Modified magnesium hydride composite hydrogen storage material and preparation method thereof

Abstract

The invention relates to a modified magnesium hydride composite hydrogen storage material and a preparation method thereof, and belongs to the technical field of hydrogen storage materials. The composite hydrogen storage material disclosed by the invention is prepared from the following components in percentage by mass: 3wt%-9wt% of a NiTi-LDH catalyst and 91wt%-97wt% of MgH2. A binary transition metal catalyst is constructed through a hydrophobic transition element Ni and a hydrophilic transition element Ti, synergistic catalysis is achieved based on electron transfer, a channel effect and a hydrogen pump effect, the hydrogen absorption and desorption performance of MgH2 is remarkably improved by adding the NiTi-LDH catalyst, and the hydrogen absorption and desorption performance of MgH2 is remarkably improved. Meanwhile, excellent low-temperature hydrogen absorption performance and stable cyclic dynamic performance are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrogen storage materials, and particularly relates to a modified magnesium hydride composite hydrogen storage material and a preparation method thereof. BACKGROUND

[0002] Hydrogen energy has the characteristics of high energy density, zero emission, high efficiency, wide source and renewable, is widely considered as the most promising clean energy in the 21st century, meets the needs of environmental protection and sustainable development, and is an ideal energy storage carrier to achieve the double carbon goal. However, the hydrogen energy industry chain system is not yet complete, and the high-density storage and transportation of hydrogen is an important link in the development of hydrogen energy, and is also a key bottleneck for the large-scale and practical application of hydrogen energy.

[0003] Compared with traditional gas storage technology, the current mainstream hydrogen storage methods include low-temperature liquid hydrogen storage, organic liquid hydrogen storage, high-pressure gaseous hydrogen storage and solid-state hydrogen storage. Hydrogen storage in the form of hydride is considered to be the best and most promising form of hydrogen storage, because hydrogen is stored in the form of atoms in the metal, the volume hydrogen storage density is high, the stability is high, the safety is strong, the storage and transportation are convenient, and the hydrogen storage performance is good. The hydrogen storage material based on magnesium has a corresponding hydride MgH2, which has the advantages of rich magnesium resources, low price, high hydrogen storage density of MgH2, high safety, green environmental protection and the like, and has become the focus in the field of hydrogen energy storage and transportation. However, the high generation enthalpy (ΔH = ~ 75 kJ / mol H2) and reaction activation energy (ΔE = 160 kJ / mol) of MgH2 lead to high hydrogen absorption and desorption temperature and poor kinetics. Therefore, it is urgent to effectively improve the hydrogen storage performance of MgH2 to achieve the goal of practical application. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a modified magnesium hydride composite hydrogen storage material and a preparation method thereof.

[0005] The technical scheme of the present application is as follows:

[0006] A modified magnesium hydride composite hydrogen storage material, according to mass percentage, the composite hydrogen storage material comprises 3wt%-9wt% of a NiTi-LDH catalyst and 91wt%-97wt% of MgH2.

[0007] In some embodiments, the composite hydrogen storage material comprises 6wt%-9wt% of the NiTi-LDH catalyst and 91wt%-94wt% of the MgH2.

[0008] The present application also provides a preparation method of the above-mentioned composite hydrogen storage material, comprising the following steps:

[0009] Preparation of a NiTi-LDH catalyst;

[0010] Calculated by mass percentage, 3wt% to 9wt% of the NiTi-LDH catalyst and 91wt% to 97wt% of the MgH2 are mixed to prepare a mixture, and the composite hydrogen storage material is prepared by mechanical ball milling.

[0011] In some embodiments, the NiTi-LDH catalyst is prepared by a co-precipitation method, comprising the following steps:

[0012] Mixing a nickel source, a titanium source, a precipitant, and a solvent to prepare a first mixed solution;

[0013] heating the first mixed solution to react and prepare a first precursor;

[0014] The first precursor is purified.

[0015] In some embodiments, the heating reaction temperature is 80°C to 90°C.

[0016] In some embodiments, the heating reaction time is 24 hours to 27 hours.

[0017] In some embodiments, the NiTi-LDH catalyst is prepared by a hydrothermal method, comprising the following steps:

[0018] Mixing a nickel source, a titanium source, a precipitant, and a solvent to prepare a second mixed solution;

[0019] preparing a second precursor by subjecting the second mixed solution to a hydrothermal reaction;

[0020] The second precursor is dried.

[0021] In some embodiments, the temperature of the hydrothermal reaction is 120°C to 150°C.

[0022] In some embodiments, the hydrothermal reaction time is 10 h to 14 h.

[0023] In some embodiments, the drying is performed by vacuum drying.

[0024] In some embodiments, the vacuum drying temperature is 50°C to 70°C.

[0025] In some embodiments, the vacuum drying time is 10 h to 15 h.

[0026] In some embodiments, the molar ratio of the nickel source to the titanium source is (3-4):1.

[0027] In some embodiments, the molar ratio of the titanium source to the precipitant is 1:(50-100).

[0028] In some embodiments, the nickel source includes one or more of nickel chloride, nickel nitrate, and nickel carbonate.

[0029] In some embodiments, the titanium source includes one or more of isopropyl titanate, butyl titanate, titanium tetrachloride, and titanium tetraisopropoxide.

