Multilayer nanostructured metal hydrides and methods for their preparation

Abstract

The application discloses a kind of multilayer nanostructure metal hydride and preparation method thereof, the preparation method includes that transition metal ion salt and carbon material are added to polar solvent mixture, heating stirring and obtain solid powder, hydrogen hot reduction reaction is carried out to solid powder and obtains functionalized carbon material;Metal hydride raw material, functionalized carbon material are added to organic solvent, ultrasonic, and mixed and obtain mixed solution, the metal hydride raw material is alkyl metal Mg compound or alkyl metal Li compound and mixture of borane compound;Under hydrogen atmosphere, the mixed solution is carried out solvothermal reaction, then centrifugation, washing, filtration, drying and obtain multilayer nanostructure metal hydride.The preparation method prepared multilayer nanostructure metal hydride has higher hydrogen absorption and hydrogen storage capacity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hydrogen storage materials and nanomaterials, and particularly relates to a multilayer nanostructured metal hydride and a preparation method thereof. BACKGROUND

[0002] Energy is the basis to support individual and social activities. The overconsumption of traditional fossil fuels not only causes energy crisis, but also brings a series of environmental pollution and health problems. Hydrogen energy, as a new type of renewable energy with abundant reserves, high energy density and clean pollution, is considered to be an ideal energy alternative in the future. However, hydrogen gas as an energy carrier in the gaseous state at room temperature and atmospheric pressure results in extremely low volumetric energy density, which leads to great challenges in its actual application in three aspects of production, storage and utilization. In particular, safe, efficient and economical hydrogen storage technology has always been a key bottleneck restricting the practicality and scale of hydrogen energy.

[0003] High-pressure gaseous hydrogen storage (room temperature, 350-700 bar) and low-temperature liquefied hydrogen storage (-253℃, 5-10 bar) are relatively mature in technology, but they cannot balance safety, hydrogen storage capacity and cost. Metal hydride, a chemical hydrogen storage material, stores hydrogen by forming chemical bonds between hydrogen atoms and materials, has good safety and high hydrogen storage capacity, and has great application and development prospects, including simple metal hydride (MgH2) and coordination hydride (LiBH4, NaAlH4) and the like.

[0004] As a typical coordination hydride, lithium borohydride (LiBH4) has high mass hydrogen storage density (18.5wt%) and volumetric hydrogen storage density (121 kg / m 3), which has attracted extensive attention of researchers. However, the high thermodynamic stability and reaction energy barrier of LiBH4 make its operation temperature high, kinetics slow and reversibility poor, which is not conducive to the application of on-board hydrogen storage. Therefore, reducing the hydrogen absorption and desorption temperature of LiBH4 and improving the reversibility have always been the focus of research in this field. At present, the modification research of LiBH4 hydrogen storage material mainly focuses on four aspects: reactant destabilization, anion and cation substitution, catalytic doping and nanocrystallization. Catalytic doping is the most commonly used modification method, which can significantly improve the hydrogen absorption and desorption kinetics of LiBH4. Based on the catalytic modification method, researchers have found that Ti-, Zr-, Nb-, Ni- and Co-based catalysts can significantly improve the dehydrogenation / hydrogenation kinetics of LiBH4. Compared with transition metal oxides and halides, metal catalysts are more suitable for the system because they are less likely to react with LiBH4 to produce byproducts LiCl during heating. In 2009, Yu et al. found that the introduction of metal Ni into LiBH4 not only improved the hydrogen desorption kinetics, but also greatly reduced the hydrogen absorption temperature. Therefore, metal-based catalysts have high catalytic effect on the hydrogen absorption and desorption of LiBH4. However, the thermodynamics of LiBH4 is relatively stable, and the improvement of the cycle stability of LiBH4 by catalyst is very limited. Nanocrystallization can not only achieve kinetic regulation, but also change the thermodynamic properties of LiBH4, thereby improving the reversibility of LiBH4. Without a carrier, LiBH4 will inevitably melt during hydrogen desorption, leading to particle agglomeration. Therefore, nanocrystallization of LiBH4 needs to be realized by nanometer confinement with the help of carrier materials. In order to further improve the comprehensive hydrogen storage performance of LiBH4, it is necessary to fully combine the advantages of catalytic doping and nanometer confinement. Therefore, the synergistic modification of nanocrystallization and nanocatalysis is very necessary.

[0005] MgH2 has become one of the high-capacity hydrogen storage materials that may be practical in recent years due to its abundant raw material reserves and high hydrogen storage content (7.6 wt%). However, due to its poor thermodynamic properties and slow kinetics, the hydrogen absorption and desorption temperature of MgH2 is too high to meet the practical requirements. Adding catalysts and nanocrystallization are effective means to reduce the hydrogen absorption and desorption kinetic energy barrier of MgH2. Similarly, the synergistic modification of nanocrystallization and nanocatalysis can also significantly improve the hydrogen absorption and desorption performance of MgH2.

[0006] At present, the research on the synergistic modification of nanocrystallization and catalytic doping cannot simultaneously meet the requirements of high hydrogen storage capacity and suitable operating temperature. SUMMARY

[0007] The application provides a preparation method of a multilayer nanostructured metal hydride, and the multilayer nanostructured metal hydride prepared by the preparation method has high hydrogen absorption and storage capacity.

