Single-atom nb substituted tio2 / tiof2 heterojunctions for catalytic hydrogenation of magnesium

Abstract

The application discloses a monatomic Nb-substituted TiO2 / TiOF2 heterojunction for catalyzing hydrogenated magnesium, and belongs to the field of hydrogen storage alloy and preparation technology thereof. The application solves the problem of poor kinetics and thermodynamics performance of the existing MgH2 hydrogen storage material, and cannot meet the actual application requirements. The application mixes tetrabutyl titanate, niobium chloride and hydrofluoric acid by using a one-step solvothermal method, limits transition metal Nb in a monatomic form on the surface of a TiO2 / TiOF2 carrier to form stable active centers, effectively reduces the dissociation energy barrier of hydrogen molecules, enhances the diffusion capacity of hydrogen atoms in a Mg matrix, realizes the rapid hydrogen absorption and release of commercial MgH2 powder in a medium temperature zone, and inhibits particle growth and agglomeration in the cycle process, so that the hydrogen absorption and release temperature and reaction rate of the material are further optimized, and good synergistic catalysis effect and excellent cycle stability are exhibited.

Description

TECHNICAL FIELD

[0001] The application relates to a single-atom Nb-substituted TiO2 / TiOF2 heterojunction for catalyzing hydrogenated magnesium, and belongs to the field of hydrogen storage alloys and preparation technologies thereof. BACKGROUND

[0002] Hydrogen energy has the advantages of high calorific value, abundant resources and good safety. The application of hydrogen energy mainly depends on three links of preparation, storage and utilization. At present, hydrogen production and hydrogen utilization technology are relatively mature, but safe, economical and efficient storage and transportation methods are still the key problems in industrial development. According to the physical state of hydrogen, common hydrogen storage methods include high-pressure gaseous hydrogen storage, liquid hydrogen storage and solid hydrogen storage. High-pressure hydrogen storage technology is applied earlier, but has the problems of low volume hydrogen storage capacity and high safety risk; liquid hydrogen storage has a high volume density, but needs complex low-temperature conditions or involves safety hazards of organic matters, so the application is limited. In comparison, solid-state hydrogen storage is considered as one of the most promising solutions due to its safety and hydrogen storage density advantages.

[0003] In the field of solid-state hydrogen storage materials, magnesium hydride is widely considered as a very potential hydrogen storage medium due to its high mass hydrogen storage density and good reversible hydrogen storage performance. However, the high thermodynamic stability and slow hydrogen absorption / desorption kinetics of the material itself seriously restrict its large-scale commercial application. Therefore, how to effectively improve the thermodynamic and kinetic performance of MgH2 hydrogen storage is the key to its industrial application. SUMMARY

[0004] In order to solve the problems of poor kinetic and thermodynamic performance of the existing MgH2 hydrogen storage material and the inability to meet the actual application requirements, the application provides a single-atom Nb-substituted TiO2 / TiOF2 heterojunction for catalyzing hydrogenated magnesium.

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

[0006] One of the purposes of the application is to provide a preparation method of the single-atom Nb-substituted TiO2 / TiOF2 heterojunction, which comprises: mixing tetrabutyl titanate, niobium chloride and hydrofluoric acid and synthesizing by one-step solvothermal method.

[0007] Further limited, the mixing amount ratio of tetrabutyl titanate, niobium chloride and hydrofluoric acid is 10-30 mL: 1.0-1.5 g: 6-10 mL.

[0008] Further limited, the reaction temperature of the one-step solvothermal method is 160-200 DEG C, and the time is 14-18 h.

[0009] The second purpose of the application is to provide a single-atom Nb-substituted TiO2 / TiOF2 heterojunction prepared by the above method.

[0010] The third object of the present application is to provide an application of the monatomic Nb-substituted TiO2 / TiOF2 heterojunction as described above, in particular as a catalyst for hydrogenating magnesium-based hydrogen storage materials.

[0011] The fourth object of the present application is to provide a magnesium-based hydrogen storage material, in particular a composite of the monatomic Nb-substituted TiO2 / TiOF2 heterojunction as described above and MgH2 powder.

