A method for preparing nanometer hydrogenated magnesium

Abstract

This invention provides a method for preparing nano-sized magnesium hydride, comprising the steps of preparing magnesium nanoparticles by gas-phase condensation, MXene-confined catalytic hydrogenation, and atomic layer deposition to construct a composite coating layer. This invention achieves the preparation of ultrafine magnesium nanoparticles through gas-phase condensation; simultaneously utilizing the three-dimensional wrinkled structure Ti3C2T x MXene not only effectively prevents the migration and aggregation of nanoparticles during cycling through physical confinement, but also lowers the energy barrier of hydrogen adsorption and desorption reactions through in-situ generated highly active catalytic phases (such as TiH2), achieving a dual synergistic effect of confinement and catalysis. A titanium dioxide-amorphous carbon composite coating layer is constructed using atomic layer deposition (ALD) technology, which, in conjunction with the MXene confinement framework, provides a dual stabilization mechanism for nano-magnesium hydride. This invention organically combines gas-phase condensation, MXene-confined hydrogenation, and ALD coating, resulting in a product with an initial dehydrogenation temperature below 100°C and a hydrogen storage capacity retention rate exceeding 95% after 3000 hydrogen adsorption and desorption cycles, demonstrating excellent comprehensive performance.

Description

Technical Field

[0001] This invention belongs to the field of new materials and new energy technology, and specifically relates to a method for preparing nano-magnesium hydride. Background Technology

[0002] Hydrogen energy, as a clean, efficient, and renewable secondary energy source, is considered an important carrier for achieving the "dual carbon" goal. However, the low density, flammability, and explosiveness of hydrogen make its storage and transportation key bottlenecks restricting the large-scale application of hydrogen energy. Solid-state hydrogen storage technology, due to its high volumetric hydrogen storage density, good safety, and operability, is considered one of the most promising hydrogen storage methods.

[0003] Among numerous solid-state hydrogen storage materials, magnesium-based hydrogen storage materials (especially magnesium hydride, MgH2) have attracted widespread attention due to their advantages such as high theoretical hydrogen storage capacity (7.6 wt%), abundant magnesium resources, low cost, and environmental friendliness. However, the practical application of MgH2 is still limited by its high dehydrogenation temperature, slow hydrogen adsorption / desorption kinetics, and poor cycle stability.

[0004] To address the aforementioned issues, research reports indicate that introducing catalysts is one of the most direct and effective methods to improve the hydrogen absorption and desorption kinetics of MgH2. In recent years, two-dimensional transition metal carbides / nitrides (MXenes) have shown great potential in the field of catalysis due to their unique layered structure, high specific surface area, excellent conductivity, and abundant surface functional groups. Existing research has shown that MXenes can significantly improve the hydrogen storage performance of MgH2. For example, Chinese patent CN120864447A discloses a magnesium hydride@TM... x+ A method for preparing a multivalent state-controlled hydrogen storage material / TM-MXene, which produces a TM-MXene with electron transfer and support functions. x+ The TM-MXene system combines confinement effects with efficient electron transport, and its multivalent state bidirectional enhancement of hydrogen absorption and dehydrogenation kinetics in Mg / magnesium hydride. However, while this method improves initial hydrogen absorption and dehydrogenation kinetics, it relies solely on the physical confinement effect of MXene and fails to address the insufficient cycling stability of nano-magnesium hydride due to particle aggregation and surface oxidation during long-term cycling.

[0005] Therefore, how to further address the problem of insufficient cycle stability caused by particle agglomeration and surface oxidation during long-term cycling, based on the efficient catalytic modification of magnesium hydride, remains a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of the above problems, the present invention provides a method for preparing nano-magnesium hydride, which can further solve the problem of insufficient cycle stability caused by particle agglomeration and surface oxidation during long-term cycling, based on the efficient catalytic modification of magnesium hydride.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] The first aspect of the present invention provides a method for preparing nano-magnesium hydride, comprising the following steps:

[0009] S1. Preparation of magnesium nanoparticles by gas-phase condensation: Under the protection of an inert gas, metallic magnesium raw material is heated and evaporated to generate magnesium vapor; the magnesium vapor is then contacted with and condensed in a mixed gas flow of hydrogen and inert gas to form magnesium nanoparticles with a particle size of 10~50nm; wherein, the volume percentage of hydrogen in the mixed gas flow is 5%~30%, and the temperature is -50~0℃.

