A novel hydrogen storage material and a preparation method thereof

Abstract

The application belongs to the technical field of material preparation, and particularly relates to a new hydrogen storage material and a preparation method thereof. A brand-new Al coordination MeAB complex, Na[Al(CH3NHBH3)4], is prepared, the successful preparation of the material expands the types and quantity of the complex, and provides more ideas for Al-based complex hydrogen storage; and compared with the AB complex of Al coordination, the MeAB has lower cost, and the methyl has weak electron-donating ability, the existence of the methyl can affect the coordination bond strength between N and Al atoms in the final complex, and allows the complex to be synthesized in a more gentle way.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation technology, and in particular relates to a novel hydrogen storage material and its preparation method. Background Technology

[0002] Ammonia borane (AB) is a novel solid-state hydrogen storage material with a theoretical hydrogen storage capacity of 19.6 wt.%. It is stable at room temperature and has low toxicity. However, its dehydrogenation temperature is above 100℃, and the dehydrogenation products contain impurities such as methaneborane and ammonia, which cannot meet the requirements for practical applications. Forming metal-coordinated amide borane complexes through mono- or multi-metal cation synthesis can effectively improve these problems. Existing research includes LiNH₂BH₃, NaNH₂BH₃, KNH₂BH₃, Mg(NH₂BH₃)₂, and their composite systems. Among them, [Al(NH₂BH₃)₄] with aluminum (Al) as the coordination element is particularly noteworthy. - The complex exhibits excellent dehydrogenation performance, with high hydrogen storage capacity, low dehydrogenation temperature, high purity hydrogen released during decomposition, and the decomposition products can be partially hydrogenated to [Al(NH2BH3)4]. - This exhibits a certain degree of reversibility. Elucidating the structures of such complexes and their dehydrogenation products is beneficial for analyzing their dehydrogenation process and mechanism; however, the structure of Al-coordinated [Al(NH2BH3)4] remains unclear. - There are few reports on the structure, which limits research on the relationship between material structure and dehydrogenation performance.

[0003] Methyl-substituted aminoboranes (CH3NH2BH3, or MeAB) exhibit certain steric hindrance compared to AB, which can stabilize intermediate products during synthesis and aid in understanding the synthetic mechanism. Furthermore, this steric hindrance is not excessive and will not hinder the formation of metal-coordinated MeAB complexes. Theoretically, methyl substitution reduces intermolecular dihydrogen bonds, thereby decreasing the energy required for thermal decomposition and hydrogen release, lowering the dehydrogenation temperature. Moreover, MeAB is cheaper to prepare than AB, making it more practical. Therefore, a novel method for preparing hydrogen storage materials is urgently needed to address these issues. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a novel hydrogen storage material and its preparation method. The novel hydrogen storage material prepared by this invention is free of impurities after dehydrogenation and has a high hydrogen storage capacity.

[0005] To achieve one of the above objectives, the present invention adopts the following technical solution:

[0006] A novel hydrogen storage material, namely Na[Al(CH3NHBH3)4], is synthesized using the following equation:

[0007] NaAlH4+4CH3NH2BH3→Na[AlH(CH3NHBH3)3]+CH3NH2BH3+3H2→Na[Al(CH3NHBH3)4]+4H2.

[0008] The second objective of this invention is to provide a method for preparing a novel hydrogen storage material, which includes the following steps:

[0009] S1. Place NaAlH4 and CH3NH2BH3 into a ball mill jar in a glove box at a stoichiometric ratio of 1:4, add stainless steel balls, seal the jar, and then remove the ball mill jar containing the balls from the glove box.

[0010] S2. The ball mill jar is placed into a ball mill for ball milling to finally obtain the hydrogen storage material Na[Al(CH3NHBH3)4].

[0011] Preferably, the reaction equation for the preparation of CH3NH2BH3 is:

[0012] CH3NH2·HCl+NaBH4→CH3NH2BH3+NaCl+H2;

[0013] The method for preparing CH3NH2BH3 includes the following steps:

[0014] S1. Add 0.1 mol of NaBH4, 0.1 mol of CH3NH2·HCl and 300 mL of tetrahydrofuran to a round-bottom flask, and replace the air in the round-bottom flask with an argon protective atmosphere.

[0015] S2. Stir the reaction at room temperature for 24 hours, and filter to remove the NaCl generated during the reaction;

[0016] S3. The solution obtained in step S2 is then subjected to a rotary evaporator to remove tetrahydrofuran, yielding CH3NH2BH3.

