Mg-based hydrogen storage material containing MOF-derived medium-high entropy alloy catalyst and preparation method thereof

Abstract

The application relates to a Mg-based hydrogen storage material containing a MOF-derived medium-high-entropy alloy catalyst and a preparation method, and belongs to the technical field of solid-state hydrogen storage materials. A high-entropy metal organic framework (HE-MOF) precursor with a ZIF structure is synthesized by adopting a mechanical chemical method with multiple acetate salts as metal precursors; after high-temperature pyrolysis treatment, high-entropy alloy nanoparticles with a face-centered cubic structure composed of five transition metal elements of Fe, Co, Ni, Cu and Mn are obtained, the particle size is about 10nm-25nm, the mixing entropy is as high as 13.031 J.mol-1.K-1, the alloy particles are uniformly embedded in the in-situ generated porous carbon skeleton, the space limited distribution is realized, and the segregation and agglomeration of the metal components in the high-temperature process are effectively prevented; the medium-high-entropy metal nanocatalyst with the carbon shell coating structure and the uniform dispersion prepared by the application can effectively improve the hydrogen storage performance of the Mg-based hydrogen storage alloy. The introduction of the HEA@C catalyst improves the kinetic behavior of the MgH2 system.

Description

Technical Field

[0001] This invention relates to the field of solid-state hydrogen storage materials technology, specifically to a Mg-based hydrogen storage material containing a MOF-derived high-entropy alloy catalyst and its preparation method. Background Technology

[0002] Currently, Mg-based hydrogen storage alloys have attracted widespread attention due to their advantages such as high hydrogen storage capacity, abundant resources, and low cost. However, the strong thermodynamic stability of Mg-based materials means that the dehydrogenation process typically requires temperatures above 300°C to proceed effectively, severely limiting their practical applications. MOFs (Metal-Organic Facility Materials) are a class of three-dimensional porous crystalline materials formed by the self-assembly of metal ions or metal clusters with organic linkers through coordination. By precisely selecting metal ions and organic ligands, the pore size, surface chemical properties, and microstructure can be effectively controlled. Furthermore, post-processing can yield nanoparticles of metals or metal oxides supported on a porous carbon framework. These derivatives can not only serve as nano-confined supports for Mg-based hydrogen storage materials, effectively inhibiting active phase aggregation and promoting hydrogen diffusion, but also act as highly efficient catalysts to significantly improve the hydrogen adsorption and desorption kinetics of the Mg / MgH₂ system.

[0003] The conventional synthesis of MOF derivatives typically involves two steps: chemical liquid-phase synthesis and subsequent thermal treatment. Introducing two or more metal elements or functional components can induce synergistic catalytic effects and significantly increase the density of surface active sites. Among these, using multi-component MOFs as precursors to prepare catalysts is considered a highly efficient and structurally controllable strategy. By precisely controlling the types of ligands, the ratio of metal nodes, and the synthesis conditions, MOF structures containing bimetallic or multimetallic centers can be constructed, transforming into highly homogeneous multi-element doped carbon-based composite materials during subsequent pyrolysis. In these materials, metal species are stably anchored in the nitrogen-doped or defect-rich carbon matrix in the form of nanoparticles, single atoms, or atomic clusters. Therefore, multi-component MOF-derived catalysts exhibit significant advantages in achieving high catalytic activity and long-term stability.

[0004] Chinese patent CN115350706A discloses a method for preparing a ternary metal MOF-derived catalyst for CO2 hydrogenation thermocatalysis. This method introduces other heteroatom-containing substances into the channels of MOFs through impregnation and other methods to functionalize carbon materials, which are then used as catalysts for CO2 hydrogenation reactions to further improve CO2 conversion and C content. 2+Product selectivity. CN119121315A discloses a method for synthesizing a silver-doped MOF-derived catalyst composite material based on a copper-based organometallic framework and its application as an electrocatalytic catalyst for the reduction of carbon dioxide to acetaldehyde. CN116943673A discloses a method for preparing an iron-molybdenum bimetallic MOF-derived catalyst and its application in the treatment of recalcitrant organic wastewater by activating persulfate. This invention successfully prepared a magnetically recyclable iron-molybdenum bimetallic composite catalyst (Fe / Mo@C) through co-precipitation and calcination. However, current research on MOF-derived multi-component doped oxide catalysts for Mg-based hydrogen storage materials is still relatively limited, with few related reports, and their mechanism of action in catalytic reactions remains unclear and requires further systematic elucidation. Therefore, the synthesis process and catalytic ability of niobium-based oxide catalysts derived from multi-component MOFs need further in-depth investigation. Summary of the Invention

[0005] In view of the above problems, this invention provides a Mg-based hydrogen storage material containing a MOF-derived medium-high entropy alloy catalyst and its preparation method, as well as a Mg-based composite nanomaterial for hydrogen storage with the addition of the MOF-derived catalyst. The uniformly dispersed medium-high entropy metal nanocatalyst with a carbon shell coating structure prepared by this method can effectively improve the hydrogen storage performance of Mg-based hydrogen storage alloys.