[0010] S2.MXene confined catalytic hydrogenation: The magnesium nanoparticles obtained in step S1 are combined with Ti3C2T x MXene nanosheets were uniformly mixed and then subjected to catalytic hydrogenation at 150-250°C in a hydrogen atmosphere with a pressure of 3-6 MPa for 2-10 h to form a MgH2@MXene complex.

[0011] S3. Atomic layer deposition to construct a composite coating layer: Using atomic layer deposition technology, a titanium dioxide layer with a thickness of 1~4 nm containing oxygen vacancies and an amorphous carbon layer with a thickness of 0.5~2 nm are sequentially deposited on the surface of the MgH2@MXene composite obtained in step S2, forming a titanium dioxide-amorphous carbon composite coating layer with a total thickness of less than 5 nm, thus obtaining nano-magnesium hydride.

[0012] Further, in step S1, the magnesium vapor is brought into contact with the mixed gas flow of hydrogen and inert gas for a time of <0.1s. Step S1 of this invention controls the contact time between the magnesium vapor and the low-temperature mixed gas flow to <0.1 seconds. Its core function is to achieve explosive nucleation and inhibited growth of magnesium atoms through extreme rapid cooling: a drastic temperature drop from >1000℃ to -50~0℃ is completed within milliseconds, causing the magnesium vapor to reach extremely high instantaneous supersaturation, triggering the formation of a large number of crystal nuclei, thereby precisely controlling the particle size within the range of 10~50nm. Ultrafine magnesium nanoparticles of 10~50nm are prepared directly from the gas phase using a gas-phase condensation method, avoiding the contamination and particle inhomogeneity problems caused by traditional mechanical ball milling, laying the foundation for the subsequent preparation of ultrafine magnesium hydride (MgH2).

[0013] Further, in step S2, the Ti3C2T xMXene nanosheets are three-dimensional wrinkled structures formed by hexadecyltrimethylammonium bromide intercalation and self-assembly, with a specific surface area >100 m². 2 / g. The MgH2@MXene composite obtained in this step is a composite structure material formed by loading magnesium hydride (MgH2) nanoparticles on the surface of MXene nanosheets or confining them in the interlayer / pores, using MXene nanosheets as the framework. This invention utilizes the three-dimensional wrinkled structure Ti3C2T x The high specific surface area and abundant nanospace of MXene nanosheets enable the physical confinement of MgH2 nanoparticles, effectively preventing their migration and aggregation during cycling. At the same time, MXene nanosheets form highly active catalytic phases (such as titanium hydride, TiH2) in situ during hydrogenation, which significantly reduces the energy barrier of hydrogenation / dehydrogenation reactions.

[0014] Further, in step S3, the titanium dioxide layer is obtained by atomic layer deposition (ALD) cycles of 20-40 times at 80-150°C using titanium and oxygen-containing sources as precursors; wherein the titanium source includes tetrakis(dimethylamino)titanium or titanium tetrachloride; the oxygen-containing source includes ozone or water; and the amorphous carbon layer is obtained by chemical vapor deposition or ALD using ethylene or propylene as a carbon source at 200-400°C. The titanium dioxide-amorphous carbon composite coating layer constructed by this invention using ALD technology has a thickness precisely controlled below 5 nm; wherein the oxygen vacancies in the titanium dioxide layer provide a rapid channel for hydrogen diffusion, while the outer amorphous carbon layer effectively isolates oxygen and water vapor, preventing MgH2 from being oxidized and corroded during storage and cycling. This titanium dioxide-amorphous carbon composite coating layer, in synergy with the confined framework (MXene), provides a dual stabilization mechanism for nano-magnesium hydride.

