Carbon nanofiber supported MnTi bimetallic microspheres, and preparation method and application thereof

Abstract

The application discloses a kind of carbon nanofiber load MnTi bimetallic microspheres, with the compound of transition metal titanium isopropyl titanate, manganese chloride tetrahydrate, polyvinylpyrrolidone PVP as raw material, carbon nanofiber load MnTi bimetallic microspheres PVP-MnTi are obtained by electrospinning method;Carbon nanofiber load MnTi bimetallic microspheres CNT-MnTi can be prepared by calcining again.The preparation method includes the following steps:1, the electrospinning of PVP-MnTi;2, the preparation of CNT-MnTi.As the application of MgH2 hydrogen storage catalyst, CNT-MnTi is ball milled with magnesium hydride, and a kind of magnesium hydride hydrogen storage material based on CNT-MnTi is obtained;Under the condition that the temperature programmed rate is 3 DEG C / min, the initial hydrogen release temperature is 180-190 DEG C;Under the condition that the hydrogen absorption pressure is 20-30bar, the hydrogen absorption temperature is 150-250 DEG C, the hydrogen absorption time is 200-600s, the hydrogen absorption amount is 5.8-6.2wt%;Under the condition that the hydrogen release temperature is 275-350 DEG C, the hydrogen release time is 240-360s, the hydrogen release amount is 4.0-6.1wt%.

Description

Technical Field

[0001] This invention relates to the field of hydrogen storage catalysis technology, specifically to a carbon nanofiber-supported MnTi bimetallic microsphere, its preparation method, and its application. Background Technology

[0002] MgH2, as a highly efficient hydrogen storage material, possesses a hydrogen storage content of 7.6 wt%, and boasts advantages such as excellent cycle performance, non-toxicity, room temperature stability, and environmental friendliness. However, MgH2 suffers from high hydrogen absorption and desorption temperatures and activation energies, resulting in slow hydrogen absorption and desorption kinetics. Therefore, catalysts are needed to improve the hydrogen absorption and desorption kinetics of MgH2. Since directly introducing catalysts can lead to agglomeration during hydrogen absorption and desorption, current conventional techniques involve loading the catalyst onto a support or adjusting its structure to improve this process. Among these techniques, electrospun thin films offer advantages such as large specific surface area and good dispersibility, effectively addressing the catalyst dispersion problem.

[0003] For example, existing literature 1 (Meng, Q.; Huang, Y.; Ye, J.; Xia, G.; Wang, G.; Dong, L.; Yang, Z.; Yu, X., Electrospun carbon nanofibers with in-situ encapsulated Ninanoparticles as catalyst for enhanced hydrogen storage of MgH2. J. Alloy. Compd. 2021, 851.) synthesized a thin film material of nickel particles encapsulated by carbon nanofibers through electrospinning and calcination, and then compounded it with MgH2 by ball milling to obtain a MgH2-10wt Ni@C composite material. This achieved a dehydrogenation capacity of 5.79wt% at 280℃. However, since the thin film of this technology contains only one metal element, i.e., a single metal thin film, even if the metal element used in this technology is the transition metal nickel, there are still few electronic configurations, i.e. the electron distribution of metal ions is relatively simple and monotonous. Therefore, this technology has the technical problem of lacking diversity of catalytic active sites, which leads to low catalytic efficiency and selectivity.

[0004] To address the technical challenges of low catalytic efficiency and selectivity caused by monometallic thin films, improvements can be made by fabricating bimetallic thin films. The basic principle is that bimetallic thin films contain two metals simultaneously, and the electronic structures of these two metals interact, resulting in a synergistic catalytic effect. This leads to increased selectivity in the catalytic process, thereby improving catalytic efficiency. Furthermore, bimetallic thin films can better disperse the two transition metals within their structure, enhancing the catalytic effect of the catalyst. For example, existing literature 2 (Wang, XS; Liu, MZ; Tian, ​​T.; Liu, F.; Wang, JL; Li, JP; Liu, G., Fibrous V / Nb bimetallic oxides with remarkable catalytic effect on hydrogen storage properties of MgH2. Int. J. Hydrog. Energy 2025, 97, 1168-1176.) discloses a method for synthesizing a thin film composed of carbon nanofiber-supported V / Nb bimetallic oxides as a catalytic material for MgH2 by adding PVP, vanadium, and nickel to ethanol in a ratio of 20:2:1 and then using electrospinning and calcination. This technical solution improves catalytic efficiency and selectivity by introducing two metal elements and utilizing the synergistic catalytic effect of the bimetals. As is known from common knowledge in the technical field of this invention, in electrospinning technology, the concentration of the electrospinning solution has a significant impact on technical characteristics, such as the viscosity of the solution, and thus a significant impact on the technical performance of the electrospinned material. Specifically, regarding the electrospinning solution containing bimetallic elements involved in this invention, increasing the element concentration significantly increases the viscosity of the electrospinning solution. Therefore, to improve the dispersibility of the metal element and obtain nanofiber negative metal composite materials, i.e., to solve the dispersibility problem, the solution adopted is to control / reduce the concentration of the metal element in the electrospinning solution, thereby improving dispersibility. However, this solution directly results in a relatively small amount of metal element added, ultimately leading to the technical problem of low catalytic performance.