[0006] This invention provides a method for preparing a Mg-based hydrogen storage material containing a MOF-derived high-entropy alloy catalyst, comprising: Step 1: Prepare a multi-metal organic framework (MOF) precursor using mechanical ball milling; the metal nodes of the multi-metal MOF precursor contain at least four metal elements. Optionally, the multi-metal MOF precursor is a medium-entropy MOF precursor, and the metal nodes include four or five metal elements.

[0007] Optionally, the multi-metal MOF precursor is a high-entropy MOF precursor, the metal nodes include 5 or 6 metal elements, and ammonium sulfate is added as a catalyst during the preparation process.

[0008] Optionally, the preparation of the medium-entropy MOF precursor includes: mixing hydrated ferric nitrate, hydrated cobalt nitrate, hydrated nickel nitrate, hydrated copper nitrate and 2-methylimidazole, adding a grinding aid, and performing ball milling.

[0009] Optionally, the preparation of the medium-entropy MOF precursor includes: mixing zinc oxide, copper oxide, hydrated cobalt acetate, hydrated nickel acetate and hydrated ferric nitrate with 2-methylimidazole, adding a grinding aid, and performing ball milling.

[0010] Optionally, the preparation of the high-entropy MOF precursor includes: mixing at least five metal sources selected from hydrated ferric nitrate, hydrated manganese nitrate, hydrated cobalt acetate, hydrated nickel acetate, copper oxide, and zinc oxide with 2-methylimidazole and ammonium sulfate, adding a grinding aid, and performing ball milling treatment.

[0011] Optionally, the molar ratio of each metal element in the medium-entropy MOF precursor, namely hydrated iron nitrate, hydrated cobalt nitrate, hydrated nickel nitrate, and hydrated copper nitrate, is (0.8–1.2):(0.8–1.2):(0.8–1.2):(0.8–1.2).

[0012] Optionally, the specific steps for preparing medium-entropy MOF (ME-MOF) precursors include: Hydrated ferric nitrate, hydrated cobalt nitrate, hydrated nickel nitrate, and hydrated copper nitrate were mixed with 2-methylimidazole to obtain mixture one, which was then added to a ball mill jar. The grinding aid was then added, and high-purity inert gas was introduced into the tank. After sealing, the tank was ball-milled to obtain product one. The product was washed three times alternately with methanol, and after centrifugation, the precipitate was obtained, dried, and the medium-entropy MOF precursor ME-MOF-1 was obtained.

[0013] Optionally, the specific steps for preparing medium-entropy MOF (ME-MOF) precursors include: Zinc oxide, copper oxide, hydrated cobalt acetate, hydrated nickel acetate and hydrated ferric nitrate were mixed with 2-methylimidazole to obtain mixture two, which was then added to a ball mill jar. Ammonium sulfate and grinding aid were then added, and high-purity inert gas was introduced into the tank. After sealing, the tank was ball-milled to obtain product two. The product was washed three times alternately with methanol, and after centrifugation, the precipitate was obtained, dried, and the medium-entropy MOF precursor ME-MOF-2 was obtained.

[0014] Optionally, in step 1, the method for preparing the high-entropy MOF precursor includes: mixing at least five metal elements, ammonium sulfate and 2-methylimidazole, adding a grinding aid, and mechanically ball milling under inert gas protection. The resulting product is washed and dried to obtain the high-entropy MOF precursor HE-MOF.

[0015] Optionally, the molar ratio of zinc oxide, copper oxide, cobalt acetate hydrate, nickel acetate hydrate and ferric nitrate hydrate in the high-entropy MOF precursor is (0.8-1.2):(0.8-1.2):(0.8-1.2):(0.8-1.2):(0.8-1.2).

[0016] Optionally, the specific steps for high-entropy MOF (HE-MOF) precursors include: Hydrated ferric nitrate, hydrated manganese nitrate, hydrated cobalt acetate, hydrated nickel acetate, copper oxide, and zinc oxide were mixed in a molar ratio of 1:1:1:1:1:1, and added to a ball mill jar along with ammonium sulfate and 2-methylimidazole. Then, a grinding aid was added, and the jar was filled with high-purity inert gas. After sealing, the mixture was ball milled to obtain product three. The product was washed three times with methanol in an alternating manner, and after centrifugation, the precipitate was obtained, dried, and the high-entropy MOF (HE-MOF) precursor was obtained.

[0017] Optionally, in step 1, the grinding aid is N,N-dimethylformamide or methanol; Optionally, the mechanical ball mill operates at a rotation speed of 150 rpm to 600 rpm, a ball-to-material ratio of (5 to 20):1, and a milling time of 5 h to 48 h.

