A2B7 type Y-Mg-Ni series hydrogen storage material and preparation method thereof

Abstract

The invention provides an A2B7 type Y-Mg-Ni series hydrogen storage material and a preparation method thereof, and belongs to the technical field of hydrogen storage materials. The general formula of the hydrogen storage material is Y1-a-bMgaCbNicDd, 0.05 < = a < = 0.25, 0 < = b < = 0.2, 3.25 < = c < = 3.45, 0 < = d < = 0.2, C is selected from at least one of Ce, Pr, Nd, Sm and Gd, and D is selected from at least one of Mn, Mo, Fe, Ti, Si and W. The pure A2B7 type hydrogen storage material is obtained by carrying out element doping and process modification on the hydrogen storage alloy material, so that the hydrogen storage capacity and hydrogen absorption and desorption cycle stability of the rare earth hydrogen storage alloy can be simultaneously improved, and the hydrogen absorption and desorption plateau pressure can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen storage materials, and more specifically to a Y-Mg-Ni-based hydrogen storage material of the A2B7 type and a preparation method thereof. Background Art

[0002] Hydrogen energy has occupied an important position in the new energy field due to its excellent environmental protection characteristics and high energy density. As a clean energy source, hydrogen only produces water after combustion and does not emit any harmful gases, including greenhouse gases and other pollutants. Therefore, its impact on the environment is almost negligible. In addition, hydrogen has an extremely high energy density, which is three times that of gasoline. This means that under the same mass, the energy released by hydrogen far exceeds that of traditional fossil fuels, giving it significant advantages in application scenarios requiring high energy output, such as heavy transportation and industrial processes. These characteristics make hydrogen energy one of the important energy sources for achieving energy transformation and combating climate change. However, in the entire hydrogen energy industrial chain, the storage and transportation of hydrogen remain the bottleneck restricting its development.

[0003] Solid-state hydrogen storage materials, as a hydrogen storage method with high safety and high volume density, have been widely regarded as an important way to break through the development bottleneck of the hydrogen energy industry in the future. Among many hydrogen storage materials, rare earth hydrogen storage materials have attracted much attention due to their easy activation and excellent kinetic properties. Although traditional AB5-type rare earth hydrogen storage materials have achieved large-scale applications, their relatively low theoretical hydrogen storage capacity (1.4 wt%) can no longer meet the current growing application requirements. Most of the research on La-Mg / Y-Ni-based rare earth hydrogen storage materials is aimed at electrochemical applications, that is, the negative electrode materials of nickel-metal hydride batteries, and they are rarely used in solid-state hydrogen storage devices. Moreover, the relative atomic mass of La is 138.9, which is much larger than those of Y (88.9) and Mg (24.3). This leads to a relatively low hydrogen storage capacity of La-Mg / Y-Ni-based hydrogen storage alloys. Compared with AB5-type alloys, the advantages are not obvious, and the reversible cycle capacity is relatively low.

[0004] Therefore, there is an urgent need for a rare earth hydrogen storage material with high hydrogen storage capacity, high hydrogen storage cycle stability, and high hydrogen absorption and desorption plateau pressure to promote its further application in solid-state hydrogen storage devices. Summary of the Invention

[0005] The purpose of the present invention is to improve the hydrogen storage capacity, cycle stability of existing rare earth-based hydrogen storage alloys, and the defect that they cannot have a relatively high hydrogen absorption and desorption plateau pressure. Element doping and process modification are carried out on the hydrogen storage alloy material to simultaneously improve the hydrogen storage capacity, hydrogen absorption and desorption cycle stability, and hydrogen absorption and desorption plateau pressure of the rare earth-based hydrogen storage alloy.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: In the first aspect of the present invention, a Y-Mg-Ni-based hydrogen storage material of the A2B7 type is provided. The structural general formula of the hydrogen storage material is: Y 1-a-b Mg a C b Ni c D d , where 0.05 ≤ a ≤ 0.25, 0 ≤ b ≤ 0.2, 3.25 ≤ c ≤ 3.45, 0 ≤ d ≤ 0.2, C is selected from at least one of Ce, Pr, Nd, Sm, and Gd, and D is selected from at least one of Mn, Mo, Fe, Ti, Si, and W.

[0007] As an embodiment of the present invention, the hydrogen storage material includes a (Y,Mg)2Ni7-2H type phase and a (Y,Mg)2Ni7-3R type phase.