[0012] Further limitation, the monatomic Nb-substituted TiO2 / TiOF2 heterojunction has a proportion of 4.5-5.5wt.%.

[0013] The fifth object of the present application is to provide a preparation method of the magnesium-based hydrogen storage material as described above, in particular a method of obtaining the monatomic Nb-substituted TiO2 / TiOF2 heterojunction and MgH2 powder through high-energy ball milling.

[0014] Further limitation, the high-energy ball milling conditions are as follows: under a protective atmosphere, a ball-to-material ratio of 60:1, a rotation speed of 400-500 rpm, an intermittent ball milling mode, 20 min of ball milling and 10 min of rest, and a total ball milling time of 8-12 h.

[0015] Further limitation, the particle size of the MgH2 powder is 2-15 μm.

[0016] Beneficial effects:

[0017] The present application mixes tetrabutyl titanate, niobium chloride and hydrofluoric acid using one-step solvothermal method, limits transition metal Nb to the surface of TiO2 / TiOF2 carrier in the form of monatomic, forms stable active centers, effectively reduces the dissociation energy barrier of hydrogen molecules, enhances the diffusion capacity of hydrogen atoms in Mg matrix, and realizes the rapid absorption and release of commercial MgH2 powder in the medium temperature zone, and inhibits particle growth and agglomeration in the cycle process, thereby further optimizing the hydrogen absorption and release temperature and reaction rate of the material, exhibiting good synergistic catalytic effect and excellent cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Transmission electron microscope image of the Nb-TiO2 / TiOF2 powder prepared in Example 1;

[0019] Figure 2 High-angle annular dark field scanning transmission electron microscope image of the Nb-TiO2 / TiOF2 powder prepared in Example 1;

[0020] Figure 3Temperature swing hydrogen desorption curve of the magnesium-based hydrogen storage material prepared for Example 1 and Comparative Example 1;

[0021] Figure 4 Temperature swing hydrogen desorption curve of the magnesium-based hydrogen storage material prepared for Example 1 and Comparative Example 1;

[0022] Figure 5 Temperature swing hydrogen desorption curve of the magnesium-based hydrogen storage material prepared for Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0023] In order to make the above objectives, features and advantages of the present application more apparent, specific embodiments of the present application are described in detail below with reference to the description and examples.

[0024] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details given herein. In other instances, well-known methods have not been described in detail in order to avoid unnecessarily obscuring the present application. Accordingly, it will be appreciated that the present application is not limited to the embodiments disclosed herein, and that the embodiments are given by way of example only.

[0025] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. The "in one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is independent or alternative to other embodiments.

[0026] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained by commercial channels by those skilled in the art.

[0027] Example 1:

[0028] (1) Preparation method of monatomic Nb-substituted TiO2 / TiOF2heterojunction:

[0029] 20 mL of tetrabutyl titanate and 1.2 g of niobium chloride were mixed to form solution A, 8 mL of hydrofluoric acid was added to solution A to form solution B, and then solution B was reacted in an autoclave at 180°C for 16 h. After reaction, centrifugal washing and drying were performed to obtain Nb-TiO2 / TiOF2powder.

[0030] The obtained monatomic Nb-substituted TiO2 / TiOF2powder was subjected to structural characterization, and the results are shown in Figures 1-2 Figure 1 The transmission electron microscope image of the TiO2 / TiOF2powder is shown in Figure 1 ​It can be seen that the Nb-TiO2 / TiOF2 powder contains a TiO2 / TiOF2 heterostructure. Figure 2 High-angle annular dark-field scanning transmission electron microscope image of Nb-TiO2 / TiOF2 powder, by Figure 2 It can be seen that a large amount of Nb is distributed in the heterostructure in the form of single atoms.

[0031] (2) Preparation of MgH2-Nb-TiO2 / TiOF2 composite hydrogen storage material:

[0032] Under an argon atmosphere, Nb-TiO2 / TiOF2 powder and MgH2 powder were mixed at mass fractions of 5 wt.% and 95 wt.%, respectively. A certain amount of zirconia beads were weighed and placed in a ball mill jar at a ball milling ratio of 60:1. High-energy ball milling was carried out at a speed of 450 rpm. Intermittent ball milling was used, with each ball milling session lasting 20 minutes and followed by a 10-minute break. The total ball milling time was 10 hours.

