Double-layer supported solid-state hydrogen storage material and preparation and recovery method thereof

Abstract

The application discloses a kind of double-layer solid-state hydrogen storage material and its preparation and recovery method, which is lignin-semi-coke composite continuous carbon skeleton as carrier, with no interface continuous network structure, inner layer load MgH2, outer layer load LaNi5, form inner hydrogen storage, outer catalysis double-layer gradient structure;Preparation process is: first load magnesium and generate MgH2 by high-pressure hydrogenation, then load lanthanum nickel precursor and make MgH2 decompose release channel space by inert atmosphere calcination, then high-pressure reduction makes lanthanum nickel alloying and distributes in carrier surface layer, finally activation.The material uses the thermal bridge and hydrogen bridge effect of continuous carbon skeleton, realizes the bidirectional cooperation of hydrogen absorption and release thermal effect and hydrogen overflow, and the hydrogen absorption and release temperature is reduced by 100-150 DEG C compared with pure MgH2, the hydrogen storage capacity is 5-7wt%, and the capacity retention rate is greater than 90% in 100 cycles.After failure, metal recovery and reagent closed loop circulation are realized by metal dissolution-three-stage precipitation-electrolysis regeneration process.

Description

Technical Field

[0001] This application relates to the field of energy storage materials technology, and in particular to a bilayer loaded solid hydrogen storage material and its preparation and recovery method. Background Technology

[0002] Hydrogen energy, as a clean secondary energy source with high energy density and pollution-free combustion products, is an important pathway to achieving carbon neutrality. Solid-state hydrogen storage is considered one of the most promising hydrogen storage methods due to its high safety, low storage pressure, and high hydrogen purity. Among various solid-state hydrogen storage materials, magnesium-based hydrogen storage materials (MgH2) have attracted much attention due to their high theoretical hydrogen storage capacity (7.6 wt%), abundant resources, and low cost. However, magnesium-based hydrogen storage materials face the following technical bottlenecks in practical applications:

[0003] (1) High thermodynamic stability: The decomposition enthalpy of MgH2 is as high as about 75kJ / mol, and the hydrogen release temperature under normal pressure needs to reach 300-400°C. The hydrogen absorption and release process requires continuous external heating, resulting in huge energy consumption.

[0004] (2) Poor kinetic performance: The diffusion rate of hydrogen atoms in the bulk phase of MgH2 is slow, and it takes tens of minutes to completely absorb hydrogen. The hydrogen release rate is also difficult to meet the needs of practical applications.

[0005] (3) Poor cycle stability: Mg / MgH2 is prone to particle sintering and agglomeration during repeated hydrogen absorption and desorption cycles, which leads to a rapid decrease in hydrogen storage capacity as the number of cycles increases;

[0006] (4) Difficulty in thermal management: The hydrogen absorption process is heat-releasing and the hydrogen release process is heat-absorbing. If the heat cannot be conducted and evenly distributed in time, it is easy to cause local overheating or local insufficient hydrogen supply, which seriously affects the stability and safety of the system operation.

[0007] To address the aforementioned issues, Chinese invention patent CN105645356A discloses a two-step method for preparing magnesium hydride hydrogen storage materials using nickel doping and a carbon mesoporous framework nanoconfined within. This method uses sucrose as a carbon source and SBA-15 as a template to prepare an ordered mesoporous carbon framework of CMK-3. Nickel is then doped into the carbon framework via nickel nitrate impregnation. Dibutylmagnesium is then used as a magnesium source, and MgH2 is generated within the nanopores of the nickel-doped carbon mesoporous framework via high-pressure hydrogenation. This method suppresses the sintering and agglomeration of MgH2 particles through the nanoconfining effect and improves the hydrogen absorption and desorption kinetics by utilizing the catalytic effect of the doped nickel, thereby reducing the hydrogen desorption temperature to some extent.

[0008] However, the method disclosed in CN105645356A still has the following shortcomings: ① The carbon mesoporous framework is prepared by a hard template method, which is complex and costly. Moreover, the resulting carbon material is an isolated particle stack with high interparticle thermal resistance and poor thermal conductivity, which is not conducive to heat transfer and management during hydrogen absorption and desorption. ② Nickel is dispersed in the carbon framework matrix as a dopant rather than existing as an independent alloy catalytic phase, resulting in a limited number and accessibility of catalytic active sites. ③ Although the hydrogen desorption temperature of MgH2 is reduced, it is still relatively high, and the increase in hydrogen absorption and desorption rate is limited. ④ The resulting material is in powder form, and in practical applications, an external binder is required for molding. The binder is prone to aging and pulverization during recycling, leading to the collapse of the carrier structure.

[0009] Furthermore, Chinese invention patent CN120328485A discloses a composite hydrogen storage material and its preparation method. First, magnesium raw material powder and lanthanum-nickel alloy (LaNi5) raw material powder are subjected to plasma nano-sizing treatment to obtain nano-sized magnesium powder and nano-sized lanthanum-nickel alloy powder, respectively. Then, the two nano-powders are uniformly mixed in an inert atmosphere, and carbon sources such as asphalt powder are added to the mixed powder. After a first calcination to form a carbon-coated precursor, a second calcination carbonization is performed to finally obtain a magnesium-lanthanum-nickel-carbon composite hydrogen storage material. This scheme utilizes a "cached + memory" staged hydrogen storage approach, leveraging the mild and rapid hydrogen absorption and desorption conditions of LaNi5 to compensate for the slow kinetics of magnesium-based materials. The carbon coating layer improves thermal conductivity and inhibits particle agglomeration, achieving better hydrogen storage performance.

[0010] However, the aforementioned existing technologies still have the following problems:

[0011] First, at the material structure design level, the materials obtained by existing technologies are micron-sized composite particles of metal particles wrapped in carbon layers. The hydrogen storage functional components are randomly distributed at the microscale. This disordered structure makes it difficult for the two functional components to exert optimal synergistic effects in actual use, and the improvement of hydrogen storage performance is significantly limited.

[0012] Secondly, in terms of thermal management and mass transport, existing carbon-coated materials only form a carbon layer on the surface of individual metal particles. Heat conduction between particles must cross the particle-particle or particle-carbon layer interface, resulting in high interfacial thermal resistance and low overall thermal conductivity. Simultaneously, the migration of hydrogen atoms between different particles is also hindered by the interface, limiting further improvements in the hydrogen spillover effect and hydrogen absorption / desorption rates.

[0013] Third, in terms of engineering application and life-cycle management, the products obtained by existing technologies are usually micron-sized powder materials. When directly filled and used, these materials suffer from problems such as large bed pressure drop, easy channeling and flow deviation. Furthermore, the fine powder is prone to further pulverization and loss under the action of cyclic expansion and contraction. In addition, when the hydrogen absorption and desorption performance of the material deteriorates and fails, existing technologies lack simple, efficient, and low-cost separation, recovery, and reagent regeneration solutions for the various valuable metal elements contained within, making it difficult to support a green and low-carbon circular economy model.

[0014] Therefore, it is necessary to propose a new technical solution to address the problems existing in the current technology. Summary of the Invention

[0015] This application provides a bilayer supported solid hydrogen storage material and its preparation and recovery method to solve the problem of poor performance of existing solid hydrogen storage materials.

[0016] To achieve the above objectives, this application provides the following technical solution:

[0017] In a first aspect, this application provides a bilayer supported solid hydrogen storage material, comprising:

[0018] A continuous carbon skeleton carrier, wherein the continuous carbon skeleton carrier is a lignin-semi-coke composite porous carbon material, having an interface-free continuous carbon skeleton network, a mesopore ratio greater than 40%, a thermal conductivity greater than 50 W / (m·K), and a lateral compressive strength greater than 80 N.

[0019] The inner hydrogen storage component is loaded inside the mesopores of the continuous carbon framework support. The inner hydrogen storage component is a magnesium-based hydrogen storage material with a loading of 40 wt% to 60 wt% based on Mg.

[0020] An outer catalytic component is supported on the surface of the continuous carbon framework support. The outer catalytic component is a lanthanum-nickel alloy with a loading of 10 wt% to 20 wt% based on LaNi5.

[0021] Furthermore, in the above technical solution, the continuous carbon framework carrier is prepared by co-pyrolysis of coal and enzymatically hydrolyzed lignin. After carbonization, the enzymatically hydrolyzed lignin is chemically bonded with semi-coke to form the interfaceless continuous carbon framework network, and the continuous carbon framework carrier retains the composite structure of natural polycyclic aromatic hydrocarbons and amorphous carbon in coal.