[0017] Preferably, the ball milling parameters are: rotation speed of 250-600 rpm, ball milling time of 3 min, interval time of 2-5 min, number of cycles ≥90, and mass ratio of stainless steel balls to material of (30-60):1.

[0018] Preferably, the ball milling parameters are: rotation speed of 600 rpm, ball milling time of 3 min, interval time of 5 min, number of cycles ≥ 90, and mass ratio of stainless steel balls to material of 60:1.

[0019] Preferably, the ball milling parameters are: rotation speed of 600 rpm, ball milling time of 3 min, interval time of 5 min, number of cycles of 120, and mass ratio of stainless steel balls to material of 30:1.

[0020] Preferably, the ball milling parameters are: rotation speed of 500 rpm, ball milling time of 3 min, interval time of 2 min, number of cycles of 200, and mass ratio of stainless steel balls to material of 60:1.

[0021] Preferably, the ball milling parameters are: rotation speed of 250 rpm, ball milling time of 3 min, interval time of 2 min, number of cycles of 240, and mass ratio of stainless steel balls to material of 60:1.

[0022] Preferably, the glove box is filled with argon protective gas; the ball mill is a Fritsch Pulverisette 7 Premium line manufactured by Fritsch; the volume of the grinding jar is 80m³; and there are 3 stainless steel balls with a diameter of 10mm.

[0023] Preferably, the round-bottom flask has a volume of 500 mL, and the reaction is carried out by stirring the round-bottom flask with a magnetic stirrer for 24 hours.

[0024] The advantages of this invention are:

[0025] (1) This invention prepares a novel Al-coordinated MeAB complex: Na[Al(CH3NHBH3)4]. The successful preparation of this material expands the types and quantities of such complexes and provides more ideas for hydrogen storage using Al-based complexes. Compared with Al-coordinated AB complexes, MeAB is cheaper and the methyl group has a weak electron-donating ability. Its presence affects the coordination bond strength between N and Al atoms in the final complex, allowing the complex to be synthesized in a milder way. The dehydrogenation temperature is lower, making it more suitable for practical applications.

[0026] (2) The present invention prepared a novel aluminum-based coordinated methyl-substituted aminoborane complex by ball milling process, and its crystal structure was analyzed by X-ray diffraction pattern.

[0027] (3) In this invention, due to the use of a ball mill jar that can monitor pressure and temperature, the intermediate product Na[AlH(CH3NHBH3)3] was discovered during the synthesis process. This product was also discovered for the first time. Since the methyl-substituted aminoborane MeAB has certain steric hindrance, the intermediate product can be relatively stable and can be extracted during the reaction process, which helps to study the reaction mechanism. Attached Figure Description

[0028] Figure 1The X-ray diffraction pattern and refined crystal structure of the product Na[Al(CH3NHBH3)4] are shown below.

[0029] Figure 2 This is a ball-and-stick model of the crystal structure of Na[Al(CH3NHBH3)4] according to the present invention.

[0030] Figure 3 This is a schematic diagram comparing the infrared spectra of the reaction raw materials NaAlH4 and CH3NH2BH3 and the product Na[Al(CH3NHBH3)4] of the present invention.

[0031] Figure 4 This is a schematic diagram showing the change of tank pressure over time during the ball milling process of the present invention.

[0032] Figure 5 This is a ball-and-stick model of the crystal structure of the intermediate product Na[AlH(CH3NHBH3)3] of this invention.

[0033] Figure 6 The thermogravimetric-mass spectrum of the Na[Al(CH3NHBH3)4]+12NaH composite system of the present invention is shown. Detailed Implementation

[0034] like Figures 1-6 As shown, a novel hydrogen storage material is Na[Al(CH3NHBH3)4], and the synthesis equation for Na[Al(CH3NHBH3)4] is as follows:

[0035] NaAlH4+4CH3NH2BH3→Na[AlH(CH3NHBH3)3]+CH3NH2BH3+3H2→Na[Al(CH3NHBH3)4]+4H2.

[0036] A method for preparing a novel hydrogen storage material Na[Al(CH3NHBH3)4] includes the following steps:

[0037] S1. Preparation of raw material CH3NH2BH3

[0038] The preparation of CH3NH2BH3 follows the reaction equation below:

[0039] CH3NH2·HCl+NaBH4→CH3NH2BH3+NaCl+H2

[0040] The specific steps are as follows:

[0041] a. Add 0.1 mol of NaBH4, 0.1 mol of CH3NH2·HCl and 300 mL of tetrahydrofuran (THF) to a 500 mL round-bottom flask, and replace the air in the round-bottom flask with an argon protective atmosphere.