[0018] Optionally, the ratio of the total amount of 2-methylimidazole to the total amount of various metal elements in the high-entropy MOF precursor or the medium-entropy MOF precursor is (0.6-1.4):1.

[0019] Optionally, the high-purity inert protective gas includes, but is not limited to, nitrogen, argon, or helium; The pressure of high-purity inert gas is 0.1 MPa to 4 MPa.

[0020] Optionally, the drying temperature is 50-90℃, and the drying time is 1 h to 18 h; Optionally, the mass ratio of the mixture to the grinding aid is 1:1.5 to 3; Optionally, the mass ratio of mixture II, ammonium sulfate and grinding aid is 1:0.01-0.02:1.5-3.

[0021] Step 2: The multi-metal MOF precursor obtained in Step 1 is calcined under a protective atmosphere to obtain carbon-coated alloy nanocatalyst. Optionally, the calcination treatment is carried out in a hydrogen-argon mixture or a hydrogen atmosphere, with a heating rate of 1-10℃ / min, a calcination temperature of 500-1000℃, a holding time of 1-10 h, and a gas flow rate of 50 mL / min-200 mL / min.

[0022] Optionally, the carbon-coated alloy nanocatalyst is a medium-entropy alloy MEA@Cx catalyst or a high-entropy alloy HEA@C catalyst, wherein x = 1, 2; Optionally, the specific preparation steps of the medium-entropy MOF-derived catalyst are as follows: the medium-entropy MOF precursor ME-MOF-1 is placed in a tube furnace, heated to 500℃ to 1000℃ at a heating rate of 1℃ / min to 10℃ / min under a hydrogen-argon mixture or hydrogen protective atmosphere, and calcined at a constant temperature for 1h to 10h under a flowing gas condition of 50 mL / min to 200 mL / min. Then, it is naturally cooled to room temperature to obtain the medium-entropy MOF-derived catalyst MEA@C-1.

[0023] Optionally, the specific preparation steps of the medium-entropy MOF-derived catalyst are as follows: the medium-entropy MOF precursor ME-MOF-2 is placed in a tube furnace, heated to 500℃ to 1000℃ at a heating rate of 1℃ / min to 10℃ / min under a hydrogen-argon mixture or hydrogen protective atmosphere, and calcined at a constant temperature for 1h to 10h under a flowing gas condition of 50 mL / min to 200 mL / min. Then, it is naturally cooled to room temperature to obtain the medium-entropy MOF-derived catalyst MEA@C-2.

[0024] Optionally, the specific preparation steps of the high-entropy MOF-derived catalyst are as follows: the high-entropy HE-MOF precursor is placed in a tube furnace, heated to 500℃ to 1000℃ at a heating rate of 1℃ / min to 10℃ / min under a hydrogen-argon mixture or hydrogen protective atmosphere, and calcined at a constant temperature for 1h to 10h under a flowing gas condition of 50 mL / min to 200 mL / min. Then, it is naturally cooled to room temperature to obtain the high-entropy MOF-derived catalyst HEA@C.

[0025] Step 3: The carbon-coated alloy nanocatalyst obtained in Step 2 is mechanically ball-milled with magnesium hydride under a hydrogen atmosphere to obtain a MgH2-alloy catalyst composite material.

[0026] Optionally, the amount of carbon-coated alloy nanocatalyst added is 5 wt.% to 10 wt.% of the total mass of the MgH2-alloy catalyst composite material; The mechanical ball milling process was carried out under hydrogen pressure of 0.1 MPa to 4 MPa, ball milling speed of 150 rpm to 600 rpm, ball-to-material ratio of (5 to 50):1, and ball milling time of 3 h to 48 h.

[0027] Optionally, the MgH2-alloy catalyst composite material can be a medium-entropy MgH2-MEA@Cx nanocomposite material or a high-entropy MgH2-HEA@C nanocomposite material.

[0028] Optionally, the specific preparation process of the medium-entropy MgH2-MEA@Cx nanocomposite is as follows: In an inert atmosphere glove box, z wt.% of the medium entropy MOF-derived catalyst MEA@C and (100-z)wt.% of MgH2 nanoparticles were weighed and transferred to a ball mill jar. After sealing, the glove box was removed and high-purity hydrogen gas of 0.1 MPa to 4 MPa was introduced into the jar. After ball milling, a medium-entropy nanocomposite material with the chemical formula MgH2-MEA@Cx, where x=1 or 2, is obtained.

[0029] Optionally, the ball milling speed is 150 rpm to 600 rpm, the ball-to-material ratio is (5 to 50):1, and the ball milling time is 3 h to 48 h.