[0022] Furthermore, the specific surface area of ​​the lignin-semi-coke composite porous carbon material is 200~500 m². 2 / g.

[0023] Furthermore, the surface of the continuous carbon skeleton support has oxygen-containing functional groups, the total amount of which is 1 mmol / g to 3 mmol / g, and the oxygen-containing functional groups include one or more of hydroxyl, carboxyl and carbonyl groups.

[0024] Furthermore, the mesopore size of the continuous carbon framework support is 5~50 nm;

[0025] Furthermore, the double-layer supported solid hydrogen storage material is a molded particle, and the particle size of the double-layer supported solid hydrogen storage material is 0.5~10 mm, preferably 5~10 mm.

[0026] Furthermore, the bilayer supported solid hydrogen storage material absorbs hydrogen at a temperature of 150℃ to 200℃, with a hydrogen storage capacity of 5wt% to 7wt%; and releases hydrogen at a temperature of 200℃ to 250℃.

[0027] Secondly, this application provides a method for preparing the above-mentioned bilayer supported solid hydrogen storage material, comprising the following steps:

[0028] S1: Immerse the particulate continuous carbon skeleton support in magnesium nitrate solution or magnesium acetate solution, dry it, and then hydrogenate and reduce it for 1 to 2 hours at 300℃~350℃ and 5~10MPa hydrogen atmosphere to reduce magnesium ions to MgH2 and load them into the mesopores of the continuous carbon skeleton support to obtain MgH2 / carbon composite particles.

[0029] S2: Immerse the MgH2 / carbon composite particles obtained in step S1 into a mixed solution of lanthanum and nickel nitrates or a mixed solution of lanthanum and nickel acetates. After drying, calcine them at 500℃~600℃ for 2~4 hours under an inert atmosphere to decompose MgH2 into metallic Mg and release the pore space. At the same time, lanthanum and nickel nitrates or lanthanum and nickel acetates decompose into La2O3 and NiO to obtain Mg / La2O3 / NiO / carbon composite particles.

[0030] S3: The Mg / La2O3 / NiO / carbon composite particles obtained in step S2 are reduced at 500℃~600℃ and 5~10MPa hydrogen atmosphere for 2~4 hours to reduce and alloy La2O3 and NiO into LaNi5, and LaNi5 is distributed on the surface of the continuous carbon skeleton support to obtain Mg / LaNi5 / carbon composite particles.

[0031] S4: The Mg / LaNi5 / carbon composite particles obtained in step S3 are activated at 300℃~350℃ and 5~10MPa hydrogen atmosphere for 1~2 hours, so that the metallic Mg is hydrogenated to MgH2 and LaNi5 is activated by hydrogen absorption to LaNi5H6, thus obtaining active MgH2 / LaNi5 / carbon composite particles, and the preparation of the double-layer supported solid hydrogen storage material is completed.

[0032] Furthermore, in step S1, the concentration of the magnesium nitrate solution is 0.5 mol / L to 2.0 mol / L.

[0033] Furthermore, in step S2, the total concentration of the lanthanum and nickel nitrate mixed solution is 0.1 mol / L to 0.5 mol / L, wherein the molar ratio of La to Ni is 1:5, and the inert atmosphere is nitrogen or argon.

[0034] Thirdly, this application provides a method for preparing a continuous carbon framework support, wherein the continuous carbon framework support is used in the above-mentioned bilayer supported solid hydrogen storage material or the above-mentioned method for preparing a bilayer supported solid hydrogen storage material, comprising the following steps:

[0035] L1: Coal powder and enzymatically hydrolyzed lignin powder are mixed, wherein the amount of enzymatically hydrolyzed lignin powder added is 10% to 20% of the coal powder mass. The mixture is subjected to supercritical carbon dioxide dynamic cyclic pyrolysis at 280℃ to 320℃ and 8 to 20MPa to carbonize the lignin in situ and form a continuous carbon skeleton network without interface with the semi-coke through chemical bonding, thus obtaining lignin-semi-coke composite carbon skeleton powder.

[0036] L2: Add the lignin-semi-coke composite carbon skeleton powder obtained in step L1 to the alkaline solution, heat and stir, separate by flotation using density difference, and collect the upper effective component.

[0037] L3: Granulate the upper effective components collected in step L2, with a particle size of 5mm to 10mm, and calcine them in an inert atmosphere at 300℃ to 500℃ to obtain continuous carbon skeleton carrier particles.

[0038] Further, in step L1, the coal powder is bituminous coal powder, and a co-solvent is added during the supercritical carbon dioxide dynamic cyclic pyrolysis process. The amount of co-solvent added is 1% to 3% of the coal powder mass. In step L2, the alkaline solution is KOH, NaOH, or Ca(OH)2 solution. In step L3, the upper effective components collected in step L2 are granulated and formed by ball rolling granulation, extrusion granulation, or spray granulation.

[0039] Furthermore, the co-solvent is n-hexane, and the amount of n-hexane added is 2% of the coal powder mass; in step L1, the amount of enzymatically hydrolyzed lignin powder added is 15% of the coal powder mass; in step L2, the concentration of the alkaline solution is 1.0 mol / L to 2.0 mol / L, the heating temperature is 80℃ to 100℃, and the stirring time is 30 to 60 minutes.

[0040] Fourthly, this application provides a method for recovering metals from a failed hydrogen storage material, wherein the failed hydrogen storage material is the material obtained after recycling the aforementioned double-layer supported solid hydrogen storage material, and the method includes the following steps:

[0041] T1: Dissolution process, the failed hydrogen storage material is put into nitric acid solution or acetic acid solution, heated and stirred so that all magnesium, lanthanum and nickel metal elements are dissolved into the solution, and the continuous carbon skeleton support is separated by filtration.

[0042] T2: Precipitation process, the filtrate obtained in step T1 is subjected to three-stage precipitation separation:

[0043] First-stage precipitation separation: Adjust the pH of the filtrate to 7.5-8.5 to precipitate La(OH)3, and recover lanthanum by filtration;

[0044] Second-stage precipitation separation: Adjust the pH of the first-stage precipitation filtrate to 6.5-7.5 to precipitate Ni(OH)2, and then filter to recover nickel;

[0045] Third-stage precipitation separation: Adjust the pH of the filtrate from the second-stage precipitation separation to 10.5-11.5 to precipitate Mg(OH)2, and then filter to recover magnesium;

[0046] T3: Electrolysis process, electrolyzing the filtrate after three-stage precipitation separation in step T2. The anode generates HNO3 or CH3COOH, which is returned to the dissolution process in step T1. The cathode generates NaOH, which is returned to the precipitation process in step T2. The cathode generates H2, which is returned to the activation process in step S4 of claim 5, thus realizing a closed-loop cycle of reagents and hydrogen.

[0047] Furthermore, in the above technical solution, the concentration of the nitric acid solution in step T1 is 5 mol / L to 7 mol / L, the heating temperature is 70℃ to 90℃, and the stirring time is 1.5 to 2.5 hours.

[0048] Compared with the prior art, this application has at least the following beneficial effects:

[0049] 1. The bilayer-supported solid-state hydrogen storage material provided in this application uses a lignin-semi-coke composite porous carbon material as a continuous carbon skeleton support. This support forms an interface-free continuous network structure through in-situ carbonization of lignin and chemical bonding with semi-coke. It can be integrally molded without the need for external binders, fundamentally eliminating the interparticle interface thermal resistance present in traditional particle-stacking porous carbon materials. On the one hand, it constructs a highly efficient "thermal bridge" with a thermal conductivity greater than 50 W / (m·K), allowing the heat released by the outer catalytic component during hydrogen absorption to be rapidly and uniformly conducted to the inner hydrogen storage component. During hydrogen release, the externally supplied heat is also uniformly transferred, effectively solving the thermal management problem caused by local overheating or uneven heating. On the other hand, it constructs a continuous "hydrogen bridge" without interface barriers, allowing hydrogen atoms to migrate freely along the surface of the continuous carbon skeleton, avoiding the transmission resistance caused by hydrogen overflow having to cross particle gaps in traditional materials, significantly improving hydrogen overflow efficiency. At the same time, through By loading magnesium-based hydrogen storage materials into the mesopores of a continuous carbon framework and loading lanthanum-nickel alloy LaNi5 onto the surface of the carbon framework, a bilayer functional gradient structure is formed, with an inner layer for hydrogen storage and an outer layer for catalysis. This allows the two functional components to occupy their respective spatial positions. Specifically, the outer LaNi5 layer acts as an "igniter" and "hydrogen pump," preferentially and rapidly absorbing hydrogen and releasing heat at low temperatures, and preferentially releasing hydrogen to reduce the partial pressure of hydrogen in the system. The inner MgH2 layer acts as the "main hydrogen storage body," providing high hydrogen storage capacity. The two layers achieve bidirectional synergy of thermal effect and hydrogen overflow through the thermal bridge and hydrogen bridge of the continuous carbon framework. Combined with the rigid framework of polycyclic aromatic hydrocarbons retained in the carbon framework and the flexible buffer of amorphous carbon, the structure effectively resists the mechanical stress generated by the approximately 30% volume change during the hydrogen absorption and desorption cycle. Thus, while significantly reducing the hydrogen absorption and desorption temperature and increasing the hydrogen absorption and desorption rate, the material maintains excellent cycle stability with a capacity retention rate of more than 90% after 100 cycles.

