A rapid method for the preparation of magnesium borohydride

Abstract

The application belongs to the technical field of hydrogen storage materials, and specifically discloses a rapid preparation method of magnesium borohydride. First, magnesium hydride and rare earth borate (yttrium borate, lanthanum borate, etc.) are uniformly mixed and then subjected to solid-phase ball milling treatment to obtain a solid-phase ball milling product, namely, magnesium borohydride; then, the solid-phase ball milling product is uniformly mixed in a solvent, and high-purity magnesium borohydride can be obtained after purification. The raw material, rare earth borate, used in the application can be synthesized by a simple hydrothermal method, and the process is simple and low in cost. The yield of nearly 50% can be achieved in only 2 hours, which has the industrial production potential of rapidly synthesizing magnesium borohydride and can ensure the high purity of the prepared magnesium borohydride.

Description

Technical Field

[0001] This invention relates to the field of hydrogen storage materials technology, and in particular to a rapid preparation method for magnesium borohydride. Background Technology

[0002] Hydrogen energy, as a high-energy-density and environmentally friendly secondary energy source, is considered one of the most promising energy carriers. However, the volumetric energy density of hydrogen is only 4.4 MJ / L. -1 However, it is difficult to meet the technical requirements for energy. In addition, hydrogen is flammable and explosive, posing certain safety hazards, which greatly limits the large-scale promotion and application of hydrogen energy.

[0003] Metal borohydrides are considered one of the most promising hydrogen storage materials due to their extremely high mass and volumetric hydrogen storage capacity, enabling effective storage and transportation of hydrogen energy. Among them, magnesium borohydride stands out for its exceptionally high mass hydrogen storage capacity (14.9 wt.%) and volumetric hydrogen storage capacity (~146 kg cm⁻¹). -1 Magnesium borohydride is considered a promising hydrogen storage material, and it can release hydrogen through hydrolysis and pyrolysis, meeting the application requirements of various environments. However, magnesium borohydride is expensive, its preparation method is cumbersome, and its hydrolysis process is irreversible, which greatly limits its widespread application as a hydrogen storage energy source. Therefore, there is an urgent need to develop a low-cost, simple, efficient, rapid, safe, and reliable method for preparing magnesium borohydride.

[0004] The currently widely used method for synthesizing magnesium borohydride is based on the ion exchange reaction between magnesium halides (such as magnesium chloride or magnesium bromide) and borohydrides (such as lithium borohydride or sodium borohydride) through methods such as heating and ball milling. The main reaction equations are shown below:

[0005] MgX2+2MBH4→Mg(BH4)2+2MX(X=Cl,Br;M=Li,Na)

[0006] According to existing reports (Angewandte Chemie International Edition, 2007, 46(30): 5765-5767), lithium borohydride and magnesium chloride were heated and refluxed in diethyl ether to successfully synthesize magnesium borohydride with a yield of 30%. However, both lithium borohydride and lithium chloride are soluble in diethyl ether solution, which makes it difficult to remove impurities such as residual and generated lithium chloride and lithium borohydride in the product, making it difficult to obtain high-purity magnesium borohydride. Meanwhile, sodium borohydride and magnesium chloride are mixed and ball-milled, and the yield can reach 50%. Then, magnesium borohydride can be purified by dissolution and desolvation. The yield can be increased to 77% by using wet ball milling. However, the cost of producing magnesium borohydride by ion exchange reaction using sodium borohydride, which is already very expensive, will undoubtedly be very high, making it difficult to promote its application (Journal of Materials Chemistry, 2007, 17(33): 3496-3503; International Journal of Hydrogen Energy, 2009, 34, 2144-2152).

[0007] There are also reports of methods for preparing magnesium borohydride by adding magnesium hydride to other derivatives such as borane. The main equations are as follows:

[0008] 3MgR2 + 4B2H6 → 3Mg(BH4)2 + 2BR3

[0009] However, the boranes and their derivatives used in this method are highly toxic and can affect human health, which limits their widespread application to some extent.

