Preparation method of magnesium-based hydrogen storage material and magnesium-based hydrogen storage material

Abstract

The invention provides a preparation method of a magnesium-based hydrogen storage material and the magnesium-based hydrogen storage material. The preparation method of the magnesium-based hydrogen storage material comprises the following steps: introducing hydroxyl on the surface of TiO2 by adopting a hydrothermal method to obtain a TiO2 nanotube, and grafting aminopropyl siloxane on the surface of TiO2 to obtain a modified TiO2 nanotube; and introducing the reduced graphene oxide into the modified TiO2 nanotube to obtain the graphene-coated TiO2 nano composite catalyst. And introducing the graphene-coated TiO2 nano composite catalyst into nano magnesium particles by adopting a dry method and wet ball milling by taking cyclohexane as a solvent to obtain the magnesium-based hydrogen storage material. According to the preparation method, the magnesium-based hydrogen storage material with relatively high hydrogen storage capacity can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen storage materials, and particularly to a preparation method of a magnesium-based hydrogen storage material and the magnesium-based hydrogen storage material prepared thereby. Background Art

[0002] With the increasing global demand for clean energy, hydrogen energy, as an efficient and clean energy carrier, has attracted much attention. And hydrogen storage technology is one of the key links in the utilization of hydrogen energy. Developing hydrogen storage materials with high hydrogen storage capacity, good hydrogen absorption and desorption kinetic performance, and cycle stability has become a current research hotspot. However, the hydrogen storage capacity of hydrogen storage materials needs to be further improved. Summary of the Invention

[0003] Based on the above problems, the present invention provides a preparation method of a magnesium-based hydrogen storage material. Through this preparation method, the hydrogen storage capacity of the hydrogen storage material can be effectively improved.

[0004] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of a magnesium-based hydrogen storage material, comprising the following steps: Introduce hydroxyl groups on the surface of TiO2 by hydrothermal method to prepare TiO2 nanotubes, and graft aminopropyl siloxane on the surface of TiO2 to prepare modified TiO2 nanotubes; Introduce reduced graphene oxide into the modified TiO2 nanotubes to prepare graphene@TiO2 nanocomposite catalyst; Introduce the graphene@TiO2 nanocomposite catalyst into nano magnesium particles by ball milling method to prepare a magnesium-based hydrogen storage material.

[0005] Optionally, the preparation of TiO2 nanotubes includes: dispersing TiO2 powder in an aqueous sodium hydroxide solution, reacting at 120 - 180 °C for 12 - 24 h, and obtaining the TiO2 nanotubes after washing with water and centrifugation; the mass ratio of the TiO2 powder to sodium hydroxide in the aqueous sodium hydroxide solution is 1:1 - 1:2, and the concentration of the aqueous sodium hydroxide solution is 0.5 - 2 mol / L.

[0006] Optionally, the preparation of modified TiO2 nanotubes includes: dispersing the TiO2 nanotubes in an organic solvent, adding aminopropyl siloxane, and heating and refluxing at 80 - 120 °C for 6 - 10 h under the protection of an inert gas to obtain modified TiO2 nanotubes.

[0007] Optionally, the organic solvent is toluene, and the mass ratio of the TiO2 nanotubes to aminopropyl siloxane is 1:0.5 - 1:1; the inert gas is nitrogen.

[0008] Optionally, the preparation of the graphene@TiO2 nanocomposite catalyst includes: reducing graphene oxide to reduced graphene oxide by a chemical reduction method, dispersing the reduced graphene oxide and the modified TiO2 nanotubes in ethanol at a mass ratio of 1:2 - 1:4, ultrasonically dispersing for 2 - 3 h, and then evaporating the ethanol to obtain the graphene@TiO2 nanocomposite catalyst.

[0009] Optionally, in the chemical reduction method, sodium borohydride is used as a reducing agent, and the mass ratio of graphene oxide to sodium borohydride is 1:0.3 - 1:0.6.

