A magnesium-based hydrogen storage composite material, its preparation method and application

Abstract

This invention relates to the field of hydrogen storage materials technology, and discloses a magnesium-based hydrogen storage composite material, its preparation method, and its applications. By pre-ball milling MgH2 powder to achieve smaller particle size and higher surface activity, and then ball-milling it with nanomaterial ZnFe2O4 powder, the dispersion of the added phase on the surface of the MgH2 particles is improved, the diffusion path between ZnFe2O4 and MgH2 is shortened, and the interfacial contact is enhanced. This also improves the uniformity of the distribution of the generated phase in the Mg / MgH2 matrix after the initial dehydrogenation, thereby reducing and shortening the temperature and time of the initial dehydrogenation. This has a positive effect on maintaining the uniformity of the dispersed phase and improving the hydrogen adsorption / desorption kinetics and cycle stability of the magnesium-based material. The preparation method of this invention is simple, low-cost, and suitable for large-scale preparation, which is beneficial for the commercial application of hydrogen storage materials.

Description

Technical Field

[0001] This invention relates to the field of hydrogen storage materials technology, specifically to a magnesium-based hydrogen storage composite material, its preparation method, and its application. Background Technology

[0002] Current research mainly focuses on improving the hydrogen storage performance of ZnFe2O4-doped MgH2 and analyzing the phase composition of the dehydrogenation products. However, there are relatively few published studies on how to further improve the dispersion state of the added phase and the uniformity of the dehydrogenated phase distribution in the matrix through the synergistic control of MgH2 pretreatment state, ZnFe2O4 particle preparation method, and composite ball milling process. Due to the high thermodynamic stability and slow kinetics of MgH2, its hydrogen absorption and desorption temperatures are high and the reaction rate is slow. Therefore, it is necessary to provide a more rationally combined process for preparing magnesium-based hydrogen storage composite materials based on the addition of ZnFe2O4 to MgH2, in order to further improve the hydrogen absorption and desorption kinetics and cycle stability of magnesium-based hydrogen storage materials. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a magnesium-based hydrogen storage composite material, its preparation method, and its applications. By pre-ball milling MgH2 powder to achieve smaller particle size and higher surface activity, and then ball-milling it with nanomaterial ZnFe2O4 powder, the dispersion of the added phase on the surface of the MgH2 particles is improved, the diffusion path between ZnFe2O4 and MgH2 is shortened, and the interfacial contact is enhanced. This also improves the uniformity of the distribution of the generated phase in the Mg / MgH2 matrix after the initial dehydrogenation, thereby reducing and shortening the temperature and time of the initial dehydrogenation. This has a positive effect on maintaining the uniformity of the dispersed phase and improving the hydrogen adsorption / desorption kinetics and cycle stability of the magnesium-based material. The preparation method of this invention is simple, low-cost, and suitable for large-scale preparation, which is beneficial for the commercial application of hydrogen storage materials.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a magnesium-based hydrogen storage composite material includes the following steps: Step (1): Preparation of pre-ball-milled MgH2 powder Mg powder is hydrogenated to obtain MgH2 powder; MgH2 powder is pre-ball-milled to obtain pre-ball-milled MgH2 powder. Step (2): Preparation of ZnFe2O4 powder Zn(NO3)2·6H2O and Fe(NO3)3·9H2O were dissolved in water and subjected to a hydrothermal reaction. After the reaction was completed, the mixture was filtered, washed with deionized water and ethanol, and dried under vacuum to obtain ZnFe2O4 powder. Step (3): Preparation of precursor composite material Pre-ball-milled MgH2 powder was mixed with ZnFe2O4 powder and ball-milled. After ball milling, the precursor composite material was obtained. Step (4) Dehydrogenation treatment The precursor composite material was subjected to dehydrogenation treatment, and after the treatment was completed, it was cooled to room temperature to obtain a magnesium-based hydrogen storage composite material.

[0005] Preferably, in step (1), the hydrogenation treatment conditions include: hydrogenation treatment at 350-420℃ and 3-4MPa hydrogen pressure.

[0006] Preferably, in step (1), the pre-ball milling conditions include: transferring MgH2 powder to a ball milling jar for pre-ball milling in a high-purity argon atmosphere for 6-8 hours, with a ball-to-material mass ratio of (30-60):1 and a ball milling speed of 400-500 r / min; opening the ball milling jar once every 4 hours during the ball milling process, tamping the sample and cleaning the jar wall under argon protection; all the above operations are carried out in a high-purity argon atmosphere to prevent sample oxidation.

