A hollow flower-shaped M-NC@TiO2 composite material, its preparation method and application

Abstract

The present invention discloses a hollow flower-shaped M-NC@TiO2 composite material. First, solid spherical TiO2 is prepared, then it is made into hollow spherical TiO2. M-MOF is orderly grown on the surface of the hollow spherical TiO2 to obtain M-MOF@TiO2, and finally it can be obtained by calcination; the hollow spherical TiO2 is a hollow spherical structure, and M-NC@TiO2 is based on the hollow spherical TiO2, and has a hollow flower-shaped structure with M-NC orderly grown on the surface. Its preparation method includes the following steps: 1. Preparation of solid spherical TiO2; 2. Preparation of hollow spherical TiO2; 3. Preparation of M-MOF@TiO2; 4. Preparation of M-NC@TiO2. And, a preparation method of an M-NC@TiO2 doped lithium aluminum hydride hydrogen storage material; and the application of the obtained LiAlH4-M-NC@TiO2 as a hydrogen storage material. When the doping amount of M-NC@TiO2 is 7 wt%, the initial hydrogen release temperature is 56.3 - 70.5 °C, and the hydrogen release amount is 7.0 - 7.3 wt%. The present invention has the characteristics of less addition amount, significantly reduced initial hydrogen release temperature and high hydrogen release amount.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen storage materials for new energy materials, and particularly relates to a hollow flower-shaped M-NC@TiO2 composite material, a preparation method thereof, and an application thereof. Background Art

[0002] At present, the development and utilization of hydrogen energy are mainly restricted by its difficulties in storage and transportation. Therefore, solid-state hydrogen storage with convenient transportation and storage is the most likely hydrogen storage method to be widely used in the future. Among solid-state hydrogen storage materials, lithium aluminum hydride LiAlH4 has the advantages of a high hydrogen storage capacity of 10.5 wt%, a high reserve of raw material Al and low cost, and a relatively low dehydrogenation temperature compared with other hydrogen storage materials. However, the high thermodynamic stability, poor kinetics, and almost irreversible characteristics of LiAlH4 limit its wide practical application.

[0003] To solve these problems, many methods have been developed, such as nanosizing, catalyst doping, and constructing an unstable system by compounding with hydrides. Among them, doping a catalyst is the most effective method to improve the dehydrogenation performance of LiAlH4, especially single-nanoparticles of transition metals. However, transition metal nanoparticles often agglomerate during synthesis and use due to the reaction heat, resulting in a significant decline in performance.

[0004] Currently, the main method to solve agglomeration is to add a suitable support material to enhance the dispersibility of the metal nanoparticle material. Classified by the type of support material, it mainly includes: carbon materials, metal-organic frameworks, metal compounds, etc.

[0005] Using porous carbon materials as support materials can effectively disperse metal nanoparticles. For example, in the existing literature 1 (Mohammad A. Wahab, Jorge N. Beltramini. Catalytic nanoconfinement effect of in-situ synthesized Ni-containing mesoporous carbon scaffold (Ni-MCS) on the hydrogen storage properties of LiAlH4 [J]. International Journal of Hydrogen Energy, 39(32), 18280-18290.), Ni nanoparticles are uniformly dispersed in the carrier mesoporous carbon scaffold through confinement, effectively increasing the contact area with LiAlH4, thereby improving the dehydrogenation performance of LiAlH4 and reducing the initial dehydrogenation temperature of LiAlH4 to 66 °C. However, the problem with this technical solution is that the carrier material has no catalytic effect on LiAlH4.

[0006] In order to solve the problem that the above-mentioned carrier cannot provide a catalytic effect, a material having a catalytic effect itself can be used as a carrier, thereby improving the catalytic effect of the composite catalyst as a whole and further reducing the initial hydrogen release temperature of LiAlH4. For example, existing document 2 (Zhaoyu Liu, Jiaxi Liu, Sheng Wei, Yongpeng Xia, Riguang Cheng, LixianSun, Fen Xu, Pengru Huang, Yiting Bu, Jian Cheng, Tianhao Zhou, Hongge Pan, ZhongCao, Julan Zeng, Hans Jurgen Seifert, Shuhui Sun, Gaixia Zhang. Improved hydrogen storage properties and mechanisms of LiAlH4 doped with Ni / C nanoparticles annealed on large-size Ti3C2T x [J]. Journal of Alloys and Compounds, 931, 167353.) uses a sheet-like metal compound Ti3C2T with catalytic properties. X As a carrier, Ni nanoparticles are loaded. This technical solution realizes the synergistic effect of the carrier and the loaded particles, improves the dehydrogenation performance, and makes the initial dehydrogenation temperature of LiAlH4 reach 56.9°C, but the hydrogen production decreases to 6.5wt%. The direct reason for the decrease in hydrogen production is that the microstructure of the metal compound carrier is a flaky structure, which directly leads to low atomic utilization during loading; and there is also the problem of easy reaction with LiAlH4 during the catalytic process, which leads to a decrease in the hydrogen production of LiAlH4.