[0005] Furthermore, the type of metal element also significantly affects the preparation process of electrospinning and the performance of the resulting material. Since there are few existing technologies for catalytic materials based on electrospinning technology applied to MgH2, this study focuses on existing technologies related to electrode materials that also involve adjusting the electronic structure, specifically electrode materials based on electrospinning technology. Among these, existing literature 3 uses nickel, existing literature 4 uses titanium, and existing literature 5 uses manganese, as detailed below.

[0006] Existing literature 3 (Luo, Z.; Xia, Y.; Huang, J.; Zeng, H.; Chen, Y.; Chen, L.; Feng, Z.; Chen, Z., Flexible electrospun carbon nanofibers-Nickel disulfide@carbonnanofibers-Carbon nanofibers sandwich structure as binder-free anode for high-performance lithium-ion batteries. Surfaces and Interfaces 2024, 54.) describes the preparation of a nickel-coated carbon nanofiber composite material by adding nickel nitrate hexahydrate and polyacrylonitrile in a 2:3 ratio to DMF via electrospinning and calcination, achieving a specific capacity of 881.1 mAh / g at a current density of 0.1 A / g.

[0007] Existing literature 4 (Li,Y.;Du,J.;Sun,X.;Lan,D.;Cui,J.;Zhao,H.;Zhang,Y.;He,W.,Preparation of TiO2 / nitrogen-doped CNF composites as high-performance lithium-ion battery anodes by electrospinning.Journal of Crystal Growth 2023,624.) describes the preparation of carbon nanofiber-encapsulated titanium composites by adding titanium dioxide and polyacrylonitrile to DMF in a 1:5 ratio and then using electrospinning and calcination methods. This resulted in a specific capacity of 590.2 mAh / g at a current density of 0.1 A / g.

[0008] Existing literature 5 (Tang,F.;He,T.;Zhang,H.;Wu,X.;Li,Y.;Long,F.;Xiang,Y.;Zhu,L.;Wu,J.;Wu,X.,The MnO@N-doped carbon composite derived from electrospinning ascathode material for aqueous zinc ion battery.Journal of ElectroanalyticalChemistry 2020,873.) describes the preparation of carbon nanofiber-encapsulated manganese composite material by adding polyvinylpyrrolidone and manganese acetate tetrahydrate in ethanol at a 1:1 ratio via electrospinning and calcination, achieving a specific capacity of 250.1 mAh / g at a current density of 0.1 A / g.

[0009] The above-mentioned technical solutions all achieve the effect of improving dispersibility through electrospinning, differing only in the metal element used: Ni, Ti, and Mn. Among these, the technical effect of introducing Ni is superior to that of introducing Ti and Mn. This is because Ni, as a Group VIII element, has a richer electronic structure than transition metals Ti and Mn, resulting in superior electron transfer capabilities. Therefore, based on the above existing technologies, it can be concluded that the technical effect obtained by introducing Ni is better than that obtained by introducing Ti and Mn.

[0010] In addition, all of the above technical solutions suffer from the problem of insufficient metal element addition. Summary of the Invention

[0011] The purpose of this invention is to provide carbon nanofiber-supported MnTi bimetallic microspheres, their preparation method, and applications. As described in the background section, simply increasing the amount of metal added leads to an increase in the concentration of the electrospinning solution, resulting in increased viscosity and ultimately causing agglomeration of the resulting material. This means that increasing the amount of metal added cannot improve the catalytic performance. Therefore, this invention addresses the technical problem of increasing the amount of metal added by introducing a bimetallic element, without increasing the concentration of the single metal, while simultaneously achieving a synergistic catalytic effect of the bimetallic element.

[0012] However, according to the inventors' research, the electrospinning solution obtained by this method also suffers from agglomeration due to increased viscosity. In other words, the bimetallic method cannot solve the technical problem of increasing the amount of metal element added. The basic principle, as is generally known in the art, is that introducing Ni, Ti, and Mn elements individually significantly enhances the electrostatic attraction between fibers in the electrospinning solution, leading to fiber agglomeration. The inventors' research also found that introducing bimetallic elements exhibits the same phenomenon of enhanced electrostatic attraction between fibers in the electrospinning solution.

