A core-shell nano-structured magnesium hydride-magnesium borohydride hydrogen generation material and a preparation method thereof

Abstract

The application discloses a kind of core-shell nanostructure magnesium hydride-magnesium borohydride hydrolysis hydrogen production materials and preparation method thereof.A kind of core-shell nanostructure magnesium hydride-magnesium borohydride hydrolysis hydrogen production material preparation method, comprising the following steps: magnesium hydride is loaded into ball mill jar vacuum, then borane gas is filled in ball mill jar, ball milling treatment is carried out, and the core-shell nanostructure magnesium hydride-magnesium borohydride hydrolysis hydrogen production material is obtained.The application uses solvent-free gas-solid reaction, ball milling method, simple, low cost;This composite method not only avoids the direct use of expensive magnesium borohydride, but also overcomes the shortcomings of other composite systems, and even improves the theoretical hydrogen release capacity;The in-situ formed magnesium borohydride nanoshell plays a key role in improving the hydrolysis kinetics of magnesium hydride by releasing heat and forming a local magnesium ion and metaborate ion solution environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-capacity controllable hydrogen release, and particularly relates to a core-shell nano-structured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material and a preparation method thereof. BACKGROUND

[0002] Hydrogen energy is an important carrier for realizing green and low-carbon transformation of energy. For the commercial application of hydrogen energy, a series of problems such as hydrogen production, storage, transportation and use must be solved. Using hydrogen through fuel cells has the advantages of high energy efficiency (~70%) and zero carbon emission. The hydrogen source for fuel cells must have the characteristics of continuity, controllability, high purity and safety. Magnesium hydride in metal hydrides has a high mass hydrogen storage density, and has been widely studied as a hydrogen source. However, the stable thermodynamics (ΔH = 76.0 kJ mol -1 ) and high kinetic energy barrier (E a = 160.0 kJ mol -1 ) of magnesium hydride lead to high pyrolysis dehydrogenation temperature and slow kinetics, which cannot meet the requirements of fuel cell hydrogen source. Hydrolysis of magnesium hydride to release hydrogen as an alternative method has become very attractive because of its high theoretical hydrogen production rate (15.2wt%), high hydrogen purity, mild operating conditions and easy recovery of by-products, and the reaction equation is as follows:

[0003] MgH2+ 2H2O → Mg(OH)2+ 2H2 ΔG 0 298 = -323 kJ mol -1

[0004] However, the formation of insoluble and dense magnesium hydroxide on the surface of magnesium hydride seriously hinders the adsorption and mass transfer process of water, resulting in slow hydrogen generation kinetics and low hydrogen production rate.

[0005] The strategies to solve the above problems are as follows: regulating the composition of the hydrolysis solution, refining magnesium hydride and compounding with other compounds. Acid (such as sulfuric acid, nitric acid, hydrochloric acid, acetic acid, citric acid) or salt solution (such as magnesium chloride, aluminum chloride, ammonium chloride) hydrolysis solution is used to dissolve or destroy the passivation layer of magnesium hydroxide. However, the use of acid will cause reactor corrosion and loss of effective hydrogen production capacity, as the stoichiometric ratio of acid needs to be consumed, and the use of ammonium chloride solution will cause ammonia impurity gas to be mixed in hydrogen gas. In the case of inactivation or modification of magnesium hydride, the use of salt solution still has challenges to obtain satisfactory hydrogen production kinetics and hydrogen production yield. Ball milling is the most commonly used method for refining magnesium hydride particles. However, only ball milling activation, the hydrogen production conversion yield of magnesium hydride is still too low, and the hydrolysis yield is less than 30% for 1 hour. Compared with only ball milling, compounding with active metals (such as calcium, lithium), hydrides (such as calcium hydride, lithium aluminum hydride) and salts (such as cobalt chloride, nickel chloride, copper chloride, magnesium chloride, calcium chloride, sodium chloride, potassium chloride) during ball milling can effectively promote the hydrolysis reaction. For example, the hydrogen production yields of MgH2-20.3mol%Ca and MgH2-20.3mol%CaH2 composites after 10 hours of ball milling are about 48% and about 80% respectively for 30 minutes of hydrolysis (J. Alloys Compd. 376 (2004) 180-185). The hydrogen conversion rate of MgH2-5 at.% LiAlH4 composite after 10 hours of ball milling is only about 25% for 60 minutes of hydrolysis (J. Alloys Compd. 353 (2003) L12-L15). The high cost of active metals or hydrides used in these composites reduces the competitiveness of large-scale applications. In addition, it is still necessary to further improve the hydrogen conversion rate and hydrogen production rate. Recently, Zhou et al. (J. Power Sources 494 (2021) 229726) studied the hydrolysis performance of MgH2 doped with 10wt% different salts, and the results showed that cobalt chloride, nickel chloride, copper chloride and magnesium chloride are much better than calcium chloride, sodium chloride, potassium chloride. Although the hydrogen production kinetics and yield can be significantly improved by compounding with salts, the loss of theoretical hydrogen release capacity is still large due to the large proportion of salts in the composite.