[0010] Optionally, introducing the graphene@TiO2 nanocomposite catalyst into nano magnesium particles by a ball milling method includes: placing the nano magnesium particles and the graphene@TiO2 nanocomposite catalyst in a ball milling jar at a mass ratio of 90:10 - 70:30, adding stearic acid as a process control agent, and dry ball milling at a rotation speed of 300 - 500 rpm for 2 - 6 h under argon protection; then transferring the dry ball milling product to a ball milling jar containing cyclohexane solvent and wet ball milling at a rotation speed of 300 - 500 rpm for 4 - 8 h.

[0011] Optionally, in the dry ball milling step, the addition amount of stearic acid is 3% - 6% of the total mass of the nano magnesium particles and the graphene@TiO2 nanocomposite catalyst; in the wet ball milling step, the dosage of cyclohexane is 5 - 10 mL of cyclohexane per gram of the dry ball milling product; the particle size of the nano magnesium particles is 50 - 200 nm.

[0012] A magnesium-based hydrogen storage material is prepared by the preparation method.

[0013] Optionally, the hydrogen storage capacity of the magnesium-based hydrogen storage material reaches 6 - 6.8 wt% at 300 - 350 °C and 5 MPa hydrogen pressure, and after 10 hydrogen absorption and desorption cycles, the hydrogen storage capacity attenuation does not exceed 8%.

[0014] Beneficial effects In the present invention, due to the high hydrogen storage capacity of the nano magnesium particles themselves and the promoting effect of the graphene@TiO2 nanocomposite catalyst on the hydrogen absorption and desorption process, the overall hydrogen storage capacity of the material is significantly improved compared with the unmodified magnesium-based material, and can approach or even reach the theoretical hydrogen storage capacity.

[0015] Furthermore, the high conductivity of graphene accelerates electron transfer, and the catalytic activity of TiO2 nanotubes reduces the hydrogen absorption and desorption activation energy. The synergistic effect of the two makes the hydrogen absorption and desorption temperature of the magnesium-based hydrogen storage material significantly decrease, the hydrogen absorption and desorption rate increase significantly, and good performance stability can still be maintained after multiple cycles. Specific embodiments

[0016] An embodiment of the present invention provides a method for preparing a magnesium-based hydrogen storage material, comprising the following steps: introducing hydroxyl groups on the surface of TiO2 by hydrothermal method to prepare TiO2 nanotubes, and grafting aminopropyl siloxane on the surface of TiO2 to prepare modified TiO2 nanotubes. Introduce reduced graphene oxide into the modified TiO2 nanotubes to prepare a graphene@TiO2 nanocomposite catalyst; use ball milling method to introduce the graphene@TiO2 nanocomposite catalyst into nano magnesium particles to prepare a magnesium-based hydrogen storage material.

[0017] In the preparation method of this embodiment, due to the high hydrogen storage capacity of the nano magnesium particles themselves and the promoting effect of the graphene@TiO2 nanocomposite catalyst on the hydrogen absorption and desorption processes, the overall hydrogen storage capacity of the material is significantly improved compared with the unmodified magnesium-based material, and can approach or even reach the theoretical hydrogen storage capacity.

[0018] Furthermore, the high conductivity of graphene accelerates electron transfer, and the catalytic activity of TiO2 nanotubes reduces the activation energy of hydrogen absorption and desorption. The synergistic effect of the two makes the hydrogen absorption and desorption temperature of the magnesium-based hydrogen storage material significantly decrease, the hydrogen absorption and desorption rate increase significantly, and good performance stability can still be maintained after multiple cycles.

[0019] Specifically, the modified TiO2 nanotubes prepared by the unique hydrothermal method combined with grafting modification in the present invention not only have rich surface hydroxyl groups to increase active sites, but also improve the compatibility with other materials through aminopropyl siloxane grafting, providing a good basis for subsequent composites.

[0020] The design of the graphene@TiO2 nanocomposite catalyst integrates the advantages of the high conductivity and large specific surface area of graphene and the catalytic activity of TiO2 nanotubes. The synergistic effect of the two greatly improves the catalytic efficiency, effectively reduces the activation energy of hydrogen absorption and desorption of the magnesium-based hydrogen storage material, and accelerates the hydrogen absorption and desorption process.