[0008] The application provides a preparation method of a multi-layer nano-structured metal hydride, comprising the following steps:

[0009] (1) adding transition metal ion salt and carbon material into a polar solvent, mixing and heating to obtain a solid powder, and performing a hydrothermal reduction reaction on the solid powder to obtain a functionalized carbon material;

[0010] (2) adding a metal hydride raw material and the functionalized carbon material into an organic solvent, and performing ultrasonic mixing to obtain a mixed solution, wherein the metal hydride raw material is a mixture of an alkyl metal Mg compound or an alkyl metal Li compound and a borane compound;

[0011] (3) performing a solvothermal reaction on the mixed solution obtained in the step (2) under a hydrogen atmosphere, and then performing centrifugation, washing, filtration and drying to obtain the multi-layer nano-structured metal hydride.

[0012] The transition metal ion salt is reduced into single transition metal by the hydrothermal reduction reaction, the single transition metal is loaded on a carbon material carrier to form a catalyst layer, then the coordination hydride is loaded on the surface of the transition metal and / or the carbon material through the solvothermal reaction to form a multi-layer nano-structure, the size of the transition metal and the metal hydride of the multi-layer nano-structure is small, and the filling rate of the carrier carbon material is high, so that the obtained multi-layer nano-structured metal hydride has a high hydrogen storage density.

[0013] Preferably, the mass ratio of the transition metal ion salt to the carbon material is 0.01-100.

[0014] By controlling the content of the transition metal ion salt, the single transition metal with a small size can be dispersedly distributed on the carbon material under the synergistic effect of the hydrothermal reduction reaction, and the single transition metal and the carbon material have good catalytic activity.

[0015] Further preferably, the mass ratio of the transition metal ion salt to the carbon material is 0.1-10.

[0016] By further controlling the content of the transition metal ion salt, the single transition metal with a high loading density and a small size is loaded on the surface of the carbon material, and the metal hydride can be mostly loaded on the active sites of the single transition metal, so that the multi-layer structure is formed.

[0017] Preferably, the transition metal ion salt comprises one or more of a transition metal metallocene compound, a transition metal nitrate and a transition metal chloride;

[0018] The transition metal metallocene compound is one of nickelocene, cobaltocene and titaniumocene;

[0019] The transition metal nitrate is one of nickel nitrate, cobalt nitrate, iron nitrate, manganese nitrate, chromium nitrate, zinc nitrate, copper nitrate, zirconium nitrate, tungsten nitrate, ruthenium nitrate, rhodium nitrate, hafnium nitrate, palladium nitrate, iridium nitrate, platinum nitrate, scandium nitrate, yttrium nitrate, lanthanum nitrate, cerium nitrate, praseodymium nitrate.

[0020] The transition metal chloride is one of titanium tetrachloride, titanium trichloride, zirconium tetrachloride, vanadium trichloride, niobium pentachloride, chromium trichloride, molybdenum pentachloride, manganese dichloride, iron trichloride, iron dichloride, cobalt dichloride, nickel dichloride, copper dichloride, ruthenium trichloride, rhodium trichloride, palladium dichloride, silver chloride, hafnium tetrachloride, tungsten hexachloride, iridium trichloride, platinum tetrachloride, gold trichloride, scandium trichloride, yttrium trichloride, lanthanum trichloride, cerium trichloride, praseodymium trichloride. The above-mentioned ionic salt can form transition metal elements under suitable hydrothermal reduction.

[0021] Further preferably, the transition metal ionic salt is a transition metal nitrate. The decomposition product under the hydrothermal reduction reaction is a metal or a gas, which can improve the purity of the product.

[0022] Preferably, the carbon material is one or more of graphene, carbon nanotube, carbon fiber, porous carbon, carbon nitride, nitrogen-doped, boron-doped, or phosphorus-doped graphene, carbon nanotube, carbon fiber, porous carbon.

[0023] Preferably, the polar solvent is water and / or ethanol. The water and / or ethanol provided by the present application can better dissolve the transition metal ionic salt and the carbon material, and the ratio of water and ethanol only affects the rate of evaporation, and does not affect the physical and chemical properties of the prepared sample.

[0024] Preferably, the temperature of the heating and stirring is 60-90 ℃, the stirring speed is 300-1000 rpm, and the stirring time is 3-12 h. By controlling the time of heating and stirring, the transition metal ionic salt can be completely dissolved in the polar solvent. Preferably, the temperature of the heating and stirring of the graphene ethanol solution of Ni(NO3)2 is 80 ℃, the stirring speed is 500 rpm, and the stirring time is 8 h.

[0025] Preferably, in the hydrothermal reduction reaction, the gas atmosphere is hydrogen, argon-hydrogen mixed gas (hydrogen volume fraction: 5%-30%), helium-hydrogen mixed gas (hydrogen volume fraction: 5%-30%), nitrogen-hydrogen mixed gas (hydrogen volume fraction: 5%-30%).

[0026] Preferably, the temperature of the hydrothermal reduction reaction is 300 °C~3000 °C. As the temperature of the hydrothermal reaction increases, the degree of reaction of the raw materials gradually increases, and the yield of the reduced metal also increases, but too high a temperature will result in an increase in the particle size of the prepared metal element, and a decrease in the catalytic activity. Therefore, the metal ions can be reduced at the reaction temperature provided by the present application. Preferably, the temperature of the hydrothermal reduction reaction of the mixture of Ni(NO3)2 and graphene is 400 °C.