[0006] Patent CN114436209A discloses a magnesium hydride-in-situ generated metal borohydride hydrolysis hydrogen production material, which is obtained by mixing magnesium hydride and metaborate and then performing solid-phase ball milling treatment. The obtained material has fast hydrolysis kinetics, and the hydrolysis conversion rate can exceed 86.3% within 1 hour. However, adding Mg(BO2)2 solid for ball milling will generate magnesium oxide (MgO) in-situ during the reaction of magnesium borohydride, and the hydrogen release capacity is low, with only 847.4 mL·g -1hydrogen. Patent CN114477091A also generates MgO by compounding MgH2 with B2O3 and B(OH)3 solid additives, and the B(OH)3 additive generates hydrogen during the ball milling process, further reducing the theoretical hydrogen release capacity of the hydrolysis of MgH2. Therefore, the hydrogen production rate of the hydrolysis of the materials described in the above two patents still has a large room for improvement.

[0007] In summary, the current methods for improving the hydrolysis performance of MgH2 still have the disadvantages of low hydrogen production rate and yield, high cost, and poor reaction controllability. Therefore, the commercial application of MgH2 hydrolysis technology is limited. SUMMARY

[0008] The present application solves the problems existing in the prior art and provides a core-shell nanostructured MgH2-Mg(BH4)2 hydrolysis hydrogen production material and a preparation method thereof. The present application adopts a strategy of ball milling MgH2 in a B2H6 atmosphere to generate in situ a nano-shell layer of Mg(BH4)2 on the surface of MgH2. The preparation conditions are mild and the process is simple. The core-shell nanostructured MgH2-Mg(BH4)2 material has high hydrogen production rate and yield.

[0009] The primary object of the present application is to provide a preparation method of a core-shell nanostructured MgH2-Mg(BH4)2 hydrolysis hydrogen production material, comprising the following steps:

[0010] The MgH2 is loaded into a ball mill jar, vacuumed, and then borane gas is filled into the ball mill jar for ball milling treatment, thereby obtaining the core-shell nanostructured MgH2-Mg(BH4)2 hydrolysis hydrogen production material.

[0011] The borane gas is obtained by heating a 1ZnCl2-2LiBH4 complex to 100-125℃. The amount of borane gas used is controlled by the mass of the 1ZnCl2-2LiBH4 complex.

[0012] Borane gas is a special gas that appears as a colorless gas at room temperature, has a special odor, is highly toxic, is easily hydrolyzed, can explode in humid air, can decompose at room temperature, and can react violently with many organic solvents and metals. Therefore, the storage conditions are very high, and it needs to be stored in a low-temperature, dry environment, away from heat sources, open flames, and oxidizing agents, halogens, and other substances. The present application adopts a strategy of generating borane gas by heating a 1ZnCl2-2LiBH4 complex to 100-125℃ and then introducing it into the ball mill jar to compound with MgH2. This strategy avoids the problem of high preparation difficulty caused by direct use of borane gas, and the entire process is simple, easy to control, safe, and economical. In addition, heating the 1ZnCl2-2LiBH4 complex to 100-125℃ generates not only borane but also hydrogen.

[0013] The 1ZnCl2-2LiBH4 composite prepared by the method comprises the following steps: ZnCl2 and LiBH4 with a molar ratio of 1:2 are loaded into a ball mill jar, a ball-to-material ratio of 30-50:1 is adopted, a ball milling atmosphere of 1 atm argon atmosphere is adopted, and the ball mill jar is placed on a swing ball mill for swing ball milling for 2-4 h, and a rotation speed of the swing ball mill is 1000-1200 r / min.

[0014] The ball milling treatment is carried out at room temperature.

[0015] Preferably, the mass of the 1ZnCl2-2LiBH4 composite is 2-6 g.

[0016] Further preferably, the mass of the 1ZnCl2-2LiBH4 composite is 4 g, the yield of the obtained hydrolysis hydrogen production material is the highest, and the comprehensive hydrolysis performance is the best.

[0017] Preferably, the mass ratio of the magnesium hydride to the 1ZnCl2-2LiBH4 composite is 1:2-6.

[0018] Preferably, the ball-to-material ratio of the ball milling treatment is 30-50:1, and the ball milling treatment time is 2-8 h.