[0007] Through the above analysis, it can be seen that the prior art has the following problems:

[0008] 1. The catalysts of lithium aluminum hydride hydrogen storage materials generally have poor dispersibility and are prone to agglomeration, which requires the introduction of carriers to solve the problem;

[0009] 2. The overall atomic utilization of the catalyst is low due to the introduction of the carrier;

[0010] 3. In the catalyst, the metal compound carrier material is easy to react with lithium aluminum hydride, which leads to a decrease in hydrogen production. Summary of the invention

[0011] The object of the present invention is to provide a method for preparing a hollow flower-like composite material M-NC@TiO2, where M = Ni, Co, Fe, Cu.

[0012] In view of the technical problems existing in the prior art, the present invention adopts the following principles and methods to solve the above problems:

[0013] 1. Since transition metal single nanoparticles can effectively improve the initial dehydrogenation temperature of LiAlH4, but metal nanoparticles are prone to agglomeration during synthesis, ball milling, and reaction processes, the method of carbonizing organometallic frameworks is selected to limit the uniform dispersion of metal nanoparticles, enabling the metal particles to fully contact with LiAlH4 during ball milling and reaction, thereby improving the dehydrogenation performance of LiAlH4;

[0014] 2. Spherical TiO2 is selected as the substrate, which can not only serve as a support material to promote the uniform growth of organometallic frameworks on its surface, increase the specific surface area of the catalyst, and further increase the contact area between the catalyst and LiAlH4 to improve the dehydrogenation performance. Moreover, TiO2 also has a catalytic effect on LiAlH4 and can jointly catalyze LiAlH4 with the metal nanoparticles in the organometallic framework after surface carbonization;

[0015] 3. Among the same volume and mass, the specific surface area of the spherical structure is the largest. Therefore, using hollow spherical TiO2 can not only effectively improve the atomic utilization rate of TiO2 but also reduce the waste of materials inside the hollow sphere;

[0016] 4. Anatase TiO2 has stable properties and will not react chemically with LiAlH4 to cause a decrease in hydrogen production.

[0017] To achieve the above object of the invention, the technical solution adopted by the present invention is as follows:

[0018] A hollow flower-like M-NC@TiO2 composite material is prepared by first preparing solid spherical TiO2, then preparing it into hollow spherical TiO2. After that, M-MOF is grown orderly on the surface of the hollow spherical TiO2 to obtain M-MOF@TiO2, and finally, the M-MOF@TiO2 is calcined to obtain the hollow flower-like M-NC@TiO2 composite material, simply referred to as hollow flower-like M-NC@TiO2;

[0019] The microscopic morphology of the hollow spherical TiO2 is a hollow spherical structure with a size of 200 nm; the microscopic morphology of the M-NC@TiO2 is a hollow flower-like structure with the hollow spherical TiO2 as the substrate and M-NC growing orderly on the surface, with a size of 1 - 3 μm.

[0020] A method for preparing a hollow flower-like M-NC@TiO2 composite material includes the following steps:

[0021] Step 1: Preparation of solid spherical TiO₂. Mix tetrabutyl titanate, potassium chloride, water, and absolute ethanol, stir, and then let it stand. After standing, the obtained product is centrifuged, washed, and dried to obtain solid spherical TiO₂.

[0022] In the said Step 1, the mass ratio of tetrabutyl titanate to potassium chloride is 1:(1 - 4), and the volume ratio of water to absolute ethanol is 1:25; the standing time is 24 h.

[0023] Step 2: Preparation of hollow spherical TiO₂. Add the solid spherical TiO₂ obtained in Step 1 and ammonium fluoride to water and stir to obtain the first hydrothermal reaction solution. Then, carry out the first hydrothermal reaction under certain conditions. After the obtained product is centrifuged, washed, and dried, hollow spherical TiO₂ is obtained.

[0024] In the said Step 2, the mass ratio of solid spherical TiO₂ to ammonium fluoride is 1:(1 - 4); the conditions for the first hydrothermal reaction are that the hydrothermal temperature is 160 - 180 °C and the hydrothermal time is 10 - 15 h.

[0025] Step 3: Preparation of M-MOF@TiO₂. Mix the hollow spherical TiO₂ obtained in Step 2, 2-aminoterephthalic acid, metal salt, N,N-dimethylformamide, and methanol to obtain the second hydrothermal reaction solution. Then, carry out the second hydrothermal reaction under certain conditions. After the obtained product is centrifuged, washed, and dried, M-MOF@TiO₂ is obtained.

[0026] In the said Step 3, the molar ratio of hollow spherical TiO₂, 2-aminoterephthalic acid, and metal salt is (1 - 2):2:(2 - 12), and the volume ratio of N,N-dimethylformamide to methanol is 9:1; the conditions for the second hydrothermal reaction are that the hydrothermal temperature is 120 - 160 °C and the hydrothermal time is 15 - 24 h.

