Preparation method of magnesium hydride-based hydrogen storage material and product thereof

Abstract

The present invention discloses a preparation method of a magnesium hydride-based hydrogen storage material. Raw materials including magnesium hydride and lanthanum vanadate are ball-milled and mixed, and a magnesium hydride-based hydrogen storage material is obtained after one cycle of activation. By in-situ introducing substances that act as a "hydrogen pump" and a hydrogen channel catalyst, the hydrogen storage and dehydrogenation performance of the magnesium hydride-based hydrogen storage material is greatly improved. The catalyst has a low cost and high activity, is suitable for large-scale industrial production. More importantly, the prepared composite hydrogen storage material is a hydrogen storage material with low hydrogen absorption and desorption temperatures, fast hydrogen absorption and desorption kinetics, and high cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen storage materials, and particularly relates to a preparation method and a product of a magnesium hydride-based hydrogen storage material with in-situ introduced hydrogen pump and hydrogen channel catalytic substances. Background Art

[0002] With the start of the industrial revolution and the increasing innovation of technologies, the demand for energy by humans is growing. One of the necessary conditions for the continuous development and application of high-tech is to find a green and renewable energy source. Renewable energy sources include geothermal energy, tidal energy, light energy, wind energy, hydrogen energy, etc. Among them, hydrogen energy has an energy calorific value as high as 142 MJ / Kg, and the reaction product is water, which is clean and pollution-free. Moreover, hydrogen energy can act as a secondary energy source and be mutually converted with other forms of energy. The application links of hydrogen energy include hydrogen production, hydrogen storage, and hydrogen utilization, and hydrogen storage is the bottleneck restricting its large-scale application. Hydrogen storage methods can be divided into gaseous hydrogen storage, liquid hydrogen storage, and solid hydrogen storage according to the physical state of hydrogen. The volumetric hydrogen storage density of gaseous hydrogen storage is relatively low, and liquid hydrogen storage requires a large amount of energy consumption during the low-temperature liquefaction process. Solid hydrogen storage has become a research hotspot in the hydrogen energy field due to its high mass / volume hydrogen storage density and convenient hydrogen storage characteristics.

[0003] The MgH2 hydrogen storage material in solid hydrogen storage is considered to be a very promising hydrogen storage material with development and application prospects due to its low cost, high abundance, 7.6 wt% hydrogen storage density, and good reversibility. However, the high stability of MgH2 itself results in a dehydrogenation enthalpy change as high as 76 kJ / mol, leading to a high dehydrogenation temperature and a slow reaction rate. Different modification methods are still needed to optimize its dehydrogenation performance for commercial application. Currently, the main modification methods for MgH2 are nanosizing, alloying, and catalysis. The operation of non-loaded nanosizing is complex and the sample yield is low, while nanoconfinement and alloying will cause serious loss of the hydrogen storage capacity of the sample. In contrast, catalysis can not only significantly improve the hydrogen absorption and desorption kinetics of the sample, lower the dehydrogenation temperature of the sample, but also maintain a relatively high hydrogen storage capacity of the system, which is the simplest and most effective modification method.

[0004] Some oxides act as stable catalysts to lower the hydrogen absorption and desorption energy barriers of MgH2. Some other oxides will react chemically with MgH2 during ball milling or dehydrogenation to form new substances as the real effective catalysts. As reported in the literature, (L.Dan, L.Hu, H.Wang and M.Zhu, Excellent catalysis of MoO3 on the hydrogen sorption of MgH2, International Journal of Hydrogen Energy. 44(2019):29249-29254.) the MgH2 + 2mol% MoO3 system can release 5wt% H2 within 900 s at 300 °C, while magnesium hydride hardly releases hydrogen under the same conditions. The good catalytic effect is mainly attributed to the fact that MoO3 can act as a hydrogen diffusion channel to improve its kinetic performance. However, the dehydrogenation temperature of 300 °C is too high and the dehydrogenation amount is also limited, so further improvement is needed.

[0005] XRD and infrared spectroscopy confirmed that ZrH was generated in the MgH2 system doped with ZrO2 during ball milling. x (2 > x > 1.5) and MgO, and the catalytic effect of ZrH x is better than that of ZrO2. The initial dehydrogenation temperature of the MgH2 system doped with 10wt% zirconia is 280 °C, and the dehydrogenation end temperature is basically after 380 °C. Therefore, more efficient catalysts need to be sought (D.Pukazhselvan, K.S.Sandhya, D.Ramasamy, A.Shaula, I.Bdikin and D.P.Fagg, Active catalytic species generated in situ in zirconia incorporated hydrogen storage material magnesium hydride, Journal of Magnesium and Alloys. 10(2022):786-796.).