[0008] As an embodiment of the present invention, the ratio of the (Y,Mg)2Ni7-2H type phase to the (Y,Mg)2Ni7-3R type phase is 1:(1 to 5).

[0009] As an embodiment of the present invention, in the structural general formula Y 1-a-b Mg a C b Ni c D d , 0.08 ≤ a ≤ 0.15.

[0010] As an embodiment of the present invention, in the structural general formula Y 1-a-b Mg a C b Ni c D d , 0 ≤ b ≤ 0.1.

[0011] As an embodiment of the present invention, in the structural general formula Y 1-a-b Mg a C b Ni c D d , 3.40 ≤ c ≤ 3.45.

[0012] As an embodiment of the present invention, in the structural general formula Y 1-a-b Mg a C b Ni c D d , 0.05 ≤ d ≤ 0.1.

[0013] As an embodiment of the present invention, in the structural general formula Y 1-a-b Mg a C b Ni c D dAmong them, 0 < b / a ≤ 0.5.

[0014] As an embodiment of the present invention, the structural general formula Y 1-a-b Mg a C b Ni c D d Among them, C is Ce or Pr, and D is selected from at least one of Mo, Ti, and W.

[0015] As an embodiment of the present invention, the hydrogen storage capacity of the hydrogen storage material at 25 °C and 5 MPa pressure is ≥ 1.75 wt%; the effective hydrogen release amount at a hydrogen release pressure of more than 0.1 MPa is ≥ 1.63 wt%; after 200 hydrogen absorption and release cycles, the capacity retention rate is ≥ 95%.

[0016] In the second aspect of the present invention, there is provided a preparation method of the A2B7 type Y-Mg-Ni series hydrogen storage material described in the first aspect of the present invention, including the following steps: after proportioning according to the stoichiometric ratio, melting to obtain a cast alloy, and annealing to obtain the A2B7 type Y-Mg-Ni series hydrogen storage material.

[0017] As an embodiment of the present invention, the raw materials for proportioning include metal raw materials or alloy raw materials.

[0018] As an embodiment of the present invention, the annealing process is as follows: first, heat up to 600 °C at a heating rate of 5 - 10 °C / min; then heat up to 750 °C - 850 °C at a heating rate of 1 - 3 °C / min and hold for 0.5 - 1.5 h; then heat up to 925 °C - 1050 °C at a heating rate of 1 - 3 °C / min and hold for 6 h - 36 h; finally, cool down.

[0019] Compared with the prior art, the beneficial effects of the present invention are: The present invention improves the hydrogen storage capacity, the hydrogen absorption and release cycle stability, and the hydrogen absorption and release platform pressure of the rare earth-based hydrogen storage alloy by element doping and process modification of the hydrogen storage alloy material. Description of the Drawings

[0020] Figure 1 It is the XRD spectrum of the A2B7 type Y-Mg-Ni series hydrogen storage material prepared in Example 1 of the present invention. Detailed Embodiments

[0021] To better illustrate the purpose, technical solutions, and advantages of the present invention, the following will further illustrate the present invention with specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field. Unless otherwise specified, the reagents and materials used in the present invention are commercially available.

[0022] In the present invention, among the technical features described in an open - ended manner, it includes a closed - ended technical solution composed of the listed features, and also includes an open - ended technical solution containing the listed features.

[0023] In the present invention, regarding numerical ranges, unless otherwise specified, the above - mentioned numerical ranges are considered continuous, and include the minimum value and the maximum value of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum value and the maximum value of the range. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub - ranges subsumed therein.

[0024] Reagents or instruments used in the present invention that are not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0025] In a first aspect of the present invention, an embodiment of the present invention provides a hydrogen storage material of the Y - Mg - Ni system of the A2B7 type. The structural general formula of the hydrogen storage material is: Y 1-a-b Mg a C b Ni c D d , where 0.05 ≤ a ≤ 0.25, 0 ≤ b ≤ 0.2, 3.25 ≤ c ≤ 3.45, 0 ≤ d ≤ 0.2, C is selected from at least one of Ce, Pr, Nd, Sm, Gd, and D is selected from at least one of Mn, Mo, Fe, Ti, Si, W.