[0013] Based on the above research results, this invention introduces Ti and Mn elements, which have the best single-metal properties, and adds PVP to coordinate with Ti and Mn elements to form a stable complex. The resulting complex has good conductivity, so bimetallic microspheres can be precipitated under the action of an electric field, thereby significantly reducing the electrostatic attraction between fibers in the electrospinning solution. Finally, a three-dimensional network structure with a dispersed structure is obtained through electrospinning.

[0014] The technical solution to achieve the objective of this invention is:

[0015] A carbon nanofiber-supported MnTi bimetallic microsphere is prepared by using isopropyl titanate, a transition metal compound, manganese chloride tetrahydrate, and polyvinylpyrrolidone (PVP) as raw materials. The carbon nanofiber-supported MnTi bimetallic microsphere PVP-MnTi is obtained by electrospinning. The carbon nanofiber-supported MnTi bimetallic microsphere CNT-MnTi is then obtained by calcination.

[0016] The microstructure of the PVP-MnTi is a three-dimensional network structure with a dispersed structure composed of PVP nanofibers. Furthermore, a microsphere structure composed of MnTi bimetal is loaded on the three-dimensional network structure. The diameter of the PVP nanofibers is 100 nm and the diameter of the bimetal microspheres is 1 μm.

[0017] The CNT-MnTi microstructure is a three-dimensional network structure composed of carbon nanofibers with a dispersed structure. Furthermore, microspheres composed of MnTi bimetallic oxides are loaded on the three-dimensional network structure. The carbon nanofibers have a diameter of 100 nm, and the bimetallic oxide microspheres have a diameter of 1 μm.

[0018] A method for preparing carbon nanofiber-supported MnTi bimetallic microspheres includes the following steps:

[0019] Step 1, electrospinning of PVP-MnTi: First, isopropyl titanate, manganese chloride tetrahydrate (MnCl2·4H2O), and polyvinylpyrrolidone (PVP) are mixed in a certain mass ratio and stirred under certain conditions to obtain an electrospinning solution. Then, under certain conditions, the electrospinning solution is electrospinned to obtain PVP nanofibers loaded with MnTi bimetallic microspheres, referred to as PVP-MnTi.

[0020] In step 1, the mass ratio of isopropyl titanate, manganese chloride tetrahydrate, and PVP is 1:1.5:0.8.

[0021] In step 1, the conditions for stirring the electrospinning solution are: stirring time of 450-550 min;

[0022] In step 1, the conditions for electrospinning are: positive voltage 14-15KV, negative voltage -3-4KV, feed speed 1.5-2.5cm / h, distance between tip and collector 8-12cm, and roller speed 80-100rpm.

[0023] In step 1, the mixed solvent is a mixed solution of N,N-dimethylformamide (DMF) and ethanol in a volume ratio of 9:1.

[0024] Step 2, Preparation of CNT-MnTi: Under certain conditions, the PVP-MnTi obtained in Step 1 is calcined to obtain carbon nanofiber-supported MnTi bimetallic microspheres, referred to as CNT-MnTi.

[0025] In step 2, the calcination conditions are as follows: under argon atmosphere, the calcination temperature is 600℃ and the calcination time is 90min.

[0026] When carbon nanofiber-supported MnTi bimetallic microspheres are used as MgH2 hydrogen storage catalysts, a CNT-MnTi-based magnesium hydride hydrogen storage material can be obtained by ball milling CNT-MnTi with magnesium hydride. The amount of CNT-MnTi added accounts for 7-12 wt% of the total mass. The ball milling conditions are as follows: under argon atmosphere, the ball-to-material ratio is (40-60):1, the ball milling speed is 350-450 rpm, and the ball milling time is 10-15 h.

[0027] A magnesium hydride hydrogen storage material based on CNT-MnTi exhibits the following characteristics: Initial hydrogen release temperature is 180-190℃ under a programmed heating rate of 3℃ / min; hydrogen absorption capacity is 5.8-6.2wt% under conditions of hydrogen absorption pressure of 20-30 bar, hydrogen absorption temperature of 150-250℃, and hydrogen absorption time of 200-600 s; and hydrogen release capacity is 4.0-6.1wt% under conditions of hydrogen release temperature of 275-350℃ and hydrogen release time of 240-360 s.

[0028] Therefore, the present invention has been shown to be identifiable by XRD, SEM, PCT, and other methods as follows:

[0029] SEM analysis revealed that the microstructure of PVP-MnTi is a three-dimensional network structure composed of PVP nanofibers with a dispersed structure, and microspheres composed of MnTi bimetals are loaded on the three-dimensional network structure.