[0007] Preferably, in step (2), the ratio of Zn(NO3)2·6H2O, Fe(NO3)3·9H2O, and water is 1 mol:(1.8-2.2) mol:(60-100) mL.

[0008] Preferably, in step (2), the hydrothermal reaction conditions include: adding 1-3 mol / L of NaOH aqueous solution to adjust the pH value to 9-11, transferring it to a high-pressure reactor, and hydrothermally reacting at 160-200℃ for 10-14 hours.

[0009] Preferably, in step (3), the mass ratio of pre-ball-milled MgH2 powder to ZnFe2O4 powder is (85-95):(5-15).

[0010] Preferably, in step (3), the ball milling conditions include: under a high-purity argon protective atmosphere with a pressure of 0.1 MPa, the pre-ball-milled MgH2 powder and ZnFe2O4 powder are mixed and loaded into a stainless steel ball milling jar, and ball milling is performed by high-energy ball milling using tungsten carbide grinding balls. The ball-to-material mass ratio is (30-60):1, the ball milling speed is 400-500 r / min, and the ball milling time is 4-8 h.

[0011] Preferably, in step (4), the dehydrogenation treatment conditions include: heating to 400-500℃ at a heating rate of 1-5℃ / min and holding at that temperature for 5-20min.

[0012] Preferably, a magnesium-based hydrogen storage composite material is prepared using the method described above.

[0013] Preferably, the application of a magnesium-based hydrogen storage composite material as described above in hydrogen storage materials.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes pre-ball milling of MgH2 powder to improve particle fineness. Pre-ball milling increases surface defects and surface activity of the MgH2 powder particles, shortening the hydrogen diffusion path and reducing dehydrogenation reaction resistance, thus improving the dehydrogenation kinetics of MgH2 powder. Simultaneously, pre-ball milling facilitates the dispersion and uniform loading of ZnFe2O4 powder on its surface, providing more adequate interfacial contact conditions for subsequent in-situ reactions. Furthermore, after mixing MgH2 and ZnFe2O4 powders to form a precursor composite material, secondary high-energy ball milling further strengthens the interfacial contact between the MgH2 and ZnFe2O4 powders, and promotes the in-situ generation of Fe and Fe3Zn. 10 The MgO phase maintains good dispersion in the matrix, thus slowing down particle sintering, agglomeration, and interfacial deactivation during hydrogen absorption and desorption cycles, thereby improving the cycling stability of the material.

[0015] The pre-ball-milled MgH2 powder prepared by this invention has a smaller particle size and higher surface activity, while the ZnFe2O4 powder obtained by hydrothermal method has nanoscale and good dispersibility. Furthermore, the secondary high-energy ball milling further enhances the interfacial contact between the two, shortens the diffusion path between ZnFe2O4 and MgH2, and strengthens the interfacial contact. Therefore, under the condition of holding at 450℃ for 10 min, ZnFe2O4 can be induced to undergo in-situ phase evolution in the MgH2 system. This condition is sufficient to complete the generation of the active phase and reduces the risk of particle sintering, phase coarsening, and interfacial degradation caused by high temperature and long-term treatment. It is beneficial to reduce particle growth, sintering, and catalytic phase coarsening, thus playing a positive role in maintaining the uniformity of the dispersed phase and improving cycle stability.

[0016] In this invention, the precursor composite material undergoes in-situ transformation to form Fe and Fe3Zn during the initial dehydrogenation process. 10 It is a dispersed phase, along with MgO. Fe promotes the dissociation of HH bonds and the migration of hydrogen atoms at the Mg / MgH2 interface, and Fe3Zn... 10MgO can act as an interfacial active phase and mass transfer channel, helping to regulate the interfacial structure of the composite system and promote electron / atom transfer during the reaction. MgO, on the other hand, can act as a stable dispersed phase to inhibit particle sintering and agglomeration, and to some extent induce the formation of more interfacial defects and diffusion channels. The above phases do not act in isolation, but rather, by constructing a multiphase dispersion structure and rich heterogeneous interfaces in the Mg / MgH2 matrix, they synergistically promote the adsorption, dissociation, diffusion, and release of hydrogen at the interface, thereby improving the hydrogen adsorption and desorption kinetics of the composite material.

