High-activity nano-magnesium powder hydrogen storage material, and preparation method and application thereof

Abstract

The application discloses high-activity nano-magnesium powder hydrogen storage material and a preparation method and application thereof. The preparation method comprises the following steps: in a closed environment of inert atmosphere or mixed atmosphere of inert atmosphere and hydrogen, a magnesium source is gasified by a high-temperature plasma method to form magnesium atom vapor; in an inert carrier gas environment, the magnesium atom vapor is cooled and uniformly nucleated to form magnesium nanoparticles; the magnesium nanoparticles enter an integrated classification system, are screened by a classification screen, are separated by gas-solid separation, and then in-situ surface passivation of the magnesium nanoparticles is performed to obtain high-activity nano-magnesium powder hydrogen storage material. The preparation method provided by the application realizes high-stability continuous production, accurate gradient classification of product particle size, significantly improves raw material utilization rate and reduces maintenance cost, and the prepared high-activity nano-magnesium powder hydrogen storage material has high stability and excellent hydrogen absorption and release activity, and can be widely applied in the field of hydrogen energy.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen energy storage materials technology, specifically relating to a highly active nano-magnesium powder hydrogen storage material, its preparation method, and its application. Background Technology

[0002] Hydrogen energy, as a clean and efficient secondary energy source, is considered a core carrier of future energy transformation. In the hydrogen energy industry chain, safe and efficient solid-state hydrogen storage technology is a crucial link connecting hydrogen production and application. Magnesium-based hydrogen storage materials are widely recognized as a commercially viable solid-state hydrogen storage medium due to their significant advantages, including a theoretical hydrogen storage capacity of up to 7.6 wt%, high abundance in the Earth's crust, low cost, and environmental friendliness. However, the excessively high thermodynamic stability of magnesium-based materials means that their hydrogen release temperature typically needs to be above 350 ℃. Furthermore, the slow diffusion rate of hydrogen in the magnesium lattice, coupled with the easy oxidation of the magnesium surface to form a dense passivation layer, severely hinders the dissociation and permeation of hydrogen molecules, limiting their practical application in low-temperature scenarios such as fuel cell vehicle hydrogen storage and distributed energy storage.

[0003] To improve the hydrogen storage performance of magnesium-based materials, existing technologies mainly employ modification methods such as high-energy ball milling, wet chemical synthesis, and physical vapor deposition. While high-energy ball milling can effectively reduce particle size and introduce catalysts, this process is typically time-consuming and energy-intensive. The intense mechanical collisions easily introduce metallic impurities such as iron and chromium, and the resulting lattice damage is often accompanied by severe amorphization and impurity defect pinning, leading to pulverization and agglomeration of the material during hydrogen adsorption and desorption cycles, resulting in poor cycle stability. Although wet chemical synthesis offers relatively mild reaction conditions, it requires the use of surfactants and organic reducing agents. These large organic molecules are difficult to completely remove, and the residues often cover the active sites on the material surface, hindering hydrogen adsorption and dissociation. Furthermore, this process involves cumbersome post-processing steps and generates large amounts of wastewater and waste liquid, making it difficult to meet green manufacturing industrial standards.

[0004] Compared to the methods mentioned above, physical vapor deposition (PVD) based on DC arc plasma can theoretically produce high-purity magnesium nanoparticles because it eliminates the need for grinding media and chemical reagents. However, in practical applications, traditional arc evaporation processes have significant technical drawbacks. First, existing technologies induce magnesium vaporization and condensation in a mixed atmosphere of Ar / acetylene and other carbon sources. While this can control particle size, the resulting carbon coating layer, as an inactive phase, not only reduces the hydrogen storage capacity per unit mass of the material but also significantly increases the resistance to hydrogen molecule penetration into the particle interior, hindering the development of low-temperature kinetic performance.

[0005] Furthermore, in terms of the system architecture, existing ultrafine metal particle preparation systems mostly use deep filtration media such as sintered tubes, filter cotton, or bag filters as the main classification and collection devices. This has significant drawbacks when processing highly active nano-magnesium powder. Since nanoparticles are very easy to enter the deep layers of the medium and cause blockage, the system back pressure will rise rapidly in a short time and cause plasma arc instability, making it difficult to maintain long-term continuous production. Moreover, existing single-stage collection devices cannot effectively remove micron-sized molten splash droplets generated during arc gasification, resulting in an excessively wide product particle size distribution and poor consistency in hydrogen storage performance. In addition, the intercepted oversized particles often adhere to the surface of the filter element or deposit at the bottom of the cavity, making it impossible to achieve in-situ real-time material recycling. This not only wastes raw materials but also significantly increases the frequency of system cleaning and maintenance.

[0006] In summary, developing a nano-magnesium powder preparation technology that can ensure atomic-level cleanliness of the material surface while possessing precise classification, automatic online material recycling, and long-term stable voltage trapping capabilities is a key technical challenge for overcoming the application bottlenecks of magnesium-based materials and promoting the industrialization of hydrogen energy. Summary of the Invention

[0007] The main objective of this invention is to provide a highly active nano-magnesium powder hydrogen storage material, its preparation method, and its application, in order to overcome the technical problems existing in the preparation technology of magnesium-based hydrogen storage materials, such as many residual impurities, uneven particle size distribution, low production efficiency, easy clogging of the collection system, and the resulting poor hydrogen absorption and desorption kinetics.