[0015] The method for preparing nano-magnesium hydride provided by this invention yields a nano-magnesium hydride composite with a three-dimensional wrinkled MXene framework and a titanium dioxide-amorphous carbon composite coating layer on the surface. The obtained nano-magnesium hydride has a particle size ≤50 nm and possesses a porous or plate-like structure; the specific surface area of ​​the obtained product is >100 m². 2 / g; the MgH2 main phase content in the obtained product is >98wt.%; the total thickness of the titanium dioxide-amorphous carbon composite coating layer on the surface of the obtained product is <5nm. The nano-magnesium hydride product prepared by this invention achieves an initial dehydrogenation temperature below 100℃, and after 3000 hydrogen adsorption / desorption cycles, the hydrogen storage capacity retention rate is still above 95%, which can be applied to solid-state hydrogen storage systems, fuel cell hydrogen supply devices, or nickel-metal hydride battery anode materials.

[0016] Compared with the prior art, the technical solution of this application has at least the following beneficial effects:

[0017] This invention achieves the clean preparation of ultrafine magnesium nanoparticles with a particle size of 10-50 nm from the source through a gas-phase condensation method, avoiding the contamination and particle inhomogeneity problems introduced by traditional ball milling methods, laying the foundation for obtaining high-purity, high-activity magnesium hydride. Simultaneously, it utilizes the three-dimensional wrinkled structure Ti3C2T formed by hexadecyltrimethylammonium bromide intercalation self-assembly. x MXene (specific surface area > 100 m²) 2 The method not only effectively prevents the migration and aggregation of nanoparticles during cycling through physical confinement, but also significantly reduces the hydrogen absorption and desorption reaction energy barrier through the in-situ generated highly active catalytic phase (such as TiH2), achieving a dual synergy of confinement and catalysis. More importantly, an atomic layer deposition technique was used to construct a titanium dioxide-amorphous carbon composite coating layer with a total thickness of <5 nm. The oxygen vacancies in the inner titanium dioxide layer provide a fast channel for hydrogen diffusion, while the outer amorphous carbon layer effectively isolates oxygen and water vapor. Together with the MXene confinement framework, it provides a dual stabilization mechanism for nano-magnesium hydride, fundamentally solving the surface oxidation problem. This invention organically combines gas-phase condensation, MXene confinement hydrogenation, and atomic layer deposition coating. The resulting product has an initial dehydrogenation temperature below 100℃, and its hydrogen storage capacity retention rate is still above 95% after 3000 hydrogen absorption and desorption cycles, demonstrating excellent comprehensive performance. Attached Figure Description

[0018] Figure 1 This is a TEM image of the nano-magnesium hydride prepared in Example 1 of this invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0020] The term "comprising" as used in this application is an open-ended inclusion, meaning "including but not limited to". The term "according to" means "at least in part according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment". Definitions of other terms will be given in the description below.

[0021] Example 1

[0022] This embodiment provides a method for preparing nano-sized magnesium hydride, including the following steps:

[0023] S1. Preparation of magnesium nanoparticles by gas-phase condensation: In an argon glove box, 1g of high-purity magnesium ingot was placed in a graphite crucible and then placed in a gas-phase condensation system. After the system was evacuated, argon gas was introduced to 0.1MPa. The crucible was heated to 750℃ to evaporate the high-purity magnesium ingot and generate magnesium vapor. A mixed gas flow consisting of 20 vol.% hydrogen and 80 vol.% argon was introduced and the temperature of the mixed gas flow was pre-cooled to -30℃. The gas flowed through the magnesium vapor condensation zone, so that the magnesium vapor came into rapid contact with the mixed gas flow of hydrogen and inert gas and condensed into nuclei. Magnesium nanoparticles with an average particle size of about 30nm were obtained by electrostatic collector.

