Vanadium oxide catalytic magnesium-based hydrogen storage material based on alkali metal enhancement and preparation method

Abstract

The invention relates to the technical field of hydrogen energy, and provides a vanadium oxide catalytic magnesium-based hydrogen storage material based on alkali metal enhancement and a preparation method. The material is prepared from spherical MgH2 powder and lamellar XV6O15 (at) C powder through a high-energy ball milling method, wherein X is one of alkali metals Li, Na and K. The material has a nanoscale composite structure, and the hydrogen storage performance can be remarkably improved. The preparation method comprises the following steps: 1) preparing XV6O15 (at) C nano powder through acid etching, alkali metal modification and heat treatment; and 2) mixing the powder with MgH2 in a protective atmosphere, and preparing the composite material by adopting high-energy ball milling. Results show that the catalyst improves the hydrogen absorption and desorption rate of MgH2, the hydrogen storage temperature is reduced to 50 DEG C for hydrogen absorption, and the hydrogen is rapidly desorbed at 200-225 DEG C. The hydrogen storage dynamics and temperature performance are remarkably optimized, an effective strategy is provided for design and application of a novel magnesium-based composite hydrogen storage material, and the method is suitable for hydrogen energy industrial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen energy, and in particular relates to an alkali metal-enhanced vanadium oxide-catalyzed magnesium-based hydrogen storage material and a preparation method thereof. Background Art

[0002] With the intensification of the global energy crisis and the increasing severity of environmental problems, finding a new and clean energy has become an urgent need in the global energy field. As a zero-carbon fuel, hydrogen has the advantages of high energy density (142MJ kg-1) and only produces water after combustion. It is considered to be an ideal choice to replace traditional fossil fuels. Hydrogen is not only environmentally friendly, green and pollution-free, but can also be used as a storage carrier for renewable energy, especially when combined with unstable energy such as wind energy and tidal energy to achieve more efficient energy conversion and storage. However, the efficient and safe storage of hydrogen remains the main challenge facing the industrialization of hydrogen energy.

[0003] Hydrogen storage technologies can be divided into three categories: solid-state hydrogen storage, low-temperature liquid hydrogen storage, and high-pressure gaseous hydrogen storage. Among them, solid-state hydrogen storage technology has become one of the most popular hydrogen storage technologies due to its high hydrogen storage density, good safety, and high recyclability. At present, solid-state hydrogen storage materials mainly include physical adsorption materials, metal hydrides, coordination hydrides, etc. Magnesium-based hydride (MgH2), as a solid-state hydrogen storage material with great potential, is considered to be one of the most promising hydrogen storage materials due to its high hydrogen storage density (theoretical value is 7.6wt%) and rich resource background. However, the slow kinetics and high dehydrogenation temperature of MgH2 in practical applications limit its widespread application. Therefore, how to improve the hydrogen absorption and desorption kinetics of MgH2 and reduce its dehydrogenation temperature has become a hot topic in current research. Summary of the invention

[0004] In view of this, in order to solve the problems of high temperature and slow kinetics of hydrogen absorption and desorption of MgH2, the present invention proposes a magnesium-based hydrogen storage material catalyzed by alkali metal-enhanced vanadium oxide and a preparation method thereof.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A magnesium-based hydrogen storage material based on alkali metal-enhanced vanadium oxide catalyst, which is composed of spherical MgH2 powder and lamellar XV6O 15 @C powder is prepared by high-energy ball milling, where X is one of Li, Na, and K, and the surface of MgH2 is uniformly coated with XV6O 15 @C, forming a nanoscale composite structure.

[0007] Furthermore, the particle size of the spherical MgH2 powder used is less than 50 μm; the lamellar XV6O 15@C powder is a micron sheet with a diameter of 50 to 100 μm, each of which is composed of a large number of nanorods; spherical MgH2 powder and lamellar XV6O 15 The mass fraction ratio of @C powder is 94:6, and the solid magnesium-based hydrogen storage material MgH2-XV6O formed after ball milling 15 The average particle size of @C is 100-500nm, and the surface of each MgH2 particle is coated with XV6O 15 @C. The nanostructure of the raw material particles is conducive to good mixing and coating of the materials during the ball milling process, promoting the improvement of material performance.

