MgH2-ZrO2-VN-coated PC composite hydrogen storage material as well as preparation method and application thereof

Abstract

The invention relates to the field of new energy hydrogen storage materials, in particular to an MgH2-ZrO2-VN-coated PC composite hydrogen storage material and a preparation method thereof. The composite hydrogen storage material comprises MgH2 and a ZrO2-VN-coated PC catalyst, the total mass of the MgH2-ZrO2-VN-coated PC composite hydrogen storage material is 100%, and the addition amount of ZrO2-VN-coated PC is 2%-10%. The preparation method comprises the following steps: step 1, preparing MgH2 with the mass fraction of 90%-98% and a ZrO2-VN-coated PC catalyst with the mass fraction of 2%-10%; and step 2, mixing and ball-milling the MgH2-ZrO2 and the VN-coated PC to obtain the MgH2-ZrO2-VN-coated PC composite hydrogen storage material. By implementing the scheme, the hydrogen storage performance of MgH2 and the safety in the preparation process are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy hydrogen storage materials, in particular to a MgH2-ZrO2-VN@PC composite hydrogen storage material, a preparation method and applications thereof. BACKGROUND

[0002] Energy transformation is undergoing a historic change from traditional fossil energy to clean and low-carbon energy system. Hydrogen energy, as a clean, efficient and sustainable energy carrier, is gradually becoming the focus of the energy field. However, due to the lack of safe and efficient storage and transportation technology, the proportion of hydrogen as an energy source is very low (less than 3%), and the strategic promotion of hydrogen energy is extremely difficult. Compared with traditional high-pressure gaseous and low-temperature liquid hydrogen storage methods, solid-state hydrogen storage has attracted widespread attention in recent years due to its high hydrogen storage density, good safety performance, and wide application scenarios, and is considered as one of the most promising hydrogen storage and transportation technologies.

[0003] Among the many solid-state hydrogen storage materials, magnesium hydride (MgH2) has the advantages of high hydrogen storage density (the theoretical mass hydrogen storage density and volume hydrogen storage density can reach 7.6 wt% and 110 g / L, respectively), abundant resources (more than 85% of global magnesium resources are in China), low cost (about 60% lower than rare earth-based materials), safety and environmental friendliness, and has shown great potential in large-scale and long-distance hydrogen transportation applications, and has received widespread attention from the domestic and foreign markets.

[0004] However, MgH2 also has problems such as high hydrogen absorption and desorption temperature and poor kinetics, which hinder its practical application. Currently, researchers have developed alloying, nanocrystallization, and doping catalysts to improve the hydrogen storage performance of MgH2.

[0005] Doping catalysts can effectively reduce the hydrogen absorption and desorption temperature of Mg / MgH2 and improve the hydrogen absorption and desorption rate, and is a simple and efficient modification method.

[0006] There are many methods for improving the hydrogen storage performance of MgH2 by doping catalysts in the prior art. For example, prior art 1 (Lu ZY, Yu HJ, Lu X, et al. Two-dimensional vanadium nanosheets as a remarkably effective catalyst for hydrogen storage in MgH2[J]. Rare Metals, 2021, 40(11): 3195-3204. doi.org / 10.1007 / s12598-021-01764-7) uses vanadium nanosheets (V NS) and MgH2 mixed ball milling to prepare a MgH2-VNS composite hydrogen storage material, which starts to release hydrogen at 187.2°C, can release 6.3 wt% of H2 within 10 min at 300°C, and the completely dehydrogenated sample can absorb hydrogen at room temperature and 3.2 MPa hydrogen pressure, effectively improving the hydrogen storage performance of MgH2. However, this technology has the following problems: 1. The ductility of vanadium metal is strong, and it is difficult to be effectively refined when mixed with MgH2 ball milling, resulting in coarse particles and uneven distribution; 2. The effective active area of vanadium metal is insufficient, and the ability to catalyze the dissociation of Mg-H / H-H bond is limited, so the hydrogen absorption and release rate of MgH2 is still slow.

