A highly active magnesium hydride-based composite hydrogen storage material and its preparation method

Abstract

This invention relates to the field of hydrogen storage, specifically disclosing a highly active magnesium hydride-based composite hydrogen storage material and its preparation method. The highly active magnesium hydride-based composite hydrogen storage material comprises the following components in parts by weight: 70-85 parts magnesium hydride, 10-30 parts calcium hydride, and 3-8 parts magnesium chloride. The preparation method of the highly active magnesium hydride-based composite hydrogen storage material includes the following steps: Step 1, weighing magnesium hydride, calcium hydride, and magnesium chloride according to the proportions; Step 2, ball milling the magnesium hydride, calcium hydride, and magnesium chloride powders under an inert atmosphere at a ball milling speed of 300-500 rpm. The highly active magnesium hydride-based composite hydrogen storage material and its preparation method of this invention can produce hydrogen more efficiently and rapidly while reducing dependence on the external chemical environment, and at the same time making the reaction process more stable and controllable.

Description

Technical Field

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

[0002] Magnesium hydride can produce hydrogen through hydrolysis, and it boasts a high theoretical hydrogen production capacity and environmentally friendly reaction byproducts, making it a commonly used chemical hydrogen storage material with broad application prospects in on-site hydrogen production scenarios such as portable fuel cells and emergency power supplies. However, the hydrolysis of magnesium hydride produces magnesium hydroxide, which forms a dense and continuous passivation layer on the surface of the magnesium hydride particles. This passivation layer severely hinders further contact between water molecules and the unreacted magnesium hydride particles, causing the hydrolysis reaction rate to rapidly decline. Ultimately, this results in a low hydrogen conversion rate, making it difficult to meet the demands of efficient and rapid hydrogen production in practical applications.

[0003] To address these issues, two approaches have emerged: physical modification and chemical promotion. Physical modification involves nano-sizing magnesium hydride materials using methods such as high-energy ball milling to reduce particle size and increase specific surface area, thereby shortening the diffusion path between reactants and products. However, actual tests have shown that even after ball milling, the conversion rate of magnesium hydride only improves to a limited extent.

[0004] Chemically promoted approaches mainly include two categories: one is to introduce acidic or salty substances into the hydrolysis reaction environment to inhibit or disrupt the formation and stability of the passivation layer by altering the solution's chemical environment. The other is to combine magnesium hydride with other material additives to accelerate the hydrolysis reaction.

[0005] However, the two methods mentioned above still have limitations: the former relies on the external solution environment, which increases the complexity of the system and the difficulty of operation; although the latter can improve the rate in the early stage of the reaction, it is often difficult to achieve stable control of the reaction process, and its effect on improving the overall conversion rate of magnesium hydride materials is limited. At the same time, it may affect the overall physical properties of the composite material due to compatibility issues. Summary of the Invention

[0006] The present invention aims to provide a highly active magnesium hydride-based composite hydrogen storage material and its preparation method, which can produce hydrogen more efficiently and quickly while reducing dependence on the external chemical environment, and at the same time make the reaction process more stable and controllable.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a highly active magnesium hydride-based composite hydrogen storage material, comprising the following components in parts by weight: 70-85 parts magnesium hydride, 10-30 parts calcium hydride, and 3-8 parts magnesium chloride.

[0008] A method for preparing a highly active magnesium hydride-based composite hydrogen storage material, comprising the following steps: Step 1: Weigh out magnesium hydride, calcium hydride and magnesium chloride according to the proportions; Step 2: The magnesium hydride, calcium hydride and magnesium chloride powders are ball-milled under an inert atmosphere at a speed of 300-500 rpm.

[0009] Further, in step 1, after weighing, magnesium hydride, calcium hydride and magnesium chloride are initially mixed to obtain a premix. In step 2, the premix is ​​ball-milled.

[0010] Furthermore, the mass ratio of balls to material in step 2 is (20:1) to (40:1).

[0011] Furthermore, the ball milling time is 5–10 hours.

[0012] Furthermore, the purity of magnesium hydride is greater than or equal to 95%.

[0013] Furthermore, the purity of calcium hydride is greater than or equal to 95%.

[0014] Furthermore, the magnesium chloride is anhydrous magnesium chloride.