[0008] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0009] The first aspect of this invention provides a method for preparing a highly active nano-magnesium powder hydrogen storage material, comprising:

[0010] In a closed environment with an inert atmosphere or a mixture of inert atmosphere and hydrogen, a high-temperature plasma method is used to vaporize the magnesium source to form magnesium atom vapor.

[0011] In an inert carrier gas environment, the magnesium atom vapor is cooled and uniformly nucleated to form magnesium nanoparticles;

[0012] The magnesium nanoparticles are introduced into an integrated classification system, screened by a classification sieve, and subjected to gas-solid separation. Then, the magnesium nanoparticles undergo in-situ surface passivation to obtain a highly active nano-magnesium powder hydrogen storage material.

[0013] A second aspect of the present invention provides a highly active nano-magnesium powder hydrogen storage material prepared by the preparation method, comprising a core and an MgO passivation layer covering the core, wherein the core has lattice distortion and a metastable phase.

[0014] A third aspect of the present invention provides the application of the aforementioned highly active nano-magnesium powder hydrogen storage material in the field of hydrogen energy.

[0015] A fourth aspect of the present invention provides a medium-low temperature solid hydrogen storage medium with an operating temperature of 150~350 °C, which includes the aforementioned highly active nano-magnesium powder hydrogen storage material.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects:

[0017] (1) The method provided by this invention significantly improves the hydrogen absorption and desorption kinetics. Unlike the existing technology that introduces carbon source gas to form a carbon coating layer, this invention uses a purely physical plasma vaporization and rapid cooling process to ensure that the nano-magnesium powder has high purity and abundant surface active sites, effectively avoiding the shielding of active sites by inactive phases or residual organic matter. At the same time, the high rapid cooling rate induces high-density lattice distortion and metastable phases inside the particles. The unique "clean surface + metastable core" structure of this application provides a fast channel for hydrogen atom diffusion and significantly reduces the reaction energy barrier, making it exhibit excellent kinetic activity under medium and low temperature conditions, which is superior to commercial Mg powder, and the hydrogen absorption and desorption kinetics are significantly improved.

[0018] (2) The method provided by this invention ensures production continuity and system stability. This invention achieves dynamic penetration of nanoparticles rather than static accumulation by using a multi-stage screen with an inclined arrangement combined with dynamic airflow shearing action. This fundamentally avoids the deep blockage problem that is very easy to occur in deep filtration media such as sintering tubes or filter cotton, and keeps the pressure drop fluctuation of the system inlet and outlet within ±2 kPa. While ensuring the continuous stability of the plasma arc, it completely solves the technical problem of the system being forced to shut down due to a surge in back pressure, and realizes the long-term continuous production of highly active nanoparticles.

[0019] (3) The method provided by this invention achieves high raw material utilization and online in-situ circulation. By utilizing the gradient interception function of the gradient grading system from 400 mesh to 1600 mesh, large-sized splashes are effectively removed through step-by-step interception and precise cutting of the end nanofiltration membrane, resulting in a narrow particle size distribution and good performance consistency of the product. Micron-sized molten splash droplets generated in the electric arc zone are effectively removed. The built-in V-shaped circulation channel is used to send the intercepted material back to the evaporation chamber for remelting in real time under the drive of gravity and differential pressure, which greatly improves the raw material utilization rate. While significantly reducing production costs, it avoids the cleaning difficulty and safety hazards caused by waste deposits on the inner wall of the chamber.

[0020] (4) The method provided by the present invention achieves precise physical control of particle size distribution. The present invention achieves precise separation of powder particle size through a gradient interception architecture composed of a stepped screen and a terminal nanofiltration membrane. This ensures the structural stability of the hydrogen storage material during multiple cycles of hydrogen charging and discharging, effectively avoids local stress concentration and material pulverization caused by uneven particle size, and improves the cycle life of the material.

[0021] (5) Through the deep integration of structural design and process innovation, this invention has fundamentally broken through the core performance bottleneck of magnesium-based hydrogen storage materials, providing key technical support for their practical application in low-temperature scenarios such as fuel cell vehicle hydrogen storage and distributed energy storage, and promoting the industrialization of the hydrogen energy industry chain. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a scanning electron microscope (SEM) image of the nano-magnesium powder prepared in Example 1 of the present invention;

[0024] Figure 2 This is a histogram of the particle size distribution of the nano-magnesium powder prepared in Example 1 of this invention;

[0025] Figure 3 This is a scanning electron microscope (SEM) image of commercially available magnesium powder in Comparative Example 1 of this invention;

[0026] Figure 4 This is an X-ray diffraction (XRD) pattern of the nano-magnesium powder prepared in Example 1 of this invention;

[0027] Figure 5 This is a kinetic curve of the nano-magnesium powder of Example 1 of the present invention at 325 °C;

[0028] Figure 6 This is the kinetic curve of commercial magnesium powder in Comparative Example 1 of this invention at 325 °C. Detailed Implementation

[0029] In view of the problems existing in the prior art, the inventors of this invention, through extensive and in-depth research, provide a highly active nano-magnesium powder hydrogen storage material, its preparation method, and its application. The invention will be further explained below.

[0030] The first aspect of this invention provides a method for preparing a highly active nano-magnesium powder hydrogen storage material, comprising:

[0031] In a closed environment with an inert atmosphere or a mixture of inert atmosphere and hydrogen, a high-temperature plasma method is used to vaporize the magnesium source to form magnesium atom vapor.