[0007] For example, prior art 2 (Chen M, Xiao X, Wang X, et al. Self-templated carbon enhancing catalytic effect of ZrO2 nanoparticles on the excellent dehydrogenation kinetics of MgH2[J]. Carbon, 2020, 166: 46-55. doi.org / 10.1016 / j.carbon.2020.05.025) provides a technology of carbon-coated nano-ZrO2 (ZrO2 / C) modified MgH2, and the initial dehydrogenation temperature of the obtained MgH2-ZrO2 / C composite material is reduced by 101°C compared with pure MgH2, and can release 5.38 wt% of H2 within 70 min at 235°C. Obviously, doping ZrO2 / C can significantly reduce the dehydrogenation temperature of MgH2 and improve the hydrogen release kinetics. However, this technology still has the following technical problems: 1. The dehydrogenation activation energy of ZrO2 / C modified MgH2 is still higher than 100 kJ / mol, and the low-temperature dehydrogenation rate of MgH2-ZrO2 / C composite material is slow; 2. ZrO2 catalyst shows obvious agglomeration after 19 cycles, and the cycle uniformity and stability need to be improved.

[0008] For example, prior art 3 (Hong F F, Shi W T, Zhao R L, et al. Improvement in hydrogen storage performance of MgH2by vanadium doped with ZIF-8 derived asingle-atom catalyst V-N-C[J]. Rare Metals, 2024, 43(6): 2623-2635. doi.org / 10.1007 / s12598-024-02639-3) uses vanadium-doped ZIF-8 as a precursor to prepare a single-atom catalyst V-N-C, which has a good promoting effect on the hydrogen storage performance of MgH2. The obtained MgH2-V-N-C can absorb 5.92 wt% of H2 in 50 min at 150°C, and the capacity retention rate after 30 cycles is 99.1%. The in-situ formed VN and metal V are uniformly dispersed in the matrix, which plays an important role in improving the hydrogen storage performance of MgH2. However, this technology has the following problems: 1. 2-methyl imidazole used in the preparation process belongs to 2B carcinogens, and zinc nitrate is an explosive hazardous chemical, and the carbonization temperature of V(acac)3@ZIF-8 is as high as 960°C, which limits the application range of this technology; 2. The catalytic active sites in the MgH2+V-N-C composite system are relatively single, and the hydrogen absorption and desorption temperature of MgH2 is still high.

[0009] For example, prior art 4 (Wu J, Liu Z, Zhang H, et al. Hydrogen storage performance of MgH2under catalysis by highly dispersed nickel-nanoparticle-doped hollow spherical vanadium nitride[J]. Journal of Magnesium and Alloys, 2024, 12(12): 5132-5143. doi.org / 10.1016 / j.jma.2023.11.010) prepares a Ni / VN catalyst by solvothermal + calcination (600°C) method. The dehydrogenation activation energy of the obtained MgH2-Ni / VN composite material is reduced by 35.4% compared with pure MgH2, and it can absorb about 6.0 wt% of hydrogen in 5 min at 150°C, showing excellent hydrogen absorption and desorption kinetics. However, this technology has the following problems: 1. The oxalic acid and concentrated nitric acid used in the preparation process are not conducive to environmental protection; 2. The dispersion of Ni / VN in MgH2 is poor, which is not conducive to the stability of long cycle process.

[0010] Therefore, it is necessary to design a hydrogen storage material with improved hydrogen storage performance of MgH2 and high safety and a method thereof. SUMMARY

[0011] One of the purposes of the present application is to provide a MgH2-ZrO2-VN@PC composite hydrogen storage material to improve the hydrogen storage performance of MgH2 and reduce pollution to the environment.

[0012] To achieve the above purpose, the present application adopts the following technical solution: a MgH2-ZrO2-VN@PC composite hydrogen storage material, comprising MgH2 and ZrO2-VN@PC catalyst, wherein the total mass of the MgH2-ZrO2-VN@PC composite hydrogen storage material is 100%, and the addition amount of the ZrO2-VN@PC is 2%-10%. Preferably, as an improvement, the addition amount of the ZrO2-VN@PC catalyst is 6%.