[0026] The present invention uses the relatively small atomic radii of Y and Mg to reduce the unit cell volume of the Y - Mg - Ni - based hydrogen storage material alloy, which can increase the hydrogen absorption and desorption plateau pressure of the hydrogen storage material; at the same time, the relative atomic masses of Y and Mg are relatively small, and under the same ratio, the Y - Mg - Ni - based alloy with Y and Mg as the substrate has a higher hydrogen storage capacity. At the same time, further doping other rare earth elements on the A side (Y - Mg phase) and doping specific metal elements on the B side (Ni phase) can also improve the alloy phase structure of the hydrogen storage material, forming (Y,Mg)2Ni7 - 2H - type phase and (Y,Mg)2Ni7 - 3R - type phase in the hydrogen storage material, significantly enhancing the hydrogen absorption capacity and cycle stability of the hydrogen storage material.

[0027] In some embodiments of the present invention, the hydrogen storage material includes a (Y,Mg)2Ni7 - 2H - type phase and a (Y,Mg)2Ni7 - 3R - type phase.

[0028] Among them, in the rare - earth superlattice structure phase, the structural stability of each phase is (Y,Mg)6Ni 24 >(Y,Mg)5Ni 19(Y,Mg)2Ni7 > (Y,Mg)Ni3 in decreasing order, but the theoretical hydrogen storage capacity shows the opposite trend, i.e., (Y,Mg)6Ni 24 (Y,Mg)5Ni 19 (Y,Mg)2Ni7 < (Y,Mg)Ni3. This property enables the (Y,Mg)2Ni7 phase to achieve an optimal balance between structural stability and hydrogen storage capacity, demonstrating excellent comprehensive hydrogen storage performance. Additionally, the superlattice structure is formed by the alternating stacking of [A2B4] and [AB5] substructures along the c-axis. Among them, the [A2B4] substructure has two crystal configurations, C14 and C15. This polymorphism leads to the simultaneous formation of the 2H-type (Y,Mg)2Ni7 phase with the P63 / mmc space group and the 3R-type (Y,Mg)2Ni7 phase with the R-3m space group during the phase formation process. The presence of the (Y,Mg)2Ni7-2H phase structure can significantly increase the hydrogen storage capacity of the hydrogen storage material; the presence of the (Y,Mg)2Ni7-3R phase structure can reduce the hydrogen absorption and desorption platform pressure. However, during the hydrogen absorption and desorption cycling process of the R-3m phase, it is prone to transform into a phase with lower symmetry (such as the monoclinic phase), resulting in capacity decay.

[0029] Therefore, by systematically regulating the type ratio and content of doping elements, the relative content of the two phases can be effectively adjusted and the unit cell structure parameters can be optimized, thereby synergistically improving the effective capacity and cycle stability of the hydrogen storage system while maintaining an appropriate reversible hydrogen absorption and desorption platform pressure.

[0030] In some embodiments of the present invention, the ratio of the (Y,Mg)2Ni7-2H phase to the (Y,Mg)2Ni7-3R phase is 1:(1~5).

[0031] In some embodiments of the present invention, in the structure general formula Y 1-a-b Mg a C b Ni c D d 0.08 ≤ a ≤ 0.15.

[0032] In some embodiments of the present invention, in the structure general formula Y 1-a-b Mg a C b Ni c D d 0 ≤ b ≤ 0.1.

[0033] In some embodiments of the present invention, in the structure general formula Y 1-a-b Mg a C b Ni c D d 3.40 ≤ c ≤ 3.45.

[0034] In some embodiments of the present invention, the general structural formula Y 1-a-b Mg a C b Ni c D d , 0.05≤d≤0.1.

[0035] In some embodiments of the present invention, the general structural formula Y 1-a-b Mg a C b Ni c D d Medium, 0

[0036] In some embodiments of the present invention, the general structural formula Y 1-a-b Mg a C b Ni c D d In the embodiment, C is Ce or Pr, and D is selected from at least one of Mn, Ti, and W. The combination of appropriate doping elements can further improve the effective hydrogen release capacity of the hydrogen storage alloy material.

[0037] The A2B7 type Y-Mg-Ni series hydrogen storage material of the present invention has a hydrogen storage capacity of ≥1.75wt% at 25°C and 5MPa pressure; an effective hydrogen release amount of ≥1.63wt% at a hydrogen release pressure of more than 0.1MPa; and a capacity retention rate of ≥95% after 200 cycles of hydrogen absorption and desorption.

[0038] In a second aspect of the present invention, an embodiment of the present invention further provides a method for preparing the A2B7 type Y-Mg-Ni series hydrogen storage material according to the first aspect of the present invention, comprising the following steps: After the ingredients are prepared according to the stoichiometric ratio, the cast alloy is obtained by smelting, and the A2B7 type Y-Mg-Ni series hydrogen storage material is obtained after annealing.