[0008] A method for preparing the above-mentioned alkali metal-enhanced vanadium oxide-catalyzed magnesium-based hydrogen storage material comprises the following steps:

[0009] (1) Synthesis of lamellar XV6O 15 @CNanomaterial powder;

[0010] (2) XV6O 15 @C powder was mixed with MgH2 powder and ball milled to obtain solid magnesium-based hydrogen storage material MgH2-XV6O 15 @C.

[0011] Furthermore, in step (1), XV6O 15 The synthesis method of @C powder comprises the following steps:

[0012] A. First, V2AlC MAX was etched with a mixed acid of HCl and HF to prepare V2C MXene: 30 ml HF and 20 ml HCl were added to the polytetrafluoroethylene liner in sequence to prepare the mixed acid;

[0013] B. In an ice bath, slowly add 2 g of V2C to the acid mixture and stir at 55 °C for 2 days. After etching, centrifuge the mixture at 6000 rpm for 5 min.

[0014] C. Wash the precipitate with clean water, centrifuge at 12000 rpm for 5 min and wash 3 times until the pH reaches (6-7) to obtain a black precipitate;

[0015] D. In order to obtain few-layer V2C MXene, 25 ml of 5% TBAOH solution was added to the black precipitate, stirred at room temperature for 24 h, and then centrifuged at 10,000 rpm for 5 min. The obtained precipitate was washed twice with ethanol until the pH was neutral; then, 150 ml of deionized water was added to the precipitate and shaken to obtain a black mixture; the black mixture was ultrasonicated for 1 h under argon protection and ice bath conditions, and then the liquid was centrifuged at 3,500 rpm for 30 min, and the upper liquid was freeze-dried for 48 h to obtain few-layer V2C MXene;

[0016] E. Add 90 mg of V2CMXene to 38 ml of deionized water and ultrasonicate for 20 min under ice bath conditions to uniformly disperse V2C in deionized water; add 5 ml of hydrazine hydrate and 5 ml of 2.5 M XOH solution to the dispersion in sequence, and then stir the mixture in a water bath at 80 ° C for 6 h at a speed of 500 rpm; then, centrifuge the reacted solution at a speed of 5000 rpm for 5 min, and wash the obtained precipitate with deionized water at a speed of 5000 rpm for 5 min three times until the black powder and pH are neutral; then, freeze-dry the precipitate for 48 h to obtain X-ion-modified V2C MXene; transfer the X-ion-modified V2CMXene to a tubular furnace and heat it at 5 ° C·min in a CO2 atmosphere. -1 The temperature was raised to 400 °C and kept at this temperature for 15 h, with a gas flow rate of 250 sccm. The final powder obtained was XV6O 15 @CNanorods.

[0017] Further, in step (2), XV6O 15 The ball milling method of @C powder and MgH2 powder is as follows: under a protective atmosphere, the ball milling beads used are stainless steel balls, wherein MgH2 and XV6O 15 The mass fraction ratio of @C is 94:6, the ball-to-material ratio is 40:1, the ball milling speed is 400rpm, and the effective ball milling time is 12h.

[0018] Furthermore, during the ball milling process, the method of running for 10 minutes and stopping for 10 minutes was adopted to avoid overheating during the ball milling process.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention proposes a magnesium-based hydrogen storage material based on alkali metal-enhanced vanadium oxide catalysis. The catalytic performance of vanadium oxide is not only related to the oxidation state of vanadium, but also affected by its crystal structure and surface active sites. In this process, the incorporation of alkali metals can effectively regulate the oxidation state of vanadium and its catalytic performance. Alkali metal ions (Li + , Na+, K + ) has a strong electron donation ability, which can effectively change the electron density of vanadium oxide, making it play a more significant catalytic role in hydrogenation / dehydrogenation reactions. By regulating the oxidation state and catalytic performance of vanadium, the hydrogen storage performance of MgH2 can be significantly improved.

[0021] 2. The high-energy ball milling method mixes powders of different materials and forms nano-scale particles under long-term grinding, thereby enhancing the surface activity of the materials, shortening the diffusion path of hydrogen atoms, and thus improving the hydrogen storage performance. At the same time, the high-energy ball milling method can also stimulate chemical reactions, using mechanical energy to promote structural changes in raw materials, and generate new active composites to further improve their hydrogen storage performance. The present invention uses the high-energy ball milling method to add a single crystal alkali metal-enhanced vanadium oxide catalyst to MgH2 to form V 2+ / V 3+ Alkali metal ions are added to the interface to stimulate V 2+ / V 3+ The catalytic activity of the interface. 15 @C nanorods were in-situ reduced to generate XVO2, VO, V2O3 and C, which significantly improved the hydrogen absorption and desorption rate of MgH2, and obtained a composite hydrogen storage material with excellent low-temperature hydrogen storage performance, that is, hydrogen absorption was achieved under low temperature conditions (50°C), and rapid hydrogen desorption kinetics was achieved at lower hydrogen desorption temperatures (e.g. 200, 225°C). At the same time, the hydrogen absorption kinetics and the total amount of hydrogen absorption and desorption were optimized and improved. This provides an effective strategy for the design of new magnesium-based composite hydrogen storage materials.