[0013] Preferably, as an improvement, the mass ratio of ZrO2 and VN is (0.21-1.90):1, and if it is greater than or less than this range, the synergistic effect between ZrO2 and VN will be affected, thereby causing the hydrogen storage performance of the MgH2-ZrO2-VN@PC composite hydrogen storage material to decrease. Preferably, the mass ratio of the two is 0.813:1.

[0014] Preferably, as an improvement, the synthesis process of the ZrO2-VN@PC comprises the following steps: S1. Solution A configuration: dissolving a carbon source, urea and a salt in deionized water at room temperature to obtain a uniform solution A; S2. Solution B configuration: dissolving a vanadium source in deionized water to obtain solution B; S3. Solution C configuration: dissolving a zirconium source in deionized water at room temperature to obtain solution C; S4. Solution mixing: under the action of magnetic stirring, solution C and solution A are sequentially added dropwise to solution B, and the mixture is uniformly mixed to obtain a mixed solution; S5. Water removal and calcination: the mixed solution is freeze-dried to obtain a yellow powder, and the yellow powder is calcined in an ammonia atmosphere at 680-800°C for 1-2 h to obtain a black powder; S6. Water etching: deionized water is added to the black powder and stirred at room temperature for 0.5-2 h, and then suction filtration and drying at 50-70°C for 5-10 h are performed to obtain the ZrO2-VN@PC catalyst.

[0015] Preferably, as an improvement, in S4, the molar ratio of Zr and V in the mixed solution is (1-5):(5-9).

[0016] Preferably, as an improvement, the mass fraction of each raw material in the ZrO2-VN@PC catalyst is: 3-4 parts of carbon source, 1-3 parts of urea, 2-3 parts of salt, 2-3 parts of vanadium source, and 2-3 parts of zirconium source.

[0017] Preferably, as an improvement, the vanadium source is ammonium metavanadate, the zirconium source is zirconium tetrachloride, the carbon source is glucose, and the salt is sodium chloride.

[0018] The second object of the present application is to provide a preparation method of MgH2-ZrO2-VN@PC composite hydrogen storage material, so as to obtain a hydrogen storage material with good hydrogen storage performance, and avoid environmental pollution and safety hazards during preparation.

[0019] The principle and advantages of the present scheme are: in practical application,

[0020] 1. In the present scheme, inexpensive sodium chloride and glucose are used as etching templates and carbon sources, respectively, and pure water is used as an etchant. For the first time, nano-ZrO2 (zirconium oxide) (average size 10 nm) and nano-VN (vanadium nitride) (average size 28 nm) are uniformly loaded on porous carbon in different size forms, and a ZrO2-VN@PC uniformly modified MgH2 composite hydrogen storage material is obtained. The sodium chloride, glucose, urea, ammonium metavanadate, and zirconium tetrachloride used in the present scheme are all common industrial raw materials, which are widely available and have low pollution, and are suitable for industrial development. The introduction of ZrO2-VN@PC can construct a high-efficiency hydrogen storage system for MgH2, which is wrapped by nano-VN, nano-ZrO2, a small amount of low-valence V / Zr-based substances, and a carbon layer, and has multiple scales and multiple active sites. The present scheme proposes a V and Zr dual-metal site synergistic enhancement effect, breaks through the limitations of single-metal catalysts in the dissociation and recombination process of H-H bond / Mg-H bond, and realizes the optimization of the whole process of Mg / MgH2 hydrogen absorption and desorption reaction.