[0010] In addition, the direct hydrogenation of MgB2, the hydrogen-evolving product of magnesium borohydride, to magnesium borohydride under high temperature and high pressure is also one of the reported methods for synthesizing magnesium borohydride. For example, magnesium borohydride has been synthesized by hydrogenation at 390℃ and 90MPa for 72 hours. However, this method requires high hydrogen pressure, is dangerous, and the high temperature results in energy loss, making it unsuitable for large-scale production.

[0011] In recent years, several methods for preparing magnesium borohydride by converting BO bonds in a boron source to BH bonds through simple room-temperature ball milling have been reported. For example, a recently reported method using direct ball milling of boron oxide and magnesium hydride achieved a yield of 76.9% after 15 hours of milling (Chemical Engineering Journal, 2022, 432: 134322). Another method uses room-temperature ball milling of magnesium borate and magnesium hydride to synthesize magnesium borohydride (Chinese patent publication number CN116374956A), achieving a yield of 57.3% after 15 hours of milling. While these methods are low-cost and simple, they require long synthesis times and consume a lot of energy, making it impossible to achieve rapid synthesis of magnesium borohydride in a short time.

[0012] In summary, current reported methods for synthesizing magnesium borohydride still suffer from problems such as high cost, complex processes, low purity, and long processing times. Existing technologies make it difficult to achieve large-scale application of magnesium borohydride. Therefore, providing a low-cost, simple, and high-purity rapid method for preparing magnesium borohydride is a pressing problem that needs to be solved in this field. Summary of the Invention

[0013] In view of this, the present invention provides a rapid preparation method for magnesium borohydride, which solves the problems of high cost, complex process, low purity, and long energy consumption and time consumption in the currently reported synthesis methods of magnesium borohydride.

[0014] To achieve the above objectives, the present invention adopts the following technical solution:

[0015] A rapid method for preparing magnesium borohydride includes the following steps:

[0016] Magnesium borohydride is obtained by mixing magnesium hydride and rare earth borate and then performing solid-phase ball milling.

[0017] Preferably, the molar ratio of magnesium hydride to rare earth borate is 4-8:1-2.

[0018] Preferably, the rare earth borates include yttrium borate and / or lanthanum borate.

[0019] Preferably, the ball-to-material ratio of the solid-phase ball mill is 25-100:1, the rotation speed of the solid-phase ball mill is 300-1800 rpm, and the solid-phase ball milling time is 0.1-5 h.

[0020] Preferably, the solid-phase ball milling is performed under a non-oxidizing atmosphere.

[0021] Preferably, the non-oxidizing atmosphere includes one or more of the following: vacuum atmosphere, argon atmosphere, hydrogen atmosphere, and nitrogen atmosphere.

[0022] Preferably, the solid-phase ball milling process further includes purification.

[0023] Preferably, the purification steps are as follows:

[0024] The mixture after solid-phase ball milling was mixed with a solvent, and the extract was obtained by separation. The extract was then dried to obtain magnesium borohydride.

[0025] Preferably, the solvent includes diethyl ether and / or dimethyl sulfide.

[0026] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. This invention uses rare earth borates as the boron source, which can be obtained by a simple hydrothermal method. The process is simple and the price is low. When yttrium borate and lanthanum borate are selected as borates, the raw materials have low toxicity and good safety.

[0028] 2. The magnesium borohydride obtained by this invention is easy to purify. The solvent used in the purification process will not dissolve metal hydrides, metal oxides, unreacted reaction raw materials, and reaction byproducts other than magnesium borohydride. This can obtain magnesium borohydride with high purity and no impurities, which solves the problem in the prior art that some metal borohydrides such as lithium borohydride or generated lithium chloride in the ion exchange reaction dissolve in organic solvents, resulting in low purity of magnesium borohydride.