[0032] In an inert carrier gas environment, the magnesium atom vapor is cooled and uniformly nucleated to form nanoparticles;

[0033] The magnesium nanoparticles are introduced into an integrated classification system, screened by a classification sieve, and subjected to gas-solid separation. Then, the magnesium nanoparticles undergo in-situ surface passivation to obtain a highly active nano-magnesium powder hydrogen storage material.

[0034] In some embodiments, the preparation method specifically includes: in a sealed cavity, using a magnesium source as the anode and a tungsten electrode as the cathode, applying a DC voltage of 20~50 V and a current of 50~150 A under the inert atmosphere or the mixed atmosphere, the generated high-temperature plasma vaporizes the magnesium source to form the magnesium atom vapor.

[0035] Furthermore, the magnesium source comprises magnesium ingots, the purity of which is above 99.9%.

[0036] Furthermore, the inert atmosphere includes argon or helium.

[0037] Furthermore, the volume ratio of inert atmosphere to hydrogen in the mixed atmosphere is 90~95:5~10.

[0038] Furthermore, the vaporization time is 5 to 60 minutes.

[0039] Furthermore, the oxygen content in the enclosed environment is ≤100 ppm.

[0040] In some embodiments, the preparation method specifically includes: introducing the magnesium atom vapor into a pressure of 0.01~0.1 MPa at a flow rate of 10~50 L·min. -1 In an inert carrier gas environment, with 10 4 ~10 6 K·s -1 The temperature is cooled to 100~300 °C at a cooling rate, so that the magnesium atom vapor can be uniformly nucleated to form magnesium nanoparticles.

[0041] Furthermore, the inert carrier gas includes helium.

[0042] Furthermore, the cooling time is 0.1 to 2 seconds.

[0043] In some embodiments, the preparation method specifically includes: introducing an airflow carrying the magnesium nanoparticles into the integrated classification system, wherein the classification screens are sequentially arranged along the airflow direction inside the integrated classification system; after being screened by each level of screens, nanoparticles with a particle size exceeding 1600 mesh are recycled and remelted; the magnesium nanoparticles that pass through the screens enter a nano-collection device for gas-solid separation; and then the screened nanoparticles undergo in-situ surface passivation to obtain the highly active nano-magnesium powder hydrogen storage material.

[0044] Furthermore, the various levels of screens are inclined relative to the horizontal plane.

[0045] Furthermore, each level of the screen is at an angle of 30° to 60° to the horizontal plane.

[0046] Furthermore, the grading screen includes a three-stage screen.

[0047] Furthermore, the diameters of the three-stage screens are 400 mesh, 800 mesh, and 1600 mesh, respectively.

[0048] Furthermore, a V-shaped circulation channel is used to circulate and remelt the ultra-sized nanoparticles.

[0049] Furthermore, the nano-capture device employs a high-temperature resistant nanofiltration membrane with a pore size of 100~800 nm.

[0050] Furthermore, the high-temperature resistant nanofiltration membrane includes at least one of polytetrafluoroethylene (PTFE) filter membrane or ceramic nanofiltration membrane.

[0051] Furthermore, the in-situ surface passivation includes: treating the nanoparticles under an oxygen partial pressure of 50~200 Pa for 10~30 min to form a 2~5 nm thick MgO passivation layer.

[0052] Specifically, the technical solution of this invention adopts "electric arc melting and condensation + integrated staged circulation", and the preparation method specifically includes the following steps:

[0053] (1) Preparation environment construction and raw material pretreatment: In a closed chamber, high-purity magnesium ingots with a purity ≥99.9% were placed in a water-cooled copper crucible (anode), and a tungsten rod was used as the cathode; the chamber was evacuated to ≤1×10 -3 Pa is filled with high-purity inert gas (Ar / He) or Ar / H2 mixture (H2 volume percentage 5~10%) to create an oxygen-free and moisture-free environment.

[0054] (2) DC arc plasma vaporization: Apply a DC voltage of 20~50 V and a current of 50~150 A to initiate an arc. The temperature at the center of the arc is extremely high, which causes the magnesium ingot to vaporize and form a high-purity magnesium atom vapor flow, avoiding impurity contamination caused by mechanical contact.

[0055] (3) Inert carrier gas transport and ultra-high-speed condensation: at 10~50 L·min -1 The flow rate forms a directional carrier gas flow, and the cavity pressure is maintained at 0.0~0.1 MPa; magnesium atom vapor is carried away from the high-temperature zone by the carrier gas, and after 10 4 ~10 6 K· Ultra-fast cooling of 0.1~2 s leads to explosive and uniform nucleation, forming nanoparticles rich in lattice defects.

[0056] (4) Online airflow classification and recycling: The airflow carrying nanoparticles enters the integrated classification system and is screened through three levels of inclined metal screens (400 mesh, 800 mesh, and 1600 mesh metal screens) set in the flow channel at an angle to the horizontal plane (each level of screen is at an angle of 30-60° to the horizontal plane). Particles of the target size pass through the 1600 mesh screen and enter the collection chamber through the nanofiltration membrane. During this process, the shear force generated by the carrier gas dynamically cleans the material adhering to the screen surface, while oversized particles and molten splashes are automatically returned to the crucible for remelting under the action of gravity or pneumatic circulation channels, realizing efficient in-situ utilization and precise classification of raw materials.

[0057] (5) In-situ surface passivation and collection: A small amount of oxygen (oxygen partial pressure 50~200 Pa) is introduced into the collection chamber and treated for 10~30 minutes to form a 2~5 nm thick MgO passivation layer; after cooling to room temperature, it is sealed and collected to ensure both material safety and activity.