[0030] Optionally, the specific process for preparing high-entropy MgH2-HEA@C nanocomposites is as follows: In an inert atmosphere glove box, weigh y wt.% of high-entropy alloy HEA@C catalyst and (100-y) wt.% of MgH2 nanoparticles, transfer them to a ball mill jar, seal it, remove the glove box, and fill the jar with 0.1MPa~4MPa of high-purity hydrogen. After ball milling, a high-entropy nanocomposite material with the chemical formula MgH2-HEA@C was obtained.

[0031] Optionally, the amount of high-entropy alloy HEA@C catalyst added is 5-10 wt.% of the total mass of MgH2 nanoparticles. y=5,7.5,10.

[0032] Optionally, the preparation steps of MgH2 nanoparticles include: Accurately weigh a certain mass of Mg nanoparticles and load them into the sample tube of the Sievert-type device. The Mg nanoparticles can be prepared by methods such as hydrogen plasma metal reaction. The Mg nanoparticles loaded into the sample tube are hydrogenated at a constant temperature of 400℃ and 4MPa high-purity hydrogen for 6 h to obtain MgH2 nanoparticles.

[0033] A Mg-based composite nanomaterial for hydrogen storage includes: a magnesium hydride (MgH2) matrix and a carbon-coated alloy nanocatalyst uniformly dispersed in the magnesium hydride matrix; the carbon-coated alloy nanocatalyst includes a carbon shell and alloy nanoparticles coated by the carbon shell. The alloy nanoparticles are medium-entropy or high-entropy alloys composed of at least four transition metal elements.

[0034] The carbon shell is derived from the pyrolysis of MOF precursors and serves to confine and prevent aggregation.

[0035] The high-entropy alloy nanoparticles have a particle size of 10–25 nm and a mixing entropy > 13 J·mol⁻¹. -1 ·K -1; The hydrogen storage material has a hydrogen absorption capacity of ≥4.5 wt.% at 250℃ and a hydrogen release capacity of ≥5.0 wt.% within 25 minutes at 300℃.

[0036] After 20 hydrogen adsorption / desorption cycles, the capacity retention rate is ≥90%.

[0037] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The medium-high entropy MOF-derived nanocatalyst with uniform carbon shell coating of the present invention has a uniform particle size distribution and strong dispersibility. (2) This invention uses various acetates as metal precursors and synthesizes high-entropy metal-organic framework (HE-MOF) precursors with ZIF structures using a mechanochemical method. After high-temperature pyrolysis treatment, high-entropy alloy nanoparticles with face-centered cubic structures composed of five transition metal elements, Fe, Co, Ni, Cu, and Mn, are obtained. The particle size is about 10 nm to 25 nm, and the mixing entropy is as high as 13 J·mol. -1 ·K -1 The alloy particles are uniformly embedded in the porous carbon skeleton generated in situ, achieving a spatially confined distribution and effectively preventing the segregation and agglomeration of metal components during high-temperature processes. (3) The introduction of high-entropy MOF-derived nanocatalysts in this invention significantly improves the hydrogen absorption and desorption kinetics of the material; (4) The introduction of the HEA@C catalyst in this invention improves the kinetic behavior of the MgH2 system. After 20 hydrogen absorption and desorption cycles, the hydrogen absorption and desorption capacity retention rates reach 91.3% and 92.8%, respectively, showing excellent cycle durability. Attached Figure Description

[0038] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0039] Figure 1 This is a schematic diagram of the transmission electron microscopy and energy-dispersive X-ray spectroscopy characterization results of the MgH2-7.5 wt.% HEA@C composite material in the embodiments of the present invention; Figure 2 This is a schematic diagram of a TEM image of MgH2-7.5 wt.% HEA@C nanoparticles in an embodiment of the present invention; Figure 3 This is a schematic diagram of a high-resolution TEM image of MgH2-7.5 wt.% HEA@C nanoparticles in an embodiment of the present invention; Figure 4 This is a schematic diagram of the HAADF image of MgH2-7.5 wt.% HEA@C nanoparticles in an embodiment of the present invention; Figure 5 This is a schematic diagram of the elemental mapping of MgH2-7.5 wt.% HEA@C nanoparticles in an embodiment of the present invention. Detailed Implementation

[0040] To better understand the above-described objectives, features, and advantages of the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other. Furthermore, the present invention can be implemented in other ways different from those described herein; therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0041] A specific embodiment of the present invention, such as Figure 1 This invention provides a Mg-based hydrogen storage material containing a MOF-derived high-entropy alloy catalyst and its preparation method, including: Example 1 Example 1: Preparation of the intermediate-entropy MOF precursor ME-MOF-1: Weigh out 2 mmol of hydrated ferric nitrate, hydrated cobalt nitrate, hydrated nickel nitrate, and hydrated copper nitrate, respectively, mix them with 16 mmol of 2-methylimidazole, and add them to a ball mill jar; Then, 5 mL of N,N-dimethylformamide was added as a grinding aid, and 0.2 MPa of high-purity argon gas was introduced into the container. After sealing, ball milling was performed. The ball milling process parameters were set as follows: rotation speed 400 rpm, ball-to-material ratio 5:1, and ball milling time 12 h. After ball milling, the product was washed three times alternately with methanol. After centrifugation, the precipitate was dried in a vacuum drying oven at 60℃ for 12 h to obtain the medium-entropy MOF precursor ME-MOF-1.