[0027] Preferably, the heating time of the hydrothermal reduction reaction is 0.5 h~5 h. As the time of the hydrothermal reaction increases, the degree of reaction of the raw materials gradually increases, and the yield of the reduced metal also increases, but too long a time will result in an increase in the particle size of the prepared metal element, and a decrease in the catalytic activity. The specific time needs to be determined by the reducibility of the specific metal salt and the temperature of the hydrothermal reaction, to ensure that the metal ions can be fully reduced and converted into the corresponding metal element within the reaction time. Preferably, the hydrothermal reduction reaction time of the mixture of Ni(NO3)2 and graphene at 400 °C is 2 h.

[0028] Preferably, the alkyl metal Li compound is n-butyllithium, and the alkyl metal Mg compound is di-n-butyl magnesium and / or dimagnesium.

[0029] Preferably, the organic solvent is one or more of n-hexane, cyclohexane, n-heptane, tetrahydrofuran, and acetone.

[0030] Further preferably, the alkyl metal Li compound is n-butyllithium, and the molar concentration of the n-butyllithium in the mixed solution of n-hexane and n-butyllithium is 0.01~2.0 mmol / ml, and the liquid environment is n-hexane.

[0031] Further preferably, the alkyl metal Li compound is n-butyllithium, and the borane compound is triethylamine borane, and the molar ratio of the n-butyllithium to the triethylamine borane is 1:3~1. The amount of triethylamine borane can be the same as or slightly more than that of the n-butyllithium, which can fully convert the nanometer hydrogenated lithium into borohydride lithium, and can completely wash away the excess organic matter. Preferably, the molar ratio of the n-butyllithium to the triethylamine borane is 1:1.3, which can fully react the nanometer hydrogenated lithium with the triethylamine borane to form borohydride lithium and avoid waste of raw materials.

[0032] Further preferably, the molar concentration of the alkyl metal Mg compound in the mixed solution of diethyl ether and n-hexane is 0.01~2.0 mmol / ml, and the organic solvent is a mixture of one or more of heptane, n-hexane, and diethyl ether. This ensures the yield of borohydride lithium in the product while avoiding agglomeration of the product due to too high a concentration. Preferably, the molar concentration of the magnesium metal alkyl compound in the reactant is 0.01~1.0 mmol / ml.

[0033] Preferably, the mass ratio of the metal hydride raw material and the functionalized carbon material is 1:5-60. Preferably, the alkyl metal Li compound is butyl lithium, and the ratio of the butyl lithium to the functional carbon material is 7:1, under which the kinetic performance of the lithium borohydride hydrogen storage material can be effectively improved, and a higher hydrogen storage capacity can be ensured.

[0034] Preferably, the power of the ultrasonic in step (2) is 100-600 W, the single ultrasonic time is 0.5-2.5 hours, the interval is 10-40 minutes, and the cumulative ultrasonic time is 3-12 hours. The setting of the reaction conditions should consider the type of the carbon material, the type of the metal alkyl compound, and the dispersion degree of the mixture, and appropriate parameters are selected to ensure uniform mixing of the system, while avoiding excessive energy consumption and solvent volatilization.

[0035] Preferably, the temperature of the solvothermal reaction is 40-200 °C, the reaction time is 15 min-24 h, and the hydrogen pressure is 20-120 bar.

[0036] By controlling the temperature, reaction time and pressure of the reaction, the metal hydride with a nanoparticle size can be obtained.

[0037] In another aspect, the application also provides a multilayer nanostructured metal hydride prepared by the preparation method of the multilayer nanostructured metal hydride.

[0038] Compared with the prior art, the application has the following beneficial effects:

[0039] In the application, the carbon material is used as a carrier, and the first-step assembly of the nano metal catalyst is realized through a hydrothermal reduction reaction of a metal ion salt; then, the second-step assembly of the multilayer metal hydride is realized through a solvothermal reaction, and a transition metal catalyzed multilayer nano metal hydride is prepared.

[0040] In the application, the carbon material added can better disperse the nano metal catalyst, avoid agglomeration and particle growth of the nano metal catalyst in the hydrothermal reduction reaction, and maintain the catalytic activity of the nano metal catalyst.

[0041] In the application, the transition metal source, the carrier material and the metal hydride are separated from each other, which enriches the selectivity of the carrier material, increases the types of the nano transition metal that can be prepared for the catalytic metal hydride, and also increases the diversity of the mutual matching of the transition metal and the carrier.

[0042] Compared with existing nano-metal catalysis and nano-limitation, the unique structure prepared by the present application separates the metal hydride from the carbon material, the transition metal layer in the middle not only limits the particle size of the metal hydride, but also efficiently plays a catalytic activity in long cycles, and always maintains the nano size of the metal hydride, while the hydrogen storage capacity of the system is high, and the hydrogen absorption and release temperature is greatly reduced compared with other technologies for preparing nano lithium borohydride. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 XRD patterns of graphene with different proportions of Ni prepared in step (1) of Example 1.

[0044] Figure 2 XRD patterns of multilayer nano LiBH4 with different proportions of Ni prepared in step (3) of Example 1.

[0045] Figure 3 TEM photos of graphene with different proportions of Ni prepared in step (1) of Example 1, Figure 3 a- Figure 3 d are TEM photos of Grs-2Ni, Grs-6Ni, Grs-10Ni and Grs-20Ni respectively.

[0046] Figure 4 SEM photos of multilayer nano LiBH4 with different proportions of Ni prepared in step (3) of Example 1, wherein Figure 4 a- Figure 4 d are SEM photos of samples LiBH4-Grs-2Ni, LiBH4-Grs-6Ni, LiBH4-Grs-10Ni and LiBH4-Grs-20Ni respectively.