[0027] In the said Step 3, the metal salt is one of nickel salt, cobalt salt, iron salt, or copper salt; the nickel salt is nickel nitrate hexahydrate, the cobalt salt is cobalt nitrate hexahydrate, the iron salt is iron nitrate nonahydrate, and the copper salt is copper nitrate hexahydrate.

[0028] Step 4: Preparation of M-NC@TiO₂. Calcinate the M-MOF@TiO₂ obtained in Step 3 under certain conditions to obtain the hollow flower-like M-NC@TiO₂ composite material, simply referred to as M-NC@TiO₂.

[0029] In the said Step 4, the calcination conditions are that under a hydrogen-argon mixed gas condition, the heating rate is 3 - 5 °C / min, the calcination temperature is 500 - 700 °C, and the calcination time is 1 - 3 h.

[0030] A preparation method of a M-NC@TiO2 doped lithium aluminum hydride hydrogen storage material, comprising: ball milling M-NC@TiO2 and lithium aluminum hydride LiAlH4 under certain conditions to obtain the M-NC@TiO2 doped lithium aluminum hydride hydrogen storage material, referred to as LiAlH4-M-NC@TiO2;

[0031] In the LiAlH4-M-NC@TiO2, the addition amount of M-NC@TiO2 accounts for 1-10wt% of the total mass;

[0032] The ball milling conditions are as follows: under argon conditions, the ball-to-material ratio is (100-300):1, the ball milling speed is 200-300 r / min, and the ball milling time is 20-40 min.

[0033] An application of LiAlH4-M-NC@TiO2 as a hydrogen storage material, when the doping amount of M-NC@TiO2 is 7wt%, the initial hydrogen decomposition temperature is 56.3-70.5°C, and the hydrogen decomposition amount is 7.0-7.3wt%.

[0034] The technical effects of the present invention have been tested and the specific contents are as follows:

[0035] The invention has been found by XRD detection that: in M-NC@TiO2 (M=Ni, Co, Fe, Cu), M exists in the form of a metal element, and TiO2 is anatase TiO2;

[0036] The present invention is known from SEM detection that: M-NC@TiO2 (M = Ni, Co, Fe, Cu) is a hollow flower-like structure with a size of 1-3 μm and orderly grown Ni-NC on the surface of hollow spherical TiO2 as the substrate;

[0037] The dehydrogenation test of the present invention shows that when the doping amount of M-NC@TiO2 (M=Ni, Co, Fe, Cu) is 7wt%, the initial dehydrogenation temperature is 56.3-70.5°C, and the dehydrogenation amount is 7.0-7.3wt%.

[0038] Therefore, the present invention has the following advantages over the prior art:

[0039] 1. The method for preparing the M-NC@TiO2 composite material of the present invention is applicable to a variety of catalysts prepared based on non-precious metals, including but not limited to Ni, Co, Fe, and Cu; and also has a significant improvement effect on the dehydrogenation performance of LiAlH4;

[0040] 2. The hollow spherical TiO2 prepared by the present invention has stable properties and structure, is not easy to collapse, and can still maintain a stable hollow spherical structure after orderly growth of M-NC on the surface;

[0041] 3. The method of the present invention for carbonizing the organic metal framework restricts the uniform dispersion of metal nanoparticles, enabling the surface metal particles to come into full contact with LiAlH4 during ball milling and reaction processes, effectively reducing the initial dehydrogenation temperature of LiAlH4;

[0042] 4. The present invention uses hollow spherical TiO2 as a substrate, which promotes the ordered growth of the organic metal framework on its surface, effectively increasing the contact area between the catalyst and LiAlH4, thereby improving the initial hydrogen release temperature of LiAlH4; at the same time, TiO2 also has a catalytic effect on LiAlH4, and together with the metal nanoparticles in the organic metal framework after surface carbonization, it jointly improves the initial hydrogen release temperature and hydrogen release amount of LiAlH4;

[0043] 5. The present invention uses hollow spherical anatase TiO2 as a substrate, which can effectively improve the atomic utilization rate and stability of TiO2. While improving the initial hydrogen release temperature of LiAlH4, it effectively increases the hydrogen release amount of LiAlH4;

[0044] 6. All raw materials used in the present invention are chemical raw materials that have been industrially produced, are commercially available, and are easily obtained. The synthesis process is simple, and the reaction process has low energy consumption and low pollution;

[0045] 7. As an application of LiAlH4 as a catalytic hydrogen storage material, the hydrogen storage material prepared by the present invention effectively improves the hydrogen release performance of lithium aluminum hydride: a lower initial hydrogen release temperature, and a high final hydrogen release amount can be obtained with the addition of a small amount of catalyst. When the doping amount of M-NC@TiO2 is 7 wt%, the initial hydrogen release temperature is 56.3 - 70.5 °C, and the hydrogen release amount is 7.0 - 7.3 wt%. The initial hydrogen release temperature of lithium aluminum hydride has decreased by 63.1 - 77.3 °C, and a high hydrogen release amount of 7.0 - 7.3 wt% is maintained.