[0029] 3. This invention avoids the problems of high cost of borohydrides (such as sodium borohydride, lithium borohydride, etc.) used in ion exchange reactions and the high risk of flammability and explosiveness of hydrogen or borane used in high temperature and high pressure synthesis methods in existing technologies.

[0030] 4. The present invention requires a short preparation time for magnesium borohydride, achieving a yield of nearly 50% in just 2 hours, which is faster than the time required by existing magnesium borohydride synthesis technologies. It can realize the rapid synthesis of magnesium borohydride in a short time and has the application potential of efficient magnesium borohydride synthesis. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0032] Figure 1 The following are the FTIR spectra of the ball-milled products in Examples 1-3;

[0033] Figure 2 The XRD pattern of magnesium borohydride prepared in Example 2 is compared with the standard PDF card of magnesium borohydride.

[0034] Figure 3 The following are the FTIR spectra of the ball-milled products in Examples 4-8;

[0035] Figure 4 The following are the FTIR spectra of the ball-milled products in Examples 9-11;

[0036] Figure 5 The following are the FTIR spectra of the ball-milled products in Examples 12-16;

[0037] Figure 6 The image shows the FTIR spectrum of the ball-milled product in Comparative Example 1.

[0038] Figure 7 XRD patterns of ball-milled samples at different ball-milling times;

[0039] Figure 8 FTIR images of ball-milled samples at different ball-milling times;

[0040] Figure 9 XPS images of ball-milled samples at different ball-milling times;

[0041] Figure 10 MS images of ball-milled samples at different ball-milling times. Detailed Implementation

[0042] This invention provides a rapid method for preparing magnesium borohydride, comprising the following steps:

[0043] Magnesium borohydride is obtained by mixing magnesium hydride and rare earth borate and then performing solid-phase ball milling.

[0044] In this invention, the molar ratio of magnesium hydride to rare earth borate is 4-8:1-2, preferably 5-7:1.2-1.8, and more preferably 6:1.5.

[0045] In this invention, the rare earth borates include yttrium borate and / or lanthanum borate; the addition of rare earth elements effectively shortens the time for ball milling to synthesize magnesium borohydride.

[0046] In this invention, when the rare earth borate used is yttrium borate, the molar ratio of magnesium hydride to yttrium borate is further preferably 6:2; when the rare earth borate used is lanthanum borate, the molar ratio of magnesium hydride to lanthanum borate is 7:2.

[0047] In this invention, the ball-to-material ratio of the solid-phase ball mill is 25–100:1, preferably 30–80:1, more preferably 50–70:1, and even more preferably 60:1; the rotational speed of the solid-phase ball mill is 300–1800 rpm, specifically 500 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, or 1600 rpm; the solid-phase ball milling time is 0.1–5 h, specifically 0.2 h, 0.5 h, 0.8 h, 1 h, 2 h, 3 h, or 4 h.

[0048] In this invention, a mechanochemical reaction occurs during the solid-phase ball milling process.

[0049] In this invention, the solid-phase ball milling is carried out under a non-oxidizing atmosphere.

[0050] In this invention, the non-oxidizing atmosphere includes one or more of the following: vacuum atmosphere, argon atmosphere, hydrogen atmosphere, and nitrogen atmosphere.

[0051] In this invention, the solid-phase ball milling process further includes purification.

[0052] In this invention, the purification step is as follows:

[0053] The mixture after solid-phase ball milling was mixed with a solvent, and the extract was obtained by separation. The extract was then dried to obtain magnesium borohydride.

[0054] In this invention, the solvent includes diethyl ether and / or dimethyl sulfide. The solvent does not dissolve metal hydrides, metal oxides, unreacted reactants, or reaction byproducts other than magnesium borohydride. The purified solution contains only magnesium borohydride.

[0055] In this invention, the drying is vacuum drying, specifically, the clarified solution obtained by filtration is first dried by vacuuming, and then desolvation treatment is performed.