[0017] The present invention has a simple process, abundant raw material sources, and low cost, making it suitable for large-scale preparation and showing good application prospects. Attached Figure Description

[0018] Figure 1 This is a SEM image of the ZnFe2O4 powder prepared in Example 1 of this invention; Figure 2 This is the XRD pattern of the ZnFe2O4 powder prepared in Example 1 of this invention; Figure 3 These are XRD patterns of the precursor composite material prepared in Example 1 of this invention and the pre-ball-milled MgH2 powder. Figure 4 The images show the XRD patterns of the precursor composite material prepared in Example 1 of this invention after the first dehydrogenation treatment, the magnesium-based hydrogen storage composite material (MgH2+10wt%ZnFe2O4) prepared in Example 1 after 10 cycles of hydrogen absorption and desorption, and the XRD pattern of the precursor composite material prepared in Example 1 of this invention. Figure 5 These are temperature-induced hydrogen desorption performance test graphs of the pre-ball-milled MgH2 powder prepared in Examples 1-3 and the unpre-ball-milled MgH2 powder prepared in Comparative Example 1. Figure 6 The graphs show the hydrogen desorption performance of MgH2+10wt%ZnFe2O4 prepared in Example 1 and the pre-ball-milled MgH2 powder prepared in Example 1. Figure 7 The graphs show the hydrogen release performance test results of MgH2+10wt%ZnFe2O4 prepared in Example 1 and MgH2+10wt%ZnFe2O4 prepared in Comparative Example 1. Figure 8 These are isothermal hydrogen desorption performance test graphs of MgH2+10wt%ZnFe2O4 prepared in Example 1 and MgH2 powder pre-ball-milled prepared in Example 1. Figure 9 The graph shows the hydrogen absorption performance test results of MgH2+10wt%ZnFe2O4 prepared in Example 1 and MgH2 powder pre-ball-milled prepared in Example 1. Figure 10 The isothermal hydrogen absorption performance test results are shown for MgH2+10wt%ZnFe2O4 prepared in Example 1 and MgH2 powder pre-ball-milled prepared in Example 1. Figure 11 This is a cycle performance test chart of MgH2+10wt%ZnFe2O4 prepared in Example 1. Detailed Implementation

[0019] The present invention will be further illustrated below through specific embodiments. The following embodiments are specific implementations of the present invention, but the implementation of the present invention is not limited to the following embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and are included within the protection scope of the present invention.

[0020] Example 1 This embodiment discloses a method for preparing a magnesium-based hydrogen storage composite material, including the following steps: Step (1): Preparation of pre-ball-milled MgH2 powder Mg powder was placed in a reactor and hydrogenated at 380°C and 3.5 MPa to fully convert it into MgH2, thus obtaining MgH2 powder. The MgH2 powder was pre-ball-milled as follows: In a high-purity argon atmosphere, the MgH2 powder was transferred to a ball mill jar for pre-ball milling for 8 hours. The ball-to-powder ratio was 50:1, the milling speed was 450 r / min, the ball mill jar was made of stainless steel, and the grinding balls were made of tungsten carbide (small tungsten carbide grinding balls with a diameter of 6 mm and a mass of 1.7 g; large tungsten carbide grinding balls with a diameter of 10 mm and a mass of 7.8 g; the ratio of large to small tungsten carbide grinding balls was 1:1; all the above tungsten carbide grinding balls were purchased from Ningbo Haishu Runchang Hard Alloy Co., Ltd.): During the ball milling process, the ball mill jar was opened every 4 hours for sample tamping and cleaning of the jar wall under argon protection. All the above operations were carried out in a high-purity argon atmosphere to prevent sample oxidation. Step (2): Preparation of ZnFe2O4 powder 1 mol of Zn(NO3)2·6H2O and 2 mol of Fe(NO3)3·9H2O were dissolved in 80 mL of deionized water. The pH value was adjusted to 9 by adding 2 mol / L NaOH aqueous solution. The resulting solution was transferred to a high-pressure reactor and hydrothermally reacted at 180 °C for 12 h. After the reaction was completed, the solution was filtered and washed with deionized water and ethanol. The solution was then vacuum dried at 80 °C for 10 h to obtain ZnFe2O4 powder. Step (3): Preparation of precursor composite material Under a high-purity argon protective atmosphere at a pressure of 0.1 MPa, pre-ball-milled MgH2 powder and ZnFe2O4 powder were mixed at a mass ratio of 90:10. The mixed powder was loaded into a stainless steel ball mill jar and ball-milled using tungsten carbide grinding balls via high-energy ball milling. The total mass of the material was 1000 mg, the ball-to-material ratio was 50:1, the ball milling speed was 450 r / min, and the ball milling time was 6 h. After ball milling, the precursor composite material was obtained. Step (4) Dehydrogenation treatment The precursor composite material underwent initial dehydrogenation treatment by heating to 450℃ at a heating rate of 2℃ / min and holding for 10 min, causing ZnFe2O4 and MgH2 to undergo in-situ phase evolution, forming Fe and Fe3Zn. 10 The MgO dispersion phase was cooled to room temperature to obtain a magnesium-based hydrogen storage composite material, denoted as MgH2+10wt%ZnFe2O4.