[0047] Figure 5 HRTEM photo of sample LiBH4-Grs-10Ni prepared in Example 1 and selected area electron diffraction (SAED) results of the corresponding area.

[0048] Figure 6 XRD patterns of different nano LiBH4 prepared in Example 1 and Comparative Example 1; wherein Figure 6 (a) is sample LiBH4-Grs-10Ni, Figure 6 (b) is a nano LiBH4 sample without adding a carrier.

[0049] Figure 7 SEM photos of different nano LiBH4 prepared in Example 1 and Comparative Example 1; wherein Figure 7 (a) is sample LiBH4-Grs-10Ni, Figure 7 (b) is a nano LiBH4 sample without adding a carrier.

[0050] Figure 8 Comparison of temperature-dependent hydrogen desorption profiles of different nano-LiBH4 prepared for Example 1 and Comparative Example 1, wherein Figure 8 (a) is for sample LiBH4-Grs-10Ni, Figure 8 (b) is for nano-LiBH4 sample without adding support.

[0051] Figure 9 Comparison of temperature-dependent hydrogen desorption and absorption profiles of single graphene supported nano-LiBH4 sample prepared for Example 1 and Comparative Example 2, wherein, Figure 9 (a) is for comparison of temperature-dependent hydrogen desorption profiles, Figure 9 (b) is for comparison of temperature-dependent hydrogen absorption profiles.

[0052] Figure 10 Comparison of TPD-MS profiles of LiBH4-Grs-2Ni, LiBH4-Grs-6Ni, LiBH4-Grs-10Ni, LiBH4-Grs-20Ni prepared for Example 1.

[0053] Figure 11 Comparison of temperature-dependent hydrogen absorption profiles of LiBH4-Grs-2Ni, LiBH4-Grs-6Ni, LiBH4-Grs-10Ni, LiBH4-Grs-20Ni prepared for Example 1.

[0054] Figure 12 Isothermal hydrogen desorption profile of LiBH4-Grs-10Ni sample prepared for Example 1.

[0055] Figure 13 Isothermal hydrogen absorption profile of LiBH4-Grs-10Ni sample prepared for Example 1, wherein (a) and (b) correspond to isothermal hydrogen absorption temperature of 350 °C, 300 °C, 325 °C and 150 °C, respectively.

[0056] Figure 14 TEM image of LiBH4-Grs-10Co sample prepared for Example 1.

[0057] Figure 15 HRTEM image of MgH2-Grs-10Ni sample prepared for Example 1. DETAILED DESCRIPTION

[0058] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application. Any modification or equivalent replacement made by those skilled in the art based on the technical solutions of the present application without departing from the spirit and scope of the present application should be covered in the protection scope of the present application. Embodiments

[0059] Preparation of Ni-catalyzed multi-layered nano LiBH4:

[0060] (1) 3 / 9 / 15 / 20 mg of Ni(NO3)2·6H2O and single-layered graphene (30 mg) were weighed according to the mass ratio of Ni (2 wt% / 6 wt% / 10 wt% / 20 wt%) and placed in 20 mL of anhydrous ethanol solution for ultrasonic stirring for 20 min. After uniform dispersion, the mixture was continuously stirred at 500 rpm for 8 h until the liquid in the mixture was completely evaporated. The powder was taken out and placed in a mixed atmosphere of 10% H2 and 90% Ar, and heated to 400 °C at a rate of 5 °C / min and kept for 2 h. After natural cooling to room temperature, functional graphene with different proportions of Ni loading was obtained, and was recorded as Grs-2Ni, Grs-6Ni, Grs-10Ni and Grs-20Ni according to the content of Ni in the product.

[0061] (2) In an inert atmosphere glove box, 30 mg of Ni-loaded functional graphene, 1.6 mL of C4H9-Li (2.0 M in hexane, Aladin) and 645 μL of (C2H5)3NBH3 were placed in 50 mL of n-hexane and ultrasonically stirred for 1 h. After mixing, it was transferred to a ventable reaction kettle.

[0062] (3) The reaction kettle was filled with 50 bar of high-purity hydrogen, and the reaction kettle was placed in an oil bath at 100 °C for heating and stirring for 3 h. After the reaction was completed and cooled to room temperature, in an inert atmosphere glove box, after centrifugation, washing, filtration and dynamic vacuum drying at 90 °C for 6 h, Ni-catalyzed multi-layered nano LiBH4 was finally obtained.

[0063] The sample prepared in the above process is: Ni-catalyzed multi-layered nano LiBH4 (LiBH4-Grs-Ni).

[0064] As shown in Figure 1 , with the increase of the amount of Ni(NO3)2·6H2O, the Ni-loaded graphene sample gradually showed the diffraction peak of Ni.

[0065] As shown in Figure 2As shown in the figure, all multilayer nano-LiBH4 samples with different Ni ratios exhibit LiBH4 diffraction peaks, indicating that LiBH4 is the primary phase. However, the intensity of these characteristic diffraction peaks is relatively weak, which is related to the reduction in LiBH4 particle size. This shows that the addition of Ni-loaded graphene not only does not affect the formation of LiBH4, but also reduces the particle size of lithium borohydride.

