Hydride hydrogen storage material and preparation method thereof

Abstract

The invention belongs to the field of hydrogen storage materials, and provides a hydride hydrogen storage material and a preparation method thereof. According to the preparation method, a block material is prepared through discharge plasma sintering forming by adopting a multi-level collaborative design of a reactive composite hydride phase formed by magnesium hydride and lithium borohydride, an ordered mesoporous carbon and hexagonal boron nitride composite carrier structure, an atomic layer deposition oxide coating layer, a niobium pentoxide and titanium hydride catalyst and a heat-conducting outer coating; the comprehensive performance that the reversible hydrogen storage mass fraction is 5.5-7.0 wt%, the capacity retention ratio after 50 times of circulation is larger than or equal to 90%, and the temperature gradient in the block is smaller than or equal to 10 DEG C / cm is achieved, and the multiple contradictions between the high hydrogen storage capacity and the block mechanical strength, between the oxide coating layer stability and the hydrogen diffusion rate and between the heat conduction uniformity and the structural integrity are solved. The method has a wide application value in a solid hydrogen storage system.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen storage materials and provides a hydride hydrogen storage material and its preparation method. Background Technology

[0002] Driven by the urgent demand for high-density clean energy in fields such as new energy vehicles, distributed energy storage, and aerospace, solid-state hydrogen storage technology has become an important technological path for hydrogen energy applications due to its high safety and large volumetric hydrogen storage density. In practical hydrogen storage systems, hydrogen storage materials need to simultaneously meet multi-dimensional performance requirements, including high reversible hydrogen storage capacity, rapid hydrogen absorption and desorption kinetics, excellent cycle stability, and good mechanical strength. Especially in on-board hydrogen storage applications, hydrogen storage materials not only need to store a sufficient mass of hydrogen within a limited volume to meet driving range requirements, but also need to maintain structural integrity and avoid pulverization failure during frequent hydrogen absorption and desorption cycles. Simultaneously, uniform heat transfer during hydrogen absorption and desorption is required to prevent localized overheating and safety hazards. Against this backdrop, developing bulk solid-state hydrogen storage materials that combine high hydrogen storage capacity, excellent cycle stability, sufficient mechanical strength, and good thermal conductivity is of great significance for promoting the practical application of hydrogen energy technology, broadening the application scope of hydrogen storage materials, and improving the overall performance of hydrogen storage systems.

[0003] Currently, magnesium hydride-based composite hydrogen storage materials have attracted widespread attention due to their high theoretical hydrogen storage capacity and abundant resources. However, there are still many shortcomings in the development of these materials. In existing technologies, although the kinetic performance of powdered magnesium hydride composite materials can be improved through nano-sizing and catalytic modification, they face problems in practical applications such as difficulty in forming powder materials, low bulk density, poor heat and mass transfer performance, and easy agglomeration and sintering during cycling, resulting in insufficient volumetric hydrogen storage density and difficulties in system integration. For example, Chinese patent CN120328484B discloses a method for preparing magnesium-based hydrogen storage materials and a magnesium-based hydrogen storage material, but it suffers from insufficient mechanical strength after bulk forming and easy pulverization or cracking during repeated hydrogen absorption and desorption. For example, Chinese patent CN108923034A discloses a method for preparing a hydrogen storage alloy with a surface-coated reduced graphene oxide-metal composite and a negative electrode material for nickel-metal hydride batteries. However, it has shortcomings such as difficulty in precisely controlling the thickness of the coating layer, excessively thick coating layers hindering hydrogen diffusion and causing a decrease in kinetic performance, and excessively thin coating layers failing to effectively suppress surface side reactions. Summary of the Invention

[0004] The purpose of this invention is to provide a hydride hydrogen storage material and its preparation method, which solves the contradiction between strength and porosity in existing solid-state hydrogen storage systems. This contradiction arises from the need to ensure hydrogen storage capacity and rapid mass transfer while maintaining a high content of reactive hydride phase (60-90 wt%) and a porosity of 5-15 vol%, while simultaneously preventing bulk pulverization or cracking. Furthermore, it addresses the contradiction between shell stability and hydrogen flux in existing solid-state hydrogen storage systems. This contradiction arises from the need to maintain hydrogen diffusion rate to achieve a reversible capacity of 5.5-7.0 wt% while suppressing side reactions and improving cycle stability with a 5-15 nm thick TiO2 / Al2O3 coating. Finally, it addresses the contradiction between strength and thermal safety in existing systems. This contradiction arises from the need to maintain structural integrity and avoid thermal stress cracking under a high volume fraction of reactive phase while controlling the temperature gradient to ≤10℃ / cm by introducing a mesoporous carbon / hexagonal boron nitride composite support and a thermally conductive outer coating.

[0005] This invention adopts a "synergistic enhancement" design concept. It constructs a core-shell structure that confines a magnesium hydride and lithium borohydride reactive composite hydride phase within an ordered mesoporous carbon and hexagonal boron nitride composite support. It also features a TiO2 / Al2O3 oxide coating layer with precisely controlled thickness achieved by atomic layer deposition, a niobium pentoxide and titanium hydride dual catalyst system, and a hexagonal boron nitride / aluminum nitride thermally conductive outer coating. Furthermore, it uses a discharge plasma sintering process to control the pore structure and relative density of the bulk material. This achieves a comprehensive balance of high hydrogen storage capacity, rapid hydrogen absorption and desorption kinetics, excellent cycle stability, sufficient mechanical strength, and good thermal conductivity. While ensuring that the bulk material has a reversible hydrogen storage mass fraction of 5.5-7.0 wt% and a capacity retention rate of ≥90% after more than 50 cycles, it ensures that the bulk material does not undergo overall pulverization or penetrating macroscopic cracks during repeated hydrogen absorption and desorption. Moreover, the internal temperature gradient of the bulk material under hydrogen absorption and desorption conditions is ≤10℃ / cm.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A hydride hydrogen storage material, which is a bulk material formed by discharge plasma sintering, the hydride hydrogen storage material comprising the following components, based on the total mass of the bulk material: A reactive composite hydride phase consisting of magnesium hydride and lithium borohydride, with a total mass fraction of 60–90 wt%, wherein the molar ratio of magnesium hydride to lithium borohydride is 1.0–1.5:1; A composite support structure composed of ordered mesoporous carbon and hexagonal boron nitride, wherein the total mass fraction of ordered mesoporous carbon and hexagonal boron nitride is 5–30 wt%. An oxide coating layer loaded on the surface of the reactive composite hydride phase particles, wherein the oxide coating layer includes a titanium dioxide coating layer and / or an aluminum oxide coating layer; A catalyst distributed in the bulk material, the catalyst comprising niobium pentoxide and titanium hydride; A thermally conductive outer coating is disposed on the outer surface of the bulk material, the thermally conductive outer coating being composed of hexagonal boron nitride powder and / or aluminum nitride powder; The overall open-pore porosity of the bulk material is 5–15 vol%, and the mass fraction of each component is selected within its corresponding range so that the sum of the mass fractions of each component does not exceed 100 wt%.

[0007] Furthermore, the reactive complex hydride phase is prepared via the following steps: A1. Raw material preparation: Weigh magnesium hydride, lithium borohydride, ordered mesoporous carbon powder and hexagonal boron nitride powder under an inert gas atmosphere. By mass, magnesium hydride is 100 parts, lithium borohydride is 55-83 parts, ordered mesoporous carbon is 5-30 parts, and hexagonal boron nitride is 5-30 parts, so that the molar ratio of magnesium hydride to lithium borohydride is 1.0-1.5:1. A2. Ball milling and mixing: The raw material powder from step A1 is placed in a closed ball mill jar filled with inert gas and ball milled and mixed to obtain a composite powder in which magnesium hydride, lithium borohydride, ordered mesoporous carbon and hexagonal boron nitride are uniformly mixed. A3. Melting and Pore Confinement: The composite powder obtained in step A2 is placed in a sealed container and kept at a temperature of 280–320°C and an atmosphere pressure of 0.1–5.0 MPa under hydrogen protection to melt and penetrate the pores of the composite support structure. Then it is cooled to room temperature to obtain a composite powder of magnesium hydride-lithium borohydride reactive composite hydride confined in an ordered mesoporous carbon and hexagonal boron nitride composite support structure. A4. Hydrogen atmosphere activation treatment: The composite powder obtained in step A3 is placed in a container and activated in a hydrogen atmosphere under hydrogen pressure and heating conditions to obtain confined reactive composite hydride powder as a raw material for subsequent processes.

[0008] Furthermore, the oxide coating layer is prepared by an atomic layer deposition process, comprising: B1. Precursor selection: When the oxide coating layer is a titanium dioxide coating layer, tetraisopropoxy titanium and water are used as alternating precursors; when the oxide coating layer is an aluminum oxide coating layer, trimethylaluminum and water are used as alternating precursors. B2. Loading and pretreatment: The confined reactive composite hydride powder obtained in step A4 is uniformly spread on the carrier disk of the atomic layer deposition reaction chamber and pretreated under heating and vacuum conditions with inert gas as carrier gas. B3. Atomic Layer Deposition: Under heating and depressurization conditions, metal-organic precursor pulses and water pulses are alternately performed. Each atomic layer deposition cycle includes a metal-organic precursor pulse, inert gas purging, water pulse, and inert gas purging again. The total number of cycles is 100–500, so that a continuous and uniform titanium dioxide film or aluminum oxide film is formed on the surface of the composite powder particles. B4. Cooling and Collection: After stopping the supply of precursors, the reaction chamber is cooled under an inert atmosphere, and the composite hydride powder with an oxide film on its surface is collected.

[0009] Furthermore, the bulk material is prepared through the following steps: discharge plasma sintering and thermally conductive outer coating construction: C1. Catalyst addition and mixing: Under an inert gas atmosphere, the atomic layer deposition coated composite powder obtained in step B4 is mixed with niobium pentoxide powder and titanium hydride powder to obtain a uniformly mixed sintering raw material powder. C2. Molding and Pre-compression: The sintered raw material powder obtained in step C1 is filled into the inner cavity of the graphite mold, and pre-compression is applied at room temperature to obtain a pre-compressed block; C3. Discharge plasma sintering: Under a protective atmosphere, a graphite mold containing pre-compressed blocks is placed in a discharge plasma sintering device, heated and held at a temperature under axial pressure for sintering. During the sintering process, the absolute pressure inside the furnace is controlled within the range of 0.01–0.1 MPa. The sintering conditions are adjusted so that the resulting block has open and interconnected pores. C4. Construction of thermally conductive outer coating: After cooling the sintered block obtained in step C3 to room temperature, a slurry prepared by hexagonal boron nitride powder and / or aluminum nitride powder with volatile solvent is coated on the outer surface of the block, and a pre-coating is formed after drying; C5. Coating curing: The pre-coating is heated in an inert gas atmosphere to enhance the bonding strength between the thermally conductive outer coating and the bulk substrate, and then cooled to room temperature to obtain a bulk material with a thermally conductive outer coating.

[0010] Furthermore, the density of the bulk material is greater than 1.0 g / cm³, and it will not undergo overall pulverization or penetrating macroscopic cracks during hydrogen absorption and desorption cycles.

[0011] Furthermore, the bulk material is pretreated as follows before first use: it is activated under heating conditions at hydrogen pressure, and subjected to multiple hydrogen pre-cycles of absorption and desorption between different hydrogen pressures.

[0012] As a concept of this invention, this invention employs a multi-level synergistic design involving a magnesium hydride and lithium borohydride reactive composite hydride phase confined within an ordered mesoporous carbon and hexagonal boron nitride composite support, atomic layer deposition oxide coating, a dual catalyst system, and a thermally conductive outer coating. This design primarily enhances the reversible hydrogen storage capacity, cycle stability, mechanical strength, and thermal uniformity of bulk hydrogen storage materials. The reactive composite hydride system composed of magnesium hydride and lithium borohydride reduces the dehydrogenation enthalpy change of each phase through chemical coupling reactions between the two phases, resulting in milder thermodynamic conditions for hydrogen absorption and desorption compared to a single hydride phase. Simultaneously, by controlling the molar ratio of magnesium hydride to lithium borohydride within the range of 1.0-1.5:1, the stoichiometric ratio of the two phases is ensured to be close to the optimal value, thereby achieving good reversibility while maintaining a high theoretical hydrogen storage capacity. The introduction of the ordered mesoporous carbon and hexagonal boron nitride composite support structure achieves nanoscale confinement of the reactive composite hydride phase through the high specific surface area and uniform pore structure of the ordered mesoporous carbon, effectively inhibiting the agglomeration and growth of hydride particles during repeated hydrogen adsorption and desorption cycles, maintaining the stability of the nanoscale active phase structure and shortening the hydrogen diffusion path. On the other hand, the high thermal conductivity of hexagonal boron nitride constructs a thermally conductive network inside the bulk material, promoting rapid heat conduction during hydrogen adsorption and desorption, reducing the internal temperature gradient of the bulk, and the chemical inertness of hexagonal boron nitride prevents it from undergoing side reactions with the hydride phase. Atomic layer deposition (ALD) technology constructs a dense coating layer of titanium dioxide or aluminum oxide on the surface of confined composite hydride powder particles, with a thickness that can be precisely controlled within the range of 5-15 nm. This ultrathin oxide coating layer serves as a gas-solid interface protective layer, effectively isolating the hydride phase from direct contact with external oxygen and water vapor, suppressing side reactions such as surface oxidation and hydrolysis, and improving the environmental stability and cycle life of the material. On the other hand, due to the nanoscale thickness of the coating layer and the presence of defects such as oxygen vacancies in the oxide lattice, hydrogen atoms can diffuse through the coating layer-hydride phase interface, thus protecting the surface without significantly reducing hydrogen diffusion kinetics. The synergistic effect of the niobium pentoxide and titanium hydride dual catalyst system lies in the fact that niobium pentoxide mainly provides catalytic active sites for the dehydrogenation and rehydrogenation processes of the lithium borohydride phase, lowering the kinetic energy barrier of the lithium borohydride phase transition reaction, while titanium hydride mainly provides catalysis for the hydrogenation-dehydrogenation reaction of the magnesium hydride phase. The combination of the two catalysts allows both phases in the reactive composite hydride system to obtain effective catalysis, thereby improving the overall hydrogen adsorption and desorption kinetics performance.The discharge plasma sintering process, through the synergistic effect of pulsed current and axial pressure, achieves rapid densification of powder particles at relatively low sintering temperatures and short holding times. Simultaneously, by precisely controlling process parameters such as sintering temperature, pressure, and holding time, the bulk material can maintain an open, interconnected porosity of 5-15 vol% while achieving sufficient mechanical strength. This porosity provides channels for rapid hydrogen mass transfer within the bulk material and acts as a buffer space for the volume expansion and contraction of the hydride phase during hydrogen absorption and desorption, preventing bulk cracking failure due to volume changes. A hexagonal boron nitride or aluminum nitride thermally conductive outer coating on the outer surface of the bulk material further enhances heat transfer between the bulk material and the external heat exchange medium. Combined with the internal thermally conductive network constructed from hexagonal boron nitride, this achieves an efficient heat conduction path from the inside of the bulk to the outer surface, ensuring that the internal temperature gradient is controlled within 10℃ / cm under hydrogen absorption and desorption conditions. This effectively avoids thermal stress concentration and structural damage caused by localized overheating or overcooling.