[0039] In the present invention, the raw materials used for the ingredients are not limited, and high-purity metal raw materials or alloy raw materials can be used, as long as the structural formula Y 1-a-b Mg a C b Ni c D d of hydrogen storage material.

[0040] ​In the present invention, the smelting process is not limited either, as long as the elements in the hydrogen storage material alloy can be evenly distributed.

[0041] In some embodiments of the present invention, the annealing process is as follows: first, heat up to 600 °C at a heating rate of 5 - 10 °C / min; then heat up to 750 - 850 °C at a heating rate of 1 - 3 °C / min and hold for 0.5 - 1.5 h; then heat up to 925 - 1050 °C at a heating rate of 1 - 3 °C / min and hold for 6 - 36 h; finally, cool down.

[0042] In the initial stage, a relatively fast heating rate is adopted to inhibit the volatilization of Mg element, and the heat preservation treatment is used to achieve the dynamic balance of magnesium element in the system. In the subsequent heating process, the heating rate needs to be strictly controlled: appropriately delaying the heating is beneficial to promoting the full dissociation of the A2B7-type phase in the as-cast alloy, and at the same time ensuring that it is completely transformed into the target A2B7-type phase through the peritectic reaction with the AB5-type phase and achieving sufficient grain growth. If the heating rate is too high, the reaction kinetics will be insufficient and the nucleation density will be reduced; if the rate is too low, it may cause secondary crystallization to form impurity phases such as A5B19-type. The temperature control needs to be maintained in the range of 925 - 1050 °C. When the treatment temperature is lower than the critical lower limit, the original impurity phase cannot be completely eliminated through the peritectic reaction; if it exceeds the upper limit, it may cause the reverse transformation of the A2B7-type phase into the A5B19-type phase or decomposition into the AB5-type phase.

[0043] After multi-stage heat preservation, during heat preservation, some non-equilibrium defects are annealed and repaired through atomic diffusion, but an appropriate amount of "functional defects" (such as low-density dislocations, nanoscale vacancy clusters) are retained to improve the stability of the hydride and the stability of the hydrogen absorption and desorption cycle. Therefore, through this progressive heating regulation, the balance optimization between the hydrogen storage capacity and the stability of the hydrogen absorption and desorption cycle of the hydrogen storage material can be achieved.

[0044] The following are specific embodiments of the present invention.

[0045] Example 1 This example provides a Y-Mg-Ni-based hydrogen storage material of the A2B7 type, with the structural general formula of Y 0.75 Mg 0.13 Ce 0.12 Ni 3.33 Mn 0.12 , and the preparation method includes the following steps: S1: According to the chemical structural general formula Y 0.75 Mg 0.13 Ce 0.12 Ni 3.33 Mn 0.12, weigh the metallic elements of Y, Mg, Ce, Ni, and Mn (with purity above 99.9% for all). It should be noted that considering the volatility of Mg, the actual addition amount of Mg needs to be 50 wt% more than the theoretical amount. After mixing the weighed metallic element raw materials evenly to obtain the mixed raw materials, place them in a quartz crucible in an induction melting furnace. After evacuating to a vacuum degree < 0.005 Pa, carry out induction melting under the protection of an argon atmosphere at 0.5 bar. Pour the molten alloy into a copper mold for cooling to obtain the as-cast alloy; S2: For the as-cast alloy prepared in step S1, use an electric grinder to polish the surface of the melted as-cast alloy until it is shiny, removing the oxide layer on the surface of the alloy ingot. Then wrap it with tantalum foil and put it into a quartz tube. Evacuate to 1×10 -3 Pa, introduce argon to 0.5 bar and seal it, and then place it in a muffle furnace for annealing according to the following process: ① Heat from room temperature to 600 °C at a heating rate of 5 °C / min → ② Then heat to 800 °C at a heating rate of 1 °C / min and hold for 1 h → ③ Then heat to 950 °C at a heating rate of 1 °C / min and hold for 12 h → ④ Subsequently, cool naturally to room temperature (below 30 °C) and take it out to obtain the A2B7-type Y-Mg-Ni-based hydrogen storage material; And conduct X-ray powder diffractometer (XRD) tests on the prepared hydrogen storage material to analyze the phase structure composition in the hydrogen storage material alloy. Use the Rietveld method to fit the XRD test results, and the fitting results are shown in Figure 1 , and the phase content, unit cell parameters, etc. can be obtained from the figure. For details, see Table 1.