[0058] In this invention, the integrated graded filtration system is fixedly connected to the sealed cavity, and the connection is sealed with a fluororubber sealing ring to ensure that the oxygen content inside the cavity is ≤100 ppm. The entire preparation process is carried out continuously in the sealed cavity.

[0059] The nano-capture device uses a high-temperature resistant nanofiltration membrane with a pore size of 100~800 nm. The nanofiltration membrane works in conjunction with the screens at each stage in the preceding stage to control the pressure drop fluctuation at the system inlet and outlet within ±2 kPa throughout the entire production process.

[0060] The method provided by this invention employs a purely physical high-speed condensation combined with trace oxygen partial pressure passivation technology to construct a discontinuous oxide layer on the atomically clean particle surface. This ensures storage safety while reserving highly efficient hydrogen adsorption sites through structural defects. Furthermore, it utilizes an inclined gradient screen system and a dual-path (working gas / carrier gas) air intake layout, leveraging dynamic airflow shear force to achieve online screen cleaning.

[0061] The second aspect of the present invention provides a highly active nano-magnesium powder hydrogen storage material prepared by the preparation method, comprising a core and an MgO passivation layer covering the core, wherein the core has lattice distortion and a metastable phase.

[0062] In some embodiments, the highly active nano-magnesium powder hydrogen storage material is in particulate form with a particle diameter of 500~800nm.

[0063] In some embodiments, the thickness of the MgO passivation layer is 2-5 nm, and the uniformity of the MgO passivation layer is ≥ 90%.

[0064] In some embodiments, the highly active nano-magnesium powder hydrogen storage material has a hydrogen absorption capacity greater than 4.9 wt% within 15 minutes under a hydrogen pressure of 3 MPa and a temperature of 325 °C.

[0065] A third aspect of the present invention provides the application of the aforementioned highly active nano-magnesium powder hydrogen storage material in the field of hydrogen energy.

[0066] In some implementations, the application includes the use of the highly active nano-magnesium powder hydrogen storage material as a medium- and low-temperature solid hydrogen storage medium in fuel cell vehicle hydrogen storage systems or distributed energy storage systems.

[0067] A fourth aspect of the present invention provides a medium-low temperature solid hydrogen storage medium with an operating temperature of 150~350°C, which includes the aforementioned highly active nano-magnesium powder hydrogen storage material.

[0068] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0069] For experiments not specifically described in the examples, the procedures or conditions can be performed according to conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified can be obtained commercially. Other unmentioned raw materials and instruments are all conventionally chosen and do not involve the core technical means of this invention.

[0070] Example 1

[0071] Step 1, Raw Material Preparation: Weigh 50 g of 99.9% pure high-purity magnesium ingots, polish the surface oxide layer with 1200-grit sandpaper, ultrasonically clean with anhydrous ethanol for 15 minutes, vacuum dry at 60 ℃ for 2 hours, and place it in a 60 mm inner diameter water-cooled copper crucible (anode), with a tungsten rod as the cathode; prepare 99.999% pure high-purity helium gas as both working gas and carrier gas. Simultaneously, connect 99.99% pure oxygen to an independent passivation gas path connected to the end collection chamber for later use in the in-situ passivation treatment of step 5. During steps 1 to 4, keep the valve of this gas path completely closed to ensure an absolutely oxygen-free and safe environment for the initial vaporization and high-temperature condensation processes.

[0072] Step 2, Cavity Pretreatment: Move the water-cooled copper crucible into the sealed cavity, install the tungsten electrodes and adjust the spacing to 3 mm; start the vacuum pump group to evacuate the cavity to a vacuum level of 5 × 10⁻⁶ mm. -4 Maintain the pressure at 0.1 MPa for 30 minutes; then fill the chamber with helium to 0.1 MPa and evacuate again to 5 × 10⁻⁶ MPa. -4 Pa, repeated 3 times.

[0073] Step 3, Arc vaporization and condensation: Activate the gas path control system and divide it into two inputs. The first input is the working gas, which is introduced through the annular nozzle at the root of the tungsten electrode to coat the cathode, with a flow rate set to 5 L·min. -1 The first channel is used to initiate and maintain a stable plasma arc flame. The second channel is the carrier gas, which is injected at high speed through a fan-shaped diffusion nozzle above the crucible side, with a flow rate set at 30 L / min. -1 A directional turbulent flow field is formed above the evaporation zone of the crucible. The DC power supply is turned on and the arc is ignited under a 30 V, 100 A helium atmosphere. Magnesium atom vapor enters the condensation zone formed by the carrier gas the instant it leaves the crucible surface, flowing at a rate of 10... 6 K·s -1 The particles were rapidly cooled to 150 °C at a rate of 0.5 s to nucleate, resulting in nanoparticles with high-density lattice distortion.

[0074] Step 4, Integrated grading and recycling: The airflow carrying nanoparticles is graded through 400-mesh, 800-mesh, and 1600-mesh sieves. Each sieve is at a 45° angle to the horizontal plane. Particles of the target size pass through the 1600-mesh sieve and enter the collection chamber through the nanofiltration membrane. Oversized particles (greater than 1600 mesh) are recycled back to the crucible for remelting, improving the utilization rate of raw materials.

[0075] Step 5, Nanofiltration Collection and In-situ Passivation: Target particle size particles enter the collection chamber through a 500 nm PTFE nanofiltration membrane. After gas-solid separation is complete, the valve of the independent passivation gas path is opened to slowly introduce oxygen into the collection chamber, controlling the oxygen partial pressure at 100 Pa, and passivating for 30 minutes. After cooling to room temperature, the product is collected and sealed for storage.