[0006] In the applicant's previous work (K. Xian, M. Wu, M. Gao, S. Wang, Z. Li, P. Gao, Z. Yao, Y. Liu, W. Sun and H. Pan, A Unique Nanoflake-Shape Bimetallic Ti-Nb Oxide of Superior Catalytic Effect for Hydrogen Storage of MgH2, Small. (2022).), when doped with only 3 wt% of two-dimensional TiNb2O7, the dehydrogenation temperature of MgH2 decreased to 178 °C, a decrease of 100 °C compared to the original magnesium hydride. However, the preparation process of two-dimensional TiNb2O7 is very complex, with low yield and high cost.

[0007] Therefore, finding a catalyst with a simple preparation method, low cost, high yield and high activity is the key to the commercialization of MgH2. Summary of the Invention

[0008] In view of the above problems existing in the prior art, the present invention discloses a preparation method of a magnesium hydride-based hydrogen storage material by in-situ introducing a hydrogen pump and a hydrogen channel catalytic substance, which is simple and controllable, low in cost, suitable for large-scale industrial production. More importantly, the prepared composite hydrogen storage material greatly improves the hydrogen absorption and desorption kinetics of MgH2, reduces its initial dehydrogenation temperature, and improves its cycle stability.

[0009] The specific technical solution is as follows:

[0010] A preparation method of a magnesium hydride-based hydrogen storage material, in which raw materials including magnesium hydride and lanthanum vanadate are ball-milled and mixed, and a magnesium hydride-based hydrogen storage material is obtained after one cycle of activation.

[0011] Preferably, the preparation method of the lanthanum vanadate is as follows:

[0012] A lanthanum source, a vanadium source, a complexing agent and deionized water are mixed, and a powder is prepared by spray drying, and then the lanthanum vanadate is obtained after high-temperature sintering;

[0013] The temperature of the high-temperature sintering is 200-600 °C, and the time is 3-12 h.

[0014] The present invention discloses a method for preparing a composite hydrogen storage material by using lanthanum vanadate prepared by spray drying as an additive, ball-milling and blending it with magnesium hydride under hydrogen pressure and then performing one cycle of hydrogen absorption and desorption activation. It has been found through experiments that the lanthanum vanadate prepared by this method contains oxygen vacancies and is in-situ converted into VH x (x ≤ 2) and La4H 12.19 , and during the hydrogen absorption and desorption process, V will react with VH xConvert to each other and act as a "hydrogen pump" to induce hydrogen absorption and desorption of Mg / MgH2; while La4H 12.19 has a high hydrogen diffusion coefficient (lanthanum hydride is ~10 -11 m 2 s -1 level, magnesium hydride is ~10 -16 m 2 s -1 level), can act as a hydrogen diffusion channel. With the mutual cooperation of the two active catalytic substances, the composite hydrogen storage material prepared by the present invention has a lower initial hydrogen desorption temperature; has a low initial hydrogen absorption temperature and can absorb hydrogen at room temperature; has faster hydrogen desorption kinetics and hydrogen absorption kinetics; and has more excellent cycle stability.

[0015] It was found through experiments that if magnesium hydride is directly blended with the above two active substances and then ball-milled and activated, rather than obtained by the in-situ transformation method in this application, the performance of the prepared composite hydrogen storage material will deteriorate, especially the cycle stability will become worse.

[0016] Compared with adding lanthanum hydride alone or adding VH alone to magnesium hydride x , in this example, lanthanum vanadate is added alone and in-situ transformed into VH x and La4H 12.19 . The prepared composite hydrogen storage material has both a low initial hydrogen desorption temperature and excellent cycle stability.

[0017] It was also found through experiments that when lanthanum vanadate is prepared by the spray drying method, the subsequent high-temperature sintering temperature has a crucial influence on the microscopic morphology of the prepared lanthanum vanadate, and further affects its activation performance for magnesium hydride.

