (1:2)]]> 96.9 <![CDATA[MgH 2 > 69.4

[0099] It can be seen from the data in Tables 2 and 3 that the V-Ni-Co / PCN+MgH 2 composite material prepared by the present invention has good cycling stability. The hydrogen storage capacity retention rates of the samples of Examples 1 to 3 reached 97.3%, 97.1%, and 96.9% respectively after 100 cycles, while that of pure MgH 2 in Comparative Example 1 was only about 69.4% after 100 cycles, far lower than that of the composite material. Although the pure V-Ni-Co / PCN in Comparative Example 2 has relatively good cycling stability, its hydrogen storage capacity is low, and the comprehensive hydrogen storage effect is slightly lower than that of the V-Ni-Co / PCN+MgH 2 composite material.

[0100] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, those skilled in the art should understand that various changes made to the present invention in form and detail without departing from the spirit and scope of the present invention defined by the appended claims all fall within the protection scope of the present invention.

Claims

1. A method for preparing a PCN-doped MOF-derived nanoporous hydrogen storage composite material, characterized in that: The following steps are involved: Step S1: Synthesis of NiCo-MOF@MPP@PER, specifically comprising: Step S11: stirring and dissolving Ni(NO3)2·6H2O and Co(NO3)2·6H2O in an organic solvent to obtain a metal salt solution A; adding melamine polyphosphate and pentaerythritol ester to the metal salt solution A to obtain a mixed solution B; Step S12: weighing an organic ligand and stirring and dissolving it in an organic solvent to obtain a ligand solution C; adding the ligand solution C to the mixed solution B under magnetic stirring, and adding a nucleating agent, and terminating the reaction after magnetic stirring to obtain a reaction product; Step S13: The obtained product is filtered and washed, and then dried to obtain NiCo-MOF@MPP@PER; Step S2: Synthesis of VNiCo-MOF@MPP@PER, specifically comprising: Step S21: Weigh NiCo-MOF@MPP@PER and a vanadium source and dissolve them in an organic solvent to obtain a suspension D; Step S22: transferring the suspension D to a high-pressure reactor for reaction to obtain a reaction product; Step S23: The reaction product is repeatedly washed with anhydrous ethanol and deionized water, and then dried to obtain VNiCo-MOF@MPP@PER; Step S3: preparation of V-Ni-Co / PCN; The VNiCo-MOF@MPP@PER composite was weighed and ground into powder in a mortar, and the powder was placed in a magnetic boat and subjected to high-temperature heat treatment in a tube furnace to obtain a V-Ni-Co / PCN hydrogen storage material; Step S4: Preparation of V-Ni-Co / PCN+MgH2, specifically comprising: Step S41: weigh V-Ni-Co / PCN and magnesium hydride, add anhydrous n-hexane as a dispersion medium, put the mixture into a stainless steel ball mill, and select steel balls with a mass of 0.1 to 1 g as ball milling media; Step S42: ball milling in a ball mill; Step S43: After the ball milling is completed, the mixture is transferred to a vacuum drying oven for drying, and finally a V-Ni-Co / PCN+MgH2 hydrogen storage composite material is obtained.

2. The method for preparing the PCN-doped MOF-derived nanoporous hydrogen storage composite material according to claim 1, characterized in that: The specific steps of step S1 are as follows: Step S11: 2.0-30 g Ni(NO3)2·6H2O and 2.0-30 g Co(NO3)2·6H2O are stirred and dissolved in 50-800 mL of an organic solvent to obtain a metal salt solution A; 0-10 g melamine polyphosphate and 0-10 g pentaerythritol ester are added to the metal salt solution A to obtain a mixed solution B; Step S12: weighing 2.0-50 g of an organic ligand and stirring and dissolving it in 50-800 mL of an organic solvent to obtain a ligand solution C; adding the ligand solution C to the mixed solution B under magnetic stirring, and adding 0-5 g of a nucleating agent, and terminating the reaction after magnetic stirring at 60-120° C. for 0.5-24 h to obtain a reaction product; Step S13: The obtained product is filtered and washed 3 to 5 times, and dried in an oven at 80 to 120° C. for 5 to 24 hours to obtain NiCo-MOF@MPP@PER.