[0030] In some embodiments, the precipitating agent comprises urea.

[0031] In some embodiments, the solvent includes water.

[0032] The present invention has the following beneficial effects:

[0033] Alloying, nano-sizing, catalytic modification, and system composite are considered to be the four main ways to effectively improve the hydrogen storage performance of MgH2. Among them, catalytic modification refers to doping MgH2 with a small amount of transition metal or its compound catalyst, which destabilizes Mg-H through the electron transfer characteristics and promotes the dissociation of hydrogen. At the same time, the diffusely distributed catalytic active sites provide more channels for the diffusion and transfer of hydrogen, which can effectively increase the hydrogen absorption / desorption rate and improve the kinetic performance of the MgH2 / Mg system. Another advantage of the catalyst is that the addition amount is usually very small, which is conducive to maintaining a high hydrogen storage capacity. The present invention constructs a binary transition metal catalyst NiTi-LDH by using the hydrophobic transition element Ni and the hydrophilic transition element Ti, and realizes synergistic catalysis based on "electron transfer", "channel effect" and "hydrogen pump effect". Through the addition of the NiTi-LDH catalyst, the hydrogen absorption and desorption performance of MgH2 is significantly improved, and it also has relatively excellent low-temperature hydrogen absorption performance and stable cycle kinetic performance.

[0034] The raw materials of the preparation method of the present invention are easily available, the preparation method is simple, easy to synthesize, environmentally friendly, and suitable for large-scale production.

[0035] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0037] Figure 1 The XRD pattern of the NiTi-LDH catalyst prepared in Example 1;

[0038] Figure 2SEM, TEM and EDS elemental mapping of the NiTi-LDH catalyst prepared in Example 1, wherein Figure 2 (a) is SEM morphology, (b) is TEM morphology, and (c) is EDS mapping corresponding to (b);

[0039] Figure 3 SEM and particle size statistics of the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1, wherein Figure 3 (a) is SEM morphology, Figure 3 (b) is particle size statistics;

[0040] Figure 4 SEM of the NiTi-LDH catalyst prepared in Examples 4-7;

[0041] Figure 5 SEM of the NiTi-LDH catalyst prepared in Examples 8-9;

[0042] Figure 6 Isothermal hydrogen desorption curves of the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1 at different temperatures;

[0043] Figure 7 Isothermal hydrogen absorption curves of the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1 at different temperatures;

[0044] Figure 8 300℃ cyclic hydrogen absorption and desorption performance of the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1;

[0045] Figure 9 Isothermal hydrogen desorption curves of the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 8 at different temperatures;

[0046] Figure 10 Temperature programmed desorption (TPD) curves of the ball-milled pure MgH2 powder of Comparative Example 1 and the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1;

[0047] Figure 11 Comparison of isothermal hydrogen desorption curves of the ball-milled pure MgH2 powder of Comparative Example 1 and the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1;

[0048] Figure 12This is a comparison diagram of the isothermal hydrogen absorption curves of the ball-milled pure MgH2 powder of Comparative Example 1 and the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1. DETAILED DESCRIPTION

[0049] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0050] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0051] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0052] Layered double hydroxides (LDHs) are composed of alternating metal ions and hydroxide ions arranged in a layered structure. They possess a large specific surface area, a stable layered structure, a high ion exchange capacity, and excellent catalytic performance. In recent years, LDHs have attracted extensive research interest as catalysts, with some progress being made. Compared to single transition metal-based catalysts, dual transition metal-based catalysts can further enhance the hydrogen storage performance of MgH2.

[0053] Currently, the design of efficient LDH catalysts to modulate the kinetics of MgH2 is rare, and there is still insufficient understanding of the structure-activity relationship and catalytic reaction mechanism of the dual transition metal-based NiTi-LDH catalyst MgH2. Therefore, it is necessary to study new magnesium-based hydrogen storage materials based on dual transition metal-based NiTi-LDH catalysts to address the shortcomings of existing magnesium-based hydrogen storage materials.

[0054] The invention provides a modified magnesium hydride composite hydrogen storage material. Calculated by mass percentage, the composite hydrogen storage material comprises 3wt% to 9wt% of a NiTi-LDH catalyst and 91wt% to 97wt% of MgH2.

[0055] The present invention dopes MgH2 with a small amount of transition metal or its compound catalyst, destabilizing the Mg-H bond through electron transfer properties and promoting hydrogen dissociation. Simultaneously, the dispersed catalytic active sites provide more channels for hydrogen diffusion and transfer, effectively increasing the hydrogen absorption and desorption rates and improving the kinetic performance of the MgH2 / Mg system. Another advantage of the catalyst is that the addition amount is typically very small, which helps maintain a high hydrogen storage capacity. Specifically, the binary transition metal catalyst, constructed from the hydrophobic transition element Ni and the hydrophilic transition element Ti, achieves synergistic catalysis based on "electron transfer," "channeling," and "hydrogen pumping effects." The addition of the NiTi-LDH catalyst significantly improves the hydrogen absorption and desorption properties of MgH2. Specifically, the composite hydrogen storage material exhibits significantly enhanced desorption kinetics. For example, for desorption, the composite material exhibits a maximum hydrogen desorption capacity of 5.91 wt.% in 5 minutes at 300°C. Even at temperatures as low as 250°C, the composite material can rapidly release 5.54 wt.% of hydrogen within 20 minutes.