[0050] 2. The continuous carbon framework support in this application is prepared by supercritical carbon dioxide pyrolysis of coal and lignin, which gives the support unique physicochemical properties of a continuous network without interface and a rigid-flexible composite structure. The continuous carbon framework network serves as both a heat conduction channel and a hydrogen atom migration channel, allowing the heat generated by the absorption of hydrogen by the outer catalytic component to be conducted to the inner hydrogen storage component through the carbon framework, and allowing hydrogen atoms dissociated from the surface of the outer catalytic component to migrate to the surface of the inner hydrogen storage component through the carbon framework. This is the structural basis for the thermal bridge, hydrogen bridge effect and anti-expansion ability.

[0051] 3. This application provides a method for preparing a bilayer supported solid hydrogen storage material. Through a unique process sequence of "inner-outer, stepwise loading, and intermediate inert atmosphere calcination," an ideal bilayer gradient structure of inner hydrogen storage and outer catalysis is precisely achieved. Specifically, magnesium is first loaded and subjected to high-pressure hydrogenation to ensure the stable formation of the main hydrogen storage component, MgH2, within the pores of the carbon framework. Subsequently, a lanthanum-nickel precursor is loaded and subjected to high-temperature calcination in an inert atmosphere. This step decomposes the inner MgH2, releasing the pore space, and simultaneously converts the lanthanum-nickel salt into oxides, providing sufficient space and phase conditions for the in-situ formation of LaNi5 on the carbon framework surface in subsequent steps. High-pressure hydrogenation reduction is then performed to alloy the surface oxide into LaNi5, while the inner magnesium remains stable under high pressure, thus forming a spatial gradient distribution of inner Mg and outer LaNi5. Finally, activation before use ensures that both functional components reach an active hydrogen storage state. The entire process is interconnected and the order cannot be reversed. This ensures the precise construction of the two functional components in their respective optimal positions, while avoiding the random distribution of components and functional interference caused by traditional blending methods, thus providing a process guarantee for maximizing the synergistic effect.

[0052] 4. This application provides a method for preparing a continuous carbon framework carrier, which uses coal powder and enzymatically hydrolyzed lignin powder as raw materials. In-situ carbonization of lignin is achieved through supercritical carbon dioxide dynamic cyclic pyrolysis, resulting in chemical bonding with semi-coke. This constructs an integrated continuous carbon framework network at the molecular level, free from interfacial thermal resistance and binders. This method overcomes the drawbacks of traditional porous carbon hard template methods, which are complex and costly. The excellent mass transfer and permeability of supercritical fluids ensure a uniform carbon framework structure. Alkali flotation effectively removes unbonded loose carbon and ash, further purifying the framework network. Granulation and inert atmosphere calcination further strengthen the structure, ultimately yielding continuous carbon framework carrier particles with high specific surface area, high porosity, ultra-high thermal conductivity, and high mechanical strength.

[0053] 5. This application provides a method for recovering metals from spent hydrogen storage materials, capable of separating and recovering a continuous carbon framework support and three valuable metals (Mg, La, Ni) from spent hydrogen storage materials. First, nitric acid or acetic acid is used to dissolve all the metal elements in the spent material into a solution, while the acid-resistant and structurally stable continuous carbon framework support remains insoluble, achieving a one-time, highly efficient separation of the continuous carbon framework support and the metal elements. Subsequently, based on the differences in solubility of La(OH)3, Ni(OH)2, and Mg(OH)2 at different pH values, the pH of the filtrate is adjusted in stages for three-stage separation. The process involves a step-by-step precipitation process to achieve highly selective, step-by-step recovery of the three metal ions, with recovery rates exceeding 95%. Finally, the remaining NaNO3 solution after recovering the metal hydroxides is electrolyzed. The anode produces HNO3, which is returned to the metal recovery and dissolution process; the cathode produces NaOH, which is returned to the metal recovery and precipitation process; and the high-purity H2 produced at the cathode is returned to the activation step in the preparation of the bilayer-supported solid-state hydrogen storage material. This achieves a fully closed-loop cycle of the three key reagents: nitric acid or acetic acid, sodium hydroxide, and hydrogen. The cost of purchased reagents is reduced by 80%, and the entire process consumes only water and electricity, essentially achieving zero waste liquid discharge. This method enables the bilayer-supported solid-state hydrogen storage material of this application to possess a green closed-loop capability throughout its entire life cycle, from preparation and use to recycling and regeneration, greatly improving the economic and environmental benefits of the technology. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. It should be understood that the specific shapes and structures shown in the drawings should not generally be regarded as limiting conditions for implementing this application. For example, based on the technical concepts disclosed in this application and the exemplary drawings, those skilled in the art are able to easily make conventional adjustments or further optimizations to the addition / reduction / classification, specific shapes, positional relationships, connection methods, and size ratios of certain units (components).

[0055] Figure 1 This is a flowchart illustrating a method for preparing a bilayer supported solid hydrogen storage material provided in this application, as one embodiment.

[0056] Figure 2 This is a flowchart illustrating a method for preparing a continuous carbon framework support provided in this application, as one embodiment.

[0057] Figure 3 This is a flowchart illustrating a method for recovering metals from a failed hydrogen storage material provided in this application, as one embodiment. Detailed Implementation

[0058] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. In the description of the present application: unless otherwise stated, expressions such as "comprising," "including," and "having" also mean "not limited to" (certain units, components, materials, steps, etc.).

[0059] Example 1

[0060] This application provides a bilayer supported solid hydrogen storage material. The material uses a continuous carbon skeleton as a carrier and forms a bilayer structure of inner MgH2 and outer LaNi5 through stepwise loading. By utilizing the thermal bridge effect and hydrogen bridge effect of the continuous carbon skeleton, the material achieves synergistic thermal effect during hydrogen absorption and hydrogen partial pressure regulation during hydrogen release. This solves the technical problems of "high temperature, slow kinetics and poor cycle" of magnesium-based hydrogen storage materials and enables efficient recovery and closed-loop recycling of metals after failure.

[0061] In a preferred embodiment of this application, the bilayer-loaded solid hydrogen storage material includes a continuous carbon framework support and a bilayer-loaded structure loaded thereon.

[0062] The continuous carbon framework carrier is a lignin-semi-coke composite porous carbon material with a specific surface area of ​​200~500 m². 2 It has a mesopore content greater than 40% and a mesopore diameter of 5-50 nm. It is prepared by co-pyrolysis of coal and enzymatically hydrolyzed lignin, possessing a continuous, interface-free carbon framework network (formed by chemical bonding between lignin carbonization and semi-coke to create a continuous, interface-free structure; its carbon structure retains the composite structure of natural polycyclic aromatic hydrocarbons (graphite microcrystals) and amorphous carbon in coal, combining rigidity and flexibility, and resisting volume expansion), requiring no external binder. Thermal conductivity >50 W / m·K (interface-free thermal resistance); lateral compressive strength >80 N (integral molding); surface oxygen-containing functional groups 1-3 mmol / g (functional groups are one or more of hydroxyl, carboxyl, and carbonyl groups).