[0022] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0024] Figure 1 For the preparation of NaV6O 15 @C X-ray diffraction (XRD) and XPS spectra of catalyst.

[0025] Figure 2 NaV6O 15 @C SEM, TEM, HRTEM, SAED and EDS spectra of nanorods.

[0026] Figure 3 MgH2-V2O5@C and MgH2-NaV6O 15 @C isothermal dehydrogenation / hydrogen absorption kinetic curve.

[0027] Figure 4 MgH2-NaV6O 15@C isothermal dehydrogenation / hydrogen absorption kinetic curve.

[0028] Figure 5 At 300℃, MgH2-NaV6O 15 @C's cyclic kinetic curve.

[0029] Figure 6 MgH2-NaV6O 15 @C XRD patterns and XPS spectra of composite hydrogen storage materials in ball-milled, dehydrogenated and hydrogen-absorbed states.

[0030] Figure 7 MgH2-V2O5@C and MgH2-NaV6O 15 @C’s cyclic hydrogen storage capacity variation diagram. DETAILED DESCRIPTION

[0031] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0032] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0033] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0034] A magnesium-based hydrogen storage material based on alkali metal-enhanced vanadium oxide catalyst, which is composed of spherical MgH2 powder and lamellar XV6O 15@C powder is prepared by high-energy ball milling, where X can be one of Li, Na, and K, and the surface of MgH2 is uniformly coated with XV6O 15 @C, forming a nanoscale composite structure.

[0035] In this embodiment, Na is used as an example. The particle size of the spherical MgH2 powder used is less than 50 μm; the lamellar NaV6O 15 @C powder is a micron sheet with a diameter of 50 to 100 μm, each of which is composed of a large number of nanorods; spherical MgH2 powder and lamellar NaV6O 15 The mass fraction ratio of @C powder is 94:6, and the solid magnesium-based hydrogen storage material MgH2-NaV6O formed after ball milling 15 The average particle size of @C is 100-500nm, and the surface of each MgH2 particle is coated with NaV6O 15 @C. The specific preparation method of the material is as follows:

[0036] (1) Preparation of NaV6O 15 @C Powder

[0037] V2C MXene was prepared by etching V2AlC MAX with a mixed acid of HCl and HF: 30 ml HF and 20 ml HCl were added to a polytetrafluoroethylene liner in sequence to prepare a mixed acid. Then, 2 g of V2C MXene was slowly added to the acid mixture under an ice bath and stirred at 55 ° C for 2 days. After etching, the mixed solution was centrifuged at 6000 rpm for 5 min. Subsequently, the precipitate was washed with clean water and centrifuged at 12000 rpm for 5 min and washed 3 times until pH = (6-7) to obtain a black precipitate. In order to obtain a few-layer V2C MXene, 25 ml of 5% TBAOH solution was added to the precipitate, stirred at room temperature for 24 h, and then centrifuged at 10000 rpm for 5 min. The precipitate was washed twice with ethanol until the pH was neutral. Subsequently, 150 ml of deionized water was added to the precipitate and shaken to obtain a black mixture. The mixture was ultrasonicated for 1 h under argon protection and ice bath conditions. Subsequently, the liquid was centrifuged at 3500 rpm for 30 min. The upper liquid layer was freeze-dried for 48 h to obtain a few-layer V2C MXene.