[0056] The composite hydrogen storage material of the present invention exhibits excellent low-temperature hydrogen absorption performance, absorbing approximately 3 wt.% of hydrogen within 30 minutes, even at a relatively low temperature of 75°C. Furthermore, the composite hydrogen storage material exhibits stable cyclic kinetics, maintaining a hydrogen storage capacity of approximately 6.0 wt.% after 100 cycles, with a capacity retention rate exceeding 95%.

[0057] In some examples, the composite hydrogen storage material includes 6 wt% to 9 wt% of the NiTi-LDH catalyst and 91 wt% to 94 wt% of MgH2, by weight. Preferably, the composite hydrogen storage material includes 6 wt% of the NiTi-LDH catalyst and 94 wt% of MgH2.

[0058] The present invention also provides a method for preparing the composite hydrogen storage material, comprising the following steps:

[0059] S100: preparing a NiTi-LDH catalyst.

[0060] In some examples, in the step S100, the NiTi-LDH catalyst is prepared by a coprecipitation method, including the following steps:

[0061] mixing a nickel source, a titanium source, a precipitant and a solvent to prepare a first mixed solution;

[0062] heating the first mixed solution to prepare a first precursor;

[0063] purifying the first precursor.

[0064] In some specific examples, the heating is performed in a water bath or in an oil bath; in some specific examples, the heating is performed under stirring at a stirring speed of 800 rpm to 1000 rpm.

[0065] In some specific examples, the heating is performed at a temperature of 80°C to 90°C.

[0066] In some specific examples, the heating is performed for a time of 24 h to 27 h.

[0067] In some specific examples, after the heating, the method further includes steps of washing and filtering. More specifically, the washing is performed by repeatedly centrifugal washing with deionized water and ethanol until the pH of the solution is neutral, and the centrifugal washing is performed at a speed of 3000 rpm to 6000 rpm. The filtering is performed by filtering the washed mixed solution to obtain a filter residue.

[0068] In some specific examples, the purifying includes steps of ultrasonic stripping, centrifugal washing, filtering to obtain a filter residue, and drying the filter residue. In some more specific examples, the ultrasonic stripping is performed by mixing the first precursor with anhydrous ethanol and ultrasonically treating at room temperature for 6 h to 18 h. In some more specific examples, the drying is performed by freeze-drying.

[0069] The NiTi-LDH catalyst with a vertical and interlaced sheet structure is prepared by a simple coprecipitation method.

[0070] In some specific examples, the NiTi-LDH catalyst has a nanosheet structure; in some more specific examples, the NiTi-LDH nanosheet has a thickness of 18 nm to 22 nm.

[0071] In some examples, in the step S100, the NiTi-LDH catalyst is prepared by a hydrothermal method, including the following steps:

[0072] mixing a nickel source, a titanium source, a precipitant and a solvent to prepare a second mixed solution;

[0073] preparing a second precursor by hydrothermal reaction of the second mixed solution;

[0074] The second precursor is dried.

[0075] In some specific examples, the hydrothermal reaction is carried out in a high-pressure reactor; in some more specific examples, the temperature of the hydrothermal reaction is 120° C. to 150° C.; in some more specific examples, the time of the hydrothermal reaction is 10 h to 14 h.

[0076] In some specific examples, the drying is carried out in a vacuum drying manner, and the vacuum drying temperature is 50°C to 70°C; more specifically, the vacuum drying temperature is 60°C.

[0077] In some specific examples, the vacuum drying time is 10 hours to 15 hours; more specifically, the vacuum drying time is 12 hours.

[0078] In some specific examples, the nickel source includes one or more of nickel chloride, nickel nitrate, and nickel carbonate; in some more specific examples, the nickel source is nickel chloride.

[0079] In some specific examples, the titanium source includes one or more of isopropyl titanate, butyl titanate, titanium tetrachloride, and titanium tetraisopropoxide; in some more specific examples, the titanium source is isopropyl titanate.

[0080] In some specific examples, the molar ratio of the nickel source to the titanium source is (3-4):1.

[0081] In some specific examples, the precipitant includes urea.

[0082] In some specific examples, the molar ratio of the titanium source to the precipitant is 1:(50-100).

[0083] In some embodiments, the solvent includes water.

[0084] S200: 3 wt% to 9 wt% of the NiTi-LDH catalyst and 91 wt% to 97 wt% of the MgH2 are mixed to prepare a mixture, and the composite hydrogen storage material is prepared by mechanical ball milling.

[0085] The present invention introduces the NiTi-LDH catalyst into the MgH2 by mechanically ball milling a mixture of the NiTi-LDH catalyst. This simple ball milling reduces the MgH2 particle size and introduces additional structural defects, shortening the diffusion distance of hydrogen, thereby enhancing surface activity. Furthermore, the flaky catalyst prepared by the present invention is uniformly dispersed on the surface of the MgH2 matrix after high-energy ball milling, resulting in a high number of catalytically active sites, thereby utilizing the synergistic catalytic effect of multiple metals.