[0030] XRD analysis revealed that CNT-MnTi contains diffraction peaks of both MnO and TiO2, indicating that Mn and Ti elements exist in oxide form after calcination.

[0031] SEM testing showed that the microstructure of CNT-MnTi was not substantially different from that of PVP-MnTi obtained in step 1, and the calcination process did not affect the microstructure of the material.

[0032] According to PCT high-temperature gas desorption tests, the initial hydrogen desorption temperature of MgH2 / CNT-MnTi material is 180-185℃ under a programmed heating rate of 3-5℃ / min.

[0033] According to PCT high-temperature gas adsorption tests, under the conditions of hydrogen adsorption temperature of 150-250℃, hydrogen adsorption pressure of 20-30 bar, and hydrogen adsorption time of 250-500s, the hydrogen adsorption capacity of MgH2 / CNT-MnTi is 5.5-6.2wt%.

[0034] PCT high-temperature gas desorption tests at different temperatures showed that, under the conditions of hydrogen release temperature of 275-350℃ and hydrogen release time of 240-360s, the hydrogen release amount of MgH2 / CNT-MnTi was 4.0-6.1wt%.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] 1. By introducing manganese and titanium, which are not the best performing single metals, a synergistic effect between the two metals is achieved, while the amount of metal added is significantly increased, thereby improving the catalytic performance of the catalyst.

[0037] 2. By adding manganese and titanium elements to the electrospinning solution, bimetallic microspheres are precipitated during electrospinning, which reduces the electrostatic attraction between nanofibers, reduces the aggregation of nanofibers, and improves the dispersibility of the material.

[0038] 3. The raw materials used in this invention are all industrially produced chemical raw materials that are available on the market and easy to obtain. The synthesis process is simple, the reaction cycle is short, and the reaction process has low energy consumption and low pollution. Attached Figure Description

[0039] Figure 1 Here is a SEM image of PVP-MnTi from Example 1;

[0040] Figure 2 The XRD patterns are of CNT-MnTi in Example 1, CNT-Mn in Comparative Example 1, CNT-Ti in Comparative Example 2, and CNT-MnTi-1.5 in Comparative Example 3.

[0041] Figure 3 Here is a SEM image of CNT-MnTi from Example 1;

[0042] Figure 4 The graph shows the hydrogen desorption performance of MgH2 / CNT-MnTi in Example 1, MgH2 / CNT-Mn in Comparative Example 1, MgH2 / CNT-Ti in Comparative Example 2, MgH2 / CNT-MnTi-1.5 in Comparative Example 3, and pure MgH2 as a function of temperature.

[0043] Figure 5 The isothermal hydrogen absorption performance of MgH2 / CNT-MnTi in Example 1, MgH2 / CNT-Mn in Comparative Example 1, MgH2 / CNT-Ti in Comparative Example 2, MgH2 / CNT-MnTi-1.5 in Comparative Example 3, and pure MgH2 is shown in the figure.

[0044] Figure 6 The graph shows the isothermal hydrogen desorption performance of MgH2 / CNT-MnTi at different temperatures in Example 1.

[0045] Figure 7 Here is a SEM image of CNT-Mn in Comparative Example 1;

[0046] Figure 8 Here is a SEM image of CNT-Ti in Comparative Example 2;

[0047] Figure 9 The image shows the SEM image of CNT-MnTi-1.5 in Comparative Example 3. Detailed Implementation

[0048] The present invention will be further described in detail through embodiments and with reference to the accompanying drawings, but this is not intended to limit the scope of the invention.

[0049] Example 1

[0050] A method for preparing carbon nanofiber-supported MnTi bimetallic microspheres includes the following steps:

[0051] Step 1, electrospinning of PVP-MnTi: First, with a mass ratio of isopropyl titanate, manganese chloride tetrahydrate (MnCl2·4H2O), and polyvinylpyrrolidone (PVP) of 1:1.5:0.8, isopropyl titanate, manganese chloride tetrahydrate, and PVP are placed in a mixed solvent and stirred for 480 min to obtain an electrospinning solution. Then, under conditions of a positive voltage of 14 kV, a negative voltage of -3 kV, a feed speed of 2 cm / h, a distance of 10 cm between the tip and the collector, and a drum rotation speed of 80 rpm, the electrospinning solution is electrospinned to obtain PVP nanofiber-supported MnTi bimetallic microspheres, abbreviated as PVP-MnTi.

[0052] The mixed solvent is a mixed solution of N,N-dimethylformamide (DMF) and ethanol in a volume ratio of 9:1.