[0076] The scanning electron microscope (SEM) image of the magnesium nanoparticles prepared in this embodiment is shown below. Figure 1 As shown, its particle size distribution histogram is as follows: Figure 2 As shown; X-ray diffraction (XRD) pattern as follows Figure 4 As shown; the kinetic curve at 325 °C is as follows. Figure 5 As shown.

[0077] Test results: The average particle size of the high-activity nano-magnesium powder hydrogen storage material in this study is approximately 500 nm, with low impurity content and a purity of approximately 99.95%. At 325 °C and 3 MPa, it reaches a saturation capacity of 5.0 wt% after 15 minutes of initial hydrogen absorption. The thickness of the MgO passivation layer is approximately 3.2 nm, with a uniformity of >95%.

[0078] Example 2

[0079] Step 1, Raw Material Preparation: Select 40 g of 99.9% pure high-purity magnesium ingots, lightly polish the surface oxide layer with 800-grit sandpaper, quickly rinse with anhydrous ethanol for 1 minute, and air dry naturally before placing it in a 60 mm inner diameter water-cooled copper crucible (anode), with a tungsten rod as the cathode; prepare 99.999% pure high-purity helium gas as both working gas and carrier gas. Simultaneously, connect 99.99% pure oxygen to an independent passivation gas path connected to the end collection chamber for later use in the in-situ passivation treatment of step 5. During steps 1 to 4, keep the valve of this gas path completely closed to ensure an absolutely oxygen-free and safe environment for the initial vaporization and high-temperature condensation processes.

[0080] Step 2, Cavity Pretreatment: Move the water-cooled copper crucible into the sealed cavity, install the tungsten electrodes and adjust the spacing to 5 mm; start the single-stage rotary vane vacuum pump to evacuate the cavity to a vacuum level of 1×10⁻⁶. -2 Maintain the pressure at 0.1 MPa for 20 minutes; then fill the cavity with argon gas to 0.1 MPa, and finally evacuate to 1 × 10⁻⁶ MPa. -2 Pa, only 2 replacements are performed to ensure that the residual oxygen content in the cavity is ≤100 ppm.

[0081] Step 3, Arc vaporization and condensation: Working gas path (argon) flow rate 5 L·min -1 Carrier gas path (helium) flow rate: 30 L / min -1The electric arc is ignited in an argon atmosphere at 20 V and 50 A. Magnesium atom vapor enters the condensation zone. Due to the decrease in arc energy density, the cooling rate is controlled at 10. 5 K·s -1 Cool to 200 ℃ for 1.5 s.

[0082] Step 4, Integrated Grading and Circulation: The airflow carrying nanoparticles enters the integrated grading and filtration system. The airflow carrying nanoparticles is graded through 400-mesh, 800-mesh, and 1600-mesh screens. Each screen is at a 30° angle to the horizontal plane. Particles of the target size pass through the 1600-mesh screen and enter the collection chamber through the nanofiltration membrane. Oversized particles (greater than 1600 mesh) are returned to the crucible through a gravity circulation channel without the need for additional power.

[0083] Step 5, Nanofiltration Collection and In-situ Passivation: Target particles passing through the classification system enter the terminal collection chamber, where gas-solid separation is performed using a ceramic nanofiltration membrane with a pore size of 800 nm. After separation, an independent passivation gas path is opened, and a trace amount of oxygen is introduced into the collection chamber, controlling the oxygen partial pressure at 150 Pa. Passivation is performed for 20 minutes. The power supply and carrier gas are then turned off, and the product is collected and sealed for storage after the chamber has naturally cooled to room temperature.

[0084] Test results: The average particle size of the high-activity nano-magnesium powder hydrogen storage material in this study is approximately 750 nm, with low impurity content and a purity of approximately 99.88%. At 325 °C and 3 MPa, it reaches a saturation capacity of 4.85 wt% after 15 minutes of initial hydrogen absorption. The thickness of the MgO passivation layer is approximately 4.1 nm, with a uniformity of >90%.

[0085] Example 3

[0086] Step 1, Raw material preparation: Select 80 g of high-purity magnesium ingots with a purity of 99.9%, process them according to the standard of Example 1, and place them in a water-cooled copper crucible with an automatic feeding device; prepare Ar / H2 mixed gas as working gas and helium gas with a purity of 99.999% as carrier gas. At the same time, prepare oxygen with a purity of 99.99% in an independent gas line outside the equipment, which is dedicated to the in-situ passivation treatment in the subsequent step 5, to ensure that the early vaporization and condensation process is in an absolutely oxygen-free environment.

[0087] Step 2, Cavity Pretreatment: Install tungsten electrodes and adjust the spacing to 3 mm, start the compound vacuum pump group, and evacuate the cavity to a vacuum level of 5 × 10⁻⁶ mm. -4 Maintain at 0.1 MPa for 30 minutes; then fill the chamber with an Ar / H2 mixture to 0.1 MPa and evacuate to 5 × 10⁻⁶ MPa. -4 Pa, replace 3 times to ensure the residual oxygen content in the chamber is ≤50 ppm; preheat the collection chamber to 80 ℃ in advance.