[0056] In this invention, the vacuum drying method is the Schlenk technique.

[0057] In this invention, the drying temperature is 10-40°C, the desolvation treatment temperature is 160-220°C, the time is 10-90 hours, and the desolvation treatment is repeated 1-3 times.

[0058] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] Example 1

[0060] At room temperature, magnesium hydride and yttrium borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 5:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and ball milled at a speed of 1000 rpm for 2 hours to obtain the ball milling product. Figure 1 Curve 1) is the FTIR spectrum of the ball-milled product, with the 2150–2400 cm⁻¹ range shown in the curve. -1 Within range and 1126cm -1 The presence of stretching absorption peaks and oscillating vibration peaks corresponding to the BH bonds in magnesium borohydride nearby confirms the synthesis of magnesium borohydride.

[0061] The ball-milled product was dissolved in anhydrous diethyl ether, and then filtered to obtain a clear filtrate. The clear filtrate was vacuum dried at 25°C using the Schlenk technique to obtain a complex of magnesium borohydride and diethyl ether. The mixture was digested by adding deionized water and hydrochloric acid to prepare a solution. After being diluted to volume with a 200 mL volumetric flask, the concentration of magnesium ions in the solution was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The yield of magnesium borohydride was determined to be 33.7% (ratio to theoretical yield, the same below).

[0062] Example 2

[0063] At room temperature, magnesium hydride and yttrium borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 6:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and milled at a speed of 1000 rpm for 2 hours to obtain the ball milling product. Figure 1 Curve 2) is the FTIR spectrum of the ball-milled product, with the curve showing a range of 2150–2400 cm⁻¹. -1 Within range and 1126cm -1 The presence of stretching absorption peaks and oscillating vibration peaks corresponding to the BH bonds in magnesium borohydride nearby confirms the synthesis of magnesium borohydride.

[0064] The ball-milled product was dissolved in anhydrous diethyl ether, and then filtered to obtain a clear filtrate. The clear filtrate was vacuum dried at 25°C using the Schlenk technique to obtain a complex of magnesium borohydride and diethyl ether. The mixture was digested by adding deionized water and hydrochloric acid to prepare a solution. After being diluted to volume with a 200 mL volumetric flask, the concentration of magnesium ions in the solution was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The yield of magnesium borohydride was determined to be 45.11%.

[0065] The obtained clarified filtrate was also dried under vacuum at 25°C using the Schlenk technique to remove most of the diethyl ether solvent, yielding a viscous complex of magnesium borohydride and diethyl ether. This complex was then desolvated at 200°C for 24 hours under vacuum. The sample was then removed, ground, and the desolvation process was repeated three times to obtain a white powder. Figure 2 The XRD pattern of the white powder is consistent with that of the PDF card of commercially available magnesium borohydride, indicating that the method of the present invention can produce magnesium borohydride.

[0066] Example 3

[0067] At room temperature, magnesium hydride and yttrium borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 7:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and ball milled at a speed of 1000 rpm for 2 hours to obtain the ball milling product. Figure 1 Curve 3) is the FTIR spectrum of the ball-milled product, with the 2150–2400 cm⁻¹ range shown in the curve. -1 Within range and 1126cm -1 The presence of stretching absorption peaks and oscillating vibration peaks corresponding to the BH bonds in magnesium borohydride nearby confirms the synthesis of magnesium borohydride.

[0068] The ball-milled product was dissolved in anhydrous diethyl ether, and then filtered to obtain a clear filtrate. The clear filtrate was vacuum dried at 25°C using the Schlenk technique to obtain a complex of magnesium borohydride and diethyl ether. Deionized water and hydrochloric acid were added to digest the mixture, and a solution was prepared. After being diluted to volume with a 200 mL volumetric flask, the concentration of magnesium ions in the solution was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The yield of magnesium borohydride was determined to be 40.62%.

[0069] Single-phase magnesium borohydride was obtained by using the same purification operation as in Example 2.