[0053] To verify the microstructure of PVP-MnTi, SEM testing was performed. The test results are as follows: Figure 1 As shown, the microstructure of PVP-MnTi is a three-dimensional network structure with a dispersed structure composed of PVP nanofibers. Furthermore, a microsphere structure composed of MnTi bimetal is loaded on the three-dimensional network structure, wherein the diameter of the PVP nanofibers is 100 nm and the particle size of the MnTi bimetal microspheres is 1 μm.

[0054] Step 2, preparation of CNT-MnTi: Under argon atmosphere, the PVP-MnTi obtained in Step 1 is calcined at a calcination temperature of 600℃ for 90 min to obtain carbon nanofiber-supported MnTi bimetallic microspheres, abbreviated as CNT-MnTi.

[0055] To verify the composition of CNT-MnTi, XRD tests were performed. The test results are as follows: Figure 2 As shown, CNT-MnT contains diffraction peaks for both MnO and TiO2. Test results indicate that after calcination in step 2, Mn and Ti elements exist in the form of oxides.

[0056] To verify the microstructure of CNT-MnTi, SEM testing was performed. The test results are as follows: Figure 3 As shown, the microstructure of CNT-MnTi is not substantially different from that of PVP-MnTi obtained in step 1. The test results indicate that the calcination process in step 2 does not affect the microstructure of the material.

[0057] To demonstrate the performance of CNT-MnTi as a MgH2 catalyst, magnesium hydride hydrogen storage materials based on CNT-MnTi were prepared and their hydrogen absorption and desorption performance was tested.

[0058] A method for preparing a magnesium hydride hydrogen storage material based on CNT-MnTi includes the following steps: under argon conditions, CNT-MnTi and MgH2 are ball-milled at a CNT-MnTi content of 10 wt% of the total mass, a ball-to-material ratio of 40:1, a ball milling speed of 400 rpm, and a ball milling time of 12 h to obtain the magnesium hydride hydrogen storage material based on CNT-MnTi, abbreviated as MgH2 / CNT-MnTi.

[0059] To demonstrate the hydrogen desorption kinetics of MgH2 / CNT-MnTi, a PCT high-temperature gas desorption test was conducted. Simultaneously, for comparison, a PCT high-temperature gas desorption test was performed on pure MgH2.

[0060] The test results for pure MgH2 are as follows: Figure 4 As shown, under a programmed heating rate of 3℃ / min, the initial hydrogen release temperature of pure MgH2 is 298℃.

[0061] The test results of MgH2 / CNT-MnTi are as follows: Figure 4 As shown, under a programmed heating rate of 3℃ / min, the initial hydrogen desorption temperature of MgH2 / CNT-MnTi is 185℃.

[0062] Test results show that introducing MgH2 / CNT-MnTi as a catalyst can significantly reduce the initial hydrogen desorption temperature of MgH2 by 113℃, meaning that MgH2 / CNT-MnTi can significantly improve the hydrogen desorption kinetics of MgH2.

[0063] To demonstrate the isothermal hydrogen adsorption kinetics of MgH2 / CNT-MnTi, a PCT high-temperature gas adsorption test was conducted. For comparison, a PCT high-temperature gas adsorption test was also performed on pure MgH2.

[0064] The test results for pure MgH2 are as follows: Figure 5 As shown, under the conditions of hydrogen absorption temperature of 200℃, hydrogen absorption pressure of 24 bar, and hydrogen absorption time of 60s, the hydrogen absorption capacity of pure MgH2 is only 0.177wt%, that is, the hydrogen absorption performance is negligible.

[0065] The test results of MgH2 / CNT-MnTi are as follows: Figure 5 As shown, under the conditions of hydrogen absorption temperature of 200℃, hydrogen absorption pressure of 24 bar, and hydrogen absorption time of 500s, the hydrogen absorption capacity of MgH2 / CNT-MnTi is 6.2wt%.

[0066] The test results show that the introduction of MgH2 / CNT-MnTi as a catalyst can significantly improve the hydrogen absorption capacity of MgH2, that is, MgH2 / CNT-MnTi can significantly improve the hydrogen absorption kinetics of MgH2.

[0067] To demonstrate the isothermal hydrogen desorption kinetics of MgH2 / CNT-MnTi, PCT high-temperature gas desorption tests were conducted at different temperatures. Meanwhile, for comparison, PCT high-temperature gas adsorption tests were performed on pure MgH2.

[0068] The test results for pure MgH2 are as follows: Figure 6 As shown, under the conditions of hydrogen release temperature of 300℃ and hydrogen release time of 180s, the hydrogen release amount of pure MgH2 is only 0.005wt%; that is, the hydrogen absorption performance is negligible.

