A method for preparing Mo-doped VO2-catalyzed magnesium hydride hydrogen storage materials and its products

Abstract

This invention discloses a method for preparing a Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material and its product. The preparation method includes: (1) mixing a vanadium source, a molybdenum source, a reducing agent, and water to obtain a raw material solution, and then preparing a Mo-doped VO2 catalyst through a hydrothermal synthesis reaction; (2) ball milling and mixing the Mo-doped VO2 catalyst prepared in step (1) with magnesium hydride to obtain the Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material. The preparation method disclosed in this invention is simple, controllable, energy-efficient, and easy to implement. The prepared composite hydrogen storage material system greatly improves the hydrogen absorption and desorption kinetics of MgH2, significantly reduces the hydrogen absorption and desorption temperature of MgH2, and improves the cycle stability of the material.

Description

Technical Field

[0001] This invention relates to the technical field of hydrogen storage materials, and in particular to a method for preparing a Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material and its product. Background Technology

[0002] Hydrogen energy boasts advantages such as extremely high energy density, cleanliness, and abundant reserves, making it one of the most promising new energy carriers of the 21st century. Developing safe, efficient, and economical hydrogen storage and transportation technologies is crucial for the widespread application of hydrogen energy. Compared to gaseous and liquid hydrogen storage methods, solid-state hydrogen storage offers higher safety and storage density, eliminates the need for high-pressure and liquefaction / compression equipment, and is cost-effective. Among these, MgH2-based hydrogen storage materials exhibit high energy density and storage capacity (up to 7.6 wt%) and 110 kg m³ / s. –3 With its high theoretical mass and volumetric hydrogen storage density, excellent reversible hydrogen absorption and desorption, and abundant resources, MgH2 has attracted much attention in the field of solid-state hydrogen storage materials. However, MgH2 itself exhibits high thermodynamic stability during hydrogen desorption (ΔH ≈ 76 kJ mol). –1 H2), kinetic energy barrier (E) a = 160 kJ mol –1 (H2), which results in a high hydrogen absorption and desorption temperature, severely hindering its practical application.

[0003] To address these issues, commonly used modification strategies include nano-sizing, alloying, composite formation, and catalyst addition. The preparation of nano-sized Mg / MgH2 systems is typically complex and suffers from particle agglomeration leading to deactivation; alloying, on the other hand, results in a loss of some of the sample's capacity. Catalytic doping, however, is a simple and efficient modification method that can effectively accelerate the hydrogen absorption and desorption kinetics of MgH2, significantly reduce the hydrogen absorption and desorption temperature of the material, and maintain a high hydrogen storage capacity.

[0004] Transition metals (such as V, Ni, and Zr) possess d or f electrons that can interact with the antibonding orbitals of H2, which is beneficial for the adsorption and dissociation of H2. Therefore, transition metals and their alloys, oxides, halides, and carbides can significantly improve the hydrogen storage performance of MgH2. Among them, vanadium has multiple valence states. Studies have shown that multivalent V species can act as electron transfer mediators in the hydrogen adsorption and desorption process, and the reversible formation of vanadium hydride acts as a "hydrogen pump," which helps to lower the hydrogen adsorption and desorption energy barrier of MgH2, thereby promoting the improvement of hydrogen storage performance.

[0005] For example, patent document CN 117401647 A discloses a method for preparing magnesium hydride-based hydrogen storage materials and its products. By adding LaVO4 catalyst, hydrogen pump and hydrogen channel catalysts are formed in situ, reducing the initial hydrogen absorption and desorption temperature of MgH2 and improving the cycle stability of the material. However, its preparation process involves further calcination, which is relatively complex and energy-intensive. Furthermore, under the condition of high catalyst doping of 15 wt%, the initial hydrogen desorption temperature of the MgH2 system drops to 185℃, and the hydrogen desorption capacity reached at 400℃ is 5.7 wt%, sacrificing some hydrogen storage capacity.

[0006] Studies (S. Milosevic; S. Kurko; L. Pasquini; L. Matovic; R. Vujasin; N. Novakovic; JG Novakovic. Fast hydrogen sorption from MgH2–VO2 (B)composite materials. J Power Sources, 2016, 307, 481–488.) have shown that B-phase VO2 with a VO6 tetrahedral structure has a certain catalytic effect on MgH2, but the initial hydrogen desorption temperature is still high, approaching 300℃, requiring further structural optimization to improve its catalytic performance. Furthermore, there are also problems such as high catalyst preparation cost and low electron transfer efficiency. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention discloses a method for preparing Mo-doped VO2-catalyzed magnesium hydride hydrogen storage materials. This method is simple, controllable, energy-efficient, and easy to implement, making it suitable for industrial production. The prepared Mo-doped VO2-catalyzed composite MgH2 hydrogen storage material system exhibits high hydrogen absorption and desorption kinetics, low absorption and desorption temperatures, and good cycle stability.

[0008] The specific technical solution is as follows:

[0009] A method for preparing a Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material includes:

[0010] (1) A raw material solution was obtained by mixing vanadium source, molybdenum source, reducing agent and water, and then prepared by hydrothermal synthesis reaction to obtain Mo-doped VO2 catalyst;

[0011] (2) The Mo-doped VO2 catalyst prepared in step (1) is ball-milled and mixed with magnesium hydride to obtain the Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material.