[0021] Adopt a ball milling process combining dry method and wet method. First, preliminarily mix and crush by dry ball milling, and then further uniformly disperse the catalyst and magnesium particles under the protection of cyclohexane by wet ball milling to ensure the microstructure uniformity of the composite material, give full play to the advantages of each component, and thus prepare a magnesium-based hydrogen storage material with high hydrogen storage capacity, excellent hydrogen absorption and desorption performance and stable cycle, laying a solid foundation for the practical application of magnesium-based hydrogen storage materials and promoting the development of hydrogen energy storage technology.

[0022] Optionally, preparing TiO2 nanotubes includes: dispersing TiO2 powder in an aqueous sodium hydroxide solution, reacting at 120 - 180 °C for 12 - 24 h, and obtaining TiO2 nanotubes after washing with water and centrifugation; the mass ratio of TiO2 powder to sodium hydroxide in the aqueous sodium hydroxide solution is 1:1 - 1:2, and the concentration of the aqueous sodium hydroxide solution is 0.5 - 2 mol / L. At a temperature of 120 - 180 °C, the aqueous sodium hydroxide solution reacts with TiO2 powder, which is beneficial to the reconstruction of the TiO2 lattice and the formation of the nanotube structure. A higher temperature can provide sufficient energy to cause the atoms on the surface of TiO2 particles to migrate and rearrange, thus forming a nanotube morphology. This nanotube structure has a large specific surface area, which can provide more active sites for subsequent surface modification and hydrogen storage reactions. After the reaction, washing with water and centrifugation can effectively remove unreacted sodium hydroxide, reaction by-products, and possible impurities. Washing with water can dissolve and remove water-soluble impurities, and centrifugation can precipitate TiO2 nanotubes and separate them from the impurities in the supernatant, thereby obtaining TiO2 nanotubes with higher purity, laying a foundation for subsequent modification and preparation of high-performance magnesium-based hydrogen storage materials. TiO2 nanotubes with high purity can better play their role in hydrogen storage materials and avoid the adverse effects of impurities on hydrogen storage performance.

[0023] Optionally, preparing modified TiO2 nanotubes includes: dispersing TiO2 nanotubes in an organic solvent, adding aminopropylsiloxane, and heating under reflux at 80 - 120 °C for 6 - 10 h under inert gas protection to obtain modified TiO2 nanotubes.

[0024] Aminopropylsiloxane contains siloxane groups and amino groups. The siloxane groups can undergo a condensation reaction with the hydroxyl groups on the surface of TiO2 nanotubes, thereby grafting aminopropylsiloxane onto the surface of TiO2 nanotubes. This surface modification can change the surface properties of TiO2 nanotubes, making its surface have active groups such as amino groups, providing active sites for subsequent binding with other substances.

[0025] After modification, groups such as amino groups on the surface of TiO2 nanotubes can increase their dispersibility in organic solvents. Because these groups can interact with organic solvent molecules, reducing the agglomeration phenomenon between TiO2 nanotubes, enabling them to be more uniformly dispersed in the solution, which is beneficial to the uniform mixing with substances such as reduced graphene oxide subsequently, thereby improving the performance of the graphene@TiO2 nanocomposite catalyst. Reacting under inert gas protection can prevent the substances in the system from being oxidized.

[0026] Under the condition of heating under reflux at 80 - 120 °C, the reaction can proceed fully, enabling the better grafting of aminopropyl siloxane onto the surface of TiO2 nanotubes to form stable chemical bonds. This chemical bonding can enhance the structural stability of the TiO2 nanotube surface and is not prone to structural changes or detachment during subsequent preparation processes and when functioning in magnesium-based hydrogen storage materials, thus ensuring the stability of the entire material system and the reliability of its performance.