[0042] Example 2: Preparation of the intermediate-entropy MOF precursor ME-MOF-2: Zinc oxide, copper oxide, hydrated cobalt acetate, hydrated nickel acetate and hydrated ferric nitrate were mixed in a molar ratio of 1:1:1:1:1, with a total metal content of 10 mmol. This mixture was then added to a ball mill jar along with 16 mmol of 2-methylimidazole. Then add 0.032 g ammonium sulfate and 5 mL N,N-dimethylformamide, fill the container with 0.2 MPa high-purity argon gas, seal it, and then perform ball milling. The ball milling process parameters are the same as in Example 1; After ball milling, the product was washed three times alternately with methanol, centrifuged, and then dried under vacuum at 60°C for 12 h to obtain the medium-entropy MOF precursor ME-MOF-2.

[0043] Example 3: Preparation of high-entropy MOF precursor HE-MOF Hydrated ferric nitrate, hydrated manganese nitrate, hydrated cobalt acetate, hydrated nickel acetate, copper oxide, and zinc oxide were mixed in a molar ratio of 1:1:1:1:1:1, with a total metal content of 12 mmol. This mixture was then added to a ball mill jar along with 16 mmol of 2-methylimidazole. Then add 0.032 g ammonium sulfate and 5 mL N,N-dimethylformamide, fill the container with 0.2 MPa high-purity argon gas, seal it, and then perform ball milling. The ball milling process parameters are the same as in Example 1; After ball milling, the sample was washed three times with methanol, centrifuged, and then vacuum dried at 60°C for 12 h to obtain the high-entropy MOF precursor HE-MOF.

[0044] Example 4: Preparation of medium-entropy alloy catalysts MEA@C-1 and MEA@C-2 The medium-entropy MOF precursors ME-MOF-1 and ME-MOF-2 prepared in Examples 1 and 2 were respectively placed in tube furnaces and heated to 800°C at a heating rate of 2°C / min under a protective atmosphere of hydrogen-argon mixture with H2 volume fraction of 5%. They were then calcined at a constant temperature for 2 h under a flowing gas condition of 150 mL / min and then naturally cooled to room temperature. The collected products were named medium-entropy alloy catalyst MEA@C-1 and medium-entropy alloy catalyst MEA@C-2, respectively.

[0045] Example 5: Preparation of high-entropy alloy catalyst HEA@C The high-entropy MOF precursor HE-MOF prepared in Example 3 was placed in a tube furnace and heated to 800°C at a heating rate of 2°C / min under a protective atmosphere of hydrogen-argon mixture with H2 volume fraction of 5%. It was then calcined at a constant temperature for 2 h under a flowing gas condition with a flow rate of 150 mL / min, and then naturally cooled to room temperature. The collected product was named high-entropy alloy catalyst HEA@C.

[0046] Example 6: Preparation of MgH2 nanoparticles Mg nanoparticles were synthesized using a hydrogen plasma metal reaction method, specifically including: placing a polished Mg ingot in a reaction chamber, initiating an arc discharge in a mixed atmosphere of 0.1 bar H2 and 0.7 bar Ar, maintaining a current of 60 A after arc initiation, and starting to generate Mg nanoparticles, which were then transported by gas flow and collected in a sleeve inside a glove box to obtain Mg nanoparticles. Subsequently, a certain mass of Mg nanoparticles was accurately weighed and loaded into the sample tube of the Sievert-type device, and hydrogenated at a constant temperature of 400℃ and 4 MPa of high-purity hydrogen for 6 h to obtain MgH2 nanoparticles.

[0047] Example 7: Preparation of medium-entropy MgH2-MEA@C nanocomposite material: 10 wt% of MEA@C-1 and MEA@C-2, and 90 wt% of MgH2 nanoparticles (prepared in Example 6) were weighed in an inert atmosphere glove box, with a total mass of 0.5 g. The weighed MEA@C-1 and MEA@C-2 were transferred to a ball mill jar along with MgH2 nanoparticles. After sealing, the glove box was removed, and the jar was filled with 2 MPa of high-purity hydrogen. The ball milling process parameters were set as follows: rotation speed 400 rpm, ball-to-material ratio 20:1, and ball milling time 4 h. After ball milling, medium-entropy nanocomposites MgH2-MEA@C-1 and MgH2-MEA@C-2 were obtained.