[0088] Step 3, Arc vaporization and condensation: Argon-hydrogen mixture is introduced into the cavity, and the cavity pressure is adjusted to 0.01 MPa and the carrier gas flow rate is adjusted to 50 L·min. -1 Turn on the DC power supply, set the voltage to 50 V and the current to 150 A, ignite the electric arc, and the H2 in the mixed gas reacts slightly with the magnesium vapor to form the MgH2 intermediate, which catalyzes and accelerates the gasification of magnesium ingots, with a gasification rate approximately 15% higher than in Example 1. The metal atom vapor and the MgH2 intermediate are rapidly cooled under the transport of helium carrier gas, with a cooling rate of 8 × 10⁻⁶. 5 K·s -1 The mixture was cooled to 120 °C for 0.8 s. The presence of H2 promoted uniform nucleation of atoms, improved nucleation efficiency, and formed a large number of nanoparticles in a short time.

[0089] Step 4, Integrated Grading and Circulation: Activate the three-stage sieves (400 mesh, 800 mesh, and 1600 mesh) of the integrated grading filtration system. Each sieve is at a 60° angle to the horizontal plane. Activate the ultrasonic airflow acceleration device to increase the airflow velocity in the grading zone to 60 m / s. -1 The screening efficiency is improved by about 20% compared to Example 1; the target particle size particles pass through a 1600-mesh sieve and enter the collection chamber through a nanofiltration membrane, while oversized particles (greater than 1600 mesh) are immediately returned to the crucible through a spiral conveyor circulation channel without the need to stop and wait, thus realizing continuous gasification-screening cycle.

[0090] Step 5, Nanofiltration Collection and In-situ Passivation: Target particles passing through the grading system enter the end-stage collection device, where gas-solid separation is performed using a 700 nm PTFE nanofiltration membrane. After collection, a "segmented passivation" process is adopted: First, an independent passivation gas path is opened, and oxygen at a partial pressure of 100 Pa is introduced for 15 minutes, followed by the introduction of a trace amount of Ar / H2 mixed gas for 5 minutes to form a surface film with both activity and stability. The collection chamber uses a continuous discharge device, collecting the product every 30 minutes without shutting down the equipment, and a single operation can produce continuously for 6 hours.

[0091] Test results: The average particle size of the high-activity nano-magnesium powder hydrogen storage material in this study is approximately 650 nm, with low impurity content and a purity of approximately 99.90%. At 325 ℃ and 3 MPa, it reaches a saturation capacity of 4.93 wt% after 15 minutes of initial hydrogen absorption. The thickness of the MgO passivation layer is approximately 2.5 nm, and the uniformity is approximately >98%.

[0092] Example 4

[0093] The difference between this embodiment and Embodiment 1 is that the working gas used is an argon-hydrogen mixture with a different ratio (Ar / H2 = 92:8).

[0094] Step 1, Raw Material Preparation: Select 80 g of high-purity magnesium ingots (99.9% purity). Polish the surface oxide layer with 1200-grit sandpaper, ultrasonically clean with anhydrous ethanol for 15 minutes, and vacuum dry at 60 ℃ for 2 hours. Place the ingots in a water-cooled copper crucible with an inner diameter of 60 mm. Prepare an Ar / H2 mixture (92:8) as the working gas and 99.999% pure helium as the carrier gas. Simultaneously, connect 99.99% pure oxygen to an independent passivation gas path connected to the end collection chamber for later use in the in-situ passivation treatment in step 5. During the operation of steps 1 to 4, keep the valve of this gas path completely closed to ensure that the initial vaporization and high-temperature condensation processes are in an absolutely oxygen-free and safe environment.

[0095] Steps 2–5 are the same as in Example 3.

[0096] Test results: The average particle size of the high-activity nano-magnesium powder hydrogen storage material in this study is approximately 630 nm, with low impurity content and a purity of approximately 99.91%. At 325 ℃ and 3 MPa, it reaches a saturation capacity of 4.95 wt% after 15 minutes of initial hydrogen absorption. The thickness of the MgO passivation layer is approximately 2.5 nm, and the uniformity is approximately >96%.

[0097] Example 5

[0098] The difference between this embodiment and Embodiment 1 is that the working gas used is an argon-hydrogen mixture with a different ratio (Ar / H2 = 90:10).

[0099] Step 1, Raw Material Preparation: Select 80 g of high-purity magnesium ingots with a purity of 99.9%, process them according to the standard of Example 1, and place them in a water-cooled copper crucible equipped with an automatic feeding device; prepare an Ar / H2 mixture (90:10) as the working gas and 99.999% pure helium as the carrier gas. Simultaneously, connect 99.99% pure oxygen to an independent passivation gas path connected to the end collection chamber for later use in the in-situ passivation treatment of Step 5. During the operation of Steps 1 to 4, keep the valve of this gas path completely closed to ensure that the initial vaporization and high-temperature condensation processes are conducted in an absolutely oxygen-free and safe environment.

[0100] Steps 2–5 are the same as in Example 3.

[0101] Test results: The average particle size of the high-activity nano-magnesium powder hydrogen storage material in this study is approximately 610 nm, with low impurity content and a purity of approximately 99.92%. At 325 °C and 3 MPa, it reaches a saturation capacity of 4.98 wt% after 15 minutes of initial hydrogen absorption. The thickness of the MgO passivation layer is approximately 2.6 nm, and the uniformity is approximately >97%.

[0102] Comparative Example 1

[0103] This comparative example uses commercial Mg powder.

[0104] Scanning electron microscope (SEM) image of commercially available magnesium powder as shown below Figure 3 As shown; Figure 6 The graph shows the kinetics of commercial magnesium powder at 325 °C. At 325 °C, the hydrogen absorption capacity is only 2.3 wt% within 45 minutes.