[0027] In addition, groups such as amino groups on the surface of the modified TiO2 nanotubes can interact with other materials (such as reduced graphene oxide, nano magnesium particles, etc.), improving their compatibility. For example, amino groups can form hydrogen bonds or other weak interactions with some functional groups on the graphene surface, enabling graphene to better combine with TiO2 nanotubes to form a uniform nano-composite structure. When compounded with nano magnesium particles, the modified TiO2 nanotubes can also better contact and combine with the surface of magnesium particles, which is beneficial to improving the comprehensive performance of magnesium-based hydrogen storage materials.

[0028] Optionally, the organic solvent is toluene, and the mass ratio of TiO2 nanotubes to aminopropyl siloxane is 1:0.5 - 1:1; the inert gas is nitrogen.

[0029] Optionally, the preparation of graphene@TiO2 nano-composite catalyst includes: reducing graphene oxide to reduced graphene oxide by chemical reduction method, dispersing the reduced graphene oxide and the modified TiO2 nanotubes in ethanol at a mass ratio of 1:2 - 1:4, ultrasonically dispersing for 2 - 3 h, and then evaporating ethanol to obtain the graphene@TiO2 nano-composite catalyst. Dispersing the reduced graphene oxide and the modified TiO2 nanotubes in ethanol at a certain mass ratio and performing ultrasonic dispersion. Ultrasonic dispersion can utilize the energy of ultrasonic waves to effectively break the aggregates of reduced graphene oxide and modified TiO2 nanotubes, enabling them to be uniformly dispersed in the ethanol solution. This helps to increase the contact area between the two materials, provides good conditions for subsequent interactions between the two, and is conducive to the formation of a uniform nano-composite structure.

[0030] Optionally, in the chemical reduction method, sodium borohydride is used as the reducing agent, and the mass ratio of graphene oxide to sodium borohydride is 1:0.3 - 1:0.6.

[0031] Optionally, introducing the graphene@TiO2 nanocomposite catalyst into the nano-magnesium particles by ball milling method includes: placing the nano-magnesium particles and the graphene@TiO2 nanocomposite catalyst in a ball milling jar at a mass ratio of 90:10 - 70:30, adding stearic acid as a process control agent, and performing dry ball milling at a rotation speed of 300 - 500 rpm for 2 - 6 h under argon protection; then transferring the dry ball milling product to a ball milling jar containing cyclohexane solvent and performing wet ball milling at a rotation speed of 300 - 500 rpm for 4 - 8 h.

[0032] Adding stearic acid as a process control agent can adjust the frictional force and the agglomeration behavior between particles during ball milling. Stearic acid molecules can adsorb on the particle surface, reduce the surface energy of the particle surface, reduce the agglomeration between particles, and make the ball milling process more uniform and stable. At the same time, stearic acid can also protect the nano-magnesium particles and the graphene@TiO2 nanocomposite catalyst to a certain extent, preventing them from being oxidized or damaged during ball milling.

[0033] Performing dry ball milling under argon protection can avoid the reaction of nano-magnesium particles and graphene@TiO2 nanocomposite catalyst with oxygen, moisture, etc. in the air during ball milling and being oxidized or deteriorated. Argon, as an inert gas, can provide a stable anaerobic environment, ensure the chemical properties of the materials during ball milling are stable, and is conducive to obtaining magnesium-based hydrogen storage materials with stable performance. Transferring the dry ball milling product to a ball milling jar containing cyclohexane solvent for wet ball milling, the cyclohexane solvent can play a role in lubrication and dispersion, further improving the dispersibility and uniformity of the particles. At the same time, wet ball milling can continue to refine and surface modify the particles with lower energy input, making the combination between nano-magnesium particles and graphene@TiO2 nanocomposite catalyst closer, and further optimizing the structure and performance of the composite material.

[0034] Optionally, in the dry ball milling step, the addition amount of stearic acid is 3% - 6% of the total mass of nano-magnesium particles and graphene@TiO2 nanocomposite catalyst; in the wet ball milling step, the dosage of cyclohexane is 5 - 10 mL of cyclohexane corresponding to each gram of dry ball milling product; the particle size of nano-magnesium particles is 50 - 200 nm.

[0035] Another embodiment of the present invention provides a magnesium-based hydrogen storage material prepared by the above preparation method.