[0070] Example 4

[0071] At room temperature, magnesium hydride and yttrium borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 5:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 100:1. The ball milling jar was then placed on a planetary ball mill and milled at a speed of 300 rpm for 2 hours to obtain the ball milling product. Figure 3 Curve 1) is the FTIR spectrum of the ball-milled product, with the 2150–2400 cm⁻¹ range shown in the curve. -1 The presence of absorption peaks corresponding to the stretching vibrations of the BH bonds in magnesium borohydride within the specified range confirms the synthesis of magnesium borohydride.

[0072] Example 5

[0073] At room temperature, magnesium hydride and yttrium borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 5:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and milled at a speed of 1000 rpm for 1 hour to obtain the ball milling product. Figure 3 Curve 2) is the FTIR spectrum of the ball-milled product, with the curve showing a range of 2150–2400 cm⁻¹. -1 The presence of absorption peaks corresponding to the stretching vibrations of the BH bonds in magnesium borohydride within the specified range confirms the synthesis of magnesium borohydride.

[0074] Example 6

[0075] At room temperature, magnesium hydride and yttrium borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 5:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and ball milled at a speed of 1000 rpm for 3 hours to obtain the ball milling product. Figure 3 Curve 3) is the FTIR spectrum of the ball-milled product, with the 2150–2400 cm⁻¹ range shown in the curve. -1 The presence of absorption peaks corresponding to the stretching vibrations of the BH bonds in magnesium borohydride within the specified range confirms the synthesis of magnesium borohydride.

[0076] Example 7

[0077] At room temperature, magnesium hydride and yttrium borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 6:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and milled at a speed of 1000 rpm for 4 hours to obtain the ball milling product. Figure 3 Curve 4) is the FTIR spectrum of the ball-milled product, with the 2150–2400 cm⁻¹ range shown in the curve. -1 The presence of absorption peaks corresponding to the stretching vibrations of the BH bonds in magnesium borohydride within the specified range confirms the synthesis of magnesium borohydride.

[0078] Example 8

[0079] At room temperature, magnesium hydride and yttrium borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 6:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and milled at a speed of 1000 rpm for 1 h 40 min to obtain the ball milling product. Figure 3 Curve 5) is the FTIR spectrum of the ball-milled product, with the 2150–2400 cm⁻¹ range shown in the curve. -1 The presence of absorption peaks corresponding to the stretching vibrations of the BH bonds in magnesium borohydride within the specified range confirms the synthesis of magnesium borohydride.

[0080] Example 9

[0081] At room temperature, magnesium hydride and lanthanum borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 6:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and ball milled at a speed of 1000 rpm for 2 hours to obtain the ball milling product. Figure 4 Curve 1) is the FTIR spectrum of the ball-milled product, with the 2150–2400 cm⁻¹ range shown in the curve. -1 Within range and 1126cm -1 The presence of stretching absorption peaks and oscillating vibration peaks corresponding to the BH bonds in magnesium borohydride nearby confirms the synthesis of magnesium borohydride.

[0082] The ball-milled product was dissolved in anhydrous diethyl ether, and then filtered to obtain a clear filtrate. The clear filtrate was vacuum dried at 25°C using the Schlenk technique to obtain a complex of magnesium borohydride and diethyl ether. Deionized water and hydrochloric acid were added to digest the mixture, and a solution was prepared. After being diluted to volume with a 200 mL volumetric flask, the concentration of magnesium ions in the solution was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The yield of magnesium borohydride was determined to be 46.39%.

[0083] Example 10

[0084] At room temperature, magnesium hydride and lanthanum borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 7:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and milled at a speed of 1000 rpm for 2 hours to obtain the ball milling product. Figure 4 Curve 2) is the FTIR spectrum of the ball-milled product, with the curve showing a range of 2150–2400 cm⁻¹. -1 Within range and 1126cm -1The presence of stretching absorption peaks and oscillating vibration peaks corresponding to the BH bonds in magnesium borohydride nearby confirms the synthesis of magnesium borohydride.