[0013] This invention also discloses a method for preparing a hydride hydrogen storage material, comprising the following steps: S1. Reactive composite hydride confined loading step: According to steps A1–A4 of claim 2, magnesium hydride, lithium borohydride, ordered mesoporous carbon and hexagonal boron nitride are mixed, and ball-milled, melt-infiltrated and activated in a hydrogen atmosphere to obtain confined reactive composite hydride powder. S2. Atomic layer deposition coating step: According to steps B1–B4 of claim 3, using tetraisopropoxy titanium and / or trimethylaluminum as atomic layer deposition precursors, perform 100–500 atomic layer deposition cycles under heating and depressurization conditions to form a titanium dioxide coating layer or an aluminum oxide coating layer on the surface of the confined reactive composite hydride powder particles, thereby obtaining atomic layer deposition coated composite powder. S3. Catalyst addition and mixing step: Niobium pentoxide powder and titanium hydride powder are added to the atomic layer deposition coated composite powder obtained in step S2 under an inert gas atmosphere, and mixed to obtain sintering raw material powder; S4. Discharge plasma sintering forming step: The sintering raw material powder from step S3 is loaded into a graphite mold, heated under a protective atmosphere and kept at a temperature under axial pressure for sintering, so that the resulting block has open and interconnected pores. S5. Thermally conductive outer coating construction steps: The outer surface of the block obtained in step S4 is coated with a slurry containing hexagonal boron nitride powder and / or aluminum nitride powder, dried and heated in an inert gas atmosphere to form a thermally conductive outer coating, thereby obtaining a hydride hydrogen storage material.

[0014] Furthermore, in step S1, the ball milling is carried out under an inert gas atmosphere, with a melt penetration temperature of 280–320°C and a penetration atmosphere pressure of 0.1–5.0 MPa.

[0015] Furthermore, in step S2, the duration of a single metal-organic precursor pulse and water pulse is 0.1–5 s, and the inert gas purging time is 1–20 s.

[0016] Furthermore, in step S4, the heat preservation stage uses a pulsed current to perform discharge plasma sintering, and after the heat preservation is completed, the pressure is released after cooling to below 200°C.

[0017] Furthermore, in one embodiment, the total mass fraction of the reactive composite hydride phase is preferably 70–85 wt%. By controlling the ratio of magnesium hydride to lithium borohydride, the phase occupies a high proportion in the bulk material, so as to balance hydrogen storage capacity and forming strength.

[0018] Furthermore, in one embodiment, the ordered mesoporous carbon preferably has an average pore size of 2–10 nm and a specific surface area of ​​800–1500 m² / g, so as to provide a large specific surface area for loading reactive complex hydrides while maintaining the confinement effect.

[0019] Furthermore, in one embodiment, hexagonal boron nitride is preferably hexagonal boron nitride powder with a particle size in the micrometer range, the total mass fraction of ordered mesoporous carbon and hexagonal boron nitride is preferably 10–20 wt%, and the mass ratio of ordered mesoporous carbon to hexagonal boron nitride is preferably 1:(0.7–1.3) to achieve a balance between thermal conductivity and confinement effect.

[0020] Furthermore, in one embodiment, the thickness of the oxide coating layer can be adjusted to the range of 5–15 nm by controlling the number of atomic layer deposition cycles. A thinner coating layer is beneficial for shortening the hydrogen diffusion path, while a thicker coating layer is beneficial for improving cycle stability.

[0021] Furthermore, in one embodiment, the mass fraction of niobium pentoxide in the catalyst is preferably 0.5–1.5 wt%, and the mass fraction of titanium hydride is preferably 2–5 wt%. The combination of this niobium-based and titanium-based catalyst can simultaneously promote the dehydrogenation and rehydrogenation processes of the lithium borohydride phase and the magnesium hydride phase.

[0022] Furthermore, in one embodiment, the average thickness of the thermally conductive outer coating is preferably 20–60 μm. Within this thickness range, the thermal conductivity of the bulk material during hydrogen absorption and desorption can be significantly improved, thereby reducing the temperature gradient and improving cycle stability.

[0023] Furthermore, in one embodiment, the overall open-connected porosity of the bulk material is preferably 5–12 vol%, with lower porosity being beneficial for improving mechanical strength, while higher porosity is beneficial for improving the mass transfer rate of hydrogen within the bulk material.

[0024] Furthermore, in one embodiment, the ball milling time in step A2 is preferably 2–6 h and the ball milling speed is preferably 200–500 r / min, so as to obtain composite powder with a particle size of 1–10 μm, which is beneficial to the uniformity of subsequent melt infiltration and discharge plasma sintering.

[0025] Furthermore, in one embodiment, the water pulse time in step B3 is preferably controlled within the range of 0.1–2 s, and the inert gas purging time is preferably controlled within the range of 1–20 s, in order to reduce the adverse side reactions between water and hydrides, while ensuring the continuity and density of the oxide coating layer.

[0026] Furthermore, in one embodiment, the discharge plasma sintering temperature in step C3 is preferably 280–380°C, and the axial pressure is preferably 30–50 MPa. By adjusting the temperature, pressure, and holding time, the relative density and open interconnected porosity of the resulting bulk material can be kept within a suitable range, thereby taking into account both hydrogen storage performance and mechanical properties.

[0027] Furthermore, in one embodiment, under the test conditions of a specific example, after the bulk material undergoes more than 50 hydrogen absorption and desorption cycles in a hydrogen atmosphere, the reversible hydrogen storage mass fraction can be maintained in the range of 5.5–7.0 wt% and the capacity retention rate is not less than 90%. Moreover, under the hydrogen absorption temperature of 250–350°C, the hydrogen desorption temperature of 200–300°C, and the hydrogen pressure of 0.5–8 MPa, the steady-state temperature gradient along the thickness direction inside the bulk material can be controlled to not exceed 10°C / cm in the embodiment.

[0028] Furthermore, in one embodiment, the density of the bulk material can be controlled at 1.1–1.6 g / cm³, the compressive strength at room temperature can reach 50–200 MPa, and the fracture toughness can reach 1–5 MPa·m¹. ², to ensure sufficient mechanical stability during repeated hydrogen absorption and desorption.

[0029] As another aspect of this invention, a multi-step synergistic preparation process is employed, primarily to enhance the controllability, reproducibility, and overall performance stability of the final product in the bulk hydrogen storage material preparation process. The reactive composite hydride confined loading step involves precisely controlling the ratio of magnesium hydride, lithium borohydride, ordered mesoporous carbon, and hexagonal boron nitride. First, high-energy ball milling is used to achieve uniform mixing of the components and preliminary particle size refinement. Then, utilizing the melting characteristics of lithium borohydride in the 280-320℃ temperature range, molten lithium borohydride is infiltrated into the mesoporous channels of the composite support under a hydrogen protective atmosphere, achieving confined loading of the reactive hydride phase at the nanoscale. Finally, activation treatment in a hydrogen atmosphere mitigates the adverse effects of surface oxidation introduced during the preparation process on hydrogen absorption and desorption performance, and the hydrogen content of the hydride phase is replenished and adjusted to a suitable level under high-pressure hydrogen. The atomic layer deposition (ALD) coating step utilizes the self-confined surface reaction mechanism of the gas-phase precursor to grow titanium dioxide or aluminum oxide films atomically layer by atomic layer on the surface of confined composite hydride powder particles. The coating thickness is precisely adjusted by controlling the deposition cycle count within the range of 100-500 cycles to ensure the uniformity and density of the coating across the entire particle surface. Simultaneously, optimizing the single pulse time and purge time avoids excessive precursor adsorption and byproduct residue, guaranteeing coating quality. The catalyst addition and mixing steps are carried out under inert gas protection to ensure that the coated composite powder does not oxidize during mixing. Niobium pentoxide and titanium hydride catalysts are mechanically mixed and uniformly dispersed in the ALD-coated composite powder, laying the foundation for the uniform distribution of the catalyst in the bulk material during subsequent sintering. The discharge plasma sintering step is a key step in the entire preparation process. By applying axial pressure under a protective atmosphere and simultaneously introducing a pulsed current, the plasma discharge effect and Joule heating effect generated at the particle contact point by the pulsed current promote particle surface activation and rapid sintering densification. Compared with traditional sintering processes, discharge plasma sintering can complete the densification process at a lower temperature and in a shorter time, thereby effectively avoiding the decomposition of hydride phases and excessive grain growth. At the same time, by precisely controlling process parameters such as sintering temperature, pressure, and holding time, it is possible to achieve sufficient mechanical strength in the bulk material while retaining 5-15 vol% of open and interconnected pores. This pore structure is crucial for ensuring the hydrogen adsorption and desorption kinetics and cycle stability of the bulk material. After sintering, depressurization after cooling to below 200°C can prevent bulk cracking caused by high-temperature depressurization. The thermally conductive outer coating construction process involves coating the outer surface of the bulk material with a slurry prepared from hexagonal boron nitride or aluminum nitride powder and a volatile solvent. After drying to remove the solvent, a pre-coating is formed. Subsequently, the material is heated in an inert gas atmosphere. This heat treatment process enhances the bonding strength between the coating powder particles and between the coating and the bulk substrate, forming a thermally conductive outer coating with good thermal conductivity and mechanical bonding strength. This coating serves as the heat conduction interface between the bulk material and the external heat exchange medium, significantly improving the overall thermal uniformity of the bulk material during hydrogen absorption and desorption.

[0030] Through the above-mentioned multi-step synergistic preparation process, the preparation method of the present invention achieves precise control over the entire process, from nanoscale hydride phase confinement loading, atomically thin surface coating, uniform catalyst dispersion, rapid densification of bulk materials, and construction of thermally conductive outer coatings. This ensures that the final bulk hydrogen storage material achieves excellent performance in terms of hydrogen storage capacity, hydrogen absorption and desorption kinetics, cycle stability, mechanical strength, and thermal conductivity.

[0031] In this invention, ordered mesoporous carbon and hexagonal boron nitride serve as a composite support structure, playing distinct yet highly synergistic roles in hydride-based hydrogen storage materials. The main function of ordered mesoporous carbon is to provide a high specific surface area and a uniform, ordered pore structure. Its 2-10 nm mesopore diameter and 800-1500 m² / g specific surface area provide an ideal spatial structure for the nanoscale confinement of reactive composite hydride phases. By confining magnesium hydride and lithium borohydride within the mesoporous channels, the agglomeration and phase separation of hydride particles during repeated hydrogen adsorption / desorption cycles are effectively suppressed, maintaining the nanoscale characteristics of the active phase and shortening the hydrogen diffusion path, thereby significantly improving the hydrogen adsorption / desorption kinetics and cycling stability. The main function of hexagonal boron nitride is to provide excellent thermal conductivity and chemical stability. Its layered crystal structure endows it with a thermal conductivity of up to 200-400 W / (m·K) along the crystal plane. In bulk materials, hexagonal boron nitride particles form a thermally conductive network by overlapping each other, which promotes the rapid conduction of heat during hydrogen absorption and desorption and reduces the internal temperature gradient of the bulk. At the same time, the chemical inertness of hexagonal boron nitride ensures that it does not undergo side reactions with the hydride phase during the entire preparation and use process, and maintains the long-term stability of the support structure. From the perspective of the mechanism of improving hydrogen storage capacity and cycle stability, ordered mesoporous carbon inhibits the particle breakage and agglomeration caused by the volume expansion of the hydride phase during hydrogen absorption and the shrinkage during hydrogen dehydrogenation through the nanoconfinement effect, maintaining the dispersed state of the hydride phase and the number of active sites, thus maintaining a high reversible hydrogen storage capacity after multiple cycles. Meanwhile, hexagonal boron nitride ensures uniform temperature distribution inside the bulk during hydrogen absorption and desorption by constructing a thermally conductive network, avoiding irreversible decomposition of the hydride phase due to local overheating or kinetic stagnation due to local undercooling, thereby ensuring that the hydrogen absorption and desorption reactions occur synchronously throughout the entire bulk, improving capacity utilization and reducing the negative impact of thermal stress caused by temperature gradients on cycle stability. More importantly, the synergistic effect of ordered mesoporous carbon and hexagonal boron nitride in the composite support structure is reflected in the fact that the combination of the two enables the bulk material to maintain high hydrogen storage capacity while also having excellent thermal conductivity. The mesoporous structure of ordered mesoporous carbon not only enables the nanoscale confinement of the hydride phase, but also provides a pore network for the rapid mass transfer of hydrogen inside the bulk material. Meanwhile, the thermally conductive network of hexagonal boron nitride ensures that the heat released or absorbed by the hydrogen absorption and desorption reaction can be rapidly conducted to the outer surface of the bulk material and exchanged with the external heat exchange medium. The synergistic effect of the two enables the bulk material to maintain good mass transfer kinetics and achieve effective thermal management during rapid hydrogen absorption and desorption, thus achieving the best balance between high hydrogen storage capacity, rapid kinetics and excellent cycle stability.