[0086] In some examples, the mechanical ball milling method uses stainless steel balls with a diameter of 5 to 10 mm as ball milling beads, argon as the ball milling atmosphere, a ball-to-material ratio of 20 to 40:1, and intermittent ball milling at a speed of 200 to 800 rpm in both forward and reverse directions for 10 to 20 hours. Preferably, the intermittent ball milling in both forward and reverse directions is performed with a pause of 5 to 20 minutes after each 5 to 20 minutes of ball milling.

[0087] In the NiTi-LDH catalyst of the present invention, the hydrophobic element Ni catalyzes the hydrogen absorption process of MgH2, while the hydrophilic element Ti catalyzes the hydrogen release process. The resulting bidirectional catalytic effect is far superior to that of a single metal. By adding a small amount of NiTi-LDH catalyst, the present invention helps maintain a high hydrogen storage capacity while also significantly improving the hydrogen absorption and desorption properties of MgH2. Specifically, the composite hydrogen storage material exhibits significantly enhanced desorption kinetics. For desorption, the amount and rate of hydrogen released are significantly increased, with a high desorption capacity (5.91 wt.%) at 300°C (5 minutes). Pure magnesium hydride releases only 0.03 wt.% of hydrogen in 5 minutes at the same temperature, virtually no hydrogen release. Extending the desorption time to 60 minutes still results in a mere 3.68 wt.% of hydrogen released. Even at temperatures as low as 250°C, the composite hydrogen storage material of the present invention rapidly releases 5.54 wt.% of hydrogen in 20 minutes. The hydrogen storage material of the present invention also has relatively excellent low-temperature hydrogen absorption performance. At 125°C, it can quickly absorb 4.28wt.% of hydrogen within 10 minutes, while pure MgH2 can only absorb 0.53wt.% of hydrogen within 10 minutes at the same temperature. When its hydrogen absorption time is extended to 60 minutes, pure magnesium hydride can only absorb 2.18wt.% of hydrogen. Even at a lower temperature of 75°C, the composite material of the present invention can absorb 2.97wt.% of hydrogen within 30 minutes.

[0088] The following are specific examples, in the following specific examples, the instruments, reagents, materials involved, if no special instructions, are existing conventional instruments, reagents, materials, can be obtained through the normal commercial channels. The experimental methods, detection methods involved in the following examples, if no special instructions, are existing conventional experimental methods, detection methods.

[0089] Examples 1 to 7 use co-precipitation method to prepare NiTi-LDH catalyst.

[0090] Example 1

[0091] (1) Co-precipitation method for preparing NiTi-LDH catalyst

[0092] 8 mmol of nickel chloride hexahydrate (NiCl2.6H2O), 2 mmol of titanium isopropoxide (C 12 H28O4Ti) and urea 0.1 mol (CH4N2O) were dissolved in 100 mL of deionized water at room temperature and magnetically stirred uniformly. Then, the uniformly mixed solution was placed in a constant temperature water bath heating pot, and stirred at 90°C for 24 h. After the reaction was completed, the mixed solution was first centrifuged with deionized water and then with anhydrous ethanol at a speed of 6000 rpm until the supernatant was neutral, and then filtered to obtain a green powder product.

[0093] The green powder product prepared in the above step was placed in 50 mL of anhydrous ethanol, and ultrasonic stripping was carried out in an ultrasonic machine at room temperature for 6 h. The obtained suspension was centrifuged at a speed of 6000 rpm, and the wet green solid powder was obtained after further freeze-drying to obtain the NiTi-LDH catalyst.

[0094] (2) Preparation of MgH2-6 wt% NiTi-LDH composite hydrogen storage material

[0095] 0.06 g of NiTi-LDH catalyst powder prepared in the above step (1) was mixed with 0.94 g of pure MgH2 powder under high-purity argon atmosphere to prepare 1 g of mixed sample. The mixed sample was subjected to high-energy mechanical ball milling under argon atmosphere for 20 h, wherein the ball-to-material ratio was 20:1, the ball milling speed was 400 rpm, the ball milling tank was a 100 mL stainless steel tank, the ball milling beads were 5 mm and 10 mm in diameter, and the stainless steel beads were used, and the positive and negative intermittent ball milling mode was used, i.e. running at a speed of 400 rpm for 10 min, then reversing for 10 min, and then running at a speed of 400 rpm for 10 min, then reversing for 10 min, and the effective ball milling time was 10 h. After ball milling, the ball milling tank was scraped in the glove box, and the product was obtained.

[0096] Example 2

[0097] (1) The steps for preparing NiTi-LDH catalyst by co-precipitation method are the same as step (1) of Example 1.

[0098] (2) Preparation of MgH2-3 wt% NiTi-LDH composite hydrogen storage material

[0099] This step is basically the same as Example 1, except that 0.03 g of the NiTi-LDH catalyst powder prepared in the above step 1 is mixed with 0.97 g of pure MgH2 powder under a high-purity argon atmosphere to prepare 1 g of a mixed sample.

[0100] Example 3

[0101] (1) The steps for preparing NiTi-LDH catalyst by co-precipitation method are the same as step (1) of Example 1.

[0102] (2) Preparation of MgH2-9 wt% NiTi-LDH composite hydrogen storage material

[0103] This step is basically the same as Example 1, except that 0.09 g of the NiTi-LDH catalyst powder prepared in the above step 1 is mixed with 0.91 g of pure MgH2 powder under a high-purity argon atmosphere to prepare 1 g of a mixed sample.