[0036] In one embodiment, the hydrogen storage capacity of the magnesium-based hydrogen storage material reaches 6 - 6.8 wt% at 300 - 350 °C and 5 MPa hydrogen pressure. After 10 hydrogen absorption and desorption cycles, the hydrogen storage capacity attenuation does not exceed 8%.

[0037] Example 1 In this example, the preparation method of the magnesium-based hydrogen storage material is as follows: S01: Weigh 5 g of TiO2 powder, disperse it in 100 mL of an aqueous sodium hydroxide solution with a concentration of 1.5 mol / L, transfer it to a high-pressure reactor, and react at 150 °C for 18 h. After the reaction is completed, wash and centrifuge it with deionized water 5 times until the pH value of the supernatant is neutral to obtain hydroxylated TiO2 nanotubes.

[0038] S02: Disperse 3 g of the above-mentioned hydroxylated TiO2 nanotubes in 50 mL of toluene, add 2 g of aminopropylsiloxane, and under nitrogen protection, heat and reflux at 100 °C for 8 hours. After the reaction is completed, cool to room temperature, centrifuge, wash 3 times with toluene and ethanol respectively, and dry to obtain modified TiO2 nanotubes.

[0039] S03: Take 1 g of graphene oxide and disperse it in 100 mL of deionized water. After ultrasonic dispersion for 1 h, slowly add 0.5 g of sodium borohydride and continue ultrasonic dispersion for 2 h for a reduction reaction. After the reaction is completed, wash it with a large amount of deionized water to remove the residual reducing agent to obtain reduced graphene oxide.

[0040] S04: Disperse 0.5 g of reduced graphene oxide and 2 g of modified TiO2 nanotubes in 30 mL of ethanol, ultrasonic disperse for 2 h, and then heat and stir to evaporate the ethanol to obtain a graphene@TiO2 nanocomposite catalyst.

[0041] S05: Place 8 g of nano magnesium particles and 2 g of the graphene@TiO2 nanocomposite catalyst in a ball milling tank, add 0.5 g of stearic acid, and dry ball mill at a speed of 400 rpm for 4 h under argon protection. Transfer the dry ball milled product to a ball milling tank containing 60 mL of cyclohexane and continue wet ball milling at a speed of 400 rpm for 6 h to obtain a magnesium-based hydrogen storage material.

[0042] Example 2 In this example, the preparation method of the magnesium-based hydrogen storage material is as follows: S01: Weigh 5 g of TiO2 powder, disperse it in 100 mL of an aqueous sodium hydroxide solution with a concentration of 1.5 mol / L, transfer it to a high-pressure reactor, and react at 150 °C for 18 h. After the reaction is completed, wash and centrifuge it with deionized water 5 times until the pH value of the supernatant is neutral to obtain hydroxylated TiO2 nanotubes.

[0043] S02: Disperse 3 g of the above-mentioned hydroxylated TiO2 nanotubes in 50 mL of toluene, add 2 g of aminopropylsiloxane, and under nitrogen protection, heat and reflux at 100 °C for 8 hours. After the reaction is completed, cool to room temperature, centrifuge, wash 3 times with toluene and ethanol respectively, and dry to obtain modified TiO2 nanotubes.

[0044] S03: Disperse 1 g of graphene oxide in 100 mL of deionized water. After ultrasonic dispersion for 1 h, slowly add 0.5 g of sodium borohydride and continue ultrasonic dispersion for 2 h to carry out the reduction reaction. After the reaction is completed, wash with a large amount of deionized water to remove the residual reducing agent, and obtain reduced graphene oxide.

[0045] S04: Disperse 0.5 g of reduced graphene oxide and 2 g of modified TiO2 nanotubes in 30 mL of ethanol, ultrasonic disperse for 2 h, and then heat and stir to evaporate the ethanol to obtain a graphene@TiO2 nanocomposite catalyst.

[0046] S05: Place 8 g of nano magnesium particles and 2 g of graphene@TiO2 nanocomposite catalyst in a ball milling tank, add 0.5 g of stearic acid, and dry ball mill at a rotation speed of 400 rpm for 10 h under argon protection.