[0032] Beneficial technical effects 1. Achieving a synergistic improvement in high reversible hydrogen storage capacity and excellent cycle stability. By constructing a core-shell structure of magnesium hydride and lithium borohydride reactive composite hydride phase confined within an ordered mesoporous carbon and hexagonal boron nitride composite support, and using atomic layer deposition technology to construct a 5-15 nm thick dense coating layer of titanium dioxide or aluminum oxide on the particle surface, combined with the synergistic catalytic effect of a niobium pentoxide and titanium hydride dual catalyst system, the bulk hydrogen storage material can maintain a high level of reversible hydrogen storage mass fraction of 5.5-7.0 wt%, while retaining a capacity retention rate of over 90% after more than 50 hydrogen adsorption / desorption cycles. This is significantly better than the shortcomings of existing single hydride systems or composite hydride materials without surface coating modification in terms of cycle stability.

[0033] 2. Effectively resolves the contradiction between mechanical strength and porosity in bulk hydrogen storage materials. By employing a discharge plasma sintering process under a protective atmosphere to rapidly densify composite powder coated with atomic layer deposition, and precisely controlling process parameters such as sintering temperature, axial pressure, and holding time, the resulting bulk material maintains a density greater than 1.0 g / cm³ and a compressive strength of 50-200 MPa while retaining an open, interconnected porosity of 5-15 vol%. This pore structure provides channels for rapid hydrogen mass transfer within the bulk material and acts as a buffer space for hydride phase volume changes during hydrogen absorption and desorption, ensuring that the bulk material does not undergo overall pulverization or penetrating macroscopic cracks during repeated hydrogen absorption and desorption cycles. This achieves an optimal balance between high hydrogen storage capacity and good mechanical stability.

[0034] 3. Significantly improves the thermal uniformity and thermal safety of bulk hydrogen storage materials. By introducing hexagonal boron nitride as a component of the composite carrier structure into the bulk material to construct an internal thermally conductive network, and building a hexagonal boron nitride or aluminum nitride thermally conductive outer coating on the outer surface of the bulk material to form an efficient thermal conduction path from the inside to the outside surface, the steady-state temperature gradient along the thickness direction of the bulk material can be controlled within 10℃ / cm under hydrogen absorption and desorption conditions. This effectively avoids the risk of thermal runaway caused by excessively high local temperatures or uneven temperature distribution, as well as structural failure caused by thermal stress concentration, thus ensuring the safe and reliable operation of bulk hydrogen storage materials in actual hydrogen storage systems.

[0035] 4. Achieving a multi-level synergistic design to comprehensively improve the overall performance of hydrogen storage materials. This invention achieves excellent performance in bulk hydrogen storage materials in multiple aspects, including nanoscale hydride phase confinement, atomically thin surface coating, micron-scale catalyst dispersion, bulk-scale pore structure control, and macroscale thermally conductive outer coating construction, through multi-level synergistic optimization design. This results in superior performance in hydrogen storage capacity, hydrogen absorption and desorption kinetics, cycle stability, mechanical strength, and thermal conductivity. Compared to existing technologies that optimize only a single performance indicator, this invention achieves a synergistic improvement in multiple performance indicators, providing a more comprehensive technical solution for the practical application of solid-state hydrogen storage materials. Attached Figure Description

[0036] Figure 1 The graph shows the effect of the mass fraction of the reactive composite hydride phase of the present invention on the reversible hydrogen storage capacity and capacity retention rate after 50 cycles.

[0037] Figure 2 This is a graph showing the effect of the molar ratio of magnesium hydride to lithium borohydride of the present invention on the reversible hydrogen storage capacity and capacity retention rate after 50 cycles.

[0038] Figure 3 This diagram illustrates the effect of the overall open-pore interconnected porosity on the 90% hydrogen absorption completion time and capacity retention rate of this invention.

[0039] Figure 4 This figure shows the effect of the number of atomic layer deposition cycles on the thickness and capacity retention of the titanium dioxide coating layer in this invention.

[0040] Figure 5 This is the XRD measured image of Example 1.

[0041] Figure 6 The image shown is the XRD pattern of Comparative Example 1.

[0042] Figure 7 The image shown is the XRD pattern of Comparative Example 2.

[0043] Figure 8 The bar chart shows the comparison of the mass fraction of each phase in Example 1, Comparative Example 1, and Comparative Example 2.

[0044] Figure 9 Box plots showing the MgH2 grain size comparison for Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0046] Example 1 (a) Reactive complex hydride confined loading step Raw material preparation: Weigh the following raw materials into a glove box filled with high-purity argon gas (purity ≥99.999%, commercially available): 100 parts by weight of magnesium hydride powder (MgH2, average particle size approximately 5 μm, purity ≥95%, commercially available) Lithium borohydride powder (LiBH4, purity ≥95%, commercially available) 69 parts by weight 10 parts by weight of ordered mesoporous carbon (CMK-3 type, average pore size 6nm, specific surface area 1100m² / g, commercially available) 10 parts by weight of hexagonal boron nitride powder (h-BN, average particle size 2μm, purity ≥99%, commercially available) The above ratio results in a molar ratio of magnesium hydride to lithium borohydride of 1.25:1 in this embodiment, which satisfies the scope of the claims.

[0047] Ball milling: The above raw material powder was transferred to a 500 mL stainless steel ball mill jar, with a filling density of approximately 30%. Stainless steel grinding balls were added at a ball-to-material ratio of 10:1. After sealing the jar, high-purity argon gas (0.15 MPa pressure) was introduced, and the mixture was ball-milled for 4 hours at 350 rpm on a planetary ball mill. During the ball milling process, a 10-minute pause was made every 30 minutes to prevent overheating. After ball milling, the uniformly mixed gray composite powder was removed from an argon-filled glove box.

[0048] Melt penetration and pore confinement: The composite powder was placed in a sealed stainless steel container, the inner wall of which was pre-coated with boron nitride to prevent adhesion. The container was placed in a tube furnace, and after evacuation to an absolute pressure below 1 Pa, high-purity hydrogen (purity ≥ 99.999%) was introduced to a pressure of 2.5 MPa. The temperature was raised to 300°C at a heating rate of 10°C / min and held at this temperature for 3 hours. Under these conditions, lithium borohydride melted (melting point approximately 280°C) and, driven by capillary action, diffused into the pores of the composite support structure composed of ordered mesoporous carbon and hexagonal boron nitride in this embodiment. After the holding period, the temperature was lowered to room temperature at a cooling rate of 5°C / min to obtain a light gray composite powder of magnesium hydride-lithium borohydride reactive composite hydride confined within the composite support structure.

[0049] Hydrogen atmosphere activation treatment: The above composite powder was loaded into a pressure-resistant reactor, evacuated, and then filled with high-purity hydrogen to a pressure of 6 MPa. It was then activated at 280°C for 2 hours. After that, it was cooled to room temperature and depressurized to atmospheric pressure to obtain the activated confined reactive composite hydride powder.

[0050] (ii) Atomic layer deposition coating steps Precursor preparation and loading: In this embodiment, the oxide coating layer is a titanium dioxide coating layer. Tetraisopropoxy titanium (TTIP, Ti[OCH(CH3)2]4, purity ≥99.999%, commercially available) and deionized water are used as alternating precursors.

[0051] The aforementioned confined reactive composite hydride powder was uniformly spread on a carrier plate of an atomic layer deposition apparatus, with a powder layer thickness of approximately 2 mm. The carrier plate was placed in the reaction chamber, and a vacuum was drawn to an absolute pressure below 10 Pa. Simultaneously, the chamber was heated to 200 °C, and high-purity nitrogen gas (purity ≥ 99.999%) was introduced as the carrier gas at a flow rate of 200 sccm. The pretreatment lasted for 30 minutes to remove surface-adsorbed moisture and impurities.

[0052] Atomic layer deposition cycle: Maintain the reaction chamber temperature at 200℃ and the chamber pressure at 100Pa. Perform 300 atomic layer deposition cycles, each cycle including the following steps: TTIP pulse: Introduce TTIP vapor for 0.5 seconds. Nitrogen purging: Introduce nitrogen for 10 seconds Water pulse: Introduce water vapor for 0.3 seconds. Nitrogen purging: Introduce nitrogen for 10 seconds The above cycle allows the composite powder particles of this embodiment to grow layer by layer to form a uniform and continuous titanium dioxide film with a thickness of about 9 nm.

[0053] Cooling and Collection: After stopping the precursor supply, the reaction chamber was naturally cooled to below 80°C under a nitrogen atmosphere, and the light brown composite hydride powder with a titanium dioxide film on its surface was collected in an argon glove box.

[0054] (III) Catalyst addition and mixing steps In an argon-filled glove box, 100 parts by weight of the above-mentioned atomic layer deposition coated composite powder were mixed with 1.0 part by weight of niobium pentoxide powder (Nb₂O₅, average particle size approximately 100 nm, purity ≥99.5%, commercially available) and 3.5 parts by weight of titanium hydride powder (TiH₂, average particle size approximately 5 μm, purity ≥98%, commercially available). The mixture was then ball-milled at 150 r / min for 1 hour using a low-energy ball mill to obtain a uniformly dispersed sintered raw material powder for the catalyst.

[0055] (iv) Discharge plasma sintering forming step Mold assembly and pre-pressing: Approximately 15g of the above-mentioned sintering raw material powder was placed into the inner cavity of a graphite mold with an inner diameter of 20mm, and graphite paper was laid on the upper and lower end faces to prevent adhesion. An axial preload of 10MPa was applied at room temperature and held for 2 minutes to obtain a pre-compacted block.

[0056] Discharge plasma sintering: A graphite mold containing a pre-compressed block was placed in a discharge plasma sintering apparatus. High-purity argon gas was introduced into the chamber, and the absolute pressure was controlled at 0.05 MPa. The temperature was increased to 330°C at a heating rate of 50°C / min, while an axial pressure of 40 MPa was applied simultaneously. The temperature was held at 330°C for 10 minutes, and discharge plasma sintering was performed using a pulsed DC current (a pulse sequence of 12 pulses on and 2 pulses off). After the holding period, heating was stopped, and the pressure was maintained. The axial pressure was removed after the temperature naturally dropped to 180°C, and the mold was further cooled to room temperature before being removed, yielding a gray block sintered part with a diameter of approximately 20 mm and a thickness of approximately 5 mm.

[0057] (V) Steps for constructing the thermally conductive outer coating Slurry preparation and coating: 10g of hexagonal boron nitride powder (h-BN, average particle size 1μm, purity ≥99%, commercially available) was mixed with 30mL of anhydrous ethanol (analytical grade, commercially available), and 0.5g of polyvinyl alcohol (PVA, degree of polymerization 1700, commercially available) was added as a binder. The mixture was stirred at 300r / min for 2 hours on a magnetic stirrer to obtain a uniform white slurry.

[0058] The slurry was evenly applied to the outer surface of the sintered block using a brush, with a coating thickness of approximately 40 μm (measured after each application, with the coating thickness measured after drying). The block was then dried in a 60°C oven for 4 hours to allow the ethanol to completely evaporate, forming a pre-coating.

[0059] Coating curing: The pre-coated block was placed in a tube furnace and heated to 400°C at a heating rate of 5°C / min under a high-purity argon atmosphere (flow rate 100 sccm). The temperature was held for 1 hour to enhance the bonding strength between the thermally conductive outer coating and the block substrate in this embodiment. Then, the block was cooled to room temperature with the furnace to obtain a hydride hydrogen storage block material with a thermally conductive outer coating.

[0060] (vi) Characterization and performance testing Structural characterization: Phase analysis of the bulk material in this embodiment was performed using an X-ray diffractometer (XRD, Cu Kα radiation, λ=0.15406nm). Scanning was performed in the range of 2θ=10-80° with a step size of 0.02° and a scan rate of 5° / min. The XRD pattern showed characteristic diffraction peaks of MgH2 at 2θ=27.8°, 40.1°, and 54.5° (corresponding to crystal planes (110), (101), and (211)), characteristic diffraction peaks of LiBH4 at 2θ=18.3°, 23.6°, and 31.2°, characteristic peak (101) of the TiO2 anatase phase at 2θ=25.3°, and characteristic peak (002) of hexagonal boron nitride at 2θ=26.6°. No obvious impurity peaks were observed, indicating that the phase composition remained stable.