[0085] The ball-milled product was dissolved in anhydrous diethyl ether, and then filtered to obtain a clear filtrate. The clear filtrate was vacuum dried at 25°C using the Schlenk technique to obtain a complex of magnesium borohydride and diethyl ether. Deionized water and hydrochloric acid were added to digest the mixture, and a solution was prepared. After being diluted to volume with a 200 mL volumetric flask, the concentration of magnesium ions in the solution was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The yield of magnesium borohydride was determined to be 48.28%.

[0086] Example 11

[0087] At room temperature, magnesium hydride and lanthanum borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 8:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and milled at a speed of 1000 rpm for 2 hours to obtain the ball milling product. Figure 4 Curve 3) is the FTIR spectrum of the ball-milled product, with the 2150–2400 cm⁻¹ range shown in the curve. -1 Within range and 1126cm -1 The presence of stretching absorption peaks and oscillating vibration peaks corresponding to the BH bonds in magnesium borohydride nearby confirms the synthesis of magnesium borohydride.

[0088] The ball-milled product was dissolved in anhydrous diethyl ether, and then filtered to obtain a clear filtrate. The clear filtrate was vacuum dried at 25°C using the Schlenk technique to obtain a complex of magnesium borohydride and diethyl ether. Deionized water and hydrochloric acid were added to digest the mixture, and a solution was prepared. After being diluted to volume with a 200 mL volumetric flask, the concentration of magnesium ions in the solution was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The yield of magnesium borohydride was determined to be 31.67%.

[0089] Example 12

[0090] At room temperature, magnesium hydride and lanthanum borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 5:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and ball milled at a speed of 1000 rpm for 3 hours to obtain the ball milling product. Figure 5 Curve 1) is the FTIR spectrum of the ball-milled product, with the 2150–2400 cm⁻¹ range shown in the curve. -1 The presence of absorption peaks corresponding to the stretching vibrations of the BH bonds in magnesium borohydride within the specified range confirms the synthesis of magnesium borohydride.

[0091] Example 13

[0092] At room temperature, magnesium hydride and lanthanum borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 6:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and ball milled at a speed of 1000 rpm for 5 hours to obtain the ball milling product. Figure 5 Curve 2) is the FTIR spectrum of the ball-milled product, with the curve showing a range of 2150–2400 cm⁻¹. -1 The presence of absorption peaks corresponding to the stretching vibrations of the BH bonds in magnesium borohydride within the specified range confirms the synthesis of magnesium borohydride.

[0093] Example 14

[0094] At room temperature, magnesium hydride and lanthanum borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 6:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and ball milled at a speed of 1000 rpm for 3 hours to obtain the ball milling product. Figure 5 Curve 3) is the FTIR spectrum of the ball-milled product, with the 2150–2400 cm⁻¹ range shown in the curve. -1 The presence of absorption peaks corresponding to the stretching vibrations of the BH bonds in magnesium borohydride within the specified range confirms the synthesis of magnesium borohydride.

[0095] Example 15

[0096] At room temperature, magnesium hydride and lanthanum borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 6:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and milled at a speed of 1000 rpm for 1 hour to obtain the ball milling product. Figure 5 Curve 4) is the FTIR spectrum of the ball-milled product, with the 2150–2400 cm⁻¹ range shown in the curve. -1 The presence of absorption peaks corresponding to the stretching vibrations of the BH bonds in magnesium borohydride within the specified range confirms the synthesis of magnesium borohydride.

[0097] Example 16

[0098] At room temperature, magnesium hydride and lanthanum borate were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 7:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and ball milled at a speed of 1000 rpm for 3 hours to obtain the ball milling product. Figure 5 Curve 5) is the FTIR spectrum of the ball-milled product, with the 2150–2400 cm⁻¹ range shown in the curve. -1 The presence of absorption peaks corresponding to the stretching vibrations of the BH bonds in magnesium borohydride within the specified range confirms the synthesis of magnesium borohydride.