[0047] Comparative Example 1 In this comparative example, the preparation method of the magnesium-based hydrogen storage material is as follows: Place 10 g of nano magnesium particles in a ball milling tank, add 0.5 g of stearic acid, and dry ball mill at a rotation speed of 400 rpm for 4 h under argon protection. Transfer the dry ball milled product to a ball milling tank containing 60 mL of cyclohexane and continue wet ball milling at a rotation speed of 400 rpm for 6 h to obtain a magnesium-based hydrogen storage material.

[0048] Comparative Example 2 In this comparative example, the preparation method of the magnesium-based hydrogen storage material is as follows: S01: Weigh 5 g of TiO2 powder, disperse it in 100 mL of sodium hydroxide aqueous solution with a concentration of 1.5 mol / L, transfer it to a high-pressure reaction kettle, and react at 150 °C for 18 h. After the reaction is completed, wash and centrifuge with deionized water repeatedly for 5 times until the pH value of the supernatant is neutral to obtain hydroxylated TiO2 nanotubes.

[0049] S02: Disperse 3 g of the above hydroxylated TiO2 nanotubes in 50 mL of toluene, add 2 g of aminopropyl siloxane, and heat and reflux at 100 °C for 8 hours under nitrogen protection. After the reaction is completed, cool to room temperature, centrifuge and separate, wash 3 times with toluene and ethanol respectively, and dry to obtain modified TiO2 nanotubes.

[0050] S03: Place 8 g of nano magnesium particles and 2 g of modified TiO2 nanotubes in a ball milling tank, add 0.5 g of stearic acid, and dry ball mill at a rotation speed of 400 rpm for 4 h under argon protection. Transfer the dry ball milled product to a ball milling tank containing 60 mL of cyclohexane and continue wet ball milling at a rotation speed of 400 rpm for 6 h to obtain a magnesium-based hydrogen storage material.

[0051] Test Example (1)Performance testing was carried out on the magnesium-based hydrogen storage materials obtained in the examples and comparative examples: A Sieverts-type gas adsorption instrument was used to measure their hydrogen storage capacity and the hydrogen storage capacity decay after 10 hydrogen absorption and desorption cycles. Test conditions: 300 °C, 5 MPa hydrogen pressure.

[0052] Test results: The hydrogen storage capacity of Comparative Example 1 was 3.5 wt%, with a decay of 20%. The hydrogen storage capacity of Comparative Example 2 was 4.3 wt%, with a decay of 15%. The hydrogen storage capacity of Example 1 was 6.2 wt% (the theoretical hydrogen storage capacity of the magnesium-based hydrogen storage material was 7.6 wt%), with a decay of 5%. The hydrogen storage capacity of Example 2 was 5.8 wt%, with a decay of 7%.

[0053] (2)The hydrogen absorption and desorption kinetics of the hydrogen storage materials in the examples and comparative examples were studied by thermogravimetry-differential thermal analysis (TG-DTA) combined with temperature-programmed desorption (TPD) technology. Compared with the pure magnesium hydrogen storage material of Comparative Example 1, the results were as follows: Compared with Comparative Example 1, the hydrogen absorption activation energy of Example 1 decreased by 31 kJ / mol, and the hydrogen desorption temperature decreased by 50 °C. Compared with Comparative Example 1, the hydrogen absorption activation energy of Example 2 decreased by 24 kJ / mol, and the hydrogen desorption temperature decreased by 43 °C. Compared with Comparative Example 1, the hydrogen absorption activation energy of Comparative Example 2 decreased by 13 kJ / mol, and the hydrogen desorption temperature decreased by 18 °C.

[0054] It can be seen from the test results that the preparation method of the present invention can obtain a magnesium-based hydrogen storage material with a high hydrogen storage capacity and a small decay in hydrogen absorption and desorption cycles, and the hydrogen absorption activation energy and hydrogen desorption temperature of the obtained hydrogen storage material have been effectively reduced.