[0061] The cross-sectional morphology of the bulk material in this embodiment was observed using scanning electron microscopy (SEM). At an accelerating voltage of 10 kV and a magnification of 5000x, the reactive composite hydride particles were observed to have a size of 2-8 μm, with interconnected open pores of 0.5-3 μm in diameter. High-magnification observation (50000x) revealed a dense TiO2 film approximately 9 nm thick coating on the particle surface.

[0062] The open-pore porosity of the bulk material in this embodiment, determined by mercury porosimetry, was 8.2 vol%, consistent with the design target. The bulk density, determined by Archimedes' displacement method, was 1.38 g / cm³.

[0063] Hydrogen storage performance test: The hydrogen storage performance of the bulk material in this embodiment was determined using the Sieverts method. The bulk material was placed in an argon glove box into a stainless steel reactor, evacuated, and then filled with high-purity hydrogen to a pressure of 5 MPa. It was activated at 300°C for 2 hours to absorb hydrogen, and then dehydrogenated at 280°C and 0.01 MPa for 2 hours. This activation cycle was repeated 3 times.

[0064] The initial hydrogen uptake was 6.8 wt%, the dehydrogenation was 6.2 wt%, and the initial coulombic efficiency was 91.2%. After 50 cycles, the reversible hydrogen storage capacity was 6.0 wt%, and the capacity retention was 96.8%.

[0065] Under the conditions of hydrogen absorption temperature of 300℃ and hydrogen pressure of 5MPa, hydrogen absorption kinetics tests showed that 90% hydrogen absorption was completed in 8 minutes. Under the conditions of hydrogen dehydrogenation temperature of 280℃ and hydrogen pressure of 0.01MPa, 90% hydrogen dehydrogenation was completed in 12 minutes.

[0066] The temperature distribution along the thickness direction of the bulk material in this embodiment during hydrogen absorption was measured using a thermocouple array. The steady-state temperature gradient was approximately 6°C / cm, indicating that the thermally conductive outer coating effectively improved the thermal conductivity of the bulk material.

[0067] Features of this embodiment: This embodiment employs moderate parameter configurations: a reactive composite hydride phase mass fraction of 75 wt%, a magnesium hydride to lithium borohydride molar ratio of 1.25:1, a composite support mass fraction of 17.5 wt%, and a porosity of 8 vol%. A good balance is achieved between hydrogen storage capacity, cycle stability, hydrogen absorption / desorption kinetics, and mechanical strength. A 9 nm thick titanium dioxide coating layer formed through 300 atomic layer deposition cycles effectively suppresses hydride oxidation and aggregation, significantly improving cycle stability. The introduction of a thermally conductive outer coating keeps the temperature gradient of the bulk material low during rapid hydrogen absorption, preventing structural damage caused by localized overheating. This embodiment is suitable for medium-sized stationary hydrogen storage systems with high requirements for hydrogen storage capacity, cycle life, and hydrogen charge / desorption rates, such as buffer hydrogen storage devices in hydrogen refueling stations or hydrogen storage modules in renewable energy storage systems.

[0068] Example 2 (a) Reactive complex hydride confined loading step Raw material preparation: Weigh the following raw materials into a glove box filled with high-purity argon gas (purity ≥99.999%, commercially available): 100 parts by weight of magnesium hydride powder (MgH2, average particle size approximately 5 μm, purity ≥95%, commercially available) 58 parts by weight of lithium borohydride powder (LiBH4, purity ≥95%, commercially available) Ordered mesoporous carbon (CMK-3 type, average pore size 5nm, specific surface area 1200m² / g, commercially available) 6 parts by weight 6 parts by weight of hexagonal boron nitride powder (h-BN, average particle size 2μm, purity ≥99%, commercially available) The above ratio results in a molar ratio of magnesium hydride to lithium borohydride of 1.4:1 in this embodiment, which satisfies the scope of the claims.

[0069] Ball milling: The above raw material powder was transferred to a stainless steel ball mill jar with a volume of 500 mL and a filling degree of approximately 30%. Stainless steel grinding balls were added at a ball-to-material ratio of 10:1. After sealing the ball mill jar, high-purity argon gas (pressure 0.15 MPa) was introduced, and the mixture was ball-milled for 3 hours at a speed of 400 rpm on a planetary ball mill. During the ball milling process, a 10-minute pause was made every 30 minutes to prevent overheating. After ball milling, the uniformly mixed gray composite powder was removed from an argon-filled glove box.

[0070] Melt penetration and pore confinement: The composite powder was placed in a sealed stainless steel container, the inner wall of which was pre-coated with boron nitride to prevent adhesion. The container was placed in a tube furnace, and after being evacuated to an absolute pressure below 1 Pa, high-purity hydrogen (purity ≥ 99.999%) was introduced to a pressure of 3.5 MPa. The temperature was increased to 310 °C at a heating rate of 10 °C / min and held at this temperature for 2.5 hours. After the holding period, the temperature was reduced to room temperature at a cooling rate of 5 °C / min to obtain a light gray composite powder of magnesium hydride-lithium borohydride reactive composite hydride confined within the composite carrier structure of this embodiment.

[0071] Hydrogen atmosphere activation treatment: The above composite powder was loaded into a pressure-resistant reactor, evacuated, and then filled with high-purity hydrogen to a pressure of 7 MPa. It was then activated at 290°C for 2 hours. After that, it was cooled to room temperature and depressurized to atmospheric pressure to obtain the activated confined reactive composite hydride powder.

[0072] (ii) Atomic layer deposition coating steps Precursor preparation and loading: In this embodiment, the oxide coating layer is a titanium dioxide coating layer. Tetraisopropoxy titanium (TTIP, Ti[OCH(CH3)2]4, purity ≥99.999%, commercially available) and deionized water are used as alternating precursors.

[0073] The confined reactive composite hydride powder was uniformly spread on the carrier plate of the atomic layer deposition apparatus, with a powder layer thickness of approximately 2 mm. The carrier plate was placed in the reaction chamber, and the vacuum was evacuated to an absolute pressure below 10 Pa. Simultaneously, the chamber was heated to 200 °C and high-purity nitrogen gas (purity ≥ 99.999%) was introduced as the carrier gas at a flow rate of 200 sccm for 30 minutes of pretreatment.

[0074] Atomic layer deposition cycle: The reaction chamber temperature was maintained at 200°C and the chamber pressure at 100 Pa. 200 atomic layer deposition cycles were performed, each cycle consisting of: a 0.5-second TTIP pulse, a 10-second nitrogen purging, a 0.3-second water pulse, and a 10-second nitrogen purging. These cycles resulted in the formation of a titanium dioxide thin film with a thickness of approximately 6 nm on the surface of the composite powder particles in this embodiment.

[0075] Cooling and Collection: After stopping the precursor supply, the reaction chamber was naturally cooled to below 80°C under a nitrogen atmosphere, and the light brown composite hydride powder with a titanium dioxide film on its surface was collected in an argon glove box.

[0076] (III) Catalyst addition and mixing steps In an argon-filled glove box, 100 parts by weight of the above-mentioned atomic layer deposition coated composite powder were mixed with 0.8 parts by weight of niobium pentoxide powder (Nb₂O₅, average particle size approximately 100 nm, purity ≥99.5%, commercially available) and 2.5 parts by weight of titanium hydride powder (TiH₂, average particle size approximately 5 μm, purity ≥98%, commercially available). The mixture was then ball-milled at 150 r / min for 1 hour using a low-energy ball mill to obtain a uniformly dispersed sintered raw material powder for the catalyst.

[0077] (iv) Discharge plasma sintering forming step Mold assembly and pre-pressing: Approximately 15g of the above-mentioned sintering raw material powder was placed into the inner cavity of a graphite mold with an inner diameter of 20mm, and graphite paper was laid on the upper and lower end faces. An axial preload of 10MPa was applied at room temperature and maintained for 2 minutes.

[0078] Discharge plasma sintering: A graphite mold containing a pre-compressed block was placed in a discharge plasma sintering apparatus. High-purity argon gas was introduced into the chamber, and the absolute pressure was controlled at 0.04 MPa. The temperature was increased to 350°C at a heating rate of 50°C / min, while an axial pressure of 45 MPa was applied simultaneously. The mold was held at 350°C for 8 minutes, and discharge plasma sintering was performed using a pulsed DC current (a pulse sequence of 12 pulses on and 2 pulses off). After the holding period, the temperature was allowed to drop to 180°C before depressurization. The mold was then allowed to cool further to room temperature before removal, yielding a gray block sintered part with a diameter of approximately 20 mm and a thickness of approximately 5 mm.

[0079] (V) Steps for constructing the thermally conductive outer coating Slurry preparation and coating: 8g of hexagonal boron nitride powder (h-BN, average particle size 1μm, purity ≥99%, commercially available) and 2g of aluminum nitride powder (AlN, average particle size 0.5μm, purity ≥99%, commercially available) (mass ratio 4:1) were mixed with 30mL of anhydrous ethanol (analytical grade, commercially available). 0.5g of polyvinyl alcohol (PVA, degree of polymerization 1700, commercially available) was added as a binder. The mixture was stirred at 300r / min for 2 hours on a magnetic stirrer to obtain a uniform white slurry.

[0080] The slurry is evenly applied to the outer surface of the sintered block using a brush, with a coating thickness of approximately 35 μm (by controlling the number of coatings). It is then dried in an oven at 60°C for 4 hours to form a pre-coating.

[0081] Coating curing: The pre-coated block was placed in a tube furnace and heated to 400°C at a heating rate of 5°C / min under a high-purity argon atmosphere (flow rate 100 sccm). The temperature was held for 1 hour, and then cooled to room temperature with the furnace to obtain a hydride hydrogen storage block material with a thermally conductive outer coating.

[0082] (vi) Characterization and performance testing Structural characterization: XRD analysis (Cu Kα radiation, 2θ=10-80°, step size 0.02°) showed characteristic peaks of MgH2, LiBH4, TiO2 anatase phase and h-BN, with no obvious impurity peaks.

[0083] SEM observation (accelerating voltage 10kV, magnification 5000x) shows that the reactive composite hydride particles in this embodiment have a size of 2-6μm, with open, interconnected pores distributed between the particles. High-magnification observation (50000x) reveals that the particle surface is coated with a TiO2 film of approximately 6nm thickness.

[0084] The open-pore porosity of this embodiment was determined to be 6.1 vol% by mercury porosimetry, and the bulk density was determined to be 1.52 g / cm³ by Archimedes method.

[0085] Hydrogen storage performance test: The Sieverts method determined the following: initial hydrogen uptake was 7.2 wt%, dehydrogenation was 6.6 wt%, and initial coulombic efficiency was 91.7%. After 50 cycles, the reversible hydrogen storage capacity was 6.5 wt%, with a capacity retention of 98.5%.

[0086] Hydrogen absorption kinetics (300℃, 5MPa): 90% hydrogen absorption was completed in 7 minutes. Dehydrogenation kinetics (280℃, 0.01MPa): 90% dehydrogenation was completed in 11 minutes.

[0087] The steady-state temperature gradient is approximately 7℃ / cm.

[0088] Features of this embodiment: This embodiment employs a high hydrogen storage capacity configuration, with a reactive composite hydride phase mass fraction reaching 85 wt% and a magnesium hydride to lithium borohydride molar ratio of 1.4:1, maximizing hydrogen storage capacity while ensuring a certain level of cycle stability. The relatively low composite support content (10 wt%) and porosity (6 vol%) result in a bulk density of 1.52 g / cm³, which is beneficial for improving the volumetric hydrogen storage density. The thin titanium dioxide coating layer (6 nm, prepared by 200 atomic layer deposition cycles) shortens the hydrogen diffusion path and improves the hydrogen absorption and desorption kinetics. The thermally conductive outer coating uses a composite formulation of hexagonal boron nitride and aluminum nitride, further enhancing thermal conductivity. This embodiment is suitable for on-board hydrogen storage systems or portable hydrogen storage devices with high requirements for volumetric hydrogen storage density and rapid hydrogen charging rates.

[0089] Example 3 (a) Reactive complex hydride confined loading step Raw material preparation: Weigh the following raw materials into a glove box filled with high-purity argon gas (purity ≥99.999%, commercially available): 100 parts by weight of magnesium hydride powder (MgH2, average particle size approximately 5 μm, purity ≥95%, commercially available) 80 parts by weight of lithium borohydride powder (LiBH4, purity ≥95%, commercially available) Ordered mesoporous carbon (CMK-3 type, average pore size 8nm, specific surface area 950m² / g, commercially available) 18 parts by weight 18 parts by weight of hexagonal boron nitride powder (h-BN, average particle size 2μm, purity ≥99%, commercially available) The above ratio results in a molar ratio of magnesium hydride to lithium borohydride of 1.05:1 in this embodiment, which satisfies the scope of the claims.

[0090] Ball milling: The above-mentioned raw material powder was transferred to a stainless steel ball mill jar with a volume of 500 mL and a filling degree of approximately 30%. Stainless steel grinding balls were added at a ball-to-material ratio of 10:1. After sealing the ball mill jar, high-purity argon gas (pressure 0.15 MPa) was introduced, and the mixture was ball-milled for 5 hours at a speed of 250 rpm on a planetary ball mill. During the ball milling process, a 10-minute pause was made every 30 minutes to prevent overheating. After ball milling, the uniformly mixed gray composite powder was removed from an argon-filled glove box.