[0069] The test results of MgH2 / CNT-MnTi are as follows: Figure 6 As shown, under the conditions of hydrogen release temperature of 325℃ and hydrogen release time of 240s, the hydrogen release amount of MgH2 / CNT-MnTi is 5.9wt%.

[0070] Test results show that CNT-MnTi can significantly improve the isothermal hydrogen desorption kinetics of MgH2.

[0071] To demonstrate the influence of each component on performance, Comparative Example 1 and Comparative Example 2 are provided, which are composite materials prepared by introducing Mn and Ti elements separately, respectively.

[0072] Comparative Example 1

[0073] A method for preparing a CNT-Mn composite material with Mn element introduced alone, the steps unless otherwise specified are the same as those in Example 1, the difference being that: in step 1, isopropyl titanate is not added, the material obtained in step 1 is named PVP-Mn, the material obtained in step 2 is named CNT-Mn, and the resulting magnesium hydride hydrogen storage material is named MgH2 / CNT-Mn.

[0074] The XRD test results of CNT-Mn are as follows: Figure 2 As shown, CNT-Mn contains diffraction peaks of MnO, proving that CNT-Mn was successfully synthesized. A comparison with Example 1 shows that the introduction of Ti does not affect the form of Mn in the composite material.

[0075] SEM test results of CNT-Mn are as follows Figure 7As shown, although the basic microstructure of CNT-Mn still exhibits a three-dimensional network structure and a microsphere structure, the nanofibers show severe aggregation, and the microspheres are encapsulated by the nanofibers due to this aggregation. Compared with Example 1, it can be seen that the introduction of Ti can transform the microstructure of the composite material from an aggregated network structure to a dispersed three-dimensional network structure, thus improving dispersibility and regulating the microstructure.

[0076] The test results of hydrogen desorption kinetics of MgH2 / CNT-Mn are as follows: Figure 4 As shown, under a programmed heating rate of 3 °C / min, the initial hydrogen decomposition temperature of MgH2 / CNT-Mn is 260 °C. Compared with Example 1, it can be seen that the introduction of Ti element can improve the hydrogen decomposition kinetics of MgH2 / CNT-Mn, that is, improve the catalytic performance of CNT-Mn. This is because the introduction of the Ti metal source allows CNT-Mn to achieve a bimetallic synergistic catalytic effect, thereby improving the catalytic performance of CNT-Mn, thus demonstrating the role of Ti element in the technical solution.

[0077] The hydrogen absorption kinetics test results of MgH2 / CNT-Mn are as follows: Figure 5 As shown, under the conditions of hydrogen absorption temperature of 200℃, hydrogen absorption pressure of 24 bar, and hydrogen absorption time of 500 s, the hydrogen absorption capacity of MgH2 / CNT-Mn is only 2.7 wt%. Compared with Example 1, it can be seen that the introduction of Ti element can significantly improve the isothermal hydrogen absorption kinetics of MgH2 / CNT-Mn, with an improvement of 129.6%, that is, improve the catalytic performance of CNT-Mn. The reason is that by introducing the Ti metal source, Ti element replaces some of the Mn element positions, making the Mn element in CNT-MnTi more dispersed than in CNT-Mn, resulting in a larger contact area between Mn element and MgH2, and a more complete reaction, thereby improving the catalytic efficiency of CNT-Mn, thus proving the role of Ti element in the technical solution.

[0078] Comparative Example 2

[0079] A method for preparing a CNT-Ti composite material with Ti element introduced separately, the steps unless otherwise specified are the same as those in Example 1, the difference being that: in step 1, manganese chloride tetrahydrate is not added, the material obtained in step 1 is named PVP-Ti, the material obtained in step 2 is named CNT-Ti, and the resulting magnesium hydride hydrogen storage material is named MgH2 / CNT-Ti.

[0080] The XRD test results of CNT-Ti are as follows: Figure 2 As shown, CNT-Ti contains diffraction peaks of TiO2, proving that CNT-Ti was successfully synthesized. A comparison with Example 1 shows that the introduction of Mn does not affect the form of Ti in the composite material.

[0081] SEM test results of CNT-Ti are as follows Figure 8 As shown, the basic microstructure of CNT-Ti is similar to that of CNT-Mn, i.e., an aggregated three-dimensional network structure encapsulating microspheres. The conclusions drawn from the test results are similar to those of Comparative Example 1, namely, the introduction of Ti can improve dispersibility and thus regulate the microstructure.

[0082] Based on the SEM test results of Example 1 and Comparative Examples 1 and 2, it can be seen that the introduction of Mn and Ti elements alone both resulted in severe aggregation, making it impossible to obtain a three-dimensional network structure with a dispersed structure. This proves that the simultaneous introduction of Mn and Ti elements causes a substantial change in the microstructure.