[0018] When the high-temperature sintering temperature is relatively low (200 °C), the product is only a smooth spherical structure, only has a primary structure, and is amorphous; when the temperature rises to 300 - 400 °C, the product also has a spherical structure, but the spherical surface is relatively rough; when the temperature rises to 500 - 600 °C, the prepared LaVO4 all shows a secondary micron spherical structure. Moreover, when the sintering temperature is 500 °C, the size of the prepared LaVO4 micron balls is relatively small, and the spherical structure is more dense and complete.

[0019] Preferably, the high-temperature sintering temperature is 500 - 600 °C; more preferably, the high-temperature sintering temperature is 500 °C. It was found through experiments that by using the continuously optimized high-temperature sintering temperature to prepare lanthanum vanadate, the hydrogen storage performance of the finally prepared composite hydrogen storage material added with lanthanum vanadate is continuously improved.

[0020] The said spray drying method can adopt the conventional technological process in the field.

[0021] The complexing agent is selected from common types in the art such as citric acid, ethylenediaminetetraacetic acid, sodium hexametaphosphate, etc. The concentration of the complexing agent in the raw material liquid is 0.2 - 0.4 mol / L.

[0022] Preferably, the mass ratio of magnesium hydride to lanthanum vanadate is (80 - 95):(5 - 20); more preferably 85:15.

[0023] It is found through experiments that with the continuous optimization of the mass ratio of the two, the hydrogen storage performance of the finally prepared composite hydrogen storage material is continuously improved; especially when the mass ratio of the two is 85:15, the finally prepared composite hydrogen storage material system has a lower hydrogen release temperature and a relatively higher hydrogen release capacity.

[0024] For the ball milling, the rotation speed is 300 - 500 revolutions per minute, the ball-to-material ratio is 120 - 180:1, the time is 6 - 18 h, and the atmosphere is selected from hydrogen.

[0025] For the first cycle activation, the reactor is evacuated, heated to not less than 400 °C, and then cooled to room temperature; hydrogen is filled into the reactor until the pressure is 3 - 10 MPa, and then heated to 200 - 400 °C and kept warm for at least 1 hour to obtain the magnesium hydride-based hydrogen storage material.

[0026] The present invention also discloses a magnesium hydride-based hydrogen storage material prepared according to the above method. The initial hydrogen release temperature is 185 - 212 °C, the initial hydrogen absorption temperature is room temperature (room temperature is generally regarded as 25 °C, and when the summer temperature is higher, it is regarded as 30 °C), and the hydrogen release amount at 300 °C is not less than 4.7 wt%. Under the optimal conditions, the prepared magnesium hydride-based hydrogen storage material has an initial hydrogen release temperature of 185 °C; after heating to 250 °C and then keeping warm for 3 minutes, 5.7 wt% H2 can be released. The hydrogen release rate is 170 times that of the original magnesium hydride under the same conditions, and 5.7 wt% H2 can be absorbed within 3 minutes under the conditions of 150 °C / 5 MPa H2. After 50 cycles, the hydrogen release amount is 5.2 wt% H2, and the capacity retention rate is 91%, showing excellent cycle stability.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] The present invention discloses a preparation method of a magnesium hydride-based hydrogen storage material with in-situ introduction of hydrogen pump and hydrogen channel catalytic substances, which is simple, controllable, low-cost, and suitable for large-scale industrial production. The prepared composite hydrogen storage material system in-situ introduces two active catalysts that can act as hydrogen pumps and hydrogen channels, greatly improving the hydrogen absorption and release kinetics of MgH2, obtaining a composite hydrogen storage material with low hydrogen release / absorption temperature, fast hydrogen release / absorption kinetics, and high cycle stability, and still having a hydrogen storage capacity of more than 5.2 wt% after 50 cycles. Description of the Drawings

[0029] Figure 1 SEM images of LaVO4 prepared for Examples 1-5 respectively;

[0030] Figure 2 SEM image of LaVO4 prepared for Example 1 and the corresponding EDS distribution maps of La, V, and O elements;

[0031] Figure 3 XRD patterns of LaVO4 prepared for Examples 1-5 respectively;

[0032] Figure 4 XPS spectrum of O element in LaVO4 prepared for Example 1;

[0033] Figure 5 EPR (electron paramagnetic resonance spectrum) pattern of LaVO4 prepared for Example 1;

[0034] Figure 6 Hydrogen desorption performance curves with temperature of the products prepared for Comparative Example 1 and Examples 1-5 respectively;