[0015] Furthermore, the ball milling was completed in a high-purity argon atmosphere.

[0016] The beneficial effects of this plan are: 1. In the composite material of this solution, magnesium hydride, calcium hydride and magnesium chloride form a ternary composite system. During hydrolysis, calcium hydride, as a highly active component, preferentially undergoes a violent exothermic reaction with water, which can quickly generate high temperature in the micro-regions inside the material, providing strong and continuous "internal heating" for the adjacent MgH2. This provides additional activation energy for the hydrolysis of magnesium hydride in this region, which is beneficial to improving the overall reaction rate. Compared with existing composite materials, it is more suitable for improving the reaction initiation performance in low-temperature environments. Moreover, this heat comes from the active components inside the material and no longer depends on external heat sources or additives. Therefore, the initiation is faster, the thermal drive is stronger, and it is not strictly limited by the water addition rate or external conditions. The compact composite structure formed by ball milling ensures that the heat can be efficiently transferred to MgH2.

[0017] Secondly, the hydrolysis product of calcium hydride is calcium hydroxide, which has a loose structure. This physically disrupts the continuity of the magnesium hydroxide passivation layer, preventing it from completely isolating water from contacting magnesium hydride. Based on this, magnesium chloride acts as an interface regulator and product guide, producing Mg²⁺ upon contact with water. + Prefers to react with OH in the solution -The combination forms a dispersed magnesium hydroxide precipitate. This process guides the product away from the reaction interface and effectively inhibits the in-situ formation of the passivation layer. Therefore, magnesium chloride in this scheme no longer only plays an "etching" role, thus enabling the composite material in this scheme to maintain a stronger and more durable passivation resistance during hydrolysis.

[0018] 2. Simultaneously, the prolonged high-speed ball milling in this scheme allows calcium hydride and magnesium chloride to be highly dispersed in the form of nanoparticles and clusters, firmly adhering to and embedding into the surface and interparticle spaces of the magnesium hydride matrix, thus forming several "reaction micro-regions." The hydrolysis reaction in these micro-regions can be initiated simultaneously, resulting in faster and more efficient hydrogen release and effectively improving the conversion rate. Furthermore, the calcium hydride in this scheme also contains hydrogen ions, which undergo hydrolysis upon contact with water, releasing hydrogen gas. Therefore, the material in this scheme not only improves the conversion rate and hydrogen production rate but also results in a larger theoretical hydrogen production capacity, making it more beneficial for practical applications. Detailed Implementation

[0019] Example This invention discloses a highly active magnesium hydride-based composite hydrogen storage material, comprising the following components in parts by weight: 70-85 parts magnesium hydride, 10-30 parts calcium hydride, and 3-8 parts magnesium chloride.

[0020] This invention also discloses a method for preparing a highly active magnesium hydride-based composite hydrogen storage material, which includes the following steps: Step 1: Weigh magnesium hydride, calcium hydride and magnesium chloride powders according to the proportions, wherein the purity of magnesium hydride is greater than or equal to 95%, the purity of calcium hydride is greater than or equal to 95%, and the magnesium chloride is anhydrous magnesium chloride. Then, perform preliminary mixing of magnesium hydride, calcium hydride and magnesium chloride to obtain a premix. Step 2: The premixed material is ball-milled for 5-10 hours under the protection of argon atmosphere, with a ball-to-material mass ratio of (20:1) to (40:1) and a ball milling speed of 300-500 rpm.

[0021] This invention discloses Examples 1 to 4, and the components and ball milling parameters of Examples 1 to 4 are shown in the following table:

[0022] The present invention also discloses Comparative Examples 1 to 5, the components and ball milling parameters of Comparative Examples 1 to 5 are shown in the table below:

[0023] The present invention tests the above-mentioned composite material through Test 1 and Test 2: Test 1: 0.5 g of the composite material was rapidly added to a three-necked flask containing 50 mL of deionized water at room temperature (25°C). The flask was immediately sealed and the gas outlet tube was connected to the water displacement collection device. The solution was kept homogeneous using a magnetic stirrer. The volume of hydrogen gas collected by water displacement was recorded at 30 min. The test results are shown in the table below:

[0024] Test 2: 0.5 g of the composite material was quickly added to a three-necked flask containing 50 mL of deionized water at 60°C. The flask was immediately sealed and the gas outlet tube was connected to the water displacement collection device. The solution was kept homogeneous using a magnetic stirrer. The volume of hydrogen gas collected by water displacement was recorded at 30 min. The test results are shown in the table below:

[0025] From the above tests, we can see that: 1. From the conversion rates of Example 1 and Comparative Examples 4-5 at 60°C, it can be seen that the conversion rate of Example 1 reaches 97%, which is significantly higher than that of the comparative examples, indicating that the composite material of the present invention has better performance. Furthermore, considering the conversion rates at 25°C, after the temperature decreases, the conversion rates of Comparative Examples 4 and 5 are 81% and 75%, respectively. The conversion rates of the comparative examples are greatly affected by temperature, but the conversion rate of Example 1 still reaches 90%, which is still relatively high, indicating that the composite material of the present invention is less affected by low temperatures.

[0026] 2. Combining the test results of Example 1 and Comparative Example 2 at 25°C, it was found that the conversion rate of Example 1 was much higher than that of Comparative Example 2, indicating the key role of MgCl2 in destroying the passivation layer and promoting the completeness of the reaction.

[0027] 3. Combining the test results of Comparative Example 1 and Comparative Example 5 at 25℃, it can be seen that the conversion rate, actual hydrogen production and average hydrogen production rate of Comparative Example 5 are much higher than those of Comparative Example 1, proving that calcium hydride plays a huge role in promoting the hydrolysis of magnesium hydride.

[0028] 4. Based on the conversion rates of Comparative Examples 4 and 6 at 25°C, it can be seen that, under the same composition, the preparation method of the present invention results in a higher conversion rate for Comparative Example 4. This is because the preparation method in this scheme disperses calcium hydride and embeds it into the surface of the magnesium hydride matrix and the interparticle gaps, forming several "reaction micro-regions" that improve the speed and efficiency of hydrogen release.

[0029] Furthermore, considering the conversion rates of Comparative Examples 4 and 7 at 25°C, it can be seen that further increasing the ball-to-material mass ratio can further improve the conversion rate. Considering the conversion rates of Comparative Examples 4 and 8 at 25°C, it can be seen that reducing the ball milling speed in Comparative Example 8 reduces the material conversion rate, further demonstrating that the preparation method of the present invention can improve the speed and efficiency of hydrogen release.

[0030] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A highly active magnesium hydride-based composite hydrogen storage material, characterized in that: It includes the following components in parts by weight: 70-85 parts magnesium hydride, 10-30 parts calcium hydride, and 3-8 parts magnesium chloride.

2. A method for preparing a highly active magnesium hydride-based composite hydrogen storage material, characterized in that: The method for preparing the hydrogen storage material of claim 1 includes the following steps: Step 1: Weigh out magnesium hydride, calcium hydride and magnesium chloride according to the proportions; Step 2: The magnesium hydride, calcium hydride and magnesium chloride powders are ball-milled under an inert atmosphere at a speed of 300-500 rpm.

3. The method for preparing a highly active magnesium hydride-based composite hydrogen storage material according to claim 2, characterized in that: Step 1 involves weighing and then initially mixing magnesium hydride, calcium hydride, and magnesium chloride to obtain a premix. Step 2 involves ball milling the premix.

4. The method for preparing a highly active magnesium hydride-based composite hydrogen storage material according to claim 3, characterized in that: The mass ratio of balls to material in step 2 is (20:1) to (40:1).

5. The method for preparing a highly active magnesium hydride-based composite hydrogen storage material according to claim 3, characterized in that: The ball milling time is 5 to 10 hours.

6. The method for preparing a highly active magnesium hydride-based composite hydrogen storage material according to claim 2, characterized in that: Magnesium hydride has a purity of 95% or higher.

7. The method for preparing a highly active magnesium hydride-based composite hydrogen storage material according to claim 2, characterized in that: The purity of calcium hydride is greater than or equal to 95%.

8. The method for preparing a highly active magnesium hydride-based composite hydrogen storage material according to claim 2, characterized in that: Magnesium chloride is anhydrous magnesium chloride.

9. The method for preparing a highly active magnesium hydride-based composite hydrogen storage material according to claim 2, characterized in that: The ball milling was performed in a high-purity argon atmosphere.

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