[0012] This invention prepares a Mo-doped VO2 catalyst via a simple one-step hydrothermal reaction, eliminating the need for high-temperature calcination in conventional methods. The process is simple and energy-efficient. By controlling the molar ratio of vanadium and molybdenum sources in the feed solution (and further, the molar ratio of V and Mo), the Mo doping level can be precisely controlled, with the doped Mo partially replacing V sites. Experiments have shown that by adjusting the molar ratio, Mo-doped VO2 catalysts with different morphologies, specific surface areas, and pore sizes can be obtained. After ball milling and mixing this catalyst with magnesium hydride, it can be converted in situ into vanadium hydride and multivalent Mo species. In the subsequent hydrogen adsorption and desorption process, V and VH... x A reversible phase transition occurs between the two phases, exerting a "hydrogen pump" effect, while VH x The hydrogen desorption temperature of Mo is lower than that of MgH2, thus reducing the hydrogen absorption and desorption energy barrier of MgH2 and promoting hydrogen diffusion; while multivalent Mo species (Mo 0 Mo 2+ Mo 4 + H can be used in the process of hydrogen absorption and desorption. – and Mg 2+ The intermediate acts as a stabilizing agent, accelerates the electron transfer process, enhances the hydrogen pumping effect of vanadium hydride, and improves the hydrogen storage performance of MgH2. Therefore, under the synergistic effect of multiple active catalysts, the composite hydrogen storage material prepared by this invention has a low hydrogen absorption / desorption temperature, fast hydrogen absorption / desorption kinetics, and high cycle stability.

[0013] In step (1):

[0014] Preferably, the vanadium source is selected from one or more of vanadium pentoxide, ammonium metavanadate, and ammonium polyvanadate; more preferably, it is vanadium pentoxide.

[0015] Preferably, the molybdenum source is selected from ammonium molybdate and / or sodium molybdate.

[0016] Preferably, the reducing agent is selected from one or more of oxalic acid, citric acid, tartaric acid, and glucose; more preferably, it is oxalic acid.

[0017] Preferably, the concentration of the vanadium source in the raw material solution is 0.05~0.1 mol / L; more preferably, it is 0.06~0.08 mol / L.

[0018] Preferably, the mass ratio of vanadium source to reducing agent in the raw material liquid is 1:(0.5~2.0); more preferably 1:(1.0~1.5).

[0019] Preferably, the molar ratio of V to Mo in the raw material liquid is 1:(0.03~0.07); more preferably 1:(0.05~0.07); and even more preferably 1:0.05.

[0020] Experiments revealed that the molar ratio of V to Mo is a key parameter in this preparation method. Adjusting this ratio allows for the acquisition of Mo-doped VO2 catalysts with different morphologies. When the Mo doping concentration is low (e.g., 1:0.03), the resulting product exhibits a mixture of nanorod-like and partially flower-like morphologies. As the Mo doping concentration increases (e.g., reaching 1:(0.05~0.07)), the product displays a nanoflower-like structure. However, if the Mo doping concentration is too high (e.g., 1:0.07), wrinkles appear at the flower-like edges, leading to a decrease in the specific surface area of ​​the product. These changes in morphology and specific surface area further affect the catalytic effect of the Mo-doped VO2 catalyst on MgH2 hydrogen storage materials.

[0021] More preferably, the molar ratio of V to Mo in the feed solution is 1:0.05. The Mo-doped VO₂ catalyst prepared under these conditions has the highest specific surface area (35.1 m²). 2 g –1 ), compared to the synthesized undoped Mo single VO2 (9.9 m) 2 g –1 The efficiency was increased by three times. This self-assembled flower-like morphology provides more catalytic active sites and shortens the transport path of substances, thus promoting electron transfer and hydrogen diffusion during the hydrogen absorption and desorption process of MgH2 and increasing the catalytic efficiency of the catalyst.

[0022] Preferably, the hydrothermal synthesis reaction is carried out at a temperature of 180~200℃ and a holding time of 18~24 h.

[0023] After the hydrothermal reaction is completed, the mixture is washed three times each with deionized water and anhydrous ethanol by centrifugation at a speed of 4000~10000 r / min for 5~15 min, until the mixture is neutral.

[0024] In step (2):

[0025] Preferably, the ball mill:

[0026] The rotation speed is 300~500 rpm, the ball-to-material ratio is (100~200):1, the time is 6~48 h, the atmosphere is selected from hydrogen, and the pressure is 1~5 MPa.

[0027] To avoid excessively high temperatures inside the tank, a bidirectional intermittent operation mode was further optimized.

[0028] Specifically, the ball milling process involves running the ball mill in the forward direction for 12 minutes, then pausing for 6 minutes, followed by running it in the reverse direction for 12 minutes, then pausing for 6 minutes, for a total milling time of 12 hours.

[0029] Preferably, the mass ratio of Mo-doped VO2 catalyst to magnesium hydride is (1~12):(88~99);

[0030] Further preferred, the mass ratio of Mo-doped VO2 catalyst to magnesium hydride is (7~12):(88~93);

[0031] More preferably, the mass ratio of Mo-doped VO2 catalyst to magnesium hydride is 10:90.

[0032] With continuous optimization of the above mass ratio, the final prepared composite hydrogen storage material has a lower hydrogen absorption / desorption temperature and a relatively higher hydrogen storage capacity.

[0033] The present invention also discloses a Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material prepared according to the above method.

[0034] With the preferred amount of Mo-doped VO2 catalyst, the initial hydrogen release temperature of this hydrogen storage material is 184~197℃, and the initial hydrogen absorption temperature is room temperature.

[0035] When heated to 300°C at room temperature, the hydrogen release is not less than 5.8 wt%, and the peak hydrogen release temperature is 224~230°C.