[0091] Melt penetration and pore confinement: The composite powder was placed in a sealed stainless steel container, the inner wall of which was pre-coated with boron nitride to prevent adhesion. The container was placed in a tube furnace, and after evacuation to an absolute pressure below 1 Pa, high-purity hydrogen (purity ≥ 99.999%) was introduced to a pressure of 1.0 MPa. The temperature was increased to 290°C at a heating rate of 10°C / min and held at this temperature for 3.5 hours. After the holding period, the temperature was reduced to room temperature at a cooling rate of 5°C / min to obtain a light gray composite powder of magnesium hydride-lithium borohydride reactive composite hydride confined within the composite carrier structure of this embodiment.

[0092] Hydrogen atmosphere activation treatment: The above composite powder was loaded into a pressure-resistant reactor, evacuated, and then filled with high-purity hydrogen to a pressure of 5 MPa. It was then activated at 270°C for 2.5 hours. After that, it was cooled to room temperature and depressurized to atmospheric pressure to obtain the activated confined reactive composite hydride powder.

[0093] (ii) Atomic layer deposition coating steps Precursor preparation and loading: In this embodiment, the oxide coating is an aluminum oxide coating. Trimethylaluminum (TMA, Al(CH3)3, purity ≥99.999%, commercially available) and deionized water are used as alternating precursors.

[0094] The confined reactive composite hydride powder was uniformly spread on the carrier plate of the atomic layer deposition equipment, with a powder layer thickness of approximately 2 mm. The carrier plate was placed in the reaction chamber, and the vacuum was evacuated to an absolute pressure below 10 Pa. Simultaneously, the chamber was heated to 180 °C and high-purity nitrogen gas (purity ≥ 99.999%) was introduced as the carrier gas at a flow rate of 200 sccm for 30 minutes of pretreatment.

[0095] Atomic layer deposition cycle: The reaction chamber temperature was maintained at 180°C and the chamber pressure at 100 Pa. 450 atomic layer deposition cycles were performed, each cycle consisting of: a 0.4-second TMA pulse, a 12-second nitrogen purging, a 0.2-second water pulse, and a 12-second nitrogen purging. These cycles resulted in the formation of an aluminum oxide film with a thickness of approximately 13 nm on the surface of the composite powder particles in this embodiment.

[0096] Cooling and Collection: After stopping the precursor supply, the reaction chamber was naturally cooled to below 80°C under a nitrogen atmosphere, and the white composite hydride powder with a thin film of aluminum oxide on its surface was collected in an argon glove box.

[0097] (III) Catalyst addition and mixing steps In an argon-filled glove box, 100 parts by weight of the above-mentioned atomic layer deposition coated composite powder were mixed with 1.4 parts by weight of niobium pentoxide powder (Nb₂O₅, average particle size approximately 100 nm, purity ≥99.5%, commercially available) and 4.8 parts by weight of titanium hydride powder (TiH₂, average particle size approximately 5 μm, purity ≥98%, commercially available). The mixture was then ball-milled at 150 r / min for 1 hour using a low-energy ball mill to obtain a uniformly dispersed sintered raw material powder for the catalyst.

[0098] (iv) Discharge plasma sintering forming step Mold assembly and pre-pressing: Approximately 15g of the above-mentioned sintering raw material powder was placed into the inner cavity of a graphite mold with an inner diameter of 20mm, and graphite paper was laid on the upper and lower end faces. An axial preload of 10MPa was applied at room temperature and maintained for 2 minutes.

[0099] Discharge plasma sintering: A graphite mold containing a pre-compressed block was placed in a discharge plasma sintering apparatus. High-purity argon gas was introduced into the chamber, and the absolute pressure was controlled at 0.08 MPa. The mold was heated to 295°C at a heating rate of 50°C / min, while an axial pressure of 35 MPa was applied simultaneously. The mold was held at 295°C for 12 minutes, and discharge plasma sintering was performed using a pulsed DC current (a pulse sequence of 12 pulses on and 2 pulses off). After the holding period, the temperature was allowed to drop to 180°C before depressurization. The mold was then allowed to cool further to room temperature before removal, yielding a gray block sintered part with a diameter of approximately 20 mm and a thickness of approximately 5 mm.

[0100] (V) Steps for constructing the thermally conductive outer coating Slurry preparation and coating: 10g of aluminum nitride powder (AlN, average particle size 0.5μm, purity ≥99%, commercially available) was mixed with 30mL of anhydrous ethanol (analytical grade, commercially available), and 0.5g of polyvinyl alcohol (PVA, degree of polymerization 1700, commercially available) was added as a binder. The mixture was stirred at 300r / min for 2 hours on a magnetic stirrer to obtain a uniform grayish-white slurry.

[0101] The slurry was evenly applied to the outer surface of the sintered block using a brush, with a coating thickness of approximately 55 μm (by controlling the number of coatings to 3). The block was then dried in an oven at 60°C for 4 hours to form a pre-coating.

[0102] Coating curing: The pre-coated block was placed in a tube furnace and heated to 400°C at a heating rate of 5°C / min under a high-purity argon atmosphere (flow rate 100 sccm). The temperature was held for 1 hour, and then cooled to room temperature with the furnace to obtain a hydride hydrogen storage block material with a thermally conductive outer coating.

[0103] (vi) Characterization and performance testing Structural characterization: XRD analysis (Cu Kα radiation, 2θ = 10-80°, step size 0.02°) showed characteristic peaks of MgH2, LiBH4 and h-BN, as well as broad scattering peaks of the Al2O3 amorphous phase, with no obvious impurity peaks.

[0104] SEM observation (accelerating voltage 10kV, magnification 5000x) shows that the reactive composite hydride particles in this embodiment have a size of 3-10μm, with numerous open interconnected pores of 1-5μm in diameter. High-magnification observation (50000x) reveals that the particle surface is coated with an Al2O3 film approximately 13nm thick.

[0105] The open-pore porosity of this embodiment was determined to be 12.1 vol% by mercury porosimetry, and the bulk density was determined to be 1.21 g / cm³ by Archimedes method.

[0106] Hydrogen storage performance test: The Sieverts method determined the following: initial hydrogen uptake was 6.2 wt%, dehydrogenation was 5.6 wt%, and initial coulombic efficiency was 90.3%. After 50 cycles, the reversible hydrogen storage capacity was 5.5 wt%, with a capacity retention of 98.2%. After 100 cycles, the capacity retention remained as high as 96.8%, demonstrating excellent cycling stability.

[0107] Hydrogen absorption kinetics (300℃, 5MPa): 90% hydrogen absorption was completed in 10 minutes. Dehydrogenation kinetics (280℃, 0.01MPa): 90% dehydrogenation was completed in 14 minutes.

[0108] The steady-state temperature gradient is approximately 4°C / cm, which is the lowest among all embodiments.

[0109] Features of this embodiment: This embodiment employs a configuration with high cycling stability and excellent thermal conductivity. The reactive composite hydride phase has a mass fraction of 65 wt%, the composite support content is as high as 28 wt%, and the molar ratio of magnesium hydride to lithium borohydride is 1.05:1. The high support content and porosity (12 vol%) provide ample channels for hydrogen mass transfer, which helps reduce diffusion resistance. The thick alumina coating (13 nm, prepared by 450 atomic layer deposition cycles) provides stronger surface protection and significantly improves cycling stability, with a capacity retention of nearly 97% after 100 cycles. The thick aluminum nitride thermally conductive outer coating (55 μm) reduces the temperature gradient of the bulk material during hydrogen absorption and desorption to 4 °C / cm, effectively avoiding localized stress concentration and structural damage caused by temperature unevenness. This embodiment is suitable for large-scale stationary hydrogen storage systems with extremely high requirements for cycle life and long-term stability, such as seasonal hydrogen energy storage devices in grid-scale energy storage systems or industrial hydrogen buffer tanks.

[0110] Example 4 (a) Reactive complex hydride confined loading step Raw material preparation: Weigh the following raw materials into a glove box filled with high-purity argon gas (purity ≥99.999%, commercially available): 100 parts by weight of magnesium hydride powder (MgH2, average particle size approximately 5 μm, purity ≥95%, commercially available) Lithium borohydride powder (LiBH4, purity ≥95%, commercially available) 55.5 parts by weight Ordered mesoporous carbon (CMK-3 type, average pore size 3nm, specific surface area 1400m² / g, commercially available) 5.5 parts by weight 5.5 parts by weight of hexagonal boron nitride powder (h-BN, average particle size 2μm, purity ≥99%, commercially available). The above ratio results in a molar ratio of magnesium hydride to lithium borohydride of 1.48:1 in this embodiment.

[0111] Ball milling: The above raw material powder was transferred to a stainless steel ball mill jar with a volume of 500 mL and a filling degree of approximately 30%. Stainless steel grinding balls were added at a ball-to-material ratio of 10:1. After sealing the ball mill jar, high-purity argon gas (pressure 0.15 MPa) was introduced, and the mixture was ball-milled for 2.5 hours at a speed of 450 rpm on a planetary ball mill. During the ball milling process, a 10-minute pause was made every 30 minutes to prevent overheating. After ball milling, the uniformly mixed gray composite powder was removed from an argon-filled glove box.

[0112] Melt penetration and pore confinement: The composite powder was placed in a sealed stainless steel container, the inner wall of which was pre-coated with boron nitride to prevent adhesion. The container was placed in a tube furnace, and after evacuation to an absolute pressure below 1 Pa, high-purity hydrogen (purity ≥99.999%) was introduced to a pressure of 0.15 MPa. The temperature was increased to 318 °C at a heating rate of 10 °C / min and held at this temperature for 2.5 hours. After the holding period, the temperature was reduced to room temperature at a cooling rate of 5 °C / min to obtain a light gray composite powder of magnesium hydride-lithium borohydride reactive composite hydride confined within the composite carrier structure of this embodiment.

[0113] Hydrogen atmosphere activation treatment: The above composite powder was loaded into a pressure-resistant reactor, evacuated, and then filled with high-purity hydrogen to a pressure of 4.5 MPa. The reactor was then activated at 285°C for 2 hours. After that, it was cooled to room temperature and depressurized to atmospheric pressure to obtain the activated confined reactive composite hydride powder.

[0114] (ii) Atomic layer deposition coating steps Precursor preparation and loading: In this embodiment, the oxide coating layer is a titanium dioxide coating layer. Tetraisopropoxy titanium (TTIP, Ti[OCH(CH3)2]4, purity ≥99.999%, commercially available) and deionized water are used as alternating precursors.

[0115] The confined reactive composite hydride powder was uniformly spread on the carrier plate of the atomic layer deposition apparatus, with a powder layer thickness of approximately 2 mm. The carrier plate was placed in the reaction chamber, and the vacuum was evacuated to an absolute pressure below 10 Pa. Simultaneously, the chamber was heated to 200 °C and high-purity nitrogen gas (purity ≥ 99.999%) was introduced as the carrier gas at a flow rate of 200 sccm for 30 minutes of pretreatment.

[0116] Atomic layer deposition cycle: The reaction chamber temperature was maintained at 200°C and the chamber pressure at 100 Pa. 120 atomic layer deposition cycles were performed, each cycle consisting of: a 0.5-second TTIP pulse, a 10-second nitrogen purging, a 0.3-second water pulse, and a 10-second nitrogen purging. These cycles resulted in the formation of a titanium dioxide thin film with a thickness of approximately 5 nm on the surface of the composite powder particles in this embodiment.

[0117] Cooling and Collection: After stopping the precursor supply, the reaction chamber was naturally cooled to below 80°C under a nitrogen atmosphere, and the light brown composite hydride powder with a titanium dioxide film on its surface was collected in an argon glove box.

[0118] (III) Catalyst addition and mixing steps In an argon-filled glove box, 100 parts by weight of the above-mentioned atomic layer deposition coated composite powder were mixed with 0.5 parts by weight of niobium pentoxide powder (Nb₂O₅, average particle size approximately 100 nm, purity ≥99.5%, commercially available) and 4.5 parts by weight of titanium hydride powder (TiH₂, average particle size approximately 5 μm, purity ≥98%, commercially available). The mixture was then ball-milled at 150 r / min for 1 hour using a low-energy ball mill to obtain a uniformly dispersed sintered raw material powder for the catalyst.

[0119] (iv) Discharge plasma sintering forming step Mold assembly and pre-pressing: Approximately 15g of the above-mentioned sintering raw material powder was placed into the inner cavity of a graphite mold with an inner diameter of 20mm, and graphite paper was laid on the upper and lower end faces. An axial preload of 10MPa was applied at room temperature and maintained for 2 minutes.

[0120] Discharge plasma sintering: A graphite mold containing a pre-compressed block was placed in a discharge plasma sintering apparatus. High-purity argon gas was introduced into the chamber, and the absolute pressure was controlled at 0.015 MPa. The mold was heated to 376°C at a heating rate of 50°C / min, while an axial pressure of 48 MPa was applied simultaneously. The mold was held at 376°C for 7 minutes, and discharge plasma sintering was performed using a pulsed DC current (a pulse sequence of 12 pulses on and 2 pulses off). After the holding period, the temperature was allowed to drop to 180°C before depressurization. The mold was then allowed to cool further to room temperature before removal, yielding a gray block sintered part with a diameter of approximately 20 mm and a thickness of approximately 5 mm.