[0099] Comparative Example 1

[0100] At room temperature, magnesium hydride and manganese borate (MnB4O7) were mixed uniformly in an argon atmosphere glove box at a pressure of 0.1 MPa at a molar ratio of 6:2. The mixed sample and stainless steel balls of different sizes were loaded into a stainless steel ball milling jar at a ball-to-material ratio of 50:1. The ball milling jar was then placed on a vibrating ball mill and ball milled at a speed of 1000 rpm for 3 hours to obtain the ball milling product. Figure 6 The image shows the FTIR spectrum of the ball-milled product, with the curve showing the range from 2150 to 2400 cm⁻¹. -1 The absence of a stretching vibration absorption peak corresponding to the BH bond in magnesium borohydride within the specified range indicates that magnesium borohydride was not synthesized.

[0101] Comparative Example 1 shows that not all borates can react with magnesium hydride to prepare magnesium borohydride.

[0102] Taking YBO3 as an example, the synthesis mechanism of this invention is as follows:

[0103] 2YBO3+7MgH2→2YH2+6MgO+Mg(BH4)2+H2 (1)

[0104] 2YBO3+2YH2+H2+MgH2→2Y2O3+Mg(BH4)2 (2)

[0105] 2YBO3+4MgH2→Y2O3+Mg(BH4)2+3MgO (3)

[0106] When the molar ratio of magnesium hydride to yttrium borate is 6:2, the XRD, FTIR, XPS, and MS spectra of the ball-milled samples at different ball-milling times correspond to... Figure 7 , Figure 8 , Figure 9 , Figure 10 .pass Figures 7-10 It can be seen that Y in yttrium borate before the ball milling reaction occurs 3+ The binding energy is a pair of double peaks, corresponding to Y respectively.3+ Y3d 5 / 2 (157.51eV) and Y3d 3 / 2 (159.57 eV), consistent with the spectrum of YBO3, and also consistent with the XRD and FTIR spectra of YBO3, confirming that the reactant is pure phase YBO3; however, when the ball milling time was extended to 1 h, the binding energy of yttrium split into two sets of doublets, indicating that the chemical environment of Y element changed, exhibiting two bonding environments, one of which is Y3d 5 / 2 157.36 eV and Y3d 3 / 2 The energy level was 159.42 eV, consistent with the binding energy of YBO3 mentioned above. The presence of YBO3 was also detected by XRD pattern, and the absorption peak of the BO bond in YBO3 was observed in the FTIR spectrum, indicating that some YBO3 remained unreacted after 1 hour of ball milling. Furthermore, the absorption peak at 2150-2400 cm⁻¹ was observed. -1 The presence of a distinct absorption peak for the BH bond within the range confirms the formation of Mg(BH4)2, while the binding energy of the other group of Y elements is Y3d. 5 / 2 156.40 eV and Y3d 3 / 2 158.46 eV, similar to YH2(Y3d) reported by Fujimori et al. 5 / 2 156.5 eV and Y3d 3 / 2 The binding energy (158.5 eV) is consistent with the diffraction peaks of YH2 detected in the XRD pattern. To determine the reaction that occurred in the initial stage of ball milling, the ball mill jar was directly connected to a mass spectrometer (PM-DEMS) after 1 hour of ball milling to detect the gas composition in the ball mill jar, such as... Figure 10 As shown in the mass spectrum, after 1 hour of ball milling, the main gas components in the milling jar were argon and hydrogen. The argon was due to the argon environment in the glove box during sample preparation, proving that H2 was generated during the ball milling process. Based on the XRD, XPS, MS, and FTIR test results of the initial raw materials and the ball-milled products, the reaction between YBO3 and MgH2 within 2 hours of ball milling is shown in Equation 1.