[0048] Example 8: Preparation of high-entropy MgH2-HEA@C nanocomposite material: 5 wt.%, 7.5 wt.%, or 10 wt.% of HEA@C prepared in Example 5, and MgH2 nanoparticles (prepared in Example 6) in the corresponding proportions were weighed in an inert atmosphere glove box, with a total mass of 0.5 g. The weighed HEA@C and MgH2 nanoparticles were transferred to a ball mill jar, sealed, and then the glove box was removed. 2 MPa of high-purity hydrogen gas was then introduced into the jar. The ball milling process parameters were set as follows: rotation speed 400 rpm, ball-to-material ratio 20:1, and ball milling time 4 h. After ball milling, high-entropy nanocomposites MgH2-5 wt.% HEA@C, MgH2-7.5 wt.% HEA@C, and MgH2-10 wt.% HEA@C were obtained, respectively.

[0049] Hydrogen storage performance of medium-entropy nanocomposites MgH2-MEA@Cx (x=1,2) and high-entropy nanocomposites MgH2-x wt.%HEA@C (x=5,7.5,10) were tested. The effects of medium-entropy catalyst MEA@Cx (x=1,2) and high-entropy catalyst HEA@C on the hydrogen storage performance of MgH2 nanoparticles were determined.

[0050] Medium-entropy nanocomposite material MgH2-MEA@Cx (x=1,2) was prepared by mechanical ball milling of MgH2 with 10 wt.% MEA@Cx (x=1,2) catalyst. The catalytic performance of MEA@C nanocatalyst for MgH2 was studied. The isothermal hydrogen adsorption and desorption properties of the medium-entropy nanocomposite MgH2-MEA@Cx (x=1,2) and the MgH2-HPMR sample without catalyst were tested.

[0051] Comparison of the isothermal hydrogen absorption curves of different catalytic systems shows that the MgH2-HPMR sample, without the introduction of a catalyst, exhibits the highest hydrogen absorption capacity at 400℃, absorbing 7.38 wt.% of hydrogen within 60 min. In contrast, the Mg-based composite materials with the addition of medium-entropy catalysts MEA@C-1 and MEA@C-2 absorbed 6.79 wt.% and 6.67 wt.% of hydrogen, respectively. Although the capacity was slightly reduced, the hydrogen absorption rate was significantly improved.

[0052] Both medium-entropy nanocomposites MgH2-MEA@C-1 and MgH2-MEA@C-2 achieved near-saturation hydrogen absorption within 90 s, while MgH2-HPMR required over 200 s to reach saturation. Furthermore, both catalyst composites exhibited excellent hydrogen absorption catalytic performance under relatively mild temperature conditions (<300℃): at 300℃, MgH2-MEA@C-1 and MgH2-MEA@C-2 rapidly absorbed 5.04 wt.% and 4.96 wt.% of hydrogen, respectively, within 5 min. MgH2-MEA@C-2, in particular, showed a significantly faster hydrogen absorption rate below 250℃, and could still absorb 2.86 wt.% of hydrogen at 200℃. This indicates that MEA nanoparticle catalysts with a well-coated carbon layer have a better catalytic effect on hydrogen absorption.

[0053] Isothermal hydrogen adsorption and desorption tests of the medium-entropy nanocomposites MgH2-MEA@Cx (x=1,2) at a hydrogen desorption temperature of 400℃ revealed that while MgH2-HPMR exhibited the highest hydrogen desorption capacity (6.52 wt.%), its hydrogen desorption rate was the slowest. When the test temperature dropped to 350℃, due to the lack of a catalyst, the hydrogen desorption rate of MgH2-HPMR remained relatively slow, and its hydrogen desorption capacity was lower than that of the MgH2-MEA@C-1 nanocomposite (5.90 wt.%). In contrast, although the hydrogen desorption capacity of the MgH2-MEA@C-2 nanocomposite was slightly lower at high temperatures, it exhibited the fastest hydrogen desorption rate, indicating that MEA@C-2 showed the best kinetic catalytic effect. Further analysis showed that the MgH2-MEA@C-2 nanocomposite exhibited the best hydrogen desorption performance under relatively mild temperature conditions. At 300℃, this material can release 4.92 wt.% hydrogen within 30 min, which is higher than the hydrogen release capacity of MgH2-HPMR and MgH2-MEA@C-1 (1.11 wt.% and 2.50 wt.%). Furthermore, the hydrogen release rate of MgH2-MEA@C-2 is significantly faster than the other two materials under the same test conditions. Comprehensive kinetic test results show that the MgH2-MEA@C-2 nanocomposite material exhibits faster hydrogen absorption and desorption rates and superior overall hydrogen absorption and desorption performance at mild temperatures (<300℃): at 300℃, its maximum hydrogen absorption capacity reaches 5.32 wt.%, and its maximum hydrogen release capacity is 4.92 wt.%. These results indicate that the MEA@C-2 catalyst, derived from the ZIF-configured ME-MOF-2 precursor, exhibits stronger catalytic activity due to its better dispersibility and nanoscale MEA catalyst, effectively promoting the improvement of hydrogen absorption and desorption kinetics performance of Mg-based hydrogen storage materials.