[0019] Preferably, the ball milling treatment adopts a swing ball mill, and the rotation speed of the swing ball mill is 1000-1200 r / min.

[0020] A second object of the present application is to protect the core-shell nano-structured magnesium hydride-magnesium borohydride hydrogen production material obtained by the preparation method.

[0021] The magnesium hydride-magnesium borohydride hydrogen production material prepared by the present application has a core-shell nanostructure with MgH2 as the core and Mg(BH4)2 as the shell. The Mg(BH4)2 shell layer is closely combined with the MgH2, uniformly and completely covers the surface of the MgH2, and under the optimal parameters, the secondary particle size of the magnesium hydride-magnesium borohydride composite is greater than 40 nm, and the thickness of the Mg(BH4)2 shell layer is about 4 nm. This structure is beneficial to the Mg(BH4)2 shell layer to preferentially hydrolyze to form a local magnesium ion and metaborate ion solution environment and release a large amount of heat, accelerating the hydrolysis of the MgH2 "core". The in-situ generated magnesium borohydride consumes the magnesium hydride, further reduces the particle size of the magnesium hydride, increases the surface area of the magnesium hydride, reduces the thickness of the magnesium hydroxide passivation layer, and shortens the diffusion mass transfer path of water to the internal particles, thereby improving the hydrolysis kinetics.

[0022] The third object of the present application is to protect the application of the above-mentioned core-shell nano-structured magnesium hydride-magnesium borohydride hydrogen production material in hydrolysis hydrogen production. The core-shell nano-structured magnesium hydride-magnesium borohydride hydrogen production material prepared by the present application can occur hydrolysis reaction at normal temperature and pressure and in pure water, has fast hydrolysis kinetics, high hydrogen production yield and high hydrogen purity, and can be directly used in hydrogen-oxygen fuel cells.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] (1) Compared with the prior art, the present application adopts a solvent-free gas-solid reaction and a room-temperature ball milling method, is simple and safe, has good controllability, and has low cost, thereby avoiding the direct use of expensive magnesium borohydride.

[0025] (2) The in-situ formed magnesium borohydride shell layer has high hydrolysis reaction activity due to the novel nano structure. The magnesium borohydride shell layer preferentially hydrolyzes to form Mg(BO2)2·xH2O and releases a large amount of heat. The heat can accelerate the hydrolysis of the magnesium hydride "core". At the same time, the rapid hydrolysis of the magnesium borohydride produces a large amount of hydrogen, improves the theoretical hydrogen production capacity of the magnesium hydride hydrolysis, and can also inhibit the agglomeration of the hydrolysis products, which is beneficial to diffusion mass transfer. More importantly, due to the low solubility of Mg(BO2)2, a local magnesium ion and metaborate ion solution environment is formed after the magnesium borohydride hydrolysis. The magnesium ions will compete with the magnesium ions on the surface of the magnesium hydride to combine with hydroxyl ions to form magnesium hydroxide dispersed in water instead of on the surface of the magnesium hydride, which weakens the influence of the passivation layer of the magnesium hydroxide and significantly promotes the hydrolysis of the magnesium hydride.

[0026] (3) The present application uses borane gas to react with magnesium hydride to generate magnesium borohydride in-situ, and the reaction equation is MgH2+B2H6→Mg(BH4)2, which will not generate inert magnesium oxide to hinder the subsequent hydrolysis hydrogen production reaction process of the material.

[0027] (4) The typical core-shell nano-structured magnesium hydride-magnesium borohydride composite in the present application can further reduce the particle size of the magnesium hydride, increase the surface area of the magnesium hydride, reduce the thickness of the passivation layer of the magnesium hydroxide, shorten the diffusion mass transfer path of water to the internal particles, and thus improve the hydrolysis kinetics.

[0028] (5) The magnesium hydride-magnesium borohydride hydrolysis hydrogen production material synthesized by the present application overcomes the disadvantage of reduced theoretical hydrogen production capacity of other composite systems, and even improves the theoretical hydrogen production capacity. The hydrolysis hydrogen production material prepared by the present application has the best hydrolysis performance in the reported magnesium hydride hydrolysis systems. The material can occur hydrolysis reaction at normal temperature (35℃) and pressure and in pure water, has fast hydrolysis kinetics, the hydrolysis rate in the first minute is 1356.7 mL g -1 min -1 H2, the hydrolysis hydrogen production rate in 1 hour is 2027.7 mL g -1 H2.