[0105] Comparative Example 2

[0106] The difference between this comparative example and Example 1 is that large pieces of magnesium powder are forcibly broken up by impact with stainless steel balls. This method mainly relies on mechanical shearing, which can refine the grains, but cannot eliminate the "hereditary" nature of the original coarse grains, and is very easy to introduce impurities such as iron and chromium from the grinding balls.

[0107] Step 1, Raw material preparation: Select 50 g of high-purity magnesium ingots with a purity of 99.9%, lightly sand the surface oxide layer with 800-grit sandpaper, rinse quickly with anhydrous ethanol for 1 minute, let it air dry naturally, cut it into small pieces, put it into a high-energy ball mill jar, add stainless steel grinding balls, and the ball-to-material ratio is 20:1.

[0108] Step 2, ball milling: Under argon protection, set the rotation speed to 400 rpm and continuously ball mill for 20 hours.

[0109] Step 3, Product Collection: After ball milling is completed, unload the material in the glove box to obtain ball-milled magnesium powder.

[0110] Test results: The particles in the comparative sample exhibited an irregular, flaky shape with an average particle size of approximately 5-10 μm (significantly larger than the 500 nm of the present invention), and their distribution was extremely uneven. Hydrogen absorption tests were conducted at 325 °C and 3 MPa, and the hydrogen absorption capacity was only 1.2 wt% within 15 minutes. Reaching saturation capacity (approximately 4.0 wt%) required more than 120 minutes, indicating that the hydrogen absorption kinetics of the material prepared by mechanical ball milling were significantly lower than those of the present invention.

[0111] Comparative Example 3

[0112] The difference between this comparative example and Example 1 is that the cooling rate is slow (cooling rate is 10). 2 K·s -1 At this point, the carrier gas flow rate is low, the heat exchange efficiency is poor, and magnesium vapor undergoes significant crystal growth and agglomeration, resulting in a substantial decrease in the material's specific surface area, thus losing its ability to rapidly absorb hydrogen under medium and low temperature conditions.

[0113] Step 1, Raw material preparation: exactly the same as in Example 1.

[0114] Step 2, cavity pretreatment: exactly the same as in Example 1.

[0115] Step 3, Arc vaporization and slow condensation: Turn on the gas path control system. Set the first working gas flow rate to 5 L·min. -1 The flow rate of the second carrier gas (helium) was significantly reduced to 2 L·min. -1 (Example 1 is 30 L·min) -1 Furthermore, the fan-shaped diffuser nozzle was removed, resulting in a low-speed laminar flow above the crucible's evaporation zone. The DC power supply was then turned on to ignite the arc. After the magnesium atom vapor detached from the crucible, the heat transfer efficiency in the condensation zone decreased significantly due to the extremely low carrier gas velocity, with a cooling rate of only 10. 2 K·s -1 about.

[0116] Step 4, grading and screening: The airflow carrying particles passes through a sieve with the same mesh size as in Example 1. Due to the slow cooling, the particles remain in space for a long time and undergo violent collisions and thermal fusion.

[0117] Step 5, trapping and passivation: Same as in the example.

[0118] Test results: Due to the excessively slow cooling rate, magnesium vapor had ample time for crystal growth, resulting in particles exhibiting severe coarsening and agglomeration. The average particle size increased to 3–8 μm (micrometer scale), with a regular surface morphology and lacking the lattice distortion and defects caused by high cooling rates. At 325 °C and 3 MPa hydrogen pressure, due to the sharp decrease in specific surface area and the absence of internal active sites, the hydrogen absorption capacity was only 1.1 wt% within 15 minutes, and it took more than 180 minutes to reach saturation capacity.

[0119] Comparative Example 4

[0120] The difference between this comparative example and Example 1 is that the integrated system only has a primary screen and no grading screen.

[0121] Steps 1-3: exactly the same as in Example 1.

[0122] Step 4, conventional collection: The airflow carrying nanoparticles passes through only a 400-mesh sieve for classification and directly enters the end collection device.

[0123] Step 5, trapping and passivation treatment: same as in Example 1.

[0124] Test results: Due to the lack of graded screening, the product contained a large number of micron-sized droplets (large particles) generated by crucible splashing, with severely polarized particle sizes. At 325 °C, due to the high proportion of large particles, the hydrogen absorption capacity after 15 minutes was only 2.8 wt%. Furthermore, due to the absence of a material return system, the raw material utilization rate was reduced by more than 40% compared to Example 1.

[0125] Comparative Example 5

[0126] The difference between this comparative example and Example 1 is that a V-shaped circulation channel was not provided.

[0127] Step 1, Raw material preparation: exactly the same as in Example 1.

[0128] Step 2, cavity pretreatment: exactly the same as in Example 1.

[0129] Step 3, Arc vaporization and condensation: exactly the same as in Example 1, maintaining the same cooling rate (10 6 K·s -1 ).

[0130] Step 4, conventional return material screening: The airflow carrying nanoparticles is graded through three levels of sieves: 400 mesh, 800 mesh, and 1600 mesh. The sieves are not inclined and no V-shaped circulation channel is installed. Large particles are returned only through simple horizontal pipes, lacking gravity-induced sliding and differential pressure backflow drive.

[0131] Step 5, Nanofiltration Capture and Continuous Operation Test: Target particles passing through the classification system enter the nanofiltration membrane device. During continuous operation, the pressure drop fluctuations at the system inlet and outlet are monitored in real time.