[0021] Example 2 The difference from Example 1 is that the pre-ball milling time in step (1) is changed from 8h to 4h, while the other parameters and conditions are the same as in Example 1.

[0022] Example 3 The difference from Example 1 is that the pre-ball milling time in step (1) is changed from 8h to 12h, while other parameters and conditions are the same as in Example 1.

[0023] Comparative Example 1 The difference from Example 1 is that the pre-ball milling time in step (1) is changed from 8h to 0h, that is, the MgH2 powder is not pre-ball milled. Other parameters and conditions are the same as in Example 1.

[0024] In the above examples and comparative examples: the Mg powder had a purity of 99.9% and an average particle size of 74 μm, and was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Zn(NO3)2·6H2O, Fe(NO3)3·9H2O and NaOH were commercially available high-purity reagents, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and were not subjected to additional purification treatment before use; the ball mill was a QM-3SP4 ball mill from Nanjing Chishun Technology Development Co., Ltd.; and the high-purity argon gas was argon gas with a purity of 99.999%.

[0025] Experimental data characterization and performance testing (1) The ZnFe2O4 powder prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown; XRD tests were performed on the MgH2 powder, ZnFe2O4 powder, precursor composite material, and magnesium-based hydrogen storage composite material (MgH2+10wt%ZnFe2O4) prepared in Example 1, and the test results are as follows. Figures 2 to 4 As shown.

[0026] from Figure 1 As can be seen, the ZnFe2O4 powder consists of uniformly sized, nanoscale particles that form a relatively loose aggregate structure. This rough surface and hierarchical packing morphology constructed by nanoparticles generally helps to increase the specific surface area and expose more potential active sites, thereby providing more interfacial reaction areas for key steps such as hydrogen atom dissociation / migration; at the same time, the pore and defect structure between particles may also provide shorter mass transfer paths for hydrogen diffusion in subsequent composite systems.

[0027] from Figure 2 As can be seen, multiple diffraction peaks of the ZnFe2O4 powder can be clearly observed, with 2θ angles located at 30.01°, 35.4°, 56.8°, and 62.4°, respectively. This indicates the successful synthesis of high-purity spinel-structured ZnFe2O4 crystals, and the absence of other impurity phases within the detected range demonstrates the good purity of the catalyst.

[0028] from Figure 3 As can be seen, compared with pre-ball-milled MgH2 powder, no new phase was formed in the precursor composite material prepared by doping ZnFe2O4 nanopowder with MgH2. Figure 3 It can be seen that the diffraction peaks of MgH2 powder mainly correspond to the MgH2 phase. After ball milling and composite, the XRD pattern of the precursor composite material still mainly shows the characteristic diffraction peaks of MgH2, while the characteristic diffraction peaks of ZnFe2O4 also appear, and a small amount of Mg diffraction peaks are detected. This indicates that ZnFe2O4 nanopowder has been successfully introduced into the MgH2 system.

[0029] Compared to pure MgH2, the diffraction peak intensity of MgH2 in the precursor composite material is significantly reduced and the peak shape is broadened. This is mainly due to the reduction in MgH2 grain size, increase in lattice defects, and decrease in crystallinity during high-energy ball milling. Meanwhile, the appearance of a small number of Mg peaks may originate from slight dehydrogenation decomposition of some MgH2 during ball milling. No obvious new phase diffraction peaks were observed in the spectra, indicating that no significant chemical reaction occurred between MgH2 and ZnFe2O4 during the ball milling composite process, and the obtained material is a precursor composite material formed by the composite of MgH2 and ZnFe2O4.