[0035] Figure 7 Hydrogen desorption performance curves with temperature and hydrogen absorption curves with temperature of the products prepared for Comparative Example 1, Example 1 and Examples 6-8 respectively;

[0036] Figure 8 Isothermal hydrogen desorption curves (a) of the composite hydrogen storage material prepared for Example 8 at 210 °C, 230 °C, and 250 °C respectively, and the hydrogen desorption curve of the product prepared for Comparative Example 1 is given for comparison; isothermal hydrogen absorption curves (b) of the composite hydrogen storage material prepared for Example 8 at 50 °C, 100 °C, and 150 °C respectively, and the hydrogen absorption curve of the product prepared for Comparative Example 1 is given for comparison;

[0037] Figure 9 Hydrogen desorption cycle curve with temperature of the composite hydrogen storage material prepared for Example 8;

[0038] Figure 10 XRD patterns of the ball-milled product prepared for Example 8, the samples after heating the ball-milled product to 250 °C, 300 °C, 350 °C, and 400 °C respectively, the finally prepared composite hydrogen storage material, and the sample after fifty hydrogen absorption cycles;

[0039] Figure 11 XPS spectra of V element in the ball-milled product, the final product, and the sample after fifty hydrogen absorption cycles of the final product prepared for Example 8;

[0040] Figure 12 Hydrogen desorption diagrams with temperature of the products prepared for Example 8 and Comparative Example 2 respectively. Detailed implementation manners

[0041] The specific implementation methods of the present invention will be further described below in conjunction with examples. It should be noted here that the specific implementation methods described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the protection scope of the present invention.

[0042] For the operating methods without specific conditions noted in the following examples, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0043] Example 1

[0044] 23.7 g of lanthanum acetate, 8.8 g of vanadium acetate, and 31.5 g of citric acid were added to 0.5 L of deionized water. The solution was mechanically stirred at room temperature for 1 h to make it fully uniform, and then connected to a spray dryer. The solution was sent to the nozzle by a peristaltic pump, and pyrolyzed by spraying under the action of high-temperature and high-pressure gas to obtain a precursor. During the spray drying process, the inlet and outlet temperatures were set at 230 °C and 100 °C respectively, and the speed of the peristaltic pump was 1 L / h. The obtained precursor was collected in a corundum crucible and placed in a box furnace for sintering treatment at 500 °C for 5 h to obtain lanthanum vanadate (LaVO4). The sintering treatment atmosphere was air, which was continuously pumped in by a blower. The heating rate was 3 °C / min, and the cooling was carried out by furnace cooling.

[0045] 80 wt% of MgH2 and 20 wt% of LaVO4 were added to the ball milling tank, the ball-to-material ratio was 150:1, the ball milling atmosphere was 5 MPa of hydrogen, and the ball milling was carried out at a rotation speed of 500 revolutions per minute for 12 h to obtain a ball milled product. Under the condition of an initial vacuum of 1×10 -3 Torr, the ball milled product was heated to 400 °C with the temperature, and after cooling to room temperature, hydrogen was filled into the ball milling tank until the pressure was 5 MPa, and then heated to 250 °C and kept warm for 1 h to obtain a composite hydrogen storage material, and the product was denoted as MgH2 + 20 wt% LaVO4 - 500 °C.

[0046] Example 2

[0047] The preparation process was basically the same as that of Example 1, except that when preparing LaVO4, the sintering temperature was replaced with 200 °C and the holding time remained unchanged, and the product was denoted as MgH2 + 20 wt% LaVO4 - 200 °C.

[0048] Example 3

[0049] The preparation process was basically the same as that of Example 1, except that when preparing LaVO4, the sintering temperature was replaced with 300 °C and the holding time remained unchanged, and the product was denoted as MgH2 + 20 wt% LaVO4 - 300 °C.

[0050] Example 4

[0051] The preparation process is basically the same as that of Example 1, except that when preparing LaVO4, the sintering temperature is replaced with 400 °C and the heat preservation time remains unchanged. The product is denoted as MgH2+20wt%LaVO4-400 °C.

[0052] Example 5

[0053] The preparation process is basically the same as that of Example 1, except that when preparing LaVO4, the sintering temperature is replaced with 600 °C and the heat preservation time remains unchanged. The product is denoted as MgH2+20wt%LaVO4-600 °C.