[0046] Examples 2 to 14, Comparative Examples 1 to 4 Provide a series of A2B7-type Y-Mg-Ni-based hydrogen storage materials, and prepare them by referring to the method of Example 1. The differences from Example 1 are as follows: There are slight differences in the types and amounts of elements in the structural general formula; and during the annealing treatment process, there are slight differences in the heating rate and the holding temperature of different holding sections; However, the annealing process needs to meet the following: First, heat to 600 °C at a heating rate of 5 - 10 °C / min; then heat to 750 °C - 850 °C at a heating rate of 1 - 3 °C / min and hold for 0.5 - 1.5 h; then heat to 925 °C - 1050 °C at a heating rate of 1 - 3 °C / min and hold for 6 h - 36 h; finally, carry out cooling; Similarly, conduct XRD characterization on the prepared different A2B7-type Y-Mg-Ni-based hydrogen storage materials. The phase composition and unit cell parameters of the hydrogen storage materials are shown in Table 1.

[0047] Table 1 Hydrogen storage materials Example 15 provides a hydrogen storage material of Y-Mg-Ni system with A2B7 type, and its general formula is Y 0.75 Mg 0.13 Ce 0.12 Ni 3.33 Mn 0.12 , and it is prepared by referring to the method of Example 1. The difference from Example 1 is that the annealing process in step S2 is as follows: ① Then, it is heated to 800 °C at a heating rate of 1 °C / min, and the holding time is 1 h → ② Then, it is heated to 950 °C at a heating rate of 1 °C / min and held for 12 h → ③ Subsequently, it is naturally cooled to room temperature (below 30 °C) and taken out to obtain the hydrogen storage material of Y-Mg-Ni system with A2B7 type.

[0048] Example 16 provides a hydrogen storage material of Y-Mg-Ni system with A2B7 type, and its general formula is Y 0.75 Mg 0.13 Ce 0.12 Ni 3.33 Mn 0.12 , and it is prepared by referring to the method of Example 1. The difference from Example 1 is that the annealing process in step S2 is as follows: ① It is heated from room temperature to 600 °C at a heating rate of 5 °C / min → ② Then, it is heated to 950 °C at a heating rate of 1 °C / min and held for 13 h → ③ Subsequently, it is naturally cooled to room temperature (below 30 °C) and taken out to obtain the hydrogen storage material of Y-Mg-Ni system with A2B7 type.

[0049] Performance test The hydrogen storage performance of the hydrogen storage materials of Y-Mg-Ni system with A2B7 type prepared in the above examples and comparative examples is tested. The specific test items and test methods are as follows: (1) The Sieverts method is used to first carry out hydrogen absorption activation at 25 °C and 5 MPa, and then test the PCT performance of the alloy and draw the PCT curve; first, the hydrogen storage material is activated. The activation conditions are: filling 5 MPa H2 at room temperature (25 °C), recording the change curve of pressure and time at the same time and calculating the saturated hydrogen absorption amount, and then dehydrogenating at 300 °C for 1 h. After activation is completed, the PCT curve is tested and drawn at room temperature.

[0050] The hydrogen release platform pressure, effective hydrogen release amount (the hydrogen release amount above the hydrogen release pressure of 0.1 MPa is recorded as the effective hydrogen release amount), etc. can be obtained from the PCT curve. The results are shown in Table 2 in detail.

[0051] (2) Hydrogen absorption and desorption cycle performance test: At room temperature (25 °C), introduce 5 MPa high-purity hydrogen (purity > 99.99%) into the container containing the activated sample to be tested. After the hydrogen absorption reaches saturation, quickly heat the reactor to 300 °C to release hydrogen for 50 min, then air-cool it to room temperature (25 °C) to absorb hydrogen for 30 min. Repeat this cycle 200 times and record the hydrogen absorption content. The results are shown in Table 2. In Table 2, the capacity retention rate (%) = η 200 / η0 * 100%, where η 200 represents the hydrogen absorption content of the sample to be tested during the 200th cycle of hydrogen absorption and release, and η0 represents the initial hydrogen absorption content of the sample to be tested under these hydrogen absorption and release conditions.