[0104] Example 4

[0105] (1) Preparation of NiTi-LDH catalyst by coprecipitation method

[0106] At room temperature, 8 mmol of nickel chloride hexahydrate (NiCl2.6H2O), 2 mmol of TiCl4, and 0.1 mol of urea (CH4N2O) were dissolved in 100 mL of deionized water and magnetically stirred. The mixed solution was then placed in a constant-temperature water bath and stirred at 90°C for 24 hours. After the reaction, the resulting mixture was washed with deionized water and then with anhydrous ethanol by centrifugation at 6000 rpm until the supernatant reached a neutral pH. The product was then filtered to obtain a green powder.

[0107] The green powder product was placed in 50 mL of anhydrous ethanol and placed in an ultrasonic machine for ultrasonic stripping at room temperature for 6 hours. The resulting suspension was centrifuged at a speed of 6000 rpm and filtered to obtain a wet green solid powder, which was then further freeze-dried to obtain the NiTi-LDH catalyst.

[0108] (2) Preparation of MgH2-6 wt% NiTi-LDH composite hydrogen storage material

[0109] The NiTi-LDH catalyst powder prepared in step (1) above was mixed with 0.94 g of pure MgH2 powder under a high-purity argon atmosphere to prepare 1 g of a mixed sample, and the mixed sample was subjected to high-energy mechanical ball milling under an argon atmosphere for 20 h, with the ball milling conditions being the same as in Example 1.

[0110] Example 5

[0111] (1) Preparation of a NiTi-LDH catalyst by coprecipitation

[0112] Step (1) was basically the same as in Example 4, except that the reaction time was different, with 27 h of stirring at a constant temperature of 90 °C in Example 5.

[0113] (2) The step of preparing a composite hydrogen storage material was basically the same as in step (2) of Example 4.

[0114] Example 6

[0115] (1) Preparation of a NiTi-LDH catalyst by coprecipitation

[0116] Step (1) was basically the same as in Example 4, except that the amount of nickel chloride hexahydrate (NiCl2.6H2O) was 6 mmol.

[0117] (2) The step of preparing a composite hydrogen storage material was basically the same as in step (2) of Example 4.

[0118] Example 7

[0119] (1) Preparation of a NiTi-LDH catalyst by coprecipitation

[0120] Step (1) was basically the same as in Example 4, except that the amount of nickel chloride hexahydrate (NiCl2.6H2O) was 6 mmol and the reaction time was different, with 27 h of stirring at a constant temperature of 90 °C in Example 9.

[0121] Examples 8 to 9 used a hydrothermal method to prepare a NiTi-LDH catalyst.

[0122] Example 8

[0123] (1) Preparation of a NiTi-LDH catalyst by a hydrothermal method

[0124] At room temperature, 8 mmol of nickel chloride hexahydrate (NiCl2.6H2O) and 2 mmol of isopropyl titanate (C 12H₂₈O₄Ti₂ and 0.1 mol of urea (CH₄N₂O) were dissolved in 100 mL of deionized water and magnetically stirred. The mixed solution was then placed in an autoclave and reacted at 120°C for 12 hours. The resulting mixture was washed with deionized water and then with anhydrous ethanol by centrifugation at 6000 rpm until the supernatant reached a neutral pH. The product was then filtered to obtain a green powder.

[0125] The green powder product was vacuum dried at 60° C. for 12 h to obtain a NiTi-LDH catalyst, which was named NiTi-LDH-vacuum.

[0126] (2) Preparation of MgH2-6 wt% NiTi-LDH-vacuum composite hydrogen storage material

[0127] 0.06 g of the NiTi-LDH-vacuum catalyst prepared in the above steps was ball-milled with 0.94 g of MgH2 powder to obtain a MgH2-6 wt.% NiTi-LDH-vacuum composite hydrogen storage material.

[0128] Example 9

[0129] (1) Preparation of NiTi-LDH catalyst by hydrothermal method

[0130] This step is basically the same as Example 8, except that the temperature of the hydrothermal reaction is different. Specifically, the uniformly mixed solution is reacted in a high-pressure reactor at 150° C. for 12 h to obtain a NiTi-LDH catalyst named NiTi-LDH-vacuum-150.

[0131] (2) Preparation of MgH2-6 wt% NiTi-LDH-vacuum-150 composite hydrogen storage material

[0132] 0.06 g of the NiTi-LDH-Vacuum-150 catalyst prepared in the above steps was ball-milled with 0.94 g of MgH2 powder to obtain a MgH2-6 wt.% NiTi-LDH-Vacuum-150 composite hydrogen storage material.

[0133] Comparative Example 1

[0134] Comparative Example 1 differs from Example 1 in that no NiTi-LDH catalyst is added, and 1 g of MgH2 powder is subjected to high-energy mechanical ball milling for 20 h under a high-purity argon atmosphere. The resulting hydrogen storage material is designated as ball-milled pure MgH2.