[0066] The graphene loaded with Ni in different proportions obtained in Example 1 was observed using transmission electron microscopy. Figure 3 As shown, Figure 3 (a)- Figure 3 (d) Grs-2Ni, Grs-6Ni, Grs-10Ni, and Grs-20Ni, respectively. The figure shows that as the amount of Ni(NO₃)₂·6H₂O increases, the amount of Ni nanoparticles loaded on the graphene surface gradually increases, with minimal change in size. Grs-10Ni reaches the maximum loading, with a particle size of 2-5 nm. As the amount of Ni(NO₃)₂·6H₂O continues to increase, the size of the nanometal Ni particles increases significantly.

[0067] Figure 4 SEM photos of multilayer nano-LiBH4 with different Ni ratios, Figure 4 (a)- Figure 4 (d) Corresponding to samples LiBH4-Grs-2Ni, LiBH4-Grs-6Ni, LiBH4-Grs-10Ni, and LiBH4-Grs-20Ni, respectively. The figure shows that when LiBH4 accounts for 70 wt%, graphene accounts for 27 wt%, and the nano-Ni metal catalyst accounts for 3 wt%, all of the LiBH4 is fully loaded on the graphene surface, and the nanoparticles show no obvious agglomeration, with particle sizes ranging from 50 to 70 nm.

[0068] Figure 5 The HRTEM image of the LiBH4-Grs-10Ni sample obtained in Example 1 and the selected area electron diffraction (SAED) results of the corresponding area are shown. The sample consists of a flake carrier, black nanoparticles and gray large nanoparticles. Region 1 with large nanoparticles shows diffraction rings corresponding to the (020) crystal plane of LiBH4, the (311) crystal plane of Ni and the (1(-1)00) crystal plane of graphene. The SAED image of region 2 where only small nanoparticles exist only shows the interplanar spacing between the (311) crystal plane of Ni and the (1(-1)00) crystal plane of graphene, indicating that the LiBH4 nanoparticles of this sample are grown on the surface of the Ni nanoparticle layer.

[0069] From the above analysis, it can be seen that the Ni-catalyzed multilayer nano LiBH4 can be successfully prepared by the method, and the addition of functional graphene can obviously reduce the particle size of lithium borohydride.

[0070] The nano LiBH4 prepared without adding a carrier is used as a comparative example, and the preparation process is as follows: in an inert atmosphere glove box, 1.6 mL of C4H9-Li (2.0 M in hexane, Aladin) and 645 μL of (C2H5)3NBH3 are weighed into 50 mL of n-hexane and ultrasonically stirred for 1 h. After being fully mixed, it is transferred to a ventable reaction kettle. The reaction kettle is filled with 50 bar of high-purity hydrogen, and the reaction kettle is placed in a 100 °C oil bath for heating and stirring for 3 h. After the reaction is completed and cooled to room temperature, in an inert atmosphere glove box, after centrifugation, washing, filtration and 90 °C dynamic vacuum drying for 6 h, the nano LiBH4 without adding a carrier is finally obtained.

[0071] Figure 6 The XRD patterns of the different nano LiBH4 prepared for Example 1 and Comparative Example 1 are shown. It can be seen that the XRD diffraction peak position of the Ni-catalyzed multilayer nano LiBH4 is consistent with that of the LiBH4 without adding a carrier, but the relative intensity of the diffraction peak corresponding to the LiBH4 (200) crystal plane of the multilayer sample is significantly reduced compared with that of the sample without adding a carrier, thereby indicating that the orientation of the two is different.

[0072] Figure 7 The SEM images of the different nano LiBH4 prepared for Example 1 and Comparative Example 1 are shown. From the SEM images of Figure 7 of Figure 7 (a) and Figure 7 (b), it can be seen that the LiBH4 with a multilayer nanostructure exists in the form of nanoparticles, which is significantly reduced compared with the nanorod-like LiBH4 (diameter: 500-800 nm) without adding a carrier, thereby showing that the LiBH4 can be successfully prepared by using the present application, and the growth mode thereof can be changed, and the agglomeration and growth thereof can be limited.

[0073] The graphene-supported nano LiBH4 without a nano Ni catalyst layer is used as a comparative example, and the preparation process is as follows:

[0074] (1) A few-layer graphene (30 mg) is weighed and placed in 20 mL of anhydrous ethanol solution and ultrasonically stirred for 20 min. After being uniformly dispersed, it is continuously heated and stirred at 500 rpm for 8 h until the liquid in the mixture is completely evaporated. The powder is taken out and placed in a mixed gas atmosphere of 10% H2 and 90% Ar, heated to 400 °C at a rate of 5 °C / min and kept for 2 h. After natural cooling to room temperature, the graphene without nickel Ni loading is obtained, which is denoted as Grs.

[0075] (2) In an inert atmosphere glove box, 30 mg of Ni-free loaded graphene, 1.6 mL of C4H9-Li (2.0 M in hexane, Aladin) and 645 μL of (C2H5)3NBH3 were added into 50 mL of n-hexane and stirred for 1 h under ultrasonic. After fully mixed, it was transferred into a gas-permeable reactor.

[0076] (3) The reactor was filled with 50 bar of high purity hydrogen and heated in an oil bath at 100 °C for 3 h. After the reaction was completed and cooled to room temperature, the final single graphene loaded nano LiBH4 was obtained after centrifugation, washing, filtration and dynamic vacuum drying at 90 °C for 6 h in an inert atmosphere glove box.