[0046] Therefore, compared with the prior art, the present invention has better hydrogen storage catalytic performance for LiAlH4, improves the stability and catalytic activity of the catalyst, and has broad application prospects in the fields of hydrogen storage materials, fuel cells, etc. Description of the Drawings

[0047] Figure 1 XRD patterns of the hollow flower-like composite materials M-NC@TiO2 prepared in Example 1, Example 2, Example 3, and Example 4 of the present invention, where M = Ni, Co, Fe, Cu and TiO2;

[0048] Figure 2 Field emission scanning image of the hollow spherical TiO2 prepared in Example 1 of the present invention;

[0049] Figure 3Field emission scanning images of the hollow flower-like composite materials M-NC@TiO2 prepared in Example 1, Example 2, Example 3, and Example 4 of the present invention, where M = Ni, Co, Fe, Cu;

[0050] Figure 4 EDS diagram of the hollow flower-like composite material Ni-NC@TiO2 prepared in Example 1 of the present invention;

[0051] Figure 5 Dehydrogenation curves of LiAlH4, LiAlH4-TiO2, and LiAlH4-M-NC@TiO2 prepared in Example 1, Example 2, Example 3, and Example 4 of the present invention, where M = Ni, Co, Fe, Cu;

[0052] Figure 6 XRD patterns of M-NC prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 of the present invention, where M = Ni, Co, Fe, Cu;

[0053] Figure 7 Field emission scanning images of M-NC prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 of the present invention, where M = Ni, Co, Fe, Cu;

[0054] Figure 8 Dehydrogenation curves of LiAlH4-M-NC prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 of the present invention, where M = Ni, Co, Fe, Cu. Detailed Description of the Invention

[0055] The present invention further elaborates on the content of the present invention through examples in combination with the accompanying drawings of the specification, but it does not limit the present invention.

[0056] Example 1

[0057] A preparation method of a Ni-based hollow flower-like M-NC@TiO2 composite material includes the following steps:

[0058] Step 1, preparation of solid spherical TiO2. After mixing 2.5 mL of tetrabutyl titanate, 0.03 g of potassium chloride, 4 mL of water, and 100 mL of absolute ethanol and stirring, it is left to stand for 24 h. After standing, the obtained product is centrifuged, washed, and dried to obtain solid spherical TiO2;

[0059] Step 2, preparation of hollow spherical TiO2, adding 0.4g of the solid spherical TiO2 obtained in step 1 and 0.4g of ammonium fluoride into water and stirring to obtain the first hydrothermal reaction liquid, then, carrying out the first hydrothermal reaction under the conditions of hydrothermal temperature of 180°C and hydrothermal time of 12h, and the obtained product is centrifugally washed and dried to obtain hollow spherical TiO2;

[0060] In order to verify the composition and structure of hollow spherical TiO2, XRD and SEM tests were performed.

[0061] The XRD test results of hollow spherical TiO2 are as follows Figure 1 As shown, the diffraction peak of hollow spherical TiO2 is consistent with the characteristic peak of standard anatase TiO2. The test results show that the composition of hollow spherical TiO2 is anatase TiO2;

[0062] The SEM test results of hollow spherical TiO2 are as follows Figure 2 As shown, the hollow spherical TiO2 has a spherical structure with a size of 200 nm, and it can be confirmed from the broken hollow spherical TiO2 that the hollow spherical TiO2 has a hollow structure.

[0063] Step 3, preparation of Ni-MOF@TiO2, 0.1 g of the hollow spherical TiO2 obtained in step 2, 8 mM 2-aminoterephthalic acid, 2 mM nickel nitrate hexahydrate, 45 mL N,N-dimethylformamide and 5 mL methanol were mixed to obtain a second hydrothermal reaction solution, and then, a second hydrothermal reaction was carried out at a hydrothermal temperature of 150° C. and a hydrothermal time of 20 h. The obtained product was centrifuged, washed and dried to obtain Ni-MOF@TiO2;

[0064] Step 4, preparation of Ni-NC@TiO2, calcining the Ni-MOF@TiO2 obtained in step 3 under hydrogen and argon mixed gas conditions at a heating rate of 3°C / min, a calcination temperature of 550°C, and a calcination time of 2h to obtain a Ni-based hollow flower-shaped M-NC@TiO2 composite material, referred to as Ni-NC@TiO2.

[0065] In order to prove the composition of Ni-NC@TiO2, XRD test was carried out. The test results are shown in Figure 1 As shown in the figure, Ni-NC@TiO2 contains the characteristic peaks of Ni metal and anatase TiO2. Combined with the XRD results of hollow spherical TiO2, it is shown that Ni-NC is successfully loaded on hollow spherical TiO2, that is, hollow flower-like M-NC@TiO2 composite materials are successfully prepared.

[0066] Since XRD cannot detect the composition of NC, EDS test was performed. The test results are as follows Figure 4As shown, in addition to Ni element, the surface of Ni-NC@TiO2 also contains N element and C element. The test results show that Ni-NC grows uniformly on the surface of TiO2.