[0063] The bilayer supported structure was prepared using a stepwise loading method, forming an inner layer of MgH2 and an outer layer of LaNi5. Specifically, the inner layer is a magnesium-based hydrogen storage layer with a loading of 40%–60 wt% based on Mg. This magnesium-based hydrogen storage layer fills the pores within the support, serving as the primary hydrogen storage medium and providing a high hydrogen storage capacity (5–7 wt%). The outer layer is a lanthanum-nickel catalyst layer with a loading of 10%–20 wt% based on LaNi5. This catalyst is supported on the surface of a continuous carbon framework support and functions to rapidly absorb and release hydrogen at low temperatures, provide a heat and hydrogen source, and regulate hydrogen partial pressure.

[0064] The double-layer supported solid hydrogen storage material is in the form of molded particles with a particle size of 0.5~10mm, preferably 5~10mm. It absorbs hydrogen at temperatures of 150℃~200℃, with a hydrogen storage capacity of 5wt%~7wt%; and releases hydrogen at temperatures of 200℃~250℃, maintaining a capacity retention of over 90% after 100 hydrogen absorption / desorption cycles.

[0065] The synergistic hydrogen storage mechanism of the bilayer loaded solid hydrogen storage material provided in this application is as follows.

[0066] 1. Synergistic effect of hydrogen absorption (thermal effect + hydrogen overflow):

[0067] Hydrogen absorption in LaNi5: LaNi5 + 3H2 → LaNi5H6, exothermic (~30kJ / mol H2), occurs rapidly at room temperature to 80℃.

[0068] The heat released by the thermal bridge is rapidly and uniformly transferred to the MgH2 particles through the continuous carbon skeleton (thermal conductivity >50W / m·K).

[0069] Hydrogen spillover: Hydrogen atoms dissociated from the LaNi5 surface migrate to the Mg surface through a continuous carbon framework and directly participate in hydrogenation.

[0070] 2. Hydrogen release synergy (hydrogen partial pressure regulation + reverse hydrogen overflow):

[0071] External heating provides the heat required for hydrogen release (200~250℃);

[0072] LaNi5H6 decomposition: LaNi5H6→LaNi5+3H2, starting at 80~150℃, reduces the partial pressure of hydrogen in the system. According to Le Chatelier's principle, the reduction in partial pressure of hydrogen promotes the decomposition reaction of MgH2 to proceed to the right.

[0073] Decomposition of MgH2: MgH2 → Mg + 2H + It occurs at 200~250℃ (100~150℃ lower than pure MgH2);

[0074] Hydrogen overflow reversed: H + The continuous carbon skeleton migrates to the LaNi5 surface, combines to form H2 for desorption, and provides a "hydrogen sink".

[0075] 3. The dual bridging function of the continuous carbon skeleton:

[0076] The thermal bridge has no interfacial thermal resistance and a thermal conductivity >50W / m·K, ensuring uniform heat transfer during hydrogen absorption and uniform heat supply during hydrogen release.

[0077] Hydrogen bridges have no interface barriers, allowing hydrogen atoms to migrate continuously, and their overflow efficiency is 3 to 5 times higher than that of traditional mesoporous carbon.

[0078] It has a stable structure, requires no external adhesive, is integrally molded, and retains more than 90% of its lateral compressive strength after 100 cycles.

[0079] Therefore, the bilayer loaded solid hydrogen storage material provided in this application achieves synergistic hydrogen storage through the dual bridging effect of its interfaceless continuous carbon skeleton network: on the one hand, it acts as a "thermal bridge"—with no interface thermal resistance and a thermal conductivity of over 50 W / (m·K), rapidly and uniformly transferring the heat released by LaNi5 to MgH2 when absorbing hydrogen, and uniformly transferring external heat when releasing hydrogen; on the other hand, it acts as a "hydrogen bridge"—with no interface barrier, hydrogen atoms can migrate freely along the surface of the continuous carbon skeleton, and the hydrogen overflow efficiency is more than 3 times higher than that of traditional mesoporous carbon.

[0080] During hydrogen absorption, the surface LaNi5 preferentially and rapidly absorbs hydrogen at low temperatures (from room temperature to 80°C), releasing approximately 30 kJ / mol H2. This heat is uniformly conducted to the inner MgH2 layer through continuous carbon framework thermal bridges, preheating the MgH2 to its effective hydrogen absorption temperature and forming a thermally self-sustaining cycle. Simultaneously, hydrogen atoms dissociated from the LaNi5 surface migrate to the Mg surface through continuous carbon framework hydrogen bridges to directly participate in the hydrogenation reaction, significantly increasing the hydrogen absorption rate. During hydrogen release, external heat (200–250°C) is uniformly transferred to the material through thermal bridges. The surface LaNi5H6 layer decomposes first at 80–150°C, releasing H2, acting like a "chemical pump" to reduce the local hydrogen partial pressure in the system. According to Le Chatelier's principle, this pulls the inner MgH2 layer to decompose at 200–250°C, lowering the hydrogen release temperature by 100–150°C compared to pure MgH2. Simultaneously, the H2 produced by the decomposition of MgH2... + The carbon skeleton migrates backward to the LaNi5 surface for binding and desorption, providing a "hydrogen sink" for the continuous hydrogen release of MgH2.

[0081] Example 2

[0082] This application provides a method for preparing a bilayer supported solid hydrogen storage material, the core of which lies in the process sequence of "inner-outer, stepwise loading, and intermediate inert atmosphere calcination," see [link to relevant documentation]. Figure 1 This includes the following steps:

[0083] ①Preparation of continuous carbon framework support particles;

[0084] ② Magnesium-based support and high-pressure hydrogenation: Carbon-based support particles are immersed in a magnesium nitrate solution with a concentration of 0.5~2.0 mol / L, dried at 80~120℃, and then placed in a high-pressure reactor. Hydrogen gas is introduced to 5~10 MPa, the temperature is raised to 300~350℃, and held at this temperature for 1~2 hours to allow the Mg to undergo hydrogenation. 2+ The carbon is reduced to MgH2 and loaded into the mesopores to obtain MgH2 / carbon composite particles;

[0085] ③ Lanthanum-nickel precursor loading and inert atmosphere calcination: MgH2 / carbon composite particles are immersed in a mixed solution of lanthanum and nickel nitrates (La:Ni=1:5, total concentration 0.1~0.5mol / L), dried, and then placed in a tube furnace. An inert gas (nitrogen or argon) is introduced, and the temperature is raised to 500~600℃ and held for 2~4 hours. During this process, MgH2 decomposes into metallic Mg and releases H2 to open the pore space. At the same time, lanthanum and nickel nitrates decompose into La2O3 and NiO, resulting in Mg / La2O3 / NiO / carbon composite particles.

[0086] ④ High-pressure hydrogenation reduction: The particles obtained in step ③ are loaded into a high-pressure reactor, hydrogen is introduced to a pressure of 5-10 MPa, the temperature is raised to 500-600℃, and the temperature is maintained for 2-4 hours. During this process, La2O3 and NiO are reduced and alloyed to LaNi5, and LaNi5 is distributed on the surface of the continuous carbon skeleton support. Mg remains in the metallic state (does not decompose under high pressure) to obtain Mg / LaNi5 / carbon composite particles.

[0087] ⑤ Activation before use: Activate the particles obtained in step ④ in a hydrogen atmosphere at 300-350℃ and 5-10MPa to hydrogenate the metallic Mg to MgH2 and activate LaNi5 to LaNi5H6, so as to obtain active MgH2 / LaNi5 / carbon composite particles, which can be directly filled and used.

[0088] In the above process steps, Mg is first loaded and hydrogenated, then LaNi5 precursor is loaded, and MgH2 is decomposed into metallic Mg through calcination in an inert atmosphere (releasing the pore space). Finally, LaNi5 is generated by high-pressure reduction and distributed on the surface of the carbon framework. This sequence ensures that LaNi5 is located on the surface (as a hydrogen inlet and heat source) and Mg is located in the inner layer (as the main hydrogen storage medium), achieving an ideal distribution of the bilayer structure.

[0089] In a preferred embodiment of this application, the magnesium nitrate solution used in step ② above can be replaced with magnesium acetate solution; in addition, the lanthanum and nickel nitrate mixed solution used in step ③ above can be replaced with lanthanum and nickel acetate mixed solution.