[0029] (6) The hydrogen production material of the core-shell nanostructure magnesium hydride-magnesium borohydride prepared by hydrolysis has high hydrogen purity, and can be directly used in a hydrogen-oxygen fuel cell. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 (a) XRD patterns and (b) FTIR spectra of the products obtained after ball milling for 4 h with different amounts of borohydride (0-6 g of 1ZnCl2-2LiBH4complex), where the spectra correspond to the following examples: 1) Comparative Example 1; 2) Example 1; 3) Example 2; 4) Example 3.

[0031] Figure 2 Hydrogen production curves of the products obtained after ball milling for 4 h with different amounts of borohydride (0-6 g of 1ZnCl2-2LiBH4complex).

[0032] Figure 3 (a) XRD patterns and (b) FTIR spectra of the products obtained after ball milling for different times under borohydride atmosphere (4 g of 1ZnCl2-2LiBH4complex) from commercial magnesium hydride (0 h), where the spectra correspond to the following examples: 1) commercial magnesium hydride; 2) Example 4; 3) Example 2; 4) Example 5; 5) Example 6.

[0033] Figure 4 Hydrogen production curves of the products obtained after ball milling for different times under borohydride atmosphere (4 g of 1ZnCl2-2LiBH4complex) from commercial magnesium hydride (0 h).

[0034] Figure 5 NMR spectra of the product obtained after ball milling for 6 h under borohydride atmosphere (4 g of 1ZnCl2-2LiBH4complex) from magnesium hydride.

[0035] Figure 6 (a, b) TEM images, (c) HRTEM image, (d) SAED image, and (e) EDS mapping of the surface of the product obtained after ball milling for 6 h under borohydride atmosphere (4 g of 1ZnCl2-2LiBH4complex) from magnesium hydride, where the inset in (a) is a SEM image.

[0036] Figure 7 Hydrogen production curves (a) and Arrhenius plot (b) of the product obtained after ball milling for 6 h under borohydride atmosphere (4 g of 1ZnCl2-2LiBH4complex) from magnesium hydride at different temperatures.

[0037] Figure 8SEM images of (a) MgH2after ball milling for 6 h (under argon atmosphere) and (b) MgH2-BH4complex after ball milling for 6 h (under diborane atmosphere (4 g 1ZnCl2-2LiBH4complex) hydrolysis products.

[0038] Figure 9 (a) XRD patterns and (b) FTIR spectra of MgH2after ball milling for 6 h (under argon atmosphere) and MgH2-BH4complex after ball milling for 6 h (under diborane atmosphere (4 g 1ZnCl2-2LiBH4complex) hydrolysis products.

[0039] Figure 10 Schematic diagrams of (a) MgH2and (b) core-shell nanostructured MgH2-BH4hydrolysis mechanism.

[0040] Figure 11 Bar charts of (a) average hydrogen evolution rate in the first minute and (b) hydrogen evolution yield within 60 min of MgH2under argon or diborane atmosphere (4 g 1ZnCl2-2LiBH4complex) at different ball milling times.

[0041] Figure 12 Mass spectrum of the gaseous products of the hydrolysis of the product obtained after ball milling of MgH2for 6 h under diborane atmosphere (4 g 1ZnCl2-2LiBH4complex) in water. DETAILED DESCRIPTION

[0042] The following examples are further illustrations of the application and are not intended to limit the same.

[0043] Unless otherwise indicated, the experimental materials and reagents used in the present application are routinely commercially available products in the art.

[0044] Typical hydrolysis experiment in the following examples: First, about 0.1 g of the hydrolysis material was loaded into a reaction flask in an argon-filled glove box, and the flask opening was sealed with a rubber plug. Then, 10 mL of deionized water was injected into the reaction flask through a syringe. The reaction was stirred by a magnetic stirrer. The generated hydrogen gas was discharged into water in a meniscus washing bottle, and the mass of the discharged water was detected and recorded using an electronic scale connected to a computer. The volume of the generated hydrogen gas was the volume of the discharged water, and the hydrolysis hydrogen production curve of the hydrolysis material could be obtained by dividing the mass of the discharged water by the density of water. In order to obtain the activation energy, the hydrolysis was carried out in water at different temperatures (0, 25, 35 °C), and the reaction flask was placed in a corresponding constant temperature water bath. After hydrolysis, the hydrolysis product was collected by freeze-drying. The hydrolysis by-products and the hydrolysis material were characterized by powder X-ray (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). In addition, some of the hydrolysis materials were analyzed by solid-state nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM).

[0045] In Example 1, the preparation method of the ZnCl2-2LiBH4 composite was as follows: In an argon glove box, ZnCl2 and LiBH4 with a molar ratio of 1:2 were loaded into a ball mill jar, using a ball-to-material ratio of 50:1, and then placed on a vibrating ball mill. The vibrating ball mill was operated at 1000 r / min for 2 hours. To prevent overheating and reduce composite decomposition, the milling was paused for 30 minutes after every 15 minutes.