[0030] Therefore, the XRD results show that ZnFe2O4 has been successfully incorporated into MgH2, and ball milling can effectively reduce the grain size of MgH2 and introduce defects, which is beneficial to the subsequent dehydrogenation reaction.

[0031] from Figure 4As can be seen, after the first dehydrogenation treatment of the precursor composite material (i.e., the first hydrogen release in the figure), ZnFe2O4 and MgH2 undergo in-situ phase evolution to form Fe and Fe3Zn. 10 And MgO dispersed phase.

[0032] The XRD pattern shows that the ball-milled composite material only exhibits characteristic peaks of MgH2 and ZnFe2O4, and no byproducts were detected, indicating that the system is relatively stable during the mechanical composite stage.

[0033] After the initial dehydrogenation, the characteristic peaks of ZnFe2O4 significantly decreased, accompanied by the appearance of diffraction peaks for MgO and metallic Fe. Simultaneously, an Fe-Zn alloy phase was observed. This significant change demonstrates that during the initial dehydrogenation process, ZnFe2O4, acting as a precursor catalyst, underwent an in-situ reaction with MgH2. The reaction equation can be deduced as follows: 40MgH2+10ZnFe2O4=17Fe+40MgO+Fe3Zn 10 +40H2↑; In subsequent cyclic tests, after 10 cycles of dehydrogenation / absorption, it can be seen that a highly reversible transformation occurs between MgH2 and Mg in the matrix phase, while Fe and Fe3Zn undergo this transformation. 10 The diffraction peaks for MgO remained stable, and no further formation of ZnFe2O4 was observed. This phenomenon indicates that nano-Fe and Fe3Zn were generated in situ during the initial dehydrogenation process. 10 In long-term cycles, MgO and MgO act as "active substances" that play a catalytic role: during hydrogen absorption, they can act as "hydrogen pumps," preferentially adsorbing hydrogen molecules and promoting their dissociation into highly active hydrogen atoms; during hydrogen release, these metal sites can effectively weaken Mg-H bonds and reduce the activation energy of hydrogen atom recombination and desorption.

[0034] (2) The hydrogen storage performance of the pre-ball-milled MgH2 powder prepared in Examples 1-3 and the un-ball-milled MgH2 powder prepared in Comparative Example 1 were tested. The test results are as follows: Figure 5 As shown.

[0035] The test method includes the following steps: MgH2 powder without pre-ball milling treatment in Comparative Example 1 and MgH2 powder with pre-ball milling treatment in Examples 1-3 (pre-ball milling times of 8h, 4h, and 12h, respectively) are used as samples. 200mg of each sample is placed in the reactor, the heater is turned on, and the temperature is increased from room temperature to 450℃ at a heating rate of 2℃ / min. The temperature is held for 10min, the amount of hydrogen released from the sample during the heating process is measured, and the heating and hydrogen release curve is plotted.

[0036] from Figure 5It can be seen that the MgH2 powder prepared in Comparative Example 1 without pre-ball milling (unmilled MgH2) only begins to significantly release hydrogen at a relatively high temperature (420℃), while the MgH2 powder prepared in Examples 1-3 with pre-ball milling treatment starts to release hydrogen at a significantly earlier temperature. Specifically, the MgH2 powder prepared in Example 1 with pre-ball milling treatment for 8 hours has an initial hydrogen release temperature of 300℃, the MgH2 powder prepared in Example 2 with pre-ball milling treatment for 4 hours has an initial hydrogen release temperature of 330℃, and the MgH2 powder prepared in Example 3 with pre-ball milling treatment for 12 hours has an initial hydrogen release temperature of 310℃. This indicates that ball milling can effectively improve the dehydrogenation kinetics of MgH2 powder. This is mainly attributed to the fact that ball milling reduces the particle size and increases the specific surface area of ​​MgH2 powder, and introduces more defects, grain boundaries, and fresh active surfaces on the particle surface, thereby shortening the hydrogen diffusion path and reducing the resistance to the dehydrogenation reaction.