[0077] The sample was tested for hydrogen release and absorption performance using the temperature-dependent hydrogen release and absorption mode. The test conditions were as follows: heating to 500 °C at a rate of 2 °C / min under vacuum (initial vacuum degree of 1 x 10 -3 Torr) and heating to 350 °C at a rate of 1 °C / min under 100 bar H2 pressure and holding for 6 h. Figure 9 The temperature-dependent hydrogen release and absorption curves of the LiBH4-Grs-10Ni sample prepared in Example 1 and the single graphene loaded nano LiBH4 prepared in Comparative Example 2 are compared. As can be seen from the graph, Figure 9 (a) and Figure 9 (b) show that the initial hydrogen release temperature of the LiBH4-Grs-10Ni sample prepared in Example 1 is 100 °C, the first step hydrogen release peak temperature is 330 °C, and the initial hydrogen release (230 °C) temperature of the single graphene loaded nano LiBH4 sample prepared in Comparative Example 2 is reduced by 130 °C, which indicates that the nano Ni catalytic layer has higher catalytic activity. When heated to 368 °C, the hydrogen release amount of the LiBH4-Grs-10Ni sample prepared in Example 1 is 7.4 wt%, indicating that this multi-layer metal hydride has a higher hydrogen storage capacity. The initial hydrogen absorption temperature of the LiBH4-Grs-10Ni sample prepared in Example 1 is 70 °C, which is reduced by 120 °C compared to the initial hydrogen absorption (190 °C) temperature of the single graphene loaded nano LiBH4 sample prepared in Comparative Example 2. This indicates that the Ni catalytic multi-layer nano LiBH4 prepared by the method of the example significantly reduces the hydrogen absorption temperature due to the unique nano catalytic layer.

[0078] The hydrogen release and absorption performance of the LiBH4-Grs-10Ni sample prepared in Example 1 was tested using the temperature-dependent hydrogen release and absorption mode, and the test conditions were as follows: heating to 500 °C at a rate of 2 °C / min under vacuum (initial vacuum degree of 1 x 10 -3Torr) at a heating rate of 2 °C / min to 500 °C and 100 bar H2pressure at a heating rate of 1 °C / min to 350 °C and holding for 6 h, the results are shown in Figure 8 and Figure 9 .

[0079] The hydrogen desorption performance of the nano LiBH4 sample without carrier prepared from Comparative Example 1 was tested by the temperature-dependent hydrogen desorption mode, and the test conditions were as follows: heating from room temperature to 500 °C at a heating rate of 2 °C / min under vacuum (initial vacuum degree was 1 x 10 -3 Torr) at a heating rate of 2 °C / min to 500 °C. Figure 8 The comparison chart of the temperature-dependent hydrogen desorption curves of the LiBH4-Grs-10Ni sample prepared from Example 1 and the nano LiBH4 sample without carrier prepared from Comparative Example 1 is shown in the figure. As can be seen from the figure, Figure 8 (a) The initial hydrogen desorption temperature of the LiBH4-Grs-10Ni sample prepared from Example 1 is 100 °C, and the first-step hydrogen desorption peak temperature is 330 °C, which is 103 °C lower than that of the nano LiBH4 sample without carrier prepared from Comparative Example 1, which indicates that the hydrogen desorption performance of LiBH4 is significantly improved by the nano confinement and nano-catalysis synergy. Figure 8 (b) The hydrogen desorption peak temperature (433 °C) of the nano LiBH4 sample without carrier prepared from Comparative Example 1 is reduced by 103 °C, which indicates that the hydrogen desorption performance of LiBH4 is significantly improved by the nano confinement and nano-catalysis synergy.

[0080] The hydrogen desorption performance of the LiBH4-Grs-2Ni, LiBH4-Grs-6Ni and LiBH4-Grs-20Ni samples prepared from Example 1 was tested by MS-TPD, and the test conditions were as follows: heating to 550 °C at a heating rate of 2 °C / min under vacuum (initial vacuum degree was 1 x 10 -3 Torr) at a heating rate of 2 °C / min to 500 °C. Figure 10 The comparison chart of the TPD-MS curves of the LiBH4-Grs-10Ni, LiBH4-Grs-2Ni, LiBH4-Grs-6Ni and LiBH4-Grs-20Ni samples of Example 1 is shown in the figure. As can be seen from the figure, when the proportion of Ni in the sample increases, the hydrogen desorption peak temperature of the sample is reduced from 360 °C to 330 °C, and the hydrogen desorption peak temperature of the LiBH4-Grs-20Ni sample is basically no longer changed, which indicates that the hydrogen desorption performance of the LiBH4-Grs-10Ni sample is the best.

[0081] The hydrogen absorption performance of the LiBH4-Grs-2Ni, LiBH4-Grs-6Ni and LiBH4-Grs-20Ni samples prepared from Example 1 was tested by the temperature-dependent hydrogen absorption mode, and the test conditions were as follows: heating to 350 °C at a heating rate of 1 °C / min under 100 bar H2pressure and holding for 6 h. Figure 11A comparison chart of temperature-dependent hydrogen absorption curves for LiBH4-Grs-10Ni, LiBH4-Grs-2Ni, LiBH4-Grs-6Ni, and LiBH4-Grs-20Ni samples of Example 1. As can be seen from the chart, as the proportion of Ni in the sample increases, the initial hydrogen absorption temperature of the sample decreases from 270 °C to 70 °C, and the reversible hydrogen storage capacity increases from 1.6 wt% to 7.6 wt%. The initial hydrogen absorption temperature of the sample LiBH4-Grs-20Ni shifts to a high temperature, and the reversible hydrogen storage capacity decreases to 4.2 wt%, indicating that the hydrogen absorption performance of the LiBH4-Grs-10Ni sample is improved most significantly.