[0046] In the following examples, ball milling was performed at room temperature.

[0047] Example 1

[0048] A core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material, the preparation method of which includes the following steps:

[0049] ① In a glove box with a 1 atm argon atmosphere, weigh 1 g of magnesium hydride, mix it, and then load it into a ball mill jar, using a ball-to-material ratio of 50:1. Subsequently, evacuate the ball mill jar.

[0050] ② After loading 2g of the 1ZnCl2-2LiBH4 complex into a 325mL high-pressure reactor, the reactor was evacuated and then heated to 120℃ and kept at that temperature for 60min.

[0051] ③ Connect the ball mill jar to the high-pressure reactor and introduce the borane gas generated in the reactor into the ball mill jar.

[0052] ④ Place the ball mill jar in a vibratory ball mill (QM-3C), mill at 1000 r / min for 4 hours, and mill for 30 minutes, then pause for 30 minutes to prevent overheating. The resulting core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material is obtained.

[0053] Figure 1 Curve 2) in a is the XRD pattern of the ball-milled product. Apart from the diffraction peaks of magnesium hydride and a small amount of iron that has been removed by ball milling, there are no diffraction peaks of other phases. Figure 1 Curve 2) in b is the FTIR spectrum of the ball-milled product, with the 2150-2400 cm⁻¹ range shown in the curve. -1 and 1100-1300cm -1 The stretching vibration of the BH bond in Mg(BH4)2 appeared at that location. Figure 1 (b in ν) and rocking vibration ( Figure 1 The δ) absorption peak in b indicates the successful preparation of a core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material, which can be corroborated by other structural characterization results in subsequent examples. The prepared core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material was hydrolyzed in pure water at 25℃, and the average hydrolysis rate in the first 1 minute was 518.7 mL·g. -1 ·min-1 Hydrogen gas was released at a rate of 1172.8 mL·g per hour. -1 Hydrogen, such as Figure 2 As shown.

[0054] Example 2

[0055] A core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material is prepared by a method that is basically the same as that in Example 1, except that the mass of the 1ZnCl2-2LiBH4 composite is 4g.

[0056] Figure 1 Curve 3) in a is the XRD pattern of the ball-milled product. Apart from the diffraction peaks of magnesium hydride and a small amount of iron that has been detached by ball milling, there are no diffraction peaks of other phases. Figure 1 Curve 3) in b is the FTIR spectrum of the ball-milled product, with the 2150-2400 cm⁻¹ range shown in the curve. -1 and 1100-1300cm -1 The stretching vibration of the BH bond in Mg(BH4)2 appeared at that location. Figure 1 (b in ν) and rocking vibration ( Figure 1 The absorption peak (δ) in b indicates the successful preparation of core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material, which can be corroborated by other structural characterization results in subsequent examples. The prepared core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material was hydrolyzed in pure water at 25°C, and its hydrolysis performance was significantly better than that of magnesium hydride ball-milled under argon atmosphere. Figure 2 ,0g), Example 1 ( Figure 2 The hydrolysis rate was significantly improved (2g), with an average hydrolysis rate of 1311.7 mL·g in the first minute. -1 ·min -1 Hydrogen gas releases 1861.8 mL·g in 1 hour at room temperature. -1 Hydrogen gas exhibits rapid hydrolysis kinetics, high hydrogen production yield, and excellent hydrogen release performance, such as... Figure 2 As shown.

[0057] Example 3

[0058] A core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material is prepared by a method that is basically the same as that in Example 1, except that the mass of the 1ZnCl2-2LiBH4 composite is 6g.

[0059] Figure 1 Curve 4) in a is the XRD pattern of the ball-milled product. Apart from the diffraction peaks of magnesium hydride and a small amount of iron that has been removed by ball milling, there are no diffraction peaks of other phases. Figure 1 Curve 4) in section b is the FTIR spectrum of the ball-milled product, with the 2150-2400 cm⁻¹ range shown in the curve. -1 and 1100-1300cm-1 The stretching vibration of the BH bond in Mg(BH4)2 appeared at that location. Figure 1 (b in ν) and rocking vibration ( Figure 1 The absorption peak (δ) in b indicates the successful preparation of core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material, which can be corroborated by other structural characterization results in subsequent examples. The prepared core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material was hydrolyzed in pure water at 25°C, and its hydrolysis performance was significantly better than that of magnesium hydride ball-milled under argon atmosphere. Figure 2 The hydrolysis rate (0g) was significantly improved, with an average hydrolysis rate of 1174.5 mL·g in the first minute. -1 ·min -1 Hydrogen gas releases 1913.5 mL·g in 1 hour at room temperature. -1 Hydrogen gas exhibits rapid hydrolysis kinetics, high hydrogen production yield, and excellent hydrogen release performance, such as... Figure 2 As shown.