[0037] Furthermore, from Figure 5 As can be seen, compared with MgH2 powder pre-ball milled for 4 hours, MgH2 powder pre-ball milled for 8 hours and 12 hours exhibited a faster hydrogen desorption rate and a lower hydrogen desorption onset temperature. This indicates that appropriately extending the ball milling time helps to further improve the activity of MgH2 powder. The hydrogen desorption curves of MgH2 powder pre-ball milled for 8 hours and 12 hours are quite similar. Considering ball milling energy consumption, process efficiency, and subsequent composite dispersion effect, the optimal pre-ball milling time for MgH2 powder is 8 hours.

[0038] (3) The hydrogen release test was performed on the MgH2+10wt%ZnFe2O4 prepared in Example 1 and the pre-ball-milled MgH2 powder. The test results are as follows: Figure 6 As shown; the MgH2+10wt%ZnFe2O4 prepared in Example 1 and the MgH2+10wt%ZnFe2O4 prepared in Comparative Example 1 were subjected to a heating hydrogen release test, and the test results are as follows. Figure 7 As shown.

[0039] The testing method includes the following steps: 200 mg of each of the two samples (MgH2 + 10 wt% ZnFe2O4 prepared in Example 1 and pre-ball-milled MgH2 powder) is placed in a reactor. The reactor is evacuated to a maximum vacuum, the heater is turned on, and the temperature is increased from room temperature to 450°C at a rate of 2°C / min, held for 10 min, and the hydrogen release rate during the heating process is measured. A heating-hydrogen release curve is plotted, and the results are as follows: Figure 6 As shown; The MgH2+10wt%ZnFe2O4 prepared in Example 1 and the MgH2+10wt%ZnFe2O4 prepared in Comparative Example 1 were used as samples, and the same method as described above was used to perform a hydrogen release test by heating. The hydrogen release curves are shown in the figure. Figure 7 As shown.

[0040] from Figure 6 It can be seen that the dehydrogenation temperature of MgH2 + 10wt% ZnFe2O4 drops to 224℃, while the pre-ball-milled MgH2 powder only begins to release hydrogen at 335℃. This shows that doping with ZnFe2O4 powder significantly reduces the initial hydrogen release temperature of the hydrogen storage material. Furthermore, from... Figure 6 As can be seen, before approximately 400°C, the hydrogen release of MgH2+10wt%ZnFe2O4 is higher than that of pre-ball-milled MgH2 powder. This is mainly attributed to ZnFe2O4 lowering the activation energy of the dehydrogenation reaction, promoting hydrogen diffusion, and accelerating the decomposition of MgH2. However, as the temperature continues to rise, the hydrogen release of the pre-ball-milled MgH2 powder gradually exceeds that of MgH2+10wt%ZnFe2O4. This is because ZnFe2O4 itself does not contribute to the effective hydrogen storage capacity, and its 10wt% addition reduces the mass fraction of MgH2 powder in the sample, thus resulting in a lower final hydrogen release of MgH2+10wt%ZnFe2O4 calculated by total mass compared to pure MgH2.

[0041] from Figure 7 It can be seen that the MgH2+10wt%ZnFe2O4 (pre-ball-milled MgH2+10wt%ZnFe2O4) prepared in Example 1 exhibits a lower initial dehydrogenation temperature and a faster hydrogen desorption rate compared with the MgH2+10wt%ZnFe2O4 (un-ball-milled MgH2+10wt%ZnFe2O4) prepared in Comparative Example 1. This indicates that pre-ball milling of MgH2 powder is beneficial to improving the dispersion state of ZnFe2O4 powder on the surface of MgH2 powder and further promoting the improvement of dehydrogenation kinetics of hydrogen storage materials.

[0042] (4) The MgH2+10wt%ZnFe2O4 prepared in Example 1 and the pre-ball-milled MgH2 powder were subjected to isothermal hydrogen release tests. The test results are as follows: Figure 8 As shown.

[0043] The testing method includes the following steps: MgH2+10wt%ZnFe2O4 prepared in Example 1 and pre-ball-milled MgH2 powder are used as samples. 200mg of each sample is placed in the reactor, the reactor is evacuated to the ultimate vacuum, the heater is turned on, and the temperature is raised to 330℃ at a rate of 5℃ / min. The temperature is maintained for 3h. After the temperature stabilizes, the reactor is turned on for testing. The test time is 60min. The amount of hydrogen released at different times is recorded, and the isothermal hydrogen release curve is plotted.