[0021] 2、The MgH2-ZrO2-VN@PC composite hydrogen storage material obtained by the scheme has excellent hydrogen storage performance. The initial hydrogen release temperature is reduced from 305°C of pure MgH2 to 209°C. At 300°C, 6.3 wt% of H2 can be released within 5 min, and at a lower temperature of 200°C, 5.4 wt% of H2 can also be released. In terms of hydrogen absorption, the dehydrogenated MgH2-ZrO2-VN@PC can absorb 5.6 wt% of H2 within 10 min at 175°C, and even at 75°C, it can complete the hydrogen absorption capacity of 3.8 wt% within 60 min. The MgH2-ZrO2-VN@PC composite hydrogen storage material exhibits more excellent hydrogen storage performance than pure MgH2, single metal V / Zr-based catalysts, and pure carbon modified MgH2. It can be seen that the porous carbon supported V and Zr-based bimetallic catalysts play a synergistic enhancement role in improving the hydrogen storage performance of MgH2.

[0022] 3、Environmentally friendly and safe preparation process: The scheme selects carbon source, urea and salt as raw materials. Such raw materials are all conventional chemical products, without carcinogenic, easily explosive and strong corrosive risks. Compared with 2-methyl imidazole (2B carcinogen) and zinc nitrate (easily explosive) of the prior art 3, and oxalic acid and concentrated nitric acid (strongly corrosive) of the prior art 4, the scheme has higher safety and smaller negative impact on the environment, and is more suitable for green production and industrial application requirements.

[0023] 4、During the synthesis of ZrO2-VN@PC, the calcination temperature is controlled at 680-800°C. If it is too low, the V source cannot be nitrided, and V-based oxides will be left. If it is too high, not only will the catalyst particles agglomerate, but also ZrO2 will be partially or completely nitrided. Within this temperature range, selective nitridation can be achieved, so that a heterogeneous composite catalyst coexisting with Zr-based oxides and V-based nitrides can be prepared, and the synergistic effect of ZrO2 and VN in the hydrogen dissociation and diffusion process can significantly improve the hydrogen absorption and desorption performance of MgH2.

[0024] 5、The scheme can effectively improve the performance of MgH2-ZrO2-VN@PC composite hydrogen storage material by precisely controlling the molar ratio range of Zr and V to make better synergistic cooperation between ZrO2 and VN. VN as a strong dissociation site can reduce the dissociation energy barrier of H2 molecules, greatly reducing the difficulty of hydrogen absorption of the material, thus playing an important catalytic role, and its molar ratio is 50%-90%. ZrO2 can be uniformly distributed on the surface of Mg / MgH2 substrate in smaller size, providing more active area and more active interface for hydrogen dissociation and diffusion, which helps the rapid diffusion of H atoms in the hydrogen absorption and release process, but its dissociation ability is weaker than VN, so the molar ratio is 10%-50%. Therefore, if the molar ratio of Zr and V is greater than or less than the range, the synergistic effect between ZrO2 and VN will be affected, and the hydrogen storage performance of MgH2-ZrO2-VIN@PC composite hydrogen storage material will decrease. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The XRD spectrum of ZrO2-VN@PC of the present embodiment.

[0026] Figure 2 The SEM spectrum of ZrO2-VN@PC of the present embodiment.

[0027] Figure 3 The SEM spectrum of ball-milled MgH2-ZrO2-VN@PC composite hydrogen storage material of the present embodiment.

[0028] Figure 4 The non-isothermal dehydrogenation curve comparison chart.

[0029] Figure 5 The hydrogen release curve comparison chart under isothermal (275°C) conditions.

[0030] Figure 6 The hydrogen absorption curve comparison chart under isothermal (125°C) conditions.

[0031] Figure 7 MgH2-ZrO2-VN@PC 31st hydrogen absorption curve.

[0032] Figure 8 The TEM-EDS spectrum of the cyclic MgH2-ZrO2-VN@PC composite hydrogen storage material. DETAILED DESCRIPTION

[0033] The following will be further described in detail through specific embodiments: Example 1 The MgH2-ZrO2-VN@PC composite hydrogen storage material comprises MgH2 and a ZrO2-VN@PC catalyst, wherein the total mass of the MgH2-ZrO2-VN@PC composite hydrogen storage material is 100%, and the addition amount of the ZrO2-VN@PC catalyst is 2%.