[0060] Comparative Example 1

[0061] First, in a glove box under a 1 atm argon atmosphere, 1 g of magnesium hydride was weighed out at a ball-to-material ratio of 50:1 and placed into a ball mill jar. The ball mill jar was then placed directly into a vibrating ball mill (QM-3C) and milled at 1000 r / min for 4 hours. To prevent overheating, milling was continued for 30 minutes followed by a 30-minute pause. The final product was magnesium hydride hydrolysis hydrogen production material.

[0062] Figure 1 Curve 1) in a is the XRD pattern of the ball-milled product. Apart from the diffraction peaks of magnesium hydride and a small amount of iron that has been detached by ball milling, there are no diffraction peaks of other phases. Figure 1 Curve 1) in Figure b is the FTIR spectrum of the ball-milled product, showing no absorption peaks for BH bond stretching and rocking vibrations. Hydrolysis of the ball-milled product in pure water at 25°C resulted in hydrogen release; the average hydrolysis rate in the first 1 minute was 740.6 mL·g. -1 ·min -1 Hydrogen gas was released, with only 1435.7 mL·g released in 1 hour. -1 Hydrogen, with a low hydrogen production rate, such as Figure 2 As shown.

[0063] Example 4

[0064] A core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material is prepared by a method that is basically the same as that in Example 1, except that the mass of the 1ZnCl2-2LiBH4 composite is 4g and the ball milling time is 2h.

[0065] Figure 3Curve 2) in a is the XRD pattern of the ball-milled product. Apart from the diffraction peaks of magnesium hydride and a small amount of iron that has been removed by ball milling, there are no diffraction peaks of other phases. Figure 3 Curve 2) in b is the FTIR spectrum of the ball-milled product, with the 2150-2400 cm⁻¹ range shown in the curve. -1 and 1100-1300cm -1 The stretching vibration of the BH bond in Mg(BH4)2 appeared at that location. Figure 3 (b in ν) and rocking vibration ( Figure 3 The absorption peak (δ) in b indicates the successful preparation of core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material, which can be corroborated by other structural characterization results in subsequent examples. The prepared core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material was hydrolyzed in pure water at 25°C, and its hydrolysis performance was significantly better than that of unmilled magnesium hydride (…). Figure 4 The hydrolysis rate improved significantly in the first 1 minute (0h), with an average hydrolysis rate of 990.9 mL·g. -1 ·min -1 Hydrogen gas releases 1896.3 mL·g in 1 hour at room temperature. -1 Hydrogen gas exhibits rapid hydrolysis kinetics, high hydrogen production yield, and excellent hydrogen release performance, such as... Figure 4 As shown.

[0066] Example 5

[0067] A core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material is prepared by a method that is basically the same as that in Example 1, except that the mass of the 1ZnCl2-2LiBH4 composite is 4g and the ball milling time is 6h.

[0068] Figure 3 Curve 4) in a is the XRD pattern of the ball-milled product. Apart from the diffraction peaks of magnesium hydride and a small amount of iron that has been removed by ball milling, there are no diffraction peaks of other phases. Figure 3 Curve 4) in section b is the FTIR spectrum of the ball-milled product, with the 2150-2400 cm⁻¹ range shown in the curve. -1 and 1100-1300cm -1 The stretching vibration of the BH bond in Mg(BH4)2 appeared at that location. Figure 3 (b in ν) and rocking vibration ( Figure 3 The absorption peak (δ) in b is obtained. 11 [BH4] appeared at -39.4 ppm in the B NMR spectrum. - Confirmation of anion resonance peaks ( Figure 5 As shown in the SEM and TEM images ( Figure 6 (a) and (b) the MgH2-Mg(BH4)2 composite particles exhibit irregular shapes, with secondary nanoparticles having a diameter >40 nm.Figure 6 Image b clearly shows that the MgH2-Mg(BH4)2 composite exhibits a core-shell nanostructure, as indicated by the white dashed line, with a shell thickness of approximately 4 nm. (High-resolution TEM (HRTEM) image) Figure 6 c) shows the amorphous shell and lattice fringes, with interplanar spacings of 0.213 nm (or 0.216 nm) and 0.260 nm, corresponding to the (111) and (101) crystal planes of β-MgH2, respectively. Selected area electron diffraction (SAED) pattern ( Figure 6 (d) mainly shows a series of diffraction rings corresponding to the β-MgH2 phase, consistent with the XRD results. EDS spectrum ( Figure 6 The result (e) indicates that Mg is located in the core, while B is concentrated on the surface. This confirms that after ball milling with B₂H₂, MgH₂ is covered by an amorphous layer of Mg(BH₄)₂, consistent with the XRD results. Therefore, ball milling of MgH₂ under a B₂H₆ atmosphere successfully prepared a core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material with MgH₂ as the core and Mg(BH₄)₂ as the shell. The prepared core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material was hydrolyzed in pure water at 25°C, and the hydrolysis performance was significantly better than that of un-ball-milled magnesium hydride (MgH₂H₄)₂. Figure 4 The hydrolysis rate improved significantly (after 0 hours), with an average hydrolysis rate of 1392.3 mL·g in the first minute. -1 ·min -1 Hydrogen gas releases 1906.0 mL·g in 1 hour at room temperature. -1 Hydrogen gas exhibits rapid hydrolysis kinetics, high hydrogen production yield, and excellent hydrogen release performance, such as... Figure 4 As shown. Furthermore, the hydrogen gas produced by hydrolysis has high purity and produces no borane, such as... Figure 12 As shown in the figure, Ar is the test carrier gas, and N2 is the gas from the air during the test.