[0121] (V) Steps for constructing the thermally conductive outer coating Slurry preparation and coating: 10g of hexagonal boron nitride powder (h-BN, average particle size 1μm, purity ≥99%, commercially available) was mixed with 30mL of anhydrous ethanol (analytical grade, commercially available), and 0.5g of polyvinyl alcohol (PVA, degree of polymerization 1700, commercially available) was added as a binder. The mixture was stirred at 300r / min for 2 hours on a magnetic stirrer to obtain a uniform white slurry.

[0122] The slurry was evenly applied to the outer surface of the sintered block using a brush, with a coating thickness of approximately 25 μm. It was then dried in an oven at 60°C for 4 hours to form a pre-coating.

[0123] Coating curing: The pre-coated block was placed in a tube furnace and heated to 400°C at a heating rate of 5°C / min under a high-purity argon atmosphere (flow rate 100 sccm). The temperature was held for 1 hour, and then cooled to room temperature with the furnace to obtain a hydride hydrogen storage block material with a thermally conductive outer coating.

[0124] (vi) Characterization and performance testing Structural characterization: XRD analysis (Cu Kα radiation, 2θ=10-80°, step size 0.02°) showed characteristic peaks of MgH2, LiBH4, TiO2 anatase phase and h-BN, with no obvious impurity peaks.

[0125] SEM observation (accelerating voltage 10kV, magnification 5000x) shows that the reactive composite hydride particles in this embodiment have a size of 2-6μm, with numerous open interconnected pores distributed between the particles. High-magnification observation (50000x) reveals that the particle surface is coated with a TiO2 film of approximately 5nm thickness.

[0126] The open-cell porosity of this embodiment was determined to be 13.8 vol% by mercury porosimetry, and the bulk density was determined to be 1.15 g / cm³ by Archimedes method.

[0127] Hydrogen storage performance test: The Sieverts method determined the following: initial hydrogen uptake was 7.0 wt%, dehydrogenation was 6.3 wt%, and initial coulombic efficiency was 90.0%. After 50 cycles, the reversible hydrogen storage capacity was 5.8 wt%, with a capacity retention of 92.1%.

[0128] Hydrogen absorption kinetics (300℃, 5MPa): 90% hydrogen absorption was completed in 9 minutes. Dehydrogenation kinetics (280℃, 0.01MPa): 90% dehydrogenation was completed in 13 minutes.

[0129] The steady-state temperature gradient is approximately 8℃ / cm.

[0130] Features of this embodiment: This embodiment employs a configuration with multiple parameters close to the boundaries of the technical solution: the reactive composite hydride phase mass fraction is 88 wt%, the molar ratio of magnesium hydride to lithium borohydride is 1.48:1, the composite support content is 6 wt%, and the porosity is 13.8 vol%. This aims to fully demonstrate the feasibility and rationality of the defined parameter range. A thinner titanium dioxide coating (5 nm, prepared by 120 atomic layer deposition cycles) and a thinner thermally conductive outer coating (25 μm) reduce manufacturing costs while ensuring basic protective functions. A higher melt penetration temperature (318 °C) and sintering temperature (376 °C), combined with a higher axial pressure (48 MPa) and a lower sintering atmosphere pressure (0.015 MPa), result in a higher porosity in the bulk, which is beneficial for rapid hydrogen mass transfer. This embodiment is suitable for short-term or emergency hydrogen storage applications that are cost-sensitive and have relatively low cycle life requirements, such as temporary hydrogen storage devices or laboratory-scale hydrogen storage systems.

[0131] Comparative Example 1: Basically the same as Example 1, except that the total mass fraction of the reactive composite hydride phase is 55 wt%, which is achieved by reducing the amount of magnesium hydride and lithium borohydride and increasing the amount of ordered mesoporous carbon and hexagonal boron nitride. The amounts of other components and preparation conditions remain unchanged.

[0132] Comparative Example 2: It is basically the same as Example 1, except that the total mass fraction of the reactive composite hydride phase is 92 wt%, which is achieved by increasing the amount of magnesium hydride and lithium borohydride and decreasing the amount of ordered mesoporous carbon and hexagonal iron nitride. The amount of other components and preparation conditions remain unchanged.

[0133] Comparative Example 3: It is basically the same as Example 1, except that the molar ratio of magnesium hydride to lithium borohydride is 0.85:1, which is achieved by reducing the amount of magnesium hydride to 100 parts by mass and increasing the amount of lithium borohydride to 95 parts by mass. The amounts of other components and preparation conditions remain unchanged.

[0134] Comparative Example 4: It is basically the same as Example 1, except that the molar ratio of magnesium hydride to lithium borohydride is 1.65:1, which is achieved by keeping the amount of magnesium hydride at 100 parts by mass and reducing the amount of lithium borohydride to 49 parts by mass. The amounts of other components and preparation conditions remain unchanged.

[0135] Comparative Example 5: It is basically the same as Example 1, except that the total mass fraction of ordered mesoporous carbon and hexagonal boron nitride is 3 wt%, which is achieved by reducing the amount of ordered mesoporous carbon to 1.8 parts by mass and the amount of hexagonal boron nitride to 1.8 parts by mass. The amounts of other components and preparation conditions remain unchanged.

[0136] Comparative Example 6: It is basically the same as Example 1, except that the total mass fraction of ordered mesoporous carbon and hexagonal boron nitride is 33 wt%, which is achieved by increasing the amount of ordered mesoporous carbon to 22 parts by mass and the amount of hexagonal boron nitride to 22 parts by mass. The amounts of other components and preparation conditions remain unchanged.

[0137] Comparative Example 7: It is basically the same as Example 1, except that the overall open-pore interconnected porosity is 3.2 vol%, which is achieved by increasing the axial pressure to 60 MPa and extending the holding time to 15 minutes in the discharge plasma sintering step. The amounts of other components and other preparation conditions remain unchanged.

[0138] Comparative Example 8: It is basically the same as Example 1, except that the overall open-pore interconnected porosity is 17.5 vol%, which is achieved by reducing the axial pressure to 25 MPa, shortening the holding time to 6 minutes, and increasing the sintering atmosphere pressure to 0.12 MPa in the discharge plasma sintering step. The amounts of other components and other preparation conditions remain unchanged.

[0139] Comparative Example 9: Basically the same as Example 1, except that the melt penetration temperature is 260°C and the melt penetration holding time is adjusted to 4 hours to compensate for the temperature reduction. The amounts of other components and other preparation conditions remain unchanged.

[0140] Comparative Example 10: It is basically the same as Example 1, except that the melt penetration temperature is 340°C, the melt penetration holding time is adjusted to 2 hours, and the amount of other components and other preparation conditions remain unchanged.

[0141] Comparative Example 11: Essentially the same as Example 1, except that the melt infiltration atmosphere pressure was 0.05 MPa, while the amounts of other components and preparation conditions remained unchanged. This comparative example was used to investigate the effect of excessively low hydrogen atmosphere pressure on the stability of the magnesium hydride phase and the suppression of side reactions during the melt infiltration of lithium borohydride.

[0142] Comparative Example 12: Basically the same as Example 1, except that the pressure of the melt infiltration atmosphere is 6.0 MPa, while the amount of other components and preparation conditions remain unchanged.

[0143] Comparative Example 13: It is basically the same as Example 1, except that the atomic layer deposition cycle is 80 times to form a titanium dioxide coating layer with a thickness of about 3 nm. The amount of other components and the preparation conditions remain unchanged.

[0144] Performance testing: Test Subject: Reversible hydrogen storage capacity and cycle stability of hydride hydrogen storage bulk materials. Test Objective: To evaluate the mass hydrogen storage capacity, initial coulombic efficiency, and capacity retention of the bulk material during repeated hydrogen adsorption / desorption cycles. Test Principle: Based on the Sieverts volumetric method, the hydrogen pressure and temperature changes in a closed reactor are monitored in real time using precision pressure and temperature sensors. The amount of hydrogen adsorbed / desorbed is calculated according to the actual gas law and then converted into a mass percentage hydrogen storage capacity. Experimental Method: The bulk material (approximately 1.0 g) is placed in a stainless steel reactor. After evacuating to an absolute pressure below 1 Pa, high-purity hydrogen is introduced to 5 MPa. Activation and hydrogen adsorption are performed at 300°C for 2 hours, followed by dehydrogenation at 280°C and 0.01 MPa for 2 hours. This cycle is repeated 3 times to complete the activation. The amount of hydrogen adsorbed and desorbed is recorded during the first cycle, and the initial coulombic efficiency is calculated. At least 50 hydrogen adsorption / desorption cycles are continued, and the reversible hydrogen storage capacity is recorded every 10 cycles to calculate the capacity retention. Key parameters: Hydrogen absorption temperature 300℃, hydrogen absorption pressure 5MPa, dehydrogenation temperature 280℃, dehydrogenation pressure 0.01MPa, number of cycles ≥50. Data processing: Hydrogen storage capacity (wt%) = (hydrogen absorption mass / sample mass) × 100%, capacity retention rate (%) = (capacity of Nth cycle / capacity of first cycle) × 100%, each data set should have at least 3 parallel samples, and the mean ± standard deviation should be reported.

[0145] Test Object: Hydrogen absorption and desorption kinetics of hydride hydrogen storage bulk materials. Test Objective: To quantitatively characterize the time required for the bulk material to complete 90% hydrogen absorption and desorption under specific temperature and pressure conditions, and to evaluate its rapid hydrogen charging and decharging capabilities. Test Principle: The Sieverts method is used to record the hydrogen pressure change curve over time during hydrogen absorption and desorption in real time. The instantaneous hydrogen absorption and desorption rate is calculated based on the pressure change rate, and the time point at which 90% of the equilibrium capacity is reached is determined. Experimental Method: The activated bulk material (approximately 1.0 g) is placed in a reactor. The hydrogen absorption kinetics test conditions are 300℃ and a hydrogen pressure of 5 MPa, recording the time required for the pressure to decrease from the initial value to the equilibrium value. The desorption kinetics test conditions are 280℃ and a hydrogen pressure of 0.01 MPa, recording the time required for the pressure to increase from the initial value to the equilibrium value. Hydrogen absorption and desorption curves over time are plotted, and the 90% completion time point is marked. Standard Basis: Refer to GB / T 26466 Kinetic Test Methods for Solid Hydrogen Storage Materials or similar standards. Key parameters: Hydrogen absorption temperature 300℃, hydrogen absorption pressure 5MPa, dehydrogenation temperature 280℃, dehydrogenation pressure 0.01MPa, sampling interval ≤10 seconds. Data processing: 90% hydrogen absorption time t 90 (Absorption) and 90% dehydrogenation time t 90 (Remove), each group should have at least 3 parallel samples, and report the mean ± standard deviation.

[0146] Test Object: Overall open-connected porosity and density of hydride hydrogen storage bulk material. Test Objective: To quantitatively determine the volume fraction of open-connected pores and the true density of the bulk material, and to evaluate the influence of its pore structure on hydrogen mass transfer and mechanical strength. Test Principle: The open-connected pores are determined using mercury intrusion porosimetry, and the porosity and pore size distribution are calculated based on the intrusion behavior of mercury into the pores under different pressures; the bulk density is determined using the Archimedes displacement method, and calculated based on mass and displacement volume. Experimental Method: During the mercury intrusion porosimetry test, the bulk material (approximately 1 cm³ in volume) is... 3 The sample is placed in the sample cell of a mercury porosimeter, and the pressure is gradually increased within the range of 0.1-400 MPa. The volume of mercury intrusion is recorded, and the pore size distribution and total porosity are calculated according to the Washburn equation. For the Archimedes method, the mass m1 of the block in air and the apparent weight m2 of the block immersed in deionized water are measured on an analytical balance, and the density ρ is calculated as ρ = m1 / (m1-m2) × ρwater. Standards: Refer to GB / T 21650.1 Mercury Porosimeter Method and GB / T 533 Archimedes Method or similar standards. Key parameters: Mercury porosimeter pressure range 0.1-400 MPa, water temperature 25℃. Data processing: Porosity (vol%) = (total pore volume / total block volume) × 100%, density (g / cm³) 3 Each group should have at least 3 parallel samples, and report the mean ± standard deviation.

[0147] Test Object: Temperature distribution uniformity of hydride hydrogen storage bulk material during hydrogen absorption and desorption. Test Objective: To evaluate the internal temperature gradient of the bulk material during rapid hydrogen absorption and verify the improvement effect of the thermally conductive outer coating on thermal management. Test Principle: The temperature field distribution is monitored in real time by embedding a thermocouple array at different depths in the bulk material. The steady-state temperature gradient along the thickness direction is calculated to evaluate thermal conductivity. Experimental Method: K-type thermocouples are embedded in the bulk material (approximately 5 mm thick) at different locations along the thickness direction (surface, 1 / 4 depth, 1 / 2 depth, 3 / 4 depth, bottom). After being placed in a reactor, a hydrogen absorption experiment is conducted (300℃, 5 MPa). After the reaction reaches a steady state (hydrogen absorption rate <0.01 wt% / min), the temperature at each measurement point is recorded. The temperature gradient is calculated as (highest temperature - lowest temperature) / bulk thickness. The experiment is repeated three times, and the average value is taken. Standard Basis: Refer to ASTM E1461 thermocouple temperature measurement method or similar standards. Key parameters: hydrogen absorption temperature 300℃, hydrogen absorption pressure 5MPa, thermocouple accuracy ±0.5℃, sampling frequency 1Hz. Data processing: steady-state temperature gradient (℃ / cm), plotting temperature-location distribution maps, with at least 3 parallel samples per group, and reporting the mean ± standard deviation.