[0054] Comparative Example 1 Nanocomposites of MgH2-5 wt% HEA@C, MgH2-7.5 wt% HEA@C, and MgH2-10 wt% HEA@C were selected. The hydrogen absorption and desorption behavior of the samples was characterized in detail under multiple temperature conditions. As can be seen from the hydrogen absorption kinetics curve, with the increase of HEA@C catalyst addition, the overall hydrogen absorption rate of the material is significantly improved, exhibiting excellent catalytic activity.

[0055] At 400℃, the maximum hydrogen storage capacities reached within 60 minutes for the MgH2-5 wt.% HEA@C, MgH2-7.5 wt.% HEA@C, and MgH2-10 wt.% HEA@C samples were 7.03 wt.%, 6.98 wt.%, and 6.71 wt.%, respectively, showing a trend of gradually decreasing with increasing catalyst content.

[0056] This phenomenon can be attributed to the fact that HEA@C itself does not participate in the hydrogen storage reaction and occupies a certain mass fraction, leading to a decrease in the relative content of the MgH2 active phase, thus slightly reducing the theoretical hydrogen storage capacity of the material. However, in terms of kinetic performance, the introduction of the catalyst plays a key role, especially in the medium and low temperature range below 300℃, where the catalytic effect is more significant.

[0057] At 250℃, samples containing 5 wt.% and 7.5 wt.% HEA@C required approximately 20 min and 15 min, respectively, to approach hydrogen absorption saturation, while the sample containing 10 wt.% HEA@C completed the hydrogen absorption process in only about 10 min, demonstrating a significant kinetic advantage.

[0058] This indicates that a higher content of HEA@C can more effectively promote the dissociation of hydrogen molecules, the surface migration and bulk diffusion of atomic hydrogen, and the hydrogenation reaction at the Mg / MgH2 interface, significantly reducing the activation energy barrier of the hydrogen absorption process and thus accelerating the reaction rate.

[0059] It is noteworthy that at a lower temperature of 200℃, the actual hydrogen absorption capacity of the material within 60 min actually increased with the increase of catalyst addition. In summary, although increasing the amount of HEA@C catalyst slightly reduces the maximum hydrogen storage capacity at high temperatures due to the dilution effect, its contribution to improving hydrogen absorption kinetics and enhancing low-temperature hydrogen absorption performance is extremely significant.

[0060] Isothermal hydrogen desorption kinetics of MgH2-x wt.% HEA@C nanocomposites were tested to investigate the effect of different HEA@C catalyst addition amounts on the hydrogen desorption behavior of MgH2.

[0061] With increasing catalyst content, the maximum hydrogen release capacity of the material under high-temperature conditions shows a certain degree of decrease. However, high catalyst content exhibits a significant advantage in improving hydrogen release kinetics.

[0062] HEA@C catalysts possess abundant multi-element active sites and excellent electronic conductivity, which can effectively reduce the reaction energy barrier during the decomposition of MgH2, promote the breaking of HH bonds and the desorption of hydrogen molecules in hydrides, and enhance atomic diffusion and phase transition kinetics at the Mg / MgH2 interface.

[0063] Therefore, with the increase of HEA@C content, the hydrogen desorption rate of the MgH2-x wt.% HEA@C nanocomposite material is significantly accelerated, exhibiting good catalytic activity. Isothermal hydrogen desorption tests conducted at 300℃ showed that the MgH2-5 wt.% HEA@C sample required approximately 50 minutes to reach near-complete hydrogen desorption, releasing 5.25 wt.% hydrogen. When the catalyst content increased to 7.5 wt.%, the hydrogen desorption time shortened to 35 minutes, and the hydrogen release reached 5.27 wt.%, with a significantly improved release rate. The sample with 10 wt.% HEA@C added completed the main hydrogen desorption process in only 25 minutes, exhibiting the best kinetic performance, but its final hydrogen release was slightly reduced to 4.97 wt.%. These results indicate that increasing the catalyst content within a certain range can significantly accelerate hydrogen desorption, but excessively high addition ratios may lead to a decrease in overall hydrogen storage efficiency. The catalytic advantage is more pronounced at lower temperatures.

[0064] For example, at 250 °C, the MgH2-7.5 wt.% HEA@C nanocomposite material can release 1.15 wt.% hydrogen gas in a relatively short time. This not only demonstrates a better hydrogen release rate than the MgH2-5 wt.% HEA@C sample, but also a higher hydrogen release capacity than the 1.10 wt.% of the MgH2-10 wt.% HEA@C sample. These results indicate that the 7.5 wt.% catalyst addition achieves an optimal balance between promoting hydrogen release kinetics and maintaining hydrogen release capacity.