[0036] Under optimal conditions, the prepared magnesium hydride composite hydrogen storage material exhibits an initial hydrogen release temperature of 184℃ and an initial hydrogen absorption temperature of room temperature. At room temperature, it can absorb 2.5 wt% H2 within 1 h and 4.5 wt% H2 within 12 h. When heated from room temperature to 300℃, the hydrogen release is 6.4 wt%. Under isothermal conditions of 250℃, it can release 5.9 wt% H2 within 15 min, and under 150℃ / 5MPa H2 conditions, it can absorb 5.6 wt% H2 within 60 min. After 30 cycles, the hydrogen release is 5.8 wt%, with a capacity retention rate of 96.6%, demonstrating good cycle stability.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The catalyst preparation process in this invention is simple and easy to control, with low raw material cost, low pollution, low energy consumption and simple process; the obtained Mo-doped VO2 catalyst has a large specific surface area, which can provide more catalytic active sites, promote electron transfer and hydrogen diffusion in the hydrogen absorption and desorption process of MgH2, and increase the catalytic efficiency of the catalyst.

[0039] (2) In this invention, during the ball milling and hydrogen absorption / desorption processes of the Mo-doped VO2 catalyst with MgH2, V and Mo species undergo a reduction reaction. During hydrogen release, elemental V is the main component, while during hydrogen absorption, vanadium hydride VH is the main component. x Mainly, elemental V and VH xThe reversibility of the cycle introduces a "hydrogen pump" effect in situ, which helps to lower the hydrogen adsorption and desorption energy barrier of MgH2 and promote hydrogen transport. Secondly, the generated multivalent Mo species (including Mo...) 0 Mo 2+ and Mo 4+ This provides more catalytic active sites, promoting H – and Mg 2+ Electron transfer between them. The synergistic effect of the above factors greatly improves the hydrogen absorption and desorption reaction kinetics of MgH2, resulting in a magnesium hydride composite hydrogen storage material with low hydrogen absorption and desorption temperature, fast hydrogen absorption and desorption kinetics, high cycle stability, and excellent overall performance. Attached Figure Description

[0040] Figure 1 The XRD patterns of Mo-doped VO2 catalysts prepared in step (1) of Examples 1-3 are shown, and the XRD patterns of undoped pure VO2 catalysts prepared in Comparative Examples 2 and 3 are given for comparison.

[0041] Figure 2 SEM images of Mo-doped VO2 catalysts prepared in different proportions in Examples 1-3 are shown, and SEM images of undoped VO2 catalysts prepared in Comparative Examples 2 and 3 are given for comparison.

[0042] Figure 3 N2 adsorption-desorption curves and pore size distribution diagrams of Mo-doped VO2 catalysts prepared in different proportions in Examples 1-3 and undoped VO2 catalysts prepared in Comparative Examples 2 and 3, respectively.

[0043] Figure 4 XPS spectra of the Mo2–VO2 catalyst prepared in Example 2 and the undoped VO2 catalyst prepared in Comparative Example 2 (a), V 2p (b), O 1s (c) and Mo 3d (d).

[0044] Figure 5 The image shows a high-angle annular dark-field image-scanning transmission electron microscope (HAADF-STEM) image (Figure a) of the Mo2–VO2 catalyst prepared in Example 2 and its corresponding EDS distribution diagrams of V, O, and Mo elements (Figures b-d).

[0045] Figure 6 The image shows a scanning electron microscope (SEM) image (a) of the ball-milled MgH2+10 wt% Mo2–VO2 composite hydrogen storage material prepared in Example 2, along with corresponding EDS distribution maps (c-f) and elemental distribution overlay map (b).

[0046] Figure 7The hydrogen desorption curves of the MgH2 composite hydrogen storage material products prepared in Examples 1-3 and Comparative Examples 1-3 are shown in the temperature-dependent hydrogen desorption curves.

[0047] Figure 8 The hydrogen absorption curves of the products prepared in Examples 1-3 and Comparative Examples 1-3 are shown as a function of temperature.

[0048] Figure 9 The hydrogen desorption curves of the products prepared in Examples 2, 4-8 and Comparative Example 1 are shown as a function of temperature.

[0049] Figure 10 The hydrogen absorption curves of the products prepared in Examples 2, 4-8 and Comparative Example 1 are shown as a function of temperature.

[0050] Figure 11 Isothermal hydrogen desorption curves of the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material prepared in Example 2 at 210℃, 230℃ and 250℃ are given for comparison with the isothermal hydrogen desorption curves of the products prepared in Comparative Example 1 and Comparative Example 3 at 250℃.

[0051] Figure 12 Isothermal hydrogen absorption curves of the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material prepared in Example 2 at 50℃, 100℃ and 150℃ are given for comparison with the isothermal hydrogen absorption curve of the product prepared in Comparative Example 1 at 150℃ (a) and the room temperature hydrogen absorption curve of the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material (b).

[0052] Figure 13 The hydrogen storage material system of MgH2+10 wt% Mo2–VO2 prepared in Example 2 is shown in (a) the hydrogen desorption curve and (b) the hydrogen absorption curve (at a specific number of cycles) at 280°C.

[0053] Figure 14 The XRD patterns of the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material prepared in Example 2 after ball milling, after one hydrogen release, after one hydrogen absorption, and after 30 hydrogen absorptions.

[0054] Figure 15 XPS spectra of elemental V in the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material prepared in Example 2 after ball milling, after one hydrogen release, after one hydrogen absorption, and after 30 hydrogen absorptions.

[0055] Figure 16 XPS spectra of elemental Mo in the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material prepared in Example 2 after ball milling, after one hydrogen release, after one hydrogen absorption, and after 30 hydrogen absorption cycles. Detailed Implementation

[0056] To make the technical problems, solutions, and advantages of this invention easier to understand, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. However, it should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Unless otherwise specified, the raw materials, reagents, and equipment involved in this invention can be purchased or obtained by known methods.