[0069] The core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material was hydrolyzed in water at different temperatures (0, 25, 35℃), and the reaction flasks were placed in constant temperature water baths at the corresponding temperatures. Figure 7 As shown in Figure a, with increasing temperature, both the hydrogen production yield and rate of the core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material significantly increased. At 35℃, the core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material achieved the fastest hydrolysis rate and the highest hydrogen production yield, with an average hydrolysis rate of 1356.7 mL·g in the first 1 minute. -1 ·min -1 Hydrogen gas releases 2027.7 mL·g in 1 hour at room temperature. -1 Hydrogen. Through fitting calculations, the core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material exhibits a very low activation energy for the hydrolysis reaction, at 9.05 kJ / mol. -1This further proves that it has fast hydrolysis reaction kinetics. Figure 7 (b).

[0070] To investigate the hydrolysis reaction mechanism, the hydrolysis products were freeze-dried and characterized using SEM, XRD, and FTIR. Under the same conditions, the magnesium hydride hydrolysis products ball-milled under argon atmosphere for 6 hours appeared as lumps. Figure 8 (a) The magnesium hydride-magnesium borohydride composite (the product of Example 5) ball-milled for 6 hours was cotton-like. Figure 8 (b) In Figure 9 In curve 1 of a), the magnesium hydride hydrolysis product after ball milling for 6 hours consists of two phases: unreacted magnesium hydride and magnesium hydroxide. (“◆” and “◆” represent the magnesium hydride phase and magnesium hydroxide phase, respectively). The magnesium hydroxide passivation layer hinders the hydrolysis reaction, and the reaction principle is illustrated in the diagram. Figure 10 As shown in a. However, the hydrolysis products of the magnesium hydride-magnesium borohydride complex did not show diffraction peaks for magnesium hydride; only broad diffraction peaks for magnesium hydroxide were observed. Furthermore, the FTIR characteristic peaks of Mg(BH4)2 (2150-2400 cm⁻¹) were also observed. -1 and 1100-1300cm -1 The BO2 component disappears, while the BO2 component corresponding to Mg(BO2)2·xH2O is at 1200-1350 cm⁻¹. -1 and 976cm -1 An absorption peak appears at ( Figure 9 (b) The above results indicate that the magnesium hydride-magnesium borohydride complex is almost completely hydrolyzed, which corresponds perfectly to the results of extremely high hydrogen production yield from hydrolysis.

[0071] The mechanism by which core-shell nanostructured magnesium hydride-magnesium borohydride improves hydrolysis performance can be found in [reference needed]. Figure 10 The explanation below focuses on b. A typical core-shell nanostructured magnesium hydride-magnesium borohydride composite can further reduce the particle size of magnesium hydride, leading to an increase in its surface area and a reduction in the influence of the magnesium hydroxide passivation layer. This facilitates water diffusion and mass transfer, thereby improving hydrolysis kinetics. The in-situ formed magnesium borohydride shell exhibits high hydrolysis reactivity due to its novel nanostructure. The magnesium borohydride shell preferentially hydrolyzes to form Mg(BO2)2·xH2O, releasing a large amount of heat. This heat accelerates the hydrolysis of the magnesium hydride "core." Simultaneously, the rapid hydrolysis of magnesium borohydride generates a large amount of hydrogen gas, increasing the theoretical hydrogen release capacity of magnesium hydride hydrolysis and inhibiting the aggregation of hydrolysis products, which is beneficial for diffusion and mass transfer. More importantly, since Mg(BO2)2 is slightly soluble in water, the hydrolysis of magnesium borohydride leads to the formation of a localized solution environment containing magnesium ions and metaborate ions. The magnesium ions will compete with the magnesium ions on the surface of magnesium hydride for binding with hydroxide ions, forming magnesium hydroxide dispersed in water rather than on the surface of magnesium hydride. This weakens the effect of the magnesium hydroxide passivation layer and significantly promotes the hydrolysis of magnesium hydride, which can be confirmed by SEM results.