[0044] from Figure 8It can be seen that the MgH2+10wt%ZnFe2O4 prepared in Example 1 can release 5.08wt% hydrogen within 10min, while the pre-ball-milled MgH2 powder only releases 0.4wt% hydrogen in the same time (10min). This shows that the hydrogen release rate of MgH2 powder is greatly improved after doping with ZnFe2O4 nanoparticles.

[0045] (5) The MgH2+10wt%ZnFe2O4 prepared in Example 1 and the pre-ball-milled MgH2 powder were subjected to a hydrogen absorption test upon heating. The test results are as follows: Figure 9 As shown.

[0046] The testing method includes the following steps: MgH2+10wt%ZnFe2O4 prepared in Example 1 and pre-ball-milled MgH2 powder are used as samples. 200mg of each sample is placed in the reactor, the reactor is evacuated to the ultimate vacuum, H2 is introduced at 3MPa under high pressure, the heater is turned on, and the temperature is increased from room temperature to 400℃ at a rate of 1℃ / min. The temperature is held for 10min, the amount of hydrogen absorbed by the sample during the heating process is measured, and the heating and hydrogen absorption curve is plotted.

[0047] from Figure 9 It can be seen that the MgH2+10wt%ZnFe2O4 prepared in Example 1 can begin to absorb hydrogen at 60℃ and can absorb 3.89wt% H2 at 200℃. In contrast, under the same conditions (200℃), the pre-ball-milled MgH2 powder only absorbs 1wt% H2. This shows that the hydrogen absorption temperature is significantly reduced after doping with ZnFe2O4 nanoparticles, allowing hydrogen absorption to be achieved at a lower temperature. Before the curves intersect, the hydrogen absorption capacity of MgH2+10wt%ZnFe2O4 is higher than that of the pre-ball-milled MgH2 powder, indicating that the addition of ZnFe2O4 improves the hydrogen absorption kinetics. Its catalytic effect is beneficial to the dissociation of hydrogen molecules, the diffusion of hydrogen atoms, and the conversion of Mg to MgH2. Therefore, MgH2+10wt%ZnFe2O4 begins to absorb hydrogen significantly at a lower temperature, with a faster absorption rate.

[0048] After the crossover point, the hydrogen absorption capacity of the pre-ball-milled MgH2 powder gradually exceeds that of the composite material. This is mainly because ZnFe2O4 itself provides virtually no hydrogen storage capacity, and the addition of 10wt% reduces the ratio of the effective hydrogen storage component Mg / MgH2 in the sample. Therefore, after sufficient hydrogen absorption at high temperature, the final hydrogen absorption capacity of MgH2 + 10wt% ZnFe2O4, calculated by total mass, is lower than that of the pre-ball-milled MgH2 powder.

[0049] (6) The MgH2+10wt%ZnFe2O4 prepared in Example 1 and the pre-ball-milled MgH2 powder were subjected to isothermal hydrogen absorption tests. The test results are as follows: Figure 10 As shown.

[0050] The testing method includes the following steps: MgH2+10wt%ZnFe2O4 prepared in Example 1 and pre-ball-milled MgH2 powder are used as samples. 200mg of each sample is placed in the reactor, the reactor is evacuated to the ultimate vacuum, and H2 is introduced at 3MPa under high pressure. The heater is turned on and the temperature is raised to 200℃ at a heating rate of 2℃ / min. The temperature is maintained for 2h. After the temperature stabilizes, the reactor is turned on for testing. The test time is 60min. The amount of hydrogen absorbed at different times is recorded, and the isothermal hydrogen absorption curve is plotted.

[0051] from Figure 10 It can be seen that the MgH2+10wt%ZnFe2O4 prepared in Example 1 can absorb 6.12wt% hydrogen within 60 min, while the pre-ball-milled MgH2 powder can only absorb 3.75wt% hydrogen under the same conditions. It is evident that the hydrogen absorption rate of MgH2 is significantly improved after doping with ZnFe2O4 nanoparticles.

[0052] (7) The cycling characteristics of MgH2+10wt%ZnFe2O4 prepared in Example 1 were tested, and the test results are as follows: Figure 11 As shown.

[0053] The testing method includes the following steps: MgH2+10wt%ZnFe2O4 prepared in Example 1 is used as a sample. 200mg of the sample is placed in the reactor, the reactor is evacuated to the ultimate vacuum, the heater is turned on, and the temperature is raised to 350℃ at a heating rate of 5℃ / min. Hydrogen absorption and desorption cycle performance is tested for 10 cycles. The hydrogen absorption and desorption time of each cycle is 30min. Cycle characteristic curves are plotted.