[0057] Example 1

[0058] (1) 0.504 g of oxalic acid and 0.364 g of vanadium pentoxide were added to 30 mL of deionized water and mechanically stirred at room temperature for 1 h to ensure thorough homogenization. Then, 20 mg of ammonium molybdate was added (in the raw material solution, the molar ratio of V to Mo was 1:0.03) and stirring was continued. The mixed solution was then transferred to a 50 mL stainless steel reactor lined with polytetrafluoroethylene and heated to 180 °C for 24 h for hydrothermal reaction. After naturally cooling to room temperature, the catalyst was washed several times by centrifugation with deionized water and anhydrous ethanol, and finally dried under vacuum at 70 °C for 12 h to obtain the Mo-doped VO2 catalyst, denoted as Mo1–VO2.

[0059] (2) In an argon atmosphere glove box, 90 wt% MgH2 and 10 wt% Mo1–VO2 were added to the ball mill jar at a ball-to-material ratio of 120:1. The ball milling atmosphere was 5 MPa H2, and the ball milling speed was 500 rpm. To avoid excessive temperature inside the jar, a bidirectional intermittent operation mode was adopted, first running forward for 12 min with a 6 min interval, then running in reverse for 12 min with a 6 min interval, for a total ball milling time of 12 h. The final product was denoted as MgH2 + 10 wt% Mo1–VO2.

[0060] Example 2

[0061] The preparation process is basically the same as in Example 1, except that in step (1):

[0062] The ammonium molybdate was replaced with 35 mg, and the molar ratio of V to Mo in the feed solution was 1:0.05. The resulting Mo-doped VO2 catalyst was denoted as Mo2–VO2; the final product was denoted as MgH2+10 wt% Mo2–VO2.

[0063] Example 3

[0064] The preparation process is basically the same as in Example 1, except that in step (1):

[0065] The ammonium molybdate was replaced with 50 mg, and the molar ratio of V to Mo in the feed solution was 1:0.07. The resulting Mo-doped VO2 catalyst was denoted as Mo3–VO2; the final product was denoted as MgH2+10 wt% Mo3–VO2.

[0066] Comparative Example 1

[0067] MgH2 was added to a ball mill jar in an argon-atmosphere glove box at a ball-to-material ratio of 120:1. The milling atmosphere was 5 MPa H2, and the milling speed was 500 rpm. To avoid excessive temperature inside the jar, a bidirectional intermittent operation mode was adopted: first, the jar was run in the forward direction for 12 minutes with a 6-minute interval, then in the reverse direction for 12 minutes with a 6-minute interval. The milling time was 12 hours. The final product was denoted as BM MgH2.

[0068] Comparative Example 2

[0069] (1) 0.504 g of oxalic acid and 0.364 g of vanadium pentoxide were added to 30 mL of deionized water and mechanically stirred at room temperature for 1 h to ensure complete homogenization. The mixture was then transferred to a 50 mL stainless steel reactor lined with polytetrafluoroethylene and heated to 180 °C for 24 h for hydrothermal reaction. After naturally cooling to room temperature, the mixture was washed several times with deionized water and anhydrous ethanol by centrifugation, and finally vacuum dried at 70 °C for 12 h to obtain a nanorod-shaped VO2 catalyst.

[0070] (2) In an argon atmosphere glove box, 90 wt% MgH2 and 10 wt% VO2 catalyst were added to the ball mill jar at a ball-to-material ratio of 120:1. The ball milling atmosphere was 5 MPa H2, and the ball milling speed was 500 rpm. To avoid excessive temperature inside the jar, a bidirectional intermittent operation mode was adopted, first running forward for 12 min with a 6 min interval, then running in reverse for 12 min with a 6 min interval, for a total ball milling time of 12 h. The final product was denoted as MgH2 + 10 wt% VO2.

[0071] Comparative Example 3

[0072] (1) 0.504 g of oxalic acid, 0.364 g of vanadium pentoxide and 0.5 g of sodium dodecyl sulfate were added to 30 mL of deionized water and mechanically stirred at room temperature for 1 h to ensure complete homogenization. The mixture was then transferred to a 50 mL stainless steel reactor lined with polytetrafluoroethylene and heated to 180 °C for 24 h for hydrothermal reaction. After naturally cooling to room temperature, the mixture was washed several times with deionized water and anhydrous ethanol by centrifugation, and finally dried under vacuum at 70 °C for 12 h to obtain the flower-like VO2 catalyst.

[0073] (2) In an argon atmosphere glove box, 90 wt% MgH2 and 10 wt% flower-shaped VO2 catalyst were added to a ball mill jar with a ball-to-material ratio of 120:1. The ball milling atmosphere was 5 MPa H2, and the ball milling speed was 500 rpm. To avoid excessive temperature inside the jar, a bidirectional intermittent operation mode was adopted, first running forward for 12 min and then intermittently for 6 min, then running in reverse for 12 min and then intermittently for 6 min, for a total ball milling time of 12 h. The final product was denoted as MgH2 + 10 wt% VO2 (flower-shaped).

[0074] Example 4

[0075] The preparation process is basically the same as in Example 2, except that in step (2):

[0076] Replace the ratio of MgH2 to Mo2–VO2 added with 99:1. The final product is denoted as MgH2 + 1 wt% Mo2–VO2.