[0054] Figure 1 SEM images of LaVO4 prepared for Examples 1-5 respectively. In the figures, (a) is LaVO4 prepared at a sintering temperature of 200 °C (Example 2), (b) is LaVO4 prepared at a sintering temperature of 300 °C (Example 3), (c) is LaVO4 prepared at a sintering temperature of 400 °C (Example 4), (d) is LaVO4 prepared at a sintering temperature of 500 °C (Example 1), and (e) is LaVO4 prepared at a sintering temperature of 600 °C (Example 5). By comparison, it is found that the LaVO4 prepared in Example 2 has a smooth spherical structure with a radius of several micrometers. The LaVO4 prepared in Examples 3 and 4 also has a spherical structure, but the spherical surface is relatively rough. The LaVO4 prepared in Examples 1 and 5 both exhibit a secondary micro-spherical structure, and the size of the micro-spheres of LaVO4 prepared in Example 1 is relatively small, and the spherical structure is more dense and complete.

[0055] Figure 2 EDS distribution maps of La, V, and O elements in LaVO4 prepared for Example 1. The results show that the three elements of La, V, and O are evenly distributed on the lanthanum vanadate spheres.

[0056] Figure 3 XRD patterns of LaVO4 prepared for Examples 1-5 respectively. It is observed that when the sintering temperature is 200 °C, the prepared LaVO4 is amorphous; when the sintering temperature increases to 300 °C, obvious diffraction peaks appear, corresponding to P21 / nLaVO4. As the sintering temperature increases, the crystallinity gradually becomes stronger.

[0057] Figure 4 XPS spectrum of O element in LaVO4 prepared for Example 1. It can be confirmed from the figure that 531.6 eV and 530.2 eV correspond to oxygen vacancies and lattice oxygen, indicating the presence of oxygen vacancies in the prepared lanthanum vanadate.

[0058] Figure 5For the EPR spectrum of LaVO4 prepared in Example 1, it can be found that there is a pair of signal peaks in the range of 3500 - 3540 G, further confirming the existence of oxygen vacancies in the LaVO4 prepared in Example 1.

[0059] Comparative Example 1

[0060] Add MgH2 to the ball milling jar with a ball-to-material ratio of 150:1. The ball milling atmosphere is 5 MPa hydrogen, and ball mill at a speed of 500 revolutions per minute for 12 hours. Under the condition of an initial vacuum of 1×10 -3 Torr, heat the ball milled product to 400 °C with temperature increase, and after cooling to room temperature, fill the ball milling jar with hydrogen until the pressure reaches 5 MPa, then heat to 250 °C and keep it warm for 1 hour to obtain the product.

[0061] Example 6

[0062] The preparation process is basically the same as that in Example 1, except that the mass ratio of MgH2 to LaVO4 is replaced with 95:5, and the product is denoted as MgH2 + 5wt% LaVO4.

[0063] Example 7

[0064] The preparation process is basically the same as that in Example 1, except that the mass ratio of MgH2 to LaVO4 is replaced with 90:10, and the product is denoted as MgH2 + 10wt% LaVO4.

[0065] Example 8

[0066] The preparation process is basically the same as that in Example 1, except that the mass ratio of MgH2 to LaVO4 is replaced with 85:15, and the product is denoted as MgH2 + 15wt% LaVO4.

[0067] Comparative Example 2

[0068] Keep lanthanum powder in an atmosphere of 450 °C / 5.0 MPa H2 for 5 hours to obtain LaH 2.3 powder.

[0069] Weigh the raw materials VCl3 and LiH according to a molar ratio of 1:3, and then seal the raw materials in a ball milling jar for ball milling. The ball milling speed is 400 rpm and the ball milling time is 6 h. Then dissolve LiCl in the solid product with tetrahydrofuran (THF), centrifuge to collect the remaining solid, and dynamically evacuate it at room temperature for about 1 h to completely remove the residual THF. The collected black powder is VH 1.17 powder.

[0070] Mix 85wt% of MgH2, 11.5wt% LaH 2.3 , 3.5wt% of VH 1.17Add to the ball milling jar with a ball-to-material ratio of 150:1. The ball milling atmosphere is hydrogen at 5 MPa, and ball mill for 12 hours at a rotation speed of 500 revolutions per minute. Under the condition of an initial vacuum of 1×10 -3 Torr, heat the ball milled product to 400 °C with temperature increase, and after cooling to room temperature, fill the ball milling jar with hydrogen until the pressure reaches 5 MPa, then heat to 250 °C and keep it warm for 1 hour to obtain the product.