[0038] NaV6O 15Preparation of @C nanorods: 90 mg of V2C was added to 38 ml of deionized water, and ultrasonicated for 20 minutes under ice bath conditions to make V2C evenly dispersed in the deionized water. 5 ml of hydrazine hydrate and 5 ml of 2.5M NaOH solution were added to the dispersion in sequence, and then the mixture was stirred in a water bath at 80 ° C for 6 hours at a speed of 500 rpm. Then, the reacted solution was centrifuged at 5000 rpm for 5 minutes. The obtained precipitate was washed three times with deionized water at a speed of 5000 rpm for 5 minutes until the black powder and pH were neutral. Subsequently, the precipitate was freeze-dried for 48 hours to obtain Na ion-modified V2C MXene. The Na ion-modified V2C was transferred to a tubular furnace and heated at 5 ° C·min in a CO2 atmosphere. -1 The temperature was raised to 400 °C and kept at this temperature for 15 h, with a gas flow rate of 250 sccm. The final powder obtained was NaV6O 15 @CNanorods.

[0039] (2) Preparation of doped NaV6O 15 @C MgH2 hydrogen storage material

[0040] In a glove box filled with argon, weigh a certain mass fraction of NaV6O 15 @C powder and mixed with MgH2, wherein MgH2 and NaV6O 15 The mass fraction ratio of @C is 94:6. Then the powder is placed in a 250ml stainless steel ball mill with a ball-to-material ratio of 40:1. The composite hydrogen storage material can be obtained by ball milling in a high-energy ball mill with a rotation speed of 400rpm for 12 hours, with each ball milling for 10 minutes and resting for 10 minutes. After the ball milling is completed, the stainless steel ball mill is placed in a glove box, and the ball-milled powder is taken out for relevant tests.

[0041] The prepared solid magnesium-based hydrogen storage material MgH2-NaV6O 15 @C tested and the results are as follows:

[0042] Figure 1 For the preparation of NaV6O 15 X-ray diffraction (XRD) and XPS spectra of @C catalyst. The XRD spectrum shows that the product is similar to NaV6O 15 All the diffraction peaks can be well matched to the PDF standard card, and no characteristic peaks of impurities are observed, indicating that the purity of the prepared product is high.

[0043] Figure 2 NaV6O 15SEM, TEM, HRTEM, SAED and EDS spectra of @C nanorods. From the SEM image, we can see that the calcined NaV6O 15 The @C sample exhibits a flake structure similar to that of V2C MXene, with a flake diameter of 50-100 μm. The SEM magnified image shows that the micron flakes are composed of a large number of nanorods. TEM tests show that the diameter of the nanorods is 100 nm and the length is 1.5 μm. HRTEM images show lattice fringes distributed along the growth direction of the nanorods, with a plane spacing of 0.950 nm, corresponding to NaV6O 15 (100) face. NaV6O 15 The SAED diffraction pattern of @C shows typical single crystal characteristics. The EDS spectrum shows that NaV6O 15 The above results show that high-purity single-crystalline NaV6O was successfully prepared by calcining Na-ion-modified V2C MXene in a CO2 atmosphere. 15 @C nanorod catalyst.

[0044] Figure 3 MgH2-V2O5@C and MgH2-NaV6O 15 @C isothermal dehydrogenation / hydrogen absorption kinetic curve. The experimental results show that NaV6O 15 @C has a better catalytic efficiency in the hydrogen absorption / desorption process of Mg / MgH2 than V2O5@C. At 200℃, MgH2-NaV6O 15 @C can release 5.0wt.% H2 in 72min; in the same time, MgH2-V2O5@C can only release 2.98wt.% H2 at 200℃, and the amount of hydrogen released is only 1.34wt.% of MgH2-NaV6O 15 @C. At the same time, at a lower temperature of 175°C, MgH2-NaV6O 15 @C can release 1.80wt.% H2 within 170min; in contrast, MgH2-V2O5@C can only release 0.90wt.% H2 in the same time at 180℃. The incorporation of Na element nearly doubles the hydrogen release rate of the material under medium temperature conditions. At the same time, Na element enhances the catalytic efficiency of vanadium oxide catalyst for Mg hydrogen absorption. The above results show that the incorporation of Na stimulates the catalytic performance of vanadium oxide. In particular, when MgH2 is dehydrogenated under medium temperature conditions (i.e., 150-200℃), MgH2-NaV6O 15 @C shows the most obvious advantage. The lower the temperature, the more obvious the improvement of Na on the hydrogen desorption kinetics of the material. At the same time, the incorporation of Na also further improves the hydrogen absorption performance of Mg at low temperatures.