[0033] Comparative Example 1:

[0034] This comparative example uses commercially available MgH2 hydrogen storage material as the magnesium-based hydrogen storage material.

[0035] The performance of the magnesium-based hydrogen storage materials of Example 1 and Comparative Example 1 was characterized, and the specific test results are as follows: Figures 3-5 As shown.

[0036] Figure 3 This is a comparison of the temperature-dependent hydrogen desorption curves of the MgH2-Nb-TiO2 / TiOF2 composite hydrogen storage material prepared in Example 1 and the commercially available MgH2 hydrogen storage material. Figure 3 It is known that the initial hydrogen release temperature of commercially available MgH2 is as high as 418.2℃, and the total hydrogen release is 7.4wt.%. The initial hydrogen release temperature of MgH2-Nb-TiO2 / TiOF2 composite hydrogen storage material is 185.7℃, which is about 232.5℃ lower than that of pure MgH2, showing the best dehydrogenation thermodynamic performance.

[0037] Figure 4 The figure shows the hydrogen desorption curves of the MgH2-Nb-TiO2 / TiOF2 composite hydrogen storage material prepared in Example 1 at different temperatures. As can be seen from the isothermal hydrogen desorption curve of the MgH2-Nb-TiO2 / TiOF2 composite hydrogen storage material at 250℃, this composite material can release 6.0 wt.% hydrogen gas in only 4.6 minutes. To further test the isothermal hydrogen absorption performance, the hydrogen desorption products of the MgH2-Nb-TiO2 / TiOF2 composite hydrogen storage material were subjected to hydrogen absorption tests at 100℃ and a hydrogen pressure of 3 MPa. The test results are as follows. Figure 5 As shown in the figure, the hydrogen-depleting product absorbs up to 5.02 wt.% of hydrogen within 15 seconds.

[0038] While the application has been disclosed in its preferred embodiments with reference to specific details, it is to be understood that various modifications and substitutions can be made by one skilled in the art without departing from the spirit and scope of the application, as defined by the following claims.

Claims

1. A method for preparing a monatomic Nb-substituted TiO2 / TiOF2 heterojunction, characterized in that, The tetrabutyl titanate, niobium chloride and hydrofluoric acid are mixed to synthesize by one-step solvothermal method.

2. The production method according to claim 1, characterized by, The tetrabutyl titanate, niobium chloride and hydrofluoric acid are mixed to synthesize by one-step solvothermal method.

3. The preparation method according to claim 1, characterized in that, The reaction temperature of the one-step solvothermal method is 160-200℃, and the time is 14-18h.

4. A monatomic Nb-substituted TiO2 / TiOF2 heterojunction prepared by the method of any one of claims 1-3.

5. Use of the monatomic Nb-substituted TiO2 / TiOF2 heterojunction according to claim 4, characterized in that, The monatomic Nb-substituted TiO2 / TiOF2 heterojunction is used as a catalyst to catalyze hydrogenation of magnesium hydrogen storage material.

6. A magnesium-based hydrogen storage material, characterized in that, The monatomic Nb-substituted TiO2 / TiOF2 heterojunction is compounded with MgH2 powder.

7. The magnesium-based hydrogen storage material of claim 6, wherein, The proportion of the monatomic Nb-substituted TiO2 / TiOF2 heterojunction is 4.5-5.5wt.%.

8. A method for producing a magnesium-based hydrogen storage material according to claim 6 or 7, characterized in that The monatomic Nb-substituted TiO2 / TiOF2 heterojunction is compounded with MgH2 powder.

9. The production method according to claim 8, characterized by, The monatomic Nb-substituted TiO2 / TiOF2 heterojunction is compounded with MgH2 powder.

10. The method of claim 8, wherein, The high-energy ball milling treatment condition is that the ball-to-material ratio is 60:1, the rotation speed is 400-500rpm, the intermittent ball milling mode is adopted, the ball milling time is 20min, the stop time is 10min, and the total ball milling time is 8-12h. The particle size of the MgH2 powder is 2-15μm.

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