[0090] Example 3

[0091] This application provides a method for preparing a continuous carbon framework support, which can be used in the preparation method of the bilayer-loaded solid hydrogen storage material in Example 1 or the bilayer-loaded solid hydrogen storage material in Example 2. See [link to relevant documentation]. Figure 2 Specifically, it includes the following steps:

[0092] 1. Mix coal powder (bituminous coal powder) with enzymatically hydrolyzed lignin powder (10% to 20% of the coal powder mass) and carry out supercritical carbon dioxide dynamic cyclic pyrolysis at 280 to 320℃ and 8 to 20 MPa to carbonize lignin in situ and form a continuous carbon skeleton network without interface with semi-coke through chemical bonding, thus obtaining lignin-semi-coke composite carbon skeleton powder.

[0093] 2. Add the above powder to an alkaline solution (such as KOH, NaOH or Ca(OH)2, with a concentration of 1.0 mol / L to 2.0 mol / L), heat and stir at 80℃ to 100℃, and separate by flotation using density difference, collecting the upper effective component;

[0094] 3. The particles are formed by ball milling, extrusion granulation or spray granulation, with the particle size controlled at 5~10mm (larger particles are preferred for fixed beds), and calcined at 300~500℃ in an inert atmosphere to obtain continuous carbon skeleton carrier particles.

[0095] In a preferred embodiment, a co-solvent (such as n-hexane, the amount of which is 1% to 3% of the coal powder mass, preferably 2%) is added during the supercritical carbon dioxide dynamic cyclic pyrolysis process.

[0096] The method for preparing a continuous carbon framework carrier provided in this application uses coal powder and enzymatically hydrolyzed lignin powder as raw materials. In-situ carbonization of lignin is achieved through supercritical carbon dioxide dynamic cyclic pyrolysis, resulting in chemical bonding with semi-coke. This constructs an integrated continuous carbon framework network at the molecular level, free from interfacial thermal resistance and binders. This method overcomes the drawbacks of traditional porous carbon hard template methods, which are complex and costly. The excellent mass transfer and permeability of supercritical fluids ensure a uniform carbon framework structure. Alkaline flotation effectively removes unbonded loose carbon and ash, further purifying the framework network. Structural strengthening is achieved through granulation and inert atmosphere calcination, ultimately yielding continuous carbon framework carrier particles with high specific surface area, high porosity, ultra-high thermal conductivity, and high mechanical strength.

[0097] Example 4

[0098] This application also provides a method for recovering metals from degraded hydrogen storage materials, see [link to relevant documentation]. Figure 3 It includes the following steps:

[0099] 1. Dissolving metals: Add the degraded hydrogen storage material to a nitric acid solution (6 mol / L), stir at 80°C for 2 hours. Mg, La, and Ni will all dissolve, while the carbon skeleton will remain insoluble. Filter to separate.

[0100] 2. Three-stage precipitation separation:

[0101] The filtrate from step 1 is discharged into pool 1 and the pH is adjusted to 7.5-8.5 to precipitate La(OH)3. Lanthanum is then recovered by filtration. The filtrate from pool 1 is discharged into pool 2 and the pH is adjusted to 6.5-7.5 to precipitate Ni(OH)2. Nickel is then recovered by filtration. The filtrate from pool 2 is discharged into pool 3 and the pH is adjusted to 10.5-11.5 to precipitate Mg(OH)2. Magnesium is then recovered by filtration.

[0102] 3. Closed-loop electrolytic regeneration:

[0103] The recovered NaNO3 solution is electrolyzed, generating HNO3 at the anode (returned to the dissolution tank) and NaOH at the cathode (returned to the precipitation tank). At the same time, high-purity H2 is generated at the cathode (returning to the activation step of the preparation method of the double-layer supported solid hydrogen storage material in Example 2), thus realizing a closed-loop cycle of reagents and hydrogen.

[0104] In a preferred embodiment of this application, the nitric acid solution used in the dissolution process of step 1 can be replaced with acetic acid solution. After the replacement, the electrolysis process in step 3 will electrolyze the recovered CH3COONa solution, generating CH3COOH at the anode (returning to the dissolution tank), generating NaOH at the cathode (returning to the precipitation tank), and generating H2 at the cathode (returning to the activation step of the preparation method of double-layer loaded solid hydrogen storage material in Example 2), thus realizing a closed-loop circulation of hydrogen.

[0105] Example 5

[0106] This embodiment provides a verification example of the preparation of a continuous carbon framework support.

[0107] Take 500g of bituminous coal powder and add 75g of enzymatically hydrolyzed lignin powder, mix well. Place the mixture into a supercritical reactor, introduce CO2, heat to 300℃, pressurize to 15MPa, add 2% (by weight of coal) of n-hexane as a co-solvent, start the circulating compressor, and dynamically circulate the reaction for 2 hours. Depressurize and cool, collect the lignin-semi-coke composite carbon skeleton powder.

[0108] Take 100g of the above powder, add 300mL of 1.5mol / L KOH solution, heat to 90℃ and stir for 40 minutes, let stand and float to separate, and collect the upper effective component. Granulate using a ball granulator, control the particle size to 5-10mm, dry at 110℃ for 4 hours, and calcine at 450℃ under nitrogen atmosphere for 3 hours to obtain continuous carbon skeleton support particles.

[0109] The obtained carrier performance test results are: specific surface area 372m². 2 The material has a porosity of 40%, a thermal conductivity of 85 W / (m·K), and a lateral compressive strength of 95 N. This carrier can be integrally molded without the need for external binders. After carbonization, the lignin forms a continuous, interface-free network with the semi-coke through chemical bonding. The carbon structure retains the microcrystalline characteristics of polycyclic aromatic hydrocarbons in coal.

[0110] Example 6

[0111] This embodiment provides a specific example of the magnesium-based loading and high-pressure hydrogenation steps in the preparation method of a bilayer loaded solid hydrogen storage material.

[0112] Take 100g of the carrier particles obtained in Example 5, immerse them in 200mL of 1.0mol / L magnesium nitrate solution, stir and impregnate at 80℃ for 2 hours, and dry at 110℃ for 4 hours. Place them in a high-pressure reactor, purge with hydrogen to 8MPa, heat to 320℃, and hold at that temperature for 1.5 hours to allow the Mg... 2+ The Mg is reduced to MgH2 and fills the pores within the support, resulting in MgH2 / carbon composite particles. Analysis showed that the Mg loading was 52 wt%.

[0113] Example 7

[0114] This embodiment provides a specific example of the lanthanum-nickel precursor loading and inert atmosphere calcination steps in the preparation method of a double-layer loaded solid hydrogen storage material.

[0115] The MgH2 / carbon composite particles obtained in Example 6 were immersed in 150 mL of a mixed solution of lanthanum and nickel nitrates (La:Ni molar ratio = 1:5, total concentration 0.3 mol / L), stirred and impregnated at 80°C for 2 hours, and dried at 110°C for 4 hours. The mixture was then placed in a tube furnace, nitrogen gas was introduced, and the temperature was raised to 550°C and held for 3 hours. In this step, MgH2 decomposes into metallic Mg and releases the pore space, while La and Ni nitrates decompose into La2O3 and NiO, respectively, yielding Mg / La2O3 / NiO / carbon composite particles.

[0116] Example 8

[0117] This embodiment provides a specific example of the high-pressure hydrogenation reduction step in the preparation method of a bilayer supported solid hydrogen storage material.

[0118] The Mg / La₂O₃ / NiO / carbon composite particles obtained in Example 7 were loaded into a high-pressure reactor, hydrogen gas was introduced to 8 MPa, and the temperature was raised to 550°C and held for 3 hours. In this step, La₂O₃ and NiO were reduced and alloyed to LaNi₅, and LaNi₅ was distributed on the surface of the continuous carbon framework support. Mg remained in a metallic state (it did not decompose under high pressure). After natural cooling, Mg / LaNi₅ / carbon composite particles were obtained. Analysis showed that the LaNi₅ loading was 15 wt%.

[0119] Example 9

[0120] This embodiment provides a specific example of the pre-activation step used in the preparation method of a bilayer supported solid hydrogen storage material.

[0121] The Mg / LaNi5 / carbon composite particles obtained in Example 8 were loaded into a high-pressure reactor, hydrogen gas was introduced to 8 MPa, the temperature was raised to 320°C, and held at that temperature for 1.5 hours. In this step, metallic Mg is hydrogenated to MgH2, and LaNi5 absorbs hydrogen to form LaNi5H6. Active MgH2 / LaNi5 / carbon composite particles (i.e., the bilayer supported solid hydrogen storage material of this invention) are obtained and can be directly loaded for use.