[0034] The synthesis process of the ZrO2-VN@PC catalyst is as follows: S1. Preparation of aqueous solution A: 0.4 g of a carbon source, 0.2 g of urea and 2.5 g of a salt are dissolved in 10 mL of deionized water at room temperature to obtain a uniform solution A; wherein the carbon source is one of glucose, sucrose and citric acid, and the salt is one of sodium chloride, potassium chloride, calcium chloride and magnesium chloride, and the embodiment preferably uses sodium chloride.

[0035] S2. Preparation of aqueous solution B: 0.25 g of ammonium metavanadate is dissolved in 10 mL of deionized water at 75°C to obtain solution B; wherein the vanadium source is one of ammonium metavanadate, sodium metavanadate, vanadium trichloride and vanadyl sulfate, and the embodiment preferably uses ammonium metavanadate.

[0036] S3. Preparation of aqueous solution C: 0.21 g of zirconium tetrachloride (ZrCl4) is dissolved in 5 mL of deionized water at room temperature to obtain solution C; wherein the zirconium source is one of zirconium tetrachloride, zirconium oxychloride octahydrate, zirconium sulfate tetrahydrate and zirconium acetate, and the embodiment preferably uses zirconium tetrachloride.

[0037] S4. Mixing of solutions: under the action of magnetic stirring, solution C and solution A are added dropwise to solution B in sequence, stirred for 10-20 min, and then ultrasonically treated for 2-5 min to obtain a mixed solution, wherein the molar ratio of Zr to V is (1-5):(5-9), specifically 1:9, 2:8, 3:7, 4:6 or 5:5, and the embodiment preferably uses 3:7. S5. Water removal and calcination: the mixed solution is freeze-dried at -40°C for 35-48 h to obtain a yellow powder, and the yellow powder is calcined at 750°C in an ammonia atmosphere for 1-2 h to obtain a black powder; S6. Water etching: 100-200 mL of deionized water is added to the above black powder and stirred at room temperature for 0.5-2 h, and then suction filtration and drying at 50-70°C for 5-10 h are performed to obtain a porous carbon-supported nano ZrO2-VN catalyst.

[0038] The preparation method of the MgH2-ZrO2-VN@PC composite hydrogen storage material comprises the following steps: Step 1: ZrO2-VN@PC and MgH2 are weighed in an argon-filled glove box, and the mass ratio of ZrO2-VN@PC to MgH2 is 2%:98%; Step 2, mix and ball mill to obtain MgH2-ZrO2-VN@PC composite hydrogen storage material.

[0039] Specifically, the weighed powder is placed in a stainless steel ball mill tank equipped with stainless steel grinding balls in a glove box, the volume of the ball mill tank is 100 mL, the mass ratio of grinding ball and grinding material is 30:1. The diameter of the grinding ball meets three types of 6 mm, 8 mm and 10 mm; The prepared ball mill tank is taken out of the glove box and installed on a planetary ball mill for ball milling. The rotation speed of the ball mill is 400 rpm, the ball milling mode is forward ball milling for 10 min, then pause for 10 min, and then reverse ball milling for 10 min, and the cycle is repeated, and the MgH2-ZrO2-VN@PC composite hydrogen storage material is obtained after ball milling for 6-12 h.

[0040] Example 2 Different from example 1 is that the addition amount of ZrO2-VN@PC catalyst is 6%; Example 3 Different from example 1 is that the addition amount of ZrO2-VN@PC catalyst is 10%; Comparative example 1 Different from example 1 is that the ZrO2-VN@PC catalyst is not added (i.e. the addition amount of ZrO2-VN@PC is 0%); Comparative example 2 Different from example 1 is that the synthesis process of ZrO2-VN@PC does not contain ammonium metavanadate and zirconium tetrachloride, and the obtained material is named PC, and the prepared composite hydrogen storage material is named MgH2-PC.