[0042] b. Stir the round-bottom flask with a magnetic stirrer at room temperature for 24 hours. The NaCl produced in the reaction is insoluble in THF. Then remove the NaCl by filtration.

[0043] c. The solution obtained in step b is then subjected to a rotary evaporator to remove the solvent THF, in order to obtain CH3NH2BH3.

[0044] Preparation of S2 and Na[Al(CH3NHBH3)4]

[0045] 1) Place NaAlH4 and CH3NH2BH3 into an 80mL ball mill jar in an argon-filled glove box at a stoichiometric ratio of 1:4. This ball mill jar can monitor temperature and pressure changes during the experiment. Place three 10mm diameter stainless steel balls in the jar, seal the lid, and then remove the ball mill jar from the glove box.

[0046] 2) Use a Fritsch Pulverisette 7 Premium line ball mill to ball mill the grinding jar. The ball mill parameters are: rotation speed 250-600 rpm, grinding time 3 min, interval time 2-5 min, number of cycles ≥90, and the mass ratio of stainless steel balls to material is (30-60):1.

[0047] 3) Collect the product from the ball mill jar to obtain the hydrogen storage material Na[Al(CH3NHBH3)4].

[0048] Example 1

[0049] S1. Preparation of raw material CH3NH2BH3;

[0050] S2. In an argon-filled glove box, put NaAlH4 and CH3NH2BH3 into an 80mL ball mill jar at a stoichiometric ratio of 1:4, and put in three 10mm diameter stainless steel balls at the same time. Cover the jar with the seal and then take it out of the glove box.

[0051] S3. The ball mill jar was ball-milled using a Fritsch Pulverisette 7 Premium line ball mill with the following parameters: rotation speed of 600 rpm, ball milling time of 3 min, interval time of 5 min, number of cycles of 90, and ball-to-material ratio of 60:1. The product was collected from the ball mill jar to obtain the hydrogen storage material Na[Al(CH3NHBH3)4].

[0052] Example 2

[0053] S1. Preparation of raw material CH3NH2BH3;

[0054] S2. In an argon-filled glove box, put NaAlH4 and CH3NH2BH3 into an 80mL ball mill jar at a stoichiometric ratio of 1:4, and put in three 10mm diameter stainless steel balls at the same time. Cover the jar with the seal and then take it out of the glove box.

[0055] S3. The ball mill jar was ball-milled using a Fritsch Pulverisette 7 Premium line ball mill with the following parameters: rotation speed of 600 rpm, ball milling time of 3 min, interval time of 5 min, number of cycles of 120, and ball-to-material ratio of 30:1. The product was collected from the ball mill jar to obtain the hydrogen storage material Na[Al(CH3NHBH3)4]2.

[0056] Example 3

[0057] S1. Preparation of raw material CH3NH2BH3;

[0058] S2. In an argon-filled glove box, put NaAlH4 and CH3NH2BH3 into an 80mL ball mill jar at a stoichiometric ratio of 1:4, and put in three 10mm diameter stainless steel balls at the same time. Cover the jar with the seal and then take it out of the glove box.

[0059] S3. The ball mill jar was ball-milled using a Fritsch Pulverisette 7 Premium line ball mill with the following parameters: rotation speed of 500 rpm, ball milling time of 3 min, interval time of 2 min, number of cycles of 200, and ball-to-material ratio of 60:1. The product was collected from the ball mill jar to obtain the hydrogen storage material Na[Al(CH3NHBH3)4].

[0060] Example 4

[0061] S1. Preparation of raw material CH3NH2BH3;

[0062] S2. In an argon-filled glove box, put NaAlH4 and CH3NH2BH3 into an 80mL ball mill jar at a stoichiometric ratio of 1:4, and put in three 10mm diameter stainless steel balls at the same time. Cover the jar with the seal and then take it out of the glove box.

[0063] S3. The ball mill jar was ball-milled using a Fritsch Pulverisette 7 Premium line ball mill with the following parameters: rotation speed 250 rpm, milling time 3 min, interval time 2 min, number of cycles 240, and ball-to-material ratio 60:1. The product was collected from the ball mill jar to obtain the hydrogen storage material Na[Al(CH3NHBH3)4] tetra.

[0064] The preparation methods of the raw material CH3NH2BH3 in Examples 1-4 above are all as described above.