[0132] Test Results: Due to the lack of self-cleaning and gravity return functions of the V-shaped channel, oversized droplets easily accumulate on the screen surface, causing a "material trapping" phenomenon and resulting in localized blockage of the flow channels. After only 40 minutes of system operation, the pressure drop fluctuation on the nanofiltration membrane surface increased from the initial ±2 MPa to ±12 MPa, forcing the production line to be interrupted for manual cleaning. Compared to Example 1 (which enables continuous production), this comparative example has an extremely short effective operating time, and due to poor material return, a large number of large particles are mistakenly trapped in the filter membrane layer, resulting in significant micron-sized particulate impurities in the finished product, with a hydrogen absorption capacity of only 3.8 wt%.

[0133] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0134] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A method for preparing a highly active nano-magnesium powder hydrogen storage material, characterized in that, include: In a closed environment with an inert atmosphere or a mixture of inert atmosphere and hydrogen, a high-temperature plasma method is used to vaporize the magnesium source to form magnesium atom vapor. In an inert carrier gas environment, the magnesium atom vapor is cooled and uniformly nucleated to form magnesium nanoparticles; The magnesium nanoparticles are introduced into an integrated classification system, screened by a classification sieve, and subjected to gas-solid separation. Then, the magnesium nanoparticles undergo in-situ surface passivation to obtain a highly active nano-magnesium powder hydrogen storage material.

2. The preparation method according to claim 1, characterized in that, Specifically, it includes: In a sealed cavity, a magnesium source is used as the anode and a tungsten electrode as the cathode. Under the inert atmosphere or the mixed atmosphere, a DC voltage of 20~50 V and a current of 50~150 A are applied. The resulting high-temperature plasma vaporizes the magnesium source to form magnesium atom vapor.

3. The preparation method according to claim 2, characterized in that: The magnesium source includes magnesium ingots, and the purity of the magnesium ingots is above 99.9%. And / or, the inert atmosphere includes argon or helium; And / or, the volume ratio of inert atmosphere to hydrogen in the mixed atmosphere is 90:10 to 95:5; And / or, the vaporization time is 5 to 60 minutes; And / or, the oxygen content in the enclosed environment is ≤100 ppm.

4. The preparation method according to claim 1, characterized in that, Specifically, it includes: The magnesium atom vapor is introduced into a system with a pressure of 0.01~0.1 MPa and a flow rate of 10~50 L·min. -1 In an inert carrier gas environment, with 10 4 ~10 6 K·s -1 The temperature is cooled to 100~300 °C at a cooling rate, so that the magnesium atom vapor is uniformly nucleated to form the magnesium nanoparticles. Preferably, the inert carrier gas includes helium; Preferably, the cooling time is 0.1 to 2 seconds.

5. The preparation method according to claim 1, characterized in that, Specifically, it includes: An airflow carrying the magnesium nanoparticles is introduced into the integrated classification system. The integrated classification system has classification screens arranged sequentially along the airflow direction. After being screened by each level of screens, nanoparticles with a particle size exceeding 1600 mesh are recycled and remelted. The magnesium nanoparticles that pass through the screens enter the nano-capture device for gas-solid separation. After that, the screened nanoparticles undergo in-situ surface passivation to obtain the highly active nano-magnesium powder hydrogen storage material.

6. The preparation method according to claim 5, characterized in that: The various levels of screens are set at an angle relative to the horizontal plane; Preferably, each level of the screen is at an angle of 30° to 60° to the horizontal plane; And / or, the grading screen includes a three-stage screen; Preferably, the diameters of the three-stage sieves are 400 mesh, 800 mesh, and 1600 mesh, respectively. And / or, a V-shaped circulation channel is used to circulate and remelt the nanoparticles with a particle size exceeding 1600 mesh; And / or, the nano-capture device uses a high-temperature resistant nanofiltration membrane with a pore size of 100~800 nm; Preferably, the high-temperature resistant nanofiltration membrane includes at least one of polytetrafluoroethylene (PTFE) filter membrane or ceramic nanofiltration membrane; And / or, the in-situ surface passivation includes: treating the nanoparticles under an oxygen partial pressure of 50~200 Pa for 10~30 min to form a 2~5 nm thick MgO passivation layer.

7. The highly active nano-magnesium powder hydrogen storage material prepared by the preparation method according to any one of claims 1-6, characterized in that, It includes a core and an MgO passivation layer covering the core, the core having lattice distortion and a metastable phase; Preferably, the highly active nano-magnesium powder hydrogen storage material is in particulate form with a particle diameter of 500~800 nm; Preferably, the thickness of the MgO passivation layer is 2~5 nm, and the uniformity of the MgO passivation layer is ≥ 90%. Preferably, the hydrogen absorption capacity of the highly active nano-magnesium powder hydrogen storage material is greater than 4.9 wt% within 15 minutes under a hydrogen pressure of 3 MPa and a temperature of 325 °C.

8. The application of the highly active nano-magnesium powder hydrogen storage material according to claim 7 in the field of hydrogen energy.

9. The application according to claim 8, characterized in that: The applications include the use of the highly active nano-magnesium powder hydrogen storage material as a medium- and low-temperature solid hydrogen storage medium in fuel cell vehicle hydrogen storage systems or distributed energy storage systems.

10. A medium- and low-temperature solid hydrogen storage medium, characterized in that, The operating temperature is 150~350℃, including the highly active nano-magnesium powder hydrogen storage material as described in claim 7.

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