[0082] The hydrogen desorption kinetics of the LiBH4-Grs-10Ni sample prepared in Example 1 was characterized using an isothermal hydrogen desorption mode: under vacuum (initial vacuum degree 1 x 10 -3 Torr), heated to 300 °C, 325 °C, and 350 °C at a heating rate of 10 °C / min and held for a certain time.

[0083] Figure 12 The isothermal hydrogen desorption curve of the LiBH4-Grs-10Ni sample prepared in Example 1 is shown in the chart, from which it can be seen that the sample completely releases 8.23 wt% of hydrogen within 50 min at 350 °C, and 6.5 wt% of hydrogen within 100 min at 300 °C, indicating that the nano-Ni catalyzed multi-layer structure significantly improves the hydrogen desorption kinetics of LiBH4.

[0084] The hydrogen absorption kinetics of the LiBH4-Grs-10Ni sample was characterized using an isothermal hydrogen absorption mode: the initial hydrogen pressure was 100 bar, heated to 350 °C, 300 °C, 325 °C, and 150 °C at a heating rate of 10 °C / min and held for a certain time, and the results are shown in Figure 13 (a) and (b).

[0085] As shown in Figure 13 (a) and (b), the hydrogen desorption product of the sample is completely hydrogenated (8.2 wt%) within 300 min at 350 °C, can absorb 7.8 wt% and 7.4 wt% of hydrogen within 400 min and 500 min at 325 °C and 300 °C, respectively. Even at 150 °C, LiBH4-Grs-10Ni can achieve complete hydrogenation. This indicates that the nano-Ni catalyzed multi-layer structure significantly improves the hydrogen absorption kinetics of LiBH4. Example

[0086] Preparation of Co catalyzed multi-layer nano LiBH4:

[0087] (1) 2.96 mg of Co(N03)2-6H20 and single-layer graphene (30 mg) were weighed according to the mass ratio (10 wt%) of Co generated, and were placed in a 20 mL anhydrous ethanol solution and ultrasonically stirred for 20 min. After uniform dispersion, the mixture was continuously stirred at 500 rpm and heated for 8 h until the liquid in the mixture was completely evaporated. The powder was taken out and placed in a mixed atmosphere of 10% H2and 90% Ar, heated to 400 °C at a rate of 5 °C / min and kept for 2 h. After natural cooling to room temperature, functional graphene with a Ni loading of 10 wt% was obtained, denoted as Grs-10Co.

[0088] (2) In an inert atmosphere glove box, 30 mg of Grs-10Co, 1.6 mL of C4H9-Li (2.7 M in hexane, Aladin), and 645 μL of (C2H5)3NBH3 were placed in 50 mL of n-hexane and ultrasonically stirred for 1 h. After mixing, it was transferred to a vented reactor.

[0089] (3) The reactor was filled with 50 bar of high-purity hydrogen, and the reactor was placed in a 100 °C oil bath for heating and stirring for 3 h. After cooling to room temperature, the Co-catalyzed multi-layer nano-LiBH4was obtained after centrifugation, washing, filtration, and dynamic vacuum drying at 90 °C for 6 h in an inert atmosphere glove box.

[0090] The sample prepared in the above process is: Co-catalyzed multi-layer nano-LiBH4(LiBH4-Grs-10Co).

[0091] Figure 14 The TEM image of the sample prepared in this example is shown in the figure, from which it can be seen that the graphene is loaded with a large number of dispersed Co nano-particles and larger LiBH4nano-particles.

[0092] Preparation of Ni-catalyzed multi-layer nano-MgH2:

[0093] (1) An appropriate amount of Ni(N03)2-6H20 and few-layer graphene (30 mg) were weighed according to the mass ratio (10 wt%) of Ni generated, and were placed in a 20 mL anhydrous ethanol solution and ultrasonically stirred for 20 min. After uniform dispersion, the mixture was continuously stirred at 500 rpm and heated for 8 h until the liquid in the mixture was completely evaporated. The powder was taken out and placed in a mixed atmosphere of 10% H2and 90% Ar, heated to 400 °C at a rate of 5 °C / min and kept for 2 h. After natural cooling to room temperature, functional graphene with a Ni loading of 10 wt% was obtained, denoted as Grs-10Ni.

[0094] (2) In an inert atmosphere glove box, 30 mg of Ni-loaded functionalized graphene and 2.7 mL of MgBu2(1.0 M in heptane, Aladin) were weighed into 50 mL of n-hexane and stirred ultrasonically for 1 h. After being mixed thoroughly, it was transferred into a gas-permeable reactor.

[0095] (3) The reactor was filled with 50 bar of high-purity hydrogen and heated in an oil bath at 150 °C for 6 h. After the reaction was completed and cooled to room temperature, the Ni-catalyzed multi-layered nano-MgH2was obtained by centrifugation, washing, filtration and dynamic vacuum drying at 40 °C for 4 h in an inert atmosphere glove box.

[0096] The sample prepared in the above process was: Ni-catalyzed multi-layered nano-MgH2(MgH2-Grs-10Ni).

[0097] Figure 15 The HRTEM image of the sample prepared in this example is shown in the figure, from which it can be seen that the graphene is loaded with a large number of dispersed Ni nanoparticles and larger MgH2nanoparticles.