[0054] from Figure 11 It can be seen that the MgH2+10wt%ZnFe2O4 prepared in Example 1 can still maintain 97.8% of the hydrogen storage capacity after 10 cycles, which shows good cycle stability.

[0055] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing a magnesium-based hydrogen storage composite material, characterized in that, Includes the following steps: Pre-ball milling of MgH2 powder is performed to improve the surface activity of MgH2 powder particles, reduce the initial hydrogen desorption temperature of MgH2 powder, and increase the interfacial contact points of ZnFe2O4 powder on the surface of MgH2 powder, thus obtaining pre-ball milled MgH2 powder. Pre-ball-milled MgH2 powder and ZnFe2O4 powder were mixed and ball-milled to obtain a precursor composite material; The precursor composite material was subjected to dehydrogenation treatment to obtain a magnesium-based hydrogen storage composite material.

2. The preparation method of the magnesium-based hydrogen storage composite material according to claim 1, characterized in that, The preparation of the MgH2 powder includes the following steps: Mg powder is hydrogenated at 350-420℃ and 3-4MPa hydrogen pressure to obtain MgH2 powder.

3. The preparation method of the magnesium-based hydrogen storage composite material according to claim 1, characterized in that, The pre-ball milling conditions include: transferring MgH2 powder to a ball milling jar for pre-ball milling in a high-purity argon atmosphere for 6-8 hours, with a ball-to-material mass ratio of (30-60):1 and a ball milling speed of 400-500 r / min.

4. The preparation method of the magnesium-based hydrogen storage composite material according to claim 1, characterized in that, The preparation of the ZnFe2O4 powder includes the following steps: Zn(NO3)2·6H2O and Fe(NO3)3·9H2O were dissolved in water and subjected to a hydrothermal reaction. After the reaction was completed, the mixture was filtered, washed, and dried to obtain ZnFe2O4 powder. The ratio of Zn(NO3)2·6H2O, Fe(NO3)3·9H2O, and water is 1 mol:(1.8-2.2) mol:(60-100) mL. The hydrothermal reaction conditions include: adding 1-3 mol / L NaOH aqueous solution to adjust the pH value to 9-11, and hydrothermally reacting at 160-200℃ for 10-14 h.

5. The method for preparing the magnesium-based hydrogen storage composite material according to claim 1, characterized in that, The mass ratio of the pre-ball-milled MgH2 powder to ZnFe2O4 powder is (85-95):(5-15).

6. The method for preparing the magnesium-based hydrogen storage composite material according to claim 1, characterized in that, The conditions for ball milling the pre-ball-milled MgH2 powder and ZnFe2O4 powder include: under a high-purity argon protective atmosphere at a pressure of 0.1 MPa, the pre-ball-milled MgH2 powder and ZnFe2O4 powder mixture is loaded into a stainless steel ball mill jar, and ball milling is performed using tungsten carbide grinding balls via high-energy ball milling. The ball-to-material mass ratio is (30-60):1, the ball milling speed is 400-500 r / min, and the ball milling time is 4-8 h.

7. The method for preparing the magnesium-based hydrogen storage composite material according to claim 1, characterized in that, The dehydrogenation treatment conditions include heating to 400-500℃ at a heating rate of 1-5℃ / min and holding at that temperature for 5-20min.

8. A method for preparing a magnesium-based hydrogen storage composite material, characterized in that, Includes the following steps: MgH2 powder was pre-ball-milled to obtain pre-ball-milled MgH2 powder. The specific process of pre-ball milling included: transferring MgH2 powder to a ball milling jar for pre-ball milling in a high-purity argon atmosphere for 6-8 hours, with a ball-to-powder mass ratio of (30-60):1 and a ball milling speed of 400-500 r / min; all the above operations were carried out in a high-purity argon atmosphere. Pre-ball-milled MgH2 powder and ZnFe2O4 powder were mixed and ball-milled to obtain a precursor composite material; The precursor composite material was subjected to dehydrogenation treatment to obtain a magnesium-based hydrogen storage composite material.

9. A magnesium-based hydrogen storage composite material prepared by the preparation method of the magnesium-based hydrogen storage composite material as described in any one of claims 1-8.

10. The application of the magnesium-based hydrogen storage composite material as described in claim 9 in hydrogen storage materials.

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