[0083] The hydrogen desorption kinetics test results of MgH2 / CNT-Ti are as follows: Figure 4 As shown, under a programmed heating rate of 3℃ / min, the initial hydrogen decomposition temperature of MgH2 / CNT-Ti is 220℃. Compared with Example 1, it can be seen that the introduction of Mn element can improve the hydrogen decomposition kinetics of MgH2 / CNT-Ti, that is, improve the catalytic performance of CNT-Ti. This is because the introduction of the Mn metal source allows CNT-Ti to achieve a bimetallic synergistic catalytic effect, thereby improving the catalytic performance of CNT-Ti, thus demonstrating the role of Mn element in the technical solution.

[0084] The test results of the hydrogen absorption kinetics of MgH2 / CNT-Ti are as follows: Figure 5 As shown, under the conditions of hydrogen absorption temperature of 200℃, hydrogen absorption pressure of 24 bar, and hydrogen absorption time of 500 s, the hydrogen absorption capacity of MgH2 / CNT-Ti is only 2.1 wt%. Compared with Example 1, it can be seen that the introduction of Mn element can significantly improve the isothermal hydrogen absorption kinetics of MgH2 / CNT-Ti, with an improvement of 195.2%, that is, improve the catalytic performance of CNT-Ti. The reason is that by introducing the Mn metal source, Mn element replaces some Ti element positions, making the Ti element in CNT-MnTi more dispersed than in CNT-Ti, resulting in a larger contact area between Ti element and MgH2, and a more complete reaction, thereby improving the catalytic efficiency of CNT-Ti, thus proving the role of Mn element in the technical solution.

[0085] Based on the test results of hydrogen desorption and hydrogen absorption kinetics of Example 1 and Comparative Examples 1 and 2, it can be seen that neither introducing Mn nor Ti elements alone can effectively improve the catalytic performance. Only by introducing Mn and Ti elements simultaneously can the catalytic performance be significantly improved, which proves that there is a synergistic effect between Mn and Ti elements in the technical solution.

[0086] To demonstrate the effect of PVP addition ratio on performance, Comparative Example 3 is provided, showing CNT-MnTi composite materials prepared by increasing the PVP addition ratio.

[0087] Comparative Example 3

[0088] A method for preparing a CNT-MnTi composite material with a high proportion of PVP is provided. Unless otherwise specified, the steps are the same as in Example 1, except that in step 1, the mass ratio of isopropyl titanate, manganese chloride tetrahydrate and PVP is 1:1.5:1.5. The material obtained in step 1 is named PVP-MnTi-1.5, the material obtained in step 2 is named CNT-MnTi-1.5, and the resulting magnesium hydride hydrogen storage material is named MgH2 / CNT-MnTi-1.5.

[0089] The XRD test results of CNT-MnTi-1.5 are as follows: Figure 2 As shown, CNT-MnTi-1.5 contains characteristic peaks of MnO and TiO2, proving that CNT-MnTi-1.5 was successfully synthesized. Comparison with Example 1 shows that changing the PVP addition ratio does not affect the presence of Mn and Ti elements in the composite material.

[0090] The SEM test results of CNT-MnTi-1.5 are as follows: Figure 9 As shown, although CNT-MnTi-1.5 still exhibits a three-dimensional network structure, the nanofibers aggregate, and microspheres are absent. Compared to Example 1, it is evident that excessive PVP addition not only leads to nanofiber aggregation but, more importantly, prevents Mn and Ti elements from forming microspheres. This demonstrates that the proportion of PVP added can significantly alter the microstructure.

[0091] The hydrogen desorption kinetics test results of MgH2 / CNT-MnTi-1.5 are as follows: Figure 4 As shown, under a programmed heating rate of 3℃ / min, the initial hydrogen desorption temperature of MgH2 / CNT-MnTi-1.5 is 190℃. Compared with Example 1, it can be seen that when the proportion of PVP is too high, the initial hydrogen desorption temperature actually increases, meaning the performance deteriorates. The reason for this, combined with the SEM test results, is that severe agglomeration of the nanofibers leads to an increase in the initial hydrogen desorption temperature of MgH2 / CNT-MnTi-1.5, thus reducing the catalytic performance of CNT-MnTi-1.5.

[0092] The hydrogen absorption kinetics test results of MgH2 / CNT-MnTi-1.5 are as follows: Figure 5As shown, under the conditions of hydrogen absorption temperature of 200℃, hydrogen absorption pressure of 24 bar, and hydrogen absorption time of 500 s, the hydrogen absorption capacity of MgH2 / CNT-MnTi-1.5 is 6.0 wt%. Compared with Example 1, it can be seen that when the proportion of PVP added is too high, the hydrogen absorption capacity decreases. The reason is consistent with the conclusion obtained from the hydrogen desorption kinetics performance test.