[0098] The preparation process is substantially the same as that of Example 1, except that the transition metal ion salt used is nickelocene, cobaltocene, titaniumocene, cobalt nitrate, iron nitrate, manganese nitrate, chromium nitrate, zinc nitrate, copper nitrate, zirconium nitrate, tungsten nitrate, ruthenium nitrate, rhodium nitrate, hafnium nitrate, palladium nitrate, iridium nitrate, platinum nitrate, scandium nitrate, yttrium nitrate, lanthanum nitrate, cerium nitrate, praseodymium nitrate, titanium tetrachloride, titanium trichloride, zirconium tetrachloride, vanadium trichloride, niobium pentachloride, chromium trichloride, molybdenum pentachloride, manganese dichloride, iron trichloride, iron dichloride, cobalt dichloride, nickel dichloride, copper dichloride, ruthenium trichloride, rhodium trichloride, palladium dichloride, silver chloride, hafnium tetrachloride, tungsten hexachloride, iridium trichloride, platinum tetrachloride, gold trichloride, scandium trichloride, yttrium trichloride, lanthanum trichloride, cerium trichloride, praseodymium trichloride, and also the metal alkyl compound used is n-dibutylmagnesium, dimethylmagnesium, and also the carbon material is carbon nanotubes, carbon fibers, porous carbon, C3N4. Table 1 lists the basic preparation parameters for synthesizing transition metal-catalyzed multi-layered nano-metal hydride using different transition metal ion salts as raw materials.

[0099] Table 1 Synthesis parameters of different transition metal-catalyzed multi-layered nano-metal hydride

[0100]

Claims

1. A method for preparing a multilayer nanostructured metal hydride, characterized in that, include: (1) adding a transition metal ion salt and a carbon material to a polar solvent, mixing, heating and stirring to obtain a solid powder, and subjecting the solid powder to a hydrogen thermal reduction reaction to obtain a functionalized carbon material, wherein the temperature of the hydrogen thermal reduction reaction is 300°C to 3000°C, and the heating time is 0.5 h to 5 h; (2) adding a metal hydride raw material and a functionalized carbon material to an organic solvent, ultrasonically treating and mixing to obtain a mixed solution, wherein the mass ratio of the metal hydride raw material to the functionalized carbon material is 1:5-60, the metal hydride raw material is a mixture of an alkyl metal Mg compound or an alkyl metal Li compound and a borane compound, the alkyl metal Li compound is n-butyl lithium, the alkyl metal Mg compound is di-n-butyl magnesium and / or dioctyl magnesium, and the molar ratio of n-butyl lithium to triethylamine borane is 1:3-1; (3) Under a hydrogen atmosphere, the mixed solution of step (2) is subjected to a solvothermal reaction at a temperature of 40 to 200 °C, a reaction time of 15 min to 24 h, and a hydrogen pressure of 20 to 120 bar. The mixture is then centrifuged, washed, filtered, and dried to obtain a multilayer nanostructured metal hydride.

2. The method for preparing a multilayer nanostructured metal hydride according to claim 1, wherein: The mass ratio of the transition metal ion salt to the carbon material is 0.01-100.

3. The method for preparing a multilayer nanostructured metal hydride according to claim 2, wherein: The mass ratio of the transition metal ion salt to the carbon material is 0.1-10.

4. The method of claim 1, wherein the multilayer nanostructured metal hydride is prepared by a process comprising: The transition metal ion salt includes one or more of transition metallocenes, transition metal nitrates, and transition metal chlorides; The transition metallocene is one or more of nickelocene, cobaltocene, and titanocene; The transition metal nitrate is one of nickel nitrate, cobalt nitrate, iron nitrate, manganese nitrate, chromium nitrate, zinc nitrate, copper nitrate, zirconium nitrate, tungsten nitrate, ruthenium nitrate, rhodium nitrate, hafnium nitrate, palladium nitrate, iridium nitrate, platinum nitrate, scandium nitrate, yttrium nitrate, lanthanum nitrate, cerium nitrate, and praseodymium nitrate; The transition metal chloride is one of titanium tetrachloride, titanium trichloride, zirconium tetrachloride, vanadium trichloride, niobium pentachloride, chromium trichloride, molybdenum pentachloride, manganese dichloride, ferric chloride, ferric dichloride, cobalt dichloride, nickel dichloride, copper dichloride, ruthenium trichloride, rhodium trichloride, palladium dichloride, silver chloride, hafnium tetrachloride, tungsten hexachloride, iridium trichloride, platinum tetrachloride, gold trichloride, scandium trichloride, yttrium trichloride, lanthanum trichloride, cerium trichloride, and praseodymium trichloride.

5. The method of claim 4, wherein the multilayered nanostructured metal hydride is prepared by the steps of: The transition metal ion salt is a transition metal nitrate.

6. The method of claim 1, wherein the multilayer nanostructured metal hydride is prepared by a method comprising: The carbon material is one or more of graphene, carbon nanotubes, carbon fibers, porous carbon, carbon nitride, graphene doped with nitrogen, boron or phosphorus atoms, carbon nanotubes, carbon fibers and porous carbon.

7. The method for preparing a multilayer nanostructured metal hydride according to claim 1, wherein: The polar solvent is water and / or ethanol.

8. The method for preparing a multilayer nanostructured metal hydride according to claim 1, wherein: The heating and stirring temperature is 60-90°C, the stirring speed is 300-1000 rpm, and the stirring time is 3-12 h.

9. A multilayer nanostructured metal hydride, characterized in that, The multilayer nanostructured metal hydride is prepared by the method for preparing a multilayer nanostructured metal hydride according to any one of claims 1 to 8.

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