[0077] Example 5

[0078] The preparation process is basically the same as in Example 2, except that in step (2):

[0079] Replace the ratio of MgH2 to Mo2–VO2 with 97:3. The final product is denoted as MgH2 + 3 wt% Mo2–VO2.

[0080] Example 6

[0081] The preparation process is basically the same as in Example 2, except that in step (2):

[0082] Replace the ratio of MgH2 to Mo2–VO2 with 95:5. The final product is denoted as MgH2 + 5 wt% Mo2–VO2.

[0083] Example 7

[0084] The preparation process is basically the same as in Example 2, except that in step (2):

[0085] Replace the ratio of MgH2 to Mo2–VO2 with 93:7. The final product is denoted as MgH2 + 7 wt% Mo2–VO2.

[0086] Example 8

[0087] The preparation process is basically the same as in Example 2, except that in step (2):

[0088] Replace the ratio of MgH2 to Mo2–VO2 with 88:12. The final product is denoted as MgH2 + 12 wt% Mo2–VO2.

[0089] Product characterization

[0090] Figure 1 The XRD patterns of Mo-doped VO2 catalysts with different proportions prepared in the first major step of Examples 1-3 are shown. The XRD patterns of undoped pure VO2 catalysts in Comparative Examples 2 and 3 are also provided for comparison. It was observed that the diffraction peaks of all samples were consistent with the standard peaks of VO2 (PDF#81–2392), indicating that VO2 was successfully prepared by the hydrothermal method. Furthermore, the phase structure of VO2 was not changed after doping with Mo. The intensity of the diffraction peaks of VO2 gradually decreased with the increase of Mo doping amount, indicating that defects were generated.

[0091] Figure 2 SEM images of the Mo-doped VO2 catalysts prepared in Examples 1-3 with different proportions are shown. SEM images of the undoped VO2 catalysts prepared in Comparative Examples 2 and 3 are also provided for comparison. It was observed that the undoped VO2 sample prepared in Comparative Example 2 has a nanorod-like structure. As the Mo doping amount increases, the morphology of the sample changes to a flower-like structure. This is because the Mo with a higher charge density causes the self-assembly of VO2 nanosheets. Specifically, Mo1–VO2 has a mixed morphology of nanorods and some flowers, Mo2–VO2 has thin nanosheets forming a relatively complete nanoflower-like structure, and the flower size of Mo3–VO2 decreases, but the flower edges show a wrinkled morphology. The undoped VO2 sample prepared in Comparative Example 3 has a flower-like structure formed by the superposition of mixed VO2 nanorods.

[0092] Figure 3 The adsorption-desorption curves and pore size distribution diagrams of Mo-doped VO2 catalyst materials prepared in different proportions in Examples 1-3 and undoped N2 catalysts prepared in Comparative Examples 2 and 3 are shown. A comparison reveals that, compared to the original VO2 material prepared in Comparative Example 2, the specific surface area of ​​the Mo-doped material is significantly increased, with Mo2–VO2 exhibiting the highest specific surface area value of 35.1 m². 2 g –1 The pore volume is 0.113 cm. –3 g –1 The specific surface area of ​​the flower-shaped VO2 material prepared after adding surfactants increased significantly. The specific surface area, pore volume, and pore size values ​​of various catalyst materials are shown in Table 1 below.

[0093] Table 1

[0094]

[0095] Figure 4XPS spectra of the Mo2–VO2 prepared in Example 2 and the undoped VO2 catalyst prepared in Comparative Example 2 are shown. The results indicate that (a) the full spectrum shows that, compared with the pure VO2 material, Mo2–VO2 exhibits a new characteristic peak at approximately 233 eV, corresponding to the peak position of Mo 3d, proving the successful doping of Mo. (b) In the figure, binding energy peaks of 524.2 eV and 516.7 eV appear in the pure VO2 material, which are attributed to V2 and V3 respectively. 4+ 2p 1 / 2 and V 4+ 2p 3 / 2 The value corresponds to the tetravalent state V; while for Mo2–VO2 catalyst materials, the binding energy peaks at 523.8 / 516.3 eV correspond to V. 4+ Furthermore, the binding energy peak located at 525.1 / 517.5 eV was observed to correspond to V. 5+ This indicates that after Mo doping, V undergoes partial oxidation, presumably because the electronegativity of Mo is stronger than that of V, resulting in a decrease in the electron density of V and causing V oxidation. In figure (c), the binding energy peaks at approximately 530.2 eV and 531.2 eV correspond to the lattice oxygen (O2) of the VO2 catalyst material, respectively. L ) and oxygen vacancies (O V Both oxygen types exist in Mo2–VO2 materials. Oxygen vacancies provide more catalytic active sites, facilitating hydrogen dissociation and diffusion, and thus can serve as active species to enhance the hydrogen absorption and desorption performance of MgH2. In figure (d), for the Mo2–VO2 catalyst material, binding energy peaks at 235.9 eV and 232.7 eV are observed in the Mo 3d peak profile, reflecting that the doped Mo is in the hexavalent state (Mo2+). 6+ ).

[0096] Figure 5 The image shows a high-angle annular dark-field image-scanning transmission electron microscope (HAADF-STEM) image of the Mo2–VO2 catalyst material prepared in Example 2, along with the corresponding EDS distribution diagrams of V, O, and Mo elements. Observation shows that V, O, and Mo elements are uniformly distributed in the material, which also proves the successful doping of Mo.

[0097] Figure 6 The image shows a scanning electron microscope (SEM) image (a) of the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material prepared in Example 2 under ball milling conditions, along with corresponding EDS distribution maps (c-f) and elemental distribution overlay map (b). The results indicate that Mg, V, O, and Mo elements are uniformly distributed in the composite hydrogen storage material, suggesting that the ball milling is uniform.