[0024] S2.MXene confined catalytic hydrogenation: 0.5g of the above magnesium nanoparticles were mixed with 2g of Ti3C2T, which has undergone CTAB intercalation treatment and has a three-dimensional wrinkled structure. x MXene nanosheets (specific surface area approximately 150 m²) 2 / g) was lightly mixed in a planetary ball mill for 1 h under argon protection; the uniformly mixed powder was transferred to a high-pressure reactor and charged with 5 MPa of high-purity hydrogen; the reactor was heated to 200 °C and kept at this temperature for 5 h to carry out the hydrogenation reaction; after the reaction was completed, it was naturally cooled to room temperature to obtain the MgH2@MXene complex.

[0025] S3. Atomic Layer Deposition to Construct Composite Coating Layer: The MgH2@MXene composite obtained in step S2 is loaded into the atomic layer deposition reaction chamber; firstly, tetrakis(dimethylamino)titanium and water are used as precursors, and 30 deposition cycles are performed at 120°C to form a titanium dioxide film with a thickness of about 2.5 nm on the particle surface. An appropriate amount of oxygen vacancies is introduced by controlling the pulse and time; then the temperature is raised to 350°C, and ethylene is used as the carbon source to perform 10 pulses of chemical vapor deposition to form a continuous amorphous carbon layer with a thickness of about 1 nm outside the titanium dioxide layer, thus obtaining the nano-magnesium hydride product.

[0026] Example 2

[0027] This embodiment provides a method for preparing nano-sized magnesium hydride, including the following steps:

[0028] S1. Preparation of magnesium nanoparticles by gas phase condensation: The mixed gas flow was adjusted to 10 vol.% hydrogen and 90 vol.% helium, the temperature of the condensation zone was controlled at -10℃, and the other conditions were the same as in Example 1, resulting in magnesium nanoparticles with an average particle size of about 45 nm.

[0029] S2.MXene confined catalytic hydrogenation: 0.8 g of the above magnesium nanoparticles and 1.5 g of Ti3C2T with a three-dimensional wrinkled structure after CTAB intercalation were taken. x MXene nanosheets were mixed; the hydrogenation conditions were adjusted to: hydrogen pressure 4 MPa, temperature 180 °C, time 8 h; the other conditions were the same as in Example 1.

[0030] S3. Construction of composite coating layer by atomic layer deposition: Titanium tetrachloride and ozone were used as precursors and 25 cycles were performed at 100°C to obtain a titanium dioxide layer with a thickness of about 2 nm; then, atomic layer deposition was performed at 300°C with propylene as carbon source for 15 cycles to obtain a carbon layer with a thickness of about 1.5 nm; the remaining conditions were the same as in Example 1.

[0031] Comparative Example 1

[0032] Catalytically modified MgH2 was prepared by conventional high-energy ball milling: 2g of magnesium powder and 5wt.% nickel catalyst were ball milled for 20h under argon protection; the ball-milled powder was hydrogenated for 5h under 3MPa hydrogen and 300℃ to obtain nano-magnesium hydride.

[0033] Comparative Example 2

[0034] Based on Example 1, only steps S1 and S2 were performed, without step S3, to construct the composite coating layer and obtain the MgH2@MXene complex.

[0035] Test method:

[0036] (1) The product’s cycle stability was tested by long-term constant temperature and pressure cycling test;

[0037] (2) The initial hydrogenation temperature of the product was tested by high-pressure differential scanning calorimetry (HP-DSC);

[0038] (3) The specific surface area of ​​the sample was tested by BET nitrogen adsorption.

[0039] (4) The morphology of the product was tested by transmission electron microscopy (TEM).

[0040] Performance verification:

[0041] (1) Ultra-long cycle stability: The test showed that the hydrogen storage capacity retention rate of the nano-magnesium hydride prepared in Example 1 of the present invention was 95.4% after 3000 cycles. This indicates that the cycle stability of the product of the present invention is significantly better than that of Comparative Example 1. This is due to the dual stabilization mechanism of the MXene confined framework and the titanium dioxide-amorphous carbon composite coating layer in the product.