[0065] The hydrogen storage materials Na[Al(CH3NHBH3)4] prepared in Examples 1-4 were analyzed, as detailed in the attached figures. Figures 1-5 As shown.

[0066] Figure 1 In the topmost peak, the black portion represents the refined simulated spectrum of Na[Al(CH3NHBH3)4]. The gray portion near the peak represents the X-ray diffraction patterns of prepared Na[Al(CH3NHBH3)4]¹ to Na[Al(CH3NHBH3)4]⁴. From bottom to top, the bottommost line represents the difference between the two. The second layer of discontinuous gray vertical lines marks the Bragg peaks of Na[Al(CH3NHBH3)4]. The third layer of gray vertical lines marks the Bragg peaks of impurity NaCl, which originates from residues during the preparation of CH3NH2BH3. The refined results show that R… exp =9.41%, R wp =16.3%, R p =18.8%, χ 2 =3, that is, the error value between the prepared Na[Al(CH3NHBH3)4] X-ray diffraction pattern and the refined simulated pattern of Na[Al(CH3NHBH3)4] is small, indicating that the generated product contains Na[Al(CH3NHBH3)4] and the impurity NaCl.

[0067] Figure 2 The crystal structures of prepared Na[Al(CH3NHBH3)4]1 to Na[Al(CH3NHBH3)4]4 are shown, in which the largest gray sphere represents Na atom, the medium gray sphere represents Al atom, the small black sphere represents N atom, the small dark gray sphere represents B atom, and the small light gray sphere represents C atom. The space group is P21 / n.

[0068] Figure 3 The medium wavenumber is 962-1218 cm⁻¹ -1 2168-2450cm -1 BH bonds were present in all samples, with a wavenumber of 1595 cm⁻¹. -13200-3298cm -1 NH bonds are present in all samples, with wavenumbers ranging from 1405 to 1495 cm⁻¹. -1 2864-3035cm -1 CH bonds were present in all samples, with wavenumbers ranging from 859 to 965 cm⁻¹. -1 CN bonds are present in all samples; additionally, CN bonds are present in samples from 502 to 640 cm. -1 A new peak appeared, corresponding to the formation of Al-N bonds, which can correspond to the bonding between atoms inside the target product Na[Al(CH3NHBH3)4], that is, the material prepared is Na[Al(CH3NHBH3)4].

[0069] Figure 4 During the formation of Na[Al(CH3NHBH3)4], the pressure change can be divided into two segments: a gray curve and a black curve. In the first step, the gray curve segment generates approximately 3 unit volumes of gas, corresponding to the formation of the intermediate product Na[AlH(CH3NHBH3)3]. In the second step, the black curve segment generates approximately 4 unit volumes of gas, corresponding to the formation of the target product. Therefore, by detecting the amount of gas generated by pressure change, it can be determined that the synthesis process of the material prepared in this invention is divided into two steps and involves the formation of an intermediate, which is consistent with the above-mentioned synthesis equation for Na[Al(CH3NHBH3)4].

[0070] Figure 5 The crystal structure of the intermediate Na[AlH(CH3NHBH3)3] is shown, in which the largest gray sphere represents Na atoms, the medium gray sphere represents Al atoms, the small black sphere represents N atoms, the light white smallest sphere connected to the largest gray sphere represents H atoms, the dark gray sphere connected to both the light white smallest sphere and the small black sphere represents B atoms, and the light gray sphere connected to the small black sphere represents C atoms.

[0071] The prepared Na[Al(CH3NHBH3)4]- to Na[Al(CH3NHBH3)4]tetra form complex systems with NaH active hydrides, and dehydrogenation experiments are performed. The results are as follows: Figure 6 As shown, by Figure 6Combining (A) and (B), it can be seen that during the heating process from 40 to 180℃, the mass of the composite system decreased by 6.2 wt%, all of which was the release of hydrogen. Specifically, as the temperature rose to around 75℃, the system began to dehydrogenate, and no other related gases (such as NH3, B2H6, CH3NH2, CH4, etc.) were detected. This indicates that Na[Al(CH3NHBH3)4], as a hydrogen storage material, can release pure hydrogen under mild conditions (i.e., dehydrogenation temperature below 100℃). Furthermore, forming a composite system between Na[Al(CH3NHBH3)4] and active hydrides such as NaH can improve the dehydrogenation performance of the material, reduce the dehydrogenation temperature, and increase the dehydrogenation rate.