3. The method for preparing the PCN-doped MOF-derived nanoporous hydrogen storage composite material according to claim 2, characterized in that: In step S1, the organic ligand is 2-methylimidazole, benzimidazole, terephthalic acid, 2-aminoterephthalic acid or trimesic acid; the organic solvent is methanol, ethanol, DMF, DMAc or deionized water; and the nucleating agent is one or more of polyvinyl pyrrolidone, sodium dodecylbenzene sulfonate, polyvinyl alcohol and sodium hydroxide.

4. The method for preparing the PCN-doped MOF-derived nanoporous hydrogen storage composite material according to claim 1, characterized in that: The specific steps of step S2 are as follows: Step S21: weigh 5-60 g NiCo-MOF@MPP@PER and 0-10 g vanadium source and dissolve them in 50-300 mL organic solvent to obtain a suspension D; Step S22: transferring the suspension D to a high-pressure reactor, reacting at 60-150° C. and 300-1000 rpm for 6-24 hours, and then terminating the reaction to obtain a reaction product; Step S23: The reaction product is repeatedly washed with anhydrous ethanol and deionized water for 3 to 5 times, and dried at 80 to 120° C. for 3 to 24 hours to obtain VNiCo-MOF@MPP@PER.

5. The method for preparing the PCN-doped MOF-derived nanoporous hydrogen storage composite material according to claim 4, characterized in that: In step S2, the vanadium source is one or more of ammonium vanadate, sodium orthovanadate, sodium metavanadate, vanadyl sulfate, vanadium acetylacetonate and vanadyl oxalate; and the organic solvent is methanol, ethanol, DMF, DMAc or deionized water.

6. The method for preparing the PCN-doped MOF-derived nanoporous hydrogen storage composite material according to claim 1, characterized in that: The specific process of step S3 is as follows: Weigh 5-50 g of VNiCo-MOF@MPP@PER composite and grind it into powder in a mortar. Place the powder in a magnetic boat and perform high-temperature heat treatment in a tube furnace. First, heat the mixture to 200-250°C at 5-7.5°C / min under the protection of N2 and keep it for 1-1.5 h. Then heat the mixture to 300-400°C at 7.5-10°C / min and keep it for 2-4 h. Then heat the mixture to 500-680°C at 10-15°C / min and keep it for 4-6 h. Finally, cool the mixture naturally to room temperature to obtain V-Ni-Co / PCN hydrogen storage material.

7. The method for preparing the PCN-doped MOF-derived nanoporous hydrogen storage composite material according to claim 1, characterized in that: The specific steps of step S4 are as follows: Step S41: weigh 0-50 g V-Ni-Co / PCN and 0-50 g magnesium hydride, add 5-100 mL anhydrous n-hexane as a dispersion medium, put the mixture into a stainless steel ball mill, and select steel balls with a mass of 0.1-1 g as ball milling media; Step S42: ball milling at a speed of 300 to 800 rpm for 2 to 12 hours in a ball mill, pausing for 10 to 30 minutes every 0.5 to 2 hours to prevent overheating; Step S43: After the ball milling is completed, the mixture is transferred to a vacuum drying oven and dried at 50-150° C. for 3-24 hours to finally obtain a V-Ni-Co / PCN+MgH2 hydrogen storage composite material.

8. The method for preparing the PCN-doped MOF-derived nanoporous hydrogen storage composite material according to claim 7, characterized in that: In the step S41, the mass ratio of the sample to the ball milling medium is 1:10-50, and the sample is V-Ni-Co / PCN and MgH2. 9 . The PCN-doped MOF-derived nanoporous hydrogen storage composite material obtained according to the method for preparing the PCN-doped MOF-derived nanoporous hydrogen storage composite material according to any one of claims 1 to 8 .

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