Monatomic Nb substituted TiO2 / TiOF2 heterojunction for catalytic magnesium hydride

Abstract

The invention discloses a monatomic Nb substituted TiO2 / TiOF2 heterojunction for catalyzing magnesium hydride, and belongs to the technical field of hydrogen storage alloys and preparation thereof. The invention solves the problem that the existing MgH2 hydrogen storage material has poor dynamic and thermodynamic properties and cannot meet the actual application requirements. Tetrabutyl titanate, niobium chloride and hydrofluoric acid are mixed, a one-step solvothermal method is adopted, transition metal Nb is confined to the surface of a TiO2 / TiOF2 carrier in a monatomic form to form a stable active center, the dissociation energy barrier of hydrogen molecules is effectively reduced, the diffusivity of hydrogen atoms in an Mg matrix is enhanced, rapid hydrogen absorption / desorption of commercial MgH2 powder in a medium-temperature zone is achieved, and the preparation method has the advantages that the preparation process is simple, and the preparation cost is low. And the growth and agglomeration of particles are inhibited in the circulation process, so that the hydrogen absorption and desorption temperature and the reaction rate of the material are further optimized, and a good synergistic catalysis effect and excellent circulation stability are shown.

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

[0006] 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.

[0007] Further limited, the reaction temperature of the one-step solvothermal method is 160-200 DEG C, and the time is 14-18 h.

[0008] The second purpose of the application is to provide the single-atom Nb-substituted TiO2 / TiOF2 heterojunction prepared by the above method.

[0009] The third object of the present application is to provide an application of the monatomic Nb-substituted TiO2 / TiOF2 heterojunction as described above, specifically as a catalyst for hydrogenating magnesium-based hydrogen storage materials.

[0010] The fourth object of the present application is to provide a magnesium-based hydrogen storage material, specifically a composite of the monatomic Nb-substituted TiO2 / TiOF2 heterojunction as described above and MgH2 powder.

[0011] Further limitation, the monatomic Nb-substituted TiO2 / TiOF2 heterojunction has a proportion of 4.5-5.5wt.%.

[0012] The fifth object of the present application is to provide a preparation method of the magnesium-based hydrogen storage material as described above, specifically a monatomic Nb-substituted TiO2 / TiOF2 heterojunction and MgH2 powder are treated by high-energy ball milling.

[0013] Further limitation, the high-energy ball milling treatment 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.

[0014] Further limitation, the particle size of the MgH2 powder is 2-15 μm.

[0015] Beneficial effects: The present application mixes tetrabutyl titanate, niobium chloride and hydrofluoric acid by 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 ability of hydrogen atoms in the Mg matrix, and in the hydrogen absorption / desorption process, Nb remains in the form of monatomic and stably distributes in the catalyst lattice, realizes the rapid hydrogen absorption / desorption of commercial MgH2 powder in the medium temperature zone, and inhibits the particle growth and agglomeration in the cycle process, thereby further optimizing the hydrogen absorption / desorption temperature and reaction rate of the material, showing good synergistic catalytic effect and excellent cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 Transmission electron microscope image of the Nb-TiO2 / TiOF2 powder prepared in Example 1; Figure 2 High-angle annular dark field scanning transmission electron microscope image of the Nb-TiO2 / TiOF2 powder prepared in Example 1; Figure 3 Temperature-variable hydrogen desorption curve of the magnesium-based hydrogen storage material prepared in Example 1 and Comparative Example 1; Figure 4Isothermal hydrogen desorption curve of the magnesium-based hydrogen storage material prepared for Example 1 and Comparative Example 1; Figure 5 Isothermal hydrogen absorption curve of the magnesium-based hydrogen storage material prepared for Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0017] In order to make the above objectives, characteristics 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.

[0018] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the concept of the present application, therefore the present application is not limited to the specific examples disclosed below.

[0019] 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. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is separate or alternative to other embodiments.

[0020] 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.

[0021] Example 1: (1) Preparation method of monatomic Nb-substituted TiO2 / TiOF2heterojunction: 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.

[0022] The obtained monatomic Nb-substituted TiO2 / TiOF2powder was subjected to structural characterization, and the results are shown in Figures 1-2 As shown in Figure 1 The transmission electron microscope image of the TiO2 / TiOF2powder, from which Figure 1 It can be seen that the Nb-TiO2 / TiOF2powder contains TiO2 / TiOF2heterostructure. Figure 2 The high-angle annular dark field scanning transmission electron microscope image of the Nb-TiO2 / TiOF2powder, from which Figure 2 It can be seen that a large amount of Nb is distributed in the heterostructure in the form of a single atom.

[0023] (2) Preparation of MgH2-Nb-TiO2 / TiOF2 composite hydrogen storage material: 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.

[0024] Comparative Example 1: This comparative example uses commercially available MgH2 hydrogen storage material as the magnesium-based hydrogen storage material.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing a single-atom Nb-substituted TiO2 / TiOF2 heterojunction, characterized in that, Tetrabutyl titanate, niobium chloride, and hydrofluoric acid were mixed and synthesized using a one-step solvothermal method.

2. The preparation method according to claim 1, characterized in that, The ratio of tetrabutyl titanate, niobium chloride and hydrofluoric acid is 10~30mL: 1.0~1.5g: 6~10mL.

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

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

5. An application of the single-atom Nb-substituted TiO2 / TiOF2 heterojunction as described in claim 4, characterized in that, Magnesium as a catalyst for catalytic hydration of hydrogen storage materials.

6. A magnesium-based hydrogen storage material, characterized in that, It is composed of TiO2 / TiOF2 heterojunction with single-atom Nb substitution as described in claim 4 and MgH2 powder.

7. The magnesium-based hydrogen storage material according to claim 6, characterized in that, The proportion of single-atom Nb-substituted TiO2 / TiOF2 heterojunctions is 4.5~5.5 wt.%.

8. A method for preparing the magnesium-based hydrogen storage material according to claim 6 or 7, characterized in that, TiO2 / TiOF2 heterojunctions with single-atom Nb substitution and MgH2 powder were obtained by high-energy ball milling.

9. The preparation method according to claim 8, characterized in that, The high-energy ball milling conditions are as follows: under a protective atmosphere, with a ball-to-material ratio of 60:1 and a rotation speed of 400-500 rpm, the ball milling is carried out in an intermittent manner, with each ball milling session lasting 20 minutes and followed by a 10-minute rest, for a total ball milling time of 8-12 hours.

10. The preparation method according to claim 8, characterized in that, The particle size of MgH2 powder is 2~15μm.

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