[0067] To prove the microscopic morphology of Ni-NC@TiO2, SEM test was carried out. The test results are as Figure 3 shown. Ni-NC@TiO2 presents a hollow flower-like structure. Due to the orderly growth of flaky Ni-NC on the surface of hollow spherical TiO2, its size increases from 200nm to 1 - 3μm. Combining with Figure 4 the results of EDS in

[0068] To prove the role of Ni-NC@TiO2 as a catalyst for lithium aluminum hydride hydrogen storage material, a Ni-based M-NC@TiO2 doped lithium aluminum hydride hydrogen storage material was prepared and its temperature-rising dehydrogenation performance was tested, which is abbreviated as LiAlH4-Ni-NC@TiO2;

[0069] Meanwhile, the temperature-rising dehydrogenation performance tests were carried out on the lithium aluminum hydride hydrogen storage material without adding Ni-NC@TiO2 and the TiO2 doped lithium aluminum hydride hydrogen storage material obtained by adding the hollow spherical TiO2 obtained in step 2 as reference experiments.

[0070] Among them, the lithium aluminum hydride hydrogen storage material without adding Ni-NC@TiO2 is abbreviated as LiAlH4;

[0071] The TiO2 doped lithium aluminum hydride hydrogen storage material obtained by adding hollow spherical TiO2 is abbreviated as LiAlH4-TiO2.

[0072] The specific method for doping the lithium aluminum hydride hydrogen storage material is as follows: under argon atmosphere, with an addition amount of 7wt%, the additive and lithium aluminum hydride are ball-milled at a ball-to-material ratio of 300:1, a ball-milling speed of 250r / min, and a ball-milling time of 30min to obtain the doped lithium aluminum hydride hydrogen storage material.

[0073] Taking the Ni-NC@TiO2 in Example 1 as an additive as an example.

[0074] A preparation method of a Ni-based M-NC@TiO2 doped lithium aluminum hydride hydrogen storage material: under argon atmosphere, 0.0140g of Ni-NC@TiO2 and 0.1860g of lithium aluminum hydride LiAlH4 are ball-milled at a ball-to-material ratio of 300:1, a ball-milling speed of 250r / min, and a ball-milling time of 30min to obtain the Ni-based M-NC@TiO2 doped lithium aluminum hydride hydrogen storage material, which is abbreviated as LiAlH4-Ni-NC@TiO2.

[0075] LiAlH4 and LiAlH4-TiO2 were prepared in the same way.

[0076] The specific method for dehydrogenation performance testing was that the heating rate was 3 °C / min, and the hydrogen release temperature was raised to 300 °C.

[0077] The dehydrogenation performance test results of LiAlH4 are as Figure 5 shown. The initial hydrogen release temperature was 133.6 °C, and the hydrogen release amount was 7.6 wt%;

[0078] The dehydrogenation performance test results of LiAlH4-TiO2 are as Figure 5 shown. The initial hydrogen release temperature was 90.9 °C, and the hydrogen release amount was 7.6 wt%;

[0079] The dehydrogenation performance test results of LiAlH4-Ni-NC@TiO2 are as Figure 5 shown. The initial hydrogen release temperature was 56.3 °C, and the hydrogen release amount was 7.3 wt%.

[0080] By comparing the above test results, the following conclusions can be obtained:

[0081] 1. Comparing LiAlH4 and LiAlH4-TiO2, it can be seen that the initial dehydrogenation temperature of LiAlH4-TiO2 decreased by 42.7 °C relative to LiAlH4;

[0082] 2. Comparing LiAlH4-TiO2 and LiAlH4-Ni-NC@TiO2, it can be seen that the initial dehydrogenation temperature of LiAlH4-Ni-NC@TiO2 decreased by 34.6 °C relative to LiAlH4-TiO2. Compared with LiAlH4-TiO2, the starting hydrogen release temperature of Ni-NC@TiO2 doped with lithium aluminum hydride is lower;

[0083] This comparative experiment can prove the role of Ni-NC in the technical solution - effectively reducing the initial dehydrogenation temperature of lithium aluminum hydride.

[0084] Therefore, the hollow flower-like composite material Ni-NC@TiO2 has a better improvement on the hydrogen production performance of lithium aluminum hydride, and the high catalytic activity of the hollow flower-like composite material Ni-NC@TiO2 for the lithium aluminum hydride hydrogen storage material does not come from the hollow spherical TiO2.

[0085] To prove the role of the hollow spherical TiO2 in the technical solution, Comparative Example 1 was provided, which is an M-NC material based on Ni and an M-NC doped lithium aluminum hydride hydrogen storage material.

[0086] Comparative Example 1

[0087] A method for preparing a Ni-based M-NC material, wherein the steps not specifically described are the same as those in Example 1, except that steps 1 and 2 are not performed, and hollow spherical TiO2 is not added in step 3, and the obtained material is named Ni-NC.

[0088] The XRD test results of Ni-NC are as follows Figure 6 As shown in Figure 2, Ni-NC only contains the characteristic peaks of Ni metal. The test results show that Ni-NC is successfully prepared.