[0135] 60 mg of ball-milled pure MgH2 powder was weighed in a glove box, and the temperature-dependent hydrogen desorption curve of the sample was tested using a PCTpro high-pressure gas adsorption instrument: the isothermal hydrogen desorption curve at 300°C and an initial hydrogen pressure of 0.01 MPa; the isothermal hydrogen absorption curve at 125°C and an initial hydrogen pressure of 3 MPa.

[0136] Test Example

[0137] (1) Structural Test

[0138] The NiTi-LDH catalyst prepared in Example 1 was subjected to XRD test, and the results are shown in FIG. 2. As can be seen from FIG. 2, the catalyst has a characteristic peak specific to a hydrotalcite-like material, indicating that the NiTi-LDH catalyst is successfully synthesized. Figure 1 Figure 1 The NiTi-LDH catalyst prepared in Example 1 was subjected to SEM, TEM test and EDS element distribution analysis, and the results are shown in FIG. 3. As can be seen from FIG. 3(a), the NiTi-LDH catalyst has a straight and interlaced sheet structure, and the thickness of the nanosheet is 18 nm to 22 nm. The TEM analysis further verifies the nanosheet structure of the material.

[0139] The NiTi-LDH catalyst prepared in Example 1 was subjected to SEM, TEM test and EDS element distribution analysis, and the results are shown in FIG. 3. As can be seen from FIG. 3(a), the NiTi-LDH catalyst has a straight and interlaced sheet structure, and the thickness of the nanosheet is 18 nm to 22 nm. The TEM analysis further verifies the nanosheet structure of the material. Figure 2 Figure 2 (b) in FIG. 3, the lattice fringe spacing of 0.156 nm corresponds to the (110) crystal plane, which matches the XRD results, confirming the successful synthesis of the nanosheet NiTi-LDH catalyst, and at the same time, Figure 2 (b) shows that the average particle size of the nanosheet is about 200 nm, which is composed of several single layers stacked. The EDS element distribution results (c) show that the elements of Ni, Ti, O and C are highly uniformly distributed on the surface of the nanosheet, and the excess C element signal is derived from the carbon film support substrate used for testing. The thin two-dimensional nanosheet structure can effectively increase the contact interface of the catalyst and MgH2, shorten the hydrogen diffusion path, and realize rapid hydrogen diffusion and electron transfer in the hydrogen absorption / desorption process, thereby improving the hydrogen storage performance of MgH2. This may be a key structural factor for the NiTi-LDH catalyst to exhibit excellent catalytic effect. Figure 2 Figure 2

[0140] Figure 3 The SEM image (left) and particle size distribution graph (right) of the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1 are shown in FIG. 4. As can be seen from FIG. 4, after mechanical ball milling, the average particle size of the composite hydrogen storage material is 0.36 μm. Figure 3

[0141] The SEM images of the NiTi-LDH catalyst materials of Example 4 to Example 7 are shown in FIG. 5. As can be seen from FIG. 5, the average particle size of the NiTi-LDH catalyst materials of Example 4 to Example 7 is about 200 nm. Figure 4 Figure 4 ​​​​​It can be seen that although these catalysts still maintain the typical layered double hydroxide phase structure, the microscopic morphology of the above samples does not show the expected nanosheet structure. Specifically, the sample surface shows a porous aggregate structure formed by the self-assembly of nanoparticles. This three-dimensional disordered stacking morphology deviates significantly from the experimental design that obtains a two-dimensional nanosheet structure by controlling experimental parameters.

[0142] Figure 5 The SEM images of the NiTi-LDH catalysts prepared in Examples 8 and 9 are as follows: Figure 5 It is shown that the NiTi-LDH catalysts prepared in Examples 8 to 9 have different morphologies compared to Example 1. The samples of Examples 8 to 9 did not form the expected highly dispersed nanostructures, but were mainly characterized by irregular block morphology, with particle size distribution concentrated in the range of 10-15 μm. The formation of such micron-sized agglomerates may be related to the Ostwald ripening effect caused by excessive precursor concentration during the synthesis process. It is worth noting that the catalyst particle size and dispersion have a key influence on the performance of its composite system. Nanoscale catalysts with high specific surface area characteristics can achieve uniform interface distribution with the MgH2 matrix through a mechanical ball milling process. This close contact heterogeneous structure can significantly improve hydrogen diffusion kinetics. In contrast, the large-sized block catalysts prepared in Examples 8 to 9 may have significantly deteriorated their catalytic performance due to a sudden drop in specific surface area and insufficient interface contact sites.

[0143] (2) Hydrogen storage performance test

[0144] The test method is as follows: 60 mg of the prepared composite hydrogen storage material was weighed in a glove box, and the temperature-dependent hydrogen desorption curve of the sample was tested using a PCTpro high-pressure gas adsorption instrument: isothermal hydrogen desorption curve at 300°C and 250°C under an initial hydrogen pressure of 0.01 MPa; isothermal hydrogen absorption curve at 75°C and 125°C under an initial hydrogen pressure of 3 MPa; and cycle curve.