[0098] Performance testing

[0099] 1. Temperature-dependent hydrogen absorption and desorption performance test:

[0100] The reaction was performed using a Sieverts-type gas-solid reactor. The hydrogen absorption and desorption of the above system were tested using a volumetric method. First, the system was heated from room temperature to 400°C at a heating rate of 2°C / min to test the hydrogen desorption curve with temperature. Then, under a hydrogen pressure of 5 MPa, the system was heated from room temperature to 250°C at a heating rate of 1°C / min and held at that temperature for 1 h to test the hydrogen absorption.

[0101] Figure 7 The hydrogen desorption curves of the products prepared in Examples 1-3 and Comparative Examples 1-3 are shown in the figure. Figure 7 It is evident that the addition of 10 wt% (Mo)–VO2 catalyst significantly reduced the initial and peak hydrogen release temperatures of the MgH2 system. The initial hydrogen release temperature of the MgH2+10 wt%VO2 (flower-like) composite hydrogen storage material was 209℃, indicating that a larger specific surface area provides more catalytic active sites, reduces the distance for electron and hydrogen transport, and facilitates electron transfer and hydrogen diffusion, thus exhibiting a lower hydrogen release temperature. Mo-doped VO2 catalysts showed a more significant improvement in the hydrogen release performance of magnesium hydride. Their catalytic effects on the hydrogen release performance of MgH2, ranked from highest to lowest, were: Mo2–VO2 > Mo3–VO2 > Mo1–VO2. Among them, the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material system had the lowest initial hydrogen release temperature of 184℃ and a peak hydrogen release temperature of 224℃, which was 110℃ lower than the original MgH2, with a final hydrogen release of 6.6 wt%. The initial hydrogen release temperature of the MgH2+10 wt% VO2 composite hydrogen storage material was 215℃, which was 67℃ lower than that of the original MgH2. However, the hydrogen storage performance of the pure VO2-catalyzed MgH2 system was still inferior to that of the VO2-catalyzed MgH2 system with different amounts of Mo added. The hydrogen release performance data of each product with temperature are listed in Table 2 below.

[0102] Table 2

[0103]

[0104] Figure 8 To obtain the hydrogen absorption curves of the products prepared in Comparative Examples 1-3 and Examples 1-3 respectively, by... Figure 8It is evident that the addition of 10 wt% (Mo)–VO2 catalyst significantly reduced the initial hydrogen absorption temperature and accelerated the hydrogen absorption rate of the MgH2 system. Specifically, the MgH2+10 wt% (Mo)–VO2 composite hydrogen storage materials all began to absorb hydrogen from room temperature (~25℃), a reduction of approximately 90℃ compared to the original MgH2 system. Although the flower-shaped VO2 catalyst with increased specific surface area exhibited better catalytic activity for MgH2 than the nanorod-shaped VO2 catalyst, it was still inferior to the Mo-doped VO2-catalyzed MgH2 composite system. For Mo-doped VO2 catalysts, their catalytic efficacy for MgH2 hydrogen absorption was ranked as follows: Mo2–VO2 > Mo3–VO2 > Mo1–VO2. Among them, the hydrogen absorption capacity of the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material at 140℃ is 5.9 wt%, while the original MgH2 can only absorb 0.7 wt% H2 under the same conditions. Moreover, this composite system exhibits the highest hydrogen absorption capacity of 6.3 wt% after holding at 250℃ for 1 h. The hydrogen absorption capacities of the MgH2+10 wt% Mo1–VO2 and MgH2+10 wt% Mo3–VO2 composite hydrogen storage materials are 5.9 and 6.2 wt%, respectively. The hydrogen absorption performance data of each product with temperature are listed in Table 3 below.

[0105] Table 3

[0106]

[0107] Therefore, Mo2–VO2 exhibits the best catalytic effect on hydrogen absorption and desorption in the MgH2 system, indicating that Mo doping enhances the catalytic effect of VO2. This may be related to its large specific surface area and mesoporous characteristics, which promote electron transfer and hydrogen diffusion during the hydrogen absorption and desorption processes. Subsequent studies have shown that Mo can act as an intermediate between Mg and H ions, facilitating electron transfer and further promoting hydrogen diffusion. Therefore, subsequent tests adjusting the catalyst content all used the Mo2–VO2 catalyst.

[0108] Figure 9 The hydrogen desorption curves of the products prepared in Examples 2, 4-8 and Comparative Example 1 are shown as a function of temperature. Figure 9It can be seen that the initial hydrogen release temperature of the MgH2 system gradually decreases with the increase of Mo2–VO2 addition. The initial hydrogen release temperature of the MgH2 composite hydrogen storage material system with 1 wt% Mo2–VO2 is 228℃; the initial hydrogen release temperatures of the MgH2 systems with 3 wt% and 5 wt% catalyst addition are similar, around 205℃; the initial hydrogen release temperatures of the MgH2 systems with 7 wt%, 10 wt%, and 12 wt% catalyst addition are similar, around 185℃. However, with the increase of catalyst addition, the theoretical hydrogen release capacity also decreases. For example, the hydrogen release capacity of the MgH2+12 wt% Mo2–VO2 composite hydrogen storage material at 350℃ is only 6.3 wt%. The composite hydrogen storage material system with 10 wt% catalyst addition has both a lower initial hydrogen release temperature and a higher hydrogen release capacity.