[0089] The SEM test results of Ni-NC are as follows Figure 7 As shown, Ni-NC presents an irregular flake structure. Comparing the test results with Ni-NC@TiO2, it can be seen that the hollow flower-like structure cannot be formed without adding hollow spherical TiO2.

[0090] A method for preparing a Ni-based M-NC doped lithium aluminum hydride hydrogen storage material, wherein the steps not specifically described are the same as those in Example 1, except that Ni-NC@TiO2 is replaced by Ni-NC, and the obtained material is referred to as LiAlH4-Ni-NC.

[0091] The dehydrogenation performance test results of LiAlH4-Ni-NC are as follows Figure 8 As shown, the initial hydrogen desorption temperature is 63.4°C and the hydrogen desorption amount is 7.5wt%.

[0092] Comparing the dehydrogenation performance test results with LiAlH4-Ni-NC@TiO2, it can be seen that the initial dehydrogenation temperature of LiAlH4-Ni-NC@TiO2 is 7.1°C lower than that of LiAlH4-Ni-NC, and the initial dehydrogenation temperature of Ni-NC@TiO2 material doped with lithium aluminum hydride is lower; this comparative experiment can prove the role of hollow spherical TiO2 in the technical solution - to promote the improvement of the catalytic performance of Ni-NC@TiO2 material.

[0093] Combining the results of SEM tests and dehydrogenation performance tests, the following conclusions can be drawn: the micromorphology of Ni-NC is adjusted by adding hollow spherical TiO2, so that irregular flake Ni-NC grows uniformly and orderly on the surface of hollow spherical TiO2 to form a hollow flower-like structure; furthermore, the hollow flower-like structure can increase the contact area between the material and lithium aluminum hydride, provide more active sites, and thus promote the improvement of the hydrogen production performance of lithium aluminum hydride.

[0094] In order to prove that the method for preparing M-NC@TiO2 composite materials by the technical solution of the present invention is applicable to other metal elements with catalytic properties, and also has a significant improvement effect on the dehydrogenation performance of LiAlH4, Examples 2, 3 and 4 are provided, namely, hollow flower-shaped M-NC@TiO2 composite materials based on Co, Fe and Cu, respectively;

[0095] Meanwhile, in order to further prove the role of hollow spherical TiO2 in the technical solution, similar to Example 1 and Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 are provided, which are M-NC materials based on Co, Fe, and Cu, and M-NC doped lithium aluminum hydride hydrogen storage materials, respectively.

[0096] Example 2

[0097] A preparation method of a Co-based hollow flower-like M-NC@TiO2 composite material. The steps not specifically described are the same as those in Example 1, except that: in step 3, nickel nitrate hexahydrate is replaced with cobalt nitrate hexahydrate, and the obtained material is named Co-NC@TiO2.

[0098] The XRD test results of Co-NC@TiO2 are as Figure 1 shown. Co-NC@TiO2 contains the characteristic peaks of both Co metal and anatase TiO2. The test results are the same as those of Ni-NC@TiO2, that is, the hollow flower-like M-NC@TiO2 composite material is successfully prepared.

[0099] The SEM test results of Co-NC@TiO2 are as Figure 3 shown, and are the same as the test results of Ni-NC@TiO2.

[0100] A preparation method of a Co-based M-NC@TiO2 doped lithium aluminum hydride hydrogen storage material. The steps not specifically described are the same as those in Example 1, except that: Ni-NC@TiO2 is replaced with Co-NC@TiO2, and the obtained material is named LiAlH4-Co-NC@TiO2.

[0101] The dehydrogenation performance test results of LiAlH4-Co-NC@TiO2 are as Figure 5 shown. The initial hydrogen release temperature is 65.3 °C, and the hydrogen release amount is 7.0 wt%.

[0102] Comparative Example 2

[0103] A preparation method of a Co-based M-NC material. The steps not specifically described in detail are the same as those in Example 2, except that steps 1 and 2 are not carried out, and hollow spherical TiO2 is not added in step 3. The obtained material is named Co-NC.

[0104] The XRD test results of Co-NC are as Figure 6 shown. Co-NC only contains the characteristic peaks of Co metal. The test results show that Co-NC is successfully prepared.

[0105] The SEM test results of Co-NC are as Figure 7As shown, the test results are the same as those of Ni-NC.

[0106] A method for preparing a Co-based M-NC doped lithium aluminum hydride hydrogen storage material, wherein the steps not specifically described are the same as those in Example 1, except that Ni-NC@TiO2 is replaced by Co-NC, and the obtained material is named LiAlH4-Co-NC.

[0107] The dehydrogenation performance test results of LiAlH4-Co-NC are as follows Figure 8 As shown, the initial hydrogen desorption temperature is 83.3°C and the hydrogen desorption amount is 7.2wt%.