[0122] Example 10

[0123] This embodiment provides a test example for testing the hydrogen absorption performance of the active MgH2 / LaNi5 / carbon composite particles prepared in Example 9.

[0124] Take 5g of the active particles obtained in Example 9, load them into a high-pressure hydrogen storage test device, and test their hydrogen absorption performance under hydrogen conditions of 200℃ and 5MPa.

[0125] Results: The initial hydrogen absorption temperature was 165℃ (i.e., significant hydrogen absorption could be detected at this temperature), the complete hydrogen absorption time was 8 minutes, and the hydrogen absorption capacity was 6.2 wt%.

[0126] This is thanks to the low-temperature rapid hydrogen absorption capability of the surface LaNi5 and the synergistic effect of the continuous carbon skeleton thermal / hydrogen bridges—LaNi5 absorbs hydrogen and releases heat to rapidly preheat the inner MgH2 layer, and the dissociated hydrogen atoms migrate rapidly to the Mg surface through the carbon skeleton.

[0127] Example 11

[0128] This embodiment provides a test example for testing the hydrogen desorption performance of the active MgH2 / LaNi5 / carbon composite particles prepared in Example 9.

[0129] Take 5g of the active particles obtained in Example 9 and measure their hydrogen release performance under programmed temperature rise at 0.1MPa hydrogen pressure.

[0130] Results: The initial hydrogen release temperature was 185℃, the peak hydrogen release temperature was 225℃, the complete hydrogen release time at 250℃ was 12 minutes, and the hydrogen release capacity was 6.1wt%.

[0131] The significant reduction in hydrogen release temperature is mainly due to the preferential decomposition of the surface LaNi5H6 in the low-temperature region, which reduces the local hydrogen partial pressure of the system. This leads to the decomposition of the inner MgH2 layer through the Le Chatelier principle, and the continuous carbon framework hydrogen bridges provide a fast migration channel for hydrogen atoms generated by the decomposition of MgH2.

[0132] Example 12

[0133] This embodiment provides a test example for the cyclic stability performance test of the active MgH2 / LaNi5 / carbon composite particles prepared in Example 9.

[0134] Take 5g of the active particles obtained in Example 9, absorb hydrogen at 200℃ and 5MPa hydrogen, and release hydrogen at 250℃ and 0.1MPa hydrogen, and cycle 100 times.

[0135] Results: After 100 cycles, the capacity retention rate was 92%, the lateral pressure retention rate was 91%, and the Mg particle size increased only slightly from the initial approximately 12 nm to approximately 15 nm (slight growth).

[0136] The hydrogen storage material of this application has excellent cycle stability, mainly due to: ① The continuous carbon skeleton does not require external binders and is integrally molded, avoiding structural collapse caused by binder aging and powdering; ② The rigid structure of polycyclic aromatic hydrocarbon graphite microcrystalline rigid skeleton and amorphous carbon flexible buffer effectively resists the mechanical stress generated by the approximately 30% volume change during the MgH2 / Mg cycle.

[0137] Example 13

[0138] This embodiment provides a specific example of metal recovery from the double-layer loaded solid hydrogen storage material prepared in Example 9 after it fails during recycling.

[0139] The bilayer supported solid hydrogen storage material prepared in Example 9 was subjected to 100 cycles of hydrogen absorption and desorption, after which 50g was added to 200mL of a 6mol / L nitric acid solution and stirred at 80°C for 2 hours. Mg, La, and Ni completely dissolved as nitrates and entered the solution, while the continuous carbon skeleton remained insoluble. Filtering yielded 45g of the carbon skeleton (specific surface area 335m²). 2 / g indicates that the carbon skeleton structure is well preserved.

[0140] The filtrate was divided into three portions, and each portion was subjected to a three-stage precipitation process:

[0141] Tank 1: The pH of the filtrate was adjusted to 8.0 with NaOH solution, resulting in a white precipitate of La(OH)3. After filtration and drying, 2.1 g of La(OH)3 was obtained. The recovery rate was 96% based on La elemental composition.

[0142] Pool 2: The filtrate from Pool 1 was taken, and the pH was adjusted to 7.0 with HNO3, resulting in a green precipitate of Ni(OH)2. After filtration and drying, 3.8 g of Ni(OH)2 was obtained. The recovery rate was 97% based on Ni elemental content.

[0143] Pool 3: Take the filtrate from Pool 2, adjust the pH to 11.0 with NaOH solution, and a white precipitate of Mg(OH)2 will form. Filter and dry to obtain 12.5g of Mg(OH)2. The recovery rate is 98% based on Mg elemental content.

[0144] Example 14

[0145] The NaNO3 solution (concentration approximately 2 mol / L) after the recovery of metal hydroxide in Example 13 was electrolyzed at a current density of 1000 A / m. 2 Electrolysis for 4 hours.

[0146] The HNO3 solution produced at the anode has a concentration of approximately 1.8 mol / L and can be recycled back to the dissolution process.

[0147] The NaOH solution produced at the cathode has a concentration of approximately 1.9 mol / L and can be recycled back to the precipitation process.

[0148] The cathode simultaneously produces high-purity H2 (99.2% purity), with a yield of 0.5 Nm. 3 / h allows you to return to the activation step for repeated use.

[0149] The electrolysis energy consumption is approximately 2.5 kWh per kilogram of NaNO3.

[0150] Therefore, this application achieves a closed-loop cycle for the three key reagents / raw materials, namely nitric acid, sodium hydroxide, and hydrogen, throughout the entire process through electrolytic regeneration and hydrogen recovery. The cost of purchased reagents is reduced by about 80% compared to the method of purchasing them entirely from outside sources, and it only consumes water and electricity with no waste liquid discharge.

[0151] Comparative Example 1

[0152] The continuous carbon framework support particles obtained in Example 5 were used to load Mg monolayer onto the support according to the process steps described in Example 6 (without the subsequent LaNi5 loading step) to obtain a monolayer Mg / carbon material. Hydrogen absorption performance, hydrogen release performance, and cycle stability performance were tested under the same conditions as in Examples 10, 11, and 12. A performance comparison table of the monolayer MgH2 / carbon material prepared in Comparative Example 1 and the bilayer loaded solid hydrogen storage material of this application is shown in Table 1 below.

[0153] Table 1. Performance Comparison of Single-Layer Mg / Carbon Materials and Bilayer Supported Solid Hydrogen Storage Materials

[0154]

[0155] The results show that monolayer Mg / carbon materials do not possess the catalytic ignition and hydrogen partial pressure regulation effects of the LaNi5 surface layer in this application, and the hydrogen absorption and desorption temperatures are significantly increased, while the kinetics and cycle stability are significantly reduced.

[0156] Comparative Example 2

[0157] Commercial mesoporous carbon (prepared by template method, specific surface area 350 m²) was used. 2The comparative sample (with a thermal conductivity of 18 W / (m·K)) was prepared using the same method as in Examples 6-9. Hydrogen absorption performance and cycle stability were tested under the same conditions as in Examples 10 and 12. A performance comparison table of the comparative sample 2 prepared in Comparative Example 2 and the bilayer supported solid hydrogen storage material of this application is shown in Table 2 below.

[0158] Table 2. Performance Comparison of Sample 2 and Bilayer Loaded Solid Hydrogen Storage Material

[0159]

[0160] Comparative Example 3

[0161] The raw material powder used in Example 5 (lignin-semi-coke composite carbon skeleton powder, without ball granulation and heat treatment for shaping) was granulated with 5% CMC (sodium carboxymethyl cellulose) binder and prepared as comparative sample 3 according to the same method as in Examples 6 to 9. The performance of comparative sample 3 and the double-layer loaded solid hydrogen storage material of this application were compared under the same conditions. The comparison results are shown in Table 3 below.

[0162] Table 3. Performance Comparison of Sample 3 and Bilayer Supported Solid Hydrogen Storage Material

[0163]

[0164] It is evident that the initial strength of the comparative sample 3, which was granulated and molded with an external binder, was lower than that of the binder-free integrally molded carrier of this application. Furthermore, the aging and pulverization of the binder during cycling resulted in a significant decrease in strength and a sharp drop in capacity retention.