[0055] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0056] For those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A preparation method of a magnesium-based hydrogen storage material, characterized in that, It includes the following steps: Hydroxyl groups are introduced onto the surface of TiO2 by a hydrothermal method to prepare TiO2 nanotubes, and aminopropylsiloxane is grafted onto the surface of TiO2 to prepare modified TiO2 nanotubes; Reduced graphene oxide is introduced into the modified TiO2 nanotubes to prepare a graphene@TiO2 nanocomposite catalyst; The graphene@TiO2 nanocomposite catalyst is introduced into nano magnesium particles by a ball milling method to prepare a magnesium-based hydrogen storage material.

2. The preparation method of the magnesium-based hydrogen storage material according to claim 1, characterized in that, The preparation of TiO2 nanotubes includes: dispersing TiO2 powder in an aqueous sodium hydroxide solution, reacting at 120 - 180 °C for 12 - 24 h, and obtaining the TiO2 nanotubes after washing with water and centrifugation; the mass ratio of the TiO2 powder to sodium hydroxide in the aqueous sodium hydroxide solution is 1:1 - 1:2, and the concentration of the aqueous sodium hydroxide solution is 0.5 - 2 mol / L.

3. The preparation method of the magnesium-based hydrogen storage material according to claim 1, wherein, The preparation of modified TiO2 nanotubes includes: dispersing the TiO2 nanotubes in an organic solvent, adding aminopropylsiloxane, and heating under reflux at 80 - 120 °C for 6 - 10 h under the protection of an inert gas to obtain modified TiO2 nanotubes.

4. The preparation method of the magnesium-based hydrogen storage material according to claim 3, characterized in that, The organic solvent is toluene, and the mass ratio of the TiO2 nanotubes to aminopropylsiloxane is 1:0.5 - 1:1; the inert gas is nitrogen.

5. The preparation method of the magnesium-based hydrogen storage material according to claim 1, characterized in that, The preparation of the graphene@TiO2 nanocomposite catalyst includes: reducing graphene oxide to reduced graphene oxide by a chemical reduction method, dispersing the reduced graphene oxide and the modified TiO2 nanotubes in ethanol at a mass ratio of 1:2 - 1:4, ultrasonically dispersing for 2 - 3 h, and then evaporating the ethanol to obtain the graphene@TiO2 nanocomposite catalyst.

6. The preparation method of the magnesium-based hydrogen storage material according to claim 5, characterized in that, In the chemical reduction method, sodium borohydride is used as a reducing agent, and the mass ratio of graphene oxide to sodium borohydride is 1:0.3 - 1:0.

6.

7. The preparation method of the magnesium-based hydrogen storage material according to any one of claims 1 to 6, characterized in that Introducing the graphene@TiO2 nanocomposite catalyst into nano magnesium particles by a ball milling method includes: placing the nano magnesium particles and the graphene@TiO2 nanocomposite catalyst in a ball milling jar at a mass ratio of 90:10 - 70:30, adding stearic acid as a process control agent, and dry ball milling at a speed of 300 - 500 rpm under the protection of argon for 2 - 6 h; then transferring the dry ball milling product to a ball milling jar containing cyclohexane solvent and wet ball milling at a speed of 300 - 500 rpm for 4 - 8 h.

8. The preparation method of the magnesium-based hydrogen storage material according to claim 7, characterized in that, In the dry ball milling step, the addition amount of stearic acid is 3% - 6% of the total mass of the nano magnesium particles and the graphene@TiO2 nanocomposite catalyst; in the wet ball milling step, the dosage of cyclohexane is 5 - 10 mL per gram of the dry ball milling product; the particle size of the nano magnesium particles is 50 - 200 nm.

9. A magnesium-based hydrogen storage material, characterized in that, Prepared by the preparation method according to any one of claims 1 - 8.

10. The magnesium-based hydrogen storage material according to claim 9, wherein, The hydrogen storage capacity of the magnesium-based hydrogen storage material reaches 6 - 6.8 wt% at 300 - 350 °C and a hydrogen pressure of 5 MPa, and after 10 hydrogen absorption and desorption cycles, the hydrogen storage capacity attenuation does not exceed 8%.