[0108] Example 3

[0109] A method for preparing a hollow flower-shaped M-NC@TiO2 composite material based on Fe, wherein the steps not specifically described are the same as those in Example 1, except that: in the step 3, nickel nitrate hexahydrate is replaced with ferric nitrate nonahydrate, and the obtained material is named Fe-NC@TiO2.

[0110] The XRD test results of Fe-NC@TiO2 are as follows Figure 1 As shown in Figure 2, Fe-NC@TiO2 contains the characteristic peaks of both Fe metal and anatase TiO2. The test results are the same as those of Ni-NC@TiO2, that is, the hollow flower-shaped M-NC@TiO2 composite material was successfully prepared.

[0111] The SEM test results of Fe-NC@TiO2 are as follows Figure 3 As shown, the test results are the same as those of Ni-NC@TiO2.

[0112] A method for preparing an Fe-based M-NC@TiO2-doped lithium aluminum hydride hydrogen storage material, wherein the steps not specifically described are the same as those in Example 1, except that: the Ni-NC@TiO2 is replaced by Fe-NC@TiO2, and the obtained material is named LiAlH4-Fe-NC@TiO2.

[0113] The dehydrogenation performance test results of LiAlH4-Co-NC@TiO2 are as follows Figure 5 As shown, the initial hydrogen desorption temperature is 68.2°C and the hydrogen desorption amount is 7.1 wt%.

[0114] Comparative Example 3

[0115] A method for preparing an Fe-based M-NC material, wherein the steps not specifically described are the same as those in Example 3, except that: Steps 1 and 2 are not performed, and hollow spherical TiO2 is not added in Step 3, and the obtained material is named Fe-NC.

[0116] The XRD test results of Fe-NC are as followsFigure 6 As shown, Fe-NC only contains the characteristic peaks of elemental Fe metal. The test results show that Co-NC was successfully prepared.

[0117] The SEM test results of Fe-NC are as Figure 7 shown, which are the same as the test results of Ni-NC.

[0118] A preparation method of an Fe-based M-NC doped lithium aluminum hydride hydrogen storage material, the steps not specifically described are the same as those in Example 1, except that: Ni-NC@TiO2 is replaced by Fe-NC, and the obtained material is named LiAlH4-Fe-NC.

[0119] The dehydrogenation performance test results of LiAlH4-Fe-NC are as Figure 8 shown, the initial hydrogen release temperature is 88.1 °C, and the hydrogen release amount is 6.8 wt%.

[0120] Example 4

[0121] A preparation method of a Cu-based hollow flower-like M-NC@TiO2 composite material, the steps not specifically described are the same as those in Example 1, except that: in step 3, nickel nitrate hexahydrate is replaced by copper nitrate hexahydrate, and the obtained material is named Cu-NC@TiO2.

[0122] The XRD test results of Cu-NC@TiO2 are as Figure 1 shown, Cu-NC@TiO2 contains the characteristic peaks of both elemental Cu metal and anatase TiO2. The test results are the same as those of Ni-NC@TiO2, that is, a hollow flower-like M-NC@TiO2 composite material was successfully prepared.

[0123] The SEM test results of Cu-NC@TiO2 are as Figure 3 shown, which are the same as the test results of Ni-NC@TiO2.

[0124] A preparation method of a Cu-based M-NC@TiO2 doped lithium aluminum hydride hydrogen storage material, the steps not specifically described are the same as those in Example 1, except that: Ni-NC@TiO2 is replaced by Cu-NC@TiO2, and the obtained material is named LiAlH4-Cu-NC@TiO2.

[0125] The dehydrogenation performance test results of LiAlH4-Cu-NC@TiO2 are as Figure 5 shown, the initial hydrogen release temperature is 70.5 °C, and the hydrogen release amount is 7.3 wt%.

[0126] Comparative Example 4

[0127] A preparation method of Cu-based M-NC material. The steps not specifically described are the same as those in Example 4, except that: steps 1 and 2 are not carried out, and hollow spherical TiO2 is not added in step 3. The obtained material is named Cu-NC.

[0128] The XRD test results of Cu-NC are as Figure 6 shown. Cu-NC only contains the characteristic peaks of metallic Cu. The test results indicate that Cu-NC is successfully prepared.

[0129] The SEM test results of Cu-NC are as Figure 7 shown, which are the same as the test results of Ni-NC.

[0130] A preparation method of a Cu-based M-NC doped lithium aluminum hydride hydrogen storage material. The steps not specifically described are the same as those in Example 1, except that Ni-NC@TiO2 is replaced by Cu-NC. The obtained material is named LiAlH4-Cu-NC.

[0131] The dehydrogenation performance test results of LiAlH4-Cu-NC are as Figure 8 shown. The initial dehydrogenation temperature is 90.9 °C, and the hydrogen release amount is 7.7 wt%.

[0132] The following conclusions can be obtained through the above examples and comparative examples:

[0133] 1. From Examples 1 and 2, Examples 3 and 4, it can be seen that the method for preparing the M-NC@TiO2 composite material in the technical solution of the present invention is applicable to other metal elements with catalytic performance, and it also has an obvious improvement effect on the dehydrogenation performance of LiAlH4;

[0134] 2. Through Examples 1 and Comparative Example 1, Examples 2 and Comparative Example 2, Examples 3 and Comparative Example 3, Examples 4 and Comparative Example 4, the role of hollow spherical TiO2 in the technical solution can be further confirmed.