[0109] Figure 10 The hydrogen absorption curves of the products prepared in Examples 2, 4-8 and Comparative Example 1 are shown as a function of temperature. Figure 10 It can be seen that with the increase of Mo2–VO2 addition, the hydrogen absorption temperature of the MgH2 composite system gradually decreases and the hydrogen absorption rate increases. Among them, when the hydrogen absorption heating temperature reaches 140℃, the hydrogen absorption capacity of the MgH2 system doped with different proportions of Mo2–VO2 is in the range of 4.6~5.9 wt%. The MgH2+10 wt% Mo2–VO2 composite hydrogen storage material system exhibits the largest hydrogen absorption capacity at 140℃, which is 5.9 wt%, and the hydrogen absorption capacity after holding at 250℃ for 1 h is 6.3 wt%.

[0110] Therefore, taking into account the initial hydrogen absorption and desorption temperature and the amount of hydrogen in the system, 10 wt% is the optimal doping ratio of Mo2–VO2 in the MgH2 system.

[0111] 2. Isothermal hydrogen absorption and desorption performance test:

[0112] The hydrogen absorption and desorption performance of the composite hydrogen storage material system at different temperatures was tested using a volumetric method. Hydrogen desorption curves were recorded when the material was heated to the target temperatures (210℃, 230℃, 250℃, and 280℃) at a heating rate of 10℃ / min. Hydrogen absorption curves were recorded when the material was heated from room temperature to the target temperatures (50℃, 100℃, 150℃, and 280℃) at an initial hydrogen pressure of 5 MPa at a heating rate of 10℃ / min.

[0113] Figure 11 Isothermal hydrogen desorption curves of the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material prepared in Example 2 at 210℃, 230℃, and 250℃ are shown, and the isothermal hydrogen desorption curves of the products prepared in Comparative Examples 1 and 3 at 250℃ are presented for comparison. Figure 11It can be seen that at 250℃, the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material system rapidly releases 5.6 wt% H2 within 5 min, and the hydrogen release amount reaches as high as 5.9 wt% H2 after 15 min, while the original MgH2 releases almost no hydrogen (0.2 wt%) under the same conditions. The MgH2+10 wt% VO2 (flower-like) composite hydrogen storage material system releases 3.3 wt% H2 within 5 min, and the hydrogen release amount after 15 min is 5.2 wt% H2. Even at low temperatures of 230℃ and 210℃, the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material can release 5.5 wt% and 2.8 wt% hydrogen respectively within 30 min.

[0114] Figure 12 Figure a shows the isothermal hydrogen absorption curves of the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material prepared in Example 2 at 50℃, 100℃, and 150℃, and compares them with the isothermal hydrogen absorption curve of the product prepared in Comparative Example 1 at 150℃. As shown in the figure, at 150℃, the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material system can absorb 5.6 wt% H2 within 60 min (including heating time), and at 100℃ and 50℃, it can absorb 5.3 wt% H2 and 4.0 wt% H2 within 60 min, respectively. In contrast, the original MgH2 only absorbs 3.0 wt% H2 within 60 min (including heating time) at 150℃. These data demonstrate that Mo2–VO2 has excellent catalytic activity and can significantly improve the hydrogen desorption and absorption kinetics of MgH2. Further testing was conducted on the room temperature hydrogen absorption performance of the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material prepared in Example 2. As shown in Figure b, the hydrogen absorption capacity can reach 2.5 wt% H2 within 1 h and 4.5 wt% H2 within 12 h.

[0115] Figure 13 The figures (a) show the hydrogen desorption / absorption curves (b) of the MgH₂ + 10 wt% Mo₂–VO₂ composite hydrogen storage material system prepared in Example 2 at 280 °C. The results show that the hydrogen absorption / absorption performance of the system remains good and shows no decline during the first 10 cycles. After 30 cycles, the reversible hydrogen storage capacity of the system changes from the initial 6.0 wt% H₂ to 5.8 wt% H₂, with a capacity retention rate of 96.6%, indicating good cycling stability.

[0116] Figure 14 The XRD patterns of the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material prepared in Example 2 after ball milling, one hydrogen release, one hydrogen absorption, and 30 hydrogen absorption cycles are shown. Figure 14It can be seen that the main peak of the ball-milled sample is MgH2, accompanied by a small amount of MgO diffraction peaks, which may originate from the chemical reaction between MgH2 and the oxide-based catalyst or oxidation during the testing process. In addition, VH was also observed at 36.5° and 42.4°. x The diffraction peaks indicate that V-related substances underwent reduction and hydrogenation during ball milling. After one hydrogen release, the main peak of the sample was Mg, indicating relatively complete dehydrogenation of MgH2. A weak V phase was also observed, indicating that VH was generated during the ball milling process. x It transforms into elemental vanadium after hydrogen release; the spectrum after a single hydrogen absorption shows a large amount of MgH2 and a small amount of VH. x The presence of [something] indicates that Mg almost completely absorbs hydrogen, and the V generated during the hydrogen release process can also be converted into VH under the hydrogen absorption conditions applied in this invention. x Furthermore, VH could still be observed in the products after 30 hydrogen absorption cycles. x The stable existence of the phase. It has been reported that the 3d electrons of metallic vanadium interact with H atoms, serving as active sites for H2 adsorption and dissociation, and readily adsorbing hydrogen under hydrogen pressure to form vanadium hydride (VH). x Vanadium hydride has a lower formation enthalpy than magnesium hydride, thus inducing and promoting its hydrogen desorption reaction. Therefore, during the hydrogen absorption and desorption cycle of magnesium hydride, the reversible stabilization between V and the vanadium hydride phases plays a "hydrogen pump" effect, which helps lower the hydrogen absorption and desorption energy barrier of MgH2 and promotes hydrogen diffusion, thereby improving the hydrogen storage performance of the MgH2 composite hydrogen storage material. However, no Mo-containing substances were observed in the XRD patterns of different states, therefore other characterization methods are needed to indicate the presence of Mo-based substances.