[0145] The hydrogen storage performance of the composite hydrogen storage materials prepared in Examples 1 to 3 was tested, and the test results are shown in Table 1 below:

[0146] Table 1

[0147]

[0148] Table 1 is a performance comparison table of the initial hydrogen desorption temperature, hydrogen desorption amount at 300°C for 5 minutes, and hydrogen absorption amount at 125°C for 10 minutes of three composite hydrogen storage materials modified with NiTi-LDH with different doping amounts obtained in Examples 1 to 3. It can be concluded from Table 1 that compared with the MgH2-3 wt.% NiTi-LDH and MgH2-9 wt.% NiTi-LDH samples, MgH2-6 wt.% NiTi-LDH not only maintains a higher hydrogen storage capacity, but also has the lowest initial hydrogen desorption temperature (230.1°C). It was preliminarily determined that the optimal doping ratio of the catalyst is 6 wt.%. In addition, the isothermal hydrogen absorption and desorption kinetics of the three groups of samples were compared. It can be seen that the MgH2-3 wt.% NiTi-LDH, MgH2-6 wt.% NiTi-LDH, and MgH2-9 wt.% NiTi-LDH composite materials released 5.71 wt.%, 5.91 wt.%, and 5.24 wt.% of hydrogen, respectively, at 300°C within 5 minutes. At 125°C, they absorbed 3.92 wt.%, 4.28 wt.%, and 4.06 wt.% of hydrogen, respectively, within 10 minutes. In summary, the MgH2-6 wt.% NiTi-LDH prepared in Example 1 has better comprehensive hydrogen storage performance than the other samples.

[0149] Figure 6 and Figure 7 They are the isothermal hydrogen desorption curve and the isothermal hydrogen absorption curve of the MgH2-6wt% NiTi-LDH composite hydrogen storage material prepared in Example 1. Figure 6 It can be seen that the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material has a large hydrogen release capacity at 300°C (5 min, 5.91 wt.%). Even at a temperature as low as 250°C, the composite material can quickly release 5.54 wt.% of hydrogen within 20 min. Figure 7 It can be seen that the MgH2-6wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1 also has relatively excellent low-temperature hydrogen absorption performance. After adding the catalyst, the composite hydrogen storage material can quickly absorb 4.28wt.% of hydrogen within 10 minutes at 125°C. Even at a lower temperature of 75°C, the composite material can absorb 2.97wt.% of hydrogen within 30 minutes.

[0150] Table 2 below summarizes the isothermal hydrogen desorption results of the MgH2-6 wt% NiTi-LDH composite hydrogen storage material at different temperatures.

[0151] Table 2

[0152]

[0153] Combine Figure 6As can be seen from Table 2, the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material exhibits excellent hydrogen desorption kinetics at different temperatures: at 300°C, it has a large hydrogen desorption capacity, with a hydrogen desorption capacity of 5.91 wt.% within 10 min; at 275°C, the hydrogen desorption capacity within 10 min is 5.81 wt.%; when the temperature is as low as 250°C, the hydrogen desorption capacity of the composite material within 10 min is 4.00 wt.%.

[0154] Figure 8 This is a graph showing the cyclic hydrogen absorption and desorption performance at 300°C of the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1. Figure 8 It can be seen that after 100 cycles of hydrogen absorption and desorption, the hydrogen desorption amount of the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material only decayed by 0.25 wt.%, the hydrogen storage capacity remained at 5.90 wt.%, and the capacity retention rate was 95.89%, showing stable cyclic reversibility.

[0155] Figure 9 This is the isothermal hydrogen desorption curve of the MgH2-6 wt.% NiTi-LDH-vacuum composite hydrogen storage material prepared in Example 8. Table 3 summarizes the isothermal hydrogen desorption results of the MgH2-6 wt.% NiTi-LDH-vacuum composite material within 10 minutes at different temperatures.

[0156] Table 3

[0157] Isothermal hydrogen desorption temperature / ℃ 300 275 250 Hydrogen release within 10 minutes / wt.% 5.57 4.90 1.15

[0158] Depend on Figure 9As shown in Table 3, the composite hydrogen storage material prepared in Example 8 exhibits a high hydrogen desorption capacity at 300°C, with a hydrogen desorption rate of 5.57 wt.% in 10 minutes, comparable to that of the composite hydrogen storage material prepared in Example 1. However, the two exhibit significant differences in their desorption kinetics: during the rapid desorption phase at 300°C, the average desorption rate of Example 8 is only 0.87 wt.% / min, a 48.2% decrease from 1.68 wt.% / min in Example 1. The difference is even more pronounced at lower temperatures, with the desorption capacity of the composite hydrogen storage material prepared in Example 8 declining significantly with decreasing temperature. At 275°C, the desorption rate in 10 minutes is 4.90 wt.% (Example 1: 5.81 wt.%). At temperatures as low as 250°C, the composite material desorbs only 1.15 wt.% (Example 1: 4.00 wt.%) in 10 minutes. By comparing the test results of Example 1 with those of Example 8, it can be seen that compared with irregular block-shaped NiTi-LDH, NiTi-LDH with a nanosheet structure has better kinetic performance. Nanosheet-shaped NiTi-LDH has more active sites, is more severely broken during ball milling with MgH2, is more dispersed in the composite hydrogen storage material, and ultimately achieves a better catalytic effect.