[0148] Test Object: Phase composition and crystal structure of hydride hydrogen storage bulk materials. Test Objective: To identify the crystal structure of the main hydride phases, oxide coatings, and thermally conductive components in the bulk material, and to verify the stability of each phase during atomic layer deposition coating and sintering. Test Principle: X-ray diffraction utilizes the Bragg diffraction effect of crystals on X-rays. The phase types, lattice parameters, and crystallinity are identified based on the position and intensity of characteristic diffraction peaks. Experimental Method: The bulk material is ground into powder (particle size <75μm) or XRD testing is performed directly on the bulk surface. Cu Kα radiation (λ=0.15406nm) is used, with a scanning range of 2θ=10-80°, a step size of 0.02°, and a scanning rate of 5° / min. The measured diffraction patterns are compared with PDF standard cards to identify the characteristic peaks of phases such as MgH2, LiBH4, TiO2 (anatase or rutile), Al2O3, and h-BN. If necessary, the relative content and lattice parameters are calculated using Rietveld refinement. Standard Basis: Refer to GB / T 6900.3 X-ray Diffraction Analysis Methods or similar standards. Key Parameters: Radiation source Cu Kα, tube voltage 40kV, tube current 40mA, scanning range 10-80°, step size 0.02°. Data Processing: Phase identification results, characteristic peak 2θ positions and relative intensities, with at least 3 parallel samples per group.

[0149] Test Object: Thickness and chemical composition of atomic layer deposition (ALD) coatings. Test Objective: To verify the actual thickness, elemental distribution, and chemical state of TiO2 or Al2O3 coatings prepared by ALD, and to confirm the continuity and compactness of the coatings. Test Principle: X-ray photoelectron spectroscopy (XPS) determines the surface elemental composition and chemical state through the photoelectric effect, combined with argon ion sputtering depth profiling to obtain the coating thickness and elemental distribution; transmission electron microscopy (TEM) directly observes the morphology and thickness of the coating. Experimental Method: During XPS testing, the powder sample is fixed on the sample stage and excited with monochromatic Al Kα rays (hν = 1486.6 eV). Characteristic spectral lines such as Ti 2p, Al 2p, O 1s, and Mg 2p are scanned. The peak position and shape are analyzed to determine the Ti 2p coating thickness. 4+ Or Al 3 + Oxidized state. Depth profiling was performed using argon-ion sputtering (sputtering rate approximately 2 nm / min), with elemental content recorded every 1 nm. The coating thickness was determined based on the attenuation of the Ti or Al signal to 10% of the matrix signal. For TEM testing, the powder was dispersed on a copper grid, and the morphology and thickness of the coating on the particle surface were observed using an accelerating voltage of 200 kV. Standards: Refer to ISO 18115 XPS analytical method or similar standards. Key parameters: XPS power 10 eV, sputtering rate 2 nm / min, TEM accelerating voltage 200 kV. Data processing: Coating thickness (nm), elemental atomic fraction (at%) depth distribution curves, with at least 3 samples per group.

[0150] Figure 1 This figure shows the effect of the mass fraction of the reactive composite hydride phase of the present invention on the reversible hydrogen storage capacity and capacity retention rate after 50 cycles. The fixed parameters are: a molar ratio of magnesium hydride to lithium borohydride of 1.25:1, a niobium pentoxide catalyst mass fraction of 1.0 wt%, a titanium hydride catalyst mass fraction of 3.5 wt%, a melt infiltration temperature of 300°C, a melt infiltration atmosphere pressure of 2.5 MPa, 300 atomic layer deposition cycles, a sintering temperature of 330°C, a sintering axial pressure of 40 MPa, a sintering atmosphere pressure of 0.05 MPa, and a thermally conductive outer coating of hexagonal boron nitride with a thickness of 40 μm. The varying parameters are: a reactive composite hydride phase mass fraction ranging from 55 wt% to 92 wt%. When the mass fraction of the reactive composite hydride phase is 80 to 85 wt%, the reversible hydrogen storage capacity and capacity retention rate reach their peak values ​​of 6.3 to 6.5 wt% and 97.5 to 98.5% respectively after 50 cycles. When the mass fraction is below 60 wt%, the insufficient reactive hydride phase results in a hydrogen storage capacity of only 4.2 wt% and a capacity retention rate of 88.5%. When the mass fraction is above 90 wt%, the low content of the composite support leads to insufficient confinement effect and thermal conductivity, causing the capacity retention rate to plummet to 94.2% and structural mismatch to occur during cycling. This demonstrates that a moderate mass fraction can simultaneously ensure high hydrogen storage capacity and excellent cycling stability.

[0151] Figure 2 This diagram illustrates the effect of the molar ratio of magnesium hydride to lithium borohydride on the reversible hydrogen storage capacity and capacity retention after 50 cycles. The fixed parameters are: total mass fraction of reactive composite hydride phase 75 wt%, ordered mesoporous carbon mass fraction 10 wt%, hexagonal boron nitride mass fraction 10 wt%, niobium pentoxide catalyst mass fraction 1.0 wt%, titanium hydride catalyst mass fraction 3.5 wt%, melt infiltration temperature 300°C, melt infiltration atmosphere pressure 2.5 MPa, atomic layer deposition cycles 300, sintering temperature 330°C, sintering axial pressure 40 MPa, and a thermally conductive outer coating of hexagonal boron nitride with a thickness of 40 μm. The varying parameters are the molar ratio of magnesium hydride to lithium borohydride from 0.85:1 to 1.65:1. When the molar ratio of magnesium hydride to lithium borohydride is 1.25 to 1.35:1, the reversible hydrogen storage capacity and capacity retention rate reach their optimal values ​​of 6.0 to 6.1 wt% and 96.8 to 97.2% after 50 cycles. When the molar ratio is below 1.0:1, the excess of lithium borohydride leads to insufficient synergistic reaction of the magnesium hydride phase, causing the capacity retention rate to drop to 88.2%. When the molar ratio is above 1.5:1, the catalytic effect of the lithium borohydride phase weakens, causing the capacity retention rate to drop to 93.8%. This verifies that the precise control of the molar ratio of the two phases is crucial to the reversible hydrogen storage performance of the composite hydride system.

[0152] Figure 3This diagram illustrates the effect of overall open-pore porosity on the 90% hydrogen absorption completion time and capacity retention rate. The fixed parameters are: total mass fraction of reactive composite hydride phase 75 wt%, molar ratio of magnesium hydride to lithium borohydride 1.25:1, mass fraction of ordered mesoporous carbon 10 wt%, mass fraction of hexagonal boron nitride 10 wt%, mass fraction of niobium pentoxide catalyst 1.0 wt%, mass fraction of titanium hydride catalyst 3.5 wt%, melt penetration temperature 300°C, atomic layer deposition cycles 300, sintering temperature 330°C, and a thermally conductive outer coating of hexagonal boron nitride with a thickness of 40 μm. The varying parameter is the overall open-pore porosity, ranging from 3.2 vol% to 17.5 vol%. When the overall open-cell porosity is 8 to 12 vol%, the hydrogen absorption completion time is as short as 7 to 8 minutes, and the capacity retention rate reaches 96.2% to 97.5%, achieving the optimal balance between kinetic performance and cycle stability. When the porosity is below 5 vol%, the hydrogen mass transfer resistance increases significantly, extending the hydrogen absorption time to 13 minutes. Although the capacity retention rate is maintained at 92.5%, the rapid hydrogen charging capability is sacrificed. When the porosity is above 15 vol%, the insufficient mechanical strength of the bulk material leads to structural damage during the cycle, causing the capacity retention rate to plummet to 92.8%, and even to 71.4% at 17.5 vol%. This indicates that an appropriate porosity is the key to simultaneously satisfying rapid hydrogen mass transfer and the integrity of the bulk structure.

[0153] Figure 4 This diagram illustrates the effect of the number of atomic layer deposition cycles on the thickness and capacity retention of the titanium dioxide coating. The fixed parameters are: total mass fraction of reactive composite hydride phase 75 wt%, molar ratio of magnesium hydride to lithium borohydride 1.25:1, mass fraction of ordered mesoporous carbon 10 wt%, mass fraction of hexagonal boron nitride 10 wt%, mass fraction of niobium pentoxide catalyst 1.0 wt%, mass fraction of titanium hydride catalyst 3.5 wt%, melt infiltration temperature 300°C, melt infiltration atmosphere pressure 2.5 MPa, sintering temperature 330°C, sintering axial pressure 40 MPa, porosity 8.2 vol%, and a thermally conductive outer coating of hexagonal boron nitride with a thickness of 40 μm. The varying parameters correspond to coating thicknesses ranging from 3 nm to 16.5 nm depending on the number of atomic layer deposition cycles, from 80 to 550. When the atomic layer deposition cycle count is 300 to 450 times, corresponding to a coating thickness of 9 to 13 nm, the capacity retention reaches a peak of 96.8% to 98.2%, demonstrating the optimal balance between surface protection and hydrogen diffusion. When the cycle count is less than 100 times, corresponding to a coating thickness of 4 nm, insufficient surface protection leads to an increase in side reactions during cycling, causing the capacity retention to drop to 85.2%. When the cycle count is more than 500 times, corresponding to a coating thickness of 15 nm, the excessively thick coating hinders hydrogen diffusion at the interface between the coating and the hydride phase, causing the capacity retention to begin to decrease to 97.5%. This proves that precise control of the coating thickness is the core of balancing surface stability and hydrogen transport kinetics.

[0154] Figure 5 The XRD pattern of Example 1 is shown below. The fixed parameters are X-ray powder diffraction characterization using Cu Kα radiation, with a 2θ scan range of 10° to 80° and a step size of approximately 0.04°. A unified Rietveld refinement procedure, background function, peak shape function, and zero-point correction strategy are used. The variable parameter is that the total content of reactive complex hydrides in Example 1 is approximately 75 wt%, and the remaining proportions are set according to the scheme. In the figure, black represents the measured XRD curve of Example 1, and red represents the curve based on MgH2, LiBH4, TiO2, and h... The Rietveld fitting curve obtained from the BN structure model, the blue line below is the difference spectrum curve obtained from the measured subfit, and the colored vertical lines at the bottom indicate MgH2, LiBH4, TiO2 and h in Example 1. The characteristic diffraction peak positions of BN are shown. It can be seen that the measured and fitted curves highly coincide across the entire 2θ range, with only minor fluctuations near zero and no systematic bias. The main peak intensities of MgH2 and LiBH4 correspond to the approximately 75 wt% mass fraction of reactive complex hydrides in the Rietveld phase quantification results. This indicates that the structural model, phase combination, and fitting parameters used in Example 1 can fully reproduce the measured diffraction data, ensuring the reliability of subsequent phase quantification and grain size analysis.

[0155] Figure 6 The XRD pattern is shown in Comparative Example 1, with parameters fixed. Figure 1 The methods were identical, employing Cu Kα radiation X-ray powder diffraction conditions, a 2θ scan range of 10° to 80°, a step size of approximately 0.04°, and a uniform Rietveld refinement strategy. The only variable parameter was that the total content of reactive complex hydrides in Comparative Example 1 was approximately 55 wt% after sample ratio adjustment, and the inert phase h... The contents of BN and TiO2 are correspondingly increased; in the figure, black represents the measured XRD curve of Comparative Example 1, red represents the Rietveld fitted curve, blue below represents the difference spectrum curve, and the colored vertical line at the bottom indicates the contents of MgH2, LiBH4, TiO2, and h in Comparative Example 1. The characteristic diffraction peak positions of BN were determined. The results show that the intensity and area of ​​the MgH2 and LiBH4 related peaks in Comparative Example 1 were significantly lower than those in Example 1, while h... The proportions of BN and TiO2 peaks increased, but the overall fitting curves still closely matched the measured curves. The difference spectrum fluctuated randomly around zero without any systematic mismatch. This indicates that when the content of reactive composite hydrides decreased to about 55 wt%, the selected diffraction model could still accurately describe the diffraction characteristics and relative contents of each phase, providing reliable basic data for subsequent comparison of different sample ratios using phase mass fraction histograms.

[0156] Figure 7The XRD pattern shown in Comparative Example 2 is obtained using the same X-ray powder diffraction test conditions with Cu Kα radiation, a 2θ range of 10° to 80°, and a step size of approximately 0.04°. Figure 1 and Figure 2 The Rietveld refinement method was consistent, with the variable parameter being that the total content of reactive complex hydrides in Comparative Example 2 was increased to approximately 92 wt%, and the inert phases TiO2 and h The BN content is significantly reduced; in the figure, black represents the measured XRD curve of Comparative Example 2, red represents the Rietveld fitted curve, blue below represents the difference spectrum curve, and the colored vertical lines at the bottom correspond to MgH2, LiBH4, TiO2, and h in Comparative Example 2. The characteristic diffraction peak positions of BN can be observed. It can be seen that the peak intensities of MgH2 and LiBH4 are significantly enhanced in Comparative Example 2, while h... The BN and TiO2 peaks were significantly weakened, but the fitted curves still closely followed the measured curves throughout the entire 2θ range, and the difference spectrum remained within a small fluctuation range. This indicates that even when the proportion of reactive complex hydrides increased significantly to approximately 92 wt%, the Rietveld refinement could still converge stably and accurately distinguish the contributions of each phase. Figure 1 and Figure 2 The results together constitute a set of comparative data that can achieve high-quality fitting at three different levels of reactive complex hydride content (low, medium, and high), structurally supporting the subsequent analytical conclusions on the influence of phase content and grain size evolution.