[0071] Performance test:

[0072] 1. The hydrogen desorption performance of the material is tested by the volume hydrogen desorption method during temperature increase. Desorb hydrogen under the condition of an initial vacuum of 1×10 -3 Torr, heat to 400 °C at a heating rate of 2 °C / min. The hydrogen absorption condition is to heat from room temperature to 250 °C at a heating rate of 2 °C / min under a hydrogen pressure of 5 MPa and keep it warm for 1 hour.

[0073] Figure 6 The hydrogen desorption performance curves during temperature increase of the products are respectively prepared for Comparative Example 1 and Examples 1 - 5. It can be seen that the order of the starting hydrogen desorption temperature from high to low is: Example 1 < Example 5 < Example 4 < Example 3 < Example 2 < Comparative Example 1. It can be seen that lanthanum vanadate (sintered at 500 °C) as an additive in Example 1 has the highest catalytic activity, and lanthanum vanadate prepared by sintering at 500 °C is added in the subsequent tests of adjusting the additive content. Generally speaking, the higher the sintering temperature, the higher the catalytic activity, which may be due to the improvement of the crystallinity of lanthanum vanadate prepared with the increase of the sintering temperature. However, the catalytic activity of Example 1 is higher than that of Example 5, probably because the secondary sphere size of lanthanum vanadate prepared in Example 1 is smaller and the structure is denser, thus obtaining more catalytic active sites, making the performance of Example 1 better than that of Example 5. Example 1 has the lowest starting hydrogen desorption temperature and ending hydrogen desorption temperature, which are 185 °C and 280 °C respectively. In contrast, the starting hydrogen desorption temperature of Comparative Example 1 is 290 °C, much higher than that of Example 1. The hydrogen desorption performance data during temperature increase of Comparative Example 1 and Examples 1 - 5 are listed in Table 1 below.

[0074] Table 1

[0075]

[0076] Figure 7For Comparative Example 1, Example 1, and Examples 6 - 8, the hydrogen desorption performance curves and hydrogen absorption curves of the prepared products with temperature were respectively obtained. As the addition amount of lanthanum vanadate increased from 5 wt% to 15 wt%, the initial hydrogen desorption temperature decreased from 197 °C to 185 °C. When the addition amount was further increased to 20 wt%, the initial hydrogen desorption temperature remained unchanged while the hydrogen desorption amount decreased. For hydrogen absorption, the initial hydrogen absorption temperature of Comparative Example 1 was 140 °C, while the systems with added lanthanum vanadate started hydrogen absorption from room temperature. Among them, the hydrogen absorption amount of the composite hydrogen storage material prepared in Example 1 was the highest after holding at 250 °C for 1 hour, which was 5.7 wt%, and was similar to Figure 7 the hydrogen desorption amount of this material heated to 400 °C in (a), showing high reversibility. From the hydrogen desorption and absorption curves, it can be analyzed that the optimal addition amount of lanthanum vanadate is 15 wt%. The hydrogen desorption and absorption performance data of the products prepared in Comparative Example 1, Example 1, and Examples 6 - 8 are listed in Table 2 below.

[0077] Table 2

[0078]

[0079] 2. The hydrogen desorption and absorption performances of the materials at different temperatures were tested by the volumetric hydrogen desorption method. The hydrogen desorption test conditions were heating to 210 °C, 230 °C, and 250 °C at a heating rate of 10 °C / min under an initial vacuum of 1×10 -3 Torr, and then holding at the preset temperature for 25 minutes. The hydrogen absorption test conditions were heating to 50 °C, 100 °C, and 150 °C at a heating rate of 10 °C / min under an initial vacuum of 1×10 -3 Torr, and then instantaneously applying a hydrogen pressure of 5 MPa to obtain the isothermal hydrogen absorption curve.

[0080] Figure 8 In (a) are the isothermal hydrogen desorption curves of the composite hydrogen storage material prepared in Example 8 at 210 °C, 230 °C, and 250 °C, and the hydrogen desorption curve of the product prepared in Comparative Example 1 is given for comparison. As Figure 8 shown, MgH2 - 15 wt% LaVO4 had released 5.4 wt% H2 when heated to 250 °C, and the capacity reached a stable value of 5.7 wt% H2 only after holding at this temperature for 3 minutes. While MgH2 prepared in Comparative Example 1 basically did not release hydrogen under the same conditions. MgH2 - 15 wt% LaVO4 released 3.0 wt% H2 and 5.2 wt% H2 respectively when held at the lower holding temperatures of 210 °C and 230 °C for 25 minutes.