[0165] Comparative Example 4

[0166] The carrier raw material powder obtained in Example 5 was granulated into carrier particles with particle sizes of 1 mm, 3 mm, 5 mm, 8 mm, and 10 mm by ball rolling. The particles were prepared using the same method as in Examples 6-9 and subjected to 100 cycles of testing as in Example 12. The performance test results of carrier particles with different particle sizes are shown in Table 4 below.

[0167] Table 4 Performance test results of carrier particles of different sizes

[0168]

[0169] The results showed that although small particles with a diameter of 1–3 mm had a large initial specific surface area, they exhibited poor resistance to pulverization during cyclic expansion and contraction, resulting in a significant increase in bed pressure drop and rapid capacity decay. Large particles with a diameter of 5–10 mm demonstrated the best resistance to pulverization and cyclic stability, while also exhibiting a smaller increase in bed pressure drop, making them suitable for loading into fixed-bed reactors. Considering both mass transfer efficiency and ease of loading, 5–10 mm was the preferred particle size range.

[0170] Comparative Example 5

[0171] Three carbon supports were prepared according to the same methods in Examples 6-9, respectively, and subjected to 100 cycles of testing under the same conditions as in Example 12. The performance comparison of the three carbon supports is shown in Table 5 below.

[0172] Table 5. Performance Comparison of Three Carbon Supports

[0173]

[0174] As can be seen, although activated carbon (sample B) has acceptable initial strength, the lack of a rigid graphite microcrystalline framework leads to structural collapse due to volume changes during cycling, resulting in a strength retention rate of only 49%. While artificial graphite (sample C) has high initial strength, its rigidity and lack of flexible buffering cause stress concentration during cycling, leading to microcrack propagation and the lowest strength retention rate (38%). In contrast, the support provided in this application utilizes a rigid polycyclic aromatic hydrocarbon framework for structural support and flexible amorphous carbon regions to absorb expansion stress, achieving a balance of rigidity and flexibility. Its cycling stability and strength retention rate are far superior to those of a single carbon structure support.

[0175] In summary, this application discloses a bilayer supported solid hydrogen storage material. The material uses a lignin-semi-coke composite continuous carbon skeleton as a carrier (mesopore >40%, thermal conductivity >50W / m·K, no external binder, retaining the rigid skeleton of polycyclic aromatic hydrocarbons). A bilayer structure of inner layer MgH2 (40~60wt%) and outer layer LaNi5 (10~20wt%) is formed by stepwise loading, and the shaped particles are 5~10mm.

[0176] The preparation method of this bilayer supported solid hydrogen storage material is as follows: first, high-pressure hydrogenation (300~350℃, 5~10MPa hydrogen atmosphere) is performed on Mg... 2+The process involves reducing MgH2 to Mg, then loading it with La and Ni nitrates (or La and Ni acetates), followed by calcination in an inert atmosphere (500-600℃) to decompose MgH2 into Mg and La / Ni nitrates (or La / Ni acetates) into oxides. High-pressure reduction (500-600℃, 5-10MPa hydrogen atmosphere) then generates LaNi5, which is distributed on the surface. Finally, activation (300-350℃, 5-10MPa hydrogen atmosphere) hydrogenates Mg and activates LaNi5. Utilizing the thermal bridges (no interfacial thermal resistance) and hydrogen bridges (continuous migration channels) of the continuous carbon framework, during hydrogen absorption, LaNi5 exothermally preheats MgH2, causing hydrogen atoms to overflow to the Mg surface. During hydrogen release, LaNi5H6 decomposes first, reducing the hydrogen partial pressure and pulling MgH2 to decompose. The material has a hydrogen storage capacity of 5-7 wt%, with hydrogen absorption and release temperatures 100-150℃ lower than pure MgH2, and a capacity retention rate of >90% after 100 cycles. After failure, the metal is dissolved in nitric acid or acetic acid, separated by three-stage precipitation (La, Ni, and Mg recovery rates >95%), and the filtrate is electrolyzed for regeneration (NaNO3 electrolysis regenerates HNO3, NaOH, and H2, or CH3COONa electrolysis regenerates CH3COOH, NaOH, and H2), achieving a closed-loop cycle of reagents and hydrogen, reducing external purchase costs by 80%. Therefore, this application solves the technical problems of "high temperature, slow kinetics, and poor cycle" in magnesium-based hydrogen storage materials, realizing a green cycle throughout the entire life cycle from preparation to recovery.

[0177] Compared with traditional hydrogen storage materials, the bilayer supported solid hydrogen storage material and its preparation and recovery method provided in this application have at least the following advantages:

[0178] 1. Unique structure of continuous carbon skeleton: The double-layer loaded solid hydrogen storage material provided in this application is integrally molded without the need for external binders. It forms an interface-free continuous carbon skeleton through in-situ carbonization of lignin, eliminating the thermal resistance between particles and the binder interface. The thermal conductivity is >50W / m·K, which is 2 to 5 times that of traditional mesoporous carbon.

[0179] 2. The anti-expansion advantage of polycyclic aromatic hydrocarbon structure: Under the mild pyrolysis of supercritical CO2 at 300℃, the natural polycyclic aromatic hydrocarbon structure in coal is selectively retained in the hydrogen storage material provided in this application, forming a composite structure of graphite microcrystals (rigid framework) and amorphous carbon (flexible buffer). It combines rigidity and flexibility to resist the mechanical stress generated by the cyclic expansion and contraction of MgH2 / Mg (volume change of about 30%). After 100 cycles, the lateral pressure strength retention rate is >90%.

[0180] 3. Ideal bilayer load structure: Through a step-by-step process of "Mg hydrogenation → inert atmosphere calcination → high-pressure reduction of LaNi5 → activation before use", LaNi5 is distributed on the surface of the carbon skeleton (igniter) and MgH2 is distributed inside the pores (main hydrogen storage body), thus achieving an ideal bilayer structure distribution.

[0181] 4. Synergistic effect of hydrogen absorption and heat release: Utilizing the low-temperature hydrogen absorption and heat release of LaNi5, MgH2 is uniformly preheated through a continuous carbon skeleton to form a thermally self-sustaining cycle.

[0182] 5. Synergistic effect of hydrogen absorption and hydrogen overflow: Hydrogen atoms dissociated from the LaNi5 surface migrate to the Mg surface through the continuous carbon skeleton and directly participate in the hydrogenation reaction, reducing the activation energy of Mg hydrogen absorption and increasing the hydrogen absorption rate by 3 to 5 times.

[0183] 6. Hydrogen partial pressure control: LaNi5H6 decomposes first at 80~150℃, reducing the hydrogen partial pressure of the system, which in turn drives MgH2 to decompose at 200~250℃, which is 100~150℃ lower than that of pure MgH2.

[0184] 7. Hydrogen overflow in reverse: Hydrogen atoms produced by the decomposition of MgH2 migrate to the surface of LaNi5 through the continuous carbon skeleton and combine to form H2 for desorption, providing a "hydrogen sink" for the continuous decomposition of MgH2.

[0185] 8. Structural stability of large particle molding: It adopts 5~10mm large particle molding, which is convenient to fill, reduces bed pressure drop, and has strong anti-pulverization ability. After 100 cycles, the capacity retention rate is >90% and the bed pressure drop increase is <10%.

[0186] 9. Hydrogen storage capacity maintenance: While achieving rapid hydrogen absorption and desorption at low temperatures, it still maintains a high hydrogen storage capacity of 5~7wt%.

[0187] 10. Metal recovery and closed-loop recycling: Metals are separated through three-stage precipitation, with La recovery rate >95%, Ni recovery rate >96%, and Mg recovery rate >98%; Nitric acid or acetic acid, sodium hydroxide, and hydrogen are all recycled in a closed loop through electrolytic regeneration, consuming only water and electricity; the cost of purchased reagents is reduced by 80%, hydrogen is self-sufficient, and there is zero waste liquid discharge.

[0188] 11. Traditional mesoporous carbon cannot achieve this: Comparative experiments have shown that traditional mesoporous carbon (isolated particles with added binder) cannot achieve the synergistic hydrogen storage effect of this application due to its large interfacial thermal resistance, low hydrogen overflow efficiency, and aging and pulverization of the binder.

[0189] The technical features of the above embodiments can be combined in any way (as long as there is no contradiction in the combination of these technical features). For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; these embodiments not explicitly written should also be considered to be within the scope of this specification.