[0157] Figure 8 The bar chart shows the comparison of the mass fraction of each phase in Example 1, Comparative Example 1, and Comparative Example 2. The parameters were fixed so that all three groups of samples used... Figures 1 to 3 The X-ray powder diffraction conditions and the unified Rietveld finishing process described herein, with the data for each column in the histogram directly derived from MgH2, LiBH4, TiO2, and h The refined mass fraction of BN was determined by the phase composition difference caused by the sample ratio. The total content of reactive complex hydrides in Example 1 was approximately 75 wt%, in Comparative Example 1 approximately 55 wt%, and in Comparative Example 2 approximately 92 wt%. The results showed that the mass fractions of MgH2 and LiBH4 in Example 1 were at a moderately high level, significantly higher than in Comparative Example 1 but lower than in Comparative Example 2. In Comparative Example 1, the contents of MgH2 and LiBH4 were relatively low, and h... BN had the highest content, while in Comparative Example 2, MgH2 and LiBH4 had the highest contents, while TiO2 and h were the most abundant. BN decreased significantly, and this distribution pattern is consistent with Figures 1 to 3The diffraction peak intensity trends of the corresponding samples MgH2 and LiBH4 are completely consistent, indicating that there is a good mutual corroboration relationship between the phase quantification results and the diffraction patterns, ensuring that the judgment on the difference in the content of reactive complex hydrides in different samples is based on repeatable quantification.

[0158] Figure 9 Box plots showing the MgH2 grain size comparison for Example 1, Comparative Example 1, and Comparative Example 2, with parameters fixed as shown in the box plots. Figures 1 to 3 Consistent X-ray powder diffraction conditions and the Rietveld refinement method were used. Peak shape analysis was employed to simultaneously separate the main peak and high-angle peaks of MgH2 by size broadening and micro-strain broadening. The variable parameters were the differences in the equivalent grain size distribution of MgH2 caused by variations in confinement degree, interface environment, and stoichiometry in different samples. Box plot results showed that the median and upper quartile values ​​of the MgH2 grain size in Example 1 were significantly lower than those in Comparative Examples 1 and 2, with the size mainly concentrated in the approximately 30 to 40 nm range and a narrow distribution. In Comparative Example 1, the grain size distribution shifted to the right and broadened, while in Comparative Example 2, the grains further coarsened to approximately 70 to 90 nm. This size evolution pattern is consistent with... Figures 1 to 3 The variation in the full width at half maximum (FWHM) and the degree of peak broadening of the corresponding MgH2 peak in the sample remained consistent, combined with Figure 4 The difference in the mass fraction of the middle phase indicates that the proportion of reactive composite hydrides and the structural design in Example 1 achieved a better balance, allowing MgH2 to maintain a small and concentrated grain size even at a high content, providing structural support for the subsequent improvement of hydrogen absorption and desorption kinetics and cycle stability.

[0159] As can be seen from the performance of the embodiments and comparative examples in Table 1, the four embodiments of the present invention exhibit excellent comprehensive performance in terms of hydrogen storage capacity, cycle stability, hydrogen adsorption and desorption kinetics, mechanical strength, and thermal management performance. Comparative Example 1, due to its low content of reactive composite hydride phase, has a hydrogen storage capacity of only 3.5 wt%, far lower than the 5.5-6.5 wt% of the embodiments; Comparative Example 2, although having a high initial capacity, suffers from poor cycle stability due to insufficient composite support content, with a capacity retention rate of only 76.5%; Comparative Examples 3 and 4, due to the deviation of the molar ratio of magnesium hydride to lithium borohydride from the preferred range, disrupt the balance of the two-phase synergistic reaction, resulting in post-cycle capacities of 4.5 wt% and 4.8 wt%, respectively; Comparative Example 5, due to its low composite support content, suffers from insufficient confinement effect and thermal conductivity, resulting in a capacity retention rate of only 70.0% and a temperature gradient as high as 11 °C / cm; Comparative Example 6, although exhibiting good cycle stability, has a hydrogen storage capacity diluted to 4.5 wt%; Comparative Example 7, due to its low porosity, suffers from poor hydrogen mass transfer... The hydrogen absorption time was extended to 18 minutes and the dehydrogenation time was extended to 25 minutes due to excessive porosity in Comparative Example 8, resulting in a bulk density of only 0.98 g / cm³, insufficient mechanical strength, and a capacity retention rate of only 71.4%. Comparative Examples 9 and 10 suffered from impaired cycle stability due to the melt penetration temperature deviating from the preferred range, leading to an undesirable microstructure of the confined composite hydride. Comparative Examples 11 and 12, while slightly inferior to the examples, showed no significant difference compared to Comparative Examples 9 and 10, indicating that atmospheric pressure within the range of 0.1-5.0 MPa has a relatively small impact on performance, but exceeding this range increases equipment costs or safety risks. Comparative Example 13 suffered from insufficient surface protection due to an excessively thin atomic layer deposition coating, resulting in a significant decrease in cycle stability and a capacity retention rate of only 75.0%. Comprehensive data show that by precisely controlling key parameters such as the content of reactive composite hydride phase, the molar ratio of magnesium hydride to lithium borohydride, the content of composite support, porosity, melt penetration temperature, and atomic layer deposition coating thickness within the range defined in the claims, this invention achieves an optimal balance of hydrogen storage capacity, cycle stability, kinetic performance, mechanical strength, and thermal management performance.

[0160] Table 1. Comparison of hydrogen storage performance and structural parameters between the examples and comparative examples.

[0161] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A hydride hydrogen storage material, which is a bulk material formed by discharge plasma sintering, characterized in that, The hydride hydrogen storage material comprises the following components, based on the total mass of the bulk material: A reactive composite hydride phase consisting of magnesium hydride and lithium borohydride, with a total mass fraction of 60–90 wt%, wherein the molar ratio of magnesium hydride to lithium borohydride is 1.0–1.5:1; A composite support structure composed of ordered mesoporous carbon and hexagonal boron nitride, wherein the total mass fraction of ordered mesoporous carbon and hexagonal boron nitride is 5–30 wt%. An oxide coating layer loaded on the surface of the reactive composite hydride phase particles, wherein the oxide coating layer includes a titanium dioxide coating layer and / or an aluminum oxide coating layer; A catalyst distributed in the bulk material, the catalyst comprising niobium pentoxide and titanium hydride; A thermally conductive outer coating is disposed on the outer surface of the bulk material, the thermally conductive outer coating being composed of hexagonal boron nitride powder and / or aluminum nitride powder; The overall open-pore porosity of the bulk material is 5–15 vol%, and the mass fraction of each component is selected within its corresponding range so that the sum of the mass fractions of each component does not exceed 100 wt%.

2. The hydride hydrogen storage material according to claim 1, characterized in that, The reactive composite hydride phase is prepared by the following steps: A1. Raw material preparation: Weigh magnesium hydride, lithium borohydride, ordered mesoporous carbon powder and hexagonal boron nitride powder under an inert gas atmosphere. By mass, magnesium hydride is 100 parts, lithium borohydride is 55-83 parts, ordered mesoporous carbon is 5-30 parts, and hexagonal boron nitride is 5-30 parts, so that the molar ratio of magnesium hydride to lithium borohydride is 1.0-1.5:

1. A2. Ball milling and mixing: The raw material powder from step A1 is placed in a closed ball mill jar filled with inert gas and ball milled and mixed to obtain a composite powder in which magnesium hydride, lithium borohydride, ordered mesoporous carbon and hexagonal boron nitride are uniformly mixed. A3. Melting and Pore Confinement: The composite powder obtained in step A2 is placed in a sealed container and kept at a temperature of 280–320°C and an atmosphere pressure of 0.1–5.0 MPa under hydrogen protection to melt and penetrate the pores of the composite support structure. Then it is cooled to room temperature to obtain a composite powder of magnesium hydride-lithium borohydride reactive composite hydride confined in an ordered mesoporous carbon and hexagonal boron nitride composite support structure. A4. Hydrogen atmosphere activation treatment: The composite powder obtained in step A3 is placed in a container and activated in a hydrogen atmosphere under hydrogen pressure and heating conditions to obtain confined reactive composite hydride powder as a raw material for subsequent processes.

3. The hydride hydrogen storage material according to claim 1, characterized in that, The oxide coating layer is prepared by atomic layer deposition, including: B1. Precursor selection: When the oxide coating layer is a titanium dioxide coating layer, tetraisopropoxy titanium and water are used as alternating precursors; when the oxide coating layer is an aluminum oxide coating layer, trimethylaluminum and water are used as alternating precursors. B2. Loading and pretreatment: The confined reactive composite hydride powder obtained in step A4 is uniformly spread on the carrier disk of the atomic layer deposition reaction chamber and pretreated under heating and vacuum conditions with inert gas as carrier gas. B3. Atomic Layer Deposition: Under heating and depressurization conditions, metal-organic precursor pulses and water pulses are alternately performed. Each atomic layer deposition cycle includes a metal-organic precursor pulse, inert gas purging, water pulse, and inert gas purging again. The total number of cycles is 100–500, so that a continuous and uniform titanium dioxide film or aluminum oxide film is formed on the surface of the composite powder particles. B4. Cooling and Collection: After stopping the supply of precursors, the reaction chamber is cooled under an inert atmosphere, and the composite hydride powder with an oxide film on its surface is collected.

4. The hydride hydrogen storage material according to claim 1, characterized in that, The bulk material is prepared by the following steps: discharge plasma sintering and thermally conductive outer coating construction: C1. Catalyst addition and mixing: Under an inert gas atmosphere, the atomic layer deposition coated composite powder obtained in step B4 is mixed with niobium pentoxide powder and titanium hydride powder to obtain a uniformly mixed sintering raw material powder. C2. Molding and Pre-compression: The sintered raw material powder obtained in step C1 is filled into the inner cavity of the graphite mold, and pre-compression is applied at room temperature to obtain a pre-compressed block; C3. Discharge plasma sintering: Under a protective atmosphere, a graphite mold containing pre-compressed blocks is placed in a discharge plasma sintering device, heated and held at a temperature under axial pressure for sintering. During the sintering process, the absolute pressure inside the furnace is controlled within the range of 0.01–0.1 MPa. The sintering conditions are adjusted so that the resulting block has open and interconnected pores. C4. Construction of thermally conductive outer coating: After cooling the sintered block obtained in step C3 to room temperature, a slurry prepared by hexagonal boron nitride powder and / or aluminum nitride powder with volatile solvent is coated on the outer surface of the block, and a pre-coating is formed after drying; C5. Coating curing: The pre-coating is heated in an inert gas atmosphere to enhance the bonding strength between the thermally conductive outer coating and the bulk substrate, and then cooled to room temperature to obtain a bulk material with a thermally conductive outer coating.

5. The hydride hydrogen storage material according to claim 1, characterized in that, The density of the bulk material is greater than 1.0 g / cm³, and it will not undergo overall pulverization or penetrating macroscopic cracks during hydrogen absorption and desorption cycles.

6. The hydride hydrogen storage material according to claim 1, characterized in that, Before first use, the bulk material is pretreated as follows: it is activated under heating conditions at hydrogen pressure, and subjected to multiple hydrogen pre-cycles of absorption and desorption between different hydrogen pressures.

7. A method for preparing a hydride hydrogen storage material as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Reactive composite hydride confined loading step: According to steps A1–A4 of claim 2, magnesium hydride, lithium borohydride, ordered mesoporous carbon and hexagonal boron nitride are mixed, and ball-milled, melt-infiltrated and activated in a hydrogen atmosphere to obtain confined reactive composite hydride powder. S2. Atomic layer deposition coating step: According to steps B1–B4 of claim 3, using tetraisopropoxy titanium and / or trimethylaluminum as atomic layer deposition precursors, perform 100–500 atomic layer deposition cycles under heating and depressurization conditions to form a titanium dioxide coating layer or an aluminum oxide coating layer on the surface of the confined reactive composite hydride powder particles, thereby obtaining atomic layer deposition coated composite powder. S3. Catalyst addition and mixing step: Niobium pentoxide powder and titanium hydride powder are added to the atomic layer deposition coated composite powder obtained in step S2 under an inert gas atmosphere, and mixed to obtain sintering raw material powder; S4. Discharge plasma sintering forming step: The sintering raw material powder from step S3 is loaded into a graphite mold, heated under a protective atmosphere and kept at a temperature under axial pressure for sintering, so that the resulting block has open and interconnected pores. S5. Thermally conductive outer coating construction steps: The outer surface of the block obtained in step S4 is coated with a slurry containing hexagonal boron nitride powder and / or aluminum nitride powder, dried and heated in an inert gas atmosphere to form a thermally conductive outer coating, thereby obtaining a hydride hydrogen storage material.

8. The preparation method according to claim 7, characterized in that, In step S1, ball milling is carried out under an inert gas atmosphere, with a melt penetration temperature of 280–320°C and a penetration atmosphere pressure of 0.1–5.0 MPa.

9. The preparation method according to claim 7, characterized in that, In step S2, the duration of a single metal-organic precursor pulse and water pulse is 0.1–5 s, and the inert gas purging time is 1–20 s.

10. The preparation method according to claim 7, characterized in that, In step S4, the heat preservation stage uses pulsed current to perform discharge plasma sintering. After the heat preservation is completed, the pressure is released after cooling to below 200°C.

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