[0041] Comparative example 3 Different from example 1 is that the synthesis process of ZrO2-VN@PC does not contain ammonium metavanadate, and the obtained material is named ZrO2@PC, and the prepared composite hydrogen storage material is named MgH2-ZrO2@PC.

[0042] Comparative example 4 Different from example 1 is that the synthesis process of ZrO2-VN@PC does not contain zirconium tetrachloride, and the obtained material is named VN@PC, and the prepared composite hydrogen storage material is named MgH2-VN@PC.

[0043] Comparative example 5 Different from example 1 is that the addition amount of ZrO2-VN@PC is 13%.

[0044] Experiment I. ZrO2-VN@PC catalyst ZrO2-VN@PC were tested by XRD and SEM, and the test results are shown in Figure 1 and Figure 2 The XRD results show that ZrO2 and VN phases are contained in ZrO2-VN@PC. The SEM results show that ZrO2-VN@PC presents a porous structure.

[0045] II. MgH2-ZrO2-VN@PC composite hydrogen storage material In order to prove the microstructure characteristics of MgH2-ZrO2-VN@PC composite hydrogen storage material, SEM test was carried out. The test results shown in Figure 3 indicate that MgH2-ZrO2-VN@PC composite hydrogen storage material is a powder made of irregular particles of different sizes.

[0046] In order to prove the influence of ZrO2-VN@PC on the hydrogen storage performance of MgH2, performance test experiment was carried out on MgH2-ZrO2-VN@PC composite hydrogen storage material, and the performance test referred to GB / T 33291-2016 Hydrogen Storage Alloy Reversible Hydrogen Absorption / Desorption Pressure-Composition- Isothermal Line (P-C-T) Test Method.

[0047]

[0048] Table 1 1. Non-isothermal hydrogen desorption test and isothermal hydrogen absorption / desorption test The test results are shown in Table 1 and Figure 4 The initial hydrogen desorption temperature of MgH2-ZrO2-VN@PC of Example 2 is 209°C, which is reduced by 96°C, 72°C, 37°C and 17°C compared with ball-milled MgH2 of Comparative Example 1, MgH2-PC of Comparative Example 2, MgH2-ZrO2@PC of Comparative Example 3 and MgH2-VN@PC of Comparative Example 4 respectively. This indicates that ZrO2-VN@PC can significantly reduce the hydrogen desorption temperature of MgH2, and the effect is better than that of porous carbon and single metal V / Zr-based catalyst, further confirming the synergistic enhancement of V and Zr bimetallic sites.

[0049] 2. Isothermal hydrogen absorption / desorption test The test results are shown in Figure 5 , Figure 6As shown in Table 1, the MgH2-ZrO2-VN@PC composite hydrogen storage material of Example 2 can release 4.60 wt% of H2 within 5 min at 275°C, and the dehydrogenated sample can absorb 5.70 wt% of H2 within 30 min at 125°C. The average hydrogen release rate of MgH2-ZrO2-VN@PC at 275°C and the average hydrogen absorption rate at 125°C are both significantly better than those of the ball-milled MgH2 and Comparative Examples 2, 3 and 4. This result shows that ZrO2-VN@PC has a significant effect on improving the hydrogen absorption and desorption kinetics of MgH2.

[0050] 3. Cycle performance test In order to prove the cycle performance of MgH2-ZrO2-VN@PC, it was subjected to 31 cycles of hydrogen absorption and desorption at 300°C, and the hydrogen absorption curve of the 31st cycle is shown in Figure 7 The results show that MgH2-ZrO2-VN@PC can store 6.31 wt% of H2 after 31 cycles, and the capacity retention rate can reach 97.4%.

[0051] 4. Dispersion test of ZrO2-VN@PC in MgH2 In order to prove the dispersion of ZrO2-VN@PC in MgH2, TEM and EDS analysis were performed on the MgH2-ZrO2-VN@PC composite hydrogen storage material after 31 cycles, and the results are shown in Figure 8 The results show that the elements Zr and V are still uniformly distributed in the matrix after cycling, which is an important reason for the stability of the cycle performance of the MgH2-ZrO2-VN@PC composite hydrogen storage material.