[0107] 2YBO3+7MgH2→2YH2+6MgO+Mg(BH4)2+H2 (1)

[0108] When the ball milling time reaches 3 hours, such as Figure 7 As shown, the diffraction peaks of YBO3 almost completely disappear, and the diffraction peaks of Y2O3 appear. Meanwhile, as... Figure 9 As shown in the XPS spectrum, the binding energy of a double peak for element Y is Y3d. 5 / 2 157.02 eV and Y3d 3 / 2 159.10 eV, consistent with the binding energy of Y2O3 reported by Uwamino et al. (Y3d 5 / 2156.8 eV and Y3d 3 / 2 (158.9 eV), further proving that Y2O3 was generated during the ball milling process, it is inferred that the reaction shown in Equation 2 occurred between 2 and 3 hours of ball milling. Combining Equations 1 and 2, the reaction equation for the ball milling of YBO3 and MgH2 to generate Mg(BH4)2 can be obtained as shown in Equation 3:

[0109] 2YBO3+2YH2+H2+MgH2→2Y2O3+Mg(BH4)2 (2)

[0110] 2YBO3+4MgH2→Y2O3+Mg(BH4)2+3MgO (3)

[0111] The synthesis mechanism of magnesium borohydride by directly ball milling boron oxide and magnesium hydride, which is similar to that of the present invention, is as shown in Formula 4, and is completely different from the inventive mechanism of the present invention.

[0112] B2O3+4MgH2→Mg(BH4)2+3MgO (4)

[0113] As can be seen from the above embodiments, this invention provides a rapid method for synthesizing magnesium borohydride. In this invention, magnesium hydride is uniformly mixed with rare earth borates (yttrium borate and lanthanum borate) and then subjected to solid-phase ball milling to obtain a ball-milled product. Subsequently, the ball-milled product is uniformly mixed in a solvent, separated, and vacuum dried to obtain magnesium borohydride. The rare earth borates used in this method can all be synthesized by a simple hydrothermal method, resulting in a simple process and low cost. Furthermore, a ball milling yield of nearly 50% can be achieved in just 2 hours, demonstrating the potential for industrial-scale rapid synthesis of magnesium borohydride. The solvent used in this invention does not dissolve metal hydrides, metal oxides, unreacted reactants, or reaction byproducts other than magnesium borohydride, ensuring the high purity of the prepared magnesium borohydride.

[0114] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0115] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A rapid preparation method for magnesium borohydride, characterized in that, Includes the following steps: Magnesium borohydride is obtained by mixing magnesium hydride and rare earth borate and then performing solid-phase ball milling. The molar ratio of magnesium hydride to rare earth borate is 4~8:1~2; The ball-to-material ratio of the solid-phase ball mill is 25~100:1, the rotation speed of the solid-phase ball mill is 300~1800 rpm, and the solid-phase ball milling time is 0.1~5h; The solid-phase ball milling was carried out under a non-oxidizing atmosphere.

2. The rapid preparation method of magnesium borohydride according to claim 1, characterized in that, The rare earth borates include yttrium borate and / or lanthanum borate.

3. The rapid preparation method of magnesium borohydride according to claim 1, characterized in that, The non-oxidizing atmosphere includes one or more of the following: vacuum atmosphere, argon atmosphere, hydrogen atmosphere, and nitrogen atmosphere.

4. A rapid preparation method for magnesium borohydride according to claim 1 or 3, characterized in that, The solid-phase ball milling process also includes purification.

5. The rapid preparation method of magnesium borohydride according to claim 4, characterized in that, The purification steps are as follows: The mixture after solid-phase ball milling was mixed with a solvent, and the extract was obtained by separation. The extract was then dried to obtain magnesium borohydride.

6. The rapid preparation method of magnesium borohydride according to claim 5, characterized in that, The solvent includes diethyl ether and / or dimethyl sulfide.

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