[0045] Figure 4MgH2-NaV6O 15 @C isothermal dehydrogenation / hydrogen absorption kinetic curve. It can be seen that at different temperatures, MgH2-NaV6O 15 @C can achieve rapid hydrogen release. For example, at 325℃, MgH2-NaV6O 15 @C can achieve 6.20wt.% hydrogen release in 1.5min. At 300℃, MgH2-NaV6O 15 @C can release 6.00wt.% H2 in 3.5min. At lower temperatures, MgH2-NaV6O 15 @C also exhibits good hydrogen desorption kinetics. At 275℃, 250℃, 225℃, 200℃ and 175℃, MgH2-NaV6O 15 @C released 5.79wt.%, 5.43wt.%, 5.17wt.%, 5.00wt.% and 1.80wt.% of H2 in 8.5min, 19min, 20min, 70min and 170min respectively. MgH2-NaV6O after complete dehydrogenation 15 @C can achieve a high hydrogen storage capacity and hydrogen absorption rate at 125℃, absorbing 5.76wt.% and 5.90wt.% of H2 in 3min and 6min respectively. At temperatures of 100℃, 75℃, 50℃ and 25℃, the dehydrogenated MgH2-NaV6O 15 @C can absorb 4.85wt.%, 4.76wt.%, 4.10wt.% and 3.05wt.% of H2 in 8.5min, 24min, 31.5min and 55.4min respectively.

[0046] Figure 5 At 300℃, MgH2-NaV6O 15 @C cycling kinetic curve. In the first cycle, the fully dehydrogenated sample absorbed 5.93wt.% H2. The agglomeration and poisoning effects of Mg / MgH2 during the cycling process caused the hydrogen storage capacity of the material to drop rapidly in the first seven cycles. After 7 cycles, the MgH2-NaV6O 15 The hydrogen storage capacity of @C decreased from 5.93wt.% to 5.49wt.%, accounting for 92.6% of the maximum hydrogen storage capacity. After the 7th cycle, the hydrogen storage capacity of Mg was activated, and its hydrogen storage capacity was positively correlated with the number of cycles. It was not until the 51st hydrogen absorption and desorption cycle that the hydrogen storage capacity began to stabilize. After 100 hydrogen absorption and desorption cycles, MgH2-NaV6O 15 @C has a hydrogen storage capacity of 6.04wt.%, and a hydrogen storage capacity retention rate of 101.9%. The test results show that NaV6O 15@C catalyst has high catalytic activity and stability.

[0047] Figure 6 MgH2-NaV6O 15 XRD patterns and XPS spectra of @C composite hydrogen storage materials in ball-milled, dehydrogenated and hydrogen-absorbed states. NaV6O 15 After C was doped into MgH2, in-situ reduction occurred to generate NaVO2, VO, V2O3 and C. Among them, C, as a grinding aid, helps the uniform distribution of the catalytic phase in Mg / MgH2. The catalytic interface composed of NaVO2, VO and V2O3 significantly improved the hydrogen storage kinetics of Mg / MgH2. Compared with the VO / V2O3 interface, the incorporation of Na ions increased the conductivity at the interface and provided a large number of free electrons to the catalytic interface, which effectively promoted the electron transfer in the dehydrogenation process of MgH2. At the same time, the existence of the catalytic interface provides a large number of sites for the nucleation and growth of Mg, reducing the reaction energy barrier of the Mg / MgH2 absorption / dehydrogenation process.

[0048] Figure 7 MgH2-V2O5@C and MgH2-NaV6O 15 @C. The results show that the addition of Na significantly improves the cyclic stability of the material. 15 @C has obvious advantages in cyclic hydrogen storage performance. It can be seen that the cyclic capacity changes of both systems show a trend of first decreasing and then increasing. The incorporation of Na effectively shortens the hydrogen storage capacity decay and activation cycle of the material. For example, the cycle period of hydrogen storage capacity decay of the material is reduced from 46 cycles to 7 cycles; MgH2-NaV6O 15 After the capacity decay of MgH2-V2O5@C, it can quickly reach stability after the 51st cycle. However, after 100 cycles, the hydrogen storage capacity of MgH2-V2O5@C still shows an upward trend. At the same time, the presence of Na also significantly improves the hydrogen storage capacity of the material. After 100 cycles, the hydrogen storage capacity of MgH2-V2O5@C and MgH2-NaV6O 15 @C have hydrogen storage capacities of 4.71wt.% and 6.03wt.% respectively; during the cycle, the minimum hydrogen storage capacity of the materials is 4.27wt.% and 5.49wt.% respectively.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A magnesium-based hydrogen storage material catalyzed by vanadium oxide enhanced by alkali metals, characterized in that: The material is composed of spherical MgH2 powder and lamellar XV6O 15 @C powder is prepared by high-energy ball milling, where X is one of Li, Na, and K, and the surface of MgH2 is uniformly coated with XV6O 15 @C, forming a nanoscale composite structure.