[0135] That is, the presence of hollow spherical TiO2 can promote the regular arrangement and growth of irregular flaky M-NC (M = Ni, Co, Fe, Cu) on the surface of hollow spherical TiO2 into a hollow flower-like morphology. At the same time, it is beneficial to improve the catalytic performance of the M-NC@TiO2 material.

[0136] Therefore, the hollow flower-like composite material M-NC@TiO2 obtained by the combination of hollow spherical TiO2 and M-NC effectively reduces the initial dehydrogenation temperature of lithium aluminum hydride and retains a relatively high hydrogen release amount. At the same time, compared with hollow spherical TiO2 and M-NC materials, the improvement of the dehydrogenation performance of lithium aluminum hydride is more prominent.

Claims

1. A hollow flower-like M-NC@TiO2 composite material, characterized in that: First, prepare solid spherical TiO₂, then convert it into hollow spherical TiO₂. After that, grow M-MOF orderly on the surface of the hollow spherical TiO₂ to obtain M-MOF@TiO₂. Finally, calcine M-MOF@TiO₂ to obtain the hollow flower-like M-NC@TiO₂ composite material, simply referred to as hollow flower-like M-NC@TiO₂. Among them, in the M-MOF and M-NC, M = Ni, Co, Fe, Cu; The microscopic morphology of the hollow spherical TiO₂ is a hollow spherical structure with a size of 200 nm. The microscopic morphology of the M-NC@TiO₂ is a hollow flower-like structure with the hollow spherical TiO₂ as the substrate and M-NC growing orderly on the surface, with a size of 1 - 3 μm. The Ni-NC contains Ni element, and also contains N element and C element, and Ni-NC is flaky.

2. A method for preparing a hollow flower-like M-NC@TiO2 composite material, characterized in that It includes the following steps: Step 1, Preparation of solid spherical TiO₂: Mix tetrabutyl titanate, potassium chloride, water, and absolute ethanol and stir, then let it stand. After standing, the obtained product is centrifuged, washed, and dried to obtain solid spherical TiO₂. In the said Step 1, the mass ratio of tetrabutyl titanate to potassium chloride is 1:(1 - 4), and the volume ratio of water to absolute ethanol is 1:

25. Step 2, Preparation of hollow spherical TiO₂: Add the solid spherical TiO₂ obtained in Step 1 and ammonium fluoride into water and stir to obtain the first hydrothermal reaction solution. Then, carry out the first hydrothermal reaction under certain conditions. The obtained product is centrifuged, washed, and dried to obtain hollow spherical TiO₂. In the said Step 2, the mass ratio of the solid spherical TiO₂ to ammonium fluoride is 1:(1 - 4). Step 3, Preparation of M-MOF@TiO₂: Mix the hollow spherical TiO₂ obtained in Step 2, 2-aminoterephthalic acid, metal salt, N,N-dimethylformamide, and methanol to obtain the second hydrothermal reaction solution. Then, carry out the second hydrothermal reaction under certain conditions. The obtained product is centrifuged, washed, and dried to obtain M-MOF@TiO₂. In the said Step 3, the molar ratio of the hollow spherical TiO₂, 2-aminoterephthalic acid, and metal salt is (1 - 2):2:(2 - 12), and the volume ratio of N,N-dimethylformamide to methanol is 9:

1. In the said Step 3, the metal salt is one of nickel salt, cobalt salt, iron salt, or copper salt. Step 4, Preparation of M-NC@TiO₂: Calcinate the M-MOF@TiO₂ obtained in Step 3 under certain conditions to obtain the hollow flower-like M-NC@TiO₂ composite material, simply referred to as M-NC@TiO₂.

3. The preparation method of the hollow flower-shaped M-NC@TiO2 composite material according to claim 2, wherein: The nickel salt is nickel nitrate hexahydrate, the cobalt salt is cobalt nitrate hexahydrate, the iron salt is iron nitrate nonahydrate, and the copper salt is copper nitrate hexahydrate.

4. The preparation method of the hollow flower-like M-NC@TiO2 composite material according to claim 2, characterized in that: The reaction conditions in the preparation method meet the following requirements. In the said Step 1, the standing time is 24 h. In the said Step 2, the conditions of the first hydrothermal reaction are: the hydrothermal temperature is 160 - 180 °C, and the hydrothermal time is 10 - 15 h. In the said Step 3, the conditions of the second hydrothermal reaction are: the hydrothermal temperature is 120 - 160 °C, and the hydrothermal time is 15 - 24 h. In the said step 4, the calcination conditions are as follows: under the condition of a hydrogen-argon mixed gas, the heating rate is 3-5 °C / min, the calcination temperature is 500-700 °C, and the calcination time is 1-3 h.

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