[0190] The present application has been described in a relatively specific and detailed manner above through general descriptions and specific embodiments. It should be understood that, based on the technical concept of the present application, several conventional adjustments or further innovations can be made to these specific embodiments; however, as long as they do not depart from the technical concept of the present application, the technical solutions obtained by these conventional adjustments or further innovations also fall within the protection scope of the claims of the present application.

Claims

1. A bilayer supported solid-state hydrogen storage material, characterized in that, include: A continuous carbon skeleton carrier, wherein the continuous carbon skeleton carrier is a lignin-semi-coke composite porous carbon material, having an interface-free continuous carbon skeleton network, a mesopore ratio greater than 40%, a thermal conductivity greater than 50 W / (m·K), and a lateral compressive strength greater than 80 N. The inner hydrogen storage component is loaded inside the mesopores of the continuous carbon framework support. The inner hydrogen storage component is a magnesium-based hydrogen storage material with a loading of 40 wt% to 60 wt% based on Mg. An outer catalytic component is supported on the surface of the continuous carbon framework support. The outer catalytic component is a lanthanum-nickel alloy with a loading of 10 wt% to 20 wt% based on LaNi5.

2. The bilayer supported solid hydrogen storage material according to claim 1, characterized in that, The continuous carbon framework carrier is prepared by co-pyrolysis of coal and enzymatically hydrolyzed lignin. After carbonization, the enzymatically hydrolyzed lignin is chemically bonded to semi-coke to form the interfaceless continuous carbon framework network. The continuous carbon framework carrier retains the composite structure of natural polycyclic aromatic hydrocarbons and amorphous carbon in coal.

3. The bilayer supported solid hydrogen storage material according to claim 1, characterized in that, The specific surface area of ​​the lignin-semi-coke composite porous carbon material is 200~500 m². 2 / g; The continuous carbon framework support has oxygen-containing functional groups on its surface, the total amount of which is 1 mmol / g to 3 mmol / g, and the oxygen-containing functional groups include one or more of hydroxyl, carboxyl and carbonyl groups; The mesopore size of the continuous carbon framework support is 5~50 nm; The dual-layer loaded solid hydrogen storage material is a molded particle with a particle size of 0.5~10mm.

4. The bilayer supported solid hydrogen storage material according to claim 1, characterized in that, The dual-layer loaded solid hydrogen storage material is a molded particle with a particle size of 5~10 mm. The bilayer supported solid hydrogen storage material absorbs hydrogen at temperatures of 150℃ to 200℃, with a hydrogen storage capacity of 5wt% to 7wt%; and releases hydrogen at temperatures of 200℃ to 250℃.

5. A method for preparing a bilayer supported solid hydrogen storage material according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1: Immerse the particulate continuous carbon skeleton support in magnesium nitrate solution or magnesium acetate solution, dry it, and then hydrogenate and reduce it for 1 to 2 hours at 300℃~350℃ and 5~10MPa hydrogen atmosphere to reduce magnesium ions to MgH2 and load them into the mesopores of the continuous carbon skeleton support to obtain MgH2 / carbon composite particles. S2: Immerse the MgH2 / carbon composite particles obtained in step S1 into a mixed solution of lanthanum and nickel nitrates or a mixed solution of lanthanum and nickel acetates. After drying, calcine them at 500℃~600℃ for 2~4 hours under an inert atmosphere to decompose MgH2 into metallic Mg and release the pore space. At the same time, lanthanum and nickel nitrates or lanthanum and nickel acetates decompose into La2O3 and NiO to obtain Mg / La2O3 / NiO / carbon composite particles. S3: The Mg / La2O3 / NiO / carbon composite particles obtained in step S2 are reduced at 500℃~600℃ and 5~10MPa hydrogen atmosphere for 2~4 hours to reduce and alloy La2O3 and NiO into LaNi5, and LaNi5 is distributed on the surface of the continuous carbon skeleton support to obtain Mg / LaNi5 / carbon composite particles. S4: The Mg / LaNi5 / carbon composite particles obtained in step S3 are activated at 300℃~350℃ and 5~10MPa hydrogen atmosphere for 1~2 hours, so that the metallic Mg is hydrogenated to MgH2 and LaNi5 is activated by hydrogen absorption to LaNi5H6, thus obtaining active MgH2 / LaNi5 / carbon composite particles, and the preparation of the double-layer supported solid hydrogen storage material is completed.

6. The method for preparing the bilayer supported solid hydrogen storage material according to claim 5, characterized in that, In step S1, the concentration of the magnesium nitrate solution is 0.5 mol / L to 2.0 mol / L; In step S2, the total concentration of the lanthanum and nickel nitrate mixed solution is 0.1 mol / L to 0.5 mol / L, wherein the molar ratio of La to Ni is 1:5, and the inert atmosphere is nitrogen or argon.

7. A method for preparing a continuous carbon framework support, wherein the continuous carbon framework support is used in the preparation method of the bilayer supported solid hydrogen storage material according to any one of claims 5 to 6, characterized in that, Includes the following steps: L1: Coal powder and enzymatically hydrolyzed lignin powder are mixed, wherein the amount of enzymatically hydrolyzed lignin powder added is 10% to 20% of the coal powder mass. The mixture is subjected to supercritical carbon dioxide dynamic cyclic pyrolysis at 280℃ to 320℃ and 8 to 20MPa to carbonize the lignin in situ and form a continuous carbon skeleton network without interface with the semi-coke through chemical bonding, thus obtaining lignin-semi-coke composite carbon skeleton powder. L2: Add the lignin-semi-coke composite carbon skeleton powder obtained in step L1 to the alkaline solution, heat and stir, separate by flotation using density difference, and collect the upper effective component. L3: Granulate the upper effective components collected in step L2, with a particle size of 5mm to 10mm, and calcine them in an inert atmosphere at 300℃ to 500℃ to obtain continuous carbon skeleton carrier particles.

8. The method for preparing a continuous carbon framework support according to claim 7, characterized in that, In step L1, the pulverized coal is bituminous coal powder, and a co-solvent is added during the supercritical carbon dioxide dynamic cyclic pyrolysis process. The amount of co-solvent added is 1% to 3% of the mass of the pulverized coal. In step L2, the alkaline solution is a KOH, NaOH, or Ca(OH)2 solution; In step L3, the upper effective components collected in step L2 are granulated and formed by ball rolling granulation, extrusion granulation or spray granulation.

9. The method for preparing a continuous carbon framework support according to claim 8, characterized in that, The co-solvent is n-hexane, and the amount of n-hexane added is 2% of the mass of the coal powder. In step L1, the amount of enzymatically hydrolyzed lignin powder added is 15% of the coal powder mass; In step L2, the concentration of the alkaline solution is 1.0 mol / L to 2.0 mol / L, the heating temperature is 80℃ to 100℃, and the stirring time is 30 to 60 minutes.

10. A method for recovering metals from a failed hydrogen storage material, wherein the failed hydrogen storage material is the material remaining after recycling of the bilayer supported solid hydrogen storage material as described in any one of claims 1 to 4, characterized in that... Includes the following steps: T1: Dissolution process, the failed hydrogen storage material is put into nitric acid or acetic acid solution, heated and stirred, so that all magnesium, lanthanum and nickel metal elements are dissolved into the solution, and the continuous carbon skeleton support is separated by filtration. T2: Precipitation process, the filtrate obtained in step T1 is subjected to three-stage precipitation separation: First-stage precipitation separation: Adjust the pH of the filtrate to 7.5-8.5 to precipitate La(OH)3, and recover lanthanum by filtration; Second-stage precipitation separation: Adjust the pH of the first-stage precipitation filtrate to 6.5-7.5 to precipitate Ni(OH)2, and then filter to recover nickel; Third-stage precipitation separation: Adjust the pH of the filtrate from the second-stage precipitation separation to 10.5-11.5 to precipitate Mg(OH)2, and then filter to recover magnesium; T3: Electrolysis process, electrolyzing the filtrate after three-stage precipitation separation in step T2. The anode generates HNO3 or CH3COOH, which is returned to the dissolution process in step T1. The cathode generates NaOH, which is returned to the precipitation process in step T2. The cathode generates H2, which is returned to the activation process in step S4 of claim 5, thus realizing a closed-loop cycle of reagents and hydrogen.

11. The method for recovering metals from failed hydrogen storage materials according to claim 10, characterized in that, The concentration of the nitric acid solution in step T1 is 5 mol / L to 7 mol / L, the heating temperature is 70℃ to 90℃, and the stirring time is 1.5 to 2.5 hours.

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