2. The alkali metal-enhanced vanadium oxide-catalyzed magnesium-based hydrogen storage material according to claim 1, characterized in that: The particle size of the spherical MgH2 powder used is less than 50 μm; the lamellar XV6O 15 @C powder is a micron sheet with a diameter of 50 to 100 μm, each of which is composed of a large number of nanorods; spherical MgH2 powder and lamellar XV6O 15 The mass fraction ratio of @C powder is 94:6, and the solid magnesium-based hydrogen storage material MgH2-XV6O formed after ball milling 15 The average particle size of @C is 100-500nm, and the surface of each MgH2 particle is coated with XV6O 15 @C.

3. A method for preparing a magnesium-based hydrogen storage material catalyzed by alkali metal-enhanced vanadium oxide as claimed in claim 2, characterized in that: The steps include: (1) Synthesis of lamellar XV6O 15 @CNanomaterial powder; (2) XV6O 15 @C powder was mixed with MgH2 powder and ball milled to obtain solid magnesium-based hydrogen storage material MgH2-XV6O 15 @C.

4. The method for preparing a magnesium-based hydrogen storage material catalyzed by alkali metal-enhanced vanadium oxide according to claim 3, characterized in that: Step (1) XV6O 15 The synthesis method of @C powder comprises the following steps: A. First, V2AlC MAX was etched with a mixed acid of HCl and HF to prepare V2C MXene: 30 ml HF and 20 ml HCl were added to the polytetrafluoroethylene liner in sequence to prepare the mixed acid; B. In an ice bath, slowly add 2 g of V2C to the acid mixture and stir at 55 °C for 2 days. After etching, centrifuge the mixture at 6000 rpm for 5 min. C. Wash the precipitate with clean water, centrifuge at 12000 rpm for 5 min and wash 3 times until the pH reaches (6-7) to obtain a black precipitate; D. In order to obtain few-layer V2C MXene, 25 ml of 5% TBAOH solution was added to the black precipitate, stirred at room temperature for 24 h, and then centrifuged at 10,000 rpm for 5 min. The obtained precipitate was washed twice with ethanol until the pH was neutral; then, 150 ml of deionized water was added to the precipitate and shaken to obtain a black mixture; the black mixture was ultrasonicated for 1 h under argon protection and ice bath conditions, and then the liquid was centrifuged at 3,500 rpm for 30 min, and the upper liquid was freeze-dried for 48 h to obtain few-layer V2C MXene; E. Add 90 mg of V2CMXene to 38 ml of deionized water and ultrasonicate for 20 min under ice bath conditions to uniformly disperse V2C in deionized water; add 5 ml of hydrazine hydrate and 5 ml of 2.5 M XOH solution to the dispersion in sequence, and then stir the mixture in a water bath at 80 ° C for 6 h at a speed of 500 rpm; then, centrifuge the reacted solution at a speed of 5000 rpm for 5 min, and wash the obtained precipitate with deionized water at a speed of 5000 rpm for 5 min three times until the black powder and pH are neutral; then, freeze-dry the precipitate for 48 h to obtain X-ion-modified V2C MXene; transfer the X-ion-modified V2CMXene to a tubular furnace and heat it at 5 ° C·min in a CO2 atmosphere. -1 The temperature was raised to 400 °C and kept at this temperature for 15 h, with a gas flow rate of 250 sccm. The final powder obtained was XV6O 15 @CNanorods.

5. The method for preparing a magnesium-based hydrogen storage material catalyzed by alkali metal-enhanced vanadium oxide according to claim 3, characterized in that: In step (2), XV6O 15 The ball milling method of @C powder and MgH2 powder is as follows: under a protective atmosphere, the ball milling beads used are stainless steel balls, wherein MgH2 and XV6O 15 The mass fraction ratio of @C is 94:6, the ball-to-material ratio is 40:1, the ball milling speed is 400rpm, and the effective ball milling time is 12h.

6. The method for preparing a magnesium-based hydrogen storage material catalyzed by alkali metal-enhanced vanadium oxide according to claim 5, characterized in that: During the ball milling process, the method of running for 10 minutes and stopping for 10 minutes was adopted to avoid overheating during the ball milling process.

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