[0052] The above is only an embodiment of the present application, and well-known specific technical solutions and / or properties in the scheme are not described in detail. It should be noted that, for those skilled in the art, without departing from the technical solutions of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect and practicality of the patent. The protection scope claimed in this application should be subject to the content of its claims, and the specific embodiments described in the specification can be used to explain the content of the claims.

Claims

1. A MgH2-ZrO2-VN@PC composite hydrogen storage material, characterized in that: The ZrO2-VN@PC catalyst is added in an amount of 6%. 2.The MgH 2-ZrO 2-VN@PC composite hydrogen storage material according to claim 1, characterized in that: The mass ratio of ZrO2 and VN in the ZrO2-VN@PC catalyst is (0.21 – 1.90):

1.

3. The MgH2-ZrO2-VN@PC composite hydrogen storage material according to claim 1, characterized in that: The synthesis process of the ZrO2-VN@PC catalyst comprises the following steps: 4.The MgH 2 -ZrO 2 -VN@PC composite hydrogen storage material according to any one of claims 1-3, characterized in that: S1. Preparation of solution A: Dissolve a carbon source, urea and a salt in deionized water at room temperature to obtain a uniform solution A; S2. Preparation of solution B: Dissolve a vanadium source in deionized water to obtain solution B; S3. Preparation of solution C: Dissolve a zirconium source in deionized water at room temperature to obtain solution C; S4. Mixing of solutions: Under the action of magnetic stirring, solution C and solution A are added dropwise to solution B in sequence, and the mixture is uniformly mixed to obtain a mixed solution; S5. Water removal and calcination: freeze-dry the mixed solution to obtain a yellow powder, and calcine the yellow powder in an ammonia atmosphere at 680-800°C for 1-2 h to obtain a black powder; S6. Water etching: add deionized water to the black powder and stir at room temperature for 0.5-2 h, then perform suction filtration and dry at 50-70°C for 5-10 h to obtain the ZrO2-VN@PC catalyst. In S4, the molar ratio of Zr to V in the mixed solution is (1-5):(5-9). 5.The MgH 2 -ZrO 2 -VN@PC composite hydrogen storage material of claim 4, characterized in that: The mass fractions of the raw materials in the ZrO2-VN@PC catalyst are as follows: 3-4 parts of a carbon source, 1-3 parts of urea, 2-3 parts of a salt, 2-3 parts of a vanadium source, and 2-3 parts of a zirconium source.

6. The MgH2-ZrO2-VN@PC composite hydrogen storage material according to claim 4, characterized in that The vanadium source is ammonium metavanadate, the zirconium source is zirconium tetrachloride, the carbon source is glucose, and the salt is sodium chloride. 7.The MgH 2 -ZrO 2 -VN@PC composite hydrogen storage material of claim 6, characterized in that: The method comprises the following steps:

8. A method for preparing MgH2-ZrO2-VN@PC composite hydrogen storage material, characterized in that: Step 1. Prepare 90%-98% by mass of MgH2 and 2%-10% by mass of the ZrO2-VN@PC catalyst; Step 2. Mix and ball mill the two to obtain the MgH2-ZrO2-VN@PC composite hydrogen storage material. In step 2, the ball milling speed is 400 rpm, the ball milling time is 6-12 h, and the ball milling mode is forward ball milling for 10 min, pausing for 10 min, and then reverse ball milling for 10 min.

9. The preparation method of the MgH2-ZrO2-VN@PC composite hydrogen storage material according to claim 8, characterized in that: The MgH2-ZrO2-VN@PC composite hydrogen storage material according to any one of claims 1-3 and 5-7 is applied to magnesium-based solid-state hydrogen storage.

10. The use of MgH2-ZrO2-VN@PC composite hydrogen storage material, characterized in that: ​

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