[0065] In summary, although increasing the amount of HEA@C catalyst reduces the maximum high-temperature hydrogen desorption capacity of MgH2-x wt.%HEA@C nanocomposites to some extent, its significant improvement on hydrogen absorption and desorption kinetics is of great importance. Especially in the medium- and low-temperature operating range, the appropriate addition of catalyst (7.5 wt.%) not only effectively increases the hydrogen desorption rate but also better maintains the hydrogen desorption capacity, thus exhibiting superior overall hydrogen absorption and desorption performance.

[0066] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a Mg-based hydrogen storage material containing a MOF-derived high-entropy alloy catalyst, characterized in that, include: Step 1: Prepare a multi-metal-organic framework (MOF) precursor using mechanical ball milling; the metal nodes of the multi-metal MOF precursor contain at least four metal elements; the multi-metal MOF precursor is a medium-entropy MOF precursor, with metal nodes containing 4 or 5 metal elements; the multi-metal MOF precursor is a high-entropy MOF precursor, with metal nodes containing 5 or 6 metal elements, and ammonium sulfate is added as a catalyst during the preparation process; Step 2: The multi-metal MOF precursor obtained in Step 1 is calcined under a protective atmosphere to obtain carbon-coated alloy nanocatalyst. Step 3: The carbon-coated alloy nanocatalyst obtained in Step 2 is mechanically ball-milled with magnesium hydride under a hydrogen atmosphere to obtain a MgH2-alloy catalyst composite material.

2. The method for preparing Mg-based hydrogen storage material containing MOF-derived high-entropy alloy catalyst according to claim 1, characterized in that, The preparation of the intermediate-entropy MOF precursor includes: mixing hydrated ferric nitrate, hydrated cobalt nitrate, hydrated nickel nitrate, hydrated copper nitrate and 2-methylimidazole, adding a grinding aid, and performing ball milling.

3. The method for preparing Mg-based hydrogen storage material containing MOF-derived high-entropy alloy catalyst according to claim 1, characterized in that, The preparation of the intermediate-entropy MOF precursor includes: mixing zinc oxide, copper oxide, hydrated cobalt acetate, hydrated nickel acetate and hydrated ferric nitrate with 2-methylimidazole, adding a grinding aid, and performing ball milling.

4. The method for preparing Mg-based hydrogen storage material containing MOF-derived high-entropy alloy catalyst according to claim 1, characterized in that, The preparation of the high-entropy MOF precursor includes: mixing at least five metal sources selected from hydrated ferric nitrate, hydrated manganese nitrate, hydrated cobalt acetate, hydrated nickel acetate, copper oxide, and zinc oxide with 2-methylimidazole and ammonium sulfate, adding a grinding aid, and performing ball milling treatment.

5. The method for preparing Mg-based hydrogen storage material containing MOF-derived high-entropy alloy catalyst according to claim 1, characterized in that, The molar ratio of hydrated ferric nitrate, hydrated cobalt nitrate, hydrated nickel nitrate, and hydrated copper nitrate is (0.8–1.2):(0.8–1.2):(0.8–1.2):(0.8–1.2).

6. The method for preparing Mg-based hydrogen storage material containing MOF-derived high-entropy alloy catalyst according to claim 1, characterized in that, The mechanical ball mill operates at a speed of 150 rpm to 600 rpm, with a ball-to-material ratio of (5 to 20):1, and a milling time of 5 h to 48 h.

7. The method for preparing Mg-based hydrogen storage material containing MOF-derived high-entropy alloy catalyst according to claim 1, characterized in that, The ratio of the total amount of various metal elements in methylimidazole to that in high-entropy MOF precursors or medium-entropy MOF precursors is (0.6-1.4):

1.

8. The method for preparing Mg-based hydrogen storage material containing MOF-derived high-entropy alloy catalyst according to claim 1, characterized in that, The calcination process involves a heating rate of 1–10 °C / min, a calcination temperature of 500–1000 °C, and a holding time of 1–10 h.

9. The method for preparing Mg-based hydrogen storage material containing MOF-derived high-entropy alloy catalyst according to claim 1, characterized in that, The amount of carbon-coated alloy nanocatalyst added is 5 wt.% to 10 wt.% of the total mass of the MgH2-alloy catalyst composite material.

10. A Mg-based hydrogen storage material containing a MOF-derived high-entropy alloy catalyst prepared by the preparation method according to any one of claims 1-9, characterized in that, include: A magnesium hydride (MgH2) matrix and a carbon-coated alloy nanocatalyst uniformly dispersed in the magnesium hydride matrix; the carbon-coated alloy nanocatalyst comprises a carbon shell and alloy nanoparticles coated by the carbon shell. The alloy nanoparticles are medium-entropy or high-entropy alloys composed of at least four transition metal elements.

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