[0081] For hydrogen absorption ( Figure 8In Figure (b), MgH2-15wt% LaVO4 absorbs 3.2wt% H2 after being held at a temperature as low as 50 °C for 30 minutes; it can absorb 4.9wt% H2 after being held at 100 °C for only 20 minutes; and it can absorb 5.7wt% H2 after being held at 150 °C for 3 minutes. The above data shows that, compared with pure MgH2, the composite hydrogen storage material prepared in this example has better hydrogen desorption kinetics and hydrogen absorption kinetics.

[0082] 3. The cyclic performance of the hydrogen storage material was tested by the volumetric hydrogen desorption method. The hydrogen desorption process was as follows: hydrogen desorption was carried out under the condition of an initial vacuum of 1×10 -3 Torr, and it was heated to 400 °C at a heating rate of 2 °C / min. The hydrogen absorption process was as follows: under a hydrogen pressure of 5 MPa, it was heated from room temperature to 250 °C at a heating rate of 2 °C / min and held for 1 hour.

[0083] Figure 9 Figure 9 shows the cyclic hydrogen desorption curve of the composite hydrogen storage material prepared in Example 8. After 50 cycles, the hydrogen desorption amount was 5.2wt% H2. Compared with the hydrogen desorption amount of 5.7wt% H2 in the first hydrogen desorption, the capacity retention rate was 91%. This shows that the composite hydrogen storage material prepared in this example has high cyclic stability.

[0084] Figure 10 Figure 13 shows the XRD patterns of the ball-milled products prepared in Example 8 heated to 250 °C, 300 °C, 350 °C, 400 °C, the finally prepared composite hydrogen storage material, and the sample after 50 hydrogen absorptions. It was observed that only the diffraction peaks of MgH2 were observed in the ball-milled samples, which may be because LaVO4 exists in an amorphous state or has a relatively small size. When heating started, hydrogen was desorbed from the ball-milled products, and the diffraction peaks of Mg appeared in the products; when the ball-milled products were heated to 400 °C, La4H 12.19 appeared in the products, which may be derived from the reaction between MgH2 and LaVO4. In addition, there were weak diffraction peaks of MgO, which may also be reaction products. In the composite hydrogen storage material prepared in Example 8 (after one cycle of activation), La4H 12.19 still existed stably, and Mg also absorbed hydrogen to be converted into MgH2. The diffraction peaks of the composite hydrogen storage material were basically the same before and after 50 hydrogen absorptions. No V-containing substances were observed in the XRD patterns at each stage. Therefore, other characterization methods are needed to show the existence form of V-based substances.

[0085] Figure 11 Figure 21 shows the XPS spectra of V elements in the ball-milled products, the final products, and the samples after 50 hydrogen absorptions of the final products prepared in Example 8. It was observed that the spin-orbit peaks of V at 525.1 eV and 517.2 eV in the ball-milled products corresponded to VO4 of LaVO4 3-, the spin - orbit peaks at 520.6 eV and 513.2 eV correspond to V2O3, indicating that LaVO4 is partially reduced. For the final product after one - cycle activation, the spin - orbit peaks at 520.3 eV and 512.8 eV in the XPS spectrum of V correspond to V metal, indicating that the oxide is completely reduced to V metal only after hydrogen release. After fifty hydrogen - absorption cycles, the XPS peaks of V are basically the same as those after one - time hydrogen release, indicating that V may still exist in the form of V metal after hydrogen absorption. However, XPS characterization cannot accurately distinguish vanadium and vanadium hydride because the sample needs to be under vacuum before detection, and this vacuum degree generally causes vanadium hydride to dehydrogenate. Vanadium can absorb hydrogen at room temperature (Luo Long, Wu Wenyuan, Bian Xue, et al. Research progress of vanadium - based solid - solution hydrogen storage alloys [J]. Rare Metals, 2017, 41(11): 1265 - 1272.), and under the hydrogen - absorption conditions applied in this invention, vanadium is easily converted into vanadium hydride. And vanadium hydride will form vanadium metal at 177 °C (S. Kumar, A. Jain, T. Ichikawa, Y. Kojima and G. K. Dey, Development of vanadium - based hydrogen storage material: A review, Renewable & Sustainable Energy Reviews. 72(2017): 791 - 800.). Therefore, it can be considered that the V - based substance in the prepared product exists in the form of vanadium hydride and is converted into vanadium metal after hydrogen release. V will x interconvert with VH