[0072] Example 6

[0073] A core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material is prepared by a method that is basically the same as that in Example 1, except that the mass of the 1ZnCl2-2LiBH4 composite is 4g and the ball milling time is 8h.

[0074] Figure 3 Curve 5 in a is the XRD pattern of the ball-milled product. Apart from the diffraction peaks of magnesium hydride and a small amount of iron that has been detached by ball milling, there are no diffraction peaks of other phases. Figure 3 Curve 5) in section b is the FTIR spectrum of the ball-milled product, with the 2150-2400 cm⁻¹ range shown in the curve. -1 and 1100-1300cm -1 The stretching vibration of the BH bond in Mg(BH4)2 appeared at that location. Figure 3 (b in ν) and rocking vibration ( Figure 3 The presence of the δ) absorption peak in b indicates the successful preparation of a core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material. The prepared core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material was hydrolyzed in pure water at 25℃, and its hydrolysis performance was significantly better than that of unmilled magnesium hydride (…). Figure 4 The hydrolysis rate improved significantly (after 0 hours), with an average hydrolysis rate of 1527.7 mL·g in the first minute. -1 ·min -1 Hydrogen gas releases 1888.7 mL·g in 1 hour at room temperature. -1 Hydrogen gas exhibits rapid hydrolysis kinetics, high hydrogen production yield, and excellent hydrogen release performance, such as... Figure 4 As shown. From Figure 4 It can be seen that the hydrolysis rate gradually increases with increasing ball milling time, while the hydrogen production yield shows a trend of first increasing and then slightly decreasing. The slight decrease in hydrogen production yield after 8 hours of ball milling may be due to increased Fe impurity shavings caused by prolonged ball milling. It is worth noting that the hydrolysis hydrogen production rate and yield of the magnesium hydride-magnesium borohydride hydrolysis hydrogen production material are significantly higher than those of magnesium hydride ball-milled under argon atmosphere for the same time. Figure 11 As shown.

[0075] The above description of the embodiments is only for the purpose of helping to understand the technical solution and core idea of ​​the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a core-shell nanostructured magnesium hydride-magnesium borohydride hydrolysis hydrogen production material, characterized by, It comprises the following steps: The magnesium hydride is loaded into a ball mill tank, vacuumized, and then borane gas is filled into the ball mill tank for ball milling treatment, so that the core-shell nano-structured magnesium hydride-magnesium borohydride hydrogen production material is obtained; the borane gas is obtained by heating 1ZnCl2-2LiBH4 composite to 100-125℃.

2. The production method according to claim 1, characterized by, The amount of borane gas used is controlled by the mass of 1ZnCl2-2LiBH4 composite, and the mass of 1ZnCl2-2LiBH4 composite is 2-6 g.

3. The production method according to claim 1, characterized by, The 1ZnCl2-2LiBH4 composite is prepared by the following method: 1:2 molar ratio of ZnCl2 and LiBH4 are swing ball milled for 2-4 h, the ball milling atmosphere is 1 atm argon atmosphere, the ball-to-material ratio is 30-50:1, and the swing ball mill speed is 1000-1200 r / min.

4. The preparation method according to claim 1, characterized in that, The mass ratio of the magnesium hydride to the 1ZnCl2-2LiBH4 composite is 1:2-6.

5. The preparation method according to claim 1, characterized in that, The swing ball mill speed is 1000-1200 r / min, and the ball-to-material ratio for ball milling treatment is 30-50:

1.

6. The method of claim 1, wherein, The ball milling treatment is carried out at room temperature, and the ball milling treatment time is 2-8 h.

7. The core-shell nano-structured magnesium hydride-magnesium borohydride hydrogen production material prepared by the preparation method of any one of claims 1-6.

8. The magnesium hydride-magnesium borohydride hydrolysis hydrogen generation material according to claim 7, characterized in that, It has a core-shell nanostructure with MgH2 as the core and Mg(BH4)2 as the shell, and the secondary particle size is 40 nm or more, and the shell thickness is 4 nm.

9. The use of the core-shell nano-structured magnesium hydride-magnesium borohydride hydrogen production material of claim 7 or 8 in hydrolysis hydrogen production.

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