[0072] In this invention, a novel Al-coordinated MeAB complex, Na[Al(CH3NHBH3)4], was prepared, and its structure was characterized for the first time by X-ray powder diffraction and infrared spectroscopy, and the reaction mechanism was elucidated. Its dehydrogenation process was analyzed by thermogravimetric-mass spectrometry.

[0073] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hydrogen storage material, characterized in that, The material is Na[Al(CH3NHBH3)4], and the synthesis equation for Na[Al(CH3NHBH3)4] is as follows: NaAlH4 + 4 CH3NH2BH3 → Na[AlH(CH3NHBH3)3] + CH3NH2BH3 + 3 H2 → Na[Al(CH3NHBH3)4] + 4 H2; The preparation method of this hydrogen storage material includes the following steps: S1. Place NaAlH4 and CH3NH2BH3 into a ball mill jar in a glove box at a stoichiometric ratio of 1:4, add stainless steel balls, seal the jar, and then remove the ball mill jar containing the balls from the glove box. S2. The ball mill jar is placed into a ball mill for ball milling to finally obtain the hydrogen storage material Na[Al(CH3NHBH3)4]; The ball milling parameters are as follows: rotation speed 250-600 rpm, ball milling time 3 min, interval time 2-5 min, number of cycles ≥90, and the mass ratio of stainless steel balls to material is (30-60):

1.

2. A method for preparing the hydrogen storage material as described in claim 1, characterized in that: The synthesis equation for Na[Al(CH3NHBH3)4] is as follows: NaAlH4 + 4 CH3NH2BH3 → Na[AlH(CH3NHBH3)3] + CH3NH2BH3 + 3 H2 → Na[Al(CH3NHBH3)4] + 4 H2; The preparation method of this hydrogen storage material includes the following steps: S1. Place NaAlH4 and CH3NH2BH3 into a ball mill jar in a glove box at a stoichiometric ratio of 1:4, add stainless steel balls, seal the jar, and then remove the ball mill jar containing the balls from the glove box. S2. The ball mill jar is placed into a ball mill for ball milling to finally obtain the hydrogen storage material Na[Al(CH3NHBH3)4]; The ball milling parameters are: rotation speed 250-600 rpm, ball milling time 3 min, interval time 2-5 min, number of cycles ≥90 times, and the mass ratio of stainless steel balls to material is (30-60):

1. The reaction equation for the preparation of CH3NH2BH3 is as follows: CH3NH2·HCl + NaBH4→CH3NH2BH3 + NaCl + H2; The method for preparing CH3NH2BH3 includes the following steps: S1. Add 0.1 mol of NaBH4, 0.1 mol of CH3NH2·HCl and 300 mL of tetrahydrofuran to a round-bottom flask, and replace the air in the round-bottom flask with an argon protective atmosphere. S2. Stir the reaction at room temperature for 24 hours, and filter to remove the NaCl generated during the reaction; S3. The solution obtained in step S2 is then subjected to a rotary evaporator to remove tetrahydrofuran, yielding CH3NH2BH3.

3. The method for preparing a hydrogen storage material according to claim 2, characterized in that: The ball milling parameters are as follows: rotation speed of 600 rpm, ball milling time of 3 min, interval time of 5 min, number of cycles ≥ 90, and mass ratio of stainless steel balls to material of 60:

1.

4. The method for preparing a hydrogen storage material according to claim 2, characterized in that: The ball milling parameters are as follows: rotation speed of 600 rpm, ball milling time of 3 min, interval time of 5 min, number of cycles of 120, and mass ratio of stainless steel balls to material of 30:

1.

5. The method for preparing a hydrogen storage material according to claim 2, characterized in that: The ball milling parameters are as follows: rotation speed of 500 rpm, ball milling time of 3 min, interval time of 2 min, number of cycles of 200, and mass ratio of stainless steel balls to material of 60:

1.

6. The method for preparing a hydrogen storage material according to claim 2, characterized in that: The ball milling parameters are as follows: rotation speed 250 rpm, ball milling time 3 min, interval time 2 min, number of cycles 240, and mass ratio of stainless steel balls to material 60:

1.

7. The method for preparing a hydrogen storage material according to claim 2, characterized in that: Argon protective gas is introduced into the glove box; the ball mill is a Fritsch Pulverisette 7 Premiumline manufactured by Fritsch; the volume of the grinding jar is 80 m³; and there are 3 stainless steel balls with a diameter of 10 mm.

8. The method for preparing a hydrogen storage material according to claim 2, characterized in that: The round-bottom flask has a volume of 500 mL, and the reaction is carried out by stirring the round-bottom flask with a magnetic stirrer for 24 hours.

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