[0052] Table 2 The above results of the above examples and comparative examples show that: By comparing Example 14 and Comparative Example 1, when the B / A value of the alloy design is less than 3.2, using the same preparation method and heat treatment process, the phase structure of the obtained alloy is the (Y,Mg)Ni3 phase. Although it has a relatively high hydrogen storage capacity, the hydrogen release platform pressure and the effective hydrogen storage amount are low, and the cycle retention rate is only 89.1%. The reason is that the structural stability of the (Y,Mg)Ni3 phase is not as good as that of the (Y,Mg)2Ni7 phase, and it is prone to hydrogen-induced amorphization during the cycle, resulting in a decrease in capacity.

[0053] In Comparative Examples 2 - 4, it is not a pure (Y,Mg)2Ni7 phase, which leads to a reduction in the hydrogen storage capacity of the alloy and further reduces the effective hydrogen release capacity.

[0054] The results of the above examples and comparative examples show that by using the general formula design and preparation method of the present invention, a Y-Mg-Ni-based hydrogen storage alloy containing only the A2B7-type structure can be obtained. This type of hydrogen storage alloy has a hydrogen release platform pressure exceeding 0.25 MPa, an effective hydrogen release amount of more than 1.63 wt%, and excellent cycle stability, and is more suitable for use in solid-state hydrogen storage devices.

[0055] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A Y-Mg-Ni based hydrogen storage material of A2B7 type, characterized in that, The structural general formula of the hydrogen storage material is: Y 1-a- b Mg a C b Ni c D d , where 0.05 ≤ a ≤ 0.25, 0 ≤ b ≤ 0.2, 3.25 ≤ c ≤ 3.45, 0 ≤ d ≤ 0.2, C is selected from at least one of Ce, Pr, Nd, Sm, Gd, and D is selected from at least one of Mn, Mo, Fe, Ti, Si, W.

2. The A2B7 type Y-Mg-Ni based hydrogen storage material according to claim 1, characterized in that, The hydrogen storage material includes a (Y, Mg) 2 Ni 7-2H type phase and a (Y, Mg) 2 Ni 7-3R type phase.

3. The A2B7 type Y-Mg-Ni hydrogen storage material according to claim 2, characterized in that, The ratio of the (Y,Mg)2Ni7-2H phase to the (Y,Mg)2Ni7-3R phase is 1:(1~5).

4. The A2B7 type Y-Mg-Ni based hydrogen storage material according to claim 1, characterized in that, General structural formula Y 1-a- b Mg a C b Ni c D d Among them, at least one of the following characteristics is satisfied: （1）0.08≤a≤0.15； （2）0≤b≤0.1； （3）3.4≤c≤3.45； （4）0.05≤d≤0.1。 5. The A2B7 type Y-Mg-Ni based hydrogen storage material according to claim 1, characterized in that, Structural general formula Y 1-a- b Mg a C b Ni c D d where 0 < b / a ≤ 0.5 6. The A2B7-type Y-Mg-Ni hydrogen storage material according to claim 1, wherein, The general structural formula Y 1-a- b Mg a C b Ni c D d wherein C is Ce or Pr, and D is selected from at least one of Mn, Ti, and W.

7. The A2B7 type Y-Mg-Ni based hydrogen storage material according to claim 1, characterized in that, The hydrogen storage capacity of the hydrogen storage material at 25°C and 5MPa pressure is ≥1.75wt%; the effective hydrogen release capacity above the hydrogen release pressure of 0.1MPa is ≥1.63wt%; After 200 cycles of hydrogen absorption and desorption, the capacity retention rate is ≥95%.

8. The preparation method of the A2B7 type Y-Mg-Ni based hydrogen storage material according to any one of claims 1 to 7, characterized in that, The steps include: After the ingredients are prepared according to the stoichiometric ratio, the cast alloy is obtained by smelting, and the A2B7 type Y-Mg-Ni series hydrogen storage material is obtained after annealing.

9. The preparation method of the A2B7 type Y-Mg-Ni based hydrogen storage material according to claim 8, characterized in that, The raw materials of the batch include metal raw materials or alloy raw materials.

10. The preparation method of the A2B7 type Y-Mg-Ni hydrogen storage material according to claim 8, characterized in that, The annealing process is: First, heat to 600℃ at a heating rate of 5~10℃ / min; then heat to 750℃~850℃ at a heating rate of 1~3℃ / min, and keep warm for 0.5~1.5h; then heat to 925℃~1050℃ at a heating rate of 1~3℃ / min, and keep warm for 6h~36h; finally cool.

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