[0159] Figure 10 The temperature-dependent hydrogen release curves (TPD curves) of the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1 and the ball-milled pure MgH2 powder of Comparative Example 1 are shown. Figure 10 It can be seen that the initial dehydrogenation temperature of the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material is 230.1°C, and the initial dehydrogenation temperature of the ball-milled pure MgH2 powder of Comparative Example 1 is 290.1°C. Obviously, the composite hydrogen storage material of Example 1 has a lower initial dehydrogenation temperature, indicating that the introduction of NiTi-LDH can significantly reduce the dehydrogenation temperature of MgH2. The composite material of Example 1 exhibits an accelerated dehydrogenation rate while maintaining a high hydrogen storage capacity.

[0160] Figure 11 The isothermal hydrogen release curve comparison diagram of the ball-milled pure MgH2 powder of Comparative Example 1 and the MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1. Figure 11It can be seen that the MgH2-6wt.%NiTi-LDH composite hydrogen storage material prepared in Example 1 significantly improves the hydrogen release capacity and rate. Ball-milled pure MgH2 releases only 0.03wt.% of hydrogen in 5 minutes at 300°C, almost no hydrogen is released. When the hydrogen release time is extended to 60 minutes, pure magnesium hydride can only release 3.68wt.% of hydrogen. MgH2-6wt.%NiTi-LDH, on the other hand, has a larger hydrogen release capacity (5.91wt.% in 5 minutes). Even at temperatures as low as 250°C, the composite material can quickly release 5.54wt.% of hydrogen in 20 minutes.

[0161] Figure 12 The isothermal hydrogen absorption curve comparison diagram of ball-milled pure MgH2 powder and MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1. Figure 12 It can be seen that pure MgH2 can only absorb 0.53 wt.% of hydrogen in 10 minutes at 125°C. When the hydrogen absorption time is extended to 60 minutes, ball-milled pure MgH2 can only absorb 2.18 wt.% of hydrogen. The MgH2-6 wt.% NiTi-LDH composite hydrogen storage material prepared in Example 1 also has relatively excellent low-temperature hydrogen absorption performance. After adding the catalyst, the composite hydrogen storage material can quickly absorb 4.28 wt.% of hydrogen in 10 minutes at 125°C. Even at a lower temperature of 75°C, the composite material can absorb 2.97 wt.% of hydrogen in 30 minutes.

[0162] In summary, the isothermal hydrogen desorption capacity of the composite hydrogen storage material obtained by doping with NiTi-LDH catalyst prepared by hydrothermal reaction is improved to a certain extent compared with ball-milled pure MgH2, but the effect is poorer than that of doping with NiTi-LDH catalyst prepared by co-precipitation method. This shows that the nanosheet NiTi-LDH catalyst has a better catalytic effect.

[0163] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A modified magnesium hydride composite hydrogen storage material, characterized in that: Calculated by mass percentage, the composite hydrogen storage material includes 3wt% to 9wt% of NiTi-LDH catalyst and 91wt% to 97wt% of MgH2.

2. The composite hydrogen storage material according to claim 1, wherein Calculated by mass percentage, the composite hydrogen storage material includes 6wt% to 9wt% of the NiTi-LDH catalyst and 91wt% to 94% of the MgH2.

3. A method for preparing the composite hydrogen storage material according to any one of claims 1 to 2, characterized in that: The steps include: Preparation of NiTi-LDH catalyst; Calculated by mass percentage, 3wt% to 9wt% of the NiTi-LDH catalyst and 91wt% to 97wt% of the MgH2 are mixed to prepare a mixture, and the composite hydrogen storage material is prepared by mechanical ball milling.

4. The preparation method according to claim 3, characterized in that The NiTi-LDH catalyst is prepared by a coprecipitation method, comprising the following steps: Mixing a nickel source, a titanium source, a precipitant, and a solvent to prepare a first mixed solution; heating the first mixed solution to react and prepare a first precursor; The first precursor is purified.

5. The preparation method according to claim 4, characterized in that The heating reaction satisfies one or more of the following conditions: (1) The heating reaction temperature is 80°C to 90°C; (2) The heating reaction time is 24h~27h.

6. The preparation method according to claim 3, characterized in that The NiTi-LDH catalyst is prepared by a hydrothermal method, comprising the following steps: Mixing a nickel source, a titanium source, a precipitant, and a solvent to prepare a second mixed solution; preparing a second precursor by subjecting the second mixed solution to a hydrothermal reaction; The second precursor is dried.

7. The preparation method according to claim 6, characterized in that The hydrothermal reaction satisfies one or more of the following conditions: (1) The temperature of the hydrothermal reaction is 120°C to 150°C; (2) The hydrothermal reaction time is 10h~14h.

8. The preparation method according to claim 6, characterized in that The drying is carried out by vacuum drying; vacuum drying satisfies one or more of the following conditions: (1) Drying temperature is 50℃~70℃; (2) Drying time is 10h~15h.

9. The preparation method according to any one of claims 3 to 8, characterized in that One or more of the following conditions are met: (1) The molar ratio of the nickel source to the titanium source is (3-4):1; (2) The molar ratio of the titanium source to the precipitant is 1:(50-100).

10. The preparation method according to any one of claims 3 to 8, characterized in that: One or more of the following conditions are met: (1) The nickel source includes one or more of nickel chloride, nickel nitrate and nickel carbonate; (2) The titanium source includes one or more of isopropyl titanate, butyl titanate, titanium tetrachloride and titanium tetraisopropoxide; (3) The precipitant includes urea; (4) The solvent includes water.

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