[0117] Figure 15 XPS spectra of elemental V in the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material prepared in Example 2 after ball milling, one hydrogen release, one hydrogen absorption, and 30 hydrogen absorption cycles. Figure 15 It can be seen that in the ball-milled sample, the XPS peaks located at 519.5 / 512.0 eV, 520.9 / 513.4 eV, and 524.0 / 516.5 eV correspond to elemental vanadium (V2, V3, V4, V5, V6, V7, V8, V9 ... 0 ), vanadium with a +2 valence (V 2+ ) and +4 valence vanadium (V 4+ V 2p 1 / 2 and V 2p 3 / 2 The spin dual orbitals indicate that Mo2–VO2 undergoes partial reduction during ball milling with MgH2. Undoped VO2 also catalyzes V reduction in the MgH2 system, but the reduction is less pronounced. Furthermore, multivalent vanadium ions (V) were still observed in the composite hydrogen storage material after one hydrogen adsorption / desorption cycle. 0 V 2+ and V 4+The coexistence of these ions promotes charge transfer between magnesium and hydrogen molecules, accelerates the hydrogen absorption and desorption reactions, and enhances the catalytic activity of the catalyst. Furthermore, the coexistence of multivalent V ions was still observed in the hydrogen storage system after 30 hydrogen absorption cycles, a phenomenon that confirms the existence of the "hydrogen pump" effect, consistent with the XRD results described above.

[0118] Figure 16 XPS spectra of elemental Mo after ball milling, one hydrogen release, one hydrogen absorption, and 30 hydrogen absorption cycles for the MgH2+10 wt% Mo2–VO2 composite hydrogen storage material prepared in Example 2. Figure 16 As can be seen, similar to element V, element Mo also exhibits multiple valence states under different conditions. For the ball-milled sample, the XPS peaks at 230.4 / 227.0 eV, 231.1 / 228.0 eV, and 232.3 / 229.3 eV correspond to zero-valent Mo (Mo₂O₃) and Mo₂O₃, respectively. 0 ), +2 valence Mo (Mo 2+ ) and Mo with +4 valence (Mo 4+ After one hydrogen release, the XPS peak of Mo shifts to higher binding energies, resulting in the appearance of Mo with a +5 valence. 5+ (234.9 / 231.8 eV). This composite hydrogen storage material also exhibited multivalent Mo states after a single hydrogen absorption. 0 Mo 2+ and Mo 4+ The coexistence of these forms, and the maintenance of this stability after 30 hydrogen adsorption / desorption cycles, demonstrates that this multivalent Mo catalytic environment provides more catalytically active sites, acting as a stabilizing intermediate to promote H2O. – and Mg 2+ Electron transfer between molecules accelerates the hydrogen absorption and desorption kinetics of MgH2, thus obtaining a composite hydrogen storage material with low hydrogen absorption and desorption temperatures.

[0119] The above-described embodiments are preferred embodiments, but the scope of protection of the present invention is not limited thereto. Those skilled in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and variations, but as long as they do not depart from the spirit of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A method for preparing a Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material, characterized in that, include: (1) A raw material solution was obtained by mixing vanadium source, molybdenum source, reducing agent and water, and then prepared by hydrothermal synthesis reaction to obtain Mo-doped VO2 catalyst; (2) The Mo-doped VO2 catalyst prepared in step (1) is ball-milled and mixed with magnesium hydride to obtain the Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material.

2. The method for preparing Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material according to claim 1, characterized in that, In step (1): The vanadium source is selected from one or more of vanadium pentoxide, ammonium metavanadate, and ammonium polyvanadate. The molybdenum source is selected from ammonium molybdate and / or sodium molybdate; The reducing agent is selected from one or more of oxalic acid, citric acid, tartaric acid, and glucose.

3. The method for preparing Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material according to claim 1, characterized in that, In step (1): The concentration of the vanadium source in the feed solution is 0.05~0.1 mol / L; In the feed liquid, the molar ratio of V to Mo is 1:(0.03~0.07).

4. The method for preparing Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material according to claim 1, characterized in that, In step (1): The hydrothermal synthesis reaction is carried out at a temperature of 180~200℃ for 18~24 h.

5. The method for preparing Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material according to claim 1, characterized in that, In step (2): The mass ratio of Mo-doped VO2 catalyst to magnesium hydride is (1~12):(88~99).

6. The method for preparing Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material according to claim 1, characterized in that, In step (2), the ball milling: The rotation speed is 300~500 rpm, the ball-to-material ratio is (100~200):1, the time is 6~48 h, the atmosphere is selected from hydrogen, and the pressure is 1~5 MPa.

7. The method for preparing Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material according to any one of claims 1 to 6, characterized in that, In step (1): In the feed liquid, the molar ratio of V to Mo is 1:(0.05~0.07).

8. The method for preparing Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material according to claim 7, characterized in that, In step (2): The mass ratio of Mo-doped VO2 catalyst to magnesium hydride is (7~12):(88~93).

9. A Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material prepared by the method according to any one of claims 1 to 8.

10. The Mo-doped VO2-catalyzed magnesium hydride hydrogen storage material according to claim 9, characterized in that, The initial hydrogen release temperature is 184~197℃, and the initial hydrogen absorption temperature is room temperature; when heated from room temperature to 300℃, the hydrogen release amount is not less than 5.8 wt%, and the peak hydrogen release temperature is 224~230℃.

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