[0042] (2) Initial dehydrogenation temperature: According to HP-DSC test, the initial dehydrogenation temperature of the nano magnesium hydride in Example 1 of this invention is 99℃, and the initial dehydrogenation temperature of the nano magnesium hydride prepared in Comparative Example 1 is 225℃. This is because the nano size of the product magnesium hydride shortens the hydrogen diffusion path and increases the surface energy. At the same time, the TiH2 catalytic phase generated in situ by MXene and the titanium dioxide layer rich in oxygen vacancies work together to serve as a highly efficient active site for hydrogen atom composite desorption, which fundamentally reduces the reaction energy barrier.

[0043] (3) Morphology and specific surface area: such as Figure 1 As shown, under transmission electron microscopy (TEM), the magnesium hydride nanoparticles prepared in Example 1 exhibit a distinct and abundant mesoporous / plate-like structure; the specific surface area of ​​the magnesium hydride nanoparticles in Example 1 of this invention is 153 m² / g, as determined by BET testing. 2 / g, significantly higher than Comparative Example 1, which is attributed to its abundant mesoporous / lamellar structure.

[0044] Table 1. Data Comparison between Embodiments of the Invention and Comparative Examples

[0045]

[0046] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing nano-magnesium hydride, characterized in that, Includes the following steps: S1. Preparation of magnesium nanoparticles by gas-phase condensation: Under the protection of an inert gas, metallic magnesium raw material is heated and evaporated to generate magnesium vapor; the magnesium vapor is then contacted with and condensed in a mixed gas flow of hydrogen and inert gas to form magnesium nanoparticles with a particle size of 10~50nm; wherein, the volume percentage of hydrogen in the mixed gas flow is 5%~30%, and the temperature is -50~0℃. S2.MXene confined catalytic hydrogenation: The magnesium nanoparticles obtained in step S1 are combined with Ti3C2T x MXene nanosheets were uniformly mixed and then subjected to catalytic hydrogenation at 150-250°C in a hydrogen atmosphere with a pressure of 3-6 MPa for 2-10 h to form a MgH2@MXene complex. S3. Atomic layer deposition to construct a composite coating layer: Using atomic layer deposition technology, a titanium dioxide layer with a thickness of 1~4 nm containing oxygen vacancies and an amorphous carbon layer with a thickness of 0.5~2 nm are sequentially deposited on the surface of the MgH2@MXene composite obtained in step S2, forming a titanium dioxide-amorphous carbon composite coating layer with a total thickness of less than 5 nm, thus obtaining nano-magnesium hydride.

2. The method for preparing nano-magnesium hydride according to claim 1, characterized in that, In step S1, the magnesium vapor is brought into contact with the mixed gas flow of hydrogen and inert gas for a time of <0.1s.

3. The method for preparing nano-magnesium hydride according to claim 1, characterized in that, In step S2, the Ti3C2T x MXene nanosheets are three-dimensional wrinkled structures formed by hexadecyltrimethylammonium bromide intercalation and self-assembly, with a specific surface area >100 m². 2 / g.

4. The method for preparing nano-magnesium hydride according to claim 1, characterized in that, In step S3, the titanium dioxide layer is obtained by performing atomic layer deposition cycles of 20 to 40 times at 80 to 150°C using titanium source and oxygen source as precursors.

5. The method for preparing nano-magnesium hydride according to claim 3, characterized in that, The titanium source includes tetra(dimethylamino)titanium or titanium tetrachloride.

6. The method for preparing nano-magnesium hydride according to claim 3, characterized in that, The oxygen source includes ozone or water.

7. The method for preparing nano-magnesium hydride according to claim 1, characterized in that, In step S3, the amorphous carbon layer is obtained by chemical vapor deposition or atomic layer deposition using ethylene or propylene as the carbon source at a temperature of 200~400℃.

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