[0086] Figure 12 are the hydrogen - release - temperature - dependent diagrams of the products prepared in Example 8 and Comparative Example 2 respectively. It can be seen that the initial hydrogen - release temperature of the composite hydrogen - storage material prepared in Example 8 is significantly lower than that of MgH2 doped with 11.5 wt% LaH 2.3 and 3.5 wt% VH 1.17 , with a difference of 25 °C. The first - stage hydrogen - release capacity and the second - stage hydrogen - release capacity of MgH2 + 15 wt% LaVO4 are both 5.7 wt%, with basically no attenuation, while

[0087] MgH2 + 11.5 wt% LaH 2.3 + 3.5 wt% VH 1.17The primary and secondary hydrogen release amounts were 5.7wt% and 5.5wt% respectively, showing relatively poor cyclic stability. This proves that the lanthanum hydride and vanadium hydride obtained in situ after adding LaVO4 and undergoing one cycle activation in the present invention have higher catalytic activity than the externally added lanthanum hydride and vanadium hydride composite catalyst, and are more conducive to improving the hydrogen release performance of MgH2. Among them, lanthanum hydride has a higher hydrogen diffusion coefficient, so the in-situ La4H 12.19 It can act as a hydrogen diffusion channel. After releasing hydrogen, vanadium hydride will turn into vanadium element. In the continuous circulation process, it can act as a hydrogen pump to transport hydrogen to MgH2. The two work together to improve the hydrogen storage performance of MgH2.

[0088] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. The above description of the present invention using specific examples is only used to help understand the present invention and is not intended to limit the present invention. Those skilled in the art of the present invention can also make several simple deductions, modifications, substitutions or combinations based on the concept of the present invention. These deductions, modifications, substitutions or combinations also fall within the scope of the claims of the present invention.

Claims

1. A preparation method of a magnesium hydride-based hydrogen storage material, characterized in that: Raw materials including magnesium hydride and lanthanum vanadate are ball-milled and mixed, and a magnesium hydride-based hydrogen storage material is obtained after one cycle of activation. The preparation method of the lanthanum vanadate is as follows: A lanthanum source, a vanadium source, a complexing agent and deionized water are mixed, and a powder is prepared by spray drying, and then the lanthanum vanadate is obtained after high-temperature sintering. The temperature of the high-temperature sintering is 200-600 °C, and the heat preservation time is 3-12 h.

2. The preparation method of the magnesium hydride-based hydrogen storage material according to claim 1, wherein The temperature of the high-temperature sintering is 500-600 °C.

3. The preparation method of the magnesium hydride-based hydrogen storage material according to claim 1, characterized in that, The temperature of the high-temperature sintering is 500 °C.

4. The preparation method of the magnesium hydride-based hydrogen storage material according to claim 1, characterized in that, The mass ratio of magnesium hydride to lanthanum vanadate is (80-95):(5-20).

5. The preparation method of the magnesium hydride-based hydrogen storage material according to claim 1, characterized in that, The mass ratio of magnesium hydride to lanthanum vanadate is 85:

15.

6. The preparation method of the magnesium hydride-based hydrogen storage material according to claim 1, wherein For the ball milling, the rotation speed is 300-500 revolutions per minute, the ball-to-material ratio is 120-180:1, the time is 6-18 h, and the atmosphere is selected from hydrogen.

7. The preparation method of the magnesium hydride-based hydrogen storage material according to claim 1, characterized in that, For the one-cycle activation, the reactor is evacuated, heated to not less than 400 °C, and then cooled to room temperature; hydrogen is filled into the reactor until the pressure is 3-10 MPa, heated to 200-400 °C, and kept warm for at least 1 hour to obtain a magnesium hydride-based hydrogen storage material.

8. A magnesium hydride-based hydrogen storage material prepared by the method according to any one of claims 1-7.

9. The magnesium hydride-based hydrogen storage material according to claim 8, characterized in that, The initial hydrogen release temperature is 185-212 °C, the initial hydrogen absorption temperature is room temperature, and the hydrogen release amount at 300 °C is not less than 4.7 wt%.

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