[0093] Therefore, as can be seen from Example 1 and Comparative Example 3, excessive PVP addition will lead to nanofiber aggregation, thus demonstrating the role of adjusting the PVP addition ratio in the technical solution.

Claims

1. A carbon nanofiber-supported MnTi bimetallic microsphere, characterized in that: Carbon nanofiber-supported MnTi bimetallic microspheres PVP-MnTi were obtained by electrospinning using transition metal compounds such as isopropyl titanate, manganese chloride tetrahydrate, and polyvinylpyrrolidone (PVP). The carbon nanofiber-supported MnTi bimetallic microspheres CNT-MnTi were then obtained by calcination. The microstructure of the PVP-MnTi is a three-dimensional network structure with a dispersed structure composed of PVP nanofibers. Furthermore, a microsphere structure composed of MnTi bimetal is loaded on the three-dimensional network structure. The diameter of the PVP nanofibers is 100 nm and the diameter of the bimetal microspheres is 1 μm. The CNT-MnTi microstructure is a three-dimensional network structure composed of carbon nanofibers with a dispersed structure. Furthermore, microspheres composed of MnTi bimetallic oxides are loaded on the three-dimensional network structure. The carbon nanofibers have a diameter of 100 nm, and the bimetallic oxide microspheres have a diameter of 1 μm. The mass ratio of isopropyl titanate, manganese chloride tetrahydrate, and PVP is 1:1.5:0.

8.

2. The carbon nanofiber-supported MnTi bimetallic microspheres according to claim 1, characterized in that: When used as a MgH2 hydrogen storage catalyst, CNT-MnTi and magnesium hydride are ball-milled together to obtain a magnesium hydride hydrogen storage material based on CNT-MnTi. The amount of CNT-MnTi added is 7-12 wt% of the total mass.

3. The carbon nanofiber-supported MnTi bimetallic microspheres according to claim 2, characterized in that: When used as a MgH2 hydrogen storage catalyst, the ball milling conditions are as follows: under argon atmosphere, the ball-to-material ratio is (40-60):1, the ball milling speed is 350-450 rpm, and the ball milling time is 10-15 h.

4. The carbon nanofiber-supported MnTi bimetallic microspheres according to claim 1, characterized in that: When used as a MgH2 hydrogen storage catalyst, the initial hydrogen release temperature is 180-190℃ under a programmed heating rate of 3℃ / min.

5. The carbon nanofiber-supported MnTi bimetallic microspheres according to claim 1, characterized in that: When used as a MgH2 hydrogen storage catalyst, under the conditions of hydrogen absorption pressure of 20-30 bar, hydrogen absorption temperature of 150-250℃, and hydrogen absorption time of 200-600 s, the hydrogen absorption capacity is 5.8-6.2 wt%. Under the conditions of hydrogen release temperature of 275-350℃ and hydrogen release time of 240-360 s, the amount of hydrogen released is 4.0-6.1 wt%.

6. A method for preparing carbon nanofiber-supported MnTi bimetallic microspheres, characterized in that... Includes the following steps: Step 1, electrospinning of PVP-MnTi: First, isopropyl titanate, manganese chloride tetrahydrate (MnCl2·4H2O), and polyvinylpyrrolidone (PVP) are mixed in a certain mass ratio and stirred under certain conditions to obtain an electrospinning solution. Then, under certain conditions, the electrospinning solution is electrospinned to obtain PVP nanofibers loaded with MnTi bimetallic microspheres, referred to as PVP-MnTi. In step 1, the mixed solvent is a mixed solution of N,N-dimethylformamide (DMF) and ethanol in a volume ratio of 9:

1. In step 1, the mass ratio of isopropyl titanate, manganese chloride tetrahydrate, and PVP is 1:1.5:0.

8. In step 1, the conditions for stirring the electrospinning solution are: stirring time of 450-550 min; In step 1, the conditions for electrospinning are: positive voltage 14-15 KV, negative voltage -3 to -4 KV, feed speed 1.5-2.5 cm / h, distance between tip and collector 8-12 cm, and roller speed 80-100 rpm. Step 2, Preparation of CNT-MnTi: Under certain conditions, the PVP-MnTi obtained in Step 1 is calcined to obtain carbon nanofiber-supported MnTi bimetallic microspheres, abbreviated as CNT-MnTi.

7. The preparation method according to claim 6, characterized in that: In step 2, the calcination conditions are as follows: under argon atmosphere, the calcination temperature is 600℃ and the calcination time is 90 min.

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